Heat transfer inhibiting sheet and battery pack

Abstract

To provide a heat transfer suppressing sheet having excellent heat insulating properties and capable of suppressing the contamination of the surroundings caused by powder falling.SOLUTION: A heat transfer suppression sheet 10 includes a heat insulating material 11 containing inorganic particles, a protective material 16 laminated on the heat insulating material 11, and a resin film 12 containing a laminate 17 including the heat insulating material 11 and the protective material 16 and having a hole 13. The plastic film 12 has a thermal insulation material side film 12b covering the surfaces of the thermal insulation material 11 and a protective material side film 12a covering the surfaces of the protective material 16, and the total area of the holes 13 in the thermal insulation material side film 12b is smaller than the total area of the holes in the protective material side film 12a.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[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] These battery cells mainly use 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 the propagation of heat from a battery cell that has experienced thermal runaway as described above is to place a heat insulating sheet between the battery cells.

[0005] However, when a heat insulating sheet is produced, for example, a heat-sensitive adhesive binder fiber is used as a binder. However, the heat-sensitive adhesive binder fiber needs to be kept in a wet state during production in order to exhibit its adhesiveness. Therefore, when a heat insulating sheet is produced using a heat-sensitive adhesive binder fiber, the heat insulating sheet needs to be produced by a wet papermaking method.

[0006] 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 they 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, it is not possible to obtain a thermal insulation sheet with a uniformly dispersed material, resulting in a decrease in quality.

[0007] 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 fall) due to pressure, impact, etc.

[0008] For example, Patent Document 1 discloses a battery cell thermal runaway barrier having a nonwoven fibrous insulation material including a fiber matrix of inorganic fibers, thermally insulating inorganic particles, and a binder, and an organic sealing layer that seals the insulation material. The battery cell thermal runaway barrier described in Patent Document 1 is configured so that when the gas trapped within the organic sealing layer is heated to a high temperature, the gas is released to the outside, for example, through an opening formed in the peripheral portion of the insulating material. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] International Publication No. 2022 / 024076 Summary of the Invention [Problem to be solved by the invention]

[0010] However, since the insulating material that prevents thermal runaway of the battery cells is generally placed inside the battery case between the battery cells, when gas is released from the periphery of the insulating material, as in the case of the thermal runaway barrier described above, inorganic particles and the like are ejected along with the gas, contaminating the inside of the battery case.

[0011] The present invention has been made in consideration of the above-mentioned problems, and has an object to provide a heat-transfer-suppressing sheet that has excellent thermal insulation properties and can suppress contamination of the surrounding area due to powder falling, and a battery pack including this heat-transfer-suppressing sheet. [Means for solving the problem]

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

[0013] [1] An insulating material containing inorganic particles; A protective material laminated on the heat insulating material; a resin film having holes and enclosing a laminate including the heat insulating material and the protective material, the resin film has a heat insulating material side film that covers a surface of the heat insulating material and a protective material side film that covers a surface of the protective material, A heat transfer-suppressing sheet, wherein the sum of the areas of the holes in the heat insulating material side film is smaller than the sum of the areas of the holes in the protection material side film.

[0014] Furthermore, preferred embodiments of the present invention relating to the heat transfer-suppressing sheet relate to the following [2] to [9].

[0015] [2] The heat transfer-suppressing sheet according to [1], wherein the number of holes in the heat insulating material side film is smaller than the number of holes in the protective material side film.

[0016] [3] The heat-transfer-suppressing sheet according to [1] or [2], wherein the protective material is an elastic sheet.

[0017] [4] The heat transfer-suppressing sheet according to [1] or [2], wherein the protective material is a fiber-reinforced plastic sheet or a fiber-reinforced plastic board.

[0018] [5] The heat-transfer-suppressing sheet according to any one of [1] to [4], wherein the heat-insulating material-side film does not have the holes.

[0019] [6] The heat transfer-suppressing sheet according to any one of [1] to [5], wherein the resin film has a fused portion at an end face side of the laminate where the resin films are fused together.

[0020] [7] The heat transfer-suppressing sheet according to any one of [1] to [6], wherein the resin film has a plurality of the holes, and the holes have an elliptical shape.

[0021] [8] The heat-transfer-suppressing sheet according to any one of [1] to [7], wherein the laminate has a rectangular shape when viewed in the stacking direction, and the holes have an elliptical shape with their major axes extending in approximately the same direction as the longitudinal direction of the rectangular faces of the laminate.

[0022] [9] The resin film has a plurality of the holes, The heat-transfer-suppressing sheet according to any one of [1] to [8], wherein the holes are arranged along the direction in which the sides of the laminate extend.

[0023] The above object of the present invention is also achieved by the following configuration

[10] relating to a battery pack.

[0024]

[10] A battery pack comprising a plurality of battery cells and the heat transfer-suppressing sheet according to any one of [1] to [9], A battery pack in which the plurality of battery cells are connected in series or in parallel. [Effects of the Invention]

[0025] The heat-transfer-suppressing sheet of the present invention has a heat-insulating material containing inorganic particles, and therefore can achieve excellent heat-insulating effects. Furthermore, the heat-transfer-suppressing sheet of the present invention has a resin film encapsulating a laminate containing a heat-insulating material and a protective material laminated on the heat-insulating material, and therefore can suppress the shedding of inorganic particles contained in the heat-insulating material. Furthermore, the heat-transfer-suppressing sheet of the present invention has a structure in which the sum of the areas of the holes in the protective material-side film covering the surface of the protective material is smaller than the sum of the areas of the holes in the heat-insulating material-side film covering the surface of the heat-insulating material, and therefore can suppress the inorganic particles contained in the heat-insulating material from being ejected in large quantities outside the heat-transfer-suppressing sheet.

