Heat transfer suppression sheet and battery pack

Abstract

To provide: a heat transfer suppression sheet that includes an elastic body and is able to handle swelling of a battery cell caused by normal charging / discharging, and being able to demonstrate elastic performance at the time of thermal runaway; and a battery pack including the heat transfer suppression sheet.SOLUTION: A heat transfer suppression sheet 10 includes an elastic body 1 that is in a compressed state below 90°C and is released from the compressed state at or above 90°C. The compressed state of the elastic body 1 is maintained by a binder substance. An insulation material 5 may be laminated thereon, and in such a case, the compressed state may be maintained by a heat shrinkable enclosure 20. Furthermore, the elastic body 1 may be configured from a plurality of elastic body fragments 1A.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a heat transfer-suppressing sheet and a battery pack having the heat transfer-suppressing sheet. [Background technology]

[0002] In recent years, from the viewpoint of environmental protection, the development of electric vehicles and hybrid vehicles driven by electric motors has been actively promoted. These electric vehicles and hybrid vehicles are equipped with a battery pack in which multiple battery cells are connected in series or parallel to serve as the power source for the driving electric motor. Note that, as the battery cells, lithium-ion secondary batteries, which have higher capacity and higher output than lead-acid batteries and nickel-metal hydride batteries, are mainly used.

[0003] In a battery pack, battery cells are generally stacked with heat-transfer-suppressing sheets interposed between adjacent battery cells. The heat-transfer-suppressing sheets suppress the transfer of heat between the battery cells and also absorb the expansion of the battery cells due to charging and discharging with an elastic material.

[0004] For example, Patent Document 1 describes a heat transfer inhibitor sheet that includes an insulating material and an elastic body laminated on the surface of the insulating material, where the elastic body has elastic protrusions that deform due to the expansion of a battery cell, and has a deformation space between the battery cell and the elastic protrusions that allows them to move in a circumferential direction perpendicular to the pressing direction.

[0005] Furthermore, Patent Document 2 describes a heat-transfer-suppressing sheet that includes a heat insulating material and an elastic body with a specific compressive elastic modulus and compressive stress. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2020 / 262080 [Patent Document 2] JP 2021-140968 A Summary of the Invention [Problem to be solved by the invention]

[0007] However, neither of the heat-transfer-suppressing sheets described in Patent Documents 1 and 2 takes into account thermal runaway of battery cells. Patent Document 2 specifies the compressive modulus and compressive stress of the elastic body, but these are values ​​specified in JIS K 6254, and the test temperature is room temperature.

[0008] In a battery pack, an internal short circuit, overcharging, or the like can cause a battery cell to suddenly rise in temperature, leading to thermal runaway in which the cell continues to generate heat, and in some cases, even ignite. The heat and flames from the battery cell that has experienced thermal runaway can then spread to other adjacent battery cells, potentially causing thermal runaway in those other battery cells. For this reason, it is reasonably assumed that the elastic body of the heat transfer suppression sheet described in Patent Documents 1 and 2 will not be able to exhibit its elastic performance during thermal runaway.

[0009] The present invention has been made in consideration of the above problems, and has an object to provide a heat-transfer-inhibiting sheet having an elastic body that can accommodate the expansion of battery cells that accompanies normal charging and discharging and can exhibit elastic performance even during thermal runaway, and a battery pack including this heat-transfer-inhibiting sheet. [Means for solving the problem]

[0010] The above object of the present invention can be achieved by the heat-transfer-suppressing sheet having the following configuration [1].

[0011] [1] A heat-transfer-suppressing sheet having an elastic body that is in a compressed state at temperatures below 90°C and is released from the compressed state at temperatures of 90°C or higher.

[0012] Further, preferred embodiments of the present invention relating to the heat-transfer-suppressing sheet relate to the following items [2] to

[10] .

[0013] [2] The heat-transfer-suppressing sheet according to [1], wherein the elastic body is maintained in a compressed state by a blended binder material. [3] The heat-transfer-suppressing sheet according to [1] or [2], characterized in that the elastic body and a heat insulating material are laminated together. [4] The heat-transfer-suppressing sheet according to [3], wherein the elastic body and the heat insulating material are bonded at least in part. [5] A heat transfer suppression sheet as described in [3] or [4], characterized in that the elastomer is composed of a plurality of elastomer segments, and the elastomer segments are scattered on the surface of the insulation material. [6] A heat transfer suppressing sheet as described in [5], characterized in that when released from a compressed state, the peripheral end faces of adjacent elastomer segments abut against each other, filling the gaps between the elastomer segments or forming mountain-shaped voids. [7] The heat-transfer-suppressing sheet according to [1], wherein the elastic body and a heat insulating material are laminated together, and the compressed state is maintained by a heat-shrinkable enclosure. [8] The heat-transfer-suppressing sheet according to [7], wherein the elastic body and the insulating material are bonded at least in part. [9] A heat transfer suppression sheet as described in [7] or [8], characterized in that the elastomer is composed of a plurality of elastomer segments, and the elastomer segments are scattered on the surface of the insulation material.

[10] A heat transfer suppressing sheet as described in [9], characterized in that when released from a compressed state, the peripheral end faces of adjacent elastomer segments abut against each other, filling the gaps between the elastomer segments or forming mountain-shaped voids.

[0014] The above object of the present invention is achieved by the following configuration

[11] relating to a battery pack.

