Heat transfer suppression sheet and battery pack

Abstract

To facilitate handling and suppress destruction of a battery case and reduction in performance of a battery caused by deformation of battery cells while suppressing propagation of heat between the battery cells in the case of abnormality.SOLUTION: A heat transfer suppression sheet 10 comprises: a tabular first elastic member (first outer member) 1 and a second elastic member (second outer member) 2 which are disposed while being opposed to each other; and a tabular heat insulation material (intermediate member) 3 which is disposed therebetween. The first elastic member 1 and the second elastic member 2 include a first projection 1a and a second projection 2a on surfaces opposed to the heat insulation material 3. The heat insulation material 3 includes a first recess 3a and a second recess 3b on surfaces opposed to the first elastic member 1 and the second elastic member 2. The first projection 1a is fitted into the first recess 3a, and the second projection 2a is fitted into the second recess 3b. Further, in a view in a lamination direction of the heat transfer suppression sheet 10, all the first projections 1a are provided at different positions from positions of all the second projections 2a.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

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

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

[0004] Furthermore, if thermal runaway occurs in a battery cell, gas is generated inside the battery, causing the internal pressure to rise and deforming the battery cell. If this deformation is significant, the battery cell itself may be destroyed. Such deformation of battery cells occurs slightly even when battery cells assembled into a battery are subjected to charge / discharge cycles (i.e., during "normal use"). When the internal pressure of the battery cells repeatedly increases and decreases during charging and discharging, the battery cells are repeatedly compressed and relaxed, causing a decrease in battery performance.

[0005] As a method for suppressing the performance degradation caused by the expansion of the battery cells, a method of placing an elastic heat insulating sheet between the battery cells has been proposed. For example, Patent Document 1 proposes a battery insulating material that undergoes compressive deformation in response to the expansion of battery cells, thereby preventing damage to the battery cells. The insulating material described in Patent Document 1 includes an insulating part and a buffer part that is more susceptible to compressive deformation than the insulating part, and the buffer part is laminated on the insulating part.

[0006] Furthermore, Patent Document 2 proposes an energy storage system in which energy storage cells, i.e., battery cells, are insulated by a device. This device is formed to separate the energy storage cells from each other, and for example, the device disclosed has a base made of a heat-resistant and dimensionally stable material on which protrusions made of a heat-resistant elastic material are formed. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2021-140968 [Patent Document 2] Special Publication No. 2020-532078 Summary of the Invention [Problem to be solved by the invention]

[0008] However, the battery insulating material described in Patent Document 1 is a laminate of an insulating part and a buffer part, and is difficult to handle if the two are not bonded together. Also, a thermal insulating material has been proposed in which the buffer part is disposed in a recessed portion on the surface of the insulating part, but if the buffer part is disposed on both sides of the insulating part, the insulating part becomes too thin in some places, resulting in reduced insulating properties.

[0009] Furthermore, in the device described in Patent Document 2, only the multiple protrusions are in direct contact with the battery cells, and when the battery cells repeatedly expand and contract, the protrusions are prone to deterioration.

[0010] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a heat transfer suppression sheet that is easy to handle and can suppress the propagation of heat between battery cells in the event of an abnormality, while suppressing destruction of the battery case and deterioration of battery performance due to deformation of the battery cells, and a battery pack that can suppress the propagation of heat between battery cells, while suppressing destruction of the battery case and deterioration of battery performance. [Means for solving the problem]

[0011] The above object of the present invention is achieved by the heat transfer-suppressing sheet having the following configuration (1) or (2).

[0012] (1) A first outer member and a second outer member, each of which is a plate-like member, disposed opposite to each other; a plate-shaped intermediate member disposed between the first outer member and the second outer member, a heat transfer suppressing sheet in which the first outer member has a first convex portion provided on a surface facing the intermediate member, the second outer member has a second convex portion provided on a surface facing the intermediate member, and the intermediate member has a first concave portion provided on a surface facing the first outer member and a second concave portion provided on a surface facing the second outer member, the first convex portion being fitted into the first concave portion and the second convex portion being fitted into the second concave portion, the first outer member and the second outer member are made of either a heat insulating material or an elastic material, the intermediate member is made of the other of the heat insulating material and the elastic member, A heat transfer suppression sheet, characterized in that, when viewed from the stacking direction of the first outer member, the intermediate member, and the second outer member, all of the first convex portions are provided at positions different from the positions of all of the second convex portions.

[0013] (2) a first outer member and a second outer member, each of which is a plate-like member, disposed opposite to each other; a plate-shaped intermediate member disposed between the first outer member and the second outer member, a heat transfer suppressing sheet in which the first outer member has a first recess provided on a surface facing the intermediate member, the second outer member has a second recess provided on a surface facing the intermediate member, and the intermediate member has a first convex portion provided on a surface facing the first outer member and a second convex portion provided on a surface facing the second outer member, the first convex portion being fitted into the first recess and the second convex portion being fitted into the second recess, the first outer member and the second outer member are made of either a heat insulating material or an elastic material, the intermediate member is made of the other of the heat insulating material and the elastic member, A heat transfer suppression sheet, characterized in that, when viewed from the stacking direction of the first outer member, the intermediate member, and the second outer member, all of the first convex portions are provided at positions different from the positions of all of the second convex portions.

[0014] Furthermore, preferred embodiments of the present invention relating to the heat transfer-suppressing sheet relate to the following (3) to (12).

[0015] (3) The first outer member and the second outer member are made of elastic members, The heat-transfer-suppressing sheet according to (1) or (2), wherein the intermediate member is made of a heat insulating material.

[0016] (4) The heat transfer-suppressing sheet according to any one of (1) to (3), characterized in that there are gaps between the first convex portions and the first concave portions, and between the second convex portions and the second concave portions.

[0017] (5) The heat-transfer-suppressing sheet according to any one of (1) to (4), wherein the first convex portions and the second convex portions have a granular or linear extending shape.

[0018] (6) The first protrusion and the second protrusion are provided in plural, the member on which the first convex portion and the second convex portion are provided is made of an elastic member, The heat transfer-suppressing sheet according to any one of (1) to (5), wherein the number density of the first convex portions and the second convex portions is higher in a central region of the surface on which the first convex portions and the second convex portions are formed than in a peripheral region.

[0019] (7) The first protrusion and the second protrusion are provided in plural, the member on which the first convex portion and the second convex portion are provided is made of a heat insulating material, The heat transfer-suppressing sheet according to any one of (1) to (5), wherein the number density of the first convex portions and the second convex portions is lower in a central region of the surface on which the first convex portions and the second convex portions are formed than in a peripheral region.

[0020] (8) The first convex portion and the second convex portion protrude in a substantially hemispherical shape, The heat-transfer-suppressing sheet according to any one of (1) to (7), wherein the first recess and the second recess are recessed in a substantially hemispherical shape.

[0021] (9) The first outer member and the second outer member are each made of an elastic member having a flat portion, and the first convex portion and the second convex portion provided on the flat portion, the intermediate member is made of a heat insulating material, The heat transfer suppressing sheet described in (1) is characterized in that the distance between any first convex portion on the first outer member and the second convex portion located closest to the any first convex portion is greater than the distance between the any first convex portion and the flat portion of the second outer member at a position opposite the any first convex portion.

[0022] (10) The intermediate member is made of an elastic member having a flat portion and the first convex portion and the second convex portion provided on the flat portion, the first outer member and the second outer member are made of a thermal insulating material, The heat-transfer-suppressing sheet according to (2), wherein the back surface side of the first convex portion of the intermediate member is a flat portion.

[0023] (11) The heat-transfer-suppressing sheet according to any one of (1) to (10), wherein the elastic member is made of rubber or elastomer.

[0024] (12) The heat-transfer-suppressing sheet according to any one of (1) to (11), wherein the heat insulating material contains at least one of inorganic particles, organic fibers, and inorganic fibers.

[0025] The above object of the present invention is also achieved by the following configuration (13) relating to the battery pack.

[0026] (13) A battery pack comprising a plurality of battery cells and the heat transfer-suppressing sheet according to any one of (1) to (12), wherein the plurality of battery cells series Or a battery pack connected in parallel. [Effects of the Invention]

[0027] The heat-transfer-suppressing sheet of the present invention is easy to handle because a pair of outer members and an intermediate member disposed between them are held together by the engagement of the recesses with the first and second protrusions, eliminating the need for adhesive. Furthermore, in the heat-transfer-suppressing sheet of the present invention, one of the outer member and the intermediate member is made of an elastic material, and the other is made of a thermal insulating material. When viewed in the stacking direction, the first and second protrusions are misaligned, thereby suppressing heat transfer between battery cells in the event of an abnormality and preventing battery case damage and battery performance degradation due to battery cell deformation.

