Heat transfer suppression sheet and battery pack

Abstract

The present invention provides a heat transfer suppression sheet having excellent heat transfer suppression effects, excellent retention of inorganic particles, and excellent shape retention at high temperatures, and a battery pack in which the heat transfer suppression sheet is interposed between battery cells. The heat transfer suppression sheet (10) includes inorganic particles (20), a first inorganic fiber (30), and a second inorganic fiber (31). The average fiber diameter of the first inorganic fiber (30) is thicker than the average fiber diameter of the second inorganic fiber (31). Further, the first inorganic fiber (30) is linear or needle-shaped, and the second inorganic fiber (31) is dendritic or curled.

Description

Technical Field

[0001] The present invention relates to a heat transfer suppression sheet and a battery pack in which the heat transfer suppression sheet is sandwiched between battery cells. Background Art

[0002] In recent years, from the aspect of environmental protection, the development of electric vehicles or hybrid vehicles driven by an electric motor has been actively carried out. In such an electric vehicle or hybrid vehicle, a battery pack in which two or more battery cells serving as a power source for a driving electric motor are connected in series or in parallel is mounted.

[0003] In addition, a lithium ion secondary battery that can achieve high capacity and high output is mainly used in the battery cell. Further, in the case of thermal runaway in which a certain battery cell rapidly heats up due to internal short circuit or overcharge of the battery and then continues to release heat, the heat from the battery cell that has experienced thermal runaway is transferred to other adjacent battery cells, which may cause thermal runaway of other battery cells.

[0004] As a technique for suppressing heat transfer from a battery cell that has experienced thermal runaway as described above, an operation of sandwiching a heat transfer suppression sheet between battery cells has been performed. For example, Patent Document 1 proposes a heat transfer suppression sheet that contains at least one of a mineral-based powder and a flame retardant, and a matrix resin selected from a thermosetting resin, a thermoplastic elastomer, and rubber.

[0005] Prior Art Documents

[0006] Patent Documents

[0007] Patent Document 1: Japanese Patent Application Laid-Open No. 2018-206605 Summary of the Invention

[0008] Problems to be Solved by the Invention

[0009] In such a heat transfer suppression sheet, it is required to satisfactorily hold the powder having a heat transfer suppression effect (i.e., suppress powder detachment), and to maintain its shape and continue to exist between battery cells even when a battery cell experiences thermal runaway and becomes high temperature. In the heat transfer suppression sheet described in Patent Document 1, a matrix resin is used to hold the mineral-based powder and / or the flame retardant, but such a matrix resin melts at high temperature. Therefore, there is a risk that the shape cannot be maintained when a battery cell experiences thermal runaway in the heat transfer suppression sheet described in Patent Document 1.

[0010] Therefore, an object of the present invention is to provide a heat transfer suppression sheet capable of suppressing the detachment of powder or the like having a heat transfer suppression effect and having excellent shape retention at high temperatures, and a battery pack in which the heat transfer suppression sheet is interposed between battery cells.

[0011] Means for Solving the Problem

[0012] The above object is achieved by the heat transfer suppression sheet of the following (1) of the present invention.

[0013] (1) A heat transfer suppression sheet comprising inorganic particles, a first inorganic fiber, and a second inorganic fiber,

[0014] The average fiber diameter of the above first inorganic fiber is larger than the average fiber diameter of the above second inorganic fiber, and

[0015] The above first inorganic fiber is linear or needle-like, and the above second inorganic fiber is dendritic or curly (contracted).

[0016] In addition, the heat transfer suppression sheet of the present invention is preferably the following (2) to (15).

[0017] (2) The heat transfer suppression sheet according to (1), wherein the average fiber diameter of the above first inorganic fiber is 1 μm or more and 20 μm or less,

[0018] The average fiber diameter of the above second inorganic fiber is 1 nm or more and less than 1 μm.

[0019] (3) The heat transfer suppression sheet according to (1) or (2), wherein

[0020] The above first inorganic fiber and the above second inorganic fiber are the same kind of fiber or different kinds of fibers from each other,

[0021] The above first inorganic fiber and the above second inorganic fiber each contain at least one selected from silica fiber, alumina fiber, aluminosilicate fiber, zirconia fiber, glass fiber, and mineral fiber.

[0022] (4) The heat transfer suppression sheet according to any one of (1) to (3), wherein

[0023] The above first inorganic fiber is a glass fiber,

[0024] The above second inorganic fiber is a mineral fiber.

[0025] (5) The heat transfer suppression sheet according to any one of (1) to (4), wherein the average secondary particle diameter of the above inorganic particles is 0.01 μm or more and 200 μm or less.

