Battery pack

Abstract

To provide a battery pack which can prevent removal of a battery stack from a case member while ensuring the battery stack to be easily housed into the case member.SOLUTION: In a battery pack 1, a battery stack 11 is housed inside a battery case 12 in such a manner that an outer surface 71 of an end plate 22 comes into contact with a wall part 52 of the battery case 12. On a cross section in a lamination direction of battery cells 31 in the battery pack 1, a battery laminate 21 is bent so as to protrude downward, and the wall part 52 of the battery case 12 is formed so as to extend in parallel to the vertical direction.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to a battery pack.

Background Art

[0002] As a conventional technique related to a battery pack, Patent Document 1 discloses a battery pack that attempts to prevent a battery stack from detaching from a battery case by forming the wall portion (side wall) of the battery case in an under shape that widens outward as it goes downward.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] As shown in FIG. 7, in the battery pack disclosed in Patent Document 1, the wall portion 152 of the battery case 112 has an under shape. Therefore, when storing the battery stack 111 in the battery case 112, it is necessary to increase the compression amount δ0 of the battery stack 111. Therefore, when the battery stack 111 is difficult to compress (the spring constant of the battery stack 111 is high), there is a possibility that the battery stack 111 cannot be stored in the battery case 112.

[0005] Therefore, the present disclosure has been made to solve the above problems, and an object thereof is to provide a battery pack that can suppress the battery stack from detaching from the case member while ensuring ease of storing the battery stack in the case member.

Means for Solving the Problems

[0006] One aspect of the present disclosure made to solve the above problems is a battery pack having a battery stack and a box-shaped case member that houses the battery stack. The battery stack includes a battery laminate composed of a plurality of battery cells to be stacked and spacers disposed between adjacent battery cells, and a pair of end plates disposed so as to contact both ends of the battery laminate in the stacking direction of the battery cells. The case member includes a bottom portion located below the battery stack and a wall portion extending upward from an outer peripheral edge portion of the bottom portion. The battery stack is housed in the case member such that a surface of the end plate opposite to the battery laminate contacts the wall portion of the case member. In a cross-section of the battery pack in the stacking direction of the battery cells, the battery laminate is curved convexly downward, and the wall portion of the case member is formed to extend parallel to the vertical direction.

[0007] According to this aspect, since the battery laminate is curved convexly downward, it is difficult for the battery laminate to move up and down when the battery pack is subjected to vibration or impact. Therefore, it is possible to suppress the battery stack including the battery laminate from being displaced vertically. Accordingly, it is possible to suppress the battery stack from detaching from the case member.

[0008] Further, the wall portion of the case member is formed to extend parallel to the vertical direction, that is, it is not formed in an under shape as in Patent Document 1. Therefore, when the battery stack is compressed and housed in the case member, the amount of compression of the battery stack can be reduced. Accordingly, even when the battery stack is difficult to compress (the spring constant of the battery stack is high), the battery stack can be housed in the case member. Therefore, it is possible to ensure the ease of housing the battery stack in the case member.

[0009] In the above aspect, the battery cell is formed in a rectangular or substantially rectangular shape, the end plate is formed such that the surface of the end plate in contact with the battery stack inclines inwardly of the case member from the lower side toward the upper side, and the surface of the end plate in contact with the wall portion of the case member is formed parallel to the vertical direction. It is preferable that the spacer is formed such that the thickness of the spacer in the stacking direction of the battery cells gradually decreases from the lower end portion to the upper end portion of the spacer.

[0010] According to this aspect, by using a spacer whose thickness gradually decreases from the lower end portion to the upper end portion and an end plate whose surface in contact with the battery stack inclines inwardly of the case member from the lower side toward the upper side, the battery stack can be easily curved convexly downward.

[0011] In the above aspect, the battery cell is formed in a rectangular or substantially rectangular shape, and the end plate is formed in a rectangular or substantially rectangular shape such that the surface of the end plate in contact with the battery stack and the surface of the end plate in contact with the wall portion of the case member are formed parallel to the vertical direction. As the spacer, a first spacer and a second spacer are used. The first spacer is formed such that the thickness of the first spacer in the stacking direction of the battery cells gradually increases from the lower end portion to the upper end portion of the first spacer, and the second spacer is formed such that the thickness of the second spacer in the stacking direction of the battery cells gradually decreases from the lower end portion to the upper end portion of the second spacer. For the plurality of spacers arranged along the stacking direction of the battery cells, the first spacer is arranged at least at both ends in the arrangement direction of the spacers, and the second spacer is arranged inside the case member with respect to the first spacer. This is preferable.

