Heat insulating material for battery pack and manufacturing method thereof

Abstract

To provide a heat insulating material for a battery pack that is excellent in deformation property against compression and in restoration property after unloading, using a pressure molded body of a composition having powder of a porous structure, and a manufacturing method thereof.SOLUTION: A heat insulating material for a battery pack comprises a pressure molded body 1 of a composition having 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 powder of the porous structure is made up of particles 10 of different shapes and sizes. A content of the powder of the porous structure in the composition is 65 mass% or more when a solid content of the composition is 100 mass%, and a porosity of the pressure molded body is 20% or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

[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 in particular to a thermal insulator using a porous structure such as an aerogel. [Background technology]

[0002] A battery pack containing a plurality of battery cells is mounted on a hybrid vehicle or an electric vehicle. In the battery pack, a battery module formed by stacking a plurality of battery cells is housed in a housing in a state in which the battery modules are fixed by fastening members from both sides in the stacking direction. A heat insulating material is arranged between adjacent battery cells in order to suppress the transfer of heat and suppress thermal runaway when the battery cells generate abnormal heat. The battery cells expand and contract as they are charged and discharged. Therefore, it is desirable that the heat insulating material arranged between the battery cells can deform in accordance with the expansion and contraction of the battery cells and maintain its heat insulating properties. More specifically, when the battery cells are charged and expanded, the thickness of the heat insulating material becomes thinner due to the compression force, and at the same time, it is necessary to generate a reaction force of a certain value or more to bias the battery cells and prevent the heat insulating material from being displaced. In addition, when the battery cells are discharged and contracted (returning to their original thickness), the thickness of the heat insulating material also needs to be restored.

[0003] Silica aerogels with low thermal conductivity are known as materials 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 excellent in flexibility and resistance to destruction against compression force. The raw silane compound satisfies 0≦Qx≦70, 30≦Tx≦100, 0≦Dx<30 (where Qx+Tx+Dx=100), where the mass percentages of a tetrafunctional silane compound, a trifunctional silane compound, and a bifunctional silane compound are Qx, Tx, and Dx, respectively. Patent Document 2 describes that in a heat insulating material having a porous structure in which a plurality of primary particles are connected to form a skeleton and pores are present between the skeletons, and a binder, the volume ratio of voids present between the porous structures is set to 10% or more and 55% or less. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-165387 [Patent Document 2] JP 2020-122544 A Summary of the Invention [Problem to be solved by the invention]

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

[0109] of the same document lists the use of aerogel powder as filling insulating windows, insulating building materials, etc., Patent Document 1 does not describe the use of aerogel powder as a heat insulating material for battery packs by pressurizing it. Therefore, Patent Document 1 does not consider the deformability during compression of the "pressurized body" of aerogel powder, the reaction force generated, and the restorability to the original shape after unloading. In addition, there is no description suggesting the porosity of the "pressurized body".

[0006] On the other hand, the heat insulating material described in the above Patent Document 2 is manufactured by applying a paint in which a porous structure is dispersed in a binder liquid to a substrate after adjusting the state of the gas in the paint, and then drying it. In this manufacturing method, by intentionally creating voids between the porous structures, shrinkage distortion during drying is reduced and the occurrence of cracks is suppressed. The heat insulating material described in Patent Document 2 is not a "pressure molded body" obtained by pressurizing and molding a powder of a porous structure. The volume ratio of the voids specified in Patent Document 2 is specified for the purpose of reducing shrinkage distortion during drying of the paint, and does not satisfy the characteristics required for a heat insulating material for a battery pack.

[0007] The present disclosure has been made in consideration of the above-mentioned circumstances, and has an objective of providing 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 after unloading, and a method for producing the same. [Means for solving the problem]

[0008] (1) In order to solve the above problems, an insulating material for a battery pack according to 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 having two or more types of silane compounds having different numbers of siloxane bonds, the powder of the porous structure being composed of particles having 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, when the powder of the porous structure is composed of spherical particles of the same size, the particles are mainly in contact with each other at points and regularly packed in the pressurized compact of the powder. This increases the rigidity of the filled particles, and the reaction force against the compressive force from the outside increases, so that the change in thickness when compressed is extremely small. 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 a pressurized compact of powder composed of particles of different shapes and sizes, the particles are in contact with each other not only at points but also at lines or surfaces, and there is no regularity in the arrangement. In this case, when compressed from the outside, the particles move in a shifted manner, so that the deformation in the thickness direction is relatively large. In addition, when voids are present in the pressurized compact, the particles are more likely to move, and the deformation amount is greater.

