Heat insulating material for battery packs and method for producing same

Abstract

This heat insulating material for battery packs includes a pressure-molded body (1) of a composition containing a powder of a porous structure, in which a plurality of primary particles are connected to form skeletal structures and pores are formed between the skeletal structures. The porous structure is produced by a sol-gel reaction of a solution having two or more kinds of silane compounds having mutually different numbers of siloxane bonds, and the powder of the porous structure is composed of particles (10) that are different in shape and size and are obtained by crushing the porous structure. The content of the powder of the porous structure in the composition is 65 mass% or more when the solid content in the composition is 100 mass %, and the porosity of the pressure-molded body (1) is 20% or less.

Description

Heat insulating material for battery pack and manufacturing method thereof

[0001] The present disclosure relates to a thermal insulator disposed between adjacent battery cells in a battery pack housing a plurality of battery cells, and particularly to a thermal insulator using a porous structure such as aerogel.

[0002] Hybrid vehicles and electric vehicles are equipped with battery packs containing multiple battery cells. In the battery pack, a battery module formed by stacking multiple battery cells is housed in a housing and secured by fastening members on both sides in the stacking direction. Insulating materials are placed between adjacent battery cells to suppress heat transfer and prevent thermal runaway when the battery cells generate abnormal heat. Battery cells expand and contract as they are charged and discharged. Therefore, it is desirable for the insulating materials placed between the battery cells to deform in response to the expansion and contraction of the battery cells and maintain their insulating properties. More specifically, when the battery cells are charged and expand, the resulting compressive force reduces the thickness of the insulating material. At the same time, a reaction force of at least a certain value must be generated to bias the battery cells and prevent the insulating material from shifting position. Furthermore, when the battery cells are discharged and contract (returning to their original thickness), the insulating material must also restore its original thickness.

[0003] Silica aerogel, which has low thermal conductivity, is known as a material for heat insulating materials. For example, Patent Document 1 describes an aerogel powder made of an aerogel, which is a hydrolysis condensation product of a silane compound, as an aerogel powder with excellent flexibility and fracture resistance against compressive force. The raw silane compound satisfies the following conditions: 0≦Qx≦70, 30≦Tx≦100, and 0≦Dx<30 (where Qx+Tx+Dx=100), where Qx, Tx, and Dx are the mass percentages of a tetrafunctional silane compound, a trifunctional silane compound, and a bifunctional silane compound, respectively. Patent Document 2 describes a heat insulating material having a porous structure in which a plurality of primary particles are connected to form a skeleton and pores are formed between the skeletons, and a binder, in which the volume fraction of voids present between the porous structures is 10% or more and 55% or less.

[0004] JP 2021-165387 A JP 2020-122544 A

[0005] The above-mentioned Patent Document 1 describes the use of a specific silane compound as a raw material for the purpose of improving the flexibility of the aerogel powder itself and its resistance to breakage during processing. However, while paragraph

[0109] of the same document lists applications of aerogel powder, such as filling it into insulating windows and insulating building materials, Patent Document 1 does not describe the use of aerogel powder pressure-molded to form a battery pack as an insulating material. Therefore, Patent Document 1 does not consider the deformability of a "pressure-molded body" of aerogel powder during compression, the generated reaction force, or the ability to return to its original shape after unloading. Furthermore, there is no mention of the porosity of the "pressure-molded body."

[0006] On the other hand, the insulating material described in Patent Document 2 is manufactured by applying a coating material in which a porous structure is dispersed in a binder liquid to a substrate after adjusting the gas state in the coating material and then drying it. In this manufacturing method, voids are intentionally created between the porous structures to reduce shrinkage distortion during drying and suppress the occurrence of cracks. The insulating material described in Patent Document 2 is not a "pressure-molded body" produced by pressurizing a powder of a porous structure. The volume fraction of voids specified in Patent Document 2 was specified for the purpose of reducing shrinkage distortion during drying of the coating material, but does not satisfy the characteristics required of an insulating material for a battery pack.

[0007] The present disclosure has been made in consideration of the above-described circumstances, and aims to provide an insulating material for a battery pack, which is formed by using a pressure-molded body of a composition having a powder of a porous structure, and which has excellent deformability against compression and recovery properties after unloading, and a method for producing the same.

[0008] (1) In order to solve the above problems, the insulating material for a battery pack of the present disclosure (hereinafter, sometimes simply referred to as the "insulating material of the present disclosure") is an insulating material for a battery pack comprising a pressure-molded body of a composition having a powder of a porous structure in which a plurality of primary particles are linked to form a skeleton and the skeleton has pores between the skeletons, the porous structure being produced by a sol-gel reaction of a solution containing two or more types of silane compounds with different numbers of siloxane bonds, the powder of the porous structure being composed of particles of different shapes and sizes obtained by pulverizing the porous structure, the content of the powder of the porous structure in the composition being 65% by mass or more when the solid content of the composition is 100% by mass, and the porosity of the pressure-molded body being 20% ​​or less.

[0009] For example, if the powder of the porous structure is composed of spherical particles of similar size, the particles in the pressed compact of the powder will be in regular contact with each other, mainly at points. This increases the rigidity of the filled particles, increasing the repulsive force against external compression forces, resulting in extremely small changes in thickness when compressed. In contrast, the powder of the porous structure used in the heat insulating material of the present disclosure is obtained by pulverizing the porous structure and is composed of particles of different shapes and sizes. In such pressed compacts of powder composed of particles of different shapes and sizes, the particles contact each other not only at points but also at lines or surfaces, resulting in no regular arrangement. In this case, when compressed from the outside, the particles move in a misaligned manner, resulting in a relatively large amount of deformation in the thickness direction. Furthermore, if voids are present in the pressed compact, the particles are more likely to move, resulting in even greater deformation.

