rexresearch.com
Lonnie JOHNSON, et al
Lithium-Air Battery
Lithium-Air Battery
Rechargeable lithium-air batteries can store 5 to 10 times the energy of a lithium-ion battery, and can be several times lighter. Here is Lonnie Johnson's leading edge design ( articles, & patents ), & a list of ~ 400 recent Li-Air Battery patents. But we might have to invade Columbia to get enough lithium for our Needful Things ...
http://www.blackenterprise.com/mag/charging-ahead/
Lonnie Johnson takes a different road
to alternative energy
by
Marcia Wade Talbert
by
Marcia Wade Talbert
With a mind toward energy independence, President Barack Obama’s administration has made it a priority to put 1 million electric cars on the road in the next four years. Atlanta-based scientist Lonnie G. Johnson has been working toward that goal for nearly 20 years. In fact, he was trying to construct a device to produce alternative sources of energy when he unexpectedly invented the Super Soaker water gun in 1989.
But Johnson, a former NASA scientist with a bachelor’s degree in mechanical engineering and a master’s degree in nuclear engineering, hopes his legacy will stand for something far more important than a children’s toy. He has put much of the money he made from the Super Soaker into two projects: the lithium air battery and the JTEC (Johnson Thermo-Electrochemical Converter) system.
The lithium air battery reacts to oxygen from its surroundings instead of reacting to corrosive metal materials that are stored inside traditional batteries. It is lighter than conventional battery cathode materials and lasts longer since oxygen is an unlimited reactant. Last year Johnson and his team became the first researchers to use a rechargeable lithium air battery to power a device. They started small by powering a remote control car—a suitable choice since the objective is to one day power electric vehicles. Johnson calls the lithium air battery “a game changer,” claiming it can power a vehicle for more than 1,000 miles on a single charge. By comparison, the Chevy Volt has a 16-kWh lithium-ion battery that lasts only 40 miles before it switches to its gas engine.
“Lithium air is a very complicated technology. The great challenge for vehicle electrification—of getting people off of petroleum—is getting a battery that is powerful enough, cheap enough, and lightweight enough to rival gasoline in terms of its energy density,” says James Greenberger, executive director of the National Alliance of Advanced Technology Batteries. “Lonnie is unquestionably one of the leading scientific minds working on that problem.”
Johnson’s other endeavor, the JTEC engine, which is still in the development phase, could potentially convert heat from the sun into electricity that is able to power entire cities, says Johnson. Popular Mechanics magazine awarded Johnson with the Breakthrough Award for the JTEC in 2008, and Paul Werbos, a program director at the National Science Foundation, believes that the engine could be worth trillions of dollars one day.
Still, obtaining funding to advance both the JTEC and the lithium air battery has been a challenge. Johnson’s companies have received contracts from the U.S. Department of Defense and the Department of Energy to develop the two technologies, but the support has been insignificant considering the president’s goal toward energy independence, he says. “More emphasis needs to be placed on these particular technologies because they are in a class all by themselves.”
http://cenvironment.blogspot.com/2011/04/lithium-air-battery.html
Saturday, April 30, 2011
Lithium Air Battery
Lonnie Johnson Develops New Battery Technology Via His Company: Excellatron
Lonnie Johnson Develops New Battery Technology Via His Company: Excellatron
The performance of conventional lithium battery systems is limited by the fundamental capacities of both the cathode and anode used in these batteries. The best cathode materials in lithium ion batteries have a specific capacity of less than 200mAh/g. The most widely used anode material, graphitic or soft carbon, has a specific capacity of 372mAh/g. Metal/air batteries have a much larger specific energy than most of the available primary and rechargeable batteries. These batteries are unique in that the active cathode material (oxygen) is not stored in the battery. Oxygen from the environment is reduced at a catalytic air electrode surface forming either an oxide or peroxide ion that then reacts with cationic species in the electrolyte.Among various metal/oxygen batteries, Li/O2 couple is especially attractive because it has the potential of the highest specific energy (5,200Wh/kg) among all the known electrochemical couples.
The specific energy of lithium air batteries is expected to be an order of magnitude larger than that achievable using conventional lithium or lithium ion batteries. Excellatron has expanded its technology base to lithium air batteries. Until now, commercialization of these batteries has been hindered by several problems such as corrosion and low capacity. The unique technology developed by Excellatron has overcome these problems and pushed Li/Air batteries closer to practical applications. Recently, we have successfully demonstrated the feasibility of a rechargeable lithium/oxygen battery, and Li/Air demonstration samples have been successfully delivered to a customer.
http://www.excellatron.com/
Lithium-Air Battery
The performance of conventional lithium battery systems is limited by the fundamental capacities of both the cathode and anode used in these batteries. The best cathode materials in lithium ion batteries have a specific capacity of less than 200mAh/g. The most widely used anode material, graphitic or soft carbon, has a specific capacity of 372mAh/g. Metal/air batteries have a much larger specific energy than most of the available primary and rechargeable batteries. These batteries are unique in that the active cathode material (oxygen) is not stored in the battery. Oxygen from the environment is reduced at a catalytic air electrode surface forming either an oxide or peroxide ion that then reacts with cationic species in the electrolyte.Among various metal/oxygen batteries, Li/O2 couple is especially attractive because it has the potential of the highest specific energy (5,200Wh/kg) among all the known electrochemical couples. The specific energy of lithium air batteries is expected to be an order of magnitude larger than that achievable using conventional lithium or lithium ion batteries. Excellatron has expanded its technology base to lithium air batteries. Until now, commercialization of these batteries has been hindered by several problems such as corrosion and low capacity. The unique technology developed by Excellatron has overcome these problems and pushed Li/Air batteries closer to practical applications. Recently, we have successfully demonstrated the feasibility of a rechargeable lithium/oxygen battery, and Li/Air demonstration samples have been successfully delivered to a customer.
Advantages
Metal/air batteries have a much higher gravimetric energy density than most available primary and rechargeable batteries. These batteries are unique in that the cathode active material is not stored in the battery. Oxygen from the environment is reduced at a catalytic air electrode surface forming either an oxide or peroxide ion that then reacts with cationic species in the electrolyte, metal air batteries have a much higher gravimetric energy density than that achieved by metal oxide/carbon couples. The Li/O2 couple is especially attractive because it has the potential for the highest gravimetric energy density (11,238 Wh/kg exclude oxygen and 5,200 Wh/kg include oxygen) among all the known electrochemical couples. Even considering a 50% weight contribution from other inactive materials (including the cathode, separator, electrolyte, and packaging), the gravimetric energy density of the lithium air battery is still much larger than that achievable using conventional lithium or lithium ion batteries.
Applications & Products
The electrochemical coupling of a reactive anode to an air electrode provides a battery with an inexhaustible cathode and, potentially, very high specific energy and energy density. The most important advantage of a metal/air battery is that its active cathode, oxygen, is not carried inside of the battery. Instead, oxygen is extracted from the surrounding ambient environment when it is used. This unique property of metal/air batteries results in a huge advantage in their specific energy (Wh/kg) that is critical for applications that are very sensitive to weight.
YouTube Videos
Johnson JTech air battery
http://www.youtube.com/watch?v=gEUZz5TtJ-k&
Suppressed Technology That Could Have Changed The World ...
http://www.youtube.com/playlist?list=PLF78B61ADE50DF166
Black Engineer Created A "FREE ENERGY" Device - YouTube
http://www.youtube.com/watch?v=gEUZz5TtJ-k
Lonnie Johnson : The Viability of High
Specific Energy Lithium-Air Batteries
[ PDF
]
http://en.wikipedia.org/wiki/Lonnie_Johnson_%28inventor%29
Lonnie Johnson (inventor)
Mobile, Alabama, United States
Occupation Engineer, Inventor
Known for Super Soaker
Lonnie George Johnson (born October 6, 1949 in Mobile, Alabama) is an American engineer. Johnson invented the Super Soaker water gun, which was the top selling toy in the United States in 1991 and 1992.
Engineering firms
In 1980 Johnson formed his own law firm and licensed the Super Soaker water gun to Larami Corporation. Two years later the Super Soaker generated over $200 million in retail sales and became the best selling toy in America. Larami Corporation was eventually purchased by Hasbro, the second largest toy manufacturer in the world. Over the years, Super Soaker sales have totaled close to one billion dollars. Johnson reinvested a majority of his earnings from the Super Soaker into research and development for his energy technology companies - "It's who I am, it's what I do."[2] Currently, Johnson holds over 80 patents, with over 20 more pending, and is the author of several publications on spacecraft power systems.[3][4]
Energy technology
Two of Johnson’s companies, Excellatron Solid State and Johnson Electro-Mechanical Systems (JEMS), are developing energy technology. Excellatron is introducing thin film batteries, a new generation of rechargeable battery technology. JEMS has developed the Johnson Thermo-Electrochemical Converter System (JTEC), listed by Popular Mechanics as one of the top 10 inventions of 2009. JTEC has potential applications in solar power plants and ocean thermal power generation. It converts thermal energy to electrical energy using a non-steam process which works by pushing hydrogen ions through two membranes, with significant advantages over alternative systems.[5][6]
Patents
HIGH CAPACITY SOLID STATE
COMPOSITE CATHODE, SOLID STATE COMPOSITE SEPARATOR,
SOLID-STATE RECHARGEABLE LITHIUM BATTERY AND METHODS OF MAKING
SAME
WO2013131005
WO2013131005
A high capacity solid state composite cathode contains an active cathode material dispersed in an amorphous inorganic ionically conductive metal oxide, such as lithium lanthanum zirconium oxide and/or lithium carbon lanthanum zirconium oxide. A solid state composite separator contains an electronically insulating inorganic powder dispersed in an amorphous, inorganic, ionically conductive metal oxide. Methods for preparing the composite cathode and composite separator are provided.
BACKGROUND OF THE INVENTION
[0003] A battery cell is a particularly useful article that provides stored electrical energy which can be used to energize a multitude of devices, including portable devices that require an electrical power source. A battery cell, which is often referred to, somewhat inaccurately, in an abbreviated form as a "battery," is an electrochemical apparatus typically formed from at least one electrolyte (also referred to as an "electrolytic conductor") disposed between a pair of spaced apart electrodes. The electrodes and electrolyte are the reactants for an electrochemical reaction that causes an electric current to flow between the electrodes when respective current collectors in contact with the electrodes are connected to an external circuit containing an object or device (generally referred to as the "load") to be powered. The flow of electrons through the free ends of the electrodes is accompanied and caused by the creation and flow of ions in and through the electrolyte.
[0004] Typically, battery performance is enhanced by improving upon one or more of the individual components, such as the electrodes and/or electrolyte, and/or improving the interaction between or among the components of the battery. Materials that serve as electrolytes may have several different forms. For example, an electrolyte material may be a liquid, a solid, or a material such as a paste that has characteristics of both a liquid and a solid. In addition to electrodes and electrolyte, batteries may also contain a separator component, which separates the electrodes from one another. Separation of the electrodes prevents the undesirable conduction of electrons directly between the electrodes, called short circuiting. Typically, some type of solid material that is capable of creating and maintaining physical spacing between electrodes is used as a separator.
[0005] In recent years, much consideration has been given to so-called "solid-state" batteries, in which no liquids are employed in the electrodes or electrolyte. In solid-state batteries, the functions of separating electrodes (separator function) and of serving as a medium for the conduction of ions between electrodes (electrolyte function) are carried out by a single component. Thus, a solid ionically conductive electrolyte often serves as both a separator and as an electrolytic conductor. Very recently, solid ionically conductive materials, such as ionically conductive metal oxides, and amorphous ionically conductive metal oxides in particular, have been investigated for use as solid electrolytes in solid-state batteries. However, some solid ionically conductive materials have flaws, such as cracks in the material, which may adversely impact battery performance. Solid ionically conductive materials are often produced from precursors via a process that may cause cracks to be formed in the final product. Such cracks may inhibit the optimum transport of ions through the solid electrolyte. In addition, cracks may provide pathways for the transport of electrons between electrodes, thereby producing short- circuits that may cause the cell to fail. Thus, it can be appreciated that it would be useful to develop a solid ionically conductive electrolyte, suitable for use in solid-state batteries, in which flaws are sufficiently diminished or eliminated and cell performance is enhanced.
[0006] Thin film sputtered cathode materials are currently being used in state of the art thin film solid-state lithium and lithium ion batteries. Because lithium atoms generally have low diffusion coefficients in active cathode materials, the capacity of thick layer cathodes can only be shallowly, not fully, accessed during charge/discharge cycles of the battery. As a result, lithium ions can only move a limited distance from their entrance point into the cathode material at reasonable charge discharge rates. This shallow access dramatically reduces the volumetric and gravimetric energy density of the resulting batteries.
[0007] Current thin film solid-state lithium-ion battery technology employs expensive substrates, including noble metals, and uses expensive sputtering processes to form the cathode material coatings. Despite high cost, high temperature-stable noble metals, such as gold, are utilized to retain the electronic conductivity of the current collectors required in such cells under the high temperature (>850[deg.]C) procedures used to crystallize films and/or layers of the cathode materials.
[0008] Accordingly, cost effective solid-state lithium batteries containing high capacity cathodes are highly desirable.
BRIEF SUMMARY OF THE INVENTION
[0009] A solid state composite cathode according to an embodiment of the invention comprises an active cathode material dispersed in an amorphous inorganic ionically conductive metal oxide.
[0010] A method of producing a solid state composite cathode according to an embodiment of the invention comprises: (a) preparing a slurry comprising an active cathode material and precursors for an amorphous inorganic ionically conductive metal oxide;
(b) forming a film from the slurry; and
(c) heating the film to form the amorphous inorganic ionically conductive metal oxide, wherein the active cathode material is dispersed in the amorphous inorganic ionically conductive metal oxide.
[0011 ] A solid composite separator according to an embodiment of the invention comprises an inorganic electronically insulating powder dispersed in an amorphous, inorganic, ionically conductive metal oxide.
[0012] A method of producing a solid composite separator according to an embodiment of the invention comprises
(a) preparing a slurry comprising an inorganic electronically insulating powder and precursors for an amorphous inorganic ionically conductive metal oxide;
(b) forming a film from the slurry; and
(c) heating the film to form the amorphous inorganic ionically conductive metal oxide, wherein the inorganic electronically insulating powder is dispersed in the amorphous inorganic ionically conductive metal oxide.
[0013] A solid state composite electrode according to another embodiment of the invention comprises an active electrode material dispersed in an amorphous inorganic ionically conductive metal oxide.
[0014] Finally, a method of producing a solid state composite electrode according to an embodiment of the invention comprises:
(a) preparing a slurry comprising an active electrode material and precursors for an amorphous inorganic ionically conductive metal oxide;
(b) forming a film from the slurry; and
(c) heating the film to form the amorphous inorganic ionically conductive metal oxide, wherein the active electrode material is dispersed in the amorphous inorganic ionically conductive metal oxide.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0015] The foregoing summary, as well as the following detailed description of the invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there are shown in the drawing embodiments which are presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown.
[0016] In the drawings:
[0017¦ Fig. 1 is a schematic cross sectional diagram of a lithium battery cell according to an embodiment of the invention;
¦0018] Fig. 2 is a schematic diagram of a complex two battery cell according to an embodiment of the invention; and
¦0019] Fig. 3 is a Nyquist plot of impedance spectrum of a composite separator prepared according to an embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
¦
0020] The invention is directed to a high capacity solid state composite cathode, a high capacity solid-state rechargeable lithium battery containing the cathode, and methods for their manufacture. The invention is also directed to a composite solid separator or electrolyte containing a solid ionically conductive material, a high capacity solid state rechargeable lithium battery containing the separator, and methods for their manufacture. The term '"battery" technically refers to a combination of two or more cells, but is commonly used to refer to a single cell. Accordingly, for the purposes of this disclosure, the term "battery" refers to both a single cell and a battery containing multiple cells.
[0021] The hereby disclosed invention and process apply particularly to oxide electrodes in lithium and lithium ion batteries which are mostly applied as cathodes, although there are examples of oxide anodes, such as lithium titanium oxide (LTO). Thus, for the purposes of this disclosure, the term "cathode" may be understood to refer not only to a cathode per se, but also to any active oxide electrode, even if it is used as an anode in a battery due to its low voltage. Additionally, although lithium batteries contain an anode made of pure lithium and lithium ion batteries contain an anode made of lithium-containing material, the terms "lithium battery" and "lithium ion battery" are used interchangeably in this disclosure.
Solid State Composite Cathode
[0022] The high capacity solid state composite cathode according to the invention comprises a an active cathode material dispersed in an amorphous inorganic ionically conductive metal oxide. The active cathode material (powder), such as, for example, LiCo0 2 or LiNio 33Coo.33Mno.33O2 (NCM), has preferably been treated to remove passivating surface impurities or coatings (films). Preferred amorphous inorganic ionically conductive materials include lithium lanthanum zirconium oxide (LLZO) and/or amorphous lithium carbon lanthanum zirconium oxide (LCLZO). Optionally, the cathode further comprises an electronically conductive material, such as carbon black or carbon nanotubes, dispersed in the amorphous inorganic ionically conductive metal oxide. As described in more detail below, the cathode is preferably formed by combining the active cathode material, precursors of the amorphous inorganic ionically conductive metal oxide, and optionally electronically conductive material, to form a slurry, and forming a film from the slurry, such as by casting. A heating and curing process converts the precursors into the amorphous material having the cathode active material dispersed therein.
[0023] When used to form a battery, the film may be cast from the slurry as a layer on a thin electronically conductive substrate, such as a metal foil, to serve as the current collector. The amorphous ionically conductive material will then function as both the electrolyte and the binder.
[0024] The active cathode material component of the composite cathode structure is prepared from a commercially available active cathode powder, such as LiCo0 2or NCM, commercially available from Pred Materials International (New York, NY). Other oxide active intercalation material powders known in the art or to be developed for use in lithium or lithium ion batteries would also be appropriate. The commercial powder is preferably washed in alcohol (such as isopropanol, for example) and dried by heating at about 200 to 650[deg.]C for about two hours in an oxygen atmosphere, ozone-rich air or air. Such treatment results in a material which is at least substantially free of surface impurities.
[0025] It has been found that commercially available cathode powders have reacted with moisture in the air, resulting in the formation of thin passivating layers, such as lithium carbonate, lithium hydroxide, and/or lithium oxide, on the surface of the cathode materials. These thin passivating layers (typically much less than 1 micron in thickness) have high impedance, and act as a barrier to the passage of lithium ions. Accordingly, it has been found that treating commercially available cathode powders to remove the surface impurities results in a superior battery.
