Heat absorber and secondary battery module provided with same

Abstract

The purpose of the present invention is to provide: a heat-absorbing body which has excellent heat-absorbing properties, heat-insulating properties, and pressure resistance, and which can be changed into a heat-insulating body in a high-temperature region; and a secondary battery module which is provided with the heat-absorbing body. The present disclosure is a heat-absorbing body and a secondary battery module provided with the heat-absorbing body. The heat-absorbing body has a pouch body capable of being filled with a content, and an aqueous solvent and a water-soluble inorganic powder which are filled as the content in the pouch body.

Description

Technical Field

[0001] This disclosure relates to a heat absorber and a secondary battery module having the heat absorber. Background Technology

[0002] Secondary batteries, which can control the time difference between energy storage and demand, are used in various applications, such as automobiles or mobile devices. From the perspective of building a low-carbon society or energy security, it is necessary to expand the introduction of renewable energy, and therefore their importance is increasing.

[0003] However, secondary batteries, such as lithium-ion batteries, pose a risk of damage due to thermal runaway when their temperature rises during high-speed charging or high-output discharging. Furthermore, with the future development of ultra-fast charging, heat generation is predicted to increase further, necessitating the development of methods to suppress temperature rise and improve battery safety. Additionally, secondary batteries can sometimes experience thermal runaway due to internal short circuits, leading to fires or smoke.

[0004] Therefore, in order to minimize the damage caused by such adverse conditions, it is necessary to have technologies that can suppress, prevent or delay chain explosions by extinguishing the heat of the 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 single cells) through heat absorption and insulation.

[0005] For example, Patent Documents 1 and 2 exemplify technologies with excellent heat insulation and fire spread prevention. Patent Document 1 describes a laminated fire spread prevention material comprising a sodium silicate layer A with a SiO2 / Na2O molar ratio of less than 3.1 and a layer B containing precipitated silica. Furthermore, according to Patent Document 1, this fire spread prevention material is used in battery packs comprising two or more individual cells, thereby suppressing heat transfer between individual cells under normal conditions and suppressing the spread of heat to adjacent individual cells under abnormal conditions.

[0006] Furthermore, Patent Document 2 describes a partition member comprising a liquid, a heat-insulating material, and an outer packaging containing the liquid and the heat-insulating material. Moreover, according to Patent Document 2, by appropriately setting the peel strength and crystallization-melting characteristics of the sealing resin layer of the sheet member in contact with the heat-insulating material, the partition member can maintain its cooling function during long-term use, and the release temperature of the cooling liquid inside the sheet member exhibits excellent stability.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: International Publication No. 2022 / 270359

[0010] Patent Document 2: Japanese Patent Application Publication No. 2020-161290 Summary of the Invention

[0011] The problem that the invention aims to solve

[0012] However, the technology in the aforementioned patent document 1 is generated by the endothermic reaction of water contained in layer A (e.g., water molecules in sodium silicate) in the temperature range of 100~300°C. Therefore, the water content is limited and a sufficient endothermic effect cannot be obtained.

[0013] Furthermore, Patent Document 2 only lists various porous materials, fibers, or particles as heat-insulating materials, but it completely fails to address the issue of how the separator itself, in batteries reaching abnormally high temperatures, exhibits heat-insulating effects to suppress heat transfer to other individual cells, thereby suppressing, preventing, or delaying chain explosions. Moreover, when using the separator or other membrane components of Patent Document 2 in stacked secondary batteries, the thickness between adjacent cells changes when individual cells expand and contract due to charging and discharging, or when individual cells rapidly expand during thermal runaway. Therefore, mechanical properties such as pressure resistance are required for the separator components. However, Patent Document 2 does not address mechanical properties such as pressure resistance. Consequently, especially during cell expansion, the distance between individual cells shortens, leading to problems such as easy heat transfer between adjacent cells.

[0014] Therefore, the purpose of this disclosure is to provide a heat absorber and a secondary battery module having the heat absorber, the heat absorber having excellent heat absorption properties and being able to transform into a heat insulator in high-temperature regions, thereby having excellent heat insulation and pressure resistance.

[0015] Methods for solving problems

[0016] The inventors have discovered that a heat absorber containing an aqueous solvent and a water-soluble inorganic powder in the bag body exhibits excellent heat absorption, heat insulation and pressure resistance, and can be transformed into a heat insulation body in high-temperature regions (e.g., above 150°C), thereby completing the following invention.

[0017] [1] This disclosure is a heat absorber having: a bag body capable of being filled with contents; and an aqueous solvent and a water-soluble inorganic powder that dissolves in 100g of water at 20°C or more as the contents to be filled into the bag body.

