Battery pack

Abstract

To provide a battery pack that is reinforced without the need for providing a reinforcing member to a battery case.SOLUTION: The battery pack includes a battery cell group and a battery case. The battery cell group includes a plurality of battery cells. The battery case houses the battery cell group. The battery case includes a pair of cross members arranged to sandwich the battery cell group therebetween in a first direction and extending along a second direction orthogonal to the first direction. The plurality of battery cells is stacked along the second direction. The battery cell group includes a reinforcement plate stacked together with the plurality of battery cells at a position closer to the center of the battery cell group than each end of the battery cell group in the second direction. The reinforcement plate is arranged to bridge between the pair of cross members.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] This disclosure relates to a battery pack.

Background Art

[0002] Patent Document 1 discloses a battery pack mounted on a vehicle. In this battery pack, cell groups are arranged on both sides sandwiching a reinforcement arranged so as to extend in the vehicle front-rear direction.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the battery pack described in Patent Document 1, the cell group alone does not have a reinforcing member. Therefore, in the structure described in Patent Document 1, it is necessary to provide a reinforcing member (reinforcement) in the battery case that houses the cell group.

[0005] This disclosure has been made in view of the above problems, and an object thereof is to provide a battery pack that is reinforced without the need to provide a reinforcing member in the battery case.

Means for Solving the Problems

[0006] The battery pack according to this disclosure comprises a group of battery cells and a battery case. The group of battery cells includes a plurality of battery cells. The battery case houses the group of battery cells. The battery case includes a pair of cross members arranged to sandwich the group of battery cells in a first direction and extending along a second direction perpendicular to the first direction. The plurality of battery cells are stacked along the second direction. The group of battery cells includes a reinforcing plate stacked with the plurality of battery cells at a position closer to the center of the group of battery cells than to each end of the group of battery cells in the second direction. The reinforcing plate is arranged to bridge the pair of cross members. [Effects of the Invention]

[0007] According to the battery pack described herein, a battery pack having a reinforcing structure against loads from a first direction can be realized without the need to provide reinforcing members to the battery case. [Brief explanation of the drawing]

[0008] [Figure 1] This diagram shows the configuration of a battery pack according to an embodiment. [Figure 2] This figure shows a cross-section of line AA in Figure 1. [Figure 3] This diagram illustrates the electrical connection paths between multiple battery cells in a battery pack according to an embodiment. [Figure 4] This figure shows an example of a thermal insulation structure for a battery cell group according to an embodiment. [Figure 5] This figure shows another example of the thermal insulation structure of a battery cell group according to the embodiment. [Modes for carrying out the invention]

[0009] 1. Basic configuration of the battery pack Figure 1 shows the configuration of a battery pack 1 according to an embodiment. The battery pack 1 is mounted on an electric vehicle such as a battery electric vehicle (BEV). The direction labeled "FR" in Figure 1 corresponds to the front direction of the vehicle on which the battery pack 1 is mounted. The direction labeled "RH" corresponds to the right direction of the vehicle.

[0010] The battery pack 1 comprises a plurality of battery cells 10 and a battery case 20. The battery case 20 houses the plurality of battery cells 10. The battery case 20 includes a lower case 21 and an upper case 22 (see Figure 2 below). Figure 1 includes a view of the plurality of battery cells 10 mounted on the lower case 21, looking down from above the electric vehicle (in the direction of "UPR" shown in Figure 2), along with an exploded perspective view to illustrate the restraint structure of the plurality of battery cells 10.

[0011] The multiple battery cells 10 are, for example, prismatic cells. If a predetermined number of battery cells 10 stacked along the second direction D2 are referred to as a battery cell group 12, then in the example shown in Figure 1, multiple battery cell groups 12 (four in one example) are arranged in a line along the first direction D1. More specifically, each of the multiple battery cells 10 is housed in the battery case 20 on top of the lower case 21 without being modularized. Thus, the battery pack 1 according to this embodiment has a so-called CTP (Cell To Pack) structure. The CTP structure does not require a modularized structure, thus effectively improving the space utilization rate and energy density of the battery pack 1.

