Operando pH measurements revealing the promoted Zn$^{2+}$ intercalation kinetics of pre-intercalated V$_2$O$_5$ 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 Zn$^{2+}$ -based aqueous electrolytes for high-performance aqueous zinc metal batteries. However, the respective role of H$^+$ and Zn$^{2+}$ de-/intercalation in the promoted electrochemical performance is not well understood due to the lack of suitable characterization methods. Herein, Zn$^{2+}$ pre-intercalated and neat bilayered V$_2$O$_5$ 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 Zn$^{2+}$ pre-intercalated V$_2$O$_5$ exhibits higher specific capacity than the neat V$_2$O$_5$ 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 Zn$^{2+}$ mainly occurs in the high voltage and low voltage regions, respectively. ... mehrAlthough the intercalation kinetics of both H$^+$ and Zn$^{2+}$ is promoted due to the enlarged interlayer distance from 11.6 to 13.4 Å, the Zn$^{2+}$ intercalation as the step limiting the specific capacity contributes more to the capacity enhancement.