Vacuum and Atmospheric Coating and Lamination Techniques Applied to Li-S Battery Fabrication

Transcription

1 Vacuum and Atmospheric Coating and Lamination Techniques Applied to Li-S Battery Fabrication AIMCAL Web Coating Conference Paper AB5, 1:00 PM Wednesday, October 26, 2011 The Rechargeable Battery Company John Affinito, Sion Power Corporation Chief Technical Officer

2 Vacuum and Atmospheric Coating and Lamination Techniques Applied to Li-S Battery Fabrication, AIMCAL Paper AB5 10/26/11, John Affinito slide 2 Outline of Presentation Li-S Basics Why develop Li-S? Specific Energy. The Li-S Discharge Characteristic. The Upper Plateau Polysulfide Shuttle. Lower Plateau Li 2 S precipitation, in relation to cathode porosity, microstructure and solvent effects. Upper Plateau: ~420 mah/gs Lower Plateau: ~1260 mah/gs 1,672 mah/gs 2,572 Wh/kg 2,835 Wh/l Sion s solutions for Li-S Cycle Life, Safety and Energy improvements. The Future Li-S Cell. Sion s Old Technology Li-S cells enabled a record setting UAV Flight. Summary. Soluble Polysulfide species diffuse from the cathode to the anode and selfdischarge the Upper Plateau, with loss of ~400 mah/gs. Leaving ~ mah/gs Li 2 S precipitation clogs the cathode, polarizes the cell and leads to ~400 mah/gs capacity loss at the end of the Lower Plateau.

3 Vacuum and Atmospheric Coating and Lamination Techniques Applied to Li-S Battery Fabrication, AIMCAL Paper AB5 10/26/11, John Affinito slide 3 Why Choose Lithium and Sulfur? For high specific energy and volumetric energy density. S e Li + 8Li 2 S ΔG ~ kj/mol The Li-S couple has the highest theoretical specific energy and energy density of any pair of solid elements. Li-S: <OCV> ~2.18 V Theoretical ~2,572 Wh/kg Theoretical ~2,835 Wh/l Compare With Li-ion Energies: Theoretical ~600 Wh/kg Theoretical ~1,800 Wh/l Li-ion is currently at/near, practical limit of ~40% of theoretical specific energy (<250 Wh/kg). At 350 Wh/kg, Sion s baseline Li-S cell is only at 14% of theoretical specific energy.

4 Vacuum and Atmospheric Coating and Lamination Techniques Applied to Li-S Battery Fabrication, AIMCAL Paper AB5 10/26/11, John Affinito slide 4 The Li-S Discharge Characteristic Tells Much, but not all, of the Story Very Low Solubility S 8 e 2 Upper Plateau 2 Li Li S Li Lower Plateau 1-Li 2 S Nucleation Polarization Begins. First Discharge Only 2S8 e 2Li Li S 2Li Li S 2-Highest Conc. Li 2 S x Species. 3-Highest Viscosity. 2S4 4e 4Li 4 4Li2S2 8e 8Li 8Li2S ~1,672 mah/g(s) Theoretical: ~2,572 Wh/kg(S+Li) ~2,835 Wh/l(S+Li) High Solubility Moderate Solubility Very Low Solubility Solid Upper Plateau - Fast Kinetics Lower Plateau - Slow Kinetics

5 Vacuum and Atmospheric Coating and Lamination Techniques Applied to Li-S Battery Fabrication, AIMCAL Paper AB5 10/26/11, John Affinito slide 5 The Li-S discharge curve looks great. But..What are the real world problems? First Problem: Polysulfide Shuttle The high solubility and fast kinetics of the Upper Plateau species leads to the Polysulfide Shuttle that results in near complete loss of the upper plateau capacity, ~400 mah/gs.