[0026] (6) The heat transfer inhibition sheet according to any one of (1) to (5), wherein the inorganic particles include at least one selected from oxide particles, carbide particles, nitride particles, and inorganic hydrate particles.

[0027] (7) The heat transfer inhibition sheet according to (6), wherein the inorganic particles include oxide particles.

[0028] (8) The heat transfer inhibition sheet according to (6) or (7), wherein the average primary particle size of the oxide particles is 0.001 μm or more and 50 μm or less.

[0029] (9) The heat transfer inhibition sheet according to any one of (6) to (8), wherein the oxide particles include at least one selected from silica, titanium dioxide, zirconia, zircon, barium titanate, zinc oxide, and alumina.

[0030] (10) The heat transfer inhibition sheet according to any one of (6) to (9), wherein the inorganic particles include at least one selected from nanoparticles, hollow particles, and porous particles.

[0031] (11) The heat transfer inhibition sheet according to (9), wherein the inorganic particles include nanoparticles.

[0032] (12) The heat transfer inhibition sheet according to any one of (1) to (11), wherein the inorganic particles include silica nanoparticles.

[0033] (13) The heat transfer inhibition sheet according to any one of (1) to (12), wherein the inorganic particles include titanium dioxide.

[0034] (14) The heat transfer inhibition sheet according to any one of (10) to (13), wherein the average primary particle size of the nanoparticles is 1 nm or more and 100 nm or less.

[0035] (15) The heat transfer inhibition sheet according to any one of (1) to (14), wherein

[0036] relative to the total mass of the heat transfer inhibition sheet,

[0037] the content of the inorganic particles is 30% by mass or more and 94% by mass or less, the content of the first inorganic fiber is 3% by mass or more and 30% by mass or less, and the content of the second inorganic fiber is 3% by mass or more and 30% by mass or less.

[0038] In addition, the above object of the present invention is achieved by the following constitution (16) of the battery pack.

[0039] (16) A battery pack formed by connecting two or more battery cells in series or in parallel, wherein

[0040] The heat transfer suppression sheet according to any one of (1) to (15) is interposed between the battery cells.

[0041] Effects of the Invention

[0042] The heat transfer suppression sheet of the present invention contains inorganic particles and inorganic fibers with excellent heat transfer suppression effects, and thus has an excellent heat transfer suppression effect.

[0043] In addition, in the heat transfer suppression sheet of the present invention, since the second inorganic fibers with a fine diameter and in a dendritic or curly shape are wound around the inorganic particles and the first inorganic fibers with a thick diameter, the inorganic particles can be well retained.

[0044] Furthermore, unlike the matrix resin, the first inorganic fiber and the second inorganic fiber do not melt at the temperature during thermal runaway of the battery cell. Therefore, the heat transfer suppression sheet of the present invention maintains its shape and continues to exist between the battery cells even during thermal runaway of the battery cell.

[0045] In addition, the heat transfer suppression sheet may be subjected to extrusion pressure due to the expansion accompanying the thermal runaway of the battery cell, or may be subjected to wind pressure accompanying the fire of the battery cell. However, in the heat transfer suppression sheet of the present invention, the thick first inorganic fiber wound around the second inorganic fiber can resist these external forces.

[0046] In the battery pack of the present invention, the heat transfer suppression sheet is interposed between the battery cells. Therefore, the battery pack of the present invention can minimize the damage caused by thermal runaway of the battery cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 It is a cross-sectional view schematically showing an embodiment of the heat transfer suppression sheet of the present invention.

[0048] Figure 2 It is an SEM photograph showing the cross-section of the heat transfer suppression sheet in the embodiment of the present invention manufactured by the dry extrusion molding method.

[0049] Figure 3 It is a cross-sectional view schematically showing an embodiment of the battery pack of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0050] Hereinafter, embodiments of the heat transfer suppression sheet and the battery pack of the present invention will be described in detail with reference to the accompanying drawings. It should be noted that the present invention is not limited to the embodiments described below. In addition, in the following drawings, components or parts that perform the same function may sometimes be denoted by the same reference numerals, and redundant descriptions may sometimes be omitted or simplified. In addition, in the embodiments described in the drawings, for the purpose of clearly illustrating the present invention, they are schematized and do not necessarily represent actual dimensions or scales.

