Thermal insulation sheet, method for manufacturing a thermal insulation sheet, and battery pack

Abstract

To provide a heat insulation sheet which suppresses peeling of a resin layer, suppresses omission of a heat insulation material component, has low thermal conductivity, and has flame retardancy, a method for manufacturing a heat insulation sheet, and a battery pack having the heat insulation sheet.SOLUTION: A heat insulation sheet 10 has a heat insulation material 2 containing inorganic particles 41, and a resin film 1 coating at least a part of a surface of the heat insulation material 2.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a heat insulation sheet, a method for manufacturing the same, and a battery pack using the heat insulation sheet.

Background Art

[0002] Conventionally, in order to suppress heat transfer from a heating element to other objects, a heat insulation sheet that is placed in proximity to the heating element or at least partially contacts the heating element is used.

[0003] In recent years, from the perspective of environmental protection, the development of electric vehicles or hybrid vehicles driven by an electric motor has been actively promoted. Such electric vehicles or hybrid vehicles are equipped with a battery pack in which a plurality of battery cells are connected in series or parallel to serve as a power source for the driving electric motor.

[0004] In this battery cell, a lithium-ion secondary battery that can have a high capacity and a high output compared to a lead storage battery or a nickel-metal hydride battery is mainly used. However, when thermal runaway occurs in one battery cell due to an internal short circuit or overcharging of the battery (i.e., in the case of "abnormal conditions"), heat may be propagated to adjacent other battery cells, causing thermal runaway of the other battery cells.

[0005] Therefore, various heat insulation materials disposed between battery cells have been studied in a power storage device such as a lithium-ion secondary battery. For example, Patent Document 1 discloses an insulator having an inorganic heat insulation material and a polymer coating layer disposed on the surface of the inorganic heat insulation material as a heat insulation material that can be disposed between battery cells, and it is described that by having the polymer coating layer, component dropout of the inorganic particle material contained in the inorganic heat insulation material can be prevented. Further, Patent Document 2 discloses a heat insulation material having a resin and expanded graphite and having a layer with a thickness of 10 μm to 3 mm on the surface.

Prior Art Documents

Patent Documents

[0006] [Patent Document 1] Special Publication No. 2019-508632 [Patent Document 2] Japanese Patent Publication No. 2020-2979 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, with the insulator described in Patent Document 1, there was a concern that the polymer coating layer would peel off from the inorganic heat insulating material due to warping caused by differences in shrinkage during processing and differences in shrinkage and expansion within the normal operating temperature range. Furthermore, the heat insulating material described in Patent Document 2 contains graphite with a high expansion coefficient in its surface layer, raising concerns that its fire resistance may be insufficient in the event of battery thermal runaway.

[0008] The present invention has been made in view of the above problems, and aims to provide an insulating sheet and a method for manufacturing the same that suppresses peeling of the resin layer, suppresses the detachment of insulating material components, has low thermal conductivity and flame retardancy. The present invention also aims to provide a battery pack having the above insulating sheet. [Means for solving the problem]

[0009] The above objective of the present invention is achieved by the configuration of the heat insulating sheet described in [1] below.

[0010] [1] An insulating material containing inorganic particles, An insulating sheet having a resin coating that covers at least a portion of the surface of the insulating material.

[0011] Furthermore, preferred embodiments of the present invention relating to the heat insulating sheet are described in [2] to

[13] below.

[0012] [2] The heat insulating sheet according to [1], wherein the average thickness of the resin coating is 1 to 95 μm. [3] The heat insulating sheet according to [1] or [2], wherein the thickness of the resin coating is greater than 0 and less than 100 μm. [4] The heat insulating sheet according to any one of [1] to [3], wherein the resin coating is irregularly curved in accordance with the surface shape of the heat insulating material. [5] The heat insulating sheet according to any one of [1] to [4], wherein the resin coating has a plurality of pores. [6] The heat insulating sheet according to [5], wherein the holes are dispersed and arranged across the entire surface of the resin coating. [7] The heat insulating sheet according to [5] or [6], wherein the ratio (A / B) of the total area A of the resin coating portion to the total area B of the pore portion, calculated by digital microscope image observation of the resin coating side, is 7 / 3 to 99 / 1. [8] The thermal insulation sheet according to any one of [1] to [7], characterized in that the inorganic particles are particles made of at least one inorganic material selected from oxide particles, carbide particles, nitride particles and inorganic hydrate particles. [9] The thermal insulation sheet according to any one of [1] to [8], wherein the thermal insulation material further comprises a first inorganic fiber and a second inorganic fiber having at least one property selected from average fiber diameter, shape and glass transition temperature that differs from each other.

[10] The average fiber diameter of the first inorganic fiber is greater than the average fiber diameter of the second inorganic fiber. The heat insulating sheet according to [9], characterized in that the first inorganic fiber is linear or needle-shaped, and the second inorganic fiber is dendritic or curly.

[11] The first inorganic fiber is an amorphous fiber, The second inorganic fiber is at least one fiber selected from amorphous fibers and crystalline fibers, each having a higher glass transition temperature than the first inorganic fiber. The thermal insulation sheet according to [9], characterized in that the average fiber diameter of the first inorganic fiber is greater than the average fiber diameter of the second inorganic fiber.

[12] The inorganic particles include at least one selected from nanoparticles, hollow particles and porous particles, The first inorganic fiber is an amorphous fiber, The heat insulation sheet according to [9], wherein the second inorganic fiber is at least one inorganic fiber selected from amorphous fibers and crystalline fibers having a glass transition point higher than that of the first inorganic fiber.

[13] The heat insulation sheet according to any one of [1] to

[12] , which is used for a battery pack in which a plurality of battery cells are connected in series or in parallel.

[0013] Further, the above object of the present invention is achieved by the following configuration

[14] related to a method for manufacturing a heat insulation sheet.

[0014]

[14] A method for manufacturing a heat insulation sheet according to any one of [1] to

[13] , comprising: a step of forming a material for a heat insulating material containing the inorganic particles into a sheet shape; a step of applying a composition for forming a resin film on the surface of the sheet-shaped heat insulating material by a screen printing method or a spray coating method to form the resin film.

[0015] Further, the above object of the present invention is achieved by the following configuration

[15] related to a battery pack.

[0016]

[15] A battery pack having a plurality of battery cells and the heat insulation sheet according to

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

Advantages of the Invention

[0017] According to the present invention, it is possible to provide a heat insulation sheet and a method for manufacturing the same that suppress peeling of the resin layer, suppress dropout of the heat insulating material component, have a low thermal conductivity, and have flame retardancy. Further, according to the present invention, it is possible to provide a battery pack including a heat insulation sheet that suppresses peeling of the resin layer, suppresses dropout of the heat insulating material component, has a low thermal conductivity, and has flame retardancy.

Brief Description of the Drawings

[0018] [Figure 1] FIG. 1 is a plan view schematically showing a heat insulation sheet according to an embodiment of the present invention. [Figure 2] Figure 2 is a schematic cross-sectional view showing a thermal insulation sheet according to an embodiment of the present invention. [Figure 3] Figure 3 is a cross-sectional SEM (scanning electron microscope) image of a heat insulating sheet according to an embodiment of the present invention. [Figure 4] Figure 4 is a schematic diagram illustrating a method for measuring the average thickness of the resin coating in a heat insulating sheet according to an embodiment of the present invention. [Figure 5] Figure 5 is a schematic cross-sectional view of an insulating sheet using an insulating material containing two types of inorganic particles. [Figure 6] Figure 6 is a schematic cross-sectional view showing an example of a battery pack to which an insulating sheet according to an embodiment of the present invention is applied. [Figure 7] Figure 7 is a photograph used as a substitute for a drawing, showing the surface of the heat-insulating sheet of Example 1, taken with a digital microscope. [Figure 8] Figure 8 is a schematic diagram illustrating the measurement method in an embodiment of the present invention. [Figure 9] Figure 9 is a schematic diagram illustrating the measurement method in an embodiment of the present invention. [Modes for carrying out the invention]

[0019] The inventors of the present invention have diligently conducted research to provide an insulating sheet that suppresses the peeling of the resin layer, inhibits the detachment of insulating material components, has low thermal conductivity, and is flame-retardant.