[0010] The porous structure is manufactured by a sol-gel reaction of a solution having two or more kinds of silane compounds with different numbers of siloxane bonds. In this specification, the siloxane bond of the silane compound means a bond (Si-O bond) between a silicon atom (Si) and an oxygen atom (O). The number of siloxane bonds is the number of oxygen atoms bonded to one silicon atom, and silane compounds are divided into four types with 1 to 4 siloxane bond numbers. Based on the knowledge that the number of siloxane bonds of a silane compound affects the elasticity of the manufactured porous structure, the present inventors have realized a porous structure having a desired elasticity, more specifically, a porous structure having a restoring ability to deform while generating a desired reaction force when compressed and to return to its original shape after unloading, by mixing and using a plurality of silane compounds with different numbers of siloxane bonds. Then, the obtained porous structure is pulverized, and a powder composed of particles with different shapes and sizes is used, thereby realizing a heat insulating material that can deform in response to slight expansion during charging of a battery cell. In this way, the heat insulating material of the present disclosure is excellent in deformability against compression and restoring ability after unloading. According to the insulating material of the present disclosure, even if the battery cells expand and contract, displacement or the like is unlikely to occur, and high insulating properties can be maintained.

[0011] (2) In the above configuration, the powder of the porous structure may have an average particle size of 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 are in contact with each other at points, lines, or surfaces, and are likely to move in a displaced manner when compressed from the outside. Therefore, the amount of deformation in the thickness direction is large.

[0013] (4) In any of the above configurations, the silane compound 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 means a silane compound having four siloxane bonds. Similarly, a trifunctional silane compound means a silane compound having three siloxane bonds, a bifunctional silane compound means a silane compound having two siloxane bonds, and a monofunctional silane compound means a silane compound having one siloxane bond. This configuration is suitable for producing a porous structure having a 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 when the total amount of the silane compounds is 100% by mass. By increasing the content of the trifunctional silane compound, the elastic deformation amount of the obtained porous structure can be increased.

[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 is small, and if it is 40% by mass or more, the skeletal strength of the porous structure is reduced.

[0016] (7) In any of the above configurations, the composition may have 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] According to the heat insulating material using the porous structure, a high heat insulating effect can be obtained by suppressing mainly conduction and convection among the three forms of heat transfer (conduction, convection, radiation). Here, radiation is a phenomenon in which heat is transferred by electromagnetic waves, and the higher the temperature, the greater the radiation energy released. For this reason, in a high temperature atmosphere, radiation is the main cause of heat transfer. Therefore, by using infrared shielding particles that can suppress heat transfer by radiation in combination, it is possible to suppress heat transfer by radiation in addition to conduction and convection, and high heat insulation can be achieved not only at room temperature but also at high temperatures of 500°C or higher. When the pressure-molded body has inorganic fibers, the mechanical strength of the pressure-molded body is improved and the falling off of the particles of the porous structure can be suppressed. The porous structure is also difficult to mix with water and difficult to disperse. Therefore, when water is used during the pulverization process, the dispersibility of the porous structure can be improved by adding a dispersant having amphipathic properties. As a result, the porous structure can be pulverized to a desired state. In this case, the composition has a powder of the porous structure and a dispersant, and is pressure-molded as it is to become a pressure-molded body.

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

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

[0020] (10) The manufacturing method of an insulating material for a battery pack disclosed herein is one form of a manufacturing method of an insulating material for a battery pack having any of the above configurations, and is characterized by having a first step of pulverizing a composition containing the porous structure manufactured 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 manufacture a powder of the porous structure composed of particles having different shapes and sizes, and a second step of placing the pulverized composition in a molding die and pressurizing it to mold 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"), the porous structure is pulverized using a dispersant (first step). This makes it possible to improve the dispersibility of the porous structure, and to pulverize the porous structure into a desired state to produce a powder consisting of particles of different shapes and sizes. In the second step, the porosity of the pressure-molded body can be set to 20% or less by adjusting the conditions during pressure molding. According to the manufacturing method of the present disclosure, the insulating material for a battery pack of the present disclosure can be easily manufactured.

