The experimental result shows that all of the test cells were seriously bulged at the end of the overcharge test. However, only the cell with a overcharge current rate of 1/8C (No.1 cell) did not suffer from thermal runaway after 15 hours. This result confirms Leising and Tobishima’s finding that thermal runaway only occurs when the charging rate is beyond 1/5C (No.2 cell). But the cell with a overcharge current rate of 1/5C suffered from thermal runaway. This demonstrates that in overcharging process whether a lithium ion cell ruptured or exploded depends on not only current rate, but also some other factors, such as cell design, manufacturing and ventilation condition.
The surface temperature of No.1 cell presented a trend of earlier increase and later decrease. The temperature finally stabilized at about 65℃. The highest surface temperature is approximately 85℃, and it didn’t reach the temperature of separator melting.
Why didn't the cell with a overcharge current rate of 1/8C (No.1 cell) suffer from thermal runway?Did the energy exchanges keep balance finally?
Thanks for sharing your work. I believe it has to do with the heat balance. At such small C-rate (1/8C), the cell has sufficient time to dissipate the heat that is being generated. Therefore the separator did not get to melt and no thermal runaway developed. On the contrary, when the cell does not have sufficient time to dissipate the heat generated, the temperature would rise beyond the threshold of Thermal runaway initiation.
I guess it also has an impact where the cell is being tested (e.g. test chamber with temperature control)
Thank you a false manoeuver made lost my former answer so i will be more contractive.
Are you sure your assumptions is true anytime ? with limits constraints and thermal control mode, interface can modify exchange conditions.
Is your model accurate enough internaly to warranty precision of predictions and safe margins at the very localized places where thermal condcuctance and flux matter more?
Proceeding with a randomly choosen batch could show statistically more dispersed values and reduced margins for this upper limite overcharge rate.
Dispersion in values, and less reproducible set of datas can drive you toward a still more reduced charge regime and the use of strength/resistance statistical method with reduced variable could show you a more accurate margin to preserve safety integrity of the device.
The present battery chargers are not controlled by thr impedance of the battery cells
A charger system h6aving this and other features are in use of Arnolds machinery storage In Dresden university lab tests were also carried out on Li ion battery pack
Once cells are not heated up you can charge with C over 1
I can provide details and protocols if interrested [email protected]
We will do more experiments in adiabatic environments（eg,in Accelerating Rate Calorimeter-ARC）, in order to explore the law of energy transfer during the overcharge process.So, the heat generated by the battery will be measured by ARC. And the capacity and surface area of the cells will also be taken into account.
Many thanks dear Dr. Vanesa for this wonderful input.
Best regards,
Xiaoqing
Many thanks dear Dr. Thierry for this input. But I can not understand your answer.
Best regards,
Xiaoqing
Many thanks dear Dr. Istvan for this wonderful input.
And We will do more experiments in adiabatic environments（eg,in Accelerating Rate Calorimeter-ARC）, in order to explore the law of energy transfer during the overcharge process .
Best regards,
Xiaoqing
@Thierry Jamin, probably that response relates to another question and was placed here by mistake ?
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