Heat transfer suppression sheet and battery pack

Abstract

The present invention provides a heat transfer suppression sheet in which it is possible to accurately align the positions of a heat insulation material and an elastic sheet, and with which it is possible to suppress destruction of a battery case and deterioration of the battery performance due to deformation of a battery cell, to further suppress propagation of heat between battery cells when an abnormality occurs, and to reduce the starting material cost. This heat transfer suppression sheet (50) has: a heat insulation material (10) which contains inorganic particles; elastic sheets (51a, 51b) which are superposed on a first surface (10a) and a second surface (10b) of the heat insulation material (10), the first and second surfaces being orthogonal to the thickness direction of the heat insulation material; and joining parts (55a, 55b) which join the heat insulation material (10) and the elastic sheets (51a, 51b) to each other. Facing regions (45a, 45b) in which the heat insulating material (10) and the elastic sheets (51a, 51b) face each other have joining regions (44a, 44b) in which the joining parts (55a, 55b) are present, and non-joining regions (41a, 41b) in which the joining parts (55a, 55b) are not present.

Description

Heat transfer suppression sheet and assembled battery

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

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

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

[0004] Furthermore, when thermal runaway occurs in a battery cell, gas is generated inside the battery, causing an increase in internal pressure, which causes deformation of the battery cell, and if this deformation is significant, it may even destroy the case. Such battery cell deformation 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 cell repeatedly increases and decreases during charge / discharge, the case repeatedly presses and releases pressure on the battery cell, 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, an insulating sheet 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 insulating sheet and adhering the 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 properties and also serves 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.

[0007] Japanese Patent Application Publication No. 2023-62546

[0008] However, the fire prevention sheet according to 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.

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

[0013] [1] A heat-transfer-suppressing sheet comprising: 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 that are orthogonal to the thickness direction; and a joint portion that joins the heat-insulating material and the elastic sheet, wherein an opposing region where the heat-insulating material and the elastic sheet face each other has a joint region where the joint portion is present and a non-joint region where the joint portion is not present.

[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 heat-transfer-suppressing sheet according to any one of [1] to [7], wherein the bonding portion is formed in only a part of the facing region to form the bonding region, and the non-bonding region extends from a boundary between the bonding region and the non-bonding 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 in 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 portion 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 an 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.

[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.

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

[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-Suppressing Sheet] [First Embodiment] Fig. 1A is a top view showing 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 A-A 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, 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 a pair of elastic sheets 51a, 51b. The heat insulating material 10 contains inorganic particles (not shown). The elastic sheets 51a, 51b are formed by processing an elastic material, described below, into a sheet shape.

[0036] In addition, to prevent misalignment between the insulating material 10 and the elastic sheet 51a, the insulating material 10 and the elastic sheet 51a are joined in multiple regions by joints 55a, thereby forming joint regions 44a. However, in this embodiment, in the opposing region 45a where the insulating material 10 and the elastic sheet 51a face each other, the insulating material 10 and the elastic sheet 51a are not joined to each other except for the joint region 44a, thereby forming non-joint regions 41a. Similarly, the insulating material 10 and the elastic sheet 51a are joined in multiple regions by joints 55b, thereby forming joint regions 44b. Furthermore, in the opposing region 45b where the insulating material 10 and the elastic sheet 51b face each other except for the joint region 44b, the insulating material 10 and the elastic sheet 51b are not joined to each other except for the non-joint region 41b, thereby forming non-joint regions 41b. The materials constituting the 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 the opposing region 45a of the thermal insulating material 10 and the elastic sheet 51a, except for 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 thermal 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 is described below as an example. FIG. 3 is a schematic diagram showing a battery pack according to an embodiment of the present invention. As shown in FIG. 3, the heat-transfer-suppressing sheet 50 can be used by interposing the heat-transfer-suppressing sheet 50 between a plurality of battery cells 20a, 20b, and 20c. The battery pack 100 is constructed by storing the plurality of battery cells 20a, 20b, and 20c in a state connected in series or parallel (the connected state is not shown) in a battery case 30. Note that, for example, lithium-ion secondary batteries are preferably used as the battery cells 20a, 20b, and 20c, but the present invention is not limited thereto and other secondary batteries can also be used.

[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, 51b are joined by joints 55a, 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 the heat insulating material and the elastic sheets to be accurately aligned. However, in this embodiment, the joints 55a, 55b are not formed over the entire surfaces of the facing regions 45a, 45b where the heat insulating material 10 and the elastic sheets 51a, 51b face each other. These facing regions 45a, 45b include joining regions 44a, 44b where the joints 55a, 55b are formed, and non-joint regions 41a, 41b where the joints 55a, 55b are not formed. Therefore, deterioration of the heat insulating performance and compression characteristics due to the presence of the joints 55a, 55b can be suppressed.

[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 environmental impact can be reduced.

[0043] In the present invention, the size of the bonding regions 44a, 44b is not particularly limited, and it is sufficient that non-bonding 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. Furthermore, in the non-bonding 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 a decrease in thermal insulation performance and compression characteristics, it is preferable that the area of ​​the bonding regions 44a, 44b be small, as long as the thermal insulating material 10 and the elastic sheets 51a, 51b are fixed to each other. For example, the area of ​​the bonding 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 positions. However, the center of the main surface of a battery cell is generally the most likely to deform and become the hottest. Therefore, when the heat-transfer-suppressing sheet 50 is interposed between the battery cells, it is preferable that the bonded regions 55a, 55b are not present in the region of the heat-transfer-suppressing sheet 50 that faces the center of the battery cell. 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, when the facing regions 45a, 45b are rectangular as shown in the first embodiment, the central region R0 refers to a 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 is 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 can be determined appropriately taking into account the shape of the facing region, and the region R0 can 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 B-B 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 denoted 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 opposing long sides 46a, 46b and a pair of opposing short sides 48a, 48b 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 the non-joining region 41a.

[0049] Here, for example, a case will be described in which the joints 55a are formed in two regions, near the short sides 48a and 48b surrounding the facing region 45a. While the specific elastic material constituting the elastic sheet will be described 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 distort, 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 insulating material 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 insulating material 10 and the elastic sheet 51a are configured to be separable at one end of the facing region 45a. Therefore, even if the elastic sheet 51a expands or contracts after the thermal insulating material 10 and the elastic sheet 51a are joined together, the thermal insulating material 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 insulating material 10 and peeling of the joint portion 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 the heat-transfer-suppressing sheet 53 according to the second embodiment.

