Heat transfer suppression sheet and battery pack

Abstract

To provide a heat transfer suppression sheet that can accurately align the positions of an insulating material and an elastic sheet, suppress the destruction of a battery case and the deterioration of battery performance due to deformation of a battery cell, further suppress the propagation of heat between battery cells in the event of an abnormality, and reduce raw material costs.SOLUTION: A heat transfer suppression sheet 50 includes a thermal insulating material 10 containing inorganic particles, elastic sheets 51a and 51b laminated on a first surface 10a and a second surface 10b perpendicular to the thickness direction of the thermal insulating material 10, and bonding portions 55a and 55b bonding the thermal insulating material 10 and the elastic sheets 51a and 51b together. Opposing regions 45a and 45b where the thermal insulating material 10 and the elastic sheets 51a and 51b face each other include bonding regions 44a and 44b where the bonding portions 55a and 55b are present, and non-bonding regions 41a and 41b where the bonding portions 55a and 55b are not present.SELECTED DRAWING: Figure 1B

Description

[Technical Field]

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

[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] Furthermore, if thermal runaway occurs in a battery cell, gas is generated inside the battery, causing the internal pressure to rise and deforming the battery cell. If this deformation is severe, the case may be destroyed. Such deformation of the battery cells occurs slightly even when the assembled battery cells are subjected to a charge / discharge cycle (i.e., during "normal use"). When the internal pressure of the battery cells repeatedly rises and falls during charging and discharging, the battery cells are repeatedly pressed and released by the case, causing a decrease in battery performance.

[0005] As a countermeasure against the occurrence of thermal runaway as described above, for example, Patent Document 1 proposes a fire spread prevention sheet comprising a rubber sheet made of a rubber-like elastic material, heat insulating sheets laminated on both sides of the rubber sheet and capable of reducing heat transfer between multiple adjacent heat sources, and an adhesive layer interposed between the rubber sheet and the heat insulating sheet and adhering the heat insulating sheet to both sides of the rubber sheet.

[0006] The fire spread prevention sheet described in Patent Document 1 includes a rubber sheet, which provides cushioning and also acts as a protective member to prevent damage to the heat insulating sheet. Patent Document 1 also describes that the adhesive layer contains a specific low thermal conductive filler, which reduces heat transfer between multiple heat sources and improves fire spread prevention performance. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 2023-62546 Summary of the Invention [Problem to be solved by the invention]

[0008] However, the fire prevention sheet disclosed in Patent Document 1 uses an adhesive layer containing a specific low thermal conductivity filler, which increases the raw material cost of the fire prevention sheet and requires a manufacturing process for the adhesive layer, potentially complicating the manufacturing process.

[0009] Furthermore, since the adhesive layer contains a low thermal conductivity filler as described above, it can reduce heat transfer between heat sources, but the effect is not sufficient. For example, because the adhesive layer has lower thermal insulation properties than the insulating material, interposing an adhesive layer between the insulating material and the rubber sheet tends to reduce the thermal insulation properties. Furthermore, during the production of the fire spread prevention sheet, if the adhesive constituting the adhesive layer penetrates into the rubber sheet or insulating sheet having pores, the pores may be blocked by the adhesive, further reducing the thermal insulation properties. Furthermore, if the adhesive layer is flammable, the adhesive layer may ignite when the fire spread prevention sheet is exposed to high temperatures, preventing it from fully fulfilling its role as a fire spread prevention sheet. Furthermore, the presence of an adhesive layer may reduce the compression properties of the fire spread prevention sheet, making it impossible to obtain the desired compression properties and resulting in reduced battery performance.

[0010] On the other hand, if an adhesive layer is not formed in order to prevent a decrease in heat insulation, the heat insulating material and the rubber sheet cannot be accurately aligned.

[0011] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a heat transfer suppression sheet that can accurately align the positions of the insulating material and the elastic sheet, can suppress destruction of the battery case and deterioration of battery performance due to deformation of the battery cells, can further suppress the propagation of heat between each battery cell in the event of an abnormality, and can reduce raw material costs, and an assembled battery that can suppress the propagation of heat between each battery cell while suppressing destruction of the battery case and deterioration of battery performance. [Means for solving the problem]

[0012] The above object of the present invention is achieved by the heat transfer-suppressing sheet having the following configuration [1].

[0013] [1] An insulating material containing inorganic particles; An elastic sheet laminated on at least one of a first surface and a second surface of the heat insulating material that are perpendicular to the thickness direction; a joining portion that joins the heat insulating material and the elastic sheet, A heat transfer suppression sheet, characterized in that the opposing region where the heat insulating material and the elastic sheet face each other has a bonded region where the bonded portion exists and a non-bonded region where the bonded portion does not exist.

[0014] Furthermore, preferred embodiments of the present invention relating to the heat transfer-suppressing sheet relate to the following [2] to

[14] .

[0015] [2] The heat-transfer-suppressing sheet according to [1], wherein the non-bonded region is located in the center of the facing region.

[0016] [3] The heat-transfer-suppressing sheet according to [1] or [2], wherein the joining region is located in the vicinity of an end of the facing region.

[0017] [4] The heat-transfer-suppressing sheet according to any one of [1] to [3], wherein the facing region is a region surrounded by three or more sides, and the joining region is located only in proximity to one of the three or more sides.

[0018] [5] The heat-transfer-suppressing sheet according to [4], wherein the bonding region is formed so as to extend along the one side.

[0019] [6] The heat-transfer-suppressing sheet according to any one of [1] to [3], wherein the facing region is a rectangular region surrounded by a pair of long sides and a pair of short sides perpendicular to the long sides, and the joining region is located only in proximity to one of the pair of short sides.

[0020] [7] The heat-transfer-suppressing sheet according to [6], wherein the bonding region is formed so as to extend along the one of the short sides.

[0021] [8] The joining region is configured by forming the joining portion only in a part of the facing region, The heat transfer-suppressing sheet according to any one of [1] to [7], characterized in that the non-bonded region extends from the boundary between the bonded region and the non-bonded region to one end of the facing region, and the heat insulating material and the elastic sheet are configured to be separable from each other at the one end of the facing region.

[0022] [9] The heat transfer-suppressing sheet according to [8], wherein the joint is formed at a position close to one end of the opposing region that faces the other end.

[0023]

[10] The heat-transfer-suppressing sheet according to any one of [1] to [9], wherein the joint is formed by an adhesive that bonds the heat insulating material and the elastic sheet together.

[0024]

[11] The heat-transfer-suppressing sheet according to any one of [1] to [9], wherein the joint is formed by a joint member that joins the heat insulating material and the elastic sheet.

[0025]

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

[11] , wherein the elastic sheet contains at least one material selected from synthetic rubber, natural rubber, and thermoplastic elastomer.

[0026]

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

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

[0027]

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

[13] , further comprising a film covering the outer peripheral surface of a laminate including the heat insulating material and the elastic sheet.

[0028] The above object of the present invention is also achieved by the following configuration

[15] relating to a battery pack.

[0029]

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

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

[0030] The heat transfer-suppressing sheet of the present invention has an insulating material containing inorganic particles, thereby achieving excellent thermal insulation. Furthermore, because an elastic sheet is laminated on the insulating material, the elastic sheet absorbs deformation of the battery cell, preventing damage to the battery case and deterioration of battery performance. Furthermore, because the opposing regions of the insulating material and the elastic sheet have bonded and non-bonded regions, the presence of the bonded regions allows the two to be accurately aligned, and the presence of the non-bonded regions prevents deterioration of insulating performance and compression characteristics, thereby reducing material costs.

[0031] The battery pack of the present invention has a heat transfer-suppressing sheet that has high thermal insulation properties and can suppress damage to the battery case and deterioration of battery performance, thereby suppressing thermal runaway of the battery cells in the battery pack and the spread of flames outside the battery case. [Brief explanation of the drawings]

[0032] [Figure 1A] FIG. 1A is a top view showing a heat-transfer-suppressing sheet according to a first embodiment of the present invention. [Figure 1B] FIG. 1B is a schematic cross-sectional view taken along line AA in FIG. 1A. [Figure 2] FIG. 2 is a schematic cross-sectional view showing another structural example of the heat-transfer-suppressing sheet according to the first embodiment of the present invention. [Figure 3] FIG. 3 is a schematic diagram showing a battery pack according to an embodiment of the present invention. [Figure 4A] FIG. 4A is a top view showing a heat-transfer-suppressing sheet according to a second embodiment of the present invention. [Figure 4B] FIG. 4B is a schematic cross-sectional view taken along line BB in FIG. 4A. [Figure 5] FIG. 5 is a schematic diagram showing a heat-transfer-suppressing sheet according to a second embodiment of the present invention, in which the heat insulating material and the elastic sheet are configured to be separable from each other in the non-bonded region. [Figure 6] FIG. 6 is a schematic cross-sectional view showing a heat-transfer-suppressing sheet according to a third embodiment of the present invention. [Figure 7]FIG. 7 is a photograph, substituted for a drawing, showing a structural example S1 of a heat insulating material used in a heat-transfer-suppressing sheet according to an embodiment of the present invention. [Figure 8] FIG. 8 is a photograph showing an enlarged view of a part of the heat insulating material shown in FIG. [Figure 9] FIG. 9 is a photograph, substituted for a drawing, showing a structural example S2 of a heat insulating material used in a heat-transfer-suppressing sheet according to an embodiment of the present invention. [Figure 10] FIG. 10 is a schematic diagram showing a structural example S3 of a heat insulating material used in a heat-transfer-suppressing sheet according to an embodiment of the present invention. [Figure 11] FIG. 11 is a schematic diagram showing an enlarged portion of FIG. [Figure 12] FIG. 12 is a photograph showing the heat insulating material shown in FIG. [Figure 13] FIG. 13 is a photograph, substituted for a drawing, showing a structural example S4 of a heat insulating material used in a heat-transfer-suppressing sheet according to an embodiment of the present invention. [Figure 14] FIG. 14 is a photograph showing an enlarged view of the structure of the heat insulating material shown in FIG. [Figure 15] FIG. 15 is a photograph showing a cross section of the heat insulating material shown in FIG. [Figure 16] FIG. 16 is a schematic diagram showing a structural example S5 of a heat insulating material used in a heat-transfer-suppressing sheet according to an embodiment of the present invention. [Figure 17] FIG. 17 is an enlarged schematic view of part A of the heat insulating material shown in FIG. [Figure 18] FIG. 18 is a photograph, substituted for a drawing, showing a structural example S6 of a heat insulating material used in a heat-transfer-suppressing sheet according to an embodiment of the present invention. [Figure 19] FIG. 19 is a photograph showing another area of ​​the heat insulating material shown in FIG. [Figure 20] FIG. 20 is a photograph showing a cross section of the heat insulating material shown in FIGS. [Figure 21] FIG. 21 is a photograph, substituted for a drawing, showing a structural example S7 of a heat insulating material used in a heat-transfer-suppressing sheet according to an embodiment of the present invention. [Figure 22]FIG. 22 is a photograph showing an enlarged view of a part of the heat insulating material shown in FIG. [Figure 23] FIG. 23 is a diagram for explaining an example of a method for defining the length of a fiber bundle, and is a photograph substituting for a drawing showing an enlarged view of part A in FIG. [Figure 24] FIG. 24 is a diagram showing a mesh-like fiber bundle, and is a photograph showing an enlarged view of part A in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0033] The inventors conducted extensive research to solve the above problems and discovered that by joining the insulating material and the elastic sheet only partially, it is possible to further suppress the transfer of heat between battery cells in the event of an abnormality and also reduce raw material costs.

