New Insight on K 2 Zn 2 V 10 O 28 as an Advanced Cathode for Rechargeable Aqueous Zinc-Ion Batteries.

Aqueous zinc-ion batteries (ZIBs) have recently attracted people's extensive attention in their application in energy storage systems resulting from their exclusive characteristics of low cost and environmental compatibility. However, finding suitable cathode materials continues to be the major challenge. Polyoxovanadates (POVs), as an important branch of polyoxometalates (POMs), are considered as a promising electrode material for reversible aqueous ZIBs relying on the flexible valence state of V. Herein, POVs (K 2 Zn 2 V 10 O 28 : KZVO) are reported as an advanced cathode for storing Zn 2+ , which delivers a high discharge capacity of 223.4 mAh g -1 at 0.1 A g -1 , considerable energy density (182.9 Wh kg -1 ) and power density (40.38 W kg -1 ), and robust cyclic performance. In addition, the dynamic properties of the KZVO/Zn battery are revealed by pseudocapacitance analysis and GITT tests. Meanwhile, the storage mechanism of Zn 2+ is further analyzed by ex situ XRD, XPS, TEM, and HRTEM. Overall, this work not only draws up a cathode material for the POMs system in aqueous ZIBs, but also demonstrates that POMs are the rising star in energy storage and electric energy applications.