[0015]

[11] A battery pack comprising a plurality of battery cells and the heat transfer-suppressing sheet according to [1], the plurality of battery cells being connected in series or in parallel. Effect of the Invention

[0016] The heat transfer-suppressing sheet of the present invention has an elastic body that maintains a compressed state at temperatures below 90°C and expands as it is released from the compressed state at temperatures of 90°C or higher. This allows the sheet to accommodate the expansion of battery cells that accompanies normal charging and discharging, and also allows the sheet to demonstrate elastic performance even during thermal runaway.

[0017] Furthermore, because the battery pack of the present invention includes the heat transfer-suppressing sheet, it can accommodate the expansion of the battery cells that accompanies normal charging and discharging and can exhibit elastic performance even in the event of thermal runaway, thereby further enhancing safety. [Brief description of the drawings]

[0018] [Figure 1] FIG. 1 is a perspective view showing the structure of a heat-transfer-suppressing sheet according to a first embodiment of the present invention. [Diagram 2] FIG. 2 is a perspective view showing an example in which the elastic body is constituted by elastic body divided pieces. [Diagram 3] FIG. 3 is a cross-sectional view showing mountain-shaped gaps formed between adjacent elastic body segments when the elastic body segments expand. [Figure 4] FIG. 4 is a cross-sectional view showing the structure of a heat-transfer-suppressing sheet according to a second embodiment of the present invention. [Diagram 5] FIG. 5 is a cross-sectional view showing one embodiment of a battery pack of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] The inventors discovered that by configuring a heat transfer-suppressing sheet with an elastic body that maintains a compressed state below 90°C and releases its compressed state and expands at temperatures of 90°C or higher, it is possible to accommodate the expansion of battery cells that accompanies normal charging and discharging, and also to demonstrate elastic performance during thermal runaway, which led to the completion of the present invention.

[0020] Hereinafter, a heat transfer-suppressing sheet and a battery pack according to an embodiment of the present invention will be described in detail. Note that the present invention is not limited to the embodiment described below, and can be modified as desired without departing from the gist of the present invention.

[0021] 1.Heat transfer suppression sheet First, the heat-transfer-suppressing sheet will be described in detail.

[0022] First Embodiment The heat transfer-suppressing sheet of the present invention comprises an elastic body that maintains a compressed state at temperatures below 90° C. and releases the compressed state and expands at temperatures equal to or higher than 90° C. The elastic body itself may be a known one, and the elastic material may be, for example, rubber or a thermoplastic elastomer.

[0023] The rubber may be either synthetic or natural rubber. Examples of synthetic rubber include styrene-butadiene rubber, butadiene rubber, chloroprene rubber, isoprene rubber, butyl rubber, ethylene-propylene rubber, nitrile rubber, silicone rubber, fluororubber, acrylic rubber, urethane rubber, polysulfide rubber, and epichlorohydrin rubber.

[0024] Examples of the thermoplastic elastomer include polystyrene-based, polyolefin-based, vinyl chloride-based, polyurethane-based, polyester-based, polyamide-based, and polybutadiene-based thermoplastic elastomers. The elastomer may be either porous or non-porous. If the elastomer is porous, the cell structure may be either closed-cell type or open-cell type.

[0025] In order to maintain the elastic body in a compressed state, in this embodiment, a binder substance is mixed with the elastic material and processed into a predetermined shape. As the binder substance, an organic binder is preferable, considering that the binder substance is melted at 90°C or higher to release the compressed state of the elastic body. Examples of the organic binder include acrylic, methacrylic, styrene, and butadiene resins. The amount of the binder substance to be mixed can be appropriately selected depending on the type of binder substance, the degree of compression of the elastic body, and the elastic ability of the elastic body, but the binder substance is appropriately 5 to 30 mass% of the total mass of the elastic body 1.

[0026] As shown in Fig. 1, a heat-transfer-suppressing sheet 10 may be formed by laminating a compressed elastic body 1 and a thermal insulating material 5. In Fig. 1, the elastic body 1 is disposed on only one side of the thermal insulating material 5, but it may be disposed on both sides of the thermal insulating material 5. The elastic body 1 and the thermal insulating material 5 may be bonded to each other over their entire surfaces, or may be bonded partially in spots. By bonding the elastic body 1 and the thermal insulating material 5, the handleability of the heat-transfer-suppressing sheet 10 is improved.

[0027] In addition, since the elastic body 1 expands in the thickness direction and the planar direction when released from the compressed state, when partially bonding, it is preferable that the central portion of the elastic body 1 be bonded to the insulating material 5 so as not to hinder the expansion in the planar direction.

[0028] As shown in the figure, the elastic body 1 is shaped to be slightly smaller than the insulating material 5, taking into consideration the expansion in the planar direction, but the elastic body 1 may be shaped to be the same as the insulating material 5. If the elastic body 1 and the insulating material 5 are shaped to be the same, when the elastic body 1 expands, it will also expand into the space around the insulating material 5, and when applied to, for example, an assembled battery, it is expected to protect battery cells adjacent to a battery cell that has experienced thermal runaway.

