Battery pack structure for vehicle

Abstract

A battery pack structure for a vehicle is provided with: a case (10) that accommodates a battery (22); and a wall section (13) that forms at least a part of the case (10) and covers the battery (22). The wall section (13) includes, in the thickness direction of the wall section (13), a first layer (14) that forms a portion on one side of the wall section (13), and a second layer (15) that is formed on the other side of the first layer (14). The first layer (14) and the second layer (15) contain reinforcing fibers (2) and a flame retardant (3). The content of the reinforcing fibers (2) contained in the first layer (14) is higher than the content of the reinforcing fibers (2) contained in the second layer (15). The flame retardant (3) content of the first layer (14) in the first layer (14) is lower than the flame retardant (3) content of the second layer (15) in the second layer (15).

Description

Technical Field

[0001] The present invention relates to a battery pack structure for a vehicle. Background Art

[0002] The battery pack housing of an electric vehicle disclosed in Patent Document 1 below is a hardened product of a molding material containing an unsaturated polyester resin composition and a reinforcing fiber. The unsaturated polyester resin composition contains an unsaturated polyester, a polymerizable monomer, a low shrinkage agent, aluminum hydroxide, and a conductive filler. The unsaturated polyester is a polymerization product of a polybasic acid and a polyhydric alcohol, and the polybasic acid contains a polybasic acid having a predetermined ratio of ethylenically unsaturated double bonds. Polyvinyl acetate as the low shrinkage agent is in a predetermined ratio with respect to the total amount of the unsaturated polyester, the polymerizable monomer, and the low shrinkage agent. Aluminum hydroxide is in a predetermined ratio with respect to the total amount of the unsaturated polyester, the polymerizable monomer, and the low shrinkage agent.

[0003] Prior art documents

[0004] Patent documents

[0005] Patent Document 1: WO2020 / 162288 Summary of the Invention

[0006] Problems to be Solved by the Invention

[0007] However, when a battery cell disposed inside the housing of a vehicle battery pack releases a high-temperature gas, the pressure inside the housing may increase due to the release of the gas, and a relatively high pressure may be input from the inside to the housing. Moreover, the temperature of the housing may rise due to the heat of the gas.

[0008] An object of the present invention is to improve the rigidity and heat resistance of the housing of a vehicle battery pack when a battery cell releases a gas.

[0009] Solutions to the Problems

[0010] A battery pack structure for a vehicle according to one aspect of the present invention includes: a housing; and a wall portion that forms at least a part of the housing, the wall portion including a first layer and a second layer, the first layer and the second layer containing a reinforcing fiber and a flame retardant, the content rate of the reinforcing fiber contained in the first layer of the first layer being higher than the content rate of the reinforcing fiber contained in the second layer of the second layer, and the content rate of the flame retardant contained in the first layer of the first layer being lower than the content rate of the flame retardant contained in the second layer of the second layer.

[0011] Effects of the Invention

[0012] According to the present invention, it is possible to improve the rigidity and heat resistance of the housing of the vehicle battery pack when the battery cell releases gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 FIG. 1 is a perspective view showing an example of the overall structure of a battery pack applicable to the vehicle battery pack structure of the first embodiment.

[0014] Figure 2 FIG. 2 is a schematic perspective view of a battery cell of the vehicle battery pack structure of the first embodiment.

[0015] Figure 3 FIG. 3 is an exploded perspective view of a battery pack applicable to the vehicle battery pack structure of the first embodiment.

[0016] Figure 4 FIG. 4 is a view for explaining the positional relationship between the opposing wall portion and the battery module of the vehicle battery pack structure of the first embodiment, and is a schematic cross-sectional view taken along line IV-IV of FIG. 3. Figure 1 of FIG. 3.

[0017] Figure 5 FIG. 5 is a chart showing an example of the distribution of the content rates of reinforcing fibers and flame retardants in the opposing wall portion of the vehicle battery pack structure of the first embodiment.

[0018] Figure 6 FIG. 6 is a chart showing an example of the distribution of the content rates of reinforcing fibers and flame retardants in the opposing wall portion of the vehicle battery pack structure of the first embodiment.

[0019] Figure 7 FIG. 7 is a view for explaining the positional relationship between the first wall portion and the battery module of the vehicle battery pack structure of the second embodiment, and is a schematic cross-sectional view corresponding to FIG. 3. Figure 4 of FIG. 3.

[0020] Figure 8 FIG. 8 is a chart showing an example of the distribution of the content rates of reinforcing fibers and flame retardants in the first wall portion of the vehicle battery pack structure of the second embodiment.

[0021] Figure 9 FIG. 9 is a chart showing an example of the distribution of the content rates of reinforcing fibers and flame retardants in the first wall portion of the vehicle battery pack structure of the second embodiment.

[0022] Figure 10 FIG. 10 is a view for explaining the wall portion of the vehicle battery pack structure of the third embodiment, and is a schematic view showing the main part in the cross-section corresponding to FIG. 3. Figure 4 of FIG. 3.

[0023] Figure 11It is a diagram showing an example of the distribution of the content rates of reinforcing fibers and flame retardants in the wall portion of a vehicle battery pack structure according to the third embodiment.

[0024] Figure 12 It is a diagram showing an example of the distribution of the content rates of reinforcing fibers and flame retardants in the wall portion of a vehicle battery pack structure according to the third embodiment. Detailed Embodiments

[0025] Hereinafter, while referring to the attached Figure 1 the vehicle battery pack structure of the embodiment will be described. In addition, in each figure, FR and RR respectively represent the front and rear in the vehicle longitudinal direction. LH and RH respectively represent the left and right in the vehicle width direction. UP and DN respectively represent the upper and lower in the vehicle vertical direction. In the following description, the left and right in the vehicle width direction, the upper and lower in the vehicle vertical direction will be simply referred to as "the left side of the vehicle", "the right side of the vehicle", "the upper side", and "the lower side", respectively. In addition, in the following description, elements having the same function are denoted by the same reference numerals, and redundant description is omitted.

[0026] The vehicle battery pack structure of the embodiment can be used, for example, as a driving power source for a vehicle (not shown) such as an electric vehicle driven by an electric motor. The vehicle is not limited to an electric vehicle. For example, the vehicle battery pack structure can also be applied to a driving power source mounted on a hybrid vehicle.

