As a promising salt for lithium-ion batteries, lithium difluoro(oxalate)borate (LiODFB) has become a research hotspot in recently. In this work, LiODFB-based electrolytes are studied. When used in Li/MCMB (mesophase carbon microbeads) cells, cell with 0.9 M LiODFB ethyl methyl carbonate (EMC)/sulfolane (SL) (1:1, v/v) electrolyte shows lower impedance than ones with 0.9 M LiODFB EMC/ethylene carbonate (EC) (1:1, v/v) electrolyte. Reduction of impedance mainly dues to the fitting nature of solid electrolyte interphase (SEI) film on carbon electrode of lithium-ion battery. The changing morphologies of SEI films with increased circulation numbers were analyzed by scanning electron microscope (SEM). And C2H5OLi, C2H5CO3Li, Li2CO3, RSO3Li, Li2SO3, LiF, C2H5F and some complicated mesh compounds based on >B-O- bond, were found in SEI film by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). It was believed that the root of impedance reduction benefits from both the rich existence of sulfurous compounds and the low content of LiF in SE! film. Crown Copyright (C) 2012 Published by Elsevier B.V. All rights reserved.