Heat insulating material for battery pack and method for producing same

Abstract

A heat insulating material for an assembled battery is provided with a press-molded body (1) 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 formed between the skeletons. The porous structure is produced by a sol-gel reaction of a solution having two or more silane compounds having different siloxane bond numbers, and the powder of the porous structure is composed of particles (10) having different shapes and sizes and obtained by pulverizing the porous structure. When the solid content in the composition is 100% by mass, the content of the powder of the porous structure in the composition is 65% by mass or more, and the porosity of the press-molded article (1) is 20% or less.

Description

Technical Field

[0001] The present disclosure relates to a thermal insulation material to be disposed between adjacent battery cells in a battery pack accommodating a plurality of battery cells, and more particularly to a thermal insulation material using a porous structure such as aerogel. Background Art

[0002] Hybrid vehicles and electric vehicles are equipped with battery packs that accommodate multiple battery cells. In the battery pack, a battery module composed of multiple stacked battery cells is housed in a frame in a state where it is fixed by fastening members from both sides in the stacking direction. Insulating materials are arranged between adjacent battery cells, etc., in order to suppress heat transfer and thermal runaway in the event of abnormal heat generation of the battery cells. Battery cells expand and contract with charging and discharging. Therefore, the insulating materials arranged between the battery cells are preferably able to deform to follow the expansion and contraction of the battery cells and maintain thermal insulation properties. In more detail, when the battery cells expand due to charging, it is necessary to generate a reaction force of a certain value or more to apply force to the battery cells while reducing the thickness of the insulating material due to its compression force, thereby avoiding positional displacement of the insulating material. In addition, when the battery cells shrink due to discharge (when returning to their original thickness), the thickness of the insulating material also needs to be restored.

[0003] As materials for thermal insulation, silica aerogels with low thermal conductivity are known. For example, in Patent Document 1, as an aerogel powder having excellent softness and resistance to damage against compression force, there is described an aerogel powder composed of an aerogel that is a hydrolysis condensate of a silane compound. When the mass percentages of a tetrafunctional silane compound, a trifunctional silane compound, and a difunctional silane compound are set to Qx, Tx, and Dx, respectively, the raw material silane compound satisfies 0≤Qx≤70, 30≤Tx≤100, and 0≤Dx<30 (where Qx+Tx+Dx=100). Patent Document 2 describes a thermal insulation material having a porous structure and a binder having pores formed by connecting a plurality of primary particles to form a skeleton, and wherein the volume ratio of the voids between the porous structures is set to be greater than 10% and less than 55%.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2021-165387

[0007] Patent Document 2: Japanese Patent Application Laid-Open No. 2020-122544 Summary of the Invention

[0008] Problems to be solved by the invention

[0009] The aforementioned Patent Document 1 describes the use of a predetermined silane compound as a raw material for the purpose of improving the softness of the aerogel powder itself and its resistance to damage during processing. However, in paragraph

[0109] of the document, as the use of aerogel powder, filling it into insulating windows, insulating building materials, etc. is listed. Patent Document 1 does not describe the use of aerogel powder by pressurizing and forming it into an insulating material for battery packs. Therefore, Patent Document 1 does not study the deformability of the "pressed compact" of aerogel powder during compression, the reaction force generated, and the recovery of the original shape after unloading. In addition, there is no record of the porosity of the "pressed compact".

[0010] On the other hand, the thermal insulation material described in Patent Document 2 is manufactured by dispersing a porous structure in a binder solution, applying the coating to a substrate after adjusting the gas state in the coating, and drying. In this manufacturing method, voids are actively created between the porous structures to reduce shrinkage strain during drying and suppress the occurrence of cracks. The thermal insulation material described in Patent Document 2 is not a "pressed compact" formed by press-molding powder of a porous structure. The volume ratio of voids specified in Patent Document 2 is determined to reduce shrinkage strain during drying of the coating and does not meet the properties required of thermal insulation materials for battery packs.

[0011] Means used to solve problems

[0012] The present disclosure has been made in view of such actual circumstances, and aims to provide a battery pack thermal insulation material and a method for producing the same, which uses a press-molded body of a powder composition having a porous structure and has excellent deformability against compression and recovery after unloading.

[0013] (1) In order to solve the above-mentioned problems, the thermal insulation material for battery packs disclosed in the present invention (hereinafter sometimes referred to as "the thermal insulation material disclosed in the present invention") is characterized in that it comprises a press-formed body having a composition, wherein the composition comprises powder of a porous structure having pores between a plurality of primary particles connected to form a skeleton, wherein the porous structure is produced by a sol-gel reaction of a solution of two or more silane compounds having different numbers of siloxane bonds, wherein the powder of the porous structure is composed of particles of different shapes and sizes obtained by pulverizing the porous structure, wherein the content of the powder of the porous structure in the composition is 65% by mass or more when the solid content in the composition is set to 100% by mass, and the porosity of the press-formed body is 20% or less.

[0014] For example, when the powder of a porous structure is composed of spherical particles of the same size, in a press-formed body of the powder, the particles are mainly regularly filled with point contact. As a result, the rigidity of the filled particles increases, and the reaction force relative to the compression force from the outside increases, so the change in thickness when compressed is extremely small. In contrast, the powder of the porous structure used in the thermal insulation material of the present invention is obtained by pulverizing the porous structure and is composed of particles of different shapes and sizes. In a press-formed body composed of such particles of different shapes and sizes, the particles are not only in point contact with each other, but also in line or surface contact, and the configuration is irregular. In this case, when compressed from the outside, the particles move in a staggered manner, thereby increasing the deformation in the thickness direction. In addition, when there are gaps in the press-formed body, the particles become easier to move and the deformation becomes even greater.

