Investigations on the Surface Degradation of LiNi_1/3Co_1/3Mn_1/3O₂ after Storage

The surface evolution of LiNi1/3Co1/3Mn1/3O2 (NCM­333) during storage is investigated detailedly in this paper. Different from the traditional awareness of NCM333 with excellent storage stability, considerable deterioration is found including specific capacity loss, cycling and rate performance decline after long-time storage especially in a high-humidity environment. Small flaky impurity particles are observed on the surface by scanning electron microscope, which are proved to be Li2CO3 and LiOH through Fourier-transform infrared spectroscopy tests. X-ray photoelectron spectroscopy depth profiling directly shows the proportion of oxygen element in the lattice of NCM333 and the impurities in different depths, revealing the degree of degradation. X-ray diffraction analysis confirms that the stored NCM333 still maintains the pristine layered crystal structure, proving surface degradation leads to the performance deterioration. During storage, the lithium ions were extracted from superficial lattice to become active Li+, which gradually react with H2O and CO2 in moist air to form lithium impurities. Therefore, the humidity of air should be controlled during the storage, which is beneficial for the production and application of NCM333 cathode material