Heat transfer suppression sheet, method of manufacturing the heat transfer suppression sheet, and battery pack

Abstract

To provide a heat transfer suppression sheet which can prevent the occurrence of sparks between battery cells and efficiently diffuse, to the outside, heat generated from the battery cells, thereby capable of suppressing a chain thermal runaway.SOLUTION: There is provided a heat transfer suppression sheet 10 which is used in a battery pack including a plurality of battery cells connected in series or parallel therein. The heat transfer suppression sheet 10 includes a pair of heat insulation materials 13a, 13b, and an insulating heat transfer layer 12 arranged between the pair of heat insulation materials 13a, 13b. Thermal conductivity of the heat transfer layer 12 in a thickness direction and the thermal conductivity thereof in a surface direction perpendicular to the thickness direction each are higher than the thermal conductivity of each of the heat insulation materials 13a, 13b, and the thermal conductivity of the heat transfer layer 12 in the surface direction is higher than the thermal conductivity in the thickness direction.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a heat-transfer-suppressing sheet suitable for use in a battery pack that serves as a power source for an electric motor that drives, for example, an electric vehicle or a hybrid vehicle, a method for producing the same, and a battery pack that uses 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 and hybrid vehicles driven by electric motors. These electric vehicles and hybrid vehicles are equipped with assembled batteries in which multiple battery cells are connected in series or parallel to serve as the power source for the drive electric motor.

[0003] These battery cells mainly use lithium-ion secondary batteries, which have higher capacity and output than lead-acid batteries or nickel-metal hydride batteries. However, if thermal runaway occurs in one battery cell due to an internal short circuit or overcharging (i.e., in the event of an "abnormal battery cell"), heat may be transmitted to other adjacent battery cells, potentially causing thermal runaway in those cells.

[0004] For example, Patent Document 1 proposes a heat transfer suppression sheet that is placed close to or in at least partial contact with a heat generating element, and that has a first insulating layer and a second insulating layer, with a metal layer sandwiched between the first insulating layer and the second insulating layer.

[0005] In the heat-transfer-suppressing sheet described in Patent Document 1, the metal layer is made of a material with high thermal conductivity and has a high heat dissipation effect in a direction perpendicular to the sheet thickness. Therefore, heat received from the heating element is insulated to a certain extent by the second insulating layer facing the heating element. However, heat that is not completely insulated by the second insulating layer actively transfers through the metal layer in a direction perpendicular to the sheet thickness, thereby suppressing heat transfer in the sheet thickness direction. As a result, even if thermal runaway occurs in one battery cell, it is possible to prevent a chain reaction of thermal runaway to adjacent battery cells. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2020-165483 Summary of the Invention [Problem to be solved by the invention]

[0007] However, the heat-transfer-suppressing sheet described in Patent Document 1 has a metal layer sandwiched between the first and second insulating layers, so when the heat-transfer-suppressing sheet is placed between heat-generating elements, i.e., battery cells, there is a risk of sparks occurring between the battery cells, which could ignite combustible materials and cause a vehicle fire. Furthermore, in the above Patent Document 1, for example, stainless steel foil is used as the metal layer, but since stainless steel has a low thermal conductivity among metals, it may be difficult to actively transfer heat in a direction perpendicular to the sheet thickness direction.

[0008] Furthermore, with the recent diversification of vehicles and the like, it is preferable that the insulating material used in the battery pack for the power source of the drive electric motor is one that has high versatility and can be used not only between battery cells but also between the battery cell and the battery case, from the viewpoint of reducing manufacturing costs, etc.

[0009] The present invention has been made in view of the above-mentioned problems, and aims to provide a heat-transfer-suppressing sheet, a method for manufacturing a heat-transfer-suppressing sheet, and a battery pack that are highly versatile and can prevent sparks from occurring between battery cells and suppress a chain reaction of thermal runaway by efficiently diffusing heat generated from the battery cells to the outside. [Means for solving the problem]

[0010] The above object of the present invention is achieved by the heat transfer-suppressing sheet having the following configuration [1].

[0011] [1] A heat transfer suppression sheet used in a battery pack in which multiple battery cells are connected in series or parallel, A pair of insulating materials; an insulating heat transfer layer disposed between the pair of heat insulating materials; The thermal conductivity of the heat transfer layer in a thickness direction and a surface direction perpendicular to the thickness direction are both higher than the thermal conductivity of the heat insulating material, A heat transfer-suppressing sheet, wherein the thermal conductivity of the heat transfer layer in the plane direction is higher than the thermal conductivity in the thickness direction.

[0012] Furthermore, preferred embodiments of the present invention relating to the heat transfer-suppressing sheet relate to the following [2] to

[14] .

[0013] [2] The heat-transfer-suppressing sheet according to [1], wherein the heat-transfer layer contains a filler made of at least one type of ceramic selected from plate-like ceramics, scaly ceramics, and fibrous ceramics.

[0014] [3] The heat-transfer-suppressing sheet according to [2], wherein the filler is oriented in the plane direction of the heat-transfer layer.

[0015] [4] The electrical resistivity of the filler is 1×10 8 The heat-transfer-suppressing sheet according to [2] or [3], characterized in that it has a resistivity of Ω·m or more.

[0016] [5] The heat-transfer-suppressing sheet according to any one of [2] to [4], wherein the ceramic constituting the filler includes at least one selected from boron nitride, aluminum nitride, alumina, silica, silicon nitride, zinc oxide, magnesia, silicon carbide, beryllium oxide, and diamond.

[0017] [6] The heat transfer layer further contains a matrix that binds the filler, The heat-transfer-suppressing sheet according to any one of [2] to [5], wherein the matrix contains at least one material selected from ceramics and resins.

[0018] [7] The heat transfer layer further contains a matrix that binds the filler, The heat-transfer-suppressing sheet according to any one of [2] to [5], wherein the matrix contains at least one material selected from aluminum phosphate, sodium silicate, silica sol, alumina sol, silicone resin, epoxy resin, acrylic resin, fluorine-based resin, and cellulose nanofiber.

[0019] [8] The electrical resistivity of the matrix is ​​1×10 8 The heat-transfer-suppressing sheet according to [6] or [7], characterized in that it has a resistivity of Ω·m or more.

[0020] [9] The heat-transfer-suppressing sheet according to any one of [1] to [8], wherein λs / λt is 2 or greater, where λs (W / mK) is the thermal conductivity of the heat-transfer layer in the plane direction and λt (W / mK) is the thermal conductivity of the heat-transfer layer in the thickness direction.

[0021]

[10] The heat-transfer-suppressing sheet according to any one of [1] to [9], wherein the heat insulating material has a thermal conductivity of less than 1 (W / m·K).

[0022]

[11] The heat-transfer-suppressing sheet according to any one of [1] to

[10] , wherein the heat-insulating material contains at least one selected from inorganic fibers, organic fibers, inorganic particles, and organic particles.

[0023]

[12] The thermal insulating material includes inorganic particles, first inorganic fibers, and second inorganic fibers; the first inorganic fibers are amorphous fibers, The heat transfer-suppressing sheet according to

[11] , wherein the second inorganic fibers are at least one type selected from amorphous fibers and crystalline fibers having a glass transition point higher than that of the first inorganic fibers.

