Heat transfer suppression sheet, method for manufacturing the same, and battery pack

Abstract

To provide a heat transfer suppression sheet that even when the heat transfer suppression sheet is pressed due to expansion of a battery cell, can maintain its shape and thus can suppress reduction in heat insulation performance, a manufacturing method therefor, and an assembly battery having the heat transfer suppression sheet.SOLUTION: A heat transfer suppression sheet comprises first inorganic particles 1, a resin binder 6, and organic fibers 3, where a glass transition point of the organic fibers 3 is higher than that of the resin binder 6. At least some of the organic fibers 3 are fused to each other to form a three-dimensional skeleton 8, a resin binder 9 is fused to a portion of the skeleton 8 and at least some of the first inorganic particles 1, and at least some of the first inorganic particles 1 are bonded to the skeleton 8.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a heat transfer suppression sheet, a method for manufacturing the same, and a battery pack having the heat transfer suppression sheet. [Background technology]

[0002] In recent years, from an environmental protection perspective, the development of electric vehicles (EVs) and hybrid vehicles (HEVs) powered by electric motors has been actively pursued. These EVs and HEVs are equipped with battery packs consisting of multiple battery cells connected in series or parallel to power the electric motors used for propulsion.

[0003] Furthermore, these battery cells primarily utilize lithium-ion secondary batteries, which offer higher capacity and output compared to lead-acid batteries and nickel-metal hydride batteries. However, if a battery cell experiences a rapid temperature rise due to an internal short circuit or overcharging, and subsequently continues to generate heat (thermal runaway), the heat from the overheated cell can propagate to adjacent battery cells, potentially causing thermal runaway in those cells as well.

[0004] A common method to suppress heat transfer from battery cells experiencing thermal runaway, as described above, is to interpose an insulating sheet between the battery cells. For example, Patent Document 1 discloses a heat insulating sheet for a battery pack that includes first particles composed of silica nanoparticles and second particles composed of a metal oxide, with a limited content of the first particles. Patent Document 1 also states that the heat insulating sheet may include a binder consisting of at least one selected from fibers, a binder, and a heat-resistant resin. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2021-34278 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] Incidentally, in the case of insulating sheets for battery packs, it is required that they maintain their shape and remain present between the battery cells even when the battery cells overheat and reach high temperatures. In particular, in recent battery packs, the capacity of battery cells has improved even further, so the expansion rate during charging and discharging has increased. Therefore, if the temperature of the battery cells rises due to a malfunction in the battery cells, it becomes difficult to maintain the overall strength of the insulating sheet, the insulating performance deteriorates, and this can cause a heat chain reaction. The thermal insulation sheet described in Patent Document 1 maintains excellent thermal insulation even when compressive stress increases, but further improvements in terms of strength are required.

[0007] The present invention has been made in view of the above-mentioned problems, and aims to provide a heat transfer suppression sheet that can maintain its shape even when exposed to high temperatures, thereby suppressing a decrease in thermal insulation performance, a method for manufacturing the same, and a battery pack having this heat transfer suppression sheet. [Means for solving the problem]

[0008] The above objective of the present invention is achieved by the configuration of the heat transfer suppression sheet described below [1].

[0009] [1] comprising first inorganic particles, a resin binder, and organic fibers, A heat transfer suppression sheet characterized in that the glass transition temperature of the organic fiber is higher than the glass transition temperature of the resin binder.

[0010] Furthermore, preferred embodiments of the present invention relating to the heat transfer suppression sheet are described in the following [2] to

[17] .

[0011] [2] At least a portion of the organic fibers are fused together to form a three-dimensional skeleton, The heat transfer suppression sheet according to [1], characterized in that the resin binder is fused to a part of the skeleton and at least a part of the first inorganic particles, and at least a part of the first inorganic particles are adhered to the skeleton.

[0012] [3] The heat transfer suppression sheet according to [1] or [2], characterized in that the glass transition temperature of the organic fiber is 250°C or lower.

[0013] [4] The heat transfer suppression sheet according to any one of [1] to [3], characterized in that the glass transition temperature of the resin binder is -10°C or higher.

[0014] [5] The heat transfer suppression sheet according to any one of [1] to [4], characterized in that the difference between the glass transition temperature of the resin binder and the glass transition temperature of the organic fiber is 10°C or more and 130°C or less.

[0015] [6] The heat transfer suppression sheet according to any one of [1] to [5], characterized in that the dissolution temperature of the organic fiber in water is 60°C or higher.

[0016] [7] The heat transfer suppression sheet according to any one of [1] to [6], characterized in that the average fiber length of the organic fibers is 0.5 mm or more and 10 mm or less.

[0017] [8] With respect to the total mass of the heat transfer suppression sheet, The content of the aforementioned organic fibers is 0.5% by mass or more and 12% by mass or less, A heat transfer suppression sheet according to any one of [1] to [7], characterized in that the resin binder content is 0.5% by mass or more and 20% by mass or less.

[0018] [9] The heat transfer suppression sheet according to any one of [1] to [8], characterized in that the resin binder comprises at least one selected from styrene-butadiene resin, acrylic resin, silicone-acrylic resin, and styrene resin.

[0019]

[10] The heat transfer suppression sheet according to any one of [1] to [9], wherein the organic fiber contains at least one selected from polyvinyl alcohol fiber, polyethylene fiber, nylon fiber, polyurethane fiber, and ethylene-vinyl alcohol copolymer fiber.

[0020]

[11] The heat transfer suppression sheet according to any one of [1] to

[10] , wherein the first inorganic particles are composed of at least one selected from oxide particles, carbide particles, nitride particles, and inorganic hydrate particles.

[0021]

[12] The heat transfer suppression sheet according to any one of [1] to

[11] , further comprising first inorganic fibers and second inorganic fibers having at least one property selected from average fiber diameter, shape, and glass transition point being different from each other.

[0022]

[13] The average fiber diameter of the first inorganic fiber is larger than the average fiber diameter of the second inorganic fiber. The heat transfer suppression sheet according to

[12] , wherein the first inorganic fiber is linear or needle-shaped, and the second inorganic fiber is dendritic or crumpled.

[0023]

[14] The first inorganic fiber is an amorphous fiber. The second inorganic fiber is at least one fiber selected from amorphous fibers having a glass transition point higher than that of the first inorganic fiber and crystalline fibers. The heat transfer suppression sheet according to

[12] , wherein the average fiber diameter of the first inorganic fiber is larger than the average fiber diameter of the second inorganic fiber.

[0024]

[15] The first inorganic particles contain at least one selected from nanoparticles, hollow particles, and porous particles. The first inorganic fiber is an amorphous fiber. The heat transfer suppression sheet according to

[12] , wherein the second inorganic fiber is at least one inorganic fiber selected from amorphous fibers and crystalline fibers, each having a higher glass transition temperature than the first inorganic fiber.

[0025]

[16] The heat transfer suppression sheet according to any one of

[12] to

[15] , characterized in that the first inorganic fiber is a fiber containing SiO2, and the second inorganic fiber is a fiber consisting of at least one selected from glass fiber, silica fiber, alumina fiber, alumina silicate fiber, zirconia fiber, glass wool, carbon fiber, soluble fiber, refractory ceramic fiber, aerogel composite material, magnesium silicate fiber, alkali earth silicate fiber, zirconia fiber, potassium titanate fiber, and mineral fiber.

[0026]

[17] The heat transfer suppression sheet according to any one of [1] to

[16] , further characterized by containing a second inorganic particle made of a metal oxide.

