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

Abstract

Provided is a heat transfer suppression sheet having excellent heat insulation performance, capable of absorbing deformation of a battery cell and thereby suppressing degradation of battery performance, and capable of suppressing positional deviation. Due to the foregoing, the heat transfer suppression sheet is capable of ensuring excellent heat insulation performance even in the event of failure. This heat transfer suppression sheet (10) comprises: a heat insulating material (11) that contains inorganic particles, and organic fibers and / or inorganic fibers, and that has a first main surface (21) and a second main surface (22) forming a pair; and an elastic body (12) that is laminated in the thickness direction of the heat insulating material (11). The first main surface of the heat insulating material (11) is disposed facing the elastic body (12). A maximum height Sz1 representing the surface roughness of the first main surface (21) is lower than a maximum height Sz2 representing the surface roughness of the second main surface (22).

Description

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

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

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

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

[0004] A common method for suppressing heat transfer from a battery cell experiencing thermal runaway is to place a heat transfer-suppressing sheet between the battery cells. Furthermore, battery cells repeatedly expand and contract as they are charged and discharged, and if this expansion and contraction repeatedly applies repulsive and relaxing forces to the battery cells themselves, battery performance may be reduced.

[0005] In response to this, heat transfer-suppressing sheets that have the effect of absorbing deformation of battery cells have been proposed. For example, Patent Document 1 describes a battery insulating material that includes a heat insulating portion and a buffer portion that is more susceptible to compressive deformation than the heat insulating portion.

[0006] Japanese Patent Application Publication No. 2021-140968

[0007] As described above, the battery cells that make up the battery pack repeatedly expand and contract during charging and discharging. For example, in a battery pack installed in an automobile, the battery cells are often charged while the automobile is parked, and the expansion of the battery cells due to charging presses and fixes the heat-transfer-suppressing sheet, so that misalignment between the battery cells and the heat-transfer sheet is unlikely to occur.

[0008] In contrast, when the vehicle is moving, the battery cells contract due to discharge, weakening the force with which the battery cells hold the heat-transfer-inhibiting sheet and making the heat-transfer-inhibiting sheet more susceptible to vibrations caused by vehicle movement. Therefore, in the case of a heat-transfer-inhibiting sheet that is a laminate of an insulating member with thermal insulation properties and an elastic member that easily absorbs deformation, misalignment is likely to occur between the insulating member and the elastic member, which in turn causes misalignment between the heat-transfer-inhibiting sheet and the battery cells. If the heat-transfer-inhibiting sheet between adjacent battery cells deviates from its desired position, creating an area between the battery cells where the heat-transfer-inhibiting sheet is not present, a sudden rise in the temperature of the battery cell could potentially cause a chain reaction of severe thermal runaway to the adjacent battery cells.

[0009] Furthermore, there is an ever-increasing demand for miniaturization and safety in battery packs installed in automobiles, etc. However, when the insulating member is made thinner to meet the demand for miniaturization of battery packs, a problem arises in that the insulating properties are reduced. The insulating material described in Patent Document 1 cannot simultaneously prevent misalignment and improve the insulating properties.

[0010] The present invention has been made in consideration of these problems, and has an object to provide a heat-transfer-suppressing sheet that has excellent thermal insulation performance, can absorb deformation of battery cells to prevent a decrease in battery performance, and can also prevent misalignment, thereby ensuring excellent thermal insulation performance even in abnormal conditions; a method for manufacturing the same; and a battery pack that includes the heat-transfer-suppressing sheet.

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

[0012] [1] A heat-transfer-suppressing sheet comprising: a thermal insulating material containing inorganic particles and at least one of organic fibers and inorganic fibers, the thermal insulating material having a pair of first and second main surfaces; and an elastic body laminated in a thickness direction of the thermal insulating material, wherein the first main surface of the thermal insulating material is disposed opposite the elastic body, and a maximum height Sz1 representing the surface roughness of the first main surface is smaller than a maximum height Sz2 representing the surface roughness of the second main surface.

[0013] Preferred embodiments of the present invention relating to the heat-transfer-suppressing sheet relate to the following [2] to

[11] : [2] The heat-transfer-suppressing sheet according to [1], wherein a difference between the maximum height Sz1 of the first main surface and the maximum height Sz2 of the second main surface is 0.2 mm or more.

[0014] [3] The heat-transfer-suppressing sheet according to [1] or [2], wherein the maximum height Sz1 of the first main surface is 0.1 mm or more and 1.0 mm or less, and the maximum height Sz2 of the second main surface is 0.5 mm or more and 1.4 mm or less.

[0015] [4] The heat-transfer-suppressing sheet according to any one of [1] to [3], characterized in that, in the first principal surface and the second principal surface of the thermal insulating material photographed by a coordinate measuring machine, a surface area ratio (Sfa2 / Sfa1) is 1.03 or more, where Sfa1 is a surface area per unit area calculated by dividing the surface area in a measurement field of view for the first principal surface by the area of ​​the measurement field, and Sfa2 is a surface area per unit area calculated by dividing the surface area in a measurement field of view for the second principal surface by the area of ​​the measurement field.

[0016] [5] The heat-transfer-suppressing sheet according to any one of [1] to [4], characterized in that in the first main surface and the second main surface of the thermal insulating material photographed by a coordinate measuring machine, a volume ratio (V2 / V1) of 2.0 or more is obtained when: a first recess having the deepest depth is selected from a measurement field of view for the first main surface; a plane including the bottom of the first recess and perpendicular to the thickness direction of the thermal insulating material is defined as a reference plane X1; and a second recess having the deepest depth is selected from a measurement field of view for the second main surface; a plane including the bottom of the second recess and perpendicular to the thickness direction of the thermal insulating material is defined as a reference plane X2; and a volume ratio (V2 / V1) of 2.0 or more is obtained when: a first recess having the deepest depth is selected from a measurement field of view for the second main surface; a plane including the bottom of the second recess and perpendicular to the thickness direction of the thermal insulating material is defined as a reference plane X2; and a second recess having the deepest depth is selected from a measurement field of view for the second main surface; a plane including the bottom of the second recess and perpendicular to the thickness direction of the thermal insulating material is defined as a reference plane X2; and a volume ratio (V2 / V1) of 2.0 or more is obtained when: a first recess having the deepest depth is selected from a measurement field of view for the first main surface; a plane including the bottom of the second recess and perpendicular to the thickness direction of the thermal insulating material is defined as a reference plane X2; and a second recess having the deepest depth is selected from a measurement field of view for the second main surface; a plane including the bottom of the second recess being

[0017] [6] The heat transfer-suppressing sheet according to any one of [1] to [5], wherein the second main surface of the heat insulating material has a fuzz portion in which at least one of the organic fibers and the inorganic fibers protrude.

[0018] [7] The heat-transfer-suppressing sheet according to any one of [1] to [6], further comprising a mica sheet laminated on the second main surface side of the heat insulating material.

