Battery pack

Abstract

A battery pack comprising: a battery block composed of a plurality of secondary battery cells, each of which is provided with a gas discharge unit for discharging gas when internal pressure increases; and an exterior case for accommodating the battery block in an internal accommodation space. In the exterior case, a plurality of case-side discharge holes communicating with the accommodation space are opened on a case main surface on an inner surface. The case main surface faces the plurality of secondary battery cells and is provided with flexibility such that the case main surface deforms so as to expand outward in accordance with pressure of gas discharged from the gas discharge unit.

Description

Battery pack

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

[0002] Battery packs that house rechargeable secondary battery cells, such as lithium-ion secondary batteries, inside an exterior case to power electrical devices are used for various purposes (see, for example, Patent Document 1). In such battery packs, if any abnormality occurs in the secondary battery cells housed in the exterior case and high-temperature, high-pressure gas is generated inside the exterior case, the gas needs to be vented to the exterior of the exterior case. For this reason, a gas vent path needs to be provided inside the exterior case to vent the high-temperature, high-pressure gas (see, for example, Patent Document 1).

[0003] However, on the other hand, there is a demand for smaller and thinner outer cans to make battery packs easier to carry and reduce the area they occupy. However, there are conflicting demands, as providing space within the outer case for a gas exhaust path would result in the outer case becoming correspondingly larger.

[0004] Japanese Patent Application Laid-Open No. 2017-212065

[0005] One object of the present disclosure is to provide a battery pack that can ensure a gas exhaust path while avoiding an increase in the size of the exterior case. Another object is to provide a battery pack that facilitates the formation of a gas exhaust path and thereby enhances safety. Note that the description of these objects and objects of the present disclosure does not preclude the existence of other objects and objects. Furthermore, it is not necessary for one embodiment of the present disclosure to solve all of these objects. Furthermore, other objects can be extracted from the description of the specification, drawings, and claims of the present disclosure.

[0006] A battery pack according to one embodiment of the present disclosure comprises a battery block composed of a plurality of secondary battery cells, each of which has a gas exhaust section for exhausting gas when internal pressure rises, and an outer case that houses the battery block in an internal storage space, wherein the outer case has a plurality of case-side exhaust holes that communicate with the storage space on its inner surface, in a main case surface that faces the plurality of secondary battery cells, and the main case surface is flexible enough to deform and bulge outward in response to the pressure of the gas exhausted from the gas exhaust section.

[0007] According to a battery pack according to one embodiment of the present disclosure, by opening a plurality of case-side exhaust holes in the main surface of the case, rigidity is weakened and flexibility is imparted, and in an emergency, the increased internal pressure of the outer case is used to inflate the outer case, forming an expansion space which is used as a gas exhaust path, without constantly ensuring space for gas exhaust within the outer case. This makes it possible to achieve both the conflicting requirements of making the battery pack thin and ensuring a gas exhaust path.

[0008] 7 is a perspective view showing a battery pack according to embodiment 1. FIG. 1 is a cross-sectional view taken along line II-II of the battery pack of FIG. 1. FIG. 1 is a cross-sectional view taken along line III-III of the battery pack of FIG. 1. FIG. 1 is an exploded perspective view of the battery pack of FIG. 1 with the label removed. FIG. 4 is a perspective view seen from diagonally below. FIG. 4 is a plan view of the battery pack of FIG. 4. FIG. 4 is a further exploded perspective view of the battery pack of FIG. 4. FIG. 7 is an exploded perspective view of the battery holder of FIG. 7. FIG. 7 is a schematic cross-sectional view showing gas being discharged from a battery pack according to a comparative example. FIG. 7 is a schematic cross-sectional view showing gas being discharged from a battery pack according to embodiment 1. FIG. 7 is a cross-sectional view showing gas being released from the battery pack of FIG. 3.

[0009] The embodiments of the present disclosure may be specified by the following configurations and features.

[0010] In a battery pack according to another aspect of the present disclosure, in the above aspect, the case main surface is deformed outward by the pressure of the gas discharged from the gas discharge portion, thereby forming an expansion space between the inner surface of the case main surface and the surface of the battery block, and the expansion space guides the gas to the plurality of case-side exhaust holes. With this configuration, in an emergency, an increase in the internal pressure of the outer case is used to inflate the outer case, and the expansion space formed is used as a gas exhaust path, thereby making it possible to achieve both the conflicting requirements of making the battery pack thin and ensuring a gas exhaust path.

