Cushioning material for battery packs

Abstract

To provide a compact and highly insulating cushioning material for battery packs. [Solution] The buffer member 21 for the battery pack is placed between adjacent secondary batteries 10, 10 in a battery pack in which multiple plate-shaped secondary batteries 10, 10 are stacked. The buffer member 21 includes a first buffer 201 and a second buffer 202. The first buffer 201 and the second buffer 202 are flat plates and are stacked in the direction in which the secondary batteries 10, 10 are stacked. The first buffer 201 and the second buffer 202 are made of the same cross-linked rubber. In the buffer member 21, the first buffer 201 and the second buffer 202 are not bonded to each other.

Description

Technical Field

[0001] The present invention relates to a buffer member for a battery pack. In particular, the present invention relates to a buffer member for a battery pack that is disposed between adjacent secondary batteries in a battery pack in which a plurality of plate-shaped secondary batteries are stacked.

Background Art

[0002] Rechargeable secondary batteries are used in a variety of applications such as electric vehicles, household appliances, and mobile phones. A secondary battery generally has an electrode body in which a positive electrode and a negative electrode are stacked via a separator, enclosed in a container together with an electrolyte. In applications such as automobiles, it is common to use a plurality of such secondary batteries as an integrated battery pack while electrically connecting them.

[0003] When a battery pack is configured by stacking plate-shaped secondary batteries, a buffer member may be disposed between adjacent secondary batteries. For example, Patent Document 1 discloses a technique related to a buffer member for a battery pack in which an adjacent member (2) is sandwiched between adjacent power storage elements (secondary batteries), and the adjacent member (2) includes a plate-shaped elastic portion (26). According to this battery pack, deformation of the holding member due to expansion of the power storage element (secondary battery) is suppressed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] By the way, secondary batteries may cause abnormal overheating or ignition. Even in such cases, it is required to suppress the chain of abnormal overheating and fire spread to adjacent secondary batteries.

[0006] However, the adjacent components (2) and elastic components (26) in the conventional technology may have poor heat resistance and fire resistance. If the secondary battery overheats or catches fire, the components may burn or be damaged by the high temperature and flames, which could result in insufficient suppression of a chain reaction of overheating or the spread of fire to adjacent secondary batteries. On the other hand, because compactness is required for battery packs, the cushioning material sandwiched between the secondary batteries must be as thin as possible.

[0007] The object of the present invention is to provide a compact and highly heat-insulating cushioning member for battery packs. [Means for solving the problem]

[0008] As a result of diligent research, the inventor discovered that the above problem could be solved by configuring the cushioning member so that a pair of cross-linked rubber cushioning bodies are laminated in a non-adherent state, and thus completed the present invention.

[0009] The present invention relates to a buffer member for a battery pack in which a plurality of plate-shaped secondary batteries are stacked, wherein the buffer member is placed between adjacent secondary batteries, and the buffer member includes a first buffer and a second buffer, the first buffer and the second buffer are flat plates, stacked in the direction in which the secondary batteries are stacked, the first buffer and the second buffer are made of the same cross-linked rubber, and the first buffer and the second buffer are not bonded to each other, thus providing a buffer member for a battery pack (First Invention).

[0010] In the first invention, preferably, the first buffer and the second buffer have substantially the same thickness, and the buffer member has a laminated structure symmetrical in the direction in which the secondary batteries are stacked (second invention). Also in the first invention, preferably, the buffer member further includes a third buffer, and the third buffer is not adhered to the first buffer and the second buffer, but is sandwiched between the first buffer and the second buffer (third invention). Also in any of the first to third inventions, preferably, the buffer member further includes a nonwoven fabric, the nonwoven fabric carrying heat-expandable, fire-resistant functional particles, the functional particles expand upon heating to improve the heat insulation properties of the nonwoven fabric, and the nonwoven fabric is laminated on the secondary battery side relative to the first buffer, or on the secondary battery side relative to the second buffer (fourth invention). [Effects of the Invention]

[0011] According to the buffering member for battery packs of the present invention (first invention), a compact (thin) buffering member for battery packs with excellent heat insulation properties can be obtained.

[0012] Furthermore, in the second invention, since the buffer member has a symmetrical laminated structure, even if the secondary battery on either side of the secondary battery sandwiching the buffer member overheats abnormally, a single buffer member can suppress the chain reaction of abnormal heat generation, and the space required for the buffer member can be significantly reduced. Furthermore, in the third invention, a third buffer, which is not bonded to the first buffer and the second buffer, is sandwiched between the first buffer and the second buffer, thus further improving heat insulation. Furthermore, as in the fourth invention, if a nonwoven fabric carrying heat-expandable fire-resistant particles is combined, the heat insulation properties of the buffering material can be further improved while also improving its fire resistance. [Brief explanation of the drawing]

[0013] [Figure 1] This is a perspective view showing the external appearance of a secondary battery. [Figure 2] This is a cross-sectional view of a secondary battery, shown in XX. [Figure 3]It is a schematic diagram showing the structure of a battery pack in which a buffer member for a battery pack according to the first embodiment is incorporated. [Figure 4] It is a cross-sectional view showing the structure of a buffer member for a battery pack according to the first embodiment. [Figure 5] It is a schematic diagram showing an example of the structure of a non-woven fabric that can be used for the buffer member for a battery pack according to the first embodiment. [Figure 6] It is a schematic diagram showing the structure of the large-diameter part and the small-diameter part of the long fibers. [Figure 7] It is a micrograph showing an example of the structure of the non-woven fabric. [Figure 8] It is a schematic diagram showing the behavior when a conventional buffer member is heated. [Figure 9] It is a schematic diagram showing the behavior when the buffer member for a battery pack according to the first embodiment is heated. [Figure 10] It is a cross-sectional view showing the structure of a buffer member for a battery pack according to the second embodiment. [Figure 11] It is a cross-sectional view showing the structure of a buffer member for a battery pack according to the third embodiment. [Figure 12] It is a cross-sectional view showing the structure of a buffer member for a battery pack according to the fourth embodiment.

