Controlling crystal structures of vanadium oxides via pH regulation and decoupling crystallographic perspective on zinc storage behaviors

Abstract

Rechargeable aqueous zinc–ion batteries (RAZIBs) hold tremendous promise for large–scale energy storage applications on account of high materials abundance, cost–effectiveness, and intrinsic safety. To date, vanadium–based oxides have been widely investigated as promising candidates for RAZIBs. The crystal structure of vanadium oxide plays a decisive role in determining Zn2+ storage behavior. In this work, we reveal that vanadium oxides with various crystal structures can be obtained from different V5+ solute species by controlling the pH value of the precursor solution. The results indicate that layered Zn0.15V2O5·0.76H2O obtained at pH = 1 exhibits reduced charge−transfer resistance and promoted Zn2+ transport kinetics. As a result, the sample demonstrates remarkable Zn2+ storage capability, that is, high capacity (320 mAh g–1 at 1 A g–1), promising rate capability (227 mAh g–1 at 8 A g–1), and reliable cycle performance (184 mAh g–1 after 3000 cycles at 4 A g–1). Controlling the pH value of precursor solution to 4 and 6, the samples are characterized as mixed–phase compounds containing ‘‘inactive’’ components (ZnV2O6 and/or water−deficient (NH4)2V6O16), leading to inferior electrochemical performance. For the pH = 10 sample, the obtained Zn2(OH)3VO3 is unfit for Zn2+ storage with negligible capacity. The reaction chemistries of vanadium oxides and the crystallographic perspective on Zn2+ storage properties are revealed, providing a new insight into the development of high−performance cathodes for RAZIBs.