[0026] The second component of the composite cathode preferably contains amorphous LLZO and/or LCLZO, which provides high ionic conductivity to the cathode and serves as the cathode binder. These materials are described in United States Patent Application Publications Nos. 2011/0053001 and 2012/0196189, the disclosures of which are herein incorporated by reference in their entirety . These application publications are hereinafter referred to as "the <v>001 application publication" and "the [Iota] 89 application publication," respectively. For the purposes of this disclosure, the term "LLZO" may be understood to refer to LLZO and/or LCLZO. It is also within the scope of the invention to utilize alternative amorphous inorganic ionically conductive metal oxides instead of or in addition to the LLZO. For example, appropriate amorphous inorganic materials are those in which one or more of the elements in LLZO has been partially or completely replaced by a different element, such as replacing zirconium with tantalum. Such alternative materials are also described in the '001 and [Iota]89 application publications and all of the materials described therein are also within the scope of the invention.
[0027] The inorganic metal oxide, such as the preferred amorphous LLZO/LCLZO, is preferably combined with the cathode material as precursors, that is, compounds of lanthanum, lithium, and zirconium. Preferably, a precursor solution of such compounds which may be preferably applied by sol gel techniques is employed. For example, appropriate precursor solutions for LLZO and LCLZO are described in detail in the '001 and ' 189 application publications, the disclosures of which are herein incorporated by reference in their entirety. In a preferred embodiment, the solution of precursors contains a lanthanum alkoxide, a lithium alkoxide, and a zirconium alkoxide dissolved in a solvent, such as an alcohol. Preferred precursors include lithium butoxide, lanthanum methoxyethoxide, and zirconium butoxide, and a preferred solvent is methoxyethanol. These precursor components are exemplary, not limiting, and alternative precursor solutions arc also within the scope of the invention, provided that they contain the required lithium, lanthanum, zirconium, and oxygen components in appropriate concentrations. It is also within the scope of the invention to prepare more than one solution, such as three solutions each containing one o f the desired lithium, lanthanum, or zirconium compounds. If an amorphous metal oxide other than or in addition to the preferred LLZO/LCLZO is to be contained in the final cathode, the appropriate precursor solution(s) should contain the desired components in appropriate concentrations.
[0028] In a preferred embodiment, the composite cathode also contains an electronically conductive material and/or at least one additional ionically conductive material in powder form. Such materials are also combined with the active cathode material and amorphous material precursor and will be dispersed in the amorphous material after casting, for example, and heating (curing). Exemplary electronically conductive materials comprise carbon, preferably commercially available standard acetylene black, carbon nanotubes, or a mixture thereof. The ionically conductive powder may be a single material or a combination of materials. Examples of suitable ionically conductive powders include, but are not limited to, lithium aluminum germanium phosphate (LAGP), lithium aluminum titanium phosphate (LATP), LLZO/LCLZO, or lithium lanthanum titanium oxide (LLTO). Thus, in a preferred embodiment, two forms of LLZO may be used to produce the composite cathode: fully formed LLZO powder (amorphous or crystalline) and a LLZO precursor solution which will become amorphous LLZO after casting and curing. ¦0029] A preferred composite cathode is formed from a slurry that contains about 3g of NCM, about 3 ml LLZO sol gel precursor solution (as described in the '001 and [Iota] 89 application publications), about 0.75 g of LAGP, and about 0.02 g of acetylene black. More generally, the solids portion of the slurry preferably comprises about 80 to 100% cathode powder, about 0 to 30% LAGP, and about 0 to 3% carbon, all percentages being by weight. The ratio of the liquid portion (LLZO sol gel precursor solution) to the solid portion of the slurry is preferably about 75 to 200% (in milliliters) liquid to about 100% (by weight in grams) solids.
[0030] The term "slurry" may be understood to encompass materials having a range of viscosity, and may include a damp powder, a thick paste, a thin paste, a free flowing material, a thick liquid, a thin liquid, etc. After combining the active material with a solution containing the precursor compounds, the majority of the solvent may be evaporated to concentrate the slurry into the form of a thicker material, such as a paste. It is also within the scope of the invention to combine the precursor compounds with the active material (and optionally additional components, as previously described) using only a minimal amount of solvent necessary for mixing of the components.
[0031 J The components of the cathode slurry may be mixed or energy milled in an inert environment to obtain a homogeneous mixture and then formed into a film, such as by casting or calendaring using known techniques. The method of mixing the components is not critical and may be determined or adjusted by routine experimentation. The film, which may also be referred to as a sheet or wafer, may be thick or thin, and may have a thickness of about 1 micron to about 1 mm. When the slurry is in the form of a thick paste or damp powder, for example, the film may also be formed by compacting or pressing it into a rigid or semi-rigid structure, such as a sheet or wafer, using a press or other device which applies pressure.
[0032] When preparing a battery, the film may be cast or calendered onto a thin electronically conductive substrate, preferably an inexpensive thin metal foil substrate, as a coating or layer. The substrate, which will serve as a current collector in the battery, preferably has a thickness of about 5 microns to about 50 microns, more preferably about 5 microns to about 30 microns. A preferred substrate is aluminum foil. It is within the scope of the invention to utilize other substrates, including other metal substrates, such as nickel foil, in place of aluminum, provided that they provide the same advantages. Specifically, other flexible foils exhibiting high electronic conductivity, such as metalized non-metal foils, composite foils, and other foils known in the art or to be developed which have similar properties are also within the scope of the invention. Preferably the coating composition is coated on the substrate to form a layer having a thickness of about 5 to 50 microns. [0033J Finally, as described in more detail below, the film (which may be self-supporting or supported on a substrate) is heated (cured) to convert the precursors into the amorphous inorganic ionically conductive metal oxide having the active material (and optional additional components) dispersed therein.
[0034] It is also within the scope of the invention to include additional layers in the cathode. For example, multiple layers of cathode composition, such as from the slurry as described above, having a thickness of about 5 to about 50 microns may be applied to the cathode film. Additionally, one or more compacting steps or calendering steps may be performed after application of the materials onto the substrate to facilitate the formation of a smooth surface battery. One or more layers of LLZO (deposited by sol-gel techniques from a precursor solution) may also be applied onto the composite cathode to further increase the ionic conductivity. Advantageously, the cathode according to the invention is formed using only low temperatures processing (up to about 350[deg.]C). Solid State Battery
[0035] A high capacity rechargeable lithium solid state battery according to an embodiment of the invention contains, in addition to the previously described cathode, a thin solid electrolyte, such as amorphous LLZO and/or lithium phosphorus oxynitride (LiPON), and/or a thick solid electrolyte, such as an amorphous LLZO based-composite separator, either of which (or their combination) is deposited onto the previously described cathode, and a lithium-based anode, such as a metal current collector, silicon, lithium, a lithium alloy, or lithium titanium oxide (LTO). Other battery parts well known in the art may also be included, such as current collectors) and outside casing. If only a metal current collector, such as a copper film, is utilized, the lithium anode will be formed upon initial charging of the battery as lithium is plated between the current collector and the separator. Thus, both lithium and lithium-ion batteries are within the scope of the invention. During synthesis of the battery, processing is performed at low temperatures (up to about 350[deg.]C), which further reduces the cost of the battery.
[0036] Additionally, the invention is directed to a solid state lithium or lithium ion battery comprising a composite solid state anode, a cathode, and a separator, in which the composite solid state anode is as described previously. In other words, solid state lithium or lithium ion batteries according to the invention comprises a composite solid state electrode according to the invention, a counter electrode, and a separator.
[0037] As previously explained, when forming the batteries according to the invention, the composite electrode may be cast or applied directly onto an electronically conductive substrate serving as a current collector.
[0038] A schematic of an exemplary solid state lithium battery according to an embodiment of the invention is shown in Fig. 1. As shown in Fig. 1, a portion of the lithium battery 1 contains a composite cathode 2 containing cathode powder, LLZO, and optionally carbon, a separator 4, and a lithium-based anode 6.
[0039] Also within the scope of the invention are complex two battery cell structures containing a single cathode current collector (thin metal foil substrate) and complete cells constructed on both sides of the substrate, as shown in Fig. 2. As shown in Fig. 2, a lithium battery 8 contains an aluminum foil current collector 16 sandwiched between two composite cathodes 14, two solid state separators 12, and two lithium anodes 10. A copper current collector 18 is present on the external surface of one of the lithium anodes.
[0040] Solid state lithium batteries according to the invention exhibit high capacity during cycling by deep harvesting the active cathode material due to the presence of a highly conducting LLZO/LCLZO or analogous network in the cathode structure. In addition to providing an enhanced ion conduction network in the cathode structure to facilitate this deep accessing of the active cathode materia!, LLZO or analogous material also binds the cathode material, providing structural integrity to the cathode without requiring high temperature sintering or any other high temperature processing step.
[0041] The batteries of the invention thus provide numerous advantages relative to prior art batteries, including high capacity, deep access of the cathode, low cost, low temperature processing, smooth surface cathodes (leading to better uniformity and coverage by the solid electrolyte separator film), and the ability to scale up to large size batteries.
Cathode and Battery Preparation
[0042] The methods for producing the cathode and battery according to the invention preferably involve at least the following steps, which will be described in more detail below.
However, some of these steps, while preferred, are not critical, and other steps may be combined or modified based on routine experimentation. The method steps include:
(1) preparing an active cathode material substantially free from surface impurities;
(2) preparing precursor compounds for an amorphous inorganic ionically conductive metal oxide, such as an LLZO/LCLZO precursor solution;
(3) preparing a slurry containing the active cathode material and the precursor compounds;
(4) forming a film from the slurry;
(5) exposing the film to ozone-rich, low humidity air,
(6) heating the film at about 70 to 130[deg.]C in ozone-rich, low humidity air,
(7) heating the film at about 280 to 350[deg.]C in low humidity air to form a cathode;
(8) depositing a solid electrolyte separator layer on the cathode; and
(9) depositing a lithium-based anode on the electrolyte layer to form the battery.
[0043] Importantly, at least steps (4) to (6) are preferably performed in an ozone-rich, low humidity environment. The term "ozone-rich" refers to an environment containing at least about 0.05 ppm ozone and the term "low humidity" describes an environment having less than about 30 percent relative humidity (RH).
(1) Active Cathode Material Preparation
[004 1 The first step in the method of the invention involves preparing an active cathode material or powder that is preferably substantially free from passivating surface films (surface impurities). The material is prepared from a commercially available cathode powder, such as L1C0O2 or NCM, available from Pred Materials International (New York, NY). Other oxide active intercalation material powders known in the art or to be developed for use in lithium or lithium ion batteries would also be appropriate. The powder is first washed in alcohol (such as isopropanol, for example) and dried by heating at about 200 to 650[deg.]C for about two hours in an oxy gen atmosphere, ozone-rich air, or air. The isopropanol washing is preferably performed by placing the cathode active powder in a pan, pouring the alcohol over the powder until all of the powder has been submerged in the liquid, briefly mixing the powder in the liquid, pouring off the excess liquid, and placing the wet powder in a furnace for the heating step.
[0045] As previously explained, it has been found that treating commercially available cathode powders to remove the passivating surface impurities, such as lithium carbonate, lithium oxide, and lithium hydroxide, which act as a high impedance barrier, results in a superior battery.
[0046] The active intercalation material is preferably NCM or LiCo0 2. However, other oxide electrode materials may also be used to form a composite solid state electrode according to the invention. For example, LTO is an oxide intercalation material that is generally considered to be an anode material due to its low voltage. Accordingly, LTO powder may also be used as an active material to form a composite solid state electrode in the same manner as described for the formation of a solid state cathode.
(2) Amorphous Ionically Conductive Material Precursor Solution Preparation
[0047] The second step in the method involves preparing precursor compounds for the amorphous inorganic ionically conductive metal oxide, preferably a solution of such precursors.
In a preferred embodiment, the step involves preparing a solution of LLZO/LCLZO precursors, namely, compounds containing lanthanum, lithium, and zirconium which may be preferably applied by sol gel techniques. For example, appropriate precursor solutions for LLZO and LCLZO are described in detail in the '001 and ' 189 application publications. In a preferred embodiment, the solution contains a lanthanum alkoxide, a lithium alkoxide, and a zirconium alkoxide dissolved in a solvent, such as an alcohol. Preferred precursors include lithium butoxide, lanthanum methoxyethoxide, and zirconium butoxide, and a preferred solvent is methoxyethanol. These precursor components are exemplary, not limiting, and alternative precursor solutions for LLZO/LCLZO are also within the scope of the invention, provided that they contain the required lithium, lanthanum, zirconium, and oxygen components in appropriate concentrations. It is also within the scope of the invention to prepare more than one solution, such as three solutions each containing one of the desired lithium, lanthanum, or zirconium components. If an amorphous material other than or in addition to LLZO/LCLZO is to be contained in the final cathode, the appropriate precursor solution(s) should contain the desired components in appropriate concentrations.
[0048] The precursor solution may be prepared by mixing the components in any sequence at room temperature. Preferably, the thoroughly-mixed precursor solution is maintained in an inert en vironment for about one to 1.5 hours to help facilitate substantially complete dissolution of the components. An "inert environment" may be understood to refer to a nitrogen or argon environment in which the moisture is low enough that lithium components are not degraded due to moisture.
(3) Slurry Preparation
[0049] After preparing the precursor compounds and active cathode material, the next step in the method involves forming a slurry containing these components. The slurry may be simply prepared by combining appropriate amounts of solution and active material and mixing, such as by energy milling in an airtight jar for about 60 to about 100 minutes, or until the resulting mixture is homogeneous by visible inspection. However, such a method of slurry preparation is by no means limiting and any appropriate method of mixing and slurry preparation is also within the scope of the invention. As previously explained, the slurry is preferably prepared in an inert (nitrogen or argon filled) environment. In a preferred embodiment, no additional solvent is added to form the slurry other than the solvent present in the precursor solution.
[0051] Each of the slurry components will play a distinct role in the final cathode. Specifically, the active cathode material intercalates lithium, and the precursors to LLZO/LCLZO or similar material functions as an ionically conductive component and, after curing, as a solid electrolyte and as a binder for the cathode. [0051] In a preferred embodiment, the slurry contains a third component, which provides electronic conductivity to the cathode. This component is a carbon material, such as the preferred commercially available standard acetylene black and/or carbon nanotubes, although other carbon materials which would provide the same function would also be appropriate. It is also within the scope of the invention to include more than one type of electronically conductive material. When carbon is included in the slurry, it may be necessary to add additional solvent in order to facilitate the formation of a homogeneous suspension. The added solvent is preferably the same solvent contained in the precursor solution, such as the preferred methoxyethanol. The amounts of carbon (and optionally solvent) to be added may be determined by routine experimentation in order to maintain the same viscosity of the suspension
[0052] Additionally, it is also within the scope of the invention to include an additional powder in the slurry to further improve the ionic conductivity. Such additional powders may- include, for example, LATP (lithium aluminum titanium phosphate), LAGP (lithium aluminum germanium phosphate), LLZO/LCLZO powder, or another oxide/phosphate based ionically conductive powder. It may be advantageous to replace some of the precursor solution, such as the preferred LLZO/LCLZO precursor solution, with one or more of these powders to increase the ionic conductivity, yield a compact structure, and reduce the drying time needed due to the decrease in the amount of solvent present from the precursor solution. Thus, in a preferred embodiment, LLZO is present in two forms in the cathode slurry: a fully formed LLZO powder (amorphous or crystalline) and a LLZO precursor solution which will become amorphous LLZO after casting and curing.
[0053] A preferred slurry contains about 3 g of NCM, about 3 ml LLZO precursor solution (as described in the '001 application publication), about 0.75 g of LAGP and about 0.02 g of acetylene black. More generally, the solids portion of the slurry preferably comprises about 80 to 100% cathode powder, about 0 to 30% LAGP, and about 0 to 3% carbon, all percentages being by weight. The ratio of the liquid portion (LLZO precursor solution) to the solid portion of the slurry is preferably about 75 to 200% (in milliliters) liquid to about 100% (by weight in grams) solids.
[0054] The term "slurry" may be understood to encompass materials having a range of viscosity, and may include a damp powder, a thick paste, a thin paste, a free flowing material, a thick liquid, a thin liquid, etc. After combining the active material with a solution containing the precursor compounds, the majority of the solvent may be evaporated to concentrate the slurry into the form of a thicker material, such as a paste. It is also within the scope of the invention to combine the precursor compounds with the active material (and optionally additional components, as previously described) using only a minimal amount of solvent necessary for mixing of the components.
(4) Forming a Film
[0055] The next step in the method involves forming a film from the slurry, such as by casting or calendering. The film preferably has a thickness of about 1 micron to about 1 mm.
[0056] It is within the scope of the invention to form a film that will be self-supporting and free standing, or to form a film from the slurry on a substrate, preferably a thin, electronically conductive substrate such as the preferred thin aluminum foil substrate, to form a layer or coating. Aluminum has several advantages, including being light weight and inexpensive, in contrast with more expensive metal substrates utilized in traditional batteries. The aluminum foil or other substrate preferably has a thickness of about 5 microns to about 50 microns, more preferably about 5 microns to about 30 microns. It is within the scope of the invention to utilize other substrates, such as other metal and non-metal electronically conductive substrates, including nickel foil, in place of aluminum, as long as they provide the same advantages and can withstand the curing processing temperature and environment. Preferably, the metal foil is cleaned prior to casting, such as by wiping with alcohol.
[0057] The casting is preferably performed by tape casting on a standard flat casting table. The method of tape casting is well known in the art and need not be described. Appropriate conditions for the tape casting are known in the art or may be determined by routine experimentation. The casting is preferably performed in an ozone-rich and low humidity environment, as previously described. The slurry may also be applied by other means, such as calendering, using known techniques.
[0058] Additionally, if the slurry is relatively viscous, such as a thick paste or damp powder, a film may be formed by compacting the slurry, such as under pressure with a press or other device known in the art, to form a rigid or semi-rigid structure.
