Electrochemical Feature of Hydrated Molybdenum Oxides in Lithium Batteries

Abstract

ABSTRACTOxide-hydrates of molybdenum [OHM] are investigated as 3-volt cathode materials for rechargeable lithium batteries. The oxides and oxide-hydrates of molybdenum have been prepared at various degrees of heat treatment. The oxide-hydrates of molybdenum with different water content showed a much better performance as cathode of the rechargeable lithium battery than that of MoO3. From these results, it was found that the crystalline-bonded water molecules play an important role for the high discharge capacity and high cyclability. We report the electrochemical characteristics of Li/OHM batteries using the oxides and oxide-hydrates of molybdenum which have been prepared with various degrees of heat treatment of molybdic acid. The oxide has a corrugated layer structure consisting of corner-shared MoO6octahedra. This structure provide electronic conductivity within a layer and high lithium ion mobility between layers. The mechanism of dehydration and structural rearrangement of molybdic acid during heat treatment were studies by thermal analysis, X-ray diffraction, Raman and infrared spectroscopy. Thermal analysis indicates a two-step dehydration and formation of orthorhombic α-MoO3and monoclinic β-MoO3. Discharge profiles and kinetics of the materials are dependent on the amount of “structural water” into the host lattice. The electro-insertion of Li ions occurs mainly in two steps in the potential range between 3.0 and 1.5 V (compositional range 0<xLi<l.5). Kinetic measurement show that Li ions are highly mobile in the OHM framework. The partial molar quantities δGx, δSx, and δHx, estimated from EMF-temperature measurements and coulometric titration.