Heat transfer suppression sheet and battery pack

Abstract

To provide: a heat transfer suppression sheet capable of maintaining the shape thereof even in cases where the heat transfer suppression sheet is exposed to high temperatures, thereby being capable of suppressing a decrease in the heat insulation performance; and a battery pack which comprises the heat transfer suppression sheet.SOLUTION: A heat transfer suppression sheet 10 contains: first organic fibers 1 that do not have a glass transition temperature at a temperature lower than 120°C; first inorganic particles 2; and a resin binder 9. The first organic fibers 1 have a melting point Tm at a temperature equal to or higher than 200°C. Preferably, the elastic modulus of the first organic fibers 1 at Tm°C is 0.1% or more of the elastic modulus of the first organic fibers 1 at 23°C.SELECTED DRAWING: Figure 1

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 parallel to serve as a power source for the drive electric motor.

[0003] Further, for this battery cell, a lithium-ion secondary battery capable of high capacity and high output is mainly used as compared with a lead storage battery, a nickel-hydrogen battery, etc. And when a certain battery cell causes thermal runaway such that it rapidly heats up due to internal short circuit or overcharging of the battery and continues to generate heat thereafter, the heat from the battery cell that has caused thermal runaway may be propagated to other adjacent battery cells, causing thermal runaway of the other battery cells.

[0004] As a method for suppressing the propagation of heat from a battery cell that has caused thermal runaway as described above, a method of interposing a heat insulating sheet between battery cells is generally performed. 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 made of a metal oxide, and limits the content of the first particles. Further, Patent Document 1 describes that the heat insulating sheet may include a binder made of at least one selected from fibers, binders, and heat-resistant resins.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[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 become hotter. 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 insulating sheet is exposed to high temperatures due to a malfunction in the battery cells, it may not be able to maintain the overall strength of the insulating sheet, the insulating performance will decrease, and this may 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, 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] A first organic fiber that does not have a glass transition temperature at temperatures below 120°C, The first inorganic particle, A heat transfer suppression sheet characterized by comprising a resin binder.

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

[16] .

[0011] [2] The heat transfer suppression sheet according to [1], characterized in that the first organic fiber is at least one of a crystalline organic fiber having a glass transition temperature of 120°C or higher and an organic fiber not having a glass transition temperature.

[0012] [3] The first organic fiber has a melting point Tm at a temperature of 200 or higher, The heat transfer suppression sheet according to [1] or [2], characterized in that the modulus of elasticity of the first organic fiber at Tm°C is 0.1% or more relative to the modulus of elasticity of the first organic fiber at 23°C.

[0013] [4] The heat transfer suppression sheet according to any one of [1] to [3], characterized in that the first organic fiber is at least one selected from polyethylene terephthalate fiber, polybutylene terephthalate fiber, polytrimethylene terephthalate fiber, polyacetal fiber, polytetrafluoroethylene fiber, polyether ether ketone fiber, polyphenylene sulfide fiber, polyamide fiber, and polyparaphenylphthalamide fiber.

[0014] [5] The heat transfer suppression sheet according to any one of [1] to [4], characterized in that the content of the first organic fiber is 1% by mass or more and 10% by mass or less with respect to the total mass of the heat transfer suppression sheet.

[0015] [6] Furthermore, it has a second organic fiber having a glass transition temperature, The heat transfer suppression sheet according to any one of [1] to [5], characterized in that, when the first organic fiber has a glass transition temperature, the glass transition temperature of the second organic fiber is higher than the glass transition temperature of the resin binder and lower than the glass transition temperature of the first organic fiber.

[0016] [7] Furthermore, it has a second organic fiber having a glass transition temperature, The heat transfer suppression sheet according to any one of [1] to [5], characterized in that, when the first organic fiber does not have a glass transition temperature, the glass transition temperature of the second organic fiber is higher than the glass transition temperature of the resin binder.

[0017] [8] The heat transfer suppression sheet according to [6] or [7], characterized in that the glass transition temperature of the second organic fiber is 250°C or lower.

[0018] [9] The second organic fiber contains at least one selected from polyvinyl alcohol fiber, polyethylene fiber, nylon fiber, polyurethane fiber, and ethylene-vinyl alcohol copolymer fiber, and is the heat transfer suppression sheet according to any one of [6] to [8].

[0019]

[10] The first inorganic particle is a particle composed of at least one inorganic material selected from oxide particles, carbide particles, nitride particles, and inorganic hydrate particles, and is the heat transfer suppression sheet according to any one of [1] to [9].

[0020]

[11] Further, it has a first inorganic fiber and a second inorganic fiber in which at least one property selected from average fiber diameter, shape, and glass transition point is different from each other, and is the heat transfer suppression sheet according to any one of [1] to

[10] .

[0021]

[12] 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

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

[0022]

[13] 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

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

[0023]

[14] The first inorganic particle contains 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

[11] , 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.

[0024]

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

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

[0025]

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

[15] , characterized in that the resin binder comprises at least one selected from styrene-butadiene resin, acrylic resin, silicone-acrylic resin, and styrene resin.

[0026] Furthermore, the above-mentioned objective of the present invention is achieved by the following configuration of the battery pack

[17] .

[0027]

[17] A battery pack comprising a plurality of battery cells and a heat transfer suppression sheet described in any one of [1] to

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

[0028] According to the heat transfer suppression sheet of the present invention, even when the heat transfer suppression sheet is exposed to high temperatures, it is possible to achieve both excellent compression characteristics and heat transfer suppression effect, thereby suppressing a decrease in thermal insulation performance.