[0015] In addition, the porous structure is manufactured by a sol-gel reaction of a solution of two or more silane compounds having different numbers of siloxane bonds. In this specification, the siloxane bond of the silane compound refers to the bond (Si-O bond) between a silicon atom (Si) and an oxygen atom (O). Moreover, the number of siloxane bonds refers to the number of oxygen atoms bonded to one silicon atom, and the number of siloxane bonds of the silane compound is divided into four types: 1 to 4. Based on the understanding that the number of siloxane bonds of the silane compound affects the elasticity of the manufactured porous structure, the inventors of the present invention have achieved a porous structure with the desired elasticity by mixing and using a plurality of silane compounds with different numbers of siloxane bonds. More specifically, a porous structure with the ability to deform while generating the desired reaction force during compression and to return to its original shape after unloading is achieved. The obtained porous structure is then pulverized, and a powder composed of particles of different shapes and sizes is used, thereby achieving an insulating material that can deform accordingly even if the battery cell expands slightly during charging. Thus, the thermal insulation material of the present disclosure has excellent deformation properties against compression and recovery properties after unloading. According to the thermal insulation material of the present disclosure, even if the battery cell expands or contracts, positional displacement is unlikely to occur, and high thermal insulation properties can be maintained.

[0016] (2) In the above configuration, the average particle size of the powder of the porous structure may be 30 μm or more and 150 μm or less. According to this configuration, a desired filling state of the particles of the porous structure can be easily achieved.

[0017] (3) In any of the above configurations, the particles of the porous structure may be randomly stacked in the press-molded body. According to this configuration, the particles of the porous structure contact each other at points, lines, or surfaces, and when compressed from the outside, the particles tend to move in a staggered manner. Consequently, the amount of deformation in the thickness direction increases.

[0018] (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 refers to a silane compound having four siloxane bonds. Similarly, a trifunctional silane compound refers to a silane compound having three siloxane bonds, a difunctional silane compound refers to a silane compound having two siloxane bonds, and a monofunctional silane compound refers to a silane compound having one siloxane bond. This configuration is suitable for producing a porous structure having desired elasticity.

[0019] (5) In the configuration of (4), 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 greater, with the total mass of the silane compound being 100% by mass. Increasing the content of the trifunctional silane compound can increase the elastic deformation of the resulting porous structure.

[0020] (6) In the configuration of (4), when the silane compound is the tetrafunctional silane compound and the monofunctional silane compound, the content of the monofunctional silane compound is 10% by mass or more and less than 40% by mass, with the total content of the silane compound being 100% by mass. If the content of the monofunctional silane compound is less than 10% by mass, the elastic deformation of the resulting porous structure decreases, while if the content is 40% by mass or more, the skeletal strength of the porous structure decreases.

[0021] (7) In any of the above configurations, the composition may include one or more selected from infrared blocking particles, inorganic fibers, and dispersants. According to this configuration, the press-molded body (thermal insulation material) includes one or more selected from infrared blocking particles, inorganic fibers, and dispersants.

[0022] Thermal insulation materials using porous structures can achieve a high thermal insulation effect by suppressing conduction and convection, the main of the three forms of heat transfer (conduction, convection, and radiation). Radiation is the phenomenon of heat transfer through electromagnetic waves. The higher the temperature, the greater the radiation energy released. Therefore, in a high-temperature atmosphere, radiation becomes the main cause of heat transfer. Therefore, if infrared blocking particles that can suppress heat transfer caused by radiation are used in combination, heat transfer caused by radiation can be suppressed in addition to suppressing heat transfer caused by conduction and convection. High thermal insulation properties can be achieved at room temperature and at temperatures above 500°C. When the pressed body contains inorganic fibers, the mechanical strength of the pressed body is improved, which can suppress the shedding of particles of the porous structure. In addition, porous structures are not easily fused with water and are not easy to disperse. Therefore, when water is used for the pulverization process, the addition of 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 comprises a powder of a porous structure and a dispersant, and is directly press-molded to form a press-molded body.

[0023] (8) In any of the above configurations, the porous structure may be a silica aerogel. Silica aerogel has a good balance between the size of its skeleton and the size of its pores, and exhibits excellent thermal insulation properties.

[0024] (9) In any of the above configurations, the composition may not contain a binder for binding the components of the press-formed body. According to this configuration, it is easy to achieve a desired filling state and porosity of the particles of the porous structure in the press-formed body.

[0025] (10) The method for manufacturing a thermal insulation material for a battery pack disclosed in the present invention is one mode of the method for manufacturing a thermal insulation material for a battery pack of any of the above-mentioned structures, and is characterized in that it comprises: a first step, in which a composition having the porous structure, a dispersant and water is pulverized to produce a powder of the porous structure composed of particles of different shapes and sizes, wherein the porous structure is produced by a sol-gel reaction of a solution of two or more silane compounds having different numbers of siloxane bonds; and a second step, in which the pulverized composition is placed in a forming mold for pressure molding.

[0026] In the method for manufacturing a thermal insulation material for a battery pack disclosed herein (hereinafter sometimes referred to as the "manufacturing method of the present disclosure"), a porous structure is pulverized using a dispersant (a first step). This improves the dispersibility of the porous structure, allowing the porous structure to be pulverized into a desired state to produce a powder composed of particles of varying shapes and sizes. Furthermore, in the second step, by adjusting the conditions during press molding, the porosity of the press molded body can be reduced to 20% or less. The manufacturing method of the present disclosure makes it possible to easily manufacture the thermal insulation material for a battery pack disclosed herein.

[0027] (11) It can also be configured such that, in the configuration of the above-mentioned (10), the composition in the first step contains one or more selected from infrared blocking particles and inorganic fibers. In this configuration, when the pressurized molded body (thermal insulation material) contains one or more selected from infrared blocking particles and inorganic fibers (hereinafter sometimes referred to as "infrared blocking particles, etc."), it is combined with a porous structure, etc. to form a composition, and then subjected to a pulverization treatment. Infrared blocking particles and inorganic fibers are harder than porous structures, and therefore are hardly pulverized under the condition that the porous structure is pulverized. According to this configuration, infrared blocking particles, etc. can be added to the porous structure and dispersed during the pulverization treatment, so there is no need for additional mixing and dispersion, and the number of working steps is reduced. Therefore, it is possible to improve production efficiency and also improve the quality of the thermal insulation material.

