Understanding the Benefit of Hybrid Electrolytes towards Vanadium Dissolution Suppression and Improved Capacity Retention in Zinc‐Aqueous Batteries using NaV3O8 Cathodes

Vanadate cathodes used in aqueous Zn‐ion batteries with ZnSO4 are hindered by capacity loss from V dissolution into the electrolyte. However, studies pinpointing the onset of dissolution as a function of electrochemical redox state and quantifying the amount of associated active material are lacking. To prevent dissolution of the NaV3O8 active material, Na+ ions were introduced into the electrolyte. Specifically, a hybrid ZnSO4 + Na2SO4 electrolyte was investigated in concert with NaV3O8 (NVO) cathodes of varied crystallinity to determine the resulting impacts on cathode dissolution and functional electrochemistry. The use of Na+ containing hybrid electrolyte, showed no significant change in Zn2+ diffusion coefficients yet improved capacity retention. Time‐resolved quantitative optical emission spectroscopy demonstrated suppression of V dissolution with the hybrid electrolyte in both pristine and cycled electrodes. Operando synchrotron x‐ray diffraction and absorption provided mechanistic insights. Hydrated NVO with wider interplanar spacing exhibited much higher H+/Zn2+ capacity, while the Na2SO4 mitigated formation of irreversible side products. This study demonstrates that use of hybrid electrolytes and control of crystallite size in the parent material can significantly improve electrochemical behavior of layered V‐based cathodes in Zn‐ion batteries, providing a general strategy toward safe and resilient aqueous battery systems.