Electrochemical properties of Li-Mg alloy electrodes for lithium batteries

Li-Mg alloy electrodes are prepared by two methods: (1) direct-alloying thr ough 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 conditio ns greatly influence the microstructures and surface morphologies, and henc e, the electrochemical properties of the Li-Mg alloy electrodes. When apply ing thr: KCVD technique, the composition of each prepared alloy is determin ed by independently varying the temperature of the molten lithium, the temp erature 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 va riable temperatures on the microstructure, morphology, and electrochemical properties of the vapor-deposited alloys has been studied. The diffusion co efficients for Lithium in the Li-Mg alloy electrodes prepared by the KCVD m ethod are in the range 1.2x10(-7) to 5.2x10(-7) cm(2) s(-1) at room tempera ture, two to three orders of magnitude larger than those in other lithium a lloy systems (e.g. 6.0x10(-10) cm(2) s(-1) in LiAl). These observations sug gest that Li-Mg alloys prepared by the KCVD method might be used effectivel y to prevent dendrite formation, improving the cycleability of lithium elec trodes 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 ele ctrodes also appear to show not only the potential for higher rate capabili ties (power densities) but also for larger capacities (energy densities) wh ich might considerably exceed those of lithiated carbon or So-based electro des for lithium batteries. (C) 2001 Elsevier Science B.V. All rights reserv ed.