Understanding the mechanism of byproduct formation with in operando synchrotron techniques and its effects on the electrochemical performance of VO2(B) nanoflakes in aqueous rechargeable zinc batteries

Abstract

Monoclinic VO₂(B) nanoflakes prepared by a hydrothermal method displayed superior electrochemical performance in 1 M ZnSO₄ electrolyte. The reaction mechanisms of VO₂(B) and the essential causes of byproduct formation in aqueous rechargeable zinc batteries (ARZBs) were comprehensively studied by electrochemical measurements combined with in operando synchrotron techniques and first-principles calculations. During the electrochemical processes, the electrode underwent a reversible solid-solution reaction between VO₂(B) and Zn_0.44VO₂ with the simultaneous formation/decomposition of the (Zn(OH)₂)₃(ZnSO₄)·5H₂O byproduct. Importantly, the formation of the byproduct was attributed to [Zn(H₂O)₆]²⁺ dehydration, where the byproduct could protect the electrode material from the corrosion of H₃O⁺ and facilitate the dehydration process of Zn²⁺ on the electrode–electrolyte interface. The byproducts could facilitate the migration of Zn²⁺ on the electrode surface due to their three-dimensional pathways. In addition, the electrochemical performance of VO₂(B) and the byproduct in ZnSO₄ electrolyte were compared with those in Zn(CF₃SO₃)₂ and Zn(NO₃)₂. An appropriate electrolyte (1 M Zn(CF₃SO₃)₂) to form a byproduct with largely expanded ionic pathways was proven to further improve the electrochemical performance of VO₂(B). This work not only provides a deep understanding of the Zn²⁺ storage mechanism in VO₂(B) but also establishes a clear relationship between the byproducts and electrochemical performance of vanadium-based electrode materials in ARZBs.