Heat transfer inhibiting sheet and battery pack

Abstract

Provided is a heat transfer inhibiting sheet and a battery pack having the heat transfer inhibiting sheet, which can maintain its shape even when exposed to high temperatures, thereby inhibiting a decrease in adiabatic performance. The heat transfer inhibiting sheet (10) includes: first organic fibers (1) having no glass transition temperature at a temperature lower than 120°C; first inorganic particles (2); and a resin binder (9). It is preferable that the first organic fibers (1) have a melting point (Tm) at a temperature of 200°C or higher, and that the elastic modulus of the first organic fibers (1) at Tm°C be 0.1% or greater relative to the elastic modulus of the first organic fibers (1) at 23°C.

Description

Technical Field

[0001] This invention relates to a heat transfer suppressor and a battery pack having the heat transfer suppressor. Background Technology

[0002] In recent years, from an environmental protection perspective, the development of electric vehicles or hybrid vehicles powered by electric motors has become increasingly popular. These electric vehicles or hybrid vehicles are equipped with battery packs consisting of multiple battery cells connected in series or parallel to power the electric motors used for driving the motors.

[0003] Furthermore, this battery cell primarily uses lithium-ion rechargeable batteries, which offer higher capacity and output compared to lead-acid and nickel-metal hydride batteries. However, in the event of thermal runaway, such as a battery cell experiencing a rapid temperature rise and continued heating due to an internal short circuit or overcharging, the heat from the thermally runaway cell can propagate to adjacent battery cells, potentially causing thermal runaway in those cells as well.

[0004] As a method to suppress the propagation of heat from battery cells that have experienced thermal runaway as described above, a common practice is to sandwich insulating sheets between the battery cells.

[0005] For example, Patent Document 1 discloses a heat insulation sheet for a battery pack, which comprises a first particle composed of silica nanoparticles and a second particle composed of metal oxides, and specifies the content of the first particle. Furthermore, Patent Document 1 describes that the heat insulation sheet may comprise a bonding material composed of at least one selected from fibers, adhesives, and heat-resistant resins.

[0006] Existing technical documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2021-34278 Summary of the Invention

[0008] The problem that the invention aims to solve

[0009] However, in battery pack insulation sheets, it is required that they maintain their shape and remain between battery cells even when the cell temperature is higher. In particular, in recent years, the capacity of battery cells in battery packs has further increased, thus increasing the expansion rate during charging and discharging. Therefore, when the insulation sheet is exposed to high temperatures due to abnormalities in the battery cells, it is impossible to maintain the overall strength of the insulation sheet, resulting in reduced insulation performance and sometimes causing thermal cascading.

[0010] The insulation sheet described in the aforementioned patent document 1 maintains excellent insulation properties even under increased compressive stress, but requires further improvements related to strength.

[0011] The present invention was made in view of the above-mentioned problems, and its object is to provide a heat transfer suppressor sheet that can maintain its shape even when exposed to high temperature, thereby suppressing the reduction of thermal insulation performance, and a battery pack having the heat transfer suppressor sheet.

[0012] Methods for solving problems

[0013] The above-mentioned objective of the present invention is achieved by the following structure of the heat transfer suppression sheet [1].

[0014] Structure [1]. A heat transfer inhibition sheet, characterized in that it comprises:

[0015] The first organic fiber, which does not have a glass transition temperature below 120°C; the first inorganic particles; and the resin adhesive.

[0016] Furthermore, the preferred embodiments of the present invention regarding the heat transfer inhibition sheet are related to the following structures [2] to

[16] .

[0017] The heat transfer suppression sheet of structure [2]. Structure [1] is characterized in that,

[0018] The first organic fiber is at least one of crystalline organic fibers with a glass transition temperature of 120°C or higher and organic fibers without a glass transition temperature.

[0019] The heat transfer suppression sheet of structure [3]. Structure [1] or [2] is characterized in that,

[0020] The first organic fiber has a melting point Tm at temperatures above 200°C.

[0021] The elastic modulus of the first organic fiber at Tm℃ is more than 0.1% relative to the elastic modulus of the first organic fiber at 23℃.

[0022] The heat transfer inhibiting sheet of any one of structures [1] to [3] is characterized in that,

[0023] The first organic fiber is at least one selected from polyethylene terephthalate fiber, polybutylene terephthalate fiber, polypropylene terephthalate fiber, polyacetal fiber, polytetrafluoroethylene fiber, polyetheretherketone fiber, polyphenylene sulfide fiber, polyamide fiber, and poly(p-phenylene terephthalamide) fiber.

[0024] The heat transfer inhibiting sheet of any one of structures [1] to [4] is characterized in that,

[0025] The content of the first organic fiber is more than 1% by mass and less than 10% by mass relative to the total mass of the heat transfer inhibiting sheet.

[0026] The heat transfer inhibiting sheet of any one of structures [1] to [5] is characterized in that,

[0027] The heat transfer inhibition sheet also includes a second organic fiber having a glass transition temperature.

[0028] When the first organic fiber has a glass transition temperature, the glass transition temperature of the second organic fiber is higher than that of the resin adhesive and lower than that of the first organic fiber.

[0029] The heat transfer inhibiting sheet of any one of structures [7]. [1] to [5] is characterized in that,

[0030] The heat transfer inhibition sheet also includes a second organic fiber having a glass transition temperature.

[0031] In the case where the first organic fiber does not have a glass transition temperature, the glass transition temperature of the second organic fiber is higher than that of the resin adhesive.

[0032] The heat transfer inhibiting sheet of structure [8]. Structure [6] or [7] is characterized in that,

[0033] The glass transition temperature of the second organic fiber is below 250°C.

[0034] The heat transfer inhibiting sheet of any one of structures [9]. Structures [6] to [8] is characterized in that,

[0035] 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.

[0036] The heat transfer inhibiting sheet of any one of structures [1] to [9] is characterized in that,

[0037] 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.

[0038] The heat transfer inhibiting sheet of any one of structures [1] to

[10] is characterized in that,

[0039] The heat transfer inhibition sheet further comprises at least one first inorganic fiber and a second inorganic fiber, selected from the average fiber diameter, shape and glass transition temperature, which are different from each other.

[0040] The heat transfer suppression sheet of structure

[12] . Structure

[11] is characterized in that,

[0041] The average fiber diameter of the first inorganic fiber is larger than that of the second inorganic fiber.

[0042] The first inorganic fiber is linear or needle-like, and the second inorganic fiber is dendritic or crimped.

[0043] The heat transfer suppression sheet of structure

[13] . Structure

[11] is characterized in that,

[0044] The first inorganic fiber is an amorphous fiber.

[0045] The second inorganic fiber is at least one type of fiber selected from crystalline fibers and amorphous fibers with a glass transition temperature higher than that of the first inorganic fiber.

[0046] The average fiber diameter of the first inorganic fiber is larger than that of the second inorganic fiber.

[0047] The heat transfer suppression sheet of structure

[14] . Structure

[11] , wherein,

[0048] The first inorganic particle comprises at least one type selected from nanoparticles, hollow particles, and porous particles.

[0049] The first inorganic fiber is an amorphous fiber.

[0050] The second inorganic fiber is at least one inorganic fiber selected from crystalline fibers and amorphous fibers with a glass transition temperature higher than that of the first inorganic fiber.

[0051] The heat transfer inhibiting sheet of any one of structures [1] to

[14] is characterized in that,

[0052] The heat transfer inhibition sheet also contains a second inorganic particle composed of metal oxides.

[0053] The heat transfer inhibiting sheet of any one of structures [1] to

[15] is characterized in that,

[0054] The resin adhesive comprises at least one selected from styrene-butadiene resin, acrylic resin, silicone-acrylic resin and styrene resin.

[0055] Furthermore, the above-mentioned objective of the present invention is achieved by the following structure

[17] relating to the battery pack.

[0056] Structure

[17] . A battery pack having:

[0057] Multiple battery cells; and a heat transfer suppressor sheet according to any one of the structures [1] to

[16] , wherein the multiple battery cells are connected in series or in parallel.

[0058] Invention Effects

[0059] According to the present invention, the heat transfer suppression sheet can maintain its shape even when exposed to high temperatures, resulting in a balance between excellent compression characteristics and heat transfer suppression effect, and suppressing the reduction of thermal insulation performance.

