Residual-carbon-supported δ-MnO2 as cathodes for aqueous zinc ion batteries with high specific capacity

Manganese-based oxides, as promising cathode materials for aqueous zinc-ion batteries (AZIBs), face limitations due to their slow reaction kinetics and low specific capacity. Therefore, this study employed a two-step acid leaching method to extract residual carbon (RC) from coal gasification fine slag and used a hydrothermal method to grow manganese dioxide nanoflowers on the RC surface. By adjusting the amount of RC incorporated, the optimal loading state and cluster morphology were achieved. Compared with the δ-MnO₂, the composite material exhibited a high specific capacity of 531 mAh g⁻¹ at 0.2 A g⁻¹. Characterization and electrochemical kinetic analysis of the composite material revealed that the unique nanoflower morphology and RC provided more active sites, shortened ion transport pathways, and increased ion diffusion rates. Furthermore, the inclusion of RC provided more oxygen vacancies, enhancing the specific capacity, and improved the reaction kinetics. Through studies on the charge and discharge mechanisms of the cathode material, it was found that the composite not only facilitated the insertion/extraction of H⁺/Zn²⁺ ions but also enhanced crystallization stability during cycling. This research offers a new approach for developing high-performance AZIBs cathode materials and opens a new avenue for utilizing coal-based solid waste.