The present invention relates to a lithium ion secondary battery, and more particularly, to a lithium ion secondary battery which makes the best use of an accommodating space in electronic apparatus in which a secondary battery is accommodated or mounted to maximize a performance of the battery. A secondary battery includes an electrode assembly in which a plurality of pocketing anode bodies and a plurality of cathode bodies are alternately stacked, in which a concavely recessed space is formed in the electrode assembly, and the space may be formed in the plurality of pocketing anode bodies and the plurality of cathode bodies excluding a cathode body disposed at the lowest end of the electrode assembly.