Heat transmission 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 having the heat transfer-suppressing sheet. [Background technology]

[0002] In recent years, from the viewpoint of environmental protection, active development of electric vehicles, hybrid vehicles, etc. that are driven by electric motors is underway. These electric vehicles, hybrid vehicles, etc. 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 mainly use lithium-ion secondary batteries, which are capable of higher capacity and higher output than lead-acid batteries, nickel-metal hydride batteries, etc. If a certain battery cell experiences thermal runaway, in which the temperature rises suddenly and the cell continues to generate heat due to an internal short circuit or overcharging, the heat from the battery cell experiencing thermal runaway may propagate to other adjacent battery cells, causing thermal runaway in the other battery cells.

[0004] As a method for suppressing the propagation of heat from a battery cell that has experienced the above-mentioned thermal runaway, a method of placing a heat insulating sheet between the battery cells is commonly used. For example, Patent Document 1 discloses a heat insulating sheet for a battery pack, which contains first particles composed of silica nanoparticles and second particles composed of a metal oxide, and in which the content of the first particles is limited. Patent Document 1 also describes that the heat insulating sheet may contain a binding material composed of at least one material selected from fibers, binders, and heat-resistant resins.

[0005] Furthermore, the above-mentioned Patent Document 1 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, when a heat insulating sheet (heat transfer suppressing sheet) is produced, for example, a heat-adhesive binder fiber is used as a binder, but the heat-adhesive binder fiber needs to be in a wet state during production in order to exhibit its adhesiveness. Therefore, when a heat-adhesive binder fiber is used, the heat insulating sheet needs to be produced by a wet papermaking method.

[0008] However, when dry silica or silica aerogel, which has low thermal conductivity, is used to further improve the thermal insulation performance, there is a problem that the thermal insulation sheet cannot be manufactured by the wet papermaking method. This is because when a material containing dry silica is molded into a sheet by the wet papermaking method, the dry silica aggregates with water, and the thermal conductivity increases. In addition, since it is generally difficult to disperse silica aerogel in water, when a material containing silica aerogel is molded by the wet papermaking method, a thermal insulation sheet in which the material is uniformly dispersed cannot be obtained, which causes a decrease in quality.

[0009] On the other hand, when inorganic particles such as dry silica or silica aerogel are used to manufacture a heat insulating sheet by a dry molding method, the inorganic particles may fall off (hereinafter, also referred to as powder falling off) due to pressure, impact, etc. In particular, in recent assembled batteries, the capacity of the battery cells has been further improved, and the expansion rate during charging and discharging has increased. Therefore, when a heat insulating sheet is placed between the battery cells of an assembled battery, if the strength of the heat insulating sheet as a whole is low, the heat insulating sheet is compressed due to the expansion of the battery cells during charging and discharging, etc., causing powder falling off, and the heat insulating performance is reduced. As a result, when the battery cells become hot due to thermal runaway, the heat insulating sheet cannot exert its effect, and a thermal chain reaction may occur. For these reasons, there is a demand for a heat insulating sheet and a manufacturing method thereof that have high strength to continue to maintain their shape, can suppress powder falling off, and can maintain excellent heat insulating properties.

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

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

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

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

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

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

[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], further 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 type of inorganic material selected from the group consisting of 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 the group consisting of titania, zircon, zirconia, silicon carbide, zinc oxide, and alumina.

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

[0023] [9] An assembled battery 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. Effect of the Invention

[0024] The heat-transfer-inhibiting sheet of the present invention has a first region on the surface having streaky fiber bundles, and a second region where no fiber bundles are present, which improves the strength of the heat-transfer-inhibiting sheet and reduces impacts and pressure on the surface of the heat-transfer-inhibiting sheet, thereby suppressing powder falling and preventing a decrease in the insulating effect due to deformation of the heat-transfer-inhibiting sheet.

