All solid‐state sodium batteries (ASSSBs) are considered a promising alternative to lithium‐ion batteries due to increased safety in employing solid‐state components and the widespread availability and low cost of sodium. As one of the indispensable components in the battery system, organic liquid electrolytes are the currently used electrolytes due to their high‐ionic conductivity (10−2 S cm−1) and good wettability; however, their low‐thermal stability, flammability, and leakage tendency pose safety concerns. The growing sodium‐ion battery technology with solid electrolytes is a viable solution due to their improved safety. However, solid electrolytes suffer from insufficient ionic conductivity at room temperature (10−4–10−3 S cm−1), poor interface stability, high charge‐transfer resistance, and low wettability, yielding inferior battery performance. Sodium rare‐earth silicates are a new class of materials with a 3D structure framework similar to sodium‐superionic conductors (NASICONs). These silicates can be used as a solid electrolyte for solid‐state sodium batteries due to their high‐ionic conduction (10−3 S cm−1) at 25 °C. Herein, the sodium rare‐earth silicate synthesis, crystal structure, ion‐conduction mechanism, doping, and electrochemical properties are discussed. This emerging type of inorganic solid electrolyte can pave the way to building next‐generation ASSSBs.

Solid-state sodium-ion batteries (ss-SIBs) are a promising alternative to commercially available lithium-ion batteries for next-generation energy storage applications due to the abundance and cost-effectiveness of sodium over lithium. Herein, using a facile solution casting process, a high sodium-ion conductive, filler-less composite solid polymer electrolyte (SPE) film based on poly(vinylidene fluoride) polymer, poly(vinyl pyrrolidone) (PVP) binder, and NaPF 6 salt for ss-SIB has been successfully fabricated. Total conductivities of 8.51 × 10 −4 and 8.36 × 10 −3 S cm −1 at 23 and 83 °C, respectively, were observed from the SPE. A hybrid symmetric half-cell assembly using Na electrode and 1 M NaClO 4 in ethylene carbonate (EC) and propylene carbonate (PC) (EC/PC = 1:1 wt %) electrolyte showed excellent Na plating−stripping performance at 10 mA cm −2 at 23 °C. The study showed that PVP binder played an important role in achieving good Na ion conductivity and excellent Na plating−stripping performance, highlighting the applicability of the as-prepared SPE in next-generation high-power rechargeable SIBs. A full cell with an SPE, a Na anode, and a Na 3 V 2 (PO 4 ) 3 cathode showed a discharge capacity of 93.2 mAh g −1 at 0.1 C with 86% capacity retention and 99.68% Coulombic efficiency for 100 cycles.

Sodium gadolinium silicate solid electrolyte showed an outstanding sodium plating/stripping performance for 1000 cycles that proves excellent interfacial contact between the sodium anode and solid electrolyte.