Heat absorbing body and secondary battery module comprising said heat absorbing body

Abstract

The purpose of the present disclosure is to provide a heat absorbing body that has an excellent heat absorption capacity and an excellent temperature increase suppressing effect, and can change from a heat absorption effect to a heat insulation effect in a high temperature range, as well as a secondary battery module that comprises said heat absorbing body.　The present disclosure is a heat absorbing body having: a bag body that can be filled with contents; and, an aqueous solvent and a mesh body composed of an inorganic material which are filled into the bag body as said contents.

Description

Heat absorber and secondary battery module equipped with the heat absorber

[0001] The present disclosure relates to a heat absorber and a secondary battery module including the heat absorber.

[0002] Secondary batteries, which can control the time lag between energy storage and demand, are used in a variety of applications, including automobiles and mobile devices. Their importance is currently increasing due to their need for expanding the adoption of renewable energy sources from the perspectives of building a low-carbon society and energy security. However, secondary batteries, such as lithium-ion batteries, are at risk of thermal runaway when their temperature rises due to heat generation during fast charging or high-output discharging. Furthermore, as ultra-fast charging becomes more common, even greater heat generation is expected, necessitating the development of methods to suppress temperature rise and improve battery safety. Secondary batteries can also experience thermal runaway due to internal short circuits, resulting in problems such as fire or smoke. Therefore, to minimize damage caused by such problems, technologies are needed to suppress, prevent, or delay battery explosions by absorbing heat from abnormally high battery temperatures or by suppressing heat transfer to other cells through heat absorption and insulation.

[0003] For example, Patent Documents 1 and 2 disclose techniques that are excellent in heat insulation and fire spread prevention. ２ / Na ２Patent Document 1 describes a laminated fire spread prevention material comprising a layer A containing sodium silicate with an O molar ratio of less than 3.1 and a layer B containing precipitated silica. Patent Document 1 describes that the fire spread prevention material is used in a battery pack having two or more cells, suppressing heat transfer between cells under normal conditions and suppressing heat spread to adjacent cells under abnormal conditions. Patent Document 2 describes an insulating sheet for a battery pack, which has an insulating layer composed of at least inorganic fibers or inorganic powder, and heat absorption layers composed of at least inorganic hydrate formed on both sides of the insulating layer. Patent Document 2 describes that when the inorganic hydrate in the outer heat absorption layer is heated by heat generated in the battery cell, the inorganic hydrate exerts an endothermic effect by absorbing the heat and releasing moisture, thereby effectively reducing the heat generation of the battery cell.

[0004] International Publication No. 2022 / 270359 Japanese Patent Application Laid-Open No. 2019-83150

[0005] However, in the technology of Patent Document 1, the water content is limited because the water contained in Layer A (e.g., water molecules in sodium silicate) undergoes an endothermic reaction in the temperature range of 100 to 300°C, resulting in an insufficient endothermic effect. Furthermore, in the technology of Patent Document 2, the heat absorption layer is made of an inorganic hydrate, resulting in an endothermic capacity of approximately 1000 J / g or less. The thickness and flexibility of the sheet limit the inorganic hydrate content, resulting in an insufficient endothermic effect. Furthermore, in the technologies of Patent Documents 1 and 2, a laminate having two or more layers is used, which necessitates a thicker laminate to achieve sufficient endothermic capacity and thermal insulation. Therefore, the present disclosure aims to provide a heat absorber that has excellent endothermic capacity and temperature rise suppression effect, and that can change from an endothermic effect to an insulating effect at high temperatures, and a secondary battery module equipped with the heat absorber.

[0006] The present inventors have discovered that a heat absorber comprising a bag, an inorganic mesh body, and an aqueous solvent has an excellent heat absorption capacity and temperature rise suppression effect, and can change from an endothermic effect to an insulating effect in the high temperature range, and have completed the present invention as described below.

[0007] [1] The present disclosure provides a heat absorber having a bag that can be filled with a content, and an inorganic mesh body and an aqueous solvent that are filled into the bag as the content.

[0008] [2] The heat absorber according to [1], further containing inorganic powder as the content.

[0009] [3] The heat absorber according to [1] or [2], wherein the contents include a hydrogel composed of a hydrogel body and the aqueous solvent, and the inorganic material mesh body.

[0010] [4] The heat absorber according to any one of [1] to [3], further containing an antifreeze agent as the content.

[0011] [5] The water vapor permeability ([g / (m ２ ・24h)]) is 50g / (m ２ - The heat absorber according to any one of [1] to [4], wherein the heat absorption time is 24 h or less.

[0012] [6] The heat absorber according to any one of [1] to [5], wherein the average porosity of the inorganic material mesh body within the heat absorber is 30 to 99.5%, as represented by the following formula (1): Average porosity (%) of inorganic material mesh body = ((1 / ρf) - (1 / ρr)) / (1 / ρf) x 100 ... formula (1) (In the above formula (1), ρf represents bulk density, and ρr represents true density.)

[0013] [7] A heat absorber having high cushioning properties, which comprises a bag body and a hydrogel and a mesh body made of an inorganic material contained in the bag body, wherein the hydrogel body has a hydrogel body formed from three-dimensional polymer chains and an aqueous solvent, and is a heat absorber according to any one of [1] to [6].

[0014] [8] The following formula (I): [Equation 1] "Cushioning property (%) = h ａ / h ｂ × 100 (in the above formula (I), h ａ is the height (mm) of the pressed part 5 minutes after pressing the surface of the heat absorber at 1 MPa for 60 seconds, and h ｂThe heat absorber according to any one of [1] to [7], which has a cushioning property of 80% or more, as expressed by the following formula: (where "height" represents the height (mm) before the surface of the heat absorber is pressed at 1 MPa for 60 seconds).

[0015] [9] A heat absorber according to any one of [1] to [8], which has excellent pressure resistance when heated, and which is composed of a bag that can be filled with contents, an aqueous solvent, and an inorganic material mesh body that is filled with the contents.

[0016]

[10] The heat absorber according to any one of [1] to [9], wherein a hydrogel composed of a hydrogel body and the aqueous solvent, and the inorganic material mesh body are filled into the contents as a composite.

[0017]

[11] The heat absorber according to any one of [1] to

[10] , wherein the thickness change rate (5) expressed by the following formula (II): [Mathematical Expression 2] "Thickness change rate (%) = (thickness of the heat absorber after pressing the surface of the heat absorber after heating at 0.5 MPa for 60 seconds) / (thickness of the heat absorber before pressing the surface of the heat absorber after heating at 0.5 MPa for 60 seconds) × 100" is 70% or more.

[0018]

[12] A secondary battery module comprising the heat absorber according to any one of [1] to

[11] .

[0019]

[13] A secondary battery module in which the heat absorber according to any one of [1] to

[11] is sandwiched between battery cells.

[0020]

[14] The heat absorber of [7] or [8] is a high-cushion heat absorber.

[0021]

[15] Any of the heat absorbers [9] to

[11] is a high pressure resistant heat absorber.

[0022] According to the heat absorber of the present disclosure, it has an excellent heat absorption capacity and a temperature rise suppression effect, and can change from a heat absorption effect to a heat insulating effect in a high temperature range. According to the present disclosure, by including a heat absorber that has an excellent heat absorption capacity and a temperature rise suppression effect, and can change from a heat absorption effect to a heat insulating effect in a high temperature range, it is possible to provide a highly safe secondary battery module.

[0023] FIG. 1 shows an example of a secondary battery module on which the heat absorber of this embodiment can be mounted. FIG. 2 is a perspective view showing a schematic exploded view of the secondary battery module of FIG. 1. FIG. 3 shows the results of a cone calorimeter test (test conditions: radiation intensity 50 kW / m) of the heat absorbers of the examples and comparative examples. ２ 1 is a graph showing the results of a test using a cone calorimeter (heating time: 20 minutes), with the vertical axis representing temperature and the horizontal axis representing elapsed time. FIG. 4 is a schematic diagram of the cone calorimeter test apparatus used in the Examples and Comparative Examples. FIG. 5 shows photographs of the heat absorber of Example 5 before and after the cone calorimeter test. (a) The heat absorber of Example 5 before the cone calorimeter test, (b) The heat absorber of Example 5 during the cone calorimeter test, and (c) The heat absorber of Example 5 after the cone calorimeter test. The results of DSC measurement of the heat absorber of Example 2 are shown. The results of DSC measurement of the heat absorber of Comparative Example 2 are shown. The results of DSC measurement of the heat absorber of Comparative Example 3 are shown.

[0024] Hereinafter, an embodiment of the present invention (hereinafter referred to as the "present embodiment") will be described in detail. However, the present disclosure is not limited to the following description and can be implemented in various modifications within the scope of the present disclosure. [Definition] In this specification, the term "mesh made of inorganic material" refers to a network structure made of inorganic material and having fine pores or voids. Therefore, it is preferable that the structure be capable of trapping gas bubbles. The term "mesh made of inorganic material" refers to, for example, a fiber aggregate in which fibers made of inorganic material are entangled with each other, or a porous body made of inorganic material, and is capable of trapping gas bubbles. Specific examples include woven or knitted fabrics, nonwoven fabrics, cotton-like bodies (including not only glass wool, rock wool, and ceramic wool, but also spongy bodies (sponge bodies)), and porous bodies. In this specification, the term "reaction raw material" refers to a compound used to obtain a target compound through a chemical reaction such as synthesis or decomposition and that partially constitutes the chemical structure of the target compound. Substances that act as chemical reaction aids, such as solvents, catalysts, and polymerization initiators, are excluded. As used herein, the term "structural unit" refers to a (repeating) unit of a chemical structure formed during a reaction or polymerization. In other words, in a compound formed by a reaction or polymerization, the term refers to a partial structure other than the structure of the chemical bonds involved in the reaction or polymerization, i.e., a residue. As used herein, a "hydrogel" refers to a three-dimensional polymer network containing an aqueous solvent such as water, such as jelly, diaper absorbents, konjac, agar, etc. The three-dimensional network polymer that forms the skeleton of the hydrogel is referred to as the hydrogel body, and the hydrogel body contains an aqueous solvent. Therefore, a hydrogel comprises a hydrogel body and an aqueous solvent.

[0025] [Heat Absorber] The heat absorber of the present disclosure comprises a bag that can be filled with contents, an inorganic mesh body filled in the bag, and an aqueous solvent. This provides excellent heat absorption and temperature rise suppression, and can change from an endothermic effect to an insulating effect at high temperatures. Heat absorption can be achieved using the latent heat of vaporization of the aqueous solvent contained in the inorganic mesh body or the aqueous solvent contained in the bag. Therefore, the latent heat of vaporization of water, which has a greater heat absorption capacity than typical hydrates, can be utilized. Furthermore, since the heat is absorbed as sensible heat of the aqueous solvent, temperature can be stabilized even at room temperature. Meanwhile, when exposed to high temperatures, such as during combustion, the aqueous solvent evaporates, creating voids within the inorganic mesh body, providing thermal insulation and fire protection. More specifically, air bubbles trapped in the inorganic mesh body or voids (e.g., gaps between fibers) within the inorganic mesh body created by the evaporation of the aqueous solvent act as pores, making the entire heat absorber porous. As a result, thermal insulation and fire protection are achieved. Therefore, in relatively low temperature ranges (e.g., above room temperature to around 100°C), it mainly functions as a heat absorber. On the other hand, in temperature ranges from the critical temperature (e.g., 150°C) to the thermal runaway temperature (e.g., around 1000°C), the entire heat absorber becomes porous, so it can also function as a heat insulator. As a result, when the heat absorber of this embodiment is placed between cells in a battery stack in which multiple cells are stacked, it can block or suppress the thermal effects on adjacent cells.

[0026] Optionally, the contents may further contain one or more components selected from the group consisting of hydrogel bodies, inorganic powders, and antifreeze agents. The inclusion of hydrogel bodies as the contents can impart cushioning and impact resistance to the heat absorber. Furthermore, the inclusion of inorganic powders as the contents can continuously absorb heat at a different endothermic temperature from that of the aqueous solvent. Furthermore, when the aqueous solvent evaporates, voids are created within the inorganic material network, and the composite containing the inorganic material network and inorganic powder is more likely to form a porous body, thereby changing from a heat absorber to an insulator, thereby enhancing both the heat absorption and insulation effects throughout the entire thickness of the heat absorber. Furthermore, the inclusion of an antifreeze agent as the contents can suppress freezing below freezing points. Furthermore, by utilizing the heat of solidification of the aqueous solvent, the temperature drop of the battery in cold environments can be suppressed. Water generates heat of solidification around 0°C. The use of an antifreeze agent can lower the temperature at which this heat of solidification occurs, thereby suppressing the temperature drop of the battery at lower temperatures.

[0027] <Characteristics of Heat Endogenous Material> The endothermic onset temperature of the heat endogenous material of this embodiment is preferably 400°C or lower, more preferably 160°C or lower, even more preferably 120°C or lower, more preferably 110°C or lower, and even more preferably 100°C or lower. The endothermic onset temperature range of the heat endogenous material of this embodiment is preferably 35°C or higher and 400°C or lower, more preferably 37°C or higher and 160°C or lower, and even more preferably 40°C or higher and 110°C or lower. The upper and lower limits of the endothermic onset temperature of the endogenous material can be adjusted as appropriate. In this specification, the endothermic onset temperature (°C) is defined as the temperature at the intersection of a straight line extending the low-temperature side baseline toward the high-temperature side in a DSC measurement curve obtained by measurement with a differential scanning calorimeter (DSC), and a tangent drawn at the point where the gradient of the low-temperature side curve of the endothermic peak associated with evaporation is maximum. However, when multiple endothermic peaks are observed, the intersection of a straight line extending the low-temperature baseline toward the high-temperature side with a tangent drawn at the point where the gradient of the low-temperature curve of each of the multiple endothermic peaks is maximum is calculated for each of the multiple endothermic peaks, and the lowest temperature among the temperatures at the multiple intersections is determined to be the endothermic onset temperature.

[0028] The endothermic peak temperature of the endothermic body of this embodiment is preferably in the range of at least 80 ° C to 400 ° C, and more preferably in the range of 90 ° C to 160 ° C. In this specification, the endothermic peak temperature refers to the temperature (° C) at the maximum value of the endothermic peak due to evaporation in a DSC measurement curve, which is the measurement result of a differential scanning calorimeter (DSC). In addition, when multiple endothermic peaks are observed, it is sufficient that at least one of the multiple endothermic peaks is present in the range of 80 ° C to 160 ° C. The endothermic amount of the endothermic body of this embodiment is not particularly limited, but at the endothermic peak temperature (in the range of 80 ° C to 160 ° C), it is preferably 100 J / g or more, more preferably 200 J / g or more, even more preferably 300 J / g or more, even more preferably 500 J / g or more, and preferably 3000 J / g or less, more preferably 2500 J / g or less, and even more preferably 2000 J / g or less. The range of the endothermic amount of the heat endotherm of this embodiment is preferably 100 J / g or more and 3000 J / g or less, more preferably 200 J / g or more and 2500 J / g or less, and even more preferably 300 J / g or more and 2000 J / g or less. The preferred range of the endothermic amount can be determined by appropriately combining the upper and lower limits. The endothermic onset temperature, endothermic peak temperature, and endothermic amount of the heat endotherm of this embodiment are values ​​determined using a differential scanning calorimeter (DSC) according to the method described in the Examples below.

