In this study, TriMethylene sulfite (TMS) was evaluated as a new electrolyte additive for improving the performances of lithium-ion batteries (LIBs). Charge-discharge, cyclic voltammetry (CV), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), and electrochemical impedance spectroscopy (EIS) were used to analyze the electrochemical reaction processes. The results showed that the initial charge capacities of the graphite electrode in electrolytes without and with TMS were 332.54 and 362.93 mAh g−1, respectively. After 100 cycles, the charge capacities were 321.05 and 353.4 mAh g−1 and the capacity retention rates were 96.6 and 97.4%, respectively. The impedance of the electrode in the electrolyte with TMS was reduced. These improvements in performance were benefited from the effective formation of a stable, compact, and smooth solid electrolyte interface (SEI) film with low resistance.