Effect of Mo doping on the structure and electrochemical performances of LiNi0.6Co0.2Mn0.2O2 cathode material at high cut-off voltage

Mo-doped nickel-rich LiNi0.6Co0.2Mn0.2O2 (NCM622) cathode material is prepared by a solid-state method to enhance the high voltage electrochemical performances of the NCM622 material for lithium-ion batteries. The molybdenum element is proved to be homogeneously distributed inside the particles of the NCM622 material according to the result from the EDS mapping of the particle cross-section. The effects of Mo doping on the crystal structure, morphology, electrochemical properties and high-temperature performances of the NCM622 material are investigated in detail. The Mo-doped sample delivers a discharge capacity of 203.1 mAh/g and a capacity retention of 82.96% after 100 cycles at 1C under a high cut-off voltage of 4.6 V. Besides, the Mo-modified material exhibits a better rate performance of 159.9 mAh/g at 8C and lower voltage fading compared with the unmodified material. The significant improvements in electrochemical properties are ascribed to the fact that trace Mo ions doped into the transition-metal layer help to enlarge the lithium slab spacing, stabilize the crystal structure and suppress the electrode polarization. It is also demonstrated that Mo doping effectively suppresses the pulverization of particles and reduces the charge transfer resistance according to the SEM and EIS analyses.