[0027] Furthermore, the above objective of the present invention is achieved by the configuration described below

[18] relating to a method for manufacturing a heat transfer suppression sheet.

[0028] A method for manufacturing a heat transfer suppression sheet described in any one of [1] to

[17] , A step of obtaining a dispersion containing the first inorganic particles, the resin binder, and the organic fibers, The process involves removing the dispersion to obtain a wet sheet, The process includes heating the wet sheet and then cooling it, A method for manufacturing a heat transfer suppression sheet, characterized in that the heating temperature for heating the wet sheet is set to be 10°C or more and 50°C or less higher than the glass transition temperature of the organic fiber.

[0029] Furthermore, preferred embodiments of the present invention relating to a method for manufacturing a heat transfer suppression sheet are described in the following

[19] .

[0030]

[19] The method for producing a heat transfer suppression sheet according to

[18] , characterized in that the dispersion is an emulsion obtained by dispersing the resin binder in water.

[0031] Furthermore, the above-mentioned objective of the present invention is achieved by the following configuration of the battery pack

[20] .

[0032]

[20] Multiple battery cells Ru A battery pack comprising a heat transfer suppression sheet described in any one of [1] to

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

[0033] The heat transfer suppression sheet of the present invention contains first inorganic particles that have excellent heat transfer suppression effects, and therefore exhibits superior heat transfer suppression effects. Furthermore, in the heat transfer suppression sheet of the present invention, the glass transition temperature of the organic fibers is higher than that of the resin binder. Therefore, during manufacturing, the organic fibers solidify to form a skeleton, and then the skeleton is reinforced with the resin binder. Thus, it is possible to achieve both excellent compression characteristics and heat transfer suppression effects, thereby suppressing a decrease in thermal insulation performance.

[0034] According to the method for manufacturing a heat transfer suppression sheet of the present invention, since the temperature during heating is appropriately controlled, a skeleton can be reliably formed with organic fibers, and excellent compression properties can be obtained.

[0035] According to the battery pack of the present invention, as described above, it has a heat transfer suppression sheet that has excellent compression characteristics and a heat transfer suppression effect, so it is possible to suppress thermal runaway of battery cells in the battery pack and the spread of flames to the outside of the battery case. [Brief explanation of the drawing]

[0036] [Figure 1] Figures 1(a) to 1(c) are schematic diagrams showing the manufacturing method of a heat transfer suppression sheet according to the first embodiment of the present invention in order of steps. [Figure 2]Figure 2 is a schematic diagram showing a heat transfer suppression sheet according to a second embodiment of the present invention. [Figure 3] Figure 3 is a schematic diagram showing a battery pack according to an embodiment of the present invention. [Figure 4] Figures 4(a) to 4(c) are schematic diagrams showing the manufacturing method of the test material for Comparative Example No. 1 in order of steps. [Figure 5] Figure 5 is a schematic diagram illustrating the compression characteristics test method. [Figure 6] Figure 6 is a schematic diagram illustrating the heat transfer test method. [Figure 7] Figure 7 is a graph showing the relationship between compressive stress and compressive ratio for each test material, with the horizontal axis representing compressive ratio and the vertical axis representing compressive stress. [Figure 8] Figure 8 is a graph showing the relationship between elapsed time and bottom surface temperature for each test material, with the horizontal axis representing elapsed time and the vertical axis representing bottom surface temperature. [Figure 9] Figure 9 is a graph showing the relationship between compressive stress and thermal resistivity for each test material, with the horizontal axis representing compressive stress and the vertical axis representing thermal resistivity. [Modes for carrying out the invention]

[0037] 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 the heat transfer suppression sheet, by having a first inorganic particle, a resin binder, and organic fibers having a higher glass transition temperature than the resin binder, can increase its resistance to pressure, and as a result, maintain excellent thermal insulation performance.

[0038] Specifically, during the manufacturing of the heat transfer suppression sheet, if the heating temperature is appropriately controlled when the wet sheet containing the above material is heated, the organic fibers become semi-molten. Then, upon subsequent cooling, the organic fibers with high glass transition points solidify first, causing the areas in contact with each other to bond and form a framework. Further cooling then causes the resin binder to solidify on the surface of the framework formed by the organic fibers, reinforcing the framework. In this way, the heat transfer suppression sheet of the present invention has a strong framework, and even when the heat transfer suppression sheet is pressed by the expansion of the battery cell, it can maintain its shape and suppress the deterioration of its heat insulation performance.

[0039] First, a method for manufacturing a heat transfer suppression sheet according to an embodiment of the present invention will be described in detail with reference to the drawings. Then, the heat transfer suppression sheet according to this embodiment and the materials constituting it will be described in detail. Furthermore, a battery pack according to this embodiment will be described. It should be noted that the present invention is not limited to the embodiments described below, and can be modified and implemented as desired without departing from the spirit of the invention.

[0040] [1. Method for manufacturing a heat transfer suppression sheet] Figures 1(a) to 1(c) are schematic diagrams showing the manufacturing method of a heat transfer suppression sheet according to the first embodiment of the present invention in order of steps. As shown in Figure 1(a), a first inorganic particle 1, an emulsion 2 obtained by dispersing a resin binder in water, an organic fiber 3 having a higher glass transition temperature than the resin binder, and an inorganic fiber 4 are prepared, and a dispersion 5 is obtained by mixing and stirring these. Next, a wet sheet is prepared by dehydrating (deliquidating) the dispersion 5.

[0041] Next, the wet sheet is heated. As shown in Figure 1(b), as the temperature rises, the water in the emulsion 2 evaporates, and molten resin binder 6 is obtained. Further heating of the sheet causes at least a portion of the surface of the organic fibers 3 to melt. Subsequently, by cooling the sheet, the organic fibers 3 fuse together to form a fused portion 7, as shown in Figure 1(c). Further cooling of the sheet forms a solidified resin binder 9, and a heat transfer suppression sheet according to this embodiment can be obtained.

[0042] In the heat transfer suppression sheet according to this embodiment, manufactured by the manufacturing method described above, since an emulsion 2 containing a resin binder is used, the entire material is uniformly dispersed, and organic fibers 3 exist in irregular directions within these dispersions. Then, during the process of heating the wet sheet to a predetermined temperature, the resin binder completely melts, and subsequently, a portion of the surface of the organic fiber 3, which has a high glass transition temperature, melts.

[0043] Furthermore, during the cooling process of the heated sheet, the molten surface portion of the organic fiber 3 solidifies first, and fused portions 7 are formed at the points where the organic fibers 3 are in contact with each other. As described above, the organic fibers 3 are present in an irregular orientation in the dispersion liquid in which the raw materials are mixed. Therefore, after a portion of the surface of the organic fibers 3 melts, when it is cooled to a temperature lower than the glass transition temperature of the organic fibers 3, at least a portion of the organic fibers 3 fuse together to form a three-dimensional skeleton 8. As a result, the resulting skeleton 8 maintains the shape of the entire heat transfer suppression sheet.

[0044] Subsequently, when the sheet is cooled to a temperature lower than the glass transition temperature of the resin binder, the molten resin binder solidifies on the surface of the skeleton 8, as well as between the skeleton 8 and the first inorganic particles 1, and between the skeleton 8 and the inorganic fibers 4. As a result, the first inorganic particles 1 and the inorganic fibers 4 adhere to the skeleton 8, and the skeleton 8 is reinforced by the solidified resin binder 9. In this way, the heat transfer suppression sheet according to this embodiment has a strong framework 8, and even when the heat transfer suppression sheet is pressed by the expansion of the battery cell, it can maintain its shape and suppress a decrease in thermal insulation performance.

