Regulating the zinc ion transport kinetics of MnO through copper doping towards high-capacity aqueous Zn-ion battery.

High working voltage, large theoretical capacity and cheapness render MnO promising cathode candidate for aqueous zinc ion batteries (AZIBs). Unfortunately, poor electrochemical activity and bad structural stability lead to low capacity and unsatisfactory cycling performance. Herein, MnO material was fabricated through a facile precipitation reaction and divalent copper ions were introduced into the crystal framework, and ultra-small Cu-doped MnO nanocrystalline cathode materials with mixed valence states of Mn, Mn and Mn were obtained via post-calcination. The presence of Cu acts as structural stabilizer by partial substitution of Mn, as well as enhance the conductivity and reactivity of MnO. Significantly, based on electrochemical investigations and ex-situ XPS characterization, a synergistic effect between copper and manganese was revealed in the Cu-doped MnO, in which divalent Cu can catalyze the transformation of Mn and Mn to divalent Mn, accompanied by the translation of Cu to Cu and Cu. Benefitting from the above advantages, the MnO cathode doped with moderate copper (abbreviated as CMO-2) delivers large discharge capacity of 352.9 mAh g at 100 mA g, which is significantly better than MnO (only 247.8 mAh g). In addition, CMO-2 holds 203.3 mAh g discharge capacity after 1000 cycles at 1 A g with 98.6 % retention, and after 1000 cycles at 5 A g, it still performs decent discharge capacity of 104.2 mAh g. This work provides new ideas and approaches for constructing manganese-based AZIBs with long lifespan and high capacity.