Operando pH measurements revealing the promoted Zn2+ intercalation kinetics of pre-intercalated V2O5 cathode in aqueous zinc metal batteries

Pre-intercalating metallic cations into the interlayer spacing of vanadium oxides is considered as a promising strategy to promote the de-/intercalation kinetics in Zn2+-based aqueous electrolytes for high-performance aqueous zinc metal batteries. However, the respective role of H+ and Zn2+ de-/intercalation in the promoted electrochemical performance is not well understood due to the lack of suitable characterization methods. Herein, Zn2+ pre-intercalated and neat bilayered V2O5 prepared via a highly efficient microwave-assisted hydrothermal method were selected as model compounds to study the effect of the pre-intercalated ions through combining operando electrolyte pH measurement with conventional structural and electrochemical characterization. The Zn2+ pre-intercalated V2O5 exhibits higher specific capacity than the neat V2O5 in a wide current rate, increasing from 281 to 355 mAh g(-1) at 50 mA g(-1), and capacity retention of 84 % after 500 cycles at 2000 mA g(-1). The mechanism study demonstrates that the de-/intercalation of H+ and Zn2+ mainly occurs in the high voltage and low voltage regions, respectively. Although the intercalation kinetics of both H+ and Zn2+ is promoted due to the enlarged interlayer distance from 11.6 to 13.4 & Aring;, the Zn2+ 2+ intercalation as the step limiting the specific capacity contributes more to the capacity enhancement.