The Study of Electrolyte Solutions Based on Ethylene and Diethyl Carbonates for Rechargeable Li Batteries I. Li Metal Anodes

The behavior of Li electrodes was studied in ethylene and diethyl carbonates (EC-DEC) solutions of LiAsF₆, LiC1O₄, LiBF₄, and LiPF₆. The correlation of the surface chemistry to the interfacial properties, morphology, and Li cycling efficiency was investigated using surface sensitive Fourier transform infrared spectroscopy and impedance spectroscopy, scanning electron microscopy, x-ray energy dispersive microanalysis, and standard electrochemical techniques. The Li surface chemistry is initially dominated by EC reduction to an insoluble species, probably (CH₂OCO₂Li)₂. Upon storage, several aging processes may take place, depending on the salt used. Their mechanisms are discussed. Although EC-DEC solutions were found to be adequate for Li ion rechargeable batteries, this work indicates that they are not suitable as electrolyte solutions for batteries with Li metal electrodes. This is mostly because Li electrodes cannot be considered stable in these systems and Li deposition is highly dendritic.