Thermally stable Al₂O₃-reinforced PVDF-HFP hybrid quasi-solid polymer electrolyte enabling high-energy lithium-ion...

Solid-state lithium-ion batteries (SSLIBs) employing nickel-rich layered oxide cathodes are essential for electric vehicles and large-scale energy storage owing to their high energy density. Although solid polymer electrolytes are promising candidates for these systems, their practical deployment remains constrained by insufficient ionic conductivity, limited oxidative stability, and safety concerns arising from polymer membrane shrinkage under thermally abusive conditions. Herein, we report a highly safe organic-inorganic hybrid quasi-solid polymer electrolyte (HQSPE) based on a poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) host matrix plasticized with ethylene carbonate and reinforced with Al₂O₃ ceramic filler. The incorporation of Al₂O₃ induces polymer chain amorphization, enhances ionic conductivity, improves thermal stability, and establishes favorable Lewis acid-base interactions that effectively regulate anion mobility. Consequently, the optimized HQSPE exhibits a high ionic conductivity of 4.13 mS cm^-1 at room temperature and an elevated Li⁺ transference number of 0.58. The electrolyte further demonstrates outstanding thermal robustness with minimal dimensional shrinkage at 200 °C and an expanded oxidative stability window approaching 4.99 V vs. Li/Li⁺. When assembled into high-loading Graphite-SiO_x||LiNi_0.8Co_0.1Mn_0.1O₂ full cells, the HQSPE delivers superior rate capability and long-term cycling stability, retaining 81% of its initial capacity after 300 cycles at 0.5C with high Coulombic efficiency. These results establish a rational design strategy for hybrid quasi-solid polymer electrolytes that effectively balance ionic transport, interfacial stability, and thermal safety, offering a viable pathway toward practical high-energy lithium-ion batteries.