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

Abstract

The purpose of the present disclosure is to provide: a heat absorbing body that demonstrates a low heat-absorption starting temperature, that has an excellent amount of heat absorption, and excellent flame retardancy and cushioning properties; and a secondary battery module comprising said heat absorbing body.　The present disclosure is a heat absorbing body that includes: a bag body that can be filled with content; and a hydrogel that is packed into the bag body as the content. The hydrogel is characterized by having a three-dimensional mesh structure and being made through synthesis in which a water-soluble organic monomer is used as a reaction material. The heat absorbing body according to the present disclosure is useful in particular as a heat absorbing body for a secondary battery.

Description

Heat absorber and secondary battery module equipped with the heat absorber

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

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

[0003] For example, Patent Document 1 discloses a technology for suppressing battery ignition and achieving excellent fire resistance. Patent Document 1 discloses a technology for using, as a battery casing material, a battery exterior film provided with a fire-resistant resin layer containing a hydrated metal compound such as aluminum hydroxide or magnesium hydroxide as a heat-absorbing agent. Patent Document 2 discloses a technology for quickly extinguishing fires caused by sudden temperature increases in batteries. Patent Document 2 discloses a technology related to a fire-resistant resin composition or a sheet thereof containing a thermoplastic resin or an elastomer resin, a metal hydroxide such as aluminum hydroxide or magnesium hydroxide, and a thermally conductive filler.

[0004] JP 2021-2425 A JP 2020-132843 A

[0005] However, both of the technologies described in Patent Documents 1 and 2 absorb heat using the laminate film itself, which limits the amount of heat-absorbing material contained due to limitations on film thickness or flexibility, resulting in insufficient heat-absorbing effect. Furthermore, the resin molding temperature used in Patent Document 2 generally requires 150°C or higher. Therefore, if calcium sulfate dihydrate is used as the heat-absorbing material, an endothermic reaction occurs at the endothermic onset temperature of 120°C, making molding difficult. Therefore, the technology described in Patent Document 2 molds the battery exterior film at 80°C, but this also creates another problem: the film does not have the strength required for use as a standalone battery exterior film. Furthermore, the technologies described in Patent Documents 1 and 2 do not address temperature control before thermal runaway, battery cell expansion, or flame-blocking properties. Therefore, the present disclosure aims to provide a heat absorber with a low endothermic onset temperature and excellent heat absorption capacity, flame retardancy, and cushioning properties, as well as a secondary battery module equipped with the heat absorber.

[0006] The present inventors have found that a heat absorber containing a bag and a hydrogel exhibits a low endothermic onset temperature and is excellent in heat absorption amount, flame retardancy, and cushioning properties, and have completed the following invention. [1] A heat absorber having a bag that can be filled with contents and a hydrogel that is filled in the bag as the contents. [2] A sheet that constitutes the bag has a water vapor permeability ([g / (m ２ ・24h)]) is 50g / (m ２24h) or less. [3] The heat absorber according to [1] or [2], wherein the hydrogel is an organic-inorganic composite hydrogel. [4] The heat absorber according to any one of [1] to [3], wherein the hydrogel is made from at least a water-soluble organic monomer and a water-swellable clay mineral as reaction raw materials. [5] The heat absorber according to any one of [1] to [4], wherein the content further contains a low-volatile solvent. [6] The heat absorber according to any one of [1] to [5], which is used in a battery. [7] The heat absorber according to [6], wherein the battery is a secondary battery. [8] A secondary battery module including the heat absorber according to any one of [1] to [7]. [9] The secondary battery module according to [8], wherein the heat absorber according to any one of [1] to [7] is sandwiched between battery cells.

[10] The secondary battery module according to [8] or [9], wherein the heat absorber according to any one of [1] to [7], has a total thickness in the range of 100 to 50,000 μm.

[0007] According to the heat absorber of the present disclosure, a highly safe secondary battery module can be provided by including a heat absorber having a low heat absorption onset temperature and excellent heat absorption capacity, flame retardancy, and cushioning properties.

[0008] Fig. 1 shows an example of a secondary battery module in which the heat absorber of this embodiment can be mounted. Fig. 2 is a perspective view schematically showing the disassembled secondary battery module of Fig. 1. Fig. 3 shows DSC measurement results showing the endothermic onset temperature and endothermic amount of the heat absorber in Example 1. Fig. 4 shows DSC measurement results showing the endothermic onset temperature and endothermic amount of the heat absorber in Example 2.

[0009] Hereinafter, embodiments of the present invention (hereinafter referred to as "present embodiments") will be described in detail. However, the present disclosure is not limited to the following description and can be practiced in various modifications within the scope of its gist. [Definitions] In this specification, "reaction raw materials" refers to compounds used to obtain a target compound through a chemical reaction such as synthesis or decomposition and that partially constitute the chemical structure of the target compound. Substances that serve as chemical reaction aids, such as solvents, catalysts, and polymerization initiators, are excluded. In this specification, "structural unit" refers to a (repeating) unit of a chemical structure formed during a reaction or polymerization. In other words, in a product compound formed by a reaction or polymerization, a partial structure other than the structure of the chemical bonds involved in the reaction or polymerization, i.e., a residue. In this specification, a "hydrogel" refers to a three-dimensional network of polymers containing an aqueous solvent such as water, and examples of such materials include jelly, diaper absorbents, konjac, and agar. The three-dimensional network polymer that forms the skeleton of the hydrogel is referred to as the hydrogel body, and the hydrogel body contains an aqueous solvent. Thus, the hydrogel has a hydrogel body and an aqueous solvent.

[0010] [Heat Absorber] The heat absorber of the present disclosure (hereinafter, sometimes simply referred to as "heat absorber") is a heat absorber having a pouch and a hydrogel filled in the pouch. The hydrogel is not particularly limited, and known hydrogels can be used. However, for example, a hydrogel in which an aqueous solvent is held within a three-dimensional network structure (three-dimensional network) whose main component is a polymer synthesized from a water-soluble organic monomer or the like is preferred. Furthermore, a hydrogel in which an aqueous solvent is held within a three-dimensional network structure (three-dimensional network) whose main component is a polymer synthesized from a water-soluble organic monomer in the presence of a water-swellable clay mineral is even more preferred. If the content of the aqueous solvent in the hydrogel is in the range of 5 to 99% by mass relative to the total hydrogel, it can exhibit a heat absorption effect at a level that can effectively prevent ignition or damage due to thermal runaway in secondary batteries, making it suitable as a heat absorber, particularly a heat absorber for batteries, particularly a heat absorber for secondary batteries. The upper limit of the aqueous solvent content in the hydrogel is preferably 99% by mass or less, more preferably 90% by mass or less, and even more preferably 80% by mass or less, based on the total mass of the gel. The lower limit of the aqueous solvent content is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 20% by mass or more. The preferred range of the aqueous solvent content can be any combination of the upper and lower limits.

[0011] Specific examples of such hydrogels include organic-inorganic composite hydrogels (NC gels), interpenetrating network hydrogels (DN gels), slide-ring gels (SR gels), and hydrogels known as aquamaterials. Among these, organic-inorganic composite hydrogels (also referred to as organic-inorganic hydrogels or NC gels (nanocomposite gels)) are preferred because of their excellent heat-absorbing properties due to the aqueous solvent contained therein, as well as their excellent cushioning and creep resistance.

[0012] The content of the hydrogel in this embodiment is preferably 100% by mass or less, more preferably 90% by mass or less, and preferably 20% by mass or more, more preferably 25% by mass or more, relative to the entire heat absorber (total amount of the contents of the bag). The preferred range of the hydrogel content in the contents can be any combination of the upper and lower limits (for example, the preferred range of the content can be 20% by mass to 100% by mass, or 25% by mass to 90% by mass).

