Secondary battery, battery module, battery pack, device, and manufacturing method

1. A secondary battery, comprising:

an electrode unit, comprising a main body portion, and a first tab and a second tab extending out from the main body portion;

a casing, comprising an accommodating cavity for accommodating the main body portion and a first opening which is in communication with the accommodating cavity;

a first cover plate capping the first opening, the first cover plate comprising a first relief hole penetrating therethrough, the first tab passing through the first relief hole and being welded to a side of the first cover plate facing away from the accommodating cavity; and

a sealing plate, which is sealingly connected to the side of the first cover plate facing away from the accommodating cavity and covers the first relief hole, wherein

an outer surface of the first cover plate facing away from the accommodating cavity is recessed toward the accommodating cavity and forms a first recess, the first recess comprises a bottom plate, and the first relief hole is located on a side of the bottom plate along a thickness direction of the secondary battery;

the first tab comprises a connecting portion and a fixing portion, the fixing portion is disposed within the first recess and connected to the bottom plate, and the connecting portion is disposed to be bent relative to the fixing portion and penetrates through the first relief hole; and

the first cover plate comprises an inner surface facing the accommodating cavity, and the bottom plate is disposed to protrude out from the inner surface in a direction facing the accommodating cavity.

2. The secondary battery according to claim 1 , wherein,

a number of the first relief hole is two, and two first relief holes are located on two sides of the bottom plate along the thickness direction; and

a number of the electrode units is two, two electrode units are arranged side by side along the thickness direction, and the first tabs of the two electrode units respectively pass through the two first relief holes, and the fixing portions of the two first tabs extend in directions approaching each other.

3. The secondary battery according to claim 1 , wherein,

the first recess comprises a first segment and a second segment which are successively arranged in a height direction of the secondary battery, and the first segment is located on a side of the second segment facing away from the accommodating cavity, and an orthographic projection of the second segment in the height direction is located within an orthographic projection of the first segment in the height direction; and

at least part of the fixing portion is accommodated in the second segment, and the sealing plate is accommodated in the first segment.

4. The secondary battery according to claim 3 , wherein

the first recess comprises a first side wall facing the first segment, a second side wall facing the second segment, and a transition portion, the first side wall and the second side wall are connected with each other by the transition portion, and the sealing plate is located on a side of the transition portion facing away from the accommodating cavity.

5. The secondary battery according to according to claim 3 , wherein,

the sealing plate comprises a welding region at an edge, a reinforcing rib is provided at the inner surface of the first cover plate facing the accommodating cavity, and an orthographic projection of the reinforcing rib in the height direction of the electrode unit covers an orthographic projection of the welding region in the height direction.

6. The secondary battery according to claim 1 , further comprising a separating plate located between the first cover plate and the main body portion, the separating plate is provided with a second relief hole penetrating therethrough, and the first tab passes through the first relief hole and the second relief hole.

7. The secondary battery according to claim 6 , wherein,

an orthographic projection of the second relief hole at least partially overlaps that of the first relief hole, in the height direction of the electrode unit.

8. The secondary battery according to claim 6 , wherein,

the separating plate comprises a first surface facing the first cover plate and a second surface facing the main body portion, the first surface is recessed toward the second surface and forms a second recess, and at least part of the bottom plate is disposed within the second recess.

9. The secondary battery according to claim 1 , wherein,

the secondary battery further comprises a first electrode terminal electrically connected with the first tab and a second electrode terminal electrically connected with the second tab, the first electrode terminal is electrically connected with the first cover plate and the casing, and the second electrode terminal is insulated from the first cover plate and the casing.

10. The secondary battery according to claim 9 , wherein,

the secondary battery further comprises a second cover plate, the casing comprises a second opening which is in communication with the accommodating cavity, and the second opening and the first opening are respectively located at two ends of the casing along the height direction of the secondary battery, the second cover plate caps the second opening, the first electrode terminal and the second electrode terminal are both disposed on the second cover plate, and the first tab is electrically connected with the first electrode terminal by the first cover plate, the casing, and the second cover plate in sequence, and the second tab is insulated from the second cover plate.

11. A manufacturing method for a secondary battery according to claim 1 , comprising:

a step of assembling an electrode unit: placing an electrode unit within an accommodating cavity of a casing, the electrode unit comprising a main body portion, and a first tab and a second tab extending out from the main body portion, the casing comprising a first opening which is in communication with the accommodating cavity, and disposing the first tab faces the first opening;

a step of capping with a first cover plate: capping the first opening with the first cover plate, the first cover plate comprising a first relief hole penetrating therethrough, and passing the first tab through the first relief hole and welding the first tab to a side of the first cover plate facing away from the accommodating cavity; and

a step of sealing: sealingly connecting a sealing plate to the side of the first cover plate facing away from the accommodating cavity, and covering the first relief hole with the sealing plate, wherein,

before the step of covering the first cover plate, the manufacturing method further comprises:

punching the first cover plate to form a first recess on a surface of the first cover plate, the first recess comprising a bottom plate, the bottom plate protruding out from an inner surface of the first cover plate facing the accommodating cavity in a direction facing the accommodating cavity, and positioning the first relief hole on a side of the bottom plate along the thickness direction of the secondary battery; and

the step of capping with the first cover plate further comprises: capping the first opening with the first cover plate, positioning the first recess on the side of the first cover plate facing away from the accommodating cavity, passing the first tab through the first relief hole, the first tab comprising a connecting portion and a fixing portion, passing the connecting portion through the first relief hole, and bending the fixing portion relative to the connecting portion, such that the fixing portion is disposed in the first recess and connected to the bottom plate.

12. The manufacturing method of the secondary battery according to claim 11 , wherein,

before the step of capping with the first cover plate, the manufacturing method further comprises:

capping the first opening with a separating plate, the separating plate being provided with a second relief hole penetrating therethrough, and passing the first tab through the second relief hole; and

the step of capping with the first cover plate further comprises: subsequently capping the separating plate with the first cover plate, and passing the first tab through the second relief hole and the first relief hole in sequence.