[0029] 2, the elastic body 1 may be composed of a plurality of elastic body segments 1A. As shown in the figure, the plurality of elastic body segments 1A are arranged at approximately equal intervals on the surface of the thermal insulation material 5, with gaps 2 being formed between adjacent elastic body segments 1A. Because the elastic body segments 1A are in a compressed state, at temperatures below 90°C, these gaps 2 become air passages, providing a cooling effect and improving the insulating performance of the heat-transfer-suppressing sheet 10.

[0030] On the other hand, when the temperature reaches 90°C or above, the individual elastic body segments 1A expand and close the gaps 2, improving the elastic performance. Also, as shown in Fig. 3, the end faces of adjacent elastic body segments 1A come into contact with each other to form mountain-shaped gaps 2A. These mountain-shaped gaps 2A act as air passages and provide a cooling effect, improving the insulating performance of the heat-transfer-suppressing sheet 10 at temperatures above 90°C.

[0031] Second Embodiment In the first embodiment, the compressed state is maintained by blending a binder substance into the elastic material, but in this embodiment, the compressed state is maintained by a heat-shrinkable packaging material.

[0032] That is, as shown in Fig. 4, the elastic body 1 made of the above-mentioned elastic material and the insulating material 5 are laminated, the front end is surrounded by a heat-shrinkable wrapping body 15, and the wrapping body 15 is heated to shrink. In the figure, the wrapping body 15 is shown by a thick solid line, and it surrounds the entire laminate of the elastic body 1 and the insulating material 5 with almost no gaps. The insulating material 5 hardly changes shape, and the elastic body 1 shrinks due to the wrapping body 15, becoming slightly smaller in area than the insulating material 5.

[0033] Similarly to the first embodiment, the elastic body 1 may be composed of a plurality of elastic body divided pieces 1A, and the elastic body 1 and the heat insulating material 5 may be bonded partially or entirely.

[0034] The packaging body 15 can be a sheet or film made of a heat-shrinkable resin, and may be either non-perforated or perforated. If the packaging body 15 has holes, the holes will cause the packaging body 15 to break at 90° C. or higher, making the elastic body 1 more likely to expand.

[0035] Examples of heat-shrinkable resins that can be used for the packaging body 15 include polyethylene, polypropylene, polystyrene, polyethylene terephthalate, and vinyl chloride. There is no limitation on the thickness of the packaging body 15 as long as it can maintain the compressed state of the elastic body 1. However, if the thickness of the packaging body 15 exceeds 1 mm, it becomes difficult to conform to the shape of the insulating material 5, and cracks and breaks may occur. Therefore, the thickness is preferably 1 mm or less, more preferably 0.1 mm or less, and even more preferably 0.05 mm or less. On the other hand, the lower limit is preferably 0.005 mm or more, and more preferably 0.01 mm or more, in order to prevent tearing due to friction with battery cells when applied to a battery pack, for example.

[0036] <Insulation material composition> In the first and second embodiments described above, other layers may be included as necessary in the laminate of the elastic body 1 and the heat insulating material 5. The heat insulating material 5 may be made of various known materials, but is preferably made of the materials shown below in terms of heat insulating performance.

[0037] [Insulation 5] The heat insulating material 5 contains organic fibers, inorganic fibers, and inorganic particles. Specific examples of each are shown below.

[0038] <Organic fiber> The organic fibers have the effect of imparting flexibility to the insulating material 5, and also have the effect of increasing the strength of the insulating material 5 by forming a skeleton of the organic fibers. Furthermore, if inorganic particles and other organic fibers are fused to the surface of the organic fibers, the effect of increasing the strength of the sheet and the effect of maintaining the shape can be further improved. Furthermore, if the insulating material 5 contains an appropriate amount of organic fibers, multiple voids are formed inside the insulating material 5, and when the insulating material 5 is heated, air and moisture can be released to the outside through the voids.

[0039] Although single-component organic fibers can be used as the organic fiber material in the thermal insulation material 5, it is preferable to use binder fibers with a core-sheath structure. Binder fibers with a core-sheath structure have a core extending in the longitudinal direction of the fiber and a sheath formed to cover the outer periphery of the core. In this case, the core is made of a first organic material, the sheath is made of a second organic material, and the melting point of the first organic material is higher than the melting point of the second organic material.

[0040] (First organic material) In the present embodiment, when a binder fiber having a core-sheath structure is used, the first organic material constituting the core is not particularly limited as long as it has a melting point higher than that of the sheath present on the outer peripheral surface of the core, i.e., the second organic material. The first organic material may be at least one selected from polyethylene terephthalate, polypropylene, and nylon.

[0041] (Second organic material) The second organic material is not particularly limited as long as it has a melting point lower than that of the first organic material constituting the organic fiber. The second organic material may be at least one selected from the group consisting of polyethylene terephthalate, polyethylene, polypropylene, and nylon. The melting point of the second organic material is preferably 90° C. or higher, and more preferably 100° C. or higher. The melting point of the second organic material is preferably 150° C. or lower, and more preferably 130° C. or lower.

[0042] (Organic fiber content) If the content of the organic fibers in the heat insulating material 5 is appropriately controlled, the effect of reinforcing the skeleton can be sufficiently obtained. The organic fiber content is preferably 5% by mass or more, and more preferably 10% by mass or more, based on the total mass of the thermal insulation material 5. If the organic fiber content is too high, the inorganic particle content will relatively decrease, so in order to obtain the desired thermal insulation performance, the organic fiber content is preferably 25% by mass or less, and more preferably 20% by mass or less, based on the total mass of the thermal insulation material 5.