[0011] In a battery pack according to another aspect of the present disclosure, in any of the above aspects, the case main surface includes a thin-walled region formed by partially reducing the thickness of the case main surface, thereby imparting flexibility that allows the case main surface to easily deform so as to bulge outward due to an increase in internal pressure of the exterior case.

[0012] In a battery pack according to another aspect of the present disclosure, in any of the above aspects, the plurality of case-side exhaust holes are opened in the thin-walled region. With this configuration, high-temperature, high-pressure gas is exhausted from the outer case through the plurality of case-side exhaust holes opened in the thin-walled region, and pressure is applied to the inner surface of the thin-walled region, making it easier to deform the case main surface.

[0013] In addition, in a battery pack according to any one of the above embodiments, a plurality of grooves are formed on the outer surface of the case main face, and the plurality of case-side exhaust holes open into the grooves. With the above configuration, forming the plurality of grooves on the outer surface of the case main face imparts flexibility to the case main face, making it easier to form gas exhaust paths.

[0014] Furthermore, in a battery pack according to another aspect of the present disclosure, in any of the above aspects, the groove portion is formed in a lattice pattern, and the multiple case-side discharge holes are opened at the intersections of the lattice pattern of the groove portion.

[0015] According to yet another aspect of the present disclosure, in any of the above battery packs, the battery pack further includes a label covering the area of ​​the outer case where the groove is formed. With this configuration, the label blocks the case discharge hole under normal circumstances, preventing foreign matter from entering the outer case. In the event of an emergency, the pressure of gas discharged through the case discharge hole causes the label to break or peel off, opening the case discharge hole and allowing the gas to be released from the outer case to the outside.

[0016] In a battery pack according to still another aspect of the present disclosure, in any of the above aspects, each of the plurality of secondary battery cells has a cylindrical outer shape, the gas exhaust portion is provided on a first cell end face among the cylindrical end faces of each of the plurality of secondary battery cells, and the plurality of secondary battery cells are arranged in a position where the first cell end faces are aligned on the same plane. With the above configuration, by aligning the cell end faces through which high-temperature and high-pressure gas is exhausted from the secondary battery cells, it is possible to easily define a path for guiding the gas to the case-side exhaust hole.

[0017] In a battery pack according to yet another aspect of the present disclosure, in any of the above aspects, the exterior case includes a first case and a second case divided in a direction along the axes of the plurality of secondary battery cells, and the joint surface between the first case and the second case is closer to the second cell end face opposite the first cell end face than to the first cell end face. With this configuration, by separating the joint surface dividing the exterior case from the first cell end face, it is possible to further facilitate deformation of the case main surface.

[0018] In a battery pack according to yet another aspect of the present disclosure, in any of the above aspects, the first case is longer than the second case in a direction along the axes of the plurality of secondary battery cells. With this configuration, the outer case is not divided equally, and the first case is made longer than the second case, making it possible to bias the joint surface between the first case and the second case toward the end face of the second cell.

[0019] In a battery pack according to yet another aspect of the present disclosure, in any of the above aspects, the plurality of case-side exhaust holes are unevenly distributed on the first case, toward the surface where the first case joins with the second case. By distributing the case-side exhaust holes unevenly on the main surface of the first case, rather than evenly distributed on the main surface of the first case, the distance that gas discharged from the first cell end face travels to the case-side exhaust holes can be increased, and the gas pressure can be reduced before the gas is safely discharged from the outer case.

[0020] In a battery pack according to yet another aspect of the present disclosure, in any of the above aspects, the second case has a plurality of second case-side exhaust holes formed therein. By providing a plurality of second case-side exhaust holes in the second case, the distance traveled by gas exhausted from the first cell end face to the second case-side exhaust holes can be further increased, thereby weakening the gas pressure and enabling the gas to be safely exhausted from the outer case.

[0021] In addition, the battery pack according to another aspect of the present disclosure is any of the above-described aspects, further including a heat-resistant plate fixed in the internal space of the exterior case in a position facing the end face of the first cell. With this configuration, when high-temperature, high-pressure gas is discharged from the gas discharge portion provided on the end face of the first cell, the heat-resistant plate can receive the gas, reflect it in the opposite direction, and guide it toward the gas discharge path.

