1. Packaged Inkjet-Printed Flexible Supercapacitors
Matthew Ervin (ARL), Linh Le (SIT), and Woo Lee (SIT)

2. Flexible Supercapacitors for Munitions
Description of Application:
Flexible printed supercapacitors for storing energy to power flexible munition electronics
POC: Brian Fuchs & Jim Zunino
address:
Important Specifications:
Stores >3 mJ at 3 V
Survive 50+ kGs, 1000 rpm
Flexible
Printable
Benefits Anticipated:
Enable flexible circuits
Reduced cost
Manufacture on demand
Reduced Obsolescence
Improved volume utilization/increased leathality
Rapid prototyping/Mission tailored

3. Thin-film Supercapacitors for Integration with Uniforms and Equipment
Description of Application:
Thin-film supercapacitors employing ionogel electrolytes to be integrated in parallel with batteries in uniforms and equipment
POCs: Stephanie Flores Zopf Natalie Pomerantz
addresses:
Important Specifications:
Energy density > 0.5 kJ/m2, > 0.5 kJ/kg
Conductivity = 1 mS/cm
Capacitance = 1µF/cm2
Electrochemical window = 2.5 V
Long term stability over charge/discharge cycles
Mechanically flexible and conformable
Lightweight
Benefits Anticipated:
Size, weight and power savings
Environmentally safer than electrolytic supercapacitors
Increased reliability over current electrolytic capacitors

4. Energy Storage Why Supercapacitors?
Supercapacitors store charge by the adsorption of ions onto the electrodes using an electric field. Since there is no dielectric, the voltage must remain low enough that there is no charge transfer or electrochemical breakdown of the electrolyte. Capacitance is proportional to accessible surface area.
Advantages:
Stable performance
Higher specific power (~100x batteries)
Millions of charge/discharge cycles
Rapid charge and discharge times
Efficiencies (98%)
Perform well at extreme temperatures
Safety
Shelf-life
Challenges:
Lower energy densities than batteries
Limited voltage rating on individual cells:
~1 V for aqueous electrolytes and
~3 V for organic electrolytes.
Voltage varies with charge
Rigid Packaging
Slow response <1Hz vs other capacitor types
Self-discharge
Supercapacitor vs. Electrolytic

5. Capacitor Types Dielectric Electrolytic Electrochemical Double Layer
Ragone Plot of Electrochemical Devices
Dielectric
Electrolytic
Electrochemical Double Layer ‘
Al foil
anode
dielectric
separator
cathode
electrolyte
permittivity
Aqueous 1V
Organic 2.7V
Ionic liquid >3.5V
Dielectric strength
Ta 50V
Al 500V
Highest power/frequency
Lowest energy
Thicker dielectric yields higher voltage, but volumetric energy density unchanged
Lower power/frequency
More energy
Lowest power/frequency
Highest energy

6. Graphene Supercapacitor Rationale
CNT/G
Goal:
To increase power and energy density of supercapacitors using graphene
Rationale:
Graphene has the highest surface area which correlates to capacitance.
2630 m2/g, external surface area (20uF/cm2 yields 550F/g theoretical)
Graphene is highly conductive which improves power performance.
Carbon has a very good electrochemical window.
The mechanical properties of graphene will enable flexible/conformal supercapacitors.
Graphene oxide makes good solutions, and it is readily reduced.
<$50/kg anticipated in 3 years for graphene.

7. Flexible Device Component Choices and Issues
Current Collector
Graphene Ink/Printing
Binder(less)
Separator(less)
Electrolyte
Substrate/Package

8. Substrate/Packaging Material
Kapton: Stable to 400oC – facilitates metal ink sintering Good dielectric properties Low outgassing But… Permeable to water, oxygen – electrolyte degradation Use metallization to improve hermetic sealing Not directly heat sealable FEP: Enables heat sealing – flows during sealing (350oC) Chemically inert Adhesion of printed features? Unstable substrate when sealing Permeable to small molecules, e.g. CO2

9. Packaging Permeability
AN/thick Kapton/FEP
Kapton permeability2.xls
IL/thick Kapton/FEP
PC/thick Kapton
H2O/thick Kapton/Al tape
H2O/thick Kapton/FEP
H2O/thin Kapton
H2O/thin Kapton/FEP

