Electrochemical cell

A high temperature rechargeable electrochemical power storage cell comprising a cell housing having an interior divided by a separator into an anode compartment and a cathode compartment, the anode compartment containing sodium as active anode material, the separator being a solid electrolyte conductor of sodium ions, the cathode compartment containing a sodium aluminium chloride molten salt electrolyte and containing a solid cathode comprising an electrolyte-permeable porous matrix impregnated with the molten salt electrolyte and which has solid active cathode material dispersed therein and is electronically conductive, the cell having an operating temperature at which the sodium and molten salt electrolyte are molten, the molten salt electrolyte comprising a substantially equimolar mixture of sodium chloride and aluminium chloride in which the proportion of aluminium chloride in all states of charge is at most 50% on a molar basis, the active cathode material comprising at least one transition metal selected from the group consisting of Fe, Ni, Cr, Co, Mn, Cu and Mo having, dispersed therein, at least one additive element selected from the group consisting of As and Sb, the atomic ratio of transition metal additive element in the active cathode material being 99:1-30:70, and the cell having a charged state in which the active cathode material is chlorinated.