[0026] The battery pack of the present invention has a heat transfer-suppressing sheet with excellent heat insulation properties and powder fall-suppressing effects as described above, which makes it possible to suppress thermal runaway of the battery cells in the battery pack and the spread of flames to the outside of the battery case, as well as to suppress contamination of the inside of the battery case. [Brief explanation of the drawings]

[0027] [Figure 1] FIG. 1 is a perspective view showing the structure of a heat-transfer-suppressing sheet according to an embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view showing the structure of a heat-transfer-suppressing sheet according to an embodiment of the present invention. [Figure 3] FIG. 3 is a cross-sectional view that schematically shows a battery pack having a heat transfer-suppressing sheet according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0028] The present inventors have conducted extensive research into a heat-transfer-suppressing sheet that can solve the above-mentioned problems. As a result, we found that it is effective to cover the laminate of the insulating material and the protective material with a resin film having holes, and to make the sum of the area of ​​the holes in the protective material side film covering the surface of the protective material smaller than the sum of the area of ​​the holes in the insulating material side film covering the surface of the insulating material.

[0029] The heat transfer-suppressing sheet (heat insulating sheet) and battery pack according to the 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.

[0030] [Heat transfer suppression sheet] FIG. 1 is a perspective view showing the structure of a heat-transfer-suppressing sheet according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view thereof. As shown in FIGS. 1 and 2, a heat-transfer-suppressing sheet 10 according to this embodiment includes a thermal insulating material 11, a protective material 16 laminated on one main surface 11a of the thermal insulating material 11, and a resin film 12 enclosing a laminate 17 of the thermal insulating material 11 and the protective material 16. The resin film 12 includes a thermal insulating material-side film 12b covering the surface of the thermal insulating material 11 and a protective material-side film 12a covering the surface of the protective material 16. Specifically, the thermal insulating material-side film 12b covers the other main surface 11b of the thermal insulating material 11 and an end surface 11c of the thermal insulating material 11. The protective material-side film 12a covers the main surface 16a of the protective material 16 opposite the thermal insulating material 11 side and an end surface 16c of the protective material 16. In this embodiment, a plurality of elliptical holes 13 are formed in the protective material-side film 12a. On the other hand, the heat insulating material side film 12b has no holes.

[0031] It is not necessary for there to be complete adhesion between the heat insulating material side film 12b and the heat insulating material 11, and between the protection material side film 12a and the protection material 16, and there may be partial gaps between them. In the following description, when there is no need to distinguish between the heat insulating material side film 12b and the protection material side film 12a, they may be collectively referred to as the resin film 12.

[0032] In this embodiment, a laminate 17 of the heat insulating material 11 and the protective material 16 is wrapped in a resin film 12, and the resin films 12 are fused together near the end face 11c of the heat insulating material 11 and the end face 16c of the protective material 16. That is, a fused portion 14 that covers at least a portion of the end face is formed on the end face side of the laminate 17. Then, as the resin film 12 is heated and shrinks, the main surface 11b and end face 11c of the heat insulating material 11 and the main surface 16a and end face 16c of the protective material 16 are covered with the resin film 12. Because the fused portion 14 is formed by the resin films 12 being heated and shrinking, the thickness of the region where the fused portion 14 is formed increases, and as a result, the fused portion 14 has higher strength than other regions.

[0033] The configuration and effects of applying the heat-transfer-suppressing sheet 10 configured as described above to a battery pack will be specifically described below. Fig. 3 is a cross-sectional view schematically showing a battery pack including a heat-transfer-suppressing sheet according to an embodiment of the present invention. Note that the detailed structure of the heat-transfer-suppressing sheet 10 shown in Figs. 1 and 2 is simplified in Fig. 3.

[0034] The battery pack 100 includes a battery case 30, a plurality of battery cells 20a, 20b, and 20c housed inside the battery case 30, and a heat-transfer-suppressing sheet 10 interposed between the battery cells 20a and 20b and between the battery cells 20b and 20c. The battery cells 20a, 20b, and 20c are connected in series or in parallel by bus bars (not shown) or the like. The battery cells 20a, 20b, and 20c are preferably, for example, lithium-ion secondary batteries, but are not limited thereto and may also be other secondary batteries.

[0035] In the battery pack 100 configured in this manner, the heat insulating material 11 contains inorganic particles and has high thermal insulation properties, thereby suppressing the transfer of heat from a battery cell that has experienced thermal runaway to adjacent battery cells. Furthermore, the heat transfer-suppressing sheet 10 has a structure in which the heat insulating material 11 and the protective material 16 are encapsulated in the resin film 12, which prevents misalignment between the heat insulating material 11 and the protective material 16 when the heat transfer-suppressing sheet 10 is incorporated into the battery pack 100, and also prevents the inorganic particles and other components from falling off.

[0036] Furthermore, for example, when the temperature of battery cell 20a rises, the heat-transfer-suppressing sheet 10 disposed between battery cell 20a and battery cell 20b is also heated. At this time, the air contained within the heat insulating material 11 and between the laminate 17 and the resin film 12 expands, and the air is discharged through the holes 13 in the resin film 12. In this embodiment, no holes are formed in the heat insulating material-side film 12b that covers the heat insulating material 11, and holes 13 are formed only in the protection material-side film 12a that covers the protection material 16. Therefore, even if inorganic particles fall off from the heat insulating material 11, the air is discharged only from the protection material 16 side, and the inorganic particles can be prevented from being discharged to the outside, thereby suppressing the spread of inorganic particle contamination within the battery case 30.

[0037] In this embodiment, the heat insulating material-side film 12b has no holes, and holes 13 are provided only in the protective material-side film 12a. Air inside the resin film 12 is only discharged through the protective material-side film 12a, thereby maximizing the effect of preventing contamination by inorganic particles. However, the heat insulating material-side film 12b does not necessarily have to be hole-free. By providing some holes in the heat insulating material-side film 12b, the internal pressure inside the resin film 12 can be controlled within a predetermined range. That is, in this embodiment, the effect of suppressing the discharge of inorganic particles to the outside can be achieved as long as the total area of ​​the holes in the heat insulating material-side film 12b is designed to be smaller than the total area of ​​the holes 13 in the protective material-side film 12a. For example, the number of holes in the heat insulating material-side film 12b may be designed to be smaller than the number of holes 13 in the protective material-side film 12a. Furthermore, the area ratio of the holes in the heat insulating material-side film 12b may be designed to be smaller than the area ratio of the holes 13 in the protective material-side film 12a.

