Abuse Testing of Lithium Ion Cells: Internal Short Circuit, Accelerated Rate Calorimetry and Nail Penetration in Large Cells (1-20 Ah)

Transcription

1 Abuse Testing of Lithium Ion Cells: Internal Short Circuit, Accelerated Rate Calorimetry and Nail Penetration in Large Cells (1-20 Ah) Battery Safety 2011, Nov 9-10, Las Vegas, NV Ann Edwards, PhD Kirby W. Beard, COO Porous Power Technologies David Wood, Wei Cai, Jianlin Li, Hsin Wang Oak Ridge National Laboratory

2 Overview Introduction Porous Power (PPT) SYMMETRIX separator types Safety enhancements via PPT s advanced separators Testing and Results Li Ion Cell Mechanical Abuse: o Nail penetration test Li Ion Cell Thermal Abuse: o Accelerated rate calorimetry (Oak Ridge National Lab.), over-heating, temperature extreme cycling Li Ion Cell Electrical Abuse: o Internal short circuit (Oak Ridge National Lab.), external short circuit, over-charging Summary

3 Introduction Porous Power Separators Generation I: SYMMETRIX HP PVDF polymer membranes: ~80% porosity, 25 μm gauge, submicron pore size, low puncture and tensile strength Generation II: SYMMETRIX HPX Composite PVDF membranes with polyester fiber non-woven web reinforcement: 60-75% porosity, 25 μm gauge, submicron pore size, enhanced puncture and tensile strength

4 Generation III: SYMMETRIX HPXF Ceramic filled separator Modified Generation II product: composite PVDF/polyester non-woven web membrane but with high temperature ceramic fillers Typical/projected separator properties 60-80% total porosity 25 μm nominal thick, sub-micron pore size Enhanced tensile and compressive strength Enhanced puncture and penetration strength Enhanced temperature resistance Enhanced safety properties/cell performance

5 SEM Photomicrograph of SYMMETRIX HPXF Ceramic particles embedded in PVDF pore walls Up to 50% Filler by weight ~ 70% Porous Sub-micron through pores

6 60% ceramic filled, yet still flexible, heatsealable and fully laminable

7 How PPT Separators Enhance Safety High Temperature Resistance High melt point non-woven web fibers & high inert filler content provide structural integrity at > 200 C High Porosity/Low Internal Impedance Allows higher operating power with less self-heating Uniform Pore Structure (and high surface porosity) Reduces potential for harmful reactions (Li dendrite growth, electrolyte oxidation, etc.) and for hard shorting (thermal runaway) on overcharge High Penetration Resistance Helps to prevent particle cut-through

8 Temperature (degree Celsius) PPT s Typical Expanded Li Ion Li Cell Ion Operating Cell Operating Range Range Charge Rate (C-Rate) C/10 1C 10C Separator melting due to overheating from high temperature exposure or electrical abuse or both PPT's Generation III separator: Expanded region of safe Li ion cell operation Li plating upon cold charge Li plating upon high rate or high volt charge Voltage (Volts)

9 Testing and Results Mechanical Abuse Nail penetration test (USABC test protocol) No adverse effects observed on single cells of lower capacity (1.2 Ah and 5 Ah sizes) Flat plate pouch cell: -LiCoO 2 / Carbon electrodes -EC/EMC/LiPF 6 electrolyte Thermocouple is placed inside the nail and positioned to correspond with center of cell after cell is fully penetrated

10 Penetration Test Set up 3 mm diameter nail with pointed tip 8 cm/sec penetration speed Tested cells: -20 Ah single cells -2 x 1.2 Ah stacked cells/parallel wiring 100% SOC (4.2 V) Hollow steel spike with thermocouple inside Pouch cell with thermocouples on both surfaces

11 Nail Penetration Test Results Commercial polyolefin separator 20 Ah

12 Nail Penetration Test Results PPT SYMMETRIX HPX4 20 Ah

13 Temperature inside "nail" (º C) Nail Penetration Test: Peak Temperature Penetration Test of 20 Ah cells 671 C- vent with fire of both electrolyte and electrodes C - vent with flash-off of electrolyte, but without oxidation or fire of the electrodes Commercial Polyolefin (JOA147-11) HPX4 (JOB24-7) 0 00: : : : :09.1 Elapsed Time (mm:ss.0)

14 Nail Penetration Test Results 2 x 1.2 Ah polyolefin separator cells in parallel

15 Nail Penetration Test Results 2 x1.2 Ah SYMMETRIX HPX4 cells in parallel

16 Nail Penetration Test Results 2 x1.2 Ah SYMMETRIX HPXF cells in parallel

17 Nail Penetration Test - Results Two 1.2 Ah SYMMETRIX HPXF cells stacked together and connected in parallel after nail penetration:

