Method for manufacturing a heat transfer inhibiting sheet

Abstract

The present invention provides a method for producing a heat transfer inhibiting sheet having strength capable of maintaining the shape of the heat transfer inhibiting sheet and high holding performance of inorganic particles, thereby maintaining excellent heat insulation performance. The method for producing a heat transfer inhibiting sheet has a processing step of processing a mixture into a sheet shape by a dry method, the mixture containing inorganic particles (4) and binder fibers (3) having a core-sheath structure. The binder fibers (3) having a 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 peripheral 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 (7) constituting the sheath portion (2).

Description

Technical Field

[0001] This invention relates to a heat transfer suppressor sheet, a method for manufacturing the same, and a battery pack having the heat transfer suppressor sheet. Background Technology

[0002] In recent years, from an environmental protection perspective, there has been active development of electric vehicles or hybrid vehicles powered by electric motors. These electric vehicles or hybrid vehicles are equipped with battery packs consisting of multiple battery cells connected in series or parallel to serve as the power source for the electric motors that drive them.

[0003] Furthermore, this battery cell primarily uses lithium-ion rechargeable batteries, which offer higher capacity and output compared to lead-acid and nickel-metal hydride batteries. Moreover, in the event of thermal runaway—where a battery cell experiences a rapid temperature increase and continues to heat up due to internal short circuits or overcharging—heat from the thermally runaway cell can propagate to adjacent battery cells, potentially causing thermal runaway in those cells as well.

[0004] As a method to suppress the propagation of heat from battery cells that have experienced thermal runaway as described above, a common practice is to sandwich heat insulation sheets between the battery cells.

[0005] For example, Patent Document 1 discloses a heat insulation sheet for battery packs, which comprises a first particle composed of silica nanoparticles and a second particle composed of metal oxides, and specifies the content of the first particle. Furthermore, Patent Document 1 describes that the heat insulation sheet may comprise a bonding material composed of at least one selected from fibers, adhesives, and heat-resistant resins.

[0006] In addition, the aforementioned patent document 1 describes the following: as the first particle, dry silica or wet silica can be used, and the heat insulation sheet can be manufactured by dry molding or wet papermaking.

[0007] Existing technical documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 2021-34278 Summary of the Invention

[0009] The technical problem that the invention aims to solve

[0010] Furthermore, a type of adhesive used in the manufacture of thermal insulation sheets is, for example, a heat-bonding adhesive fiber. However, to achieve its adhesive properties, the heat-bonding adhesive fiber needs to be in a wet state during manufacturing. Therefore, when using heat-bonding adhesive fibers, the thermal insulation sheet needs to be manufactured using a wet papermaking method.

[0011] However, when using dry silica or silica aerogel with low thermal conductivity to further improve thermal insulation performance, there is a problem that insulation sheets cannot be manufactured using the wet forming method. This is because if the material containing dry silica is formed into sheets using the wet forming method, the dry silica will condense due to water, increasing its thermal conductivity. Furthermore, silica aerogel is generally difficult to disperse in water; therefore, if the material containing silica aerogel is formed using the wet forming method, a uniformly dispersed insulation sheet cannot be obtained, leading to a reduction in quality.

[0012] On the other hand, when using inorganic particles such as dry silica or silica aerogel to manufacture heat insulation sheets via dry molding, the inorganic particles sometimes detach due to pressure, impact, etc. (hereinafter also referred to as powder shedding). Especially in recent years, the capacity of battery cells in battery packs has further increased, thus the expansion rate during charging and discharging has increased. Therefore, when heat insulation sheets are placed between battery cells in a battery pack, if the overall strength of the heat insulation sheet is low, the heat insulation sheet will be compressed due to the expansion of the battery cells during charging and discharging, resulting in powder shedding and a decrease in heat insulation performance. As a result, in the event of thermal runaway of the battery cells and high temperatures, the heat insulation sheet cannot function effectively, sometimes causing a thermal cascading effect. Therefore, there is a need to develop heat insulation sheets and their manufacturing methods that possess high strength that can maintain their shape, suppress powder shedding, and maintain excellent heat insulation performance.

[0013] The heat insulation sheet described in the aforementioned patent document 1 can maintain excellent heat insulation even under increased compressive stress, but further improvements are required regarding its heat insulation, strength, and ability to suppress powder shedding.

[0014] The present invention was made in view of the above-mentioned problems, and its object is to provide a method for manufacturing a heat transfer suppressing sheet, a heat transfer suppressing sheet, and a battery pack having the heat transfer suppressing sheet, wherein the heat transfer suppressing sheet has the strength to maintain its shape even when compressive stress is applied to the heat transfer suppressing sheet, and has high inorganic particle retention performance, thereby maintaining excellent heat insulation performance.

[0015] Means for solving technical problems

[0016] The above-mentioned objective of the present invention is achieved by the following [1] configuration involved in the manufacturing method of the heat transfer inhibition sheet.

[0017] [1] A method for manufacturing a heat transfer inhibition sheet, characterized in that it includes a processing step of processing a mixture into a sheet shape by a dry method, wherein the mixture comprises inorganic particles and adhesive fibers having a core-sheath structure.

[0018] The adhesive fiber with a core-sheath structure has a core extending along its length and a sheath formed to cover the outer peripheral surface of the core.

[0019] The melting point of the first organic material constituting the core is higher than the melting point of the second organic material constituting the sheath.

[0020] Furthermore, the preferred embodiments of the present invention relating to the method for manufacturing the heat transfer inhibition sheet are as follows [2] to [7].

[0021] [2] In the method of manufacturing the heat transfer suppression sheet of [1], the characteristic is that the melting point of the first organic material is more than 60°C higher than the melting point of the second organic material.

[0022] [3] In the method of manufacturing the heat transfer suppressing sheet of [1] or [2], the processing step is characterized by a step of pressurizing the mixture and a step of heating the mixture.

[0023] [4] In the method for manufacturing the heat transfer inhibition sheet of [3], the characteristic is that the heating temperature in the process of heating the mixture is set to a temperature that is higher than the melting point of the second organic material and lower than the melting point of the first organic material.

[0024] [5] In a method for manufacturing a heat transfer inhibition sheet according to any one of [1] to [4], the inorganic particles are characterized in that the inorganic particles comprise at least one type of particles selected from dry silica particles and silica aerogel.

[0025] [6] In the method of manufacturing the heat transfer suppression sheet of [5], the inorganic particles are characterized in that the inorganic particles further include at least one type of particles selected from titanium dioxide, zircon, zirconium oxide, silicon carbide, zinc oxide and aluminum oxide.

[0026] [7] In a method for manufacturing a heat transfer inhibiting sheet according to any one of [1] to [6], the mixture is characterized in that it comprises hot-melt powder.

[0027] Furthermore, the above-mentioned objective of the present invention is achieved by the following [8] configuration of the heat transfer suppression sheet.

[0028] [8] A heat transfer inhibition sheet, characterized in that the heat transfer inhibition sheet comprises: inorganic particles; organic fibers containing a first organic material; and a cladding portion covering the outer peripheral surface of the organic fibers.

[0029] The cladding portion comprises the inorganic particles and a second organic material having a melting point lower than that of the first organic material.

[0030] Furthermore, the preferred embodiments of the present invention relating to the heat transfer inhibition sheet are as follows [9] to

[13] .

[0031] [9] In the heat transfer suppression sheet of [8], the inorganic particles are characterized in that the inorganic particles are at least one type of particles composed of inorganic materials selected from oxide particles, carbide particles, nitride particles and inorganic hydrate particles.

[0032]

[10] In the heat transfer suppression sheet of [9], the inorganic particles are characterized in that the inorganic particles comprise at least one type of particles selected from dry silica particles and silica aerogel.

[0033]

[11] In the heat transfer suppression sheet of

[10] , the inorganic particles further comprise at least one type of particle selected from titanium dioxide, zircon, zirconium oxide, silicon carbide, zinc oxide and aluminum oxide.

[0034]

[12] A heat transfer suppressor sheet of any one of [8] to

[11] , characterized in that the melting point of the second organic material is more than 60°C lower than the melting point of the first organic material.

[0035]

[13] A heat transfer inhibiting sheet according to any one of [8] to

[12] , characterized in that the first organic material is at least one selected from polyethylene terephthalate, polypropylene and nylon.

[0036] The second organic material is at least one selected from polyethylene terephthalate, polyethylene, polypropylene and nylon.

[0037] Furthermore, the above-mentioned objective of the present invention is achieved by the following

[14] configuration of the battery pack.

[0038]

[14] A battery pack having a heat transfer suppressor sheet of any one of [8] to

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

[0039] Invention Effects

[0040] The method for manufacturing the heat transfer suppression sheet of the present invention includes a processing step of dry-processing a mixture comprising inorganic particles and adhesive fibers having a core-sheath structure into a sheet shape, wherein the melting point of the organic material constituting the core of the adhesive fibers is higher than that of the organic material constituting the sheath. Therefore, the core can be retained during manufacturing to form a skeleton, and the sheath can be melted to fuse the surrounding inorganic particles, thus preventing the inorganic particles from detaching from the heat transfer suppression sheet, resulting in a heat transfer suppression sheet that achieves both excellent strength and heat transfer suppression effect. Furthermore, according to the method for manufacturing the heat transfer suppression sheet of the present invention, since the melting points of the core and sheath of the adhesive fibers are different, temperature control for melting the sheath while retaining the core becomes easier.