[0027] First, while referring to Figures 1 to 4 an example of the structure of the battery pack 1 as a vehicle battery pack will be described. It may be that Figure 1 the illustrated battery pack 1 is a power source for vehicle driving and is disposed below the floor of the vehicle. The battery pack 1 includes a housing 10. The housing 10 is a member constituting the outer package of the battery pack 1. In the illustrated example, the housing 10 houses a battery module 20 (refer to Figure 2 ) including one or more battery cells 22 as batteries. That is, one or more battery cells 22 described later are housed inside the housing 10. The housing 10 may be a hollow member having a flat shape of a rectangular box.

[0028] The illustrated housing 10 has a wall portion 13. The wall portion 13 forms at least a part of the housing 10 and surrounds the battery cell 22. The battery cell 22 is disposed in the region inside the wall portion 13 (refer to Figure 3)。In addition, the inner side of the wall portion 13 is the direction toward the interior space of the housing 10 in the thickness direction of the wall portion. The outer side of the wall portion 13 is the direction opposite to the inner side in the thickness direction of the wall portion. The wall portion 13 may also surround the battery module 20 in the vehicle front-rear direction, vehicle width direction, and vehicle up-down direction. Additionally, the wall portion 13 may include a wall portion 13a and a wall portion 13b. The wall portion 13a forms at least a part of the upper cover 11 described later. The wall portion 13b forms at least a part of the lower housing 12 described later. The shape of the housing 10 is not limited to the illustrated example and can be appropriately set according to the shape, size, or arrangement method in the vehicle of the battery pack 1.

[0029] The wall portion 13 includes a first layer 14 and a second layer 15 (see Figure 4 , Figure 7 , and Figure 10 ). Additionally, the wall portion 13 may also include a third layer 16 described later (see Figure 10 ). Of course, the structure of the wall portion 13 is not limited to the illustrated example. For example, other layers may be formed in the region of the first layer 14 on the side opposite to the second layer 15. Additionally, other layers may be formed in the region of the second layer 15 on the side opposite to the first layer 14. Additionally, other layers may be formed in the region of the third layer 16 on the side opposite to the second layer 15.

[0030] The first layer 14 forms a part on one side in the thickness direction of the wall portion 13. The second layer 15 is formed at a position on the other side of the first layer 14 in the thickness direction of the wall portion 13. Additionally, the third layer 16 may also be formed at a position on the other side of the second layer 15 in the thickness direction of the wall portion 13. In the example shown in Figure 4 , the first layer 14 constitutes the lower side portion in the thickness direction of the wall portion 13. The second layer 15 constitutes the upper side portion in the thickness direction of the wall portion 13. In addition, in the illustrated example, the wall portion 13 is configured such that the first layer 14 is directly adjacent to the second layer 15, but it is not limited thereto. For example, one or more other layers may be included between the first layer 14 and the second layer 15. That is, the first layer 14 and the second layer 15 may be indirectly adjacent in the thickness direction of the wall portion 13. Additionally, the one or more other layers are simply referred to as the "intermediate layer".

[0031] In Figure 4In the example shown, the inner layer 14a of the first layer 14 forms the part on the inner side of the wall portion 13a. Therefore, the inner layer 14a can also partition and form at least a part of the internal space of the housing 10. In addition, the inner layer 14a can also form the part on the lower side of the upper cover 11. The outer layer 15a of the second layer 15 forms the part on the outer side of the wall portion 13a. The outer layer 15a can also form at least a part of the outer packaging surface of the housing 10. The outer layer 15a can also form the part on the upper side of the upper cover 11. In addition, the thickness of the first layer 14 or the second layer 15 in the thickness direction of the wall portion 13 is not particularly limited, but can also be set to about one-third of the thickness of the wall portion 13. For example, in a certain embodiment, the thickness of the wall portion 13 can be 1.5 mm to 6 mm, and the thickness of the first layer 14 can be 0.5 mm to 2 mm. In addition, the thickness of the second layer 15 can also be set to 0.5 mm to 2 mm.

[0032] Figure 1 The illustrated housing 10 has an upper cover 11 and a lower housing 12. The upper cover 11 and the lower housing 12 can also be fastened at their peripheral portions by fasteners such as bolts (not shown). The illustrated lower housing 12 is a bottomed box-shaped member with an upper opening in the vehicle, and has a substantially rectangular shape when viewed from above. The lower housing 12 can be formed of a metal such as aluminum, for example. A battery module 20 is disposed at the bottom of the lower housing 12. In addition, the form in which the battery module 20 is placed on the lower housing 12 is not limited to the illustrated example, and can be appropriately set according to the shape or size of the battery pack 1, for example. In addition, wiring components such as busbars (not shown) for electrically connecting the battery modules 20 to each other can be disposed inside the housing 10. The illustrated upper cover 11 is a plate-shaped member having a substantially rectangular shape when viewed from above. The upper cover 11 can be made of resin, for example. By closing the upper opening of the lower housing 12 with the upper cover 11, the inside of the housing 10 is sealed. In addition, the shape of the upper cover 11 is not limited to the illustrated example, and can be appropriately set according to the shape of the battery pack 1, for example. In addition, as Figure 3 illustrated, a plurality of battery modules 20 are accommodated inside the housing 10, but it is not limited thereto. The number of battery modules 20 disposed inside the housing 10 can be appropriately set according to the size of the battery pack 1 or the battery module 20, for example.

[0033] Figure 2The exemplified battery module 20 is a component formed by arranging and modularizing a plurality of battery cells 22. The plurality of battery cells 22 may also be arranged in the vehicle width direction. In addition, the number of battery cells 22 included in the battery module 20 may also be one. The battery module 20 may also include a module housing (not shown) as an outer packaging member that integrally houses the plurality of battery cells 22. The plurality of battery cells 22 are electrically connected to each other by wiring components such as a bus bar unit (not shown). In addition, the battery cell 22 may be formed by sealing a power generation element and an electrolyte together using a metal outer packaging member, and the power generation element is formed by laminating a positive electrode plate and a negative electrode plate with a separator therebetween. The battery cell 22 may also be a lithium-ion secondary battery.

[0034] The battery cell 22 may also have a gas release portion 25. When gas is generated inside the battery cell 22, the gas can be released from the gas release portion 25. The shape and structure of the gas release portion 25 are not particularly limited. For example, an explosion-proof valve that opens and releases the gas when the internal pressure of the battery cell 22 becomes equal to or higher than a predetermined pressure, or a sealing member that breaks and releases the gas may be used. Figure 2 The exemplified gas release portion 25 is formed in a portion on the upper side of the battery cell 22.

