The present invention provides a molten sodium secondary cell. In some cases, the secondary cell includes a sodium metal negative electrode, a positive electrode compartment that includes a positive electrode disposed in a molten positive electrolyte comprising Na-FSA (sodium-bis(fluorosulonyl)amide), and a sodium ion conductive electrolyte membrane that separates the negative electrode from the positive electrolyte. One disclosed example of electrolyte membrane material includes, without limitation, a NaSICON-type membrane. Non-limiting examples of the positive electrode include Ni, Zn, Cu, or Fe. The cell is functional at an operating temperature between about 100° C. and about 150° C., and preferably between about 110° C. and about 130° C.