Heat transfer suppression sheet and battery pack

Abstract

To provide: a heat transfer suppression sheet which has excellent thermal insulation properties and prevents ingress of water, thereby being capable of preventing ignition due to a short circuit between battery cells, and the like, and which is preferably capable of preventing a decrease in the thermal insulation properties due to ingress of an electrolyte solution; and a battery pack which comprises the heat transfer suppression sheet.SOLUTION: A heat transfer suppression sheet 10 is interposed between multiple battery cells comprises: at least one kind of fibers (glass fibers 1) which are selected from among inorganic fibers and organic fibers; and a liquid repellent substance 2 which has a surface tension that is lower than the surface tension of water.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

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

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

[0004] As a method for preventing the spread of fire from a battery cell that has experienced the above-mentioned thermal runaway, a method of placing a heat insulating material between the battery cells is commonly used. For example, Patent Document 1 discloses a thermal insulation material having a composite layer containing a fiber sheet and silica aerogel, in which the fiber sheet is folded and laminated. Patent Document 1 describes that the thermal insulation sheet can be made to follow changes in the gap between battery cells due to expansion and contraction of the battery cells. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2021-34278 Summary of the Invention [Problem to be solved by the invention]

[0006] In a conventional battery pack (battery unit), heat generation and cooling are repeated as the battery cells expand and contract during charging and discharging, and condensation water may occur inside the battery case. If the condensation water penetrates into the insulation material, the insulating properties of the insulation material may deteriorate, causing adjacent battery cells to short-circuit and possibly ignite. In addition, if a battery cell is damaged due to thermal runaway, and the electrolyte inside the battery cell penetrates into the insulation material at a high temperature, the insulating properties of the insulation material may deteriorate significantly, causing a chain reaction of thermal runaway. The heat insulating material described in the above Patent Document 1 cannot prevent deterioration of insulating properties due to infiltration of condensed water and deterioration of heat insulating properties due to infiltration of electrolyte.

[0007] The present invention has been made in consideration of the above-mentioned problems, and has an object to provide a heat-transfer-inhibiting sheet that has excellent thermal insulation properties and prevents the infiltration of moisture, thereby preventing fires and other accidents caused by short-circuiting between battery cells, and preferably prevents a decrease in thermal insulation properties due to the infiltration of electrolyte, and a battery pack having this heat-transfer-inhibiting sheet. [Means for solving the problem]

[0008] The above object of the present invention can be achieved by the heat-transfer-suppressing sheet having the following configuration [1].

[0009] [1] A heat transfer suppression sheet interposed between multiple battery cells, At least one type of fiber selected from inorganic fibers and organic fibers; and a liquid-repellent substance having a surface tension smaller than that of water.

[0010] Further, preferred embodiments of the present invention relating to the heat-transfer-suppressing sheet relate to the following items [2] to

[12] .

[0011] [2] The heat transfer-suppressing sheet according to [1], which contains inorganic particles, at least a portion of which is made of the liquid repellent substance.

[0012] [3] The heat transfer-suppressing sheet according to [2], wherein the liquid repellent substance is hydrophobic silica.

[0013] [4] Contains inorganic particles; The heat-transfer-inhibiting sheet according to [1], wherein the liquid repellent substance is attached to at least a portion of a surface of the heat-transfer-inhibiting sheet, surfaces of the inorganic particles inside the heat-transfer-inhibiting sheet, and surfaces of the fibers inside the heat-transfer-inhibiting sheet.

[0014] [5] The heat transfer-inhibiting sheet according to [4], wherein the liquid repellent substance is at least one selected from paraffin-based oils, naphthene-based oils, hydrocarbon-based synthetic oils, ester-based synthetic oils, animal and vegetable fats and oils, silicone resins, fluororesins, rosin-based sizing agents, and alkyl ketene dimer sizing agents.

[0015] [6] The heat-transfer-suppressing sheet according to [4] or [5], wherein the inorganic particles are particles made of at least one inorganic material selected from the group consisting of oxide particles, carbide particles, nitride particles and inorganic hydrate particles.

[0016] [7] The heat-transfer-suppressing sheet according to [6], wherein the inorganic particles include at least one type of particles selected from dry silica particles and silica aerogel.

[0017] [8] The heat-transfer-suppressing sheet according to [7], wherein the inorganic particles further include at least one type of particles selected from the group consisting of titania, zircon, zirconia, silicon carbide, zinc oxide, and alumina.

[0018] [9] The heat transfer-suppressing sheet of any one of [1] to [8], wherein the surface tension of the liquid repellent substance is lower than the surface tension of an electrolyte contained in the battery cell.

[0019]

[10] The heat transfer-suppressing sheet according to any one of [1] to [9], wherein the liquid repellent substance has a surface tension of 45 mN / m or less.

[0020]

[11] The heat transfer-suppressing sheet according to

[10] , wherein the liquid repellent substance is at least one selected from a silicone resin and a fluororesin.

[0021]

[12] It has multiple three-dimensionally connected pores, The heat-transfer-suppressing sheet according to any one of [1] to

[11] , wherein the pores are open toward a surface of the heat-transfer-suppressing sheet.

[0022] The above object of the present invention can be achieved by the following configuration

[13] relating to a battery pack.

[0023]

[12] An assembled battery comprising a plurality of battery cells and the heat-transfer-suppressing sheet according to any one of [1] to

[12] , the plurality of battery cells being connected in series or in parallel. Effect of the Invention

[0024] The heat-transfer-inhibiting sheet of the present invention has a liquid-repellent substance on at least a portion of its surface and interior, and because the surface tension of this liquid-repellent substance is smaller than the surface tension of water, it is possible to inhibit condensation water generated on the outside of the heat-transfer-inhibiting sheet from penetrating into the heat-transfer-inhibiting sheet. This makes it possible to prevent a decrease in the insulating properties of the heat-transfer-inhibiting sheet, which could lead to a short circuit between adjacent battery cells and fire. Furthermore, if the surface tension of the liquid-repellent substance is smaller than the surface tension of the electrolyte used in the battery cells, it is possible to inhibit the electrolyte from penetrating into the heat-transfer-inhibiting sheet, thereby preventing a decrease in heat insulation.

[0025] As described above, the battery pack of the present invention has excellent insulation properties and includes a heat transfer-inhibiting sheet that inhibits the intrusion of condensation water and electrolyte, so that it is possible to prevent short circuits between battery cells in the battery pack and to inhibit thermal runaway of the battery cells and the spread of flames to the outside of the battery case. [Brief description of the drawings]

[0026] [Figure 1] FIG. 1 is a schematic cross-sectional view showing the structure of a heat-transfer-suppressing sheet according to a first embodiment of the present invention. [Diagram 2] FIG. 2 is a cross-sectional view that typically illustrates a battery pack having a heat-transfer-suppressing sheet according to the first embodiment of the present invention. [Diagram 3] FIG. 3 is a schematic cross-sectional view showing the structure of a heat-transfer-suppressing sheet according to a second embodiment of the present invention. [Figure 4] FIG. 4 is a photograph, substituted for a drawing, showing a cross section of a heat insulating material that can be used in a heat-transfer-suppressing sheet according to an embodiment of the present invention. [Diagram 5] FIG. 5 is a schematic cross-sectional view showing the structure of a heat-transfer-suppressing sheet according to a second embodiment having pores that are three-dimensionally connected. [Figure 6] FIG. 6 is a schematic cross-sectional view showing a heat-transfer-suppressing sheet according to a second embodiment disposed adjacent to a battery cell. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] The present inventors have conducted extensive research into a heat-transfer-suppressing sheet that can solve the above-mentioned problems. As a result, it was found that by adding a liquid repellent substance to the surface of the heat transfer-suppressing sheet or adding a liquid repellent substance to the inside of the heat transfer-suppressing sheet and using a liquid repellent substance having a surface tension lower than that of water, it is possible to prevent condensation water generated outside the heat transfer sheet from penetrating into the sheet. Also, it was found that, for example, when the heat transfer sheet is placed near a battery cell, if a liquid repellent substance having a surface tension lower than that of the electrolyte filled in the battery cell is used, it is possible to prevent the electrolyte leaking from the battery cell from penetrating into the heat transfer-suppressing sheet, and a decrease in thermal insulation properties can be prevented.

