Analysis of deterioration mechanism depending on porosity of NCM811 electrode through electrochemical impedance spectroscopy

Abstract

The calendaring process of the electrode increases the volumetric capacity of the electrode, which is essential in the electrode manufacturing process. In addition, it has the characteristic of making an electrochemically uniform electrode state by controlling the porosity. However, the pressing process causes plastic deformation of the electrode surface, and furthermore, it has a problem of generating cracks in the particles. To identify the deterioration of LIBs from the electrode structure point of view, we tried to compare them by focusing on the electrode structure point of view. Herein, electrochemical impedance spectroscopy (EIS) using symmetrical cell is applied to analyze the effect of electrode structure. The electrical and mass transport can be observed at high frequency and low frequency, respectively. In particular, information on the Li-ion diffusion are investigated by applying complex capacitance analysis in low frequency. In this study, NCM811 electrodes with various porosities are examined to investigate the deterioration mechanism. The correlations between the electrode interface and resistance components with cycling are closely investigated using EIS. Ultimately, this work proves that a proper pressing process is required to prevent cracking of the electrode, and that complex capacitance can be used for analysis of electrode degradation.