Control of the structure and properties of vanadium and manganese oxides through tailored soft synthesis

Abstract

Vanadium and manganese oxides can be readily synthesized using soft chemical approaches, such as hydrothermal, sol–gel, intercalation and ion-exchange. By controlling the pH and organic reactants/templates it is possible to control the structure formed by controlling the species in solution. In the case of vanadium, its coordination number increases as the pH decreases. It is found that the higher the vanadium coordination number the better the behavior of the oxide as a cathode material in lithium cells; tetrahedral vanadium is not reduced without destruction of the structure, whereas octahedral vanadium as in the delta double sheet structure holds its structure during reduction. Manganese oxides can also be synthesized using hydrothermal methods, with layered structures formed when small cations are present and tunnel structures when larger cations or anions are present. A range of mixed vanadium manganese oxides has been prepared, the structure depending on the organic cation and vanadium-to-manganese ratio. In several cases these are pillared oxides, that readily react with intercalating cations.