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

Abstract

To provide a heat transfer suppression sheet that has excellent heat insulating performance, can absorb deformation of a battery cell to suppress deterioration of battery performance, and can maintain excellent compressive restoring force, thereby preventing displacement and ensuring excellent heat insulating performance even in abnormal situations. [Solution] The heat transfer-suppressing sheet (10) includes an insulating material (11) containing inorganic particles and at least one of organic fibers and inorganic fibers, and having a pair of first and second main surfaces (21 and 22), and an elastic body (12) laminated in the thickness direction of the insulating material (11). The second main surface (22) of the insulating material (11) is disposed opposite the elastic body (12). The maximum height (Sz2) representing the surface roughness of the second main surface (22) is greater than the maximum height (Sz1) representing the surface roughness of the first main surface (21).

Description

[Technical Field]

[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. [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. 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 the transfer of heat from a battery cell that has experienced thermal runaway as described above is to interpose a heat transfer suppression sheet between the battery cells.

[0005] For example, Patent Document 1 proposes a battery insulating material that includes an insulating section disposed opposite the surface of the battery and a buffer section that is more susceptible to compressive deformation than the insulating section, with at least a portion of the buffer section disposed closer to the battery surface than the insulating section. In the battery insulating material, when a battery cell expands and its surface protrudes toward the insulating material, the buffer section deforms in response to the deformation of the battery cell surface. Patent Document 1 describes that the insulating material can effectively prevent problems caused by excessive suppression of battery cell expansion, even if the insulating material is not susceptible to compressive deformation. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2021-140968 Summary of the Invention [Problem to be solved by the invention]

[0007] In battery packs installed in automobiles, battery cells are often charged while the automobile is parked, and the battery cells expand due to charging, pressing against the heat-insulating material (heat-transfer-reducing sheet). Meanwhile, while the automobile is moving, the battery cells contract due to discharge, releasing the pressure on the heat-transfer-reducing sheet. As a result of this repeated expansion and contraction of the battery cells, the pressure on and release from the heat-transfer-reducing sheet are repeatedly released.

[0008] In the thermal insulation material described in Patent Document 1, the buffer section functions to absorb deformation of the battery cell when excessive heat is generated in the battery cell, but depending on the material of the buffer section, repeated pressure can cause the restoring force to decrease and the elastic force to increase. As a result, the buffer section cannot adequately absorb deformation of the battery cell in the event of an abnormality, which may cause the battery cell to burst.

[0009] Furthermore, if the restoring force of the buffer section is reduced, gaps are more likely to form between the battery cells and the heat-transfer-reducing sheet when the battery cells contract due to discharge, weakening the force with which the heat-transfer-reducing sheet is sandwiched between the battery cells. In particular, when the vehicle is traveling, the heat-transfer-reducing sheet is subjected to vibrations caused by the vehicle's movement, making it more likely that the heat-transfer-reducing sheet will become misaligned with the battery cells. If the heat-transfer-reducing sheet is positioned differently from the desired position between adjacent battery cells, creating areas between the battery cells where the heat-transfer-reducing sheet is not present, a sudden rise in the temperature of the battery cell could potentially lead to a chain reaction of severe thermal runaway in the adjacent battery cells.

[0010] 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. With the insulating material described in Patent Document 1, it is difficult to achieve both excellent compression recovery and improved insulating properties.

[0011] 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 maintain excellent compressive recovery force, thereby preventing misalignment and 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. [Means for solving the problem]

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

[0013] [1] A thermal insulating material containing inorganic particles and at least one of organic fibers and inorganic fibers, and having a pair of first and second main surfaces; an elastic body laminated in a thickness direction of the heat insulating material, The second main surface of the heat insulating material is disposed opposite to the elastic body, A heat-transfer-suppressing sheet, wherein a maximum height Sz2 representing the surface roughness of the second main surface is greater than a maximum height Sz1 representing the surface roughness of the first main surface.

[0014] Furthermore, 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 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.

[0015] [3] The maximum height Sz1 of the first main surface is 0.1 mm or more and 1.0 mm or less, The heat-transfer-suppressing sheet according to [1] or [2], wherein the maximum height Sz2 of the second main surface is 0.5 mm or more and 1.4 mm or less.

[0016] [4] In the first principal surface and the second principal surface of the thermal insulation material photographed by a three-dimensional measuring machine, a surface area per unit area calculated by dividing the surface area in the measurement field of view for the first principal surface by the area of ​​the measurement field of view is defined as Sfa1; When the surface area per unit area calculated by dividing the surface area in the measurement field of view for the second principal surface by the area of ​​the measurement field of view is Sfa2, The heat-transfer-suppressing sheet according to any one of [1] to [3], wherein the surface area ratio (Sfa2 / Sfa1) is 1.03 or greater.