[0020] As a result, the inventors found that the above problem can be solved by providing a resin-containing film on at least a portion of the surface of the thermal insulation material containing inorganic particles. The heat insulating sheet according to the embodiment of the present invention has a resin coating on the surface of the heat insulating material, which can suppress the shedding of inorganic particles contained in the heat insulating material. Furthermore, if this resin coating is thin and highly flexible, it can suppress peeling from the heat insulating material due to differences in shrinkage during heating, etc. Furthermore, if the resin coating is thin, the change in the resin content of the entire insulation sheet due to the application of the resin coating is small, which helps to suppress a decrease in the flame retardancy and an increase in the thermal conductivity of the insulation sheet.

[0021] Embodiments of the present invention will be described in detail below with reference to the drawings. However, the present invention is not limited to the embodiments described below, and can be modified and implemented as desired without departing from the spirit of the invention.

[0022] [1. Insulation sheet] An embodiment of the present invention comprises a thermal insulation material containing inorganic particles and a resin coating that covers at least a portion of the surface of the thermal insulation material.

[0023] [1-1. Resin coating] In this embodiment, the heat insulating sheet has at least a portion of the surface of the heat insulating material covered with a resin coating. Figure 1 is a schematic plan view showing an insulating sheet according to an embodiment of the present invention. Figure 2 is a schematic cross-sectional view showing an insulating sheet according to an embodiment of the present invention. In the thermal insulation sheets shown in Figures 1 and 2, the thermal insulation sheet 10 according to this embodiment has a portion of the surface of the thermal insulation material 2 containing inorganic particles 41 covered with a resin film 1. The thermal insulation material 2 may also contain inorganic fibers 42. The surface of the insulation material 2 preferably has uncoated portions that are not covered by the resin coating 1, and the resin coating 1 may have a plurality of pores 31. The portions with pores 31 can be made into uncoated portions. By having a plurality of pores 31 in the resin coating 1, the flexibility of the resin coating is further improved, and peeling from the surface of the insulation material can be further suppressed. In addition, the increase in thermal conductivity and decrease in flame retardancy of the insulation sheet can be further suppressed.

[0024] Figure 3 is a scanning electron microscope (SEM) image of a cross-section of a thermal insulation sheet according to an embodiment of the present invention. Figure 4 is a schematic diagram illustrating a method for measuring the average thickness of the resin coating in a thermal insulation sheet according to an embodiment of the present invention.

[0025] The resin film 1 preferably has a non-uniform thickness, as shown in Figures 2 to 4. The non-uniform thickness of the resin film 1 allows for a balance between the film strength provided by the thicker (larger film thickness) portions and the flexibility provided by the thinner (smaller film thickness) portions. Furthermore, as shown in Figures 2 to 4, it is preferable that the resin film 1 is irregularly curved to conform to the surface shape of the heat insulating material 2. By irregularly curving the resin film, the heat conduction area with the heat-generating element can be reduced, thereby suppressing an increase in the thermal conductivity of the heat insulating sheet.

[0026] The thickness of the resin coating is preferably greater than 0 and less than 100 μm. The thickness of the resin film is more preferably 1 μm or more, even more preferably 4 μm or more, and even more preferably 8 μm or more. Furthermore, the thickness of the resin film is more preferably 50 μm or less, even more preferably 25 μm or less, and even more preferably 15 μm or less. By making the resin coating thickness greater than 0, good coating strength is achieved. Furthermore, by making the resin coating thickness less than 100 μm, it is easier to obtain effects such as suppression of peeling of the resin coating from the insulation material, suppression of increase in thermal conductivity, and suppression of decrease in flame retardancy.

[0027] The average thickness of the resin coating is preferably 1 to 95 μm. The average thickness of the resin film is preferably 1 μm or more, more preferably 4 μm or more, and even more preferably 8 μm or more. Furthermore, the average thickness of the resin film is more preferably 50 μm or less, even more preferably 25 μm or less, and even more preferably 15 μm or less. By setting the average thickness of the resin coating to 1 μm or more, good coating strength is achieved. Furthermore, by setting the average thickness of the resin coating to 95 μm or less, it is easier to obtain effects such as suppression of peeling of the resin coating from the insulation material, suppression of increase in thermal conductivity, and suppression of decrease in flame retardancy.

[0028] The thickness of the resin coating can be determined by analyzing SEM images of the cross-section of the heat-insulating sheet. The average thickness of the resin coating is the average value of the thickness of the resin coating measured at multiple locations at regular intervals. For example, as shown in Figures 3 and 4, the average thickness can be calculated by analyzing SEM images of the cross-section of the heat insulating sheet to measure the thickness of the resin coating at seven locations W1 to W7 (indicated by arrows in the figures). In Figure 4, there are seven measurement locations, but there is no particular limit to the number; seven or more locations are acceptable, and seven to ten locations are preferable. The thickness and average thickness of the resin film can be measured specifically by the method described in the examples.

[0029] As described above, the resin coating only needs to cover at least a portion of the surface of the insulation material, but it is preferable that there is a portion of the surface of the insulation material that is not covered, and it is even more preferable that the resin coating has multiple pores. Having multiple pores in the resin coating improves the flexibility of the resin coating and further suppresses peeling of the resin coating from the surface of the insulation material. In addition, it is possible to further suppress an increase in thermal conductivity and a decrease in flame retardancy. From the viewpoint of improving the above-mentioned effects, it is preferable that the pores are dispersed and arranged across the entire surface of the resin coating.

[0030] The ratio (A / B) of the total area A of the resin coating portion to the total area B of the pore portion, calculated by observing digital microscope images of the resin coating side, is preferably between 7 / 3 and 99 / 1. A / B is more preferably 8 / 2 or more, even more preferably 85 / 15 or more, and even more preferably 9 / 1 or more. Furthermore, A / B is preferably 99 / 1 or less, and more preferably 97 / 3 or less. By setting the A / B ratio to 7 / 3 or higher, it is easier to obtain effects such as suppressing the shedding of inorganic particles contained in the insulation material, suppressing the increase in thermal conductivity, and suppressing the decrease in flame retardancy. Furthermore, by setting the A / B ratio to 99 / 1 or less, it becomes easier to achieve a peeling suppression effect on the resin coating.

[0031] The A / B ratio was calculated by observing the surface of the heat-insulating sheet with the resin coating at 20x magnification using a digital microscope (KEYENCE VHX-5000). The total area of ​​the pores (B) was defined as the range of brightness settings from 96 to 255, and the total area of ​​the resin coating (A) was defined as the range of brightness settings from 0 to 96.

[0032] The type of resin used to form the resin film is not limited as long as the effects of the present invention are obtained, but it is preferably a flame-retardant resin. Examples include epoxy resin, melamine resin, silicone resin, urethane resin, polyvinyl alcohol (PVA), acrylic resin, polyester resin, etc. Resins with self-extinguishing properties or resins with a high oxygen index are more preferable.

[0033] The resin coating may contain components other than resin, such as organic fibers, inorganic fibers, organic fillers, inorganic fillers, organic pigments, and the like.

