Method for manufacturing heat transfer inhibiting sheet, heat transfer inhibiting sheet, and battery pack

Abstract

The present application provides a heat transfer inhibiting sheet manufacturing method, a heat transfer inhibiting sheet, and a battery pack. The heat transfer inhibiting sheet has strength capable of maintaining the shape of the heat transfer inhibiting sheet, and high inorganic particle holding performance, thereby maintaining excellent heat insulation performance. The heat transfer inhibiting sheet manufacturing method has a processing step of processing a mixture into a sheet shape, the mixture including inorganic particles (4), binder fibers (3) having a core-sheath structure, and a hot melt powder. The binder fibers (3) having the core-sheath structure have a core portion (1) extending in the length direction thereof, and a sheath portion (2) formed so as to cover the outer circumferential surface of the core portion (1). The melting point of a first organic material constituting the core portion (1) is higher than the melting point of a second organic material constituting the sheath portion (2) and the melting point of a third organic material constituting the hot melt powder.

Description

TECHNICAL FIELD

[0001] The present application relates to a heat transfer inhibiting sheet and a method for manufacturing the same, and a battery pack having the heat transfer inhibiting sheet. BACKGROUND

[0002] In recent years, from the viewpoint of environmental protection, development of an electric automobile or a hybrid automobile, etc. driven by an electric motor is being actively conducted. In the electric automobile or the hybrid automobile, etc., a battery pack configured by connecting a plurality of battery cells in series or in parallel is mounted as a power source for the electric motor for driving.

[0003] In addition, the battery cells mainly use a lithium ion secondary battery which can have a high capacity and a high output compared to a lead storage battery, a nickel hydrogen battery, etc. Moreover, in the case where a certain battery cell sharply heats up due to internal short circuit of the battery, overcharge, etc., and thereafter, heat runaway continues, heat from the battery cell where the heat runaway has occurred propagates to the other battery cells adjacent thereto, and thus, heat runaway of the other battery cells can be caused.

[0004] As a method for inhibiting the propagation of heat from the battery cell where the heat runaway as described above has occurred, a method of interposing a heat insulating sheet between the battery cells is generally conducted.

[0005] For example, Patent Literature 1 discloses a heat insulating sheet for a battery pack, which contains first particles composed of silicon dioxide nanoparticles and second particles composed of a metal oxide, and the content of the first particles is limited. In addition, Patent Literature 1 describes that the heat insulating sheet can contain a binding material composed of at least one selected from a fiber, a binder, and a heat-resistant resin.

[0006] PRIOR ART DOCUMENTS

[0007] Patent Literature 1: Japanese Patent Application Laid-Open No. 2021-34278 SUMMARY

[0008] PROBLEMS TO BE SOLVED BY THE INVENTION

[0009] However, in the battery pack in recent years, the capacity of the battery cell is further improved, and thus, the expansion rate at the time of charge and discharge is increased. Therefore, in the case where the heat insulating sheet is arranged between the battery cells of the battery pack, if the strength of the entire heat insulating sheet is low, the heat insulating sheet is compressed due to the expansion of the battery cell at the time of charge and discharge of the battery cell, etc., and powder is detached, and the heat insulating performance is decreased. As a result, in the case where the battery cell heat runs away and becomes high temperature, the effect of the heat insulating sheet cannot be exerted, and sometimes, heat chain is caused. Thus, development of a heat insulating sheet and a method for manufacturing the same which have a high strength capable of maintaining the shape, can inhibit powder detachment, and can maintain excellent heat insulating properties is required.

[0010] The heat-insulating sheet described in the above Patent Document 1 maintains excellent heat-insulating properties even in the case where the compressive stress is increased, but further improvement is required with respect to the properties of heat-insulating properties, strength, and suppression of powder drop.

[0011] The present application was completed in view of the above problems, and aims to provide a heat transfer suppressing sheet manufacturing method, a heat transfer suppressing sheet, and a battery pack having the heat transfer suppressing sheet, the heat transfer suppressing sheet having strength capable of maintaining its shape even in the case where a compressive stress is applied to the heat transfer suppressing sheet, and high inorganic particle holding performance, thereby being capable of maintaining excellent heat-insulating properties.

[0012] Means for solving the technical problem

[0013] The above object of the present application is achieved by the following [1] relating to the heat transfer suppressing sheet manufacturing method.

[0014] [1] A heat transfer suppressing sheet manufacturing method characterized by having a processing step of processing a mixture into a sheet shape, the mixture containing inorganic particles, a hot melt powder, and an adhesive fiber having a core-sheath structure,

[0015] the adhesive fiber having the core-sheath structure has a core portion extending in a length direction thereof and a sheath portion formed so as to cover an outer circumferential surface of the core portion,

[0016] a melting point of a first organic material constituting the core portion is higher than a melting point of a second organic material constituting the sheath portion and a melting point of a third organic material constituting the hot melt powder.

[0017] Further, the preferred embodiments of the present application relating to the heat transfer suppressing sheet manufacturing method relate to the following [2] to [9].

[0018] [2] In the heat transfer suppressing sheet manufacturing method of [1], characterized in that the melting point of the third organic material is lower than the melting point of the second organic material.

[0019] [3] In the heat transfer suppressing sheet manufacturing method of [1], characterized in that the melting point of the third organic material is higher than the melting point of the second organic material.

[0020] [4] In the heat transfer suppressing sheet manufacturing method of any one of [1] to [3], characterized in that the melting point of the first organic material is higher than the higher one of the melting point of the second organic material and the melting point of the third organic material by 60°C or more.

[0021] [5] The method for producing the heat transfer inhibiting sheet according to any one of [1] to [4], wherein the processing step includes a step of pressurizing the mixture and a step of heating the mixture.

[0022] [6] The method for producing the heat transfer inhibiting sheet according to [5], wherein the heating temperature in the step of heating the mixture is set to a temperature higher than the higher one of the melting point of the second organic material and the melting point of the third organic material and lower than the melting point of the first organic material.

[0023] [7] The method for producing the heat transfer inhibiting sheet according to any one of [1] to [6], wherein, in the processing step, the mixture is processed into a sheet shape by a dry method.

[0024] [8] The method for producing the heat transfer inhibiting sheet according to any one of [1] to [7], wherein the inorganic particles include at least one kind of particle selected from among dry silica particles and silica aerogel.

[0025] [9] The method for producing the heat transfer inhibiting sheet according to [8], wherein the inorganic particles further include at least one kind of particle selected from among titanium dioxide, zircon, zirconium oxide, silicon carbide, zinc oxide, and aluminum oxide.

[0026] Further, the above object of the present application is achieved by the structure of the heat transfer inhibiting sheet according to the following

[10] .

[0027]

[10] A heat transfer inhibiting sheet, comprising:

[0028] inorganic particles;

[0029] an organic fiber composed of a first organic material;

[0030] a cladding portion that clads an outer peripheral surface of the organic fiber; and

[0031] a solidified portion formed in a region different from the cladding portion,

[0032] the cladding portion includes the inorganic particles and a second organic material having a melting point lower than the melting point of the first organic material,

[0033] the solidified portion includes the inorganic particles and a third organic material having a melting point lower than the melting point of the first organic material.

[0034] Further, preferred embodiments of the present application relating to the heat transfer inhibiting sheet relate to the following

[11] to

[19] .

[0035]

[11] The heat transfer inhibiting sheet according to

[10] , characterized in that

[0036] the solidified portions have a plurality of solidified layers on a surface of the heat transfer inhibiting sheet,

[0037] a crack is formed between the plurality of solidified layers.

[0038]

[12] The heat transfer inhibiting sheet according to

[10] or

[11] , characterized in that

[0039] the melting point of the third organic material is lower than the melting point of the second organic material.

[0040]

[13] The heat transfer inhibiting sheet according to

[10] or

[11] , characterized in that the melting point of the third organic material is higher than the melting point of the second organic material.

[0041]

[14] The heat transfer inhibiting sheet according to any one of

[10] to

[13] , characterized in that both the melting point of the second organic material and the melting point of the third organic material are lower than the melting point of the first organic material by 60°C or more.

[0042]

[15] The heat transfer inhibiting sheet according to any one of

[10] to

[14] , characterized in that the first organic material is at least one selected from the group consisting of polyethylene terephthalate, polypropylene, and nylon,

[0043] the second organic material is at least one selected from the group consisting of polyethylene terephthalate, polyethylene, polypropylene, and nylon.

[0044]

[16] The heat transfer inhibiting sheet according to any one of

[10] to

[15] , characterized in that the third organic material is at least one selected from the group consisting of polyethylene, polyester, polyamide, and ethylene-vinyl acetate copolymer.

[0045]

[17] The heat transfer inhibiting sheet according to any one of

[10] to

[16] , characterized in that the inorganic particles are at least one kind of particles composed of inorganic material selected from the group consisting of oxide particles, carbide particles, nitride particles, and inorganic hydrate particles.

[0046]

[18] The heat transfer inhibiting sheet according to

[17] , characterized in that the inorganic particles contain at least one kind of particles selected from the group consisting of dry silica particles and silica aerogel.