[0022] Embodiments of the present disclosure will be described below with reference to the drawings. However, the embodiments described below are merely examples for embodying the technical concepts of the present disclosure, and the present disclosure is not limited to the following. Furthermore, this specification does not in any way specify the components set forth in the claims to be those of the embodiments. The dimensions, materials, shapes, relative positions, etc. of components described in the embodiments are not intended to limit the scope of the present disclosure, and are merely illustrative examples, unless otherwise specified. The size and positional relationships of components shown in the drawings may be exaggerated for clarity. Furthermore, in the following description, the same names and symbols indicate components that are identical or of the same quality, and detailed descriptions will be omitted as appropriate. Furthermore, the elements constituting the present disclosure may be configured with the same components, such that multiple elements are shared by one component, or conversely, the functions of one component may be shared by multiple components.

[0023] The battery pack of the present disclosure can be used as a driving power source for mobile objects such as electric carts, electric scooters, and assisted bicycles, as a power source for portable electrical devices such as radios, electric cleaners, and power tools, as a backup power source for servers in stationary power storage applications, as a power supply device for home, office, or factory use, and as a driving power source for vehicles such as hybrid cars and electric automobiles. Hereinafter, a battery pack used as a driving power source for an electric motorcycle will be described as one embodiment of the present invention.

[0024] [Embodiment 1] A battery pack 100 according to Embodiment 1 of the present disclosure is shown in Figures 1 to 8. In these figures, Figure 1 is a perspective view showing the battery pack 100 according to Embodiment 1, Figure 2 is a cross-sectional view of the battery pack 100 of Figure 1 taken along line II-II, Figure 3 is a cross-sectional view of the battery pack 100 of Figure 1 taken along line III-III, Figure 4 is an exploded perspective view of the battery pack 100 of Figure 1 with the label unit 20 removed, Figure 5 is a perspective view of Figure 4 viewed obliquely from below, Figure 6 is a plan view of the battery pack 100 of Figure 4, Figure 7 is a further exploded perspective view of the battery pack 100 of Figure 4, and Figure 8 is an exploded perspective view of the battery holder 5 of Figure 7. The battery pack 100 shown in these figures includes an exterior case 10 and a battery block 2.

[0025] (External Case 10) The external case 10 houses the battery block 2. The external case 10 can have any shape that provides an internal storage space. In the example shown in Figures 1 to 7, the external case 10 has a box-like shape that extends in one direction. As shown in Figures 3 and 7, the box-shaped external case 10 is composed of two halves: a first case 11 and a second case 12. This external case 10 is preferably made of a material with excellent insulating properties, such as a resin such as polycarbonate or PC-ABS alloy. An internal space for housing the battery block 2 is provided inside the external case 10. Furthermore, the external case 10 has a case main surface 14 on its inner surface that faces the multiple secondary battery cells 1. In the example shown in Figures 1 to 5, the pair of upper and lower surfaces in the figures serve as the case main surfaces 14.

[0026] (Battery Block 2) As shown in Figure 7, a battery block 2 is housed inside the exterior case 10. The battery block 2, also known as a core pack, is composed of a battery holder 5 that houses multiple rechargeable battery cells 1. A circuit board 3 may also be added to the battery holder 5.

[0027] The battery block 2 is composed of a battery holder 5. In the example shown in FIG. 8 , a large number of cylindrical secondary battery cells 1 are housed and held in a horizontal position in the battery holder 5. The multiple secondary battery cells 1 are connected in series or parallel via lead plates 4 or the like. The number of series connections or parallel connections can be set as desired according to the required specifications. In the examples shown in FIGS. 7 and 8 , eight secondary battery cells 1 are used in the battery block 2, resulting in a 4-in-4 x 2-in-4 parallel configuration. However, the present disclosure is not limited to this configuration, and any number of secondary battery cells can be used according to the required specifications to achieve any series or parallel connection. Furthermore, a battery block may be composed of multiple sub-blocks, each housing multiple secondary battery cells. Combining multiple sub-blocks to form a single battery block makes it easy to adjust the number of secondary battery cells included in the battery block.

[0028] The battery holder 5 has multiple cylindrical storage sections 6 that individually store the rechargeable battery cells 1. In the example shown in FIG. 8 , the end faces of the cylindrical storage sections 6 of the battery holder 5 are open so that the rechargeable battery cells 1 can be inserted. However, the present disclosure does not limit the battery holder to this configuration; the battery holder can also be divided into multiple sub-holders. For example, the battery holder can be divided into two sections, and the rechargeable battery cells can be sandwiched between the two cylindrical storage sections. The number of sections in the battery holder is not limited to two, and can be three or more. Such a battery holder 5 can be made of a resin with excellent insulating properties, such as polycarbonate.

