Insulation sheet between battery cells for electric vehicles

Abstract

The present invention aims to provide an inter-cell insulation sheet for electric vehicle batteries containing silica aerogel that can prevent powder shedding. [Solution] The present invention provides an electric vehicle battery cell insulation sheet comprising silica aerogel and fibers, having a plurality of voids on one surface and the other surface in the thickness direction, and the ratio of the number of voids on one surface to the number of voids on the other surface being 1.3 or more.

Description

[Technical Field]

[0001] This invention relates to an insulating sheet for use between battery cells in electric vehicles. [Background technology]

[0002] Silica aerogel is composed of multiple linked silica nanoparticles forming a framework, with pores between the framework that are smaller than the mean free path of air. This fine, porous structure results in low thermal conductivity, making it useful as a component material for insulation in automotive parts, building materials for houses, industrial equipment, and other applications.

[0003] Insulating materials containing silica aerogel often have low surface mechanical strength, and powder shedding due to impact is a problem. For example, when used as insulating material for automobile batteries, the pressure caused by the thermal expansion of the battery can lead to powder shedding, potentially degrading the performance of electronic devices. As a solution, for example, Patent Documents 1 and 2 describe that powder shedding can be suppressed by incorporating fibrous mineral fibers and hot melt powder into a silica aerogel sheet, or by sealing the surface with a film. Furthermore, Patent Document 3 describes that powder shedding can be suppressed by providing an insulating elastic member containing an elastic layer on one side of the silica aerogel sheet and a cover layer on the other side, or by covering the sheet and the entire sheet with an outer covering. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2024-97328 [Patent Document 2] Japanese Patent Publication No. 2023-132944 [Patent Document 3] Japanese Patent Publication No. 2023-35097 [Overview of the project] [Problems that the invention aims to solve]

[0005] Among the conventional technologies described above, the film-forming technology does not aim to suppress the shedding of aerogel (hereinafter referred to as powder shedding) when stress is applied to the silica aerogel sheet, as the silica aerogel, which was physically and chemically bonded to the fibers, peels off. Furthermore, according to the technology of Patent Document 2, the hardened layer formed by the hot melt powder may reduce the heat insulation performance of the sheet.

[0006] On the sheet surface, areas subjected to stress caused by battery expansion, and areas close to vibration sources, tend to experience powder shedding due to the transmission of stress and vibration. When aerogel powder shedding occurs, the concentration of aerogel within the insulation sheet becomes uneven, potentially preventing the insulation performance from being fully realized in certain areas.

[0007] The present invention aims to provide an inter-cell insulation sheet for electric vehicle batteries containing silica aerogel that can prevent powder shedding. [Means for solving the problem]

[0008] To solve the above problems, the inventors focused on the surface properties of the thermal insulation sheet. Specifically, by adjusting the surface properties of two surfaces when the sheet is viewed from the horizontal direction, such as the number (distribution) of pores, the shape of the surface roughness, and the ratio thereof between the two surfaces, to a predetermined range, one surface was formed in which the number (distribution) of pores is relatively large or the surface roughness is relatively large, and the other surface in which the number (distribution) of pores is relatively small or the surface roughness is relatively small. As a result, it was confirmed that on one side, even if the silica aerogel that was physically and chemically bonded to the fibers peeled off when stress, vibration, etc. were applied to the silica aerogel sheet, the large number (distribution) of pores or the relatively large surface roughness made it easy to capture the peeled silica aerogel, thus suppressing powder falling to the lower surface. Furthermore, on the other hand, since the stress and vibration applied to the silica aerogel sheet are minimal, and considering that the silica aerogel, which was physically and chemically bonded to the fibers, is less likely to peel off, it was confirmed that the number (distribution) of pores that cause powder shedding can be reduced, or the surface roughness can be made relatively smaller. This suppresses powder shedding throughout the entire sheet, thus preventing a decrease in thermal insulation performance. Furthermore, by having one side with a relatively large number (distribution) of pores or a relatively large surface roughness have a predetermined shape and / or by forming them with fibers, adhesion to films and the like can be improved. This suppresses delamination between the film and the silica aerogel sheet when stress, vibration, etc. are applied to the silica aerogel sheet, and as a result, powder shedding to the lower part can be suppressed. As a result, we found that the sheet's insulation performance could be maintained at a high level.

[0009] The present invention provides the following [1] to

[12] . [1] Contains silica aerogel and fibers, It has multiple voids on one surface and the other surface in the thickness direction, An electric vehicle battery cell insulation sheet in which the ratio of the number of voids on one side to the number of voids on the other side is 1.3 or greater. [2] The number of voids on one of the surfaces is 25,000 to 225,000 per square meter. 2 The sheet described in [1]. [3] The number of voids on the other surface is 10,000 to 50,000 per square meter. 2 The sheet described in [1] or [2]. [4] A sheet according to any one of items [1] to [3], wherein the difference between the surface roughness Sa of one surface and the surface roughness of the other surface is 10 μm or more. [5] A sheet according to any one of items [1] to [4], wherein the difference between the surface roughness Sa of one surface and the surface roughness of the other surface is 30 μm or more. [6] The sheet according to any one of items [1] to [5], wherein the surface roughness Sa of one of the surfaces is 60 μm or more. 〔7〕The sheet according to any one of 〔1〕~〔6〕, wherein the surface roughness Sa of the one surface is 80 to 100 μm. 〔8〕The sheet according to any one of 〔1〕~〔7〕, wherein the surface roughness Sa of the other surface is less than 60 μm. 〔9〕The sheet according to any one of 〔1〕~〔8〕, wherein the surface roughness Sa of the other surface is 30 to 50 μm. 〔10〕The sheet according to any one of 〔1〕~〔9〕, further comprising a film covering at least a part of the one surface and the other surface. 〔11〕The sheet according to any one of 〔1〕~〔9〕, further comprising an elastic body layer laminated on at least a part of the one surface and the other surface. 〔12〕The sheet according to any one of 〔1〕~〔9〕, further comprising a film covering the one surface and the other surface, and an elastic body layer laminated on the one surface or the other surface via the film.

