Silica aerogel powder used for heat insulation material for battery pack, and heat insulation material for battery pack

Abstract

This silica aerogel powder used for a heat insulation material for a battery pack has a specific surface area of 550 m2 / g or greater as measured on the basis of an adsorption isotherm obtained if the silica aerogel powder is measured using an adsorbed nitrogen amount measurement method, has a pore volume of 3.5-5.0 mL / g when the relative pressure is 0.99, and satisfies the following conditions (i) and (ii), where the pore volume with the relative pressure being 0.93 is a [mL / g], the pore volume with the relative pressure being 0.965 is b [mL / g], and the pore volume with the relative pressure being 0.99 is c [mL / g]. (i): 0 ≤ (a / c×100) ≤ 50, (ii): 50 ≤ (b / c×100) < 100

Description

Silica aerogel powder used as a heat insulating material for battery packs and heat insulating material for battery packs

[0001] The present disclosure relates to a thermal insulator disposed between adjacent battery cells in a battery pack housing a plurality of battery cells, and particularly to a thermal insulator using silica aerogel powder or silica aerogel.

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

[0003] Silica aerogel, which has low thermal conductivity, is known as a material for heat insulation. For example, Patent Document 1 describes an aerogel powder made of an aerogel, which is a hydrolysis condensation product of a silane compound, as an aerogel powder with excellent flexibility and fracture resistance against compressive force. The raw silane compound satisfies the following conditions: 0≦Qx≦70, 30≦Tx≦100, and 0≦Dx<30 (where Qx+Tx+Dx=100), where Qx, Tx, and Dx are the mass percentages of a tetrafunctional silane compound, a trifunctional silane compound, and a bifunctional silane compound, respectively. Patent Document 2 describes silica aerogel as an example of an aerogel used in an aerogel composite. Paragraphs

[0023] and

[0025] of the same document describe physical and structural properties attributable to aerogel, such as (a) an average pore diameter of 2 nm to 100 nm, (b) a porosity of 80% or more, and (c) a surface area of ​​20 m2, as determined by a nitrogen porosimetry test. ２ / g or more, and (d) a pore volume of 2.0 mL / g or more.

[0004] JP 2021-165387 A JP 2023-27128 A

[0005] Patent Document 1 discloses the use of a specific silane compound as a raw material for the purpose of improving the flexibility and fracture resistance (breakage resistance) of aerogel powder against compressive forces. However, Patent Document 1 does not disclose imparting compression recovery to silica aerogel, i.e., the ability to deform under load and return to its original state upon unloading. Patent Document 1 also discloses that the pores of aerogel are 5 nm to 100 nm when the pores are approximated by tubes and the inner diameter of the tubes is approximated by a circle. Furthermore, Patent Document 1 discloses that the inner diameter of the tube is equal to or less than the mean free path of the elemental molecules constituting air at atmospheric pressure. However, Patent Document 1 merely describes the size of the pores (pores) of the aerogel, and does not address the technical idea of ​​focusing on and specifying the pore structure to achieve desired properties. Similarly, Patent Document 2 discloses only values ​​such as surface area and pore volume as the general structure of aerogel, but does not discuss the pore structure.

[0006] The present disclosure has been made in view of the above circumstances, and aims to provide a silica aerogel powder that has excellent heat insulating properties and compression recovery and is used in a heat insulating material for a battery pack, and a heat insulating material for a battery pack that uses the silica aerogel. Another aim is to provide a heat insulating material for a battery pack that uses a silica aerogel that has excellent heat insulating properties and compression recovery.

[0007] (1) In order to solve the above problems, the silica aerogel powder of the present disclosure is a silica aerogel powder used as a heat insulating material for a battery pack, and when the silica aerogel powder is measured by a nitrogen adsorption measurement method, the specific surface area measured based on the obtained adsorption isotherm is 550 m ２ / g or more, and the pore volume at a relative pressure of 0.99 is 3.5 mL / g or more and 5.0 mL / g or less, and is characterized by satisfying the following conditions (i) and (ii) when the pore volume at a relative pressure of 0.93 is a [mL / g], the pore volume at a relative pressure of 0.965 is b [mL / g], and the pore volume at a relative pressure of 0.99 is c [mL / g]: (i) 0≦(a / c×100)≦50 (ii) 50≦(b / c×100)<100

[0008] In the present disclosure, the pore structure of the silica aerogel powder is specified to achieve the desired heat insulating property and compression recovery. ２ / g or more, the proportion of extremely small pores (so-called micropores) with a pore diameter (pore size) of about several nm is reduced. This relatively increases the proportion of pores with a pore diameter of about 30 to 68 nm, which is effective in improving thermal insulation. Secondly, by setting the pore volume at a relative pressure of 0.99 to 3.5 mL / g or more and 5.0 mL / g or less, the proportion of pores having the desired pore diameter is increased. In the nitrogen adsorption measurement method, if the pore shape is assumed to be cylindrical, the measured "pore volume at a relative pressure of 0.99" can be considered to be the volume of pores with a pore diameter of up to about 100 nm. If there are many large pores with a pore diameter exceeding 100 nm, not only will the thermal insulation properties be reduced, but the skeleton will easily collapse during compression, making it difficult to obtain the desired recovery properties. Therefore, in the silica aerogel powder of the present disclosure, the pore volume at a relative pressure of 0.99 is focused on, and by setting this within a predetermined range, the silica aerogel powder has pore sizes that contribute to heat insulation and compression recovery, except for those containing many pores with pore sizes exceeding 100 nm.

