Heat transfer suppression sheet, method for producing same, and battery pack

Abstract

Provided is a heat transfer suppression sheet having desired strength and heat insulation properties and capable of flexibly adapting to various designs such as size and heat insulation properties. A heat transfer suppression sheet (50) is formed by coupling a plurality of pieces of heat insulation material (10) containing inorganic particles. The heat insulation material (10) has a pair of main surfaces (10a, 10b), and a connection surface (10c) that connects the pair of main surfaces (10a, 10b). The connection surfaces (10c) of the plurality of pieces of heat insulation material (10) are disposed facing each other, and a coupling surface (61) for coupling the pieces of heat insulation material (10) together is formed. In a cross-sectional view orthogonal to the pair of main surfaces (10a, 10b) and parallel to a direction in which the pieces of the heat insulation material (10) are adjacent to each other, the length of the coupling surface (61) is longer than the thickness of the heat insulation material (10) in a region in which the coupling surface (61) is formed.

Description

Heat transfer suppression sheet, manufacturing method thereof, and battery pack

[0001] The present invention relates to a heat-transfer-suppressing sheet, a method for producing the same, and a battery pack including the heat-transfer-suppressing sheet.

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

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

[0004] A common method for suppressing heat transfer from a battery cell experiencing thermal runaway is to place a heat insulating sheet between the battery cells. For example, Patent Document 1 proposes a flame-resistant electrical insulating material for use in electric vehicles. The insulating material contains glass fiber, a particulate filler mixture containing a specified material, and an inorganic binder, and has a specified flammability rating.

[0005] Furthermore, Patent Document 2 also proposes a method for producing a heat-transfer-suppressing sheet by processing a mixture containing inorganic particles, binder fibers having a core-sheath structure, and hot-melt powder into a sheet by a dry method, as a method for obtaining strength and heat-insulating performance superior to conventional heat-insulating sheets.

[0006] In response to recent demands for larger battery cell capacities, long battery cells have been developed in which only one end surface of a plate-shaped battery cell is significantly longer than conventional battery cells. Therefore, the heat insulating sheets placed between such long battery cells must also be enlarged to match the size of the battery cells.

[0007] Japanese Patent Publication No. 2021-531631 Japanese Patent Publication No. 2023-132944

[0008] However, some of the long battery cells described above have longitudinal lengths exceeding 1 m. For example, if a conventional small-sized insulation sheet is joined to increase the size, the insulation performance at the joints may be reduced. On the other hand, manufacturing an insulation sheet with the desired strength and insulation performance to fit the size of a long battery cell requires new manufacturing equipment, which increases manufacturing costs. Even if a single large insulation sheet is manufactured, the insulation performance may vary depending on the region, or design may be difficult if different insulation performance is desired in different regions. Because these problems occur even with conventional small-sized insulation materials, there is a growing demand for the development of a heat-transfer-suppressing sheet that can improve design flexibility.

[0009] The present invention has been made in consideration of the above-mentioned problems, and has an object to provide a heat-transfer-inhibiting sheet that has desired strength and heat insulating properties and can flexibly accommodate a variety of designs, such as size and heat insulating properties; a method for manufacturing the heat-transfer-inhibiting sheet that can easily and inexpensively manufacture the heat-transfer-inhibiting sheet; and a battery pack that includes the heat-transfer-inhibiting sheet.

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

[0011] [1] A heat-transfer-suppressing sheet formed by bonding together a plurality of insulating materials containing inorganic particles, wherein the insulating materials have a pair of main surfaces and a connecting surface connecting the pair of main surfaces, the connecting surfaces of the plurality of insulating materials are arranged opposite each other to form a connecting surface connecting the insulating materials, and in a cross-sectional view perpendicular to the pair of main surfaces and parallel to the direction in which the insulating materials are adjacent to each other, the length of the connecting surface is longer than the thickness of the region of the insulating material where the connecting surface is formed.

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

[15] .

[0013] [2] The heat-transfer-suppressing sheet according to [1], wherein, in the cross-sectional view, at least a portion of the bonding surface extends in a direction different from the thickness direction of the heat insulating material.

[0014] [3] The heat transfer-suppressing sheet according to [2], wherein, in the cross-sectional view, at least a portion of the bonding surface has a region that forms an angle of 20° or more and 160° or less with respect to the thickness direction of the thermal insulation material.

[0015] [4] The heat transfer suppressing sheet according to any one of [1] to [3], characterized in that, when an end portion of the joining surface on one main surface side is defined as a first end portion and an end portion on the other main surface side is defined as a second end portion, the first end portion is positioned offset in a direction parallel to the main surface relative to the second end portion in the cross-sectional view.

[0016] [5] The heat transfer-suppressing sheet according to any one of [1] to [3], characterized in that, when an end portion on one main surface side of the joining surface is defined as a first end portion and an end portion on the other main surface side is defined as a second end portion, in the cross-sectional view, the first end portion and the second end portion are located at symmetrical positions in the thickness direction of the heat insulating material, and the connecting surface of one of the adjacent heat insulating materials has a convex portion, and the connecting surface of the other heat insulating material has a concave portion shaped to fit into the convex portion, and the convex portion and the concave portion fit together to join the adjacent heat insulating materials.

[0017] [6] The heat transfer-suppressing sheet according to any one of [1] to [5], characterized in that, when the density of the insulating material in a region including the bonding surface in the thickness direction of the insulating material is defined as M1 and the density of the insulating material in a region not including the bonding surface in the thickness direction of the insulating material is defined as M2, the ratio of the density M1 to the density M2 (M1 / M2) is 1.2 or more.

[0018] [7] A heat-transfer-suppressing sheet formed by bonding together a plurality of insulating materials containing inorganic particles, wherein the insulating materials have a pair of main surfaces and a connecting surface connecting the pair of main surfaces, the connecting surfaces of the plurality of insulating materials are arranged opposite each other to form a bonding surface connecting the insulating materials, and in a cross-sectional view perpendicular to the pair of main surfaces and parallel to the direction in which the insulating materials are adjacent to each other, when an end of the bonding surface on one main surface side is defined as a first end and an end of the bonding surface on the other main surface side is defined as a second end, the bonding surface has a heat-transfer-preventing portion between the first end and the second end, and the heat-transfer-preventing portion is located at a position shifted from at least one of the first end and the second end in a direction parallel to the main surfaces.

[0019] [8] The heat transfer-suppressing sheet according to [7], wherein, in the cross-sectional view, the heat transfer-blocking portion has a region that extends in a direction different from the thickness direction of the heat insulating material.

[0020] [9] The heat transfer-suppressing sheet according to [7] or [8], wherein, in the cross-sectional view, the heat transfer-preventing portion has a region that is at an angle of 20° or more and 160° or less with respect to the thickness direction of the thermal insulation material.

[0021]

[10] The heat transfer-suppressing sheet according to any one of [7] to [9], wherein, in the cross-sectional view, the first end portion is shifted in a direction parallel to the main surface with respect to the second end portion.

[0022]

[11] The heat transfer-suppressing sheet according to any one of [7] to [9], characterized in that, in the cross-sectional view, the first end and the second end are located symmetrically in the thickness direction of the thermal insulating material, and the connecting surface of one of the adjacent thermal insulating materials has a convex portion, and the connecting surface of the other thermal insulating material has a concave portion shaped to fit into the convex portion, and the adjacent thermal insulating materials are joined by fitting the convex portion and the concave portion.

[0023]

[12] The heat transfer-suppressing sheet according to any one of [7] to

[11] , characterized in that, when the density of the heat insulating material in a region in the thickness direction of the heat insulating material that includes the heat transfer-preventing portion is M1 and the density of the heat insulating material in a region in the thickness direction that does not include the heat transfer-preventing portion is M2, the ratio of the density M1 to the density M2 (M1 / M2) is 1.2 or more.

[0024]

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

[12] , wherein the heat insulating material includes organic fibers.

[0025]

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

[13] , wherein the connecting surfaces of adjacent pieces of the heat insulating material that make up the joining surface are bonded to each other in at least a partial region of the joining surface.

[0026]

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

[13] , wherein in at least a partial region of the bonding surface, connecting surfaces of adjacent pieces of the thermal insulating material that constitute the bonding surface are heat-fused to each other.

[0027] The above object of the present invention is also achieved by the following configuration

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

[0028]

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

[13] , comprising: a first processing step of processing an end face of one of the two insulating materials to be joined together so that at least a partial region of the end face of the one of the insulating materials extends in a direction different from the thickness direction of the insulating material, thereby forming a first connecting surface; a second processing step of processing the end face of the other of the two insulating materials to be joined together so that the end face of the other of the two insulating materials has a shape that conforms to the first connecting surface of the one of the insulating materials, thereby forming a second connecting surface; and a connecting surface forming step of arranging the one of the insulating materials and the other of the insulating materials so that the first connecting surface and the second connecting surface face each other, thereby forming the connecting surface where the first connecting surface and the second connecting surface are connected.

[0029] Furthermore, preferred embodiments of the present invention relating to a method for producing a heat transfer-suppressing sheet relate to the following

[17] to

[18] .

[0030]

[17] The method for producing a heat transfer-suppressing sheet according to

[16] , wherein in the bonding surface forming step, at least a part of the bonding surface is bonded with an adhesive.

[0031]

[18] The method for manufacturing a heat transfer-suppressing sheet according to

[16] , wherein in the joining surface forming step, the first joining surface and the second joining surface are heated while being pressed in a direction in which they approach each other, and at least a portion between the first joining surface and the second joining surface is fused by thermal fusion.

[0032] The above object of the present invention can also be achieved by the following configuration

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

[0033]

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

[13] , comprising: an arrangement step of arranging two sheets of heat insulating material to be joined together such that a portion of a main surface of one of the two sheets of heat insulating material overlaps with a portion of a main surface of the other of the two sheets of heat insulating material; and a joining surface forming step of applying pressure to the overlapping region of the two sheets of heat insulating material in the thickness direction of the two sheets of heat insulating material to form the joining surface where a portion of the main surface of one of the heat insulating material and a portion of the main surface of the other of the two sheets of heat insulating material are joined.

[0034] Further, preferred embodiments of the present invention relating to other methods for producing a heat transfer-suppressing sheet relate to the following

[20] to

[21] .

[0035]

[20] The method for producing a heat transfer-suppressing sheet according to

[19] , wherein in the bonding surface forming step, at least a part of the bonding surface is bonded with an adhesive.

[0036]

[21] The method for producing a heat transfer-suppressing sheet according to

[19] , characterized in that in the bonding surface forming step, the area where the two insulating materials overlap is heated while being pressed in the thickness direction of the area, and a part of the main surface of one insulating material and a part of the main surface of the other insulating material are fused by thermal fusion.

[0037] The above object of the present invention is also achieved by the following configuration

[22] relating to a battery pack.

[0038]

[22] A battery pack comprising a plurality of battery cells and the heat transfer-suppressing sheet according to any one of [1] to

[15] , the plurality of battery cells being connected in series or in parallel.

[0039] The heat-transfer-suppressing sheet of the present invention has a heat-insulating material containing inorganic particles, and therefore can provide excellent heat insulation. Furthermore, because it has a structure in which multiple heat-insulating materials are combined, it can be easily manufactured to a desired size, and it is possible to minimize variations in heat insulation depending on the location and intentionally change the heat insulation depending on the location. This simplifies the design of the heat-transfer-suppressing sheet when manufacturing it, and improves the degree of design freedom.

[0040] Furthermore, when viewed in cross section, the length of the bonding surface to which the insulating material is bonded is formed to be longer than the thickness of the area in which this bonding surface is formed, so that heat transfer in the thickness direction of the insulating material can be suppressed compared to when the bonding surface extends linearly in the thickness direction of the insulating material.

[0041] Furthermore, according to the method for producing a heat-transfer-suppressing sheet of the present invention, even if the sheet has bonding surfaces of multiple insulating materials, it is possible to suppress a decrease in insulating properties, and it is possible to easily and inexpensively produce a heat-transfer-suppressing sheet in which the properties and size of the insulating materials can be freely designed.

[0042] According to the battery pack of the present invention, the joining surface where multiple insulating materials are joined has a heat transfer suppression sheet formed so that it is longer than the thickness in the plate thickness direction in that area, which makes it possible to suppress the propagation of heat between battery cells and can flexibly adapt to the size and shape of the battery cells, thereby suppressing thermal runaway of the battery cells in the battery pack and the spread of flames outside the battery case.

[0043] FIG. 1 is a perspective view of a heat-transfer-inhibiting sheet according to embodiment 1A of the present invention. FIG. 2 is a cross-sectional view showing an enlarged portion of the heat-transfer-inhibiting sheet shown in FIG. 1. FIG. 3 is a schematic diagram showing a battery pack according to an embodiment of the present invention. FIG. 4 is a cross-sectional view showing an enlarged portion of the heat-transfer-inhibiting sheet according to embodiment 2A of the present invention. FIG. 5 is a cross-sectional view showing an enlarged portion of the heat-transfer-inhibiting sheet according to embodiment 3A of the present invention. FIG. 6 is a cross-sectional view showing an enlarged portion of the heat-transfer-inhibiting sheet according to embodiment 4A of the present invention. FIG. 7 is a schematic diagram showing a method for manufacturing the heat-transfer-inhibiting sheet shown in FIGS. 1 and 2. FIG. 8 is a schematic diagram showing a method for manufacturing the heat-transfer-inhibiting sheet shown in FIG. 6. FIG. 9 is a photograph, substituted for a drawing, showing an example structure S1 of a heat insulating material used in a heat-transfer-inhibiting sheet according to each embodiment of the present invention. FIG. 10 is a photograph, substituted for a drawing, showing an enlarged portion of the heat insulating material shown in FIG. 9. FIG. 11 is a photograph, substituted for a drawing, showing an example structure S2 of a heat insulating material used in a heat-transfer-inhibiting sheet according to each embodiment of the present invention. FIG. 12 is a schematic diagram showing an example structure S3 of a heat insulating material used in a heat-transfer-inhibiting sheet according to each embodiment of the present invention. FIG. 13 is a schematic diagram showing an enlarged portion of FIG. 12 . FIG. 14 is a photograph, substitute for a drawing, showing the insulating material shown in FIG. 12 . FIG. 15 is a photograph, substitute for a drawing, showing structural example S4 of the insulating material used in the heat-transfer-suppressing sheet according to each embodiment of the present invention. FIG. 16 is a photograph, substitute for a drawing, showing an enlarged view of the structure of the insulating material shown in FIG. 15 . FIG. 17 is a photograph, substitute for a drawing, showing a cross-section of the insulating material shown in FIG. 15 . FIG. 18 is a schematic diagram showing structural example S5 of the insulating material used in the heat-transfer-suppressing sheet according to each embodiment of the present invention. FIG. 19 is a schematic diagram showing an enlarged view of portion A of the insulating material shown in FIG. 18 . FIG. 20 is a photograph, substitute for a drawing, showing structural example S6 of the insulating material used in the heat-transfer-suppressing sheet according to each embodiment of the present invention. FIG. 21 is a photograph, substitute for a drawing, showing another region of the insulating material shown in FIG. 20 . FIG. 22 is a photograph, substitute for a drawing, showing a cross-section of the insulating material shown in FIGS. 20 and 21 . FIG. 23 is a photograph, substitute for a drawing, showing structural example S7 of the insulating material used in the heat-transfer-suppressing sheet according to each embodiment of the present invention. Fig. 24 is a photograph substituting for a drawing showing an enlarged portion of the thermal insulation material shown in Fig. 23. Fig. 25 is a photograph substituting for a drawing for explaining a method for specifying the length of the fiber bundles contained in the thermal insulation material.FIG. 26 is a photograph showing fiber bundles arranged in a mesh pattern on the surface of a heat insulating material.

