Abstract: The δ-MnO2 cathode materials in aqueous zinc-ion batteries suffers from sluggish reaction kinetics, structural instability and rapid capacity degradation. To address these issues, this study proposes a synergistic modification strategy combining Ni2+ doping and nanostructure regulation, successfully preparing Ni2+-doped δ-MnO2 nanoflower spheres (NiMnO2-n). Nanostructure regulation endows NiMnO2-n with nanosized sheet structures and a large specific surface area of 142 m2·g-1, effectively shortening ion diffusion paths and increasing electrochemical active sites. Besides, Ni2+ doping further reduces the thickness of nanosheet and expands the interlayer spacing, which not only promotes H+/Zn2+ intercalation/extraction kinetics but also significantly enhances the structural stability of NiMnO2-n. Moreover, the abundant oxygen vacancies introduced by Ni2+ doping weaken the spatial potential resistance for ion intercalation and lower the ion diffusion barrier, thereby accelerating the reaction kinetics. Benefiting from these structural advantages, NiMnO2-n exhibits faster H+ and Zn2+ diffusion characteristics and improved intercalation/extraction kinetics, leading to improved rate capability and cycling stability: it delivers a reversible capacity of 150.7 mAh·g-1 at a current density of 1.0 A·g-1 with a decay as low as 0.040% per cycle over 900 cycles. Mechanistic studies preliminarily confirm that the energy storage process in NiMnO2-n originates from the intercalation/extraction of H+ and Zn2+ and the dissolution-deposition of MnO2.

Key words: Aqueous zinc-ion battery, Doping, Structural regulation, Oxygen vacancy, Kinetics