Heat transfer suppression sheet and battery pack

Abstract

Provided is a heat transfer suppression sheet which has excellent heat insulation properties, can absorb pressing force even when the pressing force is applied to the heat transfer suppression sheet, and thereby being able to suppress powder drop and maintain the excellent heat insulation properties, and also provided is a battery pack having the heat transfer suppression sheet. A heat transfer suppression sheet (10) contains heat insulating particles (5) and organic fibers (3). The heat-insulating particles (5) include large-diameter inorganic particles (1) having an average primary particle diameter of 0.1 μm or more and silica nanoparticles (2). One part of the principal surface (10a) of the heat transfer suppression sheet (10) orthogonal to the thickness direction has a first region (11) in which the large-diameter inorganic particles (1) are eccentrically located, and the other part of the principal surface (10a) has a second region (12) in which the large-diameter inorganic particles (1), the silica nanoparticles (2), and the organic fibers (3) are dispersed.

Description

Heat transfer suppression sheet and battery pack

[0001] The present invention relates to a heat transfer-suppressing sheet and a battery pack including the heat transfer-suppressing sheet.

[0002] In recent years, from the viewpoint of environmental protection, active development has been made of electric vehicles, hybrid vehicles, and the like that are driven by electric motors. These electric vehicles, hybrid vehicles, and the like are equipped with assembled batteries in which multiple battery cells are connected in series or parallel to serve as the power source for the driving electric motor.

[0003] Furthermore, these battery cells are mainly lithium-ion secondary batteries, which have higher capacity and higher output than lead-acid batteries, nickel-metal hydride batteries, etc. If a battery cell experiences thermal runaway, where the temperature rises suddenly and continues to rise due to an internal short circuit or overcharging, the heat from the battery cell experiencing thermal runaway may be transmitted to other adjacent battery cells, potentially causing thermal runaway in those cells.

[0004] A common method for suppressing heat propagation from a battery cell experiencing thermal runaway is to interpose a heat insulating sheet between the battery cells. For example, Patent Document 1 proposes a fire-resistant sheet for suppressing thermal runaway, which includes a substrate and an inorganic particle layer. In the fire-resistant sheet for suppressing thermal runaway, the substrate contains glass fibers, moist heat adhesive binder fibers, and fibrillated heat-resistant fibers, and the inorganic particle layer contains inorganic particles and an inorganic binder. The inorganic particle layer also includes a coating layer that covers the surface of the fibers contained in the substrate and a heat insulating layer present on at least one surface of the substrate.

[0005] Patent Document 1 describes that the thermal runaway suppressing fire-resistant sheet has an inorganic particle layer as a coating layer and an inorganic particle layer as a shielding layer, and therefore the sheet has fire resistance and heat insulation properties.

[0006] Japanese Patent Application Publication No. 2021-96935

[0007] The thermal runaway suppressing fire-resistant sheet described in Patent Document 1 contains a moisture-heat adhesive binder fiber, but the moisture-heat adhesive binder fiber needs to be in a wet state during production in order to exhibit its adhesiveness. Therefore, when a moisture-heat adhesive binder fiber is used, the fire-resistant sheet needs to be produced by a wet papermaking method.

[0008] However, when dry silica or silica aerogel, which have low thermal conductivity, are used to further improve thermal insulation performance, there is a problem that fireproof sheets cannot be produced by wet papermaking. This is because when a material containing dry silica is formed into a sheet by wet papermaking, the dry silica aggregates in the presence of water, increasing the thermal conductivity. Furthermore, since silica aerogel is generally difficult to disperse in water, when a material containing silica aerogel is formed by wet papermaking, a sheet with uniformly dispersed material cannot be obtained, resulting in a decrease in quality.

[0009] On the other hand, when inorganic particles such as dry silica or silica aerogel are used to manufacture a heat insulating sheet by a dry molding method, the inorganic particles may fall off (hereinafter also referred to as powder falling) due to pressure, impact, etc. In particular, in recent battery packs, the capacity of battery cells has been further improved, resulting in an increased expansion rate during charging and discharging. Therefore, when a heat insulating sheet is placed between battery cells of a battery pack, if the strength of the heat insulating sheet as a whole is low, the expansion of the battery cells during charging and discharging, etc., can compress the heat insulating sheet, causing powder falling and reducing the heat insulating performance.

[0010] Thus, there is a need for research into heat-transfer-suppressing sheets that have even better thermal insulation properties and can suppress the deterioration of battery cell performance and the occurrence of powder falling due to external compression, thereby suppressing the deterioration of thermal insulation properties.

[0011] The present invention has been made in consideration of the above-mentioned problems, and has an object to provide a heat-transfer-inhibiting sheet that has excellent thermal insulation properties and can absorb pressure even when pressure is applied to the heat-transfer-inhibiting sheet, thereby suppressing powder falling and maintaining excellent thermal insulation properties, and a battery pack that includes this heat-transfer-inhibiting sheet.

[0012] The above object of the present invention is achieved by the heat transfer-suppressing sheet having the following configuration [1].

[0013] [1] A heat-transfer-suppressing sheet containing heat-insulating particles and organic fibers, wherein the heat-insulating particles include large-diameter inorganic particles having an average primary particle diameter of 0.1 μm or more and silica nanoparticles, the heat-transfer-suppressing sheet having, in a part of a main surface perpendicular to the thickness direction, a first region in which the large-diameter inorganic particles are unevenly distributed, and a second region in another part of the main surface in which the large-diameter inorganic particles, the silica nanoparticles, and the organic fibers are dispersed.

[0014] Further, preferred embodiments of the present invention relating to the heat transfer-suppressing sheet relate to the following [2] to [8].

[0015] [2] The heat-transfer-suppressing sheet according to [1], wherein the second region has a surface shape that is raised relative to the surface that constitutes the first region.

[0016] [3] The heat transfer-suppressing sheet according to [1] or [2], wherein the large-diameter inorganic particles have an average primary particle diameter of 50 μm or less.

[0017] [4] The heat-transfer-suppressing sheet according to any one of [1] to [3], wherein the large-diameter inorganic particles include at least one type of particles selected from metal oxides and metal carbides.

[0018] [5] The heat transfer-suppressing sheet according to any one of [1] to [3], wherein the large-diameter inorganic particles include at least one type of particles selected from titania, zirconia, zircon, barium titanate, zinc oxide, alumina, and silicon carbide.

[0019] [6] The heat transfer-suppressing sheet according to any one of [1] to [3], wherein the large-diameter inorganic particles contain titania.

[0020] [7] The heat-transfer-suppressing sheet according to any one of [1] to [6], wherein the silica nanoparticles have an average primary particle size of 1 nm or more and less than 100 nm.

[0021] [8] The heat transfer-suppressing sheet according to any one of [1] to [7], wherein the silica nanoparticles include at least one type of particles selected from wet silica, dry silica, and aerogel.

[0022] The above object of the present invention is also achieved by the following configuration [9] relating to a battery pack.

