Heat transfer suppression sheet and battery pack

Abstract

To provide a heat transmission suppression sheet that has such a strength that its shape can be maintained even in a case where an impact and a pressing force are given to the heat transmission suppression sheet, and thus can suppress fall of powder and maintain an excellent thermal insulation performance, and to provide a battery pack having the same.SOLUTION: A heat transmission suppression sheet 10 has inorganic particles 4 and organic fibers 1. In addition, on a surface of the heat transmission suppression sheet 10, a first region 2 that has a striated fiber bundle 7 made of a plurality of organic fibers 1 and a second region 3 without the fiber bundle 7 are formed.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] In recent years, from the viewpoint of environmental protection, active development has been made of electric vehicles, hybrid vehicles, and the like that are driven by electric motors. These electric vehicles, hybrid vehicles, and the like are equipped with assembled batteries in which multiple battery cells are connected in series or parallel to serve as the power source for the driving electric motor.

[0003] Furthermore, these battery cells are mainly lithium-ion secondary batteries, which have higher capacity and higher output than lead-acid batteries, nickel-metal hydride batteries, etc. If a battery cell experiences thermal runaway, where the temperature rises suddenly and continues to rise due to an internal short circuit or overcharging, the heat from the battery cell experiencing thermal runaway may be transmitted to other adjacent battery cells, potentially causing thermal runaway in those cells.

[0004] A common method for suppressing the propagation of heat from a battery cell that has experienced thermal runaway as described above is to place a heat insulating sheet between the battery cells. For example, Patent Document 1 discloses a heat insulating sheet for a battery pack, which contains first particles made of silica nanoparticles and second particles made of a metal oxide, with the content of the first particles being limited. Patent Document 1 also describes that the heat insulating sheet may contain a binding material made of at least one material selected from fibers, binders, and heat-resistant resins.

[0005] Furthermore, Patent Document 1 also describes that dry silica or wet silica can be used as the first particles, and that the heat insulating sheet can be produced by a dry molding method or a wet papermaking method. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent Publication No. 2021-34278 Summary of the Invention [Problem to be solved by the invention]

[0007] Incidentally, examples of binders used in producing a heat insulating sheet (heat transfer-suppressing sheet) include moisture-heat adhesive binder fibers, which must be kept wet during production in order to exhibit their adhesiveness. Therefore, when using moisture-heat adhesive binder fibers, the heat insulating sheet must be produced by a wet papermaking method.

[0008] However, when dry silica or silica aerogel, which have low thermal conductivity, are used to further improve thermal insulation performance, there is a problem that they cannot be produced by wet papermaking. This is because when a material containing dry silica is formed into a sheet by wet papermaking, the dry silica aggregates in the presence of water, increasing the thermal conductivity. Furthermore, since silica aerogel is generally difficult to disperse in water, when a material containing silica aerogel is formed by wet papermaking, it is not possible to obtain a thermal insulation sheet with a uniformly dispersed material, resulting in a decrease in quality.

[0009] On the other hand, when insulating sheets are manufactured using a dry molding method using inorganic particles such as dry silica or silica aerogel, the inorganic particles may fall off (hereinafter referred to as "powder shedding") due to pressure, impact, or the like. In particular, in recent battery packs, the capacity of battery cells has been further improved, resulting in an increased expansion rate during charging and discharging. Therefore, when an insulating sheet is placed between battery cells of an assembled battery, if the overall strength of the insulating sheet is low, the expansion of the battery cells during charging and discharging, etc., can compress the insulating sheet, causing powder shedding and reducing its insulating performance. As a result, if the battery cells experience thermal runaway and reach high temperatures, the insulating sheet's effectiveness cannot be fully realized, and a thermal chain reaction may occur. For these reasons, there is a need for an insulating sheet and a manufacturing method thereof that has high strength enough to maintain its shape, can suppress powder shedding, and can maintain excellent insulating properties.

[0010] The heat insulating sheet described in Patent Document 1 maintains excellent heat insulating properties even when the compressive stress increases, but further improvements are required in terms of heat insulating properties, strength, and ability to suppress powder shedding.

[0011] The present invention has been made in consideration of the above-mentioned problems, and has an object to provide a heat-transfer-inhibiting sheet that has the strength to maintain its shape even when an impact or pressure is applied to the heat-transfer-inhibiting sheet, thereby suppressing powder falling off and maintaining excellent heat insulating performance, and a battery pack including this heat-transfer-inhibiting sheet. [Means for solving the problem]

[0012] The above object of the present invention is achieved by the heat transfer-suppressing sheet having the following configuration [1].

[0013] [1] A heat transfer-suppressing sheet having inorganic particles and organic fibers, a first region having a plurality of streak-like fiber bundles made of the organic fibers on a surface thereof; and a second region in which the fiber bundles are not present.

[0014] Furthermore, preferred embodiments of the present invention relating to the heat transfer-suppressing sheet relate to the following [2] to [8].

[0015] [2] The heat transfer suppression sheet according to [1], wherein the first region has the streak-like fiber bundles passing through at least three consecutive 5 mm square imaginary frames.

[0016] [3] The heat-transfer-suppressing sheet according to [1], wherein the first region has the streak-like fiber bundles having a length of 20 mm or more.

[0017] [4] The heat-transfer-suppressing sheet according to any one of [1] to [3], comprising the second region surrounded by the first region.

[0018] [5] The heat-transfer-suppressing sheet according to any one of [1] to [4], wherein the streak-like fiber bundles are connected in a mesh-like pattern on the surface.