[0034] [1-2. Insulation Material] The thermal insulation material used in the thermal insulation sheet according to this embodiment is not particularly limited, as long as it contains inorganic particles and has a thermal insulation effect. Thermal conductivity can be cited as an indicator of thermal insulation effect, but in this embodiment, the thermal conductivity of the thermal insulation material is preferably less than 1 (W / m·K), more preferably less than 0.5 (W / m·K), and more preferably less than 0.2 (W / m·K). Furthermore, the thermal conductivity of the thermal insulation material is more preferably less than 0.1 (W / m·K), more preferably less than 0.05 (W / m·K), and particularly preferably less than 0.02 (W / m·K).

[0035] The thermal conductivity of the insulation material can be measured in accordance with the "Test Method for Thermal Conductivity of Refractory Materials" described in JIS R 2251.

[0036] As inorganic particles, inorganic particles of a single material may be used, or inorganic particles of two or more materials may be used in combination. When two or more inorganic particles with different heat transfer suppression effects are used in combination, the heat-generating element can be cooled in multiple stages, and the heat-endurance effect can be expressed over a wider temperature range, thereby improving the thermal insulation performance. When two or more inorganic particles are included, the preferred material, shape, and particle size of each inorganic particle will be described below.

[0037] Figure 5 is a schematic cross-sectional view of an insulating sheet using an insulating material containing two types of inorganic particles. However, the insulating material shown in Figure 5 also contains two types of inorganic fibers, which will be described later.

[0038] From the viewpoint of 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 as the first inorganic particles 51 and the second inorganic particles 54, and it is more preferable to use oxide particles. In addition, silica nanoparticles, metal oxide particles, inorganic balloons such as microporous particles and hollow silica particles, particles made of thermally expandable inorganic materials, particles made of water-containing porous materials, etc., can also be used. Hereinafter, inorganic particles will be described in more detail, with small-diameter inorganic particles referred to as the first inorganic particles 51 and large-diameter inorganic particles referred to as the second inorganic particles 54.

[0039] <1-2-1. The 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 inorganic particles can suppress radiative heat transfer, especially in high-temperature regions such as abnormal heat generation. As oxide particles, at least one particle selected from silica, titania, zirconia, zircon, barium titanate, zinc oxide, and alumina can be used. That is, only one of the above oxide particles that can be used as inorganic particles may be used, or two or more oxide particles may be used. In particular, silica is a component with high thermal insulation properties, and titania is a component with a high refractive index compared to other metal oxides. Since they have a high effect of diffusely reflecting light and blocking radiant heat in high-temperature regions of 500°C or higher, it is most preferable to use silica and titania as oxide particles.

[0040] (Average primary particle size of oxide particles: 0.001 μm or more and 50 μm or less) Since the particle size of oxide particles can affect the effect of reflecting radiant heat, limiting the average primary particle size to a predetermined range can result in even higher thermal insulation. In other words, if the average primary particle diameter of the oxide particles is 0.001 μm or larger, it is sufficiently larger than the wavelength of light that contributes to heating, and efficiently diffusely reflects light. As a result, radiative heat transfer within the insulating material is suppressed in the high-temperature region of 500°C or higher, further improving the insulating properties. On the other hand, if the average primary particle diameter of oxide particles is 50 μm or less, the number of contact points between particles does not increase even when compressed, making it difficult to form conductive heat transfer paths. This reduces the impact on thermal insulation, especially in the normal temperature range where conductive heat transfer is dominant. In this invention, the average primary particle diameter can be determined by observing the particles under a microscope, comparing them to a standard scale, and taking the average of 10 arbitrary particles.

[0041] (Nanoparticles) In this invention, nanoparticles refer to particles that are spherical or nearly spherical, with an average primary particle diameter of less than 1 μm and on the order of nanometers. Because nanoparticles have a low density, they suppress conductive heat transfer, and when nanoparticles are used as inorganic particles, the voids are further finely dispersed, resulting in excellent heat insulation that suppresses convective heat transfer. For this reason, it is preferable to use nanoparticles when using batteries in the normal room temperature range, as it can suppress heat conduction between adjacent nanoparticles. Furthermore, when fine particles such as silica nanoparticles are used in the thermal insulation material, the thermal insulation sheet of the present invention is more likely to suppress the shedding of thermal insulation components.

[0042] Furthermore, by using nanoparticles with a small average primary particle diameter as oxide particles, even if the insulating sheet is compressed due to expansion caused by thermal runaway of the battery cell, and the internal density increases, the increase in conductive heat transfer of the insulating sheet can be suppressed. This is thought to be because nanoparticles easily create fine voids between particles due to electrostatic repulsion, and because their bulk density is low, the particles are packed in a way that provides cushioning.

[0043] Furthermore, in this invention, when using nanoparticles as inorganic particles, the material is not particularly limited as long as it conforms to the above definition of nanoparticles. For example, silica nanoparticles are a material with high thermal insulation properties, and because the contact points between particles are small, the amount of heat conducted by silica nanoparticles is smaller compared to when silica particles with a larger particle size are used. Also, commonly available silica nanoparticles have a bulk density of 0.1 g / cm³. 3 Because of this, even if, for example, battery cells placed on both sides of the heat insulating sheet undergo thermal expansion and a large compressive stress is applied to the heat insulating sheet, the size (area) and number of contact points between silica nanoparticles will not increase significantly, and the heat insulating properties can be maintained. Therefore, it is preferable to use silica nanoparticles. As silica nanoparticles, wet silica, dry silica, aerogel, etc., can be used.

[0044] (Average primary particle size of nanoparticles: 1 nm to 100 nm) By limiting the average primary particle size of nanoparticles to a predetermined range, even higher thermal insulation can be achieved. In other words, by setting the average primary particle diameter of the nanoparticles to 1 nm or more and 100 nm or less, convective and conductive heat transfer within the insulating material can be suppressed, especially in the temperature range below 500°C, thereby further improving the insulating properties. Furthermore, even when compressive stress is applied, the voids remaining between the nanoparticles and the numerous contact points between particles suppress conductive heat transfer, maintaining the insulating properties of the insulating sheet. Furthermore, the average primary particle diameter of the nanoparticles is more preferably 2 nm or larger, and even more preferably 3 nm or larger. On the other hand, the average primary particle diameter of the nanoparticles is more preferably 50 nm or smaller, and even more preferably 10 nm or smaller.

[0045] (Inorganic hydrate particles) Inorganic hydrate particles, when exposed to heat from a heat source and exceeding their decomposition start temperature, undergo thermal decomposition, releasing their crystalline water and lowering the temperature of the heat source and its surroundings—a phenomenon known as "endothermic action." After releasing the crystalline water, they become porous, exhibiting insulating properties through their numerous air pores. 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).

[0046] For example, aluminum hydroxide contains approximately 35% crystal water, and as shown in the formula below, it undergoes thermal decomposition to release crystal water, exhibiting an endothermic effect. After releasing the crystal water, it becomes a porous alumina (Al2O3) and functions as an insulating material. 2Al(OH)3 → Al2O3 + 3H2O

[0047] As will be described later, the heat insulating sheet 10 according to this embodiment is preferably interposed between battery cells, for example. However, in a battery cell that has experienced thermal runaway, the temperature rapidly rises to over 200°C and continues to rise to around 700°C. Therefore, it is preferable that the inorganic particles consist of inorganic hydrates whose thermal decomposition initiation temperature is 200°C or higher. The thermal decomposition initiation temperatures for the inorganic hydrates listed above are approximately 200°C for aluminum hydroxide, 330°C for magnesium hydroxide, 580°C for calcium hydroxide, 200°C for zinc hydroxide, 350°C for iron hydroxide, 300°C for manganese hydroxide, 300°C for zirconium hydroxide, and 300°C for gallium hydroxide. These temperatures largely overlap with the temperature range of rapid temperature increases in battery cells experiencing thermal runaway, and can effectively suppress temperature rise, making them desirable inorganic hydrates.

