In this research, we investigated the potential application of vinyl ethylene carbonate (VEC) and ethylene carbonate (EC) as solid electrolyte interface (SEI) filmforming additive in 1-ethyl-3-methylimidazolium (EMI)-bis(trifluoromethyl-sulfonyl) imide (TFSI)-LiTFSI ionic liquid electrolyte (IL). The electrochemical performance of natural graphite (NG7) was studied in LiTFSI/EMI-TFSI containing different weight percent of EC/VEC via cyclic voltammetry (CV), electrochemical impedance spectrum (EIS), and galvanostatic charge/discharge cycles. Temperature effect on the discharge/charge performance of NG7 electrode in the researched IL electrolyte was also discussed.

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The electrochemical properties and overcharge protection mechanism of xylene as a new polymerizable electrolyte additive for overcharge protection of lithium ion batteries were studied by cyclic voltammetry tests, chargedischarge performance and battery power capacity measurements. It was found that when the battery was overcharged, xylene could electrochemically polymerize at the overcharge potential of 4.3-4.7 V (vs. Li/Li ＋ ) to form a thin polymer film on the surface of the cathode, thus preventing voltage runaway. On the other hand, the use of xylene as an overcharge protection electrolyte additive did not influence the normal performance of lithium ion batteries.