[0023] [9] A battery pack comprising a plurality of battery cells and the heat transfer-suppressing sheet according to any one of [1] to [8], the plurality of battery cells being connected in series or in parallel.

[0024] The heat-transfer-suppressing sheet of the present invention contains large-sized inorganic particles and silica nanoparticles, and therefore can provide excellent heat insulation, and has a first region in which the large-sized inorganic particles are unevenly distributed, thereby further suppressing heat transfer in the thickness direction of the sheet. Furthermore, the heat-transfer-suppressing sheet has a second region in which the large-sized inorganic particles, silica nanoparticles, and organic fibers are dispersed, which can reduce pressure on the surface of the heat-transfer-suppressing sheet and suppress deterioration of heat-insulating performance due to powder falling off.

[0025] The battery pack of the present invention has a heat transfer-suppressing sheet that has excellent thermal insulation properties and the effect of retaining thermal insulation performance as described above, and therefore can suppress thermal runaway of the battery cells in the battery pack and the spread of flames to the outside of the battery case.

[0026] Fig. 1 is a photograph, substituted for a drawing, showing the appearance of the surface of a heat-transfer-suppressing sheet according to an embodiment of the present invention. Fig. 2 is a photograph, substituted for a drawing, showing an enlarged view of a portion of the surface of a heat-transfer-suppressing sheet according to an embodiment of the present invention. Fig. 3 is a schematic diagram showing a cross section of a heat-transfer-suppressing sheet according to an embodiment of the present invention. Fig. 4 is a schematic diagram showing the reflection of infrared rays from large-diameter inorganic particles having a relatively small average primary particle size. Fig. 5 is a schematic diagram showing the reflection of infrared rays from large-diameter inorganic particles having a relatively large average primary particle size. Fig. 6 is a schematic diagram showing a battery pack including a heat-transfer-suppressing sheet according to an embodiment of the present invention.

[0027] As a result of extensive research, the inventors have found that the above-mentioned problems can be solved by providing a heat-transfer-suppressing sheet having a surface including a first region in which large-sized inorganic particles having an average primary particle diameter equal to or greater than a predetermined value are unevenly distributed, and a second region in which large-sized inorganic particles, silica nanoparticles, and organic fibers are dispersed. Specifically, the first region on the surface of the heat-transfer-suppressing sheet improves the probability of reflecting radiant heat, which accounts for the majority of heat transfer, thereby achieving the effect of suppressing heat transfer. Furthermore, the presence of the second region in which large-sized inorganic particles, silica nanoparticles, and organic fibers are dispersed provides cushioning to the surface of the heat-transfer-suppressing sheet, thereby reducing pressure on the surface of the heat-transfer-suppressing sheet and also achieving the effect of retaining the large-sized inorganic particles, silica nanoparticles, and the like, thereby achieving excellent thermal insulation.

[0028] The heat transfer-suppressing sheet, its manufacturing method, and battery pack according to embodiments of the present invention will be described in detail below. Note that the present invention is not limited to the embodiments described below, and can be modified as desired without departing from the spirit and scope of the present invention.

[0029] [Heat-transfer-suppressing sheet] Fig. 1 is a photograph showing the appearance of the surface of a heat-transfer-suppressing sheet according to an embodiment of the present invention, Fig. 2 is a photograph showing an enlarged portion of the surface, and Fig. 3 is a schematic diagram showing a cross section of the heat-transfer-suppressing sheet according to an embodiment of the present invention.

[0030] 1 to 3 , a heat-transfer-suppressing sheet 10 according to this embodiment contains heat-insulating particles 5 including large-diameter inorganic particles 1 and silica nanoparticles 2, and organic fibers 3. The heat-transfer-suppressing sheet 10 also has, in a part of its main surface 10a perpendicular to its thickness direction, a first region 11 in which the large-diameter inorganic particles 1 are unevenly distributed. The heat-transfer-suppressing sheet 10 also has, in a region of the main surface 10a excluding the first region 11, a second region 12 in which the large-diameter inorganic particles 1, silica nanoparticles 2, and organic fibers are dispersed. In FIG. 1 , the region exhibiting a dark color is the first region 11, and the region exhibiting a lighter color than the first region 11 is the second region 12.

[0031] As shown in the enlarged photograph of FIG. 2 , the main surface 10a of the heat-transfer-suppressing sheet 10 is formed with a sea portion consisting of the first regions 11 and island portions consisting of the second regions 12. The island portions are surrounded by the sea portion, forming a sea-island structure. The first regions 11 on the main surface 10a of the heat-transfer-suppressing sheet 10 are connected in a mesh-like shape. The island portions consisting of the second regions 12 vary in size and shape, with most of them being curved in one or more places, and some island portions having a constricted shape. Depending on the shape characteristics of the second regions 12, the mesh-like sea portion of the first regions 11 also has various shapes, such as being curved or partially constricted. These shape characteristics of the first regions 11 and the second regions 12 extend across the entire surface of the heat-transfer-suppressing sheet 10, thereby further enhancing the effects of reflecting radiant heat and mitigating pressure through cushioning properties.

[0032] 3 , the second regions 12 have a surface shape that is raised relative to the surface that constitutes the first regions 11. The large-diameter inorganic particles 1 are not only unevenly distributed on the surface of the heat-transfer-suppressing sheet 10, but are also unevenly distributed toward the main surface 10 a in the thickness direction of the heat-transfer-suppressing sheet 10 in a cross-sectional view.

[0033] One example of how the heat-transfer-suppressing sheet 10 can be used is by placing the heat-transfer-suppressing sheet 10 between a plurality of battery cells. Specific examples of how the heat-transfer-suppressing sheet 10 can be used are described below.

[0034] The effects of the heat transfer-suppressing sheet 10 configured as described above will be described below. Fig. 4 is a schematic diagram showing how infrared rays are reflected by large-diameter inorganic particles having a relatively small average primary particle diameter. Fig. 5 is a schematic diagram showing how infrared rays are reflected by large-diameter inorganic particles having a relatively large average primary particle diameter. Note that organic fibers are not shown in Figs. 4 and 5.

[0035] Large-sized inorganic particles have the effect of reflecting radiant heat, which accounts for most of the heat transfer, but the manner of reflection is greatly affected by the wavelength of the infrared rays and the particle size of the inorganic particles. For example, if the particle size of the large-sized inorganic particles 1 is about 1.5 μm, which is smaller than the wavelength of the infrared rays whose transfer is to be suppressed, the infrared rays 4 will pass through the large-sized inorganic particles 1 and then penetrate the heat-transfer-suppressing sheet 10, as shown in FIG. 4. However, in this embodiment, because there are first regions 11 in which the large-sized inorganic particles 1 are unevenly distributed, these first regions 11 behave like inorganic particles larger in size than the original large-sized inorganic particles 1. In other words, the heat-transfer-suppressing sheet 10 has inorganic particles of apparently large size on at least a portion of the main surface 10 a, which increases the probability of reflecting the infrared rays 4. Therefore, heat transfer within the heat-transfer-suppressing sheet 10 can be suppressed, and the heat insulation can be further improved.