[0035] In addition, the structures of the battery module 20 and the battery cell 22 are not limited to the illustrated examples. For example, the battery module 20 may be a component formed by arranging and modularizing one or more battery cells 22 in the vertical direction. In addition, the battery cell 22 may be formed by covering a plurality of laminated monomers (not shown) that are electrically connected to each other using a metal outer packaging member. The laminated monomer may be formed by sealing a power generation element and an electrolyte together using a laminated film, and the power generation element is formed by laminating a positive electrode plate and a negative electrode plate with a separator therebetween. The position of the gas release portion 25 in the battery cell 22 may also be set, for example, to release gas toward the side of the battery module 20.

[0036] Next, while referring to Figure 4, while further explaining a structural example of the wall portion 13. The first layer 14 and the second layer 15 included in the wall portion 13 contain reinforcing fibers 2 and a flame retardant 3, respectively. In the example shown in the figure, the wall portion 13a of the upper cover 11 contains the reinforcing fibers 2 and the flame retardant 3. The wall portion 13a can also be formed by integrally molding the reinforcing fibers 2, the flame retardant 3, and a resin. That is, the wall portion 13a can also contain the reinforcing fibers 2, the flame retardant 3, and a resin. The resin forming the wall portion 13a is not particularly limited. For example, a known thermosetting resin can be used. The thermosetting resin can be, for example, an unsaturated polyester resin, a phenolic resin, a melamine resin, a polyurethane resin, an epoxy resin, a vinyl ester resin, or the like. The heat resistance and stiffness of the wall portion 13a can be improved by using the thermosetting resin as the resin component of the wall portion 13a. In addition, a thermoplastic resin can be used as the resin forming the wall portion 13a. The thermoplastic resin can be, for example, a polypropylene resin, a polyethylene resin, a polyamide resin, a PEKK resin (polyetheretherketone), or the like.

[0037] The reinforcing fibers 2 are composed of multiple fibers, and the fibers can be, for example, glass fibers, carbon fibers, boron fibers, or aramid fibers. The fiber length and fiber diameter of the fibers are not particularly limited, and they can be short fibers, long fibers, or continuous fibers. In addition, the orientation of the fibers inside the wall portion 13a is not particularly limited. For example, multiple of the fibers can be bundled to form a reinforcing fiber bundle, and multiple of the reinforcing fiber bundles can be filament-wound in one direction or at an angle and laminated. Each of the multiple reinforcing fiber bundles can be tied to each other by sewing or maintained in shape by hot melting. Multiple of the fibers can also form a fabric.

[0038] The flame retardant 3 is a substance for imparting flame retardancy to the wall portion 13a. The flame retardant 3 can also be a filler dispersed in the wall portion 13a. For example, it can be composed of multiple particles, and the multiple particles are composed of hydrated metal compounds such as aluminum hydroxide, magnesium hydroxide, and calcium hydroxide. Thus, even when the temperature inside the housing 10 rises due to the gas released from the battery cell 22, the endothermic reaction of the hydrated metal compound can be used to more reliably cool the housing 10. That is, the temperature rise of the housing 10 due to the gas can be more reliably suppressed. In addition, the flame retardant 3 is not limited to these examples and can be appropriately selected according to the material of the housing 10, the manufacturing method, and the like.

[0039] In addition, the wall portion 13 containing the reinforcing fibers 2 and the flame retardant 3 is not limited to the wall portion 13a of the upper cover 11. For example, the wall portion 13b of the lower housing 12 can also be formed by integrally molding the reinforcing fibers 2, the flame retardant 3, and a resin.

[0040] In the battery pack 1 of the embodiment, the content rate of the reinforcing fiber 2 in the first layer 14 is higher than the content rate of the reinforcing fiber 2 in the second layer 15. In addition, the content rate of the flame retardant 3 in the first layer 14 is lower than the content rate of the flame retardant 3 in the second layer 15. More specifically, the content rate of the reinforcing fiber 2 contained in the first layer 14 in the first layer 14 is higher than the content rate of the reinforcing fiber 2 contained in the second layer 15 in the second layer 15. In addition, the content rate of the flame retardant 3 contained in the first layer 14 in the first layer 14 is lower than the content rate of the flame retardant 3 contained in the second layer 15 in the second layer 15. In addition, when the wall portion 13 includes an intermediate layer, the content rates of the reinforcing fiber 2 and the flame retardant 3 in the intermediate layer are not particularly limited. The intermediate layer may also be a layer formed of, for example, a resin that does not contain the reinforcing fiber 2 and the flame retardant 3.

[0041] In addition, the intermediate layer may also contain the reinforcing fiber 2 and the flame retardant 3. In a certain embodiment, the content rate of the reinforcing fiber 2 in the intermediate layer may also be lower than the content rate of the reinforcing fiber 2 in the first layer 14 and higher than the content rate of the reinforcing fiber 2 in the second layer 15. In addition, the content rate of the flame retardant 3 in the intermediate layer may also be higher than the content rate of the flame retardant 3 in the first layer 14 and lower than the content rate of the reinforcing fiber 2 in the second layer 15. Thereby, even when the wall portion 13 includes an intermediate layer, for example, compared with the case where the intermediate layer does not contain the reinforcing fiber 2 and the flame retardant 3, the stiffness of the wall portion 13 against the load in the direction perpendicular to the thickness direction can be increased.

[0042] In addition, the region of the intermediate layer on the first layer 14 side may be directly adjacent to the first layer 14. In this case, the content rate of the reinforcing fiber 2 in the region of the intermediate layer on the first layer 14 side may be substantially equal to the content rate of the reinforcing fiber 2 in the region of the first layer 14 on the intermediate layer side. In addition, the content rate of the flame retardant 3 in the region of the intermediate layer on the first layer 14 side may be substantially equal to the content rate of the flame retardant 3 in the region of the first layer 14 on the intermediate layer side. Thereby, the bonding strength between the first layer 14 and the intermediate layer can be further increased, and the stiffness of the wall portion 13 against the load input from the direction perpendicular to the thickness direction can be further increased.