[0045] In the present embodiment, the first inorganic particles 1, the emulsion 2 containing a resin binder, the organic fibers 3 having a glass transition point higher than that of the resin binder, and the inorganic fibers 4 are used as materials. However, the inorganic fibers 4 are not necessarily required. The effects obtained by adding the inorganic fibers 4 will be described later. Further, the emulsion 2 containing a resin binder does not necessarily have to be in the form of an emulsion. As long as the resin binder is uniformly dispersed in the liquid by any method, it is more preferable that all the materials are uniformly dispersed in the dispersion liquid. Therefore, the first inorganic particles 1, a resin binder (not shown), the organic fibers 3, the inorganic fibers 4, and a liquid for preparing the dispersion liquid may be mixed and dispersed. From the viewpoint of reducing the environmental load, it is preferable to use water as the liquid for dispersing the resin binder.

[0046] Next, the conditions in the manufacturing method of the heat transfer suppression sheet according to the present embodiment will be described.

[0047] <Heating temperature of the wet sheet> In the step of heating the wet sheet, the heating temperature is set to be 10°C or more and 50°C or less higher than the glass transition point of the organic fibers 3. That is, when the heating temperature of the wet sheet is t (°C) and the glass transition point of the organic fibers 3 is Tg (°C), if the relationship is t < Tg + 10, the melting on the surface of the organic fibers 3 becomes insufficient, and the adhesive force between the organic fibers 3 becomes weak, so that a strong skeleton cannot be formed. On the other hand, if the relationship is t > Tg + 50, the organic fibers 3 are completely melted by heating, and the shape as a skeleton cannot be formed. Therefore, the heating temperature t of the wet sheet is preferably Tg + 10 (°C) or more and preferably Tg + 15 (°C) or more. Further, the heating temperature t of the wet sheet is preferably Tg + 50 (°C) or less and preferably Tg + 30 (°C) or less.

[0048] [2. Heat transfer suppression sheet] (First embodiment) As shown in Figure 1(c), the heat transfer suppression sheet according to the first embodiment includes first inorganic particles 1, a resin binder 9, organic fibers 3, and inorganic fibers 4. Furthermore, the glass transition temperature of the organic fibers 3 is higher than that of the resin binder 9.

[0049] In the heat transfer suppression sheet according to the first embodiment configured in this way, the first inorganic particles 1 are made of a heat-resistant material, and countless minute spaces are formed inside the heat transfer suppression sheet where the resin binder 9 that has solidified after melting, the first inorganic particles 1, organic fibers 3, and inorganic fibers 4 are absent, and an insulating effect by air is also exhibited, thus providing an excellent heat transfer suppression effect.

[0050] Furthermore, since the glass transition temperature of the organic fiber 3 is higher than that of the resin binder 9, as explained in the above manufacturing method, the organic fiber 3 forms a skeleton during heating and cooling in the manufacturing process, and the skeleton is further reinforced by the resin binder 9. In detail, in the heat transfer suppression sheet according to this embodiment, at least a portion of the organic fibers 3 are fused to each other, thereby forming a three-dimensional skeleton 8. Furthermore, the resin binder 9 is fused to a portion of the surface of the skeleton 8, as well as to a portion of the first inorganic particles 1 and inorganic fibers 4, so that the first inorganic particles 1 and inorganic fibers 4 are bonded to the skeleton, reinforcing the skeleton 8. Therefore, the heat transfer suppression sheet according to this embodiment is high-strength and can suppress a decrease in thermal insulation performance even when a pressing force is applied.

[0051] (Second embodiment) Figure 2 is a schematic diagram showing a heat transfer suppression sheet according to a second embodiment of the present invention. As shown in Figure 2, the heat transfer suppression sheet 10 according to the second embodiment includes first inorganic particles 1, a resin binder 9, organic fibers 3, second inorganic particles 12, first inorganic fibers 31, and second inorganic fibers 32. The glass transition temperature of the organic fibers 3 is set to be higher than that of the resin binder 9. The first inorganic particles 1 and the second inorganic particles 12 are inorganic particles with different heat transfer suppression effects, and the first inorganic fibers 31 and the second inorganic fibers 32 are inorganic fibers having different properties.

[0052] In the heat transfer suppression sheet according to the second embodiment configured in this way, since the glass transition temperature of the organic fiber 3 is higher than that of the resin binder 9, at least a portion of the organic fiber 3 is fused to each other, similar to the first embodiment, thereby forming a three-dimensional skeleton 8. Furthermore, the resin binder 9 is fused to a portion of the surface of the skeleton 8, and the first inorganic particles 1, the second inorganic particles 12, the first inorganic fibers 31, and the second inorganic fibers 32 are bonded to the skeleton, thereby reinforcing the skeleton 8. Therefore, the heat transfer suppression sheet according to the second embodiment is also high-strength and can suppress a decrease in thermal insulation performance even when a pressing force is applied.

[0053] Furthermore, in this embodiment, since the first inorganic particles 1 and the second inorganic particles 12, which have different heat transfer suppression effects, are used in combination, the heat-generating element can be cooled in multiple stages, the heat-endurance effect can be expressed over a wider temperature range, and the thermal insulation performance can be further improved. Furthermore, in this embodiment, since the first inorganic fiber 31 and the second inorganic fiber 32 have at least one property that is different from each other, selected from the average fiber diameter, shape, and glass transition temperature, the mechanical strength of the heat transfer suppression sheet 10 and the retention of the first inorganic particles 1 and the second inorganic particles 12 can be improved.

[0054] The materials used in the heat transfer suppression sheet according to this embodiment will be described in detail below.

[0055] <2-1. Resin Binder> The resin binder 9 that can be used in this embodiment is not particularly limited, as long as it has a glass transition temperature lower than that of the organic fiber 3 described later. For example, a resin binder 9 containing at least one selected from styrene-butadiene resin, acrylic resin, silicone-acrylic resin, and styrene resin can be used. The glass transition temperature of the resin binder 9 is not specifically defined, but it is preferably -10°C or higher. Furthermore, if the glass transition temperature of the resin binder 9 is above room temperature, the strength of the heat transfer suppression sheet containing the resin binder 9 can be further improved when the sheet is used at room temperature. Therefore, the glass transition temperature of the resin binder 9 is more preferably 20°C or higher, even more preferably 30°C or higher, even more preferably 50°C or higher, and particularly preferably 60°C or higher.

[0056] (2-1-1. Resin binder content) In this embodiment, if the content of the resin binder 9 is appropriately controlled, the reinforcing effect of the organic fiber 3 on the skeleton can be sufficiently obtained. The content of the resin binder 9 is preferably 0.5% by mass or more, and more preferably 1% by mass or more, relative to the total mass of the heat transfer suppression sheet 10. Furthermore, it is preferably 20% by mass or less, and more preferably 10% by mass or less.

[0057] Furthermore, in the heat transfer suppression sheet 10 according to this embodiment, even if the total content of organic fibers 3 and resin binder 9 is the same as the content of organic materials in conventional heat insulating sheets, the above structure increases the strength against compression, thereby achieving both heat insulating performance and strength.

[0058] <2-2. Organic Fibers> The organic fiber 3 that can be used in this embodiment is not particularly limited, as long as it has a glass transition temperature higher than the glass transition temperature of the resin binder 9. For example, the organic fiber 3 can be made up of at least one selected from polyvinyl alcohol (PVA) fiber, polyethylene fiber, nylon fiber, polyurethane fiber, and ethylene-vinyl alcohol copolymer fiber. Furthermore, since it is difficult to raise the heating temperature above 250°C during the manufacturing of the heat transfer suppression sheet, the glass transition temperature of the organic fiber 3 is preferably 250°C or lower, and more preferably 200°C or lower.