[0048] (Average secondary particle diameter of inorganic hydrate particles: 0.01 μm or more and 200 μm or less) Furthermore, if inorganic hydrate particles are used as the first inorganic particles 51, and their average particle size is too large, it may take a certain amount of time for the first inorganic particles 51 (inorganic hydrate) near the center of the heat insulating sheet 10 to reach their thermal decomposition temperature, resulting in the first inorganic particles 51 near the center of the sheet not being completely decomposed. For this reason, the average secondary particle size 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.

[0049] (Particles made of thermally expandable inorganic material) Examples of thermally expandable inorganic materials include vermiculite, bentonite, mica, and perlite.

[0050] (Particles made of a water-containing porous material) Specific examples of water-containing porous materials include zeolite, kaolinite, montmorillonite, acid clay, diatomaceous earth, wet silica, dry silica, aerogel, mica, and vermiculite.

[0051] (Inorganic balloon) The thermal insulation material used in the present invention may contain inorganic balloons as inorganic particles. The inclusion of inorganic balloons can suppress convective or conductive heat transfer within the insulation material at temperatures below 500°C, thereby further improving the insulation performance of the insulation material. As the inorganic balloon, at least one selected from shirasu balloons, silica balloons, fly ash balloons, barlite balloons, and glass balloons can be used.

[0052] (Inorganic balloon content: 60% or less by mass relative to the total mass of the insulation material) The inorganic balloon content is preferably 60% by mass or less relative to the total mass of the insulating material.

[0053] (Average particle size of inorganic balloons: 1 μm to 100 μm) The average particle size of the inorganic balloons is preferably between 1 μm and 100 μm.

[0054] <1-2-2. The second inorganic particle> When the thermal insulation material contains two types of inorganic particles, the second inorganic particle 54 is not particularly limited as long as it differs from the first inorganic particle 51 in terms of material, particle size, etc. The second inorganic particle 54 can be 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 thermally expandable inorganic materials, particles made of water-containing porous materials, etc. Details of these are as described above.

[0055] Furthermore, nanoparticles exhibit extremely low conductive heat transfer and can maintain excellent thermal insulation even when compressive stress is applied to the thermal insulation sheet. In addition, metal oxide particles such as titania have a high effect in blocking radiant heat. Moreover, by using both large-diameter and small-diameter inorganic particles, the small-diameter inorganic particles can fill 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 51, it is preferable to further include particles made of metal oxides, which are larger in diameter than the first inorganic particles 51, as the second inorganic particles 54 in the thermal insulation material. Examples of metal oxides include silicon dioxide, titanium dioxide, aluminum oxide, barium titanate, zinc oxide, zirconium oxide, and zirconium oxide. In particular, titania has a higher refractive index compared to other metal oxides, and is highly effective in scattering light and blocking radiant heat in the high-temperature range of 500°C or higher, so titania is the most preferred choice.

[0056] (Average primary particle diameter of the second inorganic particle) When a second inorganic particle 54 made of a metal oxide is included in the thermal insulation material, if the average primary particle diameter of the second inorganic particle 54 is 1 μm or more and 50 μm or less, radiant heat transfer can be efficiently suppressed in the high-temperature region of 500°C or higher. It is more preferable that the average primary particle diameter of the second inorganic particle 54 be 5 μm or more and 30 μm or less, and most preferably 10 μm or less.

[0057] (Content of the first inorganic particles and the second inorganic particles) When the first inorganic particles 51 are silica nanoparticles and the second inorganic particles 54 are metal oxides, if the content of the first inorganic particles 51 is 60% by mass or more and 95% by mass or less relative to the total mass of the first inorganic particles 51 and the second inorganic particles 54, the amount of metal oxide particles necessary for suppressing radiative heat transfer and the amount of silica nanoparticles necessary for suppressing conductive and convective heat transfer and for cushioning can be optimized. As a result, it is believed that a well-balanced and high level of thermal insulation can be obtained even when external compressive force is applied, across a wide temperature range from the temperature during normal battery use to high temperatures of 500°C or higher.

[0058] <1-2-3. First inorganic fiber and second inorganic fiber> The thermal insulation material may also preferably have a first inorganic fiber 52 and a second inorganic fiber 53, each having at least one property selected from average fiber diameter, shape, and glass transition temperature that differs from each other. By including two inorganic fibers with different properties, the mechanical strength and inorganic particle retention of the thermal insulation sheet can be improved.

[0059] (Two types of inorganic fibers with different average fiber diameters and fiber shapes) When the thermal insulation material contains two types of inorganic fibers, it is preferable that the average fiber diameter of the first inorganic fiber 52 is larger than the average fiber diameter of the second inorganic fiber 53, that the first inorganic fiber 52 is linear or needle-shaped, and that the second inorganic fiber 53 is dendritic or curly-shaped. The first inorganic fiber 52, which has a larger average fiber diameter (larger diameter), has the effect of improving the mechanical strength and shape retention of the thermal insulation sheet. The above effect can be obtained by making one of the two types of inorganic fibers, for example, the first inorganic fiber 52, larger in diameter than the second inorganic fiber 53. Since thermal insulation sheets may be subjected to external impacts, the inclusion of the first inorganic fiber 52 in the thermal insulation material increases its impact resistance. Examples of external impacts include the compressive force due to the expansion of battery cells and the wind pressure due to the ignition of battery cells. Furthermore, in order to improve the mechanical strength and shape retention of the heat insulating sheet, it is particularly preferable that the first inorganic fibers 52 are linear or needle-shaped. Linear or needle-shaped fibers refer to fibers whose crimp degree, as described later, is, for example, less than 10%, preferably 5% or less.

[0060] 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 52 is preferably 1 μm or more, and more preferably 3 μm or more. If the first inorganic fiber 52 is too thick, the moldability and processability of the heat insulating material may decrease, so the average fiber diameter of the first inorganic fiber 52 is preferably 20 μm or less, and more preferably 15 μm or less. Furthermore, since excessive length of the first inorganic fiber 52 may reduce moldability and processability, it is preferable to keep the fiber length 100 mm or less. Additionally, since excessively short length of the first inorganic fiber 52 may reduce shape retention and mechanical strength, it is preferable to keep the fiber length 0.1 mm or more.

[0061] On the other hand, the second inorganic fiber 53, which has a smaller average fiber diameter (small diameter), improves the retention of other inorganic fibers and inorganic particles, and also enhances the flexibility of the thermal insulation material. Therefore, it is preferable to make the second inorganic fiber 53 smaller in diameter than the first inorganic fiber 52.

[0062] More specifically, in order to improve the retention of other inorganic fibers and inorganic particles, it is preferable that the second inorganic fiber 53 is easily deformable and flexible. Therefore, the second inorganic fiber 53, which is small in diameter, preferably has an average fiber diameter of less than 1 μm, and more preferably 0.1 μm or less. However, if the small-diameter inorganic fiber is too thin, it is prone to breakage, and the retention ability of other inorganic fibers and inorganic particles decreases. In addition, a large proportion of the fibers remain entangled in the insulation material without retaining other inorganic fibers and inorganic particles, resulting in a decrease in the retention ability of other inorganic fibers and inorganic particles, as well as inferior moldability and shape retention. Therefore, the average fiber diameter of the second inorganic fiber 53 is preferably 1 nm or more, and more preferably 10 nm or more. Furthermore, since the moldability and shape retention of the second inorganic fiber 53 decrease if it becomes too long, it is preferable that the fiber length of the second inorganic fiber 53 be 0.1 mm or less.

