Secondary battery
According to the present disclosure, a secondary battery in which a gas discharge valve has excellent operational stability is provided. A battery case of the secondary battery disclosed herein includes a flat rectangular sealing plate, and a gas discharge valve provided in the sealing plate. In addition, in the secondary battery, a thickness T1 of the sealing plate, a length L1 of a short side of the sealing plate, a length L2 of a long side of the sealing plate, and a length L3 of the gas discharge valve in a short side direction satisfy expression (1) represented by T1/L1≤0.1, expression (2) represented by L2/L1≥6, and expression (3) represented by L3/L1≥0.4. As a result, when an internal pressure of the case rises to a desired pressure, the sealing plate is easily bent and deformed, so that the gas discharge valve can be stably operated by the bending deformation.
1 . A secondary battery, comprising:
an electrode body including a positive electrode and a negative electrode; and
a battery case configured to house the electrode body,
wherein
the battery case includes
an exterior body that is a flat quadrangular container of which one surface side forms an opening portion,
a flat rectangular sealing plate configured to close the opening portion of the exterior body, the sealing plate includes short sides extending along a short side direction of the sealing plate, and long sides longer than the short side and extending along a long side direction, wherein the sealing plate is fitted into the opening portion of the exterior body, and a welded portion is formed to straddle between an upper surface of the exterior body forming an outer edge of the opening portion and an outer surface of the sealing plate, and
a gas discharge valve provided in the sealing plate, and
the exterior body includes
a pair of first side walls each joined to one of the short sides of the sealing plate, and
a pair of second side walls each joined to one of the long sides of the sealing plate,
a thickness of each of the pair of first side walls is larger than a thickness of each of the pair of second side walls,
the welded portion includes
a first welded portion straddling between a long side of the long sides of the sealing plate and a second side wall of the pair of second side walls joined to the long side of the sealing plate, and
a second welded portion straddling between a short side of the short sides of the sealing plate and a first side wall of the pair of first side walls joined to the short side of the sealing plate,
a depth of the first welded portion is larger than a depth of the second welded portion,
the gas discharge valve includes a central portion, a peripheral portion around the central portion, and an annular breakable groove at the peripheral portion and surrounding the central portion,
a geometrical moment of inertia of the central portion is larger than a geometrical moment of inertia of the peripheral portion, and
a thickness T1 of the sealing plate, a length L1 of a short side of the short sides of the sealing plate, a length L2 of a long side of the long sides of the sealing plate, and a length L3 of the gas discharge valve in the short side direction of the sealing plate satisfy the following expressions (1) to (3):
T 1/ L 1≤0.1 (1)
L 2/ L 1≥6.5 (2)
L 3/ L 1≥0.4 (3).
2 . The secondary battery according to claim 1 , wherein the sealing plate is fitted into the opening portion of the exterior body, and a welded portion is formed to bridge between an upper surface of the exterior body forming an outer edge of the opening portion and an outer surface of the sealing plate.
3 . The secondary battery according to claim 2 , wherein a heat insulating groove extending in the long side direction of the sealing plate is formed between a long side of the long sides of the sealing plate and the gas discharge valve.
4 . The secondary battery according to claim 1 , wherein a plurality of the electrode bodies are housed inside the battery case.
5 . The secondary battery according to claim 1 , further comprising a pair of electrode terminals penetrating the sealing plate, wherein
the sealing plate includes two terminal insertion holes into which the pair of electrode terminals is inserted, respectively, and
the length L1 of the short side of the sealing plate and the shortest distance L4 from the gas discharge valve to the terminal insertion holes in the long side direction of the sealing plate satisfy the following expression (4):
L 4/ L 1≥3 (4).
6 . The secondary battery according to claim 1 , wherein
the sealing plate includes a liquid injection hole communicating with an internal space of the exterior body, the liquid injection hole being sealed by a sealing member, and
the length L1 of the short side of the sealing plate and a distance L5 from the gas discharge valve to the liquid injection hole in the long side direction of the sealing plate satisfy the following expression (5):
L 5/ L 1≥1 (5).
7 . The secondary battery according to claim 1 , further comprising:
a pair of electrode terminals penetrating the sealing plate;
an external conductive member connected to the electrode terminals outside the sealing plate; and
an external insulating member interposed between an outer surface of the sealing plate and the external conductive member,
wherein
the length L1 of the short side of the sealing plate and a shortest distance L6 from the gas discharge valve to the external insulating member in the long side direction of the sealing plate satisfy the following expression (6):
L 6/ L 1≥2 (6).
8 . The secondary battery according to claim 1 , wherein the length L3 of the gas discharge valve in the short side direction of the sealing plate and a length L7 of the gas discharge valve in the long side direction of the sealing plate satisfy the following expression (7):
0.8≤ L 3/ L 7≤2 (7).
9 . The secondary battery according to claim 1 , wherein
a bottom surface of the gas discharge valve protrudes from an inner surface of the sealing plate toward the electrode body,
an internal insulating member is disposed between the sealing plate and the electrode body, and
a distance from the bottom surface of the gas discharge valve to the electrode body in a direction perpendicular to the sealing plate is larger than a thickness of the internal insulating member.
10 . The secondary battery according to claim 1 , wherein
a bottom surface of the gas discharge valve protrudes from an inner surface of the sealing plate toward the electrode body,
the sealing plate includes a liquid injection hole communicating with an internal space of the exterior body,
the liquid injection hole is sealed by a sealing member protruding from the inner surface of the sealing plate toward the electrode body, and
in a direction perpendicular to the sealing plate, a distance from the bottom surface of the gas discharge valve to the electrode body is larger than a distance from the sealing member to the electrode body.
11 . The secondary battery according to claim 1 , wherein the length L1 of the short side of the sealing plate is 30 mm or more.
12 . The secondary battery according to claim 8 , wherein the length L3 of the gas discharge valve in the short side direction of the sealing plate and the length L7 of the gas discharge valve in the long side direction of the sealing plate satisfy the following expression (8):
0.8≤ L 3/ L 7≤1.2(8).