[0012] In the example shown in Figure 1, the first direction D1 is parallel to the vehicle's longitudinal direction. Furthermore, when viewing the battery pack 1 from above as shown in Figure 1, the first direction D1 is perpendicular to the second direction D2, which is the stacking direction of the battery cells 10 in each battery cell group 12. The second direction D2 is parallel to the vehicle's lateral direction (vehicle width direction). Figure 1 The reinforcing plate 13 shown is related to the "reinforcing structure against front-to-back loads" described later, and details of the reinforcing plate 13 will be described later.

[0013] The lower case 21 includes a pair of side reinforcements 23 and a plurality of cross members 24 as reinforcing members for the lower case 21. These side reinforcements 23 and cross members 24 are fixed to the main body of the lower case 21 so as to surround each of the plurality of battery cells 10 (each battery cell group 12).

[0014] More specifically, as shown in Figure 1, the side reinforcements 23 are positioned outside each end of the battery cell group 12 in the second direction D2 (vehicle width direction) and extend along the first direction D1 (vehicle longitudinal direction). In addition, some of the multiple cross members 24 are positioned between two adjacent battery cell groups 12 in the first direction D1 and extend along the second direction D2. The remaining cross members 24 extend along the second direction D2 adjacent to the battery cell groups 12 located at each end of the first direction D1. Both ends of each cross member 24 are connected to a pair of side reinforcements 23. Focusing on one battery cell group 12, in other words, the lower case 21 includes a pair of cross members 24 that are positioned to sandwich the battery cell group 12 in the first direction D1 and are formed to extend along the second direction D2 which is perpendicular to the first direction D1.

[0015] In order to restrain multiple battery cells 10 (each battery cell group 12) in the second direction D2 (stacking direction), the battery pack 1 has a hybrid restraint structure in which a cross member 24 integrally provides a cross member as a reinforcing member and a restraint band for the battery cell group 12.

[0016] Specifically, as shown in Figure 1, each cross member 24 has a facing wall 24a that faces the adjacent battery cell group 12. In addition, a cross member 24 located between two battery cell groups 12 in the first direction D1 has two facing walls 24a. The cross member 24 is joined to the battery cell group 12 via adhesive 30 applied to the facing walls 24a.

[0017] In addition, engaging portions 24b are formed at each end of each cross member 24 in the second direction D2. The engaging portion 24b engages with the engaging portion 31a of the restraining member 31 on the battery cell group 12 side. The restraining member 31 is provided at each end of the battery cell group 12 in the second direction D2. By engaging the engaging portion 24b with the engaging portion 31a in a state where a compressive load along the second direction D2 is applied to the battery cell group 12, the battery cell group 12 is restrained by the cross member 24 with a predetermined restraining force in the second direction D2.

[0018] As described above, according to the hybrid restraint structure, the battery cell group 12 is restrained in the second direction D2 (lamination direction) by the restraint using the adhesive 30 and the mechanical restraint using the engaging portions 24b and 31a (double structure). Thereby, while reducing the number of parts, the gap between the cross member 24 and the battery cell group 12 can be reduced well, and the restraint in the second direction D2 can be realized by a method excellent in space efficiency.

[0019] In addition, a restraining band 32 may be used to restrain the battery cell group 12 in the second direction D2. According to the restraining band 32, by engaging the engaging portions 32a at each end of the restraining band 32 with the engaging portion 31b of the restraining member 31, the battery cell group 12 can be restrained from above. Further, in order to achieve more reliable restraint, the restraining band 32 may be joined to the upper surface 10a of each battery cell 10 included in the battery cell group 12 via an adhesive 33 (see FIG. 2).

