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

Abstract

The present invention provides a heat-absorbing material that exhibits excellent heat absorption, heat insulation, and pressure resistance, and can transform into a heat-insulating material in high-temperature ranges, as well as a secondary battery module equipped with the heat-absorbing material. [Solution] The secondary battery module comprises a heat-absorbing body 1 having a bag into which contents can be filled, and an aqueous solvent and a water-soluble inorganic powder that are filled into the bag as contents. The heat-absorbing body has a bag into which contents can be filled, and an aqueous solvent and a water-soluble inorganic powder that dissolves at a rate of 1 g or more per 100 g of water at 20°C, which are filled into the bag as contents. As a result, it has excellent heat absorption, heat insulation, and pressure resistance, and can transform into a heat-insulating body in high-temperature ranges.

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. Furthermore, Patent Document 2 describes a partition member comprising a liquid, an insulating material, and an outer casing that contains the liquid and the insulating material. According to Patent Document 2, by appropriately setting the peel strength of the sealant resin layer of the sheet-like member in contact with the insulating material and the crystal melting characteristics of the sealant resin layer, the partition member maintains its cooling function during long-term use and exhibits excellent stability in the release temperature of the cooling liquid inside the sheet-like member. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] International Publication No. 2022 / 270359 [Patent Document 2] Japanese Patent Publication No. 2020-161290 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, the technology described in Patent Document 1 above is produced by an endothermic reaction of water contained in layer A (for example, water molecules in sodium silicate) in the temperature range of 100 to 300°C, which limits the amount of water that can be contained and prevents obtaining a sufficient endothermic effect. Furthermore, the technology described in Patent Document 2 merely lists various porous materials, fibrous materials, or particles as thermal insulation materials, and does not consider at all how the partition member itself exhibits a thermal insulation effect in a battery that has reached abnormally high temperatures, thereby suppressing, preventing, or delaying chain explosions by inhibiting heat transfer to other cells. Moreover, when separator members such as the partition members described in Patent Document 2 are used in a stacked secondary battery, the thickness between adjacent cells changes when the cells themselves expand and contract due to charging and discharging, or when cells rapidly expand during thermal runaway, so the separator member is required to have certain mechanical properties such as pressure resistance. However, since mechanical properties such as pressure resistance are not considered in Patent Document 2, a problem arises in which heat is easily transferred between adjacent cells, especially when cells expand, because the distance between cells shortens. Therefore, an object of the present disclosure is to provide a heat absorber having excellent heat absorption properties and capable of changing into a heat insulator in a high-temperature region, thereby having excellent heat insulation properties and pressure resistance, 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 an aqueous solvent and a water-soluble inorganic powder in a bag exhibits excellent heat absorption, heat insulation, and pressure resistance, and can change into a heat insulator in a high-temperature region (for example, 150°C or higher), and have completed the following present invention. [1] The present disclosure is a heat absorber having a bag capable of filling contents, and an aqueous solvent and a water-soluble inorganic powder that is filled into the bag as the contents and dissolves 1 g or more in 100 g of water at 20°C.

[0007] [2] The heat absorber according to [1], wherein the water-soluble inorganic powder has a solubility (g) in water at 20°C of 5 g / 100 g or more.

[0008] [3] The heat absorber according to [1] or [2], further containing one or more selected from the group consisting of an antifreeze and inorganic fibers in the contents.

[0009] [4] The heat absorber according to any one of [1] to [3], wherein the water-soluble inorganic powder is one or more selected from chlorides, sulfates, carbonates, nitrates, phosphates, acetates, alkali metal oxides, and alkaline earth metal oxides.

[0010] [5] The heat absorber according to any one of [1] to [4], wherein an aqueous solution containing the aqueous solvent and the water-soluble inorganic powder is filled in the contents, and the content of the water-soluble inorganic powder in the aqueous solution is 5 to 80% by mass based on the total amount of the aqueous solution.

[0011] [6] The heat absorber according to any one of [1] to [5], wherein the contents change into a porous body when heated to 120°C or higher.

[0012] [7] The following equation (I): [Mathematics 1] "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 The heat absorber was heated using the specified amount of heat until the temperature of the side opposite to the heating surface (back surface) reached a predetermined temperature. Then, the heat absorber was allowed to dissipate heat at room temperature, and naturally cooled until the surface temperature of the heat absorber returned to room temperature. The percentage change in thickness before and after heating was then calculated. The heating surface of the heat absorber was subjected to pressure of 0.5 MPa for 60 seconds. A heat-absorbing body according to any of [1] to [6], wherein the thickness change rate represented by is 70% or more.

[0013] A secondary battery module equipped with a heat absorber as described in any of [8][1] to [7].

[0014] A secondary battery module in which a heat-absorbing material described in any of [9][1] to [7] is sandwiched between battery cells. [Effects of the Invention]

[0015] The heat-absorbing material of this disclosure provides a heat-absorbing material that is excellent in heat absorption and can transform into an insulating material in the high-temperature range, thereby providing a heat-absorbing material with excellent thermal insulation and pressure resistance. According to this disclosure, by providing a heat-absorbing material that has excellent heat absorption properties and can transform into an insulating material in high-temperature ranges, a highly safe secondary battery module can be provided, which also has excellent heat insulation and pressure resistance properties. [Brief explanation of the drawing]

[0016] [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 is a graph showing the results of a cone calorimeter test (test conditions: radiant intensity 50 kW / m2, heating time 20 minutes) for the heat absorber of the example and the sheet of the comparative example, with the vertical axis representing temperature and the horizontal axis representing elapsed time. [Figure 4] Figure 4 shows a schematic diagram of the cone calorimeter test apparatus used in the examples and comparative examples. [Figure 5] Figure 5(a) is an image showing that the heat-absorbing body (1) prepared in Example 1 has changed into a porous body. Figure 5(b) is an image showing that the heat-absorbing body (2) prepared in Example 2 has changed into a porous body. Both Figures 5(a) and (b) are images showing the state after the edge of the porous body has been cut. [Modes for carrying out the invention]

[0017] 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.