[0047]

[19] The heat transfer inhibiting sheet according to

[18] , characterized in that the inorganic particles further contain at least one kind of particles selected from the group consisting of titanium dioxide, zircon, zirconium oxide, silicon carbide, zinc oxide, and aluminum oxide.

[0048] Further, the above object of the present application is achieved by the following

[20] relating to the structure of a battery pack.

[0049]

[20] A battery pack having the heat transfer inhibiting sheet of any one of

[10] to

[19] and a plurality of battery cells connected in series or in parallel.

[0050] Effects of the Invention

[0051] The manufacturing method of the heat transfer inhibiting sheet of the present application has a processing step of processing a mixture into a sheet shape, the mixture containing inorganic particles, a hot melt powder, and an adhesive fiber having a core-sheath structure, the melting point of a first organic material constituting a core portion of the adhesive fiber being higher than the melting points of a second organic material constituting a sheath portion and a third organic material constituting the hot melt powder. Therefore, the core portion can be left to form a skeleton at the time of manufacturing, and the sheath portion is melted to fuse the surrounding inorganic particles, and further, even in a region where the sheath portion is not present, the hot melt powder is melted to form a solidified portion together with the surrounding inorganic particles, so that the inorganic particles can be inhibited from falling off from the heat transfer inhibiting sheet, and a heat transfer inhibiting sheet achieving both excellent strength and heat transfer inhibiting effect can be obtained. Further, according to the manufacturing method of the heat transfer inhibiting sheet of the present application, the melting point of the core portion of the adhesive fiber is higher than the melting points of the sheath portion and the hot melt powder, so that temperature control for leaving only the core portion and melting the sheath portion and the hot melt powder becomes easy.

[0052] Further, according to the heat transfer inhibiting sheet of the present application, since the inorganic particles having excellent heat transfer inhibiting effect are contained, excellent thermal insulation can be obtained. Further, according to the heat transfer inhibiting sheet of the present application, an organic fiber and a cladding portion cladding the outer peripheral surface thereof are provided, and by the cladding portion, the apparent fiber diameter of the organic fiber becomes thick, so that the strength of the skeleton constituted by the organic fiber can be improved. Furthermore, according to the heat transfer inhibiting sheet of the present application, in a region other than the skeleton constituted by the organic fiber and the cladding portion, a solidified portion in which the hot melt powder is solidified together with the inorganic particles is also provided. Therefore, excellent strength can be obtained, and thereby, powder falling can be prevented, and excellent thermal insulation performance can be maintained.

[0053] According to the battery pack of the present application, since the heat transfer inhibiting sheet having high strength and excellent thermal insulation performance as described above is provided, heat runaway of the battery cells in the battery pack and expansion of the flame to the outside of the battery case can be inhibited. BRIEF DESCRIPTION OF DRAWINGS

[0054] Figure 1 is a schematic view showing the state after mixing of raw materials in a part of the manufacturing method of the heat transfer inhibiting sheet of the embodiment of the present application.

[0055] Figure 2is a schematic view showing a structure of a heat transfer inhibiting sheet manufactured by a manufacturing method according to an embodiment of the present application.

[0056] Figure 3 is a photographic substitute drawing showing a surface of a heat transfer inhibiting sheet according to an embodiment of the present application.

[0057] Figure 4 is a photographic substitute drawing showing states of particles of wet silica and dry silica.

[0058] Figure 5 is a graph showing changes in thermal conductivities of wet silica and dry silica at respective temperatures.

[0059] Figure 6 is a schematic view showing a battery pack according to an embodiment of the present application.

[0060] Figure 7 is a photographic substitute drawing showing a surface of Example 1.

[0061] Figure 8 is a photographic substitute drawing showing a surface of Comparative Example 1.

[0062] Figure 9 is a schematic view showing a method for measuring a flying rate.

[0063] Figure 10 is a graph showing changes in a flying rate with a number of hits in a case where a vertical axis is the flying rate and a horizontal axis is the number of hits.

[0064] Explanation of Reference Numerals

[0065] 1: core portion;

[0066] 2: sheath portion;

[0067] 3: binder fiber;

[0068] 4: inorganic particle;

[0069] 5: fusion-bonded portion;

[0070] 6: fiber portion;

[0071] 9: mixture;

[0072] 12: crack;

[0073] 13: heat transfer inhibiting sheet;

[0074] 16: cured portion;

[0075] 17: cured layer;

[0076] 20a, 20b, 20c: battery cell;

[0077] 30: battery case

[0078] 100: battery pack DETAILED DESCRIPTION

[0079] The inventors of the present application have intensively studied a heat transfer inhibiting sheet capable of solving the above-described technical problems.

[0080] As a result, it has been found that by using an adhesive fiber of a core-sheath structure having a core portion with a high melting point and a sheath portion with a low melting point, and a hot melt powder, the core portion can be made to serve as a skeleton to obtain high strength, and even in regions other than the skeleton, the hot melt powder is solidified to increase the strength, and furthermore, by causing the sheath portion and the hot melt powder to melt and hold the inorganic particles, it is possible to inhibit the powder from falling off.

[0081] Specifically, at the time of manufacturing the heat transfer inhibiting sheet, when heating the sheet material, if the heating temperature is set so as not to melt the core portion, only the sheath portion having a lower melting point than the core portion and the hot melt powder can be caused to melt. Then, by cooling, the sheath portion is re-melted on the core portion in a state of containing the inorganic particles around it. In addition, the hot melt powder is solidified in a state of containing the inorganic particles around it. Therefore, after cooling, the core portion and the re-melted portion containing the inorganic particles become the skeleton, and between the skeletons, the solidified portion containing the hot melt powder and the inorganic particles supports the skeleton, so it is possible to increase the strength of the heat transfer inhibiting sheet. In addition, the sheath portion is melted and re-melted on the core portion together with the inorganic particles, and the hot melt powder is solidified on the surface of the heat transfer inhibiting sheet to form a plurality of solidified layers, whereby the inorganic particles on the surface of the heat transfer inhibiting sheet are held to the surface of the sheet, so it is possible to inhibit the powder from falling off. As a result, even in the case where pressure and impact are applied to the heat transfer inhibiting sheet, it is possible to maintain high thermal insulation performance.

[0082] Hereinafter, the manufacturing method of the heat transfer inhibiting sheet, the heat transfer inhibiting sheet, and the battery pack according to the embodiments of the present application will be described in detail. Furthermore, the present application is not limited to the embodiments described below, and can be arbitrarily changed and implemented within the scope of the gist of the present application.

[0083] [1. Manufacturing method of heat transfer inhibiting sheet]

[0084] Figure 1 is a schematic view showing the state after mixing raw materials in a part of the manufacturing method of the heat transfer inhibiting sheet according to the embodiments of the present application. Figure 2 is a schematic view showing the structure of the heat transfer inhibiting sheet manufactured by the manufacturing method according to the embodiments of the present application. In addition, Figure 3 is a photographic substitute view showing the surface of the heat transfer inhibiting sheet according to the embodiments of the present application.

[0085] (Processing steps)

[0086] like Figure 1 As shown, firstly, adhesive fibers 3 with a core-sheath structure, inorganic particles 4, and hot-melt powder 14 are added to a mixer such as a V-type mixer in a predetermined ratio to prepare mixture 9. In this embodiment, when manufacturing the heat transfer suppression sheet by a dry method, solvents such as water required for molding by a wet method are not added to mixture 9. However, during the manufacture of the heat transfer suppression sheet, a small amount of solvent such as water may be added to prevent the handling of raw materials from becoming difficult due to the flying of inorganic particles and other powders. For example, by adding a small amount of solvent such as water to mixture 9, the scattering of inorganic particles during manufacturing can be further suppressed.

[0087] Furthermore, the adhesive fiber 3 has a core 1 extending along the length of the fiber and a sheath 2 formed to cover the outer peripheral surface of the core 1. The core 1 is made of a first organic material, and the sheath 2 is made of a second organic material. Additionally, the melting point of the first organic material is higher than that of the second organic material.

[0088] Furthermore, the hot-melt powder 14 is formed by molding a third organic material, such as ethylene-vinyl acetate copolymer (EVA), into a powder form. Additionally, the melting point of the first organic material constituting the core 1 is higher than the melting point of the third organic material constituting the hot-melt powder 14. The hot-melt powder 14 will be described later.

[0089] Then, the obtained mixture 9 is placed into a prescribed mold, pressurized using a stamping press or the like, and heated, thereby melting the sheath 2 of the adhesive fiber 3 to form a molten portion (not shown) containing inorganic particles 4 surrounding the core 1. Simultaneously, the hot-melt powder also melts, forming a molten portion (not shown) in the area outside the core 1. Then, as... Figure 2 As shown, by cooling the heated mixture 9, the molten sheath 2 is re-clad onto the core 1, forming a cladding portion 5 comprising a second organic material constituting the sheath 2 and inorganic particles 4. The cladding portion 5 covers at least a portion of the surface of the core 1 and together with the core 1 forms a fiber portion 6. Furthermore, the molten hot-melt powder 14 solidifies while containing the surrounding inorganic particles 4, forming a solidified portion 16 in all regions between the plurality of fiber portions 6. The solidified portion 16 further comprises the inorganic particles 4 and a third organic material constituting the hot-melt powder 14. In this way, a heat transfer suppression sheet 13 processed into a sheet shape can be obtained.