[0038] Here, the area ratio of the holes 13 in the protection material-side film 12a refers to the ratio of the area of ​​the holes 13 formed in the protection material-side film 12a to the total area of ​​the protection material-side film 12a. Also, the area ratio of the holes in the insulation material-side film 12b refers to the ratio of the area of ​​the holes formed in the insulation material-side film 12b to the total area of ​​the insulation material-side film 12b.

[0039] For example, the battery cell 20a and the heat-transfer-suppressing sheet 10, and the battery cell 20b and the heat-transfer-suppressing sheet 10, are not in complete contact with each other, but rather there are areas where they are in close contact with each other and areas where they are slightly separated. If the hole 13 were completely blocked by the areas of close contact, it would be difficult for air to escape through the hole 13, increasing the internal pressure in the resin film 12 and potentially causing damage to the resin film 12. Therefore, to prevent the hole 13 from being completely blocked by an adjacent battery cell, it is preferable that the shape of the hole 13 be an ellipse that extends long in one direction.

[0040] Furthermore, when the laminate 17 has a rectangular shape in a plan view (when viewed in the stacking direction), it is more preferable that the holes 13 have an elliptical shape with the major axis in approximately the same direction as the longitudinal direction of the rectangular surface of the laminate 17. When the major axis of the elliptical holes 13 is oriented in the above-mentioned direction, it is possible to prevent adjacent holes 13 from being too close to each other, thereby reducing the strength and causing cracks in the resin film 12. Furthermore, when the protection material side film 12a has multiple holes 13, if the holes 13 are arranged in the direction in which the sides of the laminate 17 extend, it is possible to prevent adjacent holes 13 from being too close to each other, thereby causing cracks in the protection material side film 12a.

[0041] In this embodiment, the protective material 16 is not particularly limited as long as it has the desired heat insulating properties and does not allow particles to fall off. In other words, it is sufficient if it has the function of protecting the heat insulating material 11 and preventing particles from being discharged through the holes 13 in the resin film 12 even if they fall off the heat insulating material 11. Specifically, an elastic sheet, a mica sheet, or the like can be used as the elastic sheet.

[0042] In recent battery packs, the capacity of the battery cells has been further improved, resulting in an increased expansion rate during charging and discharging. Therefore, when the internal pressure of the battery cells 20a, 20b, and 20c repeatedly increases and decreases during charging and discharging, the battery cells 20a, 20b, and 20c are repeatedly pressed and released by the case, causing a decrease in battery performance. In this embodiment, using an elastic sheet as the protective material 16 can generate stress when the battery cells expand, thereby reducing the pressure on the battery cells 20a, 20b, and 20c, thereby maintaining battery performance.

[0043] Furthermore, in this embodiment, laminate 17, in which heat insulating material 11 and protective material 16 are laminated, is configured to be enclosed in resin film 12, but the present invention is not limited to this, and a functional member having another function may be disposed between heat insulating material 11 and protective material 16. In other words, if one of the multiple laminated members located on the outermost side is heat insulating material 11 and the other member is protective material 16, the effects of the present invention can be obtained.

[0044] The heat insulating material 11, the protective material 16, and the resin film 12 that constitute the heat transfer-suppressing sheet 10 according to this embodiment will be described in detail below.

[0045] [Insulation material] The heat insulating material used in the heat transfer-suppressing sheet according to this embodiment is not particularly limited as long as it contains inorganic particles and has a heat insulating effect. Thermal conductivity can be used as an index of heat insulating effect, and in this embodiment, the heat conductivity of the heat insulating material is preferably less than 1 (W / m·K), more preferably less than 0.5 (W / m·K), and even more preferably less than 0.2 (W / m·K). Furthermore, the heat conductivity of the heat insulating 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 heat insulating material can be measured in accordance with the "Test method for thermal conductivity of refractories" described in JIS R 2251.

[0046] (Insulation size) The size of the insulating material 11 can be designed arbitrarily depending on the size of the protective material 16 to be laminated on the insulating material 11 and the size of the battery cells 20a, 20b, and 20c shown in FIG. 3. For example, the size of the main surface of the insulating material 11 perpendicular to the thickness direction and the size of the main surface of the protective material 16 perpendicular to the thickness direction may be substantially the same or different. When the main surfaces of the insulating material 11 and the protective material 16 are designed to have substantially the same size, "substantially the same" means that the difference between their 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%.

[0047] Next, the materials that make up the heat insulating material will be described.

[0048] <Inorganic particles> The heat insulating material contains inorganic particles. A single inorganic particle may be used as the inorganic particle, or two or more types of inorganic particles may be used in combination. From the viewpoint of the heat transfer suppression effect, it is preferable to use particles made of at least one inorganic material selected from oxide particles, carbide particles, nitride particles, and inorganic hydrate particles, and it is more preferable to use 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 use at least one type selected from nanoparticles, hollow particles, porous particles, and scale-like particles. Specific examples of inorganic particles that can be used 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 hydrous porous bodies. Furthermore, particles made of mica can also be used as the inorganic particles.

[0049] When the average secondary particle diameter of the inorganic particles is 0.01 μm or more, they are easily available and the increase in production costs can be suppressed. Furthermore, when the average secondary particle diameter 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.

