Heat transfer inhibiting sheet and method for manufacturing the same, and battery pack

Abstract

The present application provides a heat transfer inhibiting sheet and a method for manufacturing the same, and a battery pack having the heat transfer inhibiting sheet, the heat transfer inhibiting sheet being capable of maintaining a shape even when being pressed due to expansion of a battery cell, thereby being capable of inhibiting a decrease in adiabatic performance. The heat transfer inhibiting sheet includes first inorganic particles (1), a resin binder (6), and organic fibers (3), the organic fibers (3) having a glass transition temperature higher than that of the resin binder (6). In addition, at least a portion of the organic fibers (3) are fused to each other to form a three-dimensional skeleton (8), the resin binder (9) is fused to a portion of the skeleton (8) and at least a portion of the first inorganic particles (1), and at least a portion of the first inorganic particles (1) are bonded to the skeleton (8).

Description

Technical Field

[0001] This invention relates to a heat transfer suppressor sheet, a method for manufacturing the same, and a battery pack having the heat transfer suppressor sheet. Background Technology

[0002] In recent years, from an environmental protection perspective, the development of electric vehicles or hybrid vehicles powered by electric motors has become increasingly popular. These electric vehicles or hybrid vehicles are equipped with battery packs consisting of multiple battery cells connected in series or parallel to power the electric motors used for driving the motors.

[0003] Furthermore, this battery cell primarily uses lithium-ion rechargeable batteries, which offer higher capacity and output compared to lead-acid and nickel-metal hydride batteries. However, in the event of thermal runaway, such as a battery cell experiencing a rapid temperature rise and continued heating due to an internal short circuit or overcharging, the heat from the thermally runaway cell can propagate to adjacent battery cells, potentially causing thermal runaway in those cells as well.

[0004] As a method to suppress the propagation of heat from battery cells that have experienced thermal runaway as described above, a common practice is to sandwich insulating sheets between the battery cells.

[0005] For example, Patent Document 1 discloses a heat insulation sheet for a battery pack, which comprises a first particle composed of silica nanoparticles and a second particle composed of metal oxides, and specifies the content of the first particle. Furthermore, Patent Document 1 describes that the heat insulation sheet may comprise a bonding material composed of at least one selected from fibers, adhesives, and heat-resistant resins.

[0006] Existing technical documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2021-34278 Summary of the Invention

[0008] The problem that the invention aims to solve

[0009] However, in battery pack insulation sheets, it is required that they maintain their shape and remain between battery cells even if the cells experience thermal runaway and reach high temperatures. In particular, in recent years, the capacity of battery cells in battery packs has further increased, resulting in a higher rate of expansion during charging and discharging. Therefore, when the temperature of battery cells rises due to abnormalities, it becomes difficult to maintain the overall strength of the insulation sheet, leading to a decrease in insulation performance and sometimes causing a thermal cascading effect.

[0010] The insulation sheet described in the aforementioned patent document 1 maintains excellent insulation properties even under increased compressive stress, but requires further improvements related to strength.

[0011] The present invention was made in view of the above-mentioned problems, and its object is to provide a heat transfer suppressor sheet that can maintain its shape even when exposed to high temperature, thereby suppressing the reduction of thermal insulation performance, a method for manufacturing the same, and a battery pack having the heat transfer suppressor sheet.

[0012] Methods for solving problems

[0013] The above-mentioned objective of the present invention is achieved by the following structure of the heat transfer suppression sheet [1].

[0014] Structure [1]. A heat transfer inhibition sheet, characterized in that,

[0015] The heat transfer inhibition sheet comprises first inorganic particles, resin binder, and organic fibers.

[0016] The glass transition temperature of the organic fiber is higher than that of the resin adhesive.

[0017] Furthermore, the preferred embodiments of the present invention regarding the heat transfer inhibition sheet are related to the following structures [2] to

[17] .

[0018] The heat transfer suppression sheet of structure [2]. Structure [1] is characterized in that,

[0019] At least a portion of the organic fibers are fused together to form a three-dimensional skeleton.

[0020] The resin adhesive is fused to a portion of the skeleton and at least a portion of the first inorganic particles, with at least a portion of the first inorganic particles bonded to the skeleton.

[0021] The heat transfer suppression sheet of structure [3]. Structure [1] or [2] is characterized in that,

[0022] The glass transition temperature of the organic fiber is below 250°C.

[0023] The heat transfer inhibiting sheet of any one of structures [1] to [3] is characterized in that,

[0024] The glass transition temperature of the resin adhesive is above -10°C.

[0025] The heat transfer inhibiting sheet of any one of structures [1] to [4] is characterized in that,

[0026] The difference between the glass transition temperature of the resin adhesive and the glass transition temperature of the organic fiber is greater than 10°C and less than 130°C.

[0027] The heat transfer inhibiting sheet of any one of structures [1] to [5] is characterized in that,

[0028] The organic fiber has a water solubility temperature of 60°C or higher.

[0029] The heat transfer inhibiting sheet of any one of structures [1] to [6] is characterized in that,

[0030] The average fiber length of the organic fiber is 0.5 mm or more and 10 mm or less.

[0031] The heat transfer inhibiting sheet of any one of structures [1] to [7] is characterized in that,

[0032] The content of the organic fiber is 0.5% by mass or more and 12% by mass or less relative to the total mass of the heat transfer inhibiting sheet, and the content of the resin adhesive is 0.5% by mass or more and 20% by mass or less.

[0033] The heat transfer inhibiting sheet of any one of structures [1] to [8] is characterized in that,

[0034] The resin adhesive comprises at least one selected from styrene-butadiene resin, acrylic resin, silicone-acrylic resin and styrene resin.

[0035] The heat transfer inhibiting sheet of any one of structures [1] to [9] is characterized in that,

[0036] The organic fiber comprises at least one selected from polyvinyl alcohol fiber, polyethylene fiber, nylon fiber, polyurethane fiber and ethylene-vinyl alcohol copolymer fiber.

[0037] The heat transfer inhibiting sheet of any one of structures [1] to

[10] is characterized in that,

[0038] The first inorganic particle is composed of at least one selected from oxide particles, carbide particles, nitride particles and inorganic hydrate particles.

[0039] Structure

[12] . A heat transfer inhibiting sheet of any one of structures [1] to

[11] , characterized in that,

[0040] The heat transfer inhibition sheet further comprises at least one first inorganic fiber and a second inorganic fiber, selected from the average fiber diameter, shape and glass transition temperature, which are different from each other.

[0041] The heat transfer suppression sheet of structure

[13] . Structure

[12] is characterized in that,

[0042] The average fiber diameter of the first inorganic fiber is larger than that of the second inorganic fiber.

[0043] The first inorganic fiber is linear or needle-like, and the second inorganic fiber is dendritic or crimped.

[0044] The heat transfer suppression sheet of structure

[14] . Structure

[12] is characterized in that,

[0045] The first inorganic fiber is an amorphous fiber.

[0046] The second inorganic fiber is at least one type of fiber selected from crystalline fibers and amorphous fibers with a glass transition temperature higher than that of the first inorganic fiber.

[0047] The average fiber diameter of the first inorganic fiber is larger than that of the second inorganic fiber.

[0048] The heat transfer suppression sheet of structure

[15] . Structure

[12] , wherein,

[0049] The first inorganic particle comprises at least one type selected from nanoparticles, hollow particles, and porous particles.

[0050] The first inorganic fiber is an amorphous fiber.

[0051] The second inorganic fiber is at least one inorganic fiber selected from crystalline fibers and amorphous fibers with a glass transition temperature higher than that of the first inorganic fiber.

[0052] The heat transfer suppressor sheet of any one of structures

[16] .

[12] to

[15] is characterized in that,

[0053] The first inorganic fiber is a fiber containing SiO2, and the second inorganic fiber is a fiber composed of at least one of the following fibers: glass fiber, silica fiber, alumina fiber, aluminum silicate fiber, zirconium oxide fiber, glass wool, carbon fiber, soluble fiber, refractory ceramic fiber, aerogel composite material, magnesium silicate fiber, alkaline earth silicate fiber, zirconium oxide fiber, potassium titanate fiber, and natural mineral fiber.

[0054] The heat transfer inhibiting sheet of any one of structures [1] to

[16] is characterized in that,

[0055] The heat transfer inhibition sheet also contains a second inorganic particle composed of metal oxides.

[0056] Furthermore, the above-mentioned objective of the present invention is achieved by the structure of the following

[18] involved in the manufacturing method of the heat transfer suppression sheet.

[0057] Structure

[18] . A method for manufacturing a heat transfer suppressor sheet according to any one of structures [1] to

[17] , characterized in that it has:

[0058] The process of obtaining a dispersion containing the first inorganic particles, the resin binder, and the organic fibers;

[0059] The process of dehydrating the dispersion to obtain a wetted tablet; and

[0060] The process of heating and then cooling the humidified sheet.

[0061] The heating temperature for heating the wetted sheet is set to be at least 10°C higher than the glass transition temperature of the organic fiber and less than 50°C higher.

[0062] Furthermore, the preferred embodiment of the present invention relating to the method of manufacturing the heat transfer inhibition sheet is related to the following structure

[19] .

[0063] The method for manufacturing the heat transfer suppression sheet of structure

[19] . Structure

[18] is characterized in that,

[0064] The dispersion is an emulsion in which the resin adhesive is dispersed in water.

[0065] Furthermore, the above-mentioned objective of the present invention is achieved by the structure of the battery pack described below

[20] .