[0009] In the nitrogen adsorption measurement method, it is believed that the pore volume, including pores with a pore diameter of more than 100 nm, cannot be measured when the relative pressure is 0.99 or less. However, in the present disclosure, since the pores that contribute to the heat insulating property and compression recovery of the silica aerogel powder are the target, the "pore volume at a relative pressure of 0.99" is assumed to be close to the "total pore volume," and the above conditions (i) and (ii) are set. In the nitrogen adsorption measurement method, if the pore shape is assumed to be cylindrical, the "pore volume at a relative pressure of 0.93" can be considered to be the volume of pores with a pore diameter of up to about 30 nm, and the "pore volume at a relative pressure of 0.965" can be considered to be the volume of pores with a pore diameter of up to about 68 nm.

[0010] Under condition (i), when the ratio of pore volume (a) at a relative pressure of 0.93 is 50% or less, the number of pores with a pore size of up to about 30 nm decreases, and the number of pores with relatively large pore sizes increases, which is advantageous for improving compression recovery. Under condition (ii), when the ratio of pore volume (b) at a relative pressure of 0.965 is 50% or more, the number of pores with a pore size equal to or smaller than the mean free path of air (68 nm) increases. Pores with a pore size smaller than the mean free path of air suppress the heat conduction of air. Therefore, increasing the number of such pores is advantageous for improving thermal insulation. Thus, the silica aerogel powder of the present disclosure, which has a specific surface area and a pore volume at a relative pressure of 0.99 within a predetermined range and satisfies conditions (i) and (ii), has high thermal insulation and excellent compression recovery.

[0011] (2) A first insulating material for a battery pack according to the present disclosure includes the silica aerogel powder having the configuration described in (1) above. According to the insulating material for a battery pack according to the present disclosure, the insulating material deforms in response to the expansion and contraction of the battery cells, thereby suppressing misalignment and maintaining high insulating properties. Furthermore, the insulating material appropriately maintains the expansion and contraction of the battery cells, thereby contributing to extending the life of the battery cells.

[0012] (3) In the configuration of (2), the insulating material for a battery pack according to the present disclosure may include a pressure-molded body of a composition containing the silica aerogel powder, in which silica aerogel particles are in contact with each other at points, lines, or surfaces, and when compressed from the outside, the particles move in a shearing manner, resulting in a large deformation in the thickness direction.

[0013] (4) In the configuration of (2) or (3), the insulating material for a battery pack of the present disclosure may further include one or more selected from infrared shielding particles, inorganic fibers, and dispersants. In the configuration of (3), a composition containing silica aerogel powder and one or more selected from infrared shielding particles, inorganic fibers, and dispersants may be prepared, and a pressure-molded body may be produced from the composition.

[0014] Insulating materials using silica aerogel powder can achieve high thermal insulation by suppressing conduction and convection, among the three forms of heat transfer (conduction, convection, and radiation). Radiation is the phenomenon in which heat is transferred by electromagnetic waves, and the higher the temperature, the greater the amount of radiant energy released. Therefore, radiation is the primary cause of heat transfer in high-temperature environments. Infrared-shielding particles absorb heat from the heat source and re-emit it from the surface of the heat source, thereby blocking radiant heat from the heat source. Therefore, the use of infrared-shielding particles that can suppress heat transfer due to radiation can suppress heat transfer due to radiation in addition to conduction and convection, achieving high thermal insulation not only at room temperature but also at high temperatures above 500°C. Furthermore, the addition of inorganic fibers improves the mechanical strength of the insulating material and suppresses the shedding of silica aerogel particles. Silica aerogel powder is poorly compatible with water and difficult to disperse. Therefore, the addition of an amphiphilic dispersant can improve the dispersibility of silica aerogel powder when water is used in the manufacturing process of the insulating material. Furthermore, by adding a dispersant, the press moldability of the silica aerogel powder can be improved.

[0015] (5) In any one of the above (2) to (4), the silica aerogel powder may have an average particle size of 30 μm to 150 μm, which is preferable from the viewpoints of improving heat insulation, maintaining strength, and suppressing the shedding of silica aerogel particles.

[0016] (6) In any of the configurations (2) to (5) above, the insulating material for a battery pack of the present disclosure may be configured to be used in an automobile. With this configuration, even if vibrations or the like occur while the automobile is running, displacement of the battery cells or the like is suppressed, and high insulating properties can be maintained.

[0017] (7) A second insulating material for a battery pack according to the present disclosure is an insulating material for a battery pack having silica aerogel, and when the silica aerogel is measured by a nitrogen adsorption measurement method, the specific surface area measured based on the obtained adsorption isotherm is 550 m ２ / g or more, and the pore volume at a relative pressure of 0.99 is 3.5 mL / g or more and 5.0 mL / g or less, and is characterized by satisfying the following conditions (i) and (ii) when the pore volume at a relative pressure of 0.93 is a [mL / g], the pore volume at a relative pressure of 0.965 is b [mL / g], and the pore volume at a relative pressure of 0.99 is c [mL / g]: (i) 0≦(a / c×100)≦50 (ii) 50≦(b / c×100)<100

[0018] The silica aerogel constituting the second battery pack insulating material of the present disclosure, like the silica aerogel powder described in (1) above, has a specific surface area and a pore volume at a relative pressure of 0.99 within a predetermined range, satisfying conditions (i) and (ii). Therefore, the silica aerogel in this configuration has high thermal insulation properties and excellent compression recovery. Therefore, according to the second battery pack insulating material of the present disclosure, the insulating material deforms in response to the expansion and contraction of the battery cells, thereby suppressing misalignment and maintaining high thermal insulation properties. Furthermore, the insulating material appropriately maintains the expansion and contraction of the battery cells, thereby contributing to a longer battery cell life.