[0010] The porous structure is also manufactured by a sol-gel reaction of a solution containing two or more silane compounds with different numbers of siloxane bonds. In this specification, the siloxane bond in a silane compound refers to a bond between a silicon atom (Si) and an oxygen atom (O) (Si—O bond). The number of siloxane bonds refers to the number of oxygen atoms bonded to one silicon atom, and silane compounds are divided into four types, with siloxane bond numbers ranging from 1 to 4. Based on the finding that the number of siloxane bonds in a silane compound affects the elasticity of the manufactured porous structure, the present inventors have realized a porous structure with the desired elasticity, more specifically, a porous structure that deforms while generating a desired reaction force when compressed and has the ability to return to its original shape after unloading, by mixing and using multiple silane compounds with different numbers of siloxane bonds. The obtained porous structure is then pulverized, and a powder composed of particles of different shapes and sizes is used to realize an insulating material that can deform even when a battery cell expands slightly during charging. As such, the insulating material disclosed herein exhibits excellent deformability against compression and excellent recovery after unloading. According to the heat insulating material of the present disclosure, even if the battery cells expand and contract, displacement and the like are unlikely to occur, and high heat insulating properties can be maintained.

[0011] (2) In the above configuration, the average particle diameter of the powder of the porous structure may be 30 μm or more and 150 μm or less. With this configuration, it is easy to achieve a desired packing state of the particles in the porous structure.

[0012] (3) In any of the above configurations, the particles of the porous structure may be randomly stacked in the pressure-molded body. With this configuration, the particles of the porous structure contact each other at points, lines, or surfaces, and are likely to move in a displaced manner when compressed from the outside. This increases the amount of deformation in the thickness direction.

[0013] (4) In any of the above configurations, the silane compounds may be a tetrafunctional silane compound and a trifunctional silane compound, or a tetrafunctional silane compound and a monofunctional silane compound. In this specification, a tetrafunctional silane compound refers to a silane compound with four siloxane bonds. Similarly, a trifunctional silane compound refers to a silane compound with three siloxane bonds, a bifunctional silane compound refers to a silane compound with two siloxane bonds, and a monofunctional silane compound refers to a silane compound with one siloxane bond. This configuration is suitable for producing a porous structure having desired elasticity.

[0014] (5) In the above configuration (4), when the silane compound is the tetrafunctional silane compound and the trifunctional silane compound, the content of the trifunctional silane compound may be 50% by mass or more, where the total amount of the silane compounds is 100% by mass. Increasing the content of the trifunctional silane compound can increase the elastic deformation of the resulting porous structure.

[0015] (6) In the above configuration (4), when the silane compound is the tetrafunctional silane compound and the monofunctional silane compound, the content of the monofunctional silane compound may be 10% by mass or more and less than 40% by mass, where the total amount of the silane compounds is 100% by mass. If the content of the monofunctional silane compound is less than 10% by mass, the elastic deformation amount of the resulting porous structure will be small, and if it is 40% by mass or more, the skeletal strength of the porous structure will be reduced.

[0016] (7) In any of the above configurations, the composition may contain one or more selected from infrared shielding particles, inorganic fibers, and dispersants. According to this configuration, the pressure-molded body (thermal insulating material) contains one or more selected from infrared shielding particles, inorganic fibers, and dispersants.

[0017] Insulating materials using porous structures can achieve high thermal insulation by suppressing mainly conduction and convection, among the three forms of heat transfer (conduction, convection, and radiation). Radiation is a phenomenon in which heat is transferred by electromagnetic waves, and the higher the temperature, the greater the radiant energy released. Therefore, in high-temperature environments, radiation is the primary cause of heat transfer. Therefore, by using infrared-shielding particles that can suppress heat transfer due to radiation, heat transfer due to radiation can be suppressed in addition to conduction and convection, achieving high thermal insulation not only at room temperature but also at high temperatures of 500°C or higher. When the pressed body contains inorganic fibers, the mechanical strength of the pressed body is improved and the detachment of particles from the porous structure can be suppressed. Porous structures are also poorly compatible with water and difficult to disperse. Therefore, when water is used during the pulverization process, adding an amphiphilic dispersant can improve the dispersibility of the porous structure. As a result, the porous structure can be pulverized to the desired state. In this case, the composition contains a powder of the porous structure and a dispersant, and is pressure-molded as is to form a pressed body.

[0018] (8) In any of the above configurations, the porous structure may be made of silica aerogel. Silica aerogel has a good balance between the size of its skeleton and the size of its pores, and exhibits excellent heat insulating properties.

[0019] (9) In any of the above configurations, the composition may be configured to not contain a binder that binds the constituent components of the pressure-molded body. This configuration makes it easier to achieve a desired particle packing state and porosity of the porous structure in the pressure-molded body.

[0020] (10) The method for producing an insulating material for a battery pack according to the present disclosure is one form of the method for producing an insulating material for a battery pack having any of the above configurations, and is characterized by comprising: a first step of pulverizing a composition comprising the porous structure produced by a sol-gel reaction of a solution containing two or more types of silane compounds having different numbers of siloxane bonds, a dispersant, and water to produce a powder of the porous structure composed of particles of different shapes and sizes; and a second step of placing the pulverized composition in a mold and pressure-molding it.

[0021] In the manufacturing method of the insulating material for a battery pack of the present disclosure (hereinafter, sometimes simply referred to as the "manufacturing method of the present disclosure"), a porous structure is pulverized using a dispersant (first step). This improves the dispersibility of the porous structure, and the porous structure can be pulverized to a desired state to produce a powder composed of particles of different shapes and sizes. In addition, in the second step, by adjusting the conditions during pressure molding, the porosity of the pressure-molded body can be reduced to 20% or less. The manufacturing method of the present disclosure allows the insulating material for a battery pack of the present disclosure to be easily manufactured.