[0028] According to this configuration, a press-molded body containing infrared-blocking particles and the like is manufactured. As with the configuration (7) above, if the press-molded body contains infrared-blocking particles, heat transfer due to radiation can be suppressed in addition to heat transfer due to conduction and convection, achieving high thermal insulation properties at temperatures ranging from room temperature to high temperatures exceeding 500°C. If the press-molded body contains inorganic fibers, the mechanical strength of the press-molded body is improved, and the shedding of particles from the porous structure can be suppressed.

[0029] Effects of the Invention

[0030] The battery pack insulation material disclosed herein exhibits excellent deformation resistance against compression and recovery after unloading. Therefore, even when battery cells expand or contract, they are less likely to shift position, maintaining high thermal insulation properties. The method for manufacturing a battery pack insulation material disclosed herein improves the dispersibility of the porous structure during pulverization, making it easy to produce a powder of the porous structure composed of particles of varying shapes and sizes. This facilitates the manufacture of the battery pack insulation material disclosed herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a schematic diagram showing the filling state of particles in the porous structure of the thermal insulation material of the present disclosure.

[0032] Figure 2 This is a cross-sectional SEM photograph of the sample of Example 1 (magnification 200 times). DETAILED DESCRIPTION

[0033] The following describes in detail the battery pack insulation material and its manufacturing method of the present disclosure. The insulation material of the present disclosure is not limited to the following embodiments and can be implemented in various forms with modifications and improvements that can be made by those skilled in the art without departing from the scope of the present disclosure.

[0034] <Thermal insulation materials for battery packs>

[0035] The press-formed body constituting the thermal insulation material for a battery pack of the present disclosure is produced by press-forming a powder composition having a porous structure.

[0036] [Porous structure]

[0037] In a porous structure, multiple primary particles are linked to form a skeleton, with pores located between the skeletons. The diameter of the primary particles forming the skeleton is preferably approximately 2 to 5 nm, and the size of the pores formed between the skeletons is preferably approximately 10 to 50 nm. When the pores are mostly so-called mesopores, which are 50 nm or less in size, the mesopores are smaller than the mean free path of air, thus restricting air convection and hindering heat transfer.

[0038] [Method for producing porous structure]

[0039] The porous structure is manufactured by a sol-gel reaction of a solution of two or more silane compounds having different numbers of siloxane bonds (hereinafter sometimes referred to as a "solution containing a silane compound"). The silane compound only needs to contain compounds with different numbers of siloxane bonds, or it can contain multiple compounds with the same number of siloxane bonds. The solution containing a silane compound can be prepared by adding a compound appropriately selected from a tetrafunctional silane compound, a trifunctional silane compound, a difunctional silane compound, and a monofunctional silane compound to the solution. In addition, when a catalyst is added to an aqueous solution of sodium silicate, silane compounds with different numbers of siloxane bonds are generated according to the pH of the aqueous solution, the molar ratio of SiO2 to Na2O, the type and concentration of the catalyst, etc. Therefore, sodium silicate can also be used as a starting material and its hydrolysis reaction can be used to prepare a solution containing a silane compound. From the viewpoint of increasing the elastic deformation of the obtained porous structure, the silane compound is preferably in a form consisting of a tetrafunctional silane compound and a trifunctional silane compound, or in a form consisting of a tetrafunctional silane compound and a monofunctional silane compound.

[0040] Among them, in the former mode, when the overall amount of the silane compound is set to 100% by mass, the content of the trifunctional silane compound is preferably 50% by mass or more. More preferably, it is 60% by mass or more, and further preferably 65% by mass or more. If the content of the trifunctional silane compound is increased, the -O-Si-O-bonding ratio is reduced in the resulting porous structure, and therefore the elastic deformation of the porous structure can be increased. In addition, in order to give play to the effect of mixing silane compounds with different siloxane bond numbers, when the overall amount of the silane compound is set to 100% by mass, the content of the tetrafunctional silane compound in this mode is preferably at least 20% by mass or more.

[0041] In the latter embodiment, when the total amount of the silane compound is 100% by mass, the content of the monofunctional silane compound is preferably 10% by mass or more. More preferably, it is 15% by mass or more. If the content of the monofunctional silane compound is less than 10% by mass, the elastic deformation of the resulting porous structure decreases. In addition, from the perspective of suppressing the reduction of the skeletal strength of the porous structure, when the total amount of the silane compound is 100% by mass, the content of the monofunctional silane compound is preferably less than 40% by mass. More preferably, it is 30% by mass or less.

[0042] The silane compound used in the manufacture of the porous structure can be made of solid 29 Si-NMR is analyzed by DD (Dipolar Decoupling) method. 29 In the Si-NMR spectrum, the presence ratios of the Q unit, T unit, D unit, and M unit calculated based on the signal areas of the Q unit of a silicon atom bonded to four oxygen atoms, the T unit of a silicon atom bonded to three oxygen atoms, the D unit of a silicon atom bonded to two oxygen atoms, and the M unit of a silicon atom bonded to one oxygen atom are consistent with the content ratios of the tetrafunctional silane compound, trifunctional silane compound, difunctional silane compound, and monofunctional silane compound contained in the solution containing the silane compound.