[0019] (8) In the configuration described in (7) above, the insulating material for a battery pack of the present disclosure may further include one or more selected from infrared-shielding particles and dispersants. As described in (4) above, the use of infrared-shielding particles in combination can suppress heat transfer due to radiation in addition to conduction and convection, thereby achieving high thermal insulation not only at room temperature but also at high temperatures of 500°C or higher. Furthermore, silica aerogel is poorly compatible with water and difficult to disperse. Therefore, adding an amphiphilic dispersant can improve the dispersibility of silica aerogel when water is used in the process of producing the insulating material.

[0020] (9) In the configuration of (7) or (8) above, the insulating material for a battery pack of the present disclosure may be configured to be used in an automobile. With this configuration, even if vibrations or the like occur while the automobile is running, displacement of the battery cells or the like is suppressed, and high insulating properties can be maintained.

[0021] (10) In any of the configurations (7) to (9), the insulating material for a battery pack according to the present disclosure may further include a fiber material. This configuration can improve the mechanical strength of the insulating material.

[0022] The silica aerogel powder and silica aerogel of the present disclosure have a unique pore structure with a large proportion of pores that contribute to thermal insulation and compression recovery, and therefore have high thermal insulation properties and excellent compression recovery.The insulating material for a battery pack of the present disclosure, which uses the silica aerogel powder or silica aerogel of the present disclosure, is deformable to follow the deformation of the mating member and exhibits a high thermal insulation effect.

[0023] 1 is a graph showing the adsorption isotherms of silica aerogel powders of Examples and Comparative Examples; FIG. 2 is a schematic diagram showing the configuration of an upper jig and a lower jig that constitute a compression device; FIG. 3 is a schematic diagram showing the state of the same device at maximum compression; FIG. 4 is a schematic diagram showing the state of the same device at unloading; and FIG. 5 is a graph showing the relationship between compression ratio and compressive stress in the 10th compression-unloading cycle.

[0024] The silica aerogel powder and the insulating material for a battery pack according to the present disclosure are described in detail below. The silica aerogel powder and the insulating material for a battery pack according to the present disclosure are not limited to the following forms, and can be embodied in various forms including modifications and improvements that can be made by those skilled in the art without departing from the gist of the present disclosure.

[0025] <Silica Aerogel Powder> Silica aerogel particles are composed of a skeleton formed by a plurality of primary particles linked together, with pores between the skeletons. The diameter of the primary particles forming the skeleton is preferably about 2 to 5 nm. The specific surface area and pore volume of the silica aerogel powder of the present disclosure are measured based on an adsorption isotherm obtained by a nitrogen adsorption measurement method. The nitrogen adsorption measurement method is a method for measuring the phenomenon in which nitrogen gas molecules physically adsorb to the surface of a solid (silica aerogel) due to intermolecular forces at low temperatures (liquid nitrogen temperature). The adsorption isotherm is a curve plotted by measuring the adsorption amount by increasing the pressure of nitrogen gas, with the relative pressure of nitrogen gas on the horizontal axis and the adsorption amount of nitrogen gas on the vertical axis, as shown in Figure 1 below. The relative pressure on the horizontal axis is the ratio between the adsorption equilibrium pressure (P) of nitrogen gas and the saturated vapor pressure (P０ ) and the ratio (P / P ０ )

[0026] The values ​​of specific surface area and pore volume used in this specification are values ​​obtained by measuring the amount of nitrogen gas adsorption using an Anton Paar high-vacuum physical / chemical adsorption analyzer "Autosorb iQ." The specific surface area is a value calculated by the BET multipoint method using the nitrogen gas adsorption values ​​between relative pressures of 0.1 and 0.3. The pore volumes at relative pressures of 0.99, 0.965, and 0.93 are values ​​calculated by the BJH method using the respective nitrogen gas adsorption values.

[0027] [Specific surface area] The specific surface area of ​​the silica aerogel powder of the present disclosure is 550 m ２ / g or more. ２ If the pore size is less than 1 / g, the proportion of very small pores with a pore size of about several nm increases, and the proportion of pores with a pore size of about 30 to 68 nm, which are effective in improving heat insulation, decreases.

[0028] [Pore Volume at Relative Pressure of 0.99] The pore volume of the silica aerogel powder of the present disclosure measured by a nitrogen adsorption measurement method at a relative pressure of 0.99 is 3.5 mL / g or more and 5.0 mL / g or less. Under this condition, silica aerogel powder containing many pores with pore sizes exceeding 100 nm is eliminated, thereby realizing a silica aerogel powder containing many pores with pore sizes that contribute to heat insulation and compression recovery.

[0029] [Conditions (i) and (ii)] When the pore volume at a relative pressure of 0.93, b, and c, measured by nitrogen adsorption measurement, is a [mL / g], the pore volume at a relative pressure of 0.965, and the pore volume at a relative pressure of 0.99, respectively, the silica aerogel powder of the present disclosure satisfies the following conditions (i) and (ii): (i) 0≦(a / c×100)≦50 (ii) 50≦(b / c×100)<100 Condition (i) is a condition related mainly to compression recovery and indicates that there are few or no pores with a pore size of up to about 30 nm. Condition (ii) is a condition related mainly to heat insulation and indicates that there are many pores with a pore size of up to about 68 nm.

