Rational Design of MnO2/Mn2O3 Core-Shell Heterojunctions via MnCl2-Assisted Synthesis for Advanced Aqueous Zinc-Ion Batteries.

Manganese-based oxides have garnered extensive scientific attention in the field of aqueous Zn-ion batteries due to their abundant resources, diverse oxidation states, and high output voltage. However, their low intrinsic electronic conductivity, susceptibility to significant phase changes, and structural collapse lead to rapid capacity degradation during cycling. Therefore, the design of novel manganese oxide structures through appropriate methods remains a key challenge in the development of high-performance cathode materials. In this study, MnO2 was modified using an MnCl2-assisted hydrothermal method to precisely construct MnO2/Mn2O3 core-shell heterojunctions, which significantly enhanced the crystallinity of MnO2. Subsequently, the crystalline phase of MnO2 was transformed into MnOOH via the reduction effect of Mn2+ ions adsorbed onto or embedded within the surface layer at elevated temperatures, and finally, the MnOOH phase was converted into Mn2O3 via thermal annealing, resulting in the formation of MnO2/Mn2O3 core-shell heterojunctions. Benefiting from the unexpected abundance of the interfaces of the heterostructures involving a built-in electric field, the as-obtained MnO2/Mn2O3 electrode delivers a high capacity of 563.6 mA h g-1 for 286 cycles at 0.3 A g-1 and shows excellent rate capability up to 3 A g-1 with a capacity of 178.13 mA h g-1. Its cycling stability was remarkably improved, retaining 261.8 mA h g-1 with 80.5% capacity retention after 1000 cycles at 1 A g-1. The MnO2/Mn2O3 electrode exhibited an outstanding energy density of 788.03 W h kg-1 at a power density of 41.8 W kg-1. All these performances are significantly superior to those of MnO2. This work provides a new path for long-life and fast-discharging electrode materials.