Thermal insulation material sheet for use between electric vehicle battery cells and method for manufacturing same
Patent Information
- Application Number
- PCT/JP2025/012703
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2025-03-28
- Publication Date
- 2026-10-01
Smart Images
Figure JP2025012703_01102026_PF_FP_ABST
Abstract
Description
Insulating Material Sheet Between Battery Cells for Electric Vehicles and Method for Manufacturing the Same
[0001] The present invention relates to an insulating material sheet used for heat insulation between battery cells of electric vehicles and a method for manufacturing the same.
[0002] Silica aerogel has a porous structure provided with pores having a diameter smaller than the mean free path of air, and the skeleton thereof is formed by connecting a plurality of silica fine particles. Due to this fine porous structure, silica aerogel has low thermal conductivity and is useful as a constituent material for heat insulating materials in vehicle-mounted components, residential building materials, industrial equipment and the like.
[0003] On the other hand, heat insulating materials containing silica aerogel often have low surface mechanical strength. Therefore, when an external force is applied to the heat insulating material, a phenomenon called powder falling, in which powder formed of the constituent material of the heat insulating material falls off from the heat insulating material, tends to easily occur. For example, heat insulating materials used for heat insulation between battery cells of electric vehicles are repeatedly subjected to loads caused by heat and expansion of the battery during charging. Furthermore, heat insulating materials for automobiles are subjected to vibration generated during driving of the automobile. Therefore, when a sheet containing silica aerogel is used as a heat insulating material for automobile batteries, the aforementioned load and vibration cause powder falling from the sheet, which may lead to a decrease in heat insulating performance.
[0004] Furthermore, powder falling tends to easily occur in portions of the sheet surface that receive stress accompanying battery expansion and portions close to vibration sources. Therefore, when powder falling occurs, a bias occurs in the composition distribution within the heat insulating material, and there is also a risk that a portion with low heat insulating performance may be formed in a part of the heat insulating material.
[0005] Accordingly, as a technique for suppressing the occurrence of powder falling, for example, Patent Document 1 describes a technique of blending hot melt powder into a sheet containing silica aerogel, a technique of sealing the surface of the sheet with a film, and the like. Furthermore, Patent Document 2 describes a technique in which a heat-insulating elastic member including an elastic layer is provided on one surface of a silica aerogel sheet, a cover layer is provided on the other surface, or the sheet and the entire body are covered with an exterior body.
[0006] Japanese Patent Publication No. 2023-132944 Japanese Patent Publication No. 2023-35097
[0007] However, when a sheet containing silica aerogel is covered with a film or the like, repeated external forces applied to the insulating material over a long period of time can cause the film to peel off the sheet, leading to powder shedding. In particular, if the sheet contains relatively high-density substances such as silicon carbide, these high-density substances are more likely to detach from the sheet, which can lead to a decrease in thermal insulation performance. Furthermore, according to the technology described in Patent Document 2, the hardened layer formed by the hot-melt powder may reduce the thermal insulation performance of the sheet.
[0008] This invention has been made in view of the above background, and aims to provide an inter-cell insulation sheet for electric vehicle batteries that can maintain good thermal insulation performance over a long period of time, and a method for manufacturing the same.
[0009] One aspect of the present invention is an insulating sheet for use in insulating the space between battery cells of an electric vehicle, comprising silica aerogel, fibers, and infrared shielding particles, wherein a photograph of the cross-section of the insulating sheet shows first particles consisting of infrared shielding particles having a major axis of 0.5 μm to 1 μm, and second particles consisting of infrared shielding particles having a major axis of 5 μm to 10 μm.
[0010] Another aspect of the present invention is a method for manufacturing an inter-cell thermal insulation sheet for electric vehicles according to the above aspect, comprising: preparing a sheet precursor in which a wet gel containing silica fine particles and infrared shielding particles dispersed in the gel are impregnated into the fibers, and forming the thermal insulation sheet by drying the gel in the sheet precursor.
[0011] The aforementioned battery cell insulation sheet for electric vehicles (hereinafter referred to as the "insulation sheet") contains silica aerogel, fibers, and infrared shielding particles. The infrared shielding particles also contain first and second particles having the aforementioned specific major axis. The infrared shielding particles have the effect of increasing insulation by blocking radiant heat. It is known that the effect of blocking radiant heat by infrared shielding particles increases as the particle size of the infrared shielding particles increases. On the other hand, when the particle size of infrared shielding particles increases, the infrared shielding particles tend to connect with each other within the insulation sheet. As a result, heat transfer paths containing infrared shielding particles tend to form, leading to a decrease in insulation performance. Therefore, conventionally, in this type of insulation sheet, in order to increase the radiant heat blocking effect while avoiding the connection of infrared shielding particles with each other, infrared shielding particles with a particle size below a predetermined value and with small particle size variation have been used.
[0012] In contrast to this common technical practice, by deliberately using infrared shielding particles including first and second particles, it is possible to suppress the detachment of the first and second particles from the thermal insulation sheet even when external forces or vibrations are applied to the thermal insulation sheet. Furthermore, by retaining the first and second particles within the thermal insulation sheet for a long period of time, the good thermal insulation performance of the thermal insulation sheet can be maintained over a long period of time.
[0013] Therefore, according to the above embodiment, it is possible to provide an insulating sheet and a method for manufacturing the same that can maintain good insulating performance over a long period of time.
[0014] Figure 1 is a schematic cross-sectional view showing a cross-section parallel to the thickness direction of the insulation sheet.
[0015] (Insulation sheet) The structure of the insulation sheet is described below.
[0016] [Silica Aerogel] Silica aerogel is a porous structure composed of silica nanoparticles and has pores. The pores of silica aerogel are usually mesopores with a diameter of 50 nm or less. Since the diameter of mesopores is smaller than the mean free path of air, using silica aerogel can suppress convection of air within the pores. As a result, heat transfer by convection can be suppressed, and the thermal insulation performance can be improved. The lower limit of the pore diameter is not particularly limited from the viewpoint of suppressing convection of air within the pores, but it is preferable that the pore diameter is, for example, 10 nm or more.
[0017] The silica aerogel framework is mainly composed of secondary particles formed by the aggregation of primary silica nanoparticles. The average particle size of the silica nanoparticles (primary particles) is typically around 2 to 5 nm. The average particle size of the silica nanoparticles can be measured by electron microscopy.
[0018] The average particle diameter of the particles (mainly secondary particles) constituting the silica aerogel skeleton is preferably 1 μm or more, and more preferably 10 μm or more. While there is no particular upper limit to the average particle diameter of the skeleton particles from the viewpoint of improving thermal insulation performance, it is preferable that the average particle diameter of the skeleton particles be, for example, 200 μm or less. The average particle diameter of the skeleton particles is the median diameter (i.e., D50) determined from the volume-based particle size distribution measured by laser diffraction / scattering.
[0019] The silica aerogel content in the insulation sheet is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more. In this case, the effect of improving the insulation performance due to silica aerogel can be obtained more reliably.
[0020] On the other hand, the silica aerogel content in the thermal insulation sheet is preferably 60% by mass or less, more preferably 50% by mass or less, and even more preferably 40% by mass or less. In this case, a decrease in the mechanical strength of the thermal insulation sheet can be more easily avoided. As a result, the occurrence of powder shedding from the thermal insulation sheet can be made less likely.
