Related Illustration on thermal propagation

Prof. Xiao Chengwei (TF5 team leader)2015/06/03

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

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）

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

Probability of thermal propagation

TonsetPropagation

time / s130 (PE) 21170 (PP) 35

200 60260 259290 433446 549

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 6th meeting in Korea

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.

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

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?

Research result of the initiation of thermal runaway

From Japan

Nail pickPartial heating

Nail penetration

AVoltage drop(V)(1h later) 0.32 0 Max→0

Cell temperature(℃) (1h later) 44 192

Phenomenon Nothing Smoke

BVoltage drop(V)(1h later) 0.12 0 0.41

Cell temperature(℃) (1h later) 30 119

Phenomenon Nothing Smoke

C

Voltage drop(V)(1h later) 0.04 Max→0

Cell temperature(℃) (1h later) 45 634

Phenomenon NothingSmoke

Propagation

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

From KoreaThermal 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 item Test condition Drawbacks

Heating

400W heater within the cellsHeating until thermal runaway

Heating powerSeverity of thermal runaway heating temperature ∝Max temp. 1/cell size (constant heater power)∝ Difficult to specify heater power for various cell design

Overcharge1cell 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).

<Schematic>

Research result of the initiation of thermal runaway

From China

Test items Overcharge Nail Heat

Thermal runaway temperature 300℃ 100℃～ 400

℃ 250℃

Test result Venting and leakage Smoke or fire Most serious, Venting and leakage or fire

Operational Better normal Good

Successful Good normal Better

Influence factors Active Protection device, like PTC or CID Material Thermal 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

From other organizations/countries

OICA?

Others?

Research result of the initiation of thermal runaway

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

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?

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?

……

Thanks!