[0036] 5, when the particle size of the large-sized inorganic particles 1 is, for example, about 5 μm, infrared rays 4 having a wavelength similar to this particle size are reflected by the large-sized inorganic particles 1, thereby achieving a heat transfer suppression effect. On the other hand, when the wavelength of the infrared rays 4 exceeds 5 μm or when the infrared rays 4 pass through dispersed large-sized inorganic particles 1, the infrared rays 4 are reflected by the first region where the large-sized inorganic particles 1 are unevenly distributed. Therefore, as in the case shown in FIG. 4, heat transfer within the heat transfer-suppressing sheet 10 can be suppressed, and heat insulation can be further improved. That is, in this embodiment, heat transfer by infrared rays 4 of a wide range of wavelengths can be suppressed regardless of the particle size of the large-sized inorganic particles 1.

[0037] Regardless of which main surface of the heat-transfer-suppressing sheet 10 the heat (infrared rays 4) is generated from, the heat can be reflected as shown in Figures 4 and 5. Therefore, when the heat-transfer-suppressing sheet 10 is interposed between multiple battery cells, for example, it is possible to suppress the transfer of heat from one battery cell to another adjacent battery cell via the heat-transfer-suppressing sheet 10, thereby preventing thermal runaway.

[0038] Furthermore, in this embodiment, the island portions formed by the second regions 12 have a surface shape that is raised relative to the surface forming the sea portion formed by the first regions 11, and the raised regions (second regions 12) contain a higher content of silica nanoparticles 2 and organic fibers 3 than the first regions 11. Therefore, the second regions 12 are softer and have better cushioning properties than the first regions. Therefore, when an impact or pressure is applied to the heat-transfer-suppressing sheet 10, the raised second regions 12 absorb and mitigate the impact or pressure, resulting in a lower pressure on the first regions 11 than when the second regions 12 are not raised. As a result, it is possible to prevent the large-diameter inorganic particles 1 and the silica nanoparticles 2 from falling off from the main surface 10a of the heat-transfer-suppressing sheet 10, and to suppress a decrease in thermal insulation properties.

[0039] As described above, in this embodiment, the organic fibers 3 are also present inside the heat transfer-suppressing sheet 10, and therefore the effect of retaining the large-diameter inorganic particles 1 and the silica nanoparticles 2 can be sufficiently obtained, and excellent sheet strength can be obtained.

[0040] The materials constituting the heat transfer-suppressing sheet according to this embodiment will be described in detail below.

[0041] <Organic Fibers> The organic fibers 3 impart flexibility to the heat transfer-suppressing sheet 10 and have the effect of improving the strength and shape of the sheet. While single-component organic fibers can be used as the material for the organic fibers 3 in the heat transfer-suppressing sheet 10, it is preferable to use binder fibers with a core-sheath structure. Binder fibers with a core-sheath structure have a core extending in the longitudinal direction of the fiber and a sheath formed to cover the outer surface of the core. The core is made of a first organic material, and the sheath is made of a second organic material, with the melting point of the first organic material being higher than the melting point of the second organic material.

[0042] Whether single-component organic fibers or binder fibers with a core-sheath structure are used as the material for the organic fibers 3, when the heat transfer-suppressing sheet 10 is manufactured, a portion of the surface of the fibers melts due to heating, and subsequent cooling forms a welded portion (not shown) around the organic fibers 3. The welded portion welds the heat insulating particles 5, including the large-diameter inorganic particles 1 and the silica nanoparticles 2, to the surface of the organic fibers 3 and also welds the organic fibers 3 together, so that the formation of the welded portion allows for excellent sheet strength to be obtained.

[0043] When binder fibers with a core-sheath structure are used as the material, the core of the heat-transfer-suppressing sheet 10 corresponds to the organic fibers 3. If binder fibers with a core-sheath structure are used during the manufacture of the heat-transfer-suppressing sheet 10, fiber bundles are more likely to be formed in which adjacent binder fibers are fused to each other, thereby further increasing the sheet strength. Furthermore, when binder fibers with a core-sheath structure are used, the second organic material that constitutes the sheath melts and then solidifies again in a state that includes the surrounding heat-insulating particles 5, thereby improving the retention of the heat-insulating particles 5.

[0044] (First Organic Material) When binder fibers having a core-sheath structure are used as the material for the organic fibers 3, the first organic material constituting the core, i.e., the organic fibers 3, is not particularly limited as long as it has a melting point higher than that of the sheath, i.e., the second organic material, which is present on the outer surface of the organic fibers 3. Examples of the first organic material include at least one selected from polyethylene terephthalate, polypropylene, and nylon.

[0045] (Second Organic Material) When binder fibers having a core-sheath structure are used as the material for the organic fibers 3, the second organic material constituting the sheath portion is not particularly limited as long as it has a melting point lower than that of the first organic material constituting the organic fibers 3. 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. The melting point of the second organic material is preferably 150°C or lower, and more preferably 130°C or lower.

[0046] (Organic Fiber Content) In the present embodiment, when the content of the organic fibers 3 in the heat-transfer-inhibiting sheet 10 is appropriately controlled, the effects of improving the strength of the heat-transfer-inhibiting sheet 10, retaining the heat-insulating particles 5, and providing cushioning properties to the heat-transfer-inhibiting sheet 10 can be sufficiently obtained. The content of the organic fibers 3 is preferably 2 mass% or more, and more preferably 4 mass% or more, relative to the total mass of the heat-transfer-inhibiting sheet 10. Furthermore, if the content of the organic fibers 3 is too high, the contents of the large-diameter inorganic particles 1 and the silica nanoparticles 2 will relatively decrease. Therefore, in order to obtain the desired heat-insulating performance, the content of the organic fibers is preferably 10 mass% or less, and more preferably 8 mass% or less, relative to the total mass of the heat-transfer-inhibiting sheet 10.

[0047] (Fiber Length of Organic Fibers) The fiber length of the organic fibers 3 is not particularly limited, but from the viewpoint of ensuring moldability and processability, the average fiber length of the organic fibers 3 is preferably 10 mm or less. On the other hand, from the viewpoint of improving the strength of the heat transfer-suppressing sheet, the average fiber length of the organic fibers 3 is preferably 0.5 mm or more.

[0048] <Heat-insulating particles> The heat-transfer-suppressing sheet 10 according to this embodiment contains, as the heat-insulating particles 5, large-diameter inorganic particles having an average primary particle diameter of 0.1 μm or more and silica nanoparticles. When inorganic particles with different heat-transfer-suppressing effects, such as large-diameter inorganic particles 1 and silica nanoparticles 2, are used in combination, a heat-generating body can be cooled in multiple stages, and the heat-absorbing effect can be exerted over a wider temperature range. The silica nanoparticles and large-diameter inorganic particles will be described in more detail below.