[0028] Furthermore, since the battery pack of the present invention has multiple battery cells and the heat transfer sheet, it is possible to suppress the transfer of heat between the battery cells in the event of an abnormality, and the elastic member flexibly deforms in response to deformation of the battery cells, thereby suppressing damage to the battery case and deterioration of battery performance. [Brief explanation of the drawings]

[0029] [Figure 1] FIG. 1 is a cross-sectional view schematically showing a heat-transfer-suppressing sheet according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a plan view showing the heat transfer suppressing sheet shown in FIG. [Figure 3] FIG. 3 is a cross-sectional view showing the positional relationship between the first convex portion and the second convex portion. [Figure 4] FIG. 4 is a plan view showing an example of the positions where the first convex portion and the second convex portion are formed. [Figure 5] FIG. 5 is a perspective view showing examples of the shapes of the first convex portions and the second convex portions in the heat-transfer-suppressing sheet according to the embodiment of the present invention. [Figure 6] FIG. 6 is a plan view showing another example of the shape of the first protrusions and the second protrusions in the heat-transfer-suppressing sheet according to the embodiment of the present invention. [Figure 7] FIG. 7 is a cross-sectional view schematically showing a heat-transfer-suppressing sheet according to a second embodiment of the present invention. [Figure 8] FIG. 8 is a plan view illustrating a preferable position of the protrusions in the heat-transfer-suppressing sheet according to the second embodiment. [Figure 9] FIG. 9 is a schematic diagram showing a battery pack according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0030] The inventors have conducted extensive research to provide a battery pack that is easy to handle, suppresses heat propagation between battery cells in the event of an abnormality, and does not affect the performance of the battery case or batteries even if the battery cells are deformed. As a result, the inventor discovered that the above problem can be solved by providing a convex portion on either the insulating material or the elastic member and a concave portion on the other, so that the convex portion is offset when viewed in a plane, and assembling a heat transfer suppression sheet by engaging the convex portion with the concave portion.

[0031] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments described below, and can be implemented with any modifications within the scope of the gist of the present invention.

[0032] [Heat transfer suppression sheet] (First embodiment) Fig. 1 is a cross-sectional view schematically showing a heat-transfer-suppressing sheet according to a first embodiment of the present invention, Fig. 2 is a plan view showing the heat-transfer-suppressing sheet shown in Fig. 1. As shown in Fig. 1, this embodiment includes a plate-shaped first elastic member (first outer member) 1 and a plate-shaped second elastic member (second outer member) 2 arranged opposite each other, and a plate-shaped heat insulating material (intermediate member) 3 arranged between them. The first elastic member 1 has a first protrusion 1a on the surface facing the heat insulating material 3. The second elastic member 2 also has a second protrusion 2a on the surface facing the heat insulating material 3.

[0033] Meanwhile, the heat insulating material 3 has a first recess 3a formed on the surface facing the first elastic member 1 at a position facing the first protrusion 1a. Similarly, a second recess 3b is formed on the surface of the heat insulating material 3 opposite the surface on which the first recess 3a is formed, i.e., the surface facing the second elastic member 2, at a position facing the second protrusion 2a of the second elastic member 2. The first protrusion 1a of the first elastic member 1 is fitted into the first recess 3a of the heat insulating material 3, and the second protrusion 2a of the second elastic member 2 is fitted into the second recess 3b of the heat insulating material 3, thereby assembling the heat transfer-suppressing sheet 10.

[0034] Furthermore, as shown in Figure 2, when the first elastic member 1, the insulating material 3, and the second elastic member 2 are assembled and viewed from the upper surface side of the first elastic member 1, i.e., from the stacking direction of the first elastic member 1, the insulating material 3, and the second elastic member 2, all of the first convex portions 1a are located at positions different from the positions of all of the second convex portions 2a.

[0035] For example, if heat transfer-suppressing sheet 10 configured in this manner is placed between battery cells, and if thermal runaway occurs in one battery cell due to an abnormality, the presence of heat insulating material 3 will suppress the transfer of heat to the adjacent battery cell. This prevents the adjacent battery cell from being exposed to heat, preventing a chain reaction of thermal runaway.

[0036] Furthermore, the heat transfer-suppressing sheet 10 according to this embodiment has a heat insulating material 3 between the first elastic member 1 and the second elastic member 2. The first elastic member 1 and the second elastic member 2 have the effect of suppressing deformation of the battery cell and the effect of absorbing the deformation of the battery cell. In other words, if the battery cell deforms due to an abnormality, the first elastic member 1 and the second elastic member 2 suppress the deformation of the battery cell while also deforming flexibly in response to the deformation of the battery cell. Therefore, it is possible to suppress the application of unnecessary pressure to the battery cell.

[0037] Furthermore, in this embodiment, the first elastic member 1 and the second elastic member 2 are disposed on the outside of the heat-transfer-suppressing sheet 10, and the heat-insulating material 3 is disposed in the center. As will be described later, the heat-insulating material 3 may contain inorganic particles with extremely small particle diameters, such as nanoparticles. Disposing the heat-insulating material between a pair of elastic members prevents the inorganic particles from falling out of the heat-insulating material. Furthermore, when the heat-transfer-suppressing sheet 10 according to this embodiment is disposed between multiple battery cells, the first elastic member 1 and the second elastic member 2 are disposed in positions that contact the battery cells. Therefore, even if any of the battery cells expands or contracts, the heat-transfer-suppressing sheet 10 can follow the deformation of the battery cells.

[0038] Furthermore, in this embodiment, the positions of all first convex portions 1a on the first elastic member 1 are offset from the positions of all second convex portions 2a on the second elastic member 2. If the positions of the first convex portions 1a and the second convex portions 2a were aligned in a plan view, the thickness of the insulating material 3 would be reduced where the first convex portions 1a and the second convex portions 2a were formed, resulting in a reduction in the insulating effect. On the other hand, in this embodiment, as described above, the positions of the first convex portions 1a and the second convex portions 2a are offset from each other, minimizing the reduction in the insulating effect due to the formation of the first convex portions 1a and the second convex portions 2a. As such, it is preferable to appropriately select the positional relationship between the elastic member and the insulating material, taking into consideration the material of the insulating material, and the heat resistance, elasticity, durability, etc. of the elastic member.

[0039] A preferred positional relationship between the first convex portion 1a and the second convex portion 2a will be described in more detail. Fig. 3 is a cross-sectional view showing the positional relationship between the first convex portion 1a and the second convex portion 2a. If the thickness of the heat insulating material 3 is d0, then, for example, at the position where the second convex portion 2a is provided on the second elastic member 2, the thickness of the heat insulating material 3 is a distance d1 reduced by the thickness of the second convex portion 2a. Since the thinner the thickness of the heat insulating material 3, the lower the insulating performance. Therefore, if the first elastic member 1 has a flat portion 1b and a first convex portion 1a on the surface facing the heat insulating material 3, it is preferable that the position facing the second convex portion 2a be at least the flat portion 1b.

[0040] If the positions of the first convex portion 1a and the second convex portion 2a are simply misaligned, and the second convex portion 2a and the first convex portion 1a are close to each other, these distances d2 and d3 will be smaller than the distance d1 between the second convex portion 2a and the opposing flat portion 1b, which may result in a decrease in heat insulation. Therefore, it is more preferable that the distance (e.g., distance d2) between any second convex portion 2a in the second elastic member 2 and the first convex portion 1a provided closest to this second convex portion 2a be greater than the distance d1 between the second convex portion 2a and the flat portion 1b of the first elastic member 1 at a position opposing it.

[0041] Although not shown in the figures, it is also preferable that the distance between any first convex portion 1a on the first elastic member 1 and the second convex portion 2a located closest to this first convex portion 1a is greater than the distance between the first convex portion 1a and the flat portion 2b of the second elastic member 2 at the position opposite it.

