A Thin and Ultrahigh‐Ionic‐Conductivity Composite Electrolyte With 3D Aramid Nanofiber Networks Toward Ambient‐Temperature Lithium Metal Batteries

Abstract The low ambient‐temperature ionic conductivity and undesired compatibility with electrode materials are hindering the practical application of solid‐state electrolytes in high‐safety and high‐energy‐density lithium metal batteries. Herein, an ultrahigh ionic conductivity composite electrolyte is prepared by introducing a 3D aramid nanofiber (ANF) framework in succinonitrile (SN)‐lithium bis (trifluoromethylsulphonyl) imide (LiTFSI) electrolytes. Theoretical calculations and experimental characterizations reveal that the ANF framework‐based composite electrolyte (CPE) has dual fast‐ion pathways: one Li + pathway along the 3D ANF frameworks with the coordination interaction between the amide groups and Li + (especially Li + pathway between SN and ANF), and another Li + pathway along the SN molecules in the form of Li(SN) x + cluster. Meanwhile, the hydrogen bonding interaction between the –NH groups of the ANF and the cyano groups of SN captures the free SN molecules, improving the chemical compatibility with Li metal. The well‐designed CPE membrane with a small thickness of 24 µm exhibits a high Li + conductivity of 1.69 × 10 −3 S cm −1 . Notably, the Li|CPE|LiFePO 4 cell shows a long cycle life at 30 °C (0.5 C, >300 cycles, a capacity retention of 94.3%). The all‐solid‐state Li||LiNi 0.5 Co 0.2 Mn 0.3 O 2 battery with an ultrahigh active mass loading of 20 mg cm −2 also displays excellent cycle performance.