Embodiments for Carrying Out the Invention

[0014] Hereinafter, embodiments of the invention will be described by taking as an example a battery pack used in an electric vehicle and a buffer member for a battery pack incorporated in the battery pack, while referring to the drawings. The invention is not limited to the individual embodiments shown below, and the form can be changed and implemented.

[0015] FIGS. 1 and 2 show the appearance and structure of the secondary battery 10 incorporated in the battery pack. FIG. 2 is a cross-sectional view taken along the X-X cross-section of FIG. 1. FIG. 3 schematically shows the structure of the battery pack 20 having a structure in which the secondary batteries 10 and 10 are stacked. FIG. 3 is drawn from the same direction as FIG. 2.

[0016] As shown in Figure 3, the battery pack 20 of this embodiment is constructed by electrically connecting and integrating multiple secondary batteries 10, 10. The battery pack 20 is constructed by stacking multiple flat secondary batteries 10, 10. In Figure 3, the left-right direction of the diagram is the direction in which the batteries are stacked.

[0017] Although not mandatory, typically, the positive electrode members 13 and negative electrode members 14 of each secondary battery are connected by busbars 23 to establish an electrical connection. Buffer members 21, 21 are also placed between the individual secondary batteries 10, 10. Typically, end plates 22, 22 are provided to sandwich the stacked structure of these secondary batteries 10, 10 and buffer members 21, 21, and the stacked structure of the battery pack 20 is maintained by fastening the end plates 22, 22 with fasteners such as bolts or bands. Known materials can be used for the busbars 23 and end plates 22 as appropriate.

[0018] The battery pack 20 can be housed in a battery case (not shown) or the like and installed in a vehicle such as a hybrid car. Typically, cooling air is blown through the battery case or the like to cool the battery pack 20, thereby cooling the individual secondary batteries 10, 10. Note that the means of cooling the batteries is not limited to air cooling using cooling air, but may also be liquid cooling using a coolant. Although not shown in Figure 3, a member for forming a passage for the coolant or cooling air to flow along the batteries may be placed between the secondary batteries 10, 10 in a stacked manner with the buffer member 21.

[0019] The buffer member 21 will now be described. The buffer member 21 has a structure in which multiple components are stacked. Figure 4 schematically shows the stacked structure of the buffer member 21. Figure 4 is drawn from the same direction as Figure 3. The left-right direction in Figure 4 corresponds to the direction in which the secondary batteries are stacked in the battery pack. The cushioning member 21 includes the cushioning body 200. Although not essential, the cushioning member 21 may also include a nonwoven fabric 1 laminated on the cushioning body 200, as in this embodiment.

[0020] The buffer 200 includes a first buffer 201 and a second buffer 202. The first and second buffers are plate-shaped. A third buffer may also be included, as in other embodiments described later. In this embodiment, the first buffer 201 and the second buffer 202 are stacked in the direction in which the secondary batteries are stacked to constitute the buffer 200.

[0021] The first buffer 201 and the second buffer 202 are made of crosslinked rubber. Furthermore, the first buffer 201 and the second buffer 202 are made of the same crosslinked rubber. Here, "the same crosslinked rubber" means that the main polymer of the rubber composition is the same, the main physical properties of the rubber such as hardness and permanent compression set are substantially the same, and the behavior of the rubber when exposed to heat is substantially the same. For example, rubber materials that differ only in coloring pigment and have the same other formulations are treated as the same rubber. By crosslinking the rubber, a predetermined elasticity is given to the first buffer 201 and the second buffer 202, and they function as buffers.

[0022] The crosslinked rubber constituting the first buffer 201 and the second buffer 202 is not particularly limited, but examples include silicone rubber, urethane rubber, acrylic rubber (ACM), ethylene propylene diene rubber (EPDM), and acrylonitrile butadiene rubber (NBR). The rubber is preferably flame-retardant.

[0023] The first buffer 201 and the second buffer 202 constituting the buffer 200 are flat plates. The first buffer 201 and the second buffer 202 may be solid rubber sheets or rubber plates. The first buffer 201 and the second buffer 202 may be made of foamed cross-linked rubber. Grooves or protrusions may be provided on the surfaces of the first buffer 201 and the second buffer 202. Although not essential, the surfaces of the first buffer 201 and the second buffer 202 may be decorated with fine irregularities (e.g., a fabric pattern transfer), or the surfaces of the first buffer 201 and the second buffer 202 may be roughened with a textured, matte, or hairline finish.

[0024] Furthermore, holes or conduits may be provided inside the first buffer 201 and the second buffer 202, or the first buffer 201 and the second buffer 202 may be formed in a flat bag shape. The shape of the plates of the buffer 200 and the first buffer 201 and the second buffer 202 is not particularly limited, but is typically rectangular, similar to the plate-shaped secondary battery 10. The first buffer 201 and the second buffer 202 can be manufactured using conventional methods for manufacturing rubber sheets, rubber plates, rubber components, etc., such as press molding, roll molding, extrusion molding, and injection molding.

[0025] The first buffer 201 and the second buffer 202 are not bonded to each other. They are stacked and, in this embodiment, in contact with each other, but are not bonded. Bonding here includes bonding with adhesives, crosslinking, and bonding with adhesives. The first buffer 201 and the second buffer 202, which are not bonded, can be easily separated.

[0026] While not essential, preferably, the buffer member 21 is configured to have a symmetrical structure in the stacking direction, that is, a line-symmetric structure with respect to the axis extending vertically in Figure 4, as shown in the embodiment in Figure 4. The buffer member may be asymmetrical, but a symmetrical structure like the buffer member 21 is efficient because it can similarly suppress the propagation of heat and flame to the battery on the opposite side regardless of which of the adjacent secondary batteries malfunctions.