[0018] [2] According to the heat absorber described in [1], the water-soluble inorganic powder has a water solubility (g) of 5 g / 100 g or more at 20 °C.

[0019] [3] The heat absorber according to [1] or [2], wherein the contents further contain one or more of the following: selected from the group consisting of antifreeze and inorganic fibers.

[0020] [4] The heat absorber according to any one of [1] to [3], wherein the water-soluble inorganic powder is selected from one or more of chlorides, sulfates, carbonates, nitrates, phosphates, acetates, alkali metal oxides and alkaline earth metal oxides.

[0021] [5] The heat absorber according to any one of [1] to [4], wherein the contents are filled with an aqueous solution containing the aqueous solvent and the water-soluble inorganic powder, wherein the content of the water-soluble inorganic powder in the aqueous solution is 5 to 80% by mass relative to the total amount of the aqueous solution.

[0022] [6] The heat absorber according to any one of [1] to [5], wherein when the contents are heated to 120°C or higher, the contents change into a porous body.

[0023] [7] The heat absorber according to any one of [1] to [6], wherein the thickness change rate represented by the following formula (I) is 70% or more.

[0024] [Number 1]

[0025] "Thickness change rate (%) = (Thickness of the heat absorber after pressing its surface with 0.5 MPa for 60 seconds under the heating conditions described below) / (Thickness of the heat absorber before pressing its surface with 0.5 MPa for 60 seconds under the heating conditions described below) × 100"

[0026] Heating conditions:

[0027] "Utilizing radiant heat at 50kW / m 2 After the heat is applied to the surface (back side) of the heat absorber opposite to the heating surface to reach a predetermined temperature, the heat absorber is allowed to release heat at room temperature and naturally cool until the surface temperature of the heat absorber reaches room temperature. The thickness change rate (%) before and after heating is then calculated. Additionally, the heating surface of the heat absorber is subjected to a 0.5 MPa pressurization for 60 seconds.

[0028] [8] A secondary battery module, characterized in that it comprises a heat absorber as described in any one of [1] to [7].

[0029] [9] A secondary battery module, wherein a heat absorber as described in any one of [1] to [7] is sandwiched between battery cells.

[0030] Invention Effects

[0031] According to the heat absorber disclosed herein, a heat absorber with excellent heat absorption properties and excellent insulation and pressure resistance is provided by being able to change into an insulation material in a high-temperature region.

[0032] According to this disclosure, a highly safe secondary battery module can be provided by having a heat absorber with excellent heat absorption properties and the ability to change into a heat insulation material in high-temperature regions, thereby providing excellent heat insulation and pressure resistance. Attached Figure Description

[0033] [ Figure 1 ] Figure 1 This describes an example of a secondary battery module capable of carrying the heat absorber of this embodiment.

[0034] [ Figure 2 ] Figure 2 It is a general indication that will Figure 1 A 3D view of the disassembled secondary battery module.

[0035] [ Figure 3 ] Figure 3 This refers to the cone calorimeter test of the absorber of the embodiment and the sheet of the comparative example (test conditions: radiation intensity 50 kW / m²). 2 The graph shows the results of heating for 20 minutes, with the vertical axis representing temperature and the horizontal axis representing time.

[0036] [ Figure 4 ] Figure 4 This is a schematic diagram of the cone calorimeter test apparatus used in the embodiments and comparative examples.

[0037] [ Figure 5 ] Figure 5 (a) is an image showing the transformation of the heat absorber (1) prepared in Example 1 into a porous material. Figure 5 (b) is an image showing the transformation of the absorber (2) prepared in Example 2 into a porous material. Furthermore, Figure 5 (a) and (b) are also images showing the state of cutting off the edge of the porous material. Detailed Implementation

[0038] Hereinafter, embodiments of the present invention (referred to as "this embodiment") will be described in detail, but this disclosure is not limited to the following description and can be implemented in various ways within the scope of its spirit.

[0039] [Endothermic body]

[0040] The heat absorber disclosed herein comprises: a bag capable of being filled with contents; and an aqueous solvent and a water-soluble inorganic powder, which dissolves in 1 g or more of water at 20°C per 100 g of water, and is filled in the bag as the contents.

[0041] Therefore, it has excellent heat absorption, heat insulation and pressure resistance, and can be transformed into a heat insulation material in high-temperature regions.