[0034] A heat-transfer-suppressing sheet, a manufacturing method thereof, and a battery pack according to an embodiment of the present invention will be described in detail below. Note that the present invention is not limited to the embodiment described below, and can be implemented with any modifications within the scope of the present invention. First, a heat-transfer-suppressing sheet according to an embodiment of the present invention will be described.

[0035] [Heat transfer suppression sheet] [First embodiment] FIG. 1A is a top view of a heat-transfer-suppressing sheet according to a first embodiment of the present invention, and FIG. 1B is a schematic cross-sectional view taken along line AA in FIG. 1A. As shown in FIGS. 1A and 1B, a heat-transfer-suppressing sheet 50 according to the first embodiment includes a heat-insulating material 10 and elastic sheets 51a and 51b laminated on a first surface 10a and a second surface 10b, respectively, that are perpendicular to the thickness direction of the heat-insulating material 10. That is, in the heat-transfer-suppressing sheet 50 according to the first embodiment, the heat-insulating material 10 is sandwiched between the pair of elastic sheets 51a and 51b. The heat-insulating material 10 contains inorganic particles (not shown). The elastic sheets 51a and 51b are formed by processing an elastic material (described later) into a sheet shape.

[0036] In addition, the heat insulating material 10 and the elastic sheet 51a are joined in multiple regions by joints 55a to prevent misalignment, thereby forming joint regions 44a. However, in this embodiment, in the opposing region 45a where the heat insulating material 10 and the elastic sheet 51a face each other, the heat insulating material 10 and the elastic sheet 51a are not joined to each other except for the joint region 44a, thereby forming non-joined regions 41a. Similarly, the heat insulating material 10 and the elastic sheet 51a are joined in multiple regions by joints 55b to form joint regions 44b. In the opposing region 45b where the heat insulating material 10 and the elastic sheet 51b face each other except for the joint region 44b, the heat insulating material 10 and the elastic sheet 51b are not joined to each other except for the non-joined regions 41b. The materials constituting the heat insulating material 10 and the elastic sheets 51a and 51b will be described in detail later.

[0037] FIG. 2 is a schematic cross-sectional view showing another example of the structure of the heat-transfer-suppressing sheet according to the first embodiment of the present invention. The heat-transfer-suppressing sheet 52 shown in FIG. 2 includes a thermal insulating material 10 and an elastic sheet 51a laminated on a first surface 10a of the thermal insulating material 10, the first surface 10a being perpendicular to the thickness direction. The thermal insulating material 10 and the elastic sheet 51a are bonded together in multiple regions, forming bonded regions 44a. In an opposing region 45a between the thermal insulating material 10 and the elastic sheet 51a, excluding the bonded region 44a, the thermal insulating material 10 and the elastic sheet 51a are not bonded together, forming non-bonded regions 41a. The materials constituting the thermal insulating material 10, the elastic sheet 51a, and the bonded portions 55a are the same as those of the thermal insulating material, the elastic sheets 51a and 51b, and the bonded portions 55a and 55b of the heat-transfer-suppressing sheet 50 shown in FIGS. 1A and 1B.

[0038] In this embodiment, the bonded portions 55a, 55b may be areas that spread over a surface or may be dot-like. When multiple dot-like bonded portions are densely arranged, the bonded regions 44a, 44b may represent an aggregate of multiple dot-like bonded portions. In this embodiment, the heat insulating material 10 and the elastic sheets 51a, 51b are bonded with an adhesive, and the bonded portions 55a, 55b are areas where the adhesive has solidified. However, the bonded portions 55a, 55b do not necessarily have to be made of an adhesive. The structure and materials of the bonded portions 55a, 55b will be described in detail later.

[0039] A specific use of the heat-transfer-suppressing sheet 50 shown in FIGS. 1A and 1B will be 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 where they are connected in series or in 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.

[0040] 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 multiple battery cells 20a, 20b, and 20c. Therefore, for example, if an abnormality occurs in the battery cell 20a and the temperature rises, heat transfer to the battery cell 20b can be sufficiently suppressed. Furthermore, in the first embodiment, elastic sheets 51a and 51b are laminated on the first surface 10a and the second surface 10b of the insulating material 10. The elastic sheets 51 have the effect of suppressing deformation of the battery cells 20a, 20b, and 20c and the effect of absorbing the deformation of the battery cells 20a, 20b, and 20c. In other words, when the battery cells 20a, 20b, and 20c deform during charging / discharging or an abnormality, the elastic sheets 51 flexibly deform in response to the deformation of the battery cells 20a, 20b, and 20c while suppressing the deformation of the battery cells 20a, 20b, and 20c. Therefore, it is possible to prevent unnecessary pressure from being applied to the battery cells 20a, 20b, and 20c.

[0041] Furthermore, because the heat insulating material 10 and the elastic sheets 51a and 51b are joined by joints 55a and 55b, respectively, misalignment between the heat-transfer-suppressing sheet 50 and the elastic sheets can be prevented during transportation or installation in the battery case 30, allowing for accurate alignment of the heat insulating material and the elastic sheets. However, in this embodiment, the joints 55a and 55b are not formed over the entire surfaces of the facing regions 45a and 45b where the heat insulating material 10 and the elastic sheets 51a and 51b face each other. These facing regions 45a and 45b include joining regions 44a and 44b where the joints 55a and 55b are formed, and non-joining regions 41a and 41b where the joints 55a and 55b are not formed. This prevents degradation of the heat insulating performance and compression characteristics due to the presence of the joints 55a and 55b.

[0042] Furthermore, because the joints 55a, 55b are formed only in a portion of the opposing regions 45a, 45b between the thermal insulation material 10 and the elastic sheets 51a, 51b, the amount of adhesive used can be reduced when bonding the thermal insulation material 10 and the elastic sheets 51a, 51b together. Furthermore, the reduction in thermal insulation performance due to the presence of the joints can be suppressed without using an adhesive containing a specific low-thermal-conductivity material. Therefore, when using an adhesive, the manufacturing process for the adhesive can be simplified, the material cost of the heat-transfer-suppressing sheet can be reduced, and the burden on the environment can be reduced.

[0043] In the present invention, the size of the bonded regions 44a, 44b is not particularly limited. It is sufficient that non-bonded regions 41a, 41b exist in at least a portion of the opposing regions 45a, 45b between the thermal insulating material 10 and the elastic sheets 51a, 51b. In the non-bonded regions, the thermal insulating material 10 and the elastic sheets 51a, 51b may be in contact with or spaced apart from each other. To prevent deterioration in thermal insulation performance and compression characteristics, it is preferable that the area of ​​the bonded regions 44a, 44b be small, as long as the thermal insulating material 10 and the elastic sheets 51a, 51b are secured to each other. For example, the area of ​​the bonded regions 44a, 44b is preferably 50% or less, more preferably 30% or less, and even more preferably 20% or less of the area of ​​the opposing regions 45a, 45b between the thermal insulating material 10 and the elastic sheets 51a, 51b.

[0044] Furthermore, in the present invention, the positions of the bonded regions 44a, 44b and the non-bonded regions 41a, 41b are not particularly limited and can be selected at any desired locations. However, the center of a battery cell's main surface is generally the area most likely to deform and become hottest. Therefore, when a heat-transfer-suppressing sheet 50 is interposed between battery cells, it is preferable that no bonded regions 55a, 55b exist in the area of ​​the heat-transfer-suppressing sheet 50 facing the center of the battery cells. In other words, of the facing regions 45a, 45b between the thermal insulator 10 and the elastic sheets 51a, 51b, at least the central region R0 shown in FIG. 1A is preferably the non-bonded region 41a, 41b.

[0045] In this specification, as shown in the first embodiment, when the facing regions 45a, 45b are rectangular, the central region R0 refers to the region including the center X, which is the intersection of one bisector L1 and the other bisector L2 of two pairs of facing sides. Specifically, the region R0 may be set so that the center X is located at the center of the region R0. The area of ​​the region R0 is preferably 10% or more, and more preferably 20% or more, of the area of ​​the entire facing region 45a. If the facing region between the heat insulating material and the elastic sheet is not rectangular, the center X does not need to be set precisely. The center X may be determined appropriately taking into account the shape of the facing region, and the region R0 may be set so that the center X is included.