[0027] Although not essential, in the buffer member 21 of this embodiment, the first buffer 201 and the second buffer 202 have substantially the same thickness, and the buffer member 21 and buffer 200 have a laminated structure that is symmetrical in the direction in which the secondary batteries are stacked. Also, although not essential, preferably, as in the buffer member 21 of this embodiment, nonwoven fabrics 1,1 having fire resistance and heat insulation properties are arranged on both sides of the buffer 200.

[0028] Furthermore, although not essential, preferably, as in other embodiments described later (Figures 11 and 12), the buffer members 29 and 27 may further include third buffers 203A and 203B, where the third buffers 203A and 203B are not adhered to either the first buffer 201 or the second buffer 202, but are sandwiched between the first buffer 201 and the second buffer 202. Specific examples of the third buffer include nonwoven fabric, woven fabric, fiber sheet, paper, rubber sheet, and resin plate. It is preferable that the third buffer also has flame retardancy or fire resistance.

[0029] Furthermore, although not essential, preferably as in this embodiment, the buffer member 21 further includes nonwoven fabrics 1,1, the nonwoven fabrics 1,1 supporting fire-resistant functional particles that have thermal expansion properties, and the thermal insulation properties of the nonwoven fabric are improved when heated as the functional particles expand. The nonwoven fabrics 1,1 are arranged in a laminated configuration either on the secondary battery side relative to the first buffer body 201, or on the secondary battery side relative to the second buffer body 202.

[0030] In the embodiment shown in Figure 4, the cushioning member 21 is constructed by laminating nonwoven fabrics 1,1 on both sides of the buffer body 200. If necessary, the nonwoven fabric 1 may be laminated on only one side of the buffer body 200. Although it is not essential to integrate the nonwoven fabric 1 with the buffer body 200, integration makes handling the cushioning member easier. The means of integration are not particularly limited, and it is sufficient that the buffer body 200 and the nonwoven fabric 1 are integrated to the extent that they do not separate when the cushioning member 21 is assembled into the battery pack. For example, the nonwoven fabric 1 may be integrated using an adhesive, adhesive, double-sided tape, etc., or it may be integrated by directly forming the nonwoven fabric 1 on the surface of the buffer body 200. Alternatively, the buffer body 200 may be placed in a nonwoven fabric bag and the two may be integrated.

[0031] In the laminated configuration of the buffer 200 and the nonwoven fabric 1, it is preferable that the nonwoven fabric 1 is sandwiched between the portions where the secondary battery 10 and the buffer 200 face each other and press against one another. That is, it is preferable that the nonwoven fabric 1 is positioned so that it blocks the space between the buffer 200 and the secondary battery 10. There may be portions of the buffer 200 that are not covered by the nonwoven fabric 1, and there may be portions of the nonwoven fabric 1 that protrude from the buffer 200.

[0032] Furthermore, preferably, as shown in the embodiment of Figure 10, the buffer member 28 may be configured such that an aluminum glass cloth 205 is placed between the nonwoven fabric 1 and the buffer body 200. The aluminum glass cloth is a material formed by laminating and integrating a glass fiber woven fabric and aluminum foil. The aluminum foil may be formed by vapor deposition or the like.

[0033] The nonwoven fabric 1 that can be used for the cushioning members 21, 28, and 27 will be described in detail below. The nonwoven fabric 1 supports heat-expandable, fire-resistant functional particles 4, 4. When heated, the heat-expandable functional particles 4, 4 expand, improving the heat insulation properties of the nonwoven fabric 1. Furthermore, the functional particles 4, 4 are fire-resistant and will not burn up for a predetermined time even when exposed to high temperatures such as flames. The expansion start temperature at which the functional particles 4, 4 begin to expand is set higher than the temperature during normal operation of the secondary battery 10. When the secondary battery is operating normally, the functional particles 4, 4 do not expand, but expand when the nonwoven fabric 1 is exposed to high temperatures due to abnormal overheating of the secondary battery or a fire. For example, a preferred range for the expansion start temperature of the heat-expandable, fire-resistant functional particles 4, 4 may be set to 250°C to 400°C.

[0034] Furthermore, it is preferable that the nonwoven fabric 1 is permeable to gas or liquid. For example, if the nonwoven fabric 1 is placed facing a location through which cooling air passes, it is preferable that the nonwoven fabric 1 is configured to allow air to pass through.

[0035] Examples of thermally expandable functional particles 4,4 include thermally expandable graphite and aluminum phosphite. Preferably, the functional particles 4,4 are inorganic particles that do not melt even when exposed to high temperatures and maintain their function as a fire-resistant heat insulating layer for a predetermined time (e.g., 10 to 30 minutes).

[0036] The form in which the nonwoven fabric 1 used for the buffer member 21 carries the thermally expandable functional particles 4, 4 is not particularly limited, and the functional particles may be carried on the fibers constituting the nonwoven fabric using a binder or the like. Preferably, as in the nonwoven fabric 1 of the embodiment shown in Figure 5, the thermally expandable functional particles 4, 4 are carried so as to be contained in and integrated with long fibers made of synthetic resin. When integrated in this form, the functional particles are less likely to fall off, and even if a large amount of functional particles are carried, air and liquid can easily pass through the nonwoven fabric. The structure of the nonwoven fabric 1 in the embodiment shown in Figure 5 will be described in detail below.

[0037] The nonwoven fabric 1 of the embodiment shown in Figure 5 is a nonwoven fabric containing long fibers made of synthetic resin, into which thermally expandable functional particles 4,4 are integrated. Here, long fibers refer to long fibers in contrast to short fibers in the fibers that make up the nonwoven fabric. Long fibers are also called filament yarns. Short fibers are called staple fibers, etc., and their length is generally several millimeters to several tens of centimeters, whereas long fibers are fibers that have not been cut into short pieces. Long fibers are typically spun by melt-blown, electrospinning, or spunbond methods and then stacked to form a nonwoven fabric. The nonwoven fabric 1 does not need to be composed only of long fibers; it may also contain short fibers, or long fibers and short fibers may be blended in a way that they are intertwined.