[0029] The battery holder 5 also has a connection window 7 on the end surface of the cylindrical storage tube 6 so that the cell end surfaces 1 a of the secondary battery cells 1 stored in the cylindrical storage tube 6 can be connected to the lead plates 4 from outside the battery holder 5. The connection window 7 is formed large enough to expose part of the cell end surfaces 1 a.

[0030] (Circuit Board 3) As shown in Figure 7, the battery block 2 is connected to the circuit board 3 via lead plates 4. The circuit board 3 is equipped with a charge / discharge circuit that charges and discharges the rechargeable battery cells 1, and a protection circuit that monitors the voltage and temperature of the rechargeable battery cells 1 and cuts off the current in the event of an abnormality. The circuit board 3 is made of a glass epoxy board or the like. A board holder for holding such a circuit board 3 may also be provided. The board holder can be connected to the battery holder.

[0031] (Lead Plates 4) The lead plates 4 connect the electrodes on the cell end faces 1a of the secondary battery cells 1 to each other, connecting multiple secondary battery cells 1 in series or parallel. In the example of Fig. 7, a lead plate 4 is disposed on each cell end face 1a of the secondary battery cells 1. Each cell end face 1a may also be divided into multiple lead plates 4. Each lead plate 4 is formed in a plate shape and connects the electrodes provided on the cell end faces 1a of the secondary battery cells 1 to each other.

[0032] These lead plates 4 are made of metal plates with excellent conductivity, such as aluminum or nickel. If necessary, a coating of nickel or other material may be added to the surface of the lead plate 4. The lead plate 4 is fixed to the cell end surface 1a of the secondary battery cell 1 by laser welding, spot welding, projection welding, or the like.

[0033] (Secondary battery cell 1) Each secondary battery cell 1 can be a secondary battery cell with a cylindrical or rectangular outer shape. In the example shown in FIG. 8 etc., cylindrical secondary battery cells 1 are used arranged in a row in a horizontal position. However, the number and arrangement of secondary battery cells 1 are not limited to this example, and any number and arrangement can be used as appropriate. For example, cylindrical secondary battery cells may be stacked in multiple stages. Furthermore, the multiple-stage stacked secondary battery cells may be arranged in a staggered pattern, or in a grid or matrix pattern.

[0034] The cylindrical secondary battery cell 1 has cell end faces 1a on both sides of the cylinder. The pair of cell end faces 1a is made up of a first cell end face 1a1 and a second cell end face 1a2.

[0035] Each secondary battery cell 1 has a positive and negative electrode, which are preferably provided on a first cell end surface 1a1 of the secondary battery cell 1. Such secondary battery cells 1 can be any known secondary battery, such as a lithium-ion secondary battery, a nickel-metal hydride battery, or a nickel-cadmium battery.

[0036] (Gas exhaust section 1c) The outer can of each secondary battery cell 1 is provided with a gas exhaust section 1c. The gas exhaust section 1c releases gas inside the outer can to the outside when the internal pressure of the outer can increases. The gas exhaust section 1c is provided on one of the cell end faces 1a of the secondary battery cell 1. In the example shown in FIG. 8 etc., the gas exhaust section 1c is provided on the first cell end face 1a1, which is on the positive electrode side of the secondary battery cell 1. Such a gas exhaust section 1c can be configured as a gas exhaust valve that opens in response to an increase in internal pressure of the outer can.

[0037] The multiple secondary battery cells 1 are held in the storage tube 6 of the battery holder 5 and are arranged so that the first cell end faces 1a1 are aligned on the same plane. This arrangement concentrates the surfaces from which high-temperature, high-pressure gas is discharged from the secondary battery cells 1 on one side, making it easier to define the gas discharge path 8 within the exterior case 10 that guides the gas to the case-side discharge hole 13.

[0038] (Case-side exhaust holes 13) Meanwhile, the exterior case 10 has case-side exhaust holes 13 formed in a portion thereof for discharging high-pressure gas to the outside when the gas exhaust portion 1c of the secondary battery cell 1 is opened and the gas is discharged. Specifically, a plurality of case-side exhaust holes 13 that communicate with the storage space are opened in the case main surface 14 of the exterior case 10. In the example shown in FIGS. 4 to 6 , the case-side exhaust holes 13 are provided on the front side of the first case 11 of the exterior case 10. In this example, the case-side exhaust holes 13 are circular, but the shape of the case-side exhaust hole is not limited to this shape and may be rectangular, chamfered rectangular, polygonal such as octagonal, hexagonal, or square, or circular, track-shaped, elliptical, or the like.