[0022] (11) In the above configuration (10), the composition in the first step may have one or more selected from infrared shielding particles and inorganic fibers. In this configuration, when one or more selected from infrared shielding particles and inorganic fibers (hereinafter, sometimes referred to as "infrared shielding particles, etc.") are contained in the pressure-molded body (thermal insulation material), this is mixed with a porous structure, etc. to form a composition, and then pulverized. Since 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, so there is no need to mix or disperse them separately, and the number of work steps is reduced. This can increase production efficiency and also lead to improved quality of the thermal insulation material.

[0023] According to this configuration, a pressure-molded body having infrared shielding particles and the like is manufactured. As in 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 from room temperature to high temperatures of 500°C or higher. When inorganic fibers are contained in the pressure-molded body, the mechanical strength of the pressure-molded body is improved, and falling off of particles in the porous structure can be suppressed. Effect of the Invention

[0024] The insulating material for a battery pack according to the present disclosure has excellent deformability against compression and recovery after unloading. Therefore, even if the battery cell expands and contracts, it is difficult for displacement to occur and high insulating properties can be maintained. According to the manufacturing method for the insulating material for a battery pack according to the present disclosure, the dispersibility of the porous structure in the pulverization process can be improved, and a powder of the porous structure composed of particles of different shapes and sizes can be easily manufactured. This makes it possible to easily manufacture the insulating material for a battery pack according to the present disclosure. [Brief description of the drawings]

[0025] [Figure 1] FIG. 2 is a schematic diagram showing the particle packing state of a porous structure in a thermal insulating material according to the present disclosure. [Diagram 2] 1 is a cross-sectional SEM photograph of a sample of Example 1 (magnification: 200 times). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[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 may be embodied in various forms that include modifications and improvements that can be made by those skilled in the art without departing from the gist of the present disclosure.

[0027] <Insulation material for battery packs> The pressure-molded body constituting the insulating material for a battery pack of the present disclosure is produced by pressure-molding a composition having a powder of a porous structure.

[0028] [Porous structure] The porous structure has a skeleton formed by connecting a plurality of primary particles, and has 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, so that air convection is restricted and heat transfer is inhibited.

[0029] [Method of manufacturing porous structure] The porous structure is manufactured by a sol-gel reaction of a solution having two or more kinds 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, and may contain a plurality of compounds with the same number of siloxane bonds. The silane compound-containing solution may be prepared by adding a compound appropriately selected from a tetrafunctional silane compound, a trifunctional silane compound, a bifunctional silane compound, and a monofunctional silane compound to the solution. In addition, when a catalyst is added to an aqueous solution of sodium silicate, a silane compound with a different number of siloxane bonds is generated depending on the pH of the aqueous solution, the molar ratio of SiO2 to Na2O, the type and concentration of the catalyst, and the like. Therefore, the 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 amount of the obtained porous structure, it is desirable that the silane compound is in the form of a tetrafunctional silane compound and a trifunctional silane compound, or a tetrafunctional silane compound and a monofunctional silane compound.

[0030] Among these, in the former embodiment, the content ratio of the trifunctional silane compound is preferably 50% by mass or more when the total amount of the silane compounds is 100% by mass. More preferably, it is 60% by mass or more, and even more preferably 65% ​​by mass or more. When the content ratio of the trifunctional silane compound is increased, the -O-Si-O- bond ratio in the obtained porous structure is decreased, so that the elastic deformation amount of the porous structure can be increased. In addition, in order to exert the effect of mixing silane compounds having different numbers of siloxane bonds, the content ratio of the tetrafunctional silane compound in this embodiment is preferably at least 20% by mass or more when the total amount of the silane compounds is 100% by mass.

[0031] In the latter embodiment, the content of the monofunctional silane compound is desirably 10% by mass or more, based on 100% by mass of the entire silane compounds. It is more preferable that it is 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 is small. In addition, from the viewpoint of suppressing a decrease in the skeletal strength of the porous structure, it is desirably 40% by mass or less, based on 100% by mass of the entire silane compounds. It is more preferable that it is 30% by mass or less.

