Japanese Researchfor Thermal Propagation

EVS-GTR IWG #9 in China14th-18th Sep, 2015

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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

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Definition of Thermal Runaway and Propagation*Thermal Runaway

**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

“Thermal runaway” means the phenomena of uncontrollable heat generation with continuous temperature rise caused by exothermal chain reaction in the cell.

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Criteria of Thermal PropagationCriteria: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.

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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

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Image of thermal propagation test

Cell

Visible validation

・　・

　

・　・　

Vehicle/Battery pack

Thermal runaway cell

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.

Initiation method of in the research

Internal short circuit

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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 : 25x25x1.75mmCapacity : 100V-555W

Overcharge Charge with the rate of 1C Constant Current.

Heating Heat battery pack with the rate of 60 ゜ C/min.【 Spec of heater 】Size : 5,000x40mmCapacity : 100V-1,000W

Heater

Charge

Heater

Current

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Nail

Test sampleSample Type of

batteryType of cell SOC Nail Partial

HeatingOvercharge Heating

A HEV Prismatic cellhard case

100%

ㇾ ㇾ ㇾ －

B BEV Prismatic cellhard case ㇾ ㇾ － ㇾ

C PHEV Prismatic cellhard case ㇾ ㇾ ㇾ －

D BEV Pouch cell － ㇾ ㇾ －

Sample B

Sample C

Sample D

ㇾ : Administered－ : Unadministered

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Sample A

Nail In each sample, single cell internal short circuit and thermal runaway occurred.

Time / min

Vol

tage

/ V

Tem

pera

ture

/ ℃

Sample A(Full penetration)

Cell Voltage

Cell Temperature

Internal short circuit occurred

Time / min

Vol

tage

/ V

Tem

pera

ture

/ ℃

Sample C(Partial penetration)

Cell Temperature

Cell Voltage

Internal short circuit occurred

Time / min

Vol

tage

/ V

Tem

pera

ture

/ ℃

Sample B(Full penetration)

Cell Temperature

Cell Voltage

Internal short circuit occurred

Time / min

Vol

tage

/ V

Tem

pera

ture

/ ℃

Sample C(Prick)

Cell Temperature

Internal short circuit occurred

Cell Voltage

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.

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Voltage drop(heated cell)Stop heating

Sample D

Sample A

Sample B

Time / min

Time / min Time / min

Vol

tage

/ V

Vol

tage

/ V

Vol

tage

/ V

Tem

pera

ture

/ ℃

Tem

pera

ture

/ ℃

Tem

pera

ture

/ ℃

Time / min

Vol

tage

/ V

Tem

pera

ture

/ ℃

Break down of heater

Cell Voltage

Sample C

Cell Voltage

Cell Temperature

Cell Temperature

Cell Temperature

Cell Temperature

Break down of heater

Cell Voltage

Internal short circuit occurred

Internal short circuit occurred

Cell Voltage

Thermal propagation occurred

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.

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Time / min

Vol

tage

/ V

Tem

pera

ture

/ ℃

Current Cutoff system operated

Sample A

Sample C Multiple cellsthermal runaway

occurred

Sample D

Time / min

Vol

tage

/ V

Tem

pera

ture

/ ℃

Time / min

Vol

tage

/ V

Tem

pera

ture

/ ℃

Cell Voltage

Cell Temperature

Cell Voltage

Cell Temperature

Cell 1&2Voltage

Cell 1 Temperature

Cell 2 Temperature

Internal short circuit occurred

Burning of plastic parts

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

Time / min

Vol

tage

/ V

Tem

pera

ture

/ ℃

Cell1Voltage

Cell1 Temperature

Cell2 Temperature

Cell2Voltage

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Multiple cellsthermal runaway

occurred

Sample Nail Partial Heating Overcharge Heating

A ㇾ ㇾ ㇾ －

B ㇾ (X) － (M)

C ㇾ (X) (X) －

D － ㇾ (M) －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.

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.

Test Results

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

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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.

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Type of Cell Structure of Battery

ConfigurationStructure of electrode

Protection device

Series connecting Parallel connecting

Cylindrical WindingWith 　

Without 　

Prismatic

WindingWith Sample C

Without Sample A Sample B 　

StackingWith 　 　

Without 　 　

Pouch

WindingWith 　 　

Without 　 　

StackingWith 　 　

Without Sample D

⇒Nail

⇒Partial 　Heating

⇒Partial Heating?

⇒Nail?

Battery pack sample Battery pack drilled a hole for nail insertion

Enlarged view

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.

Technical issues for Initiation methods

Bracket around cells

Hole made for inserting nail

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Summary and Proposal

Summary 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.

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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.