Advantages of the Invention

[0010] According to the present invention, it is possible to provide a battery heat insulating material sheet for an electric vehicle that can prevent powder shedding and exhibit good heat insulating properties. That is, according to the present invention, it is possible to suppress the occurrence of powder shedding corresponding to the difference in stress on both sides of the sheet, so that the heat insulating performance of the sheet can be improved as a whole, and it is useful as a heat insulating material sheet between battery cells for an electric vehicle.

Brief Description of the Drawings

[0011] [Figure 1] FIG. 1 is a diagram showing an example of an image when one surface (surface A) of the sheet of the present invention is binarized. [Figure 2] FIG. 2 is a diagram showing an example of an image when the other surface (surface B) of the sheet of the present invention is binarized.

Embodiments for Carrying Out the Invention

[0012] Next, embodiments of the present invention will be described in detail. However, the present invention is not limited to this embodiment.

[0013] In this specification, when "X~Y" (where X and Y are any numbers) is written, unless otherwise specified, it means "X or greater and Y or less," and also includes the meanings of "preferably greater than X" or "preferably less than Y."

[0014] In this specification, unless otherwise specified, the upper or lower limits of numerical ranges described in stages may be arbitrarily combined with the upper or lower limits of numerical ranges in other stages. Furthermore, in numerical ranges described in this specification, the upper or lower limits of those ranges may be replaced with the values ​​shown in the examples.

[0015] In this specification, "X and / or Y (where X and Y are any combination)" means at least one of X and Y, and can mean X only, Y only, or X and Y, unless otherwise specified.

[0016] [1. Materials for insulation sheets] The insulation sheet is a sheet containing silica aerogel and fibers.

[0017] [1.1 Silica Aerogel] In this specification, silica aerogel is a structure formed by the aggregation of primary silica nanoparticles to form secondary particles, with a framework mainly composed of these particles and pores between them.

[0018] -Average particle size of primary particles- The diameter of the silica nanoparticles (primary particles) that form the backbone of silica aerogel is typically around 2 to 5 nm.

[0019] In this specification, the average particle size is the median diameter (D50) determined from the volume-based particle size distribution measured by laser diffraction and scattering.

[0020] -Pore size- The pores in silica aerogel are typically mostly mesopores. Mesopores have a diameter of 50 nm or less, which is smaller than the mean free path of air. Therefore, air convection is restricted and heat transfer is inhibited, resulting in thermal insulation performance. There is no particular lower limit, but 10 nm or more is preferred.

[0021] The shape of silica aerogel is not particularly limited; it can be spherical, irregularly shaped, or as a lump. For example, in the case of a spherical shape, it is easier to achieve close packing, allowing for a larger amount to be used, which greatly enhances the effect of improving thermal insulation.

[0022] -Average particle diameter of secondary particles- The average particle size of the particles (mainly secondary particles) constituting silica aerogel is usually 1 μm or larger, preferably 10 μm or larger. Larger particle sizes result in smaller surface area and larger pore volume, which can improve the thermal insulation effect. There is no particular upper limit, but for example, it is 200 μm or less. The average particle size can be measured by electron microscopy.

[0023] The insulation sheet may contain one type of silica aerogel, or it may contain two or more different types of silica aerogel, preferably two or more silica aerogels with different particle sizes. This allows the smaller diameter silica aerogels to fill the gaps between the larger diameter silica aerogels, increasing the filling volume and further improving the insulation performance.

[0024] Silica aerogel may be formed by impregnating fibers with a liquid coating solution (including a slurry) containing a binder, as described later, and then drying it. Alternatively, silica aerogel may be formed by impregnating fibers with its precursor sol, then gelling it by heating, and finally drying it.

[0025] Silica aerogel may be synthesized as needed, or a commercially available product may be used.

[0026] [1.2 Fibers (Reinforcement Fibers)] Examples of fibers include inorganic fibers such as glass fibers, ceramic fibers, quartz fibers, alumina fibers, silica fibers, silicon carbide fibers, boron fibers, and metal fibers (e.g., aluminum, iron); and organic 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-phenylene benzbisoxazole) (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. The fibers may also be natural fibers such as wood fibers, silk, hemp, and wool fibers. Of these, fibers having strength and / or heat resistance are preferred, inorganic fibers are more preferred, and glass fibers are even more preferred. The fibers are discontinuous fibers; bundles of fibers; and fabrics such as nonwoven or woven fabrics, or a combination thereof. The fibers contained in the heat insulating sheet preferably include fabric, more preferably nonwoven fabric. This allows for further improvement of mechanical strength. By using fabrics that have been perforated or treated to create a napped surface (preferably nonwoven fabric, more preferably glass nonwoven fabric) as fibers, the porosity ratio and surface roughness of the sheet surface can be easily adjusted.

[0027] [1.3 Optional components] The insulating material may contain optional components other than silica aerogel and fibers. Examples of optional components include binders and thickeners.

[0028] -binder- By adding a binder, degradation in high-temperature environments can be reduced and crack formation can be suppressed. The binder can be either an inorganic or organic material. Inorganic materials include talc, carbon black, kaolinite, montmorillonite, mica, silica (e.g., precipitated silica, gel silica, fused silica), wollastonite, magnesium silicate, titania, metal carbides (e.g., silicon carbide, 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, and slaked lime. Combinations of these materials are also possible. From these, appropriate materials can be selected as needed. For example, silica is preferred because it is easily compatible with silica aerogel, inexpensive, and readily available. Furthermore, hydraulic materials are preferable because they can form a high-strength insulating layer by reacting with water, a solvent commonly used in the production of silica aerogels, and filling the gaps between silica particles to create a binder; they are also inexpensive and readily available. Additionally, materials with a large specific surface area and hardness may be selected.