[0022] (11) In the configuration of (10) above, the composition in the first step may contain one or more types selected from infrared-shielding particles and inorganic fibers. In this configuration, when one or more types selected from infrared-shielding particles and inorganic fibers (hereinafter sometimes referred to as "infrared-shielding particles, etc.") are incorporated into a pressure-molded body (thermal insulating material), the composition is blended with a porous structure, etc. to form a composition, which is then pulverized. Because the infrared-shielding particles and inorganic fibers are harder than the porous structure, they are hardly pulverized under the conditions for pulverizing the porous structure. According to this configuration, the infrared-shielding particles, etc. can be added to the porous structure and dispersed during the pulverization process, eliminating the need for separate mixing and dispersion, and reducing the number of work steps. This can increase production efficiency and improve the quality of the thermal insulating material.

[0023] According to this configuration, a pressure-molded body containing infrared-shielding particles and the like is produced. As with the configuration (7) above, when the pressure-molded body contains infrared-shielding particles, heat transfer by radiation in addition to conduction and convection can be suppressed, and high thermal insulation can be achieved at temperatures ranging from room temperature to high temperatures of 500°C or higher. When the pressure-molded body contains inorganic fibers, the mechanical strength of the pressure-molded body is improved, and particle detachment from the porous structure can be suppressed.

[0024] The insulating material for a battery pack disclosed herein has excellent deformability against compression and recovery after unloading. Therefore, even when the battery cell expands and contracts, it is less likely to shift position, and high insulating properties can be maintained. According to the manufacturing method for the insulating material for a battery pack disclosed herein, the dispersibility of the porous structure in the pulverization process can be improved, making it possible to easily produce a powder of the porous structure composed of particles of different shapes and sizes. This makes it possible to easily manufacture the insulating material for a battery pack disclosed herein.

[0025] 1 is a schematic diagram showing the state of particle packing in the porous structure of the heat insulating material of the present disclosure. 2 is a cross-sectional SEM photograph of the sample of Example 1 (magnification: 200 times).

[0026] The insulating material for a battery pack and a method for manufacturing the same according to the present disclosure are described in detail below. The insulating material according to the present disclosure is not limited to the following forms, and can be embodied in various forms including modifications and improvements that can be made by those skilled in the art without departing from the gist of the present disclosure.

[0027] <Thermal Insulating Material for Battery Pack> The pressure-molded body constituting the thermal insulating material for a battery pack of the present disclosure is produced by pressure-molding a composition containing powder of a porous structure.

[0028] [Porous Structure] The porous structure has a skeleton formed by connecting a plurality of primary particles, with pores between the skeletons. The diameter of the primary particles forming the skeleton is preferably about 2 to 5 nm, and the size of the pores formed between the skeletons is preferably about 10 to 50 nm. When most of the pores are so-called mesopores with a size of 50 nm or less, the mesopores are smaller than the mean free path of air, which restricts air convection and inhibits heat transfer.

[0029] [Method for producing porous structure] The porous structure is produced by a sol-gel reaction of a solution containing two or more types of silane compounds with different numbers of siloxane bonds (hereinafter, sometimes referred to as a "silane compound-containing solution"). The silane compound may contain compounds with different numbers of siloxane bonds, or may contain multiple types of compounds with the same number of siloxane bonds. The silane compound-containing solution may be prepared by adding to the solution a compound appropriately selected from tetrafunctional silane compounds, trifunctional silane compounds, bifunctional silane compounds, and monofunctional silane compounds. Furthermore, adding a catalyst to an aqueous solution of sodium silicate can change the pH of the aqueous solution, SiO ２ and Na ２ The number of silane bonds in a silane compound varies depending on the molar ratio of O to the catalyst, the type and concentration of the catalyst, and other factors. Therefore, a silane compound-containing solution may be prepared by using sodium silicate as a starting material and utilizing its hydrolysis reaction. From the viewpoint of increasing the elastic deformation of the resulting porous structure, the silane compound is preferably a tetrafunctional silane compound and a trifunctional silane compound, or a tetrafunctional silane compound and a monofunctional silane compound.

[0030] In the former embodiment, the content of the trifunctional silane compound is preferably 50% by mass or more, based on 100% by mass of the total silane compounds. It is more preferable to set it to 60% by mass or more, and even more preferably 65% ​​by mass or more. Increasing the content of the trifunctional silane compound reduces the —O—Si—O— bond ratio in the resulting porous structure, thereby increasing the amount of elastic deformation of the porous structure. In order to maximize the effect of mixing silane compounds with different numbers of siloxane bonds, it is desirable that the content of the tetrafunctional silane compound in this embodiment be at least 20% by mass or more, based on 100% by mass of the total silane compounds.

[0031] In the latter embodiment, the content of the monofunctional silane compound is preferably 10% by mass or more, based on 100% by mass of the total silane compounds. It is more preferable that it be 15% by mass or more. If the content of the monofunctional silane compound is less than 10% by mass, the amount of elastic deformation of the resulting porous structure will be small. Furthermore, from the viewpoint of suppressing a decrease in the skeletal strength of the porous structure, it is preferable that the content of the monofunctional silane compound is less than 40% by mass, based on 100% by mass of the total silane compounds. It is more preferable that it be 30% by mass or less.

[0032] The composition of the silane compound used to fabricate the porous structure is solid ２９ Using Si-NMR, analysis can be performed by the DD (Dipolar Decoupling) method. ２９ In the Si-NMR spectrum, the abundance ratios of Q units, T units, D units, and M units calculated from the signal areas of Q units, which are silicon atoms bonded to four oxygen atoms, T units, which are silicon atoms bonded to three oxygen atoms, D units, which are silicon atoms bonded to two oxygen atoms, and M units, which are silicon atoms bonded to one oxygen atom, correspond to the contents of tetrafunctional silane compounds, trifunctional silane compounds, difunctional silane compounds, and monofunctional silane compounds contained in the silane compound-containing solution.