18 Temperature inside "nail" (º C) Nail Penetration Test: Peak Temperature Nail penetration of two stacked 1.2 Ah cells connected in parallel 664 C: fast vent 564 C: slow vent with electrolyte flash off, but without oxidation/fire of electrodes C: no thermal events Commercial Polyolefin (JOB26-1&2) HPX4 (JOA149-6&7) HPXF (JOB15-7&8) 0 00: : : : :45.6 Elapsed Time (mm:ss.0)

19 Testing and Results Thermal Abuse Accelerated rate calorimetry Overheating Extreme temperature cycling

20 Cell Accelerated Rate Calorimetry 1.2 Ah flat plate pouch cells, 4 each: Commercial polyolefin separator PPT s SYMMETRIX HPX4 NW web reinforced separator Test procedure (per ORNL) Charge cell to specified limits (~ V) Increase calorimeter temperature at set rate Stop heating at onset of self-heating Measure exothermic reactions: Peak temp., time to peak temp., self-heat rate etc.

21 Maximum Temperature (ºC) Cell Accelerated Rate Calorimetry: Maximum Temperature Results SYMMETRIX HPX4 Commercial polyolefin Initial Charge Voltage (V)

22 Time to failure (minutes) Cell Accelerated Rate Calorimetry: Time to Peak Temperature SYMMETRIX HPX4 Commercial polyolefin Initial Charge Voltage (V)

23 Exotherm Temperature Rise (º C) Cell Accelerated Rate Calorimetry: ARC profile 4.1 V initial charge voltage Peak Temp.: 551 ºC Peak Temp. : 442 ºC HPX4 Commercial polyolefin Exotherm Time (minutes)

24 Exotherm Temperature Rise (ºC) Cell Accelerated Rate Calorimetry: ARC profile 4.4 V initial charge voltage Peak Temp.: 745 ºC Peak Temp.: 623 ºC HPX4 Commercial polyolefin Exotherm Time (minutes)

25 Li Ion Cell Overheating - Set up Cells at 100% SOC (4.2 V pre-charge) 1.2 Ah flat plate pouch cells Cells heated in oven from ~25 ºC at a rate of ~5 ºC per minute to 150 ºC Oven held at 150 ºC until failure Thermocouples externally located on top and bottom of cell pouch used to record cell temperatures

26 Temperature (º C) Cell Overheating - Results Oven Heating of 1.2Ah Cells After reaching 150 C, time until exotherm: Polyolefin ~25 minutes HPXF ~40 minutes 274 C 245 C Polyolefin (JOB26-3) HPXF (JOB15-9) 0 0:00:00 0:28:48 0:57:36 1:26:24 1:55:12 Time (h:mm:ss)

27 Varied Temperature/Rate Cycling: Test Set up 1.2 Ah flat plate pouch cells Cells cycled at 60 ºC, 40 ºC, 20 ºC & 0 ºC Initial results of discharge rate capability reported (C/10 to 6C) Long term cycling capacity testing in progress (up to 3000 cycles planned)

28 Discharge Capacity (Ah) Capacity at 60 ºC at Varied Discharge Rate: 1.2 Ah C/EC, EMC, LiPF 6 /LiCoO 2 Cells Discharge Capacity at 60 ºC Polyolefin HPX4 HPXF C-rate (Current in 1/hr)

29 Capacity at 40 ºC at Varied Discharge Rate: 1.2 Ah C/EC, EMC, LiPF 6 /LiCoO 2 Cells Discharge Capacity (Ah) Discharge Capacity at 40 ºC Polyolefin HPX4 HPXF C-rate (Current in 1/hr)

30 Discharge Capacity (Ah) Capacity at 20 ºC at Varied Discharge Rate: 1.2 Ah C/EC, EMC, LiPF 6 /LiCoO 2 Cells Discharge Capacity at 20 ºC Polyolefin HPX4 HPXF C-rate (Current in 1/hr)

31 Capacity at 0 ºC at Varied Discharge Rate: 1.2 Ah C/EC, EMC, LiPF 6 /LiCoO 2 Cells Discharge Capacity (Ah) Discharge capacity at 0 ºC Polyolefin HPX4 HPXF C-rate (Current in 1/hr)

32 Discharge Capacity (Ah) Percent of Full Capacity Extreme Temperature Cycling at -20 C (PPT s Gen. II vs. commercial polyolefin separators) Cycling Capacity of PPT's Gen II vs. Commercial Polyolefin at -20 C [C/5 Discharge, C/5 Charge] Generation II commercial product Commercial Polyolefin Cycle Number

33 Testing and Results Electrical Abuse of Charge Li Ion cells Internal short circuit External short circuit Overcharge

34 Internal Short Circuit Set up ORNL Pinch Test shorts cells between two metal spheres (spheres do not penetrate cell pouch) Variable parameters: Sphere Size Loading Speed Return Mode Voltage