[0044] The present inventors conducted extensive research into a heat-transfer-suppressing sheet that can solve the above-mentioned problems. For example, when a large heat-transfer-suppressing sheet is manufactured by butting the end faces of multiple thermal insulating materials together and bonding them with an adhesive or the like, the insulating properties of the adhesive portion of the bonded surfaces are lower than those of other areas, resulting in a decrease in the insulating properties of the heat-transfer-suppressing sheet itself. Therefore, the present inventors discovered that by bonding the thermal insulating materials together so that the length of the bonding surface joining the end faces is longer, the decrease in insulating properties can be suppressed compared to when the bonding surface extends parallel to the thickness direction of the thermal insulating materials.

[0045] The following describes in detail a method for manufacturing a heat transfer-suppressing sheet, a heat transfer-suppressing sheet, and a battery pack according to embodiments of the present invention. Note that the present invention is not limited to the embodiments described below, and can be modified as desired without departing from the spirit and scope of the present invention.

[0046] [Heat-transfer-suppressing sheet] [Embodiment 1A] Fig. 1 is a perspective view showing a heat-transfer-suppressing sheet according to embodiment 1A of the present invention. Fig. 2 is an enlarged cross-sectional view showing a part of the heat-transfer-suppressing sheet shown in Fig. 1.

[0047] As shown in Fig. 1, the heat transfer-suppressing sheet 50 according to the first embodiment is formed by bonding together a plurality of insulating materials 10. The insulating materials 10 contain inorganic particles, and the materials constituting the insulating materials 10 will be described in detail later. Each insulating material 10 has a pair of main surfaces 10a, 10b and a connecting surface 10c connecting the main surfaces 10a and 10b. The connecting surfaces 10c of adjacent insulating materials 10 are arranged opposite each other, forming a bonding surface 61 along which the insulating materials 10 are bonded together.

[0048] The joining surface 61 will be described in more detail using Figure 2. Figure 2 shows a cross section perpendicular to the pair of main surfaces 10a, 10b and parallel to the direction in which adjacent thermal insulating materials 10 adjoin each other. In the cross-sectional view shown in Figure 2, the end of the joining surface 61 on one main surface 10a side is designated as a first end 63a, and the end on the other main surface 10b side is designated as a second end 63b. For ease of explanation, Figure 2 shows a gap between adjacent thermal insulating materials 10, but in reality, it is preferable that there is no gap between adjacent thermal insulating materials 10, and it is more preferable that the connecting surfaces 10c are in complete contact over the entire surface.

[0049] In the first embodiment, the joining surface 61 includes a first thickness-direction portion 64a extending from the first end 63a in the thickness direction (thickness direction) to approximately the center of the thermal insulation material 10, a second thickness-direction portion 64b extending from the second end 63b in the thickness direction to approximately the center of the thermal insulation material 10, and a main surface-direction portion 64c connecting the first thickness-direction portion 64a and the second thickness-direction portion 64b near the center of the thickness. That is, the length of the stepped joining surface 61 is the sum of the lengths of the first thickness-direction portion 64a, the second thickness-direction portion 64b, and the main surface-direction portion 64c, and is longer than the thickness T1 of the region where the joining surface is formed. Furthermore, in this cross-sectional view, the first end 63a of the joining surface 61 of the heat transfer-suppressing sheet 50 is offset from the second end 63b in a direction parallel to the main surfaces 10a and 10b.

[0050] The connecting surfaces 10c arranged opposite each other do not have to be joined, but because the heat-transfer-suppressing sheet 50 according to embodiment 1A has a simple shape and the joining surface 61 is prone to slippage, it is preferable that adjacent thermal insulating materials 10 are fixed in a joined state. For example, the connecting surfaces 10c of adjacent thermal insulating materials 10 that make up the joining surface 61 may be adhered to each other with an adhesive or the like, or may be joined by thermal fusion.

[0051] A specific use of the heat-transfer-suppressing sheet 50 shown in FIGS. 1 and 2 is described below as an example. FIG. 3 is a schematic diagram showing a battery pack according to an embodiment of the present invention. As shown in FIG. 3, the heat-transfer-suppressing sheet 50 can be used by interposing the heat-transfer-suppressing sheet 50 between a plurality of battery cells 20a, 20b, and 20c. The battery pack 100 is constructed by storing the plurality of battery cells 20a, 20b, and 20c in a state connected in series or parallel (the connected state is not shown) in a battery case 30. Note that, for example, lithium-ion secondary batteries are preferably used as the battery cells 20a, 20b, and 20c, but the present invention is not limited thereto and other secondary batteries can also be used.

[0052] Furthermore, the battery cells 20a, 20b, and 20c may be of a normal size or may be larger than a normal size. If the battery cells 20a, 20b, and 20c shown in FIG. 3 are large, the battery cells 20a, 20b, and 20c may be assumed to extend elongatedly in a direction perpendicular to the paper surface. Therefore, the heat transfer-suppressing sheet 50 is also arranged to extend elongatedly in a direction perpendicular to the paper surface, and the joining surface 61 does not appear in FIG. 3.

[0053] The heat-transfer-suppressing sheet 50 according to the first embodiment includes the insulating material 10 containing inorganic particles, thereby achieving excellent thermal insulation between the plurality of battery cells 20a, 20b, and 20c. Therefore, for example, if an abnormality occurs in the battery cell 20a and the temperature rises, the heat transfer to the battery cell 20b can be sufficiently suppressed. Furthermore, because the heat-transfer-suppressing sheet 50 can be formed by joining together a plurality of insulating materials 10, it can be easily manufactured to a desired size. If the insulating material contains organic fibers, the effect of retaining the inorganic fibers can be improved.

[0054] Furthermore, when attempting to manufacture a large heat-transfer-suppressing sheet made from a single piece of thermal insulation material, there is a risk of variations in thermal insulation properties. However, by combining multiple small thermal insulation materials 10 to manufacture a heat-transfer-suppressing sheet, as in the present embodiment, it is possible to minimize variations in thermal insulation properties depending on the location. Furthermore, combining multiple small thermal insulation materials 10 also makes it possible to intentionally vary the thermal insulation properties. Therefore, the multiple thermal insulation materials may all have the same properties, or may have different properties. This facilitates design and increases the degree of freedom in design when manufacturing a heat-transfer-suppressing sheet with different thermal insulation properties depending on the region.

[0055] Furthermore, if two sheets of insulating material having end faces extending in the thickness direction were joined together to form a heat-transfer-suppressing sheet, the joint surface would have lower insulating properties than the insulating material, resulting in increased heat transfer at the joint and reduced insulating properties of the heat-transfer-suppressing sheet. In contrast, in this embodiment, as shown in Figure 2, the joining surface 61 extends in a direction different from the thickness direction at least in part from one main surface 10a to the other main surface 10b. As a result, the length of the joining surface 61 where the insulating materials 10 are joined is longer than the thickness T1 of the region where the joining surface 61 is formed, thereby suppressing heat transfer at the joining surface 61 compared to when the joining surface extends linearly in the thickness direction.

[0056] [First Embodiment (Example of Functional Expression)] Next, a first embodiment (first embodiment) will be described with reference to Figures 1 and 2. The first embodiment (first embodiment) is a functional description of the heat transfer-suppressing sheet according to the first embodiment (first embodiment).

[0057] In the first embodiment, the heat transfer-suppressing sheet 50 is also formed by bonding together a plurality of insulating materials 10 containing inorganic particles. Each insulating material 10 has a pair of main surfaces 10a, 10b and a connecting surface 10c connecting the pair of main surfaces 10a, 10b. The connecting surfaces 10c of the insulating materials 10 are arranged opposite each other to form a bonding surface 61 that bonds the insulating materials 10 together. The bonding surface 61 has a heat transfer-blocking portion. In the cross-sectional view shown in FIG. 2 , the heat transfer-blocking portion is formed between a first end 63a on one main surface 10a side of the bonding surface 61 and a second end 63b on the other main surface 10b side. The heat transfer-blocking portion refers to a region of the bonding surface 61 that is offset from at least one of the first end 63a and the second end 63b in a direction parallel to the main surfaces 10a, 10b. Specifically, the heat transfer prevention portion in the first B embodiment corresponds to the main surface direction portion 64c in FIG.

[0058] Even in the first embodiment configured in this manner, the joining surface 61 does not extend linearly in the plate thickness direction from one main surface 10a to the other main surface 10b, but has a heat transfer blocking portion (main surface direction portion 64c) that extends in a direction different from the plate thickness direction in at least a portion thereof. Therefore, even if there is a joining surface 61 that joins multiple insulating materials 10, the presence of the heat transfer blocking portion makes it possible to suppress heat transfer in the plate thickness direction of the insulating materials 10.

[0059] [Embodiment 2A] Fig. 4 is an enlarged cross-sectional view of a portion of a heat-transfer-suppressing sheet according to embodiment 2A of the present invention. In embodiment 2A shown in Fig. 4, the same components as those in embodiment 1A are designated by the same reference numerals, and detailed descriptions thereof will be omitted or simplified. Furthermore, the heat-transfer-suppressing sheet 52 according to embodiment 2A can be used in place of the heat-transfer-suppressing sheet 50 of the battery pack 100 shown in Fig. 3. For ease of explanation, Fig. 4 shows gaps between adjacent insulating materials 10. However, in practice, it is preferable that there be no gaps between adjacent insulating materials 10, and it is more preferable that the connecting surfaces be in complete contact over the entire surface.

[0060] In the heat transfer-suppressing sheet 52 according to the second embodiment, the first end 63a and the second end 63b are located symmetrically in the thickness direction of the thermal insulating material 10, and the connecting surface of one of the thermal insulating materials 10 has a convex portion 65, while the connecting surface of the other of the thermal insulating materials 10 has a concave portion 66 shaped to fit into the convex portion 65. The convex portion 65 and the concave portion 66 fit together to form a joining surface 61 where adjacent thermal insulating materials 10 are joined together.

[0061] Specifically, the joining surface 61 is composed of a first thickness direction portion 67a extending in the thickness direction from the first end portion 63a, a first main surface direction portion 67d extending from the tip of the first thickness direction portion 67a in a direction parallel to the main surfaces 10a, 10b, a second thickness direction portion 67b extending in the thickness direction from the second end portion 63b, a second main surface direction portion 67e extending from the tip of the second thickness direction portion 67b in a direction parallel to the main surfaces 10a, 10b, and a third thickness direction portion 67c connecting the first main surface direction portion 67d and the second main surface direction portion 67e and extending in a direction parallel to the main surfaces 10a, 10b. Therefore, the length of the bonding surface 61 is the total length of the first thickness direction portion 67a, the first main surface direction portion 67d, the second thickness direction portion 67b, the second main surface direction portion 67e, and the third thickness direction portion 67c, and is longer than the thickness T2 of the region where the bonding surface is formed. Note that in Figure 4, the thickness of the region where the bonding surface 61 is formed is the same as the thickness of the thermal insulation material 10, so the thickness T2 is shown on the outside of the thermal insulation material 10.

[0062] The heat transfer-suppressing sheet 52 thus configured also has a structure in which multiple thermal insulating materials 10 are combined, thereby suppressing variations in functionality and improving design freedom. Furthermore, the bonding surface 61 does not extend linearly in the thickness direction from one main surface 10a to the other main surface 10b, but rather the length of the bonding surface 61 is formed longer than the thickness T1 of the region in which the bonding surface 61 is formed. Therefore, heat transfer at the bonding surface 61 can be suppressed.

[0063] Furthermore, in this embodiment, the convex portions 65 and the concave portions 66 are fitted together to join the insulating materials 10 together. Therefore, even if the joining surfaces 61 are not glued or fused, the insulating materials 10 will not easily come apart, making them easy to handle. However, as in the first A embodiment, if the connecting surfaces of adjacent insulating materials 10 are joined together by glueing or fusion, the handling can be further improved.

[0064] [Embodiment 2B (Example of Functional Expression)] Next, embodiment 2B will be described with reference to Fig. 4. Embodiment 2B is a functional description of the heat transfer-suppressing sheet according to embodiment 2A.

[0065] In the heat transfer suppressing sheet according to embodiment 2B, the convex portions 65 and the concave portions 66 are fitted together to form a joining surface 61 where adjacent thermal insulators 10 are joined together. The joining surface 61 includes, in order from the main surface 10a side, a first thickness direction portion 67a, a first main surface direction portion 67d, a third thickness direction portion 67c, a second main surface direction portion 67e, and a second thickness direction portion 67b. Of these, the convex portion 65 is positioned offset in a direction parallel to the main surfaces 10a and 10b from at least one of the first end portion 63a and the second end portion 63b. In other words, the convex portion 65, comprised of the first main surface direction portion 67d, the third thickness direction portion 67c, and the second main surface direction portion 67e, corresponds to the heat transfer blocking portion.

[0066] The heat transfer-suppressing sheet according to the second embodiment B configured in this manner also has the convex portions 65 that serve as heat transfer-blocking portions. Therefore, even if there are joining surfaces 61 that join multiple pieces of heat insulating material 10 together, the presence of the heat transfer-blocking portions makes it possible to suppress the transfer of heat in the thickness direction of the heat insulating material 10.

[0067] [Embodiment 3A] Fig. 5 is an enlarged cross-sectional view of a portion of a heat-transfer-suppressing sheet according to embodiment 3A of the present invention. In embodiment 3A shown in Fig. 5, the same components as those in embodiment 1A are designated by the same reference numerals, and detailed description thereof will be omitted or simplified. Furthermore, the heat-transfer-suppressing sheet 53 according to embodiment 3A can be used in place of the heat-transfer-suppressing sheet 50 of the battery pack 100 shown in Fig. 3. For ease of explanation, Fig. 5 shows gaps between adjacent insulating materials 10. However, in practice, it is preferable that there be no gaps between adjacent insulating materials 10, and it is more preferable that the connecting surfaces be in complete contact over the entire surface.

[0068] In the heat transfer-suppressing sheet 53 according to the third embodiment, the first end 63a is offset from the second end 63b in a direction parallel to the main surfaces 10a and 10b, and the inclined surface connecting the first end 63a and the second end 63b forms the joining surface 61. Therefore, the length of the joining surface (inclined surface) 61 in a cross-sectional view is longer than the thickness T3 of the region where the joining surface 61 is formed. In FIG. 5, the thickness of the region where the joining surface 61 is formed is the same as the thickness of the thermal insulation 10, so the thickness T3 is shown outside the thermal insulation 10.

[0069] The heat-transfer-suppressing sheet 53 configured in this manner can also achieve the same effects as those of the first embodiment. In the cross-sectional view shown in FIG. 5 , the bonding surface 61 is inclined with respect to the thickness direction V of the thermal insulation material 10, as indicated by the dashed line in the figure, and is formed at a predetermined angle with respect to the thickness direction V. If the angle A between the bonding surface 61 and the thickness direction V is 20° or greater, a decrease in the thermal insulation performance of the thermal insulation material in the thickness direction can be suppressed. Furthermore, if the angle A between the bonding surface 61 and the thickness direction V is 90°, the bonding surface 61 is parallel to the main surfaces 10a and 10b. For example, the main surface direction portion 64c of the heat-transfer-suppressing sheet 50 shown in FIG. 2 and the first main surface direction portion 67d and the second main surface direction portion 67e of the heat-transfer-suppressing sheet 52 shown in FIG. 4 are examples of this. Furthermore, if the angle A between the bonding surface 61 and the thickness direction V is greater than 90° and less than 160°, the length of the bonding surface 61 is longer than the thickness T3 of the region where the bonding surface 61 is formed, thereby suppressing a decrease in thermal insulation performance. Therefore, it is preferable that at least a portion of the joining surface 61 has an area that is at an angle of 20° or more and 160° or less with respect to the thickness direction of the insulation material 10, and it is more preferable that the angle with respect to the plate thickness direction V over the entire surface of the joining surface 61 is 20° or more and 160° or less.

