Separator‐Free In Situ Dual‐Curing Solid Polymer Electrolytes with Enhanced Interfacial Contact for Achieving Ultrastable Lithium‐Metal Batteries

Abstract Solid polymer electrolytes (SPEs) are expected to possess high ionic conductivity and conformal interfacial contact with all cell components for all‐solid‐state lithium‐ion batteries. However, the commonly used in situ separator‐assisted approach reduces the ionic conductivity because of the use of inert and non‐ion‐conducting separators. Here, a facile separator‐free dual‐curing strategy combining UV‐curing outside the cell and subsequent thermal‐curing inside the cell is reported, in which the second thermal polymerization process provides improved interfacial properties without sacrificing ionic conductivity. The resulting DC‐SPEs possess high ionic conductivity (0.3 mS cm⁻¹ at 25 °C), a wide electrochemical stability window (4.64 V vs Li/Li⁺), and improved interfacial properties. The in situ‐formed DC‐SPE can effectively suppress the growth of Li dendrites and achieve stable Li symmetric cell cycling performance at high current density (over 700 h at 0.2 mA cm⁻² and 0.2 mAh cm⁻²). The all‐solid‐state lithium metal batteries (LMBs) with LiFePO₄ demonstrate high coulombic efficiency (>99.93%) and ultrastable cycling stability (900 cycles) at 1C rate under 40 °C. The dual‐curing strategy provides a brand new in situ processing method to avoid the use of expensive and inert separators, which can be widely applied to the development of all‐solid‐state LMBs.