[0041] Furthermore, the heat transfer suppression sheet according to the present invention, due to containing inorganic particles with excellent heat transfer suppression effect, can achieve excellent thermal insulation properties. Additionally, the heat transfer suppression sheet according to the present invention has organic fibers and a cladding portion covering its outer peripheral surface. Through this cladding portion, the apparent fiber diameter of the organic fibers becomes thicker, thereby increasing the strength of the skeleton composed of organic fibers. Therefore, excellent strength can be obtained, thereby preventing powder shedding and maintaining excellent thermal insulation performance.

[0042] According to the present invention, the battery pack, having a heat transfer suppression sheet with high strength and excellent heat insulation performance as described above, can suppress thermal runaway of the battery cells in the battery pack and the spread of flames to the outside of the battery casing. Attached Figure Description

[0043] Figure 1 This is a schematic diagram showing a part of the manufacturing method of the heat transfer inhibition sheet according to the first embodiment of the present invention, and a schematic diagram showing the state after the raw materials are mixed.

[0044] Figure 2 This is a schematic diagram showing the structure of a heat transfer suppression sheet manufactured by a manufacturing method according to a first embodiment of the present invention.

[0045] Figure 3 This is a schematic cross-sectional view showing the structure of a heat transfer suppression sheet manufactured by the manufacturing method according to the first embodiment of the present invention.

[0046] Figure 4 The accompanying drawing is a photograph showing an enlarged view of the heat transfer suppression sheet according to the first embodiment of the present invention.

[0047] Figure 5 This is a schematic diagram showing the structure of a heat transfer suppressing sheet manufactured by the manufacturing method of the heat transfer suppressing sheet according to the second embodiment of the present invention.

[0048] Figure 6The accompanying photograph is a magnified view of the heat transfer suppression sheet according to the second embodiment of the present invention.

[0049] Figure 7 The accompanying photograph is a substitute photograph showing the state of wet silica and dry silica particles.

[0050] Figure 8 This is a graph showing the change in thermal conductivity of wet silica and dry silica at various temperatures.

[0051] Figure 9 This is a schematic diagram illustrating a battery pack according to an embodiment of the present invention.

[0052] Figure 10 This is a schematic diagram illustrating the method for determining the scattering rate.

[0053] Figure 11 This is a graph showing the changes in thermal conductivity of Comparative Example 3 and Example 1 at various temperatures.

[0054] Figure 12 The accompanying drawings are substitute photographs showing the surfaces and cross-sections of Comparative Example 5 and Example 1.

[0055] Figure 13 It is a graph showing the change in the scattering rate with the number of hits, with the vertical axis representing the scattering rate and the horizontal axis representing the number of hits.

[0056] Label Explanation

[0057] 1: Core;

[0058] 2: Sheath;

[0059] 3: Adhesive fibers;

[0060] 4: Inorganic particles;

[0061] 5: Cladding section;

[0062] 6: Fiber section;

[0063] 7: Second organic material;

[0064] 8: Base Material Section;

[0065] 9: Mixture;

[0066] 10, 13: Heat transfer inhibition tablets;

[0067] 12: Cracks;

[0068] 16: Curing part;

[0069] 17: Curing layer;

[0070] 20a, 20b, 20c: Battery cells;

[0071] 30: Battery casing;

[0072] 100: Battery pack. Detailed Implementation

[0073] The inventors of this invention have conducted in-depth research on heat transfer suppression sheets that can solve the above-mentioned technical problems.

[0074] The results showed that by using adhesive fibers with a core-sheath structure having a high melting point core and a low melting point sheath, heat transfer suppression sheets can be manufactured using a dry method. This allows the core to act as a skeleton to achieve high strength, while the sheath melts to retain inorganic particles, thereby suppressing powder shedding.

[0075] Specifically, during the manufacture of the heat transfer suppression sheet, if the heating temperature is set so as not to melt the core when heating the sheet material, only the low-melting-point sheath can be melted. Then, by cooling, the sheath, containing the surrounding inorganic particles, is re-fused onto the core. Therefore, after cooling, the core and the fused portion containing inorganic particles form a skeleton, which can improve the strength of the heat transfer suppression sheet. In addition, since the sheath melts and is fused onto the core together with the inorganic particles, the inorganic particles on the surface of the heat transfer suppression sheet are retained on the sheet surface, thus preventing powder shedding. As a result, high thermal insulation performance can be maintained even when pressure or impact is applied to the heat transfer suppression sheet.

[0076] The following provides a detailed description of the manufacturing method of the heat transfer suppression sheet, the heat transfer suppression sheet, and the battery pack according to embodiments of the present invention. Furthermore, the present invention is not limited to the embodiments described below, and can be implemented in any way without departing from the spirit of the invention.

[0077] [1. Manufacturing method of heat transfer inhibition sheet]

[0078] <First Implementation>

[0079] Figure 1 This is a schematic diagram illustrating the state of raw materials after mixing in a part of the heat transfer inhibition sheet manufacturing method according to the first embodiment of the present invention. Figure 2 This is a schematic diagram illustrating the structure of a heat transfer suppression sheet manufactured by the manufacturing method according to the first embodiment of the present invention. Figure 3 This is its sectional view. Additionally, Figure 4 The accompanying drawing is a photograph showing an enlarged view of the heat transfer suppression sheet according to the first embodiment of the present invention.

[0080] (Processing steps)

[0081] like Figure 1As shown, firstly, inorganic particles 4 and adhesive fibers 3 with a core-sheath structure are fed into a mixer such as a V-type mixer in a predetermined ratio to prepare mixture 9. In this embodiment, since the heat transfer suppression sheet is manufactured by a dry process, solvents such as water, which are required for wet molding, are not added to mixture 9. However, in order to prevent the handling of raw materials from becoming difficult due to the flying of inorganic particles and other powders during the manufacture of the heat transfer suppression sheet, a small amount of solvent such as water may be added within the range of dry processes in this embodiment. 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.

[0082] 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. In addition, the melting point of the first organic material is higher than that of the second organic material.

[0083] Then, the obtained mixture 9 is placed into a specified mold, and pressure is applied using a stamping press or the like, while the resulting molded body (not shown) is heated. At this time, through heating, the sheath 2 of the adhesive fiber 3 melts, forming a molten portion (not shown) containing inorganic particles present around the core 1. Then, as... Figure 2 and Figure 3 As shown, by cooling the heated mixture, the molten sheath 2 is re-clad onto the core 1, forming a fiber portion 6 comprising a clad portion 5 and the core 1. The clad portion 5 comprises a second organic material 7 constituting the sheath 2 and inorganic particles 4. Furthermore, a base material portion 8 containing inorganic particles 4 is formed between the plurality of fiber portions 6. Thus, a heat transfer suppression sheet 10 processed into a sheet shape can be obtained.

[0084] According to the manufacturing method of this embodiment, 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. Therefore, when the mixture 9 is heated, the core 1 can be retained while the sheath 2 melts. Thus, the strength of the heat transfer suppression sheet 10 can be ensured by the core 1. In addition, after cooling, the outer peripheral surface of the core 1 is covered by the second organic material 7 containing inorganic particles 4, forming a cladding portion 5, thus retaining the inorganic particles 4. Furthermore, the resulting fiber portion 6 has a structure with a larger fiber diameter due to the core 1 and the cladding portion 5, thus achieving higher strength than the core 1 alone. Moreover, in the mixture 9, the adhesive fibers 3 exist in an irregular orientation, and sometimes the adhesive fibers 3 are in partial contact with each other. Thus, as Figure 4 As shown in the contact portion 11, when the molten sheath portion 2 is cooled, adjacent core portions 1 are fused together through the cladding portion 5 to form a three-dimensional skeleton. As a result, the overall shape of the heat transfer suppression sheet can be maintained with higher strength.

[0085] Furthermore, as a raw material for the heat transfer suppression sheet, the mixture 9 may also contain binders such as hot-melt powder, as will be described in detail later. By appropriately adjusting the type and content of the binder contained in the mixture 9, the holding power of the inorganic particles 4 can be improved, further suppressing powder shedding.

[0086] Furthermore, even when using organic fibers without a core-sheath structure as adhesive fibers, the core of the adhesive fiber can be retained while only the surface melts, allowing inorganic particles to coat the surface, by setting the temperature. However, during the manufacture of heat transfer suppression sheets, heating is typically performed from one or both sides perpendicular to the thickness direction. Due to the use of materials with high thermal insulation properties, it is difficult to reach the same temperature on the surface side and the center side in the thickness direction of the sheet. That is, on the surface side of the sheet, if the temperature is set to melt only the surface of the organic fibers, the surface of the organic fibers will not melt on the center side of the sheet, reducing the holding force of the inorganic particles 4. In addition, if the temperature is set to melt the surface of the organic fibers on the center side of the sheet, the organic fibers will melt to the radial center on the surface side, making it difficult to ensure the strength of the sheet.