[0063] Furthermore, the second inorganic fiber 53 is preferably dendritic or crimped. When the second inorganic fiber 53 has such a shape, it intertwines with other inorganic fibers and inorganic particles in the thermal insulation material. As a result, the ability to hold other inorganic fibers and inorganic particles is improved. In addition, when the thermal insulation sheet is subjected to compressive force or wind pressure, the sliding movement of the second inorganic fiber 53 is suppressed, thereby improving the mechanical strength, especially against external compressive force and impact.

[0064] Furthermore, a dendritic structure is a structure that branches out in two or three dimensions, such as a feathery, tetrapod-shaped, radial, or three-dimensional network-like structure. When the second inorganic fiber 53 is dendritic, its average fiber diameter can be obtained by measuring the diameters of the trunk and branches at several points using SEM and calculating the average value of these measurements.

[0065] Furthermore, a crimped structure is one in which fibers are bent in various directions. One method for quantifying the crimp morphology is to calculate the degree of crimp from electron microscope images, which can be calculated, for example, using the following formula. Crimping (%) = (Fiber length - Distance between fiber ends) / (Fiber length) × 100 Here, both the fiber length and the distance between fiber ends are measured values ​​obtained from electron microscope images. That is, these are the fiber length and distance between fiber ends projected onto a two-dimensional plane, and are shorter than the actual values. Based on this formula, the crimp of the second inorganic fiber 53 is preferably 10% or more, and more preferably 30% or more. If the crimp is small, the ability to hold other inorganic fibers or inorganic particles, and the formation of entanglement (network) between the second inorganic fibers 53 and between the first inorganic fiber 52 and the second inorganic fiber 53 becomes difficult.

[0066] In the above-described embodiment, a first inorganic fiber 52 and a second inorganic fiber 53 having different average fiber diameters and fiber shapes are used as a method to improve the mechanical strength, shape retention, and retention of inorganic particles and inorganic fibers of the heat transfer suppression sheet. However, the mechanical strength, shape retention, and particle retention of the heat transfer suppression sheet can also be improved by using the first inorganic fiber 52 and the second inorganic fiber 53 having different glass transition temperatures and average fiber diameters.

[0067] As described above, in this embodiment, it is preferable to use various combinations of inorganic fibers in order to improve the mechanical strength, shape retention, and particle retention of the heat transfer suppression sheet. Below, a first and second combination of inorganic fibers different from the embodiment shown in Figure 5 will be described, but for convenience, other embodiments relating to inorganic fibers will be described using Figure 5 in this specification.

[0068] (Two types of inorganic fibers with different glass transition temperatures) When the thermal insulation material contains two types of inorganic fibers, it is preferable that the first inorganic fiber 52 is an amorphous fiber, and the second inorganic fiber 53 is at least one fiber selected from amorphous fibers and crystalline fibers that have a higher glass transition temperature than the first inorganic fiber 52. Furthermore, the thermal insulation performance can be further improved by using first inorganic particles 51 that include at least one selected from nanoparticles, hollow particles, and porous particles, together with the two types of inorganic fibers.

[0069] The melting point of crystalline inorganic fibers is usually higher than the glass transition point of amorphous inorganic fibers. Therefore, when the first inorganic fiber 52 is exposed to high temperatures, its surface softens before the second inorganic fiber 53, and it binds to other inorganic fibers and inorganic particles. Consequently, by incorporating the first inorganic fiber 52 as described above into the insulation material, the mechanical strength of the insulation layer can be improved. Specifically, the first inorganic fiber 52 is preferably an inorganic fiber with a melting point of less than 700°C, and many amorphous inorganic fibers can be used. Among these, it is preferable that the fiber contains SiO2, and more preferably that it is glass fiber because it is inexpensive, readily available, and has excellent handling properties.

[0070] As described above, the second inorganic fiber 53 is a fiber consisting of at least one selected from amorphous fibers and crystalline fibers, having a higher glass transition temperature than the first inorganic fiber 52. Many crystalline inorganic fibers can be used as the second inorganic fiber 53. If the second inorganic fiber 53 is made of crystalline fibers or has a higher glass transition temperature than the first inorganic fiber 52, then even if the first inorganic fiber 52 softens when exposed to high temperatures, the second inorganic fiber 53 will not melt or soften. Therefore, it can maintain its shape and remain present between battery cells even during thermal runaway of the battery cell. Furthermore, if the second inorganic fiber 53 does not melt or soften, the minute spaces between each particle, between particles and fibers, and between each fiber in the insulating material are maintained, so that the insulating effect of air is exerted and excellent heat transfer suppression performance can be maintained.

[0071] When the second inorganic fiber 53 is crystalline, the second inorganic fiber 53 can be ceramic fibers such as alumina fibers, alumina silicate fibers, and zirconia fibers, silica fibers, glass fibers, glass wool, rock wool, carbon fibers, basalt fibers, soluble fibers, refractory ceramic fibers, aerogel composites, magnesium silicate fibers, alkali earth silicate fibers, zirconia fibers, potassium titanate fibers, wollastonite, and other mineral fibers. Among the fibers listed as the second inorganic fiber 53, if the melting point exceeds 1000°C, the second inorganic fiber 53 will not melt or soften even if thermal runaway occurs in the battery cell, and will be able to maintain its shape, making it suitable for use. Furthermore, among the fibers listed as the second inorganic fiber 53 above, it is more preferable to use ceramic fibers such as silica fibers, alumina fibers, and aluminasilicate fibers, as well as mineral fibers, and among these, it is even more preferable to use those with a melting point exceeding 1000°C.

[0072] Furthermore, even if the second inorganic fiber 53 is amorphous, it can be used as long as it has a higher glass transition temperature than the first inorganic fiber 52. For example, a glass fiber with a higher glass transition temperature than the first inorganic fiber 52 may be used as the second inorganic fiber 53. Furthermore, the second inorganic fiber 53 may be any of the various inorganic fibers exemplified, either individually or in a mixture of two or more.

[0073] As described above, the first inorganic fiber 52 has a lower glass transition temperature than the second inorganic fiber 53, and when exposed to high temperatures, the first inorganic fiber 52 softens first, allowing it to bind other inorganic fibers or inorganic particles. However, if, for example, the second inorganic fiber 53 is amorphous and its fiber diameter is smaller than that of the first inorganic fiber 52, and the glass transition temperatures of the first inorganic fiber 52 and the second inorganic fiber 53 are close together, the second inorganic fiber 53 may soften first. Therefore, when the second inorganic fiber 53 is an amorphous fiber, the glass transition temperature of the second inorganic fiber 53 is preferably 100°C or more higher than the glass transition temperature of the first inorganic fiber 52, and more preferably 300°C or more higher.

[0074] Furthermore, the fiber length of the first inorganic fiber 52 is preferably 100 mm or less, and preferably 0.1 mm or more. The fiber length of the second inorganic fiber 53 is preferably 0.1 mm or less. The reasons for these preferences are as described above.

[0075] (Two types of inorganic fibers with different glass transition temperatures and average fiber diameters) When the thermal insulation material contains two types of inorganic fibers, the first inorganic fiber 52 is an amorphous fiber, and the second inorganic fiber 53 is at least one fiber selected from amorphous fibers and crystalline fibers, having a higher glass transition temperature than the first inorganic fiber 52, and it is preferable that the average fiber diameter of the first inorganic fiber 52 is greater than the average fiber diameter of the second inorganic fiber 53.

