A THERMODYNAMIC, STRUCTURAL AND KINETIC-STUDY OF THE ELECTROCHEMICAL LITHIUM INTERCALATION INTO THE XEROGEL V2O5.1.6 H2O IN A PROPYLENE CARBONATE SOLUTION

The electrochemical lithium insertion reaction into the vanadium pentoxide xerogel V2O5.1.6 H2O (noted VXG) in a propylene carbonate solution has been investigated by structural, thermodynamic and kinetic studies. This material, obtained via a sol-gel process, is a lamellar compound whose high anisotropic structure is characterized by the stacking of ribbons in the c direction. The presence of propylene carbonate in the starting material leads to a basal distance of 21.6 angstrom (1 angstrom = 10(-10) m). About 1.8 Li+ ions can be accommodated between the ribbons of this lamellar compound at the same energetic level of approximately 3.1 V vs. Li/Li+. Entropy measurements, X-ray diffraction experiments and particle size determinations have given evidence for the existence of two one-phase regions for the composition ranges 0 < x < 0.1 and 0.2 < x < 1.8, and a two phase region for the narrow lithium content 0.1 < x < 0.2. Between x = 0.1 and x = 0.2, lithium insertion causes the removal of the propylene carbonate from the inter-ribbon space to give rise to a collapsed VXG form. With a theoretical faradaic capacity of 250 Ah/kg, the reversibility of the lithium insertion process being proven, VXG constitutes a promising intercalation material. Nevertheless, even with a high diffusion coefficient D(Li) approximately > 5 X 10(-11) cm2 s-1, its low electronic conductivity hinders utilisation of high current densities. Cycling experiments have shown a satisfactory behaviour since for a current density j = 0.05 mA CM-2, about 70% of the initial capacity, ie. 70 Ah/kg, is recovered after the 30th cycle.