[0060] The battery pack according to the present invention has a heat transfer suppression sheet as described above, which has excellent compression characteristics and heat transfer suppression effect, and thus can suppress thermal runaway of the battery cells in the battery pack. Attached Figure Description

[0061] Figure 1 This is a schematic diagram illustrating the structure of the heat transfer suppression sheet according to the first embodiment of the present invention.

[0062] Figure 2 This is a schematic diagram illustrating a battery pack according to an embodiment of the present invention.

[0063] Figure 3 This is a schematic diagram illustrating the structure of the heat transfer suppression sheet according to the second embodiment of the present invention.

[0064] Figure 4A , Figure 4B and Figure 4C This is a schematic diagram illustrating the manufacturing method of the heat transfer suppression sheet according to the process sequence of embodiments of the present invention.

[0065] Label Explanation

[0066] 1: First organic fiber;

[0067] 2: First inorganic particles;

[0068] 3: Second inorganic particles;

[0069] 4: Second organic fiber;

[0070] 5: First inorganic fiber;

[0071] 6: Second inorganic fiber;

[0072] 9: Resin adhesive;

[0073] 11: Skeleton;

[0074] 10, 20: Heat transfer inhibition sheets;

[0075] 100: Battery pack;

[0076] 101: Battery cell;

[0077] 110: Battery casing. Detailed Implementation

[0078] The inventors have conducted in-depth research on heat transfer suppression sheets that can solve the above-mentioned problems.

[0079] The results showed that the heat transfer inhibition sheet, which has inorganic particles, resin binder, and a first organic fiber that does not have a glass transition temperature below 120°C, can maintain its shape even when exposed to high temperatures, resulting in excellent thermal insulation performance.

[0080] First, refer to the appendix Figure 1 The structure of the heat transfer suppression sheet according to embodiments of the present invention will be described in detail below. Furthermore, the embodiments described in the accompanying drawings are schematic for the purpose of clearly illustrating the present invention and may not accurately represent actual dimensions or scales.

[0081] Furthermore, the present invention is not limited to the embodiments described below, and can be implemented in any way without departing from the spirit of the present invention.

[0082] [1. Heat transfer inhibitory tablets]

[0083] <1-1. Structure of the heat transfer inhibition sheet>

[0084] Figure 1 This is a schematic diagram showing the structure of the heat transfer suppression sheet according to the first embodiment of the present invention. Additionally, Figure 2 This is a schematic diagram illustrating a battery pack according to an embodiment of the present invention.

[0085] like Figure 1 As shown, the heat transfer inhibiting sheet 10 of the first embodiment includes a first organic fiber 1, a first inorganic particle 2, and a resin binder 9. Additionally, although not essential materials in this invention, a second inorganic particle 3 and a second organic fiber 4 are also included in this embodiment. Furthermore, the first organic fiber 1 is an organic fiber that does not have a glass transition temperature below 120°C, such as crystalline polyethylene terephthalate (PET) fiber. The second organic fiber 4 is an organic fiber with a glass transition temperature higher than that of the resin binder, such as polyvinyl alcohol (PVA) fiber. The first inorganic particle 2 is, for example, silica nanoparticles, and the second inorganic particle is, for example, titanium dioxide. The first organic fiber 1, the first inorganic particle 2, the second inorganic particle 3, and the second organic fiber 4 are held in a sheet-like form by the resin binder 9.

[0086] As a specific example of the use of the heat transfer suppression sheet 10, such as Figure 2As shown, an example is illustrated where a heat transfer suppression sheet 10 is sandwiched between multiple battery cells 101. Furthermore, the multiple battery cells 101 are connected in series or in parallel (the connected state is not shown in the diagram), and are housed in a battery casing 110 to form a battery pack 100. In addition, the battery cells 101 are suitable for, for example, lithium-ion secondary batteries, but are not particularly limited to this, and can also be applied to other secondary batteries.

[0087] In the heat transfer suppression sheet 10 constructed in this way, the first inorganic particles 2 and the second inorganic particles 3 are both heat-resistant materials. Furthermore, countless tiny spaces are formed between the particles, between the particles and the fibers, and between the fibers, which also play an air-based heat insulation role. Therefore, excellent heat transfer suppression performance can be obtained.

[0088] Furthermore, the heat transfer suppression sheet 10 includes a first organic fiber 1 that does not have a glass transition temperature below 120°C. The fact that the first organic fiber 1 does not have a glass transition temperature below 120°C means that it will not soften within a temperature range from room temperature to below 120°C. Even in the event of an abnormal high temperature in which the battery cell 101 malfunctions and the second organic fiber 4 softens, the first organic fiber 1 will act as a framework, maintaining the strength of the heat transfer suppression sheet and supporting its shape. Therefore, it is possible to suppress the reduction in the thickness of the heat transfer suppression sheet and the reduction in thermal insulation performance caused by such a small reduction in space.

[0089] Furthermore, by containing a first organic fiber 1 that does not have a glass transition temperature below 120°C, the first organic fiber 1 functions as the skeleton of the heat transfer suppression sheet even at room temperature. Therefore, the softness and processability of the heat transfer suppression sheet can be improved.

[0090] Furthermore, the heat transfer suppression sheet 10 of this embodiment also contains a second organic fiber 4 having a glass transition temperature higher than that of the resin adhesive. During heating 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 particle 2, and the second inorganic particle 3 fuse to the second organic fiber 4, forming a more robust three-dimensional framework. Thus, through 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.

[0091] Furthermore, the heat transfer suppression sheet 10 of this embodiment comprises first inorganic particles 2 composed of silica nanoparticles and second inorganic particles 3 composed of metal oxides such as titanium dioxide. The silica nanoparticles are low-density, thus suppressing conductive heat transfer, and their finely dispersed pores provide excellent thermal insulation, suppressing convective heat transfer. Therefore, during battery use in normal ambient temperature ranges, heat conduction between adjacent silica nanoparticles can be suppressed.

[0092] Furthermore, the high refractive index of the second inorganic particles 3, composed of metal oxides, results in excellent diffuse light reflection, thus suppressing radiative heat transfer, particularly in high-temperature regions such as those experiencing abnormal heat generation. Therefore, if these first inorganic particles 2 and second inorganic particles 3 are included in the heat transfer suppression sheet 10, excellent thermal insulation can be achieved over a wide temperature range, from the normal operating temperature of the battery to temperatures exceeding 500°C.

[0093] Furthermore, in the first embodiment described above, an example was shown in which the heat transfer inhibiting sheet 10 also includes a second organic fiber 4 and a second inorganic particle 3 in addition to the first organic fiber 1, the first inorganic particle 2, and the resin binder 9. However, the present invention is not limited to such a structure. As described above, it is acceptable as long as at least one type of inorganic particle, the aforementioned specific organic fiber, and the resin binder are included. For example, it is preferable that the heat transfer inhibiting sheet 10 includes two different types of inorganic fibers.

[0094] As described above, if the heat transfer suppression sheet 10 contains specified organic fibers, it can maintain its shape even when exposed to high temperatures. Furthermore, even if the organic fibers contained in the heat transfer suppression sheet 10 rise to a combustion temperature, the organic fibers will not completely burn away, leaving some residue. Therefore, the strength of the heat transfer suppression sheet 10 can be maintained through the remaining organic fibers.

[0095] Furthermore, as shown below, if the heat transfer suppression sheet 10 contains inorganic fibers, it can maintain its shape as inorganic fibers even if some organic fibers burn, thus further improving the high-temperature strength of the heat transfer suppression sheet 10. In particular, if it contains two or more types of inorganic fibers with different properties, the retention of inorganic particles can also be improved. Hereinafter, examples of heat transfer suppression sheets 10 containing first and second inorganic fibers with different properties will be described.

[0096] Figure 3 This is a schematic diagram illustrating the structure of the heat transfer suppression sheet according to the second embodiment of the present invention. Figure 3 In the second embodiment shown, for the... Figure 1The same parts as those in the first embodiment are labeled with the same reference numerals, and their detailed descriptions are omitted. Furthermore, the heat transfer suppressor sheet of the second embodiment, like that of the first embodiment, can be used for... Figure 2 Therefore, the following will explain the effect of placing the heat transfer suppression sheet 20 of the second embodiment between the plurality of battery cells 101 in the battery pack shown.