[0020] Next, the relationship between the plurality of battery cells 10 and the battery case 20 (lower case 21) will be described. The lower surface 10b of each battery cell 10 is joined to the lower case 21 via a thermally conductive adhesive 34 (see FIG. 2). That is, each battery cell 10 is restrained by the adhesive force of the thermally conductive adhesive 34 so as not to separate from the lower case 21. Additionally, as shown in FIG. 2, each cross member 24 is disposed on the lower case 21 (more specifically, for example, a reinforcing member 25 included in the lower case 21). In order to make the restraint of the assembly of the battery cell group 12 and the cross member 24 more reliable, each cross member 24 may be fixed to the lower case 21 (reinforcing member 25) using fasteners such as bolts and nuts. Further, by using the thermally conductive adhesive 34, when a cooler 40 is provided so as to contact the lower surface of the lower case 21 as in the example shown in FIG. 2, the heat dissipation from the lower surface 10b of each battery cell 10 can be promoted using the thermally conductive adhesive 34.

[0021] Also, in order to achieve more reliable restraint, the upper surface 10a of each battery cell 10 may be joined to the upper case 22 via a thermally conductive adhesive 35 (see FIG. 2). According to such a configuration, when a cooler 41 is provided so as to contact the upper surface of the upper case 22 as in the example shown in FIG. 2, the heat dissipation from the upper surface 10a of each battery cell 10 can be promoted using the thermally conductive adhesive 35. Note that only the thermally conductive adhesive 35 may be used without using the adhesive 33 in combination for the restraint on the side of the upper surface 10a of each battery cell 10.

[0022] 2. Reinforcement structure for front and rear loads For the description of the reinforcing plate ١٣, FIGS. 1 and 2 are additionally referred to. FIG. 2 is a view showing a cross section taken along line A-A in FIG. 1, and shows the reinforcing plate 13 and the surrounding configuration as viewed from the second direction D2.

[0023] Each battery cell group 12 includes a reinforcing plate 13. As shown in Figure 1, the reinforcing plate 13 is positioned in the center of the battery cell group 12 in the second direction D2 and is stacked together with the multiple battery cells 10 that make up the battery cell group 12. The reinforcing plate 13 is formed using, for example, a metal material. The position of the reinforcing plate 13 in the battery cell group 12 is not necessarily limited to the center in the second direction D2, but can be any position closer to the center of the battery cell group 12 than to any of the ends of the battery cell group 12 in the second direction D2. In addition, the position of the reinforcing plate 13 in the second direction D2 being close to the center as described above is preferable for effectively receiving front-to-back loads together with the skeletal structural members (side reinforcement 23 and cross member 24) on the battery case 20 side, compared to an example where the position is close to one end of the battery cell group 12.

[0024] Each reinforcing plate 13 is positioned to bridge the gap between a pair of cross members 24. More specifically, each reinforcing plate 13 has a size equivalent to that of the battery cell 10, at least in the first direction D1 and the vehicle's longitudinal direction (height direction). Similar to the battery cell 10, each reinforcing plate 13 is joined to the cross members 24 (a pair of cross members) located at each end of the first direction D1, as shown in Figure 2. In the example shown in Figure 2, the joining of the reinforcing plate 13 to the cross members 24 is also done by bonding with adhesive 30, as shown in Figure 2. More broadly speaking, the joining of the reinforcing plate 13 to the cross members 24 does not necessarily have to be by adhesive, and other joining methods such as fastening with fasteners (e.g., bolts and nuts) may be used.

[0025] (effect) As described above, in the battery pack 1 according to this embodiment, the battery cell group 12 includes a reinforcing plate 13 that is stacked together with a plurality of battery cells 10 at a position closer to the center of the battery cell group 12 than to each end of the battery cell group 12 in the second direction D2. The reinforcing plate 13 is arranged to bridge between a pair of cross members 24. As a result, when a load (front-rear load) from the vehicle's front-rear direction (first direction D1) acts on the battery pack 1, each reinforcing plate 13 functions as a reinforcing member that receives the load. In this way, the battery pack 1 has a reinforcing structure against front-rear loads in the battery cell group 12 itself. For this reason, a battery pack 1 having a reinforcing structure against front-rear loads can be suitably realized without the need to provide reinforcing members in the battery case 20.