[0032] The composition of the silane compound used to fabricate the porous structure is solid 29 It can be analyzed by the DD (Dipolar Decoupling) method using Si-NMR. 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 a Q unit, a silicon atom to which four oxygen atoms are bonded, a T unit, a silicon atom to which three oxygen atoms are bonded, a D unit, a silicon atom to which two oxygen atoms are bonded, and an M unit, a silicon atom to which one oxygen atom is bonded, correspond to the abundance ratios of tetrafunctional silane compounds, trifunctional silane compounds, difunctional silane compounds, and monofunctional silane compounds contained in the silane compound-containing solution.

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

[0034] The method for producing a porous structure using a sol-gel reaction is not particularly limited, but the porous structure can be produced, for example, through a sol production process, a gelling process, and a drying process. When the drying process is performed at normal pressure, a solvent replacement process in which moisture adhering to the gel is replaced with an organic solvent that can be dried at normal pressure may be performed before the drying process. First, in the sol production 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 non-polar components in the side chain, and the like may be added. In addition, when sodium silicate is used as a starting material, an acid catalyst may be added to an aqueous solution of sodium silicate and hydrolyzed under a specific pH to produce a sol. Next, in the gelling process, a basic catalyst is added to the produced sol, and the sol is polycondensed to gel it. After the basic catalyst is added, it is preferable to leave it to stand under heating at about 80 to 120 ° C. to proceed with the polycondensation reaction. Then, in the drying process, the produced gel is dried. The drying method may be either a supercritical drying method or a non-supercritical drying method (normal pressure drying method, freeze drying method). The obtained porous structure may be directly subjected to the pulverization treatment of the present disclosure, that is, the pulverization treatment for converting the porous structure into a desired powder consisting of particles of different shapes and sizes, or the porous structure 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 manufacture the aerogel, the one dried at normal pressure is called "xerogel" and the one dried at supercritical pressure is called "aerogel", but in this specification, both are referred to as "aerogel". Silica aerogel is suitable because it has a good balance between the size of the skeleton and the size of the 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 manufactured 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 preferable.

[0037] The average particle diameter 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 insulation. Powders with an average particle diameter of less than 30 μm are difficult to obtain by pulverization, and fine voids are likely to occur between the particles, which may cause the pressed compact to become brittle. A suitable average particle diameter is 50 μm or more. On the other hand, from the viewpoint of ease of forming into a sheet and suppression of particle falling off, the average particle diameter is desirably 150 μm or less. Powders with an average particle diameter of more than 150 μm are unlikely to cause voids between the particles, but the size of the voids is likely to be large. A suitable average particle diameter is 120 μm or less. The average particle diameter of the powder of the porous structure is determined by the median diameter (D 50 ) can be adopted.

[0038] [Composition] The composition having the powder of the porous structure may be composed only of the powder of the porous structure, 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 insulation in the pressure-molded body, the content of the powder of the porous structure in the composition is 65% by mass or more when the solid content of the composition is 100% by mass. It is preferable to make it 70% by mass or more. Here, the solid content is a component 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. In addition, from the viewpoint of easily realizing the desired filling state and porosity of the particles of the porous structure in the pressure-molded body, it is desirable that the composition does not have 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, especially at high temperatures. From the viewpoint of filling the gaps (voids) between the porous structures and suppressing the connection between the infrared shielding particles and other components to make it difficult to form a heat transfer path, it is desirable for the particle diameter of the infrared shielding particles to be relatively small. However, if the particle diameter is too small, it becomes difficult for infrared rays to hit the particles, and further, the scattering of infrared rays becomes insufficient, so that the radiant heat blocking effect is difficult to be exhibited. From this viewpoint, it is preferable that the average particle diameter of the infrared shielding particles is 0.3 μm or more and 22 μm or less. The shape of the infrared shielding particles is not particularly limited to a spherical shape, a flat shape, etc. The average particle diameter of the infrared shielding particles is also determined by the median diameter (D 50 ) can be used, and when using a commercially available product, the catalog value can be used.