[0029] The organic material is preferably an aqueous binder (a binder that is soluble or dispersible in water (capable of forming an emulsion)), and may be a substance that imparts hydrophilic groups to the silica aerogel, or a so-called surfactant.

[0030] The glass transition temperature (Tg) of the organic material is preferably -5°C or lower, and more preferably -20°C or lower. This can result in good adhesion to silica aerogel, improve the flexibility of the sheet, and suppress cracking.

[0031] Examples of organic binders include resins such as acrylic resin, urethane resin, and mixtures of acrylic and urethane resin; and rubbers such as styrene-butadiene rubber (SBR), nitrile rubber, silicone rubber, urethane rubber, and acrylic rubber, with urethane resin and SBR being preferred. This improves the flexibility of the sheet, enabling the creation of a flexible sheet. When using a binder, a crosslinking agent may also be used in combination. This allows the binder to be crosslinked, further improving the strength of the sheet.

[0032] -Thickener- By using a thickening agent, the dispersibility of silica aerogel in a solvent (usually water) can be improved, thereby enhancing its processability. Furthermore, it is possible to impart flexibility to the sheet and suppress cracking. 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.

[0033] -Flame retardant- The flame retardancy of the sheet can be enhanced by using a flame retardant. Examples of flame retardants include halogen-based, phosphorus-based, and metal hydroxide-based flame retardants. Phosphorus-based flame retardants (e.g., ammonium polyphosphate, red phosphorus, phosphate ester) are preferred, water-insoluble phosphorus-based flame retardants are more preferred, and ammonium polyphosphate is even more preferred.

[0034] The optional components are not limited to those listed above. For example, one or more selected from preservatives, colorants, infrared shielding particles, and radiation absorbing / reflecting materials may be used.

[0035] [1.4 Composition] -Silica aerogel content- The silica aerogel content in the thermal insulation sheet is typically 10% by mass or more, preferably 20% by mass or more, and more preferably 30% by mass or more, based on 100% by mass of the total mass of the thermal insulation sheet. This allows for better thermal insulation. The upper limit is typically 60% by mass or less, preferably 50% by mass or less, and more preferably 40% by mass or less. This suppresses a decrease in mechanical strength and reduces so-called powder shedding.

[0036] -Fiber content- The fiber content in the insulation sheet is typically 20% by mass or more, preferably 30% by mass or more, based on 100% of the total mass of the insulation sheet. This can further improve the mechanical strength. The upper limit is typically 70% by mass or less, preferably 60% by mass or less. This allows the sheet to exhibit mechanical strength commensurate with its fiber content.

[0037] [2. Insulation sheet] The insulation sheet is preferably made of the above materials and satisfies one or more of the following shapes and physical properties.

[0038] [2.1 Sheet Thickness] The insulation sheet is usually flat. The thickness of the sheet is not particularly limited, but for example, it can be 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 sheet's strength to be maintained within an appropriate thickness range. The lower limit is usually 0.1 mm or more, preferably 0.5 mm or more, or 1 mm or more. The thickness is preferably approximately uniform, and the thickness variation may be, for example, 5% or less, 4% or less, or 3% or less.

[0039] [2.2 Surface Shape] The insulation sheet has irregularities, voids (openings), etc., on its surface (one side and the other side when viewed from the horizontal direction). There are usually multiple voids, and they may be randomly located. The shape of the voids is not particularly limited and may be circular, polygonal, or irregular. The irregularities are usually not uniform and may be unevenly distributed.

[0040] The properties of the sheet surface differ between the two surfaces of the sheet, i.e., one side and the other side when viewed from the thickness direction of the sheet. As a result, for example, on one side (hereinafter referred to as surface A), where the number (distribution) of pores is relatively large or the surface roughness is relatively large, even if the silica aerogel that was physically and chemically bonded to the fibers delaminates when stress, vibration, etc. is applied to the silica aerogel sheet, the large number (distribution) of pores or the large surface roughness makes it easy to capture the delaminate silica aerogel, thus suppressing powder falling to the lower surface. Furthermore, since surface A has a predetermined shape and / or is formed of fibers, adhesion to films, etc. can be enhanced, so when stress, vibration, etc. is applied to the silica aerogel sheet, delamination of the film, etc. and silica aerogel is suppressed, and as a result, powder falling to the lower surface can be suppressed.

[0041] On the other hand, on the other surface (hereinafter referred to as surface B), where the number (distribution) of pores is relatively small, or the surface roughness is relatively small, the stress and vibrations applied to the silica aerogel sheet are small. Therefore, considering that the silica aerogel that was physically and chemically bonded to the fibers is less likely to peel off, the number (distribution) of pores that cause powder shedding, or the size of the surface roughness, can be reduced.

[0042] As explained above, the different surface properties of the sheets help to suppress powder shedding throughout the sheet, thus preventing a decrease in thermal insulation performance.

[0043] -Number of voids- The number of voids is different between surfaces A and B. The ratio of the number of voids on surface A to the number of voids on surface B is preferably 1.3 or more, 2.0 or more, more preferably 2.2 or more, still more preferably 2.7 or more, and 4.0 or more. The upper limit is preferably 9.0 or less, more preferably 8.0 or less, and still more preferably 7.0 or less. Therefore, the preferable range of the ratio is 1.3 or more, more preferably 1.3 to 9.0, 1.3 to 8.0, 1.3 to 7.0, 2.0 to 9.0, 2.0 to 8.0, 2.0 to 7.0, 2.2 to 9.0, 2.2 to 8.0, 2.2 to 7.0, 2.7 to 9.0, 2.7 to 8.0, 2.7 to 7.0, 4.0 to 9.0, 4.0 to 8.0, 4.0 to 7.0. Thereby, surface B can better prevent powder shedding and exhibit better heat insulation performance, and surface A can better prevent powder shedding and improve adhesion, thereby better exhibiting heat insulation performance.