[0043] Examples of tetrafunctional silane compounds include tetraalkoxysilane and tetraacetoxysilane. The number of carbon atoms in the alkoxy group of tetraalkoxysilane is preferably 1 to 9. Examples include tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, and tetraisopropoxysilane. Examples of trifunctional silane compounds include trialkoxysilane and triacetoxysilane. The number of carbon atoms in the alkoxy group of trialkoxysilane is preferably 1 to 9. Examples include methyltrimethoxysilane, ethyltrimethoxysilane, propyltrimethoxysilane, hexyltrimethoxysilane, octyltrimethoxysilane, methyltriethoxysilane, ethyltriethoxysilane, propyltriethoxysilane, pentyltriethoxysilane, hexyltriethoxysilane, and octyltriethoxysilane. Examples of difunctional silane compounds include dialkoxysilane and diacetoxysilane. The number of carbon atoms in the alkoxy group of dialkoxysilane is preferably 1 to 9. Examples include dimethyldimethoxysilane, diethyldimethoxysilane, and diisobutyldimethoxysilane. Examples of monofunctional silane compounds include methoxytrimethylsilane, isopropoxytrimethylsilane, ethoxytrimethylsilane, tert-butoxytrimethylsilane, ethoxytriethylsilane, methoxydimethyl(phenyl)silane, trimethyl(vinyloxy)silane, and isopropenyloxytrimethylsilane.

[0044] The method for producing a porous structure utilizing a sol-gel reaction is not particularly limited. The porous structure can be produced, for example, through a sol generation step, a gelation step, and a drying step. When the drying step is performed under normal pressure, a solvent replacement step can be performed before the drying step to replace the water adhering to the gel with an organic solvent that can be dried under normal pressure. First, in the sol generation step, a predetermined silane compound is added to an aqueous solution containing an acid catalyst and hydrolyzed to produce a sol. Optionally, a surfactant or a water-soluble oligomer having both polar and non-polar side chains can be added. Furthermore, when sodium silicate is used as the starting material, an acid catalyst is added to the aqueous sodium silicate solution and hydrolyzed at a predetermined pH to produce a sol. Next, in the gelation step, an alkaline catalyst is added to the generated sol to cause polycondensation and gelation. After the addition of the alkaline catalyst, the solution can be heated to approximately 80-120°C for curing to promote the polycondensation reaction. Next, in the drying step, the generated gel is dried. The drying method may be any of supercritical drying and non-supercritical drying methods (normal pressure drying and freeze drying). The resulting porous structure may be directly subjected to the pulverization process disclosed herein, i.e., a pulverization process for converting the porous structure into a desired powder composed of particles of varying shapes and sizes. Alternatively, a pre-pulverized porous structure may be subjected to the pulverization process disclosed herein.

[0045] Examples of porous structures include silica aerogels. Depending on the drying method used to produce the aerogel, materials dried under normal pressure are sometimes referred to as "xerogels" and those dried under supercritical pressure are sometimes referred to as "aerogels." However, in this specification, the term "aerogel" encompasses both. Silica aerogels are preferred because they have a good balance between the size of their skeleton and the size of their pores.

[0046] [Powder of porous structure]

[0047] The powder of the porous structure constituting the press-molded body is composed of particles of varying shapes and sizes obtained by pulverizing the porous structure produced by the aforementioned sol-gel method. The pulverization process can be performed using a medium-free pulverizing and mixing device such as a jet mill, a blender, or the like. The porous structure can be formed into various shapes by pulverizing, preferably shapes other than spherical.

[0048] From the viewpoint of increasing the pore volume and improving the thermal insulation, the average particle size of the powder of the porous structure is preferably 30 μm or more. In addition to being difficult to obtain by pulverization, powders with an average particle size of less than 30 μm are also prone to produce fine voids between the particles, so there is a hidden danger that the pressurized compact becomes brittle. The preferred average particle size is 50 μm or more. On the other hand, from the viewpoint of ease of forming into a sheet shape and suppressing particle shedding, the average particle size is preferably 150 μm or less. Although powders with an average particle size greater than 150 μm are less likely to produce voids between the particles, the size of the voids tends to become larger. The preferred average particle size is 120 μm or less. The average particle size of the powder of the porous structure is the median particle size (D 50 ) can be used.

[0049] [Composition]

[0050] The composition of the powder of the porous structure can be composed only of the powder of the porous structure, or it can be composed by containing other components within the scope of not hindering the effect exerted by the present disclosure. From the viewpoint of ensuring the desired thermal insulation of the press-formed body, when the solid content of the composition is set to 100% by mass, the content of the powder of the porous structure in the composition is 65% by mass or more. Preferably, it is 70% by mass or more. Here, the solid content refers to the component after removing volatile substances such as organic solvents and water. As other ingredients, for example, infrared blocking particles, inorganic fibers, dispersants, reinforcing inorganic particles, flame retardants, etc. can be listed. In addition, in the press-formed body, from the viewpoint of easily achieving the desired filling state and porosity of the particles of the porous structure, the composition preferably does not have a binder that bonds the constituent components of the press-formed body such as the particles of the porous structure.

[0051] (1) Infrared blocking particles

[0052] Infrared blocking particles absorb heat from a heat source and release it again from the surface on the heat source side, thereby blocking radiant heat from the heat source, and are particularly helpful in improving thermal insulation properties at high temperatures. From the viewpoint of filling the gaps (voids) between the porous structures, inhibiting the connection between the infrared blocking particles and other components, and making it difficult to form a heat transfer path, it is preferred that the particle size of the infrared blocking particles is smaller. However, if the particle size is too small, infrared rays are difficult to irradiate, and the scattering of infrared rays also becomes insufficient, making it difficult to exert the radiant heat blocking effect. From this viewpoint, the average particle size of the infrared blocking particles can be greater than 0.3 μm and less than 22 μm. The shape of the infrared blocking particles is spherical, flat, etc., and is not particularly limited. As for the average particle size of the infrared blocking particles, as with the powder of the porous structure, the median particle size (D 50 ) is sufficient. When using commercially available products, catalog values can also be used.

