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

Abstract

The present invention provides an elastic sheet and a method for manufacturing the same, which can suppress the blocking phenomenon that occurs during storage and transportation, thereby ensuring excellent workability during the assembly of battery packs and the like, as well as an elastic sheet with good heat insulation properties, a heat transfer suppression sheet having this elastic sheet, and a battery pack having this elastic sheet or heat transfer suppression sheet. [Solution] The elastic sheet 10 is made of foam and has a first main surface 12a and a second main surface 12b perpendicular to the thickness direction. The elastic sheet 10 also has partition walls 13 made of the material constituting the foam and air bubbles 14 that are sealed and surrounded by the partition walls 13, and the first main surface 12a and the second main surface 12b have openings 18 through which a part of the air bubbles 14 is open.

Description

Technical Field

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

Background Art

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

[0003] In addition, for this battery cell, a lithium-ion secondary battery capable of high capacity and high output is mainly used as compared with a lead storage battery or a nickel-hydrogen battery. However, when a certain battery cell undergoes thermal runaway due to internal short circuit or overcharging of the battery, and then continues to generate heat rapidly, the heat from the battery cell that has undergone thermal runaway may propagate to other adjacent battery cells, causing thermal runaway of the other battery cells. [[ID=​​​​​For example, Patent Document 1 proposes a thermoplastic resin foam molded article that has high thermal insulation performance as well as excellent cushioning, good flexibility, and good bendability. In this foam molded article, an intermediate skin layer is provided between front and back skin layers made of non-foamed layers, with a first foam layer fused to the opposing surfaces of the front skin layer and the intermediate skin layer, and a second foam layer fused to the opposing surfaces of the back skin layer and the intermediate skin layer. Furthermore, a first core layer and a second core layer, made of countless elongated short fibrous resin bodies, are formed between the first foam layers and between the second foam layers. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2015-33849 [Overview of the project] [Problems that the invention aims to solve]

[0007] Incidentally, when storing and transporting resin and rubber materials, they are sometimes stacked to save space. However, depending on the surrounding environment, the surfaces of the resin materials may become sticky, causing a blocking phenomenon where the surfaces stick together.

[0008] In the foamed molded bodies described in Patent Document 1, if they are stored or transported in a stacked state, the skin layers of the foamed molded bodies may adhere to each other, potentially causing a blocking phenomenon. Therefore, when assembling battery packs, for example, if one foamed molded body is to be removed one by one using an assembly device, it may be necessary to separate the adhered foamed molded bodies, which can lead to a decrease in work efficiency. As a result, misalignment may occur, making it difficult to accurately position the foamed molded bodies between battery cells. Furthermore, when laminating foamed molded bodies with insulating materials, the skin layer of the foamed molded bodies may adsorb components contained in the insulating materials, potentially damaging the surface condition of the insulating materials.

[0009] This invention has been made in view of the above problems, and aims to provide an elastic sheet and a method for manufacturing the same, which suppress the blocking phenomenon that occurs during storage and transportation, thereby ensuring excellent workability when assembling battery packs and the like, and which also has good heat insulation properties, as well as a heat transfer suppression sheet having this elastic sheet, and a battery pack having this elastic sheet and heat transfer suppression sheet. [Means for solving the problem]

[0010] The above objective of the present invention is achieved by the following configuration [1] relating to the elastic sheet.

[0011] [1] An elastic sheet made of foam, having a first main surface and a second main surface perpendicular to the thickness direction, The foam has a partition made of the material constituting the foam, and a sealed bubble cell surrounded by the partition, An elastic sheet characterized in that the first main surface and the second main surface have openings in which a portion of the bubble cells are open.

[0012] Furthermore, preferred embodiments of the present invention relating to elastic sheets are described in the following [2]-[3].

[0013] [2] The elastic sheet according to [1], characterized in that the first main surface and the second main surface are the cut surfaces of the foam.

[0014] [3] The elastic sheet according to [1] or [2], characterized in that the foam comprises at least one selected from polyurethane, polyethylene and silicone.

[0015] The above objective of the present invention is achieved by the configuration described below [4] relating to a method for manufacturing an elastic sheet.

[0016] A method for manufacturing an elastic sheet as described in any one of [4] [1] to [3], An elastic sheet precursor manufacturing step of manufacturing an elastic sheet precursor having a pair of main surfaces orthogonal to the thickness direction, A cutting step of removing one main surface and the other main surface of the elastic sheet precursor by cutting along these main surfaces, and A method for manufacturing an elastic sheet, characterized in that a pair of cut surfaces formed by cutting are used as the first main surface and the second main surface of the elastic sheet.

[0017] Moreover, a preferred embodiment of the present invention related to the method for manufacturing an elastic sheet relates to the following [5] to [6].

[0018] [5] The elastic sheet precursor manufacturing step The method for manufacturing an elastic sheet according to [4], characterized in that it has a step of injecting the material of the foam into a mold, heating it, and foaming it.

[0019] [6] The elastic sheet precursor manufacturing step A step of processing the material of the foam into a predetermined shape to produce a foamed material, and The method for manufacturing an elastic sheet according to [4], characterized in that it has a step of heating and foaming the foamed material while sandwiching it with a sandwiching material.

[0020] The above object of the present invention is achieved by the configuration of the following [7] related to the heat transfer suppression sheet.

[0021] [7] A heat transfer suppression sheet, characterized in that it has the elastic sheet according to any one of [1] to [3] and a heat insulating material laminated on at least one of the first main surface and the second main surface of the elastic sheet.

[0022] The above object of the present invention is achieved by the configuration of the following [8] to [9] related to the assembled battery.

[0023] [8] An assembled battery, characterized in that it has a plurality of battery cells and the elastic sheet according to any one of [1] to [3], and the plurality of battery cells are connected in series or in parallel.

[0024] [9] A battery pack comprising a plurality of battery cells and the heat transfer suppression sheet according to [7], wherein the plurality of battery cells are connected in series or in parallel.

Advantages of the Invention

[0025] <00啊00101>According to the elastic sheet of the present invention, openings are formed on the surface of the elastic sheet to expose the inner wall surfaces of the air cells, and the contact area when the elastic sheets are stacked is significantly reduced, so that the blocking phenomenon can be suppressed. Further, according to the heat insulation sheet of the present invention, air cells are contained inside the elastic sheet, and air exists inside the air cells. Therefore, due to the effect of air heat insulation, the elastic sheet can have high heat insulation properties.