[0043] (Organic fiber length) The fiber length of the organic fibers is not particularly limited, but from the viewpoint of ensuring moldability and processability, it is preferable that the average fiber length of the organic fibers is 10 mm or less. On the other hand, from the standpoint of allowing the organic fibers to function as a skeleton and ensuring the compressive strength of the heat-transfer-suppressing sheet, the average fiber length of the organic fibers is preferably 0.5 mm or greater.

[0044] <Inorganic particles> As the inorganic particles, a single inorganic particle may be used, or two or more types of inorganic particles may be used in combination. As the type of inorganic particles, from the viewpoint of the heat transfer suppression effect, it is preferable to use particles made of at least one inorganic material selected from oxide particles, carbide particles, nitride particles, and inorganic hydrate particles, and it is more preferable to use oxide particles. In addition, the shape is not particularly limited, but it is preferable to include at least one selected from nanoparticles, hollow particles, and porous particles, and specifically, silica nanoparticles, metal oxide particles, inorganic balloons such as microporous particles and hollow silica particles, particles made of thermally expandable inorganic materials, particles made of water-containing porous bodies, etc. can also be used.

[0045] If the average secondary particle diameter of the inorganic particles is 0.01 μm or more, they are easily available and the increase in production costs can be suppressed. If the average secondary particle diameter is 200 μm or less, the desired heat insulating effect can be obtained. Therefore, the average secondary particle diameter of the inorganic particles is preferably 0.01 μm or more and 200 μm or less, and more preferably 0.05 μm or more and 100 μm or less.

[0046] In addition, when two or more kinds of inorganic particles having different heat transfer suppression effects are used in combination, the heating body can be cooled in multiple stages, and the heat absorption effect can be expressed in a wider temperature range. Specifically, it is preferable to use a mixture of large-diameter particles and small-diameter particles. For example, when nanoparticles are used as one inorganic particle, it is preferable to include inorganic particles made of metal oxide as the other inorganic particle. Hereinafter, the inorganic particles will be described in more detail, with the small-diameter inorganic particles being referred to as the first inorganic particles and the large-diameter inorganic particles being referred to as the second inorganic particles.

[0047] <First inorganic particle> (Oxide particles) Since oxide particles have a high refractive index and a strong effect of scattering light, when oxide particles are used as the first inorganic particles, radiation heat transfer can be suppressed, particularly in high temperature regions such as abnormal heat generation. As the oxide particles, at least one type of particle selected from silica, titania, zirconia, zircon, barium titanate, zinc oxide, and alumina can be used. That is, among the above oxide particles that can be used as inorganic particles, only one type may be used, or two or more types of oxide particles may be used. In particular, silica is a component with high heat insulation properties, and titania is a component with a high refractive index compared to other metal oxides, and has a high effect of scattering light and blocking radiant heat in high temperature regions of 500°C or more, so it is most preferable to use silica and titania as the oxide particles.

[0048] (Average primary particle size of oxide particles: 0.001 μm to 50 μm) The particle size of the oxide particles can affect the effect of reflecting radiant heat, so if the average primary particle size is limited to a predetermined range, even higher heat insulation can be obtained. In other words, when the average primary particle size of the oxide particles is 0.001 μm or more, the average primary particle size is sufficiently larger than the wavelength of light that contributes to heating and efficiently diffuses light, thereby suppressing the radiation of heat transfer within the heat-transfer-inhibiting sheet in the high-temperature range of 500° C. or more, and further improving the thermal insulation properties. On the other hand, if the average primary particle size of the oxide particles is 50 μm or less, the number and number of contact points between the particles do not increase even when compressed, making it difficult to form a conductive heat transfer path, thereby reducing the impact on insulation, especially in the normal temperature range where conductive heat transfer is dominant.

[0049] In the present invention, the average primary particle size can be determined by observing particles under a microscope, comparing with a standard scale, and taking the average of any ten particles.

[0050] (Nanoparticles) In the present invention, nanoparticles refer to particles of the order of nanometers that are spherical or nearly spherical and have an average primary particle diameter of less than 1 μm. Nanoparticles have a low density and therefore suppress conductive heat transfer, and when nanoparticles are used as the first inorganic particles, finer voids are dispersed, resulting in excellent heat insulation that suppresses convective heat transfer. For this reason, it is preferable to use nanoparticles in order to suppress the conduction of heat between adjacent nanoparticles when the battery is used in the normal room temperature range. Furthermore, if nanoparticles with a small average primary particle size are used as the oxide particles, an increase in conductive heat transfer in the heat-transfer-suppressing sheet can be suppressed even if the heat-transfer-suppressing sheet is compressed due to expansion accompanying thermal runaway of the battery cell, causing the internal density to increase. This is thought to be because nanoparticles are prone to forming small voids between particles due to static electricity repulsion, and because their bulk density is low, the particles are packed in a way that provides cushioning properties.