[0051] [1. Heat transfer suppression sheet]

[0052] Figure 1 FIG. is a cross-sectional view schematically showing an embodiment of the heat transfer suppression sheet of the present invention. The heat transfer suppression sheet 10 shown in the figure includes inorganic particles 20, thick first inorganic fibers 30, and thin second inorganic fibers 31. The inorganic particles 20, the first inorganic fibers 30, and the second inorganic fibers 31 are all heat-resistant materials, and furthermore, numerous minute spaces are formed between the particles, between the particles and the fibers, and between the fibers, and the heat insulation effect based on air is also exerted, so the heat transfer suppression performance is excellent.

[0053] Next, the inorganic particles 20, the first inorganic fibers 30, the second inorganic fibers 31, and other mixed materials constituting the heat transfer suppression sheet 10, and the thickness of the heat transfer suppression sheet 10 will be described in turn.

[0054] <1-1. Inorganic particles>

[0055] The material of the inorganic particles 20 is not particularly limited. From the aspect of the heat transfer suppression effect, the inorganic particles 20 preferably contain at least one selected from oxide particles, carbide particles, nitride particles, and inorganic hydrate particles, and more preferably contain oxide particles.

[0056] In addition, the shape and size of the inorganic particles 20 are not particularly limited, and preferably contain at least one selected from nanoparticle, hollow particles, and porous particles, and more preferably contain nanoparticle.

[0057] It should be noted that as the inorganic particles 20, a single inorganic particle can be used, or two or more kinds of inorganic particles 20 can be used in combination. If two or more kinds of inorganic particles 20 having different heat transfer suppression effects are used together, the heat generating body can be cooled in multiple stages, and the heat absorption effect can be exhibited in a wider temperature range.

[0058] In addition, the inorganic particles 20 also preferably use a mixture of large-diameter particles and small-diameter particles. If the small-diameter inorganic particles 20 are squeezed into the gaps between the large-diameter inorganic particles 20, a denser structure can be formed, and the heat transfer suppression effect can be improved.

[0059] If the average secondary particle diameter of the inorganic particles 20 is 0.01 μm or more, they are easily obtained, and an increase in the manufacturing cost can be suppressed. In addition, if it is 200 μm or less, the desired heat insulation effect can be obtained. Therefore, the average secondary particle diameter of the inorganic particles 20 is preferably 0.01 μm or more and 200 μm or less, more preferably 0.05 μm or more and 100 μm or less.

[0060] Next, an example of the material or shape of the particles that can be used as the inorganic particles 20 will be described in detail.

[0061] (1-1-1. Oxide particles)

[0062] Oxide particles have a high refractive index and a strong effect of diffusing light. Therefore, when oxide particles are used as inorganic particles, radiation heat transfer can be particularly suppressed in high-temperature regions such as abnormal heat release. As the oxide particles, at least one selected from silica, titanium dioxide, zirconium oxide, zircon, barium titanate, zinc oxide, and aluminum oxide can be used. That is, only 1 type of the above-mentioned oxide particles that can be used as inorganic particles can be used, or 2 or more types of oxide particles can be used. In particular, silica is a component with high heat insulation, and titanium dioxide is a component with a refractive index higher than other metal oxides, and has a high effect of diffusing light and blocking radiant heat in a high-temperature region of 500 °C or more. Therefore, it is most preferable to use at least one of silica and titanium dioxide as the oxide particles.

[0063] (Average primary particle diameter of oxide particles: 0.001 μm or more and 50 μm or less)

[0064] Since the particle diameter of the oxide particles sometimes affects the effect of reflecting radiant heat, when the average primary particle diameter is limited to a specified range, higher heat insulation can be further obtained.

[0065] That is, 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 the light that acts during heating, and light is efficiently diffused, so that radiation heat transfer of heat in the heat transfer suppression sheet can be suppressed in a high-temperature region of 500 °C or more, and the heat insulation can be further improved.

[0066] On the other hand, when the average primary particle diameter of the oxide particles is 50 μm or less, even if compressed, the contacts or the number between the particles do not increase, and it is not easy to form a path for conduction heat transfer. Therefore, the influence on heat insulation in the normal temperature region where conduction heat transfer is dominant can be particularly reduced.

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

[0068] It should be noted that regarding the average primary particle diameter in the present invention, the particles can be observed under a microscope, compared with a standard scale, and the average value of any 10 particles can be taken to obtain the average primary particle diameter.

[0069] (1-1-2. Nanoparticles)

[0070] The nanoparticles in the present invention refer to nanoparticles in the nanometer order with an average primary particle diameter less than 1 μm that are spherical or nearly spherical. Since the density of the nanoparticles is low, conduction heat transfer can be suppressed. When using nanoparticles as inorganic particles, the voids are more finely dispersed, so convective heat transfer can be suppressed and excellent heat insulation can be achieved. Therefore, when using a battery in a normal room temperature region, heat conduction between adjacent nanoparticles can be suppressed. From this aspect, it is preferable to use nanoparticles.