[0013] This allows for the provision of a heat absorber with a low endothermic onset temperature and excellent flame retardancy, heat absorption capacity, and cushioning properties. As a result, the inclusion of this heat absorber allows for the heat absorption properties to be fully utilized, suppressing the temperature impact on other battery cells and providing a highly safe secondary battery module. Furthermore, the heat absorber of the present disclosure has sufficient strength to be used alone. If necessary, the pouch may further contain one or more low-volatile solvents and additives. The endothermic onset temperature of the heat absorber of this embodiment is preferably 160°C or lower, more preferably 150°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 lower limit of the endothermic onset temperature is not particularly limited, but is preferably 70°C or higher, more preferably 80°C or higher, and even more preferably 90°C or higher. The upper and lower limits of the preferred range of the endothermic onset temperature can be appropriately combined (for example, 70°C to 160°C, 70°C to 150°C, 80°C to 120°C, and 90°C to 100°C can be preferred ranges of the endothermic onset temperature). In this specification, the endothermic onset temperature (°C) is defined as the temperature at the intersection of a line extending the low-temperature baseline toward the high-temperature side in a DSC measurement curve obtained by measurement with a differential scanning calorimeter (DSC) and a tangent drawn at the point where the gradient is maximum on the low-temperature side of the endothermic peak associated with evaporation. However, when multiple endothermic peaks are observed, the intersection of a line extending the low-temperature side of the baseline toward the high-temperature side and a tangent drawn at the point where the gradient is maximum on the low-temperature side of each of the multiple endothermic peaks is calculated for each of the multiple endothermic peaks, and the lowest temperature among the temperatures at the intersections is defined as the endothermic onset temperature. The endothermic peak temperature of the endothermic body of this embodiment is preferably at least in the range of 80°C to 160°C, and more preferably in the range of 90°C to 150°C. In this specification, the endothermic peak temperature refers to the temperature (°C) at the maximum value of the endothermic peak due to evaporation in a DSC measurement curve, which is the measurement result of a differential scanning calorimeter (DSC). When 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 160°C.The endothermic amount of the heat endotherm of this embodiment is not particularly limited, but at the endothermic peak temperature (in the range of 80 ° C to 160 ° C), it is preferably 100 J / g or more, more preferably 200 J / g or more, even more preferably 300 J / g or more, and even more preferably 500 J / g or more, preferably 3000 J / g or less, more preferably 2500 J / g or less, and even more preferably 2000 J / g or less. The preferred range of the endothermic amount can be an appropriate combination of the upper and lower limits (for example, the endothermic amount can be in the range of 100 J / g to 3000 J / g, 200 J / g to 2500 J / g, 300 J / g to 2000 J / g, or 500 J / g to 2000 J / g). The endothermic onset temperature, endothermic peak temperature, and endothermic amount of the heat endotherm of this embodiment are values ​​determined using a differential scanning calorimeter (DSC) according to the method described in the Examples below.

[0014] The shape or size of the heat absorber of this embodiment is not particularly limited and may be, for example, substantially spherical, substantially flat, or amorphous, and is appropriately selected depending on the size of the secondary battery to be used. For example, a substantially flat heat absorber is preferable because it is easy to install between adjacent battery cells. The average thickness of the substantially flat heat absorber of this embodiment is not particularly limited, but may be, for example, in the range of 100 μm to 50,000 μm. The lower limit of the average thickness is preferably 100 μm or more, more preferably 200 μm or more, even more preferably 500 μm or more, and particularly preferably 1,000 μm or more. The upper limit of the average thickness is preferably 50,000 μm or less, more preferably 20,000 μm or less, even more preferably 10,000 μm or less, and particularly preferably 8,000 μm or less. The preferred range of the average thickness can be any combination of the upper and lower limits (for example, the preferred range of the average thickness can be 200 μm to 20,000 μm, 500 μm to 10,000 μm, or 1,000 μm to 8,000 μm). Below, the essential components of the heat absorber of this embodiment, namely the bag and the hydrogel (including the aqueous solvent contained in the hydrogel), and the optional components such as a low-volatile solvent and additives that are blended as necessary will be described.

[0015] (Bag) The bag of this embodiment is not particularly limited as long as the contents, i.e., the hydrogel or aqueous solvent, do not leak to the outside. A preferred example of such a bag is a three-sided bag having an opening at the top end, a body portion closed at the bottom end, and a structure in which the opening is heat-sealed to close after the contents, i.e., the hydrogel and aqueous solvent, are contained. The three-sided bag is constructed by bonding the bottom ends and side portions of two sheets together, and then sealing the bag after filling the contents through the opening. This structure provides excellent airtightness, and its substantially flat shape makes it easy to insert between battery cells. The bag of this embodiment is preferably made of a sheet. A preferred embodiment of the bag of this embodiment is constructed by stacking two films of a desired size and shape (e.g., rectangular or (substantially) circular) depending on the intended use, and then heat-pressing a predetermined heat-sealed region (e.g., the edge of the film) to form an opening. This allows the creation of a three-sided bag having an internal space region capable of being filled with contents, an opening through which the contents can be filled into the internal space region, and a heat-sealed region between the two sheets. After filling the contents, the contents can be sealed by crimping and heat-sealing the openings together. Note that "sealed" in this specification refers to a state in which the interior and exterior of the bag are substantially isolated from each other. For example, as long as the contents do not escape to the outside, the permeation of trace amounts of gases such as water vapor is permitted. The sheets used in the bag body of this embodiment are not particularly limited as long as they are water-proof, and examples include known resin films, resin films with a metal layer, and films with a metal layer. The average thickness of the sheets used in the bag body of this embodiment is not particularly limited, but is preferably 30 μm to 200 μm, and more preferably 60 μm to 150 μm. Examples of materials for the resin film include one or more resins such as polyester resin, nylon resin, polycarbonate resin, polypropylene resin, polyethylene resin, cyclic polyolefin resin, polystyrene resin, fluororesin, and elastomer.These plastics can be used for bags in the form of films, sheets, tubes, etc. In addition, the resin film having the metal layer may be laminated to the resin film with a metal such as aluminum or a metal oxide such as silica or alumina as a metal foil, vapor-deposited film, etc. The use of a resin film having a metal layer can reduce the water vapor permeability of the resin film. The water vapor permeability of the sheet can be adjusted by selecting, thickness, and combination of materials. Examples of lamination methods include dry lamination, extrusion lamination, thermal lamination, coextrusion, multilayer blow molding, laminate injection molding, and coating. A preferred form of the resin film having a metal layer is an aluminum laminate film (a film formed by integrating aluminum foil (including an aluminum vapor-deposited layer) with a thermoplastic resin film (e.g., polyethylene film, PP film, PET film) laminated on at least one side thereof). In this embodiment, an adhesive layer may be formed in the heat-sealed area and the closed opening for sealing purposes. Examples of the adhesive layer that can be used include laminate adhesives such as polyester-based adhesives, polyether-based adhesives, and polyurethane-based adhesives. Furthermore, the properties of the adhesive are not particularly limited, and any of solvent-based, solventless, and aqueous adhesives can be used. For example, in the present invention, a bag formed by sealing a resin film having an aluminum-deposited layer on the outside via a polyurethane-based laminate adhesive layer can be suitably used. Examples include the Gas Barrier Aluminum Bag AB Series (manufactured by Mitsubishi Gas Chemical Company, Inc.) and Lamizip AL Type (manufactured by Seisan Nippon Co., Ltd.). The higher the melting temperature (e.g., 120 to 140°C) of the adhesive used to close the opening of the bag or in the heat-sealed region of the present embodiment, the stronger the strength and the more likely it is to withstand internal pressure.

[0016] The water vapor permeability ([g / (m ２ ・24h)]) is 50g / (m ２ 24h) or less, and ２ 24h) or less, and more preferably 5g / (m２ It is more preferable that the water vapor permeability of the sheet constituting the bag is 50 g / (m ２ If the water vapor permeability ([g / (m ２ The lower limit of the viscosity of the polymer is preferably 0 g / (m ２ 24h) or more, more preferably 0 g / (m ２ The preferred range of the water vapor permeability may be, for example, 0 g / (m ２ ・24h) or more 50g / (m ２ ・24h) or less, or 0g / (m ２ ・24h) or more 10g / (m ２ From another viewpoint, the preferable range of the water vapor permeability is 0 g / (m ２ ・24h) More than 50g / (m ２ 24h) or less.) The water vapor transmission rate ([g / (m ２ The temperature and humidity are measured in accordance with JIS K7129 at a temperature of 40°C and a relative humidity of 90%.