[0030] <Method for Producing Silica Aerogel Powder> The silica aerogel powder of the present disclosure may be produced by a sol-gel reaction of a silane compound. From the viewpoint of easily designing the skeleton and pore structure of the silica aerogel to a desired state, it is preferable to use two or more types of compounds with different numbers of siloxane bonds as the silane compound. In this specification, the siloxane bond of a silane compound refers to a bond between a silicon atom (Si) and an oxygen atom (O) (Si—O bond). The number of siloxane bonds refers to the number of oxygen atoms bonded to one silicon atom, and silane compounds are divided into four types with 1 to 4 siloxane bonds. The silane compound may contain compounds with different numbers of siloxane bonds, or may contain multiple types of compounds with the same number of siloxane bonds.

[0031] From the viewpoint of increasing the elastic deformation of the silica aerogel powder, the silane compound is preferably a tetrafunctional silane compound and a trifunctional silane compound. In this case, the content of the trifunctional silane compound is preferably 65% ​​by mass or more, based on 100% by mass of the total silane compounds. 70% by mass or more, and even 80% by mass or more, are more preferable. Increasing the content of the trifunctional silane compound reduces the —O—Si—O— bond ratio in the resulting silica aerogel powder. Furthermore, the proportion of pores with relatively large pore sizes increases. This increases the elastic deformation of the silica aerogel powder. On the other hand, from the viewpoint of increasing the proportion of relatively small pore sizes, which are effective in improving thermal insulation, the content of the tetrafunctional silane compound is preferably 5% by mass or more, and even 10% by mass or more, based on 100% by mass of the total silane compounds.

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

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

[0034] The method for producing silica aerogel powder using the sol-gel reaction consists of a sol generation process, a gelation process, and a drying process. The chemicals used and the conditions, such as the temperature and time, of each process can be adjusted appropriately to obtain the desired pore structure. First, in the sol generation process, a specific silane compound is added to an aqueous solution containing an acid catalyst and hydrolyzed to produce a sol. The aqueous solution may also contain organic solvents, surfactants, and water-soluble oligomers with both polar and nonpolar side chains. Considering compatibility after hydrolysis of the silane compound with the acid catalyst, alcohol-based solvents are preferred as organic solvents. Examples include methanol, ethanol, and isopropyl alcohol. Next, in the gelation process, a basic catalyst is added to the produced sol to polycondense the sol to form a gel. A quaternary ammonium salt, such as tetramethylammonium hydroxide, is suitable as the basic catalyst. After adding the basic catalyst, the mixture is allowed to stand for 6 to 12 hours at 90 to 120°C for aging to promote the polycondensation reaction and form the desired pore structure. Subsequently, in the drying step, the produced gel is dried. The drying method may be either supercritical drying or non-supercritical drying (atmospheric pressure drying or freeze-drying). For example, drying at atmospheric pressure may be performed for 2 to 3 hours under heating at 80 to 100°C. Note that aerogels such as silica aerogels may be referred to as "xerogels" when dried at atmospheric pressure, "aerogels" when dried supercritically, and "cryogels" when freeze-dried, depending on the drying method used in their production; however, in this specification, these are collectively referred to as "aerogels."

[0035] When drying at atmospheric pressure, a solvent substitution step may be performed before the drying step, in which moisture adhering to the gel is replaced with an organic solvent that can be dried at atmospheric pressure. Furthermore, when drying at atmospheric pressure, drying proceeds more slowly than with supercritical drying, and the pores may shrink due to the action of the basic catalyst remaining in the gel, potentially preventing the desired pore structure from being obtained. From the perspective of suppressing pore shrinkage during drying, it is desirable to perform a washing step to remove the basic catalyst from the gel before the drying step. The gel can be washed, for example, by heating it to 40-50°C and adding the organic solvent used in the sol generation step to release the basic catalyst due to the concentration difference between the inside and outside of the gel. On the other hand, with supercritical drying, drying proceeds quickly, so the pores are less likely to shrink even if the basic catalyst remains in the gel. However, if the basic catalyst remains in the silica aerogel, it may cause thermal degradation, etc. Therefore, even when using supercritical drying, it is desirable to perform a washing step to remove the basic catalyst from the gel before the drying step. The silica aerogel powder may be produced by pulverizing the obtained silica aerogel using a media-less pulverizing and mixing device such as a jet mill, a stirrer, or the like.

[0036] <Insulating Material for Battery Pack> A first insulating material for a battery pack according to the present disclosure is constructed using the silica aerogel powder according to the present disclosure. A first embodiment of the insulating material for a battery pack according to the present disclosure includes a pressure-molded body of a composition containing silica aerogel powder. A second embodiment includes a thermal insulating layer produced by applying a liquid (including a slurry) composition obtained by adding a solvent such as water to silica aerogel powder to a substrate and drying the composition. These two compositions may be constructed solely from silica aerogel powder, or may be constructed by adding other components to silica aerogel powder. Furthermore, a second insulating material for a battery pack according to the present disclosure may use silica aerogel produced by the sol-gel reaction of a silane compound as is without powdering it.

[0037] When silica aerogel powder is used, the average particle size is preferably 10 μm or more from the viewpoint of improving heat insulation. In the form of a pressure-molded body, the average particle size is preferably 30 μm or more, and even 50 μm or more, from the viewpoint of reducing fine voids between particles and increasing strength. On the other hand, from the viewpoint of ease of forming into a sheet and suppressing particle detachment, the average particle size is preferably 150 μm or less, and even more preferably 120 μm or less. When producing a heat-insulating layer, the average particle size is preferably 100 μm or less, taking into consideration the stability of the liquid composition and ease of application. The average particle size of the silica aerogel powder is determined by the median diameter (D ) calculated from the volume-based particle size distribution measured by laser diffraction / scattering. ５０ ) can be adopted.

