Rational Regulation of Optimal Oxygen Vacancy Concentrations on VO 2 for Superior Aqueous Zinc-Ion Battery Cathodes.

VO 2 with its special tunnel structure and high theoretical capacity is an ideal candidate for cathode materials for aqueous zinc-ion batteries (ZIBs). However, the slow kinetics and structural instability due to the strong electrostatic interactions between the host structure of VO 2 and Zn 2+ hinder its application. Defect engineering is a well-recognized strategy for improving the intrinsic ion-electron dynamics and structural stability of this material. However, the preparation of oxygen vacancies poses significant difficulties, and it is challenging to control their concentration effectively. Excessive or insufficient vacancy concentration can have a negative effect on the cathode material. Herein, we propose electrode materials with controlled oxygen vacancies prepared in situ on carbon nanofibers (CNF) by a simple, one-step hydrothermal process (Ov-VO 2 @CNF). This method can balance the adsorption energy and migration energy barrier easily, and we maximized the adsorption energy of Zn 2+ while minimizing the adsorption energy barrier. Notably, the O v2 -VO 2 @CNF electrode delivered a high specific capacity (over 450 mAh g -1 at 0.1 A g -1 ) and excellent cycle stability (318 mAh g -1 at 5 A g -1 capacity after 2000 cycles with a capacity retention of 85%). This rational design of precisely regulated defect engineering provides a way to obtain advanced electrode materials with excellent comprehensive properties.