[0017] (Hydrogel) The hydrogel of this embodiment preferably comprises an aqueous solvent and a three-dimensional polymer network structure that retains the aqueous solvent therein. The hydrogel comprises an aqueous solvent and a hydrogel body that is a three-dimensional polymer network structure containing a water-swellable clay mineral and a water-soluble organic monomer structural unit, at least a portion of which is dissolved or dispersed in the aqueous solvent. Examples of the hydrogel include interpenetrating network gels in which two types of acrylic polymers each form a three-dimensional network structure, slide-ring gels in which cyclodextrin forms the three-dimensional network structure skeleton, and aquamaterials in which a multi-branched dendrimer forms the three-dimensional network structure skeleton and a water-swellable clay mineral is added. However, the following description focuses on an organic-inorganic composite hydrogel, which is one aspect of this embodiment. The organic-inorganic composite hydrogel of this embodiment comprises a three-dimensional network structure containing a water-soluble organic monomer structural unit and a water-swellable clay mineral as the hydrogel body. More specifically, the hydrogel body of the organic-inorganic composite hydrogel (hereinafter also referred to as the organic-inorganic composite hydrogel body) is considered to be a polymer gel (i.e., a three-dimensional network structure) in which polymer chains composed of multiple water-soluble organic monomer structural units are crosslinked via water-swellable clay minerals that function as binding points. The organic-inorganic composite hydrogel can swell 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 has heat-absorbing properties and exhibits excellent cushioning properties that allow it to adapt to relatively short-term deformations such as expansion and contraction caused by charging and discharging a battery cell, but also exhibits excellent creep resistance that can relieve internal pressure due to expansion of the battery cell over time. The organic-inorganic composite hydrogel preferably has a three-dimensional network structure and is made from a water-soluble organic monomer and a water-swellable clay mineral as reaction raw materials.

[0018] The organic-inorganic composite hydrogel according to one aspect of this embodiment is produced using at least a water-soluble organic monomer structural unit and a water-swellable clay mineral as reaction raw materials. A preferred method for producing the organic-inorganic composite hydrogel according to one aspect of this embodiment involves polymerizing the water-soluble organic monomer in a dispersion (a) containing a water-soluble organic monomer, a water-swellable clay mineral, an aqueous solvent, and, if necessary, a polymerization initiator and additives, since this method allows for the easy production of an organic-inorganic composite hydrogel having a three-dimensional network structure. The resulting polymer of the water-soluble organic monomer forms a three-dimensional network structure together with the water-swellable clay mineral, becoming a component of the organic-inorganic composite hydrogel.

[0019] The lower limit of the content of the hydrogel body according to this embodiment is preferably 1% by mass or more, more preferably 10% by mass or more, relative to the total amount of the hydrogel. Meanwhile, the upper limit of the content of the hydrogel body is preferably 50% by mass or less, more preferably 40% by mass or less. The preferred range of the content of the hydrogel body can be an appropriate combination of the upper and lower limits (e.g., the preferred range of the content can be 1% by mass to 50% by mass, or 10% by mass to 40% by mass). For example, when the hydrogel body is composed of water-soluble organic monomer structural units described below, the content of the hydrogel body can be the total amount of the water-soluble organic monomer structural units and the water-swellable clay mineral. The content of the hydrogel body is calculated by the mass change (%) before and after drying the hydrogel at 120°C for 2 hours.

[0020] <Water-Soluble Organic Monomer> The water-soluble organic monomer used in this embodiment constitutes the organic-inorganic hybrid hydrogel body as the water-soluble organic monomer structural unit. The lower limit of the content of the water-soluble organic monomer structural unit in the hydrogel according to this embodiment may be preferably 0.9% by mass or more, more preferably 1% by mass or more, and even more preferably 5% by mass or more, based on the total amount of the hydrogel. Meanwhile, the upper limit of the content of the water-soluble organic monomer structural unit may be 50% by mass or less, 40% by mass or less, or 30% by mass or less. The preferred range of the content of the water-soluble organic monomer structural unit in the hydrogel can be any combination of the above upper and lower limits (e.g., the preferred range of the content may be 0.9% by mass to 50% by mass, 1% by mass to 40% by mass, or 5% by mass to 30% by mass). The type of water-soluble organic monomer used in this embodiment is not particularly limited, and examples include monomers having a (meth)acrylamide group, monomers having a (meth)acryloyloxy group, and acrylic monomers having a hydroxyl group. In this specification, "(meth)acrylamide" refers to either or both of acrylamide and methacrylamide, "(meth)acryloyloxy" refers to either or both of acryloyloxy and (meth)acryloyloxy, "(meth)acrylate" refers to either or both of acrylate and methacrylate, and "(meth)acrylic monomer" refers to either or both of acrylic monomer and methacrylic monomer.

[0021] Examples of the monomer having a (meth)acrylamide group include acrylamide, N,N-dimethylacrylamide, N,N-diethylacrylamide, N-methylacrylamide, N-ethylacrylamide, N-isopropylacrylamide, N-cyclopropylacrylamide, N,N-dimethylaminopropylacrylamide, N,N-diethylaminopropylacrylamide, acryloylmorpholine, methacrylamide, N,N-dimethylmethacrylamide, N,N-diethylmethacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, N-isopropylmethacrylamide, N-cyclopropylmethacrylamide, N,N-dimethylaminopropylmethacrylamide, and N,N-diethylaminopropylmethacrylamide. Preferred examples of the monomer having a (meth)acrylamide group include acrylamide, N,N-dimethylacrylamide, N-methylacrylamide, N-ethylacrylamide, acryloylmorpholine, methacrylamide, N,N-dimethylmethacrylamide, N-methylmethacrylamide, and N-ethylmethacrylamide.

[0022] Examples of the monomer having a (meth)acryloyloxy group include methoxyethyl acrylate, ethoxyethyl acrylate, methoxyethyl methacrylate, ethoxyethyl methacrylate, methoxymethyl acrylate, and ethoxymethyl acrylate.

[0023] Examples of the acrylic monomer having a hydroxyl group include hydroxyethyl acrylate, hydroxyethyl methacrylate, etc. As the water-soluble organic monomer used in this embodiment, the acrylic monomer having a hydroxyl group may be used alone or in combination of two or more thereof.

[0024] In this embodiment, when a homopolymer is obtained from a water-soluble organic monomer, the resulting homopolymer preferably has a lower critical solution temperature (°C) of 50°C or higher, more preferably 60°C or higher. It is preferable that the homopolymer does not have a lower critical solution temperature (°C), i.e., that the lower critical solution temperature (°C) cannot be observed in an aqueous solvent. This prevents the polymer chains of water-soluble organic monomer structural units constituting the organic-inorganic composite hydrogel from undergoing phase transition below 50°C, thereby achieving both superior cushioning properties and heat absorption capacity even at high temperatures. More specifically, the organic-inorganic composite hydrogel according to one aspect of this embodiment has, as a constituent component, a polymer chain composed of water-soluble organic monomer structural units obtained by polymerization or reaction of a water-soluble organic monomer. Therefore, when the temperature rises above the lower critical solution temperature (°C) of the polymer chain composed of the water-soluble organic monomer structural units, the polymer chain undergoes a phase transition due to desolvation, separating into a phase containing the polymer chain and a phase containing the aqueous solvent. As a result, the three-dimensional network structure of the organic-inorganic composite hydrogel encapsulating the aqueous solvent cannot be maintained, making it difficult to exhibit cushioning properties. Therefore, the lower critical solution temperature (°C) of the organic-inorganic composite hydrogel in an aqueous solvent is preferably 50°C or higher, more preferably 60°C or higher, and preferably does not have a lower critical solution temperature (°C), i.e., the lower critical solution temperature (°C) cannot be observed in an aqueous solvent.