[0050] In addition, by using two or more inorganic particles with different heat transfer suppression effects in combination, it is possible to cool a heat generating body in multiple stages, and the heat absorption effect can be exerted over a wider temperature range. Specifically, it is preferable to use a mixture of large-diameter particles and small-diameter particles. For example, when nanoparticles are used as one of the inorganic particles, it is preferable to include inorganic particles made of a metal oxide as the other inorganic particle. Hereinafter, the inorganic particles will be described in more detail, with the small-diameter inorganic particles referred to as the first inorganic particles and the large-diameter inorganic particles referred to as the second inorganic particles.

[0051] <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 radiant heat transfer, particularly in high-temperature regions such as those caused by abnormal heat generation. The oxide particles can be at least one type of particle selected from silica, titania, zirconia, zircon, barium titanate, zinc oxide, and alumina. That is, among the above oxide particles that can be used as inorganic particles, only one type or two or more types of oxide particles can be used. In particular, silica is a component with high heat insulating properties, and titania is a component with a higher refractive index than other metal oxides, and is highly effective in diffusely reflecting light and blocking radiant heat in high-temperature regions of 500°C or higher. Therefore, it is most preferable to use silica and titania as the oxide particles.

[0052] (Average primary particle size of oxide particles: 0.001 μm to 50 μm) The particle size of the oxide particles can affect the effect of reflecting radiant heat, so if the average primary particle size is limited to a predetermined range, even higher heat insulating properties can be obtained. In other words, when the average primary particle diameter of the oxide particles is 0.001 μm or more, the particle diameter is sufficiently larger than the wavelength of light that contributes to heating, and the light is efficiently diffused, thereby suppressing the radiative heat transfer within the thermal insulation material in the high temperature range of 500°C or higher, thereby further improving the thermal insulation properties. On the other hand, if the average primary particle size of the oxide particles is 50 μm or less, the number and number of contact points between the particles do not increase even when compressed, making it difficult to form paths for conductive heat transfer. This reduces the impact on thermal insulation, particularly in the normal temperature range where conductive heat transfer is dominant.

[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] (nanoparticles) In the present invention, nanoparticles refer to particles on the order of nanometers that are spherical or nearly spherical and have an average primary particle diameter of less than 1 μm. Nanoparticles have low density, which suppresses conductive heat transfer. When nanoparticles are used as the first inorganic particles, finer voids are dispersed, resulting in excellent heat insulation that suppresses convective heat transfer. Therefore, it is preferable to use nanoparticles because they can suppress heat transfer between adjacent nanoparticles during normal use of the battery at room temperature. Furthermore, if nanoparticles with a small average primary particle size are used as oxide particles, the increase in conductive heat transfer through the insulating material can be suppressed even when the insulating material is compressed due to expansion caused by thermal runaway in the battery cell, increasing the internal density. This is thought to be because nanoparticles are prone to forming small voids between particles due to electrostatic repulsion, and because their bulk density is low, the particles are packed together to provide cushioning.

[0055] In the present invention, when nanoparticles are used as the first inorganic particles, there are no particular limitations on the material as long as they comply with the definition of nanoparticles. For example, silica nanoparticles are a material with high heat insulating properties, and 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 diameter are used. Furthermore, 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 a large compressive stress is applied to the insulating material, the size (area) and number of contact points between the silica nanoparticles do not increase significantly, and 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 that are particularly suitable for this embodiment will be described below.

[0056] Generally, wet silica particles are agglomerated, while dry silica particles can be dispersed. Because heat conduction is predominant in the temperature range below 300°C, dry silica, which can disperse particles, can achieve superior heat insulation performance compared to wet silica. The heat insulating material according to this embodiment is preferably produced by a manufacturing method in which a mixture containing the material is processed into a sheet by a dry method. Therefore, it is preferable to use dry silica, silica aerogel, or the like, which has low thermal conductivity, as the inorganic particles.

[0057] (Average primary particle diameter of nanoparticles: 1 nm to 100 nm) If the average primary particle size of the nanoparticles is limited to a predetermined range, even higher heat insulating properties can be obtained. That is, when the average primary particle diameter of the nanoparticles is 1 nm or more and 100 nm or less, convective heat transfer and conductive heat transfer within the thermal insulation material can be suppressed, particularly in the temperature range below 500°C, and the thermal insulation properties can be further improved. Furthermore, even when compressive stress is applied, the voids remaining between the nanoparticles and the contact points between many particles suppress conductive heat transfer, allowing the thermal insulation properties of the thermal insulation material to be maintained. The average primary particle size of the nanoparticles is more preferably 2 nm or more, and even more preferably 3 nm or more, while the average primary particle size of the nanoparticles is more preferably 50 nm or less, and even more preferably 10 nm or less.

[0058] (Inorganic hydrate particles) When inorganic hydrate particles receive heat from a heating element and reach a temperature above their thermal decomposition initiation temperature, they undergo thermal decomposition and release their own water of crystallization, lowering the temperature of the heating element and its surroundings, thereby exhibiting a so-called "endothermic effect." After releasing the water of crystallization, the particles become porous, and the numerous air holes provide thermal insulation. 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).

[0059] For example, aluminum hydroxide has 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 (Al2O3) and functions as a heat insulating material. 2Al(OH)3 → Al2O3 + 3H2O

[0060] As described above, the heat-transfer-suppressing sheet 10 according to this embodiment is preferably interposed between battery cells, for example, but in a battery cell that experiences thermal runaway, the temperature rises sharply to over 200°C and continues to rise to around 700°C. Therefore, the inorganic particles contained in the thermal insulating material 11 are preferably made of an inorganic hydrate whose thermal decomposition temperature starts at 200°C or higher. The thermal decomposition starting 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.All of these temperatures roughly overlap with the temperature range in which a battery cell experiencing thermal runaway experiences a sudden rise in temperature, and can efficiently suppress temperature rise, making these inorganic hydrates preferable.