[0019] [6] The heat-transfer-suppressing sheet according to any one of [1] to [5], wherein the inorganic particles are particles made of at least one inorganic material selected from oxide particles, carbide particles, nitride particles, and inorganic hydrate particles.

[0020] [7] The heat-transfer-suppressing sheet according to [6], wherein the inorganic particles include at least one type of particles selected from dry silica particles and silica aerogel.

[0021] [8] The heat-transfer-suppressing sheet according to [7], wherein the inorganic particles further include at least one type of particles selected from titania, zircon, zirconia, silicon carbide, zinc oxide, and alumina.

[0022] The above object of the present invention is also achieved by the following configuration [9] relating to the battery pack.

[0023] [9] A battery pack comprising a plurality of battery cells and the heat-transfer-suppressing sheet according to any one of [1] to [8], the plurality of battery cells being connected in series or in parallel. [Effects of the Invention]

[0024] The heat-transfer-inhibiting sheet of the present invention has a first region on its surface that has streaky fiber bundles and a second region that has no fiber bundles. This improves the strength of the heat-transfer-inhibiting sheet and reduces the impact and pressure on the surface of the heat-transfer-inhibiting sheet, thereby suppressing powder fall-off and preventing a decrease in the heat insulating effect due to deformation of the heat-transfer-inhibiting sheet.

[0025] The battery pack of the present invention includes a heat transfer-suppressing sheet that has high strength and the effect of maintaining thermal insulation performance as described above, and therefore can suppress thermal runaway of the battery cells in the battery pack and the spread of flames to the outside of the battery case. [Brief explanation of the drawings]

[0026] [Figure 1] FIG. 1 is a photograph, substituted for a drawing, showing the surface of a heat-transfer-suppressing sheet according to an embodiment of the present invention. [Figure 2] FIG. 2 is a photograph showing an enlarged portion of FIG. [Figure 3] FIG. 3 is a photograph, substituted for a drawing, showing a cross section of a heat-transfer-suppressing sheet according to an embodiment of the present invention. [Figure 4] FIG. 4 is a diagram for explaining an example of a method for defining the length of a fiber bundle, and is a photograph substituting for a drawing showing an enlarged view of part A in FIG. [Figure 5] FIG. 5 is a diagram showing a mesh-like fiber bundle, and is a photograph showing an enlarged view of part A in FIG. [Figure 6] FIG. 6 is a schematic diagram showing a battery pack having a heat transfer-suppressing sheet according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0027] The present inventors have conducted extensive research into a heat-transfer-suppressing sheet that can solve the above-mentioned problems. As a result, it was discovered that by forming a first region having streaky fiber bundles and a second region having no fiber bundles on the surface of the heat transfer-inhibiting sheet, the strength of the heat transfer-inhibiting sheet can be improved, thereby maintaining high thermal insulation performance.

[0028] The heat transfer-suppressing sheet, its manufacturing method, and battery pack according to embodiments of the present invention will be described in detail below. Note that the present invention is not limited to the embodiments described below, and can be modified as desired without departing from the spirit and scope of the present invention.

[0029] [Heat transfer suppression sheet] Fig. 1 is a photograph showing the surface of a heat-transfer-suppressing sheet according to an embodiment of the present invention, Fig. 2 is a photograph showing an enlarged portion of the surface, and Fig. 3 is a photograph showing a cross section of a heat-transfer-suppressing sheet according to an embodiment of the present invention.

[0030] 1 to 3, a heat-transfer-suppressing sheet 10 according to this embodiment includes inorganic particles 4 and organic fibers 1. The surface of the heat-transfer-suppressing sheet 10 is formed with first regions 2 having streak-like fiber bundles 7 made of a plurality of organic fibers 1, and second regions 3 having no fiber bundles 7. In this specification, the fiber bundles 7 are defined as 10 or more entangled organic fibers 1 that extend in streak-like patterns in a direction substantially parallel to the surface of the heat-transfer-suppressing sheet 10.

[0031] That is, when the surface of the heat transfer-suppressing sheet 10 is observed, a plurality of organic fibers 1 are observed to be entangled in the first region 2, as shown in Fig. 2. On the other hand, in the second region 3, although several organic fibers 1 are observed in some places, fiber bundles 7 in which a plurality of organic fibers 1 are entangled are not observed. In this embodiment, the first region 2 and the second region 3 have a sea-island structure, and the second region 3 corresponding to the island portion is formed so as to be surrounded by the first region 2 corresponding to the sea portion.

[0032] One example of how the heat-transfer-suppressing sheet 10 can be used is by placing the heat-transfer-suppressing sheet 10 between a plurality of battery cells. Specific examples of how the heat-transfer-suppressing sheet 10 can be used are described below.

[0033] In the present embodiment configured as described above, fiber bundles 7 formed by entanglement of organic fibers 1 are present on the surface of heat-transfer-inhibiting sheet 10 in stripes, thereby improving the strength of heat-transfer-inhibiting sheet 10. Furthermore, since the entire surface is not covered with fiber bundles 7, and there are first regions 2 where fiber bundles 7 are present and second regions where fiber bundles 7 are not present, heat-transfer-inhibiting sheet 10 also has excellent flexibility. Furthermore, because fiber bundles 7 are present on the surface of heat-transfer-inhibiting sheet 10, even if heat-transfer-inhibiting sheet 10 is subjected to impact or pressure, the fiber bundles 7 can absorb and mitigate the impact or pressure. This prevents inorganic particles 4 from falling off (powdering), and prevents a decrease in the heat insulating performance of heat-transfer-inhibiting sheet 10.