[0025] From the viewpoint of suppressing the phase transition of the organic-inorganic composite hydrogel, the preferred water-soluble organic monomer used in this embodiment is a water-soluble organic monomer having a homopolymer repeating unit that does not have a lower critical solution temperature in an aqueous solvent. Specifically, (meth)acrylamide, N,N-dimethyl(meth)acrylamide, acryloylmorpholine, methoxyethyl acrylate, ethoxyethyl acrylate, methoxyethyl methacrylate, ethoxyethyl methacrylate, methoxymethyl acrylate, ethoxymethyl acrylate, hydroxyethyl acrylate, or hydroxyethyl methacrylate is preferred. When the organic-inorganic composite hydrogel is heated to or above the lower critical solution temperature (°C) of the organic-inorganic composite hydrogel or the polymer chains constituting the organic-inorganic composite hydrogel, the organic-inorganic composite hydrogel undergoes a phase transition and separates into a phase in which polymer chains containing water-soluble organic monomer structural units constituting the organic-inorganic composite hydrogel are aggregated and a phase of the aqueous solvent contained within the organic-inorganic composite hydrogel. Therefore, it is particularly preferred that the polymer chains constituting the organic-inorganic composite hydrogel do not have a lower critical solution temperature in an aqueous solvent. Therefore, a water-soluble organic monomer capable of forming a highly hydrophilic polymer chain is preferred. Furthermore, when the polymer chain constituting the organic-inorganic composite hydrogel is constituted by two or more water-soluble organic monomers, from the viewpoint of reducing a decrease in cushioning property or liquid leakage due to phase transition, the copolymer constituted by the two or more water-soluble organic monomers preferably has a lower critical solution temperature (°C) of 50°C or higher, more preferably 60°C or higher, and preferably does not have a lower critical solution temperature (°C), i.e., the lower critical solution temperature (°C) cannot be observed in an aqueous solvent.

[0026] Among the above water-soluble organic monomers, from the viewpoints of solubility and cushioning properties of the resulting organic-inorganic hybrid hydrogel, it is preferable to use a monomer having a (meth)acrylamide group, it is more preferable to use acrylamide, N,N-dimethylacrylamide, or acryloylmorpholine, it is even more preferable to use N,N-dimethylacrylamide or acryloylmorpholine, and from the viewpoint of ease of polymerization, N,N-dimethylacrylamide is particularly preferable. The above water-soluble organic monomers may be used alone or in combination of two or more.

[0027] <Water-Swellable Clay Mineral> The water-swellable clay mineral used in this embodiment forms a three-dimensional network structure together with the polymer chain having the water-soluble organic monomer structural unit (polymer having the water-soluble organic monomer structural unit), and serves as a component of the organic-inorganic composite hydrogel and the organic-inorganic composite hydrogel body. The water-swellable clay mineral used in this embodiment is not particularly limited, and examples thereof include water-swellable smectite and water-swellable mica. Examples of the water-swellable smectite include water-swellable hectorite, water-swellable montmorillonite, and water-swellable saponite. Examples of the water-swellable mica include water-swellable synthetic mica. Among these, from the viewpoint of dispersibility, it is preferable to use water-swellable hectorite and water-swellable montmorillonite, and it is more preferable to use water-swellable hectorite.

[0028] The water-swellable clay mineral used in this embodiment may be naturally occurring, synthetic, or surface-modified. Examples of surface-modified water-swellable clay minerals include phosphonic acid-modified hectorite and fluorine-modified hectorite. From the viewpoint of the heat absorption and cushioning properties of the resulting organic-inorganic composite hydrogel, it is preferable to use phosphonic acid-modified hectorite. The above-mentioned water-swellable clay minerals may be used alone or in combination of two or more.

[0029] The phosphonic acid-modified hectorite forms a three-dimensional network structure with the polymer of the water-soluble organic monomer, becoming a component of the organic-inorganic composite hydrogel. Examples of the phosphonic acid-modified hectorite include pyrophosphate-modified hectorite, etidronic acid-modified hectorite, alendronic acid-modified hectorite, methylenediphosphonic acid-modified hectorite, and phytic acid-modified hectorite. These phosphonic acid-modified hectorites may be used alone or in combination of two or more. The content of the water-swellable clay mineral of this embodiment is preferably 50% by mass or less, more preferably 30% by mass or less, even more preferably 20% by mass or less, and particularly preferably 10% by mass or less, based on the total amount of the polymer derived from the water-soluble organic monomer contained in the organic-inorganic composite hydrogel, the water-swellable clay mineral, the polymerization initiator, and the aqueous solvent. The lower limit of the content of the water-swellable clay mineral is preferably 0.1% by mass or more, more preferably 1% by mass or more, even more preferably 2% by mass or more, and particularly preferably 3% by mass or more. The upper and lower limits of the content of the water-swellable clay mineral in the organic-inorganic composite hydrogel can be appropriately combined (preferable ranges of the content can be, for example, 0.1% by mass to 50% by mass, 1% by mass to 30% by mass, 2% by mass to 20% by mass, or 3% by mass to 10% by mass).

[0030] <Reaction Raw Materials> In one aspect of this embodiment, the heat absorber contains a bag and an organic-inorganic composite hydrogel as the content of the bag. The organic-inorganic composite hydrogel, which is one aspect of this embodiment, 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. Alternatively, the water-soluble organic monomer and the water-swellable clay mineral, which are reaction raw materials for the organic-inorganic composite hydrogel, may be filled into the bag together with an aqueous solvent (an organic solvent and a polymerization initiator may also be added as necessary), and then the water-soluble organic monomer and the water-swellable clay mineral inside the bag may be gelled while the bag is sealed.

[0031] A preferred method for producing an organic-inorganic composite hydrogel according to one aspect of this embodiment involves polymerizing the water-soluble organic monomer in a dispersion (a) containing reaction raw materials (a water-soluble organic monomer and a water-swellable clay mineral), a polymerization initiator, and an aqueous solvent, as this method allows for a simple production of the organic-inorganic composite hydrogel. The content of the water-soluble organic monomer in the dispersion (a) is, for example, in the range of 0.9% to 50% by mass, based on the total amount (mass) of the water-soluble organic monomer, the water-swellable clay mineral, and the aqueous solvent. The lower limit of the water-soluble organic monomer content is preferably 0.9% by mass or more, more preferably 1% by mass or more, and even more preferably 5% by mass or more. The upper limit of the water-soluble organic monomer content is preferably 50% by mass or less, more preferably 30% by mass or less. The upper and lower limits of the content can be appropriately combined. A water-soluble organic monomer content of 0.9% by mass or more is preferred 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 preferred because it facilitates the 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, based on the total amount (mass) of the water-soluble organic monomer, the water-swellable clay mineral, and the aqueous solvent. The lower limit of the content of the water-swellable clay mineral is preferably 0.1% by mass or more, more preferably 1% by mass or more, and even more preferably 3% by mass or more. The upper limit of the content of the water-swellable clay mineral is preferably 50% by mass or less, more preferably 30% by mass or less, and even more preferably 10% by mass or less. The upper and lower limits of the content can be appropriately combined (for example, the content can be in the range of 1% by mass to 30% by mass, or 3% by mass to 10% by mass). A content of the water-swellable clay mineral of 0.1% by mass or more is preferred because the mechanical properties of the resulting hydrogel are further improved. On the other hand, a content of the water-swellable clay mineral of 50% by mass or less is preferred because the increase in viscosity of the dispersion (a) can be further suppressed.The use of phosphonic acid-modified hectorite as the water-swellable clay mineral in the dispersion (a) improves storage stability, but other water-swellable clay minerals may also be included as long as storage stability is not impaired. The content of the aqueous solvent in the dispersion (a) is, for example, in the range of 50% to 99% by mass, based on the total amount (mass) of the water-soluble organic monomer, the water-swellable clay mineral, and the aqueous solvent. The lower limit of the aqueous solvent content is preferably 50% by mass or more, more preferably 60% by mass or more. The upper limit of the aqueous solvent content is preferably 99% by mass or less, more preferably 90% by mass or less. The upper and lower limits of the content can be appropriately combined (for example, the content can be in the range of 50% by mass to 90% by mass, or in the range of 60% by mass to 90% by mass). A content of the aqueous solvent of 90% by mass or less is preferred because it allows for the production of a hydrogel with excellent mechanical properties. On the other hand, if the content of the aqueous solvent is 60% by mass or more, it is possible to easily prepare a dispersion liquid (a) in which each component is uniformly dispersed. In addition, in addition to the water-soluble organic monomer and water-swellable clay mineral, which are reaction raw materials, the polymerization initiator, and the aqueous solvent, one or more selected from the group consisting of low-volatile solvents and additives described below may be mixed into the dispersion liquid (a).