[0029] <Preferred Shape of Heat Absorber> The shape or size of the heat absorber of this embodiment is not particularly limited and may be, for example, substantially spherical, substantially flat, or irregular, and is appropriately selected depending on the intended use. For example, a substantially flat heat absorber is preferable because it is easily installed between adjacent battery cells. The average thickness of the substantially flat heat absorber of this embodiment is not particularly limited, but may be, for example, in the range of 100 μm to 50,000 μm. The lower limit of the average thickness is preferably 100 μm or more, more preferably 200 μm or more, even more preferably 500 μm or more, and particularly preferably 1,000 μm or more. The upper limit of the average thickness is preferably 50,000 μm or less, more preferably 20,000 μm or less, even more preferably 10,000 μm or less, and particularly preferably 8,000 μm or less. The upper and lower limits of the preferred range of the average thickness can be appropriately adjusted. The following describes the essential components of the heat absorber of this embodiment, namely, the bag body, the inorganic material mesh body, and the aqueous solvent, as well as optional components such as hydrogel (including the aqueous solvent encapsulated in the hydrogel), inorganic powder, antifreeze agent, and additives, which may be blended as needed.

[0030] (Bag) The bag of this embodiment is not particularly limited as long as it can be filled with contents such as an aqueous solvent or an inorganic mesh. A preferred example of the bag is a three-sided bag having an opening at the top end, a body portion with a closed bottom end, and a structure in which the opening is heat-sealed to close after the inorganic mesh and the aqueous solvent are completely contained. The three-sided bag is constructed by bonding the bottom ends and side portions of two sheets together, and then sealing the bag after filling the contents through the opening. This provides excellent airtightness, and its substantially flat shape makes it easy to insert between battery cells. The bag of this embodiment is preferably made of a sheet. A preferred embodiment of the bag of this embodiment is one in which two films of a desired size and shape (e.g., rectangular or (substantially) circular) are stacked on top of each other, and a predetermined heat-sealed region (e.g., the edge of the film) is heat-pressed to form an opening. This allows the creation of a three-sided bag having an internal space region capable of being filled with contents, an opening through which the contents can be filled into the internal space region, and a heat-sealed region between the two sheets. After filling the bag with contents, the openings can be heat-sealed by crimping the openings together. In this specification, "sealed" refers to a state in which the interior and exterior of the bag are substantially isolated from each other. The sheets used in the bag of this embodiment are not particularly limited as long as they are water-proof, and examples include known resin films, resin films with metal layers, and films with metal layers. The average thickness of the sheets used in the bag of this embodiment is not particularly limited, but is preferably 30 μm to 200 μm, and more preferably 60 μm to 150 μm. Examples of materials for the resin film include one or more resins such as polyester resin, nylon resin, polycarbonate resin, polypropylene resin, polyethylene resin, cyclic polyolefin resin, polystyrene resin, fluororesin, and elastomer. These plastics can be used for the bag as films, sheets, tubes, etc.Furthermore, the resin film having the metal layer may be laminated to the resin film with a metal such as aluminum or a metal oxide such as silica or alumina as a metal foil, vapor-deposited film, or the like. The use of a resin film having a metal layer can reduce the water vapor permeability of the resin film. Furthermore, the water vapor permeability of the sheet can be adjusted by the selection, thickness, and combination of materials. Examples of lamination methods include dry lamination, extrusion lamination, thermal lamination, coextrusion, multilayer blow molding, laminate injection molding, and coating. A preferred form of the resin film having a metal layer is an aluminum laminate film (a film in which aluminum foil (including an aluminum vapor-deposited layer) is integrated with a thermoplastic resin film (e.g., a polyethylene film, a PP film, or a PET film) laminated on at least one side thereof). In this embodiment, an adhesive layer may be formed in the heat seal area and the closed opening for sealing purposes. Suitable adhesive layers include laminate adhesives such as polyester-based adhesives, polyether-based adhesives, and polyurethane-based adhesives. Furthermore, the nature of the adhesive is not particularly limited, and any of solvent-based, solventless, and aqueous adhesives can be used. For example, in the present invention, a bag-shaped product made from a laminate film is preferred. The porous laminate film is preferably a film laminated with a metal foil and a resin film, and an example of such a laminate film is a three-layer structure consisting of an outer resin film, a metal foil, and an inner resin film. Specifically, a bag made from a resin film having an aluminum-deposited layer on the outside is sealed via a polyurethane-based laminate adhesive layer; a bag made from a three-layer laminate film having an outer nylon film, a central aluminum foil, and an inner adhesive layer such as modified polypropylene, sealed via a polyurethane-based laminate adhesive layer; or a bag made from a laminate film having a PET layer, an aluminum layer, and a polyethylene layer, sealed via a polyurethane-based laminate adhesive layer. Examples include the Gas Barrier Aluminum Bag AB Series (manufactured by Mitsubishi Gas Chemical Company, Inc.) and the Lamizip AL Type (manufactured by Seisan Nippon Co., Ltd.).The higher the melting temperature (for example, 120 to 140° C.) of the adhesive used to close the opening of the bag body of this embodiment or applied to the heat-sealed area, the stronger the bag body will be and the more likely it will be able to withstand internal pressure.

[0031] The water vapor permeability ([g / (m ２ ・24h)]) is 50g / (m ２ 24h) or less, and ２ 24h) or less, and more preferably 5g / (m ２ It is more preferable that the water vapor permeability of the sheet constituting the bag is 50 g / (m ２ When the water vapor permeability ([g / (m ２ The temperature and humidity are measured in accordance with JIS K7129 at a temperature of 40°C and a relative humidity of 90%.

[0032] (Mesh made of inorganic material) The mesh made of inorganic material of this embodiment is a general term for a network structure (= three-dimensional mesh structure) made of an inorganic material and having fine pores or voids. The mesh made of inorganic material may have a structure capable of trapping air bubbles, and may be, for example, a fiber aggregate in which fibers made of an inorganic material are entangled with each other, or a porous body made of an inorganic material. Specific examples include woven or knitted fabrics (glass cloth or silica cloth), nonwoven fabrics (made of glass fiber or ceramic fiber (e.g., glass wool, rock wool, or ceramic wool)), or porous bodies made of inorganic materials. The mesh made of inorganic material of this embodiment preferably has a heat resistance of 300°C or higher, more preferably 700°C or higher, and even more preferably 1200°C or higher. The heat resistance refers to the temperature at which the rate of volume change (in the thickness direction) reaches -20% when a test specimen is heated from 200 to 700°C in 100°C increments and held at each temperature for 30 minutes. When the inorganic mesh body of this embodiment is a porous body having at least one of a specific airflow resistance, a specific porosity, a specific tortuosity, and a specific void ratio, the entire heat absorber becomes a relatively stable porous body even in a high temperature range (a temperature range from a critical temperature (e.g., 150°C) to a thermal runaway temperature (e.g., around 1000°C)), and therefore tends to function as a thermal insulator. In particular, when the inorganic mesh body has a specific void ratio, it can become an even better thermal insulator when combined with an inorganic powder.

[0033] <Porosity> The average porosity of the inorganic material mesh body of this embodiment is preferably 30% to 99.7%, more preferably 50% to 99.5%, even more preferably 70% to 99.3%, and particularly preferably 90% to 99%. In this specification, the average porosity of the inorganic material mesh body is a value calculated from the bulk density and true density described below, and is a density based on the volume occupied by the inorganic material mesh body. The bulk density is a density based on the volume including the voids contained in the inorganic material mesh body. In contrast, the true density is a density based on the volume occupied by the material of the inorganic material mesh body. The average porosity (%) can be calculated from the bulk density ρf and true density ρr described below using the following formula (1): Average porosity (%) = ((1 / ρf) - (1 / ρr)) / (1 / ρf) × 100 ... formula (1)

[0034] <Bulk density> The bulk density ρf of the inorganic material mesh body of this embodiment is 0.020 g / cm ３ 1g / cm or more ３ Preferably, it is 0.022 g / cm or less, more preferably 0.022 g / cm ３ 0.5g / cm or more ３ More preferably, 0.024 g / cm or less ３ 0.1g / cm or more ３ Particularly preferably 0.026 g / cm ３ 0.07g / cm or more ３ The dimensions of the inorganic material mesh body are measured, and the bulk volume V of the inorganic material mesh body is calculated. Then, the mass M of the inorganic material mesh body is measured using a precision balance. From the obtained mass M and bulk volume V, the bulk density of the inorganic material mesh body can be calculated using the following formula (2). Bulk density ρf (g / cm ３ )=M / V...Formula (2)

[0035] <True Density> The true density ρr of the inorganic material mesh body of this embodiment is 0.5 g / cm ３ 10g / cm or more ３ Preferably, it is less than 1 g / cm ３ 7g / cm or more ３ More preferably, 1.5 g / cm or less ３ 5g / cm or more３ Particularly preferably 2 g / cm ３ 3g / cm or more ３ The true density ρr of the inorganic mesh body is not particularly limited, but can be calculated by the sink-float method using a mixed solution consisting of n-heptane, carbon tetrachloride, and ethylene dibromide. Specifically, first, an appropriate-sized sample piece of inorganic mesh body is placed in a stoppered test tube. Next, a mixed solvent of three solvents is added to the test tube, and the tube is immersed in a thermostatic bath at 30°C. If the sample piece floats, n-heptane, which has a low density, is added. On the other hand, if the test piece sinks, ethylene dibromide, which has a high density, is added. This procedure is repeated until the test piece floats in the liquid. Finally, the density of the mixed solvent is measured using a Gay-Lussac pycnometer.

[0036] <Composition of inorganic mesh body> Examples of materials constituting the inorganic mesh body of this embodiment or inorganic materials contained in the inorganic mesh body include elements selected from the group consisting of silicon, titanium, barium, zirconium, zinc, calcium, magnesium, cerium, aluminum, indium, tin, and lanthanum, single oxides of the elements or composite oxides of the elements, single sulfides of the elements or composite sulfides of the elements, and single phosphate compounds of the elements or composite phosphate compounds of the elements, with silicon, titanium, zirconium, magnesium, aluminum, indium, tin, and single or composite oxides thereof being preferred. Specific examples of inorganic materials constituting the inorganic mesh body include glass, shirasu, silica, silica gel, alumina, clay, ceramics, vermiculite, bentonite, perovskite compounds (strontium titanate), talc, mica, wollastonite, potassium titanate, calcium oxide, basic magnesium sulfate, sepiolite, xonotlite, perlite, zeolite, apatite, hydroxyapatite, kaolinite, montmorillonite, acid clay, diatomaceous earth, basalt, wet silica, dry silica, aerogel, mica, and vermiculite. Of these, alumina and silica are particularly preferred from the viewpoint of heat resistance.

[0037] <Shape of inorganic material mesh body> The shape of the inorganic material mesh body of this embodiment is not particularly limited as long as the inorganic material mesh body as a whole has a porous structure, and can be selected according to the mode of use, such as powder, particles, plates, threads, fibers, fiber bundles, fiber aggregates, cotton, woven or knitted fabrics, nonwoven fabrics, pellets, or rods. Note that in this specification, "woven or knitted fabrics" refers to woven fabrics or knitted fabrics.

[0038] When the inorganic material mesh body according to this embodiment is a woven fabric, known weaving methods such as plain weave, twill weave, satin weave, tatami weave, leno weave, and cord weave can be appropriately used as the weave of the fabric. Among these weaving methods, it is preferable to use a weaving method that provides a predetermined range of resistance to fluid passage between the communicating holes, i.e., between the spaces per mesh formed by the intersection of the warp and weft lines (for example, the airflow resistance described below). From these perspectives, it is preferable to use a weaving method such as plain weave, twill weave, satin weave, leno weave, or tatami weave.

[0039] When the inorganic material mesh body according to this embodiment is a knitted fabric, the knitting method can be any known knitting method, including warp knitting, which is knitted in the vertical direction, such as lace knitting, raschel knitting, tricot knitting, and vandyke knitting, and weft knitting, which is knitted in the horizontal direction, such as flat knitting, plain knitting, rib knitting, tubular knitting, jersey knitting, canard knitting, rib knitting, and jacquard knitting. Among these knitting methods, it is preferable to use a knitting method that provides a predetermined range of resistance to passage of a fluid through the communicating holes (for example, the airflow resistance described below). Various knitting machines may be used, including warp knitting machines, flat knitting machines, circular knitting machines, and raschel knitting machines.

[0040] When the inorganic material mesh body according to this embodiment is a woven or knitted fabric, the woven or knitted yarn used is not particularly limited, and the fineness is preferably 50 dtex or more and 8000 dtex or less, more preferably 100 dtex or more and 3000 dtex or less. The twisting method of the woven or knitted yarn is also not particularly limited, and the twisting method may be dry twisting, wet twisting performed by immersion in water, or a combination of these. Furthermore, the twisting direction is also not particularly limited, and may be right-handed twisting, left-handed twisting, or a combination of these. The woven or knitted yarn used in this embodiment may be false-twisted yarn, filament yarn, or yarn processed using the POY-DTY method or the PTY (Producers Textured Yarn) method. The conditions for the woven or knitted yarn used can be appropriately selected depending on the purpose of use, the type of aqueous solvent, etc. The material of the woven or knitted yarn is the material constituting the inorganic mesh body described above or the inorganic material contained in the inorganic mesh body.

[0041] When the inorganic mesh body of this embodiment is in powder or particulate form, the inorganic mesh body is preferably a porous powder or particle of an inorganic material selected from the group consisting of silica gel, shirasu balloons, silica aerogel, mesoporous silica, diatomaceous earth, activated carbon, zeolite, alumina, metal-organic frameworks, and porous concrete. This allows the inorganic mesh body of porous powder or particle to be dispersed as the contents in an aqueous solvent. The average particle diameter of the inorganic mesh body of powder or particle is preferably 0.01 to 2000 μm, more preferably 0.02 to 1500 μm, and even more preferably 0.02 to 1300 μm. The average particle size of the inorganic material mesh body is measured by photographing the particulate or powdered inorganic material mesh body with a scanning electron microscope (SEM) and measuring the maximum length between two points on the contour lines of 50 randomly selected primary particles (i.e., primary particles) that constitute the aggregates in the two-dimensional image. The BET specific surface area of ​​the powdered or particulate inorganic material mesh body is 0.3 to 5,000 m. ２ / g, and 10 to 2000m ２ / g, and 30 to 1600m ２ The BET specific surface area of ​​the inorganic material mesh body may be measured using a specific surface area meter (BELSORP-mini, manufactured by Microtrac-Bell Corporation), and the surface area per 1 g of the sample measured from the amount of nitrogen gas adsorbed by the BET method may be defined as the specific surface area (m ２ / g).

[0042] When the inorganic mesh body of this embodiment is composed of a nonwoven fabric, the average fiber diameter of all fibers (fibers made of the inorganic raw material) constituting the nonwoven fabric is preferably 1 to 100 μm, more preferably 2 to 10 μm. It is preferable that the average fiber diameter of the fibers constituting the nonwoven fabric is within the above range, as this makes it easier to ensure the desired porosity. The average fiber diameter can be measured by microscope observation or image analysis using a fiber length measuring device (e.g., KAJAANI Fiber Lab.).