[0021] In determining a preferred range for the silica aerogel content, the upper and lower limits of the silica aerogel content described above can be arbitrarily combined. For example, the preferred range for the silica aerogel content in the thermal insulation sheet may be 10% by mass or more and 60% by mass or less, 20% by mass or more and 50% by mass or less, or 30% by mass or more and 40% by mass or less.
[0022] Silica aerogels can be obtained, for example, by gelling a sol containing silica nanoparticles and a liquid dispersion medium for dispersing the silica nanoparticles, then drying the sol to remove the liquid dispersion medium from the gel. The method of drying the gel is not particularly limited; for example, drying can be carried out in an atmosphere of normal pressure or in a supercritical fluid. The gel can also be dried by freeze-drying or drying under ambient pressure.
[0023] It should be noted that gels obtained by drying in an atmosphere of normal pressure are sometimes called "xerogels," gels obtained by drying in a supercritical fluid are sometimes called "aerogels," gels obtained by freeze-drying are sometimes called "cryogels," and gels obtained by drying under ambient pressure are sometimes called "ambigels." However, the silica aerogel contained in the aforementioned heat insulating sheet may be manufactured by any of these methods. In other words, "silica aerogel" as used herein includes "aerogels," "xerogels," "cryogels," and "ambigels" that consist of silica fine particles.
[0024] Silica aerogels may undergo hydrophobic treatment during their manufacturing process. Performing the hydrophobic treatment of the gel before the drying process eliminates the need for drying in a supercritical fluid, allowing drying in an atmospheric pressure environment. Therefore, this simplifies the silica aerogel manufacturing process and further reduces manufacturing costs.
[0025] [Infrared Shielding Particles] Infrared shielding particles have the effect of absorbing heat from a heat source and re-emitting it from the surface on the heat source side, as well as scattering infrared rays. Therefore, by incorporating infrared shielding particles into the insulation sheet, it is possible to block radiant heat from the heat source and improve the insulation performance, especially at high temperatures.
[0026] The infrared shielding particles appearing in the photograph of the cross-section of the thermal insulation sheet include at least a first particle having a major axis of 0.5 μm to 1 μm and a second particle having a major axis of 5 μm to 10 μm. In addition to the first and second particles, the photograph may also include infrared shielding particles having major axes outside the aforementioned ranges. By using infrared shielding particles such that both the first and second particles appear in the photograph of the cross-section of the thermal insulation sheet, the thermal insulation sheet can maintain good thermal insulation performance over a long period of time.
[0027] The reasons why the aforementioned effects are obtained by the first and second particles are thought to be as follows: The first particles have a relatively small particle size, so the mass of each particle is small and the ratio of surface area to mass is large. Therefore, even when vibration or repeated loads are applied to the insulation sheet, it is thought that they are less likely to fall downward from their initial position. On the other hand, the second particles have a relatively large particle size, so when vibration or repeated loads are applied to the insulation sheet and they fall downward from their initial position, it is thought that they are more likely to be captured by fibers, etc.
[0028] Therefore, by using infrared shielding particles such that both the first and second particles appear in a photograph of the cross-section of the insulation sheet, it is believed that the shedding of the first and second particles will be less likely to occur even when the insulation sheet is subjected to vibration or repeated loads. Furthermore, it is believed that the insulation performance can be maintained by retaining the first and second particles in the insulation sheet over a long period of time.
[0029] From the viewpoint of more reliably obtaining the aforementioned effects, the ratio of the number of first particles to the number of second particles present in the photograph is preferably first particles:second particles = 1:4 to 4:1, preferably 1:4 to 3:1, more preferably 1:4 to 2:1, and even more preferably 1:4 to 1:1. From a similar viewpoint, in the photograph, the sum of the ratio of the number of first particles to the ratio of the number of second particles among the infrared shielding particles having a major axis of 0.5 μm or more is preferably 5% to 30%, more preferably 10% to 30%, even more preferably 15% to 30%, and particularly preferably 20% to 30%.
[0030] It is preferable that the infrared shielding particles appearing in the photograph of the cross-section of the thermal insulation sheet further contain third particles having a major axis greater than 1 μm and less than 5 μm. Because the third particles have a moderately large particle size, they have high performance in blocking radiant heat from a heat source. In addition, since the third particles do not easily connect within the thermal insulation sheet, the formation of heat transfer paths including the third particles can be easily avoided. Therefore, by using infrared shielding particles such that third particles appear in the photograph of the cross-section of the thermal insulation sheet, the initial thermal insulation performance of the thermal insulation sheet can be further enhanced. From the viewpoint of obtaining this effect more reliably, it is preferable that the ratio of the number of third particles to the infrared shielding particles present in the photograph be 70% or more and 95%, and more preferably 70% or more and 90%.
[0031] One method for adjusting the number of first particles, second particles, and other particles present in the photograph is to adjust the particle size distribution of the infrared shielding particles used in the manufacture of the heat-insulating sheet. More specifically, the number of first particles, second particles, and other particles present in the photograph can be adjusted to a desired range by methods such as classifying the infrared shielding particles, mixing and using multiple types of infrared shielding particles having different particle size distributions, or combining these methods.
[0032] The method for determining the presence or absence of the first and second particles, and the method for measuring the number of these particles, are as follows. First, the insulation sheet is cut and a test piece of a predetermined size is taken. After forming a platinum coating on the surface of this test piece, the test piece is processed using a sample cross-section processing device (for example, "Cross-Section Polisher (registered trademark) SM09010" manufactured by JEOL Ltd.) under the conditions of an acceleration voltage of 4 kV and a processing time of 20 hours, to expose a cross section that is approximately parallel to the thickness direction of the insulation sheet.
[0033] After forming an osmium coating on the processed cross-section, the backscattered electron image of this cross-section is observed using an electron microscope (for example, Hitachi, Ltd.'s "SEM S-3400N") under conditions of an acceleration voltage of 15 kV and a magnification of 200x. Based on this backscattered electron image, a photograph of the cross-section of the test piece is obtained. Figure 1 shows a schematic diagram of the photograph of the cross-section. The photograph of the cross-section of the thermal insulation sheet 1 shows silica aerogel 2, infrared shielding particles 4, and fibers 3. The infrared shielding particles 4 have, for example, a polygonal contour. The fibers 3 have, for example, a circular or elliptical contour. For each infrared shielding particle 4 present in this photograph, the rectangle with the smallest area among the rectangles circumscribing the particle is identified. The length of the long side of the rectangle thus identified is taken as the major axis of each infrared shielding particle 4.
[0034] Based on the major axis determined in this way, it is possible to determine whether each infrared shielding particle 4 is a first particle 41, a second particle 42, or another particle. The number of first particles 41 and second particles 42 can be obtained by counting the number of each particle present in the photograph after identifying the first particles 41 and second particles 42 using the method described above. If particles other than the first and second particles, such as a third particle, are present in the photograph, the major axis and number of these particles can be measured using the same method as described above.
[0035] The above process can also be performed using image processing software. For example, the method for measuring the major axis of a particle using ImageJ is as follows: First, a cross-sectional image with dimensions of 960 pixels vertically and 1280 pixels horizontally is created from the backscattered electron image. Next, binarization is performed based on the pixel value of each pixel to identify the regions of infrared shielding particles and glass fibers. After that, region division is performed to create a measurement image in which only the regions of infrared shielding particles are extracted. At this time, regions with an area of 1 pixel are judged as noise and are excluded from the measurement of the major axis of the infrared shielding particles.
