Provided is an electrochemical device comprising two types of separators having different energy to break, wherein the outermost electrode layer of the electrode assembly includes an active material non-coated cathode, an active material non-coated anode, and a separator (second separator) disposed between the cathode and anode and having relatively low energy to break compared to that of separators (first separator) in other electrode layers. Therefore, it is possible to remarkably improve safety of the battery by inducing primary short-circuiting in the outermost electrode layer of a battery, thus facilitating heat dissipation of the battery, upon application of external impact.