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

• Published in: ACS applied energy materials 2022-01, Vol.5 (1), p.1085-1094
• Main Authors: Aoki, Yasuhito, Oda, Mami, Kojima, Sachiko, Ishihama, Taihei, Nagashima, Tsuyoshi, Doi, Takayuki, Inaba, Minoru
• Format: Article
• Language: English
• ISSN: 2574-0962; 2574-0962
• DOI: 10.1021/acsaem.1c03450

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.