Lithium difluoro(oxalato)borate (LiODFB) (99.5%, by weight) is synthesized by an improved method, with the co-product of LiBF4 (99.5%, by weight). The electrochemical behaviors of sulfolane (SL) with LiODFB are studied by employment dimethyl sulfite (DMS) as a mixed solvent. It shows that 0.9molL−1 LiODFB-SL/DMS (1:1, by volume) electrolyte has considered stability against oxidative decomposition (>5.5V) and satisfactory conductivity. Electrochemical reductions of SL and DMS would occur nearly at the same level of ODFB anions. Further studies show that SL is the main and key reason during the formation process of an excellent solid electrolyte interphase (SEI) layer. When used in Li/MCMB cells, 0.9molL−1 LiODFB-SL/DMS electrolyte exhibits not only excellent film-forming characteristics, but also stable cycle performance. Besides, when used in LiFePO4/Li cells, 0.9molL−1 LiODFB-SL/DMS electrolyte exhibits several advantages, for example, the more stable electrochemical performances even at elevated and relatively low temperatures.