Aqueous zinc-ion batteries (AZIBs) are emerging as promising candidates for sustainable energy storage because of their intrinsic safety, low cost, environmental compatibility, and the high theoretical capacity of metallic zinc. However, their practical performance remains limited by sluggish Zn²⁺ diffusion, structural instability of cathode materials, and interfacial polarization during repeated Zn²⁺ insertion and extraction. In this work, we investigate interface- and defect-engineered Ni–Co–MnO2 cathodes as advanced host materials for aqueous Zn-ion storage. The material design combines Co incorporation into the MnO2 framework with subsequent Ni modification, aiming to regulate the local electronic structure, induce favorable lattice distortion, and increase the accessibility of electrochemically active sites. This compositional and interfacial engineering strategy is expected to facilitate Zn²⁺ transport while improving charge-transfer kinetics and structural stability during cycling. The synthesized cathodes were characterized by X-ray diffraction, Raman spectroscopy, electron microscopy, and surface-sensitive spectroscopic techniques to establish correlations between crystal structure, defect chemistry, morphology, and local chemical environment. Their electrochemical behavior was evaluated in aqueous Zn-based electrolytes using cyclic voltammetry, galvanostatic charge–discharge, electrochemical impedance spectroscopy, rate-capability measurements, and long-term cycling. Compared with unmodified MnO2, the Ni–Co– MnO2 electrodes exhibit improved charge-storage behavior, enhanced rate performance, and more stable cycling, which are associated with faster interfacial charge transfer, improved electronic transport, and a higher density of accessible redox-active sites. Beyond conventional Zn-ion storage, this material platform is also being explored for photo-assisted zinc-ion batteries, where photoexcitation may provide an additional driving force for charge generation and interfacial electrochemical reactions. The integration of electrochemically active transition-metal oxides with photoresponsive functionality therefore offers a promising route toward multifunctional systems capable of combining solar-energy conversion and electrochemical energy storage within the same device architecture.

Overall, this study demonstrates how controlled transition-metal incorporation and interface engineering can enhance Zn²⁺ storage in MnO2-based cathodes while providing a materials platform for the future development of sustainable photo-assisted electrochemical energy-storage systems.