A heat absorber and a secondary battery module equipped with the heat absorber.

Abstract

The purpose of the present disclosure is to provide: a heat-absorbing body that has exceptional pressure resistance, heat absorption, and temperature-increase-suppressing effects, and that can change from having a heat absorption effect to having a heat insulation effect in a high temperature region; and a secondary battery module comprising said heat-absorbing body.　The present disclosure is a heat-absorbing body having: a bag body that can be filled with contents; and a hydrogel and an inorganic powder that are filled into the bag body as the contents.

Description

[Technical Field]

[0001] This disclosure relates to a heat absorber and a secondary battery module equipped with the heat absorber. [Background technology]

[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 as they are necessary for expanding the introduction of renewable energy from the perspective of building a low-carbon society or energy security. However, rechargeable batteries, such as lithium-ion batteries, are susceptible to thermal runaway and subsequent battery damage if their temperature rises due to heat generated during high-speed charging or high-power discharge. Furthermore, as ultra-high-speed charging advances, the amount of heat generated is expected to increase even further, necessitating the development of methods to suppress temperature rise and enhance battery safety. In addition, rechargeable batteries can also experience thermal runaway due to internal short circuits and other causes, leading to malfunctions such as fire or smoke emission. Therefore, in order to minimize the damage caused by such malfunctions, there is a need for technologies that can suppress, prevent, or delay chain explosions by extinguishing the heat of a battery that has become abnormally hot through heat absorption, or by suppressing heat transfer to other battery cells (hereinafter sometimes referred to as battery cells or simply cells) through heat absorption and heat insulation.

[0003] For example, Patent Documents 1 and 2 are cited as technologies that excel in heat insulation and fire spread prevention. Patent Document 1 describes a fire spread prevention material made of a laminate comprising layer A containing sodium silicate with an SiO2 / Na2O molar ratio of less than 3.1 and layer B containing precipitated silica. According to Patent Document 1, since this fire spread prevention material is used in a battery pack having two or more cells, heat transfer between cells is suppressed under normal conditions, and the spread of heat to adjacent cells is suppressed in abnormal conditions. In addition, Patent Document 2 describes a heat insulation sheet for a laminated battery having a heat insulation layer made of at least inorganic fibers or inorganic powder, and heat absorption layers formed on both surfaces of the heat insulation layer and made of at least inorganic hydrates. According to Patent Document 2, when the inorganic hydrates in the outer heat absorption layer are heated by the heat generated in the battery cell, the inorganic hydrates exhibit a heat absorption effect of absorbing heat and releasing moisture, so that the heat generation amount of the battery cell can be effectively reduced.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the technology of Patent Document 1 above, since the water contained in layer A (for example, water molecules in sodium silicate) undergoes an endothermic reaction in the temperature range of 100 to 300 °C, the water content is limited and a sufficient endothermic effect cannot be obtained. Further, in the technology of Patent Document 2 above, since a heat absorption layer made of inorganic hydrates is used, the heat absorption amount is about 1000 J / g or less, and the content of inorganic hydrates is limited due to restrictions on the thickness or flexibility of the sheet, and a sufficient endothermic effect cannot be obtained. Furthermore, in the technologies of Patent Documents 1 and 2 above, since a laminate having two or more layers is used, in order to achieve a sufficient heat absorption amount and heat insulation effect, it is necessary to increase the thickness of the laminate. In addition, when the battery temperature rises and the melt-down of the separator begins, the battery cell expands, so cushioning properties or mechanical strength of the expanded battery cell is required. However, in the technologies of Patent Documents 1 and 2 above, mechanical properties such as shock absorption of the laminate have not been studied. Therefore, an object of the present disclosure is to provide a heat absorber that is excellent in pressure resistance, heat absorption amount, and temperature rise suppression effect, and can change from a heat absorption effect to a heat insulation effect in a high temperature range, and a secondary battery module including the heat absorber. **Means for Solving the Problems**

[0006] The inventors of the present invention have found that a heat absorber containing a hydrogel and inorganic powder in a bag is excellent in cushioning property, heat absorption amount, and temperature rise suppression effect, and can change from a heat absorption effect to a heat insulation effect in a high temperature range, and have completed the following present invention.

[0007] [1] The present disclosure is a heat absorber having a bag body capable of filling contents, and a hydrogel and inorganic powder filled in the bag body as the contents.

[0008] [2] The heat absorber according to [1] above, wherein the hydrogel is composed of a hydrogel main body and an aqueous solvent.

[0009] [3] The heat absorber according to [1] or [2] above, further containing an antifreeze as the content.

[0010] [4] The water vapor permeability ([g / (m 2 ·24h)]) of the sheet constituting the bag body is 50 g / (m 2 ·24h) or less, and the heat absorber according to any one of [1] to [3] above.

[0011] [5] The heat absorber according to [2] above, wherein the hydrogel main body uses at least a water-soluble organic monomer and a water-swellable clay mineral as reaction raw materials.

[0012] [6] A heat absorber having high cushioning property, including a bag body, a hydrogel composed of a hydrogel main body formed from a three-dimensional polymer chain and an aqueous solvent included as the content of the bag body, and inorganic powder.

[0013] [7] The following formula (I): [Equation 1] "Cushioning property (%) = h a / h b ×100 (In the above formula (I), h a This is the height (mm) of the pressed area after 5 minutes have elapsed since pressing the surface of the heat absorber at 1 MPa for 60 seconds. b This represents the height (mm) of the heat absorber surface before it is pressed down at 1 MPa for 60 seconds. A heat absorber according to any of [1] to [6], wherein the cushioning effect represented by is 90% or more.

[0014] [8] A heat-absorbing element according to any one of [1] to [7], wherein the contents are filled into a bag, the aqueous solvent and the hydrogel are filled into the contents, and the bag has excellent pressure resistance when heated.

[0015] [9] The heat-absorbing material according to any one of [1] to [8], wherein the hydrogel and the inorganic powder are filled into the contents as a composite.

[0016]

[10] Formula (II) below: [Math 2] "Percentage change in thickness (%) = (Thickness of the heat absorber after applying pressure at 0.5 MPa for 60 seconds to the surface of the heat absorber heated under the following heating conditions) / (Thickness of the heat absorber before applying pressure at 0.5 MPa for 60 seconds to the surface of the heat absorber heated under the following heating conditions) × 100" Heating conditions: "50 kW / m² due to radiant heat" 2 After heating the heat-absorbing body with the heat energy required until the temperature of the side opposite to the heating surface (back surface) reached a predetermined temperature, the heat-absorbing body was allowed to dissipate heat at room temperature and naturally cool until the surface temperature of the heat-absorbing body reached room temperature, and the percentage change in thickness before and after heating was calculated. Furthermore, pressure was applied to the heating surface of the heat-absorbing element by pressing it down at 0.5 MPa for 60 seconds. A heat absorber according to any of [1] to [9], wherein the thickness change rate (%) expressed as is 70% or more.

[0017]

[11] The endothermic onset temperature is 400°C or lower, and the endothermic peak temperature is in the range of at least 80°C to 400°C, and the following equation (II): [Math 3] "Percentage change in thickness (%) = (Thickness of the heat absorber after applying pressure at 0.5 MPa for 60 seconds to the surface of the heat absorber heated under the following heating conditions) / (Thickness of the heat absorber before applying pressure at 0.5 MPa for 60 seconds to the surface of the heat absorber heated under the following heating conditions) × 100" Heating conditions: "50 kW / m² due to radiant heat" 2 After heating the heat-absorbing body with the heat energy required until the temperature of the side opposite to the heating surface (back surface) reached a predetermined temperature, the heat-absorbing body was allowed to dissipate heat at room temperature and naturally cool until the surface temperature of the heat-absorbing body reached room temperature, and the percentage change in thickness before and after heating was calculated. Furthermore, pressure was applied to the heating surface of the heat-absorbing element by pressing it down at 0.5 MPa for 60 seconds. A heat-absorbing material whose thickness change rate (%), expressed as , is 70% or more.

[0018] A secondary battery module equipped with a heat absorber as described in any of

[12] [1] to

[11] .

[0019] A secondary battery module in which a heat-absorbing material described in any of

[13] [1] to

[11] is sandwiched between battery cells.

[0020] One of the heat-absorbing materials

[14] [8] to

[10] is a high-pressure heat-absorbing material. [Effects of the Invention]

[0021] The heat-absorbing material of this disclosure exhibits excellent pressure resistance, heat absorption capacity, and temperature rise suppression effect, and can change from a heat-absorbing effect to a heat-insulating effect in the high-temperature range. According to this disclosure, a highly safe secondary battery module can be provided by equipping a heat-absorbing element that is excellent in pressure resistance, heat absorption capacity, and temperature rise suppression effect, and that can change from an endothermic effect to an insulating effect in the high-temperature range. [Brief explanation of the drawing]

[0022] [Figure 1] Figure 1 shows an example of a secondary battery module on which the heat-absorbing element of this embodiment can be mounted. [Figure 2] Figure 2 is a schematic perspective view showing the disassembled secondary battery module from Figure 1. [Figure 3] Figure 3 shows a schematic diagram of the cone calorimeter test apparatus used in the examples and comparative examples. [Figure 4] Figure 4 shows a photograph of the heat absorber of Example 1 after the cone calorimeter test. Figure 4(a) shows a photograph of the heat absorber of Example 1 after the cone calorimeter test (top), Figure 4(b) shows a photograph of the heat absorber of Example 1 after the cone calorimeter test (perspective view), and Figure 4(c) shows a magnified photograph of (b) above. [Figure 5] This graph shows the results of a cone calorimeter test (test conditions: radiant intensity 50 kW / m2, heating time 20 minutes) for the heat-absorbing material of the example and the sheet of the comparative example, with the vertical axis representing temperature and the horizontal axis representing elapsed time. [Modes for carrying out the invention]

[0023] The embodiments of the present invention (hereinafter referred to as "these embodiments") will be described in detail below, but this disclosure is not limited to the following description and can be implemented in various ways within the scope of its gist. [Definition] In this specification, "reaction material" refers to a compound used to obtain a target compound through a chemical reaction such as combination or decomposition, and which partially constitutes the chemical structure of the target compound. Substances that act as aids to chemical reactions, such as solvents, catalysts, and polymerization initiators, are excluded. In this specification, "structural unit" refers to a (repeating) unit of chemical structure formed during a reaction or polymerization. In other words, in a compound formed by a reaction or polymerization, it refers to a substructure other than the chemical bond structure involved in the reaction or polymerization, and is commonly known as a residue. In this specification, "hydrogel" refers to a three-dimensional network of polymers containing an aqueous solvent such as water, and examples include jelly, diaper absorbent material, konjac, and agar. The three-dimensional network of polymers that forms the backbone of the hydrogel is called the hydrogel body, and the aqueous solvent is contained within the hydrogel body. Therefore, a hydrogel consists of a hydrogel body and an aqueous solvent.

[0024] [Heat absorber] The heat-absorbing element of this disclosure comprises a bag into which contents can be filled, a hydrogel, and an inorganic powder. The hydrogel and the inorganic powder are filled into the bag as contents. The hydrogel contains a hydrogel body and an aqueous solvent. This results in excellent cushioning, heat absorption, and temperature rise suppression effects, and the effect can change from heat absorption to heat insulation in high-temperature ranges. The hydrogel itself within the endothermic material exhibits a swollen state at room temperature (around 20°C to 27°C), containing the hydrogel body, which is composed of a three-dimensional network polymer that forms the matrix of the hydrogel, and the aqueous solvent incorporated into the hydrogel body. Therefore, because it absorbs heat as the sensible heat of the aqueous solvent, the temperature can be stabilized even at room temperature. The endothermic material has excellent cushioning and shock absorption properties. When heat is applied from the outside to this state, an endothermic effect is produced due to the latent heat of vaporization of the aqueous solvent incorporated into the hydrogel. Furthermore, if the inorganic powder contained within the endothermic material has an endothermic effect, a higher endothermic effect (for example, an endothermic effect in different temperature ranges) can be produced by the latent heat of vaporization of the aqueous solvent and the inorganic powder. Next, when the endothermic material is exposed to high heat due to combustion or the like, the so-called gel water within the hydrogel evaporates, and the contents of the bag form an inorganic foam, exhibiting heat insulation and fire prevention effects. More specifically, the entire heat-absorbing material can become porous due to voids within the hydrogel created by bubbles incorporated into the hydrogel or by the evaporation of the aqueous solvent. As a result, it is thought to exhibit heat insulation and fire-resistant effects. Furthermore, when the heat-absorbing material reaches higher temperatures, an inorganic porous body can be formed by the sintering of inorganic powder. Therefore, this inorganic porous body can exhibit fire resistance and heat insulation effects as an inorganic heat-insulating material.

[0025] In other words, the heat absorber of this disclosure functions primarily as a heat absorber with excellent cushioning and shock absorption properties at relatively low temperatures (e.g., above room temperature to around 100°C). On the other hand, in the range from around 100°C to near the critical temperature (e.g., 150°C), the entire heat absorber becomes porous due to the evaporation of the gel water, so the hydrogel body, which is the substantial contents, can impart heat insulation, cushioning, and shock resistance to the heat absorber. Furthermore, in the temperature range from the critical temperature (e.g., 150°C) to the runaway temperature (e.g., around 1000°C), the entire heat absorber becomes porous due to the evaporation of the gel water, so it also acts as a heat insulator. In addition, the inorganic powder inside can be sintered using the porous body as a scaffold to form an inorganic porous body in which the inorganic powder is sintered, so the overall strength (compression resistance and fire resistance) of the heat absorber is thought to be further improved. As a result, for example, when the heat-absorbing material of this embodiment is placed between the cells of a battery stack (battery module) in which multiple battery cells (hereinafter sometimes referred to as battery cells or simply cells) are stacked, the heat-absorbing material can exhibit both heat absorption and heat insulation effects more effectively across its entire thickness, and can become an inorganic porous material with excellent mechanical strength, thus exhibiting an extremely excellent effect in blocking or suppressing thermal influence on adjacent cells. Furthermore, in the temperature range from the critical temperature (e.g., 150°C) to the runaway thermal temperature (e.g., around 1000°C), the material changes from a heat-absorbing material to a heat-insulating material, so both heat absorption and heat insulation effects can be exhibited across its entire thickness. This also results in excellent space-saving properties by effectively utilizing space.

[0026] If the heat absorber of this disclosure contains a hydrogel body as its contents, cushioning and impact resistance can be imparted to the heat absorber. Furthermore, if inorganic powder is included as a contents, heat can be absorbed continuously at a different endothermic temperature than that of an aqueous solvent. In addition, when the aqueous solvent evaporates, voids are created within the hydrogel, and the composite containing the hydrogel and inorganic powder tends to form a porous body. As a result, the heat absorber changes from an endothermic to an insulating body, allowing it to exhibit both heat absorption and insulating effects more effectively across its entire thickness. Furthermore, if an antifreeze is included as an optional component, freezing below freezing point can be suppressed. Moreover, by utilizing the heat of solidification of the aqueous solvent, the temperature drop of the battery in cold environments can be suppressed. In the case of water, the heat of solidification occurs at around 0°C, but by using an antifreeze, the temperature at which this heat of solidification occurs can be lowered, thereby suppressing the temperature drop of the battery at even lower temperatures. Furthermore, when the hydrogel itself is included as a component, it exhibits superior shape retention when placed vertically compared to when the hydrogel itself is not included, or the effect of maintaining the dispersion state of the inorganic powder. The heat-absorbing material of this disclosure exhibits excellent shape retention when placed vertically between cells, and also exhibits excellent shape retention when placed, for example, on the top plate of a housing (case) that houses battery cells. Specifically, when placed on the top plate of a housing that houses battery cells, it can suppress the uneven distribution of the hydrogel and dispersed inorganic powder within the bag due to its own weight, thereby maintaining its shape. In addition, if the bag is damaged by heat or the like, the hydrogel's shape retention makes it difficult for the hydrogel to leak out from the damaged area of ​​the bag, so even if the bag is damaged, the function of the hydrogel and inorganic powder is not easily lost. Furthermore, since the heat-absorbing element of this disclosure exhibits not only a heat-absorbing effect but also effects such as heat insulation, it can be more precisely described as a component capable of absorbing and insulating heat from the outside, that is, a heat control component that controls heat from the outside.

