Battery pack and battery pack manufacturing method

1. A battery pack comprising:

a cell group obtained by stacking a plurality of unit cells in a thickness direction, the unit cells each including a cell body having a power generation element and a flat shape, and an electrode tab protruding out from the cell body, and the electrode tabs having distal end portions bent in a stacking direction of the unit cells; and

a flat plate shape bus bar connecting the distal end portions of the electrode tabs of the unit cells while facing the distal end portions, and electrically connecting the electrode tabs of at least two of the unit cells with each other, wherein:

each of the distal end portions of the electrode tabs of at least two of the unit cells and a surface of the bus bar that faces the unit cells are in contact and welded to each other,

the distal end portions of the electrode tabs that are electrically connected by the bus bar are bent in a same direction,

the cell group comprises spacers disposed between the electrode tabs of the unit cells that are stacked, the spacers including supporting portions that abut the electrode tabs from an opposite side of the bus bar to support the distal end portions of the electrode tabs, and

each of the spacers are attached to a respective one of the unit cells.

2. The battery pack according to claim 1 , wherein

the electrode tabs are each formed by being bent in an L shape from proximal end portions adjacent to the cell bodies to the distal end portions as seen from a side of the unit cells, and are each mutually joined where flat portions of the distal end portions and the bus bar overlap.

3. The battery pack according to claim 1 , wherein

the spacers include recesses having an opening along a direction that intersects with the stacking direction in positions corresponding to welding areas of the bus bar and the electrode tabs.

4. The battery pack according to claim 3 , wherein

the recesses seal at least a portion of a periphery of the welding areas of the electrode tabs.

5. The battery pack according to claim 4 , wherein

the recesses each includes a bottom surface positioned on a lower side of the stacking direction of the unit cells that is larger than a top surface positioned on an upper side of the stacking direction of the unit cells.

6. The battery pack according to claim 1 , wherein

the bus bar electrically connects the electrode tabs on a positive electrode side of one group of the unit cells in parallel, and electrically connects the electrode tabs on a negative electrode side of another group of the unit cells in parallel.

7. The battery pack according to claim 1 , wherein

the bus bar includes a first bus bar bonded to the electrode tabs on the positive electrode side of one of the unit cells, and a second bus bar bonded to the electrode tabs on the negative electrode side of another of the unit cells.

8. The battery pack according to claim 7 , further comprising

a bus bar holder for integrally holding the first bus bar and the second bus bar.

9. The battery pack according to claim 8 , wherein

the bus bar holder comprises an insulating portion having insulating properties that protrudes between the bus bars that are adjacent along the stacking direction.

10. The battery pack according to claim 1 , wherein

each of the electrode tabs on the positive electrode side and the negative electrode side of the unit cells protrudes out from one edge from among edges of the cell body, and the electrode tabs of all of the unit cells are disposed on a same side.