[0042] The first convex portions 1a of the first elastic member 1 and the first concave portions 3a of the heat insulating material 3, and the second convex portions 2a of the second elastic member 2 and the second concave portions 3b of the heat insulating material 3 may be fitted together without any gaps, or there may be some voids 5. The voids 5 form an air-insulating insulating layer, further improving the heat insulating effect. Furthermore, to assemble the convex portions and concave portions without any gaps during the manufacture of the heat-transfer-suppressing sheet 10, the first convex portions 1a and the second convex portions 2a, and the first concave portions 3a and the second concave portions 3b must be precisely aligned in size and position, requiring high-precision manufacturing. On the other hand, the presence of voids 5 between the first convex portions 1a of the first elastic member 1 and the first concave portions 3a of the heat insulating material 3, and between the second convex portions 2a of the second elastic member 2 and the second concave portions 3b of the heat insulating material 3, facilitates the manufacture of the heat-transfer-suppressing sheet 10.

[0043] There are no particular limitations on the method for forming the first convex portions 1a of the first elastic member 1 and the second convex portions 2a of the second elastic member 2. For example, convex-shaped elastic components may be prepared and adhered to a plate-shaped elastic material with an adhesive or the like, or the first convex portions 1a and the second convex portions 2a may be formed by placing adhesive itself at a predetermined position on the elastic material. Alternatively, the first elastic member 1 and the second elastic member 2 may be formed by molding.

[0044] There is no particular limitation on the method for forming the heat insulating material 3. For example, the heat insulating material 3 can be formed by preparing a flat plate having heat insulating properties and forming the first recess 3a and the second recess 3b by cutting or the like. Alternatively, the heat insulating material 3 may be formed by molding.

[0045] The positions at which the first protrusions 1a and the second protrusions 2a are formed are not particularly limited. As shown in the plan view of FIG. 2, the first protrusions 1a and the second protrusions 2a may be formed so that they are alternately arranged at equal intervals in a grid pattern. Furthermore, in the heat-transfer-suppressing sheet 20 shown in FIG. 4, the number density of the first protrusions 1a and the second protrusions 2a is higher in the central region of the surface where the multiple first protrusions 1a and the multiple second protrusions 2a are formed than in the peripheral region. With this configuration, when the heat-transfer-suppressing sheet 20 is interposed between multiple battery cells, the first elastic member 1 and the second elastic member 2 have increased thickness in the central region where the battery cells expand and contract the most, making it easier to absorb the expansion of the battery cells.

[0046] Furthermore, when the positional relationship between the first protrusions 1a and the second protrusions 2a is as shown in FIG. 2, the positions of the first protrusions 1a formed on the first elastic member 1 and the second protrusions 2a formed on the second elastic member 2 can be made the same. That is, when two identical elastic members are prepared and one of the elastic members is flipped over so that the surfaces on which the protrusions are formed face each other, the first protrusions 1a and the second protrusions 2a are offset from each other in plan view. This eliminates the need to design elastic members with two different shapes, and allows the heat-transfer-suppressing sheet 10 to be easily manufactured.

[0047] Similarly, in the heat transfer-suppressing sheet 20 shown in FIG. 4 , for example, the positions of the first protrusions 1 a formed on the first elastic member 1 and the second protrusions 2 a formed on the second elastic member 2 can be the same. That is, as shown in FIG. 4 , a first elastic member 1 having the first protrusions 1 a formed thereon and an identical second elastic member 2 are prepared. The second elastic member 2 is then inverted and rotated, for example, by 90° so that the first protrusions 1 a and the second protrusions 2 a face each other. This results in the first protrusions 1 a and the second protrusions 2 a being offset from each other in a plan view. In this way, it is preferable to design the positions of the first protrusions 1 a and the second protrusions 2 a so that the positions of the first protrusions 1 a and the second protrusions 2 a on the first elastic member 1 and the second elastic member 2 are the same, and then one of them is inverted or inverted and then rotated by a predetermined angle, so that the first protrusions 1 a and the second protrusions 2 a are offset from each other in a plan view.

[0048] The shapes of the first protrusions 1a and the second protrusions 2a are not particularly limited. As shown in FIGS. 1 and 2, they may be cylindrical. Alternatively, as shown in the schematic cross-sectional view of the heat-transfer-suppressing sheet 10 in FIG. 5, the first protrusions 1a and the second protrusions 2a may be hemispherically protruding and the first recesses 3a and the second recesses 3b may be hemispherically recessed. This is preferable because such shapes are easy to manufacture and the first protrusions 1a and the first recesses 3a, and the second protrusions 2a and the second recesses 3b can be easily fitted together. These shapes do not need to be exact hemispherical, but may be approximately hemispherical. The first protrusions 1a and the second protrusions 2a may be various other shapes, such as prismatic, conical, or pyramidal.

[0049] Furthermore, the first convex portions 1a and the second convex portions 2a need not necessarily be granular as described above, but may instead be linearly extending, as shown in the plan view of the heat transfer-suppressing sheet 10 in FIG. 6. Furthermore, no matter what shapes the first convex portion 1a and the second convex portion 2a have, the first recess 3a and the second recess 3b may have any shape as long as the first convex portion 1a and the second convex portion 2a can be fitted into them.

[0050] (Second embodiment) 7 is a cross-sectional view schematically illustrating a heat-transfer-suppressing sheet according to a second embodiment of the present invention. In the second embodiment, the first protrusions 1a and second protrusions 2a shown in the first embodiment are formed in the intermediate insulating material, rather than in the outer elastic member.

[0051] 7, in the second embodiment, a first convex portion 13a and a second convex portion 13b are provided on both surfaces perpendicular to the thickness direction of a heat insulating material (intermediate member) 13. The first convex portion 13a provided on one surface of the heat insulating material 13 and the second convex portion 13b provided on the other surface are provided at different positions in a plan view seen from the thickness direction of the heat insulating material 13. Furthermore, a plate-shaped first elastic member (first outer member) 11 and a plate-shaped second elastic member (second outer member) 12 are arranged on both surfaces of the heat insulating material 13 so as to face each other.

[0052] The first elastic member 11 has a first recess 11a at a position facing the first protrusion 13a of the heat insulating material 13. Similarly, the second elastic member 12 has a second recess 12a at a position facing the second protrusion 13b of the heat insulating material 13. The first protrusion 13a of the heat insulating material 13 is fitted into the first recess 11a of the first elastic member 11, and the second protrusion 13b of the heat insulating material 13 is fitted into the second recess 12a of the second elastic member 12, thereby assembling the heat transfer-suppressing sheet 30.

[0053] In the second embodiment configured in this manner, the same effects as in the first embodiment can be obtained.

[0054] In this embodiment, the first protrusions 13a and second protrusions 13b are provided on the heat insulating material 13, so their positional relationship does not reduce the heat insulating properties. However, if the first protrusions 13a and second protrusions 13b were formed in the same position on both sides of the heat insulating material 13, the sum of the thicknesses of the first elastic member 11 and the second elastic member 12 at that position would be small, and the heat insulating material 13 would not be able to adequately follow the expansion and contraction of the battery cells. Therefore, the positions of the first protrusions 13a and the second protrusions 13b are assumed to be different in plan view.

[0055] FIG. 8 is a plan view illustrating a preferred position of the protrusions in a heat-transfer-suppressing sheet according to the second embodiment. Unlike the first embodiment, the heat-transfer-suppressing sheet 40 shown in FIG. 6 has multiple first protrusions 13a and multiple second protrusions 13b formed on a heat insulating material 13 that has lower elasticity than the first elastic members 11 and the second elastic members 12. Therefore, when the heat-transfer-suppressing sheet 40 is interposed between multiple battery cells, it is preferable to lower the number density of the first protrusions 13a and second protrusions 13b in the central region, where the battery cells expand and contract most frequently, than in the peripheral region. This configuration ensures a certain degree of thickness for the first elastic members 11 and second elastic members 12 in the central region, making it easier to absorb the expansion of the battery cells.

[0056] As in the first embodiment, the first convex portion 13a and the second convex portion 13b can have various shapes, such as a cylindrical shape, a substantially hemispherical shape, a prismatic shape, a conical shape, a pyramidal shape, a linear shape, etc. Furthermore, the same methods as in the first embodiment can be used to form the heat insulating material 13 having the first convex portion 13a and the second convex portion 13b, the first elastic member 11 having the first recess 11a, and the second elastic member 12 having the second recess 12a.