[0059] The lower limit of the glass transition temperature of the organic fiber 3 is not particularly limited, but if the difference between it and the glass transition temperature of the resin binder 9 is 10°C or more, the resin binder will solidify after the semi-molten organic fiber 3 has completely solidified during the cooling process in manufacturing, thus allowing for sufficient reinforcement of the skeleton by the resin binder 9. Therefore, the difference between the glass transition temperature of the resin binder 9 and the glass transition temperature of the organic fiber 3 is preferably 10°C or more, and more preferably 30°C or more. On the other hand, if the difference between the glass transition temperatures of the two is 130°C or less, the time from when the organic fiber 3 is completely solidified until the resin binder begins to solidify can be appropriately adjusted, and the resin binder solidifies while maintaining a good dispersion state, thus further enhancing the reinforcing effect of the skeleton 8. Therefore, the difference between the glass transition temperature of the resin binder 9 and the glass transition temperature of the organic fiber 3 is preferably 130°C or less, more preferably 120°C or less, even more preferably 100°C or less, even more preferably 80°C or less, and particularly preferably 70°C or less.

[0060] In the heat transfer suppression sheet according to this embodiment, if it contains two or more types of organic fibers, at least one of the organic fibers may act as a skeleton, that is, an organic fiber having a glass transition temperature higher than the glass transition temperature of the resin binder. The difference between the glass transition temperature of the resin binder 9 and the glass transition temperature of at least one type of organic fiber is preferably 10°C or higher, more preferably 30°C or higher, preferably 130°C or lower, more preferably 120°C or lower, even more preferably 100°C or lower, even more preferably 80°C or lower, and particularly preferably 70°C or lower.

[0061] In this embodiment, if the content of the organic fiber 3 and the resin binder 9 is appropriately controlled, the function of the organic fiber 3 as a skeleton can be sufficiently obtained, and the reinforcing effect of the skeleton by the resin binder 9 can be sufficiently obtained. The content of the organic fiber 3 is preferably 0.5% by mass or more, more preferably 1% by mass or more, relative to the total mass of the heat transfer suppression sheet. Furthermore, it is preferably 12% by mass or less, and more preferably 8% by mass or less. When the heat transfer suppression sheet contains multiple organic fibers having a glass transition temperature higher than the glass transition temperature of the resin binder, it is preferable that the total amount of these multiple organic fibers is within the range of the organic fiber 3 content described above.

[0062] As described above, in the heat transfer suppression sheet according to this embodiment, if it contains two or more types of organic fibers, it is sufficient that at least one type of organic fiber has a glass transition temperature higher than the glass transition temperature of the resin binder, but it is more preferable that the other organic fibers include organic fibers in a crystalline state that do not have a glass transition temperature. Since organic fibers in a crystalline state that do not have a glass transition point do not have a softening point, in this embodiment, the overall strength of the heat transfer suppression sheet can be maintained even when exposed to high temperatures that would cause the organic fibers forming the skeleton to soften. Furthermore, by including organic fibers in a crystalline state that do not have a glass transition temperature, these organic fibers also act as the backbone of the heat transfer suppression sheet at room temperature. Therefore, the flexibility and handling of the heat transfer suppression sheet can be improved. Polyester (PET) fibers are an example of organic fibers in a crystalline state that do not have a glass transition temperature.

[0063] Furthermore, as described above, in this embodiment, it is preferable to use water as the liquid for dispersing the resin binder. Therefore, when using water, it is preferable to use organic fibers with low solubility in water. In this embodiment, the dissolution temperature in water is used as an indicator of solubility in water. That is, the dissolution temperature in water of the organic fiber 3 is preferably 60°C or higher, more preferably 70°C or higher, and even more preferably 80°C or higher.

[0064] While there are no particular limitations on the fiber length of the organic fiber 3, it is preferable that the average fiber length of the organic fiber 3 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 3 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 3 be 0.5 mm or more.

[0065] <2-3. Inorganic particles> 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. As inorganic particles, a single inorganic particle may be used, or two or more types of inorganic particles (first inorganic particle 1 and second inorganic particle 12) may be used in combination. 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 as the first inorganic particle 1 and second inorganic particle 12, and it is more preferable to use oxide particles. Furthermore, there are no particular limitations on the shape of the first inorganic particle 1 and second inorganic particle 12, 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 also be used.

[0066] 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 the small-diameter inorganic particles referred to as the first inorganic particle 1 and the large-diameter inorganic particles as the second inorganic particle 12.

[0067] <2-3-1. The 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 particle 1 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.

[0068] (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.

[0069] 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.

[0070] (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 and on the order of nanometers. Because nanoparticles have low density, they suppress conductive heat transfer, and when nanoparticles are used as the first inorganic particle 1, the voids are further finely dispersed, 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.

[0071] In this invention, when nanoparticles are used as the first inorganic particle 1, 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, even if, for example, battery cells placed on both sides of the heat insulating sheet undergo thermal expansion and a large compressive stress is applied to the heat insulating sheet, the size (area) and number of contact points between silica nanoparticles will not increase significantly, and the heat insulating properties can be maintained. Therefore, it is preferable to use silica nanoparticles. As silica nanoparticles, wet silica, dry silica, aerogel, etc., can be used.

[0072] (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.

[0073] (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).

[0074] 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

[0075] 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.

[0076] (Average secondary particle diameter of inorganic hydrate particles: 0.01 μm or more and 200 μm or less) Furthermore, if inorganic hydrate particles are used as the first inorganic particles 1, and their average particle size is too large, the first inorganic particles 1 (inorganic hydrate) near the center of the heat transfer suppression sheet 10 will take a certain amount of time to reach their thermal decomposition temperature, and the first inorganic particles 1 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.

[0077] (Particles made of thermally expandable inorganic material) Examples of thermally expandable inorganic materials include vermiculite, bentonite, mica, and perlite.

[0078] (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.

[0079] (Inorganic balloon) The thermal insulation material used in the present invention may include inorganic balloons as the first inorganic particles 1. 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.

[0080] (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.

[0081] (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.

[0082] <2-3-2. The second inorganic particle> When the heat transfer suppression sheet contains two types of inorganic particles, the second inorganic particle 12 is not particularly limited as long as it differs from the first inorganic particle 1 in material, particle size, etc. The second inorganic particle 12 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.

[0083] 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 1, it is preferable to further include particles made of metal oxides, which are larger in diameter than the first inorganic particles 1, as the second inorganic particles 12 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.

[0084] (Average primary particle diameter of the second inorganic particle) When a second inorganic particle 12 made of a metal oxide is included in the heat transfer suppression sheet, if the average primary particle diameter of the second inorganic particle 12 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 12 is 5 μm or more and 30 μm or less, and most preferably 10 μm or less.

[0085] <2-4. First Inorganic Fiber and Second Inorganic Fiber> In this embodiment, the heat transfer suppression sheet preferably has a first inorganic fiber 31 and a second inorganic fiber 32 having at least one property that is different from each other, selected from the average fiber diameter, shape, and glass transition temperature. As described in the second embodiment above, by including two inorganic fibers with different properties, the mechanical strength of the heat transfer suppression sheet and the retention of the first inorganic particles 1 and the second inorganic particles 12 can be improved.