[0052] In the heat transfer-suppressing sheet 53, the bonding portions 55a are formed only in a portion of the area adjacent to the short side 48a. However, the location of the bonding portions 55a can be appropriately selected as needed. For example, the bonding 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 a region 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 of the side or end. 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, it is preferable that the bonding region 44a be 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 region 44a only in a position close to one of the pair of short sides, and it is even more preferable that the joint region 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 region 44a be only in a position close to one of the three or more sides, as in the case of the rectangle. It is even more preferable that the joint region 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 Figs. 4A and 4B are denoted 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 insulating material 10, an elastic sheet 51a laminated on the first surface 10a of the thermal insulating material 10, and a joint 55a joining these together, and further includes a film 22 covering the outer surface of a laminate 19 including the thermal insulating material 10 and the elastic sheet 51a. The position of the joint region 44a and other features are the same as those in the second embodiment. In this embodiment, the elastic sheet 51a is formed to have the same size as the thermal insulating material 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 can prevent, for example, the inorganic particles that make up the thermal insulation material 10 from falling off. Furthermore, if the film 22 is configured to be in close contact with the laminate 19, the thermal insulation 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 insulation material 10 and the elastic sheet 51a in the process 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 an elastic sheet 51a only on the first surface 10a of the thermal insulation material 10. However, the elastic sheet may be laminated on at least one surface of the thermal insulation 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 insulation material 10. Alternatively, the elastic sheet 51 may be sandwiched between a pair of thermal insulation materials 10, or the thermal insulation material 10 may be sandwiched between a pair of elastic sheets 51. Furthermore, various sheets other than the thermal insulation material 10 and the elastic sheet 51 may be laminated. The relative sizes of the thermal insulation material and the elastic sheets are not particularly limited. The elastic sheets 51a and 51b may be smaller or larger than the thermal insulation material 10, or the thermal insulation material 10 and the elastic sheets 51a and 51b may be the same size.

[0059] [Method of Manufacturing Heat Transfer-Inhibiting Sheet] In the present invention, the method of manufacturing the heat transfer-inhibiting sheet is not particularly limited. 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 dried while pressure is applied in the thickness direction. This completes the manufacturing process of the heat transfer-inhibiting sheet 50. The heat transfer-inhibiting sheet 52 shown in FIG. 2 and the heat transfer-inhibiting 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 the third embodiment, the steps up to the step of joining the thermal 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 an example of a method for shrink-packaging the laminate 19 using a shrink film will be described below.

[0061] First, similar to the manufacturing method of 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, and the film is folded to cover the upper surface of the laminate 19 as well. The film on the lower surface of the laminate 19 and the film on the upper surface of the laminate 19 are then bonded by heating while 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, thereby 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 near 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 non-bonded region side end surface 49b, 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 in the traveling direction. Therefore, even after the elastic sheet 51a is cooled and returns to its original size, the adhesion to the film may not be sufficient, or the bend of the elastic sheet 51a may remain.

[0063] Therefore, when a heat-transfer-suppressing sheet 54 having a film 22 covering the outer peripheral surface is manufactured using a shrink device, it is preferable to pass the sheet through a shrink film tunnel with the bonded region side end face 49a facing forward. In this way, the heat insulating material 10 and the elastic sheet 51a are fixed together by the film from the bonded side, but because the heat insulating material 10 and the elastic sheet 51a can be separated at the non-bonded region side end face 49b, it is possible to prevent the elastic sheet 51a 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 bonding portion 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 bonding portion 55a is formed in a region adjacent to one of the short sides 48a, 48b. Furthermore, it is particularly preferable that the bonding portion 55a be located close to the adjacent side. In either case, it is more preferable that the bonding portion 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] [Thermal Insulation Material] The thermal insulation material used in the heat transfer-suppressing sheet according to this embodiment is not particularly limited as long as it has a thermal insulation effect. Thermal conductivity can be used as an index of the thermal insulation effect. In this embodiment, the thermal conductivity of the thermal insulation material is preferably less than 1 (W / m·K), more preferably less than 0.5 (W / m·K), and even more preferably less than 0.2 (W / m·K). Furthermore, the thermal conductivity of the thermal insulation material is more preferably less than 0.1 (W / m·K), more preferably less than 0.05 (W / m·K), and particularly preferably less than 0.02 (W / m·K). The thermal conductivity of the thermal insulation material can be measured in accordance with the "Test Method for Thermal Conductivity of Refractories" described in JIS R 2251.

[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] <Thermal insulation (Structural example S1)> FIG. 7 is a photograph substituting a drawing showing structural example S1 of a thermal insulation used in a heat transfer-suppressing sheet according to an embodiment of the present invention, and FIG. 8 is a photograph substituting a drawing showing an enlarged portion of the thermal insulation shown in FIG. 7.

[0069] 7 and 8 , the thermal insulation material 10 has inorganic particles 4 and organic fibers 1. The thermal insulation 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 covering 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 enhances the flexibility of the insulating material 10 but also makes it easier for the organic fibers 1 to entangle with each other, thereby improving sheet strength. Therefore, damage to a heat-transfer-suppressing sheet including such insulating material 10 can be suppressed. Furthermore, the presence of pores 7 in the insulating material 10 improves the cushioning properties of the entire sheet. Therefore, when the battery cells 20a, 20b, and 20c expand during charging and discharging, the insulating material 10, together with the elastic sheet 51, absorbs the expansion of the battery cells, further suppressing deterioration 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 insulation material 10 and open outward. With the pores 7 configured in this manner, even if the adjacent battery cells 20a, 20b, 20c experience thermal runaway and the thermal insulation material 10 becomes hot and the organic fibers 1 and the like are decomposed, the decomposition gas will not remain inside the sheet but will be released to the outside through the pores 7. Therefore, from this point of view as well, the effect of preventing destruction of the sheet can be obtained.

[0072] Furthermore, when the welded portions 5 on the outer peripheral surfaces of the organic fibers 1 fix the inorganic particles 4 to the organic fibers 1, it is possible to obtain the effect of suppressing the falling off (powdering) of the inorganic particles 4. Therefore, even if, for example, a portion of the battery cells 20a, 20b, 20c expands and applies compressive stress or impact to the heat transfer-suppressing sheet 50, it is possible to further enhance the effect of maintaining the shape of the thermal insulation material 10, and to prevent a decrease in the thermal insulation effect due to compressive deformation of the thermal insulation material 10.

[0073] The welded portion 5 does not need to completely cover the outer periphery of the organic fiber 1, and there may be areas where the welded portion 5 is not present. In the thermal insulation material 10, binder fibers with a sheath-core structure, which will be described later, can be used as the material for the organic fiber 1, but if the sheath portion peels off during the manufacturing process, the core portion of the organic fiber 1 may be partially exposed. Even in such a case, the effect of holding the inorganic particles 4 can be sufficiently obtained.