[0018] [Heat absorber] The heat-absorbing body of this disclosure comprises a bag into which contents can be filled, and a water-soluble inorganic powder that dissolves in 1 g or more of water at 20°C, which is filled into the bag as the contents, and consists of an aqueous solvent. This results in excellent heat absorption, heat insulation, and pressure resistance, and the ability to transform into an insulating material at high temperatures. The material can absorb heat through the latent heat of vaporization of the aqueous solvent inside the bag or through the water-soluble inorganic powder. Therefore, it can utilize 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, it can stabilize the temperature even at room temperature. On the other hand, when exposed to high temperatures such as combustion, the aqueous solvent evaporates, but the presence of the water-soluble inorganic powder provides heat insulation and fire prevention effects. More specifically, at relatively low temperatures (e.g., above room temperature to around 100°C), it mainly acts as a heat absorber. 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 water-soluble inorganic powder inside the heat absorber changes into a porous material, so it can also act as a heat insulator. As a result, when the heat absorber of this embodiment is placed between the battery cells of a battery stack (battery module) in which multiple battery cells are stacked, the thermal influence on adjacent cells can be blocked or suppressed.

[0019] Furthermore, the heat-absorbing material of this disclosure has fluid contents at relatively low temperatures, making it easy to conform to and adhere to cells, and it can exhibit cushioning properties that absorb stress even when cells expand and contract due to heat. On the other hand, at temperatures exceeding the thermal runaway temperature, the water-soluble inorganic powder inside the heat-absorbing material sintersects and deforms into a hard, plate-like porous body, thereby increasing its compressive strength. As a result, the distance between cells can be kept constant, thus maintaining effective heat insulation, controlling thermal conductivity, and effectively suppressing chain explosions between cells.

[0020] In the endothermic body of this disclosure, the aqueous solvent may, if necessary, be included in the contents of this embodiment as a hydrogel composed of a hydrogel body and an aqueous solvent. By including a hydrogel body as the contents, cushioning and impact resistance can be imparted to the heat-absorbing material. 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.

[0021] The contents of the heat-absorbing body of this embodiment may further contain one or more selected from the group consisting of inorganic fibers, antifreeze agents, and additives. Further inclusion of inorganic fibers as contents can impart cushioning and pressure resistance to the heat-absorbing material, or the inorganic fibers can act as foaming nuclei, making it easier for the water-soluble inorganic powder to form a foam (=porous material). In addition, the inorganic fibers included as contents retain water, making it easier to mold the heat-absorbing material into a desired shape. Furthermore, when the aqueous solvent evaporates, voids are created within the inorganic fibers, and the composite containing the inorganic fibers and water-soluble inorganic powder becomes more likely to form a porous material. As a result, the material changes from a heat-absorbing material to an insulating material, allowing it to exhibit both heat absorption and insulating effects more effectively across its entire thickness. Furthermore, by including an antifreeze as part of the contents, freezing below freezing point can be suppressed. In addition, by utilizing the heat of solidification of an 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.

[0022] <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 heat-absorbing element in this embodiment is preferably in the range of at least 80°C to 400°C, and more preferably in the range of 90°C to 160°C. In this specification, the endothermic peak temperature refers to the temperature (°C) at the maximum value of the endothermic peak due to evaporation in 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 160°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 160°C), it is preferably in the range of 100 J / g to 3000 J / g, more preferably 200 J / g to 2500 J / g, even more preferably 300 J / g to 2000 J / g, and even more preferably 500 J / g to 1500 J / g. The preferred range of heat absorbed can be achieved by appropriately 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.

[0023] <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 average thickness is preferably 100 μm or more, more preferably 200 μm to 20,000 μm, even more preferably 500 μm to 10,000 μm, and particularly preferably 1,000 μm to 8,000 μm. The preferred range of the average thickness can be achieved by appropriately combining the above upper and lower limits. The following describes the essential components of the heat-absorbing body of this embodiment, which include a bag, a water-soluble inorganic powder that dissolves in 1 g or more of water at 20°C, and an aqueous solvent, as well as optional components such as inorganic fibers, antifreeze, and additives that may be added as needed.

[0024] (Bag body) The bag of this embodiment is not particularly limited as long as it can be filled with contents such as an aqueous solvent and a water-soluble inorganic powder that dissolves in 1 g or more of water at 20°C. A preferred bag is a three-sided bag having an opening at the top and a closed bottom, and a structure that allows the opening to be heat-sealed after all the contents, such as the aqueous solvent and water-soluble inorganic powder, have been contained. The three-sided bag is constructed by joining the lower ends and sides of two sheets together, and then sealing it after filling it with contents through the opening. As such, it offers excellent airtightness and, due to its 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. 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). 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.

[0025] For example, in the present invention, a bag-like body made of a laminate film is preferred, and as the laminate film, a film made by laminating a metal foil and a resin film is preferred, and a laminated film with a three-layer structure consisting of an outer resin film / metal foil / inner resin film is an example. Specifically, a bag body made by sealing a resin-based film having an aluminum vapor-deposited layer on the outside via a polyurethane-based laminate adhesive layer, a bag body made by sealing 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 via a polyurethane-based laminate adhesive layer, or a bag body made by sealing a laminate film having a PET layer, an aluminum layer and a polyethylene layer via a polyurethane-based laminate adhesive layer can be suitably used. For example, gas barrier aluminum bag AB series (manufactured by Mitsubishi Gas Chemical Company, Inc.) and Lamizip AL type (manufactured by Seisan Nipponsha Co., Ltd.) can be cited. The higher the melting temperature (e.g., 120-140°C) of the adhesive used to close the opening of the bag in this embodiment or the adhesive provided in the heat-sealed area, the higher the strength and the greater the ability to withstand internal pressure.