(5) - (7) Forming the Cathode
[0059] After film forming, the film is preferably exposed to low humidity, ozone-rich air, such as for about one hour, heated at about 70 to 130[deg.]C in ozone-rich, low humidity air, such as for about one hour, and then heated at about 280 to 350[deg.]C in low humidity air, such as for about one hour to form a cathode. More preferably, the first heating step is performed at about 75 to 90[deg.]C, more preferably about 80[deg.]C, and the second heating step preferably performed at about 300 to about 310[deg.]C. The specific drying and heating times and temperatures may be varied, but are preferably performed at no higher than about 350[deg.]C. It is also within the scope of the invention to omit the first exposure step and proceed with the two heating steps after casting. After these heating steps, the cathode is now complete.
[0060] Importantly, the lower temperature heating is preferably performed in an ozone-rich (containing at least about 0.05 ppm ozone) and low humidity (less than about 30 percent relative humidity) environment, and the higher temperature heating is performed in low humidity air. Without wishing to be bound by theory, it is believed that the lower temperature heating gently evaporates the alcohol components from the precursor solution without destroying the soft and sensitive structure of the solid material. Subsequently, the higher temperature heating step serves to solidify the active material in the amorphous material.
[0061] It is also within the scope of the invention to perform additional steps during production of the cathode. For example, after film forming and before heating, in a preferred embodiment, a layer or film of LLZO precursor solution may be spin coated onto the cast film. Upon subsequent heating to about 70 to 130[deg.]C and drying at about 280 to 350[deg.]C. this additional LLZO layer helps to improve the ionic conductivity and mechanical integrity of the cathode.
[0062] It is also within the scope of the invention to perform a compacting step to compact the film. If compacting is performed, it is preferably performed after the lower temperature heating step but before the higher temperature heating step. It has been found that after heating to about 350[deg.]C, an amorphous solid material has been formed, and compacting is not possible without cracking of the material. Compacting may be performed by any method known in the art, such as calendering, and may be performed in an inert or low humidity environment.
[0063] If compacting is performed, it is also within the scope of the invention to subsequently spin coat an additional layer of amorphous inorganic ionically conductive metal oxide, such as an LLZO/LCLZO layer (from a precursor solution) onto the cathode, followed by two heating steps as previously described.
[0064] Thus, in a preferred embodiment, the method comprises casting forming a film from the slurry, optionally applying a layer of amorphous LLZO/LCLZO from a precursor solution, drying at about 70-130[deg.]C, compacting the slurry and LLZO/LCLZO layer, and applying a second layer of LLZO/LCLZO from a sol-gel precursor solution and drying, followed by a final heating step at about 280-350[deg.]C.
(8) Depositing Electrolyte Separator Layer
[0065] To form a battery, a separator (electrolyte) layer is subsequently deposited onto the completed cathode, more preferably onto a completed cathode/current collector combination.
As noted above, the cathode may be formed directly on an electronically conductive substrate, such as a metal foil, which serves as the current collector. Alternatively, the cathode may be formed as a self-supporting, free-standing structure. If so, a current collector may be coated onto the cathode using known techniques.
[0066] The specific electrolyte material used for the separator is not critical, and may be one known in the art or to be developed for solid-state batteries. In preferred embodiments, the electrolyte is preferably a layer of lithium phosphorus oxynitride (UPON), which may be vacuum sputtered to a thickness of about 1.5 to 2 microns, or a layer of LLZO deposited from a sol-gel precursor solution to a thickness of 1-2 microns, exposed to low humidity, ozone-rich air, and heated at about 70-130[deg.]C and then at about 280-350[deg.]C as previously described. The separator may also be the composite separator described in more detail below. Other methods for depositing solid electrolyte separator materials on top of a solid cathode are well known in the art and need not be described.
(9) Depositing Lithium Anode
[0067] Finally, a lithium-based anode (preferably about 2 microns in thickness) is deposited on the electrolyte (separator) layer to complete the solid-state battery. The anode may be any anode material known in the art or to be developed, such as a metal current collector, silicon, lithium, a lithium alloy, or lithium titanium oxide (LTO). If only a metal current collector, such as a copper film, is utilized, the lithium anode will be formed upon initial charging of the battery as lithium is plated between the current collector and the separator. Methods for depositing anode materials on top of a solid electrolyte are well known in the art and need not be described.
[0068] According to the invention, high capacity solid-state batteries are achieved by deep accessing the cathode material, which is made possible by the presence of a highly ionically conducting network, such as an LLZO/LCLZO network, in the cathode structure. Processing of the cathode at low temperature (about 350[deg.]C), compared with high temperature processed (sintered) cathodes, is enabled by utilizing a highly ionically conductive amorphous material, such as LLZO, as a binder. This low temperature processing helps reduce the cost of solid-state battery manufacturing. The use of inexpensive thin aluminum foil as a substrate in the battery, rather than expensive substrates such as gold, is also possible because of the low temperature processing. Finally, the ability to achieve a smooth cathode surface leads to better uniformity and coverage of the separator film. This method also allows scale up of the size of the battery.
Solid State Composite Separator
[0069] The solid state composite separator according to the invention is formed from a composite ionically conductive solid material. Because this ionically conductive solid material is capable of serving as both a separator and an electrolyte, it may be understood that the description of "separator" in this section also refers to an "electrolyte." The ionically conductive material is a composite comprising an inorganic powder dispersed in a binder of amorphous, inorganic, ionically conductive metal oxide, such as LLZO/LCLZO. To form a working battery, the separator is cast onto a cathode, which serves as a substrate for the separator. The presence of the inorganic powder increases the thickness of the layer of amorphous material, thus reducing defects induced by debris which are present in very thin films, and which destroy their functionality as separators. Thus, the presence of the inorganic powder increases the reliability of the amorphous material and provides a better separator material. Inorganic Powder
[0070] A variety of inorganic powders, both amorphous and crystalline, are appropriate for use as the inorganic powder in the invention provided that the powder is an electronic insulator. Preferred powders include LLZO, which is ionically conductive, and aluminum oxide, which is non-conductive.
[0071] Other electronically insulating materials may also be used alone or in combination, provided that they bond well with the binder, described below. Exemplary non- conductive inorganic powders include, without limitation, inorganic single metal/multi-metal/non-metal oxides, carbides, phosphates, and nitrides, such as AI2O3, TiO?, ZnO, Si0 2, BaTiO^, L1AIO3, BC, BN, etc. Appropriate particle sizes may be selected based on routine experimentation.
[0072] It is also within the scope of the invention to include an ionic ally -conductive inorganic powder in addition to or instead of the electronically insulating powders described above to enhance the ion-transport capability of the separator. While not required, inclusion of one or more ionically conductive inorganic powders is advantageous and a preferred embodiment of the invention. Exemplary ionically conductive inorganic powders include, for example, crystalline or amorphous LLZO. crystalline or amorphous LCLZO, lithium aluminum titanium phosphate (LATP), lithium aluminum germanium phosphate (LAGP) and lithium lanthanum titanium oxide (LLTO). The inorganic powders listed above are exemplary, not limiting, and it i s also within the scope of the invention to utilize other inorganic powder materials that are known in the art or to be developed which would provide the same benefits as the materials described herein. Appropriate particle sizes may be selected based on routine experimentation .
Ionically Conductive Metal Oxide
[0073] Presently preferred inorganic, amorphous, ionically conductive metal oxide materials include amorphous LLZO and amorphous LCLZO as previously described, that is, a solution containing precursor compounds. It is also within the scope of the invention to utilize alternative amorphous inorganic ionically conductive materials instead of or in addition to the LLZO. Other preferred materials are also amorphous, oxide-based compounds. For example, appropriate amorphous inorganic materials are those in which one or more of the elements in LLZO has been partially or completely replaced by a different element, such as replacing zirconium with tantalum, provided that the resulting material exhibits the desired properties. Such alternative materials are also described in the '001 and [Iota] 89 application publications and incorporated by reference herein.
¦0074] The ionically conductive material is preferably prepared from a sol gel precursor solution containing the desired elements, as previously described. Specifically, the preferred LLZO/LCLZO is preferably prepared from a solution containing compounds of lanthanum, lithium, and zirconium which may be preferably applied by sol gel techniques. For example, appropriate precursor solutions for LLZO and LCLZO are described in detail in the '001 and ' 189 application publications. In a preferred embodiment, the solution contains a lanthanum alkoxide, a lithium alkoxide, and a zirconium alkoxide dissolved in a solvent, such as an alcohol. Preferred precursors include lithium butoxide, lanthanum methoxyethoxide, and zirconium butoxide, and a preferred solvent is methoxyethanol. These precursor components are exemplary, not limiting, and alternative precursor solutions are also within the scope of the invention, provided that they contain the required lithium, lanthanum, zirconium, and oxygen components in appropriate concentrations. It is also within the scope of the invention to prepare more than one solution, such as three solutions each containing one of the desired lithium, lanthanum, or zirconium components. If an amorphous material other than or in addition to LLZO/LCLZO is to be contained in the final cathode, the appropriate precursor solution(s) should contain the desired components in appropriate concentrations.
Separator and Method of Formation
[0075¦ The separator according to the invention may be formed by any known method for dispersing a powder into primary ingredient(s) or precursor(s) and for producing a substantially solid medium in which the particles of powder will be dispersed. A preferred method for producing the separator involves first creating a slurry by mixing together the inorganic powder with one or more liquid precursor(s) of the amorphous, inorganic ionically conducting material, then forming a film of the slurry. Finally, the film is subjected to a thermal curing process (heating) whereby the precursors are converted into the amorphous ionically conductive material. These steps are described in detail above with respect to the preparation of the composite cathode; differing only in the fact that the electronically insulating inorganic powder is used instead of the cathode active material and optional electronically conductive material.
[0076] When LLZO or LCLZO is utilized as the amorphous ionically conductive metal oxide, the drying and curing process preferably involves two sequential heating steps that are performed in specific ozone and humidity atmospheres, as described previously. When alternative inorganic ionically conductive materials are utilized, appropriate slurry components and reaction conditions may be determined by routine experimentation.
[00771 For forming a battery comprising the composite separator, the film from the slurry of inorganic pow <!>der and precursor of amorphous ionically conductive metal oxide is cast onto an electrode, typically a cathode, which serves as a substrate, and then dried and cured as previously described to form the composite separator on the electrode. Appropriate electrodes are well known in the art and need not be described. However, it is also within the scope of the invention to produce the separator as a free-standing, self-supporting structure by forming a self-supporting film from the slurry, as previously described with respect to the composite cathode. It is also within the scope of the invention to utilize the composite cathode according to an embodiment of the invention, described previously, in the battery. Subsequently, the battery may be produced from the separator/electrode combination using known methods.
[0078] In a composi te separator according to an embodiment of the invention, particles of electronically insulating inorganic powder are dispersed in a medium comprising an amorphous, inorganic, ionically conductive metal oxide serving as a binder for the powder. The dispersion of inorganic powder may be uniform or may be random and non-uniform without adversely affecting the effectiveness of the separator. The separator is a separator in the functional and traditional sense of serving to separate electrodes from one another; however, the separator is also an electrolyte (or electrolytic conductor) because it comprises predominantly ionically conductive material. The separator is substantially free of cracks because inorganic powder has been added to the amorphous, inorganic, ionically conductive metal oxide, which would typically be used alone to form a separator. The added inorganic powder changes the structural and chemical composition of the mixture of precursors for the amorphous, inorganic, ionically conductive metal oxide such that cracks are not typically formed during the process of forming the final product. Because the amorphous, inorganic material is ionically conductive, it serves the dual purpose of binder for the inorganic powder and electrolyte for the transport of ions.
[0079] The separator according to the invention is suitable for use in a cell (or battery) comprising a cathode and an anode separated by a separator. The invention is particularly suitable for use in a lithium battery, in which the lithium ions will be transported through the separator/electrolyte.
[0080] This invention will now be described in connection with the following, non-limiting examples.
Example 1 : Preparation of Composite Cathode and Lithium Battery
[0081] A dried cathode material (NCM) (obtained from Pred Materials International (New York, NY)) was washed in isopropanol and dried at 200[deg.]C in an ozone-rich air environment for about two hours. A LLZO sol gel precursor solution was prepared by dissolving about 4.5 grams of a lanthanum methoxyethoxide solution (about 12% by weight in methoxyethanol), about 0.65 gram of lithium butoxide and about 0.77 gram of a zirconium butoxide solution (about 80% by weight in butanol) in about 5 grams of methoxyethanol (all chemicals obtained from Gelest, Inc. (Morrisville, PA) or Alfa Acsar). The thoroughly-mixed precursor solution was left in a bottle in an inert environment for about 1 to 1.5 hours to help facilitate substantially complete dissolution of the lithium butoxide.
[0082] In an inert environment, a slurry was prepared by combining 6 g of the dried cathode material, 1.2 g LAGP (electrolyte powder), 6 ml of the LLZO sol-gel precursor solution, and 0.03 g acetylene black (obtained from Alfa Aesar), and then energy milled for about 80 minutes in an airtight jar. A thin aluminum foil (approximately 50 [mu][eta][iota]) was cleaned using isopropanol, and the slurry was then cast onto the cleaned foil and exposed to an ozone-rich and low humidity air environment for about one hour. To the exposed cathode structure, more LLZO sol gel solution was infiltrated by spin coating and again exposed to ozone-rich and low humidity air environment for about one hour. Subsequently, the coated substrate was heated to 80[deg.]C for about one hour in the ozone-rich and low humidity air environment. Thereafter, it was calendered for compaction and surface smoothcning. To this, an extra layer of LLZO sol gel layer was spin-coated, exposed at ambient temperature for one hour and then heated at 80[deg.]C for one hour, all in the ozone-rich and low humidity air environment.
[0083] To complete production of the cathode, the resulting structure was heated to 300[deg.]C in air for about one hour. On this novel cathode-separator combination, a thin layer of LiPON (1.5 - 2 micron thick) electrolyte was sputtered. Finally, an approximately 2-micron thick lithium anode was evaporated on the LiPON to complete the solid-state battery.
[0084] Analysis of the resulting low cost solid-state lithium battery demonstrated that high capacity was achieved and that deep cathode material was accessed during charge-discharge cycling.
Example 2: Preparation of Composite Separator
[0085] Aluminum oxide powder from Sigma- Aldrich in the form of nanoparticles (size -60 nm) was dried at about 150[deg.]C under vacuum for about 24 h. About 2g of the dried A1 20 3powder was mixed with 2ml of LLZO sol gel precursor solution as described in Example 1 into an energy milling jar. The jar was air tight sealed in the inert environment and was energy milled for about 80 min. A 45-micron thick aluminum foil was prepared by wiping with isopropanol and drying at about 80[deg.]C for about one hour. The homogeneously milled slurry was cast onto the clean and dried foil inside an ozone-rich (at least 0.05 ppm) and low humidity (less than about 30 percent relative humidity) air environment to form a sheet. The sheet was let to dry and cure for about one hour in the ozone-rich and low humidity air environment. Subsequently, the sheet was compacted using a clean roller inside the same air environment. Thereafter, one square inches pieces were cut from the sheet and further cured at about 80[deg.]C for about one hour in an ozone-rich and low humidity air environment. The pieces of the sheet were heated at 300[deg.]C for about one hour in air, thus forming a sample of composite separator.
[0086] The ionic conductivity of the composite separator pieces was measured using a Solectron Si 1260 Impedance Analyzer. The Al foil substrate served as one electrode for the measurement while the other electrode was formed by sputtered gold. The impedance spectrum of the composite separator sample (Fig. 3) demonstrates ionic conduction and a lack of short circuits.
[0087J It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims.
IMPREGNATED SINTERED SOLID STATE COMPOSITE
ELECTRODE, SOLID STATE BATTERY, AND METHODS OF PREPARATION
WO2013130983
WO2013130983
An impregnated solid state composite cathode is provided. The cathode contains a sintered porous active material, in which pores of the porous material are impregnated with an inorganic ionically conductive amorphous solid electrolyte. A method for producing the impregnated solid state composite cathode involves forming a pellet containing an active intercalation cathode material; sintering the pellet to form a sintered porous cathode pellet; impregnating pores of the sintered porous cathode pellet with a liquid precursor of an inorganic amorphous ionically conductive solid electrolyte; and curing the impregnated pellet to yield the composite cathode.
BACKGROUND OF THE INVENTION
[0003] Solid-state lithium batteries have recently garnered a great deal of attention due to their many advantages over batteries that use liquid electrolytes. Safety is a major issue with liquid electrolyte batteries and constrains the use of batteries in some applications, such as the car industry. Benefits of solid-state batteries include improved safety and longer life because they do not contain any combustible organics and can operate at high temperatures, if needed.
[0004] Some of the major drawbacks in solid-state battery development have included achieving high energy density and capacity, which are inhibited by factors such as thickness of the cathode, the percentage of the cathode that can be accessed during discharge, and the rate at which the cathode can be accessed. The percentage of the cathode that can be accessed during charge/discharge is limited because lithium atoms generally have low diffusion coefficients in active intercalation cathode materials, so that lithium ions can only move a very limited distance from their entrance point into the intercalation material during a given period of time. In order to access the full capacity of a thick cathode at reasonable charge and discharge rates, the cathode must be rich in lithium ion conducting pathways that are connected and stretch throughout the body of the cathode. This goal is easily achievable using an organic liquid electrolyte which fills the pores of the cathode, providing the desired ionic pathways, but at a significant safety risk. The ability to replace the liquid electrolyte with a chemically stable and safe solid electrolyte, while maintaining the same high access of the liquid electrolyte battery, has been one of the main objectives of all solid state battery development.
[0005] Active cathode materials are generally oxides or oxide-based materials, such as transition metal oxides, phosphates and silicates. Large solid structures of these materials are usually prepared by sintering the corresponding powders. It would be expected that sintering an active cathode powder with a lithium ionically conductive solid electrolyte powder would form a high access cathode structure. However, it has been found that sintering a cathode material with a solid electrolyte normally induces solid-state reactions between the cathode and electrolyte, and may result in electrochemical deactivation of the interface.
[0006] Many attempts have been made to develop and commercialize solid-state lithium batteries with high access, capacity, and energy density. For example, Nagata and Nanno {Journal of Power Sources; 174; 832-837 (2007)) attempted to eliminate the solid-state reaction between cathode and electrolyte and the resulting deactivation of the interface by utilizing lithium aluminum titanium phosphate (LATP) as an electrolyte and lithium iron phosphate or lithium cobalt phosphate as an cathode active material. They were able to sinter the two materials without observing any significant additional new material phase at the interface between the cathode and electrolyte.
