A number of vanadium oxides can function as host materials for the insertion of lithium and sodium. These materials are of interest as they can be utilized as electrodes in high capacity secondary batteries.
Although most of these systems are not thermodynamically stable over the entire composition interval spanned by the inserted ion, the kinetic stability of the vanadiumoxygen lattice is sufficient to ensure reversible operation at temperatures below 200 - 300°C. However, after transgression of the reversible composition interval some electrode materials exhibit characteristic changes in the voltage vs. composition curves. Depending on the guest/host system the phase formed can be either a new crystalline host phase, or an amorphous, highly defect material characterized by a smooth emf curve.
The materials studied were predominantly of two-dimensional nature: Vanadium pentoxide and its molybdenum substituted analogue, which have layerlike structures due to some of the V--O bonds being long and weak, and a series of layered trivanadates. Even in their highest oxidation state the latter host structures contain an amount of interlayer alkali metal ions, balancing the otherwise strong electrostatic repulsion between adjacent oxygen layers.