[0028] Hereinafter, a heat transfer-suppressing sheet, a manufacturing method thereof, and a battery pack according to an embodiment of the present invention will be described in detail. Note that the present invention is not limited to the embodiment described below, and can be modified as desired without departing from the gist of the present invention.

[0029] [Heat transfer suppression sheet] <First embodiment> Fig. 1 is a schematic cross-sectional view showing the structure of a heat-transfer-suppressing sheet according to a first embodiment of the present invention, and Fig. 2 is a schematic cross-sectional view showing a battery pack having the heat-transfer-suppressing sheet according to the first embodiment of the present invention.

[0030] 1, a heat transfer-suppressing sheet 10 according to this embodiment has a liquid repellent substance 2 attached to the surface of a heat insulating material 9. The heat insulating material 9 has nanosilica 4 and titania 3 as inorganic particles, and glass fibers 1 as fibers. The liquid repellent substance 2 has a surface tension smaller than that of water, and is, for example, a rosin-based sizing agent.

[0031] 2, the heat-transfer-suppressing sheet 10 can be used by being interposed between a plurality of battery cells 20a, 20b, and 20c. The plurality of battery cells 20a, 20b, and 20c are connected in series or parallel (the connected state is not shown) and stored in a battery case 30 to form a battery pack 100. The battery cells 20a, 20b, and 20c are preferably, for example, lithium-ion secondary batteries, but are not limited thereto and may also be other secondary batteries.

[0032] In the battery pack 100 configured as described above, during operation (charging and discharging), the temperatures of the battery cells 20a, 20b, and 20c rise, and the temperature inside the battery case 30 also rises. When the operation of the battery pack 100 is subsequently stopped and the air inside the battery case 30 is cooled, condensed water adheres to the battery cells 20a, 20b, and 20c and the inner surface of the battery case 30. At this time, the heat-transfer-suppressing sheet 10 according to the first embodiment has a liquid-repellent substance 2 attached to its surface, which has a surface tension lower than that of water, and because this liquid-repellent substance 2 has the property of repelling water, it is possible to suppress the infiltration of the condensed water 5 into the heat-transfer-suppressing sheet 10. This makes it possible to suppress a decrease in the insulating properties of the heat-transfer-suppressing sheet, and to prevent adjacent battery cells, for example battery cell 20a and battery cell 20b, from shorting out and catching fire.

[0033] In addition, in the battery pack 100, if the battery cell 20c expands due to thermal runaway, breaks, and the electrolyte filled in the battery cell 20c leaks out, if this electrolyte penetrates the insulating material at a high temperature, the insulating properties of the insulating material will be significantly reduced, causing a chain reaction of thermal runaway. In such a case, if a fluororesin is used as the liquid repellent material 2, the fluororesin has a surface tension smaller than that of the electrolyte filled in the battery cells 20a, 20b, and 20c, such as dimethyl carbonate (DMC). Therefore, the fluororesin exhibits liquid repellency not only to the condensed water 5 but also to the electrolyte, and can inhibit the electrolyte from penetrating into the heat-transfer-suppressing sheet 10, thereby preventing a chain reaction of thermal runaway.

[0034] In the first embodiment, when the heat-transfer-inhibiting sheet 10 has the liquid-repellent substance 2 on its surfaces 10a and 10b, if the liquid-repellent substance 2 is attached to at least a part of the surfaces 10a and 10b, it is possible to obtain an effect of preventing the infiltration of condensed water and electrolyte into the heat-transfer-inhibiting sheet 10, compared to a case in which the liquid-repellent substance 2 is not attached. However, it is preferable that the liquid-repellent substance 2 is attached so as to completely cover the entire surfaces 10a and 10b. In this way, if the liquid-repellent substance 2 is attached to the entire surfaces 10a and 10b of the heat-transfer-inhibiting sheet 10, it is possible to reliably prevent the infiltration of condensed water and electrolyte into the heat-transfer-inhibiting sheet 10. A method for manufacturing the heat-transfer-inhibiting sheet 10 according to the first embodiment will be described later.

[0035] Furthermore, since the heat-transfer-inhibiting sheet 10 according to this embodiment has glass fibers 1, which are inorganic fibers, as the fibers, the glass fibers 1 act as aggregates for the heat-transfer-inhibiting sheet 10, and a high compressive strength can be obtained. As shown in FIG. 2, the heat-transfer-inhibiting sheet 10 according to this embodiment is interposed between a plurality of battery cells 20a, 20b, and 20c, and the battery cells 20a, 20b, and 20c arranged adjacent to the heat-transfer-inhibiting sheet 10 expand or contract due to charging and discharging. At this time, since the heat-transfer-inhibiting sheet 10 has a high compressive strength, it is possible to maintain its shape without being significantly deformed even when pressed by the battery cells 20a, 20b, and 20c. Therefore, it is possible to prevent a decrease in the heat insulation property due to a decrease in the thickness of the heat-transfer-inhibiting sheet 10 due to compression or due to inorganic particles or the like falling off the heat-transfer-inhibiting sheet 10. Furthermore, since the inorganic fibers have a high high-temperature strength, the heat-transfer-inhibiting sheet 10 can maintain its shape even when exposed to high temperatures.

[0036] Furthermore, the heat-transfer-suppressing sheet 10 according to this embodiment contains nanosilica 4 and titania 3 as inorganic particles, and these inorganic particles exhibit heat insulating properties over a wide temperature range, thereby achieving excellent heat insulating properties.

[0037] <Second embodiment> Fig. 3 is a schematic cross-sectional view showing the structure of a heat-transfer-suppressing sheet according to a second embodiment of the present invention. The heat-transfer-suppressing sheet 10 according to the first embodiment has a liquid-repellent substance 2 attached to the surface of a heat insulating material 9, but in the second embodiment, the region where the liquid-repellent substance 2 is attached is different from that in the first embodiment. However, since other materials and the like are similar to those of the first embodiment, in Fig. 3, the same elements as those in Fig. 1 are given the same reference numerals and detailed descriptions thereof are omitted.

[0038] As shown in FIG. 3, the heat transfer-suppressing sheet 10 according to the second embodiment has a so-called internally added structure in which a liquid repellent substance 2 is attached to at least a portion of the surface of the fibers (glass fibers 1) or inorganic particles (nanosilica 4 and titania 3) inside the heat insulating material 9.

