Pipeline and Hazardous Material Administration (PHMSA) Department of Transportation

1. 1 Pipeline and Hazardous Material Administration (PHMSA) Department of Transportation AN OVERVIEW OF INTERNAL SHORT CIRCUIT SCREENING TEST METHODS FOR LITHIUM BATTERIES and a Proposal for Test T.6 Modification Presented at 1st Workshop on Lithium Batteries, Brussels, Belgium March 17-18, 2015 Steve Hwang, Ph.D. steve.hwang@dot.gov

2. 2 UN Test Guidelines TestsTest NamePurposeRequirement Primary Secondary CellBatteryCellBattery T1 Altitude Vacuum @ 11.6 kPa 1 yes yes yes yes T2 Thermal -40 – 72 oC 1 yes yes yes yes T3 Vibration 7 Hz – 200 Hz 1 yes yes yes yes T4 Shock Small 150 g 6 ms 1 yes yes yes yes Large 50 g 11 ms T5 External Short External short 2 yes yes yes yes T6 Impact/Crush Internal short by 2 yes no yes no applying external impact T7 Overcharge <18 V 3 no no no yes > 18 V x 1.2 T8 Forced Discharge Maximum discharge 3 yes no yes no current 1. No leakage, no venting, no disassembly, no rupture, no fire, <90% of V 2. Not exceeding 170 oC, no disassembly, no rupture, no fire 3. disassembly, no fire

3. 3 Causes of Internal Short-Circuiting • Causes Why can this Can it be managed? • happen? • Shock or Dropping Physical Abuse Strong casing by design • Formation of Dendrite Lithium Plating New Techniques needed • Existence of Impurities Manufacturing New Techniques needed • due to Poor Quality Control defects • during Manufacturing • Imbalance of Voltage Voltage BMS • among Cells Imbalance • High Charging Voltage High Charging BMS • applied to a cell Voltage • 6. Propagation of Thermal Damaged Cell Proper venting, insulation • Runaway can raise temp. • of surrounding • cells • Separator Failure Temp, Defects, wear- T control, quality • out, puncture, degrad. control, struct.

4. 4 Cases of Thermal Runaway as it relates to Internal Shorts (Metal particle in cathode slurry) Nail Penetration - Did not cause thermal runaway Manufacturing Defects – Possible thermal runaway Cell Crushing - Can cause massive internal shorts and thermal runaway Metal Plating (Dendrite) - Can reach 200 oC with thermal runaway Elevated Temp - Can cause thermal runaway @ >170 oC

5. 5 • How Applied Method for As a Test Requirement • Inducing ISCfor Prevention • NREL During Manufacturing Heat to ~55 oC Can reduce IS with 1 • ISC Device Process to Melt Wax Shut-down Separator • UL Indentation Rounded Tip Pressure Safety Level req’d 1 • Induced ISC Nail in the Market • IEC (62133) Nickel Powder Pressure Safe Cell Design 1 • Forced ISC Tech • Nail Nail Piecing Safety Level req’d 1 • Penetration in the Market • Impact/Crash Small: Steel Bar Drop weight Survival of 2 • (UN 38.3) Large: Flat Surface Force applied Deformation • Propagation Insulated Heating of a Proper Venting 3 • Test Thermal Chamber Cell • 1. No Fire • 2. No fire, No disassembly , not exceeding 170 oC • 3. No external fire, No battery case rupture Comparison of Internal Shorts Screening Tests

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8. 8 Cell Separator Deformation from Indentation Test

9. 9 Data Search Test Type (Li Ion cells) % of Explosion or Fire Indentation ISC 58 Forced Nickel Powder None NREL ISC Device Depending on existence of shut-down separator Techniques

10. 10 -10 oC 5 oC 20 oC DENDRITE GROWTH PATTERN

11. 11 Separator vs. Dendrite Mechanical Interaction: Compressive Stress Polymer Property: Brittle Failure Mode*: Crack Propagation & Growth Desire Property: High Bulk Modulus; Low Compressibility Ideal Material: Large Pore Size OK; High Ductility

12. 12 SUMMARY Many companies are testing cells and batteries to determine their integrity as it relates to ISC using the test methods of their choosing. None of the ISC screening methods can address the basic concern on IS prevention. It is not clear why these tests are conducted by he manufacturers. No recommendable test methods for preventing occurrence of ISC can be identified from literature search. Though many field failures are reported to be caused by IS resulting from manufacturing defects or impurities inadvertently incorporated during manufacturing, no tools presently exist to detect or mitigate these defects.

13. 13 SUMMARY (cont’d) Recent research information indicates that dendrite formed at the anode migrates to the cathode through the separator membrane to cause an internal short circuiting. A corollary to the finding is that the integrity of separator membranes plays a significant role in retarding or preventing the dendrite penetration through the membrane. It is important to test for the desired mechanical properties of the separator membranes to mitigate the occurrence of internal short-circuiting and thermal runaway.