[0017] [5] In the first principal surface and the second principal surface of the thermal insulation material photographed by a three-dimensional measuring machine, A first recess having the deepest depth is selected from the measurement field of view for the first main surface, and 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 the volume of the portion protruding outward from the reference plane X1 is defined as V1; A second recess having the deepest depth is selected from the measurement field of view for the second main surface, and 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. When the volume of the portion protruding outward from the reference plane X2 is defined as V2, The heat-transfer-suppressing sheet according to any one of [1] to [4], wherein the volume ratio (V2 / V1) is 2.0 or greater.

[0018] [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 fluffed portion in which at least one of the organic fibers and the inorganic fibers protrude.

[0019] [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.

[0020] [8] The heat-transfer-suppressing sheet according to any one of [1] to [7], further comprising a mica sheet laminated on the surface of the elastic body opposite the surface facing the heat insulating material.

[0021] [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 the group consisting of oxide particles, carbide particles, nitride particles, and inorganic hydrate particles.

[0022]

[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.

[0023]

[11] The inorganic particles may further include titania, zircon, zirconia, silicon carbide, zinc oxide, and The heat-transfer-suppressing sheet according to any one of [1] to

[10] , comprising particles of at least one kind selected from the group consisting of silica and alumina.

[0024] 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.

[0025]

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

[11] , a heat insulating material manufacturing step of manufacturing the heat insulating material having a pair of main surfaces perpendicular to the thickness direction, the surface roughnesses of which are different from each other; a lamination step of laminating the elastic body and the heat insulating material so that the second main surface of the heat insulating material faces the elastic body, with the main surface of the pair of main surfaces having a smaller surface roughness designated as the first main surface and the other designated as the second main surface.

[0026] 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] .

[0027]

[13] The heat insulating material manufacturing process 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 performing a polishing or cutting process on the heat insulating precursor along a direction perpendicular to the thickness direction of the heat insulating precursor, so that the polished or cut surface is the second main surface and the unpolished or uncut surface is the first main surface.

[0028]

[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.

[0029] The above object of the present invention is achieved by the following configuration

[15] relating to a battery pack.

[0030]

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

[11] , wherein the plurality of battery cells are connected in series or in parallel. [Effects of the Invention]

[0031] According to the heat-transfer-suppressing sheet of the present invention, an elastic body is laminated on a thermal insulating material, and the second main surface of the thermal insulating material has a greater maximum height than the first main surface. When the battery cell expands, the convex portions on the second main surface create depressions in the elastic body, allowing the sheet to easily follow the deformation of the battery cell. Furthermore, because the convex portions are less likely to be crushed when the heat-transfer-suppressing sheet is pressed, excellent restoring force can be obtained when the battery cell contracts. On the side of the first main surface, which has a smaller maximum height, the first main surface abuts against the harder battery cell or the like during compression, preventing a decrease in restoring force due to crushing of the convex portions. Furthermore, because a gap is formed between the second main surface of the thermal insulating material and the elastic body, thermal insulation performance can be further improved.

[0032] 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.

[0033] Furthermore, the battery pack of the present invention has a heat-transfer-suppressing sheet that has high thermal insulation performance as described above and can maintain excellent compression recovery force, and therefore can suppress thermal runaway of the battery cells in the battery pack and the spread of flames to the outside of the battery case. [Brief explanation of the drawings]

[0034] [Figure 1] FIG. 1 is a schematic cross-sectional view showing a heat-transfer-suppressing sheet according to an embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view that schematically shows a battery pack having a heat transfer-suppressing sheet according to an embodiment of the present invention. [Figure 3] FIG. 3 is a diagram showing the shape of the second main surface of the heat insulating material measured by a coordinate measuring machine. [Figure 4] FIG. 4 is a diagram showing the shape of the first main surface of the heat insulating material measured by a coordinate measuring machine. [Figure 5A]FIG. 5A is a cross-sectional view showing a step of preparing a heat insulating precursor in the method for producing a heat transfer sheet according to this embodiment. [Figure 5B] FIG. 5B is a cross-sectional view showing a processing step in the method for producing a heat transfer sheet according to this embodiment. [Figure 5C] 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. DETAILED DESCRIPTION OF THE INVENTION

[0035] 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 when the insulating material constituting the heat-transfer-suppressing sheet has a pair of main surfaces with different maximum heights, it is effective for achieving both improved insulating performance and maintaining excellent compressive recovery. Specifically, by arranging the second main surface, which has a larger maximum height, facing an elastic body, the heat-transfer-suppressing sheet can be deformed with less force, allowing it to follow the deformation of battery cells, etc. Furthermore, by arranging the first main surface, which has a smaller maximum height, facing a hard battery cell, etc., it is possible to prevent a decrease in recovery force after deformation.

[0036] 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.

[0037] [Heat transfer suppression 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 second main surface 22 facing the elastic body 12. The first main surface 21 of the thermal insulating material 11 may be substantially flat, or may have multiple protrusions 21a protruding outward from the heat-transfer-suppressing sheet 10 and multiple recesses 21b recessed toward the elastic body 12. When the protrusions 21a and the 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 toward the elastic body 12 and concave portions 22b that are recessed in a direction away from the elastic body 12, and for example, a sea-island structure is formed in which the convex portions 22a are island portions and the concave portions 22b are sea portions.

