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

A zinc-ion battery study that elucidates the dissolution mechanism of the NaV₃O₈ (NVO) cathode with ZnSO₄ (ZS) electrolytes. Comparisons between three NVO morphologies and crystallinities found an improved cycling behavior with a hydrated (h-NVO) active material. Dissolution suppression of NVO with a ZS + Na₂SO₄ hybrid electrolyte improved capacity retention and decreased contributions from irreversible byproducts.

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 are introduced into the electrolyte. Specifically, a hybrid ZnSO₄ + Na₂SO₄ electrolyte is 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 shows no significant change in Zn²⁺ diffusion coefficients yet improved capacity retention. Time-resolved quantitative optical emission spectroscopy demonstrates the suppression of V dissolution with the hybrid electrolyte in both pristine and cycled electrodes. Operando synchrotron X-ray diffraction and absorption provide mechanistic insights. Hydrated NVO with wider interplanar spacing exhibits much higher H⁺/Zn²⁺ capacity, while the Na₂SO₄ mitigates the formation of irreversible side products. This study demonstrates that the 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.

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