Nonstoichiometric molybdenum oxides as cathodes for lithium cells. Part V. Thermodynamic, kinetic and structural aspects of the behaviour of Mo8O23 and Mo18O52.

A deeper insight in the electrochemical behaviour of Li cells based on two non-stoichiometric Mo oxides, Mo8O23 and Mo18O52, was obtained by determining the OCV's, the diffusion coefficients and the variations of lattice parameters as a function of depth of discharge. The first material is a monoclinic framework-structured compound endowed with large channels which provide easy paths for Li+. Occupation of sites in the cavities of this structure produces at first a shrinkage of the unit cell, followed by a moderate re-expansion. Mo18O52 is a triclinic step-layered material which markedly expands upon Li+ intercalation. Li+ diffuses in it relatively slowly for x<1, i.e. before increasing the interlayer distance, and for x>0.4 due to coulombic repulsion between Li+ ions.