[0040] Examples of the 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 effect of blocking radiant heat, it is preferable that the infrared shielding particles have high emissivity particles having an 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. From the viewpoint of scattering the incident infrared rays and enhancing the effect of blocking radiant heat, a form having particles with a high refractive index in the infrared wavelength region is also effective. For example, high refractive index particles with a refractive index of 2.0 or more in the visible light wavelength region 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, so that their heat capacity is large and the particles themselves do not heat up easily. In this respect, they also contribute to improving the heat insulation of the pressure-molded body (insulating material). In addition, they also have high heat resistance, so they also contribute to improving the heat resistance of the pressure-molded body. In particular, silicon carbide is 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 intertwined around the porous structure, thereby improving the mechanical strength of the pressure-molded body and suppressing the falling off of particles of the porous structure. The type of inorganic fiber is not particularly limited, but considering heat resistance, mechanical strength, etc., ceramic fibers such as glass fiber and alumina fiber are preferable. The length of the inorganic fiber is desirably 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 The dispersant may be used when the porous structure is pulverized. Suitable dispersants include surfactants and water-soluble oligomers having both polar and non-polar components in the side chain. Examples of surfactants include ionic surfactants (cationic surfactants, anionic surfactants, amphoteric surfactants) and non-ionic surfactants. For example, the use of ionic surfactants can increase the viscosity of the composition even in a relatively small amount, and can stabilize the dispersion of materials such as the porous structure in the composition. Examples of ionic surfactants include sodium carboxymethylcellulose (CMC-Na), polycarboxylate amine salts, polycarboxylate ammonium salts, polycarboxylate sodium salts, and TEMPO-oxidized cellulose nanofibers (CNF-Na). The use of non-ionic surfactants makes it easier for materials such as the porous structure to be incorporated into the solvent when preparing the composition. In addition, when these materials aggregate or separate in the composition, they become easier to redisperse, and the solvent is easier to discharge when pressure molding is performed. Examples of non-ionic surfactants include polyethylene oxide (PEO) and polyvinyl alcohol (PVA).

[0044] (4) Reinforcing inorganic particles From the viewpoint of improving 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, barium sulfate, etc., can be used.

[0045] (5) Flame retardants From the viewpoint of imparting flame retardancy to the pressure-molded body, a flame retardant may be contained in the composition. As the flame retardant, a known one such as a halogen-based, phosphorus-based, or metal hydroxide-based one may be used. In consideration of the environmental load, it is preferable to use a phosphorus-based flame retardant. Examples of phosphorus-based flame retardants include ammonium polyphosphate, red phosphorus, and phosphoric ester. Among them, those that are insoluble in water or coated with a water-resistant resin are preferable because the flame retardant is unlikely to flow out even when it comes into contact with moisture during use, and for example, ammonium polyphosphate and resin-coated ammonium polyphosphate are suitable.

[0046] [Pressure-molded body] In a pressurized compact obtained by pressurizing a composition having a powder of a porous structure, the particles of the porous structure are preferably stacked randomly. FIG. 1 is a schematic diagram showing the packed state of the particles of the porous structure in the heat insulating material of the present disclosure. The schematic diagram shown in FIG. 1 shows a cross section in the thickness direction of the heat insulating material (pressurized compact). In FIG. 1, hatching of the particles of the porous structure is omitted. As shown in FIG. 1, in the heat insulating material 1, a plurality of particles 10 of the porous structure are arranged so as to be stacked. Many of the 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 shape of "nozura-mi" seen in the stone walls of Japanese castles and the like. "Nozura-mi" is a stone masonry method in which natural stones or roughly broken stones are stacked as they are without processing. There are a few voids 11 between the particles 10 of the porous structure and 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 there is no regularity in the arrangement. Therefore, when compressed from the outside in the thickness direction, the particles 10 of the porous structure move and deform so as to shift from each other. In addition, since the particles 10 of the porous structure have elasticity, they deform while generating a desired reaction force when the heat insulating material 1 is compressed, and return to their original shape when the load is removed.

