Mechanism of the Enhanced Electrochemical Properties of LiNi1/3Co1/3Mn1/3O2 Cathode Materials by a Pre-Sintering Process

α-NaFeO2 layered LiNi1/3Co1/3Mn1/3O2 cathode materials were synthesized by mechanical milling accompanied by the solid phase sintering. The sample exhibited a good crystallinity and layered structure while sintered at 900°C, which can be further improved by adding a pre-sintering process at 500°C before high temperature sintering. The sample with a pre-sintering process presents an average particle size about 0.6 μm, and a hexagonal crystalline structure. The optimally fabricated sample showed a first charge capacity of 210.2 mA h/g, discharge capacity of 171.2 mA h/g with a current rate of 0.2 C within the voltage range of 2.7~4.5 V. With increasing the current rate to 1 C, the charge–discharge capacity faded quickly during the cycling process, which can be partially recovered while operated at a low current rate. However, the capacity fading at a current rate of 2 C was largely irreversible. The evolution of the surface chemical states was evaluated using X-ray photoelectron spectroscopy on the charged and discharged samples to understand the high rate capacity fading.