[0026] Further, according to the method for manufacturing the elastic sheet of the present invention, by simply cutting and removing one main surface and the other main surface of the elastic sheet precursor along these main surfaces, the contact area when the elastic sheets are laminated can be reduced, so that an elastic sheet capable of suppressing the blocking phenomenon can be easily manufactured.

[0027] Furthermore, according to the heat transfer suppression sheet of the present invention, it is possible to achieve both high deformation followability by the elastic sheet and even higher heat insulation properties, and it is also possible to suppress the elastic sheet from adsorbing components contained in the heat insulating material. Therefore, the surface state of the heat insulating material is not impaired, and the characteristics of the heat insulating material can be maintained.

[0028] Furthermore, according to the battery pack of the present invention, since it includes an elastic sheet having good heat insulation performance and high followability to deformation as described above, it is possible to suppress thermal runaway of the battery cells in the battery pack, deterioration of battery performance, and spread of flames to the outside of the battery case.

Brief Description of the Drawings

[0029] [Figure 1A] FIG. 1A is a schematic cross-sectional view showing an elastic sheet according to an embodiment of the present invention. <00001亮17> [Figure 1B] Figure 1B is a photographic representation of a drawing showing two elastic sheets according to an embodiment of the present invention, arranged with their first and second main surfaces facing upwards. [Figure 2] Figure 2 is a schematic cross-sectional view showing two elastic sheets stacked together according to an embodiment of the present invention. [Figure 3A] Figure 3A is a photograph used as a substitute for a drawing, showing a cross-section of an elastic sheet made from silicone rubber. [Figure 3B] Figure 3B is a photographic representation of a cross-section of an elastic sheet made from silicone rubber using a different method than that shown in Figure 3A. [Figure 4] Figure 4 is a schematic cross-sectional view showing a battery pack having an elastic sheet according to an embodiment of the present invention. [Figure 5] Figure 5 is a schematic cross-sectional view showing another example of the battery pack shown in Figure 4. [Figure 6A] Figure 6A is a cross-sectional view showing the process for producing an elastic sheet precursor. [Figure 6B] Figure 6B is a cross-sectional view showing the cutting process for cutting the elastic sheet precursor. [Figure 6C] Figure 6C is a cross-sectional view showing the elastic sheet precursor after the cutting process. [Figure 7A] Figure 7A is a photograph used as a substitute for a diagram to illustrate the blocking test method. [Figure 7B] Figure 7B is a photograph used as a substitute for a diagram to illustrate the blocking test method. [Modes for carrying out the invention]

[0030] The inventors diligently studied elastic sheets that could solve the above problems. As a result, they found that when elastic sheets are laminated in contact with each other, minimizing the contact area as much as possible can suppress the blocking phenomenon and ensure high workability during assembly. Therefore, the inventors found that if openings are formed on both sides of the elastic sheet to expose the inner wall surface of the bubble cell, the contact area between the elastic sheets can be significantly reduced.

[0031] The present invention is based on the above findings. Hereinafter, an elastic sheet according to an embodiment of the present invention will be briefly described with reference to the drawings. However, 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.

[0032] [Elastic sheet] Figure 1A is a schematic cross-sectional view showing an elastic sheet according to an embodiment of the present invention. Figure 1B is a photograph in lieu of a drawing showing two elastic sheets according to an embodiment of the present invention, arranged with their first and second main surfaces facing upward. The elastic sheet 10 according to this embodiment has a first main surface 12a and a second main surface 12b perpendicular to the thickness direction. The elastic sheet 10 is made of foam and has a partition wall portion 13 made of the material constituting the foam, and a sealed bubble cell 14 surrounded by this partition wall portion 13.

[0033] Furthermore, as shown in Figure 1B, the first main surface 12a and the second main surface 12b of the elastic sheet 10 are, for example, cut surfaces obtained by cutting the main surfaces on both sides of the foam, which is a precursor of the elastic sheet 10. At least a portion of the partition wall 13 is removed, a portion of the bubble cell 14 opens, and a plurality of openings 18 are formed.

[0034] Typically, components that make up a battery pack are stored and transported in a stacked state during the pre-assembly process. Therefore, elastic sheets are also sometimes stacked and held together to save space.

[0035] Figure 2 is a schematic diagram showing the state when the elastic sheets 10 according to this embodiment shown in Figure 1A are stacked. As mentioned above, there are openings 18 on the first main surface 12a and the second main surface 12b of the elastic sheet 10. Therefore, when one elastic sheet 10 is stacked on top of another elastic sheet 10, the area of ​​the opening 18 on the first main surface 12a of the lower elastic sheet 10 does not come into contact with the second main surface 12b of the upper elastic sheet 10. Similarly, the area of ​​the opening 18 on the second main surface 12b of the upper elastic sheet 10 does not come into contact with the first main surface 12a of the lower elastic sheet 10. As a result, the contact area between the elastic sheets 10 is reduced, making it difficult for them to stick together, and thus the occurrence of blocking phenomena can be suppressed. This means that when assembling a battery pack or the like, for example, when trying to remove foam molded bodies one by one using an assembly device, it is not necessary to peel apart the foam molded bodies that are sticking together, and high workability can be ensured. In addition, the occurrence of misalignment is suppressed, and it becomes possible to accurately position the foam molded bodies between the battery cells.

[0036] Furthermore, as described above, the elastic sheet 10 has air bubbles 14 that are sealed and surrounded by partition walls 13. Because air is present inside the air bubbles 14, the elastic sheet can have high thermal insulation properties due to the effect of air insulation. Moreover, the elastic sheet 10 can be easily deformed by the compression of the air inside the air bubbles 14 in response to pressure from other members, and when the pressure is released, it can be restored to its original shape by the restorative force of the air. Therefore, it can have high conformability to other members.

[0037] Figures 3A and 3B are photographic representations of cross-sections of elastic sheets made from silicone rubber. In both Figures 3A and 3B, only the first main surface is shown in enlargement. Note that Figures 3A and 3B are manufactured using different methods. The elastic sheet 41 shown in Figure 3A is made of millable silicone rubber and can be manufactured by kneading the raw materials with rollers, processing them into a sheet, and then foaming it. On the other hand, the elastic sheet 42 shown in Figure 3B is made of two-component condensation-type liquid silicone rubber and can be manufactured by mixing two types of liquid raw materials that have been mixed and stirred, processing them into a sheet, and then foaming it. In elastic sheets 41 and 42, elements identical to those in elastic sheet 10 shown in Figure 1A are given the same reference numerals, and detailed explanations are omitted or simplified.