[0087] In contrast, in this embodiment, the melting point of the first organic material constituting the core 1 is higher than that of the second organic material constituting the sheath 2, so it is extremely easy to set the temperature for retaining the core 1 while melting the sheath 2. Moreover, in the resulting heat transfer suppression sheet, the core 1 serves as a skeleton for maintaining the strength of the sheet on either the surface side or the center side, thereby achieving an ideal structure in which a cladding portion 5 containing inorganic particles 4 is formed on the surface of the core 1.

[0088] As a result, the heat transfer suppression sheet 10 manufactured by the manufacturing method of this embodiment has a strong skeleton, which can maintain its shape even when pressure or impact is applied to the heat transfer suppression sheet, can suppress powder shedding, and can maintain excellent heat insulation performance.

[0089] Furthermore, to further suppress powder shedding, the surface of the heat transfer suppressing sheet 10 can be covered with a film or the like. Examples of polymer films include those made of polyimide, polycarbonate, PET, p-phenylene sulfide, polyetherimide, cross-linked polyethylene, flame-retardant chloroprene rubber, polyvinyl fluoride, rigid vinyl chloride, polybutylene terephthalate, PTFE, PFA, FEP, ETFE, rigid PCV, flame-retardant PET, polystyrene, polyethersulfone, polyamide-imide, polyacrylonitrile, polyethylene, polypropylene, and polyamide. The method of covering the surface of the heat transfer suppressing sheet 10 with a film is not particularly limited; examples include methods such as bonding with adhesives, wrapping the heat transfer suppressing sheet 10 with a film, and containing the heat transfer suppressing sheet 10 in a bag-like film.

[0090] <Second Implementation>

[0091] Figure 5 This is a schematic diagram showing the structure of a heat transfer suppression sheet manufactured by the manufacturing method of the heat transfer suppression sheet according to the second embodiment of the present invention. Furthermore, Figure 6 The accompanying photograph is a magnified view of the heat transfer suppression sheet according to the second embodiment of the present invention. Furthermore, the second embodiment differs from the first embodiment only in the material; the manufacturing process is the same as that of the heat transfer suppression sheet according to the first embodiment. Therefore, in... Figure 5 and Figure 6 In the middle, to and Figures 1 to 4 The same parts are labeled with the same number, and their descriptions are omitted or simplified.

[0092] (Processing steps)

[0093] like Figure 1 As shown, firstly, adhesive fibers 3 having a core-sheath structure, inorganic particles 4, and hot-melt powder (not shown) are added in a predetermined ratio to a mixer such as a V-type mixer to prepare a mixture. The hot-melt powder is formed by molding a third organic material, such as ethylene-vinyl acetate copolymer (EVA), into a powder form. Furthermore, the melting point of the hot-melt powder is lower than the melting point of the first organic material constituting the core 1.

[0094] Then, the obtained mixture is placed into a specified mold, and pressure is applied using a stamping press or the like. The resulting molded body is heated, thereby melting the sheath 2 of the adhesive fiber 3 and the hot-melt powder. Then, by cooling the heated mixture, the molten sheath 2 is re-clad onto the core 1, forming a cladding portion 5 containing a second organic material 7 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, it constitutes the fiber portion 6. Furthermore, the molten hot-melt powder solidifies while containing the surrounding inorganic particles 4, forming a solidified portion 16 containing a third organic material constituting the hot-melt powder and inorganic particles 4 in all regions between the plurality of fiber portions 6. Thus, the heat transfer suppression sheet 13 of the second embodiment can be obtained.

[0095] Furthermore, as described above, if hot melt powder is added as the material for the heat transfer suppressor sheet, the hot melt powder, which melts upon heating, is prone to segregation on the surface of the molded body. Therefore, a thinner cured layer 17 is formed on the surface of the heat transfer suppressor sheet 13. Moreover, the cured portion 16 includes thin cured layers 17 dispersed in multiple regions, and sometimes cracks 12 form between the multiple cured layers 17.

[0096] According to the manufacturing method of the second embodiment, 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 and the melting point of the third organic material constituting the hot-melt powder. Therefore, when the mixture 9 is heated, the core 1 can be retained while the sheath 2 and the hot-melt powder are melted. Thus, the strength of the heat transfer suppression sheet 13 can be ensured by the core 1.

[0097] Furthermore, through cooling, the sheath 2 is re-clad onto the core 1 while still containing the surrounding inorganic particles 4, forming a cladding portion 5, and the hot-melt powder solidifies while still containing the surrounding inorganic particles 4, forming a solidified portion 16. Therefore, not only are the inorganic particles 4 retained by the cladding portion 5, but the inorganic particles 4 can also be retained by the solidified portion 16 in areas other than the cladding portion 5. In particular, as described above, the hot-melt powder that melts upon heating tends to segregate on the surface of the molded body, and the surface of the heat transfer inhibiting sheet 13 becomes covered by a thinner solidified layer 17, thus further suppressing the shedding of the inorganic particles 4.

[0098] Furthermore, in this embodiment, if cracks 12 are formed between the thin cured layers 17 dispersed in multiple regions, and a heat transfer suppression sheet 13 is disposed between multiple battery cells, the heat transfer suppression sheet 13 is prone to deformation due to the expansion and contraction of the battery cells during charging and discharging. Therefore, damage to the heat transfer suppression sheet 13 can be suppressed, and the load on adjacent battery cells can also be reduced.

[0099] Furthermore, between the skeleton composed of fiber sections 6, the cured section 16, which contains hot-melt powder and inorganic particles 4, supports the skeleton, thus enabling the overall shape of the heat transfer suppression sheet to be maintained at a higher strength. As a result, even when pressure or impact is applied to the heat transfer suppression sheet, high thermal insulation performance can be maintained.

[0100] Furthermore, in the second embodiment, to further suppress powder shedding, the surface of the heat transfer suppression sheet 13 may be coated with a film or the like. The types of films and the methods of coating with films are the same as described above.

[0101] Next, the adhesive fibers and heating conditions used in the manufacturing method of the heat transfer inhibition sheet of this embodiment will be described.

[0102] <Adhesive Fibers>

[0103] The adhesive fiber 3 that can be used in this embodiment is not particularly limited, 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 for the core 1, at least one selected from polyethylene terephthalate, polypropylene, and nylon can be chosen. Furthermore, as the second organic material for the sheath 2, at least one selected from polyethylene terephthalate, polyethylene, polypropylene, and nylon can be chosen.

[0104] 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 temperature setting margin in the heating process can be expanded, and the temperature setting for obtaining the desired structure can be more easily achieved. 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, and even more preferably 80°C or more.

[0105] Furthermore, adhesive fibers with the aforementioned core-sheath structure are commonly sold on the market, and the materials constituting the core and sheath can be the same or different. Examples of adhesive fibers where the core 1 and sheath 2 are made of the same material but have different melting points include: adhesive fibers where the core 1 and sheath 2 are made of polyethylene terephthalate; adhesive fibers where the core 1 and sheath 2 are made of polypropylene; and adhesive fibers where the core 1 and sheath 2 are made of nylon. Examples of adhesive fibers where the core 1 and sheath 2 are made of different materials include: adhesive fibers where the core 1 is made of polyethylene terephthalate and the sheath 2 is made of polyethylene; and adhesive fibers where the core 1 is made of polypropylene and the sheath 2 is made of polyethylene.

[0106] In this embodiment, the melting point of the second organic material constituting the sheath of the adhesive fiber represents the melting temperature at which the second organic material begins to melt and deform, and softening accompanied by shape change is also judged as a type of melting and deformation. The melting point of the sheath of the adhesive fiber can be determined, for example, by the following method.

[0107] The adhesive fiber, which is the object of the test, is placed in contact with glass fiber, which has a higher melting point. It is heated from room temperature to, for example, 200°C at a heating rate of 5°C / min, and then cooled to room temperature. If the surface of the adhesive fiber undergoes melting deformation and fuses with the glass fiber at the point of contact, or if the cross-sectional shape of the adhesive fiber changes, it can be determined that the melting point of the second organic material constituting the sheath is below 200°C. In this embodiment, by varying the heating temperature and observing the fusion state of the adhesive fiber and glass fiber, or the cross-sectional shape of the adhesive fiber after cooling, using the above method, the melting point of the second organic material constituting the sheath can be determined.

[0108] (Content of adhesive fibers)

[0109] In this embodiment, if the content of adhesive fiber 3 in the mixture 9 is properly controlled, the strengthening effect of the skeleton in the obtained heat transfer inhibition sheet 10 can be fully obtained.

[0110] The content of adhesive fiber 3 relative to the total mass of mixture 9 is preferably 5% by mass or more, more preferably 10% by mass or more. In addition, if the content of adhesive fiber 3 is too high, the content of inorganic particles 4 will be relatively reduced. Therefore, in order to obtain the desired thermal insulation performance, the content of adhesive fiber 3 relative to the total mass of mixture 9 is preferably 25% by mass or less, more preferably 20% by mass or less.

[0111] <Inorganic Particles>

[0112] The types of inorganic particles 4 that can be used in this embodiment will be described later.

[0113] (Content of inorganic particles)

[0114] In this embodiment, if the content of inorganic particles 4 in the mixture 9 is properly controlled, the heat insulation performance of the obtained heat transfer suppression sheet 10 can be adequately ensured.

