Interface-Compatible Gel-Polymer Electrolyte Enabled by NaF-Solubility-Regulation toward All-Climate Solid-State Sodium Batteries.

Abstract

Gel-polymer electrolyte (GPE) is a pragmatic choice for high-safety sodium batteries but still plagued by interfacial compatibility with both cathode and anode simultaneously. Here, salt-in-polymer fibers with NaF salt inlaid in polylactide (PLA) fiber network was fabricated via electrospinning and subsequent in situ forming gel-polymer electrolyte in liquid electrolytes. The obtained PLA-NaF GPE achieves a high ion conductivity (2.50×10-3 S cm-1) and large Na+ transference number (0.75) at ambient temperature. Notably, the dissolution of NaF salt occupies solvents leading to concentrated-electrolyte environment, which facilitates aggregates with increased anionic coordination (anion/Na+ >1). Aggregates with higher HOMO realize the preferential oxidation on the cathode so that inorganic-rich and stable CEI covers cathode' surface, preventing particles' breakage and showing good compatibility with different cathodes (Na3V2(PO4)3, Na2+2xFe2-x(SO4)3, Na0.72Ni0.32Mn0.68O2, NaTi2(PO4)3). While, passivated Na anode induced by the lower LUMO of aggregates, and the lower surface tension between Na anode and PLA-NaF GPE interface, leading to the dendrites-free Na anode. As a result, the assembled Na || Na3V2(PO4)3 cells display excellent electrochemical performance at all-climate conditions.