[0066] Structure

[20] . A battery pack having:

[0067] Multiple battery cells and a heat transfer suppressor sheet of any one of the structures [1] to

[17] , wherein the multiple battery cells are connected in series or in parallel.

[0068] Invention Effects

[0069] According to the heat transfer suppression sheet of the present invention, the heat transfer suppression sheet contains first inorganic particles with excellent heat transfer suppression effect, thus achieving excellent heat transfer suppression effect. Furthermore, according to the heat transfer suppression sheet of the present invention, the glass transition temperature of the organic fibers is higher than the glass transition temperature of the resin adhesive; therefore, during manufacturing, after the organic fibers have cured to form a skeleton, the skeleton is reinforced by the resin adhesive. Therefore, it is possible to achieve both excellent compression characteristics and heat transfer suppression effect, thereby suppressing the reduction of thermal insulation performance.

[0070] According to the method for manufacturing the heat transfer inhibition sheet of the present invention, by appropriately controlling the temperature during heating, a skeleton can be reliably formed by organic fibers, thereby obtaining excellent compression characteristics.

[0071] The battery pack according to the present invention has a heat transfer suppression sheet as described above, which has excellent compression characteristics and heat transfer suppression effect. Therefore, it is possible to suppress thermal runaway of the battery cells in the battery pack and the spread of flames to the outside of the battery casing. Attached Figure Description

[0072] Figure 1A , Figure 1B and Figure 1C This is a schematic diagram illustrating the manufacturing method of the heat transfer suppression sheet according to the process sequence of the first embodiment of the present invention.

[0073] Figure 2 This is a schematic diagram illustrating the heat transfer suppression sheet according to the second embodiment of the present invention.

[0074] Figure 3 This is a schematic diagram illustrating a battery pack according to an embodiment of the present invention.

[0075] Figure 4A , Figure 4B and Figure 4C This is a schematic diagram showing the manufacturing method of the test material for Comparative Example 1 in the order of the production process.

[0076] Figure 5 This is a schematic diagram illustrating the compression characteristic test method.

[0077] Figure 6 This is a schematic diagram illustrating the heat transfer test method.

[0078] Figure 7 It is a graph showing the relationship between compressive stress and compressive rate in each test material when the horizontal axis is set as compressibility and the vertical axis is set as compressive stress.

[0079] Figure 8 It is a graph showing the relationship between the lower surface temperature of each test material and the elapsed time, with the horizontal axis set to elapsed time and the vertical axis set to the lower surface temperature.

[0080] Figure 9 It is a graph showing the relationship between thermal resistivity and compressive stress in each test material when the horizontal axis is set as compressive stress and the vertical axis is set as thermal resistivity.

[0081] Label Explanation

[0082] 1: First inorganic particle;

[0083] 2: Emulsion;

[0084] 3: Organic fibers;

[0085] 4, 14: Inorganic fibers;

[0086] 5, 15: Dispersion;

[0087] 6, 9, 16, 19: Resin adhesives;

[0088] 7: Welded section;

[0089] 8: Skeleton;

[0090] 10: Heat transfer inhibitor;

[0091] 12: Second inorganic particles;

[0092] 20a, 20b, 20c: Battery cells;

[0093] 30: Battery casing;

[0094] 31: First inorganic fiber;

[0095] 32: Second inorganic fiber;

[0096] 100: Battery pack. Detailed Implementation

[0097] The inventors have conducted in-depth research on heat transfer suppression sheets that can solve the above-mentioned problems.

[0098] The results showed that the heat transfer inhibition sheet, by having a first inorganic particle, a resin binder, and an organic fiber having a higher glass transition temperature than the resin binder, can improve its strength against extrusion, resulting in the maintenance of excellent thermal insulation performance.

[0099] Specifically, during the manufacture of the heat transfer suppression sheet, when heating the wet sheet containing the aforementioned materials, if the heating temperature is appropriately controlled, the organic fibers are in a semi-molten state. Furthermore, upon subsequent cooling, the organic fibers with high glass transition temperatures solidify first, thus bonding the contacting parts to form a framework. Then, through further cooling, the resin adhesive solidifies on the surface of the framework formed by the organic fibers, strengthening the framework. In this way, the heat transfer suppression sheet of the present invention has a robust framework, maintaining its shape even when compressed due to the expansion of the battery cells, and suppressing a decrease in thermal insulation performance.

[0100] First, the manufacturing method of the heat transfer suppression sheet according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings. Next, the heat transfer suppression sheet of this embodiment and the materials constituting the heat transfer suppression sheet will be described in detail. Furthermore, the battery pack of this embodiment will be described.

[0101] Furthermore, the present invention is not limited to the embodiments described below, and can be implemented in any way without departing from the spirit of the present invention.

[0102] [1. Manufacturing method of heat transfer inhibition sheet]

[0103] Figures 1A to 1C This is a schematic diagram illustrating the manufacturing method of the heat transfer suppression sheet according to the process sequence of the first embodiment of the present invention.

[0104] like Figure 1A As shown, a first inorganic particle 1, an emulsion 2 in which a resin binder is dispersed in water, an organic fiber 3 having a higher glass transition temperature than the resin binder, and an inorganic fiber 4 are prepared. They are mixed and stirred to obtain a dispersion 5. Next, a wetted sheet is made by dehydrating (de-liquidizing) the dispersion 5.

[0105] Next, the moistened sheet is heated. At this time, as... Figure 1B As shown, as the temperature rises, the water in emulsion 2 evaporates, and molten resin binder 6 is obtained. Then, by further heating the sheet, at least a portion of the surface of the organic fiber 3 melts.

[0106] Then, by cooling the plate, such as... Figure 1C As shown, organic fibers 3 are fused together to form a welded portion 7. Furthermore, by further cooling the sheet, a cured resin adhesive 9 is formed, thus obtaining the heat transfer suppression sheet of this embodiment.

[0107] In the heat transfer suppression sheet of this embodiment manufactured by the manufacturing method described above, an emulsion 2 containing a resin binder is used, so the material is uniformly dispersed overall, and in these dispersions, organic fibers 3 exist in an irregular orientation.

[0108] Furthermore, during the process of heating the wet sheet to the specified temperature, the resin adhesive completely melts, and then a portion of the surface of the organic fiber 3 with a high glass transition temperature melts.

[0109] Furthermore, during the cooling process of the heated sheet, the molten surface portion of the organic fiber 3 solidifies first, forming a welded portion 7 at the point where the organic fibers 3 come into contact with each other.

[0110] As described above, in the dispersion containing the raw materials, the organic fibers 3 exist in an irregular orientation. Therefore, after a portion of the surface of the organic fibers 3 melts, when cooled to a temperature lower than the glass transition temperature of the organic fibers 3, at least a portion of the organic fibers 3 fuses together to form a three-dimensional skeleton 8. As a result, the resulting skeleton 8 maintains the overall shape of the heat transfer inhibition sheet.

[0111] Subsequently, as the sheet cools to a temperature lower than the glass transition temperature of the resin adhesive, the molten resin adhesive solidifies on the surface of the skeleton 8, and also between the skeleton 8 and the first inorganic particles 1, and between the skeleton 8 and the inorganic fibers 4. Thus, the first inorganic particles 1 and the inorganic fibers 4 are bonded to the skeleton 8, and the skeleton 8 is strengthened by the solidified resin adhesive 9.

[0112] Thus, the heat transfer suppression sheet of this embodiment has a robust skeleton 8, which can maintain its shape even if the heat transfer suppression sheet is squeezed due to the expansion of the battery cell, and can suppress the reduction of heat insulation performance.

[0113] Furthermore, in this embodiment, the materials used are first inorganic particles 1, emulsion 2 containing resin binder, organic fiber 3 having a higher glass transition temperature than the resin binder, and inorganic fiber 4, but inorganic fiber 4 is not necessarily required. The effects obtained by adding inorganic fiber 4 will be described later. Regarding the emulsion 2 containing resin binder, it does not necessarily have to be in emulsion form; it is sufficient that the resin binder is uniformly dispersed in the liquid using some method. More preferably, all materials are uniformly dispersed in the dispersion. Therefore, the first inorganic particles 1, resin binder (not shown), organic fiber 3, inorganic fiber 4, and liquid used to prepare the dispersion are mixed and dispersed. Furthermore, from the viewpoint of reducing environmental impact, water is preferred as the liquid used to disperse the resin binder.

[0114] Next, the conditions in the manufacturing method of the heat transfer suppression sheet of this embodiment will be explained.

[0115] <Heating temperature of the moistened sheet>

[0116] In the process of heating the above-mentioned wetted sheet, the heating temperature is set to be at least 10°C higher than the glass transition temperature of the organic fiber 3 and less than 50°C.

[0117] That is, when the heating temperature of the wetted sheet is set to t (°C) and the glass transition temperature of the organic fiber 3 is set to Tg (°C), if the relationship is t < Tg + 10, the melting of the surface of the organic fiber 3 becomes insufficient, the adhesion between the organic fibers 3 becomes weak, and therefore, a strong skeleton cannot be formed.

[0118] On the other hand, if the relationship is t > Tg + 50, then the organic fiber 3 will completely melt due to heating and will not be able to form a shape that serves as a skeleton.

[0119] Therefore, the heating temperature t of the moistened sheet is set to Tg+10 (°C) or higher, preferably Tg+15 (°C) or higher. Furthermore, the heating temperature t of the moistened sheet is set to Tg+50 (°C) or lower, preferably Tg+30 (°C) or lower.