[0057] In the first and second embodiments, a heat insulating material is disposed between a pair of elastic members. However, the present invention is not limited to this. An elastic member may be disposed between a pair of heat insulating materials. In this case, the first and second convex portions may be formed on either the elastic member side or the heat insulating material side. Referring to FIG. 1, a pair of heat insulating materials having convex portions may be disposed in place of the first elastic member 1 and the second elastic member 2, and an elastic member having concave portions may be disposed in place of the heat insulating material 3. As mentioned above, the convex portions and concave portions may be reversed.

[0058] In addition, when an elastic member is disposed between a pair of heat insulating materials and the elastic member has a flat portion and a first convex portion and a second convex portion, it is preferable to prevent a decrease in heat insulating properties due to a partial thinning of the thickness of the heat insulating material. Therefore, it is preferable that the back sides of the first convex portion and the second convex portion are both flat portions.

[0059] When the heat transfer-suppressing sheet configured as described above is interposed between multiple battery cells, the insulating material is arranged so as to contact the battery cells, but the elastic member does not contact the battery cells. Therefore, when the battery cells become hot due to an abnormality, heat is less likely to reach the elastic member, preventing melting of the elastic member. Furthermore, even if the temperature of the battery cells changes during normal operation, the insulating material arranged between the elastic member and the battery cells reduces the temperature change applied to the elastic member, preventing deterioration of the elastic member. In this way, it is preferable to appropriately select the positional relationship between the elastic member and the heat insulating material, taking into consideration the quality of the heat insulating material, the heat resistance, elasticity, durability, etc. of the elastic member.

[0060] In the various embodiments described above, the heat-transfer-suppressing sheet is manufactured by fitting the protrusions and recesses. Therefore, compared to, for example, stacking a flat insulating material and an elastic member, an adhesive or the like is not required to bond the insulating material and the elastic member. In a heat-transfer-suppressing sheet in which the insulating material and the elastic member are bonded with an adhesive, depending on the type of adhesive, if the temperature of a battery cell rises significantly, the adhesive may burn, making heat more likely to be transferred to adjacent battery cells, potentially causing a thermal chain reaction. Therefore, the heat-transfer-suppressing sheet according to the present invention, which does not require an adhesive, is extremely effective in preventing a thermal chain reaction.

[0061] However, if the adhesive is properly selected, the possibility of combustion is reduced even when the temperature rises. Therefore, a suitable adhesive may be used between the elastic member and the insulating material. In this case, the bonding area is larger than when flat plates are bonded together, and the bonding strength can be further increased.

[0062] Next, the heat insulating material and the elastic member that constitute the battery pack according to this embodiment will be described in detail.

[0063] [Insulation material] In the heat-transfer-suppressing sheet according to this embodiment, either the pair of first and second outer members or the intermediate member is made of a heat insulating material. The heat insulating material preferably contains at least one of organic fibers and inorganic fibers, and more preferably contains inorganic particles as needed. In this embodiment, these materials can be processed into, for example, a sheet. Since it is important that the material constituting the heat insulating material has heat insulating properties, the material is selected from materials with high heat insulating performance.

[0064] Thermal conductivity can be used as an index of thermal insulation performance, and 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).

[0065] The thermal conductivity of the heat insulating material can be measured in accordance with the "Test method for thermal conductivity of refractories" described in JIS R 2251.

[0066] <Inorganic particles> The inorganic particles are preferably made of a heat-resistant compound, and inorganic particles of a single material may be used, or inorganic particles of two or more materials may be used in combination. The combined use of two or more inorganic particles with different heat transfer suppression effects allows the heat-generating body to be cooled in multiple stages, allowing the heat absorption effect to be exerted over a wider temperature range, thereby improving the heat insulating performance. When two or more types of inorganic particles are contained, the preferred material, shape, and particle size of each inorganic particle are described below.

[0067] As an example, the heat insulating material may contain, in addition to first inorganic particles and second inorganic particles, two types of inorganic fibers (first inorganic fibers and second inorganic fibers) described below, organic fibers, and a binder.

[0068] From the viewpoint of the heat transfer suppression effect, the first inorganic particles and the second inorganic particles are preferably particles made of at least one inorganic material selected from oxide particles, carbide particles, nitride particles, and inorganic hydrate particles, and more preferably oxide particles. Also usable are silica nanoparticles, metal oxide particles, inorganic balloons such as microporous particles and hollow silica particles, particles made of thermally expandable inorganic materials, and particles made of hydrous porous bodies. Hereinafter, inorganic particles will be described in more detail, with small-diameter inorganic particles referred to as the first inorganic particles and large-diameter inorganic particles referred to as the second inorganic particles.

[0069] <First inorganic particle> (oxide particles) Oxide particles have a high refractive index and a strong effect of scattering light. Therefore, when oxide particles are used as inorganic particles, they can suppress radiative heat transfer, especially in high-temperature areas such as those where abnormal heat is generated. Examples of oxide particles include silica (SiO2), titania (TiO2), and mullite (Al6O 13 Examples of suitable oxide particles include, but are not limited to, silica (Si2), zirconia (ZrO2), magnesia (MgO), zircon (ZrSiO4), barium titanate (BaTiO3), zinc oxide (ZnO), and alumina (Al2O3). In other words, only one of the above oxide particles that can be used as inorganic particles 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 scattering 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 oxide particles.

[0070] (Average primary particle size of oxide particles: 0.001 μm to 50 μm) The particle size of the oxide particles can affect the effect of reflecting radiant heat, so if the average primary particle size is limited to a predetermined range, even higher heat insulating properties can be obtained. In other words, when the average primary particle diameter of the oxide particles is 0.001 μm or more, the particle diameter is sufficiently larger than the wavelength of light that contributes to heating, and the light is efficiently diffused, thereby suppressing the radiative heat transfer within the thermal insulation material in the high temperature range of 500°C or higher, thereby further improving the thermal insulation properties. On the other hand, if the average primary particle size of the oxide particles is 50 μm or less, the number and number of contact points between the particles do not increase even when compressed, making it difficult to form paths for conductive heat transfer. This reduces the impact on thermal insulation, particularly in the normal temperature range where conductive heat transfer is dominant. 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.

[0071] (nanoparticles) In the present invention, nanoparticles refer to particles on the order of nanometers that are spherical or nearly spherical and have an average primary particle diameter of less than 1 μm. Nanoparticles have a low density, which suppresses conductive heat transfer. Furthermore, when nanoparticles are used as inorganic particles, the finely dispersed voids provide excellent heat insulation, suppressing convective heat transfer. Therefore, the use of nanoparticles is preferred because they can suppress heat transfer between adjacent nanoparticles during normal use at room temperature.

[0072] Furthermore, if nanoparticles with a small average primary particle size are used as oxide particles, the increase in conductive heat transfer through the insulating material can be suppressed even when the insulating material is compressed due to expansion caused by thermal runaway in the battery cell, increasing the internal density of the insulating material. This is thought to be because nanoparticles are prone to forming tiny voids between particles due to electrostatic repulsion, and their low bulk density allows the particles to be packed together in a cushioning manner.

[0073] In the present invention, when nanoparticles are used as 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 size are used. Furthermore, commonly available silica nanoparticles have a bulk density of 0.1 (g / cm 3 ), for example, even if a battery cell placed adjacent to the insulating material undergoes thermal expansion and a large compressive stress is applied to the insulating material, the size (area) and number of contact points between the silica nanoparticles in the flame retardant do not increase significantly, and the insulating properties can be maintained. Therefore, it is preferable to use silica nanoparticles as the nanoparticles. Wet silica, dry silica, aerogel, etc. can be used as the silica nanoparticles.

[0074] (Average primary particle diameter of nanoparticles: 1 nm to 100 nm) If the average primary particle size of the nanoparticles is limited to a predetermined range, even higher heat insulating properties can be obtained. That is, when the average primary particle diameter of the nanoparticles is 1 nm or more and 100 nm or less, convective heat transfer and conductive heat transfer within the thermal insulation material can be suppressed, particularly in the temperature range below 500°C, and the thermal insulation properties can be further improved. Furthermore, even when compressive stress is applied, the voids remaining between the nanoparticles and the contact points between many particles suppress conductive heat transfer, allowing the thermal insulation properties of the thermal insulation material to be maintained. The average primary particle size of the nanoparticles is more preferably 2 nm or more, and even more preferably 3 nm or more, while the average primary particle size of the nanoparticles is more preferably 50 nm or less, and even more preferably 10 nm or less.

