Simultaneous interlayer expansion and structural stabilization of δ-MnO₂ via sodium/molybdenum co-doping for ultra-stable aqueous zinc-ion batteries

Although δ-MnO₂ is a promising cathode for aqueous zinc-ion batteries (AZIBs), its practical application is hindered by structural instability, Mn dissolution, and irreversible phase transitions during cycling. Herein, we address these challenges by developing a dual Na+/Mo6+ doped δ-MnO₂ (NaMo-MnO₂) cathode via a hydrothermal-annealing method. Na+ acts as an interlayer pillar to expand the spacing and facilitate Zn2+ diffusion, while Mo6+ doping stabilizes the layered framework and suppresses detrimental phase transitions. This synergistic effect endows NaMo-MnO₂ with exceptional cycling stability (100% capacity retention after 6500 cycles at 3 A g−1) and a high reversible capacity (250 mAh g−1 at 0.1 A g−1). Mechanistic studies reveal that optimized activation (30 cycles) induces an irreversible phase transformation to ZnMnO₃, enabling subsequent stable Zn2+/H+ co-intercalation and controlled Mn dissolution/deposition. This work provides a rational design strategy for high-performance MnO₂ cathodes in AZIBs.