[0033] Examples of tetrafunctional silane compounds include tetraalkoxysilane and tetraacetoxysilane. The alkoxy group of the tetraalkoxysilane preferably has 1 to 9 carbon atoms. Examples include tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, and tetraisopropoxysilane. Examples of trifunctional silane compounds include trialkoxysilane and triacetoxysilane. The alkoxy group of the trialkoxysilane preferably has 1 to 9 carbon atoms. Examples include methyltrimethoxysilane, ethyltrimethoxysilane, propyltrimethoxysilane, hexyltrimethoxysilane, octyltrimethoxysilane, methyltriethoxysilane, ethyltriethoxysilane, propyltriethoxysilane, pentyltriethoxysilane, hexyltriethoxysilane, and octyltriethoxysilane. Examples of bifunctional silane compounds include dialkoxysilane and diacetoxysilane. The alkoxy group of the dialkoxysilane preferably has 1 to 9 carbon atoms. Examples of the monofunctional silane compound include dimethyldimethoxysilane, diethyldimethoxysilane, diisobutyldimethoxysilane, etc. Examples of the monofunctional silane compound include methoxytrimethylsilane, isopropoxytrimethylsilane, ethoxytrimethylsilane, tert-butoxytrimethylsilane, ethoxytriethylsilane, methoxydimethyl(phenyl)silane, trimethyl(vinyloxy)silane, and isopropenyloxytrimethylsilane.

[0034] The method for producing a porous structure using a sol-gel reaction is not particularly limited. The porous structure can be produced, for example, through a sol generation process, a gelation process, and a drying process. When the drying process is performed at normal pressure, a solvent substitution process may be performed before the drying process, in which moisture adhering to the gel is replaced with an organic solvent that can be dried at normal pressure. First, in the sol generation process, a specific silane compound is added to an aqueous solution containing an acid catalyst and hydrolyzed to produce a sol. If necessary, a surfactant, a water-soluble oligomer having both polar and nonpolar components in the side chain, or the like may be added. When sodium silicate is used as the starting material, an acid catalyst is added to an aqueous solution of sodium silicate and hydrolyzed at a predetermined pH to produce a sol. Next, in the gelation process, a basic catalyst is added to the produced sol, and the sol is polycondensed to form a gel. After the basic catalyst is added, the mixture is allowed to stand and age at a temperature of approximately 80 to 120°C to promote the polycondensation reaction. Subsequently, in the drying process, the produced gel is dried. The drying method may be either supercritical drying or non-supercritical drying (atmospheric drying or freeze-drying). The obtained porous structure may be directly subjected to the pulverization treatment of the present disclosure, i.e., the pulverization treatment for converting the porous structure into a desired powder consisting of particles of different shapes and sizes, or may be pre-pulverized and then subjected to the pulverization treatment of the present disclosure.

[0035] An example of a porous structure is silica aerogel. Depending on the drying method used to produce the aerogel, aerogels dried at normal pressure are sometimes called "xerogels" and those dried under supercritical conditions are sometimes called "aerogels." In this specification, however, both are referred to as "aerogels." Silica aerogels are suitable because they have a good balance between the size of their skeleton and the size of their pores.

[0036] [Porous Structure Powder] The powder of the porous structure constituting the pressure-molded body is composed of particles of different shapes and sizes obtained by pulverizing the porous structure produced by the sol-gel method described above. For the pulverization, a media-less pulverizing and mixing device such as a jet mill, a stirrer, or the like may be used. The porous structure can be pulverized into various shapes, but a shape other than spherical is desirable.

[0037] The average particle size of the powder of the porous structure is desirably 30 μm or more from the viewpoint of increasing the pore volume and improving the heat insulating properties. Powders with an average particle size of less than 30 μm are difficult to obtain by pulverization, and fine voids are likely to occur between the particles, which may result in the compact being brittle. A suitable average particle size is 50 μm or more. On the other hand, from the viewpoint of ease of forming into a sheet and preventing particles from falling off, the average particle size is desirably 150 μm or less. Powders with an average particle size of more than 150 μm are less likely to generate voids between the particles, but the size of the voids is likely to become large. A suitable average particle size is 120 μm or less. The average particle size of the powder of the porous structure is determined by the median diameter (D ) calculated from the volume-based particle size distribution measured by laser diffraction / scattering method. ５０ ) can be adopted.

[0038] [Composition] The composition containing the porous structure powder may be composed solely of the porous structure powder, or may contain other components within a range that does not impair the effects achieved by the present disclosure. From the viewpoint of ensuring the desired heat insulating properties of the pressure-molded body, the content of the porous structure powder in the composition is 65% by mass or more, assuming that the solid content of the composition is 100% by mass. 70% by mass or more is preferable. Here, the solid content refers to components excluding volatile substances such as organic solvents and water. Examples of other components include infrared shielding particles, inorganic fibers, dispersants, reinforcing inorganic particles, and flame retardants. Note that, from the viewpoint of easily achieving the desired packing state and porosity of the particles of the porous structure in the pressure-molded body, it is desirable that the composition does not contain a binder that binds the constituent components of the pressure-molded body, such as the particles of the porous structure.

[0039] (1) Infrared Shielding Particles Infrared shielding particles absorb heat from a heat source and re-emit it from the surface on the heat source side, thereby blocking radiant heat from the heat source and contributing to improving heat insulation, particularly at high temperatures. It is desirable for the particle diameter of the infrared shielding particles to be relatively small, as they fill the gaps (voids) between the porous structure and suppress bonding between the infrared shielding particles and other components, making it difficult to form a heat transfer path. However, if the particle diameter is too small, infrared rays are less likely to hit the particles, and further, the scattering of infrared rays is insufficient, making it difficult to achieve the radiant heat blocking effect. From this perspective, the average particle diameter of the infrared shielding particles is preferably 0.3 μm or more and 22 μm or less. The shape of the infrared shielding particles is not particularly limited, such as spherical or flat. The average particle diameter of the infrared shielding particles is also determined, as with the powder of the porous structure, by the median diameter (D ) calculated from the volume-based particle size distribution measured by laser diffraction / scattering method. ５０ ) can be used, and when using a commercially available product, the catalog value can be used.