[0090] In this embodiment, the material of the heat transfer suppression sheet 13 includes hot-melt powder 14, which, when melted by heating, easily segregates on the surface of the molded body. Therefore, as... Figure 3As shown, a thin solidified layer 17 is formed on the surface of the heat transfer inhibiting sheet 13. In addition, the solidified portion 16 includes the thin solidified layers 17 dispersed in a plurality of regions, and a crack 12 is sometimes formed between the plurality of solidified layers 17.

[0091] According to the manufacturing method related to the present embodiment, the first organic material constituting the core portion 1 has a higher melting point than the second organic material constituting the sheath portion 2 and the third organic material constituting the hot melt powder 14, and thus, when the mixture 9 is heated, the core portion 1 can be left while the sheath portion 2 and the hot melt powder 14 are melted. Therefore, by the core portion 1, the strength of the heat transfer inhibiting sheet 13 can be ensured.

[0092] In addition, by cooling, the sheath portion 2 is re-melted to the core portion 1 in a state of including the surrounding inorganic particles 4, and a build-up portion 5 is formed, and the hot melt powder 14 is solidified in a state of including the surrounding inorganic particles 4, and a solidified portion 16 is formed. Therefore, the outer peripheral surface of the core portion 1 is covered with the build-up portion 5, and the inorganic particles 4 can be held. In addition, in a region other than the build-up portion 5, the inorganic particles 4 can also be held by the solidified portion 16. In particular, as described above, the hot melt powder 14 that is melted by heating is likely to segregate on the surface of the molded body, and a thin solidified layer 17 is formed on the surface of the heat transfer inhibiting sheet 13, and thus a very high powder drop-out inhibiting effect can be obtained.

[0093] Further, in the present embodiment, if the crack 12 is formed between the thin solidified layers 17 dispersed in a plurality of regions, when the heat transfer inhibiting sheet 13 is arranged between a plurality of battery cells, the heat transfer inhibiting sheet 13 is likely to deform along with the expansion and contraction of the battery cells at the time of charge and discharge. Therefore, the breakage of the heat transfer inhibiting sheet 13 can be inhibited, and the load on the adjacent battery cells can also be reduced.

[0094] In addition, the fiber portion 6 constituted by the core portion 1 and the build-up portion 5 has a relatively thick fiber diameter, and thus has a higher strength than the strength of the core portion 1 alone. In addition, in the mixture 9, the binder fibers 3 exist in an irregular direction, and the binder fibers 3 sometimes contact each other at a portion. Thus, as shown in the contact portion 11 of FIG. 1, when the melted sheath portion 2 is cooled, the adjacent core portions 1 are fused to each other by the build-up portion 5, and a three-dimensional skeleton is formed. Furthermore, since the solidified portion 16 including the hot melt powder 14 and the inorganic particles 4 supports the skeleton between the skeletons, the shape of the entire heat transfer inhibiting sheet can be maintained to be higher in strength, and as a result, even when a pressure or an impact is applied to the heat transfer inhibiting sheet, the high heat insulating performance can be maintained. Figure 2 Figure 3 In addition, the fiber portion 6 constituted by the core portion 1 and the build-up portion 5 has a relatively thick fiber diameter, and thus has a higher strength than the strength of the core portion 1 alone. In addition, in the mixture 9, the binder fibers 3 exist in an irregular direction, and the binder fibers 3 sometimes contact each other at a portion. Thus, as shown in the contact portion 11 of FIG. 1, when the melted sheath portion 2 is cooled, the adjacent core portions 1 are fused to each other by the build-up portion 5, and a three-dimensional skeleton is formed. Furthermore, since the solidified portion 16 including the hot melt powder 14 and the inorganic particles 4 supports the skeleton between the skeletons, the shape of the entire heat transfer inhibiting sheet can be maintained to be higher in strength, and as a result, even when a pressure or an impact is applied to the heat transfer inhibiting sheet, the high heat insulating performance can be maintained.

[0095] ​Further, as the binder fiber, even in the case where an organic fiber not having a core-sheath structure is used, the core of the binder fiber can be left and only the surface can be melted by temperature setting, so that the inorganic particles are coated on the surface. However, in the production of the heat transfer inhibiting sheet, heating is generally performed from one side or both sides in the direction perpendicular to the thickness direction, and since a material having high heat insulation performance is used, the temperature is difficult to be raised to the same degree on the surface side and the center side in the thickness direction of the sheet. That is, in the case where the temperature is set so that only the surface of the organic fiber is melted on the surface side of the sheet, the surface of the organic fiber does not melt on the center side of the sheet, and the holding force of the inorganic particles 4 is reduced. Further, in the case where the temperature is set so that the surface of the organic fiber is melted on the center side of the sheet, the organic fiber is melted to the radial center on the surface side of the sheet, and it is difficult to ensure the strength of the sheet.

[0096] On the contrary, in the present embodiment, the melting point of the first organic material constituting the core portion 1 is higher than the melting point of the second organic material constituting the sheath portion 2, and thus the temperature for leaving the core portion 1 and melting the sheath portion 2 can be extremely easily set. Further, the obtained heat transfer inhibiting sheet has the core portion 1 as a skeleton for maintaining the strength of the sheet on either side of the surface side and the center side, and thus has a desirable structure in which the cladding portion 5 containing the inorganic particles 4 is formed on the surface of the core portion 1.

[0097] As a result, the heat transfer inhibiting sheet 13 produced by the production method according to the present embodiment has a strong skeleton, and can maintain its shape even when a pressing force or an impact is applied to the heat transfer inhibiting sheet, can inhibit powder shedding, and can maintain excellent heat insulation performance.

[0098] Further, in order to further inhibit powder shedding, the surface of the heat transfer inhibiting sheet 13 can be covered with a film or the like. As the polymer film, a film formed of polyimide, polycarbonate, PET, p-phenylene sulfide, polyether imide, cross-linked polyethylene, flame-retardant chloroprene rubber, polyfluoroethylene, hard chlorovinyl, polybutylene terephthalate, PTFE, PFA, FEP, ETFE, hard PCV, flame-retardant PET, polystyrene, polyether sulfone, polyamide imide, polyacrylonitrile, polyethylene, polypropylene, polyamide, or the like can be given. Further, the method for covering the surface of the heat transfer inhibiting sheet 13 with a film is not particularly limited, and a method in which the film is adhered using an adhesive or the like, a method in which the heat transfer inhibiting sheet 13 is wrapped with a film, a method in which the heat transfer inhibiting sheet 13 is accommodated in a bag-shaped film, or the like can be given.

[0099] Next, the binder fiber and the heating conditions used in the production method of the heat transfer inhibiting sheet according to the present embodiment will be described.

[0100] <Binder fiber>

[0101] As the binder fiber 3 that can be used in the present embodiment, there is no particular limitation as long as it has a core-sheath structure and the melting point of the first organic material constituting the core 1 is higher than the melting point of the second organic material constituting the sheath 2. As the first organic material that becomes the core 1, at least one selected from among polyethylene terephthalate, polypropylene, and nylon can be chosen. In addition, as the second organic material that becomes the sheath 2, at least one selected from among polyethylene terephthalate, polyethylene, polypropylene, and nylon can be chosen.

[0102] If the melting point of the first organic material constituting the core 1 is sufficiently higher than the melting point of the second organic material constituting the sheath 2, the setting margin of the heating temperature in the heating process can be enlarged, and the temperature setting for obtaining the desired structure can be performed more easily. For example, the melting point of the first organic material is preferably 60°C or more higher than the melting point of the second organic material, more preferably 70°C or more higher, and further preferably 80°C or more higher.

[0103] In addition, the binder fiber having the above-described core-sheath structure is generally sold on the market, and the materials constituting the core and the sheath can be the same or different from each other. As examples of the binder fiber in which the core 1 and the sheath 2 are made of the same material and have different melting points, for example, there are a binder fiber in which the core 1 and the sheath 2 are made of polyethylene terephthalate, a binder fiber in which the core 1 and the sheath 2 are made of polypropylene, a binder fiber in which the core 1 and the sheath 2 are made of nylon, and the like. As examples of the binder fiber in which the core 1 and the sheath 2 are made of different materials, there are a binder fiber in which the core 1 is made of polyethylene terephthalate and the sheath 2 is made of polyethylene, a binder fiber in which the core 1 is made of polypropylene and the sheath 2 is made of polyethylene, and the like.

[0104] In the present embodiment, the melting point of the second organic material constituting the sheath of the binder fiber indicates the melting temperature at which the second organic material starts to be deformed by melting, and softening accompanied by a change in shape is also judged as one kind of deformation by melting. The melting point of the sheath of the binder fiber can be measured, for example, by the following method.

