Heat-transmission controlling sheet and battery pack

Abstract

To provide: a heat-transmission controlling sheet, where, even if a compressive stress applied to the heat-transmission controlling sheet is increased, the sheet can maintain heat insulating properties and prevent breakage of the sheet itself when an adjacent battery cell undergoes thermal runaway; and a battery pack with the heat-transmission controlling sheet.SOLUTION: A heat-transmission controlling sheet 10 includes inorganic particles 4 and organic particles 1, and also includes a plurality of voids 7 which are three-dimensionally linked.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a heat transfer suppression sheet and a battery pack having the heat transfer suppression sheet.

Background Art

[0002] In recent years, from the viewpoint of environmental protection, the development of electric vehicles or hybrid vehicles driven by an electric motor has been actively promoted. Such electric vehicles or hybrid vehicles are equipped with a battery pack in which a plurality of battery cells are connected in series or in parallel to serve as a power source for the drive electric motor.

[0003] In addition, for this battery cell, a lithium-ion secondary battery that can achieve high capacity and high output compared to lead-acid batteries, nickel-metal hydride batteries, etc. is mainly used. And when a thermal runaway occurs due to internal short circuit or overcharge of the battery, etc., causing a certain battery cell to rapidly heat up and continue to generate heat thereafter, the heat from the battery cell that has experienced thermal runaway may be propagated to other adjacent battery cells, causing thermal runaway of other battery cells.

[0004] As a method for suppressing the propagation of heat from a battery cell that has experienced thermal runaway as described above, a method of interposing a heat insulation sheet between battery cells is generally performed. For example, Patent Document 1 discloses a heat insulation sheet for a battery pack that includes first particles composed of silica nanoparticles and second particles composed of a metal oxide, and limits the content of the first particles. Patent Document 1 also describes that the heat insulation sheet may contain a binder made of at least one selected from fibers, binders, and heat-resistant resins.

[0005] Patent Document 1 also describes that dry silica or wet silica can be used as the first particles, and this heat insulation sheet can be manufactured by a dry forming method or a wet papermaking method.

Prior Art Documents

Patent Documents

[0006] [Patent Document 1] Japanese Patent Publication No. 2021-34278 [Overview of the project] [Problems that the invention aims to solve]

[0007] Incidentally, when manufacturing heat-insulating sheets (heat transfer suppression sheets), one example of a binder is a moist heat-adhesive binder fiber. However, moist heat-adhesive binder fibers need to be kept wet during manufacturing in order to exhibit their adhesive properties. Therefore, when using moist heat-adhesive binder fibers, the heat-insulating sheet must be manufactured using a wet papermaking method.

[0008] However, when using dry silica or silica aerogel, which have low thermal conductivity, to further improve insulation performance, there is a problem in that insulation sheets cannot be manufactured using the wet papermaking method. This is because when materials containing dry silica are formed into a sheet using the wet papermaking method, the dry silica aggregates with water, increasing its thermal conductivity. In addition, silica aerogel is generally difficult to disperse in water, so when materials containing silica aerogel are formed using the wet papermaking method, it is not possible to obtain an insulation sheet with uniformly dispersed material, leading to a decrease in quality.

[0009] Furthermore, in recent battery packs, the capacity of battery cells has improved even further, resulting in an increased expansion rate during charging and discharging. Therefore, when an insulating sheet is placed between the battery cells of a battery pack, depending on the structure of the insulating sheet, the insulating sheet may be compressed by the expansion of the battery cells during charging and discharging, reducing its insulating performance. As a result, if the battery cells overheat and reach high temperatures, a heat chain reaction is more likely to occur.

[0010] While the thermal insulation sheet described in Patent Document 1 maintains excellent thermal insulation even when compressive stress increases, there is a growing demand for a heat transfer suppression sheet that can maintain high thermal insulation for an even longer period and prevent the sheet from being destroyed by decomposition gases, etc., during thermal runaway of battery cells.

[0011] The present invention has been made in view of the above problems, and aims to provide a heat transfer suppression sheet that can maintain its heat insulation properties even when the compressive stress on the heat transfer suppression sheet increases, and that can prevent the sheet itself from being destroyed when an adjacent battery cell experiences thermal runaway, and a battery pack having this heat transfer suppression sheet. [Means for solving the problem]

[0012] The above objective of the present invention is achieved by the configuration of the heat transfer suppression sheet described below [1].

[0013] [1] A heat transfer suppression sheet having inorganic particles and organic fibers, A heat transfer suppression sheet characterized by having multiple three-dimensionally connected voids.

[0014] Furthermore, preferred embodiments of the present invention relating to the heat transfer suppression sheet are described in the following [2] to

[11] .

[0015] [2] The heat transfer suppression sheet according to [1], characterized in that the organic fiber has a welded portion covering at least a part of its surface, and at least a part of the inorganic particles are welded to the organic fiber by the welded portion.

[0016] [3] The heat transfer suppression sheet according to [1] or [2], further characterized by having inorganic fibers.

[0017] [4] The heat transfer suppression sheet according to [2], characterized in that at least a portion of the first and second surfaces perpendicular to the thickness direction has a fiber layer in which at least a portion of the plurality of organic fibers are welded together by the welding portion.

[0018] [5] Further, it has inorganic fibers, The heat transfer suppression sheet according to [4], wherein the fiber layer contains the inorganic fibers.

[0019] [6] The organic fiber is made of a first organic material, and the welded portion contains a second organic material, The heat transfer suppression sheet according to any one of [2] to [5], wherein the melting point of the second organic material is lower than the melting point of the first organic material.

[0020] [7] The heat transfer suppression sheet according to [6], wherein the melting point of the second organic material is 60°C or more lower than the melting point of the first organic material.

[0021] [8] The first organic material is at least one selected from polyethylene terephthalate, polypropylene, and nylon, The heat transfer suppression sheet according to [6] or [7], wherein the second organic material is at least one selected from polyethylene terephthalate, polyethylene, polypropylene, and nylon.

[0022] [9] The inorganic particles are particles made of at least one inorganic material selected from oxide particles, carbide particles, nitride particles, and inorganic hydrate particles, and the heat transfer suppression sheet according to any one of [1] to [8].

[0023]

[10] The heat transfer suppression sheet according to [9], wherein the inorganic particles contain at least one particle selected from dry silica particles and silica aerogel.

[0024]

[11] The heat transfer suppression sheet according to

[10] , wherein the inorganic particles further contain at least one particle selected from titania, zircon, zirconia, silicon carbide, zinc oxide, and alumina.

[0025] Further, the above object of the present invention is achieved by the following configuration

[12] related to a battery pack.

[0026]

[12] A battery pack having a plurality of battery cells and a heat transfer suppression sheet according to any one of [1] to

[11] , wherein the plurality of battery cells are connected in series or in parallel.

