Deciphering the Role of Binder Reaction Exothermicity in Thermal Runaway of Lithium-Ion Cells

Thermal safety associated with lithium-ion cells as power sources remains a critical industry concern. A comprehensive understanding of how internal exothermic side reactions contribute to temperature rise is fundamental for accurately analyzing thermal runaway processes and predicting the thermal safety of lithium-ion cells. While various side-reactions, such as decomposition of solid electrolyte interphase layer, reaction between anode materials and electrolyte, reaction between cathode materials and electrolyte, and electrolyte decomposition, have been identified as heat generation sources in previous studies, the quantification of these reactions remains insufficiently standardized. Particularly, the impact of heat generation from binder decomposition (most commonly polyvinylidene difluoride) at elevated temperatures on the thermal runaway process of lithium-ion cells has not been fully elucidated. Therefore, in this study, an electro-thermal coupled numerical model was developed for 18650-type lithium-ion cells to systematically investigate the synergistic effects of these five major side-reactions under high-temperature conditions leading to thermal runaway. Special emphasis was placed on precisely quantifying the contribution from binder decomposition heat during the thermal runaway process. The results demonstrate that once the ambient temperature exceeds the threshold required to initiate cascading exothermic side reactions, the inclusion or exclusion of the binder reaction in the model does not affect the overall assessment results of thermal runaway for lithium-ion cells. However, under these conditions, the heat contribution from binder decomposition to the total heat release increases significantly and therefore becomes one of the dominant heat sources for temperature rise during the thermal runaway propagation. Conversely, when ambient temperatures do not reach the threshold, the heat contribution from binder decomposition is negligible. Additionally, the improved electro-thermal coupling model serves as an effective simulation tool for designing battery systems with enhanced safety, selecting appropriate binder materials to mitigate the adverse effects of thermal runaway, and optimizing thermal management during battery development. This approach significantly reduces the research and development cycle. These findings establish appropriate heat source selection criteria for electro-thermal models under varying precision requirements and provide a theoretical foundation for both model simplification and high-fidelity optimization in lithium-ion battery design.