[0115] The content of all inorganic particles 4 in the mixture 9 is preferably 60% by mass or more, more preferably 70% by mass or more, relative to the total mass of the mixture 9. In addition, if the content of inorganic particles 4 is too high, the content of adhesive fibers 3 will be relatively reduced. Therefore, in order to obtain sufficient reinforcement effect of the skeleton, the content of inorganic particles 4 is preferably 95% by mass or less, more preferably 90% by mass or less, relative to the total mass of the mixture 9.

[0116] <Hot Melt Powder>

[0117] In this embodiment, in addition to the adhesive fibers 3 and inorganic particles 4 described above, the mixture 9 may also contain a hot-melt powder (not shown). The hot-melt powder is, for example, a powder containing a third organic material different from the first and second organic materials described above, and having the property of melting upon heating. By including the hot-melt powder in the mixture 9 and heating it, the hot-melt powder melts, and upon cooling, it solidifies while still containing the surrounding inorganic particles 4, forming a solidified portion 16. As described above, the solidified portion 16 includes a thin solidified layer 17 dispersed in multiple regions on the surface of the heat transfer suppressing sheet 13. Since the surface of the heat transfer suppressing sheet 13 is covered by this thin solidified layer, it is possible to further suppress the inorganic particles 4 from detaching from the heat transfer suppressing sheet 13.

[0118] As a hot-melt powder, various hot-melt powders with different melting points can be cited, but considering the melting points of the core 1 and sheath 2 of the adhesive fiber 3 used, a hot-melt powder with an appropriate melting point can be selected. For example, if the melting point of the hot-melt powder is lower than the melting point of the core 1, a heating temperature can be set to melt the sheath 2 and the hot-melt powder while retaining the core 1. Furthermore, if the melting point of the hot-melt powder is lower than the melting point of the sheath 2, the heating temperature during manufacturing only needs to be set between the melting points of the core 1 and the sheath 2, thus making it easier to set the heating temperature.

[0119] On the other hand, the type of hot-melt powder used can be selected such that its melting point is between the melting point of the core 1 and the melting point of the sheath 2. If a hot-melt powder with such a melting point is used, after both the sheath 2 and the hot-melt powder melt, upon cooling and solidification, the hot-melt powder in all areas except the organic fibers (core 1) and the surrounding molten sheath 2 solidifies first. As a result, the position of the organic fibers can be fixed, and then the molten sheath 2 fused to the organic fibers, thereby easily forming a three-dimensional skeleton. Therefore, the overall strength of the sheet can be further improved.

[0120] If the melting point of the third organic material constituting the hot-melt powder is sufficiently lower than the melting point of the first organic material constituting the core 1, the temperature setting margin in the heating process can be expanded, making it easier to use a temperature setting that yields a more desired structure. 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, and even more preferably 80°C or more.

[0121] Furthermore, components constituting hot melt powder include polyethylene, polyester, polyamide, ethylene vinyl acetate copolymer, etc.

[0122] (Content of hot melt powder)

[0123] In order to suppress the shedding of inorganic particles, even if the content of hot-melt powder in the mixture 9 is trace, the effect of suppressing powder shedding can be obtained. Therefore, the content of hot-melt powder relative to the total mass of the mixture 9 is preferably 0.5% by mass or more, and more preferably 1% by mass or more.

[0124] On the other hand, if the content of hot melt powder is increased, the content of inorganic particles 4 will be relatively reduced. Therefore, in order to obtain the desired heat insulation performance, the content of hot melt powder relative to the total mass of mixture 9 is preferably 5% by mass or less, more preferably 4% by mass or less.

[0125] <Heating conditions>

[0126] As a process for processing the mixture 9 into a sheet, examples include pressing the mixture 9 and heating the mixture 9. The heating temperature in the heating process is preferably set to a temperature higher than the melting point of the second organic material constituting the sheath 2 and lower than the melting point of the first organic material constituting the core 1. By setting the heating temperature to such a temperature, as described above, the core 1 can ensure the strength of the sheet on either the surface side or the center side, and the cladding portion 5 can retain the inorganic particles 4.

[0127] Furthermore, 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 temperature setting margin in the heating process can be expanded, and the temperature setting for obtaining the desired structure can be more easily achieved. 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 even more preferably 80°C or more higher.

[0128] Furthermore, the heating temperature in the heating process is preferably set to be at least 10°C higher than the melting point of the second organic material constituting the sheath 2, and more preferably at least 20°C higher. On the other hand, the heating temperature is preferably set to be at least 10°C lower than the melting point of the first organic fiber constituting the core 1, and more preferably at least 20°C lower.

[0129] There is no particular limitation on the heating time, but it is preferable to set a heating time that allows the sheath 2 to melt sufficiently. For example, it can be set to a heating time of 3 minutes or more but less than 15 minutes.

[0130] As described in the second embodiment above, when the material includes hot-melt powder as a heat transfer suppressor sheet, the heating temperature in the heating process is preferably set to be at least 10°C higher than the higher of the melting point of the second organic material constituting the sheath 2 and the melting point of the third organic material constituting the hot-melt powder, more preferably at least 20°C higher. On the other hand, the heating temperature is preferably set to be at least 10°C lower than the melting point of the first organic material constituting the core 1, more preferably at least 20°C lower. By setting the heating temperature to such a level, as described above, the strength of the sheet can be further improved by utilizing the skeleton formed by the fiber portion 6 and the curing portion 16, and the detachment of the inorganic particles 4 can be prevented by utilizing the cladding portion 5 and the curing layer 17.

[0131] [2. Heat transfer inhibition tablets]

[0132] (First Implementation)

[0133] Hereinafter, a first embodiment of a heat transfer suppression sheet manufactured by the manufacturing method of the heat transfer suppression sheet according to the first embodiment described above will be described.

[0134] like Figures 2 to 4As shown, the heat transfer suppression sheet according to this embodiment has inorganic particles 4, organic fibers (core 1) containing a first organic material, and a cladding portion 5 covering the outer peripheral surface of the organic fibers. As described above, the cladding portion 5 includes a second organic material 7 having a melting point lower than that of the first organic material, and the inorganic particles 4.

[0135] In the heat transfer suppression sheet 10 of this embodiment, as described above in [1. Method for manufacturing heat transfer suppression sheet], the organic fiber (core 1) and the cladding portion 5 function as a framework, thus achieving excellent strength and shape retention. Furthermore, on either the surface side or the center side of the heat transfer suppression sheet 10, the cladding portion 5 covering the outer peripheral surface of the organic fiber fixes the inorganic particles 4 to the organic fiber (core 1), thereby suppressing powder shedding. Therefore, for example, by arranging the heat transfer suppression sheet 10 of this embodiment between multiple battery cells (described later), excellent thermal insulation performance can be maintained even when the battery cells expand and apply compressive stress or impact to the heat transfer suppression sheet 10.

[0136] In this embodiment, the mechanism by which inorganic particles 4 are suppressed from detaching from the sheet surface (powder shedding) is uncertain, but one reason is believed to be that the organic fibers (core 1) and the cladding portion 5 form a three-dimensional and robust skeleton, maintaining the shape of the heat transfer suppression sheet 10 and thus suppressing deformation or compression of the heat transfer suppression sheet 10. Furthermore, the fiber portion 6, composed of the organic fibers (core 1) exposed on the sheet surface and the cladding portion 5, can absorb the impact applied to the heat transfer suppression sheet 10, which is also considered a reason for retaining the inorganic particles 4.

[0137] And, as Figure 4 As shown, in the heat transfer suppression sheet 10, the cladding portion 5 does not need to completely cover the outer peripheral surface of the organic fiber (core 1), and the organic fiber (core 1) can be partially exposed. In the manufacturing method of the heat transfer suppression sheet according to this embodiment, since the adhesive fiber 3 with a core-sheath structure is used, the sheath portion 2 may sometimes peel off during the manufacturing process, but even when the organic fiber (core 1) is partially exposed, the effects of the present invention can be fully obtained.

[0138] (Second Implementation)

[0139] Hereinafter, a second embodiment of the heat transfer suppression sheet manufactured by the manufacturing method of the heat transfer suppression sheet according to the second embodiment described above will be described. Figure 5 and Figure 6 As shown, regarding the heat transfer suppression sheet 13, and Figure 4Similarly, in the example of the heat transfer suppression sheet according to the first embodiment shown, the sheath of the adhesive fiber in the core-sheath structure is again fused to the core 1. Specifically, the fiber portion 6 is composed of the fused portion 5, which includes a second organic material and inorganic particles 4 constituting the sheath, and the core 1. In addition, adjacent core portions 1 are fused to each other through the fused portion 5 to form a contact portion 11. Moreover, in the area other than the plurality of fiber portions 6, a cured portion 16 is formed, which includes a third organic material and inorganic particles constituting the hot melt powder. Furthermore, the cured portion 16 has a plurality of cured layers 17 on the surface of the heat transfer suppression sheet 13, and cracks 12 are formed between the plurality of cured layers 17.

