Lithium is a soft metal, with a Young's modulus in the range of 5 - 8 GPa. Yield strength is about 0.6 - 0.8 MPa. Elongation is about 50%. Therefore it is plastically deformed at very low stress levels. When exposed to air it will immediately oxidize to Li2O which is a brittle ceramic. Li will oxidize even at very low oxygen partial pressures (~10-40 bar). Therefore, if lithium is used as a solid state lubricant to reduce the friction between two mating surfaces, the lithium needs to be coated with an impervious layer of lubricant that completely prevents oxidation of lithium. Formation of Li2O will cause scoring of the surface.
Probably it's because that the in-situ produced large size ion pairs have a boundary adsorption capability on the rubbing surfaces that will enhance the formation of a physical adsorption film.
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