[0039] (Case main surface 14) The case main surface 14 is flexible enough to deform and swell outward in response to the pressure of the gas discharged from the gas discharge portion 1c. In this way, by opening a plurality of case-side discharge holes 13 in the case main surface 14, rigidity is weakened and flexibility is imparted. In an emergency, an increase in the internal pressure of the outer case 10 is used to inflate the outer case 10, forming an expansion space ES, which is used as the gas discharge path 8, without requiring a space for constant gas discharge within the outer case 10. This makes it possible to achieve the conflicting requirements of making the battery pack 100 thinner and ensuring a gas discharge path 8.

[0040] 9 , a battery pack 900 according to a comparative example has a gas exhaust path 908 formed between the outer surface of the battery block 902 and the inner surface of the exterior case 910. The gas exhaust path 908 is a path for guiding high-temperature, high-pressure gas discharged from one of the secondary battery cells 901 into the interior of the exterior case 910 in an emergency, so that the gas is discharged through a case-side exhaust hole 913 opened in the exterior case 910. On the other hand, under normal circumstances, the gas exhaust path 908 is not used but is present inside the exterior case 910. For this reason, the thickness D2 of the battery pack 900 is always increased by the amount of the gas exhaust path 908.

[0041] In contrast, in the battery pack 100 according to the first embodiment, the gap between the outer surface of the battery block 2 and the inner surface of the exterior case 10 is narrowed as shown in FIG. 10 . This allows the thickness D1 of the battery pack 100 to be thinner than that of the comparative example by the amount corresponding to the absence of a gas exhaust path 8 during normal operation. On the other hand, in an emergency, i.e., when high-temperature, high-pressure gas is exhausted from one of the secondary battery cells 1, the gas increases the internal pressure of the exterior case 10. In response to this, the case main surface 14 of the exterior case 10 is pushed out from the inside and deformed in a bulging direction, as shown in FIG. 11 . This forms an expansion space ES between the outer surface of the battery block 2 and the inner surface of the exterior case 10. By using this expansion space ES as the gas exhaust path 8, it is possible to guide the gas to the case-side exhaust hole 13. In this way, the battery pack 100 according to the first embodiment maintains a thin profile while still providing a gas exhaust path 8 during an emergency.

[0042] In particular, by constructing the exterior case 10 from resin, it is possible to provide flexibility that allows it to easily deform elastically. Furthermore, by providing a plurality of case-side exhaust holes 13 on each of the pair of case main surfaces 14 of the exterior case 10, the rigidity is reduced and flexibility is further increased, making it easier to deform due to the pressure when gas is released.

[0043] (Thin-Walled Regions 15) The case main surface 14 preferably includes thin-walled regions 15 formed by partially thinning the wall thickness. By forming the case main surface 14 in this manner as a thin portion, the rigidity is further weakened, making it easier for the case main surface 14 to bulge outward due to the pressure of the high-temperature, high-pressure gas discharged into the exterior case 10 from the gas discharge portion 1c. Such thin-walled regions 15 are preferably provided on the case main surface 14 on the first case 11 side. More preferably, as shown in Figures 3 and 4, the thin-walled regions 15 are unevenly distributed in a region of the first case 11 close to the joint surface 16 with the second case 12. In other words, the side of the secondary battery cell 1 far from the first cell end surface 1a1 where the gas discharge portion 1c is provided is made easier to deform. This increases the rigidity of the area close to the gas exhaust section 1c, i.e., the area that is exposed to high-pressure gas that has just been released from the gas exhaust section 1c, thereby preventing gas from leaking to the outside from unintended locations due to breakage or deformation of the outer case 10, and guiding the gas along the intended gas exhaust path 8, increasing the possibility of safely exhausting the gas from the outer case 10 to the outside.

[0044] 3, 10, 11, etc., the plurality of case-side exhaust holes 13 are preferably opened in the thin-walled region 15. This defines a gas exhaust path 8 for exhausting high-temperature, high-pressure gas from the outer case 10 through the plurality of case-side exhaust holes 13 opened in the thin-walled region 15, guiding the gas to the case-side exhaust holes 13 where the pressure is relatively low, and applying pressure to the inner surface of the thin-walled region 15 makes it easier to deform the case main surface 14.

