Evidence for Reversible Formation of Metallic Cu in Cu_0.1V₂O₅ Xerogel Cathodes during Intercalation Cycling of Li⁺ Ions as Detected by X-Ray Absorption Spectroscopy

Vanadium pentoxide materials prepared through sol-gel processes (xerogel, aerogel, and aerogel-like) act as excellent intercalation hosts for lithium as well as polyvalent cations. The large lithium insertion capacity of these materials makes them attractive for use as cathodes in high-capacity lithium batteries. Copper-doped V₂O₅-based cathodes have excellent properties in terms of high intercalation rate and very good reversibility upon cycling with no capacity fading after more than 450 cycles. This paper reports in situ X-ray absorption spectroscopy (XAS) investigations of copper-doped V₂O₅ xerogel. The K-edge X-ray absorption thresholds of V and Cu were studied. The local structure around copper is found to change dramatically during individual insertion/ release cycles for Li⁺ ions. The XAS analysis indicates that the lithiation of the Cu_0.1V₂O₅ xerogel cathode proceeds with concurrent formation of copper metal. However, the starting compound is regenerated upon releasing the inserted lithium (charging the cathode), thus revealing the foundation for excellent structural and electronic reversibility of the material.