Active Carbon-Induced Electron Transfer and Active Site Control for Improved Reversibility in MnO ₂ Dissolution-Deposition Reactions

Manganese-based materials are considered highly promising cathode materials for aqueous zinc-ion batteries (AZIBs) due to their low cost, environmental friendliness, and high voltage window. However, the limited electron transfer caused by the poor conductivity of MnO2 hinders the complete redox reaction of Mn, leading to the formation of inactive “dead Mn,” which severely deteriorates the electrochemical performance, severely limiting their practical applications. In this study, activated carbon (AC) coating layer on MnO2 electrode (C-MnO2) were employed as a case to effectively suppress dead Mn and enhance manganese utilization. Structural characterization reveals that the well-developed microporous structure of activated carbon offers abundant active sites for Mn2+ dissolution-deposition, while its high specific surface area and superior conductivity synergistically improve the reversibility of the Mn two-electron redox reaction, thus effectively mitigating the accumulation of electrochemically inactive dead Mn. Furthermore, comparative analysis reveals a significant positive correlation between the electrochemically deposited area and the specific capacity. Benefiting from these modifications, the C-MnO2 cathode maintains a high capacity retention of 99% after 500 cycles at 0.5 A/g and delivers a reversible capacity of 146 mAh/g even after 2000 cycles at a high current density of 1 A/g. This study provides new insights and a theoretical foundation for designing manganese-based cathode materials with high capacity and long cycle life.