A secondary battery comprising a cathode, an anode, a separator and an electrolyte that comprises a eutectic mixture formed of: an amide group-containing compound, and an ionizable lithium salt. The anode comprises a metal or metal oxide having a potential vs. lithium potential (Li/Li+) within electrochemical window of the eutectic mixture. Because the secondary battery uses a eutectic mixture as an electrolyte in combination with an anode having a potential vs. lithium potential (Li/Li+) within the electrochemical window of the eutectic mixture, problems such as decomposition of an electrolyte and degradation of the quality of a battery are avoided. Also, due to the thermal and chemical stability, high conductivity and a broad electrochemical window of a eutectic mixture, it is possible to improve the quality as well as safety of a battery.