An asymmetric bilayer polymer-ceramic solid electrolyte for high-performance sodium metal batteries

Manufacturing an excellent solid electrolyte compatible with a high-voltage cathode is viewed as a critical tactic for improving the energy density of solid-state sodium-ion batteries (SSIBs). A novel asymmetric bilayer solid electrolyte of the PEO-SN-NaClO4|NZSP-NSO with an anti-reduction PEO-SN-NaClO4 layer close to the Na side is constructed by solution casting. The ionic conductivity is enhanced by using succinonitrile (SN) in polyethylene oxide (PEO) polymer electrolyte. The anti-oxidation layer of Na3Zr2Si2PO12 with Na2SiO3 (NZSP-NSO) is served as the support of the membrane on the cathode, which could improve the interface compatibility and electrochemical performance of SSIBs. The asymmetric bilayer solid electrolyte simultaneously features a wide electrochemical stability window (4.65 V vs. Na+/Na) and a high conductivity (2.68 × 10–4 S cm−1). Furthermore, the solid electrolyte demonstrates stable Na plating/stripping over 700 h and remarkably improves cycling stability in Na/Na3V2(PO4)3 batteries with an ultra-high capacity retention of 99.6% after 100 cycles at 50 °C and 0.5 C. This study provides an effective strategy for designing asymmetric high sodium ion conductivity solid-state electrolytes for high-performance SSIBs.