[0047] The amount of voids in the pressure-molded body affects the heat insulation. When the voids increase, that is, when the porosity increases, the heat transfer due to air convection increases, and the heat insulation decreases. Therefore, if only the original purpose of heat insulation is taken into consideration, it is preferable that there are no voids. However, when there are few voids, the particles of the porous structure are less likely to shift when compressed from the outside, and the amount of deformation may be small. On the other hand, when there are too many voids, the contact points formed by any of the points, lines, and faces of the porous structure, or a combination of these, are reduced, and the elasticity of the porous structure is less likely to be exhibited, and the recovery rate may decrease. Therefore, in the heat insulating material of the present disclosure, the porosity is set to 20% or less in consideration of heat insulation, deformability, and recovery. A suitable porosity is 15% or less. The porosity may be 0%, that is, no voids may be detected in the following measurement method.

[0048] The porosity in the present disclosure is a value determined by photographing a cross section of the pressure-molded body in the thickness direction with 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 a magnification of 200 times. (2) Next, the captured SEM image is subjected to contrast adjustment, noise removal, and binarization processing in that order. The contrast adjustment was performed using the CLAHE (Contrast Limited Adaptive Histogram Equalization) algorithm. The parameters were Contrast Limit: 2.0 and Grid Size: (8,8). The noise removal was performed using the Non-Local Means Filter. The parameters were h: 40, Template Window Size: 23, and Search Window Size: 39. Here, h is the strength of the filter, Template Window Size is the size of the part to be searched, and Search Window Size is the size of the area to be searched. The binarization processing was performed using adaptive binarization. The parameters were Block Size: 219 and C: 40. Here, Block Size is the range to be referenced when calculating the threshold, and C is the correction of the threshold. The threshold was calculated using the average value of the range to be referenced. Finally, to remove extremely small noise, structures smaller than 15 μm (32 pixels) were removed from the image 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 the pressure-molded body, or may be composed of a base material supporting the pressure-molded body, an exterior material housing the pressure-molded body, and the like. The base material may be arranged only on one side of the heat insulating material in the thickness direction, or may be arranged on both sides so as to sandwich the heat insulating material. In addition, the heat insulating material may be covered with a single base material, and the base material may be used as an exterior material. An adhesive layer may be interposed between the heat insulating material and the base material. The adhesive layer may contain a flame retardant in addition to the adhesive component.

[0050] Examples of the material of the substrate include cloth, resin, paper, and steel plate. Examples of the 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 them, AES fiber is safer because it is biosoluble. Examples of resins include polyethylene terephthalate (PET), polyimide, polyamide, and PPS. Examples of paper include pulp and composite materials 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, a fabric (woven fabric) or nonwoven fabric made from inorganic fibers such as glass fiber or metal fiber, or fireproof insulation paper made as a composite of pulp and magnesium silicate, has a relatively low thermal conductivity and is highly shape-retaining even in a high-temperature atmosphere. In addition, the use of a fireproof substrate further improves safety. Substrates with high heat resistance 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 of manufacturing heat insulating material for battery packs> The method for producing an insulating material for a battery pack according to the present disclosure is one embodiment of the method for producing an 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 process is a process for producing a powder of a porous structure consisting of particles of different shapes and sizes by pulverizing a composition containing a porous structure produced by the sol-gel reaction of a solution containing two or more types of silane compounds with different numbers of siloxane bonds, a dispersant, and water. 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 a manufactured state or may be pre-pulverized after production (both include purchased products). The pulverization process may be performed using a media-less pulverizing and mixing device, a stirrer, or the like.

[0054] As the dispersant, as described above, a surfactant, a water-soluble oligomer having both polar and non-polar components in the side chain, etc. may be used. If a dispersant is present in the pressure-molded body, a heat transfer path may be formed through the dispersant. In addition, the organic components may decompose and deteriorate at high temperatures, generating gas or causing cracks in the pressure-molded body. Therefore, taking into consideration the balance with exerting the dispersing function, the amount of the dispersant to be blended is desirably 5% by mass or less, and more desirably 2% by mass or less, when the solid content of the composition is 100% by mass.

[0055] In this process, one or more selected from infrared shielding particles and inorganic fibers may be blended with the composition and pulverized. Since 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 and the like to the composition and pulverizing it together with the porous structure, there is no need to mix and disperse the infrared shielding particles and the like separately, and the number of work steps can be reduced. This can increase production efficiency and also lead to improved quality of the heat insulating material.