[0025] The battery pack of the present invention has a heat-transfer-suppressing sheet that has high strength and the effect of retaining thermal insulation performance as described above, so that it is possible to suppress thermal runaway of the battery cells in the battery pack and the spread of flames to the outside of the battery case. [Brief description of the drawings]

[0026] [Figure 1] FIG. 1 is a photograph, substituted for a drawing, showing the state of the surface of a heat-transfer-suppressing sheet according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a photograph showing an enlarged portion of FIG. [Diagram 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 a drawing showing an enlarged view of part A in FIG. [Diagram 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 PREFERRED EMBODIMENTS

[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 found 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 insulation performance.

[0028] Hereinafter, a heat transfer-suppressing sheet, a manufacturing method thereof, 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.

[0029] [Heat transfer suppression sheet] Fig. 1 is a photograph showing the appearance of 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 the 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. A first region 2 having streak-like fiber bundles 7 made of a plurality of organic fibers 1 and a second region 3 in which no fiber bundles 7 are present are formed on the surface of the heat-transfer-suppressing sheet 10. In this specification, the fiber bundles 7 are 10 or more organic fibers 1 entangled with one another and extend in streak-like fashion in a direction approximately 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 an island portion is formed so as to be surrounded by the first region 2 corresponding to a sea portion.

[0032] One example of how the heat-transfer-suppressing sheet 10 can be used is to place 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, the fiber bundles 7 in which the organic fibers 1 are entangled are present on the surface of the heat-transfer-inhibiting sheet 10 so as to extend in stripes, thereby improving the strength of the heat-transfer-inhibiting sheet 10. Furthermore, the entire surface is not covered with the fiber bundles 7, and there are a first region 2 in which the fiber bundles 7 are present and a second region in which the fiber bundles 7 are not present, so that the flexibility of the heat-transfer-inhibiting sheet 10 is excellent. Furthermore, since the fiber bundles 7 are present on the surface of the heat-transfer-inhibiting sheet 10, even if the heat-transfer-inhibiting sheet 10 is subjected to an impact or pressure, the fiber bundles 7 can absorb and mitigate the impact or pressure. Therefore, the inorganic particles 4 can be prevented from falling off (powdering), and a decrease in the heat insulating performance of the heat-transfer-inhibiting sheet 10 can be prevented.

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

[0035] In this embodiment, it is preferable that the length of the fiber bundles 7 formed so as to extend over the surface of the heat-transfer-suppressing sheet 10 is relatively long. An example of a method for determining the length of the fiber bundles 7 will be described with reference to 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 effect of improving the strength of the heat-transfer-suppressing sheet 10 is sufficient.

[0036] It is also possible to simply measure the length of the fiber bundles 7 extending in stripes. For example, a method can be used in which a string or the like is placed on the surface of the heat-transfer-suppressing sheet 10 along the fiber bundles 7, and then the length of the string is measured. When the length of continuous fiber bundles 7 is measured, as long as 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 has the effect of improving the strength and shape of the sheet. Although 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 periphery of the core. 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] Whether a single-component organic fiber or a binder fiber with a core-sheath structure is used as the material for the organic fibers 1, when the heat-transfer-suppressing sheet 10 is manufactured, a part of the surface of the fiber melts by heating, and then cooling forms a welded part (not shown) around the organic fibers 1. The welded part welds the inorganic particles 4 to the surface of the organic fibers 1 and also welds the organic fibers 1 to each other, so that the formation of the welded part provides excellent sheet strength.

[0041] When binder fibers with a core-sheath structure are used as the material, the core of the heat-transfer-suppressing sheet 10 corresponds to the organic fibers 1. When binder fibers with a core-sheath structure are used during the manufacture 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 core-sheath structure are used, the second organic material that constitutes the sheath melts and then solidifies again in a state that includes the inorganic particles 4 present around it, thereby improving the retention of the inorganic particles 4.