[0053] As infrared blocking particles, there can be listed particles selected from silicon carbide, kaolinite, montmorillonite, titanium oxide, silicon nitride, mica, aluminum oxide, 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, titanium iron oxide, zirconium, zirconium oxide, zirconium silicate, barium titanate, manganese dioxide, chromium oxide, titanium carbide, tungsten carbide, tungsten oxide, niobium oxide, indium tin oxide, cerium oxide, or particles of a mixture of two or more thereof. Among them, from the viewpoint of improving the blocking effect of radiant heat, infrared blocking particles preferably have a high emissivity particle with an emissivity of 0.6 or more in the wavelength region of infrared light. As high emissivity particles, there can be listed particles such as silicon carbide, kaolinite, silicon nitride, mica, aluminum oxide, zirconium oxide, aluminum nitride, zirconium silicate, cerium oxide, boron carbide, manganese oxide, tin oxide, iron oxide, etc. In addition, from the perspective of scattering incident infrared light and improving the radiant heat blocking effect, a method using particles having a high refractive index in the infrared wavelength region is also effective. For example, high-refractive-index particles having a refractive index of 2.0 or greater in the visible light wavelength region are preferred. Examples of high-refractive-index particles include silicon carbide, titanium oxide, zirconium oxide, 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.

[0054] For example, silicon carbide, titanium oxide, silicon nitride, mica, aluminum oxide, aluminum nitride, boron carbide, iron oxide, and magnesium oxide have high specific heat and therefore high heat capacity, making it difficult for the particles themselves to heat up. This also helps improve the thermal insulation of the pressurized compact (insulating material). Furthermore, since it also has high heat resistance, it also helps improve the heat resistance of the pressurized compact. In particular, silicon carbide is preferred because its thermal conductivity increases little even in a high-temperature atmosphere of around 800°C.

[0055] (2) Inorganic fiber

[0056] The inorganic fibers are physically entangled around the porous structure, thereby increasing the mechanical strength of the pressurized compact and suppressing the shedding of particles from the porous structure. The type of inorganic fibers is not particularly limited; however, considering heat resistance, mechanical strength, and other factors, ceramic fibers such as glass fibers and alumina fibers are preferred. Considering both the reinforcing effect and the suppression of the formation of heat transfer paths, the length of the inorganic fibers is preferably 16 mm or less.

[0057] (3) Dispersant

[0058] The dispersant can be used when the porous structure is subjected to a pulverization treatment. As a dispersant, a surfactant, a water-soluble oligomer having polar and non-polar side chains, etc. is preferred. As a surfactant, there are ionic surfactants (cationic surfactants, anionic surfactants, amphoteric surfactants) and non-ionic surfactants. For example, if an ionic surfactant is used, even a relatively small amount can make the composition highly viscous, or the porous structure and other materials in the composition can be dispersed and stabilized. As an ionic surfactant, sodium carboxymethylcellulose (CMC-Na), polycarboxylic acid amine salts, polycarboxylic acid ammonium salts, polycarboxylic acid sodium salts, TEMPO oxidized cellulose nanofibers (CNF-Na) and the like can be listed. If a non-ionic surfactant is used, when preparing the composition, the porous structure and other materials can easily enter the solvent. In addition, when these materials aggregate and separate in the composition, it becomes easy to redisperse, or the solvent becomes easy to discharge during press forming. As a non-ionic surfactant, polyethylene oxide (PEO), polyvinyl alcohol (PVA) and the like can be listed.

[0059] (4) Enhanced inorganic particles

[0060] From the perspective of improving the mechanical strength of the pressed 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 high hardness and a large specific surface area, such as precipitated silica, gel-process silica, fused silica, wollastonite, potassium titanate, magnesium silicate, glass flakes, calcium carbonate, and barium sulfate, may be used.

[0061] (5) Flame retardant

[0062] From the perspective of imparting flame retardancy to the press-formed body, a flame retardant may be included in the composition. Halogen-based, phosphorus-based, metal hydroxide-based, and other known flame retardants may be used as flame retardants. Taking environmental load into consideration, phosphorus-based flame retardants are preferably used. Examples of phosphorus-based flame retardants include ammonium polyphosphate, red phosphorus, and phosphate esters. Among these, water-insoluble flame retardants and flame retardants coated with water-resistant resins are preferred, as they are less likely to flow out even when in contact with moisture during use. For example, ammonium polyphosphate and resin-coated ammonium polyphosphate are preferred.

[0063] [Pressure-molded body]

[0064] In a pressed compact formed by press-molding a composition of powder having a porous structure, it is preferred that the particles of the porous structure are randomly stacked. Figure 1 Schematic diagram showing the filling state of the particles of the porous structure in the thermal insulation material of the present disclosure. Figure 1 The schematic diagram shown in FIG. 1 shows a cross section of the heat insulating material (pressed molded body) in the thickness direction. Figure 1 In the figure, the hatching of the particles of the porous structure is omitted. Figure 1 As shown, in the thermal insulation material 1, a plurality of porous structure particles 10 are arranged in a stacked manner. Most of the porous structure particles 10 have shapes other than spherical, and each has a different shape and size. The filling state of the porous structure particles 10 is similar to the "no-face stacking" seen in the stone walls of Japanese castles, etc. "No-face stacking" is a stone stacking method that directly stacks natural stone or rough-cut stone without processing. There are small gaps 11 between the porous structure particles 10. The porous structure particles 10 contact each other at any one of points, lines and surfaces, or a combination of these, and the arrangement form is irregular. Therefore, if compressed from the outside in the thickness direction, the porous structure particles 10 move in a staggered manner and deform. In addition, the porous structure particles 10 are elastic, so when the thermal insulation material 1 is compressed, they generate the desired reaction force and deform, and return to their original shape when unloaded.

