Enhanced electrochemical performance enabled by ionic-liquid-coated Na3SbS4 electrolyte encapsulated in flexible filtration membrane

Na3SbS4-based solid electrolytes show the merits of a high ionic conductivity and aqueous-processible syntheses. However, Na3SbS4 (NSS) is incompatible with metallic Na and Na alloys. Incorporation of an ionic liquid can solve this issue, but it is hard to coat it on sulfide powders homogeneously in a minimal quantity. Herein, a facile preparation is realized by using a PVDF filtration membrane with submicro-size vertical channels to constrain the flow of the liquid. By this constraint effect, the well mixed BMPTFSI and a NSS aqueous solution are soaked by the vertical channels and inhibited the segregation. Homogeneous BMPTFSI coating layers on NSS particles with a thickness less than 500 nm are encapsulated in the vertical channels after evaporating the water. The coating layers not only improve the physical contact of the NSS particles for enhanced ion transport, but more importantly effectively stabilize the interface between NSS and the metallic Na. The Na3V2(PO4)3||Na half cells with this composite electrolyte demonstrate superior cycling stability and good rate capability. This green method provides a facile way to optimize the interfacial performance for solid state batteries using ionic liquid.