Progress in sodium silicates for all-solid-state sodium batteries—a review

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.