There are a numbers of triggers for battery therml runaway, induction heating offers a way of heating a cell in a targetted way.
Induction heating [1] works with any ferromagnetic and electrically conductive material immersed in an alternating electromagnetic field in the frequency range of kHz to MHz can be heated up by induction. Therefore, inductive heating has been used at industrial scale for numerous applications for decades to heat up various specimens.
The failures of the 18650 cells as tested [1] show significant case deformation.
The resultant rupturing of the cell case would not bode well for a test of thermal propagation at module or pack level as side rupture tends to result in rapid failure of neighbouring cells.
The advantages as listed [1] are:
- Only 1–4 s energy injection is needed
- Possible to achieve volumetric heating, heats also the internal layers not only the casing
- Accurate control of energy and power input
- No thermal contact required between heater and cell.
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Jin et al [2] use induction heating as a trigger for pouch cell thermal runaway, they show that induction heating is a very controllable way of initiating thermal runaway and hence made some interesting observations:
- At the instant of TR, gas pressure is generated, causing venting to occur in all test samples. The process of TRP is accompanied by the propagation of short circuits and the drifting of sparks. Toward the end of the TR process the electrolyte boiling was observed.
- The disassembly results of the debris of the test revealed that the separators and anode electrode materials were nearly untraceable, as they were mixed with substances such as graphite and adhered to the relatively intact copper foils in the debris. The shape of the copper foils was no longer flat but exhibited a wavy pattern, with numerous dendritic grooves on the surface.
- The analysis of the CT data further indicates that the unevenness of the copper foils, as well as the occurrence of TR exothermic reactions on both sides of the copper foils, leads to the formation of holes and cracks on their surfaces due to overheating. There are materials with higher density (gray-scale values) than copper foils, which are distributed in scattered, fragmented forms.
We see that induction heating is very controllable in terms of heating time, thus making it a useful trigger for some observations. However, the induction coil is bulky and is not as precise in terms of heating location as the laser radiation trigger.
One of the most representative but easy to implement which I use for small cylindrical is to intensely but locally heat the can, enough for the separator to melt, triggering the internal short-circuit and the ensuing chain of events.
Energy Storage Testing & Verification Engineer
The intense but very localised heating is obtained by using the cell can as a conductor for a separate electrical circuit, which can be regulated. This external circuit typically needs 500A+ to generate enough heat in a short period of time.
Nothing is perfect, but the locality of the heat source and time delay from initiation to full cell TR ensures that the can structure is not compromised due to the triggering method.
References
- Akos Kriston, Algirdas Kersys, Adriano Antonelli, Stefan Ripplinger, Stefan Holmstrom, Sebastian Trischler, Harry Döring, Andreas Pfrang, Initiation of thermal runaway in Lithium-ion cells by inductive heating, Journal of Power Sources, Volume 454, 2020
- Changyong Jin, Yuedong Sun, Yuejiu Zheng, Jian Yao, Yu Wang, Xin Lai, Chengshan Xu, Huaibin Wang, Fangshu Zhang, Huafeng Li, Jianfeng Hua, Xuning Feng, Minggao Ouyang, In situ observation of thermal runaway propagation in lithium-ion battery electrodes triggered by high-frequency induction heating, Cell Reports Physical Science, Volume 4, Issue 7, 2023