However, in this method, the active cathode material was not sintered to itself to form excellent electrical conductivity because there were other LATP particles in the cathode. In addition, the final sintered structure was still very porous, and thus exhibited undesirably low density and low performance. Sintering of LATP powder with lithium cobalt oxide (L1C0O 2) powder was also reported, in which a new material phase was detected after the sintering, most likely making the interface electrochemically inactive. The resulting structures displayed very low performance as electrodes in electrochemical cells. It was concluded that a sintering process could be used to construct all solid state batteries, but only by selecting appropriately matched materials, not for general cathode/solid electrolyte material combinations.
[0007] Sun et al. {Journal of Power Sources; 196; 6507-651 1 (201 1 )) report making an all solid lithium ion electrode by sintering at 950[deg.]C lithium titanium oxide (LTO) as an active material component, lithium lanthanum titanium oxide (LLTO) as a Li ion conducting electrolyte component, and silver as an electronically conducting component. Both the active and the electrolyte materials were titanium oxides, thus representing a special matching materials case. In addition, the reported battery cycling results were only for a liquid electrolyte, not a solid electrolyte, thus preventing any real insight into the quality of the cathode for an all solid state battery. The LTO electrode has relatively low voltage and is frequently used and/or envisioned to be used as an anode in a battery, although its Li intercalation mechanism corresponds to a cathode.
[0008] Kotobuki et al. {Journal of the Electrochemical Society, 157 (4); A493-A498 (2010)) fabricated a sintered electrode by first forming a honeycomb structure of LLTO electrolyte, infiltrating the honeycomb pores with suspensions of lithium cobalt oxide and/or lithium manganese oxide particles, then sintering at > 700[deg.]C. The produced battery cells were able to be cycled, but showed unacceptably high interface impedance of over 20 kOhm-cm <2>.
[0009] Machida et al. {Journal of the Electrochemical Society, 149 (6) A688-A693 (2002)) also studied an all solid-state battery containing lithium cobalt nickel oxide as an active cathode material and an amorphous sulfide electrolyte. These cathode and electrolyte materials were milled and pressed into pellets along with acetylene black, i.e., no sintering was performed to compact the cathode and electrolyte material powders. A working battery of these materials was assembled by compacting and maintaining them under constant pressure of 300MPa (3000 atm). The metallic fixture required to apply and maintain this high pressure severely reduces the volumetric and gravimetric capacities and energies of the battery, making it impractical.
[0010] Lee et al. {Journal of Ceramic Processing Research; Vol. 8, No. 2, pp. 106-109 (2007)) studied the production of lithium cobalt oxide (LiCo0 2) thick cathode films using screen-printing to produce an all solid-state micro-battery. Lee et al. mixed a sol gel precursor of L1C0O 2with LiCo0 2powder and then screen printed, achieving crack-free cathodes greater than 10 [mu][iota][eta] in thickness. However, for characterization purpose, the cell was analyzed using a liquid electrolyte for a lithium ion battery. It was concluded that even though liquid electrolyte was used for cycling and there were no signs of cracks due to cycle stress of the half cells tested, the cathode had good potential to form an all solid state battery. However, the sintered thick cathode described by Lee et al. consisted solely of lithium cobalt oxide, which is an active intercalation cathode material. No solid electrolyte (to provide ionically conductive pathways) was used in the battery cell fabrication or testing. Thus, the cell of Lee et al. was not an all solid state battery.
[0011] Other experimental work has focused on developing novel materials and structures for solid-state lithium cathodes, particularly with an emphasis on improving stability and structure. For example, Thackeray et al. (U.S. Patent Application Publication No. 2004/0081888 Al and U.S. Patent No. 7,732,096) describe stable cathode materials with various transition metal oxides.
[0012] Finally, Johnson et al. (U.S. Patents Nos. 6,242,129 and 7,540,886) disclose methods of manufacturing thin film lithium batteries. The thin film lithium batteries have high charge/discharge rates and operate over a wide temperature range, but their energy density and specific energy are low, due to the unavoidable presence of an inactive but prohibitively large substrate. Johnson et al. (U.S. Patent Application Publication No. 2009/0092903) also disclose a solid state battery that consists of a sintered composite cathode and a sintered composite or Li metal anode. The sintered composite electrodes consist of an active intercalation material and a Li ion conducting solid electrolyte material. [0013] The sintered electrodes described above, which exhibit favorable properties, also exhibit either higher interface resistance than desirable between the active intercalation material and the solid electrolyte material or belong to a specially matched pair of active and electrolyte materials (LTO and LLTO, as an example). Most of the high specific capacity active materials are oxides of cobalt, manganese, nickel and their combinations. However, because there are no known high Li ionically conductive solid electrolytes that are based on Co/Mn/Ni oxides, no matched active material/solid electrolyte pair exists. It is thus difficult to achieve high performance all solid state lithium ion batteries using sintering, and there remains a need in the art for improved, low cost, high access cathodes (and low voltage oxide electrodes such as LTO) for all solid state batteries.
SUMMARY OF THE INVENTION
[0014] A method of producing an impregnated solid state composite cathode according to an embodiment of the invention comprises:
(a) forming at least one pellet comprising an active intercalation cathode material;
(b) sintering the at least one pellet to form at least one sintered porous cathode pellet;
(c) impregnating pores of the at least one sintered porous cathode pellet with a liquid precursor of an inorganic amorphous ionically conductive solid electrolyte; and
(d) curing the at least one impregnated pellet to yield the composite cathode.
[0015] An impregnated solid state composite cathode according to an embodiment of the invention comprises a sintered porous active intercalation material, wherein pores of the porous material are impregnated with an inorganic amorphous ionically conductive solid electrolyte.
[0016] An impregnated solid state composite electrode according to another embodiment of the invention comprises a sintered porous active material, wherein pores of the porous material are impregnated with an amorphous inorganic ionically conductive solid electrolyte.
[0017] A method of producing an impregnated solid state composite electrode according to another embodiment of the invention comprises:
(a) forming at least one pellet comprising an active electrode material;
(b) sintering the at least one pellet to form at least one sintered porous electrode pellet;
(c) impregnating pores of the at least one sintered porous electrode pellet with a liquid precursor of an inorganic amorphous ionically conductive solid electrolyte; and
(d) curing the at least one impregnated pellet to yield the composite electrode.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0018] The foregoing summary, as well as the following detailed description of the invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there are shown in the drawings embodiments which are presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown.
[0019] In the drawings:
[0020] Fig. 1 is an SEM image of the surface of a sintered porous cathode material according to an embodiment of the invention;
[0021] Fig. 2 is an SEM image of a cross section of a sintered porous cathode material according to an embodiment of the invention;
[0022] Fig. 3 is an SEM image of a cross section of a cathode filled with LLZO solid electrolyte according to an embodiment of the invention;
[0023] Fig. 4 is a Nyquist plot of a cured amorphous LLZO film prepared from a 25% condensed LLZO precursor solution;
[0024] Fig. 5 is a Nyquist plot of a cured amorphous LLZO film prepared from a 50% condensed LLZO precursor solution;
[0025] Fig. 6 is a Nyquist plot of a cured amorphous LLZO film prepared from a 75% condensed LLZO precursor solution;
[0026] Fig. 7 is a graph of ionic conductivity of amorphous LLZO films as a function of concentration level of their precursor solution; and
[0027] Fig. 8 is a Nyquist plot of a cured amorphous LLZO film prepared from a 75% LLZO condensed precursor solution condensed in ozone.
DETAILED DESCRIPTION OF THE INVENTION
[0028] This invention is directed to a process for producing an impregnated, sintered composite cathode, such as for use in an all solid state battery, the cathode produced by the process, and a solid state battery containing the cathode. The process for producing the cathode involves four basic steps: preparing pellets from an active (intercalation) cathode material, sintering the pellets at high temperature to form a sintered porous cathode pellet structure, impregnating the pores with a liquid precursor of an inorganic amorphous ionically conductive solid electrolyte, and drying and curing the impregnated material to convert the precursor into an inorganic amorphous solid electrolyte and yield the composite cathode. Each of these process steps will be described in more detail below.
[0029] The hereby disclosed invention and process apply particularly to oxide electrodes in lithium and lithium ion batteries which are mostly applied as cathodes, although there are examples of oxide anodes, such as lithium titanium oxide (LTO). Thus, for the purposes of this disclosure, the term "cathode" may be understood to refer not only to a cathode per se, but also to any active oxide electrode, even if it is used as an anode in a battery due to its low voltage. Additionally, although lithium batteries contain an anode made of pure lithium and lithium ion batteries contain an anode made of lithium-containing material, the terms "lithium battery" and "lithium ion battery" are used interchangeably in this disclosure.
Pellets from Active Cathode Powder
[0030] The first step in the method for producing the composite cathode involves preparing pellets from an active (intercalation) cathode material, such as an active powder. For forming a cathode, the active cathode powder for use in the invention is preferably LiMni/3 ii 3Coi 30 2 ("NCM"), which is commercially available, such as from Pred Materials International (New York, NY). Other oxide active intercalation material powders known in the art, such as LiCo0 2, or to be developed for use in lithium or lithium ion batteries would also be appropriate.
[0031] Active intercalation materials, particularly those used in cathodes of lithium or lithium ion batteries, are generally electronically conductive, including the preferred NCM and LiCo0 2.
However, other oxide electrode materials may also be used to form a composite solid state electrode according to the invention. For example, LTO is an oxide intercalation material that is generally considered to be an anode material due to its low voltage. Because LTO is not electronically conductive, an electronically conductive material, such as silver, should be added to LTO to form the sintered composite structure. It is also within the scope of the invention to add silver (or another suitable electronically conductive material) to the active intercalation material prior to sintering, even if it is electronically conductive, to enhance the electronic conductivity of the composite all solid state structure.
[0032] To form the pellets, a slurry is first prepared by mixing the cathode powder with solvents, such as xylene and ethanol, binder(s), such as polyvinyl butyral (PVB), and/or plasticizer(s), such as butyl benzyl phthalate. A preferred mixture contains about 150 g of active cathode powder, about 30 g of xylene, about 30 g of ethanol, about 7 g of PVB, and about 3.5 g of butyl benzyl phthalate. Other solvent, binder and plasticizer materials may be used in different material proportions provided that they form a slurry whose properties, such as viscosity, are suitable for tape casting as described in "Tape Casting: Theory and Practice" (R. E. Mistier and E.R. Twiname (Wiley-ACS, 2000)), which is herein incorporated by reference.
[0033] The combination of powder, solvents, binder(s), and/or plasticizer(s) is mixed thoroughly, such as by ball milling, to form a homogeneous slurry, then cast into a sheet by tape casting on a standard flat casting table. The method of tape casting is well known in the art and need not be described. Appropriate conditions for the tape casting are known in the art or may be determined by routine experimentation.
[0034] The resulting sheet is then dried, such as for about two hours at room temperature, and rolled. In order to obtain uniformity and desired density, the sheet is folded and calendered (compacted), such as between rollers, to the desired thickness, preferably about 6 mil (150 microns), but generally in the approximate range of about 40 to 500 microns. The resulting uniform sheet is then punched into pellets of a desired size and heated to remove the organic components. For example, the sheet may be punched into pellets of about 3/4" diameter using a round puncher and heated at about 400[deg.]C in air for about two hours in order to remove the organic components from the pellets. These pellet diameters and heating conditions are merely exemplary, and other pellet diameters, shapes, thicknesses, techniques for compacting the sheet, punching the pellets, and heating protocols to remove the organics are also within the scope of the invention. Additionally, it is also within the scope of the invention to prepare cathode shapes other than pellets, such as sheets, wafers, or other shapes, provided that such shapes will function as desired, such as in a battery. If the composite cathode is desired in sheet or wafer form, it is not necessary to punch pellets from the sheet as previously described. Rather, the whole sheet itself may be sintered, as described below, to form the cathode. Accordingly, the description herein of pellets may be understood to encompass other cathode shapes as well.
Sintering of Pellets
[0035] The pellets prepared from the active cathode powder are next sintered at a high temperature of about 800-1100[deg.]C, preferably about 900[deg.]C, in either oxygen or air, for about ten minutes to about twelve hours, preferably about one hour, to produce a self supporting porous cathode pellet structure. The sintering process (time and temperature profiles) is controlled so that the resulting structure will have sufficient porosity to allow for impregnation with the electrolyte solution. [0036] The sintered porous pellet structure has good cathode powder particle-to-particle contact because the particles merge during sintering. The cathode pellet also forms electronically conductive pathways because the active cathode materials are usually electronic conductors. If a particular oxide electrode material is not an electronic conductor (such as LTO), a suitable electronically conductive additive (silver, for example) may be added to the slurry to form the electronically conductive pathways in the sintered pellets.
[0037] Another notable feature of the sintered cathode pellet is that it is very uniform due to the tape casting method and the calendering process. This uniformity provides a good structure to fill with electrolyte in the subsequent step and yield an excellent composite high access cathode. SEM images of the surface and cross section structure of an exemplary sintered cathode material are shown in Figs. 1 and 2, respectively, which clearly show the uniformity of the porous structure. The typical density of the sintered cathode pellet without solid electrolyte is estimated from SEM images of its surface and cross section to be about 60%. However, the porosity may be greater or less than this amount and this density (porosity) is exemplary, not limiting.
Impregnation of Porous Pellet Structure
[0038] For an all solid state lithium or lithium ion battery to have high access, capacity, and energy density, it must have effective pathways for the lithium ions and electrons to move throughout the body of the cathode during charge and discharge of the battery. As previously explained, the sintered porous pellets have effective electron pathways. In order to provide effective ionic pathways in the body of the cathode pellet of an all solid state battery, it is necessary to fill the pores of the pellet with a solid inorganic electrolyte.
[0039] Thus, the next step in the method involves filling the pores in the sintered pellet with a liquid precursor solution of an inorganic amorphous ionically conductive solid electrolyte to form ionic pathways. Preferred solid electrolytes for use in the invention are amorphous lithium lanthanum zirconium oxide (LLZO), lithium carbon lanthanum zirconium oxide (LCLZO), and lithium lanthanum titanium oxide (LLTO). LLZO and LCLZO are described in United States Patent Application Publications Nos. 2011/0053001 and 2012/0196189, the disclosures of which are herein incorporated by reference in their entirety. These application publications will hereinafter be referred to as "the '001 publication" and "the [Iota]89 publication," respectively. For the purposes of this disclosure, the term "LLZO" may be understood to refer to LLZO and/or LCLZO. It is also within the scope of the invention to utilize alternative amorphous inorganic ionically conductive materials instead of or in addition to the LLZO. Other preferred materials are also amorphous, oxide-based compounds. For example, appropriate amorphous inorganic materials are those in which one or more of the elements in LLZO has been partially or completely replaced by a different element, such as replacing zirconium with tantalum. Such alternative materials are also described in the '001 and [Iota] 89 application publications and all of the materials described therein are also within the scope of the invention.
[0040] The process of inserting an inorganic solid electrolyte into the pores of the sintered pellets begins by impregnating the cathode pores with an inorganic solid electrolyte precursor solution and then curing the solution to form the solid inorganic electrolyte. This process has its challenges. A main challenge is due to surface tension of the electrolyte precursor solution. The surface tension controls the wetting of the cathode surface by the precursor solution ,which is necessary to fully impregnate the cathode pores. It has been found that the surface tension of the preferred LLZO precursor solution is adequate for wetting the porous sintered cathode pores.
Another challenge is due to high shrinkage of the electrolyte precursor when forming the solid inorganic electrolyte.
[0041] According to an embodiment of the invention, the pores of the sintered porous cathode are first evacuated to remove all of the air, such as, for example, with a small vacuum pump. The pores are then impregnated with a precursor solution for the inorganic solid amorphous electrolyte. For example, appropriate precursor solutions for LLZO and LCLZO are described in detail in U.S. Patent Application Publications Nos. 201 1/0053001 and 2012/0196189. In a preferred embodiment, the solution contains a lanthanum alkoxide, a lithium alkoxide, and a zirconium alkoxide dissolved in a solvent, such as an alcohol. Preferred precursors include lithium butoxide, lanthanum methoxyethoxide, and zirconium butoxide, and a preferred solvent is methoxyethanol. These precursor components are exemplary, not limiting, and alternative precursor solutions are also within the scope of the invention, provided that they contain the required lithium, lanthanum, zirconium, and oxygen components in appropriate concentrations. It is also within the scope of the invention to prepare more than one solution, such as three solutions each containing one of the desired lithium, lanthanum, or zirconium components. If an amorphous material other than or in addition to LLZO/LCLZO is to be contained in the final cathode, the appropriate precursor solution(s) should contain the desired components in appropriate concentrations.
[0042] Appropriate precursor solutions for LLTO, another preferred electrolyte, are described in detail in U.S. Patent No. 8,21 1 ,496, the disclosure of which is herein incorporated by reference in its entirety. These precursor solutions are exemplary, not limiting, and even the preferred LLZO and LCLZO may be applied from alternative precursor solutions, provided that they contain the required lithium, lanthanum, zirconium, and oxygen components in appropriate concentrations.
Impregnation is preferably performed by casting the solution over the surface of the pellet, so that the solution impregnates the evacuated pores by capillary action.
[0043] It has been found that the preferred LLZO precursor solution, which is prepared from commercially available metal precursors, some of which (such as lanthanum methoxyethoxide and zirconium butoxide) are obtained in solution, exhibits high volume shrinkage of about 90% when cured to form an amorphous solid LLZO electrolyte. This high shrinkage is inconvenient because it requires many impregnation cycles of the pores with the precursor solution in order to reach an adequate level of pore filling, defined by formation of fast lithium ion conductive pathways through the amorphous solid electrolyte that is present in the pores. It has been found that a number of the impregnation steps may be eliminated by utilizing a condensed (concentrated) precursor solution (containing less solvent than the original precursor solution but the same amounts of the other components) that shrinks less during the curing process than the dilute solution. If the precursor solution for the solid electrolyte is prepared in more concentrated form, it is not necessary to perform such a condensation step.
[0044] Condensation of the precursor solution may be accomplished by heating a dilute precursor solution, such as the LLZO precursor solution previously described, in an inert environment, such as nitrogen or argon. A preferred heating temperature is about 80[deg.]C, although it may vary in a wide range from about room temperature to about 100[deg.]C.
[0045] High ionic conductivity of the amorphous electrolyte is necessary for its successful application in a lithium ion battery. The ionic conductivity of amorphous LLZO/LCLZO samples prepared from condensed precursor solutions having different condensation levels was measured in order to determine the optimal condensation level.