[0140] Furthermore, if the mixture of materials contains hot-melt powder, the hot-melt powder is present in all areas of the molded body. Therefore, if cooling is performed after heating during the manufacturing process, a third organic material, which is a component of the hot-melt powder, is sometimes included in the cladding section 5. Similarly, near the organic fibers, a second organic material, which is a component of the sheath section 2, is sometimes included in the curing section 16. In either case, the effectiveness of the present invention is not affected.

[0141] In the heat transfer suppression sheet 13 of the second embodiment, similar to the first embodiment described above, a solidified portion 16 containing hot-melt powder and inorganic particles 4 supports the skeleton, thus maintaining the overall shape of the heat transfer suppression sheet with higher strength. Furthermore, the outer peripheral surface of the organic fibers is covered by the cladding portion 5, and a solidified portion 16 is also formed in areas other than the cladding portion 5, thus retaining the inorganic particles 4. Furthermore, a thin solidified layer 17 is formed on the surface of the heat transfer suppression sheet 13, thus achieving a high powder shedding suppression effect. Moreover, when cracks 12 are formed, the heat transfer suppression sheet 13 easily deforms with the expansion and contraction of the battery cells during charging and discharging. Therefore, for example, by arranging the heat transfer suppression sheet 13 of this embodiment between multiple battery cells (described later), excellent heat insulation performance can be maintained even when the battery cells expand and apply compressive stress or impact to the heat transfer suppression sheet 13.

[0142] The materials constituting the heat transfer suppression sheet of this embodiment will be described in detail below.

[0143] <Organic Fiber>

[0144] In the heat transfer suppression sheet 10, the core 1, made of a first organic material, functions as an organic fiber that maintains the strength and shape of the sheet. The first organic material constituting the organic fiber is not particularly limited as long as its melting point is higher than that of the second organic material present on the outer periphery of the organic fiber. Examples of the first organic material include at least one selected from polyethylene terephthalate, polypropylene, and nylon.

[0145] (Organic fiber content)

[0146] In this embodiment, if the content of organic fibers in the heat transfer inhibition sheet 10 is properly controlled, the reinforcement effect of the skeleton can be fully obtained.

[0147] The content of organic fibers relative to the total mass of the heat transfer inhibiting sheet 10 is preferably 2% by mass or more, more preferably 4% by mass or more. In addition, if the content of organic fibers is too high, the content of inorganic particles 4 will be relatively reduced. Therefore, in order to obtain the desired heat insulation performance, the content of organic fibers relative to the total mass of the heat transfer inhibiting sheet 10 is preferably 10% by mass or less, more preferably 8% by mass or less.

[0148] (Fiber length of organic fibers)

[0149] There is no particular limitation on the fiber length of organic fibers. From the point of view of ensuring formability and processability, the average fiber length of organic fibers is preferably less than 10 mm.

[0150] On the other hand, from the viewpoint of enabling the organic fiber to function as a skeleton and ensuring the compressive strength of the heat transfer suppression sheet, the average fiber length of the organic fiber is preferably 0.5 mm or more.

[0151] <Clad Section>

[0152] The cladding section 5 is formed by temporarily melting the sheath 2 of the adhesive fiber 3 with a core-sheath structure through heating and then cooling it, and contains a second organic material 7 and inorganic particles 4.

[0153] (Second Organic Material)

[0154] There are no particular limitations on the second organic material, as long as its melting point is lower than that of the first organic material constituting the aforementioned organic fiber. Examples of the second organic material include at least one selected from polyethylene terephthalate, polyethylene, polypropylene, and nylon.

[0155] Furthermore, the melting point of the second organic material is preferably 90°C or higher, more preferably 100°C or higher. Additionally, the melting point of the second organic material is preferably 150°C or lower, more preferably 130°C or lower.

[0156] <Cure Department>

[0157] As a material for a heat transfer suppression sheet, when it contains hot-melt powder, the manufactured heat transfer suppression sheet has a curing portion 16. The curing portion 16 is formed by temporarily melting the hot-melt powder by heating and then cooling it, and includes a third organic material constituting the hot-melt powder and inorganic particles 4.

[0158] (Third Organic Material)

[0159] As described above, there is no particular limitation on the third organic material, which is a component of the hot-melt powder, as long as its melting point is lower than that of the first organic material constituting the aforementioned organic fiber. To facilitate control of the heating temperature during manufacturing, the melting point of the hot-melt powder (third organic material) is preferably below that of the second organic material constituting the sheath. However, for the purpose of forming a more three-dimensional framework and improving the strength of the heat transfer inhibition sheet, the melting point of the third organic material may be positioned between the melting points of the first and second organic materials.

[0160] Furthermore, the melting point of the hot-melt powder (third organic material) is preferably 80°C or higher, more preferably 90°C or higher. Additionally, the melting point of the hot-melt powder (third organic material) is preferably 180°C or lower, more preferably 150°C or lower. Furthermore, the third organic material constituting the hot-melt powder is preferably at least one selected from polyethylene, polyester, polyamide, and ethylene vinyl acetate copolymer.

[0161] (Inorganic particles)

[0162] As inorganic particles, a single inorganic particle can be used, or two or more inorganic particles can be used in combination. From the viewpoint of heat transfer inhibition, particles composed of at least one inorganic material selected from oxide particles, carbide particles, nitride particles, and inorganic hydrate particles are preferred, with oxide particles being more preferred. Furthermore, there are no particular limitations on the shape, but it is preferable to include at least one type selected from nanoparticles, hollow particles, and porous particles. Specifically, inorganic hollow spheres such as silica nanoparticles, metal oxide particles, microporous particles, and hollow silica particles, particles composed of thermally expandable inorganic materials, and particles composed of hydrous porous bodies can also be used.

[0163] When the average secondary particle size of the inorganic particles is 0.01 μm or more, it is readily available, which helps to suppress the increase in manufacturing costs. Furthermore, when it is 200 μm or less, the desired heat insulation effect can be obtained. Therefore, the average secondary particle size of the inorganic particles is preferably 0.01 μm or more and 200 μm or less, more preferably 0.05 μm or more and 100 μm or less.

[0164] Furthermore, by using two or more types of inorganic particles with different heat transfer inhibition effects, multi-stage cooling of the heating element can be achieved, enabling endothermic effects over a wider temperature range. Specifically, it is preferable to use a mixture of large-diameter and small-diameter particles. For example, when using nanoparticles as one type of inorganic particle, it is preferable that the other type of inorganic particle comprises inorganic particles composed of metal oxides. Hereinafter, small-diameter inorganic particles will be referred to as the first type of inorganic particle, and large-diameter inorganic particles as the second type of inorganic particle, for a more detailed explanation of the inorganic particles.

[0165] <First Inorganic Particle>

[0166] (Oxide particles)

[0167] Oxide particles have a high refractive index, resulting in strong light diffuse reflection. Therefore, when oxide particles are used as the first inorganic particle, they can suppress radiative heat transfer, especially in high-temperature regions such as those experiencing abnormal heating. As oxide particles, at least one type of particle selected from silicon dioxide, titanium dioxide, zircon, barium titanate, zinc oxide, and aluminum oxide can be used. That is, only one type of the aforementioned oxide particles that can be used as inorganic particles can be used, or two or more types of oxide particles can be used. In particular, silicon dioxide is a component with high thermal insulation properties, and titanium dioxide is a component with a higher refractive index compared to other metal oxides. Both are highly effective at diffusely reflecting light and blocking radiative heat in high-temperature regions above 500°C. Therefore, silicon dioxide and titanium dioxide are most preferably used as oxide particles.

[0168] (Average primary particle size of oxide particles: greater than 0.001 μm and less than 50 μm)

[0169] The particle size of oxide particles can sometimes affect the effectiveness of reflecting radiant heat. Therefore, if the average primary particle size is limited to a specified range, higher thermal insulation can be achieved.

[0170] That is, when the average primary particle size of the oxide particles is greater than 0.001 μm, it is large enough compared to the wavelength of light that helps to heat up, so that the light is diffusely reflected efficiently. Therefore, in the high temperature region above 500°C, the radiative heat transfer of heat in the heat transfer suppression sheet is suppressed, which can further improve the heat insulation performance.

[0171] On the other hand, when the average primary particle size of oxide particles is less than 50 μm, even when compressed, the number of contact points between particles does not increase, making it difficult to form a conductive heat transfer path. Therefore, it can reduce the influence of the typical temperature range, where conductive heat transfer is dominant, on insulation performance.

[0172] Furthermore, in this invention, the average primary particle size can be obtained by observing the particles under a microscope, comparing them with a standard scale, and taking the average of any 10 particles.

[0173] (Nanoparticles)

[0174] In this invention, nanoparticles refer to nanoscale particles that are spherical or nearly spherical with an average primary particle size of less than 1 μm. Because nanoparticles are low-density, they suppress conductive heat transfer. If nanoparticles are used as the first inorganic particle, the voids are further finely dispersed, thus achieving excellent thermal insulation by suppressing convective heat transfer. Therefore, in battery use within typical ambient temperature ranges, nanoparticles are preferred from the perspective of suppressing thermal conduction between adjacent nanoparticles.