Effects of the Invention

[0027] Since the heat transfer suppression sheet of the present invention has a plurality of three-dimensionally connected pores, excellent heat insulation can be maintained even when the compressive stress increases. Further, when an adjacent battery cell undergoes thermal runaway and the heat transfer suppression sheet becomes high temperature and internal organic fibers or the like are decomposed, the decomposition gas is discharged to the outside through the pores without remaining inside the sheet, so that destruction of the sheet can be prevented.

[0028] Since the battery pack of the present invention has a heat transfer suppression sheet having high heat insulation performance and a shape retention effect as described above, thermal runaway of battery cells in the battery pack and spread of flames to the outside of the battery case can be suppressed.

Brief Description of the Drawings

[0029] [Figure 1] FIG. 1 is a drawing substitute photograph showing the structure of a heat transfer suppression sheet according to the first embodiment of the present invention. [Figure 2] FIG. 2 is a drawing substitute photograph showing an enlarged part of the heat transfer suppression sheet according to the first embodiment of the present invention. [Figure 3] FIG. 3 is a cross-sectional view schematically showing a battery pack having a heat transfer suppression sheet according to the first embodiment of the present invention. [Figure 4] FIG. 4 is a drawing substitute photograph showing the structure of a heat transfer suppression sheet according to the second embodiment of the present invention.

Modes for Carrying Out the Invention

[0030] The inventors of this invention have diligently studied a heat transfer suppression sheet that can solve the above problems. As a result, we found that when three-dimensionally connected pores are formed in the heat transfer suppression sheet, excellent heat insulation can be obtained through air insulation, and the presence of pores in the sheet improves cushioning, giving it the strength to withstand the increase in compressive stress when the battery cell expands, thereby maintaining high heat insulation performance. Furthermore, we found that when multiple three-dimensionally connected pores are present in the heat transfer suppression sheet and these pores are in communication with the surface of the heat transfer suppression sheet, even if the heat transfer suppression sheet becomes hot and the internal organic fibers decompose, the decomposition gases can be easily released to the outside through the pores, thus preventing the destruction of the heat transfer suppression sheet.

[0031] The following describes in detail a heat transfer suppression sheet, a method for manufacturing the same, and a battery pack according to embodiments of the present invention. It should be noted that the present invention is not limited to the embodiments described below, and can be modified and implemented as necessary without departing from the spirit of the invention.

[0032] [Heat transfer suppression sheet] <First Embodiment> Figure 1 is a photographic substitute for a drawing showing the structure of a heat transfer suppression sheet according to the first embodiment of the present invention, and Figure 2 is a photographic substitute for a drawing showing an enlarged view of a part of the heat transfer suppression sheet according to the first embodiment of the present invention. Figure 3 is a schematic cross-sectional view showing a battery pack having a heat transfer suppression sheet according to the first embodiment of the present invention.

[0033] As shown in Figures 1 and 2, the heat transfer suppression sheet 10 according to this embodiment has inorganic particles 4 and organic fibers 1. The heat transfer suppression sheet 10 also has a plurality of three-dimensionally connected voids 7 between the inorganic particles 4 and the organic fibers 1. The organic fibers 1 have welded portions 5 that cover at least a portion of their surface, and at least a portion of the inorganic particles 4 are welded to the surface of the organic fibers 1 by the welded portions 5. As a result, the surface of the organic fibers 1 is covered with inorganic particles 4.

[0034] As shown in Figure 3, the heat transfer suppression sheet 10 can be used by interposing it between multiple battery cells 20a, 20b, and 20c. The battery pack 100 is then constructed by housing the battery case 30 with the multiple battery cells 20a, 20b, and 20c connected in series or parallel (the connected state is not shown in the figure). While lithium-ion secondary batteries are preferably used as the battery cells 20a, 20b, and 20c, the design is not limited to these and can be applied to other secondary batteries as well.

[0035] In the heat transfer suppression sheet 10 according to the first embodiment configured in this way, since it has a plurality of three-dimensionally connected voids 7, the effect of air insulation can be obtained and the heat insulation performance can be improved. Furthermore, since the heat transfer suppression sheet 10 according to this embodiment contains organic fibers 1 that have high flexibility, the flexibility of the heat transfer suppression sheet 10 can be increased, and the organic fibers 1 can be more easily intertwined with each other, resulting in an effect of improving the strength of the sheet. Moreover, because the voids 7 in the heat transfer suppression sheet 10 improve the cushioning of the entire sheet, when the battery cells 20a, 20b, and 20c expand during charging and discharging, the heat transfer suppression sheet 10 can absorb the expansion of the battery cells. Therefore, damage to the sheet can be suppressed.

[0036] Furthermore, in this embodiment, it is preferable that at least a portion of the voids 7 communicates with the surface of the heat transfer suppression sheet and opens outward. When the voids 7 are configured in this way, even if the heat transfer suppression sheet 10 becomes hot and the organic fibers 1 etc. decompose when adjacent battery cells 20a, 20b, 20c experience thermal runaway, the decomposition gas will not remain inside the sheet but will be released to the outside through the voids 7. Therefore, from this point as well, the effect of preventing damage to the sheet can be obtained.

[0037] Furthermore, as shown in the first embodiment, if the welded portion 5 on the outer surface of the organic fiber 1 fixes the inorganic particles 4 to the organic fiber 1, the effect of suppressing the shedding (dropping of powder) of the inorganic particles 4 can be obtained. Therefore, for example, even if a part of the battery cells 20a, 20b, and 20c expands and compressive stress or impact is applied to the heat transfer suppression sheet 10, the effect of maintaining the shape can be further enhanced, and a decrease in the heat insulation effect due to compressive deformation of the heat transfer suppression sheet 10 can be prevented.

[0038] In this specification, the welded portion 5 refers to a portion where the surface of the organic fiber 1 has melted and then solidified again, and is formed in the manufacturing process of the heat transfer suppression sheet 10, which will be described later. In this embodiment, since inorganic particles 4 are welded to the surface of the organic fiber 1 by the welded portion 5, the apparent fiber diameter of the organic fiber 1 becomes thicker, which supports the shape of the heat transfer suppression sheet 10 and allows for high strength to be obtained.

[0039] Furthermore, the welded portion 5 does not need to completely cover the outer surface of the organic fiber 1, and there may be areas where the welded portion 5 is not present. In the heat transfer suppression sheet 10 according to this embodiment, a binder fiber with a core-sheath structure, as described later, can be used as the material for the organic fiber 1. However, if the sheath peels off during the manufacturing process, the core portion of the organic fiber 1 may be partially exposed. Even in such cases, the effect of holding the inorganic particles 4 can be sufficiently obtained.