[0024]

[13] The heat-transfer-suppressing sheet according to

[11] or

[12] , wherein the heat insulating material contains at least one selected from silica nanoparticles, titania, alumina fiber, carbon fiber, mica, basalt fiber, soluble fiber, refractory ceramic fiber, glass fiber, aerogel composite, microporous particles, hollow silica particles, thermally expandable inorganic material, aerogel, silica, zirconia, zircon, barium titanate, zinc oxide, alumina, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, zinc hydroxide, iron hydroxide, manganese hydroxide, zirconium hydroxide, gallium hydroxide, fiber containing SiO2, silica fiber, alumina fiber, ceramic fiber, rock wool, alkaline earth silicate fiber, zirconia fiber, and mineral fiber.

[0025]

[14] The heat-transfer-suppressing sheet according to any one of [1] to

[13] , which is interposed between the plurality of battery cells.

[0026] The above object of the present invention is also achieved by the following configuration

[15] relating to a method for producing a heat transfer-suppressing sheet.

[0027]

[15] A method for producing the heat transfer-suppressing sheet according to any one of [1] to

[14] , a coating step of coating a heat transfer layer material on one surface of one of the pair of heat insulating materials, the surface being perpendicular to the thickness direction; a pressurizing step of pressing the applied heat transfer layer material in a thickness direction; a lamination step of laminating another heat insulating material on the surface on which the heat transfer layer material has been applied, between the application step and the pressurizing step or after the pressurizing step.

[0028] The above object of the present invention can be achieved by the following battery pack configuration

[16] or

[17] .

[0029]

[16] A battery case; a plurality of battery cells housed inside the battery case and connected in series or in parallel; a heat transfer-suppressing sheet according to any one of [1] to

[14] interposed between the plurality of battery cells; and

[0030]

[17] A battery case; a plurality of battery cells housed inside the battery case and connected in series or in parallel; a heat transfer-suppressing sheet according to any one of [1] to

[14] interposed between the plurality of battery cells; a heat transfer member provided between the plurality of battery cells and the battery case; and The battery pack according to claim 1, wherein at least a portion of the heat transfer layer of the heat transfer-suppressing sheet is in contact with the heat transfer member. [Effects of the Invention]

[0031] The heat transfer-suppressing sheet of the present invention has a heat transfer layer disposed between a pair of thermal insulators, and is designed so that the thermal conductivity of the heat transfer layer in both the thickness direction and the plane direction perpendicular to the thickness direction is higher than that of the thermal insulators, and the thermal conductivity of the heat transfer layer in the plane direction is higher than that in the thickness direction. This allows for efficient external diffusion of heat generated from a heat source, thereby suppressing the chain reaction of thermal runaway. Furthermore, the heat transfer layer is insulating, which prevents sparks from occurring between battery cells.

[0032] Furthermore, the method for manufacturing a heat transfer-suppressing sheet of the present invention involves applying a heat transfer layer material to one side of a heat insulating material and then applying pressure in the thickness direction, making it easy to form a heat transfer layer whose thermal conductivity in the surface direction is higher than that in the thickness direction.

[0033] Furthermore, in the battery pack of the present invention, the heat transfer suppression sheet is interposed between multiple battery cells, which prevents sparks from occurring between the battery cells and efficiently diffuses heat generated from the battery cells to the outside, thereby suppressing a chain reaction of thermal runaway. [Brief explanation of the drawings]

[0034] [Figure 1] FIG. 1 is a cross-sectional view that schematically shows a heat-transfer-suppressing sheet according to an embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing the heat transfer layer of the heat transfer-suppressing sheet according to this embodiment. [Figure 3] FIG. 3 is a cross-sectional view that schematically shows a battery pack to which the heat transfer-suppressing sheet according to this embodiment is applied. [Figure 4] FIG. 4 is a cross-sectional view showing the process steps of a method for producing a heat-transfer-suppressing sheet according to an embodiment of the present invention. [Figure 5] FIG. 5 is a diagram showing the orientation of the heat transfer layer for the test materials of the examples and comparative examples. DETAILED DESCRIPTION OF THE INVENTION

[0035] The inventors conducted extensive research to provide a heat transfer-suppressing sheet that can prevent sparks from occurring between battery cells and efficiently diffuse heat generated from the battery cells to the outside.

[0036] As a result, the inventors discovered that the above problem can be solved by disposing an insulating heat transfer layer between a pair of insulating materials, the insulating layer having a higher thermal conductivity than the insulating materials and a higher thermal conductivity in the surface direction than the thermal conductivity in the thickness direction.

[0037] That is, the heat generated by the battery cells is reduced by the heat insulating material before reaching the heat transfer layer between the pair of heat insulating materials. Because the heat transfer layer has a higher thermal conductivity in its surface direction than in its thickness direction, the heat that reaches the heat transfer layer is diffused in the surface direction of the thermal diffusion sheet by conductive heat transfer. In this way, if a battery cell becomes too hot, heat transfer is suppressed before it reaches adjacent battery cells, allowing the heat to be diffused to the outside, thereby preventing a chain reaction of thermal runaway. Furthermore, since the heat transfer layer is insulating, sparks can be prevented from occurring between the battery cells.

[0038] A heat-transfer-suppressing sheet according to an embodiment of the present invention, a method for manufacturing the same, and a battery pack using the heat-transfer-suppressing sheet will be described in detail below with reference to the drawings. The heat-insulating material and heat-transfer layer that make up the heat-transfer-suppressing sheet according to this embodiment will also be described. 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.

[0039] [1. Heat transfer suppression sheet] Fig. 1 is a cross-sectional view schematically showing a heat-transfer-suppressing sheet according to an embodiment of the present invention, and Fig. 2 is a schematic diagram showing a heat-transfer layer of the heat-transfer-suppressing sheet according to this embodiment. Heat-transfer-suppressing sheet 10 has a pair of heat insulating materials 13a and 13b, and an insulating heat-transfer layer 12 disposed between heat insulating materials 13a and 13b.

[0040] 2, heat transfer layer 12 contains fillers 15 made of, for example, boron nitride (BN), and matrix 16 made of resin for binding fillers 15 and maintaining the shape of heat transfer layer 12. Fillers 15 have a scale-like shape, and when a cross section of heat transfer layer 12 is observed, fillers 15 are oriented in a plane perpendicular to the thickness direction of heat transfer layer 12.

[0041] The thickness direction of the heat transfer layer 12 refers to the direction in which the heat insulating material 13a, the heat transfer layer 12, and the heat insulating material 13b are stacked. The surface direction of the heat transfer layer 12 refers to the direction perpendicular to the thickness direction and the surface direction in which the heat transfer layer 12 and the heat insulating materials 13a and 13b are in contact. Hereinafter, these terms are simply referred to as the thickness direction and surface direction of the heat transfer layer 12. In this embodiment, the heat transfer layer 12 and the heat insulating material 13a, and the heat transfer layer 12 and the heat insulating material 13b are in contact with each other, but they do not need to be completely bonded; they may be partially bonded or simply stacked. Therefore, non-bonded portions (not shown) may exist between the heat transfer layer 12 and the heat insulating material 13a and between the heat transfer layer 12 and the heat insulating material 13b. The heat transfer layer 12 and the heat insulating materials 13a and 13b may be completely bonded with an adhesive or the like, and non-bonded portions may not exist.

[0042] 2, the filler 15 contained in the heat transfer layer 12 is oriented in the plane direction, so that the thermal conductivity of the heat transfer layer 12 in the plane direction is higher than the thermal conductivity in the thickness direction. Furthermore, the materials of the heat transfer layer 12 and the thermal insulating materials 13a and 13b are selected so that the thermal conductivity of the heat transfer layer 12 in all directions is higher than the thermal conductivity of the thermal insulating materials.

