Understanding the Stabilizing Effects of Nanoscale Metal Oxide and Li-Metal Oxide Coatings on Lithium-Ion Battery Positive Electrode Materials.

Nickel-rich layered oxides, such as LiNi0.6Co0.2Mn0.2O2 (NMC622), are high-capacity electrode materials for lithium-ion batteries. However, this material faces issues, such as poor durability at high cut-off voltages (>4.4 V vs Li/Li+), which mainly originate from an unstable electrode-electrolyte interface. To reduce the side reactions at the interfacial zone and increase the structural stability of the NMC622 materials, nanoscale (<5 nm) coatings of TiOx (TO) and LixTiyOz (LTO) were deposited over NMC622 composite electrodes using atomic layer deposition. It was found that these coatings provided a protective surface and also reinforced the electrode structure. Under high-voltage range (3.0-4.6 V) cycling, the coatings enhance the NMC electrochemical behavior, enabling longer cycle life and higher capacity. Cyclic voltammetry, X-ray photoelectron spectroscopy, and X-ray diffraction analyses of the coated NMC electrodes suggest that the enhanced electrochemical performance originates from reduced side reactions. In situ dilatometry analysis shows reversible volume change for NMC-LTO during the cycling. It revealed that the dilation behavior of the electrode, resulting in crack formation and consequent particle degradation, is significantly suppressed for the coated sample. The ability of the coatings to mitigate the electrode degradation mechanisms, illustrated in this report, provides insight into a method to enhance the performance of Ni-rich positive electrode materials under high-voltage ranges.