[0012] According to this aspect, while making the shape of the end plate a simple shape such as a rectangle or a substantially rectangular shape, by using two types of spacers (that is, a first spacer and a second spacer), the battery stack can be easily curved convex downward.

[0013] Another aspect of the present disclosure made to solve the above problems is a battery pack having a battery stack and a box-shaped case member that houses the battery stack. The battery stack includes a battery laminate composed of a plurality of stacked battery cells and a spacer disposed between adjacent battery cells, and a pair of end plates disposed so as to contact both ends in the stacking direction of the battery cells in the battery laminate. The case member includes a bottom portion located below the battery stack and a wall portion extending upward from an outer peripheral edge portion of the bottom portion. The battery stack is housed in the case member such that a surface of the end plate opposite to the battery laminate contacts the wall portion of the case member. In a cross-section in the stacking direction of the battery cells in the battery pack, the battery laminate is curved convex downward, and the wall portion of the case member is formed to be inclined outward of the case member as it extends from the lower side to the upper side.

[0014] According to this aspect, since the battery laminate is curved convex downward, when the battery pack is subjected to vibration or impact, it is difficult for the battery laminate to move up and down. Therefore, it is possible to suppress the battery stack including the battery laminate from being displaced up and down. Accordingly, it is possible to suppress the battery stack from detaching from the case member.

[0015] Further, the wall portion of the case member is formed to be inclined outward of the case member as it extends from the lower side to the upper side, that is, it is not formed in an under shape as in Patent Document 1. Therefore, when the battery stack is compressed and housed in the case member, the amount of compression of the battery stack can be reduced. Accordingly, even when the battery stack is difficult to compress, the battery stack can be housed in the case member. Therefore, it is possible to ensure the ease of housing the battery stack in the case member.

[0016] Further, since the wall portion of the case member is formed to incline outward of the case member as it goes from the lower side to the upper side, and the draft angle during the molding of the case member is ensured, the productivity of the case member can be improved.

[0017] In the above aspect, the battery cell is formed in a rectangular or substantially rectangular shape, and the end plate is formed such that the surface of the end plate in contact with the battery laminate inclines inward of the case member as it goes from the lower side to the upper side, and the surface of the end plate in contact with the wall portion of the case member inclines outward of the case member as it goes from the lower side to the upper side. The spacer is preferably formed such that the thickness of the spacer in the stacking direction of the battery cells gradually decreases as it goes from the lower end portion to the upper end portion of the spacer.

[0018] According to this aspect, by using a spacer whose thickness gradually decreases as it goes from the lower end portion to the upper end portion, and an end plate whose surface in contact with the battery laminate inclines inward of the case member as it goes from the lower side to the upper side, the battery laminate can be easily curved convexly downward.

[0019] In the above aspect, the battery cell is formed in a rectangular or substantially rectangular shape, and the end plate is formed such that the surface of the end plate that contacts the battery stack is parallel to the vertical direction, and the surface of the end plate that contacts the wall portion of the case member is formed to be inclined outward of the case member as it goes from the lower side to the upper side. As the spacer, a first spacer and a second spacer are used. The first spacer is formed such that the thickness of the first spacer in the stacking direction of the battery cells gradually increases from the lower end portion to the upper end portion of the first spacer. The second spacer is formed such that the thickness of the second spacer in the stacking direction of the battery cells gradually decreases from the lower end portion to the upper end portion of the second spacer. For the plurality of spacers arranged along the stacking direction of the battery cells, the first spacer is arranged at at least both ends in the arrangement direction of the spacers, and the second spacer is arranged inside the case member with respect to the first spacer, which is preferable.

[0020] According to this aspect, while forming the surface of the end plate that contacts the wall portion of the case member in accordance with the inclination of the wall portion of the case member, it is possible to easily curve the battery stack convex downward by using two types of spacers (that is, the first spacer and the second spacer).