[0046] Next, a heat-transfer-suppressing sheet in which the heat insulating material and the elastic sheet are joined at a more preferable position will be described below using a second embodiment as an example.

[0047] [Second embodiment] Fig. 4A is a top view showing a heat-transfer-suppressing sheet according to a second embodiment of the present invention, and Fig. 4B is a schematic cross-sectional view taken along line BB in Fig. 4A. In the second embodiment shown in Fig. 4A and Fig. 4B, the same components as those in the first embodiment shown in Fig. 1A and Fig. 1B are designated by the same reference numerals, and detailed descriptions thereof will be omitted or simplified.

[0048] In the heat-transfer-suppressing sheet 53 according to the second embodiment, as in the first embodiment, the facing region 45a between the thermal insulator 10 and the elastic sheet 51a is rectangular and is surrounded by long sides 46a, 46b and short sides 48a, 48b. Specifically, the facing region 45a is surrounded by a pair of facing long sides 46a, 46b and a pair of facing short sides 48a, 48b that are perpendicular to the long sides 46a, 46b. A joint 55a is formed along only one of the short sides 48a, 48b, adjacent to the short side 48a, thereby forming a joining region 44a. The region of the facing region 45a where the joint 55a is not formed is a non-joining region 41a.

[0049] Here, for example, a case will be described in which joints 55a are formed in two regions surrounding the short side 48a and the short side 48b surrounding the facing region 45a. While the elastic material constituting the elastic sheet will be described in detail later, elastic sheets are generally materials that expand and contract significantly depending on the ambient temperature. Therefore, for example, if a heat-transfer-suppressing sheet is manufactured by joining an insulating material and an elastic sheet in a high-temperature environment and then moved to a low-temperature environment, the elastic sheet may shrink. Conversely, if a heat-transfer-suppressing sheet manufactured in a low-temperature environment is moved to a high-temperature environment, the elastic sheet may expand and sag. As a result, depending on the insulating material, the insulating material may deform and become distorted, or a load may be applied to the joint, causing the joint to separate, resulting in the elastic sheet becoming detached from the insulating material.

[0050] On the other hand, in the heat transfer-suppressing sheet 53 according to the second embodiment, a joint portion 55a joining the thermal insulator 10 and the elastic sheet 51a is formed only in a portion of the heat transfer-suppressing sheet 53 near the short side 48a, thereby forming the joint region 44a. Therefore, as shown in FIG. 5, the non-joined region 41a extends from the boundary 34 between the joint region 44a and the non-joined region 41a to one end of the facing region 45a. Furthermore, as shown by arrow D1, the thermal insulator 10 and the elastic sheet 51a are configured to be separable from one end of the facing region 45a. Therefore, even if the elastic sheet 51a expands or contracts after the thermal insulator 10 and the elastic sheet 51a are joined together, the thermal insulator 10 and the elastic sheet 51a are not fixed from the boundary 34 to the end of the facing region 45a, and therefore deformation of the thermal insulator 10 and peeling of the joint region do not occur.

[0051] Thus, depending on the materials of the heat insulating material and elastic sheet, and the environment during manufacturing and transportation of the heat-transfer-suppressing sheet, it is preferable to select the structure shown in heat-transfer-suppressing sheet 53 according to the second embodiment.

[0052] Although the bonded portions 55a of the heat transfer-suppressing sheet 53 are formed only in a portion of the area adjacent to the short side 48a, the position of the bonded portions 55a can be appropriately selected as needed. For example, the bonded portions 55a may be formed along the long side 46a or 46b in a portion of the area adjacent to the long side 46a or 46b, or may be formed in an area spaced apart from the long side 46a, 46b, or the short side 48a, 48b. In this specification, a position adjacent to a side or end refers to a position that contacts the side or end or a position in the vicinity thereof. In this embodiment, as described above, it is preferable that the non-bonded region 41a be located in the center of the facing region 45a. Therefore, the bonded region 44a is preferably located closer to the other end of the facing region 45a that faces the one end.

[0053] However, because the degree of temperature-dependent expansion and contraction of the elastic sheet 51a is greater on the longitudinal side of the facing region 45a, forming the joint 55a along the long sides 46a, 46b would likely result in stress being applied to the joint 55a. Therefore, if the facing region is rectangular, it is preferable to have the joint 44a only in a position close to one of the pair of short sides, and it is more preferable that the joint 44a be formed so as to extend along this one short side. Even if the facing region 45a is not rectangular but a polygonal region surrounded by three or more sides, it is preferable that the joint 44a be only in a position close to one of the three or more sides, as in the case of the rectangle. It is also more preferable that the joint 44a be formed along this one side.

[0054] Furthermore, the bonded portions 55a do not need to be formed continuously within the bonded region 44a. For example, a plurality of point-like bonded portions may be formed that are spaced apart enough to be unaffected by the expansion and contraction of the elastic sheet.

[0055] [Third embodiment] Fig. 6 is a schematic cross-sectional view showing a heat-transfer-suppressing sheet according to a third embodiment of the present invention. In the third embodiment shown in Fig. 6, the same components as those in the second embodiment shown in Fig. 4A and Fig. 4B are designated by the same reference numerals, and detailed descriptions thereof will be omitted or simplified.

[0056] The heat-transfer-suppressing sheet 54 according to the third embodiment includes a thermal insulator 10, an elastic sheet 51a laminated on a first surface 10a of the thermal insulator 10, and a joining portion 55a joining these together, and further includes a film 22 covering the outer surface of a laminate 19 including the thermal insulator 10 and the elastic sheet 51a. The position of the joining region 44a is the same as in the second embodiment. In this embodiment, the elastic sheet 51a is formed to have the same size as the thermal insulator 10.

[0057] In the heat-transfer-suppressing sheet 54 configured in this manner, the outer peripheral surface of the laminate 19 is covered with the film 22, which makes it possible to prevent, for example, the inorganic particles that make up the thermal insulating material 10 from falling off. Furthermore, if the film 22 is configured to be in close contact with the laminate 19, the thermal insulating material 10 and the elastic sheet 51a can be fixed together even more firmly. When manufacturing the heat-transfer-suppressing sheet 54 having the film 22, it is important to have the joint 55a in order to prevent misalignment between the thermal insulating material 10 and the elastic sheet 51a in the step of covering the laminate 19 with the film 22.

[0058] In the second and third embodiments, the heat transfer-suppressing sheets 53 and 54 are configured by laminating the elastic sheet 51a only on the first surface 10a of the thermal insulating material 10. However, the elastic sheet may be laminated on at least one surface of the thermal insulating material 10. That is, as shown in FIGS. 1A and 1B , the elastic sheets 51a and 51b may be laminated on the first surface 10a and the second surface 10b of the thermal insulating material 10. Alternatively, the elastic sheet 51 may be sandwiched between a pair of thermal insulating materials 10, or the thermal insulating material 10 may be sandwiched between a pair of elastic sheets 51. Furthermore, various sheets other than the thermal insulating material 10 and the elastic sheet 51 may be laminated. The relative sizes of the thermal insulating material and the elastic sheets are not particularly limited. The elastic sheets 51a and 51b may be smaller or larger than the thermal insulating material 10, or the thermal insulating material 10 and the elastic sheets 51a and 51b may be the same size.

[0059] [Method for manufacturing heat transfer-suppressing sheet] The present invention does not limit the manufacturing method of the heat-transfer-suppressing sheet. For example, the first embodiment will be described below with reference to FIGS. 1A and 1B. First, a heat insulating material 10 and elastic sheets 51a and 51b made from the preferred materials described below are prepared. Next, bonding regions 44a and 44b and non-bonding regions 41a and 41b are defined in the heat insulating material 10 or the elastic sheets 51a and 51b, and adhesive is applied to the bonding regions 44a and 44b. Subsequently, the elastic sheet 51a is laminated on the first surface 10a of the heat insulating material 10, and the elastic sheet 51b is laminated on the second surface 10b. The adhesive is then dried while pressure is applied in the thickness direction. This completes the manufacturing process of the heat-transfer-suppressing sheet 50. The heat-transfer-suppressing sheet 52 shown in FIG. 2 and the heat-transfer-suppressing sheet 53 shown in FIGS. 4A and 4B can also be manufactured in a similar manner. The manufacturing method of the heat insulating material will be described in detail later.

[0060] 6 according to a third embodiment, the steps up to the step of joining the heat insulating material 10 and the elastic sheet 51a can be performed in the same manner as the manufacturing method of the heat transfer-suppressing sheet 50. There are no particular limitations on the method for covering the outer peripheral surface of the laminate 19 with a film, but here, an example of a method for shrink-packaging the laminate 19 using a shrink film will be described below.

[0061] First, similar to the method for manufacturing the heat-transfer-suppressing sheet 50, the desired bonding area 44a is selected so that the thermal insulating material 10 and the elastic sheet 51a are bonded at the bonding portion 55a shown in FIG. 6 , and the two are bonded to produce the laminate 19. Next, the laminate 19 is placed on a planar film, which is then folded to cover the top surface of the laminate 19. The films on the bottom and top surfaces of the laminate 19 are then bonded together by heating and applying pressure around the periphery of the laminate 19, thereby obtaining the laminate 19 enclosed in the film. The laminate 19 enclosed in the film is then placed on a conveyor belt of a shrinking device and passed through a shrink tunnel into which hot air is sprayed. This causes the film to thermally shrink and adhere to the outer peripheral surface of the laminate 19, producing the heat-transfer-suppressing sheet 54.

