Transcript EVSTF-03-21e

Related Illustration on thermal
propagation
Prof. Xiao Chengwei (TF5 team leader)
2015/06/03
Contents
 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
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）
Characteristic and severity of ISC
 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.
Presentation from CAMX Power in 32th Annual International
Battery Seminar & Exhibit in Florida in March, 2015.
Probability of thermal propagation



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.
Tonset
130 (PE)
170 (PP)
200
260
290
446
Propagation
time / s
21
35
60
259
433
549
From Chinese presentation in 6th meeting in Korea
Objective of thermal propagation
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.
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
A
B
C
Nail pick
Partial
heating
Nail
penetration
Voltage drop(V)(1h later)
0.32
0
Max→0
Cell temperature(℃) (1h later)
44
192
Phenomenon
Nothing
Smoke
Voltage drop(V)(1h later)
0.12
Cell temperature(℃) (1h later)
30
119
Phenomenon
Nothing
Smoke
Voltage drop(V)(1h later)
0.04
Max→0
Cell temperature(℃) (1h later)
45
634
Phenomenon
Nothing
Smoke
Propagation
0
0.41
Research result of the initiation of thermal runaway
 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 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 item
Test condition
Heating
400W heater within the cells
Heating until thermal runaway
Overcharge
Internal short
1cell overcharging
- 1C charging until thermal
runaway
Ceramic nail with metal tip
- Test on single cell in module
- Test condition : same with
cell level ceramic nail test.
Drawbacks
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
Usually multiple cells are exposed in overcharge condition.
Not applicable for cells with overcharge protection.
Same issues with cell test.
- Case weakening.
- Precision control (less than 5mV).
<Schematic>
Research result of the initiation of thermal runaway
 From China
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.
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
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.
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!