[0038] As described above, both elastic sheets 41 and 42 have a partition wall portion 13 and a sealed bubble cell 14 surrounded by the partition wall portion 13 inside. The bubble cell 14 can be a single cell 14a in which one bubble (spherical space) is sealed by the partition wall portion 13, or a continuous cell 14b in which multiple consecutive bubbles are sealed by the partition wall portion 13. Since the continuous cell 14b has a larger volume than the single cell 14a, convection is more likely to occur inside it. Also, since the single cell 14a has a smaller volume than the continuous cell 14b, the repulsive force from the air when pressed is higher. Therefore, it is preferable that the volume of a sealed single cell 14a in the elastic sheet is larger than the volume of a sealed continuous cell 14b.

[0039] The configuration and effects of applying the elastic sheet 10 configured as described above to a battery pack will be explained in detail below. Figure 4 is a schematic cross-sectional view showing a battery pack having an elastic sheet according to an embodiment of the present invention. Note that some of the structure of the elastic sheet 10 shown in Figure 1A is simplified in Figure 4.

[0040] The battery pack 100 comprises a battery case 30 and a plurality of battery cells 20a, 20b, and 20c housed inside the battery case 30. Elastic sheets 10 are interposed between battery cells 20a and 20b, and between battery cells 20b and 20c. The plurality of battery cells 20a, 20b, and 20c are connected in series or parallel by busbars (not shown). While lithium-ion secondary batteries are preferably used for the battery cells 20a, 20b, and 20c, the design is not limited to these and can be applied to other types of secondary batteries as well.

[0041] As described above, the battery pack 100 in Figure 4 has an elastic sheet 10. Therefore, in Figure 4, even if the battery cells expand due to charging, the elastic sheet 10 is compressed, so a high repulsive force is not applied to the battery cells, and a decrease in battery performance can be suppressed. Furthermore, when the pressure is relieved by the discharge of the battery cells, the thickness of the elastic sheet 10 returns to its original state due to the restorative force of the air in the bubble cells 14 of the elastic sheet 10, so that the force that adjacent battery cells hold the elastic sheet 10 can be maintained.

[0042] [Heat transfer suppression sheet] The heat transfer suppression sheet according to an embodiment of the present invention comprises the elastic sheet according to the above-described embodiment of the present invention and an insulating material laminated on at least one of the first main surface and the second main surface of the elastic sheet. The configuration and effects when the heat transfer suppression sheet according to this embodiment is applied to a battery pack will be described below.

[0043] Figure 5 is a schematic cross-sectional view showing a battery pack having a heat transfer suppression sheet according to an embodiment of the present invention. In Figure 5, the same reference numerals are used for elements identical to those in the battery pack 100 shown in Figure 4, and detailed explanations are omitted or simplified. As shown in Figure 5, the heat transfer suppression sheet 50 comprises an elastic sheet 10 and a heat insulating material 11 laminated on one main surface of the elastic sheet 10. As shown in Figure 5, the battery pack 100 may have the heat transfer suppression sheet 50, in which the elastic sheet 10 and the heat insulating material 11 are laminated, interposed between the battery cells. In the battery pack 100 shown in Figure 5, preferred materials for the heat insulating material 11 will be described in detail later, but for example, using materials containing inorganic particles can provide high heat insulation and further suppress the transfer of heat from a battery cell experiencing thermal runaway to an adjacent battery cell.

[0044] Furthermore, the elastic sheet 10 according to the embodiment of the present invention has multiple openings on its surface, and since the contact area with the laminated heat insulating material 11 is small, it is possible to suppress the adsorption of components contained in the heat insulating material 11 by the elastic sheet 10. Therefore, the surface condition of the heat insulating material 11 is not impaired, and its properties can be maintained.

[0045] Similarly, in the battery pack 100 shown in Figure 5, the elastic sheet 10 has a sealed bubble cell 14 surrounded by a partition wall 13, so it can deform in response to the pressing force when the battery cell expands and return to its original shape when it contracts, thus having high conformability. As a result, it can follow the thermal runaway of the battery cell and deformation due to charging and discharging, thereby suppressing a decrease in battery performance and the spread of flames to the outside of the battery case.

[0046] In the battery pack 100 shown in Figure 5, one insulating material 11 is laminated on one main surface (for example, the first main surface) of one elastic sheet 10 and sandwiched between battery cells. However, the heat transfer suppression sheet 50 in the present invention may have a three-layer structure consisting of two elastic sheets 10 and an insulating material 11 sandwiched between these elastic sheets 10. Alternatively, it may have a three-layer structure in which the insulating material 11 is laminated on both the first and second main surfaces of one elastic sheet 10.

[0047] (Materials that make up the elastic sheet) The elastic sheet 10 is made of foam and is flexible enough to deform in response to the deformation of the battery cells 20a, 20b, and 20c. The foam can be made of materials including, for example, at least one selected from polyurethane, polyethylene, and silicone. Specifically, foamed silicone is one example.

[0048] (Thickness of the elastic sheet) The thickness of the elastic sheet 10 is not particularly limited, but it is preferable to set it to 1 mm or more and 10 mm or less in order to effectively obtain the above-mentioned effects of the elastic sheet 10. Furthermore, it is preferable that the shape and size of the first main surface 12a and the second main surface 12b of the elastic sheet 10 are substantially the same as the shape and size of the battery cells 20a, 20b, and 20c in Figure 4, and the surface of the heat insulating material 11 facing the elastic sheet 10 in Figure 5.

[0049] <Insulation material> As shown in Figure 5, when the elastic sheet 10 and the thermal insulation material 11 are laminated according to this embodiment, the thermal insulation material 11 is not particularly limited as long as it has, for example, inorganic particles and has a thermal insulation effect. Thermal conductivity can be cited as an indicator of the thermal insulation effect, but in this embodiment, the thermal conductivity of the thermal insulation material is preferably less than 1 (W / m·K), more preferably less than 0.5 (W / m·K), and more preferably less than 0.2 (W / m·K). Furthermore, the thermal conductivity of the thermal insulation material is more preferably less than 0.1 (W / m·K), more preferably less than 0.05 (W / m·K), and particularly preferably less than 0.02 (W / m·K). The thermal conductivity of the insulation material can be measured in accordance with the "Test Method for Thermal Conductivity of Refractory Materials" described in JIS R 2251.

