Integrating Flame‐Retardant Li‐Cu Anode With Self‐Extinguishing Polymer Electrolyte for Coordinated Thermal Runaway Suppression in Solid‐State Li Metal Batteries

Solid‐state polymer electrolytes have emerged as a safer alternative to liquid electrolytes for lithium metal batteries, yet their flammability and the inherent combustion risks of lithium metal anodes during thermal runaway remain critical safety concerns. Herein, we propose a cost‐effective lithium‐copper composite anode that synergistically addresses both safety and lithium dendrite suppression challenges. The composite anode enables cells to achieve a fourfold enhancement in cycle lifespan compared with conventional lithium metal anodes. By integrating this non‐flammable composite anode with a flame‐retardant polymer electrolyte, we establish a dual‐protection strategy for battery safety. Notably, the total heat release of composite anode‐based batteries decreases by 80% compared to conventional lithium metal counterparts. This study provides a materials engineering solution that simultaneously improves both electrochemical performance and safety metrics for solid‐state lithium metal batteries, paving the way for practical high‐energy‐density battery applications.