[0043] Furthermore, when the inorganic mesh body of this embodiment is composed of a nonwoven fabric, the average fiber length of all fibers (raw fibers) constituting the nonwoven fabric is preferably 3 mm to 200 mm, more preferably 5 mm to 100 mm, and more preferably 10 mm to 50 mm. It is preferable that the average fiber length of all fibers constituting the nonwoven fabric is within the above range, as this makes it easier to ensure the desired porosity. The average fiber length can be measured by microscope observation or the average fiber diameter based on image analysis results using a fiber length measuring device (e.g., KAJAANI Fiber Lab.). When the inorganic mesh body of this embodiment is formed from a cotton-like material, the average fiber length of all fibers (raw fibers) constituting the cotton-like material is preferably 0.5 μm to 50 μm, more preferably 0.8 μm to 32 μm, and more preferably 1 μm to 25 μm. It is preferable that the average fiber length of all fibers constituting the cotton-like material is within the above range, since it is easier to ensure the desired void ratio. The average fiber length can be measured by microscope observation or the average fiber diameter from image analysis results using a fiber length measuring device (e.g., KAJAANI Fiber Lab.). In this specification, cotton-like material is also a type of nonwoven fabric, but it is defined as a cotton-like material that is in the form of fibers and has a shape other than a cloth (or flat plate).

[0044] <Preferred Embodiments of Mesh Body Made of Inorganic Material> Preferred embodiments of the mesh body made of inorganic material in this embodiment are glass cloth, plate-like zeolite or plate-like silica, porous powder made of silica gel, ceramic wool, rock wool, and glass wool.

[0045] The upper limit of the content of the inorganic material mesh body of this embodiment is preferably 50% by mass or less, more preferably 30% by mass or less, even more preferably 10% by mass or less, preferably 5% by mass or less, and particularly preferably 3% by mass or less, relative to the total amount (100% by mass) of the contents of the heat absorber. The lower limit of the content of the inorganic material mesh body is preferably 1% by mass or more, relative to the total amount (100% by mass) of the contents of the heat absorber. The content of the inorganic material mesh body of this embodiment is preferably 1% by mass or more to 50% by mass or less, more preferably 2% by mass or more to 30% by mass or less, and even more preferably 2.3% by mass or more to 10% by mass or less, relative to the total amount (100% by mass) of the contents of the heat absorber. The preferred range of the content of the inorganic material mesh body can be determined by appropriately combining the upper and lower limits. When the content of the inorganic material mesh body is within the above range, the heat absorption capacity and temperature rise suppression effect are superior, and the heat absorption effect can be changed to an insulating effect at high temperatures.

[0046] (Aqueous Solvent) The heat absorber of the present embodiment contains an aqueous solvent as its content. This allows heat absorption using the latent heat of vaporization of the aqueous solvent, particularly water, within the bag. This allows for utilization of the latent heat of vaporization of water, which has a greater heat absorption capacity than typical hydrates. Furthermore, since the heat is absorbed as sensible heat of the aqueous solvent, the temperature can be stabilized even at room temperature. Meanwhile, when exposed to high temperatures, such as during combustion, the aqueous solvent evaporates, creating voids within the inorganic material mesh, potentially providing thermal insulation and fire protection. In this embodiment, the aqueous solvent may be filled into the bag alone, or may be filled into the bag as a hydrogel composed of a hydrogel body and the aqueous solvent. In other words, a preferred embodiment of the heat absorber of the present disclosure includes a bag capable of being filled with a content, and the content includes a hydrogel composed of a hydrogel body and the aqueous solvent, and an inorganic material mesh. It is preferred that the aqueous solvent is primarily present in the hydrogel, such as an organic-inorganic composite hydrogel.

[0047] The aqueous solvent of this embodiment may contain water as the main component, and refers to water or a solvent containing water as the main component. Therefore, aqueous solvents encompass mixed solvents with solvents other than water, aqueous solutions containing salts (e.g., buffer solutions, electrolyte solutions), and the like. In this specification, "containing water as the main component" refers to a water content of 45% by mass or more relative to the total amount of the aqueous solvent. Furthermore, purified water, pure water, ultrapure water, distilled water, and the like can be used as the water without any particular limitation. Examples of the salt include alkali metal halides such as sodium chloride or potassium chloride; alkaline earth metal halides such as magnesium chloride or calcium chloride; and salts with buffering capacity such as tris-hydrochloric acid, glycine hydrochloride, citric acid-sodium citrate, acetic acid-sodium acetate, citric acid-disodium hydrogen phosphate, sodium dihydrogen phosphate-disodium hydrogen phosphate, glycine-sodium hydroxide, and sodium carbonate-sodium bicarbonate. Furthermore, Good's buffers such as HEPES or MOPS may also be used as the aqueous solvent. Examples of the solvent other than water that constitutes the mixed solvent include organic solvents that are uniformly miscible with water (for example, lower alcohols, lower ketones, etc.), and low-volatility solvents that are used as antifreeze agents.

[0048] The upper limit of the water content in the aqueous solvent of this embodiment is preferably 100% by mass or less, more preferably 99% by mass or less, even more preferably 90% by mass or less, and particularly preferably 80% by mass or less, relative to the total amount of the aqueous solvent. The lower limit of the water content is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 20% by mass or more, and particularly preferably 45% by mass or more. In this embodiment, the water content in the aqueous solvent may be preferably 5% by mass or more to 100% by mass or less, more preferably 10% by mass or more to 100% by mass or less, relative to the total amount of the aqueous solvent (100% by mass). The preferred range of the water content in the aqueous solvent can be determined by appropriately combining the upper and lower limits. The upper limit of the water solvent content of this embodiment is preferably 99% by mass or less, more preferably 90% by mass or less, even more preferably 80% by mass or less, and particularly preferably 70% by mass or less, relative to the total amount of the contents of the heat endotherm (100% by mass). The lower limit of the content of the aqueous solvent is preferably 15% by mass or more, preferably 20% by mass or more, preferably 30% by mass or more, and preferably 50% by mass or more, relative to the total amount (100% by mass) of the contents of the heat endotherm. In this embodiment, the content of the aqueous solvent may be preferably 15% by mass or more and 99% by mass or less, more preferably 20% by mass or more and 90% by mass or less, and even more preferably 30% by mass or more and 80% by mass or less, relative to the total amount (100% by mass) of the contents of the heat endotherm. The preferred range of the content of the aqueous solvent can be determined by appropriately combining the above upper and lower limits. When the content of the aqueous solvent is within the above range, the composition has a better heat absorption and temperature rise suppression effect, and can change from an endothermic effect to an insulating effect in a high temperature range.

[0049] <Antifreezing Agent> In this embodiment, an antifreezing agent may be added to the aqueous solvent as needed, since this can improve the effect of suppressing a temperature drop below freezing. In particular, adding an antifreezing agent to the contents of the heat absorber can maintain high cushioning properties over a wide temperature range. The antifreezing agent of this embodiment may be an inorganic or organic antifreezing agent. The antifreezing agent may be in the form of a liquid, powder, solid, or the like. Preferred inorganic antifreezing agents are chlorides such as sodium chloride, calcium chloride, or magnesium chloride (including hydrates such as magnesium chloride hexahydrate). On the other hand, preferred organic antifreezing agents are salts of organic acids or low-volatility substances (low-volatility solvents or urea), with salts of organic acids or low-volatility solvents being more preferred. As the salts (including hydrates) of the organic acids, it is preferable to use salts of sodium, potassium, magnesium, ammonium, etc. of formic acid, acetic acid, propionic acid, succinic acid, etc., and examples thereof include sodium acetate (including hydrates such as sodium acetate trihydrate), potassium acetate (including hydrates such as calcium acetate monohydrate), magnesium acetate (including hydrates such as magnesium acetate tetrahydrate), disodium succinate (including hydrates such as disodium succinate hexahydrate), and sodium propionate. In addition, examples of the low-volatility substances include urea or low-volatility solvents (for example, polyhydric alcohols). Examples of the low-volatility solvent include ethylene glycol, diethylene glycol, glycerin, dipropylene glycol, propylene glycol, butyrolactone, N,N-dimethylformamide, glycerol, 1,3-propanediol, glycol ether, glycol ether, glycol monoether, ethylene glycol, diethylene glycol, propylene glycol, isopropanol, propylene glycol monomethyl ether, di- or tripropylene glycol monomethyl ether, cyclohexanol, glucose, mannose, fructose, galactose, sucrose, lactose, maltose, xylose, arabinose, sorbitol, mannitol, trehalose, and raffinose.

[0050] The low-volatility solvent of this embodiment has a volatility of 1 cm in an open system at 60°C and 1 atmosphere. ２ ・0.1g or less per hour (0.1g / cm ２ More preferably, an organic solvent of 0.05 g or less, and even more preferably 0.01 g or less is used. Specifically, a solvent that is easily miscible with water is preferred, and therefore glycerin (0.001 g or less / cm ２ hr 60 ° C 1 atm), diglycerin (0.001 g or less / cm ２ hr 60°C 1 atm), ethylene glycol (0.01 g or less / cm ２ hr 60 ° C 1 atm), propylene glycol (0.001 g or less / cm ２ hr 60°C 1 atm), polyethylene glycol (0.001 g or less / cm ２Polyhydric alcohols such as ethanol (water, ethanol, ethanol 1000 hr, 60°C, 1 atm) are preferred, with glycerin and diglycerin being more preferred. These low-volatile solvents may be used alone or in combination of two or more. It is also preferred that these low-volatile solvents be uniformly contained in the organic-inorganic composite hydrogel. By including a low-volatile solvent, particularly a polyhydric alcohol, as the content of the heat endotherm of this embodiment, volatilization of the aqueous solvent is suppressed or prevented, or a decrease in cushioning properties at low temperatures is suppressed (improved anti-freeze effect). When a low-volatile solvent is used as an optional component, the mass ratio of the aqueous solvent to the low-volatile solvent (aqueous solvent / low-volatile solvent) in the content of the heat endotherm of this embodiment is preferably 95 / 5 to 30 / 70, more preferably 90 / 10 to 50 / 50, and even more preferably 85 / 15 to 65 / 35. In this embodiment, the upper limit of the content of the antifreeze agent is preferably 70% by mass or less, more preferably 50% by mass or less, even more preferably 35% by mass or less, and particularly preferably 30% by mass or less, relative to the total amount (100% by mass) of the contents of the heat endotherm. The lower limit of the content of the antifreeze agent is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and particularly preferably 20% by mass or more, relative to the total amount (100% by mass) of the contents of the heat endotherm. In this embodiment, the content of the antifreeze agent may be preferably 5% by mass or more to 70% by mass or less, more preferably 10% by mass or more to 50% by mass or less, and even more preferably 15% by mass or more to 35% by mass or less, relative to the total amount (100% by mass) of the contents of the heat endotherm. The preferred range of the content of the antifreeze agent can be determined by appropriately combining the upper and lower limits. Furthermore, when the antifreeze agent is contained within the above range, the battery is less likely to freeze even at -20°C, allowing it to be used over a wide temperature range.

[0051] <Hydrogel> In the heat absorber of this embodiment, the hydrogel may be composed of a hydrogel body and an aqueous solvent, with the aqueous solvent filling the pouch. Furthermore, the hydrogel of this embodiment preferably comprises an aqueous solvent and a three-dimensional polymer network structure (i.e., the hydrogel body) that retains the aqueous solvent. While the hydrogel is not particularly limited and any known hydrogel can be used, it is more preferable for the hydrogel body to comprise an aqueous solvent and a three-dimensional polymer network structure containing a water-swellable clay mineral and a water-soluble organic monomer structural unit, at least a portion of which is dissolved or dispersed in the aqueous solvent. In other words, the hydrogel of this embodiment preferably comprises an aqueous solvent retained in a three-dimensional network structure (three-dimensional network) primarily composed of a polymer synthesized from a water-soluble organic monomer, etc., and even more preferably comprises an aqueous solvent retained in a three-dimensional network structure (three-dimensional network) primarily composed of a polymer synthesized from a water-soluble organic monomer in the presence of a water-swellable clay mineral. When the heat absorber of this embodiment includes a hydrogel, the content of the aqueous solvent in the hydrogel is in the range of 5 to 99% by mass relative to the entire hydrogel, and thus the hydrogel is suitable as a heat absorber because it can exhibit a heat absorption effect at a level that can effectively prevent fire or damage due to thermal runaway in secondary batteries. The upper limit of the aqueous solvent content in the hydrogel is preferably 99% by mass or less, more preferably 90% by mass or less, and even more preferably 80% by mass or less, relative to the entire gel. The lower limit of the aqueous solvent content is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 20% by mass or more. The preferred range of the aqueous solvent content can be achieved by appropriately combining the above upper and lower limits.

[0052] Specific examples of such hydrogels include organic-inorganic composite hydrogels (NC gels), interpenetrating network hydrogels (DN gels), slide-ring gels (SR gels), and hydrogels known as aquamaterials. Among these, organic-inorganic composite hydrogels (also referred to as organic-inorganic hydrogels or NC gels (nanocomposite gels)) are preferred because of their excellent heat-absorbing properties due to the aqueous solvent contained therein, as well as their excellent cushioning and creep resistance.

[0053] When the heat absorber of this embodiment contains a hydrogel, the upper limit of the hydrogel content is preferably 95% by mass or less, preferably 80% by mass or less, preferably 70% by mass or less, preferably 50% by mass or less, preferably 40% by mass or less, and more preferably 30% by mass or less, relative to the total amount of the contents of the heat absorber. The lower limit of the hydrogel content is preferably 10% by mass or more, more preferably 15% by mass or more, relative to the total amount of the contents of the heat absorber (100% by mass). In this embodiment, the hydrogel content is preferably 10% by mass or more to 95% by mass or less, more preferably 15% by mass or more to 80% by mass or less, and even more preferably 15% by mass or more to 40% by mass or less, relative to the total amount of the contents of the heat absorber (100% by mass). The preferred range of the hydrogel content can be determined by appropriately combining the upper and lower limits. When the hydrogel content is within the above range, a heat absorber with excellent cushioning properties can be provided. As a result, the inclusion of the heat absorber allows the heat absorption properties to be exerted, suppressing the temperature effect on other battery cells and providing a highly safe secondary battery module. The heat absorber of the present disclosure has sufficient strength to be used alone. If necessary, an additive may be further filled into the pouch.

[0054] Preferred hydrogels of this embodiment include interpenetrating network gels in which two types of acrylic polymers each form a three-dimensional network structure, slide-ring gels in which cyclodextrin forms the backbone of the three-dimensional network structure, and aquamaterials in which a hyperbranched dendrimer forms the main backbone of the three-dimensional network structure and a water-swellable clay mineral is added. However, this disclosure will be described below based on an organic-inorganic composite hydrogel, which is one aspect of this embodiment. The organic-inorganic composite hydrogel of this embodiment has a three-dimensional network structure containing water-soluble organic monomer structural units and a water-swellable clay mineral as the hydrogel body. More specifically, the hydrogel body of the organic-inorganic composite hydrogel (hereinafter also referred to as the organic-inorganic composite hydrogel body) is considered to be a polymer gel (i.e., a three-dimensional network structure) in which polymer chains composed of multiple water-soluble organic monomer structural units are crosslinked via water-swellable clay minerals that function as binding points. The organic-inorganic composite hydrogel can swell by incorporating an aqueous solvent such as water into the three-dimensional network structure of the polymer gel. As a result, the swollen organic-inorganic composite hydrogel not only has heat absorption properties and exhibits excellent cushioning properties that allow it to adapt to relatively short-term deformations such as expansion and contraction due to charging and discharging of the battery cell, but also exhibits excellent creep resistance that can alleviate internal pressure due to expansion of the battery cell over time. The organic-inorganic composite hydrogel preferably has a three-dimensional network structure and is made from a water-soluble organic monomer and a water-swellable clay mineral as reaction raw materials.

