The present invention relates to a cathode mixture having improved conductivity, a cathode and an electrochemical device containing the same. According to an embodiment of the present invention, in a lithium manganese-based oxide having a spinel structure, a conductive polymer is located on the surface of a shell part that is present in a tetragonal structure. Thus, the present invention improves electrical conductivity, thereby increasing the degree of participation in a reaction in region 3 V, and provides a conductive path to thereby improve the capacity, cycle life characteristics and rate capability of an electrochemical device.