[0040] Furthermore, the heat transfer suppression sheet 10 according to the first embodiment preferably contains inorganic fibers. The effects obtained by including inorganic fibers will be explained in the second embodiment below.

[0041] <Second Embodiment> Figure 4 is a photographic substitute for a drawing showing the structure of a heat transfer suppression sheet according to a second embodiment of the present invention. In the second embodiment shown in Figure 4, the same reference numerals are used for parts identical to those in the first embodiment shown in Figures 1 and 2, and detailed descriptions are omitted. Furthermore, since the heat transfer suppression sheet according to the second embodiment can be used in place of the heat transfer suppression sheet 10 described in the battery pack 100 shown in Figure 3, the following description will assume that the heat transfer suppression sheet according to the second embodiment is applied to the battery pack 100.

[0042] As shown in Figure 4, the heat transfer suppression sheet 40 according to the second embodiment has inorganic fibers 15. Furthermore, the heat transfer suppression sheet 40 has a fiber layer 11 formed on at least a portion of the first surface 40a and a second surface (not shown) perpendicular to its thickness direction. The fiber layer 11 is formed in a layered manner on the surface (first surface and second surface) of the heat transfer suppression sheet 40 by welding at least a portion of a plurality of organic fibers 1 to each other at welding points. That is, the fiber layer 11 is a layer formed by the aggregation of 10 or more organic fibers 1 on the surface of the heat transfer suppression sheet 40, and extends, for example, in a streaky manner in a direction substantially parallel to the surface.

[0043] Furthermore, a composite layer (not shown) is formed between the fiber layer 11 and the base layer 13 containing inorganic particles 4 and organic fibers 1, in which a portion of the fiber layer 11 and a portion of the inorganic particles 4 are mixed. Specifically, the composite layer is a region containing a plurality of organic fibers 1, at least a portion of which are welded to each other by welding portions, and inorganic particles 4 welded to the organic fibers 1 by welding portions.

[0044] In the second embodiment shown in Figure 4, the inorganic fibers 15 are contained in the base layer 13 which contains inorganic particles 4 and organic fibers 1, but they may also be contained in the fiber layer 11. In Figure 4, the inorganic fibers 15 in the fiber layer 11 cannot be distinguished and are therefore not shown.

[0045] Furthermore, the heat transfer suppression sheet 40 has fiber bundles 6 formed by welding at least a portion of multiple organic fibers 1 together at welding portions 5. The fiber bundles 6 are formed by 10 or more organic fibers 1 intertwining with each other and welding some of the organic fibers 1 together, and are arranged in any direction within the heat transfer suppression sheet 10.

[0046] The heat transfer suppression sheet 40 according to the second embodiment, configured in this way, contains inorganic fibers 15 that are resistant to decomposition even at high temperatures. Therefore, for example, if a battery cell 20a experiences thermal runaway and the heat transfer suppression sheet 40, which is located adjacent to the battery cell 20a, is exposed to high temperatures, even if the organic fibers 1 decompose, the inorganic fibers 15 remain, thus reliably maintaining the shape of the heat transfer suppression sheet 40. Furthermore, because the flexible organic fibers 1 easily intertwine with the relatively hard inorganic fibers 15, a three-dimensional skeleton is formed by the inorganic fibers 15 and the organic fibers 1, further improving the strength of the heat transfer suppression sheet 40.

[0047] Furthermore, if the heat transfer suppression sheet 40 has a fiber layer 11 on its surface and a fiber bundle 6 inside, it can obtain even higher sheet strength compared to the case where organic fibers 1 are dispersed. Note that the fiber layer 11 is not simply placed on the base layer 13, but rather there is a composite layer between the fiber layer 11 and the base layer 13 in which a part of the fiber layer 11 and a part of the inorganic particles 4 are mixed. Therefore, the fiber layer 11 is securely constrained to the surface of the heat transfer suppression sheet 10. Consequently, the fiber layer 11 does not detach, and a heat transfer suppression sheet 40 with high strength can be obtained.

[0048] Furthermore, if a fiber layer 11 is formed on the surface of the heat transfer suppression sheet 40, this fiber layer 11 can absorb the impact applied to the heat transfer suppression sheet 10, thereby further improving the effect of preventing powder from falling off.

[0049] The materials constituting the heat transfer suppression sheet according to this embodiment will be described in detail below, with heat transfer suppression sheet 10 as an example. However, the materials used for heat transfer suppression sheet 40 are the same as those used for heat transfer suppression sheet 10.

[0050] <Organic Fibers> The organic fiber 1 provides flexibility to the heat transfer suppression sheet 10, and also maintains the strength and shape of the sheet by welding inorganic particles 4 and other organic fibers 1 to its surface. As the material for the organic fiber 1 in the heat transfer suppression sheet 10, a single-component organic fiber can be used, but it is preferable to use a binder fiber with a core-sheath structure. The binder fiber with a core-sheath structure has a core portion that extends in the longitudinal direction of the fiber and a sheath portion formed to cover the outer surface of the core portion. The core portion is made of a first organic material, and the sheath portion 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. When a binder fiber with a core-sheath structure is used as the material, the core portion in the heat transfer suppression sheet 10 corresponds to the organic fiber 1. Also, during the manufacture of the heat transfer suppression sheet 10, the second organic material constituting the sheath portion melts and then solidifies again, so in the heat transfer suppression sheet 10, the sheath portion becomes a welded portion 5.

[0051] When a binder fiber with a core-sheath structure is used as the material for the organic fiber 1, the core portion, i.e., the first organic material constituting the organic fiber 1, is not particularly limited as long as its melting point is higher than that of the sheath portion, i.e., the second organic material present on the outer surface of the organic fiber 1. Examples of the first organic material include at least one selected from polyethylene terephthalate, polypropylene, and nylon.

[0052] (Organic fiber content) In this embodiment, if the content of organic fibers 1 in the heat transfer suppression sheet 10 is appropriately controlled, a sufficient reinforcing effect on the skeleton can be obtained. The content of organic fiber 1 is preferably 2% by mass or more, and more preferably 4% by mass or more, relative to the total mass of the heat transfer suppression sheet 10. Furthermore, if the content of organic fiber 1 becomes too high, the content of inorganic particles 4 will relatively decrease. Therefore, in order to obtain the desired heat insulation performance, the content of organic fiber is preferably 10% by mass or less, and more preferably 8% by mass or less, relative to the total mass of the heat transfer suppression sheet 10.

[0053] (Fiber length of organic fibers) While there are no particular limitations on the fiber length of organic fiber 1, it is preferable that the average fiber length of the organic fiber be 10 mm or less from the viewpoint of ensuring moldability and processability. On the other hand, from the viewpoint of allowing the organic fiber 1 to function as a backbone and ensuring the compressive strength of the heat transfer suppression sheet, it is preferable that the average fiber length of the organic fiber 1 be 0.5 mm or more.