[0026] The water vapor permeability of the sheet constituting the bag body of this embodiment is ([g / (m³) 2 (24h)) is 50g / (m 2 It is preferable that it is 24 hours or less, and 10 g / (m 2 It is more preferable that it be 24 hours or less, and 5 g / (m 2 It is even more preferable that it be 24 hours or less. The water vapor permeability of the sheet constituting the bag is 50 g / m². 2 If the time is within the range of 24 hours or less, it is possible to prevent moisture inside the bag from leaking out to the outside, which is preferable from the viewpoint of preventing a decrease in heat absorption performance over time. Water vapor transmission rate in this specification ([g / (m 2 The 24h measurement was taken in accordance with the JIS K7129 standard, under conditions of 40°C and 90% relative humidity.

[0027] (A water-soluble inorganic powder that dissolves at least 1 g in 100 g of water at 20°C (hereinafter also referred to as water-soluble inorganic powder)). The heat-absorbing body of this embodiment contains a water-soluble inorganic powder. This water-soluble inorganic powder dissolves at a rate of 1 g or more per 100 g of water at 20°C. Because the water-soluble inorganic powder exhibits hydrophilicity, it readily dissolves in aqueous solvents, allowing for a uniform distribution of the 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 easily forms a homogeneous porous body, effectively acting as an insulator. Furthermore, when water-soluble inorganic powder and an aqueous solvent are present in the contents of the heat absorber, a synergistic effect with the heat absorption 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 heat absorber is exposed to high temperatures, the water-soluble inorganic powder can become porous (see, for example, the photographs in Figures 5 and 6 described later). As a result, it exhibits excellent heat insulation and fire prevention effects. Therefore, a heat absorber containing water-soluble inorganic powder mainly functions as a heat absorber in a relatively low temperature range (e.g., above room temperature to around 100°C). On the other hand, in the temperature range from the critical temperature (e.g., 150°C) to the runaway thermal temperature (e.g., around 1000°C), the entire water-soluble inorganic powder becomes porous, and can therefore also act as a heat absorber. As a result, when the heat absorber of this embodiment is placed between cells in a battery stack in which multiple cells are stacked, the thermal influence on adjacent cells can be blocked or suppressed. 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 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 effectively suppressing chain explosions between cells.

[0028] 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.

[0029] The solubility of the water-soluble inorganic powder in this embodiment is 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.

[0030] 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.

[0031] 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 calculated by appropriately rearranging the above upper and lower limits.

[0032] 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 calculated by appropriately rearranging the above upper and lower limits.

[0033] 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.

[0034] The method for measuring solubility in this specification is as follows: After weighing a specified amount of the water-soluble inorganic powder to be measured into a glass bottle, 100 g of pure water (pH=7) is added to the glass bottle, and the mixture 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 mixture 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

[0035] 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.

[0036] The heat absorbed by the water-soluble inorganic powder (= 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 heat absorbed by the water-soluble inorganic powder is not particularly limited, but is preferably 4000 J / g or less. The heat absorbed by the water-soluble inorganic powder is preferably 100 J / g or more and 4000 J / g or less, more preferably 500 J / g or more and 4000 J / g or less. The upper and lower limits of the heat absorbed by the water-soluble inorganic powder can be changed as appropriate. When the amount of heat absorbed by the above-mentioned water-soluble 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-mentioned content can be combined as appropriate. The heat absorption of water-soluble inorganic powders can be measured using a differential scanning calorimeter (DSC), as described in the Examples section.

[0037] The thermal decomposition initiation temperature of the water-soluble 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. Having the thermal decomposition initiation temperature of the water-soluble inorganic powder within the above range allows the water-soluble inorganic powder itself to decompose rapidly, making it easier to suppress ignition. The upper and lower limits of the thermal decomposition initiation temperature can be appropriately rearranged. The thermal decomposition initiation temperature can be measured using a differential scanning calorimeter (DSC).

[0038] The shape of the water-soluble inorganic powder in this embodiment is not particularly limited and can be, for example, in powder, particulate, crystalline, or plate form. Furthermore, the water-soluble inorganic powder in this embodiment is preferably one that has an endothermic effect, and preferred embodiments of the water-soluble inorganic powder include porous powder, solid particles, or hollow particles. The water-soluble inorganic powder may be in any shape or form as long as it is dissolved in an aqueous solvent. When the water-soluble inorganic powder is in powder or particulate form, the average particle size of the water-soluble inorganic powder is preferably 0.01 to 200 μm, more preferably 0.1 to 140 μm, and even more preferably 10 to 100 μm. By setting the average particle size within the above range, the water-soluble inorganic powder disperses easily within 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.

[0039] 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. 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 within the bag, the hydrate of the water-soluble inorganic powder usually exists as an anhydrous form.

[0040] 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.

[0041] The content of the water-soluble inorganic powder in this embodiment can be 1 to 90% by mass, 3 to 80% by mass, preferably 5 to 60% by mass, more preferably 10 to 50% by mass, more preferably 10 to 35% by mass, and even more preferably 15 to 30% by mass, based on the total amount (100% by mass) of the contents of the endotherm. When the content of water-soluble inorganic powder is within the above range, the heat-absorbing material readily sintersects when exposed to high heat, forming a homogeneous porous body. Furthermore, when the water-soluble inorganic powder is a hydrate, the content of the water-soluble inorganic powder does not include the water content contained in the hydrate that is the water-soluble inorganic powder. The above upper and lower limits for the content of the water-soluble inorganic powder can be adjusted as appropriate.

[0042] 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. The temperature at which the contents change into a porous material is preferably 150°C or higher, preferably 180°C or higher, preferably 200°C or higher, preferably 210°C or higher, preferably 240°C or higher, and preferably 250°C or higher. When a heat-absorbing material is exposed to high temperatures due to combustion or other means, the aqueous solvent evaporates, but a porous body can be formed by the sintering of water-soluble inorganic powders. As a result, the heat-absorbing material can exhibit heat insulation and fire-preventive effects on adjacent components (e.g., battery cells). In particular, when a component (e.g., a battery cell) is sandwiched or surrounded by two or more heat-absorbing elements of this embodiment, it is considered that heat from the component is less likely to leak to the outside. For example, when the component is exposed to high heat, the water-soluble inorganic powder inside the heat-absorbing element forms a porous body through sintering, and this porous body acts as a firewall, thus exhibiting excellent heat insulation and fire prevention effects. Therefore, when the heat-absorbing elements of this embodiment are placed in a secondary battery module such as a stacked battery described later, heat transfer to other cells can be suppressed, prevented, or delayed to suppress chain explosions.