[0027] In addition to the hydrogel and inorganic powder, the contents of the heat-absorbing body of this embodiment may further contain, if necessary, one or more selected from the group consisting of inorganic fibers, antifreeze agents, and additives. When inorganic fibers are included as contents, the inorganic powder acts as a foaming nucleating agent, making it easier for the material to form a porous body. Furthermore, when the inorganic powder transforms into a porous body, a porous composite containing the inorganic fibers and inorganic powder can be formed. As a result, for example, when the temperature exceeds the thermal runaway temperature, it acts as a composite material, making it easier to form an insulating wall with the desired mechanical strength. Including an antifreeze as a component can suppress freezing below freezing point. In this case, by utilizing the heat of solidification of the aqueous solvent, the temperature drop of the battery in cold environments can be suppressed. In the case of water, the heat of solidification occurs at around 0°C, but by using an antifreeze, the temperature at which the heat of solidification of the antifreeze occurs can be lowered, and the surrounding environment in which the heat absorber is placed at lower temperatures, for example, by placing the heat absorber of this embodiment between the cells of a battery stack (battery module) in which multiple cells are stacked, the temperature drop of the battery stack (battery module) can be suppressed.

[0028] <Characteristics of heat absorbers> The endothermic start temperature of the heat-absorbing element in this embodiment is preferably 400°C or lower, more preferably 160°C or lower, even more preferably 120°C or lower, even more preferably 110°C or lower, and even more preferably 100°C or lower. The range of the endothermic start temperature for the heat-absorbing element in this embodiment is preferably 35°C to 400°C, more preferably 37°C to 160°C, and even more preferably 40°C to 110°C. The upper and lower limits of the heat absorption start temperature of the heat absorption element 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 baseline towards the high-temperature side of the differential scanning calorimetry (DSC) measurement curve, and a tangent line drawn at the point where the slope is maximum on the low-temperature side curve of the endothermic peak associated with evaporation. However, if multiple endothermic peaks are observed, the intersection point of the straight line extending the low-temperature baseline towards the high-temperature side and the tangent line drawn at the point where the slope is maximum on the low-temperature side curve of each of the multiple endothermic peaks is calculated for each of the multiple endothermic peaks, and the lowest temperature among these multiple intersection points is defined as the endothermic onset temperature. The endothermic peak temperature of the endothermic element in this embodiment is preferably in the range of at least 80°C to 400°C, more preferably in the range of 90°C to 350°C, even more preferably in the range of 102°C to 280°C, and even more preferably in the range of 110°C to 240°C. In another embodiment, it is more preferable that the endothermic peak temperature is in the range of 90°C to 160°C. The preferred range of the endothermic peak temperature can be appropriately combined with the above upper and lower limits. In this specification, the endothermic peak temperature refers to the temperature (°C) at the maximum value of the endothermic peak due to evaporation in the DSC measurement curve, which is the measurement result of a differential scanning calorimetry (DSC). If multiple endothermic peaks are observed, it is sufficient that at least one of the multiple endothermic peaks is in the range of 80°C to 400°C. The amount of heat absorbed by the heat absorber in this embodiment is not particularly limited, but at the endothermic peak temperature (in the range of 80°C to 400°C), it 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, even more preferably 300 J / g or more and 2000 J / g or less, and even more preferably 500 J / g or more and 1500 J / g or less. The heat absorption range of the heat absorption element in 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 above heat absorption amount can be appropriately determined by combining the above upper and lower limits. The endothermic start temperature, endothermic peak temperature, and amount of heat absorbed by the heat absorber in this embodiment were determined using a differential scanning calorimetry (DSC) and the method described in the examples below.

[0029] <Preferred shape of heat absorber> The shape or size of the heat-absorbing element in this embodiment is not particularly limited and may be, for example, approximately spherical, approximately flat, or irregularly shaped, and can be appropriately selected depending on the application. For example, an approximately flat heat-absorbing element is preferable because it is easy to install between adjacent battery cells. The average thickness of the heat-absorbing element in this embodiment, when it is substantially flat, is not particularly limited, but for example, it can be in the range of 100 μm to 50,000 μm. The above average thickness is more preferably 200 μm or more and 20,000 μm or less, even more preferably 500 μm or more and 10,000 μm or less, and particularly preferably 1,000 μm or more and 8,000 μm or less. The preferred range of the above average thickness can be appropriately combined with the above upper and lower limits.

[0030] The following describes the essential components of the heat-absorbing body of this embodiment, which consist of a bag, a hydrogel (including an aqueous solvent contained within the hydrogel), and an inorganic powder, as well as optional components such as antifreeze and additives that may be added as needed.

[0031] (Bag body) The bag of this embodiment is not particularly limited as long as it can be filled with contents such as hydrogel or inorganic powder. Preferably, the bag is a three-sided bag having an opening at the upper end and a closed lower end, and having a structure that is heat-sealed so that the opening is closed after all of the contents such as hydrogel or inorganic powder have been contained. This three-sided bag has a structure in which the lower ends and sides of two sheets are bonded together, and the contents are filled in through the opening and then sealed. As such, it has excellent airtightness and, because it has a roughly flat shape, is easy to insert between battery cells. The bag of this embodiment is preferably made of sheets. In addition, a preferred form of the bag of this embodiment is to overlap two films of a desired size and shape (for example, rectangular or (approximately) circular) depending on the purpose of use, and then heat-seal a predetermined heat-seal area (for example, the edge of the film) is heat-sealed to form an opening, thereby bonding the heat-seal area. This makes it possible to create a three-sided bag that has an opening through which the contents can be filled into the internal space, and in which the heat-seal areas of the two sheets are bonded together. After filling with contents, the contents can be sealed by heat-sealing the openings together. In this specification, "sealed" means a state in which the inside and outside of the bag are substantially separated.

[0032] The sheet used in the bag of this embodiment is not particularly limited as long as it exhibits water-impermeable properties, and examples include known resin films, resin films having a metal layer, or films having a metal layer. The average thickness of the sheet 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 above-mentioned 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, or elastomer. These plastics can be used in bags as films, sheets, tubes, etc. Furthermore, as the resin film having the metal layer, metals such as aluminum, or metal oxides such as silica and alumina may be laminated onto the resin film as metal foil, a vapor-deposited film, etc. By using a resin film having a metal layer, the water vapor permeability of the resin film can be reduced. The water vapor permeability of the sheet can also be adjusted by selecting materials, thickness, combination, etc. Examples of lamination methods include dry lamination, extrusion lamination, thermal lamination, co-extrusion, multilayer blow molding, laminated 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) and a thermoplastic resin film (e.g., polyethylene film, PP film, PET film) laminated on at least one of its surfaces are integrated).

[0033] In this embodiment, an adhesive layer may be formed in the heat-sealed region and the closed opening for sealing purposes. Suitable adhesives for this layer include, for example, polyester-based adhesives, polyether-based adhesives, or polyurethane-based adhesives, such as laminate adhesives. Furthermore, the properties of the adhesive are not particularly limited; for example, solvent-based, solvent-free, or aqueous types can be used. For example, in the present invention, a bag-shaped body formed by making a laminate film into a bag shape is preferable. As the laminate film, a film obtained by laminating a metal foil and a resin film is preferable, and a laminated film having a three-layer structure composed of an outer resin film / metal foil / inner resin film is exemplified. Specifically, a resin film having an aluminum vapor-deposited layer on the outside, a bag body sealed through a polyurethane-based laminate adhesive layer, a three-layer laminate film having a nylon film on the outside, an aluminum foil in the center, and an adhesive layer such as modified polypropylene on the inside, a bag body sealed through a polyurethane-based laminate adhesive layer, or a laminate film having a PET layer, an aluminum layer, and a polyethylene layer, a bag body sealed through a polyurethane-based laminate adhesive layer can be preferably used. For example, a gas barrier aluminum bag AB series (manufactured by Mitsubishi Gas Chemical Company, Inc.), a Lamzip AL type (manufactured by Seisan Nippon Co., Ltd.), and the like can be mentioned. The higher the melting temperature (for example, 120 to 140 ° C) of the adhesive that closes the opening of the bag body of the present embodiment or is provided in the heat seal area, the higher the strength and the tendency to withstand the internal pressure.

[0034] The water vapor permeability ([g / (m 2 ·24h)]) of the sheet constituting the bag body of the present embodiment is preferably 50 g / (m 2 ·24h) or less, more preferably 10 g / (m 2 ·24h) or less, and even more preferably 5 g / (m 2 ·24h) or less. When the water vapor permeability of the sheet constituting the bag body is in the range of 50 g / (m 2 ·24h) or less, it is possible to prevent the moisture inside the bag body from leaking to the outside, which is preferable from the viewpoint of preventing the deterioration of the heat absorption performance over time. The water vapor permeability ([g / (m 2 ·24h)]) in this specification is measured in an environment of a temperature of 40 ° C and a relative humidity of 90% in accordance with the standard of JIS K7129.

[0035] (Hydrogel) In the endothermic body of this embodiment, a hydrogel composed of a hydrogel body and an aqueous solvent can be filled into a bag. Furthermore, it is preferable that the hydrogel of this embodiment has an aqueous solvent and a three-dimensional polymer network structure (=hydrogel body) that holds the aqueous solvent inside. By further incorporating the hydrogel body as a component, pressure resistance and impact resistance can be imparted to the heat absorber. Furthermore, even if the bag is ruptured, the hydrogel can retain the aqueous solvent, making it difficult for the aqueous solvent to leak out. As a result, when the heat absorber is installed inside a battery, it is less likely to wet the inside with the aqueous solvent. In addition, the shape of the heat absorber can be easily molded into the desired shape. Therefore, when a heat absorber containing hydrogel as a component is placed vertically, it exhibits excellent shape retention when placed vertically, or the effect of maintaining the dispersion state of the inorganic powder component. Furthermore, the hydrogel is not particularly limited, and known hydrogels can be used, but it is more preferable that it comprises an aqueous solvent and a hydrogel body which is a three-dimensional network structure of a polymer containing a water-swellable clay mineral and water-soluble organic monomer structural units, at least a portion of which is dissolved or dispersed in the aqueous solvent. In other words, as the hydrogel of this embodiment, for example, it is preferable that the aqueous solvent is held within a three-dimensional network structure (three-dimensional network) mainly composed of a polymer synthesized from water-soluble organic monomers, and it is even more preferable that the aqueous solvent is held within a three-dimensional network structure (three-dimensional network) mainly composed of a polymer synthesized from water-soluble organic monomers in the presence of a water-swellable clay mineral. The aqueous solvent content in the hydrogel of this embodiment is suitable as a heat absorber if it is in the range of 5 to 99% by mass relative to the total hydrogel, as it can exhibit an endothermic effect at a level that can effectively prevent ignition and damage due to thermal runaway of secondary batteries. The aqueous solvent content in the hydrogel is preferably 5% to 99% by mass, more preferably 10% to 90% by mass, and even more preferably 20% to 80% by mass, relative to the total gel. The preferred range for the aqueous solvent content can be appropriately adjusted by combining the above upper and lower limits.

[0036] Specific examples of such hydrogels include organic-inorganic composite hydrogels (NC gels), interpenetrating network structure hydrogels (DN gels), cyclic gels (SR gels), and hydrogels called aquamaterials. Of these, organic-inorganic composite hydrogels (also referred to as organic-inorganic hydrogels or NC gels (nanocomposite gels)) are preferred because they have excellent endothermic properties due to the aqueous solvent contained within, as well as excellent cushioning and creep resistance.

[0037] The hydrogel content included in the contents of the heat absorber of this embodiment is preferably 10% by mass or more and 95% by mass or less, preferably 20% by mass or more and 90% by mass or less, preferably 30% by mass or more and 80% by mass or less, and preferably 40% by mass or more and 70% by mass or less, based on the total amount of contents of the heat absorber. The preferred range for the hydrogel content can be determined by appropriately combining the above 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, by incorporating this heat absorber, the heat absorber exhibits its heat-absorbing properties, suppressing the temperature influence on other battery cells and providing a highly safe secondary battery module. Furthermore, the heat absorber of this disclosure has sufficient strength to be used as a standalone material. In addition, additives may be further filled into the bag if necessary. The hydrogel of this embodiment preferably comprises an aqueous solvent and a three-dimensional network structure of polymers that holds the aqueous solvent internally, and comprises an aqueous solvent and a hydrogel body which is a three-dimensional network structure of polymers containing a water-swellable clay mineral and water-soluble organic monomer structural units, at least a portion of which are dissolved or dispersed in the aqueous solvent.

[0038] Preferred hydrogels in this embodiment include interpenetrating network gels in which two types of acrylic polymers each separately form a three-dimensional network structure, cyclic gels in which cyclodextrin forms the backbone of a three-dimensional network structure, and aquamaterials in which multi-branched dendrimers form the main backbone of a three-dimensional network structure and water-swellable clay minerals are added. However, in this disclosure, the following description will be 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 water-swellable clay minerals 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 (= three-dimensional network structure) in which polymer chains composed of a plurality of 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 when an aqueous solvent such as water is incorporated into the three-dimensional network structure of the polymer gel. As a result, the swollen organic-inorganic composite hydrogel not only possesses endothermic properties and exhibits excellent cushioning that can follow relatively short-term deformations such as expansion and contraction due to charging and discharging of battery cells, but also exhibits excellent creep resistance that can alleviate internal pressure caused by the expansion of battery cells over time. The aforementioned organic-inorganic composite hydrogel has a three-dimensional network structure, and preferably uses water-soluble organic monomers and water-swellable clay minerals as reaction raw materials.

[0039] In one aspect of this embodiment, the organic-inorganic composite hydrogel preferably uses at least water-soluble organic monomer structural units and water-swellable clay minerals as reaction raw materials. As a method for producing the organic-inorganic composite hydrogel in one aspect of this embodiment, a method is preferred in which the water-soluble organic monomer is polymerized in a dispersion (a) containing the water-soluble organic monomer, water-swellable clay minerals, an aqueous solvent, and optionally a polymerization initiator and additives, since an organic-inorganic composite hydrogel having a three-dimensional network structure can be easily obtained. The resulting polymer of water-soluble organic monomer forms a three-dimensional network structure together with the water-swellable clay minerals and becomes a component of the organic-inorganic composite hydrogel (hydrogel body).

[0040] The hydrogel body content in this embodiment may preferably be 1% to 95% by mass, more preferably 10% to 90% by mass, and even more preferably 20% to 80% by mass, relative to the total amount of hydrogel. Furthermore, the upper limit of the hydrogel body content may preferably be 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less. For example, if the hydrogel body is composed of water-soluble organic monomer structural units as described later, the hydrogel body content may be the total amount of water-soluble organic monomer structural units and water-swellable viscosity minerals. The preferred range for the content of the hydrogel body described above can be determined by appropriately combining the above upper and lower limits. The hydrogel content is calculated by determining the percentage change in mass before and after drying the hydrogel at 120°C for 2 hours.

