Method for assembling battery pack, and battery pack

1. A method for assembling a battery pack having a cell group including a plurality of unit cells stacked in a thickness direction, each of the unit cells including a cell body having a flat shape by sealing a power generation element using laminate films, and an electrode tab protruding out from the cell body, and the battery pack further having a bus bar electrically connecting the unit cells, the method comprising:

a step of stacking the plurality of the unit cells such that distal end portions of the electrode tabs of the unit cells are bent along a stacking direction of the unit cells;

a step of disposing a pair of first cover members on an outer side of both ends of the unit cells in the stacking direction;

a step of disposing a pair of second cover members on the outer side of both ends of the unit cells in a direction that intersects with the stacking direction and that also intersects with a direction in which the electrode tabs extend;

a step of welding the first cover members and the second cover members while the cell group obtained by stacking the unit cells is pressurized from both sides of the cell group in the stacking direction using the first cover members, the welding of the first cover members and the second cover members being performed prior to electrically connecting the unit cells by the bus bar; and

a step of laser-welding the bus bar to distal end portions of the electrode tabs that are bent along the stacking direction after the first cover members and the second cover members are welded.

2. The method according to claim 1 , wherein

the welding of the first cover members and the second cover members is performed in a spot or linear manner.

3. The method according to claim 1 , wherein

the cell group further comprises a spacer disposed between the unit cells that are adjacent in the stacking direction at an end portion of a direction in which the unit cells extend in the flat shape, the spacer is disposed before the first cover members and the second cover members are welded, and

the spacer in the cell group is fixed in a position by welding the first cover members and the second cover members when pressurizing force is imparted to the cell group by the first cover members.

4. The method according to claim 1 , further comprising

disposing an elastic member is in any position in the stacking direction to generate resilient force in the elastic member along the stacking direction upon the welding of the first cover members and the second cover members.

5. The method according to claim 4 , wherein

the elastic member includes a leaf spring, and

the welding of the first cover members and the second cover members generates the resilient force more inward than an outer perimeter when the leaf spring is viewed from the stacking direction.

6. The method according to claim 4 , wherein

the elastic member includes a plurality of leaf springs being arranged adjacent to each other, and

adjacent ones of the leaf springs are joined to each other at a more outward location than a location where the resilient force is generated when viewed from the stacking direction.

7. The method according to claim 5 , wherein

the elastic member is disposed between one of the unit cells and one of the first cover members, and further comprising

clamping the first cover member using a clamp member that enters a hole on the one of the first cover member.

8. The method according to claim 4 , further comprising

disposing a flat intermediate member between the elastic member and one of the unit cells that is adjacent to the elastic member in the stacking direction or in a position adjacent to one of the first cover members in the stacking direction.

9. The method according to claim 1 , further comprising

disposing another spacer that is connected with one of the unit cells that is adjacent to at least one end portion of the cell group in the stacking direction, and

the another spacer and at least one of the first cover members that are adjacent to the another spacer being engaged with each other to align the at least one of the first cover members with respect to the cell group.

10. The method according to claim 9 , wherein

at least one of the second cover members and the first cover members are engaged with each other to align the at least one of the second cover members with respect to the first cover members.

11. The method according to claim 10 , wherein

alignment of the first cover member with respect to the cell group and alignment of the second cover member with respect to the first cover members are carried out at a plurality of locations.

12. A battery pack comprising:

a cell group including a plurality of unit cells stacked in a thickness direction, each of the unit cells including a cell body having a flat shape by sealing a power generation element using laminate films and an electrode tab protruding out from the cell body;

a bus bar electrically connecting the unit cells; and

a pair of first cover members covering the cell group from both sides in a stacking direction of the unit cells; and a pair of second cover members covering the cell group from both sides in a direction that intersects with the stacking direction and that also intersects with a direction in which the electrode tabs extend,

the pair of first cover members covering the cell group such that the cell group is pressurized along the stacking direction of the unit cells,

the electrode tabs having bent distal end portions that are bent in the stacking direction of the unit cells, and the bus bar being laser-welded to the bent distal end portions, and

the electrode tabs and bus bar being disposed on an open portion of the pair of first cover members and the pair of second cover members, the open portion of the pair of first cover members and the pair of second cover members being disposed adjacent to the cell group in the direction in which the electrode tabs extend.

13. The battery pack according to claim 12 , wherein

the first cover members and the second cover members are joined by joining points between the first cover members and the second cover members in a spot or a linear manner.

14. The battery pack according to claim 12 , wherein

the cell group further comprises a spacer disposed between the unit cells that are adjacent in the stacking direction, the spacer being disposed at an end portion of a direction in which the unit cells extend in a flat shape.

15. The battery according to claim 12 , wherein further comprising an elastic member disposed in any position in the stacking direction for generating resilient force along the stacking direction.

16. The battery pack according to claim 15 , wherein

the elastic member comprises a leaf spring, and

the resilient force is generated more inward than an outer perimeter when the leaf spring is viewed from the stacking direction.

17. The battery pack according to claim 16 , wherein

the elastic member comprises a plurality of leaf springs that are adjacent to each other, and

the leaf springs are joined to each other at locations more outward than a location where the resilient force is generated when the leaf springs are viewed from the stacking direction.

18. The battery pack according to claim 15 , wherein

the elastic member is disposed between one of the unit cells and one of the first cover members, and

the one of the first cover members includes a hole through which a clamp member for clamping the one first cover member passes from outside with respect to the one of the first cover members at a location more outward than the location where the resilient force is generated when the one of the first cover members is viewed from the stacking direction.

19. The battery pack according to claim 15 , further comprising

a flat intermediate member disposed between the elastic member and one of the unit cells that is adjacent to the elastic member in the stacking direction or in a position adjacent to one of the first cover members in the stacking direction.

20. The battery pack according to claim 12 , further comprising

another spacer connected to one of the unit cells adjacent to at least one end portion of the cell group in the stacking direction, and

the another spacer and at least one of the first cover members that are adjacent to the another spacer, each comprises an engagement portion that is engaged with another engagement portion to align the one of the first cover members with respect to the cell group.

21. The battery pack according to claim 20 , wherein

at least one of the second cover members and the first cover members, respectively, comprise engagement portions that are engaged with each other to align the at least one of the second cover member with respect to the first cover members.

22. The battery pack according to claim 20 , wherein

the another spacer includes a plurality of the engagement portions and the first cover member includes a plurality of the other engagement portions.

23. The method according to claim 1 , further comprising a step of assembling the bus bars to the cell group after the step of welding the first cover members and the second cover members, wherein:

the step of welding the first cover members and the second cover members is performed in a state in which the bus bars are not assembled to the cell group, and

the step of laser-welding the bus bar to the distal end portions of the electrode tabs is performed after the bus bars are assembled to the cell group.

24. The battery pack according to claim 12 , further comprising a protective cover erected along the stacking direction, wherein:

the pair of first cover members compresses the cell group in a state in which the cell group is housed inside the pair of first cover members and the pair of second cover members, and

the protective cover comprises openings where the electrode tabs and the bus bar are arranged in a state in which the cell group is housed inside the pair of first cover members and the pair of second cover members.