[0043] 3 is a cross-sectional view schematically illustrating a battery pack incorporating a heat-transfer-suppressing sheet according to this embodiment. The battery pack 100 includes a battery case 30, multiple battery cells 20a, 20b, and 20c housed within 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 multiple battery cells 20a, 20b, and 20c are connected in series or in parallel by bus bars (not shown). A plate-shaped heat transfer member 21 is disposed between the bottom surface of the battery case 30 and the multiple battery cells 20a, 20b, and 20c, and at least a portion of the heat transfer layer 12 is in contact with the heat transfer member 21.

[0044] The heat transfer member 21 is a member that transfers heat from the battery cells 20a, 20b, and 20c or the heat transfer suppression sheet 10 to the heat transfer member 21 to promote heat dissipation, and includes, for example, a heat sink, a heat storage material, and also a thermal interface material (TIM) arranged between the heat sink or heat storage material and the battery cells 20a, 20b, and 20c.

[0045] The battery cells 20a, 20b, and 20c are preferably, for example, lithium ion secondary batteries, but are not particularly limited to this and may also be other secondary batteries.

[0046] In the embodiment configured as described above, for example, when the temperature of the battery cell 20a rises, the heat generated from the battery cell 20a is reduced by the heat insulating material 13a and then passes through the interface between the heat insulating material 13a and the heat-transfer layer 12. At this time, as described above, if there is a non-adhesive portion between the heat insulating material 13a and the heat-transfer layer 12, heat conduction in the thickness direction of the heat-transfer-suppressing sheet can be suppressed. The heat then reaches the heat-transfer layer 12. In this embodiment, the heat-transfer layer 12 has a higher thermal conductivity than the heat insulating materials 13a and 13b and also has high thermal conductivity in the planar direction of the heat-transfer layer 12, so the heat is diffused in the planar direction of the heat-transfer layer 12. Furthermore, at least a portion of the end surface of the heat-transfer layer 12 is in contact with the heat-transfer member 21, so that the heat can be efficiently released via the heat-transfer member 21.

[0047] Then, some of the heat reduced by the heat-transfer layer 12 passes through the interface with the heat-insulating material 13b arranged on the battery cell 20b side. Even at this stage, if there is a non-adhesive portion between the heat-transfer layer 12 and the heat-insulating material 13b, heat conduction in the thickness direction of the heat-transfer-suppressing sheet can be suppressed. The heat that passes through the interface between the heat-transfer layer 12 and the heat-insulating material 13b is further reduced by passing through the heat-insulating material 13b.

[0048] In this way, by arranging the battery cell 20a and the battery cell 20b via the heat transfer suppression sheet 10, when heat is generated from the battery cell 20a, the heat can be efficiently diffused and the propagation of heat between the battery cells can be suppressed, thereby preventing a chain reaction of thermal runaway. Furthermore, since the heat transfer layer is insulating, sparks can be prevented from occurring between the battery cells.

[0049] Furthermore, in this embodiment, the heat transfer layer 12 is disposed on the surface of the heat insulating material 13a opposite to the surface facing the battery cell 20a. Therefore, even when the temperature rise of the battery cell 20a stops, the heat stored in the heat insulating material 13a moves toward the heat transfer layer 12. This prevents the heat stored in the heat insulating material from returning to the battery cell 20a or being transferred to the battery cell 20b, and allows the heat to be released to the outside via the heat transfer layer 12.

[0050] Even if a heat-transfer-suppressing sheet with a structure in which a thermal insulator is disposed between a pair of thermal conduction layers is applied to the battery pack 100, the heat generated from the battery cell 20a reaches the thermal conduction layer and is then transferred in the planar direction of the thermal conduction layer. However, because the thermal conduction layer is in contact with the battery cell 20a, there is a possibility that the heat may return to the battery cell 20a while being transferred in the planar direction of the thermal conduction layer, preventing the required thermal insulation effect from being fully achieved. Therefore, in this embodiment, it is important to place the thermal conduction layer 12 between the pair of thermal insulators 13a, 13b.

[0051] The heat-transfer-suppressing sheet 10 is configured symmetrically in the thickness direction around the heat-transfer layer 12. Therefore, even if heat is generated from the battery cell 20b, this heat is gradually reduced toward the battery cell 20a by passing through the heat-insulating material 13b, the heat-transfer layer 12, and the heat-insulating material 13a in this order, thereby suppressing the propagation of heat to the battery cell 20a.

[0052] Similarly, the heat generated from battery cell 20b is gradually reduced by passing through insulating material 13a, heat transfer layer 12, and insulating material 13b in this order toward battery cell 20c, thereby suppressing the transmission of heat to battery cell 20c.

[0053] The orientation direction of the filler 15 contained in the heat transfer layer 12 does not need to be completely parallel to the surface direction. It is sufficient that the orientation of the filler 15 is controlled so that the thermal conductivity in the surface direction of the heat transfer layer 12 is higher than the thermal conductivity in the thickness direction. For example, some of the filler 15 may be contained in the heat transfer layer 12 so as to extend in the thickness direction.

[0054] In addition, in this embodiment, the heat transfer layer 12 has filler 15 and matrix 16, but as long as the fillers 15 can be fixed to each other and the heat transfer layer 12 can be formed, the matrix 16 does not have to be included.

[0055] Next, the heat insulating material, heat transfer layer, and other components that make up the heat transfer-suppressing sheet according to this embodiment will be described in detail.

[0056] <1-1.Insulation materials> The heat insulating material used in the heat transfer-suppressing sheet according to this embodiment is not particularly limited as long as it 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.

[0057] As such a heat insulating material, for example, a material containing at least one selected from inorganic fibers, organic fibers, inorganic particles, and organic particles can be used. Examples of inorganic fibers that can be used include alumina fibers, carbon fibers, basalt fibers, soluble fibers, refractory ceramic fibers, glass fibers, and aerogel composite materials. As the organic fiber, cellulose fiber or the like can be used. These fibers may be used alone or in combination of two or more types.

[0058] As the inorganic particles, mica, microporous particles, hollow silica particles, thermally expandable inorganic materials, and aerogels can be used. Examples of thermally expandable inorganic materials include vermiculite, bentonite, mica, and perlite. As the organic particles, hollow polystyrene particles or the like can be used.

[0059] Among these materials for the heat insulating material, alumina fiber, glass fiber, aerogel composite material, etc. can be suitably used.

[0060] Another example of a heat insulating material is specifically a material containing inorganic particles, first inorganic fibers, and second inorganic fibers, where the first inorganic fibers are amorphous fibers and the second inorganic fibers are at least one type selected from amorphous fibers having a higher glass transition point than the first inorganic fibers and crystalline fibers. The inorganic particles, the first inorganic fibers, and the second inorganic fibers are all heat-resistant materials, and furthermore, countless tiny spaces are formed between the particles, between the particles and the fibers, and between the fibers, and the air also provides an insulating effect, resulting in excellent heat transfer suppression performance. The inorganic particles, first inorganic fibers, and second inorganic fibers that may be contained in the heat insulating material will be described in detail below.

[0061] <1-1-1. Inorganic particles> The material of the inorganic particles is not particularly limited, but from the viewpoint of the heat transfer suppression effect, the inorganic particles are preferably made of at least one type selected from oxide particles, carbide particles, nitride particles, and inorganic hydrate particles, and more preferably contain oxide particles. The shape and size of the inorganic particles are not particularly limited, but they preferably contain at least one type selected from nanoparticles, hollow particles, and porous particles, and more preferably contain nanoparticles.