[0043] (Aqueous solvent) The heat-absorbing body of this embodiment contains an aqueous solvent as its contents. This allows it to absorb heat using the latent heat of vaporization of the aqueous solvent inside the bag, particularly water, which has a larger heat absorption capacity than typical hydrates. Furthermore, because it absorbs heat as the sensible heat of the aqueous solvent, it can stabilize the temperature even at room temperature. On the other hand, when the heat-absorbing body is exposed to high temperatures due to combustion or the like, the aqueous solvent evaporates, but a porous body formed by sintering water-soluble inorganic powder can be created, thus providing heat insulation and fire protection effects to the heat-absorbing body and adjacent components.

[0044] 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, and 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.

[0045] 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. In this embodiment, the content of the aqueous solvent is preferably 10% to 95% by mass, more preferably 20% to 90% by mass, even more preferably 30% to 80% by mass, and particularly preferably 50% to 70% by mass, based on the total amount (100% by mass) of the contents of the endotherm. 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 heat absorption, heat insulation, and pressure resistance, and can transform into a heat insulating material in high-temperature ranges.

[0046] The above describes the essential components of this disclosure: the bag, the water-soluble inorganic powder, and the aqueous solvent. The following describes the optional components of this disclosure: the inorganic fiber, the antifreeze, and the additives.

[0047] The contents of the heat-absorbing body in this embodiment may contain one or more selected from the group consisting of inorganic fibers and antifreeze agents. (Inorganic fibers) The inorganic fibers of this embodiment are a fiber aggregate in which fibers made of inorganic material are intertwined, or a porous body made of inorganic material, and the water-soluble inorganic powder acts as a foaming nucleating agent, facilitating the formation of the porous body. Furthermore, when the soluble water-soluble inorganic powder transforms into a porous body, a porous composite containing the inorganic fibers and the water-soluble 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.

[0048] 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 (temperature ranges from the critical temperature (e.g., 150°C) to the runaway thermal temperature (e.g., around 1000°C)), thus tending to act as an insulator. In particular, if the inorganic fibers have a specific void ratio, they can be combined with water-soluble inorganic powders to become an even better insulator.

[0049] <Porosity> The average porosity of the inorganic fibers in this embodiment is preferably 30% or more and 99.7% or less, more preferably 50% or more and 99.5% or less, still more preferably 70% or more and 99.3% or less, and particularly preferably 90% or more and 99% or less. In this specification, the average porosity of the inorganic fibers is a value obtained from the bulk density and the true density described below, and is the density based on the volume occupied by the inorganic fibers. The bulk density is the density based on the volume including the voids contained in the inorganic fibers. In contrast, the true density is the density based on the volume occupied by the material of the inorganic fibers. The average porosity (%) can be obtained from the following bulk density ρf and true density ρr using the following formula (1). Average porosity (%) = ((1 / ρf) - (1 / ρr)) / (1 / ρf) × 100 ··· Formula (1)

[0050] <Bulk density> The bulk density ρf of the inorganic fibers in this embodiment is preferably 0.020 g / cm 3 or more and 1 g / cm 3 or less, more preferably 0.022 g / cm 3 or more and 0.5 g / cm 3 or less, still more preferably 0.024 g / cm 3 or more and 0.1 g / cm 3 or less, and particularly preferably 0.026 g / cm 3 or more and 0.07 g / cm 3 or less. After measuring the dimensions of the inorganic fibers and calculating the bulk volume V of the inorganic fibers, the mass M of the inorganic fibers is measured using a precision balance. The bulk density of the inorganic fibers can be obtained from the obtained mass M and bulk volume V using the following formula (2). Bulk density ρf (g / cm 3 ) = M / V ·· Formula (2)

[0051] <True density> The true density ρr of the inorganic fibers in this embodiment is preferably 0.5 g / cm 3 or more and 10 g / cm 3 or less, more preferably 1 g / cm 3 or more and 7 g / cm 3More 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.

[0052] <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.

[0053] <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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] The BET specific surface area of ​​inorganic fibers ranges from 0.3 to 5000 m². 2 It can also be / g, and 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).

[0058] 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.).

[0059] 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).

[0060] <Preferred embodiment of inorganic fiber> Preferred embodiments of the inorganic fibers in this embodiment are glass cloth, ceramic wool, rock wool, and glass wool.

[0061] 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 the high-temperature range.

[0062] <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 or contents as needed. In particular, by adding an antifreeze agent to the contents of the heat-absorbing body, 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 such as formic acid, propionic acid, or succinic acid, and 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.

[0063] 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. 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 amount of the antifreeze can be adjusted by appropriately combining the above upper and lower limits. Furthermore, by including the antifreeze within the above range, freezing is difficult even at -20°C, allowing the battery to be used over a wide temperature range.

[0064] (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.

[0065] 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.

[0066] 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.

[0067] 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).