[0042] (First organic material) When a binder fiber having a core-sheath structure is used as the material of the organic fiber 1, the core, i.e., the first organic material constituting 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 peripheral 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 a binder fiber having a core-sheath structure is used as the material of the organic fiber 1, the second organic material constituting the sheath is not particularly limited as long as it has a melting point lower than that of the first organic material constituting the organic fiber 1. The second organic material may be 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, when 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 mass % or more, and more preferably 4 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, so in order to obtain the desired heat insulation performance, the content of organic fibers is preferably 10 mass % or less, and more preferably 8 mass % or less, relative to the total mass of heat-transfer-suppressing sheet 10.

[0045] (Organic fiber length) 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 is 10 mm or less. On the other hand, from the standpoint 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> 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.

[0047] 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.

[0048] 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.

[0049] <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.

[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 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.

[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 ten particles.

[0052] (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, the voids are finely 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 by 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 fine gaps between particles due to static electricity repulsion, and because they have a low bulk density, the particles are packed together to provide a cushioning effect.

[0053] In the present invention, when nanoparticles are used as the first inorganic particles, there is no particular limitation on the material as long as it meets 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.

[0054] Generally, wet silica particles are aggregated, whereas dry silica particles can be dispersed. In the temperature range below 300℃, heat conduction is dominated by conductive heat transfer, so dry silica particles can be dispersed, which provides better heat insulation performance than 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.

[0055] (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.

[0056] (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).

[0057] 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

[0058] As 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 rapidly to over 200° C. and continues to rise to around 700° C. Therefore, the inorganic particles are preferably made of inorganic hydrates whose thermal decomposition starting temperature is 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.

[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 a certain amount of 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 the thermally expandable inorganic material include vermiculite, bentonite, mica, and perlite.

[0061] (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.

[0062] (Inorganic balloon) 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., and the heat insulating properties of the heat-transfer-suppressing sheet can be further improved. As the inorganic balloons, at least one selected from the group consisting of 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, particles made of a water-containing porous body, etc., 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 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.

[0067] 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 is used as the second inorganic particles, in order to obtain excellent heat insulating performance within a temperature range of 300° 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 of 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 of the total mass of the inorganic particles.

[0068] On the other hand, in order to obtain excellent heat insulating performance within a temperature range exceeding 300° 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.

[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 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.

[0070] (Inorganic particle content) In this embodiment, when 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 the inorganic particles 4 is preferably 60 mass % or more, and more preferably 70 mass % or more, relative to the total mass of the heat-transfer-suppressing sheet 10. Furthermore, if the total content of the inorganic particles 4 is too high, the content of the organic fibers 1 will relatively decrease, and therefore, in order to fully obtain the effect of improving the sheet strength by the organic fibers 1, the total content of the inorganic particles 4 is preferably 95 mass % or less, and more preferably 90 mass % or less, relative to the total mass of the heat-transfer-suppressing sheet 10.

[0071] The amount of inorganic particles 4 contained 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 remainder.

[0072] The heat-transfer-suppressing sheet 10 according to the present 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 the present embodiment will be described below.

[0073] <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.

[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 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.

[0075] 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 heat-transfer-suppressing sheet 10 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 lead to continuous voids and thus to a reduction in heat insulation.

[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. 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.

[0077] (Inorganic fiber content) In this embodiment, when heat-transfer-suppressing sheet 10 contains inorganic fibers, the content of inorganic fibers is preferably 3 mass % or more and 15 mass % or less relative to the total mass of heat-transfer-suppressing sheet 10.

[0078] The content of the inorganic fibers is more preferably 5% by mass or more and 10% by mass or less with respect to the total mass of the heat-transfer-suppressing sheet 10. This content allows the shape retention, pressing force resistance, wind pressure resistance, and inorganic particle retention ability of the inorganic fibers to be exhibited in a well-balanced manner. By appropriately controlling the content of the inorganic fibers, the organic fibers 1 and the inorganic fibers are entangled with each other to form a three-dimensional network, which further improves the effect of retaining the inorganic particles 4 and other blended materials described below.

