Surface Li₂CO₃ Mediated Phosphorization Enables Compatible Interfaces of Composite Polymer Electrolyte for Solid‐State Lithium Batteries

Abstract Composite polymer electrolytes (CPEs) are subject to interface incompatibilities due to the space charge layer of ceramic and polymer phases. The intensive dehydrofluorination of poly(vinylidene fluoride‐co‐hexafluoropropylene) (PVDF‐HFP) incorporating Li 7 La 3 Zr 2 O 12 (LLZO) significantly compromises electro‐chemo‐mechanical properties and compatibilities with electrodes. Herein, this study addresses the challenges by precisely phosphatizing LLZO surfaces through a surface Li 2 CO 3 mediated chemical reaction. The designed neutral chemical environment of LLZO surfaces ensures high air stability and effective suppression of PVDF‐HFP dehydrofluorination. This greatly facilitates the uniform distribution of ceramic and polymer phases, and fast interfacial Li + exchange, establishing high‐throughput ion percolation pathways and distinctly enhancing ionic conductivity and transference number. Moreover, the dramatically reduced formation of dehydrofluorination products and an in situ formed interphase layer between phosphatized surface and a Li metal anode stabilize the Li/CPE and cathode/CPE interfaces, which provide a symmetric Li/Li cell and solid‐state Li/LiFePO 4 and Li/LiNi 0.8 Co 0.1 Mn 0.1 O 2 cells an exceptional cycling performance at room temperature. This study emphasizes the vital importance of achieving electro‐chemo‐mechanical compatibilities for CPEs and provides a new waste to wealth route.