[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 binder fibers having a core-sheath structure are used as the material for the organic fiber 1, the welded portion 5 contains the second organic material that constitutes the sheath portion. In this embodiment, because the inorganic particles 4 are welded to the surface of the organic fiber 1 by the welded portion 5, the apparent fiber diameter of the organic fiber 1 becomes thicker, which supports the shape of the thermal insulating material 10 and achieves high strength.

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

[0077] As shown in Figure 9, the thermal insulation material 40 has inorganic fibers 15. The thermal insulation material 40 also has a fiber layer 11 formed on at least a portion of a first surface 40a and a second surface (not shown) perpendicular to the thickness direction of the thermal insulation material 40. The fiber layer 11 is formed by welding at least a portion of a plurality of organic fibers 1 to each other at welding portions, and is formed in a layer on the surface (first surface and second surface) of the thermal insulation material 40. In other words, the fiber layer 11 is a layer formed by gathering 10 or more organic fibers 1 on the surface of the thermal insulation material 40, and extends, for example, in stripes, in a direction approximately parallel to the surface.

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

[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 insulation material 40, this fiber layer 11 can absorb the impact given to the insulation material 40, and therefore, even on surfaces where the elastic sheet 51 is not laminated, the effect of preventing the inorganic particles contained in the insulation material 40 from falling off can be obtained.

[0084] <Thermal Insulation (Structural Example S3)> Fig. 10 is a schematic diagram showing structural example S3 of a thermal insulation 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 thermal insulation 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 thermal insulation material 60 shown in Figs. 10 to 12 can be used, for example, in place of the thermal insulation material 10 of the heat-transfer-suppressing sheets 50, 52, 53, and 54.

[0085] As shown in FIGS. 10 to 12 , the thermal insulating material 60 includes inorganic particles 4, organic fibers 1 made of a first organic material, and welded portions 5 covering the outer surfaces of the organic fibers 1. As described above, the welded portions 5 include a second organic material 17 having a melting point lower than that of the first organic material, and inorganic particles 4. In this embodiment, the organic fibers are binder fibers 3 having a sheath-core structure with a core and a sheath covering the outer surface of the core, with the organic fibers 1 corresponding to the core. The welded portions 5 are formed by heating and then cooling the sheath of the binder fibers 3 having a sheath-core structure. Furthermore, as shown in FIG. 12 , the organic fibers 1 and the welded portions 5 containing the inorganic particles 4 form fiber portions 16, and matrix portions 18 containing inorganic particles are formed between the multiple fiber portions 16. When the molten sheath portions are cooled, adjacent organic fibers 1 are fused to each other at contact portions 31, forming a three-dimensional skeleton.

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

[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 periphery of the organic fiber 1, and the organic fiber 1 may be partially exposed. Because the thermal insulation material 60 uses binder fiber 3 with a core-sheath structure, the sheath portion may peel off during the manufacturing process of the thermal insulation material 60, but even if the organic fiber 1 is partially exposed, the effect of the present invention can be fully obtained.

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

[0090] 13 and 14 , the heat insulating material 70 has a matrix 14 containing inorganic particles 4 and organic fibers 1 three-dimensionally oriented in this matrix 14. The organic fibers 1 have welded parts 5 covering at least a part of their surfaces, and the organic fibers 1 are welded to each other by the welded parts 5. Similarly, the inorganic particles 4 are welded to the surfaces of the organic fibers 1, so that the surfaces of the organic fibers 1 are covered with the inorganic particles 4.

[0091] 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 welds 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 a portion of a plurality of organic fibers 1 welded together by welded portions 5. A composite layer 12 is formed between the fiber layer 11 and a base layer 13 containing a matrix 14 and the organic fibers 1. The composite layer 12 is a layer in which a portion of the fiber layer 11 and a portion of the matrix 14 are mixed. Specifically, the composite layer 12 is a region containing a plurality of organic fibers 1 at least a portion of which are welded to each other by welded portions 5, and inorganic particles 4 welded to the organic fibers 1 by welded portions 5.

[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 three-dimensionally oriented in the matrix 14, and 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 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 to each other by the welded portions 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 insulating material 70 can prevent the inorganic particles 4 from falling off from the sheet surface is thought to be similar to that of the insulating material 60 of the above-mentioned structural example S3.

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

[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, thereby obtaining the effect of improving the sheet strength.

[0099] Furthermore, the thermal insulation material 70 has a plurality of voids 7 in the matrix 14 and voids 8 between the plurality of organic fibers 1 that make up the fiber bundle 6, thereby improving the thermal insulation performance. Furthermore, the presence of the voids 8 makes it difficult for the organic fibers 1 to be constrained in the matrix 14, thereby further improving the flexibility and strength of the thermal insulation material 70. The voids 8 do not need to be formed in the entire region between the plurality of organic fibers 1; as long as the voids 8 are formed in at least a portion of the regions between the organic fibers 1, the effect of suppressing heat transfer can be obtained.

[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 that the fiber layer 11 is securely bound to the surface of the thermal insulation material 70. Therefore, a thermal insulation material 70 with high strength can be obtained.

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

[0102] 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 around a portion of the inorganic fibers 15. The organic fibers 1 also have welded portions 5 on a portion of their surface, and at least a portion of the inorganic fibers 15 is welded to the organic fibers 1 by the welded portions 5. Furthermore, at least a portion of the inorganic particles 4 is welded to the organic fibers 1 by the welded portions 5.

[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 a skeleton, providing high strength. Therefore, even if the heat transfer-suppressing sheet 50 is compressed due to expansion of the battery cells 20a, 20b, and 20c during charging and discharging, the shape of the thermal insulation material 80 can be maintained. As a result, it is possible to suppress 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 the highly flexible organic fibers 1, the flexibility of the heat insulating material 80 can be increased, and the organic fibers 1 are more likely to become entangled with the inorganic fibers 15 to form a three-dimensional web structure, thereby improving strength. Furthermore, if the heat insulating material 80 contains the inorganic fibers 15, for example, when the 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, a heat transfer-suppressing sheet that has a good balance of both flexibility and strength can be obtained.

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

[0107] Furthermore, in the insulating material 80, the organic fibers 1 have welded portions 5 that cover at least a portion of the surface. The welded portions 5 refer to areas where the surfaces of the organic fibers 1 melt and then solidify again, and are formed during the manufacturing process of the insulating material 80. When at least a portion of the inorganic fibers 15 are welded to the organic fibers 1 by the welded portions 5, the entangled organic fibers 1 and inorganic fibers 15 are fixed, thereby making it possible to obtain an insulating material 80 with even higher strength.