[0021] In the above aspect, it is preferable that the battery stack is housed in the case member in a state compressed in the stacking direction of the battery cells.

[0022] According to this aspect, it is possible to more reliably suppress the battery stack from detaching from the case member.

[0023] In the above aspect, it is preferable that the upper surface of the bottom portion of the case member is curved convex downward.

[0024] According to this aspect, it is possible to stably maintain the state in which the battery stack is curved convex downward.

Advantages of the Invention

[0025] According to the battery pack of the present disclosure, it is possible to suppress the battery stack from detaching from the case member while ensuring ease of accommodation of the battery stack within the case member of the battery stack.

Brief Description of the Drawings

[0026]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Modes for Carrying Out the Invention

[0027] Hereinafter, embodiments of the battery pack of the present disclosure will be described.

[0028] <Regarding the overall outline of the battery pack> First, the overall outline of the battery pack 1 of the present embodiment will be described.

[0029] As shown in FIG. 1, the battery pack 1 of the present embodiment includes a battery stack 11 and a box-shaped battery case 12 that houses the battery stack 11. Note that the battery case 12 is an example of the "case member" of the present disclosure.

[0030] The battery stack 11 includes a battery laminate 21 and a pair of end plates 22.

[0031] The battery laminate 21 is composed of a plurality of rectangular battery cells 31 stacked and arranged in the X direction shown in FIG. 1, and spacers 32 arranged between adjacent battery cells 31. In this embodiment, two battery stacks 11 are arranged side by side in the Y direction shown in FIG. 1.

[0032] The battery cell 31 is provided with two electrode terminals 42 on its upper surface 41. One of the two electrode terminals 42 is a positive electrode terminal and the other is a negative electrode terminal.

[0033] A pair of end plates 22 are arranged so as to be in contact with both ends of the battery cells 31 in the stacking direction of the battery laminate 21.

[0034] The battery case 12 is a box-shaped member with an open upper part, and includes a bottom part 51 and a wall part 52.

[0035] The bottom part 51 is located below the battery stack 11 (below in the Z direction). Also, the wall part 52 is located on both sides of the battery stack 11 (both sides in the X direction and the Y direction). And the wall part 52 is formed so as to extend upward in the height direction (Z direction) of the battery pack 1 from the outer peripheral edge part 61 (see FIG. 2 etc.) of the bottom part 51.

[0036] Such a battery case 12 has two storage spaces for the battery stack 11 formed by being surrounded by the bottom part 51 and the wall part 52. And the battery stack 11 is stored in each of these two storage spaces.

[0037] <Examples of the battery stack and the battery case> Next, examples of the battery stack 11 and the battery case 12 will be described.

[0038] (First Embodiment) First, the first embodiment will be described.

[0039] As shown in FIG. 2, the battery stack 11 is housed in the battery case 12 such that the outer surface 71 (i.e., the surface opposite to the battery laminate 21) of its end plate 22 contacts the wall portion 52 of the battery case 12. Note that the battery stack 11 is housed in the battery case 12 in a state compressed in the stacking direction of the battery cells 31.

[0040] And in this embodiment, in the cross section shown in FIG. 2, that is, in the cross section in the stacking direction of the battery cells 31 in the battery pack 1 (cross-sectional view taken along line A-A in FIG. 1), the battery laminate 21 is curved convex downward. Also, the upper surface 81 of the bottom portion 51 of the battery case 12 is also curved convex downward.

[0041] Also, the wall portion 52 of the battery case 12 is formed to extend parallel in the vertical direction (Z direction).

[0042] Also, the inner surface 72 (i.e., the surface that contacts the battery laminate 21) of the end plate 22 is formed to incline inward of the battery case 12 as it goes from the lower side to the upper side. On the other hand, the outer surface 71 of the end plate 22 is formed parallel in the vertical direction. Note that the battery cell 31 is formed in a rectangular or substantially rectangular shape.

[0043] The spacer 32 is formed such that the thickness T of the spacer 32 in the stacking direction of the battery cells 31 gradually decreases as it goes from the lower end portion 91 to the upper end portion 92. Note that the lower end surface 73 of the end plate 22 and the lower end portion 91 of the spacer 32 are in contact with the upper surface 81 of the bottom portion 51 of the battery case 12.