[0068] (Method for manufacturing a heat absorber) A preferred method for manufacturing the heat-absorbing body of this embodiment includes the steps of filling a bag with an aqueous solvent, a water-soluble inorganic powder, and one or more selected from the group consisting of inorganic fibers and additives, which are added as needed, through the opening of the bag, and sealing the bag by sealing the opening of the bag. The aqueous solvent, the water-soluble inorganic powder, and one or more selected from the group consisting of inorganic fibers and additives, which may be added as needed, may be filled separately through the opening of the bag, or a mixed solution (1) may be prepared in advance by impregnating or dispersing the water-soluble inorganic powder and the inorganic fibers and additives, which may be added as needed, in the aqueous solvent, and then the mixed solution may be filled through the opening of the bag. The mixed solution (1) preferably contains the aqueous solvent and the water-soluble inorganic powder, and more preferably contains the aqueous solvent, the water-soluble inorganic powder, and one or more selected from the group consisting of inorganic fibers and additives, which are added as needed. The mixed solution (1) is, relative to the total amount (100% by mass) of the mixed solution (1), Preferably, the mixture contains 0-50% by mass of inorganic fibers, 10-95% by mass of aqueous solvent, 0-50% by mass of antifreeze, 5-90% by mass of water-soluble inorganic powder (including water in the case of hydrates), and 0-10% by mass of additives. Preferably, it contains 0-30% by mass of inorganic fibers, 10-95% by mass of aqueous solvent, 0-50% by mass of antifreeze, 5-70% by mass of water-soluble inorganic powder (including water in the case of hydrates), and 0-10% by mass of additives. More preferably, it contains 1-12% by mass of inorganic fibers, 20-94% by mass of aqueous solvent, 0-25% by mass of antifreeze, 5-50% by mass of water-soluble inorganic powder (including water in the case of hydrates), and 0-50% by mass of additives. The amount of "water-soluble inorganic powder (including water in the case of a hydrate)" relative to the total amount (100% by mass) of the above mixed solution (1) refers to the amount blended. Therefore, if the water-soluble inorganic powder is a hydrate, the amount of "water-soluble inorganic powder (including water in the case of a hydrate)" includes the amount of water contained in the water-soluble inorganic powder which is a hydrate.

[0069] A suitable heat-absorbing body in this embodiment may be a bag containing, as its contents, inorganic fibers (for example, 4-9% by mass of rock wool relative to the total amount of contents), an aqueous solvent (for example, 20-60% by mass of water relative to the total amount of contents), and a water-soluble inorganic powder (for example, 10-50% by mass of magnesium sulfate relative to the total amount of contents). This makes it possible to provide a heat-absorbing body that has superior heat absorption capacity and pressure resistance, 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 aqueous solvent and the water-soluble inorganic powder contained in the contents of the bag may be preferably 79 to 100% by mass, more preferably 91 to 99.5% by mass, even more preferably 94 to 99% by mass, and even more preferably 96 to 99.4% by mass, relative to the total amount (100% by mass) of the contents of the bag. In this embodiment, the total content of the aqueous solvent, inorganic fibers, and water-soluble inorganic powder contained in the contents of the bag may be preferably 80 to 100% by mass, more preferably 92 to 99.5% by mass, even more preferably 93 to 99.4% by mass, and even more preferably 96 to 99.1% by mass, relative to the total amount (100% by mass) of the contents of the bag. In this embodiment, the total content of the aqueous solvent, inorganic fibers, water-soluble inorganic powder, antifreeze, and additives contained in the contents of the bag may be preferably 83 to 100% by mass, more preferably 94 to 99.8% by mass, even more preferably greater than 95% by mass and 99.6% by mass or less, and even more preferably greater than 96% by mass and 99.5% 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.

[0070] (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 has a bag and contents filled in the bag, wherein the contents include an aqueous solvent (preferably water) and a water-soluble inorganic powder (preferably magnesium sulfate), exhibiting high cushioning properties. More preferably, the heat-absorbing body exhibits high cushioning properties and includes a bag and contents filled in the bag, which include an aqueous solvent (preferably water), a water-soluble inorganic powder (preferably magnesium sulfate), and inorganic fibers (preferably ceramic wool). 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 inorganic fibers, there is a tendency for it 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 2] "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. Furthermore, in the heat-absorbing body of this embodiment, when cushioning is important, the lower limit of the total amount of aqueous solvent, inorganic fiber, water-soluble inorganic powder, and antifreeze contained in the contents may be preferably more than 30% by mass, more preferably 50% by mass or more, even more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, and particularly preferably 100% by mass, relative to the total amount of contents (100% by mass) of the heat-absorbing body. On the other hand, the upper limit of the total amount of aqueous solvent, inorganic fiber, water-soluble inorganic powder, and antifreeze contained in the contents may be preferably 100% by mass or less, and more preferably 50% by mass or less, relative to the total amount (100% by mass) of the contents of the heat absorber. It is believed that when the total amount of inorganic fibers, aqueous solvent, and water-soluble inorganic powder increases relative to the total amount of contents, the inorganic fibers and water-soluble inorganic powder reinforce the elasticity of the contents, resulting in high cushioning properties.

