Nanoscale electrical characterization of ambient-induced surface impurities on high-nickel cathode materials for lithium-ion batteries

One of the most critical points in the study of LIB-related materials is the extremely high reactivity of Li. In addition to pure Li metal, many Li-containing materials employed in LIBs are highly reactive under ambient conditions. Therefore, they should be stored and treated in an inert environment, such as vacuum chambers and gloveboxes filled with inert gases. In particular, most pristine cathode materials contain Li and are more reactive in air than pristine anode materials are. For instance, various impurities, mostly Li₂CO₃, are grown on the surface of pristine NCA (LiNi_xCo_yAl_zO₂, x + y + z = 1) materials. The precise characterization of these ambient-induced surface impurities is critical for understanding the intrinsic properties of these cathode materials. In this study, we directly image and characterize ambient-induced surface impurities formed on the surface of high-Ni NCA (LiNi_0.8Co_0.15Al_0.05O₂) materials using Kelvin probe force microscopy (KPFM) and scanning spreading resistance microscopy (SSRM). The ambient-induced surface impurities show clearly distinguishable work functions and resistance features compared with the pristine NCA surface. In particular, it is confirmed that the resistance of ambient-induced impurities is significantly higher than that of pristine NCA materials, which can deteriorate the performance of LIB cells. This study provides direction for the fabrication, storage, and processing of LIB cathode materials.