THE REACTION OF CLEAN LI SURFACES WITH SMALL MOLECULES IN ULTRAHIGH-VACUUM

Reactions at the Li/H2O interface were studied at 160 to 290 K in ultr ahigh vacuum by a combination of spectroscopic ellipsometry and Anger electron spectroscopy. Ice multilayers, ca. 100 ML thick, were deposit ed on clean Li at 160 K. The evaporation rate of water at 160 K is suf ficiently slow that the ice layer remains on the surface for about 1 h . After 10 mill at 160 k, a pure LiOH layer ca. 70 Angstrom thick is p roduced, and after 1 h there is evidence of a slow conversion of LiOH to Li2O in the layer, probably at the Li/LiOH interface. Raising the t emperature to 240 K results in desorption of the adsorbed water and co nversion of all the LiOH to a porous (60% void) layer composed mostly of Li2O (35%) with some metallic Li mixed in. Raising the temperature further to 290 K results in densification of the layer by both collaps e of the voids and by diffusion of Li into the interstices of the Li2O , increasing the Li content to 27% and shrinking the film thickness to 26 Angstrom. Based on these results, a model for the behavior of smal l amounts of water in Li battery electrolyte is presented.