[0041] <<Water-soluble organic monomers>> The water-soluble organic monomer used in this embodiment constitutes the organic-inorganic composite hydrogel body as the water-soluble organic monomer structural unit. Furthermore, 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 and 50% by mass or less, more preferably 1% by mass or more and 40% by mass or less, and even more preferably 5% by mass or more and 30% by mass or less, relative to the total amount of the hydrogel. The preferred range for the content of the above-mentioned water-soluble organic monomer structural units can be appropriately determined by combining the above-mentioned upper and lower limits. The types of water-soluble organic monomers used in this embodiment are not particularly limited, but 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" means either or both acrylamide and methacrylamide; "(meth)acryloyloxy" means either or both acryloyloxy and (meth)acryloyloxy; "(meth)acrylate" means either or both acrylate and methacrylate; and "(meth)acrylic monomer" means either or both acrylic monomer and methacrylic monomer.

[0042] Examples of monomers having the (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, acryloylmorpholin, methacrylamide, N,N-dimethylmethacrylamide, N,N-diethylmethacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, N-isopropylmethacrylamide, N-cyclopropylmethacrylamide, N,N-dimethylaminopropylmethacrylamide, and N,N-diethylaminopropylmethacrylamide. Preferred monomers having the (meth)acrylamide group include, for example, acrylamide, N,N-dimethylacrylamide, N-methylacrylamide, N-ethylacrylamide, acryloylmorpholin, methacrylamide, N,N-dimethylmethacrylamide, N-methylmethacrylamide, and N-ethylmethacrylamide.

[0043] Examples of monomers having the (meth)acryloyloxy group include methoxyethyl acrylate, ethoxyethyl acrylate, methoxyethyl methacrylate, ethoxyethyl methacrylate, methoxymethyl acrylate, and ethoxymethyl acrylate.

[0044] Examples of acrylic monomers having a hydroxyl group include hydroxyethyl acrylate and hydroxyethyl methacrylate. Furthermore, the water-soluble organic monomer used in this embodiment may be the acrylic monomer having a hydroxyl group used alone or in combination of two or more types.

[0045] In this embodiment, when a homopolymer is obtained from a water-soluble organic monomer, the lower critical eutectic temperature (°C) of the obtained homopolymer is preferably 50°C or higher, more preferably 60°C or higher, and preferably does not have a lower critical eutectic temperature (°C), that is, it is preferable that the lower critical eutectic temperature (°C) cannot be observed in an aqueous solvent. The upper limit of the lower critical eutectic temperature (°C) of the homopolymer may be, for example, 100°C. As a result, the polymer chains that make up the water-soluble organic monomer structural units of the organic-inorganic composite hydrogel do not undergo a phase transition below 50°C, thus enabling superior cushioning and heat absorption even at high temperatures. More specifically, one aspect of this embodiment, the organic-inorganic composite hydrogel, has polymer chains composed of water-soluble organic monomer structural units obtained by polymerization or reaction of water-soluble organic monomers. Therefore, when the temperature exceeds the lower critical eutectic temperature (°C) of the polymer chains composed of these water-soluble organic monomer structural units, the polymer chains undergo a phase transition due to desolvation, separating into a phase containing the polymer chains and a phase containing an aqueous solvent. As a result, the three-dimensional network structure of the organic-inorganic composite hydrogel containing the aqueous solvent can no longer be maintained, making it difficult to exhibit cushioning properties. Therefore, it is preferable that the lower critical eutectic temperature (°C) of the organic-inorganic composite hydrogel in an aqueous solvent be 50°C or higher, more preferably 60°C or higher, and even preferable that it does not have a lower critical eutectic temperature (°C), i.e., that a lower critical eutectic temperature (°C) cannot be observed in an aqueous solvent. The upper limit of the lower critical eutectic temperature (°C) of the organic-inorganic composite hydrogel may be, for example, 100°C.

[0046] From the viewpoint of suppressing the phase transition of the organic-inorganic composite hydrogel, the preferred water-soluble organic monomers used in this embodiment are water-soluble organic monomers having repeating units in a homopolymer that do not have a lower critical eutectic 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 are preferred. When an organic-inorganic composite hydrogel is heated above the lower critical eutectic 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 in which the aqueous solvent contained within the organic-inorganic composite hydrogel is contained. Therefore, it is particularly preferable that the polymer chains constituting the organic-inorganic composite hydrogel do not have a lower critical eutectic temperature in the aqueous solvent. Accordingly, water-soluble organic monomers capable of forming highly hydrophilic polymer chains are 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 properties due to phase transition or reducing leakage, it is preferable that the lower critical eutectic temperature (°C) of the copolymer composed of the two or more water-soluble organic monomers be 50°C or higher, more preferably 60°C or higher, and preferably have no lower critical eutectic temperature (°C), that is, it is preferable that the lower critical eutectic temperature (°C) cannot be observed in an aqueous solvent. The upper limit of the lower critical eutectic temperature (°C) of the copolymer composed of the two or more water-soluble organic monomers may be, for example, 100°C.

[0047] Furthermore, among the water-soluble organic monomers mentioned above, monomers having a (meth)acrylamide group are preferred from the viewpoint of solubility and cushioning properties of the resulting organic-inorganic composite hydrogel. Acrylamide, N,N-dimethylacrylamide, and acryloylmorpholine are more preferred, N,N-dimethylacrylamide and acryloylmorpholine are even more preferred, and N,N-dimethylacrylamide is particularly preferred from the viewpoint of easy polymerization. The water-soluble organic monomers mentioned above may be used individually or in combination of two or more.

[0048] <<Water-swellable clay minerals>> 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 becomes 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, but examples 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 or water-swellable montmorillonite, and more preferably to use water-swellable hectorite.

[0049] The water-swellable clay minerals used in this embodiment can be naturally derived, synthesized, or surface-modified. Examples of surface-modified water-swellable clay minerals include phosphonic acid-modified hectorite and fluorine-modified hectorite, but from the viewpoint of the endothermic and cushioning properties of the resulting organic-inorganic composite hydrogel, phosphonic acid-modified hectorite is preferred. The aforementioned water-swellable clay minerals may be used individually or in combination of two or more types.

[0050] The phosphonic acid-modified hectorite forms a three-dimensional network structure together 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, alendronate-modified hectorite, methylenediphosphonic acid-modified hectorite, and phytic acid-modified hectorite. These phosphonic acid-modified hectorites may be used individually or in combination of two or more types. In this embodiment, the content of the water-swellable clay mineral is preferably 0.1% to 50% by mass, more preferably 1% to 30% by mass, even more preferably 2% to 20% by mass, and particularly preferably 3% to 10% by mass, 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 for the content of water-swellable clay minerals in the above organic-inorganic composite hydrogel can be adjusted as appropriate.

[0051] <Reaction materials for hydrogels> In one aspect of this embodiment, the heat-absorbing body preferably comprises a bag and contains an aqueous solvent and an organic-inorganic composite hydrogel as its contents. The organic-inorganic composite hydrogel 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 and then the bag may be sealed, or the water-soluble organic monomer and water-swellable clay mineral, which are the reaction raw materials for the organic-inorganic composite hydrogel, may be filled into the bag together with the aqueous solvent (an organic solvent and polymerization initiator may be added as needed), and then the water-soluble organic monomer and water-swellable clay mineral inside may be gelled while the bag is sealed.

[0052] One aspect of this embodiment is a method for producing an organic-inorganic composite hydrogel, which allows for the simple acquisition of an organic-inorganic composite hydrogel. This method involves polymerizing a water-soluble organic monomer in a dispersion (a) containing a water-soluble organic monomer and a water-swellable clay mineral as reaction raw materials, a polymerization initiator, and an aqueous solvent. More specifically, a method is preferred in which the dispersion (a) (containing the water-soluble organic monomer and water-swellable clay mineral as reaction raw materials, a polymerization initiator, and an aqueous solvent) is filled into a bag together with inorganic powder, and then the bag is sealed while the water-soluble organic monomer is polymerized under predetermined polymerization conditions. 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, relative to the total amount (mass) of the water-soluble organic monomer, the water-swellable clay mineral, and the aqueous solvent. The content of the water-soluble organic monomer is preferably 0.9% by mass or more and 50% by mass or less, more preferably 1% by mass or more and 40% by mass or less, and even more preferably 5% by mass or more and 30% by mass or less. The above upper and lower limits of the content can be changed as appropriate. A water-soluble organic monomer content of 0.9% by mass or more is preferable because it allows for the production of a hydrogel with excellent mechanical properties. On the other hand, a water-soluble organic monomer content of 50% by mass or less is preferable because it allows for the easy preparation of the dispersion. 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, relative to the total amount (mass) of the water-soluble organic monomer, the water-swellable clay mineral, and the aqueous solvent. The lower limit of the water-swellable clay mineral content 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 water-swellable clay mineral content 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 combined as appropriate. A water-swellable clay mineral content of 0.1% by mass or more is preferable because it further improves the mechanical properties of the resulting hydrogel. On the other hand, a water-swellable clay mineral content of 50% by mass or less is preferable because it further suppresses the increase in viscosity of the dispersion (a). Furthermore, the dispersion (a) has better storage stability when phosphonic acid-modified hectorite is used as the water-swellable clay mineral, but it may also contain other water-swellable clay minerals as long as it does not impair storage stability. The content of the aqueous solvent in the dispersion (a) is, for example, in the range of 50 to 99% by mass, and more preferably 60% to 90% by mass, relative to the total amount (mass) of the water-soluble organic monomer, the water-swellable clay mineral, and the aqueous solvent. The upper and lower limits of the above content can be combined as appropriate. A content of 90% by mass or less of the aqueous solvent is preferable because it allows for the production of a hydrogel with excellent mechanical properties. On the other hand, a content of 60% by mass or more of the aqueous solvent is preferable because it facilitates the preparation of a dispersion (a) in which each component is uniformly dispersed. The upper and lower limits of the above content can be combined as appropriate. Furthermore, the dispersion (a) may contain one or more substances selected from the group consisting of low-volatility solvents and additives described later, in addition to the reaction raw materials: water-soluble organic monomers and water-swellable clay minerals, polymerization initiators, and aqueous solvents.

[0053] The dispersion (a) of this embodiment preferably contains a polymerization initiator. The polymerization initiator is not particularly limited, but examples include water-soluble peroxides and water-soluble azo compounds. Examples of the water-soluble peroxides mentioned above include potassium peroxodisulfate, ammonium peroxodisulfate, sodium peroxodisulfate, and t-butyl hydroperoxide. Examples of the aforementioned water-soluble azo compounds include 2,2'-azobis(2-methylpropionamidine) dihydrochloride and 4,4'-azobis(4-cyanovaleric acid). Among these, from the viewpoint of interaction with water-swellable clay minerals, it is preferable to use water-soluble peroxides, more preferably potassium peroxodisulfate, ammonium peroxodisulfate, or sodium peroxodisulfate, and even more preferably sodium peroxodisulfate or ammonium peroxodisulfate. The polymerization initiators mentioned above may be used individually or in combination of two or more.

[0054] In one aspect of this embodiment, the polymerization initiator is not essential, but if used, the molar ratio of the polymerization initiator to the water-soluble organic monomer in the dispersion (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.

[0055] The polymerization initiator content in the dispersion (a) is not essential, but if used, it is preferably 0.1 to 10% by mass, and more preferably 0.2 to 5% by mass, relative to the total amount (mass) of the water-soluble organic monomer, water-swellable clay mineral, aqueous solvent, and polymerization initiator. A polymerization initiator content of 0.1% by mass or more is preferable 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% by mass or less is preferable because it allows the dispersion to be used without aggregation before polymerization, improving handling.

[0056] The dispersion (a) contains a water-soluble organic monomer, a water-swellable clay mineral, and an aqueous solvent, but may further contain an organic solvent, a catalyst, an organic crosslinking agent, a preservative, a thickener, etc., as needed. Examples of the aforementioned organic solvents 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 dispersibility of water-swellable clay minerals, it is preferable to use alcohol compounds, more preferably methanol, ethanol, n-propyl alcohol, or isopropyl alcohol, and even more preferably methanol or ethanol. These organic solvents may be used individually or in combination of two or more.

[0057] The catalyst has the function of increasing the polymerization rate when polymerizing water-soluble organic monomers. The catalyst is not particularly limited, but examples include tertiary amine compounds, thiosulfates, and ascorbic acids. Examples of tertiary amine compounds include N,N,N',N'-tetramethylethylenediamine and 3-dimethylaminopropionitrile. Examples of the thiosulfate include sodium thiosulfate and ammonium thiosulfate. Examples of the aforementioned 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 more preferably to use N,N,N',N'-tetramethylethylenediamine. The catalysts mentioned above may be used individually or in combination of two or more. Although a catalyst is not essential, when a catalyst is used, the catalyst content in the dispersion (a) is preferably 0.01 to 1% by mass, and more preferably 0.05 to 0.5% by mass, relative to the total amount (mass) of the water-soluble organic monomer, water-swellable clay mineral, aqueous solvent, and catalyst. A catalyst content of 0.01% by mass or more is preferable because it efficiently promotes the synthesis of hydrogels obtained from water-soluble organic monomers. On the other hand, a catalyst content of 1% by mass or less is preferable because the dispersion can be used without aggregation before polymerization, improving handling.

[0058] Examples of methods for preparing the dispersion (a) include a method of mixing a water-soluble organic monomer, a water-swellable clay mineral, a polymerization initiator, and an aqueous solvent such as water all at once; and a multi-liquid mixing method in which a dispersion (a1) containing a water-soluble organic monomer and a solution (a2) containing a polymerization initiator are prepared as separate dispersions or solutions and mixed immediately before use. However, from the viewpoint of dispersibility, storage stability, viscosity control, etc., the multi-liquid mixing method is preferred.

[0059] Examples of the dispersion (a1) containing the water-soluble organic monomer include a dispersion obtained by mixing a water-soluble organic monomer with a water-swellable clay mineral.

[0060] Examples of the solution (a2) containing the polymerization initiator include aqueous solutions obtained by mixing the polymerization initiator with water.

[0061] The organic-inorganic composite hydrogel is obtained by polymerizing a water-soluble organic monomer in the dispersion (a). The polymerization method is not particularly limited and can be carried out by known methods. Specifically, examples include radical polymerization by heating or ultraviolet irradiation, and radical polymerization utilizing redox reactions.

[0062] The polymerization temperature for polymerizing the organic-inorganic composite hydrogel is preferably 10 to 80°C, and more preferably 20 to 80°C. A polymerization temperature of 10°C or higher is preferable because radical reactions can proceed in a chain reaction. On the other hand, a polymerization temperature of 80°C or lower is preferable because polymerization can occur without the water contained in the dispersion (a) boiling. The polymerization time for organic-inorganic composite hydrogels varies depending on the type of polymerization initiator and catalyst, but it is typically between several tens of seconds and 24 hours. In particular, for radical polymerization using heating or redox, a polymerization time of 1 to 24 hours is preferred, and 5 to 24 hours is more preferred. A polymerization time of 1 hour or more is preferable because the polymer of water-swellable clay minerals and water-soluble organic monomers can form a three-dimensional network structure. On the other hand, since the polymerization reaction is almost completed within 24 hours, a polymerization time of 24 hours or less is preferable.

[0063] The heat-absorbing material of this embodiment contains a hydrogel body along with an aqueous solvent as its contents. On the other hand, when exposed to high temperatures such as combustion, the aqueous solvent evaporates, creating pores within the hydrogel, which can exhibit heat insulation and fire prevention effects.

[0064] <Aqueous solvents> The heat-absorbing material of this embodiment contains an aqueous solvent along with the hydrogel body as its contents. This allows for heat absorption through the latent heat of vaporization of the aqueous solvent within the bag, particularly water, thus utilizing the latent heat of vaporization of water, which has a larger heat absorption capacity than typical hydrates. Furthermore, because it absorbs heat as the sensible heat of the aqueous solvent, the temperature can be stabilized even at room temperature. It contains a hydrogel (including at least the hydrogel body and the aqueous solvent). This allows for heat absorption through the latent heat of vaporization of the aqueous solvent within the hydrogel, particularly water, thus utilizing the latent heat of vaporization of water, which has a larger heat absorption capacity than typical hydrates. On the other hand, when exposed to high temperatures such as combustion, the aqueous solvent evaporates, creating pores within the hydrogel, which can exhibit heat insulation and fire-preventive effects. The aqueous solvent is preferably mainly present in the hydrogel, for example, an organic-inorganic composite hydrogel.