[0034] In this embodiment, as shown in the cross-sectional photograph of Fig. 3, the organic fibers 1 and fiber bundles 7 formed by entanglement of the organic fibers 1 are present not only on the surface of the heat-transfer-suppressing sheet 10 but also inside the sheet, thereby achieving even greater sheet strength.

[0035] In this embodiment, it is preferable that the length of the fiber bundles 7 formed to extend over the surface of the heat-transfer-suppressing sheet 10 is relatively long. An example of a method for specifying the length of the fiber bundles 7 will be described with reference to FIG. As shown in Fig. 4, rectangular imaginary frames 21 are arranged along the streak-like fiber bundles 7 on the surface of the heat-transfer-suppressing sheet 10. In this embodiment, the size of the imaginary frames 21 is 5 mm square, and these imaginary frames 21 are arranged so that they are continuous with each other. In this case, if there are fiber bundles 7 that penetrate at least three continuous imaginary frames 21, it can be determined that the strength of the heat-transfer-suppressing sheet 10 is sufficiently improved.

[0036] Alternatively, the length of the fiber bundles 7 extending in stripes can be simply measured. For example, a string or the like can be placed on the surface of the heat-transfer-suppressing sheet 10 along the fiber bundles 7, and the length of the string can then be measured. When measuring the length of continuous fiber bundles 7, if there are fiber bundles 7 with a length of 20 mm or more, the effect of improving the strength of the heat-transfer-suppressing sheet 10 can be sufficiently obtained.

[0037] Furthermore, as shown in FIG. 5, if the fiber bundles 7 are connected in a mesh pattern on the surface of the heat-transfer-suppressing sheet 10, the sheet strength can be further improved.

[0038] The materials constituting the heat transfer-suppressing sheet according to this embodiment will be described in detail below.

[0039] <Organic fiber> The organic fiber 1 provides flexibility to the heat-transfer-suppressing sheet 10 and also has the effect of improving the strength and shape of the sheet. While single-component organic fibers can be used as the material for the organic fiber 1 in the heat-transfer-suppressing sheet 10, 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 surface of the core. The core is made of a first organic material, and the sheath is made of a second organic material, with the melting point of the first organic material being higher than that of the second organic material.

[0040] Whether single-component organic fibers or binder fibers with a core-sheath structure are used as the material for the organic fibers 1, heating during production of the heat transfer-suppressing sheet 10 melts part of the surface of the fibers, and subsequent cooling forms welded parts (not shown) around the organic fibers 1. The welded parts fuse the inorganic particles 4 to the surfaces of the organic fibers 1 and fuse the organic fibers 1 together, so the formation of the welded parts provides excellent sheet strength.

[0041] When binder fibers with a sheath-core structure are used as the material, the core of the heat-transfer-suppressing sheet 10 corresponds to the organic fiber 1. If binder fibers with a sheath-core structure are used during the production of the heat-transfer-suppressing sheet 10, adjacent binder fibers are fused to each other, making it easier to form fiber bundles 7 and further increasing the sheet strength. Furthermore, when binder fibers with a sheath-core structure are used, the second organic material that makes up the sheath melts and then solidifies again in a state that includes the surrounding inorganic particles 4, thereby improving the retention of the inorganic particles 4.

[0042] (First organic material) When a binder fiber with a core-sheath structure is used as the material for the organic fiber 1, the first organic material constituting the core, i.e., the organic fiber 1, is not particularly limited as long as it has a melting point higher than that of the sheath, i.e., the second organic material present on the outer surface of the organic fiber 1. The first organic material may be at least one selected from polyethylene terephthalate, polypropylene, and nylon.

[0043] (Second organic material) When binder fibers having a core-sheath structure are used as the material for the organic fibers 1, the second organic material constituting the sheath portion is not particularly limited as long as it has a melting point lower than that of the first organic material constituting the organic fibers 1. Examples of the second organic material include at least one selected from 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.

[0044] (organic fiber content) In this embodiment, if the content of the organic fibers 1 in the heat-transfer-suppressing sheet 10 is appropriately controlled, the effect of improving the strength of the heat-transfer-suppressing sheet 10 can be sufficiently obtained. The content of organic fibers 1 is preferably 2% by mass or more, and more preferably 4% by mass or more, relative to the total mass of heat-transfer-suppressing sheet 10. Furthermore, if the content of organic fibers 1 is too high, the content of inorganic particles 4 will relatively decrease. Therefore, in order to obtain the desired heat insulating performance, the content of organic fibers is preferably 10% by mass or less, and more preferably 8% by mass or less, relative to the total mass of heat-transfer-suppressing sheet 10.

[0045] (fiber length of organic fiber) The fiber length of the organic fibers 1 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 be 10 mm or less. On the other hand, from the viewpoint of improving the strength of the heat transfer-suppressing sheet, the average fiber length of the organic fibers 1 is preferably 0.5 mm or more.

[0046] <Inorganic particles> The inorganic particles may be a single inorganic particle or a combination of two or more 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. The shape of the inorganic particles is not particularly limited, but it is preferable to use at least one selected from nanoparticles, hollow particles, and porous particles. Specific examples include silica nanoparticles, metal oxide particles, inorganic balloons such as microporous particles and hollow silica particles, particles made of thermally expandable inorganic materials, and particles made of hydrous porous bodies.

[0047] When 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. Furthermore, when 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.

[0048] In addition, by using two or more inorganic particles with different heat transfer suppression effects in combination, it is possible to cool a heat generating body in multiple stages, and the heat absorption effect can be exerted over 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 of the inorganic particles, it is preferable to include inorganic particles made of a metal oxide as the other inorganic particle. Hereinafter, the inorganic particles will be described in more detail, with the small-diameter inorganic particles referred to as the first inorganic particles and the large-diameter inorganic particles referred to as the second inorganic particles.