[0043] In addition, the region of the intermediate layer on the second layer 15 side may be directly adjacent to the second layer 15. In this case, the content rate of the reinforcing fiber 2 in the region of the intermediate layer on the second layer 15 side may be substantially equal to the content rate of the reinforcing fiber 2 in the region of the second layer 15 on the intermediate layer side. In addition, the content rate of the flame retardant 3 in the region of the intermediate layer on the second layer 15 side may be substantially equal to the content rate of the flame retardant 3 in the region of the second layer 15 on the intermediate layer side. Thereby, the bonding strength between the second layer 15 and the intermediate layer can be further increased, and the stiffness of the wall portion 13 against the load input from the direction perpendicular to the thickness direction can be further increased.

[0044] The content ratio may also be the volume content ratio or the weight content ratio of each layer of the wall portion 13, or each position in the thickness direction, of the reinforcing fiber 2 or the flame retardant 3. The volume content ratio is the ratio of the volume of the particles of the reinforcing fiber 2 or the flame retardant 3 to the volume of any part of the wall portion 13. The weight content ratio is the ratio of the weight of the particles of the reinforcing fiber 2 or the flame retardant 3 to the weight of any part of the wall portion 13.

[0045] The determination of the volume content ratio can also be carried out by cross-sectional observation using, for example, SEM (Scanning Electron Microscope) and EDX (Energy Dispersive X-rays pectroscopy). For example, the wall portion 13 is cut in the thickness direction at an arbitrary part to form a cross-section. And the volume content ratio of the reinforcing fiber 2 or the flame retardant 3 can be calculated based on the ratio occupied by the reinforcing fiber 2 or the flame retardant 3 in the image of this cross-section. In addition, the weight content ratio can be calculated based on this volume content ratio and the specific gravity of the reinforcing fiber 2 or the flame retardant 3. In addition, it can also be that an arbitrary part of the wall portion 13 is sliced in a direction perpendicular to the thickness direction and divided into a plurality of layers, and the ratio of the reinforcing fiber 2 or the flame retardant 3 contained in each of the plurality of layers is calculated, so as to obtain the volume content ratio or the weight content ratio. For example, by heating each of the plurality of layers respectively, or immersing each of the plurality of layers in an organic solvent to remove the resin component. And it can also be that the volume content ratio or the weight content ratio of the reinforcing fiber 2 or the flame retardant 3 in each of the plurality of layers is calculated by obtaining the volume or weight of the reinforcing fiber 2 or the flame retardant 3 contained in each of the plurality of layers.

[0046] [First Embodiment]

[0047] Next, while referring to Figures 4 to 6 while explaining the structure of the battery pack 1 of the first embodiment. As Figure 4 illustrated by way of example, the gas release portion 25 may also be provided in a portion on the upper side of the battery cell 22. The illustrated housing 10 has an opposing wall portion 17 as the wall portion 13. The opposing wall portion 17 is a wall portion that is at least opposed to the gas release portion 25 in the direction of gas release from the gas release portion 25. In the illustrated example, when gas is generated inside the battery cell 22, the gas is released upward as shown by the arrow A in the figure. Therefore, the opposing wall portion 17 forms at least a part of the upper cover 11. In addition, the opposing wall portion 17 may have a substantially rectangular shape extending in the vehicle width direction in a plan view, and in addition, a plurality of them may be provided on the upper cover 11 (refer to Figure 1 ).

[0048] In the battery pack 1 illustrated in the figure, a plurality of battery cells 22 are arranged side by side in the vehicle width direction (refer toFigure 2 and Figure 3 ), a plurality of gas release portions 25 are arranged in a substantially linear shape in the vehicle width direction. Therefore, the opposing wall portion 17 can also extend in the vehicle width direction from the left end portion of the vehicle of the wall portion 13a to the right end portion of the vehicle so as to cover the plurality of gas release portions 25. Of course, the shape of the opposing wall portion 17 is not limited to the illustrated example, and can be appropriately set according to the position of the gas release portion 25, or the shape or size of the battery pack 1, for example.

[0049] The first layer 14 illustrated in the figure forms an inner layer 14a. The inner layer 14a is a portion of the opposing wall portion 17 on the side closer to the battery cell 22. The second layer 15 forms an outer layer 15a. That is, the outer layer 15a forms a portion of the opposing wall portion 17 on the side opposite to the inner layer 14a in the thickness direction of the opposing wall portion 17. The outer layer 15a can also form at least a part of the outer packaging surface of the housing 10.

[0050] In the opposing wall portion 17, the content rate of the reinforcing fiber 2 of the inner layer 14a is set to be relatively high. Therefore, the strength of the inner layer 14a is relatively high, and the opposing wall portion 17 is more reliably strengthened by the inner layer 14a. Hereinafter, the layer formed for one of the main purposes of strengthening the wall portion 13 will be simply referred to as a reinforcing layer. In addition, the reinforcing fiber 2 contained in the inner layer 14a may also include continuous fibers oriented in the length direction of the opposing wall portion 17. In the illustrated example, the vehicle width direction corresponds to the length direction of the opposing wall portion 17.

[0051] In addition, in the opposing wall portion 17 illustrated in the figure, the content rate of the flame retardant 3 of the outer layer 15a is set to be relatively high. Therefore, the outer layer 15a can more reliably impart flame retardancy to the opposing wall portion 17. Hereinafter, the layer formed for one of the main purposes of imparting flame retardancy will be simply referred to as a flame retardant layer.

[0052] Next, while referring to Figure 5 and Figure 6 while an example of the change in the content rate of the reinforcing fiber 2 and the flame retardant 3 in the thickness direction of the opposing wall portion 17 will be described. By configuring as illustrated in the figure, the inner layer 14a functions as a reinforcing layer. In addition, the outer layer 15a functions as a flame retardant layer.

[0053] Figure 5 and Figure 6 In the chart illustrated, the horizontal axis represents each position in the thickness direction of the opposing wall portion 17. The positive direction of the horizontal axis corresponds to the upper side of the opposing wall portion 17, and the negative direction of the horizontal axis corresponds to the lower side of the opposing wall portion 17. The vertical axis of this chart represents the content rate of the reinforcing fiber 2 or the flame retardant 3 in each part of the opposing wall portion 17. In addition, in the illustrated example, the content rate of the reinforcing fiber 2 at each position in the thickness direction is represented by a solid line, and the content rate of the flame retardant 3 is represented by a dashed line.