[0075] (Inorganic hydrate particles) When inorganic hydrate particles receive heat from a heating element and reach a temperature above their thermal decomposition initiation temperature, they undergo thermal decomposition and release their own water of crystallization, lowering the temperature of the heating element and its surroundings, thereby exhibiting a so-called "endothermic effect." After releasing the water of crystallization, the particles become porous, and the numerous air holes provide thermal insulation. Specific examples of inorganic hydrates include aluminum hydroxide (Al(OH)3), magnesium hydroxide (Mg(OH)2), calcium hydroxide (Ca(OH)2), zinc hydroxide (Zn(OH)2), iron hydroxide (Fe(OH)2), manganese hydroxide (Mn(OH)2), zirconium hydroxide (Zr(OH)2), and gallium hydroxide (Ga(OH)3).

[0076] For example, aluminum hydroxide has about 35% water of crystallization, and as shown in the following formula, it thermally decomposes, releasing the water of crystallization and exhibiting an endothermic effect. After releasing the water of crystallization, it becomes a porous alumina (Al2O3) and functions as a heat insulating material. 2Al(OH)3 → Al2O3 + 3H2O

[0077] As will be described later, the heat insulating material and elastic member according to this embodiment are preferably interposed between battery cells, for example, but in a battery cell that has experienced thermal runaway, the temperature rises sharply to over 200° C. and continues to rise to around 700° C. Therefore, it is also preferable that the inorganic particles be made of an inorganic hydrate whose thermal decomposition starting temperature is 200° C. or higher. The thermal decomposition starting temperatures of the inorganic hydrates listed above are approximately 200°C for aluminum hydroxide, approximately 330°C for magnesium hydroxide, approximately 580°C for calcium hydroxide, approximately 200°C for zinc hydroxide, approximately 350°C for iron hydroxide, approximately 300°C for manganese hydroxide, approximately 300°C for zirconium hydroxide, and approximately 300°C for gallium hydroxide.All of these temperatures roughly overlap with the temperature range in which a battery cell experiencing thermal runaway experiences a sudden rise in temperature, and can efficiently suppress temperature rise, making these inorganic hydrates preferable.

[0078] (Average secondary particle diameter of inorganic hydrate particles: 0.01 μm or more and 200 μm or less) Furthermore, when inorganic hydrate particles are used as the first inorganic particles, if their average particle diameter is too large, it takes some time for the first inorganic particles (inorganic hydrate) near the center of the thermal insulating material to reach their thermal decomposition temperature, and the first inorganic particles near the center of the thermal insulating material 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.

[0079] (nitride particles) Suitable examples of nitride particles include boron nitride (BN).

[0080] (carbide particles) Suitable examples of carbide particles include boron carbide (B4C).

[0081] (Particles made of thermally expandable inorganic material) Examples of thermally expandable inorganic materials include vermiculite, bentonite, mica, and perlite.

[0082] (Particles made of hydrous porous material) Specific examples of the hydrous porous material include zeolite, kaolinite, montmorillonite, acid clay, diatomaceous earth, wet silica, dry silica, aerogel, mica, and vermiculite.

[0083] (inorganic balloons) The heat insulating material used in the present invention may contain inorganic balloons as inorganic particles. When inorganic balloons are contained, convective or conductive heat transfer within the heat insulating material can be suppressed in the temperature range below 500°C, and the heat insulating properties of the heat insulating material can be further improved. As the inorganic balloons, at least one selected from shirasu balloons, silica balloons, fly ash balloons, barite balloons, and glass balloons can be used.

[0084] (Inorganic balloon content: 60% or less by mass of the total mass of the insulation material) The content of the inorganic balloons is preferably 60 mass % or less based on the total mass of the heat insulating material.

[0085] (Average particle size of inorganic balloons: 1 μm to 100 μm) The average particle size of the inorganic balloons is preferably 1 μm or more and 100 μm or less.

[0086] <Second inorganic particles> When two types of inorganic particles are contained in a heat insulating material, the second inorganic particles are not particularly limited as long as they are different from the first inorganic particles in terms of material, particle size, etc. Examples of the second inorganic particles that can be used include oxide particles, carbide particles, nitride particles, inorganic hydrate particles, silica nanoparticles, metal oxide particles, inorganic balloons such as microporous particles and hollow silica particles, particles made of a thermally expandable inorganic material, and particles made of a hydrous porous body, the details of which are as described above.

[0087] Nanoparticles have extremely low conductive heat transfer and can maintain excellent heat insulation even when compressive stress is applied to the insulating material. Metal oxide particles such as titania are also effective in blocking radiant heat. Furthermore, when large-diameter inorganic particles and small-diameter inorganic particles are used, the small-diameter inorganic particles penetrate into the gaps between the large-diameter inorganic particles, resulting in a denser structure and improving the heat transfer suppression effect. Therefore, when nanoparticles are used as the first inorganic particles, it is preferable to further include second inorganic particles made of a metal oxide that are larger in diameter than the first inorganic particles in the insulating material. Examples of metal oxides include silicon oxide, titanium oxide, aluminum oxide, barium titanate, zinc oxide, zircon, zirconium oxide, etc. In particular, titania is a component with a higher refractive index than other metal oxides, and is highly effective in scattering light and blocking radiant heat in a high temperature range of 500°C or higher, so it is most preferable to use titania.

[0088] (Average primary particle size of second inorganic particles) When second inorganic particles made of a metal oxide are contained in a thermal insulating material, if the average primary particle size of the second inorganic particles is 1 μm or more and 50 μm or less, radiation heat transfer can be efficiently suppressed in a high temperature range of 500° C. or more. The average primary particle size of the second inorganic particles is more preferably 5 μm or more and 30 μm or less, and most preferably 10 μm or less.

[0089] (Content of first inorganic particles and second inorganic particles) When the first inorganic particles are silica nanoparticles and the second inorganic particles are metal oxide, if the content of the first inorganic particles is 60 mass% or more and 95 mass% or less relative to the total mass of the first inorganic particles and the second inorganic particles, the amount of metal oxide particles required to suppress radiative heat transfer and the amount of silica nanoparticles required to suppress conductive and convective heat transfer and to provide cushioning can be optimized. As a result, it is believed that balanced, high thermal insulation can be achieved over a wide temperature range, from temperatures during normal battery use to temperatures above 500°C, even when external compressive force is applied.

[0090] <Inorganic fibers> Examples of inorganic fibers include ceramic fibers such as silica fiber, alumina fiber, alumina silicate fiber, zirconia fiber, carbon fiber, soluble fiber, refractory ceramic fiber, aerogel composite material, magnesium silicate fiber, alkaline earth silicate fiber, potassium titanate fiber, and potassium titanate whisker fiber; glass fibers such as glass fiber and glass wool; and mineral fibers such as rock wool, basalt fiber, and wollastonite. These inorganic fibers are preferred in terms of heat resistance, strength, availability, etc. Among the inorganic fibers, silica-alumina fibers, alumina fibers, silica fibers, rock wool, alkaline earth silicate fibers, and glass fibers are particularly preferred in terms of ease of handling.

[0091] 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.

[0092] Unless the inorganic fibers have special properties as described below, 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 intertwine 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 is obtained, the inorganic fibers may not be able to intertwine tightly with each other, or may curl up with a single inorganic fiber, which may result in continuous voids and reduce the insulating properties.

[0093] Unless the inorganic fibers have special properties as described below, 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, resulting in a decrease in thermal insulation properties, and the moldability and strength of the thermal insulation material may be impaired.

[0094] The inorganic fibers may be used alone or in combination of two or more. As shown in Figure 3, the heat insulating material preferably has first and second inorganic fibers that are different from each other in at least one property selected from the group consisting of average fiber diameter, shape, and glass transition point. By including two types of inorganic fibers that are different from each other in properties, the mechanical strength of the heat insulating material and its ability to retain inorganic particles can be improved.

[0095] (Two types of inorganic fibers with different average fiber diameters and fiber shapes) When the thermal insulating material contains two types of inorganic fibers, it is preferable that the average fiber diameter of the first inorganic fibers be larger than that of the second inorganic fibers, that the first inorganic fibers be linear or needle-like, and that the second inorganic fibers be dendritic or crimped. The first inorganic fibers with a larger average fiber diameter (larger diameter) have the effect of improving the mechanical strength and shape retention of the thermal insulating material. The above effect can be achieved by making one of the two types of inorganic fibers, for example, the first inorganic fibers, larger in diameter than the second inorganic fibers. Because the thermal insulating material may be subjected to external impacts, the inclusion of the first inorganic fibers in the thermal insulating material improves its impact resistance. Examples of external impacts include compressive force due to expansion of a battery cell and wind pressure due to a battery cell ignition. In order to improve the mechanical strength and shape retention of the heat insulating material, it is particularly preferable that the first inorganic fibers are linear or needle-shaped. Note that linear or needle-shaped fibers refer to fibers having a crimp degree (described later), for example, of less than 10%, preferably 5% or less.

