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 ultrahigh vacuum by a combination of spectroscopic ellipsometry and Anger electron spectroscopy. Ice multilayers, ca. 100 ML thick, were deposited on clean Li at 160 K. The evaporation rate of water at 160 K is sufficiently 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 produced, 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 temperature to 240 K results in desorption of the adsorbed water and conversion 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 collapse 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 small amounts of water in Li battery electrolyte is presented.