Localized Water Confinement via Micellar Electrolyte for Aqueous Zinc‐Vanadium Batteries

Highly reactive water-induced cascade failures, including vanadium dissolution, proton intercalation, hydrogen evolution reactions, and interfacial side reactions, limit the recyclability of vanadium-based aqueous zinc-ion batteries. These failures are more severe at low current densities (< 0.5 A g^-1). Current studies on electrolyte optimization stabilize the zinc anode but neglect the vanadium-based cathode. Here, from a vanadium-based cathode perspective, a micellar electrolyte is developed using the surfactant cetyltrimethylammonium bromide (CTAB), in which water is locally confined and Br^- restructures Zn²⁺ solvation, collectively inhibiting the water-induced cascade failures. Concomitantly, electrostatic interactions enable CTA⁺ intercalation into V─O layers (forming expanded-spacing cathode (CTA, Ca)VO) and cathode-surface electric double layer generation, which enhances pseudocapacitance to offset water confinement-induced kinetic losses. Additionally, cycling-induced CTA⁺ degradation participates in the formation of solid-state electrolyte interphases (CEI/SEI) to provide further effective cathode/anode interfacial protection. The micellar electrolyte balances water confinement and charge transfer to achieve breakthrough full-cell performance: 93.57%/98.78%/82.17% retention after 150/300/17 700 cycles at 0.1/0.2/4.0 A g^-1 (25 °C) and 99.77% retention after 420 cycles at 0.1 A g^-1 (-20 °C). This micellar electrolyte strategy can be extended to other vanadium-based cathodes (e.g., NaVO, BaVO), quasi-solid-state cells, and anode-free cells, providing a viable paradigm for electrolyte design.