[0038] In this embodiment, the maximum height Sz2 representing the surface roughness of the second main surface 22 is designed to be larger than the maximum height Sz1 representing the surface roughness of the first main surface 21. 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. Note that 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.

[0039] 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.

[0040] 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 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.

[0041] In the battery pack 100 configured in this manner, the heat insulating material 11 contains inorganic particles and has high heat insulating properties, so that it is possible to suppress the propagation of heat from a battery cell that has experienced thermal runaway to adjacent battery cells.

[0042] Furthermore, the second main surface of the heat insulating material 11 facing the elastic body 12 in the heat transfer-suppressing sheet 10 has a greater maximum height than the first main surface, and high protrusions 22a are formed on it, reducing the contact area between the heat insulating material 11 and the elastic body 12. As a result, when the battery cells 20a, 20b, and 20c expand and apply a compressive force to the heat transfer-suppressing sheet 10, even a small compressive force presses the protrusions 22a into the surface of the elastic body 12. In this way, in addition to the inherent deformation absorption capacity of the elastic body 12, the protrusions 22a on the second main surface 22 of the heat insulating material 11 create depressions in the surface of the elastic body 12, allowing the heat transfer-suppressing sheet 10 to be easily deformed with a small force and easily follow the deformation of the battery cells 20a, 20b, and 20c.

[0043] If heat-transfer-suppressing sheet 10 has a low recovery force when it is released from compression after being deformed in the thickness direction due to compression, the force with which heat-transfer-suppressing sheet 10 is sandwiched between battery cells 20a, 20b, and 20c will be weak. As described above, if the fixing force of heat-transfer-suppressing sheet 10 is weak, particularly while the vehicle is traveling, vibrations will cause misalignment between heat-transfer-suppressing sheet 10 and battery cells 20a, 20b, and 20c, making it difficult to maintain sufficient thermal insulation in the event of an abnormality.

[0044] In contrast, in this embodiment, the elastic body 12 is easily elastically deformed according to the shape of the protrusions 22a of the heat insulating material 11, making the protrusions 22a less likely to collapse. Therefore, when the battery cells 20a, 20b, and 20c contract and the pressing force on the heat-transfer-suppressing sheet 10 is released, the restoring force of the elastic body 12 applies a force that pushes back the protrusions 22a. Meanwhile, although the first main surface 21 of the heat insulating material 11 faces the hard battery cells 20a and 20b, the protrusions 21a are less likely to collapse because the maximum height of the protrusions 21a is low and the contact area between the heat insulating material 11 and the battery cells 20a and 20b is large. Therefore, the heat-transfer-suppressing sheet 10 easily returns to its original thickness before deformation, allowing the force that sandwiches the heat-transfer-suppressing sheet 10 between adjacent battery cells to be maintained, preventing a chain reaction of thermal runaway.

[0045] Furthermore, abnormalities tend to occur in the battery cells 20a, 20b, and 20c during discharge, and at this time, the battery cells 20a, 20b, and 20c contract, forming a relatively large gap 24 between the heat insulating material 11 and the elastic body 12, as shown in Fig. 2. Therefore, the heat insulating properties can be further improved compared to when the second main surface 22 of the heat insulating material 11 is nearly flat.

[0046] In this embodiment, second main surface 22 preferably has a fluffy portion (not shown) in which at least one of organic fibers and inorganic fibers protrudes. If second main surface 22 has a fluffy portion, voids are also generated within the fluffy portion, thereby further improving the heat insulation properties of heat-transfer-suppressing sheet 10.

[0047] Furthermore, in the heat-transfer-suppressing sheet 10 of this embodiment, a mica sheet (not shown) may be laminated on the first main surface 21 side 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.

[0048] Next, the first main surface 21 and the second main surface 22 will be described in more detail.

[0049] <Difference between the maximum height Sz1 of the first principal surface and the maximum height Sz2 of the second principal surface: 0.2 mm or more> As described above, the second main surface 22 of the heat insulating material 11, which faces the elastic body 12, and the first main surface 21, which is the opposite surface, have different surface roughnesses. By making the maximum height Sz2 of the second main surface greater than that of the first main surface, it is possible to improve the heat insulating performance of the heat transfer-suppressing sheet 10 while maintaining excellent compressive recovery. In this embodiment, the difference between the maximum heights Sz1 and Sz2 is not particularly limited. For example, if the difference is 0.2 mm or more, the effect of substantially different surface roughnesses can be obtained. Therefore, the difference between the maximum heights Sz1 and Sz2 is preferably 0.2 mm or more, more preferably 0.3 mm or more, and even more preferably 0.4 mm or more.

[0050] 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 also becomes large. If the maximum height Sz2 of the second main surface 22 becomes too large, the recesses 22b become too deep, which may cause the heat insulating material 11 to become thin in parts 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.

