Copper-doped layered Fe₂VO₄ nanorods for aqueous zinc-ion batteries

Zinc-ion batteries (ZIBs) have attracted an increasing attention as a potential low-cost, environmentally friendliness, and high-safety energy storage system. Among them, transition metal vanadates with high oxidation state vanadium have great potential in ZIBs cathode research due to their high theoretical capacity. However, many vanadate particles still inevitably suffer from low ion mobility, low electrical conductivity and stability. Cation doping or compositing is an effective pathway capable of enhancing electrical conductivity. In this work, layered Cu-Fe₂VO₄ porous nanorods are obtained by introducing Cu²⁺ into MIL-88A(Fe) (a metal-organic framework; MIL stands for materials from Institute Lavoisier) and further ion-exchanged with NH₄VO₃, exhibiting excellent zinc storage properties as an cathode. The existence of oxygen vacancies and the change of electronic structure caused by Cu²⁺ substituting part of Fe²⁺ enhanced the conductivity and electron transfer rate. It delivers a reversible discharge capacity of 237 mAh/g at 0.3 A/g and a satisfactory high rate capacity of 126 mAh/g after 30 cycles at 5 A/g, and stable cycling performance (198 mAh/g after 1000 cycles at 1 A/g). Furthermore, the energy density can reached to 230.97 Wh kg^-1 at 208.6 W kg^-1. The assembled quasi-solid-state ZIBs maintain a high capacitance retention of 75% after 8000 cycles at 1 A/g.