35 Internal Short Circuit Set up Test parameters used: 1.2Ah flat plate pouch cells Room temperature 1 inch diameter brass spheres Load speed of inches/second Various charged open circuit voltages were investigated

36 Internal Short Circuit - Results Cell number Separator type Open circuit voltage before test Thermal runaway JOA143-2 Polyolefin 4.1 No JOA143-4 Polyolefin 4.2 No JOA143-1 Polyolefin 4.2 Yes JOA143-3 Polyolefin 4.3 Yes JOA143-6 HPX No JOA143-9 HPX No JOA143-7 HPX No JOA143-8 HPX Yes JOA147-1 HPX No JOA147-3 HPX No JOA147-4 HPX No JOA147-2 HPX Yes JOB4-13 HPXF 4.2 No JOB4-14 HPXF 4.4 No JOB4-12 HPXF 4.4 No JOB4-15 HPXF 4.45 No

37 External Short Circuit Set up Test parameters used: 1.2 Ah flat plate pouch cells All cells at 100% SOC (~4.2 V) Hard short applied to terminals in <0.1 second Shorting resistance ~ 5 mω

38 Short Circuit Current, amp External Short Circuit: Discharge Current Discharge Short Circuit Test of 1.2 Ah Cells: External Shorting Current, amp Greater peak currents as compared to commercial polyolefin Commercial Polyolefin Separator, 1.2 Ah HPX4, 1.2 Ah HPXF, 1.2 Ah Discharge Time, sec.

39 External Cell Temperature (ºC) External Short Circuit: Cell Temperature Discharge Short Circuit Test of 1.2 Ah Cells: External Cell Temperature, deg. C Cells with PPT separators reach higher temperatures due to higher current, but still quickly and safely cool down Discharge Time (seconds) Cells with polyolefin separators continue to heat up over a period of >6 minutes...despite the apparent "shut-down" of the cell by the melted separator. Commercial polyolefin separator, 1.2 Ah HPX4, 1.2 Ah HPXF, 1.2 Ah

40 Short Circuit Current (amps) External Short Circuit: Discharge Current Discharge Short Circuit Test of 5 Ah Cells: External Shorting Current, amp Greater peak currents as compared to commercial polyolefin Commercial Polyolefin Separator, 5 Ah HPX4, 5 Ah HPXF, 5 Ah Discharge Time (seconds)

41 External Cell Temperature (ºC) External Short Circuit: Cell Temperature Discharge Short Circuit Test of 5 Ah Cells: External Cell Temperature, deg. C PPT separator cells show gradual, controlled cooling after sustaining high initial shorting currents Larger capacity cells with polyolefin shutdown separators reach higher initial peak temperatures Polyolefin separators also show a secondary thermal event after a period of >6 minutes Commercial Polyolefin Separator, 5 Ah HPX4, 5 Ah HPXF, 5 Ah Discharge Time (seconds)

42 Overcharge Set up 5 Ah flat plate pouch cells 100% SOC starting condition (~4.2 V) 2 C charge rate Overcharge until cell failure

43 Cell Temperature (ºC) Overcharge: Cell Temperature Cell Failures Under Abuse Overcharge (5 Ah cells, 2C Charge Rate) Commercial Polyolefin HPX4 HPXF Commercial polyolefin in thermal runaway at 50 C external cell temperature and 77% overcharge Increased thermal abuse resistance of PPT separators: no thermal runaway until >75 C and ~100% overcharge % Overcharge, fully charged cells

44 Cell Voltage (Volts) Overcharge: Cell Voltage Cell Failures Under Abuse Overcharge (5 Ah cells, 2C Charge Rate) Commercial Polyolefin HPX4 HPXF Cell voltage spike as a result of Shutdown of polyolefin separator - followed by thermal runaway at 77% overcharge PPT separators show a lower voltage spike at thermal runaway at 97% overcharge % Overcharge, fully charged cells

45 Summary PPT s SYMMETRIX HPX4 & HPXF provide: Improved cell safety performance (mechanical, thermal and electrical abuse) Exceptional cell rate capability and cycle life (even at extreme hot and cold temperatures) ORNL compressive cycle fatigue results same or better than various polyolefin separators SYMMETRIX HPXF also provides: Excellent particle penetration resistance Cost reduction (via use of low cost fillers)

46 Acknowledgement Project supported in part by CRADA No. NFE The research at Oak Ridge National Laboratory, managed by UT Battelle, LLC, for the U.S. Department of Energy under contract DE-AC05-00OR22725, was sponsored by the Industrial Technologies and Vehicle Technologies Programs of the Office of Energy Efficiency and Renewable Energy.

47 Thank You, For Further Details Contact: Porous Power Technologies, LLC Technical and Engineering Center 5115 Campus Drive Plymouth Meeting, PA Kirby W. Beard, Co-founder & COO/CTO Corporate Headquarters: Porous Power Technologies, LLC 2765 Dagny Way, Lafayette, CO Office: , Fax: