A long-life aqueous Zn-ion battery based on Na3V2(PO4)2F3 cathode

Aqueous “rocking-chair” Zn-ion batteries based on the intercalation/deintercalation chemistry of divalent Zn2+ ions are appealing area, but the lack of suitable cathodes to tolerate the stable insertion/extraction of Zn2+ ions as well as practical approaches to minimize the dendrite growth of zinc anode are still the major challenges. Here, we report a rechargeable aqueous Zn-ion battery based on a new intercalated Na3V2(PO4)2F3 cathode coupled with a carbon film functionalizing Zn anode and 2 M Zn(CF3SO3)2 electrolyte. This battery exhibits a high voltage of 1.62 V, energy density of 97.5 W h kg−1, as well as superior cyclability of 95% capacity retention over 4000 cycles. The remarkable performance originates from the dendrite-free of Zn anode assisted by a carbon film changing the deposition behavior of Zn, the protective layer of “solid electrolyte interphase” on Na3V2(PO4)2F3 cathode and the highly reversible insertion/extraction chemistry of Zn2+ ions in Na3V2(PO4)2F3 with a much small volume change of 0.22% as evidenced by ex-situ XPS and XRD analysis. Moreover, this system can be delicately designed as a flexible soft package battery with both good flexibility and cyclability (80.6% capacity retention over 600 cycles).