Ultrafast thermo-responsive electrolyte for enhanced safety in lithium metal batteries

Short circuits in lithium metal batteries caused by separator failure at elevated temperatures present a critical thermal safety challenge. Smart, temperature-responsive materials offer a promising way to prevent short circuits, yet practical systems with sufficiently fast response times have not been realized. Here we propose a thermo-responsive electrolyte that undergoes a rapid liquid-to-solid phase transition upon heating, offering a highly effective strategy to enhance lithium metal battery safety. The electrolyte leverages LiPF 6 to initiate cationic polymerization, enabling solidification within seconds at a temperature threshold near the separator’s melting point. This fast phase change forms an effective heat shield that prevents internal short circuits and thermal runaway. Demonstrated in LiFePO 4 ||Li pouch cells, the electrolyte ensures stable operation up to 90 °C and completely suppresses thermal runaway. Notably, the transition temperature can be tuned between 100 °C and 150 °C, allowing compatibility with various commercial separators. This ultrafast thermo-responsive electrolyte offers a pathway towards the design of intrinsically safe lithium metal batteries.