Insight into the Kinetic Degradation of Stored Nickel-Rich Layered Cathode Materials for Lithium-Ion Batteries

As the cathode materials for lithium-ion batteries (LIBs), nickel-rich LiNixCoyMn1–x–yO2 (nickel-rich NCM, 0.6 ≤ x < 1) materials have attracted increasing attention. However, during the practical production, transportation, and storage processes, they would suffer from poor storage stability in air, which seriously affects their electrochemical performance. Although researchers have made much effort to understand the degradation mechanism of the storage performance, the relationship between the structural evolution and electrochemical performance degradation still remains ambiguous. In this work, through the detailed structural and electrochemical characterization, the structure–performance relationship of nickel-rich NCM materials during storage in air is established from the aspect of the Li+ kinetics. It is found that the increased cation mixing would gradually slow down the kinetics of the solid-phase Li+ diffusion, and the adsorbed species (adsorbed hydroxyl, bicarbonate, carbonated, etc.), impurities (LiOH and Li2CO3), and rock salt structure formed on the material surface can significantly weaken the charge transfer kinetics at the electrode/electrolyte interface. In addition, the Li+ kinetic degradation during charge is much more serious than that during discharge, thereby becoming the dominant factor for the capacity fading during storage. Interestingly, the self-regeneration of the interfacial charge transfer kinetics is found, in which the surface impurities would be decomposed at the end of the first charge (4.0–4.3 V). Therefore, the results obtained in this work is conducive to further understanding the performance degradation mechanism of nickel-rich NCM materials during storage and can provide favorable guidance for the modification research.