[0062] Here, the direction in which the laminate passes through the shrink tunnel will be described. As shown in FIG. 6, when the bonded portion 55a is formed in proximity to one of the short sides 48a surrounding the facing region 45b, the end face closest to the bonded portion 55a is referred to as the bonded region end face 49a, and the end face away from the bonded portion 55a is referred to as the non-bonded region end face 49b. If the laminate 19 enclosed in the film is passed through the shrink tunnel with the non-bonded region end face 49b facing forward, the film will shrink from the non-bonded region end face 49b toward the bonded region end face 49a. At this time, the elastic sheet 51a shifts toward the bonded region end face 49a, and the contraction of the film fixes the elastic sheet 51a to the thermal insulation material 10. At the same time, the elastic sheet 51a in the heated region stretches. On the other hand, at the rear end portion, which is the end surface 49b on the non-bonded region side, the elastic sheet 51a and the thermal insulating material 10 are fixed by the bonding portion 55a, so the elastic sheet 51a is adhered to the film in a bent state at the center portion in the traveling direction. Therefore, even after the elastic sheet 51a is cooled and returns to its original size, the adhesion to the film is not sufficient, or the bend in the elastic sheet 51a remains.

[0063] Therefore, when using a shrink device to manufacture heat-transfer-suppressing sheet 54 having film 22 covering the outer peripheral surface, it is preferable to pass the sheet through a shrink film tunnel with bonded region side end face 49a facing forward. In this way, heat insulating material 10 and elastic sheet 51a are fixed by the film from the bonded side, but because heat insulating material 10 and elastic sheet 51a can be separated at non-bonded region side end face 49b, elastic sheet 51a can be prevented from being fixed in a bent state even if it stretches.

[0064] That is, when the heat transfer-suppressing sheet 54 is manufactured using a shrink machine, it is preferable to use a laminate in which the joint 55a is formed in a region adjacent to one of the short sides 48a, 48b or the long sides 46a, 46b. It is even more preferable to use a laminate in which the joint 55a is formed in a region adjacent to one of the short sides 48a, 48b. Furthermore, it is particularly preferable that the joint 55a be structured close to the adjacent side. In either case, it is more preferable that the joint 55a be formed along the adjacent side.

[0065] The components of the heat-transfer-suppressing sheet according to this embodiment will be described below. First, the heat insulating material will be described in detail.

[0066] [Insulation material] The heat insulating material used in the heat transfer-suppressing sheet according to this embodiment is not particularly limited as long as it has a heat insulating effect. Thermal conductivity can be used as an index of heat insulating effect, and in this embodiment, the heat conductivity of the heat insulating 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 heat conductivity of the heat insulating 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 heat insulating material can be measured in accordance with the "Test method for thermal conductivity of refractories" described in JIS R 2251.

[0067] In the heat transfer-suppressing sheet according to the embodiment of the present invention, the heat insulating material may contain inorganic particles, but may also contain organic fibers for the purposes of improving the strength of the heat insulating material and preventing powder falling off. Examples of the structure of a heat insulating material containing inorganic particles and organic fibers are described in detail below.

[0068] <Insulating material (Structure example S1)> FIG. 7 is a photograph showing an example structure S1 of an insulating material used in a heat transfer suppression sheet according to an embodiment of the present invention, and FIG. 8 is a photograph showing an enlarged portion of the insulating material shown in FIG. 7.

[0069] As shown in Figures 7 and 8, the heat insulating material 10 has inorganic particles 4 and organic fibers 1. The heat 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.

[0070] 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 increases 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. This makes it possible to prevent damage to a heat-transfer-suppressing sheet that includes such insulating material 10. 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 charge and discharge, the insulating material 10, together with the elastic sheet 51, absorbs the expansion of the battery cells, further preventing a decrease in battery cell performance.

[0071] Furthermore, in this embodiment, it is preferable that at least some of the pores 7 communicate with the surface of the thermal insulator 10 and open outward. With the pores 7 configured in this manner, even if the adjacent battery cells 20a, 20b, and 20c experience thermal runaway and the thermal insulator 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.

[0072] Furthermore, if the welded portions 5 on the outer peripheral surface 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 insulating material 10, and to prevent a decrease in the insulating effect due to compressive deformation of the thermal insulating material 10.

[0073] 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. 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. However, 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.

[0074] 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 a binder fiber having a core-sheath structure is used as the material for the organic fiber 1, the welded portion 5 contains a second organic material that constitutes the sheath portion. In this embodiment, the welded portion 5 welds the inorganic particles 4 to the surface of the organic fiber 1, thereby increasing the apparent fiber diameter of the organic fiber 1, supporting the shape of the thermal insulating material 10 and achieving high strength.

[0075] 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.

[0076] <Insulating material (Structure example S2)> Fig. 9 is a photograph showing a structural example S2 of a heat insulating material used in a heat-transfer-suppressing sheet according to an embodiment of the present invention. In structural example S2 shown in Fig. 9, the same components as those in structural example S1 shown in Figs. 7 and 8 are designated by the same reference numerals, and detailed description thereof will be omitted. Note that the heat insulating material 40 shown in Fig. 9 can be used, for example, in place of the heat insulating material 10 of the heat-transfer-suppressing sheets 50, 52, 53, and 54 described above.

[0077] As shown in FIG. 9, the heat insulating material 40 has inorganic fibers 15. The heat insulating 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 heat insulating material 40. The fiber layer 11 is formed by welding at least some of the organic fibers 1 together at welding portions, and is formed in a layer on the surface (first surface and second surface) of the heat insulating material 40. That is, the fiber layer 11 is a layer formed by gathering 10 or more organic fibers 1 on the surface of the heat insulating material 40, and extends, for example, in stripes, in a direction approximately parallel to the surface.

[0078] 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.

[0079] In the heat insulating material 40 shown in Fig. 9, 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. 9, the inorganic fibers 15 in the fiber layer 11 cannot be distinguished and are therefore not shown.

[0080] 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.

[0081] 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, allowing the thermal insulation material 40 to reliably maintain its shape. Furthermore, the flexible organic fibers 1 easily become entangled with the relatively hard inorganic fibers 15, and the inorganic fibers 15 and organic fibers 1 form a three-dimensional skeleton, further improving the strength of the thermal insulation material 40.

[0082] Furthermore, when the insulating material 40 has a fiber layer 11 on its surface and 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 since the elastic sheet 51 is laminated on this insulating material 40, the pressure on the base layer 13 can be further reduced.

[0083] Furthermore, when a fiber layer 11 is formed on the surface of the insulating material 40, this fiber layer 11 can absorb the impact given to the insulating material 40, and therefore, even on the surface where the elastic sheet 51 is not laminated, the effect of preventing the inorganic particles contained in the insulating material 40 from falling off can be obtained.

[0084] <Insulating material (Structure example S3)> Fig. 10 is a schematic diagram showing a structural example S3 of a heat insulating material used in a heat-transfer-suppressing sheet according to an embodiment of the present invention, and Fig. 11 is a schematic diagram showing an enlarged portion of Fig. 10. Fig. 12 is a photograph showing the heat insulating material shown in Fig. 10. In structural example S3 shown in Figs. 10 to 12, the same components as those in structural example S1 shown in Figs. 7 and 8 are designated by the same reference numerals, and detailed description thereof will be omitted. Note that the heat insulating material 60 shown in Figs. 10 to 12 can be used, for example, in place of the heat insulating material 10 of the heat-transfer-suppressing sheets 50, 52, 53, and 54.

[0085] As shown in FIGS. 10 to 12, the heat 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, binder fibers 3 having a sheath-core structure with a core and a sheath covering the outer surface of the core are used as the organic fibers, and the organic fibers 1 correspond to the core. The welded portions 5 are formed by heating and then melting the sheath of the binder fibers 3 having a sheath-core structure, followed by cooling. As shown in FIG. 12, a fiber portion 16 is formed by the organic fibers 1 and the welded portions 5 containing the inorganic particles 4, and a matrix portion 18 containing inorganic particles is formed between the multiple fiber portions 16. When the melted sheath portions are cooled, adjacent organic fibers 1 are fused to each other at contact portions 31, forming a three-dimensional skeleton.

[0086] 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, on both the surface and center sides of the thermal insulation material 60, the welded portions 5 covering the outer periphery of the organic fibers fix the inorganic particles 4 to the organic fibers 1, thereby preventing powder from falling off. Therefore, for example, if the heat-transfer-suppressing sheet 50 according to this embodiment is disposed between multiple battery cells, and the battery cells expand, applying compressive stress or impact to the heat-transfer-suppressing sheet 50, the excellent thermal insulation performance can be maintained.

[0087] 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. In addition, since the elastic sheet 51 is laminated on at least one of the first and second surfaces of the insulating material 60, the pressure on the insulating material 60 is reduced, which is also thought to contribute to preventing the inorganic particles 4 from falling off. Note that, regardless of whether the elastic sheet 51 is present on the surface of the insulating material 60, the fiber portion 16 exposed on the surface of the insulating material 60 can absorb impacts applied to the insulating material 60, which is also thought to be a reason why the inorganic particles 4 are retained.

[0088] 12, in the thermal insulation material 60, the welded portion 5 does not need to completely cover the outer peripheral surface 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 the present invention can be fully obtained.

[0089] <Insulating material (Structure example S4)> Fig. 13 is a photograph, substituted for a drawing, showing a structural example S4 of a heat insulating material used in a heat-transfer-suppressing sheet according to an embodiment of the present invention, and Fig. 14 is a photograph, substituted for a drawing, showing an enlarged view of the structure of the heat insulating material shown in Fig. 13. Fig. 15 is a photograph, substituted for a drawing, showing a cross section of the heat insulating material shown in Fig. 13. In structural example S4 shown in Figs. 13 to 15, the same components as those in structural example S1 shown in Figs. 7 and 8 are designated by the same reference numerals, and detailed description thereof will be omitted. Note that the heat insulating material 70 shown in Figs. 13 to 15 can be used, for example, in place of the heat insulating material 10 of the heat-transfer-suppressing sheets 50, 52, 53, and 54 described above.

[0090] 13 and 14, the heat insulating material 70 has a matrix 14 containing inorganic particles 4 and organic fibers 1 oriented three-dimensionally 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.

[0091] As shown in the cross-sectional view of Fig. 15, 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 welded portions 5 not shown in Fig. 15, thereby forming fiber bundles 6, and voids 8 are formed between the plurality of organic fibers 1 constituting the fiber bundles 6.