[0019] [8] The heat-transfer-suppressing sheet according to any one of [1] to [7], further comprising a mica sheet laminated on a surface of the elastic body opposite to a surface facing the thermal insulating material.

[0020] [9] The heat-transfer-suppressing sheet according to any one of [1] to [8], wherein the inorganic particles are particles made of at least one inorganic material selected from oxide particles, carbide particles, nitride particles, and inorganic hydrate particles.

[0021]

[10] The heat transfer-suppressing sheet according to any one of [1] to [9], wherein the inorganic particles include at least one type of particles selected from dry silica particles and silica aerogel.

[0022]

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

[10] , wherein the inorganic particles further include at least one type of particles selected from titania, zircon, zirconia, silicon carbide, zinc oxide, and alumina.

[0023] The above object of the present invention is achieved by the following configuration

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

[0024]

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

[11] , comprising: an insulating material fabrication step of fabricating the insulating material having a pair of main surfaces perpendicular to the thickness direction that have different surface roughnesses; and a lamination step of laminating the elastic body and the insulating material, with one of the pair of main surfaces having a smaller surface roughness as the first main surface and the other as the second main surface, so that the first main surface of the insulating material faces the elastic body.

[0025] Furthermore, preferred embodiments of the present invention relating to a method for producing a heat transfer-suppressing sheet relate to the following

[13] to

[14] .

[0026]

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

[12] , wherein the heat insulating material preparation step includes: a heat insulating precursor preparation step of preparing a heat insulating precursor containing the inorganic particles and at least one of the organic fibers and the inorganic fibers; and a processing step of polishing or cutting the heat insulating precursor along a direction perpendicular to a thickness direction thereof, so that the polished or cut surface is the second main surface and the unpolished or uncut surface is the first main surface.

[0027]

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

[13] , wherein in the heat insulating precursor producing step, the heat insulating precursor is produced by a dry method.

[0028] The above object of the present invention is 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 [9], wherein the plurality of battery cells are connected in series or in parallel.

[0030] According to the heat transfer-suppressing sheet of the present invention, an elastic body is laminated on the insulating material, allowing the sheet to conform to deformation of the battery cells, thereby suppressing deterioration of battery performance. Furthermore, the first and second main surfaces of the insulating material have different surface roughnesses, and the first main surface, which has a smaller maximum height, is positioned facing the elastic body, ensuring a large contact area between the insulating material and the elastic body and preventing misalignment between the insulating material and the elastic body. Furthermore, the second main surface, which has a larger maximum height, is positioned on the heat-generating side of the battery cells, etc., forming a gap between the second main surface and the battery cells, etc., further improving insulating performance and providing a cushioning effect via the second main surface.

[0031] Furthermore, according to the present invention, a heat insulating material having a pair of main surfaces with different surface roughnesses can be produced, and a heat transfer suppression sheet with excellent performance can be easily manufactured simply by adjusting the surface of the heat insulating material that faces the elastic body, thereby reducing manufacturing costs.

[0032] Furthermore, the battery pack of the present invention has high thermal insulation performance as described above, and also includes a heat transfer-suppressing sheet that prevents slippage, thereby making it possible to suppress thermal runaway of the battery cells in the battery pack and the spread of flames to the outside of the battery case.

[0033] FIG. 1 is a schematic cross-sectional view showing a heat-transfer-suppressing sheet according to an embodiment of the present invention. FIG. 2 is a cross-sectional view showing a battery pack having a heat-transfer-suppressing sheet according to an embodiment of the present invention. FIG. 3 is a diagram showing the shape of a first main surface of a heat insulating material measured by a coordinate measuring machine. FIG. 4 is a diagram showing the shape of a second main surface of a heat insulating material measured by a coordinate measuring machine. FIG. 5A is a cross-sectional view showing a heat insulating precursor preparation step in the method for producing a heat transfer sheet according to this embodiment. FIG. 5B is a cross-sectional view showing a processing step in the method for producing a heat transfer sheet according to this embodiment. FIG. 5C is a cross-sectional view showing the state after the processing step in the method for producing a heat transfer sheet according to this embodiment.

[0034] The present inventors conducted extensive research into a heat-transfer-suppressing sheet that can solve the above-mentioned problems. As a result, they discovered that a heat-transfer-suppressing sheet comprising a pair of main surfaces with different maximum heights is effective in both improving heat-insulating performance and preventing misalignment. Specifically, by arranging the first main surface, which has a smaller maximum height, facing the elastic body, a large contact area between the heat-insulating material and the elastic body can be ensured, preventing misalignment between the heat-insulating material and the elastic body. Furthermore, by arranging the second main surface, which has a larger maximum height, facing the battery cells, etc., a buffering effect can be obtained between the heat-insulating material and the battery cells, and a gap can be formed between the second main surface and the battery cells, further improving heat-insulating performance.

[0035] The present invention has been made based on the above findings. A heat transfer-suppressing sheet according to an embodiment of the present invention will be described in detail below with reference to the drawings. It should be noted that the present invention is not limited to the embodiment described below, and can be modified as desired without departing from the spirit and scope of the present invention.

[0036] [Heat Transfer-Suppressing Sheet] FIG. 1 is a schematic cross-sectional view showing a heat transfer-suppressing sheet according to an embodiment of the present invention. The heat transfer-suppressing sheet 10 according to this embodiment includes a thermal insulating material 11 and an elastic body 12 laminated in the thickness direction of the thermal insulating material 11. The thermal insulating material 11 contains inorganic particles and at least one of organic fibers and inorganic fibers. The insulating material contained in the thermal insulating material 11 will be described in detail later. The thermal insulating material 11 also has a pair of first and second main surfaces 21 and 22, with the first main surface 21 facing the elastic body 12. The first main surface 21 of the thermal insulating material 11 may be substantially flat, or may have a plurality of protrusions 21a protruding toward the elastic body 12 and recesses 21b recessed in a direction away from the elastic body 12. When the protrusions 21a and recesses 21b are formed, a sea-island structure may be formed in which the protrusions 21a form island portions and the recesses 21b form a sea portion. On the other hand, the second main surface 22 of the insulating material 11 is formed with a plurality of convex portions 22a that protrude outward from the heat transfer suppression sheet 10 and concave portions 22b that are recessed toward the elastic body 12, and a sea-island structure is formed in which the convex portions 22a are island portions and the concave portions 22b are sea portions.

[0037] In this embodiment, the maximum height Sz1 representing the surface roughness of the first main surface 21 is designed to be smaller than the maximum height Sz2 representing the surface roughness of the second main surface 22. The maximum height Sz1 of the first main surface 21 represents the difference in height between the highest protruding convex portion and the deepest recessed portion on the first main surface 21. Furthermore, the maximum height Sz2 of the second main surface 22 represents the difference in height between the highest protruding convex portion and the deepest recessed portion on the second main surface 22. The maximum heights Sz1 and Sz2 can be measured using a three-dimensional measuring machine (for example, a one-shot 3D shape measuring machine VR-3000 (manufactured by Keyence Corporation)) that photographs the uneven shapes of the first main surface 21 and the second main surface 22.