[0051] <Maximum height Sz1 of the first principal 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 insulator 11, the larger the contact area with the battery cells 20a, 20b, making the protrusions 21a less likely to be crushed and improving the effectiveness of maintaining compression recovery. However, if the maximum height Sz1 of the first main surface 21 is to be less than 0.1 mm, a special manufacturing method would be required, which could increase manufacturing costs. Therefore, it is preferable that the maximum height Sz1 of the first main surface 21 be 0.1 mm or greater.

[0052] On the other hand, if the maximum height Sz1 of the first main surface 21 of the thermal insulator 11 becomes too large, the contact area with the battery cells 20a, 20b becomes small, the protrusions 21a become easily crushed, and the compressive recovery force 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.

[0053] <Maximum height Sz2 of the second principal 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 insulator 11 is too small, the amount of deformation of the elastic body 12 when the heat-transfer-suppressing sheet 10 is compressed will be small, making it difficult to fully accommodate the deformation of the battery cells 20a, 20b, and 20c. Furthermore, the volume of the voids 24 that are effective in achieving a thermal insulating effect will decrease. Therefore, the maximum height Sz2 of the second main surface 22 is preferably 0.5 mm or greater, more preferably 0.6 mm or greater, and even more preferably 0.7 mm or greater.

[0054] On the other hand, the larger the maximum height Sz2 of the second main surface 22 of the thermal insulator 11, the greater the amount of deformation of the elastic body 12 and the more effectively it follows the deformation of the battery cells 20a, 20b, 20c. However, as mentioned above, if the recesses 22b become too deep, the thermal insulator 11 may become thin in parts, which may result 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.

[0055] 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, if there are slight scratches or dust particles on the first main surface 21 or the second main surface 22, the measured values ​​may fall outside the above-mentioned preferable range. However, the presence of scratches or dust particles is a unique phenomenon, and the effects of the present invention can be fully obtained even if scratches or dust particles are present in some areas. Therefore, if there are any unusual points due to scratches or dust particles in the above-mentioned measured values, it is preferable to determine whether the values ​​are within the preferable range after excluding these points.

[0056] 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 insulating 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 21a on the first main surface 21 to the convex portions 22a 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.

[0057] Fig. 3 is a diagram showing the shape of the second main surface of the thermal insulation material measured by a coordinate measuring machine, and Fig. 4 is a diagram showing the shape of the first main surface thereof. In Fig. 3, shape diagram 40a shows the cross-sectional shape along line AA on the second main surface 22 side of the thermal insulation material 11, and shape diagram 40b shows the cross-sectional shape along line BB on the second main surface 22 side of the thermal insulation material 11. Also, in Fig. 4, 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 DD on the first main surface 21 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.

[0058] 3 and 4, the coordinate measuring machine is set so that the centers of the measurement fields R2 and R1 are located at the centers of the second main surface 22 and the first main surface 21 of the thermal insulation material 11, and images are taken of the surfaces of the second main surface 22 and the first main surface 21. 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.

[0059] 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.

[0060] <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 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 recessed portions 21b is approximately the same as the area of ​​the first main surface 21 in a planar view.

[0061] In this embodiment, the surface area ratio (Sfa2 / Sfa1) between the surface area Sfa2 of the second main surface 22 per unit area and the surface area Sfa1 of the first main surface 21 per unit area can be used as an index for determining the surface quality 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 protrusions 22a and recesses 22b with appropriate heights and shapes. Therefore, the surface area ratio (Sfa2 / Sfa1) between the surface area Sfa2 of the second main surface 22 per unit area and 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.

[0062] Furthermore, if the value of 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.

[0063] 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 of view. 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 of view. 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.

[0064] <Volume ratio (V2 / V1): 2.0 or more> Similarly to the surface area ratio, the second main surface 22 of the thermal insulator 11 has large protruding convex portions 22a and large recessed portions 22b, while the first main surface 21 has small convex portions 21a and recessed portions 21b. A large volume of the second main surface 22 does not mean that there are a small number of small convex portions, but rather that there are convex portions of a desired size. 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 insulator can be determined to have even better surface quality. When the volume ratio (V2 / V1) is 2.0 or greater, it can be determined that the second main surface 22 has convex portions 22a and recessed portions 22b with appropriate heights and shapes. Therefore, the volume ratio (V2 / V1) of the volume V2 of the convex portion 22a on the second main surface 22 to the volume V1 of the convex portion 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.

[0065] 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.

[0066] The volume V1 measured by the three-dimensional measuring machine refers to the volume of the portion that protrudes outward from the reference plane X1, for example, as shown in the shape diagram 40c of Figure 4, 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 the reference plane X1 is a plane that includes the bottom of this first recess 41 and is perpendicular to the thickness direction of the insulation material 11. Similarly, volume V2 represents the volume of the portion that protrudes outward from reference plane X2, for example, as shown in the shape diagram 40a of Figure 3, when the second recess 42 having the deepest depth is selected from the measurement field of view R2 of the second main surface, and the reference plane X2 is a plane that includes the bottom of this second recess 42 and is perpendicular to the thickness direction of the insulation material 11.