[0065] The amount of voids in the press-formed body affects the thermal insulation. If the voids increase, that is, the porosity increases, the heat transfer caused by the convection of the air increases, and thus the thermal insulation decreases. Therefore, if only the thermal insulation as the original purpose is considered, it is preferable to have no voids. However, if there are few voids, there is a risk that the particles of the porous structure will be difficult to stagger when compressed from the outside, and the deformation amount will be reduced. On the contrary, if there are too many voids, the contact points formed by any one of the points, lines and surfaces of the porous structure, or their combination, will decrease, and there is a risk that it will be difficult to exert the elasticity of the porous structure and the recovery rate will be reduced. Therefore, in the thermal insulation material disclosed in the present invention, taking into account the thermal insulation, deformation and recovery, the void ratio is set to 20% or less. The preferred void ratio is 15% or less. The void ratio can also be 0%, that is, no voids can be detected in the following measurement method.

[0066] The porosity in the present disclosure is a value obtained by photographing a cross section of a press-molded body in the thickness direction using a scanning electron microscope (SEM) and binarizing the obtained cross-sectional photograph.

[0067] (1) First, a SEM photograph of a cross section in the thickness direction of the press-molded body is taken at a magnification of 200 times.

[0068] (2) Next, the SEM photographs were subjected to contrast adjustment, noise removal, and binarization in sequence. CLAHE (Contrast Limited Adaptive Histogram Equalization) algorithm was used for contrast adjustment. The parameters at this time were Contrast Limit: 2.0 and Grid Size: (8,8). Non-Local Means Filter was used for noise removal. The parameters at this time 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. Adaptive binarization was used for binarization. The parameters at this time were Block Size: 219 and C: 40. Here, BlockSize is the range referenced when calculating the threshold, and C is the threshold correction. The method for calculating the threshold was set to the average value of the referenced range. Finally, in order to remove extremely small noise, structures smaller than 15 μm (32 pixels) were removed from the binarized image.

[0069] (3) The structures remaining in the image are regarded as voids, and the void ratio is calculated using the following formula (I).

[0070] Void ratio (%) = area of voids / area of the entire screen × 100 (I)

[0071] <Usage form>

[0072] The thermal insulation material disclosed herein may consist solely of a press-formed body, or may include a substrate supporting the press-formed body, an outer packaging material for housing the press-formed body, and the like. The substrate may be disposed only on one side of the thermal insulation material in the thickness direction, or may be disposed on both sides of the thermal insulation material so as to sandwich the thermal insulation material. Alternatively, the thermal insulation material may be coated with a single substrate, and the substrate may be used as an outer packaging material. Alternatively, an adhesive layer may be interposed between the thermal insulation material and the substrate. In addition to adhesive components, the adhesive layer may also contain a flame retardant, etc.

[0073] The material of the substrate can be cloth, resin, paper, steel plate, etc. As the fibers constituting the cloth, glass fiber, rock wool, ceramic fiber, alumina fiber, silica fiber, carbon fiber, metal fiber, polyimide fiber, aramid fiber, polyphenylene sulfide (PPS) fiber, etc. are listed. As ceramic fibers, refractory ceramic fiber (RCF), polycrystalline alumina fiber (Polycrystalline Wool: PCW), and alkaline earth silicate (AES) fiber are known. Among them, AES fiber is biosoluble and therefore safer. As resins, polyethylene terephthalate (PET), polyimide, polyamide, PPS, etc. are listed. As paper, pulp, a composite material of pulp and magnesium silicate, etc. are listed. As steel plates, hot-dip galvanized steel plates (Galvalume) (registered trademark), galvanized plates, stainless steel (SUS) plates, iron plates, titanium plates, etc. are listed. The shape of the substrate is not particularly limited, and can be listed as woven fabrics, non-woven fabrics, films, sheets, etc. The substrate may be composed of a single layer, or may be a laminate in which two or more layers of the same material or different materials are laminated.

[0074] For example, glass cloth etc. are made of the cloth (woven fabric), nonwoven fabrics, the fire-resistant insulation paper made as the composite material of pulp and magnesium silicate by the inorganic fibers such as glass fiber and metal fiber, and the thermal conductivity is less, even if shape retention is also high under high temperature atmosphere. In addition, if adopting the base material with fire resistance, then safety is further improved. The base material with high heat resistance is made by glass fiber, rock wool, ceramic fiber, polyimide, PPS etc., specifically, can be listed as glass fiber nonwoven fabric, glass cloth, aluminum glass cloth, AES wool paper, polyimide fiber nonwoven fabric etc.

[0075] <Method for manufacturing thermal insulation material for battery pack>

[0076] The method for producing a thermal insulation material for a battery pack disclosed herein is one embodiment of the method for producing a thermal insulation material for a battery pack disclosed herein, and includes a first step and a second step. Each step will be described in order.

[0077] [First process]

[0078] This process is a process of pulverizing a composition having a porous structure, a dispersant and water to produce a powder of a porous structure composed of particles of different shapes and sizes. The porous structure is produced by a sol-gel reaction of a solution of two or more silane compounds having different numbers of siloxane bonds. 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 a porous structure in a state after manufacture, or a porous structure that has been pre-pulverized after manufacture (both including commercially available porous structures). The pulverization process may be carried out using a medium-free pulverizing and mixing device, a blender, or the like.

[0079] As the dispersant, as described above, a surfactant, a water-soluble oligomer having polar and non-polar side chains, etc. can be used. In addition, if a dispersant is present in the press-formed body, there is a hidden danger of forming a heat transfer path via the dispersant. In addition, there is a hidden danger of generating gas due to decomposition and degradation of the organic component at high temperatures, or generating cracks in the press-formed body. Therefore, in consideration of the balance with the dispersion function, when the solid content of the composition is set to 100% by mass, the amount of the dispersant is preferably 5% by mass or less, more preferably 2% by mass or less.

[0080] In this process, the composition may be mixed with one or more selected from infrared blocking particles and inorganic fibers and then subjected to a pulverization process. Infrared blocking particles and inorganic fibers are harder than the porous structure and therefore are rarely pulverized under conditions where the porous structure is pulverized. Therefore, by adding infrared blocking particles and the like to the composition and pulverizing them together with the porous structure, there is no need for separate mixing and dispersion of the infrared blocking particles, resulting in fewer operational steps. This can improve production efficiency and also enhance the quality of the thermal insulation material.