[0092] 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 some of the 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 some of the fiber layer 11 and some of the matrix 14 are mixed. Specifically, the composite layer 12 is a region containing a plurality of organic fibers 1 at least partially welded to each other by welded portions 5, and inorganic particles 4 welded to the organic fibers 1 by the welded portions 5.

[0093] 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.

[0094] In the thermal insulation material 70 configured in this manner, the organic fibers 1 are oriented three-dimensionally 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 have melted and then solidified 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 together 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.

[0095] 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.

[0096] The mechanism by which the heat 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 heat insulating material 60 of the above-mentioned structural example S3.

[0097] In the heat insulating material 70, the welded portions 5 do not need to completely cover the outer periphery of the organic fibers 1, and there may be areas where the welded portions 5 are not present. Even in such a case, the effect of holding the inorganic particles 4 can be sufficiently obtained.

[0098] 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, which has the effect of improving the sheet strength.

[0099] Furthermore, the heat insulating material 70 has a plurality of pores 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 heat insulating 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 heat insulating material 70. The voids 8 do not need to be formed in the entire area between the plurality of organic fibers 1; as long as the voids 8 are formed in at least a portion of the area between the organic fibers 1, the effect of suppressing heat transfer can be obtained.

[0100] 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 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.

[0101] <Insulation material (Structure example S5)> Fig. 16 is a schematic diagram showing a structural example S5 of a heat insulating material used in a heat-transfer-suppressing sheet according to an embodiment of the present invention, and Fig. 17 is a schematic diagram showing an enlarged view of part A of the heat insulating material shown in Fig. 16. In structural example S5 shown in Figs. 16 and 17, the same components as those in structural example S1 of the heat insulating material shown in Figs. 7 and 8 are designated by the same reference numerals, and detailed description thereof will be omitted. Note that heat insulating material 80 shown in Figs. 16 to 17 can be used, for example, in place of heat insulating material 10 of the heat-transfer-suppressing sheets 50, 52, 53, and 54 described above.

[0102] As shown in Figures 16 and 17, 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 in a portion around 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.

[0103] 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.

[0104] 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 the 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.

[0105] Furthermore, because the heat insulating material 80 contains highly flexible organic fibers 1, the flexibility of the heat insulating material 80 can be increased, and the organic fibers 1 are easily 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 inorganic fibers 15, for example, when a battery cell 20a experiences thermal runaway and the heat-transfer-suppressing sheet disposed adjacent to the battery cell 20a is exposed to high temperatures, the shape of the heat-transfer-suppressing sheet can be maintained even if the organic fibers 1 are decomposed. 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, it is possible to obtain a heat-transfer-suppressing sheet that has a good balance of both flexibility and strength.

[0106] 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 air layers 28 formed around the inorganic fibers 15 can suppress heat transfer between the inorganic fibers 15 and the matrix 14. The air layers 28 are formed in the manufacturing process of the thermal insulation material 80, but it is not necessary for the air layers 28 to be formed around the entire area around the inorganic fibers 15. As long as the air layers 28 are formed on at least a portion of the outer circumferential surface of the inorganic fibers 15, the effect of suppressing heat transfer can be obtained. When the inorganic fibers 15 are uniformly dispersed in the matrix 14, the air spaces 28 in the matrix 14 are also uniformly dispersed and disposed, so that the heat insulating material 80 can obtain high heat insulating properties evenly.

[0107] Furthermore, in the insulating material 80, the organic fibers 1 have welded portions 5 that cover at least a portion of their surfaces. 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.

[0108] Similarly, in this embodiment, 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, 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, excellent heat insulating performance can be maintained.

[0109] 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 by the welded portions 5 to form a three-dimensional, strong skeleton, which maintains the shape of the thermal insulation material 80 and prevents deformation or compression of the heat-transfer-suppressing sheet. Furthermore, regardless of whether or not an elastic sheet 51 is present on the surface of the thermal insulation material 80, when the organic fibers 1 and the inorganic fibers 15 are exposed on the surface of the thermal insulation material 80, they are able to absorb impacts applied to the thermal insulation material 80, and the inorganic particles 4 are thought to be held in place.

[0110] In the heat insulating material 80, the welded portions 5 do not need to completely cover the outer periphery of the organic fibers 1, and there may be areas where the welded portions 5 are not present. Even in such a case, the effect of holding the inorganic particles 4 can be sufficiently obtained.

[0111] <Insulating material (Structure example S6)> Fig. 18 is a photograph, substitute for a drawing, showing structural example S6 of the heat insulating material used in the heat-transfer-suppressing sheet according to an embodiment of the present invention, and Fig. 19 is a photograph, substitute for a drawing, showing another region of the heat insulating material shown in Fig. 18. Fig. 20 is a photograph, substitute for a drawing, showing a cross section of the heat insulating material shown in Figs. 18 and 19. In structural example S6 shown in Figs. 18 to 20, the same components as those in structural example S4 of the heat insulating material shown in Figs. 13 to 15 are designated by the same reference numerals, and detailed description thereof will be omitted. Note that the heat insulating material 90 shown in Figs. 18 to 20 can be used, for example, in place of the heat insulating material 10 of the heat-transfer-suppressing sheets 50, 52, 53, and 54.

[0112] As shown in Fig. 18, 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 consisting of 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.

[0113] 19 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. 19 have a base 32 and branches 33 extending from the base 32 in five directions, namely, directions D1, D2, D3, D4, and D5, and the base 32 is thicker than the multiple branches 33.

[0114] Furthermore, as shown in FIGS. 18 and 19, 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.

[0115] 20, a plurality of voids 7 are formed in the heat insulating material 90. Furthermore, a plurality of organic fibers 1 are at least partially welded together in the heat insulating material 90 to form fiber bundles 6, and gaps 8 are formed between the plurality of organic fibers 1 constituting the fiber bundles 6. Note that, also in FIG. 20, the organic fibers 1 can be seen to have a branched structure consisting of a base 32 and branch portions 33 extending in three directions from the base 32.

[0116] Furthermore, a fiber layer 11 may be formed on at least a portion of the first and second surfaces of the thermal insulation 90 that are perpendicular to the thickness direction. 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 90. Furthermore, a composite layer 12 may be formed between the fiber layer 11 and a base layer 13 that contains 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 that contains a plurality of organic fibers 1 that are welded to each other and inorganic particles 4 that are welded to the organic fibers 1.

[0117] 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.

[0118] 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, allowing the shape of the thermal insulation material 90 to be maintained. 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 portions of the multiple 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, allowing the strength of the thermal insulation material 90 to be significantly improved.

[0119] In the thermal insulating material 90, at least some of the organic fibers 1 have a branched structure consisting of a base 32 and branch portions 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 branch portions 33 extending from the base 32 in at least three directions. The base 32 and branch portions 33 will be described in more detail below.

[0120] (Base (fusion part)) The fused portion is formed by heating and melting the sheath portion of the binder fiber at the portion where the plurality of binder fibers are in contact with each other when a binder fiber with a core-sheath structure is used as the material for the thermal insulation material 90, and then cooling the sheath portion. When a binder fiber with a core-sheath structure is used as the material for the thermal insulation material 90, the fused portion contains the second organic material that constitutes the sheath portion. Thus, in the manufacturing process of the heat transfer-suppressing sheet 50, when the sheaths in the contacting regions of the binder fibers are melted by heating, 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.

[0121] (Branch) The support portions 33 extend in at least three directions from the base portion 32 and have the effect of holding the inorganic particles 4. Furthermore, the base portion 32 and the support portions 33 form a skeleton, which can also improve the strength of the heat transfer-suppressing sheet 50. This makes it possible to obtain a high effect of suppressing powder falling. When a binder fiber with a core-sheath structure is used as the organic fiber 1, the branch portion 33 is a part of the binder fiber with a core-sheath structure, and has a core portion made of a first organic material and a sheath portion made of a second organic material.

[0122] 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, which allows the formation of a three-dimensional, strong skeleton.

[0123] In the thermal insulating 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 prevention 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 insulating material 90 can be maintained. As a result, shedding (powder shedding) of the inorganic particles 4 can be prevented, and a decrease in the insulating effect of the thermal insulating material 90 due to compressive deformation can be prevented.

[0124] The mechanism by which the inorganic particles 4 can be prevented from falling off from 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.

[0125] 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.

[0126] 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, which has the effect of improving the sheet strength.

[0127] 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 leaves the organic fibers 1 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 area between the plurality of organic fibers 1; as long as the voids 8 are formed in at least a portion of the area between the organic fibers 1, the effect of suppressing heat transfer can be obtained.

[0128] Furthermore, since the thermal insulation 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 thermal insulation material 90. Therefore, the strength of the thermal insulation material 90 can be improved.

[0129] <Insulating material (Structure example S7)> Fig. 21 is a photograph, substitute for a drawing, showing structural example S7 of a heat insulating material used in a heat-transfer-suppressing sheet according to an embodiment of the present invention, and Fig. 22 is a photograph, substitute for a drawing, showing an enlarged portion of the heat insulating material shown in Fig. 21. In structural example S7 shown in Figs. 21 and 22, the same components as those in structural example S2 of the heat insulating material shown in Fig. 9 are given the same reference numerals, and detailed explanations will be omitted. Note that the heat insulating material 110 shown in Figs. 21 and 22 can be used, for example, in place of the heat insulating material 10 of the heat-transfer-suppressing sheets 50, 52, 53, and 54 described above.

[0130] 21 and 22, the thermal insulating material 110 has inorganic particles 4 and organic fibers 1. On the surface of the thermal insulating material 110, 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. 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.

[0131] That is, when the surface of the thermal insulating material 110 is observed, a state in which a plurality of organic fibers 1 are entangled is observed in the first region 42, as shown in Fig. 22. On the other hand, in the second region 43, although there are some places where a few organic fibers 1 are observed, 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 an island portion, is formed so as to be surrounded by the first region 42, which corresponds to a sea portion.