[0051] When nanoparticles are used as the first inorganic particles, there are no particular limitations on the material as long as they meet the above definition of nanoparticles. For example, silica nanoparticles are a material with high heat insulation properties, and since the contact points between particles are small, the amount of heat conducted by silica nanoparticles is smaller than that when silica particles with a large particle size are used. Furthermore, silica nanoparticles that are generally available have a bulk density of 0.1 (g / cm 3), for example, even if the battery cells arranged on both sides of the heat-transfer-suppressing sheet thermally expand and a large compressive stress is applied to the heat-transfer-suppressing sheet, the size (area) and number of contacts between the silica nanoparticles do not increase significantly, and heat insulation can be maintained. Therefore, it is preferable to use silica nanoparticles as the nanoparticles. Examples of silica nanoparticles include wet silica, dry silica, and aerogel, but silica nanoparticles that are particularly suitable for this embodiment will be described below.

[0052] Generally, wet silica particles are aggregated, whereas dry silica particles can be dispersed. In the temperature range below 90℃, heat conduction is dominated by conductive heat transfer, so dry silica particles can be dispersed, and therefore can provide superior heat insulation performance compared to wet silica. The heat-transfer-suppressing sheet according to the present embodiment is preferably produced by a manufacturing method in which a mixture containing materials is processed into a sheet shape by a dry method, and therefore, it is preferable to use dry silica, silica aerogel, or the like, which have low thermal conductivity, as the inorganic particles.

[0053] (Average primary particle size of nanoparticles: 1 nm to 100 nm) By limiting the average primary particle size of the nanoparticles to a predetermined range, even higher heat insulation properties can be obtained. That is, when the average primary particle size of the nanoparticles is 1 nm or more and 100 nm or less, convective heat transfer and conductive heat transfer within the heat-transfer-suppressing sheet can be suppressed, particularly in a temperature range below 500° C., and the heat insulation can be further improved. Even when compressive stress is applied, the voids remaining between the nanoparticles and the contact points between many of the particles suppress conductive heat transfer, and the heat insulation of the heat-transfer-suppressing sheet can be maintained. The average primary particle size of the nanoparticles is more preferably 2 nm or more, and even more preferably 3 nm or more, while the average primary particle size of the nanoparticles is more preferably 50 nm or less, and even more preferably 10 nm or less.

[0054] (Inorganic hydrate particles) When inorganic hydrate particles receive heat from a heating element and reach a temperature above the thermal decomposition initiation temperature, they undergo thermal decomposition and release their own water of crystallization to lower the temperature of the heating element and its surroundings, thus exerting the so-called "endothermic effect". After releasing the water of crystallization, the particles become porous and exert a heat insulating effect due to the countless air holes. Specific examples of inorganic hydrates include aluminum hydroxide (Al(OH)3), magnesium hydroxide (Mg(OH)2), calcium hydroxide (Ca(OH)2), zinc hydroxide (Zn(OH)2), iron hydroxide (Fe(OH)2), manganese hydroxide (Mn(OH)2), zirconium hydroxide (Zr(OH)2), and gallium hydroxide (Ga(OH)3).

[0055] For example, aluminum hydroxide has about 35% water of crystallization, and as shown in the formula below, it decomposes thermally and releases the water of crystallization, exerting an endothermic effect. After releasing the water of crystallization, it becomes a porous material called alumina (Al2O3), and functions as a heat insulating material. 2Al(OH)3 → Al2O3 + 3H2O

[0056] As described above, it is preferable that the heat-transfer-suppressing sheet 10 is interposed between battery cells, for example, but in a battery cell that experiences thermal runaway, the temperature rises rapidly to over 200° C. and continues to rise to around 700° C. Therefore, the inorganic particles contained in the thermal insulating material 5 are preferably made of inorganic hydrates with a thermal decomposition onset temperature of 200° C. or higher. The thermal decomposition onset temperatures of the inorganic hydrates listed above are approximately 200°C for aluminum hydroxide, approximately 330°C for magnesium hydroxide, approximately 580°C for calcium hydroxide, approximately 200°C for zinc hydroxide, approximately 350°C for iron hydroxide, approximately 300°C for manganese hydroxide, approximately 300°C for zirconium hydroxide, and approximately 300°C for gallium hydroxide. All of these temperatures roughly overlap with the temperature range of the sudden temperature rise in a battery cell that has experienced thermal runaway, and can efficiently suppress the temperature rise, making these inorganic hydrates preferable.

[0057] (Average secondary particle diameter of inorganic hydrate particles: 0.01 μm or more and 200 μm or less) Furthermore, when inorganic hydrate particles are used as the first inorganic particles, if the average particle diameter is too large, it takes a certain amount of time for the first inorganic particles (inorganic hydrate) near the center of the thermal insulation material 5 to reach their thermal decomposition temperature, and the first inorganic particles near the center of the thermal insulation material 5 may not be completely thermally decomposed. For this reason, the average secondary particle diameter of the inorganic hydrate particles is preferably 0.01 μm or more and 200 μm or less, and more preferably 0.05 μm or more and 100 μm or less.

[0058] (Particles made of thermally expandable inorganic material) Examples of the thermally expandable inorganic material include vermiculite, bentonite, mica, and perlite.

[0059] (Particles made of water-containing porous material) Specific examples of the hydrous porous body include zeolite, kaolinite, montmorillonite, acid clay, diatomaceous earth, wet silica, dry silica, aerogel, mica, and vermiculite.

[0060] (Inorganic balloon) The heat insulating material used in the present invention may contain inorganic balloons as the first inorganic particles. When inorganic balloons are contained, convection heat transfer or conductive heat transfer within the insulating material can be suppressed in the temperature range below 500° C., and the insulating properties of the insulating material can be further improved. As the inorganic balloons, at least one selected from shirasu balloons, silica balloons, fly ash balloons, barite balloons, and glass balloons can be used.