[0096] More specifically, in order to improve the mechanical strength and shape retention of the thermal insulating material, the average fiber diameter of the first inorganic fibers is preferably 1 μm or more, more preferably 3 μm or more. If the first inorganic fibers are too thick, there is a risk that the moldability and processability into the thermal insulating material may decrease, so the average fiber diameter of the first inorganic fibers is preferably 20 μm or less, more preferably 15 μm or less. If the first inorganic fibers are too long, moldability and processability may decrease, so the fiber length is preferably 100 mm or less.Furthermore, if the first inorganic fibers are too short, shape retention and mechanical strength may decrease, so the fiber length is preferably 0.1 mm or more.

[0097] On the other hand, the second inorganic fibers having a small average fiber diameter (thin diameter) have the effect of improving the retention of other inorganic fibers, inorganic particles, etc., and also increasing the flexibility of the heat insulating material. Therefore, it is preferable that the second inorganic fibers have a smaller diameter than the first inorganic fibers.

[0098] More specifically, to improve the retention of other inorganic fibers, inorganic particles, etc., the second inorganic fibers are preferably easily deformed and flexible. Therefore, the average fiber diameter of the thin second inorganic fibers is preferably less than 1 μm, and more preferably 0.1 μm or less. However, if the thin inorganic fibers are too thin, they are prone to breakage, reducing their ability to retain other inorganic fibers, inorganic particles, etc. Furthermore, a large proportion of the fibers remain entangled in the insulating material without retaining other inorganic fibers, inorganic particles, etc., resulting in a decrease in the ability to retain other inorganic fibers, inorganic particles, etc., as well as poor moldability and shape retention. Therefore, the average fiber diameter of the second inorganic fibers is preferably 1 nm or more, and more preferably 10 nm or more. If the second inorganic fibers are too long, moldability and shape retention will decrease, so the fiber length of the second inorganic fibers is preferably 0.1 mm or less.

[0099] The second inorganic fibers are preferably dendritic or crimped. When the second inorganic fibers have such a shape, they become entangled with other inorganic fibers, inorganic particles, etc. in the thermal insulation material. This improves the ability to retain other inorganic fibers, inorganic particles, etc. Furthermore, when the thermal insulation material and the elastic member are subjected to pressure or wind pressure, the entanglement of the first inorganic fibers and the second inorganic fibers prevents the thermal insulation material from sliding and moving, thereby improving the mechanical strength, particularly against external pressure and impact.

[0100] The term "dendritic" refers to a two-dimensionally or three-dimensionally branched structure, such as feather-like, tetrapod-like, radial, or three-dimensional mesh-like. When the second inorganic fibers are dendritic, the average fiber diameter can be obtained by measuring the diameters of the trunk and branches at several points using an SEM and calculating the average value of these.

[0101] The crimped structure refers to a structure in which fibers are bent in various directions. One method for quantifying the crimped structure is to calculate the crimp degree from an electron microscope photograph, which can be calculated, for example, using the following formula: Crimp degree (%) = (fiber length - distance between fiber ends) / (fiber length) × 100 Here, both the fiber length and the distance between fiber ends are measured values ​​on an electron microscope photograph. In other words, they are the fiber length and the distance between fiber ends projected onto a two-dimensional plane, and are shorter than the actual values. Based on this formula, the crimp degree of the second inorganic fiber is preferably 10% or more, and more preferably 30% or more. If the crimp degree is low, it becomes difficult to retain other inorganic fibers or inorganic particles, and it becomes difficult to form entanglements (networks) between the second inorganic fibers and between the first inorganic fibers and the second inorganic fibers.

[0102] In the above-described embodiment, the first inorganic fibers and the second inorganic fibers having different average fiber diameters and fiber shapes are used as a method for improving the mechanical strength and shape retention of the thermal insulating material, as well as the retention of inorganic particles, inorganic fibers, etc. However, the mechanical strength, shape retention, and particle retention of the thermal insulating material can also be improved by using the first inorganic fibers and the second inorganic fibers having different glass transition points and average fiber diameters.

[0103] As described above, in this embodiment, it is preferable to use various combinations of inorganic fibers in order to improve the mechanical strength, shape retention, and particle retention of the heat insulating material.

[0104] (Two types of inorganic fibers with different glass transition temperatures) When the thermal insulating material contains two types of inorganic fibers, it is preferable that the first inorganic fibers are amorphous fibers, and the second inorganic fibers are at least one type of fiber selected from amorphous fibers having a higher glass transition temperature than the first inorganic fibers and crystalline fibers. Furthermore, by using first inorganic particles including at least one type selected from nanoparticles, hollow particles, and porous particles together with the two types of inorganic fibers, the thermal insulating performance can be further improved.

[0105] The melting point of crystalline inorganic fibers is usually higher than the glass transition point of amorphous inorganic fibers. Therefore, when exposed to high temperatures, the surface of the first inorganic fibers softens before the second inorganic fibers, and binds other inorganic fibers, inorganic particles, etc. Therefore, by incorporating the above-mentioned first inorganic fibers into a thermal insulation material, the mechanical strength of the thermal insulation material can be improved. Specifically, the first inorganic fiber is preferably an inorganic fiber having a melting point of less than 700°C, and many amorphous inorganic fibers can be used. Among them, a fiber containing SiO2 is preferable, and glass fiber is more preferable because it is inexpensive, easily available, and has excellent handleability.

[0106] As described above, the second inorganic fibers are at least one type of fibers selected from amorphous fibers and crystalline fibers having a glass transition temperature higher than that of the first inorganic fibers. Many crystalline inorganic fibers can be used as the second inorganic fibers. If the second inorganic fibers are crystalline fibers or have a higher glass transition temperature than the first inorganic fibers, the second inorganic fibers will not melt or soften when exposed to high temperatures, even if the first inorganic fibers soften, and therefore will be able to maintain their shape and remain present between the battery cells even during thermal runaway. Furthermore, if the second inorganic fibers do not melt or soften, tiny spaces are maintained between each particle, between the particles and the fibers, and between each fiber contained in the insulating material, thereby providing an insulating effect through air and maintaining excellent heat transfer suppression performance.

[0107] When the second inorganic fiber is crystalline, examples of the second inorganic fiber that can be used 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, and potassium titanate fiber; glass fibers such as glass fiber and glass wool; and mineral fibers such as rock wool, basalt fiber, and wollastonite. Among the fibers listed as the second inorganic fiber, those with a melting point exceeding 1000°C are suitable for use because even if thermal runaway occurs in the battery cell, the second inorganic fiber will not melt or soften and will be able to maintain its shape. Among the fibers listed as the second inorganic fibers, it is more preferable to use ceramic fibers such as silica fibers, alumina fibers, and alumina silicate fibers, as well as mineral fibers, and it is even more preferable to use fibers with a melting point of over 1000°C.

[0108] Furthermore, even if the second inorganic fibers are amorphous, they can be used as long as they have a higher glass transition temperature than the first inorganic fibers. For example, glass fibers having a higher glass transition temperature than the first inorganic fibers may be used as the second inorganic fibers. As the second inorganic fiber, the various inorganic fibers exemplified above may be used alone or in combination of two or more kinds.

[0109] As described above, the first inorganic fibers have a lower glass transition point than the second inorganic fibers, and when exposed to high temperatures, the first inorganic fibers soften first, allowing the first inorganic fibers to bind other inorganic fibers, inorganic particles, etc. However, for example, if the second inorganic fibers are amorphous and have a smaller fiber diameter than the first inorganic fibers, and the glass transition points of the first and second inorganic fibers are close to each other, the second inorganic fibers may soften first. Therefore, when the second inorganic fibers are amorphous fibers, the glass transition point of the second inorganic fibers is preferably at least 100° C. higher, and more preferably at least 300° C. higher, than the glass transition point of the first inorganic fibers.