[0042] Heat absorption can be achieved through the latent heat of vaporization of the aqueous solvent or the water-soluble inorganic powder within the bag. Therefore, the latent heat of vaporization of water, which has a higher heat absorption capacity than typical hydrates, can be utilized. Furthermore, since the sensible heat of the aqueous solvent is absorbed, temperature stabilization is achieved even at room temperature. On the other hand, if exposed to high temperatures such as during combustion, the aqueous solvent evaporates, but the presence of the water-soluble inorganic powder provides insulation and fire resistance. More specifically, it primarily functions as a heat absorber in relatively low temperature ranges (e.g., above room temperature to around 100°C). On the other hand, in temperature ranges from the critical temperature (e.g., 150°C) to above the thermal runaway temperature (e.g., around 1000°C), the water-soluble inorganic powder within the heat absorber transforms into a porous material, thus also functioning as a heat absorber. As a result, if the heat absorber of this embodiment is arranged between the battery cells of a battery stack (battery module) containing multiple battery cells, the thermal impact on adjacent individual cells can be blocked or suppressed.

[0043] Furthermore, the endotherm of this disclosure exhibits fluidity of its contents at relatively low temperatures, thus easily following and adhering to the single cell. Even if the single cell expands and contracts due to heat, it can still exhibit stress-absorbing buffering properties. On the other hand, in temperature ranges exceeding the thermal runaway temperature, the water-soluble inorganic powder within the endotherm sinters and deforms into a hard, plate-like porous body, thereby increasing its compressive strength. As a result, the distance between the single cells can be kept constant, thus maintaining effective thermal insulation and controlling thermal conductivity, effectively suppressing the chain reaction of explosions between single cells.

[0044] In the heat absorber disclosed herein, an aqueous solvent may be included in the contents of this embodiment as a hydrogel composed of a hydrogel body and an aqueous solvent, as needed.

[0045] When the contents contain a hydrogel matrix, it can impart cushioning and impact resistance to the heat absorber.

[0046] It should be noted that the heat absorber disclosed herein not only has the effect of heat absorption, but also has the effect of heat insulation. Therefore, strictly speaking, the heat absorber can be called a component that can absorb and insulate heat from the outside, that is, a heat control component that controls heat from the outside.

[0047] The contents of the heat absorber in this embodiment may further contain one or more selected from the group consisting of inorganic fibers, antifreeze agents and additives.

[0048] If inorganic fibers are further included as a component, the absorber can be further endowed with buffering and pressure resistance. Alternatively, the inorganic fibers can act as a foaming nucleating agent, and the water-soluble inorganic powder easily forms a foam (=porous body). Furthermore, by retaining water through the inorganic fibers included as a component, the absorber can be easily shaped into the desired form. Moreover, if the aqueous solvent evaporates, voids are created within the inorganic fibers, and the composite containing inorganic fibers and water-soluble inorganic powder easily forms a porous body. Therefore, by transforming it from an absorber to an insulator, both heat absorption and insulation effects can be further enhanced throughout the overall thickness of the absorber.

[0049] Furthermore, if an antifreeze is included as a component, freezing below the freezing point can be suppressed. Additionally, by utilizing the heat of solidification of aqueous solvents, the temperature drop of the battery in cold environments can be suppressed. In the case of water, heat of solidification is generated at around 0°C, but by using an antifreeze, the temperature at which this heat of solidification is generated can be lowered, thus suppressing the temperature drop of the battery at even lower temperatures.

[0050] Properties of heat absorbers

[0051] The heat absorption start temperature of the heat absorber in this embodiment is preferably below 400°C, more preferably below 160°C, even more preferably below 120°C, more preferably below 110°C, and even more preferably below 100°C.

[0052] The heat absorption start temperature range of the heat absorber in this embodiment is preferably 35°C or higher and 400°C or lower, more preferably 37°C or higher and 160°C or lower, and even more preferably 40°C or higher and 110°C or lower.

[0053] The upper and lower limits of the heat absorption start temperature of the above-mentioned heat absorber can be appropriately reorganized.

[0054] The endothermic onset temperature (°C) in this specification is the temperature at the intersection of a straight line extending from the low-temperature side to the high-temperature side of the DSC measurement curve (resulting from differential scanning calorimetry), and the tangent line drawn from the point of maximum slope on the low-temperature side of the curve accompanying the evaporation endothermic peak. However, when multiple endothermic peaks are observed, the lowest temperature among these intersection points is taken as the endothermic onset temperature, calculated for each of the multiple endothermic peaks and using the lowest temperature among them.

[0055] The heat absorption peak temperature of the heat absorber 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.

[0056] The endothermic peak temperature in this specification refers to the temperature (°C) at the maximum value of the endothermic peak based on evaporation in the DSC measurement curve, which is the result of the differential scanning calorimetry (DSC) instrument. Furthermore, if multiple endothermic peaks are observed, at least one of the multiple endothermic peaks need to be within the range of 80°C to 160°C.