[0038] The configuration and effects of applying the heat-transfer-suppressing sheet 10 configured as described above to a battery pack will be described in detail below. Fig. 2 is a cross-sectional view schematically showing a battery pack including a heat-transfer-suppressing sheet according to an embodiment of the present invention. Note that part of the structure of the heat-transfer-suppressing sheet 10 shown in Fig. 1 is simplified in Fig. 2.

[0039] The battery pack 100 includes a battery case 30, a plurality of battery cells 20a, 20b, and 20c housed inside the battery case 30, and a heat-transfer-suppressing sheet 10 interposed between the battery cells 20a and 20b and between the battery cells 20b and 20c. The plurality of battery cells 20a, 20b, and 20c are connected in series or in parallel by bus bars (not shown) or the like. The battery cells 20a, 20b, and 20c are preferably, for example, lithium-ion secondary batteries, but are not limited thereto and may also be other secondary batteries.

[0040] In the battery pack 100 configured in this manner, the insulating material 11 contains inorganic particles and has high insulating properties, thereby suppressing the transfer of heat from a battery cell that has experienced thermal runaway to adjacent battery cells. The heat-transfer-suppressing sheet 10 also includes the insulating material 11 and the elastic body 12 laminated on the insulating material 11. Therefore, after the heat-transfer-suppressing sheet 10 is compressed in its thickness direction during battery cell charging, when the pressure is relieved by the battery cell discharging, the restoring force of the elastic body 12 causes the heat-transfer-suppressing sheet 10 to return to its original thickness, maintaining the force holding the heat-transfer-suppressing sheet 10 between adjacent battery cells.

[0041] Regardless of the material, the surface of the elastic body 12 often contains numerous small holes. If the second main surface 22, which has a larger maximum height, were positioned facing the elastic body 12 and the convex portions 22 a of the second main surface 22 were fitted into the holes on the surface of the elastic body 12, the convex portions 22 a would act as anchors, firmly securing the thermal insulator 11 and the elastic body 12. However, in this embodiment, the diameter of the holes in the elastic body 12 is significantly smaller than the size of the convex portions 22 a of the thermal insulator 11 in a planar view, so no anchor effect can be achieved. Furthermore, because the height and shape of the convex portions 22 a of the thermal insulator are irregular, the pressing force between the thermal insulator 11 and the elastic body 12 becomes uneven, potentially resulting in localized, unexpected stress. Therefore, if the battery cell contracts and the pressing force on the heat transfer-suppressing sheet 10 decreases, the ability to suppress misalignment becomes weak.

[0042] In contrast, in this embodiment, the first main surface 21, which has a smaller maximum height, is disposed opposite the elastic body 12, and therefore the contact area between the thermal insulator 11 and the elastic body 12 is larger than when the second main surface 22, which has a larger maximum height, faces the elastic body 12. Furthermore, because the contact area between the thermal insulator 11 and the elastic body 12 is large even when no pressure is applied to the heat transfer-suppressing sheet 10, a large contact area can be ensured between the first main surface 21 and the elastic body 12 during both expansion and contraction of the battery cell, and pressure is applied evenly across the entire surface when pressed. This improves the ability to suppress misalignment.

[0043] Furthermore, because the second main surface 22, which has a greater maximum height, is located outside the heat transfer-suppressing sheet 10, when the second main surface 22 is pressed by a battery cell, for example, a cushioning effect can be obtained by the convex portions 22a and concave portions 22b of the second main surface 22. In particular, in this embodiment, the elastic body 12 is disposed only on one main surface (first main surface 21) of the heat insulating material 11, and no elastic body 12 is disposed on the other main surface (second main surface 22). Therefore, when a cushioning effect is obtained on the second main surface 22 side, it is possible to further suppress a decrease in battery performance caused by expansion and contraction of the battery cell.

[0044] Furthermore, according to this embodiment, as shown in Figure 2, a relatively large gap 24 is formed between the battery cell and the recess 22b on the second main surface 22 of the thermal insulator 11. Therefore, superior thermal insulation can be achieved compared to when the second main surface 22 of the thermal insulator 11 is nearly flat.

[0045] In the present embodiment, it is preferable that the second main surface 22 has a fluffy portion (not shown) in which at least one of the organic fibers and the inorganic fibers protrudes. When the second main surface 22 has a fluffy portion, voids are also generated within the fluffy portion, thereby further improving the heat insulating properties of the heat transfer-suppressing sheet 10.

[0046] Furthermore, in the heat-transfer-suppressing sheet 10 of this embodiment, a mica sheet (not shown) may be laminated on the second main surface 22 of the thermal insulator 11 or on the main surface 25 of the elastic body 12 opposite the surface facing the thermal insulator 11. The mica sheet is resistant to heat and impact. Therefore, if an abnormality occurs in a battery cell adjacent to the heat-transfer-suppressing sheet and a fire breaks out, the mica sheet can protect the thermal insulator 11 and the elastic body 12, thereby preventing the fire from spreading to other battery cells.

[0047] Next, the first main surface 21 and the second main surface 22 will be described in more detail.

[0048] <Difference Between Maximum Height Sz1 of First Main Surface and Maximum Height Sz2 of Second Main Surface: 0.2 mm or More> As described above, by having different surface roughnesses on the first main surface 21 of the heat insulating material 11 facing the elastic body 12 and the second main surface 22 on the opposite side thereof, it is possible to improve the heat insulating performance of the heat transfer-suppressing sheet 10 while suppressing misalignment. In this embodiment, the difference between the maximum height Sz1 and the maximum height Sz2 is not particularly limited. For example, if the difference is 0.2 mm or more, the effect of substantially different surface roughness can be obtained. Therefore, the difference between the maximum height Sz1 and the maximum height Sz2 is preferably 0.2 mm or more, more preferably 0.3 mm or more, and even more preferably 0.4 mm or more.

[0049] On the other hand, if the difference between the maximum height Sz1 and the maximum height Sz2 is large, the maximum height Sz2 of the second main surface 22 becomes large. If the maximum height Sz2 of the second main surface 22 becomes too large, the position of the recess 22b will be too close to the elastic body 12, which may cause the heat insulating material 11 to become partially thin and reduce its heat insulating properties. Therefore, the difference between the maximum height Sz1 and the maximum height Sz2 is preferably 1.5 mm or less, more preferably 1.0 mm or less, and even more preferably 0.8 mm or less.

