Battery pack and vehicle

1. A battery pack, comprising:

a box assembly; and

a plurality of battery units arranged in the box assembly, wherein the battery units are divided into a plurality of battery unit groups;

wherein the box assembly comprises:

a box body; and

a plurality of fixed beams arranged in parallel in the box body, wherein one or more battery unit groups are placed between two fixed beams;

a plurality of constraint components, wherein each constrain component covers the one or more battery unit groups placed between the two fixed beams, and is attached to the two fixed beams; and

an outer cover attached to the box body, covering the constraint components;

wherein each battery unit comprises:

a shell; and

an electrode assembly arranged in the shell;

wherein the electrode assembly comprises a first pole piece, a second pole piece, and a diaphragm arranged between the first pole piece and the second ole piece; and

wherein

the electrode assembly is of a wound structure and is flat, the outer surface of the electrode assembly comprises two flat surfaces, and the two flat surfaces are oppositely arranged along a height direction of the battery pack; or

the electrode assembly is of a laminated structure, and the first pole piece and the second pole piece are stacked along a height direction of the battery pack.

2. The battery pack according to claim 1 , wherein each of the battery unit groups has at least two battery units.

3. The battery pack according to claim 1 , wherein the plurality of battery units are divided into several battery unit groups along a length direction of the battery pack, and the fixed beam extends along a width direction of the battery pack.

4. The battery pack according to claim 1 , wherein the plurality of battery units are divided into several battery unit groups along a width direction of the battery pack, and the fixed beam extends along a length direction of the battery pack.

5. The battery pack according to claim 1 , wherein the constraint components respectively cover different groups of the battery units.

6. The battery pack according to claim 5 , wherein each constraint component comprises:

a limiting portion covering the same group of battery units; and

two mounting portions, respectively connected to the both sides of the limiting portion along a grouping direction of the battery units,

wherein the two mounting portions are respectively fixed with the fixed beams on the both sides of the same group of battery units.

7. The battery pack according to claim 6 , wherein the limiting portion protrudes relative to the mounting portion toward a direction away from the battery units.

8. The battery pack according to claim 6 , wherein there is only one fixed beam arranged between two adjacent groups of battery units, each of the two adjacent mounting portions fixed with the fixed beam comprises a plurality of mounting blocks, the plurality of mounting blocks are arranged along an extension direction of the fixed beam at intervals, and the plurality of mounting blocks of the two adjacent mounting portions are alternately arranged.

9. The battery pack according to claim 1 , wherein at least one constraint component is of a split structure covering at least part of the surface of the corresponding battery units.

10. The battery pack according to claim 1 , wherein there is a gap between an inner surface of the outer cover and an outer surface of the constraint components.

11. The battery pack according to claim 10 , wherein the gap ranges from 2 mm to 100 mm.

12. The battery pack according to claim 6 , wherein the box assembly further comprises:

a depression bar and a fastener,

wherein the mounting portions are arranged between the depression bar and the fixed beam, and the fastener passes through the depression bar and the mounting portions, and is fixed with the fixed beam to fix the mounting portions to the fixed beam.

13. The battery pack according to claim 1 , further comprising a sealing member, wherein the sealing member is arranged between the outer cover and the box body to seal the open end of the box body.

14. The battery pack according to claim 1 , wherein a bonding layer is arranged between the battery units on the bottommost layer and an inner bottom surface of the box body.

15. The battery pack according to claim 1 , wherein a bonding layer is arranged between two adjacent battery units in each group of battery units.

16. The battery pack according to claim 1 , wherein a bonding layer is arranged between the constraint component and the battery units on the topmost layer.

17. A vehicle, comprising:

the battery pack according to claim 1 ; and

a vehicle body provided with the battery pack.

18. A device powered by a secondary battery, wherein the secondary battery comprises the battery pack according to claim 1 .