[0061] (Average secondary particle diameter of inorganic hydrate particles: 0.01 μm or more and 200 μm or less) Furthermore, when inorganic hydrate particles are used as the first inorganic particles, if the average particle diameter is too large, it takes some time for the first inorganic particles (inorganic hydrate) near the center of the thermal insulating material 11 to reach their thermal decomposition temperature, and the first inorganic particles near the center of the thermal insulating material 11 may not be completely thermally decomposed. For this reason, the average secondary particle diameter 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.

[0062] (Particles made of thermally expandable inorganic material) Examples of thermally expandable inorganic materials include vermiculite, bentonite, mica, and perlite.

[0063] (Particles made of hydrous porous material) Specific examples of the hydrous porous material include zeolite, kaolinite, montmorillonite, acid clay, diatomaceous earth, wet silica, dry silica, aerogel, mica, and vermiculite.

[0064] (inorganic balloons) The heat insulating material used in the present invention may contain inorganic balloons as the first inorganic particles. When inorganic balloons are contained, convective or conductive heat transfer within the heat insulating material can be suppressed in the temperature range below 500°C, and the heat insulating properties of the heat insulating material can be further improved. As the inorganic balloons, at least one selected from shirasu balloons, silica balloons, fly ash balloons, barite balloons, and glass balloons can be used.

[0065] (Inorganic balloon content: 60% or less by mass of the total mass of the insulation material) The content of the inorganic balloons is preferably 60 mass % or less based on the total mass of the heat insulating material.

[0066] (Average particle size of inorganic balloons: 1 μm to 100 μm) The average particle size of the inorganic balloons is preferably 1 μm or more and 100 μm or less.

[0067] <Second inorganic particles> When two types of inorganic particles are contained in a heat insulating material, the second inorganic particles are not particularly limited as long as they are different from the first inorganic particles in terms of material, particle size, etc. Examples of the second inorganic particles that can be used include 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 a thermally expandable inorganic material, and particles made of a hydrous porous body, the details of which are as described above.

[0068] Nanoparticles have extremely low conductive heat transfer and can maintain excellent heat insulation even when compressive stress is applied to the insulating material. Metal oxide particles such as titania are also effective in blocking radiant heat. Furthermore, when large-diameter inorganic particles and small-diameter inorganic particles are used, the small-diameter inorganic particles penetrate into 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 second inorganic particles made of a metal oxide that are larger in diameter than the first inorganic particles in the insulating material. Examples of metal oxides include silicon oxide, titanium oxide, aluminum oxide, barium titanate, zinc oxide, zircon, zirconium oxide, etc. In particular, titanium oxide (titania) is a component with a higher refractive index than other metal oxides, and is highly effective in scattering light and blocking radiant heat in a high temperature range of 500°C or higher, so it is most preferable to use titania.

[0069] When the first inorganic particles are at least one type of particles selected from dry silica particles and silica aerogel, and the second inorganic particles are at least one type of particles selected from titania, zircon, zirconia, silicon carbide, zinc oxide, and alumina, the first inorganic particles preferably account for 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more of the total mass of the inorganic particles, in order to obtain excellent heat insulating performance within a temperature range of 300° C. or less. Furthermore, the first inorganic particles preferably account for 95% by mass or less, more preferably 90% by mass or less, and even more preferably 80% by mass or less of the total mass of the inorganic particles.

[0070] On the other hand, in order to obtain excellent heat insulating performance in a temperature range exceeding 300° C., the content 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. Also, the content 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.

[0071] (Average primary particle size of second inorganic particles) When second inorganic particles made of a metal oxide are contained in a thermal insulating material, if the average primary particle size of the second inorganic particles is 1 μm or more and 50 μm or less, radiation heat transfer can be efficiently suppressed in a high temperature range of 500° C. or more. The average primary particle size of the second inorganic particles is more preferably 5 μm or more and 30 μm or less, and most preferably 10 μm or less.

[0072] (Inorganic particle content) In this embodiment, if the total content of inorganic particles in the heat insulating material 11 is appropriately controlled, the heat insulating property of the heat insulating 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 is too high, the content of organic fibers will relatively decrease, so in order to fully obtain the skeleton reinforcing effect and the inorganic particle retention effect, 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.

[0073] The content of inorganic particles in the heat insulating material 11 can be calculated, for example, by heating the heat insulating material 11 at 800° C., decomposing the organic components, and then measuring the mass of the remaining portion.

[0074] The heat insulating material of the heat transfer sheet according to this embodiment may contain, in addition to the inorganic particles, organic fibers, inorganic fibers, etc. The organic fibers and inorganic fibers that are preferably contained in the heat insulating material will be described below.

[0075] <Organic fiber> The organic fibers have the effect of imparting flexibility to the insulating material 11, and by forming a skeleton, they have the effect of increasing the strength of the insulating material 11. Furthermore, if inorganic particles and other organic fibers are fused to the surface of the organic fibers, the effect of increasing the strength of the sheet and the effect of maintaining its shape can be further improved. Furthermore, if the insulating material 11 contains an appropriate amount of organic fibers, multiple voids are formed inside the insulating material 11, and when the insulating material 11 is heated, air and moisture can be released to the outside through the voids.

[0076] Although single-component organic fibers can be used as the organic fiber material in the thermal insulation material 11, 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. In this case, the core is made of a first organic material, and the sheath is made of a second organic material, and the melting point of the first organic material is higher than that of the second organic material.

[0077] (First organic material) In this embodiment, when a core-sheath binder fiber is used, 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. The first organic material may be at least one selected from polyethylene terephthalate, polypropylene, and nylon.

[0078] (Second organic material) The second organic material is not particularly limited as long as it has a melting point lower than that of the first organic material constituting the organic fiber, and 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.

[0079] (organic fiber content) In this embodiment, if the content of organic fibers in the heat insulating material 11 is appropriately controlled, the skeleton can be sufficiently reinforced. 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 thermal insulation material 11. Furthermore, if the organic fiber content is too high, the inorganic particle content will relatively decrease, so in order to obtain the desired thermal 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 thermal insulation material 11.

