The invention relates to an electrode unit for an electrochemical device, comprising (i) a solid electrolyte, which separates a space for molten cathode material selected from the group consisting of elemental sulfur and polysulfide of the alkali metal anode material and a space for molten alkali metal anode material, and (ii) a porous solid electrode, which is located in the space for the cathode material directly adjacent to the solid electrolyte. Situated between the solid electrode and the solid electrolyte is a non-electron-conducting intermediate layer S, characterized in that prior to the first charging of the electrochemical device, said intermediate layer S is completely saturated with a polysulfide composition containing (A) clean polysulfide met where met = alkali metal of the alkali metal anode material selected from lithium, sodium, potassium, and x is a function of the alkali metal, and for Na = 2, 3, 4, or 5, and for Li = 2, 3, 4, 5, 6, 7, 8 and for K = 2, 3, 4, 5, 6, or (B) mixtures of the polysulphides of one and the same alkali metal from (A) between each other.