[0049] <First inorganic particle> (oxide particles) Oxide particles have a high refractive index and a strong effect of diffusely reflecting light. Therefore, using oxide particles as the first inorganic particles can suppress radiant heat transfer, particularly in high-temperature regions such as those caused by abnormal heat generation. The oxide particles can be at least one type of particle selected from silica, titania, zirconia, zircon, barium titanate, zinc oxide, and alumina. That is, among the above oxide particles that can be used as inorganic particles, only one type or two or more types of oxide particles can be used. In particular, silica is a component with high heat insulating properties, and titania is a component with a higher refractive index than other metal oxides, and is highly effective in diffusely reflecting light and blocking radiant heat in high-temperature regions of 500°C or higher. Therefore, it is most preferable to use silica and titania as the oxide particles.

[0050] (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 insulating properties can be obtained. That is, 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 light is efficiently diffused, thereby suppressing the radiative heat transfer within the heat transfer-suppressing sheet in the high-temperature range of 500°C or higher, thereby further improving the heat 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 paths for conductive heat transfer. This reduces the impact on thermal insulation, particularly in the normal temperature range where conductive heat transfer is dominant.

[0051] 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 10 particles.

[0052] (nanoparticles) In the present invention, nanoparticles refer to particles on the order of nanometers that are spherical or nearly spherical and have an average primary particle diameter of less than 1 μm. Nanoparticles have low density, which suppresses conductive heat transfer. Furthermore, when nanoparticles are used as the first inorganic particles, the voids are finely dispersed, resulting in excellent heat insulation that suppresses convective heat transfer. Therefore, it is preferable to use nanoparticles because they can suppress heat transfer between adjacent nanoparticles during normal use of the battery at room temperature. Furthermore, if nanoparticles with a small average primary particle size are used as the oxide particles, an increase in conductive heat transfer through the heat-transfer-suppressing sheet can be suppressed even when the sheet is compressed due to expansion caused by thermal runaway in the battery cell, increasing its internal density. This is thought to be because nanoparticles are prone to forming tiny voids between them due to electrostatic repulsion, and their low bulk density allows the particles to be packed together in a cushioning manner.

[0053] In the present invention, when nanoparticles are used as the first inorganic particles, there are no particular limitations on the material as long as they comply with the definition of nanoparticles. For example, silica nanoparticles are a material with high heat insulating properties, and the contact points between particles are small, so the amount of heat conducted by silica nanoparticles is smaller than when silica particles with a large particle diameter are used. Furthermore, commonly available silica nanoparticles 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 contact points between the silica nanoparticles do not increase significantly, and heat insulation properties 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.

[0054] Generally, wet silica particles are agglomerated, while dry silica particles can be dispersed. Because heat conduction is predominant in the temperature range below 300°C, dry silica, which can disperse particles, can achieve superior heat insulation performance compared to wet silica. The heat transfer-suppressing sheet according to this embodiment is preferably produced by a dry process in which a mixture containing the materials is processed into a sheet, and therefore, dry silica, silica aerogel, or the like, which have low thermal conductivity, is preferably used as the inorganic particles.

[0055] (Average primary particle diameter of nanoparticles: 1 nm to 100 nm) If the average primary particle size of the nanoparticles is limited to a predetermined range, even higher heat insulating 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 the temperature range below 500° C., and thermal insulation can be further improved. Furthermore, even when compressive stress is applied, the voids remaining between the nanoparticles and the contact points between many particles suppress conductive heat transfer, allowing the thermal insulation of the heat-transfer-suppressing sheet to 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.

[0056] (Inorganic hydrate particles) When inorganic hydrate particles receive heat from a heating element and reach a temperature above their thermal decomposition initiation temperature, they undergo thermal decomposition and release their own water of crystallization, lowering the temperature of the heating element and its surroundings, thereby exhibiting a so-called "endothermic effect." After releasing the water of crystallization, the particles become porous, and the numerous air holes provide thermal insulation. 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).

[0057] For example, aluminum hydroxide has about 35% water of crystallization, and as shown in the following formula, it thermally decomposes, releasing the water of crystallization and exhibiting an endothermic effect. After releasing the water of crystallization, it becomes a porous alumina (Al2O3) and functions as a heat insulating material. 2Al(OH)3 → Al2O3 + 3H2O

[0058] As will be described later, the heat transfer-suppressing sheet 10 according to this embodiment is preferably interposed between battery cells, for example, but in a battery cell that has experienced thermal runaway, the temperature rises sharply to over 200° C. and continues to rise to around 700° C. Therefore, the inorganic particles are preferably made of an inorganic hydrate whose thermal decomposition temperature is 200° C. or higher. The thermal decomposition starting 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 in which a battery cell experiencing thermal runaway experiences a sudden rise in temperature, and can efficiently suppress temperature rise, making these inorganic hydrates preferable.

[0059] (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 their average particle size is too large, it takes some time for the first inorganic particles (inorganic hydrate) near the center of the heat transfer-suppressing sheet 10 to reach their thermal decomposition temperature, and the first inorganic particles near the center of the sheet may not be completely thermally decomposed. For this reason, the average secondary particle size 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.

[0060] (Particles made of thermally expandable inorganic material) Examples of thermally expandable inorganic materials include vermiculite, bentonite, mica, and perlite.

[0061] (Particles made of hydrous porous material) Specific examples of the hydrous porous material include zeolite, kaolinite, montmorillonite, acid clay, diatomaceous earth, wet silica, dry silica, aerogel, mica, and vermiculite.