[0054] In Figure 5 In the structure illustrated in the diagram of Figure 5 , the content rate of the reinforcing fiber 2 with respect to the opposing wall portion 17 is set to be higher as it goes downward. Therefore, the content rate of the reinforcing fiber 2 in the inner layer 14a is higher than the content rate of the reinforcing fiber 2 in the outer layer 15a. In addition, the content rate of the flame retardant 3 with respect to the opposing wall portion 17 is set to be higher as it goes upward. Therefore, the content rate of the flame retardant 3 in the inner layer 14a is lower than the content rate of the flame retardant 3 in the outer layer 15a.

[0055] In Figure 6 In the structure illustrated in the diagram of Figure 6 , between the inner layer 14a and the outer layer 15a, the content rates of the reinforcing fiber 2 and the flame retardant 3 are set to increase or decrease discontinuously in a stepped manner. In addition, in the inner layer 14a and the outer layer 15a respectively, the content rates of the reinforcing fiber 2 and the flame retardant 3 are substantially constant in the thickness direction. The content rate of the reinforcing fiber 2 in the inner layer 14a illustrated in the figure is higher than the content rate of the reinforcing fiber 2 in the outer layer 15a. In addition, the content rate of the flame retardant 3 in the inner layer 14a is lower than the content rate of the flame retardant 3 in the outer layer 15a.

[0056] [Second Embodiment]

[0057] Next, while referring to Figures 7 to 9 while explaining the structure of the battery pack 1 of the second embodiment. In this embodiment, as Figure 7 illustrated, the gas release portion 25 is provided on the side portion of the battery cell 22. The illustrated housing 10 has a first wall portion 18 as the wall portion 13. The first wall portion does not face the gas release portion 25. That is, the first wall portion 18 is the portion of the housing 10 other than the opposing wall portion 17. In the illustrated example, when gas is generated inside the battery cell 22, the gas is released to the left side or the right side of the vehicle as shown by the arrow B in the figure. At this time, since the first wall portion 18 does not face the gas release portion 25, the jet flow of the gas does not directly collide with the first wall portion 18. The first wall portion 18 may also form at least a part of the upper cover 11.

[0058] In the illustrated example, the outer layer 14b as the first layer 14 forms the outer side portion of the wall portion 13. That is, the outer layer 14b forms the portion of the first wall portion 18 opposite to the side of the battery cell 22. The outer layer 14b may also form at least a part of the outer packaging surface of the housing 10. The outer layer 14b may also form the upper side portion of the upper cover 11. In addition, in the illustrated example, the inner layer 15b as the second layer 15 forms the inner side portion of the wall portion 13. Therefore, the inner layer 15b may also divide and form at least a part of the internal space of the housing 10. The inner layer 15b may also form the lower side portion of the upper cover 11.

[0059] In Figure 7 the illustrated first wall portion 18, the content rate of the reinforcing fiber 2 in the outer layer 14b is set relatively high. Therefore, the strength of the outer layer 14b is relatively high, and the first wall portion 18 is more reliably strengthened by the outer layer 14b. In addition, in the illustrated first wall portion 18, the content rate of the flame retardant 3 in the inner layer 15b is set relatively high. Therefore, the first wall portion 18 can be more reliably imparted with flame retardancy by the inner layer 15b.

[0060] Next, while referring to Figure 8 and Figure 9 , an example of the change in the content rate of the reinforcing fiber 2 and the flame retardant 3 in the thickness direction in the first wall portion 18 will be described. By being configured as illustrated in the figure, the outer layer 14b functions as a reinforcing layer. In addition, the inner layer 15b functions as a flame-retardant layer.

[0061] Figure 8 and Figure 9 In the chart illustrated in, the horizontal axis represents each position in the thickness direction of the first wall portion 18. The positive direction of the horizontal axis corresponds to the upper side of the first wall portion 18, and the negative direction of the horizontal axis corresponds to the lower side of the first wall portion 18. The vertical axis of this chart represents the content rate of the reinforcing fiber 2 or the flame retardant 3 in each part of the first wall portion 18. In addition, in the illustrated example, the content rate of the reinforcing fiber 2 at each position in the thickness direction is represented by a solid line, and the content rate of the flame retardant 3 is represented by a dashed line.

[0062] In Figure 8 the structure illustrated in the chart, the content rate of the reinforcing fiber 2 in the first wall portion 18 is set to be higher as it goes upward. Therefore, the content rate of the reinforcing fiber 2 in the outer layer 14b is higher than the content rate of the reinforcing fiber 2 in the inner layer 15b. In addition, the content rate of the flame retardant 3 in the first wall portion 18 is set to be higher as it goes downward. Therefore, the content rate of the flame retardant 3 in the outer layer 14b is lower than the content rate of the flame retardant 3 in the inner layer 15b.

[0063] In Figure 9 the structure illustrated in the chart, between the outer layer 14b and the inner layer 15b, the content rates of the reinforcing fiber 2 and the flame retardant 3 are set to increase or decrease discontinuously in a stepped manner. In addition, in the outer layer 14b and the inner layer 15b respectively, the content rates of the reinforcing fiber 2 and the flame retardant 3 are substantially constant in the thickness direction. The content rate of the reinforcing fiber 2 in the illustrated outer layer 14b is higher than the content rate of the reinforcing fiber 2 in the inner layer 15b. In addition, the content rate of the flame retardant 3 in the outer layer 14b is lower than the content rate of the flame retardant 3 in the inner layer 15b.

[0064] [Third Embodiment]

[0065] Next, while referring to Figures 10 to 12 FIG. 188, the structure of the battery pack 1 of the third embodiment will be described by taking the wall portion 13a of the upper cover 11 as an example. In the present embodiment, the wall portion 13a includes a first layer 14, a second layer 15, and a third layer 16. In the illustrated example, the first layer 14 forms an inner layer 14c. The inner layer 14c is the wall portion on the inner side of the housing 10 in the wall portion 13a. That is, the inner layer 14c forms the portion of the wall portion 13a on the side closer to the battery cell 22. The second layer 15 forms a first outer layer 15c. The first outer layer 15c is formed at a position above the inner layer 14c in the thickness direction of the wall portion 13a. The third layer 16 forms a second outer layer 16c. The second outer layer 16c is formed at a position above the first outer layer 15c in the thickness direction of the wall portion 13a.

[0066] In addition, the positional relationship among the first layer 14, the second layer 15, and the third layer 16 in the wall portion 13a is not limited to the illustrated example. For example, the wall portion 13a may be configured by reversing the illustrated up-and-down direction, the second outer layer 16c may constitute the first layer 14, the first outer layer 15c may constitute the second layer 15, and the inner layer 14c may constitute the third layer 16. That is, the third layer 16 corresponds to the first layer 14. In addition, in the illustrated example, the second layer 15 and the third layer 16 are directly adjacent to each other, but an intermediate layer may be interposed therebetween. That is, the second layer 15 and the third layer 16 may be directly or indirectly adjacent to each other.