[0065] In this embodiment, the aqueous solvent only needs to contain water as its main component, and means water or a solvent whose main component is water. Therefore, the aqueous solvent includes mixed solvents with solvents other than water, or aqueous solutions containing salts (e.g., buffer solutions, electrolyte solutions). In this specification, "containing water as its main component" means that the aqueous solvent contains 45% by mass or more of water relative to the total aqueous solvent. Furthermore, the water used is not particularly limited and can be purified water, pure water, ultrapure water, or distilled water, etc. Examples of such salts include alkali metal halides such as sodium chloride or potassium chloride; alkaline earth metal halides such as magnesium chloride or calcium chloride; and buffering salts such as Tris-hydrochloric acid, glycine hydrochloride, citrate-sodium citrate, acetate-sodium acetate, citrate-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 be used as the aqueous solvent. Other solvents that make up the mixed solvent include organic solvents that can be uniformly mixed with water (e.g., lower alcohols, lower ketones, etc.), or low-volatility solvents used as antifreeze agents.

[0066] In this embodiment, the water content in the aqueous solvent is preferably 50% to 100% by mass, more preferably 80% to 100% by mass, even more preferably 90% to 100% by mass, and particularly preferably 95% to 100% by mass, relative to the total aqueous solvent. The preferred range for the water content in the aqueous solvent can be determined by appropriately combining the upper and lower limits mentioned above. The content of the aqueous solvent in this embodiment can be 1% by mass or more and 94% by mass or less, more preferably 10% by mass or more and 90% by mass or less, and even more preferably 20% by mass or more and 80% by mass or less, based on the total amount (100% by mass) of the contents of the endothermic body. It is particularly preferable that the amount is between 30% by mass and 70% by mass. The preferred range for 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, it exhibits superior endothermic and heat rise suppression effects, and can change from an endothermic effect to an insulating effect in the high-temperature range.

[0067] <Antifreezing agent> In this embodiment, since the effect of suppressing temperature drop below freezing point can be improved, an antifreeze agent may be added to the aqueous solvent as needed. In particular, by adding an antifreeze agent to the contents of the heat-absorbing material, high cushioning properties can be maintained over a wide temperature range. The antifreeze agent in this embodiment may be an inorganic antifreeze agent or an organic antifreeze agent. Furthermore, the antifreeze agent may be in liquid, powder, or solid form. The inorganic antifreeze is preferably a chloride such as sodium chloride, calcium chloride, or magnesium chloride (including hydrates such as magnesium chloride hexahydrate). On the other hand, organic antifreeze agents are preferably salts of organic acids or low-volatility substances (low-volatility solvents or urea), and more preferably salts of organic acids or low-volatility solvents. As the salt (including hydrate) of the aforementioned organic acid, it is preferable to use a salt of sodium, potassium, magnesium, or ammonia of formic acid, acetic acid, propionic acid, or succinic acid. Examples include disodium succinate (including hydrates such as disodium succinate hexahydrate) or sodium propionate. Furthermore, examples of the low-volatility substance include urea or low-volatility solvents (e.g., polyhydric alcohols). Examples of such low-volatility solvents 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, or raffinose.

[0068] The low-volatility solvent in this embodiment is one whose volatility is 1 cm in an open system at 60°C and 1 atm. 2 • Less than 0.1g per hour (0.1g / cm³) 2 An organic solvent (hr, 60℃, 1 atm or less) is more preferably used, even more preferably 0.05 g or less, and even more preferably 0.01 g or less. Specifically, since a solvent that is easily miscible with water is preferred, glycerin (0.001 g or less / cm³) is preferred. 2 ·hr·60℃·1atm), diglycerin (0.001g or less / cm³) 2 ·hr·60℃·1atm), ethylene glycol (0.01g or less / cm³) 2 ·hr·60℃·1atm), propylene glycol (0.001g or less / cm³) 2 ·hr·60℃·1atm), polyethylene glycol (0.001g or less / cm³) 2 Polyhydric alcohols such as (hr·60℃·1atm) are preferred, and glycerin and diglycerin are more preferred. These low-volatility solvents may be used alone or in combination of two or more. Furthermore, it is preferable that these low-volatility solvents are uniformly contained in the organic-inorganic composite hydrogel. By including a low-volatility solvent, particularly a polyhydric alcohol, as the contents of the heat-absorbing element in this embodiment, the volatilization of aqueous solvents is suppressed and prevented, or the decrease in cushioning properties at low temperatures is suppressed (improving the antifreeze effect). When a low-volatility solvent is used as an optional component, the mass ratio (water-based solvent / low-volatility solvent) of the aqueous solvent to the low-volatility solvent in the contents of the endothermic body 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. The amount of the antifreeze in this embodiment can be 0% to 70% by mass relative to the total amount (100% by mass) of the contents of the heat absorber, preferably 5% to 60% by mass, more preferably 10% to 50% by mass, even more preferably 15% to 35% by mass, and particularly preferably 20% to 30% by mass. The preferred range for the content of the above-mentioned antifreeze agent can be adjusted by appropriately combining the above-mentioned upper and lower limits. Furthermore, when the antifreeze agent is contained within the above range, it is less likely to freeze even at -20°C, allowing the battery to be used over a wide temperature range.

[0069] (Inorganic powder) The heat-absorbing body of this embodiment essentially contains inorganic powder. When the heat-absorbing body is exposed to high temperatures, the internal aqueous solvent evaporates, and the hydrogel and inorganic powder are calcined. As a result, an inorganic porous body is formed from the inorganic powder, exhibiting excellent heat insulation and fire prevention effects. More specifically, it exhibits a synergistic effect with the endothermic properties of aqueous solvents, allowing for continuous heat absorption at different endothermic temperatures than those of aqueous solvents. Furthermore, even when exposed to high temperatures, the presence of inorganic powder as a component of the heat absorber acts as bubbles incorporated into the hydrogel body, allowing the inorganic powder and hydrogel as a whole to form a porous composite (see, for example, the photograph in Figure 4 described later). As a result, it exhibits excellent heat insulation and fire prevention effects. Therefore, a heat absorber containing 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 exceeding the critical temperature (e.g., 150°C) to the thermal runaway temperature (e.g., around 1000°C), the inorganic powder and hydrogel as a whole become porous, and can therefore also function as a heat absorber. As a result, placing the heat absorber of this embodiment between cells in a battery stack made up of multiple stacked cells can block or suppress the thermal influence on adjacent cells. Furthermore, if the inorganic powder has an endothermic effect (for example, if it absorbs external heat and undergoes thermal decomposition), it may exhibit a synergistic effect with the endothermic effect of the aqueous solvent. Furthermore, when thermal runaway occurs, the cells expand, compressing the heat-absorbing material itself between the cells, reducing the void space and preventing it from exhibiting effective thermal insulation performance. If inorganic powder is included as the contents of the heat-absorbing material in this embodiment, the inorganic powder itself will sinter when heated to high temperatures due to thermal runaway, etc., thereby increasing the pressure resistance strength of the entire heat-absorbing material. This maintains effective thermal insulation, thereby effectively suppressing chain explosions between cells. The inorganic powder used in this embodiment is preferably an inorganic powder that has an endothermic effect, and more preferably one or more selected from the group consisting of heat-absorbing materials, porous powders, hollow particles, and other inorganic powders. The amount of heat absorbed by the inorganic powder (= amount of heat absorbed when heated from room temperature (23°C) to 1000°C (J / g)) is preferably 100 J / g or more, more preferably 500 J / g or more, and even more preferably 700 J / g or more. On the other hand, the upper limit of the amount of heat absorbed by the inorganic powder is not particularly limited, but is preferably 4000 J / g or less. The heat absorbed by the inorganic powder is preferably 100 J / g or more and 4000 J / g or less. When the amount of heat absorbed by the inorganic powder is within the above range, the endothermic effect is enhanced, resulting in a synergistic effect with the endothermic effect of the aqueous solvent, making it easier to suppress ignition. The upper and lower limits of the above content can be combined as appropriate. The upper and lower limits of the amount of heat absorbed by the inorganic powder can be rearranged as appropriate. The heat absorption of inorganic powders can be measured using a differential scanning calorimeter (DSC), as described in the Examples section.

[0070] The thermal decomposition initiation temperature of the inorganic powder in this embodiment is preferably 80°C to 800°C, more preferably 90°C to 500°C, even more preferably 100°C to 350°C, and still more preferably 110°C to 150°C. By setting the thermal decomposition initiation temperature of the inorganic powder to be below the above upper limits, the inorganic powder itself decomposes rapidly, making it easier to suppress ignition. The above upper and lower limits for the thermal decomposition initiation temperature of the inorganic powder can be appropriately rearranged. The thermal decomposition initiation temperature can be measured using a differential scanning calorimeter (DSC).

[0071] The shape of the inorganic powder in this embodiment is not particularly limited and can be, for example, in powder, particulate, or plate form. Furthermore, a water-soluble inorganic powder with an endothermic effect is preferred as the inorganic powder in this embodiment. Preferred embodiments of the inorganic powder include porous powder, solid particles, or hollow particles. 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 more easily dispersed in the system. Note that the above average particle diameter may be the median diameter (D50) value measured by a laser diffraction / scattering particle size distribution analyzer.

[0072] The inorganic powder material in this embodiment is not particularly limited, but it is preferably one or more compounds consisting of an inorganic cation and a combination of organic-inorganic anions. Examples of the inorganic cations include alkali metal ions, alkaline earth metal ions, aluminum ions, zinc ions, silver ions, copper(I) ions, and copper(II) ions, and it is preferable that they be one or more selected from the group consisting of potassium ions, calcium ions, magnesium ions, and aluminum ions. The organic and inorganic anions are preferably one or more selected from oxygen ions, sulfate ions, halogen ions (chloride ions, fluoride ions, bromide ions, etc.), nitrate ions, carbonate ions, acetate ions, and phosphate ions.

[0073] The inorganic powder in this embodiment is preferably one or more selected from the group consisting of hydrated metal compounds, inorganic materials other than hydrated metal compounds, hollow materials, and porous powders, and a hydrated metal compound having a thermal decomposition initiation temperature of 350°C or lower and an endothermic amount of 700 J / g or higher 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, sodium acetate (including hydrates such as sodium acetate trihydrate), potassium acetate (including hydrate), calcium acetate (including hydrates such as calcium acetate monohydrate), magnesium acetate (including hydrates such as magnesium acetate tetrahydrate), aluminum oxide, talc, kaolin clay, dawsonite, boehmite, hydrotalcite, calcium aluminate, alum, and magnesium sulfate heptahydrate. Moreover, from the viewpoint 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 preferable. Furthermore, the alum is R 3 R 1 This refers to a double salt of a sulfate, represented as (SO4)2·12H2O. 3R represents a trivalent metal atom (for example, Al, Fe, or Cr), 1 This represents a monovalent cation (for example, K, NH4, or Na), and includes potassium alum (especially potassium aluminum sulfate dodecahydrate: AlK(SO4)2·12H2O) and ammonium alum (especially ammonium aluminum sulfate dodecahydrate: AlNH4(SO4)2·12H2O). Among the above, aluminum hydroxide or calcium sulfate dihydrate are particularly preferred as the hydrated metal compound. In this specification, "heat-absorbing material" refers to a material that has the property of absorbing heat through physical changes, desorption of crystal water, phase transition, dissolution, or chemical reaction, and may be a material in which an endothermic peak can be measured in the range of approximately 80°C to 400°C by thermal analysis such as differential scanning calorimetry (DSC). "Porous powder" refers to a material in the form of powder particles that has multiple continuous or independent pores within the powder particles. "Hollow particle" refers to a material that has a single independent pore within the powder particles. Furthermore, "other inorganic powder" refers to a material that does not have the above properties (for example, a thermal decomposition initiation temperature of 350°C or less and a heat absorption amount of 500 J / g or more), but can be reinforced as a heat-absorbing material by sintering. Examples of the hollow material or porous powder 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 or composite oxides of the elements, single sulfides or composite sulfides of the elements, and single phosphate compounds or composite phosphate compounds of the elements. Silicon, titanium, zirconium, magnesium, aluminum, indium, tin, and their single or composite oxides are preferred, and materials other than the examples of hydrated metal compounds described above are preferred. Specifically, inorganic materials 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 inorganic powder content in this embodiment can be 1 to 90% by mass, preferably 3 to 80% by mass, relative to the total amount (100% by mass) of the contents of the heat-absorbing body. More preferably 5 to 70% by mass, and even more preferably 10 to 60% by mass. More preferably 20-50% by mass, and even more preferably 25-35% by mass. The content of inorganic powder can be set within the above range regardless of its type, but in particular, when the inorganic powder is water-soluble inorganic powder, the content of water-soluble inorganic powder can be 1 to 90% by mass, may be 3 to 80% by mass, preferably 5 to 60% by mass, most preferably 10 to 50% by mass, and even more preferably 15 to 35% by mass. Furthermore, when the inorganic powder is a water-soluble inorganic powder and a hydrate as described later, the inorganic powder content does not include the water content contained in the hydrate of the inorganic powder. In this embodiment, it is preferable that the contents of the heat-absorbing body change into a porous material when heated to 120°C or higher. More preferably, the temperature at which the contents change into a porous material is 150°C or higher, even more preferably 180°C or higher, even more preferably 210°C or higher, and even more preferably 240°C or higher, or 250°C or higher. When a heat-absorbing material is exposed to high temperatures due to combustion or other means, the aqueous solvent evaporates. However, since the inorganic powder can form a porous body through sintering, it can be physically isolated from adjacent components (e.g., battery cells), thus providing thermal insulation and fire protection to the heat-absorbing material and adjacent components (e.g., battery cells).

[0074] <<Preferred inorganic powders>> A preferred inorganic powder in this embodiment is an inorganic powder that dissolves in 1 g or more of water at 20°C. In this specification, an inorganic powder that dissolves in 1 g or more of water at 20°C is referred to as a water-soluble inorganic powder. In other words, a water-soluble inorganic powder in this specification refers to an inorganic powder that dissolves in 1 g or more of water at 20°C. On the other hand, inorganic powders that dissolve in less than 1 g per 100 g of water at 20°C are called sparingly soluble inorganic powders. By using water-soluble inorganic powder as the inorganic powder, the water-soluble inorganic powder exhibits hydrophilicity, making it easily soluble in the aqueous solvent in the hydrogel, and thus facilitating the uniform distribution of the water-soluble inorganic powder within the contents. As a result, at temperatures exceeding the thermal runaway temperature (e.g., around 1000°C), the entire water-soluble inorganic powder is more likely to form a homogeneous porous body, allowing it to act more effectively as an insulator. Furthermore, when water-soluble inorganic powder, an aqueous solvent, and a hydrogel body are present in the contents of the endothermic body, a synergistic effect with the endothermic effect of the aqueous solvent is observed, allowing for continuous heat absorption at a different endothermic temperature than that of the aqueous solvent. Even when the endothermic body is exposed to high temperatures, the uniformly dispersed water-soluble inorganic powder can become a homogeneous porous body (see, for example, the photograph in Figure 4 described later). As a result, superior heat insulation and fire prevention effects are achieved. Therefore, an endothermic body containing water-soluble inorganic powder primarily functions as an endothermic body in a relatively low temperature range (e.g., above room temperature to around 100°C). On the other hand, in the temperature range exceeding the critical temperature (e.g., 150°C) to the thermal runaway temperature (e.g., around 1000°C), the entire water-soluble inorganic powder becomes a homogeneous porous body, and can therefore also act as an insulator. As a result, it is believed that placing the endothermic body of this embodiment between cells in a battery stack made up of multiple stacked cells can further block or suppress the thermal influence on adjacent cells. For example, when thermal runaway occurs, the cells expand, compressing the heat-absorbing material between cells. This drastically reduces the distance between cells, making it difficult to achieve effective thermal insulation. However, if the heat-absorbing material in this embodiment contains water-soluble inorganic powder, when heated to high temperatures due to thermal runaway, the uniformly dispersed water-soluble inorganic powder itself sintersects to form a porous body with a certain strength, thereby increasing the pressure resistance. This allows the distance between cells to be kept constant, maintaining effective thermal insulation and more effectively suppressing chain explosions between cells. In this embodiment, when prioritizing the amount of heat absorbed and delaying the time required to reach the meltdown temperature, it is preferable to use a water-soluble inorganic powder as the heat absorber.