[0105] The binder fiber to be measured is arranged so as to be in contact with a glass fiber having a higher melting point, heated from room temperature to, for example, 200°C at a temperature increase rate of 5°C / minute, and then cooled to room temperature. At this time, if the surface of the binder fiber is deformed by melting and fused in the portion in contact with the glass fiber, or the cross-sectional shape of the binder fiber is changed, it can be judged that the melting point of the second organic material constituting the sheath is 200°C or lower. In the present embodiment, the heating temperature is changed variously, and the fusion state of the binder fiber and the glass fiber after cooling, or the cross-sectional shape of the binder fiber is observed by the above-described method, whereby the melting point of the second organic material constituting the sheath can be determined.

[0106] (Content of binder fiber)

[0107] In the present embodiment, if the content of the binder fiber 3 in the mixture 9 is appropriately controlled, the reinforcing effect of the skeleton in the obtained heat transfer suppressing sheet 13 can be sufficiently obtained.

[0108] The content of the binder fiber 3 is preferably 5% by mass or more, more preferably 10% by mass or more, with respect to the total mass of the mixture 9. In addition, if the content of the binder fiber 3 is too much, the content of the inorganic particles 4 is relatively reduced, and thus the content of the binder fiber 3 is preferably 25% by mass or less, more preferably 20% by mass or less, with respect to the total mass of the mixture 9, in order to obtain the desired heat insulating properties.

[0109] <Inorganic particles>

[0110] The kind of the inorganic particles 4 that can be used in the present embodiment is described later.

[0111] (Content of inorganic particles)

[0112] In the present embodiment, if the content of the inorganic particles 4 in the mixture 9 is appropriately controlled, the heat insulating properties of the obtained heat transfer suppressing sheet 13 can be sufficiently ensured.

[0113] The content of the entire inorganic particles 4 contained in the mixture 9 is preferably 60% by mass or more, more preferably 70% by mass or more, with respect to the total mass of the mixture 9. In addition, if the content of the inorganic particles 4 is too much, the content of the binder fiber 3 is relatively reduced, and thus the content of the inorganic particles 4 is preferably 95% by mass or less, more preferably 90% by mass or less, with respect to the total mass of the mixture 9, in order to sufficiently obtain the reinforcing effect of the skeleton.

[0114] <Thermofusible powder>

[0115] The thermofusible powder is, for example, a powder that contains a third organic material different from the above-described first and second organic materials and has a property of being fused by heating. By containing the thermofusible powder in the mixture 9 and heating, the thermofusible powder is fused, and then, when cooled, the fused powder is solidified in a state of containing the surrounding inorganic particles 4, forming the solidified portion 16. As described above, the solidified portion 16 includes the thin solidified layer 17 dispersed in a plurality of regions on the surface of the heat transfer suppressing sheet 13, and the surface of the heat transfer suppressing sheet 13 is covered with the thin solidified layer, and thus the falling of the inorganic particles 4 from the heat transfer suppressing sheet 13 can be further suppressed.

[0116] As the hot-melt powder, hot-melt powders having various melting points can be mentioned, but a hot-melt powder having an appropriate melting point can be selected in consideration of the melting points of the core portion 1 and the sheath portion 2 of the binder fiber 3 used. In the present embodiment, the melting point of the first organic material constituting the core portion 1 is higher than the melting points of the second organic material constituting the sheath portion 2 and the third organic material constituting the hot-melt powder 14, and thus the heating temperature for retaining the core portion 1 while melting the sheath portion 2 and the hot-melt powder 14 can be set. Furthermore, if the melting point of the hot-melt powder 14 is lower than the melting point of the sheath portion 2, the heating temperature at the time of production can be set to be between the melting point of the core portion 1 and the melting point of the sheath portion 2, and thus the heating temperature can be more easily set.

[0117] On the other hand, the kind of the hot-melt powder 14 used can also be selected so that the melting point of the hot-melt powder 14 is between the melting point of the core portion 1 and the melting point of the sheath portion 2. When a hot-melt powder 14 having such a melting point is used, after both the sheath portion 2 and the hot-melt powder 14 are melted, the hot-melt powder 14 present in all regions other than the organic fiber (core portion 1) and the molten sheath portion 2 around the same solidifies at the time of cooling. As a result, the position of the organic fiber can be fixed, and thereafter the molten sheath portion 2 is fused to the organic fiber, and thus a three-dimensional skeleton can be easily formed. Therefore, the strength of the entire sheet can be further improved.

[0118] If the melting point of the third organic material constituting the hot-melt powder 14 is sufficiently lower than the melting point of the first organic material constituting the core portion 1, the setting margin of the heating temperature in the heating process can be enlarged, and the temperature setting for obtaining a more desirable configuration can be made easy. For example, the melting point of the first organic material is preferably 60°C or more higher than the melting point of the third organic material, more preferably 70°C or more higher, and further preferably 80°C or more higher.

[0119] Furthermore, as the component constituting the hot-melt powder 14, polyethylene, polyester, polyamide, ethylene-vinyl acetate copolymer, and the like can be mentioned.

[0120] (Content of hot-melt powder)

[0121] Even if the content of the hot-melt powder 14 is a trace amount, an effect of suppressing powder drop-off can be obtained. Therefore, the content of the hot-melt powder 14 is preferably 0.5% by mass or more, and more preferably 1% by mass or more, with respect to the total mass of the mixture 9.

[0122] On the other hand, if the content of the hot-melt powder 14 is increased, the content of the inorganic particles 4 is relatively reduced, and thus the content of the hot-melt powder 14 is preferably 5% by mass or less, and more preferably 4% by mass or less, with respect to the total mass of the mixture 9, in order to obtain a desired thermal insulation performance.

[0123] <Heating conditions>

[0124] As the process of processing the mixture 9 into a sheet, a process of pressurizing the mixture 9 and a process of heating the mixture 9 can be given. The heating temperature in the heating process is preferably set to a temperature higher than the higher one of the melting point of the second organic material constituting the sheath portion 2 and the melting point of the third organic material constituting the hot-melt powder 14 and lower than the melting point of the first organic material constituting the core portion 1. By setting the heating temperature to such a temperature, as described above, the strength of the sheet can be further increased using the skeleton constituted by the fiber portion 6 and the solidified portion 16, and the falling of the inorganic particles 4 can be prevented using the melt-coated portion 5 and the solidified layer 17.

[0125] Further, if the melting point of the first organic material constituting the core portion 1 is sufficiently higher than the melting point of the second organic material constituting the sheath portion 2, the setting margin of the heating temperature in the heating process can be enlarged, and the temperature setting for obtaining the desired structure can be more easily performed. For example, the melting point of the first organic material is preferably 60°C or more higher than the melting point of the second organic material, more preferably 70°C or more higher, and further preferably 80°C or more higher. That is, in order to sufficiently enlarge the setting margin of the heating temperature, the melting point of the first organic material is preferably 60°C or more higher than the higher one of the melting point of the second organic material and the melting point of the third organic material, more preferably 70°C or more higher, and further preferably 80°C or more higher.

[0126] Further, the heating temperature in the heating process is preferably set to a temperature higher than the higher one of the melting point of the second organic material constituting the sheath portion 2 and the melting point of the third organic material constituting the hot-melt powder 14, more preferably 10°C or more higher, and further preferably 20°C or more higher. On the other hand, the heating temperature is preferably set to a temperature lower than the melting point of the first organic fiber constituting the core portion 1, more preferably 10°C or lower, and further preferably 20°C or lower.

[0127] The heating time is not particularly limited, and a heating time for sufficiently melting the sheath portion 2 and the hot-melt powder 14 is preferably set. For example, it can be set to 3 minutes or more and 15 minutes or less.

[0128] [2. Heat transfer inhibiting sheet]

[0129] Hereinafter, an embodiment of the heat transfer inhibiting sheet manufactured by the manufacturing method of the heat transfer inhibiting sheet according to the present application described above will be described.

[0130] As Figure 2 and Figure 3As shown, the heat transfer inhibiting sheet 13 of the present embodiment has the inorganic particles 4, the organic fiber (core portion 1) composed of the first organic material, the cladding portion 5 that clads the outer peripheral surface of the organic fiber, and the solidified portion 16 formed in a region different from the cladding portion 5. As described above, the cladding portion 5 contains the second organic material having the inorganic particles 4 and a lower melting point than the first organic material. In addition, the solidified portion 16 contains the inorganic particles 4 and a third organic material having a lower melting point than the first organic material. Further, the solidified portion 16 has a plurality of solidified layers 17 on the surface of the heat transfer inhibiting sheet 13, and the cracks 12 are formed between the plurality of solidified layers 17.

[0131] Further, in the present embodiment, the hot melt powder 14 is contained in the mixture of the materials, and the hot melt powder 14 is present in all regions of the molded body, and thus, when cooling is performed after heating in the manufacturing process, the cladding portion 5 sometimes contains the third organic material as a component of the hot melt powder 14. Likewise, in the vicinity of the organic fiber (core portion 1), the second organic material as a component of the sheath portion 2 is sometimes contained in the solidified portion 16. In either case, the effects of the present application are not affected.

