Realizing excellent cycle stability of Zn/Na 3 V 2 (PO 4 )3 batteries by suppressing dissolution and structural degradation in non-aqueous Na/Zn dual-salt electrolytes

The low-cost and high-safety rechargeable zinc-ion batteries (ZIBs) show promising applications for large-scale energy storage. However, the (de)intercalation of divalent zinc ions with high charge density restricts cathode materials’ choice. Na3V2(PO4)3 (NVP) is one of the sodium (Na) super-ionic conductor materials that shows feasible utilization in aqueous ZIBs but universally has poor cycle life, commonly limited to 200 cycles or less. In this study, we investigate the capacity degradation mechanism of NVP systematically and then propose a novel organic dual-salt electrolyte to realize excellent cycling stability. We find a spontaneous dissolution of NVP when immersed in the static aqueous electrolyte, and there is an irreversible phase change during the first discharge process, leading to a fast capacity fading in aqueous electrolytes. The dissolution problem can be effectively suppressed by non-aqueous Zn2+-containing electrolytes. However, the sluggish reaction of Zn2+ intercalation into NVP causes poor reversibility. We develop a non-aqueous Na/Zn hybrid system by adding Na+ ions as charge carriers to address this issue. Highly reversible co-insertion of Na/Zn ions into the NVP enables a high capacity of 84 mA h−1 and an outstanding lifetime of 600 cycles at 500 mA g−1 without capacity loss. This work provides valuable views on the NVP’s failure mechanisms that will be helpful for ZIB development.