Defect Engineering via Copper Doping on Oxygen‐Deficient Manganese Oxide for Durable Aqueous Zinc‐Ion Battery

Aqueous Zn‐ion batteries (ZIBs) have triggered an astounding research surge because of their high safety, affordability, and impressive electrochemical properties. However, the smooth implementation of this promising technology is hindered by severe structural degradation and sluggish reaction kinetics of the cathode materials. Here, the defect engineering is demonstrated by the substitution doping of Cu 2+ in layered δ‐MnO 2 to boost the electrochemical reactivity for Zn‐ion storage. Benefited from the nanoscale morphology and oxygen‐deficient structural features, this Zn/MnO 2 battery is able to deliver a high reversible capacity of 296.8 mAh g −1 with a capacity retention of 94.9% over 120 cycles (at 0.1 A g −1 ) and a desirable energy density of 441 Wh kg −1 , as well as an ultra‐long cycle life up to 6000 cycles, which is also intensively associated with the facilitated Zn 2+ diffusion and charge transfer rates after the Cu 2+ dopants, based on the electrochemical kinetics analysis. The effortless but effective defect engineering arising from element doping can provide significant enlightenment to design high‐performance cathode materials for ZIBs.