Evidence for reversible formation of metallic Cu in Cu0.1V2O5 xerogel cathodes during intercalation cycling of Li+ ions as detected by X-ray absorption spectroscopy

Vanadium pentoxide materials prepared through sol-gel processes (xerogel. a erogel. and aerogel-like) act as excellent intercalation hosts for lithium as well as polyvalent cations. The large lithium insertion capacity of thes e materials makes them attractive for use as cathodes in high-capacity lith ium batteries. Copper-doped V2O5-based cathodes have excellent properties i n terms of high intercalation rate and very good reversibility upon cycling with no capacity hiding after more than 450 cycles. This paper reports in situ X-ray absorption spectroscopy (XAS) investigations of copper-doped V2O 5 xerogel. The K-edge X-ray adsorption thresholds of V and Cu were studied. The local structure around copper is found to change dramatically during i ndividual insertion/ release cycles for Li+ ions. The XAS analysis indicate s that the lithiation of the Cu0.1V2O5 xerogel cathode proceeds with concur rent formation of copper metal. However. the starting compound is regenerat ed upon releasing the inserted lithium (charging the cathode), thus reveali ng the foundation for excellent structural and electronic reversibility of the material. (C) 2001 The Electrochemical Society.