High-temperature rechargeable cell having solid electrolyte separator with projecting lobes in polygonal housing

In a high temperature rechargeable electrochemical cell (10) has a housing (10) containing an anode (38) and a cathode (34), and divided by a sodium ion-conducting solid electrolyte separator (16), into an anode compartment and a cathode compartment, containing respectively molten sodium active anode material and active cathode material, the separator is tubular, having a closed end and an open end, and a plurality of circumferentially spaced radially outwardly projecting ribs or lobes (46), the housing is a tubular canister which is polygonal in cross-section, so that it has a plurality of circumferentially spaced corners (14) corresponding in number to the number of lobes (46) of the separator (16), and the separator is concentrically located in the housing (12), each lobe (46) of the separator (16) being circumferentially aligned with, and projecting radially from the separator towards, one of said corners (14).