[0075] The water-soluble inorganic powder of this embodiment dissolves in an aqueous solvent. This makes it easier to dissolve in an aqueous solvent, thus ensuring that the water-soluble inorganic powder is uniformly distributed within the contents. In this specification, "water-soluble" means dissolving 1 g or more in 100 g of water at 20°C. Therefore, the water-soluble inorganic powder of this embodiment may be an inorganic powder that dissolves 1 g or more in 100 g of water at 20°C.

[0076] In this embodiment, the solubility of the water-soluble inorganic powder is preferably 1 g or more per 100 g of water at 20°C. From the viewpoint of the stability and dispersibility of the water-soluble inorganic powder in the endothermic body and sinterability upon high-temperature heating, the solubility of the water-soluble inorganic powder (per 100 g of water at 20°C) is preferably 1 g or more and 100 g or less, more preferably 2 g or more and 90 g or less, even more preferably 3 g or more and 80 g or less, even more preferably 5 g or more and 70 g or less, even more preferably 15 g or more and 60 g or less, and particularly preferably 25 g or more and 50 g or less. The solubility of water-soluble inorganic powders in 100g of water at 20°C can be determined by appropriately combining the above upper and lower limits. Since the solubility of the water-soluble inorganic powder at 20°C is within the above range, solubility is ensured, and the water-soluble inorganic powder is uniformly dissolved or dispersed in the aqueous solvent, making it easier to form a homogeneous porous body during sintering.

[0077] The solubility of the water-soluble inorganic powder in this embodiment is preferably 10 g or more per 100 g of water at 60°C. The solubility of the water-soluble inorganic powder (per 100 g of water at 60°C) is preferably 10 g or more and 150 g or less, more preferably 15 g or more and 120 g or less, even more preferably 20 g or more and 100 g or less, even more preferably 25 g or more and 80 g or less, even more preferably 30 g or more and 60 g or less, and particularly preferably 35 g or more. The solubility of water-soluble inorganic powders in 100g of water at 60°C can be determined by appropriately adjusting the above upper and lower limits.

[0078] The solubility of the water-soluble inorganic powder in this embodiment is preferably 15 g or more per 100 g of water at 80°C. The solubility of the water-soluble inorganic powder (per 100 g of water at 80°C) is preferably 15 g or more and 160 g or less, more preferably 20 g or more and 120 g or less, even more preferably 25 g or more and 100 g or less, even more preferably 30 g or more and 80 g or less, and particularly preferably 35 g or more and 60 g or less. The solubility of water-soluble inorganic powders in 100g of water at 80°C can be determined by appropriately rearranging the above upper and lower limits.

[0079] The solubility of the water-soluble inorganic powder in this embodiment is preferably 15 g or more per 100 g of water at 100°C. The solubility of the water-soluble inorganic powder (per 100 g of water at 100°C) can be, for example, 15 g or more and 170 g or less, preferably 20 g or more and 130 g or less, more preferably 25 g or more and 100 g or less, even more preferably 30 g or more and 80 g or less, and particularly preferably 35 g or more and 60 g or less. The solubility of water-soluble inorganic powders in 100g of water at 100°C can be adjusted by appropriately rearranging the above upper and lower limits.

[0080] The preferred solubility of the water-soluble inorganic powder in this embodiment is 1 g to 90 g per 100 g of water at 20°C, more preferably 5 g to 90 g, 5 g to 100 g per 100 g of water at 40°C, 10 g to 150 g per 100 g of water at 60°C, 15 g to 160 g per 100 g of water at 80°C, and 15 g to 170 g per 100 g of water at 100°C. It is preferable, from the viewpoint of exhibiting suitable endothermic and pressure-resistant properties, that the solubility of the water-soluble inorganic powder at each temperature falls within the above range. The solubility of water-soluble inorganic powders in 100g of water at 20°C can be adjusted by appropriately rearranging the above upper and lower limits.

[0081] The method for measuring solubility in this specification is as follows: After weighing a specified amount of the inorganic powder to be measured into a glass bottle, 100 g of pure water (pH=7) is added to the glass bottle, and a mixed solution is prepared by stirring at a rotation speed of 80 rpm on a mix rotor for 24 hours at 20°C, 40°C, 60°C, 80°C, and 100°C at 1 atm. The transmittance of the mixed solution after 24 hours of stirring is then measured under the following conditions. In this process, the transmittance is measured by changing the amount of water-soluble inorganic powder dissolved, and the upper limit amount (g) at which the transmittance reaches 99% is defined as the solubility of the water-soluble inorganic powder in water. <Transmittance measurement conditions> Dynamic light scattering (DLS) measurement Equipment: DLS-8000 DLS measuring device manufactured by Otsuka Electronics Laser wavelength, power output: 488nm / 100mW Sample cell: NMR tube

[0082] In this embodiment, the water-soluble inorganic powder is preferably solid at room temperature. Furthermore, in the endothermic body of this embodiment, it is preferable that an aqueous solution containing a water-based solvent and the water-soluble inorganic powder is filled into a bag as the contents of the endothermic body. Since the endothermic body is filled with an aqueous solution containing an aqueous solvent and water-soluble inorganic powder, the water-soluble inorganic powder is completely dissolved in the aqueous solvent, resulting in a uniform distribution of water-soluble inorganic powder within the contents, and thus a homogeneous porous body can be formed. The transmittance of the aqueous solution is preferably 99% or higher, and more preferably 99.5% or higher.

[0083] The heat absorption amount and thermal decomposition start temperature of the water-soluble inorganic powder can be within a preferred range for the inorganic powder. Similarly, the preferred shape and form of the water-soluble inorganic powder can also be within a preferred range for the inorganic powder.

[0084] The water-soluble inorganic powder material of this embodiment is preferably composed of a water-soluble inorganic salt. Furthermore, the water-soluble inorganic salt is preferably one or more compounds consisting of an inorganic cation and a combination of organic-inorganic anions, similar to the inorganic powder described above. Examples of the inorganic cations include alkali metal ions, alkaline earth metal ions, aluminum ions, zinc ions, silver ions, copper(I) ions, and copper(II) ions, and it is preferable that they be one or more selected from the group consisting of potassium ions, calcium ions, magnesium ions, and aluminum ions. The organic and inorganic anions are preferably one or more selected from oxygen ions, sulfate ions, halogen ions (chloride ions, fluoride ions, bromide ions, etc.), nitrate ions, carbonate ions, acetate ions, and phosphate ions. The water-soluble inorganic powder of this embodiment is preferably composed of one or more compounds selected from the group consisting of chlorides, sulfates, carbonates, nitrates, phosphates, acetates, alkali metal oxides, and alkaline earth metal oxides. This allows for excellent solubility in aqueous solvents. The water-soluble inorganic powder before mixing with the aqueous solvent may be anhydrous or hydrated, as long as it exhibits the desired solubility described above. Note that the hydrate usually exists as an anhydrous form within the bag.

[0085] The water-soluble inorganic powder or water-soluble inorganic salt of this embodiment is preferably, specifically, a chloride such as sodium chloride, potassium chloride, or ammonium chloride; a sulfate such as sodium sulfate, potassium sulfate, magnesium sulfate, aluminum sulfate, or alum; a carbonate such as sodium bicarbonate, sodium sesquicarbonate, sodium carbonate, potassium carbonate, potassium sesquicarbonate, or ammonium carbonate; a nitrate such as sodium nitrate, potassium nitrate, or calcium nitrate; a phosphate such as sodium phosphate, sodium dihydrogen phosphate, dipotassium hydrogen phosphate, or sodium polyphosphate; an acetate such as zinc acetate, sodium acetate, potassium acetate, copper(I) acetate, or copper(II) acetate; an oxide such as chromium oxide, barium oxide, or boric acid oxide; or a hydrate thereof. Among the above, magnesium sulfate or magnesium sulfate heptahydrate is particularly preferred. The water-soluble inorganic powders of this embodiment may be used individually or in combination with the examples described above.

[0086] (Inorganic fibers) The contents of the heat-absorbing element in this embodiment may optionally contain inorganic fibers. The inorganic fibers are a fiber aggregate in which fibers made of inorganic material are intertwined, or a porous body made of inorganic material, and the inorganic powder acts as a foaming nucleating agent, facilitating the formation of the porous body. Furthermore, when the inorganic powder transforms into a porous body, a porous composite containing the inorganic fibers and inorganic powder can be formed. This makes it easier to form an insulating wall with desired mechanical strength when the temperature exceeds the thermal runaway temperature, for example. In this embodiment, when prioritizing the amount of heat absorbed and delaying the time required to reach the meltdown temperature, it is preferable to use inorganic fibers as the heat-absorbing element.

[0087] Specifically, the inorganic fibers include woven fabrics (glass cloth or silica cloth), nonwoven fabrics (glass fibers or ceramic fibers), and cotton-like materials (including not only glass wool, rock wool, and ceramic wool, but also spongy materials). The inorganic fibers of this embodiment preferably have 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 is defined as the temperature at which the rate of change in volume (in the thickness direction) becomes -20% when the test specimen is held at each temperature for 30 minutes while its temperature is changed in 100°C increments from 200°C to 700°C. The inorganic fibers of this embodiment are porous materials having at least one of a specific air permeability resistance, specific porosity, specific tortuousity, or specific void ratio. This makes it easier for the entire heat-absorbing material to form a relatively stable porous material even in high-temperature ranges (temperatures exceeding the critical temperature (e.g., 150°C) to the runaway thermal temperature (e.g., around 1000°C)), thus making it easier to act as an insulator. In particular, if the inorganic fibers have a specific void ratio, they can be combined with inorganic powder to become an even better insulator.

[0088] <Porosity> The average porosity of the inorganic fibers in 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 inorganic fibers is a value obtained from the bulk density and true density described below, and is a density based on the volume occupied by the inorganic fibers. Bulk density is a density based on the volume including the voids contained in the inorganic fibers. In contrast, true density is a density based on the volume occupied by the material of the inorganic fibers. The average porosity (%) can be calculated from the bulk density ρf and true density ρr shown below using the following equation (1). Average porosity (%)=((1 / ρf)-(1 / ρr)) / (1 / ρf)×100...Equation (1)

[0089] <Bulk density> The bulk density ρf of the inorganic fiber in this embodiment is 0.020 g / cm³. 3 More than 1g / cm 3 The following is preferred, and more preferably, 0.022 g / cm³. 3 More than 0.5g / cm 3 More preferably, 0.024 g / cm³ 3 More than 0.1g / cm 3 The following is particularly preferred: 0.026 g / cm³ 3 More than 0.07g / cm 3 The following applies: After measuring the dimensions of the inorganic fiber and calculating its bulk volume V, the mass M of the inorganic fiber is measured using a precision balance. From the obtained mass M and bulk volume V, the bulk density of the inorganic fiber can be determined using the following equation (2). Bulk density ρf(g / cm³) 3 )=M / V · Formula (2)

[0090] <True density> The true density ρr of the inorganic fiber in this embodiment is 0.5 g / cm³. 3 More than 10g / cm 3 The following is preferable, and more preferably, 1 g / cm³ 3 More than 7g / cm 3 More preferably, 1.5 g / cm³ 3 More than 5g / cm 3 The following is particularly preferable: 2 g / cm³ 3 More than 3g / cm 3 The following applies: There are no particular restrictions on the method for measuring the true density ρr of inorganic fibers, but it can be calculated by the buoyancy method using a mixed solution consisting of n-heptane, carbon tetrachloride, and ethylene dibromide. Specifically, first, a sample piece of inorganic fiber of an appropriate size is placed in a stoppered test tube. Next, a mixed solvent, which is a mixture of the three solvents in appropriate proportions, is added to the test tube, and it is immersed in a 30°C constant temperature bath. 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 operation is repeated until the test piece floats in the liquid. Finally, the density of the mixed solvent is measured using a Gay-Lussac gravity bottle.

[0091] <Composition of inorganic fibers> Examples of materials constituting the inorganic fibers of this embodiment or inorganic materials contained in said inorganic fibers include elements selected from the group consisting of silicon, titanium, barium, zirconium, zinc, calcium, magnesium, cerium, aluminum, indium, tin, and lanthanum, single oxides or composite oxides of said elements, single sulfides or composite sulfides of said elements, and single phosphate compounds or composite phosphate compounds of said elements, with silicon, titanium, zirconium, magnesium, aluminum, indium, tin, and their single or composite oxides being preferred. Specifically, the inorganic materials constituting the inorganic fibers 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.

[0092] <Shape of inorganic material fibers> The inorganic fiber shape of this embodiment can be selected from yarn-like, fibrous, fiber bundle-like, fiber aggregate-like, cotton-like, woven / knitted, nonwoven fabric-like, etc. In this specification, "woven / knitted" refers to a woven or knitted fabric.

[0093] If the inorganic fibers according to this embodiment are woven fabric, then known weaving methods such as plain weave, twill weave, satin weave, leno weave, and blind weave can be appropriately adopted as the weaving method of the fabric. From among these weaving methods, it is preferable to adopt a weaving method in which the resistance of fluid passage through the spaces between the connecting holes, that is, the spaces for each individual (eye) formed by the intersection of the warp and weft lines (for example, the air permeability resistance described later) is within a predetermined range. From these viewpoints, it is preferable to adopt weaving methods such as plain weave, twill weave, satin weave, leno weave, and leno weave.

[0094] If the inorganic fiber according to this embodiment is a knitted fabric, the knitting method for the fabric may include warp knitting, which knits vertically, such as lace knitting, raschel knitting, tricot knitting, and van dyke knitting, and weft knitting, which knits horizontally, such as weft knitting, plain knitting, rib knitting, tubular knitting, jersey knitting, kanako knitting, rib knitting, and jacquard knitting, and known knitting methods can be appropriately adopted. From among these knitting methods, it is preferable to adopt a knitting method in which the resistance of fluid passage through the communication holes (for example, the air permeability resistance described later) is within a predetermined range. Furthermore, various knitting machines such as warp knitting machines, weft knitting machines, circular knitting machines, and raschel knitting machines may be used.

[0095] When the inorganic fibers according to this embodiment are woven or knitted fabrics, the woven or knitted yarn used is not particularly limited, and its fineness is preferably 50 dtex or more and 8000 dtex or less, more preferably 100 dtex or more and 3000 dtex or less. Furthermore, the twisting method of the woven or knitted yarn is not limited, and the twisting method may be dry twisting, wet twisting by immersion in water, or a combination thereof. Moreover, the direction of the twist is not particularly limited, and may be right-hand twist, left-hand twist, or a combination thereof. The woven or knitted yarn used in this embodiment may be false-twisted yarn, filament yarn, or yarn processed by the POY·DTY method or the PTY (Producers Textured Yarn) method. The conditions for the woven or knitted yarn used as described above can be appropriately selected depending on the intended use or the type of aqueous solvent. Furthermore, the material of the woven or knitted yarn may be the materials constituting the inorganic fibers described above or the inorganic materials contained within those inorganic fibers.