[0071] <High-pressure heat-absorbing material> A preferred heat-absorbing body of this embodiment comprises a bag and contents filled in the bag, wherein the contents comprise an aqueous solvent (preferably water) and a water-soluble inorganic powder (preferably magnesium sulfate), and is a heat-absorbing body with excellent pressure resistance when heated. More preferably, a heat-absorbing body comprises a bag and contents filled in the bag, wherein the contents comprise an aqueous solvent (preferably water), a water-soluble inorganic powder, and inorganic fibers, and is a heat-absorbing body with 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. "Exhibiting pressure resistance during heating" means that the heat-absorbing material exhibits 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 having a bag into which contents can be filled, an aqueous solvent, water-soluble inorganic powder, and inorganic fibers, wherein the inorganic fibers and water-soluble inorganic powder are composite and filled into the contents. In this case, since the water-soluble inorganic powder exhibits excellent solubility in water, the water-soluble inorganic powder can be uniformly dispersed or dissolved in the contents. When inorganic fibers and water-soluble inorganic powders coexist, they temporarily form 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 coexistence of inorganic fibers and water-soluble inorganic powders results in a synergistic effect of high pressure resistance, as the inorganic fibers support the water-soluble inorganic powders and the inorganic fibers promote the dispersibility of the water-soluble inorganic powders. In detail, in this embodiment of the high-pressure heat-absorbing material, heating causes the aqueous solvent (water component) within the heat-absorbing material to exhibit an endothermic effect, evaporating while forming a foamed film. At this time, the decrease in the aqueous solvent creates voids between the inorganic fibers, improving the heat insulation performance. In addition, water-soluble inorganic powder precipitates and is supported on the inorganic fibers during the evaporation process of the aqueous solvent. If the water-soluble inorganic powder is a hydrate, as heating progresses, the water component contained in the hydrate also evaporates while exhibiting an endothermic effect. At this time, if the water-soluble inorganic powder can be uniformly dispersed or dissolved in the aqueous solvent, it is possible to suppress the uneven distribution and support of the water-soluble inorganic powder on the inorganic fibers. As heating progresses, the water-soluble inorganic powder supported on the inorganic fibers sintersects, firmly reinforcing the network structure of the inorganic fibers. Furthermore, the inorganic powder forms a porous structure within the inorganic fibers, further improving the heat insulation properties. As described above, the dispersed presence of the water-soluble inorganic powder enables reinforcement of the network structure and formation of porous structures throughout the entire inorganic fiber region. As a result, the high-pressure heat-absorbing material of this embodiment exhibits a synergistic effect of heat insulation and high pressure resistance. Uniform dispersion means, for example, that when the composite material is removed, the difference in concentration (mass%) of the water-soluble 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-absorbing body 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 body 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%. [Math 3] 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 that has been heated to a predetermined temperature or higher, preferably under the following heating conditions (approximately within 20 minutes from immediately after pressing). 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 high-pressure heat absorber" is the average thickness (arithmetic mean of the thicknesses at any 5 locations) of the heat absorber after heating one surface of the high-pressure heat absorber to a predetermined temperature or higher, preferably under the following heating conditions, and before applying pressure at 0.5 MPa for 60 seconds to one surface of the high-pressure heat absorber. Heating conditions: "50 kW / m² due to radiant heat" 2 After 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-absorbing material can become porous, and can be set according to the operating environment of the heat-absorbing material, 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-absorbing material, heated until the temperature of the side opposite to the heating surface (the side to which radiant heat is directly applied) reaches 150°C, then the heat-absorbing material can achieve a thickness change rate of 150°C or higher even in the temperature range of 150°C or higher. When high pressure resistance is important, it is preferable that the contents of the heat absorber in this embodiment include inorganic fibers, an aqueous solvent, and a water-soluble inorganic powder.

[0072] [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.

[0073] 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 cell (or battery cell) constituting the secondary battery module may be a battery cell in which, for example, a battery outer film is 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 is 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.

[0074] 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, and the battery element 10 do not come into direct contact. Therefore, a preferred heat absorber for secondary batteries in this embodiment is a bag filled with an aqueous solvent, a water-soluble inorganic powder, and inorganic fibers, but the contents of the bag are not such that the aqueous solvent and the battery element 10 come into direct contact, and more preferably, the contents of the heat absorber bag for secondary batteries do not include the battery element 10.

[0075] 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-absorbing body 1 sandwiched between the battery elements 10 absorbs the heat generated during charging of the secondary battery, 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. When the heat-absorbing body 1 is sandwiched between the battery elements 10, the temperature influence between the battery elements 10 can be suppressed by its insulating properties, and it is also thought to 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. On the other hand, when the battery elements 10 experience thermal runaway due to excessive heat generation, the water-soluble inorganic powder in the heat-absorbing body 1 sintersects and changes into a hard, plate-like porous body, thereby increasing its pressure resistance and decreasing its thermal conductivity. As a result, the heat-absorbing body 1 can maintain a constant distance between cells, maintain effective insulating properties, control thermal conductivity, and effectively suppress chain explosions of the battery elements 10.

[0076] 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]

[0077] 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 (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 water-soluble inorganic powder used in the measurement.

[0078] (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, or being unable to measure" was marked with "×".

[0079] (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 4, 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 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. Then, the temperature change until the back surface of the heat-absorbing material 1 reached 200°C was measured using the 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.

[0080] (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 addition, the indentation test was performed at two locations on the surface of the heat absorber after the heating experiment using the cone calorimeter described above, 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. Formula (II): Thickness change rate (%) = (Thickness of the heat absorber after pressing it against the surface of the heat absorber at 0.5 MPa for 60 seconds after heating) / (Thickness of the heat absorber before pressing it against the surface of the heat absorber at 0.5 MPa for 60 seconds after heating) × 100 (Evaluation criteria for the rate of change in thickness) 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 within the range of 0-39% or unmeasurable 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.

[0081] Furthermore, in Example 1, during the heating experiment using the cone calorimeter described above, when the back surface of the heat absorber 1 reached temperatures of 150°C, 160°C, 170°C, 180°C, and 240°C, the heat absorber was allowed to cool naturally until its surface temperature reached room temperature, and the percentage change in thickness before and after heating at each temperature was calculated. The results are shown in Table 2 below.

[0082] (5) Methods for measuring average porosity, true density, and bulk density The average porosity of inorganic fibers was calculated from the bulk density ρf and true density ρr measured by the following method using the following formula (1). Average porosity (%)=((1 / ρf)-(1 / ρr)) / (1 / ρf)×100...Equation (1) <Measurement of true density> Inorganic fibers removed from the contents of the endothermic body, or inorganic fibers before being sealed in the bag, were thoroughly washed with distilled water and dried overnight. The dried inorganic fibers were then placed in a stoppered test tube, and a mixed solvent, prepared by appropriately mixing three types of solvents, was added to the stoppered test tube. The test tube was then immersed in a 30°C constant temperature bath. If the inorganic fibers floated, low-density n-heptane was added. On the other hand, if the inorganic fibers sank, high-density ethylene dibromide was added. This operation was repeated until the inorganic fibers floated in the liquid, and the density of the mixed solvent was measured using a Gay-Lussac specific gravity bottle. <Measurement of bulk density> Inorganic fibers removed from the contents of the heat-absorbing body, or inorganic fibers before being sealed in the bag, were thoroughly washed with distilled water and dried overnight. The dimensions of the dried inorganic fibers were then measured to calculate the bulk volume V of the inorganic fibers. Subsequently, the mass M of the inorganic fibers was measured using a precision balance. From the obtained mass M and bulk volume V, the bulk density of the inorganic fibers was calculated using the following formula (2). Bulk density ρf(g / cm³) 3 )=M / V · Formula (2)