[0050] (Size of insulation material) The size of the thermal insulation material 11 can be arbitrarily designed depending on the size of the elastic sheet 10 laminated on the thermal insulation material 11 and the battery cells 20a, 20b, and 20c shown in Figure 5. To obtain the desired thermal insulation performance, it is preferable that the size of the first main surface 12a of the elastic sheet 10 and the size of the main surface perpendicular to the thickness direction of the thermal insulation material 11 are approximately the same. When designing the main surfaces of the thermal insulation material 11 and the elastic sheet 10 to be approximately the same size, "approximately the same" means that the difference between the two sizes is preferably up to ±5% of the average value of the two, more preferably up to ±3%, and even more preferably up to ±1%.

[0051] (Inorganic particles) The thermal insulation material preferably contains inorganic particles. A single inorganic particle may be used, or a combination of two or more inorganic particles may be used. From the viewpoint of heat transfer suppression, it is preferable to use particles made of at least one inorganic material selected from oxide particles, carbide particles, nitride particles, and inorganic hydrate particles, and more preferably oxide particles. Particles mainly composed of multiple metal oxides can also be used. The shape of the inorganic particles is not particularly limited, but it is preferable to include at least one selected from nanoparticles, hollow particles, porous particles, and flake-like particles. Specifically, the inorganic particles can include silica nanoparticles, metal oxide particles, inorganic balloons such as microporous particles and hollow silica particles, particles made of thermally expandable inorganic materials, and particles made of water-containing porous materials. Furthermore, particles made of mica can also be used as inorganic particles.

[0052] (Method of manufacturing insulation material) When laminating the thermal insulation material 11 onto the elastic sheet according to this embodiment, the method for manufacturing the thermal insulation material is not particularly limited. A thermal insulation material raw material containing inorganic particles and, if necessary, organic fibers or inorganic fibers in a predetermined ratio is put into a mixer such as a V-type mixer to produce a mixture. Then, the obtained mixture is put into a predetermined mold, pressurized with a press or the like, and then heated to produce the thermal insulation material 11. The thermal insulation material 11 can be produced by either a wet method or a dry method, but from the viewpoint of thermal insulation performance, it is preferable to produce it by a dry method.

[0053] If the average secondary particle diameter of the inorganic particles is 0.01 μm or more, they are readily available and manufacturing costs can be kept down. Furthermore, if it is 200 μm or less, the desired heat insulating effect can be obtained. Therefore, the average secondary particle diameter of the inorganic particles is preferably 0.01 μm or more and 200 μm or less, and more preferably 0.05 μm or more and 100 μm or less.

[0054] Furthermore, by using two or more inorganic particles with different heat transfer suppression effects, the heat-generating element can be cooled in multiple stages, and the endothermic effect can be exhibited over a wider temperature range. Specifically, it is preferable to use a mixture of large-diameter and small-diameter particles. For example, when nanoparticles are used as one type of inorganic particle, it is preferable to include inorganic particles made of metal oxides as the other type of inorganic particle. Below, the inorganic particles will be described in more detail, with small-diameter inorganic particles referred to as the first inorganic particles and large-diameter inorganic particles as the second inorganic particles.

[0055] <First inorganic particle> (Oxide particles) Oxide particles have a high refractive index and a strong effect of diffusely reflecting light. Therefore, using oxide particles as the first inorganic particles can suppress radiative heat transfer, especially in high-temperature regions such as abnormal heat generation. As oxide particles, at least one particle selected from silica, titania, zirconia, zircon, barium titanate, zinc oxide, and alumina can be used. That is, only one of the above oxide particles that can be used as inorganic particles may be used, or two or more oxide particles may be used. In particular, silica is a component with high thermal insulation properties, and titania is a component with a high refractive index compared to other metal oxides. Since they have a high effect of diffusely reflecting light and blocking radiant heat in high-temperature regions of 500°C or higher, it is most preferable to use silica and titania as oxide particles.

[0056] (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 light. As a result, radiative heat transfer within the insulating material is suppressed in the high-temperature region of 500°C or higher, further improving the insulating properties. 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.

[0057] 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.

[0058] (Nanoparticles) In this invention, nanoparticles refer to particles that are spherical or nearly spherical, with an average primary particle diameter of less than 1 μm on the order of nanometers. Because nanoparticles have low density, they suppress conductive heat transfer, and when nanoparticles are used as the first inorganic particles, even finer voids are dispersed, resulting in excellent heat insulation that suppresses convective heat transfer. For this reason, it is preferable to use nanoparticles when using batteries in the normal room temperature range, as it can suppress heat conduction between adjacent nanoparticles. Furthermore, by using nanoparticles with a small average primary particle diameter as oxide particles, it is possible to suppress the increase in conductive heat transfer through the insulating material, even when the insulating material is compressed and its internal density increases due to expansion caused by thermal runaway of the battery cell. This is thought to be because nanoparticles easily form 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.

[0059] In this invention, when nanoparticles are used as the first inorganic particles, the material is not particularly limited as long as it conforms to the above definition of nanoparticles. For example, silica nanoparticles are a material with high thermal insulation properties, and because the contact points between particles are small, the amount of heat conducted by silica nanoparticles is smaller compared to when silica particles with a larger particle size are used. Also, commonly available silica nanoparticles have a bulk density of 0.1 g / cm³. 3 Because of this, for example, even if battery cells arranged on both sides of the heat transfer suppression sheet undergo thermal expansion and a large compressive stress is applied to the insulating material, the size (area) and number of contact points between silica nanoparticles do not increase significantly, and the insulating properties can be maintained. Therefore, it is preferable to use silica nanoparticles as the nanoparticles. Examples of silica nanoparticles include wet silica, dry silica, and aerogel, but silica nanoparticles particularly suitable for this embodiment will be described below.

[0060] Generally, wet silica has aggregated particles, while dry silica allows for particle dispersion. In the temperature range below 300°C, conduction is the dominant method of heat transfer, so dry silica, which allows for particle dispersion, can provide superior thermal insulation compared to wet silica. In this embodiment, it is preferable to use a manufacturing method in which a mixture containing the materials is processed into a sheet by a dry process. Therefore, it is preferable to use dry silica, silica aerogel, or the like as the inorganic particles, as they have low thermal conductivity.

[0061] (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 insulating material can be suppressed, especially in the temperature range below 500°C, thereby further improving the insulating properties. 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 insulating properties of the insulating material. 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.

[0062] (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).

[0063] 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

[0064] As described above, the heat transfer suppression sheet 15 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 contained in the heat insulating material 11 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.