[0040] Examples of infrared-shielding particles include particles of one kind selected from 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, and cerium oxide, or particles of a mixture of two or more kinds selected from these. Among these, from the viewpoint of enhancing the radiant heat blocking effect, it is desirable that the infrared-shielding particles have a high emissivity of 0.6 or more in the infrared wavelength region. Examples of high-emissivity particles include silicon carbide, kaolinite, silicon nitride, mica, alumina, zirconia, aluminum nitride, zirconium silicate, cerium oxide, boron carbide, manganese oxide, tin oxide, and iron oxide. Furthermore, from the viewpoint of scattering incident infrared rays and enhancing the radiant heat blocking effect, a form having particles with a high refractive index in the infrared wavelength range is also effective. For example, high-refractive-index particles with a refractive index of 2.0 or more in the visible light wavelength range are suitable. Examples of high-refractive-index particles include 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.

[0041] For example, silicon carbide, titanium oxide, silicon nitride, mica, alumina, aluminum nitride, boron carbide, iron oxide, magnesium oxide, etc. have a relatively large specific heat capacity, and therefore the particles themselves do not heat up easily. In this respect, they also contribute to improving the thermal insulation of the pressed compact (insulating material). In addition, they have high heat resistance, which also contributes to improving the heat resistance of the pressed compact. Silicon carbide is particularly suitable because its thermal conductivity does not increase much even in a high-temperature atmosphere of about 800°C.

[0042] (2) Inorganic Fibers The inorganic fibers are physically entangled around the porous structure, thereby improving the mechanical strength of the pressure-molded body and suppressing particle shedding of the porous structure. The type of inorganic fiber is not particularly limited, but ceramic fibers such as glass fiber and alumina fiber are preferred in consideration of heat resistance, mechanical strength, etc. The length of the inorganic fiber is preferably 16 mm or less, taking into consideration both the reinforcing effect and the suppression of the formation of a heat transfer path.

[0043] (3) Dispersant A dispersant may be used when pulverizing the porous structure. Suitable dispersants include surfactants and water-soluble oligomers with both polar and nonpolar side chains. Examples of surfactants include ionic surfactants (cationic surfactants, anionic surfactants, and amphoteric surfactants) and nonionic surfactants. For example, the use of ionic surfactants can increase the viscosity of the composition even in relatively small amounts and stabilize the dispersion of materials such as the porous structure in the composition. Examples of ionic surfactants include sodium carboxymethylcellulose (CMC-Na), polycarboxylic acid amine salts, polycarboxylic acid ammonium salts, polycarboxylic acid sodium salts, and TEMPO-oxidized cellulose nanofibers (CNF-Na). The use of nonionic surfactants facilitates the incorporation of materials such as the porous structure into the solvent during the preparation of the composition. Furthermore, when these materials aggregate or separate in the composition, they are easily redispersed, and the solvent is easily removed during pressure molding. Examples of nonionic surfactants include polyethylene oxide (PEO) and polyvinyl alcohol (PVA).

[0044] (4) Reinforcing Inorganic Particles In order to improve the mechanical strength of the pressure-molded body, the composition may contain reinforcing inorganic particles. The type of reinforcing inorganic particles is not particularly limited, and for example, particles having a relatively large hardness and specific surface area, such as precipitated silica, gel silica, fused silica, wollastonite, potassium titanate, magnesium silicate, glass flakes, calcium carbonate, and barium sulfate, can be used.

[0045] (5) Flame Retardant From the viewpoint of imparting flame retardancy to the pressure-molded body, a flame retardant may be contained in the composition. Known flame retardants, such as halogen-based, phosphorus-based, and metal hydroxide-based flame retardants, may be used. Considering the environmental impact, it is desirable to use a phosphorus-based flame retardant. Examples of phosphorus-based flame retardants include ammonium polyphosphate, red phosphorus, and phosphate esters. Among these, water-insoluble flame retardants and those coated with a water-resistant resin are desirable because they are less likely to leak even when in contact with moisture during use. For example, ammonium polyphosphate and resin-coated ammonium polyphosphate are preferred.

[0046] [Pressure-molded body] In a pressure-molded body obtained by pressure-molding a composition containing a powder of a porous structure, the particles of the porous structure are preferably randomly stacked. FIG. 1 is a schematic diagram showing the packed state of the particles of the porous structure in the thermal insulation material of the present disclosure. The schematic diagram shown in FIG. 1 shows a cross section in the thickness direction of the thermal insulation material (pressure-molded body). In FIG. 1, hatching of the particles of the porous structure is omitted. As shown in FIG. 1, in the thermal insulation material 1, multiple particles 10 of the porous structure are arranged so as to be stacked. Many of the multiple particles 10 of the porous structure have shapes other than spherical, and each has a different shape and size. The packed state of the particles 10 of the porous structure is similar to the "nozura-zumi" (pile-like) stone wall found in Japanese castles and other buildings. "Nozura-zumi" is a masonry construction method in which natural stone or roughly broken stone is stacked without processing. Small voids 11 exist between the particles 10 of the porous structure. The particles 10 of the porous structure contact each other at points, lines, or surfaces, or a combination of these, and are arranged without any regularity. Therefore, when compressed from the outside in the thickness direction, the particles 10 of the porous structure move and deform, causing them to slip. Furthermore, because the particles 10 of the porous structure are elastic, they deform while generating a desired reaction force when the thermal insulation material 1 is compressed, and return to their original shape when the load is removed.