[0097] like Figure 3 As shown, the heat transfer inhibiting sheet 20 of the second embodiment contains a first organic fiber 1 and a first inorganic particle 2, and also contains a first inorganic fiber 5 and a second inorganic fiber 6, which are held together by a resin adhesive 9. The first inorganic fiber 5 and the second inorganic fiber 6 are fibers with at least one different property selected from those with different average fiber diameters, shapes, and glass transition temperatures. For example, the average fiber diameter of the first inorganic fiber 5 is larger than that of the second inorganic fiber 6, the first inorganic fiber 5 is linear or needle-like, and the second inorganic fiber 6 is dendritic or crimped.

[0098] In this second embodiment, similar to the first embodiment, since it includes the first organic fiber 1, even when the temperature of the battery cell 101 rises, the first organic fiber 1 serves as a framework, supporting the sheet shape of the heat transfer suppression sheet. Furthermore, the heat transfer suppression sheet 20 includes first inorganic particles 2 composed of silicon dioxide nanoparticles, thus suppressing both conductive and convective heat transfer, resulting in excellent thermal insulation.

[0099] Furthermore, in the heat transfer suppression sheet 20, the fine-diameter and dendritic or coiled second inorganic fiber 6 exists in a state of interweaving with the first inorganic particle 2 and the coarse-diameter first inorganic fiber 5, thus effectively retaining the inorganic particles.

[0100] Furthermore, the first inorganic fiber 5 and the second inorganic fiber 6 will not melt even at the temperature during thermal runaway of the battery cell. Therefore, even when the heat transfer suppression sheet 20 is exposed to high temperature, it can maintain its shape and maintain its heat insulation effect.

[0101] Furthermore, the properties of the two different inorganic fibers can be selected, but are not limited to those described above. As the first inorganic fiber 5, an amorphous inorganic fiber with an average fiber diameter larger than that of the second inorganic fiber 6 can be used. Additionally, as the second inorganic fiber 6, at least one inorganic fiber selected from crystalline fibers and amorphous fibers with a glass transition temperature higher than that of the first inorganic fiber 5 can be used.

[0102] The melting point of crystalline inorganic fibers is generally higher than the glass transition temperature of amorphous inorganic fibers. Therefore, when the first inorganic fiber 5 is exposed to high temperature, its surface softens before that of the second inorganic fiber 6, bonding the first inorganic particle 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.

[0103] Furthermore, if the second inorganic fiber 6 is composed of crystalline fibers, or has a higher glass transition temperature than the first inorganic fiber 5, then when exposed to high temperatures, even if the first inorganic fiber 5 softens, the second inorganic fiber 6 will not melt or soften. Therefore, it can maintain its shape even during thermal runaway of the battery cell and can continue to exist between the battery cells.

[0104] Furthermore, the first inorganic fiber 5 with a coarse average fiber diameter has the effect of improving the mechanical strength and shape retention of the heat transfer suppression sheet 20. By making the first inorganic fiber 5 coarse, it is possible to soften only the surface when exposed to high temperatures, thus further improving the bonding effect of the first inorganic particle 2, the first organic fiber 1, and the second inorganic fiber 6.

[0105] Furthermore, preferably, the first inorganic particle 2 includes at least one selected from nanoparticles, hollow particles and porous particles; the first inorganic fiber 5, which is one of two different inorganic fibers, is an amorphous fiber; and the second inorganic fiber is at least one selected from crystalline fibers and amorphous fibers with a glass transition temperature higher than that of the first inorganic fiber.

[0106] <1-2. Thickness of the heat transfer suppression sheet>

[0107] The thickness of the heat transfer suppression sheet in this embodiment is not particularly limited, but it is preferably 0.05 mm or more and 10 mm or less. When the thickness is 0.05 mm or more, sufficient compressive strength can be obtained. On the other hand, when the thickness is 10 mm or less, good thermal insulation properties of the heat transfer suppression sheet can be obtained.

[0108] [2. Manufacturing method of heat transfer inhibition sheet]

[0109] Next, as an example of a method for manufacturing a heat transfer suppression sheet, a detailed description of the manufacturing method and conditions of the heat transfer suppression sheet according to the second embodiment of the present invention will be provided.

[0110] <2-1. Manufacturing method of heat transfer inhibition sheet>

[0111] Figures 4A to 4C This is a schematic diagram showing the structure of the heat transfer suppression sheet according to the manufacturing process sequence of the second embodiment of the present invention. Furthermore, in Figures 4A to 4C In China, regarding Figure 1The second inorganic particle 3 shown is omitted from the description.

[0112] like Figure 4A As shown, a first organic fiber 1, a first inorganic particle 2, an emulsion 7 in which a resin binder is dispersed in water, and a second organic fiber 4 having a higher glass transition temperature than the resin binder are prepared. They are mixed and stirred to obtain a dispersion 8. Next, the dispersion 8 is dehydrated (dehydrated) to produce a wetted sheet.

[0113] Then, the moistened sheet is heated. At this time, as... Figure 4B As shown, as the temperature rises, the water in the emulsion 7 evaporates, and a molten resin binder 13 is obtained. Furthermore, by further heating the sheet, at least a portion of the surface of the second organic fiber 4 melts.

[0114] Then, by cooling the plate, such as... Figure 4C As shown, the second organic fibers 4 are fused together to form a welded portion 12. Furthermore, by further cooling the sheet to form a cured resin adhesive 9, the heat transfer suppression sheet of this embodiment can be obtained.

[0115] In the heat transfer suppression sheet of the second embodiment manufactured by the manufacturing method described above, an emulsion 7 containing a resin binder is used, so the material is uniformly dispersed overall, and in these dispersions, the first organic fiber 1 and the second organic fiber 4 exist in an irregular orientation.

[0116] Furthermore, during the process of heating the wet sheet to the specified temperature, the resin adhesive completely melts, and then a portion of the surface of the second organic fiber 4, which has a high glass transition temperature, melts.

[0117] Furthermore, during the cooling process of the heated sheet, the molten surface portion of the second organic fiber 4 solidifies first, forming a welded portion 12 at the point where the second organic fibers 4 come into contact with each other.

[0118] As described above, in the dispersion containing the raw materials, the first organic fiber 1 and the second organic fiber 4 exist in an irregular orientation. Therefore, after a portion of the surface of the second organic fiber 4 melts, if 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 to form a three-dimensional skeleton 11. As a result, the resulting skeleton 11 maintains the overall shape of the heat transfer inhibition sheet.

[0119] In addition, as it cools, the first organic fiber 1, the first inorganic particle 2, and the second inorganic particle (not shown) that are in contact with the surface of the second organic fiber 4 become fixed to the surface of the second organic fiber 4, thus making the skeleton 11 more robust.

[0120] Subsequently, if the sheet is cooled to a temperature lower than the glass transition temperature of the resin adhesive, the molten resin adhesive 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. Thus, the first organic fibers 1, the first inorganic particles 2, and the second inorganic particles are bonded to the skeleton 11, and the skeleton 11 is further strengthened by the solidified resin adhesive 9.

[0121] By manufacturing in this way, the heat transfer suppression sheet of this embodiment has a robust skeleton 11. In addition, in this embodiment, the first organic fiber 1, which does not have a glass transition temperature at temperatures below 120°C, exists in the heat transfer suppression sheet in an irregular orientation. Therefore, when the heat transfer suppression sheet is used, even if the second organic fiber 4 softens due to exposure to high temperatures, its shape and strength can be maintained, and the reduction in heat insulation performance can be suppressed.

[0122] Furthermore, 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 glass transition temperature higher than that of the resin binder. However, the second inorganic particle and the second organic fiber 4 are not essential. For example, as shown in the second embodiment described above, it may contain the first inorganic fiber and the second inorganic fiber, or it may contain all of the second inorganic particle, the second organic fiber 4, the first inorganic fiber, and the second inorganic fiber. In addition, 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. More preferably, all materials are uniformly dispersed in the dispersion. Therefore, it is sufficient to mix and disperse 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 used to prepare the dispersion. Furthermore, from the viewpoint of reducing environmental impact, water is preferred as the liquid used to disperse the resin binder.

[0123] Next, the conditions in the manufacturing method of the heat transfer suppression sheet of this embodiment will be explained.

[0124] <2-2. Heating temperature of the moistened sheet>

[0125] In the process of heating the above-mentioned wetted sheet, the heating temperature is set to be 10°C or more higher than the glass transition temperature of the second organic fiber 4 and 50°C or less.

[0126] That is, when the heating temperature of the wetted sheet is set to t (°C) and the glass transition temperature of the second organic fiber 4 is set to Tg (°C), if the relationship is t < Tg + 10, the melting of the surface of the second organic fiber 4 becomes insufficient, the adhesion between the second organic fibers 4 becomes weak, and therefore, a strong skeleton cannot be formed.

