RECENT STUDIES OF THE LITHIUM LIQUID ELECTROLYTE INTERFACE - ELECTROCHEMICAL, MORPHOLOGICAL AND SPECTRAL STUDIES OF A FEW IMPORTANT SYSTEMS

Our recent studies on the correlation between Li-cycling efficiency, morphology, interfacial properties and surface chemistry in a variety of Li battery electrolyte solutions are reviewed. The solvent systems include alkyl carbonate mixtures, ether and ether alkyl carbonate mixtures, and methyl formate solutions. The techniques include surface sensitive Fourier-transform infrared spectroscopy, both in situ and ex situ modes, energy dispersive analysis of X-rays, scanning electron microscopy, impedance spectroscopy and standard electrochemical techniques. The principal points are: (i) the surface chemistry of Li is determined by a delicate balance between reduction processes of the solvents, salts and common contaminants; (ii) the surface films initially formed are subjected to ageing processes which gradually change their structure and properties; (iii) the heterogeneous chemical structure of the Li electrode's surface films induces non-uniform Li deposition; (iv) the cycling efficiency is high in systems where Li deposition is smooth and/or the Li deposited is efficiently passivated by the surface species instantaneously formed on it, and (v) it is evident that less hygroscopic surface species passivate the active metal in solution (e.g., Li2CO3, LiF) more effectively.