[0038] While not essential, preferably, the amount of functional particles 4,4 blended with nonwoven fabric 1 is approximately 10 to 500 g / m².

[0039] Furthermore, the nonwoven fabric may be a single layer, or it may be a laminated nonwoven fabric in which multiple nonwoven layers, films, sheets, woven fabrics, etc. are laminated together. Alternatively, the nonwoven fabric may be a composite nonwoven fabric in which a layer of nonwoven long fibers is laminated on top of a woven fabric or mesh material. The synthetic resin long fibers, into which the functional particles 4,4 are integrated, may be contained in only one of the nonwoven layers. Preferably, as shown in the embodiment of Figure 10, an aluminum glass cloth 203 may be laminated with a nonwoven fabric or composite nonwoven fabric containing the layer of nonwoven long fibers. The laminate of aluminum glass cloth and nonwoven fabric 1 has excellent fire resistance and heat insulation properties, and the nonwoven fabric becomes stronger and easier to handle.

[0040] Furthermore, while all of the long fibers contained in the nonwoven fabric 1 may be long fibers made of synthetic resin with functional particles integrated into them, the nonwoven fabric 1 may also contain other long fibers, such as long fibers without integrated functional particles. Although not essential, the nonwoven fabric 1 in the embodiment shown in Figure 5 is a single-layer nonwoven fabric made by electrospinning long fibers of synthetic resin in which functional particles are integrated.

[0041] Figure 5 schematically illustrates the structure of the nonwoven fabric 1 that can be used as a buffer member 21 for a battery pack in the first embodiment. Figure 7 is a micrograph of an example of the nonwoven fabric in the embodiment shown in Figure 5. In Figure 5, the small diameter portions 3,3 are represented by a single solid line. The long fibers contained in nonwoven fabric 1 have a diameter that changes along the longitudinal direction of the fiber, with multiple large-diameter sections 2,2 and small-diameter sections 3,3 arranged alternately. In other words, the long fibers are structured like a string of beads, with large-diameter sections 2,2 and small-diameter sections 3,3 linked together. That is, the diameter of the long fibers changes along the longitudinal direction of the fiber.

[0042] The small-diameter portions 3,3 of the long fibers are monofilaments formed from the synthetic resin. The synthetic resin is not particularly limited as long as it can be formed into fibers, but it is preferable that it is a synthetic resin suitable for producing long fibers by melt-blown or electrospinning methods. Furthermore, it is preferable that the synthetic resin is a resin that adheres to the functional particles described later. Preferably, the synthetic resin used as the raw material for the long fibers can be, for example, polyurethane resin or polyvinyl chloride resin.

[0043] The monofilament forming the small-diameter sections 3,3 may be composed solely of the aforementioned synthetic resin, but may also contain other compounding materials, such as particles with a diameter smaller than the diameter of the small-diameter sections, including reinforcing materials and bulking agents, or agents that improve the properties of the synthetic resin.

[0044] Although not mandatory, the fiber diameter of the small-diameter sections 3,3 is preferably 100 nanometers or more and 10 micrometers or less. Particularly preferably, the fiber diameter of the small-diameter sections 3,3 is 500 nanometers or more and 3 micrometers or less. Here, fiber diameter refers to the diameter of the fiber measured in a direction perpendicular to the direction of fiber extension, and is determined by taking a microscopic photograph of the nonwoven fabric 1 and measuring the fiber diameter of the small-diameter sections on the photograph. Preferably, the fiber diameter is measured at 10 to 20 small-diameter sections and the average of these measurements is treated as the fiber diameter of the small-diameter sections.

[0045] The large-diameter portions 2,2 contain thermally expandable functional particles 4,4. Although not essential, at least a portion of the large-diameter portions 2,2 is formed by solidifying multiple functional particles 4,4 with the synthetic resin into a string-like or ball-like shape. Here, "string-like" means that, with respect to the shape of the large-diameter portion, the length in the direction of fiber extension is greater than the length in the direction perpendicular to the direction of fiber extension, preferably three times or more. "Ball-like" means that, with respect to the shape of the large-diameter portion, the length in the direction of fiber extension is approximately the same as the length in the direction perpendicular to the direction of fiber extension, preferably 1 / 2 to 2 times. Note that the long fibers may also contain large-diameter portions that do not contain functional particles or large-diameter portions that contain only one functional particle.

[0046] The diameter of the large-diameter sections 2,2 is larger than the fiber diameter of the small-diameter sections 3,3. The diameter of the large-diameter sections is the diameter measured in a direction perpendicular to the direction of fiber extension. Preferably, the diameter is measured at 10 to 20 large-diameter sections and the average of these measurements is used as the diameter of the large-diameter sections. Although not essential, preferably the diameter of the large-diameter sections 2,2 is 150 nanometers or more and 300 micrometers or less. Particularly preferably the diameter of the large-diameter sections 2,2 is 1 micrometer or more and 50 micrometers or less. Also preferably, the diameter of the large-diameter sections 2,2 is 3 to 20 times the fiber diameter of the small-diameter sections 3,3, and particularly preferably 4 to 10 times.

[0047] Figure 6 schematically shows the structure of the large-diameter sections 2,2 and small-diameter sections 3,3 in a long fiber. The large-diameter section 2 contains multiple thermally expandable functional particles 4,4. In the illustrated form, these functional particles 4,4 are encased or bonded with the same synthetic resin that constitutes the small-diameter section, and solidified into a string-like or ball-like shape. In the large-diameter sections 2,2, the functional particles 4,4 may be bonded to each other by the synthetic resin, or they may be encased in a film-like or mesh-like synthetic resin. In the large-diameter sections 2,2, there may be only one functional particle in the radial direction of the fiber, or there may be multiple functional particles in the radial direction of the fiber. At the ends of the large-diameter sections 2,2, the large-diameter section 2 and the small-diameter section 3 are continuous so that the synthetic resin contained in the large-diameter section becomes the monofilament of the small-diameter section 3,3.