[0044] Thus, in this embodiment, since the battery laminate 21 is curved convex downward, when the battery pack 1 is subjected to vibration or impact, it is difficult for the battery laminate 21 to move up and down. Therefore, it is possible to suppress the battery stack 11 including the battery laminate 21 from being displaced vertically. Accordingly, it is possible to suppress the battery stack 11 from detaching from the battery case 12.

[0045] In addition, the wall portion 52 of the battery case 12 is formed to extend parallel to the vertical direction, that is, it is not formed in an under shape like that of Patent Document 1. Therefore, as shown in FIG. 3, when the battery stack 11 is compressed (pressurized) and housed in the battery case 12, the compression amount δ1 (<δ0) of the battery stack 11 can be made small. Accordingly, even when the battery stack 11 is difficult to compress (the spring constant of the battery stack 11 is high), the battery stack 11 can be housed in the battery case 12. Thus, the ease of housing the battery stack 11 in the battery case 12 can be ensured.

[0046] In addition, the wall portion 52 of the battery case 12 may be formed to extend parallel to the vertical direction, and it is not necessary to form it in a complicated under shape like that of Patent Document 1. Therefore, the battery case 12 can be manufactured at low cost.

[0047] Also, by using the spacer 32 whose thickness T gradually decreases from the lower end portion 91 toward the upper end portion 92 and the end plate 22 whose inner surface 72 inclines toward the inside of the battery case 12 from the lower side toward the upper side, the battery laminate 21 can be easily curved convexly downward.

[0048] (Second Embodiment) Next, the second embodiment will be described, mainly focusing on the differences from the first embodiment.

[0049] In this embodiment, in the cross section shown in FIG. 4, that is, in the cross section in the stacking direction of the battery cells 31 in the battery pack 1 (cross-sectional view taken along line A-A in FIG. 1), similarly to the first embodiment, the battery laminate 21 is curved convexly downward.

[0050] On the other hand, as a difference from the first embodiment, the end plate 22 is formed in a rectangular or substantially rectangular shape such that the inner surface 72 and the outer surface 71 of the end plate 22 are formed parallel to the vertical direction.

[0051] In addition, as the spacer 32, a first spacer 32A and a second spacer 32B are used. Specifically, the first spacer 32A is formed such that the thickness T of the battery cell 31 in the stacking direction of the first spacer 32A gradually increases from the lower end portion 91 toward the upper end portion 92. Further, the second spacer 32B is formed such that the thickness T of the battery cell 31 in the stacking direction of the second spacer 32B gradually decreases from the lower end portion 91 toward the upper end portion 92.

[0052] Then, with respect to the plurality of spacers 32 arranged along the stacking direction of the battery cells 31 in this manner, the first spacers 32A are arranged at least at both ends in the arrangement direction of the spacers 32, and the second spacers 32B are arranged inside the battery case 12 with respect to the first spacers 32A. In the example shown in FIG. 4, specifically, a total of four first spacers 32A are arranged at both end portions in the arrangement direction of the spacers 32 and at one inner portion (inside the battery case 12). Further, a total of four second spacers 32B are arranged at a portion inside the battery case 12 with respect to these first spacers 32A.

[0053] Thus, in this embodiment, while the shape of the end plate 22 is made into a simple shape such as a rectangle or a substantially rectangle, by using two types of spacers 32 (that is, the first spacer 32A and the second spacer 32B), the battery stack 21 can be easily curved convex downward.

[0054] (Third Embodiment) Next, the third embodiment will be described, mainly focusing on the differences from the first and second embodiments.

[0055] In this embodiment, in the cross section shown in FIG. 5, that is, in the cross section in the stacking direction of the battery cells 31 in the battery pack 1 (cross-sectional view taken along line A-A in FIG. 1), similar to the first and second embodiments, the battery stack 21 is curved convex downward.

[0056] On the other hand, as a difference from the first and second embodiments, the wall portion 52 of the battery case 12 is formed so as to incline outward of the battery case 12 as it goes from the lower side to the upper side. Here, the inclination angle θ of the wall portion 52 is, for example, greater than 0° and within 10°. The inclination angle θ is the angle at which the wall portion 52 inclines outward of the battery case 12 with respect to the vertical direction, and serves as the draft angle during the molding of the battery case 12, as shown in FIG. 5.