[0070] [Embodiment 3B (Example of Functional Expression)] Next, embodiment 3B will be described with reference to Fig. 5. Embodiment 3B is a functional description of the heat transfer-suppressing sheet according to embodiment 3A.

[0071] In the heat transfer-suppressing sheet according to embodiment 3B, the first end 63a is positioned at a position offset in a direction parallel to the principal surfaces 10a, 10b with respect to the second end 63b, and a continuous inclined surface (joint surface 61 in FIG. 5) is formed from the first end 63a to the second end 63b. That is, since the inclined surface is positioned at a position offset in a direction parallel to the principal surfaces 10a, 10b from at least one of the first end 63a and the second end 63b, this inclined surface (joint surface 61) corresponds to a heat transfer-blocking portion.

[0072] In the heat transfer-suppressing sheet according to the third embodiment configured in this manner, the presence of the heat transfer-blocking portion also makes it possible to suppress heat transfer in the thickness direction of the thermal insulation material 10. As in the third embodiment, the angle A formed by the inclined surface constituting the heat transfer-blocking portion and the thickness direction V is preferably in the range of 20° to 160°.

[0073] [Embodiment 4A] Fig. 6 is an enlarged cross-sectional view of a portion of a heat-transfer-suppressing sheet according to embodiment 4A of the present invention. In embodiment 4A shown in Fig. 6, the same components as those in embodiment 1A are designated by the same reference numerals, and detailed description thereof will be omitted or simplified. Furthermore, the heat-transfer-suppressing sheet 54 according to embodiment 4A can be used in place of the heat-transfer-suppressing sheet 50 of the battery pack 100 shown in Fig. 3. For ease of explanation, Fig. 6 shows gaps between adjacent insulating materials 10. However, in practice, it is preferable that there be no gaps between adjacent insulating materials 10, and it is more preferable that the connecting surfaces be in complete contact over the entire surface.

[0074] In the heat-transfer-suppressing sheet 54 according to the fourth embodiment, the first end 63a is offset from the second end 63b in a direction parallel to the main surfaces 10a and 10b, forming an inclined surface from the first end 63a to the second end 63b. While a detailed manufacturing method for the heat-transfer-suppressing sheet 54 will be described later, in this embodiment, a portion of the main surface 10a of one insulating material 10 is overlapped with a portion of the main surface 10b of the other insulating material 10 and pressed in the thickness direction to form the inclined surface, which serves as the joining surface 61. In this embodiment, the curved or linear joining surface 61 connecting the first end 63a and the second end 63b is longer than the thickness T4 of the region in which the joining surface 61 is formed.

[0075] The heat-transfer-suppressing sheet 54 configured in this manner can achieve the same effects as in the first embodiment. Note that the larger the size of the heat-transfer-suppressing sheet 54, the more likely it is that the regions farther from its end faces will lack strength. Furthermore, since the central portion of the main surface of large battery cells 20a, 20b, and 20c is more likely to bulge than that of small battery cells, the heat-transfer-suppressing sheet must also be strong enough to withstand pressure. In this embodiment, because the end portions of the thermal insulation material 10 are compressed in the thickness direction, the density M1 of the region R1 that includes the bonding surface 61 in the thickness direction is higher than the density M2 of the region R2 that does not include the bonding surface 61 in the thickness direction. Therefore, the presence of the high-density region R1 extending along the main surface of the heat-transfer-suppressing sheet 54 not only maintains the strength of the heat-transfer-suppressing sheet itself but also improves its strength against pressure from the battery cells 20a, 20b, and 20c.

[0076] Assuming that the density of the insulating material in region R1, which includes the bonding surface 61 in the thickness direction, is M1 and the density of the insulating material in region R2, which does not include the bonding surface 61 in the thickness direction, is M2, if the ratio of density M1 to density M2 (M1 / M2) is 1.2 or greater, the effect of improving the strength of the heat transfer-suppressing sheet can be achieved as described above. Therefore, the ratio (M1 / M2) is preferably 1.2 or greater, and more preferably 1.5 or greater. However, as the density of the insulating material increases, the insulating properties tend to decrease. Therefore, it is preferable to control the ratio (M1 / M2) of density M1 to density M2, taking into account the required insulating properties and strength.

[0077] As in the first embodiment, in the third and fourth embodiments, the connecting surfaces of adjacent insulating materials 10 can be joined by adhesion, fusion, or the like to further improve ease of handling.

[0078] [Functional Expression Example of 4B Embodiment] Next, a functional expression example of 4B embodiment will be described with reference to Fig. 6. 4B embodiment is a functional description of the heat transfer suppressing sheet according to the above-described 4A embodiment.

[0079] In the fourth embodiment, a portion of the main surface 10a of one thermal insulator 10 is overlapped with a portion of the main surface 10b of the other thermal insulator 10, and pressure is applied in the thickness direction to form an inclined surface. Therefore, a joint surface 61 is formed by a portion of the main surface 10a and a portion of the main surface 10b, and the joint surface 61 corresponds to the heat transfer blocking portion.

[0080] In the heat-transfer-suppressing sheet according to the fourth embodiment configured in this manner, the density M1 of the region R1 that includes the heat-transfer-suppressing portion in the thickness direction is also higher than the density M2 of the region R2 that does not include the heat-transfer-suppressing portion in the thickness direction. Therefore, the presence of the high-density region R1 not only maintains the strength of the heat-transfer-suppressing sheet itself but also improves its strength against pressure from the battery cells 20 a, 20 b, and 20 c.

[0081] Furthermore, the ratio (M1 / M2) of the density M1 of the insulating material in the region R1 including the heat transfer blocking portion in the thickness direction of the plate to the density M2 of the insulating material in the region R2 not including the heat transfer blocking portion in the thickness direction of the plate is preferably 1.2 or more, and more preferably 1.5 or more.

[0082] [Method for Producing Heat-Transfer-Suppressing Sheet] Methods for producing heat-transfer-suppressing sheets having the various structures described above will be described below with reference to examples.

[0083] [Method of Manufacturing Heat-Transfer-Suppressing Sheet According to Embodiment 1A and Embodiment 1B] Fig. 7 is a schematic diagram showing a method of manufacturing the heat-transfer-suppressing sheet shown in Fig. 1 and Fig. 2. For convenience, Fig. 7 illustrates a method of manufacturing a heat-transfer-suppressing sheet using a heat insulating material 10 and a heat insulating material 9 bonded to this heat insulating material 10.

[0084] 7, an insulating material 10 having main surfaces 10a and 10b and an insulating material 9 having main surfaces 9a and 9b are prepared. Next, a first connecting surface 10e is processed on an end surface of one of the two insulating materials 10, 9. Specifically, a notch 10d is formed at the corner between the end surface of the insulating material 10 and the main surface 10b, thereby creating a first connecting surface 10e in at least a portion of which extends in a direction different from the thickness direction of the insulating material.

[0085] <Second Processing Step> Thereafter, the end face of the insulating material 9 is processed to form a second connecting surface 9e so that the end face of the other insulating material 9 to be joined to the insulating material 10 has a shape that conforms to the first connecting surface 10e of one of the insulating materials 10. Specifically, a notch 9d is formed at the corner between the end face and the main surface 9a of the insulating material 9. The notches 10d, 9d in the first processing step and the second processing step may be formed by cutting the end face of the plate-shaped insulating board, or may be formed by pressing the end faces of the insulating materials 10, 9 with a mold.

[0086] <Joint surface forming step (heat transfer blocking portion forming step)> Then, the thermal insulation material 10 and the thermal insulation material 9 are arranged so that the first connecting surface 10e of the thermal insulation material 10 faces the second connecting surface 9e of the thermal insulation material 9. As a result, the first connecting surface 10e and the second connecting surface 9e are connected to form the connecting surface 61, as shown in Fig. 2. In the first B embodiment, a heat transfer blocking portion is formed on a part of the connecting surface 61.

[0087] In the bonding surface forming step, at least a portion of the bonding surface 61 may be bonded with an adhesive or fused by thermal fusion. When bonding by thermal fusion, the first bonding surface 10e and the second bonding surface 9e are heated while being pressed in a direction that brings them closer to each other, for example, in the direction of the arrows shown in FIG. 7 . This allows at least a portion of the first bonding surface 10e and the second bonding surface 9e to be thermally fused. When the insulating material contains organic fibers, the heating temperature during thermal fusion is preferably set to a temperature at which the organic fibers melt, as described below. Furthermore, when bonding the first bonding surface 10e and the second bonding surface 9e by thermal fusion, cutting is preferably used as a method for forming the notches 10d and 9d.

[0088] According to the method for manufacturing a heat-transfer-suppressing sheet according to the above embodiment, even if the heat-transfer-suppressing sheet has a bonding surface where multiple heat-insulating materials are bonded, it is possible to suppress a decrease in heat-insulating properties, and it is possible to easily manufacture a heat-transfer-suppressing sheet of a desired size at low cost. Furthermore, because the heat-transfer-suppressing sheet can be manufactured by combining multiple heat-insulating materials, the properties of the heat-insulating material can be freely designed by changing the position of the heat-transfer-suppressing sheet.

[0089] In this embodiment, the size of the notches 10d and 9d may be adjusted in advance, and the density of the overlapping region of the thermal insulating material 10 and the thermal insulating material 9 may be increased by applying pressure to this region. As described above, the strength of the heat-transfer-suppressing sheet can be improved by applying pressure so that the ratio of density M1 to density M2 (M1 / M2) is 1.2 or greater. Furthermore, even when the end faces of the thermal insulating materials 10 and 9 are pressed with a mold and processed into a desired shape, the density of the pressed region is increased. Therefore, even when the first connecting surface 10e and the second connecting surface 9e pressed with a mold are joined, a heat-transfer-suppressing sheet having excellent strength at the joining surface 61 can be obtained.

[0090] The heat transfer suppressing sheet 52 according to the second embodiment A and the second embodiment B shown in FIG. 4 and the heat transfer suppressing sheet 53 according to the third embodiment A and the third embodiment B shown in FIG. 5 can be manufactured in the same manner as the heat transfer suppressing sheet 50 according to the first embodiment A and the first embodiment B, and therefore the manufacturing methods thereof will not be described here.

[0091] [Method of Manufacturing Heat-Transfer-Suppressing Sheet According to Embodiment 4A and Embodiment 4B] Fig. 8 is a schematic diagram showing a method of manufacturing the heat-transfer-suppressing sheet 54 shown in Fig. 6. For convenience, Fig. 8 also describes a method of manufacturing a heat-transfer-suppressing sheet using a heat insulating material 10 and a heat insulating material 9 bonded to this heat insulating material 10.

[0092] <Arranging Step> As shown in FIG. 8, two thermal insulating materials 10 and 9 are arranged so that a part of the main surface 10b of one thermal insulating material 10 overlaps a part of the main surface 9a of the other thermal insulating material 9.

[0093] <Joint surface forming process (heat transfer blocking portion forming process)> Pressure is applied to the overlapping region of the insulating material 10 and the insulating material 9 in the thickness direction of the insulating material 10 and the insulating material 9, i.e., in the direction indicated by the arrow in FIG. 8 . As a result, the insulating material 10 and the insulating material 9 are compressed as they approach their end faces, forming a joint surface 61 in which a portion of the main surface 10b of one insulating material 10 and a portion of the main surface 9a of the other insulating material 9 are joined, as shown in FIG. 6 . In this embodiment, the joint surface 61 is not a region where the end faces of the insulating materials 10 and 9 face each other, but a region where the main surfaces 10b and 9a face each other, so that the joint surface 61 is formed by portions of the main surfaces 10b and 9a. Note that in the first embodiment, this joint surface 61 serves as a heat transfer blocking portion.

[0094] The manufacturing methods for the heat-transfer-suppressing sheet according to the 4A and 4B embodiments, like the heat-transfer-suppressing sheets according to the 1A and 1B embodiments, allow for easy and low-cost production of heat-transfer-suppressing sheets of desired sizes with excellent thermal insulation properties, while also improving design flexibility. Furthermore, unlike the manufacturing method shown in FIG. 7 , the end faces of the heat insulating material do not need to be pre-processed. The joining surface formation process allows for simultaneous formation of the connecting surface and the bonding surface, further simplifying the manufacturing process. Furthermore, because the end faces of the heat insulating material are compressed during the bonding surface formation process, the density M1 of the heat insulating material in region R1 is increased, and the ratio of density M1 to density M2 (M1 / M2) can easily be set to 1.2 or greater. Therefore, according to this embodiment, a heat-transfer-suppressing sheet with excellent strength at the bonding surface 61 can be easily obtained.

[0095] When the manufacturing methods for the heat transfer-inhibiting sheet according to the above-described embodiments 4A and 4B are used, the shape of the joining surface 61 in cross section may vary depending on the hardness of the insulating materials 10 and 9, resulting in a stepped joining surface, as shown in FIG. 2 . Furthermore, depending on the pressure applied to the insulating materials 10 and 9 in their thickness direction, the ends of the insulating materials 10 and 9 may protrude from the main surfaces 10a and 10b. However, regardless of the surface shape of the joining surface 61 or the heat transfer-inhibiting sheet, as long as the length of the joining surface 61 is longer than the thickness of the heat transfer-inhibiting sheet in that region, a decrease in the insulating properties at the joining surface can be sufficiently suppressed. Furthermore, as shown in FIG. 6 , if a heat transfer blocking portion is formed at a position offset from at least one of the first end 63a and the second end 63b in a direction parallel to the main surfaces 10a and 10b of the insulating material 10, a decrease in the insulating properties at the joining surface can be sufficiently suppressed.

[0096] In the bonding surface forming step, at least a portion of the bonding surface 61 may be adhered with an adhesive or the like, or may be fused by thermal fusion. When fusion is performed by thermal fusion, the area where the insulating material 10 and the insulating material 9 overlap is heated while being pressed in the thickness direction of this area. This allows a portion of the main surface 10b of one insulating material 10 to a portion of the main surface 9a of the other insulating material 9 to be fused by thermal fusion. When the insulating material contains organic fibers, the heating temperature during thermal fusion is preferably set to a temperature equal to or higher than the melting temperature of the organic fibers, as described below.

[0097] The components of the heat transfer-suppressing sheet according to each embodiment of the present invention will be described below. First, the heat insulating material will be described in detail.

[0098] [Thermal Insulation Material] The thermal insulation material used in the heat transfer-suppressing sheet according to this embodiment is not particularly limited as long as it has a thermal insulation effect. Thermal conductivity can be used as an index of the thermal insulation effect. In this embodiment, the thermal conductivity of the thermal insulation material is preferably less than 1 (W / m·K), more preferably less than 0.5 (W / m·K), and even more preferably less than 0.2 (W / m·K). Furthermore, the thermal conductivity of the thermal insulation material is more preferably less than 0.1 (W / m·K), more preferably less than 0.05 (W / m·K), and particularly preferably less than 0.02 (W / m·K). The thermal conductivity of the thermal insulation material can be measured in accordance with the "Test Method for Thermal Conductivity of Refractories" described in JIS R 2251.

[0099] In the heat transfer-suppressing sheet according to each embodiment of the present invention, the insulating material may contain inorganic particles. However, examples of the structure of insulating materials that have even better insulating properties and contain organic fibers will be described in detail below.

