Eu-doped β-MnO₂ for synergistically enhancing the specific capacity and cycling stability of aqueous zinc-ion battery cathodes

Aqueous zinc-ion batteries (AZIBs) have emerged as a research focus in large-scale energy storage due to their advantages of high safety, low cost, and abundant zinc resources. However, manganese dioxide (MnO₂) cathode materials suffer from poor cycle stability and insufficient rate capability, limiting their practical applications. Herein, β-MnO₂ cathode materials with different Eu doping contents were prepared via a microwave hydrothermal method. Pure-phase β-MnO₂ exhibited a slender nanorod-like structure but suffered from agglomeration, delivering a specific capacity of only 142 mAh g⁻ 1 at 0.1 A g⁻ 1 . In contrast, Eu-doped MnO₂ materials formed a tunnel structure with a larger lattice constant, along with more uniformly distributed nanorods and reduced agglomeration. Electrochemical tests revealed that the Eu-doped MnO₂ cathode achieved a specific capacity of 425 mAh g⁻ 1 at 0.1 A g⁻ 1 (three times that of pure β-MnO₂). After 1000 cycles at 1 A g⁻ 1 , it retained 59.4% of its initial capacity, significantly outperforming the pure phase (44.7%). Kinetic analysis indicated that Eu doping enhanced the surface pseudocapacitive effect, shifted the reaction mechanism toward diffusion-capacitance mixed control, and improved reversibility and active site utilization efficiency remarkably.