With the great progress being made in the development of cathodes in advanced lithium-sulfur (Li-S) batteries, the cycling stability of Li-metal anode has become an extremely urgent challenge presently. Herein, we report a new sulfonimide salt, namely lithium (trifluoromethanesulfonyl)(n-nonafluorobutanesulfonyl) imide (LiTNFSI), which can not only afford the excellent cycling and C-rate performances in Li-S batteries, but also deliver the superior cycling stability and comparable cycling efficiency for Li-metal anode, compared with conventional used LiTFSI (Li[(CF3SO2)(2)N]). It is demonstrated that the solid-electrolyte-interphase (SEI) films formed on the Li-metal anode in the LiTNFSI-based electrolyte are more stable than those formed in the LiTFSI-based one, due to the different surface chemistry developed on the Li-metal anode, essentially originated from the different anionic structures of Li salts (i.e., TNFSI- vs. TFSI-). (C) 2016 The Electrochemical Society. All rights reserved.