[0026] Furthermore, in the battery pack 1 according to this embodiment, the reinforcing plate 13 is joined to each of the pair of cross members 24 together with the multiple battery cells 10 via adhesive 30. In other words, like the multiple battery cells 10, the reinforcing plate 13 is arranged without gaps with each of the pair of cross members 24. More specifically, as shown in Figure 2, with respect to the first direction D1 (vehicle longitudinal direction), the multiple reinforcing plates 13 are arranged continuously without gaps with the cross members 24 interposed between the individual reinforcing plates 13. With such a reinforcing structure, excellent effects are obtained in terms of improving the resistance of the battery pack 1 to crushing or front / rear impacts (front or rear collision of an electric vehicle) due to front / rear loads, as follows.

[0027] To explain the above effects, a battery pack in which a group of battery cells, including a reinforcing plate similar to the reinforcing plate 13, are modularized as a battery module without a CTP structure is referred to here as a comparative example. In the battery pack according to this comparative example, in order to assemble the battery module in the space within the battery case partitioned by multiple cross members, it is necessary to secure a gap between the battery module and the cross member. This gap occurs between each of the battery modules, which are arranged in a line in the first direction D1 (vehicle longitudinal direction), and the cross member. As a result, when the above longitudinal load acts on the battery pack, the reinforcing plate in each battery module that receives the longitudinal load strokes in the first direction D1 by the amount of the gap. This stroke of the reinforcing plate causes deformation in the battery module. More specifically, when the battery pack is viewed from above, the battery module deforms into a V-shape. For this reason, it is difficult to appropriately improve resistance to crushing or longitudinal impacts due to longitudinal loads in the structure of the comparative example. In contrast, according to the reinforcing structure of the battery pack 1 according to this embodiment, the reinforcing plate 13 is arranged without a gap with the cross member 24. Therefore, compared to the above comparative example, it is possible to significantly improve resistance to crushing or impacts caused by longitudinal loads.

[0028] Next, other effects resulting from each battery cell group 12 being equipped with a reinforcing plate 13 will be explained with reference to Figure 3. Figure 3 is a diagram illustrating the electrical connection paths between multiple battery cells 10 in a battery pack 1 according to this embodiment. The electrical connection paths here are formed by busbars 54 connecting the positive terminal 50 and the negative terminal 52 of the battery pack 1.

[0029] In a battery pack comprising multiple battery cell groups, such as battery cell group 12, an alternative configuration to the one shown in Figure 3 for the electrical connection path could be adopted. Specifically, the multiple battery cells within each battery cell group are first electrically connected in series. Then, adjacent battery cell groups are electrically connected in series. However, adopting such a configuration would increase the length of the busbars connecting the battery cell groups. An increased busbar length for the entire battery pack is undesirable, for example, from the perspective of increasing the cost of the battery pack and protecting the busbars from external inputs.

[0030] In contrast, in the electrical connection path according to this embodiment, as shown in Figure 3, the busbar 54 connects multiple battery cells 10 in series not in units of 12 battery cell groups, but in each of the eight sections A to H, which are divided by the cross member 24 and the reinforcing plate 13. The busbar 54 then connects the sections A to H in series sequentially. This electrically formed electrical connection path effectively shortens the overall length of the busbar 54 for the battery pack 1. More specifically, the busbar 54 is formed to connect the four sections A, B, C, and D located on one side of the second direction D2, separated by the reinforcing plate 13 of each battery cell group 12, in series sequentially, and then connect the four sections E, F, G, and H located on the other side of the second direction D2, in series sequentially.