[0049] <Silica Nanoparticles> Silica is a highly insulating component, and nanoparticles, due to their low density, are effective in suppressing conductive heat transfer. Nanoparticles refer to nanometer-order particles with a spherical or nearly spherical shape and an average primary particle diameter of less than 1 μm. When silica nanoparticles 2 are contained in the heat-transfer-suppressing sheet 10, fine voids are dispersed within the sheet, resulting in excellent thermal insulation that suppresses convective heat transfer. Therefore, heat conduction between adjacent nanoparticles can be suppressed during normal battery use at room temperature. Furthermore, when silica nanoparticles 2 are contained in the heat-transfer-suppressing sheet 10, an increase in conductive heat transfer through the heat-transfer-suppressing sheet can be suppressed even when the heat-transfer-suppressing sheet is compressed by expansion associated with thermal runaway of the battery cell, increasing its internal density. This is thought to be because silica nanoparticles are prone to forming fine voids between particles due to electrostatic repulsion, and their low bulk density allows the particles to be packed together to provide cushioning.

[0050] Silica nanoparticles are a material with high heat insulating properties, and in addition, the contact points between particles are small, so the amount of heat conducted by silica nanoparticles is smaller than when silica particles with a large particle size are used. In addition, commonly available silica nanoparticles have a bulk density of 0.1 (g / cm ３), for example, even if the battery cells arranged on both sides of the heat-transfer-suppressing sheet thermally expand and apply a large compressive stress to the heat-transfer-suppressing sheet, the size (area) and number of contact points between the silica nanoparticles do not increase significantly, and excellent heat insulation properties can be maintained. Examples of silica nanoparticles include wet silica, dry silica, and aerogel. Note that the silica nanoparticles preferably contain at least one type of particle selected from wet silica, dry silica, and aerogel, and may also be a mixture of at least two types of these. Silica nanoparticles that are particularly suitable for this embodiment are described below.

[0051] Generally, wet silica particles are aggregated, whereas dry silica particles can be dispersed. Because conductive heat transfer is dominant in the temperature range of 300°C or less, dry silica, which allows particles to be dispersed, can provide superior heat insulating performance compared to wet silica. The heat transfer-suppressing sheet according to this embodiment is preferably produced using a manufacturing method in which a mixture containing materials is processed into a sheet by a dry process. Therefore, it is preferable to use dry silica, silica aerogel, or the like, which has low thermal conductivity, as the silica nanoparticles.

[0052] (Average primary particle diameter of silica nanoparticles: 1 nm or more and less than 100 nm) Limiting the average primary particle diameter of silica nanoparticles to a predetermined range can achieve even higher thermal insulation. That is, when the average primary particle diameter of silica nanoparticles is 1 nm or more and less than 100 nm, convective heat transfer and conductive heat transfer within the heat-transfer-suppressing sheet can be suppressed, particularly in a temperature range below 500°C, thereby further improving thermal insulation. Furthermore, even when compressive stress is applied, the voids remaining between the silica nanoparticles and the contact points between many particles suppress conductive heat transfer, thereby maintaining the thermal insulation of the heat-transfer-suppressing sheet. The average primary particle diameter of the silica nanoparticles is more preferably 2 nm or more, and even more preferably 3 nm or more. On the other hand, the average primary particle diameter of the silica nanoparticles is more preferably 50 nm or less, and even more preferably 20 nm or less.

[0053] In the present invention, the average primary particle size can be determined by observing particles under a microscope, comparing with a standard scale, and taking the average of any 10 particles.

[0054] <Large-Sized Inorganic Particles> The heat-transfer-suppressing sheet 10 contains the silica nanoparticles 2 and large-sized inorganic particles 1 having an average primary particle diameter of 0.1 μm or more. The large-sized inorganic particles 1 have a high refractive index and a strong effect of diffusely reflecting light. Therefore, when the heat-transfer-suppressing sheet 10 contains the large-sized inorganic particles 1, radiant heat transfer can be suppressed, particularly in high-temperature regions such as those caused by abnormal heat generation. The large-sized inorganic particles preferably contain at least one type of particle selected from metal oxides and metal carbides. Other examples of the large-sized inorganic particles 1 that can be contained in the heat-transfer-suppressing sheet 10 include inorganic hydrate particles, inorganic balloons such as microporous particles and hollow silica particles, particles made of a thermally expandable inorganic material, and particles made of a hydrated porous material. Metal oxides, metal carbides, inorganic hydrate particles, particles made of a thermally expandable inorganic material, particles made of a hydrated porous material, and inorganic balloons are described in detail below.

[0055] (Metal Oxide Particles) Specific examples of metal oxide particles include titanium oxide (titania), zirconia, zircon, barium titanate, zinc oxide, and alumina.

[0056] (Metal Carbide Particles) Examples of metal carbide particles include silicon carbide.

[0057] (Inorganic hydrate particles) When inorganic hydrate particles receive heat from a heating element and reach a temperature above the thermal decomposition initiation temperature, they undergo thermal decomposition, releasing their own water of crystallization to lower the temperature of the heating element and its surroundings, thereby exhibiting the so-called "endothermic effect." After releasing the water of crystallization, they become porous, and exhibit heat insulating properties due to the countless air holes. 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 ), gallium hydroxide (Ga(OH) ３ ) etc.

[0058] For example, aluminum hydroxide contains about 35% water of crystallization, and as shown in the following formula, it thermally decomposes, releasing the water of crystallization and exhibiting an endothermic effect. After releasing the water of crystallization, it becomes a porous alumina (Al ２ O ３ ) and functions as a heat insulating material. 2Al(OH) ３ →Al ２ O ３ +3H ２ O

[0059] As will be described later, the heat-transfer-suppressing sheet 10 according to this embodiment is preferably interposed between battery cells, for example. In a battery cell that has experienced thermal runaway, the temperature rises sharply to over 200°C and continues to rise to around 700°C. Therefore, the heat-transfer-suppressing sheet 10 preferably contains an inorganic hydrate whose thermal decomposition onset temperature is 200°C or higher. The thermal decomposition onset temperatures of the inorganic hydrates listed above are approximately 200°C for aluminum hydroxide, approximately 330°C for magnesium hydroxide, approximately 580°C for calcium hydroxide, approximately 200°C for zinc hydroxide, approximately 350°C for iron hydroxide, approximately 300°C for manganese hydroxide, approximately 300°C for zirconium hydroxide, and approximately 300°C for gallium hydroxide. These inorganic hydrates are all preferred because they substantially overlap the temperature range of the rapid temperature rise in a battery cell that has experienced thermal runaway and can efficiently suppress temperature rise.

[0060] (Particles Made of Thermally Expandable Inorganic Material) Examples of thermally expandable inorganic materials include vermiculite, bentonite, mica, and perlite.

[0061] (Particles Made of Hydrous Porous Material) Specific examples of hydrous porous materials include zeolite, kaolinite, montmorillonite, acid clay, diatomaceous earth, mica, and vermiculite.

