Simulation and understanding of degraded lithium-ion battery self-heating ignition

Self-heating ignition is an important form of failure when lithium-ion batteries are not in use, such as when stored or transported. Despite being widely studied, existing studies have only focused on fresh batteries. However, it is of more practical use to understand self-heating ignition for degraded cells, regardless of how they are used. In this study, we develop a physics-based model that integrates multiple coupled degradation and thermal runaway mechanisms to simulate and understand changes in self-heating ignition behaviours with battery degradation. Prior to use, the model is validated against experiments and demonstrates its capability of replicating the measured critical temperature for self-heating ignition. Using the model, we examine the effects of degradation on self-heating ignition and find a strong dependence on degradation mechanisms and thus degradation paths, with lithium plating being the most hazardous. Considering heat transfer effects, a self-heating ignition criticality map is proposed, which uses a criticality boundary to distinguish between conditions that will and will not lead to self-heating ignition. For batteries subjected to low-temperature cycling, rapid lithium plating reduces their critical temperatures and shifts their criticality boundaries from heat dissipation-limited to heat generation-limited. Conversely, batteries exposed to high-temperature cycling, where the solid electrolyte interphase layer growth and electrolyte dry-out dominate the performance fade, show a slight increase in their critical temperatures, with the criticality boundaries remaining heat dissipation-limited as at their beginning of life. Our study bridges degradation and self-heating ignition, guiding efforts to enhance the safety of degraded batteries in storage or standby conditions.