[0036] Then, after detecting the contours of the regions of individual infrared shielding particles present in the measurement image, rectangular fitting is used to identify the rectangle with the smallest area among the rectangles circumscribing each region. After measuring the length of the longer side of this rectangle (in pixels), the major axis of the infrared shielding particle (in μm) is obtained by converting the units.
[0037] In the aforementioned photograph, it is preferable that the infrared shielding particles are concentrated near the fibers. More specifically, it is preferable that the number of infrared shielding particles present within 13 μm of the fiber surface is greater than the number of infrared shielding particles present outside this range. In this case, since a relatively large number of infrared shielding particles are present around the fibers, radiant heat from a heat source is more easily blocked by the infrared shielding particles before it reaches the fibers. As a result, the fibers can be protected from radiant heat, and their heat resistance can be improved. In addition, the second particle, which has a relatively large particle size, is easily captured by the fibers. Therefore, because a relatively large number of infrared shielding particles are present near the fibers, powder shedding is less likely to occur even when vibration or repeated loading is applied to the insulation sheet, and it is expected that the insulation performance can be maintained for a longer period of time.
[0038] From the viewpoint of more reliably obtaining the aforementioned effects, it is preferable that 70% or more of the infrared shielding particles in the photograph are located within a range of 13 μm from the surface of the fiber.
[0039] From the viewpoint of obtaining the effect of protecting the fibers from radiant heat, in the above photograph, all of the first, second, and third particles may be unevenly distributed near the fibers, or one or two of the first, second, and third particles may be unevenly distributed near the fibers. On the other hand, from the viewpoint of suppressing powder shedding, it is preferable that at least the second particles are unevenly distributed near the fibers. That is, it is preferable that the number of second particles present within a range of 13 μm from the surface of the fibers is greater than the number of second particles present outside that range.
[0040] Examples of substances constituting the infrared shielding particles include silicon carbide, kaolinite, montmorillonite, titanium oxide, silicon nitride, mica, alumina, aluminum nitride, boron carbide, iron oxide, magnesium oxide, tin oxide, zinc oxide, tantalum oxide, manganese ferrite, manganese oxide, nickel oxide, nickel, silver oxide, silver, bismuth oxide, carbon black, graphite, titanium, iron titanium oxide, zirconium, zirconia, zirconium silicate, barium titanate, manganese dioxide, chromium oxide, titanium carbide, tungsten carbide, tungsten oxide, niobium oxide, indium tin oxide, cerium oxide, and mixtures of the foregoing. The heat insulating sheet may include infrared shielding particles composed of one type of the above substances, or may include two or more types of infrared shielding particles composed of mutually different substances.
[0041] From the viewpoint of further enhancing the radiant heat blocking effect, the infrared shielding particles are preferably composed of a substance having an emissivity of 0.6 or more in the infrared wavelength region. Examples of such substances include silicon carbide, kaolinite, silicon nitride, mica, alumina, zirconia, aluminum nitride, zirconium silicate, cerium oxide, boron carbide, manganese oxide, tin oxide, and iron oxide. Further, from the viewpoint of scattering incident infrared rays to enhance the radiant heat blocking effect, it is also effective to use infrared shielding particles composed of a substance having a high refractive index in the infrared wavelength region. Examples of such substances include substances having a refractive index of 2.0 or more in the visible light wavelength region, such as silicon carbide, titanium oxide, zirconia, silicon nitride, aluminum nitride, zinc oxide, tantalum oxide, tungsten oxide, niobium oxide, cerium oxide, manganese oxide, tin oxide, bismuth oxide, iron oxide, and barium titanate.
[0042] Further, by forming the infrared shielding particles from a material having a relatively large specific heat, the heat capacity of the infrared shielding particles can be increased, and an increase in the temperature of the particles themselves can be suppressed. In addition, such materials are also excellent in heat resistance. Therefore, by using infrared shielding particles formed of such a material, the heat insulating performance and heat resistance of the heat insulating sheet can be further improved. As the material having a relatively large specific heat, for example, silicon carbide, titanium oxide, silicon nitride, mica, alumina, aluminum nitride, boron carbide, iron oxide, magnesium oxide and the like can be preferably used. In particular, silicon carbide is preferable because it has little increase in thermal conductivity even in a high-temperature atmosphere of about 800°C.
[0043] The content of the infrared shielding particles in the heat insulating sheet is preferably 5% by mass or more, and more preferably 10% by mass or more. In this case, the effect of suppressing heat transfer due to radiation can be obtained more reliably. On the other hand, from the viewpoint of reducing contact between infrared shielding particles and contact with other components to make it difficult to form a heat transfer path, the content of the infrared shielding particles in the heat insulating sheet is preferably 30% by mass or less, more preferably 20% by mass or less.
[0044] In configuring the preferred range of the content of the infrared shielding particles, the aforementioned upper limit and lower limit of the content of the infrared shielding particles can be arbitrarily combined. For example, the preferred range of the content of the infrared shielding particles in the heat insulating sheet may be 5% by mass or more and 30% by mass or less, or may be 10% by mass or more and 20% by mass or less.
[0045] [Fibers] The fibers in the heat insulating sheet ensure the mechanical strength of the heat insulating sheet, and have the effect of suppressing powder falling of silica aerogel and infrared shielding particles. The fibers may be inorganic fibers or organic fibers. As the inorganic fibers, for example, glass fibers, ceramic fibers, quartz fibers, alumina fibers, silica fibers, silicon carbide fibers, boron fibers, metal fibers (e.g., aluminum, iron) and the like can be used.
[0046] As organic fibers, for example, chemical fibers such as polyamide fibers, polyimide fibers, aromatic polyamide fibers (aramid fibers), polyolefin fibers (e.g., polyethylene fibers, polypropylene fibers), fluorine fibers (e.g., polytetrafluoroethylene fibers), acrylic fibers, poly(p-phenylenebensbisoxazole) (PBO) fibers, polyarylate fibers, nylon fibers, polyurethane fibers, polyamide fibers, polyetheretherketone (PEEK) fibers, polyethersulfone (PES) fibers, polyetherimide (PEI) fibers, polyetherketone (PEK) fibers, and polyphenylene sulfide (PPS) fibers can be used, as well as natural fibers such as wood fibers, silk, hemp, and wool fibers. The insulation sheet may contain one type of fiber or two or more types of fibers.
[0047] The fibers contained in the insulation sheet are preferably those that have strength and / or heat resistance. From this viewpoint, the fibers contained in the insulation sheet are more preferably inorganic fibers, and even more preferably glass fibers.
[0048] In a photograph of the cross-section of the insulation sheet, the average diameter of the fibers is preferably 0.6 to 2 times the average major axis of the second particle, more preferably 0.7 to 1.7 times, and even more preferably 0.8 to 1.5 times. In this case, since the diameter of the fibers is appropriately large compared to the major axis of the second particle, it is thought that even if the insulation sheet is subjected to vibration or repeated loads and falls downward from its initial position, the second particle will be more easily captured by the fibers. As a result, powder shedding of the second particle is less likely to occur, and the insulation performance can be maintained for a longer period of time.
