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

Abstract 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 Zn 2+ 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.