Electrochemical properties of Li-Mg alloy electrodes for lithium batteries

Li-Mg alloy electrodes are prepared by two methods: (1) direct-alloying through the melting of mole percent specific mixtures of Li and ME metal under vacuum and (2) the kinetically-controlled vapor formation and deposition (KCVD) of a Li-Mg alloy on a substrate. It is found that processing conditions greatly influence the microstructures and surface morphologies, and hence, the electrochemical properties of the Li-Mg alloy electrodes. When applying thr: KCVD technique, the composition of each prepared alloy is determined by independently varying the temperature of the molten lithium, the temperature of magnesium with which the lithium interacts, and the temperature of the substrate on which the intimately mixed Li-Mg mixture is deposited. Here, the required temperature for lithium induced Mg vaporization is more than 200 degreesC below the magnesium melting point. The effect of these variable temperatures on the microstructure, morphology, and electrochemical properties of the vapor-deposited alloys has been studied. The diffusion coefficients for Lithium in the Li-Mg alloy electrodes prepared by the KCVD method are in the range 1.2x10(-7) to 5.2x10(-7) cm(2) s(-1) at room temperature, two to three orders of magnitude larger than those in other lithium alloy systems (e.g. 6.0x10(-10) cm(2) s(-1) in LiAl). These observations suggest that Li-Mg alloys prepared by the KCVD method might be used effectively to prevent dendrite formation, improving the cycleability of lithium electrodes and the rechargeability of lithium batteries as a result of the high diffusion coefficient of lithium atoms in the Li-Mg alloy. Li-Mg alloy electrodes also appear to show not only the potential for higher rate capabilities (power densities) but also for larger capacities (energy densities) which might considerably exceed those of lithiated carbon or So-based electrodes for lithium batteries. (C) 2001 Elsevier Science B.V. All rights reserved.