THE STUDY OF ELECTROLYTE-SOLUTIONS BASED ON ETHYLENE AND DIETHYL CARBONATES FOR RECHARGEABLE LI BATTERIES .1. LI METAL ANODES

The behavior of Li electrodes was studied in ethylene and diethyl carb onates (EC-DEC) solutions of LiAsF6, LiClO4, LiBF4, and LiPF6. The cor relation of the surface chemistry to the interfacial properties, morph ology, and Li cycling efficiency was investigated using surface sensit ive Fourier transform. infrared spectroscopy and impedance spectroscop y, 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 bat teries, this work indicates that they are not suitable as electrolyte solutions for batteries with ii metal electrodes. This is mostly becau se Li electrodes cannot be considered stable in these systems and Li d eposition is highly dendritic.