Research advances on thermal runaway mechanism of lithium-ion batteries and safety improvement

Lithium-ion batteries have found widespread applications in automotive, energy storage, and numerous other fields, attributed to their remarkable features such as high energy density, extended cycle life, and the absence of a memory effect. Nevertheless, these batteries are prone to various forms of abuse, including electrical, thermal, and mechanical stress, which can lead to internal short circuits and subsequently thermal runaway. This thermal runaway poses a significant threat to the safe operation of lithium-ion batteries. In this paper, we delve into the working principles of lithium-ion batteries and provide a comprehensive overview of the reaction characteristics of critical components, including the solid electrolyte interphase (SEI) film, electrolyte, electrode, and separator, during the thermal runaway process. It is found that the decomposition of SEI film and electrolyte occur at 80 and 100 °C, respectively, among which the chemical reactions between the negative electrode and the electrolyte could occur as well, while the diaphragm starts to undergo melting at 110 °C. It is crucial to highlight that various cathode materials exhibit distinct thermal decomposition temperatures, falling within a range of 150–300 °C. Notably, the melting of the diaphragm constitutes an endothermic reaction, efficiently absorbing a portion of heat, whereas all other reactions observed were exothermic. Furthermore, we conduct a detailed analysis and summary of how battery materials, battery state, external environmental conditions, and the initiating factors of thermal runaway impact voltage, temperature, and the type and concentration of gases produced during this process. Moreover, we summarize the current research efforts aimed at enhancing the safety performance of lithium-ion batteries, focusing on three key areas: thermal runaway prevention, thermal runaway early warning systems, and thermal runaway fire prevention technology. Finally, we identify the shortcomings of current technologies and provide insights into future prospects for addressing these challenges.