6 The Polysulfide Shuttle Causes Massive Self-Discharge of Li-S Cells Vacuum and Atmospheric Coating and Lamination Techniques Applied to Li-S Battery Fabrication, AIMCAL Paper AB5 10/26/11, John Affinito slide 6 Polysulfide Shuttle Soluble Li 2 S x species on the Upper Plateau diffuse to the anode where they are reduced to Li 2 S. This results in Rapid Self- Discharge and loss of the Upper Plateau capacity, ~400 mah/gs.

7 Vacuum and Atmospheric Coating and Lamination Techniques Applied to Li-S Battery Fabrication, AIMCAL Paper AB5 10/26/11, John Affinito slide 7 About ¼ of Total Li-S Cell Discharge Capacity is Lost Due to the Polysulfide Shuttle. Still ~400 mah/gs missing?

8 Vacuum and Atmospheric Coating and Lamination Techniques Applied to Li-S Battery Fabrication, AIMCAL Paper AB5 10/26/11, John Affinito slide 8 Second Problem: Li 2 S Precipitation With typical cathodes and solvents used in Li-S cells, the low solubility and slow kinetics of the Lower Plateau species, and clogging susceptible cathode structures, result in polarization that is responsible for loss of another ~400 mah/gs: this time from the end of the Lower Plateau. This effect becomes more severe as the discharge rate is increased and/or as solvent is depleted in parasitic Li- Solvent reactions. Controlling cathode porosity, detailed cathode microstructure, solvent type and solvent level are absolutely critical to optimize specific energy.

9 Cathode Diffusion Limitations, and Li 2 S Precipitation at the End of the Lower Voltage Plateau, Limit Li-S Cell Capacity Anode facing cathode surface at the end of the lower voltage plateau after the 20 th discharge. Li 2 S deposits block cathode porosity on anode facing surface, limiting capacity to <1,250 mah/gs, in current high energy-high rate Li-S cell designs. Without anode protection, solvent is also lost on each cycle, further increaseing Li 2 S precipitation and capacity loss on each cycle. Vacuum and Atmospheric Coating and Lamination Techniques Applied to Li-S Battery Fabrication, AIMCAL Paper AB5 10/26/11, John Affinito slide 9

10 Vacuum and Atmospheric Coating and Lamination Techniques Applied to Li-S Battery Fabrication, AIMCAL Paper AB5 10/26/11, John Affinito slide 10 Sion s Electrochemical Model Predicts that Blocking of the Cathode Porosity Leads to End of Cycle Cathode Blocking of Baseline Cathode as a Function of State of Charge and Distance from Anode Surface, at C/5 discharge rate Porosity is not blocked on the Upper Plateau (blue trace) due to the high solubility of upper plateau polysulfides. Blocking begins as the lower plateau discharge begins, due to the low solubility of species. Polarization spikes up, ending the cycle as blockage of the anode facing surface of the cathode reaches the percolation limit (~16% open, red trace) at a sulfur utilization of ~70%.

11 Vacuum and Atmospheric Coating and Lamination Techniques Applied to Li-S Battery Fabrication, AIMCAL Paper AB5 10/26/11, John Affinito slide 11 Cell Capacity is Strongly Influenced by Electrolyte/Solvent Selection Cathode Specific Capacity vs. Solvent Type, at C/5 Discharge Rates (350 Wh/kg design, No Anode Protection and Cells Not Cycled Under Externally Applied Pressure) Solvent 7 Solvent 6 Solvent 5 Solvent 4 Solvent 3 Many solvent systems can resolubilize Li 2 S. However, to be useful with an unprotected metallic Li anode, the solvent must be relatively benign towards metallic Li. Solvent 2 Solvent 1 Specific Capacity for 5 hour discharge (mah/g) (for 350 Wh/kg cell formats) To date, this has limited S-Utilization to less than about 1,250 mah/gs at reasonable discharge rates (>C/5).