[0086] (2-4-1. Two types of inorganic fibers with different average fiber diameters and fiber shapes) When the heat transfer suppression sheet contains two types of inorganic fibers, it is preferable that the average fiber diameter of the first inorganic fiber 31 is larger than the average fiber diameter of the second inorganic fiber 32, that the first inorganic fiber 31 is linear or needle-shaped, and that the second inorganic fiber 32 is dendritic or crimped. The first inorganic fiber 31, which has a large average fiber diameter (large diameter), has the effect of improving the mechanical strength and shape retention of the heat transfer suppression sheet. The above effect can be obtained by making one of the two types of inorganic fibers, for example, the first inorganic fiber 31, larger in diameter than the second inorganic fiber 32. Since the heat transfer suppression sheet may be subjected to external impacts, the inclusion of the first inorganic fiber 31 in the heat transfer suppression sheet increases its impact resistance. Examples of external impacts include the compressive force due to the expansion of battery cells and the wind pressure due to the ignition of battery cells. Furthermore, in order to improve the mechanical strength and shape retention of the heat transfer suppression sheet, it is particularly preferable that the first inorganic fiber 31 be linear or needle-shaped. Linear or needle-shaped fibers refer to fibers whose crimp degree, as described later, is, for example, less than 10%, preferably 5% or less.

[0087] More specifically, in order to improve the mechanical strength and shape retention of the heat transfer suppression sheet, the average fiber diameter of the first inorganic fiber 31 is preferably 1 μm or more, and more preferably 3 μm or more. If the first inorganic fiber 31 is too thick, the moldability and processability of the heat transfer suppression sheet may decrease, so the average fiber diameter of the first inorganic fiber 31 is preferably 20 μm or less, and more preferably 15 μm or less. Furthermore, since excessive length of the first inorganic fiber 31 may reduce moldability and processability, it is preferable to keep the fiber length 100 mm or less. Additionally, since excessively short length of the first inorganic fiber 31 may reduce shape retention and mechanical strength, it is preferable to keep the fiber length 0.1 mm or more.

[0088] On the other hand, the second inorganic fiber 32, which has a smaller average fiber diameter (small diameter), improves the retention of the organic fiber 3 and the first inorganic particle 1, and also enhances the flexibility of the heat transfer suppression sheet. Therefore, it is preferable to make the second inorganic fiber 32 smaller in diameter than the first inorganic fiber 31.

[0089] More specifically, in order to improve the retention of organic fibers 3 and first inorganic particles 1, it is preferable that the second inorganic fibers 32 are easily deformable and flexible. Therefore, the second inorganic fibers 32, which are small in diameter, preferably have an average fiber diameter of less than 1 μm, and more preferably 0.1 μm or less. However, if the small-diameter inorganic fibers are too thin, they are prone to breakage, and the retention ability of organic fibers 3 and first inorganic particles 1 decreases. In addition, a large proportion of the fibers remain entangled in the heat transfer suppression sheet without retaining the organic fibers 3 and first inorganic particles 1, resulting in a decrease in the retention ability of organic fibers 3 and first inorganic particles 1, as well as inferior moldability and shape retention. Therefore, the average fiber diameter of the second inorganic fibers 32 is preferably 1 nm or more, and more preferably 10 nm or more. Furthermore, since the moldability and shape retention of the second inorganic fiber 32 decrease if it becomes too long, it is preferable that the fiber length of the second inorganic fiber 32 be 0.1 mm or less.

[0090] Furthermore, the second inorganic fiber 32 is preferably dendritic or crimped. When the second inorganic fiber 32 has such a shape, it intertwines with the organic fiber 3 and the first inorganic particle 1 in the heat transfer suppression sheet. As a result, the holding ability of the organic fiber 3 and the first inorganic particle 1 is improved. In addition, when the heat transfer suppression sheet is subjected to pressing force or wind pressure, the sliding movement of the second inorganic fiber 32 is suppressed, thereby improving the mechanical strength to withstand external pressing force and impact in particular.

[0091] Furthermore, a dendritic structure is a structure that branches out in two or three dimensions, such as a feathery, tetrapod-shaped, radial, or three-dimensional network-like structure. When the second inorganic fiber 32 is dendritic, its average fiber diameter can be obtained by measuring the diameters of the trunk and branches at several points using a scanning electron microscope (SEM) and calculating the average value of these measurements.

[0092] Furthermore, a crimped structure is one in which fibers are bent in various directions. One method for quantifying the crimp morphology is to calculate the degree of crimp from electron microscope images, which can be calculated, for example, using the following formula. Crimping (%) = (Fiber length - Distance between fiber ends) / (Fiber length) × 100 Here, both the fiber length and the distance between fiber ends are measured values ​​obtained from electron microscope images. That is, these are the fiber length and distance between fiber ends projected onto a two-dimensional plane, and are shorter than the actual values. Based on this formula, the crimp of the second inorganic fiber 32 is preferably 10% or more, and more preferably 30% or more. If the crimp is small, the holding ability of the organic fiber 3 and the first inorganic particle 1 decreases, making it difficult to form entanglements (networks) between the second inorganic fibers 32 and between the first inorganic fiber 31 and the second inorganic fiber 32.

[0093] In the above-described embodiment, a first inorganic fiber 31 and a second inorganic fiber 32 having different average fiber diameters and fiber shapes are used as a method to improve the mechanical strength and shape retention of the heat transfer suppression sheet, as well as the retention of the organic fiber 3 and the first inorganic particle 1. However, the mechanical strength, shape retention, and particle retention of the heat transfer suppression sheet can also be improved by using the first inorganic fiber 31 and the second inorganic fiber 32 having different glass transition temperatures and average fiber diameters.

[0094] As described above, in this embodiment, it is preferable to use various combinations of inorganic fibers in order to improve the mechanical strength, shape retention, and particle retention of the heat transfer suppression sheet. Below, we will describe first and second inorganic fiber combinations that differ from those of the second embodiment shown in Figure 2, but for convenience, other embodiments relating to inorganic fibers will be described using Figure 2 in this specification.

[0095] (2-4-2. Two types of inorganic fibers with different glass transition temperatures) When the heat transfer suppression sheet contains two types of inorganic fibers, it is preferable that the first inorganic fiber 31 is an amorphous fiber, and the second inorganic fiber 32 is at least one fiber selected from amorphous fibers and crystalline fibers that have a higher glass transition temperature than the first inorganic fiber 31. Furthermore, by using the first inorganic particles 1, which include at least one selected from nanoparticles, hollow particles, and porous particles, together with the two types of inorganic fibers, the heat insulation performance can be further improved.

[0096] The melting point of crystalline inorganic fibers is usually higher than the glass transition point of amorphous inorganic fibers. Therefore, when the first inorganic fiber 31 is exposed to high temperatures, its surface softens before the second inorganic fiber 32, binding the organic fiber 3 and the first inorganic particles 1 to it. Consequently, by incorporating the first inorganic fiber 31 as described above into the heat transfer suppression sheet, the mechanical strength of the heat insulating layer can be improved. Specifically, the first inorganic fiber 31 is preferably an inorganic fiber with a melting point of less than 700°C, and many amorphous inorganic fibers can be used. Among these, it is preferable that the fiber contains SiO2, and more preferably that it is glass fiber because it is inexpensive, readily available, and has excellent handling properties.