[0065] (Average secondary particle diameter of inorganic hydrate particles: 0.01 μm or more and 200 μm or less) Furthermore, if inorganic hydrate particles are used as the first inorganic particles, and their average particle size is too large, it may take a certain amount of time for the first inorganic particles (inorganic hydrates) near the center of the insulation material 11 to reach their thermal decomposition temperature, resulting in the first inorganic particles near the center of the insulation material 11 not being 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.

[0066] (Particles made of thermally expandable inorganic material) Examples of thermally expandable inorganic materials include vermiculite, bentonite, mica, and perlite.

[0067] (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.

[0068] (Inorganic balloon) The thermal insulation material used in the present invention may include inorganic balloons as the first inorganic particles. The inclusion of inorganic balloons can suppress convective or conductive heat transfer within the insulation material at temperatures below 500°C, thereby further improving the insulation performance of the insulation material. As the inorganic balloon, at least one selected from shirasu balloons, silica balloons, fly ash balloons, barlite balloons, and glass balloons can be used.

[0069] (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.

[0070] (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.

[0071] <Second inorganic particle> When two types of inorganic particles are contained in the thermal insulation material, the second inorganic particle is not particularly limited as long as it differs from the first inorganic particle in terms of material, particle size, etc. The second inorganic particle can be oxide particles, carbide particles, nitride particles, inorganic hydrate particles, silica nanoparticles, metal oxide particles, inorganic balloons such as microporous particles and hollow silica particles, particles made of thermally expandable inorganic materials, particles made of water-containing porous materials, etc. Details of these are as described above.

[0072] Furthermore, nanoparticles exhibit extremely low conductive heat transfer and can maintain excellent thermal insulation properties even when compressive stress is applied to the insulation material. In addition, metal oxide particles such as titania have a high effect in blocking radiant heat. Moreover, by using both large-diameter and small-diameter inorganic particles, the small-diameter inorganic particles can fill the gaps between the large-diameter inorganic particles, resulting in a denser structure and improving the heat transfer suppression effect. Therefore, when nanoparticles are used as the first inorganic particles, it is preferable to further include metal oxide particles, which are larger in diameter than the first inorganic particles, as a second inorganic particle in the insulation material. 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.

[0073] When using at least one particle selected from dry silica particles and silica aerogel as the first inorganic particle, and at least one particle selected from titania, zircon, zirconia, silicon carbide, zinc oxide, and alumina as the second inorganic particle, in order to obtain excellent thermal insulation performance within a temperature range of 300°C or less, the first inorganic particle is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more, based on the total mass of the inorganic particles. Furthermore, the first inorganic particle is preferably 95% by mass or less, more preferably 90% by mass or less, and even more preferably 80% by mass or less, based on the total mass of the inorganic particles.

[0074] On the other hand, in order to obtain excellent heat insulation performance in a temperature range exceeding 300°C, the amount of the second inorganic particles is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 20% by mass or more, based on the total mass of the inorganic particles. Furthermore, the amount of the second inorganic particles is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less, based on the total mass of the inorganic particles.

[0075] (Average primary particle diameter of the second inorganic particle) When a second inorganic particle made of a metal oxide is included in the thermal insulation material, if the average primary particle diameter of the second inorganic particle is 1 μm or more and 50 μm or less, radiant heat transfer can be efficiently suppressed in the high-temperature region of 500°C or higher. It is more preferable that the average primary particle diameter of the second inorganic particle is 5 μm or more and 30 μm or less, and most preferably 10 μm or less.

[0076] (Content of inorganic particles) In this embodiment, if the total amount of inorganic particles in the thermal insulation material 11 is appropriately controlled, the thermal insulation properties of the thermal insulation material 11 can be sufficiently ensured. The total content of inorganic particles is preferably 60% by mass or more, and more preferably 70% by mass or more, relative to the total mass of the thermal insulation material 11. Furthermore, if the total content of inorganic particles becomes too high, the content of organic fibers will relatively decrease. Therefore, in order to obtain sufficient structural reinforcement and inorganic particle retention effects, the total content of inorganic particles is preferably 95% by mass or less, and more preferably 90% by mass or less, relative to the total mass of the thermal insulation material 11.

[0077] The amount of inorganic particles in the thermal insulation material 11 can be calculated, for example, by heating the thermal insulation material 11 to 800°C to decompose the organic components and then measuring the mass of the remaining material.

[0078] The heat transfer sheet according to this embodiment contains, in addition to the inorganic particles, at least one of organic fibers and inorganic fibers. The organic and inorganic fibers contained in the heat transfer sheet are described below.

[0079] <Organic Fibers> Organic fibers have the effect of giving flexibility to the insulation material 11, and also have the effect of increasing the strength of the insulation material 11 by forming a framework with organic fibers. Furthermore, if inorganic particles and other organic fibers are welded to the surface of the organic fibers, the effect of improving the strength of the sheet and the effect of maintaining its shape can be further improved. In addition, if the insulation material 11 contains organic fibers in an appropriate amount, multiple voids are formed inside the insulation material 11, and when the insulation material 11 is heated, air and moisture can be released to the outside through these voids.

[0080] As the material for the organic fibers in the thermal insulation material 11, single-component organic fibers can be used, but it is preferable to use binder fibers with a core-sheath structure. Binder fibers with a core-sheath structure have a core portion that extends in the longitudinal direction of the fiber and a sheath portion formed to cover the outer surface of the core portion. In this case, the core portion is made of a first organic material, and the sheath portion is made of a second organic material, and the melting point of the first organic material is higher than the melting point of the second organic material.

[0081] (First organic material) In this embodiment, when using binder fibers with a core-sheath structure, the first organic material constituting the core is not particularly limited as long as it has a melting point higher than that of the sheath present on the outer surface of the core, i.e., the second organic material. Examples of the first organic material include at least one selected from polyethylene terephthalate, polypropylene, and nylon.

[0082] (Second organic material) The second organic material is not particularly limited, as long as its melting point is lower than that of the first organic material constituting the organic fiber. Examples of the second organic material include at least one selected from polyethylene terephthalate, polyethylene, polypropylene, and nylon. The melting point of the second organic material is preferably 90°C or higher, and more preferably 100°C or higher. Furthermore, the melting point of the second organic material is preferably 150°C or lower, and more preferably 130°C or lower.