[0175] Furthermore, if nanoparticles with small average primary particle size are used as oxide particles, the increase in conductive heat transfer of the heat transfer suppressor can be suppressed even when the heat transfer suppressor is compressed due to the expansion accompanying the thermal runaway of the battery cell, resulting in an increase in internal density. This is believed to be because the nanoparticles easily form small gaps between them due to the repulsive force generated by electrostatics, resulting in low bulk density, thus allowing the particles to be filled in a buffering manner.

[0176] Furthermore, in this invention, when using nanoparticles as the first inorganic particle, there are no particular limitations on the material as long as they meet the above definition of nanoparticles. For example, silica nanoparticles are highly insulating materials, and the contact points between the particles are small, therefore the heat conducted through silica nanoparticles is less compared to using silica particles with larger particle sizes. Additionally, the bulk density of silica nanoparticles typically obtained is 0.1 g / cm³. 3 Therefore, even if the battery cells disposed on both sides of the heat insulation sheet undergo thermal expansion and apply large compressive stress to the heat insulation sheet, the size (area) and number of contact points between the silica nanoparticles will not increase significantly, thus maintaining heat insulation performance. Therefore, silica nanoparticles are preferred as nanoparticles. Examples of silica nanoparticles include wet silica, dry silica, and aerogel; the silica nanoparticles particularly suitable for this embodiment will be described below.

[0177] Figure 7 This is a substitute photograph illustrating the state of wet and dry silica particles. Additionally, Figure 8 This is a graph showing the change in thermal conductivity of wet and dry silica at various temperatures. For example... Figure 7 As shown, wet silica particles agglomerate, while dry silica particles disperse. In the temperature range below 300°C, conduction dominates heat transfer; therefore, as... Figure 8 As shown, compared with wet silica, dry silica, which allows for particle dispersion, can achieve superior thermal insulation performance.

[0178] Furthermore, in the method for manufacturing the heat transfer suppression sheet according to this embodiment, the mixture containing the material is processed into a sheet shape using a dry process. Therefore, as inorganic particles, dry silica, silica aerogel, or the like with low thermal conductivity are preferably used.

[0179] (Average primary particle size of nanoparticles: greater than 1 nm and less than 100 nm)

[0180] If the average primary particle size of the nanoparticles is limited to a specified range, higher thermal insulation performance can be obtained.

[0181] That is, when the average primary particle size of the nanoparticles is set to be greater than 1 nm and less than 100 nm, especially in the temperature range below 500 °C, convective and conductive heat transfer within the heat transfer suppression sheet can be suppressed, thereby further improving the thermal insulation performance. In addition, even under compressive stress, the voids remaining between the nanoparticles and the contacts between multiple particles can also suppress conductive heat transfer, maintaining the thermal insulation performance of the heat transfer suppression sheet.

[0182] Furthermore, the average primary particle size of the nanoparticles is more preferably 2 nm or more, and even more preferably 3 nm or more. On the other hand, the average primary particle size of the nanoparticles is more preferably 50 nm or less, and even more preferably 10 nm or less.

[0183] (Inorganic hydrate particles)

[0184] When inorganic hydrate particles are heated by a heat source and reach a temperature above the initiation temperature of thermal decomposition, they undergo thermal decomposition, releasing their own water of crystallization and thus lowering the temperature of the heat source and its surroundings, exhibiting what is known as "endothermic effect." Furthermore, after releasing the water of crystallization, they become porous, exhibiting a thermal insulating effect through numerous air pores.

[0185] Specific examples of inorganic hydrates include aluminum hydroxide (Al(OH)3), magnesium hydroxide (Mg(OH)2), calcium hydroxide (Ca(OH)2), zinc hydroxide (Zn(OH)2), iron hydroxide (Fe(OH)2), manganese hydroxide (Mn(OH)2), zirconium hydroxide (Zr(OH)2), and gallium hydroxide (Ga(OH)3).

[0186] For example, aluminum hydroxide contains about 35% water of crystallization, as shown in the following formula. It undergoes thermal decomposition to release the water of crystallization, exhibiting an endothermic effect. Moreover, after releasing the water of crystallization, it becomes alumina (Al2O3), a porous material, which functions as a heat insulation component.

[0187] 2Al(OH)3 → Al2O3 + 3H2O

[0188] Furthermore, as described later, the heat transfer suppression sheet 10 involved in this embodiment is preferably located between battery cells, but in a battery cell where thermal runaway has occurred, the temperature rises sharply to over 200°C and continues to rise to around 700°C. Therefore, as inorganic particles, it is preferable to be composed of inorganic hydrates with a thermal decomposition start temperature of 200°C or higher.

[0189] Regarding the thermal decomposition start temperatures of the inorganic hydrates listed above, aluminum hydroxide is approximately 200°C, magnesium hydroxide is approximately 330°C, calcium hydroxide is approximately 580°C, zinc hydroxide is approximately 200°C, iron hydroxide is approximately 350°C, manganese hydroxide is approximately 300°C, zirconium hydroxide is approximately 300°C, and gallium hydroxide is approximately 300°C. These temperatures all roughly overlap with the temperature range of a rapidly rising battery cell that has experienced thermal runaway. They can effectively suppress the temperature rise and are therefore considered preferred inorganic hydrates.

[0190] (Average secondary particle size of inorganic hydrate particles: greater than 0.01 μm and less than 200 μm)

[0191] Furthermore, when inorganic hydrate particles are used as the first inorganic particles, if their average particle size is too large, the first inorganic particles (inorganic hydrates) located near the center of the heat transfer inhibition sheet 10 will require a certain amount of time before reaching their thermal decomposition temperature. Therefore, there is a possibility that the first inorganic particles near the center of the sheet may not be completely thermally decomposed. Therefore, the average secondary particle size of the inorganic hydrate particles is preferably 0.01 μm or more and 200 μm or less, more preferably 0.05 μm or more and 100 μm or less.

[0192] (Particles composed of thermally expanding inorganic materials)

[0193] Examples of thermally expandable inorganic materials include vermiculite, bentonite, mica, and perlite.

[0194] (Particles composed of hydrous porous materials)

[0195] Specific examples of hydrous porous materials include zeolite, kaolinite, montmorillonite, acid clay, diatomaceous earth, wet silica, dry silica, aerogel, mica, vermiculite, etc.

[0196] (Inorganic hollow sphere)

[0197] The heat insulation component used in this invention may contain inorganic hollow spheres as the first inorganic particles.

[0198] If it contains inorganic hollow spheres, it can suppress convective or conductive heat transfer within the insulation component in temperature ranges below 500°C, thereby further improving the insulation performance of the insulation component.

[0199] As an inorganic hollow sphere, at least one of the following can be used: white sand hollow sphere, silica hollow sphere, fly ash hollow sphere, barite hollow sphere, and glass hollow sphere.

[0200] (Inorganic hollow sphere content: less than 60% by mass relative to the total mass of the insulation component)

[0201] The content of inorganic hollow spheres is preferably 60% by mass or less relative to the total mass of the insulation component.

[0202] (Average particle size of inorganic hollow spheres: greater than 1 μm and less than 100 μm)

[0203] The average particle size of the inorganic hollow spheres is preferably 1 μm or more and 100 μm or less.

[0204] <Second Inorganic Particles>

[0205] When the heat transfer suppression sheet contains two types of inorganic particles, there are no particular limitations on the second inorganic particle, as long as its material, particle size, etc., differ from the first inorganic particle. The second inorganic particle can be made of inorganic hollow spheres such as oxide particles, carbide particles, nitride particles, inorganic hydrate particles, silica nanoparticles, metal oxide particles, microporous particles, or hollow silica particles; particles composed of thermally expandable inorganic materials; particles composed of hydrous porous bodies; and so on. Details of these particles are as described above.

[0206] Furthermore, nanoparticles exhibit extremely low thermal conductivity and maintain excellent thermal insulation even under compressive stress applied to the heat transfer suppression sheet. Additionally, metal oxide particles such as titanium dioxide are highly effective at shielding radiant heat. Moreover, if both large-diameter and small-diameter inorganic particles are used, the small-diameter particles will intersect within the gaps between the large-diameter particles, resulting in a denser structure and improved heat transfer suppression. Therefore, when using, for example, nanoparticles as the first inorganic particle, it is preferable to further include particles composed of metal oxides with a diameter larger than the first inorganic particles as the second inorganic particle in the heat transfer suppression sheet.

[0207] Examples of metal oxides include silicon dioxide, titanium dioxide, aluminum oxide, barium titanate, zinc oxide, zircon, and zirconium oxide. In particular, titanium dioxide has a higher refractive index than other metal oxides, and it is highly effective at scattering light and blocking radiant heat in high-temperature regions above 500°C. Therefore, titanium dioxide is the preferred choice.

[0208] When using at least one type of particle selected from dry silica particles and silica aerogel as the first inorganic particle, and using at least one type of particle selected from titanium dioxide, zircon, zirconium oxide, silicon carbide, zinc oxide, and alumina as the second inorganic particle, in order to obtain excellent thermal insulation performance in a temperature range below 300°C, the first inorganic particle's mass relative to the total mass of the inorganic particles is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more. Furthermore, the first inorganic particle's mass relative to the total mass of the inorganic particles is preferably 95% by mass or less, more preferably 90% by mass or less, and even more preferably 80% by mass or less.

