An electrolyte includes a eutectic mixture composed of (a) an alkoxy alkyl group-containing amide compound having a specific chemistry formula; and (b) an ionizable lithium salt. The eutectic mixture contained in the electrolyte has excellent high temperature stability as well as inherent characteristics of eutectic mixtures such as excellent thermal stability and excellent chemical stability, so it contributes to improvement of high temperature stability and decrease the lowest limit of a electrochemical window. Thus, the electrolyte may be usefully applied to electrochemical devices using various anode materials.