[0076] As described above, when the thermal insulation material according to this embodiment contains two types of inorganic fibers, it is preferable that the average fiber diameter of the first inorganic fiber 52 is larger than that of the second inorganic fiber 53. Furthermore, it is preferable that the large-diameter first inorganic fiber 52 is amorphous, and the small-diameter second inorganic fiber 53 is composed of at least one type of fiber selected from amorphous fibers and crystalline fibers, each having a higher glass transition point than the first inorganic fiber 52. As a result, the glass transition point of the first inorganic fiber 52 is low, and it softens quickly, becoming film-like and hardening as the temperature rises. On the other hand, if the small-diameter second inorganic fiber 53 is composed of at least one type of fiber selected from amorphous fibers and crystalline fibers, each having a higher glass transition point than the first inorganic fiber 52, the small-diameter second inorganic fiber 53 remains in its fibrous shape even as the temperature rises, thus maintaining the structure of the thermal insulation sheet and preventing powder shedding.

[0077] Even in this case, the fiber length of the first inorganic fiber 52 is preferably 100 mm or less, and preferably 0.1 mm or more. The fiber length of the second inorganic fiber 53 is preferably 0.1 mm or less. The reasons for these are as described above.

[0078] Furthermore, the insulation material may contain different inorganic fibers in addition to the first inorganic fiber 52 and the second inorganic fiber 53 described above.

[0079] (Content of the first inorganic fiber and the second inorganic fiber) When the thermal insulation material contains two types of inorganic fibers, the content of the first inorganic fiber 52 is preferably 3% by mass or more and 30% by mass or less relative to the total mass of the thermal insulation material, and the content of the second inorganic fiber 53 is preferably 3% by mass or more and 30% by mass or less relative to the total mass of the thermal insulation material.

[0080] Furthermore, the content of the first inorganic fiber 52 is more preferably 5% by mass or more and 15% by mass or less relative to the total mass of the insulation material, and the content of the second inorganic fiber 53 is more preferably 5% by mass or more and 15% by mass or less relative to the total mass of the insulation material. By using such content, the shape retention, compressive force resistance, and wind pressure resistance of the first inorganic fiber 52, and the inorganic particle holding ability of the second inorganic fiber 53 are expressed in a well-balanced manner.

[0081] <1-2-4. Other Materials> In addition to the first inorganic particles 51 and the second inorganic particles 54, the first inorganic fibers 52 and the second inorganic fibers 53 described above, the thermal insulation material used in the present invention may also contain organic fibers that have the effect of improving the strength of the thermal insulation material, as well as binders, colorants, and other components necessary for forming the thermal insulation material. The other components will be described in detail below.

[0082] (Binding material) In the present invention, the thermal insulation material can be formed by sintering or the like even if it does not contain a binder. However, especially when the thermal insulation material contains silica nanoparticles, it is preferable to add a binder in an appropriate amount to maintain its shape as a thermal insulation material. In the present invention, the binder can be anything that holds inorganic particles together to maintain them, and its form is not limited to a binder that provides adhesion, fibers that physically entangle the particles, or a heat-resistant resin that adheres by adhesive force. The first inorganic fiber 52 and the second inorganic fiber 53 also function as binders.

[0083] Organic binders, inorganic binders, etc., can be used as binders. The present invention does not particularly limit these types, but as organic binders, polymer flocculants and acrylic emulsions can be used, and as inorganic binders, for example, silica sol, alumina sol, aluminum sulfate, etc., can be used. These function as adhesives when the solvent such as water is removed.

[0084] While not particularly limited, organic fibers can be used, including synthetic fibers, natural fibers, and pulp. Specifically, examples include polyvinyl alcohol (PVA) fibers, polyethylene fibers, nylon fibers, polyurethane fibers, ethylene-vinyl alcohol copolymer fibers, polyethylene terephthalate fibers, polybutylene terephthalate fibers, polytrimethylene terephthalate fibers, polyacetal fibers, polytetrafluoroethylene fibers, polyetheretherketone fibers, polyphenylene sulfide fibers, polyamide fibers, and poly-p-phenylphthalamide fibers.

[0085] In the thermal insulation material used in the present invention, the binder content is preferably 60% by mass or less, and more preferably 50% by mass or less, based on the total mass of the thermal insulation material. In the thermal insulation material used in the present invention, the binder content is preferably 10% by mass or more, and more preferably 20% by mass or more, based on the total mass of the thermal insulation material.

[0086] The thickness of the thermal insulation material used in this invention is not particularly limited, but it is preferably in the range of 0.1 mm to 30 mm. When the thickness of the thermal insulation material is within the above range, sufficient mechanical strength can be obtained and it can be easily molded.

[0087] [2. Method for manufacturing heat-insulating sheets] Next, a method for manufacturing a heat-insulating sheet according to the present invention will be described.

[0088] The method for manufacturing the heat insulating sheet according to this embodiment is not particularly limited, but for example, it can be obtained by forming a sheet of heat insulating material containing inorganic particles, applying a resin film-forming composition to the sheet, and drying it. However, since the heat insulating sheet according to this embodiment preferably has a resin film thickness of less than 100 μm, it is preferable to appropriately select a method for forming the resin film.

[0089] [2-1. Forming of insulation material] Thermal insulation materials may be manufactured by molding a thermal insulation material containing inorganic particles using a wet papermaking method, a dry molding method, or a wet molding method, or by extrusion molding. The manufacturing methods for obtaining thermal insulation materials using each molding method are described below.

[0090] <2-1-1. Method for manufacturing thermal insulation materials using the wet papermaking method> In the wet papermaking method, inorganic particles, along with inorganic fibers, organic fibers, or organic binders as needed, are first mixed in water and stirred with a stirrer to prepare a mixture. Then, the resulting mixture is dewatered through a filtration mesh to produce a wet sheet. Finally, the resulting wet sheet is heated and pressurized to obtain an insulating material. Before the heating and pressurizing steps, a ventilated drying treatment may be performed by passing hot air through the wet sheet to dry it; however, this ventilated drying treatment may be omitted, and the sheet may be heated and pressurized while still wet.

[0091] <2-1-2. Method for manufacturing heat-insulating sheets by dry molding method> In the dry molding method, inorganic particles, along with inorganic fibers, organic fibers, or organic binders as needed, are first introduced into a mixer such as a V-type mixer in a predetermined ratio. After the materials introduced into the mixer are thoroughly mixed, the mixture is placed into a predetermined mold and pressed to obtain the heat insulating material. Heating may be used during pressing as needed.

[0092] The above-mentioned press pressure is preferably in the range of 0.98 to 9.80 MPa. If the press pressure is less than 0.98 MPa, the resulting insulation material may not be able to maintain its strength and may collapse. On the other hand, if the press pressure exceeds 9.80 MPa, excessive compression may reduce workability, and furthermore, the bulk density will increase, which may increase solid heat transfer and reduce the insulation performance.

[0093] <2-1-3. Method for manufacturing heat-insulating sheets by extrusion molding> In the extrusion molding method, first, water is added to inorganic particles, and optionally to a binder such as inorganic fibers, organic fibers, or an organic binder, and the mixture is kneaded in a kneader to prepare a paste. Then, the resulting paste is extruded through a slit-shaped nozzle using an extrusion molding machine and further dried to obtain an insulating material. As the organic binder, it is preferable to use methylcellulose and water-soluble cellulose ether, but any organic binder commonly used in the extrusion molding method can be used without particular limitation.

[0094] [2-2. Formation of resin coatings] The method for forming the resin film is not particularly limited, but for example, it can be formed by applying a resin film-forming composition to a heat insulating material and drying it.

