Free-Standing, Robust, and Stable Li⁺Conductive Li(Sr,Zr)₂(PO₄)₃/PEO Composite Electrolytes for Solid-State Batteries

We developed promising soft-rigid and free-standing composite electrolytes by mixing a Sr-doped LiZr2(PO4)3 compound with a poly(ethylene oxide) (PEO)-based polymer for Li+-ion conductors. Using crystal formation modeling, we synthesized a thermodynamically stable Li(Sr,Zr)2(PO4)3 compound with the formation of composite electrolytes via PEO-based in situ radical polymerization, which possessed a good ionic conductivity (5.75 × 10-4 S cm-1). The cell with Li/composite electrolyte/LiFePO4 showed a capacity retention rate of 80% after 100 cycles at room temperature. The corresponding composite electrolyte film demonstrated superior electrochemical behavior even when assembling pouch-type cells without any interfacial control during the cell assembly, that is, without post-treatment such as soaking liquid electrolytes or over-coated interlayers. This suggested that the optimal phosphate composition followed by the formation of a PEO-based polymer electrolyte will be suitable for Li+-ion transporting films and/or the Li metal protection layer for solid-state Li+-ion rechargeable batteries operating at room temperature.