[0108] Similarly, in this embodiment, the welded portions 5 on the outer peripheral surfaces of the organic fibers 1 also fix the inorganic particles 4 to the organic fibers 1, thereby achieving an even greater powder shedding suppression effect. Therefore, even if, for example, a portion of the battery cells 20 a, 20 b, 20 c expands and applies compressive stress or impact to the heat transfer-suppressing sheet, excellent heat insulating performance can be maintained.

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

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

[0111] <Thermal Insulation (Structural Example S6)> Figure 18 is a photograph substituting a drawing showing structural example S6 of the thermal insulation used in the heat-transfer-suppressing sheet according to an embodiment of the present invention, and Figure 19 is a photograph substituting a drawing showing another region of the thermal insulation shown in Figure 18. Also, Figure 20 is a photograph substituting a drawing showing a cross section of the thermal insulation shown in Figures 18 and 19. In structural example S6 shown in Figures 18 to 20, the same components as those in structural example S4 of the thermal insulation shown in Figures 13 to 15 are designated by the same reference numerals, and detailed description thereof will be omitted. It should be noted that the thermal insulation 90 shown in Figures 18 to 20 can be used, for example, in place of the thermal insulation 10 of the heat-transfer-suppressing sheets 50, 52, 53, and 54.

[0112] 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 including a base 32 and branches 33 extending from the base 32. In this embodiment, the branches 33 extend from the base 32 in four directions: direction D1, direction D2, direction D3, and direction D4. The base 32 and the multiple branches 33 form a skeleton.

[0113] 19 also contains organic fibers 1 having a branched structure made up 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, i.e., directions D1, D2, D3, D4, and D5, and the base 32 is thicker than the multiple branches 33.

[0114] Furthermore, as shown in Figures 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 thermal insulation material 90. Furthermore, a plurality of organic fibers 1 are at least partially welded together in the thermal insulation material 90 to form fiber bundles 6, and gaps 8 are formed between the plurality of organic fibers 1 that make up the fiber bundles 6. Note that, also in FIG. 20, the organic fibers 1 having a branched structure consisting of a base 32 and branches 33 extending in three directions from the base 32 can be seen.

[0116] Furthermore, a fiber layer 11 may be formed on at least a portion of the first and second surfaces perpendicular to the thickness direction of the thermal insulation material 90. The fiber layer 11 is formed by welding at least a portion of a plurality of organic fibers 1 to each other and forming a layer on the surface (first and second surfaces) of the thermal insulation material 90. Furthermore, a composite layer 12 may be formed between the fiber layer 11 and a base layer 13 containing inorganic particles 4 and the organic fibers 1. The composite layer 12 is a layer in which a portion of the fiber layer 11 and a portion of the inorganic particles 4 are mixed. Specifically, the composite layer 12 is a region containing a plurality of organic fibers 1 welded to each other and inorganic particles 4 welded to the organic fibers 1.

[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 to maintain the shape of the thermal insulation material 90. In this embodiment, the bases 32 are formed by fused portions where the organic fibers 1 are fused to each other. Specifically, the bases 32 are portions where a plurality of organic fibers 1 come into contact with each other, melt together, and then solidify, and are therefore thicker than the branches 33. Therefore, the bases 32 can firmly support the entire skeleton, and the strength of the thermal insulation material 90 can be significantly improved.

[0119] In the thermal insulating material 90, at least a portion of the organic fibers 1 have a branched structure consisting of a base 32 and branches 33 extending from the base 32 in at least three directions. The branched structure can be confirmed in a cross-sectional photograph of the thermal insulating material 90, but an easier way to confirm the branched structure is to observe a cross section of the thermal insulating material 90 torn in a plane direction perpendicular to its thickness direction. In this way, by observing the cross section, it is possible to easily confirm that the organic fibers 1 have a branched structure consisting of a base 32 and branches 33 extending from the base 32 in at least three directions. The base 32 and branches 33 will be described in more detail below.

[0120] (Base (Fused Portion)) When binder fibers with a sheath-core structure are used as the material for the thermal insulation material 90, the fused portion is formed by first melting the sheath of the binder fiber by heating and then cooling it in the area where multiple binder fibers are in contact with each other. When binder fibers with a sheath-core structure are used as the material for the thermal insulation material 90, the fused portion contains the second organic material that constitutes the sheath. In this way, when the sheath in the area where multiple binder fibers are in contact is melted by heating in the manufacturing process of the heat transfer-suppressing sheet 50, the amount of melted sheath (second organic material) is greater than when the sheath of a single binder fiber is melted, and a thick fused portion (base 32) is formed after cooling. As a result, the skeleton is firmly supported by the base 32.

[0121] (Branch) The branch 33 extends in at least three directions from the base 32 and has the effect of holding the inorganic particles 4. Furthermore, the base 32 and branch 33 form a skeleton, which can also improve the strength of the heat transfer-suppressing sheet 50. This can achieve a high powder shedding suppression effect. When a core-sheath binder fiber is used as the organic fiber 1, the branch 33 is part of the core-sheath binder fiber and has a core made of a first organic material and a sheath made of a second organic material.

[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, thereby forming a three-dimensional, strong skeleton.

[0123] In the thermal insulation material 90, the multiple support portions 33 extend from the base portion 32, allowing the inorganic particles 4 to be held by these support portions 33. This, combined with the improved sheet strength achieved by the formation of a skeleton, provides a high powder shedding suppression effect. Therefore, for example, even if a portion of the battery cells 20a, 20b, and 20c expands during charging and discharging, causing compressive stress or impact on the heat transfer-suppressing sheet, the shape of the thermal insulation material 90 can be maintained. As a result, shedding (powder shedding) of the inorganic particles 4 can be suppressed, and a decrease in the insulating effect of the thermal insulation material 90 due to compressive deformation can be prevented.

[0124] The mechanism by which the inorganic particles 4 can be prevented from falling off the surface of the insulating material 90 is thought to be due to the same effect as that of the insulating material 60 of the above structural example S3, as well as the effect of the support parts 33 to hold the inorganic particles 4. Furthermore, when the inorganic particles 4 are fused to the surface of the organic fibers 1, the organic fibers 1 appear to have a thicker fiber diameter, which makes them stronger than the strength of the organic fibers 1 alone, and also provides a high holding effect for the inorganic particles 4.