[0097] As described above, the second inorganic fiber 32 is a fiber consisting of at least one type selected from amorphous fibers and crystalline fibers, which have a higher glass transition temperature than the first inorganic fiber 31. Many crystalline inorganic fibers can be used as the second inorganic fiber 32. If the second inorganic fiber 32 is made of crystalline fibers or has a higher glass transition temperature than the first inorganic fiber 31, then even if the first inorganic fiber 31 softens when exposed to high temperatures, the second inorganic fiber 32 will not melt or soften. Therefore, it can maintain its shape and remain present between battery cells even during thermal runaway of the battery cell. Furthermore, if the second inorganic fiber 32 does not melt or soften, the minute spaces between each particle, between the particles and the fibers, and between each fiber in the heat transfer suppression sheet are maintained, so that the insulating effect of air is exerted and excellent heat transfer suppression performance can be maintained.

[0098] When the second inorganic fiber 32 is crystalline, the second inorganic fiber 32 can be a variety of materials, such as 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, and potassium titanate fibers, glass fibers such as glass wool, and mineral fibers such as rock wool, basalt fibers, and wollastonite. Among the fibers listed as the second inorganic fiber 32, if the melting point exceeds 1000°C, the second inorganic fiber 32 will not melt or soften even if thermal runaway occurs in the battery cell, and will be able to maintain its shape, making it suitable for use. Furthermore, among the fibers listed as the second inorganic fiber 32 above, it is more preferable to use ceramic fibers such as silica fibers, alumina fibers, and aluminasilicate fibers, as well as mineral fibers, and among these, it is even more preferable to use those with a melting point exceeding 1000°C.

[0099] Furthermore, even if the second inorganic fiber 32 is amorphous, it can be used as long as it has a higher glass transition temperature than the first inorganic fiber 31. For example, a glass fiber with a higher glass transition temperature than the first inorganic fiber 31 may be used as the second inorganic fiber 32. Furthermore, the second inorganic fiber 32 may be any of the various inorganic fibers exemplified, either individually or in a mixture of two or more types.

[0100] As described above, the first inorganic fiber 31 has a lower glass transition temperature than the second inorganic fiber 32, and when exposed to high temperatures, the first inorganic fiber 31 softens first, allowing the first inorganic fiber 31 to bind the organic fiber 3 and the first inorganic particles 1, etc. However, if, for example, the second inorganic fiber 32 is amorphous and its fiber diameter is smaller than that of the first inorganic fiber 31, and the glass transition temperatures of the first inorganic fiber 31 and the second inorganic fiber 32 are close together, the second inorganic fiber 32 may soften first. Therefore, when the second inorganic fiber 32 is an amorphous fiber, the glass transition temperature of the second inorganic fiber 32 is preferably 100°C or more higher than the glass transition temperature of the first inorganic fiber 31, and more preferably 300°C or more higher.

[0101] Furthermore, the fiber length of the first inorganic fiber 31 is preferably 100 mm or less, and preferably 0.1 mm or more. The fiber length of the second inorganic fiber 32 is preferably 0.1 mm or less. The reasons for these preferences are as described above.

[0102] (2-4-3. Two types of inorganic fibers with different glass transition temperatures and average fiber diameters) When the heat transfer suppression sheet contains two types of inorganic fibers, it is preferable that the first inorganic fiber 31 is an amorphous fiber, and the second inorganic fiber 32 is at least one fiber selected from amorphous fibers and crystalline fibers that have a higher glass transition temperature than the first inorganic fiber 31, and that the average fiber diameter of the first inorganic fiber 31 is greater than the average fiber diameter of the second inorganic fiber 32.

[0103] As described above, when the heat transfer suppression sheet according to this embodiment contains two types of inorganic fibers, it is preferable that the average fiber diameter of the first inorganic fiber 31 is larger than that of the second inorganic fiber 32. Furthermore, it is preferable that the large-diameter first inorganic fiber 31 is amorphous, and the small-diameter second inorganic fiber 32 is composed of at least one type of fiber selected from amorphous fibers and crystalline fibers, each having a higher glass transition point than the first inorganic fiber 31. As a result, the glass transition point of the first inorganic fiber 31 is low, and it softens quickly, becoming film-like and hardening as the temperature rises. On the other hand, if the small-diameter second inorganic fiber 32 is composed of at least one type of fiber selected from amorphous fibers and crystalline fibers, each having a higher glass transition point than the first inorganic fiber 31, the small-diameter second inorganic fiber 32 remains in its fiber shape even as the temperature rises, thus maintaining the structure of the heat transfer suppression sheet and preventing powder shedding.

[0104] Even in this case, the fiber length of the first inorganic fiber 31 is preferably 100 mm or less, and preferably 0.1 mm or more. The fiber length of the second inorganic fiber 32 is preferably 0.1 mm or less. The reasons for these are as described above.

[0105] Furthermore, the heat transfer suppression sheet according to this embodiment may contain different inorganic fibers in addition to the first inorganic fiber 31 and the second inorganic fiber 32 described above.

[0106] (2-4-4. Content of the first inorganic fiber and the second inorganic fiber) When the heat transfer suppression sheet contains two types of inorganic fibers, the content of the first inorganic fiber 31 is preferably 3% by mass or more and 30% by mass or less relative to the total mass of the heat transfer suppression sheet, and the content of the second inorganic fiber 32 is preferably 3% by mass or more and 30% by mass or less relative to the total mass of the heat transfer suppression sheet.

[0107] Furthermore, the content of the first inorganic fiber 31 is more preferably 5% by mass or more and 15% by mass or less relative to the total mass of the heat transfer suppression sheet, and the content of the second inorganic fiber 32 is more preferably 5% by mass or more and 15% by mass or less relative to the total mass of the heat transfer suppression sheet. By using such content, the shape retention, pressure resistance, and wind pressure resistance of the first inorganic fiber 31 and the inorganic particle retention ability of the second inorganic fiber 32 are expressed in a well-balanced manner.

[0108] <2-5. 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.

[0109] [3. Battery Packs] Figure 3 is a schematic diagram showing a battery pack according to an embodiment of the present invention. The battery pack 100 according to this embodiment 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.

[0110] 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, since the heat transfer suppression sheet 10 according to this embodiment has high compressive strength, 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, suppress the decrease in heat insulation performance, and prevent thermal runaway of the battery cells. In addition, because the effect of suppressing thermal expansion can prevent deformation of the battery cells, the load on the battery case 30 can be reduced.

[0111] Furthermore, the battery pack 100 of this embodiment is not limited to the battery pack illustrated in Figure 3, and the heat transfer suppression sheet 10 can 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.

[0112] 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.

[0113] 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 cell 101, 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 cell can be tolerated even if the temperature of one of the battery cells rises and its volume expands.

[0114] Furthermore, the heat transfer suppression sheet 10 according to this embodiment can be easily bent depending on the type and thickness of the material selected. Therefore, it can be adapted to any shape, regardless of the shape of the battery cells 20a, 20b, 20c and the battery case 30. Specifically, it can be applied to prismatic batteries, as well as cylindrical batteries, flat-plate batteries, and the like. [Examples]

[0115] The present invention will be described in detail below with reference to examples and comparative examples, but the present invention is not limited to these.