[0132] In the heat transfer inhibiting sheet 13 of the present embodiment thus configured, as described above in [1. Manufacturing method of heat transfer inhibiting sheet], the fiber portion 6 composed of the organic fiber (core portion 1) and the cladding portion 5 functions as a skeleton, and the solidified portion 16 containing the hot melt powder 14 and the inorganic particles 4 between the skeletons supports the skeleton, and thus, it is possible to maintain the shape of the entire heat transfer inhibiting sheet in a higher strength. In addition, the outer peripheral surface of the organic fiber is clad by the cladding portion 5, and the solidified portion 16 is also formed in a region other than the cladding portion 5, and thus, it is possible to maintain the inorganic particles 4. Further, since the thin solidified layers 17 are formed on the surface of the heat transfer inhibiting sheet 13, it is possible to obtain a very high powder drop-out inhibiting effect. Further, when the cracks 12 are formed, the heat transfer inhibiting sheet 13 easily follows the deformation of the battery cell accompanying the expansion and contraction at the time of charge and discharge. Thus, for example, when the heat transfer inhibiting sheet 13 of the present embodiment is arranged between a plurality of battery cells as described later, even in the case where the battery cell expands and exerts a compressive stress or an impact on the heat transfer inhibiting sheet 13, it is possible to maintain excellent heat insulation performance.

[0133] In the present embodiment, as a mechanism capable of inhibiting the detachment (powder detachment) of the inorganic particles 4 from the surface of the sheet, it can be considered that a three-dimensional and strong skeleton is formed by the organic fiber (core portion 1) and the fused portion 5, the shape of the heat transfer inhibiting sheet 13 is maintained, and thus the deformation or compression of the heat transfer inhibiting sheet 13 is inhibited. In addition, the fiber portion 6, the thin solidified layer 17 formed on the surface of the sheet, and the fiber portion 6 composed of the exposed organic fiber (core portion 1) and the fused portion 5 cover the surface of the heat transfer inhibiting sheet 13 and can absorb the impact applied to the heat transfer inhibiting sheet 13, and this is also considered to be a reason for maintaining the inorganic particles 4.

[0134] Also, as shown in FIG. 1, in the heat transfer inhibiting sheet 13, the fused portion 5 does not need to completely cover the outer peripheral surface of the organic fiber (core portion 1), and the organic fiber (core portion 1) can be partially exposed. In the manufacturing method of the heat transfer inhibiting sheet of the present embodiment, since the adhesive fiber 3 of the core-sheath structure is used, the sheath portion 2 is sometimes peeled off in the manufacturing process, but even in the case where the organic fiber (core portion 1) is partially exposed, the effects of the present application can be sufficiently obtained. Figure 3

[0135] Hereinafter, the materials constituting the heat transfer inhibiting sheet of the present embodiment will be described in detail.

[0136] <Organic Fiber>

[0137] In the heat transfer inhibiting sheet 13, the core portion 1 composed of the first organic material functions as an organic fiber that maintains the strength and shape of the sheet. The melting point of the first organic material constituting the organic fiber is not particularly limited as long as it is higher than the melting point of the second organic material present on the outer peripheral surface of the organic fiber and the melting point of the third organic material contained in the solidified portion 16. As the first organic material, at least one selected from polyethylene terephthalate, polypropylene, and nylon can be cited.

[0138] (Content of Organic Fiber)

[0139] In the present embodiment, if the content of the organic fiber in the heat transfer inhibiting sheet 13 is appropriately controlled, the reinforcing effect of the skeleton can be sufficiently obtained.

[0140] The content of the organic fiber is preferably 2% by mass or more, and more preferably 4% by mass or more, with respect to the total mass of the heat transfer inhibiting sheet 13. In addition, if the content of the organic fiber is too much, the content of the inorganic particles 4 is relatively reduced, and thus in order to obtain the desired heat insulating performance, the content of the organic fiber is preferably 10% by mass or less, and more preferably 8% by mass or less, with respect to the total mass of the heat transfer inhibiting sheet 13.

[0141] (Fiber Length of Organic Fiber)

[0142] ​The fiber length of the organic fiber is not particularly limited, and the average fiber length of the organic fiber is preferably 10 mm or less from the viewpoint of ensuring moldability and processability.

[0143] On the other hand, the average fiber length of the organic fiber is preferably 0.5 mm or more from the viewpoint of allowing the organic fiber to function as a skeleton and ensuring the compression strength of the heat transfer-inhibiting sheet.

[0144] <Overcoat>

[0145] The overcoat 5 is formed by cooling the sheath portion 2 of the binder fiber 3 having a core-sheath structure after temporarily melting the sheath portion 2 by heating, and the overcoat 5 contains the second organic material and the inorganic particles 4.

[0146] (Second Organic Material)

[0147] The second organic material is not particularly limited as long as the melting point thereof is lower than that of the first organic material constituting the above-mentioned organic fiber. As the second organic material, at least one selected from the group consisting of polyethylene terephthalate, polyethylene, polypropylene, and nylon can be mentioned.

[0148] Further, the melting point of the second organic material is preferably 90°C or higher, and more preferably 100°C or higher. In addition, the melting point of the second organic material is preferably 150°C or lower, and more preferably 130°C or lower.

[0149] <Solidified Portion>

[0150] The solidified portion 16 is formed by cooling the hot-melt powder after temporarily melting the hot-melt powder by heating, and contains the inorganic particles 4 and a third organic material constituting the hot-melt powder.

[0151] (Third Organic Material)

[0152] As mentioned above, the third organic material as a component constituting the hot-melt powder is not particularly limited as long as the melting point thereof is lower than that of the first organic material constituting the above-mentioned organic fiber. In order to make the control of the heating temperature at the time of production easy, the melting point of the hot-melt powder (third organic material) is preferably lower than the melting point of the second organic material constituting the sheath portion. However, for the purpose of forming a more three-dimensional skeleton and improving the strength of the heat transfer-inhibiting sheet, the melting point of the third organic material can be higher than the melting point of the above-mentioned second organic material, i.e., can be between the melting point of the first organic material and the melting point of the second organic material.

[0153] As mentioned above, in order to sufficiently expand the setting margin of the heating temperature, the melting point of the second organic material and the melting point of the third organic material are each preferably 60°C or more lower than the melting point of the first organic material, more preferably 70°C or more lower, and further preferably 80°C or more lower.

[0154] Further, the melting point of the hot-melt powder (third organic material) is preferably 80°C or higher, more preferably 90°C or higher. In addition, the melting point of the hot-melt powder (third organic material) is preferably 180°C or lower, more preferably 150°C or lower. In addition, the third organic material constituting the hot-melt powder is preferably at least one selected from the group consisting of polyethylene, polyester, polyamide, and ethylene-vinyl acetate copolymer.

[0155] (Inorganic particles)

[0156] As the inorganic particles, a single inorganic particle can be used, or two or more kinds of inorganic particles can be used in combination. As the kind of the inorganic particles, from the viewpoint of heat transfer inhibition effect, it is preferable to use at least one kind of particles composed of inorganic material selected from the group consisting of oxide particles, carbide particles, nitride particles, and inorganic hydrate particles, and more preferably oxide particles. In addition, there is no particular limitation on the shape, but it is preferable to contain at least one selected from the group consisting of nanoparticles, hollow particles, and porous particles, and specifically, inorganic hollow spheres such as silica nanoparticles, metal oxide particles, microporous particles, hollow silica particles, particles composed of thermally expandable inorganic material, particles composed of hydrous porous body, and the like can be used.

[0157] When the average secondary particle diameter of the inorganic particles is 0.01 μm or more, it is easy to obtain an increase in manufacturing cost. In addition, when it is 200 μm or less, the desired heat insulation 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.

[0158] Further, if two or more kinds of inorganic particles having different heat transfer inhibition effects are used in combination, the heat generating body can be cooled in multiple stages, and the endothermic action can be exhibited in a larger temperature range. Specifically, it is preferable to use a large-diameter particle and a small-diameter particle in combination. For example, in the case where nanoparticles are used as one kind of inorganic particles, as the other kind of inorganic particles, it is preferable to contain inorganic particles composed of metal oxide. Hereinafter, the small-diameter inorganic particles will be described as first inorganic particles, and the large-diameter inorganic particles will be described as second inorganic particles.

[0159] <First inorganic particles>

[0160] (Oxide particles)

[0161] The refractive index of the oxide particles is high, and the light diffusion reflection effect is strong, so when the oxide particles are used as the first inorganic particles, radiation heat transfer can be suppressed particularly in a high temperature region such as abnormal heating. As the oxide particles, at least one kind of particle selected from among silica, titanium dioxide, zirconium oxide, zircon, barium titanate, zinc oxide, and aluminum oxide can be used. That is, among the above oxide particles that can be used as inorganic particles, only one kind can be used, or two or more kinds of oxide particles can be used. In particular, silica is a component having high thermal insulation properties, and titanium dioxide is a component having a high refractive index compared to other metal oxides, and has a high effect of diffusing light and shielding radiation heat in a high temperature region of 500°C or higher, so silica and titanium dioxide are most preferably used as the oxide particles.

