Impact of carbon additives on alpha-MnO2 cathode performance in aqueous zinc ion batteries: Towards high energy density and stability

Manganese oxides (MnO2) have emerged as a promising cathode material for aqueous zinc-ion batteries (AZIBs) owing to their high specific capacity and wide potential window. However, they face critical challenges, such as low electrochemical stability and poor electronic conductivity, which hinder their practical application in largescale energy storage systems (ESS). To address these issues, various strategies have been proposed, including nanostructuring the cathode, incorporating conductive additives, and doping MnO2 with third elements. In this study, we introduce different carbon additives, including carbon black, carbon nanotubes, and reduced graphene oxide (rGO), into alpha-MnO2 cathodes using a conventional slurry casting process. The effects of these additives on the mass loading, capacity, stability, and electrode kinetics of the active materials are systematically investigated. Through comprehensive material and electrochemical characterization, we identify the optimal conductive carbon composition and characteristics that significantly enhance the energy density and stability of MnO2-based cathodes. The MnO2 with highly porous, conductive rGO additive achieves a high specific capacity of 246.4 mAh g- 1 at 0.4C in the first cycle, with stable capacity retention of approximately 76.1 % after 150 cycles. When the rGO content is reduced to 10 wt%, the MnO2 still maintains a specific capacity of 238.5 mAh g- 1 and a capacity retention of 78.6 % after 150 cycles at 0.4C. Our findings provide a strategic approach to designing high-performance MnO2 cathodes, which is crucial for advancing the development of robust and efficient AZIBs for large-scale ESS applications.