[0067] For three different thermal 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.

[0068] [Table 1]

[0069] 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.

[0070] [Insulation material] The heat insulating material used in the heat transfer-suppressing sheet according to this embodiment is not particularly limited as long as it contains inorganic particles and at least one of organic and inorganic fibers and has a heat insulating effect. Thermal conductivity can be used as an index of heat insulating effect. In this embodiment, the heat conductivity of the heat insulating material is preferably less than 1 (W / m·K), more preferably less than 0.5 (W / m·K), and even more preferably less than 0.2 (W / m·K). Furthermore, the heat conductivity of the heat insulating material is more preferably less than 0.1 (W / m·K), more preferably less than 0.05 (W / m·K), and even more preferably less than 0.02 (W / m·K). The thermal conductivity of the heat insulating material can be measured in accordance with the "Test method for thermal conductivity of refractories" described in JIS R 2251.

[0071] (Insulation size) 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 main surfaces of the insulating material 11 and the elastic body 12 are designed to have approximately the same size, "approximately the same" means that the difference in size between them is preferably up to ±5% of the average value of both, more preferably up to ±3%, and even more preferably up to ±1%.

[0072] Next, the materials that make up the heat insulating material will be described.

[0073] <Inorganic particles> The heat insulating material contains inorganic particles. A single inorganic particle may be used as the inorganic particle, 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 use 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.

[0074] When the average secondary particle diameter of the inorganic particles is 0.01 μm or more, they are easily available and the increase in production costs can be suppressed. Furthermore, when the average secondary particle diameter is 200 μm or less, the desired heat insulating effect can be obtained. Therefore, the average secondary particle diameter of the inorganic particles is preferably 0.01 μm or more and 200 μm or less, and more preferably 0.05 μm or more and 100 μm or less.

[0075] In addition, by using two or more inorganic particles with different heat transfer suppression effects in combination, it is possible to cool a heat generating body in multiple stages, and the heat absorption effect can be exerted over a wider temperature range. Specifically, it is preferable to use a mixture of large-diameter particles and small-diameter particles. For example, when nanoparticles are used as one of the inorganic particles, it is preferable to include inorganic particles made of a metal oxide as the other inorganic particle. Hereinafter, the inorganic particles will be described in more detail, with the small-diameter inorganic particles referred to as the first inorganic particles and the large-diameter inorganic particles referred to as the second inorganic particles.

[0076] <First inorganic particle> (oxide particles) Oxide particles have a high refractive index and a strong effect of diffusely reflecting light. Therefore, using oxide particles as the first inorganic particles can suppress radiant heat transfer, particularly in high-temperature regions such as those caused by abnormal heat generation. The oxide particles can be at least one type of particle selected from silica, titania, zirconia, zircon, barium titanate, zinc oxide, and alumina. That is, among the above oxide particles that can be used as inorganic particles, only one type 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.

[0077] (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.

[0078] 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.

[0079] (nanoparticles) In the present invention, nanoparticles refer to particles on the order of nanometers that are spherical or nearly spherical and have an average primary particle diameter of less than 1 μm. Nanoparticles have low density, which suppresses conductive heat transfer. When nanoparticles are used as the first inorganic particles, finer voids are dispersed, resulting in excellent heat insulation that suppresses convective heat transfer. Therefore, it is preferable to use nanoparticles because they can suppress heat transfer between adjacent nanoparticles during normal use of the battery at room temperature. Furthermore, if nanoparticles with a small average primary particle size are used as oxide particles, the increase in conductive heat transfer through the insulating material can be suppressed even when the insulating material is compressed due to expansion caused by thermal runaway in the battery cell, increasing the internal density. This is thought to be because nanoparticles are prone to forming small voids between particles due to electrostatic repulsion, and because their bulk density is low, the particles are packed together to provide cushioning.

[0080] 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.

[0081] Generally, wet silica particles are agglomerated, while dry silica particles can be dispersed. Because heat conduction is predominant in the temperature range below 300°C, dry silica, which can disperse particles, can achieve superior heat insulation performance compared to wet silica. The heat insulating material according to this embodiment is preferably produced by a manufacturing method in which a mixture containing the material is processed into a sheet 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.

[0082] (Average primary particle size 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.

[0083] (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).

[0084] 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

[0085] As described above, the heat-transfer-suppressing sheet 10 according to this embodiment is preferably interposed between battery cells, for example, but in a battery cell that experiences 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 an inorganic hydrate whose thermal decomposition temperature starts at 200°C or higher. The thermal decomposition starting temperatures of the inorganic hydrates listed above are approximately 200°C for aluminum hydroxide, approximately 330°C for magnesium hydroxide, approximately 580°C for calcium hydroxide, approximately 200°C for zinc hydroxide, approximately 350°C for iron hydroxide, approximately 300°C for manganese hydroxide, approximately 300°C for zirconium hydroxide, and approximately 300°C for gallium hydroxide.All of these temperatures roughly overlap with the temperature range in which a battery cell experiencing thermal runaway experiences a sudden rise in temperature, and can efficiently suppress temperature rise, making these inorganic hydrates preferable.