[0055] The organic-inorganic composite hydrogel according to one aspect of this embodiment preferably uses at least a water-soluble organic monomer structural unit and a water-swellable clay mineral as reaction raw materials. A preferred method for producing the organic-inorganic composite hydrogel according to one aspect of this embodiment involves polymerizing the water-soluble organic monomer in a dispersion (a) containing a water-soluble organic monomer, a water-swellable clay mineral, an aqueous solvent, and, if necessary, a polymerization initiator and additives, since this method allows for the easy production of an organic-inorganic composite hydrogel having a three-dimensional network structure. The resulting polymer of the water-soluble organic monomer forms a three-dimensional network structure together with the water-swellable clay mineral, becoming a component of the organic-inorganic composite hydrogel (the hydrogel main body).

[0056] When the heat absorber of this embodiment includes a hydrogel, the lower limit of the content of the hydrogel body according to this embodiment may be preferably 1% by mass or more, more preferably 10% by mass or more, and even more preferably 20% by mass or more, relative to the total amount (100% by mass) of the hydrogel. On the other hand, the upper limit of the content of the hydrogel body may be preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less. For example, when the hydrogel body is composed of a water-soluble organic monomer structural unit as described below, the content of the hydrogel body may be the total amount of the water-soluble organic monomer structural unit and the water-swellable clay mineral. In this embodiment, the content of the hydrogel body may be preferably 1% by mass or more and 50% by mass or less, more preferably 10% by mass or more and 40% by mass or less, and even more preferably 20% by mass or more and 30% by mass or less, relative to the total amount (100% by mass) of the hydrogel. The preferred range of the content of the hydrogel body can be determined by appropriately combining the above upper and lower limits. The content of the hydrogel body was calculated by the mass change (%) before and after drying the hydrogel at 120°C for 2 hours.

[0057] <<Water-Soluble Organic Monomer>> The water-soluble organic monomer used in this embodiment constitutes the organic-inorganic hybrid hydrogel body as the water-soluble organic monomer structural unit. Furthermore, the lower limit of the content of the water-soluble organic monomer structural unit in the hydrogel according to this embodiment may be preferably 0.9% by mass or more, more preferably 1% by mass or more, and even more preferably 5% by mass or more, relative to the total amount of the hydrogel. Meanwhile, the upper limit of the content of the water-soluble organic monomer structural unit may be 50% by mass or less, 40% by mass or less, or 30% by mass or less. In this embodiment, the content of the water-soluble organic monomer structural unit may be preferably 0.9% by mass or more to 50% by mass or less, more preferably 1% by mass or more to 40% by mass or less, and even more preferably 5% by mass or more to 30% by mass, relative to the total amount of the hydrogel (100% by mass). The preferred range of the content of the water-soluble organic monomer structural unit can be determined by appropriately adjusting the upper and lower limits. The type of water-soluble organic monomer used in this embodiment is not particularly limited, and examples include monomers having a (meth)acrylamide group, monomers having a (meth)acryloyloxy group, and acrylic monomers having a hydroxyl group. In this specification, "(meth)acrylamide" refers to either or both of acrylamide and methacrylamide, "(meth)acryloyloxy" refers to either or both of acryloyloxy and (meth)acryloyloxy, "(meth)acrylate" refers to either or both of acrylate and methacrylate, and "(meth)acrylic monomer" refers to either or both of acrylic monomer and methacrylic monomer.

[0058] Examples of the monomer having a (meth)acrylamide group include acrylamide, N,N-dimethylacrylamide, N,N-diethylacrylamide, N-methylacrylamide, N-ethylacrylamide, N-isopropylacrylamide, N-cyclopropylacrylamide, N,N-dimethylaminopropylacrylamide, N,N-diethylaminopropylacrylamide, acryloylmorpholine, methacrylamide, N,N-dimethylmethacrylamide, N,N-diethylmethacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, N-isopropylmethacrylamide, N-cyclopropylmethacrylamide, N,N-dimethylaminopropylmethacrylamide, and N,N-diethylaminopropylmethacrylamide. Preferred examples of the monomer having a (meth)acrylamide group include acrylamide, N,N-dimethylacrylamide, N-methylacrylamide, N-ethylacrylamide, acryloylmorpholine, methacrylamide, N,N-dimethylmethacrylamide, N-methylmethacrylamide, and N-ethylmethacrylamide.

[0059] Examples of the monomer having a (meth)acryloyloxy group include methoxyethyl acrylate, ethoxyethyl acrylate, methoxyethyl methacrylate, ethoxyethyl methacrylate, methoxymethyl acrylate, and ethoxymethyl acrylate.

[0060] Examples of the acrylic monomer having a hydroxyl group include hydroxyethyl acrylate, hydroxyethyl methacrylate, etc. As the water-soluble organic monomer used in this embodiment, the acrylic monomer having a hydroxyl group may be used alone or in combination of two or more thereof.

[0061] In this embodiment, when a homopolymer is obtained from a water-soluble organic monomer, the resulting homopolymer preferably has a lower critical solution temperature (°C) of 50°C or higher, more preferably 60°C or higher. It is preferable that the homopolymer does not have a lower critical solution temperature (°C), i.e., that the lower critical solution temperature (°C) cannot be observed in an aqueous solvent. The upper limit of the lower critical solution temperature (°C) of the homopolymer may be, for example, 100°C. This prevents the polymer chains of water-soluble organic monomer structural units constituting the organic-inorganic composite hydrogel from undergoing a phase transition at temperatures below 50°C, thereby achieving both superior cushioning properties and heat absorption capacity even at high temperatures. More specifically, the organic-inorganic composite hydrogel according to one aspect of this embodiment has, as a constituent component, a polymer chain composed of water-soluble organic monomer structural units obtained by polymerization or reaction of a water-soluble organic monomer. Therefore, when the temperature reaches or exceeds the lower critical solution temperature (°C) of the polymer chain composed of the water-soluble organic monomer structural units, the polymer chains undergo a phase transition due to desolvation, resulting in separation into a phase containing the polymer chains and a phase containing the aqueous solvent. As a result, the three-dimensional network structure of the organic-inorganic composite hydrogel encapsulating the aqueous solvent cannot be maintained, making it difficult to exhibit cushioning properties. Therefore, the lower critical solution temperature (°C) of the organic-inorganic composite hydrogel in an aqueous solvent is preferably 50°C or higher, more preferably 60°C or higher, and preferably does not have a lower critical solution temperature (°C), i.e., it is not possible to observe a lower critical solution temperature (°C) in an aqueous solvent. The upper limit of the lower critical solution temperature (°C) of the organic-inorganic composite hydrogel can be, for example, 100°C.

[0062] From the viewpoint of suppressing the phase transition of the organic-inorganic composite hydrogel, the preferred water-soluble organic monomer used in this embodiment is a water-soluble organic monomer having a homopolymer repeating unit that does not have a lower critical solution temperature in an aqueous solvent. Specifically, (meth)acrylamide, N,N-dimethyl(meth)acrylamide, acryloylmorpholine, methoxyethyl acrylate, ethoxyethyl acrylate, methoxyethyl methacrylate, ethoxyethyl methacrylate, methoxymethyl acrylate, ethoxymethyl acrylate, hydroxyethyl acrylate, or hydroxyethyl methacrylate is preferred. When the organic-inorganic composite hydrogel is heated to or above the lower critical solution temperature (°C) of the organic-inorganic composite hydrogel or the polymer chains constituting the organic-inorganic composite hydrogel, the organic-inorganic composite hydrogel undergoes a phase transition and separates into a phase in which polymer chains containing water-soluble organic monomer structural units constituting the organic-inorganic composite hydrogel are aggregated and a phase of the aqueous solvent contained within the organic-inorganic composite hydrogel. Therefore, it is particularly preferred that the polymer chains constituting the organic-inorganic composite hydrogel do not have a lower critical solution temperature in an aqueous solvent. Therefore, a water-soluble organic monomer capable of forming a highly hydrophilic polymer chain is preferred. Furthermore, when the polymer chain constituting the organic-inorganic composite hydrogel is composed of two or more water-soluble organic monomers, from the viewpoint of reducing the decrease in cushioning property or liquid leakage due to phase transition, the lower critical solution temperature (°C) of the copolymer composed of the two or more water-soluble organic monomers is preferably 50°C or higher, more preferably 60°C or higher, and preferably does not have a lower critical solution temperature (°C), i.e., the lower critical solution temperature (°C) cannot be observed in an aqueous solvent. The upper limit of the lower critical solution temperature (°C) of the copolymer composed of the two or more water-soluble organic monomers can be, for example, 100°C.

[0063] Among the above water-soluble organic monomers, from the viewpoints of solubility and cushioning properties of the resulting organic-inorganic hybrid hydrogel, it is preferable to use a monomer having a (meth)acrylamide group, it is more preferable to use acrylamide, N,N-dimethylacrylamide, or acryloylmorpholine, it is even more preferable to use N,N-dimethylacrylamide or acryloylmorpholine, and from the viewpoint of ease of polymerization, N,N-dimethylacrylamide is particularly preferable. The above water-soluble organic monomers may be used alone or in combination of two or more.

[0064] <<Water-Swellable Clay Mineral>> The water-swellable clay mineral used in this embodiment forms a three-dimensional network structure together with the polymer chain having the water-soluble organic monomer structural unit (polymer having the water-soluble organic monomer structural unit), and serves as a component of the organic-inorganic composite hydrogel and the organic-inorganic composite hydrogel body. The water-swellable clay mineral used in this embodiment is not particularly limited, and examples thereof include water-swellable smectite and water-swellable mica. Examples of the water-swellable smectite include water-swellable hectorite, water-swellable montmorillonite, and water-swellable saponite. Examples of the water-swellable mica include water-swellable synthetic mica. Among these, from the viewpoint of dispersibility, it is preferable to use water-swellable hectorite and water-swellable montmorillonite, and it is more preferable to use water-swellable hectorite.

[0065] The water-swellable clay mineral used in this embodiment may be naturally occurring, synthetic, or surface-modified. Examples of surface-modified water-swellable clay minerals include phosphonic acid-modified hectorite and fluorine-modified hectorite. From the viewpoint of the heat absorption and cushioning properties of the resulting organic-inorganic composite hydrogel, it is preferable to use phosphonic acid-modified hectorite. The above-mentioned water-swellable clay minerals may be used alone or in combination of two or more.

[0066] The phosphonic acid-modified hectorite forms a three-dimensional network structure with the polymer of the water-soluble organic monomer, becoming a component of the organic-inorganic composite hydrogel. Examples of the phosphonic acid-modified hectorite include pyrophosphate-modified hectorite, etidronic acid-modified hectorite, alendronic acid-modified hectorite, methylenediphosphonic acid-modified hectorite, and phytic acid-modified hectorite. These phosphonic acid-modified hectorites may be used alone or in combination of two or more. The content of the water-swellable clay mineral of this embodiment is preferably 50% by mass or less, more preferably 30% by mass or less, even more preferably 20% by mass or less, and particularly preferably 10% by mass or less, based on the total amount of the polymer derived from the water-soluble organic monomer contained in the organic-inorganic composite hydrogel, the water-swellable clay mineral, the polymerization initiator, and the aqueous solvent. The lower limit of the content of the water-swellable clay mineral is preferably 0.1% by mass or more, more preferably 1% by mass or more, even more preferably 2% by mass or more, and particularly preferably 3% by mass or more. In this embodiment, the content of the water-swellable clay mineral is preferably 0.1% by mass or more and 50% by mass or less, more preferably 2% by mass or more and 30% by mass or less, and even more preferably 3% by mass or more and 20% by mass or less, based on the total amount of the polymer derived from the water-soluble organic monomer contained in the organic-inorganic composite hydrogel, the water-swellable clay mineral, the polymerization initiator, and the aqueous solvent. The upper and lower limits of the content of the water-swellable clay mineral in the organic-inorganic composite hydrogel can be adjusted as appropriate.

[0067] <<Reaction Raw Materials for Hydrogel>> In one aspect of this embodiment, when the heat absorber of this embodiment includes a hydrogel, the heat absorber includes a bag, and as contents of the bag, an organic-inorganic composite hydrogel and an inorganic mesh body. The organic-inorganic composite hydrogel of one aspect of this embodiment preferably uses at least a water-swellable clay mineral and a water-soluble organic monomer as reaction raw materials. In this case, the organic-inorganic composite hydrogel may be filled into the bag as a gel together with the inorganic mesh body, and the bag may then be sealed. Alternatively, the water-soluble organic monomer and the water-swellable clay mineral, which are reaction raw materials for the organic-inorganic composite hydrogel, may be filled into the bag together with an aqueous solvent and the inorganic mesh body (optionally, an organic solvent and a polymerization initiator may be added), and the water-soluble organic monomer and the water-swellable clay mineral inside the bag may then be gelled while the bag is sealed.

[0068] A preferred method for producing an organic-inorganic composite hydrogel according to one aspect of this embodiment involves polymerizing a water-soluble organic monomer in a dispersion (a) containing the reaction raw materials (a water-soluble organic monomer, a water-swellable clay mineral, a polymerization initiator, and an aqueous solvent), as this method allows for easy production of the organic-inorganic composite hydrogel. More specifically, a preferred method involves filling a bag with the dispersion (a) (containing the reaction raw materials (a water-soluble organic monomer, a water-swellable clay mineral, a polymerization initiator, and an aqueous solvent) together with an inorganic mesh body, and then polymerizing the water-soluble organic monomer under predetermined polymerization conditions while the bag is sealed. The content of the water-soluble organic monomer in the dispersion (a) is, for example, in the range of 0.9 to 50% by mass, based on the total amount (mass) of the water-soluble organic monomer, the water-swellable clay mineral, and the aqueous solvent. The lower limit of the content of the water-soluble organic monomer is preferably 0.9% by mass or more, more preferably 1% by mass or more, and even more preferably 5% by mass or more. The upper limit of the content of the water-soluble organic monomer is preferably 50% by mass or less, more preferably 30% by mass or less. The upper and lower limits of the content can be appropriately combined. A content of the water-soluble organic monomer of 0.9% by mass or more is preferable because a hydrogel with excellent mechanical properties can be obtained. On the other hand, a content of the water-soluble organic monomer of 50% by mass or less is preferable because the dispersion can be easily prepared.