[0039] In the heat-transfer-suppressing sheet 10 according to the second embodiment configured as described above, the liquid-repellent substance 2 is added thereto, and although condensed water 5 and electrolyte may penetrate from the surfaces 10a, 10b to a certain depth, complete penetration can be prevented. This makes it possible to suppress deterioration of the insulating properties of the heat-transfer-suppressing sheet, prevent ignition due to a short circuit between adjacent battery cells, and prevent deterioration of the insulating properties due to the penetration of high-temperature electrolyte.

[0040] Furthermore, as shown in the second embodiment, when a liquid-repellent substance 2 is incorporated into the heat-transfer-suppressing sheet 10, even if the surfaces 10a, 10b of the heat-transfer-suppressing sheet 10 are damaged, the infiltration of the condensed water 5 can be prevented midway.

[0041] As shown in the second embodiment, a liquid-repellent substance 2 is attached to at least a portion of the surface of the fibers (glass fibers 1) or inorganic particles (nanosilica 4 and titania 3) inside the insulating material 9, and as shown in the first embodiment, a heat transfer-inhibiting sheet having the excellent effects of both can be obtained by attaching the liquid-repellent substance 2 to the surface of the insulating material 9.

[0042] <Third embodiment> Although the third embodiment is not shown in the drawings, it will be described with reference to Fig. 1. A heat transfer-suppressing sheet 10 according to the third embodiment does not have a liquid repellent substance 2 attached to its surface as shown in Fig. 1, but uses inorganic particles having liquid repellency. That is, at least a part of the inorganic particles in the heat insulating material 9 is made of a liquid repellent substance. An example of such inorganic particles is hydrophobic silica (fumed silica).

[0043] Even in the third embodiment configured in this manner, since inorganic particles having liquid repellency are present on the surface, it is possible to easily prevent the infiltration of condensed water 5 into the interior without carrying out a process of adhering a liquid repellent substance 2 to the surface of the heat transfer-inhibiting sheet 10. If heat-transfer-suppressing sheet 10 were manufactured using only inorganic particles made of liquid-repellent substance 2, without including at least one type of fiber selected from inorganic fibers and organic fibers, the inorganic particles would aggregate together and cracks would be likely to occur if condensed water 5 penetrated into heat-transfer-suppressing sheet 10. In the present embodiment, the inorganic particles are suppressed from aggregating together, and cracks can be prevented by including fibers (glass fibers 1).

[0044] Next, a heat insulating material that can be used in the heat transfer-suppressing sheet according to an embodiment of the present invention will be described in more detail. FIG. 4 is a drawing substitute photograph showing a cross section of a heat insulating material that can be used in the heat transfer-suppressing sheet according to an embodiment of the present invention. The heat insulating material 19 shown in FIG. 4 contains inorganic particles 14 and organic fibers 6. As shown in the first and second embodiments, nanosilica, titania, etc. can be used as the inorganic particles 14. Also, polyethyleneterephthalate (PET) fibers, etc. can be used as the organic fibers 6. Furthermore, as shown in the first and second embodiments, inorganic fibers such as glass fibers 1 may be included.

[0045] The heat insulating material 19 has a plurality of three-dimensionally connected pores 7 between the inorganic particles 14, between the inorganic particles 14 and the organic fibers 6, etc. At least a portion of the pores 7 communicates with the surface 19a of the heat insulating material 19 and has an opening 7a that opens outward.

[0046] As shown in Fig. 4, the insulating material 19 used in this embodiment has a surface 19a on which the inorganic particles 14 are exposed and on which extremely fine irregularities are formed, so that the insulating material 19 has an inherently water-repellent structure. In addition, in the first and second embodiments, a liquid-repellent substance is attached to the surface 19a of the insulating material 19, or to the surfaces of the inorganic particles 14 and organic fibers 6 inside the insulating material, and in the third embodiment, inorganic particles made of a liquid-repellent substance are used. Therefore, compared with the case where a liquid-repellent substance is applied to an insulating material that does not contain a predetermined amount of inorganic particles and does not have fine irregularities formed on the surface, the effect of preventing the intrusion of condensation water and electrolyte can be significantly improved.

[0047] As shown in FIG. 4, when the heat insulating material 19 has three-dimensionally connected pores 7 and the pores 7 have openings 7a, when a liquid repellent substance is applied from the surface side of the heat insulating material 19, the liquid repellent substance easily penetrates into the heat insulating material 19 through the openings 7a. In particular, when hydrophobic silica is used as the inorganic particles 14, if an attempt is made to further attach a liquid repellent substance to the surface of the heat insulating material 19, the inorganic particles 14 may exhibit liquid repellency, making attachment difficult. In contrast, as shown in FIG. 4, when the heat insulating material 19 has pores 7 having openings 7a, the liquid repellency of the liquid repellent substance can easily penetrate into the heat insulating material 19, and the liquid repellency can be improved.

[0048] Fig. 5 is a schematic cross-sectional view showing a structure in which the heat-transfer-suppressing sheet according to the second embodiment has three-dimensionally connected pores, and Fig. 6 is a schematic cross-sectional view showing the heat-transfer-suppressing sheet according to the second embodiment disposed adjacent to a battery cell. 5, when heat-transfer-suppressing sheet 10 has three-dimensionally connected pores 7 and pores 7 have openings 7a, inlet / drainage paths 8 are formed that connect openings 7a to pores 7. Therefore, even if condensed water 5 infiltrates into heat-transfer-suppressing sheet 10 through openings 7a of pores 7 or other portions, condensed water 5 can be discharged to the outside through inlet / drainage paths 8.

[0049] Furthermore, as shown in Fig. 6, when the temperature of the battery cell 20c rises during operation and the temperature of the heat-transfer-inhibiting sheet 10 also rises to a certain extent, the moisture present inside the heat-transfer-inhibiting sheet 10 evaporates into water vapor, which can be discharged to the outside via the inlet / drainage path 8. Furthermore, when the battery cell 20c expands during operation, the gap between the battery cell 20c and battery cell 20b (not shown in Fig. 6) narrows, and the heat-transfer-inhibiting sheet 10 is pressed. If moisture has penetrated the heat-transfer-inhibiting sheet 10 at this time, condensed water 5 is easily discharged via the inlet / drainage path 8.

[0050] The materials constituting the heat-transfer-suppressing sheet according to this embodiment will be described in detail below.

[0051] <Liquid repellent material> The liquid repellent substance 2 is an important component that has the effect of preventing the infiltration of condensed water 5 into the heat-transfer-suppressing sheet 10. In order to prevent the infiltration of condensed water 5, the surface tension of the liquid repellent substance 2 needs to be lower than the surface tension of water. Furthermore, if the surface tension of the liquid repellent substance 2 is lower than the surface tension of the electrolyte contained in the battery cell disposed near the heat-transfer-suppressing sheet 10, the infiltration of the electrolyte can also be prevented.

[0052] Since the surface tension of water at 25° C. is approximately 72.0 (mN / m), the specific value of the surface tension of the liquid repellent material is, for example, 70.0 (mN / m) or less, and preferably 65 (mN / m) or less. In order to suppress the infiltration of the electrolyte, the surface tension of the liquid repellent material is more preferably 45 (mN / m) or less, and even more preferably 25 (mN / m) or less.