[0049] The method for calculating the average fiber diameter in a photograph of the cross-section of an insulating sheet is as follows. First, a photograph of the cross-section of the insulating sheet, roughly parallel to the thickness direction, is obtained using the same method as described above. If the cross-sectional shape of fiber 3 is circular and extends in a direction roughly perpendicular to the cross-section, the cross-section of fiber 3a appearing in the photograph will be circular, as shown in Figure 1. Therefore, in this case, the diameter of the circle becomes the diameter of fiber 3a. On the other hand, if fiber 3 extends in a direction inclined with respect to the cross-section, the cross-section of fiber 3b appearing in the photograph will be elliptical. Therefore, in this case, the minor axis of the ellipse becomes the diameter of fiber 3b.
[0050] Therefore, after determining the diameter of each individual fiber present in the photograph using the method described above, the average diameter of the fibers can be calculated by taking the arithmetic mean of these values. Furthermore, the average major axis of the second particle can be obtained by measuring the major axes of all second particles in the photograph using the method described above, and then taking the arithmetic mean of these values.
[0051] The fibers in the thermal insulation sheet can exist in various forms. For example, the fibers in the thermal insulation sheet may exist separately from each other, or multiple fibers may form bundles. Furthermore, the fibers in the thermal insulation sheet may form fabrics such as woven or nonwoven fabrics. In addition, the fibers in the thermal insulation sheet may exist in two or more of these forms.
[0052] The fibers in the thermal insulation sheet preferably constitute a cloth, and more preferably a nonwoven fabric. In this case, the mechanical strength of the thermal insulation sheet can be further improved. Furthermore, by using a cloth (preferably a nonwoven fabric, more preferably a glass fiber nonwoven fabric) that has been perforated or treated to create a napped surface during the manufacturing process of the thermal insulation sheet, the porosity and surface roughness of the thermal insulation sheet surface can be easily adjusted.
[0053] The fiber content in the thermal insulation sheet is preferably 20% by mass or more, and more preferably 30% by mass or more. In this case, the mechanical strength of the thermal insulation sheet can be further increased. On the other hand, from the viewpoint of obtaining mechanical strength commensurate with the fiber content, the fiber content in the thermal insulation sheet is preferably 70% by mass or less, and more preferably 60% by mass or less.
[0054] In determining a preferred range for the fiber content, the aforementioned upper and lower limits for the fiber content can be arbitrarily combined. For example, the preferred range for the fiber content in the insulation sheet may be 20% by mass or more and 70% by mass or less, or 30% by mass or more and 60% by mass or less.
[0055] [Other Components] The insulation sheet may consist of silica aerogel, infrared shielding particles, and fibers, and may also contain other components. Optional components that may be incorporated into the insulation sheet include, for example, binders, thickeners, flame retardants, preservatives, colorants, and radiation absorbers / reflectors.
[0056] The binder can reduce degradation in high-temperature atmospheres and suppress crack formation. The binder may be composed of inorganic materials or organic materials.
[0057] Examples of inorganic binders include talc, carbon black, kaolinite, montmorillonite, mica, silica (e.g., precipitated silica, gel silica, fused silica), wollastonite, magnesium silicate, titania, metal carbides (e.g., titanium carbide or tungsten carbide), metal oxides (e.g., manganese oxide, nickel oxide, tin oxide, silver oxide, bismuth trioxide, chromium oxide, iron oxide, alumina, zirconia, manganese dioxide), metal nitrides (e.g., silicon nitride, aluminum nitride), ilmenite, zirconium silicate, potassium titanate), glass flakes, water glass (sodium silicate), calcium carbonate, barium sulfate, hydraulic materials (e.g., cement, gypsum, magnesium silicate), quicklime, slaked lime, etc. The insulation sheet may contain one type of inorganic binder, or two or more types of inorganic binders.
[0058] The type of inorganic binder added to the thermal insulation sheet is not particularly limited, and an appropriate inorganic binder should be blended according to its properties. For example, silica is preferred because it is easily compatible with silica aerogel and is inexpensive and readily available. Hydraulic materials are also preferred because they react with water, which is a solvent commonly used in the manufacture of silica aerogel, and can form a high-strength thermal insulation sheet by bonding the constituent materials together while filling the gaps between silica nanoparticles, and are inexpensive and readily available. In addition, inorganic binders with a large specific surface area and hardness may be selected.
[0059] As the organic binder, it is preferable to use an aqueous binder that is soluble or dispersible in water (capable of forming an emulsion). Alternatively, as the organic binder, a substance that imparts hydrophilic groups to silica aerogel or a so-called surfactant can also be used.
[0060] The glass transition temperature (Tg) of the organic binder is preferably -5°C or lower, and more preferably -20°C or lower. Such organic binders exhibit excellent adhesion to silica aerogel. Furthermore, by using an organic binder whose glass transition temperature is within the aforementioned specific range, the flexibility of the thermal insulation sheet can be improved and crack formation can be suppressed.
[0061] Examples of organic binders include resins such as acrylic resin, urethane resin, and mixtures of acrylic resin and urethane resin; and rubbers such as styrene-butadiene rubber (SBR), nitrile rubber, silicone rubber, urethane rubber, and acrylic rubber. Among these, the organic binder is preferably urethane resin and / or SBR. In this case, the flexibility of the insulation sheet can be further improved, resulting in a flexible sheet. When using an organic binder, a crosslinking agent may also be used in combination. In this case, the organic binder is crosslinked, further improving the strength of the sheet.
[0062] • Thickening agents: Thickening agents can improve the dispersibility of silica aerogel in a solvent (usually water) and enhance processability. They can also improve the flexibility of the insulation sheet and suppress crack formation. Examples of thickening agents include polysaccharides such as carboxymethylcellulose (CMC), polyethylene oxide (PEO), carboxyethylcellulose, carboxypropylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, xanthan gum, agarose, carrageenan, and glucomannan; and polyvinyl alcohol.
[0063] Flame retardants can enhance the flame retardancy of the insulation sheet. Examples of flame retardants that can be used include halogen-based flame retardants, phosphorus-based flame retardants, and metal hydroxide-based flame retardants. It is preferable to use phosphorus-based flame retardants (e.g., ammonium polyphosphate, red phosphorus, phosphate esters), more preferable to use phosphorus-based flame retardants that are insoluble in water, and even more preferable to use ammonium polyphosphate.
[0064] [Structure of the insulation sheet] The thickness of the insulation sheet is not particularly limited, but may be, for example, 10 mm or less, 8 mm or less, 3 mm or less, 2.5 mm or less, or 2 mm or less. This allows the strength of the sheet to be maintained within an appropriate thickness range. The lower limit of the thickness of the insulation sheet may be, for example, 0.1 mm. The lower limit of the thickness of the insulation sheet is preferably 0.5 mm, and more preferably 1 mm. It is preferable that the thickness of the insulation sheet is generally uniform throughout. For example, the variation in the thickness of the insulation sheet may be 5% or less, 4% or less, or 3% or less.
[0065] At least one surface of the insulation sheet in the thickness direction may have an uneven shape or multiple voids. The position and shape of the voids in the insulation sheet are not particularly limited and can take various forms. For example, the voids may be arranged at regular intervals on the surface of the insulation sheet, or they may be arranged randomly. The shape of the voids may be circular, polygonal, or irregular. The uneven shape provided on the insulation sheet may be arranged over the entire surface of the insulation sheet, or it may be arranged on a part of the surface. Furthermore, the recesses and protrusions in the uneven shape may be arranged uniformly over the entire surface, or they may be unevenly distributed on a part of the surface.
