Predictive Characterization of SEI Formed on Graphite Negative Electrodes for Efficiently Designing Effective Electrolyte Solutions

The solid electrolyte interphase (SEI) formed on graphite in highly concentrated electrolyte solutions was thoroughly characterized by a combined experimental and computational study. The comprehensive understanding revealed that a chemical composition of SEI, as well as the chemical species vulnerable to reduction, can be predicted by a profound understanding of density functional theory (DFT) calculation results of the solvates containing a counteranion. More specifically, in this study, highly concentrated LiPF6/carbonate ester electrolyte solutions were prepared by using two kinds of carbonate ester solvents to obtain quite different types of SEI and different charge/ discharge behavior of graphite negative electrodes. The solvation structures were determined by Raman spectroscopy to evaluate electron affinity (EA) and LUMO of the solvates containing a PF6- anion by DFT calculations. The chemical composition of SEI was quantitatively analyzed by X-ray photoelectron spectroscopy (XPS), and the results were consistent with a prediction based on the calculation. In addition, the stability of the SEI against reduction was clarified by correlating the chemical composition with the charge/discharge behavior. These results indicate that electrolyte solutions can be efficiently designed by predicting the physicochemical properties of SEI through the more effective utilization of DFT calculations.

Automated summary

The solid electrolyte interphase (SEI) formed on graphite in highly concentrated electrolyte solutions was thoroughly characterized by a combined experimental and computational study. The study revealed that the chemical composition and reduction vulnerability of SEI can be predicted through a profound understanding of density functional theory (DFT) calculations. The results indicate the potential for efficient design of electrolyte solutions by utilizing DFT calculations to predict the physicochemical properties of SEI.