Regulating the zinc ion transport kinetics of Mn3O4 through copper doping towards high-capacity aqueous Zn-ion battery

High working voltage, large theoretical capacity and cheapness render Mn 3 O 4 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, Mn 3 O 4 material was fabricated through a facile precipitation reaction and divalent copper ions were introduced into the crystal framework, and ultra-small Cu-doped Mn 3 O 4 nanocrystalline cathode materials with mixed valence states of Mn 2+ , Mn 3+ and Mn 4+ 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 Mn 3 O 4 . Significantly, based on electrochemical investigations and ex-situ XPS characterization, a synergistic effect between copper and manganese was revealed in the Cu-doped Mn 3 O 4 , in which divalent Cu 2+ can catalyze the transformation of Mn 3+ and Mn 4+ to divalent Mn 2+ , accompanied by the translation of Cu 2+ to Cu 0 and Cu + . Benefitting from the above advantages, the Mn 3 O 4 cathode doped with moderate copper (abbreviated as CMO-2) delivers large discharge capacity of 352.9 mAh g −1 at 100 mA g −1 , which is significantly better than Mn 3 O 4 (only 247.8 mAh g −1 ). In addition, CMO-2 holds 203.3 mAh g −1 discharge capacity after 1000 cycles at 1 A g −1 with 98.6 % retention, and after 1000 cycles at 5 A g −1 , it still performs decent discharge capacity of 104.2 mAh g −1 . This work provides new ideas and approaches for constructing manganese-based AZIBs with long lifespan and high capacity.