Electrode assembly having improved safety of use by means of structure in which local site in exterior material is reinforced with elastic polymer film, and lithium-ion secondary battery having same

A secondary battery, comprising:

• an electrode assembly;
• and
• a case covering the outside of the electrode assembly,
• wherein the electrode assembly includes one or more unit cells each equipped with a pair of electrodes having different polarities with a separator interposed therebetween;
• an electrode mixture coated on one or both surfaces of the pair of electrodes;
• and
• electrode tabs protruding from the respective electrodes, wherein
• the electrode tabs include an electrode parallel connection tab and an electrode lead connection tab,
• the electrode lead connection tab is formed on a first end of an outermost electrode among the electrodes included in the electrode assembly,
• the electrode parallel connection tab is formed on a second end opposite to the first end of the outermost electrode, and
• an elastic polymer film is provided at between the electrode lead connection tab of the outermost electrode and the electrode parallel connection tab of the outermost electrode and facing an outer surface of the outermost electrode inside the case such that internal electrodes included in the electrode assembly are put in a shutdown state by inducing a cutting of the outermost electrode facing the elastic polymer film before breakage of the case during repeated bending of the secondary battery, and
• wherein a thickness of the elastic polymer film is 0.5 mm or more and 1 mm or less, and
• wherein a local portion of the outermost electrode on which the elastic polymer film is overlapped is X which is equal to 1/15 to ⅓ of an entire length L of the case,
• wherein the case has upper stamped portions and lower stamped portions that are repeatedly formed, and the elastic polymer film is thermally compressed on valleys formed by the upper stamped portions and the lower stamped portions.