Degradation of Nickel-Rich layered oxides in ambient air and its inhibition by surface coating and doping

Abstract

Nickel-rich layered cathode materials [LiNixCoyMn1-x-yO2 (x ≥ 0.6), NCM] have been considered as one of the most promising cathode materials for high energy lithium-ion batteries (LIBs) due to the low cost and high energy density. However, NCM can easily degrade in the air·H2O and CO2 will react with NCM to produce surface impurities mainly consisting of LiOH and Li2CO3. These impurity species have a negative impact on LIBs, such as slurry gelation and side reactions, which hinder the practical application of NCM materials. Here, we use ambient pressure X-ray photoelectron spectroscopy (APXPS) to monitor the NCM surface reactions in air and identify the degradation mechanism. Then, surface coating and surface doping are deployed on NCM by the combination of atomic layer deposition (ALD) and post-annealing. We prove that ZrO2 surface coating and Zr4+ surface doping can significantly inhibit the formation of LiOH and Li2CO3 on NCM surface in air through thermogravimetric analysis (TGA) and titration and hence eliminate the electrochemical performance degradation of the battery. This simple modification method is expected to be a potential solution to the problem of residual lithium in the large-scale production of nickel-rich layered cathode materials.