Solid state ionics of manganese and vanadium oxides

摘要

The layered structure Li_xTiS_2 and Li_xCoO_2 compounds are excellent reversible cathodes for lithium batteries. However, the corresponding Li_xMnO_w is metastable reverting to a disordered spinel form on cycling. MnO_2 may be stabilized in the layer form by pillaring of the layers with larger ions such as potassium, which minimizes the diffusion of the manganese ions. The low conductivity of manganese oxide compounds can be substantially increased by doping with cobalt or iron. This doping was accomplished under both hydrothermal and high temperature reactions, and was found to enhance the conductivity by two orders of magnitude relative to pure K_xMnO_2. A wide variety of vanadium oxide strutures have been formed under hydrothermal conditions. The vanadium oxides containing double sheets of vanadium oxide appear particularly promising for ionics applications. Examples include xerogel H_xV_2O_5, V_6O_13, and Mn_0.6 V_2O_5. Tunnel structures of both manganese and vanadium oxides also exhibit solid state ionic behavior.