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

[0057] [Other forms] In the above-mentioned first step, the infrared shielding particles and the like are blended into the composition and 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 into the composition obtained by pulverizing the porous structure, and the mixture may be subjected to the pressure molding in the second step. EXAMPLES

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

[0059] <Production of insulation samples> [Preparation of the 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 with 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 was added as a porous structure and completely wetted in the liquid. Then, glass fiber was added as inorganic fiber, and the mixture was stirred at 800 rpm for 30 minutes to perform a pulverization process. After that, the mixture was further stirred at 1000 rpm for 10 minutes to perform a second pulverization process. In this way, the average particle diameter (D 50A composition having a silica aerogel powder with a particle size of 70 μm was produced. The composition had a clay-like appearance with particulate matter with a diameter of 5 mm or less. The content of the silica aerogel powder in the composition was 73.7% by mass when 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 having a silica aerogel powder with a particle size of 150 μm was produced. Specifically, the stirring time after the addition of the silica aerogel was set to 5 minutes, and the additional stirring time was set to 5 minutes.

[0061] Details of the materials used are as follows: Silica aerogel: A crushed product of Cabot Corporation's "Aerogel Particles P200", with an average particle size of 100 μm. 29 Analysis by Si-NMR with 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 mass% and the proportion of M units was 21.7 mass%. From this analysis result, it was confirmed that the silane compounds used in the production of this product, assuming the total to be 100 mass%, consisted of 78.3 mass% tetrafunctional silane compounds and 21.7 mass% 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: "ECS03-615" manufactured by Central Glass Fiber Co., Ltd., length 3 mm, fiber diameter 9 μm.

[0062] [Production of pressure-molded body] The clay-like composition produced was pressure-molded as follows. First, a base was prepared in which a first spacer plate made of SUS was layered on top of glass fiber paper. A square injection hole of 150 mm square was formed in the center of the first spacer plate. The produced 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, glass fiber paper was layered from above, and a second spacer plate was placed on top of that to produce a laminate consisting of "glass fiber paper / composition / glass fiber paper / second spacer plate". A square injection hole of 150 mm square was also formed in the center of the second spacer plate, similar to the first spacer plate, and the molded composition was contained in the injection hole of the second spacer plate. The thicknesses of the first spacer plate and the second spacer plate were adjusted so that the insulation sample had the desired porosity.

[0063] Separately, a first plate material made of aluminum, 5 mm thick and 320 mm square, and a second plate material made of aluminum, 1 mm thick and 320 mm square, were prepared. A plurality of grooves were formed on one side of the first plate material. Each of the plurality of grooves was linear, 2.5 mm wide, 3 mm deep, and 200 mm long, and was formed in parallel at 5 mm intervals. Punched holes with a diameter of 1 mm were formed on the entire surface of the second plate material at 2 mm intervals. The second plate material was placed on one side of the first plate material, and a laminate was placed on top of it. Then, the second plate material was placed on the laminate, and the first plate material was further placed on top of it so that the side on which the grooves were formed was the second plate material side. In this state, pressure molding was performed by hot pressing for 10 minutes at a temperature of 165°C and a load of about 980kN. After that, it was allowed to cool to room temperature (20°C ± 5°C), and the first plate material, the second plate material, the second spacer plate, and the upper and lower glass fiber papers were removed to obtain a square plate-shaped pressure molded body. 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 heat insulating material samples in the thickness direction were observed by SEM. As an example, FIG. 2 shows a cross-sectional SEM photograph (magnification 200 times) 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 insulation samples> [Thermal insulation] The thermal conductivity of the insulation sample 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, the insulation samples were stacked to prepare two laminates with a thickness of about 20 mm. The laminates were placed on the upper and lower sides of the probe so as to sandwich the probe, and a weight of about 5 kg was placed on top of the laminate to prevent it from being crushed, and the laminate was placed in an electric furnace. Then, the temperature in the electric furnace was raised to 600°C, and the thermal conductivity was measured after the temperature in the furnace stabilized. 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 more was evaluated as fail (indicated by a cross in the same table).