[0045] (Groove 17) Furthermore, multiple grooves 17 can be formed on the outer surface of the case main surface 14. This further weakens the rigidity of the case main surface 14, increasing its flexibility and making it easier to deform. In the example shown in Figures 4 and 6, the grooves 17 are formed in the thin-walled region 15. The grooves 17 are formed in a lattice pattern with multiple lines crossing each other vertically and horizontally. The grooves 17 formed in this lattice pattern can be interconnected. The width and depth of the grooves 17 are designed according to the volume of the outer case 10 and the battery capacity of the secondary battery cells 1. For example, the width of the grooves 17 is 0.5 to 2.0 mm, and the depth is 0.1 to 1.0 mm.

[0046] It is also preferable that a plurality of case-side discharge holes 13 open into groove portions 17. This allows gas discharged from case-side discharge holes 13 to be guided to groove portions 17 as well. More preferably, each case-side discharge hole 13 opens at an intersection of the grid-like groove portions 17. This makes it easier for gas discharged from case-side discharge holes 13 to be guided so that it spreads up, down, left, and right along groove portions 17 that extend vertically and horizontally.

[0047] The number of case-side discharge holes 13 and the spacing between adjacent case-side discharge holes 13, i.e., the pitch, are also designed according to the volume of the outer case 10 and the battery capacity of the secondary battery cells 1. For example, the inner diameter of the case-side discharge holes 13 is set to φ=0.5 to 2.0 mm, and the pitch is set to 5 to 20 mm.

[0048] (Label 20) The battery pack 100 can also include a label 20 that is attached to the exterior case 10. The label 20 preferably covers the area where the groove 17 is formed. In this way, under normal circumstances, the label 20 blocks the case discharge hole 13, preventing unintended foreign matter from entering the interior of the exterior case 10 through the case discharge hole 13. In addition, in the event of an abnormality, the pressure of the gas discharged from the case discharge hole 13 causes the label 20 to break or peel off, opening the case discharge hole 13 and allowing the gas to be released from the exterior case 10 to the outside.

[0049] In the examples shown in Figures 4 and 5, the label 20 is attached to the thin-walled region 15. As a result, a closed space CS in the groove 17 is formed between the label 20 and the thin-walled region 15, as shown in Figure 3. Forming the groove 17 on the outside of the outer case 10 and forming the closed space CS between the label 20 and the groove 17 is effective in preventing clogging of the case-side exhaust hole 13. Specifically, when high-temperature, high-pressure gas is exhausted from the secondary battery cell 1, foreign matter such as broken pieces of the electrode assembly may be exhausted from the inside of the outer can of the secondary battery cell 1 along with the gas. If the foreign matter clogs the case-side exhaust hole 13, the gas may not be exhausted from the outer case 10, and the internal pressure of the storage space may increase. In response to this, forming the closed space CS on the outside of the outer case 10 and communicating it with the closed space CS outside the outer case 10 through the multiple case-side exhaust holes 13 allows some of the high-temperature, high-pressure gas released from the case-side exhaust hole 13 to the outside of the outer case 10 to be supplied to the closed space CS. As a result, high-temperature, high-pressure gas is supplied to the area where foreign matter is clogged in the case-side discharge hole 13 through the other case-side discharge holes 13. This applies pressure to the case-side discharge hole 13 from outside the outer case 10, pushing the foreign matter clogged in the case-side discharge hole 13 back inward, increasing the likelihood that the clog will be cleared. In this way, by forming the groove 17 on the surface of the outer case 10 and forming the closed space CS with the label 20, it is possible to eliminate or suppress clogging of some of the case-side discharge holes 13 by foreign matter.

[0050] The label 20 is made of a material that can be torn by pressure or temperature when gas is discharged to open the case-side discharge hole 13. For example, the label 20 can be made of a resin such as polycarbonate or polypropylene, or a paper base material impregnated with or coated with resin.

[0051] Furthermore, it is preferable to design the thickness of the label portion 20 and the thickness of the thin portion so that, when the label portion 20 is attached to the thin-walled region 15, the surface of the label portion 20 and the case main surface 14 are substantially flush with each other, as shown in FIG. 3 and other figures. It is preferable to pre-print information about the battery pack 100, such as the model number, manufacturer name, battery capacity, and ratings, on the label portion 20. The outer shape of the label portion 20 is rectangular in the examples of FIGS. 4 and 5 . However, the shape of the label portion is not limited to this and may be a horizontally elongated rectangle with chamfered corners, or a vertically elongated polygonal shape such as a square or octagon. Furthermore, at least a portion of the back side of the label portion 20 has an adhesive surface for affixing the label portion 20. Double-sided tape may be affixed to the periphery of the label portion to provide an adhesive surface. Adhesives or other adhesives may also be used to adhere the label portion, rather than being limited to double-sided tape.