[0066] When both the first and second surfaces of an insulating sheet are provided with an uneven surface and / or voids in the thickness direction, the properties of the first surface and the second surface may be the same or different. From the viewpoint of more effectively suppressing powder shedding from the insulating sheet, it is preferable that the properties of the first surface and the second surface of the insulating sheet are different. That is, for example, when voids are provided on both the first and second surfaces, it is preferable that the number of voids provided on the first surface be greater than the number of voids provided on the second surface. Also, for example, when both the first and second surfaces are provided with an uneven surface, it is preferable that the surface roughness of the first surface be greater than the surface roughness of the second surface.
[0067] When the aforementioned heat insulating sheet is placed between battery cells, the magnitude of external force or vibration applied to one surface in the thickness direction of the heat insulating sheet may be greater than the magnitude of external force or vibration applied to the other surface. In this case, by arranging the heat insulating sheet such that the magnitude of external force or vibration applied to the first surface is greater than the magnitude of external force or vibration applied to the second surface, powder of the constituent material of the heat insulating sheet generated from the first surface due to external force or vibration can be easily captured by pores or recesses on the surface. Furthermore, since the first surface has a predetermined shape and / or is formed of fibers, adhesion to films, etc., can be improved. Therefore, even when external force or vibration is applied to the heat insulating sheet, peeling between the film, etc. and silica aerogel, etc. can be suppressed.
[0068] On the other hand, by arranging the insulation sheets as described above, the magnitude of external forces and vibrations applied to the second surface can be reduced, and the amount of powder generated from the constituent materials of the insulation sheets by external forces and vibrations on the second surface can be reduced. Therefore, even if the number of pores on the second surface is less than that of the first surface, or if the surface roughness of the second surface is less than that of the first surface, the powder generated from the constituent materials of the insulation sheets on the second surface can be easily captured. Furthermore, since pores and uneven shapes on the surface themselves can cause powder shedding, reducing the number of pores on the second surface or reducing the surface roughness of the second surface can suppress powder shedding caused by pores and uneven shapes.
[0069] Therefore, by arranging insulation sheets, each having different surface properties, in orientations corresponding to the magnitude of external forces and vibrations, powder shedding from the insulation sheets can be suppressed.
[0070] [Applications] The heat-insulating sheet offers an excellent balance between its powder-shedding suppression effect and heat insulation properties, making it suitable for use as a heat-insulating sheet between automotive battery cells. More specifically, by placing the heat-insulating sheet between the cells of an automotive battery, heat transfer between cells can be reduced.
[0071] If the properties of the first surface and the second surface of the thermal insulation sheet are different, as described above, it is preferable to position the thermal insulation sheet so that the stress generated on the first surface, i.e., the surface with a large number of pores and / or a large surface roughness, is greater than the stress generated on the second surface. More specifically, it is preferable that the first surface is positioned closer to the battery cell, closer to the vibration source, or closer to the motor than the second surface. By positioning the thermal insulation sheet in this way, powder shedding from the thermal insulation sheet can be suppressed, and the thermal insulation performance can be further improved.
[0072] (Thermal insulation) A thermal insulation material can be obtained by laminating the thermal insulation sheet with other components. The thermal insulation material may include, for example, a film, an elastic layer, a base layer, and an adhesive layer, in addition to the thermal insulation sheet.
[0073] [Film] The thermal insulation material may further include a film that covers at least one surface of the thermal insulation material sheet in the thickness direction. Covering the surface of the thermal insulation material sheet with a film can further suppress powder shedding from the surface. The film may cover only one surface of the thermal insulation material sheet in the thickness direction. Alternatively, the entire thermal insulation material sheet may be covered and sealed with a film.
[0074] If the properties of the first surface and the second surface of the thermal insulation sheet are different, it is preferable that the film covers at least the first surface, that is, the surface with a large number of pores and / or a large surface roughness, and it is more preferable that the film covers both the first and second surfaces. By covering at least the first surface of the thermal insulation sheet with the film in this way, powder shedding can be suppressed more effectively. From the viewpoint of further enhancing this effect, it is preferable to arrange the thermal insulation sheet in a direction in which the external force and vibration applied to the first surface are greater than the external force and vibration applied to the second surface.
[0075] The materials that make up the film are not particularly limited. For example, the film may be composed of polyimide, polycarbonate, PET, p-phenylene sulfide, polyetherimide, crosslinked polyethylene, flame-retardant chloroprene rubber, polyvinyldenium fluoride, rigid polyvinyl chloride, polybutylene terephthalate, PTFE, PFA, FEP, ETFE, rigid PCV, flame-retardant PET, polystyrene, polyethersulfone, polyamideimide, polyacrylonitrile, polyethylene, polypropylene, polyamide, etc.
[0076] [Elastic Layer] The thermal insulation material may have an elastic layer to relieve stress generated in the thermal insulation sheet and to apply a compressive load to the battery cells. The elastic layer may be provided on one surface in the thickness direction of the thermal insulation sheet, or on both surfaces. If the properties of the first surface and the second surface of the thermal insulation sheet are different, it is preferable that the elastic layer be provided on at least the first surface. In this case, the stress-relieving effect described above can be utilized more effectively. From the viewpoint of further enhancing this effect, it is preferable to arrange the thermal insulation sheet in a direction in which the external force or vibration applied to the first surface is greater than the external force or vibration applied to the second surface.
[0077] As the material constituting the elastic layer, a material having rubber elasticity can be used. For example, the elastic layer may be made of natural rubber or synthetic rubber. The main component of the elastic layer is preferably polyisoprene, hydrogenated polyisoprene, polybutadiene, styrene-butadiene copolymer, isobutylene-isoprene copolymer, ethylene-propylene copolymer, ethylene-propylene-diene ternary copolymer (EPDM), or silicone.
[0078] The shape of the elastic layer can take various forms. Preferably, the elastic layer has a raised ridge on the back surface of the surface in contact with the thermal insulation sheet (for example, the surface in contact with the cells). In this case, the stress generated in the thermal insulation sheet can be further relieved. As a result, powder shedding can be suppressed more effectively.
[0079] [Lamination Method] Various methods can be used to laminate the insulation sheet with other layers. For example, the insulation sheet and other layers can be laminated by applying a slurry containing the constituent materials of the insulation sheet to at least one surface of the layer to be laminated with the insulation sheet, and then drying the slurry. For applying the slurry, known coating devices such as blade coaters, bar coaters, die coaters, comma coaters (registered trademarks), roll coaters, and brushes can be used as needed. The temperature for drying the slurry can be appropriately set from, for example, within the range of 80 to 180°C. The drying time for the slurry can be appropriately set from, for example, within the range of several minutes to several tens of minutes.
[0080] Alternatively, the insulation sheet and other layers may be prepared separately and then laminated together by bonding them via an adhesive layer. Examples of materials that make up the adhesive layer include epoxy resin, phenolic resin, acrylic resin, melamine resin, vinyl acetate resin, silicone resin, urethane resin, polyethylene, and polypropylene.
[0081] Furthermore, for example, the insulation sheet can be sealed by placing it inside a film formed into a bag shape and then closing the opening of the film.
[0082] (Method for manufacturing the thermal insulation sheet) The method for manufacturing the thermal insulation sheet can take various forms. For example, the thermal insulation sheet can be manufactured by compressing a mixture containing silica aerogel particles, infrared shielding particles, fibers, and a suitable dispersion medium, and then drying the dispersion medium. The thermal insulation sheet obtained by this method has a structure in which infrared shielding particles and fibers are held in the gaps between the silica aerogel particles.
