Monoclinic VO₂(D) hollow nanospheres with super-long cycle life for aqueous zinc ion batteries

Abstract

Vanadium dioxide (VO₂) is a very promising cathode material for aqueous zinc ion batteries (AZIBs) because of its high reversible specific capacity, excellent rate performance and fast diffusion kinetics. However, its long-term cycle stability and compatibility with electrolytes have not met expectations. In this study, another metastable phase of vanadium dioxide-monoclinic VO₂(D)-is demonstrated to be a better choice as a cathode for AZIBs. Electrochemical results revealed that the as-prepared VO₂(D) hollow nanospheres delivered high reversible discharge capacity (up to 408 mA h g^-1 at 0.1 A g^-1), exceptional rate performance (200 mA h g^-1 at 20 A g^-1), and long cyclic endurance stability (cycling for 30 000 cycles with a low capacity fading rate of 0.0023% per cycle) in inexpensive 3 M ZnSO₄ electrolyte. Furthermore, the electrochemical reaction mechanism was corroborated using ex situ XRD, HRTEM and XPS, showing that an interesting electrochemically induced phase transition from VO₂(D) to V₂O₅·xH₂O occured with the insertion/extraction of zinc ions. Finally, the prototype batteries assembled with our as-prepared VO₂(D) hollow nanospheres and the impressive performance of this electrode under high active material mass loading further reveal its high potential in practical applications.