[0054] <Welded part> The welded portion 5 is formed when the surface of the organic fiber 1, or the sheath portion of a binder fiber having a core-sheath structure, is heated, melted, and then cooled. It welds inorganic particles 4 to the surface of the organic fiber 1 and also welds the organic fibers 1 to each other. When a binder fiber with a core-sheath structure is used as the material for the organic fiber 1, the welded portion 5 includes a second organic material that constitutes the sheath portion.

[0055] (Second organic material) The second organic material is not particularly limited, as long as its melting point is lower than that of the first organic material constituting the organic fiber 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. Furthermore, the melting point of the second organic material is preferably 150°C or lower, and more preferably 130°C or lower.

[0056] <Inorganic particles> As inorganic particles, a single inorganic particle may be used, or a combination of two or more inorganic particles may be used. From the viewpoint of 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. Furthermore, there are no particular limitations on the shape, but it is preferable to include at least one selected from nanoparticles, hollow particles, and porous particles. 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 materials, etc., can be used.

[0057] If the average secondary particle diameter of the inorganic particles is 0.01 μm or more, they are readily available and manufacturing costs can be kept down. Furthermore, if it 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.

[0058] Furthermore, by using two or more inorganic particles with different heat transfer suppression effects, the heat-generating element can be cooled in multiple stages, and the endothermic effect can be exhibited over a wider temperature range. Specifically, it is preferable to use a mixture of large-diameter and small-diameter particles. For example, when nanoparticles are used as one type of inorganic particle, it is preferable to include inorganic particles made of metal oxides as the other type of inorganic particle. Below, the inorganic particles will be described in more detail, with small-diameter inorganic particles referred to as the first inorganic particles and large-diameter inorganic particles as the second inorganic particles.

[0059] <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 radiative heat transfer, especially in high-temperature regions such as abnormal heat generation. As oxide particles, at least one particle selected from silica, titania, zirconia, zircon, barium titanate, zinc oxide, and alumina can be used. That is, only one of the above oxide particles that can be used as inorganic particles may be used, or two or more oxide particles may be used. In particular, silica is a component with high thermal insulation properties, and titania is a component with a high refractive index compared to other metal oxides. Since they have a high effect of diffusely reflecting light and blocking radiant heat in high-temperature regions of 500°C or higher, it is most preferable to use silica and titania as oxide particles.

[0060] (Average primary particle size of oxide particles: 0.001 μm or more and 50 μm or less) Since the particle size of oxide particles can affect the effect of reflecting radiant heat, limiting the average primary particle size to a predetermined range can result in even higher thermal insulation. In other words, if the average primary particle diameter of the oxide particles is 0.001 μm or larger, it is sufficiently larger than the wavelength of light that contributes to heating, and efficiently diffusely reflects the light. As a result, radiative heat transfer within the heat transfer suppression sheet is suppressed in the high-temperature region of 500°C or higher, further improving the heat insulation performance. On the other hand, if the average primary particle diameter of oxide particles is 50 μm or less, the number of contact points between particles does not increase even when compressed, making it difficult to form conductive heat transfer paths. This reduces the impact on thermal insulation, especially in the normal temperature range where conductive heat transfer is dominant.

[0061] In this invention, the average primary particle diameter can be determined by observing the particles under a microscope, comparing them to a standard scale, and taking the average of 10 arbitrary particles.

[0062] (Nanoparticles) In this invention, nanoparticles refer to particles that are spherical or nearly spherical, with an average primary particle diameter of less than 1 μm on the order of nanometers. Because nanoparticles have low density, they suppress conductive heat transfer, and when nanoparticles are used as the first inorganic particles, the three-dimensionally connected pores 7 are further refined, resulting in excellent heat insulation that suppresses convective heat transfer. For this reason, it is preferable to use nanoparticles when using batteries in the normal room temperature range, as it can suppress heat conduction between adjacent nanoparticles. Furthermore, by using nanoparticles with a small average primary particle diameter as oxide particles, even if the heat transfer suppression sheet is compressed due to expansion associated with thermal runaway of the battery cell, and the internal density increases, the increase in conductive heat transfer of the heat transfer suppression sheet can be suppressed. This is thought to be because nanoparticles easily create fine voids between particles due to electrostatic repulsion, and because their bulk density is low, the particles are packed in a way that provides cushioning.

[0063] In this invention, when nanoparticles are used as the first inorganic particles, the material is not particularly limited as long as it conforms to the above definition of nanoparticles. For example, silica nanoparticles are a material with high thermal insulation properties, and because the contact points between particles are small, the amount of heat conducted by silica nanoparticles is smaller compared to when silica particles with a larger particle size are used. Also, commonly available silica nanoparticles have a bulk density of 0.1 g / cm³. 3 Because of this, for example, even if the battery cells arranged on both sides of the heat transfer suppression sheet undergo thermal expansion and a large compressive stress is applied to the heat transfer suppression sheet, the size (area) and number of contact points between silica nanoparticles will not increase significantly, and the 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 particularly suitable for this embodiment will be described below.

[0064] Generally, wet silica has aggregated particles, while dry silica allows for particle dispersion. In the temperature range below 300°C, conduction is the dominant method of heat transfer, so dry silica, which allows for particle dispersion, can provide superior thermal insulation compared to wet silica. In this embodiment, it is preferable to use a manufacturing method in which a mixture containing the material is processed into a sheet by a dry process. Therefore, it is preferable to use dry silica, silica aerogel, or the like as the inorganic particles, as they have low thermal conductivity.

[0065] (Average primary particle size of nanoparticles: 1 nm to 100 nm) By limiting the average primary particle size of nanoparticles to a predetermined range, even higher thermal insulation can be achieved. In other words, by setting the average primary particle diameter of the nanoparticles to 1 nm or more and 100 nm or less, convective and conductive heat transfer within the heat transfer suppression sheet can be suppressed, especially in the temperature range below 500°C, thereby further improving the thermal insulation performance. Furthermore, even when compressive stress is applied, the voids remaining between the nanoparticles and the numerous contact points between particles suppress conductive heat transfer, maintaining the thermal insulation performance of the heat transfer suppression sheet. Furthermore, the average primary particle diameter of the nanoparticles is more preferably 2 nm or larger, and even more preferably 3 nm or larger. On the other hand, the average primary particle diameter of the nanoparticles is more preferably 50 nm or smaller, and even more preferably 10 nm or smaller.

[0066] (Inorganic hydrate particles) Inorganic hydrate particles, when exposed to heat from a heat source and exceeding their decomposition start temperature, undergo thermal decomposition, releasing their crystalline water and lowering the temperature of the heat source and its surroundings—a phenomenon known as "endothermic action." After releasing the crystalline water, they become porous, exhibiting insulating properties through their numerous air pores. 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).