12 Cell Performance as a Function of Cathode Structure (without anode protection) Cycling with Cathode Structure Typical of Current Li-S Cathodes Cycling with Cathode with Engineered Topology, Microstructure and Porosity Li DoD ~50% Increasing Cycle # s With conventional cathode structure: The pores plug while cycling. Cell reaches polarization induced voltage cut-off at lower capacity with each cycle as solvent depletes. With engineered cathode structure: Pores don t plug while cycling. Cathode polarization is reduced and capacity stays higher longer, even as solvent depletes. Vacuum and Atmospheric Coating and Lamination Techniques Applied to Li-S Battery Fabrication, AIMCAL Paper AB5 10/26/11, John Affinito slide 12

13 Cycle Life, Safety and Capacity issues with the 1 st Generation of Li-S Cells (the last 40 years) When the shuttle is stopped, solvent depletion, due to the metallic Li anode reacting with the electrolyte, limits cycle life. Safety is limited by metallic Li reacting with sulfur species. Specific Energy is limited by Upper Plateau self-discharge, through the Polysulfide Shuttle, by Lower Plateau precipitation of Li 2 S/cathode clogging and by cell design. The shuttle can be suppressed by Sion s NO x additives, or by physical membranes protecting the anode. NO x additives do not stop solvent depletion, membranes can. Li 2 S precipitation can be mitigated by either, or both, of: Solvents more aggressive to Li 2 S x in the cathode; or A high permeability/high throughput cathode microstructure that doesn t clog and improves overall transport through the cathode. Vacuum and Atmospheric Coating and Lamination Techniques Applied to Li-S Battery Fabrication, AIMCAL Paper AB5 10/26/11, John Affinito slide 13

14 Vacuum and Atmospheric Coating and Lamination Techniques Applied to Li-S Battery Fabrication, AIMCAL Paper AB5 10/26/11, John Affinito slide 14 How can the Li-S cycle life, safety and capacity issues be overcome? What are Sion s approaches?

15 Increasing Li-S Cycle Life (the Future Cell) Key to increasing cycle life is stopping the metallic Li anode from reacting with solvents and controlling Li morphology. Sion s Approach Protect the Metallic Lithium Anode and Decouple the Anode and Cathode Chemistries: An atmospherically coated, thin film, releasable substrate; A vacuum deposited current collector; Vacuum Deposited Li (VDLi); Vacuum Deposited Anode Stabilization Laminates (ASLs); comprising multi-layer ceramic/polymer protective coatings; A compliant, atmospherically coated, polymer gel separator; A dual phase solvent system; and Externally applied uniaxial pressure (controls morphology). Cathode issues are secondary with respect to cycle life. Vacuum and Atmospheric Coating and Lamination Techniques Applied to Li-S Battery Fabrication, AIMCAL Paper AB5 10/26/11, John Affinito slide 15

16 Vacuum and Atmospheric Coating and Lamination Techniques Applied to Li-S Battery Fabrication, AIMCAL Paper AB5 10/26/11, John Affinito slide 16 Functional Description of Sion s Future Li-S EV Cell Layered Elements Stabilizes Li Morphology and ASL structure Increases Li smoothness and specific energy Increases cycle life/smoothness, carries current Allows thinner, smoother, Li. Allows reactive doping of Li to improve electrochemistry Blocks solvents from contacting, and reacting with, metallic Li anode Transmits pressure uniformly to Li, stabilizes ASL, reservoir for dual phase anode solvent Reservoir for polysulfide aggressive dual phase cathode solvent, increases S-utilization Structurally stable cathode does not collapse under applied pressure, and optimized pore structure increases S-utilization Tie layer adheres cathode to current collector Carries current to/from cathode Stabilizes Li Morphology and ASL structure

17 In Sion s Future Li-S EV Cell Construction, All Major Elements are Coated Vacuum and Atmospheric Coating and Lamination Techniques Applied to Li-S Battery Fabrication, AIMCAL Paper AB5 10/26/11, John Affinito slide 17 Atmospherically Coated Vacuum Coated Atmospherically Coated

