Inorganic sodium solid-state electrolyte and interface with sodium metal for room-temperature metal solid-state batteries

Metal solid-state batteries are regarded as the next-generation energy storage systems with high energy density and high safety. A robust and intimate solid-state interfacial contact between the sodium metal with the solid-state electrolyte (SSE) is vital to achieve good cyclic stability at high current density. However, inorganic SSEs suffer from poor stability when cycling at a current density below 2 mA cm−2. This can be ascribed to the dendrite formation through the SSE due to plating process or void formation during the stripping process. Furthermore, simply direct application of a sodium metal on SSE shows poor interfacial contact and low critical current density. In this review, the recent development of inorganic sodium-ion electrolytes, such as oxide-, sulphide-, and halide-based, are briefly discussed. More particularly, the dendrite formation through the SSE and the loss of solid-solid contact at the sodium/SSE interface are reviewed. Additionally, different engineering approaches to integrate the sodium metal with the solid-state electrolytes and its correlation with the electrochemical performance are discussed. Finally, perspectives in future researches are identified.