[0062] (Inorganic Balloons) The heat-transfer-suppressing sheet 10 according to this embodiment may contain inorganic balloons such as microporous particles or hollow silica particles as the heat-insulating particles 5. The inclusion of inorganic balloons can suppress convective or conductive heat transfer within the heat-transfer-suppressing sheet 10 in a temperature range of less than 500°C, further improving the heat insulating properties of the heat-transfer-suppressing sheet 10. The inorganic balloons can be at least one selected from shirasu balloons, silica balloons, fly ash balloons, barite balloons, and glass balloons.

[0063] It is preferable to use at least one type of particle selected from metal oxide particles and metal carbide particles among these large-diameter inorganic particles 1. Specifically, it is preferable to use at least one type of particle selected from titania, zirconia, zircon, barium titanate, zinc oxide, alumina, and silicon carbide as the large-diameter inorganic particles 1.

[0064] In particular, titania is particularly preferred as the large-diameter inorganic particles because titania has a higher refractive index than other metal oxides and is highly effective at scattering light and blocking radiant heat in high-temperature regions of 500° C. or higher. When large-diameter inorganic particles 1 and small-diameter silica nanoparticles 2 are contained in heat-transfer-suppressing sheet 10 in this manner, the small-diameter silica nanoparticles 2 enter the gaps between the large-diameter inorganic particles 1, resulting in a denser structure and an improved heat-transfer-suppressing effect.

[0065] (Average primary particle diameter of large-sized inorganic particles) By using large-sized inorganic particles 1 having an average primary particle diameter of 0.1 μm or more, radiant heat transfer can be efficiently suppressed in a desired high-temperature range. Furthermore, by using large-sized inorganic particles 1 having an average primary particle diameter of 1 μm or more, radiant heat transfer can be efficiently suppressed in a high-temperature range of, for example, 500° C. or more. Therefore, the average primary particle diameter of the large-sized inorganic particles 1 is set to 0.1 μm or more, preferably 1 μm or more, and more preferably 5 μm or more. Meanwhile, the average primary particle diameter of the large-sized inorganic particles 1 is preferably 50 μm or less, more preferably 30 μm or less, and even more preferably 10 μm or less.

[0066] In this embodiment, the heat transfer-suppressing sheet 10 contains large-sized inorganic particles 1 and silica nanoparticles 2, and in order to obtain excellent heat insulating performance within a predetermined temperature range, it is preferable to appropriately adjust the contents of the large-sized inorganic particles 1 and silica nanoparticles 2. For example, in order to obtain excellent heat insulating performance within a temperature range of 300°C or less, the content of the silica nanoparticles 2 is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more, relative to the total mass of the heat insulating particles. Furthermore, the content of the silica nanoparticles 2 is preferably 95% by mass or less, more preferably 90% by mass or less, and even more preferably 80% by mass or less, relative to the total mass of the heat insulating particles.

[0067] On the other hand, in order to obtain excellent heat insulating performance within a temperature range exceeding 300° C., the content of the large-sized inorganic particles 1 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 heat insulating particles. Furthermore, the content of the large-sized inorganic particles 1 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 heat insulating particles.

[0068] (Thermal Insulating Particle Content) In the present embodiment, when the total content of the thermal insulating particles 5 in the heat-transfer-inhibiting sheet 10 is appropriately controlled, the thermal insulating properties of the heat-transfer-inhibiting sheet 10 can be sufficiently ensured. The total content of the thermal insulating particles 5 is preferably 60 mass % or more, more preferably 65 mass % or more, and even more preferably 70 mass % or more, relative to the total mass of the heat-transfer-inhibiting sheet 10. Furthermore, the total content of the thermal insulating particles 5 is even more preferably 75 mass % or more, even more preferably 80 mass % or more, and particularly preferably 85 mass % or more, relative to the total mass of the heat-transfer-inhibiting sheet 10. On the other hand, if the total content of the thermal insulating particles 5 is too high, the content of the organic fibers 3 will relatively decrease. Therefore, in order to sufficiently obtain the sheet strength improving effect of the organic fibers 3, the total content of the thermal insulating particles 5 is preferably 95 mass % or less, and more preferably 90 mass % or less, relative to the total mass of the heat-transfer-inhibiting sheet 10. The content of the heat-insulating particles 5 in the heat-transfer-suppressing sheet 10 can be calculated, for example, by heating the heat-transfer-suppressing sheet 10 at 800°C, decomposing the organic components, and then measuring the mass of the remaining portion.

[0069] In this embodiment, the total content of the heat-insulating particles 5 and the organic fibers 3 is preferably 65% ​​by mass or more, more preferably 70% by mass or more, and even more preferably 75% by mass or more, relative to the total mass of the heat-transfer-suppressing sheet 10. The total content of the heat-insulating particles 5 and the organic fibers 3 is even more preferably 80% by mass or more, even more preferably 85% by mass or more, and particularly preferably 90% by mass or more, relative to the total mass of the heat-transfer-suppressing sheet 10. The total content of the heat-insulating particles 5 and the organic fibers 3 may be 100% by mass, relative to the total mass of the heat-transfer-suppressing sheet 10.

[0070] The heat-transfer-suppressing sheet 10 according to this embodiment may contain, in addition to the organic fibers 3 and the heat-insulating particles 5, organic fibers made of an organic material different from the first organic material, inorganic fibers, etc. When the heat-transfer-suppressing sheet 10 contains inorganic fibers, the inorganic fibers that are preferably contained in this embodiment will be described below.

[0071] <Inorganic Fibers> As the inorganic fibers, a single inorganic fiber may be used, or two or more inorganic fibers may be used in combination. Examples of inorganic fibers include ceramic fibers such as silica fiber, alumina fiber, alumina silicate fiber, zirconia fiber, carbon fiber, soluble fiber, refractory ceramic fiber, aerogel composite material, magnesium silicate fiber, alkaline earth silicate fiber, potassium titanate fiber, silicon carbide fiber, and potassium titanate whisker fiber; glass fibers such as glass fiber, glass wool, and slag wool; and mineral fibers such as rock wool, basalt fiber, wollastonite, and mullite fiber. These inorganic fibers are preferred in terms of heat resistance, strength, and availability. Among the inorganic fibers, silica-alumina fiber, alumina fiber, silica fiber, rock wool, alkaline earth silicate fiber, and glass fiber are particularly preferred from the viewpoint of handleability.

[0072] The cross-sectional shape of the inorganic fiber is not particularly limited, and examples thereof include a circular cross section, a flat cross section, a hollow cross section, a polygonal cross section, a core cross section, etc. Among these, modified cross section fibers having a hollow cross section, a flat cross section, or a polygonal cross section are preferably used because they have slightly improved heat insulation properties.

