Battery pack

Abstract

To solve a problem in which, in conventional battery packs, the load on the battery pack, in which multiple battery stacks are housed in a single stack case, cannot be reduced.SOLUTION: A battery pack according to the present invention includes a first battery stack Fr and a second battery stack Rr in which a plurality of secondary batteries are stacked, and a stack case that stores the first battery stack Fr and the second battery stack Rr in parallel, and the first battery stack Fr and the second battery stack Rr are stored in the stack case so as to have different Young's moduli when stored in the stack case.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a battery pack that constitutes a battery stack in which a plurality of secondary batteries are stacked, and houses at least two battery stacks in one stack case.

Background Art

[0002] In a battery pack, a battery stack in which a plurality of secondary batteries are stacked is housed so as to be fixed in a stack case to prevent deformation of the battery stack. Therefore, techniques related to a method of housing a battery stack in a stack case are disclosed in Patent Documents 1-4.

[0003] The battery pack described in Patent Document 1 is a battery pack in which a battery module is housed in a housing. The battery module includes an array including a plurality of battery cells arranged along one direction, a pair of fixing members respectively arranged at the array ends of the array and fixed to the wall surface of the housing, and a fastening member that applies a restraint load to the array in the arrangement direction of the battery cells. Each of the plurality of battery cells has a first side surface facing the wall surface, the plurality of battery cells are arranged so as to be convex toward the wall surface, and the angle formed by the first side surface and the wall surface is larger for the battery cells arranged closer to the array end with respect to the central portion of the array.

[0004] In the method for manufacturing a battery described in Patent Document 2, the battery includes a battery module having a plurality of single cells stacked in one direction, a bottom portion in contact with the battery module, and a pair of side wall portions rising from the bottom portion and facing each other in the stacking direction of the single cells. The battery further includes a battery case for housing the battery module, and a pair of wedge members inserted between each of the pair of side wall portions and the battery module. The wedge member has a contact surface that contacts the battery module and is inclined such that the distance from the side wall portion increases as the wedge member moves away from the bottom portion. The method for manufacturing the battery includes a step of stacking a plurality of the single cells and arranging a pair of the wedge members on both sides of the stacked plurality of the single cells, and a step of arranging the battery module and the pair of the wedge members in the battery case while applying a compressive force from both sides of the pair of the wedge members so that the battery module is deformed convexly toward the bottom portion.

[0005] A battery pack described in Patent Document 3 includes a stack in which a plurality of battery cells and a plurality of resin frames are alternately stacked in an arrangement direction, and a lower case that houses the stack in a state of being compressed in the arrangement direction. In the battery pack, the resin frame has a plurality of comb teeth extending in the arrangement direction on at least one of the surfaces facing the battery cells. The plurality of comb teeth include a plurality of upper comb teeth located above the central portion of the battery cell in the height direction. The plurality of upper comb teeth are configured such that the comb tooth height in the arrangement direction decreases as the upper comb teeth are located lower in the height direction.

[0006] The battery pack described in Patent Document 4 is a battery pack having a battery stack and a box-shaped case member for housing the battery stack. The battery stack includes a battery laminate composed of a plurality of stacked battery cells 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 the outer peripheral edge of the bottom portion. 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 of the battery cells in the stacking direction of the battery pack, the battery laminate is curved convexly downward, and the wall portion of the case member is formed to extend parallel to the vertical direction.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0008] However, when a battery stack is housed in a stack case, a problem occurs in that the load applied to the stack case increases when the vibration applied to the battery stack coincides with the resonance frequency of the battery stack. In particular, when a plurality of battery stacks are housed in the stack case, the load applied to the stack case due to resonance becomes several times the number of battery stacks to be housed, which becomes an even greater problem. In response to such a problem, for example, in Patent Document 2, a proposal has been made to suppress the resonance phenomenon of the assembled battery, but no solution has been presented for the problems that occur when the number of battery stacks housed in one stack case increases. That is, even by referring to Patent Document 2, the problem of the increased load on the stack case for housing a plurality of battery stacks cannot be solved. Also, even by referring to Patent Documents 1, 3, and 4, no means for dealing with the magnitude of the load on the stack case for housing a plurality of battery stacks is disclosed.

[0009] The present invention has been made in view of the above circumstances, and an object thereof is to reduce the load on a battery pack in which a plurality of battery stacks are housed in one stack case.