[0044] The number of voids on surface A is preferably 25,000 per m 2 or more, more preferably 35,000 per m 2 or more, still more preferably 50,000 per m 2 or more. Thereby, the powder falling off from the sheet surface can be captured, and powder shedding can be suppressed. The upper limit is preferably 225,000 per m 2 or less, more preferably 200,000 per m 2 or less, still more preferably 150,000 per m 2 or less. Thereby, the shedding of the voids themselves from the sheet surface can be suppressed, and powder shedding can be suppressed. Therefore, it is preferably 25,000 to 225,000 per m 2 more preferably 35,000 to 200,000 per m 2 still more preferably 50,000 to 150,000 per m 2 or less.

[0045] The number of voids on surface B is preferably 10,000 per m 2 or more, more preferably 20,000 per m 2 or more. Thereby, the powder falling off from the sheet surface can be captured, and powder shedding can be suppressed. The upper limit is preferably 50,000 per m 2 or less, more preferably 30,000 per m2 The following is the result. This suppresses the shedding of the voids themselves from the sheet surface and reduces powder fallout. Therefore, a density of 10,000 to 50,000 voids / m is preferred. 2 more preferably 20,000 to 30,000 pieces / m 2 That is the case.

[0046] The number of voids can be counted using the following method: Cut the sheet into 15cm x 15cm pieces and photograph five arbitrary locations on the sheet surface using a digital camera (e.g., Canon PowerShot SX720 HS). Using image processing software (e.g., ImageJ), extract a 2cm x 2cm (200 pixels x 200 pixels) image from the captured images. Use ImageJ's binarization function to binarize areas with a brightness of 125 or less as voids (for example, Figures 1 and 2 show examples of binarized surfaces A and B, respectively). Next, use ImageJ's particle analysis function to remove particles smaller than 4 pixels² as noise and count them as voids. In this way, calculate the average value of the five locations and use that as the number of voids. Furthermore, voids may be covered by glass fibers or other materials, and voids that penetrate from the surface to the back surface are also included. In addition, the diameter of voids counted under the above conditions is larger than 0.2 μm.

[0047] The degree of unevenness on the sheet surface can be expressed by the surface roughness Sa (arithmetic mean height). The lower limit of the surface roughness of surface A is preferably 60 μm or more, more preferably 65 μm or more, and even more preferably 70 μm or more, 80 μm or more, or 90 μm or more. This allows for the capture of powder that falls off the sheet surface and suppresses powder shedding.

[0048] The upper limit of the surface roughness of surface A is preferably 130 μm or less, more preferably 120 μm or less, even more preferably 110 μm or less, and 100 μm or less. This suppresses the shedding of the voids themselves from the sheet surface and suppresses powder shedding. Therefore, the surface roughness of surface A is preferably 60 to 130 μm, more preferably 65 to 110 μm, even more preferably 70 to 100 μm, 80 to 100 μm, and 90 to 100 μm.

[0049] The lower limit of the surface roughness of surface B is preferably 20 μm or more, 25 μm or more, more preferably 30 μm or more, and even more preferably 40 μm or more. This allows for the capture of powder that falls off the sheet surface and suppresses powder shedding. The upper limit of the surface roughness of surface B is preferably less than 60 μm, more preferably 55 μm or less, and even more preferably 50 μm or less. This suppresses the shedding of the voids themselves from the sheet surface and suppresses powder shedding. Therefore, the surface roughness of surface B is preferably 20 to less than 60 μm, 25 to less than 60 μm, more preferably 30 to less than 60 μm, and even more preferably 30 to 50 μm, 40 to 50 μm, and 40 to 45 μm.

[0050] The surface roughness of surface A is preferably greater than the surface roughness of surface B, and the difference between the two (AB) is usually 10 μm or more, preferably 20 μm or more, more preferably 30 μm or more, or 40 μm or more. The upper limit is not particularly limited, but for example, it is 100 μm or less, 90 μm or less, or 80 μm or less.

[0051] The ratio of the surface roughness of surface A to the surface roughness of surface B (A / B) is preferably 1.3 or higher, more preferably 1.5 or higher, even more preferably 2.3 or higher, 2.7 or higher, or 4.5 or higher. The upper limit is usually 7.0 or lower, preferably 6.5 or lower, and more preferably 6.0 or lower. Therefore, preferably 1.3 or higher, more preferably 1.3 to 7.0, 1.3 to 7.0, 1.3 to 6.5, 1.3 to 6.0, 1.5 to 7.0, 1.5 to 6.5, 1.5 to 6.0, 2.3 to 7.0, 2.3 to 6.5, 2.3 to 6.0, 2.7 to 7.0, 2.7 to 6.5, 2.7 to 6.0, 4.5 to 7.0, 4.5 to 6.5, or 4.5 to 6.0.

[0052] Surface roughness Sa is the arithmetic mean height, and is the average of values ​​measured at any five locations in accordance with ISO 25178. The surface roughness Sa of surfaces A and B can be measured by observation using a microscope (for example, Keyence's "One-Shot 3D Shape Measuring Machine VR-6000"). A 15cm x 15cm measurement sheet is prepared, and with 0.13kg weights placed at both ends at 3cm intervals when viewed from the front to flatten the sheet surface, the value calculated using the surface roughness mode in the analysis program (program name: KEYENCE VR-6000 Analysis Application) of the image taken at 12x magnification in the central area (18mm x 24mm) can be used as the surface roughness Sa.

[0053] [3. Method for manufacturing insulation sheets] One method for manufacturing an insulating sheet is to dissolve a silica material in a solvent to prepare a reaction solution (sol), then gel it, remove impurities such as the solvent and unreacted substances from the resulting wet gel, and then coat and dry it in a frame.

