Identification of an unconventional zinc coordination site in anhydrous Zn_xV₂O₅ aerogels from x-ray absorption spectroscopy

V₂O₅ aerogel (ARG) has been studied as an insertion host for lithium ions and for several polyvalent cations. The stability, reversibility, and capacity for ion insertion and release processes make the amorphous ARG an interesting material for battery applications. The local structural modifications resulting from the chemical insertion of Zn²⁺ ions into the host have been investigated by X-ray absorption spectroscopy (XAS). X-ray absorption nearedge structure (XANES) spectra at the V K-edge of Zn_xV₂O₅ did not shown any substantive change as a function of increasing amounts of intercalated ions, thus indicating the absence of interactions between the intercalated ions and the vanadium ions. To study the structural sites of the polyvalent ions, EXAFS (extended X-ray absorption fine structure) spectra have been recorded at the Zn K-edge. The EXAFS analysis showed that the Zn²⁺ ions are 4-fold coordinated by almost coplanar oxygens. In addition, differences in the first shell of the inserted Zn²⁺ as a function of the intercalation level have been observed. The first-shell Zn-O bond length shortened and the EXAFS Debye-Waller factor increased. This suggests a decrease of the local geometrical order of the first shell as polyvalent cations are inserted.