Reversible phase transition poly(benzyl methacrylate)/ionic liquid electrolytes for effective overheating protection in lithium batteries

Battery safety is influenced by various factors, with thermal runaway being one of the most significant concerns. While most studies have concentrated on developing one-time, self-activating mechanism for thermal protection, such as temperature-responsive electrodes, and thermal-shutdown separators, these methods only provide irreversible protection. Recently, reversible temperature-sensitive electrolytes have emerged as promising alternatives, offering both thermo-reversibility and self-protective properties. However, further research is crucial to fully understand these thermal-shutdown electrolytes. In this study, we propose lower critical solution temperature (LCST) phase behavior poly(benzyl methacrylate)/imidazolium-based ionic liquid mixtures to prepare temperature-sensitive electrolytes that provide reversible thermal shutdown protection of batteries. This electrolyte features an appropriate protection temperature (∼105 °C) and responds quickly within a 1 min at 105 °C, causing cells to hardly discharge as the voltage suddenly drops to 3.38 V, and providing efficient thermal shutdown protection within 30 min. Upon cooling back to room temperature, the battery regains its original performance. Additionally, the electrolyte exhibits excellent cycling stability with the capacity retention of the battery is 91.6% after 500 cycles. This work provides a viable solution for preventing batteries from thermal runaway triggered by overheating.