[0054] Examples of silica materials include methyltrimethoxysilane (MTMS), trimethylmethoxysilane (TMS), dimethyldimethoxysilane (DMS), trimethylethoxysilane, dimethyldiethoxysilane (DMDS), methyltriethoxysilane (MTES), ethyltriethoxysilane (ETES), diethyldiethoxysilane, ethyltriethoxysilane, propyltrimethoxysilane, propyltriethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane (PhTES), hexamethyldisilazane, and hexaethyldisilazane.

[0055] Suitable solvents include, for example, water, methanol, ethanol, isopropanol, ethyl acetate, ethyl acetoethyl acetate, acetone, dichloromethane, and tetrahydrofuran. Of these, acidic aqueous solutions are preferred, and aqueous acetic acid solutions are more preferred. The reaction solution usually contains a hydrolyzable compound (e.g., urea) and may optionally contain a surfactant (e.g., aliphatic ammonium, alkylbenzylammonium). When preparing the sol, ice cooling and stirring may be performed as needed. Drying is usually performed using supercritical drying, but atmospheric pressure drying is also acceptable. Supercritical drying involves repeatedly exchanging the solvent (e.g., 2-propanol, ethanol, or other alcohols) with a supercritical fluid (e.g., supercritical carbon dioxide) one or more times. Pressurization may be applied during drying as needed. This allows for uniformity of sheet thickness. The timing for adding the fibers is preferably during the gelation stage from the preparation of the reaction solution (for example, impregnating the nonwoven fabric of fibers into the reaction solution once or twice or more) and / or the drying stage, and it is more preferable to impregnate the fibers into the reaction solution (sol). The method of gelation is not particularly limited and can be carried out by, for example, letting the reaction solution stand (for example, letting it stand in a sealed device, preferably under heating in a sealed device (e.g., 50°C or higher, 60°C or higher)), adding a catalyst, or irradiating with ultraviolet light, etc., with standing being preferred. The porosity ratio and surface roughness of the sheet surface can also be adjusted by the gelation conditions and the fiber addition conditions (number of impregnations). In this specification, the term "silica aerogel" includes not only silica aerogel in the narrow sense (silica aerogel obtained by supercritical drying) but also silica aerogel obtained by other drying methods (for example, xerogel (produced by drying at atmospheric pressure), cryogel (produced by freeze-drying), and ambigel (produced by drying under ambient pressure)). At any stage of manufacturing, voids can be formed, for example, by methods such as perforation. This allows for adjustment of the void ratio and surface roughness of the sheet surface.

[0056] Furthermore, hydrophobic treatment (for example, conversion of silica surface functional groups (e.g., hydroxyl groups) to hydrophobic trimethylsilyl groups) may be performed at any stage, and it is preferable to perform it before the drying process. Hydrophobic treatment can be performed by adding a hydrophobic agent such as a trimethylsilylating agent. When hydrophobic treatment is performed, the content of hydrophobic silica relative to the total aerosilica gel sheet obtained after the treatment is preferably 5% by mass or more, more preferably 7% by weight or more, with an upper limit of preferably 30% by weight or less, and more preferably 25% by weight or less. In addition, the weight ratio of hydrophobic silica to non-hydrophobic silica (hydrophobic / non-hydrophobic) is preferably 0.1 or more, more preferably 0.2 or more, with an upper limit of preferably 1.5 or less, more preferably 1.2 or less, and even more preferably 1.0 or less.

[0057] [4. Other layers] The insulation sheet may form a laminate (insulation material) together with other components. Other components include films, elastic layers, and adhesive layers.

[0058] [4.1 Film] The thermal insulation material may further have a film that covers (seals) at least one surface (preferably only surface A, or both surfaces A and B). This further suppresses powder shedding. It is preferable to cover surface A, or to cover both surfaces. This more efficiently suppresses powder shedding. This effect can be further enhanced by positioning sheet surface A on the side of the cells that receives greater stress.

[0059] Examples of polymer films include films made from polyimide, polycarbonate, PET, p-phenylene sulfide, polyetherimide, crosslinked polyethylene, flame-retardant chloroprene rubber, polyvinyldenide fluoride, rigid polyvinyl chloride, polybutylene terephthalate, PTFE, PFA, FEP, ETFE, rigid PCV, flame-retardant PET, polystyrene, polyethersulfone, polyamideimide, polyacrylonitrile, polyethylene, polypropylene, polyamide, and the like.

[0060] [4.2 Adhesive layer] If other components are provided with the insulation material, an adhesive layer may be further included. The adhesive layer can be made of a material capable of bonding the insulation sheet to the other components. Examples of materials for the adhesive layer include epoxy resin, phenolic resin, acrylic resin, melamine resin, vinyl acetate resin, silicone resin, urethane resin, polyethylene, and polypropylene.

[0061] [4.3 Elastic material layer] The elastic layer is a layer that relieves stress generated in the insulation sheet and applies a constant compressive load to the battery cells. In particular, covering surface A can further enhance the stress relief effect. This effect can be further exhibited by positioning surface A, which is covered with the elastic layer, on the side of the cell that receives greater stress. The material of the elastic layer may be natural rubber or synthetic rubber, and is preferably mainly composed of polyisoprene, hydrogenated polyisoprene, polybutadiene, styrene-butadiene copolymer, isobutylene-isoprene copolymer, ethylene-propylene copolymer, ethylene-propylene-diene ternary copolymer (EPDM), or silicone. The shape of the elastic body is not particularly limited, and the shape of its surface is not particularly limited, but it is preferable to have protrusions such as irregularities on the surface that does not come into contact with the insulation sheet (for example, the surface that comes into contact with the cells). This can further enhance the powder fall prevention effect by relieving stress on the sheet.

