ELECTRONIC-STRUCTURE IN RELATION TO THE REACTIVITY OF NONSTOICHIOMETRIC AXMX2 LAYERED COMPOUNDS

The data concerning the character of the discharge curve for various materials are collected and correlated with the microscopic electronic parameters such as the metal-metal distances in the corresponding materials. On the basis of this correlation an electronic model of alkali metal ion intercalation into A(x)MX2 (A = Li, Na; M = V, Cr, Mn, Co, Ni; X = O, S, Se) cathode materials is proposed. The potential changes accompanying electrochemical intercalation are ascribed to the changes of the Fermi level position in the cathode material. Consequently, the step-like shape of the discharge curve is linked with the step-like shape of the density-of-states curve. Comparison of the actual metal-metal distance R(M-M) with the critical distance R(c) given by Goodenough allows the prediction of the properties of oxide cathode materials. The materials for which R(M-M) < R(c) prove to be among the best materials for use in batteries.