[0061] (Inorganic balloon content: 60% or less by mass of the total mass of the insulation material) The content of the inorganic balloons is preferably 60 mass % or less based on the total mass of the heat insulating material.

[0062] (Average particle size of inorganic balloons: 1 μm to 100 μm) The average particle size of the inorganic balloons is preferably 1 μm or more and 100 μm or less.

[0063] <Second inorganic particles> When two types of inorganic particles are contained in the heat-transfer-suppressing sheet 10, the second inorganic particles are not particularly limited as long as they are different from the first inorganic particles in terms of material, particle size, etc. Examples of the second inorganic particles that can be used include oxide particles, carbide particles, nitride particles, inorganic hydrate particles, silica nanoparticles, metal oxide particles, inorganic balloons such as microporous particles and hollow silica particles, particles made of a thermally expandable inorganic material, particles made of a water-containing porous body, and the like, the details of which are as described above.

[0064] Nanoparticles have extremely low conductive heat transfer and can maintain excellent heat insulation even when compressive stress is applied to the heat transfer-suppressing sheet. Metal oxide particles such as titania have a high effect of blocking radiant heat. Furthermore, when large-diameter inorganic particles and small-diameter inorganic particles are used, the small-diameter inorganic particles enter the gaps between the large-diameter inorganic particles, resulting in a denser structure and improving the heat transfer suppression effect. Therefore, when nanoparticles are used as the first inorganic particles, it is preferable to further include particles made of a metal oxide larger in diameter than the first inorganic particles as the second inorganic particles in the heat transfer-suppressing sheet. Examples of metal oxides include silicon oxide, titanium oxide, aluminum oxide, barium titanate, zinc oxide, zircon, zirconium oxide, etc. In particular, titanium oxide (titania) is a component with a higher refractive index than other metal oxides, and is highly effective in scattering light and blocking radiant heat in a high temperature range of 500°C or higher, so it is most preferable to use titania.

[0065] When at least one type of particles selected from dry silica particles and silica aerogel is used as the first inorganic particles, and at least one type of particles selected from titania, zircon, zirconia, silicon carbide, zinc oxide and alumina are used as the second inorganic particles, in order to obtain excellent heat insulating performance within a temperature range of 90° C. or less, the first inorganic particles are preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more, based on the total mass of the inorganic particles. In addition, the first inorganic particles are preferably 95% by mass or less, more preferably 90% by mass or less, and even more preferably 80% by mass or less, based on the total mass of the inorganic particles.

[0066] On the other hand, in order to obtain excellent heat insulating performance within a temperature range exceeding 90° C., the second inorganic particles are preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 20% by mass or more, based on the total mass of the inorganic particles. Also, the second inorganic particles are preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less, based on the total mass of the inorganic particles.

[0067] (Average primary particle size of second inorganic particles) When second inorganic particles made of a metal oxide are contained in the heat transfer-suppressing sheet, if the average primary particle size of the second inorganic particles is from 1 μm to 50 μm, radiation heat transfer can be efficiently suppressed in a high temperature range of 500° C. or more. The average primary particle size of the second inorganic particles is more preferably from 5 μm to 30 μm, and most preferably 10 μm or less.

[0068] (Inorganic particle content) In this embodiment, when the total content of the inorganic particles in the heat insulating material 5 is appropriately controlled, the heat insulating property of the heat insulating material 5 can be sufficiently ensured. The total content of the inorganic particles is preferably 60% by mass or more, and more preferably 70% by mass or more, based on the total mass of the thermal insulation material 5. If the total content of the inorganic particles is too high, the content of the organic fibers is relatively reduced, so that in order to sufficiently obtain the effect of reinforcing the skeleton and the effect of retaining the inorganic particles, the total content of the inorganic particles is preferably 95% by mass or less, and more preferably 90% by mass or less, based on the total mass of the thermal insulation material 5.

[0069] The content of inorganic particles in the heat insulating material 5 can be calculated, for example, by heating the heat insulating material 5 at 800° C., decomposing the organic matter, and then measuring the mass of the remaining portion.

[0070] In addition to the organic fibers and inorganic particles, the heat insulating material 5 may contain organic fibers made of an organic material different from the first organic material, inorganic fibers, etc. When the heat insulating material 5 contains inorganic fibers, the inorganic fibers that are preferably contained in this embodiment will be described below.

[0071] <Inorganic fibers> As the inorganic fiber, a single inorganic fiber may be used, or two or more inorganic fibers may be used in combination. Examples of the inorganic fiber include ceramic fibers such as silica fiber, alumina fiber, alumina silicate fiber, zirconia fiber, carbon fiber, soluble fiber, refractory ceramic fiber, aerogel composite material, magnesium silicate fiber, alkaline earth silicate fiber, potassium titanate fiber, silicon carbide fiber, and potassium titanate whisker fiber, glass fibers such as glass fibers, glass wool, and slag wool, and mineral fibers such as rock wool, basalt fiber, wollastonite, and mullite fiber. These inorganic fibers are preferred in terms of heat resistance, strength, availability, etc. Among the inorganic fibers, silica-alumina fibers, alumina fibers, silica fibers, rock wool, alkaline earth silicate fibers, and glass fibers are particularly preferred in terms of ease of handling.