Means for Solving the Problem

[0010] One aspect of the battery pack according to the present invention includes a first battery stack and a second battery stack in which a plurality of secondary batteries are stacked, a stack case for housing the first battery stack and the second battery stack in parallel, and the first battery stack and the second battery stack are housed in the stack case so as to have different Young's moduli in a state of being housed in the stack case.

[0011] Another aspect of the battery pack according to the present invention includes a first battery stack and a second battery stack in which a plurality of secondary batteries are stacked, a stack case for housing the first battery stack and the second battery stack in parallel, and the first battery stack and the second battery stack are housed in the stack case so as to have different natural vibration frequencies in a state of being housed in the stack case. [Effect of the Invention]

[0012] According to the secondary battery of the present invention, the load on the battery pack in which a plurality of battery stacks are housed in one stack case can be reduced. [Brief Description of the Drawings]

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

[0014] For the sake of clarity of explanation, the following descriptions and drawings are appropriately omitted and simplified. In each drawing, the same elements are denoted by the same reference numerals, and redundant explanations are omitted as necessary.

[0015] Embodiment 1 FIG. 1 shows a schematic view of a battery pack 1 according to Embodiment 1. The battery pack 1 according to Embodiment 1 is mounted on, for example, an automobile as a power source. The automobile vibrates greatly during operation. Therefore, the battery pack 1 is fixed to the chassis or the like of the automobile using a fixing member so as to withstand this vibration. Further, the stack case is designed to ensure rigidity that can withstand the load caused by the shaking of the battery stack to be housed. Also, the fixing member is required to have high rigidity in order to cope with the shaking of the battery pack 1. In particular, the larger the battery pack 1 becomes, the higher the rigidity required for the fixing member. On the other hand, in order to simplify the stack case and the fixing member and reduce the weight and volume, it is important to suppress the shaking of the battery pack 1 itself.

[0016] As shown in FIG. 1, the battery pack 1 according to Embodiment 1 includes a stack case 10, a first battery stack Fr, and a second battery stack Rr. In FIG. 1, for the sake of clarity of the configuration, the lid provided on the stack case 10 to cover the battery stack is not shown. Also, in FIG. 1, only the state in which the first battery stack Fr and the second battery stack Rr are housed in the stack case 10 is shown in a simplified manner, and actually, more configurations are included.

[0017] The first battery stack Fr and the second battery stack Rr are each formed by stacking a plurality of secondary batteries (hereinafter referred to as battery cells). The first battery stack Fr and the second battery stack Rr are housed in parallel in the stack case 10. Here, the first battery stack Fr and the second battery stack Rr each have a natural frequency in a state of being housed in the stack case 10.

[0018] Therefore, a diagram for explaining the relationship between the change in the amount of cell floating of the battery cells in the battery stack according to Embodiment 1 and the natural frequency of the battery stack is shown in FIG. 2. In the graph shown in FIG. 2, the horizontal axis represents the position of the battery cells in the battery stack, and the vertical axis represents the amount of cell floating from the reference position (the position where the amount of cell floating is zero) for each battery cell. In the graph shown in FIG. 2, when a undulation that draws an arc convex upward occurs in the battery stack, a change occurs in the natural frequency of the battery stack. Also, a difference occurs in the natural frequency of the battery stack depending on the shape of the undulation.

[0019] Such a difference in natural frequency occurs due to a difference in the Young's modulus of the battery stack. Therefore, a table for explaining the difference in the Young's modulus of the battery stack according to Embodiment 1 and the difference in the natural frequency of the battery stack is shown in FIG. 3. The table shown in FIG. 3 is based on the condition that the first battery stack Fr and the second battery stack Rr are composed of the same number of battery cells, and the Young's moduli of the first battery stack Fr and the second battery stack Rr are unified to a reference value (Ref). Under comparison condition A where the Young's modulus of the first battery stack Fr is set to 1 / 10 times that of the second battery stack Rr, and comparison condition B where the Young's modulus of the first battery stack Fr is set to 10 times that of the second battery stack Rr, the natural frequency of the first battery stack Fr is verified.

[0020] As shown in FIG. 3, by changing the Young's modulus, the natural frequency changes by about +0.4 Hz for the first battery stack Fr under comparison condition A and by about +0.5 Hz for the first battery stack Fr under comparison condition B with respect to the reference condition. That is, it can be seen that the natural frequencies of the two battery stacks can be shifted by increasing or decreasing the Young's modulus of the first battery stack Fr housed in one stack case 10 with respect to the second battery stack Rr.