[0062] The inorganic particles may be a single type or a combination of two or more types. When two or more types of inorganic particles with different heat transfer suppression effects are used in combination, the heat-generating body can be cooled in multiple stages, and the heat absorption effect can be exerted over a wider temperature range. It is also preferable to use a mixture of large and small inorganic particles. When small inorganic particles fill the gaps between the large inorganic particles, a denser structure is formed, thereby improving the heat transfer suppression effect.

[0063] 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.

[0064] Next, examples of the material or shape of particles that can be used as inorganic particles will be described in detail below.

[0065] (1-1-1-1. Oxide particles) Oxide particles have a high refractive index and a strong effect of diffusely reflecting light. Therefore, using oxide particles as inorganic particles can suppress radiant heat transfer, particularly in high-temperature regions such as those affected 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 therefore highly effective at 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 oxide particles.

[0066] (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 insulation material in the high temperature range of 500°C or higher, thereby further improving the 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.

[0067] When two or more types of oxide particles are used, it is also preferable to use a mixture of large-diameter particles and small-diameter particles (nanoparticles). In this case, the average primary particle size of the large-diameter particles is more preferably 1 μm or more and 50 μm or less, even more preferably 5 μm or more and 30 μm or less, and most preferably 10 μm or less. 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.

[0068] (1-1-1-2. 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 a low density, which suppresses conductive heat transfer. Furthermore, when nanoparticles are used as inorganic particles, the finely dispersed voids provide excellent heat insulation, suppressing convective heat transfer. Therefore, the use of nanoparticles is preferred because they can suppress heat transfer between adjacent nanoparticles during normal use at room temperature.

[0069] In the present invention, it is preferable that at least one of oxide particles, carbide particles, nitride particles, and inorganic hydrate particles selected as inorganic particles is a nanoparticle. Furthermore, if nanoparticles with a small average primary particle size are used as the oxide particles, it is possible to suppress an increase in conductive heat transfer through the insulation material, even if the heat transfer-suppressing sheet is compressed due to expansion caused by thermal runaway in the battery cell, increasing the internal density. This is thought to be because the nanoparticles are easily filled with tiny voids due to electrostatic repulsion, and their low bulk density allows the particles to be packed together in a cushioning manner.

[0070] In the present invention, when nanoparticles are used as inorganic particles, there is no particular limitation 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 size are used. Furthermore, commonly available silica nanoparticles have a bulk density of 0.1 g / cm. 3Therefore, even if, for example, battery cells arranged on both sides of the heat-transfer-suppressing sheet thermally expand and a large compressive stress is applied to the heat-transfer-suppressing sheet, the size (area) and number of contact points between the silica nanoparticles do not increase significantly, and heat insulation properties can be maintained. Therefore, it is preferable to use silica nanoparticles as the nanoparticles. Wet silica, dry silica, aerogel, etc. can be used as the silica nanoparticles.

[0071] As described above, titania has a high effect of blocking radiant heat, and silica nanoparticles have extremely low conductive heat transfer and can maintain excellent heat insulation even when compressive stress is applied to the heat insulating material. Therefore, it is most preferable to use both titania and silica nanoparticles as the inorganic particles.

[0072] (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.

[0073] (1-1-1-3.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).

[0074] 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

[0075] As will be described later, the battery pack of the present invention has heat-transfer-suppressing sheet 10 interposed between battery cells, and 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, it is preferable that the inorganic particles be made of an inorganic hydrate whose thermal decomposition temperature is 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.

[0076] Furthermore, when inorganic hydrate particles are used as inorganic particles, if their average particle size is too large, it takes a certain amount of time for the inorganic particles (inorganic hydrate) near the center of the insulating material to reach their thermal decomposition temperature, and the inorganic particles near the center of the insulating material may not be completely thermally decomposed. Therefore, the average secondary particle size of the inorganic hydrate particles is preferably 0.01 μm or more and 200 μm or less, and more preferably 0.05 μm or more and 100 μm or less.

[0077] <1-1-2. The first inorganic fiber> The first inorganic fibers are amorphous fibers, and the second inorganic fibers are at least one type of fiber selected from amorphous fibers having a higher glass transition point than the first inorganic fibers and crystalline fibers. Note that the melting point of crystalline inorganic fibers is usually higher than the glass transition point of amorphous inorganic fibers. Therefore, when exposed to high temperatures, the surface of the first inorganic fibers softens before the second inorganic fibers, bonding the inorganic particles and the second inorganic fibers together, thereby improving the mechanical strength of the thermal insulation material. Specifically, the first inorganic fiber is preferably an inorganic fiber having a melting point of less than 700°C, and many amorphous inorganic fibers can be used. Among them, a fiber containing SiO2 is preferable, and glass fiber is more preferable because it is inexpensive, easily available, and has excellent handleability.

[0078] <1-1-3. Second inorganic fiber> As described above, the second inorganic fibers are at least one type of fibers selected from amorphous fibers and crystalline fibers having a glass transition temperature higher than that of the first inorganic fibers. Many crystalline inorganic fibers can be used as the second inorganic fibers. If the second inorganic fibers are crystalline fibers or have a higher glass transition temperature than the first inorganic fibers, the second inorganic fibers will not melt or soften when exposed to high temperatures, even if the first inorganic fibers soften, and therefore will be able to maintain their shape and remain present between the battery cells even during thermal runaway. Furthermore, if the second inorganic fibers do not melt or soften, tiny spaces are maintained between the inorganic particles, between the inorganic particles and the first inorganic fibers and the second inorganic fibers, and between the first inorganic fibers and the second inorganic fibers, thereby providing an insulating effect through air and maintaining excellent heat transfer suppression performance.

[0079] When the second inorganic fiber is crystalline, examples of the second inorganic fiber include ceramic fibers such as silica fiber, alumina fiber, alumina silicate fiber, and zirconia fiber, as well as mineral fibers such as rock wool, alkaline earth silicate fiber, zirconia fiber, potassium titanate fiber, and wollastonite. Among the fibers listed as the second inorganic fiber, those with a melting point exceeding 1000°C are suitable for use because even if thermal runaway occurs in the battery cell, the second inorganic fiber will not melt or soften and will be able to maintain its shape. Among the fibers listed as the second inorganic fibers, it is more preferable to use ceramic fibers such as silica fibers, alumina fibers, and alumina silicate fibers, as well as mineral fibers, and it is even more preferable to use fibers with a melting point of over 1000°C. Furthermore, even if the second inorganic fibers are amorphous, they can be used as long as they have a higher glass transition temperature than the first inorganic fibers. For example, glass fibers having a higher glass transition temperature than the first inorganic fibers may be used as the second inorganic fibers. As the second inorganic fiber, the various inorganic fibers exemplified above may be used alone or in combination of two or more kinds.

[0080] As described above, the first inorganic fibers have a lower glass transition point than the second inorganic fibers, and therefore soften first when exposed to high temperatures, allowing the first inorganic fibers to bind the inorganic particles and the second inorganic fibers. However, for example, if the second inorganic fibers are amorphous and have a smaller fiber diameter than the first inorganic fibers, and the glass transition points of the first and second inorganic fibers are close to each other, the second inorganic fibers may soften first. Therefore, when the second inorganic fibers are amorphous fibers, the glass transition point of the second inorganic fibers is preferably at least 100° C. higher, and more preferably at least 300° C. higher, than the glass transition point of the first inorganic fibers.