[0071] In addition, in the present invention, it is preferable that at least one of the oxide particles, carbide particles, nitride particles, and inorganic hydrate particles preferably selected as inorganic particles is a nanoparticle.

[0072] Furthermore, when using nanoparticles with a small average primary particle diameter as oxide particles, even when the heat transfer suppression sheet is compressed due to the expansion accompanying thermal runaway of the battery cell and the internal density increases, an increase in the conduction heat transfer of the heat transfer suppression sheet can be suppressed. It is considered that the reason is that the nanoparticles are likely to form fine voids between the particles under the action of electrostatic repulsive force and have a low packing density, so the particles are filled in a manner with a buffering characteristic.

[0073] It should be noted that in the present invention, when using nanoparticles as inorganic particles, as long as they meet the above definition of nanoparticles, there is no particular limitation on their material. For example, silica nanoparticles are materials with high heat insulation, and in addition, the contact points between the particles are small, so the heat conducted by silica nanoparticles is less than that in the case of using silica particles with a large particle diameter. In addition, the packing density of usually obtained silica nanoparticles is 0.1 g / cm 3Therefore, for example, even when the battery cells disposed on both sides of the heat insulating sheet undergo thermal expansion and apply a large compressive stress to the heat insulating sheet, the size (area) and number of the contacts between the silica nanoparticles do not increase significantly, and the heat insulation property can be maintained. Therefore, silica nanoparticles are preferably used as the nanoparticles. As the silica nanoparticles, wet silica, dry silica, aerogel, etc. can be used.

[0074] In addition, in the present invention, at least one of the oxide particles, carbide particles, nitride particles, and inorganic hydrate particles preferably selected as the inorganic particles is a nanoparticle. As described above, titanium dioxide has a high effect of blocking radiant heat, the heat conduction of silica nanoparticles is extremely small, and excellent heat insulation can be maintained even when a compressive stress is applied to the heat insulating sheet. Therefore, both titanium dioxide and silica nanoparticles are most preferably used as the inorganic particles.

[0075] (Average primary particle size of nanoparticles: 1 nm or more and 100 nm or less)

[0076] If the average primary particle size of the nanoparticles is limited to a specified range, higher heat insulation can be further obtained.

[0077] That is, if the average primary particle size of the nanoparticles is 1 nm or more and 100 nm or less, particularly in the temperature range below 500 °C, convective heat transfer and conductive heat transfer of heat in the heat transfer suppression sheet can be suppressed, and the heat insulation property can be further improved. In addition, even when a compressive stress is applied, the voids remaining between the nanoparticles and the contacts between a large number of particles will suppress conductive heat transfer, and the heat insulation property of the heat transfer suppression sheet can be maintained.

[0078] It should be noted that the average primary particle size of the nanoparticles is more preferably 2 nm or more, and further preferably 3 nm or more. On the other hand, the average primary particle size of the nanoparticles is more preferably 50 nm or less, and further preferably 10 nm or less.

[0079] (1-1-3. Inorganic hydrate particles)

[0080] When the inorganic hydrate particles receive heat from the heat generating body and reach a temperature above the thermal decomposition starting temperature, they will undergo thermal decomposition, release the crystal water they possess, and reduce the temperature of the heat generating body and its surroundings, that is, exhibit the so-called "endothermic effect". In addition, after releasing the crystal water, it becomes a porous body and exhibits an adiabatic effect through numerous air holes.

[0081] Specific examples of the inorganic hydrate can include aluminum hydroxide (Al(OH) 3 ), magnesium hydroxide (Mg(OH) 2 ), calcium hydroxide (Ca(OH)2 ) Zinc hydroxide (Zn(OH) 2 ) Iron(III) hydroxide (Fe(OH) 2 ) Manganese(II) hydroxide (Mn(OH) 2 ) Zirconium(IV) hydroxide (Zr(OH) 2 ) Gallium(III) hydroxide (Ga(OH) 3 ) etc.

[0082] For example, aluminum hydroxide has about 35% water of crystallization. As shown in the following formula, it undergoes thermal decomposition to release the water of crystallization, showing an endothermic effect. Moreover, after releasing the water of crystallization, it becomes alumina (Al 2 O 3 ), which functions as a heat-insulating material.