[0116] <Preparation of test specimens> (Example No. 1) As organic fibers, polyester (PET) fibers, which are crystalline organic fibers without a glass transition temperature, and polyvinyl alcohol (PVA) fibers, which have a glass transition temperature, were prepared. As a resin binder, a latex solution with a glass transition temperature of 58°C was prepared. As first and second inorganic particles, silica particles and titanium dioxide particles were prepared. As other components, silica-based fibers and glass fibers, which are inorganic fibers, were also prepared. The specific content and names of each component are shown below. • Polyester fiber (3 parts): 0.1 decitex x 3 mm (average fiber length) • PVA fiber (5 parts): VPB053 (manufactured by Kuraray Co., Ltd.), 0.55 decitex x 3mm • Latex solution (5 parts styrene-butadiene resin): Glass transition temperature 58°C • First inorganic particles, second inorganic particles (70 parts in total): Silica particles and titanium oxide particles • First inorganic fiber (7 parts): Silica-based fiber • Second inorganic fiber (10 parts): Glass fiber, CS 3J-888S (manufactured by Nitto Boseki Co., Ltd.), fiber diameter 10 μm x fiber length 6 mm

[0117] The above materials were dispersed in water using a pulper to prepare a uniform papermaking slurry (dispersion), and then dewatered using a papermaking machine to obtain a wet sheet. Subsequently, the sheet was dried using a Yankee dryer with a surface temperature of 140°C, and then heated to 250°C by hot air drying to obtain a dried sheet. After that, the dried sheet was cooled to obtain a basis weight of 600 g / m². 2 A test material for Example No. 1, with a thickness of 1.5 mm, was prepared. In addition, of the total mass of the test material obtained in Example No. 1, the polyester fiber content was 3% by mass, the PVA fiber content was 5% by mass, and the resin binder (styrene-butadiene resin) content was 5% by mass.

[0118] (Example No. 2) As organic fibers, polyester (PET) fibers, which are crystalline organic fibers without a glass transition temperature, and polyvinyl alcohol (PVA) fibers, which have a glass transition temperature, were prepared. As a resin binder, a latex solution with a glass transition temperature of -9°C was prepared. As inorganic particles, silica particles were prepared. In addition, as other components, silica-based fibers and glass fibers, which are inorganic fibers, were prepared. • Polyester fiber (3 parts): 0.1 decitex x 3mm • PVA fiber (5 parts): VPB053 (manufactured by Kuraray Co., Ltd.), 0.55 decitex x 3 mm (average fiber length) • Latex solution (5 parts acrylic resin): Glass transition temperature -9°C • First inorganic particles, second inorganic particles (70 parts in total): Silica particles and titanium oxide particles • First inorganic fiber (7 parts): Silica-based fiber • Second inorganic fiber (10 parts): Glass fiber, CS 3J-888S (manufactured by Nitto Boseki Co., Ltd.), fiber diameter 10 μm x fiber length 6 mm

[0119] Subsequently, a wet sheet was prepared in the same manner as in Example No. 1, heated, dried, and then cooled, resulting in a basis weight of 600 g / m². 2 A test material for Example No. 2, with a thickness of 1.5 mm, was prepared. In addition, of the total mass of the test material obtained in Example No. 2, the polyester fiber content was 3% by mass, the PVA fiber content was 5% by mass, and the resin binder (acrylic resin) content was 5% by mass.

[0120] (Comparative Example No. 1) To clarify the differences from the examples, the manufacturing method of Comparative Example No. 1 will be described with reference to the drawings. Figures 4(a) to (c) are schematic diagrams showing the manufacturing method of the test material of Comparative Example No. 1 in order of steps.

[0121] As shown in Figure 4(a), a latex solution with a glass transition temperature of -9°C was prepared as the resin binder, silica particles and titanium oxide particles were prepared as inorganic particles 11, and silica-based fibers and glass fibers were prepared as other components, which are inorganic fibers 14. • Polyester fiber (3 parts): 0.1 decitex x 3mm • Latex solution (10 parts acrylic resin): Glass transition temperature -9°C • Inorganic particles 11 (first inorganic particles, second inorganic particles) (70 parts in total): Silica particles and titanium oxide particles • Inorganic fiber 14 (first inorganic fiber, second inorganic fiber): Silica-based fiber (7 parts), glass fiber (10 parts), CS 3J-888S (manufactured by Nitto Boseki Co., Ltd.), fiber diameter 10 μm x fiber length 6 mm

[0122] The above materials were dispersed in water using a pulper to prepare a uniform papermaking slurry (dispersion 15), and then dewatered using a papermaking machine to obtain a wet sheet. Subsequently, the material was dried using a Yankee dryer with a surface temperature of 140°C, and then heated to 250°C in a hot air dryer. As a result, as shown in Figure 4(b), the moisture evaporated as the temperature rose, and molten resin binder 16 was obtained. Subsequently, by cooling, the inorganic particles 11 and inorganic fibers 14 were bonded together by the solidified resin binder 19, as shown in Figure 4(c). In this way, the basis weight is 600 (g / m²). 2A test material for Comparative Example No. 1, with a thickness of 1.5 mm, was prepared.

[0123] The glass transition temperatures of the materials used for each test specimen are shown in Table 1 below. The glass transition temperatures of resin binders and organic fibers are determined by differential scanning calorimetry (DSC) and dynamic viscoelasticity measurements. It can be calculated by Dynamic Mechanical Analysis (DMA) or Thermomechanical Analysis (TMA). However, of the two types of organic fibers used in the above examples and comparative examples, polyester (PET) fiber is a crystalline organic fiber that does not have a glass transition temperature, as described above. Therefore, the glass transition temperature of the organic fibers shown in Table 1 below represents the glass transition temperature of polyvinyl alcohol (PVA) fiber, which does have a glass transition temperature.

[0124] [Table 1]

[0125] <Evaluation method for test materials> For each test material, compression properties tests, heat transfer properties tests, and thermal insulation performance tests were conducted, and the compression properties and thermal insulation performance were evaluated.

[0126] (Compression characteristics test) As shown in Figure 5, a universal testing machine was used, with the test specimen 23 placed between the upper plate 21 and the lower plate 22. The test specimen 23 was then compressed by moving the upper plate 21 downwards. The size of the test specimen 23 was set to 25 mm × 25 mm × 1.5 mm, the compression speed to 0.5 mm / min, and the maximum compressive stress to 5 MPa. Then, the initial thickness of the test material 23 is D0 (mm), and the amount of compression (thickness reduction) is D d The compression ratio C (%) was calculated using the following formula, where (mm) is used. C=D d / D0×100 In addition, the compression characteristic test was conducted for Example No. 1 and Comparative Example No. 1.

[0127] (Heat transfer property test) As shown in FIG. 6, an iron upper plate 24 and a lower plate 25 were prepared, and a test specimen 26 was placed on the lower plate 25. Next, the upper plate 24 heated to 800° C. was placed on the upper surface 26a of the test specimen 26, and pressure was applied downward at 3.5 MPa. At this time, a temperature sensor (not shown) was installed between the lower surface 26b of the test specimen 26 and the lower plate 25 to measure the lower surface temperature T c (° C.), and a temperature sensor (not shown) was installed between the upper surface 26a of the test specimen 26 and the upper plate 24 to measure the upper surface temperature T h (° C.). Then, the change in the lower surface temperature T c (° C.) with respect to time was observed.

[0128] (Heat insulation performance test) For the heat insulation performance, first, among the methods for measuring the thermal conductivity, the hot wire method corresponding to the unsteady method was used to measure the thermal conductivity λ (W / m·K) at room temperature to obtain the thermal conductivity λ (W / m·K) of the test specimen. Thereafter, using the thermal conductivity λ (W / m·K), the initial thickness D0 (m), and the compression ratio C (%) of the test specimen, the thermal resistance value R (m 2 ·K / W) was calculated by the following formula. R = D0 / λ × (100 - C) / 100

[0129] <Evaluation results of the test specimen> (Compression characteristic test results) FIG. 7 is a graph showing the relationship between the compression stress and the compression ratio for each test specimen when the horizontal axis is the compression ratio and the vertical axis is the compression stress. As shown in FIG. 7, it was shown that Example No. 1 and Example No. 2 had a lower compression ratio and excellent compression characteristics when the same pressure was applied compared to Comparative Example No. 1. In particular, Example No. 1 had a glass transition point of the resin binder of 20° C. or more and a difference in the glass transition points between the organic fiber and the resin binder of 62° C., both within the preferable range of the present invention, so that excellent compression characteristics could be obtained.