[0048] The functional particles 4,4 contained in the large-diameter sections 2,2 have thermal expandability and fire resistance. Preferably, in the nonwoven fabric 1, thermally expandable particles are used as functional particles. Examples of thermally expandable particles include thermally expandable microcapsules, thermally expandable graphite, and aluminum phosphite. An example of thermally expandable aluminum phosphite particles is "APA-100" from Taihei Chemical Industry Co., Ltd. Among aluminum phosphite particles, aluminum hydrogen phosphite particles (such as "NSF" from Taihei Chemical Industry Co., Ltd.) are particularly preferred. These particles have the property of expanding when heated to a predetermined temperature. When thermally expandable particles are included in the large-diameter sections 2,2, when the nonwoven fabric is heated, the large-diameter sections 2,2 expand, reducing the size and narrowing of the voids in the nonwoven fabric, resulting in a decrease in the air permeability of the nonwoven fabric. Furthermore, as the functional particles 4,4 expand, the particles themselves become foamed and form a hollow structure, making them less conductive to heat, and thus improving the heat insulation properties of the nonwoven fabric 1.

[0049] Preferably, the fiber diameter Ds of the small-diameter sections 3,3 is less than or equal to the diameter Dp of the functional particles 4,4 contained in the large-diameter sections 2,2. The fiber diameter Ds of the small-diameter sections 3,3 and the diameter Dp of the functional particles 4,4 may be substantially the same. In this invention, the diameter Dp of the functional particles 4,4 refers to the volume-average diameter. The diameter Dp of the functional particles 4,4 contained in the large-diameter sections is typically 300 nanometers or more and 200 micrometers or less. Although not essential, preferably, the fiber diameter Ds of the small-diameter sections 3,3 is 1 / 100 or more of the diameter Dp of the functional particles 4,4.

[0050] An example of a method for manufacturing the nonwoven fabric 1 of the above embodiment will be described. The nonwoven fabric 1 can be manufactured by applying the melt-blown method or the electrospinning method.

[0051] First, in the first step, the liquefied synthetic resin and the thermally expandable functional particles are mixed. The synthetic resin is liquefied by heating and melting it, or by dissolving it with a solvent. The functional particles 4,4 are mixed and dispersed in the liquefied synthetic resin. Alternatively, the functional particles may be kneaded into the synthetic resin beforehand, then heated and melted to obtain a liquid synthetic resin in which the functional particles are dispersed, or the synthetic resin may be dissolved with a solvent or the like to liquefy it, and then the functional particles may be mixed and dispersed.

[0052] In this embodiment, polyurethane resin was dissolved in a solvent to liquefy it, and aluminum hydrogen phosphite powder (manufactured by Taihei Chemical Industry Co., Ltd., NSF, volume average diameter 5 micrometers) was mixed in as functional particles 4,4 and stirred to disperse.

[0053] Next, as a second step, following the first step, the liquid synthetic resin in which the functional particles 4,4 are dispersed is spun into long fibers by melt-blown or electrospinning and deposited to form a nonwoven fabric.

[0054] The liquid synthetic resin extruded from the spinning nozzle is stretched by centrifugal force, gravity, electrostatic force, etc., to form thin fibers. These thin fibers become the small-diameter portions 3,3 of the long fibers. At this time, when functional particles 4,4 are extruded from the nozzle together with the liquid synthetic resin, the portions where the functional particles 4,4 are gathered solidify into string-like or ball-like structures to form large-diameter portions 2,2, while the excess synthetic resin is stretched to form small-diameter portions 3,3, resulting in a continuous chain of long fibers in which large-diameter portions 2,2 and small-diameter portions 3,3 are alternately linked together. The resulting long fibers solidify as the solvent evaporates and the temperature drops, accumulating on the base of the spinning apparatus to produce the nonwoven fabric 1.

[0055] Although not mandatory, the second step may be performed using rubber sheets or rubber plates that will become the buffer 200, first buffer 201, and second buffer 202 as a base material, and the nonwoven fabric 1 may be directly formed on the surface of the buffer 200, etc., and integrated with the buffer 200. In this way, the step of integrating the buffer 200 and the nonwoven fabric 1 can be omitted, and the nonwoven fabric 1 is easier to handle. When forming the nonwoven fabric 1 by spinning the rubber material that will become the buffer 200 using an electrospinning method, it is preferable to adjust the conductivity of the rubber material itself or adjust its electrostatic properties by spray treatment, etc.

[0056] (Specific examples of nonwoven fabrics) In a specific example, aluminum hydrogen phosphite, or "NSF" (average particle diameter 5 micrometers), was used as a functional particle to obtain a nonwoven fabric 1 in which the diameter of the large-diameter sections 2,2 was approximately 2 to 10 micrometers (average diameter 6 micrometers), and the diameter of the small-diameter sections 3,3 was approximately 0.5 to 1.5 micrometers (average diameter 0.9 micrometers). The amount of functional particles 4,4 blended into the obtained nonwoven fabric 1 was approximately 100 g / m². By layering many long fibers, the amount of functional particles 4,4 blended per unit area in the nonwoven fabric 1 can be increased further. Figure 7 shows a micrograph of the specific nonwoven fabric. In Figure 7, only a small portion of the layers in the thickness direction of the nonwoven fabric is photographed so that the fiber morphology can be clearly seen.

[0057] By adjusting the amount of functional particles mixed, the viscosity and dispensing speed of the liquid synthetic resin, the nozzle diameter, the applied electrostatic voltage, the distance from the nozzle to the base, the ambient temperature, etc., the size, length, diameter, and ratio between the large-diameter sections 2,2 and the small-diameter sections 3,3 can be adjusted.

[0058] When the above nonwoven fabric 1 is manufactured using the melt-blown method or the electrospinning method, the synthetic resin is drawn out from the large-diameter portion to the small-diameter portion during spinning, so that less synthetic resin remains in the large-diameter portion. As a result, the synthetic resin coating covering the functional resin in the large-diameter portion becomes thinner or more mesh-like. This thinning or mesh-like synthetic resin coating allows the thermal expansion properties of the functional particles to be exhibited more quickly and effectively, which is preferable.