[0029] According to the battery pack of the present invention, since it has a heat transfer suppression sheet that has excellent compression characteristics and a heat transfer suppression effect as described above, it is possible to suppress thermal runaway of battery cells in the battery pack. [Brief explanation of the drawing]

[0030] [Figure 1] Figure 1 is a schematic diagram showing the structure of a heat transfer suppression sheet according to the first embodiment of the present invention. [Figure 2]Figure 2 is a schematic diagram showing a battery pack according to an embodiment of the present invention. [Figure 3] Figure 3 is a schematic diagram showing the structure of a heat transfer suppression sheet according to a second embodiment of the present invention. [Figure 4] Figures 4(a) to 4(c) are schematic diagrams showing, in order of steps, a method for manufacturing a heat transfer suppression sheet according to an embodiment of the present invention. [Modes for carrying out the invention]

[0031] 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 comprising inorganic particles, a resin binder, and a first organic fiber that does not have a glass transition temperature at temperatures below 120°C, can maintain its shape even when exposed to high temperatures, and as a result, can maintain excellent thermal insulation performance.

[0032] First, the structure of the heat transfer suppression sheet according to an embodiment of the present invention will be described in detail with reference to the drawings. Note that the embodiments shown in the drawings are schematic for the purpose of clearly illustrating the present invention and do not necessarily accurately represent the actual size or scale. Furthermore, 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.

[0033] [1. Heat transfer suppression sheet] <1-1. Configuration of the heat transfer suppression sheet> Figure 1 is a schematic diagram showing the configuration of a heat transfer suppression sheet according to the first embodiment of the present invention. Figure 2 is a schematic diagram showing a battery pack according to an embodiment of the present invention. As shown in Figure 1, the heat transfer suppression sheet 10 according to the first embodiment comprises a first organic fiber 1, a first inorganic particle 2, and a resin binder 9. In addition, although not essential materials in the present invention, this embodiment further comprises a second inorganic particle 3 and a second organic fiber 4. The first organic fiber 1 is an organic fiber that does not have a glass transition temperature at temperatures below 120°C, for example, a crystalline polyethylene terephthalate (PET) fiber. The second organic fiber 4 is an organic fiber that has a glass transition temperature higher than the glass transition temperature of the resin binder, for example, a polyvinyl alcohol (PVA) fiber. Furthermore, the first inorganic particle 2 is, for example, silica nanoparticles, and the second inorganic particle is, for example, titania. The first organic fiber 1, the first inorganic particle 2, the second inorganic particle 3, and the second organic fiber 4 are held together in a sheet shape by the resin binder 9.

[0034] A specific example of using the heat transfer suppression sheet 10 is to interpose it between multiple battery cells 101, as shown in Figure 2. The multiple battery cells 101 are then connected in series or parallel (the connected state is not shown in the figure) and housed in a battery case 110 to form a battery pack 100. While lithium-ion secondary batteries are preferably used as the battery cells 101, the sheet is not limited to these and can be applied to other types of secondary batteries as well.

[0035] In the heat transfer suppression sheet 10 configured in this way, both the first inorganic particles 2 and the second inorganic particles 3 are made of heat-resistant material. Furthermore, countless minute spaces are formed between the particles, between the particles and fibers, and between the fibers, and an insulating effect due to air is also achieved, thus providing excellent heat transfer suppression performance. Furthermore, the heat transfer suppression sheet 10 contains a first organic fiber 1 that does not have a glass transition temperature at temperatures below 120°C. The fact that the first organic fiber 1 does not have a glass transition temperature at temperatures below 120°C means that the first organic fiber 1 does not soften in the temperature range from room temperature to below 120°C. Even if an abnormality occurs in the battery cell 101 and the temperature rises to such a high level that the second organic fiber 4 softens, the first organic fiber 1 acts as a framework, maintaining the strength of the heat transfer suppression sheet and supporting the sheet shape. Therefore, it is possible to reduce the thickness of the heat transfer suppression sheet and suppress the decrease in thermal insulation performance due to the reduction of the minute spaces mentioned above.

[0036] Furthermore, by including a first organic fiber 1 that does not have a glass transition temperature at temperatures below 120°C, the first organic fiber 1 acts as the backbone of the heat transfer suppression sheet even at room temperature. Therefore, the flexibility and handling of the heat transfer suppression sheet can be improved.

[0037] Furthermore, the heat transfer suppression sheet 10 according to this embodiment also contains a second organic fiber 4 having a glass transition temperature higher than that of the resin binder. When heated in the manufacturing process described later, at least a portion of the surface of the second organic fiber 4 melts. Therefore, upon subsequent cooling, the second organic fibers 4 fuse together, and the first organic fiber 1, the first inorganic particles 2, and the second inorganic particles 3 fuse to the second organic fibers 4, forming an even stronger, three-dimensional skeleton. Thus, due to the synergistic effect of the first organic fiber 1 and the second organic fiber 4, a heat transfer suppression sheet 10 with extremely excellent shape retention can be obtained.

[0038] Furthermore, the heat transfer suppression sheet 10 according to this embodiment includes first inorganic particles 2 made of silica nanoparticles and second inorganic particles 3 made of a metal oxide such as titania. Silica nanoparticles have excellent heat insulation properties, suppressing conductive heat transfer due to their low density and further suppressing convective heat transfer due to their finely dispersed voids. Therefore, when using a battery at normal room temperature, it is possible to suppress heat conduction between adjacent silica nanoparticles. Furthermore, the second inorganic particles 3, which are made of metal oxides, have a high refractive index and a high effect of diffusely reflecting light, so they can suppress radiative heat transfer, especially in high-temperature regions such as abnormal heat generation. Therefore, when these first inorganic particles 2 and second inorganic particles 3 are included in the heat transfer suppression sheet 10, excellent heat insulation can be obtained over a wide temperature range from the temperature during normal battery use to high temperatures of 500°C or higher.

[0039] In the first embodiment described above, an example was shown in which, in addition to the first organic fiber 1, the first inorganic particle 2, and the resin binder 9, the heat transfer suppression sheet 10 also includes a second organic fiber 4 and a second inorganic particle 3. However, the present invention is not limited to such a configuration. As stated above, it is sufficient for the heat transfer suppression sheet 10 to include at least one type of inorganic particle, the specific organic fiber described above, and the resin binder, but it is preferable, for example, for the heat transfer suppression sheet 10 to include two different types of inorganic fibers.