[0046] It was found that condensing the LLZO precursor solution in ozone maintains the high ionic conductivity, allowing for the use of a more concentrated solution to fill the pores of the cathode and reducing the number of impregnations necessary to achieve the desired ionic conductivity levels. Consequently, if the precursor solution is determined to be too dilute (resulting from the fact that the desired precursors are commercially obtained in solution), the precursor solution is preferably condensed prior to impregnation into the pores of the sintered cathode. If the LLZO precursor solution described previously is utilized, it is preferably condensed by about 25% to about 50%. However, it is preferred to prepare a more concentrated precursor solution so that the condensation process is not required, yet high conductivity and low shrinkage can still be achieved. [0047] The SEM image of a cathode partially filled with solid LLZO electrolyte is shown in Fig. 3. It can be seen that the amorphous solid electrolyte partially fills the pores or coats the NCM sintered particles, based on the amorphous material seen in the image, forming continuous pathways for lithium ions. It is not necessary to completely fill the pores with solid electrolyte; the pores only need to be partially filled to establish the desired high conductivity.
Curing the Electrolyte
[0048] The final step in the process of producing an impregnated sintered composite solid state cathode involves curing the liquid precursor solution of the inorganic amorphous solid electrolyte by drying and heating the impregnated pellets. For example, drying and heating may be effected by maintaining the samples in an ozone-rich and low humidity air environment for about one hour followed by heating at approximately 70 to 130[deg.]C, more preferably about 75 to 90[deg.]C, most preferably about 80[deg.]C for about 30 minutes, preferably in an ozone-rich air and low humidity environment, followed by heating at approximately 280 to 350[deg.]C, more preferably about 300-310[deg.]C for about 30 minutes in low-humidity air. The specific drying and heating times and temperatures may be varied, but are preferably performed at no higher than about 350[deg.]C. Importantly, the lower temperature curing is performed in an ozone-rich (preferably containing at least about 0.05 ppm ozone) and low humidity (preferably less than about 30 percent relative humidity) environment, and the higher temperature heating is performed in low humidity air. The resulting composite solid state cathode containing impregnated amorphous solid electrolyte may be used to form a solid state battery, but is not limited to this application.
[0049] As previously explained, the method for producing an impregnated sintered composite solid state cathode may also be used to produce any other electrode in which the active material operates by intercalation and can be sintered. For example, lithium titanium oxide (LTO) is an intercalation oxide that can be sintered, and the above described impregnation and curing steps may be used to form a functional electrode from a sintered LTO pellet. The LTO electrode is used as an anode in a battery due to its low voltage, although in every other way it is and behaves as a cathode.
Composite Solid State Cathode
[0050] The invention is also directed to an impregnated sintered solid-state composite cathode, such as for an all solid state battery. The composite cathode contains a sintered active intercalation material having pores impregnated with an inorganic ionically conductive amorphous solid electrolyte. The active intercalation material is sintered in the form of a compact porous structure and is preferably in the form of sintered pellets prepared from an active cathode powder, as previously described. However, the invention is not limited to composite cathodes in the shape of pellets. Rather, it is also within the scope of the invention for the composite cathode to be the shape of a sheet, wafer, or any other shape, provided that it contains the desired components and will function as desired, such as in a battery.
[0051] Active intercalation materials, particularly those used in cathodes of lithium or lithium ion batteries, are generally electronically conductive. However, other oxide electrode materials may also be used to form a composite solid state electrode according to the invention. For example, LTO is an oxide intercalation material that is generally considered to be an anode material due to its low voltage. Because LTO is not electronically conductive, an electronically conductive material, such as silver, must be added to LTO to form the sintered structure. It is also within the scope of the invention to add silver (or another suitable electronically conductive material) to the active intercalation material even if it is electronically conductive to enhance the electronic conductivity of the composite all solid state structure.
[0052] The inorganic amorphous solid electrolyte in the solid state cathode is most preferably amorphous solid LLZO and/or LCLZO, as previously described. Preferably, the inorganic amorphous solid electrolyte is impregnated into the pores of the sintered cathode as a liquid precursor solution and then subjected to a thermal drying and curing process to convert the precursor solution into the amorphous solid electrolyte. Although LLZO and LCLZO are most preferred, it is also within the scope of the invention to utilize other inorganic ionically conductive materials, provided that they can be impregnated into the pores of the cathode as a liquid and then solidified after a relatively low temperature curing process. For example, a mixed electronic/ionic conductor, such as amorphous LLTO, may also be used to impregnate the electrode pores in another preferred embodiment. Other preferred amoiphous inorganic materials are oxide-based materials. Further, other appropriate amorphous inorganic materials are those in which one or more of the elements in LLZO has been partially or completely replaced by a different element, such as replacing zirconium with tantalum. Such alternative materials are also described in the '001 and ' 189 application publications and all of the materials described therein are also within the scope of the invention. [0053] As previously explained, the invention is also directed to other solid state composite electrodes, such as anodes, which have the same structure as described above with respect to the cathode. In particular, an LTO electrode having an impregnated sintered structure is also included in the invention. [0054] The cathodes and low voltage oxide electrodes according to the invention thus fulfill a need in the art for improved, low cost, high access electrodes, which may be used in the production of all solid state batteries. Solid State Battery
[0055] Finally, the invention is directed to a solid state lithium or lithium ion battery comprising an impregnated sintered composite solid state cathode, an anode, and a separator, in which the composite solid state cathode is as described previously. The separator may be any solid electrolyte known in the art or to be developed, such as UPON, crystalline LLZO, amorphous LLZO, etc. The anode may be any anode material known in the art or to be developed, such as lithium metal, alloys thereof, and LTO. Methods for depositing the solid electrolyte separator and anode materials on top of a solid cathode are well known in the art and need not be described. Methods for producing solid state batteries from cathode, anode, and separator components are also well known in the art and also need not be described.
[0056] Additionally, the invention is directed to a solid state lithium or lithium ion battery comprising an impregnated sintered composite solid state anode, a cathode, and a separator, in which the composite solid state anode is as described previously. In other words, a solid state lithium or lithium ion battery according to an embodiment of the invention comprises an impregnated sintered composite state electrode as described previously, a lithium-containing counter electrode, and a separator.
[0057] The invention addresses problems with prior art electrodes by providing a freestanding high-access cathode structure with thickness of 1 [Omicron][Omicron][mu][eta][iota] or greater, if desired. The invention also overcomes disadvantages of prior art electrodes with regard to low energy density and access of the cathode, thus improving capacity and rate capability of the resulting battery. Specifically, enhancing access of the cathode by providing ionic and electronic pathways for lithium ions and electrons to travel during the charge and discharge processes is achieved by filling the pores of a highly electronically conductive cathode with a highly ionically conductive material, such as amorphous LLZO. This is effectively achieved by concentrating an electrolyte precursor solution, such that shrinkage after curing is much less than a regular unconcentrated precursor solution of the material.
[0058] Another problem addressed by the present invention is that of solid-state reactions when sintering the cathode material and the solid electrolyte. This problem is resolved by first sintering the cathode to obtain excellent electronic conductivity, and then filling the pores of the sintered cathode with a liquid precursor solution of the amorphous solid electrolyte, which cures in the pores to form the solid amorphous electrolyte and the composite solid state structure. By this method, a safe solid state cathode having higher access, capacity and energy density compared to currently available cathodes is obtained. The invention also provides low voltage cathodes, such as LTO, which may be used as anodes in solid state batteries.
[0059] The current invention is thus an improvement on both liquid electrolyte and thin film batteries whereby a novel freestanding cathode, between about 50 and 400[mu][eta][iota] thick, is fabricated with enhanced safety, access, capacity and energy density by a low-cost process.
[0060] This invention will now be described in connection with the following, non-limiting examples.
EXAMPLE 1 : Preparation of Cathode Pellet
[0061] A slurry was prepared from 150 g of cathode powder (NCM), obtained from Pred Materials International (New York, NY), about 30 g of xylene, about 30 g of ethanol, about 7 g of PVB, and about 3.5 g of butyl benzyl phthalate. The combination of powder, solvents, binder(s), and plasticizer(s) was mixed thoroughly by ball milling to form a homogeneous slurry, then cast into a sheet by tape casting on a standard flat casting table.
[0062] The resulting sheet was dried for about two hours at room temperature, folded, and calendered (compacted) between rollers using a roller-compactor apparatus to the desired thickness of about 6 mil (150 microns). The resulting uniform sheet was then punched into pellets of about 3/4" diameter using a round puncher and heated at about 400[deg.]C in air for about two hours in order to remove the organic components from the pellets. The pellets were then sintered at 900[deg.]C in oxygen for about one hour to produce a self supporting porous cathode pellet structure. SEM images of the sintered porous pellets are shown in Figs. 1 and 2.
[0063] A LLZO sol gel precursor solution was prepared by dissolving about 9 grams of a lanthanum methoxyethoxide solution (about 12% by weight in methoxyethanol), about 1.3 grams of lithium butoxide and about 1.54 gram of a zirconium butoxide solution (about 80% by weight in butanol) in about 10 grams of methoxyethanol. The precursor components were obtained from either Gelest or Alfa Aesar. The thoroughly-mixed precursor solution was left in a bottle in an inert environment for about 1 to 1.5 hours to help facilitate substantially complete dissolution of the lithium butoxide. The solution was then condensed to 75%o condensed precursor solution by heating at 80[deg.]C for about 3 hours. [0064] The pores of the sintered porous cathode were evacuated with a small vacuum pump to remove the air, then impregnated with the LLZO precursor solution by casting the solution over the surface of the pellets, so that the solution impregnated the evacuated pores by capillary action.
[0065] Finally, the precursor solution was dried and cured by maintaining the impregnated pellets in an ozone-rich (at least 0.05 ppm) and low humidity (less than about 30%) air environment for about 1 hour, heating at approximately 80[deg.]C for about 30 minutes in an ozone-rich air and low humidity environment, followed by heating at approximately 300[deg.]C for about 30 minutes in air. The SEM image of a cross section of an LLZO impregnated sintered pellet is shown in Fig. 3. EXAMPLE 2: Comparison of Precursor Solution Concentration
[0066] Measurements were performed by spin coating differently condensed precursor solutions onto glass substrates with conductive aluminum strips. After curing of the spin-coated layers by the regular LLZO curing process, a second layer of gold contacts was sputtered on top.
[0067] The impedance of the resulting amorphous LLZO films was measured using an electrochemical impedance spectroscopy (EIS) instrument. The EIS data for the amorphous LLZO films prepared from 25%, 50% and 75% condensed precursor solutions (75% represents the highest concentration) are shown in Figs. 4, 5 and 6, respectively. The resistance used to calculate the conductivity of the LLZO films is taken at the high frequency real axis intercept of the Nyquist plot, which is more clearly shown in the inset of the graphs. Using this resistance and the thickness and the geometry of the sample, the conductivity may be estimated. Fig. 7 is a graph of the conductivity of the amorphous films for the three concentration levels of the precursor solutions as a function of concentration. It can be seen that the ionic conductivity decreases as the concentration level increases, although it did not change drastically from the 25% to the 50% condensed solution (6E-4 S/cm vs. 5E-4 S/cm). The conductivities of the 25% and 50% condensed solutions are both adequate for use in all solid state lithium batteries.
[0068] As described in U.S. Patent Application Publication No. 2011/0053001 , the amorphous solid LLZO drying and gelling environment is controlled by relative humidity, ambient temperature, and ozone level. Accordingly, the influence of ozone on the LLZO precursor solution condensation process was tested to ensure mutual compatibility. Fig. 8 shows the Nyquist plot for an amorphous LLZO film prepared from a 75% condensed precursor solution that was condensed in an ozone rich environment (at least 0.05 ppm).
[0069] It was found that the ionic conductivity of this amorphous LLZO material was 5.9E-4 S/cm, which is essentially the same as for the film prepared from the 25% condensed solution. [0070] It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims.
AMORPHOUS IONICALLY-CONDUCTIVE METAL
OXIDES, METHOD OF PREPARATION, AND BATTERY
WO2013085557
WO2013085557
A method for forming an amorphous ionically conductive metal oxide, such as lithium lanthanum zirconium oxide (LLZO), by chemical vapor deposition (CVD), as well as to the ionically conductive material formed by the method, are provided. Such a material may be utilized as a solid electrolyte and/or as a solid separator in an all solid state lithium battery.
BACKGROUND OF THE INVENTION
[0003] This invention relates to a method for forming an amorphous ionically conductive metal oxide, such as lithium lanthanum zirconium oxide (LLZO), by chemical vapor deposition (CVD), as well as to the ionically conductive material formed by the method. Such a material may be utilized as a solid electrolyte and/or a solid separator in an all solid state, or ceramic, battery cell.
[0004] A battery cell is a particularly useful article that provides stored electrical energy that can be used to energize a multitude of devices, particularly portable devices that require an electrical power source. A battery cell, which is often referred to in an abbreviated form as a "battery," is an electrochemical apparatus typically formed of at least one electrolyte (also referred to as an "electrolytic conductor") disposed between a pair of spaced apart electrodes. Upon completion of a circuit between the electrodes, the battery discharges electrical current as ions flow from a negative electrode (anode) to a positive electrode (cathode).
[0005] Rechargeable batteries, also known as secondary batteries, are useful because the energy available for discharge can be replenished by reversing the flow of current between the electrodes such that ions flow from the positive cathode to the negative anode. The type of electrolyte used in rechargeable batteries is important. It is desirable to utilize an electrolyte that promotes optimum transport of ions but that is compatible with the electrode materials and does not adversely affect performance over time or contribute to safety issues. For example, lithium is a desirable anode material because it possesses high energy density. However, the use of lithium as an anode material has presented problems because many materials that are otherwise very effective as electrolytes react adversely with lithium. As another example, many ionically-conductive liquids are effective for ion transport but contribute to diminished performance over time and safety issues.
[0006] In the context of the present invention, all solid state batteries are batteries that contain solid electrodes and solid inorganic electrolytes. All solid state lithium and lithium-ion batteries typically contain at least three major components: (1) a cathode, normally made of transition metal oxide powder (such as lithium cobalt oxide, lithium manganese oxide, or lithium manganese nickel cobalt oxide). The cathode material may be sintered to achieve the required electronic conductivity and structural integrity or it may be mixed with carbon or graphite powder to provide electronic conductivity and act as a binder for structural integrity, (2) an anode, made of Li, a Li alloy, or another material capable of intercalating lithium, such as carbon, silicon, lithium titanium oxide, etc., and (3) a solid electrolyte that also serves as a separator between the cathode and anode.
Although lithium batteries contain an anode made of pure lithium and lithium ion batteries contain an anode made of lithium-containing material, the terms "lithium battery" and "lithium ion battery" are used interchangeably in this disclosure.
[0007] The solid electrolyte is a key element in an all solid state lithium or lithium ion battery. For optimal battery performance, the solid electrolyte should have high Li ion conductivity but negligible electronic conductivity, have long term chemical stability against chemical reactions with metallic lithium, and have high voltage stability (higher than 5.5V). (See, for example, Kotobuki et al; J.Electrochem. Soc. 157, A1076- 1079 (2010)). Using a solid electrolyte in a lithium battery eliminates the formation of a solid electrolyte interphase (SEI) layer between Li metal and liquid electrolyte. In liquid electrolyte systems, a SEI film forms during the first electrochemical charge due to the electrochemical reduction of species present in the electrolyte. (See Xu Kang, Chem. Rev, 104, 4303-4417 (2004)). Its formation causes irreversible battery capacity loss associated with the active lithium consumption during the initial SEI layer formation. Additional SEI layer growth in subsequent charge-discharge cycles further lowers the battery capacity by irreversible depletion of the active lithium, also limiting the cycle life of the battery. Accordingly, utilizing a solid electrolyte in an all solid state battery will allow a battery to reach high energy density and utilize metallic lithium anode without detriment to the battery operation. In addition, using an inorganic oxide as an electrolyte prevents loss of oxygen from the cathode materials at high charge voltages, thereby increasing the stability of the cathode and improving the cycle life of the battery.
[0008] Different types of materials have been reported as Li-ion conducting materials, including Li3N, Li-P-alumina, LiSi04, L13PO4, LiSICON (lithium superionic conductors, e.g., Lii4Z Ge40i6), lithium phosphorus oxynitride (LiPON), lanthanum lithium titanate (LLTO), lithium titanium phosphate (LTP), lithium aluminum germanium phosphate (LAGP), and garnet-like crystalline structure compounds having the formula LisLa3M20i2 (M=Nb, Ta) or Li7La3Zr20i2. (See Ramzy et al.; Applied Materials & Interfaces 2, 385-390 (2010)). A limitation of the reported compounds is that they have either high ionic conductivity or high electrochemical stability, but not both.
[0009] Crystalline Li7La3Zr20i2 (cLLZ) has been recently reported as a new type of garnet-like structure with high lithium-ion conductivity and stability with lithium metal. (See Murugan et al.; Ang w. Chem. Int. Ed. 46, 7778-7781 (2007) and Kokal et al.; Solid State Ionics, 185, 42-46 (201 1)). This powder material has been synthesized by a solid-state reaction or sol-gel high temperature synthesis and sintered into a pellet for characterization, reportedly having high ionic conductivity in the 10<"4> to 10<"3> S/cm range. cLLZ has also been reported to be stable with molten lithium and when exposed to air and moisture. Thus, it appears that cLLZ satisfied all the major criteria for a lithium ion solid electrolyte. However, in an attempt to cycle a LiCo02/cLLZ/Li cell, the discharge capacity was very low, much lower than expected based on the quantity of LiCo02 cathode involved, which was mostly attributed to the high interfacial resistance between the cLLZ pellet and electrodes. A study of the interface between LiCo02 and cLLZ revealed the formation of a thick intermediate layer of La2Co04 at the <?LLZ/LiCo02 interface that was believed to be created by a mutual diffusion of elements during deposition and processing at 700[deg.]C (Kim et al.; J. of Power Sources, 196, 764-767 (201 1)). This diffusion layer undergoes further changes during electrochemical charge-discharge cycles and severely limits the performance of the solid state battery. Thus, lowering the deposition temperature can substantially decrease or eliminate the diffusion process and lower the interface resistance.