[0038] To ensure the desired thermal insulation properties, the content of silica aerogel powder in the composition is preferably 65% ​​by mass or more, based on 100% by mass of the solid content of the composition. A content of 70% by mass or more is preferable. Here, the solid content refers to the components excluding volatile substances such as organic solvents and water. Examples of components other than silica aerogel powder that may be contained in the insulating material for a battery pack of the present disclosure include infrared shielding particles, inorganic fibers, dispersants, reinforcing inorganic particles, and flame retardants. It is also possible to include a binder that binds the components to prevent the silica aerogel particles from falling off. However, this may create a heat transfer path through the binder and may impair the effects achieved by the pore structure of the silica aerogel powder. Therefore, it is desirable that the insulating material for a battery pack of the present disclosure does not contain a binder that binds the components, such as the silica aerogel powder. The other components are described below.

[0039] [Infrared Shielding Particles] Infrared shielding particles absorb heat from a heat source and re-emit it from the surface facing the heat source, thereby blocking radiant heat from the heat source and contributing to improved thermal insulation, particularly at high temperatures. From the viewpoint of filling the gaps (voids) between silica aerogel particles and suppressing the bonding of the infrared shielding particles with each other or with other components, making 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, infrared rays are less likely to hit the particles and the scattering of infrared rays is insufficient, making it difficult to achieve the radiant heat blocking effect. From this viewpoint, the average particle diameter of the infrared shielding particles is preferably 0.3 μm or more and 22 μm or less. The shape of the infrared shielding particles is not particularly limited, and may be spherical, flat, or the like. The average particle diameter of the infrared shielding particles is also determined, as with silica aerogel powder, by the median diameter (D ) calculated from the volume-based particle size distribution measured by laser diffraction / scattering method. ５０ ) can be used, and when using a commercially available product, the catalog value can be used.

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

[0041] For example, silicon carbide, titanium oxide, silicon nitride, mica, alumina, aluminum nitride, boron carbide, iron oxide, magnesium oxide, etc. have a relatively large specific heat capacity, and therefore the particles themselves do not heat up easily. In this respect, they also contribute to improving the thermal insulation properties of the insulating material. In addition, they have high heat resistance, which also contributes to improving the heat resistance of the insulating material. Silicon carbide is particularly suitable because its thermal conductivity does not increase much even in high-temperature atmospheres of around 500 to 800°C.

[0042] [Inorganic Fibers] The inorganic fibers are physically entangled around the silica aerogel particles, thereby improving the mechanical strength of the heat insulating material and preventing the silica aerogel particles from falling off. The type of inorganic fiber is not particularly limited, but ceramic fibers such as glass fiber and alumina fiber are preferred in consideration of heat resistance and mechanical strength. The length of the inorganic fiber is preferably 16 mm or less, taking into consideration both the reinforcing effect and the prevention of the formation of heat transfer paths.

[0043] [Dispersant] The use of a dispersant during the pulverization process of silica aerogel or during the preparation of a liquid composition for producing a thermal insulating layer can improve the dispersibility of silica aerogel powder. Suitable dispersants include surfactants and water-soluble oligomers with both polar and nonpolar side chains. Examples of surfactants include ionic surfactants (cationic surfactants, anionic surfactants, and amphoteric surfactants) and nonionic surfactants. For example, the use of an ionic surfactant can increase the viscosity of the composition even in relatively small amounts and stabilize the dispersion of materials such as silica aerogel powder in the composition. Examples of ionic surfactants include sodium carboxymethylcellulose (CMC-Na), polycarboxylic acid amine salts, polycarboxylic acid ammonium salts, polycarboxylic acid sodium salts, and TEMPO-oxidized cellulose nanofibers (CNF-Na). The use of a nonionic surfactant facilitates the incorporation of materials such as silica aerogel powder into the solvent during the preparation of the composition. Furthermore, when these materials aggregate or separate in the composition, they are more easily redispersed, and the solvent is more easily removed during pressure molding. Examples of nonionic surfactants include polyethylene oxide (PEO) and polyvinyl alcohol (PVA).

[0044] [Reinforcing inorganic particles] From the viewpoint of improving the mechanical strength of the heat insulating material, reinforcing inorganic particles may be contained. The type of reinforcing inorganic particles is not particularly limited, and for example, particles having a relatively large hardness and specific surface area, such as precipitated silica, gel silica, fused silica, wollastonite, potassium titanate, magnesium silicate, glass flakes, calcium carbonate, and barium sulfate, can be used.

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

[0046] <Method for Manufacturing a Thermal Insulating Material for a Battery Pack> When producing the first type of pressure-molded body as the first thermal insulating material for a battery pack of the present disclosure, the composition is placed in a mold and heated at a temperature of about 100 to 160°C while applying a surface pressure of about 0.1 to 2.0 MPa. The thermal insulating material for a battery pack of the present disclosure may be composed of only the pressure-molded body, or may also be composed of a substrate supporting the pressure-molded body and an exterior material housing the pressure-molded body. The substrate may be disposed on only one side of the thermal insulating material in the thickness direction, or on both sides so as to sandwich the thermal insulating material. Alternatively, the thermal insulating material may be covered with a single substrate, and the substrate may be used as an exterior material. An adhesive layer may be interposed between the thermal insulating material and the substrate. The adhesive layer may contain a flame retardant in addition to the adhesive component.

[0047] When producing the second type of insulating layer as the first battery pack insulating material of the present disclosure, the composition may be applied to a substrate by brushing, or by using a coating machine such as a blade coater, bar coater, die coater, Comma Coater (registered trademark), or roll coater, or by spraying. Alternatively, the composition may be produced by immersing the substrate in the composition or by forming the composition on the substrate by a papermaking method. Drying may be carried out at a temperature of 80 to 180°C for several minutes to several tens of minutes.