[0080] (fiber length of organic fiber) There are no particular limitations on the fiber length of the organic fibers, but from the viewpoint of ensuring moldability and processability, it is preferable that the average fiber length of the organic fibers be 10 mm or less. On the other hand, from the viewpoint of making the organic fibers function as a skeleton and ensuring the compressive strength of the heat insulating material, it is preferable that the average fiber length of the organic fibers is 0.5 mm or more.

[0081] <Inorganic fibers> The inorganic fibers may be a single inorganic fiber or a combination of two or more inorganic fibers. 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 natural mineral fibers other than these fibers, such as rock wool, basalt fiber, wollastonite, and mullite fiber. These inorganic fibers are preferred in terms of heat resistance, strength, availability, etc. Among the above inorganic fibers, the heat insulating material preferably contains at least one type selected from silica-alumina fiber, alumina fiber, silica fiber, rock wool, alkaline earth silicate fiber, and glass fiber, from the viewpoint of ease of handling.

[0082] 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.

[0083] The preferred lower limit of the average fiber length of the inorganic fibers is 0.1 mm, more preferably 0.5 mm. On the other hand, 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 intertwine with each other, which may reduce the mechanical strength of the thermal insulation material 11. On the other hand, if the average fiber length exceeds 50 mm, although a reinforcing effect is obtained, the inorganic fibers may not be able to intertwine tightly with each other or may curl up individually, which may result in reduced thermal insulation.

[0084] 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 heat transfer through the inorganic fibers may increase, leading to a decrease in thermal insulation properties, and the moldability and strength of the thermal insulation material may be deteriorated.

[0085] (Inorganic fiber content) In this embodiment, when the heat insulating material 11 contains inorganic fibers, the content of the inorganic fibers is preferably 3 mass % or more and 15 mass % or less with respect to the total mass of the heat insulating material 11.

[0086] Furthermore, the content of inorganic fibers is more preferably 5% by mass or more and 10% by mass or less of the total mass of the thermal insulation material 11. By setting the content in this range, the shape retention, compressive force resistance, wind pressure resistance, and inorganic particle retention ability of the inorganic fibers are exhibited in a balanced manner. Furthermore, by appropriately controlling the content of inorganic fibers, the organic fibers and inorganic fibers become entangled with each other to form a three-dimensional network, which further improves the effect of retaining inorganic particles and other compounding materials described below.

[0087] <Other compounding materials> (hot melt powder) In this embodiment, in addition to the binder fibers and inorganic particles, the mixture may contain hot-melt powder. The hot-melt powder is a powder that contains, for example, a third organic material different from the first and second organic materials and has the property of melting when heated. When the hot-melt powder is added to the mixture and heated, it melts, and when cooled, it hardens in a state that includes the surrounding inorganic particles. This further prevents the inorganic particles from falling off the insulating material 11.

[0088] Hot melt powders with various melting points can be used. A hot melt powder with an appropriate melting point can be selected based on 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.

[0089] 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), the molten sheath around them, and the hot melt powder present in the gaps between the inorganic particles harden first. As a result, the position of the organic fibers can be fixed, and then the molten sheath will fuse to the organic fibers, facilitating the formation of a three-dimensional skeleton. This further improves the strength of the entire sheet.

[0090] 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 latitude 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.

[0091] 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. Components constituting the hot melt powder include polyethylene, polyester, polyamide, and ethylene vinyl acetate.

[0092] (Hot melt powder content) When hot melt powder is added to the insulating material to prevent the inorganic particles from falling off, even a small amount of hot melt powder can be used to prevent 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, of the total mass of the insulating material. On the other hand, when the content of hot melt powder is increased, the content of inorganic particles and the like is relatively decreased. Therefore, in order to obtain the desired heat insulating performance, the content of hot melt powder is preferably 5 mass % or less, and more preferably 4 mass % or less, of the total mass of the heat insulating material.

[0093] When the material for the insulating material 11 contains a hot melt powder, the heating temperature in the heating step is preferably set to be at least 10°C higher, and more preferably at least 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 at least 20°C lower, than the melting point of the first organic material constituting the core. Setting the heating temperature at this level allows for the formation of a strong skeleton, further improving the strength of the sheet and preventing the inorganic particles from falling off.

[0094] The heat insulating material 11 may further contain other binders, colorants, etc. as needed. These are all useful for the purpose of reinforcing the heat insulating material 11 and improving its formability, and the total amount of these additives relative to the total mass of the heat insulating material 11 is preferably 10 mass % or less.

[0095] In addition to the heat insulating material 11 having the above-mentioned materials, a mica sheet containing mica can also be used as the heat insulating material in this embodiment. Below, a mica sheet that can be used as the heat insulating material will be specifically described.

[0096] <Mica sheet> In this embodiment, a mica sheet can be used alone as a thermal insulator, or in combination with a material other than the mica sheet, such as the thermal insulators described above. The mica sheet is a mica sheet material containing inorganic particles processed into a sheet shape. Mica has excellent heat resistance and insulating properties, and a mica sheet made by processing a material containing mica into a sheet shape also has excellent impact resistance. Therefore, for example, if the battery cell 20a explodes due to high temperature and generates debris, the thermal insulator containing the mica sheet can be prevented from being damaged. As a result, high thermal insulation can be maintained between the battery cell 20a and the battery cell 20b.

[0097] The mica sheet material preferably includes oxide particles, oxide fibers, etc. in addition to mica. Specific examples include SiO2, Al2O3, Ti2O3, etc., but the present invention is not limited to these materials. It is more preferable to use a mica sheet made of natural minerals. The sheet shape may be a flat sheet without holes or may have holes. Providing holes in at least a portion of the center or other regions of the mica sheet allows the mica sheet to conform to the battery cells 20a, 20b, 20c without cracking when the battery cells 20a, 20b, 20c expand and contract.