[0132] In the thermal insulating material 110, fiber bundles 47 formed by entanglement of organic fibers 1 are present on the surface of the thermal insulating material 110 in a streak-like manner, thereby improving the strength of the thermal insulating 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, so the flexibility of the thermal insulating material 110 is also excellent. Furthermore, because the fiber bundles 47 are present on the surface of the thermal insulating material 110, even if an impact or pressure is applied to the thermal insulating material 110, the fiber bundles 47 can absorb and mitigate the impact or pressure. Therefore, it is possible to suppress the inorganic particles 4 from falling off (powdering), and it is possible to prevent a decrease in the thermal insulating performance of the thermal insulating material 110.

[0133] 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 allows for even greater strength to be obtained.

[0134] It is preferable that the length of the fiber bundles 47 formed so as to extend on the surface of the heat insulating material 110 is relatively long. An example of a method for specifying the length of the fiber bundles 47 will be described with reference to FIG. 23, rectangular imaginary frames 21 are arranged along the streak-like fiber bundles 47 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 arranged so that they are 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 effect of improving the strength of the thermal insulation material 110 is sufficient.

[0135] 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.

[0136] Furthermore, as shown in FIG. 24, 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.

[0137] While structural examples S1 to S7 of the thermal insulation material have been described above, the structure of the thermal insulation material is not limited thereto, and thermal insulation materials having various structures can be used. Specifically, the thermal insulation materials of structural examples S1 to S7 have excellent thermal insulation effects and also have various properties such as the effect of suppressing powder falling, the effect of further improving strength, and the effect of maintaining shape. Therefore, as shown in Figures 1 to 6, a heat-transfer-suppressing sheet in which elastic sheets 51a and 51b are laminated on the thermal insulation material 10, 40, 60, 70, 80, 90, and 110 can obtain the various effects described above and can prevent unnecessary pressure from being applied to the battery cells 20a, 20b, and 20c.

[0138] As described above, the heat insulating material contains inorganic particles, and may contain at least one selected from organic fibers, inorganic fibers, and organic particles as other components. Each material will be described with reference to Figs. 7 to 23.

[0139] <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, the type of inorganic particles 4 is preferably particles made of at least one inorganic material selected from oxide particles, carbide particles, nitride particles, and inorganic hydrate particles, and more preferably oxide particles. Furthermore, the shape of the inorganic particles 4 is not particularly limited, but preferably includes at least one type selected from nanoparticles, hollow particles, and porous particles. Specific examples of the inorganic particles that can be used include silica nanoparticles, metal oxide particles, inorganic balloons such as microporous particles and hollow silica particles, particles made of thermally expandable inorganic materials, and particles made of hydrous porous bodies.

[0140] 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. Furthermore, 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.

[0141] 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.

[0142] <First inorganic particle> (oxide particles) Oxide particles have a high refractive index and a strong effect of diffusely reflecting light. Therefore, using oxide particles as the first inorganic particles can suppress radiant heat transfer, particularly in high-temperature regions such as those caused by abnormal heat generation. The oxide particles can be at least one type of particle selected from silica, titania, zirconia, zircon, barium titanate, zinc oxide, and alumina. That is, among the above oxide particles that can be used as inorganic particles, only one type or two or more types of oxide particles can 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.

[0143] (Average primary particle size of oxide particles: 0.001 μm to 50 μm) The particle size of the oxide particles can affect the effect of reflecting radiant heat, so if the average primary particle size is limited to a predetermined range, even higher heat insulating properties can be obtained. In other words, when the average primary particle diameter of the oxide particles is 0.001 μm or more, the particle diameter is sufficiently larger than the wavelength of light that contributes to heating, and the light is efficiently diffused, thereby suppressing the radiative heat transfer within the thermal insulation material in the high temperature range of 500°C or higher, thereby further improving the thermal insulation properties. On the other hand, if the average primary particle size of the oxide particles is 50 μm or less, the number and number of contact points between the particles do not increase even when compressed, making it difficult to form paths for conductive heat transfer. This reduces the impact on thermal insulation, particularly in the normal temperature range where conductive heat transfer is dominant.

[0144] 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.

[0145] (nanoparticles) In the present invention, nanoparticles refer to particles on the order of nanometers that are spherical or nearly spherical and have an average primary particle diameter of less than 1 μm. Nanoparticles have low density, which suppresses conductive heat transfer. When nanoparticles are used as the first inorganic particles, the three-dimensionally connected pores 7 become finer, resulting in excellent heat insulation that suppresses convective heat transfer. Therefore, it is preferable to use nanoparticles because they can suppress heat transfer between adjacent nanoparticles during normal use of the battery at room temperature. Furthermore, if nanoparticles with a small average primary particle size are used as oxide particles, the increase in conductive heat transfer through the insulating material can be suppressed even when the insulating material is compressed due to expansion caused by thermal runaway in the battery cell, increasing the internal density. This is thought to be because nanoparticles are prone to forming tiny voids between particles due to electrostatic repulsion, and because their bulk density is low, the particles are packed together to provide cushioning.

[0146] 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.

[0147] Generally, wet silica particles are aggregated, whereas dry silica particles can be dispersed. Because heat conduction is dominated by conductive heat transfer 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.

[0148] (Average primary particle diameter of nanoparticles: 1 nm to 100 nm) If the average primary particle size of the nanoparticles is limited to a predetermined range, even higher heat insulating properties can be obtained. That is, when the average primary particle diameter of the 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, and the thermal insulation properties can be further improved. Furthermore, even when compressive stress is applied, the voids remaining between the nanoparticles and the contact points between many particles suppress conductive heat transfer, allowing the thermal insulation properties of the thermal insulation material to be maintained. The average primary particle size of the nanoparticles is more preferably 2 nm or more, and even more preferably 3 nm or more, while the average primary particle size of the nanoparticles is more preferably 50 nm or less, and even more preferably 10 nm or less.

[0149] (Inorganic hydrate particles) When inorganic hydrate particles receive heat from a heating element and reach a temperature above their thermal decomposition initiation temperature, they undergo thermal decomposition and release their own water of crystallization, lowering the temperature of the heating element and its surroundings, thereby exhibiting a so-called "endothermic effect." After releasing the water of crystallization, the particles become porous, and the numerous air holes provide thermal insulation. Specific examples of inorganic hydrates include aluminum hydroxide (Al(OH)3), magnesium hydroxide (Mg(OH)2), calcium hydroxide (Ca(OH)2), zinc hydroxide (Zn(OH)2), iron hydroxide (Fe(OH)2), manganese hydroxide (Mn(OH)2), zirconium hydroxide (Zr(OH)2), and gallium hydroxide (Ga(OH)3).

[0150] For example, aluminum hydroxide has 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 (Al2O3) and functions as a heat insulating material. 2Al(OH)3 → Al2O3 + 3H2O

[0151] The heat transfer-suppressing sheet 50 according to this embodiment is preferably interposed between battery cells, for example, but in a battery cell that has experienced thermal runaway, the temperature rises 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 temperature starts at 200°C or higher. The thermal decomposition starting temperatures of the inorganic hydrates listed above are approximately 200°C for aluminum hydroxide, approximately 330°C for magnesium hydroxide, approximately 580°C for calcium hydroxide, approximately 200°C for zinc hydroxide, approximately 350°C for iron hydroxide, approximately 300°C for manganese hydroxide, approximately 300°C for zirconium hydroxide, and approximately 300°C for gallium hydroxide.All of these temperatures roughly overlap with the temperature range in which a battery cell experiencing thermal runaway experiences a sudden rise in temperature, and can efficiently suppress temperature rise, making these inorganic hydrates preferable.

[0152] (Average secondary particle diameter of inorganic hydrate particles: 0.01 μm or more and 200 μm or less) Furthermore, when inorganic hydrate particles are used as the first inorganic particles, if their average particle size is too large, it takes some 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 size of the inorganic hydrate particles is preferably 0.01 μm or more and 200 μm or less, and more preferably 0.05 μm or more and 100 μm or less.

[0153] (Particles made of thermally expandable inorganic material) Examples of thermally expandable inorganic materials include vermiculite, bentonite, mica, and perlite.

[0154] (Particles made of hydrous porous material) Specific examples of the hydrous porous material include zeolite, kaolinite, montmorillonite, acid clay, diatomaceous earth, wet silica, dry silica, aerogel, mica, and vermiculite.

[0155] (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 or conductive heat transfer within the heat insulating material can be suppressed in the temperature range below 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.

[0156] (Inorganic balloon content: 60% or less by mass of the total mass of the insulation material) The content of the inorganic balloons is preferably 60 mass % or less based on the total mass of the heat insulating material.

[0157] (Average particle size of inorganic balloons: 1 μm to 100 μm) The average particle size of the inorganic balloons is preferably 1 μm or more and 100 μm or less.

[0158] <Second inorganic particles> When two types of inorganic particles are contained in a 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.

[0159] 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 also effective in 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 improving the heat transfer suppression effect. Therefore, when nanoparticles are used as the first inorganic particles, it is preferable to further include second inorganic particles made of a metal oxide that are 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, zircon, zirconium oxide, etc. In particular, titanium oxide (titania) is a component with a higher refractive index than other metal oxides, and is highly effective in scattering light and blocking radiant heat in a high temperature range of 500°C or higher, so it is most preferable to use titania.

[0160] When the first inorganic particles are at least one type of particles selected from dry silica particles and silica aerogel, and the second inorganic particles are at least one type of particles selected from titania, zircon, zirconia, silicon carbide, zinc oxide, and alumina, the first inorganic particles preferably account for 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more of the total mass of the inorganic particles, in order to obtain excellent heat insulating performance within a temperature range of 300° C. or less. Furthermore, the first inorganic particles preferably account for 95% by mass or less, more preferably 90% by mass or less, and even more preferably 80% by mass or less of the total mass of the inorganic particles.