[0096] The BET specific surface area of ​​inorganic fibers ranges from 0.3 to 5000 m². 2 It can also be / g, 10-2000m 2 It can also be / g, 30-1600m 2 / g is also acceptable. The BET specific surface area of ​​the inorganic fiber described above is measured using a specific surface area meter (BELSORP-mini, manufactured by Microtrac-Bel Co., Ltd.), and the surface area per gram of sample, measured from the amount of nitrogen gas adsorbed by the BET method, is used as the specific surface area (m²).2 It was calculated as ( / g).

[0097] When the inorganic fibers of this embodiment are composed of a nonwoven fabric, the average fiber diameter of all the fibers constituting the nonwoven fabric (fibers made from the inorganic raw material) 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 be within the above range because it is easier to secure the desired porosity. The average fiber diameter can be measured by microscopic observation or by image analysis results using a fiber length measuring device (e.g., KAJAANI Fiber Lab.).

[0098] Furthermore, when the inorganic fibers of this embodiment are composed of a nonwoven fabric, the average fiber length of all the fibers (raw material 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 the fibers constituting the nonwoven fabric is within the above range, as this makes it easier to secure the desired porosity. The average fiber length can be determined by measuring the average fiber diameter by microscopic observation or by image analysis results using a fiber length measuring device (e.g., KAJAANI Fiber Lab.). When the inorganic fibers of this embodiment are formed from a cotton-like material, the average fiber length of all the fibers (raw material 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 the fibers constituting the cotton-like material is within the above range, as this makes it easier to secure the desired porosity. The average fiber length can be determined by measuring the average fiber diameter using microscopic observation or image analysis results from a fiber length measuring device (e.g., KAJAANI Fiber Lab.). In this specification, although cotton-like material is a type of nonwoven fabric, it refers to material that is in the form of fibers and in a shape other than cloth (or flat plate).

[0099] <Preferred embodiment of inorganic fiber> Preferred embodiments of the inorganic fibers in this embodiment are glass cloth, ceramic wool, rock wool, and glass wool.

[0100] In this embodiment, the inorganic fiber content is preferably 0% to 50% by mass, more preferably 1% to 30% by mass, even more preferably 1% to 10% by mass, preferably 1% to 5% by mass, and particularly preferably 1% to 3% by mass, based on the total amount (100% by mass) of the contents of the heat absorber. The preferred range for the inorganic fiber content can be determined by appropriately combining the above upper and lower limits. When the inorganic fiber content is within the above range, it exhibits superior heat absorption and pressure resistance, and can change from a heat absorption effect to a heat insulating effect in high-temperature ranges.

[0101] (Additives) The contents or dispersion (a) of the heat absorber in this embodiment may optionally 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. While these additives are optional components, when used, it is preferable to use them in proportions appropriate to the purpose of each additive and without impairing the effects of the present disclosure. Although such proportions cannot be determined in general terms, the content of the various additives is preferably 0% by mass or more and 50% by mass or less, and more preferably 10% by mass or more and 40% by mass or less, relative to the total amount (mass) of the aqueous solvent and various additives used in the present disclosure. Furthermore, the preferred range for the content of each additive can be appropriately adjusted by combining the above upper and lower limits.

[0102] Examples of the above-mentioned UV absorbers 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'-xanthen carboxy-5'-methylphenyl)benzotriazole, 2-(2'-o-nitrobenzyloxy-5'-methylphenyl)benzotriazole, 2-xanthen carboxy-4-dodecyloxybenzophenone, and 2-o-nitrobenzyloxy-4-dodecyloxybenzophenone. These UV absorbers can be used alone or in combination of two or more.

[0103] Examples of the above-mentioned antioxidants include "Sumiriser BBM-S" and "Sumiriser GA-80" manufactured by Sumitomo Chemical Co., Ltd. Examples of the above-mentioned organic solvents 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. These organic solvents can be used individually or in combination of two or more. Examples of the inorganic fillers mentioned above include fused silica, crystalline silica, alumina, silicon nitride, and aluminum hydroxide. Examples of viscosity modifiers such as the thickening agents mentioned above include various tackifying resins such as rosin-based, polymerized rosin-based, polymerized rosin ester-based, rosin phenol-based, stabilized rosin ester-based, disproportionated rosin ester-based, terpene-based, terpene phenol-based lipids, and petroleum resin-based resins. Examples of known crosslinking agents include isocyanates, epoxys, aziridines, polyvalent metal salts, metal chelates, ketohydrazides, oxazolines, carbodiimides, silanes, and glycidyl(alkoxy)epoxysilanes.

[0104] Examples of the above flame retardants include inorganic phosphorus compounds such as red phosphorus, monoammonium phosphate, diammonium phosphate, triammonium phosphate, polyammonium phosphate, and other ammonium phosphates; phosphate ester compounds, phosphonic acid compounds, phosphinic acid compounds, phosphine oxide compounds, phospholane compounds, organic nitrogen-containing phosphorus compounds, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, and 10-(2,5-dihydrooxyphenyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxy Examples of flame retardants include cyclic organophosphorus compounds such as 10-(2,7-dihydrooxynaphthyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxide, and derivatives 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 phenothiazines; silicone-based flame retardants such as silicone oil, silicone rubber, and silicone resins; 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 individually or in combination of two or more. When using these flame retardants, it is preferable that the amount is in the range of 0.1 to 20% by mass relative to the entire contents of the endothermic body or the entire dispersion (a).

[0105] (Method for manufacturing a heat absorber) As an example of a method for manufacturing the endothermic body of this embodiment, as described above, the method includes the steps of: (1) preparing a dispersion (a) containing a water-soluble organic monomer and a water-swellable clay mineral, which are reaction raw materials for the hydrogel body, an aqueous solvent, and a polymerization initiator, catalyst, and / or additives as needed; (2) filling the bag with the dispersion (a) and sealing the bag; and (3) gelling the water-soluble organic monomer inside the bag at a desired polymerization temperature. The inorganic powder of this embodiment can be added as a contents during steps (1) and (2) above. Furthermore, in one aspect of this embodiment, an alternative method for producing the endothermic body includes the steps of: (4) preparing a dispersion (a) by mixing a water-soluble organic monomer and a water-swellable clay mineral, which are reaction raw materials for the hydrogel body, a polymerization initiator, and an aqueous solvent or organic solvent; (5) heating the dispersion (a) to gel and prepare an organic-inorganic composite hydrogel body; (6) impregnating the organic-inorganic composite hydrogel body in an aqueous solvent for a desired time to swell the organic-inorganic composite hydrogel in the aqueous solvent; and (7) filling the opening of the bag with the swollen organic-inorganic composite hydrogel or a mixture (1) containing the swollen organic-inorganic composite hydrogel, and then sealing the opening of the bag. The inorganic powder of this embodiment can be added in any of the above steps (4) to (7). Furthermore, as an alternative method for manufacturing the heat-absorbing body, after step (5) above, instead of steps (6) and (7) above, a step (8) may be provided in which the hydrogel body, aqueous solvent, and inorganic powder are separately filled into the opening of the bag, and then the opening of the bag is sealed. Furthermore, instead of step (6), a step (9) may be provided in which a mixture (including a mixed liquid) (1) is prepared in advance by impregnating or dispersing the hydrogel body and / or inorganic powder in the aqueous solvent, and then the mixture (1) is filled into the opening of the bag, and the opening of the bag is sealed. The mixture (1) contains a hydrogel body and an aqueous solvent, and may optionally contain one or more selected from the group consisting of antifreeze and additives. The mixture (1) preferably contains 1 to 50% by mass (preferably 4 to 35% by mass) of the hydrogel body, 1 to 98% by mass (preferably 2 to 91% by mass) of the aqueous solvent, 1 to 80% by mass (preferably 3 to 75% by mass) of the inorganic powder, 0 to 50% by mass of the antifreeze agent, and 0 to 10% by mass of the additives, based on the total amount (100% by mass) of the mixture (1). More preferably, it contains 5 to 30% by mass of the hydrogel body, 10 to 80% by mass of the aqueous solvent, 5 to 70% by mass of the inorganic powder, 0 to 40% by mass of the antifreeze agent, and 0 to 10% by mass of the additives. In one aspect of this embodiment, the method for producing the heat-absorbing body includes, as described above, the steps of: preparing a dispersion (a) containing a water-soluble organic monomer and a water-swellable clay mineral as reaction raw materials, an aqueous solvent, and optionally a polymerization initiator, catalyst, low-volatility solvent and / or additives; filling the bag with the dispersion (a) and inorganic powder through the opening and then sealing it; and gelling the water-soluble organic monomer inside the bag at a desired polymerization temperature. Instead of the aforementioned dispersion (a), a dispersion (b) may be used, which is a mixture of dispersion (a) with an antifreeze and / or additives added as needed. Furthermore, in another aspect of this embodiment, an alternative method for producing the endothermic body includes the steps of: preparing a mixed solution (2) by mixing a water-soluble organic monomer and a water-swellable clay mineral as reaction raw materials, a polymerization initiator, an aqueous solvent or organic solvent, and an inorganic powder; heating the mixed solution (2) to gel it and prepare an organic-inorganic composite hydrogel body; impregnating the inorganic powder and the organic-inorganic composite hydrogel body in an 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 powder through the opening of a bag and then sealing it. In the heat absorption method of this embodiment, even when inorganic powder is incorporated into the contents of the heat absorption body, the heat absorption body can be molded by the above method. The mixed solution (2) preferably contains 1 to 80% by mass of inorganic powder and 20 to 99% by mass of dispersion (a) based on the total amount (100% by mass) of the mixed solution (2).

[0106] A suitable heat-absorbing body of this embodiment may be a bag containing, as contents of the bag, an aqueous solvent (for example, 20-60% by mass of water relative to the total amount of contents), a hydrogel body (for example, 10-30% by mass of NC gel relative to the total amount of contents), and an inorganic powder (for example, 10-50% by mass of aluminum hydroxide relative to the total amount of contents). This makes it possible to provide a heat-absorbing body that has a better heat absorption capacity and a temperature rise suppression effect, and that can change from an endothermic effect to an insulating effect in the high-temperature range. In this embodiment, the total content of the contents of the bag, consisting of an aqueous solvent, a hydrogel body, and inorganic powder, is preferably 80 to 100% by mass, more preferably 92 to 99.5% by mass, and even more preferably 93 to 99% by mass, relative to the total amount of contents of the bag (100% by mass). In this embodiment, the total content of the contents of the bag, consisting of an aqueous solvent, a hydrogel body, inorganic powder, an antifreeze, and additives, 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, relative to the total amount of contents of the bag (100% by mass). The upper and lower limits of the total content mentioned above can be adjusted as appropriate.

[0107] (Preferred embodiment of the heat absorber) The heat-absorbing element of this embodiment preferably exhibits high cushioning properties and / or excellent pressure resistance when heated. Each preferred embodiment will be described in detail below. <High-cushioning heat-absorbing material> A preferred heat-absorbing body of this embodiment is a heat-absorbing body exhibiting high cushioning properties, comprising a bag and a hydrogel and an inorganic powder as contents of the bag, wherein the hydrogel comprises a hydrogel body formed from a three-dimensional polymer chain and an aqueous solvent. In this specification, a heat-absorbing material exhibiting high cushioning properties is also referred to as a high-cushioning heat-absorbing material. The term "exhibiting high cushioning properties" refers to having excellent cushioning capabilities, and when the contents of the bag include a hydrogel (hydrogel body and an aqueous solvent), it tends to exhibit high cushioning properties. Furthermore, "exhibiting high cushioning properties" specifically means that the cushioning percentage (%) represented by the following formula (I) is preferably 90% or higher, and more preferably 93% or higher. By exhibiting cushioning properties of 90% or higher, the material becomes more responsive to relatively short-term deformations such as expansion and contraction due to charging and discharging of battery cells. The upper limit of the high cushioning properties may be 100%. [Math 4] "Cushioning (%) = h"a / h b ×100 Equation (I) (In the above formula (I), h a This is the height (mm) of the pressed area after pressing the surface of a high-cushioning heat absorber at 1 MPa for 60 seconds, and then releasing the pressure, and 5 minutes have passed. b This represents the height (mm) before pressing the surface of the high-cushioning heat absorber for 60 seconds at 1 MPa. In the heat-absorbing body of this embodiment, when cushioning is important, it is preferable not only that the cushioning (%) represented by formula (I) be 90% or more, but also that the content of the antifreeze is controlled to a predetermined value or less. That is, when cushioning is important, the content of the antifreeze can be 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 especially preferably substantially none (0.5% by mass or less) with respect to the total amount of contents. When the amount of antifreeze exceeds a predetermined amount relative to the total volume of contents, the number of crosslinking points in the gel decreases, making it more flexible and consequently reducing its cushioning properties. On the other hand, under high-temperature heating conditions, the gel vaporizes, which helps to lubricate and flow the inorganic powder, allowing it to be uniformly distributed, and consequently increasing its strength. Furthermore, in the heat-absorbing body of this embodiment, when cushioning is important, not only the amount of antifreeze, but also the amount of hydrogel contained in the contents, preferably the total amount of hydrogel (hydrogel body and aqueous solvent) and inorganic powder, can be preferably more than 80% by mass, more preferably 83% by mass or more, even more preferably 87% by mass or more, even more preferably 91% by mass or more, even more preferably 94% by mass or more, even more preferably 98% by mass or more, and particularly preferably 100% by mass, relative to the total amount of contents. It is thought that when the total amount of hydrogel and inorganic powder increases relative to the total amount of contents, the inorganic powder reinforces the hydrogel, which has a high recovery rate after deformation, resulting in high cushioning properties.