[0069] The content of the water-swellable clay mineral in the dispersion (a) is, for example, in the range of 0.1 to 50% by mass, based on the total amount (mass) of the water-soluble organic monomer, the water-swellable clay mineral, and the aqueous solvent. The lower limit of the content of the water-swellable clay mineral is preferably 0.1% by mass or more, more preferably 1% by mass or more, and even more preferably 3% by mass or more. The upper limit of the content of the water-swellable clay mineral is preferably 50% by mass or less, more preferably 30% by mass or less, and even more preferably 10% by mass or less. The upper and lower limits of the content can be appropriately combined. A content of the water-swellable clay mineral of 0.1% by mass or more is preferred because the mechanical properties of the resulting hydrogel are further improved. On the other hand, a content of the water-swellable clay mineral of 50% by mass or less is preferred because the increase in viscosity of the dispersion (a) can be further suppressed. The dispersion (a) has better storage stability when phosphonic acid-modified hectorite is used as the water-swellable clay mineral, but may contain other water-swellable clay minerals as long as the storage stability is not impaired.

[0070] The content of the aqueous solvent in the dispersion (a) is, for example, in the range of 50 to 99% by mass, based on the total amount (mass) of the water-soluble organic monomer, the water-swellable clay mineral, and the aqueous solvent. The lower limit of the aqueous solvent content is preferably 50% by mass or more, more preferably 60% by mass or more. The upper limit of the aqueous solvent content is preferably 99% by mass or less, more preferably 90% by mass or less. The upper and lower limits of the content can be appropriately combined. A content of the aqueous solvent of 90% by mass or less is preferred because a hydrogel with excellent mechanical properties can be obtained. On the other hand, a content of the aqueous solvent of 60% by mass or more is preferred because it facilitates the preparation of a dispersion (a) in which each component is uniformly dispersed. In addition to the reaction raw materials, namely the water-soluble organic monomer, the water-swellable clay mineral, the polymerization initiator, and the aqueous solvent, the dispersion (a) may also contain one or more low-volatile solvents and additives, as described below.

[0071] The dispersion liquid (a) of this embodiment preferably contains a polymerization initiator. Examples of the polymerization initiator include, but are not limited to, water-soluble peroxides and water-soluble azo compounds. Examples of the water-soluble peroxides include potassium peroxodisulfate, ammonium peroxodisulfate, sodium peroxodisulfate, and t-butyl hydroperoxide. Examples of the water-soluble azo compounds include 2,2'-azobis(2-methylpropionamidine) dihydrochloride and 4,4'-azobis(4-cyanovaleric acid). Among these, in terms of interaction with the water-swellable clay mineral, it is preferable to use water-soluble peroxides, and it is more preferable to use potassium peroxodisulfate, ammonium peroxodisulfate, or sodium peroxodisulfate, with sodium peroxodisulfate and ammonium peroxodisulfate being even more preferable. The above-mentioned polymerization initiators may be used alone or in combination of two or more.

[0072] In one aspect of the present embodiment, the polymerization initiator is not essential. However, when used, the molar ratio of the polymerization initiator to the water-soluble organic monomer in the dispersion liquid (a) (polymerization initiator / water-soluble organic monomer) is preferably 0.01 or more, more preferably 0.02 to 0.1, and even more preferably 0.04 to 0.1.

[0073] The content of the polymerization initiator in the dispersion (a) is not essential, but when used, it is preferably 0.1 to 10 mass% and more preferably 0.2 to 5 mass% relative to the total amount (mass) of the water-soluble organic monomer, the water-swellable clay mineral, the aqueous solvent, and the polymerization initiator. A polymerization initiator content of 0.1 mass% or more is preferred because it enables polymerization of the water-soluble organic monomer even in an air atmosphere. On the other hand, a polymerization initiator content of 10 mass% or less is preferred because it allows the dispersion to be used without agglomeration before polymerization, improving handleability.

[0074] The dispersion liquid (a) contains a water-soluble organic monomer, a water-swellable clay mineral, and an aqueous solvent, and may further contain an organic solvent, a catalyst, an organic crosslinking agent, a preservative, a thickener, etc., as necessary. Examples of the organic solvent include alcohol compounds such as methanol, ethanol, propanol, isopropyl alcohol, and 1-butanol; ether compounds such as ethyl ether and ethylene glycol monoethyl ether; amide compounds such as dimethylformamide and N-methylpyrrolidone; and ketone compounds such as acetone and methyl ethyl ketone. Among these, from the viewpoint of the dispersibility of the water-swellable clay mineral, it is preferable to use an alcohol compound, and it is more preferable to use methanol, ethanol, n-propyl alcohol, and isopropyl alcohol, and it is even more preferable to use methanol and ethanol. These organic solvents may be used alone or in combination of two or more.

[0075] The catalyst has the function of increasing the polymerization rate when polymerizing a water-soluble organic monomer. Examples of the catalyst include, but are not limited to, tertiary amine compounds, thiosulfates, and ascorbic acids. Examples of the tertiary amine compounds include N,N,N',N'-tetramethylethylenediamine and 3-dimethylaminopropionitrile. Examples of the thiosulfates include sodium thiosulfate and ammonium thiosulfate. Examples of the ascorbic acids include L-ascorbic acid and sodium L-ascorbate. Among these, from the viewpoint of dispersion stability, it is preferable to use a tertiary amine compound, and it is more preferable to use N,N,N',N'-tetramethylethylenediamine. The above-mentioned catalysts may be used alone or in combination of two or more. Although a catalyst is not essential, when a catalyst is used, the content of the catalyst in the dispersion (a) is preferably 0.01 to 1 mass %, more preferably 0.05 to 0.5 mass %, relative to the total mass of the water-soluble organic monomer, the water-swellable clay mineral, the aqueous solvent, and the catalyst. A catalyst content of 0.01 mass % or more is preferred because it can efficiently promote the synthesis of a hydrogel obtained from the water-soluble organic monomer. On the other hand, a catalyst content of 1 mass % or less is preferred because it allows the dispersion to be used without flocculation before polymerization, improving handleability.

[0076] Examples of methods for preparing the dispersion liquid (a) include a method in which a water-soluble organic monomer, a water-swellable clay mineral, a polymerization initiator, an aqueous solvent such as water, and the like are mixed all at once; and a multi-liquid mixing method in which a dispersion liquid (a1) containing a water-soluble organic monomer and a solution (a2) containing a polymerization initiator are prepared as separate dispersion liquids or solutions and then mixed immediately before use. However, from the viewpoints of dispersibility, storage stability, viscosity control, and the like, the multi-liquid mixing method is preferred.

[0077] The dispersion (a1) containing the water-soluble organic monomer may be, for example, a dispersion in which a water-soluble organic monomer and a water-swellable clay mineral are mixed.

[0078] The solution (a2) containing the polymerization initiator may be, for example, an aqueous solution obtained by mixing a polymerization initiator with water.

[0079] The organic-inorganic composite hydrogel can be obtained by polymerizing a water-soluble organic monomer in the dispersion liquid (a), and the polymerization method is not particularly limited and can be performed by a known method. Specific examples include radical polymerization by heating or ultraviolet irradiation, and radical polymerization using a redox reaction.

[0080] The polymerization temperature for polymerizing the organic-inorganic composite hydrogel is preferably 10 to 80°C, more preferably 20 to 80°C. A polymerization temperature of 10°C or higher is preferred because the radical reaction can proceed in a chain reaction. On the other hand, a polymerization temperature of 80°C or lower is preferred because the water contained in the dispersion (a) can be polymerized without boiling. The polymerization time for the organic-inorganic composite hydrogel varies depending on the type of polymerization initiator and catalyst, but is typically between several tens of seconds and 24 hours. In particular, in the case of radical polymerization using heat or redox, a polymerization time of 1 to 24 hours is preferred, more preferably 5 to 24 hours. A polymerization time of 1 hour or more is preferred because the polymer of the water-swellable clay mineral and the water-soluble organic monomer can form a three-dimensional network structure. On the other hand, since the polymerization reaction is nearly complete within 24 hours, a polymerization time of 24 hours or less is preferred.

[0081] (Inorganic Powder) The heat absorber of this embodiment preferably contains an inorganic powder as its content. This provides a synergistic effect with the heat absorption of the aqueous solvent, allowing for continuous heat absorption at a different endothermic temperature than the aqueous solvent. Furthermore, even when exposed to high temperatures, if the inorganic powder is present as a content of the heat absorber, air bubbles trapped in the inorganic material mesh or voids within the inorganic material mesh created by the evaporation of the aqueous solvent act as pores, allowing the inorganic powder and the inorganic material mesh as a whole to form a porous composite (see, for example, the photograph in Figure 5 below). As a result, excellent thermal insulation and fire protection are achieved. Therefore, a heat absorber containing an inorganic powder primarily functions as a heat absorber in relatively low temperature ranges (e.g., above room temperature to around 100°C). On the other hand, in temperature ranges from the critical temperature (e.g., 150°C) to above the thermal runaway temperature (e.g., around 1000°C), the inorganic powder and the inorganic material mesh as a whole become porous, allowing it to also function as a thermal insulator. As a result, when the heat absorber of this embodiment is disposed between cells in a battery stack in which multiple cells are stacked, it is possible to block or suppress the thermal influence on adjacent cells.

[0082] Furthermore, when thermal runaway occurs, the cells expand, compressing the inorganic material mesh between the cells, reducing the void space and preventing effective thermal insulation. When an inorganic powder is included as the content of the heat absorber of this embodiment, the inorganic powder itself sinters when heated to a high temperature due to thermal runaway or the like, thereby increasing the pressure resistance of the inorganic material mesh. This maintains effective thermal insulation, effectively suppressing the explosion of cells. The inorganic powder of this embodiment is preferably an inorganic powder with a heat absorption effect, and more preferably one or more selected from the group consisting of heat absorption materials, porous powders, hollow particles, and other inorganic powders. The heat absorption capacity of the inorganic powder (= the heat absorption capacity (J / g) when heated from room temperature (23°C) to 1000°C) is preferably 100 J / g or more, more preferably 500 J / g or more, and even more preferably 700 J / g or more. Meanwhile, the upper limit of the heat absorption capacity of the inorganic powder is not particularly limited, but is preferably 4000 J / g or less. The endothermic capacity of the inorganic powder is preferably 100 J / g or more and 4000 J / g or less. When the endothermic capacity of the inorganic powder is within the above range, the endothermic effect is improved, resulting in a synergistic effect with the endothermic capacity of the aqueous solvent, making it easier to suppress ignition. The upper and lower limits of the endothermic capacity of the inorganic powder can be appropriately adjusted. The endothermic capacity of the inorganic powder can be measured using a differential scanning calorimeter (DSC) as described in the Examples section.

[0083] The upper limit of the thermal decomposition onset temperature of the inorganic powder of this embodiment is preferably 800°C or lower, more preferably 500°C or lower, even more preferably 350°C or lower, and even more preferably 150°C or lower. By setting the thermal decomposition onset temperature of the inorganic powder to the above upper limit or lower, the inorganic powder itself decomposes quickly, making it easier to suppress ignition. Furthermore, the lower limit of the thermal decomposition onset temperature of the inorganic powder is, for example, 80°C or higher, preferably 90°C or higher, more preferably 100°C or higher, and even more preferably 110°C or higher. The thermal decomposition onset temperature of the inorganic powder may be preferably 80°C or higher and 800°C or lower, more preferably 90°C or higher and 500°C or lower. The upper and lower limits of the thermal decomposition onset temperature can be appropriately adjusted. The thermal decomposition onset temperature can be measured using a differential scanning calorimeter (DSC).

[0084] The shape of the inorganic powder of this embodiment is not particularly limited, and examples thereof include powder, particle, and plate shapes. The average particle diameter of the inorganic powder is preferably 0.1 to 200 μm, more preferably 1 to 140 μm, and even more preferably 10 to 100 μm. By setting the average particle diameter within the above range, the inorganic powder is easily dispersed in the system. The average particle diameter may be the median diameter (D50) value measured using a laser diffraction / scattering particle size distribution analyzer.

[0085] The inorganic powder of this embodiment is not particularly limited, but is preferably one or more selected from the group consisting of hydrated metal compounds, inorganic materials other than the hydrated metal compounds, hollow materials, and porous powders. A hydrated metal compound having a thermal decomposition onset temperature of 350°C or less and an endothermic heat of 700 J / g or more is preferred. Furthermore, the hydrated metal compound is preferably one or more selected from the group consisting of aluminum hydroxide, magnesium hydroxide, sodium acetate (including anhydrous and trihydrate), calcium hydroxide, calcium sulfate, calcium sulfate 0.5-hydrate, calcium sulfate dihydrate, zinc borate, calcium carbonate, basic magnesium carbonate, magnesium oxide, aluminum oxide, talc, karyon clay, dawsonite, boehmite, hydrotalcite, calcium aluminate, and magnesium sulfate heptahydrate. Furthermore, from the viewpoints of fire resistance, pinhole resistance, and moldability, one or more selected from the group consisting of sodium acetate, aluminum hydroxide, magnesium hydroxide, calcium sulfate dihydrate, and magnesium sulfate heptahydrate is more preferred. Among the above, aluminum hydroxide or calcium sulfate dihydrate is particularly preferred as a hydrated metal compound. In this specification, the term "endothermic material" refers to a material that has the ability to absorb heat through physical changes, elimination of water of crystallization, phase transition, dissolution, or chemical reaction, and can be a material that exhibits an endothermic peak measured in the range of approximately 80°C to 400°C by thermal analysis using a differential scanning calorimeter (DSC) or other similar device. "Porous powder" refers to a powder particle-like material having multiple continuous or independent pores within the powder particles. "Hollow particles" refers to a material having a single, independent pore within the powder particles. Furthermore, "other inorganic powders" refer to materials that do not have the above characteristics (e.g., a thermal decomposition onset temperature of 350°C or less and an endothermic heat of 500 J / g or more) but can reinforce an inorganic network by sintering. Examples of hollow materials or porous powders include hollow silica, shirasu balloons, hollow calcium carbonate particles, and glass balloons.Examples of inorganic materials other than the hydrated metal compounds include elements selected from the group consisting of silicon, titanium, barium, zirconium, zinc, calcium, magnesium, cerium, aluminum, indium, tin, and lanthanum, single oxides of the elements or composite oxides of the elements, single sulfides of the elements or composite sulfides of the elements, and single phosphate compounds of the elements or composite phosphate compounds of the elements. Silicon, titanium, zirconium, magnesium, aluminum, indium, tin, and single or composite oxides thereof, other than the above-mentioned examples of hydrated metal compounds, are preferred. Specific examples of the inorganic material include clay, ceramics, vermiculite, bentonite, perovskite compounds (strontium titanate), mica, wollastonite, potassium titanate, calcium oxide, basic magnesium sulfate, sepiolite, xonotlite, perlite, zeolite, apatite, hydroxyapatite, kaolinite, montmorillonite, acid clay, diatomaceous earth, basalt, wet silica, dry silica, aerogel, mica, and vermiculite. The content of the inorganic powder in this embodiment is preferably 10 to 60% by mass, more preferably 20 to 50% by mass, and even more preferably 25 to 35% by mass, relative to the total amount (100% by mass) of the contents of the heat absorber.

[0086] (Additives) The heat absorber content or dispersion liquid (a) of this embodiment may contain various additives, such as ultraviolet absorbers, antioxidants, organic solvents, inorganic fillers other than the water-swellable clay minerals, viscosity modifiers such as thickeners, crosslinking agents, and flame retardants, as needed. Although the various additives are optional components, when used, they are preferably used in proportions that do not impair the effects of the present disclosure and that correspond to the purpose of each additive. While the proportions cannot be determined in general, the content of the various additives is preferably 0% by mass or more, and more preferably 10% by mass or more, relative to the total amount (mass) of the aqueous solvent and various additives used in the present disclosure. Furthermore, it is preferably 50% by mass or less, and more preferably 40% by mass or less.

