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U.S. Army Research, Development and Engineering Command Matthew Ervin (ARL), Linh Le (SIT), and Woo Lee (SIT) Packaged Inkjet-Printed Flexible Supercapacitors.

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Presentation on theme: "U.S. Army Research, Development and Engineering Command Matthew Ervin (ARL), Linh Le (SIT), and Woo Lee (SIT) Packaged Inkjet-Printed Flexible Supercapacitors."— Presentation transcript:

1 U.S. Army Research, Development and Engineering Command Matthew Ervin (ARL), Linh Le (SIT), and Woo Lee (SIT) Packaged Inkjet-Printed Flexible Supercapacitors

2 2 of 22 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 3 of 22 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/m 2, > 0.5 kJ/kg Conductivity = 1 mS/cm Capacitance = 1µF/cm 2 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 4 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 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 5 of 22 Capacitor Types Ta 50V Al 500V Highest power/frequency Lowest energy Thicker dielectric yields higher voltage, but volumetric energy density unchanged DielectricElectrolyticElectrochemical Double Layer ‘ Al foil anode dielectric separator cathode electrolyte permittivity Dielectric strength Lower power/frequency More energy Ragone Plot of Electrochemical Devices Lowest power/frequency Highest energy Aqueous 1V Organic 2.7V Ionic liquid >3.5V

6 6 of 22 Graphene Supercapacitor Rationale Rationale: Graphene has the highest surface area which correlates to capacitance m 2 /g, external surface area (20uF/cm 2 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. Goal:  To increase power and energy density of supercapacitors using graphene CNT/G

7 7 of 22 Flexible Device Component Choices and Issues Current Collector Graphene Ink/Printing Binder(less) Separator(less) Electrolyte Substrate/Package

8 8 of 22 Substrate/Packaging Material Kapton: Stable to 400 o C – 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 (350 o C) Chemically inert But… Adhesion of printed features? Unstable substrate when sealing Permeable to small molecules, e.g. CO 2

9 9 of 22 Kapton permeability2.xls Packaging Permeability AN/thick Kapton/FEP IL/thick Kapton/FEP PC/thick Kapton H2O/thick Kapton/Al tape H2O/thick Kapton/FEP H2O/thin Kapton/FEP H2O/thin Kapton

10 10 of 22 Inkjet Printing Graphene Oxide N D D Print Head IR Heat Lamp Substrate Dreyer el al., Chem. Soc. Rev., 2010, 39, Suspension Stable, Hydrophilic Graphene Oxide (GO) in Water (2mg/ml), no surfactant 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 11 of 22 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 12 of nm 100 Printed Layers: Cross-Section Stacks of horizontal sheets of graphene

13 13 of 22 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 insertedElectrolyte injected to wet the separator/electrodes The final heat seal is made

14 14 of 22 LL0114A03 3/25/14 LL0114B04 5/7/14 LL0114A03 3/25/14 LL0114A01 3/25/14 per rGO mass only Prototype CV Results Cyclic Voltamogram Charge/Discharge 1M H 2 SO 4 0-1V BMIMBF 4 0-3V Capacitance (F/g) 20mV/s 20mV/s Energy Density (Wh/kg) 0.25 A/g 0.25 A/g Power Density (kW/kg) 10 A/g 10 A/g

15 15 of 22 LL0114A Good capacitive behavior at low frequencies Prototype EIS Results with H2SO Ohms mHz mHz

16 16 of 22 Bending expt xls Bending Test

17 17 of 22 Flex tests xlsm Bending Cycles 150FN019 packaging 1M H2SO4 electrolyte

18 18 of 22 Flex cycle life tests 5 14.xls EIS at 0V shows only a loss of 20% capacitance Cycle-Life Testing

19 19 of 22 Flex cycle life tests 5 14.xls 104 F/g 89 F/g 124 F/g 67 F/g Cycle-Life Testing 140 F/g 153 F/g Dropcast, coin cells Inkjet printed, Flex Kapton cell

20 20 of 22 Flex Ragone plots.xlsm Bending Cycles 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 per rGO mass

21 21 of 22 Flex Ragone plots.xlsm Bending Cycles 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 per rGO mass per package mass

22 22 of 22 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 Conclusions


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