Richard KANER & Maher EL-KADY
Lightscibe DVD Burner Production of
Flexible Thermoelectric Converters ...
Nature Communications, Vol.4, Article number: 1475
12 February 2013
Scalable fabrication of high-power
for flexible and on-chip energy storage
Maher F. El-Kady // Richard B. Kaner
Maher F El-Kady Richard
The rapid development of miniaturized electronic devices has
increased the demand for compact on-chip energy storage.
Microscale supercapacitors have great potential to complement or
replace batteries and electrolytic capacitors in a variety of
applications. However, conventional micro-fabrication techniques
have proven to be cumbersome in building cost-effective
micro-devices, thus limiting their widespread application. Here we
demonstrate a scalable fabrication of graphene
micro-supercapacitors over large areas by direct laser writing on
graphite oxide films using a standard LightScribe DVD burner. More
than 100 micro-supercapacitors can be produced on a single disc in
30?min or less. The devices are built on flexible substrates for
flexible electronics and on-chip uses that can be integrated with
MEMS or CMOS in a single chip. Remarkably, miniaturizing the
devices to the microscale results in enhanced charge-storage
capacity and rate capability. These micro-supercapacitors
demonstrate a power density of ~200uW/cm-3, which is among
the highest values achieved for any supercapacitor.
Figure 1: Fabrication of LSG-MSC
(a–c) Schematic diagram showing the fabrication process for an LSG
micro-supercapacitor. A GO film supported on a PET sheet is placed
on a DVD media disc. The disc is inserted into a LightScribe DVD
drive and a computer-designed circuit is etched onto the film. The
laser inside the drive converts the golden-brown GO into black LSG
at precise locations to produce interdigitated graphene circuits
(a). Copper tape is applied along the edges to improve the
electrical contacts, and the interdigitated area is defined by
polyimide (Kapton) tape (b). An electrolyte overcoat is then added
to create a planar micro-supercapacitor (c). (d,e) This
technique has the potential for the direct writing of
micro-devices with high areal density. More than 100
micro-devices can be produced on a single run. The micro-devices
are completely flexible and can be produced on virtually any
[ Ed. Note -- Combine this with Palmer CRAIG's bismuth power device ]
Characterization of LSG micro-devices
Figure 2: Characterization of LSG micro-devices
(a) A digital photograph of the laser-scribed micro-devices with 4
(LSG-MSC4), 8 (LSG-MSC8) and 16 interdigitated electrodes
(b) An optical microscope image of LSG-MSC16 shows interdigitated
fingers with 150-µm spacings. The dark area corresponds to LSG and
the light area is GO. Scale bar, 200?µm. (c) A tilted-view (45°)
SEM image shows the direct reduction and expansion of the GO film
after exposure to the laser beam. Scale bar, 10?µm. (d) and (e)
show the I–V curves of GO and LSG, respectively. LSG exhibits a
current enhanced by about 6 orders of magnitude, confirming the
change from nearly insulating GO to conducting LSG. (f) A
comparison of electrical conductivity values for GO and LSG.
Electrochemical performance of the LSG-MSC in PVA-H2SO4 gelled
Figure 3: Electrochemical performance of the LSG-MSC in
PVA-H2SO4 gelled electrolyte
CV profiles of LSG-MSC in sandwich and interdigitated structures
with 4, 8 and 16 electrodes at scan rates of (a) 1,000?mV?s-1, (b)
5,000?mV?s-1 and (c) 10,000?mV?s-1. (d) Evolution of the specific
capacitance of the different supercapacitors as a function of the
scan rate. Symbol key for a–d: sandwich (black), MSC(4) (red),
MSC(8) (green) and MSC(16) (blue). (e) Galvanostatic
charge/discharge curves of micro-supercapacitors based on
interdigitated structures with 4, 8 and 16 electrodes, all
operated at an ultrahigh current density of 1.68 × 104?mA?cm-3.
(f) Volumetric stack capacitance of LSG-MSC in the sandwich and
interdigitated structures as calculated from the charge/discharge
curves at different current densities. Data for a commercial AC-SC
are shown for comparison. (g) Complex plane plot of the impedance
of a LSG-MSC(16) with a magnification of the high-frequency region
is provided in the inset. (h) Impedance phase angle versus
frequency for LSG-MSC(16) compared with commercial AC-SC and
aluminium electrolytic capacitors. (i) The LSG-MSC(16) shows
excellent stability, losing only about 4% of its initial
capacitance over 10,000 cycles.
Behaviour of LSG-MSC under mechanical stress and in
Figure 4: Behaviour of LSG-MSC under mechanical stress and in
(a) A photograph of LSG-MSC(16) bent with a tweezers demonstrates
the flexibility of the micro-device. (b) Bending/twisting the
device has almost no effect on its performance, as can be seen
from these CVs collected under different bending and twisting
conditions at 1,000?mV?s-1. (c) Performance durability of the
micro-device when tested under bending and twisting conditions.