[0161] 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. Also, the content of the second inorganic particles 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.

[0162] (Average primary particle size 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 size 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 size of the second inorganic particles is more preferably 5 μm or more and 30 μm or less, and most preferably 10 μm or less.

[0163] (Inorganic particle content) In this embodiment, if the total content of the inorganic particles 4 in the heat insulating material is appropriately controlled, the heat insulating property of the heat insulating material can be sufficiently ensured. The total content of the inorganic particles 4 is preferably 60% by mass or more, and more preferably 70% by mass or more, based on the total mass of the thermal insulation material. If the total content of the inorganic particles 4 is too high, the content of the organic fibers will relatively decrease, so in order to sufficiently obtain the skeleton reinforcing effect and the inorganic particle retention effect, the total content of the inorganic particles 4 is preferably 95% by mass or less, and more preferably 90% by mass or less, based on the total mass of the thermal insulation material.

[0164] 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.

[0165] <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, and the melting point of the first organic material is higher than that of the second organic material. When the binder fiber with a core-sheath structure is used as a material, the core in the thermal insulation material corresponds to the organic fiber 1. Furthermore, during the manufacturing 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.

[0166] (organic fiber content) In this embodiment, if the content of the organic fiber 1 in the heat insulating material is appropriately controlled, the skeleton can be sufficiently reinforced. The content of organic fiber 1 is preferably 2% by mass or more, and more preferably 4% by mass or more, based on the total mass of the thermal insulation material. If the content of organic fiber 1 is too high, the content of inorganic particles 4 will relatively decrease, so in order to obtain the desired thermal insulation performance, the content of organic fiber is preferably 10% by mass or less, and more preferably 8% by mass or less, based on the total mass of the thermal insulation material.

[0167] (fiber length of organic fiber) The fiber length of the organic fibers 1 is not particularly limited, but from the viewpoint of ensuring moldability and processability, it is preferable that the average fiber length of the organic fibers be 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 heat insulating material, it is preferable that the average fiber length of the organic fibers 1 is 0.5 mm or more.

[0168] (binder fiber) When binder fibers having a core-sheath structure are used as the material for the organic fibers 1, the melting point of the first organic material constituting the core, i.e., the organic fibers 1, is not particularly limited as long as it is higher than the melting point of the second organic material constituting the sheath, i.e., the second organic material, present on the outer surface of the organic fibers 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.

[0169] 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.

[0170] If the melting point of the first organic material constituting the core is sufficiently higher than that of the second organic material constituting the sheath, 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 second organic material, more preferably 70°C or more higher, and even more preferably 80°C or more higher.

[0171] When binder fibers with a core-sheath structure are used as the material for the thermal insulation, the sheath can be melted while leaving the core when the material mixture is heated during the production of the thermal insulation. After cooling, the outer surface of the core (organic fiber 1) is covered 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 strength greater than that of 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 the areas where the binder fibers are in contact with each other, forming a three-dimensional skeleton. As a result, the overall shape of the thermal insulation can be maintained with even greater strength.

[0172] 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.

[0173] 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 intact. 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 surfaces 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.

[0174] 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, but softening accompanied by a change in shape is also considered to be a type of melting deformation. The melting point of the sheath of the binder fiber can be measured, for example, by the following method. The binder fiber to be measured is placed in contact with a glass fiber having a higher melting point, and is heated from room temperature to, for example, 200°C at a temperature increase 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 identifying the melting point of the second organic material constituting the sheath.

[0175] (Binder fiber content) In this embodiment, when binder fibers 3 having a core-sheath structure are used as the material, if the content of binder fibers in the mixture is appropriately controlled, the skeleton of the resulting insulating material can be sufficiently reinforced. The content of the binder fibers 3 is preferably 5% by mass or more, and more preferably 10% by mass or more, based on the total mass of the mixture. If the content of the binder fibers 3 is too high, the content of the inorganic particles 4 will relatively decrease. Therefore, in order to obtain the desired heat insulating performance, the content of the binder fibers 3 is preferably 25% by mass or less, and more preferably 20% by mass or less, based on the total mass of the mixture.

[0176] <Inorganic fibers> A single inorganic fiber may be used, or two or more types of inorganic fibers may be used in combination as the inorganic fiber 15. 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 material, 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, availability, etc. Among the inorganic fibers, silica-alumina fibers, alumina fibers, silica fibers, rock wool, alkaline earth silicate fibers, and glass fibers are particularly preferred in terms of ease of handling.

[0177] 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.

[0178] The preferred lower limit of the average fiber length of the inorganic fibers is 0.1 mm, more preferably 0.5 mm. Meanwhile, 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 intertwine with each other, which may reduce the mechanical strength of the insulating material. Meanwhile, if the average fiber length exceeds 50 mm, although a reinforcing effect is obtained, the inorganic fibers may not be able to intertwine tightly with each other, or may curl up with a single inorganic fiber, which may result in continuous voids and reduce the insulating properties.

[0179] 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.

[0180] (Inorganic fiber content) In this 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 relative to the total mass of the heat insulating material.

[0181] 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 balanced. 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 retention effect of the inorganic particles 4 and other compounding materials described below.

[0182] <Hot melt powder> In this embodiment, the insulating material may contain hot melt powder as a binder material in addition to the organic fibers 1 and inorganic particles 4. The hot melt powder is a powder that contains, for example, a third organic material different from the first and second organic materials and has the property of melting when heated. When the hot melt powder is added to the 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.

[0183] Hot melt powders with various melting points can be used. A hot melt powder with an appropriate melting point can be selected based on 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.

[0184] 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, the sheath and hot melt powder melt together, and then when they cool and harden, the organic fibers (core) 1, the molten sheath around them, and the hot melt powder present in the gaps between the inorganic particles 4 harden first. As a result, the position of the organic fibers 1 can be fixed, and then the molten sheath will fuse to the organic fibers, facilitating the formation of a three-dimensional skeleton. This further improves the strength of the entire sheet.

[0185] 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 latitude 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.

[0186] 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. Components constituting the hot melt powder include polyethylene, polyester, polyamide, and ethylene vinyl acetate.

[0187] (Hot melt powder content) When hot-melt powder is added to the mixture to prevent the inorganic particles from falling off, even a small amount of hot-melt powder can be effective in preventing the particles from falling off. Therefore, the hot-melt powder content is preferably 0.5% by mass or more, and more preferably 1% by mass or more, based on the total mass of the mixture. On the other hand, when the content of the hot melt powder is increased, the content of the inorganic particles 4 and the like is relatively decreased, so in order to obtain the desired heat insulating performance, the content of the hot melt powder is preferably 5 mass% or less, and more preferably 4 mass% or less, relative to the total mass of the mixture.

[0188] <Other compounding materials> The heat insulating material may further contain binders, colorants, etc., as needed. These are all useful for reinforcing the heat insulating material and improving its formability, and the total amount of these additives is preferably 10 mass % or less based on the total mass of the heat insulating material.

[0189] <Insulating material manufacturing method> The method for manufacturing the heat insulating material will be described in detail below, particularly taking the method for manufacturing the heat insulating material of structural example S2 as an example. For example, binder fibers (not shown) having a core-sheath structure, inorganic particles 4, and inorganic fibers 15 are put into a mixer such as a V-type mixer in a predetermined ratio to prepare a mixture. As mentioned above, it is preferable to use a core-sheath fiber as the binder fiber, which has a core made of a first organic material and a sheath made of a second organic material, where the melting point of the first organic material is higher than that of the second organic material.

[0190] The resulting mixture is then placed in a mold and pressurized with a press or the like, and 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 the binder fibers are also fused to each other in the areas where they were in contact with each other. This allows for the production of a sheet-shaped insulating material 40.

[0191] 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.

[0192] 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.

[0193] (Heating conditions) When a core-sheath binder fiber is used as the material for the thermal insulation material, the heating temperature in the heating step is preferably 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.

[0194] 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, while 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.

[0195] The heating time is not particularly limited, but it is preferable to set the heating time so that the sheath can be sufficiently melted, for example, from 3 minutes to 15 minutes.

[0196] 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, and more preferably at least 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. Meanwhile, the heating temperature is preferably set to be at least 10°C lower, and more preferably at least 20°C lower, than the melting point of the first organic material constituting the core. Setting the heating temperature at this level allows for the formation of a strong skeleton, further improving the strength of the sheet, and preventing the inorganic particles 4 from falling off due to the welded portions 5, etc.

[0197] As described above, the insulating material may be manufactured by either a dry method or a wet method, but the dry method is preferred. 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 the raw materials difficult to handle, 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.

[0198] [Elastic sheet] The elastic sheets 51a and 51b used in the heat transfer-suppressing sheets 50, 52, 53, and 54 according to the first to fourth embodiments are made by processing an elastic material into a sheet shape. Any known elastic material can be used. Specifically, sheets made of rubber or thermoplastic elastomer that has elasticity that allows them to flexibly deform in response to deformation of the battery cells 20a, 20b, and 20c can be used.

[0199] The rubber may be either synthetic or natural rubber, and examples of synthetic rubber include styrene-butadiene rubber, butadiene rubber, chloroprene rubber, isoprene rubber, butyl rubber, ethylene-propylene rubber, nitrile rubber, silicone rubber, fluororubber, acrylic rubber, urethane rubber, polysulfide rubber, epichlorohydrin rubber, and foamed silicone.

[0200] Examples of thermoplastic elastomers include polystyrene-based, polyolefin-based, vinyl chloride-based, polyurethane-based, polyester-based, polyamide-based, and polybutadiene-based thermoplastic elastomers. The elastomer may be either porous or non-porous. If the elastomer is porous, the cell structure may be either closed-cell or open-cell.

[0201] (Elastic sheet size) There are no particular limitations on the thickness of the elastic sheet, but in order to effectively obtain the effects of the elastic sheet, it is preferable that the thickness be 1 mm or more and 10 mm or less.

