Hierarchical Porous Metallic VO@C for Advanced Aqueous Zinc-Ion Batteries.

Aqueous Zn-ion batteries (ZIBs) are a potential electrochemical energy storage device because of their highly intrinsic safety, low cost, and large capacity. However, it is still in the primary stage because of the limited selection of cathode materials with high rate and long-life cycling stability. In addition, the energy storage mechanisms of ZIBs have not been well established. In this work, we report the synthesis of porous VO@C materials with high conductivity and further illustrate its application as the intercalation cathode for aqueous zinc-ion batteries. The unique channel and appropriate pore size distribution of corundum-type VO are beneficial to the rapid zinc ion intercalation and removal, leading to a high rate capability. Also, the carbon framework structure achieves a high cyclic stability. The porous VO@C cathode delivers high capacities of 350 mA h g at 100 mA g, an excellent rate capability (250 mA h g at 2 A g), and an impressive long-life cycling stability with 90% capacity retention over 4000 cycles at 5 A g. The storage mechanism of zinc ions in the Zn/VO system was studied by various analytical methods and first-principles calculation.