[0100] <Thermal Insulation (Structural Example S1)> Fig. 9 is a photograph substituting a drawing showing structural example S1 of a thermal insulation material used in the heat-transfer-suppressing sheet according to each embodiment of the present invention, and Fig. 10 is a photograph substituting a drawing showing an enlarged portion of the thermal insulation material shown in Fig. 9. Note that the thermal insulation material 10 in Figs. 9 and 10 can be used as the thermal insulation material 10 in Figs. 1 to 8 and the thermal insulation material 9 in Figs. 7 and 8.

[0101] 9 and 10 , the thermal insulating material 10 has inorganic particles 4 and organic fibers 1. The thermal insulating material 10 also has a plurality of three-dimensionally connected pores 7 between the inorganic particles 4 and the organic fibers 1. The organic fibers 1 have welded portions 5 that cover at least a portion of their surfaces, and at least a portion of the inorganic particles 4 are welded to the surfaces of the organic fibers 1 by the welded portions 5. As a result, the surfaces of the organic fibers 1 are covered with the inorganic particles 4.

[0102] The insulating material 10 configured in this manner has multiple three-dimensionally connected pores 7, which provide the effect of air insulation and improve thermal insulation performance. Furthermore, the insulating material 10 contains highly flexible organic fibers 1, which not only enhances the flexibility of the insulating material 10 but also makes it easier for the organic fibers 1 to entangle with each other, thereby improving sheet strength. Therefore, damage to a heat-transfer-suppressing sheet including such insulating material 10 can be suppressed. Furthermore, the presence of pores 7 in the insulating material 10 improves the cushioning properties of the entire sheet. Therefore, when the battery cells 20a, 20b, and 20c expand during charging and discharging, the insulating material 10 absorbs the expansion of the battery cells, further suppressing deterioration in battery cell performance.

[0103] Furthermore, in this embodiment, it is preferable that at least some of the pores 7 communicate with the surface of the thermal insulation material 10 and open outward. With the pores 7 configured in this manner, even if the adjacent battery cells 20a, 20b, 20c experience thermal runaway and the thermal insulation material 10 becomes hot and the organic fibers 1 and the like are decomposed, the decomposition gas will not remain inside the sheet but will be released to the outside through the pores 7. Therefore, from this point of view as well, the effect of preventing destruction of the sheet can be obtained.

[0104] Furthermore, when the welded portions 5 on the outer peripheral surfaces of the organic fibers 1 fix the inorganic particles 4 to the organic fibers 1, it is possible to obtain the effect of suppressing the falling off (powdering) of the inorganic particles 4. Therefore, even if, for example, a portion of the battery cells 20a, 20b, 20c expands and applies compressive stress or impact to the heat transfer-suppressing sheet 50, it is possible to further enhance the effect of maintaining the shape of the thermal insulation material 10, and to prevent a decrease in the thermal insulation effect due to compressive deformation of the thermal insulation material 10.

[0105] The welded portion 5 does not need to completely cover the outer periphery of the organic fiber 1, and there may be areas where the welded portion 5 is not present. In the thermal insulation material 10, binder fibers with a sheath-core structure, which will be described later, can be used as the material for the organic fiber 1, but if the sheath portion peels off during the manufacturing process, the core portion of the organic fiber 1 may be partially exposed. Even in such a case, the effect of holding the inorganic particles 4 can be sufficiently obtained.

[0106] In this specification, the welded portion 5 refers to a portion on the surface of the organic fiber 1, or a portion where the sheath portion of a binder fiber having a core-sheath structure is melted by heating and then cooled and solidified again, and is formed during the manufacturing process of the thermal insulating material 10 described below. The welded portion 5 welds the inorganic particles 4 to the surface of the organic fiber 1 and also welds the organic fibers 1 together. When binder fibers having a core-sheath structure are used as the material for the organic fiber 1, the welded portion 5 contains the second organic material that constitutes the sheath portion. In this embodiment, because the inorganic particles 4 are welded to the surface of the organic fiber 1 by the welded portion 5, the apparent fiber diameter of the organic fiber 1 becomes thicker, which supports the shape of the thermal insulating material 10 and achieves high strength.

[0107] Furthermore, it is preferable that the heat insulating material 10 contains inorganic fibers. The effect obtained by containing inorganic fibers will be explained in the following structural example S2 of the heat insulating material.

[0108] <Thermal Insulation (Structural Example S2)> Figure 11 is a photograph showing structural example S2 of a thermal insulation material used in the heat-transfer-suppressing sheet according to each embodiment of the present invention. In structural example S2 shown in Figure 11, the same components as those in structural example S1 shown in Figures 9 and 10 are designated by the same reference numerals, and detailed description thereof will be omitted. Note that the thermal insulation material 40 shown in Figure 11 can be used in place of, for example, the thermal insulation material 10 of the heat-transfer-suppressing sheets 50, 52, 53, and 54, or the thermal insulation material 9 shown in Figures 7 and 8.

[0109] As shown in Figure 11, the thermal insulation material 40 has inorganic fibers 15. The thermal insulation material 40 also has a fiber layer 11 formed on at least a portion of a first surface 40a and a second surface (not shown) perpendicular to the thickness direction of the thermal insulation material 40. The fiber layer 11 is formed by welding at least a portion of a plurality of organic fibers 1 together at welding portions, and is formed in a layer on the surface (first surface and second surface) of the thermal insulation material 40. In other words, the fiber layer 11 is a layer formed by gathering 10 or more organic fibers 1 on the surface of the thermal insulation material 40, and extends, for example, in stripes, in a direction approximately parallel to the surface.

[0110] Furthermore, a composite layer (not shown) containing a mixture of part of the fiber layer 11 and part of the inorganic particles 4 is formed between the fiber layer 11 and the base layer 13 containing the inorganic particles 4 and the organic fibers 1. Specifically, the composite layer is a region containing a plurality of organic fibers 1 at least partially welded to one another by welded portions, and inorganic particles 4 welded to the organic fibers 1 by welded portions.

[0111] In the heat insulating material 40 shown in Fig. 11, the inorganic fibers 15 are contained in the base layer 13 containing the inorganic particles 4 and the organic fibers 1, but may also be contained in the fiber layer 11. In Fig. 11, the inorganic fibers 15 in the fiber layer 11 cannot be distinguished, and are therefore not shown.

[0112] Furthermore, the thermal insulating material 40 has fiber bundles 6 formed by welding at least some of the organic fibers 1 together at welding portions 5. The fiber bundles 6 are formed by entangling 10 or more organic fibers 1 with one another and welding some of the organic fibers 1 together, and are arranged in any direction within the thermal insulating material 40.

[0113] The thermal insulation material 40 configured in this manner contains inorganic fibers 15 that are resistant to decomposition even at high temperatures. Therefore, for example, if the battery cell 20a experiences thermal runaway and the heat-transfer-suppressing sheet 50 disposed adjacent to the battery cell 20a is exposed to high temperatures, even if the organic fibers 1 in the thermal insulation material 40 decompose, the inorganic fibers 15 remain, thereby reliably maintaining the shape of the thermal insulation material 40. Furthermore, the flexible organic fibers 1 easily become entangled with the relatively hard inorganic fibers 15, and the inorganic fibers 15 and the organic fibers 1 form a three-dimensional skeleton, further improving the strength of the thermal insulation material 40.

[0114] Furthermore, when the insulating material 40 has the fiber layer 11 on its surface and the fiber bundles 6 inside, it can obtain even higher strength compared to when the organic fibers 1 are dispersed. Note that the fiber layer 11 is not simply disposed on the base layer 13, but has a composite layer between the fiber layer 11 and the base layer 13, in which part of the fiber layer 11 and part of the inorganic particles 4 are mixed, so that the fiber layer 11 is securely bound to the surface of the insulating material 40. Therefore, the fiber layer 11 alone does not fall off, and an insulating material 40 having high strength can be obtained, and the pressure on the base layer 13 can be further reduced.

[0115] Furthermore, when a fiber layer 11 is formed on the surface of the insulation material 40, this fiber layer 11 can absorb the impact given to the insulation material 40, thereby preventing the inorganic particles contained in the insulation material 40 from falling off.

[0116] <Thermal Insulation (Structural Example S3)> Figure 12 is a schematic diagram showing structural example S3 of the thermal insulation used in the heat transfer-suppressing sheet according to each embodiment of the present invention, and Figure 13 is a schematic diagram showing an enlarged portion of Figure 12. Figure 14 is a photograph showing the thermal insulation shown in Figure 12. In structural example S3 shown in Figures 12 to 14, the same components as those in structural example S1 shown in Figures 9 and 10 are designated by the same reference numerals, and detailed description will be omitted. Note that the thermal insulation 60 shown in Figures 12 to 14 can be used, for example, in place of the thermal insulation 10 of the heat transfer-suppressing sheets 50, 52, 53, and 54, or the thermal insulation 9 shown in Figures 7 and 8.

[0117] As shown in FIGS. 12 to 14 , the thermal insulating material 60 includes inorganic particles 4, organic fibers 1 made of a first organic material, and welded portions 5 covering the outer surfaces of the organic fibers 1. As described above, the welded portions 5 include a second organic material 17 having a melting point lower than that of the first organic material, and inorganic particles 4. In this embodiment, the organic fibers are binder fibers 3 having a sheath-core structure with a core and a sheath covering the outer surface of the core, with the organic fibers 1 corresponding to the core. The welded portions 5 are formed by heating and then cooling the sheath of the binder fibers 3 having a sheath-core structure. Furthermore, as shown in FIG. 14 , the organic fibers 1 and the welded portions 5 containing the inorganic particles 4 form fiber portions 16, and matrix portions 18 containing inorganic particles are formed between the multiple fiber portions 16. When the molten sheath portions are cooled, adjacent organic fibers 1 are fused to each other at contact portions 31, forming a three-dimensional skeleton.

[0118] In the thermal insulation material 60 configured in this manner, the organic fibers 1 and the welded portions 5 act as a skeleton, thereby achieving excellent strength and shape retention. Furthermore, the welded portions 5 covering the outer periphery of the organic fibers on both the surface and center sides of the thermal insulation material 60 fix the inorganic particles 4 to the organic fibers 1, thereby suppressing powder shedding. Therefore, for example, if the heat-transfer-suppressing sheet 50 according to this embodiment is disposed between multiple battery cells, excellent thermal insulation performance can be maintained even if the battery cells expand and apply compressive stress or impact to the heat-transfer-suppressing sheet 50.

[0119] Although the mechanism by which the above-mentioned insulating material 60 is able to prevent the inorganic particles 4 from falling off (powdering) is not clear, one possible reason is that the organic fibers 1 and the welded portions 5 form a three-dimensional, strong skeleton, which maintains the shape of the insulating material 60 and thus prevents deformation or compression of the insulating material 60. Another possible reason for the inorganic particles 4 being retained is that the fiber portions 16 exposed on the surface of the insulating material 60 can absorb impacts applied to the insulating material 60.

[0120] 14 , in the thermal insulation material 60, the welded portion 5 does not need to completely cover the outer periphery of the organic fiber 1, and the organic fiber 1 may be partially exposed. Because the thermal insulation material 60 uses binder fiber 3 with a core-sheath structure, the sheath portion may peel off during the manufacturing process of the thermal insulation material 60, but even if the organic fiber 1 is partially exposed, the effect of suppressing powder fall-off can be sufficiently obtained.

[0121] <Thermal Insulation (Structural Example S4)> Figure 15 is a photograph, substituted for a drawing, showing structural example S4 of the thermal insulation used in the heat-transfer-suppressing sheet according to each embodiment of the present invention, and Figure 16 is a photograph, substituted for a drawing, showing an enlarged view of the structure of the thermal insulation shown in Figure 15. Figure 17 is a photograph, substituted for a drawing, showing a cross section of the thermal insulation shown in Figure 15. In structural example S4 shown in Figures 15 to 17, the same components as those in structural example S1 shown in Figures 9 and 10 are designated by the same reference numerals, and detailed description will be omitted. Note that the thermal insulation 70 shown in Figures 15 to 17 can be used, for example, in place of the thermal insulation 10 of the heat-transfer-suppressing sheets 50, 52, 53, and 54, or the thermal insulation 9 shown in Figures 7 and 8.

[0122] 15 and 16 , the heat insulating material 70 has a matrix 14 containing inorganic particles 4 and organic fibers 1 three-dimensionally oriented in this matrix 14. The organic fibers 1 have welded parts 5 covering at least a part of their surfaces, and the organic fibers 1 are welded to each other by the welded parts 5. Similarly, the inorganic particles 4 are welded to the surfaces of the organic fibers 1, so that the surfaces of the organic fibers 1 are covered with the inorganic particles 4.

[0123] As shown in the cross-sectional view of Fig. 17, a plurality of voids 7 are formed in the matrix 14 of the thermal insulating material 70. Furthermore, at least some of the plurality of organic fibers 1 are welded together in the matrix 14 by welds 5 (not shown in Fig. 17), thereby forming fiber bundles 6, and voids 8 are formed between the plurality of organic fibers 1 constituting the fiber bundles 6.

[0124] Furthermore, a fiber layer 11 is formed on at least a portion of the first surface 70a and the second surface (not shown) perpendicular to the thickness direction of the thermal insulation material 70. The fiber layer 11 is formed in a layer on the surfaces (first and second surfaces) of the thermal insulation material 70, with at least a portion of a plurality of organic fibers 1 welded together by welded portions 5. A composite layer 12 is formed between the fiber layer 11 and a base layer 13 containing a matrix 14 and the organic fibers 1. The composite layer 12 is a layer in which a portion of the fiber layer 11 and a portion of the matrix 14 are mixed. Specifically, the composite layer 12 is a region containing a plurality of organic fibers 1 at least a portion of which are welded to each other by welded portions 5, and inorganic particles 4 welded to the organic fibers 1 by welded portions 5.

[0125] The fiber bundles 6 are formed by entangling 10 or more organic fibers 1 with some of the organic fibers 1 being welded to one another, and are arranged in any direction in the matrix 14 of the thermal insulation material 70. On the other hand, the fiber layer 11 is a layer formed by assembling 10 or more organic fibers 1 on the surface of the thermal insulation material 70, and extends, for example, in stripes in a direction substantially parallel to the surface.

[0126] In the thermal insulation material 70 configured in this manner, the organic fibers 1 are three-dimensionally oriented in the matrix 14, and the organic fibers 1 have welded parts 5 that cover at least a portion of their surfaces. The welded parts 5 refer to areas where the surfaces of the organic fibers 1 melt and then solidify again, and are formed during the manufacturing process of the thermal insulation material 70. In the thermal insulation material 70, the three-dimensionally oriented organic fibers 1 are welded to each other by the welded parts 5, and this structure serves as a skeleton to support the shape of the thermal insulation material 70, thereby achieving high strength.

[0127] Similarly, in the thermal insulating material 70, the welded portions 5 on the outer peripheral surface of the organic fibers 1 also fix the inorganic particles 4 to the organic fibers 1, thereby achieving an even greater powder shedding suppression effect. Therefore, for example, even if a portion of the battery cells 20a, 20b, and 20c expands during charging and discharging, causing compressive stress or impact on the heat transfer-suppressing sheet 50, the shape of the thermal insulating material 70 can be maintained. As a result, shedding (powder shedding) of the inorganic particles 4 can be suppressed, and a decrease in the insulating effect of the thermal insulating material 70 due to compressive deformation can be prevented.

[0128] The mechanism by which the insulating material 70 can prevent the inorganic particles 4 from falling off from the sheet surface is thought to be similar to that of the insulating material 60 of the above-mentioned structural example S3.