[0083] (Organic fiber content) In this embodiment, if the content of organic fibers in the thermal insulation material 11 is appropriately controlled, a sufficient reinforcing effect on the framework can be obtained. The organic fiber content is preferably 5% by mass or more, and more preferably 10% by mass or more, relative to the total mass of the insulation material 11. Furthermore, if the organic fiber content becomes too high, the inorganic particle content will relatively decrease. Therefore, in order to obtain the desired insulation performance, the organic fiber content is preferably 25% by mass or less, and more preferably 20% by mass or less, relative to the total mass of the insulation material 11.

[0084] (Fiber length of organic fibers) While there are no particular limitations on the fiber length of the organic fibers, it is preferable that the average fiber length of the organic fibers be 10 mm or less from the viewpoint of ensuring moldability and processability. On the other hand, from the viewpoint of using organic fibers as a framework and ensuring the compressive strength of the thermal insulation material, it is preferable that the average fiber length of the organic fibers be 0.5 mm or more.

[0085] <Inorganic Fibers> When the insulation material 11 contains inorganic fibers, a single inorganic fiber may be used, or two or more types of inorganic fibers may be used in combination. Examples of inorganic fibers include ceramic fibers such as silica fibers, alumina fibers, alumina silicate fibers, zirconia fibers, carbon fibers, soluble fibers, refractory ceramic fibers, aerogel composites, magnesium silicate fibers, alkali earth silicate fibers, potassium titanate fibers, silicon carbide fibers, potassium titanate whisker fibers, glass fibers, glass wool, slag wool, and other natural mineral fibers such as rock wool, basalt fiber, wollastonite, and mullite fiber. These inorganic fibers are preferable in terms of heat resistance, strength, and availability. From the viewpoint of handling, the thermal insulation material preferably contains at least one of the above inorganic fibers selected from silica-alumina fibers, alumina fibers, silica fibers, rock wool, alkali earth silicate fibers, and glass fibers.

[0086] The cross-sectional shape of inorganic fibers is not particularly limited and includes circular, flat, hollow, polygonal, and core cross-sections. Among these, fibers with irregular cross-sections, such as hollow, flat, or polygonal cross-sections, can be suitably used because they slightly improve thermal insulation.

[0087] The preferred lower limit for the average fiber length of the inorganic fibers is 0.1 mm, and the more preferred lower limit is 0.5 mm. On the other hand, the preferred upper limit for the average fiber length of the inorganic fibers is 50 mm, and the more preferred upper limit is 10 mm. If the average fiber length of the inorganic fibers is less than 0.1 mm, entanglement between the inorganic fibers is unlikely to occur, which may reduce the mechanical strength of the insulation material 11. On the other hand, if it exceeds 50 mm, although a reinforcing effect can be obtained, the inorganic fibers may not be able to entangle tightly with each other, or a single inorganic fiber may curl up, which may lead to a decrease in insulation performance.

[0088] The preferred lower limit for the average fiber diameter of inorganic fibers is 1 μm, a more preferred lower limit is 2 μm, and an even more preferred lower limit is 3 μm. On the other hand, the preferred upper limit for the average fiber diameter of inorganic fibers is 15 μm, and a more preferred upper limit is 10 μm. If the average fiber diameter of inorganic fibers is less than 1 μm, the mechanical strength of the inorganic fibers themselves may decrease. Furthermore, from the viewpoint of the impact on human health, it is preferable that the average fiber diameter of inorganic fibers be 3 μm or more. On the other hand, if the average fiber diameter of inorganic fibers is greater than 15 μm, solid heat transfer through the inorganic fibers may increase, leading to a decrease in thermal insulation performance, and the moldability and strength of the thermal insulation material may deteriorate.

[0089] (Inorganic fiber content) In this embodiment, when the thermal insulation material 11 contains inorganic fibers, it is preferable that the inorganic fiber content is 3% by mass or more and 15% by mass or less of the total mass of the thermal insulation material 11.

[0090] Furthermore, it is more preferable that the inorganic fiber content be between 5% and 10% by mass relative to the total mass of the thermal insulation material 11. By using such a content, the shape retention, compressive force resistance, wind pressure resistance, and inorganic particle holding ability of the inorganic fibers are well-balanced. In addition, by appropriately controlling the inorganic fiber content, the organic and inorganic fibers intertwine to form a three-dimensional network, thereby improving the effect of holding inorganic particles and other compounding materials described later.

[0091] <Other ingredients> (Hot melt powder) In this embodiment, in addition to the inorganic particles and organic fibers mentioned above, hot melt powder may be included in the material mixture. The hot melt powder is a powder that contains, for example, a third organic material different from the first and second organic materials mentioned above, and has the property of melting when heated. By including the hot melt powder in the mixture and heating it, the hot melt powder melts, and then when cooled, it hardens while containing the surrounding inorganic particles. Therefore, the shedding of inorganic particles from the heat insulating material 11 can be suppressed.

[0092] While various types of hot melt powders have different melting points, it is best to select a hot melt powder with an appropriate melting point, taking into account the melting points of the core and sheath of the binder fiber used. Specifically, if the melting point of the third organic material constituting the hot melt powder is lower than that of the first organic material constituting the organic fiber, the heating temperature can be set to melt the sheath and the hot melt powder while leaving the core intact. For example, if the melting point of the hot melt powder is lower than or equal to the melting point of the sheath, the heating temperature during manufacturing can be set between the melting points of the core and the sheath, making it even easier to set the heating temperature.

[0093] Alternatively, the type of hot melt powder used can be selected so that its melting point falls between the melting point of the core and the melting point of the sheath. When a hot melt powder with such a melting point is used, after both the sheath and the hot melt powder melt and then cool and harden, the hot melt powder present in the gaps between the organic fibers (core), the surrounding molten sheath, and the inorganic particles hardens first. As a result, the position of the organic fibers can be fixed, and then the molten sheath fuses to the organic fibers, making it easier to form a three-dimensional structure. Therefore, the overall strength of the sheet can be further improved.

[0094] If the melting point of the third organic material constituting the hot melt powder is sufficiently lower than the melting point of the first organic material constituting the core, the margin for setting the heating temperature in the heating process can be widened, making it easier to set the temperature to obtain the desired structure. For example, the melting point of the first organic material is preferably 60°C or more higher than the melting point of the third organic material, more preferably 70°C or more higher, and even more preferably 80°C or more higher.