[0053] Examples of liquid repellent substances include commonly used water repellents, oil repellents, and sizing agents. Specific examples of water repellents include paraffin-based oils, naphthene-based oils, hydrocarbon synthetic oils, ester synthetic oils, animal and vegetable oils, etc. Specific examples of oil repellents include silicone resins and fluororesins. Specific examples of sizing agents include rosin (pine resin), alkyl ketene dimer (AKD), etc. Among these liquid repellent substances, silicone resin and fluororesin are examples of liquid repellent substances having a surface tension smaller than that of the electrolyte. Note that the surface tension of silicone resin is 16 to 30 (mN / m), and the surface tension of fluororesin is 10 to 25 (mN / m).

[0054] As shown in the third embodiment, inorganic particles can be used as the liquid repellent substance. In this case, examples of the liquid repellent substance include hydrophobic silica (fumed silica).

[0055] (Content of liquid repellent substance) In this embodiment, if the content of the liquid repellent substance 2 relative to the total mass of the heat transfer-suppressing sheet is appropriately controlled, sufficient liquid repellency against condensed water 5 and electrolyte can be obtained. The content of the liquid repellent substance 2 is preferably 5 mass % or more, and more preferably 10 mass % or more, relative to the total mass of the heat transfer-inhibiting sheet 10. Furthermore, if the content of the liquid repellent substance 2 is too high, the content of the inorganic particles and fibers will relatively decrease, so in order to obtain the desired heat insulating performance, the content of the liquid repellent substance 2 is preferably 35 mass % or less, and more preferably 20 mass % or less, relative to the total mass of the heat transfer-inhibiting sheet 10.

[0056] <Inorganic particles> As the inorganic particles, a single inorganic particle may be used, or two or more types of inorganic particles may be used in combination. As the type of inorganic particles, from the viewpoint of the heat transfer suppression effect, it is preferable to use particles made of at least one inorganic material selected from oxide particles, carbide particles, nitride particles, and inorganic hydrate particles, and it is more preferable to use oxide particles. In addition, the shape is not particularly limited, but it is preferable to include at least one selected from nanoparticles, hollow particles, and porous particles, and specifically, silica nanoparticles, metal oxide particles, inorganic balloons such as microporous particles and hollow silica particles, particles made of thermally expandable inorganic materials, particles made of water-containing porous bodies, etc. can also be used.

[0057] If 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. If 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.

[0058] In addition, when two or more kinds of inorganic particles having different heat transfer suppression effects are used in combination, the heating body can be cooled in multiple stages, and the heat absorption effect can be expressed in a wider temperature range. Specifically, it is preferable to use a mixture of large-diameter particles and small-diameter particles. For example, as shown in the first and second embodiments, when nanoparticles (nanosilica 4) are used as one inorganic particle, it is preferable to include inorganic particles (titania 3) made of metal oxide as the other inorganic particle. Hereinafter, the inorganic particles will be described in more detail, with the small-diameter inorganic particles being referred to as the first inorganic particles and the large-diameter inorganic particles being referred to as the second inorganic particles.

[0059] <First inorganic particle> (Oxide particles) Since oxide particles have a high refractive index and a strong effect of scattering light, when oxide particles are used as the first inorganic particles, radiation heat transfer can be suppressed, particularly in high temperature regions such as abnormal heat generation. As the oxide particles, at least one type of particle selected from silica, titania, zirconia, zircon, barium titanate, zinc oxide, and alumina can be used. That is, among the above oxide particles that can be used as inorganic particles, only one type may be used, or two or more types of oxide particles may be used. In particular, silica is a component with high heat insulation properties, and titania is a component with a high refractive index compared to other metal oxides, and has a high effect of scattering light and blocking radiant heat in high temperature regions of 500°C or more, so it is most preferable to use silica and titania as the oxide particles.

[0060] (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 insulation can be obtained. In other words, when the average primary particle size of the oxide particles is 0.001 μm or more, the average primary particle size is sufficiently larger than the wavelength of light that contributes to heating and efficiently diffuses light, thereby suppressing the radiation of heat transfer within the heat-transfer-inhibiting sheet in the high-temperature range of 500° C. or more, and further improving the thermal insulation properties. On the other hand, if the average primary particle size of the oxide particles is 50 μm or less, the number and number of contact points between the particles do not increase even when compressed, making it difficult to form a conductive heat transfer path, thereby reducing the impact on insulation, especially in the normal temperature range where conductive heat transfer is dominant.

[0061] 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 ten particles.

[0062] (Nanoparticles) In the present invention, nanoparticles refer to particles of 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 and therefore suppress conductive heat transfer. When nanoparticles are used as the first inorganic particles, the three-dimensionally connected pores 7 are further refined, and excellent heat insulation properties that suppress convective heat transfer can be obtained. For this reason, it is preferable to use nanoparticles in that heat transfer between adjacent nanoparticles can be suppressed when the battery is used in the normal room temperature range. Furthermore, if nanoparticles with a small average primary particle size are used as the oxide particles, an increase in conductive heat transfer in the heat-transfer-suppressing sheet can be suppressed even if the heat-transfer-suppressing sheet is compressed by expansion accompanying thermal runaway of the battery cell, causing the internal density to increase. This is thought to be because nanoparticles are prone to forming fine gaps between particles due to static electricity repulsion, and because they have a low bulk density, the particles are packed together to provide a cushioning effect.

[0063] Furthermore, when nanoparticles are contained in the insulating material of the heat transfer-inhibiting sheet 10 of this embodiment, fine irregularities are formed on the surface of the insulating material, and as described above, the liquid repellency obtained by applying the liquid repellent substance 2 can be further improved.

[0064] In the present invention, when nanoparticles are used as the first inorganic particles, there is no particular limitation on the material as long as it meets the above definition of nanoparticles. For example, silica nanoparticles are a material with high heat insulation properties, and since the contact points between particles are small, the amount of heat conducted by silica nanoparticles is smaller than that when silica particles with a large particle size are used. Furthermore, silica nanoparticles that are generally available have a bulk density of 0.1 (g / cm 3), for example, even if the battery cells arranged on both sides of the heat-transfer-suppressing sheet thermally expand and a large compressive stress is applied to the heat-transfer-suppressing sheet, the size (area) and number of contacts between the silica nanoparticles do not increase significantly, and heat insulation can be maintained. Therefore, it is preferable to use silica nanoparticles as the nanoparticles. Examples of silica nanoparticles include wet silica, dry silica, and aerogel, but silica nanoparticles that are particularly suitable for this embodiment will be described below.

[0065] Generally, wet silica particles are aggregated, whereas dry silica particles can be dispersed. In the temperature range below 300℃, heat conduction is dominated by conductive heat transfer, so dry silica particles can be dispersed, which provides better heat insulation performance than wet silica. The heat-transfer-suppressing sheet according to the present embodiment is preferably produced by a method in which a mixture containing the materials is processed into a sheet by a dry method. Therefore, it is preferable to use dry silica, silica aerogel, or the like, which has low thermal conductivity, as the inorganic particles. It is also preferable to use hydrophobic silica, as shown in the heat-transfer-suppressing sheet according to the third embodiment.