[0050] <Maximum height Sz1 of first main surface: 0.1 mm or more and 1.0 mm or less> The smaller the maximum height Sz1 of the first main surface 21 of the thermal insulation material 11, the larger the contact area with the elastic body 12, improving the effect of suppressing slippage. However, if the maximum height Sz1 of the first main surface 21 is to be less than 0.1 mm, a special manufacturing method must be used, which may increase manufacturing costs. Therefore, it is preferable that the maximum height Sz1 of the first main surface 21 be 0.1 mm or more.

[0051] On the other hand, if the maximum height Sz1 of the first main surface 21 of the thermal insulation material 11 becomes too large, the contact area with the elastic body 12 becomes small, and the effect of suppressing slippage decreases. Therefore, the maximum height Sz1 of the first main surface 21 is preferably 1.0 mm or less, more preferably 0.5 mm or less, and even more preferably 0.3 mm or less.

[0052] <Maximum height Sz2 of second main surface: 0.5 mm or more and 1.4 mm or less> If the maximum height Sz2 of the second main surface 22 of the thermal insulation material 11 is too small, the volume of the voids 24 that are effective for obtaining a thermal insulating effect decreases. Therefore, the maximum height Sz2 of the second main surface 22 is preferably 0.5 mm or more, more preferably 0.6 mm or more, and even more preferably 0.7 mm or more.

[0053] On the other hand, the larger the maximum height Sz2 of the second main surface 22 of the thermal insulation material 11, the larger the volume of the voids 24 and the better the thermal insulation effect, but as mentioned above, there is a risk that the position of the recesses 22b will be too close to the elastic body 12, resulting in a decrease in thermal insulation. Therefore, the maximum height Sz2 of the second main surface 22 is preferably 1.4 mm or less, and more preferably 1.2 mm or less.

[0054] It should be noted that when measuring the difference between the maximum height Sz1 of the first main surface 21 and the maximum height Sz2 of the second main surface 22, or the maximum height Sz1 of the first main surface 21 or the maximum height Sz2 of the second main surface 22, the presence of even slight scratches or dust on the first main surface 21 or the second main surface 22 may cause the measured values ​​to fall outside the above-described preferable range. However, the presence of scratches or dust is a unique phenomenon, and the effects of the present invention can be fully obtained even if scratches or dust are present in some areas. Therefore, if there are any singular points in the measured values ​​due to scratches or dust, it is preferable to determine whether the measured values ​​are within the preferable range after excluding the singular points.

[0055] In addition, in this embodiment, the difference in surface properties between the first main surface 21 and the second main surface 22 of the thermal insulation material 11 can be determined by the ratio of the surface areas of the first main surface 21 and the second main surface 22, and the volume ratio of the convex portions 21 a on the first main surface 21 to the convex portions 22 a on the second main surface 22. Below, a method for measuring the surface shape and preferred ranges for the surface area ratio and volume ratio on each surface will be described.

[0056] Fig. 3 is a diagram showing the shape of the first main surface of the thermal insulation material measured by a coordinate measuring machine, and Fig. 4 is a diagram showing the shape of the second main surface. In Fig. 3, shape diagram 40c shows the cross-sectional shape along line CC on the first main surface 21 side of the thermal insulation material 11, and shape diagram 40d shows the cross-sectional shape along line D-D on the first main surface 21 side of the thermal insulation material 11. Also, in Fig. 4, shape diagram 40a shows the cross-sectional shape along line A-A on the second main surface 22 side of the thermal insulation material 11, and shape diagram 40b shows the cross-sectional shape along line B-B on the second main surface 22 side of the thermal insulation material 11. Here, a one-shot 3D shape measuring machine VR-3000 (manufactured by Keyence Corporation) was used as the three-dimensional measuring machine.

[0057] 3 and 4, the coordinate measuring machine is set so that the centers of the measurement fields R1 and R2 are located at the centers of the first main surface 21 and the second main surface 22 of the thermal insulation material 11, and images are taken of the surfaces of the first main surface 21 and the second main surface 22. Note that if the thermal insulation material 11 is warped, accurate measurement of unevenness will not be possible, so the corners of the thermal insulation material 11 are pressed and fixed to perform measurements without being affected by the warping.

[0058] By photographing the measurement fields R1 and R2 on the first principal surface 21 and the second principal surface 22 using the three-dimensional measuring machine, it is possible to measure the surface area and the volume of the convex portions, which will be described later.

[0059] <Surface Area Ratio (Sfa2 / Sfa1): 1.03 or More> As shown in FIG. 1 , the second main surface 22 of the thermal insulator 11 has large protruding convex portions 22a and large recessed portions 22b. Therefore, the surface area of ​​the second main surface 22 measured along the convex portions 22a and the recessed portions 22b is larger than the area of ​​the second main surface 22 in a planar view. Furthermore, a large surface area of ​​the second main surface 22 does not indicate the presence of large convex portions or large recessed portions in a planar view, but rather the presence of numerous convex portions 22a and recessed portions 22b. On the other hand, the first main surface 21 of the thermal insulator 11 is substantially flat, and the height of the convex portions 21a and the depth of the recessed portions 21b are smaller than those of the second main surface 22. Therefore, the surface area of ​​the first main surface 21 measured along the convex portions 21a and the recessed portions 21b is approximately the same as the area of ​​the first main surface 21 in a planar view.

[0060] In this embodiment, the surface area ratio (Sfa2 / Sfa1) of the surface area Sfa2 of the second main surface 22 per unit area to the surface area Sfa1 of the first main surface 21 per unit area can be used as an index for determining the surface texture of each surface. That is, if the surface area ratio (Sfa2 / Sfa1) is 1.03 or greater, it can be determined that the second main surface 22 has convex portions 22a and concave portions 22b with appropriate heights and shapes, and that the first main surface 21 is flatter than the second main surface 22. Therefore, the surface area ratio (Sfa2 / Sfa1) of the surface area Sfa2 of the second main surface 22 per unit area to the surface area Sfa1 of the first main surface 21 per unit area is preferably 1.03 or greater, more preferably 1.04 or greater, and even more preferably 1.05 or greater.

[0061] Furthermore, if the surface area ratio (Sfa2 / Sfa1) becomes too large, the maximum height Sz2 of the second main surface 22 also becomes large, which may result in a decrease in heat insulation, as described above. Therefore, the surface area ratio (Sfa2 / Sfa1) is preferably 1.1 or less, and more preferably 1.08 or less.

[0062] In the above surface area ratio, the surface area Sfa1 of the first principal surface 21 per unit area is a value calculated by dividing the surface area in the measurement field of view for the first principal surface by the area of ​​the measurement field. Furthermore, the surface area Sfa2 of the second principal surface 22 per unit area is a value calculated by dividing the surface area in the measurement field of view for the second principal surface by the area of ​​the measurement field. The surface area in the measurement field of view is an area measured along the irregularities of the surface. The area of ​​the measurement field of view is an area in a planar view in the measurement field of view, and is a value that is not affected by the convex portions 22 a and the concave portions 22 b.