[0040] As described above, if the heat transfer suppression sheet 10 contains a predetermined organic fiber, it can maintain its shape even when exposed to high temperatures. Furthermore, even if the temperature rises to the point where the organic fiber contained in the heat transfer suppression sheet 10 burns, the organic fiber will not burn completely but will partially remain, and the remaining organic fiber will maintain the strength of the heat transfer suppression sheet 10.

[0041] Furthermore, as shown below, if the heat transfer suppression sheet 10 contains inorganic fibers, even if some organic fibers burn, they can maintain their shape as inorganic fibers, thereby further increasing the high-temperature strength of the heat transfer suppression sheet 10. In particular, if two or more inorganic fibers having different properties are included, the retention of inorganic particles can also be improved. An example in which the heat transfer suppression sheet 10 contains a first inorganic fiber and a second inorganic fiber having different properties will be described below.

[0042] Figure 3 is a schematic diagram 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 3, the same reference numerals are used for parts identical to those in the first embodiment shown in Figure 1, and their detailed descriptions are omitted. Furthermore, since the heat transfer suppression sheet according to the second embodiment can be used in the battery pack shown in Figure 2, similar to the first embodiment, the effects and other aspects will be described below assuming that the heat transfer suppression sheet 20 according to the second embodiment is interposed between a plurality of battery cells 101.

[0043] As shown in Figure 3, the heat transfer suppression sheet 20 according to the second embodiment contains a first organic fiber 1 and a first inorganic particle 2, and further contains a first inorganic fiber 5 and a second inorganic fiber 6, which are held together by a resin binder 9. The first inorganic fiber 5 and the second inorganic fiber 6 are fibers that differ from each other in at least one property selected from average fiber diameter, shape, and glass transition temperature. For example, the average fiber diameter of the first inorganic fiber 5 is larger than the average fiber diameter of the second inorganic fiber 6, the first inorganic fiber 5 is linear or needle-shaped, and the second inorganic fiber 6 is dendritic or curly.

[0044] In the second embodiment configured in this way, similar to the first embodiment, the first organic fiber 1 is included, so even when the temperature of the battery cell 101 rises, the first organic fiber 1 acts as a framework and can support the sheet shape of the heat transfer suppression sheet. Furthermore, since the heat transfer suppression sheet 20 contains first inorganic particles 2 made of silica nanoparticles, conductive and convective heat transfer can be suppressed, and excellent heat insulation can be obtained.

[0045] Furthermore, in the heat transfer suppression sheet 20, the small-diameter, dendritic or crimped second inorganic fibers 6 are intertwined with the first inorganic particles 2 and the large-diameter first inorganic fibers 5, thus enabling good retention of the inorganic particles. Furthermore, since the first inorganic fiber 5 and the second inorganic fiber 6 do not melt even at the temperature during thermal runaway of the battery cell, the heat transfer suppression sheet 20 can maintain its shape and heat insulation effect even when exposed to high temperatures.

[0046] Furthermore, the properties that can be selected as two different types of inorganic fibers are not limited to those described above. As the first inorganic fiber 5, an amorphous inorganic fiber having an average fiber diameter larger than the average fiber diameter of the second inorganic fiber 6 can be used. Also, as the second inorganic fiber 6, at least one inorganic fiber selected from amorphous fibers and crystalline fibers having a higher glass transition temperature than the first inorganic fiber 5 can be used.

[0047] 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 5 is exposed to high temperatures, its surface softens before that of the second inorganic fiber 6, binding the first inorganic particles 2, the first organic fiber 1, and the second inorganic fiber 6 together, thereby improving the mechanical strength of the heat transfer suppression sheet 20. Furthermore, if the second inorganic fiber 6 is made of crystalline fibers or has a higher glass transition temperature than the first inorganic fiber 5, then even if the first inorganic fiber 5 softens when exposed to high temperatures, the second inorganic fiber 6 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.

[0048] Furthermore, the first inorganic fibers 5, which have a larger average fiber diameter (larger diameter), have the effect of improving the mechanical strength and shape retention of the heat transfer suppression sheet 20. By making the first inorganic fibers 5 larger in diameter, only the surface can be softened when exposed to high temperatures, thereby further enhancing the binding effect between the first inorganic particles 2, the first organic fibers 1, and the second inorganic fibers 6.

[0049] Furthermore, it is preferable that the first inorganic particle 2 includes at least one selected from nanoparticles, hollow particles, and porous particles, and that, among two different types of inorganic fibers, the first inorganic fiber 5 is amorphous, and the second inorganic fiber is at least one selected from amorphous fibers and crystalline fibers, which have a higher glass transition temperature than the first inorganic fiber.

[0050] <1-2. 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.

[0051] [2. Method for manufacturing a heat transfer suppression sheet] Next, as an example of a heat transfer suppression sheet manufacturing method, the manufacturing method and conditions for the heat transfer suppression sheet according to the second embodiment of the present invention will be described in detail.

[0052] <2-1. Method for manufacturing a heat transfer suppression sheet> Figures 4(a) to 4(c) are schematic diagrams showing the structure of the heat transfer suppression sheet according to the second embodiment of the present invention in order of the manufacturing process. Note that in Figures 4(a) to 4(c), the second inorganic particle 3 shown in Figure 1 is omitted from the description. As shown in Figure 4(a), a first organic fiber 1, a first inorganic particle 2, an emulsion 7 obtained by dispersing a resin binder in water, and a second organic fiber 4 having a higher glass transition temperature than the resin binder are prepared, and a dispersion 8 is obtained by mixing and stirring these together. Next, a wet sheet is prepared by dehydrating (removing the liquid from) the dispersion 8.

[0053] Next, the wet sheet is heated. As shown in Figure 4(b), as the temperature rises, the water in the emulsion 7 evaporates, and molten resin binder 13 is obtained. Further heating of the sheet causes at least a portion of the surface of the second organic fiber 4 to melt. Subsequently, by cooling the sheet, the second organic fibers 4 fuse together to form a fused portion 12, as shown in Figure 4(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.