[0048] Examples of substrate materials include cloth, resin, paper, and steel plate. Examples of fibers constituting the cloth include glass fiber, rock wool, ceramic fiber, alumina fiber, silica fiber, carbon fiber, metal fiber, polyimide fiber, aramid fiber, and polyphenylene sulfide (PPS) fiber. Examples of ceramic fibers include refractory ceramic fiber (RCF), polycrystalline alumina fiber (Polycrystalline Wool: PCW), and alkaline earth silicate (AES) fiber. Among these, AES fiber is biosoluble and therefore more safe. Examples of resins include polyethylene terephthalate (PET), polyimide, polyamide, and PPS. Examples of paper include pulp and composites of pulp and magnesium silicate. Examples of steel plates include Galvalume Steel Plate (registered trademark), galvanized sheet, stainless steel (SUS) plate, iron plate, and titanium plate. The shape of the substrate is not particularly limited, and examples include woven fabric, nonwoven fabric, film, and sheet. The substrate may be a single layer or a laminate of two or more layers of the same or different materials.

[0049] For example, glass cloth, fabrics (woven fabrics) and nonwoven fabrics made from inorganic fibers such as glass fiber and metal fiber, and fireproof insulating paper made as a composite of pulp and magnesium silicate have relatively low thermal conductivity and high shape retention even in high-temperature environments. Furthermore, the use of a fire-resistant substrate further improves safety. Highly heat-resistant substrates can be made from glass fiber, rock wool, ceramic fiber, polyimide, PPS, etc., and specific examples include glass fiber nonwoven fabric, glass cloth, aluminum glass cloth, AES wool paper, and polyimide fiber nonwoven fabric.

[0050] The second insulating material for a battery pack according to the present disclosure may be manufactured using the silica aerogel produced through the aforementioned sol production process, gelation process, drying process, etc., without powdering it. For example, a fibrous material may be added to the produced sol during the gelation process. Adding a fibrous material can strengthen the insulating material. The fibrous material may be not only thread-like but also cloth-like, such as a nonwoven fabric or a woven fabric (corresponding to the aforementioned substrate). When using cloth, the sol may be applied to the cloth or immersed in the sol to gel it. The fibrous material may be either inorganic or organic fiber, or may contain both. When the fibrous material is thread-like, the fibrous material is dispersed within the insulating material and physically entangled with the silica aerogel, thereby improving the mechanical strength of the insulating material. When the fibrous material is cloth-like, the cloth and the silica aerogel are bonded to each other, thereby improving the mechanical strength of the insulating material.

[0051] The specific surface area and pore volume of the silica aerogel constituting the second battery pack insulating material of the present disclosure can be measured by the same method as the method for measuring the specific surface area and pore volume of the silica aerogel powder described above. For example, the silica aerogel may be crushed and the nitrogen gas adsorption amount of the powder obtained may be measured.

[0052] Next, the present disclosure will be described more specifically with reference to examples. (1) Pore Structure and Compression Recovery of Silica Aerogel Powder <Production of Silica Aerogel Powder> [Example 1] First, tetramethoxysilane (a tetrafunctional silane compound), methyltrimethoxysilane (a trifunctional silane compound), water, and methanol were mixed at room temperature (20°C ± 5°C) by stirring. Then, acetic acid was added as an acid catalyst and stirred for 10 minutes to hydrolyze the silane compound and generate a sol (sol generation process). The tetramethoxysilane and methyltrimethoxysilane were mixed in a mass ratio of 10:90. Next, methanol and tetramethylammonium hydroxide (a basic catalyst) were added to the generated sol, stirred for 1 minute, and then allowed to stand in a sealed container at room temperature for 1 hour. The mixture was then left to stand (heat treated) for 6 hours at 90°C to polycondense and gelate the sol (gelation process). Methanol was then added to the gel at 40°C to remove the basic catalyst from the gel (washing process). Then, the washed gel was dried at normal pressure and 80° C. for 2 hours to produce the silica aerogel of Example 1 (drying step).

[0053] [Example 2, Comparative Examples 1 to 3] Four types of silica aerogels, Example 2 and Comparative Examples 1 to 3, were produced in the same manner as Example 1, except that the blending ratio of the tetrafunctional silane compound (tetramethoxysilane) and the trifunctional silane compound (methyltrimethoxysilane) was changed. The blending ratio of the silane compound in each silica aerogel is shown in Table 1 below. The produced silica aerogels were pulverized into powder using a Henschel mixer and subjected to the following measurements.

[0054] <Measurement of Specific Surface Area and Pore Volume> The nitrogen gas adsorption capacity of the produced silica aerogel powder was measured at liquid nitrogen temperature (-196°C), and the specific surface area and pore volume were calculated based on the resulting adsorption isotherm. The nitrogen gas adsorption capacity was measured using an Anton Paar Autosorb iQ high-vacuum physical / chemical adsorption analyzer at a relative pressure range of 0.025 to 0.995. The specific surface area was determined by the BET multipoint method using the nitrogen gas adsorption capacity values ​​between relative pressures of 0.1 and 0.3. The pore volumes at relative pressures of 0.93, 0.965, and 0.99 were determined by the BJH method using the respective nitrogen gas adsorption capacity values. The silica aerogel powder samples were degassed prior to measurement as follows: First, the samples were placed in a dry heat oven and maintained at 117°C for 3 hours. Next, the sample was set in the measuring device and degassed under reduced pressure at 120° C. for 2 hours.

[0055] The adsorption isotherms of the silica aerogel powders of the examples and comparative examples are shown in Figure 1. Table 1 shows the specific surface area and pore volume of the silica aerogel powders.

