Molecular engineering of Mn-based cathode for enhanced intrinsic conductivity towards high mass-loading aqueous zinc-ion batteries

Manganese dioxide (MnO2) is a promising cathode for aqueous zinc-ion batteries (ZIBs) because of its low cost, high energy density and environmental friendliness. However, the intrinsic poor electrical conductivity and sluggish reaction kinetics lead to inferior rate capability, especially under high mass loading, which hinders its commercialization. Herein, we report a molecular engineering strategy that can enhance the intrinsic electrical/ionic conductivity of MnO2 and accelerate reaction kinetics. Electrochemical analysis reveals that boron-modified MnO2 (B-MnO2) delivers improved reaction kinetics since the tailored boron atoms with lower electronegativity can abate the strong electrostatic interactions between the cations and cathode. Theoretical calculations demonstrate that B-MnO2 possesses a smaller bandgap than MnO2, which can enhance its electrical conductivity. As a result, the developed Zn/B-MnO2 batteries display a high specific capacity (325.3 mAh/g at 200 mA g−1) and remarkable rate capability (99.4 mAh/g at 10 A/g). More importantly, at high mass loadings of 25 and 30 mg cm−2, the B-MnO2 cathodes can still deliver high specific capacity of 197.2 and 176.5 mAh/g, respectively. This work will pave a way toward the commercial applications of Mn-based cathodes.