[0110] The fiber length of the first inorganic fibers is preferably 100 mm or less, and more preferably 0.1 mm or more, and the fiber length of the second inorganic fibers is preferably 0.1 mm or less, for the reasons described above.

[0111] (Two types of inorganic fibers with different glass transition temperatures and average fiber diameters) When the heat insulating material contains two types of inorganic fibers, it is preferable that the first inorganic fibers are amorphous fibers, the second inorganic fibers are at least one type of fiber selected from amorphous fibers having a glass transition point higher than that of the first inorganic fibers and crystalline fibers, and the average fiber diameter of the first inorganic fibers is larger than the average fiber diameter of the second inorganic fibers.

[0112] As described above, when the thermal insulating material according to this embodiment contains two types of inorganic fibers, it is preferable that the average fiber diameter of the first inorganic fibers be larger than that of the second inorganic fibers. Furthermore, it is preferable that the thick first inorganic fibers be amorphous fibers, and the thin second inorganic fibers be at least one type of fiber selected from amorphous fibers and crystalline fibers having a higher glass transition point than the first inorganic fibers. This allows the first inorganic fibers to have a low glass transition point and soften quickly, forming a film and hardening as the temperature rises. On the other hand, if the thin second inorganic fibers are at least one type of fiber selected from amorphous fibers and crystalline fibers having a higher glass transition point than the first inorganic fibers, the thin second inorganic fibers remain in their fibrous form even when the temperature rises, thereby maintaining the structure of the thermal insulating material and preventing powder shedding.

[0113] Even in this case, the fiber length of the first inorganic fibers is preferably 100 mm or less, and more preferably 0.1 mm or more. The fiber length of the second inorganic fibers is preferably 0.1 mm or less. The reasons for this are as described above.

[0114] Furthermore, the heat insulating material may contain different inorganic fibers in addition to the first and second inorganic fibers.

[0115] (Contents of first inorganic fibers and second inorganic fibers) When the insulating material contains two types of inorganic fibers, the content of the first inorganic fibers is preferably 3% by mass or more and 30% by mass or less relative to the total mass of the insulating material, and the content of the second inorganic fibers is preferably 3% by mass or more and 30% by mass or less relative to the total mass of the insulating material.

[0116] The content of the first inorganic fibers is more preferably 5% by mass to 15% by mass, both inclusive, of the total mass of the thermal insulation material, and the content of the second inorganic fibers is more preferably 5% by mass to 15% by mass, both inclusive, of the total mass of the thermal insulation material. By setting the contents in this range, the shape retention, compression force resistance, and wind pressure resistance provided by the first inorganic fibers, and the inorganic particle retention ability provided by the second inorganic fibers are exhibited in a balanced manner.

[0117] <Organic fiber> The organic fibers are not particularly limited, and synthetic fibers, natural fibers, pulp, etc. can be used. As the synthetic fibers, fibers made of thermosetting resins or thermoplastic resins can be selected, and examples of synthetic fibers that can be used include modified polyethylene terephthalate (PET) fibers, polyethylene (PE) fibers, polypropylene fibers, polyester fibers, nylon fibers, polybutylene terephthalate fibers, polyvinyl alcohol (PVA) fibers, polyurethane fibers, ethylene-vinyl alcohol copolymer fibers, polytrimethylene terephthalate fibers, polyacetal fibers, polytetrafluoroethylene fibers, polyether ether ketone fibers, polyphenylene sulfide fibers, polyamide fibers, and polyparaphenylphthalamide fibers.

[0118] The types and structures of synthetic fibers that can be used in this embodiment will be described in more detail below. Vinylon: A fiber made from a long-chain synthetic polymer containing more than 65% vinyl alcohol units by mass. Vinylal: Fibers made from long-chain synthetic polymers of polyvinyl alcohol with varying levels of acetalization. Polyvinyl chloride (chlorofiber): A fiber made from a long-chain synthetic polymer primarily composed of vinyl chloride units. Polyvinylidene chloride (chlorofiber): A fiber made of a long-chain synthetic polymer primarily composed of vinylidene chloride units (-CH2-CCl2-). Acrylic: Fiber made from a long-chain synthetic polymer containing 85% or more repeating units of acrylonitrile groups by mass. Acrylic (modacrylic): Fibers made from long-chain synthetic polymers containing 35% or more but less than 85% repeating units of acrylonitrile groups by mass. Nylon (polyamide): A fiber made from a long-chain synthetic polymer in which 85% or more of the repeating amide bonds are linked to aliphatic or cycloaliphatic units. Aramid: A fiber made of a long-chain synthetic polymer in which amide or imide bonds directly bonded to two benzene rings account for 85% or more by mass, and if imide bonds are present, their number does not exceed the number of amide bonds. Polyester: A fiber made from a long-chain synthetic polymer containing 85% or more ester units of terephthalic acid and dihydric alcohol by mass. Polyethylene terephthalate (PET): A fiber made from a long-chain synthetic polymer containing 85% or more ester units of terephthalic acid and ethylene glycol by mass. Polytrimethylene terephthalate (PTT): A fiber made from a long-chain synthetic polymer containing 85% or more ester units of terephthalic acid and 1,3-propanediol by mass. Polybutylene terephthalate (PBT): A fiber made from a long-chain synthetic polymer containing 85% or more ester units of terephthalic acid and 1,4-butanediol by mass. Polyethylene (PE): A polymer composed of unsubstituted saturated aliphatic hydrocarbons, a fiber made from long-chain synthetic polymers. Polypropylene (PP): A polymer composed of saturated aliphatic hydrocarbons with a methyl group side chain on one carbon atom per two carbon atoms. It has stereoregularity and is a fiber made from a long-chain synthetic polymer with no other substituents. Polyurethane: A fiber made of a long-chain synthetic polymer that contains 85% or more polyurethane segments by mass and that, when stretched to three times its length without tension, immediately returns to its original length when the tension is removed. Polylactic acid: A fiber made from a long-chain synthetic polymer containing 50% or more lactic acid ester units by mass. The preferred ranges of the average fiber length and average fiber diameter of the organic fibers are the same as those of the inorganic fibers.

[0119] <Other ingredients> The heat insulating material that can be used in this embodiment may contain, in addition to the first and second inorganic particles, the first and second inorganic fibers, and the organic fibers, components necessary for forming the heat insulating material, such as a binder, a colorant, etc. These other components will be described in detail below.

[0120] (Binding material) The insulating material of the present invention can be formed by sintering or the like even if it does not contain a binding material such as a binder. However, when the insulating material contains silica nanoparticles, it is preferable to add a binding material in an appropriate amount to maintain the shape of the insulating material. In the present invention, the binding material may be anything that holds the inorganic particles together, and may be in any form, such as a binder that provides adhesion, a fiber that physically entangles the particles, or a heat-resistant resin that adheres by adhesive force. The first inorganic fiber and the second inorganic fiber also function as binding agents.

[0121] The binder may be an organic binder, an inorganic binder, or the like. Although the present invention is not particularly limited to these types, the organic binder may be a polymer flocculant or an acrylic emulsion, and the inorganic binder may be, for example, silica sol, alumina sol, aluminum sulfate, or the like. These function as adhesives when the solvent, such as water, is removed.

[0122] In the heat insulating material used in the present invention, the content of the binder is preferably 60% by mass or less, more preferably 50% by mass or less, based on the total mass of the heat insulating material. In the heat insulating material used in the present invention, the content of the binder is preferably 10% by mass or more, more preferably 20% by mass or more, based on the total mass of the heat insulating material.

[0123] The thickness of the heat insulating material used in the present invention is not particularly limited, but is preferably in the range of 0.1 mm to 30 mm. When the thickness of the heat insulating material is within the above range, sufficient heat insulating properties and mechanical strength can be obtained, and the heat insulating material can be easily molded.

[0124] [Elastic member] In the heat-transfer-suppressing sheet according to this embodiment, one of the pair of first and second outer members or the intermediate member is made of the above-mentioned insulating material, and the other is made of an elastic member. When the heat-transfer-suppressing sheet is interposed between multiple battery cells, the elastic member can be one that flexibly deforms in response to deformation of the battery cells and has the elasticity to absorb the expansion and contraction of the battery cells. Examples of such elastic members that can be used include rubber and elastomer.