[0209] On the other hand, in order to obtain excellent thermal insulation performance in 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 in terms of the total mass of the inorganic particles. Furthermore, 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 in terms of the total mass of the inorganic particles.

[0210] (Average primary particle size of the second inorganic particle)

[0211] (Average primary particle size of the second inorganic particle)

[0212] When the heat transfer suppression sheet contains second inorganic particles composed of metal oxides, if the average primary particle size of the second inorganic particles is 1 μm or more and 50 μm or less, radiative heat transfer can be efficiently suppressed in high-temperature regions above 500°C. The average primary particle size of the second inorganic particles is further preferably 5 μm or more and 30 μm or less, and most preferably 10 μm or less.

[0213] (Content of inorganic particles)

[0214] In this embodiment, if the content of inorganic particles 4 in the heat transfer inhibition sheet 10 is properly controlled, the heat insulation performance of the heat transfer inhibition sheet 10 can be adequately ensured.

[0215] The content of inorganic particles 4 relative to the total mass of the heat transfer inhibiting sheet 10 is preferably 60% by mass or more, more preferably 70% by mass or more. Furthermore, if the content of inorganic particles 4 is too high, the content of organic fibers and the cladding portion will be relatively reduced. Therefore, in order to fully obtain the reinforcing effect of the skeleton and the retention effect of the inorganic particles, the content of inorganic particles 4 relative to the total mass of the heat transfer inhibiting sheet 10 is preferably 95% by mass or less, more preferably 90% by mass or less. Moreover, the content of inorganic particles in the heat transfer inhibiting sheet 10 can be calculated, for example, by heating the heat transfer inhibiting sheet at 800°C to decompose the organic components, measuring the mass of the remaining portion, and thus calculating the content of inorganic particles in the heat transfer inhibiting sheet 10.

[0216] Furthermore, in addition to the aforementioned organic fibers, cladding portion 5, and inorganic particles 4, the heat transfer suppression sheet of this embodiment may also include organic fibers, inorganic fibers, etc., made of an organic material different from the aforementioned first organic material. Additionally, the base material portion 8 may contain an organic material different from the aforementioned first and second organic materials, and the inorganic particles may be retained within this organic material.

[0217] <Thickness of the heat transfer suppression sheet>

[0218] The thickness of the heat transfer suppression sheet in this embodiment is not particularly limited, but it 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 properties of the heat transfer suppression sheet can be obtained.

[0219] [3. Battery Pack]

[0220] Figure 9 This is a schematic diagram illustrating a battery pack according to an embodiment of the present invention. The battery pack 100 of this embodiment has a plurality of battery cells 20a, 20b, 20c and a heat transfer suppression sheet according to this embodiment, wherein the plurality of battery cells are connected in series or in parallel.

[0221] For example, such as Figure 9 As shown, the heat transfer suppression sheet 10 of this embodiment is sandwiched between battery cell 20a and battery cell 20b, and between battery cell 20b and battery cell 20c. Furthermore, battery cells 20a, 20b, and 20c, as well as the heat transfer suppression sheet 10, are housed within the battery casing 30.

[0222] Furthermore, the contents of the heat transfer inhibition sheet 10 are as described above.

[0223] In the battery pack 100 configured in this way, even if a certain battery cell 20a becomes hot, the heat transfer suppression sheet 10 with heat transfer suppression effect is present between it and the battery cell 20b, so the heat transfer to the battery cell 20b can be suppressed.

[0224] Furthermore, the heat transfer suppression sheet 10 of this embodiment has high compressive strength, thus suppressing the thermal expansion of the battery cells 20a, 20b, and 20c even during charging and discharging. Therefore, it ensures the distance between the battery cells, maintains excellent thermal insulation performance, and prevents thermal runaway of the battery cells. Additionally, because it suppresses powder shedding, it can be easily processed.

[0225] Furthermore, the battery pack 100 in this embodiment is not limited to... Figure 9 The illustrated battery pack may also have heat transfer suppression sheets 10 disposed not only between battery cells 20a and 20b, and between battery cells 20b and 20c, but also between battery cells 20a, 20b, 20c and the battery casing 30.

[0226] In the battery pack 100 configured in this way, in the event of a fire in a battery cell, the spread of flames to the outside of the battery casing 30 can be suppressed.

[0227] For example, the battery pack 100 described in this embodiment is sometimes used in electric vehicles (EVs) and is located under the passenger's floor. In this case, even if the battery cell catches fire, the safety of the passenger can be ensured.

[0228] In addition, since the heat transfer suppression sheet 10 can be positioned not only between each battery cell, but also between the battery cells 20a, 20b, 20c and the battery casing 30, there is no need to remake fireproof components, etc., and a low-cost and safe battery pack 100 can be easily constructed.

[0229] In the battery pack of this embodiment, the heat transfer suppression sheet 10 disposed between the battery cells 20a, 20b, 20c and the battery casing 30 can be in contact with the battery cells or may have a gap. However, if there is a gap between the heat transfer suppression sheet 10 and the battery cells 20a, 20b, 20c, the deformation of the battery cells can be allowed even if the temperature of any one of the battery cells rises and its volume expands.

[0230] Furthermore, the heat transfer suppression sheet 10 of this embodiment can be manufactured into various shapes using its manufacturing method. Therefore, it is not affected by the shape of the battery cells 20a, 20b, 20c and the battery casing 30, and can accommodate any shape. Specifically, in addition to prismatic batteries, it can also be applied to cylindrical batteries, flat batteries, etc.

[0231] [Example]

[0232] The present invention will now be described in detail with reference to embodiments and comparative examples, but the present invention is not limited to these embodiments and comparative examples.

[0233] [Experiment 1]

[0234] Test specimens of heat transfer inhibition sheets were prepared using various materials and by dry or wet methods to evaluate their thermal insulation performance and powder shedding inhibition performance (scattering rate).

[0235] <Preparation of the test specimen>

[0236] (Example 1)

[0237] Dry silica and titanium dioxide were prepared as inorganic particles, and adhesive fibers for the core-sheath structure were also prepared. The specific content and names of each component are shown below.

[0238] • Inorganic particles: Dry silica (60% by mass, average primary particle size: 0.012 μm)

[0239] • Inorganic particles: Titanium dioxide (25% by mass, average primary particle size: 8 μm)

[0240] • Adhesive fiber (15% by weight, average fiber length: 5mm)

[0241] Core: Polyethylene terephthalate (melting point: 240℃)

[0242] Sheath: Low-melting-point polyethylene terephthalate (melting point: 110℃)

[0243] The above materials are fed into a mixer to prepare a mixture. Then, the resulting mixture is poured into a pre-designed mold, pressurized, heated, and cooled using a stamping press or similar device, thereby obtaining a product with a basis weight of 740 g / m³. 2 The test specimen of Example 1 was 2 mm thick. The heating conditions were set to 150°C for 15 minutes. Furthermore, the content of organic fiber (core) in the obtained test specimen was 7% by mass relative to the total mass of the test specimen.

[0244] (Comparative Example 1)

[0245] Dry silica and titanium dioxide were prepared as inorganic particles, and single-component adhesive fibers were also prepared. The specific content and names of each component are shown below.

[0246] • Inorganic particles: Dry silica (60% by mass, average primary particle size: 0.012 μm)

[0247] • Inorganic particles: Titanium dioxide (25% by mass, average primary particle size: 8 μm)

[0248] • Adhesive fiber: Low melting point polyethylene terephthalate (15% by mass, melting point: 130°C, average fiber length: 5mm)

[0249] Then, using the same dry method as in Example 1, a sample with a basis weight of 740 (g / m³) was prepared. 2 The test material of Comparative Example 1 was 2 mm thick. The heating conditions were set to 160°C for 15 minutes.

[0250] (Comparative Example 2)

[0251] Wet silica and titanium dioxide were prepared as inorganic particles, and single-component adhesive fibers were also prepared. The specific content and names of each component are shown below.

[0252] • Inorganic particles: wet silica (60% by mass, average primary particle size: 0.014 μm)

[0253] • Inorganic particles: Titanium dioxide (25% by mass, average primary particle size: 8 μm)

[0254] • Adhesive fiber: Low melting point polyethylene terephthalate (15% by mass, melting point: 130°C, average fiber length: 5mm)

[0255] Then, using the same dry method as in Example 1, a sample with a basis weight of 740 (g / m³) was prepared. 2 The test piece of Comparative Example 2, with a thickness of 2 mm, was used. The heating conditions were set to 160°C for 15 minutes.

[0256] (Comparative Example 3)

[0257] Wet silica and titanium dioxide were prepared as inorganic particles, and single-component adhesive fibers were also prepared. The specific content and names of each component are shown below.

[0258] • Inorganic particles: wet silica (60% by mass, average primary particle size: 0.014 μm)

[0259] • Inorganic particles: Titanium dioxide (25% by mass, average primary particle size: 8 μm)

[0260] • Adhesive fiber: Low melting point polyethylene terephthalate (15% by mass, melting point: 130°C, average fiber length: 5mm)

[0261] The above materials are dispersed in water using a pulper to prepare a uniform papermaking pulp (dispersion). This pulp is then dewatered using a paper machine to obtain wet sheets. These wet sheets are then dried using a Yankee dryer at a surface temperature of 140°C, followed by hot air drying to 250°C to obtain dried sheets. The dried sheets are then cooled to produce a sheet with a basis weight of 740 g / m³. 2 The test piece of Comparative Example 3, with a thickness of 2 mm.

