Robust and sulfur-containing ingredient surface film to improve the electrochemical performance of LiDFOB-based high-voltage electrolyte

In order to optimize the electrolyte system of lithium difluoro (oxalato) borate (LiDFOB)-ethyl methyl carbonate (EMC)/ethylene carbonate (EC)/adiponitrile (ADN) to overcome the drawback of low discharge capacity at room temperature and the easily decomposition of ADN under lower potential, three sulfur-containing solvents, ethylene sulfite (ES), dimethyl sulfite (DMS) and sulfolane (SL) are introduced. AC impedances, cycling performance, cyclic voltammetry tests as well as compatibilities between electrolytes and positive/negative electrodes are evaluated, respectively. Both of the solution systems of 0.7 M LiDFOB-EMC/ES/ADN (49: 49: 2, vol. % ratio) and 0.7 M LiDFOB-EMC/SL/ADN (65.3: 32.7: 2, vol. % ratio) are recommended as alternative electrolytes for 5 V high-voltage lithium ion batteries, benefitting from the synergistic effect between LiDFOB salt and sulfur-containing solvents. Besides, the effect on the performance of sulfur-containing solvents on the positive and negative electrodes is studied by theoretical calculation. This paper provides a promising candidate for improving the electrochemical performance of the battery by optimization of electrolyte formula, especially by a combination of lithium salt and solvent mixture.