[0010] U.S. Patent Application Publication No. 201 1/0053001 of Babic et al. describes a novel lithium ionic conductor material, amorphous lithium lanthanum zirconium oxide (aLLZO), which exhibits high ionic conductivity (~10<"3> S/cm), high transport number (~1), is stable with metallic lithium, and has a high voltage stability window (up to 10V). The aLLZO film taught in the '001 publication is prepared from a sol-gel process, yielding crack-free and precipitate-free sol gel aLLZO films with a smooth surface. However, some pinholes can occur during film nucleation and could propagate without filling in as the layer thickness increases. Since even a single remaining pinhole may result in the failure of a cell, a second continuous layer of solid electrolyte may be applied. For example, a thin layer of lithium phosphorus oxynitride (LiPON) (2 [mu][eta][iota]) may be used to fill the pores in electrolyte films. However, such films require expensive vacuum equipment for sputtering and are unstable in air (Nimisha et al., Solid State Ionics 185, 47-51 (201 1)), making sample handling and transferring during manufacturing very complicated and expensive.
[0011] Thus, alternative solid electrolyte materials for high performance all solid state batteries are desirable. Such materials would desirably provide a high level of ion transport, be defect free, and be effective for charge and discharge but not interact adversely with lithium, adversely affect performance over time, or contribute to safety issues.
BRIEF SUMMARY OF THE INVENTION
[0012] A method is provided for synthesizing an amorphous ionically conductive metal oxide having formula MwM'xM"yM" 'zCa, wherein
M is at least one alkali metal;
M' is at least one metal selected from the group consisting of lanthanides, barium, strontium, calcium, indium, magnesium, yttrium, scandium, chromium, aluminum, and alkali metals, provided that when M' is an alkali metal, M' further contains at least one non-alkali M' metal;
M" is at least one metal selected from the group consisting of zirconium, tantalum, niobium, antimony, tin, hafnium, bismuth, tungsten, silicon, selenium, gallium and germanium;
M' ' ' comprises oxygen and optionally at least one element selected from the group consisting of sulfur and halogens; and
w, x, y, and z are positive numbers, including various combinations of integers and fractions or decimals, and "a" may be zero or a positive number. The method comprises:
(a) introducing a precursor mixture comprising at least one reactant gas and at least one precursor material for each of M, M', and M" into a CVD reactor chamber;
(b) providing a substrate in the CVD chamber; and
(c) energizing the CVD reactor such that the amorphous ionically conductive metal oxide is deposited on the substrate.
[0013] An amorphous ionically conductive metal oxide material according to the invention has formula MwM'xM"yM' "zCa, wherein
M is at least one alkali metal;
M' is at least one metal selected from the group consisting of lanthanides, barium, strontium, calcium, indium, magnesium, yttrium, scandium, chromium, aluminum, and alkali metals, provided that when M' is an alkali metal, M' further contains a non-alkali M' metal;
M' ' is at least one metal selected from the group consisting of zirconium, tantalum, niobium, antimony, tin, hafnium, bismuth, tungsten, silicon, selenium, gallium and germanium;
M' " comprises oxygen and optionally at least one element selected from the group consisting of sulfur and halogens; and w, x, y, and z are positive numbers, including various combinations of integers and fractions or decimals, and "a" may be zero or a positive number. The metal oxide is prepared by a method comprising:
(a) introducing a precursor mixture comprising at least one reactant gas and at least one precursor material for each of , M', and M" into a CVD reactor chamber;
(b) providing a substrate in the CVD chamber; and
(c) energizing the CVD reactor such that the amorphous ionically conductive metal oxide is deposited on the substrate.
[0014] A solid state battery according to the invention comprises an anode, a cathode, and a solid electrolyte or solid separator comprising the amorphous ionically conductive metal oxide described previously.
RECHARGEABLE LITHIUM AIR BATTERY
HAVING ORGANOSILICON-CONTAINING ELECTROLYTE
US2013130131
US2013130131
A rechargeable lithium air battery comprises a non-aqueous electrolyte disposed between a spaced-apart pair of a lithium anode and an air cathode. The electrolyte includes including a lithium salt and an additive containing an alkylene group or a lithium salt and an organosilicon compound. The alkylene additive may be alkylene carbonate, alkylene siloxane, or a combination of alkylene carbonate and alkylene siloxane. The alkylene carbonate may be vinylene carbonate, butylene carbonate, or a combination of vinylene carbonate and butylene carbonate. The alkylene siloxane may be a polymerizable silane such as triacetoxyvinylsilane. In preferred embodiments, the organosilicon compound is a silane containing polyethyleneoxide side chain(s).
BACKGROUND OF THE INVENTION
[0002] A battery cell is a particularly useful article that provides stored electrical energy which can be used to energize a multitude of devices requiring an electrical power source. A battery cell, which is often referred to, somewhat inaccurately, in an abbreviated form as a "battery," is an electrochemical apparatus typically formed of at least one electrolyte (also referred to as an "electrolytic conductor") disposed between a pair of spaced apart electrodes. The electrodes and electrolyte are the reactants for a chemical reaction that causes an electric current to flow between the electrodes when the electrode ends that are not in contact with the electrolyte are connected to one another through an object or device (generally referred to as the "load") to be powered. The flow of electrons through the free ends of the electrodes is accompanied and caused by the creation and flow of ions in and through the electrolyte under a reaction potential between the electrodes.
[0003] In a non-rechargeable battery cell, the chemical reaction that produces the flow of electric current also causes one or more of the reactants to be consumed or degraded over time as the cell discharges, thereby depleting the cell. In contrast, in a rechargeable battery cell, after the cell has partially or fully discharged its electrical potential, the chemical reaction may be reversed by applying an electric current to the cell that causes electrons to flow in an opposite direction between the electrodes and an associated flow of ions. Thus, it can be appreciated that rechargeable battery cells are extremely useful as a source of electrical power that can be replenished.
[0004] A problem in utilizing rechargeable batteries is that it is often difficult to return the reactants to their original, pre-use state, that is, the pristine or ideal (or as close as possible) condition that the reactants are in before the cell is used. This problem relates to specific problems associated with returning each individual reactant to its original state.
[0005] Lithium air batteries are attractive batteries because they provide high energy density from easily-obtainable and inexpensive electrode reactant materials, namely, lithium and air. In a lithium air battery, lithium serves as the anode and the cathode is formed of a light-weight, inexpensive substrate that is capable of supporting a catalyst for facilitating oxygen's role as a reactant.
[0006] A problem with rechargeable lithium air batteries is that they are particularly difficult to recharge multiple times due to the characteristics of lithium. Specifically, it is often difficult to return the lithium anode to its pre-discharge condition because of imperfections formed on the surface of the anode during the discharge-recharge cycling. Imperfection problems include a roughening of the surface of the anode and the formation of pores in the anode. Another serious imperfection problem is that the surface of the lithium anode that is in contact with the electrolyte may be degraded by the formation of dendrites. Dendrites are thin protuberances that can grow upon and outwardly of a surface of an electrode during recharging of the cell. Recharging causes a re-plating of the lithium anode. Not only do dendrites inhibit proper plating or re-plating of the electrode, but also, one or more branches of dendrites may grow long enough so as to extend through the electrolyte between the anode and cathode and thereby provide a direct connection that can electrically short circuit the cell. An electrical short is undesirable in and of itself but, in addition, the current passing through an electrical short may cause the temperature through the electrolyte to increase to a point wherein the electrolyte is no longer effective and/or the electrolyte and/or the cell itself may ignite. Thus, known lithium air batteries have a very limited useful life. It can thus be appreciated that it would be useful to develop a rechargeable lithium air battery cell that can be discharged and recharged effectively many times.
[0007] A concern in recharging a rechargeable battery is how much electrical energy will be required to restore the battery to its pre-discharged state and potential. This level of electrical is typically greater than the electrical energy initially provided by the battery. However, it is desirable that the electrical energy required to recharge a rechargeable battery be minimized so as to reduce the cost of operation and to prevent damage to the battery. Thus, it can be appreciated that it would be useful to develop a rechargeable lithium air battery in which the voltage level and amount of energy required to recharge the battery are minimized. The excess energy required during recharge is associated with a difficulty in reversing the reactions that take place in an air cathode. Reactions in the cathode are plagued with parasitic reactions involving the electrolyte. These reactions can consume the electrolyte and cause degradations in performance. Therefore, a more stable electrolyte is needed.
[0008] Most battery systems developed to date are based on aqueous-based alkaline electrolytes. A popular example is the zinc/oxygen battery that is in commercial use for hearing aids. Electric Fuel Corp. produces primary zinc air batteries for cellular phone applications. Electrically rechargeable zinc air batteries use bifunctional oxygen electrodes so that both the charge and discharge processes take place within the battery structure. AER Energy Resources, Inc. (Atlanta, Ga.) designed an electrically rechargeable zinc air cell; however, the cyclability of this battery is too low to satisfy the requirements of many commercial applications.
[0009] In recent years, there has been a renewed interest in the development of lithium oxygen batteries. To overcome water corrosion problems, non-aqueous electrolytes typically used in lithium and lithium ion batteries have been utilized. For example, U.S. Pat. No. 5,510,209 describes a lithium oxygen battery based on an organic electrolyte using carbon powder as an air electrode and cobalt phthalocyanine as a catalyst. The battery was shown to have an open-circuit potential of approximately 3V and an operating voltage between 2.0 to 2.8V.
[0010] Although the '209 patent suggests that the lithium/oxygen batteries were rechargeable, no more than two complete cycles were reported. On the other hand, the formation of Li2O2 in the discharged air electrode was observed by chemical titration analysis, but the disappearance of Li2O2 in the recharged (not original) air electrode was not shown. Therefore, the rechargeability of this lithium oxygen battery is not conclusive.
[0011] The discharge mechanism of a lithium oxygen battery is primarily the deposition of Li2O2 in the carbon-based air electrode. Since the reduction of O2 to O<2-> occurs only in the presence of a catalyst, the product is often the peroxide, O2<2->. The reactions of lithium with oxygen are:
[0000]
2Li+O2->Li2O2 E[deg.]=3.10 V
[0000]
4Li+O2->2Li2O E[deg.]=2.91V
[0012] Before completely forming peroxide, an oxygen molecule can reduce to form a superoxide radical which links with one lithium cation, forming lithium superoxide. This intermediate can precipitate within the cathode, forming peroxide, which may support ongoing cycling or attack carbonate based solvents through nucleophilic mechanisms, thus choking off cycling. Lithium superoxide is not a stable compound and will convert to peroxide, but this in part depends upon the stability of the solvent. The superoxide reaction is expected to proceed as follows:
[0000]
O2+Li<+>+e<->->LiO2
[0000]
2LiO2->Li2O2+O2
[0013] There remains a need in the art for further improvements in battery structure to maximize the potential of rechargeable lithium air and lithium oxygen batteries.
BRIEF SUMMARY OF THE INVENTION
[0014] This invention relates to rechargeable battery cells, and more particularly, the invention relates to electrolytes for rechargeable, lithium air battery cells.
[0015] According to the present invention, a rechargeable lithium air battery comprises a non-aqueous, organic-solvent-based electrolyte including a lithium salt and an additive containing an alkylene group, disposed between a spaced apart pair of an anode and an air cathode.
[0016] In one embodiment of the invention, the alkylene additive is selected from the group consisting of alkylene carbonate, alkylene siloxane, and a combination of alkylene carbonate and alkylene siloxane.
[0017] In an aspect of this embodiment, alkylene carbonate is selected from the group consisting of vinylene carbonate, butylene carbonate, and a combination of vinylene carbonate and butylene carbonate.
[0018] In another aspect of this embodiment, alkylene siloxane is a polymerizable silane. And in a further aspect, the polymerizable silane is triacetoxyvinylsilane.
[0019] In another embodiment of the invention, a separator is disposed between the air cathode and the anode and is infused with the non-aqueous, organic-solvent-based electrolyte including a lithium salt and an alkylene additive.
[0020] The invention also relates to a rechargeable lithium air battery comprising a lithium based anode, an air cathode, and a non-aqueous electrolyte, wherein the electrolyte comprises a lithium salt and at least one organosilicon compound, and wherein the anode and the cathode are spaced apart from one another and electrochemically coupled to one another by the electrolyte.
[0021] Additionally, a cathode for a rechargeable lithium air battery comprises a carbon-based, porous electrode and a non-aqueous electrolyte comprising a lithium salt and at least one organosilicon compound.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0022] The foregoing summary, as well as the following detailed description of the invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there are shown in the drawings embodiments which are presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown.
[0023] FIG. 1 is a schematic representation of a rechargeable battery cell according to an embodiment of the present invention.
[0024] FIG. 2 is a schematic representation of a rechargeable battery cell according to a second embodiment of the present invention.
[0025] FIG. 3 is a schematic representation of a cell assembly having a double-cell structure comprising a single anode flanked on both sides by a cathode according to an embodiment the present invention.
[0026] FIG. 4 is a schematic representation of a step in the construction of a sealed cell according to an embodiment of the present invention.
[0027] FIG. 5 is a schematic representation of another step in the construction of a sealed cell according to an embodiment of the present invention.
[0028] FIG. 6 is a schematic representation of a further step in the construction of a sealed cell according to an embodiment of the present invention.
[0029] FIG. 7 is a box-plot graph comparing performance characteristics (Rest Voltage Before Cycling) of inventive and comparative cells.
[0030] FIG. 8 is a box-plot graph comparing performance characteristics (Discharge Voltage During Second Cycle) of inventive and comparative cells.
[0031] FIG. 9 is a box-plot graph comparing performance characteristics (Charge Voltage During Second Cycle) of inventive and comparative cells.
[0032] FIG. 10 shows cycling data for a comparative lithium-O2 cell with PC/glyme solvent.
[0033] FIG. 11 shows cycling data for a Lithium/Oxygen cell with silane electrolyte.
DETAILED DESCRIPTION OF THE INVENTION
[0034] Embodiments of the present invention are described herein. The disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms, and combinations thereof. As used herein, the word "exemplary" is used expansively to refer to embodiments that serve as illustrations, specimens, models, or patterns. The figures are not necessarily to scale and some features may be exaggerated or minimized to show details of particular components. In other instances, well-known components, systems, materials, or methods have not been described in detail in order to avoid obscuring the present invention. Therefore, at least some specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention.
Overview
[0035] As an overview, the invention teaches a first electrolyte for a rechargeable battery that has a lithium anode and an air cathode, which improved electrolyte helps to increase the useful life and effectiveness of the battery. This electrolyte according to the invention also optimizes (lowers) the level of charge voltage required by the battery during recharging, thereby further increasing the usefulness of the battery. The electrolyte is also stable in the presence of the superoxide radical.
[0036] Non-aqueous electrolytes are often used with lithium cells to avoid undesirable reactions between lithium and water-based electrolytes. However, in a cell, a film will typically form on a lithium electrode immersed in a non-aqueous electrolyte. These films form when the lithium metal immersed in the non-aqueous liquid electrolyte generally reacts with the electrolyte solvent, the electrolyte salt, and trace impurities or dissolved gases to form the film. Rather than leaving the nature of the surface film that forms to chance, in one embodiment, the invention modifies the film by introducing additives to the electrolyte solution. These additives are tailored to react with the electrode surfaces and form a surface stabilizing film that is conducive to lithium cycling. This electrolyte of the invention changes the chemical composition of the film such that it adopts characteristics that inhibit the growth of dendrites on the lithium electrode. The invention thus converts the natural presence of the film to a beneficial use in fighting dendrite growth. To convert the film to a desirable composition, the invention uses as additives a class of organic compounds that are capable of being dissolved in the electrolyte solution and capable of polymerizing when placed in contact with lithium metal.
[0037] A second electrolyte according to the invention contains an organosilicon compound. These compounds have been found to improve the reversibility of batteries. Silicon-based electrolytes are advantageous due to high conductivity, safety, and favorable electrochemical and chemical properties. The premise behind organosilicon based electrolytes is that they are not susceptible to nucleophilic attack, but maintain properties needed for lithium air cycling. Thus, silicon-containing electrolytes represent a growing area of interest as a means for improving the safety of lithium air batteries.
[0038] As a further aspect of this overview and introduction, it is to be noted that the air cathode that is utilized in the invention comprises a porous substrate which supports a material that serves as a catalyst to facilitate oxygen's role in the electrochemical reaction that produces energy. In a lithium air battery, oxygen is the cathode reactant for the overall electrochemical reaction that creates electricity. Oxygen is placed in condition for reacting at the substrate that forms the cathode support member. The cathode may employ a catalyst that facilitates oxygen's participation in the electrochemical reaction. The oxygen may be in an isolated (or pure state), or the cathode may use oxygen that is present in ambient air. The oxygen in ambient air is a natural component of air. Hence, the use of the term "air battery" or "lithium air battery." For the purposes of this disclosure, the term "lithium air battery" may also be understood to encompass "lithium oxygen batteries." In both systems, lithium reacts with oxygen, forming Li2O or Li2O2. The distinction between lithium air and lithium-oxygen batteries is the type of oxygen source that is used: oxygen from a tank or oxygen from air. The electrolytes according to the invention are appropriate for both types of systems.
Invention Described in Detail
[0039] Although the term "battery" technically may more properly define a combination of two or more cells, it has come to be used popularly to refer to a single cell. Thus the term battery by itself is sometimes used herein for convenience of explanation to refer to what is actually a single cell. The teachings herein that are applicable to a single cell are applicable equally to each cell of a battery containing multiple cells.
[0040] Referring now to the drawings, wherein like numerals indicate like elements throughout the several views, the drawings illustrate certain of the various aspects of exemplary embodiments.
[0041] Referring first to FIG. 1, therein is illustrated a schematic representation of a rechargeable battery cell 10 according to an embodiment of the invention. A non-aqueous electrolyte 16 is disposed between a spaced-apart pair of a lithium anode 12 and an air cathode 14. The electrolyte 16 includes a lithium salt and further includes an additive comprising an alkylene compound or includes an organosilicon compound according to the invention, as described in more detail below.
[0042] Referring now to FIG. 2, therein is illustrated a schematic representation of a rechargeable battery cell 20 according to a second embodiment of the present invention. In this embodiment, a separator 25 is disposed between and separates a lithium anode 22 and an air cathode 24. The separator 25 is infused with a non-aqueous electrolyte 26. The electrolyte 26 includes a lithium salt and further includes an additive comprising an alkylene compound or includes an organosilicon compound according to the invention, as described in more detail below. The lithium anode 22 adjoins an anode current-collector 30. The anode current-collector 30 may be formed of copper metal or a copper alloy.