[0066] (Average primary particle size of nanoparticles: 1 nm to 100 nm) By limiting the average primary particle size of the nanoparticles to a predetermined range, even higher heat insulation properties can be obtained. That is, when the average primary particle size of the nanoparticles is 1 nm or more and 100 nm or less, convective heat transfer and conductive heat transfer within the heat-transfer-suppressing sheet can be suppressed, particularly in a temperature range below 500° C., and the heat insulation can be further improved. Even when compressive stress is applied, the voids remaining between the nanoparticles and the contact points between many of the particles suppress conductive heat transfer, and the heat insulation of the heat-transfer-suppressing sheet can 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.

[0067] (Inorganic hydrate particles) When inorganic hydrate particles receive heat from a heating element and reach a temperature above the thermal decomposition initiation temperature, they undergo thermal decomposition and release their own water of crystallization to lower the temperature of the heating element and its surroundings, thus exerting the so-called "endothermic effect". After releasing the water of crystallization, the particles become porous and exert a heat insulating effect due to the countless air holes. A specific example of an inorganic hydrate is aluminum hydroxide (Al(OH) 3 ), magnesium hydroxide (Mg(OH) 2 ), calcium hydroxide (Ca(OH) 2 ), zinc hydroxide (Zn(OH) 2 ), iron hydroxide (Fe(OH) 2 ), manganese hydroxide (Mn(OH) 2 ), zirconium hydroxide (Zr(OH) 2 ), gallium hydroxide (Ga(OH) 3 ) etc.

[0068] For example, aluminum hydroxide contains about 35% water of crystallization, and as shown in the following formula, it decomposes thermally and releases the water of crystallization, thereby exerting an endothermic effect. After releasing the water of crystallization, it becomes a porous alumina (Al 2 O 3 ) and acts as a thermal insulator. 2Al(OH) 3 →Al 2 O 3 +3H 2 O

[0069] As described later, the heat transfer-suppressing sheet 10 according to this embodiment is preferably interposed between battery cells, for example, but in a battery cell that has experienced thermal runaway, the temperature rises rapidly to over 200° C. and continues to rise to around 700° C. Therefore, the inorganic particles are preferably made of inorganic hydrates whose thermal decomposition starting temperature is 200° C. or higher. The thermal decomposition onset temperatures of the inorganic hydrates listed above are approximately 200°C for aluminum hydroxide, approximately 330°C for magnesium hydroxide, approximately 580°C for calcium hydroxide, approximately 200°C for zinc hydroxide, approximately 350°C for iron hydroxide, approximately 300°C for manganese hydroxide, approximately 300°C for zirconium hydroxide, and approximately 300°C for gallium hydroxide. All of these temperatures roughly overlap with the temperature range of the sudden temperature rise in a battery cell that has experienced thermal runaway, and can efficiently suppress the temperature rise, making these inorganic hydrates preferable.

[0070] (Average secondary particle diameter of inorganic hydrate particles: 0.01 μm or more and 200 μm or less) Furthermore, when inorganic hydrate particles are used as the first inorganic particles, if their average particle size is too large, it takes a certain amount of time for the first inorganic particles (inorganic hydrate) near the center of the heat-transfer-suppressing sheet 10 to reach their thermal decomposition temperature, and the first inorganic particles near the center of the sheet may not be completely thermally decomposed. For this reason, the average secondary particle size of the inorganic hydrate particles is preferably 0.01 μm or more and 200 μm or less, and more preferably 0.05 μm or more and 100 μm or less.

[0071] (Particles made of thermally expandable inorganic material) Examples of the thermally expandable inorganic material include vermiculite, bentonite, mica, and perlite.

[0072] (Particles made of water-containing porous material) Specific examples of the hydrous porous body include zeolite, kaolinite, montmorillonite, acid clay, diatomaceous earth, wet silica, dry silica, aerogel, mica, and vermiculite.

[0073] (Inorganic balloon) The heat insulating material used in the present invention may contain inorganic balloons as the first inorganic particles. When inorganic balloons are contained, convective or conductive heat transfer within the insulating material can be suppressed in the temperature range below 500° C., and the insulating properties of the insulating material can be further improved. As the inorganic balloons, at least one selected from the group consisting of shirasu balloons, silica balloons, fly ash balloons, barite balloons, and glass balloons can be used.

[0074] (Inorganic balloon content) The content of the inorganic balloons is preferably 60 mass % or less based on the total mass of the heat-transfer-suppressing sheet.

[0075] (Average particle size of inorganic balloons: 1 μm to 100 μm) The average particle size of the inorganic balloons is preferably 1 μm or more and 100 μm or less.

[0076] <Second inorganic particles> When the heat-transfer-suppressing sheet contains two types of inorganic particles, the second inorganic particles are not particularly limited as long as they are different from the first inorganic particles in terms of material, particle size, etc. Examples of the second inorganic particles that can be used include oxide particles, carbide particles, nitride particles, inorganic hydrate particles, silica nanoparticles, metal oxide particles, inorganic balloons such as microporous particles and hollow silica particles, particles made of a thermally expandable inorganic material, particles made of a water-containing porous body, etc., the details of which are as described above.

[0077] Nanoparticles have extremely low conductive heat transfer and can maintain excellent heat insulation even when compressive stress is applied to the heat transfer-suppressing sheet. Metal oxide particles such as titania have a high effect of blocking radiant heat. Furthermore, when large-diameter inorganic particles and small-diameter inorganic particles are used, the small-diameter inorganic particles enter the gaps between the large-diameter inorganic particles, resulting in a denser structure and improving the heat transfer suppression effect. Therefore, when nanoparticles are used as the first inorganic particles, it is preferable to further include particles made of a metal oxide larger in diameter than the first inorganic particles as the second inorganic particles in the heat transfer-suppressing sheet. Examples of metal oxides include silicon oxide, titanium oxide, aluminum oxide, barium titanate, zinc oxide, zircon, zirconium oxide, etc. In particular, titanium oxide (titania) is a component with a higher refractive index than other metal oxides, and is highly effective in scattering light and blocking radiant heat in a high temperature range of 500°C or higher, so it is most preferable to use titania.

[0078] When at least one type of particles selected from dry silica particles and silica aerogel is used as the first inorganic particles, and at least one type of particles selected from titania, zircon, zirconia, silicon carbide, zinc oxide and alumina is used as the second inorganic particles, in order to obtain excellent heat insulating performance within a temperature range of 300° C. or less, the first inorganic particles are preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more of the total mass of the inorganic particles. In addition, the first inorganic particles are preferably 95% by mass or less, more preferably 90% by mass or less, and even more preferably 80% by mass or less of the total mass of the inorganic particles.

[0079] On the other hand, in order to obtain excellent heat insulating performance within a temperature range exceeding 300° C., the second inorganic particles are preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 20% by mass or more, based on the total mass of the inorganic particles. Also, the second inorganic particles are preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less, based on the total mass of the inorganic particles.

[0080] (Average primary particle size of second inorganic particles) When second inorganic particles made of a metal oxide are contained in the heat transfer-suppressing sheet, if the average primary particle size of the second inorganic particles is from 1 μm to 50 μm, radiation heat transfer can be efficiently suppressed in a high temperature range of 500° C. or more. The average primary particle size of the second inorganic particles is more preferably from 5 μm to 30 μm, and most preferably 10 μm or less.