[0062] [4.4 Lamination Method] The method of laminating other layers onto the sheet is not particularly limited and includes methods of laminating other layers required for the insulation sheet. The lamination process can be, for example, by applying an adhesive to at least one surface of the insulation sheet (using equipment and tools such as a blade coater, bar coater, die coater, comma coater®, roll coater, or brush as needed), drying (for example, at 80 to 180°C for several minutes to several tens of minutes), or by bonding pre-prepared other layers via an adhesive or adhesive layer. In the case of a film, for example, a method of attaching the film to the sheet surface with an adhesive, or a method of housing it in a bag-shaped film can be used.

[0063] [5. Uses of insulation sheets] The insulation sheet offers a good balance of both thermal insulation and thermal insulation properties. Therefore, it can be used as an insulation sheet between automotive battery cells. When used between automotive battery cells, the sheet can be placed between the cells.

[0064] It is preferable to position surface A of the sheet facing the side that experiences greater stress, such as the side where the battery expands and generates stress, the vibration source side, or the side with greater motor vibration. This effectively suppresses powder shedding while maintaining adhesion, while surface B maintains its heat insulation and adhesion properties, thus providing overall heat insulation performance. [Examples]

[0065] The present invention will be explained with reference to examples. The following examples are merely illustrative and do not limit the present invention.

[0066] Example 1 (Preparation of glass fiber reinforced aerogel sheet) As a cationic surfactant, 1.00 g of cetyltrimethylammonium bromide (also known as hexadecyltrimethylammonium bromide: manufactured by Nacalai Tesque Co., Ltd., hereinafter abbreviated as "CTAB") was dissolved in 10.00 g of a 0.01 mol / L aqueous acetic acid solution, which is an acidic aqueous solution. Then, 0.50 g of urea (manufactured by Nacalai Tesque Co., Ltd.) was added as a hydrolyzable compound and dissolved. To this acidic aqueous solution, 5.0 mL of methyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., LS-530 (specific gravity: 0.95), hereinafter abbreviated as "MTMS") was added as a silica material. The mixture was then stirred and mixed under ice cooling for 30 minutes to allow the hydrolysis reaction of MTMS to occur and produce a sol. The sol was then impregnated into a perforated glass fiber nonwoven fabric (manufactured by Nippon Glass Fiber Industry Co., Ltd., Nitigura Mat, MNA-300-1000-30m, thickness 3 mm) placed on a polypropylene film (thickness 50 μm). The mixture was allowed to stand in a sealed container at 60°C for 3 hours to gel. The gel was then allowed to mature by standing in the sealed container for an additional 96 hours. After removing the mixture from the sealed container, it was immersed in 2-propanol for solvent replacement. This process was repeated twice: the first time at 60°C for 24 hours, and the second time at 60°C for 48 hours with fresh 2-propanol.

[0067] Next, the aerogel sheets were supercritically dried under the following conditions. A 400 mL autoclave was filled with 2-propanol, and the aerogel sheet, whose solvent had been replaced, was placed inside. The lid was closed, and liquefied carbon dioxide was introduced to create a pressure of approximately 882 N / cm². 2 (approx. 90kgf / cm 2 While maintaining the condition, the first liquid phase replacement operation was performed (time required: 1.5 hours).

[0068] After the first liquid phase displacement was completed, the valve was closed and the pressure was maintained while liquefied carbon dioxide was diffused into the gel over a period of 17.5 hours. Subsequently, similar to the first liquid phase displacement, the pressure was set to approximately 882 N / cm². 2 (approx. 90kgf / cm 2 While maintaining the state, a second liquid phase displacement was performed (time required: 1 hour). After the second liquid phase displacement was completed, the valve was closed and the pressure was maintained, as in the first case, and liquefied carbon dioxide was diffused into the gel over a period of 5 hours. Subsequently, similar to the first liquid phase displacement, approximately 882 N / cm² was used. 2 (approx. 90kgf / cm 2 While maintaining the condition, a third liquid phase displacement was performed in the same manner (time required: 0.75 hours).

[0069] Once the third liquid phase displacement was complete, the valve was closed and the autoclave was heated from room temperature to 80°C over 1.5 hours. After reaching 80°C, the pressure was 4.9 N / cm². 2 min(0.5kgf / cm) 2 The pressure was reduced at a rate of (min). After reaching atmospheric pressure, the autoclave was cooled to room temperature over a period of two hours. Afterward, the autoclave was opened, the aerogel sheet was removed, and the supercritical drying process was completed. This allowed us to produce the glass fiber reinforced aerogel sheet (3 mm thick) of Example 1. The side in contact with the film is the B-side.

[0070] Example 2 (Preparation of glass fiber reinforced aerogel sheet 2) The glass fiber reinforced aerogel sheet of Example 2 was prepared in the same manner as in Example 1, except that the generated sol was heated at 60°C for 0.5 hours, impregnated into a glass fiber nonwoven fabric, and allowed to stand in a sealed container at 60°C for 2.5 hours to gel.

[0071] Example 3 (Preparation of glass fiber reinforced aerogel sheet 3) The glass fiber reinforced aerogel sheet of Example 3 was prepared in the same manner as in Example 1, except that the generated sol was heated at 60°C for 1 hour, then impregnated into a glass fiber nonwoven fabric, and allowed to stand in a sealed container at 60°C for 2 hours to gel.

[0072] Example 4 (Preparation of glass fiber reinforced aerogel sheet 4) A glass fiber reinforced aerogel sheet of Example 4 was prepared in the same manner as in Example 2, except that a nonwoven fabric impregnated with sol was sandwiched between polypropylene films, squeegeeed from side A, and then the polypropylene film on side A was peeled off.

[0073] Example 5 (Preparation of glass fiber reinforced aerogel sheet 5) A glass fiber reinforced aerogel sheet of Example 5 was prepared in the same manner as in Example 2, except that holes were punched into the glass fiber nonwoven fabric from the B-side.

[0074] Example 6 The glass fiber reinforced aerogel sheet of Example 6 was prepared in the same manner as in Example 1, except that the nonwoven fabric impregnated with sol was left to stand in a sealed container at 60°C for 1 hour, then removed from the sealed container and impregnated with sol again.