[0086] (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 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.

[0087] (Particles made of thermally expandable inorganic material) Examples of thermally expandable inorganic materials include vermiculite, bentonite, mica, and perlite.

[0088] (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.

[0089] (inorganic balloons) The heat insulating material used in the present invention may contain inorganic balloons as the first inorganic particles. When inorganic balloons are contained, convective or conductive heat transfer within the heat insulating material can be suppressed in the temperature range below 500°C, and the heat insulating properties of the heat insulating material can be further improved. As the inorganic balloons, at least one selected from shirasu balloons, silica balloons, fly ash balloons, barite balloons, and glass balloons can be used.

[0090] (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.

[0091] (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.

[0092] <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.

[0093] Nanoparticles have extremely low conductive heat transfer and can maintain excellent heat insulation even when compressive stress is applied to the insulating material. Metal oxide particles such as titania are also effective in blocking radiant heat. Furthermore, when large-diameter inorganic particles and small-diameter inorganic particles are used, the small-diameter inorganic particles penetrate into the gaps between the large-diameter inorganic particles, resulting in a denser structure and improving the heat transfer suppression effect. Therefore, when nanoparticles are used as the first inorganic particles, it is preferable to further include second inorganic particles made of a metal oxide that are larger in diameter than the first inorganic particles in the insulating material. Examples of metal oxides include silicon oxide, titanium oxide, aluminum oxide, barium titanate, zinc oxide, zircon, zirconium oxide, etc. In particular, titanium oxide (titania) is a component with a higher refractive index than other metal oxides, and is highly effective in scattering light and blocking radiant heat in a high temperature range of 500°C or higher, so it is most preferable to use titania.

[0094] When the first inorganic particles are at least one type of particles selected from dry silica particles and silica aerogel, and the second inorganic particles are at least one type of particles selected from titania, zircon, zirconia, silicon carbide, zinc oxide, and alumina, the first inorganic particles preferably account for 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more of the total mass of the inorganic particles, in order to obtain excellent heat insulating performance within a temperature range of 300° C. or less. Furthermore, the first inorganic particles preferably account for 95% by mass or less, more preferably 90% by mass or less, and even more preferably 80% by mass or less of the total mass of the inorganic particles.

[0095] On the other hand, in order to obtain excellent heat insulating performance in a temperature range exceeding 300° C., the content of the second inorganic particles is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 20% by mass or more, based on the total mass of the inorganic particles. Also, the content of the second inorganic particles is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less, based on the total mass of the inorganic particles.

[0096] (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.

[0097] (Inorganic particle content) In this embodiment, if the total content of inorganic particles in the heat insulating material 11 is appropriately controlled, the heat insulating property of the heat insulating 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 is too high, the content of organic fibers will relatively decrease, so in order to fully 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.

[0098] 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.

[0099] 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.

[0100] <Organic fiber> 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 an appropriate amount of organic fibers, 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.

[0101] 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. 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.

[0102] (First organic material) In this embodiment, when a core-sheath binder fiber 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. The first organic material may be at least one selected from polyethylene terephthalate, polypropylene, and nylon.

[0103] (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, and 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, and more preferably 100° C. or higher. The melting point of the second organic material is preferably 150° C. or lower, and more preferably 130° C. or lower.

[0104] (organic fiber content) In this embodiment, if the content of organic fibers in the heat insulating material 11 is appropriately controlled, the skeleton can be sufficiently reinforced. The organic fiber content is preferably 5% by mass or more, and more preferably 10% by 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, so in order to obtain the desired thermal insulation performance, the organic fiber content is preferably 25% by mass or less, and more preferably 20% by mass or less, relative to the total mass of the thermal insulation material 11.

[0105] (fiber length of organic fiber) There are no particular limitations on the fiber length of the organic fibers, but from the viewpoint of ensuring moldability and processability, it is preferable that the average fiber length of the organic fibers be 10 mm or less. On the other hand, from the viewpoint of making the organic fibers function as a skeleton and ensuring the compressive strength of the heat insulating material, it is preferable that the average fiber length of the organic fibers is 0.5 mm or more.

[0106] <Inorganic fibers> When the heat insulating material 11 contains inorganic fibers, a single inorganic fiber may be used as the inorganic fiber, or two or more types of inorganic fibers may be used in combination. Examples of inorganic fibers include ceramic fibers such as silica fiber, alumina fiber, alumina silicate fiber, zirconia fiber, carbon fiber, soluble fiber, refractory ceramic fiber, aerogel composite material, magnesium silicate fiber, alkaline earth silicate fiber, potassium titanate fiber, silicon carbide fiber, and potassium titanate whisker fiber, glass fibers such as glass fiber, glass wool, and slag wool, and 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, availability, etc. Among the above inorganic fibers, the heat insulating material preferably contains at least one type selected from silica-alumina fiber, alumina fiber, silica fiber, rock wool, alkaline earth silicate fiber, and glass fiber, from the viewpoint of ease of handling.