[0063] <Volume Ratio (V2 / V1): 2.0 or More> As with the surface area ratio, the second main surface 22 of the thermal insulating material 11 has large protruding convex portions 22a and large recessed portions 22b, while the convex portions 21a and recessed portions 21b of the first main surface 21 are small. A large volume of the second main surface 22 does not indicate the presence of a small number of small convex portions, but rather the presence of convex portions of a desired size. Furthermore, a small volume of the first main surface 21 indicates high flatness and a large contact area with the elastic body 12. Therefore, when the volume ratio (V2 / V1) of the volume V2 of the convex portions 22a on the second main surface 22 to the volume V1 of the convex portions 21a on the first main surface 21 and the surface area ratio (Sfa2 / Sfa1) are within a predetermined range, the thermal insulating material can be determined to have even better surface properties. If the value of the volume ratio (V2 / V1) is 2.0 or more, it can be determined that the second main surface 22 has convex portions 22a and concave portions 22b with appropriate heights and shapes, and the effect of further preventing slippage between the first main surface 21 and the elastic body 12 can be obtained. Therefore, the volume ratio (V2 / V1) of the volume V2 of the convex portions 22a on the second main surface 22 to the volume V1 of the convex portions 21a on the first main surface 21 is preferably 2.0 or more, more preferably 2.5 or more, even more preferably 3.0 or more, even more preferably 3.5 or more, and particularly preferably 4.0 or more.

[0064] Furthermore, if the value of the volume ratio (V2 / V1) becomes too large, the maximum height Sz2 of the second main surface 22 also becomes large, which may result in a decrease in heat insulation. Therefore, the volume ratio (V2 / V1) is preferably 7.0 or less, and more preferably 5.0 or less.

[0065] The volume V1 measured by the coordinate measuring machine refers to, for example, as shown in the shape diagram 40c of Fig. 3, when the first recess 41 having the deepest depth is selected from the measurement field of view R1 of the first main surface 21, and a plane including the bottom of this first recess 41 and perpendicular to the thickness direction of the thermal insulation material 11 is set as the reference plane X1, and the volume V2 refers to, for example, as shown in the shape diagram 40a of Fig. 4, when the second recess 42 having the deepest depth is selected from the measurement field of view R2 of the second main surface, and a plane including the bottom of this second recess 42 and perpendicular to the thickness direction of the thermal insulation material 11 is set as the reference plane X2, and the volume V2 refers to, for example, the volume of the portion protruding outward from the reference plane X2.

[0066] For three different insulating materials, the surface areas and volumes of the first and second main surfaces are measured, and the surface area ratio and volume ratio are calculated, resulting in the values ​​shown in Table 1 below, for example.

[0067]

[0068] The heat insulating material 11 and elastic body 12 that constitute the heat transfer-suppressing sheet 10 according to this embodiment, as well as the mica sheet that may be laminated thereon, will be described in detail below.

[0069] [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 contains inorganic particles and at least one of organic fibers and inorganic fibers and 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 even more preferably less than 0.02 (W / m·K). The thermal conductivity of the thermal insulation material can be measured in accordance with JIS R 2251, "Test Method for Thermal Conductivity of Refractories."

[0070] (Size of the insulating material) The size of the insulating material 11 can be designed arbitrarily depending on the size of the elastic body 12 to be laminated on the insulating material 11 and the size of the battery cells 20a, 20b, and 20c shown in Figure 2. To obtain the desired thermal insulation properties, it is preferable that the size of the first main surface 21 and the second main surface 22 of the insulating material 11 and the size of the main surfaces 23 and 25 of the elastic body 12 are approximately the same. When the sizes of the main surfaces of the insulating material 11 and the elastic body 12 are designed to be approximately the same, "approximately the same" means that the difference between the sizes is preferably up to ±5% of the average value of the two, more preferably up to ±3%, and even more preferably up to ±1%.

[0071] Next, the materials that make up the heat insulating material will be described.

[0072] <Inorganic Particles> The heat insulating material contains inorganic particles. As the inorganic particles, 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. Particles mainly composed of multiple metal oxides can also be used. The shape of the inorganic particles is not particularly limited, but it is preferable to include at least one type selected from nanoparticles, hollow particles, porous particles, and scale-like particles. Specific examples of inorganic particles that can be used include silica nanoparticles, metal oxide particles, inorganic balloons such as microporous particles and hollow silica particles, particles made of thermally expandable inorganic materials, and particles made of hydrous porous bodies. Furthermore, particles made of mica can also be used as the inorganic particles.

[0073] 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.

[0074] In addition, when two or more inorganic particles having different heat transfer suppression effects are used in combination, the heat generating body can be cooled 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 being referred to as the first inorganic particles and the large-diameter inorganic particles being referred to as the second inorganic particles.

[0075] <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.

[0076] (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.

[0077] 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.

[0078] (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. When nanoparticles are used as the first inorganic particles, the fine voids are dispersed, resulting in 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, when nanoparticles with a small average primary particle diameter are used as oxide particles, an 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 its internal density. This is thought to be because nanoparticles are prone to forming fine voids between particles due to electrostatic repulsion, and their low bulk density allows the particles to be packed together to provide cushioning.

[0079] 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 heat transfer-suppressing sheet 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 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.

[0080] Generally, wet silica has agglomerated particles, whereas dry silica allows particles to be dispersed. In the temperature range of 300°C or less, heat conduction is dominated by conductive heat transfer, so dry silica, which allows particles to be dispersed, can provide superior heat insulating performance compared to wet silica. Note that the heat insulating material according to this embodiment is preferably produced using a manufacturing method in which a mixture containing the materials is processed into a sheet shape by a dry method. Therefore, it is preferable to use dry silica, silica aerogel, or the like, which has low thermal conductivity, as the inorganic particles.

[0081] (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 the 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 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 nanoparticles is more preferably 50 nm or less, and even more preferably 10 nm or less.

[0082] (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.

[0083] 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

[0084] As described above, the heat transfer-suppressing sheet 10 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 contained in the thermal insulating material 11 are preferably made of inorganic hydrates with a thermal decomposition onset temperature of 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 preferred because they can efficiently suppress temperature rises and are within the temperature range of the rapid temperature rise in a battery cell that has experienced thermal runaway.

[0085] (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 some time for the first inorganic particles (inorganic hydrate) near the center of the thermal insulating material 11 to reach their thermal decomposition temperature, and therefore the first inorganic particles near the center of the thermal insulating material 11 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.

[0086] (Particles Made of Thermally Expandable Inorganic Material) Examples of thermally expandable inorganic materials include vermiculite, bentonite, mica, and perlite.

[0087] (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.

[0088] (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.

[0089] (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.

[0090] (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.

[0091] <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.

[0092] 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.

[0093] 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.

[0094] 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.

[0095] (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.