[0075] Example 7 A glass fiber reinforced aerogel sheet of Example 7 was prepared in the same manner as in Example 6, except that a nonwoven fabric with a napped surface (A) was used.

[0076] Example 8 A glass fiber reinforced aerogel sheet of Example 8 was prepared in the same manner as in Example 1, except that a nonwoven fabric impregnated with sol was sandwiched between polypropylene films, squeegeeed from side A, and then the polypropylene film on side A was peeled off.

[0077] Example 9 Except for using a nonwoven fabric with a napped surface on side B, the glass fiber reinforced aerogel sheet of Example 9 was prepared in the same manner as in Example 8.

[0078] Example 10 The glass fiber reinforced aerogel sheet of Example 10 was prepared in the same manner as in Example 3, except that the nonwoven fabric impregnated with sol was left to stand in a sealed container at 60°C for 1 hour, then removed from the sealed container and impregnated with sol again.

[0079] Comparative Example 1 A glass fiber reinforced aerogel sheet of Comparative Example 1 was prepared in the same manner as in Example 1, except that the generated sol was heated at 60°C for 2 hours, then impregnated into a glass fiber nonwoven fabric, and allowed to stand in a sealed container at 60°C for 1 hour to gel.

[0080] Comparative Example 2 A glass fiber reinforced aerogel sheet for Comparative Example 2 was prepared in the same manner as in Example 1, except that the generated sol was impregnated into a glass fiber nonwoven fabric (Nitto Boseki, Chopped Strand Mat, MC-600A, 1 mm thick) with the B side fluffed up to a thickness of 3 mm, and then left to gel in a sealed container at 60°C for 3 hours.

[0081] Comparative Example 3 The glass fiber reinforced aerogel sheet of Comparative Example 3 was prepared in the same manner as in Example 4, except that the generated sol was impregnated into a glass fiber nonwoven fabric (Nitto Boseki, Chopped Strand Mat, MC-600A, 1 mm thick) layered to a thickness of 3 mm, sandwiched between polypropylene films, squeegeeed from side A, the film on side A was peeled off to impregnate with the sol, and then sandwiched again between polypropylene films.

[0082] Reference example 1 A glass fiber-reinforced aerogel sheet for Reference Example 1 was prepared in the same manner as in Comparative Example 1, except that the generated sol was fuzzed on side A.

[0083] Reference example 2 A glass fiber reinforced aerogel sheet for Reference Example 2 was prepared in the same manner as in Example 2, except that the generated sol was impregnated into a layer of glass fiber nonwoven fabric (Nitto Boseki, Chopped Strand Mat, MC-600A, 1 mm thick) to a thickness of 3 mm.

[0084] [Testing methods for physical properties] - Evaluation method for "powder shedding properties" - (1) A measurement sheet (prepared by cutting to a surface area of 5×5 cm) was coated with a PET film (thickness 50 μm) and adhered to a rubber sheet to prepare a sample. The rubber sheet had a structure in which a plurality of ridge unit (in cross-section, having a base width of 10.86 mm, a height of about 7 mm, a 60° taper, and consisting of a convex portion extending in the width direction and a concave portion around it, with a width including the concave and convex portions of about 20.5 mm) were connected. The measurement sheet and the rubber sheet were arranged such that the concave portion of the ridge was on the A-side surface. In a vibrator equipped with a jig consisting of a pair of metal plates and a powder receiver, the sample was sandwiched (vertically) between the metal plates so that the surface of the sample was in a substantially vertical direction, pressurized and fixed to a state of 50% compression, and given vibrations of 3G / 15Hz×800,000 times. (2) Thereafter, with the sample standing in a substantially horizontal direction, the film was peeled off, and the amount of aerogel drop on each of the A and B surfaces was visually confirmed. It was judged which of the evaluation criteria in (3) the amount of aerogel drop on surface A corresponded to that of surface A in Comparative Example 1, and on surface B corresponded to that of surface B in Comparative Example 2. (3) Evaluation criteria (evaluated with surface A of Comparative Example 1 and surface B of Comparative Example 2 as the respective reference) For those where the amount of aerogel drop is 1 / 3 or less with respect to the reference... A For those where the amount of aerogel drop exceeds 1 / 3 and is 1 / 2 or less with respect to the reference... B For those where the amount of aerogel drop exceeds 1 / 2 with respect to the reference... C

[0085] - Method for evaluating "adhesion"- Samples with adhesive tapes (manufactured by Sekisui Chemical Co., Ltd., thickness 0.15 mm, green) attached to the A and B surfaces of the heat insulation material sheet were prepared. A 180° peel test (conforming to JIS Z 0237:2009, tensile speed 300 mm / min) was performed at the interface between the heat insulation material sheet and the adhesive tape using a tabletop tensile tester ("AGS-1kNG" manufactured by Minebea), and the peel force was measured and taken as the interfacial adhesion force between the layers. <Reference for A surface> Those with a tensile load of 5 N / 25 mm or more were rated as having good adhesion "A", those with a tensile load of 0.5 - 5 N / 25 mm were rated as having adhesion "B", and those with a tensile load of less than 0.5 N / 25 mm were rated as having poor adhesion "C". <Standard for the B side> Those with a tensile load of 0.5 N / 25 mm or more were rated as having good adhesion "A", and those with a tensile load of less than 0.5 N / 25 mm were rated as having poor adhesion "C".

[0086] - Evaluation method for "Overall evaluation"- The overall evaluation was carried out based on the following criteria. When all are A... ◎ When there are A and B... 〇 When there is even one C... ×

[0087] [Test method for the surface properties of the sheet] - Surface roughness- The surface roughness Sa was measured by the following method. The sheet was cut into a size of 15 cm × 15 cm, and with 0.13 kg weights placed at both ends at an interval of 3 cm when viewed from the front direction to flatten the sheet surface. In the central area (18 mm × 24 mm) of the sheet measurement surface, the average value of the values calculated for any 5 locations in the surface roughness mode of the analysis program (program name: KEYENCE VR-6000 analysis application) of the image taken at 12 times magnification using a microscope (Keyence's "One-shot 3D shape measuring machine VR-6000") was defined as the surface roughness Sa.