[0081] (Average fiber diameter of inorganic fibers) In the present invention, inorganic fibers with a large average fiber diameter (large diameter) have the effect of improving the mechanical strength and shape retention of the thermal insulation material. This effect can be achieved by making either the first inorganic fibers or the second inorganic fibers large in diameter. Since the heat transfer-suppressing sheet may be subjected to external impacts, the inclusion of large diameter inorganic fibers in the thermal insulation material increases impact resistance. Examples of external impacts include pressure caused by expansion of battery cells and wind pressure caused by ignition of battery cells. In order to improve the mechanical strength and shape retention of the thermal insulating material, it is particularly preferable that the large-diameter inorganic fibers are linear or needle-shaped. Note that linear or needle-shaped fibers refer to fibers having a crimp degree (described later), for example, of less than 10%, preferably 5% or less.

[0082] More specifically, in order to improve the mechanical strength and shape retention of the thermal insulating material, the average fiber diameter of the thick inorganic fibers is preferably 1 μm or more, more preferably 3 μm or more. However, if the thick inorganic fibers are too thick, there is a risk that the moldability and processability into the thermal insulating material may decrease, so the average fiber diameter is preferably 20 μm or less, more preferably 15 μm or less. If the thick inorganic fibers are too long, moldability and processability may decrease, so the fiber length is preferably 100 mm or less.Furthermore, if the thick inorganic fibers are too short, shape retention and mechanical strength may decrease, so the fiber length is preferably 0.1 mm or more.

[0083] On the other hand, inorganic fibers with a small average fiber diameter (thin diameter) have the effect of improving the retention of inorganic particles and increasing the flexibility of the insulating material. Therefore, by making the other of the first inorganic fibers and the second inorganic fibers thin in diameter, the above effect can be obtained.

[0084] More specifically, to improve the inorganic particle retention, it is preferable that the small-diameter inorganic fibers be easily deformed and flexible. Therefore, the small-diameter inorganic fibers preferably have an average fiber diameter of less than 1 μm, more preferably 0.1 μm or less. However, if the small-diameter inorganic fibers are too thin, they are prone to breakage, reducing their inorganic particle retention ability. Furthermore, the proportion of fibers remaining entangled without retaining inorganic particles increases in the insulating material, which not only reduces the inorganic particle retention ability but also leads to poor moldability and shape retention. Therefore, the average fiber diameter of the small-diameter inorganic fibers is preferably 1 nm or more, more preferably 10 nm or more. In addition, if the fine inorganic fibers are too long, moldability and shape retention will decrease, so the fiber length is preferably 0.1 mm or less.

[0085] The fine inorganic fibers are preferably dendritic or crimped. When the fine inorganic fibers have such a shape, they become entangled with the thick inorganic fibers and inorganic particles in the insulating material. This improves the inorganic particle retention capacity. Furthermore, when the insulating material is subjected to pressure or wind pressure, the fine inorganic fibers are prevented from sliding and moving, thereby improving the mechanical strength, particularly against external pressure and impact.

[0086] The term "dendritic" refers to a two-dimensionally or three-dimensionally branched structure, such as feather-like, tetrapod-like, radial, or three-dimensional mesh-like. When the fine inorganic fibers are dendritic, the average fiber diameter can be obtained by measuring the diameters of the trunk and branches at several points using an SEM and calculating the average value.

[0087] The crimped structure refers to a structure in which fibers are bent in various directions. One method for quantifying the crimped structure is to calculate the crimp degree from an electron microscope photograph, which can be calculated, for example, using the following formula: Crimp degree (%) = (fiber length - distance between fiber ends) / (fiber length) × 100 Here, both the fiber length and the distance between fiber ends are measured values ​​on an electron microscope photograph. In other words, they are the fiber length and the distance between fiber ends projected onto a two-dimensional plane, and are shorter than the actual values. Based on this formula, the crimp degree of the small-diameter inorganic fibers is preferably 10% or more, and more preferably 30% or more. If the crimp degree is low, it becomes difficult to retain inorganic particles and to form entanglements (networks) between large-diameter inorganic fibers and between large-diameter inorganic fibers.

[0088] As described above, it is preferable that the average fiber diameter of either the first inorganic fibers or the second inorganic fibers is larger than the average fiber diameter of the other. In the present invention, however, it is more preferable that the average fiber diameter of the first inorganic fibers is larger than the average fiber diameter of the second inorganic fibers. When the average fiber diameter of the first inorganic fibers is large, the first inorganic fibers have a low glass transition point and soften quickly, so that they become film-like and harden as the temperature rises. On the other hand, when the average fiber diameter of the second inorganic fibers is small, the small-diameter second inorganic fibers remain in their fibrous form even when the temperature rises, so that the structure of the thermal insulating material can be maintained and powder shedding can be prevented.

[0089] It is most preferable to use both thick, linear or needle-like inorganic fibers and thin, dendritic or crimped inorganic fibers as the first inorganic fibers, and to use both thick, linear or needle-like inorganic fibers and thin, dendritic or crimped inorganic fibers as the second inorganic fibers, since this can further enhance the inorganic particle retention effect, mechanical strength, and shape retention.

[0090] (Contents of inorganic particles, first inorganic fibers, and second inorganic fibers) The content of the above inorganic particles is preferably 30% by mass or more and 94% by mass or less relative to the total mass of the insulating material, the content of the first inorganic fibers is preferably 3% by mass or more and 30% by mass or less relative to the total mass of the insulating material, and the content of the second inorganic fibers is preferably 3% by mass or more and 30% by mass or less relative to the total mass of the insulating material.

[0091] More preferably, the content of inorganic particles is 60% by mass or more and 90% by mass or less, the content of first inorganic fibers is 5% by mass or more and 15% by mass or less, and the content of second inorganic fibers is 5% by mass or more and 15% by mass or less, based on the total mass of the thermal insulating material. By setting the contents in this range, a good balance is achieved between the heat absorption and heat insulation effects of the inorganic particles, the shape retention, compression force resistance, and wind pressure resistance of the first inorganic fibers, and the inorganic particle retention ability of the second inorganic fibers.

[0092] <1-1-4. Other ingredients> The heat insulating material may contain organic fibers, organic binders, etc. as needed. These are all useful for reinforcing the heat insulating material and improving its formability, and the total amount of these is preferably 10 mass % or less based on the total mass of the heat insulating material.

[0093] <1-2. Heat transfer layer> The heat transfer layer used in the heat transfer-suppressing sheet according to this embodiment has the effect of diffusing heat that reaches the heat transfer layer by conductive heat transfer. Therefore, the heat transfer layer has a higher thermal conductivity than the insulating material in both the thickness direction and the surface direction. When the thermal conductivity of the heat transfer layer in the thickness direction is λt (W / mK) and the thermal conductivity of the heat transfer layer in the surface direction is λs (W / mK), the specific values ​​of these are as follows: λt (thermal conductivity in the thickness direction) is preferably 5 (W / m·K) or less, and more preferably 2 (W / m·K) or less. Furthermore, λs (thermal conductivity in the surface direction) is preferably 10 (W / m·K) or more, and more preferably 30 (W / m·K) or more.

[0094] Furthermore, if the thermal conductivity of the heat transfer layer in the thickness direction is higher than the thermal conductivity in the plane direction, the heat that reaches the heat transfer layer cannot be diffused and is likely to be transferred to the adjacent heat insulating material. Therefore, in this embodiment, the thermal conductivity of the heat transfer layer in the plane direction (λs) is higher than the thermal conductivity of the heat transfer layer in the thickness direction (λt) (λs > λt), and it is preferable that λs / λt is 2 or more.