[0120] [2. Heat transfer inhibition tablets]

[0121] (First Implementation)

[0122] like Figure 1C As shown, the heat transfer inhibiting sheet of the first embodiment includes first inorganic particles 1, resin binder 9, organic fibers 3, and inorganic fibers 4. Furthermore, the glass transition temperature of the organic fibers 3 is higher than that of the resin binder 9.

[0123] In the heat transfer suppression sheet of the first embodiment with such a configuration, the first inorganic particles 1 are heat-resistant materials. In addition, numerous tiny spaces are formed inside the heat transfer suppression sheet, consisting of resin adhesive 9, first inorganic particles 1, organic fibers 3 and inorganic fibers 4 that do not solidify after melting, which also provides an air-based heat insulation effect. Therefore, an excellent heat transfer suppression effect can be obtained.

[0124] Furthermore, the glass transition temperature of the organic fiber 3 is higher than that of the resin adhesive 9. Therefore, as described in the manufacturing method above, during the heating and cooling process, the organic fiber 3 forms a skeleton, and the skeleton is strengthened by the resin adhesive 9.

[0125] In detail, at least a portion of the organic fibers 3 of the heat transfer inhibiting sheet in this embodiment are fused together to form a three-dimensional skeleton 8. In addition, the resin adhesive 9 is fused to a portion of the surface of the skeleton 8 and also to a portion of the first inorganic particles 1 and the inorganic fibers 4. Therefore, the first inorganic particles 1 and the inorganic fibers 4 are bonded to the skeleton, and the skeleton 8 is strengthened.

[0126] Therefore, the heat transfer suppression sheet of this embodiment has high strength and can suppress the decrease in heat insulation performance even when extrusion is applied.

[0127] (Second Implementation)

[0128] Figure 2 This is a schematic diagram illustrating the heat transfer suppression sheet according to the second embodiment of the present invention.

[0129] like Figure 2 As shown, the heat transfer inhibition sheet 10 of the second embodiment includes first inorganic particles 1, resin binder 9, organic fibers 3, second inorganic particles 12, first inorganic fibers 31, and second inorganic fibers 32. Furthermore, the glass transition temperature of the organic fibers 3 is higher than that of the resin binder 9. Additionally, the first inorganic particles 1 and the second inorganic particles 12 are inorganic particles with different heat transfer inhibition effects, and the first inorganic fibers 31 and the second inorganic fibers 32 are inorganic fibers with different properties.

[0130] In the heat transfer suppression sheet of the second embodiment, the glass transition temperature of the organic fiber 3 is higher than that of the resin adhesive 9. Therefore, as in the first embodiment, at least a portion of the organic fiber 3 is fused together to form a three-dimensional skeleton 8.

[0131] In addition, the resin adhesive 9 is fused to a portion of the surface of the skeleton 8, and the first inorganic particles 1, the second inorganic particles 12, the first inorganic fiber 31 and the second inorganic fiber 32 are bonded to the skeleton, thereby strengthening the skeleton 8.

[0132] Therefore, the heat transfer suppression sheet of the second embodiment also has high strength, and can suppress the decrease in heat insulation performance even when extrusion is applied.

[0133] In addition, in this embodiment, first inorganic particles 1 and second inorganic particles 12 with different heat transfer inhibition effects are used. Therefore, the heating element can be cooled in multiple stages, and heat absorption can be exhibited over a wider temperature range, thereby further improving the thermal insulation performance.

[0134] Furthermore, in this embodiment, at least one first inorganic fiber 31 and a second inorganic fiber 32 with different properties selected from average fiber diameter, shape and glass transition temperature are provided. Therefore, the mechanical strength of the heat transfer suppression sheet 10 and the retention of the first inorganic particles 1 and the second inorganic particles 12 can be improved.

[0135] The materials used in the heat transfer suppression sheet of this embodiment will be described in detail below.

[0136] <2-1. Resin Adhesives>

[0137] As for the resin adhesive 9 that can be used in this embodiment, there are no particular limitations as long as it has a glass transition temperature lower than that of the organic fiber 3 described later. For example, a resin adhesive 9 comprising at least one selected from styrene-butadiene resin, acrylic resin, silicone-acrylic resin, and styrene resin can be used.

[0138] The glass transition temperature of the resin binder 9 is not specifically specified, but is preferably above -10°C.

[0139] Furthermore, if the glass transition temperature of the resin binder 9 is above room temperature, the strength of the heat transfer suppressing sheet can be further improved when the heat transfer suppressing sheet with the resin binder 9 is used at room temperature.

[0140] Therefore, the glass transition temperature of the resin adhesive 9 is more preferably 20°C or higher, more preferably 30°C or higher, even more preferably 50°C or higher, and particularly preferably 60°C or higher.

[0141] (2-1-1. Resin binder content)

[0142] In this embodiment, if the content of the resin adhesive 9 is properly controlled, the reinforcement effect of the skeleton based on the organic fiber 3 can be fully obtained.

[0143] The content of resin binder 9 relative to the total mass of heat transfer inhibiting sheet 10 is preferably 0.5% by mass or more, more preferably 1% by mass or more. Furthermore, it is preferably 20% by mass or less, more preferably 10% by mass or less.

[0144] Furthermore, in the heat transfer suppression sheet 10 of this embodiment, even if the total content of organic fiber 3 and resin adhesive 9 is the same as the content of organic material in conventional insulation sheets, the strength against compression is increased by the above structure, and a balance between insulation performance and strength can be achieved.

[0145] <2-2. Organic Fibers>

[0146] As for the organic fiber 3 that can be used in this embodiment, there is no particular limitation as long as it has a glass transition temperature higher than that of the resin adhesive 9 described above. For example, an organic fiber 3 comprising at least one selected from polyvinyl alcohol (PVA) fiber, polyethylene fiber, nylon fiber, polyurethane fiber, and ethylene-vinyl alcohol copolymer fiber can be used.

[0147] Furthermore, it is difficult to raise the heating temperature above 250°C during the manufacture of the heat transfer suppression sheet. Therefore, the glass transition temperature of the organic fiber 3 is preferably set to 250°C or below, and more preferably to 200°C or below.

[0148] The lower limit of the glass transition temperature of the organic fiber 3 is not particularly limited, but if the difference between its glass transition temperature and that of the resin adhesive 9 is 10°C or more, then during the cooling process in manufacturing, after the semi-molten organic fiber 3 has completely solidified, the resin adhesive will also solidify. Therefore, the reinforcing effect of the resin adhesive 9 on the skeleton can be fully obtained. Thus, the difference between the glass transition temperature of the resin adhesive 9 and that of the organic fiber 3 is preferably 10°C or more, and more preferably 30°C or more.

[0149] On the other hand, if the difference in glass transition temperatures between the two is 130°C or less, the time from the complete curing of the organic fiber 3 to the beginning of curing of the resin adhesive can be appropriately adjusted, and the resin adhesive cures in a well-dispersed state. Therefore, the reinforcing effect of the skeleton 8 can be further obtained. Therefore, the difference between the glass transition temperature of the resin adhesive 9 and the glass transition temperature of the organic fiber 3 is preferably 130°C or less, more preferably 120°C or less, further preferably 100°C or less, even more preferably 80°C or less, and particularly preferably 70°C or less.

[0150] In the heat transfer suppression sheet of this embodiment, when two or more types of organic fibers are included, at least one type of organic fiber is required to function as a framework, i.e., an organic fiber having a glass transition temperature higher than that of the resin binder. Furthermore, as described above, the difference between the glass transition temperature of the resin binder 9 and the glass transition temperature of at least one type of organic fiber is preferably 10°C or more, more preferably 30°C or more, preferably 130°C or less, more preferably 120°C or less, further preferably 100°C or less, even more preferably 80°C or less, and particularly preferably 70°C or less.

[0151] In this embodiment, by appropriately controlling the content of organic fiber 3 and resin binder 9, the function of the organic fiber 3-based skeleton can be sufficiently obtained, and the reinforcing effect of the resin binder 9 on the skeleton can be sufficiently obtained. The content of organic fiber 3 relative to the total mass of the heat transfer suppressing sheet is preferably 0.5% by mass or more, more preferably 1% by mass or more. Furthermore, it is preferably 12% by mass or less, more preferably 8% by mass or less. In addition, when the heat transfer suppressing sheet contains multiple organic fibers having a glass transition temperature higher than that of the resin binder, the total amount of these multiple organic fibers is preferably within the range of the aforementioned organic fiber 3 content.

[0152] As described above, in the heat transfer suppression sheet of this embodiment, when two or more organic fibers are included, it is acceptable as long as at least one organic fiber has a glass transition temperature higher than that of the resin adhesive. However, as other organic fibers, it is preferable to include organic fibers in a crystalline state that do not have a glass transition temperature.

[0153] Organic fibers in a crystalline state that do not have a glass transition temperature do not have a softening point. Therefore, even when exposed to high temperatures, such as when the organic fibers that form the skeleton soften, in this embodiment, the overall strength of the heat transfer suppression sheet can be maintained.

[0154] Furthermore, by incorporating organic fibers in a crystalline state that do not possess a glass transition temperature, these organic fibers also function as the framework of the heat transfer suppression sheet at room temperature. Therefore, the flexibility and processability of the heat transfer suppression sheet can be improved.

[0155] In addition, polyester (PET) fiber is an example of an organic fiber that is in a crystalline state and does not have a glass transition temperature.