[0095] The raw material resin included in the resin film-forming composition is not limited as long as the effects of the present invention are obtained, but it is preferably a flame-retardant resin. Examples include epoxy resin, melamine resin, silicone resin, urethane resin, polyvinyl alcohol (PVA), acrylic resin, polyester resin, etc. Resins with self-extinguishing properties or resins with a high oxygen index are more preferable.

[0096] The resin film-forming composition may contain components other than resin, such as organic fibers, inorganic fibers, organic fillers, inorganic fillers, organic pigments, and the like.

[0097] The solvent used in the resin film-forming composition is not particularly limited, but examples include water and organic solvents, and water is preferred from the viewpoint of versatility.

[0098] The resin concentration (resin content relative to the total mass of the resin film-forming composition) in the resin film-forming composition is preferably 25 to 100% by mass. This range facilitates the formation of resin films with desired thickness and shape.

[0099] Methods for applying the composition include dip coating, die coating, barcode coating, spin coating, offset coating, and spray coating, as well as printing methods such as inkjet printing, screen printing, offset printing, flexographic printing, and gravure printing. The method for applying the resin film-forming composition is not particularly limited, but it is preferable to use a screen printing method or a spray coating method, and more preferably a screen printing method, because it is easier to form a resin film with the desired thickness and shape.

[0100] [3. Uses of insulation sheets] The heat insulating sheet according to an embodiment of the present invention is used in a battery pack in which multiple battery cells are connected in series or parallel. For example, it is preferably used in a battery pack interposed between the battery cells. When using an embodiment of the present invention as a battery pack, it is preferable that a resin coating is formed on any of the surfaces of the heat insulating sheet that come into contact with the battery cells.

[0101] [4. Battery Pack] A battery pack according to an embodiment of the present invention comprises a plurality of battery cells and a heat insulating sheet according to this embodiment, wherein the plurality of battery cells are connected in series or in parallel. Figure 6 is a schematic cross-sectional view showing an example of a battery pack to which an insulating sheet according to an embodiment of the present invention is applied. For example, as shown in Figure 6, the battery pack 100 according to an embodiment of the present invention has a plurality of battery cells 20a, 20b, and 20c arranged side by side, connected in series or parallel and housed in a battery case 30, with an insulating sheet 10 interposed between the battery cells 20a, 20b, and 20c.

[0102] In the battery pack 100 configured in this way, the heat insulating sheet 10 has a resin coating that covers at least a portion of the surface of the heat insulating material. This makes it possible to suppress peeling of the resin coating from the surface of the heat insulating material, as well as suppress an increase in thermal conductivity and a decrease in flame retardancy. Furthermore, when the heat insulating sheet 10 is interposed between each battery cell 20a, 20b, and 20c, heat transfer between each battery cell 20a, 20b, and 20c can be suppressed during normal use. Furthermore, even if one of the multiple battery cells 20a, 20b, and 20c experiences thermal runaway, becomes overheated, expands, or catches fire, the presence of the heat-insulating sheet 10 according to this embodiment can suppress the propagation of heat between the battery cells 20a, 20b, and 20c. Therefore, a chain reaction of thermal runaway can be prevented, minimizing adverse effects on other battery cells.

[0103] Furthermore, the battery pack 100 of this embodiment is not limited to the battery pack illustrated in Figure 6. The heat insulating sheet 10 can be placed not only between battery cells 20a and 20b, and between battery cells 20b and 20c, but also between battery cells 20a, 20b, and 20c and the battery case 30.

[0104] In a battery pack configured in this way, if a battery cell ignites, it is possible to suppress the spread of flames outside the battery case 30. For example, the battery pack 100 according to this embodiment may be used in electric vehicles (EVs) and placed under the passenger floor. In this case, even if the battery cells catch fire, the safety of the passengers can be ensured. Furthermore, since the heat insulating sheet 10 can be placed not only between each battery cell, but also between the battery cells 20a, 20b, and 20c and the battery case 30, there is no need to newly manufacture fire-retardant materials, and a safe battery pack 100 can be easily constructed at low cost.

[0105] In the battery pack of this embodiment, the heat insulating sheet 10, which is placed between the battery cells 20a, 20b, 20c and the battery case 30, may be in contact with the battery cells 20a, 20b, 20c, or there may be a gap between them. However, if there is a gap between the heat insulating sheet 10 and the battery cells 20a, 20b, 20c, deformation of the battery cells can be tolerated even if the temperature of one of the battery cells rises and its volume expands.

[0106] Furthermore, the heat-insulating sheet according to this embodiment can be easily bent depending on the type and thickness of the resin coating and heat-insulating material selected. Therefore, it can be adapted to any shape, regardless of the shape of the battery cells 20a, 20b, 20c and the battery case 30. Specifically, it can be applied to prismatic batteries, as well as cylindrical batteries, flat-plate batteries, and the like. [Examples]

[0107] The following describes examples of the heat-insulating sheet according to this embodiment, but the present invention is not limited to these examples.

[0108] <Comparative Example 1> The following inorganic particles and binders were prepared, and these materials were thoroughly stirred and mixed to prepare a slurry. Using the obtained slurry, an insulating material was formed by papermaking.

[0109] A slurry was prepared by adding 56% by mass of silica nanoparticles (average particle size 5 nm), 24% by mass of titania (average particle size 8 μm) (silica nanoparticles:titania particles = 70% by mass:30% by mass), and as a binder, 11% by mass of glass fibers (average fiber diameter 10 μm, average fiber length 5 mm) and 8% by mass of pulp fibers, and thoroughly stirring and mixing. An insulating material was obtained by papermaking from the above slurry, and the insulating material without a resin layer on the surface was used as the insulating sheet of Comparative Example 1. The drying process was carried out at 110°C, and the resulting insulation material had dimensions of 80 mm in width, 80 mm in length, and 1 mm in thickness.

[0110] <Comparative Examples 2 and 3> As a composition for forming the resin layer, an aqueous solution of acrylic resin with a resin concentration of 50% by mass was used. Resin layers with thicknesses of 60 μm and 300 μm were formed on the above-mentioned heat insulating material by coating with a bar coater, and the heat insulating sheets of Comparative Examples 2 and 3 were obtained by heating and drying at 140°C. Visual inspection of the resin layered surfaces of the insulation sheets in Comparative Examples 2 and 3 revealed that cracks were observed in the resin layer of all insulation sheets.

[0111] <Example 1> As the resin film-forming composition, an aqueous solution of polyvinyl alcohol (PVA) resin with a resin concentration of 10% by mass was used. The resin film-forming composition was applied to the above-mentioned heat insulating material using a screen printing machine, and a resin film was formed by heating and drying at 130°C, thereby obtaining the heat insulating sheet of Example 1.

[0112] Visual observation of the surface of the heat insulating sheet in Example 1, it was confirmed that the resin coating in Example 1 was free of cracks and that multiple pores were distributed across the entire surface of the resin coating. Figure 7 is a photograph used as a substitute for a drawing, showing the surface of the heat-insulating sheet of Example 1, taken with a digital microscope. In Figure 7, the white areas represent pores, and the black areas represent the resin coating. As shown in Figure 7, the images obtained using a digital microscope also confirmed that multiple holes were distributed throughout the entire field of view. Furthermore, the ratio (A / B) of the total area A of the resin coating to the total area B of the holes, calculated from the digital microscope image observation, was 17.5.

[0113] Furthermore, for example, observation of the cross-sectional SEM image of the heat insulating sheet shown in Figure 3 confirmed that the resin coating 1 of the heat insulating sheet 10 is irregularly curved along the surface shape of the heat insulating material 2 and has a width in thickness. Under the conditions described below, the thickness of the resin coating was measured at 45 points from SEM images of the cross-section of the insulation sheet. The thickness ranged from over 0 to 40.3 μm, with an average thickness of 13.8 μm. Note that the thickness was not measured at the locations of pores.

