Enhanced Safety and Performance of High-Voltage Solid-State Sodium Battery through Trilayer, Multifunctional Electrolyte Design

Solid-state electrolytes are promising to resolve the safety hazards and low energy density of traditional liquid batteries. However, the practical application of these electrolytes has been impaired by the low ionic conductivity and an unstable interface present with a high-voltage cathode. Here, an improvement of ionic conductivity, interface, and safety was achieved by impregnating anti-oxidation polyacrylonitrile (PAN) and anti-reduction poly(ethylene oxide) (PEO) into a sandwich sodium superionic conductor (NASICON) framework with a dense core and porous outer layers. Using this sandwich composite electrolyte (SCE), a high ionic conductivity of 4.13×10−4 S cm−1 at 30°C was obtained owing to long-range and continuous ionic conduction pathways in the porous network. The interfacial resistance was greatly improved through the creation of a compact and stable interface. More importantly, the safety of this SCE is improved through the in-situ formation of a central, dense NASICON layer, which suppressed dendrite growth. Furthermore, a high-voltage solid-state battery combining Na3V2(PO4)2F3 (NVPF) with this SCE exhibited an impressive rate performance with long cycle life. This study offers a promising strategy to design ultra-safe, high energy density, solid-state batteries.