[0127] On the other hand, if the relationship is t < Tg + 50, only the surface of the second organic fiber 4 melts due to heating, and can form a shape as a skeleton. However, even if t ≥ Tg + 50, the molten second organic fiber 4 will also melt on the surface of the first organic fiber 1, and can form a solid skeleton based on the first organic fiber 1.

[0128] Therefore, the heating temperature t of the humidified sheet is set to Tg+10 (°C) or higher, preferably Tg+15 (°C) or higher. Furthermore, the heating temperature t of the humidified sheet is preferably Tg+50 (°C) or lower, more preferably Tg+30 (°C) or lower.

[0129] [3. Materials constituting the heat transfer inhibition sheet and their content]

[0130] Next, the first organic fiber 1, the second organic fiber 4, the first inorganic particle 2, the second inorganic particle 3, the first inorganic fiber 5, the second inorganic fiber 6, and the resin adhesive 9 constituting the heat transfer inhibition sheet of the first and second embodiments described above will be described in detail below.

[0131] <3-1. First Organic Fiber>

[0132] As described above, preferably, the first organic fiber 1 does not have a glass transition temperature at temperatures below 120°C; that is, the first organic fiber 1 is at least one of crystalline organic fibers with a glass transition temperature of 120°C or higher and organic fibers without a glass transition temperature. By including such a first organic fiber 1 in the heat transfer suppression sheet, the sheet shape can be maintained even if abnormal conditions occur in the heat transfer suppression sheet.

[0133] Organic fibers that do not possess a glass transition temperature, when their mechanical behavior is represented graphically using elastic modulus and strength, exhibit the following behavior: as the temperature rises from room temperature to the melting point Tm, the elastic modulus decreases gradually, then drops sharply at the melting point Tm. Specifically, the crystals are arranged without gaps, and even when the temperature rises to near the melting point Tm, they become crystalline in a state where crystallization is extremely difficult.

[0134] This state can be represented by the following formula related to the elastic modulus.

[0135] When the first organic fiber 1 has a melting point Tm at a temperature above 200°C, 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 preferably 0.1% or more.

[0136] If (G1 / G0)×100 is less than 0.1%, then when the temperature is increased from 23°C, the elastic modulus will decrease significantly before reaching the melting point Tm, and it may be difficult to fully achieve the effect of maintaining the shape of the heat transfer inhibition sheet.

[0137] For example, regarding crystalline polyethylene terephthalate (PET) fiber, the ratio of the above elastic moduli was investigated. The elastic moduli G0 at room temperature (23°C) is 50,000 MPa, and the elastic moduli G1 at the melting point Tm (approximately 230°C) is 200 MPa. Therefore, (G1 / G0)×100=0.4 (%).

[0138] (Refer to "Temperature Dependence of Elastic Modulus of SPS Biaxially Stretchable Film": idemitsu.com, SPS Biaxially Stretchable Film - Film Characteristics - Temperature Dependence of Elastic Modulus of SPS Biaxially Stretchable Film, Idemitsu Kosan Co., Ltd., [online], [accessed December 21, 2005], Internet)<URL:https: / / www.idemitsu.com / jp / business / ipc / products / sps / oshidashi / nizikuenshin_2.ht ml> )

[0139] As the first organic fiber 1, it is preferably selected from at least one of the following: polyethylene terephthalate fiber, polybutylene terephthalate fiber, polypropylene terephthalate fiber, polyacetal fiber, polytetrafluoroethylene fiber, polyetheretherketone fiber, polyphenylene sulfide fiber, polyamide fiber, and poly(p-phenylene terephthalamide) fiber.

[0140] (3-1-1. Content of the first organic fiber)

[0141] If the content of the first organic fiber 1 is too low, it may be insufficient to maintain 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 the first inorganic particles 2 and the resin binder 9, which are other essential components, will decrease, making it difficult to obtain the desired heat insulation effect and the retention effect of the resin binder 9 on the first inorganic particles 2, etc. Therefore, the content of the first organic fiber 1 is preferably 1% by mass or more and 10% by mass or less relative to the total mass of the heat transfer suppression sheet.

[0142] (3-1-2. Average fiber length of the first organic fiber)

[0143] The fiber length of the first organic fiber 1 is not particularly limited. From the viewpoint of ensuring formability and processability, the average fiber length of the first organic fiber 1 is preferably 10 mm or less.

[0144] On the other hand, from the viewpoint of enabling the first organic fiber 1 to function as a skeleton and ensuring the compressive strength of the heat transfer suppression sheet, the average fiber length of the first organic fiber 1 is preferably 0.5 mm or more.

[0145] <3-2. Second Organic Fiber>

[0146] As the second organic fiber 4 that can be used in this embodiment, a fiber having a glass transition temperature higher than that of the resin adhesive 9 can be used. For example, an organic fiber comprising at least one selected from polyvinyl alcohol (PVA) fiber, polyethylene fiber, nylon fiber, polyurethane fiber, and ethylene-vinyl alcohol copolymer fiber can be used.

[0147] Furthermore, when the first organic fiber 1 has a glass transition temperature, the second organic fiber 4, which has a glass transition temperature that is higher than that of the resin adhesive 9 and lower than that of the first organic fiber 1, can be used as the second organic fiber 4.

[0148] Furthermore, if the first organic fiber 1 does not have a glass transition temperature, then as the second organic fiber 4 having a glass transition temperature, a fiber with a glass transition temperature higher than that of the resin adhesive 9 can be used.

[0149] During the manufacture of the heat transfer suppression sheet, it is difficult to raise the heating temperature above 250°C. Therefore, the glass transition temperature of the second organic fiber 4 is preferably below 250°C, and more preferably below 200°C.

[0150] The lower limit of the glass transition temperature of the second organic fiber 4 is not particularly limited, but if the difference between its glass transition temperature and that of the resin adhesive 9 is 10°C or more, then during the cooling process in manufacturing, the semi-molten organic fiber will completely solidify, and the resin adhesive will solidify. Therefore, the reinforcing effect on the skeleton based on the resin adhesive 9 can be fully obtained. Therefore, the difference between the glass transition temperature of the resin adhesive 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.

[0151] On the other hand, if the difference in glass transition temperature between the second organic fiber 4 and the resin adhesive 9 is 130°C or less, the time from the complete curing of the second organic fiber 4 to the beginning of curing of the resin adhesive can be appropriately adjusted, and the resin adhesive cures in a well-dispersed state. Therefore, the reinforcing effect of the skeleton 11 can be further obtained. Therefore, the difference in glass transition temperature between the resin adhesive 9 and the second organic fiber 4 is preferably 130°C or less, more preferably 120°C or less, further preferably 100°C or less, even more preferably 80°C or less, and particularly preferably 70°C or less.

[0152] In the first embodiment described above, two types of organic fibers are included: a first organic fiber 1 and a second organic fiber 4. However, if the first organic fiber 1 has a glass transition temperature, the glass transition temperature of the first organic fiber 1 is preferably 10°C or more higher than that of the second organic fiber 4, and more preferably 20°C or more higher. Furthermore, other organic fibers may be included as needed.

[0153] (3-2-1. The total content of the first organic fiber and the second organic fiber)

[0154] In this embodiment, by appropriately controlling the content of the first organic fiber 1 and the second organic fiber 4, the function of the organic fiber as a framework can be sufficiently 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 inhibiting sheet. Furthermore, it is preferably 12% by mass or less, more preferably 8% by mass or less.

[0155] (3-2-2. Average fiber length of the second organic fiber)

[0156] The fiber length of the second organic fiber 4 is not particularly limited. From the point of view of ensuring formability and processability, the average fiber length of the second organic fiber 4 is preferably less than 10 mm.

[0157] On the other hand, similar to the first organic fiber 1, from the viewpoint of enabling the second organic fiber 4 to function as a skeleton and ensuring the compressive strength of the heat transfer suppression sheet, the average fiber length of the second organic fiber 4 is preferably 0.5 mm or more.

[0158] (3-2-3. Solubility temperature of the first and second organic fibers in water)

[0159] Furthermore, as described above, in this embodiment, water is preferably used as the liquid for dispersing the resin adhesive. Therefore, when water is used as the dispersion liquid, organic fibers with low water solubility are preferably used as the first and second organic fibers. In this embodiment, the water solubility is indicated by the water dissolution temperature. That is, the water dissolution temperature of the first and second organic fibers is preferably 60°C or higher, more preferably 70°C or higher, and even more preferably 80°C or higher.

