Balancing defect activation and framework stability: oxygen-vacancy-regulated MnO₂ cathodes for aqueous zinc-ion...

Aqueous zinc-ion batteries have attracted increasing attention owing to their intrinsic safety, low cost, resource abundance, and environmental compatibility. Among various cathode candidates, MnO₂ has been widely investigated because of its high theoretical capacity, tunable crystal structures, and suitable operating voltage. However, the practical application of MnO₂ cathodes is still limited by intrinsically poor electronic conductivity, sluggish Zn²⁺/H⁺ transport, Mn dissolution, structural distortion, and complex interfacial side reactions. Oxygen vacancies, as typical point defects in MnO₂, can regulate local Mn-O coordination, Mn³⁺/Mn⁴⁺ valence distribution, defect-induced electronic states, and surface adsorption behavior, thereby improving charge transfer, ion diffusion, interfacial reaction kinetics, and structural adaptability. Nevertheless, excessive oxygen vacancies may weaken the Mn-O framework, promote the accumulation of low-valence Mn species, and aggravate irreversible phase evolution or Mn loss. This review summarizes recent progress in oxygen-vacancy-regulated MnO₂ cathodes for aqueous zinc-ion batteries, with emphasis on vacancy construction strategies and the corresponding mechanisms associated with electronic-structure regulation, Zn²⁺/H⁺ transport, interfacial reactivity, Zn-storage pathways, MnO₂/Mn²⁺ conversion, and structural stability. This work aims to provide mechanistic guidance for the rational design of high-performance MnO₂ cathodes based on a balance between defect activation and framework stability. The optimum vacancy level is therefore treated as a multidimensional operational window defined within matched sample series, rather than as a universally transferable atomic percentage.