INTERCALATION COMPOUNDS - SOME RECENT DEVELOPMENTS AND FUTURE-TRENDS IN MIXED CONDUCTORS

Intercalation compounds are formed by the injection of guest ions (e.g. Li+) and their charge compensating electrons into a solid host (e.g. TiS2). Such compounds are mixed, ionic and electronic conductors.

Recent developments concerning three aspects of intercalation are discussed in this article. (1) Ionic diffusion. Results are presented for the self-diffusion coefficient of Li+ in both layered and cubic titanium disulphide which permits comparison of Li+ diffusion in two and three dimensions within a chemically identical environment. In both cases the activation energy and pre-exponential factor for self-diffusion exhibit a dramatic variation with Li+ ion content. These variations and possible interpretations are discussed. (2) Thermodynamics of intercalation. The variation in the chemical potential of lithium in cubic TiS2 is presented and interpreted in terms of interactions between both the ions and electrons; the interactions follow a cube root dependence on composition. (3) New intercalation compounds. New sodium intercalation compounds are described and the future prospects for other monovalent and divalent cation intercalation compounds discussed.