Spider-egg-like structured α-MnO₂ as an efficient cathode material for aqueous rechargeable zinc-ion batteries

This study reports the direct hydrothermal growth of α-MnO₂ on carbon fiber textile without the use of polymeric binders, yielding a unique “spider-egg-like” morphology. Unlike conventional MnO₂-based cathodes, where active materials require binders and conductive additives, this approach ensures strong adhesion to the substrate while maintaining high conductivity and mechanical stability. SEM revealed spherical MnO₂ structures entangled within a nanowire network, creating a porous, interconnected architecture that enhances ion diffusion and charge transfer. XRD confirmed the formation of crystalline α-MnO₂, while EDS and XPS validated its elemental composition and mixed-valence states, highlighting its redox activity. Electrochemical characterization demonstrated its potential as a cathode for ARZIBs, delivering an initial capacity of 367 mAh/g. The composite maintained stable discharge capacities of 218, 120, 102, and 79 mAh/g at 0.1C, 0.3C, 0.5C, and 1C, respectively, with 88.94% capacity retention over 350 cycles. Its long-term stability and nearly 100% Coulombic efficiency confirm the robustness of the direct-growth architecture in facilitating reversible Zn²⁺ intercalation. The binder-free synthesis method presents a scalable and eco-friendly alternative to conventional electrode fabrication, reducing processing steps while improving electrochemical performance. This study introduces a novel approach to designing MnO₂ cathodes, offering a high-performance, mechanically stable, and conductive material for next-generation ARZIBs.