A rechargeable Zn-ion battery is a promising aqueous system, where coinsertion of Zn2+ and H+ could address the obstacles of the sluggish ionic transport in cathode materials imposed by multivalent battery chemistry. However, there is a lack of fundamental understanding of this dual-ion transport, especially the potentiodynamics of the storage process. Here, a quantitative analysis of Zn2+ and H+ transport in a disordered sodium vanadate (NaV3O8) cathode material has been reported. Collectively, synchrotron X-ray analysis shows that both Zn2+ and H+ storages follow an intercalation storage mechanism in NaV3O8 and proceed in a sequential manner, where intercalations of 0.26 Zn2+ followed by 0.24 H+ per vanadium atom occur during discharging, while reverse dynamics happens during charging. Such a unique and synergistic dual-ion sequential storage favors a high capacity (265 mA h g–1) and an energy density (221 W h kg–1) based on the NaV3O8 cathode and a great cycling life (a capacity retention of 78% after 2000 cycles) in Zn/NaV3O8 full cells.

Aqueous Zn-ion batteries (AZIBs) are promising alternatives to lithium-ion batteries in stationary storage. However, limited storage capacity and cyclic life impede their large-scale implementation. We report reversible electrochemical insertion of multi-ions into sodium vanadate (NaV3O8) cathode materials for AZIBs, achieving a maximum storage capacity of 450 mAh g–1 at 0.05 A g–1 and a capacity retention of 82% after 500 cycles at 0.4 A g–1. In addition to Zn2+ and H+ insertion, in situ X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) collectively provide explicit evidence on vanadyl ions (VO2+) conversion–intercalation at the NaV3O8 cathode, showing the deintercalation of VO2+ from NaV3O8 and the consequent conversion of VO2+ into V2O5 on charging, and vice versa on discharging. Our study is the first to report on the cation conversion–intercalation mechanism in AZIBs. This reversible multi-ion storage mechanism provides a design principle for developing high-capacity aqueous electrode materials by engaging both the intercalation and conversion of charge carriers.

We reported that the incorporation of conductive polymer into V2O5 materials resulted in an increased interlayer distance of 2.2 nm, favoring K-ion storage in an aqueous electrolyte. In situ X-ray...