Forming a stable SEI layer by the synergy effect of methyl p-toluenesulfonate electrolyte additive in Li-ion batteries.

In this study, a novel S-based compound, methyl p-toluene sulfonate (MPTS) has been investigated as film-forming additive in Li/graphite cells. According to the density functional theory (DFT) investigation of electron affinity energy of MPTS and carbonate solvents, MPTS has more negative electron affinity energy of −2.17 eV, while it is only −1.03 eV for ethylene carbonate (EC) and −0.73 eV for dimethyl carbonate (DMC). It confirms the highest reductive activity of MPTS, which was consistent with the CV test result. The physicochemical features of the graphite electrode were studied using Fourier-transform infrared (FT-IR) spectroscopy, field-emission scanning microscopy (FESEM), X-ray photoelectron spectroscopy (XPS) analysis, and transmission electron microscopy (TEM). The electrochemical test results showed that the battery with 1.5% wt% MPTS exhibited a low impedance on the electrode interface and remarkable cyclability, maintaining 93.17% of its initial capacity at 0.2 C after 100 cycles, approximately 11% more than the conventional electrolyte. These outstanding performances are ascribed to the preferential absorption of MPTS and the as-created interface. TEM and XPS analysis confirmed that MPTS forms a thinner SEI layer containing sulfur on the graphite electrode, predicted by the recommended mechanism via theoretical calculations. This protective sulfur-containing film promotes faster lithium intercalation/deintercalation kinetics via declining the charge transfer resistance. [ABSTRACT FROM AUTHOR]