[0031] Furthermore, according to the electrical connection path shown in Figure 3, the potential difference between distant compartments (for example, between compartment A and compartment H, between compartment B and compartment G, and between compartment C and compartment F) becomes large. Therefore, when an electrical short circuit occurs due to the action of an external input or thermal runaway of the battery cell 10, a heat chain reaction or sparking of the battery cell 10 due to the high potential difference is likely to occur. In response to this problem, the battery pack 1 according to this embodiment has a reinforcing plate 13 interposed between compartments where a high potential difference occurs. Therefore, the presence of the reinforcing plate 13 ensures sufficient insulation distance between the battery cells 10 in two compartments where a high potential difference occurs, and also strengthens resistance to the occurrence of the heat chain reaction and sparking mentioned above.

[0032] 3. Thermal insulation structure of the battery cell group If the battery pack 1 includes a busbar 54 having the electrical connection path shown in Figure 3, it may also include a battery cell group 14 shown in Figure 4 or a battery cell group 16 shown in Figure 5 instead of the battery cell group 12.

[0033] Figure 4 shows an example of a thermal insulation structure for a battery cell group according to an embodiment. The battery cell group 14 shown in Figure 4 includes a thermal insulation material 15 interposed between the reinforcing plate 13 and the battery cell 10 in the second direction D2 (stacking direction). More specifically, the thermal insulation material 15 is placed between each of the battery cells 10 adjacent to both ends of the reinforcing plate 13 in the second direction D2. With a thermal insulation structure using the thermal insulation material 15, when thermal runaway occurs in a battery cell 10, it is possible to more reliably suppress the occurrence of a heat chain that extends beyond the compartments within the same battery cell group 12.

[0034] Figure 5 shows another example of the thermal insulation structure of a battery cell group according to the embodiment. The battery cell group 16 shown in Figure 5 includes a reinforcing plate 17 instead of a reinforcing plate 13. The reinforcing plate 17 is formed using a resin material. More specifically, the reinforcing plate 17 is formed using, for example, a fiber-reinforced resin material with high thermal resistance. This thermal insulation structure, using a reinforcing plate 17 with higher thermal resistance compared to a metal reinforcing plate 13, can more reliably prevent the occurrence of a heat chain across compartments within the same battery cell group 12 when thermal runaway occurs in the battery cell 10. [Explanation of Symbols]

[0035] 1 Battery pack, 10 Battery cells, 12, 14, 16 Battery cell groups, 13, 17 Reinforcement plates, 15 Insulation material, 20 Battery case, 21 Lower case, 22 Upper case, 23 Side reinforcement, 24 Cross member, 30 Adhesive, 50 Positive terminal, 52 Negative terminal, 54 Busbar

Claims

1. Multiple battery cell groups, each containing multiple battery cells, A battery case housing the aforementioned group of battery cells, A battery pack equipped with, The battery case includes a pair of cross members that are arranged to sandwich the battery cell group in a first direction and extend along a second direction perpendicular to the first direction, with respect to each of the battery cell groups. In each of the aforementioned battery cell groups, the plurality of battery cells are stacked along the second direction, Each of the aforementioned battery cell groups includes a reinforcing plate stacked together with the plurality of battery cells at a position closer to the center of each battery cell group than to each end of each battery cell group in the second direction, In each of the aforementioned battery cell groups, the reinforcing plate is positioned to bridge the gap between the pair of cross members. In each of the aforementioned battery cell groups, the plurality of battery cells and the reinforcing plate are joined to the pair of cross members via an adhesive. The battery pack further comprises a busbar connecting the positive terminal and the negative terminal of the battery pack. In each of the aforementioned battery cell groups, when a portion of the plurality of battery cells located on one side of the second direction with respect to the reinforcing plate is referred to as a plurality of first battery cells, and the remaining portion of the plurality of battery cells located on the other side of the second direction is referred to as a plurality of second battery cells, the busbar is formed to connect the plurality of first battery cells of each battery cell group located on one side of the second direction in sequential series, and then connect the plurality of second battery cells of each battery cell group located on the other side of the second direction in sequential series. A battery pack characterized by the following features.

2. Each of the aforementioned battery cell groups includes a heat insulating material interposed between the reinforcing plate and the battery cell in the second direction. The battery pack according to feature 1.

3. The reinforcing plate is formed using a resin material. The battery pack according to feature 1.

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