Dimensional Engineering‐Driven V/O Defect Modulation for Ultrahigh‐Energy‐Density Aqueous Zinc‐Ion Batteries

Achieving high energy density in aqueous zinc‐ion batteries (AZIBs) while simultaneously optimizing Zn 2+ migration kinetics and redox activity remains a formidable challenge. Herein, a novel in situ strategy is developed using glutamic acid as a structural regulator during hydrothermal synthesis, enabling a dimensional transformation of ammonium vanadate and inducing a high density of V/O defects. This engineered structure, featuring abundant V/O defects and interlayer water, facilitates a significant increase in V 4+ content, thereby enhancing redox kinetics and reaction reversibility. As a cathode material for AZIBs, the resulting defect‐rich ammonium vanadate (denoted as V/O‐NHVO) delivers a high specific capacity of 567.9 mAh g −1 at 0.1 A g −1 , an energy density of 433 Wh kg −1 , and a peak power density of 3575 W kg −1 , along with excellent cycling stability—retaining 87.9% of its capacity over 2000 cycles. Moreover, the material exhibits promising performance in aqueous magnesium‐ion batteries, demonstrating remarkable versatility. This work offers a compelling design paradigm for in situ structure and defect engineering toward high‐performance cathode materials for aqueous multivalent‐ion batteries.