[0096] (Inorganic Particle Content) In the present embodiment, if the total content of inorganic particles in the thermal insulation material 11 is appropriately controlled, the thermal insulation properties of the thermal insulation material 11 can be sufficiently ensured. The total content of inorganic particles is preferably 60% by mass or more, and more preferably 70% by mass or more, relative to the total mass of the thermal insulation material 11. Furthermore, if the total content of inorganic particles becomes 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 is preferably 95% by mass or less, and more preferably 90% by mass or less, relative to the total mass of the thermal insulation material 11.

[0097] The content of inorganic particles in the heat insulating material 11 can be calculated, for example, by heating the heat insulating material 11 at 800° C., decomposing the organic components, and then measuring the mass of the remaining portion.

[0098] The heat insulating material of the heat transfer sheet according to this embodiment contains at least one of organic fibers and inorganic fibers in addition to the inorganic particles. The organic fibers and inorganic fibers contained in the heat insulating material will be described below.

[0099] <Organic Fibers> The organic fibers have the effect of imparting flexibility to the insulating material 11, and by forming a skeleton, they have the effect of increasing the strength of the insulating material 11. Furthermore, if inorganic particles and other organic fibers are fused to the surface of the organic fibers, the effect of increasing the strength of the sheet and the effect of maintaining its shape can be further improved. Furthermore, if the insulating material 11 contains organic fibers in an appropriate content, multiple voids are formed inside the insulating material 11, and when the insulating material 11 is heated, air and moisture can be released to the outside through the voids.

[0100] Although single-component organic fibers can be used as the organic fiber material in the thermal insulation material 11, it is preferable to use binder fibers with a core-sheath structure. The binder fibers with a core-sheath structure have a core extending in the longitudinal direction of the fiber and a sheath formed to cover the outer surface of the core. In this case, the core is made of a first organic material, and the sheath is made of a second organic material, and the melting point of the first organic material is higher than that of the second organic material.

[0101] (First Organic Material) In the present embodiment, when a binder fiber having a core-sheath structure is used, the first organic material constituting the core is not particularly limited as long as it has a melting point higher than that of the sheath present on the outer surface of the core, i.e., the second organic material. Examples of the first organic material include at least one selected from polyethylene terephthalate, polypropylene, and nylon.

[0102] (Second Organic Material) The second organic material is not particularly limited as long as it has a melting point lower than that of the first organic material constituting the organic fiber. Examples of the second organic material include at least one selected from polyethylene terephthalate, polyethylene, polypropylene, and nylon. The melting point of the second organic material is preferably 90°C or higher, more preferably 100°C or higher. The melting point of the second organic material is preferably 150°C or lower, more preferably 130°C or lower.

[0103] (Organic Fiber Content) In this embodiment, if the organic fiber content in the thermal insulation material 11 is appropriately controlled, a sufficient skeleton reinforcement effect can be obtained. The organic fiber content is preferably 5 mass% or more, and more preferably 10 mass% or more, relative to the total mass of the thermal insulation material 11. Furthermore, if the organic fiber content is too high, the inorganic particle content will relatively decrease. Therefore, in order to obtain the desired thermal insulation performance, the organic fiber content is preferably 25 mass% or less, and more preferably 20 mass% or less, relative to the total mass of the thermal insulation material 11.

[0104] (Fiber length of organic fibers) The fiber length of the organic fibers 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 function as a skeleton and ensuring the compressive strength of the thermal insulating material, the average fiber length of the organic fibers is preferably 0.5 mm or more.

[0105] <Inorganic Fibers> When the thermal insulation material 11 contains inorganic fibers, the inorganic fibers may be a single inorganic fiber or a combination of two or more 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, 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 natural 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. From the standpoint of handleability, it is preferable that the thermal insulation material contain at least one type of inorganic fiber selected from silica-alumina fiber, alumina fiber, silica fiber, rock wool, alkaline earth silicate fiber, and glass fiber.

[0106] 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.

[0107] The preferred lower limit of the average fiber length of the inorganic fibers is 0.1 mm, more preferably 0.5 mm. Meanwhile, the preferred upper limit of the average fiber length of the inorganic fibers is 50 mm, more preferably 10 mm. If the average fiber length of the inorganic fibers is less than 0.1 mm, the inorganic fibers are less likely to intertwine with each other, which may reduce the mechanical strength of the thermal insulation material 11. Meanwhile, if the average fiber length exceeds 50 mm, although a reinforcing effect is obtained, the inorganic fibers may not be able to intertwine tightly with each other, or may curl up on their own, which may result in reduced thermal insulation.

[0108] 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.

[0109] (Inorganic Fiber Content) In the present embodiment, when the heat insulating material 11 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 11 .

[0110] Furthermore, the content of inorganic fibers is more preferably 5% by mass or more and 10% by mass or less of the total mass of the thermal insulation material 11. By setting the content in this range, the shape retention, compressive force resistance, wind pressure resistance, and inorganic particle retention capacity of the inorganic fibers are exhibited in a balanced manner. Furthermore, by appropriately controlling the content of inorganic fibers, the organic fibers and inorganic fibers are entangled with each other to form a three-dimensional network, thereby improving the effect of retaining inorganic particles and other compounding materials described below.

[0111] <Other Compounding Materials> (Hot Melt Powder) In this embodiment, in addition to the inorganic particles, organic fibers, and inorganic fibers, the material mixture may contain a hot melt powder. The hot melt powder contains, for example, a third organic material different from the first and second organic materials, and is a powder that melts when heated. When the hot melt powder is added to the mixture and heated, it melts, and when cooled, it hardens in a state that includes the surrounding inorganic particles. This prevents the inorganic particles from falling off the insulating material 11.

[0112] 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.

[0113] Alternatively, the type of hot melt powder used can be selected so that its melting point lies between the melting points of the core and the sheath. When a hot melt powder with such a melting point is used, the sheath and hot melt powder melt together, and then when they cool and harden, the organic fibers (core), the molten sheath around them, and the hot melt powder present in the gaps between the inorganic particles harden first. As a result, the position of the organic fibers can be fixed, and then the molten sheath is fused to the organic fibers, facilitating the formation of a three-dimensional skeleton. This further improves the strength of the entire sheet.

[0114] 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.

[0115] 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.

[0116] (Hot melt powder content) When hot melt powder is contained in the insulating material 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 mass% or more, more preferably 1 mass% or more, based on the total mass of the insulating material. On the other hand, since increasing the hot melt powder content relatively reduces the content of inorganic particles, etc., in order to obtain the desired insulating performance, the hot melt powder content is preferably 5 mass% or less, more preferably 4 mass% or less, based on the total mass of the insulating material.

[0117] When the insulating material 11 contains a hot melt powder, the heating temperature in the heating step is preferably set to be at least 10°C higher, more preferably at least 20°C higher, than the higher of the melting point of the second organic material constituting the sheath and the melting point of the third organic material constituting the hot melt powder. On the other hand, the heating temperature is preferably set to be at least 10°C lower, more preferably at least 20°C lower, than the melting point of the first organic material constituting the core. Setting the heating temperature at such a temperature allows for the formation of a strong skeleton, further improving the strength of the sheet and preventing the inorganic particles from falling off.

