Inhibition of phase transition from δ-MnO2 to α-MnO2 by Mo-doping and the application of Mo-doped MnO2 in aqueous zinc-ion batteries

MnO2 is an oxide with many crystalline phases and is often used as a cathode material for aqueous zinc-ion batteries. However, its poor electrical conductivity and structural instability limit its further application. In the present work, Mo-doped MnO2 microflowers are successfully prepared by a facile hydrothermal method. Interestingly, it is found that the doping of Mo inhibits the phase transition from δ-MnO2 to α-MnO2, which may be related to the low crystallinity of Mo doped MnO2. Compared with undoped MnO2, Mo-doped MnO2 maintains two-dimensional morphology with a large specific surface area and mesoporous structure. In addition, the electronic conductivity and reversibility of Zn2+ insertion/extraction are improved in Mo doped MnO2. Therefore, Mo-doped MnO2 exhibits high reversible capacity and long cycling stability. For example, a high reversible capacity of 72.6 mA h g-1 can be achieved at a current density of 2000 mA g-1 after 2500 cycles.