Surface Modification of Li(Ni_0.6Co_0.2Mn_0.2)O₂ Cathode Materials by Nano-Al₂O₃ to Improve Electrochemical Performance in Lithium-Ion Batteries

Al₂O₃-coated Li(Ni_0.6Co_0.2Mn_0.2)O₂ cathode materials were prepared by simple surface modification in water media through a sol-gel process with a dispersant. The crystallinity and surface morphology of the samples were characterized through X-ray diffraction analysis and scanning electron microscopy observation. The Li(Ni_0.6Co_0.2Mn_0.2)O₂ cathode material was of a polycrystalline hexagonal structure and agglomerated with particles of approximately 0.3 to 0.8 μm in diameter. The nanosized Al₂O₃ particles of low concentration (0.06-0.12 wt %) were uniformly coated on the surface of Li(Ni_0.6Co_0.2Mn_0.2)O₂. Measurement of electrochemical properties showed that Li(Ni_0.6Co_0.2Mn_0.2)O₂ coated with Al₂O₃ of 0.08 wt % had a high initial discharge capacity of 206.9 mAh/g at a rate of 0.05 C over 3.0-4.5 V and high capacity retention of 94.5% at 0.5 C after 30 cycles (cf. uncoated sample: 206.1 mAh/g and 90.8%, respectively). The rate capability of this material was also improved, i.e., it showed a high discharge capacity of 166.3 mAh/g after 5 cycles at a rate of 2 C, whereas the uncoated sample showed 155.8 mAh/g under the same experimental conditions.