[0162] (Average primary particle diameter of oxide particles: 0.001 μm or more and 50 μm or less)

[0163] The particle diameter of the oxide particles sometimes affects the effect of reflecting radiation heat, so if the average primary particle diameter is limited to a prescribed range, higher thermal insulation properties can be obtained.

[0164] That is, when the average primary particle diameter of the oxide particles is 0.001 μm or more, it is sufficiently large compared to the wavelength of light that contributes to heating, and light is diffused efficiently, so in a high temperature region of 500°C or higher, the radiation heat transfer of heat within the heat transfer suppressing sheet is suppressed, and the thermal insulation properties can be further improved.

[0165] On the other hand, when the average primary particle diameter of the oxide particles is 50 μm or less, even if the particles are compressed, the number of contacts between the particles does not increase, and it is difficult to form a path for conduction heat transfer, so the influence on the thermal insulation properties in a normal temperature region where conduction heat transfer is dominant can be particularly reduced.

[0166] Also, in the present application, the average primary particle diameter can be found by observing the particles with a microscope, comparing them with a standard scale, and taking the average of any 10 particles.

[0167] (Nanoparticles)

[0168] In the present application, nanoparticles mean nanoscale particles that are spherical or nearly spherical and have an average primary particle diameter of less than 1 μm. Since the nanoparticles are low in density, conduction heat transfer is suppressed, and if nanoparticles are used as the first inorganic particles, the voids are further finely dispersed, so excellent thermal insulation properties that suppress convection heat transfer can be obtained. Therefore, in the use of the battery in a normal room temperature region, it is preferable to use nanoparticles from the viewpoint of being able to suppress heat conduction between adjacent nanoparticles.

[0169] Further, as the oxide particles, if a nanoparticle having a small average primary particle diameter is used, even in a case where the heat transfer suppressing sheet is compressed and the density inside is increased due to expansion accompanying thermal runaway of the battery cell, the increase in the conductive heat transfer of the heat transfer suppressing sheet can be suppressed. The reason is considered to be that the nanoparticle easily forms a fine gap between the particles due to the repulsive force generated by static electricity, and the bulk density is low, so the particles are filled in a manner having a cushioning property.

[0170] Further, in the present application, in a case where a nanoparticle is used as the first inorganic particles, the material is not particularly limited as long as the definition of the nanoparticle described above is satisfied. For example, a silica nanoparticle is a material having high thermal insulation properties, and the contact of the particles with each other is small, so the heat conducted through the silica nanoparticle is smaller than in a case where a silica particle having a large particle diameter is used. In addition, the bulk density of a generally obtained silica nanoparticle is about 0.1 (g / cm 3 ) or less, so for example, even in a case where the battery cell disposed on both sides of the heat insulating sheet thermally expands and a large compressive stress is applied to the heat insulating sheet, the size (area) and the number of the contacts of the silica nanoparticles with each other do not significantly increase, and the thermal insulation properties can be maintained. Therefore, as the nanoparticle, a silica nanoparticle is preferably used. As the silica nanoparticle, a wet-type silica, a dry-type silica, an aerogel, and the like can be given, and the silica nanoparticle particularly suitable for the present embodiment will be described below.

[0171] Figure 4 is a photograph showing the state of the particles of the wet-type silica and the dry-type silica. In addition, Figure 5 is a graph showing the change in the thermal conductivity of the wet-type silica and the dry-type silica at each temperature. As shown in Figure 4 , the particles of the wet-type silica agglomerate together, and in contrast to this, the dry-type silica enables the particles to be dispersed. In a temperature range of 300°C or less, the conductive heat transfer is dominant in the conduction of heat, so, as shown in Figure 5 , the dry-type silica enabling the particles to be dispersed can obtain excellent thermal insulation properties, and is more preferable than the wet-type silica.

[0172] Further, as described above, in a case where a dry-type silica, a silica aerogel, or the like having a low thermal conductivity is used as the inorganic particles for the purpose of further improving the thermal insulation properties, it is preferable that the mixture containing the material is processed into a sheet shape by a dry method.

[0173] (Nanoparticle: average primary particle diameter of 1 nm or more and 100 nm or less)

[0174] If the average primary particle diameter of the nanoparticle is limited to a prescribed range, higher thermal insulation properties can be obtained.

[0175] That is, when the average primary particle diameter of the nanoparticles is 1 nm or more and 100 nm or less, particularly in a temperature region of less than 500°C, the heat convection and conduction heat in the heat transfer-inhibiting sheet can be inhibited, and the heat insulation property can be further improved. In addition, even in the case where a compressive stress is applied, the conduction heat can be inhibited by the voids remaining between the nanoparticles and the contacts between the plurality of particles, and the heat insulation property of the heat transfer-inhibiting sheet can be maintained.

[0176] In addition, the average primary particle diameter 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 diameter of the nanoparticles is more preferably 50 nm or less and further preferably 10 nm or less.

[0177] (Inorganic Hydrate Particles)

[0178] The inorganic hydrate particles undergo thermal decomposition when they reach a temperature of the thermal decomposition initiation temperature or higher due to heat from the heat generating body, release the crystal water they have, and lower the temperature of the heat generating body and its surroundings, exhibiting so-called "heat absorption". In addition, after the release of the crystal water, they become porous bodies and exhibit heat insulation through the innumerable air pores.

[0179] Specific examples of the inorganic hydrate include aluminum hydroxide (Al(OH)3), magnesium hydroxide (Mg(OH)2), calcium hydroxide (Ca(OH)2), zinc hydroxide (Zn(OH)2), iron hydroxide (Fe(OH)2), manganese hydroxide (Mn(OH)2), zirconium hydroxide (Zr(OH)2), gallium hydroxide (Ga(OH)3), and the like.

[0180] For example, aluminum hydroxide has about 35% of crystal water, as shown in the following formula, and undergoes thermal decomposition to release the crystal water, exhibiting heat absorption. Furthermore, after the release of the crystal water, it becomes aluminum oxide (Al2O3) as a porous body and functions as a heat insulating member.

[0181] 2Al(OH)3→ Al2O3 + 3H2O

[0182] In addition, as described later, the heat transfer-inhibiting sheet 13 according to the present embodiment is preferably interposed between battery cells, for example, but in a battery cell in which thermal runaway has occurred, the temperature sharply rises to more than 200°C, and the temperature continues to rise to around 700°C. Therefore, as the inorganic particles, it is preferable that the inorganic hydrate having a thermal decomposition initiation temperature of 200°C or higher be used.

[0183] As for the thermal decomposition start temperature of the above-mentioned inorganic hydrate, 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 hydroxide is about 350°C, manganese hydroxide is about 300°C, zirconium hydroxide is about 300°C, and gallium hydroxide is about 300°C, all of which approximately overlap with the temperature range of the rapid temperature increase of the battery cell in which thermal runaway occurs, and can efficiently suppress temperature rise, and thus can be said to be preferable inorganic hydrates.

[0184] (Average secondary particle diameter of inorganic hydrate particles: 0.01 μm or more and 200 μm or less)

[0185] In addition, in the case where the inorganic hydrate particles are used as the first inorganic particles, if the average particle diameter thereof is too large, the first inorganic particles (inorganic hydrate) located near the center of the heat transfer inhibiting sheet 13 requires a certain degree of time until reaching the thermal decomposition temperature thereof, and thus there is a case where the first inorganic particles near the center of the sheet cannot be completely thermally decomposed. Therefore, the average secondary particle diameter of the inorganic hydrate particles is preferably 0.01 μm or more and 200 μm or less, and more preferably 0.05 μm or more and 100 μm or less.

[0186] (Particles composed of thermally expandable inorganic material)

[0187] As the thermally expandable inorganic material, vermiculite, bentonite, mica, perlite, and the like can be given.

[0188] (Particles composed of hydrous porous body)

[0189] As specific examples of the hydrous porous body, zeolite, kaolinite, montmorillonite, acid clay, diatomite, wet-type silica, dry-type silica, aerogel, mica, vermiculite, and the like can be given.

[0190] (Inorganic hollow sphere)

[0191] The heat insulating member used in the present application can contain an inorganic hollow sphere as the first inorganic particles.

[0192] If the inorganic hollow sphere is contained, in the temperature region lower than 500°C, the convection heat transfer or the conduction heat transfer of heat within the heat insulating member can be suppressed, and the heat insulating property of the heat insulating member can be further improved.

[0193] As the inorganic hollow sphere, at least one selected from the group consisting of white sand hollow sphere, silica hollow sphere, fly ash hollow sphere, barite hollow sphere, and glass hollow sphere can be used.

[0194] (Content of inorganic hollow sphere: 60 mass% or less with respect to the total mass of the heat insulating member)

[0195] The content of the inorganic hollow spheres is preferably 60% by mass or less relative to the total mass of the thermal insulation member.

[0196] (the average particle diameter of the inorganic hollow spheres: 1 μm or more and 100 μm or less)

[0197] The average particle diameter of the inorganic hollow spheres is preferably 1 μm or more and 100 μm or less.