[0073] The preferred lower limit of the average fiber length of the inorganic fibers is 0.1 mm, more preferably 0.5 mm. Meanwhile, the preferred upper limit of the average fiber length of the inorganic fibers is 50 mm, more preferably 10 mm. If the average fiber length of the inorganic fibers is less than 0.1 mm, the inorganic fibers are less likely to be entangled with each other, which may reduce the mechanical strength of the heat transfer-suppressing sheet 10. Meanwhile, if the average fiber length exceeds 50 mm, although a reinforcing effect can be obtained, the inorganic fibers may not be able to be tightly entangled with each other, or may be curled up by a single inorganic fiber, which may result in continuous voids and reduce the heat insulating properties.

[0074] The preferred lower limit of the average fiber diameter of the inorganic fibers is 1 μm, more preferably 2 μm, and even more preferably 3 μm. On the other hand, the preferred upper limit of the average fiber diameter of the inorganic fibers is 15 μm, and more preferably 10 μm. If the average fiber diameter of the inorganic fibers is less than 1 μm, the mechanical strength of the inorganic fibers themselves may be reduced. Furthermore, from the viewpoint of the effects on human health, the average fiber diameter of the inorganic fibers is preferably 3 μm or more. On the other hand, if the average fiber diameter of the inorganic fibers is greater than 15 μm, solid-state heat transfer via the inorganic fibers may increase, resulting in a decrease in thermal insulation, and the formability and strength of the heat transfer-suppressing sheet may be impaired.

[0075] (Inorganic Fiber Content) In the present embodiment, when the heat-transfer-suppressing sheet 10 contains inorganic fibers, the inorganic fiber content is preferably 3 mass % or more and 15 mass % or less relative to the total mass of the heat-transfer-suppressing sheet 10 .

[0076] Furthermore, the content of the inorganic fibers is more preferably 5% by mass or more and 10% by mass or less with respect to the total mass of the heat transfer-suppressing sheet 10. By setting the content in this range, the shape retention, pressing force resistance, wind pressure resistance, and heat insulating particle retention ability of the inorganic fibers are exhibited in a balanced manner. Furthermore, by appropriately controlling the content of the inorganic fibers, the organic fibers 3 and the inorganic fibers become entangled with each other to form a three-dimensional network, which further improves the effect of retaining the heat insulating particles and other compounded materials described below.

[0077] <Other Compounding Materials> The heat-transfer-suppressing sheet according to this embodiment may further contain binders, colorants, and the like, as necessary. These are all useful for reinforcing the heat-transfer-suppressing sheet and improving its formability, and the total amount of these additives is preferably 10% by mass or less relative to the total mass of the heat-transfer-suppressing sheet. When binder fibers with a core-sheath structure are used as the material for producing the heat-transfer-suppressing sheet, the sheath melts during production, and only the core remains in the heat-transfer-suppressing sheet in the form of organic fibers. In this case, the content of the organic welded portion formed by the melting of the sheath is preferably 5% by mass or more and 15% by mass or less relative to the total mass of the heat-transfer-suppressing sheet 10.

[0078] [Method of Manufacturing Heat Transfer-Suppressing Sheet] An example of a method of manufacturing the heat transfer-suppressing sheet 10 according to this embodiment is described below. For example, organic fibers and heat insulating particles including silica nanoparticles and large-diameter inorganic particles are introduced into a mixer such as a V-type mixer in a predetermined ratio to prepare a mixture. It is preferable to use binder fibers with a core-sheath structure having a core made of a first organic material and a sheath made of a second organic material as the organic fibers. In this case, the melting point of the first organic material is set to be higher than the melting point of the second organic material.

[0079] The resulting mixture is then poured into a predetermined mold, and the mold is vibrated to smooth the surface, causing some of the large-diameter inorganic particles 1, which have a large mass, to move downward. The resulting molded body is then heated by applying pressure using a press or the like, thereby melting the sheaths of the binder fibers. The heated molded body is then cooled, solidifying the molten sheaths on the surface of the molded body, and fusing the organic fibers 3 together and the organic fibers 3 to the heat-insulating particles 5. Depending on the type of large-diameter inorganic particles 1 selected, the second regions 12 may have a raised shape relative to the surface constituting the first regions 11 due to differences in shrinkage rates caused by heating and cooling. In this way, a heat-transfer-suppressing sheet 10 can be produced that has, on a portion of its main surface, first regions in which the large-diameter inorganic particles 1 are unevenly distributed.

[0080] In this embodiment, it is preferable to manufacture the heat-transfer-suppressing sheet 10 by a dry method. When using the dry method, dry silica nanoparticles suitable for the dry method are used as the silica nanoparticles, and a solvent such as water, which is required when forming by a wet method, is not added to the mixture. However, to prevent powder such as dry silica nanoparticles from flying around during the manufacture of the heat-transfer-suppressing sheet 10 and making it difficult to handle the raw materials, a small amount of solvent such as water can be added within the range required for the dry method. For example, adding a small amount of solvent such as water to the mixture can suppress the scattering of heat-insulating particles during production.

[0081] According to the production method of this embodiment, first regions in which the large-sized inorganic particles 1 are unevenly distributed are formed in parts of the main surface 10a of the heat-transfer-suppressing sheet 10, and the large-sized inorganic particles 1 and the first regions 11 can reflect infrared rays 4 over a wide wavelength range, thereby producing a heat-transfer-suppressing sheet 10 with excellent heat insulation properties. Furthermore, second regions in which the large-sized inorganic particles 1, silica nanoparticles 2, and organic fibers 3 are dispersed are formed in other parts of the main surface, and a heat-transfer-suppressing sheet 10 with excellent strength and heat-insulating particle retention can be produced. Furthermore, if the second regions 12 are formed in a shape raised relative to the surface constituting the first regions 11, the pressing force on the first regions 11 is further reduced, and a heat-transfer-suppressing sheet 10 that can maintain excellent heat insulation properties can be produced.

[0082] Even when organic fibers 3 not having a core-sheath structure are used, it is possible to obtain the effect of holding the heat-insulating particles 5. In this case, appropriate temperature control may be performed to melt only the surfaces of the organic fibers and to coat the surfaces with heat-insulating particles or to fuse the organic fibers together. Regardless of the type of organic fiber used, when the organic fibers 3 are fused together inside or on the surface of the heat-transfer-suppressing sheet, this forms a framework that improves the strength of the sheet, and therefore a heat-transfer-suppressing sheet 10 with excellent strength can be obtained.

[0083] As will be described in detail later, an adhesive such as hot melt powder may be contained in the mixture as a raw material for the heat transfer-suppressing sheet 10. By appropriately adjusting the type and content of the adhesive contained in the mixture, the holding power of the heat insulating particles 5 can be improved and powder falling can be further suppressed.