[0081] [Second process]

[0082] This step involves placing the pulverized composition into a mold and performing pressure molding. The pressure molding conditions can be appropriately determined so that the resulting press-molded body has the desired porosity (20% or less). For example, the pressure can be applied while heating to approximately 100-160°C and applying a surface pressure of approximately 0.1-2.0 MPa.

[0083] [Other methods]

[0084] In the first step described above, infrared-blocking particles, etc., are added to the composition and then pulverized together with the porous structure. However, if the press-molded body contains infrared-blocking particles, infrared-blocking particles, etc., can also be separately mixed with the composition after the porous structure has been pulverized, and then subjected to press-molding in the second step.

[0085] Example

[0086] Next, the present disclosure will be described in more detail with reference to examples.

[0087] <Manufacturing of Thermal Insulation Material Samples>

[0088] [Manufacturing of Composition]

[0089] (1) First composition

[0090] First, water is weighed in a resin container, a surfactant as a dispersant is added, and an air-driven blade stirrer is used to stir at 800 rpm for 60 minutes to dissolve the surfactant in the water. After stopping the stirring, silicon carbide (SiC) powder as infrared insulation particles is added, and further stirring is performed at 800 rpm for 15 minutes. While continuing to stir in this state, silica aerogel as a porous structure is added to completely wet it in the liquid. Then, glass fiber as an inorganic fiber is added, and stirring is performed at 800 rpm for 30 minutes, thereby performing a crushing process. After that, additional stirring is performed at 1000 rpm for 10 minutes, and a second crushing process is performed. In this way, a particle having an average particle size (D 50 ) is a composition containing silica aerogel powder having a diameter of 70 μm. The composition exhibits a clay-like texture composed of aggregated particles having a diameter of 5 mm or less. When the solid content of the composition is set to 100% by mass, the silica aerogel powder content in the composition is 73.7% by mass. Similarly, the surfactant content in the composition is 2.9% by mass, the silicon carbide powder content is 15.1% by mass, and the glass fiber content is 8.3% by mass.

[0091] (2) Second composition

[0092] A granular composition having an average particle size (D 50 ) is a second composition of silica aerogel powder having a particle size of 150 μm. Specifically, the stirring time after adding the silica aerogel was set to 5 minutes, and the additional stirring time was set to 5 minutes.

[0093] The details of the materials used are as follows.

[0094] Silica aerogel: A pulverized product of "Aerogel Particles P200" manufactured by Cabot Corporation, with an average particle size of 100 μm. 29 Si-NMR analysis of this product using the DD method at a MAS speed of 10 kHz and a pulse waiting time of 5 seconds revealed a Q unit ratio of 78.3% by mass and an M unit ratio of 21.7% by mass. Based on these analysis results, it was confirmed that, with the total silane compound used in the manufacture of this product being 100% by mass, the tetrafunctional silane compound accounted for 78.3% by mass and the monofunctional silane compound accounted for 21.7% by mass.

[0095] Silicon carbide powder: "FUJI RUNDUM GC#4000" manufactured by Fuji Manufacturing Co., Ltd., average particle size 5 μm.

[0096] Surfactant: Polyethylene oxide "PEO-8" manufactured by Sumitomo Seika Co., Ltd., with a viscosity-average molecular weight of 1.7 million to 2.2 million.

[0097] Glass fiber: "ECS03-615" manufactured by Central Glass Fiber Co., Ltd., 3 mm in length, 9 μm in fiber diameter.

[0098] [Manufacturing of Pressed Formed Body]

[0099] The manufactured clay-like composition is press-formed as follows. First, a base is prepared in which a first partition made of SUS is overlapped on glass fiber paper. A square injection hole of 150 mm square is formed in the center of the first partition. The manufactured composition is filled into the injection hole of the first partition and formed into a square plate. Next, the first partition is removed, and the glass fiber paper is overlapped from above, and the second partition is further arranged from above to manufacture a laminate consisting of "glass fiber paper / composition / glass fiber paper / second partition". A square injection hole of 150 mm square is also formed in the center of the second partition in the same manner as the first partition, and the formed composition is accommodated in the injection hole of the second partition. The thickness of the first partition and the second partition is adjusted so that the insulating material sample is formed to have the desired porosity.

[0100] Separately, a first aluminum plate having a thickness of 5 mm and a square of 320 mm and a second aluminum plate having a thickness of 1 mm and a square of 320 mm were prepared. A plurality of grooves were formed on one side of the first plate. The plurality of grooves were straight lines with a width of 2.5 mm, a depth of 3 mm, and a length of 200 mm, and were formed in parallel at intervals of 5 mm. Punches with a diameter of 1 mm were formed as a whole on the second plate at intervals of 2 mm. The second plate was overlapped on one side of the first plate, and a laminate was arranged thereon. Then, the second plate was placed on the laminate, and the first plate was overlapped so that the side with the groove formed became the side of the second plate. In this state, press-forming was performed by hot pressing for 10 minutes at a temperature of 165°C and a load of approximately 980 kN. Afterwards, it was cooled to room temperature (20°C ± 5°C), and the first plate, the second plate, the second partition, and the upper and lower glass fiber papers were removed to obtain a square plate-shaped press-formed body. The thickness of the first partition and the second partition was changed to produce seven press-formed bodies with different porosities. The produced press-molded body was used as a thermal insulation material sample.

[0101] The cross-sections of seven thermal insulation material samples in the thickness direction were observed using SEM. Figure 2 The cross-sectional SEM photograph of the sample of Example 1 is shown in FIG (magnification 200 times). Figure 2 As shown, in all samples, silica aerogel particles of different shapes and sizes were randomly stacked. Most of the silica aerogel particles had shapes other than spherical, and silicon carbide particles and glass fibers were arranged between the silica aerogel particles.

