A study on the catalytic and structural viewpoints for enhancement of cathodes performance for lithium-ion batteries

Abstract

In this study, two researches on the catalytic and structural viewpoints on the high-performance cathodes for lithium-ion batteries (LIBs) are introduced. First, the catalytic effect of non-conductive metal oxides is investigated in lithium-sulfur batteries. Metal oxides are known as materials that suppress the polysulfide dissolution and accelerate the sulfur redox reaction in lithium-sulfur batteries. However, due to its non-conductivity, it is inevitable to involve strategies for improving electrical conductivity. Herein, to demonstrate the intrinsic catalytic effect of the non-conductive metal oxides, pompon-like ZnO microspheres (p-ZnO) are synthesized and used as a host material of sulfur (p-ZnO/S). The composite of p-ZnO/S significantly enhances the sulfur utilization and rate capability without additional efforts to improve electrical conductivity. In addition, the decrease of reaction resistance and charge-transfer resistance was shown in electrochemical impedance spectroscopy (EIS) and galvanostatic intermittent titration technique (GITT) results. Moreover, the mechanism of the catalytic effect is demonstrated by analyzing the lithium-ion diffusion coefficient and the change in the chemical composition on the cathode surface during the discharge process. Second, the correlation between electrode structures and electrochemical performances is investigated by using NMC532 thick electrodes designed with various laser-structuring parameters. Although the 3-dimensional electrodes processed by laser-structuring have shown the superior improvement of electrochemical performance, the material loss by the laser structuring leads to the usable capacity loss of electrode. Therefore, the structuring condition to minimize material loss and processing time and to maximize performance improvement should be fundamentally studied. Herein, the correlation between the physical and electrochemical characteristics according to the various structuring parameters is investigated. Furthermore, the various resistance components depending on the structuring parameters are elucidated by EIS measurement using a conventional half-cell and a blocking symmetric cell.