U.S. Army Research, Development and
Engineering Command
Packaged
Inkjet-Printed
Flexible
Supercapacitors
Matthew Ervin (ARL), Linh Le (SIT), and Woo Lee (SIT)
Flexible Supercapacitors for
Munitions
Description of Application:
•Flexible printed supercapacitors
for storing energy to power
flexible munition electronics
POC: Brian Fuchs & Jim Zunino
Email address:
brian.edward.fuchs@us.army.mil
james.l.zunino.civ@mail.mil
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
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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
Email addresses:
stephanie.f.zopf.civ@mail.mil
natalie.l.pomerantz.civ@mail.mil
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 3 of 22
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
Supercapacitor vs. Electrolytic
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
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Capacitor Types
Ragone Plot of Electrochemical Devices
Dielectric
Electrolytic
dielectric
Electrochemical
Double Layer
cathode
Al foil
Al foil
anode
separator
‘
electrolyte
permittivity
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
Aqueous 1V
Organic 2.7V
Ionic liquid >3.5V
Lowest power/frequency
Highest energy
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Graphene Supercapacitor
Rationale
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.
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Flexible Device Component
Choices and Issues
•
•
•
•
•
•
Current Collector
Graphene Ink/Printing
Binder(less)
Separator(less)
Electrolyte
Substrate/Package
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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
But…
Adhesion of printed features?
Unstable substrate when sealing
Permeable to small molecules, e.g. CO2
8 of 22
Packaging Permeability
AN/thick Kapton/FEP
Electrolyte Mass (g)
0.2
Kapton permeability2.xls
0.15
IL/thick Kapton/FEP
PC/thick Kapton
0.1
H2O/thick Kapton/Al tape
0.05
H2O/thick Kapton/FEP
H2O/thin Kapton
H2O/thin Kapton/FEP
0
0
10
20
30
40
50
60
70
80
Time (days)
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Inkjet Printing Graphene Oxide
Suspension Stable,
Hydrophilic Graphene
Oxide (GO) in Water
(2mg/ml), no surfactant
Dreyer el al., Chem. Soc. Rev.,
2010, 39, 228-240
IR Heat Lamp
Print Head
Inkjet Printing Attributes
N • Micropatternable at 50 um resolution
D
D
• Additive, net-shape manufacturing with
minimum nanomaterial use and waste
• Scale-up and integration readiness with
rapidly emerging printed electronics
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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
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100 Printed Layers:
Cross-Section
500 nm
Stacks of horizontal sheets of graphene
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Packaged Prototype Assembly
Graphene printed on
evaporated Ti/Au on Kapton
Separator inserted
Double-side FEP coated
Kapton used for sealing
Electrolyte injected to wet the
separator/electrodes
Device sealed on three sides
The final heat seal is made
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Prototype CV Results
Cyclic Voltamogram
LL0114A01
3/25/14
1M H2SO4
0-1V
Capacitance
(F/g)
Energy Density
(Wh/kg)
LL0114A03
192
3/25/14
@ 20mV/s
5.0
@ 0.25 A/g
perDensity
rGO mass only
Power
10
(kW/kg)
@ 10 A/g
BMIMBF4
Charge/Discharge
0-3V
LL0114B04
5/7/1473
@ 20mV/s
5.5
@ 0.25 A/g
19
@ 10 A/g
LL0114A03
3/25/14
14 of 22
Prototype EIS Results
with H2SO4
-79 deg @ 10mHz
LL0114A02
3-25-14
0
50
100 150 200
Ohms
8.2 mF @ 10mHz
•
Good capacitive behavior at
low frequencies
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Bending Test
Capacitance vs Bending Experiment
Normalized Capacitance
1
0.8
0.6
Bending expt 2 04 11 13.xls
0.4
0.2
0
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
1/radius of curvature (mm-1)
(flat, 65, 40, 34, 25, 14, flat)
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Bending Cycles
Normalized Capacitance
8.25mm Radius flexing
1
0.8
0.6
Flex tests 3 25 14.xlsm
0.4
0.2
0
0
50
100
150
Number of Flex Cycles
200
250
•
•
150FN019 packaging
1M H2SO4 electrolyte
Normalized Capacitance
4mm Radius flexing
1
0.8
0.6
Flex tests 3 25 14.xlsm
0.4
0.2
0
0
20
40
60
Number of Flex Cycles
80
100
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Cycle-Life Testing
Cycle-Life Test in 1M H2SO4
Normalized Capacitance
1.2
1
Flex cycle life tests 5 14.xls
0.8
0.6
0.4
0.2
Cycle-Life Test in IL
0
100
200
300
400
500
Cycle number
•
EIS at 0V shows only a loss of 20%
capacitance
600
1.2
Normalized Capacitance
0
1
0.8
Flex cycle life tests 5 14.xls
0.6
0.4
0.2
0
0
10
20
30
40
50
60
70
Cycle Number
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Cycle-Life Testing
Cycle Life Test in 0.5M K2SO4
1.4
124 F/g
104 F/g
89 F/g
1
•
Dropcast,
coin cells
0.8
67 F/g
0.6
140C 16hrs
225C 4hrs
0.4
Flex cycle life tests 5 14.xls
0.2
Cycle Life Test in 0.5M K2SO4
0
0
50
100
150
Cycle #
•
200
250
1.2
Normalized Capacitance
Normalized Capacitance
1.2
Inkjet printed,
Flex Kapton cell
153 F/g
1
140 F/g
0.8
Flex cycle life tests 5 14.xls
0.6
225C 4hrs
0.4
0.2
0
0
50
100
150
200
250
Cycle #
19 of 22
Bending Cycles
Ragone Plots
100
per rGO mass
10
KW/kg
1
H2SO4
0.1
BMIMBF4
Flex Ragone plots.xlsm
0.01
0.001
0.001
•
•
0.01
0.1
1
Wh/kg
10
100
1000
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
20 of 22
Bending Cycles
Ragone Plots
100
Flex Ragone plots.xlsm
per rGO mass
10
1
KW/kg
H2SO4
BMIMBF4
IL packaged
0.1
Li Ion
Comm 80mF
0.01
per package mass
0.001
0.001
•
•
•
0.01
0.1
1
Wh/kg
10
100
1000
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: 0.0010 Wh/kg pkg at 0.25 A/g, 0.063 kW/kg pkg at 10 A/g
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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
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