[0083] Alternatively, the thermal insulation sheet may be produced by, for example, creating a sheet precursor in which a wet gel containing silica fine particles and infrared shielding particles dispersed in the gel are impregnated into the fibers, and then drying the gel in the sheet precursor to form the thermal insulation sheet. In this case, a thermal insulation sheet with the desired properties can be obtained more easily.
[0084] Various methods can be used to produce the sheet precursor. For example, a sheet precursor can be obtained by impregnating fibers with a dispersion containing a hydrolyzable silane compound and infrared shielding particles, hydrolyzing the silane compound in the dispersion to form a silica microparticle sol, and then gelling the sol. Alternatively, a sheet precursor can be obtained by dispersing infrared shielding particles in a silica microparticle sol, impregnating the fibers with this dispersion, and then gelling the sol. Furthermore, a sheet precursor can be obtained by mixing a wet gel with infrared shielding particles to prepare a dispersion, and then impregnating the fibers with this dispersion. By drying the sheet precursor obtained by these methods, a thermal insulation sheet can be obtained having a structure in which silica aerogel fills the gaps between fibers and infrared shielding particles are dispersed in the silica aerogel. From the viewpoint of more easily obtaining a thermal insulation sheet with desired properties, it is more preferable that the sheet precursor be produced by gelling a silica microparticle sol impregnated into fibers.
[0085] A sol containing silica nanoparticles can be obtained, for example, by preparing a silane solution containing a hydrolyzable silane compound and infrared shielding particles, and then hydrolyzing the silane compound in the silane solution. During hydrolysis, the silane solution may be cooled with ice or stirred as needed. Alternatively, the hydrolysis of the silane compound can be carried out with the fibers impregnated in the silane solution.
[0086] Examples of hydrolyzable silane compounds include methyltrimethoxysilane (MTMS), trimethylmethoxysilane (TMS), dimethyldimethoxysilane (DMS), trimethylethoxysilane, dimethyldiethoxysilane (DMDS), methyltriethoxysilane (MTES), ethyltriethoxysilane (ETES), diethyldiethoxysilane, ethyltriethoxysilane, propyltrimethoxysilane, propyltriethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane (PhTES), hexamethyldisilazane, and hexaethyldisilazane.
[0087] Suitable solvents for the silane solution include, for example, water, methanol, ethanol, isopropanol, ethyl acetate, ethyl acetoethyl acetate, acetone, dichloromethane, and tetrahydrofuran. The solvent for the silane solution is preferably an acidic aqueous solution, and more preferably an aqueous acetic acid solution. The silane solution may also contain hydrolyzable compounds such as urea. Furthermore, the silane solution may optionally contain surfactants such as aliphatic ammonium or alkylbenzylammonium.
[0088] The method for gelling a sol containing silica nanoparticles is not particularly limited. For example, methods such as letting the sol stand in a sealed container, adding a suitable catalyst to the sol, or irradiating the sol with energy rays such as ultraviolet light can be employed. Among these, gelling by letting the sol stand in a sealed container is preferred. When letting the sol stand in a sealed container, the sol can be heated to a temperature of, for example, 50°C or 60°C or higher, as needed.
[0089] A wet gel is formed by gelling the sol. Silica aerogel can be obtained by drying the wet gel and removing the liquid dispersion medium and unreacted products from the gel. Various methods can be used to dry the wet gel, such as supercritical drying, atmospheric pressure drying, freeze-drying, and drying under ambient pressure. When performing supercritical drying, the wet gel is brought into contact with a supercritical fluid such as supercritical carbon dioxide, and the supercritical fluid is exchanged for the liquid dispersion medium, etc. During drying, the sheet precursor may be compressed as needed. This can reduce unevenness in the thickness of the thermal insulation sheet.
[0090] During the manufacturing process of the insulation sheet, voids may be formed as needed by methods such as puncturing. This allows for adjustment of the surface properties of the sheet. The timing of void formation is not particularly limited; voids can be formed at any stage during the manufacturing process of the insulation sheet.
[0091] Furthermore, during the manufacturing process of the thermal insulation sheet, a hydrophobic treatment of the gel may be performed as needed. In the hydrophobic treatment, a trimethylsilylating agent is reacted with the wet gel or silica aerogel. This converts hydrophilic functional groups (e.g., hydroxyl groups) on the silica surface to hydrophobic functional groups (e.g., trimethylsilyl groups). The timing of the hydrophobic treatment can be after the formation of silica fine particles. From the viewpoint of further simplifying the manufacturing process of the thermal insulation sheet, it is preferable to perform the hydrophobic treatment on the wet gel.
[0092] When performing hydrophobic treatment, it is preferable to perform the treatment so that the content of hydrophobic silica relative to the mass of the insulation sheet is 5% by mass or more, and more preferably 7% by mass or more. On the other hand, the content of hydrophobic silica relative to the mass of the insulation sheet is preferably 30% by mass or less, and more preferably 25% by mass or less. Furthermore, the mass ratio of hydrophobic silica to non-hydrophobic silica (hydrophobic / non-hydrophobic) is preferably 0.1 or more, and more preferably 0.2 or more. On the other hand, the mass ratio of hydrophobic silica to non-hydrophobic silica is preferably 1.5 or less, more preferably 1.2 or less, and even more preferably 1.0 or less.
[0093] Experimental examples of the aforementioned heat-insulating sheet and its manufacturing method are described below.
[0094] (Experimental Example 1) The thermal insulation sheet in this example is produced by creating a sheet precursor in which a wet gel containing silica fine particles and infrared shielding particles dispersed in the gel are impregnated into the fibers, and then drying the gel in the sheet precursor. The method for producing the thermal insulation sheet in this example is described in detail below.
[0095] First, 1.00 g of cetyltrimethylammonium bromide (also known as hexadecyltrimethylammonium bromide: manufactured by Nacalai Tesque Co., Ltd., hereinafter abbreviated as "CTAB"), a cationic surfactant, was dissolved in 10.00 g of acetic acid aqueous solution with a concentration of 0.01 mol / L. To this acidic aqueous solution, 0.50 g of urea (manufactured by Nacalai Tesque Co., Ltd.), a hydrolyzable compound, was added and dissolved.
[0096] Subsequently, 5.0 mL of methyltrimethoxysilane (LS-530, manufactured by Shin-Etsu Chemical Co., Ltd., specific gravity: 0.95, hereinafter abbreviated as "MTMS"), a hydrolyzable silane compound, was added to the acidic aqueous solution. The acidic aqueous solution after the addition of MTMS was stirred and mixed under ice cooling for 30 minutes to hydrolyze the MTMS and form silica nanoparticles in the aqueous solution. Thus, a sol of silica nanoparticles was prepared. 0.7 g of silicon carbide particles with adjusted particle size was added to this sol to prepare a dispersion in which silicon carbide particles were dispersed in the sol. The dispersion was then allowed to stand for 3 hours in a 60°C atmosphere, causing a portion of the sol in the dispersion to gel.
[0097] The silicon carbide particles used in this example are obtained by classifying a mixed powder of silicon carbide powder with a particle size of #400 and silicon carbide powder with a particle size of #6000. For classifying the mixed powder, known classifiers such as centrifugal classifiers (e.g., "Turboplex®" manufactured by Hosokawa Micron Corporation) or airflow classifiers (e.g., "Elbowjet®" manufactured by Nippon Steel Mining Co., Ltd.) can be used.