[0160] <3-3. Resin Adhesives>

[0161] As the resin adhesive 9 that can be used in this embodiment, for example, when the heat transfer inhibiting sheet 10 contains the aforementioned second organic fiber 4, a resin adhesive having a glass transition temperature lower than that of the second organic fiber 4 can be used. For example, a resin adhesive 9 containing at least one selected from styrene-butadiene resin, acrylic resin, silicone-acrylic resin, and styrene resin can be used.

[0162] The glass transition temperature of the resin binder 9 is not specifically specified, but is preferably above -10°C.

[0163] Furthermore, if the glass transition temperature of the resin binder 9 is above room temperature, the strength of the heat transfer suppressing sheet can be further improved when using the heat transfer suppressing sheet with the resin binder 9 at room temperature.

[0164] Therefore, the glass transition temperature of the resin adhesive 9 is more preferably 20°C or higher, more preferably 30°C or higher, even more preferably 50°C or higher, and particularly preferably 60°C or higher.

[0165] (3-3-1. Resin binder content)

[0166] In this embodiment, if the content of the resin adhesive 9 is properly controlled, the strengthening effect of the organic fiber-based skeleton can be fully obtained.

[0167] The content of resin binder 9 relative to the total mass of the heat transfer inhibiting sheet is preferably 0.5% by mass or more, more preferably 1% by mass or more. Furthermore, it is preferably 20% by mass or less, more preferably 10% by mass or less.

[0168] Furthermore, in the heat transfer suppression sheet of this embodiment, even if the total content of the first organic fiber 1 and other organic fibers and the resin adhesive 9 is the same as the content of organic materials in conventional insulation sheets, the strength relative to compression is also increased by the above-described structure, thus achieving a balance between insulation performance and strength.

[0169] <3-4. Inorganic Particles>

[0170] As inorganic particles, a single inorganic particle can be used, or two or more inorganic particles (first inorganic particle 2 and second inorganic particle 3) can be used in combination. From the viewpoint of inhibiting heat transfer, particles composed of at least one inorganic material selected from oxide particles, carbide particles, nitride particles, and inorganic hydrate particles are preferred as first inorganic particle 2 and second inorganic particle 3, and oxide particles are more preferred. Furthermore, the shape of first inorganic particle 2 and second inorganic particle 3 is not particularly limited, but preferably includes at least one selected from nanoparticles, hollow particles, and porous particles. Specifically, inorganic hollow spheres such as silica nanoparticles, metal oxide particles, microporous particles, and hollow silica particles, particles composed of thermally expandable inorganic materials, and particles composed of hydrous porous bodies can also be used. Hereinafter, small-diameter inorganic particles will be referred to as first inorganic particle 2, and large-diameter inorganic particles as second inorganic particle 3, for a more detailed explanation of the inorganic particles.

[0171] Furthermore, if two or more types of inorganic particles with different heat transfer inhibition effects are used together, the heating element can be cooled in multiple stages, and the endothermic effect can be exhibited over a wider temperature range. Therefore, when using nanoparticles as the first inorganic particle 2, it is preferable to include the second inorganic particle 3, which is composed of metal oxides and will be described later, as another inorganic particle.

[0172] Next, an example of the material or shape of the particles that can be used as the first inorganic particle 2 will be described in detail below.

[0173] <3-4-1. First Inorganic Particle>

[0174] (Oxide particles)

[0175] Oxide particles have a high refractive index, resulting in strong light diffuse reflection. Therefore, when oxide particles are used as inorganic particles, they can suppress radiative heat transfer, especially in high-temperature regions such as those experiencing abnormal heating. At least one type of oxide particle selected from silicon dioxide, titanium dioxide, zircon, barium titanate, zinc oxide, and aluminum oxide can be used as the oxide particle. That is, only one of the aforementioned oxide particles that can be used as inorganic particles can be used, or two or more oxide particles can be used. In particular, silicon dioxide is a component with high thermal insulation properties, and titanium dioxide is a component with a high refractive index compared to other metal oxides. Both are effective at diffusely reflecting light and blocking radiative heat in high-temperature regions above 500°C. Therefore, silicon dioxide and titanium dioxide are most preferably used as oxide particles.

[0176] (Average primary particle size of oxide particles: greater than 0.001 μm and less than 50 μm)

[0177] The particle size of oxide particles can sometimes affect the effectiveness of reflecting radiant heat. Therefore, if the average primary particle size is limited to a specified range, higher thermal insulation can be obtained.

[0178] That is, when the average primary particle size of the oxide particles is greater than 0.001 μm, it is large enough compared to the wavelength of light that helps to heat up, so that the light is diffusely reflected efficiently. Therefore, in the high temperature region above 500°C, the radiative heat transfer of heat in the heat transfer suppression sheet is suppressed, which can further improve the thermal insulation.

[0179] On the other hand, when the average primary particle size of oxide particles is less than 50 μm, even when compressed, the number of contact points between particles will not increase, making it difficult to form a conductive heat transfer pathway. Therefore, it can reduce the influence of conductive heat transfer on the insulation of the dominant normal temperature range.

[0180] Furthermore, in this invention, the average primary particle size can be determined by observing the particles under a microscope, comparing them with a standard scale, and taking the average of any 10 particles.

[0181] (Nanoparticles)

[0182] In this invention, nanoparticles refer to nanoscale particles that are spherical or nearly spherical with an average primary particle size of less than 1 μm. Nanoparticles have low density, thus suppressing conductive heat transfer. If nanoparticles are used as inorganic particles, the voids are further finely dispersed, thereby achieving excellent thermal insulation to suppress convective heat transfer. Therefore, from the perspective of suppressing heat conduction between adjacent nanoparticles during battery use in the normal ambient temperature range, the use of nanoparticles is preferred.

[0183] Furthermore, if nanoparticles with a small average primary particle size are used as oxide particles, even if the heat transfer suppressor is compressed due to the expansion accompanying the thermal runaway of the battery cell, resulting in an increase in internal density, the increase in conductive heat transfer of the heat transfer suppressor can still be suppressed. This is believed to be because nanoparticles easily form small gaps between particles due to electrostatic repulsion, resulting in low bulk density. Therefore, the particles are filled in a buffering manner.

[0184] Furthermore, in this invention, when using nanoparticles as inorganic particles, the material is not particularly limited as long as it meets the above definition of nanoparticles. For example, silica nanoparticles are highly insulating materials, and the contact points between the particles are small; therefore, the heat conducted through silica nanoparticles is less compared to the case where larger silica particles are used. Additionally, the bulk density of silica nanoparticles typically obtained is 0.1 g / cm³. 3Therefore, even if the battery cells positioned on both sides of the insulation sheet undergo thermal expansion, applying large compressive stress to the insulation sheet, the size (area) and number of contact points between the silica nanoparticles will not increase significantly, thus maintaining thermal insulation. Therefore, silica nanoparticles are preferred as nanoparticles. Wet silica, dry silica, and aerogels can be used as silica nanoparticles.

[0185] (Average primary particle size of nanoparticles: greater than 1 nm and less than 100 nm)

[0186] If the average primary particle size of the nanoparticles is limited to a specified range, higher thermal insulation can be obtained.

[0187] That is, if the average primary particle size of the nanoparticles is set to be greater than 1 nm and less than 100 nm, then, especially in the temperature range below 500 °C, convective and conductive heat transfer within the heat transfer suppression sheet can be suppressed, thereby further improving the thermal insulation. In addition, even under the condition of applied compressive stress, the voids remaining between the nanoparticles and the contacts between multiple particles can also suppress conductive heat transfer, thus maintaining the thermal insulation of the heat transfer suppression sheet.

[0188] Furthermore, the average primary particle size of the nanoparticles is more preferably 2 nm or more, and even more preferably 3 nm or more. On the other hand, the average primary particle size of the nanoparticles is more preferably 50 nm or less, and even more preferably 10 nm or less.

[0189] (Inorganic hydrate particles)

[0190] When inorganic hydrate particles are heated by a heat source and reach a temperature above the initiation temperature of thermal decomposition, they undergo thermal decomposition, releasing their own water of crystallization and thus lowering the temperature of the heat source and its surroundings, exhibiting the so-called "endothermic effect." Furthermore, after releasing the water of crystallization, they become porous, exhibiting an insulating effect through numerous air pores.

[0191] 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).

