Surface chemistries of lithium: Detailed characterization of the reactions of H2S, SO2, and SO2Cl2 using XPS and EELS

The surface chemical reactions of clean lithium with H₂S, SO₂ and SO₂Cl₂ have been studied by a combination of XPS and EELS. The reactions with H₂S lead entirely to the formation of sulfide product layers, which propagate only to the extent of a few monolayers. The reactions with SO₂ are more complicated, the first monolayer consists of oxide and sulfide from the full dissociation of the SO₂ molecule. Subsequent reaction occurs to form sulfide, sulfite and SO₂ (ads), probably as the radical anion form. At exposures of SO₂ up to atmospheric pressure, the product layer composition, within the XPS sampling depth, becomes exclusively sulfite. The reaction with SO₂Cl₂ occurs along similar pathways. The first monolayer is exclusively the oxide, sulfide and chloride, while subsequent reactions occur to form sulfite and SO₂ (ads), in the presence of additional chloride. These studies are important first steps toward the understanding of electrochemical processes of these interfaces.