Sea urchin-like hierarchical structured Ag-doped MnO2 cathode material for stable aqueous zinc-ion batteries

Rechargeable aqueous zinc-ion batteries (RAZIBs) have emerged as promising candidates for large-scale energy storage systems, owing to their low cost, high safety, and environmental benignity. However, their practical application is hindered by intrinsic limitations of cathode materials, including sluggish Zn 2+ diffusion kinetics, poor electrical conductivity, and structural degradation during cycling. Herein, we report a facile hydrothermal strategy to synthesize Ag-doped MnO 2 cathode with uniform urchin-like nanostructures surrounded by nanowires as high-performance cathodes for RAZIBs. The optimal 5 wt% Ag doping yields denser nanowire arrays, namely 5Ag/MnO 2 , increases accessible active sites, and introduces lattice defects while preserving the tetragonal MnO 2 crystal structure ( I 4 /m ). The electrochemical characterization demonstrated that 5Ag/MnO 2 exhibited significantly enhanced kinetics, including lower charge-transfer resistance, reduced polarization, and higher Zn 2+ diffusion coefficient. Consequently, the 5Ag/MnO 2 cathode delivered a high initial discharge capacity of 153.4 mAh g −1 at 1 A g −1 and superior long-term cycling stability (the discharge specific capacity remained at 135.5 mAh g −1 and 88.3% capacity retention after 500 cycles). Mechanism studies via ex situ XRD, XPS, and CV reveal a reversible Zn 2+ /H + storage mechanism involving phase transformation between MnO 2 and ZnMn 2 O 4 , with mixed capacitive and intercalation behavior. The enhanced performance is attributed to Ag doping facilitating rapid ion diffusion, improving electronic conductivity, and stabilizing the hierarchical structure. This work provides a viable strategy for designing high-performance MnO 2 -based cathodes for advanced zinc-ion batteries, advancing the practical application of RAZIBs.