[0021] Methods for changing the Young's modulus include, for example, as described in FIG. 2, changing the amount of undulation or the undulation shape of the battery stack in a state where the battery stack is housed in the stack case 10, changing the restraint load applied to the battery stack, devising the shape of the spacers included in the battery stack, and the like. Note that methods for changing the restraint load applied to the battery stack include changing the housing length of the battery stack when housed in the stack case 10 between the first battery stack Fr and the second battery stack Rr, changing the thickness of the spacers included in the battery stack between the first battery stack Fr and the second battery stack Rr, and the like. Further, by changing the shape of the end plates provided at both ends of the battery stack between the first battery stack Fr and the second battery stack Rr, or by making at least some of the spacers included in one of the first battery stack Fr and the second battery stack Rr into a wedge shape, it is conceivable to change the amount of undulation or the undulation shape of the battery stack.

[0022] Here, a method for setting the amount of undulation or the undulation shape of the battery stack using the difference in the shape of the end plates will be described. In the following description, an example of changing one of a pair of end plates provided at both ends of the battery stack in the stacking direction of the batteries will be described, but a structure in which the battery stack is bent with respect to both of the pair of end plates may be adopted. Further, in FIGS. 4 to 6 described below, an example in which the battery cells 20 and the spacers 21 are alternately stacked as the battery stack is shown. Although it is possible to bend the battery stack by changing a part of the spacer 21 into a wedge shape, in the example described in FIGS. 4 to 6, an example using a flat spacer 21 with no change in the thickness in the vertical direction will be described. Further, in the example described in FIGS. 4 to 6, the back end plate 22 provided at the end of the battery stack on the side opposite to the side pushed in by the pressing jig PS when the battery stack is housed in the stack case 10 will be of a common shape.

[0023] First, FIG. 4 shows a diagram for explaining the shape of the first end plate type combined with the battery stack according to Embodiment 1. The first end plate type EP1 shown in FIG. 4 uses a combination of a front end plate 23 and an end spacer 24. The front end plate 23 and the end spacer 24 have wall surfaces facing each other in the vertical direction (the depth direction of the stack storage area of the stack case 10) having vertical surfaces. By using such a front end plate 23 and end spacer 24, a restraining force parallel to the stacking direction is applied to the battery stack, so that the deflection of the battery stack becomes extremely small.

[0024] Subsequently, FIG. 5 shows a diagram for explaining the shape of the second end plate type combined with the battery stack according to Embodiment 1. The second end plate type EP2 shown in FIG. 5 uses a combination of a front end plate 33 and an end spacer 34. The front end plate 33 has a forwardly inclined surface such that the lower thickness in the vertical direction is thin and the upper thickness is thick. The end spacer 34 has a contact surface with an angle inclined rearward so as to be in close contact with the forwardly inclined surface of the front end plate 33. In such a combination of the front end plate 33 and the end spacer 34, since a force causing the front end plate 43 to shift upward is generated, the restraining force is weak on the upper side of the battery stack and strong on the lower side of the battery stack. Therefore, a deflection convex upward occurs in the battery stack.

[0025] Next, FIG. 6 shows a diagram for explaining the shape of a third end plate type combined with the battery stack according to Embodiment 1. The third end plate type EP3 shown in FIG. 6 uses a combination of a front end plate 43 and an end spacer 44. The front end plate 43 has a rearwardly inclined surface such that the thickness is greater on the lower side in the vertical direction and smaller on the upper side. The end spacer 44 has a contact surface with a forwardly inclined angle so as to be in close contact with the rearwardly inclined surface of the front end plate 43. In such a combination of the front end plate 43 and the end spacer 44, since a force that causes the front end plate 33 to shift downward is generated, the restraining force is strong on the upper side of the battery stack and weak on the lower side, so that the battery stack has a deflection that is convex downward.