[0083] (2) Raw materials used <Water-soluble inorganic powder> The water-soluble inorganic powders used in the examples and comparative examples are as follows: • Magnesium sulfate heptahydrate: (Product name "Magnesium sulfate heptahydrate, Grade 1," manufactured by Kanto Chemical Co., Ltd., solubility in 100g of water at 20°C (g / 100g): 71g) • 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) • Sodium acetate: (Product name "Sodium Acetate Grade 1", manufactured by Kanto Chemical Co., Ltd., solubility in 100g of water at 20℃ (g / 100g): 46.5g) • Calcium sulfate dihydrate: (Product name "Calcium Sulfate Dihydrate Grade 1", manufactured by Kanto Chemical Co., Ltd., solubility in 100g of water at 20℃ (g / 100g): 0.2g) 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, while calcium sulfate dihydrate exists as a hydrate. <Bag body> The water vapor permeability of the aluminum pouch bag used in Examples 1-4 described below ([g / (m³) 2 (24h)) is 50g / (m 2We confirmed that it was less than 24 hours.

[0084] (3) Examples and Comparative Examples <Example 1> A water-soluble inorganic powder-containing aqueous solution (1) was prepared by mixing 32 parts by mass of magnesium sulfate heptahydrate (including the amount of water in the hydrate) with 60 parts by mass of pure water. Then, 92 parts by mass of the water-soluble inorganic powder-containing aqueous solution (1) and 8 parts by mass of ceramic wool (average porosity 96.9%, true density 3, bulk density 0.093) were placed inside a container made of 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. Next, the aluminum pouch was filled with the aqueous solution (1) containing the water-soluble inorganic powder, and the opening was sealed 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 (1). The obtained heat absorber (1) was then evaluated according to the procedure described in the evaluation section above. The results are shown in Table 1 and Figure 3. Furthermore, when the heat-absorbing body (1) prepared in Example 1 was heated to 200°C using a cone calorimeter, it was confirmed that the heat-absorbing body (1) prepared in Example 1 changed into a porous material at temperatures above 150°C. Figure 5(a) shows a cross-sectional photograph of the heat-absorbing body (1) that has changed into a porous material.

[0085] <Example 2> A water-soluble inorganic powder-containing aqueous solution (2) was prepared by mixing 27 parts by mass of sodium acetate with 64 parts by mass of pure water. Then, 91 parts by mass of the water-soluble inorganic powder-containing aqueous solution (2) and 9 parts by mass of ceramic wool (average porosity 96.8%, true density 3, bulk density 0.096) were placed inside a container made of 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. Next, the aluminum pouch was filled with the aqueous solution (2) containing the water-soluble inorganic powder, and the opening was sealed 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 (2). The obtained heat absorber (2) was then evaluated according to the procedure described in the evaluation section above. The results are shown in Table 1 and Figure 3. Furthermore, when the heat-absorbing body (1) prepared in Example 2 was heated to 200°C using a cone calorimeter, it was confirmed that the heat-absorbing body (2) prepared in Example 2 changed into a porous material at temperatures above 180°C. Figure 5(b) shows a cross-sectional photograph of the heat-absorbing body (2) that has changed into a porous material.

[0086] <Example 3> A water-soluble inorganic powder-containing aqueous solution (3) was prepared by mixing 35 parts by mass of magnesium sulfate heptahydrate (including the amount of water in the hydrate) with 65 parts by mass of pure water. Then, 100 parts by mass of the water-soluble inorganic powder-containing aqueous solution (3) was placed inside a container made of 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. Next, the aluminum pouch was filled with the aqueous solution (3) containing the water-soluble inorganic powder, and the opening was sealed 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 (3). The obtained heat absorber (3) was then evaluated according to the procedure described in the evaluation section above. The results are shown in Table 1 and Figure 3. Furthermore, when the heat-absorbing body (3) prepared in Example 3 was heated to 200°C using a cone calorimeter, it was confirmed that at temperatures above 180°C, the heat-absorbing body (3) prepared in Example 3 also transformed into a porous body, similar to the heat-absorbing bodies of Examples 1 and 2.

[0087] <Example 4> A water-soluble inorganic powder-containing aqueous solution (4) was prepared by mixing 25 parts by mass of anhydrous magnesium sulfate (including the amount of water in the hydrate) with 75 parts by mass of pure water. Then, 100 parts by mass of the water-soluble inorganic powder-containing aqueous solution (4) was placed inside a container made of 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. Next, the aluminum pouch was filled with the aqueous solution (4) containing the water-soluble inorganic powder, and the opening was sealed 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-absorbing body (4). The obtained heat-absorbing body (4) was then evaluated according to the procedure described in the evaluation section above. As a result, the evaluation results for heat absorption, meltdown temperature, heat absorption start temperature, heat absorption peak temperature, pressure resistance, and cushioning properties were all similar to those of Example 2.

[0088] <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 the comparison sheet (C1). The nominal thickness of the silica aerogel mat material in Comparative Example 1 was 3 mm. The obtained comparison sheet (C1) was then evaluated according to the procedure described in the evaluation section above. The results are shown in Table 1 and Figure 3. Furthermore, since the material used in Comparative Example 1, "Xiaomei silica aerogel mat material," has virtually no endothermic capacity, "Substantially no endothermic capacity" is indicated in the "Endothermic start temperature (°C), Endothermic peak temperature (°C), Heat absorbed (J / g or mJ / mg)" column of the table. In addition, although the bulk density of the material used in Comparative Example 1 could be measured, the true density could not be measured, so "Unmeasurable" is indicated in the "True density" and "Average porosity" columns of the table.