[0192] For example, aluminum hydroxide contains about 35% water of crystallization, as shown in the following formula. It decomposes thermally to release this water of crystallization, exhibiting an endothermic effect. Furthermore, after releasing the water of crystallization, it becomes alumina (Al₂O₃), a porous material, which functions as a thermal insulation material.

[0193] 2Al(OH)3→Al2O3+3H2O

[0194] Furthermore, as described later, the heat transfer suppression sheet 10 of this embodiment is preferably sandwiched between battery cells, but in a battery cell where thermal runaway occurs, the temperature rises sharply to over 200°C and continues to rise to around 700°C. Therefore, as inorganic particles, it is preferable to use inorganic hydrates with a thermal decomposition start temperature of 200°C or higher.

[0195] Regarding the thermal decomposition start temperatures of the inorganic hydrates listed above, aluminum hydroxide is approximately 200°C, magnesium hydroxide is approximately 330°C, calcium hydroxide is approximately 580°C, zinc hydroxide is approximately 200°C, iron hydroxide is approximately 350°C, manganese hydroxide is approximately 300°C, zirconium hydroxide is approximately 300°C, and gallium hydroxide is approximately 300°C. These temperatures largely overlap with the temperature range of the rapidly rising battery cells that experience thermal runaway, effectively suppressing temperature rise. Therefore, they can be considered preferred inorganic hydrates.

[0196] (Average secondary particle size of inorganic hydrate particles: greater than 0.01 μm and less than 200 μm)

[0197] Furthermore, when inorganic hydrate particles are used as the first inorganic particle 2, if their average particle size is too large, the first inorganic particle 2 (inorganic hydrate) located near the center of the heat transfer inhibition sheet 10 will require a certain amount of time to reach its thermal decomposition temperature. Therefore, there is a possibility that the first inorganic particle 2 near the center of the sheet may not be completely thermally decomposed. Therefore, the average secondary particle size of the inorganic hydrate particles is preferably 0.01 μm or more and 200 μm or less, more preferably 0.05 μm or more and 100 μm or less.

[0198] (Particles composed of thermally expanding inorganic materials)

[0199] Examples of thermally expandable inorganic materials include vermiculite, bentonite, mica, and perlite.

[0200] (Particles composed of hydrous porous materials)

[0201] Specific examples of hydrous porous materials include zeolite, kaolinite, montmorillonite, acid clay, diatomaceous earth, wet silica, dry silica, aerogel, mica, vermiculite, etc.

[0202] (Inorganic hollow sphere)

[0203] The thermal insulation material used in this invention may contain inorganic hollow spheres as inorganic particles.

[0204] If it contains inorganic hollow spheres, it can suppress convective or conductive heat transfer within the insulation material in temperature ranges below 500°C, thereby further improving the insulation performance of the insulation material.

[0205] As an inorganic hollow sphere, at least one of the following can be used: white sand hollow sphere, silica hollow sphere, fly ash hollow sphere, barite hollow sphere, and glass hollow sphere.

[0206] (Inorganic hollow sphere content: less than 60% by mass relative to the total mass of the insulation material)

[0207] The content of inorganic hollow spheres, relative to the total mass of the insulation material, is preferably 60% by mass or less.

[0208] (Average particle size of inorganic hollow spheres: greater than 1 μm and less than 100 μm)

[0209] The average particle size of the inorganic hollow spheres is preferably 1 μm or more and 100 μm or less.

[0210] <3-4-2. Second Inorganic Particles>

[0211] When the heat transfer suppression sheet contains two types of inorganic particles, the second inorganic particle 3 is not particularly limited as long as its material, particle size, etc., are different from the first inorganic particle 2. As the second inorganic particle 3, it can be inorganic hollow spheres such as oxide particles, carbide particles, nitride particles, inorganic hydrate particles, silica nanoparticles, metal oxide particles, microporous particles or hollow silica particles, particles made of thermally expandable inorganic materials, particles made of hydrous porous bodies, etc., as detailed above.

[0212] Furthermore, nanoparticles exhibit extremely low thermal conductivity and maintain excellent thermal insulation even when compressive stress is applied to the heat transfer suppression sheet. Additionally, metal oxide particles such as titanium dioxide are highly effective at blocking radiant heat. Moreover, when using both large-diameter and small-diameter inorganic particles, the small-diameter particles can penetrate the gaps between the large-diameter particles, resulting in a denser structure and improved heat transfer suppression. Therefore, when using nanoparticles as the first inorganic particle 2, it is preferable to further include particles composed of metal oxides with a diameter larger than the first inorganic particle 2 as the second inorganic particle 3 in the heat transfer suppression sheet.

[0213] Examples of metal oxides include silicon dioxide, titanium dioxide, aluminum oxide, barium titanate, zinc oxide, zircon, and zirconium oxide. In particular, titanium dioxide has a higher refractive index than other metal oxides, and it is highly effective in blocking radiant heat by diffuse reflection of light in high-temperature regions above 500°C. Therefore, titanium dioxide is the preferred choice.

[0214] (Average primary particle size of the second inorganic particle)

[0215] When the heat transfer suppression sheet contains second inorganic particles 3 composed of metal oxides, if the average primary particle size of the second inorganic particles 3 is 1 μm or more and 50 μm or less, radiative heat transfer can be efficiently suppressed in high-temperature regions above 500°C. The average primary particle size of the second inorganic particles 3 is further preferably 5 μm or more and 30 μm or less, and most preferably 10 μm or less.

[0216] <3-5. First Inorganic Fiber and Second Inorganic Fiber>

[0217] The heat transfer suppression sheet of this embodiment preferably has at least one first inorganic fiber 5 and a second inorganic fiber 6 with different properties selected from average fiber diameter, shape and glass transition temperature. As explained in the second embodiment above, by containing two inorganic fibers with different properties, the mechanical strength of the heat transfer suppression sheet and the retention of inorganic particles can be improved.

[0218] (3-5-1. Two types of inorganic fibers with different average fiber diameters and fiber shapes)

[0219] When the heat transfer suppressing sheet 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. The first inorganic fiber 5 is linear or needle-like, and the second inorganic fiber 6 is dendritic or crimped. The first inorganic fiber 5 with a larger average fiber diameter (coarse diameter) has the effect of improving the mechanical strength and shape retention of the heat transfer suppressing sheet. By making one of the two inorganic fibers, for example, the diameter of the first inorganic fiber 5, larger than that of the second inorganic fiber 6, the above-mentioned effect can be obtained. Since there are cases where external impacts act on the heat transfer suppressing sheet, the inclusion of the first inorganic fiber 5 in the heat transfer suppressing sheet improves impact resistance. Examples of external impacts include the compressive force based on the expansion of the battery cell, the wind pressure caused by the fire of the battery cell, etc.

[0220] Furthermore, to improve the mechanical strength and shape retention of the heat transfer suppression sheet, it is particularly preferred that the first inorganic fiber 5 is linear or needle-like. Moreover, linear or needle-like fibers refer to fibers with a crimp degree of, for example, less than 10%, preferably less than 5%, as described later.

[0221] 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 coarse, the formability and processability of the heat transfer suppression sheet may be reduced. Therefore, the average fiber diameter of the first inorganic fiber 5 is preferably 20 μm or less, and more preferably 15 μm or less.

[0222] Furthermore, if the first inorganic fiber 5 is too long, its formability and processability may be reduced. Therefore, it is preferable to set the fiber length to 100 mm or less. Moreover, if the first inorganic fiber 5 is too short, its shape retention and mechanical strength will also be reduced. Therefore, it is preferable to set the fiber length to 0.1 mm or more.

[0223] On the other hand, the second inorganic fiber 6, with a smaller average fiber diameter, has the effect of improving the retention of the first organic fiber 1 and the first inorganic particles 2, and improving the softness of the heat transfer suppression sheet. Therefore, it is preferable that the diameter of the second inorganic fiber 6 is smaller than the diameter of the first inorganic fiber 5.

[0224] More specifically, in order to improve the retention of the first organic fiber 1 and the first inorganic particles 2, the second inorganic fiber 6 is preferably easily deformable and flexible. Therefore, the average fiber diameter of the fine-diameter second inorganic fiber 6 is preferably less than 1 μm, more preferably less than 0.1 μm. However, if the fine-diameter inorganic fiber is too thin, it is prone to breakage, and the retention capacity of the first organic fiber 1 and the first inorganic particles 2 is reduced. In addition, the proportion of fibers that do not retain the first organic fiber 1 and the first inorganic particles 2 and exist in an interwoven state in the heat transfer suppression sheet increases, which not only reduces the retention capacity of the first organic fiber 1 and the first inorganic particles 2, but also worsens the formability and shape retention. Therefore, the average fiber diameter of the second inorganic fiber 6 is preferably 1 nm or more, more preferably 10 nm or more.

