We develop a new co-solvent for wide temperature lithium ion battery electrolytes: 2,2,2-Trifluoroethyl N-caproate (TFENH) in this work and particularly investigate the effect of TFENH content on the electrochemical properties of the mixed electrolytes. The results show that the improved low and high temperature performances of LiCoO₂/graphite can be achieved if the volume ratio of TFENH co-solvent is kept between 17 and 25 Vol%. Carbon nuclear magnetic resonance spectroscopy (¹³C NMR) indicate that TFENH co-solvent is prior to distribute in the bulk of electrolyte, which help to reduce the viscosity and enhance the ionic conductivity of the electrolyte at low temperature. Electrochemical impedance spectroscopy (EIS) show that few TFENH co-solvent incorporation is beneficial to decrease the resistance of SEI film. X-ray photoelectron spectroscopy (XPS) demonstrate that a thin and stable CH₃(CH₂)₄COOLi film decomposed by TFENH is formed on the surface of graphite, which plays an crucial role in improving low temperature performance and cycling stability of lithium-ion batteries.