Tuesday, 15 October 2019: 11:20
Room 217 (The Hilton Atlanta)
Multivalent (MV) ion storage remains to be a key thrust in the development of prospective “beyond lithium-ion” technology. In the field of Zn2+-based MV batteries, lingering questions regarding Zn2+ intercalation remain due to the divalent nature of this positively-charged cation. In the present study, we explore the charge-storage properties of a V-based Na+ superionic conductor (NASICON), Na3V2(PO4)3 (NVP), by X-ray synchrotron characterization to unravel potential-dependent structure-property relationships. We posit that a two-stage intercalation of Na+ and Zn2+ may be responsible for the overall electrochemical behavior. The initial charging profile at C/20 indicates Na+ extraction from Na3V2(PO4)3 to NaV2(PO4)3, observed by a single plateau in the galvanostatic charge/discharge profile, while subsequent discharge results in two plateaus occurring at 1.35 and 1.2 V. Operando X-ray diffraction of the cells were collected to examine the changes associated with the first charge/discharge cycle, which showed reversible behavior based on the shifting of X-ray reflections associated with the NVP structure. To examine distinct changes linked with the suggested Na+ and Zn2+ two-stage intercalation process, electrodes were prepared ex situ for Rietveld refinement to understand variations in the lattice parameters. Furthermore, changes in V oxidation state, V-O coordination, and the presence of Zn2+ was studied by ex situ X-ray absorption spectroscopy. The results of this work present a rigorous analysis of the charge-storage property of MV Zn2+ intercalation for a well-established NASICON framework, and may provide further insight into the other related structures.