[0087] Examples of the ultraviolet absorber include triazine derivatives such as 2-[4-{(2-hydroxy-3-dodecyloxypropyl)oxy}-2-hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine and 2-[4-{(2-hydroxy-3-tridecyloxypropyl)oxy}-2-hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine, 2-(2'-xanthenecarboxy-5'-methylphenyl)benzotriazole, 2-(2'-o-nitrobenzyloxy-5'-methylphenyl)benzotriazole, 2-xanthenecarboxy-4-dodecyloxybenzophenone, 2-o-nitrobenzyloxy-4-dodecyloxybenzophenone, etc. These ultraviolet absorbers can be used alone or in combination of two or more.

[0088] Examples of the antioxidant include "Sumilizer BBM-S" and "Sumilizer GA-80" manufactured by Sumitomo Chemical Co., Ltd. Examples of the organic solvent include aromatic hydrocarbons such as toluene and xylene; glycols such as ethylene glycol and propylene glycol; polyether glycols, which are polymers thereof; cellosolves; carbitols; and aliphatic alcohols such as methanol. The organic solvents can be used alone or in combination of two or more. Examples of the inorganic filler include fused silica, crystalline silica, alumina, silicon nitride, and aluminum hydroxide. Examples of the viscosity modifier such as the thickener include various tackifying resins such as rosin, polymerized rosin, polymerized rosin ester, rosin phenol, stabilized rosin ester, disproportionated rosin ester, terpene, terpene phenol, and petroleum resin. Examples of the crosslinking agent include known crosslinking agents such as isocyanate-based, epoxy-based, aziridine-based, polyvalent metal salt-based, metal chelate-based, ketohydrazide-based, oxazoline-based, carbodiimide-based, silane-based, and glycidyl (alkoxy) epoxy silane-based crosslinking agents.

[0089] Examples of the flame retardant include inorganic phosphorus compounds such as red phosphorus, ammonium phosphates such as monoammonium phosphate, diammonium phosphate, triammonium phosphate, and ammonium polyphosphate, and phosphoric acid amides; phosphoric acid ester compounds, phosphonic acid compounds, phosphinic acid compounds, phosphine oxide compounds, phosphorane compounds, organic nitrogen-containing phosphorus compounds, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, 10-(2,5-dihydroxyphenyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxy Examples of suitable flame retardants include organic phosphorus compounds such as cyclic organic phosphorus compounds such as 10-(2,7-dihydroxynaphthyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxide and derivatives thereof obtained by reacting them with compounds such as epoxy resins and phenolic resins; nitrogen-based flame retardants such as triazine compounds, cyanuric acid compounds, isocyanuric acid compounds, and phenothiazine; silicone-based flame retardants such as silicone oil, silicone rubber, and silicone resin; and inorganic flame retardants such as metal hydroxides, metal oxides, metal carbonate compounds, metal powders, boron compounds, and low-melting-point glass. These flame retardants can be used alone or in combination of two or more. When these flame retardants are used, their amount is preferably in the range of 0.1 to 20% by mass based on the entire contents of the heat endotherm or the entire dispersion liquid (a).

[0090] (Method for Manufacturing Heat Absorber) A preferred example of a method for manufacturing a heat absorber according to this embodiment includes the steps of filling a bag with an aqueous solvent and an inorganic mesh through an opening thereof, and sealing the opening of the bag to seal the bag. The aqueous solvent and the inorganic mesh may be filled separately through the opening of the bag. Alternatively, a mixed solution (1) may be prepared in advance by impregnating or dispersing the inorganic mesh in the aqueous solvent, and the mixed solution may then be filled through the opening of the bag. The mixed solution (1) contains an inorganic mesh and an aqueous solvent, and optionally contains one or more additives selected from the group consisting of antifreeze agents, inorganic powders, and additives. As described above, the inorganic powder is preferably one or more additives selected from the group consisting of heat absorption materials, porous powders, hollow particles, and other inorganic powders. The mixed solution (1) preferably contains 2 to 30% by mass of an inorganic mesh body, 10 to 98% by mass of an aqueous solvent, 0 to 50% by mass of an antifreeze agent, 0 to 60% by mass of an inorganic powder, and 0 to 10% by mass of an additive, relative to the total amount (100% by mass) of the mixed solution (1), and more preferably contains 3 to 12% by mass of an inorganic mesh body, 20 to 95% by mass of an aqueous solvent, 0 to 25% by mass of an antifreeze agent, 0 to 50% by mass of an inorganic powder, and 0 to 50% by mass of an additive. In one aspect of this embodiment, when the contents of the heat absorber contain a hydrogel, the method for producing the heat absorber, as described above, includes the steps of preparing dispersion (a) containing reaction raw materials (a water-soluble organic monomer and a water-swellable clay mineral), an aqueous solvent, and optionally blended polymerization initiator, catalyst, low-volatile solvent, and / or additives, filling dispersion (a) and an inorganic material mesh into a bag through an opening thereof, followed by sealing, and gelling the water-soluble organic monomer in the bag at a desired polymerization temperature. Instead of dispersion (a), dispersion (b) may be used, which is a mixture of dispersion (a) and optionally blended inorganic powder, antifreeze, and additives.In another aspect of this embodiment, when the contents of the heat absorber contain a hydrogel, another method for producing the heat absorber includes the steps of preparing a mixed solution (2) by mixing reaction raw materials (a water-soluble organic monomer and a water-swellable clay mineral), a polymerization initiator, an aqueous solvent or organic solvent, and an inorganic network, heating the mixed solution (2) to gel and prepare an organic-inorganic composite hydrogel body, impregnating the inorganic network and the organic-inorganic composite hydrogel body in the aqueous solvent for a desired time to swell the organic-inorganic composite hydrogel in the aqueous solvent, and filling the swollen organic-inorganic composite hydrogel and the inorganic network body into a bag through an opening and then sealing the bag. In this method for producing a heat absorber, the heat absorber can be formed by the above method even when the contents of the heat absorber contain an inorganic powder. The mixed solution (2) preferably contains 4 to 10% by mass of inorganic material mesh and 90 to 96% by mass of dispersion liquid (a) relative to the total amount (100% by mass) of the mixed solution (2).

[0091] A suitable heat absorber of this embodiment may be a heat absorber including a bag and, as the contents of the bag, an inorganic mesh body (e.g., 4 to 9% by mass of rock wool relative to the total amount of the contents), an aqueous solvent (e.g., 20 to 60% by mass of water relative to the total amount of the contents), a hydrogel body (e.g., 5 to 30% by mass of NC gel relative to the total amount of the contents), and an inorganic powder (e.g., 10 to 50% by mass of aluminum hydroxide relative to the total amount of the contents). This makes it possible to provide a heat absorber that has a superior heat absorption capacity and temperature rise suppression effect, and that can change from a heat absorption effect to a heat insulation effect in a high temperature range.

[0092] In this embodiment, the total content of the inorganic mesh body, aqueous solvent, hydrogel body, and inorganic powder as the contents of the bag is preferably 80 to 100% by mass, more preferably 92 to 99.5% by mass, and even more preferably 93 to 99% by mass, based on the total amount (100% by mass) of the contents of the bag. In this embodiment, the total content of the inorganic mesh body, aqueous solvent, hydrogel body, inorganic powder, antifreeze agent, and additives as the contents of the bag is preferably 83 to 100% by mass, more preferably 94 to 99.5% by mass, and even more preferably more than 95% by mass and 99% by mass or less, based on the total amount (100% by mass) of the contents of the bag. The upper and lower limits of the above total content can be adjusted as appropriate.

[0093] (Preferred Aspects of Heat Absorber) The heat absorber of this embodiment preferably exhibits high cushioning properties and / or excellent pressure resistance during heating. Each preferred aspect will be described in detail below. <High-Cushioning Heat Absorber> A preferred heat absorber of this embodiment exhibits high cushioning properties and includes a bag body and, as the contents of the bag, a hydrogel and an inorganic material mesh body. The hydrogel body includes a hydrogel body formed from three-dimensional polymer chains and an aqueous solvent. In this specification, a heat absorber exhibiting high cushioning properties is also referred to as a high-cushioning heat absorber. "Exhibiting high cushioning properties" refers to excellent cushioning properties, and when the contents of the bag contain hydrogel (hydrogel body and aqueous solvent), high cushioning properties tend to be exhibited. Furthermore, "exhibiting high cushioning properties" specifically refers to a cushioning property (%) expressed by the following formula (I): 80% or more, more preferably 90% or more, and even more preferably 93% or more. By exhibiting the above-mentioned cushioning property of 90% or more, it becomes easier to follow deformations that occur over a relatively short period of time, such as expansion and contraction due to charging and discharging of the battery cell. The upper limit of the high cushioning property can be 100%. [Equation 3] "Cushioning property (%) = h ａ / h ｂ × 100 Formula (I) (wherein, h ａis the height (mm) of the pressed part 5 minutes after the surface of the high-cushion heat absorber is pressed at 1 MPa for 60 seconds and then released, and h ｂ represents the height (mm) before the surface of the high-cushioning heat absorber is pressed at 1 MPa for 60 seconds. In the heat absorber of this embodiment, when cushioning is important, it is preferable that not only is the cushioning (%) represented by formula (I) 90% or more, but also that the content of the antifreeze agent be controlled to a predetermined value or less. That is, when cushioning is important, the content of the antifreeze agent is preferably 40% by mass or less, more preferably 30% by mass or less, even more preferably 20% by mass or less, even more preferably 12% by mass or less, even more preferably 9% by mass or less, even more preferably 6% by mass or less, and particularly preferably substantially absent (0.5% by mass or less) relative to the total amount of the contents. If the content of the antifreeze agent exceeds a predetermined amount relative to the total amount of the contents, the number of crosslinking points in the gel decreases, making the gel more flexible, and as a result, cushioning properties are thought to be reduced. On the other hand, under high-temperature heating conditions, the gel acts to smoothly flow the inorganic powder during the vaporization process, allowing the inorganic powder to be uniformly distributed within the inorganic material network, which is thought to result in increased strength. Furthermore, in the heat absorber of this embodiment, when cushioning is important, not only the content of the antifreeze agent but also the amount of hydrogel contained in the contents, preferably the total amount of the inorganic material mesh body, hydrogel (hydrogel main body and aqueous solvent), and optional inorganic powder, relative to the total amount of the contents, can be preferably more than 80% by mass, more preferably 83% by mass or more, even more preferably 87% by mass or more, still more preferably 91% by mass or more, even more preferably 94% by mass or more, still more preferably 98% by mass or more, and particularly preferably 100% by mass. It is thought that as the total amount of the inorganic material mesh body, hydrogel, and inorganic powder increases relative to the total amount of the contents, the inorganic material mesh body and inorganic powder reinforce the hydrogel, which has a high recovery rate after deformation, thereby exhibiting high cushioning properties.

[0094] <Particularly preferred form of heat absorber> A particularly preferred form of the heat absorber of this embodiment has a bag that can be filled with a content, and an inorganic material mesh body and an aqueous solvent that are filled into the bag as the content, and the cushioning property (%) is expressed by the following formula (I): [Number 4] "Cushioning property (%) = h ａ / h ｂ × 100 (in the above formula (I), h ａ is the height (mm) of the pressed part after 5 minutes have passed since the surface of the high-cushion heat absorber was pressed at 1 MPa for 60 seconds and then the pressing force was released, and h ｂ indicates the height (mm) before the surface of the high-cushioning heat absorber is pressed at 1 MPa for 60 seconds. The heat absorber has a cushioning property of 80% or more, as expressed by the formula (1). The heat absorber exhibits high cushioning properties. Furthermore, a combination of an inorganic mesh body with inorganic powder and / or hydrogel tends to exhibit high cushioning properties. High cushioning properties can absorb the expansion and contraction of the battery and facilitate placement between multiple battery elements, thereby better suppressing the spread of heat to adjacent battery elements in the event of an abnormality. This results in superior heat absorption and temperature rise suppression effects, as well as excellent cushioning properties, which facilitate a stable transition from a heat absorption effect to a heat insulating effect in high-temperature ranges.

[0095] <High-Pressure-Resistant Heat Endotherm> A preferred heat endotherm of this embodiment has excellent pressure resistance when heated, and is composed of a bag that can be filled with a content, an aqueous solvent, and an inorganic mesh body that are filled with the content. Herein, a heat endotherm that has excellent pressure resistance when heated is also referred to as a high-pressure-resistant heat endotherm. Such a high-pressure-resistant heat endotherm tends to exhibit excellent pressure resistance when heated to high temperatures (e.g., 800°C or higher) due to thermal runaway of a battery or the like. "Exhibiting pressure resistance when heated" refers to the heat endotherm exhibiting high pressure resistance when heated. When the bag further contains a hydrogel (hydrogel body and aqueous solvent), the pressure resistance is improved. Similarly, when the bag further contains an inorganic powder, the pressure resistance is improved. In particular, when the bag contains both a hydrogel (hydrogel body and aqueous solvent) and an inorganic powder, the pressure resistance tends to be particularly excellent when heated.

[0096] Therefore, a preferred embodiment of the high-pressure-resistant heat absorber of this embodiment may be a high-pressure-resistant heat absorber comprising a bag capable of being filled with contents, a hydrogel composed of hydrogel bodies and an aqueous solvent, and an inorganic mesh body, wherein the hydrogel and the inorganic mesh body form a composite and are filled into the contents. A more preferred embodiment of the high-pressure-resistant heat absorber of this embodiment may be a high-pressure-resistant heat absorber comprising a bag capable of being filled with contents, a hydrogel composed of hydrogel bodies and an aqueous solvent, an inorganic mesh body, and inorganic powder, wherein the hydrogel and the inorganic mesh body form a composite and are filled into the contents. In this case, it is preferable that the inorganic powder is uniformly dispersed in the contents. The coexistence of hydrogel and inorganic powder temporarily forms a foam film during thermal runaway, and it is believed that this foam film acts as a dispersion reinforcement. Furthermore, the coexistence of hydrogel and inorganic powder is thought to exhibit a synergistic effect of high pressure resistance because the hydrogel promotes the dispersibility of the inorganic powder. Note that the uniform dispersion may mean, for example, that when the composite content is removed, the difference in the concentration (% by mass) of the inorganic powder at both ends of the composite within approximately 3 mm from the end of the composite is within ±15%. Furthermore, "exhibiting high pressure resistance upon heating" specifically means that the thickness change rate (%) represented by the following formula (II) is preferably 70% or more, more preferably 75% or more, and even more preferably 85% or more. By exhibiting the above-mentioned thickness change rate of 70% or more, excellent pressure resistance can be achieved, thereby effectively suppressing and preventing inter-cell explosions. Note that the upper limit of the thickness change rate may be 100%. [Mathematical Expression 5] Equation (II): "Thickness change rate (%) = (thickness of high pressure resistant heat absorber after pressing the surface of the high pressure resistant heat absorber at 0.5 MPa for 60 seconds) / (thickness of high pressure resistant heat absorber before pressing the surface of the high pressure resistant heat absorber at 0.5 MPa for 60 seconds) × 100" When high pressure resistance is important, the heat absorber of this embodiment preferably contains an inorganic material mesh body, a hydrogel (hydrogel main body and aqueous solvent), and an inorganic powder.

