Battery pack

Abstract

To provide a battery pack in which joints in a battery case are resistant to corrosion.SOLUTION: A battery pack is configured to be mountable on a vehicle. The battery pack includes a battery case, battery cells housed in the battery case, and a protective layer formed on the battery case. The battery case includes a first case portion, a second case portion, and a joint portion. The first case portion and the second case portion form the outer surface of the battery case. The joint portion joins the first case portion and the second case portion. The protective layer is formed so as to be in close contact with the joint portion from the outside of the battery case.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a battery pack configured to be mountable on a vehicle. Background Art

[0002] For example, Patent Document 1 describes a battery pack configured to be mountable on a vehicle. The battery pack described in Patent Document 1 includes a battery case and battery cells housed in the battery case. Prior Art Documents Patent Documents

[0003] Patent Document 1 Japanese Unexamined Patent Publication No. 2021-120244 Summary of the Invention Problem to be Solved by the Invention

[0004] The present inventors studied configuring this type of battery pack such that the battery case has two portions forming the outer surface of the battery case and a joint joining these two portions. However, it has been found that when the battery case is configured in this manner, the joint may not have excellent corrosion resistance in some cases.

[0005] One aspect of the present disclosure provides a battery pack in which the joint in the battery case is less prone to corrosion. Means for Solving the Problem

[0006] One aspect of the present disclosure is a battery pack configured to be mounted on a vehicle. The battery pack comprises a battery case, battery cells housed in the battery case, and a protective layer formed on the battery case. The battery case has a first case portion, a second case portion, and a joint portion. The first and second case portions constitute the outer surface of the battery case. The joint portion joins the first and second case portions. The protective layer is formed to adhere closely to the joint portion from the outside of the battery case.

[0007] With this configuration, corrosion of the joints in the battery case can be made less likely in the battery pack.

[0008] In one aspect of this disclosure, the first case portion and the second case portion may constitute the upper surface of the outer surface of the battery case. Even in such a configuration, where the problem of poor corrosion resistance of the joint portion is relatively likely to occur, it is possible to make the joint portion of the battery case less susceptible to corrosion.

[0009] In one aspect of this disclosure, the joint and protective layer may be formed in a position that does not overlap with the battery cell when viewed from above. With such a configuration, deterioration of the protective layer due to heat from the battery cell can be suppressed. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic perspective view of a battery pack. [Figure 2] This is a schematic cross-sectional view of the battery pack when mounted on the underside of the vehicle. [Figure 3] This is a schematic top view of the battery pack. [Figure 4] This is a schematic perspective view showing a modified example of the joint. [Figure 5] Figure 5A is a schematic cross-sectional view showing a first modified example of the protective layer. Figure 5B is a schematic cross-sectional view showing a second modified example of the protective layer. [Modes for carrying out the invention]

[0011] Hereinafter, exemplary embodiments of the present disclosure will be described with reference to the drawings.

[0012] [1. Structure] The battery pack 1 shown in Figures 1 to 3 is configured to be mounted on a vehicle such as an electric vehicle. For example, as shown in Figure 2, the battery pack 1 is positioned below the floor panel F of the vehicle. The floor panel F is a component that constitutes the floor of the passenger compartment in the vehicle. When mounted on the vehicle, the battery pack 1 supplies power to, for example, the motor that drives the vehicle. In this description and in the drawings, "top" and "bottom" refer to the top and bottom of the battery pack 1 when it is mounted on the vehicle.

[0013] As shown in Figures 1 and 2, the battery pack 1 comprises a battery case 2, a plurality of battery cells 3, and a protective layer 4.

[0014] The battery case 2 is a component that houses multiple battery cells 3. In this embodiment, each of the multiple battery cells 3 is a rectangular plate-shaped component. The multiple battery cells 3 are housed in the battery case 2 in a stacked or aligned state.

[0015] The external shape of the battery case 2 in this embodiment is generally that of a rectangular parallelepiped. The battery case 2 is made of metal. Preferably, the battery case 2 is made of a metal with high corrosion resistance. Examples of metals with high corrosion resistance include zinc-plated steel sheets and stainless steel.

[0016] The battery case 2 comprises an upper member 21 and a lower member 22. The upper member 21 and the lower member 22 are members that form a housing space 23 for housing the battery cells 3.

[0017] The upper member 21 is a box-shaped member with an open bottom. The upper member 21 has a ceiling wall 211, a side wall 212, and a flange 213.

