Nickel-rich cathodes such as LiNi_0.6Co_0.2Mn_0.2O₂ (NCM622) have received considerable attention as a result of their high delivered capacity. However, owing to high nickel content, NCM622 cathodes suffer from reduced cycle life and thermal stability compared to lower nickel content NCM523 and NCM333 cathodes. (1) Traditional approaches to coating and doping, including exploration of various coating (Al₂O₃, AlF₃, SiO₂) and dopant (Al³⁺, Mg²⁺, F^-) species which either act as a passivating layer between the cathode surface and reactive electrolyte or to stabilize the structure of the material, have been employed in the past to improve the performance of Ni-rich cathodes. (2-9)

This presentation demonstrates the effectiveness of a large batch (i.e. 500 grams) coating process to deposit either AlF₃ or ZnO on NCM622 cathode material. The process is a dry mixing technique wherein the coating is applied using powerful mechanical energy to induce mechano-chemical reactions between the surface of NCM622 and AlF₃ or ZnO. SEM imaging and EDX mapping illustrate that the size or morphology of the secondary particles is not affected by the process and the coating species is well-distributed among the bulk. Differential scanning calorimetry (DSC) and temperature-depending X-ray diffraction (XRD) were conducted to monitor the thermal stability of AlF₃ and ZnO coated NCM622. Temperature-dependent XRD shows the structural degradation of the layered NCM622 structure to a non-layered rock-salt structure as a function of temperature. The peak positions in the DSC correspond directly to the c lattice parameter decreasing, which is caused by oxygen release, and the conversion to a rock-salt phase. These results indicate how AlF₃ and ZnO coatings alter the collapse and phase transition of the delithiated NCM622 during heating.

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