[0129] In the heat insulating material 70, the welded portion 5 does not need to completely cover the outer surface of the organic fiber 1, and there may be areas where the welded portion 5 is not present. Even in such a case, the effect of holding the inorganic particles 4 can be sufficiently obtained.

[0130] Furthermore, since the insulating material 70 contains organic fibers 1 that have high flexibility, the flexibility of the insulating material 70 can be increased and the organic fibers 1 can be easily entangled with each other, thereby obtaining the effect of improving the sheet strength.

[0131] Furthermore, the thermal insulation material 70 has a plurality of voids 7 in the matrix 14 and voids 8 between the plurality of organic fibers 1 that make up the fiber bundle 6, thereby improving the thermal insulation performance. Furthermore, the presence of the voids 8 makes it difficult for the organic fibers 1 to be constrained in the matrix 14, thereby further improving the flexibility and strength of the thermal insulation material 70. The voids 8 do not need to be formed in the entire region between the plurality of organic fibers 1; as long as the voids 8 are formed in at least a portion of the regions between the organic fibers 1, the effect of suppressing heat transfer can be obtained.

[0132] Furthermore, since the thermal insulation material 70 has the fiber bundles 6 and the fiber layer 11, it can have even higher strength than when the organic fibers 1 are dispersed. Furthermore, the fiber layer 11 is not simply disposed on the base layer 13, but has a composite layer 12 between the fiber layer 11 and the base layer 13, in which part of the fiber layer 11 and part of the inorganic particles 4 that make up the matrix 14 are mixed, so that the fiber layer 11 is securely bound to the surface of the thermal insulation material 70. Therefore, a thermal insulation material 70 with high strength can be obtained.

[0133] <Thermal Insulation (Structural Example S5)> Figure 18 is a schematic diagram showing structural example S5 of the thermal insulation used in the heat-transfer-suppressing sheet according to each embodiment of the present invention, and Figure 19 is a schematic diagram showing an enlarged view of section A of the thermal insulation shown in Figure 18. In structural example S5 shown in Figures 18 and 19, the same components as those in structural example S1 of the thermal insulation shown in Figures 9 and 10 are designated by the same reference numerals, and detailed description thereof will be omitted. Note that the thermal insulation 80 shown in Figures 18 to 19 can be used, for example, in place of the thermal insulation 10 of the heat-transfer-suppressing sheets 50, 52, 53, and 54, or the thermal insulation 9 shown in Figures 7 and 8.

[0134] 18 and 19 , the heat insulating material 80 has a matrix 14 containing inorganic particles 4, inorganic fibers 15 dispersed in the matrix 14, and organic fibers 1. The organic fibers 1 and the inorganic fibers 15 are entangled with each other to form a three-dimensional web structure. In this embodiment, an air layer 28 is formed around a portion of the inorganic fibers 15. The organic fibers 1 also have welded portions 5 on a portion of their surface, and at least a portion of the inorganic fibers 15 is welded to the organic fibers 1 by the welded portions 5. Furthermore, at least a portion of the inorganic particles 4 is welded to the organic fibers 1 by the welded portions 5.

[0135] In this specification, the term "dispersed" of the inorganic fibers 15 means that the inorganic fibers 15 are not distributed unevenly but are spread out over the entire surface.

[0136] In the thermal insulation material 80 configured in this manner, the organic fibers 1 and inorganic fibers 15 are entangled with each other to form a three-dimensional web structure, and this structure serves as a skeleton, providing high strength. Therefore, even if the heat transfer-suppressing sheet 50 is compressed due to expansion of the battery cells 20a, 20b, and 20c during charging and discharging, the shape of the thermal insulation material 80 can be maintained. As a result, it is possible to prevent the inorganic particles 4 from falling off (powdering), and to prevent a decrease in the thermal insulation effect of the thermal insulation material 80 due to compression and deformation.

[0137] Furthermore, because the heat insulating material 80 contains the highly flexible organic fibers 1, the flexibility of the heat insulating material 80 can be increased, and the organic fibers 1 are more likely to become entangled with the inorganic fibers 15 to form a three-dimensional web structure, thereby improving the strength. Furthermore, if the heat insulating material 80 contains the inorganic fibers 15, the shape of the heat transfer-inhibiting sheet can be maintained even if, for example, the battery cell 20a experiences thermal runaway and the heat transfer-inhibiting sheet disposed adjacent to the battery cell 20a is exposed to high temperatures, causing the organic fibers 1 to decompose. Therefore, by including the highly flexible organic fibers 1 and the inorganic fibers 15 that do not decompose even at high temperatures in the heat insulating material 80, a heat transfer-inhibiting sheet that has a good balance of both flexibility and strength can be obtained.

[0138] Furthermore, in this embodiment, air layers 28 are formed around the inorganic fibers 15 dispersed in the matrix 14. The inorganic fibers 15 have a higher thermal conductivity than the organic fibers 1, but as described above, the formation of the air layers 28 around the inorganic fibers 15 can suppress heat transfer between the inorganic fibers 15 and the matrix 14. The air layers 28 are formed during the manufacturing process of the thermal insulation material 80, but the air layers 28 do not need to be formed around the entire area around the inorganic fibers 15. The heat transfer suppression effect can be obtained as long as the air layers 28 are formed on at least a portion of the outer surface of the inorganic fibers 15. If the inorganic fibers 15 are uniformly dispersed in the matrix 14, the air layers 28 in the matrix 14 will also be uniformly dispersed and disposed, allowing the thermal insulation material 80 to achieve high, uniform thermal insulation properties.

[0139] Furthermore, in the insulating material 80, the organic fibers 1 have welded portions 5 that cover at least a portion of the surface. The welded portions 5 refer to areas where the surfaces of the organic fibers 1 melt and then solidify again, and are formed during the manufacturing process of the insulating material 80. When at least a portion of the inorganic fibers 15 are welded to the organic fibers 1 by the welded portions 5, the entangled organic fibers 1 and inorganic fibers 15 are fixed, thereby making it possible to obtain an insulating material 80 with even higher strength.

[0140] Similarly, in this embodiment, the welded portions 5 on the outer peripheral surfaces of the organic fibers 1 also fix the inorganic particles 4 to the organic fibers 1, thereby achieving an even greater powder shedding suppression effect. Therefore, even if, for example, a portion of the battery cells 20 a, 20 b, 20 c expands and applies compressive stress or impact to the heat transfer-suppressing sheet, excellent heat insulating performance can be maintained.

[0141] In this embodiment, the mechanism by which the inorganic particles 4 are prevented from falling off from the sheet surface is thought to be that the organic fibers 1 and the inorganic fibers 15 are welded to each other at the welded portions 5 to form a three-dimensional, strong skeleton, which maintains the shape of the heat insulating material 80 and prevents deformation or compression of the heat transfer-suppressing sheet. Furthermore, when the organic fibers 1 and the inorganic fibers 15 are exposed on the surface of the heat insulating material 80, they are able to absorb impacts applied to the heat insulating material 80, thereby presumably holding the inorganic particles 4 in place.

[0142] In the heat insulating material 80, the welded portion 5 does not need to completely cover the outer surface of the organic fiber 1, and there may be areas where the welded portion 5 is not present. Even in such a case, the effect of holding the inorganic particles 4 can be sufficiently obtained.

[0143] <Thermal Insulation (Structural Example S6)> Figure 20 is a photograph showing structural example S6 of the thermal insulation used in the heat-transfer-suppressing sheet according to each embodiment of the present invention, and Figure 21 is a photograph showing another region of the thermal insulation shown in Figure 20. Also, Figure 22 is a photograph showing a cross section of the thermal insulation shown in Figures 20 and 21. In structural example S6 shown in Figures 20 to 22, the same components as those in structural example S4 of the thermal insulation shown in Figures 15 to 17 are designated by the same reference numerals, and detailed description will be omitted. The thermal insulation 90 shown in Figures 20 to 22 can be used, for example, in place of the thermal insulation 10 of the heat-transfer-suppressing sheets 50, 52, 53, and 54, or the thermal insulation 9 shown in Figures 7 and 8.

[0144] 20 , the heat insulating material 90 includes inorganic particles 4 and organic fibers 1. At least some of the organic fibers 1 have a branched structure including a base 32 and branches 33 extending from the base 32. In this embodiment, the branches 33 extend from the base 32 in four directions: direction D1, direction D2, direction D3, and direction D4. The base 32 and the multiple branches 33 form a skeleton.

[0145] 21 also contains organic fibers 1 having a branched structure consisting of a base 32 and branches 33 extending from the base 32. The organic fibers 1 shown in Fig. 21 have a base 32 and branches 33 extending from the base 32 in five directions, i.e., directions D1, D2, D3, D4, and D5, and the base 32 is thicker than the multiple branches 33.

[0146] Furthermore, as shown in Figures 20 and 21, in this embodiment, inorganic particles 4 are welded to the surface of the organic fiber 1, so that the surface of the organic fiber 1 is covered with the inorganic particles 4.

[0147] 22, a plurality of voids 7 are formed in the thermal insulation material 90. Furthermore, a plurality of organic fibers 1 are at least partially welded together in the thermal insulation material 90 to form fiber bundles 6, and gaps 8 are formed between the plurality of organic fibers 1 that make up the fiber bundles 6. Note that, also in FIG. 22, it is possible to see the organic fibers 1 having a branched structure consisting of a base 32 and branches 33 extending in three directions from the base 32.

[0148] Furthermore, a fiber layer 11 may be formed on at least a portion of the first and second surfaces perpendicular to the thickness direction of the thermal insulation material 90. The fiber layer 11 is formed by welding at least a portion of a plurality of organic fibers 1 to each other and forming a layer on the surface (first and second surfaces) of the thermal insulation material 90. Furthermore, a composite layer 12 may be formed between the fiber layer 11 and a base layer 13 containing inorganic particles 4 and the organic fibers 1. The composite layer 12 is a layer in which a portion of the fiber layer 11 and a portion of the inorganic particles 4 are mixed. Specifically, the composite layer 12 is a region containing a plurality of organic fibers 1 welded to each other and inorganic particles 4 welded to the organic fibers 1.

[0149] The fiber bundles 6 are formed by entangling 10 or more organic fibers 1 with some of the organic fibers 1 being welded to one another, and are arranged in any direction inside the thermal insulation material 90. On the other hand, the fiber layer 11 is a layer formed by assembling 10 or more organic fibers 1 on the surface of the thermal insulation material 90, and extends, for example, in stripes in a direction substantially parallel to the surface.

[0150] In the thermal insulation material 90 configured in this manner, at least some of the organic fibers 1 have a branched structure consisting of bases 32 and branches 33, and the organic fibers 1 serve as a skeleton to maintain the shape of the thermal insulation material 90. In this embodiment, the bases 32 are formed by fused portions where the organic fibers 1 are fused to each other. Specifically, the bases 32 are portions where a plurality of organic fibers 1 come into contact with each other, melt together, and then solidify, and are therefore thicker than the branches 33. Therefore, the bases 32 can firmly support the entire skeleton, and the strength of the thermal insulation material 90 can be significantly improved.

[0151] In the thermal insulating material 90, at least a portion of the organic fibers 1 have a branched structure consisting of a base 32 and branches 33 extending from the base 32 in at least three directions. The branched structure can be confirmed in a cross-sectional photograph of the thermal insulating material 90, but an easier way to confirm the branched structure is to observe a cross section of the thermal insulating material 90 torn in a plane direction perpendicular to its thickness direction. In this way, by observing the cross section, it is possible to easily confirm that the organic fibers 1 have a branched structure consisting of a base 32 and branches 33 extending from the base 32 in at least three directions. The base 32 and branches 33 will be described in more detail below.

[0152] (Base (Fused Portion)) When binder fibers with a sheath-core structure are used as the material for the thermal insulation material 90, the fused portion is formed by first melting the sheath of the binder fiber by heating and then cooling it in the area where multiple binder fibers are in contact with each other. When binder fibers with a sheath-core structure are used as the material for the thermal insulation material 90, the fused portion contains the second organic material that constitutes the sheath. In this way, when the sheath in the area where multiple binder fibers are in contact is melted by heating in the manufacturing process of the heat transfer-suppressing sheet 50, the amount of melted sheath (second organic material) is greater than when the sheath of a single binder fiber is melted, and a thick fused portion (base 32) is formed after cooling. As a result, the skeleton is firmly supported by the base 32.

[0153] (Branch) The branch 33 extends in at least three directions from the base 32 and has the effect of holding the inorganic particles 4. Furthermore, the base 32 and branch 33 form a skeleton, which can also improve the strength of the heat transfer-suppressing sheet 50. This can achieve a high powder shedding suppression effect. When a core-sheath binder fiber is used as the organic fiber 1, the branch 33 is part of the core-sheath binder fiber and has a core made of a first organic material and a sheath made of a second organic material.

[0154] As long as the branches 33 extending from the base 32 extend in at least three directions, a skeleton made of the organic fibers 1 can be formed. Furthermore, it is preferable that these multiple branches 33 extend in different three-dimensional directions, thereby forming a three-dimensional, strong skeleton.

[0155] In the thermal insulation material 90, the multiple support portions 33 extend from the base portion 32, allowing the inorganic particles 4 to be held by these support portions 33. This, combined with the improved sheet strength achieved by the formation of a skeleton, provides a high powder shedding suppression effect. Therefore, for example, even if a portion of the battery cells 20a, 20b, and 20c expands during charging and discharging, causing compressive stress or impact on the heat transfer-suppressing sheet, the shape of the thermal insulation material 90 can be maintained. As a result, shedding (powder shedding) of the inorganic particles 4 can be suppressed, and a decrease in the insulating effect of the thermal insulation material 90 due to compressive deformation can be prevented.

[0156] The mechanism by which the inorganic particles 4 can be prevented from falling off the surface of the insulating material 90 is thought to be due to the same effect as that of the insulating material 60 of the above structural example S3, as well as the effect of the support parts 33 to hold the inorganic particles 4. Furthermore, when the inorganic particles 4 are fused to the surface of the organic fibers 1, the organic fibers 1 appear to have a thicker fiber diameter, which makes them stronger than the strength of the organic fibers 1 alone, and also provides a high holding effect for the inorganic particles 4.

[0157] In the heat insulating material 90, there may be a region where the inorganic particles 4 are not partially welded to the outer peripheral surface of the organic fibers 1. Even in such a case, the effect of holding the inorganic particles 4 can be sufficiently obtained.

[0158] Furthermore, since the insulating material 90 contains organic fibers 1 that have high flexibility, the flexibility of the insulating material 90 can be increased and the organic fibers 1 can be easily entangled with each other, thereby obtaining the effect of improving the sheet strength.

[0159] Furthermore, the heat insulating material 90 preferably has a plurality of pores 7 and voids 8 between the plurality of organic fibers 1 constituting the fiber bundle 6, thereby obtaining the effect of air insulation and improving the heat insulating performance. Furthermore, the presence of the voids 8 causes the organic fibers 1 to be in a completely unconstrained state, further improving the flexibility and strength of the heat insulating material 90. The voids 8 do not need to be formed in the entire region between the plurality of organic fibers 1; as long as the voids 8 are formed in at least a portion of the regions between the organic fibers 1, the effect of suppressing heat transfer can be obtained.

[0160] Furthermore, since the insulating material 90 has the fiber bundles 6 and the fiber layer 11, it can obtain a sheet strength that is even higher than when the organic fibers 1 are dispersed. Furthermore, when the fiber layer 11 is present, the fiber layer 11 is not simply disposed on the base layer 13, but has a composite layer 12 between the fiber layer 11 and the base layer 13, in which part of the fiber layer 11 and part of the inorganic particles 4 are mixed, so that the fiber layer 11 is securely bound to the surface of the insulating material 90. Therefore, the strength of the insulating material 90 can be improved.

