Designing a Self-Extinguishing System in a Composite Electrolyte for Highly Safe Solid-State Lithium Metal Batteries

The thermal runaway issue of polymer electrolytes (solid polymer electrolytes (SPEs)) at high temperatures, particularly the irreconcilable contradiction between thermal safety and electrochemical performance, remains a great challenge for SPEs that can be applied to solid-state lithium batteries. Here, an intelligent self-extinguishing system originating from the core-shell structure of microcapsules is designed to snuff out the possibility of thermal runaway and provides a high-performance solid-state Li metal battery. The polymer shell of the microcapsules not only serves as a barrier to eliminate detrimental interactions of the flame retardant with the electrolyte or the active lithium metal anode but also acts as a thermoresponsive agent to release the flame retardant. The ion hopping points on the shell of the microcapsules further contribute to the ion conducting nature of the SPE, boosting the ionic conductivity to be 9.3 × 10^-4 S cm^-1. Significantly, the Li//Li symmetric cells exhibit stable long-term cycling for over 3400 h, and the solid-state Li metal battery shows a capacity retention of 87.4% after 500 cycles. Meanwhile, the SPE displays superior flame retardancy with a self-expansion time of 3 s g^-1. This work offers a versatile strategy for designing truly safe and high-performance solid-state Li-metal batteries.