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

Multivalent (MV) ion storage remains to be a key thrust in the development of prospective “beyond lithium-ion” technology. In the field of Zn 2+ -based MV batteries, lingering questions regarding Zn 2+ 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), Na 3 V 2 (PO 4 ) 3 (NVP), by X-ray synchrotron characterization to unravel potential-dependent structure-property relationships. We posit that a two-stage intercalation of Na + and Zn 2+ may be responsible for the overall electrochemical behavior. The initial charging profile at C/20 indicates Na + extraction from Na 3 V 2 (PO 4 ) 3 to NaV 2 (PO 4 ) 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 Zn 2+ 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 Zn 2+ 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 Zn 2+ intercalation for a well-established NASICON framework, and may provide further insight into the other related structures.