[0083] 2Al(OH) 3 →Al 2 O 3 +3H 2 O

[0084] It should be noted that, as described below, in the battery pack of the present invention, the heat transfer suppression sheet 10 is sandwiched between battery cells. In a battery cell that has experienced thermal runaway, the temperature rises sharply to exceed 200°C and continues to rise to around 700°C. Therefore, the inorganic particles preferably include inorganic hydrates with a thermal decomposition start temperature of 200°C or higher.

[0085] Regarding the thermal decomposition start temperature of the above-mentioned inorganic hydrates, aluminum hydroxide is about 200°C, magnesium hydroxide is about 330°C, calcium hydroxide is about 580°C, zinc hydroxide is about 200°C, iron(III) hydroxide is about 350°C, manganese(II) hydroxide is about 300°C, zirconium(IV) hydroxide is about 300°C, and gallium(III) hydroxide is about 300°C. They all roughly overlap with the temperature range of the sharp temperature rise of the battery cell that has experienced thermal runaway and can efficiently suppress the temperature rise. Therefore, they can be said to be preferred inorganic hydrates.

[0086] In addition, when inorganic hydrate particles are used as the inorganic particles 20, if their average particle size is too large, the inorganic particles 20 (inorganic hydrates) near the center of the heat transfer suppression sheet 10 require a certain amount of time to reach their thermal decomposition temperature. Therefore, the inorganic particles 20 near the center of the sheet may not be completely thermally decomposed. Therefore, the average secondary particle size of the inorganic hydrate particles is preferably 0.01 μm or more and 200 μm or less, more preferably 0.05 μm or more and 100 μm or less.

[0087] <1-2. First inorganic fiber>

[0088] The average fiber diameter of the first inorganic fiber 30 is set to be thicker than that of the second inorganic fiber 31. By using thick-diameter fibers in the form of wires or needles as the first inorganic fiber 30, the mechanical strength and shape retention of the heat transfer inhibition sheet 10 against extrusion or wind pressure from the battery cell can be improved. An external impact may act on the heat transfer inhibition sheet 10. By including the thick-diameter first inorganic fiber 30 therein, the impact resistance can be improved. Examples of the external impact include the extrusion force based on the expansion of the battery cell and the wind pressure based on the fire of the battery cell. It should be noted that the wire-shaped or needle-shaped fibers refer to fibers with a crimp ratio, for example, less than 10%, preferably 5% or less, as described later.

[0089] To exhibit such an effect, the average fiber diameter of the first inorganic fiber 30 is preferably 1 μm or more, more preferably 3 μm or more. However, if the first inorganic fiber 30 is too thick, the moldability and processability of forming the heat transfer inhibition sheet 10 may be reduced. Therefore, the average fiber diameter is preferably 20 μm or less, more preferably 15 μm or less.

[0090] In addition, if the first inorganic fiber 30 is too long, the moldability and processability may also be reduced. Therefore, the fiber length is preferably 100 mm or less. Furthermore, if the first inorganic fiber 30 is too short, the shape retention and mechanical strength will also be reduced. Therefore, the fiber length is preferably 0.1 mm or more.

[0091] <1-3. The second inorganic fiber>

[0092] Compared with the first inorganic fiber 30, the second inorganic fiber 31 is a fine-diameter fiber. In addition, its shape is dendritic or curly. By making the shape of the second inorganic fiber 31 dendritic or curly, it can become a fiber that is easily deformable and has flexibility. Therefore, the second inorganic fiber 31 is intricately wound with the first inorganic fiber 30 and the inorganic particles 20, improving the retention performance of the inorganic particles 20.

[0093] In addition, by winding the first inorganic fiber 30 and the second inorganic fiber 31 around each other, it is possible to prevent the heat transfer inhibition sheet from sliding or changing its angle when subjected to extrusion force or wind pressure. Thus, the effect of resisting external extrusion force or impact can be particularly exerted.

[0094] It should be noted that the dendritic shape is a two-dimensional or three-dimensional branched structure, such as a feather shape, a quadrangular pyramid shape, a radial shape, or a three-dimensional mesh shape.

[0095] In addition, the curly shape is a structure in which the fiber is bent in various directions. As one method for quantifying the curly form, it is known that the crimp ratio can be calculated based on an electron microscope photograph, for example, it can be calculated by the following formula.

[0096] Degree of crimp (%) = (fiber length - distance between fiber ends) / (fiber length) × 100

[0097] Here, both the fiber length and the distance between fiber ends are measured values on the electron microscope photograph. That is, the fiber length and the distance between fiber ends projected on a two-dimensional plane are shorter than the actual values. Based on this formula, the degree of crimp of the second inorganic fiber 31 is preferably 10% or more, more preferably 30% or more. If the degree of crimp is small, it is not easy to form the holding ability of the inorganic particles 20, the entanglement (network) between the second inorganic fibers 31, and with the first inorganic fiber 30.