[0067] In the wall portion 13a, the content ratios of the reinforcing fibers 2 in the inner layer 14c as the first layer 14 and the second outer layer 16c as the third layer 16 are set relatively high. Therefore, the inner layer 14c and the second outer layer 16c function as reinforcing layers. In addition, in the wall portion 13a, the content ratio of the flame retardant 3 in the first outer layer 15c as the second layer 15 is set relatively high. Therefore, the first outer layer 15c functions as a flame-retardant layer. In addition, the wall portion 13a of the present embodiment may also be a facing wall portion 17 or a first wall portion 18. In addition, in the case where the facing wall portion 17 is configured like the wall portion 13a of the present embodiment, at least one of the inner layer 14c and the second outer layer 16c may contain continuous fibers oriented in the longitudinal direction of the facing wall portion 17 as the reinforcing fibers 2.

[0068] Figure 11 and Figure 12 In the chart illustrated in FIG. 196, the horizontal axis represents each position in the thickness direction of the wall portion 13a. The positive direction of the horizontal axis corresponds to the upper side of the wall portion 13a, and the negative direction of the horizontal axis corresponds to the lower side of the wall portion 13a. The vertical axis of this chart represents the content ratio of the reinforcing fibers 2 or the flame retardant 3 in each part of the wall portion 13a. In addition, in the illustrated example, the content ratio of the reinforcing fibers 2 at each position in the thickness direction is represented by a solid line, and the content ratio of the flame retardant 3 is represented by a dotted line.

[0069] In Figure 11 the structure illustrated in the diagram, the content rate of the reinforcing fiber 2 in the wall portion 13a is set to be lower as it approaches the vicinity of the central portion in the thickness direction of the wall portion 13a. Therefore, the content rate of the reinforcing fiber 2 in each of the inner layer 14c and the second outer layer 16c is higher than the content rate of the reinforcing fiber 2 in the first outer layer 15c. In addition, the change in the content rate of the reinforcing fiber 2 in the thickness direction is not limited to the illustrated example. For example, it may be that the content rate is the lowest in the region on the inner layer 14c side or the region on the second outer layer 16c side compared to the vicinity of the central portion in the thickness direction of the wall portion 13a.

[0070] In addition, the content rate of the flame retardant 3 in the wall portion 13a is set to be higher as it approaches the vicinity of the central portion in the thickness direction of the wall portion 13a. Therefore, the content rate of the flame retardant 3 in each of the inner layer 14c and the second outer layer 16c is lower than the content rate of the flame retardant 3 in the first outer layer 15c. In addition, the change in the content rate of the flame retardant 3 in the thickness direction is not limited to the illustrated example. For example, it may be that the content rate is the highest in the region on the inner layer 14c side or the region on the second outer layer 16c side compared to the vicinity of the central portion in the thickness direction of the wall portion 13a.

[0071] In Figure 12 the example shown in the diagram, between the inner layer 14c and the first outer layer 15c and between the first outer layer 15c and the second outer layer 16c, the content rates of the reinforcing fiber 2 and the flame retardant 3 are configured to increase or decrease discontinuously in a stepped manner. In addition, in the inner layer 14c, the first outer layer 15c, and the second outer layer 16c respectively, the content rates of the reinforcing fiber 2 and the flame retardant 3 are substantially constant in the thickness direction. The content rate of the reinforcing fiber 2 in the inner layer 14c illustrated in the diagram is higher than the content rate of the reinforcing fiber 2 in the first outer layer 15c. The content rate of the flame retardant 3 in the inner layer 14c is lower than the content rate of the flame retardant 3 in the first outer layer 15c. In addition, the content rate of the reinforcing fiber 2 in the second outer layer 16c is higher than the content rate of the reinforcing fiber 2 in the first outer layer 15c. The content rate of the flame retardant 3 in the second outer layer 16c is lower than the content rate of the flame retardant 3 in the first outer layer 15c.

[0072] In addition, Figure 11 and Figure 12 in the example shown, there is no particular limitation on the magnitude relationship between the content rate of the reinforcing fiber 2 or the content rate of the flame retardant 3 in each of the inner layer 14c and the second outer layer 16c. For example, the content rate of the reinforcing fiber 2 in the inner layer 14c and the content rate of the reinforcing fiber 2 in the second outer layer 16c may be substantially equal. In addition, the content rate of the flame retardant 3 in the inner layer 14c and the content rate of the flame retardant 3 in the second outer layer 16c may be substantially equal.

[0073] The form of increase or decrease in the thickness direction of the content rates of the reinforcing fiber 2 and the flame retardant 3 is not limited to Figure 5 , Figure 8 , and Figure 11 the examples shown. The content rate may increase or decrease linearly, or may increase or decrease curvilinearly. In addition, the content rate may increase or decrease continuously. For example, the wall portion 13 may also include a layer in which the content rate of the reinforcing fiber 2 decreases as it goes from the first layer 14 toward the second layer 15 in the thickness direction of the wall portion 13, and the content rate of the flame retardant 3 increases as it goes from the first layer 14 toward the second layer 15 in the thickness direction of the wall portion 13. In a certain embodiment, the wall portion 13 may also include a layer in which the content rates of the reinforcing fiber 2 and the flame retardant 3 increase or decrease continuously in the thickness direction of the wall portion 13. In Figure 5 the example shown, the relative wall portion 17 includes a layer in which the content rate of the reinforcing fiber 2 decreases as it goes from the lower side portion of the inner layer 14a upward, and the content rate of the flame retardant 3 increases as it goes from the lower side portion of the inner layer 14a upward. In Figure 8 the example shown, the first wall portion 18 includes a layer in which the content rate of the reinforcing fiber 2 decreases as it goes from the upper side portion of the outer layer 14b downward, and the content rate of the flame retardant 3 increases as it goes from the upper side portion of the outer layer 14b downward. In Figure 10 the example shown, the wall portion 13a includes a layer in which the content rate of the reinforcing fiber 2 decreases as it goes from the lower side portion of the inner layer 14c upward, and the content rate of the flame retardant 3 increases as it goes from the lower side portion of the inner layer 14c upward. That is, the wall portion 13 may also include a layer in which the content rate of the reinforcing fiber 2 decreases as it goes from a portion on one side of the first layer 14 toward the other side in its thickness direction, and the content rate of the flame retardant 3 increases as it goes from a portion on one side of the first layer 14 toward the other side.

