an electrode assembly including positive electrodes, of which positive electrode tabs are connected to each other, and negative electrodes, of which negative electrode tabs are connected to each other, the electrode assembly having a quadrangular shape with four sides, wherein a space part that is an empty space is defined between two sides of the four sides facing each other, and the positive electrode tabs and the negative electrode tabs are positioned within the space part;

a positive electrode lead having a first end connected to the positive electrode tabs;

a negative electrode lead having a first end connected to the negative electrode tabs; and

a pouch in which the electrode assembly is embedded, wherein a second end of the positive electrode lead and a second end of the negative electrode lead pass through the pouch to protrude from one of the largest surfaces of the pouch to the outside,

wherein the pouch has a quadrangular shape with four sides,

wherein one side is opened in a state in which a remaining three sides are closed so that the electrode assembly is inserted into the pouch through the opened one side,

when the electrode assembly is inserted, the opened one side and a portion, through which each of the positive electrode lead and the negative electrode lead protrudes, are sealed,

wherein the pouch includes two major surfaces opposite each other, the four sides are four minor surfaces joining the two major surfaces to each other, and

wherein only one of the two major surfaces has a cutout, the positive electrode lead and the negative electrode lead extending through the cutout.