STRUCTURAL, PHYSICAL AND ELECTROCHEMICAL CHARACTERISTICS OF A VANADIUM OXYSULFIDE, A CATHODE MATERIAL FOR LITHIUM BATTERIES

A vanadium oxysulfide is obtained by a reaction between water solution s of a vanadyl salt and sodium sulfide at room temperature. After dryi ng under mild conditions, the formulation of this phase is V2O3S . 3H( 2)O. Thermogravimetric analyses show that it is not possible to remove completely water without losing sulfur. This is in agreement with pro ton nuclear magnetic resonance experiments which prove that water mole cules are tightly bonded to vanadium. Magnetic susceptibility and X-ra y absorption spectroscopy measurements allow to define the oxidation s tates of vanadium and sulfur, (IV) and (-II) respectively. From extend ed X-ray absorption fine structure spectroscopy at the vanadium K edge and infrared spectroscopy, the local structure around vanadium can be defined as a distorted octahedron, with a vanadyl bond and an opposit e sulfur atom. Magnetic susceptibility and X-ray absorption spectrosco py measurements on chemically lithiated compounds show a complex charg e transfer from lithium to the host structure upon lithium intercalati on. If it appears that vanadium atoms are reduced, a possible role of sulfur atoms in the redox process has to be considered. Cycling tests of lithium batteries whose positive consists of oxysulfide are promisi ng with 70 cycles under a regime of C/8, without noticeable loss in ca pacity of 120 Ah/kg.