The device retains ~97% of its initial capacitance after 1,000
cycles under the bent state, followed by another 1,000 cycles
under the twisted state. Galvanostatic charge/discharge curves for
four tandem micro-supercapacitors connected (d) in series, (e) in
parallel and (f) in a combination of series and parallel. A single
device is shown for comparison. Both the tandem devices and the
single device were operated at the same charge/discharge current.
(Insets) the tandem micro-supercapacitor can be used to power a
light-emitting diode (LED).
Fabrication and characterization of LSG-MSC on a chip
Figure 5: Fabrication and characterization of LSG-MSC on a chip
LightScribe can be used to produce LSG-MSC directly on a chip
that contains integrated circuits, which they can then power.
(a) An ionogel electrolyte was used in the assembly of the
device. It is prepared by mixing together the ionic liquid
with fumed silica nanopowder. (b) Schematic of the device;
(c) Photograph of the micro-devices. (d) CV profile of LSG-MSC(16)
at various scan rates, from low to high: 1000 (black), 2000 (red),
5000 (green) and 10000 (blue)?mV?s-1. (e) Galvanostatic
charge/discharge curves of LSG-MSC(16) collected at different
current densities: 1.06 × 104 (black), 5.05 × 103 (red), 2.42 ×
103 (green) and 1.38 × 103 (blue)?mA?cm-3.
Testing the self-discharge rate of LSG-MSC
Figure 6: Testing the self-discharge rate of LSG-MSC
(a) Leakage current measurement of an LSG micro-supercapacitor
(with 16 interdigitated electrodes) and two commercially available
supercapacitors. A DC voltage (the voltage at which the
supercapacitor is operated, Vmax) was applied across the
capacitor; the current required to retain that voltage was
measured over a period of 12?h. (b) Self-discharge curves of the
respective supercapacitors obtained immediately after precharging
to Vmax in the previous test. This involves measuring the
open-circuit voltage across the supercapacitors between Vmax and
½Vmax versus the course of time. This involves 3.5?V/25?mF
commercial supercapacitor (black), 2.75?V/44?mF commercial
supercapacitor (red) and LSG micro-supercapacitor assembled using
ionogel electrolyte (green).
Energy and power densities of LSG-MSCs compared with
commercially available energy-storage systems
Figure 7: Energy and power densities of LSG-MSCs compared
with commercially available energy-storage systems
LSG-MSCs exhibit ultrahigh power and energy densities compared
with a commercially available AC-SC, an aluminium electrolytic
capacitor and a lithium thin-film battery. LSG micro-devices
can deliver ultrahigh power density comparable to those of an
aluminium electrolytic capacitor, while providing three orders
of magnitude higher energy density. Data for the Li battery
are reproduced from ref. 2.
Self-Charged Graphene Battery Harvests
Electricity from Thermal Energy of the Environment
Authors: Zihan Xu, Guoan Tai, Yungang Zhou, Fei Gao, Kin Hung
Abstract : The energy of ionic thermal motion presents
universally, which is as high as 4 kJ\bullet kg-1\bullet K-1 in
aqueous solution, where thermal velocity of ions is in the order
of hundreds of meters per second at room temperature1,2. Moreover,
the thermal velocity of ions can be maintained by the external
environment, which means it is unlimited. However, little study
has been reported on converting the ionic thermal energy into
electricity. Here we present a graphene device with asymmetric
electrodes configuration to capture such ionic thermal energy and
convert it into electricity. An output voltage around 0.35 V was
generated when the device was dipped into saturated CuCl2
solution, in which this value lasted over twenty days. A positive
correlation between the open-circuit voltage and the temperature,
as well as the cation concentration, was observed. Furthermore, we
demonstrated that this finding is of practical value by lighting a
commercial light-emitting diode up with six of such graphene
devices connected in series. This finding provides a new way to
understand the behavior of graphene at molecular scale and
represents a huge breakthrough for the research of self-powered
technology. Moreover, the finding will benefit quite a few
applications, such as artificial organs, clean renewable energy
and portable electronics.
February 19, 2013
UCLA researchers develop new technique
to scale up production of graphene micro-supercapacitors
While the demand for ever-smaller electronic devices has spurred
the miniaturization of a variety of technologies, one area has
lagged behind in this downsizing revolution: energy-storage units,
such as batteries and capacitors.
Now, Richard Kaner, a member of the California NanoSystems
Institute at UCLA and a professor of chemistry and biochemistry,
and Maher El-Kady, a graduate student in Kaner's laboratory, may
have changed the game.
The UCLA researchers have developed a groundbreaking technique
that uses a DVD burner to fabricate micro-scale graphene-based
supercapacitors — devices that can charge and discharge a
hundred to a thousand times faster than standard batteries. These
micro-supercapacitors, made from a one-atom–thick layer of
graphitic carbon, can be easily manufactured and readily
integrated into small devices such as next-generation pacemakers.