[0059] Let me explain the secondary battery 10. As shown in Figures 1 and 2, the secondary battery 10 is constructed by sealing electrode bodies 11 together with an electrolyte (not shown) in a container 12. Each electrode body 11 is a single power generation unit. As in this embodiment, one electrode body 11 may be housed in the container 12, but multiple electrode bodies 11, 11 may be housed in the container 12. The secondary battery 10 is sometimes called a single cell or battery element in contrast to the battery pack 20. The shape of the secondary battery 10 is not particularly limited and may be cylindrical, but it is preferably flat, as in this embodiment. A flat secondary battery is sometimes called a rectangular battery.

[0060] In the secondary battery 10, known components can be used as the electrode body 11, electrolyte, container 12, positive electrode member 13, and negative electrode member 14 as appropriate. These components can be assembled into the secondary battery 10 by known methods.

[0061] The electrode body 11 comprises a positive electrode, a separator, and a negative electrode. The positive electrode, separator, and negative electrode are in sheet form. The positive electrode and negative electrode are stacked with the separator sandwiched between them, and the stacked material is wound up to form the electrode body 11. In this embodiment, the electrode body is flat (plate-shaped).

[0062] Suitable and known materials can be used for the positive electrode, negative electrode, and separator. The positive electrode is conductive and contains a positive electrode active material (e.g., lithium transition metal composite oxide). The negative electrode is conductive and contains a negative electrode active material (e.g., graphite). The separator may be a porous resin film.

[0063] The electrolyte can be appropriately selected from known electrolytes. The electrolyte may be a non-aqueous electrolyte containing a non-aqueous solvent (e.g., ethylene carbonate) and an electrolyte salt (e.g., an inorganic lithium salt). Alternatively, the electrolyte may be a solid electrolyte.

[0064] The container 12 is not particularly limited as long as it can enclose the electrode body 11 and the electrolyte. The container 12 may be made of resin or metal.

[0065] The positive electrode of electrode body 11 is connected to positive electrode member 13, which is exposed outside the container 12. The negative electrode of electrode body 11 is connected to negative electrode member 14, which is also exposed outside the container 12. The positive electrode member 13 and the negative electrode member 14 become the external terminals of the secondary battery 10 and are electrically connected to a busbar 23 or the like.

[0066] When assembling the secondary batteries 10,10 and the buffer members 21,21 to manufacture the battery pack 20, the two are stacked alternately to obtain the battery pack 20 with a stacked structure as shown in Figure 3. In this case, if the buffer member 21 includes a nonwoven fabric 1, it is preferable to arrange the buffer members 21,21 between adjacent secondary batteries 10,10 so that the nonwoven fabric 1 blocks the space between the buffer body 200 and the secondary batteries 10. Furthermore, if the buffer member 21 includes an aluminum glass cloth 203, it is preferable to arrange the aluminum glass cloth 203 between the nonwoven fabric 1 and the buffer body 200.

[0067] The effects of a buffer member in which the first buffer and the second buffer are laminated without being bonded together, as described above, will now be explained. The buffer member of the above embodiment is a compact (thin) buffer member for a battery pack with excellent heat insulation properties. That is, compared to a single-layer buffer member of the same thickness, the buffer member of the above embodiment has superior heat insulation properties and can keep the temperature of the side opposite to the side being heated lower.

[0068] First, we will describe the behavior of a conventional cushioning material, which is a single-layer rubber sheet (3 mm thick) made of cross-linked rubber (EPDM), when a secondary battery placed on one side of the cushioning material overheats abnormally.

[0069] As a simple test for abnormal battery overheating, a hot iron plate heated to approximately 700°C was placed on one side, simulating an overheated battery. A buffer material was then pressed against the hot iron plate for a predetermined time (e.g., 5 minutes) at a predetermined pressure P, and its behavior was observed.

[0070] Cross-linked rubber cushioning materials maintain their shape up to around 300°C even when heat H is applied, because they are cross-linked. However, when they come into contact with a hot iron plate and the temperature rises further, decomposition of polymers and other materials occurs, resulting in plasticity and fluidity. As a result, in the case of conventional single-layer rubber sheet cushioning materials, the plasticized rubber material is pushed out by pressure P and protrudes from the edges of the sheet. This is schematically shown in Figure 8, with the edge of the cushioning material before protrusion shown by a dashed line and the behavior of protrusion due to heating shown by a white arrow.

[0071] In Figure 8, the lower part of the figure corresponds to a heated iron plate, with heat H applied to the buffer member from below and pressure P applied to the buffer member from above. The same applies to Figure 9. In the conventional single-layer rubber sheet cushioning member 99, as shown in Figure 8, the plasticized rubber material was extruded along the entire length in the thickness direction at the edge of the rubber sheet. This means that in the conventional single-layer rubber sheet cushioning member 99, the heat H transmitted from below was transmitted to the entire thickness direction of the rubber sheet, causing the entire rubber sheet to become plasticized. In other words, in the conventional single-layer rubber sheet cushioning member 99, the temperature reached above the temperature at which the crosslinked rubber becomes plasticized was reached on the side opposite to the heated side (the lower side in Figure 8) (the upper side in Figure 8).

[0072] On the other hand, a similar test was performed on a cushioning member in which the first cushioning body 201 and the second cushioning body 202 were laminated without being bonded together (only the cushioning body 200, without the nonwoven fabrics 1,1), corresponding to the cushioning member 21 of the above embodiment. The thickness of the first cushioning body 201 and the second cushioning body 202 was 1.5 mm each, and the total thickness of the laminated cushioning member was 3 mm, which is the same as the single-layer cushioning member of the prior art. The rubber material was also the same as that of the single-layer cushioning member 99.