[0047] The amount of voids in a pressure-molded body affects its thermal insulation properties. When the number of voids increases, i.e., the porosity increases, heat transfer due to air convection increases, resulting in decreased thermal insulation properties. Therefore, if only the original purpose of thermal insulation is considered, it is desirable to have no voids. However, if there are few voids, the particles of the porous structure may not easily shift when compressed from the outside, resulting in a small amount of deformation. Conversely, if there are too many voids, the number of contact points formed by any one or a combination of points, lines, and surfaces of the porous structure may decrease, making it difficult for the porous structure to exhibit its elasticity and reducing the recovery rate. Therefore, in the thermal insulation material of the present disclosure, the porosity is set to 20% or less, taking into consideration thermal insulation properties, deformability, and recovery properties. A suitable porosity is 15% or less. A porosity of 0%, i.e., no voids may be detected in the following measurement method.

[0048] The porosity in this disclosure is a value obtained by photographing a cross section of the pressure-molded body in the thickness direction using a scanning electron microscope (SEM) and binarizing the resulting cross-sectional photograph. The procedure is described below. (1) First, a cross-sectional SEM photograph of the pressure-molded body in the thickness direction is taken at 200x magnification. (2) Next, the SEM photograph is subjected to contrast adjustment, noise removal, and binarization in this order. The contrast adjustment was performed using the CLAHE (Contrast Limited Adaptive Histogram Equalization) algorithm. The parameters used were Contrast Limit: 2.0 and Grid Size: (8, 8). The noise removal was performed using a Non-Local Means Filter. The parameters used were h: 40, Template Window Size: 23, and Search Window Size: 39. Here, h is the filter strength, Template Window Size is the size of the search area, and Search Window Size is the size of the search area. Adaptive binarization was used for the binarization process. The parameters used at that time were Block Size: 219, C: 40. Here, Block Size is the range referenced when calculating the threshold, and C is the threshold correction. The threshold was calculated using the average value of the reference range. Finally, to remove extremely small noise, structures smaller than 15 μm (32 pixels) were removed from the screen after binarization processing. (3) The structures remaining on the screen were considered to be voids, and the void ratio was calculated using the following formula (I): Porosity (%) = Area of ​​voids / Area of ​​entire screen × 100 (I)

[0049] <Usage Form> The heat insulating material of the present disclosure may be composed of only a pressure-molded body, or may also be composed of a substrate that supports the pressure-molded body, an exterior material that houses the pressure-molded body, and the like. The substrate may be arranged on only one side of the heat insulating material in the thickness direction, or on both sides so as to sandwich the heat insulating material. Alternatively, the heat insulating material may be covered with a single substrate, and the substrate may be used as an exterior material. An adhesive layer may be interposed between the heat insulating material and the substrate. The adhesive layer may contain a flame retardant in addition to an adhesive component.

[0050] Examples of substrate materials include cloth, resin, paper, and steel plate. Examples of fibers constituting the cloth include glass fiber, rock wool, ceramic fiber, alumina fiber, silica fiber, carbon fiber, metal fiber, polyimide fiber, aramid fiber, and polyphenylene sulfide (PPS) fiber. Examples of ceramic fibers include refractory ceramic fiber (RCF), polycrystalline alumina fiber (Polycrystalline Wool: PCW), and alkaline earth silicate (AES) fiber. Among these, AES fiber is biosoluble and therefore more safe. Examples of resins include polyethylene terephthalate (PET), polyimide, polyamide, and PPS. Examples of paper include pulp and composites of pulp and magnesium silicate. Examples of steel plates include Galvalume Steel Plate (registered trademark), galvanized sheet, stainless steel (SUS) plate, iron plate, and titanium plate. The shape of the substrate is not particularly limited, and examples include woven fabric, nonwoven fabric, film, and sheet. The substrate may be a single layer or a laminate of two or more layers of the same or different materials.

[0051] For example, glass cloth, fabrics (woven fabrics) and nonwoven fabrics made from inorganic fibers such as glass fiber and metal fiber, and fireproof insulating paper made as a composite of pulp and magnesium silicate have relatively low thermal conductivity and high shape retention even in high-temperature environments. Furthermore, the use of a fire-resistant substrate further improves safety. Highly heat-resistant substrates can be made from glass fiber, rock wool, ceramic fiber, polyimide, PPS, etc., and specific examples include glass fiber nonwoven fabric, glass cloth, aluminum glass cloth, AES wool paper, and polyimide fiber nonwoven fabric.

[0052] <Method for manufacturing a thermal insulating material for a battery pack> The method for manufacturing a thermal insulating material for a battery pack according to the present disclosure is one embodiment of the method for manufacturing a thermal insulating material for a battery pack according to the present disclosure, and includes a first step and a second step. Each step will be described in order.

[0053] [First Step] This step involves pulverizing a composition containing a porous structure produced by the sol-gel reaction of a solution containing two or more silane compounds with different numbers of siloxane bonds, a dispersant, and water to produce a powder of the porous structure composed of particles of different shapes and sizes. The method for producing a porous structure using a silane compound and a sol-gel reaction is as described above. The porous structure may be in the as-produced state or may be pre-pulverized after production (both include purchased products). The pulverization process may be carried out using a media-less pulverizing mixer, agitator, or the like.

[0054] As described above, the dispersant may be a surfactant, a water-soluble oligomer having both polar and non-polar components in the side chain, or the like. The presence of a dispersant in the pressure-molded body may create a heat transfer path through the dispersant. Furthermore, the organic components may decompose or deteriorate at high temperatures, resulting in the generation of gas or cracks in the pressure-molded body. Therefore, taking into account the balance with the ability to exert dispersing function, the amount of dispersant blended is preferably 5% by mass or less, and more preferably 2% by mass or less, based on 100% by mass of the solids content of the composition.

[0055] In this process, one or more types selected from infrared-shielding particles and inorganic fibers may be blended with the composition and then pulverized. Because the infrared-shielding particles and inorganic fibers are harder than the porous structure, they are hardly pulverized under the conditions for pulverizing the porous structure. Therefore, by adding infrared-shielding particles or the like to the composition and pulverizing them together with the porous structure, there is no need to separately mix or disperse the infrared-shielding particles or the like, and fewer work steps are required. This can increase production efficiency and also lead to improved quality of the thermal insulation material.

