STEM-EELS analysis of improved cycle life of lithium-ion cells with Al2O3-coated LiNi0.8Co0.1Mn0.1O2 cathode active material

Abstract

Abstract The effect of Al2O3 on the cycle performance of 1 Ah-class LiNi0.8Co0.1Mn0.1O2 (NCM811)/graphite lithium-ion cells was studied by exploiting STEM-EELS analysis. Al2O3 was coated on NCM811 particles by a mechanochemical process with the coating from 0.5 to 3 wt%. All cells with the Al2O3-coated NCM811 cathode demonstrated better cycle performance than that with bare NCM811 independent of the coating amount. Analysis by STEM-EELS for the cells after 200 cycles revealed that the 3 wt%- Al2O3-coated NCM811 cathode had a solid solution layer of Al and NCM and also AlF3 on the surface of NCM particles. Moreover, the Al2O3-coated NCM811 cathode showed suppression of the growth of NiO-like layer on the Ni-based cathode material surface to degrade the cell performance. It is, therefore, concluded that the cycle performance was improved mainly by the solid solution and AlF3 layers to suppress the growth of the surface deposit and NiO-like layer formed by the reaction between NCM and electrolyte solution.