[0056] 1, the silica aerogel powders of Examples 1 and 2 and Comparative Example 1, which contained a relatively large proportion of the trifunctional silane compound, had a large pore volume (total pore volume) at a relative pressure of 0.99, and the proportion of pores with small pore diameters was smaller than that of the silica aerogel powders of Comparative Examples 2 and 3. Furthermore, as shown in Table 1, the silica aerogel powders of Examples 1 and 2 satisfied all of the specific surface area, pore volume at a relative pressure of 0.99, and conditions (i) and (ii).

[0057] <Evaluation of Compression Recovery> The compression recovery of the produced silica aerogel powder was measured using the compression device shown in Figures 2A to 2C. Figure 2A is a schematic diagram showing the configuration of the upper and lower jigs constituting the compression device, Figure 2B is a schematic diagram showing the state of the device at maximum compression, and Figure 2C is a schematic diagram showing the state of the device at unloading. As shown in Figure 2A, the compression device 8 includes an upper jig 80 and a lower jig 81. The upper jig 80 is made of stainless steel and has a disk-shaped base 800 and a cylindrical piston 801 located in the center of the base 800 and protruding downward. The diameter D1 of the base 800 is 50 mm, and the diameter D2 of the piston 801 is 11.3 mm. The length of the piston 801 is 27 mm, the same as the depth L of the recess 810 of the lower jig 81 described below. The lower jig 81 is also made of stainless steel and has a cylindrical shape with the same diameter D1 as the base 800 of the upper jig 80. A cylindrical recess 810 is formed in the center of the lower jig 81 to accommodate the piston 801. The depth L of the recess 810 is 27 mm.

[0058] The compression recovery was measured as follows. First, the produced silica aerogel powder was sieved through a stainless steel sieve with a 125 μm mesh, and the powder that passed through was then sieved again through a stainless steel sieve with a 75 μm mesh. The powder with a particle size of 75 μm to 125 μm that remained on the sieve was used to measure the compression recovery. Next, the sieved silica aerogel powder was filled into the recess 810 of the lower jig 81 by tapping the lower jig 81 up and down. The silica aerogel powder was filled to a height of 13 mm ± 1 mm from the bottom of the recess 810. Using a Tensilon universal testing machine "RTF1350" manufactured by A&D Co., Ltd., the upper jig 80 was moved downward at a speed of 12 mm / min, as indicated by the downward white arrow in Figure 2B, and the silica aerogel powder 82 was compressed with the piston part 801 until the compressive stress reached 3.0 MPa. 2C, the upper jig 80 was moved upward at a speed of 12 mm / min to unload the material until the compressive stress reached 0 MPa. This compression-unloading operation was repeated 10 times, and the recovery rate was calculated from the displacement of the filling height of the silica aerogel powder 82 in the 10th compression-unloading cycle.

[0059] The recovery rate was calculated by the following formula (I), where L2 (mm) is the packed height of the silica aerogel powder under a compressive stress of 3.0 MPa (see FIG. 2B) and L1 (mm) is the packed height of the silica aerogel powder when unloaded (see FIG. 2C). A recovery rate of 25% or more was evaluated as pass (indicated by a circle in Table 1 above), and a recovery rate of less than 25% was evaluated as fail (indicated by an x ​​in the same table). Table 1 above summarizes the evaluation results of the compression recovery of each silica aerogel powder. Recovery rate (%) = (L1 - L2) / L1 × 100 ... (I)

[0060] 3 is a graph showing the relationship between the compression ratio and the compressive stress after the 10th compression-unloading cycle. The compression ratio on the horizontal axis of the graph in FIG. 3 is a value calculated by the following formula (II): Compression ratio (%) = Compression displacement of silica aerogel powder (mm) / Initial (unloaded) filling height of silica aerogel powder (mm) × 100 (II).

[0061] As shown in Table 1, the silica aerogel powders of Examples 1 and 2 were confirmed to have high compression recovery. On the other hand, the silica aerogel powders of Comparative Examples 2 and 3 had small pore volumes (total pore volumes) at a relative pressure of 0.99, and also had large values ​​of a / c under condition (i), resulting in a high proportion of pores with small pore diameters, resulting in low elasticity and poor compression recovery.

[0062] (2) Heat Insulation Properties of Silica Aerogel Powder The produced silica aerogel powder was pressure-molded to produce a heat insulating material sample, and its heat insulating properties were evaluated.

[0063] <Production of Heat Insulating Material Sample> [Production of Composition] First, water was weighed into a resin container, and a surfactant (PEO) was added as a dispersant. The mixture was stirred for 60 minutes at 800 rpm using an air-driven blade stirrer to dissolve the surfactant in the water. After stopping the stirring, silicon carbide (SiC) powder was added as infrared heat shielding particles, and the mixture was further stirred for 15 minutes at 800 rpm. While continuing the stirring, silica aerogel powder was added and completely wetted in the liquid. Then, glass fiber was added as inorganic fiber, and the mixture was stirred for 30 minutes at 800 rpm. After that, the mixture was further stirred for 10 minutes at 1000 rpm. In this way, the average particle diameter (D５０ A composition containing silica aerogel powder with a particle size of 70 μm was produced. The composition had a clay-like structure consisting of aggregates of particles with a diameter of 5 mm or less. The content of the silica aerogel powder in the composition was 73.7% by mass, where the solid content of the composition was 100% by mass. Similarly, the content of the surfactant in the composition was 2.9% by mass, the content of the silicon carbide powder was 15.1% by mass, and the content of the glass fiber was 8.3% by mass.

[0064] Details of the materials other than the silica aerogel powder are as follows: 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.