[0156] Furthermore, as described above, in this embodiment, water is preferably used as the liquid for dispersing the resin adhesive. Therefore, when using water, it is preferable to use organic fibers with low water solubility. In this embodiment, the water solubility is indicated by the water dissolution temperature. That is, the water dissolution temperature of the organic fiber 3 is preferably 60°C or higher, more preferably 70°C or higher, and even more preferably 80°C or higher.

[0157] The fiber length of organic fiber 3 is not particularly limited, but from the point of view of ensuring formability and processability, the average fiber length of organic fiber 3 is preferably less than 10 mm.

[0158] On the other hand, from the viewpoint of enabling the organic fiber 3 to function as a skeleton and ensuring the compressive strength of the heat transfer suppression sheet, the average fiber length of the organic fiber 3 is preferably 0.5 mm or more.

[0159] <2-3. Inorganic Particles>

[0160] When the average secondary particle size of the inorganic particles is 0.01 μm or more, it is readily available, which helps to suppress the increase in manufacturing costs. Furthermore, when the average secondary particle size of the inorganic particles is 200 μm or less, the desired thermal insulation effect can be obtained. Therefore, the average secondary particle size of the inorganic particles is preferably 0.01 μm or more and 200 μm or less, more preferably 0.05 μm or more and 100 μm or less.

[0161] As inorganic particles, a single inorganic particle can be used, or two or more inorganic particles (first inorganic particle 1 and second inorganic particle 12) can be combined. From the viewpoint of inhibiting heat transfer, particles composed of at least one inorganic material selected from oxide particles, carbide particles, nitride particles, and inorganic hydrate particles are preferred as first inorganic particle 1 and second inorganic particle 12, and oxide particles are more preferred. Furthermore, the shape of first inorganic particle 1 and second inorganic particle 12 is not particularly limited, but it is preferable to include at least one of nanoparticles, hollow particles, and porous particles. Specifically, inorganic hollow spheres such as silica nanoparticles, metal oxide particles, microporous particles, and hollow silica particles, particles composed of thermally expandable inorganic materials, and particles composed of hydrous porous bodies can also be used.

[0162] Furthermore, by using two or more types of inorganic particles with different heat transfer inhibition effects, multi-stage cooling of the heating element can be achieved, resulting in endothermic effects over a wider temperature range. Specifically, it is preferable to use a mixture of large-diameter and small-diameter particles. For example, when using nanoparticles as one type of inorganic particle, it is preferable to include inorganic particles composed of metal oxides as the other type of inorganic particle. Hereinafter, small-diameter inorganic particles will be referred to as the first inorganic particle 1, and large-diameter inorganic particles as the second inorganic particle 12, for a more detailed explanation of the inorganic particles.

[0163] <2-3-1. First Inorganic Particle>

[0164] (Oxide particles)

[0165] Oxide particles have a high refractive index, resulting in strong light diffuse reflection. Therefore, when oxide particles are used as the first inorganic particle 1, they can suppress radiative heat transfer, especially in high-temperature regions such as those experiencing abnormal heating. As oxide particles, at least one type selected from silicon dioxide, titanium dioxide, zircon, zirconia, barium titanate, zinc oxide, and aluminum oxide can be used. That is, only one of the aforementioned oxide particles that can be used as inorganic particles can be used, or two or more oxide particles can be used. In particular, silicon dioxide is a component with high thermal insulation properties, and titanium dioxide is a component with a high refractive index compared to other metal oxides. Both are effective at diffusely reflecting light and blocking radiative heat in high-temperature regions above 500°C. Therefore, silicon dioxide and titanium dioxide are most preferably used as oxide particles.

[0166] (Average primary particle size of oxide particles: greater than 0.001 μm and less than 50 μm)

[0167] The particle size of oxide particles can sometimes affect the effectiveness of reflecting radiant heat. Therefore, if the average primary particle size is limited to a specified range, higher thermal insulation can be obtained.

[0168] That is, when the average primary particle size of the oxide particles is greater than 0.001 μm, it is large enough compared to the wavelength of light that helps to heat up, so that the light is diffusely reflected efficiently. Therefore, in the high temperature region above 500°C, the radiative heat transfer of heat in the heat transfer suppression sheet is suppressed, which can further improve the thermal insulation.

[0169] On the other hand, when the average primary particle size of oxide particles is less than 50 μm, even when compressed, the number of joints between particles will not increase, making it difficult to form a conductive heat transfer pathway. Therefore, it can reduce the influence of conductive heat transfer on the insulation of the dominant normal temperature range.

[0170] Furthermore, in this invention, the average primary particle size can be determined by observing the particles under a microscope, comparing them with a standard scale, and taking the average of any 10 particles.

[0171] (Nanoparticles)

[0172] In this invention, nanoparticles refer to nanoscale particles that are spherical or nearly spherical with an average primary particle size of less than 1 μm. Nanoparticles have low density, thus suppressing conductive heat transfer. If nanoparticles are used as the first inorganic particle 1, the voids are further finely dispersed, thereby achieving excellent thermal insulation to suppress convective heat transfer. Therefore, from the perspective of suppressing heat conduction between adjacent nanoparticles during battery use in the normal ambient temperature range, the use of nanoparticles is preferred.

[0173] Furthermore, if nanoparticles with a small average primary particle size are used as oxide particles, even if the heat transfer suppressor is compressed due to the expansion accompanying the thermal runaway of the battery cell, resulting in an increase in internal density, the increase in conductive heat transfer of the heat transfer suppressor can still be suppressed. This is believed to be because nanoparticles easily form small gaps between particles due to electrostatic repulsion, resulting in low bulk density. Therefore, the particles are filled in a buffering manner.

[0174] Furthermore, in this invention, when nanoparticles are used as the first inorganic particle 1, the material is not particularly limited as long as it meets the definition of nanoparticles described above. For example, silica nanoparticles are highly insulating materials, and the contact points between particles are small; therefore, the heat conducted through silica nanoparticles is less compared to the case where larger silica particles are used. Additionally, the bulk density of silica nanoparticles typically obtained is 0.1 g / cm³. 3 Therefore, even if the battery cells positioned on both sides of the insulation sheet undergo thermal expansion, applying large compressive stress to the insulation sheet, the size (area) and number of the contact points between the silica nanoparticles will not increase significantly, thus maintaining the insulation properties. Therefore, silica nanoparticles are preferred as nanoparticles. Wet silica, dry silica, and aerogels can be used as silica nanoparticles.

[0175] (Average primary particle size of nanoparticles: greater than 1 nm and less than 100 nm)

[0176] If the average primary particle size of the nanoparticles is limited to a specified range, higher thermal insulation can be obtained.

[0177] That is, if the average primary particle size of the nanoparticles is set to be greater than 1 nm and less than 100 nm, then, especially in the temperature range below 500 °C, convective and conductive heat transfer within the heat transfer suppression sheet can be suppressed, thereby further improving the thermal insulation. In addition, even under compressive stress, the voids remaining between the nanoparticles and the junctions between multiple particles can suppress conductive heat transfer, thus maintaining the thermal insulation of the heat transfer suppression sheet.

[0178] Furthermore, the average primary particle size of the nanoparticles is more preferably 2 nm or more, and even more preferably 3 nm or more. On the other hand, the average primary particle size of the nanoparticles is more preferably 50 nm or less, and even more preferably 10 nm or less.

[0179] (Inorganic hydrate particles)

[0180] When inorganic hydrate particles are heated by a heat source and reach a temperature above the initiation temperature of thermal decomposition, they undergo thermal decomposition, releasing their own water of crystallization and thus lowering the temperature of the heat source and its surroundings, exhibiting the so-called "endothermic effect." Furthermore, after releasing the water of crystallization, they become porous, exhibiting an insulating effect through numerous air pores.

[0181] 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).

[0182] For example, aluminum hydroxide contains about 35% water of crystallization, as shown in the following formula. It decomposes thermally to release this water of crystallization, exhibiting an endothermic effect. Furthermore, after releasing the water of crystallization, it becomes alumina (Al₂O₃), a porous material, which functions as a thermal insulation material.

[0183] 2Al(OH)3→Al2O3+3H2O

[0184] Furthermore, as described later, the heat transfer suppression sheet 10 of this embodiment is preferably sandwiched between battery cells, but in a battery cell where thermal runaway occurs, the temperature rises sharply to over 200°C and continues to rise to around 700°C. Therefore, as inorganic particles, it is preferable to use inorganic hydrates with a thermal decomposition start temperature of 200°C or higher.

[0185] Regarding the thermal decomposition start temperatures of the inorganic hydrates listed above, aluminum hydroxide is approximately 200°C, magnesium hydroxide is approximately 330°C, calcium hydroxide is approximately 580°C, zinc hydroxide is approximately 200°C, iron hydroxide is approximately 350°C, manganese hydroxide is approximately 300°C, zirconium hydroxide is approximately 300°C, and gallium hydroxide is approximately 300°C. These temperatures largely overlap with the temperature range of the rapidly rising battery cells that experience thermal runaway, effectively suppressing temperature rise. Therefore, they can be considered preferred inorganic hydrates.

