Effects of electrolyte additive on the electrochemical performance of Si/C anode for lithium-ion batteries

Additives play critical roles on the performances of electrolytes. Vinyl tris(2-methoxyethoxy) silane (VTMS) was utilized as additive in the ethylene carbonate (EC)/ethyl methyl carbonate (EMC) electrolyte. Scanning electron microscopy (SEM) was used to examine the morphological evolution of electrodes after cycling. The morphology of the SEI film for Si/C electrode was observed by transmission electron microscopy (TEM). X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectra (EIS) techniques were employed to understand the effect of electrolytes containing VTMS on the formation of the SEI layer. Our experiments reveal that the capacity and cyclability of Si/C anode are improved due to formation of a stable SEI on the anode surface. These behaviors are confirmed by constant current charge–discharge and electrochemical impedance spectra (EIS) study. In particular, 5 wt.% VTMS in EC:DEC (3:7 wt.%) shows the most optimal reversible capacity and best cycle stability. Such a performance can be attributed to the formation of a more flexible SEI containing Li2CO3, LiF, and organosilicone compounds, which can reduce further reduction of electrolyte.