Potassium manganese-vanadium oxide cathodes prepared by hydrothermal synthesis

Hydrothermal reactions between potassium permanganate and vanadyl sulfate h ave been used to synthesize new forms of vanadium oxides. Depending on the reactant ratios and pH values of the reaction mixtures, two different layer ed materials have been identified. The first one formed at a pH value of 1. 6 has an interlayer distance of 10.90 Angstrom and a composition of K0.16Mn 0.04V2O4.94.0.14H(2)O, while the second one formed at pH Values higher than 3.0 has an interlayer distance of 9.45 Angstrom and a composition of K0.44 V2O4.96 Structural analysis indicates that they have a delta -type structur e with potassium ions residing in between double sheets of vanadium oxide. The structure and composition of these materials have a profound effect on their charge and discharge properties when used as cathodes in Lithium batt eries. The sample prepared at a pH value of 2.3 shows best overall performa nce considering both reversible capacity and cyclability, which is explaine d with the coexistence of two layered phases in the material. This material has a capacity of over 200 mA h/g between 3.6 and 2.2 V and retains a capa city of 190 mA h/g after 30 cycles. increase of manganese to vanadium ratio during synthesis leads to a gradual loss of the layered structure and decr eased lithium insertion capacity. (C) 2001 Elsevier Science B.V. All rights reserved.