[0186] (Average secondary particle size of inorganic hydrate particles: greater than 0.01 μm and less than 200 μm)

[0187] Furthermore, when inorganic hydrate particles are used as the first inorganic particle 1, if their average particle size is too large, the first inorganic particle 1 (inorganic hydrate) located near the center of the heat transfer inhibition sheet 10 will require a certain amount of time to reach its thermal decomposition temperature. Therefore, there is a possibility that the first inorganic particle 1 near the center of the sheet may not be completely thermally decomposed. Therefore, the average secondary particle size of the inorganic hydrate particles is preferably 0.01 μm or more and 200 μm or less, more preferably 0.05 μm or more and 100 μm or less.

[0188] (Particles composed of thermally expanding inorganic materials)

[0189] Examples of thermally expandable inorganic materials include vermiculite, bentonite, mica, and perlite.

[0190] (Particles composed of hydrous porous materials)

[0191] Specific examples of hydrous porous materials include zeolite, kaolinite, montmorillonite, acid clay, diatomaceous earth, wet silica, dry silica, aerogel, mica, vermiculite, etc.

[0192] (Inorganic hollow sphere)

[0193] The thermal insulation material used in this invention may contain inorganic hollow spheres as the first inorganic particles 1.

[0194] If it contains inorganic hollow spheres, it can suppress convective or conductive heat transfer within the insulation material in temperature ranges below 500°C, thereby further improving the insulation performance of the insulation material.

[0195] As an inorganic hollow sphere, at least one of the following can be used: white sand hollow sphere, silica hollow sphere, fly ash hollow sphere, barite hollow sphere, and glass hollow sphere.

[0196] (Inorganic hollow sphere content: less than 60% by mass relative to the total mass of the insulation material)

[0197] The content of inorganic hollow spheres, relative to the total mass of the insulation material, is preferably 60% by mass or less.

[0198] (Average particle size of inorganic hollow spheres: greater than 1 μm and less than 100 μm)

[0199] The average particle size of the inorganic hollow spheres is preferably 1 μm or more and 100 μm or less.

[0200] <2-3-2. Second Inorganic Particles>

[0201] When the heat transfer suppression sheet contains two types of inorganic particles, the second inorganic particle 12 is not particularly limited as long as its material, particle size, etc., are different from the first inorganic particle 1. As the second inorganic particle 12, inorganic hollow spheres such as oxide particles, carbide particles, nitride particles, inorganic hydrate particles, silica nanoparticles, metal oxide particles, microporous particles or hollow silica particles, particles made of thermally expandable inorganic materials, particles made of hydrous porous bodies, etc., can be used, and their details are as described above.

[0202] Furthermore, nanoparticles exhibit extremely low thermal conductivity and maintain excellent thermal insulation even when compressive stress is applied to the heat transfer suppression sheet. Additionally, metal oxide particles such as titanium dioxide are highly effective at blocking radiant heat. Moreover, when using both large-diameter and small-diameter inorganic particles, the small-diameter particles can penetrate the gaps between the large-diameter particles, resulting in a denser structure and improved heat transfer suppression. Therefore, when using nanoparticles as the first inorganic particle 1, it is preferable to further include particles composed of metal oxides with a diameter larger than the first inorganic particle 1 as the second inorganic particle 12 in the heat transfer suppression sheet.

[0203] Examples of metal oxides include silicon dioxide, titanium dioxide, aluminum oxide, barium titanate, zinc oxide, zircon, and zirconium oxide. In particular, titanium dioxide has a higher refractive index than other metal oxides, and it is highly effective in blocking radiant heat by diffuse reflection of light in high-temperature regions above 500°C. Therefore, titanium dioxide is the preferred choice.

[0204] (Average primary particle size of the second inorganic particle)

[0205] When the heat transfer suppression sheet contains second inorganic particles 12 composed of metal oxides, if the average primary particle size of the second inorganic particles 12 is 1 μm or more and 50 μm or less, radiative heat transfer can be efficiently suppressed in high-temperature regions above 500°C. The average primary particle size of the second inorganic particles 12 is further preferably 5 μm or more and 30 μm or less, and most preferably 10 μm or less.

[0206] <2-4. First Inorganic Fiber and Second Inorganic Fiber>

[0207] The heat transfer suppression sheet of this embodiment preferably has at least one first inorganic fiber 31 and a second inorganic fiber 32 with different properties selected from average fiber diameter, shape and glass transition temperature. As explained in the second embodiment above, by containing two inorganic fibers with different properties, the mechanical strength of the heat transfer suppression sheet and the retention of the first inorganic particles 1 and the second inorganic particles 12 can be improved.

[0208] (2-4-1. Two types of inorganic fibers with different average fiber diameters and fiber shapes)

[0209] When the heat transfer suppressing sheet contains two types of inorganic fibers, it is preferable that the average fiber diameter of the first inorganic fiber 31 is larger than that of the second inorganic fiber 32. The first inorganic fiber 31 is linear or needle-like, while the second inorganic fiber 32 is dendritic or crimped. The first inorganic fiber 31 with a larger average fiber diameter (coarse diameter) has the effect of improving the mechanical strength and shape retention of the heat transfer suppressing sheet. By making one of the two inorganic fibers, for example, the diameter of the first inorganic fiber 31, larger than that of the second inorganic fiber 32, the above-mentioned effect can be obtained. Since there are cases where external impacts act on the heat transfer suppressing sheet, the inclusion of the first inorganic fiber 31 in the heat transfer suppressing sheet improves impact resistance. Examples of external impacts include the compressive force based on the expansion of the battery cell, the wind pressure caused by the fire of the battery cell, etc.

[0210] Furthermore, to improve the mechanical strength and shape retention of the heat transfer suppression sheet, it is particularly preferred that the first inorganic fiber 31 is linear or needle-like. Moreover, linear or needle-like fibers refer to fibers with a crimp degree of, for example, less than 10%, preferably less than 5%, as described later.

[0211] More specifically, in order to improve the mechanical strength and shape retention of the heat transfer suppression sheet, the average fiber diameter of the first inorganic fiber 31 is preferably 1 μm or more, and more preferably 3 μm or more. If the first inorganic fiber 31 is too coarse, the formability and processability of the heat transfer suppression sheet may be reduced. Therefore, the average fiber diameter of the first inorganic fiber 31 is preferably 20 μm or less, and more preferably 15 μm or less.

[0212] Furthermore, if the first inorganic fiber 31 is too long, its formability and processability may be reduced. Therefore, it is preferable to set the fiber length to 100 mm or less. Moreover, if the first inorganic fiber 31 is too short, its shape retention and mechanical strength will also be reduced. Therefore, it is preferable to set the fiber length to 0.1 mm or more.

[0213] On the other hand, the second inorganic fiber 32 with a smaller average fiber diameter has the effect of improving the retention of the organic fiber 3 and the first inorganic particle 1, and improving the softness of the heat transfer suppression sheet. Therefore, it is preferable that the diameter of the second inorganic fiber 32 is smaller than the diameter of the first inorganic fiber 31.

[0214] More specifically, in order to improve the retention of the organic fiber 3 and the first inorganic particle 1, the second inorganic fiber 32 is preferably easily deformable and flexible. Therefore, the average fiber diameter of the fine-diameter second inorganic fiber 32 is preferably less than 1 μm, more preferably less than 0.1 μm. However, if the fine-diameter inorganic fiber is too thin, it is prone to breakage, and the retention ability of the organic fiber 3 and the first inorganic particle 1 will decrease. In addition, if the proportion of the organic fiber 3 and the first inorganic particle 1 are not retained and the fibers exist in an interwoven state in the heat transfer suppression sheet increases, in addition to the decrease in the retention ability of the organic fiber 3 and the first inorganic particle 1, the formability and shape retention will also deteriorate. Therefore, the average fiber diameter of the second inorganic fiber 32 is preferably 1 nm or more, more preferably 10 nm or more.

[0215] Furthermore, if the second inorganic fiber 32 is too long, its formability and shape retention will decrease. Therefore, the fiber length of the second inorganic fiber 32 is preferably 0.1 mm or less. Conversely, if the second inorganic fiber 32 is too short, its shape retention and mechanical strength will decrease. Therefore, the fiber length of the second inorganic fiber 32 is preferably 1 μm or more.

[0216] Furthermore, the second inorganic fiber 32 is preferably dendritic or crimped. If the second inorganic fiber 32 has this shape, it will interweave with the organic fiber 3 and the first inorganic particles 1 in the heat transfer suppression sheet. Therefore, the retention capacity of the organic fiber 3 and the first inorganic particles 1 is improved. In addition, when the heat transfer suppression sheet is subjected to compressive force or wind pressure, the sliding movement of the second inorganic fiber 32 is suppressed, thereby improving its mechanical strength, particularly its resistance to external compressive force and impact.

[0217] In addition, dendritic refers to a structure that branches in two or three dimensions, such as feather-like, tetrap-like, radial, or three-dimensional mesh-like structures.

[0218] In the case where the second inorganic fiber 32 is dendritic, its average fiber diameter can be obtained by using SEM to measure the diameter of the trunk and branches at multiple points and calculating their average value.

[0219] Furthermore, crimped refers to a structure in which fibers bend in various directions. As one method for quantifying crimped morphology, it is known to calculate the degree of crimp based on electron microscope images, for example, using the following formula.

[0220] crimp (%) = (fiber length - distance between fiber ends) / (fiber length) × 100

[0221] Here, the fiber length and the distance between fiber ends are measured values ​​from electron microscope images. That is, the fiber length and the distance between fiber ends projected onto a two-dimensional plane are shorter than the actual values. According to this formula, the crimp of the second inorganic fiber 32 is preferably 10% or more, more preferably 30% or more. If the crimp is small, the retention capacity of the organic fiber 3 and the first inorganic particle 1 is reduced, making it difficult to form an interweaving (web) between the second inorganic fibers 32 and between the first inorganic fiber 31 and the second inorganic fiber 32.