[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, thereby obtaining 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 causes the organic fibers 1 to be in a completely unconstrained state, further improving the flexibility and strength of the heat insulating material 90. The voids 8 do not need to be formed in the entire region between the plurality of organic fibers 1; as long as the voids 8 are formed in at least a portion of the regions between the organic fibers 1, the effect of suppressing heat transfer can be obtained.

[0128] Furthermore, since the insulating material 90 has the fiber bundles 6 and the fiber layer 11, it can obtain a sheet strength that is even higher than when the organic fibers 1 are dispersed. Furthermore, when the fiber layer 11 is present, the fiber layer 11 is not simply disposed on the base layer 13, but has a composite layer 12 between the fiber layer 11 and the base layer 13, in which part of the fiber layer 11 and part of the inorganic particles 4 are mixed, so that the fiber layer 11 is securely bound to the surface of the insulating material 90. Therefore, the strength of the insulating material 90 can be improved.

[0129] <Thermal Insulation (Structural Example S7)> Figure 21 is a photograph, substitute for a drawing, showing structural example S7 of the thermal insulation used in the heat-transfer-suppressing sheet according to an embodiment of the present invention, and Figure 22 is a photograph, substitute for a drawing, showing an enlarged portion of the thermal insulation shown in Figure 21. In structural example S7 shown in Figures 21 and 22, the same components as those in structural example S2 of the thermal insulation shown in Figure 9 are designated by the same reference numerals, and detailed description thereof will be omitted. Note that the thermal insulation 110 shown in Figures 21 and 22 can be used, for example, in place of the thermal insulation 10 of the heat-transfer-suppressing sheets 50, 52, 53, and 54.

[0130] 21 and 22 , the thermal insulating material 110 includes inorganic particles 4 and organic fibers 1. A first region 42 having streak-like fiber bundles made of a plurality of organic fibers 1 and a second region 43 having no fiber bundles 47 are formed on the surface of the thermal insulating material 110. In this specification, the fiber bundles 47 are 10 or more organic fibers 1 entangled with one another, and extend in streak-like fashion in a direction substantially parallel to the surface of the thermal insulating material 110.

[0131] That is, when the surface of the thermal insulating material 110 is observed, as shown in Fig. 22, a state in which a plurality of organic fibers 1 are entangled is observed in the first region 42. On the other hand, in the second region 43, although a few organic fibers 1 are observed in some places, fiber bundles 47 in which a plurality of organic fibers 1 are entangled are not observed. In this embodiment, the first region 42 and the second region 43 have a sea-island structure, and the second region 43, which corresponds to the island portion, is formed so as to be surrounded by the first region 42, which corresponds to the sea portion.

[0132] In the thermal insulation material 110, fiber bundles 47 formed by intertwining organic fibers 1 are present on the surface of the thermal insulation material 110 in a streak-like manner, thereby improving the strength of the thermal insulation material 110. Furthermore, the entire surface is not covered with fiber bundles 47, and there are first regions 42 where fiber bundles 47 are present and second regions where fiber bundles 47 are not present, thereby improving the flexibility of the thermal insulation material 110. Furthermore, because the fiber bundles 47 are present on the surface of the thermal insulation material 110, even if the thermal insulation material 110 is subjected to impact or pressure, the fiber bundles 47 can absorb and mitigate the impact or pressure. Therefore, shedding (powdering) of the inorganic particles 4 can be suppressed, and a decrease in the thermal insulation performance of the thermal insulation material 110 can be prevented.

[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 makes it possible to obtain even greater strength.

[0134] It is preferable that the length of the fiber bundles 47 formed to extend on the surface of the thermal insulation material 110 be relatively long. An example of a method for specifying the length of the fiber bundles 47 will be described with reference to FIG. 23 . As shown in FIG. 23 , rectangular imaginary frames 21 are placed along the fiber bundles 47 extending in stripes on the surface of the thermal insulation material 110. In this embodiment, the size of the imaginary frames 21 is 5 mm square, and these imaginary frames 21 are placed so as to be continuous with each other. In this case, if there are fiber bundles 47 that penetrate at least three continuous imaginary frames 21, it can be determined that the fiber bundles 47 have a sufficient effect of improving the strength of the thermal insulation material 110.

[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 various properties, such as suppressing powder shedding, further improving strength, and maintaining shape. Therefore, as shown in Figures 1 to 6, heat transfer-suppressing sheets in which elastic sheets 51a and 51b are laminated on the thermal insulation materials 10, 40, 60, 70, 80, 90, and 110 can achieve 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 material 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, it is preferable to use particles made of at least one inorganic material selected from oxide particles, carbide particles, nitride particles, and inorganic hydrate particles, and it is more preferable to use oxide particles. Furthermore, the shape of the inorganic particles 4 is not particularly limited, but it is preferable to include at least one type selected from nanoparticles, hollow particles, and porous particles. Specifically, it is also possible to use inorganic balloons such as silica nanoparticles, metal oxide particles, microporous particles, and hollow silica particles, particles made of a thermally expandable inorganic material, particles made of a hydrous porous body, and the like.

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

[0143] (Average primary particle diameter of oxide particles: 0.001 μm or more and 50 μm or less) The particle diameter of the oxide particles can affect the effect of reflecting radiant heat, so limiting the average primary particle diameter to a predetermined range can achieve even higher thermal insulation. That is, when the average primary particle diameter of the oxide particles is 0.001 μm or more, the particles are sufficiently larger than the wavelength of light that contributes to heating and efficiently diffusely reflect light, thereby suppressing radiant heat transfer within the thermal insulation material in high-temperature regions of 500°C or more, thereby further improving thermal insulation. On the other hand, when the average primary particle diameter of the oxide particles is 50 μm or less, the number and number of contact points between particles do not increase even when compressed, making it difficult to form a path for conductive heat transfer, thereby reducing the impact on thermal insulation, particularly in normal temperature regions 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 nanometer order that are spherical or nearly spherical and have an average primary particle diameter of less than 1 μm. Nanoparticles have a low density, which suppresses conductive heat transfer. Using nanoparticles as the first inorganic particles further refines the three-dimensionally connected pores 7, thereby achieving excellent thermal insulation that suppresses convective heat transfer. Therefore, nanoparticles are preferred because they can suppress heat conduction between adjacent nanoparticles during normal battery operation at room temperature. Furthermore, using nanoparticles with a small average primary particle diameter as oxide particles can suppress an increase in conductive heat transfer through the insulating material, even when the insulating material is compressed due to expansion associated with thermal runaway in the battery cell, increasing its internal density. This is thought to be because nanoparticles are prone to forming small voids between particles due to electrostatic repulsion, and their low bulk density allows the particles to be packed together to provide cushioning.