[0108] <High-pressure heat-absorbing material> A preferred heat-absorbing body of this embodiment comprises a bag into which contents can be filled, an aqueous solvent, and inorganic powder, which are filled into the contents, and exhibits excellent pressure resistance when heated. In this specification, a heat absorber exhibiting excellent pressure resistance when heated is also referred to as a high-pressure heat absorber. Such high-pressure heat absorbers tend to exhibit excellent pressure resistance when heated to high temperatures (for example, 800°C or higher) due to thermal runaway of a battery or the like. The statement that the endothermic material exhibits high pressure resistance when heated means that it exhibits high pressure resistance when heated, and if the contents of the bag further include hydrogel (hydrogel body and aqueous solvent), it shows an effect of improving pressure resistance. Similarly, if the contents of the bag include inorganic powder, it shows an effect of improving pressure resistance. In particular, because the contents of the bag include both hydrogel (hydrogel body and aqueous solvent) and inorganic powder, it tends to exhibit particularly excellent high pressure resistance when heated. Therefore, a preferred embodiment of the high-pressure heat-absorbing body of this embodiment may be a high-pressure heat-absorbing body comprising a bag into which contents can be filled, a hydrogel composed of a hydrogel body and an aqueous solvent, and an inorganic powder, wherein the hydrogel and the inorganic powder are a composite and filled into the contents. A more preferred embodiment of the high-pressure heat-absorbing body of this embodiment may include a bag into which contents can be filled, a hydrogel composed of a hydrogel body and an aqueous solvent, and an inorganic powder, wherein the hydrogel and the inorganic powder form a composite and are filled into the contents. In this case, it is preferable that the inorganic powder is uniformly dispersed as the contents. The presence of hydrogel and inorganic powder together temporarily forms a foamed film during thermal runaway, and it is considered that this foamed film acts as a reinforcing dispersion. Furthermore, it is thought that the presence of hydrogel and inorganic powder together enhances the dispersibility of the inorganic powder, resulting in a synergistic effect that enhances high pressure resistance. Furthermore, uniform dispersion means, for example, that when the composite material is removed, the difference in concentration (mass%) of the inorganic powder at both ends of the composite material, up to approximately 3 mm from the edge, can be within ±15%. Furthermore, "exhibiting high pressure resistance when heated" specifically means that, after heating the heat absorber until the side opposite to the heating surface reaches a predetermined temperature, the thickness change rate (%) represented by the following formula (II) is preferably 70% or more, more preferably 75% or more, even more preferably 85% or more, and particularly preferably 90% or more. By exhibiting the above thickness change rate of 70% or more, the heat absorber has excellent pressure resistance, and thus can effectively suppress and prevent chain explosions between cells. The upper limit of the thickness change rate may be 100%. [Number 5] Formula (II): "Thickness change rate (%) = (Thickness of the heat absorber after pressing it with 0.5 MPa for 60 seconds against the surface of the heated high-pressure heat absorber) / (Thickness of the heat absorber before pressing it with 0.5 MPa for 60 seconds against the surface of the heated high-pressure heat absorber) × 100" In the above formula (II), "the thickness of the heat-absorbing body after being pressed at 0.5 MPa for 60 seconds against the surface of the heated high-pressure heat-absorbing body" is the average thickness of the heat-absorbing body (arithmetic mean of the thicknesses at any 5 locations) after being pressed at 0.5 MPa for 60 seconds against one surface of the high-pressure heat-absorbing body after it has been heated to a predetermined temperature or higher (preferably against one surface of the high-pressure heat-absorbing body after it has been heated under the following heating conditions (the heated surface which is the surface to which radiant heat is directly applied)) (approximately within 20 minutes from immediately after pressurization). Similarly, in formula (II) above, "the thickness of the heat absorber before applying pressure at 0.5 MPa for 60 seconds to the surface of the heated heat absorber" is the average thickness of the heat absorber (arithmetic mean of the thicknesses at any five locations) after heating one surface of the heat absorber to a predetermined temperature or higher (preferably after heating under the heating conditions described below) and before applying pressure at 0.5 MPa for 60 seconds to one heated surface of the heat absorber. Heating conditions: "50 kW / m² due to radiant heat" 2After heating the heat-absorbing body with the amount of heat required until the temperature of the side opposite to the heating surface (back surface) reached a predetermined temperature, the heat-absorbing body was allowed to dissipate heat at room temperature (22-28°C) and naturally cooled until the surface temperature of the heat-absorbing body returned to room temperature (22-28°C), and the percentage change in thickness before and after heating was calculated. Furthermore, pressure was applied to the heating surface of the heat-absorbing element by pressing it down at 0.5 MPa for 60 seconds. In the above heating conditions, the "predetermined temperature" is the temperature at which the heat absorber can become porous, and can be set according to the operating environment of the heat absorber, the required explosion-proof properties, and the assumed thermal runaway initiation temperature. The "predetermined temperature" can be, for example, 240°C (240°C or higher), preferably 200°C (200°C or higher), more preferably 180°C (180°C or higher), even more preferably 160°C (160°C or higher), even more preferably 150°C or higher, and particularly preferably 120°C (120°C or higher). For example, if the thickness change rate (%) after heating of a heat absorber heated until the temperature of the side opposite to the heating surface (back surface) reaches 150°C is greater than or equal to a predetermined value, then the heat absorber can achieve a thickness change rate greater than or equal to a predetermined value even in the temperature range of 150°C or higher. In the heat-absorbing element of this embodiment, when high pressure resistance is important, it is preferable to include a hydrogel (hydrogel body and aqueous solvent) and an inorganic powder.

[0109] (Other preferred forms of heat absorbers) Another preferred embodiment of the heat absorber of this disclosure is one in which the endothermic onset temperature is 400°C or less and the endothermic peak temperature is in the range of at least 80°C to 400°C, and is given by the following equation (II): [Number 6] "Percentage change in thickness (%) = (Thickness of the heat absorber after applying pressure at 0.5 MPa for 60 seconds to the surface of the heat absorber heated under the following heating conditions) / (Thickness of the heat absorber before applying pressure at 0.5 MPa for 60 seconds to the surface of the heat absorber heated under the following heating conditions) × 100" Heating conditions: "50 kW / m² due to radiant heat" 2After heating the heat-absorbing body with the amount of heat required until the temperature of the side opposite to the heating surface (back surface) reached a predetermined temperature, the heat-absorbing body was allowed to dissipate heat at room temperature (22-28°C) and naturally cool until the surface temperature of the heat-absorbing body returned to room temperature (22-28°C), and the percentage change in thickness before and after heating was calculated. Furthermore, pressure was applied to the heating surface of the high-pressure heat-absorbing material by pressing it down at 0.5 MPa for 60 seconds. This is a heat-absorbing material whose thickness change rate (%), expressed as , is 70% or more. This results in excellent pressure resistance, heat absorption capacity, and temperature rise suppression effect, and the effect can change from heat absorption to heat insulation in the high-temperature range. The "specified temperature" in the above heating conditions is as explained earlier.

[0110] <Particularly preferred form of heat absorber> In this embodiment, when pressure resistance is important, the endothermic body comprises a bag into which contents can be filled, and a hydrogel and an inorganic powder filled into the bag as contents, wherein the inorganic powder is a sparingly soluble inorganic powder. As described above, the sparingly soluble inorganic powder is an inorganic powder that dissolves in less than 1 g per 100 g of water at 20°C, and examples include compounds excluding water-soluble inorganic powders from the compounds exemplified in the (inorganic powder) section above, such as aluminum hydroxide and calcium sulfate dihydrate. The combination of poorly soluble inorganic powders and hydrogels can further improve the mechanical strength of the heat-absorbing body after sintering. On the other hand, in this embodiment, when emphasizing the amount of heat absorbed and the effect of suppressing temperature rise, it is preferable that the endotherm has a bag that can be filled with contents, and that the contents filled in the bag are a hydrogel and an inorganic powder, and that the inorganic powder is a water-soluble inorganic powder. As described above, the sparingly soluble inorganic powder is an inorganic powder that dissolves at a rate of 1 g or more in 100 g of water at 20°C, and examples include water-soluble inorganic powders such as magnesium sulfate heptahydrate. For the water-soluble inorganic powder, refer to the contents of the "Preferred Inorganic Powder" section above. By using water-soluble inorganic powder as the inorganic powder, it becomes easier to dissolve in the aqueous solvent in the hydrogel, and the water-soluble inorganic powder is more likely to be uniformly present within the contents. As a result, the heat absorption and temperature rise suppression effect are further improved, and at temperatures exceeding the thermal runaway temperature (e.g., around 200°C), the entire water-soluble inorganic powder tends to form a homogeneous porous body, allowing it to act more effectively as an insulator.

[0111] [Secondary battery module] The type of secondary battery on which the heat-absorbing element of this embodiment can be mounted is not particularly limited, and examples include lithium-ion batteries, lithium-ion polymer batteries, lead-acid batteries, nickel-metal hydride batteries, nickel-cadmium batteries, nickel-iron batteries, nickel-zinc batteries, silver oxide-zinc batteries, metal-air batteries, polyvalent cation batteries, capacitors, and the like. Among these, lithium-ion batteries are a particularly suitable application.

[0112] The secondary battery module capable of mounting a heat-absorbing element according to this embodiment is a secondary battery mounted on a mobile device such as a vehicle or an aircraft (especially a drone), and has a plurality of battery cells and a case that houses such plurality of battery cells. The battery cells constituting the secondary battery module (hereinafter also referred to as battery cells) can be, for example, battery outer film used as the outer material, and a battery element comprising 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 enclosed within the outer material. The secondary battery module capable of mounting the heat-absorbing element of this embodiment will be described below with reference to Figure 1. Figure 1 shows a cross-sectional view of a stacked battery 20 as an example of a secondary battery. However, the secondary battery capable of mounting the heat-absorbing element of this embodiment is not limited to the flat-shaped stacked battery 20 shown in Figure 1. The secondary battery capable of mounting the heat-absorbing element of this embodiment may be cylindrical in shape, such as a wound-type secondary battery, or a cylindrical secondary battery may be modified to a rectangular, flat shape. In this embodiment, the stacked battery 20 has a structure in which a flattened, roughly rectangular battery element 10, on which the charge-discharge reaction substantially proceeds, is sealed inside the battery casing materials 18a,b. The battery element 10 has a configuration 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 positive electrode active material is arranged 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 negative electrode active material is arranged on both sides of a negative electrode current collector 17. One positive electrode material layer 11 and a negative electrode material layer 16 adjacent to the positive electrode material layer 11 are arranged to face each other via the electrolyte layer 14, and the positive electrode, electrolyte layer 14, and negative electrode are stacked sequentially. As a result, adjacent positive electrodes, electrolyte layers 14, and negative electrodes form one single cell body. The stacked battery 20 shown in Figure 1 has a configuration in which multiple such single cell bodies are stacked and electrically connected in parallel. Furthermore, an activated carbon layer 19 is installed to adsorb components derived from the positive electrode active material that may melt or sublimate when the battery is exposed to high temperatures. Furthermore, as shown in Figure 1, the positive electrode current collector 12 and the negative electrode current collector 17 are each attached to a positive electrode terminal 13 and a negative electrode terminal 15, to which the positive and negative electrodes are electrically connected, and are structured to be led out to the outside of the battery casing materials 18a and b so as to be sandwiched between the ends of the battery casing materials 18a and b. The positive electrode terminal 13 and the negative electrode terminal 15 can be attached to the positive electrode current collector 12 and the negative electrode current collector 17 of each electrode by welding or other means via positive electrode leads and negative electrode leads (not shown) as needed. The battery casing materials 18a and 18b are made of laminate film, and typically the sealant layers formed on the surfaces of the battery casing films 18a and 18b are heat-sealed together. In addition, the periphery of the battery casing materials 18a and 18b has a region where the sealant layers are in close contact with each other due to heat sealing.

[0113] Next, a secondary battery module equipped with the heat absorber of this embodiment will be described using Figure 2. Figure 2 is a schematic perspective view showing the secondary battery module of Figure 1 disassembled. The battery element 10 shown in Figure 2 has a configuration in which a positive electrode formed on a positive electrode current collector 12 (aluminum foil, etc.) having a positive electrode terminal 13 and a negative electrode placed on a negative electrode current collector 17 (metal foil, etc.) having a negative electrode terminal 15 are stacked facing each other via a separator 14 containing an electrolyte. Multiple battery elements 10 are stacked and sealed with battery casing materials 18a,b (for example, aluminum laminate casings, etc.). The heat absorber 1 of this embodiment is positioned to be in contact with the negative electrode current collector 17. The heat absorber 1 may be positioned to be in contact not only with the negative electrode current collector 17 but also with the positive electrode current collector 12. Therefore, a secondary battery module equipped with a heat absorber 1 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, etc.) having a positive electrode terminal 13, a separator 14 containing an electrolyte, and a negative electrode placed on a negative electrode current collector 17 (metal foil, etc.) having a negative electrode terminal 15 are sequentially stacked, and one or more heat absorbers 1 may be arranged so that they come into contact with the positive electrode current collector 12 and / or the negative electrode current collector 17, but not with the separator 14. Furthermore, when using solid electrolytes or gel electrolytes, these electrolytes can be interposed between the electrodes instead of the separator 14. On the other hand, the aqueous solvent, which is the contents of the heat absorber in this embodiment, does not come into direct contact with the battery element 10. Therefore, a suitable heat absorber for a secondary battery in this embodiment has a hydrogel, a bag filled with the aqueous solvent, and inorganic powder, but the contents of the bag are not such that the hydrogel or aqueous solvent comes into direct contact with the battery element 10, and more preferably the contents of the bag of the heat absorber for a secondary battery do not include the battery element 10.

[0114] The secondary battery module of this disclosure may have the heat-absorbing body 1 of this embodiment sandwiched between multiple cases (not shown) or multiple adjacent battery elements 10 (also referred to as battery cells) housed in battery outer casing films 18a,b. The cases can be made of, for example, aluminum, iron, or a metal material containing these, or a resin material such as polyphenylene sulfide. If made of a resin material, it can contribute to reducing the weight of the secondary battery module. The heat-absorbing body 1 can be sandwiched between multiple battery elements 10 by means of, for example, adhesive, fusion (ultrasonic fusion, high-frequency fusion, thermal fusion), or other adhesives. With this configuration, the heat generated during charging of the secondary battery is absorbed by the heat-absorbing body 1 sandwiched between the battery elements 10, thereby suppressing a rapid rise in the temperature of the battery elements 10 and preventing deterioration, ignition, and other problems of the battery elements 10. Furthermore, if the heat-absorbing body 1 contains a hydrogel that has absorbed an aqueous solvent, the heat-absorbing body 1 sandwiched between the battery elements 10 can suppress the temperature influence between the battery elements 10 due to its insulating properties. In addition, the cushioning properties of the swollen hydrogel act as a buffer against volume changes due to the expansion of the battery elements 10, making it easier to mitigate the rise in internal pressure of the secondary battery module.

[0115] Furthermore, in a secondary battery module, the heat-absorbing element of this embodiment may be placed in a case or battery casing film that houses multiple battery elements (battery cells). [Examples]

[0116] The present invention will be specifically described below with reference to examples and comparative examples. However, the present invention is not limited to the examples listed below. (1) Measurement of endothermic onset temperature, endothermic peak temperature, and amount of heat absorbed The endothermic temperatures and peak endothermic temperatures of the endothermic bodies prepared in this example and comparative example were measured as follows. Using a differential scanning calorimetry analyzer (DSC; DSC-7020, Hitachi High-Tech Corporation), the temperature was increased 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 low-temperature baseline of the DSC measurement curve toward the high-temperature side and a tangent line drawn at the point where the slope of the low-temperature endothermic peak curve associated with evaporation is maximum was defined as the endothermic onset temperature (°C). The point where the difference from the baseline of the DSC measurement curve is maximum was defined as the endothermic peak temperature (°C). Furthermore, the heat absorbed (J / g or mJ / mg) was defined as the integral value of the endothermic peak relative to the baseline of the DSC measurement curve, divided by the mass of the inorganic powder used in the measurement.

[0117] (2) Evaluation of cushioning The cushioning properties of the heat absorbers prepared in this example and comparative example were evaluated using the following method. Specifically, at room temperature (23°C), the heat absorbers, measuring 100 mm (length) x 100 mm (width) x 4.8 mm (height), were placed in a Tensilon universal testing machine (Orientec Co., Ltd. "RTE-1210") equipped with a 7 mmφ indentation jig, and an indentation test was performed. In this indentation test, the surface of the heat absorber was pressed at 1 MPa for 60 seconds, and then the height (mm) of the indented area on the surface was measured 5 minutes after the indentation was released. a And the height (mm) h before pressing the surface of the heat absorber for 60 seconds at 1 MPa. b The following measurements were taken, and the cushioning (also referred to as the degree of return) was observed and evaluated according to the following criteria using the following formula (I). In the above indentation test, the indentation was performed at two locations on the surface of the heat absorber, and the height (or thickness) was measured at each location. The cushioning (%) was calculated from the following formula (I), and the average values ​​are shown in Table 1. Formula (I): Cushioning (%) = h a / h b ×100 (Criteria for evaluating cushioning) "Returning to 90% or more of the original height" was marked with "◎". "Returning to 80% or more of the original height" was marked with a "○". "Returning to 70% or more of the original height" is marked with "△". "Returning to less than 70% of the original height" was marked with "×".