[0032] The dispersion liquid (a) of this embodiment preferably contains a polymerization initiator. The polymerization initiator is not particularly limited, but examples thereof include water-soluble peroxides and water-soluble azo compounds.

[0033] Examples of the water-soluble peroxides include potassium peroxodisulfate, ammonium peroxodisulfate, sodium peroxodisulfate, and t-butyl hydroperoxide. Examples of the water-soluble azo compounds include 2,2'-azobis(2-methylpropionamidine) dihydrochloride and 4,4'-azobis(4-cyanovaleric acid). Among these, from the viewpoint of interaction with the water-swellable clay mineral, it is preferable to use water-soluble peroxides, and it is more preferable to use potassium peroxodisulfate, ammonium peroxodisulfate, and sodium peroxodisulfate, and it is even more preferable to use sodium peroxodisulfate and ammonium peroxodisulfate. The above-mentioned polymerization initiators may be used alone or in combination of two or more.

[0034] In one aspect of the present embodiment, the polymerization initiator is not essential. However, when used, the molar ratio of the polymerization initiator to the water-soluble organic monomer in the dispersion liquid (a) (polymerization initiator / water-soluble organic monomer) is preferably 0.01 or more, more preferably 0.02 to 0.1, and even more preferably 0.04 to 0.1.

[0035] The content of the polymerization initiator in the dispersion (a) is not essential, but when used, it is preferably 0.1% by mass to 10% by mass, and more preferably 0.2% by mass to 5% by mass, based on the total amount (mass) of the water-soluble organic monomer, the water-swellable clay mineral, the aqueous solvent, and the polymerization initiator. A polymerization initiator content of 0.1% by mass or more is preferred because it enables polymerization of the water-soluble organic monomer even in an air atmosphere. On the other hand, a polymerization initiator content of 10% by mass or less is preferred because it allows the dispersion to be used without agglomeration before polymerization, improving handleability.

[0036] The dispersion liquid (a) contains a water-soluble organic monomer, a water-swellable clay mineral, and an aqueous solvent, and may further contain an organic solvent, a catalyst, an organic crosslinking agent, a preservative, a thickener, etc., as necessary. Examples of the organic solvent include alcohol compounds such as methanol, ethanol, propanol, isopropyl alcohol, and 1-butanol; ether compounds such as ethyl ether and ethylene glycol monoethyl ether; amide compounds such as dimethylformamide and N-methylpyrrolidone; and ketone compounds such as acetone and methyl ethyl ketone. Among these, from the viewpoint of the dispersibility of the water-swellable clay mineral, it is preferable to use an alcohol compound, and it is more preferable to use methanol, ethanol, n-propyl alcohol, and isopropyl alcohol, and it is even more preferable to use methanol and ethanol. These organic solvents may be used alone or in combination of two or more.

[0037] The catalyst has the function of increasing the polymerization rate when polymerizing a water-soluble organic monomer. Examples of the catalyst include, but are not limited to, tertiary amine compounds, thiosulfates, and ascorbic acids. Examples of the tertiary amine compounds include N,N,N',N'-tetramethylethylenediamine and 3-dimethylaminopropionitrile. Examples of the thiosulfates include sodium thiosulfate and ammonium thiosulfate. Examples of the ascorbic acids include L-ascorbic acid and sodium L-ascorbate. Among these, from the viewpoint of dispersion stability, it is preferable to use a tertiary amine compound, and it is more preferable to use N,N,N',N'-tetramethylethylenediamine. The above-mentioned catalysts may be used alone or in combination of two or more. Although a catalyst is not essential, when a catalyst is used, the content of the catalyst in the dispersion (a) is preferably 0.01% by mass to 1% by mass, and more preferably 0.05% by mass to 0.5% by mass, relative to the total amount (mass) of the water-soluble organic monomer, the water-swellable clay mineral, the aqueous solvent, and the catalyst. A catalyst content of 0.01% by mass or more is preferred because it can efficiently promote the synthesis of a hydrogel obtained from the water-soluble organic monomer. On the other hand, a catalyst content of 1% by mass or less is preferred because it allows the dispersion to be used without agglomeration before polymerization, improving handleability.

[0038] Examples of methods for preparing the dispersion liquid (a) include a method in which a water-soluble organic monomer, a water-swellable clay mineral, a polymerization initiator, an aqueous solvent such as water, and the like are mixed all at once; and a multi-liquid mixing method in which a dispersion liquid (a1) containing a water-soluble organic monomer and a solution (a2) containing a polymerization initiator are prepared as separate dispersion liquids or solutions and then mixed immediately before use. However, from the viewpoints of dispersibility, storage stability, viscosity control, and the like, the multi-liquid mixing method is preferred.

[0039] The dispersion (a1) containing the water-soluble organic monomer may be, for example, a dispersion in which a water-soluble organic monomer and a water-swellable clay mineral are mixed.

[0040] The solution (a2) containing the polymerization initiator may be, for example, an aqueous solution obtained by mixing a polymerization initiator with water.

[0041] The organic-inorganic composite hydrogel can be obtained by polymerizing a water-soluble organic monomer in the dispersion liquid (a), and the polymerization method is not particularly limited and can be performed by a known method. Specific examples include radical polymerization by heating or ultraviolet irradiation, and radical polymerization using a redox reaction.

[0042] The polymerization temperature for polymerizing the organic-inorganic composite hydrogel is preferably 10°C to 80°C, and more preferably 20°C to 80°C. A polymerization temperature of 10°C or higher is preferred because the radical reaction can proceed in a chain reaction. On the other hand, a polymerization temperature of 80°C or lower is preferred because the water contained in the dispersion (a) can be polymerized without boiling. The polymerization time for the organic-inorganic composite hydrogel varies depending on the type of polymerization initiator and catalyst, but is preferably between several tens of seconds and 24 hours. In particular, in the case of radical polymerization using heat or redox, a polymerization time of 1 hour to 24 hours is preferred, and 5 hours to 24 hours is more preferred. A polymerization time of 1 hour or more is preferred because the polymer of the water-swellable clay mineral and the water-soluble organic monomer can form a three-dimensional network structure. On the other hand, since the polymerization reaction is nearly complete within 24 hours, a polymerization time of 24 hours or less is preferred.

[0043] (Aqueous Solvent) The heat absorber of this embodiment contains an aqueous solvent as its content. The aqueous solvent is preferably present primarily in the hydrogel, for example, an organic-inorganic composite hydrogel. The aqueous solvent of this embodiment may contain water as the main component, and refers to water or a solvent containing water as the main component. Therefore, the aqueous solvent encompasses mixed solvents with solvents other than water, or aqueous solutions containing salts (e.g., buffer solutions, electrolyte solutions). In this specification, "containing water as the main component" means that the aqueous solvent contains 45% or more by mass of water relative to the total mass of the aqueous solvent. Furthermore, the water may be purified water, pure water, ultrapure water, distilled water, or the like, without any particular limitation. Examples of the salt include alkali metal halides such as sodium chloride or potassium chloride; alkaline earth metal halides such as magnesium chloride or calcium chloride; and salts having buffering capacity such as tris-hydrochloric acid, glycine hydrochloride, citric acid-sodium citrate, acetic acid-sodium acetate, citric acid-disodium hydrogen phosphate, sodium dihydrogen phosphate-disodium hydrogen phosphate, glycine-sodium hydroxide, and sodium carbonate-sodium bicarbonate. Furthermore, Good's buffer such as HEPES or MOPS may be used as the aqueous solvent. Examples of solvents other than water that constitute the mixed solvent include organic solvents that are uniformly miscible with water (e.g., lower alcohols, lower ketones, etc.). The upper limit of the water content in the aqueous solvent of this embodiment is preferably 100% by mass or less, more preferably 99% by mass or less, even more preferably 90% by mass or less, and particularly preferably 80% by mass or less, based on the total amount of the aqueous solvent. The lower limit of the water content is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 20% by mass or more, and particularly preferably 45% by mass or more. A preferred range of the water content in the aqueous solvent can be determined by appropriately combining the above upper and lower limits (for example, the preferred range of the water content can be 5% by mass to 100% by mass, 10% by mass to 99% by mass, 20% by mass to 90% by mass, or 45% by mass to 80% by mass).