[0074] In addition, for example, when an intermediate layer is included between the first layer 14 and the second layer 15, the content rates of the reinforcing fiber 2 and the flame retardant 3 may also increase or decrease continuously from the first layer 14 to the second layer 15. That is, the content rate of the reinforcing fiber 2 may also decrease continuously from the first layer 14 to the second layer 15. In addition, the content rate of the flame retardant 3 may also increase continuously from the first layer 14 to the second layer 15.

[0075] In addition, in Figure 5 , Figure 8 , and Figure 11 the examples shown, the content rates of the reinforcing fiber 2 and the flame retardant 3 increase or decrease continuously and smoothly as a whole in the vertical direction, but are not limited thereto. The change in the content rate may also be discontinuous. For example, in Figure 6In the example shown, the content rate of the reinforcing fiber 2 is kept substantially constant in the thickness direction of the inner layer 14a, decreases relatively greatly in the portion of the outer layer 15a closer to the inner layer 14a side, and is ensured to be substantially constant in the thickness direction of the outer layer 15a. That is, the content rate decreases stepwise from the inner layer 14a to the outer layer 15a. Similarly, the content rate of the reinforcing fiber 2 increases stepwise from the inner layer 15b to the outer layer 14b in the example shown. In addition, in the example shown, the content rate decreases stepwise from the inner layer 14c to the first outer layer 15c and increases stepwise from the first outer layer 15c to the second outer layer 16c. Thus, the wall portion 13 may also include a region where the content rate of the reinforcing fiber 2 increases or decreases stepwise in its thickness direction. Similarly, the wall portion 13 may also include a region where the content rate of the flame retardant 3 increases or decreases stepwise in its thickness direction. That is, the content rates of the reinforcing fiber 2 and the flame retardant 3 may also increase or decrease stepwise in the thickness direction of the wall portion 13. In addition, "increasing or decreasing stepwise" means that, for example, the content rate increases or decreases stepwise while remaining constant in a predetermined interval. That is, the forms of increase or decrease of the content rates of the reinforcing fiber 2 and the flame retardant 3 in the thickness direction of the wall portion 13 may also be discrete. Figure 9 In the example shown, the content rate increases stepwise from the inner layer 15b to the outer layer 14b. In addition, in Figure 12 the example shown, the content rate decreases stepwise from the inner layer 14c to the first outer layer 15c and increases stepwise from the first outer layer 15c to the second outer layer 16c. Thus, the wall portion 13 may also include a region where the content rate of the reinforcing fiber 2 increases or decreases stepwise in its thickness direction. Similarly, the wall portion 13 may also include a region where the content rate of the flame retardant 3 increases or decreases stepwise in its thickness direction. That is, the content rates of the reinforcing fiber 2 and the flame retardant 3 may also increase or decrease stepwise in the thickness direction of the wall portion 13. In addition, "increasing or decreasing stepwise" means that, for example, the content rate increases or decreases stepwise while remaining constant in a predetermined interval. That is, the forms of increase or decrease of the content rates of the reinforcing fiber 2 and the flame retardant 3 in the thickness direction of the wall portion 13 may also be discrete.

[0076] Next, a method for forming the wall portion 13 of the battery pack 1 according to the embodiment will be described. For example, a wall portion 13 in which the content rates of the reinforcing fiber 2 and the flame retardant 3 continuously change in the thickness direction as shown Figure 5 may also be formed by RTM (Resin Transfer Molding). In RTM, the wall portion 13 is formed by injecting resin into a mold in which a preform as a base material containing the reinforcing fiber 2 is laminated and arranged, heating, and applying pressure. In the case where the content rate of the reinforcing fiber 2 is higher as it is closer to the lower part of the wall portion 13, a plurality of preforms are laminated and arranged inside the mold in such a manner that the density of the reinforcing fiber 2 is higher as it is closer to the lower part. For example, the preform arranged on the lower side may be an NCF (Non Crimp Fabric), and the preform arranged on the upper side may be a fabric. The flame retardant 3 may also be added in advance to the resin injected into the mold. If such resin is injected into the mold, the density of the flame retardant 3 becomes higher on the upper side and lower on the lower side inside the mold according to the change in the density of the laminated preforms. After that, the wall portion 13 containing the reinforcing fiber 2 and the flame retardant 3 is integrally formed by heating and pressurizing. In addition, the method for forming the wall portion 13 is not limited to RTM, and known methods such as VaRTA (Vacuum assisted Resin Transfer Molding) may also be appropriately used.

[0077] In addition, the wall portion 13 can also be formed by stamping a sheet-like base material. For example, it can also be the case where the wall portion 13 in which the content rates of the reinforcing fiber 2 and the flame retardant 3 vary discontinuously in the thickness direction, as shown in Figure 6 FIG. is formed by stacking a base material containing the reinforcing fiber 2 and the flame retardant 3 inside the die of a stamping machine and performing thermocompression molding. The base material is previously added with the reinforcing fiber 2 and the flame retardant 3 to the resin and formed into a sheet shape. The base material can also be, for example, SMC (Sheet Molding Compound) previously added with the flame retardant 3. In the case where the content rates of the reinforcing fiber 2 and the flame retardant 3 are set as exemplified in Figure 6 FIG., a base material with a relatively high content rate of the reinforcing fiber 2 and a relatively low content rate of the flame retardant 3 is arranged on the lower side inside the die. Then, a base material with a relatively low content rate of the reinforcing fiber 2 and a relatively high content rate of the flame retardant 3 is overlapped and arranged on this base material. After that, the wall portion 13 containing the reinforcing fiber 2 and the flame retardant 3 is integrally formed by performing thermocompression molding.

[0078] Hereinafter, the effects of the vehicle battery pack structure of the embodiment will be described.

[0079] (1) The vehicle battery pack structure of the embodiment includes: a housing 10 that houses the battery 22; and a wall portion 13 that forms at least a part of the housing 10 and covers the battery 22. The wall portion 13 includes a first layer 14 that forms a part on one side of the wall portion 13 and a second layer 15 that is formed at a position on the other side of the first layer 14 in the thickness direction of the wall portion 13. The first layer 14 and the second layer 15 contain the reinforcing fiber 2 and the flame retardant 3. The content rate of the reinforcing fiber 2 contained in the first layer 14 in the first layer 14 is higher than the content rate of the reinforcing fiber 2 contained in the second layer 15 in the second layer 15. The content rate of the flame retardant 3 contained in the first layer 14 in the first layer 14 is lower than the content rate of the flame retardant 3 contained in the second layer 15 in the second layer 15.

