Understanding the phenomenon of increasing capacity of layered 0.65Li[Li1/3Mn2/3]O2·0.35Li(Ni1/3Co1/3Mn1/3)O2

The layered 0.65Li[Li1/3Mn2/3]O2·0.35Li(Ni1/3Co1/3Mn1/3)O2 solid solution was synthesized by low-heating solid-state reaction. When the sample was cycled between 2.5 V and 4.6 V at 0.5 C, a phenomenon that the capacity increased with the cycle number was observed. The synthesized electrode delivered 97 mAh/g in the first discharge and reached the maximum of 229 mAh/g in the 24th cycle. The dQ/dV curves showed that the increasing capacity resulted from the redox-reaction of Mn. Then the cells were tested in different voltage at different rates, revealing that the main reason of the growing Mn peak is the relatively low cut-off potential. The influence of current density on the increasing capacity was also studied.