Doped V2O5-Based Cathode Materials: Where Does the Doping Metal Go? An X-ray Absorption Spectroscopy Study

Abstract X-ray Absorption Spectroscopy (XAS) has been used to probe the local structure of doped vanadium pentoxide materials prepared through sol-gel processes. The doped samples have been analyzed at the vanadium k-edge as well as at the doping metal K-edge (copper and zinc). The presence of two metals sites gives two independent absorption signals, even if we are investigating the same compound, for this reason the reliability of the analysis is enhanced. The strategy in determining the local structure will be discussed. The local structural modifications resulting from low to high doping concentration in the best performing copper doped - V2O5 aerogel like material is reported. Similar measurements were done using zinc as doping metal, in both aerogel-like and xerogel form. The EXAFS analysis shows that the vanadium atomic environment is not altered by the doping metal insertion and that 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 in both xerogel and aerogel-like oxide hosts. The use of the metal-metal interaction while analyzing data concerning sample of high doping level played a key role in the determination of the preferred metal sites.