[0095] The thermal conductivity of the heat transfer layer can be calculated by a cyclic heating method. Specifically, for example, the thermal diffusivity of the heat transfer layer in the thickness direction and in the surface direction can be measured using an apparatus for measuring thermal diffusivity using a cyclic heating method (Thermowave Analyzer TA, manufactured by Bethel Co., Ltd.).

[0096] In addition, in this embodiment, the heat transfer layer has insulating properties, which can suppress the occurrence of sparks between battery cells. Specifically, the electrical resistivity of the heat transfer layer is 1×10 8 It is preferable that it is Ω·m or more.

[0097] Furthermore, to obtain a sufficient heat diffusion effect from the heat-transfer layer, the thickness of the heat-transfer layer is preferably 2.5% or more, more preferably 5% or more, and even more preferably 15% or more of the total thickness of the heat-transfer-suppressing sheet. On the other hand, taking into consideration the total thickness of the heat-transfer-suppressing sheet, the thickness of the heat-transfer layer is preferably 50% or less, more preferably 35% or less of the total thickness of the heat-transfer-suppressing sheet.

[0098] Furthermore, the heat transfer layer may consist of a single layer or may be a laminate of multiple thin films made of the same or different materials. When the heat transfer layer is formed by laminating multiple thin films, the filler can be more easily oriented in the planar direction of the heat transfer layer, thereby improving the heat diffusion effect.

[0099] <1-2-1. Filler> The heat transfer layer preferably contains a filler made of at least one ceramic selected from plate-like ceramics, scaly ceramics, and fibrous ceramics. As described above, when the filler contained in the heat transfer layer is oriented in the plane direction of the heat transfer layer, the thermal conductivity in the plane direction can be made higher than the thermal conductivity in the thickness direction.

[0100] In this embodiment, it is not necessary for all fillers to be perfectly oriented in the planar direction, but it is sufficient that the orientation of the fillers in the heat transfer layer is controlled so that high thermal conductivity is obtained in the planar direction of the heat transfer layer. The anisotropy of the thermal conductivity of the heat transfer layer is preferably confirmed by measurement using the cyclic heating method.

[0101] Here, regarding the measurement of the orientation of the material constituting the filler, taking boron nitride (h-BN) in the atmospheric pressure phase as an example, the degree of orientation of h-BN particles contained in the heat transfer layer can be confirmed by X-ray diffraction (XRD). Specifically, for hexagonal boron nitride, the degree of orientation can be evaluated by measuring the diffraction intensity of the (002) and (100) planes using the following formula:

[0102] Orientation degree=I(002) / I(100)

[0103] In the above formula, I(002) represents the diffraction intensity on the (002) plane, and I(100) represents the diffraction intensity on the (100) plane. If the degree of orientation calculated by the above formula is 6.7 or more, it can be determined that the film is oriented in the plane direction, and the higher the degree of orientation, the higher the degree of orientation in the plane direction.

[0104] In order to obtain an insulating heat transfer layer, the filler preferably has insulating properties. Specifically, the filler has an electrical resistivity of 1×10 8 A resistance of Ω·m or more is preferable because it can sufficiently prevent sparks from occurring between battery cells. When the heat transfer layer contains fillers made of a plurality of materials, it is preferable that the electrical resistivities of all the fillers satisfy the above range.

[0105] The ceramics constituting the filler preferably include at least one selected from boron nitride (BN), aluminum nitride (AlN), alumina (Al2O3), silica (SiO2), silicon nitride (Si3N4), zinc oxide (ZnO), magnesia (MgO), silicon carbide (SiC), beryllium oxide (BeO), and diamond. Among these ceramics, boron nitride has anisotropic thermal conductivity in the material itself, and is available in flake or plate-like and fibrous forms. For example, in flake (plate-like) boron nitride, the thermal conductivity in the planar direction perpendicular to the thickness direction is significantly higher than the thermal conductivity in the thickness direction. Furthermore, in fibrous boron nitride, the thermal conductivity in the longitudinal direction is significantly higher than the thermal conductivity in the radial direction. For this reason, it is most preferable to use boron nitride as the ceramic.

[0106] The planar direction of scaly (plate-like) boron nitride refers to the plane parallel to its widest plane, and the thickness direction refers to the direction perpendicular to the planar direction. The longitudinal direction of fibrous boron nitride refers to the direction in which the fibers extend, and the radial direction refers to the direction perpendicular to the longitudinal direction.

[0107] Furthermore, it is more preferable to use flaky silica as the ceramics constituting the filler, since this not only provides anisotropy in thermal conductivity due to the shape, but also acts as a matrix to bind the filler together.

[0108] In this embodiment, the filler content is preferably 60% by volume or more relative to the total volume of the heat transfer layer, and the higher the filler content, the more the thermal conductivity can be improved. Therefore, if flaky silica is used as one of the ceramics constituting the filler, the filler content relative to the total volume of the heat transfer layer can be 100% by volume, and the thermal conductivity can be further improved.

[0109] <1-2-2. Matrix> The heat transfer layer preferably further contains a matrix for binding the filler and maintaining the shape of the heat transfer layer, and the matrix preferably contains at least one material selected from ceramics, resins, and other materials.

[0110] When the matrix contains ceramics, examples of the ceramics include aluminum phosphate, sodium silicate, silica sol, alumina sol, etc. When the matrix contains resin, examples of the resin include silicone resin, epoxy resin, acrylic resin, fluorine-based resin, etc. Another material that is preferably contained in the matrix is ​​cellulose nanofiber.

[0111] Like the filler, the matrix preferably has insulating properties, specifically, an electrical resistivity of 1×10 8 A resistance of Ω·m or more is preferable because it can sufficiently prevent sparks from occurring between battery cells.

[0112] (Thickness of heat transfer suppression sheet) In this embodiment, the thickness of the heat-transfer-suppressing sheet is not particularly limited, but is preferably in the range of 0.05 to 6 mm. A thickness of 0.05 mm or more provides the heat-transfer-suppressing sheet with sufficient mechanical strength. On the other hand, a thickness of 6 mm or less provides good assembly properties.

[0113] [2. Method for manufacturing heat transfer suppression sheet] 4A to 4C are cross-sectional views showing the steps of a method for manufacturing a heat-transfer-suppressing sheet according to an embodiment of the present invention. The method for manufacturing a heat-transfer-suppressing sheet according to this embodiment will be described below with reference to FIG.

[0114] (Coating process) 4(a), a pair of the above-mentioned heat insulating materials is first prepared, and the heat-conductive layer material 14 is applied to one surface of one of the heat insulating materials 13b, perpendicular to the thickness direction, to a thickness of, for example, 0.5 mm. The heat-conductive layer material 14 can be prepared, for example, by mixing the above-mentioned filler with a diluent or the like. In addition to the filler, the heat transfer layer material 14 may contain a matrix, and may also contain other agents such as a coupling agent, a dispersant, a flocculating agent, and a diluent.

[0115] (Lamination process) Next, as shown in FIG. 4(b), the other heat insulating material 13a is laminated on the surface of the heat insulating material 13b on which the heat transfer layer material 14 has been applied.