[0198] <Second Inorganic Particles>

[0199] In the case where two kinds of inorganic particles are contained in the heat transfer inhibiting sheet, the second inorganic particles are not particularly limited as long as the material, particle diameter, and the like are different from those of the first inorganic particles. As the second inorganic particles, an oxide particle, a carbide particle, a nitride particle, an inorganic hydrate particle, a silica nanoparticle, a metal oxide particle, a microporous particle, or an inorganic hollow sphere such as hollow silica particle, a particle composed of a thermally expandable inorganic material, a particle composed of a hydrous porous body, and the like can be used, and details thereof are as described above.

[0200] Further, the nanoparticle has extremely small conductive heat transfer, and can maintain excellent thermal insulation even in the case where a compressive stress is applied to the heat transfer inhibiting sheet. In addition, the metal oxide particle such as titanium dioxide has a high effect of shielding radiant heat. Furthermore, if a large-diameter inorganic particle and a small-diameter inorganic particle are used, the small-diameter inorganic particle enters the gap between the large-diameter inorganic particles, thereby forming a more dense structure, and the heat transfer inhibiting effect can be improved. Therefore, in the case where, for example, a nanoparticle is used as the first inorganic particle described above, it is preferable to further contain, as the second inorganic particle, a particle composed of a metal oxide having a larger diameter than the first inorganic particle in the heat transfer inhibiting sheet.

[0201] As the metal oxide, silicon oxide, titanium oxide, aluminum oxide, barium titanate, zinc oxide, zircon, zirconium oxide, and the like can be exemplified. In particular, titanium oxide (titanium dioxide) is a component having a high refractive index compared to other metal oxides, and has a high effect of diffusely reflecting light and shielding radiant heat in a high temperature region of 500°C or higher, and thus titanium dioxide is most preferably used.

[0202] For example, in the case where at least one kind of particle selected from among dry silica particles and silica aerogel is used as the first inorganic particle, and at least one kind of particle selected from among titanium dioxide, zircon, zirconia, silicon carbide, zinc oxide, and alumina is used as the second inorganic particle, in order to obtain excellent heat shielding performance in a temperature range of 300°C or lower, the first inorganic particle is preferably 50% by mass or more, more preferably 60% by mass or more, and further preferably 70% by mass or more, with respect to the total mass of the inorganic particles. In addition, the first inorganic particle is preferably 95% by mass or less, more preferably 90% by mass or less, and further preferably 80% by mass or less, with respect to the total mass of the inorganic particles.

[0203] On the other hand, in order to obtain excellent heat shielding performance in a temperature range exceeding 300°C, the second inorganic particle is preferably 5% by mass or more, more preferably 10% by mass or more, and further preferably 20% by mass or more, with respect to the total mass of the inorganic particles. In addition, the second inorganic particle is preferably 50% by mass or less, more preferably 40% by mass or less, and further preferably 30% by mass or less, with respect to the total mass of the inorganic particles.

[0204] (Average primary particle diameter of the second inorganic particle)

[0205] In the case where the second inorganic particle composed of a metal oxide is contained in the heat transfer suppressing sheet, if the average primary particle diameter of the second inorganic particle is 1 μm or more and 50 μm or less, radiation heat transfer can be efficiently suppressed in a high-temperature region of 500°C or higher. The average primary particle diameter of the second inorganic particle is further preferably 5 μm or more and 30 μm or less, and most preferably 10 μm or less.

[0206] (Content of the inorganic particle)

[0207] In the present embodiment, if the content of the inorganic particle 4 in the heat transfer suppressing sheet 13 is appropriately controlled, the heat shielding property of the heat transfer suppressing sheet 13 can be sufficiently ensured.

[0208] The content of the inorganic particle 4 with respect to the total mass of the heat transfer suppressing sheet 13 is preferably 60% by mass or more, and more preferably 70% by mass or more. In addition, when the content of the inorganic particle 4 is too much, the content of the organic fiber and the clad portion relatively decreases, and thus in order to sufficiently obtain the reinforcement effect of the skeleton and the holding effect of the inorganic particle, the content of the inorganic particle 4 with respect to the total mass of the heat transfer suppressing sheet 13 is preferably 95% by mass or less, and more preferably 90% by mass or less.

[0209] Further, the content of the inorganic particle in the heat transfer suppressing sheet 13 can be calculated, for example, as follows: the heat transfer suppressing sheet is heated at 800°C, and after the organic component is decomposed, the mass of the remaining portion is measured, whereby the content of the inorganic particle in the heat transfer suppressing sheet 13 is calculated.

[0210] In addition, in the heat transfer inhibiting sheet 13 of the present embodiment, in addition to the above-mentioned organic fiber (core portion 1), inorganic particles 4, fused portion 5, and solidified portion 16, an organic fiber, inorganic fiber, or the like made of an organic material different from the above-mentioned first organic material can be included. Furthermore, an organic material different from the above-mentioned first to third organic materials can be present in the heat transfer inhibiting sheet 13, and inorganic particles can be held in the organic material.

[0211] <Thickness of heat transfer inhibiting sheet>

[0212] The thickness of the heat transfer inhibiting sheet of the present embodiment is not particularly limited, and is preferably 0.05 mm or more and 10 mm or less. When the thickness is 0.05 mm or more, sufficient compressive strength can be obtained. On the other hand, when the thickness is 10 mm or less, good thermal insulation of the heat transfer inhibiting sheet can be obtained.

[0213] [3. Battery pack]

[0214] Figure 6 is a schematic view showing a battery pack to which the present embodiment relates. The battery pack 100 of the present embodiment has a plurality of battery cells 20a, 20b, 20c and the heat transfer inhibiting sheet to which the present embodiment relates, which are connected in series or in parallel.

[0215] For example, as shown in Figure 6 , the heat transfer inhibiting sheet 13 to which the present embodiment relates is interposed between the battery cell 20a and the battery cell 20b, and between the battery cell 20b and the battery cell 20c. Furthermore, the battery cells 20a, 20b, and 20c and the heat transfer inhibiting sheet 13 are housed in the battery case 30.

[0216] Also, as to the heat transfer inhibiting sheet 13, the content is as described above.

[0217] In the battery pack 100 thus configured, even in the case where a certain battery cell 20a becomes high temperature, since the heat transfer inhibiting sheet 13 having a heat transfer inhibiting effect is present between it and the battery cell 20b, heat propagation to the battery cell 20b can be inhibited.

[0218] In addition, the heat transfer inhibiting sheet 13 of the present embodiment has high compressive strength, and thus even at the time of charge and discharge of the battery cells 20a, 20b, 20c, thermal expansion of these battery cells can be inhibited. Therefore, the distance between the battery cells can be ensured, excellent thermal insulation performance can be maintained, and thermal runaway of the battery cells can be prevented. In addition, since the effect of inhibiting powder fall-off is obtained, handling can be easily performed.

[0219] Furthermore, the battery pack 100 of the present embodiment is not limited to Figure 6The battery pack illustrated can also be configured with the heat transfer inhibiting sheet 13 not only between the battery cell 20a and the battery cell 20b and between the battery cell 20b and the battery cell 20c but also between the battery cells 20a, 20b, 20c and the battery case 30.

[0220] In the battery pack 100 thus configured, in the event of a fire in a certain battery cell, the spread of the flame to the outside of the battery case 30 can be inhibited.

[0221] For example, the battery pack 100 according to the present embodiment is sometimes used in an electric vehicle (EV: Electric Vehicle) or the like and is disposed under the floor of an occupant. In this case, even if a battery cell catches fire, the safety of the occupant can be ensured.

[0222] Further, since the heat transfer inhibiting sheet 13 can be interposed not only between the battery cells but also between the battery cells 20a, 20b, 20c and the battery case 30, it is not necessary to newly produce a fireproof member or the like, and a low-cost and safe battery pack 100 can be easily configured.

[0223] In the battery pack according to the present embodiment, the heat transfer inhibiting sheet 13 disposed between the battery cells 20a, 20b, 20c and the battery case 30 can be in contact with the battery cells or can have a gap. However, if a gap is provided between the heat transfer inhibiting sheet 13 and the battery cells 20a, 20b, 20c, even in the event of a temperature rise and volume expansion of any one of the plurality of battery cells, the deformation of the battery cells can be allowed.

[0224] Further, the heat transfer inhibiting sheet 13 according to the present embodiment can be produced in various shapes by its production method. Therefore, any shape can be dealt with without being affected by the shapes of the battery cells 20a, 20b, 20c and the battery case 30. Specifically, in addition to prismatic batteries, it can be applied to cylindrical batteries, flat-type batteries, and the like.

[0225] [EMBODIMENT]

[0226] Hereinafter, the present application will be described in detail by citing examples and comparative examples, but the present application is not limited thereto.

[0227] [TEST 1]

[0228] Test pieces of the heat transfer inhibiting sheets of the examples and the comparative examples were produced, the surfaces of the test pieces were observed, and the powder drop-off inhibiting performance (flying rate) was evaluated.

