High voltage and safe electrolytes based on ionic liquid and sulfone for lithium-ion batteries

Novel binary electrolytes based on ionic liquid (N-butyl-methyl piperidinium bis(trifluoro-methylsulfonyl)imide, PP14-TFSI) and sulfone (tetramethylene sulfone, TMS) have been prepared and examined for use in lithium-ion batteries. The addition of sulfone is expected to improve the lithium salts solvability, ionic conductivity and electrode compatibility of the ionic liquid greatly. More importantly, the addition of sulfone is not expected to deteriorate the peculiar properties of the ionic liquid, such as the wide electrochemical window and non-flammability. Experimental results have shown that the reversible discharge capacities of the Li/LiFePO4 half-cell, which contains a 0.5 M LiTFSI/(60%) PP14-TFSI/(40%) TMS mixed electrolyte at a current density of 0.05 C and 1 C, can reach up to 160 and 150 mAh g−1, respectively, which are much higher than the discharge capacity achieved using the pure ionic liquid electrolyte under the same conditions. Furthermore, lithium difluoro(oxalato)borate (LiDFOB) has been found to have positive effects on the battery performance of the mixed electrolytes. The 0.5 M LiDFOB/(60%) PP14-TFSI/(40%) TMS mixed electrolyte exhibits better compatibility with the Li1.2Ni0.2Mn0.6O2 cathode than conventional electrolytes, where an initial discharge capacity of 255 mAh g−1 is obtained and a stable capacity of above 230 mAh g−1 is retained after 30 cycles.

Mixed electrolytes based on ionic liquid and sulfone have been developed and demonstrated to show high safety, good electrochemical stability and good electrode compatibility.Figure optionsDownload as PowerPoint slideHighlights
► Mixed electrolytes based on ionic liquid and sulfone.
► The electrolytes exhibit wide electrochemical windows and non-flammability.
► The addition of sulfone improve electrode compatibility of the electrolytes greatly.
► Lithium difluoro(oxalato)borate also has positive effects on the battery performance.