1. Related Illustration on thermal propagation Prof. Xiao Chengwei (TF5 team leader) 2015/06/03

2. About thermal runaway (internal short circuit) Objective of thermal propagation How to do thermal propagation test Research of the test methods from different countries （ Japan, USA, Korea, China ） Suggestions Contents

3. Definition of internal short circuit The Internal short circuit (ISC) of the cell is an unintentional electrical connection between the anode and the cathode inside an electrochemical cell, bypassing the normal electrical conduction path. （ from OICA ）

4. Presentation from CAMX Power in 32th Annual International Battery Seminar & Exhibit in Florida in March, 2015. ISC of single cell is cannot be detectable and controlled through the battery pack design. ISC can directly result in the thermal runaway reaction occurrence of a single cell. Characteristic and severity of ISC

5. Probability of thermal propagation T onset Propagation time / s 130 (PE)21 170 (PP)35 20060 260259 290433 446549 The thermal runaway reaction of a single cell caused by ISC is inevitable and undetectable. The thermal runaway of a single cell can propagate to the adjacent cells which is affected by SOC, battery internal resistance, thermal control system, etc. The thermal runaway failure may occur at any time in the field. From Chinese presentation in 6 th meeting in Korea

6. The thermal propagation can cause serious consequences. Battery pack should be designed to achieve ”occupant protection (e.g. keeping enough time for occupant to evacuate)” under the situation of the thermal propagation occurrence. Objective of thermal propagation

7. How to do thermal propagation test Initiate one single cell thermal runaway reaction, see whether the battery pack can keep the normal function for a certain time on the condition of the battery pack thermal propagation or not. What has been discussed is not to find the best way to simulate the ISC, just to find the method to initiate the thermal runaway reaction of a single cell to test the battery pack thermal propagation behavior and to set requirements. Which method is the acceptable option to initiate the thermal runaway of a single cell?

8. Research result of the initiation of thermal runaway From Japan Nail pick Partial heating Nail penetration A Voltage drop(V)(1h later)0.320Max→0 Cell temperature( ℃ ) (1h later) 44192 PhenomenonNothingSmoke B Voltage drop(V)(1h later)0.1200.41 Cell temperature( ℃ ) (1h later) 30119 PhenomenonNothingSmoke C Voltage drop(V)(1h later)0.04Max→0 Cell temperature( ℃ ) (1h later) 45634 PhenomenonNothing Smoke Propagation

9. From USA The following methods were tested: a. Conductive heating: cells wrapped in Nichrome wire. b. Mechanical damage: nail penetration. c. Conductive heating: hand-made film heater. d. Conductive heating: off-the-shelf film heater. e. Conductive heating: multiple off-the shelf film heaters. f. Conductive heating: thick film resistor. See the document of EVS-06-35e. Research result of the initiation of thermal runaway

10. From Korea Thermal runaway trigger should be internal short circuit test. Alternative test method of ceramic nail with metal tip can be applicable on module level for propagation test purpose. Test itemTest conditionDrawbacks Heating 400W heater within the cells Heating until thermal runaway Heating power Severity of thermal runaway ∝ heating temperature Max temp. ∝ 1/cell size (constant heater power)  Difficult to specify heater power for various cell design Overcharge 1cell overcharging - 1C charging until thermal runaway Usually multiple cells are exposed in overcharge condition. Not applicable for cells with overcharge protection. Internal short Ceramic nail with metal tip - Test on single cell in module - Test condition : same with cell level ceramic nail test. Same issues with cell test. - Case weakening. - Precision control (less than 5mV). Research result of the initiation of thermal runaway

11. From China Test itemsOverchargeNailHeat Thermal runaway temperature 300 ℃ 100 ℃～ 400 ℃ 250 ℃ Test resultVenting and leakageSmoke or fire Most serious, Venting and leakage or fire OperationalBetternormalGood SuccessfulGoodnormalBetter Influence factors Active Protection device, like PTC or CID MaterialThermal diffusion All three methods are applicable for the thermal runaway initiation of a single cell for thermal propagation test; Based on the extent of operational complexity, the method of overcharge is preferred. Research result of the initiation of thermal runaway

12. From other organizations/countries OICA? Others? Research result of the initiation of thermal runaway

13. Summary Seen from the research results mentioned above, nail penetration, overcharge, heating are all acceptable test method options to initiate the thermal runaway of a single cell for the battery pack thermal propagation. Research result of the initiation of thermal runaway

14. Suggestions for thermal propagation Suggested test procedure: Adjust the SOC to full charged state. Overcharge one single cell until thermal runaway occurs. (The temperature over 130 ℃, or fire, or explosion?) Penetrate one single cell until thermal runaway occurs. (The temperature over 130 ℃, or fire, or explosion?) Heat one single cell until thermal runaway occurs. (The temperature over 130 ℃, or fire, or explosion?) Requirements: no fire, no explosion, keep normal function for ** minutes for the occupant to response and escape?

15. Further Research on thermal propagation What’s the definition of the exact initiation point of thermal runaway reaction? What’s the requirements of the battery pack thermal propagation? No fire, no explosion, no smoke, keep normal function for 5 minutes? 10 minutes? ……

16. Thanks!