Metal Ion‐Induced Fast Gelation of 2D MnO ₂ Nanosheets With Cationic Vacancies for Durable Aqueous Zinc‐Ion Batteries

ABSTRACT Delta manganese dioxide (δ‐MnO ₂ ) has been extensively investigated as an attractive cathode material for aqueous zinc‐ion batteries (AZIBs) owing to its large interlayer spacing that facilitates ion storage and transport. However, the random restacking of 2D MnO ₂ nanosheets significantly limits their accessible surface area and increases diffusion resistance, thereby severely degrading electrochemical performance. Herein, we report a scalable synthesis of 3D structured aerogels from defect‐rich MnO ₂ nanosheets via a divalent metal ion‐initiated self‐assembly process for durable aqueous zinc‐ion batteries. The addition of metal ions enables MnO ₂ nanosheets in solution to assemble into a 3D network by neutralizing electrostatic repulsion and serving as intersheet linkers. The obtained 3D Mn vacancy‐rich MnO ₂ aerogel (A‐MnO ₂ ) cathode demonstrate greatly enhanced electrochemical performance, especially superior rate performance (146.3 mAh g ⁻¹ at 5 A g ⁻¹ ), and long‐term cycling stability (90.6% capacity retention after 5000 cycles at 5 A g ⁻¹ ). Moreover, the experimental analysis and theoretical calculations reveal that A‐MnO ₂ delivers improved conductivity, fast reaction kinetics, and superior structural stability, owing to abundant Mn vacancies and a 3D porous structure. This work may provide new insight for guiding the structural design of 2D electrode materials in AZIBs.