[0095] The melting point of the hot melt powder (third organic material) is preferably 80°C or higher, and more preferably 90°C or higher. Furthermore, the melting point of the hot melt powder (third organic material) is preferably 180°C or lower, and more preferably 150°C or lower. Examples of components constituting the hot melt powder include polyethylene, polyester, polyamide, and ethylene vinyl acetate.

[0096] (Hot melt powder content) When incorporating hot melt powder into the insulating material to suppress the shedding of inorganic particles, even a small amount of the powder can be used to achieve the effect of suppressing powder shedding. Therefore, the hot melt powder content is preferably 0.5% by mass or more, and more preferably 1% by mass or more, relative to the total mass of the insulating material. On the other hand, increasing the content of hot melt powder relatively decreases the content of inorganic particles, etc. Therefore, in order to obtain the desired thermal insulation performance, the content of hot melt powder is preferably 5% by mass or less, and more preferably 4% by mass or less, relative to the total mass of the thermal insulation material.

[0097] When the insulating material 11 includes hot melt powder, the heating temperature in the heating process is preferably set at least 10°C higher than the higher of the melting point of the second organic material constituting the sheath and the melting point of the third organic material constituting the hot melt powder, and more preferably at least 20°C higher. On the other hand, the heating temperature is preferably set at least 10°C lower than the melting point of the first organic material constituting the core, and more preferably at least 20°C lower. By setting the heating temperature in this manner, a strong framework can be formed, the strength of the sheet can be further improved, and the shedding of inorganic particles can be prevented.

[0098] Furthermore, the thermal insulation material 11 may contain other binders, colorants, etc., as needed. These are all useful for reinforcing the thermal insulation material 11 or improving its moldability, and it is preferable that the total amount of these binders be 10% by mass or less, more preferably 8% by mass or less, and even more preferably 5% by mass or less, relative to the total mass of the thermal insulation material 11.

[0099] Furthermore, in this embodiment, in addition to the heat insulating material 11 and the elastic sheet 10, a mica sheet containing mica can be laminated. The mica sheet will be described in detail below.

[0100] <Mica Sheet> The mica sheet is made by processing a mica sheet material containing mica, an inorganic particle, into a sheet. Mica has excellent heat resistance and insulation properties, and the mica sheet, which is made by processing a mica-containing material into a sheet, also has excellent impact resistance. Therefore, for example, if the battery cell 20a ruptures due to high temperature and flying debris is generated, damage to the insulation material 11 and the elastic sheet 10 can be suppressed. As a result, high thermal insulation can be maintained between the battery cell 20a and the battery cell 20b.

[0101] The mica sheet material preferably contains, in addition to mica, oxide particles, oxide fibers, etc. Specifically, examples include SiO2, Al2O3, Ti2O3, etc., but the present invention is not limited to these materials. It is even more preferable to use a mica sheet composed of natural minerals. The sheet shape is usually a flat sheet without holes, or it may have holes. If holes are provided in the center or at least a part of other regions of the mica sheet, the mica sheet can follow the battery cells 20a, 20b, and 20c as they expand and contract without cracking.

[0102] [Method for manufacturing elastic sheets] Next, an example of a method for manufacturing an elastic sheet according to an embodiment of the present invention will be described below with reference to Figures 6A to 6C. Figure 6A is a cross-sectional view showing the process of producing an elastic sheet precursor, which will be the material for the elastic sheet. Figure 6B is a cross-sectional view showing the cutting process for cutting the elastic sheet precursor. Figure 6C is a cross-sectional view showing the state of the elastic sheet precursor after the cutting process. The elastic sheets shown in Figures 6A to 6C are simplified versions of the elastic sheet 10 shown in Figure 1A, and the same reference numerals are used for the same components as in the elastic sheet shown in Figure 1A, while detailed explanations are omitted or simplified.

[0103] <Process for producing elastic sheet precursors> The process for producing an elastic sheet precursor is a process for producing an elastic sheet precursor having a pair of main surfaces perpendicular to the thickness direction. In this embodiment, the process when foamed silicone is used as the material for the elastic sheet will be described. Although not shown in the figures, an elastic sheet precursor 19 is produced by kneading a silicone-containing material with a crosslinking agent and a foaming agent as the material for the foam, injecting this foam material into a mold, and heating it to cause foaming. At this time, due to the effect of the foaming agent, bubble cells are formed inside the elastic sheet precursor 19, and partitions are formed that surround and seal the bubble cells. Furthermore, when the foam material is injected into the mold, the material is cooled and solidified on the inner wall surface of the mold. As a result, an elastic sheet precursor 19 having a skin layer 16 on its surface is formed, as shown in Figure 6A.

[0104] The materials used for the foam are not limited to those mentioned above; for example, a mixture of two types of liquid silicone raw materials can also be used.

[0105] Furthermore, as a method for producing the elastic sheet precursor, a method can also be used in which the foam material is processed into a predetermined shape, such as a sheet, to produce a foamed material, and then the obtained foamed material is heated while being held between clamping materials such as a carrier film to cause foaming. This forms a skin layer on the surface held between the clamping materials. When the foamed material is in the form of a sheet, it is sufficient to clamp at least one pair of main surfaces of the foamed material with the clamping material, but the end surfaces connecting the pair of main surfaces may also be clamped with other clamping materials.

[0106] <Cutting process> Next, as shown in Figure 6B, one main surface and the other main surface of the elastic sheet precursor 19 are removed by cutting the elastic sheet precursor 19 along cutting lines 4 parallel to these main surfaces using a cutting tool 3 such as a knife. This forms cut surfaces 19c and 19d, as shown in Figure 6C. Although not shown in Figures 6A to 6C, the elastic sheet precursor has countless air bubble cells and surrounding partition walls. Therefore, by cutting and removing one main surface and the other main surface of the elastic sheet precursor 19 with the cutting tool 3, openings 18 with some of the air bubble cells open are formed in the cut surfaces 19c and 19d, and recesses are formed where some of the inner wall surfaces of the air bubble cells 14 are exposed. In this way, an elastic sheet 10 can be produced with the pair of cut surfaces 19c and 19d formed by cutting as the first main surface 12a and the second main surface 12b.

[0107] In Figure 6B, the elastic sheet precursor 19 is cut along a cutting line 4 that allows for the removal of the skin layer 16. However, in the present invention, the cutting method and cutting location are not particularly limited. Cutting methods include cutting, polishing, and shaping. For example, one main surface 19a and the other main surface 19b of the elastic sheet precursor 19 can be polished using a grinding wheel or brush to remove a portion of the partition wall. This method allows for the production of an elastic sheet 10 of a desired thickness.