[0054] In the heat transfer suppression sheet according to the second embodiment, manufactured by the manufacturing method described above, an emulsion 7 containing a resin binder is used, so the entire material is uniformly dispersed, and the first organic fibers 1 and the second organic fibers 4 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 second organic fiber 4, which has a high glass transition temperature, melts.

[0055] Furthermore, during the cooling process of the heated sheet, the molten surface portion of the second organic fiber 4 solidifies first, and fused portions 12 are formed at the points where the second organic fibers 4 are in contact with each other. As described above, the first organic fiber 1 and the second organic fiber 4 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 second organic fiber 4 melts, when it is cooled to a temperature lower than the glass transition temperature of the second organic fiber 4, at least a portion of the second organic fiber 4 fuses together with each other, and a three-dimensional skeleton 11 is formed. As a result, the obtained skeleton 11 maintains the shape of the entire heat transfer suppression sheet. Furthermore, as cooling occurs, the first organic fiber 1, the first inorganic particles 2, and the second inorganic particles (not shown) that were in contact with the surface of the second organic fiber 4 become fixed to the surface of the second organic fiber 4, making the framework 11 even stronger.

[0056] 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 11, and also solidifies between the first organic fibers 1, the first inorganic particles 2, the second inorganic particles, and between each fiber and each particle. As a result, the first organic fibers 1, the first inorganic particles 2, and the second inorganic particles adhere to the skeleton 11, and the skeleton 11 is further reinforced by the solidified resin binder 9. By manufacturing in this manner, the heat transfer suppression sheet according to this embodiment has a strong framework 11. Furthermore, in this embodiment, since the first organic fibers 1, which do not have a glass transition temperature at temperatures below 120°C, are present in the heat transfer suppression sheet in an irregular direction, even if the second organic fibers 4 soften when exposed to high temperatures during use, the shape and strength can be maintained, and a decrease in thermal insulation performance can be suppressed.

[0057] In this embodiment, the materials used are a first organic fiber 1, a first inorganic particle 2, a second inorganic particle (not shown), an emulsion 7 containing a resin binder, and a second organic fiber 4 having a higher glass transition temperature than the resin binder. However, the second inorganic particle and the second organic fiber 4 are not necessarily required. For example, as shown in the second embodiment described above, the first inorganic fiber and the second inorganic fiber may be included, or the second inorganic particle, the second organic fiber 4, the first inorganic fiber, and the second inorganic fiber may all be included. Furthermore, the emulsion 7 containing the resin binder does not necessarily have to be in the form of an emulsion; it is sufficient that the resin binder is uniformly dispersed in the liquid by some method, and it is more preferable that all materials are uniformly dispersed in the dispersion. Therefore, the first organic fiber 1, the first inorganic particle 2, the second inorganic particle, the resin binder, the second organic fiber 4, and the liquid for making the dispersion can be mixed and dispersed. Furthermore, from the viewpoint of reducing environmental impact, it is preferable to use water as the liquid for dispersing the resin binder.

[0058] Next, the conditions for the manufacturing method of the heat transfer suppression sheet according to this embodiment will be described.

[0059] <2-2. Heating temperature of the wet sheet> In the process of heating the wet sheet described above, the heating temperature shall be set to be higher than the glass transition temperature of the second organic fiber 4, within a range of 10°C to 50°C. That is, when the heating temperature of the wet sheet is t (°C) and the glass transition point of the second organic fiber 4 is Tg (°C), if the relationship t < Tg + 10 holds, the melting on the surface of the second organic fiber 4 becomes insufficient, and the adhesive force between the second organic fibers 4 becomes weak, so that a strong skeleton cannot be formed. On the other hand, if the relationship t < Tg + 50 holds, only the surface of the second organic fiber 4 melts due to heating, and a shape as a skeleton can be formed. However, even if t ≥ Tg + 50, the melted second organic fiber 4 melts on the surface of the first organic fiber 1, and a strong skeleton by the first organic fiber 1 can be formed. Therefore, the heating temperature t of the wet sheet is preferably Tg + 10 (°C) or higher, and more preferably Tg + 15 (°C) or higher. Also, the heating temperature t of the wet sheet is preferably Tg + 50 (°C) or lower, and more preferably Tg + 30 (°C) or lower.

[0060] [3. Materials Constituting the Heat Transfer Suppression Sheet and Their Contents] Next, the first organic fiber 1, the second organic fiber 4, the first inorganic particles 2, the second inorganic particles 3, the first inorganic fiber 5, the second inorganic fiber 6, and the resin binder 9 that constitute the heat transfer suppression sheet according to the above first and second embodiments will be described in detail below.

[0061] <3-1. First Organic Fiber> As described above, the first organic fiber 1 preferably has no glass transition point at a temperature below 120 °C. That is, the first organic fiber 1 is preferably at least one of a crystalline organic fiber having a glass transition point of 120 °C or higher and an organic fiber having no glass transition point. By including such a first organic fiber 1 in the heat transfer suppression sheet, even when an abnormality occurs in the heat transfer suppression sheet, the sheet shape can be maintained.

[0062] Organic fibers that do not have a glass transition temperature exhibit a behavior where, when their mechanical behavior is represented graphically using elastic modulus and strength, the elastic modulus gradually decreases as the temperature rises from room temperature to the melting point Tm, and then drops sharply at the melting point Tm. Specifically, the crystals are tightly aligned, and the crystals do not move easily even when the temperature is raised near the melting point Tm.

[0063] This condition can be expressed by the following equation relating to the modulus of elasticity. When the first organic fiber 1 has a melting point Tm at a temperature of 200°C or higher, it is preferable that the ratio of the elastic modulus G1 of the first organic fiber at Tm°C to the elastic modulus G0 of the first organic fiber at 23°C, i.e., (G1 / G0) × 100, is 0.1% or higher. If (G1 / G0) × 100 is less than 0.1%, when the temperature is raised from 23°C, the modulus of elasticity will decrease significantly before reaching the melting point Tm, making it difficult to fully obtain the effect of maintaining the shape of the heat transfer suppression sheet.