[0262] (Comparative Example 4)

[0263] As inorganic particles, dry silica and titanium dioxide, the same as in Example 1, were prepared, along with adhesive fibers for the core-sheath structure. The specific content and names of each component are shown below.

[0264] • Inorganic particles: Dry silica (60% by mass, average primary particle size: 0.012 μm)

[0265] • Inorganic particles: Titanium dioxide (25% by mass, average primary particle size: 8 μm)

[0266] • Adhesive fiber (15% by weight, average fiber length: 5mm)

[0267] Core: Polyethylene terephthalate (melting point: 240℃)

[0268] Sheath: Low-melting-point polyethylene terephthalate (melting point: 110℃)

[0269] Then, using the same wet process as Comparative Example 3, a sample with a basis weight of 740 (g / m³) was prepared. 2 The test piece of Comparative Example 4 was 2 mm thick. Furthermore, the heating conditions were set to the same conditions as those of Comparative Example 3.

[0270] <Evaluation of Test Specimens>

[0271] For each test specimen, the thermal conductivity was measured to evaluate the thermal insulation performance, and the scattering rate was measured to evaluate the powder shedding suppression performance. The test specimen preparation conditions and evaluation results are shown in Table 1 below.

[0272] (Determination of thermal conductivity)

[0273] Thermal conductivity (W / m·K) was measured at room temperature (25°C). The thermal conductivity was determined using the unsteady-state hot wire method according to ISO 8894-1. A thermal conductivity of 0.05 or less was considered good insulation, while a thermal conductivity exceeding 0.05 was considered poor insulation.

[0274] (Determination of scattering rate)

[0275] Figure 10 This is a schematic diagram illustrating the method for determining the scattering rate. For example... Figure 10 As shown, an apparatus was used in which an arm 25 was mounted so as to rotate at the apex of a support 24, and a test piece 23 was mounted at the end of the arm 25. First, after mounting the test piece 23 at the end of the arm 25, the arm 25 was lifted and fixed at an arbitrary angle, then released and allowed to fall, thereby causing the support 24 to collide with the arm 25 to apply an impact. The test piece 23 was 50mm × 50mm in size, the arm length was 915mm, the number of impacts was 1, and the angle between the support and the arm was 90°. Then, the mass of the test piece 23 before impact was set as F0 (g), and the mass of the test piece 23 after impact was set as Fw (g). The dispersion rate E (the amount of inorganic particles detached) (mass%) was calculated using the following formula.

[0276] Scattering rate E = (F0 - Fw) / F0

[0277] In the above evaluation method, if the scattering rate E is less than 0.15% by mass, it is judged to have good powder shedding suppression performance.

[0278] [Table 1]

[0279]

[0280] Figure 11 This is a graph showing the change in thermal conductivity of Comparative Example 3 and Example 1 at various temperatures. See Table 1 and... Figure 11 As shown, Example 1 is an example of a heat transfer suppression sheet manufactured using a dry method, thus achieving superior thermal insulation compared to the comparative example. Furthermore, since titanium dioxide is used as the inorganic particle, excellent thermal insulation is achieved even in temperature ranges above 300°C. Moreover, because Example 1 contains adhesive fibers with a core-sheath structure as the material, the scattering rate E is less than 0.15% by mass, resulting in good powder shedding suppression performance.

[0281] In contrast, Comparative Examples 1 to 4 used single-component adhesive fibers as materials or prepared test specimens by a wet method, and therefore at least one of the evaluation results for thermal insulation and powder shedding inhibition performance was poor.

[0282] [Experiment 2]

[0283] Next, for the test pieces of Comparative Example 5 manufactured by a method different from that of the present invention and the test pieces of Example 1 above, photographs were taken using a scanning electron microscope (SEM) to confirm the structure.

[0284] Furthermore, the test piece of Comparative Example 5 contained wet silica and glass fiber, and was manufactured by a wet process.

[0285] Figure 12 These are substitute photographs showing the surfaces and cross-sections of Comparative Example 5 and Example 1. Figure 12 As shown, in Comparative Example 5, because glass fiber was used, no inorganic particles were clad onto the surface of the fiber, and the fibers were not fused together. Furthermore, because the test specimen was fabricated using a wet method, the inorganic particles agglomerated together. In contrast, in Example 1, because a core-sheath structure of adhesive fiber was used, a cladding portion containing inorganic particles was formed on the outer peripheral surface of the organic fiber serving as the core, resulting in a coarse-diameter fiber portion. Furthermore, it can be observed that at locations where multiple organic fibers are close to each other, the multiple organic fibers are fixed by the cladding portion, thus forming a three-dimensional and robust framework in the coarse-diameter fiber portion.

[0286] [Experiment 3]

[0287] The powder shedding suppression performance based on the presence or absence of hot-melt powder was compared.

[0288] <Preparation of the test specimen>

[0289] (Example 2)

[0290] Dry silica and titanium dioxide were prepared as inorganic particles, and adhesive fibers for the core-sheath structure were also prepared. The specific content and names of each component are shown below.

[0291] • Inorganic particles: Dry silica (60% by mass, average primary particle size: 0.012 μm)

[0292] • Inorganic particles: Titanium dioxide (25% by mass, average primary particle size: 8 μm)

[0293] • Adhesive fiber: PET / low melting point PET fiber (TJ04CN: manufactured by Teijin Frontier Co., Ltd.: 15% by mass, average fiber length: 5mm)

[0294] Core: Polyethylene terephthalate (melting point: 240℃)

[0295] Sheath: Low-melting-point polyethylene terephthalate (melting point: 110℃)

[0296] Then, using the same dry method as in Example 1, a basis weight of 740 (g / m³) was obtained. 2 The test piece of Example 2 had a thickness of 2 mm. The heating conditions were set to 150°C for 15 minutes.

[0297] (Example 3)

[0298] The material prepared in Example 2 above has hot-melt powder added. The specific content and name of each component are shown below.

[0299] • Inorganic particles: Dry silica (57.7% by mass, average primary particle size: 0.012 μm)

[0300] • Inorganic particles: Titanium dioxide (24.7% by mass, average primary particle size: 8 μm)

[0301] • Hot melt powder: Powdered resin (PR D60C-Z: manufactured by Tokyo Ink Co., Ltd., 2.6% by mass, melting point: 100°C) • Adhesive fiber: PET / low melting point PET fiber (TJ04CN: manufactured by Teijin Frontier Co., Ltd., 15% by mass, average fiber length: 5mm)

[0302] Core: Polyethylene terephthalate (melting point: 240℃)

[0303] Sheath: Low-melting-point polyethylene terephthalate (melting point: 110℃)

[0304] Then, using the same dry method as in Example 1, a basis weight of 740 (g / m³) was obtained. 2 The test piece of Example 3 had a thickness of 2 mm. The heating conditions were set to 150°C for 15 minutes.

[0305] <Evaluation of Test Specimens>

[0306] For each test piece, the scattering rate was measured multiple times using the same method as in Test 1 above, and the powder shedding suppression performance was compared. Figure 13 This is a graph showing the change in scattering rate with the number of hits, where the vertical axis represents the scattering rate and the horizontal axis represents the number of hits. For example... Figure 13 As shown, Example 3 is an example of a test piece made using a material containing hot-melt powder to suppress heat transfer. Therefore, compared with Example 2 which does not contain hot-melt powder, it can obtain excellent powder shedding suppression performance.

Claims

1. A method for manufacturing a heat transfer inhibition sheet, characterized in that, It has a processing step of dry-processing a mixture into a sheet-like form, the mixture comprising inorganic particles, adhesive fibers with a core-sheath structure, and hot-melt powder. The adhesive fiber with a core-sheath structure has a core extending along its length and a sheath formed to cover the outer peripheral surface of the core. The melting point of the first organic material constituting the core is higher than the melting point of the second organic material constituting the sheath. The adhesive fibers exist in an irregular orientation, and the adhesive fibers are in contact with each other in a portion. Adjacent cores are fused together through cladding portions to form a three-dimensional skeleton.

2. The method for manufacturing the heat transfer suppression sheet according to claim 1, characterized in that, The melting point of the first organic material is more than 60°C higher than that of the second organic material.

3. The method for manufacturing the heat transfer suppression sheet according to claim 1, characterized in that, The processing steps include pressing the mixture and heating the mixture.

4. The method for manufacturing the heat transfer suppression sheet according to claim 3, characterized in that, The heating temperature in the process of heating the mixture is set to a temperature that is higher than the melting point of the second organic material and lower than the melting point of the first organic material.

5. The method for manufacturing the heat transfer suppressor sheet according to any one of claims 1 to 4, characterized in that, The inorganic particles comprise at least one type of particle selected from dry silica particles and silica aerogels.

6. The method for manufacturing the heat transfer suppressor sheet according to claim 5, characterized in that, The inorganic particles further include at least one type of particle selected from titanium dioxide, zircon, zirconium oxide, silicon carbide, zinc oxide, and aluminum oxide.

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