18 Improving Li-S Safety (the Future Cell) Key to improving safety is stopping the metallic Li anode from reacting with sulfur and controlling Li morphology. Sion s Approach Protect the Metallic Lithium Anode and Decouple the Anode and Cathode Chemistries: (all the same methods used to increase cycle life on the previous slide) An atmospherically coated, thin film, releasable substrate; A vacuum deposited current collector; Vacuum Deposited Li (VDLi); Vacuum Deposited Anode Stabilization Laminates (ASLs); comprising multi-layer ceramic/polymer protective coatings; A compliant, atmospherically coated, polymer gel separator; A dual phase solvent system; and Externally applied uniaxial pressure. Cathode issues are secondary with respect to safety. Vacuum and Atmospheric Coating and Lamination Techniques Applied to Li-S Battery Fabrication, AIMCAL Paper AB5 10/26/11, John Affinito slide 18

19 Vacuum and Atmospheric Coating and Lamination Techniques Applied to Li-S Battery Fabrication, AIMCAL Paper AB5 10/26/11, John Affinito slide 19 Improved Safety with Sion-BASF Compliant Gel Layer Cycling Under Pressure (the Future Cell) Thermal Ramp Test: Fully charged Li-S cells ramped at. 5 o C/min after 20 cycles, Li DoD ~50%.

20 Vacuum and Atmospheric Coating and Lamination Techniques Applied to Li-S Battery Fabrication, AIMCAL Paper AB5 10/26/11, John Affinito slide 20 Metallic Li Anode Morphology is Stabilized by Uniaxial Pressure: Smoother is Safer and Promotes Cycle Life A highly mud cracked coated cathode. 500 µm Very smooth plateaus separated by large mud-cracks 100 µm 2 Anodes initially 50 µm thick, cycled from each side, after 50 cycles At a Li DoD of ~50%. 100 µm Top: Cycled under pressure: Remains dense Li metal; Retains original 50 µm thickness; and Is very smooth except for extrusion into cathode mud-cracks and negative impressions of the cathode the surface. Bottom: Cycled without pressure: Becomes highly mossy; Is over 200 µm thick; and Is very rough on all scales and surfaces.

21 Vacuum and Atmospheric Coating and Lamination Techniques Applied to Li-S Battery Fabrication, AIMCAL Paper AB5 10/26/11, John Affinito slide 21 Under Pressure, Anode Surfaces Mimic Cathode Surfaces and Cathode Imprints are Muted by a Gel Layer A differently coated cathode. Relatively smooth, without mud-cracks and with relatively small features. A single anode. 50 µm 50 µm Initially 50 µm thick, cycled from each side, after 450 cycles - with a semi-compliant gel layer between anode and cathode. Cycled at a Li DoD of ~50%. Anode cycled under pressure: Remains dense Li metal; Retains original 50 µm thickness; Is very smooth and approximately mimics the cathode surface; and Cathode features are muted on anode surface due to intervening gel layer.

22 Vacuum and Atmospheric Coating and Lamination Techniques Applied to Li-S Battery Fabrication, AIMCAL Paper AB5 10/26/11, John Affinito slide 22 Increasing Li-S Capacity (the Future Cell) Key to increasing Li-S capacity is reduction of cell mass, increasing S-utilization by optimizing porosity, solvent type and solvent level. Sion s Approaches: A variety of anode protection methods reduce solvent loss and maintain proper cathode function/capacity while minimizing solvent requirements; Optimize cell design to minimize the mass of inactive components. With the anode protected, and employing Sion s dual phase electrolyte methodology, use solvents more aggressive towards polysulfides, particularly towards Li 2 S, on the cathode side of the cell to increase sulfur utilization; Engineer cathode topology, microstructure and porosity to limit pore blocking to increase transport and permeability to increase S-utilization. While the previous two techniques/bullets improve cathode function/sulfur utilization, resulting in a small cycle life increase, the cells will still fail due to solvent depletion, eventually, without anode protection. Anode issues are secondary with respect to energy.