[0161] <Thermal Insulation (Structural Example S7)> Figure 23 is a photograph, substitute for a drawing, showing structural example S7 of the thermal insulation used in the heat-transfer-suppressing sheet according to each embodiment of the present invention, and Figure 24 is a photograph, substitute for a drawing, showing an enlarged portion of the thermal insulation shown in Figure 23. In structural example S7 shown in Figures 23 and 24, the same components as those in structural example S2 of the thermal insulation shown in Figure 11 are given the same reference numerals, and detailed description will be omitted. Note that the thermal insulation 110 shown in Figures 23 and 24 can be used, for example, in place of the thermal insulation 10 of the heat-transfer-suppressing sheets 50, 52, 53, and 54, or the thermal insulation 9 shown in Figures 7 and 8.

[0162] 23 and 24 , the thermal insulating material 110 includes inorganic particles 4 and organic fibers 1. A first region 42 having streak-like fiber bundles made of a plurality of organic fibers 1 and a second region 43 having no fiber bundles 47 are formed on the surface of the thermal insulating material 110. In this specification, the fiber bundles 47 are 10 or more organic fibers 1 entangled with one another, and extend in streak-like fashion in a direction substantially parallel to the surface of the thermal insulating material 110.

[0163] That is, when the surface of the thermal insulating material 110 is observed, as shown in Fig. 24, a state in which a plurality of organic fibers 1 are entangled is observed in the first region 42. On the other hand, in the second region 43, although a few organic fibers 1 are observed in some places, fiber bundles 47 in which a plurality of organic fibers 1 are entangled are not observed. In this embodiment, the first region 42 and the second region 43 have a sea-island structure, and the second region 43, which corresponds to the island portion, is formed so as to be surrounded by the first region 42, which corresponds to the sea portion.

[0164] In the thermal insulation material 110, fiber bundles 47 formed by intertwining organic fibers 1 are present on the surface of the thermal insulation material 110 in a streak-like manner, thereby improving the strength of the thermal insulation material 110. Furthermore, the entire surface is not covered with fiber bundles 47, and there are first regions 42 where fiber bundles 47 are present and second regions where fiber bundles 47 are not present, thereby improving the flexibility of the thermal insulation material 110. Furthermore, because the fiber bundles 47 are present on the surface of the thermal insulation material 110, even if the thermal insulation material 110 is subjected to impact or pressure, the fiber bundles 47 can absorb and mitigate the impact or pressure. Therefore, shedding (powdering) of the inorganic particles 4 can be suppressed, and a decrease in the thermal insulation performance of the thermal insulation material 110 can be prevented.

[0165] In the heat insulating material 110, the organic fibers 1 and the fiber bundles 47 formed by entanglement of the organic fibers 1 are present not only on the surface of the heat insulating material 110 but also inside the heat insulating material 110. This makes it possible to obtain even greater strength.

[0166] It is preferable that the length of the fiber bundles 47 formed to extend on the surface of the thermal insulation material 110 be relatively long. An example of a method for specifying the length of the fiber bundles 47 will be described with reference to FIG. 25 . As shown in FIG. 25 , rectangular imaginary frames 21 are placed along the fiber bundles 47 extending in stripes on the surface of the thermal insulation material 110. In this embodiment, the size of the imaginary frames 21 is 5 mm square, and these imaginary frames 21 are placed so as to be continuous with each other. In this case, if there are fiber bundles 47 that penetrate at least three continuous imaginary frames 21, it can be determined that the fiber bundles 47 have a sufficient effect of improving the strength of the thermal insulation material 110.

[0167] It is also possible to simply measure the length of the fiber bundles 47 extending in a stripe shape. For example, a method can be used in which a string or the like is placed on the surface of the thermal insulation material 110 along the fiber bundles 47, and then the length of the string is measured. When the length of continuous fiber bundles 47 is measured, if there are fiber bundles 47 with a length of 20 mm or more, the effect of improving the strength of the thermal insulation material 110 can be sufficiently obtained.

[0168] Furthermore, as shown in FIG. 26, if the fiber bundles 47 are connected in a mesh pattern on the surface of the heat insulating material 110, the sheet strength can be further improved.

[0169] While structural examples S1 to S7 of the insulating material have been described above, the structure of the insulating material is not limited thereto, and insulating materials having various structures can be used. Specifically, the insulating materials of structural examples S1 to S7 contain inorganic particles and organic fibers, and have excellent insulating properties as well as various properties such as suppressing powder shedding, further improving strength, and maintaining shape. Therefore, as shown in Figures 1 to 6, a heat-transfer-suppressing sheet formed by combining and bonding the insulating materials 9, 10, 40, 60, 70, 80, 90, and 110 can achieve excellent insulating properties and the various effects described above. However, in the present invention, the insulating material does not necessarily need to contain organic fibers. Even a heat-transfer-suppressing sheet having an insulating material that does not contain organic fibers can achieve the effect of the present invention, which increases the design freedom regarding size and insulating properties.

[0170] As described above, the heat insulating material contains inorganic particles, and as other components, for example, at least one selected from organic fibers, inorganic fibers, and organic particles. Each material will be described with reference to Figures 9 to 25.

[0171] <Inorganic Particles> As the inorganic particles 4, a single inorganic particle may be used, or two or more types of inorganic particles may be used in combination. From the viewpoint of the heat transfer suppression effect, it is preferable to use particles made of at least one inorganic material selected from oxide particles, carbide particles, nitride particles, and inorganic hydrate particles, and it is more preferable to use oxide particles. Furthermore, the shape of the inorganic particles 4 is not particularly limited, but it is preferable to include at least one type selected from nanoparticles, hollow particles, and porous particles. Specifically, it is also possible to use inorganic balloons such as silica nanoparticles, metal oxide particles, microporous particles, and hollow silica particles, particles made of a thermally expandable inorganic material, particles made of a hydrous porous body, and the like.

[0172] When the average secondary particle diameter of the inorganic particles is 0.01 μm or more, they are easily available and the increase in production costs can be suppressed. When the average secondary particle diameter is 200 μm or less, the desired heat insulating effect can be obtained. Therefore, the average secondary particle diameter of the inorganic particles is preferably 0.01 μm or more and 200 μm or less, and more preferably 0.05 μm or more and 100 μm or less.

[0173] In addition, by using two or more inorganic particles 4 with different heat transfer suppression effects in combination, it is possible to cool a heat generating body in multiple stages, and the heat absorption effect can be exerted over a wider temperature range. Specifically, it is preferable to use a mixture of large-diameter particles and small-diameter particles. For example, when nanoparticles are used as one of the inorganic particles, it is preferable to include inorganic particles made of a metal oxide as the other inorganic particle. Hereinafter, the inorganic particles will be described in more detail, with the small-diameter inorganic particles referred to as the first inorganic particles and the large-diameter inorganic particles referred to as the second inorganic particles.

[0174] <First Inorganic Particles> (Oxide Particles) Oxide particles have a high refractive index and a strong effect of diffusely reflecting light. Therefore, when oxide particles are used as the first inorganic particles, radiant heat transfer can be suppressed, particularly in high-temperature regions such as abnormal heat generation. As the oxide particles, at least one type of particle selected from silica, titania, zirconia, zircon, barium titanate, zinc oxide, and alumina can be used. That is, among the above oxide particles that can be used as inorganic particles, only one type may be used, or two or more types of oxide particles may be used. In particular, silica is a component with high heat insulating properties, and titania is a component with a higher refractive index than other metal oxides, and is highly effective in diffusely reflecting light and blocking radiant heat in high-temperature regions of 500°C or higher. Therefore, it is most preferable to use silica and titania as the oxide particles.

[0175] (Average primary particle diameter of oxide particles: 0.001 μm or more and 50 μm or less) The particle diameter of the oxide particles can affect the effect of reflecting radiant heat, so limiting the average primary particle diameter to a predetermined range can achieve even higher thermal insulation. That is, when the average primary particle diameter of the oxide particles is 0.001 μm or more, the particles are sufficiently larger than the wavelength of light that contributes to heating and efficiently diffusely reflect light, thereby suppressing radiant heat transfer within the thermal insulation material in high-temperature regions of 500°C or more, thereby further improving thermal insulation. On the other hand, when the average primary particle diameter of the oxide particles is 50 μm or less, the number and number of contact points between particles do not increase even when compressed, making it difficult to form a path for conductive heat transfer, thereby reducing the impact on thermal insulation, particularly in normal temperature ranges where conductive heat transfer is dominant.

[0176] In the present invention, the average primary particle size can be determined by observing particles under a microscope, comparing with a standard scale, and taking the average of any 10 particles.

[0177] (Nanoparticles) In the present invention, nanoparticles refer to particles on the nanometer order that are spherical or nearly spherical and have an average primary particle diameter of less than 1 μm. Nanoparticles have a low density, which suppresses conductive heat transfer. Using nanoparticles as the first inorganic particles further refines the three-dimensionally connected pores 7, thereby achieving excellent thermal insulation that suppresses convective heat transfer. Therefore, nanoparticles are preferred because they can suppress heat conduction between adjacent nanoparticles during normal battery operation at room temperature. Furthermore, using nanoparticles with a small average primary particle diameter as oxide particles can suppress an increase in conductive heat transfer through the insulating material, even when the insulating material is compressed due to expansion associated with thermal runaway in the battery cell, increasing its internal density. This is thought to be because nanoparticles are prone to forming small voids between particles due to electrostatic repulsion, and their low bulk density allows the particles to be packed together to provide cushioning.

[0178] In the present invention, when nanoparticles are used as the first inorganic particles, there are no particular limitations on the material as long as they comply with the definition of nanoparticles. For example, silica nanoparticles are a material with high heat insulating properties, and the contact points between particles are small, so the amount of heat conducted by silica nanoparticles is smaller than when silica particles with a large particle diameter are used. Furthermore, commonly available silica nanoparticles have a bulk density of 0.1 (g / cm ３ ), for example, even if the battery cells arranged on both sides of the insulating material thermally expand and a large compressive stress is applied to the insulating material, the size (area) and number of contact points between the silica nanoparticles do not increase significantly, and the insulating properties can be maintained. Therefore, it is preferable to use silica nanoparticles as the nanoparticles. Examples of silica nanoparticles include wet silica, dry silica, and aerogel, but silica nanoparticles that are particularly suitable for this embodiment will be described below.

[0179] Generally, wet silica particles are aggregated, whereas dry silica particles can be dispersed. Because conductive heat transfer is dominant in the temperature range below 300°C, dry silica, which allows particles to be dispersed, can achieve superior insulating performance compared to wet silica. While the insulating materials shown in the structural examples S1 to S7 above are examples of insulating materials manufactured by a dry process, insulating materials may also be manufactured by a wet process. However, to further improve insulating properties, it is preferable to use a manufacturing method in which a mixture containing the materials is processed into a sheet by a dry process. Therefore, it is preferable to use dry silica, silica aerogel, or the like, which has low thermal conductivity, as the inorganic particles.

[0180] (Average primary particle diameter of nanoparticles: 1 nm or more and 100 nm or less) Limiting the average primary particle diameter of nanoparticles to a predetermined range can achieve even higher thermal insulation. That is, when the average primary particle diameter of nanoparticles is 1 nm or more and 100 nm or less, convective heat transfer and conductive heat transfer within the thermal insulation material can be suppressed, particularly in the temperature range below 500°C, thereby further improving thermal insulation. Furthermore, even when compressive stress is applied, the voids remaining between the nanoparticles and the contact points between many particles suppress conductive heat transfer, thereby maintaining the thermal insulation properties of the thermal insulation material. The average primary particle diameter 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 diameter of the nanoparticles is more preferably 50 nm or less, and even more preferably 10 nm or less.

[0181] (Inorganic hydrate particles) When inorganic hydrate particles receive heat from a heating element and reach a temperature above the thermal decomposition initiation temperature, they undergo thermal decomposition, releasing their own water of crystallization to lower the temperature of the heating element and its surroundings, thereby exhibiting the so-called "endothermic effect." After releasing the water of crystallization, they become porous, and exhibit heat insulating properties due to the countless air holes. 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 ), gallium hydroxide (Ga(OH) ３ ) etc.

[0182] For example, aluminum hydroxide contains about 35% water of crystallization, and as shown in the following formula, it thermally decomposes, releasing the water of crystallization and exhibiting an endothermic effect. After releasing the water of crystallization, it becomes a porous alumina (Al ２ O ３ ) and functions as a heat insulating material. 2Al(OH) ３ →Al ２ O ３ +3H ２ O

[0183] The heat transfer-suppressing sheet 50 according to this embodiment is preferably interposed between battery cells, for example. In a battery cell that has experienced thermal runaway, the temperature rises sharply to over 200°C and continues to rise to around 700°C. Therefore, the inorganic particles are preferably made of inorganic hydrates whose thermal decomposition onset temperature is 200°C or higher. The thermal decomposition onset temperatures of the inorganic hydrates listed above are approximately 200°C for aluminum hydroxide, approximately 330°C for magnesium hydroxide, approximately 580°C for calcium hydroxide, approximately 200°C for zinc hydroxide, approximately 350°C for iron hydroxide, approximately 300°C for manganese hydroxide, approximately 300°C for zirconium hydroxide, and approximately 300°C for gallium hydroxide. These inorganic hydrates are all preferred because they substantially overlap the temperature range of the rapid temperature rise in a battery cell that has experienced thermal runaway and can efficiently suppress temperature rise.

[0184] (Average secondary particle diameter of inorganic hydrate particles: 0.01 μm or more and 200 μm or less) Furthermore, when inorganic hydrate particles are used as the first inorganic particles, if the average particle diameter is too large, it takes a certain amount of time for the first inorganic particles (inorganic hydrate) near the center of the heat insulating material to reach their thermal decomposition temperature, and the first inorganic particles near the center of the sheet may not be completely thermally decomposed. For this reason, the average secondary particle 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.

[0185] (Particles Made of Thermally Expandable Inorganic Material) Examples of thermally expandable inorganic materials include vermiculite, bentonite, mica, and perlite.

[0186] (Particles Made of Hydrous Porous Material) Specific examples of hydrous porous materials include zeolite, kaolinite, montmorillonite, acid clay, diatomaceous earth, wet silica, dry silica, aerogel, mica, and vermiculite.

[0187] (Inorganic Balloons) The heat insulating material used in the present invention may contain inorganic balloons as the first inorganic particles. When inorganic balloons are contained, convective heat transfer or conductive heat transfer within the heat insulating material can be suppressed in a temperature range of less than 500°C, and the heat insulating properties of the heat insulating material can be further improved. As the inorganic balloons, at least one selected from shirasu balloons, silica balloons, fly ash balloons, barite balloons, and glass balloons can be used.

[0188] (Content of inorganic balloons: 60 mass % or less based on the total mass of the heat insulating material) The content of inorganic balloons is preferably 60 mass % or less based on the total mass of the heat insulating material.

[0189] (Average Particle Diameter of Inorganic Balloons: 1 μm or More and 100 μm or Less) The average particle diameter of the inorganic balloons is preferably 1 μm or more and 100 μm or less.

[0190] <Second inorganic particles> When two types of inorganic particles are contained in the heat insulating material, the second inorganic particles are not particularly limited as long as they are different from the first inorganic particles in terms of material, particle size, etc. Examples of the second inorganic particles that can be used include oxide particles, carbide particles, nitride particles, inorganic hydrate particles, silica nanoparticles, metal oxide particles, inorganic balloons such as microporous particles and hollow silica particles, particles made of a thermally expandable inorganic material, and particles made of a hydrous porous body, the details of which are as described above.

