Calcium ion pinned vanadium oxide cathode for high-capacity and long-life aqueous rechargeable zinc-ion batteries

Rechargeable aqueous zinc ion batteries (ZIBs), with the easy operation, cost effectiveness, and high safety, are emerging candidates for high-energy wearable/portable energy storage systems. Unfortunately, the unsatisfactory energy density and undesired long-term cycling performance of the cathode hinder the development of ZIBs. Here, we report the chemical pre-intercalation of a small amount of calcium ions into V2O5 as the cathode material. The cathode of Ca0.04V2O5•1.74H2O (CVO) was demonstrated to have a high specific capacity of 400 mA h g−1 at the current density of 0.05 A g−1 and 187 mA h g−1 at 10 A g−1, along with impressive capacity retention (100% capacity retention at 10 A g−1 for 3,000 cycles). Meanwhile, the CVO// Zn battery exhibits a high energy density of 308 Wh kg−1 and a power density of 467 W kg−1 at 0.5 A g−1. The superior performance originates from the pinning effect of the calcium ions and the lubricating effect of the structural water. The energy storage mechanism of the CVO cathode was also investigated in detail. The new phase (Zn3(OH)2V2O7•2H2O) generated upon cycling participates in the electrochemical reaction and thus contributes to the excellent electrochemical performance. The small amount of Ca2+ pre-inserted into the interlayer of V2O5 sheds light on constructing cathodes with high energy density for ZIBs.