The present invention relates to a sodium-ion battery comprising a positive electrode compartment comprising a positive electrode, said positive electrode comprising a Na-insertion compound; a negative electrode compartment comprising a negative electrode, said negative electrode comprising metallic sodium; and an electrolyte composition comprising a solid sodium-ion conductive ceramic electrolyte and a catholyte comprising a metallic salt with formula MY, wherein M is a cation selected from an alkali metal and an alkali-earth metal; and Y is an anion selected from [R1SO2NSO2R2], CF3SO3−, C(CN)3−, B(C2O4)2− and BF2(C2O4)−, wherein R1 and R2 are independently selected from fluorine or a fluoroalkyl group. The device is able to operate below the melting point of the anode component.