[0072] The cross-sectional shape of the inorganic fiber is not particularly limited, and examples thereof include a circular cross section, a flat cross section, a hollow cross section, a polygonal cross section, a core cross section, etc. Among them, modified cross section fibers having a hollow cross section, a flat cross section, or a polygonal cross section are preferably used because they have slightly improved heat insulation properties.

[0073] The preferred lower limit of the average fiber length of the inorganic fibers is 0.1 mm, and more preferably 0.5 mm. On the other hand, the preferred upper limit of the average fiber length of the inorganic fibers is 50 mm, and more preferably 10 mm. If the average fiber length of the inorganic fibers is less than 0.1 mm, the inorganic fibers are less likely to be entangled with each other, and the mechanical strength of the insulating material 5 may be reduced. On the other hand, if the average fiber length exceeds 50 mm, although a reinforcing effect is obtained, the inorganic fibers may not be able to be tightly entangled with each other, or may be curled up by a single inorganic fiber, which may result in a reduction in thermal insulation.

[0074] The preferred lower limit of the average fiber diameter of the inorganic fibers is 1 μm, more preferably 2 μm, and even more preferably 3 μm. On the other hand, the preferred upper limit of the average fiber diameter of the inorganic fibers is 15 μm, and more preferably 10 μm. If the average fiber diameter of the inorganic fibers is less than 1 μm, the mechanical strength of the inorganic fibers themselves may be reduced. From the viewpoint of the effect on human health, the average fiber diameter of the inorganic fibers is preferably 3 μm or more. On the other hand, if the average fiber diameter of the inorganic fibers is more than 15 μm, the solid heat transfer through the inorganic fibers may increase, leading to a decrease in heat insulation, and the moldability and strength of the heat transfer-suppressing sheet may be deteriorated.

[0075] (Inorganic fiber content) In this embodiment, when the heat insulating material 5 contains inorganic fibers, the content of the inorganic fibers is preferably 3 mass % or more and 15 mass % or less with respect to the total mass of the heat insulating material 5.

[0076] Furthermore, the content of inorganic fibers is more preferably 5% by mass or more and 10% by mass or less with respect to the total mass of the thermal insulation material 5. By setting the content in this range, the shape retention, pressing force resistance, wind pressure resistance, and inorganic particle retention ability of the inorganic fibers are exhibited in a well-balanced manner. Furthermore, by appropriately controlling the content of inorganic fibers, the organic fibers and inorganic fibers are entangled with each other to form a three-dimensional network, so that the effect of retaining inorganic particles and other compounding materials described later can be further improved.

[0077] <Other compounding materials> (Hot melt powder) In addition to the binder fibers and inorganic particles, the heat-transfer-suppressing sheet 10 may contain hot-melt powder in the mixture. The hot-melt powder is, for example, a powder containing a third organic material different from the first organic material and the second organic material, and has the property of melting when heated. When the hot-melt powder is contained in the mixture and heated, the hot-melt powder melts, and when cooled, it hardens in a state including the surrounding inorganic particles. Therefore, the falling off of the inorganic particles of the heat insulating material 5 can be further suppressed.

[0078] There are various types of hot melt powders having various melting points, and a hot melt powder having an appropriate melting point can be selected in consideration of the melting points of the core and sheath of the binder fiber to be used. Specifically, if the third organic material, which is a component constituting the hot melt powder, has a melting point lower than that of the first organic material constituting the organic fiber, the heating temperature can be set to melt the sheath and hot melt powder while leaving the core. For example, if the melting point of the hot melt powder is lower than the melting point of the sheath, the heating temperature during production can be set between the melting points of the core and the sheath, making it even easier to set the heating temperature.

[0079] On the other hand, the type of hot melt powder used can be selected so that the melting point of the hot melt powder is between the melting points of the core and the sheath. When a hot melt powder having such a melting point is used, when the sheath and the hot melt powder are both melted and then cooled and hardened, the hot melt powder present in the organic fiber (core) and the molten sheath around it, and in the gaps between the inorganic particles hardens first. As a result, the position of the organic fiber can be fixed, and then the molten sheath is welded to the organic fiber, making it easier to form a three-dimensional skeleton. Therefore, the strength of the entire sheet can be further improved.

[0080] If the melting point of the third organic material constituting the hot melt powder is sufficiently lower than that of the first organic material constituting the core, the heating temperature setting margin in the heating step can be expanded, and the temperature setting for obtaining a desired structure can be made easier. For example, the melting point of the first organic material is preferably 60° C. or more higher than the melting point of the third organic material, more preferably 70° C. or more higher, and even more preferably 80° C. or more higher.

[0081] The melting point of the hot melt powder (third organic material) is preferably 80° C. or higher, and more preferably 90° C. or higher. The melting point of the hot melt powder (third organic material) is preferably 180° C. or lower, and more preferably 150° C. or lower. Components constituting the hot melt powder include polyethylene, polyester, polyamide, ethylene vinyl acetate, and the like.

[0082] (Hot melt powder content) When hot melt powder is contained in the material of the insulating material 5 in order to suppress the falling off of inorganic particles, the effect of suppressing powder falling can be obtained even with a small amount of the content. Therefore, the content of the hot melt powder is preferably 0.5 mass % or more, and more preferably 1 mass % or more, based on the total mass of the insulating material. On the other hand, when the content of the hot melt powder is increased, the content of inorganic particles and the like is relatively decreased. Therefore, in order to obtain the desired insulation performance, the content of the hot melt powder is preferably 5 mass % or less, and more preferably 4 mass % or less, based on the total mass of the insulation material.