[0081] (Inorganic particle content) In this embodiment, when the total content of inorganic particles in the heat-transfer-suppressing sheet 10 is appropriately controlled, the heat insulation properties of the heat-transfer-suppressing sheet 10 can be sufficiently ensured. The total content of the inorganic particles is preferably 30 mass % or more, and more preferably 50 mass % or more, relative to the total mass of the heat-transfer-inhibiting sheet 10. Furthermore, if the total content of the inorganic particles is too high, the fiber content will relatively decrease, so in order to obtain an appropriate strength for the heat-transfer-inhibiting sheet 10, the total content of the inorganic particles is preferably 80 mass % or less, and more preferably 70 mass % or less, relative to the total mass of the heat-transfer-inhibiting sheet 10.

[0082] <Textile> The heat transfer-suppressing sheet 10 according to this embodiment has at least one type of fiber selected from inorganic fibers and organic fibers.

[0083] <Organic fiber> The organic fibers impart flexibility to the heat-transfer-suppressing sheet 10, and also have the effect of retaining the inorganic particles and improving the effect of retaining the strength and shape of the sheet. In addition to single-component organic fibers, binder fibers with a core-sheath structure can also be used as the organic fiber material in the heat-transfer-suppressing sheet 10. Binder fibers with a core-sheath structure have a core extending in the longitudinal direction of the fiber and a sheath formed so as to cover the outer circumferential surface of the core.

[0084] Whether a single-component organic fiber or a binder fiber with a core-sheath structure is used as the organic fiber material, part of the fiber surface melts when heated during production of heat-transfer-suppressing sheet 10, and then inorganic particles and other fibers are fused to the periphery of the organic fiber by cooling, thereby achieving excellent sheet strength.

[0085] When binder fibers having a core-sheath structure are used as the organic fiber material, the first organic material constituting the core and the second organic material constituting the sheath will be described below.

[0086] (First organic material) When a binder fiber having a core-sheath structure is used as the fiber, the first organic material constituting the core is not particularly limited as long as it has a melting point higher than that of the sheath present on the outer peripheral surface of the core, i.e., the second organic material. The first organic material may be at least one selected from polyethylene terephthalate, polypropylene, and nylon.

[0087] (Second organic material) When a binder fiber having a core-sheath structure is used as the organic fiber, the second organic material constituting the sheath is not particularly limited as long as it has a melting point lower than that of the first organic material constituting the core. The second organic material may be at least one selected from the group consisting of polyethylene terephthalate, polyethylene, polypropylene, and nylon. The melting point of the second organic material is preferably 90° C. or higher, and more preferably 100° C. or higher. The melting point of the second organic material is preferably 150° C. or lower, and more preferably 130° C. or lower.

[0088] (Organic fiber content) In the present embodiment, when the heat-transfer-inhibiting sheet 10 contains organic fibers, the effect of improving the strength of the heat-transfer-inhibiting sheet 10 can be sufficiently obtained by appropriately controlling the content of the organic fibers in the heat-transfer-inhibiting sheet 10. The organic fiber content is preferably 2 mass % or more, and more preferably 4 mass % or more, relative to the total mass of the heat-transfer-suppressing sheet 10. Furthermore, if the organic fiber content is too high, the inorganic particle content will relatively decrease, so in order to obtain the desired heat insulation performance, the organic fiber content is preferably 10 mass % or less, and more preferably 8 mass % or less, relative to the total mass of the heat-transfer-suppressing sheet 10.

[0089] (Organic fiber length) The fiber length of the organic fibers is not particularly limited, but from the viewpoint of ensuring moldability and processability, it is preferable that the average fiber length of the organic fibers is 10 mm or less. On the other hand, from the standpoint of improving the strength of heat-transfer-suppressing sheet 10, the average fiber length of the organic fibers is preferably 0.5 mm or more.

[0090] <Inorganic fibers> Because inorganic fibers have excellent strength, they act as aggregates for heat-transfer-inhibiting sheet 10, and can provide high compressive strength. Therefore, even when heat-transfer-inhibiting sheet 10 is interposed between battery cells 20a, 20b, and 20c and pressed by these battery cells, it is not significantly deformed and can retain its shape. In addition, because inorganic fibers have high high-temperature strength, heat-transfer-inhibiting sheet 10 can maintain its shape even when exposed to high temperatures.

[0091] As the inorganic fiber, a single inorganic fiber may be used, or two or more inorganic fibers may be used in combination. Examples of the inorganic fiber include ceramic fibers such as silica fiber, alumina fiber, alumina silicate fiber, zirconia fiber, carbon fiber, soluble fiber, refractory ceramic fiber, aerogel composite material, magnesium silicate fiber, alkaline earth silicate fiber, potassium titanate fiber, silicon carbide fiber, and potassium titanate whisker fiber, glass fibers such as glass fibers, glass wool, and slag wool, and mineral fibers such as rock wool, basalt fiber, wollastonite, and mullite fiber. These inorganic fibers are preferred in terms of heat resistance, strength, availability, etc. Among the inorganic fibers, silica-alumina fibers, alumina fibers, silica fibers, rock wool, alkaline earth silicate fibers, and glass fibers are particularly preferred in terms of ease of handling.

[0092] The cross-sectional shape of the inorganic fiber is not particularly limited, and examples thereof include a circular cross section, a flat cross section, a hollow cross section, a polygonal cross section, a core cross section, etc. Among them, modified cross section fibers having a hollow cross section, a flat cross section, or a polygonal cross section are preferably used because they have slightly improved heat insulation properties.

[0093] The preferred lower limit of the average fiber length of the inorganic fibers is 0.1 mm, and more preferably 0.5 mm. On the other hand, the preferred upper limit of the average fiber length of the inorganic fibers is 50 mm, and more preferably 10 mm. If the average fiber length of the inorganic fibers is less than 0.1 mm, the inorganic fibers are less likely to be entangled with each other, and the mechanical strength of the heat transfer-suppressing sheet may be reduced. On the other hand, if the average fiber length exceeds 50 mm, although a reinforcing effect is obtained, the inorganic fibers may not be tightly entangled with each other, or may be curled up by a single inorganic fiber, which may lead to continuous voids, which may result in a decrease in heat insulation.

[0094] The preferred lower limit of the average fiber diameter of the inorganic fibers is 1 μm, more preferably 2 μm, and even more preferably 3 μm. On the other hand, the preferred upper limit of the average fiber diameter of the inorganic fibers is 15 μm, and more preferably 10 μm. If the average fiber diameter of the inorganic fibers is less than 1 μm, the mechanical strength of the inorganic fibers themselves may be reduced. From the viewpoint of the effect on human health, the average fiber diameter of the inorganic fibers is preferably 3 μm or more. On the other hand, if the average fiber diameter of the inorganic fibers is more than 15 μm, the solid heat transfer through the inorganic fibers may increase, leading to a decrease in heat insulation, and the moldability and strength of the heat transfer-suppressing sheet may be deteriorated.

[0095] (Inorganic fiber content) In this embodiment, when the heat-transfer-suppressing sheet 10 contains inorganic fibers, the content of the inorganic fibers is preferably 3 mass % or more and 15 mass % or less relative to the total mass of the heat-transfer-suppressing sheet.