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

[0148] (Average primary particle diameter of nanoparticles: 1 nm or more and 100 nm or less) Limiting the average primary particle diameter of nanoparticles to a predetermined range can achieve even higher thermal insulation. That is, when the average primary particle diameter of nanoparticles is 1 nm or more and 100 nm or less, convective heat transfer and conductive heat transfer within the thermal insulation material can be suppressed, particularly in the temperature range below 500°C, thereby further improving thermal insulation. Furthermore, even when compressive stress is applied, the voids remaining between the nanoparticles and the contact points between many particles suppress conductive heat transfer, thereby maintaining the thermal insulation properties of the thermal insulation material. The average primary particle diameter of the nanoparticles is more preferably 2 nm or more, and even more preferably 3 nm or more. On the other hand, the average primary particle diameter of the nanoparticles is more preferably 50 nm or less, and even more preferably 10 nm or less.

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

[0150] For example, aluminum hydroxide contains about 35% water of crystallization, and as shown in the following formula, it thermally decomposes, releasing the water of crystallization and exhibiting an endothermic effect. After releasing the water of crystallization, it becomes a porous alumina (Al ２ O ３ ) and functions as a heat insulating material. 2Al(OH) ３ →Al ２ O ３ +3H ２ O

[0151] The heat transfer-suppressing sheet 50 according to this embodiment is preferably interposed between battery cells, for example. In a battery cell that has experienced thermal runaway, the temperature rises sharply to over 200°C and continues to rise to around 700°C. Therefore, the inorganic particles are preferably made of inorganic hydrates whose thermal decomposition onset temperature is 200°C or higher. The thermal decomposition onset temperatures of the inorganic hydrates listed above are approximately 200°C for aluminum hydroxide, approximately 330°C for magnesium hydroxide, approximately 580°C for calcium hydroxide, approximately 200°C for zinc hydroxide, approximately 350°C for iron hydroxide, approximately 300°C for manganese hydroxide, approximately 300°C for zirconium hydroxide, and approximately 300°C for gallium hydroxide. These inorganic hydrates are all preferred because they substantially overlap the temperature range of the rapid temperature rise in a battery cell that has experienced thermal runaway and can efficiently suppress temperature rise.

[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 the average particle diameter is too large, it takes a certain amount of time for the first inorganic particles (inorganic hydrate) near the center of the heat insulating material to reach their thermal decomposition temperature, and the first inorganic particles near the center of the sheet may not be completely thermally decomposed. For this reason, the average secondary particle diameter of the inorganic hydrate particles is preferably 0.01 μm or more and 200 μm or less, and more preferably 0.05 μm or more and 100 μm or less.

[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 hydrous porous materials 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 heat transfer or conductive heat transfer within the heat insulating material can be suppressed in a temperature range of less than 500°C, and the heat insulating properties of the heat insulating material can be further improved. As the inorganic balloons, at least one selected from shirasu balloons, silica balloons, fly ash balloons, barite balloons, and glass balloons can be used.

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

[0157] (Average Particle Diameter of Inorganic Balloons: 1 μm or More and 100 μm or Less) The average particle diameter of the inorganic balloons is preferably 1 μm or more and 100 μm or less.

[0158] <Second inorganic particles> When two types of inorganic particles are contained in the heat insulating material, the second inorganic particles are not particularly limited as long as they are different from the first inorganic particles in terms of material, particle size, etc. Examples of the second inorganic particles that can be used include oxide particles, carbide particles, nitride particles, inorganic hydrate particles, silica nanoparticles, metal oxide particles, inorganic balloons such as microporous particles and hollow silica particles, particles made of a thermally expandable inorganic material, and particles made of a hydrous porous body, the details of which are as described above.

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

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

[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, and is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less, based on the total mass of the inorganic particles.

[0162] (Average primary particle diameter of second inorganic particles) When second inorganic particles made of a metal oxide are contained in a thermal insulating material, if the average primary particle diameter of the second inorganic particles is 1 μm or more and 50 μm or less, radiation heat transfer can be efficiently suppressed in a high temperature range of 500° C. or more. The average primary particle diameter of the second inorganic particles is more preferably 5 μm or more and 30 μm or less, and most preferably 10 μm or less.

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

[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, with the melting point of the first organic material being higher than that of the second organic material. When the binder fiber with a core-sheath structure is used as a material, the core corresponds to the organic fiber 1 in the thermal insulation material. Furthermore, during the manufacturing process of the thermal insulation material, the second organic material constituting the sheath melts and then solidifies again, so that the sheath becomes the welded portion 5 in the thermal insulation material.

[0166] (Organic Fiber Content) In this embodiment, if the content of organic fiber 1 in the thermal insulation material is appropriately controlled, a sufficient skeleton reinforcing effect can be obtained. The content of organic fiber 1 is preferably 2 mass% or more, and more preferably 4 mass% or more, relative to the total mass of the thermal insulation material. Furthermore, if the content of organic fiber 1 is too high, the content of inorganic particles 4 will relatively decrease. Therefore, in order to obtain the desired thermal insulation performance, the content of organic fiber is preferably 10 mass% or less, and more preferably 8 mass% or less, relative to the total mass of the thermal insulation material.

[0167] (Fiber length of organic fibers) The fiber length of the organic fibers 1 is not particularly limited, but from the viewpoint of ensuring moldability and processability, the average fiber length of the organic fibers is preferably 10 mm or less. On the other hand, from the viewpoint of making the organic fibers 1 function as a skeleton and ensuring the compressive strength of the thermal insulating material, the average fiber length of the organic fibers 1 is preferably 0.5 mm or more.

[0168] (Binder Fiber) When a binder fiber having a core-sheath structure is used as the material for the organic fiber 1, the melting point of the first organic material constituting the core, i.e., the organic fiber 1, is not particularly limited as long as it is higher than the melting point of the second organic material constituting the sheath present on the outer surface of the organic fiber 1. Binder fibers 3 having such a core-sheath structure are generally commercially available, and the materials constituting the core and sheath may be the same or different. Examples of binder fibers in which the core (first organic material) and sheath (second organic material) are made of the same material but have different melting points include those in which the core and sheath are made of polyethylene terephthalate, polypropylene, or nylon. Examples of binder fibers in which the core and sheath are made of different materials include those in which the core is made of polyethylene terephthalate and the sheath is made of polyethylene, and those in which the core is made of polypropylene and the sheath is made of polyethylene.