[0088] - Number of pores per unit area- The number of voids was measured using the following method: The sheet was cut into 15cm x 15cm sections, and five arbitrary locations on the sheet surface were photographed using a digital camera (Canon PowerShot SX720 HS). Using image processing software (ImageJ), a 2cm x 2cm (200 pixels x 200 pixels) image was extracted from the captured images. Using ImageJ's binarization function, areas with a brightness of 125 or less were binarized as voids. Next, using ImageJ's particle analysis function, particles smaller than 4 pixels² were removed as noise and counted as the number of voids. The average value for the five locations was then calculated. Furthermore, voids may be covered by glass fibers or other materials, and voids that penetrate from the surface to the back surface are also included. In addition, the diameter of voids counted under the above conditions is larger than 0.2 μm.

[0089] [Table 1]

[0090] [Table 2]

[0091] [Table 3]

[0092] [Footnotes for the table] In the table, the number of voids refers to the number of voids observed in a 2cm × 2cm (200 pixels × 200 pixels) area, and 1m 2 The number of items per unit (indicated in parentheses) is also shown.

[0093] Compared to Comparative Examples 1 and 2, which had a void count of less than 1.3 and received an overall evaluation of ×, Examples 1 to 10, which had a void count of 1.3 or more, all received an overall evaluation of ○ or ◎. In addition, Reference Examples 1 and 2, which had a surface roughness difference of 30 or more, also received an overall evaluation of ○.

[0094] The following observations were made regarding the number of pores on surface A. Comparing Examples 1 and 2, the powder shedding performance of surface A in Example 1 was rated B, while in Example 2, where surface A had a relatively small number of pores, it was rated A. Furthermore, comparing Examples 3 and 10 with Example 2, the powder shedding performance in Examples 3 and 10 was rated B, while in Example 2, where surface A had a relatively large number of pores, it was rated A. These results indicate that a smaller number of pores on surface A tends to suppress the shedding of the pores themselves, while a larger number of pores tends to trap powder more easily.

[0095] The following observations were made regarding the number of voids on surface B. Comparing Examples 4 and 2, the powder shedding performance of surface B in Example 4 was rated B, while in Example 2, where surface B had a relatively large number of voids, it was rated A. Similarly, comparing Examples 5 and 10 with Example 2, the powder shedding performance of surface B in Examples 5 and 10 was rated B, while in Example 2, where surface B had a relatively large number of voids, it was rated A. These results indicate that, similar to surface A, a smaller number of voids on surface B tends to suppress the shedding of the voids themselves, while a larger number of voids tends to trap powder more easily.

[0096] The surface roughness of surface A was examined as follows. Comparing Example 6 and Example 2, the powder shedding performance of surface A in Example 6 was rated B, while in Example 2, where surface A had a relatively large surface roughness, it was rated A. Furthermore, comparing Example 7 and Example 2, the powder shedding performance in Example 7 was rated B, while in Example 2, where surface A had a relatively small surface roughness, it was rated A. These results indicate that a larger surface roughness of surface A tends to trap powder with voids, while a smaller surface roughness tends to suppress the shedding of the voids themselves.

[0097] The surface roughness of surface B was examined as follows. Comparing Example 8 and Example 2, the powder shedding performance of surface B in Example 8 was rated B, while in Example 2, where surface B had a relatively large surface roughness, it was rated A. Similarly, comparing Example 9 and Example 2, the powder shedding performance in Example 9 was rated B, while in Example 2, where surface A had a relatively small surface roughness, it was rated A. These results indicate that, similar to surface A, a larger surface roughness of surface B tends to trap powder more effectively due to the voids, while a smaller surface roughness tends to suppress the shedding of the voids themselves.

[0098] The above results demonstrate that the thermal insulation sheet of the present invention exhibits good thermal insulation properties and is useful as thermal insulation material between automotive battery cells.

Claims

1. Contains silica aerogel and fibers, It has multiple voids on one surface and the other surface in the thickness direction, An electric vehicle battery cell insulation sheet in which the ratio of the number of voids on one side to the number of voids on the other side is 1.3 or greater.

2. The number of voids on one of the aforementioned surfaces is 25,000 to 225,000 per square meter. ２ The sheet according to claim 1.

3. The number of voids on the other surface is 10,000 to 50,000 per square meter. ２ The sheet according to claim 1 or 2.

4. The sheet according to claim 1 or 2, wherein the difference between the surface roughness of one surface and the surface roughness Sa of the other surface is 10 μm or more.

5. The sheet according to claim 1 or 2, wherein the difference between the surface roughness of one surface and the surface roughness Sa of the other surface is 30 μm or more.

6. The sheet according to claim 1 or 2, wherein the surface roughness Sa of one of the aforementioned surfaces is 60 μm or more.

7. The sheet according to claim 1 or 2, wherein the surface roughness Sa of one of the aforementioned surfaces is 80 to 100 μm.

8. The sheet according to claim 1 or 2, wherein the surface roughness Sa of the other surface is less than 60 μm.

9. The sheet according to claim 1 or 2, wherein the surface roughness Sa of the other surface is 30 to 50 μm.

10. The sheet according to claim 1 or 2, further comprising a film covering at least a portion of one of the aforementioned surfaces and the other surface.

11. The sheet according to claim 1 or 2, further comprising an elastic layer laminated on at least a portion of one surface and the other surface.

12. The sheet according to claim 1 or 2, further comprising a film covering one surface and the other surface, and an elastic layer laminated on the one surface or the other surface via the film.

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