[0067] For example, aluminum hydroxide contains approximately 35% crystal water, and as shown in the formula below, it undergoes thermal decomposition to release crystal water, exhibiting an endothermic effect. After releasing the crystal water, it becomes a porous alumina (Al2O3) and functions as an insulating material. 2Al(OH)3 → Al2O3 + 3H2O

[0068] As will be described later, the heat transfer suppression sheet 10 according to this embodiment is preferably interposed between battery cells, for example. However, in a battery cell that has experienced thermal runaway, the temperature rapidly rises to over 200°C and continues to rise to around 700°C. Therefore, it is preferable that the inorganic particles consist of inorganic hydrates whose thermal decomposition initiation temperature is 200°C or higher. The thermal decomposition initiation temperatures for the inorganic hydrates listed above are approximately 200°C for aluminum hydroxide, 330°C for magnesium hydroxide, 580°C for calcium hydroxide, 200°C for zinc hydroxide, 350°C for iron hydroxide, 300°C for manganese hydroxide, 300°C for zirconium hydroxide, and 300°C for gallium hydroxide. These temperatures largely overlap with the temperature range of rapid temperature increases in battery cells experiencing thermal runaway, and can effectively suppress temperature rise, making them desirable inorganic hydrates.

[0069] (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 may take a certain amount of time for the first inorganic particles (inorganic hydrates) near the center of the heat transfer suppression sheet 10 to reach their thermal decomposition temperature, and the first inorganic particles near the center of the sheet may not be completely 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.

[0070] (Particles made of thermally expandable inorganic material) Examples of thermally expandable inorganic materials include vermiculite, bentonite, mica, and perlite.

[0071] (Particles made of a water-containing porous material) Specific examples of water-containing porous materials include zeolite, kaolinite, montmorillonite, acid clay, diatomaceous earth, wet silica, dry silica, aerogel, mica, and vermiculite.

[0072] (Inorganic balloon) The thermal insulation material used in the present invention may include inorganic balloons as the first inorganic particles. The inclusion of inorganic balloons can suppress convective or conductive heat transfer within the insulation material at temperatures below 500°C, thereby further improving the insulation performance of the insulation material. As the inorganic balloon, at least one selected from shirasu balloons, silica balloons, fly ash balloons, barlite balloons, and glass balloons can be used.

[0073] (Inorganic balloon content: 60% or less by mass relative to the total mass of the insulation material) The inorganic balloon content is preferably 60% by mass or less relative to the total mass of the insulating material.

[0074] (Average particle size of inorganic balloons: 1 μm to 100 μm) The average particle size of the inorganic balloons is preferably between 1 μm and 100 μm.

[0075] <Second inorganic particle> When the heat transfer suppression sheet contains two types of inorganic particles, the second inorganic particle is not particularly limited as long as it differs from the first inorganic particle in terms of material, particle size, etc. The second inorganic particle can be 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 thermally expandable inorganic materials, particles made of water-containing porous materials, etc. Details of these are as described above.

[0076] Furthermore, nanoparticles exhibit extremely low conductive heat transfer and can maintain excellent thermal insulation even when compressive stress is applied to the heat transfer suppression sheet. In addition, metal oxide particles such as titania have a high effect in blocking radiant heat. Moreover, by using both large-diameter and small-diameter inorganic particles, the small-diameter inorganic particles can fill 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 metal oxide particles, which are larger in diameter than the first inorganic particles, as second inorganic particles in the heat transfer suppression sheet. Examples of metal oxides include silicon dioxide, titanium dioxide, aluminum oxide, barium titanate, zinc oxide, zircon, and zirconium oxide. In particular, titanium dioxide (titania) has a higher refractive index compared to other metal oxides, and is highly effective in scattering light and blocking radiant heat in the high-temperature range of 500°C or higher, so using titania is most preferable.

[0077] When using at least one particle selected from dry silica particles and silica aerogel as the first inorganic particle, and at least one particle selected from titania, zircon, zirconia, silicon carbide, zinc oxide, and alumina as the second inorganic particle, in order to obtain excellent thermal insulation performance within a temperature range of 300°C or less, the first inorganic particle is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more, based on the total mass of the inorganic particles. Furthermore, the first inorganic particle is preferably 95% by mass or less, more preferably 90% by mass or less, and even more preferably 80% by mass or less, based on the total mass of the inorganic particles.

[0078] On the other hand, in order to obtain excellent heat insulation performance in a temperature range exceeding 300°C, the amount 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. Furthermore, the amount 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.

[0079] (Average primary particle diameter of the second inorganic particle) When a second inorganic particle made of a metal oxide is included in the heat transfer suppression sheet, if the average primary particle diameter of the second inorganic particle is 1 μm or more and 50 μm or less, radiant heat transfer can be efficiently suppressed in the high temperature region of 500°C or higher. It is more preferable that the average primary particle diameter of the second inorganic particle is 5 μm or more and 30 μm or less, and most preferably 10 μm or less.

[0080] (Content of inorganic particles) In this embodiment, if the total content of inorganic particles 4 in the heat transfer suppression sheet 10 is appropriately controlled, the heat insulation properties of the heat transfer suppression 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, relative to the total mass of the heat transfer suppression sheet 10. Furthermore, if the total content of inorganic particles 4 becomes too high, the content of organic fibers will relatively decrease. Therefore, in order to obtain sufficient reinforcing effects on the skeleton and retention effects on inorganic particles, the total content of inorganic particles 4 is preferably 95% by mass or less, and more preferably 90% by mass or less, relative to the total mass of the heat transfer suppression sheet 10.

[0081] The amount of inorganic particles 4 in the heat transfer suppression sheet 10 can be calculated, for example, by heating the heat transfer suppression sheet 10 to 800°C, decomposing the organic components, and then measuring the mass of the remaining material.

[0082] In addition to the organic fibers 1, welded portions 5, and inorganic particles 4, the heat transfer suppression sheets 10 and 40 according to the first and second embodiments of the present invention preferably contain inorganic fibers 15. The inorganic fibers that are preferably included in the heat transfer suppression sheets according to the above embodiments are described below.

[0083] <Inorganic Fibers> As inorganic fibers, a single inorganic fiber may be used, or two or more types of inorganic fibers may be used in combination. Examples of inorganic fibers include silica fibers, alumina fibers, alumina silicate fibers, zirconia fibers, carbon fibers, soluble fibers, refractory ceramic fibers, aerogel composites, ceramic fibers such as magnesium silicate fibers, alkali earth silicate fibers, potassium titanate fibers, silicon carbide fibers, potassium titanate whisker fibers, glass fibers, glass fibers such as glass wool, slag wool, and mineral fibers such as rock wool, basalt fibers, wollastonite, and mullite fibers. These inorganic fibers are preferable in terms of heat resistance, strength, and availability. Among the inorganic fibers, silica-alumina fibers, alumina fibers, silica fibers, rock wool, alkali earth silicate fibers, and glass fibers are particularly preferred from the viewpoint of ease of handling.