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

[0171] When a core-sheath binder fiber is used as a material for the insulating material, the sheath can be melted while leaving the core intact when the material mixture is heated during the manufacturing process. After cooling, the outer surface of the core (organic fiber 1) is coated with a second organic material containing inorganic particles 4, thereby holding the inorganic particles 4 in place. The organic fiber 1 with the inorganic particles 4 fused to it appears to have a thicker fiber diameter, resulting in a higher strength than the organic fiber 1 alone. Furthermore, because the binder fibers are present in an irregular orientation in the mixture, the organic fibers 1 are fused to each other in areas where the binder fibers contact each other, forming a three-dimensional skeleton. As a result, the overall shape of the insulating material can be maintained with even greater strength.

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

[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. However, softening accompanied by a change in shape is also considered to be a type of melting deformation. The melting point of the binder fiber sheath can be measured, for example, by the following method. The binder fiber to be measured is placed in contact with glass fiber, which has a higher melting point, and heated from room temperature to, for example, 200°C at a heating rate of 5°C / min, and then cooled to room temperature. If the surface of the binder fiber melts and deforms and the area in contact with the glass fiber is fused, or if the cross-sectional shape of the binder fiber changes, it can be determined that the melting point of the second organic material constituting the sheath is 200°C or lower. In this embodiment, the heating temperature is varied and the fusion state between the binder fiber and the glass fiber or the cross-sectional shape of the binder fiber after cooling is observed using the above method, thereby determining the melting point of the second organic material constituting the sheath.

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

[0176] <Inorganic Fibers> As the inorganic fibers 15, a single inorganic fiber may be used, or two or more types of inorganic fibers may be used in combination. Examples of inorganic fibers include ceramic fibers such as silica fiber, alumina fiber, alumina silicate fiber, zirconia fiber, carbon fiber, soluble fiber, refractory ceramic fiber, aerogel composite, magnesium silicate fiber, alkaline earth silicate fiber, potassium titanate fiber, silicon carbide fiber, and potassium titanate whisker fiber; glass fibers such as glass fiber, glass wool, and slag wool; and mineral fibers other than these fibers, such as rock wool, basalt fiber, wollastonite, and mullite fiber. These inorganic fibers are preferred in terms of heat resistance, strength, and availability. Among the inorganic fibers, silica-alumina fiber, alumina fiber, silica fiber, rock wool, alkaline earth silicate fiber, and glass fiber are particularly preferred from the standpoint of handleability.

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

[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 the present embodiment, when the heat insulating material contains inorganic fibers, the content of the inorganic fibers is preferably 3 mass % or more and 15 mass % or less with respect to the total mass of the heat insulating material.

[0181] The content of inorganic fibers is more preferably 5% by mass or more and 10% by mass or less of the total mass of the thermal insulating material. By setting the content in this range, the shape retention, compressive force resistance, wind pressure resistance, and inorganic particle retention ability of the inorganic fibers are exhibited in a balanced manner. Furthermore, by appropriately controlling the content of inorganic fibers, the organic fibers 1 and the inorganic fibers are entangled with each other to form a three-dimensional network, which further improves the effect of retaining the inorganic particles 4 and other compounding materials described below.

[0182] <Hot Melt Powder> In this embodiment, in addition to the organic fibers 1 and inorganic particles 4, the insulating material may contain hot melt powder as a binder material. The hot melt powder is a powder that contains, for example, a third organic material different from the first organic material and the second organic material, and has the property of melting when heated. When the hot melt powder is added to a mixture used to manufacture the insulating material and heated, the hot melt powder melts, and when cooled, it hardens in a state that includes the surrounding inorganic particles 4. This further prevents the inorganic particles 4 from falling off from the insulating material.

[0183] Hot melt powders with various melting points can be used, but a hot melt powder with an appropriate melting point can be selected taking into account the melting points of the core and sheath of the binder fiber used. Specifically, if the third organic material constituting the hot melt powder has a melting point lower than that of the first organic material constituting the organic fiber, the heating temperature can be set to melt the sheath and hot melt powder while leaving the core. For example, if the melting point of the hot melt powder is lower than that of the sheath, the heating temperature during production can be set between the melting points of the core and the sheath, making it even easier to set the heating temperature.

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

[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 margin in the heating step can be expanded, making it easier to set the temperature to obtain the desired structure. For example, the melting point of the first organic material is preferably 60°C or more higher than that of the third organic material, more preferably 70°C or more higher, and even more preferably 80°C or more higher.

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

[0188] <Other Compounding Materials> The heat insulating material may further contain, as necessary, a binder, a colorant, etc. All of these are useful for the purposes of reinforcing the heat insulating material, improving its formability, etc., and the total amount of these is preferably 10 mass % or less based on the total mass of the heat insulating material.

[0189] <Method of Manufacturing Insulating Material> The method of manufacturing the insulating material will be described in detail below, particularly using the method of manufacturing the insulating material of structural example S2 as an example. For example, a binder fiber (not shown) having a core-sheath structure, inorganic particles 4, and inorganic fibers 15 are added to a mixer such as a V-type mixer in a predetermined ratio to prepare a mixture. As described above, it is preferable to use a fiber having a core-sheath structure with a core made of a first organic material and a sheath made of a second organic material as the binder fiber. In this case, the melting point of the first organic material is higher than the melting point of the second organic material.

[0190] The resulting mixture is then placed in a mold and pressurized with a press or the like. The resulting molded body is heated to melt the sheath of the binder fiber. The heated molded body is then cooled, and the second organic material constituting the molten sheath and the inorganic particles 4 present around the binder fiber are fused to the core (organic fiber 1), and are also fused to each other in areas where the binder fibers were in contact with each other. This allows for the production of a sheet-shaped insulating material 40.

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

[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. On the other hand, the heating temperature is preferably set to be 10° C. or more lower, more preferably 20° C. or more lower, than the melting point of the first organic material constituting the core.

[0195] The heating time is not particularly limited, but is preferably set to a time sufficient to melt the sheath, for example, from 3 minutes to 15 minutes.

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

[0197] As described above, the insulating material may be manufactured by either a dry method or a wet method, but it is preferable to use the dry method. When using the dry method, inorganic particles 4 suitable for the dry method are used, and a solvent such as water, which is required when forming by a wet method, is not added to the mixture. However, to prevent powder such as inorganic particles 4 from flying around during the manufacturing of the insulating material and making it difficult to handle the raw materials, a small amount of solvent such as water can be added within the range required for the dry method. For example, adding a small amount of solvent such as water to the mixture can suppress the scattering of inorganic particles during manufacturing.