[0202] [Joint part] In the above embodiment, the joint was formed by drying an adhesive, but the structure of the joint in the present invention is not limited to this. In addition to chemical joining methods such as adhesives, joining (physical joining methods) using joining members such as stitching, staples, tag pins, etc. can also be used to join the insulating material and the elastic sheet. When joining using stitching, staples, tag pins, etc., the insulating material and the elastic sheet may be joined at a single point or at multiple closely spaced points. When forming a joint using an adhesive, the type of adhesive is not particularly limited, and commonly used adhesives can be used, but it is preferable to use a flame-retardant adhesive. Specifically, the flame-retardant inorganic adhesive can be a heat-curing, heat-resistant inorganic adhesive whose main components are a refractory ceramic such as alumina and an inorganic polymer. The flame-retardant organic adhesive can be an adhesive containing, for example, 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.

[0203] [film] As shown in the fourth embodiment, the outer peripheral surface of the laminate of the heat insulating material and the elastic sheet may be covered with a film or the like. Examples of polymer films include films made of polyimide, polycarbonate, polyethylene terephthalate (PET: Poly Ethylene Terephthalate), p-phenylene sulfide, polyetherimide, cross-linked polyethylene, flame-retardant chloroprene rubber, polyvinyldenfluoride, rigid vinyl chloride, polybutylene terephthalate, polytetrafluoroethylene (PTFE: Poly Tetra Fluoro Ethylene), perfluoroalkoxy alkane (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP: Fluorinated Ethylene Propylene), tetrafluoroethylene-ethylene copolymer (ETFE: Ethylene Tetra Fluoro Ethylen), rigid polyvinyl chloride (PCV: Polyvinyl Chloride), flame-retardant PET, nylon, acrylic, epoxy resin, polyurethane, polyether ether ketone, polycarbonate, aramid, polystyrene, polyethersulfone, polyamideimide, polyacrylonitrile, polyethylene, polypropylene, polyamide, and the like.

[0204] When the entire surface of the laminate is covered with a film, it is preferable to use shrink packaging. Therefore, it is preferable to use a film made of a material suitable for shrink packaging. Such materials include polyethylene, polypropylene, polystyrene, polyethylene terephthalate, and polyvinyl chloride.

[0205] If a shrink machine is used to cover the surface with film, it is preferable to use a heat-transfer-suppressing sheet 54 having a joint 55a formed in a position close to one end face (end face 49a on the bonding region side) of the laminate 19 so as to extend along the end face 49a, as shown in the fourth embodiment. Other methods for covering the outer periphery of the laminate with film include a method of attaching the films together with an adhesive or the like, a method of wrapping the heat insulating material and elastic sheet 51 in film and bonding them together at some points, and a method of housing the heat insulating material and elastic sheet 51 in a bag-shaped film.

[0206] (film thickness) The film preferably has an appropriate thickness because it adheres to the outer surface of the laminate, preventing particles from falling off and preventing misalignment between the heat insulating material and the elastic sheet. Furthermore, the film preferably has appropriate flexibility so that it can conform to the shape of the laminate and adhere to at least a portion of the laminate. If the film thickness exceeds 1 mm, it becomes difficult to conform to the shape of the laminate, and cracks or breaks may occur in the film. Therefore, the film thickness is preferably 1 mm or less, more preferably 0.1 mm or less, and even more preferably 0.05 mm or less. On the other hand, there is no particular lower limit to the thickness of the film, but in order to prevent the film from being easily torn due to friction with the battery cell or the like and to obtain the desired strength, the thickness is preferably 0.005 mm or more, and more preferably 0.01 mm or more.

[0207] (Other materials contained in the film) Furthermore, since the film is required to be resistant to high temperatures of the battery cells 20a, 20b, and 20c, it is preferable that the film be flame-retardant, specifically, it is preferable that the film contain an inorganic substance or a flame-retardant material. Other materials that can be contained in the film include inorganic substances such as talc, calcium carbonate, aluminum hydroxide, titanium oxide, vermiculite, zeolite, synthetic silica, zirconia, zircon, barium titanate, zinc oxide, and alumina, and flame-retardant substances such as bromine-based flame retardants, chlorine-based flame retardants, phosphorus-based flame retardants, boron-based flame retardants, silicone-based flame retardants, and nitrogen-containing compounds.

[0208] <Thickness of heat transfer suppression sheet> The thickness of the heat-transfer-suppressing sheet according to this embodiment 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 insulation of the heat-transfer-suppressing sheet.

[0209] [Battery pack] An example of a battery pack using a heat-transfer-suppressing sheet 50 according to an embodiment of the present invention is shown in FIG. 3 above. The configuration and effects of the battery pack will now be described in detail with reference to FIG. 3. As mentioned 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, the heat insulating material 10 can be replaced with other heat insulating materials within the scope of the present invention, in addition to the heat insulating materials having the various structures described above.

[0210] 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 suppressing sheet 50 is as described above.

[0211] In the battery pack 100 configured in this manner, the heat-transfer-suppressing sheet has high thermal insulation properties, so even if a certain battery cell 20a becomes hot, the heat transfer to battery cell 20b can be suppressed because 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. Furthermore, in the battery pack according to this embodiment, the heat-transfer-suppressing sheet is an elastic sheet, so unnecessary pressure is prevented from being applied to the battery cells during charging / discharging or when an abnormality occurs. As a result, deterioration of battery performance can be suppressed and durability can be improved.

[0212] 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.

[0213] In the battery pack 100 configured in this manner, if a battery cell catches fire, it is possible to prevent the flame 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 catches fire, the safety of the passengers can be ensured. Furthermore, the heat transfer suppression sheet 50 can be placed not only between each battery cell, but also between the battery cells 20a, 20b, 20c and the battery case 30, eliminating the need to fabricate new flame retardant materials, etc., and allowing for the easy, low-cost, and safe construction of the assembled battery 100.

[0214] In the battery pack of this embodiment, the heat-transfer-reducing sheet 50, which is 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. Because the heat-transfer-reducing sheet 50 is an elastic sheet, it can tolerate deformation of the battery cells even if the temperature of one of the battery cells rises and the volume expands. Furthermore, in the heat-transfer-reducing sheet of this embodiment, the insulating material and the elastic sheet are joined together at a joint, so they do not shift relative to each other even if there is a gap, and the elastic sheet can fully tolerate deformation of the battery cells. Furthermore, because there is a non-jointed region between the insulating material and the elastic sheet, where no joint exists, a decrease in thermal insulation between the battery cells can be suppressed.

[0215] 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, regardless of the shape 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. [Explanation of symbols]

[0216] 1. Organic Fiber 3. Binder Fiber 4 Inorganic particles 5 Welded area 6,47 Fiber bundles 10,40,60,70,80,90,110 Insulation 11 Fiber layer 14. Matrix 15 Inorganic fibers 19 Laminate 20a, 20b, 20c battery cells 22 Film 30 Battery case 32 Base 33 branches 41a,41b Non-bonded area 42 First area 43 Second area 44a,44b Junction area 45a,45b Opposing area 46a, 46b long side 48a, 48b short side 49a Joint area side end face 49b Non-bonded area side end face 50, 52, 53, 54 Heat transfer suppression sheet 51, 51a, 51b Elastic sheet 55a,55b joint 100 battery packs

Claims

1. a heat insulating material containing inorganic particles; an elastic sheet laminated on at least one of a first surface and a second surface of the heat insulating material, the first surface and the second surface being perpendicular to the thickness direction; a joining portion that joins the heat insulating material and the elastic sheet, A heat transfer suppression sheet, characterized in that the opposing region where the heat insulating material and the elastic sheet face each other has a bonded region where the bonded portion exists and a non-bonded region where the bonded portion does not exist.

2. The heat transfer suppressing sheet according to claim 1 , wherein the non-bonded region is located in a central portion of the facing region.

3. The heat transfer suppressing sheet according to claim 1 , wherein the joining region is located in the opposing region near an end portion.

4. The heat transfer suppressing sheet according to claim 1, wherein the facing region is a region surrounded by three or more sides, and the joining region is located only in a position close to one of the three or more sides.

5. The heat transfer suppressing sheet according to claim 4 , wherein the bonding region is formed so as to extend along the one side.

6. 2. The heat transfer suppression sheet according to claim 1, wherein the opposing region is a rectangular region surrounded by a pair of long sides and a pair of short sides perpendicular to the long sides, and the joining region is located only in a position close to one of the pair of short sides.

7. The heat transfer suppressing sheet according to claim 6, wherein the bonding region is formed so as to extend along the one of the short sides.

8. The joining region is configured by forming the joining portion only in a part of the facing region, The heat transfer suppression sheet according to claim 1, characterized in that the non-bonding region extends from the boundary between the bonding region and the non-bonding region to one end of the facing region, and the insulating material and the elastic sheet are configured to be separated at one end of the facing region.

9. 9. The heat transfer suppressing sheet according to claim 8, wherein the joint portion is formed in a position close to one end of the opposing region that faces the other end.

10. The heat transfer suppressing sheet according to claim 1 , wherein the joint is formed by an adhesive that bonds the heat insulating material and the elastic sheet together.

11. The heat transfer suppressing sheet according to claim 1 , wherein the joint portion is formed by a joint member that joins the heat insulating material and the elastic sheet together.

12. The heat transfer-suppressing sheet according to claim 1 , wherein the elastic sheet contains at least one material selected from the group consisting of synthetic rubber, natural rubber, and thermoplastic elastomer.

13. The heat transfer suppressing sheet according to claim 1 , wherein the heat insulating material further contains organic fibers.

14. 14. The heat-transfer-suppressing sheet according to claim 1, further comprising a film covering an outer peripheral surface of a laminate including the heat insulating material and the elastic sheet.

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

16. An assembled battery comprising a plurality of battery cells and the heat transfer-suppressing sheet according to claim 14, wherein the plurality of battery cells are connected in series or in parallel.

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