[0096] The content of inorganic fibers is more preferably 5% by mass or more and 10% by mass or less based on the total mass of the heat-transfer-suppressing sheet. By setting the content at such a level, the shape retention, pressing force resistance, wind pressure resistance, and inorganic particle retention ability of the inorganic fibers are exhibited in a well-balanced manner. Furthermore, when the heat-transfer-suppressing sheet 10 contains organic fibers and inorganic fibers as fibers, the content of inorganic fibers can be appropriately controlled so that the organic fibers and inorganic fibers are entangled with each other to form a three-dimensional network, thereby further improving the effect of retaining inorganic particles, etc.

[0097] <Other compounding materials> The heat-transfer-suppressing sheet according to this embodiment can further contain, as necessary, a binder, a colorant, etc. All of these are useful for the purposes of reinforcing the heat-transfer-suppressing sheet and improving its formability, and the total amount of these is preferably 10 mass % or less based on the total mass of the heat-transfer-suppressing sheet.

[0098] (Hot melt powder) For example, hot melt powder can be used as the binder. Hot melt powder is a powder that has the property of melting when heated. By adding hot melt powder to a mixture of materials and heating it, the hot melt powder melts, and when cooled, it hardens in a state containing the materials, such as fibers and inorganic particles. Therefore, the shape retention of the heat transfer-suppressing sheet can be improved. As the hot melt powder, those having various melting points can be used, so a hot melt powder having an appropriate melting point can be selected according to the manufacturing conditions of the heat transfer-suppressing sheet.

[0099] (Hot melt powder content) When hot melt powder is added to the mixture of materials, even a small amount of the hot melt powder can improve the shape retention of the heat-transfer-suppressing sheet. Therefore, the hot melt powder content is preferably 0.5 mass % or more, and more preferably 1 mass % or more, relative to the total mass of the mixture. On the other hand, when the content of the hot melt powder is increased, the content of the inorganic particles and fibers is relatively decreased, so in order to obtain the desired heat insulating performance, the content of the hot melt powder is preferably 5 mass% or less, and more preferably 4 mass% or less, relative to the total mass of the mixture.

[0100] [Method of manufacturing heat transfer suppression sheet] <Method of manufacturing the heat transfer-suppressing sheet according to the first embodiment> An example of a method for producing the heat transfer-suppressing sheet according to the first embodiment will be described below with reference to FIG. For example, fibers (glass fibers 1), inorganic particles (titania 3, nanosilica 4), and a binder (not shown) are charged in a predetermined ratio into a mixer such as a V-type mixer to prepare a mixture. The mixture obtained is then charged into a predetermined mold and pressed with a press or the like. The resulting molded body is heated and then cooled to obtain a heat insulating material 9 processed into a sheet shape.

[0101] Thereafter, the heat insulating material 9 is immersed in a solution containing the liquid repellent substance 2 and then dried, thereby producing the heat transfer-suppressing sheet 10 having the liquid repellent substance 2 adhered to the sheet surface.

[0102] In the manufacturing method according to the first embodiment described above, the insulating material 9 is immersed in a solution containing the liquid-repellent substance 2 and then dried, so that the liquid-repellent substance 2 penetrates between the fine inorganic particles on the sheet surface and can be adhered to the sheet surface without any gaps, thereby obtaining excellent liquid repellency.

[0103] 4, when voids 7 having openings 7a are formed in the heat insulating material 9, the liquid repellent substance 2 penetrates into the heat insulating material 9 through the openings 7a, and the inner wall portions of the three-dimensionally connected voids 7 are also imparted with liquid repellency. Therefore, even if cracks occur in the area of ​​the sheet surface to which the liquid repellent substance 2 is attached and condensed water 5 or the like penetrates into the interior, the three-dimensionally connected voids 7 can suppress further penetration of the condensed water 5. Furthermore, even if condensed water 5 or the like penetrates into the heat transfer-inhibiting sheet 10 through the openings 7a during use of the battery, the inner wall portions of the voids 7 have liquid repellency, so that the condensed water 5 or the like does not penetrate into other portions and is easily discharged from the openings 7a.

[0104] <Method of manufacturing heat transfer-suppressing sheet according to the second embodiment> An example of a method for producing the heat-transfer-suppressing sheet according to the second embodiment will be described below with reference to FIG. First, fibers (glass fibers 1), inorganic particles (titania 3, nanosilica 4), etc. are mixed in a predetermined ratio with a solution containing a liquid repellent substance 2, and after stirring with a stirrer, the resulting mixture is dried. This produces a mixture in which the liquid repellent substance 2 is attached to at least a portion of the surfaces of the fibers and inorganic particles. Thereafter, the resulting mixture and a binder (not shown) are placed in a predetermined mold, and pressure is applied with a press or the like. The resulting molded body is heated and then cooled to produce the heat-transfer-suppressing sheet 10 processed into a sheet shape.

[0105] In the manufacturing method according to the second embodiment, since the liquid repellent substance is attached to the surfaces of the fibers and inorganic particles used as materials, even if condensation water 5 or the like penetrates from the surface to a certain extent, it does not penetrate completely, and further penetration can be prevented by the fibers and inorganic particles having the liquid repellent substance 2 attached to their surfaces. Therefore, it is possible to prevent a decrease in insulation due to the penetration of condensation water 5, and by appropriately selecting the liquid repellent substance 2, it is possible to prevent a decrease in insulation due to the penetration of the electrolyte.

[0106] As shown in the manufacturing method of the heat transfer-inhibiting sheet according to the second embodiment, a liquid-repellent substance 2 is first applied to the surface of the material, which is then processed into a sheet, and then, following the manufacturing method according to the first embodiment, further liquid-repellent substance 2 is applied to the sheet surface, thereby making it possible to further improve the liquid repellency.

[0107] As described above, the heat transfer-suppressing sheet 10 according to the first and second embodiments is preferably produced by a dry method. When using the dry method, it is preferable to use at least one type of inorganic particles selected from dry silica and silica aerogel, which are suitable for the dry method.

[0108] <Method of manufacturing heat transfer-suppressing sheet according to the third embodiment> An example of a method for producing the heat-transfer-suppressing sheet according to the third embodiment will be described below. Fibers (glass fibers 1), liquid-repellent inorganic particles (hydrophobic silica), and a binder (not shown) are charged in a predetermined ratio into a mixer such as a V-type mixer to prepare a mixture. The mixture thus obtained is then charged into a predetermined mold and pressed with a press or the like to obtain a molded body, which is then heated and cooled to obtain a heat-transfer-suppressing sheet processed into a sheet shape.

[0109] In the manufacturing method according to the third embodiment, since the inorganic particles used as the material have a liquid-repellent effect, there is no need to perform a liquid-repellent treatment on the material stage or the heat insulating material processed into a sheet after processing into a sheet, and the heat insulating material can be easily manufactured. Note that only a part of the inorganic particles used as the material may be hydrophobic silica, and the rest may be other inorganic particles, and even with such a configuration, the water-repellent effect can be obtained.