[0073] Surprisingly, the test results differed from those of the conventional single-layer rubber sheet cushioning member 99. Despite being heated (H) and pressed (P) under the same conditions, in the laminated cushioning member corresponding to the cushioning member 21 of the above embodiment, as shown in Figure 9, the portion of the first cushioning body 201 that was heated became very hot and plasticization progressed, with the plasticized rubber material being extruded from the edges. On the other hand, the portion of the second cushioning body 202 opposite to the heated side hardly had any plasticized rubber material extruded. This means that less heat was transferred to the second cushioning body 202, and the temperature of the second cushioning body 202 did not rise enough to plasticize.

[0074] In other words, in the above embodiment, the cushioning member consists of a first cushioning body 201 and a second cushioning body 202 made of the same cross-linked rubber, which are laminated without being bonded to each other. Therefore, compared to a single-layer cushioning member of the same thickness, less heat is transferred to the opposite side of the cushioning member, and the temperature rise on the opposite side can be suppressed. In other words, it has become a compact yet highly insulating cushioning member for battery packs. Such a cushioning member is suitable for suppressing the chain reaction of overheating and the spread of fire in the event of abnormal overheating or fire in a secondary battery.

[0075] Although the detailed mechanism by which the buffer member 21 (buffer body 200) of the above embodiment can limit heat transfer compared to the conventional technology, even though it is made of the same material and has the same thickness, is unknown, it is presumed that because the first buffer body 201 and the second buffer body 202 are not bonded to each other, the first buffer body 201 and the second buffer body 202 are discontinuous at a microscopic level, and a fine gap exists between them as a thermal gap. This thermal gap suppresses heat conduction from the first buffer body 201 to the second buffer body 202, thereby suppressing the temperature rise and plasticization of the second buffer body 202.

[0076] Although not mandatory, from the viewpoint of further enhancing the effect of the thermal gap between the first buffer 201 and the second buffer 202, talc powder or the like may be dusted onto the contact surfaces of the first buffer 201 and the second buffer 202, or the surface may be roughened by creating fine irregularities such as a pear-skin pattern, texture, or matte finish, or grooves, ridges, protrusions, or depressions may be provided. Note that these surface roughenings, grooves, ridges, and protrusions may be provided on only one of the first buffer 201 or the second buffer 202.

[0077] Furthermore, as with the buffer member 21 of the first embodiment described above, if the first buffer 201 and the second buffer 202 have substantially the same thickness and have a stacked structure symmetrical in the direction in which the secondary batteries are stacked, then the heat transfer characteristics from one side of the buffer member 21 and the heat transfer characteristics from the opposite side can be ensured to be equal. In this way, even if abnormal overheating occurs in the secondary battery on either side, a single buffer member can suppress the chain reaction of abnormal overheating, and the buffer member can be made more compact.

[0078] Furthermore, as with the buffer members 29 and 27 of other embodiments described later, if the buffer members 29 and 27 further include third buffer bodies 203A and 203B, and the third buffer bodies 203A and 203B are not bonded to the first buffer body 201 and the second buffer body 202 but are sandwiched between the first buffer body 201 and the second buffer body 202, the thermal insulation effect is further improved. This is because the number of non-bonded thermal gaps increases.

[0079] The third buffers 203A and 203B may be nonwoven fabrics, woven fabrics, rubber sheets, plastic sheets, etc. Nonwoven fabrics and woven fabrics are particularly preferred from the viewpoint of reliably creating a thermal gap because they do not adhere well to the first buffer 201 and the second buffer 202. It is particularly preferable to use nonwoven fabrics or woven fabrics made of heat-resistant, fire-resistant, and flame-retardant fibers such as carbon fibers and aramid fibers as the third buffer.

[0080] Furthermore, as with the buffer member 21 of the first embodiment described above, the buffer member further includes nonwoven fabrics 1,1, and the nonwoven fabrics 1,1 carry fire-resistant functional particles that have thermal expansion properties, and when heated, the functional particles expand, improving the thermal insulation properties of the nonwoven fabric. When the nonwoven fabrics 1,1 are laminated on the secondary battery side of the first buffer body 201 or on the secondary battery side of the second buffer body 202, the thermal insulation effect of the buffer member 21 becomes more pronounced due to the thermal insulation and fire resistance exhibited by the nonwoven fabrics. In other words, if a nonwoven fabric carrying fire-resistant particles with thermal expansion properties is combined with the secondary battery side, the thermal insulation properties of the buffer member can be further improved while also improving its fire resistance.

[0081] The invention is not limited to the embodiments described above and can be implemented with various modifications. Other embodiments of the invention will be described below, but in the following description, the focus will be on the parts that differ from the embodiments described above, and detailed descriptions of parts that are similar will be omitted. Furthermore, these embodiments can be implemented by combining or substituting parts of each other.

[0082] Figure 10 shows a buffer member 28 for a battery pack according to the second embodiment. Although not essential, in this embodiment, the surfaces of the first buffer body 201A and the second buffer body 202A each have a plurality of parallel grooves, and the first buffer body 201A and the second buffer body 202A are stacked so that the surfaces with grooves face each other. Although not essential, the grooves on the first buffer body 201A extend in a direction perpendicular to the plane of the paper in Figure 10, and the grooves on the second buffer body 202A extend in the vertical direction of Figure 10, and they are stacked so that their grooves are perpendicular to each other.

[0083] In addition to the fact that the first buffer 201A and the second buffer 202A are not bonded together, the provision of grooves on the contact surfaces of the first buffer 201A and the second buffer 202A ensures that a thermal gap is more reliably created at the contact surface, thereby improving the thermal insulation performance of the buffer member 28. Furthermore, if the grooves are configured to be perpendicular to each other, the buffer member 28 can withstand stronger pressure while maintaining space or gaps between the first buffer 201A and the second buffer 202A.

[0084] In the embodiment shown in Figure 10, grooves are provided on both the first buffer 201A and the second buffer 202A, but grooves may be provided on only one of the buffers.