[0064] For example, when the percentage of the elastic modulus was investigated for crystalline polyethylene terephthalate fiber (PET fiber), the elastic modulus G0 at room temperature (23°C) is 50,000 MPa, and the elastic modulus G1 at the melting point Tm (approximately 230°C) is 200 MPa, so (G1 / G0) × 100 = 0.4 (%). (See "Temperature Dependence of Elastic Modulus of SPS Biaxially Oriented Film": idemitsu.com, SPS Biaxially Oriented Film - Film Characteristics - Temperature Dependence of Elastic Modulus of SPS Biaxially Oriented Film, Idemitsu Kosan Co., Ltd., [online], [Accessed December 21, 2021], Internet)<URL:https: / / www.idemitsu.com / jp / business / ipc / products / sps / oshidashi / nizikuenshin_2.html> )

[0065] Specifically, it is preferable to select at least one of the following as the first organic fiber 1: polyethylene terephthalate fiber, polybutylene terephthalate fiber, polytrimethylene terephthalate fiber, polyacetal fiber, polytetrafluoroethylene fiber, polyetheretherketone fiber, polyphenylene sulfide fiber, polyamide fiber, and polyparaphenylphthalamide fiber.

[0066] (3-1-1. Content of the first type of organic fiber) If the content of the first organic fiber 1 is too low, it may not be possible to obtain sufficient effect in maintaining the shape of the heat transfer suppression sheet. On the other hand, if the content of the first organic fiber 1 is too high, the content of other essential components, namely the first inorganic particles 2 and the resin binder 9, will decrease, making it difficult to obtain the desired heat insulation effect and the effect of the resin binder 9 in maintaining the shape of the first inorganic particles 2, etc. Therefore, it is preferable that the content of the first organic fiber 1 be between 1% by mass and 10% by mass relative to the total mass of the heat transfer suppression sheet.

[0067] (3-1-2. Average fiber length of the first organic fiber) The fiber length of the first organic fiber 1 is not particularly limited, but from the viewpoint of ensuring moldability and processability, it is preferable that the average fiber length of the first organic fiber 1 be 10 mm or less. On the other hand, from the viewpoint of allowing the first 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 first organic fiber 1 be 0.5 mm or more.

[0068] <3-2. Second Organic Fiber> In this embodiment, the second organic fiber 4 that can be used has a glass transition temperature, and that is higher than the glass transition temperature of the resin binder 9. For example, an organic fiber containing at least one selected from polyvinyl alcohol (PVA) fiber, polyethylene fiber, nylon fiber, polyurethane fiber, and ethylene-vinyl alcohol copolymer fiber can be used.

[0069] Furthermore, if the first organic fiber 1 has a glass transition temperature, the second organic fiber 4 having a glass transition temperature can be one that is higher than the glass transition temperature of the resin binder 9 and lower than the glass transition temperature of the first organic fiber 1. Furthermore, if the first organic fiber 1 does not have a glass transition temperature, the second organic fiber 4 having a glass transition temperature can be one that has a higher glass transition temperature than the resin binder 9. 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 second organic fiber 4 is preferably 250°C or lower, and more preferably 200°C or lower.

[0070] The lower limit of the glass transition temperature of the second organic fiber 4 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 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 second organic fiber 4 is preferably 10°C or more, and more preferably 30°C or more. On the other hand, if the difference in glass transition temperatures between the second organic fiber 4 and the resin binder 9 is 130°C or less, the time from when the second organic fiber 4 is completely solidified until the resin binder begins to solidify can be appropriately adjusted, and the resin binder solidifies while remaining in a good dispersion state, thereby further enhancing the reinforcing effect of the skeleton 11. Therefore, the difference between the glass transition temperature of the resin binder 9 and the glass transition temperature of the second organic fiber 4 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.

[0071] In the first embodiment described above, the material contains two types of organic fibers: a first organic fiber 1 and a second organic fiber 4. When the first organic fiber 1 has a glass transition temperature, it is preferable that the glass transition temperature of the first organic fiber 1 is 10°C or more higher than that of the second organic fiber 4, and more preferably 20°C or more higher. In addition, other organic fibers may be included as needed.

[0072] (3-2-1. Total content of the first and second organic fibers) In this embodiment, if the content of the first organic fiber 1 and the second organic fiber 4 is appropriately controlled, the function of the organic fibers as a skeleton can be fully obtained. When the second organic fiber 4 and other organic fibers are included in addition to the first organic fiber 1, the total content of all organic fibers 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.

[0073] (3-2-2. Average fiber length of the second organic fiber) The fiber length of the second organic fiber 4 is not particularly limited, but from the viewpoint of ensuring moldability and processability, it is preferable that the average fiber length of the second organic fiber 4 be 10 mm or less. On the other hand, similar to the first organic fiber 1, it is preferable that the average fiber length of the second organic fiber 4 be 0.5 mm or more, from the viewpoint of ensuring the compressive strength of the heat transfer suppression sheet by allowing the second organic fiber 4 to function as a skeleton.

[0074] (3-2-3. Dissolution temperatures in water of the first and second organic fibers) As described above, in this embodiment, it is preferable to use water as the liquid for dispersing the resin binder. Therefore, when using water as the dispersion liquid, it is preferable to use organic fibers with low solubility in water as the first organic fiber and the second organic fiber. 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 first organic fiber and the second organic fiber is preferably 60°C or higher, more preferably 70°C or higher, and even more preferably 80°C or higher.

[0075] <3-3. Resin Binder> As the resin binder 9 that can be used in this embodiment, for example, when the heat transfer suppression sheet 10 contains the second organic fiber 4, a resin binder 9 having a glass transition temperature lower than that of the second organic fiber 4 can be used. 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.