[0110] As shown in the manufacturing method of the heat transfer-inhibiting sheet according to the third embodiment, even when inorganic particles having liquid repellency are used as the liquid repellent substance 2, the liquid repellency can be further improved by processing this into a sheet and then further attaching the liquid repellent substance 2 to the sheet surface in accordance with the manufacturing method according to the first embodiment.

[0111] <Other manufacturing methods> The manufacturing method of the present invention is not particularly limited as long as it can manufacture a heat-transfer-suppressing sheet that satisfies the requirements of the present invention. In addition to the manufacturing methods of the heat-transfer-suppressing sheet according to the above first to third embodiments, for example, a method of using inorganic particles in which silicone, synthetic resin, or the like is attached to the surface of oxide particles to perform a liquid-repellent treatment can be used. A heat-transfer-suppressing sheet having liquid repellency can be manufactured by a method similar to that of the manufacturing method of the heat-transfer-suppressing sheet according to the third embodiment.

[0112] (Heating temperature) When a core-sheath binder fiber is used as the fiber, the melting point of the first organic material constituting the core is higher than that of the second organic material constituting the sheath, so that when the mixture is heated, a heating temperature is selected that melts the sheath while leaving the core. In this way, by appropriately adjusting the heating temperature, other fibers and inorganic particles can be attached to the outer peripheral surface of the core after cooling, and the inorganic particles can be held while a three-dimensional, strong skeleton is formed. As a result, the shape of the entire heat transfer-suppressing sheet can be held with even higher strength.

[0113] (Thickness of heat transfer suppression sheet) The thickness of the heat-transfer-suppressing sheet according to the present embodiment is not particularly limited, but is preferably 0.05 mm or more and 10 mm or less. If the thickness is 0.05 mm or more, sufficient compressive strength can be obtained while ensuring thermal insulation. On the other hand, if the thickness is 10 mm or less, a desired size for the battery pack can be achieved.

[0114] [Battery pack] An example of a battery pack to which the heat-transfer-suppressing sheet 10 according to the embodiment of the present invention is applied is shown in Fig. 2. The configuration and effects of the battery pack will now be described in detail with reference to Fig. 2. As mentioned above, the heat-transfer-suppressing sheet 10 shown in Fig. 2 can be replaced with other heat-transfer-suppressing sheets within the scope of the present invention.

[0115] As shown in FIG. 2, the battery pack 100 includes a plurality of battery cells 20a, 20b, and 20c, and a heat-transfer-suppressing sheet according to this embodiment, and the plurality of battery cells are connected in series or in parallel. 2, the heat-transfer-restricting sheet 10 according to this embodiment is interposed between battery cell 20a and battery cell 20b, and between battery cell 20b and battery cell 20c. Furthermore, the battery cells 20a, 20b, and 20c and the heat-transfer-restricting sheet 10 are housed in a battery case 30. The heat-transfer-suppressing sheet 10 is as described above.

[0116] In the battery pack 100 configured in this manner, when the temperature of a certain battery cell is repeatedly increased and cooled and condensation water 5 forms on the surface of the battery cell, the heat transfer suppression sheet 10 is present between the battery cells, which can prevent the intrusion of moisture, and therefore it is possible to prevent short circuits between the battery cells. Furthermore, if the temperature of a battery cell rises significantly and is damaged due to expansion or the like, if the liquid-repellent material attached to the heat-transfer-suppressing sheet 10 is appropriately selected, it is possible to suppress the intrusion of the leaked electrolyte, thereby preventing a chain reaction of thermal runaway caused by the intrusion of high-temperature electrolyte.

[0117] In the battery pack of this embodiment, the heat-transfer-suppressing sheet 10 arranged between the battery cells 20a, 20b, 20c and the battery case 30 may be in contact with the battery cells or may have a gap therebetween. However, if there is a gap between the heat-transfer-suppressing sheet 10 and the battery cells 20a, 20b, 20c, the allowable deformation of the battery cells can be increased even if the temperature of any one of the multiple battery cells rises and the volume expands.

[0118] The heat-transfer-suppressing sheet 10 according to this embodiment can be manufactured into various shapes depending on the manufacturing method. Therefore, it can be adapted to any shape without being affected by the shapes of the battery cells 20a, 20b, 20c and the battery case 30. Specifically, it can be applied to cylindrical batteries, flat batteries, etc. in addition to square batteries. [Explanation of symbols]

[0119] 1. Glass fiber 2 Liquid repellent material 3. Titania 4. Nano Silica 5 Condensation water 6. Organic Fibers 7 Vacancies 7a opening 8 Intake and drainage paths 9,19 Insulation 10. Heat transfer suppression sheet 14 Inorganic particles 20a, 20b, 20c Battery cells 30 Battery case 100 battery packs

Claims

1. A heat transfer suppression sheet interposed between a plurality of battery cells, At least one type of fiber selected from inorganic fibers and organic fibers; a liquid-repellent substance having a surface tension smaller than that of water; Contains inorganic particles, A heat transfer-suppressing sheet, wherein the inorganic particles are a mixture of large-diameter particles and small-diameter particles.

2. A heat transfer suppression sheet as described in claim 1, wherein at least a portion of the inorganic particles are the liquid-repellent substance.

3. The heat transfer suppressing sheet according to claim 2 , wherein the liquid repellent material is hydrophobic silica.

4. A heat transfer inhibitor sheet as described in claim 1, characterized in that the liquid repellent substance is adhered to at least a portion of the surface of the heat transfer inhibitor sheet, the surface of the inorganic particles inside the heat transfer inhibitor sheet, and the surface of the fibers inside the heat transfer inhibitor sheet.

5. 5. The heat transfer-suppressing sheet according to claim 4, wherein the liquid-repellent substance is at least one selected from the group consisting of paraffin-based oils, naphthene-based oils, hydrocarbon-based synthetic oils, ester-based synthetic oils, animal and vegetable oils, silicone resins, fluororesins, rosin-based sizing agents, and alkyl ketene dimer sizing agents.

6. 5. The heat transfer-suppressing sheet according to claim 4, wherein the inorganic particles are particles made of at least one inorganic material selected from the group consisting of oxide particles, carbide particles, nitride particles, and inorganic hydrate particles.

7. The heat transfer-suppressing sheet according to claim 6, wherein the inorganic particles include at least one type of particles selected from the group consisting of dry silica particles and silica aerogel.

8. 8. The heat transfer-suppressing sheet according to claim 7, wherein the inorganic particles further include particles of at least one type selected from the group consisting of titania, zircon, zirconia, silicon carbide, zinc oxide, and alumina.

9. The heat transfer-suppressing sheet according to claim 1 , wherein the surface tension of the liquid repellent material is lower than the surface tension of the electrolyte contained in the battery cell.

10. 10. The heat transfer-suppressing sheet according to claim 9, wherein the liquid repellent substance has a surface tension of 45 mN / m or less.

11. 11. The heat transfer-suppressing sheet according to claim 10, wherein the liquid repellent material is at least one selected from the group consisting of silicone resin and fluororesin.

12. It has a plurality of three-dimensionally connected pores, The heat-transfer-suppressing sheet according to claim 1 , wherein the pores are open toward a surface of the heat-transfer-suppressing sheet.

13. 13. A battery pack comprising a plurality of battery cells and the heat transfer-suppressing sheet according to claim 1, the plurality of battery cells being connected in series or in parallel.

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