X-ray Absorption Spectroscopy Study of Cu_0.25V₂O ₅ and Zn_0.25V₂O₅ Aerogel-Like Cathodes for Lithium Batteries

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. The local structural modifications resulting from low dopant concentration (copper and zinc) in V₂O₅ aerogel-like material have been investigated by X-ray absorption spectroscopy (XAS). To study the structural sites of the polyvalent ions, extended X-ray absorption fine structure (EXAFS) spectra have been recorded at the vanadium, zinc, and copper K edges. The EXAFS analysis shows that the vanadium atomic environment is almost the same for Cu_0.25V₂O₅ and Zn _0.25V₂O₅. Furthermore, the doping metals (Cu and Zn) are found to be in the same site. Copper and zinc are 4-fold coordinated by almost-coplanar oxygens. This suggests a preferred site for the doping metal (M) and the same interaction between the vanadium and the doping metals. M-O first-shell distances are shorter for the copper compared to those for the zinc, and we have found higher disorder in the Zn_0.25V₂O ₅ compound compared to that in Cu_0.25V₂O ₅. No interactions between metal-metal sites were found because the metal doping level was too small.