[0098] In order to exhibit such an effect, the average fiber diameter of the second inorganic fiber 31 is preferably less than 1 μm, more preferably 0.1 μm or less. However, if the second inorganic fiber 31 is too thin, it is easily broken and the holding ability of the inorganic particles 20 is reduced. In addition, the proportion of fibers that are wound directly without holding the inorganic particles 20 in the sheet increases, which not only reduces the holding ability of the inorganic particles 20 but also deteriorates the moldability and shape retention. Therefore, the average fiber diameter of the second inorganic fiber 31 is preferably 1 nm or more, more preferably 10 nm or more. When the second inorganic fiber 31 is dendritic, its average fiber diameter can be obtained by measuring the fiber diameters at several points of the trunk part and the branch part using SEM and calculating their average value.

[0099] In addition, if the second inorganic fiber 31 is too long, the moldability and shape retention will be reduced. Therefore, the fiber length is preferably 0.1 mm or less.

[0100] <1-4. Types of inorganic fibers>

[0101] Both the first inorganic fiber 30 and the second inorganic fiber 31 preferably have excellent heat resistance. For example, ceramic fibers such as silica fiber, alumina fiber, aluminosilicate fiber, and zirconia fiber, and glass fiber can be cited. Among the first inorganic fiber 30 and the second inorganic fiber 31, the above inorganic fibers can be used alone or in combination of two or more. In addition, the first inorganic fiber 30 and the second inorganic fiber 31 can be the same type of fiber or different types of fibers from each other. In particular, glass fiber is preferably used as the first inorganic fiber 30, and at least one of glass fiber, silica fiber, and mineral fiber is preferably used as the second inorganic fiber 31, and mineral fiber is more preferably used.

[0102] It should be noted that, preferably, either the first inorganic fiber 30 or the second inorganic fiber 31 is an amorphous fiber, and the other contains at least one selected from amorphous fibers having a glass transition temperature higher than that of the above-mentioned one fiber and crystalline fibers. In such a case, when the heat transfer inhibiting sheet is exposed to a high temperature, the surface of one inorganic fiber softens relatively quickly, bonding the other inorganic fiber and the inorganic particles 20, thereby improving the mechanical strength.

[0103] However, more preferably, the first inorganic fiber 30 having a larger average fiber diameter is an amorphous fiber, and the second inorganic fiber 31 having an average fiber diameter smaller than that of the first inorganic fiber 30 is a fiber containing at least one selected from amorphous fibers having a glass transition temperature higher than that of the first inorganic fiber 30 and crystalline fibers.

[0104] <1-5. Contents of each of the inorganic particles, the first inorganic fiber, and the second inorganic fiber>

[0105] The content of the above-mentioned inorganic particles 20 is preferably 30% by mass or more and 94% by mass or less relative to the total mass of the heat transfer inhibiting sheet 10, the content of the first inorganic fiber 30 is preferably 3% by mass or more and 30% by mass or less relative to the total mass of the heat transfer inhibiting sheet 10, and the content of the second inorganic fiber 31 is preferably 3% by mass or more and 30% by mass or less relative to the total mass of the heat transfer inhibiting sheet 10.

[0106] More preferably, relative to the total mass of the heat transfer inhibiting sheet 10, the content of the inorganic particles 20 is 60% by mass or more and 90% by mass or less, the content of the first inorganic fiber 30 is 5% by mass or more and 15% by mass or less, and the content of the second inorganic fiber 31 is 5% by mass or more and 15% by mass or less. With such contents, the heat absorption - heat insulation effect based on the inorganic particles 20, the shape retention property, extrusion pressure resistance, and wind pressure resistance based on the first inorganic fiber 30, and the holding ability of the inorganic particles 20 based on the second inorganic fiber 31 can be exhibited with good balance.

[0107] <1-6. Other compounding materials>

[0108] Organic fibers, organic binders, etc. can be compounded as needed in the heat transfer inhibiting sheet 10. They are all useful for the purpose of strengthening the heat transfer inhibiting sheet 10 and improving the formability, and are preferably 10% by mass or less in total relative to the total mass of the heat transfer inhibiting sheet.

[0109] It should be noted that the types of the organic fibers and organic binders used are not particularly limited. Examples of the organic fibers include pulp and polyester fibers. In addition, as the organic binder, a preferred binder can be selected according to the manufacturing method. The organic binders that can be selected in the present invention are described below.