[0097] [Secondary Battery Module] The type of secondary battery that can be equipped with the heat absorber of this embodiment is not particularly limited, and examples thereof include lithium ion batteries, lithium ion polymer batteries, lead storage batteries, nickel-metal hydride storage batteries, nickel-cadmium storage batteries, nickel-iron storage batteries, nickel-zinc storage batteries, silver oxide-zinc storage batteries, metal-air batteries, polyvalent cation batteries, condensers, and capacitors, etc. Among these, lithium ion batteries are preferred.

[0098] The secondary battery module capable of mounting the heat absorber of this embodiment is a secondary battery mounted on a mobile object such as a vehicle or an aircraft (particularly a drone), and includes a plurality of battery cells and a case for housing the plurality of battery cells. The battery cells (hereinafter also referred to as battery cells) constituting the secondary battery module can be battery cells in which, for example, a battery exterior film is used as an exterior material and battery elements including at least a positive electrode material layer, a negative electrode material layer, a separator, a positive electrode current collector, and a negative electrode current collector are enclosed within the exterior material.

[0099] A secondary battery module capable of mounting the heat absorber of this embodiment will be described below with reference to FIG. 1. FIG. 1 shows a cross-sectional view of a stacked battery 20 as an example of a secondary battery. Note that the secondary battery capable of mounting the heat absorber of this embodiment is not limited to the flat stacked battery 20 shown in FIG. 1. The secondary battery capable of mounting the heat absorber of this embodiment may be cylindrical, such as a wound secondary battery, or may be a cylindrical secondary battery modified to have a flat rectangular shape.

[0100] In this embodiment, the stacked battery 20 has a structure in which a flat, approximately rectangular battery element 10, in which charge and discharge reactions essentially proceed, is sealed inside battery exterior materials 18a, b. The battery element 10 has a structure in which a positive electrode, an electrolyte layer (or separator) 14, and a negative electrode are stacked. The positive electrode has a structure in which a positive electrode material layer 11 containing a positive electrode active material is disposed on both sides of a positive electrode current collector 12. The negative electrode has a structure in which a negative electrode material layer 16 containing a negative electrode active material is disposed on both sides of a negative electrode current collector 17. One positive electrode material layer 11 and the negative electrode material layer 16 adjacent to the positive electrode material layer 11 are arranged to face each other with the electrolyte layer 14 interposed therebetween, and the positive electrode, electrolyte layer 14, and negative electrode are stacked in sequence. As a result, adjacent positive electrodes, electrolyte layers 14, and negative electrodes form a single cell body. The stacked battery 20 shown in FIG. 1 has a structure in which a plurality of such cell bodies are stacked and electrically connected in parallel. In addition, an activated carbon layer 19 is provided to adsorb components derived from the positive electrode active material due to melting or sublimation of the positive electrode active material when the battery is exposed to high temperatures.

[0101] As shown in FIG. 1 , the positive electrode current collector 12 and the negative electrode current collector 17 are respectively attached with a positive electrode terminal 13 and a negative electrode terminal 15, which electrically connect the positive and negative electrodes, and are structured to be sandwiched between the ends of the battery exterior materials 18a and 18b and extend outside the battery exterior materials 18a and 18b. The positive electrode terminal 13 and the negative electrode terminal 15 may be attached to the positive electrode current collector 12 and the negative electrode current collector 17 of each electrode by welding or the like via a positive electrode lead and a negative electrode lead (not shown), as necessary. The battery exterior materials 18a and 18b are made of laminated film, and typically, sealant layers formed on the surfaces of the battery exterior films 18a and 18b are heat-sealed to each other. The battery exterior materials 18a and 18b have a region at their peripheries where the sealant layers are in close contact with each other by heat sealing.

[0102] Next, a secondary battery module incorporating the heat absorber of this embodiment will be described with reference to FIG. 2 . FIG. 2 is a perspective view schematically illustrating the disassembled state of the secondary battery module of FIG. 1 . The battery element 10 shown in FIG. 2 has a configuration in which a positive electrode formed on a positive electrode current collector 12 (e.g., aluminum foil) having a positive electrode terminal 13 and a negative electrode disposed on a negative electrode current collector 17 (e.g., metal foil) having a negative electrode terminal 15 are stacked so as to face each other with a separator 14 containing an electrolyte interposed therebetween. A plurality of battery elements 10 are stacked and sealed with battery exterior materials 18 a, b (e.g., aluminum laminate exteriors). The heat absorber 1 of this embodiment is arranged so as to contact the negative electrode current collector 17. The heat absorber 1 may be arranged so as to contact not only the negative electrode current collector 17 but also the positive electrode current collector 12. Therefore, a secondary battery module having a heat absorber 1 mounted on a battery element 10 has one or more laminates in which a positive electrode formed on a positive electrode current collector 12 (aluminum foil or the like) having a positive electrode terminal 13, a separator 14 containing an electrolyte, and a negative electrode disposed on a negative electrode current collector 17 (metal foil or the like) having a negative electrode terminal 15 are sequentially laminated, and the one or more heat absorbers 1 can be arranged so as to abut against the positive electrode current collector 12 and / or the negative electrode current collector 17 but not against the separator 14. When a solid electrolyte or a gel electrolyte is used as the electrolyte, it is also possible to use a configuration in which the electrolyte is interposed between the electrodes instead of the separator 14.

[0103] On the other hand, the aqueous solvent, which is the content of the heat absorber of this embodiment, does not come into direct contact with the battery element 10. Therefore, a suitable heat absorber for a secondary battery of this embodiment has an aqueous solvent or a hydrogel, a bag filled with the aqueous solvent, and an inorganic material mesh body, but the content of the bag does not include the hydrogel or aqueous solvent so as to bring the battery element 10 into direct contact with the battery element 10, and more preferably, the content of the bag of the heat absorber for a secondary battery does not include the battery element 10.

[0104] The secondary battery module of the present disclosure may include a heat absorber 1 of the present embodiment sandwiched between adjacent battery elements 10 (also referred to as battery cells) housed in multiple cases (not shown) or multiple battery exterior films 18a, b. The cases may be formed, for example, from aluminum, iron, or a metal material containing these, or a resin material such as polyphenylene sulfide. Forming the cases from a resin material contributes to reducing the weight of the secondary battery module. The heat absorber 1 may be sandwiched between the multiple battery elements 10 using, for example, adhesives, fusion (ultrasonic fusion, high-frequency fusion, or heat fusion), or pressure-sensitive adhesives. With this configuration, the heat absorber 1 sandwiched between the battery elements 10 absorbs heat generated during charging of the secondary battery, thereby suppressing a sudden temperature rise in the battery elements 10 and preventing deterioration, fire, and the like of the battery elements 10. Furthermore, when the heat absorber 1 contains a hydrogel that has absorbed an aqueous solvent, if the heat absorber 1 is sandwiched between the battery elements 10, the thermal insulation properties can suppress the temperature influence between the battery elements 10, and further, the cushioning properties of the swollen hydrogel act as a buffer for volume changes due to expansion of the battery elements 10, which is thought to make it easier to alleviate the rise in internal pressure of the secondary battery module.

[0105] The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to the examples given below.

[0106] (1) [Measurement of endothermic onset temperature, endothermic peak temperature, and endothermic amount] For the endotherms prepared in the present examples and comparative examples, the endothermic onset temperature and endothermic peak temperature were measured as follows. Using a differential scanning calorimeter (DSC; DSC-7020 manufactured by Hitachi High-Tech Corporation), the temperature was raised from 20 ° C. to 350 ° C. at a rate of 1 ° C. / min under a nitrogen atmosphere. The temperature at the intersection of a straight line extending the baseline on the low-temperature side of the DSC measurement curve to the high-temperature side and a tangent drawn at the point where the gradient of the curve on the low-temperature side of the endothermic peak associated with evaporation is maximum was taken as the endothermic onset temperature (° C.), and the point where the difference from the baseline of the DSC measurement curve is maximum was taken as the endothermic peak temperature (° C.). In addition, the integral value of the endothermic peak based on the baseline of the DSC measurement curve divided by the mass of the inorganic powder used in the measurement was taken as the endothermic amount (J / g or mJ / mg).

[0107] (2) Evaluation of cushioning properties The cushioning properties of the heat absorbers prepared in the present examples and comparative examples were evaluated using the following method. Specifically, at room temperature (23°C), the heat absorber was placed in a Tensilon universal testing machine ("RTE-1210" manufactured by Orientec Co., Ltd.) with a size of 100 mm length x 100 mm width x 4.8 mm height and equipped with a 7 mmφ indentation jig, and an indentation test was performed. The indentation test was performed by indenting the surface of the heat absorber at 1 MPa for 60 seconds, and then releasing the indentation and measuring the height (mm) h of the indented part on the surface 5 minutes later. ａ and the height (mm) h before pressing the surface of the heat absorber at 1 MPa for 60 seconds ｂ The cushioning property (also referred to as the degree of return) was observed and evaluated according to the following criteria using the following formula (I). The indentation test was performed at two points on the surface of the heat absorber, and the height (or thickness) was measured at each point. The cushioning property (%) was calculated using the following formula (I), and the average value is shown in Table 1. Formula (I): Cushioning property (%) = h ａ / h ｂ × 100 (Evaluation criteria for cushioning) "Returns to 90% or more of its original height" was marked as "◎". "Returns to 80% or more of its original height" was marked as "◯". "Returns to 70% or more of its original height" was marked as "△". "Returns to less than 70% of its original height" was marked as "X".

[0108] (2) [Evaluation of Freezing Resistance] The heat absorbers produced in the present examples and comparative examples were placed in a freezer at -20°C, and then their hardness was measured using a type E durometer in accordance with JIS K6253 (Durometer hardness of vulcanized rubber and thermoplastic rubber) to confirm the frozen state. The results were evaluated according to the following criteria. (Evaluation criteria for freezing resistance) A durometer hardness in the range of 0 to 80 was rated as "Good". A durometer hardness in the range of more than 80 to 100 was rated as "Fair". Note that when the durometer hardness was in the range of more than 80 to 100, it was confirmed by appearance that the material was frozen.

[0109] (3) [Heating Experiment Using a Cone Calorimeter] The heat absorbers prepared in the present example and comparative examples were directly heated by radiant heat using a cone calorimeter 30 (manufactured by Toyo Seiki Co., Ltd.) shown in Fig. 4 in accordance with JIS A 1316. More specifically, the cone calorimeter 30 is based on the principle that the amount of heat generated in combustion is 13.1 MJ per kg of oxygen, regardless of the type of organic material, and calculates the heat release rate, total heat release, etc., from the oxygen consumption method by measuring the oxygen concentration and exhaust gas flow rate in the combustion exhaust gas. The heat absorber 1 was placed at the top of the holder 32 as a test specimen, and a 50 kW / m radiator was used to measure the heat release rate and total heat release rate from the cone 31. ２ Then, the change in temperature until the temperature reached 160° C. was measured by the thermocouple 33 on the back surface of the heat absorber 1. In addition to the temperature change, the presence or absence of combustion was also observed.

[0110] (4) Evaluation of Pressure Resistance of Test Specimens After Heating Experiments After conducting heating experiments using the cone calorimeter described above, the heat absorbers prepared in the present examples and comparative examples were evaluated for pressure resistance using the following method. Specifically, an indentation test was performed by placing the heat absorbers at room temperature (23°C) in a Tensilon universal testing machine ("RTE-1210" manufactured by Orientec Co., Ltd.) equipped with a 7 mmφ indentation jig. The indentation test measured the indentation amount when indented at 0.5 MPa for 60 seconds (= when pressurized). From the indentation amount, the thickness change rate when pressurized was calculated according to the following formula (II) and evaluated according to the following criteria. Note that the indentation test was performed at two locations on the surface of the heat absorber after heating using the cone calorimeter described above. The height (or thickness) was measured at each location, and the thickness change rate was calculated using the following formula (II). The average values ​​are shown in Table 1. Equation (II): Thickness change rate (%) = (thickness of the heat absorber after pressing the surface of the heat absorber after heating at 0.5 MPa for 60 seconds) / (thickness of the heat absorber before pressing the surface of the heat absorber after heating at 0.5 MPa for 60 seconds) × 100 (Evaluation criteria for thickness change rate) A thickness change rate in the range of 70 to 100% was rated as "◎". A thickness change rate in the range of 40 to 69% was rated as "◯". A thickness change rate in the range of 0 to 39% was rated as "△". Note that a thickness change rate in the range of 70 to 100% has the best pressure resistance. A lower value of the pressing amount (= crushed amount) indicates better pressure resistance.

[0111] (5) Measurement Method of Average Porosity, True Density, and Bulk Density The average porosity of the inorganic mesh body was calculated using the following formula (1) from the bulk density ρf and true density ρr measured by the following method: Average Porosity (%) = ((1 / ρf) - (1 / ρr)) / (1 / ρf) × 100 Formula (1) <Measurement of True Density> The inorganic mesh body removed from the heat absorber or the inorganic mesh body before being sealed in a bag was thoroughly washed with distilled water and dried overnight. The dried inorganic mesh body was then placed in a stoppered test tube, and a mixed solvent of three solvents was added to the stoppered test tube and immersed in a constant temperature bath at 30°C. If the inorganic mesh body floats, n-heptane, which has a low density, was added. On the other hand, if the inorganic mesh body sinks, ethylene dibromide, which has a high density, was added. This operation was repeated until the inorganic mesh body was floating in the liquid, and the density of the mixed solvent was measured using a Gay-Lussac pycnometer. <Measurement of bulk density> The inorganic mesh body removed from the contents of the heat absorber or the inorganic mesh body before being sealed in a bag was thoroughly washed with distilled water and dried overnight, and then the dimensions of the dried inorganic mesh body were measured to calculate the bulk volume V of the inorganic mesh body. Thereafter, the mass M of the inorganic mesh body was measured using a precision balance. From the obtained mass M and bulk volume V, the bulk density of the inorganic mesh body was calculated using the following formula (2). Bulk density ρf (g / cm ３ )=M / V...Formula (2)

[0112] <Inorganic Powders> The inorganic powders used in the Examples and Comparative Examples are as follows: Aluminum hydroxide: (product name "Aluminum Hydroxide Grade 1", manufactured by Kanto Chemical Co., Ltd.) Calcium sulfate dihydrate: (product name "Calcium sulfate dihydrate Special Grade", manufactured by Kanto Chemical Co., Ltd.) Sodium bicarbonate: (product name "Sodium bicarbonate Special Grade", manufactured by Kanto Chemical Co., Ltd.)

[0113] <Bag> The water vapor permeability ([g / (m ２ ・24h)]) is 50g / (m ２ - We confirmed that the time is less than 24 hours.

