A High-Rate and Ultrastable Aqueous Zinc-Ion Battery with a Novel MgV2 O6 ·1.7H2 O Nanobelt Cathode.

High-safety and low-cost aqueous Zn-ion batteries have triggered an astounding investigation surge in the last 5 years and are becoming competitive alternatives for grid-scale energy storage. However, the implementation of this promising technology is still plagued by the lack of effective and affordable cathode materials that can enable high energy densities and an exceptional cycling stability. Herein, a novel vanadium-based oxide cathode based on MgV2 O6 ·1.7H2 O nanobelts, which delivers a high capacity (425.7 mAh g-1 at 0.2 A g-1 ), a robust rate capability (182.1 mAh g-1 at 10 A g-1 ), and an ultrastable cycle without any visible deterioration, as well as an adequate energy density (331.6 Wh kg-1 ), is developed. Such excellent electrochemical Zn-ion storage performance is believed to result from the fast ion-diffusion kinetics boosted by a stable layered structure and an ultrahigh intercalation pseudocapacitance reaction, which are also benefited by a typical H+ /Zn2+ co-insertion mechanism, accompanied by an atypical Zn2+ intercalation chemistry with a partial but irreversible Mg2+ -Zn2+ ion-exchange reaction during the initial discharge. These results provide key and enlightening insights into the design of high-performance vanadium oxide cathode materials.