[0108] [Battery pack] An example of a battery pack, which is an example of an energy storage device to which the elastic sheet 10 according to an embodiment of the present invention is applied, is illustrated in Figures 4 and 5 above. The configuration and effects of the battery pack are also as described above. In other words, the elastic sheet 10 has excellent heat insulation performance and can absorb deformation of battery cells, thereby suppressing a decrease in battery performance, and thus a battery pack that can maintain excellent safety even in abnormal situations can be obtained.

[0109] It should be noted that the battery pack 100 of this embodiment is not limited to the battery pack illustrated in Figures 4 and 5. For example, the elastic sheet 10 may be placed not only between battery cells 20a and 20b, and between battery cells 20b and 20c, but also between battery cells 20a, 20b, and 20c and the battery case 30, or it may be attached to the inner surface of the battery case 30.

[0110] In the battery pack 100 configured in this way, if a battery cell ignites or experiences thermal runaway, it is possible to suppress the spread of flames to the outside of the battery case 30, and it is also possible to absorb impacts to the battery case 30 and prevent damage to the battery case 30. For example, the battery pack 100 according to this embodiment may be used in electric vehicles (EVs) and placed under the passenger floor. In this case, even if the battery cells catch fire, the safety of the passengers can be ensured. Furthermore, since the elastic sheet 10 can be interposed not only between each battery cell, but also between the battery cells 20a, 20b, and 20c and the battery case 30, there is no need to newly manufacture flame-retardant materials, and a safe battery pack 100 can be easily constructed at low cost. [Examples]

[0111] The following describes examples and comparative examples of the elastic sheet according to this embodiment.

[0112] [Preparation of test specimens] As an example of the invention, test specimens 61 and 62 were prepared using the manufacturing method described with reference to Figures 6A to 6C, with the first and second main surfaces having openings in which a portion of the bubble cells were open. As a comparative example, test specimens 71 and 72 having a skin layer on the surface, as shown in Figure 6A, were also prepared. Ten sets of test specimens each of the example of the invention and the comparative example were prepared.

[0113] [Blocking Test] Figures 7A and 7B are photographic representations illustrating the blocking test method. In the inventive example, test pieces 61 and 62 were stacked with their faces facing each other, and a load of approximately 4 kg was applied in the stacking direction for 24 hours. Then, as shown in Figure 7A, the upper test piece 62 was lifted by hand in the direction of the arrow to check for the occurrence of the blocking phenomenon. Also, as shown in Figure 7B, the occurrence of the blocking phenomenon was checked in the same manner as in the inventive example using the comparative example test pieces 71 and 72. The results of the blocking test for the inventive example and comparative example test pieces are shown in Table 1 below. In the "Occurrence or Absence of Blocking Phenomenon" column in Table 1 below, if the lower test piece did not adhere to the upper test piece when the upper test piece was lifted, and only the upper test piece was lifted, it was marked with ○ (No Blocking Phenomenon Occurred). Furthermore, when the upper test piece was lifted, if the lower test piece adhered to the upper test piece and was lifted together with the upper piece, it was marked as × (blocking phenomenon occurred).

[0114] [Table 1]

[0115] As shown in Table 1 and Figure 7A above, in all of the invention examples No. 1 to 10, when the upper test piece 62 was lifted in the direction of the arrow, the lower test piece 61 did not lift. Therefore, the occurrence rate of the blocking phenomenon was 0%, and the blocking phenomenon was completely prevented.

[0116] On the other hand, as shown in Table 1 and Figure 7B above, in nine of the comparative examples No. 1 to 10, a blocking phenomenon occurred in which the lower test piece 71 lifted when the upper test piece 72 was lifted in the direction of the arrow. In comparative example No. 3, however, the blocking phenomenon did not occur, resulting in a blocking phenomenon occurrence rate of 90%. This indicates that using the elastic sheet of the present invention, in which the skin layer has been removed and some of the air cell openings have been opened, can prevent a decrease in workability during product assembly and transportation. [Explanation of Symbols]

[0117] 3 Cutting tools 4 Cutting line 10,41,42 Elastic Sheet 11. Insulation 12a First main surface 12b Second main surface 13 Bulkhead 14 Bubble Cells 14a Single cell 14b Contiguous Cells 16 skin layers 18 Opening 19. Elastic sheet precursor 19a,19b Main surface 19c,19d Cut surface 20a, 20b, 20c battery cells 30 Battery Cases 50 Heat transfer suppression sheets 100 battery packs

Claims

1. An elastic sheet made of foam, having a first main surface and a second main surface perpendicular to the thickness direction, The foam has a partition made of the material constituting the foam, and a sealed bubble cell surrounded by the partition, An elastic sheet characterized in that the first main surface and the second main surface have openings in which a portion of the bubble cells are open.

2. The elastic sheet according to claim 1, characterized in that the first main surface and the second main surface are the cut surfaces of the foam.

3. The elastic sheet according to claim 1, characterized in that the foam comprises at least one selected from polyurethane, polyethylene, and silicone.

4. A method for manufacturing an elastic sheet according to any one of claims 1 to 3, An elastic sheet precursor manufacturing step for producing an elastic sheet precursor having a pair of main surfaces perpendicular to the thickness direction, The process includes a cutting step of removing one main surface and the other main surface of the elastic sheet precursor by cutting along these main surfaces, A method for manufacturing an elastic sheet, characterized in that a pair of cut surfaces formed by cutting are the first main surface and the second main surface of the elastic sheet.

5. The elastic sheet precursor manufacturing step is as follows: A method for manufacturing an elastic sheet according to claim 4, characterized by comprising the step of injecting the foam material into a mold and heating it to cause foaming.

6. The elastic sheet precursor manufacturing step is as follows: A step of processing the aforementioned foam material into a predetermined shape to produce a foam material, A method for manufacturing an elastic sheet according to claim 4, characterized by comprising the step of heating the foamed material while it is held between clamping materials to cause foaming.

7. A heat transfer suppression sheet characterized by comprising an elastic sheet according to any one of claims 1 to 3, and a heat insulating material laminated on at least one of the first main surface and the second main surface of the elastic sheet.

8. A battery pack comprising a plurality of battery cells and an elastic sheet according to any one of claims 1 to 3, wherein the plurality of battery cells are connected in series or in parallel.

9. A battery pack comprising a plurality of battery cells and a heat transfer suppression sheet as described in claim 7, wherein the plurality of battery cells are connected in series or in parallel.

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