Microemulsion synthesis of ZnMn2O4/Mn3O4 sub-microrods for Li-ion batteries and their conversion reaction mechanism

The hierarchical ZnMn2O4/Mn3O4 composite sub-microrods were synthesized via a water-in-oil micro- emulsion method followed by calcination. The ZnMn2O4/Mn3O4 electrode displays an intriguing capacity increasing from 440 to 910 mA·h/g at 500 mA/g during 550 consecutive discharge/charge cycles, and delivers an ultrahigh capacity of 1276 mA·h/g at 100 mA/g, which is much greater than the theoretical capacity of either ZnMn2O4 or Mn3O4 electrode. To investigate the underlying mechanism of this phenomenon, cyclic voltammetry and differential capacity analysis were applied, both of which reveal the emergence and the growth of new reversible redox reactions upon charge/discharge cycling. The new reversible conversions are probably the results of an activation process of the electrode material during the cycling process, leading to the climbing charge storage. However, the capacity exceeding the theoretical value indicates that there are still other factors contributing to the increasing capacity.