[0110] <1-7. Thickness of the heat transfer suppression sheet>

[0111] The thickness of the heat transfer suppression sheet 10 is not particularly limited, and is preferably 0.05 mm or more and 5 mm or less. If the thickness is less than 0.05 mm, sufficient mechanical strength cannot be imparted to the heat transfer suppression sheet 10. On the other hand, if the thickness exceeds 5 mm, the molding of the heat transfer suppression sheet 10 itself may become difficult.

[0112] [2. Manufacturing method of the heat transfer suppression sheet]

[0113] The heat transfer suppression sheet 10 is manufactured by molding a material containing at least the inorganic particles 20, the first inorganic fiber 30, and the second inorganic fiber 31 by a dry molding method or a wet molding method using a mold. Regarding the dry molding method, for example, a compression molding method (dry compression molding method) and an extrusion molding method (dry extrusion molding method) can be used.

[0114] <2-1. Manufacturing method using the dry compression molding method>

[0115] In the dry compression molding method, the inorganic particles 20, the first inorganic fiber 30, the second inorganic fiber 31, and, if necessary, organic fibers and organic binders are put into a mixer such as a V-type mixer at a specified ratio. And, after sufficiently mixing the materials put into the mixer, the mixture is put into a specified mold and compression molded, whereby the heat transfer suppression sheet 10 can be obtained. Heating can also be performed as needed during compression molding.

[0116] It should be noted that the pressing pressure during compression molding is preferably in the range of 0.98 MPa or more and 9.80 MPa or less. If the pressing pressure is less than 0.98 MPa, the strength may not be maintained in the obtained heat transfer suppression sheet 10 and it may be damaged. On the other hand, if the pressing pressure exceeds 9.80 MPa, the workability may be reduced due to excessive compression, or the solid heat transfer may increase due to an increase in the bulk density, and the heat insulation may be reduced.

[0117] In addition, in the case of using the dry compression molding method, as the organic binder, polyvinyl alcohol (PVA: PolyVinyl Alcohol) is preferably used, but any organic binder commonly used in the case of using the dry compression molding method can be used without particular limitation.

[0118] <2-2. Manufacturing method using the dry extrusion molding method>

[0119] In the dry extrusion molding method, water is added to inorganic particles 20, first inorganic fibers 30, second inorganic fibers 31, and optionally organic fibers and organic binders as binding materials, and the mixture is kneaded using a kneader to prepare a paste. Thereafter, the obtained paste is extruded from a slit-shaped nozzle using an extrusion molding machine and further dried, whereby a heat transfer suppression sheet 10 can be obtained. In the case of using the dry extrusion molding method, methyl cellulose, water-soluble cellulose ether, etc. are preferably used as the organic binder, but any organic binder commonly used in the case of using the dry extrusion molding method can be used without particular limitation.

[0120] Figure 2 is an SEM photograph showing a cross section of the heat transfer suppression sheet in the embodiment of the present invention manufactured by the dry extrusion molding method. As Figure 2 shown, the heat transfer suppression sheet includes inorganic particles 20, thick first inorganic fibers 30, and thin second inorganic fibers 31. Innumerable minute spaces are formed between the particles of the inorganic particles 20, between the inorganic particles 20 and the inorganic fibers 30, 31, and between the inorganic fibers 30, 31, and the heat insulation effect based on air is also exerted, so the heat transfer suppression performance is excellent.

[0121] <2-3. Manufacturing method using the wet molding method>

[0122] In the wet molding method, inorganic particles 20, first inorganic fibers 30, second inorganic fibers 31, and optionally an organic binder as a binding material are mixed in water and stirred using a stirrer to prepare a mixed liquid. Thereafter, the obtained mixed liquid is caused to flow into a former having a filtration net formed on the bottom surface, and the mixed liquid is dehydrated by means of the net to produce a wet sheet. Thereafter, the obtained wet sheet is heated and pressed, whereby a heat transfer suppression sheet 10 can be obtained.

[0123] It should be noted that before the heating and pressing step, the wet sheet can be subjected to a ventilation drying treatment in which hot air is passed through to dry the sheet, but the ventilation drying treatment can also be omitted and the sheet can be heated and pressed in a wet state.

[0124] In addition, in the case of using the wet molding method, cationized starch, acrylic resin, etc. can be selected as the organic binder.

[0125] [3. Battery pack]

[0126] In the battery pack of the present invention, the above-mentioned heat transfer suppression sheet 10 is interposed between battery cells. Specifically, as Figure 3As shown, in the battery pack 100, two or more battery cells 101 are arranged and connected in series or in parallel, and are housed in the battery case 110. A heat transfer suppression sheet 10 is interposed between the battery cells 101.