[0018] The ceiling wall 211 is a plate-shaped portion that constitutes the top surface of the outer surface of the battery case 2. The ceiling wall 211 of the present embodiment is substantially rectangular. A plurality of ribs 214 are formed on the top surface of the ceiling wall 211. The rib 214 is a groove-shaped portion. The rib 214 of the present embodiment extends linearly. Note that illustration of the rib 214 is omitted in FIG. 2 and FIG. 3.

[0019] As shown in FIG. 1 and FIG. 2, the side wall 212 is a plate-shaped portion extending from the outer peripheral edge of the ceiling wall 211 toward the lower surface side of the ceiling wall 211. The side wall 212, together with a side wall 222 of the lower member 22 described later, constitutes a side surface of the outer surface of the battery case 2.

[0020] The flange 213 is a plate-shaped portion extending outward from an edge of the side wall 212 on the opposite side to the ceiling wall 211 side. The "outward" referred to here can also be rephrased as the side opposite to the ceiling wall 211 side with the side wall 212 interposed therebetween. A plurality of insertion holes 215 for inserting the fixture 5 are formed in the flange 213. Specific examples of the fixture 5 include bolts, rivets, and the like.

[0021] The upper member 21 is configured by joining a first case portion 21a and a second case portion 21b via a joining portion 21c. That is, the upper member 21 includes the first case portion 21a, the second case portion 21b, and the joining portion 21c.

[0022] The first case portion 21a and the second case portion 21b are portions that constitute the outer surface of the battery case 2. The first case portion 21a and the second case portion 21b of the present embodiment can also be rephrased as respective portions when the upper member 21 is divided into two in a top view. That is, the first case portion 21a and the second case portion 21b of the present embodiment each constitute a part of the top surface and a part of the side surface among the outer surface of the battery case 2.

[0023] The joint 21c is the part that joins the first case portion 21a and the second case portion 21b. The joint 21c is formed by joining the first case portion 21a and the second case portion 21b, for example, by welding. When the first case portion 21a and the second case portion 21b are joined by welding, the joint 21c is also called the weld line. When the first case portion 21a and the second case portion 21b are joined by welding, the method of joining the first case portion 21a and the second case portion 21b is not particularly limited.

[0024] As shown in Figure 3, the joint portion 21c is positioned so as not to overlap with the multiple battery cells 3 in a top view. In this embodiment, the joint portion 21c extends in a straight line in a top view.

[0025] In this embodiment, since the first case portion 21a and the second case portion 21b constitute a part of the top surface and a part of the side surface of the battery case 2, respectively, the joining portion 21c that joins them also constitutes a part of the top surface and a part of the side surface of the battery case 2. The top wall 211, the side wall 212, and the flange 213 each include a part of the first case portion 21a, the second case portion 21b, and the joining portion 21c.

[0026] As shown in Figures 1 and 2, the lower member 22 is a box-shaped member with an open top. The lower member 22 has a bottom wall 221, side walls 222, and flanges 223.

[0027] The bottom wall 221 is a plate-like portion that constitutes the lower surface of the outer surface of the battery case 2. In this embodiment, the bottom wall 221 is generally rectangular in shape.

[0028] The side wall 222 is a plate-like portion that extends from the outer peripheral edge of the bottom wall 221 to the upper surface of the bottom wall 221. Together with the side wall 212 of the upper member 21 described above, the side wall 222 constitutes one of the side surfaces of the outer surface of the battery case 2.

[0029] The flange 223 is a plate-like portion that extends outward from the edge of the side wall 222 opposite to the bottom wall 221. Here, "outside" can also be described as the side opposite to the bottom wall 221, with the side wall 222 in between. The flange 223 has a plurality of through holes 224 for inserting the fastener 5. The through holes 224 communicate with the through holes 215 of the upper member 21 when the lower member 22 is positioned below the upper member 21.

[0030] The upper member 21 and the lower member 22 are arranged to overlap vertically. Specifically, the upper member 21 is positioned above the lower member 22 such that the flanges 213 and 223 are in contact with each other, and the ceiling wall 211 and bottom wall 221 face each other with a gap between them. The ceiling wall 211 and side wall 212 of the upper member 21 and the bottom wall 221 and side wall 222 of the lower member 22 form a housing space 23. Fixing devices 5 are inserted through the insertion holes 215 and 224 of the upper member 21 and the lower member 22. The upper member 21 is fixed to the lower member 22 by these fixing devices 5.