[0222] In the above embodiments, as a method to improve the mechanical strength, shape retention, and retention of organic fibers 3 and first inorganic particles 1 of the heat transfer suppression sheet, first inorganic fibers 31 and second inorganic fibers 32 with different average fiber diameters and fiber shapes are used. However, by using first inorganic fibers 31 and second inorganic fibers 32 with different glass transition temperatures and average fiber diameters, the mechanical strength, shape retention, and particle retention of the heat transfer suppression sheet can also be improved.

[0223] As described above, in this embodiment, in order to improve the mechanical strength, shape retention, and particle retention of the heat transfer suppression sheet, various combinations of inorganic fibers are preferably used. Hereinafter, [the following will discuss the...] Figure 2 The second embodiment shown will be described using different combinations of the first and second inorganic fibers, but for convenience, in this specification, we will use... Figure 2 Other embodiments related to inorganic fibers are described.

[0224] (2-4-2. Two types of inorganic fibers with different glass transition temperatures)

[0225] When the heat transfer suppressing sheet contains two types of inorganic fibers, it is preferable that the first inorganic fiber 31 is an amorphous fiber, and the second inorganic fiber 32 is at least one type of fiber selected from crystalline fibers and amorphous fibers with a glass transition temperature higher than that of the first inorganic fiber 31. Furthermore, by using a first inorganic particle 1 containing at least one type selected from nanoparticles, hollow particles, and porous particles in conjunction with the aforementioned two types of inorganic fibers, the thermal insulation performance can be further improved.

[0226] The melting point of crystalline inorganic fibers is generally higher than the glass transition temperature of amorphous inorganic fibers. Therefore, if the first inorganic fiber 31 is exposed to high temperatures, its surface softens before the second inorganic fiber 32, bonding the organic fiber 3 and the first inorganic particles 1 together. Thus, by including the first inorganic fiber 31 as described above in the heat transfer suppression sheet, the mechanical strength of the insulation layer can be improved.

[0227] Specifically, the first inorganic fiber 31 is preferably an inorganic fiber with a melting point below 700°C, and many amorphous inorganic fibers can be used. Among them, fibers containing SiO2 are preferred, and glass fibers are more preferred from the perspectives of low price, easy availability, and excellent processability.

[0228] As described above, the second inorganic fiber 32 is a fiber composed of at least one selected from crystalline fibers and amorphous fibers with a glass transition temperature higher than that of the first inorganic fiber 31. Many crystalline inorganic fibers can be used as the second inorganic fiber 32.

[0229] If the second inorganic fiber 32 is composed of crystalline fibers, or has a higher glass transition temperature than the first inorganic fiber 31, then when exposed to high temperatures, even if the first inorganic fiber 31 softens, the second inorganic fiber 32 will not melt or soften. Therefore, it can maintain its shape and continue to exist between battery cells even during thermal runaway.

[0230] In addition, if the second inorganic fiber 32 does not melt or soften, the tiny spaces between the particles, between the particles and the fibers, and between the fibers contained in the heat transfer inhibition sheet are maintained. Therefore, it can exert an air-based insulation effect and maintain excellent heat transfer inhibition performance.

[0231] When the second inorganic fiber 32 is crystalline, the second inorganic fiber 32 can be made of silica fiber, alumina fiber, aluminum silicate fiber, zirconium oxide fiber, carbon fiber, soluble fiber, refractory ceramic fiber, aerogel composite material, magnesium silicate fiber, alkaline earth silicate fiber, potassium titanate fiber and other ceramic fibers, glass fiber, glass wool and other glass fibers, asbestos, basalt fiber, etc., and other mineral fibers such as wollastonite and other natural mineral fibers.

[0232] If the fiber listed as the second inorganic fiber 32 has a melting point exceeding 1000°C, then even if thermal runaway of the battery cell occurs, the second inorganic fiber 32 will not melt or soften and can maintain its shape, thus it can be used appropriately.

[0233] Furthermore, it is more preferable to use ceramic fibers such as silica fibers, alumina fibers and aluminosilicate fibers, as well as natural mineral fibers, which are listed as the second inorganic fiber 32 above. Among them, it is even more preferable to use fibers with a melting point of more than 1000°C.

[0234] Furthermore, even if the second inorganic fiber 32 is amorphous, it can be used as long as it is a fiber with a glass transition temperature higher than that of the first inorganic fiber 31. For example, a glass fiber with a glass transition temperature higher than that of the first inorganic fiber 31 can also be used as the second inorganic fiber 32.

[0235] Furthermore, as the second inorganic fiber 32, various inorganic fibers, as exemplified, can be used alone, or two or more can be used in combination.

[0236] As described above, the glass transition temperature of the first inorganic fiber 31 is lower than that of the second inorganic fiber 32. When exposed to high temperatures, the first inorganic fiber 31 softens first. Therefore, the first inorganic fiber 31 can be used to bond organic fibers 3 and first inorganic particles 1, etc. However, for example, if the second inorganic fiber 32 is amorphous and its fiber diameter is smaller than that of the first inorganic fiber 31, and if the glass transition temperatures of the first inorganic fiber 31 and the second inorganic fiber 32 are close, the second inorganic fiber 32 may soften first.

[0237] Therefore, when the second inorganic fiber 32 is an amorphous fiber, the glass transition temperature of the second inorganic fiber 32 is preferably 100°C or more higher than the glass transition temperature of the first inorganic fiber 31, and more preferably 300°C or more higher.

[0238] Furthermore, the fiber length of the first inorganic fiber 31 is preferably 100 mm or less, and more preferably 0.1 mm or more. The fiber length of the second inorganic fiber 32 is preferably 0.1 mm or less. These reasons are as described above.

[0239] (2-4-3. Two types of inorganic fibers with different glass transition temperatures and average fiber diameters)

[0240] When the heat transfer suppressing sheet contains two types of inorganic fibers, it is preferable that the first inorganic fiber 31 is an amorphous fiber, and the second inorganic fiber 32 is at least one type of fiber selected from crystalline fibers and amorphous fibers with a glass transition temperature higher than that of the first inorganic fiber 31, and the average fiber diameter of the first inorganic fiber 31 is larger than that of the second inorganic fiber 32.

[0241] As described above, when the heat transfer suppression sheet of this embodiment contains two types of inorganic fibers, it is preferable that the average fiber diameter of the first inorganic fiber 31 is larger than that of the second inorganic fiber 32. Furthermore, it is preferable that the coarser first inorganic fiber 31 is an amorphous fiber, and the finer second inorganic fiber 32 is a fiber composed of at least one selected from crystalline fibers and amorphous fibers with a glass transition temperature higher than that of the first inorganic fiber 31. Therefore, the first inorganic fiber 31 has a low glass transition temperature and softens earlier, thus hardening into a film as the temperature rises. On the other hand, if the finer second inorganic fiber 32 is a fiber composed of at least one selected from crystalline fibers and amorphous fibers with a glass transition temperature higher than that of the first inorganic fiber 31, then even if the temperature rises, the finer second inorganic fiber 32 remains in a fiber shape, thus maintaining the structure of the heat transfer suppression sheet and preventing powder shedding.

[0242] Furthermore, even in this case, the fiber length of the first inorganic fiber 31 is preferably 100 mm or less, and more preferably 0.1 mm or more. The fiber length of the second inorganic fiber 32 is preferably 0.1 mm or less. These reasons are as described above.

[0243] In addition, the heat transfer suppression sheet of this embodiment may contain different inorganic fibers besides the first inorganic fiber 31 and the second inorganic fiber 32 described above.

[0244] (2-4-4. The respective contents of the first and second inorganic fibers)

[0245] When the heat transfer inhibition sheet contains two kinds of inorganic fibers, the content of the first inorganic fiber 31 is preferably 3% or more and 30% or less by mass relative to the total mass of the heat transfer inhibition sheet, and the content of the second inorganic fiber 32 is preferably 3% or more and 30% or less by mass relative to the total mass of the heat transfer inhibition sheet.

[0246] Furthermore, the content of the first inorganic fiber 31 is more preferably 5% by mass and less than 15% by mass relative to the total mass of the heat transfer inhibiting sheet, and the content of the second inorganic fiber 32 is more preferably 5% by mass and less than 15% by mass relative to the total mass of the heat transfer inhibiting sheet. By setting such contents, the shape retention, extrusion resistance, and wind pressure resistance based on the first inorganic fiber 31 and the retention ability of the inorganic particles based on the second inorganic fiber 32 are well balanced.

[0247] <2-5. Thickness of the heat transfer suppression sheet>

[0248] The thickness of the heat transfer suppression sheet in this embodiment is not particularly limited, but it is preferably 0.05 mm or more and 10 mm or less. When the thickness is 0.05 mm or more, sufficient compressive strength can be obtained. On the other hand, when the thickness is 10 mm or less, good thermal insulation properties of the heat transfer suppression sheet can be obtained.

[0249] [3. Battery Pack]

[0250] Figure 3 This is a schematic diagram illustrating a battery pack according to an embodiment of the present invention. The battery pack 100 of this embodiment has a plurality of battery cells 20a, 20b, 20c and a heat transfer suppression sheet of this embodiment, wherein the plurality of battery cells are connected in series or in parallel.

