Suppressing Electric-Field-Induced Cathodic Salt Crystallization for Stable Zinc-Ion Batteries

Aqueous zinc-ion batteries (AZIBs) hold promise for sustainable energy storage but suffer rapid capacity decay, particularly at subzero conditions. Beyond cathode instability and side reactions, we unveil an interfacial failure pathway: electric-field-induced phase separation that triggers catastrophic interfacial salt crystallization (CISC). The insulating crystalline layer rapidly engulfs the cathode, precipitating accelerated degradation. Mechanistic studies pinpoint solvent depletion and anion enrichment within the electric double layer as the origin of CISC. Molecular dynamics simulations and experimental observations demonstrate that sulfolane (TS) disrupts interfacial ion ordering, elevates the crystallization barrier, and thereby effectively suppresses CICS. This strategy stabilizes the cathode structure, enhances zinc availability, facilitates the V₂O₅ activation phase transition, increases the Zn²⁺ transference number, and promotes uniform Zn²⁺ deposition. Consequently, V₂O₅||Zn batteries display remarkable stability, retaining 378.9 mAh g^-1 after 300 cycles at room temperature and sustaining nearly invariant capacity over 20 000 cycles at -20°C. These findings expose interfacial salt crystallization as a critical failure pathway in AZIBs and provide a molecular-level design strategy for electrolyte engineering.