An electrolyte includes an eutectic mixture composed of (a) a hetero cyclic compound having a predetermined chemistry figure, and (b) an ionizable lithium salt. An electrochemical device having the electrolyte. The eutectic mixture included in the electrolyte exhibits inherent characteristics of an eutectic mixture such as excellent thermal stability and excellent chemical stability, thereby improving the problems such as evaporation, ignition and side reaction of an electrolyte caused by the usage of existing organic solvents.