[0107] 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.

[0108] 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 thermal insulation material 11. 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 individually, which may result in reduced thermal insulation.

[0109] 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.

[0110] (Inorganic fiber content) In this 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.

[0111] 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 become entangled with each other to form a three-dimensional network, thereby improving the effect of retaining inorganic particles and other compounding materials described below.

[0112] <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 is a powder that contains, for example, a third organic material different from the first and second organic materials and melts when heated. When the hot melt powder is added to the mixture and heated, it melts and then hardens, taking the surrounding inorganic particles with it when cooled. This prevents the inorganic particles from falling off the insulating material 11.

[0113] Hot melt powders with various melting points can be used. A hot melt powder with an appropriate melting point can be selected based on the melting points of the core and sheath of the binder fiber used. Specifically, if the third organic material constituting the hot melt powder has a melting point lower than that of the first organic material constituting the organic fiber, the heating temperature can be set to melt the sheath and hot melt powder while leaving the core. For example, if the melting point of the hot melt powder is lower than that of the sheath, the heating temperature during production can be set between the melting points of the core and the sheath, making it even easier to set the heating temperature.

[0114] Alternatively, the type of hot melt powder used can be selected so that its melting point is between the melting points of the core and sheath. When a hot melt powder with such a melting point is used, the sheath and hot melt powder melt together, and then when they cool and harden, the organic fibers (core), 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 will fuse to the organic fibers, facilitating the formation of a three-dimensional skeleton. This further improves the strength of the entire sheet.

[0115] If the melting point of the third organic material constituting the hot melt powder is sufficiently lower than that of the first organic material constituting the core, the heating temperature setting latitude in the heating step can be expanded, making it easier to set the temperature to obtain the desired structure. For example, the melting point of the first organic material is preferably 60°C or more higher than that of the third organic material, more preferably 70°C or more higher, and even more preferably 80°C or more higher.

[0116] The melting point of the hot melt powder (third organic material) is preferably 80° C. or higher, and more preferably 90° C. or higher. The melting point of the hot melt powder (third organic material) is preferably 180° C. or lower, and more preferably 150° C. or lower. Components constituting the hot melt powder include polyethylene, polyester, polyamide, and ethylene vinyl acetate.

[0117] (Hot melt powder content) When hot melt powder is added to the insulating material to prevent the inorganic particles from falling off, even a small amount of hot melt powder can be used to prevent powder falling off. Therefore, the hot melt powder content is preferably 0.5% by mass or more, and more preferably 1% by mass or more, of the total mass of the insulating material. On the other hand, when the content of hot melt powder is increased, the content of inorganic particles and the like is relatively decreased. Therefore, in order to obtain the desired heat insulating performance, the content of hot melt powder is preferably 5 mass% or less, and more preferably 4 mass% or less, of the total mass of the heat insulating material.

[0118] When the material for 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, and more preferably at least 20°C higher, than the higher of the melting point of the second organic material constituting the sheath and the melting point of the third organic material constituting the hot melt powder. Meanwhile, the heating temperature is preferably set to be at least 10°C lower, and more preferably at least 20°C lower, than the melting point of the first organic material constituting the core. Setting the heating temperature at this level allows for the formation of a strong skeleton, further improving the strength of the sheet and preventing the inorganic particles from falling off.

[0119] 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.

[0120] <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, and 20c, and is obtained by processing an elastic material into a sheet. Examples of such an elastic body include rubber and elastomer. Specific examples of rubber include foamed silicone.

[0121] (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.

[0122] 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.

[0123] <Mica sheet> The mica sheet is a mica sheet material containing inorganic particles, mica, processed into a sheet. Mica has excellent heat resistance and insulating properties, and a mica sheet made by processing a material containing mica into a sheet 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.

[0124] The mica sheet material preferably includes oxide particles, oxide fibers, etc. in addition to mica. Specific examples include SiO2, Al2O3, Ti2O3, etc., but the present invention is not limited to these materials. It is more preferable to use a mica sheet made of natural minerals. The sheet shape may be a flat sheet without holes or may have holes. Providing holes in at least a portion of the center or other regions of the mica sheet allows the mica sheet to conform to the battery cells 20a, 20b, 20c without cracking when the battery cells 20a, 20b, 20c expand and contract.

[0125] [Method of manufacturing heat transfer suppression 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 insulating 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.

[0126] <Insulation material manufacturing process> In the insulating material preparation process, an insulating material having a pair of main surfaces perpendicular to the thickness direction and different surface roughnesses is prepared. The insulating material preparation process includes the insulating precursor preparation process and the processing process described below. These processes will be described in more detail below.

[0127] (Adiabatic precursor production process) 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.