[0052] (First Case 11) The exterior case 10 is divided into a first case 11 and a second case 12. In the examples shown in FIGS. 3 and 7 , the first case 11 and the second case 12 are divided in a direction along the axis of the exterior can of the secondary battery cell 1, which in this embodiment is the longitudinal direction of the secondary battery cell 1. The joint surface 16 between the first case 11 and the second case 12 is closer to the second cell end surface 1a2 than to the first cell end surface 1a1. This configuration separates the joint surface 16 that divides the exterior case 10 from the first cell end surface 1a1, making it easier to deform the case main surface 14. In other words, if the joint surface 16 between the first case 11 and the second case 12 were closer to the first cell end surface 1a1, high-pressure gas that had just been released from the gas exhaust portion 1c provided on the first cell end surface 1a1 would be irradiated onto the joint surface 16 between the first case 11 and the second case 12, potentially causing gas leakage or damage to the joint. Therefore, by separating the joint surface 16 as far as possible from the gas exhaust port, such a risk can be reduced and safety can be improved.

[0053] Specifically, the first case 11 is longer than the second case 12 in the longitudinal direction of the secondary battery cell 1. By not dividing the outer case 10 equally in this way and making the first case 11 longer than the second case 12, it is possible to position the joint surface 16 between the first case 11 and the second case 12 closer to the second cell end surface 1a2.

[0054] Furthermore, the plurality of case-side exhaust holes 13 are biased toward the joining surface 16 of the first case 11 with the second case 12. In this way, by biasing the case-side exhaust holes 13 toward the joining surface 16 with the second case 12 rather than providing them evenly on the main surface of the first case 11, the distance that gas discharged from the first cell end surface 1a1 travels to the case-side exhaust holes 13 is lengthened, and the gas pressure can be weakened before it is safely discharged from the outer case 10.

[0055] (Second Case Discharge Hole 13B) Grooves and case discharge holes can also be provided in the second case, not just the first case. In the example shown in FIG. 3 , the second case 12 has multiple second case discharge holes 13B formed in its second main surface, which intersects with the first main surface. By providing multiple second case discharge holes 13B in the second case 12, the distance traveled by gas discharged from the first cell end face 1a1 to the second case discharge holes 13B can be further increased, reducing the gas pressure and allowing the gas to be safely discharged from the outer case 10. The second case discharge holes 13B are also formed in the second groove 17B of the second thin-walled region 15B of the second case 12. A second label 20B is attached to the second thin-walled region 15B. The second thin-walled region 15B and second label 20B can be configured similarly to the thin-walled region 15 and label 20 of the first case 11.

[0056] (Heat-Resistant Plate 50) A heat-resistant plate 50 may also be placed between the surface of the battery holder 5 and the inner surface of the exterior case 10. In the example shown in FIG. 7 , the heat-resistant plate 50 is sized to cover the entire first cell end faces 1a1 of all of the secondary battery cells 1 in the battery block 2. By using the heat-resistant plate 50, which covers the battery holder 5 to improve impact resistance, to cover the cell end faces 1a where the gas exhaust ports 1c are located, even if high-temperature, high-pressure gas is exhausted from the gas exhaust port 1c of one of the secondary battery cells 1, this prevents the gas from immediately escaping from the battery pack and prevents a flame from igniting the gas from directly leaking outside the battery pack. This heat-resistant plate 50 can be made of a material with excellent insulating and fire-resistant properties, such as mica.

[0057] Thus, according to the present disclosure, even if a space for constant gas discharge is not secured within the outer case, in an emergency, an increase in the internal pressure of the outer case can be used to create an expansion space which can be used as a gas discharge path, thereby making it possible to achieve both the conflicting requirements of making the battery pack thinner and ensuring a gas discharge path.

[0058] In the above example, the battery pack is used as a power source for an electric scooter. However, the present disclosure is not limited to this. The battery pack can also be used for other purposes, such as attaching it to an electric device to be driven and supplying power to the electric device. Examples of electric devices include mobile objects such as electric vehicles and electric carts, as well as portable electric devices. In such electric devices, when the remaining capacity of the battery pack becomes low or the battery pack deteriorates over time, the battery pack can be replaced to continue using the electric device. However, the present disclosure is not limited to replaceable battery packs that mainly house secondary battery cells, but can also be applied to battery packs in which secondary battery cells are housed within the housing of the electric device. In the present disclosure, a battery pack is defined as a battery pack that houses secondary battery cells in a case, and also includes battery packs in which secondary battery cells for driving the electric device are built into the housing of the electric device itself. In other words, the present disclosure is not limited to replaceable battery packs, but can also be applied to electric devices that house secondary battery cells.

