NOVELTY - A surface-treated electrode active material (20) comprises a bulk metal oxide layer (21) comprising n types of metal elements, and a surface metal oxide layer comprising the same n types of metal elements as those of the bulk metal oxide layer, where the degree of reduction of a metal element included in surface metal oxide layer is higher than the degree of reduction of a corresponding metal element included in the bulk metal oxide layer.    USE - As surface-treated electrode active material such as cathode active material or an anode active material, used in a battery, particularly lithium secondary battery (claimed) which is used in electric vehicles or power storage devices.    ADVANTAGE - The surface-treated electrode active material provides cell characteristics, specifically lifetime characteristics at a high temperature of the surface-treated electrode active material, can be improved. As such, as the lifetime characteristics at a high temperature are improved, the lithium secondary battery employing the surface-treated electrode active material may operate in a harsh environment usually generated when used in electric vehicles and/or power storage devices because side reactions of the electrolyte or elution of the electrode active material accompanied by high temperatures or high voltages is satisfactorily suppressed on the surface of the electrode active material modified via the surface treatment.    DETAILED DESCRIPTION - A surface-treated electrode active material comprises a bulk metal oxide layer comprising n types of metal elements; and a surface metal oxide layer comprising the same n types of metal elements as those of the bulk metal oxide layer, where the degree of reduction having formula ((M(q+)/M(p+))(surface)) of a metal element included in surface metal oxide layer is higher than the degree of reduction having formula ((M(q+)/M(p+))(bulk)) of a corresponding metal element included in the bulk metal oxide layer.    n= greater than or equal to 2;    M=metal element, preferably manganese;    p and q= greater than or equal to 0.    INDEPENDENT CLAIMS are included for the following:    (1) surface treating (M1) an electrode active material, involving forming a mixture by adding an untreated electrode active material comprising a metal oxide, and at least one of a basic material and a reducing material to a solvent; and stirring the mixture;    (2) electrode comprising the surface-treated electrode active material; and    (3) lithium secondary battery comprising the electrode, where the electrode is a cathode.    DESCRIPTION OF DRAWING(S) - The figure shows cross-sectional view of surface-coated electrode active material.    Surface-coated electrode active material (20)    Bulk metal oxide layer (21)    Coating particles (22)