Nasicon Na3V2(PO4)3 Facilitates Anomalous Two-Stage Na+ and Zn2+ Intercalation for Zinc-Ion Batteries

Tuesday, 15 October 2019: 11:20
Room 217 (The Hilton Atlanta)
J. S. Ko, P. P. Paul (SLAC National Accelerator Laboratory, USA), N. Seitzman (Colorado School of Mines), R. DeBlock, B. S. Dunn (University of California, Los Angeles), and J. N. Weker (SLAC National Accelerator Laboratory, USA)
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.