[0059] The battery pack according to the present invention can be suitably used as a driving power source for mobile objects such as electric scooters, electric carts and assisted bicycles, as a power source for radios, and as a power source for portable electrical equipment such as electric cleaners and power tools, as a backup power source for servers and the like, and as a stationary power storage device for home, office and factory use, etc.

[0060] DESCRIPTION OF SYMBOLS 100...Battery pack 1...Secondary battery cell 1a...Cell end face 1a1...First cell end face 1a2...Second cell end face 1c...Gas exhaust portion 2...Battery block 3...Circuit board 4...Lead plate 5...Battery holder 6...Storage cylinder 7...Connection window 8...Gas exhaust path 10...Outer case 11...First case 12...Second case 13...Case-side exhaust hole 13B...Second case-side exhaust hole 14...Case main surface 15...Thin-walled area 15B...Second thin-walled area 16...Joint surface 17...Groove portion 17B...Second groove portion 20...Label portion 20B...Second label portion 50...Heat-resistant plate 900...Battery pack 901...Secondary battery cell 902...Battery block 908...Gas exhaust path 910...Outer case 913...Case-side exhaust hole ES...Expansion space CS...Closed space D1: Thickness of the battery pack according to the first embodiment D2: Thickness of the battery pack according to the comparative example

Claims

1. A battery pack comprising: a battery block composed of multiple secondary battery cells, each having a gas exhaust section for exhausting gas when the internal pressure rises; and an exterior case that houses the battery block in an internal storage space, wherein the exterior case has multiple case-side exhaust holes that communicate with the storage space on its inner surface, in the main case surface that faces the multiple secondary battery cells, and the main case surface is flexible enough to deform and bulge outward in response to the pressure of the gas exhausted from the gas exhaust section.

2. A battery pack as claimed in claim 1, wherein the case main surface is deformed outward by the pressure of the gas discharged from the gas discharge section, forming an expansion space between the inner surface of the case main surface and the surface of the battery block, and the expansion space is used to guide the gas to the multiple case-side discharge holes.

3. A battery pack according to claim 1, wherein the main surface of the case is provided with a thin-walled area formed by partially reducing the wall thickness.

4. A battery pack according to claim 3, wherein the plurality of case-side discharge holes are opened in the thin-walled area.

5. A battery pack according to claim 4, wherein a plurality of grooves are formed on the outer surface of the main face of the case, and the plurality of case-side discharge holes are opened into the grooves.

6. A battery pack according to claim 5, wherein the plurality of grooves are formed in a lattice pattern, and the plurality of case-side discharge holes are opened at the intersections of the plurality of grooves.

7. A battery pack according to claim 6, further comprising a label portion that covers the plurality of grooves of the exterior case.

8. A battery pack according to any one of claims 1 to 7, wherein each of the plurality of secondary battery cells has a cylindrical outer shape, and each of the plurality of secondary battery cells has the gas exhaust section provided on a first cell end face of the cylindrical end faces of the plurality of secondary battery cells, and the first cell end faces of the plurality of secondary battery cells are aligned on the same plane.

9. A battery pack as set forth in claim 8, wherein the exterior case comprises a first case and a second case divided along the respective axes of the plurality of secondary battery cells, and the joint surface between the first case and the second case is closer to the end face of the second cell opposite to the end face of the first cell than to the end face of the first cell.

10. A battery pack according to claim 9, wherein the first case is longer than the second case in a direction along the axes of the plurality of secondary battery cells.

11. A battery pack according to claim 9, wherein the plurality of case-side discharge holes are unevenly distributed on the side of the first case that joins with the second case.

12. A battery pack according to claim 11, wherein the second case has a plurality of second case side discharge holes.

13. A battery pack according to claim 8, further comprising a heat-resistant plate fixed in the interior space of the outer case so as to face the end face of the first cell.

14. A battery pack as claimed in claim 11, wherein the number of the case-side exhaust holes closer to the joining surface with the second case is greater than the number of the case-side exhaust holes farther from the longitudinal centre of the first case towards the joining surface with the second case.

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