[0079] <Other compounding materials> The heat-transfer-suppressing sheet according to this embodiment can further contain, as necessary, a binder, a colorant, etc. Any of these are useful for the purposes of reinforcing the heat-transfer-suppressing sheet or 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 producing 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 described above, it is preferable to use, as the binder fiber, fibers having a core-sheath structure with a core made of a first organic material and a sheath made of a second organic material, in which the melting point of the first organic material is higher than that of the second organic material.

[0081] The mixture thus obtained is then placed in a predetermined mold and pressed with a press or the like, and the resulting molded body is heated to melt the sheath of the binder fiber. The heated molded body is then cooled, and the molten sheath on the surface of the molded body solidifies, fusing the cores (organic fibers 1) together to form fiber bundles 7 on the surface of the heat-transfer-suppressing sheet 10. Inside the molded body, the second organic material constituting the molten sheath and the inorganic particles 4 present around the binder fibers are fused to the cores, and are 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 according to 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 a dry method, inorganic particles 4 suitable for the dry method are used, and a solvent such as water, which is necessary when forming by a wet method, is not added to the mixture. However, in order to prevent powder such as the inorganic particles 4 from flying around during the manufacture of the heat-transfer-suppressing sheet 10 and making it difficult to handle the raw materials, a small amount of solvent such as water can be added within the range that is considered to be a dry method. For example, by adding a small amount of solvent such as water to the mixture, it is possible to suppress scattering of the inorganic particles during the manufacture.

[0083] According to the manufacturing method of the present embodiment, since fiber bundles 7 made of organic fibers 1 are formed on the surface, a heat-transfer-suppressing sheet 10 having excellent strength can be manufactured. In addition, since the melting point of the first organic material constituting the core is higher than that of the second organic material constituting the sheath, when the mixture is heated, the sheath can be melted while leaving the core. After cooling, the outer peripheral surface of the core is covered with the second organic material containing inorganic particles 4, so that the inorganic particles 4 can be held. The organic fibers 1 to which the inorganic particles 4 are welded have an apparent thick fiber diameter, so that the strength is higher than that of the organic fibers 1 alone. Furthermore, since the binder fibers are present in an irregular direction in the mixture, the organic fibers 1 are welded together in the region where the binder fibers are in contact with each other, forming a three-dimensional skeleton. As a result, the shape of the entire heat-transfer-suppressing sheet can be held with even higher strength.

[0084] It is possible to form fiber bundles 7 extending in stripes on the surface even when organic fibers not having a core-sheath structure are used as binder fibers. However, when manufacturing a heat-transfer-suppressing sheet, it is common to heat the sheet from one or both sides perpendicular to the thickness direction, and since a material with high heat insulating performance is used, it is difficult to raise the temperature to the same level on the surface side and inside of the sheet. Strict temperature control is required to control the temperature so that the multiple organic fibers on the surface side of the sheet do not melt too much, and to melt only the surfaces of the organic fibers inside the sheet, to coat the surfaces with inorganic particles, or to fuse the organic fibers together, thereby manufacturing a heat-transfer-suppressing sheet 10 with even higher sheet strength.

[0085] In contrast, if binder fibers having 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 very easy to set the temperature for melting the sheath while leaving the core. 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 side and the center side to form a skeleton that improves the strength of the sheet, and the inorganic particles 4 are fused to the surfaces of the organic fibers 1. Therefore, it is preferable to use binder fibers having the above-mentioned core-sheath structure as the material for the heat-transfer-suppressing sheet 10.

[0086] As described in detail below, 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 retention force of the inorganic particles 4 can be improved and powder falling can be further suppressed. As a result, the heat-transfer-inhibiting 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-inhibiting sheet, thereby preventing powder from falling off and maintaining excellent heat insulating performance.