[0084] The cross-sectional shape of inorganic fibers is not particularly limited and includes circular, flat, hollow, polygonal, and core cross-sections. Among these, fibers with irregular cross-sections, such as hollow, flat, or polygonal cross-sections, can be suitably used because they slightly improve thermal insulation.

[0085] The preferred lower limit for the average fiber length of inorganic fibers is 0.1 mm, and the more preferred lower limit is 0.5 mm. On the other hand, the preferred upper limit for the average fiber length of inorganic fibers is 50 mm, and the more preferred upper limit is 10 mm. If the average fiber length of inorganic fibers is less than 0.1 mm, entanglement between inorganic fibers is less likely to occur, which may reduce the mechanical strength of the heat transfer suppression sheet. On the other hand, if it exceeds 50 mm, although a reinforcing effect can be obtained, the inorganic fibers may not be able to entangle tightly with each other, or a single inorganic fiber may curl up, which may lead to the creation of continuous voids and thus reduce the thermal insulation performance.

[0086] The preferred lower limit for the average fiber diameter of inorganic fibers is 1 μm, a more preferred lower limit is 2 μm, and an even more preferred lower limit is 3 μm. On the other hand, the preferred upper limit for the average fiber diameter of inorganic fibers is 15 μm, and a more preferred upper limit is 10 μm. If the average fiber diameter of inorganic fibers is less than 1 μm, the mechanical strength of the inorganic fibers themselves may decrease. Furthermore, from the viewpoint of the impact on human health, it is preferable that the average fiber diameter of inorganic fibers be 3 μm or more. On the other hand, if the average fiber diameter of inorganic fibers is greater than 15 μm, solid heat transfer using the inorganic fibers as a medium may increase, leading to a decrease in thermal insulation, and the moldability and strength of the heat transfer suppression sheet may deteriorate.

[0087] (Inorganic fiber content) In this embodiment, when the heat transfer suppression sheet contains inorganic fibers, it is preferable that the inorganic fiber content is 3% by mass or more and 15% by mass or less of the total mass of the heat transfer suppression sheet.

[0088] Furthermore, it is more preferable that the inorganic fiber content be between 5% and 10% by mass relative to the total mass of the heat transfer suppression sheet. By using such a content, the shape retention, compressive force resistance, wind pressure resistance, and inorganic particle holding ability of the inorganic fibers are well-balanced. In addition, by appropriately controlling the inorganic fiber content, the organic fibers 1 and inorganic fibers intertwine to form a three-dimensional network, thereby further improving the effect of holding the inorganic particles 4 and other compounding materials described later.

[0089] <Other ingredients> Furthermore, the heat transfer suppression sheet according to this embodiment may contain binders, colorants, etc., as needed. These are all useful for reinforcing the heat transfer suppression sheet and improving its moldability, and it is preferable that the total amount of these additives is 10% by mass or less of the total mass of the heat transfer suppression sheet.

[0090] [Method for manufacturing a heat transfer suppression sheet] An example of a method for manufacturing a heat transfer suppression sheet according to this embodiment will be described below, using the heat transfer suppression sheet 40 according to the second embodiment as an example. For example, binder fibers having a core-sheath structure (not shown), inorganic particles 4, and inorganic fibers 15 are put into a mixer such as a V-type mixer in a predetermined ratio to produce a mixture. As mentioned above, it is preferable to use a core-sheath structure fiber as the binder fiber, which has a core made of a first organic material and a sheath made of a second organic material. In this case, the melting point of the first organic material should be higher than the melting point of the second organic material.

[0091] Subsequently, the obtained mixture is placed into a predetermined mold and pressurized using a press or the like to heat the resulting molded body, causing the sheath portion of the binder fibers to melt. Then, by cooling the heated molded body, the second organic material constituting the molten sheath portion and the inorganic particles 4 present around the binder fibers are welded to the core portion (organic fiber 1), and the areas where the binder fibers were in contact with each other are also welded to each other. This makes it possible to obtain a heat transfer suppression sheet 40 processed into a sheet shape.

[0092] The heat transfer suppression sheet 10 according to the first embodiment can also be manufactured in the same manner as the heat transfer suppression sheet 40 described above, and the use of inorganic fibers 15 can be arbitrarily selected.

[0093] Furthermore, when the above materials are mixed, pressurized, and heated, the entangled organic fibers 1 exposed on the surface are heated and formed as a fiber layer 11 on the surface of the heat transfer suppression sheet 40. The fiber layer 11 thus obtained has the effect of improving the strength of the heat transfer suppression sheet 40 and mitigating impacts to the surface of the heat transfer suppression sheet 40.

[0094] The heat transfer suppression sheets 10 and 40 according to the first and second embodiments described above are preferably manufactured by a dry process. When using a dry process, inorganic particles 4 suitable for the dry process are used, and no solvents such as water required for molding by a wet process are added to the mixture. However, in order to prevent the inorganic particles 4 and other powders from becoming airborne and making it difficult to handle the raw materials during the manufacture of the heat transfer suppression sheet 10, a small amount of solvent such as water may be added within the scope of the dry process. For example, by adding a small amount of solvent such as water to the mixture, the scattering of inorganic particles during manufacture can be suppressed.

[0095] In the above manufacturing method, binder fibers with a core-sheath structure are used as the material. 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 the core remains intact. After cooling, the outer surface of the core (organic fiber 1) is covered with the second organic material containing inorganic particles 4, thus retaining the inorganic particles 4. The organic fiber 1 to which the inorganic particles 4 are welded has an apparently thicker fiber diameter, resulting in higher strength than the organic fiber 1 alone. Furthermore, because the binder fibers are present in an irregular direction in the mixture, the organic fibers 1 are welded together in the regions where the binder fibers are in contact, forming a three-dimensional skeleton. As a result, the overall shape of the heat transfer suppression sheet can be maintained with even greater strength.

[0096] Furthermore, even when using organic fibers without a core-sheath structure as binder fibers, it is possible, depending on the temperature setting, to melt only the surface while leaving the core of the organic fiber intact, thereby adhering inorganic particles to the surface or welding the organic fibers together. However, when manufacturing heat transfer suppression sheets, heating is generally done from one or both sides perpendicular to the thickness direction, and since materials with high thermal insulation performance are used, strict temperature control is necessary to raise the temperature to approximately the same level on both the surface and the center of the sheet in the thickness direction.