[0102] <Evaluation of Thermal Insulation Material Samples>

[0103] [Thermal insulation]

[0104] The thermal conductivity of the insulating material sample at 600°C was measured using the "Rapid Thermal Conductivity Meter QTM-700" and the "High-Temperature Corresponding Probe PD-31N" manufactured by Kyoto Electronics Industry Co., Ltd. as follows. First, the insulating material samples were overlapped to prepare two stacks with a thickness of about 20 mm. The stack was arranged one on the upper side and one on the lower side of the probe in a manner of clamping the probe, and a weight of about 5 kg was placed from above to prevent the stack from being crushed and placed in an electric furnace. Then, the temperature in the electric furnace was raised to 600°C, and after the temperature in the furnace stabilized, the thermal conductivity was measured. In this embodiment, the case where the measured thermal conductivity was less than 0.12 W / m·K was evaluated as qualified (indicated by the ○ mark in Table 1 described later), and the case where the thermal conductivity was 0.12 W / m·K or more was evaluated as unqualified (indicated by the × mark in the table).

[0105] [Resilience]

[0106] A compression test was conducted using a Tensilon universal material testing machine "RTF1350" manufactured by A&D Co., Ltd., in which a compression terminal with a diameter of 60 mm was used to press the central part of a thermal insulation material sample (a square plate with a length of 150 mm, a width of 150 mm, and any thickness). The compression test was conducted as follows: the upper limit of the compressive stress was set to 2.0 MPa, the compression terminal was reciprocated at a speed of 1 mm / minute, and the compressive stress range of 0.02 MPa→2.0 MPa→0.02 MPa was used as one cycle, and three cycles were repeated. Based on the data obtained by the compression test, a stress-compression rate curve was prepared with the horizontal axis as the compression rate and the vertical axis as the compressive stress. The compression rate of the horizontal axis is the value calculated by the following formula (II).

[0107] Compression rate (%) = Depth of compression terminal after the compression stress reaches 0.01 MPa during one pressing cycle (mm) / Thickness of insulation material sample when the compression stress reaches 0.01 MPa during one pressing cycle (mm) × 100 (II)

[0108] In the stress-compression rate curve for the second cycle, the value obtained by subtracting the compression rate at a compressive stress of 0.02 MPa at the end of the cycle from the compression rate at a compressive stress of 2.0 MPa was used as an indicator of the thermal insulation material sample's resilience. In this example, a resilience index value of 10% or greater was considered acceptable (indicated by a circle in Table 1 below), while a value of less than 10% was considered unacceptable (indicated by an x in the table).

[0109] [Evaluation results]

[0110] Table 1 shows the evaluation results of the porosity, average particle size of the silica aerogel powder, thermal insulation properties, and restorability of the thermal insulation material samples.

[0111]

[0112] As shown in Table 1, it was confirmed that the samples of Examples 1 to 6 with a porosity of 20% or less had excellent thermal insulation at high temperatures and high resilience. In addition, although not shown in Table 1, it was confirmed that the deformation amount (compression rate) was also large in these samples. Comparing the samples of Examples 1 to 4, it was confirmed that the resilience decreased if the porosity increased. It is speculated that if the porosity increases, the contact points between the silica aerogel particles decrease, thereby reducing the friction between the particles. Even if the voids are flattened due to compression, the voids do not have resilience, so the resilience decreases. In addition, it was confirmed that, as in the sample of Example 6, resilience was also exerted when the porosity was 0%. In contrast, the sample of Comparative Example 1 with a porosity of 25% resulted in poor thermal insulation and resilience.

[0113] Description of Reference Numerals

[0114] 1: thermal insulation material (pressed compact); 10: particles of the porous structure; 11: voids.

Claims

1. A thermal insulation material for a battery pack, characterized in that: The thermal insulation material for battery packs comprises a press-formed 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 formed between the skeletons. The porous structure is produced by a sol-gel reaction of solutions of two or more silane compounds having different numbers of siloxane bonds, and the powder of the porous structure is composed of particles of different shapes and sizes obtained by pulverizing the porous structure. When the solid content in the composition is 100% by mass, the content of the powder of the porous structure in the composition is 65% by mass or more, The porosity of the press-formed body is 20% or less.

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

3. The thermal insulation material for a battery pack according to claim 1, wherein: In the press-formed body, particles of the porous structure are randomly stacked.

4. The thermal insulation 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 thermal insulation material for a battery pack according to 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% by mass or more when the total amount of the silane compound is 100% by mass.

6. The thermal insulation material for a battery pack according to claim 4, wherein: When the silane compound is the tetrafunctional silane compound and the monofunctional silane compound, the content of the monofunctional silane compound is 10% by mass or more and less than 40% by mass, with the total amount of the silane compound being 100% by mass.

7. The thermal insulation material for a battery pack according to claim 1, wherein: The composition comprises at least one selected from infrared blocking particles, inorganic fibers, and a dispersant.

8. The thermal insulation material for a battery pack according to claim 1, wherein: The porous structure is silica aerogel.

9. The thermal insulation material for a battery pack according to claim 1, wherein: The composition does not contain a binder for binding the components of the press-formed body.

10. A method for manufacturing a thermal insulation material for a battery pack, which is the method for manufacturing a thermal insulation material for a battery pack according to claim 1, characterized in that: The method for manufacturing the thermal insulation material for a battery pack comprises: a first step of pulverizing a composition comprising the porous structure, a dispersant, and water to produce a powder of the porous structure composed of particles of different shapes and sizes, wherein the porous structure is produced by a sol-gel reaction of a solution of two or more silane compounds having different numbers of siloxane bonds; as well as In the second step, the pulverized composition is placed in a molding die and pressure-molded.

11. The method for manufacturing a thermal insulation material for a battery pack according to claim 10, wherein: The composition in the first step contains at least one selected from infrared blocking particles and inorganic fibers.

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