[0128] Here, we will further explain an example of a method for producing the heat insulating precursor 1. For example, inorganic fibers or binder fibers having a core-sheath structure and inorganic particles are put into a mixer such as a V-type mixer in a predetermined ratio to produce a mixture. The binder fibers are preferably fibers with a core-sheath structure having a core made of a first organic material and a sheath made of a second organic material, where the melting point of the first organic material is higher than that of the second organic material.

[0129] 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 surrounding 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 organic fibers. This results in a sheet-shaped heat insulating precursor 1. 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.

[0130] (Processing process) 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 or brush. This method allows the production of insulating materials 11 having a thickness approximately equal to that of the insulating precursor 1.

[0131] When cutting is performed using 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 cutting tool 3, as shown in Fig. 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 used as second main surface 22 of thermal insulation material 11, which has a high 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 used as first main surface 21, which has a low surface roughness.

[0132] 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 heat insulating material 11 is greater 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.

[0133] <Lamination process> After the heat insulating material preparation step, a lamination step is carried out. In the lamination step, one of, for example, two sheets of heat insulating material 11 obtained in the heat insulating material preparation step 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, and the elastic body 12 and the heat insulating material 11 are laminated together so that the second main surface 22 of the heat insulating material 11 faces the elastic body 12 prepared in advance. In this way, the heat transfer-suppressing sheet 10 can be produced.

[0134] 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.

[0135] 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. 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. This increases the rate at which the cutting edge of the cutting tool 3 cuts the fibers, making them more likely 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 process is preferably performed by a dry method.

[0136] 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 having different maximum heights on the main surfaces 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.

[0137] [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 an embodiment of the present invention is applied is 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 maintain excellent compressive recovery force, thereby ensuring safety in the event of an abnormality and providing a highly safe battery pack.

[0138] 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.

[0139] In the battery pack 100 configured in this manner, if a battery cell catches fire, the flames 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 area. 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 30, eliminating the need to fabricate new flame retardant materials, etc., and allowing for the easy, low-cost, and safe construction of the assembled battery 100. [Explanation of symbols]

[0140] 1. Adiabatic precursor 2, 23, 25 main surfaces 3 Cutting tools 4 Cutting line 10 Heat transfer suppression sheet 11. Insulation 12 Elastic Body 20a, 20b, 20c battery cells 21 First main surface 21a, 22a convex part 21b, 22b Recess 22 Second main surface 24 Cavity 30 Battery case 100 battery packs

Claims

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

2. 2 . The heat-transfer-suppressing sheet according to claim 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.

3. The maximum height Sz1 of the first main surface is 0.1 mm or more and 1.0 mm or less, The heat-transfer-suppressing sheet according to claim 2 , wherein the maximum height Sz2 of the second main surface is not less than 0.5 mm and not more than 1.4 mm.

4. In the first principal surface and the second principal surface of the thermal insulating material photographed by a three-dimensional measuring machine, A surface area per unit area calculated by dividing a surface area in a measurement field of view for the first principal surface by an area of ​​the measurement field of view is defined as Sfa1, When the surface area per unit area calculated by dividing the surface area in the measurement field of view for the second principal surface by the area of ​​the measurement field of view is Sfa2, 2. The heat transfer-suppressing sheet according to claim 1, wherein the surface area ratio (Sfa2 / Sfa1) is 1.03 or greater.

5. In the first principal surface and the second principal surface of the thermal insulating material photographed by a three-dimensional measuring machine, A first recess having the deepest depth is selected from the measurement field of view for the first main surface, and 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 the volume of a portion protruding outward from the reference plane X1 is defined as V1; A second recess having the deepest depth is selected from the measurement field of view for the second main surface, and 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. When the volume of the portion protruding outward from the reference plane X2 is defined as V2, 2. The heat transfer-suppressing sheet according to claim 1, wherein 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 in which 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. 2. The heat transfer-suppressing sheet according to claim 1, further comprising a mica sheet laminated on a surface of the elastic body opposite to a surface facing the heat insulating material.

9. 2. 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 7, wherein the inorganic particles include at least one type of particles selected from the group consisting of dry silica particles and silica aerogel.

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

12. A method for producing the heat transfer-suppressing sheet according to any one of claims 1 to 11, a heat insulating material manufacturing step of manufacturing the heat insulating material having a pair of main surfaces perpendicular to the thickness direction, the surface roughnesses of which are different from each other; a lamination process of laminating the elastic body and the insulating material so that the second main surface of the insulating material faces the elastic body, with the main surface of the pair of main surfaces having a smaller surface roughness as the first main surface and the other as the second main surface.

13. The heat insulating material manufacturing process 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; a processing step of polishing or cutting the heat insulating precursor along a direction perpendicular to a thickness direction thereof, 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. 14. The method for producing a heat transfer-suppressing sheet according to claim 13, wherein in the heat insulating precursor producing step, the heat insulating precursor is produced by a dry method.

15. 12. 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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