[0057] Further, corresponding to the wall portion 52 of the battery case 12 that inclines in this way, the outer surface 71 of the end plate 22 is formed so as to incline outward of the battery case 12 as it goes from the lower side to the upper side.

[0058] Note that the inner surface 72 of the end plate 22 is formed so as to incline inward of the battery case 12 as it goes from the lower side to the upper side. Also, the spacer 32 is formed such that the thickness T of the spacer 32 in the stacking direction of the battery cells 31 gradually decreases as it goes from the lower end portion 91 to the upper end portion 92.

[0059] In this way, in this embodiment, since the battery stack 21 is curved convexly downward, it is difficult for the battery stack 21 to move up and down when the battery pack 1 receives vibration or impact. Therefore, it is possible to suppress the vertical displacement of the battery stack 11 including the battery stack 21. Accordingly, it is possible to suppress the battery stack 11 from detaching from the battery case 12.

[0060] Further, the wall portion 52 of the battery case 12 is formed so as to incline outward of the battery case 12 as it goes from the lower side to the upper side, that is, it is not formed in an under shape as in Patent Document 1. Therefore, when the battery stack 11 is compressed and housed in the battery case 12, the amount of compression of the battery stack 11 can be reduced. Accordingly, even when the battery stack 11 is difficult to compress, the battery stack 11 can be housed in the battery case 12. Therefore, it is possible to ensure the ease of housing the battery stack 11 in the battery case 12.

[0061] In addition, the wall portion 52 of the battery case 12 is formed so as to incline outwardly of the battery case 12 from the lower side toward the upper side, and since the draft angle during the molding of the battery case 12 is ensured, the productivity of the battery case 12 can be improved.

[0062] Further, by using a spacer 32 whose thickness T gradually decreases from the lower end portion 91 toward the upper end portion 92 and an end plate 22 whose inner surface 72 inclines inwardly of the battery case 12 from the lower side toward the upper side, the battery laminate 21 can be easily curved convexly downward.

[0063] (Fourth Embodiment) Next, the fourth embodiment will be described, mainly focusing on the differences from the first, second, and third embodiments.

[0064] In this embodiment, as shown in FIG. 6, the outer surface 71 of the end plate 22 is formed so as to incline outwardly of the battery case 12 from the lower side toward the upper side in correspondence with the inclined wall portion 52 of the battery case 12. Also, the inner surface 72 of the end plate 22 is formed parallel to the vertical direction. Furthermore, as the spacer 32, a first spacer 32A and a second spacer 32B are used.

[0065] Thus, in this embodiment, while forming the outer surface 71 of the end plate 22 in accordance with the inclination of the wall portion 52 of the battery case 12, by using two types of spacers 32 (that is, the first spacer 32A and the second spacer 32B), the battery laminate 21 can be easily curved convexly downward.

[0066] It should be noted that the above-described embodiments are merely illustrative and do not limit the present disclosure in any way. Needless to say, various improvements and modifications can be made without departing from the gist thereof.

[0067] For example, the lower surface 82 of the bottom portion 51 of the battery case 12 (see FIG. 2 etc.) may be curved convexly downward, or from a manufacturing perspective, it may not be curved convexly downward (for example, it may be a flat surface). Also, the lower end portion 91 of the spacer 32 and the upper surface 81 of the bottom portion 51 of the battery case 12 may not be in contact with each other.

Explanation of Reference Numerals

[0068] 1 Battery pack 11 Battery stack 12 Battery case 21 Battery laminate 22 End plate 31 Battery cell 32 Spacer 32A First spacer 32B Second spacer 51 Bottom portion 52 Wall portion 61 Outer peripheral edge portion 71 Outer surface 72 Inner surface 81 Upper surface 91 Lower end portion 92 Upper end portion T Thickness δ0, δ1 Compression amount θ Inclination angle

Claims

1. A battery stack, A box-shaped case member for housing the battery stack, In a battery pack having: The battery stack is A battery laminate composed of a plurality of stacked battery cells and a spacer disposed between adjacent battery cells, A pair of end plates disposed so as to contact both ends in the stacking direction of the battery cells in the battery laminate, Comprising The case member is A bottom portion located below the battery stack, A wall portion extending upward from the outer peripheral edge of the bottom portion, Comprising The battery stack is housed in the case member such that the surface of the end plate opposite to the battery laminate contacts the wall portion of the case member, In a cross-section in the stacking direction of the battery cells in the battery pack, The battery laminate is curved convexly downward, The wall portion of the case member is formed to extend parallel to the vertical direction, A battery pack characterized by the above.

