Dual-Layer Composite Polymer Electrolyte Enabling Stable Lithium- Ion Transport in Quasi-Solid-State Batteries

Composite polymer electrolytes (CPEs) offer an attractive route to safer lithium metal batteries, yet their practical deployment is often limited by a persistent trade-off between ionic conductivity and mechanical integrity, together with unstable electrode/electrolyte interfaces. In this work, a dual-layer PVDF-based composite electrolyte (PVLC CPE) is constructed, consisting of a lithium aluminum titanium phosphate (LATP)-rich layer to facilitate Li + transport and a cerium oxide (CeO 2 ) nanofiber-reinforced layer to strengthen the mechanical robustness of membrane and stabilize Li deposition. The optimized PVLC CPE exhibits a high ionic conductivity of 1.02 × 10 –4 S cm –1 at 30 °C with a low activation energy of 0.127 eV and robust thermal stability up to 120 °C. A Li/PVLC/Li symmetric cell delivers stable stripping/plating for over 1800 h at 0.1 mA cm –2 . Full cell assembled with LiFePO 4 cathode, the electrolyte enables 95.7 mA h·g –1 after 200 cycles at 1 C with near-100% Coulombic efficiency. These results demonstrate that a rational dual-layer architecture can simultaneously promote fast Li + transport and mechanically regulate the interface, offering a practical design principle for durable quasi-solid-state batteries.