[0062] (inorganic balloons) The heat transfer-suppressing sheet 10 according to this embodiment may contain inorganic balloons as the first inorganic particles. When inorganic balloons are contained, convective or conductive heat transfer within the heat-transfer-suppressing sheet can be suppressed in the temperature range of less than 500°C, thereby further improving the heat insulating properties of the heat-transfer-suppressing sheet. As the inorganic balloons, at least one selected from shirasu balloons, silica balloons, fly ash balloons, barite balloons, and glass balloons can be used.

[0063] (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.

[0064] (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.

[0065] <Second inorganic particles> When the heat-transfer-suppressing sheet contains two types of inorganic particles, 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, and particles made of a hydrous porous body, the details of which are as described above.

[0066] 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 are highly effective at blocking radiant heat. Furthermore, when large-diameter inorganic particles and small-diameter inorganic particles are used, the small-diameter inorganic particles penetrate into the gaps between the large-diameter inorganic particles, resulting in a denser structure and improved heat-transfer suppression. Therefore, when nanoparticles are used as the first inorganic particles, it is preferable to further include second inorganic particles made of a metal oxide that are larger in diameter than the first 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.

[0067] When the first inorganic particles are at least one type of particles selected from dry silica particles and silica aerogel, and the second inorganic particles are at least one type of particles selected from titania, zircon, zirconia, silicon carbide, zinc oxide, and alumina, the first inorganic particles preferably account for 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more of the total mass of the inorganic particles, in order to obtain excellent heat insulating performance within a temperature range of 300° C. or less. Furthermore, the first inorganic particles preferably account for 95% by mass or less, more preferably 90% by mass or less, and even more preferably 80% by mass or less of the total mass of the inorganic particles.

[0068] On the other hand, in order to obtain excellent heat insulating performance in a temperature range exceeding 300° C., the content of the second inorganic particles is 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 content of the second inorganic particles is 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.

[0069] (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 1 μm or more and 50 μm or less, 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 5 μm or more and 30 μm or less, and most preferably 10 μm or less.

[0070] (Inorganic particle content) In this embodiment, if the total content of the inorganic particles 4 in the heat-transfer-suppressing sheet 10 is appropriately controlled, the heat insulation properties of the heat-transfer-suppressing sheet 10 can be sufficiently ensured. The total content of inorganic particles 4 is preferably 60% by mass or more, and more preferably 70% by mass or more, of the total mass of heat-transfer-suppressing sheet 10. If the total content of inorganic particles 4 is too high, the content of organic fibers 1 will relatively decrease. Therefore, in order to fully obtain the sheet strength-enhancing effect of organic fibers 1, the total content of inorganic particles 4 is preferably 95% by mass or less, and more preferably 90% by mass or less, of the total mass of heat-transfer-suppressing sheet 10.

[0071] The content of inorganic particles 4 in heat-transfer-suppressing sheet 10 can be calculated, for example, by heating heat-transfer-suppressing sheet 10 at 800° C. to decompose the organic components, and then measuring the mass of the remaining portion.

[0072] The heat-transfer-suppressing sheet 10 according to this embodiment may contain, in addition to the organic fibers 1 and inorganic particles 4, organic fibers made of an organic material different from the first organic material, inorganic fibers, etc. When the heat-transfer-suppressing sheet 10 contains inorganic fibers, the inorganic fibers that are preferably contained in this embodiment will be described below.

[0073] <Inorganic fibers> The inorganic fibers may be a single inorganic fiber or a combination of two or more inorganic fibers. Examples of the inorganic fibers 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 fiber, 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.

[0074] 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 these, 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.

[0075] The preferred lower limit of the average fiber length of the inorganic fibers is 0.1 mm, more preferably 0.5 mm. Meanwhile, the preferred upper limit of the average fiber length of the inorganic fibers is 50 mm, 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 intertwine with each other, which may reduce the mechanical strength of the heat-transfer-suppressing sheet 10. 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 intertwine closely with each other or may curl up individually, which may result in continuous voids and reduce the heat insulating properties.

[0076] 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. Meanwhile, 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. Furthermore, from the viewpoint of the effects on human health, the average fiber diameter of the inorganic fibers is preferably 3 μm or more. Meanwhile, if the average fiber diameter of the inorganic fibers is greater than 15 μm, solid-state heat transfer via the inorganic fibers may increase, resulting in reduced thermal insulation, and the formability and strength of the heat transfer-suppressing sheet may be impaired.

[0077] (Inorganic fiber content) In this embodiment, when the heat-transfer-suppressing sheet contains inorganic fibers, the content of the inorganic fibers is preferably 3 mass % or more and 15 mass % or less relative to the total mass of the heat-transfer-suppressing sheet .

[0078] The inorganic fiber content is more preferably 5% by mass or more and 10% by mass or less, based on the total mass of the heat transfer-suppressing sheet 10. This content allows the inorganic fibers to exhibit a good balance of shape retention, pressure resistance, wind pressure resistance, and inorganic particle retention. By appropriately controlling the inorganic fiber content, the organic fibers 1 and the inorganic fibers become entangled with each other to form a three-dimensional network, further improving the retention of the inorganic particles 4 and other blended materials described below.

[0079] <Other compounding materials> The heat-transfer-suppressing sheet according to this embodiment may further contain, as needed, a binder, a colorant, etc. These are all useful for reinforcing the heat-transfer-suppressing sheet and improving its formability, and the total amount of these is preferably 10 mass % or less based on the total mass of the heat-transfer-suppressing sheet.