23 Vacuum and Atmospheric Coating and Lamination Techniques Applied to Li-S Battery Fabrication, AIMCAL Paper AB5 10/26/11, John Affinito slide 23 Use Of New Technologies (the Future Cell) Dramatically Improves Li-S Cycle Life The new technology cells are still cycling End of Life of Old Technology Cells End of Life of New Technology Cells

24 First Commercial Li-S Application is Unmanned Aerial Vehicles UAVs (using Sion s old technology Li-S cells) Vacuum and Atmospheric Coating and Lamination Techniques Applied to Li-S Battery Fabrication, AIMCAL Paper AB5 10/26/11, John Affinito slide 24 QinetiQ's Zephyr 7 UAV Exceeds Official World Record for Longest Duration Unmanned Flight. Flew to >70,000 ft where temperature is < -60 o C. Used solar power to fly & recharge batteries by day. Flight was powered by Sion Li-S batteries at night. Official world record: >14 days of continuous flight. July, meter Wing Span

25 Projected Discharge Capacity of Sion EV Cell by the End of 2013 (the Future Cell) Vacuum and Atmospheric Coating and Lamination Techniques Applied to Li-S Battery Fabrication, AIMCAL Paper AB5 10/26/11, John Affinito slide 25

26 It is Unlikely that Li-ion Specific Energy Will Match Even 2010 Li-S Specific Energy by 2020 For Li-ion to continue on this trend line will require either new anode materials, new cathode materials or both. Li-S requires a new cathode structure and anode protection. Vacuum and Atmospheric Coating and Lamination Techniques Applied to Li-S Battery Fabrication, AIMCAL Paper AB5 10/26/11, John Affinito slide 26

27 Comparison of 2010 Li-S Performance Parameters to Projected 2013 Li-S Cells Current Sion Li-S Cell 63 mm x 43 mm x 11.5 mm 2.8 Ah, 350 Wh/kg, 320 Wh/l, cycles Wound Prismatic Design Projected Sion Li-S Cell in 2013 (the Future Cell) 121 mm x 106 mm x 8.5 mm 25 Ah, >500 (Wh/kg, Wh/l, cycles) Stacked Plate Design Project: >600 (Wh/kg, Wh/l) and >1,000 cycles by 2016 Vacuum and Atmospheric Coating and Lamination Techniques Applied to Li-S Battery Fabrication, AIMCAL Paper AB5 10/26/11, John Affinito slide 27

28 Summary Li-S cycle life is dominated by anode-electrolyte reactions. The cathode plays a secondary role in Li-S cycle life. Li-S safety is dominated by anode-sulfur reactions. The cathode plays a secondary role in Li-S safety. Li-S specific energy is dominated by cathode structure, solvent and discharge product volume requirements. Solvent type and cell design also play important roles. When nitrates or barrier layers control Upper Plateau capacity loss due to the shuttle, the anode plays only a secondary role in Li-S cell specific energy. With Sion s new hardware coming online, cells fabricated with Sion s new anode and cathode coating technologies are beginning to show dramatic cycle life improvement over old technology Li-S cells. Vacuum and Atmospheric Coating and Lamination Techniques Applied to Li-S Battery Fabrication, AIMCAL Paper AB5 10/26/11, John Affinito slide 28

29 Some of the Sion Team and One of the Anode Vacuum Web Coaters Thank You. Now hiring, process Scientists, Engineers and Technicians for both Vacuum and Atmospheric coating. Call: (520) Any Questions? Acknowledgements: This work has been supported in part by the United States Department of Energy, Advanced Research Projects Agency Energy (ARPA-E), under Award Number DE-AR Vacuum and Atmospheric Coating and Lamination Techniques Applied to Li-S Battery Fabrication, AIMCAL Paper AB5 10/26/11, John Affinito slide 29