Ultra‐Stable Vanadium‐Based Zinc‐Ion Batteries via Complete Confinement of Free Water Into Bound Water by an Organic–Inorganic Viscoelastic Solid Electrolyte

Vanadium‐based zinc‐ion batteries suffer from severe vanadium dissolution, cathode collapse, and an unstable zinc anode interface in free‐water dominated aqueous electrolytes, particularly under low current densities where long‐term cyclability remains unattainable. Here, we design a bound‐water dominated organic–inorganic viscoelastic solid electrolyte (VSE) to realize ultra‐stable vanadium‐based ZIBs. The VSE can completely convert free water into bound water through abundant hydrogen‐bonding sites from PEG4000 and SiO 2 components. Density functional theory calculations reveal that PEG4000 preferentially adsorbs on the NH 4 V 4 O 10 (NVO) surface with a binding energy of −0.942 eV, raising the vanadium vacancy formation energy to 0.838 eV and thus fundamentally suppressing vanadium dissolution. Meanwhile, this bound‐water dominated solidified electrolyte significantly stabilizes the zinc anode interface, suppressing the diffusion of soluble vanadium species, and the viscoelastic structure simultaneously provides high ionic conductivity (3.14 mS cm −1 ). Consequently, the Zn|VSE|Zn symmetric cell achieves an ultra‐long cycling life exceeding 8500 h, and the Zn|VSE|NVO full cell can stably cycle more than 8000 cycles at 1.0 A g −1 and maintain 93.2% capacity retention over 1084 cycles even at 0.2 A g −1 . This work establishes a “water confinement” electrolyte strategy to resolve cathode degradation and anode instability, offering a practical path toward durable ZIBs.