[0225] Furthermore, if the second inorganic fiber 6 is too long, its formability and shape retention will decrease. Therefore, the fiber length of the second inorganic fiber 6 is preferably 0.1 mm or less. Also, if the second inorganic fiber 6 is too short, its shape retention and mechanical strength will decrease. Therefore, the fiber length of the second inorganic fiber 6 is preferably 1 μm or more.

[0226] Furthermore, the second inorganic fiber 6 is preferably dendritic or crimped. If the second inorganic fiber 6 has this shape, it will interweave with the first organic fiber 1 and the first inorganic particles 2 in the heat transfer suppression sheet. Therefore, the retention capacity of the first organic fiber 1 and the first inorganic particles 2 is improved. In addition, when the heat transfer suppression sheet is subjected to compressive force or wind pressure, the sliding movement of the second inorganic fiber 6 is suppressed, thereby improving its mechanical strength, particularly its resistance to external compressive force and impact.

[0227] In addition, dendritic refers to a structure that branches in two or three dimensions, such as feather-like, tetrap-like, radial, or three-dimensional mesh-like structures.

[0228] In the case where the second inorganic fiber 6 is dendritic, its average fiber diameter can be obtained by using SEM to measure the diameter of the trunk and branches at multiple points and calculating their average value.

[0229] Furthermore, crimped refers to a structure in which fibers bend in various directions. As one method for quantifying crimped morphology, it is known to calculate the degree of crimp based on electron microscope images, for example, using the following formula.

[0230] crimp (%) = (fiber length - distance between fiber ends) / (fiber length) × 100

[0231] Here, the fiber length and the distance between fiber ends are measured values ​​from electron microscope images. That is, the fiber length and the distance between fiber ends projected onto a two-dimensional plane are shorter than the actual values. According to this formula, the crimp of the second inorganic fiber 6 is preferably 10% or more, more preferably 30% or more. If the crimp is small, the retention capacity of the first organic fiber 1 and the first inorganic particles 2, etc., is reduced, making it difficult to form an interweaving (network) between the second inorganic fibers 6 and between the first inorganic fiber 5 and the second inorganic fiber 6.

[0232] In the above embodiments, as a method to improve the mechanical strength, shape retention, and retention of the first organic fiber 1 and the first inorganic particles 2 of the heat transfer suppression sheet, a first inorganic fiber 5 and a second inorganic fiber 6 with different average fiber diameters and fiber shapes are used. However, by using first inorganic fibers 5 and second inorganic fibers 6 with different glass transition temperatures and average fiber diameters, it is also possible to improve the mechanical strength, shape retention, and particle retention of the heat transfer suppression sheet.

[0233] As described above, in this embodiment, in order to improve the mechanical strength, shape retention, and particle retention of the heat transfer suppression sheet, it is preferable to use various combinations of inorganic fibers. Hereinafter, [the following will discuss the...] Figure 3 The second embodiment shown will be described using different combinations of the first and second inorganic fibers, but for convenience, in this specification, we will use... Figure 3 Other embodiments related to inorganic fibers are described.

[0234] (3-5-2. Two inorganic fibers with different glass transition temperatures)

[0235] When the heat transfer suppressing 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 type of fiber selected from crystalline fibers and amorphous fibers with a glass transition temperature higher than that of the first inorganic fiber 5. Furthermore, by using a first inorganic particle 2 containing at least one type selected from nanoparticles, hollow particles, and porous particles in conjunction with the aforementioned two types of inorganic fibers, the thermal insulation performance can be further improved.

[0236] The melting point of crystalline inorganic fibers is generally higher than the glass transition temperature of amorphous inorganic fibers. Therefore, if the first inorganic fiber 5 is exposed to high temperatures, its surface softens before the second inorganic fiber 6, bonding the first organic fiber 1 and the first inorganic particles 2 together. Thus, by including the first inorganic fiber 5 as described above in the heat transfer suppression sheet, the mechanical strength of the insulation layer can be improved.

[0237] Specifically, the first inorganic fiber 5 is preferably an inorganic fiber with a melting point below 700°C, and many amorphous inorganic fibers can be used. Among them, fibers containing SiO2 are preferred, and glass fibers are even more preferred from the perspectives of low price, easy availability, and excellent processability.

[0238] As described above, the second inorganic fiber 6 is a fiber composed of at least one selected from crystalline fibers and amorphous fibers with a glass transition temperature higher than that of the first inorganic fiber 5. Many crystalline inorganic fibers can be used as the second inorganic fiber 6.

[0239] If the second inorganic fiber 6 is composed of crystalline fibers, or has a higher glass transition temperature than the first inorganic fiber 5, then when exposed to high temperatures, even if the first inorganic fiber 5 softens, the second inorganic fiber 6 will not melt or soften. Therefore, it can maintain its shape and continue to exist between battery cells even during thermal runaway.

[0240] In addition, if the second inorganic fiber 6 does not melt or soften, the tiny spaces between the particles, between the particles and the fibers, and between the fibers contained in the heat transfer inhibition sheet are maintained. Therefore, it can exert an air-based insulation effect and maintain excellent heat transfer inhibition performance.

[0241] When the second inorganic fiber 6 is crystalline, the second inorganic fiber 6 can be ceramic fibers such as alumina fiber, aluminosilicate fiber and zirconium oxide fiber, silica fiber, glass fiber, glass wool, asbestos, carbon fiber, basalt fiber, soluble fiber, refractory ceramic fiber, aerogel composite material, magnesium silicate fiber, alkaline earth silicate fiber, zirconium oxide fiber, potassium titanate fiber, etc., and as a mineral fiber other than the above, natural mineral fibers such as wollastonite can be used.

[0242] If the fiber listed as the second inorganic fiber 6 has a melting point exceeding 1000°C, then even if thermal runaway of the battery cell occurs, the second inorganic fiber 6 will not melt or soften and can maintain its shape, thus it can be used appropriately.

[0243] Furthermore, it is more preferable to use ceramic fibers such as silica fibers, alumina fibers and aluminosilicate fibers, as well as natural mineral fibers, which are listed as the second inorganic fiber 6 above. Among them, it is even more preferable to use fibers with a melting point of more than 1000°C.

[0244] Furthermore, even if the second inorganic fiber 6 is amorphous, it can be used as long as it has a glass transition temperature higher than that of the first inorganic fiber 5. For example, a glass fiber with a glass transition temperature higher than that of the first inorganic fiber 5 can also be used as the second inorganic fiber 6.

[0245] Furthermore, as the second inorganic fiber 6, various inorganic fibers, as exemplified, can be used alone, or two or more can be used in combination.

[0246] As described above, the glass transition temperature of the first inorganic fiber 5 is lower than that of the second inorganic fiber 6. When exposed to high temperatures, the first inorganic fiber 5 softens first. Therefore, the first inorganic fiber 5 can be used to bond the first organic fiber 1 and the first inorganic particles 2, etc. However, for example, if the second inorganic fiber 6 is amorphous and its fiber diameter is smaller than that of the first inorganic fiber 5, and if the glass transition temperatures of the first inorganic fiber 5 and the second inorganic fiber 6 are close, the second inorganic fiber 6 may soften first.

[0247] 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.

[0248] Furthermore, the fiber length of the first inorganic fiber 5 is preferably 100 mm or less, and more preferably 0.1 mm or more. The fiber length of the second inorganic fiber 6 is preferably 0.1 mm or less. These reasons are as described above.

[0249] (3-5-3. Two types of inorganic fibers with different glass transition temperatures and average fiber diameters)

[0250] When the heat transfer suppressing sheet contains two kinds of inorganic fibers, it is preferred that the first inorganic fiber 5 is an amorphous fiber, and the second inorganic fiber 6 is at least one kind of fiber selected from crystalline fibers and amorphous fibers with a glass transition temperature higher than that of the first inorganic fiber 5, and the average fiber diameter of the first inorganic fiber 5 is larger than that of the second inorganic fiber 6.

