Effect of TiO₂ Coating on Structure and Electrochemical Performance of LiNi_0.6Co_0.2Mn_0.2O₂ Cathode Material for...

High-nickel ternary LiNi_0.6Co_0.2Mn_0.2O₂ (NCM622) is a promising cathode material for lithium-ion batteries due to its high discharge-specific capacity and energy density. However, problems of NCM622 materials, such as unstable surface structure, lithium-nickel co-segregation, and intergranular cracking, led to a decrease in the cycling performance of the material and an inability to fully utilize high specific capacity. Surface coating was the primary approach to address these problems. The effect of TiO₂ coating prepared by the sol-gel method on the performance of LiNi_0.6Co_0.2Mn_0.2O₂ was studied, mainly including the morphology, cell structure, and electrochemical properties. LiNi_0.6Co_0.2Mn_0.2O₂ was coated by TiO₂ with a thickness of about 5 nm. Compared with the pristine NCM622 electrode, the electrochemical performance of the TiO₂-coated NCM622 electrodes is improved. Among all TiO₂-coated NCM622, the NCM622 cathode with TiO₂ coating content of 0.5% demonstrates the highest capacity retention of 89.3% and a discharge capacity of 163.9 mAh g^-1, in contrast to 80.9% and145 mAh g^-1 for the pristine NCM622 electrode, after 100 cycles at 0.3 C between 3 and 4.3 V. The cycle life of the 5 wt% TiO₂-coated NCM622 electrode is significantly improved at a high cutoff voltage of 4.6 V. The significantly enhanced cycling performance of TiO₂-coated NCM622 materials could be attributed to the TiO₂ coating layer that could block the contact between the material surface and the electrolyte, reducing the interface side reaction and inhibiting the transition metal dissolution. At the same time, the coating layer maintained the stability of layered structures, thus reducing the polarization phenomenon of the electrode and alleviating the irreversible capacity loss in the cycle process.