The Surface Film Formed on a Lithium Metal Electrode in a New Imide Electrolyte, Lithium Bis(perfluoroethylsulfonylimide)   LiN (  C 2 F 5 SO 2 ) 2 

A newly developed imide electrolyte salt, (LiBETI) was found to give very uniform, thin, and stable surface films on a lithium metal electrode in the propylene carbonate (PC) solution. LiBETI/PC was studied and compared to determine its ability to form such a stable surface film, with conventional electrolyte systems such as , , and (LiTFSI/PC). The surface film formed in LiBETI/PC system was a hemispherical, and the composition of the film consisted mainly of LiF, which is similar to that in a system. Quartz crystal microbalance (QCM) and cyclic voltammetry (after the tenth cycle) indicated that the surface film formed in LiBETI/PC (ca. 50 nm) was thinner than those in (ca. 90 nm), LiTFSI/PC (ca. 140 nm), or (ca. 255 nm). The variation of the resonance resistance (ΔR) obtained from in situ CV/QCM measurement, which has been demonstrated to be a good measure of the surface roughness, also suggested that LiBETI/PC system gave a compact and smooth surface topology during lithium deposition‐dissolution cycles. Impedance spectroscopy together with preliminary cycling tests showed that the LiBETI/PC system provides the highest cycling efficiency and improved cycleability among existing electrolyte salt systems in rechargeable battery systems employing lithium metal anodes. © 1999 The Electrochemical Society. All rights reserved.