[0251] For example, such as Figure 3 As shown, in this embodiment, the heat transfer suppression sheet 10 is sandwiched between battery cell 20a and battery cell 20b, and between battery cell 20b and battery cell 20c. Furthermore, battery cells 20a, 20b, 20c and the heat transfer suppression sheet 10 are housed within the battery casing 30.

[0252] Furthermore, the same applies to the heat transfer inhibition sheet 10 as described above.

[0253] In the battery pack 100 configured in this way, even if a certain battery cell 20a is at a high temperature, there is a heat transfer suppression sheet 10 with a heat transfer suppression effect between it and the battery cell 20b, so the heat transfer to the battery cell 20b can be suppressed.

[0254] Furthermore, the heat transfer suppression sheet 10 of this embodiment has high compressive strength, thus suppressing the thermal expansion of the battery cells 20a, 20b, and 20c even during charging and discharging. Therefore, it ensures the distance between the battery cells, suppresses the reduction in thermal insulation performance, and prevents thermal runaway of the battery cells. Additionally, by suppressing thermal expansion, it prevents deformation of the battery cells, thereby reducing the load on the battery casing 30.

[0255] Furthermore, the battery pack 100 in this embodiment is not limited to... Figure 3 The illustrated battery pack may also have heat transfer suppression sheets 10 disposed not only between battery cells 20a and 20b, and between battery cells 20b and 20c, but also between battery cells 20a, 20b, 20c and the battery casing 30.

[0256] In the battery pack 100 configured in this way, in the event of a fire in a battery cell, the spread of flames to the outside of the battery casing 30 can be suppressed.

[0257] For example, the battery pack 100 of this embodiment is sometimes used in electric vehicles (EVs) and is located under the passenger's floor. In this case, it is assumed that even if the battery cell catches fire, the safety of the passenger can be ensured.

[0258] In addition, besides sandwiching the heat transfer suppressor 10 between each battery cell, the heat transfer suppressor 10 can also be disposed between the battery cells 20a, 20b, 20c and the battery casing 30. Therefore, there is no need to remake flame-retardant materials, etc., and a low-cost and safe battery pack 100 can be easily constructed.

[0259] In the battery pack of this embodiment, the heat transfer suppression sheet 10 disposed between the battery cells 20a, 20b, 20c and the battery casing 30 can be in contact with the battery cells 101 or may have a gap. However, if there is a gap between the heat transfer suppression sheet 10 and the battery cells 20a, 20b, 20c, the deformation of the battery cells can be allowed even if the temperature of any one of the multiple battery cells rises and its volume expands.

[0260] Furthermore, the heat transfer suppression sheet 10 of this embodiment can be easily bent depending on the type and thickness of the material chosen. Therefore, it is not affected by the shape of the battery cells 20a, 20b, 20c and the battery casing 30, and can accommodate structures of any shape. Specifically, in addition to prismatic batteries, it can also be applied to cylindrical batteries, flat batteries, etc.

[0261] [Example]

[0262] The present invention will now be described in detail with reference to embodiments and comparative examples, but the present invention is not limited to these embodiments and comparative examples.

[0263] <Preparation of Experimental Materials>

[0264] (Example 1)

[0265] As organic fibers, polyester (PET) fibers, which are crystalline organic fibers without a glass transition temperature, and polyvinyl alcohol (PVA) fibers, which have a glass transition temperature, were prepared. As resin binders, a latex solution with a glass transition temperature of 58°C was prepared. As the first and second inorganic particles, silica particles and titanium dioxide particles were prepared. As other components, silica-based fibers and glass fibers were prepared as inorganic fibers. The specific content and names of each component are shown below.

[0266] • Polyester fiber (3 parts): 0.1 dtex × 3 mm (average fiber length)

[0267] • PVA fiber (5 parts): VPB 053 (manufactured by Kuraray Co., Ltd.), 0.55 dtex × 3 mm

[0268] • Latex solution (5 parts styrene-butadiene resin): Glass transition temperature 58℃

[0269] • First inorganic particles and second inorganic particles (70 parts in total): silica particles and titanium dioxide particles

[0270] • First inorganic fiber (7 parts): silica-based fiber

[0271] • Second inorganic fiber (10 parts): Glass fiber, CS 3J-888S (manufactured by Nittobo Co., Ltd.), fiber diameter 10μm × fiber length 6mm

[0272] The above materials are dispersed in water using a pulper to prepare a uniform papermaking pulp (dispersion liquid). Then, the pulp is dewatered using a papermaking machine to obtain wet sheets.

[0273] Then, after drying using a Yankee dryer with a surface temperature of 140°C, the product is heated to 250°C by hot air drying to obtain dried sheets. The dried sheets are then cooled, thereby producing a product with a basis weight of 600 g / m³. 2 The test material of Example 1 with a thickness of 1.5 mm.

[0274] Furthermore, relative to the total mass of the test materials obtained in Example 1, the content of polyester fiber was 3% by mass, the content of PVA fiber was 5% by mass, and the content of resin adhesive (styrene-butadiene resin) was 5% by mass.

[0275] (Example 2)

[0276] As organic fibers, polyester (PET) fibers, which are organic fibers in a crystalline state without a glass transition temperature, and polyvinyl alcohol (PVA) fibers, which have a glass transition temperature, are prepared. As resin adhesives, latex solutions with a glass transition temperature of -9°C are prepared. As inorganic particles, silica particles are prepared. As other components, silica-based fibers and glass fibers are prepared as inorganic fibers.

[0277] • Polyester fiber (3 parts): 0.1 dtex × 3 mm

[0278] • PVA fiber (5 parts): VPB 053 (manufactured by Kuraray Co., Ltd.), 0.55 dtex × 3 mm (average fiber length)

[0279] • Latex solution (5 parts acrylic resin): Glass transition temperature is -9℃

[0280] • First inorganic particles and second inorganic particles (70 parts in total): silica particles and titanium dioxide particles

[0281] • First inorganic fiber (7 parts): silica-based fiber

[0282] • Second inorganic fiber (10 parts): Glass fiber, CS 3J-888S (manufactured by Nittobo Co., Ltd.), fiber diameter 10μm × fiber length 6mm

[0283] Then, as in Example 1, a wetted sheet was prepared, heated, dried, and then cooled to produce a sheet with a basis weight of 600 g / m³. 2 The test material of Example 2 with a thickness of 1.5 mm.

[0284] Furthermore, relative to the total mass of the test materials obtained in Example 2, the content of polyester fiber was 3% by mass, the content of PVA fiber was 5% by mass, and the content of resin adhesive (acrylic resin) was 5% by mass.

[0285] (Comparative Example 1)

[0286] To clarify the differences from the embodiments, the manufacturing method of Comparative Example 1 will be described with reference to the accompanying drawings. Figures 4A to 4C This is a schematic diagram showing the manufacturing method of the test material for Comparative Example 1 in the order of the production process.

[0287] like Figure 4A As shown, a latex solution with a glass transition temperature of -9°C was prepared as the resin adhesive, silica particles and titanium dioxide particles were prepared as inorganic particles 11, and silica-based fibers and glass fibers were prepared as inorganic fibers 14 as other components.

[0288] • Polyester fiber (3 parts): 0.1 dtex × 3 mm

[0289] • Latex solution (10 parts acrylic resin): Glass transition temperature is -9℃

[0290] • Inorganic Particles 11 (First Inorganic Particles, Second Inorganic Particles) (Total 70 parts): Silica particles and titanium dioxide particles

[0291] • Inorganic Fiber 14 (First Inorganic Fiber, Second Inorganic Fiber): Silica-based fiber (7 parts), glass fiber (10 parts), CS 3J-888S (manufactured by Nittobo Co., Ltd.), fiber diameter 10μm × fiber length 6mm

[0292] The above materials are dispersed in water using a pulper to prepare a uniform paper pulp (dispersion liquid 15). Then, the pulp is dewatered using a paper machine to obtain wet sheets.

[0293] Then, after drying using a Yankee dryer with a surface temperature of 140°C, it is heated to 250°C using a hot air dryer. Thus, as... Figure 4B As shown, the moisture evaporates as the temperature rises, resulting in a molten resin binder 16.

[0294] Then, by cooling, such as Figure 4C As shown, inorganic particles 11 and inorganic fibers 14 are bonded together by a cured resin adhesive 19.

[0295] Thus, the basis weight is 600 (g / m³). 2 The test material of Comparative Example 1, with a thickness of 1.5 mm.

[0296] The glass transition temperatures of the materials used in each test are shown in Table 1 below.

[0297] Furthermore, the glass transition temperatures of resin adhesives and organic fibers can be calculated using differential scanning calorimetry (DSC), dynamic viscoelasticity measurement (DMA), and thermomechanical analysis (TMA).

[0298] Among the two types of organic fibers used in the above embodiments and comparative examples, polyester (PET) fiber is an organic fiber in a crystalline state that does not have a glass transition temperature, as described above. Therefore, the glass transition temperatures of the organic fibers shown in Table 1 below represent the glass transition temperatures of polyvinyl alcohol (PVA) fibers that have a glass transition temperature.

[0299] [Table 1]

[0300]

[0301] <Evaluation Methods for Test Materials>

[0302] Compression characteristics, heat transfer, and insulation properties were tested on each test material to evaluate their compression characteristics and insulation properties.

[0303] (Compression characteristics test)

[0304] like Figure 5 As shown, a universal testing machine is used, and the test material 23 is placed between the upper plate 21 and the lower plate 22. The upper plate 21 is moved downward, thereby compressing the test material 23. In addition, the dimensions of the test material 23 are set to 25mm × 25mm × 1.5mm, the compression speed is set to 0.5 (mm / min), and the maximum compressive stress is set to 5MPa.