[0044] (Low Volatility Solvent) In this embodiment, a low volatility solvent can be used as an optional component because it is possible to achieve a balance between endothermic performance and cushioning properties. In particular, by adding a low volatility solvent to the contents of the endothermic body, high cushioning properties can be maintained over a wide temperature range. The low volatility solvent of this embodiment has a volatility of 1 cm in an open system at 60°C and 1 atmosphere. ２ ・0.1g or less per hour (0.1g / cm ２ Preferably, an organic solvent having a concentration of 0.05 g or less, more preferably 0.01 g or less, is used. Specifically, a solvent that is easily miscible with water is preferred, and therefore, glycerin (0.001 g or less / cm ２ hr 60 ° C 1 atm), diglycerin (0.001 g or less / cm ２ hr 60°C 1 atm), ethylene glycol (0.01 g or less / cm ２ hr 60 ° C 1 atm), propylene glycol (0.001 g or less / cm ２ hr 60°C 1 atm), polyethylene glycol (0.001 g or less / cm ２ Polyhydric alcohols such as ethanol (water, ethanol, ethanol 1000 vol / hr, 60°C, 1 atm) are preferred, with glycerin and diglycerin being more preferred. These low-volatile solvents may be used alone or in combination of two or more. It is also preferred that these low-volatile solvents be uniformly contained in the organic-inorganic composite hydrogel. By including a low-volatile solvent, particularly a polyhydric alcohol, as the content of the heat endotherm of this embodiment, volatilization of the aqueous solvent is suppressed or prevented, or a decrease in cushioning properties at low temperatures is suppressed (improved anti-freeze properties). When a low-volatile solvent is used as an optional component, the mass ratio of the aqueous solvent to the low-volatile solvent (aqueous solvent / low-volatile solvent) in the content of the heat endotherm of this embodiment is preferably 60 / 40 to 20 / 80, and more preferably 50 / 50 to 30 / 70, in order to obtain an organic-inorganic composite hydrogel that is excellent in various physical properties, such as heat-absorbing performance and cushioning properties over a wide temperature range.

[0045] (Additives) The heat absorber content or dispersion liquid (a) of this embodiment may contain various additives, such as ultraviolet absorbers, antioxidants, organic solvents, inorganic fillers other than the water-swellable clay minerals, viscosity modifiers such as thickeners, crosslinkers, and flame retardants, as needed. While the various additives are optional components, when used, they are preferably used in proportions that do not impair the effects of the present invention and that correspond to the purpose of each additive. While the proportions cannot be determined in general, the content of the various additives is preferably 0% by mass or more, and more preferably 10% by mass or more, relative to the total amount (mass) of the hydrogel and various additives used in the present disclosure. Furthermore, it is preferably 50% by mass or less, and more preferably 40% by mass or less.

[0046] Examples of the ultraviolet absorber include triazine derivatives such as 2-[4-{(2-hydroxy-3-dodecyloxypropyl)oxy}-2-hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine and 2-[4-{(2-hydroxy-3-tridecyloxypropyl)oxy}-2-hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine, 2-(2'-xanthenecarboxy-5'-methylphenyl)benzotriazole, 2-(2'-o-nitrobenzyloxy-5'-methylphenyl)benzotriazole, 2-xanthenecarboxy-4-dodecyloxybenzophenone, 2-o-nitrobenzyloxy-4-dodecyloxybenzophenone, etc. These ultraviolet absorbers can be used alone or in combination of two or more.

[0047] Examples of the antioxidant include "Sumilizer BBM-S" and "Sumilizer GA-80" manufactured by Sumitomo Chemical Co., Ltd. Examples of the organic solvent include aromatic hydrocarbons such as toluene and xylene; glycols such as ethylene glycol and propylene glycol; polyether glycols, which are polymers thereof; cellosolves; carbitols; and aliphatic alcohols such as methanol. The organic solvents can be used alone or in combination of two or more. Examples of the inorganic filler include fused silica, crystalline silica, alumina, silicon nitride, and aluminum hydroxide. Examples of the viscosity modifier such as the thickener include various tackifying resins such as rosin, polymerized rosin, polymerized rosin ester, rosin phenol, stabilized rosin ester, disproportionated rosin ester, terpene, terpene phenol, and petroleum resin. Examples of the crosslinking agent include known crosslinking agents such as isocyanate-based, epoxy-based, aziridine-based, polyvalent metal salt-based, metal chelate-based, ketohydrazide-based, oxazoline-based, carbodiimide-based, silane-based, and glycidyl (alkoxy) epoxy silane-based crosslinking agents.

[0048] Examples of the flame retardant include inorganic phosphorus compounds such as red phosphorus, ammonium phosphates such as monoammonium phosphate, diammonium phosphate, triammonium phosphate, and ammonium polyphosphate, and phosphoric acid amides; phosphoric acid ester compounds, phosphonic acid compounds, phosphinic acid compounds, phosphine oxide compounds, phosphorane compounds, organic nitrogen-containing phosphorus compounds, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, 10-(2,5-dihydroxyphenyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxy Examples of suitable flame retardants include organic phosphorus compounds such as cyclic organic phosphorus compounds such as 10-(2,7-dihydroxynaphthyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxide, and derivatives thereof obtained by reacting such compounds with compounds such as epoxy resins and phenolic resins; nitrogen-based flame retardants such as triazine compounds, cyanuric acid compounds, isocyanuric acid compounds, and phenothiazine; silicone-based flame retardants such as silicone oil, silicone rubber, and silicone resin; and inorganic flame retardants such as metal hydroxides, metal oxides, metal carbonate compounds, metal powders, boron compounds, and low-melting-point glass. These flame retardants can be used alone or in combination of two or more. When such flame retardants are used, their content is preferably in the range of 0.1% by mass to 20% by mass relative to the entire contents of the heat endotherm or the entire dispersion liquid (a).

[0049] (Method for Producing Heat Ender) In one aspect of this embodiment, a method for producing a heat endomer includes, as described above, the steps of preparing a dispersion (a) containing the reaction raw materials (a water-soluble organic monomer and a water-swellable clay mineral), an aqueous solvent, and optionally a polymerization initiator, a catalyst, a low-volatile solvent, and / or an additive, filling a bag with the dispersion (a) through an opening thereof and sealing the bag, and gelling the water-soluble organic monomer in the bag at a desired polymerization temperature. In another aspect of this embodiment, a method for producing a heat endomer includes the steps of preparing a mixed solution by mixing the reaction raw materials (a water-soluble organic monomer and a water-swellable clay mineral), a polymerization initiator, and an aqueous solvent or an organic solvent, heating the mixed solution to gel it and preparing an organic-inorganic composite hydrogel body, immersing the organic-inorganic composite hydrogel body in the aqueous solvent for a desired time to cause the organic-inorganic composite hydrogel to swell in the aqueous solvent, and filling the bag with the swollen organic-inorganic composite hydrogel through an opening thereof and sealing the bag. In the method for producing a heat absorber of this embodiment, even when a heat absorbing agent is blended into the contents of the heat absorber, the heat absorber can be molded at a molding temperature of 120°C by the above method.

[0050] (Uses of Heat Absorber) As described above, the heat absorber of this embodiment can exhibit a heat absorption effect at a level that can effectively prevent fire and damage due to thermal runaway of secondary batteries, and therefore can be suitably used for battery applications, particularly secondary battery applications. Furthermore, the use of the heat absorber of this embodiment is not limited to battery applications, and can be used in general applications where prevention of fire spread is required. For example, the heat absorber of this embodiment can be used together with building materials such as ceilings, walls, and kitchen components.

