Carbon-Integrated Vanadium Oxide Hydrate as a High-Performance Cathode Material for Aqueous Zinc-Ion Batteries

The hydration of bilayer vanadium oxides has become the focus of several recent studies toward increasing the interlayer spacing and improving their structural stability, which is favorable for the reversible (de)insertion of Zn2+ ions. However, there is limited understanding on the optimal level of H2O molecules to be incorporated within the vanadium oxide structure. Herein, we investigate the effects of the interlayer H2O content in a vanadium(IV,V) oxide-based cathode material toward the electrochemical performance of a zinc-ion battery (ZIB). A simple solvothermal synthetic route was employed to synthesize carbon-integrated hydrated vanadium oxides with varying H2O contents, CHVO (V5O12middot2.7H2O) and CHVOLW (V5O12middot0.4H2O). CHVO material displays a high capacity of 396 mA h g-1 at a specific current of 250 mA g-1 and an excellent rate capability (187 W h kg-1 at a high-power density of 4.5 kW kg-1). In contrast, CHVO-LW delivers a higher capacity of 582 mA h g-1 at 200 mA g-1 in the initial cycles, however, suffers a rapid capacity decay and cell failure in subsequent cycles. Electrochemical characterizations revealed that structural pillars, such as H2O molecules, can indeed provide significant structural stability, yet too many of them can block intercalation pathways leading to lower capacity. This study shows the importance of adjusting the hydration level to sustain a balance between the high capacity and long-term stability of hydrated vanadium oxide cathode-based ZIBs.