A Robust Composite Solid Polymer Electrolyte with LLTO Filler for Long-Life Solid-State Lithium Metal Batteries

Solid-state lithium–metal batteries are considered a promising strategy to address the safety concerns associated with conventional liquid electrolytes. Among them, solid-state polymer electrolytes are widely utilized due to their excellent mechanical stability, good electrode compatibility, and cycling performance. In this study, Li3xLa2/3–xTiO3 (LLTO) filler was synthesized via a high-temperature solid-state reaction and incorporated into a composite polymer matrix of poly(vinylidene fluoride)-hexafluoropropylene (PVDF-HFP) and poly(acrylonitrile) (PAN). A freestanding LLTO/PVDF-HFP composite solid-state electrolyte (CSE) with a thickness of 47 μm was prepared by solution casting. The ionic conductivity of the resulting CSE reached 7.13 × 10–4 S·cm–1 at 30 °C. A solid-state battery configured with a LiFePO4 cathode and a lithium metal anode delivered an initial discharge capacity of 140 mAh·g–1 and retained 93.4% of its capacity after 500 cycles at room temperature under 1C rate. These results demonstrate that the LLTO/PVDF-HFP/PAN CSE holds great promise for application in solid-state lithium–metal batteries.