[0080] [Method of manufacturing heat transfer suppression sheet] An example of a method for manufacturing the heat transfer-suppressing sheet 10 according to this embodiment will be described below. For example, binder fibers (not shown) having a core-sheath structure and inorganic particles 4 are put into a mixer such as a V-type mixer at a predetermined ratio to prepare a mixture. As mentioned above, it is preferable to use a core-sheath fiber as the binder fiber, which has a core made of a first organic material and a sheath made of a second organic material, where the melting point of the first organic material is higher than that of the second organic material.

[0081] The resulting mixture is then placed in a predetermined mold and pressurized with a press or the like. The resulting molded body is heated, melting the sheaths of the binder fibers. The heated molded body is then cooled, solidifying the molten sheaths on the surface of the molded body and fusing the cores (organic fibers 1) together, forming fiber bundles 7 on the surface of the heat-transfer-suppressing sheet 10. Inside the molded body, the second organic material that constitutes the molten sheaths and the inorganic particles 4 that were present around the binder fibers are fused to the cores and also fused to each other in the regions where the binder fibers were in contact with each other. This allows the heat-transfer-suppressing sheet 10 of this embodiment to be obtained.

[0082] In this embodiment, it is preferable to manufacture the heat-transfer-suppressing sheet 10 by a dry method. When using the dry method, inorganic particles 4 suitable for the dry method are used, and a solvent such as water, which is required when forming by a wet method, is not added to the mixture. However, to prevent powder such as the inorganic particles 4 from flying around during the manufacture of the heat-transfer-suppressing sheet 10 and making the raw materials difficult to handle, a small amount of solvent such as water can be added within the range required for the dry method. For example, adding a small amount of solvent such as water to the mixture can prevent the inorganic particles from scattering during production.

[0083] According to the manufacturing method of this embodiment, fiber bundles 7 made of organic fibers 1 are formed on the surface, thereby producing a heat-transfer-suppressing sheet 10 with excellent strength. Furthermore, because the melting point of the first organic material constituting the core is higher than that of the second organic material constituting the sheath, the sheath can be melted while leaving the core intact when the mixture is heated. After cooling, the outer surface of the core is coated with the second organic material containing inorganic particles 4, thereby retaining the inorganic particles 4. The organic fibers 1 to which the inorganic particles 4 are fused have an apparent thicker fiber diameter, resulting in a strength greater than that of the organic fibers 1 alone. Furthermore, because the binder fibers are present in an irregular orientation in the mixture, the organic fibers 1 are fused together in areas where the binder fibers are in contact, forming a three-dimensional skeleton. As a result, the overall shape of the heat-transfer-suppressing sheet can be maintained with even greater strength.

[0084] Even when organic fibers without a core-sheath structure are used as binder fibers, it is possible to form fiber bundles 7 extending in stripes on the surface. However, when manufacturing a heat-transfer-suppressing sheet, heating is generally performed from one or both sides perpendicular to the thickness direction, and because a material with high thermal insulation performance is used, it is difficult to raise the temperature to the same level on the surface and inside of the sheet. Strict temperature control is required to prevent the organic fibers on the surface of the sheet from melting too much, while melting only the surfaces of the organic fibers inside the sheet, thereby coating the surface with inorganic particles or fusing the organic fibers together, thereby manufacturing a heat-transfer-suppressing sheet 10 with even greater sheet strength.

[0085] In contrast, if binder fibers with a sheath-core structure in which the melting point of the first organic material constituting the core is higher than the melting point of the second organic material constituting the sheath are used, it is extremely easy to set the temperature to melt the sheath while leaving the core intact. As a result, the obtained heat-transfer-suppressing sheet has an ideal structure in which the organic fibers 1 are fused to each other on both the surface and center sides to form a skeleton that improves the sheet's strength, and the inorganic particles 4 are fused to the surfaces of the organic fibers 1. Therefore, it is preferable to use binder fibers with the above-mentioned sheath-core structure as the material for the heat-transfer-suppressing sheet 10.

[0086] As will be described in detail later, an adhesive such as hot melt powder may be contained in the mixture as a raw material for the heat transfer-suppressing sheet. By appropriately adjusting the type and content of the adhesive contained in the mixture, the holding power of the inorganic particles 4 can be improved and powder fall-off can be further suppressed. As a result, the heat-transfer-suppressing sheet 10 manufactured by the manufacturing method according to this embodiment has even greater strength, and can maintain its shape even when pressure or impact is applied to the heat-transfer-suppressing sheet, preventing powder from falling off, and maintaining excellent heat-insulating performance.

[0087] To further suppress powder falling, the surface of heat-transfer-suppressing sheet 10 may be coated with a film or the like. Examples of polymer films include films made of polyimide, polycarbonate, PET, p-phenylene sulfide, polyetherimide, cross-linked polyethylene, flame-retardant chloroprene rubber, polyvinyl fluoride, rigid polyvinyl chloride, polybutylene terephthalate, PTFE, PFA, FEP, ETFE, rigid PVC, flame-retardant PET, polystyrene, polyethersulfone, polyamideimide, polyacrylonitrile, polyethylene, polypropylene, polyamide, etc. The method for covering the surface of heat-transfer-suppressing sheet 10 with a film is not particularly limited, and examples include a method of attaching the film with an adhesive, a method of wrapping heat-transfer-suppressing sheet 10 in a film, and a method of housing heat-transfer-suppressing sheet 10 in a bag-shaped film.

[0088] Next, binder fibers and heating conditions that are preferably used in the method for producing a heat transfer-suppressing sheet according to this embodiment will be described.

[0089] <Binder fiber> In this embodiment, when a core-sheath binder fiber is used, the melting point of the first organic material constituting the core is not particularly limited as long as it is higher than the melting point of the second organic material constituting the sheath. The first organic material constituting the core can be at least one selected from polyethylene terephthalate, polypropylene, and nylon. The second organic material constituting the sheath can be at least one selected from polyethylene terephthalate, polyethylene, polypropylene, and nylon.

