The Lithium-ion battery (LIB) is an important technology for the present and future of energy storage, transport, and consumer electronics. However, many LIB types display a tendency to ignite or release gases. Although statistically rare, LIB fires pose hazards which are significantly different to other fire hazards in terms of initiation route, rate of spread, duration, toxicity, and suppression. For the first time, this paper collects and analyses the safety challenges faced by LIB industries across sectors, and compares them to the research contributions found in all the review papers in the field. The comparison identifies knowledge gaps and opportunities going forward. Industry and research efforts agree on the importance of understanding thermal runaway at the component and cell scales, and on the importance of developing prevention technologies. But much less research attention has been given to safety at the module and pack scales, or to other fire protection layers, such as compartmentation, detection or suppression. In order to close the gaps found and accelerate the arrival of new LIB safety solutions, we recommend closer collaborations between the battery and fire safety communities, which, supported by the major industries, could drive improvements, integration and harmonization of LIB safety across sectors.

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Lithium-ion batteries (LIBs) are widely used as energy storage devices. However, a disadvantage of these batteries is their tendency to ignite and burn, thereby creating a fire hazard. Ignition of LIBs can be triggered by abuse conditions (mechanical, electrical or thermal abuse) or internal short circuit. In addition, ignition could also be triggered by self-heating when LIBs are stacked during storage or transport. However, the open circuit self-heating ignition has received little attention and seems to be misunderstood in the literature. This paper quantifies the self-heating behaviour of LIB by means of isothermal oven experiments. Stacks of 1, 2, 3 and 4 Sanyo prismatic LiCoO2 cells at 30% state of charge were studied. The surface and central temperatures, voltage, and time to ignition were measured. Results show that self-heating ignition of open circuit LIBs is possible and its behaviour has three stages: heating up, self-heating and thermal runaway. We find for the first time that, for this battery type, as the number of cells increases from 1 to 4, the critical ambient temperature decreases from 165.5°C to 153°C. A Frank-Kamenetskii analysis using the measured data confirms that ignition is caused by self-heating. Parameters extracted from Frank-Kamenetskii theory are then used to upscale the laboratory results, which shows large enough LIB ensembles could self-ignite at even ambient temperatures. This is the first experimental study of the effect of the number of cells on self-heating ignition of LIBs, contributing to the understanding of this new fire hazard.

Many thermal events have been reported during storage and transport of large numbers of Lithium-ion batteries (LIBs), raising industry concerns and research interests in its mechanisms. Apart from electrochemical failure, self-heating ignition, driven by poor heat transfer could also be a possible cause of fire in large-scale ensembles of LIBs. The classical theories and models of self-heating ignition assume a homogeneous lumped system, whereas LIBs storage involves complex geometry and heterogeneous material composition due to the packaging and insulation, which significantly changes the heat transfer within the system. These effects on the self-heating behaviour of LIBs have not been studied yet. In this study, the self-heating ignition behaviour of a box containing 100 LiCoO2 (LCO) type of cylindrical cells with different insulation is numerically modelled using COMSOL Multiphysics with a multi-step reaction scheme. The model predicts that the critical ambient temperature triggering self-ignition of the box is 125°C, which is 30°C lower than that for a single cell, and the time to thermal runaway is predicted to be 15 times longer. The effects of different insulating materials and packing configurations are also analysed. This work provides novel insights into the self-heating of large-scale LIBs.