[0031] The protective layer 4 is a layer that protects at least the joints 21c of the battery case 2 from corrosive substances. Corrosive substances are substances that can corrode the battery case 2. Specific examples of corrosive substances include water such as rainwater and saltwater, acids contained in de-icing agents, and oxygen contained in the atmosphere. Acids, for example, make the battery case 2 more susceptible to corrosion when they are present with water.

[0032] The protective layer 4 has properties that suppress the permeation of corrosive substances. Specific examples of properties that suppress the permeation of corrosive substances include water resistance and poor oxygen permeability. Furthermore, the protective layer 4 can be bonded to the joint 21c mechanically, chemically, or physically. Mechanical bonding is achieved by the protective layer 4 fitting into the irregularities on the surface of the joint 21c (the so-called anchoring effect). Chemical bonding is achieved by chemical bonds (e.g., covalent bonds) between atoms of the joint 21c and the protective layer 4. Physical bonding is achieved by intermolecular interactions (e.g., hydrogen bonds, electrostatic interactions, van der Waals forces) between the joint 21c and the protective layer 4.

[0033] The protective layer 4 is, for example, a coating film, an adhesive film, or a tack film. The coating film is a film formed by applying paint. Specific examples of paints include cationic paints. The adhesive film is a film formed by applying adhesive. Specific examples of adhesives include urethane adhesives, modified silicone adhesives, and epoxy adhesives. The tack film is a film formed by applying tack. Specific examples of tacks include urethane tacks.

[0034] The protective layer 4 is formed on the battery case 2 so as to be in close contact with at least the joint 21c from the outside (more specifically, the top) of the battery case 2. Close contact with the joint 21c can also be described as adhering to the joint 21c without any gaps. The protective layer 4 exhibits high adhesion to the joint 21c by mechanically, chemically, or physically bonding to the joint 21c.

[0035] In this embodiment, as shown in Figure 3, the protective layer 4 is formed to adhere closely to the entire area of ​​the joint 21c. The protective layer 4 extends in a straight line when viewed from above. The protective layer 4 is formed so as not to overlap with the multiple battery cells 3 when viewed from above.

[0036] Furthermore, in this embodiment, the protective layer 4 is formed to adhere closely not only to the joint portion 21c but also to the regions adjacent to the joint portion 21c in the first case portion 21a and the second case portion 21b. In other words, the protective layer 4 is not formed in the first case portion 21a and the second case portion 21b except in the regions adjacent to the joint portion 21c.

[0037] [2. Effects] (2a) When the battery pack 1 is installed in the vehicle, the battery case 2 may come into contact with corrosive substances. For example, if the battery pack 1 is located below the vehicle's floor panel F as shown in Figure 2, the battery case 2 may be exposed to rainwater splashed up from the tires while the vehicle is in motion. Rainwater, as mentioned above, is an example of a corrosive substance.

[0038] In the battery case 2, among the first case portion 21a, the second case portion 21b, and the joint portion 21c, the joint portion 21c is relatively more susceptible to corrosion. Therefore, a protective layer 4 is formed on the battery case 2 so as to be in close contact with the joint portion 21c from the outside of the battery case 2. With this configuration, because the protective layer 4 is formed to be in close contact with the joint portion 21c, the intrusion of corrosive substances into the interface between the joint portion 21c and the protective layer 4 can be suppressed. Thus, the joint portion 21c can be made less likely to come into contact with corrosive substances. As a result, the joint portion 21c can be made less susceptible to corrosion.

[0039] (2b) In addition, the joint portion 21c may have lower strength compared to the first case portion 21a and the second case portion 21b. With the above configuration, the protective layer 4 is formed to be in close contact with the joint portion 21c, thereby reinforcing the joint portion 21c.

[0040] (2c) The protective layer 4 may be formed over the entire outer surface of the battery case 2, for example. That is, the protective layer 4 may be formed from the outside of the battery case 2 so as to be in close contact with the entire first case portion 21a, the entire second case portion 21b, and the entire joint portion 21c. In this case, not only the joint portion 21c but also the first case portion 21a and the second case portion 21b can be made less likely to come into contact with corrosive substances. On the other hand, the time and cost required to form the protective layer 4 in the manufacture of the battery pack 1 tend to increase. For example, if the protective layer 4 is a paint film, it often takes a long time for the paint to dry. Also, a large amount of carbon dioxide may be emitted when the paint dries.