[0229] <Production of Test Pieces>

[0230] (Example 1)

[0231] As the inorganic particles, dry silica and titanium dioxide were prepared, and a hot melt powder and binder fibers of core-sheath configuration were prepared. The specific content and name of each component are shown below.

[0232] • Inorganic particles: Dry silica (57.7 mass%, average primary particle diameter: 0.012 μm)

[0233] • Inorganic particles: Titanium dioxide (24.7 mass%, average primary particle diameter: 8 μm)

[0234] • Hot melt powder: Powder resin (PR D60C-Z: manufactured by Tokyo Ink Co., Ltd., 2.6 mass%, melting point: 100°C)

[0235] Core: Polyethylene terephthalate (melting point: 240°C)

[0236] Sheath: Low-melting polyethylene terephthalate (melting point: 110°C)

[0237] The above-described materials were put into a mixer to make a mixture. Then, the obtained mixture was put into a prescribed mold, and was subjected to pressurization by a press machine or the like and was subjected to heating, cooling, whereby a test piece of Example 1 having a basis weight of 740 (g / m 2 ), a thickness of 2 mm was obtained. Also, the heating condition was set to 15 minutes at 150°C.

[0238] (Comparative Example 1)

[0239] In the above-described materials of Example 1, a material in which only the hot melt powder was not contained was prepared. The specific content and name of each component are shown below.

[0240] • Inorganic particles: Dry silica (59.2 mass%, average primary particle diameter: 0.012 μm)

[0241] • Inorganic particles: Titanium dioxide (25.4 mass%, average primary particle diameter: 8 μm)

[0242] • Binder fibers: PET / low-melting PET fibers (TJ04CN: manufactured by Teijin Frontier Co., Ltd.: 15 mass%, average fiber length: 5 mm)

[0243] Core: Polyethylene terephthalate (melting point: 240°C)

[0244] Sheath: Low-melting polyethylene terephthalate (melting point: 110°C)

[0245] Then, by the same dry method as in Example 1, a test material of Comparative Example 1 having a basis weight of 740 (g / m 2 ), and a thickness of 2 mm was produced. Also, the heating conditions were set to 15 minutes at 150°C.

[0246] <Observation of the surface of the test piece>

[0247] For the surface of each test piece, a photograph was taken using a scanning electron microscope (SEM: Scanning Electron Microscope) to observe the appearance of the surface.

[0248] Figure 7 is a diagrammatic substitute photograph showing the surface of Example 1. Also, Figure 8 is a diagrammatic substitute photograph showing the surface of Comparative Example 1. As Figure 7 indicated, Example 1, in which the binder fiber of the core-sheath structure was used, had a fusion coated portion 5 containing inorganic particles 4 formed on the outer peripheral surface of the organic fiber as the core portion 1, and a fiber portion 6 of a large diameter was obtained. Also, on the surface, cracks 12 were observed at a plurality of portions, and thus it was found that the surface of the test piece of Example 1 had a plurality of cured layers 17.

[0249] On the other hand, as Figure 8 indicated, Comparative Example 1 had a fusion coated portion 5 containing inorganic particles 4 formed on the outer peripheral surface of the organic fiber as the core portion 1, and although a fiber portion 6 of a large diameter was formed, a cured layer covering the surface was not formed.

[0250] <Evaluation of the test piece>

[0251] For each test piece, the flying rate was measured, and the powder drop-off inhibiting performance was evaluated.

[0252] (Measurement of the flying rate)

[0253] Figure 9 is a schematic diagram showing the measurement method of the flying rate. As Figure 9 indicated, a device in which an arm 25 is installed so as to operate at the top of a support 24 and a test piece 23 is installed at the end of the arm 25 was used. First, after the test piece 23 was installed at the end of the arm 25, the arm 25 was lifted and fixed to an arbitrary angle, and then the fixing was released and it was allowed to fall, whereby the support 24 and the arm 25 collided to apply an impact. Also, the size of the test piece 23 was 50 mm x 50 mm, the length of the arm was 915 mm, the number of times of applying the impact was 1, and the angle of the support and the arm was 90°. Then, the mass of the test piece 23 before the impact was set to F0 (g), the mass of the test piece 23 after the impact was set to Fw (g), and the flying rate E (amount of drop-off of inorganic particles) (mass %) was calculated by the following equation.

[0254] Emission rate E = (F0 - Fw) / F0

[0255] Figure 10 is a graph showing the change in emission rate with the number of blows in the case where the vertical axis is the emission rate and the horizontal axis is the number of blows. As shown in Figure 10 Example 1 used a material containing hot melt powder to produce a test piece of a heat transfer inhibiting sheet, and a cured layer 17 having a coated surface was formed, so that superior powder drop-off inhibiting performance could be obtained compared to Comparative Example 1 which did not contain hot melt powder.

Claims

1. A method for producing a heat transfer inhibiting sheet, characterized by comprising a processing step of processing a mixture into a sheet shape, the mixture containing inorganic particles, a hot melt powder, and binder fibers having a core-sheath structure, the binder fibers having the core-sheath structure have a core portion extending in a length direction thereof and a sheath portion formed so as to cover an outer circumferential surface of the core portion, a melting point of a first organic material constituting the core portion is higher than a melting point of a second organic material constituting the sheath portion and a melting point of a third organic material constituting the hot melt powder.

2. The method for producing a heat transfer inhibiting sheet according to claim 1, characterized in that the melting point of the third organic material is lower than the melting point of the second organic material.

3. The method for producing a heat transfer inhibiting sheet according to claim 1, characterized in that the melting point of the third organic material is higher than the melting point of the second organic material.

4. The method for producing a heat transfer inhibiting sheet according to any one of claims 1 to 3, characterized in that the melting point of the first organic material is higher than the melting point of the higher one of the second organic material and the third organic material by 60°C or more.

5. The method for producing a heat transfer inhibiting sheet according to any one of claims 1 to 3, characterized in that the processing step has a step of pressurizing the mixture and a step of heating the mixture.

6. The method for producing a heat transfer inhibiting sheet according to claim 5, characterized in that a heating temperature in the step of heating the mixture is set to a temperature higher than the melting point of the higher one of the second organic material and the third organic material and lower than the melting point of the first organic material.

7. The method for producing a heat transfer inhibiting sheet according to any one of claims 1 to 3, characterized in that in the processing step, the mixture is processed into a sheet shape by a dry method.

8. The method for producing a heat transfer inhibiting sheet according to any one of claims 1 to 3, characterized in that the inorganic particles contain at least one kind of particle selected from among dry silica particles and silica aerogel.

9. The method for producing a heat transfer inhibiting sheet according to claim 8, characterized in that the inorganic particles further contain at least one kind of particle selected from among titanium dioxide, zircon, zirconium oxide, silicon carbide, zinc oxide, and aluminum oxide.

10. A heat transfer inhibiting sheet, characterized by comprising: inorganic particles; organic fibers constituted of a first organic material; a cladding portion that covers an outer circumferential surface of the organic fibers; and a solidified portion formed in a region different from the cladding portion, the cladding portion contains the inorganic particles and a second organic material having a melting point lower than a melting point of the first organic material, the solidified portion contains the inorganic particles and a third organic material having a melting point lower than the melting point of the first organic material.

11. The heat transfer inhibiting sheet according to claim 10, characterized in that the solidified portion has a plurality of solidified layers on a surface of the heat transfer inhibiting sheet, ​ ​ A crack is formed between the plurality of cured layers.

12. The heat transfer inhibiting sheet according to claim 10 or 11, wherein The melting point of the third organic material is lower than the melting point of the second organic material.

13. The heat transfer inhibiting sheet according to claim 10 or 11, wherein The melting point of the third organic material is higher than the melting point of the second organic material.

14. The heat transfer inhibiting sheet according to claim 10 or 11, wherein The melting point of the second organic material and the melting point of the third organic material are each 60°C or more lower than the melting point of the first organic material.

15. The heat transfer inhibiting sheet according to claim 10 or 11, wherein The first organic material is at least one selected from the group consisting of polyethylene terephthalate, polypropylene, and nylon, The second organic material is at least one selected from the group consisting of polyethylene terephthalate, polyethylene, polypropylene, and nylon.

16. The heat transfer inhibiting sheet according to claim 10 or 11, wherein The third organic material is at least one selected from the group consisting of polyethylene, polyester, polyamide, and ethylene-vinyl acetate copolymer.

17. The heat transfer inhibiting sheet according to claim 10 or 11, wherein The inorganic particles are at least one kind of particles composed of inorganic material selected from the group consisting of oxide particles, carbide particles, nitride particles, and inorganic hydrate particles.

18. The heat transfer inhibiting sheet according to claim 17, wherein The inorganic particles include at least one kind of particles selected from the group consisting of dry silica particles and silica aerogel.

19. The heat transfer inhibiting sheet according to claim 18, wherein The inorganic particles further include at least one kind of particles selected from the group consisting of titanium dioxide, zircon, zirconium oxide, silicon carbide, zinc oxide, and aluminum oxide.

20. A battery pack having: the heat transfer inhibiting sheet according to any one of claims 10 to 19; and a plurality of battery cells, The plurality of battery cells are connected in series or connected in parallel.

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