[0114] (2) Examples and Comparative Examples (Example 1) 10 parts by mass of ceramic wool (average porosity 97%, true density 3, bulk density 0.092) was inserted into a container containing an aluminum pouch ("Gas Barrier Bag" manufactured by Mitsubishi Gas Chemical Company, Inc., 0.094 mm thick, laminated with PET, aluminum foil, and polyethylene) in a bag shape measuring 116 mm long x 116 mm wide. Next, 100 parts by mass of pure water was poured into the aluminum pouch to fill the bag shape, and the inlet was closed by heat sealing. The aluminum pouch bag was then placed flat between 4.8 mm thick gap materials, and a flat plate was placed on top of it and allowed to stand at 20 ° C. for 10 minutes to produce a 4.8 mm thick sheet-like heat absorber (I). The obtained heat absorber (I) was then evaluated according to the procedures described in the evaluation section above. The results are shown in Table 1 and FIG. 3. In the system of Example 1, data on the endothermic heat (J / g or mJ / mg) could not be obtained because DSC could not be measured for a liquid. Therefore, the literature value of 2257 J / g was approximated to 2000 J / g and entered in the table.

[0115] Example 2 20 parts by mass of N,N-dimethylacrylamide (hereinafter abbreviated as "DMAA"), 4.8 parts by mass of water-swellable synthetic hectorite (manufactured by BYK Japan K.K., "Laponite RD"), 0.5 parts by mass of sodium peroxodisulfate (hereinafter abbreviated as "NPS"), and 0.8 parts by mass of N,N,N',N'-tetramethylethylenediamine (hereinafter abbreviated as "TEMED") were mixed and stirred in 100 parts by mass of pure water to obtain a uniform dispersion (a-1). First, 6 parts by mass of ceramic wool (average porosity 98%, true density 3, bulk density 0.049) were inserted into a container prepared by forming an aluminum pouch (manufactured by Mitsubishi Gas Chemical Company, Inc., "Gas Barrier Bag" thickness 0.094 mm, composed of a laminate of PET, aluminum foil, and polyethylene) into a bag-like container measuring 116 mm long x 116 mm wide. Next, 100 parts by mass of the dispersion liquid (a-1) was injected into the aluminum pouch bag to fill it, and the injection port was closed by heat sealing. The aluminum pouch bag was then placed flat between 4.8 mm thick gap materials, a flat plate was placed on top of it, and the mixture was left to stand at 20 ° C for 15 hours to produce a 4.8 mm thick sheet-like heat absorber (H). The obtained heat absorber (H) was then evaluated according to the procedures described in the evaluation section above. The results are shown in Table 1 and FIG. 3. Furthermore, the endothermic peak temperature and endothermic amount of the heat absorber (H) of Example 2 were evaluated under the above DSC measurement conditions. Note that although the ceramic wool in Example 2 and the ceramic wool in Example 8 described below use the same type of material, the amount of aqueous solvent was changed to maintain a constant aluminum pouch thickness, resulting in a slight difference in the average porosity between the two.

[0116] Example 3: 14 parts by mass of ceramic wool (average porosity 97%, true density 3, bulk density 0.094) was inserted into a container prepared by forming an aluminum pouch similar to that used in Example 1 into a bag-shaped container measuring 116 mm long x 116 mm wide. Next, a dispersion (a-2) prepared by mixing 43 parts by mass of aluminum hydroxide with 100 parts by mass of pure water was poured into the bag-shaped aluminum pouch to fill it, and the inlet was closed by heat sealing. The aluminum pouch bag was then placed flat between 4.8 mm thick gap materials, and a flat plate was placed on top of it and allowed to stand at 20 ° C for 10 minutes to produce a 4.8 mm thick sheet-shaped heat absorber (J). The obtained heat absorber (J) was then evaluated according to the procedures described in the evaluation section above. The results are shown in Table 1 and FIG. 3. Note that in the system of Example 3, since DSC of the liquid could not be measured, data on the endothermic capacity (J / g or mJ / mg) could not be obtained. Therefore, the calculated value of 1650 J / g is entered in the table.

[0117] Example 4 A dispersion (a-3) was prepared by mixing 43 parts by mass of calcium sulfate dihydrate instead of the "43 parts by mass of aluminum hydroxide" in the dispersion (a-2) of Example 3. A sheet-like heat endogenous material (K) having a thickness of 4.8 mm was produced in the same manner as in Example 3, except that the dispersion (a-3) was injected instead of the dispersion (a-2) of Example 3. The obtained heat endogenous material (K) was then subjected to various evaluations according to the procedures described in the evaluation column above. The results are shown in Table 1 and FIG. 3. Note that, in the system of Example 4, DSC of the liquid could not be measured, and therefore data on the endothermic capacity (J / g or mJ / mg) could not be obtained. Therefore, the calculated value of 1628 J / g is entered in the table.

[0118] (Example 5) Dispersion (a-4) was prepared by mixing 100 parts by mass of the dispersion (a-1) described in Example 2 with 100 parts by mass of aluminum hydroxide. 8 parts by mass of ceramic wool (average porosity 98%, true density 3, bulk density 0.049) was inserted into a container in the form of a bag made of an aluminum pouch (Mitsubishi Gas Chemical Company, Inc. "Gas Barrier Bag" thickness 0.094 mm, laminated with PET, aluminum foil and polyethylene) measuring 116 mm in length and 116 mm in width. Next, 200 parts by mass of the dispersion (a-4) was poured into the bag of the aluminum pouch to fill it, and the injection port was closed by heat sealing. The aluminum pouch bag was placed flat between 4.8 mm thick gap materials, and a flat plate was placed on top of it and left to stand at 20 ° C. for 15 hours to produce a 4.8 mm thick sheet-shaped heat absorber (L). The obtained heat absorber (L) was then subjected to various evaluations according to the procedures described in the above evaluation section. The results are shown in Table 1 and FIG.

[0119] (Example 6) Dispersion (a-5) was prepared by mixing 43 parts by mass of sodium acetate with 100 parts by mass of the dispersion (a-1) described in Example 2. 7 parts by mass of ceramic wool (average porosity 98%, true density 3, bulk density 0.049) was inserted into a container in the form of a bag made of an aluminum pouch (Mitsubishi Gas Chemical Company, Inc. "Gas Barrier Bag" thickness 0.094 mm, laminated with PET, aluminum foil, and polyethylene) measuring 116 mm in length and 116 mm in width. Next, 143 parts by mass of the dispersion (a-5) was injected into the bag of the aluminum pouch to fill it, and the injection port was closed by heat sealing. The aluminum pouch bag was placed flat between 4.8 mm thick gap materials, and a flat plate was placed on top of it and left to stand at 20 ° C. for 15 hours to produce a 4.8 mm thick sheet-shaped heat absorber (E). The obtained endothermic material (E) was evaluated according to the procedures described in the above evaluation section, and the results are shown in Table 1 and FIG.

[0120] Example 7 39 parts by mass of glycerin, 20 parts by mass of N,N-dimethylacrylamide (hereinafter abbreviated as "DMAA"), 4.8 parts by mass of water-swellable synthetic hectorite (manufactured by BYK Japan K.K., "Laponite RD"), 0.5 parts by mass of sodium peroxodisulfate (hereinafter abbreviated as "NPS"), and 0.8 parts by mass of N,N,N',N'-tetramethylethylenediamine (hereinafter abbreviated as "TEMED") were mixed and stirred in 60 parts by mass of pure water to obtain a uniform dispersion (a-6). 43 parts by mass of aluminum hydroxide was further mixed with 100 parts by mass of the dispersion (a-6) to obtain a dispersion (a-7). Ceramic wool (average porosity 98.4%, true density 3, bulk density 0.047) 7 parts by mass was made into a bag-shaped body of 116 mm length x 116 mm width, and inserted into an aluminum pouch container similar to that of Example 1. Next, 143 parts by mass of the dispersion (a-7) was poured and filled, and the inlet was closed by heat sealing. The aluminum pouch bag-shaped body was then placed flat between gap materials of 4.8 mm thickness, and a flat plate was placed on top and allowed to stand at 20 ° C. for 15 hours to produce a sheet-like heat absorber (F) of 4.8 mm thickness. Then, the obtained heat absorber (F) was subjected to various evaluations according to the procedures described in the evaluation column above. The results are shown in Table 1 and FIG. 3.

[0121] (Example 8) A sheet-like heat absorber (G) having a thickness of 4.8 mm was produced in the same manner as in Example 7, except that 7 parts by mass of rock wool (average porosity 98.4%, true density 3, bulk density 0.046) was inserted instead of the ceramic wool used in Example 7. The obtained heat absorber (G) was then subjected to various evaluations according to the procedures described in the evaluation section above. The results are shown in Table 1 and FIG. 3.

[0122] Comparative Example 1: In Comparative Example 1, a commercially available material, "Xiaomei silica aerogel mat material, thickness 4.8 mm (measured), thermal conductivity: 0.012 to 0.018 W / m·K," was used as the comparative sheet (A). The silica aerogel mat material of Comparative Example 1 had a nominal thickness of 3 mm. The obtained comparative sheet (A) was then subjected to various evaluations according to the procedures described in the evaluation section above. The results are shown in Table 1 and FIG. 3. Because the material of Comparative Example 1, "Xiaomei silica aerogel mat material," does not substantially have heat absorption, the "Heat absorption onset temperature (°C), endothermic peak temperature (°C), and endothermic amount (J / g or mJ / mg)" columns in the table are marked "substantially no heat absorption." Furthermore, although the bulk density of the material used in Comparative Example 1 could be measured, the true density could not be measured. Therefore, the true density and average porosity columns in the table are marked "not measurable."

[0123] Comparative Example 2: 100 parts by mass of resin 1 ("Boncoat 5400EF" (product name, water-dispersible acrylic resin emulsion, nonvolatile content 50%, manufactured by DIC Corporation)), 6 parts by mass of foam stabilizer 1 ("DICNAL M-40" (product name, sulfonic acid-type anionic surfactant, manufactured by DIC Corporation)), and 3 parts by mass of crosslinker 1 ("DICNAL GX" (product name, oxazoline group-containing polymer, manufactured by DIC Corporation)) were blended and stirred and mixed in a disper (2000 rpm, 3 minutes) to prepare a mechanical foaming binder. The prepared binder was stirred and foamed to double the foaming ratio, and 174 parts by mass of calcium sulfate dihydrate was blended thereto as an inorganic powder. Stirring was continued for an additional 5 minutes to obtain a foamable mixture. The resulting foamable mixture was applied to a polyethylene terephthalate (PET) film using an applicator. The sheet was then pre-dried at 105°C for 5 minutes, then heated at 120°C for 3 minutes, and then turned over and further heat-treated at 120°C for 3 minutes to harden it, producing a comparative sheet (B) (=resin foam sheet) with a thickness of 4.8 mm. All of the comparative sheets (B) to (D) of Comparative Examples 2 to 4 were found to have burned in the combustion evaluation in the heating experiment using the cone calorimeter, and therefore were found to be ineffective as a heat insulating material.

[0124] Comparative Example 3 A comparative sheet (C) (=resin foam sheet) having a thickness of 4.8 mm was produced in the same manner as in Comparative Example 3, except that 525 parts by mass of sodium bicarbonate was blended instead of calcium sulfate dihydrate, which was the endothermic material in Comparative Example 2. The obtained comparative sheets (B) and (C) were then evaluated according to the procedures described in the evaluation section above. The results are shown in Table 1 and FIG. 3.

[0125] (Comparative Example 4) 100 parts by mass of the dispersion (a-1) was poured into a bag-shaped container made of an aluminum pouch similar to that used in Example 1, measuring 116 mm long and 116 mm wide, and the inlet was closed by heat sealing. The aluminum pouch was then placed flat between gap materials 4.8 mm thick, and a flat plate was placed on top of it. The mixture was then left to stand at 20 ° C. for 15 hours to produce a 4.8 mm thick sheet for comparison (D). Note that the contents of Comparative Example 4 did not contain an inorganic material mesh, and the contents were essentially only the gel body and the aqueous solvent. Therefore, the true density, bulk density, and average porosity of the inorganic material mesh were not measured, and the corresponding items in the table were marked with "-".

[0126]

[0127] From the above experimental results, it was confirmed that the heat absorber of this embodiment, because the filled contents and the pouch as a whole act as a porous body, has a sufficient heat absorption effect, flame retardancy, and changes from a heat absorber to a heat insulator even when the battery temperature rises or over time. Note that the values ​​of the content contents in Table 1 are rounded to the nearest whole number.

[0128] [Explanation of symbols] 1 heat absorber 10 battery element 11 positive electrode material layer 12 positive electrode current collector 13 positive electrode terminal 14 electrolyte layer or separator 15 negative electrode terminal 16 negative electrode material layer 17 negative electrode current collector 18a, b battery exterior material 19 activated carbon layer 20 stacked battery 30 cone calorimeter 31 cone (heater) 32 stainless steel holder 33 aluminum foil cover 34 thermocouple 35 stainless steel holder 36 ceramic wool (large) 37 ceramic wool (small)

[0129] This application claims the benefit of priority to three applications: a Japanese patent application filed on July 3, 2023 (Patent Application No. 2023-109644), a Japanese patent application filed on December 25, 2023 (Patent Application No. 2023-218613), and a Japanese patent application filed on December 25, 2023 (Patent Application No. 2023-218614), the contents of which are incorporated herein by reference.

Claims

1. A bag body capable of being filled with a content, The content includes an inorganic powder, a mesh body made of an inorganic material, and an aqueous solvent filled in the bag body, and An endothermic body in which the average porosity of the mesh body made of an inorganic material in the endothermic body represented by the following formula (1) is 30 to 99.5%. Average porosity of the mesh body made of inorganic material (%) = ((1 / ρf) - (1 / ρr)) / (1 / ρf) × 100... Formula (1) (In the above formula (1), ρf represents the bulk density, and ρr represents the true density.)

2. The endothermic body according to claim 1, wherein the content includes a hydrogel composed of a hydrogel main body and the aqueous solvent, and the mesh body made of an inorganic material.

3. The endothermic body according to claim 1 or 2, further containing an antifreeze as the content.

4. The water vapor permeability of the sheet forming the bag body ([g / (m ２ ·24 h)]) is 50 g / (m ２ ·24 h) or less. The heat absorber according to claim 1 or 2.

5. A bag body, A high-cushioning endothermic body having high cushioning properties, including an inorganic powder, a hydrogel, and a mesh body made of an inorganic material included as the content of the bag body, and The high-cushioning endothermic body, wherein the hydrogel main body has a hydrogel main body formed from a three-dimensional polymer chain and an aqueous solvent.

6. The following formula (I): 【Number 1】 The high-cushioning endothermic body according to claim 5, having a cushioning property of 80% or more represented by.

7. A bag body capable of being filled with a content, A high-pressure-resistant endothermic body excellent in pressure resistance during heating, in which an aqueous solvent, an inorganic powder, and a mesh body made of an inorganic material are filled in the content.

8. The high-pressure-resistant endothermic body according to claim 7, wherein a hydrogel composed of a hydrogel main body and the aqueous solvent and the mesh body made of an inorganic material are filled in the content as a composite.

9. The following formula (I): 【Number 2】 The high-pressure-resistant endothermic body according to claim 7 or 8, having a thickness change rate of 70% or more represented by.

10. A secondary battery module including the endothermic body according to claim 1 or 2.

11. A secondary battery module including the high-cushioning endothermic body according to claim 5 or the high-pressure-resistant endothermic body according to claim 7.

12. A secondary battery module in which the endothermic body according to claim 1 or 2 is sandwiched between battery cells.

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