[0041] Therefore, in this embodiment, the protective layer 4 is not formed on the first case portion 21a and the second case portion 21b, except for the area adjacent to the joint portion 21c. With this configuration, it is possible to reduce the time and cost required to form the protective layer 4 while making it less likely for the relatively corroded joint portion 21c to come into contact with corrosive substances. Furthermore, the weight of the battery pack 1 can be reduced by the amount of the protective layer 4 that has been reduced.

[0042] (2d) In this embodiment, the protective layer 4 is formed to adhere closely not only to the joint portion 21c but also to the regions adjacent to the joint portion 21c in the first case portion 21a and the second case portion 21b.

[0043] For example, if the joint 21c is formed by welding the first case portion 21a and the second case portion 21b, the region adjacent to the joint 21c in the first case portion 21a and the second case portion 21b may have a slightly different composition compared to other regions due to the heat generated during welding. In this case, the region adjacent to the joint 21c in the first case portion 21a and the second case portion 21b may have reduced corrosion resistance compared to other regions.

[0044] However, with the above configuration, the protective layer 4 is formed to adhere closely to the region adjacent to the joint 21c in the first case portion 21a and the second case portion 21b, so that region is also less likely to come into contact with corrosive substances. Therefore, even if the corrosion resistance of that region is reduced, it is still possible to make that region less susceptible to corrosion.

[0045] (2e) The battery case 2 is made of, for example, a highly corrosion-resistant metal. With such a configuration, even if the protective layer 4 is not formed on the first case portion 21a and the second case portion 21b, the first case portion 21a and the second case portion 21b can be made less susceptible to corrosion.

[0046] (2f) The first case portion 21a and the second case portion 21b constitute the upper surface of the outer surface of the battery case 2. With this configuration, corrosive substances tend to accumulate on the surfaces of the first case portion 21a and the second case portion 21b, compared to the case where the first case portion 21a and the second case portion 21b constitute, for example, the side or bottom surface of the outer surface of the battery case 2. When corrosive substances accumulate on the surfaces of the first case portion 21a and the second case portion 21b, the joint portion 21c that joins them together is more likely to come into contact with the corrosive substances. In other words, the problem that the joint portion 21c may not have good corrosion resistance is likely to occur. Therefore, it is even more useful to form a protective layer 4 so as to adhere closely to the joint portion 21c, thereby making it difficult for the joint portion 21c to come into contact with corrosive substances.

[0047] (2g) Furthermore, when the first case portion 21a and the second case portion 21b constitute the upper surface of the battery case 2, the joint portion 21c that joins them also constitutes the upper surface of the battery case 2. The protective layer 4 is formed to be in close contact with the joint portion 21c from the upper side of the battery case 2.

[0048] With this configuration, for example, if the battery pack 1 is positioned below the vehicle's floor panel F as shown in Figure 2, the protective layer 4 is located between the floor panel F and the battery case 2. Therefore, if the battery case 2 bulges due to heat from the battery cells 3, the protective layer 4 can prevent contact between the battery case 2 and the floor panel F. In other words, the protective layer 4 can function as a buffer.

[0049] (2h) The joint portion 21c and the protective layer 4 are formed in a position that does not overlap with the battery cell 3 when viewed from above. With this configuration, the joint portion 21c and the protective layer 4 can be made less susceptible to the effects of heat from the battery cell 3. Therefore, deterioration of the protective layer 4 due to heat from the battery cell 3 can be suppressed.

[0050] [3. Other Embodiments] While embodiments of this disclosure have been described above, it goes without saying that this disclosure is not limited to the embodiments described above and can take various forms.

[0051] (3a) In the above embodiment, the protective layer 4 is formed on the battery case 2 so as to be in close contact with at least the joint portion 21c. Specifically, the protective layer 4 is formed on the battery case 2 so as to be in close contact with the entire joint portion 21c and the areas of the first case portion 21a and the second case portion 21b adjacent to the protective layer 4. However, the area on the battery case 2 in which the protective layer is formed is not particularly limited. The protective layer may be formed so as to be in close contact with, for example, only the entire joint portion 21c. Alternatively, the protective layer may be formed so as to be in close contact with the entire joint portion 21c, the entire first case portion 21a, and the entire second case portion 21b (i.e., in close contact with the entire outer surface of the battery case 2).

[0052] (3b) In the above embodiment, the joint portion 21c extends in a straight line when viewed from above. However, the shape of the joint portion is not particularly limited. For example, as shown in Figure 4, the joint portion 24c that joins the first case portion 24a and the second case portion 24b may extend while bending at least at one point when viewed from above. Figure 4 shows the upper member 24 in a state in which the protective layer has not been formed.

