Fumed Silica-Infused PVDF-HFP Electrolytes Enable Exceptional Cycle Life Solid-State Sodium Metal Batteries

Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP)-based polymer sodium solid-state batteries represent a promising alternative to liquid lithium-ion batteries, offering advantages including enhanced safety, high energy density, resource abundance, favorable ionic conductivity, good interfacial contact, and processability. However, the commonly employed sodium salt, sodium bis(trifluoromethylsulfonyl)imide (NaTFSI), promotes corrosion of aluminum current collectors under high-voltage operation, while interfacial stability, mechanical robustness, and electrochemical window limitations persist within PVDF-HFP-based electrolytes. Here, PVDF-HFP-based polymer electrolytes with excellent mechanical properties and thermal stability are obtained by incorporating fumed silica (F-SiO₂) as a filler. As verified, the interaction between F-SiO₂ and TFSI^- effectively suppresses anion decomposition under high voltage, extending the oxidative stability limit to 4.99 V versus Na⁺/Na. This confinement mechanism concurrently mitigates aluminum current collector corrosion at the cathodes by restricting TFSI^- migration and corrosive byproducts formation, and contributes to the formation of a desirable solid-electrolyte interphase at anodes. Consequently, Na || FPEM (F-SiO₂ modified solid polymer electrolytes) || Na symmetric cell achieves 480 h stable cycling at 0.1 mA cm^-2/0.1 mAh cm^-2, while Na₃V₂(PO₄)₃ || FPEM || Na cell retains 77.35% capacity after 1000 cycles at 1C. The cycling stability is significantly improved in comparison with that without F-SiO₂.