[0305] Then, the initial thickness of the test material 23 is set as D0 (mm), and the compression amount (the reduction in thickness) is set as D. d (mm), the compression ratio C (%) is calculated using the following formula.

[0306] C = D d / D0×100

[0307] In addition, compression characteristic tests were performed on Example 1 and Comparative Example 1.

[0308] (Heat transferability test)

[0309] like Figure 6 As shown, an upper iron plate 24 and a lower iron plate 25 are prepared, and the test material 26 is placed on the lower iron plate 25. Next, the upper iron plate 24, heated to 800°C, is placed on the upper surface 26a of the test material 26, and pressure is applied downwards at 3.5 MPa. At this time, a temperature sensor (not shown) is placed between the lower surface 26b of the test material 26 and the lower iron plate 25 to measure the temperature T of the lower surface. c (°C), and a temperature sensor (not shown) is placed between the upper surface 26a of the test material 26 and the upper plate 24 to measure the upper surface temperature T. h (°C). Furthermore, observe the lower surface temperature T. c (°C) change over time.

[0310] (Insulation performance test)

[0311] Regarding thermal insulation performance, firstly, the thermal conductivity λ (W / m·K) at room temperature was measured using the hot wire method, which is equivalent to the unsteady-state method in the method of thermal conductivity determination, to obtain the thermal conductivity λ (W / m·K) of the test material.

[0312] Then, using the thermal conductivity λ (W / m·K), initial thickness D0 (m), and compressibility C (%) of the test material, the thermal resistance R (m) was calculated using the following formula. 2 ·K / W).

[0313] R = D0 / λ × (100 - C) / 100

[0314] <Evaluation Results of Test Materials>

[0315] (Compression characteristic test results)

[0316] Figure 7 It is a graph showing the relationship between compressive stress and compressive rate in each test material when the horizontal axis is set as compressibility and the vertical axis is set as compressive stress.

[0317] like Figure 7As shown, in Examples 1 and 2, the compression ratio was lower and the compression characteristics were superior compared to Comparative Example 1 under the same applied pressure. In particular, compared to Example 2, the glass transition temperature of the resin adhesive in Example 1 was 20°C or higher, and the difference between the glass transition temperatures of the organic fiber and the resin adhesive was 62°C, both of which are within the preferred range of the present invention. Therefore, excellent compression characteristics can be obtained.

[0318] (Results of heat transfer test)

[0319] Figure 8 It is a graph showing the relationship between the lower surface temperature of each test material and the elapsed time, with the horizontal axis set to elapsed time and the vertical axis set to the lower surface temperature.

[0320] like Figure 8 As shown, Example 1 exhibits a lower peak temperature on the lower surface compared to Comparative Example 1. This demonstrates that Example 1 possesses excellent thermal insulation properties.

[0321] In addition, such as Figure 4C As shown, Comparative Example 1 did not form an organic fiber-based skeleton. Therefore, by heating with the upper plate 24 at 800°C, the strength of the test material deteriorated, and by extrusion, defects 29 were formed, resulting in a decrease in compressive strength.

[0322] (Results of thermal insulation performance test)

[0323] Figure 9 It is a graph showing the relationship between thermal resistivity and compressive stress in each test material when the horizontal axis is set as compressive stress and the vertical axis is set as thermal resistivity.

[0324] like Figure 9 As shown, compared to Comparative Example 1, Examples 1 and 2 exhibit high thermal resistivity under any compressive stress. In particular, compared to Example 2, the glass transition temperature of the resin adhesive and the difference between the glass transition temperatures of the organic fiber and the resin adhesive are both within the preferred range of the present invention. Therefore, even if the compressive stress is increased, the reduction in thermal resistivity is minimal.

[0325] The various embodiments have been described above, but the present invention is not limited to these examples. Those skilled in the art will obviously be able to conceive of various modifications or alterations within the scope of the claims, and it should be understood that these also fall within the technical scope of the present invention. Furthermore, the constituent elements of the above embodiments can be combined arbitrarily without departing from the spirit of the invention.

Claims

1. A heat transfer suppressor sheet used in a battery pack, characterized in that, The heat transfer suppression sheet is located between the battery cells of the battery pack or between the battery cell and the battery casing of the battery pack. The heat transfer inhibition sheet comprises first inorganic particles, resin binder, and organic fibers. The glass transition temperature of the organic fiber is higher than that of the resin adhesive. At least a portion of the organic fibers are fused together to form a three-dimensional skeleton. The resin adhesive is fused to a portion of the skeleton and at least a portion of the first inorganic particles, with at least a portion of the first inorganic particles bonded to the skeleton.

2. The heat transfer suppression sheet according to claim 1, characterized in that, The glass transition temperature of the organic fiber is below 250°C.

3. The heat transfer suppression sheet according to claim 1 or 2, characterized in that, The glass transition temperature of the resin adhesive is above -10°C.

4. The heat transfer suppression sheet according to claim 1 or 2, characterized in that, The difference between the glass transition temperature of the resin adhesive and the glass transition temperature of the organic fiber is greater than 10°C and less than 130°C.

5. The heat transfer suppression sheet according to claim 1 or 2, characterized in that, The organic fiber has a water solubility temperature of 60°C or higher.

6. The heat transfer suppression sheet according to claim 1 or 2, characterized in that, The average fiber length of the organic fiber is 0.5 mm or more and 10 mm or less.

7. The heat transfer suppression sheet according to claim 1 or 2, characterized in that, The content of the organic fiber is 0.5% by mass or more and 12% by mass or less relative to the total mass of the heat transfer inhibiting sheet, and the content of the resin adhesive is 0.5% by mass or more and 20% by mass or less.

8. The heat transfer suppression sheet according to claim 1 or 2, characterized in that, The resin adhesive comprises at least one selected from styrene-butadiene resin, acrylic resin, silicone-acrylic resin and styrene resin.

9. The heat transfer suppression sheet according to claim 1 or 2, characterized in that, The organic fiber comprises at least one selected from polyvinyl alcohol fiber, polyethylene fiber, nylon fiber, polyurethane fiber and ethylene-vinyl alcohol copolymer fiber.

10. The heat transfer suppression sheet according to claim 1 or 2, characterized in that, The first inorganic particle is composed of at least one selected from oxide particles, carbide particles, nitride particles and inorganic hydrate particles.

11. The heat transfer suppression sheet according to claim 1 or 2, characterized in that, The heat transfer inhibition sheet further comprises at least one first inorganic fiber and a second inorganic fiber, selected from the average fiber diameter, shape and glass transition temperature, which are different from each other.

12. The heat transfer suppression sheet according to claim 11, characterized in that, The average fiber diameter of the first inorganic fiber is larger than that of the second inorganic fiber. The first inorganic fiber is linear or needle-like, and the second inorganic fiber is dendritic or crimped.

13. The heat transfer suppression sheet according to claim 11, characterized in that, The first inorganic fiber is an amorphous fiber. The second inorganic fiber is at least one type of fiber selected from crystalline fibers and amorphous fibers with a glass transition temperature higher than that of the first inorganic fiber. The average fiber diameter of the first inorganic fiber is larger than that of the second inorganic fiber.

14. The heat transfer inhibiting sheet according to claim 11, wherein, The first inorganic particle comprises at least one type selected from nanoparticles, hollow particles, and porous particles. The first inorganic fiber is an amorphous fiber. The second inorganic fiber is at least one inorganic fiber selected from crystalline fibers and amorphous fibers with a glass transition temperature higher than that of the first inorganic fiber.

15. The heat transfer suppression sheet according to claim 11, characterized in that, The first inorganic fiber is a fiber containing SiO2, and the second inorganic fiber is a fiber composed of at least one of the following fibers: glass fiber, silica fiber, alumina fiber, carbon fiber, refractory ceramic fiber, aerogel composite material, potassium titanate fiber, and natural mineral fiber.

16. The heat transfer suppression sheet according to claim 15, characterized in that, The second inorganic fiber is glass wool.

17. The heat transfer suppression sheet according to claim 15, characterized in that, The second inorganic fiber is zirconium oxide fiber.

18. The heat transfer suppression sheet according to claim 15, characterized in that, The second inorganic fiber is an alkaline earth silicate fiber.

19. The heat transfer suppression sheet according to claim 18, characterized in that, The second inorganic fiber is aluminum silicate fiber or magnesium silicate fiber.

20. The heat transfer suppression sheet according to claim 1 or 2, characterized in that, The heat transfer inhibition sheet also contains a second inorganic particle composed of metal oxides.

21. A method for manufacturing a heat transfer suppressor sheet according to any one of claims 1 to 20, characterized in that, have: The process of obtaining a dispersion containing the first inorganic particles, the resin binder, and the organic fibers; The process of dehydrating the dispersion to obtain a wetted tablet; and The process of heating and then cooling the humidified sheet. The heating temperature for heating the wetted sheet is set to be at least 10°C higher than the glass transition temperature of the organic fiber and less than 50°C higher.

22. The method for manufacturing the heat transfer suppression sheet according to claim 21, characterized in that, The dispersion is an emulsion in which the resin adhesive is dispersed in water.

23. A battery pack having: Multiple battery cells and the heat transfer suppression sheet according to any one of claims 1 to 20, These multiple battery cells are connected in series or in parallel.

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