A thermodynamic, structural and kinetic study of the electrochemical lithium intercalation into the xerogel V 2O 5 · 1.6 H 2O in a propylene

Abstract

The electrochemical lithium insertion reaction into the vanadium pentoxide xerogel V 2O 5·.1.6 H 2O (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 Å (1 Å = 10 −10 m). About 1.8 Li + ions can be accomodated between the ribbons of this lamellar compound at the same energetic level of ~ 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 spacc 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 $ ̃ > 5sx 10 −11 cm 2 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.