[0116] (Pressure process) 4(c), the heat insulating materials 13a and 13b are pressed toward each other (in the direction indicated by the arrows in the figure), compressing the heat transfer layer material 14 in its thickness direction. Heating is also performed simultaneously with the pressing, evaporating and drying the diluent and other materials contained in the heat transfer layer material 14. Note that heating is not necessarily required as long as the diluent and other materials contained in the heat transfer layer material 14 can be dried. This allows the production of a heat transfer-suppressing sheet 10 in which a heat transfer layer 12 with a thickness of approximately 0.2 mm is formed between the heat insulating materials 13a and 13b.

[0117] According to the manufacturing method of this embodiment, the heat-transfer layer material 14 is applied to the surface of the heat insulating material 13b. Therefore, when the heat-transfer layer material 14 contains a filler made of plate-like ceramics, scaly ceramics, fibrous ceramics, or the like, the filler can be oriented in the plane direction to some extent. The heat-transfer layer material 14 is then compressed in its thickness direction, further enhancing the filler orientation. Therefore, it is possible to easily manufacture a heat-transfer-suppressing sheet 10 whose thermal conductivity in the plane direction is higher than that in the thickness direction.

[0118] Furthermore, by thinly laminating the heat transfer layer material 14 on the surface of the heat insulating material 13b, the orientation of the filler in the surface direction can be further increased, and by repeating thin lamination multiple times, even higher orientation can be obtained.

[0119] In addition, in the manufacturing method shown in Figures 4(a) to 4(c) above, after the application process of applying the heat transfer layer material 14 onto one side of one of the insulating materials 13b, a lamination process of laminating the other insulating material 13a is carried out, and then a pressurization process of applying pressure to the heat transfer layer material 14 in the thickness direction is carried out, but in the present invention, the lamination process may be carried out after the pressurization process. In other words, the heat transfer inhibiting sheet of this embodiment can be manufactured by carrying out a coating process in which the heat transfer layer material 14 is applied to one side of one of the insulating materials 13b, followed by a pressurizing process in which pressure is applied to the heat transfer layer material 14 in the thickness direction, and then a lamination process in which the other insulating material 13a is laminated.

[0120] [3. Battery pack] 3, the battery pack 100 according to this embodiment includes a battery case 30, a plurality of battery cells 20a, 20b, and 20c housed inside the battery case 30 and connected in series or parallel, a heat-transfer-suppressing sheet 10 described above in [1. Heat-transfer-suppressing sheet] interposed between the plurality of battery cells 20a, 20b, and 20c, and a heat-transfer member 21 provided between the plurality of battery cells 20a, 20b, and 20c and the battery case 30. At least a portion of the heat-transfer layer 12 of the heat-transfer-suppressing sheet 10 is in contact with the heat-transfer member 21.

[0121] In the battery pack according to this embodiment, the heat-transfer-suppressing sheet 10 described in [1. Heat-transfer-suppressing sheet] above is interposed between the battery cells 20a, 20b, and 20c, preventing sparks from occurring between the battery cells 20a, 20b, and 20c. Furthermore, when heat is generated from one battery cell, the heat transfer is reduced by the insulating materials 13a and 13b, and the heat is diffused and released in the planar direction by the heat-transfer layer 12. Furthermore, in this embodiment, the heat-transfer layer 12 is in contact with the heat-transfer member 21, so the heat is transferred to the heat-transfer member 21, further promoting heat diffusion. Therefore, heat transfer between the battery cells can be suppressed, preventing a chain reaction of thermal runaway.

[0122] In the present invention, the heat transfer member 21 is not necessarily required, and the battery cells 20 a, 20 b, 20 c and the heat transfer-suppressing sheet 10 may be placed directly on the inner bottom surface of the battery case 30. Even in such a case, because heat-transfer-suppressing sheet 10 has heat-transfer layer 12, the heat that reaches heat-transfer layer 12 is diffused in the planar direction and released from the end faces. This provides an excellent effect of suppressing heat transfer between battery cells, minimizing adverse effects on other battery cells.

[0123] Furthermore, the heat transfer-suppressing sheet according to this embodiment can be easily bent depending on the type and thickness of the heat insulating material and heat transfer layer. Therefore, it can be adapted to any shape, regardless of the shape 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.

[0124] Furthermore, although not shown in the drawings, the heat-transfer-suppressing sheet described in [1. Heat-transfer-suppressing sheet] above can be disposed not only between multiple battery cells, but also between a battery cell and a battery case, etc. This provides high versatility and is effective in preventing a chain reaction of thermal runaway caused by heat transfer between adjacent battery cells. It also prevents the flames from spreading outside the battery case if a battery cell catches fire.

[0125] For example, the battery pack 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 were to catch fire, the safety of the passengers can be ensured. In this case, the heat transfer suppression sheet or the like that is interposed between each battery cell can also be placed between the battery cell and the battery case, so there is no need to create new flame retardant materials or the like, and a safe battery pack can be easily constructed at low cost. [Example]

[0126] Hereinafter, an example of a method for manufacturing a heat transfer-suppressing sheet will be described in comparison with a comparative example in terms of the orientation of the heat transfer layer. Note that, since this example is intended to compare the orientation of the heat transfer layer according to the manufacturing method, aluminum foil is used instead of the heat insulating material 13b shown in FIG. 4(a).

[0127] [Manufacturing of heat transfer suppression sheets] (Preparation of test material in Example 1) First, a heat transfer layer material was applied to one side of an aluminum foil to a thickness of 0.5 mm, and a heat insulating material was laminated on the side on which the heat transfer layer material was applied. The aluminum foil and the heat insulating material were then pressed in the direction of the arrow at a surface pressure of 0.6 kPa to compress the heat transfer layer material in the thickness direction, and then dried. This resulted in the test material of Example 1, which had a heat transfer layer with a thickness of 0.28 mm. As described above, in this example, the heat transfer layer material was applied to the aluminum foil, but since a passage for water vapor or the like is required when drying under pressure, a heat insulating material was laminated on the side on which the heat transfer layer material was applied.

[0128] (Preparation of test material for Comparative Example 1) The heat transfer layer material was dropped onto one side of an aluminum foil and dried to obtain a test material of Comparative Example 1 having a heat transfer layer with a thickness of 3 mm.

[0129] (Preparation of test material of Comparative Example 2) The heat transfer layer material was applied to one side of an aluminum foil in a thickness of 0.5 mm and dried to obtain a test material of Comparative Example 2 having a heat transfer layer of 0.31 mm in thickness. Note that no pressure was applied in either Comparative Example 1 or Comparative Example 2.

[0130] The heat insulating material used in Example 1 was a heat insulating material containing nanosilica, titania, and glass fiber. The heat transfer layer material used was one in which, when the heat transfer layer was formed, the BN content was 80 vol % and the SiO content was 20 vol % relative to the total volume of the heat transfer layer.

[0131] [Measurement of heat transfer layer orientation] The diffraction intensity of the heat transfer layer of each test material was measured from the surface of the heat transfer layer using an X-ray diffractometer. The measurement conditions using the X-ray diffractometer are shown below.

[0132] X-ray diffraction equipment: Rigaku SmartLab Tube current: 30mA Tube voltage: 40kV Scan speed: 10° / min Scan range: 20°~50° Measurement scan step: 0.01°

[0133] The diffraction intensities (I(002) and I(100)) of the (002) and (100) planes of the h-BN contained in the heat transfer layer were measured, and the degree of orientation of the heat transfer layer was calculated using the following formula.

