1. for Thermal Propagation
Japanese Research
for Thermal Propagation
EVS-GTR IWG #9 in China
14th-18th Sep, 2015

2. Background Japan will give a presentation as shown below.
The definition of thermal runaway and thermal propagation
The criteria of thermal propagation
Report for research about initiation method for thermal propagation
EVS-08-12e-revised

3. Definition of Thermal Runaway and Propagation
“Thermal runaway” means the phenomena of uncontrollable heat generation with continuous temperature rise caused by exothermal chain reaction in the cell.
**Thermal Propagation
“Thermal propagation” means the sequential occurrence of thermal runaway within a battery system triggered by thermal runaway of a cell in that battery system.
EVS-06-23

4. Criteria of Thermal Propagation
No evidence of fire or explosion by visible validation.
(Within 1 hour observation period since the test initiation)
Note:
The existing all criteria for REESS safety test are defined for protection for the persons inside or in the vicinity of the vehicle. The applicable criteria from the existing criteria should also be chosen taking account of the event assumed for the thermal propagation test.
The thermal propagation test should be also provided with the observation period (1 hour) because the same thought for existing criteria should be consistently applied.
The existing criteria for REESS
Applicable / Not applicable
Leakage
Since the thermal propagation test is premised on occurring the defect of a single cell, this criterion is not applicable.
Rupture
Since this criterion is for mechanical endurance , this criterion is not applicable.
Isolation resistance
Since this criterion is the protection from electric shock, this criteria is not applicable.
Fire, explosion
This criteria are appropriate to the thermal propagation test.

5. Research about initiation method of Thermal Propagation
Japan presented research results in IWG#6 and TF5 meeting(Beijing).
Methods which can easily cause internal short circuit and thermal runaway of a cell in battery pack are different depending on cell type and battery structure.
We did research with additional initiation method for thermal propagation test. (Nail, Partial Heating, Overcharge, Heating)
EVS-06-23
EVS-06-23

6. Initiation method of in the research
Thermal propagation test is to confirm if vehicle or battery pack achieve occupant protection when a single cell internal short circuit and thermal runaway occurs in vehicle or battery pack.
We assumed to cause a single cell internal short circuit and thermal runaway for initiation method of propagation test.
We researched initiation methods which can achieve this with various battery packs.
Thermal runaway cell
Visible validation
・　・　
Internal short circuit
・　・　
Vehicle/
Battery pack
Cell
Image of thermal propagation test

7. Initiation methods Method Test condition Image of test Nail
Insert nail until a single cell internal short circuit and thermal runaway occurred.
This includes prick, partial penetration, or full penetration of nail regardless the material of the nail.
Partial Heating
Heat a cell partially with the rate of 100゜C/min.
【Spec of heater】
Size : 25x25x1.75mm
Capacity : 100V-555W
Overcharge
Charge with the rate of 1C Constant Current.
Heating
Heat battery pack with the rate of 60゜C/min.
Size : 5,000x40mm
Capacity : 100V-1,000W
Nail
Heater
Charge
Current
Heater

8. Test sample A HEV ㇾ － B BEV C PHEV D Sample C Sample A Sample B
Type of battery
Type of cell
SOC
Nail
Partial Heating
Overcharge
Heating A
HEV
Prismatic cell
hard case
100% ㇾ － B
BEV C
PHEV D
Pouch cell
ㇾ : Administered
－ : Unadministered
Sample C
Sample A
Sample B
Sample D

9. Nail
In each sample, single cell internal short circuit and thermal runaway occurred.
Sample A(Full penetration)
Sample C(Partial penetration)
Internal short circuit occurred
Internal short circuit occurred
Voltage / V
Cell Temperature
Temperature / ℃
Voltage / V
Temperature / ℃
Cell Temperature
Cell Voltage
Cell Voltage
Time / min
Time / min
Sample B(Full penetration)
Sample C(Prick)
Cell Voltage
Cell Voltage
Voltage / V
Voltage / V
Cell Temperature
Temperature / ℃
Internal short circuit occurred
Temperature / ℃
Cell Temperature
Internal short circuit occurred
Time / min
Time / min

