Method for manufacturing secondary battery and pouch for secondary battery

1. A method for manufacturing a secondary battery, the method comprising:

a forming step of pressing a pouch sheet by using a press die so that left and right accommodation grooves, which are bilaterally symmetrical to each other and are opened upward, and a bridge connecting the left and right accommodation grooves to each other are formed in the pouch sheet, wherein the bridge protrudes upward with respect to bottom surfaces of the left and right accommodation grooves, and a curved portion having a rounded shape is formed on an upper end of the bridge;

a seating step of seating an electrode assembly in one of the left and right accommodation grooves; and

a folding step of folding the pouch sheet so that the left and right accommodation grooves face each other,

wherein, in the forming step, a first bending part having a shape in which outer side surfaces of the left and right accommodation grooves are respectively bent downward with respect to outer circumferential surfaces of the pouch sheet has a first curved surface having a rounded shape,

a second bending part having a shape in which the outer side surfaces of the left and right accommodation grooves are respectively bent upward with respect to the bottom surfaces of the left and right accommodation grooves has a second curved surface having a rounded shape, and

the pouch sheet is formed so that a width of each of inflection surfaces of the outer side surfaces that are formed between the first curved surface and the second curved surface is 0.5 mm or less,

wherein, in the forming step, the pouch sheet is formed so that each of the inflection surfaces has a planar shape, and

each of an angle between each of the outer circumferential surfaces and each of the inflection surfaces of the pouch sheet and an angle between each of the inflection surfaces and each of the bottom surfaces of the left and right accommodation grooves is 93° to 98°.

2. The method of claim 1 , wherein, in the forming step, the pouch sheet is formed so that the bottom surfaces of the left and right accommodation grooves are inclined to be bilaterally symmetrical to each other,

wherein the bottom surfaces of the left and right accommodation grooves have inclinations decreasing in a direction that is away from the bridge.

3. The method of claim 2 , wherein, in the forming step, the inclination of each of the bottom surfaces of the left and right accommodation grooves decreases at an angle of 1.5° to 3°.

4. The method of claim 1 , wherein, in the forming step, the pouch sheet is formed so that the upper end of the bridge has a semicircular shape.

5. The method of claim 1 , wherein, in the forming step, when a length along the pouch sheet between a portion, which contacts a lower edge of the electrode assembly adjacent to the bridge, and the bridge is d 1 , a length along the pouch sheet between a portion, which contacts an upper edge of the electrode assembly adjacent to the bridge, and the bridge is d 2 , a length along the pouch sheet of the bridge is d 3 , and a height of the electrode assembly seated on the pouch sheet is h, the pouch sheet is formed to satisfy following conditional expression: h≤d 1 +d 2 +d 3 .

6. The method of claim 5 , wherein, in the forming step, the pouch sheet is formed so that the bridge has a width of 4 mm or less.

7. The method of claim 6 , wherein, in the forming step, the pouch sheet is formed so that the bridge has a width of 1 mm to 2 mm.

8. The method of claim 7 , wherein, in the forming step, when a height of the electrode assembly seated on the pouch sheet is h, and a protruding height of the bridge with respect to the bottom surfaces of the pouch sheet is a, the pouch sheet is formed to satisfy following conditional expression: h/2≥a.

9. The method of claim 7 , wherein the bridge has a width defined by a width of a protrusion protruding between the left and right accommodation grooves, and

end points of the width of the protrusion are defined by inflection points between bending parts adjacent the bottom surfaces of the left and right accommodation grooves and side surfaces of the protrusion.

10. A pouch for a secondary battery, the pouch comprising:

a pouch sheet, wherein in an unfolded form, the pouch sheet includes:

left and right accommodation grooves for accommodating an electrode assembly when the pouch sheet is in a folded form and which are bilaterally symmetrical to each other and are opened upward; and

a bridge connecting the left and right accommodation grooves to each other,

wherein the bridge protrudes upward with respect to bottom surfaces of the left and right accommodation grooves, and a curved portion having a rounded shape is formed on an upper end of the bridge,

wherein a first bending part having a shape in which outer side surfaces of the left and right accommodation grooves are respectively bent downward with respect to outer circumferential surfaces of the pouch sheet is formed with a first curved surface having a rounded shape,

a second bending part having a shape in which the outer side surfaces of the left and right accommodation grooves are respectively bent upward with respect to the bottom surfaces of the left and right accommodation grooves has a second curved surface having a rounded shape, and

a width of each of inflection surfaces of the outer side surfaces that are formed between the first curved surface and the second curved surface is 0.5 mm or less,

each of the inflection surfaces has a planar shape, and

each of an angle between each of the outer circumferential surfaces and each of the inflection surfaces of the pouch sheet and an angle between each of the inflection surfaces and each of the bottom surfaces of the left and right accommodation grooves is 93° to 98°.

11. The pouch of claim 10 , wherein, in the pouch sheet, in its unfolded form, the bridge has a width of 1 mm to 2 mm.

12. A secondary battery comprising:

a pouch of claim 10 ; and

an electrode assembly accommodated in the left and right accommodation grooves with the pouch sheet in a folded form so that the left and right accommodation grooves face each other.

13. The pouch of claim 10 , wherein:

when a length along the pouch sheet between a portion, which is configured to contact a lower edge of the electrode assembly adjacent to the bridge, and the bridge is d 1 , a length along the pouch sheet between a portion, which is configured to contact an upper edge of the electrode assembly adjacent to the bridge, and the bridge is d 2 , a length along the pouch sheet of the bridge is d 3 , a height of the electrode assembly seated on the pouch sheet is h, and a protruding height of the bridge with respect to the bottom surfaces of the pouch sheet is a,

the pouch sheet is formed to satisfy following conditional expressions: h≤d 1 +d 2 +d 3 and h/2≥a.