[0130] (Heat transfer test results) Figure 8 is a graph showing the relationship between elapsed time and bottom surface temperature for each test material, with the horizontal axis representing elapsed time and the vertical axis representing bottom surface temperature. As shown in Figure 8, Example No. 1 exhibited a lower peak value for the bottom surface temperature compared to Comparative Example No. 1. This indicates that Example No. 1 has superior thermal insulation properties.

[0131] As shown in Figure 4(c), in Comparative Example No. 1, since no organic fiber skeleton was formed, the strength of the test material deteriorated when heated on the upper plate 24 at 800°C, and defects 29 were formed when pressed, resulting in a decrease in compressive strength.

[0132] (Insulation performance test results) Figure 9 is a graph showing the relationship between compressive stress and thermal resistivity for each test material, with the horizontal axis representing compressive stress and the vertical axis representing thermal resistivity. As shown in Figure 9, Examples No. 1 and No. 2 showed higher thermal resistivity at all compressive stresses compared to Comparative Example No. 1. In particular, compared to Example No. 2, Example No. 1 showed less decrease in thermal resistivity even when the compressive stress was increased, because both the glass transition temperature of the resin binder and the difference between the glass transition temperatures of the organic fibers and the resin binder were within the preferred range of the present invention. [Explanation of symbols]

[0133] 1. First inorganic particle 2 Emulsion 3 Organic Fibers 4,14 Inorganic Fibers 5,15 Dispersion 6,9,16,19 Resin Binder 7 Fusion part 8 Skeleton 10 Heat transfer suppression sheet 12. The second inorganic particle 20a, 20b, 20c battery cells 30 Battery Cases 31. First inorganic fiber 32 Second inorganic fiber 100 battery packs

Claims

1. comprising first inorganic particles, a resin binder, and organic fibers, The glass transition temperature of the organic fiber is higher than that of the resin binder. Furthermore, the material comprises a first inorganic fiber and a second inorganic fiber having at least one property selected from average fiber diameter, shape, and glass transition temperature that differs from each other. The average fiber diameter of the first inorganic fiber is greater than the average fiber diameter of the second inorganic fiber. A heat transfer suppression sheet characterized in that the first inorganic fiber is linear or needle-shaped, and the second inorganic fiber is dendritic or curly.

2. comprising first inorganic particles, a resin binder, and organic fibers, The glass transition temperature of the organic fiber is higher than that of the resin binder. Furthermore, the material comprises a first inorganic fiber and a second inorganic fiber having at least one property selected from average fiber diameter, shape, and glass transition temperature that differs from each other. The first inorganic fiber is an amorphous fiber, The second inorganic fiber is at least one fiber selected from amorphous fibers and crystalline fibers, each having a higher glass transition temperature than the first inorganic fiber. A heat transfer suppression sheet characterized in that the average fiber diameter of the first inorganic fiber is greater than the average fiber diameter of the second inorganic fiber.

3. comprising first inorganic particles, a resin binder, and organic fibers, The glass transition temperature of the organic fiber is higher than that of the resin binder. Furthermore, the material comprises a first inorganic fiber and a second inorganic fiber having at least one property selected from average fiber diameter, shape, and glass transition temperature that differs from each other. The first inorganic particle comprises at least one selected from nanoparticles, hollow particles, and porous particles. The first inorganic fiber is an amorphous fiber, A heat transfer suppression sheet characterized in that the second inorganic fiber is at least one inorganic fiber selected from amorphous fibers and crystalline fibers, each having a higher glass transition temperature than the first inorganic fiber.

4. At least a portion of the aforementioned organic fibers are fused together to form a three-dimensional skeleton. The heat transfer suppression sheet according to any one of claims 1 to 3, characterized in that the resin binder is fused to a part of the skeleton and at least a part of the first inorganic particles, and at least a part of the first inorganic particles is adhered to the skeleton.

5. The heat transfer suppression sheet according to any one of claims 1 to 4, characterized in that the glass transition temperature of the organic fiber is 250°C or lower.

6. The heat transfer suppression sheet according to any one of claims 1 to 5, characterized in that the glass transition temperature of the resin binder is -10°C or higher.

7. The heat transfer suppression sheet according to any one of claims 1 to 6, characterized in that the difference between the glass transition temperature of the resin binder and the glass transition temperature of the organic fiber is 10°C or more and 130°C or less.

8. The heat transfer suppression sheet according to any one of claims 1 to 7, characterized in that the dissolution temperature of the organic fiber in water is 60°C or higher.

9. The heat transfer suppression sheet according to any one of claims 1 to 8, characterized in that the average fiber length of the organic fibers is 0.5 mm or more and 10 mm or less.

10. With respect to the total mass of the heat transfer suppression sheet, The content of the aforementioned organic fibers is 0.5% by mass or more and 12% by mass or less, The heat transfer suppression sheet according to any one of claims 1 to 9, characterized in that the content of the resin binder is 0.5% by mass or more and 20% by mass or less.

11. The heat transfer suppression sheet according to any one of claims 1 to 10, characterized in that the resin binder comprises at least one selected from styrene-butadiene resin, acrylic resin, silicone-acrylic resin, and styrene resin.

12. The heat transfer suppression sheet according to any one of claims 1 to 11, characterized in that the organic fiber comprises at least one selected from polyvinyl alcohol fiber, polyethylene fiber, nylon fiber, polyurethane fiber, and ethylene-vinyl alcohol copolymer fiber.

13. The heat transfer suppression sheet according to any one of claims 1 to 12, characterized in that the first inorganic particles consist of at least one selected from oxide particles, carbide particles, nitride particles, and inorganic hydrate particles.

14. The first inorganic fiber is SiO ２ A heat transfer suppression sheet according to any one of claims 1 to 13, characterized in that the second inorganic fiber is a fiber comprising at least one selected from glass fiber, silica fiber, alumina fiber, alumina silicate fiber, zirconia fiber, glass wool, carbon fiber, soluble fiber, refractory ceramic fiber, aerogel composite material, magnesium silicate fiber, alkali earth silicate fiber, zirconia fiber, potassium titanate fiber, and mineral fiber.

15. Furthermore, the heat transfer suppression sheet according to any one of claims 1 to 14 is characterized by containing a second inorganic particle made of a metal oxide.

16. A method for manufacturing a heat transfer suppression sheet according to any one of claims 1 to 15, A step of obtaining a dispersion containing the first inorganic particles, the resin binder, and the organic fibers, The process involves removing the dispersion to obtain a wet sheet, The process includes heating the wet sheet and then cooling it, A method for manufacturing a heat transfer suppression sheet, characterized in that the heating temperature for heating the wet sheet is set to be 10°C or more and 50°C or less higher than the glass transition temperature of the organic fiber.

17. The method for producing a heat transfer suppression sheet according to claim 16, characterized in that the dispersion is an emulsion obtained by dispersing the resin binder in water.

18. A battery pack comprising a plurality of battery cells and a heat transfer suppression sheet according to any one of claims 1 to 15, wherein the plurality of battery cells are connected in series or in parallel.

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