[0127] In such a battery pack 100, even when one battery cell 101 undergoes thermal runaway and becomes high temperature, expands, or catches fire, the heat transfer suppression sheet 10, which is excellent in heat transfer suppression effect, shape retention at high temperature, crush resistance, and wind pressure resistance, can suppress its influence on other adjacent battery cells 101. Therefore, in the battery pack of the present invention, a chain reaction of thermal runaway of the battery cells can be suppressed, and even if one battery cell 101 undergoes thermal runaway, the damage can be minimized.

[0128] Although various embodiments have been described above with reference to the drawings, the present invention is of course not limited to these examples. Those skilled in the art can clearly conceive of various modification examples or correction examples within the scope described in the claims, and it is of course understood that these also belong to the technical scope of the present invention. In addition, within the scope not departing from the gist of the invention, the constituent elements in the above embodiments can be arbitrarily combined.

[0129] It should be noted that this application is based on a Japanese patent application (Japanese Patent Application No. 2020-119429) filed on July 10, 2020, and its content is incorporated herein by reference.

[0130] Explanation of reference numerals

[0131] 10 Heat transfer suppression sheet

[0132] 20 Inorganic particles

[0133] 30 First inorganic fiber

[0134] 31 Second inorganic fiber

[0135] 100 Battery pack

[0136] 110 Battery case

Claims

1. A heat transfer suppression sheet, which comprises inorganic particles, a first inorganic fiber, and a second inorganic fiber, wherein the average fiber diameter of the first inorganic fiber is 1 μm or more and 20 μm or less, the average fiber diameter of the second inorganic fiber is 1 nm or more and less than 1 μm, and the first inorganic fiber is a linear or needle-shaped amorphous fiber, the second inorganic fiber is a dendritic or curly crystalline fiber, and the second inorganic fiber is wound around the inorganic particles and the first inorganic fiber.

2. The heat transfer suppression sheet according to claim 1, wherein, the first inorganic fiber is a glass fiber, and the second inorganic fiber is a crystalline mineral fiber.

3. The heat transfer suppression sheet according to claim 2, wherein, the crystalline mineral fiber is at least one selected from silica fiber, alumina fiber, aluminosilicate fiber, and zirconia fiber.

4. The heat transfer suppression sheet according to claim 1 or 2, wherein, the average secondary particle diameter of the inorganic particles is 0.01 μm or more and 200 μm or less.

5. The heat transfer suppression sheet according to claim 1 or 2, wherein, the inorganic particles include at least one selected from oxide particles, carbide particles, nitride particles, aluminum hydroxide particles, magnesium hydroxide particles, calcium hydroxide particles, zinc hydroxide particles, iron hydroxide particles, manganese hydroxide particles, zirconium hydroxide particles, and gallium hydroxide particles.

6. The heat transfer suppression sheet according to claim 5, wherein, the inorganic particles include oxide particles.

7. The heat transfer suppression sheet according to claim 6, wherein, the average primary particle diameter of the oxide particles is 0.001 μm or more and 50 μm or less.

8. The heat transfer suppression sheet according to claim 6 or 7, wherein, the oxide particles include at least one selected from silica, titanium dioxide, zirconia, zircon, barium titanate, zinc oxide, and alumina.

9. The heat transfer suppression sheet according to claim 5, wherein, the inorganic particles include hollow particles.

10. The heat transfer suppression sheet according to claim 5, wherein, the inorganic particles include nanoparticles.

11. The heat transfer suppression sheet according to claim 10, wherein, the nanoparticles are silica nanoparticles.

12. The heat transfer suppression sheet according to claim 10 or 11, wherein, the average primary particle diameter of the nanoparticles is 1 nm or more and 100 nm or less.

13. The heat transfer suppression sheet according to any one of claims 9 to 11, wherein, the oxide particles include titanium dioxide.

14. The heat transfer suppression sheet according to claim 5, wherein, the inorganic particles include porous particles.

15. The heat transfer suppression sheet according to any one of claims 1, 2, 6, 7, 9 to 11, 14, wherein, relative to the total mass of the heat transfer suppression sheet, the content of the inorganic particles is 30% by mass or more and 94% by mass or less, the content of the first inorganic fiber is 3% by mass or more and 30% by mass or less, and the content of the second inorganic fiber is 3% by mass or more and 30% by mass or less.

16. A battery pack formed by connecting two or more battery cells in series or in parallel, wherein, the heat transfer inhibition sheet according to any one of claims 1 to 15 is interposed between the battery cells.

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