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Experimental study of the effect of the state of charge on self-heating ignition of large ensembles of Lithium-ion batteries in storage

Research output: Contribution to journalArticlepeer-review

Xuanze He, Zhenwen Hu, Francesco Restuccia, Jun Fang, Guillermo Rein

Original languageEnglish
Article number118621
JournalAPPLIED THERMAL ENGINEERING
Volume212
Early online date3 May 2022
DOIs
E-pub ahead of print3 May 2022
Published25 Jul 2022

Bibliographical note

Funding Information: The authors thank the support from the China Scholarship Council (CSC) to XH and ZH, and the support from the Great Britain-China Educational Trust (GBCET) to XH. Many thanks to Yue Zhang (University of Science and Technology of China) for the help with the experiments. Publisher Copyright: © 2022

King's Authors

Abstract

Self-heating can cause the ignition of open-circuit Lithium-ion batteries. Current safety literature focuses on the self-heating chemistry of a single cell, ignoring the effects of heat transfer. However, a large ensemble of batteries has a non-uniform temperature distribution and therefore self-heating ignition is dominated by both heat transfer and chemistry. This type of ignition is of importance when batteries are stored for long periods of time and in large ensembles but has been rarely studied to date. This paper studies the effect of the state of charge (SOC) on the self-heating behavior of LiCoO2 prismatic cells. The SOC of 0% (of interest in the safety of waste facilities), 30% (transport), 50% (storage), 80% (aged battery) and 100% (fully-charged battery), and 1, 2 and 4 cells stacked together were studied using oven experiments. Results show that cells at all SOC can self-ignite. Flames were only observed for SOC larger than 80%. We compare two temperature criteria: the temperature of the middle cell using the critical increase rate of 10 ℃/min defined in standard SAE-J2464, and the ambient temperature around the ensemble when triggering ignition. Both temperature criteria decrease with increasing SOC showing that the hazard grows with energy density. The cell temperature criterion is independent of the number of cells, while the ambient temperature criterion decreases as the number of cells increases, which indicates the increased risk of self-heating ignition when cells are stacked together in ensembles. Thus, the ambient temperature criterion should be used to design safe storage rather than the standard cell temperature increase rate, which does not represent well the criticality of ignition. The effective kinetics and thermal properties at different SOCs are extracted based on the Frank-Kamenetskii theory and are used to upscale laboratory results to storage conditions. The results in this work can improve the safety of the storage and provide scientific insight for safety standards

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