[0080] According to the vehicle battery pack structure of the embodiment, the wall portion 13 of the housing 10 includes the reinforcing fiber 2 and the flame retardant 3. In addition, the wall portion 13 at least includes the first layer 14 in which the content rate of the reinforcing fiber 2 is set relatively high. Thus, the rigidity of the housing 10 can be improved. Therefore, it is possible to increase the rigidity of the housing against the increase in the internal pressure of the housing 10 when gas is released from the battery cell 22. In addition, the wall portion 13 at least includes the second layer 15 in which the content rate of the flame retardant 3 is set relatively high. Thus, the heat resistance of the housing 10 can be improved, and the housing 10 can be more reliably protected from the heat of the gas released from the battery cell 22.

[0081] (2) Alternatively, the battery 22 may have a gas release portion 25 that releases gas. The wall portion 13 is an opposing wall portion 17 that is at least opposed to the gas release portion 25 in the gas release direction, and the first layer 14 forms an inner layer 14a on the battery 22 side of the opposing wall portion 17.

[0082] Thus, the gas generated within the battery cell 22 is released from the gas release portion 25 toward the opposing wall portion 17. Among them, the inner layer 14a of the opposing wall portion 17 is constituted by the first layer 14 that functions as a reinforcing layer. Therefore, the dynamic pressure of the released gas is input to the first layer 14 with higher stiffness. Thereby, the stiffness of the housing 10 against this dynamic pressure can be further improved. In addition, the content rate of the flame retardant 3 in the outer layer 15a is set higher than the content rate of the flame retardant 3 in the inner layer 14a. Therefore, even if the area near the first layer 14 is likely to be worn due to the impinging jet of this gas, the usage amount of the flame retardant 3 in this area can be reduced, and at the same time, the housing 10 can be more reliably protected against the heat of this gas.

[0083] (3) Alternatively, the battery 22 may have a gas release portion 25 that releases gas. Alternatively, the wall portion 13 is a portion 18 in the housing 10 other than the opposing wall portion 17 that is at least opposed to the gas release portion 25 in the gas release direction, and the first layer 14 forms an outer layer 14b on the side opposite to the battery 22 side of the portion 18 other than the opposing wall portion.

[0084] When the pressure inside the housing 10 rises due to the release of this gas, tensile stress may be input to the outer layer 14b. However, since the outer layer 14b is constituted by the first layer 14, the stiffness of the outer layer 14b against tensile stress is set higher. Thereby, the housing 10 can be more reliably protected against the rise in the internal pressure due to the release of this gas. In addition, the content rate of the flame retardant 3 is set relatively high in the inner layer 15b of the first wall portion 18. Therefore, even when the heat of this gas is transferred to the first wall portion 18, the housing 10 can be more reliably protected against this heat.

[0085] (4) Alternatively, the wall portion 13 may include a layer in which the content rate of the reinforcing fiber 2 decreases as it goes from the first layer 14 toward the second layer 15 in the thickness direction of the wall portion 13, and the content rate of the flame retardant 3 increases as it goes from the first layer 14 toward the second layer 15 in the thickness direction of the wall portion 13.

[0086] Thereby, the content rates of the reinforcing fiber 2 and the flame retardant 3 contained in the wall portion 13 continuously change in the thickness direction of the wall portion 13. Therefore, for example, when a load in a direction perpendicular to the thickness direction is input to the wall portion 13, the stiffness of the wall portion 13 against this load can be further improved.

[0087] (5) It is also possible that the content rates of the reinforcing fiber 2 and the flame retardant 3 in the wall portion 13 increase or decrease stepwise in the thickness direction of the wall portion 13.

[0088] Thereby, the change in the content rates of the reinforcing fiber 2 and the flame retardant 3 in the thickness direction of the wall portion 13 can be controlled more simply. Therefore, the vehicle battery pack structure of the embodiment can be more easily configured.

[0089] Explanation of reference numerals

[0090] 1. Battery pack (vehicle battery pack); 2. Reinforcing fiber; 3. Flame retardant; 10. Housing; 13, 13a, 13b. Wall portion; 14. First layer; 14a. Inner layer; 14b. Outer layer; 15. Second layer; 17. Opposite wall portion; 18. First wall portion (portion other than the opposite wall portion); 22. Battery cell (battery); 25. Gas release portion.

Claims

1. A battery pack structure for a vehicle, comprising: a housing that houses a battery; and a wall portion that forms at least a part of the housing and covers the battery, the wall portion includes a first layer that forms a part on one side of the wall portion in the thickness direction of the wall portion and a second layer that is formed at a position on the other side relative to the first layer, the first layer and the second layer contain reinforcing fibers and a flame retardant, the content rate of the reinforcing fibers contained in the first layer in the first layer is higher than the content rate of the reinforcing fibers contained in the second layer in the second layer, the content rate of the flame retardant contained in the first layer in the first layer is lower than the content rate of the flame retardant contained in the second layer in the second layer.

2. The battery pack structure for a vehicle according to claim 1, wherein the battery has a gas release portion that releases gas, the wall portion is a relative wall portion that is at least opposite to the gas release portion in the direction of releasing the gas, the first layer is formed as an inner layer on the battery side of the relative wall portion.

3. The battery pack structure for a vehicle according to claim 1, wherein the battery has a gas release portion that releases gas, the wall portion is a portion of the housing other than the relative wall portion that is at least opposite to the gas release portion in the direction of releasing the gas, the first layer forms an outer layer on the side opposite to the battery side of the portion other than the relative wall portion.

4. The battery pack structure for a vehicle according to any one of claims 1 to 3, wherein the wall portion includes a layer in which the content rate of the reinforcing fibers decreases as it goes from the first layer to the second layer in the thickness direction of the wall portion, and the content rate of the flame retardant increases as it goes from the first layer to the second layer in the thickness direction of the wall portion.

5. The battery pack structure for a vehicle according to any one of claims 1 to 3, wherein the content rates of the reinforcing fibers and the flame retardant in the wall portion increase or decrease stepwise in the thickness direction of the wall portion.

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