2. In the battery pack according to claim 1, The battery cell is formed in a rectangular or substantially rectangular shape, The end plate is The surface of the end plate that contacts the battery laminate is formed to be inclined inward of the case member as it goes from the lower side to the upper side, And The surface of the end plate that contacts the wall portion of the case member is formed parallel to the vertical direction, The spacer is formed such that the thickness of the spacer in the stacking direction of the battery cells gradually decreases from the lower end of the spacer to the upper end of the spacer, A battery pack characterized by the above.

3. In the battery pack according to claim 1, The battery cell is formed in a rectangular or substantially rectangular shape, The end plate is The surface of the end plate that contacts the battery laminate and the surface that contacts the wall portion of the case member are formed parallel to the vertical direction, and is formed in a rectangular or substantially rectangular shape, As the spacer, a first spacer and a second spacer are used, The first spacer is formed such that the thickness of the first spacer in the stacking direction of the battery cells gradually increases from the lower end of the first spacer to the upper end of the first spacer, The second spacer is formed such that the thickness of the second spacer in the stacking direction of the battery cells gradually decreases from the lower end portion to the upper end portion of the second spacer. Regarding the plurality of spacers arranged along the stacking direction of the battery cells, the first spacers are arranged at least at both ends in the arrangement direction of the spacers. the second spacer is arranged inside the case member with respect to the first spacer. A battery pack characterized by the above.

4. A battery stack, a box-shaped case member for housing the battery stack, In a battery pack having: the battery stack is a battery laminate composed of a plurality of stacked battery cells and spacers arranged between adjacent battery cells, a pair of end plates arranged so as to be in contact with both ends in the stacking direction of the battery cells in the battery laminate, and is provided with the case member is a bottom portion located below the battery stack, a wall portion extending upward from the outer peripheral edge portion of the bottom portion, and is provided with the battery stack is housed in the case member such that the surface of the end plate opposite to the battery laminate is in contact with the wall portion of the case member, In a cross-section in the stacking direction of the battery cells in the battery pack, the battery laminate is curved convexly downward, the wall portion of the case member is formed so as to incline outward of the case member from the lower side to the upper side. A battery pack characterized by the above.

5. In the battery pack according to claim 4, the battery cells are formed in a rectangular or substantially rectangular shape, the end plate is the surface of the end plate in contact with the battery laminate is formed so as to incline inward of the case member from the lower side to the upper side, and the surface of the end plate in contact with the wall portion of the case member is formed so as to incline outward of the case member from the lower side to the upper side, the spacer is formed such that the thickness of the spacer in the stacking direction of the battery cells gradually decreases from the lower end portion to the upper end portion of the spacer. A battery pack characterized by the above.

6. In the battery pack according to claim 4, the battery cells are formed in a rectangular or substantially rectangular shape, the end plate is The surface of the end plate that contacts the battery stack is formed parallel to the vertical direction. And The surface of the end plate that contacts the wall portion of the case member is formed to be inclined outward of the case member as it goes from the lower side to the upper side. As the spacer, a first spacer and a second spacer are used. The first spacer is formed such that the thickness of the first spacer in the stacking direction of the battery cells gradually increases from the lower end portion to the upper end portion of the first spacer. The second spacer is formed such that the thickness of the second spacer in the stacking direction of the battery cells gradually decreases from the lower end portion to the upper end portion of the second spacer. Regarding the plurality of spacers arranged along the stacking direction of the battery cells, The first spacer is arranged at at least both ends in the arrangement direction of the spacers. The second spacer is arranged inside the case member with respect to the first spacer. A battery pack characterized by the above.

7. In the battery pack according to any one of Claims 1 to 6, The battery stack is housed in the case member in a state compressed in the stacking direction of the battery cells. A battery pack characterized by the above.

8. In the battery pack according to any one of Claims 1 to 7, The upper surface of the bottom portion of the case member is curved convex downward. A battery pack characterized by the above.

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