[0090] If the melting point of the first organic material constituting the core is sufficiently higher than that of the second organic material constituting the sheath, the heating temperature setting margin in the heating step can be expanded, making it easier to set the temperature to obtain the desired structure. For example, the melting point of the first organic material is preferably 60°C or more higher than that of the second organic material, more preferably 70°C or more higher, and even more preferably 80°C or more higher.

[0091] Note that binder fibers having a core-sheath structure such as the one described above are generally commercially available, and the materials constituting the core and sheath may be the same or different. Examples of binder fibers in which the core and sheath are made of the same material but have different melting points include those in which the core and sheath are made of polyethylene terephthalate, polypropylene, or nylon. Examples of binder fibers in which the core and sheath are made of different materials include those in which the core is made of polyethylene terephthalate and the sheath is made of polyethylene, and those in which the core is made of polypropylene and the sheath is made of polyethylene.

[0092] In this embodiment, the melting point of the second organic material constituting the sheath of the binder fiber refers to the melting temperature at which the second organic material begins to melt and deform, but softening accompanied by a change in shape is also considered to be a type of melting and deformation. The melting point of the sheath of the binder fiber can be measured, for example, by the following method. The binder fiber to be measured is placed in contact with a glass fiber having a higher melting point, and is heated from room temperature to, for example, 200°C at a temperature increase rate of 5°C / min, and then cooled to room temperature. If the surface of the binder fiber melts and deforms, and the area in contact with the glass fiber is fused, or if the cross-sectional shape of the binder fiber changes, it can be determined that the melting point of the second organic material constituting the sheath is 200°C or lower. In this embodiment, the heating temperature is varied and the fusion state between the binder fiber and the glass fiber or the cross-sectional shape of the binder fiber after cooling is observed using the above method, thereby identifying the melting point of the second organic material constituting the sheath.

[0093] (Binder fiber content) In this embodiment, when binder fibers with a core-sheath structure are used as the material, if the content of the binder fibers in the mixture is appropriately controlled, fiber bundles 7 of an appropriate length can be formed on the surface of the obtained heat transfer-suppressing sheet 10, and excellent sheet strength can be obtained. The content of the binder fiber is preferably 5% by mass or more, more preferably 10% by mass or more, based on the total mass of the mixture. If the content of the binder fiber is too high, the content of the inorganic particles 4 will relatively decrease. Therefore, in order to obtain the desired heat insulating performance, the content of the binder fiber is preferably 25% by mass or less, more preferably 20% by mass or less, based on the total mass of the mixture.

[0094] <Hot melt powder> In this embodiment, in addition to the binder fibers and inorganic particles 4, the mixture may contain hot-melt powder. The hot-melt powder is a powder that contains, for example, a third organic material different from the first and second organic materials 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 that includes the surrounding inorganic particles 4. This further prevents the inorganic particles 4 from falling off from the heat-transfer-suppressing sheet 10.

[0095] Hot melt powders with various melting points can be used. A hot melt powder with an appropriate melting point can be selected based on the melting points of the core and sheath of the binder fiber used. Specifically, if the third organic material 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 that 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.

[0096] Alternatively, the type of hot melt powder used can be selected so that its melting point is between the melting points of the core and sheath. When a hot melt powder with such a melting point is used, the sheath and hot melt powder melt together, and then when they cool and harden, the organic fibers (core) 1, the molten sheath around them, and the hot melt powder present in the gaps between the inorganic particles 4 harden first. As a result, the position of the organic fibers 1 can be fixed, and then the molten sheath will fuse to the organic fibers, facilitating the formation of a three-dimensional skeleton. This further improves the strength of the entire sheet.

[0097] 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 latitude in the heating step can be expanded, making it easier to set the temperature to obtain the desired structure. For example, the melting point of the first organic material is preferably 60°C or more higher than that of the third organic material, more preferably 70°C or more higher, and even more preferably 80°C or more higher.

[0098] 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, and ethylene vinyl acetate.

[0099] (Hot melt powder content) When hot-melt powder is added to the mixture to prevent the inorganic particles from falling off, even a small amount of hot-melt powder can be effective in preventing the particles from falling off. Therefore, the hot-melt powder content is preferably 0.5% by mass or more, and more preferably 1% by mass or more, based on the total mass of the mixture. On the other hand, when the content of the hot melt powder is increased, the content of the inorganic particles 4 and the like is relatively decreased, so in order to obtain the desired heat insulating performance, the content of the hot melt powder is preferably 5 mass% or less, and more preferably 4 mass% or less, relative to the total mass of the mixture.

[0100] <Heating conditions> The process for processing the mixture into a sheet includes a process for pressing the mixture and a process for heating the mixture. When a binder fiber having a core-sheath structure is used as the material for the heat transfer-suppressing sheet 10, the heating temperature in the heating process is preferably higher than the melting point of the second organic material constituting the sheath and lower than the melting point of the first organic material constituting the core. By setting the heating temperature in this manner, as described above, the strength of the sheet can be ensured by the core on both the surface side and the center side of the sheet, and the inorganic particles 4 can be held by the fused sheath.

[0101] Specifically, the heating temperature in the heating step is preferably set to be 10°C or more higher, more preferably 20°C or more higher, than the melting point of the second organic material constituting the sheath, while the heating temperature is preferably set to be 10°C or more lower, more preferably 20°C or more lower, than the melting point of the first organic material constituting the core.