[0087] In order to further suppress powder falling off, the surface of heat-transfer-suppressing sheet 10 may be covered 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 denfluoride, rigid polyvinyl chloride, polybutylene terephthalate, PTFE, PFA, FEP, ETFE, rigid PCV, 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 thereof include a method of attaching the sheet with an adhesive or the like, a method of wrapping heat-transfer-suppressing sheet 10 with a film, a method of housing heat-transfer-suppressing sheet 10 in a bag-shaped film, etc.

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

[0089] <Binder fiber> In this embodiment, when using a binder fiber having a core-sheath structure, 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 may be at least one selected from polyethylene terephthalate, polypropylene, and nylon. The second organic material constituting the sheath may 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 shell, 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 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 the above-mentioned core-sheath structure 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, and 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 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 the glass fiber having a higher melting point, heated from room temperature to, for example, 200°C at a heating rate of 5°C / min, and then cooled to room temperature. At this time, if the surface of the binder fiber melts and deforms and is fused at the part in contact with the glass fiber or 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 less. In this embodiment, the heating temperature is changed in various ways, 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 by the above-mentioned method, whereby the melting point of the second organic material constituting the sheath can be specified.

[0093] (Binder fiber content) In this embodiment, when binder fibers having 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 is relatively reduced, so 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, for example, a powder containing a third organic material different from the first organic material and the second organic material, and having the property of melting when heated. By adding the hot melt powder to the mixture and heating it, the hot melt powder melts, and when cooled, it hardens in a state including the surrounding inorganic particles 4. Therefore, it is possible to further suppress the falling off of the inorganic particles 4 from the heat transfer-suppressing sheet 10.

[0095] 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.

[0096] 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 organic fiber (core) 1 and the molten sheath around it, and the hot melt powder present in the gaps between the inorganic particles 4 harden first. As a result, the position of the organic fiber 1 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.

[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 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.

[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, ethylene vinyl acetate, and the like.

[0099] (Hot melt powder content) When hot melt powder is added to the mixture to suppress the falling off of inorganic particles, the effect of suppressing powder falling can be obtained even with a small amount of hot melt powder. Therefore, the content of hot melt powder is preferably 0.5% by mass or more, 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 of processing the mixture into a sheet includes a process of pressing the mixture and a process of 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 such a heating temperature, 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 set preferably 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 set preferably 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 material of the heat transfer-suppressing sheet contains a hot melt powder, the heating temperature in the heating step is set preferably at least 10°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, and more preferably at least 20°C higher. On the other hand, the heating temperature is preferably set at least 10°C lower than the melting point of the first organic material constituting the core, and more preferably at least 20°C 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 inorganic particles 4 can be prevented from falling off.

[0104] <Thickness of heat transfer suppression sheet> The thickness of the heat-transfer-suppressing sheet according to the present embodiment is not particularly limited, but is preferably 0.05 mm or more and 10 mm or less. If the thickness is 0.05 mm or more, sufficient compressive strength can be obtained. On the other hand, if the thickness is 10 mm or less, the heat-transfer-suppressing sheet can have good heat insulation properties.

[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 the present embodiment, and the 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 stored 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, and has the effect of absorbing shock and resisting pressure, so that it can suppress thermal expansion of the battery cells 20a, 20b, and 20c even when these battery cells are charged and discharged. Therefore, it is possible to ensure the distance between the battery cells and maintain excellent heat insulating performance, so that it is possible to prevent thermal runaway of the battery cells. In addition, it is easy to handle because it has the effect of suppressing powder falling off.

[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 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.

[0109] In the battery pack of this embodiment, the heat-transfer-suppressing sheet 10 arranged between the battery cells 20a, 20b, 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, 20c, deformation of the battery cells can be tolerated even if the temperature of any 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 without being affected by 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 square batteries. [Explanation of symbols]

[0111] 1. Organic Fibers 2 First area 3 Second area 4 Inorganic particles 7 Fiber bundle 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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