The electrochemical behaviour and thermal stability of functional electrolyte additives for Li-ion batteries is investigated. The Li-ion cell systems is comprised of an anode of mesocarbon microbeads (MCMB) and a cathode (LiCoO2) in a solution of 1.1M LiPF6 dissolved in ethylene carbonate and ethylmethyl carbonate (EC:EMC; 4:6, v/v). Vinyl acetate (VA) and vinylene carbonate (VC) in an ionic electrolyte containing triphenylphosphate (TPP) are tested as functional electrolyte additives. The main analysis tools used in this study are cyclic voltammetry (CV), differential scanning calorimetry (DSC), electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM). Cells containing VA or VC exhibit excellent irreversible capacity, coulombic efficiency, rate capability and cycleability. These features confirming the effectiveness of VC addition for improving both the cell performance and the thermal stability of electrolytes in TPP-containing solutions for Li-ion batteries.