[0097] In contrast, by using binder fibers with a core-sheath 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, it becomes extremely easy to set a temperature that preserves the core while melting the sheath. As a result, the resulting heat transfer suppression sheet has an ideal structure in which the organic fibers 1 are welded together to form a framework that maintains the strength of the sheet, both on the surface and the center, and welded portions 5 containing inorganic particles 4 are formed on the surface of the organic fibers 1. Therefore, it is preferable to use binder fibers having the above-described core-sheath structure as the material for the heat transfer suppression sheet.

[0098] As will be explained in more detail later, the mixture may contain an adhesive such as hot melt powder as a raw material for the heat transfer suppression sheet. By appropriately adjusting the type and amount of adhesive contained in the mixture, the skeleton formed by the organic fibers 1 can be sufficiently fixed, the holding power of the inorganic particles 4 can be improved, and powder shedding can be further suppressed. As a result, the heat transfer suppression sheet manufactured by the manufacturing method according to this embodiment has an even stronger framework, and even when pressure or impact is applied to the heat transfer suppression sheet, it can maintain its shape, suppress powder shedding, and maintain excellent heat insulation performance.

[0099] Furthermore, to further suppress powder shedding, the surface of the heat transfer suppression sheet may be covered with a film or the like. Examples of polymer films include those made of polyimide, polycarbonate, PET, p-phenylene sulfide, polyetherimide, crosslinked polyethylene, flame-retardant chloroprene rubber, polyvinyldenide fluoride, rigid polyvinyl chloride, polybutylene terephthalate, PTFE, PFA, FEP, ETFE, rigid PCV, flame-retardant PET, polystyrene, polyethersulfone, polyamideimide, polyacrylonitrile, polyethylene, polypropylene, polyamide, and the like. The method of covering the surface of the heat transfer suppression sheet with a film is not particularly limited and includes methods such as attaching it with an adhesive, wrapping the heat transfer suppression sheet with a film, or housing the heat transfer suppression sheet in a bag-shaped film.

[0100] Next, the binder fibers and heating conditions that are preferable to use in the method for manufacturing a heat transfer suppression sheet according to this embodiment will be described.

[0101] <Binder Fiber> In this embodiment, when using binder fibers with 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 that forms the core can be selected from at least one of polyethylene terephthalate, polypropylene, and nylon. The second organic material that forms the sheath can be selected from at least one of polyethylene terephthalate, polyethylene, polypropylene, and nylon.

[0102] If the melting point of the first organic material constituting the core is sufficiently higher than the melting point of the second organic material constituting the sheath, the margin for setting the heating temperature in the heating process can be widened, 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 the melting point of the second organic material, more preferably 70°C or more higher, and even more preferably 80°C or more higher.

[0103] Binder fibers having the core-sheath structure described above are generally available on the market, 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, or those in which the core is made of polypropylene and the sheath is made of polyethylene.

[0104] In this embodiment, the melting point of the second organic material constituting the sheath of the binder fiber represents the melting temperature at which the second organic material begins to melt and deform. However, softening accompanied by a change in shape is also considered 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 a glass fiber that has a higher melting point, and heated from room temperature to, for example, 200°C at a heating rate of 5°C / min, and then cooled back to room temperature. At this time, if the surface of the binder fiber melts and deforms, and fuses with the glass fiber at the point of contact, 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, by varying the heating temperature and observing the fusion state between the binder fiber and the glass fiber after cooling using the method described above, or by observing the cross-sectional shape of the binder fiber, the melting point of the second organic material constituting the sheath can be determined.

[0105] (Binder fiber content) In this embodiment, when binder fibers with a core-sheath structure are used as the material, if the content of binder fibers in the mixture is appropriately controlled, a sufficient reinforcing effect on the skeleton of the resulting heat transfer suppression sheet can be obtained. The binder fiber content is preferably 5% by mass or more, and more preferably 10% by mass or more, relative to the total mass of the mixture. Furthermore, if the binder fiber content becomes too high, the inorganic particle 4 content will relatively decrease. Therefore, in order to obtain the desired thermal insulation performance, the binder fiber content is preferably 25% by mass or less, and more preferably 20% by mass or less, relative to the total mass of the mixture.

[0106] <Hot Melt Powder> In this embodiment, in addition to the binder fibers and inorganic particles 4, the mixture may also 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. By including the hot melt powder in the mixture and heating it, the hot melt powder melts, and then when cooled, it hardens while containing the surrounding inorganic particles 4. Therefore, the shedding of inorganic particles 4 from the heat transfer suppression sheet can be further suppressed.

[0107] While various types of hot melt powders have different melting points, it is best to select a hot melt powder with an appropriate melting point, taking into account the melting points of the core and sheath of the binder fiber used. Specifically, if the melting point of the third organic material constituting the hot melt powder is lower than that of the first organic material constituting the organic fiber, the heating temperature can be set to melt the sheath and the hot melt powder while leaving the core intact. For example, if the melting point of the hot melt powder is lower than or equal to the melting point of the sheath, the heating temperature during manufacturing can be set between the melting points of the core and the sheath, making it even easier to set the heating temperature.

[0108] Alternatively, the type of hot melt powder used can be selected so that its melting point falls between the melting point of the core and the melting point of the sheath. When a hot melt powder with such a melting point is used, after both the sheath and the hot melt powder melt and then cool and harden, the hot melt powder present in the gaps between the organic fiber (core) 1, the surrounding molten sheath, and the inorganic particles 4 hardens first. As a result, the position of the organic fiber 1 can be fixed, and then the molten sheath fuses to the organic fiber, making it easier to form a three-dimensional structure. Therefore, the overall strength of the sheet can be further improved.

[0109] If the melting point of the third organic material constituting the hot melt powder is sufficiently lower than the melting point of the first organic material constituting the core, the margin for setting the heating temperature in the heating process can be widened, 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 the melting point of the third organic material, more preferably 70°C or more higher, and even more preferably 80°C or more higher.

[0110] The melting point of the hot melt powder (third organic material) is preferably 80°C or higher, and more preferably 90°C or higher. Furthermore, the melting point of the hot melt powder (third organic material) is preferably 180°C or lower, and more preferably 150°C or lower. Examples of components constituting the hot melt powder include polyethylene, polyester, polyamide, and ethylene vinyl acetate.

[0111] (Hot melt powder content) When hot melt powder is included in the mixture to suppress the shedding of inorganic particles, even a small amount of the powder can be used to suppress shedding. Therefore, the hot melt powder content is preferably 0.5% by mass or more, and more preferably 1% by mass or more, relative to the total mass of the mixture. On the other hand, increasing the content of hot melt powder relatively decreases the content of inorganic particles 4, etc. Therefore, in order to obtain the desired thermal insulation performance, the content of hot melt powder is preferably 5% by mass or less, and more preferably 4% by mass or less, relative to the total mass of the mixture.