[0053] (3c) In the above embodiment, the joint portion 21c is formed in a position that does not overlap with the battery cell 3 in a top view. However, the arrangement of the joint portion on the upper member 21 is not particularly limited. The joint portion may be formed in a position that overlaps with the battery cell 3 in a top view, in addition to or instead of the position as in the above embodiment. In that case, the protective layer may also be formed in a position that overlaps with the battery cell 3 in a top view, in addition to or instead of the position as in the above embodiment, corresponding to the position of the joint portion. In other words, the arrangement of the protective layer on the upper member 21 is not particularly limited.

[0054] (3d) In the above embodiment, the protective layer 4 extends linearly along the linearly extending joint portion 21c when viewed from above. However, the shape of the protective layer is not particularly limited and may be appropriately changed, for example, depending on the shape of the joint portion.

[0055] (3e) Furthermore, the cross-sectional shape perpendicular to the extension direction of the protective layer is not particularly limited. For example, as in the embodiment shown in Figure 2, the cross-sectional shape perpendicular to the extension direction of the protective layer 4 may be rectangular. Also, for example, as in the first modified example shown in Figure 5A, the cross-sectional shape perpendicular to the extension direction of the protective layer 4A may be triangular. Also, for example, as in the second modified example shown in Figure 5B, the cross-sectional shape perpendicular to the extension direction of the protective layer 4B may be semicircular.

[0056] (3f) In the above embodiment, the protective layer 4 has the property of suppressing the permeation of corrosive substances. The protective layer may further have elasticity, for example. When the protective layer can function as a buffer member, as in the above embodiment, it is useful for the protective layer to have elasticity.

[0057] (3g) In the above embodiment, a rib 214 is formed on the ceiling wall 211 of the upper member 21. When a rib is formed on the ceiling wall of the upper member in this way, the shape of the rib is not particularly limited. For example, the rib may be a groove-shaped portion (so-called concave rib) as in the above embodiment, or a portion that protrudes from the ceiling wall (so-called convex rib). Also, for example, the rib may be a portion that extends in a straight line as in the above embodiment, or a portion that extends in a curved shape (for example, a wave shape). Also, for example, when multiple ribs are formed as in the above embodiment, the multiple ribs may be formed side by side as in the above embodiment, or they may be formed to spread out radially. Also, for example, a rib does not necessarily have to be formed on the ceiling wall of the upper member.

[0058] (3h) In the above embodiment, the upper member 21 has a first case portion 21a and a second case portion 21b. However, the upper member may have, for example, three or more case portions, or four or more case portions.

[0059] (3i) In the above embodiment, the first case portion 21a and the second case portion 21b constitute the upper surface of the battery case 2. That is, the portion that constitutes the upper surface of the battery case 2 (the ceiling wall 211 in the above embodiment) is composed of the first case portion 21a and the second case portion 21b. However, the portion of the battery case 2 that is composed of two or more case portions is not limited to the portion that constitutes the upper surface of the battery case 2. For example, in addition to or instead of the portion that constitutes the upper surface of the battery case 2, the portion that constitutes the side or bottom surface of the battery case 2 (the side walls 212, 222 or the bottom wall 221 in the above embodiment) may be composed of two or more case portions.

[0060] (3j) The functions of one component in the above embodiment may be distributed among multiple components, or the functions of multiple components may be integrated into one component. Also, some parts of the configuration of the above embodiment may be omitted. Also, at least some parts of the configuration of the above embodiment may be added to, replaced with, etc., the configuration of other above embodiments. [Explanation of Symbols]

[0061] 1...Battery pack, 2...Battery case, 21...Upper member, 21a...First case section, 21b...Second case section, 21c...Joint section, 22...Lower member, 23...Housing space, 3...Battery cell, 4...Protective layer, F...Floor panel.

Claims

[Claim 1] A battery pack configured to be mounted on a vehicle, A battery case made of metal, The battery cells housed in the aforementioned battery case, A protective layer formed on the aforementioned battery case, Equipped with, The aforementioned battery case is The first case portion and the second case portion constitute the upper surface of the outer surface of the battery case, A joint that joins the first case portion and the second case portion by welding, It has, The protective layer is formed so as to be in close contact with the joint from the outside of the battery case. A battery pack in which the joint and the protective layer are formed in a position that does not overlap with the battery cell when viewed from above.

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