[0098] [Protective material] As described above, the protective material 16 is a member that protects the heat insulating material 11, and it is sufficient if it has the function of preventing particles from being discharged through the holes 13 in the resin film 12 even if they fall off the heat insulating material 11. Examples of members that can be used as the protective material 16 will be described below.

[0099] <Elastic sheet> In this embodiment, an elastic sheet having elasticity that allows it to flexibly deform in response to deformation of the battery cells 20a, 20b, and 20c can be used as the protective material 16. For example, rubber, elastomer, etc. can be used as such an elastic sheet. Specific examples of rubber include foamed silicone.

[0100] (Elastic sheet thickness) The thickness of the elastic sheet is not particularly limited, but is preferably 1 mm or more and 10 mm or less to effectively obtain the above-mentioned effects of the elastic sheet. In addition, it is preferable that the shape and size of the surface of the elastic sheet in the direction perpendicular to the thickness direction be approximately the same as those of the main surfaces 11a and 11b of the thermal insulation material 11.

[0101] The protective material used in this embodiment is not limited to the elastic sheet, and sheets having other functions may also be used. Examples of other materials that can be used as the protective material 16 will be described below.

[0102] <Fiber reinforced plastic sheet or board> A fiber-reinforced plastic sheet or board can be used as the protective material. Examples of fiber-reinforced plastics include composite materials in which resins such as polyester, epoxy, vinyl ester, and phenol are reinforced with glass fiber or other fiber materials. In this embodiment, it is particularly preferable to select polyethylene phthalate or polypropylene reinforced with glass fiber as the fiber-reinforced plastic sheet or board used as the protective material, as these have excellent strength and heat resistance.

[0103] [Resin film] The resin film 12 contains the above-mentioned insulating material 11 and protective material 16, and has the effect of preventing particles and the like contained in the insulating material 11 from falling off, as well as the effect of suppressing the occurrence of misalignment between the insulating material 11 and the protective material 16. The material constituting the resin film can be at least one resin selected from polyethylene, polypropylene, polystyrene, vinyl chloride, nylon, acrylic, epoxy resin, polyurethane, polyether ether ketone, polyetherimide, polyethylene terephthalate, polyphenyl sulfide, polycarbonate, and aramid.

[0104] In this embodiment, it is preferable to use shrink packaging when covering the heat insulating material 11 and the protective material 16 with the resin film 12. Therefore, it is more preferable to use a resin film 12 made of a material suitable for shrink packaging. Examples of such materials include polyethylene, polypropylene, polystyrene, polyethylene terephthalate, and polyvinyl chloride.

[0105] <Resin film thickness> In this embodiment, the resin film 12 preferably has an appropriate thickness in order to adhere to the outer surface of the heat insulating material, etc., and to have the effect of preventing particles, etc. from falling off. Furthermore, since the resin film 12 preferably has a configuration in which at least a portion thereof adheres to the shape of the laminate 17 of the heat insulating material 11 and the protective material 16, the resin film 12 preferably has appropriate flexibility. If the thickness of resin film 12 exceeds 1 mm, it becomes difficult for resin film 12 to conform to the shape of laminate 17, and cracks or breaks may occur. Therefore, the thickness of resin film 12 is preferably 1 mm or less, more preferably 0.1 mm or less, and even more preferably 0.05 mm or less. On the other hand, there is no particular lower limit to the thickness of the resin film 12, but in order to prevent tearing due to friction with the battery cell, etc., it is preferably 0.005 mm or more, and more preferably 0.01 mm or more.

[0106] <Other materials contained in the resin film> Furthermore, since resin film 12 comes into contact with battery cells 20a, 20b, and 20c, it is preferable that resin film 12 be flame-retardant, and specifically, it preferably contains an inorganic substance or a flame-retardant material. Materials constituting resin film 12 include inorganic substances such as talc, calcium carbonate, aluminum hydroxide, titanium oxide, vermiculite, zeolite, synthetic silica, zirconia, zircon, barium titanate, zinc oxide, and alumina, and flame-retardant materials such as bromine-based flame retardants, chlorine-based flame retardants, phosphorus-based flame retardants, boron-based flame retardants, silicone-based flame retardants, and nitrogen-containing compounds.

[0107] [Method of manufacturing heat transfer suppression sheet] An example of a method for manufacturing the heat transfer-suppressing sheet 10 according to this embodiment will be described below with reference to FIGS. First, inorganic particles and, if necessary, organic fibers or inorganic fibers are charged into a mixer such as a V-type mixer in a predetermined ratio to prepare a mixture. Next, the mixture is charged into a predetermined mold and pressed with a press or the like. The resulting molded body is heated and further cooled to obtain the insulating material 11 processed into a sheet shape.

[0108] Next, the heat insulating material 11 and the protective material 16 prepared in advance are laminated together, and the laminate 17 consisting of the heat insulating material 11 and the protective material 16 is placed on a planar resin film without holes, with the heat insulating material 11 facing downward. A planar resin film with holes 13 is then placed on top of the laminate 17. The planar resin film on the lower surface and the planar resin film on the upper surface of the laminate 17 are then heated while applying pressure around the periphery of the laminate 17 to form fused portions 14. The resin film around the periphery of the laminate 17 is then shrunk by heating, and the outer surface of the laminate 17 is covered with the resin film 12. This allows the production of a heat-transfer-suppressing sheet 10 having a structure in which the laminate 17 is covered with the heat insulating material-side film 12b without holes and the protective material-side film 12a with holes 13.

[0109] Other methods for manufacturing the heat transfer-suppressing sheet 10 so that the sum of the areas of the holes in the heat insulating material-side film 12b is smaller than the sum of the areas of the holes 13 in the protection material-side film 12a include the following: For example, there is a method in which the holes in the region that will become the protection material-side film 12a are made larger than the holes in the region that will become the heat insulating material-side film 12b, or a method in which the number of holes in the region that will become the protection material-side film 12a is made greater than the number of holes in the region that will become the heat insulating material-side film 12b.

