Improved lithium capacity of defective V2O5 materials

We demonstrate that point defects may be introduced into a metal oxide to increase its Li-ion capacity by using various heat treatments to modify the defect structure of polycrystalline V2O5 and then comparing the Li capacity of the materials. The V2O5 that is heated under O-2/H O-2 at 460 degreesC has a 23% higher Li capacity than the as-received material despite no change to its long-range structure. Other heating conditions lower the Li capacity, of the V2O5. We infer that heating under O-2/H2O introduces defects, such as cation vacancies associated with lithiated oxygen sites, which can electrochemically exchange Li ions and serve as additional charge-storage sites. This study may also explain how metal oxides synthesized from sol-gels, such as xerogels and aerogels, insert lithium ions without concomitant reduction of transition-metal-ion sites-high-surface-area metal oxides are likely to be nonstoichiometric and rich with surface point defects which can serve as additional charge-storage sites. (C) 2002 Published by Elsevier Science B.V.