Secondary battery
A secondary battery includes a diaphragm which is disposed on a current path between a current collector plate connected to a wound electrode group in a battery container and an external terminal, deforms when an internal pressure of the battery container increases, and breaks the current path. The diaphragm has a convex portion which protrudes to the current collector plate. The current collector plate has a through-hole into which the convex portion is inserted. An inner wall portion of the through-hole and a side wall portion of the convex portion facing each other are welded.
1. A secondary battery including a diaphragm, which is disposed on a current path between a current collector plate connected to a wound electrode group in a battery container and an external terminal, that deforms when an internal pressure of the battery container increases, and breaks the current path,
wherein the diaphragm has a convex portion with a stepped structure which protrudes to the current collector plate,
the current collector plate has a through-hole into which the convex portion is inserted, and
an inner wall portion of the through-hole, which faces a center of the through-hole, and a side wall portion of the convex portion, which faces the inner wall portion, are welded to each other.
2. The secondary battery according to claim 1 , wherein
a welding portion is formed between the diaphragm and the current collector plate by welding the inner wall portion and the side wall portion.
3. The secondary battery according to claim 2 , wherein
the convex portion is hollow.
4. The secondary battery according to claim 2 , wherein
the convex portion is formed in a shape of a rib having an inner side wall portion facing an inner side of the through-hole at a side opposite to the side wall portion and extends along a circumferential direction of the through-hole.
5. The secondary battery according to claim 3 , wherein
a thickness of the convex portion is equal to or smaller than a thickness of the diaphragm of a portion adjacent to the convex portion.
6. The secondary battery according to claim 3 , wherein
a thickness of the convex portion is larger than a thickness of the diaphragm of a portion adjacent to the convex portion.
7. The secondary battery according to claim 2 , wherein
the convex portion is solid.
8. The secondary battery according to claim 4 , wherein
the diaphragm includes a plurality of the convex portions.
9. The secondary battery according to claim 8 , wherein
the current collector plate includes a plurality of the through-holes.
10. The secondary battery according to claim 9 , wherein
the current collector plate has a thin portion which surrounds the welding portion and is fractured by deformation of the diaphragm.
11. The secondary battery according to claim 10 , wherein
the plurality of through-holes are disposed at positions centering at individual apexes of a regular polygon, respectively, and
the thin portion is formed of an annular groove centering at a gravity center of the regular polygon.
12. The secondary battery according to claim 10 , wherein
the battery container includes a flat rectangular battery can which accommodates the flat wound electrode group and a rectangular battery lid which seals the battery can,
the diaphragm has a dimension of a longitudinal direction of the battery lid larger than a dimension of a short direction of the battery lid,
the thin portion is formed of an annular groove surrounding the plurality of through-holes, and
the plurality of through-holes are provided on a center line of the annular groove along the longitudinal direction.
13. The secondary battery according to claim 12 , wherein
the annular groove is elliptical, and
the through-holes are provided at positions of focal points of the annular groove.
14. The secondary battery according to claim 12 , wherein
the annular groove has a field track shape in which circular arc-shaped portions of both ends of the longitudinal direction are continuous by a linear portion, and
the through-holes are provided at center positions of the circular arc-shaped portions.
15. The secondary battery according to claim 12 , wherein
the current collector plate has a base portion which is disposed to face the battery lid and is provided with the through-holes and a terminal portion which extends from the base portion and is connected to the wound electrode group.
16. The secondary battery according to claim 1 , wherein
the inner wall portion of the through-hole and the side wall portion of the convex portion face each other in a horizontal direction.