[0076] (3-3-1. Resin binder content) In this embodiment, if the content of the resin binder 9 is appropriately controlled, the reinforcing effect of the organic fiber 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. Furthermore, it is preferably 20% by mass or less, and more preferably 10% by mass or less.

[0077] Furthermore, in the heat transfer suppression sheet according to this embodiment, even if the total content of the first organic fiber 1 and other organic fibers and the 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.

[0078] <3-4. Inorganic particles> As inorganic particles, a single inorganic particle may be used, or a combination of two or more inorganic particles (first inorganic particle 2 and second inorganic particle 3) 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 as the first inorganic particle 2 and second inorganic particle 3, and it is more preferable to use oxide particles. Furthermore, there are no particular limitations on the shape of the first inorganic particle 2 and second inorganic particle 3, 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. Hereinafter, inorganic particles will be described in more detail, with small-diameter inorganic particles referred to as the first inorganic particle 2 and large-diameter inorganic particles referred to as the second inorganic particle 3.

[0079] Furthermore, by using two or more inorganic particles with different heat transfer suppression effects in combination, the heat-generating element can be cooled in multiple stages, and the endothermic effect can be exhibited over a wider temperature range. Therefore, when nanoparticles are used as the first inorganic particle 2, it is preferable to include the second inorganic particle 3, which consists of a metal oxide and will be described later, as the other inorganic particle.

[0080] Next, an example of the material or shape of particles that can be used as the first inorganic particle 2 will be described in detail below.

[0081] <3-4-1. 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 inorganic particles can suppress radiative heat transfer, especially in high-temperature regions such as those associated with 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.

[0082] (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. 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.

[0083] (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 a low density, they suppress conductive heat transfer, and when nanoparticles are used as inorganic particles, 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.

[0084] 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.

[0085] Furthermore, in this invention, when using nanoparticles as 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 Therefore, even if, for example, battery cells placed 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 thermal insulation properties can be maintained. For this reason, it is preferable to use silica nanoparticles. As silica nanoparticles, wet silica, dry silica, aerogel, etc., can be used.

[0086] (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.

[0087] (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).

[0088] 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

[0089] 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.

[0090] (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 2, if their average particle size is too large, it may take a certain amount of time for the first inorganic particles 2 (inorganic hydrates) near the center of the heat transfer suppression sheet 10 to reach their thermal decomposition temperature, and the first inorganic particles 2 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.

[0091] (Particles made of thermally expandable inorganic material) Examples of thermally expandable inorganic materials include vermiculite, bentonite, mica, and perlite.

[0092] (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.

[0093] (Inorganic balloon) The thermal insulation material used in the present invention may contain inorganic balloons as 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.

[0094] (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.

[0095] (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.

[0096] <3-4-2. The second inorganic particle> When the heat transfer suppression sheet contains two types of inorganic particles, the second inorganic particle 3 is not particularly limited as long as it differs from the first inorganic particle 2 in material, particle size, etc. As the second inorganic particle 3, 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.

[0097] 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 2, it is preferable to further include particles made of metal oxides, which are larger in diameter than the first inorganic particles 2, as the second inorganic particles 3 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.

[0098] (Average primary particle diameter of the second inorganic particle) When a second inorganic particle 3 made of a metal oxide is included in the heat transfer suppression sheet, if the average primary particle diameter of the second inorganic particle 3 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 3 is 5 μm or more and 30 μm or less, and most preferably 10 μm or less.

[0099] <3-5. First Inorganic Fiber and Second Inorganic Fiber> In this embodiment, the heat transfer suppression sheet preferably has a first inorganic fiber 5 and a second inorganic fiber 6 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 and inorganic particle retention of the heat transfer suppression sheet can be improved.

[0100] (3-5-1. Two types of inorganic fibers with different average fiber diameters and fiber shapes) When a heat transfer suppression sheet contains two types of inorganic fibers, it is preferable that the average fiber diameter of the first inorganic fiber 5 is greater than the average fiber diameter of the second inorganic fiber 6, that the first inorganic fiber 5 is linear or needle-shaped, and that the second inorganic fiber 6 is dendritic or crimped. The first inorganic fiber 5, 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 5, larger in diameter than the second inorganic fiber 6. Since the heat transfer suppression sheet may be subjected to external impacts, the inclusion of the first inorganic fiber 5 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 5 is linear or needle-shaped. Linear or needle-shaped fibers refer to fibers whose crimping degree, as described later, is, for example, less than 10%, preferably 5% or less.

[0101] 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 5 is preferably 1 μm or more, and more preferably 3 μm or more. If the first inorganic fiber 5 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 5 is preferably 20 μm or less, and more preferably 15 μm or less. Furthermore, since excessive length of the first inorganic fiber 5 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 5 may reduce shape retention and mechanical strength, it is preferable to keep the fiber length 0.1 mm or more.

[0102] On the other hand, the second inorganic fiber 6, which has a smaller average fiber diameter (small diameter), improves the retention of the first organic fiber 1 and the first inorganic particle 2, and also enhances the flexibility of the heat transfer suppression sheet. Therefore, it is preferable to make the second inorganic fiber 6 smaller in diameter than the first inorganic fiber 5.

[0103] More specifically, in order to improve the retention of the first organic fiber 1 and the first inorganic particle 2, it is preferable that the second inorganic fiber 6 is easily deformable and flexible. Therefore, the second inorganic fiber 6, which is small in diameter, preferably has an average fiber diameter of less than 1 μm, and more preferably 0.1 μm or less. However, if the small-diameter inorganic fiber is too thin, it is prone to breakage, and the retention ability of the first organic fiber 1 and the first inorganic particle 2 decreases. In addition, a large proportion of the fibers remain entangled in the heat transfer suppression sheet without retaining the first organic fiber 1 and the first inorganic particle 2, resulting in a decrease in the retention ability of the first organic fiber 1 and the first inorganic particle 2, as well as inferior moldability and shape retention. For this reason, the average fiber diameter of the second inorganic fiber 6 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 6 decrease if it becomes too long, it is preferable that the fiber length of the second inorganic fiber 6 be 0.1 mm or less.