[0191] Nanoparticles have extremely low conductive heat transfer and can maintain excellent heat insulation even when compressive stress is applied to the insulating material. Metal oxide particles such as titania are highly effective at blocking radiant heat. Furthermore, when large-diameter inorganic particles and small-diameter inorganic particles are used, the small-diameter inorganic particles penetrate into the gaps between the large-diameter inorganic particles, resulting in a denser structure and improved heat transfer suppression. Therefore, when nanoparticles are used as the first inorganic particles, it is preferable to further include second inorganic particles made of a metal oxide larger in diameter than the first inorganic particles in the insulating material. Examples of metal oxides include silicon oxide, titanium oxide, aluminum oxide, barium titanate, zinc oxide, zirconium oxide, and the like. Titanium oxide (titania), in particular, has a higher refractive index than other metal oxides and is highly effective at scattering light and blocking radiant heat in high-temperature regions above 500°C. Therefore, titania is the most preferable.

[0192] When at least one type of particles selected from dry silica particles and silica aerogel is used as the first inorganic particles and at least one type of particles selected from titania, zircon, zirconia, silicon carbide, zinc oxide, and alumina is used as the second inorganic particles, in order to obtain excellent heat insulating performance within a temperature range of 300° C. or less, the content of the first 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, based on the total mass of the inorganic particles. Furthermore, the content of the first 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, based on the total mass of the inorganic particles.

[0193] On the other hand, in order to obtain excellent heat insulating performance in a temperature range exceeding 300° C., the content of the second inorganic particles is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 20% by mass or more, based on the total mass of the inorganic particles, and is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less, based on the total mass of the inorganic particles.

[0194] (Average primary particle diameter of second inorganic particles) When second inorganic particles made of a metal oxide are contained in a thermal insulating material, if the average primary particle diameter of the second inorganic particles is 1 μm or more and 50 μm or less, radiation heat transfer can be efficiently suppressed in a high temperature range of 500° C. or more. The average primary particle diameter of the second inorganic particles is more preferably 5 μm or more and 30 μm or less, and most preferably 10 μm or less.

[0195] (Inorganic Particle Content) In this embodiment, if the total content of inorganic particles 4 in the thermal insulation material is appropriately controlled, the thermal insulation properties of the thermal insulation material can be sufficiently ensured. The total content of inorganic particles 4 is preferably 60 mass% or more, and more preferably 70 mass% or more, relative to the total mass of the thermal insulation material. Furthermore, if the total content of inorganic particles 4 is too high, the content of organic fibers will relatively decrease. Therefore, in order to sufficiently obtain the skeleton reinforcing effect and the inorganic particle retention effect, the total content of inorganic particles 4 is preferably 95 mass% or less, and more preferably 90 mass% or less, relative to the total mass of the thermal insulation material.

[0196] The content of the inorganic particles 4 in the heat insulating material can be calculated, for example, by heating the heat insulating material at 800° C., decomposing the organic components, and then measuring the mass of the remaining portion.

[0197] <Organic Fiber> The organic fiber 1 provides flexibility to the thermal insulation material, and by welding the inorganic particles 4 and other organic fibers 1 to its surface, it has the effect of maintaining the strength and shape of the sheet. While single-component organic fibers can be used as the organic fiber 1 material in the thermal insulation material, it is preferable to use a binder fiber with a core-sheath structure. The binder fiber with a core-sheath structure has a core extending in the longitudinal direction of the fiber and a sheath formed to cover the outer surface of the core. The core is made of a first organic material, and the sheath is made of a second organic material, with the melting point of the first organic material being higher than that of the second organic material. When the binder fiber with a core-sheath structure is used as a material, the core corresponds to the organic fiber 1 in the thermal insulation material. Furthermore, during the manufacturing process of the thermal insulation material, the second organic material constituting the sheath melts and then solidifies again, so that the sheath becomes the welded portion 5 in the thermal insulation material.

[0198] (Organic Fiber Content) In this embodiment, if the content of organic fiber 1 in the thermal insulation material is appropriately controlled, a sufficient skeleton reinforcing effect can be obtained. The content of organic fiber 1 is preferably 2 mass% or more, and more preferably 4 mass% or more, relative to the total mass of the thermal insulation material. Furthermore, if the content of organic fiber 1 is too high, the content of inorganic particles 4 will relatively decrease. Therefore, in order to obtain the desired thermal insulation performance, the content of organic fiber is preferably 10 mass% or less, and more preferably 8 mass% or less, relative to the total mass of the thermal insulation material.

[0199] (Fiber length of organic fibers) The fiber length of the organic fibers 1 is not particularly limited, but from the viewpoint of ensuring moldability and processability, the average fiber length of the organic fibers is preferably 10 mm or less. On the other hand, from the viewpoint of making the organic fibers 1 function as a skeleton and ensuring the compressive strength of the thermal insulating material, the average fiber length of the organic fibers 1 is preferably 0.5 mm or more.

[0200] (Binder Fiber) When a binder fiber having a core-sheath structure is used as the material for the organic fiber 1, the melting point of the first organic material constituting the core, i.e., the organic fiber 1, is not particularly limited as long as it is higher than the melting point of the second organic material constituting the sheath present on the outer surface of the organic fiber 1. Binder fibers 3 having such a core-sheath structure are generally commercially available, and the materials constituting the core and sheath may be the same or different. Examples of binder fibers in which the core (first organic material) and sheath (second organic material) are made of the same material but have different melting points include those in which the core and sheath are made of polyethylene terephthalate, polypropylene, or nylon. Examples of binder fibers in which the core and sheath are made of different materials include those in which the core is made of polyethylene terephthalate and the sheath is made of polyethylene, and those in which the core is made of polypropylene and the sheath is made of polyethylene.

[0201] The melting point of the second organic material is preferably 90° C. or higher, and more preferably 100° C. or higher. The melting point of the second organic material is preferably 150° C. or lower, and more preferably 130° C. or lower.

[0202] If the melting point of the first organic material constituting the core is sufficiently higher than that of the second organic material constituting the shell, the heating temperature setting margin in the heating step can be expanded, making it easier to set the temperature to obtain a desired structure. For example, the melting point of the first organic material is preferably 60°C or more higher than that of the second organic material, more preferably 70°C or more higher, and even more preferably 80°C or more higher.

[0203] When a core-sheath binder fiber is used as a material for the insulating material, the sheath can be melted while leaving the core intact when the material mixture is heated during the manufacturing process. After cooling, the outer surface of the core (organic fiber 1) is coated with a second organic material containing inorganic particles 4, thereby holding the inorganic particles 4 in place. The organic fiber 1 with the inorganic particles 4 fused to it appears to have a thicker fiber diameter, resulting in a higher strength than the organic fiber 1 alone. Furthermore, because the binder fibers are present in an irregular orientation in the mixture, the organic fibers 1 are fused to each other in areas where the binder fibers contact each other, forming a three-dimensional skeleton. As a result, the overall shape of the insulating material can be maintained with even greater strength.

[0204] Even when organic fibers without a core-sheath structure are used as binder fibers, it is possible to melt only the surface of the organic fibers while leaving the center of the organic fibers, thereby coating the surface with inorganic particles or fusing the organic fibers together, depending on the temperature setting. However, when manufacturing a heat insulating material, it is common to heat from one or both sides perpendicular to the thickness direction, and because a material with high heat insulating performance is used, strict temperature control is required to raise the temperature to the same level on the surface side and the center side in the thickness direction of the sheet.

[0205] In contrast, if binder fibers with a sheath-core structure in which 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 are used, it is extremely easy to set the temperature to melt the sheath while leaving the core. As a result, the resulting insulating material has an ideal structure in which the organic fibers 1 are fused together on both the surface and center to form a skeleton that maintains the strength of the sheet, and fused portions 5 containing inorganic particles 4 are formed on the surface of the organic fibers 1. Therefore, it is preferable to use binder fibers with the above-mentioned sheath-core structure as a material for insulating materials.

[0206] In this embodiment, the melting point of the second organic material constituting the sheath of the binder fiber 3 refers to the melting temperature at which the second organic material begins to melt and deform. However, softening accompanied by a change in shape is also considered to be a type of melting deformation. The melting point of the binder fiber sheath can be measured, for example, by the following method. The binder fiber to be measured is placed in contact with glass fiber, which has a higher melting point, and 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 binder fiber melts and deforms and the area in contact with the glass fiber is fused, or if the cross-sectional shape of the binder fiber changes, it can be determined that the melting point of the second organic material constituting the sheath is 200°C or lower. In this embodiment, the heating temperature is varied and the fusion state between the binder fiber and the glass fiber or the cross-sectional shape of the binder fiber after cooling is observed using the above method, thereby determining the melting point of the second organic material constituting the sheath.

[0207] (Binder Fiber Content) In this embodiment, when a core-sheath binder fiber 3 is used as a material, if the binder fiber content in the mixture is appropriately controlled, the skeleton of the resulting insulating material can be sufficiently reinforced. The binder fiber 3 content is preferably 5% by mass or more, and more preferably 10% by mass or more, relative to the total mass of the mixture. Furthermore, if the binder fiber 3 content is too high, the content of the inorganic particles 4 will relatively decrease. Therefore, in order to obtain the desired insulating performance, the binder fiber 3 content is preferably 25% by mass or less, and more preferably 20% by mass or less, relative to the total mass of the mixture.

[0208] <Inorganic Fibers> As the inorganic fibers 15, a single inorganic fiber may be used, or two or more types of inorganic fibers may be used in combination. Examples of inorganic fibers include ceramic fibers such as silica fiber, alumina fiber, alumina silicate fiber, zirconia fiber, carbon fiber, soluble fiber, refractory ceramic fiber, aerogel composite, magnesium silicate fiber, alkaline earth silicate fiber, potassium titanate fiber, silicon carbide fiber, and potassium titanate whisker fiber; glass fibers such as glass fiber, glass wool, and slag wool; and mineral fibers other than these fibers, such as rock wool, basalt fiber, wollastonite, and mullite fiber. These inorganic fibers are preferred in terms of heat resistance, strength, and availability. Among the inorganic fibers, silica-alumina fiber, alumina fiber, silica fiber, rock wool, alkaline earth silicate fiber, and glass fiber are particularly preferred from the standpoint of handleability.

[0209] The cross-sectional shape of the inorganic fiber is not particularly limited, and examples thereof include a circular cross section, a flat cross section, a hollow cross section, a polygonal cross section, a core cross section, etc. Among these, modified cross section fibers having a hollow cross section, a flat cross section, or a polygonal cross section are preferably used because they have slightly improved heat insulation properties.

[0210] The preferred lower limit of the average fiber length of the inorganic fibers is 0.1 mm, more preferably 0.5 mm. On the other hand, the preferred upper limit of the average fiber length of the inorganic fibers is 50 mm, more preferably 10 mm. If the average fiber length of the inorganic fibers is less than 0.1 mm, the inorganic fibers are less likely to be entangled with each other, which may reduce the mechanical strength of the insulating material. On the other hand, if the average fiber length exceeds 50 mm, although a reinforcing effect can be obtained, the inorganic fibers may not be able to be tightly entangled with each other, or may be curled up by a single inorganic fiber, which may result in continuous voids being easily generated, which may reduce the insulating properties.

[0211] The preferred lower limit of the average fiber diameter of the inorganic fibers is 1 μm, more preferably 2 μm, and even more preferably 3 μm. On the other hand, the preferred upper limit of the average fiber diameter of the inorganic fibers is 15 μm, and more preferably 10 μm. If the average fiber diameter of the inorganic fibers is less than 1 μm, the mechanical strength of the inorganic fibers themselves may be reduced. Furthermore, from the viewpoint of the effects on human health, the average fiber diameter of the inorganic fibers is preferably 3 μm or more. On the other hand, if the average fiber diameter of the inorganic fibers is greater than 15 μm, solid heat transfer through the inorganic fibers may increase, leading to a decrease in thermal insulation properties, and the moldability and strength of the thermal insulation material may be deteriorated.

[0212] (Inorganic Fiber Content) In the present embodiment, when the heat insulating material contains inorganic fibers, the content of the inorganic fibers is preferably 3 mass % or more and 15 mass % or less with respect to the total mass of the heat insulating material.

[0213] Furthermore, the content of inorganic fibers is more preferably 5% by mass or more and 10% by mass or less of the total mass of the thermal insulating material. By setting the content in this range, the shape retention, compressive force resistance, wind pressure resistance, and inorganic particle retention ability of the inorganic fibers are exhibited in a balanced manner. Furthermore, by appropriately controlling the content of inorganic fibers, the organic fibers 1 and the inorganic fibers are entangled with each other to form a three-dimensional network, which further improves the effect of retaining the inorganic particles 4 and other compounding materials described below.

[0214] <Hot Melt Powder> In this embodiment, in addition to the organic fibers 1 and inorganic particles 4, the insulating material may contain hot melt powder as a binder material. The hot melt powder is a powder that contains, for example, a third organic material different from the first organic material and the second organic material, and has the property of melting when heated. When the hot melt powder is added to a mixture used to manufacture the insulating material and heated, the hot melt powder melts, and when cooled, it hardens in a state that includes the surrounding inorganic particles 4. This further prevents the inorganic particles 4 from falling off from the insulating material.

[0215] Hot melt powders with various melting points can be used, but a hot melt powder with an appropriate melting point can be selected taking into account the melting points of the core and sheath of the binder fiber used. Specifically, if the third organic material constituting the hot melt powder has a melting point lower than that of the first organic material constituting the organic fiber, the heating temperature can be set to melt the sheath and hot melt powder while leaving the core. For example, if the melting point of the hot melt powder is lower than that of the sheath, the heating temperature during production can be set between the melting points of the core and the sheath, making it even easier to set the heating temperature.

[0216] Alternatively, the type of hot melt powder used can be selected so that its melting point is between the melting points of the core and sheath. When a hot melt powder with such a melting point is used, when the sheath and hot melt powder melt together and then cool and harden, the organic fiber (core) 1, the molten sheath around it, and the hot melt powder present in the gaps between the inorganic particles 4 harden first. As a result, the position of the organic fiber 1 can be fixed, and then the molten sheath is fused to the organic fiber, facilitating the formation of a three-dimensional skeleton. This further improves the strength of the entire sheet.

[0217] If the melting point of the third organic material constituting the hot melt powder is sufficiently lower than that of the first organic material constituting the core, the heating temperature setting margin in the heating step can be expanded, making it easier to set the temperature to obtain the desired structure. For example, the melting point of the first organic material is preferably 60°C or more higher than that of the third organic material, more preferably 70°C or more higher, and even more preferably 80°C or more higher.

[0218] The melting point of the hot melt powder (third organic material) is preferably 80° C. or higher, and more preferably 90° C. or higher. The melting point of the hot melt powder (third organic material) is preferably 180° C. or lower, and more preferably 150° C. or lower. Examples of components constituting the hot melt powder include polyethylene, polyester, polyamide, and ethylene vinyl acetate.

[0219] (Hot-melt powder content) When hot-melt powder is added to the mixture to suppress the shedding of inorganic particles, even a small amount of hot-melt powder can be used to suppress powder shedding. Therefore, the hot-melt powder content is preferably 0.5% by mass or more, more preferably 1% by mass or more, relative to the total mass of the mixture. On the other hand, since increasing the hot-melt powder content relatively reduces the content of inorganic particles 4 and the like, in order to obtain the desired heat insulating performance, the hot-melt powder content is preferably 5% by mass or less, more preferably 4% by mass or less, relative to the total mass of the mixture.