The new cost-effective fabrication method, described in a study
published this week in the journal Nature Communications, holds
promise for the mass production of these supercapacitors, which
have the potential to transform electronics and other fields.
"The integration of energy-storage units with electronic circuits
is challenging and often limits the miniaturization of the entire
system," said Kaner, who is also a professor of materials science
and engineering at UCLA's Henry Samueli School of Engineering and
Applied Science. "This is because the necessary energy-storage
components scale down poorly in size and are not well suited to
the planar geometries of most integrated fabrication processes."
"Traditional methods for the fabrication of micro-supercapacitors
involve labor-intensive lithographic techniques that have proven
difficult for building cost-effective devices, thus limiting their
commercial application," El-Kady said. "Instead, we used a
consumer-grade LightScribe DVD burner to produce graphene
micro-supercapacitors over large areas at a fraction of the cost
of traditional devices. Using this technique, we have been able to
produce more than 100 micro-supercapacitors on a single disc in
less than 30 minutes, using inexpensive materials."
The process of miniaturization often relies on flattening
technology, making devices thinner and more like a geometric plane
that has only two dimensions. In developing their new
micro-supercapacitor, Kaner and El-Kady used a two-dimensional
sheet of carbon, known as graphene, which only has the thickness
of a single atom in the third dimension.
Kaner and El-Kady took advantage of a new structural design during
the fabrication. For any supercapacitor to be effective, two
separated electrodes have to be positioned so that the available
surface area between them is maximized. This allows the
supercapacitor to store a greater charge. A previous design
stacked the layers of graphene serving as electrodes, like the
slices of bread on a sandwich. While this design was functional,
however, it was not compatible with integrated circuits.
In their new design, the researchers placed the electrodes side by
side using an interdigitated pattern, akin to interwoven fingers.
This helped to maximize the accessible surface area available for
each of the two electrodes while also reducing the path over which
ions in the electrolyte would need to diffuse. As a result, the
new supercapacitors have more charge capacity and rate capability
than their stacked counterparts.
Interestingly, the researchers found that by placing more
electrodes per unit area, they boosted the micro-supercapacitor's
ability to store even more charge.
Kaner and El-Kady were able to fabricate these intricate
supercapacitors using an affordable and scalable technique that
they had developed earlier. They glued a layer of plastic onto the
surface of a DVD and then coated the plastic with a layer of
graphite oxide. Then, they simply inserted the coated disc into a
commercially available LightScribe optical drive — traditionally
used to label DVDs — and took advantage of the drive's own laser
to create the interdigitated pattern. The laser scribing is so
precise that none of the "interwoven fingers" touch each other,
which would short-circuit the supercapacitor.
"To label discs using LightScribe, the surface of the disc is
coated with a reactive dye that changes color on exposure to the
laser light. Instead of printing on this specialized coating, our
approach is to coat the disc with a film of graphite oxide, which
then can be directly printed on," Kaner said. "We previously found
an unusual photo-thermal effect in which graphite oxide absorbs
the laser light and is converted into graphene in a similar
fashion to the commercial LightScribe process. With the precision
of the laser, the drive renders the computer-designed pattern onto
the graphite oxide film to produce the desired graphene circuits."
"The process is straightforward, cost-effective and can be done at
home," El-Kady said. "One only needs a DVD burner and graphite
oxide dispersion in water, which is commercially available at a
The new micro-supercapacitors are also highly bendable and
twistable, making them potentially useful as energy-storage
devices in flexible electronics like roll-up displays and TVs,
e-paper, and even wearable electronics.
The researchers showed the utility of their new laser-scribed
graphene micro-supercapacitor in an all-solid form, which would
enable any new device incorporating them to be more easily shaped
and flexible. The micro-supercapacitors can also be fabricated
directly on a chip using the same technique, making them highly
useful for integration into micro-electromechanical systems (MEMS)
or complementary metal-oxide-semiconductors (CMOS).
These micro-supercapacitors show excellent cycling stability, an
important advantage over micro-batteries, which have shorter
lifespans and which could pose a major problem when embedded in
permanent structures — such as biomedical implants, active
radio-frequency identification tags and embedded micro-sensors —
for which no maintenance or replacement is possible.
As they can be directly integrated on-chip, these
micro-supercapacitors may help to better extract energy from
solar, mechanical and thermal sources and thus make more efficient
self-powered systems. They could also be fabricated on the
backside of solar cells in both portable devices and rooftop
installations to store power generated during the day for use
after sundown, helping to provide electricity around the clock
when connection to the grid is not possible.
"We are now looking for industry partners to help us mass-produce
our graphene micro-supercapacitors," Kaner said.
Kaner's micro-scale graphene-based supercapacitor research is
supported by Maxwell Technologies Inc., a global leader in
manufacturing carbon-based supercapacitors and other energy
Self-Charged Graphene Battery Harvests
Electricity from Thermal Energy of the Environment
Zihan Xu, et al.
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