[0065] [Production of Pressed Molded Body] The produced clay-like composition was press-molded as follows. First, a base was prepared by stacking a first spacer plate made of SUS on top of glass fiber paper. The first spacer plate was 7 mm thick and had a 150 mm square injection hole formed in its center. 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, and glass fiber paper was placed on top, followed by a second spacer plate on top of that, to produce a laminate consisting of "glass fiber paper / composition / glass fiber paper / second spacer plate." The second spacer plate was 6 mm thick and, like the first spacer plate, had a 150 mm square injection hole formed in its center. The molded composition was contained in the injection hole of the second spacer plate.

[0066] Separately, a 5 mm thick, 320 mm square aluminum first plate and a 1 mm thick, 320 mm square aluminum second plate were prepared. Multiple grooves were formed on one side of the first plate. Each groove was linear, 2.5 mm wide, 3 mm deep, and 200 mm long, and was formed parallel to the first plate at 5 mm intervals. Punched holes with a diameter of 1 mm were formed throughout the second plate at 2 mm intervals. A second plate was placed on one side of the first plate, and a laminate was placed on top of it. The second plate was then placed on top of the laminate, and the first plate was then placed on top of the second plate, with the grooved side facing the second plate. In this state, pressure molding was performed using a hot press at a temperature of 165°C and a load of approximately 980 kN for 10 minutes. The product was then allowed to cool to room temperature, and the first plate, second plate, second spacer plate, and upper and lower glass fiber papers were removed to obtain a 6 mm thick square plate-shaped pressure-molded product. The produced pressure-molded body is used as a heat insulating material sample, and is referred to as a sample of Example 1, etc., in accordance with the silica aerogel powder used.

[0067] <Evaluation of Thermal Insulation> The thermal conductivity of the thermal insulation material samples at 600°C was measured using a "Quick Thermal Conductivity Meter QTM-700" and a "High-Temperature Probe PD-31N" manufactured by Kyoto Electronics Manufacturing Co., Ltd., as follows. First, two laminates approximately 20 mm thick were prepared by stacking the thermal insulation material samples. These laminates were placed on either side of the probe, one above the other, and placed in an electric furnace with a weight of approximately 5 kg on top to prevent the laminate from being crushed. The temperature inside the electric furnace was then raised to 600°C, and after the temperature inside the furnace stabilized, the thermal conductivity was measured. In this example, a measured thermal conductivity of less than 0.12 W / m·K was evaluated as "pass" (indicated by a circle in Table 1 above), and a thermal conductivity of 0.12 W / m·K or greater was evaluated as "fail" (indicated by an "x" in the same table). The evaluation results of thermal insulation are summarized in Table 1 above.

[0068] As shown in Table 1, the samples of Examples 1 and 2 were confirmed to have excellent thermal insulation properties. On the other hand, the sample of Comparative Example 1 had a small value of b / c in condition (ii) and few pores with pore diameters up to approximately 68 nm, resulting in poor thermal insulation properties. Furthermore, the samples of Comparative Examples 2 and 3 had a value of b / c in condition (ii) within the desired range, but had a small pore volume (total pore volume) at a relative pressure of 0.99, resulting in poor thermal insulation properties. In summary, the silica aerogel powders of Examples 1 and 2 were confirmed to have excellent compression recovery properties, and the insulating material samples using them were confirmed to have excellent thermal insulation properties at high temperatures.

[0069] 8: Compression device, 80: Upper jig, 800: Base, 801: Piston, 81: Lower jig, 810: Recess, 82: Silica aerogel powder.

Claims

1. Silica aerogel powder used as an insulating material for battery packs, When the silica aerogel powder is measured by a nitrogen adsorption measurement method, The specific surface area, measured based on the obtained adsorption isotherms, is 550 m². ２ The pore volume is 3.5 mL / g or more and 5.0 mL / g or less at a relative pressure of 0.

99. A silica aerogel powder used as an insulating material for battery packs, characterized in that it satisfies the following conditions (i) and (ii), when the pore capacity at a relative pressure of 0.93 is a [mL / g], the pore capacity at a relative pressure of 0.965 is b [mL / g], and the pore capacity at a relative pressure of 0.99 is c [mL / g]. (i) 0≦(a / c×100)≦50 (ii) 50≦(b / c×100)<100

2. A battery pack insulation material having the silica aerogel powder described in claim 1.

3. The thermal insulation material for a battery pack according to claim 2, comprising a pressure-molded body of the composition having the silica aerogel powder.

4. Furthermore, the heat insulating material for a battery pack according to claim 2, further comprising one or more selected from infrared shielding particles, inorganic fibers, and a dispersant.

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

6. An insulating material for a battery pack, as described in claim 2, used in automobiles.

7. A thermal insulation material for battery packs having silica aerogel, When the silica aerogel is measured by a nitrogen adsorption measurement method, The specific surface area, measured based on the obtained adsorption isotherms, is 550 m². ２ The pore volume is 3.5 mL / g or more and 5.0 mL / g or less at a relative pressure of 0.

99. A battery pack insulation material characterized by satisfying the following conditions (i) and (ii), where a [mL / g] is the pore capacity at a relative pressure of 0.93, b [mL / g] is the pore capacity at a relative pressure of 0.965, and c [mL / g] is the pore capacity at a relative pressure of 0.

99. (i) 0≦(a / c×100)≦50 (ii) 50≦(b / c×100)<100

8. Furthermore, the heat insulating material for a battery pack according to claim 7, further comprising one or more selected from infrared shielding particles and dispersants.

9. An insulating material for a battery pack, as described in claim 7, used in automobiles.

10. Furthermore, the battery pack insulation material according to claim 7, further comprising a fibrous material.