[0125] [Battery pack] 9 is a schematic diagram showing a battery pack according to an embodiment of the present invention. The battery pack 100 according to this embodiment includes a plurality of battery cells 20a, 20b, and 20c and a heat-transfer-suppressing sheet 10 according to this embodiment. The plurality of battery cells 20a, 20b, and 20c are connected in series or in parallel. 9, the heat-transfer-suppressing sheet 10 according to this embodiment is interposed between the battery cell 20a and the battery cell 20b, and between the battery cell 20b and the battery cell 20c. Furthermore, the battery cells 20a, 20b, and 20c and the heat-transfer-suppressing sheet 10 are housed in a battery case 50.

[0126] The heat-transfer-suppressing sheet 10 is as described above. However, instead of the heat-transfer-suppressing sheet 10 shown in Figures 1 and 2, etc., it is possible to use the heat-transfer-suppressing sheet 20 shown in Figure 4, the heat-transfer-suppressing sheet 30 shown in Figure 7, the heat-transfer-suppressing sheet 40 shown in Figure 8, etc., or other heat-transfer-suppressing sheets of the present invention.

[0127] In the battery pack 100 configured in this manner, even if a certain battery cell 20a becomes too hot, the heat transfer suppression sheet 10, which has a heat transfer suppression effect, is present between the battery cell 20a and the battery cell 20b, so the transfer of heat to the battery cell 20b can be suppressed, and a chain reaction of thermal runaway can be prevented. Furthermore, the heat-transfer-suppressing sheet 10 according to this embodiment uses elastic members as the first outer member, the second outer member, or the intermediate member, and therefore has 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. For example, if the battery cell 20a deforms due to an abnormality, the first elastic member 1 suppresses the deformation of the battery cell 20a while also deforming flexibly in response to the deformation of the battery cell 20a. Therefore, damage to the battery cell 20a and the battery case 50 can be suppressed.

[0128] The battery cells 20a, 20b, and 20c are slightly deformed even during charge and discharge cycles during normal use. That is, if the gap between the battery cells 20a, 20b, and 20c and the battery case 50 is small, the battery cells 20a, 20b, and 20c are subjected to pressure from the battery case 50 when they expand, and the pressure from the battery case 50 is released when they contract. In this way, repeated compression and relaxation of the battery cells 20a, 20b, and 20c can cause a decrease in battery performance. In this embodiment, the first elastic member 1 and the second elastic member 2 flexibly deform even in response to slight deformation of the battery cells 20a, 20b, and 20c during the charge / discharge cycle, which is normal use, thereby suppressing deterioration in the battery performance of the battery cells 20a, 20b, and 20c.

[0129] In this embodiment, the battery cells 20a, 20b, and 20c may be rectangular or round.

[0130] Furthermore, the battery pack according to the present invention is not limited to the battery pack illustrated in FIG. 9, and the heat transfer suppression sheet 10 can be disposed not only between adjacent battery cells 20a, 20b, 20c, but also between the battery cells 20a, 20b, 20c and the battery case 50 disposed outside them.

[0131] In a battery pack configured in this manner, if a battery cell catches fire, the flames can be prevented from spreading outside the battery case 50. For example, the battery pack 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 were to catch fire, the safety of the passengers can be ensured. Furthermore, the heat transfer suppression sheet 10 can be placed not only between each battery cell, but also between the battery cells 20a, 20b, 20c and the battery case 50, eliminating the need to fabricate new flame retardant materials, etc., and allowing for the easy construction of a safe battery pack at low cost.

[0132] In the battery pack of this embodiment, when the heat-transfer-suppressing sheet 10 is disposed between the battery cells 20a, 20b, and 20c and the battery case 50, the heat-transfer-suppressing sheet 10 may be in contact with the battery cells 20a, 20b, and 20c, or there may be gaps between them. However, even if there are no gaps between the heat-transfer-suppressing sheet 10 and the battery cells 20a, 20b, and 20c, the heat-transfer-suppressing sheet 10 has the first elastic members 1 and the second elastic members 2, and therefore can allow deformation of the battery cells when the temperature of any of the battery cells rises and the volume expands. [Explanation of symbols]

[0133] 1, 11 First elastic member (first outer member) 1a, 13a First convex part 1b,2b Plane part 2, 12 Second elastic member (second outer member) 2a, 13b Second convex part 3,13 Heat insulation material (intermediate member) 3a, 11a First recess 3b,12a 2nd recess 5 Cavity 10, 20, 30, 40 Heat transfer suppression sheet 20a, 20b, 20c battery cells 100 battery packs

Claims

1. a first outer member and a second outer member in a plate shape arranged opposite to each other; a plate-shaped intermediate member disposed between the first outer member and the second outer member, a heat transfer suppressing sheet in which the first outer member has a first convex portion provided on a surface facing the intermediate member, the second outer member has a second convex portion provided on a surface facing the intermediate member, and the intermediate member has a first concave portion provided on a surface facing the first outer member and a second concave portion provided on a surface facing the second outer member, the first convex portion being fitted into the first concave portion and the second convex portion being fitted into the second concave portion, the first outer member and the second outer member are made of either a heat insulating material or an elastic material, the intermediate member is made of the other of the heat insulating material and the elastic member, A heat transfer suppression sheet, characterized in that, when viewed from the stacking direction of the first outer member, the intermediate member, and the second outer member, all of the first convex portions are located at positions different from the positions of all of the second convex portions.

2. a first outer member and a second outer member in a plate shape arranged opposite to each other; a plate-shaped intermediate member disposed between the first outer member and the second outer member, a heat transfer suppressing sheet in which the first outer member has a first recess provided on a surface facing the intermediate member, the second outer member has a second recess provided on a surface facing the intermediate member, and the intermediate member has a first convex portion provided on a surface facing the first outer member and a second convex portion provided on a surface facing the second outer member, the first convex portion being fitted into the first recess and the second convex portion being fitted into the second recess, the first outer member and the second outer member are made of either a heat insulating material or an elastic material, the intermediate member is made of the other of the heat insulating material and the elastic member, A heat transfer suppression sheet, characterized in that, when viewed from the stacking direction of the first outer member, the intermediate member, and the second outer member, all of the first convex portions are located at positions different from the positions of all of the second convex portions.

3. the first outer member and the second outer member are made of elastic members, 3. The heat transfer suppressing sheet according to claim 1, wherein the intermediate member is made of a heat insulating material.

4. The heat transfer-suppressing sheet according to any one of claims 1 to 3, characterized in that there are gaps between the first convex portions and the first concave portions, and between the second convex portions and the second concave portions.

5. 5. The heat-transfer-suppressing sheet according to claim 1, wherein the first convex portions and the second convex portions have a granular or linear extending shape.

6. a plurality of the first convex portions and a plurality of the second convex portions are provided, a member on which the first convex portion and the second convex portion are provided is made of an elastic member, 6. The heat transfer suppressing sheet according to claim 1, wherein a central region of the surface on which the first convex portions and the second convex portions are formed has a higher number density of the first convex portions and the second convex portions than a peripheral region.

7. a plurality of the first convex portions and a plurality of the second convex portions are provided, a member on which the first convex portion and the second convex portion are provided is made of a heat insulating material, 6. The heat transfer suppressing sheet according to claim 1, wherein a central region of the surface on which the first convex portions and the second convex portions are formed has a lower number density of the first convex portions and the second convex portions than a peripheral region of the surface.

8. the first convex portion and the second convex portion protrude in a substantially hemispherical shape, 8. The heat transfer suppressing sheet according to claim 1, wherein the first recess and the second recess are recessed in a substantially hemispherical shape.

9. the first outer member and the second outer member are each made of an elastic member having a flat portion, and the first convex portion and the second convex portion provided on the flat portion, the intermediate member is made of a heat insulating material, 2. The heat transfer suppression sheet according to claim 1, wherein the distance between any first convex portion on the first outer member and the second convex portion closest to the any first convex portion is greater than the distance between the any first convex portion and the flat portion of the second outer member at a position opposite the any first convex portion.

10. the intermediate member is made of an elastic member having a flat portion, and the first convex portion and the second convex portion provided on the flat portion, the first outer member and the second outer member are made of a thermal insulating material, The heat transfer suppressing sheet according to claim 2 , wherein a rear surface side of the first protrusion of the intermediate member is a flat surface.

11. The heat transfer-suppressing sheet according to any one of claims 1 to 10, wherein the elastic member is made of rubber or elastomer.

12. The heat-transfer-suppressing sheet according to any one of claims 1 to 11, wherein the heat insulating material contains at least one of inorganic particles, organic fibers, and inorganic fibers.

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

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