A.C. Marschilok, K.J. Takeuchi, E.S. Takeuchi
Stony Brook University,
Keywords: battery, zinc, aqueous
Summary:The electrochemical charge storage of sodium vanadate (NaV3O8 or NVO) cathodes in aqueous Zn-ion batteries has been hypothesized to be influenced by the inclusion of structural water for facilitating ion transfer in the material. Materials properties considered important (morphology, crystallite and particle size, surface area) are studied for two NVO materials, NaV3O8·0.34H2O and NaV3O8·0.05H2O with different water content, acicular morphologies with different size and surface area achieved via post-synthesis heat treatment. The electrochemistry of the two materials was evaluated in aqueous Zn cells using a mildly acidic electrolyte using galvanostatic cycling and rate capability testing. Thinner nanobelts with higher structural water demonstrate greater specific capacities and higher effective diffusion coefficients relative to the thicker nanorods. Structural changes accompanying electrochemical cycling are elucidated via X-ray diffraction, transmission electron microscopy, and V K-edge X-ray absorption spectroscopy (XAS). The results verify that electron transfer corresponds directly to change in vanadium oxidation state, affirming vanadium redox as the governing electrochemical process for both materials.