Room temperature conversion of X 0.3 V 2 O 5 . nH 2 O phase into X2V6O16. nH2O phase Influence of the nature of the cati
- PDF / 1,033,214 Bytes
- 6 Pages / 595 x 842 pts (A4) Page_size
- 72 Downloads / 163 Views
FF1.3.1
Room temperature conversion of X0.3V2O5. nH2O phase into X2V6O16. nH2O phase Influence of the nature of the cation X+ Olivier Durupthy, Saïd Es-salhi, Nathalie Steunou, Thibaud Coradin and Jacques Livage Laboratoire Chimie de la Matière Condensée, UMR CNRS 7574 Tour 54 E5, Université P. et M. Curie (Paris 6), 4 place Jussieu, 75252 Paris Cedex 05, France. ABSTRACT Various cations (Li+, Na+, K+, NH4+, Cs+, Mg2+,Ca2+, Ba2+) were introduced during the formation of a V2O5. nH2O gel. Cation intercalated Xy V2O5. nH2O (y = 0.3 for X = Li+, Na+, K+, NH4+ or y = 0.15 for Mg2+, Ca2+, Ba2+) were first obtained at room temperature but some of them evolve upon ageing into a new phase: XV3O8. nH2O for X = Na+, K+, NH4+ and Cs+ or XV6O16. nH2O for X = Mg2+, Ca2+, Ba2+. All the vanadium oxide phases were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and infrared spectroscopy (IR); the supernatant solutions were analysed by 51V NMR spectroscopy. These vanadium oxide phases exhibit a layered structure with cations and water molecules intercalated within the interlayer space. The formation of the different phases depends mainly on the pH of the supernatant solution and on the nature of the cation. INTRODUCTION Vanadium oxide based materials have been extensively studied for their electronic and ionic properties [1-4]. Some of them appear as promising candidates as reversible cathodes in lithium batteries but their properties strongly depend on their structural features [2, 5]. For instance, the low-temperature form of the trivanadate phase LixV3O8 is able to accommodate 4.5 mol of Li+ ions per formula unit, instead of 3 for the high temperature trivanadate [6]. Moreover, the nature of the cation in the trivanadate structure has an influence on the lithium insertion rate [4, 7]. Solution chemistry is a suitable method to design new materials with interesting properties since the polymerization reactions are performed at room temperature allowing a control over the nucleation and growth of the vanadium oxide. We have already shown that it was possible to form NaV3O8.1.5H2O phase from aqueous solutions around room temperature by controlling the synthesis parameters. The initially formed Na0.3V2O5. nH2O phase redissolves at higher pH giving rise to the trivanadate phase [8]. In this work, we have studied the addition of monovalent or divalent cation as base (MOH or M(OH)2) or salt (MCl or MCl2) to the vanadium oxide precursors obtained at room temperature after acidification of a metavanadate solution. The various vanadium oxides obtained through this approach were characterized by infrared spectroscopy (IR), X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). Solution 51V NMR spectroscopy was used to analyse the supernatant solutions. The evolution of the precipitated phases upon ageing is described, showing the conversion, at room temperature, of the initial poorly ordered X0.3V2O5. nH2O precipitate into the crystalline XV3O8.nH2O or X2V6O16.nH2O phase. Finally, the effect of the natu
Data Loading...
