Enthalpy‐Driven Molecular Engineering Enables High‐Performance Quasi‐Solid‐State Electrolytes for Long Life Lithium Metal Batteries

Abstract The advancement of lithium metal batteries toward their theoretical energy density potential remains constrained by safety and performance issues inherent to liquid electrolytes. Quasi‐solid‐state electrolytes (QSSEs) based on poly‐1,3‐dioxolane (poly‐DOL) represent a promising development, yet challenges in achieving satisfactory Coulombic efficiency and long‐term stability have impeded their practical implementation. While lithium nitrate addition can enhance efficiency, its incorporation results in prohibitively slow polymerization rates spanning several months. In this work, high‐polymerization‐enthalpy 1,1,1‐trifluoro‐2,3‐epoxypropane is introduced as a co‐polymerization promoter, successfully integrating lithium nitrate into poly‐DOL‐based QSSEs. The resulting electrolyte demonstrates exceptional performance with 2.23 mS cm −1 of ionic conductivity at 25 °C, a Coulombic efficiency of 99.34% in Li|Cu cells, and stable lithium metal interfaces sustained through 1300 h of symmetric cell cycling. This co‐polymerization approach also suppresses poly‐DOL crystallization, enabling Li|LiFePO 4 cells to maintain stability beyond 2000 cycles at 1C. Scale‐up validation in a ≈1 Ah Li|NCM811 pouch cell achieves 94.4% capacity retention over 60 cycles. This strategy establishes a new pathway for developing high‐performance, in situ polymerized quasi‐solid‐state batteries for practical energy storage applications.