[0134] Orientation degree=I(002) / I(100)

[0135] [Evaluation results of the orientation of the heat transfer layer] Figure 5 shows the orientation of the heat transfer layer for the test materials of the examples and comparative examples. In Figure 5, the SEM images are electron images of cross sections parallel to the thickness direction of each test material taken with a scanning electron microscope (SEM). Figure 5 also shows the degree of orientation of each heat transfer layer. As mentioned above, the anisotropy of the thermal conductivity in the heat transfer layer varies depending on various conditions, and therefore the actual anisotropy of the thermal conductivity in Example 1, Comparative Example 1, and Comparative Example 2 differs from the degree of orientation shown in Fig. 5. However, since the same heat transfer layer material is used in this example, the thermal conductivity of the heat transfer layer in each Example and Comparative Example can be compared by comparing the diffraction intensities of the (002) and (100) planes in the h-BN contained in the heat transfer layer.

[0136] As shown in Figure 5, Example 1 had a significantly higher degree of orientation because the heat transfer layer material was applied to one side of the heat insulating material and then pressed. This indicates that the filler was oriented in the planar direction, and the heat that reached the heat transfer layer could be sufficiently diffused in the planar direction.

[0137] On the other hand, in Comparative Example 1, the heat transfer layer was formed by dropping the heat transfer layer material onto one side of the heat insulating material and drying it, so the degree of orientation was lower than in Example 1. In addition, in Comparative Example 2, the heat transfer layer material was only applied to one side of the heat insulating material without being pressed, so the degree of orientation was lower than in Example 1. From these facts, it can be seen that in Comparative Examples 1 and 2, the filler is oriented in the plane direction to a certain extent, so that heat that reaches the heat transfer layer can be diffused in the plane direction, but the diffusion effect is lower than in Example 1. [Explanation of symbols]

[0138] 10 Heat transfer suppression sheet 12 Heat Transfer Layer 13a, 13b Insulation material 14 Heat Transfer Layer Materials 15 Filler 16. Matrix 20a, 20b, 20c battery cells 21 Heat transfer member 30 Battery case 100 battery packs

Claims

1. A heat transfer suppression sheet used in a battery pack in which a plurality of battery cells are connected in series or in parallel, A pair of insulating materials; an insulating heat transfer layer disposed between the pair of heat insulating materials; The thermal conductivity of the heat transfer layer in a thickness direction and a surface direction perpendicular to the thickness direction are both higher than the thermal conductivity of the heat insulating material, The thermal conductivity of the heat transfer layer in the plane direction is higher than the thermal conductivity in the thickness direction, The heat transfer suppressing sheet is characterized in that the heat insulating material and the heat transfer layer are partially bonded to each other, with non-bonded portions existing between them.

2. 2. The heat transfer-suppressing sheet according to claim 1, wherein the heat transfer layer contains a filler made of at least one ceramic material selected from the group consisting of plate-like ceramics, scaly ceramics, and fibrous ceramics.

3. The heat transfer-suppressing sheet according to claim 2 , wherein the filler is oriented in a plane direction of the heat transfer layer.

4. The electrical resistivity of the filler is 1×10 ８ The heat transfer-suppressing sheet according to claim 2 or 3, wherein the resistance is Ω·m or more.

5. The heat transfer-suppressing sheet according to any one of claims 2 to 4, wherein the ceramic constituting the filler includes at least one selected from the group consisting of boron nitride, aluminum nitride, alumina, silica, silicon nitride, zinc oxide, magnesia, silicon carbide, beryllium oxide, and diamond.

6. the heat transfer layer further contains a matrix that binds the filler, 6. The heat-transfer-suppressing sheet according to claim 2, wherein the matrix contains at least one material selected from the group consisting of ceramics and resins.

7. the heat transfer layer further contains a matrix that binds the filler, The heat transfer-suppressing sheet according to any one of claims 2 to 5, wherein the matrix contains at least one selected from aluminum phosphate, sodium silicate, silica sol, alumina sol, silicone resin, epoxy resin, acrylic resin, fluorine-based resin, and cellulose nanofiber.

8. The electrical resistivity of the matrix is ​​1×10 ８ The heat transfer-suppressing sheet according to claim 6 or 7, having a resistivity of Ω·m or more.

9. 9. The heat transfer-suppressing sheet according to claim 1, wherein λs / λt is 2 or more, where λs (W / mK) is the thermal conductivity of the heat transfer layer in the plane direction and λt (W / mK) is the thermal conductivity of the heat transfer layer in the thickness direction.

10. 10. The heat transfer-suppressing sheet according to claim 1, wherein the heat insulating material has a thermal conductivity of less than 1 (W / m·K).

11. The heat-transfer-suppressing sheet according to any one of claims 1 to 10, wherein the heat-insulating material contains at least one selected from inorganic fibers, organic fibers, inorganic particles, and organic particles.

12. the thermal insulating material includes inorganic particles, first inorganic fibers, and second inorganic fibers; the first inorganic fibers are amorphous fibers, The heat transfer-suppressing sheet according to claim 11, wherein the second inorganic fibers are at least one type selected from the group consisting of amorphous fibers and crystalline fibers having a glass transition point higher than that of the first inorganic fibers.

13. The heat insulating material may be selected from the group consisting of silica nanoparticles, titania, alumina fiber, carbon fiber, mica, basalt fiber, soluble fiber, refractory ceramic fiber, glass fiber, aerogel composite, microporous particles, hollow silica particles, thermally expandable inorganic material, aerogel, silica, zirconia, zircon, barium titanate, zinc oxide, alumina, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, zinc hydroxide, iron hydroxide, manganese hydroxide, zirconium hydroxide, gallium hydroxide, SiO ２ 13. The heat transfer-suppressing sheet according to claim 11 or 12, comprising at least one fiber selected from the group consisting of fibers containing hydroxybenzoates, silica fibers, alumina fibers, ceramic fibers, rock wool, alkaline earth silicate fibers, zirconia fibers, and mineral fibers.

14. The heat transfer-suppressing sheet according to any one of claims 1 to 13, wherein the heat transfer-suppressing sheet is interposed between the plurality of battery cells.

15. Used in a battery pack in which multiple battery cells are connected in series or parallel, A pair of insulating materials; an insulating heat transfer layer disposed between the pair of heat insulating materials; The thermal conductivity of the heat transfer layer in a thickness direction and a surface direction perpendicular to the thickness direction are both higher than the thermal conductivity of the heat insulating material, A method for producing a heat transfer-suppressing sheet, wherein the thermal conductivity of the heat transfer layer in the planar direction is higher than the thermal conductivity in the thickness direction, a coating step of coating a heat transfer layer material on one surface of one of the pair of heat insulating materials, the surface being perpendicular to the thickness direction; a pressurizing step of pressing the applied heat transfer layer material in a thickness direction; a lamination step of laminating another heat insulating material on the surface on which the heat transfer layer material has been applied, between the application step and the pressurizing step or after the pressurizing step.

16. A battery case and a plurality of battery cells housed inside the battery case and connected in series or in parallel; A battery pack comprising: the heat transfer-suppressing sheet according to any one of claims 1 to 14, interposed between the plurality of battery cells.

17. A battery case and a plurality of battery cells housed inside the battery case and connected in series or in parallel; the heat transfer-suppressing sheet according to any one of claims 1 to 14, which is interposed between the plurality of battery cells; a heat transfer member provided between the plurality of battery cells and the battery case; and The battery pack according to claim 1, wherein at least a portion of the heat transfer layer of the heat transfer-suppressing sheet is in contact with the heat transfer member.

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