[0043] An anode current-collector rod 32 is disposed in contact with the anode current-collector 30 and provides an anode connecting point for the cell 20. The anode current-connector rod 32 may be formed of a copper-based material such as copper metal or a copper alloy. A cathode current-connector rod 34 is disposed in contact with the air cathode 24 and provides a cathode connecting point for the cell 20. The cathode current-connector rod 34 may be formed of an aluminum material, such as aluminum metal or an aluminum alloy (aluminum fused with zinc or copper, for example), or may be carbon mesh or an alternative carbon material. The above structures may be supported by a base 40 of rigid, non-reactive, non-electrically conductive material, such as the polymer sold in block form under the brand name Teflon(R).
[0044] All of the various components described above in the second embodiment of the rechargeable cell 20 may be secured in a housing 50 forming a container. The components may be secured together and to the housing 50 by various securing mechanisms such as nuts 42, 44 that help secure the lower ends of the current-collector rods 32, 34 to the base 40 and nuts 48 that help secure the upper ends of the current-collector rods 32, 34 to the housing. Spacer elements 46 press the electrode stack together while allowing oxygen to reach the cathode 24. The anode current-collector rod 32 extends through and helps secure the position of the separator 25 and the anode current-collector 30 while the cathode current-collector rod 34 extends though and helps secure the position of the separator 25 and air cathode 24. The anode 22 is secured at least in part by being sandwiched between the separator 25 and anode current-connector 30. The housing 50 may contain a quantity of oxygen or air 52 for reaction with the air cathode 24. The housing 50 may have an orifice or aperture 54 through which oxygen or ambient air 52 is introduced into the interior of the housing 50. A removable orifice cover 56 may be used to seal the orifice 54 until injection of oxygen or air is desired.
[0045] In either the first or second embodiment described above, the lithium anode 12, 22 is formed of lithium metal, a lithium-metal based alloy, a lithium-intercalation compound, or lithium titanate (Li2TiO3). As used herein, the term "lithium-intercalation compound" means those substances having a layered structure that is suitable for receiving and storing lithium compounds for later use (such as in a reaction). Thus, these materials may also be considered "lithium-storage materials." These lithium-intercalation, or lithium-intercalating compounds, are typically types of carbon. Lithium titanate functions similarly to a lithium-loaded intercalation compound when used as an anode material in a battery cell.
[0046] The air cathode 14, 24, described in more detail below, is predominantly a porous substrate, and may be infused with an oxygen-reduction catalyst to facilitate the oxygen reaction at the air cathode. Suitable oxygen-reduction catalysts comprise at least one of electrolytic manganese (IV) dioxide, ruthenium (IV) oxide, copper (II) oxide, copper (II) hydroxide, iron (II) oxide, iron (II,III) oxide, cobalt (II,III) oxide, nickel (II) oxide, silver, platinum and iridium.
[0047] The separator 25 is preferably made of a non-conductive polymer. The non-conductive polymer material may be porous, for example, in the nature of a sponge, so as to effectively hold the electrolyte described herein.
[0048] An embodiment of a cell constructed in accordance with the teachings of the invention is sealed in an enclosure wherein oxygen or air is injected to a predetermined pressure. Suitable operating pressure is in the range from about 0.1 atm to about 100 atm, and an optimum range is from about 0.5 atm to about 20 atm.
[0049] Referring to FIG. 3, a cell assembly 120 is comprised of a lithium metal, lithium alloy, or lithium intercalation anode 112 that is sandwiched between two separators 125. The anode terminal 130 is connected to the specific anode. The separators 125 may be composed of a conductive or non-conductive polymer and may be porous or nonporous. Air electrodes 114 are adhered to the separator via chemical bonding (such as surface modifications or doping) and/or physical bonding (such as by using pressure or gluing agents). The air electrode 114 is comprised of a carbon component, a polymer binder component, and a catalyst component. Specific additives such as lithium peroxide may or may not be included. The cathodes are connected via electrical structure 136. The cathode terminal 134 is either connected to the cathode via chemical or physical processes or may be embedded within the cathode.
[0050] Reference is now made generally to FIGS. 4, 5 and 6, which are schematic representations of a cell assembly 120 placed within a bag container 200 to form a completed, sealed cell 300 in accordance with the present invention. First, reference is made specifically to FIG. 4, in which a bag 200 made of multilayer polymer and metal laminate is pre-sealed completely on three sides and has a fourth side that is partially pre-sealed. A suitable polymer is polypropylene, such as the thin-sheet polypropylene product manufactured and sold by E. I. du Pont de Nemours and Company under the trademark DuPont(TM) Surlyn(R). In FIG. 4, sealing is indicated by spaced-apart double lines with cross-hatching which double lines extend across the lower-most edge 210 and parallel side edges 212, 214. The fourth side, which is an upper-most edge in the orientation of FIG. 4, has an opening 216 along a portion of its length adjacent a sealed portion 218 of the upper-most edge. The partially-sealed bag essentially forms a pouch that is open at the top. An inner seal 220 extends parallel to one sealed side edge 212 for a substantial distance. The inner seal 220, parallel side edge 212 and partial seal 218 of the upper-most edge form a substantially U-shaped cavity. The upper-edge partial seal 218 seals a shaft 232 of a hypodermic needle 230 in the U-shaped cavity. The hypodermic needle 230 has an uppermost end 234 that is adapted for receiving an instrument for injection of a gas. The uppermost end 234 is particularly adapted for receiving a syringe (not shown) through which oxygen or air (that contains oxygen) is infused into the hag 200. Prior to placement of the needle 230 in the bag 200, the upper end 234 of the needle 230 may be sealed with epoxy or by other known means to prevent moisture from being introduced into the bag (because of the undesirable interaction of water with lithium). After ensuring that the cathode is not peeling from the separator, the cell assembly 120 is soaked in the electrolyte for at least 5 to 10 minutes, and then inserted (as shown by the direction arrow 3) into the preassembled pouch/partially sealed bag 200 with the anode current-collector tab 130 and the cathode current-collector tab 134 extending outwardly of the upper edge of the bag 200.
[0051] Referring now to FIG. 5, after the cell assembly 120 has been inserted, the bag container 200 is sealed across the current-collector mesh tabs, thus forming the completed upper-most seal 226. The fully-sealed bag 200 is then removed from the glove box and oxygen or air is injected into the bag. For example, a syringe (not shown) may be connected to the upper end 234 of the needle 230 so as to penetrate the sealed (epoxy or otherwise) opening and inject oxygen or air 5 into the bag 220.
[0052] Referring now to FIG. 6, after oxygen 5 has been injected into the bag 200, the partial inner seal 220 is fully extended between the upper-most sealed edge 226 and lower-most sealed edge 210 of the bag 200, thus segregating the needle shaft 232. Sealing may be accomplished through use of a heat-sealing device commonly known as an impulse sealer. The needle-containing portion of the bag then may be removed by simple cutting, trimming, or other conventional means leaving a completed, sealed cell 300 in accordance with the teachings of the invention.
Electrolytes Containing Alkylene Additive
[0053] In one embodiment, the invention modifies the lithium film that forms on a lithium electrode to produce a film that is conducive to lithium cycling (that is, discharging and recharging the cell). The film is modified by providing an electrolyte containing one or more additives that react with the electrode surfaces to form a surface-stabilizing film that is conducive to cycling.
[0054] An electrolyte for a battery cell typically comprises a salt dissolved in a solvent, often water. The invention employs a non-aqueous, organic-solvent-based electrolyte including a lithium salt and an alkylene additive. A non-aqueous electrolyte is used to avoid the damaging effects that water has upon lithium.
[0055] A suitable lithium salt for producing the electrolyte comprises at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bis(trifluorosulfonyl)imide, lithium bis(perfluoroethylsulfonyl)imide, lithium triflate, lithium bis(oxalato)borate, lithium tris(pentafluoroethyl)trifluorophosphate, lithium bromide, and lithium iodide. For convenience, the following table provides (molecular) chemical formulas for these salts:
[0000]
Lithium Salts Suitable For Use In Producing An Electrolyte
Molecular Common Name or Alternative Name(s) or Formula Acronym(s)
LiPF6 lithium hexafluorophosphate
LiBF4 lithium tetrafluoroborate
LiAsF6 lithium hexafluoroarsenate
LiClO4 lithium perchlorate
LiB(C2O4)2 lithium bis(oxalato)borate; [LiBOB]
LiN(SO2CF3)2 lithium bis(trifluorosulfonyl) imide; lithium trifluoromethanesulfonimide; lithium trifluoromethanesulphonylimide; lithium bis(trifluoromethane sulfone)imide; lithium bistrifluoromethanesulfonamide; [LiTFSI]
LiN(SO2CF2CF3)2 lithium bis(perfluoroethylsulfonyl) imide
CF3SO3Li lithium triflate; primary chemical name-
lithium trifluoromethanesulfonate; also known as trifluoromethanesulfonic acid
lithium salt
LiBr lithium bromide
LiI lithium iodide
Li(C2F5)3PF3 lithium tris(pentafluoroethyl) trifluorophosphate
[0056] To form the electrolyte solution, one or more of the above salts is dissolved in a solvent. Salt concentrations may range from 0.01-5 molar, but the preferred range is 0.5-1.5 molar. Examples of suitable solvents include two solvent mixtures: 1:2 (w:w) propylene carbonate and tetraglyme (PC:Tetraglyme) ("tetraglyme" is an amalgam of "tetraethylene glycol dimethyl ether") and 1:2 (w:w) propylene carbonate and 1,2-dimethoxyethane (PC:DME).
[0057] Other suitable electrolyte solutions that may be employed in the invention are electrolyte solutions that are typically used for lithium-ion batteries. Such electrolyte solutions contain solvents that are based upon carbonates, esters, ethers, amines, amides, nitriles and sulfones. Such solvents include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethylene carbonate, 1,2-dimethoxyethane, diethyl carbonate, ethyl methyl carbonate, gamma-butyrolactone, sulfolane, 1,3-dioxolane, tetrahydrofuran, dimethoxyethane, diglyme, tetraglyme, diethyl ether, 2-methyl tetrahydrofuran, tetrahydropyran, pyridine, n-methyl pyrrolidone, dimethyl sulfone, ethyl methyl sulfone, ethyl acetate, dimethyl formamide, dimethyl sulfoxide, acetonitrile, and methyl formate.
[0058] Suitable proportions of alkylene additives range from less than 1% up to 10% by weight based on the weight of the electrolyte solution.
[0059] The additive for the non-aqueous, organic-solvent-based electrolyte comprises an alkylene compound. Suitable alkylene compounds are capable of dissolving in the electrolyte solution and also capable of polymerizing when coming into contact with lithium metal. Suitable alkylene compounds are alkylene carbonates, alkylene siloxanes, and combinations of alkylene carbonate and alkylene siloxane.
[0060] Suitable alkylene carbonates are vinylene carbonate, butylene carbonate, and a combination of vinylene carbonate and butylene carbonate. Vinylene carbonate, which for convenience is sometimes herein abbreviated as "VC," has the following structural formula:
[0000]
[0061] A suitable alkylene siloxane is a polymerizable silane such as triacetoxyvinylsilane. Triacetoxyvinylsilane, which for convenience is sometimes herein abbreviated as "VS," has the following structural formula:
[0000]
Organosilicon-Containing Electrolyte
[0062] In a second embodiment, the electrolyte used in the lithium air cell contains at least one organosilicon compound. Such compounds have been found to improve the reversibility of batteries. Silicon-based electrolytes are advantageous due to high conductivity, safety, and favorable electrochemical and chemical properties. Thus, silicon-containing electrolytes represent a growing area of interest as a means for improving the safety of lithium air batteries.
[0063] Preferably, the organosilicon compound is a silane compound or a siloxane compound. The term "siloxane" technically describes a class of compounds containing alternate silicon and oxygen atoms with the silicon atoms bound to hydrogen atoms or organic groups. Silanes are compounds containing silicon-carbon bonds, analogous to alkanes. However, the terms "silane" and "siloxane" are often used interchangeably and incorrectly in the literature, and, for the purposes of this disclosure, these terms are not meant to be limited to the literal definitions thereof.
[0064] Preferred organosilicon compounds for use in the electrolyte according to the invention are those containing polyethylene oxide (PEO) side chains. Most preferred organosilicon compounds are trimethylsilane compounds having Formula (1) below, in which "n" is an integer representing the number of ethylene oxide units in the molecule and may range from 1 to about 20. Other preferred compounds are silanes containing more than one PEO side chain on the central silicon atom, including silanes having two, three, and four PEO side chains on the central silicon atom. Substituents on the silicon which are not PEO side chains may be hydrogen, substituted or unsubstituted alkyl groups having at least one carbon atom (methyl), or other substituted or unsubstituted organic groups. It is also within the scope of the invention for the electrolyte to contain more than one organosilicon compound.
[0000]
[0065] The electrolyte further contains a salt, preferably a lithium salt as previously described. Preferred salts are LiBOB and LiTFSI. In a preferred embodiment, the electrolyte contains only the organosilicon compound with salt dissolved therein, preferably at a concentration of about 1 molar. No additional solvent is present in the electrolyte in a preferred embodiment. The electrolyte may contain additional organosilicon compound(s) and/or task specific additives in amounts of up to about 10 weight percent based on the total weight of the electrolyte. Such additives are known in the art or may be determined by routine experimentation.
Anode, Air Cathode, and Separator: General Construction and Materials
[0066] Suitable anode materials include, but are not limited to lithium metal, lithium-metal-based alloys (for example, Li-Al, Li-Sn, and Li-Si), lithium-intercalating compounds that are typically used in lithium ion batteries (such as but not limited to graphite, mesocarbon microbead (MCMB) carbon, and soft carbon), and lithium titanate, which is also frequently used in lithium ion batteries.
[0067] The invention also encompasses cathode materials and air cathodes, such as for lithium air and/or lithium oxygen batteries. An air electrode according to the invention contains a carbon-based porous electrode (containing cathode active material, binder, and optionally oxidation reduction catalyst) and the non-aqueous electrolyte containing a lithium salt and an organosilicon compound or an alkylene additive according to the invention. Exemplary and preferred lithium salts, organosilicon compounds, and alkylene additives have been previously described.
[0068] The air cathode may be infused with or contain an oxidation reduction catalyst to facilitate oxygen reduction at the air cathode. Suitable oxidation reduction catalysts comprise at least one of electrolytic manganese (IV) dioxide, ruthenium (IV) oxide, copper (II) oxide, copper (II) hydroxide, iron (II) oxide, iron (II,III) oxide, cobalt (II,III) oxide, nickel (II) oxide, silver, platinum and iridium.
[0069] An exemplary reversible air cathode according to the invention initially contains about 14% lithium peroxide (Li2O2); however, the cell will operate effectively if the air cathode contains from about 0.5% to about 50% Li2O2. The addition of lithium peroxide to the air cathode helps facilitate the preservation of initial porosity of the air cathode. The lithium peroxide initially attaches to the porous structure of the substrate and then, when the cell is charged, the lithium peroxide participates in a chemical reaction that causes it to vacate the porous substrate, thereby increasing the porosity of the substrate. The lithium peroxide thus helps preserve the intended initial porosity by essentially serving as a placeholder for open space in the air cathode.
[0070] Battery capacity increases with increasing proportion of active carbon and porosity. Suitable porous cathode active materials include but are not limited to Calgon(TM) carbon (activated carbon), carbon black (such as Timcal Super P Li carbon), metal powders (such as Ni powder), activated carbon cloths, porous carbon fiber papers, and metal foams.
[0071] Suitable binders for the carbon electrodes include, but are not limited to, carboxymethyl cellulose (CMC), polyimide (PI), polyvinylidene fluoride (PVDF) fluoropolymer resin, polytetrafluoroethylene (PTFE) fluoropolymer resin, Teflon(R) AF amorphous fluoropolymers (Teflon(R) is a registered trademark of E. I. du Pont de Nemours and Company), and fluorinated ethylene propylene (FEP).
[0072] The separator included in the battery according to the invention is preferably made of a non-conductive polymer. The non-conductive polymer material may be porous, for example, in the nature of a sponge, so as to effectively hold the electrolyte described herein. Appropriate separator materials are well known in the art and need not be described. Thus, a battery according to the invention contains, in a preferred embodiment, electrolyte between the cathode and the anode, as well as electrolyte contained in the separator and in the air cathode.
[0073] The term "air" as used herein is not intended to be limited to ambient air, but includes other combinations of gases containing oxygen as well as pure oxygen. As previously noted herein, oxygen is a reactant in the electrochemical process of the invention and references to the term "air" are meant to imply that it is the oxygen in air that is applicable. Thus this broad definition of "air" applies to all uses of that term herein, including but not limited to lithium air, air battery, air cathode, and air supply.
[0074] It is to be understood that the described invention may include a battery that has not yet formed the active material of the anode or a battery which includes a preformed anode containing active material. When the battery does not yet include active anode material, the active anode material is formed upon initial charging of the battery.
[0075] The invention provides a lithium air battery (battery cell) having an electrolyte that is non-volatile, stable in contact with metallic lithium, stable against cathode oxidation during lithium air charging and able to improve the round-trip charge/discharge efficiency. The invention also provides a battery having an electrolyte that contains at least one organosilicon compound, which provides high conductivity, safety, and favorable electrochemical and chemical properties.
EXAMPLES
[0076] The invention will now be described in connection with the following, non-limiting examples. It should be understood, however, that the invention is not limited to the specific details set forth in the example. Parts and percentages set forth herein are by weight unless otherwise specified.
Example 1
Production of Air Cathode using PVDF Resin Binder
[0077] Cathodes were prepared by milling 3 g KS10 graphite (carbon), 3 g Super P(R) Li (carbon black, Timcal SA/Timcal AG/Timcal Ltd Corporation of Switzerland), 0.75 g vapor-grown carbon fiber (VGCF) 24 LD carbon fiber (such as the carbon nanofibers manufactured by Pyrograf Products, Inc., an affiliate of Applied Sciences, Inc.), 2.09 g Kynar(R) PVDF, 1.16 g EMD (electrolytic manganese dioxide, MnO2), and 70 g ZrO2 milling media with 130 mL acetone in a ZrO2 jar at 300 rpm for 17.5 hours in a planetary mill. The milling media was removed by passing the resulting slurry through a wire screen. Cathodes were cast by spreading the slurry at a depth of 20 mil wet thickness onto a 19 cm*39 cm sheet of 0.2 oz/yd<2 >(6.8 g/m<2>) non-woven carbon veil. The cathodes were allowed to dry under a cover with a [1/4]'' wide slot down the center, and cut into individual cathodes using a punch. The cathodes were then weighed and a group having a narrow mass range was selected to minimize variation due to the cathode during observation and testing.