[0056] [Second Step] This step involves placing the pulverized composition in a mold and pressure-molding it. The pressure-molding conditions may be appropriately determined so that the resulting pressure-molded body has the desired porosity (20% or less). For example, the composition may be heated to a temperature of about 100 to 160°C while applying a surface pressure of about 0.1 to 2.0 MPa.

[0057] [Other Embodiments] In the above-described first step, the infrared-shielding particles and the like are blended into the composition, and then pulverized together with the porous structure. However, when the infrared-shielding particles and the like are to be contained in the pressure-molded body, the infrared-shielding particles and the like may be separately mixed with the composition obtained by pulverizing the porous structure, and the mixture may be subjected to pressure molding in the second step.

[0058] Next, the present disclosure will be described more specifically with reference to examples.

[0059] <Production of Heat Insulating Material Samples> [Production of Composition] (1) First Composition First, water was weighed into a resin container, a surfactant was added as a dispersant, and the mixture was stirred for 60 minutes at 800 rpm using an air-driven blade stirrer to dissolve the surfactant in the water. After stopping the stirring, silicon carbide (SiC) powder was added as infrared heat shielding particles, and the mixture was further stirred for 15 minutes at 800 rpm. While continuing the stirring, silica aerogel as a porous structure was added and completely wetted in the liquid. Then, glass fiber as inorganic fiber was added, and a pulverization treatment was carried out by stirring for 30 minutes at 800 rpm. After that, additional stirring was carried out for 10 minutes at 1000 rpm, and a second pulverization treatment was carried out. In this way, the average particle diameter (D ５０ A composition containing silica aerogel powder with a particle size of 70 μm was produced. The composition had a clay-like structure consisting of aggregates of particles with a diameter of 5 mm or less. The content of the silica aerogel powder in the composition was 73.7% by mass, where the solid content of the composition was 100% by mass. Similarly, the content of the surfactant in the composition was 2.9% by mass, the content of the silicon carbide powder was 15.1% by mass, and the content of the glass fiber was 8.3% by mass.

[0060] (2) Second Composition The average particle diameter (D ５０ A second composition containing silica aerogel powder having a particle size of 150 μm was prepared. Specifically, the stirring time after adding the silica aerogel was set to 5 minutes, and the additional stirring time was set to 5 minutes.

[0061] The details of the materials used are as follows: Silica aerogel: Aerogel Particles P200 manufactured by Cabot Corporation, pulverized, with an average particle size of 100 μm. ２９ Analysis using Si-NMR by the DD method at a MAS rotation speed of 10 kHz and a pulse waiting time of 5 seconds revealed that the proportion of Q units was 78.3% by mass and the proportion of M units was 21.7% by mass. From these analysis results, it was confirmed that the silane compounds used in the production of this product, taken as 100% by mass, consisted of 78.3% by mass of tetrafunctional silane compounds and 21.7% by mass of monofunctional silane compounds. Silicon carbide powder: Fuji Random GC #4000 manufactured by Fuji Manufacturing Co., Ltd., average particle size 5 μm. Surfactant: Polyethylene oxide "PEO-8" manufactured by Sumitomo Seika Chemicals Co., Ltd., viscosity average molecular weight 1.7 million to 2.2 million. Glass fiber: Central Glass Fiber Co., Ltd., "ECS03-615", length 3 mm, fiber diameter 9 μm.

[0062] [Preparation of Pressed Molded Body] The clay-like composition was press-molded as follows. First, a base was prepared by stacking a first spacer plate made of stainless steel on glass fiber paper. A square injection hole measuring 150 mm on each side was formed in the center of the first spacer plate. The prepared composition was filled into the injection hole of the first spacer plate and molded into a square plate. Next, the first spacer plate was removed, and glass fiber paper was placed on top, followed by a second spacer plate on top of that, to produce a laminate consisting of "glass fiber paper / composition / glass fiber paper / second spacer plate." A square injection hole measuring 150 mm on each side, similar to the first spacer plate, was formed in the center of the second spacer plate, and the molded composition was placed in the injection hole of the second spacer plate. The thicknesses of the first and second spacer plates were adjusted so that the insulation sample had the desired porosity.

[0063] Separately, a 5 mm thick, 320 mm square aluminum first plate and a 1 mm thick, 320 mm square aluminum second plate were prepared. Multiple grooves were formed on one side of the first plate. Each groove was linear, 2.5 mm wide, 3 mm deep, and 200 mm long, and was formed parallel to the first plate at 5 mm intervals. Punched holes with a diameter of 1 mm were formed throughout the second plate at 2 mm intervals. A second plate was placed on one side of the first plate, and a laminate was placed on top of it. The second plate was then placed on top of the laminate, and the first plate was then placed on top of the second plate, with the grooved side facing the second plate. In this state, pressure molding was performed using a hot press at a temperature of 165°C and a load of approximately 980 kN for 10 minutes. The product was then allowed to cool to room temperature (20°C ± 5°C), and the first plate, second plate, second spacer plate, and upper and lower glass fiber papers were removed to obtain a square plate-shaped pressure-molded product. Seven types of pressure-molded bodies with different porosities were manufactured by changing the thicknesses of the first spacer plate and the second spacer plate. The pressure-molded bodies thus manufactured were used as heat insulating material samples.

[0064] The cross sections of the seven types of thermal insulation samples in the thickness direction were observed using an SEM. As an example, FIG. 2 shows a cross-sectional SEM photograph (magnification: 200x) of the sample of Example 1. As shown in FIG. 2, in all samples, silica aerogel particles of different shapes and sizes were randomly stacked. Many of the silica aerogel particles had shapes other than spherical, and silicon carbide particles and glass fibers were arranged between the silica aerogel particles.