[0251] As described above, when the heat transfer suppression sheet of 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 coarser first inorganic fiber 5 is an amorphous fiber, and the finer second inorganic fiber 6 is a fiber composed of at least one selected from crystalline fibers and amorphous fibers with a glass transition temperature higher than that of the first inorganic fiber 5. Therefore, the first inorganic fiber 5 has a low glass transition temperature and softens first, thus hardening into a film as the temperature rises. On the other hand, if the finer second inorganic fiber 6 is a fiber composed of at least one selected from crystalline fibers and amorphous fibers with a glass transition temperature higher than that of the first inorganic fiber 5, then even if the temperature rises, the finer second inorganic fiber 6 remains in a fiber shape, thus maintaining the structure of the heat transfer suppression sheet and preventing powder shedding.

[0252] Furthermore, even in this case, the fiber length of the first inorganic fiber 5 is preferably 100 mm or less, and more preferably 0.1 mm or more. The fiber length of the second inorganic fiber 6 is preferably 0.1 mm or less. These reasons are as described above.

[0253] In addition, the heat transfer suppression sheet of this embodiment may contain different inorganic fibers besides the first inorganic fiber 5 and the second inorganic fiber 6 described above.

[0254] (3-5-4. The respective contents of the first and second inorganic fibers)

[0255] When the heat transfer suppressing sheet contains two kinds 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 suppressing 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 suppressing sheet.

[0256] Furthermore, the content of the first inorganic fiber 5 is more preferably 5% by mass and less than 15% by mass relative to the total mass of the heat transfer inhibiting sheet, and the content of the second inorganic fiber 6 is more preferably 5% by mass and less than 15% by mass relative to the total mass of the heat transfer inhibiting sheet. By setting such contents, the shape retention, extrusion resistance, wind pressure resistance based on the first inorganic fiber 5 and the retention ability of the inorganic particles based on the second inorganic fiber 6 are well balanced.

[0257] [4. Battery Pack]

[0258] Figure 2This is a schematic diagram illustrating a battery pack according to an embodiment of the present invention. The battery pack 100 of this embodiment is formed by connecting multiple battery cells 101 in series or in parallel. Furthermore, a heat transfer suppression sheet 10 of this embodiment is sandwiched between the battery cells 101, for example. The battery cells 101 and the heat transfer suppression sheet 10 are housed in a battery casing 110.

[0259] Furthermore, the heat transfer inhibition sheet 10 is as described above.

[0260] Thus, when the heat transfer suppression sheet 10 is sandwiched between each battery cell 101, the heat transfer suppression sheet 10 has the effect of suppressing heat transfer, and therefore, it can suppress the propagation of heat to the battery cell adjacent to the battery cell that has become hot.

[0261] Furthermore, the heat transfer suppression sheet 10 of this embodiment has high compressive strength, thus suppressing the thermal expansion of the battery cells 101 during charging and discharging. Therefore, the distance between the battery cells can be ensured, the reduction in thermal insulation performance can be suppressed, and thermal runaway of the battery cells can be prevented. In addition, by suppressing thermal expansion, deformation of the battery cells can be prevented, thus reducing the load on the battery casing 110.

[0262] Furthermore, the battery pack 100 in this embodiment is not limited to... Figure 2 The illustrated battery pack may also have heat transfer suppression sheets 10 disposed not only between the battery cells 101, but also between the battery cells 101 and the battery casing 110.

[0263] In the battery pack 100 configured in this way, in the event of a fire in a battery cell, the spread of flames to the outside of the battery casing 110 can be suppressed.

[0264] For example, the battery pack 100 of this embodiment is sometimes used in electric vehicles (EVs) and is located under the passenger's floor. In this case, it is assumed that even if the battery cell catches fire, the safety of the passenger can be ensured.

[0265] In addition, besides being able to sandwich the heat transfer suppressor 10 between each battery cell, the heat transfer suppressor 10 can also be disposed between the battery cell 101 and the battery casing 110. Therefore, there is no need to remake flame-retardant materials, etc., and a low-cost and safe battery pack 100 can be easily constructed.

[0266] In the battery pack of this embodiment, the heat transfer suppression sheet 10 disposed between the battery cell 101 and the battery casing 110 can be in contact with the battery cell 101 or may have a gap. However, if there is a gap between the heat transfer suppression sheet 10 and the battery cell 101, the deformation of the battery cell can be allowed even if the temperature of any one of the battery cells rises and its volume expands.

[0267] Furthermore, the heat transfer suppression sheet 10 of this embodiment can be easily bent depending on the type and thickness of the material chosen. Therefore, it is not affected by the shape of the battery cell 101 and the battery casing 110, and can accommodate any shape. Specifically, in addition to prismatic batteries, it can also be applied to cylindrical batteries, flat batteries, etc.

[0268] The various embodiments have been described above, but the present invention is not limited to these examples. Those skilled in the art will obviously be able to conceive of various modifications or alterations within the scope of the claims, and it should be understood that these also fall within the technical scope of the present invention. Furthermore, the constituent elements of the above embodiments can be combined arbitrarily without departing from the spirit of the invention.

Claims

1. A heat transfer suppressor sheet used in a battery pack, characterized in that, The heat transfer suppression sheet is located between the battery cells of the battery pack or between the battery cell and the battery casing of the battery pack. The heat transfer inhibiting sheet comprises: The first organic fiber does not have a glass transition temperature below 120°C; First inorganic particles; Resin adhesives; as well as The second organic fiber with a glass transition temperature If the first organic fiber does not have a glass transition temperature, the glass transition temperature of the second organic fiber is higher than that of the resin adhesive. The first organic fiber is at least one selected from polybutylene terephthalate fiber, polypropylene terephthalate fiber, polyacetal fiber, polytetrafluoroethylene fiber, polyetheretherketone fiber, polyphenylene sulfide fiber, polyamide fiber, and poly(p-phenylene terephthalamide) fiber.

2. The heat transfer suppression sheet according to claim 1, characterized in that, The first organic fiber is at least one of crystalline organic fibers with a glass transition temperature of 120°C or higher and organic fibers without a glass transition temperature.

3. The heat transfer suppression sheet according to claim 1 or 2, characterized in that, The first organic fiber has a melting point Tm at temperatures above 200°C. The elastic modulus of the first organic fiber at Tm℃ is more than 0.1% relative to the elastic modulus of the first organic fiber at 23℃.

4. The heat transfer suppression sheet according to claim 1 or 2, characterized in that, The content of the first organic fiber is more than 1% by mass and less than 10% by mass relative to the total mass of the heat transfer inhibiting sheet.

5. The heat transfer suppression sheet according to claim 1 or 2, characterized in that, The glass transition temperature of the second organic fiber is below 250°C.

6. The heat transfer suppression sheet according to claim 1, 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.

7. The heat transfer suppression sheet according to claim 1 or 2, characterized in that, 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.

8. The heat transfer suppression sheet according to claim 1 or 2, characterized in that, The heat transfer inhibition sheet further comprises at least one first inorganic fiber and a second inorganic fiber, selected from the average fiber diameter, shape and glass transition temperature, which are different from each other.

9. The heat transfer suppression sheet according to claim 8, characterized in that, The average fiber diameter of the first inorganic fiber is larger than that of the second inorganic fiber. The first inorganic fiber is linear or needle-like, and the second inorganic fiber is dendritic or crimped.

10. The heat transfer suppression sheet according to claim 8, characterized in that, The first inorganic fiber is an amorphous fiber. The second inorganic fiber is at least one type of fiber selected from crystalline fibers and amorphous fibers with a glass transition temperature higher than that of the first inorganic fiber. The average fiber diameter of the first inorganic fiber is larger than that of the second inorganic fiber.

11. The heat transfer inhibiting sheet according to claim 8, wherein, The first inorganic particle comprises at least one type selected from nanoparticles, hollow particles, and porous particles. The first inorganic fiber is an amorphous fiber. The second inorganic fiber is at least one inorganic fiber selected from crystalline fibers and amorphous fibers with a glass transition temperature higher than that of the first inorganic fiber.

12. The heat transfer suppression sheet according to claim 1 or 2, characterized in that, The heat transfer inhibition sheet also contains a second inorganic particle composed of metal oxides.

13. The heat transfer suppression sheet according to claim 1 or 2, characterized in that, The resin adhesive comprises at least one selected from styrene-butadiene resin, acrylic resin, silicone-acrylic resin and styrene resin.

14. A battery pack comprising: A plurality of battery cells; and a heat transfer suppressor sheet according to any one of claims 1 to 13, wherein the plurality of battery cells are connected in series or in parallel.

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