[0051] [Secondary Battery Module] The type of secondary battery that can be equipped with the heat absorber of this embodiment is not particularly limited, and examples thereof include lithium ion batteries, lithium ion polymer batteries, lead-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, condensers, and capacitors. Among these, lithium ion batteries are preferred. The heat absorber of this embodiment can also be suitably used in all-solid-state batteries as the secondary battery. Similar to lithium ion batteries, all-solid-state batteries can also be susceptible to fires and damage due to thermal runaway, as well as expansion and contraction due to charging and discharging. Therefore, the incorporation of the heat absorber of this embodiment can provide beneficial effects.

[0052] The secondary battery module capable of mounting the heat absorber of this embodiment is a secondary battery mounted on a mobile object such as a vehicle or an aircraft (particularly a drone), and includes multiple battery cells and a case for housing the multiple battery cells. The battery cells (hereinafter also referred to as battery cells) constituting the secondary battery module may be battery cells in which, for example, a battery exterior film is used as an exterior material and battery elements including at least a positive electrode material layer, a negative electrode material layer, a separator, a positive electrode current collector, and a negative electrode current collector are enclosed within the exterior material. A secondary battery module capable of mounting the heat absorber of this embodiment will be described below with reference to FIG. 1 . FIG. 1 shows a cross-sectional view of a stacked battery 20 as an example of a secondary battery. It should be noted that the secondary battery capable of mounting the heat absorber of this embodiment is not limited to the flat stacked battery 20 shown in FIG. 1 . The secondary battery capable of mounting the heat absorber of this embodiment may be cylindrical, such as a wound secondary battery, or may be a cylindrical secondary battery modified to have a flat rectangular shape. In this embodiment, the stacked battery 20 has a structure in which a flat, approximately rectangular battery element 10, in which charge and discharge reactions essentially proceed, is sealed inside battery exterior materials 18a, b. The battery element 10 has a structure in which a positive electrode, an electrolyte layer (or separator) 14, and a negative electrode are stacked. The positive electrode has a structure in which a positive electrode material layer 11 containing a positive electrode active material is disposed on both sides of a positive electrode current collector 12. The negative electrode has a structure in which a negative electrode material layer 16 containing a negative electrode active material is disposed on both sides of a negative electrode current collector 17. One positive electrode material layer 11 and the negative electrode material layer 16 adjacent to the positive electrode material layer 11 are arranged to face each other with the electrolyte layer 14 interposed therebetween, and the positive electrode, electrolyte layer 14, and negative electrode are stacked in sequence. As a result, adjacent positive electrodes, electrolyte layers 14, and negative electrodes form a single cell body. The stacked battery 20 shown in FIG. 1 has a structure in which a plurality of such cell bodies are stacked and electrically connected in parallel. In addition, an activated carbon layer 19 is provided to adsorb components derived from the positive electrode active material due to melting or sublimation of the positive electrode active material when the battery is exposed to high temperatures.As shown in FIG. 1 , the positive electrode current collector 12 and the negative electrode current collector 17 are respectively attached with a positive electrode terminal 13 and a negative electrode terminal 15, which electrically connect the positive and negative electrodes, and are structured to be sandwiched between the ends of the battery exterior materials 18a and 18b and extend outside the battery exterior materials 18a and 18b. The positive electrode terminal 13 and the negative electrode terminal 15 may be attached to the positive electrode current collector 12 and the negative electrode current collector 17 of each electrode by welding or the like via a positive electrode lead and a negative electrode lead (not shown), as necessary. The battery exterior materials 18a and 18b are made of laminated film, and typically, sealant layers formed on the surfaces of the battery exterior films 18a and 18b are heat-sealed to each other. The battery exterior materials 18a and 18b have a region at their peripheries where the sealant layers are in close contact with each other by heat sealing.

[0053] Next, a secondary battery module incorporating the heat absorber of this embodiment will be described with reference to FIG. 2 . FIG. 2 is a perspective view schematically illustrating the disassembled state of the secondary battery module of FIG. 1 . The battery element 10 shown in FIG. 2 has a configuration in which a positive electrode formed on a positive electrode current collector 12 (e.g., aluminum foil) having a positive electrode terminal 13 and a negative electrode disposed on a negative electrode current collector 17 (e.g., metal foil) having a negative electrode terminal 15 are stacked so as to face each other with a separator 14 containing an electrolyte interposed therebetween. A plurality of battery elements 10 are stacked and sealed with battery exterior materials 18 a, b (e.g., aluminum laminate exteriors). The heat absorber 1 of this embodiment is arranged so as to contact the negative electrode current collector 17. The heat absorber 1 may be arranged so as to contact not only the negative electrode current collector 17 but also the positive electrode current collector 12. Therefore, a secondary battery module having a heat absorber 1 mounted on a battery element 10 has one or more laminates in which a positive electrode formed on a positive electrode current collector 12 (e.g., aluminum foil) having a positive electrode terminal 13, a separator 14 containing an electrolyte, and a negative electrode disposed on a negative electrode current collector 17 (e.g., metal foil) having a negative electrode terminal 15 are sequentially stacked, and the one or more heat absorbers 1 can be arranged so as to abut the positive electrode current collector 12 and / or the negative electrode current collector 17 but not to abut the separator 14. When a solid electrolyte or a gel electrolyte is used as the electrolyte, the electrolyte can be interposed between the electrodes instead of the separator 14. On the other hand, the hydrogel or aqueous solvent contained in the heat absorber of this embodiment does not come into direct contact with the battery element 10. Therefore, a suitable heat sink for a secondary battery in this embodiment has a hydrogel and a bag filled with the hydrogel, but the contents of the bag do not include the hydrogel or aqueous solvent so that the battery element 10 comes into direct contact with the hydrogel or aqueous solvent, and more preferably, the contents of the bag for the heat sink for a secondary battery do not include the above-mentioned battery element 10.

[0054] The secondary battery module of the present disclosure may include a heat absorber 1 of the present embodiment sandwiched between adjacent battery elements 10 (also referred to as battery cells) housed in multiple cases (not shown) or multiple battery exterior films 18a, b. The cases may be formed, for example, from aluminum, iron, or a metal material containing these, or a resin material such as polyphenylene sulfide. Forming the cases from a resin material contributes to reducing the weight of the secondary battery module. The heat absorber 1 may be sandwiched between the multiple battery elements 10 using, for example, adhesives, fusion (ultrasonic fusion, high-frequency fusion, or heat fusion), or pressure-sensitive adhesives. With this configuration, the heat absorber 1 sandwiched between the battery elements 10 absorbs heat generated during charging of the secondary battery, thereby suppressing a sudden temperature rise in the battery elements 10 and preventing deterioration, fire, and the like of the battery elements 10. Furthermore, since the heat absorber 1 contains a hydrogel that has absorbed an aqueous solvent, when the heat absorber 1 is sandwiched between the battery elements 10, the thermal insulation properties can suppress the temperature influence between the battery elements 10, and furthermore, the cushioning properties of the swollen hydrogel act as a buffer for volume changes due to expansion of the battery elements 10, which is thought to make it easier to alleviate the rise in internal pressure of the secondary battery module.

[0055] The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to the examples given below.

[0056] (1) Evaluation Method [Measurement of Endothermic Onset Temperature, Endothermic Peak Temperature, and Endothermic Amount] The endothermic onset temperature and endothermic peak temperature of the hydrogels prepared in this example were measured as follows. Using a differential scanning calorimeter (DSC; DSC-7020, manufactured by Hitachi High-Tech Corporation), the temperature was raised from 20°C to 350°C at a rate of 1°C / min under a nitrogen atmosphere. The endothermic onset temperature (°C) was determined as 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 drawn at the point where the gradient of the low-temperature side curve of the endothermic peak associated with evaporation is maximum. The endothermic onset temperature (°C) was determined as the point where the difference from the baseline of the DSC measurement curve was maximum. The endothermic amount (J / g or mJ / mg) was determined by dividing the integral of the endothermic peak based on the baseline of the DSC measurement curve by the mass of the endothermic agent used in the measurement.

