Battery pack

1 . A battery pack comprising:

multiple battery cells; and

a cell holder assembled with the multiple battery cells, the cell holder comprising:

a rim portion around an outer circumference of a first battery cell from among the multiple battery cells;

multiple protrusions at positions along the rim portion and protruding from the rim portion in a height direction; and

a divergence point between adjacent protrusions of the multiple protrusions,

wherein side surfaces of the multiple protrusions facing the outer circumference of the first battery cell have a gradient in the height direction, and

wherein a lower end of the first battery cell protrudes by a depth from a lowermost surface of the rim portion in a direction opposite the height direction.

2 . The battery pack of claim 1 , wherein the side surfaces of the multiple protrusions define a trajectory having a diameter that increases in the height direction.

3 . The battery pack of claim 1 , wherein the side surfaces of the multiple protrusions define a trajectory having a diameter that decreases in an assembly direction of the first battery cell in the height direction.

4 . The battery pack of claim 1 , wherein the side surfaces of the multiple protrusions extend from the rim portion forming a common support base of the multiple protrusions to protruding end portions of the multiple protrusions opposite to the rim portion.

5 . The battery pack of claim 4 , wherein the side surfaces of the multiple protrusions connect the rim portion to the protruding end portions in the height direction.

6 . The battery pack of claim 4 , wherein a diameter of a first trajectory defined by the side surfaces of the multiple protrusions in contact with the protruding end portions is greater than a diameter of a second trajectory defined by the side surfaces of the multiple protrusions in contact with the rim portion, and the diameters of the first and second trajectories are greater than a diameter of the first battery cell.

7 . The battery pack of claim 1 , wherein the multiple battery cells comprise six satellite battery cells around the first battery cell in a direction of the outer circumference of the first battery cell,

wherein valleys are provided between every two neighboring satellite battery cells and the first battery cell in the direction of the outer circumference of the first battery cell,

wherein a total number of six valleys are in the direction of the outer circumference of the first battery cell, and

wherein the multiple protrusions comprise a first protrusion, a second protrusion, and a third protrusion provided in valleys at alternate positions along the rim portion around the outer circumference of the first battery cell.

8 . The battery pack of claim 7 , further comprising supports having a round shape and concavely recessed toward an outer circumferential surface of the first battery cell from valleys from among the valleys that are at three alternate positions at which the first protrusion, the second protrusion, and the third protrusion are not formed along the rim portion around the first battery cell, and the multiple protrusions and the supports being alternately arranged on the valleys at alternate positions along the rim portion around the first battery cell.

9 . The battery pack of claim 8 , wherein the rim portion comprises a narrow portion having a narrow width and concavely recessed between a protrusion from among the first protrusion, the second protrusion, and the third protrusion and a support from among the supports along the rim portion around the first battery cell.

10 . The battery pack of claim 9 , wherein the narrow portion comprises multiple narrow portions at six positions along the rim portion around the first battery cell.

11 . The battery pack of claim 9 , wherein the narrow portion comprises a contact protrusion protruding toward the outer circumference of the first battery cell.

12 . The battery pack of claim 11 , wherein the contact protrusion protrudes toward the outer circumferential surface of the first battery cell to form an interference fit with the outer circumferential surface of the first battery cell.

13 . The battery pack of claim 11 , wherein the narrow portion comprises multiple narrow portions, and

wherein the contact protrusion comprises multiple contact protrusions protruding from the multiple narrow portions at six symmetrical positions along the rim portion around the first battery cell.

14 . The battery pack of claim 7 , wherein the cell holder comprises multiple rim portions including the rim portion around the outer circumference of the first battery cell, and

wherein the multiple rim portions are around the first battery cell and two neighboring satellite battery cells in the direction of the outer circumference of the first battery cell and directions of outer circumferences of the two neighboring satellite battery cells, respectively, and diverge at the divergence point in each of the valleys.

15 . The battery pack of claim 14 , wherein the multiple rim portions diverge in an angular form from the divergence point in three directions.

16 . The battery pack of claim 14 , wherein a curved surface is provided at six divergence points along the outer circumference of the first battery cell, the curved surface facing the outer circumference of the first battery cell through the multiple protrusions and supports alternately provided at alternate positions.

17 . The battery pack of claim 16 , wherein a side surface of a protrusion from among the multiple protrusions and an end portion of the support from among the supports facing the outer circumference of the first battery cell provide curved surfaces having a concave shape facing the outer circumference of the first battery cell.

18 . The battery pack of claim 17 , wherein the rim portion comprises a narrow portion having a narrow width and concavely recessed between the protrusion and the support along the rim portion around the first battery cell.

19 . The battery pack of claim 18 , wherein the narrow portion is consecutively connected between the protrusion and the support and provides a curved surface having a concave shape facing the outer circumference of the first battery cell.

20 . The battery pack of claim 1 , wherein the cell holder comprises multiple rim portions including the rim portion around the outer circumference of the first battery cell, the multiple rim portions being connected to one another to surround the multiple battery cells so as to form a main surface of the cell holder,

wherein the lower end of the first battery cell protrudes by a fixing depth from the main surface of the cell holder in the direction opposite the height direction, and

wherein the first battery cell is assembled on the cell holder from the lower end of the first battery cell to an upper end thereof in the height direction.

21 . The battery pack of claim 1 , wherein the divergence point is separated from the adjacent protrusions.

22 . A battery pack comprising:

multiple battery cells; and

a cell holder assembled with the multiple battery cells, the cell holder comprising:

a rim portion around an outer circumference of a first battery cell from among the multiple battery cells; and

multiple protrusions at positions along the rim portion and protruding from the rim portion in a height direction,

wherein side surfaces of the multiple protrusions facing the outer circumference of the first battery cell have a gradient in the height direction,

wherein the first battery cell comprises first and second electrodes at an upper end of the first battery cell, and

wherein a lower end of the first battery cell protrudes by a depth from a lowermost surface of the rim portion in a direction opposite the height direction.