[0065] <Evaluation of Insulating Material Samples> [Insulating Properties] The thermal conductivity of the insulating material samples at 600°C was measured using a "Quick Thermal Conductivity Meter QTM-700" and a "High-Temperature Probe PD-31N" manufactured by Kyoto Electronics Manufacturing Co., Ltd., as follows. First, two insulating material samples were stacked to prepare laminates approximately 20 mm thick. These laminates were placed one on top of the probe and one on the bottom of the probe, sandwiching the probe. A weight of approximately 5 kg was placed on top of the laminate to prevent it from being crushed, and the laminate was then placed in an electric furnace. The temperature inside the electric furnace was then raised to 600°C, and after the temperature inside the furnace stabilized, the thermal conductivity was measured. In this example, a measured thermal conductivity of less than 0.12 W / m K was evaluated as "pass" (indicated by a circle in Table 1 below), and a thermal conductivity of 0.12 W / m K or greater was evaluated as "fail" (indicated by an "x" in the same table).

[0066] [Resilience] A compression test was conducted using a Tensilon universal material testing machine "RTF1350" manufactured by A&D Co., Ltd., in which the center of an insulation sample (a square plate of 150 mm length, 150 mm width, and arbitrary thickness) was pressed with a 60 mm diameter compression terminal. The compression test was conducted with the upper limit of compressive stress set to 2.0 MPa and the compression terminal moved back and forth at a speed of 1 mm / min. Three cycles were repeated, with one cycle being the period in which the compressive stress changed from 0.02 MPa to 2.0 MPa to 0.02 MPa. Based on the data obtained from the compression test, a stress-compression curve was created with the compression ratio on the horizontal axis and the compressive stress on the vertical axis. The compression ratio on the horizontal axis was calculated using the following formula (II). Compression rate (%) = Push-in distance (mm) of compression terminal after compressive stress reaches 0.01 MPa during pressing in one cycle / Thickness (mm) of insulation sample when compressive stress reaches 0.01 MPa during pressing in one cycle × 100 (II)

[0067] In the stress-compression curve of the second cycle, the value obtained by subtracting the compressibility when the compressive stress was 0.02 MPa at the end of the cycle from the compressibility when the compressive stress was 2.0 MPa was used as the index value of the restorability of the insulating material sample. In this example, a restorability index value of 10% or more was evaluated as pass (indicated by a circle in Table 1 below), and a value of less than 10% was evaluated as fail (indicated by an x ​​in the same table).

[0068] [Evaluation Results] Table 1 shows the evaluation results of the porosity of the heat insulating material samples, the average particle size of the silica aerogel powder, the heat insulating properties, and the restorability.

[0069] As shown in Table 1, the samples of Examples 1 to 6, which had a porosity of 20% or less, were confirmed to have excellent heat insulating properties at high temperatures and high recovery. Furthermore, although not shown in Table 1, these samples were also confirmed to have large deformation amounts (compression rates). Comparing the samples of Examples 1 to 4, it was confirmed that the recovery rate decreased as the porosity increased. It is presumed that as the porosity increased, the number of contact points between silica aerogel particles decreased, reducing friction between particles. Even when the voids were crushed by compression, the voids did not have recovery properties, resulting in a decrease in recovery. It was also confirmed that recovery properties were exhibited even when the voids were 0%, as in the sample of Example 6. In contrast, the sample of Comparative Example 1, which had a porosity of 25%, exhibited poor heat insulating properties and recovery properties.

[0070] 1: heat insulating material (pressure-molded body), 10: particles of porous structure, 11: voids.

Claims

1. An insulating material for a battery pack comprising a pressure-molded body of a composition having a powder of a porous structure in which a plurality of primary particles are linked to form a skeleton and pores are present between the skeletons, the porous structure being produced by a sol-gel reaction of a solution having two or more types of silane compounds with different numbers of siloxane bonds, the powder of the porous structure being composed of particles of different shapes and sizes obtained by pulverizing the porous structure, the content of the powder of the porous structure in the composition being 65% by mass or more when the solid content of the composition is 100% by mass, and the porosity of the pressure-molded body being 20% ​​or less.

2. The insulating material for a battery pack according to claim 1, wherein the powder of the porous structure has an average particle size of 30 μm or more and 150 μm or less.

3. The insulating material for a battery pack according to claim 1, wherein in the pressure-molded body, the particles of the porous structure are randomly stacked.

4. The insulating material for a battery pack according to claim 1, wherein the silane compound is a tetrafunctional silane compound and a trifunctional silane compound, or a tetrafunctional silane compound and a monofunctional silane compound.

5. The insulating material for a battery pack as described in claim 4, wherein when the silane compound is the tetrafunctional silane compound and the trifunctional silane compound, the content of the trifunctional silane compound is 50 mass% or more when the total amount of the silane compounds is 100 mass%.

6. The insulating material for a battery pack as described in claim 4, wherein the silane compound is the tetrafunctional silane compound and the monofunctional silane compound, the content of the monofunctional silane compound is 10 mass% or more and less than 40 mass% when the total amount of the silane compounds is 100 mass%.

7. The insulating material for a battery pack according to claim 1, wherein the composition comprises one or more selected from the group consisting of infrared shielding particles, inorganic fibers, and dispersants.

8. The insulating material for a battery pack according to claim 1, wherein the porous structure is silica aerogel.

9. The insulating material for a battery pack according to claim 1, wherein the composition does not contain a binder that binds the constituent components of the pressure-molded body.

10. A method for producing an insulating material for a battery pack as described in claim 1, comprising: a first step of pulverizing a composition containing the porous structure produced by a sol-gel reaction of a solution containing two or more types of silane compounds having different numbers of siloxane bonds, a dispersant, and water to produce a powder of the porous structure consisting of particles of different shapes and sizes; and a second step of placing the pulverized composition in a mold and pressurizing it to form it.

11. The method for producing an insulating material for a battery pack according to claim 10, wherein the composition in the first step contains at least one type selected from the group consisting of infrared shielding particles and inorganic fibers.

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