Electrochemical Feature of Hydrated Molybdenum Oxides in Lithim batteries

摘要

Oxide-hydrates of molybdenum [OHM] are investigaed as 3-volt cathode materials for rechargeable lithium batteries. The oxides and oxide-hydrates ofmolybdenum have been prepared at various degrees of heat treatment. The oxide-hydrats of molybdenum with different water content showed a much better performance as cathode of the rechargeable lithium battery than that of MoO_3. From these results, it was found that the crystallien-bonde water molecules play an important role for the high discharge capacity and high cyclability. We report the electrochemicla characteristics of Li/OHM batteries using hte oxides and oxide-hydreates of molybdenum which have been prepared with various degrees of heat tretment of molybdic acid. The oxide has a corrugated layer structure consisitng of corner-shared MOO_6 octahedra. This structue provide electronic conductivity within a laryer and high lithium ion mobility betwee nlayers. The mechanism of dehydration and structural rearrangement of molybdicacid during heat treatment were studies by thermal analysis. X-ray diffraction, Raman and infrared spectroscopyl Thermal analysis indicates a two-stwp dehydration and formation of orthorhombic #alpha#-MOO_3 and monoclinic #beta#-MoO_3. Discharge profiles and kinetics of teh materials are dependent on theamount of "structural water" ito the host lattice. The eelctro-insertion of Li ions occurs mainly in tow steps in the potential range between 3.0 and 1.5 V. Kinetic measurement show that Li ions are highly mobile in the OHM framework. The patial molar quantiites triangle openG_x, triangle openS_x and triangle openH_x, wstimated from EMF-temperature measurements and coulometric titration.