[0057] [Evaluation of cushioning properties] Hydrogels were removed from the heat absorbers (1) and (2) prepared in this example, and the cushioning properties of each were evaluated as follows. Specifically, at room temperature (23°C), the hydrogels were cut into pieces measuring 10 cm length x 10 cm width x 1 cm height, and placed in a tabletop precision universal testing machine ("Autograph AGS-X" manufactured by Shimadzu Corporation) equipped with a 5 mmφ indentation jig, and an indentation test was performed. The indentation test was performed by observing the return of the surface after 5 minutes of indentation at 1 MPa for 60 seconds, and evaluating the return according to the following criteria: Returned to 90% or more of the original height: ◎ Returned to 80% or more of the original height: ◯ Returned to 70% or more of the original height: △ Returned to less than 70% of the original height: ×

[0058] [Evaluation of Flame Retardancy] Each dispersion used in the examples was poured into a 1 mm thick container and polymerized at 20°C to obtain a 1 mm thick sheet of organic-inorganic composite hydrogel. This sheet was cut into 125 mm x 13 mm and measured in accordance with the 20 mm vertical flame test (IEC 60695-11-10B, ASTM D38 01) of the UL94 flame test to evaluate flame retardancy. Flame retardancy of V-1 is satisfactory for practical use, and V-0 is preferred. Good: UL94 standard V-0 Pass: UL94 standard V-1 Fail: UL94 standard less than V-1

[0059] [Evaluation of Freezing Resistance] The endotherms (1) and (2) prepared in the examples were placed in a freezer at −20° C. and left for 24 hours, after which the above-mentioned [Evaluation of cushioning properties] was carried out to evaluate the freezing resistance.

[0060] (2) Examples and Comparative Examples Example 1 20 parts by mass of N,N-dimethylacrylamide (hereinafter abbreviated as "DMAA"), 4.8 parts by mass of water-swellable synthetic hectorite (manufactured by BYK Japan K.K., "Laponite RD"), 0.5 parts by mass of sodium peroxodisulfate (hereinafter abbreviated as "NPS"), and 0.8 parts by mass of N,N,N',N'-tetramethylethylenediamine (hereinafter abbreviated as "TEMED") were mixed and stirred in 100 parts by mass of pure water to obtain a uniform dispersion (a-1) (see Table 1). Subsequently, the dispersion (a-1) was poured into a bag-shaped container (manufactured by Mitsubishi Gas Chemical Company, Inc., "Gas Barrier Bag" length 100 mm x width 300 mm x thickness 0.094 mm, composed of a laminate of PET, aluminum foil, and polyethylene), and the inlet was closed by heat sealing. The aluminum pouch was placed flat between 1 cm thick gap materials, a flat plate was placed on top of it, and the resulting mixture was allowed to stand at 20°C for 15 hours to produce a 1 cm thick sheet-like heat absorber (1). The resulting heat absorber (1) was then evaluated according to the procedures described above in the "Evaluation of cushioning properties" and "Evaluation of flame retardancy." The results are shown in Table 1. The swollen organic-inorganic composite hydrogel contained in the heat absorber (1) of Example 1 was removed, and the endothermic peak temperature and endothermic amount were evaluated under the DSC measurement conditions described above. The DSC curve is shown in Figure 3.

[0061] Example 2 20 parts by mass of DMAA, 4.8 parts by mass of water-swellable synthetic hectorite (manufactured by BYK Japan K.K., "Laponite RDS"), 0.5 parts by mass of NPS, and 0.8 parts by mass of TEMED were mixed and stirred in 100 parts by mass of a mixed solution consisting of 80 parts by mass of pure water and 20 parts by mass of glycerin to obtain a uniform dispersion (a-2). A sheet-shaped heat absorber (2) was then produced in the same manner as in Example 1 (see Table 1). The obtained heat absorber (2) was then evaluated according to the procedures described above in the "Evaluation of cushioning properties" and "Evaluation of flame retardancy." The results are shown in Table 1. The swollen organic-inorganic composite hydrogel contained in the heat absorber (2) of Example 2 was removed, and the endothermic peak temperature and endothermic amount were evaluated under the DSC measurement conditions described above. The DSC curve is shown in FIG. 4.

[0062]

[0063] It was confirmed that the DSC measurement curves of the endotherms of Examples 1 and 2 descended from the start of the measurement. Furthermore, the endothermic onset temperatures of the endotherms of Examples 1 and 2 were determined from the DSC measurement curves according to the method for measuring endothermic onset temperature described in the above section [Measurement of endothermic onset temperature, endothermic peak temperature, and endothermic amount]. As a result, the endothermic onset temperatures were around 100°C for the endothermic endotherm (1) of Example 1, and around 125°C for the endothermic endotherm (2) of Example 2. Therefore, it was confirmed that the endothermic endotherms of Examples 1 and 2 have low endothermic onset temperatures and endothermic peak temperatures, and also exhibit excellent endothermic amounts, cushioning properties, and flame retardancy. Furthermore, when the endothermic endotherms (1) and (2) of Examples 1 and 2 were placed in a freezer at -20°C for 24 hours and then removed from the refrigerator to evaluate their cushioning properties, the cushioning properties of the endothermic endotherm (1) of Example 1 were reduced, while the cushioning properties of the endothermic endotherm (2) of Example 2 were maintained, and therefore the endothermic endotherm (2) of Example 2 had excellent freeze resistance. In this embodiment, without a pouch containing the hydrogel or aqueous solvent, the contents of the hydrogel or aqueous solvent would dissipate, and as the battery temperature rises or over time, sufficient heat absorption, flame retardancy, and cushioning properties would not be obtained. However, the heat absorber of this embodiment prevents the contents from dissipating because the pouch keeps the contents inside, and sufficient heat absorption, flame retardancy, and cushioning properties can be obtained even when the battery temperature rises or over time.

[0064] [Explanation of symbols] 1 laminate 10 battery element 11 positive electrode material layer 12 positive electrode current collector 13 positive electrode terminal 14 electrolyte layer (or separator) 15 negative electrode terminal 16 negative electrode material layer 17 negative electrode current collector 18a, b battery exterior material 19 activated carbon layer 20 laminated battery

Claims

1. The device has a bag that can be filled with a content, and a hydrogel that is filled in the bag as the content, The water vapor permeability ([g / (m 2 ·24 h)]) of the sheet constituting the bag body is greater than 0 g / (m 2 ·24 h) and not greater than 50 g / (m 2 ·24 h); The hydrogel is an organic-inorganic composite hydrogel made from at least a water-soluble organic monomer and a water-swellable clay mineral as reaction raw materials, and the content of the hydrogel is in the range of 20% by mass to 100% by mass with respect to the total amount of the contents of the bag, and the heat absorption onset temperature is 160°C or lower.

2. The heat sink according to claim 1 , wherein the hydrogel has a cushioning property of 90% or more as determined by the following evaluation method. Evaluation method: At room temperature (23°C), the hydrogel was cut into a size of 10 cm length x 10 cm width x 1 cm height, and placed in a tabletop precision universal tester equipped with a 5 mm diameter pressing tool. The hydrogel was pressed at 1 MPa for 60 seconds, and then the degree to which the hydrogel surface returned to its original height after 5 minutes had elapsed was evaluated.

3. The heat absorber described in claim 1, wherein the content of the water-swellable clay mineral contained in the dispersion liquid (a) containing the reaction raw materials, namely the water-soluble organic monomer and the water-swellable clay mineral, a polymerization initiator, and an aqueous solvent, is in the range of 0.1 mass % to 50 mass % relative to the total amount (mass) of the water-soluble organic monomer, the water-swellable clay mineral, and the aqueous solvent.

4. The heat absorber described in claim 1, wherein the amount of heat absorbed at the endothermic peak temperature (in the range of 80°C to 160°C) is in the range of 100 J / g or more and 3000 J / g or less.

5. The heat absorber according to any one of claims 1 to 4, further comprising a low-volatility solvent as the content.

6. The heat absorber according to any one of claims 1 to 4, which is used in a secondary battery.

7. A secondary battery module comprising the heat absorber according to any one of claims 1 to 4.

8. The secondary battery module according to claim 7 , wherein the heat sink is sandwiched between battery cells.

9. 8. The secondary battery module according to claim 7, wherein the heat sink has a total thickness in the range of 100 to 50,000 μm.