An electrode assembly according to an embodiment of the present invention for achieving the above object comprises: a first electrode formed in the form of a single sheet and repetitively in-folded and out-folded at a predetermined interval; a second electrode formed into a plurality of pieces and respectively interposed in spaces formed by folding the first electrode; and a separator formed in the form of a single sheet and interposed between the first electrode and the second electrode so as to be repetitively in-folded and out-folded at a predetermined interval together with the first electrode, wherein the first electrode is a single-sided electrode in which a first electrode active material is applied to only one surface of a first electrode collector, and the second electrode is a double-sided electrode in which a second electrode active material is applied to all both surfaces of a second electrode collector.