Abstract: The invention relates to a rechargeable high temperature electrochemical cell having a molten sodium anode, a molten halide salt liquid electrolyte, a compatible cathode in contact with the liquid electrolyte, and a beta-alumina solid electrolyte between the anode and liquid electrolyte and isolating them from each other. The liquid electrolyte is non-acidic and contains sodium cations as its only alkali metal cations, aluminum cations and chloride anions and is doped with fluoride anions to combat progressively increasing internal resistance of the cell associated with cyclic charging and discharging thereof.