[0112] <Heating conditions> The process of processing the above mixture into a sheet includes a step of pressurizing the mixture and a step of heating the mixture. When a binder fiber with a core-sheath structure is used as the material for the heat transfer suppression sheet, it is preferable that the heating temperature in the heating step be 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 way, as described above, the strength of the sheet can be ensured by the core on both the surface and the center side of the sheet, and the inorganic particles 4 can be held by the welded portion 5.

[0113] Specifically, the heating temperature in the heating process is preferably set at least 10°C higher than the melting point of the second organic material constituting the sheath, 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.

[0114] While there are no particular limitations on the heating time, it is preferable to set a heating time that allows the sheath to melt sufficiently. For example, it can be set to between 3 minutes and 15 minutes.

[0115] When the heat transfer suppression sheet material includes hot melt powder, the heating temperature in the heating process is preferably set 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 in this manner, a strong skeleton can be formed, further improving the strength of the sheet, and preventing the inorganic particles 4 from falling off at the welded parts 5, etc.

[0116] <Thickness of the heat transfer suppression sheet> The thickness of the heat transfer suppression sheet according to this embodiment is not particularly limited, but it is preferably 0.05 mm or more and 10 mm or less. A thickness of 0.05 mm or more allows for sufficient compressive strength. On the other hand, a thickness of 10 mm or less allows for good heat insulation of the heat transfer suppression sheet.

[0117] [Battery pack] An example of a battery pack to which the heat transfer suppression sheet 10 according to an embodiment of the present invention is applied is shown in Figure 3 above. Here, the configuration and effects of the battery pack will be specifically explained using Figure 3. As mentioned above, the heat transfer suppression sheet 10 shown in Figure 3 can be replaced with the heat transfer suppression sheet 40, or with other heat transfer suppression sheets within the scope of the present invention.

[0118] As shown in Figure 3, the battery pack 100 has a plurality of battery cells 20a, 20b, 20c and a heat transfer suppression sheet according to this embodiment, and the plurality of battery cells are connected in series or in parallel. For example, as shown in Figure 3, the heat transfer suppression sheet 10 according to this embodiment is interposed between battery cell 20a and battery cell 20b, and between battery cell 20b and battery cell 20c. Furthermore, the battery cells 20a, 20b, 20c and the heat transfer suppression sheet 10 are housed in a battery case 30. The heat transfer suppression sheet 10 is as described above.

[0119] In the battery pack 100 configured in this way, even if a battery cell 20a becomes hot, the heat transfer suppression sheet 10, which has a heat transfer suppression effect, is present between it and the battery cell 20b, thus suppressing the transfer of heat to the battery cell 20b. Furthermore, the heat transfer suppression sheet 10 according to this embodiment has high compressive strength, so it can suppress the thermal expansion of the battery cells 20a, 20b, and 20c even during charging and discharging. Therefore, it is possible to maintain distance between the battery cells, maintain excellent heat insulation performance, and prevent thermal runaway of the battery cells. In addition, it has the effect of suppressing powder shedding, making it easy to handle.

[0120] It should be noted that the battery pack 100 in this embodiment is not limited to the battery pack illustrated in Figure 3. For example, the heat transfer suppression sheet 10 may be placed not only between battery cells 20a and 20b, and between battery cells 20b and 20c, but also between battery cells 20a, 20b, and 20c and the battery case 30, or it may be attached to the inner surface of the battery case 30.

[0121] In the battery pack 100 configured in this way, if a battery cell ignites, it is possible to suppress the spread of flames outside the battery case 30. For example, the battery pack 100 according to this embodiment may be used in electric vehicles (EVs) and placed under the passenger floor. In this case, even if the battery cells catch fire, the safety of the passengers can be ensured. Furthermore, since the heat transfer suppression sheet 10 can be placed not only between each battery cell, but also between the battery cells 20a, 20b, and 20c and the battery case 30, there is no need to newly manufacture flame retardant materials, and a safe battery pack 100 can be easily constructed at low cost.

[0122] In the battery pack of this embodiment, the heat transfer suppression sheet 10, which is placed between the battery cells 20a, 20b, and 20c and the battery case 30, may be in contact with the battery cells or there may be a gap between them. However, if there is a gap between the heat transfer suppression 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 battery cells rises and its volume expands.

[0123] Furthermore, the heat transfer suppression sheet 10 according to this embodiment can be manufactured in various shapes depending on the manufacturing method. Therefore, it is not affected by the shape of the battery cells 20a, 20b, 20c and the battery case 30, and can be used with any shape. Specifically, it can be applied not only to prismatic batteries but also to cylindrical batteries, flat-plate batteries, and the like. [Explanation of Symbols]

[0124] 1. Organic Fibers 4 Inorganic particles 5 Welded area 6 Fiber bundles 7 Holes 10,40 Heat transfer suppression sheet 11 Fiber layer 13 Base layer 15 Inorganic Fibers 20a, 20b, 20c battery cells 30 Battery Cases 100 battery packs

Claims

1. A heat transfer-suppressing sheet including inorganic particles and organic fibers, It has a plurality of three-dimensionally connected pores, A heat-transfer-suppressing sheet, wherein at least some of the pores communicate with the surface of the heat-transfer-suppressing sheet and open outward.

2. 2. The heat transfer-suppressing sheet according to claim 1, wherein the organic fibers have welded portions covering at least a portion of a surface thereof, and at least a portion of the inorganic particles are welded to the organic fibers by the welded portions.

3. The heat transfer-suppressing sheet according to claim 1 , further comprising inorganic fibers.

4. 3. The heat transfer-suppressing sheet according to claim 2, wherein at least a portion of a first surface and a second surface perpendicular to the thickness direction has a fiber layer formed by welding at least some of the organic fibers together at the welding portions.

5. Further, the material has inorganic fibers, The heat transfer suppressing sheet according to claim 4 , wherein the fiber layer contains the inorganic fiber.

6. the organic fiber is made of a first organic material, and the welded portion includes a second organic material; The heat transfer suppressing sheet according to claim 2 , wherein the melting point of the second organic material is lower than the melting point of the first organic material.

7. 7. The heat transfer-suppressing sheet according to claim 6, wherein the melting point of the second organic material is lower than the melting point of the first organic material by 60[deg.] C. or more.

8. the first organic material is at least one selected from polyethylene terephthalate, polypropylene, and nylon; 7. The heat transfer-suppressing sheet according to claim 6, wherein the second organic material is at least one selected from the group consisting of polyethylene terephthalate, polyethylene, polypropylene, and nylon.

9. 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.

10. The heat transfer-suppressing sheet according to claim 9, wherein the inorganic particles include at least one type of particles selected from the group consisting of dry silica particles and silica aerogel.

11. 11. The heat transfer-suppressing sheet according to claim 10, 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.

12. 12. 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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