Probing local electronic and geometric changes of hydrated calcium vanadium oxide (Ca_xV₂O₅·yH₂O) upon Zn ion intercalation

An interesting nanostructured non-stoichiometric vanadium oxide bronze (CaxV2O5•yH2O) is incorporated as the active material in an aqueous zinc-ion intercalation device. Simple solvothermal synthesis route produces highly crystalline and strongly oriented nanobelt structures as characterized by microscopy. Upon cycling, the cathode materials are recovered for an X-ray absorption investigation of local electronic and geometric changes for both the host vanadium oxide and the intercalated zinc ion as a function of voltage. This multi-edge study presents changes in Zn–O coordination and suggests Zn-ion occupancy site through theoretical calculations. The layered vanadium host shows gradual oxidation state reduction from charge density donation during intercalation while the Zn ion maintains the +2 oxidation state. The findings add understanding to the mechanisms involved in aqueous electrochemical storage devices.