[0084] To further suppress powder falling, the surface of the heat-transfer-suppressing sheet 10 may be coated with a film or the like. Examples of polymer films include films made of polyimide, polycarbonate, PET, p-phenylene sulfide, polyetherimide, cross-linked polyethylene, flame-retardant chloroprene rubber, polyvinyl denfluoride, rigid polyvinyl chloride, polybutylene terephthalate, PTFE, PFA, FEP, ETFE, rigid PVC, flame-retardant PET, polystyrene, polyethersulfone, polyamideimide, polyacrylonitrile, polyethylene, polypropylene, polyamide, etc. The method for covering the surface of the heat-transfer-suppressing sheet 10 with a film is not particularly limited, and examples include a method of attaching the film with an adhesive or the like, a method of wrapping the heat-transfer-suppressing sheet 10 in a film, and a method of housing the heat-transfer-suppressing sheet 10 in a bag-shaped film.

[0085] Next, organic fibers and heating conditions that are preferably used in the method for producing a heat transfer-suppressing sheet according to this embodiment will be described.

[0086] <Organic Fiber> In the present embodiment, when a core-sheath organic fiber is used, there are no particular limitations as long as the melting point of the first organic material constituting the core is higher than the melting point of the second organic material constituting the sheath. The first organic material constituting the core can be at least one selected from polyethylene terephthalate, polypropylene, and nylon. The second organic material constituting the sheath can be at least one selected from polyethylene terephthalate, polyethylene, polypropylene, and nylon.

[0087] If the melting point of the first organic material constituting the core is sufficiently higher than that of the second organic material constituting the shell, the heating temperature setting margin in the heating step can be expanded, making it easier to set the temperature to obtain a desired structure. For example, the melting point of the first organic material is preferably 60°C or more higher than that of the second organic material, more preferably 70°C or more higher, and even more preferably 80°C or more higher.

[0088] Organic fibers having the above-described core-sheath structure are generally commercially available, and the materials constituting the core and sheath may be the same or different. Examples of organic fibers in which the core and sheath are made of the same material but have different melting points include those in which the core and sheath are made of polyethylene terephthalate, polypropylene, nylon, etc. Examples of organic fibers in which the core and sheath are made of different materials include those in which the core is made of polyethylene terephthalate and the sheath is made of polyethylene, and those in which the core is made of polypropylene and the sheath is made of polyethylene.

[0089] In this embodiment, the melting point of the second organic material constituting the sheath of the organic fiber refers to the melting temperature at which the second organic material begins to melt and deform. However, softening accompanied by a change in shape is also considered to be a type of melting deformation. The melting point of the sheath of the binder fiber can be measured, for example, by the following method. The organic fiber to be measured is placed in contact with glass fiber, which has a higher melting point, and heated from room temperature to, for example, 200°C at a heating rate of 5°C / min, and then cooled to room temperature. If the surface of the organic fiber melts and deforms and is fused to the glass fiber at the contact point, or if the cross-sectional shape of the organic fiber changes, it can be determined that the melting point of the second organic material constituting the sheath is 200°C or lower. In this embodiment, the heating temperature is varied and the fusion state between the organic fiber and the glass fiber or the cross-sectional shape of the organic fiber after cooling is observed using the above method, thereby identifying the melting point of the second organic material constituting the sheath.

[0090] (Organic Fiber Content) In this embodiment, when using organic fibers with a core-sheath structure, if the content of organic fibers in the mixture is appropriately controlled, excellent heat insulating performance and heat insulating particle retention can be obtained, and excellent sheet strength can be obtained. The content of organic fibers is preferably 5% by mass or more, more preferably 10% by mass or more, relative to the total mass of the mixture. Furthermore, if the content of organic fibers is too high, the content of heat insulating particles will relatively decrease. Therefore, in order to obtain the desired heat insulating performance, the content of organic fibers is preferably 25% by mass or less, more preferably 20% by mass or less, relative to the total mass of the mixture.

[0091] <Hot Melt Powder> In this embodiment, in addition to the organic fibers and heat-insulating particles, the mixture may contain a hot melt powder. The hot melt powder is a powder that contains, for example, a third organic material different from the first organic material and the second organic material and has the property of melting when heated. When the hot melt powder is contained in the mixture and heated, the hot melt powder melts, and when cooled, it hardens in a state that includes the surrounding heat-insulating particles. This further prevents the heat-insulating particles from falling off from the heat-transfer-suppressing sheet 10.

[0092] Hot melt powders with various melting points can be used, but a hot melt powder with an appropriate melting point can be selected taking into account the melting points of the core and sheath of the binder fiber used. Specifically, if the third organic material constituting the hot melt powder has a melting point lower than that of the first organic material constituting the organic fiber, the heating temperature can be set to melt the sheath and hot melt powder while leaving the core. For example, if the melting point of the hot melt powder is lower than that of the sheath, the heating temperature during production 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 is between the melting points of the core and sheath. When a hot melt powder with such a melting point is used, the sheath and hot melt powder melt together, and then when they cool and harden, the organic fibers (core) 3, the molten sheath around them, and the hot melt powder present in the gaps between the insulating particles harden first. As a result, the position of the organic fibers 3 can be fixed, and the molten sheath then fuses to the organic fibers, facilitating the formation of a three-dimensional skeleton. This further improves the strength of the entire sheet.

[0094] If the melting point of the third organic material constituting the hot melt powder is sufficiently lower than that of the first organic material constituting the core, the heating temperature setting margin in the heating step can be expanded, 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 that 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. 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 hot-melt powder is added to the mixture to prevent the heat-insulating particles 5 from falling off, even a small amount of hot-melt powder can be effective in preventing powder falling off. Therefore, the hot-melt powder content is preferably 0.5% by mass or more, and more preferably 1% by mass or more, relative to the total mass of the mixture. On the other hand, since increasing the hot-melt powder content relatively reduces the content of the heat-insulating particles 5 and the like, in order to obtain the desired heat-insulating performance, the hot-melt powder content is preferably 5% by mass or less, and more preferably 4% by mass or less, relative to the total mass of the mixture.

[0097] <Heating Conditions> The process of processing the mixture into a sheet includes a process of pressing the mixture and a process of heating the mixture. When an organic fiber having a core-sheath structure is used as the material for the heat transfer-suppressing sheet 10, the heating temperature in the heating process is preferably higher than the melting point of the second organic material constituting the sheath and lower than the melting point of the first organic material constituting the core. By setting the heating temperature in this manner, as described above, the strength of the sheet can be ensured by the core on both the surface side and the center side of the sheet, and the heat-insulating particles 5 can be held by the fused sheath.

[0098] Specifically, the heating temperature in the heating step is preferably set to be 10° C. or more higher, more preferably 20° C. or more higher, than the melting point of the second organic material constituting the sheath. On the other hand, the heating temperature is preferably set to be 10° C. or more lower, more preferably 20° C. or more lower, than the melting point of the first organic material constituting the core.

[0099] The heating time is not particularly limited, but is preferably set to a time sufficient to melt the sheath, for example, from 3 minutes to 15 minutes.