[0098] Next, a glass fiber nonwoven fabric (Nitigura Mat MNA-300-1000-30m, manufactured by Nippon Glass Fiber Industry Co., Ltd., 3 mm thick) placed on a 50 μm thick polypropylene film was impregnated with the dispersion, and then sealed together with the polypropylene film in a sealed container. After that, it was left to stand in the sealed container for a further 96 hours to completely gel the sol in the nonwoven fabric and to mature the gel. As a result, a sheet precursor containing a wet gel was obtained.
[0099] After removing the sheet precursor obtained in this manner from the sealed container, the water in the sheet precursor was replaced with 2-propanol. More specifically, the sheet precursor was immersed in 2-propanol at 60°C for 24 hours, and then the insulating sheet was removed from the 2-propanol. After replacing the 2-propanol, solvent replacement was performed by immersing it in 2-propanol at 60°C for 48 hours.
[0100] Next, the gel in the sheet precursor was dried using the following method to obtain a silica aerogel. First, the sheet precursor, after solvent replacement, was placed in a 400 mL autoclave filled with 2-propanol. After closing the lid of the autoclave, the pressure inside the autoclave was increased to 882 N / cm using liquefied carbon dioxide. 2 (approx. 90 kgf / cm 2 The autoclave was pressurized until the following pressure was reached. This pressure was maintained for 1.5 hours to perform the first liquid phase displacement. After the first liquid phase displacement was completed, the supply of liquefied carbon dioxide was stopped. The autoclave was then left to stand for 17.5 hours while maintaining its sealed state, allowing the liquefied carbon dioxide to diffuse into the gel.
[0101] Next, using liquefied carbon dioxide, the pressure inside the autoclave was increased to 882 N / cm². 2 (approx. 90 kgf / cm 2 The autoclave was pressurized again until the pressure reached 0. This pressure was maintained for one hour to perform the second liquid phase displacement. After the second liquid phase displacement was completed, the supply of liquefied carbon dioxide was stopped. The autoclave was then left to stand for five hours while maintaining its sealed state, allowing the liquefied carbon dioxide to diffuse into the gel.
[0102] Next, using liquefied carbon dioxide, the pressure inside the autoclave was increased to 882 N / cm². 2 (approx. 90 kgf / cm 2 The autoclave was pressurized again until the pressure reached 0.75 hours, and the third liquid phase displacement was performed. After the third liquid phase displacement was completed, the supply of liquefied carbon dioxide was stopped. Then, while keeping the autoclave sealed, the temperature inside the autoclave was raised from room temperature to 80°C over 1.5 hours.
[0103] After the temperature inside the autoclave reaches 80°C, 4.9 N / cm 2 ・min) (0.5kgf / (cm 2 The pressure inside the autoclave was reduced to atmospheric pressure at a rate of min)). After the pressure inside the autoclave reached atmospheric pressure, the autoclave was cooled to room temperature over a period of 2 hours.
[0104] The thermal insulation sheet of Experimental Example 1 was obtained using the method described above. The thickness of the thermal insulation sheet of Experimental Example 1 is 3 mm. Of the surfaces of the thermal insulation sheet of Experimental Example 1 in the thickness direction, the surface roughness of the surface not in contact with the film was greater than the surface roughness of the surface in contact with the film. Therefore, in the thermal insulation sheet of this example, the surface not in contact with the film becomes the first surface, and the surface in contact with the film becomes the second surface.
[0105] (Experimental Examples 2-8) The method for preparing the insulating sheets in these experimental examples is generally the same as the method for preparing the insulating sheet in Experimental Example 1, except that the particle size distribution of silicon carbide particles was changed.
[0106] (Ratio of First to Third Particles) Tables 1 and 2 show the ratio of the number of first, second, and third particles present in the cross-sectional photographs of the thermal insulation sheets for Experimental Examples 1 to 8. In Tables 1 and 2, "third particle" refers to a particle with a major axis exceeding 1 μm and less than 5 μm in the aforementioned photographs. The method for measuring the major axis of each particle and the method for calculating the ratio of the number of each particle are as described above.
[0107] (Evaluation of powder fall suppression effect) A thermal insulation sheet was cut to create small square pieces with sides of 5 cm. Both sides of these pieces were covered with a PET film with a thickness of 50 μm, and then one of the PET films was bonded to a rubber sheet to create a sample. The rubber sheet had a structure in which multiple ridged units (in cross-section, the base has a width of 10.86 mm, a height of approximately 7 mm, and consists of a convex part that extends in the width direction with a 60° taper and a concave part around it, with a total width of approximately 20.5 mm including the concave and convex parts) were connected, and the concave parts of the ridged units were positioned to face the film.
[0108] Next, the sample was attached to the jig of the vibration machine. The jig consists of a pair of metal plates and a powder tray. The sample was placed upright between the metal plates so that the surface in the thickness direction of the insulation sheet was approximately vertical, and then the sample was fixed in place while being compressed to 50%.
[0109] After mounting the sample to the jig as described above, a vibration test was performed on the sample by applying vibrations 800,000 times under conditions of acceleration 3G and frequency 5Hz. After the vibration test was completed, the rubber sheet was removed from the sample. Then, the film was peeled off the surface of the insulation sheet, and the powder that fell from the insulation sheet was collected.
[0110] Next, the mass ratio of silicon carbide particles contained in the powder that fell from the insulation sheet was calculated using the following method. First, a predetermined mass of silica aerogel, silicon carbide particles, and a mixture of silica aerogel and silicon carbide particles in a mass ratio of 1:1 were prepared, and their volumes were measured. Next, the volumes of silica aerogel, silicon carbide particles, and their mixture were plotted on a graph with the mass ratio of silicon carbide particles on the vertical axis and volume on the horizontal axis. Then, a calibration curve was created by approximating these three plotted points with a straight line.
[0111] Next, a sample of the same mass as the silica aerogel used to create the calibration curve was taken from the powder that fell from the insulation sheet, and the volume of the sample was measured. Then, based on the calibration curve described above, the volume of the sample was converted to the mass ratio of silicon carbide particles in the sample.
[0112] The powder shedding suppression effect was evaluated based on the mass ratio of silicon carbide particles in the sample obtained as described above. In the "Powder Shedding Suppression Effect" column of Tables 1 and 2, the symbol "A" was entered when the mass ratio of silicon carbide particles was 1 / 5 or less, "B" when it was greater than 1 / 5 but 1 / 4 or less, "C" when it was greater than 1 / 4 but 1 / 3 or less, "D" when it was greater than 1 / 3 but 1 / 2 or less, and "E" when it was greater than 1 / 2. The symbol "-" was entered in the "Powder Shedding Suppression Effect" column for Experimental Example 6, which was the standard.
[0113]
[0114]
[0115] As shown in Table 1, the cross-sectional photographs of the thermal insulation sheets in Experimental Examples 1 to 5 show the presence of both first particles, which consist of infrared shielding particles with a major axis of 0.5 μm to 1 μm, and second particles, which consist of infrared shielding particles with a major axis of 5 μm to 10 μm. Therefore, these thermal insulation sheets were able to suppress powder shedding more effectively than the thermal insulation sheet in Experimental Example 6 (see Table 2), which did not contain the second particles. Furthermore, since the thermal insulation sheets in Experimental Examples 1 to 5 are less prone to powder shedding than the thermal insulation sheet in Experimental Example 6, the state in which infrared shielding particles are retained within the thermal insulation sheet can be maintained for a long period of time. Consequently, the thermal insulation sheets in Experimental Examples 1 to 5 can maintain good thermal insulation performance for a long period of time.