[0089] <Comparative Example 2> 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 (amount including water in the hydrate) 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 comparative sheet (C2). The obtained comparative sheet (C2) was then evaluated according to the procedure described in the evaluation section above. The results are shown in Table 1 and Figure 3. In Comparative Example 2, 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)

[0090] <Comparative Example 3> 91 parts by mass of pure water and 9 parts by mass of ceramic wool (average porosity 96.9%, true density 3, bulk density 0.092) were placed inside a container made of 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. Next, the aluminum pouch was filled with the pure water and ceramic wool, and the opening was sealed with 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 comparative sheet (C3). The obtained comparative sheet (C3) was then evaluated according to the procedure described in the evaluation section above. The results are shown in Table 1 and Figure 3.

[0091] <Comparative Example 4> A dispersion (1) was prepared by mixing 27 parts by mass of aluminum hydroxide (solubility of 0.0001 g in 100 g of water at 20°C) with 64 parts by mass of pure water. Then, 91 parts by mass of the dispersion (1) and 9 parts by mass of ceramic wool (average porosity 96.8%, true density 3, bulk density 0.096) were placed inside a container made of 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. Next, the aluminum pouch was filled with the dispersion (1), the opening was sealed with heat seal, and the aluminum pouch was laid flat between 4.8 mm thick gap materials. A flat plate was placed on top of it and left to stand at 20°C for 10 minutes to produce a 4.8 mm thick comparative sheet (C4). The obtained comparative sheet (C4) was then evaluated according to the procedure described in the evaluation section above. The results are shown in Table 1 and Figure 3.

[0092] For Examples 1 and 3, in Table 1, the "Contents (Amount Blended During Preparation)" column shows the "Contents (Amount Blended During Preparation)" for water-soluble inorganic powder (mass%), the "Contents (Inside the Bag)" column shows the "Contents (Amount Blended During Preparation)" for water-soluble inorganic powder (mass%), the "Contents (Amount Blended During Preparation)" column shows the "Contents (Amount Blended During Preparation)" for water-soluble inorganic powder (anhydrous), and the "Contents (Amount Blended During Preparation)" column shows the "Contents (Amount Blended During Preparation)" including the amount of water removed from the hydrate of the water-soluble inorganic powder. Furthermore, for Comparative Examples 2 and 4, the "Contents (Amount Blended During Preparation)" in Table 1, and the "Contents (Amount Blended During Preparation)" and the "Contents (Amount Blended During Preparation)" in Table 1 refer to the content (amount blended during preparation of contents (amount blended during preparation during preparation) in

[0093] [Table 1]

[0094] [Table 2]

[0095] From the experimental results above, it was confirmed that the heat-absorbing material of this embodiment, because the entire structure of the filled contents and the bag acts as a porous material, exhibits sufficient heat absorption, pressure resistance, and transformation from a heat-absorbing material to an insulating material, even when the battery temperature rises or time passes. Heat-absorbing materials using non-water-soluble inorganic powders (Comparative Examples 2 and 4) showed particularly inferior pressure resistance compared to heat-absorbing materials containing water-soluble inorganic powders. Note that the values ​​of each content in the composition of the contents in Table 1 are rounded to the nearest whole number. Figure 3 also shows graphs of the results of cone calorimeter tests for the heat absorbers (1) to (3) prepared in Examples 1 to 4 and the comparative sheets (C1), (C3), and (C4) prepared in Comparative Examples 1, 3, and 4. In Figure 3, the vertical axis represents temperature (°C), and the horizontal axis represents elapsed time (seconds). Therefore, (1) to (3) and (C1), (C3), and (C4) in Figure 3 correspond to the heat absorbers (1) to (3) and comparative sheets (C1), (C3), and (C4) of the Examples and Comparative Examples. From the experimental results in Figure 3, it was confirmed that the heat absorbers (1) to (3) produced in these examples 1 to 3 have higher heat absorption capacity compared to the heat absorber of the comparative example, thus delaying the time it takes for the heat absorber's temperature to reach 200°C.

[0096] [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)

[0097] This application claims priority to three Japanese patent applications filed on 3 July 2023 (Japanese Patent Application No. 2023-109644), filed on 25 December 2023 (Japanese Patent Application No. 2023-218613), and filed on 25 December 2023 (Japanese Patent Application No. 2023-218614), the contents of which are incorporated herein by reference.

Claims

1. A bag that can be filled with contents, The contents to be filled into the bag are an aqueous solvent and a water-soluble inorganic powder that dissolves in 1 g or more of water at 20°C, A heat-absorbing body having [a certain characteristic].

2. The heat-absorbing body according to claim 1, wherein the water-soluble inorganic powder has a solubility (g) in water at 20°C of 5 g / 100 g or more.

3. The heat-absorbing body according to claim 1 or 2, further comprising one or more selected from the group consisting of antifreeze and inorganic fibers in the contents.

4. The heat absorber according to claim 1 or 2, wherein the water-soluble inorganic powder is one or more selected from chlorides, sulfates, carbonates, nitrates, phosphates, acetates, alkali metal oxides, and alkaline earth metal oxides.

5. The endotherm according to claim 1 or 2, wherein the contents are filled with an aqueous solution containing the aqueous solvent and the water-soluble inorganic powder, and the content of the water-soluble inorganic powder in the aqueous solution is 5 to 80% by mass with respect to the total amount of the aqueous solution.

6. The heat-absorbing body according to claim 1 or 2, wherein the contents change into a porous body when the contents are heated to 120°C or higher.

7. The following equation (I): [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 The heat absorber was heated with a certain amount of heat until the temperature of the side opposite to the heating surface (back surface) reached a predetermined temperature. Then, the heat absorber was allowed to dissipate heat at room temperature, and naturally cooled until the surface temperature of the heat absorber returned to room temperature. The percentage change in thickness before and after heating was then calculated. The heating surface of the heat absorber was subjected to pressure of 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.

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

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

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