[0102] The heating time is not particularly limited, but it is preferable to set the heating time so that the sheath can be sufficiently melted, for example, from 3 minutes to 15 minutes.

[0103] When the heat transfer-suppressing sheet contains a hot-melt powder as its material, the heating temperature in the heating step is preferably set to be at least 10°C higher, and more preferably at least 20°C 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. Meanwhile, the heating temperature is preferably set to be at least 10°C lower, and more preferably at least 20°C lower, than the melting point of the first organic material constituting the core. Setting the heating temperature in this range allows for the formation of a strong skeleton, further improving the strength of the sheet and preventing the inorganic particles 4 from falling off.

[0104] <Thickness of heat transfer suppression sheet> The thickness of the heat-transfer-suppressing sheet according to this embodiment is not particularly limited, but is preferably 0.05 mm or more and 10 mm or less. A thickness of 0.05 mm or more ensures sufficient compressive strength. On the other hand, a thickness of 10 mm or less ensures good heat insulation of the heat-transfer-suppressing sheet.

[0105] [Battery pack] Fig. 6 is a schematic diagram showing a battery pack including a heat-transfer-suppressing sheet according to an embodiment of the present invention. As shown in Fig. 6, a battery pack 100 includes a plurality of battery cells 20a, 20b, and 20c and a heat-transfer-suppressing sheet 10 according to this embodiment, and these plurality of battery cells 20a, 20b, and 20c are connected in series or in parallel. Specifically, the heat transfer-suppressing sheet 10 is interposed between the battery cell 20a and the battery cell 20b, and between the battery cell 20b and the battery cell 20c. The battery cells 20a, 20b, and 20c are connected in series or parallel (the connected state is not shown) and housed in the battery case 30 to form the battery pack 100. The battery cells 20a, 20b, and 20c are preferably, for example, lithium-ion secondary batteries, but are not limited thereto and may also be other secondary batteries. The heat-transfer-suppressing sheet 10 is as described above.

[0106] In the battery pack 100 configured in this manner, even if a certain battery cell 20a becomes hot, the heat transfer to the battery cell 20b can be suppressed because the heat transfer suppression sheet 10, which has a heat transfer suppression effect, is present between the battery cell 20a and the battery cell 20b. Furthermore, the heat-transfer-suppressing sheet 10 according to this embodiment has high strength, shock absorption, and resistance to pressure, thereby suppressing thermal expansion of the battery cells 20a, 20b, and 20c even during charging and discharging. This ensures sufficient distance between the battery cells, maintaining excellent thermal insulation performance and preventing thermal runaway of the battery cells. Furthermore, the sheet is easy to handle because it suppresses powder shedding.

[0107] The battery pack 100 of this embodiment is not limited to the battery pack illustrated in Fig. 6. 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.

[0108] 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 area. In this case, even if a battery cell were to catch fire, the safety of the passengers can be ensured. Furthermore, the heat transfer suppression sheet 10 can be placed not only between each battery cell, but also between the battery cells 20a, 20b, 20c and the battery case 30, eliminating the need to fabricate new flame retardant materials, etc., and allowing for the easy, low-cost, and safe construction of the assembled battery 100.

[0109] In the battery pack of this embodiment, the heat-transfer-suppressing sheet 10 disposed between the battery cells 20a, 20b, and 20c and the battery case 30 may be in contact with the battery cells or may have a gap therebetween. However, if there is a gap between the heat-transfer-suppressing sheet 10 and the battery cells 20a, 20b, and 20c, deformation of the battery cells can be tolerated even if the temperature of one of the multiple battery cells rises and the volume expands.

[0110] The heat transfer-suppressing sheet 10 according to this embodiment can be manufactured into various shapes depending on the manufacturing method. Therefore, it can be adapted to any shape, regardless of the shapes of the battery cells 20a, 20b, 20c and the battery case 30. Specifically, it can be applied to cylindrical batteries, flat batteries, etc., in addition to prismatic batteries. [Explanation of symbols]

[0111] 1. Organic Fiber 2 First area 3 Second area 4 Inorganic particles 7 Fiber bundles 10 Heat transfer suppression sheet 20a, 20b, 20c battery cells 21 Virtual Frame 30 Battery case 100 battery packs

Claims

1. A heat transfer-suppressing sheet including inorganic particles and organic fibers, a first region having a surface including a plurality of streak-like fiber bundles made of the organic fibers; a second region in which the fiber bundles are not present, The heat transfer suppressing sheet, wherein the first region and the second region form a sea-island structure.

2. The heat transfer suppressing sheet according to claim 1 , wherein the first region has the streak-like fiber bundles passing through at least three consecutive imaginary frames each measuring 5 mm square.

3. The heat transfer suppressing sheet according to claim 1 , wherein the first region has the streak-like fiber bundles having a length of 20 mm or more.

4. The heat transfer suppressing sheet according to claim 1 , wherein the second region is surrounded by the first region.

5. The heat transfer suppressing sheet according to claim 1 , wherein the streak-like fiber bundles are connected in a mesh-like pattern on the surface.

6. 2. The heat transfer-suppressing sheet according to claim 1, wherein the inorganic particles are particles made of at least one inorganic material selected from the group consisting of oxide particles, carbide particles, nitride particles, and inorganic hydrate particles.

7. The heat transfer-suppressing sheet according to claim 6, wherein the inorganic particles include at least one type of particles selected from the group consisting of dry silica particles and silica aerogel.

8. 8. The heat transfer-suppressing sheet according to claim 7, wherein the inorganic particles further include particles of at least one type selected from the group consisting of titania, zircon, zirconia, silicon carbide, zinc oxide, and alumina.

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

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