10. Partial Heating
In sample A and D, a single cell internal short circuit and thermal runaway occurred.
In sample B and C, a single cell internal short circuit did not occurred.
Because cells in sample B and C have high thermal conductivity, heat from the heater was diffused and couldn’t cause internal short circuit in a cell.
Sample A
Sample C
Cell Voltage
Cell Voltage
Break down of heater
Voltage / V
Internal short circuit occurred
Temperature / ℃
Voltage / V
Temperature / ℃
Cell Temperature
Cell Temperature
Time / min
Time / min
Sample B
Sample D
Cell Voltage
Voltage drop
(heated cell)
Stop heating
Cell Temperature
Voltage / V
Temperature / ℃
Voltage / V
Thermal propagation occurred
Temperature / ℃
Break down of heater
Cell Temperature
Cell Voltage
Internal short circuit occurred
Time / min
Time / min

11. Overcharge
In sample A, a single cell internal short circuit and thermal runaway occurred.
In sample C, current cutoff system operated and couldn’t cause internal short circuit.
In sample D, simultaneous internal short circuit and thermal runaway of multiple cells occurred because cells are parallel-connected in sample D.
Sample A
Sample D
Internal short circuit occurred
Cell 1 Temperature
Cell Voltage
Burning of plastic parts
Cell 2 Temperature
Voltage / V
Temperature / ℃
Voltage / V
Temperature / ℃
Cell 1&2
Voltage
Cell Temperature
Time / min
Time / min
Sample C
Multiple cells
thermal runaway occurred
Cell Voltage
Current Cutoff system operated
Voltage / V
Temperature / ℃
Cell Temperature
Time / min

12. thermal runaway occurred
Heating
In sample B, simultaneous internal short circuit and thermal runaway of multiple cells occurred because multiple initiation were heated by simultaneous heating.
Sample B
Cell1
Voltage
Cell2
Voltage
Multiple cells
thermal runaway occurred
Voltage / V
Temperature / ℃
Cell1 Temperature
Cell2 Temperature
Time / min

13. Summary of test result
For prismatic cells(Sample A,B,C), Nail is suitable.
For pouch cell(SampleD), Partial Heating is suitable.
Overcharge is unsuitable for the battery with cutoff system and parallel connecting structure.
Heating is unsuitable because multiple cell initiation occurred simultaneously.
ㇾ: Able to cause a single cell internal short circuit and thermal runaway
(M): Unable to cause “a single cell” internal short circuit and thermal runaway
（Multiple cells thermal runaway occur）
(X) : Unable to cause internal short circuit and thermal runaway
－ : Unadministered
Test Results
Sample
Nail
Partial Heating
Overcharge
Heating A ㇾ － B
(X)
(M) C D
Inapplicable to cells with high heat conductivity
・Inapplicable to cells with shutdown device
・Inapplicable to　the battery multiple cells are parallel-connected.
Whole battery is heated and multiple cells are damaged.

14. Structure of electrode
Initiation methods
It is necessary to consider several parameters battery pack as shown below in deciding initiation methods of thermal propagation.
We assume Nail and Partial Heating may be applicable.
Even though these initiation methods still have remaining technical issues.
Type of Cell
Structure of Battery
Configuration
Structure of electrode
Protection device
Series connecting
Parallel connecting
Cylindrical
Winding
With
Without
Prismatic
Sample C
Sample A
Sample B　
Stacking
Pouch
Sample D
⇒Nail?
⇒Nail
⇒Partial
Heating?
⇒Partial　Heating

15. Technical issues for Initiation methods
If there are chassis or bracket around cells of tested-device, it is necessary to process / modify them in order to insert nail or to set a heater.
We need to consider the influence of processing effect on test result.
Hole made for inserting nail
Bracket around cells
Enlarged view
Battery pack sample
Battery pack drilled a hole for nail insertion

16. Summary and Proposal Summary Proposal
We investigated appropriate initiation methods.
For Prismatic cell : Nail , For Pouch cell : Partial heating
Suitable initiation method should be selected based on battery type and connecting structure.
There are still remaining technical issues as mentioned below.
<Technical issues>
1)Applicability of initiation methods for all batteries.
To confirm the applicability for the batteries other than our tested devices.
To justify the reason for choosing the initiation method for the battery.
2)Appropriateness as GTR.
To consider the influence of actual processing for certification test.
3)Repeatability and reproducibility of tests.
Proposal
To ask TF5 validates test methods for variety of batteries to establish test method as GTR.
To request TF5 to address the technical issues as shown in above.