From “Lab Prototype” to “Practical Device”: Cycling Stability Challenges of MnO ₂ ‐Based Cathodes for Zinc‐Ion Batteries

Aqueous zinc‐ion batteries (ZIBs) are a promising alternative to lithium‐ion systems, offering intrinsic safety, environmental friendliness, and low cost. Among candidate cathode materials, manganese dioxide (MnO ₂ ) stands out for its high theoretical capacity and abundance. However, translating MnO ₂ ‐based ZIBs from lab prototypes to practical devices remains challenging due to severe cycling stability issues. Key failure modes, including structural degradation of the MnO ₂ cathode, manganese dissolution into the electrolyte with “dead” byproduct formation, sluggish Zn ²⁺ diffusion and poor electronic conductivity, and unstable electrode/electrolyte interfaces, cause progressive capacity fade. These problems are further exacerbated under realistic operating conditions (thick electrodes, limited electrolyte, and prolonged cycling) required for commercial‐level cells. This review provides a comprehensive analysis of these degradation mechanisms and critically surveys recent mitigation strategies such as MnO ₂ nanostructuring and doping, protective surface coatings, and optimized aqueous electrolytes with additives. We also highlight the persistent performance gap between coin‐cell demonstrations and real‐world devices, emphasizing the need for in situ/operando diagnostic techniques, multiscale modeling, scalable electrode fabrication, and standardized testing protocols to better bridge that gap. By uniting fundamental insights with engineering solutions, this work offers guidelines to advance MnO ₂ ‐based ZIBs toward durable, high‐performance energy storage devices suitable for broad application.