[0104] Furthermore, the second inorganic fiber 6 is preferably dendritic or crimped. When the second inorganic fiber 6 has such a shape, it intertwines with the first organic fiber 1 and the first inorganic particles 2 in the heat transfer suppression sheet. As a result, the ability to hold the first organic fiber 1 and the first inorganic particles 2 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 6 is suppressed, thereby improving the mechanical strength to withstand external pressing force and impact in particular.

[0105] 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 6 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.

[0106] 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 6 is preferably 10% or more, and more preferably 30% or more. If the crimp is small, the ability to hold the first organic fiber 1 and the first inorganic particles 2, etc., and the entanglement (network) between the second inorganic fibers 6 and between the first inorganic fibers 5 and the second inorganic fibers 6 becomes difficult to form.

[0107] In the above-described embodiment, as a method to improve the mechanical strength and shape retention of the heat transfer suppression sheet, as well as the retention of the first organic fiber 1 and the first inorganic particles 2, first inorganic fibers 5 and second inorganic fibers 6 having different average fiber diameters and fiber shapes are used. However, the mechanical strength, shape retention, and particle retention of the heat transfer suppression sheet can also be improved by using first inorganic fibers 5 and second inorganic fibers 6 having different glass transition temperatures and average fiber diameters.

[0108] As described above, in this embodiment, it is preferable to use various combinations of inorganic fibers 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 different from those of the second embodiment shown in Figure 3, but for convenience, other embodiments relating to inorganic fibers will be described using Figure 3 in this specification.

[0109] (3-5-2. 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 5 is an amorphous fiber, and the second inorganic fiber 6 is at least one fiber selected from amorphous fibers and crystalline fibers that have a higher glass transition temperature than the first inorganic fiber 5. Furthermore, by using the first inorganic particles 2, 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.

[0110] 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 5 is exposed to high temperatures, its surface softens before the second inorganic fiber 6, binding the first organic fiber 1 and the first inorganic particles 2 to it. Consequently, by incorporating the first inorganic fiber 5 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 5 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.

[0111] As described above, the second inorganic fiber 6 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 5. Many crystalline inorganic fibers can be used as the second inorganic fiber 6. If the second inorganic fiber 6 is made of crystalline fibers or has a higher glass transition temperature than the first inorganic fiber 5, then even if the first inorganic fiber 5 softens when exposed to high temperatures, the second inorganic fiber 6 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 6 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, allowing the insulating effect of air to be exerted and excellent heat transfer suppression performance to be maintained.

[0112] When the second inorganic fiber 6 is crystalline, the second inorganic fiber 6 can be ceramic fibers such as alumina fibers, alumina silicate fibers, and zirconia fibers, silica fibers, glass fibers, glass wool, rock wool, carbon fibers, basalt fibers, soluble fibers, refractory ceramic fibers, aerogel composites, magnesium silicate fibers, alkali earth silicate fibers, zirconia fibers, potassium titanate fibers, wollastonite, and other mineral fibers. Among the fibers listed as the second inorganic fiber 6, if the melting point exceeds 1000°C, the second inorganic fiber 6 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 6 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.

[0113] Furthermore, even if the second inorganic fiber 6 is amorphous, it can be used as long as it has a higher glass transition temperature than the first inorganic fiber 5. For example, a glass fiber with a higher glass transition temperature than the first inorganic fiber 5 may be used as the second inorganic fiber 6. Furthermore, the second inorganic fiber 6 may be any of the various inorganic fibers exemplified, either individually or in a mixture of two or more.

[0114] As described above, the first inorganic fiber 5 has a lower glass transition temperature than the second inorganic fiber 6, and when exposed to high temperatures, the first inorganic fiber 5 softens first, allowing the first inorganic fiber 5 to bind the first organic fiber 1 and the first inorganic particles 2, etc. However, if, for example, the second inorganic fiber 6 is amorphous and its fiber diameter is smaller than that of the first inorganic fiber 5, and the glass transition temperatures of the first inorganic fiber 5 and the second inorganic fiber 6 are close together, the second inorganic fiber 6 may soften first. Therefore, when the second inorganic fiber 6 is an amorphous fiber, the glass transition temperature of the second inorganic fiber 6 is preferably 100°C or more higher than the glass transition temperature of the first inorganic fiber 5, and more preferably 300°C or more higher.

[0115] Furthermore, the fiber length of the first inorganic fiber 5 is preferably 100 mm or less, and preferably 0.1 mm or more. The fiber length of the second inorganic fiber 6 is preferably 0.1 mm or less. The reasons for these preferences are as described above.

[0116] (3-5-3. 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 5 is an amorphous fiber, and the second inorganic fiber 6 is at least one fiber selected from amorphous fibers and crystalline fibers that have a higher glass transition temperature than the first inorganic fiber 5, and that the average fiber diameter of the first inorganic fiber 5 is greater than the average fiber diameter of the second inorganic fiber 6.

[0117] 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 5 is larger than that of the second inorganic fiber 6. Furthermore, it is preferable that the large-diameter first inorganic fiber 5 is amorphous, and the small-diameter second inorganic fiber 6 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 5. As a result, the glass transition point of the first inorganic fiber 5 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 6 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 5, the small-diameter second inorganic fiber 6 remains in its fiber shape even as the temperature rises, thus maintaining the structure of the heat transfer suppression sheet and preventing powder shedding.

[0118] Even in this case, the fiber length of the first inorganic fiber 5 is preferably 100 mm or less, and preferably 0.1 mm or more. The fiber length of the second inorganic fiber 6 is preferably 0.1 mm or less. The reasons for these are as described above.

[0119] Furthermore, the heat transfer suppression sheet according to this embodiment may contain different inorganic fibers in addition to the first inorganic fiber 5 and the second inorganic fiber 6 described above.