10. Inkjet Printing Graphene Oxide
Dreyer el al., Chem. Soc. Rev.,
2010, 39,
Suspension Stable, Hydrophilic Graphene Oxide (GO) in Water (2mg/ml), no surfactant N D
Print Head
IR Heat Lamp
Substrate
Inkjet Printing Attributes
Micropatternable at 50 um resolution
Additive, net-shape manufacturing with minimum nanomaterial use and waste
Scale-up and integration readiness with rapidly emerging printed electronics

11. Ink Preparation Concentration (2mg/ml)
Less aggregation and nozzle clogging, but requires more printing
Solvent
Using water with graphene oxide, pvdf not soluble in water
Could use N-methyl pyrrolidone with graphene and pvdf binder (more robust)
Graphene oxide functionalization/activation
Introduces defects that can decrease conductivity.
Requires reduction step: photo/thermal/chemical
Functional groups can introduce pseudocapacitance which may or may not be desirable.
Decomposition of functional groups/impurities can result in gas liberation which can rupture the package.
Surfactants
Generally nonconductive, must be removed
Sonication
Aids in solubilization but may damage graphene
Inclusion of sacrificial porogens to tailor porosity
Inclusion of pseudocapacitive materials

12. 500 nm 100 Printed Layers: Cross-Section
Stacks of horizontal sheets of graphene

13. Packaged Prototype Assembly
Graphene printed on evaporated Ti/Au on Kapton
Double-side FEP coated Kapton used for sealing
Device sealed on three sides
Separator inserted
Electrolyte injected to wet the separator/electrodes
The final heat seal is made

14. Energy Density (Wh/kg)
Prototype CV Results
Cyclic Voltamogram
LL0114A01
3/25/14
Charge/Discharge
1M H2SO4
0-1V
BMIMBF4
0-3V
Capacitance (F/g)
192
@ 20mV/s 73
Energy Density (Wh/kg)
5.0
@ 0.25 A/g
5.5
Power Density (kW/kg) 10
@ 10 A/g 19
LL0114A03
3/25/14
LL0114B04
5/7/14
LL0114A03
3/25/14
per rGO mass only

15. Prototype EIS Results with H2SO4
-79 10mHz
LL0114A02
Ohms
8.2 10mHz
Good capacitive behavior at low frequencies

16. Bending Test
Bending expt xls

17. Bending Cycles Flex tests 3 25 14.xlsm Flex tests 3 25 14.xlsm
150FN019 packaging
1M H2SO4 electrolyte

18. Cycle-Life Testing Flex cycle life tests 5 14.xls
EIS at 0V shows only a loss of 20% capacitance
Flex cycle life tests 5 14.xls

19. Cycle-Life Testing Dropcast, coin cells Flex cycle life tests 5 14.xls
124 F/g
Dropcast, coin cells
104 F/g
89 F/g
67 F/g
Flex cycle life tests 5 14.xls
153 F/g
140 F/g
Flex cycle life tests 5 14.xls
Inkjet printed, Flex Kapton cell

20. Bending Cycles per rGO mass Flex Ragone plots.xlsm
With H2SO4: 3.3 Wh/kg rGO at 0.25 A/g, 6.8 kW/kg rGO at 10 A/g, 0-1V
With BMIMBF4: 6.2 Wh/kg rGO at 0.25 A/g, 39.2 kW/kg rGO at 10 A/g, 0-3V

21. Bending Cycles Flex Ragone plots.xlsm per rGO mass per package mass
With H2SO4: 3.3 Wh/kg rGO at 0.25 A/g, 6.8 kW/kg rGO at 10 A/g,
With BMIMBF4: 6.2 Wh/kg rGO at 0.25 A/g, 39.2 kW/kg rGO at 10 A/g
BMIMBF4 packaged: Wh/kg pkg at 0.25 A/g, kW/kg pkg at 10 A/g

22. Conclusions
Demonstrated Inkjet-printed, flexible packaged supercapacitors
No need for binders
7 mF in 3 x 3 cm package of 0.23 g demonstrated with BMIMBF4.
Need to optimize: package, current collector, electrode thickness, electrolyte, etc.
Ink development difficult, limited range of metal inks available for current collectors
Slow Deposition Rates-dilute inks, thick electrodes difficult – need new printing methods
Graphene activation, electrolyte optimization, or inclusion of pseudocapacitive materials could increase power or energy density.
Need to investigate rGO cycle life in different electrolytes
Shelf life needs to be investigated – water permeation into IL