The present invention provides a sodium-aluminum secondary cell. The cell includes a sodium metal negative electrode, a positive electrode compartment that includes an aluminum positive electrode disposed in a positive electrolyte mixture of NaAl2X7 and NaAlX4, where X is a halogen atom or mixture of different halogen atoms selected from chlorine, bromine, and iodine, and a sodium ion conductive electrolyte membrane that separates the negative electrode from the positive electrolyte. In such cases, the electrolyte membrane can include any suitable material, including, without limitation, a NaSICON-type membrane. Generally, when the cell functions, both the sodium negative electrode and the positive electrolyte are molten and in contact with the electrolyte membrane. Additionally, the cell is functional at an operating temperature between about 100° C. and about 200° C.