[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 of an elastic material processed into a sheet shape. Any known elastic material can be used. Specifically, sheets made of rubber or thermoplastic elastomer that have 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] (Size of Elastic Sheet) The thickness of the elastic sheet is not particularly limited, but in order to effectively obtain the effects of the elastic sheet, it is preferable that the thickness is 1 mm or more and 10 mm or less.

[0202] [Joint] 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, and tag pins 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, for example, 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, for example, an adhesive containing a halogen-based, phosphorus-based, silicone-based, or nitrogen-based flame-retardant material. It is also effective to use the flame-retardant inorganic adhesive in combination with a flame-retardant organic adhesive.

[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 polyimide, polycarbonate, polyethylene terephthalate (PET: Poly Ethylene Terephthalate), p-phenylene sulfide, polyetherimide, cross-linked polyethylene, flame-retardant chloroprene rubber, polyvinyl fluoride, rigid vinyl chloride, polybutylene terephthalate, polytetrafluoroethylene (PTFE: Poly Tetra Fluoro Ethylene), perfluoroalkoxyalkane (PFA: Perfluoroalkoxy Alkane), tetrafluoroethylene-hexafluoropropylene copolymer (FEP: Fluorinated Ethylene Propylene), tetrafluoroethylene-ethylene copolymer (ETFE: Ethylene Tetra Fluoro Ethylene), rigid polyvinyl chloride (PCV: Polyvinyl Examples of the film include films made of polyethylene terephthalate (PET), flame-retardant PET, nylon, acrylic, epoxy resin, polyurethane, polyether ether ketone, polycarbonate, aramid, polystyrene, polyether sulfone, polyamide imide, polyacrylonitrile, polyethylene, polypropylene, polyamide, etc.

[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 a 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 a 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 a 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 and the like from falling off, and also preventing misalignment between the heat insulating material and the elastic sheet. Furthermore, the film preferably has appropriate flexibility so that at least a portion of the film adheres to the shape 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 film thickness, but in order to prevent tearing due to friction with battery cells and the like and to obtain the desired strength, it is preferably 0.005 mm or more, and more preferably 0.01 mm or more.

[0207] (Other Materials Included in the Film) Furthermore, since the film is required to be resistant to high temperatures of the battery cells 20 a, 20 b, and 20 c, it is preferable that the film be flame-retardant, and specifically, it is preferable that the film contain an inorganic substance or a flame-retardant material. Examples of other materials included 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 materials 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-Suppressing 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 Assembly] An example of a battery assembly using the heat-transfer-suppressing sheet 50 according to an embodiment of the present invention is as shown in FIG. 3 above. The configuration and effects of the battery assembly will now be described in detail with reference to FIG. 3. As 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-reducing 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 the 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 in the event of an abnormality. 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 ignites, the flame can be prevented from spreading outside the battery case 30. For example, the battery pack 100 according to this embodiment may be used in an electric vehicle (EV) or the like and placed under the floor of a passenger compartment. In this case, even if a battery cell ignites, the safety of the passengers can be ensured. Furthermore, since the heat transfer suppression sheet 50 can be placed not only between the battery cells but also between the battery cells 20a, 20b, and 20c and the battery case 30, there is no need to fabricate additional flame retardant materials, and a safe battery pack 100 can be easily configured at low cost.

[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 includes an elastic sheet, deformation of the battery cells can be tolerated 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 by 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, a non-jointed region, where no joint exists, exists between the insulating material and the elastic sheet, which can suppress a decrease in thermal insulation between the battery cells.

[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 without being affected by the shapes of the battery cells 20a, 20b, 20c and the battery case 30. Specifically, it can be applied to cylindrical batteries, flat batteries, etc. in addition to prismatic batteries.

[0216] Although various embodiments have been described above with reference to the drawings, it goes without saying that the present invention is not limited to such examples. It is clear that a person skilled in the art can conceive of various modifications or alterations within the scope of the claims, and it is understood that these also naturally fall within the technical scope of the present invention. Furthermore, the components of the above-described embodiments may be combined in any manner without departing from the spirit of the invention.

[0217] This application is based on a Japanese patent application (Patent Application No. 2024-028786) filed on February 28, 2024, the contents of which are incorporated herein by reference.

[0218] REFERENCE SIGNS LIST 1 organic fiber 3 binder fiber 4 inorganic particle 5 welded portion 6, 47 fiber bundle 10, 40, 60, 70, 80, 90, 110 heat insulating material 11 fiber layer 14 matrix 15 inorganic fiber 19 laminate 20a, 20b, 20c battery cell 22 film 30 battery case 32 base 33 support portion 41a, 41b non-bonded region 42 first region 43 second region 44a, 44b bonded region 45a, 45b opposing region 46a, 46b long side 48a, 48b short side 49a bonded region side end surface 49b non-bonded region side end surface 50, 52, 53, 54 heat transfer suppressing sheet 51, 51a, 51b elastic sheet 55a, 55b bonded portion 100 battery packs

Claims

1. A heat-transfer-suppressing sheet comprising: a thermal insulating material containing inorganic particles; an elastic sheet laminated on at least one of a first surface and a second surface of the thermal insulating material that are orthogonal to the thickness direction; and a joint portion joining the thermal insulating material and the elastic sheet, wherein an opposing region where the thermal insulating material and the elastic sheet face each other has a joint region where the joint portion is present and a non-joint region where the joint portion is not present.

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

3. The heat transfer suppressing sheet according to claim 1, wherein the joining region is located in the vicinity of an end of the facing region.

4. The heat transfer suppression sheet according to claim 1, wherein the facing region is an area surrounded by three or more sides, and the joining region is located only in proximity to one of the three or more sides.

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

6. A heat transfer suppression sheet as described in claim 1, characterized in that 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 bonding 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 area is formed so as to extend along the one of the short sides.

8. The heat transfer suppressing sheet according to claim 1, wherein the bonding portion is formed in only a portion of the opposing region to form the bonding region, and the non-bonding region extends from the boundary between the bonding region and the non-bonding region to one end of the opposing region, and the heat insulating material and the elastic sheet are configured to be separable at one end of the opposing region.

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

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 is formed by a joint member that joins the heat insulating material and the elastic sheet.

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 suppression sheet according to claim 1, wherein the heat insulating material further contains organic fibers.

14. The heat transfer-suppressing sheet according to any one of claims 1 to 13, further comprising a film covering the outer periphery of a laminate including the heat insulating material and the elastic sheet.

15. A battery pack comprising a plurality of battery cells and the heat transfer suppression sheet according to any one of claims 1 to 13, the plurality of battery cells being connected in series or parallel.

16. A battery pack comprising a plurality of battery cells and the heat transfer suppression sheet according to claim 14, the plurality of battery cells being connected in series or parallel.

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