Plasticized Composite Electrolyte with Al₂O₃ Nanofiller-Reinforced PVDF-HFP for Solid-State Lithium–Metal Batteries

Solid-state lithium–metal batteries (LMB) are promising next-generation energy storage systems (NESS), offering improved safety and higher energy density over liquid electrolyte-based batteries. This study presents a composite electrolyte based on a poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), one-dimensional Al2O3 nanofillers and plastic crystal plasticizer succinonitrile. The Al2O3 nanofillers, synthesized via electrospinning, facilitate the formation of efficient ion migration pathways and significantly enhance lithium-ion conductivity. The addition of nanofillers enhances the electrolyte’s mechanical strength, battery’s safety, performance, and durability. The optimized electrolyte exhibits an impressive ionic conductivity of 6.46 × 10–4 S cm–1, a Li+ ion transference number of 0.69, and an electrochemical stability window extending to 4.9 V at 60 °C. It also shows excellent compatibility with lithium metal anodes, enabling stable cycling in lithium symmetric cells for over 800 h at 0.1 mA cm–2. When paired with high-voltage NCM622, the cells deliver a high discharge capacity of 158.2 mAh g–1 at 0.1 C and maintain a capacity retention of 75% over 100 cycles at 1 C and 60 °C. These results demonstrate the potential of PVDF-HFP based composite electrolyte to enhance solid-state LMB performance and safety, with improved ionic conductivity, mechanical strength, and cycling stability, making it a promising candidate for NESS.