La ₂ O ₃ ‐Reinforced Polymer Electrolyte with Enhanced Interfacial Lithium‐Ion Conductivity for High Stability Lithium Metal Batteries

Abstract Solid‐state polymer electrolytes (SPEs) are attracted significant attention for their potential to enhance safety and energy density in energy storage systems. However, two major challenges persist, namely low ionic conductivity and interface instability. A composite polymer electrolyte with superior ionic conductivity and interface stability is developed using PVDF‐HFP/PAN as the polymer matrix and La ₂ O ₃ fillers. La atoms on the surface of the La ₂ O ₃ fillers act as adsorption sites to bind TFSI ⁻ , promoting lithium salt dissociation and increasing the concentration of free lithium ions. Simultaneously, the La ₂ O ₃ fillers enable anchoring with N, N‐dimethylformamide (DMF) and mitigate side reactions between DMF and lithium metal. Consequently, the composite polymer electrolyte achieves a high lithium transference number (0.64) and optimal ionic conductivity (0.31 mS cm ⁻¹ ). Besides, the LiFePO ₄ ||Li cell achieves excellent capacity retention of 90.92% after 300 cycles at 0.5C under ambient conditions. It also exhibits almost 100% capacity retention after 50 cycles (0.2C) across a temperature range of RT to −10 °C. Similarly, when coupled with LiNi _0.8 Co _0.1 Mn _0.1 O ₂ cathode, the batteries demonstrate stable cycling (capacity retention > 83% over 180 cycles, 0.5C, 25C). This work offers a promising approach for advancing the construction of high‐performance composite polymer electrolytes.