Improving Electrochemical Stability by Transition Metal Cation Doping for Manganese in Lithium-rich Layered Cathode, Li1.2Ni0.13Co0.13Mn0.54-xMxO2 (M = Co, Cr and Fe)

The capacity of high manganese containing lithium-rich cathodes tends to fade quickly upon cycling. In this work, we studied the effect of cation doping for manganese in Li1.2Ni0.13Co0.13Mn0.54-xMxO2 (M = Co, Cr and Fe and x < 0.15) in improving the cycling stability. The Cr+3 and Fe+3 doped samples exhibit considerable suppression of oxygen loss during the first charge. The first cycle irreversible capacity loss also decreased upon substitution. Further, there is significant improvement in cycling stability; after 50 cycles the pristine sample exhibits only 75% capacity retention which is improved to 88% with Co+3 doping (x = 0.10) and to 93.7% with Cr+3 doping (x = 0.10). Similarly Fe+3 doping (x = 0.05) also improves the capacity retention to 90%. Another notable observation from charge-discharge profiles is that the voltage decay during cycling has been reduced for doped samples. The charge-discharge derivative (dQ/ dV) data indicate that Cr+3 and Fe+3 doping retards spinel phase formation during long cycling thereby reducing the voltage decay. These studies further highlight the importance of fine tuning the composition of lithium-rich cathodes for optimizing the performance in terms of decreasing irreversible capacity loss, capacity degradation and voltage decay