The electrochemical behavior of lithium bis(trifluoromethanesulfonyl)imide in ethyl methyl sulfone was studied. The coulombic efficiencies for the oxidation-reduction of lithium at platinum, aluminum, and mercury electrodes were 50, 93, and 99%, respectively. A comparison of the results with Pt, Al, and Hg electrodes suggests that chemical reactions of lithium with the electrolyte contribute to the efficiency loss with the Pt and Al electrodes. Low coulombic efficiencies for lithium on the Pt substrate were due to chemical reactions involving elemental lithium and the low reduction-oxidation reversibility of the lithium in Li-Pt alloys. For the Al substrate, the chemical reactions produced protective films on the surface of the Li-Al alloys. The self-discharge rate of the lithium on the Al substrate was very low, 0.3 muA/cm(2). The electrochemical reduction of lithium on mercury occurred at the least negative potential because of the amalgam formation. The lithium amalgam did not react with the electrolyte, resulting in the high coulombic efficiency.