[0114] [Measurement and Evaluation] The following measurements and evaluations were performed on the thermal insulation sheets of Example 1 and Comparative Example 1.

[0115] (Ratio of the total surface area A of the sebum film to the total surface area B of the pores (A / B)) The ratio (A / B) of the total area A of the resin coating portion to the total area B of the pore portion was calculated by observing digital microscope images of the resin coating side. The A / B ratio was calculated by observing the surface of the heat-insulating sheet with the resin coating at 20x magnification using a digital microscope (KEYENCE VHX-5000). The total area of ​​the pores (B) was defined as the range of brightness settings from 96 to 255, and the total area of ​​the resin coating (A) was defined as the range of brightness settings from 0 to 96.

[0116] (Thickness of the resin coating) The thickness of the resin coating is, for example, the average value of 45 measurements taken at 9 locations with 35.8 μm intervals in cross-sectional SEM images of 5 locations on the heat insulating sheet, as shown in Figure 3.

[0117] (Powder falling off) As shown in Figure 8, in a device in which an arm 25 is attached to the top of a support column 24 so as to be movable, and a test material 23 is attached to the tip of the arm 25, the arm 25 was raised to an arbitrary angle and fixed, and then the fixation was released and it was dropped, causing a collision between the support column 24 and the arm 25 and applying an impact. The size of the test material 23 was 100 mm x 100 mm, the length of the arm was 915 mm, the number of impacts was 3, and the angle between the support column and the arm was 90°. The weight before impact was F0 (g) and the weight after impact was Fw (g), and the amount of powder fallout E (amount of inorganic particles detached) (g / m) was calculated using the following formula. 2 ) was evaluated. E = (F0 - Fw) / Test material area In the evaluation method described above, the powder fallout was 0.5 g / m². 2 If the value is less than this, it can be said that the powder fall prevention performance is good.

[0118] (Flame retardant) The flame retardancy test was conducted in accordance with UL94 (Flame retardancy test for polymer materials) of the UL testing standards. Products that meet the 94V-0 criteria in the UL94 testing standard can be considered to have good flame retardancy.

[0119] (Thermal conductivity) The thermal conductivity (W / m·K) was measured at room temperature (25°C). The thermal conductivity was measured in accordance with the "Method for measuring the thermal resistance and thermal conductivity of thermal insulating materials, Part 2: Heat flow meter method (HFM method)" described in JIS A 1412-2.

[0120] (Compression ratio) As shown in Figure 9, a universal testing machine was used, and the test specimen 23 was placed between the upper plate 21 and the lower plate 22. The test specimen 23 was then compressed by moving the upper plate 21 downwards. The size of the test specimen 23 was set to 25 mm x 25 mm, the compression speed to 0.5 mm / min, and the compressive stress to 0.5 and 3.5 MPa. Then, the initial thickness of the test material 23 is D0 (mm), and the amount of compression (thickness reduction) is D d The compression ratio C (%) was calculated using the following formula, where (mm) is used. C=(D d / D0)×100 The compression ratio was measured for the thermal insulation sheets (test material 23) of Example 1 and Comparative Example 1.

[0121] The evaluation results are shown in Table 1.

[0122] [Table 1]

[0123] In the heat-insulating sheet of Example 1, which has a resin coating, powder shedding was suppressed by approximately 90% compared to the heat-insulating sheet of Comparative Example 1, which does not have a resin coating. Furthermore, because the resin layer is thin and in the form of a film, the decrease in flame retardancy and increase in thermal conductivity due to the formation of the resin layer were suppressed, and it was found that good flame retardancy and thermal conductivity equivalent to that of the sheet without a resin coating could be maintained. Furthermore, it was confirmed that the compression ratio is lower than that of Comparative Example 1, which does not have a resin coating, and that it can be suitably used, for example, as an interposition between battery cells in a battery pack. [Explanation of Symbols]

[0124] 1. Resin coating 2. Insulation 10 Insulation Sheets 20a, 20b, 20c battery cells 21 Top plate 22 Lower plate 23 Test material 24 Posts 25 Arms 30 Battery Cases 31 holes 41 Inorganic particles 42 Inorganic Fibers 100 battery packs

Claims

1. Insulating material containing inorganic particles, The insulation material has a resin coating that covers at least a portion of its surface, The resin coating has a plurality of pores, An insulating sheet used in battery packs where multiple battery cells are connected in series or parallel.

2. The heat insulating sheet according to claim 1, wherein the average thickness of the resin coating is 1 to 95 μm.

3. The heat insulating sheet according to claim 1 or 2, wherein the thickness of the resin coating is greater than 0 and less than 100 μm.

4. The thermal insulation sheet according to any one of claims 1 to 3, wherein the resin coating is irregularly curved in accordance with the surface shape of the thermal insulation material.

5. The heat insulating sheet according to any one of claims 1 to 4, wherein the holes are dispersed and arranged across the entire surface of the resin coating.

6. The heat insulating sheet according to any one of claims 1 to 5, wherein the ratio (A / B) of the total area A of the resin coating portion to the total area B of the pore portion, calculated by digital microscope image observation of the surface on the resin coating side, is between 7 / 3 and 99 / 1.

7. The thermal insulation sheet according to any one of claims 1 to 6, characterized in that the inorganic particles are particles made of at least one inorganic material selected from oxide particles, carbide particles, nitride particles, and inorganic hydrate particles.

8. The thermal insulation sheet according to any one of claims 1 to 7, further characterized in that the thermal insulation material has a first inorganic fiber and a second inorganic fiber having at least one property that is different from each other, selected from average fiber diameter, shape and glass transition temperature.

9. The average fiber diameter of the first inorganic fiber is greater than the average fiber diameter of the second inorganic fiber. The heat insulating sheet according to claim 8, characterized in that the first inorganic fiber is linear or needle-shaped, and the second inorganic fiber is dendritic or curly.

10. The first inorganic fiber is an amorphous fiber, The second inorganic fiber is at least one fiber selected from amorphous fibers and crystalline fibers, each having a higher glass transition temperature than the first inorganic fiber. The heat insulating sheet according to claim 8, characterized in that the average fiber diameter of the first inorganic fiber is greater than the average fiber diameter of the second inorganic fiber.

11. The inorganic particles include at least one selected from nanoparticles, hollow particles, and porous particles. The first inorganic fiber is an amorphous fiber, The thermal insulation sheet according to claim 8, wherein the second inorganic fiber is at least one inorganic fiber selected from amorphous fibers and crystalline fibers, each having a higher glass transition temperature than the first inorganic fiber.

12. A method for manufacturing an insulating sheet according to any one of claims 1 to 11, A step of forming the thermal insulation material containing the inorganic particles into a sheet, A method for manufacturing an insulating sheet, comprising the steps of applying a resin film-forming composition to the surface of the sheet-like insulating material by a screen printing method or a spray-coating method to form the resin film.

13. A thermal insulation material containing inorganic particles, The insulation material has a resin coating that covers at least a portion of its surface, The resin coating is a method for manufacturing a heat insulating sheet having a plurality of pores, A step of forming the thermal insulation material containing the inorganic particles into a sheet, A method for manufacturing an insulating sheet, comprising the steps of applying a resin film-forming composition to the surface of the sheet-like insulating material by a screen printing method or a spray-coating method to form the resin film.

14. A battery pack comprising a plurality of battery cells and an insulating sheet according to any one of claims 1 to 11, wherein the plurality of battery cells are connected in series or in parallel.

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