Operando Raman observation of lithium-ion battery graphite composite electrodes with various densities and thicknesses

Abstract

Understanding the mechanisms of inhomogeneous charging and discharging reactions in an electrode is critical to improving the rate capability of lithium-ion batteries. Various methods have been developed to observe the distribution of electrode structure or lithium ions within an electrode; however, most of these methods require large-scale equipment or entail complex procedures. To simplify reaction distribution measurements within electrodes, this study developed specially designed cells and conducted operando observations of reaction distribution in graphite composite electrodes using Raman spectroscopy. Behaviors on both the electrolyte and current collector sides of the electrodes were compared, and electrodes of various densities and thicknesses were examined. For electrodes with low density, the changes in graphite structure were almost simultaneous on the electrolyte and current collector sides and were hardly dependent on the electrode thickness. In contrast, the changes in electrode structure with increased density were dependent on their thickness. This implies that the ion transportation length is responsible for the reaction distribution in the electrodes when ion channels connecting the current collector and electrolyte sides decrease owing to the increased electrode density. The simple method developed in this study is expected to further contribute to the understanding of the distribution of reactions within graphite composite electrodes.