Copper containing high temperature cell

A method of making an electrochemical cell comprises loading into the cathode compartment of a cell housing comprising an anode compartment separated from a cathode compartment by a separator which is a solid conductor of ions of alkali metal M or is a micromolecular sieve which contains alkali metal M sorbed therein; an alkali metal aluminium halide molten salt electrolyte having the formula MAlHal4 wherein M is the alkali metal of the anode and Hal is a halide; Cu as an active cathode substance; and an alkali metal halide MHal wherein M and Hal are respectively an alkali metal and a halide; thereby to make an electrochemical cell precursor. The precursor is charged at a temperature at which the molten salt electrolyte and alkali metal M are molten, thereby to halogenate the Cu, with alkali metal being produced and passing through the separator into the anode compartment, the proportions of alkali metal halide MHal, Cu and molten salt electrolyte loaded into the cathode compartment being selected so that when the cell is fully charged and all the available active cathode substance has been halogenated, the proportion of alkali metal ions and aluminium ions is such that the solubility of the active cathode substance in the molten electrolyte is at or near its minimum.