Example 2
Production of Air Cathode using PTFE Resin Binder
[0078] An air cathode was prepared using a fluoropolymer resin binder as a negatively charged, hydrophobic colloid, containing approximately 60% (by total weight) of 0.05 to 0.5 [mu]m polytetrafluoroethylene (PTFE) resin particles suspended in water containing approximately 6% (by weight of PTFE) of a nonionic wetting agent and stabilizer. To produce a Teflon(R)-bonded cell, a Calgon(TM) carbon (activated carbon, Calgon Carbon Corporation)-based air cathode was prepared by first wetting 14.22 g of Calgon(TM) carbon (activated carbon), 0.56 g of Acetylene Black (carbon black pigment), and 0.38 g of electrolytic manganese dioxide with a 60 ml mixture of isopropanol and water (1:2 ratio). The electrolytic manganese dioxide is an oxygen-reduction catalyst, optimally provided in a concentration of 1% to 30% by weight; ruthenium oxide, silver, platinum, or iridium could have been used as alternatives.
[0079] Next, 2.92 g of Teflon(R) 30 (60% Teflon(R) emulsion in water) were added to the above mixture, mixed, and placed in a bottle with ceramic balls to mix overnight on a roller-run jar mill. Alternatively, the slurry could be planetary milled for 6 hours. After mixing, the slurry/paste was dried in an oven at 110[deg.] C. for at least 6 hours to evaporate the water and yield a dry, fibrous mixture. The dry mixture was again wetted by a small quantity of water to form a thick paste, which was then spread over a clean glass plate (or polyester sheet). The mixture was kneaded to the desired thickness as it dried on the glass plate. After drying, it was cold pressed on an Adcote(TM)-brand-adhesive-coated aluminum mesh at 4000 psi for 3 minutes. To remove any cracks in the paste, the cathode assembly was passed through stainless steel rollers. The cathode was then cut into smaller pieces such that the active area of the cathode was 2'' by 2''. A small portion of the aluminum mesh was exposed so that it could be used as the cathode current-collector tab.
Example 3
Cell Assembly
[0080] Cell assembly was performed inside of an argon-filled glove box to reduce or eliminate undesirable effects on the lithium electrode that are caused by water (particularly water vapor, or moisture, in air).
[0081] The cathode was wetted by a non-aqueous, organic-solvent based electrolyte including a lithium salt and an alkylene carbonate and/or an alkylene siloxane additive. Specifically, the electrolyte contained lithium hexafluorophosphate dissolved in a mixture of propylene carbonate and dimethyl ether to a 1 molar concentration (1M LiPF6 in PC:DME). A pressure-sensitive, porous polymeric separator membrane, such as Policell type B38 (product of Policell Technologies, Inc.) was loaded with a non-aqueous, organic-solvent based electrolyte including a lithium salt and an alkylene additive (vinylene carbonate, butylene carbonate, or an alkylene siloxane such as triacetoxyvinylsilane. The electrolyte-loaded separator membrane was placed on the cathode with the shiny side of the membrane facing away from the cathode. Next, thin lithium foil was placed on the shiny side of the wetted separator, and a 1.5 cm by 4 cm strip of copper mesh is placed along one edge of the thin lithium foil (to serve as an anode current-collector tab), away from the aluminum-mesh cathode current-collector tab. Another cathode piece wetted by the electrolyte and covered with a second electrolyte-loaded separator was placed directly on top of the lithium foil and copper-mesh strip. This is an example of a "double-cell assembly," illustrated schematically in FIG. 3, because there is a single substantially planar anode flanked on either side by a substantially planar cathode. FIG. 3 illustrates the arrangement of a pair of spaced-apart air cathodes 114, each having a separator 125 separating the cathodes 114 from the centrally-disposed, thin lithium foil anode 112. An anode current-collector tab 130 extends from the anode 112. A cathode current-collector tab 134 extends from one of the cathodes 114 and a cathode current-collector connector 136 connects the current collector portions of the cathodes 114.
[0082] The double-cell assembly was laminated on a hot press at 100[deg.] C. and 500 lb pressure for 30 to 40 seconds. After the sample was withdrawn from the press, the heat-activated separator bound the sample together.
Example 4
Production of Completed, Enclosed Cells
[0083] Completed, enclosed cells were produced comprising a cell assembly placed in an enclosure with an electrolyte and then activated for use. The cell assembly comprises the cathode-anode-separator assembly, such as the double-cell assembly described above. Although the example described above is based upon a double cell, the teachings of the invention are equally applicable to a single-cell configuration or a multiple-cell configuration other than the single anode-dual cathode configuration described. The completed cells were also assembled in a glove box to isolate the components.
[0084] Various samples of completed cells were prepared for testing, in which the liquid electrolyte employed contained no additive or one of two general types of additives: (a) 2% by weight VS (triacetoxyvinylsilane, a polymerizable silane according to the invention) or (b) 5% by weight VC (vinylene carbonate, an alkylene carbonate additive).
[0085] Liquid electrolytes used for testing were 1 M solutions of lithium trifluoromethanesulfonimide (LiTFSI) or lithium hexafluorophosphate (LiPF6). The lithium salts were used in solvent mixtures containing a 1:2 (w:w) ratio of propylene carbonate and tetraglyme (PC:Tetraglyme) or a 1:2 (w:w) ratio of propylene carbonate and 1,2-dimethoxyethane (PC:DME). Cells constructed in accordance with the teachings of the invention were sealed in an enclosure wherein oxygen or air was injected to a predetermined pressure, preferably about 0.1 atm to about 100 atm, and more preferably about 0.5 atm to about 20 atm.
Example 5
Testing of Inventive and Comparative Cells
[0086] Embodiments of cells incorporating the teachings of the invention and comparative cells were tested to compare their performances. Three performance characteristics were tested: Rest Voltage Before Cycling, Discharge Voltage During Second Cycle, and Charge Voltage During Second Cycle.
[0087] FIGS. 7-9 are box-plot graphs of data recorded for these three characteristics. A "cycle" that is referred to in the testing described herein refers to the period in which a fully-charged cell is discharged to a predetermined level and then re-charged to maximum capacity. Charge to more than 4.6V will enhance the desired decomposition of Li2O2. Suitable voltage ranges for charging and discharging are 4 to 4.8V for charging and 3 to 1.5V for discharging. Increasing charging voltage significantly increases the reversibility of the battery.
[0088] The results of testing were compared and analyzed utilizing the statistics methodology known as Analysis of Variance (ANOVA). Measurements taken during the second cycle exhibited differences that were considered to be statistically significant and have been described herein.
[0089] Referring to FIG. 7, therein is shown a box-plot graph of rest voltage, in volts (V), before cycling for cells tested. The rest voltage (V) for each cell was recorded at the end of the initial rest (or "pre-charging" period, prior to the first discharge). Cells containing the VS additive and the VC additive showed increases in rest voltage relative to the non-additive cells, which increases are statistically significant by ANOVA. Although the rest voltage for the VS sample appears higher than for VC in the box plot of FIG. 7, review using ANOVA principals indicates that they are statistically indistinguishable.
[0090] Referring now to FIG. 8, therein is shown a box-plot graph of discharge voltage (V) during the second cycle. This is a representation of the average voltage discharged or dissipated in the second cycle. Battery cells that did not contain an additive according to the present invention gave a statistically higher voltage than cells containing the VC additive according to the invention. However, discharge voltage for cell embodiments containing the VS additive according to the invention were indistinguishable from discharge voltage for cells containing no additive and the discharge voltage for cell embodiments containing the VC additive according to the invention was indistinguishable from the discharge voltage for cells containing the VS additive according to the invention.
[0091] Referring now to FIG. 9, therein is shown a box-plot graph comparing charge voltage (V) during a second cycle, that is, the voltage (V) that was required to fully charge the cells. The charge voltage for the second cycle was lowest for cell embodiments containing VC additive, second lowest for cell embodiments containing VS additive, and highest for cells containing no additive.
[0092] When the VS additive was utilized in combination with a nonvolatile, liquid electrolyte such as 1 M LiTFSI in 2:1 (PC):tetraglyme, the VS additive served to increase the round-trip efficiency by reducing the charge voltage. Round-trip efficiency is a tool that may be used to compare the effectiveness of one rechargeable cell to another. Round-trip efficiency may be described as a ratio of the total discharge energy Edis (watt-hours) that is dissipated by a cell during a cycle as compared to the total energy Ech (watt hours) required to be applied to fully re-charge a cell after discharge during a cycle. The relationship may be described mathematically as follows:
[0000] [mathematical formula]
[0000] wherein
n=cycle number
Edis=Total energy discharged during the cycle "n."
Ech=Total energy that is applied to re-charge a battery cell at the end of the preceding cycle, that is "n-1."
[0096] As noted above, Round-Trip Efficiency is expressed as a percentage (%).
[0097] The invention provides a cell that requires a lesser amount of charge energy Ech, thus increasing the round-trip efficiency.
Comparative Example 1
[0098] For testing, a standard carbon based cathode was coupled to lithium metal anode via a porous propylene separator (Celgard) to form a lithium/oxygen battery. The electrolyte solution was comprised of propylene carbonate (PC) and tetraglyme in a specific ratio with LITFSI at one molar. As shown in FIG. 10, the cell showed a symmetric charge/discharge voltage vs. time profile, indicating reversibility. However, over the course of 20 cycles, the fade rate of this cell was near 50% per 20 cycles. Upon disassembly of the battery, the cell components and both electrodes appeared to be intact, which indicated that the fading mechanisms were related to the electrolyte solution.
Example 6
Preparation and Testing of Inventive Cell Containing PEO-Silane Electrolyte
[0099] A battery cell was prepared in which an air cathode was cycled versus lithium metal anode using an electrolyte containing an organosilicon compound having Formula (1) in which n=2 (obtained from Argonne National Labs, IL.) The electrolyte was composed of LiTFSI salt dissolved in 1NM2 organosilicon solvent to 1 molar. The cycling data was recorded on a Maccor battery tester and is presented in FIG. 11. Virtually no observable fading occurred over the first 20 cycles. Without wishing to be bound by theory, it is believed that this stability is due to the stability of the silane solvent from nucleophilic attack by the superoxide anion. The superoxide anion is present in the cell because it participates in charge and discharge electrochemical reaction in Li-O2 cells. In the case of PC based electrolyte solvents, the superoxide anion nucleophilically attacks ethereal carbon in PC leading to its decomposition. The effect is especially pronounced at higher cell voltages.
[0100] It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims.
NON-VOLATILE CATHODES FOR LITHIUM OXYGEN
BATTERIES AND METHOD OF PRODUCING SAME
US2013084507
US2013084507
An air lithium battery is provided having two equal halves (60, 69) that are joined together along a centerline. Each half includes a porous substrate (64), an oxygen cathode (67) having a non-volatile lithium ion conductive electrolyte cathode, a non-volatile electrolyte (66), and an anode (65). The electrolyte may include alternating layers of ion conductive glass or ceramic layer and ion conductive polymer layer.
Lithium Oxygen Batteries Having a Carbon
Cloth Current Collector and Method of Producing Same
US2012270115
WO2013049460
US2012270115
WO2013049460
A lithium oxygen or air battery (80) is disclosed having two halves (81) that are joined together along their edges. Each battery half (81) has a carbon cloth or mesh cathode current collector (82), a cathode (83), a cathode terminal (84), an anode (85), an anode current collector, anode terminal (88) and a solid separator (87). The cathode includes randomly distributed carbon fibers throughout. The manufacturing of the cathode includes embedding a carbon cloth between two layers of cathode material in a slurry state
Lithium Oxygen Battery Having Enhanced
Anode Environment
US2010266901
US2010266901
An anode environment mitigates undesired effects of oxygen upon the anode of a lithium-oxygen electrochemical cell. As a means of mitigating oxygen effect, a lithium anode and an air cathode are separated from one another by a lithium-ion-conductive electrolyte separator including material having low oxygen permeability that reduces the amount of oxygen that contacts the anode. As another means of mitigating oxygen effect, a cell comprises lithium-affinity anode material capable of receiving and retaining lithium in a state that is not significantly adversely affected by the presence of oxygen during cell charging and recharging and an air cathode separated by a lithium-ion-conductive electrolyte separator. Lithium-affinity material is capable of drawing lithium thereinto during charging of the cell and retaining the lithium substantially until discharge of the cell. A cell having a lithium-affinity anode may also have a lithium-ion-conductive electrolyte separator including material having low oxygen permeability.
OXYGEN BATTERY SYSTEM
WO2009117496
WO2009117496
Also published as: WO2009117496 (A3) US2009239132 (A1)
A lithium oxygen cell system (10) includes a battery cell (15), a containment vessel (106) having an air inlet conduit (114) and an air outlet conduit (112). An access control valve (101), a one way check valve (102), a H2O scrubber (103) and a CO2 scrubber (104) are mounted within inlet conduit. A one way check valve (107) and a forced air device (108) are mounted within outlet conduit. A charge controller (109) is coupled to battery and to the air device. The pair of one way check valves insure that the inside of the containment vessel (106) may be sealed. The system further includes a safety controller (111) coupled to an environmental sensor (110), and to control valve (101). When an unsafe temperature or pressure condition is detected, it closes control valve to shut down operation of the battery and thereby prevent a catastrophic event.
Non-volatile cathodes for lithium oxygen
batteries and method of producing same
TW200933953
TW200933953
Also published as: US2008070087 (A1) WO2009067425 (A1)
An air lithium battery is provided having two equal halves (60, 69) that are joined together along a centerline. Each half includes a porous substrate (64), an oxygen cathode (67) having a non-volatile lithium ion conductive electrolyte cathode, a non-volatile electrolyte (66), and an anode (65). The electrolyte may include alternating layers of ion conductive glass or ceramic layer and ion conductive polymer layer.
AIR BATTERY AND MANUFACTURING METHOD
KR20080106574
KR20080106574
Also published as: US2008070087 (A1) WO2009067425 (A1)
An air lithium battery is provided having two equal halves (60, 69) that are joined together along a centerline. Each half includes a porous substrate (64), an oxygen cathode (67) having a non-volatile lithium ion conductive electrolyte cathode, a non-volatile electrolyte (66), and an anode (65). The electrolyte may include alternating layers of ion conductive glass or ceramic layer and ion conductive polymer layer.
LOW COST SOLID STATE RECHARGEABLE BATTERY
AND METHOD OF MANUFACTURING SAME
WO2009029746
WO2009029746
Also published as: US2009092903 (A1)
A solid state Li battery and an all ceramic Li-ion battery are disclosed. The all ceramic battery has a solid state battery cathode comprised of a mixture of an active cathode material, an electronically conductive material, and a solid ionically conductive material. The cathode mixture is sintered. The battery also has a solid state battery anode comprised of a mixture of an active anode material, an electronically conductive material, and a solid ionically conductive material. The anode mixture is sintered. The battery also has a solid state separator positioned between said solid state battery cathode and said solid state battery anode. In the solid state Li battery the all ceramic anode is replaced with an evaporated thin film Li metal anode.
RECHARGEABLE AIR BATTERY AND MANUFACTURING
METHOD
KR20090020521
KR20090020521
Also published as: US2009053594 (A1) JP2009170400 (A) CN101409376 (A)
An air battery, and an air battery cathode used in the air battery are provided to improve rechargeability and to obtain a specific very high energy and a relatively flat discharge profile. An air battery(10) comprises an air cathode(11); a separator(13) which is mounted together with an organic solvent-based electrolyte containing a lithium salt and an alkylene carbonate additive; a cathode current collector(12); an anode; an anode current collector(15); and a housing which accommodates the cathode, the separator, the cathode current collector, the anode, the anode current collector, and an air supplier.
LITHIUM OXIDE BATTERY AND MANUFACTURING METHOD THEREFOR
JP2005235774
PROBLEM TO BE SOLVED: To provide a lithium oxide battery improved to solve the problems of rapid deterioration upon exposure to environmental air. ; SOLUTION: The air lithium battery (10) is provided with equal halves (11) that are jointed together along a center line (12). Each half includes a substrate (13), a carbon-based cathode (14), a solid electrolyte (15), an anode (16), an anode current collector (17), and end seals (19). The solid electrolyte includes alternating layers of ion conductive glass (21) and ion conductive polymer (22) materials.
JOHNSON : THIN-FILM LITHIUM BATTERY PATENTS
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ELECTROCHEMICAL CONVERSION SYSTEM
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THIN LITHIUM FILM BATTERY
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Systems and methods for producing multilayer thin film energy storage devices
US2002110733
METHOD OF MANUFACTURING A THIN LITHIUM FILM BATTERY
WO03050901
Thin lithium film battery.
ZA200108166
Method of producing a thin film battery
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Composite separator and electrode
TW412879
RECHARGEABLE BATTERY POWER SUPPLY OVERCHARGE PROTECTION CIRCUIT
WO9904476
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MICROWAVE DRYING OF LITHIUM-ION BATTERY MATERIALS
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STRUCTURED SILICON PARTICLES
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LI-AIR BATTERIES HAVING ETHER-BASED ELECTROLYTES
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ELECTROLYTE AND LITHIUM AIR BATTERY INCLUDING THE SAME
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POROUS CARBONACEOUS COMPOSITE MATERIAL, CATHODE AND LITHIUM AIR BATTERY
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BIFUNCTIONAL HOLLANDITE Ag2Mn8O16 CATALYST FOR LITHIUM-AIR BATTIERIES
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PROPYLENE RESIN MICROPOROUS FILM, BATTERY SEPARATOR, BATTERY, AND METHOD FOR PRODUCING PROPYLENE RESIN MICROPOROUS FILM
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PROTECTED ANODE, LITHIUM AIR BATTERY
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ELECTROLYTE FOR LITHIUM AIR RECHARGEABLE BATTERy
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PART SOLID, PART FLUID AND FLOW ELECTROCHEMICAL CELLS INCLUDING METAL-AIR AND LI-AIR BATTERY SYSTEMS
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LITHIUM AIR SECONDARY BATTERY
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LITHIUM AIR SECONDARY BATTERY AND MANUFACTURING METHOD FOR AIR ELECTRODE THEREOF
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LITHIUM-AIR BATTERY WITH HIGH OXYGEN SATURATION
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LITHIUM AIR BATTERY APPARATUS
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