[0026] Here, FIG. 7 shows a diagram for explaining the difference in cell floating amount due to the difference in end plates. The graph shown in FIG. 7 shows the position of the battery cells in the battery stack on the horizontal axis and the cell floating amount from the reference position (the position where the cell floating amount is zero) for each battery cell on the vertical axis. As shown in FIG. 7, when the first end plate type EP1 is adopted, the cell floating amount of the battery stack is suppressed regardless of the arrangement position of the battery cells. On the other hand, when the second end plate type EP2 is adopted, the battery stack has a convex shape on the upper side, and the floating amount of the battery cell amount is also larger than when the first end plate type EP1 is adopted. That is, when the second end plate type EP2 is adopted, the battery stack has a large undulation that is convex upward. Further, when the third end plate type EP3 is adopted, the battery stack has an undulation that is convex downward, but since the battery stack contacts the bottom surface of the stack case 10, the downward cell floating amount is limited by the distance between the bottom surface of the stack case 10 and the storage position of the battery stack.

[0027] From the above description, in the battery pack 1 according to the first embodiment, by housing the first battery stack Fr and the second battery stack Rr in the stack case so as to have different Young's moduli, the natural vibration frequencies of the two battery stacks can be shifted. As a result, even when vibrations of the same frequency as the natural vibration frequency of one of the battery stacks are applied to the battery pack 1, the two battery stacks do not resonate simultaneously, so that the stress applied to the stack case 10 can be reduced. By reducing the stress applied to the stack case 10 in this way, it becomes possible to reduce the rigidity required for the stack case 10 and lighten the stack case 10.

[0028] Also, by adopting a configuration for reducing the stress applied to the stack case 10, it becomes possible to reduce the rigidity required for the fixing member that fixes the battery pack 1 to the vehicle body and lighten the fixing member.

[0029] As described above, as a specific example for setting the natural vibration frequencies of at least two battery stacks housed in one stack case 10, the following examples can be considered. In the first form, the first battery stack Fr is housed in the stack case with a pair of first end plates provided at both ends in the stacking direction of the battery cells assembled, and the second battery stack Rr is housed in the stack case with a pair of second end plates provided at both ends in the stacking direction of the battery cells assembled, and at least one of the first end plates is set to a shape that deflects the first battery stack Fr in either the upward or downward direction with respect to the second battery stack Rr. In the second form, the first battery stack Fr and the second battery stack Rr are housed in the stack case 10 in a state where different restraint loads are applied. In the third form, a plurality of first spacers between adjacent battery cells in the stacking direction of the battery cells in the first battery stack Fr and a plurality of second spacers sandwiched between adjacent battery cells in the stacking direction of the battery cells in the second battery stack Rr are used, and at least a part of one of the plurality of first spacers and the plurality of second spacers is made to have a different shape.

[0030] Note that the present invention is not limited to the above-described embodiments, and can be appropriately modified without departing from the spirit thereof.

Description of Reference Numerals

[0031] 1 Battery pack 10 Stack case 20 Battery cell 21 Spacer 22 Rear end plate 23, 33, 43 Front end plate 24, 34, 44 End spacer PS Pressing jig Fr First battery stack Rr Second battery stack

Claims

1. A first battery stack and a second battery stack in which a plurality of secondary batteries are stacked, A stack case for accommodating the first battery stack and the second battery stack in parallel, The first battery stack and the second battery stack are battery packs housed in the stack case so as to have different Young's moduli in a state of being housed in the stack case.

2. The first battery stack is housed in the stack case with a pair of first end plates provided at both ends in the stacking direction of the secondary batteries assembled thereto, The second battery stack is housed in the stack case with a pair of second end plates provided at both ends in the stacking direction of the secondary batteries assembled thereto, The battery pack according to claim 1, wherein at least one of the first end plates has a shape that deflects the first battery stack in any one direction in the vertical direction with respect to the second battery stack.

3. The battery pack according to claim 1, wherein the first battery stack and the second battery stack are housed in the stack case under different restraint loads.

4. The first battery stack has a plurality of first spacers sandwiched between adjacent secondary batteries in the stacking direction of the secondary batteries, The second battery stack has a plurality of second spacers sandwiched between adjacent secondary batteries in the stacking direction of the secondary batteries, The battery pack according to claim 1, wherein at least some of the plurality of first spacers and the plurality of second spacers have different shapes.

5. A first battery stack and a second battery stack in which a plurality of secondary batteries are stacked, A stack case for accommodating the first battery stack and the second battery stack in parallel, The first battery stack and the second battery stack are battery packs housed in the stack case so as to have different natural vibration frequencies in a state of being housed in the stack case.

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