Synthesis of Li1+ αV3O8 via a Gel Precursor:  Part II, from Xerogel to the Anhydrous Material

The synthesis of anhydrous Li1+ αV3O8 from its xerogel has been studied by using thermodiffractometry and variable temperature 51V magic-angle spinning NMR spectroscopy. Completion of dehydration leads to a sample characterized by a bimodal grain size distribution, the larger and smaller sized particles coming from the two components of the xerogel (liquid and solid components), respectively. The specific reactions undergone by these two components have been identified: the solid component gradually loses water by undergoing a series of phase transitions involving layered phases with decreasing water concentrations, the hewettite framework being maintained throughout the reaction, whereas in the case of the dried liquid component of the xerogel, the formation of anhydrous Li1+ αV3O8 occurs through the decomposition of lithium vanadates, which is followed by the formation and then progressive dehydration of a hydrated hewettite structure. It is shown that the biphasic nature of the pristine gel precursor has an impact on the electrochemical behavior of anhydrous Li1+ αV3O8.