[0085] Furthermore, although not essential, in the buffer member of the second embodiment, an aluminum glass cloth 205 is laminated between the nonwoven fabric 1 and the first buffer 201A and the second buffer 202A. In particular, from the viewpoint of fire resistance and heat insulation, it is preferable that the aluminum glass cloth 205 is laminated such that the aluminum is on the side of the nonwoven fabric 1 and the glass cloth is on the side of the first buffer 201A and the second buffer 202A.

[0086] When aluminum glass cloth 205 is placed between the nonwoven fabric 1 and the buffer, fire resistance and resistance to the spread of flames are more reliably improved. Although the aluminum glass cloth itself is easily burned when exposed to flames, if the nonwoven fabric 1 is placed on the side of the secondary battery (flame) that is closer to the aluminum glass cloth, the amount of heat reaching the aluminum glass cloth is reduced due to the fire resistance and heat insulation properties of the nonwoven fabric 1, making it less likely to burn. In addition, the aluminum glass cloth acts as a backup material for the nonwoven fabric 1, making it less likely to collapse or dissipate even when the nonwoven fabric 1 is exposed to flames or gas emissions, thus maintaining the high fire resistance and heat insulation properties of the buffer material.

[0087] Furthermore, even if the nonwoven fabric 1 is thin and easily torn, if the nonwoven fabric 1 is formed using an electrospinning method with aluminum glass cloth 205 as the base material, and the two are laminated and integrated, the nonwoven fabric 1 becomes more tear-resistant, which is advantageous as it makes handling easier during the assembly of the cushioning member 28 and the battery pack.

[0088] Figure 11 shows a buffer member 29 for a battery pack according to the third embodiment. As with the buffer member 29 of this embodiment, the buffer member 29 does not necessarily have to be made of nonwoven fabric. In addition, in the buffer member 29 of this embodiment, a third buffer member 203A is laminated between the first buffer member 201 and the second buffer member 202. The third buffer member 203A is not bonded to either the first buffer member 201 or the second buffer member 202.

[0089] According to the buffer member 29 for the battery pack of the third embodiment, since the third buffer 203A is laminated without adhesive, the buffer 200A has two non-adhesive contact surfaces that form a thermal gap, thereby further improving heat insulation. In addition, if a woven or non-woven fabric made of fire-resistant fibers is used as the third buffer 203A, the heat insulation is particularly improved.

[0090] Figure 12 shows a buffer member 27 for a battery pack according to the fourth embodiment. As with the buffer member 27 of this embodiment, the buffer member 27 may have a nonwoven fabric 1 on only one side. In this embodiment, the buffer body 200B constituting the buffer member 27 is constructed by laminating a first buffer body 201, a second buffer body 202, and a third buffer body 203B, all made of the same cross-linked rubber, in a non-adherent state. Even with this configuration, the buffer body 200B has two non-adherent contact surfaces, which further enhances its heat insulation properties. Furthermore, if the third buffer body 203B is made of rubber, the buffer body 200B becomes less prone to deformation, making it a buffer more suitable for a battery pack.

[0091] In the above description of the embodiment, examples were given of the nonwoven fabric 1 being attached to one or both sides of a plate-shaped buffer 200, but the form is not limited to these. For example, the nonwoven fabric 1 may be folded into a U shape to cover two sides of a flat buffer 200. Alternatively, the nonwoven fabric 1 may be wrapped around the buffer 200. Alternatively, the buffer 200 may be inserted into a bag-shaped nonwoven fabric 1.

[0092] The field in which the secondary battery 10 is used is not particularly limited. It can be applied to other technical fields other than those exemplified in the above embodiment. For example, while the secondary battery 10 can be used in electric vehicles and hybrid vehicles, the applications of batteries and battery packs are not limited to automobiles. For example, secondary batteries can also be used in electric bicycles. Secondary batteries and battery packs may also be used as power sources for trains, ships, and aircraft. Furthermore, secondary batteries and battery packs may be used as backup power sources for computers, auxiliary storage batteries for wind power generators and solar power generators, and auxiliary or backup power sources for industrial equipment. Furthermore, the secondary battery may be, for example, a lithium-ion battery, or it may be an all-solid-state battery. [Industrial applicability]

[0093] The buffer member for the battery pack in the above embodiment can be incorporated into a battery pack used as a power source for electric vehicles, etc., which can suppress the spread of fire within the battery and has high industrial value. [Explanation of Symbols]

[0094] 1 Nonwoven fabric 2. Large diameter section 3 Small diameter section 4 Functional particles 10 Secondary battery 11 Electrode body 12 containers 13 Positive electrode component 14 Negative electrode component 20 battery packs 21 Cushioning material 200 buffer 201 First buffer 202 Second buffer 22 End Plates

Claims

1. In a battery pack in which multiple plate-shaped secondary batteries are stacked, a buffer member for the battery pack is placed between adjacent secondary batteries, The cushioning member includes a first cushioning body and a second cushioning body. The first and second buffers are flat plates and are stacked in the direction in which the secondary batteries are stacked. The first and second buffers are made of the same cross-linked rubber. The first buffer and the second buffer are not bonded to each other. Cushioning material for battery packs.

2. The first buffer and the second buffer have substantially the same thickness. The buffer member has a stacked structure that is symmetrical in the direction in which the secondary batteries are stacked. A buffer member for a battery pack according to claim 1.

3. The aforementioned buffering member further includes a third buffering body, The third buffer is not attached to the first and second buffers, but is sandwiched between them. A buffer member for a battery pack according to claim 1.

4. The cushioning member further includes a nonwoven fabric, The aforementioned nonwoven fabric is supported with heat-expandable, fire-resistant functional particles, and when heated, the functional particles expand, improving the heat insulation properties of the nonwoven fabric. The nonwoven fabric is arranged in a laminated configuration on the secondary battery side relative to the first buffer, or on the secondary battery side relative to the second buffer. A buffer member for a battery pack according to any one of claims 1 to 3.

Images