[0110] The holes 13 may be formed in an elliptical shape beforehand, or may be formed into circular holes 13 and then heat-shrunk the resin film 12 to form an elliptical shape. When heat-shrunking the resin film to form an elliptical shape, a method can be used in which the lengths of a pair of sides of the laminate 17 and the lengths of the sides of the planar resin film are adjusted. For example, when a resin film is used that has a first side that is approximately the same length as the pair of sides of the laminate and a second side that is sufficiently longer than the other side of the laminate, the force that causes the resin film to shrink in the direction parallel to the first side is strong. Therefore, an elliptical hole 13 with a major axis in the direction parallel to the first side can be formed.

[0111] There are no particular limitations on the method for enclosing laminate 17 of heat insulating material 11 and protective material 16 in resin film 12, and examples include shrink packaging in which the film is shrunk as described above, a method in which laminate 17 is wrapped in resin film and then attached with an adhesive or the like, and a method in which laminate 17 is housed in a bag-shaped film. Whichever method is used, it is sufficient that resin film 12 is configured so that the sum of the areas of the holes in heat insulating material-side film 12b is smaller than the sum of the areas of the holes in protective material-side film 12a.

[0112] [Battery pack] An example of a battery pack, which is an example of a power storage device, to which the heat transfer-suppressing sheet 10 according to an embodiment of the present invention is applied, is as shown in Fig. 3. The configuration and effects of the battery pack will now be described in detail with reference to Fig. 3. As shown in FIG. 3, the battery pack 100 includes a plurality of battery cells 20a, 20b, and 20c and the heat transfer-suppressing sheet 10 according to this embodiment, and the plurality of battery cells are connected in series or in parallel. 3, the heat-transfer-suppressing sheet 10 according to this embodiment is interposed between the battery cell 20a and the battery cell 20b, and between the battery cell 20b and the battery cell 20c. Furthermore, the battery cells 20a, 20b, and 20c and the heat-transfer-suppressing sheet 10 are housed in a battery case 30. The heat-transfer-suppressing sheet 10 is as described above.

[0113] 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 suppression sheet 10, which has a heat transfer suppression effect, is present between the battery cell 20a and the battery cell 20b. Furthermore, in the heat-transfer-suppressing sheet 10 according to this embodiment, the insulating material 11 and the protective material 16 are enclosed within the insulating-material-side film 12b and the protective-material-side film 12a. This prevents powder from falling off when the heat-transfer-suppressing sheet 10 is fitted between the battery cells 20a, 20b, and 20c, improving workability. Furthermore, in this embodiment, the sum of the areas of the holes in the insulating-material-side film 12b is smaller than that of the protective-material-side film 12a. Therefore, when the battery cells generate heat and the temperature of the insulating material 11 in the heat-transfer-suppressing sheet 10 rises, air containing particles enclosed in the resin film 12 is prevented from escaping from the insulating material 11 side, thereby preventing contamination inside the battery case 30.

[0114] The battery pack 100 of this embodiment is not limited to the battery pack illustrated in Fig. 2. 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.

[0115] In the battery pack 100 configured in this manner, if a battery cell catches fire, the flames 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 area. In this case, even if a battery cell were to catch fire, the safety of the passengers can be ensured. Furthermore, the heat transfer suppression sheet 10 can be placed not only between each battery cell, but also between the battery cells 20a, 20b, 20c and the battery case 30, eliminating the need to fabricate new flame retardant materials, etc., and allowing for the easy, low-cost, and safe construction of the assembled battery 100. [Explanation of symbols]

[0116] 10 Heat transfer suppression sheet 11. Insulation 11a,11b,16a Main surface 11c,16c end face 12 Resin film 12a Protective film 12b Insulation side film 13 holes 14 Fusion part 16 Protective materials 17 Laminate 20a, 20b, 20c battery cells 30 Battery case 100 battery packs

Claims

1. a heat insulating material containing inorganic particles; A protective material laminated on the heat insulating material; a resin film having holes and enclosing a laminate including the heat insulating material and the protective material, the resin film has a heat insulating material side film that covers a surface of the heat insulating material and a protective material side film that covers a surface of the protective material, A heat transfer-suppressing sheet, wherein the sum of the areas of the holes in the heat insulating material side film is smaller than the sum of the areas of the holes in the protection material side film.

2. The heat transfer-suppressing sheet according to claim 1 , wherein the number of holes in the heat insulating material side film is smaller than the number of holes in the protection material side film.

3. The heat transfer suppressing sheet according to claim 1 , wherein the protective material is an elastic sheet.

4. 2. The heat transfer suppressing sheet according to claim 1, wherein the protective material is a fiber-reinforced plastic sheet or a fiber-reinforced plastic board.

5. The heat transfer-suppressing sheet according to claim 1 , wherein the heat insulating material side film does not have the holes.

6. The heat transfer-suppressing sheet according to claim 1 , wherein the resin film has a fused portion at an end face side of the laminate where the resin films are fused together.

7. The heat transfer suppressing sheet according to claim 1 , wherein the resin film has a plurality of the holes, each of the holes having an elliptical shape.

8. 8. The heat transfer suppressing sheet according to claim 7, wherein the laminate has a rectangular shape when viewed in the stacking direction, and the holes have an elliptical shape with a major axis extending in approximately the same direction as the longitudinal direction of the rectangular surface of the laminate.

9. the resin film has a plurality of the holes, The heat transfer suppressing sheet according to claim 1 , wherein the holes are arranged along a direction in which the sides of the laminate extend.

10. A battery pack according to any one of claims 1 to 9, comprising: a plurality of battery cells; and a heat transfer-suppressing sheet according to any one of claims 1 to 9, A battery pack in which the plurality of battery cells are connected in series or in parallel.

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