[0116] On the other hand, as shown in Table 2, the insulation sheet in Experimental Example 7, like that in Experimental Example 6, does not contain the second particle. Therefore, the insulation sheet in Experimental Example 7 was prone to powder shedding, similar to the insulation sheet in Experimental Example 6.
[0117] The insulation sheet in Experimental Example 8 does not contain the first particle. Therefore, the insulation sheet in Experimental Example 8 was more prone to powder shedding than the insulation sheets in Experimental Examples 1 to 5. On the other hand, a comparison between Experimental Examples 6 and 7 and Experimental Example 8 shows that the insulation sheet in Experimental Example 8 was able to suppress powder shedding more effectively than Experimental Examples 6 and 7. Possible reasons for this include the fact that the second particle, which has a relatively large particle size, is more easily captured by the fibers and retained inside the insulation sheet even if it detaches from the silica aerogel.
[0118] Although the embodiments of the thermal insulation sheet and its manufacturing method have been described above based on experimental examples, the specific embodiments of the thermal insulation sheet and its manufacturing method according to the present invention are not limited to those of the experimental examples, and the configuration can be appropriately modified without impairing the spirit of the present invention.
[0119] For example, the thermal insulation sheet may take the following forms [1-1] to [1-8].
[0120] [1-1] An insulating sheet used for insulating the space between battery cells of an electric vehicle, comprising silica aerogel, fibers, and infrared shielding particles, wherein a photograph of the cross-section of the insulating sheet shows first particles consisting of infrared shielding particles having a major axis of 0.5 μm to 1 μm, and second particles consisting of infrared shielding particles having a major axis of 5 μm to 10 μm.
[0121] [1-2] The thermal insulation sheet according to [1-1], wherein the ratio of the number of first particles to the number of second particles present in the photograph is first particles:second particles = 1:4 to 4:1. [1-3] The thermal insulation sheet according to [1-1] or [1-2], wherein in the photograph, the sum of the ratio of the number of first particles to the ratio of the number of second particles to the number of infrared shielding particles having a major axis of 0.5 μm or more is 5% or more and 30% or less.
[0122] [1-4] An electric vehicle battery cell insulation sheet according to any one of [1-1] to [1-3], wherein in the photograph, the number of infrared shielding particles present within a range of 13 μm from the surface of the fiber is greater than the number of infrared shielding particles present outside that range. [1-5] An insulation sheet according to any one of [1-1] to [1-4], wherein 70% or more of the first particles and second particles in the photograph are present within a range of 13 μm from the surface of the fiber.
[0123] [1-6] The thermal insulation sheet according to any one of [1-1] to [1-5], wherein the average diameter of the fibers in the photograph is 0.6 times or more and 2 times or less the average major diameter of the second particle. [1-7] The thermal insulation sheet according to any one of [1-1] to [1-6], wherein the silica aerogel is filled in the gaps between the fibers and the infrared shielding particles are dispersed in the silica aerogel. [1-8] The thermal insulation sheet according to any one of [1-1] to [1-7], wherein the infrared shielding particles include silicon carbide particles.
[0124] Furthermore, the method for manufacturing the thermal insulation sheet may take the form described in [1-9] below. A method for manufacturing a thermal insulation sheet according to any one of [1-9] to [1-8], comprising: preparing a cloth composed of the fibers; impregnating the cloth with a silica sol containing silica fine particles, infrared shielding particles, and a liquid dispersion medium for dispersing them to produce a sheet precursor; and forming the thermal insulation sheet by removing the liquid dispersion medium from the sheet precursor.
[0125] Furthermore, the thermal insulation sheet may take the following forms [2-1] to [2-7].
[0126] [2-1] An insulating sheet used for insulating between battery cells of an electric vehicle, comprising silica aerogel, fibers, and infrared shielding particles, wherein a photograph of the cross-section of the insulating sheet shows third particles consisting of infrared shielding particles having a major axis of more than 1 μm and less than 5 μm, and second particles consisting of infrared shielding particles having a major axis of 5 μm or more and 10 μm or less.
[0127] [2-2] The thermal insulation sheet according to [2-1], wherein in the photograph, the ratio of the number of second particles to the number of infrared shielding particles having a major axis of 0.5 μm or more is 5% or more and 30% or less. [2-3] The thermal insulation sheet for electric vehicle battery cells according to [2-1] or [2-2], wherein in the photograph, the number of infrared shielding particles present within 13 μm from the surface of the fiber is greater than the number of infrared shielding particles present outside that range. [2-4] The thermal insulation sheet according to any one of [2-1] to [2-3], wherein 70% or more of the second particles and third particles in the photograph are present within 13 μm from the surface of the fiber.
[0128] [2-5] The thermal insulation sheet according to any one of [2-1] to [2-4], wherein the average diameter of the fibers in the photograph is 0.6 times or more and 2 times or less the average major diameter of the second particle. [2-6] The thermal insulation sheet according to any one of [2-1] to [2-5], wherein the silica aerogel is filled in the gaps between the fibers and the infrared shielding particles are dispersed in the silica aerogel. [2-7] The thermal insulation sheet according to any one of [2-1] to [2-6], wherein the infrared shielding particles include silicon carbide particles.
Claims
1. An insulating sheet for use in insulating the space between battery cells of an electric vehicle, comprising silica aerogel, fibers, and infrared shielding particles, wherein a photograph of the cross-section of the insulating sheet shows first particles consisting of infrared shielding particles having a major axis of 0.5 μm to 1 μm, and second particles consisting of infrared shielding particles having a major axis of 5 μm to 10 μm.
2. The battery cell insulation sheet for electric vehicles according to claim 1, wherein the ratio of the number of first particles to the number of second particles present in the photograph is first particles:second particles = 1:4 to 4:
1.
3. The electric vehicle battery cell insulation sheet according to claim 1 or 2, wherein in the photograph, the sum of the ratio of the number of first particles to the number of second particles among the infrared shielding particles having a major axis of 0.5 μm or more is 5% or more and 30% or less.
4. The electric vehicle battery cell insulation sheet according to claim 1 or 2, wherein in the photograph, the number of infrared shielding particles present within 13 μm of the surface of the fiber is greater than the number of infrared shielding particles present outside that range.
5. The electric vehicle battery cell insulation sheet according to claim 1 or 2, wherein 70% or more of the infrared shielding particles in the photograph are located within a range of 13 μm from the surface of the fiber.
6. The electric vehicle battery cell insulation sheet according to claim 1 or 2, wherein the average diameter of the fibers in the photograph is 0.6 times or more and 2 times or less the average major diameter of the second particle.
7. The electric vehicle battery cell insulation sheet according to claim 1 or 2, wherein the silica aerogel is filled in the gaps between the fibers and the infrared shielding particles are dispersed in the silica aerogel.
8. The electric vehicle battery cell insulation sheet according to claim 1 or 2, wherein the infrared shielding particles include silicon carbide particles.
9. A method for manufacturing an inter-cell thermal insulation sheet for electric vehicles according to claim 1 or 2, comprising: preparing a sheet precursor in which a wet gel containing silica fine particles and infrared shielding particles dispersed in the gel are impregnated into the fibers; and forming the thermal insulation sheet by drying the gel in the sheet precursor.