[0120] (3-5-4. 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 5 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 6 is preferably 3% by mass or more and 30% by mass or less relative to the total mass of the heat transfer suppression sheet.

[0121] Furthermore, the content of the first inorganic fiber 5 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 6 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 5 and the inorganic particle holding ability of the second inorganic fiber 6 are expressed in a well-balanced manner.

[0122] [4. Battery Packs] Figure 2 is a schematic diagram showing a battery pack according to an embodiment of the present invention. The battery pack 100 according to this embodiment consists of a plurality of battery cells 101 connected in series or in parallel. Furthermore, a heat transfer suppression sheet 10 according to this embodiment is interposed between the battery cells 101. In addition, the battery cells 101 and the heat transfer suppression sheet 10 are housed in a battery case 110. The heat transfer suppression sheet 10 is as described above.

[0123] Thus, when the heat transfer suppression sheet 10 is interposed between each battery cell 101, the heat transfer suppression sheet 10 has the effect of suppressing heat transfer, and can therefore suppress the transfer of heat from a high-temperature battery cell to an adjacent battery cell. 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 101 during charging and discharging. Therefore, it is possible to maintain distance between 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 110 can be reduced.

[0124] It should be noted that the battery pack 100 of this embodiment is not limited to the battery pack illustrated in Figure 2, and the heat transfer suppression sheet 10 can be placed not only between the battery cells 101, but also between the battery cells 101 and the battery case 110.

[0125] 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 110. 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 cell 101 and the battery case 110, there is no need to newly manufacture flame retardant materials, and a safe battery pack 100 can be easily constructed at low cost.

[0126] In the battery pack of this embodiment, the heat transfer suppression sheet 10, which is placed between the battery cell 101 and the battery case 110, 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 cell 101, deformation of the battery cell can be tolerated even if the temperature of one of the battery cells rises and its volume expands.

[0127] 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 is not affected by the shape of the battery cell 101 and the battery case 110, and can be adapted to 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]

[0128] 1. First organic fiber 2. First inorganic particle 3. Second inorganic particle 4. Second Organic Fiber 5. First inorganic fiber 6. Second inorganic fiber 9. Resin Binder 11 Skeleton 10,20 Heat transfer suppression sheet 100 battery packs 101 battery cells 110 Battery Case

Claims

1. A first organic fiber that does not have a glass transition temperature at a temperature of less than 120°C, The first inorganic particle, Includes a resin binder, The first organic fiber has a melting point Tm at a temperature of 200°C or higher. A heat transfer suppression sheet characterized in that the modulus of elasticity of the first organic fiber at Tm°C is 0.1% or more compared to the modulus of elasticity of the first organic fiber at 23°C.

2. A first organic fiber that does not have a glass transition temperature at a temperature of less than 120°C, The first inorganic particle, Includes a resin binder, Furthermore, it has a second organic fiber having a glass transition temperature, A heat transfer suppression sheet characterized in that, when the first organic fiber has a glass transition temperature, the glass transition temperature of the second organic fiber is higher than the glass transition temperature of the resin binder and lower than the glass transition temperature of the first organic fiber.

3. A first organic fiber that does not have a glass transition temperature at a temperature of less than 120°C, The first inorganic particle, Includes a resin binder, Furthermore, it has a second organic fiber having a glass transition temperature, A heat transfer suppression sheet characterized in that, when the first organic fiber does not have a glass transition temperature, the glass transition temperature of the second organic fiber is higher than the glass transition temperature of the resin binder.

4. The heat transfer suppression sheet according to claim 2 or 3, characterized in that the glass transition temperature of the second organic fiber is 250°C or lower.

5. The heat transfer suppression sheet according to any one of claims 2 to 4, characterized in that the second organic fiber comprises at least one selected from polyvinyl alcohol fiber, polyethylene fiber, nylon fiber, polyurethane fiber, and ethylene-vinyl alcohol copolymer fiber.

6. A first organic fiber that does not have a glass transition temperature at a temperature of less than 120°C, The first inorganic particle, Includes a 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.

7. A first organic fiber that does not have a glass transition temperature at a temperature of less than 120°C, The first inorganic particle, Includes a 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.

8. A first organic fiber that does not have a glass transition temperature at a temperature of less than 120°C, The first inorganic particle, Includes a 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 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.

9. The heat transfer suppression sheet according to any one of claims 1 to 8, characterized in that the first organic fiber is at least one of a crystalline organic fiber having a glass transition temperature of 120°C or higher and an organic fiber not having a glass transition temperature.

10. The heat transfer suppression sheet according to any one of claims 1 to 9, characterized in that the first organic fiber is at least one selected from polyethylene terephthalate fiber, polybutylene terephthalate fiber, polytrimethylene terephthalate fiber, polyacetal fiber, polytetrafluoroethylene fiber, polyetheretherketone fiber, polyphenylene sulfide fiber, polyamide fiber, and polyparaphenylphthalamide fiber.

11. The heat transfer suppression sheet according to any one of claims 1 to 10, characterized in that the content of the first organic fiber is 1% by mass or more and 10% by mass or less with respect to the total mass of the heat transfer suppression sheet.

12. The heat transfer suppression sheet according to any one of claims 1 to 11, characterized in that the first inorganic particles are particles made of at least one inorganic material selected from oxide particles, carbide particles, nitride particles, and inorganic hydrate particles.

13. Furthermore, the heat transfer suppression sheet according to any one of claims 1 to 12 is characterized by containing a second inorganic particle made of a metal oxide.

14. The heat transfer suppression sheet according to any one of claims 1 to 13, characterized in that the resin binder comprises at least one selected from styrene-butadiene resin, acrylic resin, silicone-acrylic resin, and styrene resin.

15. A battery pack comprising a plurality of battery cells and a heat transfer suppression sheet according to any one of claims 1 to 14, wherein the plurality of battery cells are connected in series or in parallel.

Images