[0083] When the material of the heat insulating material 5 contains hot melt powder, the heating temperature in the heating step is preferably set to be 10°C or more higher than the higher of the melting point of the second organic material constituting the sheath and the melting point of the third organic material constituting the hot melt powder, and more preferably set to be 20°C or more higher. On the other hand, the heating temperature is preferably set to be 10°C or more lower than the melting point of the first organic material constituting the core, and more preferably set to be 20°C or more lower. By setting the heating temperature at such a level, a strong skeleton can be formed, the strength of the sheet can be further improved, and the falling off of inorganic particles can be prevented.

[0084] The heat insulating material 5 may further contain other binders, colorants, etc., as necessary. Any of these are useful for the purpose of reinforcing the heat insulating material 5 or improving its formability, and the total amount of these is preferably 10 mass % or less based on the total mass of the heat insulating material 5.

[0085] 2. Battery pack Next, the battery pack will be described in detail.

[0086] The battery pack of the present invention includes the heat-transfer-restricting sheet 10. That is, as shown in Fig. 5, the battery pack 100 includes a plurality of battery cells 20a, 20b, 20c and the heat-transfer-restricting sheet 10, with the battery cells 20a, 20b, 20c connected in series or in parallel. The heat-transfer-restricting sheet 10 is interposed between the battery cells 20a and 20b, and between the battery cells 20b and 20c. The battery cells 20a, 20b, 20c and the heat-transfer-restricting sheet 10 are housed in a battery case 30.

[0087] In the battery pack 100 configured in this manner, the expansion of the battery cells 20a, 20b, and 20c that accompanies charging and discharging is absorbed by the elastic body 1 at temperatures below 90°C. On the other hand, at temperatures above 90°C, the elastic body 1 expands, widening the gap between the battery cell that has experienced thermal runaway and the adjacent battery cells to provide protection. In addition, the heat insulating material 5 can suppress the transfer of heat to the adjacent battery cells.

[0088] The battery pack 100 is not limited to the battery pack 100 illustrated in Fig. 5. For example, the heat-transfer-suppressing sheet 10 may be disposed not only between the battery cells 20a and 20b and between the battery cells 20b and 20c, but also between the battery cells 20a, 20b, and 20c and the battery case 30, or may be attached to the inner surface of the battery case 30.

[0089] In the battery pack 100 configured in this manner, if a battery cell catches fire, the flames can be prevented from spreading outside the battery case 30. For example, the battery pack 100 according to this embodiment may be used in an electric vehicle (EV) or the like and placed under the floor of a passenger compartment. In this case, even if a battery cell were to catch fire, the safety of the passengers can be ensured. Furthermore, since the heat transfer suppression sheet 10 can be disposed not only between each battery cell but also between the battery cells 20a, 20b, 20c and the battery case 30, there is no need to fabricate new flame retardant materials, etc., and a safe battery pack 100 can be easily constructed at low cost. [Explanation of symbols]

[0090] 1 Elastic body 1A Elastic body segment 2,2A air gap 5. Insulation 10. Heat transfer suppression sheet 15 Packaging 20a, 20b, 20c Battery cells 30 Battery case 100 battery packs

Claims

1. A heat transfer-suppressing sheet having an elastic body that is in a compressed state at temperatures below 90°C and that is released from the compressed state at temperatures of 90°C or higher, wherein the elastic body uses a thermoplastic elastomer having a closed-cell or open-cell cell structure.

2. 2. The heat transfer suppressing sheet according to claim 1, wherein the elastic body is maintained in a compressed state by a blended binder material.

3. The heat transfer suppressing sheet according to claim 2 , wherein the elastic body and a heat insulating material are laminated together.

4. 4. The heat transfer suppressing sheet according to claim 3, wherein the elastic body and the heat insulating material are at least partially bonded together.

5. 5. The heat transfer suppressing sheet according to claim 3, wherein the elastic body is made up of a plurality of elastic body segments, and the elastic body segments are scattered on the surface of the heat insulating material.

6. 6. The heat transfer suppressing sheet according to claim 5, wherein when released from a compressed state, the peripheral end faces of adjacent elastic segments abut against each other, filling gaps between the elastic segments or forming mountain-shaped voids.

7. 2. The heat transfer-suppressing sheet according to claim 1, wherein the elastic body and a heat insulating material are laminated together, and the compressed state is maintained by a heat-shrinkable envelope.

8. 8. The heat transfer suppressing sheet according to claim 7, wherein the elastic body and the heat insulating material are at least partially bonded together.

9. 9. The heat transfer suppressing sheet according to claim 7, wherein the elastic body is made up of a plurality of elastic body segments, and the elastic body segments are scattered on the surface of the heat insulating material.

10. 10. The heat transfer suppressing sheet according to claim 9, wherein when released from a compressed state, the peripheral end faces of adjacent elastic segments abut against each other, filling gaps between the elastic segments or forming mountain-shaped voids.

11. A battery pack comprising a plurality of battery cells and the heat transfer-suppressing sheet according to claim 1, the plurality of battery cells being connected in series or in parallel.

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