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Discussion paper on Current Status on TF5 test items

Xiao Chengwei

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1. Test procedure proposals and requirements of cell/module level sent to the Secretary for distribution to be reviewed by group member, excluding system level on Feb. 15th, 2014;

2. Feedback from Korea collected on Feb. 27th, 2014; Comments from SK, Continental on Dec. 16th, 2013; and the feedback of OICA is on 20th Mar., 2014;

3. Teleconference held on April 9th.

General status on TF5

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China gave explanations for the Japan side concerns on the contents of TF5 which includes cell/module/system. The contents of cell/module were newly added based on the suggestions of 4th meeting in Beijing, and listed as a parallel part as that of the system requirement which is already described in GTR draft. And China provided the definition of module for further discussion, which is A group of cells connected together either in a series and/or parallel configuration with or without protective devices (e.g. fuse or PTC) and monitoring circuitry. It can be transported and replaced when the battery system is maintained.

General status on TF5

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Some participants expressed the viewpoint that the whole vehicle and system design could guarantee the EV safety, China agreed that point, but also expressed that cell/module are the most important components in the EV power system and are of importance to EV safety, some safety risks belongs to the characteristics of cell/module itself, typically the short circuit of a cell in a module happens, which may cause the cell venting, burning, or even explosion and lead to thermal propagation between cells in module. The phenomena of internal short circuit couldn’t be monitored and controlled by BMS, would cause serious safety consequences once happens. China proposes test items to simulate to those which internal short circuit and thermal propagation may happen.

General status on TF5

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Nail penetration test

Internal short circuit test

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Thermal runaway of LiFePO4/C: meltdown temp. of the separator is the key factor.Meltdown temp. lower than 493K, the internal short circuit is the major cause for thermal runaway of the cell;Meltdown temp. higher than 493K, decomposition of anode and cathode materials are the major cause for thermal runaway of the cell.

0 5000 10000 15000 20000 25000

400

420

440

460

480

Hea

ting

rate

/K s

-1

Temperature Heating rate

Time/s

Tem

pera

ture

/K

419K 3580s

0.0022Ks-1

453K 23311s 0.005Ks-1

461K 24211s 0.04Ks-1

24348s

0.0

0.1

0.2

0.3

0.4

0.5

0.6

400 410 420 430 440 450 460 470 480

0.0

0.1

0.2

0.3

0.4

0.5

0.6

400 420 4400.000

0.004

0.008

0.012

0.00000

0.00005

0.00010

Re

act

ion

ra

te/s

-1

Heating rate

Temperature/K

He

atin

g r

ate

/K s

-1

0.0000

0.0005

0.0010

0.0015

0.0020

0.0025

0.0030

0.0035

0.0040

Positive Negative Electrolyte SEI Gasifying Solvent

Internal short circuit leads to thermal runaway

Adiabatic Simulation

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The current Internal short circuit test method is recommended, such as JIS 8714 of Japan.

Nail penetration test

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The state of the membrane after nail penetration test: the perforation membrane become thin and transparent, and some membrane melt at the edges of contact with the needle. A small amount of active powder fell off the plate and stuck to the membrane. Internal short circuit can be simulated excellently by nail penetration test.

Nail penetration test

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before test

after test

valve openTest begin

Temp. reach100℃ Temp. reach 200℃

before test

Nail penetration test

10t=6s t=7s t=8s t=10s t=12s t=20s

Nail penetration test is the more effective alternative test method for the Internal short circuit phenomena.

Nail penetration test

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Oven test is not the normal reliability test item, but the safety abuse test item for thermal stability. Except that considering the application environment temperature, more attention should be paid to the key factors for cell thermal stability itself. And oven test can be used for the simulation of thermal propagation ( for example, if the temp. of one cell increases rapidly at the condition of internal short circuit, this phenomena inserts serious affect on the surrounding cells, thermal propagation will happen).

(UL1642 Environmental Test - Heating Test 、 IEC62660 Reliability and abuse tests - High temperature endurance 、 SAE J2464 Thermal Abuse Test – Thermal Stability Test)

Oven Test @130℃

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At 130℃, SEI starts to decompose and exothermic reaction begins, thermal runaway will probably happen with the heat accumulation. And the membrane starts to melt at about 130℃, which leads to higher short circuit risks.

Oven Test @130℃

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The cell may be crushed when vehicle accident happens.

The crush pressure range is between 210-950 kN at the critical point of fire or explosion, and the deformation range of the cell from 10% to 40% according to the verification data by battery companies and 3rd test agency.

Crush test items can be used for the simulation of cell deformation for safety consideration after vehicle accident.

Crush test

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1. Nail penetration item can be used for the simulation of internal short circuit phenomena.2. Oven test item is recommended for the simulation of thermal propagation phenomena.3. Crush test item can be used for the simulation of cell deformation for the safety consideration after vehicle crash.

Conclusion

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Thank you!