[0220] <Other Compounding Materials> The heat insulating material may further contain, as necessary, a binder, a colorant, etc. All of these are useful for the purposes of reinforcing the heat insulating material, improving its formability, etc., and the total amount of these is preferably 10 mass % or less based on the total mass of the heat insulating material.

[0221] <Method of Manufacturing Insulating Material> The method of manufacturing the insulating material will be described in detail below, particularly using the method of manufacturing the insulating material of structural example S2 as an example. For example, a binder fiber (not shown) having a core-sheath structure, inorganic particles 4, and inorganic fibers 15 are added to a mixer such as a V-type mixer in a predetermined ratio to prepare a mixture. As described above, it is preferable to use a fiber having a core-sheath structure with a core made of a first organic material and a sheath made of a second organic material as the binder fiber. In this case, the melting point of the first organic material is higher than the melting point of the second organic material.

[0222] The resulting mixture is then placed in a mold and pressurized with a press or the like. The resulting molded body is heated to melt the sheath of the binder fiber. The heated molded body is then cooled, and the second organic material constituting the molten sheath and the inorganic particles 4 present around the binder fiber are fused to the core (organic fiber 1), and are also fused to each other in areas where the binder fibers were in contact with each other. This allows for the production of a sheet-shaped insulating material 40.

[0223] The heat insulating material 10 that does not contain the inorganic fibers 15 can also be obtained by the same manufacturing method as the heat insulating material 40, and the use of the inorganic fibers 15 can be selected arbitrarily.

[0224] When the materials for the heat insulating material are mixed and then pressurized and heated, the entangled organic fibers 1 exposed on the surface are heated and formed as a fiber layer 11 on the surface of the heat insulating material 40. The fiber layer 11 thus obtained improves the strength of the heat insulating material 40 and also has the effect of mitigating impacts on the surface of the heat insulating material 40.

[0225] (Heating Conditions) When a binder fiber having a core-sheath structure is used as the material for the thermal insulating material, the heating temperature in the heating step is preferably set to a temperature higher than the melting point of the second organic material constituting the sheath and lower than the melting point of the first organic material constituting the core. By setting such a heating temperature, as described above, the strength of the sheet can be ensured by the core on both the surface side and the center side of the sheet, and the inorganic particles 4 can be held in place by the fused parts 5.

[0226] Specifically, the heating temperature in the heating step is preferably set to be 10° C. or more higher, more preferably 20° C. or more higher, than the melting point of the second organic material constituting the sheath. On the other hand, the heating temperature is preferably set to be 10° C. or more lower, more preferably 20° C. or more lower, than the melting point of the first organic material constituting the core.

[0227] The heating time is not particularly limited, but is preferably set to a time sufficient to melt the sheath, for example, from 3 minutes to 15 minutes.

[0228] When the insulating material contains a hot melt powder, the heating temperature in the heating step is preferably set to be at least 10°C higher, more preferably 20°C higher, than the higher of the melting point of the second organic material constituting the sheath and the melting point of the third organic material constituting the hot melt powder. On the other hand, the heating temperature is preferably set to be at least 10°C lower, more preferably 20°C lower, than the melting point of the first organic material constituting the core. Setting the heating temperature at such a temperature allows a strong skeleton to be formed, further improving the strength of the sheet and preventing the inorganic particles 4 from falling off due to the welded portions 5, etc.

[0229] As described above, the insulating material may be manufactured by either a dry method or a wet method, but it is preferable to use the dry method. When using the dry method, inorganic particles 4 suitable for the dry method are used, and a solvent such as water, which is required when forming by a wet method, is not added to the mixture. However, to prevent powder such as inorganic particles 4 from flying around during the manufacturing of the insulating material and making it difficult to handle the raw materials, a small amount of solvent such as water can be added within the range required for the dry method. For example, adding a small amount of solvent such as water to the mixture can suppress the scattering of inorganic particles during manufacturing.

[0230] <Adhesive> In this embodiment, the bonding surfaces 61 of the two insulating materials can be bonded using an adhesive or the like. The adhesive for bonding the bonding surfaces 61 is not particularly limited, and a commonly used adhesive can be used, but a flame-retardant adhesive is preferably used. Specifically, the flame-retardant inorganic adhesive can be a heat-curing, heat-resistant inorganic adhesive whose main components are a fire-resistant ceramic such as alumina and an inorganic polymer. The flame-retardant organic adhesive can be an adhesive containing a halogen-based, phosphorus-based, silicone-based, or nitrogen-based flame-retardant material. It is also effective to use the flame-retardant inorganic adhesive in combination with a flame-retardant organic adhesive. By using an adhesive, the adhesive can penetrate into the pores in the bonding surfaces 61 of the two insulating materials, thereby more firmly bonding them together.

[0231] <Thickness of Heat-Transfer-Suppressing Sheet> The thickness of the heat-transfer-suppressing sheet according to this embodiment is generally the same as that of the heat insulating material and is not particularly limited, but is preferably 0.05 mm or more and 10 mm or less. A thickness of 0.05 mm or more ensures sufficient compressive strength. On the other hand, a thickness of 10 mm or less ensures good heat insulating properties of the heat-transfer-suppressing sheet.

[0232] [Battery Assembly] An example of a battery assembly using the heat-transfer-suppressing sheet 50 according to each embodiment of the present invention is as shown in FIG. 3 above. The configuration and effects of the battery assembly will now be described in detail with reference to FIG. 3. As described above, the heat-transfer-suppressing sheet 50 shown in FIG. 3 can be replaced with heat-transfer-suppressing sheets 52, 53, and 54 having other structures, as well as with heat-transfer-suppressing sheets having other structures within the scope of the present invention. Furthermore, in addition to the heat-insulating materials having the various structures described above, the heat-insulating material 10 can also be replaced with other heat-insulating materials within the scope of the present invention.

[0233] 3, the battery pack 100 includes a plurality of battery cells 20a, 20b, and 20c and a heat-transfer-reducing sheet 50 according to the present embodiment, with the plurality of battery cells connected in series or parallel. For example, the heat-transfer-reducing sheet 50 according to the present embodiment is interposed between the battery cells 20a and 20b, and between the battery cells 20b and 20c. The battery cells 20a, 20b, and 20c and the heat-transfer-reducing sheet 50 are housed in a battery case 30. The heat-transfer-reducing sheet 50 is as described above.

[0234] In the battery pack 100 configured in this manner, because the heat-transfer-suppressing sheet has high thermal insulation properties, even if a certain battery cell 20a becomes hot, the heat-transfer-suppressing sheet 50, which has a heat-transfer-suppressing effect, is present between the battery cell 20a and the battery cell 20b, thereby suppressing the transfer of heat to the battery cell 20b and preventing thermal runaway of the battery cells. Furthermore, because the battery pack according to this embodiment has a heat-transfer-suppressing sheet in which multiple thermal insulators are bonded together and in which a decrease in thermal insulation properties is suppressed at the bonded surfaces, it can flexibly accommodate various sizes of battery cells 20a, 20b, and 20c and can provide desired thermal insulation in desired areas.

[0235] The battery pack 100 of this embodiment is not limited to the battery pack illustrated in Fig. 3. For example, the heat transfer-suppressing sheet 50 may be disposed not only between the battery cells 20a and 20b and between the battery cells 20b and 20c, but also between the battery cells 20a, 20b, and 20c and the battery case 30, or may be attached to the inner surface of the battery case 30.

[0236] In the battery pack 100 configured in this manner, if a battery cell ignites, the flame can be prevented from spreading outside the battery case 30. For example, the battery pack 100 according to this embodiment may be used in an electric vehicle (EV) or the like and placed under the floor of a passenger compartment. In this case, even if a battery cell ignites, the safety of the passengers can be ensured. Furthermore, the heat-transfer-reducing sheet 50 can be placed not only between the battery cells but also between the battery cells 20a, 20b, and 20c and the battery case 30. The size and heat-insulating performance of the heat-transfer-reducing sheet according to this embodiment can be freely designed and easily manufactured, so it can be suitably used in places other than between the battery cells.

[0237] In the battery pack of this embodiment, the heat-transfer-suppressing sheet 50 disposed between the battery cells 20a, 20b, and 20c and the battery case 30 may be in contact with the battery cells or may have a gap therebetween. If the formation of a gap is undesirable, a thicker insulating material may be combined in areas where a gap may be formed than in other areas. In particular, when the battery cells 20a, 20b, and 20c are large, there is a variation in the contact between the battery cells 20a, 20b, and 20c and the heat-transfer-suppressing sheet 50 in some areas and not in other areas. Therefore, according to this embodiment, not only the insulating performance of the insulating material but also various characteristics such as thickness and elasticity can be combined to form a single heat-transfer-suppressing sheet that meets various requirements, thereby obtaining a battery pack with even better characteristics.

[0238] As described above, the heat transfer-suppressing sheet according to this embodiment can be manufactured into various shapes depending on the manufacturing method. Therefore, it can be adapted to any shape without being affected by the shapes of the battery cells 20a, 20b, 20c and the battery case 30. Specifically, it can be applied to cylindrical batteries, flat batteries, etc. in addition to prismatic batteries.

[0239] Although various embodiments have been described above with reference to the drawings, it goes without saying that the present invention is not limited to such examples. It is clear that a person skilled in the art can conceive of various modifications or alterations within the scope of the claims, and it is understood that these also naturally fall within the technical scope of the present invention. Furthermore, the components of the above-described embodiments may be combined in any manner without departing from the spirit of the invention.

[0240] This application is based on a Japanese patent application (Patent Application No. 2024-018666) filed on February 9, 2024, the contents of which are incorporated herein by reference.

[0241] REFERENCE SIGNS LIST 1 organic fiber 3 binder fiber 4 inorganic particle 5 welded portion 9, 10, 40, 60, 70, 80, 90, 110 heat insulating material 9e second connecting surface 10c connecting surface 10e first connecting surface 11 fiber layer 14 matrix 15 inorganic fiber 16 fiber portion 20a, 20b, 20c battery cell 30 battery case 32 base portion 33 support portion 42 first region 43 second region 50, 52, 53, 54 heat transfer suppressing sheet 61 connecting surface 63a first end portion 63b second end portion 65 convex portion 66 concave portion 100 battery pack

Claims

1. A heat-transfer-suppressing sheet formed by bonding together a plurality of insulating materials containing inorganic particles, wherein the insulating materials have a pair of main surfaces and a connecting surface connecting the pair of main surfaces, the connecting surfaces of the plurality of insulating materials are arranged opposite each other to form a connecting surface connecting the insulating materials, and in a cross-sectional view perpendicular to the pair of main surfaces and parallel to the direction in which the insulating materials are adjacent to each other, the length of the connecting surface is longer than the thickness of the region of the insulating materials where the connecting surface is formed.

2. The heat transfer suppressing sheet according to claim 1, wherein, in the cross-sectional view, at least a portion of the joining surface extends in a direction different from the thickness direction of the heat insulating material.

3. The heat transfer suppression sheet according to claim 2, wherein, in the cross-sectional view, at least a portion of the bonding surface has an area that forms an angle of 20° or more and 160° or less with respect to the thickness direction of the heat insulating material.

4. A heat transfer suppressing sheet as described in claim 1, characterized in that when the end of the joining surface on one main surface side is defined as a first end and the end on the other main surface side is defined as a second end, in the cross-sectional view, the first end is located at a position shifted in a direction parallel to the main surface relative to the second end.

5. The heat transfer suppressing sheet of claim 1, characterized in that, when the end of the joining surface on one main surface side is defined as a first end and the end of the joining surface on the other main surface side is defined as a second end, in the cross-sectional view, the first end and the second end are located at symmetrical positions in the thickness direction of the insulating material, and of the adjacent insulating materials, the connecting surface of one insulating material has a convex portion and the connecting surface of the other insulating material has a concave portion shaped to fit into the convex portion, and the adjacent insulating materials are joined by fitting the convex portion and the concave portion together.

6. A heat transfer suppression sheet as described in claim 1, characterized in that when the density of the insulating material in the region including the bonding surface in the thickness direction of the insulating material is defined as M1 and the density of the insulating material in the region not including the bonding surface in the thickness direction of the insulating material is defined as M2, the ratio of density M1 to density M2 (M1 / M2) is 1.2 or more.

7. A heat transfer-suppressing sheet formed by bonding together a plurality of insulating materials containing inorganic particles, wherein the insulating materials have a pair of main surfaces and a connecting surface connecting the pair of main surfaces, the connecting surfaces of the plurality of insulating materials are arranged opposite each other to form a bonding surface connecting the insulating materials, and in a cross-sectional view perpendicular to the pair of main surfaces and parallel to the direction in which the insulating materials adjoin, when an end of the bonding surface on one main surface side is defined as a first end and an end of the bonding surface on the other main surface side is defined as a second end, the bonding surface has a heat transfer-preventing portion between the first end and the second end, and the heat transfer-preventing portion is located at a position shifted from at least one of the first end and the second end in a direction parallel to the main surfaces.

8. The heat transfer suppression sheet according to claim 1, wherein the heat insulating material comprises organic fibers.

9. The heat transfer suppressing sheet according to claim 1, wherein the connecting surfaces of adjacent pieces of the heat insulating material that make up the joining surface are bonded together in at least a partial area of the joining surface.

10. The heat transfer suppression sheet according to claim 1, characterized in that the connecting surfaces of adjacent pieces of the heat insulating material that make up the connecting surface are heat-sealed together in at least a partial area of the connecting surface.

11. A method for producing a heat transfer-suppressing sheet as defined in any one of claims 1 to 8, comprising: a first processing step of processing an end face of one of two insulating materials to be joined together so that at least a partial area of the end face of the one of the insulating materials extends in a direction different from the thickness direction of the insulating material, thereby creating a first connecting surface; a second processing step of processing an end face of the other of the two insulating materials to be joined together so that the end face of the other of the two insulating materials to be joined together has a shape that conforms to the first connecting surface of the one of the insulating materials, thereby creating a second connecting surface; and a connecting surface forming step of arranging the one of the insulating materials and the other of the insulating materials so that the first connecting surface and the second connecting surface face each other, and forming the connecting surface where the first connecting surface and the second connecting surface are joined.

12. The method for producing a heat transfer-suppressing sheet according to claim 11, wherein in the bonding surface forming step, at least a portion of the bonding surface is bonded with an adhesive.

13. A method for manufacturing a heat transfer suppressing sheet as described in claim 11, characterized in that in the joining surface forming step, the first joining surface and the second joining surface are heated while being pressurized in a direction to bring them closer to each other, and at least a portion of the space between the first joining surface and the second joining surface is fused by thermal fusion.

14. A method for producing a heat transfer suppression sheet as defined in any one of claims 1 to 8, comprising: an arrangement step of arranging two sheets of heat insulating material to be joined together so that a portion of the main surface of one of the sheets of heat insulating material overlaps a portion of the main surface of the other sheet of heat insulating material; and a joining surface forming step of applying pressure to the overlapping area of the two sheets of heat insulating material in the thickness direction of the two sheets of heat insulating material to form the joining surface where a portion of the main surface of one of the sheets of heat insulating material is joined to a portion of the main surface of the other sheet of heat insulating material.

15. The method for producing a heat transfer-suppressing sheet according to claim 14, wherein in the bonding surface forming step, at least a portion of the bonding surface is bonded with an adhesive.

16. A method for manufacturing a heat transfer suppressing sheet as described in claim 14, characterized in that in the joining surface forming process, the area where the two insulating materials overlap is heated while being pressed in the thickness direction of the area, and a portion of the main surface of one insulating material is fused to a portion of the main surface of the other insulating material by thermal fusion.

17. A battery pack comprising a plurality of battery cells and the heat transfer suppression sheet according to any one of claims 1 to 10, the plurality of battery cells being connected in series or parallel.

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