Effect of TiO_x Surface Modification on the Electrochemical Performances of Ni-Rich (NMC-622) Cathode Material for Lithium-Ion Batteries

Ni-rich layered lithium transition metal oxides (LiNixMnyCozO2) have gained significant attention as high-capacity positive electrode materials for lithium-ion batteries. However, their poor cyclability, capacity retention, and rate capability at higher working potentials limit their applications in commercial batteries. Here, we demonstrate a cost-effective chemical solution deposition route of a thin TiOx shell on LiNi0.6Mn0.2Co0.2O2 (NMC-622) particles and the effect of surface modification on the electrochemical properties. The crystallinity and morphology of the NMC-622 particles are unaffected by the deposition step and verified by powder X-ray diffraction and electron microscopy. High-resolution transmission electron microscopy (HR-TEM) and selected area electron diffraction (SAED) analysis showed that the TiOx surface layer is amorphous and prone to enhance the electronic conductivity of the cathode material. The TiOx-coated material has an improved rate performance and experiences a lower charge-transfer resistance compared to the pristine material. The effect of the surface modification on the electrochemical performance of NMC-622 was investigated further by the assembly of NMC-622/Li4Ti5O12 (LTO) full cells. The beneficial impact of the TiOx coating on the electrochemical performance of NMC-622 positive electrodes in lithium-ion battery applications was showcased by the higher initial Coulombic efficiency and lower aging rates during 150 cycles at 1C in NMC-622/LTO cells.