Disclosed herein is an electrode assembly including unit cells, each of which is constituted by an electrode plate stack configured to have a structure in which a separator is disposed between electrode plates comprising positive electrodes or negative electrodes, wherein the electrode assembly includes a combination of two or more kinds of unit cells having different sizes, the unit cells are stacked in a height direction on the basis of a plane, two or more of the unit cells located at a lower part of the electrode assembly, i.e. two or more base unit cells, are wound using a single sheet-type separation film to constitute an integrated base structure, and the others of the unit cells excluding the base unit cells, i.e. sub unit cells, are stacked in a state in which a separator is disposed between the respective sub unit cells.