[0118] The heat insulating material 11 may further contain other binders, colorants, etc. as needed. These are all useful for the purpose of reinforcing the heat insulating material 11 or improving its formability, and the total amount of these additives relative to the total mass of the heat insulating material 11 is preferably 10% by mass or less, more preferably 8% by mass or less, and even more preferably 5% by mass or less.

[0119] <Elastic Body> The heat transfer-suppressing sheet 10 according to this embodiment has an elastic body 12 laminated in the thickness direction of the heat insulating material 11. The elastic body 12 flexibly deforms in response to deformation of the battery cells 20a, 20b, 20c, and is obtained by processing an elastic material into a sheet shape. Examples of such an elastic body include rubber and elastomer. Specific examples of rubber include foamed silicone.

[0120] (Thickness of Elastic Body) The thickness of the elastic body 12 is not particularly limited, but is preferably 1 mm or more and 10 mm or less in order to effectively obtain the above-mentioned effects of the elastic body 12. In addition, it is preferable that the shape and size of the surface of the elastic body 12 in a direction perpendicular to the thickness direction be approximately the same as the first main surface 21 and the second main surface 22 of the thermal insulation material 11.

[0121] In this embodiment, a mica sheet containing mica can be laminated in addition to the heat insulating material 11 and the elastic body 12. The mica sheet will be specifically described below.

[0122] <Mica Sheet> The mica sheet is a mica sheet material containing inorganic particles, mica, processed into a sheet shape. Mica has excellent heat resistance and insulating properties, and a mica sheet made by processing a material containing mica into a sheet shape also has excellent impact resistance. Therefore, for example, if the battery cell 20a explodes due to high temperature and debris is generated, damage to the insulating material 11 and the elastic body 12 can be suppressed. As a result, high thermal insulation can be maintained between the battery cell 20a and the battery cell 20b.

[0123] The mica sheet material preferably contains oxide particles, oxide fibers, etc. in addition to mica. ２ , Al ２ O ３ , Ti ２ O ３However, the present invention is not limited to these materials. It is more preferable to use a mica sheet made of a natural mineral. The sheet shape may be a flat sheet without holes or may have holes. If holes are provided in at least a portion of the center or other regions of the mica sheet, the mica sheet can follow the battery cells 20a, 20b, 20c without cracking when the battery cells 20a, 20b, 20c expand and contract.

[0124] [Method for manufacturing a heat transfer-suppressing sheet] Next, an example of a method for manufacturing a heat transfer-suppressing sheet according to an embodiment of the present invention will be described below. Fig. 5A is a cross-sectional view showing a heat insulation precursor preparation step in the method for manufacturing a heat transfer sheet according to this embodiment. Fig. 5B is a cross-sectional view showing a processing step in the method for manufacturing a heat transfer sheet according to this embodiment. Fig. 5C is a cross-sectional view showing the state after the processing step in the method for manufacturing a heat transfer sheet according to this embodiment.

[0125] <Insulating Material Producing Step> In the insulating material producing step, an insulating material having a pair of main surfaces perpendicular to the thickness direction and different surface roughnesses is produced. The insulating material producing step will be described in more detail.

[0126] (Heat-insulating precursor preparation step) As shown in FIG. 5A, a heat-insulating precursor 1 containing inorganic particles and at least one of organic fibers and inorganic fibers is prepared.

[0127] Here, an example of a method for producing the heat insulating precursor 1 will be further described. For example, inorganic fibers or binder fibers having a core-sheath structure and inorganic particles are introduced into a mixer such as a V-type mixer in a predetermined ratio to produce a mixture. It is preferable to use fibers 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 fibers. In this case, the melting point of the first organic material is set to be higher than the melting point of the second organic material.

[0128] The resulting mixture is then placed in a mold and pressurized using a press or similar device. 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 present around the binder fiber are fused to the core (organic fiber), and the binder fibers are also fused to each other in the areas where they were in contact with each other. A matrix containing inorganic particles is formed between the multiple organic fibers. This allows the heat insulating precursor 1 to be processed into a sheet. The pair of main surfaces 2 of the heat insulating precursor 1 are pressed by a press or similar device, and therefore have a shape that follows the shape of the press surface. In other words, using a press with a smooth press surface reduces the surface roughness of the main surfaces 2.

[0129] (Processing Step) Next, as shown in FIG. 5B , the insulating precursor 1 is cut along a cutting line 4 perpendicular to the thickness direction of the insulating precursor 1 using a cutting tool 3 such as a knife. This allows two insulating materials 11, as shown in FIG. 5C , to be produced. Note that in FIG. 5B , the cutting is performed so as to divide the thickness of the insulating precursor 1 into approximately two equal parts, but the cutting method and cutting position are not particularly limited in the present invention. For example, a method can be used in which one of the pair of main surfaces 2 of the insulating precursor 1 is polished using a grindstone, brush, or the like. This method allows the production of insulating materials 11 having a thickness approximately equal to that of the insulating precursor 1.

[0130] When cutting is performed using the cutting tool 3 in the processing step, convex portions 22a and concave portions 22b are formed on the cut surface due to shaking, vibration, etc. of the cutting tool 3, as shown in Figure 5C. Even when polishing is performed using a grindstone, brush, etc., unevenness is likely to be formed on the polished surface. Therefore, the surface that has been polished or cut can be the second main surface 22 of the thermal insulation material 11, which has a large surface roughness, and the surface that has not been polished or cut, i.e., the surface that has been pressed by a press or the like in the thermal insulation precursor production step, can be the first main surface 21, which has a small surface roughness.

[0131] If a surface with low surface roughness is produced by cutting or polishing, there is no need to use the pressed surface as the first main surface 21 and the cut or polished surface as the second main surface 22. Since it is sufficient that the maximum height of one of the main surfaces of the thermal insulation material 11 is smaller than the maximum height of the other main surface, if the maximum height of the cut or polished surface is small, a press with an uneven press surface should be used.

[0132] <Lamination Process> After the above-described insulating material preparation process, the lamination process is carried out. In the lamination process, one of, for example, two sheets of insulating material 11 obtained in the insulating material preparation process is selected. Then, the main surface 2 with the smaller surface roughness is designated as the first main surface 21, and the other is designated as the second main surface 22. The elastic body 12 and the insulating material 11 are laminated such that the first main surface 21 of the insulating material 11 faces the elastic body 12 prepared in advance. In this manner, the heat transfer-suppressing sheet 10 can be manufactured.

[0133] Thereafter, a mica sheet may be laminated on the insulating material 11 side or the elastic body 12 side of the laminate of the insulating material 11 and the elastic body 12, or on both sides.

