Nickel-rich LiNixMnyCo1-x-yO2 (NMC) has gained a great interest for electric vehicle (EV) applications based on its high specific capacity and low cost (i.e., low cobalt content). However, Ni-rich NMC has been known to be vulnerable to moisture attack, which makes it challenging to store and process powder materials. In this study, we performed a systematic investigation on the effect of (1) Ni-content x in NMC and (2) degree of wetness on the properties of NMC which include surficial reactions, crystal structure, and electrochemical properties. We selected four commercially available NMC powder samples with different chemical compositions: LiNi1/3Mn1/3Co1/3O2, LiNi0.5Mn0.2Co0.3O2, LiNi0.6Mn0.2Co0.2O2, and LiNi0.8Mn0.1Co0.1O2. These samples were stored in humid chamber or soaked in deionized water, followed by vacuum drying. X-ray diffraction (XRD) and Rietveld refinement showed a trend of increasing lattice parameters and decreasing c/a ratio after the moisture attack, which suggests a Li migration at the surface and cation mixing in the layered structure. Surface analysis using Fourier transform infrared (FTIR) spectroscopy showed a formation of Li2CO3 and LiOH on the surface of NMC. Electrochemical impedance spectroscopy (EIS) revealed an increase in the interfacial impedance of cathode/electrolyte after the moisture attack due to the surficial byproducts. In addition, charge-transfer reactions become sluggish due to the cation mixing in the layered structure. Based on the systematic design of experiments, we will present a strong relationship of chemical composition (i.e., Ni-content in NMC) – degree of wetness – performance degradation. From the results, we will discuss about the mitigation strategy to resolve the vulnerability of Ni-rich NMC to the moisture, which is critical for their broader applications for EVs.

Understanding degradation of Ni-Rich LiNixMnyCo1-x-yO2 (NMC): Moisture impact and chemical composition relationship

2019 Fall National Meeting

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.