[0066] [Resilience] A compression test was conducted by pressing the center of an insulation sample (square plate of 150mm length, 150mm width, and arbitrary thickness) with a 60mm diameter compression terminal using A&D's Tensilon universal material testing machine "RTF1350". The compression test was conducted by moving the compression terminal back and forth at a speed of 1mm / min with the upper limit of compressive stress set to 2.0MPa, and three cycles were repeated, with the section in which the compressive stress changed from 0.02MPa to 2.0MPa to 0.02MPa being one cycle. 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 is a value calculated using the following formula (II). Compression rate (%) = the amount of compression terminal pushed in (mm) after the compressive stress reaches 0.01 MPa during the pressing process in one cycle / the thickness of the insulation sample when the compressive stress reaches 0.01 MPa during the pressing process in one cycle (mm) × 100 (II)

[0067] In the stress-compression curve of the second cycle, the index value of the restorability of the heat insulating material sample was determined 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. In this example, the index value of the restorability of 10% or more was evaluated as pass (indicated by a circle in Table 1 below), and the index value of less than 10% was evaluated as fail (indicated by a cross in the same table).

[0068] [Evaluation Results] Table 1 shows the evaluation results of the porosity of the insulation sample, the average particle size of the silica aerogel powder, and the insulation and restoration properties. [Table 1]

[0069] As shown in Table 1, it was confirmed that the samples of Examples 1 to 6, which have a porosity of 20% or less, have excellent heat insulation at high temperatures and high recovery. In addition, although not shown in Table 1, it was confirmed that these samples also have a large deformation amount (compression rate). Comparing the samples of Examples 1 to 4, it was confirmed that the recovery rate decreases as the porosity increases. It is presumed that the recovery rate decreases because the contact points between the silica aerogel particles decrease with an increase in porosity, which reduces friction between the particles and causes the voids to have no recovery even if they are crushed by compression. It was also confirmed that the recovery rate is exhibited even when the void rate is 0%, as in the sample of Example 6. In contrast, the sample of Comparative Example 1, which has a porosity of 25%, shows poor results in both heat insulation and recovery. [Explanation of symbols]

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

Claims

1. A thermal 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 connected to form a skeleton and pores are formed between the skeletons, The powder of the porous structure is composed of particles of different shapes and sizes, The content of the powder of the porous structure in the composition is 65% by mass or more when the solid content of the composition is 100% by mass, The pressure-molded body has a porosity of 20% or less.

2. 2. The insulating material for a battery pack according to claim 1, wherein the porous structure is produced by a sol-gel reaction of a solution containing two or more kinds of silane compounds having different numbers of siloxane bonds.

3. 2. The insulating material for a battery pack according to claim 1, wherein the powder of the porous structure is obtained by pulverizing the porous structure.

4. The insulating material for a battery pack according to claim 1 , wherein the pressure-molded body has a porosity of 1.7% or more and 8.0% or less.

5. 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.

6. 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.

7. The insulating material for a battery pack according to claim 2 , wherein the silane compound is a tetrafunctional silane compound and a trifunctional silane compound, or a tetrafunctional silane compound and a monofunctional silane compound.

8. 8. The insulating material for a battery pack according to claim 7, wherein when the silane compound is the tetrafunctional silane compound and the trifunctional silane compound, the content of the trifunctional silane compound is 50% by mass or more when the total amount of the silane compounds is 100% by mass.

9. 8. The insulating material for a battery pack according to claim 7, wherein the silane compound is the tetrafunctional silane compound and the monofunctional silane compound, and the content of the monofunctional silane compound is 10% by mass or more and less than 40% by mass, where the total amount of the silane compounds is 100% by mass.

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

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

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

13. A method for producing the insulating material for a battery pack according to claim 1, A method for producing an insulating material for a battery pack, comprising a pressure molding step of placing a composition having a powder of the porous structure composed of particles of different shapes and sizes, a dispersant, and water in a mold and pressure molding the composition.

14. The method for producing an insulating material for a battery pack according to claim 13, wherein the porous structure is produced by a sol-gel reaction of a solution having two or more kinds of silane compounds having different numbers of siloxane bonds.

15. 14. The method for producing an insulating material for a battery pack according to claim 13, further comprising, prior to the pressure molding step, a composition production step of producing the composition by pulverizing a dispersion liquid having the porous structure, the dispersant, and the water.

16. The method for producing an insulating material for a battery pack according to claim 13, wherein the composition comprises at least one selected from the group consisting of infrared shielding particles and inorganic fibers.

Images