[0100] When the heat transfer-suppressing sheet contains a hot-melt powder as its material, the heating temperature in the heating step is preferably set to be at least 10°C higher, and more preferably 20°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. Meanwhile, the heating temperature is preferably set to be at least 10°C lower, and more preferably 20°C lower, than the melting point of the first organic material constituting the core. Setting the heating temperature in this range makes it possible to form a strong skeleton, further improving the strength of the sheet and preventing the heat-insulating particles 5 from falling off.

[0101] <Thickness of Heat-Transfer-Suppressing Sheet> The thickness of the heat-transfer-suppressing sheet 10 according to this embodiment is not particularly limited, but is preferably 0.05 mm or more and 10 mm or less. A thickness of 0.05 mm or more ensures sufficient compressive strength. On the other hand, a thickness of 10 mm or less ensures good heat insulation of the heat-transfer-suppressing sheet 10.

[0102] [Battery Pack] FIG. 6 is a schematic diagram showing a battery pack including a heat-transfer-suppressing sheet according to an embodiment of the present invention. As shown in FIG. 6, the battery pack 100 includes multiple battery cells 20a, 20b, and 20c and the heat-transfer-suppressing sheet 10 according to this embodiment, with the multiple battery cells 20a, 20b, and 20c connected in series or parallel. Specifically, the heat-transfer-suppressing sheet 10 is interposed between the battery cells 20a and 20b, and between the battery cells 20b and 20c. The battery pack 100 is configured by storing the multiple battery cells 20a, 20b, and 20c in a series- or parallel-connected state (the connected state is not shown) in a battery case 30. The battery cells 20a, 20b, and 20c are preferably, for example, lithium-ion secondary batteries, but are not limited thereto and may also be applied to other secondary batteries. The heat-transfer-suppressing sheet 10 is as described above.

[0103] In the battery pack 100 configured in this manner, even if a certain battery cell 20a becomes hot, the heat transfer to the battery cell 20b can be suppressed because the heat-transfer-suppressing sheet 10, which has an excellent heat-transfer-suppressing effect, is present between the battery cell 20a and the battery cell 20b. Furthermore, the heat-transfer-suppressing sheet 10 according to this embodiment has high strength and is effective in absorbing shock and resisting pressure, thereby suppressing thermal expansion of the battery cells 20a, 20b, and 20c during charging and discharging. This ensures a sufficient distance between the battery cells, maintaining excellent thermal insulation performance and preventing thermal runaway of the battery cells. Furthermore, the heat-transfer-suppressing sheet 10 is easy to handle because it suppresses powder shedding.

[0104] The battery pack 100 of this embodiment is not limited to the battery pack illustrated in Fig. 6. For example, the heat transfer-suppressing sheet 10 may be disposed not only between the battery cells 20a and 20b and between the battery cells 20b and 20c, but also between the battery cells 20a, 20b, and 20c and the battery case 30, or may be attached to the inner surface of the battery case 30.

[0105] In the battery pack 100 configured in this manner, if a battery cell ignites, the flame can be prevented from spreading outside the battery case 30. For example, the battery pack 100 according to this embodiment may be used in an electric vehicle (EV) or the like and placed under the floor of a passenger compartment. In this case, even if a battery cell ignites, the safety of the passengers can be ensured. Furthermore, since the heat transfer-suppressing sheet 10 can be placed not only between the battery cells but also between the battery cells 20a, 20b, and 20c and the battery case 30, there is no need to fabricate additional flame retardant materials, and a safe battery pack 100 can be easily configured at low cost.

[0106] In the battery pack of this embodiment, the heat-transfer-suppressing sheet 10, which is disposed between the battery cells 20a, 20b, and 20c and the battery case 30, may be in contact with the battery cells or may have gaps therebetween. For example, if the heat-transfer-suppressing sheet 10 is in contact with the battery cells 20a, 20b, and 20c, the heat-transfer-suppressing sheet 10 is fixed between the battery cells, preventing performance degradation due to misalignment. Furthermore, if there are gaps between the heat-transfer-suppressing sheet 10 and the battery cells 20a, 20b, and 20c, deformation of the battery cells can be tolerated even if the temperature of one of the multiple battery cells rises and the volume expands.

[0107] The heat transfer-suppressing sheet 10 according to this embodiment can be manufactured into various shapes depending on the manufacturing method. Therefore, it can be adapted to any shape without being affected by the shapes of the battery cells 20a, 20b, 20c and the battery case 30. Specifically, it can be applied to cylindrical batteries, flat batteries, etc. in addition to prismatic batteries.

[0108] Although various embodiments have been described above with reference to the drawings, it goes without saying that the present invention is not limited to such examples. It is clear that a person skilled in the art can conceive of various modifications or alterations within the scope of the claims, and it is understood that these also naturally fall within the technical scope of the present invention. Furthermore, the components of the above-described embodiments may be combined in any manner without departing from the spirit of the invention.

[0109] This application is based on a Japanese patent application (Patent Application No. 2024-056366) filed on March 29, 2024, the contents of which are incorporated herein by reference.

[0110] REFERENCE SIGNS LIST 1 large-diameter inorganic particles 2 silica nanoparticles 3 organic fibers 4 infrared rays 5 heat-insulating particles 10 heat-transfer-suppressing sheet 11 first region 12 second region 20a, 20b, 20c battery cell 30 battery case 100 assembled battery

Claims

1. A heat-transfer-suppressing sheet containing heat-insulating particles and organic fibers, wherein the heat-insulating particles include large-diameter inorganic particles having an average primary particle diameter of 0.1 μm or more and silica nanoparticles, the heat-transfer-suppressing sheet having a first region in which the large-diameter inorganic particles are unevenly distributed in one part of a main surface perpendicular to the thickness direction, and a second region in which the large-diameter inorganic particles, the silica nanoparticles, and the organic fibers are dispersed in another part of the main surface.

2. The heat transfer suppressing sheet according to claim 1, wherein the second region has a surface shape that is raised relative to the surface that constitutes the first region.

3. The heat transfer-suppressing sheet according to claim 1, wherein the large-diameter inorganic particles have an average primary particle size of 50 μm or less.

4. The heat transfer-suppressing sheet according to claim 1, wherein the large-diameter inorganic particles include at least one type of particles selected from the group consisting of metal oxides and metal carbides.

5. The heat transfer-suppressing sheet according to claim 1, wherein the large-diameter inorganic particles include particles of at least one type selected from the group consisting of titania, zirconia, zircon, barium titanate, zinc oxide, alumina, and silicon carbide.

6. The heat transfer suppressing sheet according to claim 1, wherein the large-diameter inorganic particles include titania.

7. The heat transfer-suppressing sheet according to claim 1, wherein the silica nanoparticles have an average primary particle size of 1 nm or more and less than 100 nm.

8. The heat transfer suppression sheet according to claim 1, wherein the silica nanoparticles include at least one type of particles selected from wet silica, dry silica, and aerogel.

9. A battery pack comprising a plurality of battery cells and the heat transfer suppression sheet according to any one of claims 1 to 8, the plurality of battery cells being connected in series or parallel.

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