[0134] In this embodiment, the material of the insulating precursor 1 contains at least one of organic fibers and inorganic fibers. When cutting is performed in the processing step, the fibers are cut, forming a fuzzed portion (not shown) on the cut surface. As described above, the fuzzed portion has the effect of further improving the thermal insulation. When the insulating precursor 1 is produced by a wet method, the fibers tend to be oriented along the cutting line 4 of the insulating precursor 1, and the cutting edge of the cutting tool 3 slides along the surface of the fibers, making it difficult to cut the fibers. In contrast, when produced by a dry method, many fibers in the insulating precursor 1 are distributed in directions oblique or perpendicular to the cutting line 4, so the cutting edge of the cutting tool 3 frequently cuts the fibers, making it easier for the fibers to be exposed. Therefore, the method for producing the insulating precursor 1 may be a wet method or a dry method. However, when intentionally forming a fuzzed portion, the insulating precursor production step is preferably performed by a dry method.

[0135] Although the manufacturing method of the present invention is not particularly limited, the above-described manufacturing method makes it possible to extremely easily produce two sheets of heat insulating material 11 whose main surfaces have different maximum heights simply by cutting heat insulating precursor 1 in the direction along main surface 2. As a result, heat transfer-suppressing sheet 10 can be easily manufactured without increasing manufacturing costs.

[0136] [Battery Pack] An example of a battery pack, which is an example of a power storage device, to which the heat-transfer-suppressing sheet 10 according to the embodiment of the present invention is applied is as shown in Fig. 2 above. The configuration and effects of the battery pack are also as described above. That is, the heat-transfer-suppressing sheet 10 has excellent heat insulating performance and can suppress misalignment, thereby ensuring safety in the event of an abnormality, and thus a highly safe battery pack can be obtained.

[0137] The battery pack 100 of this embodiment is not limited to the battery pack illustrated in Fig. 2. For example, the heat transfer-suppressing sheet 10 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.

[0138] 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-suppressing sheet 10 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.

[0139] 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.

[0140] This application is based on a Japanese patent application (Patent Application No. 2024-148468) filed on August 30, 2024, the contents of which are incorporated herein by reference.

[0141] REFERENCE SIGNS LIST 1 Heat insulating precursor 2, 23, 25 Main surface 3 Cutting tool 4 Cutting line 10 Heat transfer suppressing sheet 11 Heat insulating material 12 Elastic body 20a, 20b, 20c Battery cell 21 First main surface 21a, 22a Convex portion 21b, 22b Concave portion 22 Second main surface 24 Void portion 30 Battery case 100 Assembled battery

Claims

1. A heat-transfer-suppressing sheet comprising: a thermal insulating material containing inorganic particles and at least one of organic and inorganic fibers, the thermal insulating material having a pair of first and second principal surfaces; and an elastic body laminated in the thickness direction of the thermal insulating material, wherein the first principal surface of the thermal insulating material is disposed opposite the elastic body, and a maximum height Sz1 representing the surface roughness of the first principal surface is smaller than a maximum height Sz2 representing the surface roughness of the second principal surface.

2. The heat transfer suppressing sheet according to claim 1, wherein the difference between the maximum height Sz1 of the first main surface and the maximum height Sz2 of the second main surface is 0.2 mm or more.

3. The heat transfer suppressing sheet according to claim 2, wherein the maximum height Sz1 of the first main surface is 0.1 mm or more and 1.0 mm or less, and the maximum height Sz2 of the second main surface is 0.5 mm or more and 1.4 mm or less.

4. The heat transfer suppressing sheet according to claim 1, characterized in that, in the first principal surface and the second principal surface of the thermal insulating material photographed by a coordinate measuring machine, the surface area per unit area calculated by dividing the surface area in the measurement field for the first principal surface by the area of ​​the measurement field is Sfa1, and the surface area per unit area calculated by dividing the surface area in the measurement field for the second principal surface by the area of ​​the measurement field is Sfa2, the surface area ratio (Sfa2 / Sfa1) is 1.03 or more.

5. The heat-transfer-suppressing sheet according to claim 1, wherein in the first principal surface and the second principal surface of the thermal insulating material photographed by a coordinate measuring machine, a first recess having the greatest depth is selected from the measurement field for the first principal surface, a plane including the bottom of the first recess and perpendicular to the thickness direction of the thermal insulating material is defined as reference plane X1, and the volume of the portion protruding outward from reference plane X1 is defined as V1; and a second recess having the greatest depth is selected from the measurement field for the second principal surface, a plane including the bottom of the second recess and perpendicular to the thickness direction of the thermal insulating material is defined as reference plane X2, and the volume of the portion protruding outward from reference plane X2 is defined as V2; the volume ratio (V2 / V1) is 2.0 or more.

6. The heat transfer suppressing sheet according to claim 1, wherein the second main surface of the heat insulating material has a fluffed portion where at least one of the organic fibers and the inorganic fibers protrudes.

7. The heat transfer suppressing sheet according to claim 1, further comprising a mica sheet laminated on the second main surface side of the heat insulating material.

8. The heat transfer suppressing sheet according to claim 1, further comprising a mica sheet laminated on the surface of said elastic body opposite to the surface facing said heat insulating material.

9. The heat transfer-suppressing sheet according to claim 1, wherein the inorganic particles are particles made of at least one inorganic material selected from the group consisting of oxide particles, carbide particles, nitride particles, and inorganic hydrate particles.

10. The heat transfer suppressing sheet according to claim 9, wherein the inorganic particles include at least one type of particles selected from the group consisting of dry silica particles and silica aerogel.

11. The heat transfer-suppressing sheet according to claim 10, wherein the inorganic particles further include particles of at least one type selected from the group consisting of titania, zircon, zirconia, silicon carbide, zinc oxide, and alumina.

12. A method for producing a heat transfer-inhibiting sheet as claimed in any one of claims 1 to 11, comprising: an insulating material producing step of producing the insulating material having a pair of main surfaces perpendicular to the thickness direction which have different surface roughnesses; and a laminating step of laminating the elastic body and the insulating material so that the first main surface of the insulating material faces the elastic body, with the main surface of the pair of main surfaces having the smaller surface roughness designated as the first main surface and the other designated as the second main surface.

13. The method for manufacturing a heat transfer suppressing sheet according to claim 12, characterized in that the heat insulating material preparation process comprises: a heat insulating precursor preparation process for preparing a heat insulating precursor containing the inorganic particles and at least one of the organic fibers and the inorganic fibers; and a processing process for polishing or cutting the heat insulating precursor along a direction perpendicular to the thickness direction, so that the surface that has been polished or cut is the second main surface and the surface that has not been polished or cut is the first main surface.

14. The method for producing a heat transfer-suppressing sheet according to claim 13, wherein in the heat insulating precursor production step, the heat insulating precursor is produced by a dry method.

15. A battery pack comprising a plurality of battery cells and a heat transfer suppression sheet according to any one of claims 1 to 11, the plurality of battery cells being connected in series or parallel.

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