[0118] (3) Heating experiment using a cone calorimeter The heat-absorbing elements prepared in this example and comparative example were directly heated by radiant heat using the cone calorimeter 30 (manufactured by Toyo Seiki Co., Ltd.) shown in Figure 3, in accordance with the JIS A 1316 standard. More specifically, the cone calorimeter 30 calculates the heat generation rate, total heat generation amount, etc., from the oxygen consumption method by measuring the oxygen concentration in the combustion exhaust gas and the exhaust gas flow rate, based on the principle that the amount of heat generated in combustion is 13.1 MJ per 1 kg of oxygen, regardless of the type of organic material. The heat-absorbing element 1 was placed as a test specimen at the top of the holder 32, and 50 kW / m³ was emitted from the cone 31. 2 The material was heated with a certain amount of heat (radiant intensity). Then, the temperature change until the back surface of the heat-absorbing material 1 reached 200°C was measured using a thermocouple 33 on the back surface of the heat-absorbing material 1. In addition, the presence or absence of combustion was observed in conjunction with the temperature change.

[0119] (4) Evaluation of pressure resistance of test specimens after heating experiment The heat absorbers prepared in this embodiment and comparative example were subjected to heating experiments using the cone calorimeter described above, and then their pressure resistance was evaluated using the following method. Specifically, at room temperature (23°C), the absorbers were placed in a Tensilon universal testing machine (Orientec Co., Ltd. "RTE-1210") equipped with a 7 mmφ indentation jig, and an indentation test was performed. In this indentation test, the amount of indentation was measured when the absorber was pressed at 0.5 MPa for 60 seconds (= under pressure). From this amount of indentation, the rate of change in thickness under pressure was calculated according to the following formula (II), and evaluated according to the following criteria. In the above indentation test, the indentation was performed at two locations on the surface of the heat absorber after heating with the cone calorimeter, and the height (or thickness) was measured at each location. The rate of change in thickness was calculated from the following formula (II), and the average values ​​are shown in Table 1. Equation (II): Thickness change rate (%) = (Thickness of the heat absorber after pressing it against the surface of the heated heat absorber at 0.5 MPa for 60 seconds) / (Thickness of the heat absorber before pressing it against the surface of the heated heat absorber at 0.5 MPa for 60 seconds) × 100 (Evaluation criteria for thickness change rate) A thickness change rate in the range of 70-100% was marked with "◎". A thickness change rate in the range of 40-69% was marked with "○". A thickness change rate in the range of 0-39% was marked with "×". Furthermore, the material exhibits the best pressure resistance when the thickness change rate is in the range of 70-100%. A lower value for the amount of compression (= amount of crushing) indicates superior pressure resistance.

[0120] <Inorganic powder> 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., solubility in 100g of water at 20°C (g / 100g): less than 0.1g) • Calcium sulfate dihydrate: (Product name "Calcium Sulfate Dihydrate, Special Grade", manufactured by Kanto Chemical Co., Ltd., solubility in 100g of water at 20°C (g / 100g): 0.2g) • Magnesium sulfate heptahydrate: (Product name "Magnesium sulfate heptahydrate, Special Grade", manufactured by Kanto Chemical Co., Ltd., solubility in 100g of water at 20°C (g / 100g): 71g) The solubility of the above hydrates in their anhydrous form is as follows: • Solubility of anhydrous magnesium sulfate in 100g of water at 20°C (g / 100g): 30g • Solubility of anhydrous calcium sulfate in 100g of water at 20°C (g / 100g): 0.2g Within the endothermic body, magnesium sulfate heptahydrate exists as an anhydrous substance, and calcium sulfate dihydrate exists as a hydrate.

[0121] <Bag body> The water vapor permeability of the aluminum pouch bag used in Examples 1-3 described below ([g / (m³) 2(24h)) is 50g / (m 2 We confirmed that it was less than 24 hours.

[0122] (Example 1) In 100 parts by mass of pure water, 20 parts by mass of N,N-dimethylacrylamide (hereinafter abbreviated as "DMAA"), 4.8 parts by mass of water-swellable synthetic hectorite (manufactured by BIC Chemie Japan Co., Ltd., "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 to obtain a homogeneous dispersion (a-1) (see Table 1). An aluminum pouch (Mitsubishi Gas Chemical Co., Ltd.'s "Gas Barrier Bag," 0.094 mm thick, constructed by laminating PET, aluminum foil, and polyethylene) was made into a bag-like container measuring 116 mm in length and 116 mm in width. 50 parts by mass of the above dispersion (a-1) and 50 parts by mass of calcium sulfate dihydrate powder were injected into the aluminum pouch to fill it, and the injection port was closed with a heat seal. The aluminum pouch was then laid flat between 4.8 mm thick gap materials, a flat plate was placed on top, and it was left to stand at 20°C for 15 hours to produce a 4.8 mm thick sheet-like heat absorber (E). The obtained heat absorber (E) was then evaluated according to the procedure described in the evaluation section above. The results are shown in Table 1 and Figure 5. Furthermore, when the heat-absorbing material (E) prepared in Example 1 was heated to 200°C using a cone calorimeter, it was confirmed that it transformed into a porous material at temperatures above 150°C.

[0123] (Example 2) Dispersion (a-2) was prepared by mixing 30 parts by mass of the above dispersion (a-1) described in the section for Example 1 with an additional 70 parts by mass of aluminum hydroxide. A container was prepared by forming an aluminum pouch (Mitsubishi Gas Chemical Co., Ltd.'s "Gas Barrier Bag," 0.094 mm thick, constructed by laminating PET, aluminum foil, and polyethylene) into a bag-like body measuring 116 mm in length and 116 mm in width. Next, 100 parts by mass of the above dispersion (a-2) was poured into the bag-like body of the aluminum pouch to fill it, and the pouring opening was closed with a heat seal. Then, the bag-like body of the aluminum pouch was laid flat between 4.8 mm thick gap materials, a flat plate was placed on top of it, and it was left to stand at 20°C for 15 hours to produce a sheet-like heat absorber (F) with a thickness of 4.8 mm. The obtained heat absorber (F) was then evaluated according to the procedure described in the evaluation section above. The results are shown in Table 1 and Figure 5. Furthermore, when the heat absorber (F) prepared in Example 2 was heated to 200°C using a cone calorimeter, the heat absorber (F) prepared in Example 2 exhibited the same properties as the heat absorber in Example 1. It was confirmed that the material transformed into a porous material at temperatures above 150°C.

[0124] (Example 3) In the section for Example 1, 54 parts by mass of magnesium sulfate heptahydrate were dissolved in 100 parts by mass of the dispersion (a-1) to prepare a water-soluble inorganic powder-containing aqueous solution (3). Then, 91 parts by mass of the water-soluble inorganic powder-containing aqueous solution (3) and 9 parts by mass of ceramic wool (average porosity 96.9%, true density 3, bulk density 0.093) were filled into an aluminum pouch measuring 116 mm in length and 116 mm in width. After closing the opening with a heat seal, the aluminum pouch was placed flat between 4.8 mm thick gap materials, a flat plate was placed on top, and it was left to stand at 20°C for 15 hours to produce a 4.8 mm thick sheet-like heat absorber (G). The obtained heat absorber (G) was then evaluated according to the procedure described in the evaluation section above. The results are shown in Table 1 and Figure 5. Furthermore, when the heat-absorbing body ((G)) prepared in Example 3 was heated to 200°C using a cone calorimeter, it was confirmed that the heat-absorbing body ((G)) prepared in Example 3 also changed into a porous body at 150°C or higher, similar to the heat-absorbing bodies of Examples 1 and 2.

[0125] (Comparative Example 1) As Comparative Example 1, a commercially available material, "Xiaomei silica aerogel mat material, 4.8 mm thick (measured), thermal conductivity: 0.012~0.018 W / m·K," was used as comparison sheet (A). The nominal thickness of the silica aerogel mat material in Comparative Example 1 was 3 mm. The obtained comparison sheet (A) was then evaluated according to the procedure described in the evaluation section above. The results are shown in Table 1 and Figure 5. Furthermore, since the material used in Comparative Example 1, "Xiaomei silica aerogel mat material," has virtually no endothermic capacity, "virtually no endothermic capacity" is indicated in the "Endothermic start temperature (°C), endothermic peak temperature (°C), and heat absorption amount (J / g or mJ / mg)" column of the table.

[0126] (Comparative Example 2) Resin 1 ("Boncoat 5400EF" (product name, water-dispersible acrylic resin emulsion, 50% non-volatile content, manufactured by DIC Corporation)) 100 parts by mass, Foam stabilizer 1 ("DICNAL M-40" (product name, sulfonic acid type anionic surfactant, manufactured by DIC Corporation)) 6 parts by mass, Crosslinking agent 1 ("DICNAL GX" (product name, oxazoline group-containing polymer, manufactured by DIC Corporation) )3 parts by mass and were mixed together and stirred in a disperser (2000 rpm, 3 minutes) to prepare a binder for mechanical foaming. 39 parts by mass of the binder, which is an acrylic resin prepared, was stirred to create foam so that the foaming ratio doubled. 61 parts by mass of calcium sulfate dihydrate was added as an inorganic powder, and stirring was continued for a further 5 minutes to obtain a foaming mixture. The resulting foamed mixture was applied to a polyethylene terephthalate (PET) film using an applicator. Next, as a pre-drying step, it was heated at 105°C for 5 minutes, then at 120°C for 3 minutes. After that, it was flipped over and heat-treated at 120°C for another 3 minutes to cure it, producing a comparative sheet (B) (=resin foam sheet) with a thickness of 4.8 mm. Furthermore, comparative sheet (B) of Comparative Example 2 was burned during the combustion evaluation of the heating experiment using the cone calorimeter described above, resulting in a poor performance as an insulating material.

[0127] (Comparative Example 3) An aluminum pouch (Mitsubishi Gas Chemical Co., Ltd.'s "Gas Barrier Bag," 0.094 mm thick, constructed by laminating PET, aluminum foil, and polyethylene) was made into a bag-like container measuring 116 mm in length and 116 mm in width. 100 parts by mass of the dispersion (a-1) described in the section for Example 1 were injected into the aluminum pouch to fill it, and the injection port was closed with a heat seal. The aluminum pouch was then laid flat between 4.8 mm thick gap materials, a flat plate was placed on top, and it was left to stand at 20°C for 15 hours to produce a 4.8 mm thick sheet-like heat absorber (C). The obtained heat absorber (C) was then evaluated according to the procedure described in the evaluation section above. The results are shown in Table 1 and Figure 5.

[0128] (Comparative Example 4) An aluminum pouch (Mitsubishi Gas Chemical Co., Ltd.'s "Gas Barrier Bag," 0.094 mm thick, constructed by laminating PET, aluminum foil, and polyethylene) measuring 116 mm in length and 116 mm in width was prepared. Next, 33 parts by mass of pure water and 67 parts by mass of calcium sulfate dihydrate as an inorganic powder were filled into the aluminum pouch, and the opening was closed with a heat seal. The aluminum pouch was then laid flat between 4.8 mm thick gap materials, a flat plate was placed on top, and it was left to stand at 20°C for 10 minutes to produce a 4.8 mm thick sheet-like heat absorber (D). The obtained heat absorber (D) was then evaluated according to the procedure described in the evaluation section above. The results are shown in Table 1 and Figure 5. In Comparative Example 4, since the DSC of the liquid could not be measured, data on the endothermic heat (J / g or mJ / mg) could not be obtained. Therefore, the value of 1170 J / g, calculated based on an approximate value of 2000 J / g (100°C) from the literature value of 2257 J / g, is entered in the table. (Specifically, the approximate value of the heat absorbed by water is 2000 J / g × 33% + the heat absorbed by calcium sulfate (measured value) is 762 J / g × 67% = 1170 J / g)

[0129] Note that the inorganic powder in Example 3 is water-soluble. Also, in Table 1, the "Inorganic Powder Content (mass%)" in "Contents (Amount Blended During Preparation)" indicates the content in the hydrate state, the "Inorganic Powder Content (mass%)" in "Contents (Inside the Bag)" indicates the content in the state from which water has been removed from the hydrate (anhydrous), and the "Aqueous Solvent Content (mass%)" indicates the content of the aqueous solvent during preparation, including the amount of water removed from the hydrate of the inorganic powder. Furthermore, the inorganic powders used in Example 1 and Comparative Examples 2 and 4 are non-water soluble, and the "content of inorganic powder (mass%)" in the "contents (inside the bag)" refers to the content including the amount of water in the hydrate, while the "content of aqueous solvent (mass%)" is the same as the content of the aqueous solvent during preparation.

[0130] [Table 1]

[0131] When the heat-absorbing bodies (E) to (G) prepared in Examples 1 to 3 above were sandwiched between two plates with a 4.8 mm gap between them, and placed upright with the sides of the heat-absorbing bodies (E) to (G) facing the bottom, and left to stand, the heat-absorbing bodies (E) to (G) maintained their original position and shape even after a whole night. On the other hand, when the heat-absorbing body (D) of Comparative Example 4 was similarly sandwiched between two plates with a 4.8 mm gap between them, and placed vertically with the side of the heat-absorbing body (D) facing the bottom, and left to stand for 1 hour, the heat-absorbing body (D) had become crushed under its own weight and was unable to maintain its original position and shape. In this embodiment, the heat-absorbing material, including the filled contents and the bag, acts as a porous material. Therefore, even when the battery temperature rises or time passes, sufficient heat absorption, flame retardancy, and transformation from a heat-absorbing material to an insulating material are confirmed.

[0132] [Explanation of symbols] 1. Heat absorber 10 Battery elements 11 Cathode material layer 12 Positive electrode current collector 13 Positive terminal 14. Electrolyte layer or separator 15 Negative terminal 16 Negative electrode material layer 17 Negative electrode current collector 18a,b Battery exterior material 19 Activated carbon layer 20 Stacked Battery 30 Corn Calorimeter 31. Cone (heater) 32 Stainless Steel Holder 33 Aluminum foil cover 34 Thermocouples 35 Stainless Steel Holder 36 Ceramic Wool (Large) 37 Ceramic Wool (Small)

Claims

1. A bag that can be filled with contents, The contents of the bag are a hydrogel and an inorganic powder, The hydrogel is composed of a hydrogel body and an aqueous solvent, and the hydrogel body uses at least a water-soluble organic monomer and a water-swellable clay mineral as reaction raw materials. A heat-absorbing body in which the entire contents form a porous body in the temperature range of 150°C to 1000°C.

2. The heat-absorbing body according to claim 1, further comprising an antifreeze agent as the contents.

3. The water vapor permeability of the sheet constituting the bag body ([g / (m²)) ２ ・24h) is 50g / (m ２ The heat-absorbing body according to claim 1 or 2, wherein the heat absorption period is 24 hours or less.

4. The endothermic onset temperature is 400°C or lower, and the endothermic peak temperature is in the range of at least 80°C to 400°C, and the following equation (II): [Mathematics 1] "Percentage change in thickness (%) = (Thickness of the heat absorber after being pressed at 0.5 MPa for 60 seconds on the surface of the heat absorber heated under the following heating conditions) / (Thickness of the heat absorber before being pressed at 0.5 MPa for 60 seconds on the surface of the heat absorber heated under the following heating conditions) × 100" Heating conditions: "50 kW / m² due to radiant heat" ２ After heating the heat-absorbing body with the heat energy required until the temperature of the side opposite to the heating surface (back surface) reached a predetermined temperature, the heat-absorbing body was allowed to dissipate heat at room temperature and naturally cool until the surface temperature of the heat-absorbing body reached room temperature, and the percentage change in thickness before and after heating was calculated. Furthermore, pressure was applied to the heating surface of the heat-absorbing element by pressing it down at 0.5 MPa for 60 seconds. The heat-absorbing body according to claim 1 or 2, wherein the thickness change rate (%) represented by is 70% or more.

5. A secondary battery module comprising the heat-absorbing element according to claim 1 or 2.

6. The secondary battery module according to claim 1 or 2, wherein the heat-absorbing element is sandwiched between battery cells.

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