A number of composite polyphase electrode systems employing the mixed-conducting matrix principle have been proposed in this laboratory as alternatives to single lithium alloy systems for use as negative electrodes in both room and intermediate temperature lithium-based cells. Further, a composite hydroxide ion conducting electrolyte has been considered for use at intermediate temperatures which utilises liquid lithium hydroxide formed in situ and contained within a lithium aluminium oxide ceramic matrix.
Both these, and other, composite electrochemical cell component systems serve to overcome certain disadvantages found in simpler, non-composite designs. In order to operate effectively, the electrode and electrolyte systems described here must satisfy certain thermodynamic, kinetic and mechanical criteria. In this work, these criteria are discussed, using, among others, the examples given above, with particular emphasis on the thermodynamic phase stability conditions which must be satisfied by a viable composite electrode or electrolyte system.