[0057] The heat absorption capacity of the heat absorber in this embodiment is not particularly limited. At the peak endothermic temperature (range 80°C to 160°C), it is preferably 100 J / g or more and 3000 J / g or less, more preferably 200 J / g or more and 2500 J / g or less, even more preferably 300 J / g or more and 2000 J / g or less, and even more preferably 500 J / g or more and 1500 J / g or less. The preferred range of heat absorption capacity can be appropriately rearranged from the aforementioned upper and lower limits.

[0058] It should be noted that the heat absorption start temperature, heat absorption peak temperature, and heat absorption of the heat absorber in this embodiment are values ​​obtained using a differential scanning calorimeter (DSC) through the method described in the embodiments below.

[0059] <Preferred shape of the heat absorber>

[0060] The shape or size of the heat absorber in this embodiment is not particularly limited. For example, it can be approximately spherical, approximately flat, or irregular in shape, and can be appropriately selected according to the application. For example, if it is an approximately flat heat absorber, it is easy to place between adjacent battery cells, so it is preferred.

[0061] In this embodiment, the average thickness of the heat absorber when it is substantially flat is not particularly limited, and for example, a range of 100 μm to 50,000 μm can be cited. The average thickness is preferably 100 μm or more, more preferably 200 μm or more and 20,000 μm or less, further preferably 500 μm or more and 10,000 μm or less, and particularly preferably 1,000 μm or more and 8,000 μm or less. The preferred range of the average thickness can be appropriately rearranged from the aforementioned upper and lower limits.

[0062] Hereinafter, the essential components of the heat absorber in this embodiment, namely the bag body, the water-soluble inorganic powder and aqueous solvent that dissolve at least 1g of water per 100g of water at 20°C, and any other components such as inorganic fibers, antifreeze and additives that may be added as needed, will be described.

[0063] (Bag)

[0064] There are no particular limitations on the bag body in this embodiment, as long as it can be filled with an aqueous solvent and water-soluble inorganic powder that dissolves at least 1g in 100g of water at 20°C. For example, a preferred bag body is a three-side sealed flat bag with a main body 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, including the aqueous solvent and water-soluble inorganic powder, are contained.

[0065] The three-sided sealed flat bag is a structure in which the lower ends and sides of two sheets are glued together and sealed after the contents are filled from the opening. Therefore, it has excellent airtightness and has a roughly flat shape, making it easy to insert between battery cells.

[0066] The bag body in this embodiment is preferably made of sheet material. Furthermore, as a preferred method of bag body in this embodiment, depending on the intended use, two sheets of film of a desired size and shape (e.g., rectangular or (approximately) circular) are overlapped, and an opening is formed by heat-pressing a predetermined heat-sealing area (e.g., the edge of the film) together, thereby bonding the heat-sealing area. This creates an internal space area capable of being filled with contents, and allows the production of a three-sided sealing strip with an opening into which the contents are filled, and where the heat-sealing areas of the two sheets are bonded together. Moreover, after filling with contents, the contents can be sealed by pressing the openings together and heat-sealing.

[0067] Furthermore, the term "sealed" in this instruction manual refers to a state in which the inside and outside of the bag are substantially separated.

[0068] In this embodiment, there are no particular limitations on the sheet material used in the bag body, as long as it is a sheet material that exhibits water resistance. Examples include known resin films, resin films with metal layers, or thin films with metal layers.

[0069] The average thickness of the sheet material used in the bag body of this embodiment is not particularly limited, but is preferably 30μm to 200μm, and more preferably 60μm to 150μm.

[0070] Examples of resin films include one or more resins selected from polyester resin, nylon resin, polycarbonate resin, polypropylene resin, polyethylene resin, cyclic polyolefin resin, polystyrene resin, fluoropolymer resin, or elastomers. These plastics can be used as films, sheets, tubes, etc., for bag bodies.

[0071] Furthermore, as a resin film having the aforementioned metal layer, metals such as aluminum, metal oxides such as silicon dioxide and aluminum oxide, or vapor-deposited films can be laminated onto the resin film as metal foils. By using a resin film with a metal layer, the water vapor permeability of the resin film can be reduced. Additionally, the water vapor permeability of the sheet can be adjusted by the selection, thickness, and combination of materials. Moreover, as a lamination method, examples include dry lamination, extrusion lamination, hot lamination, co-extrusion, multilayer blow molding, lamination injection molding, and coating. It should be noted that, as a preferred type of resin film with a metal layer, an aluminum laminate film (a film integrally formed of 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 side thereof) can be cited.

[0072] In this embodiment, an adhesive layer can be formed in the heat-sealed area and the closed opening for sealing purposes. As this adhesive layer, laminated adhesives such as polyester-based adhesives, polyether-based adhesives, or polyurethane-based adhesives can be suitably used. Furthermore, the properties of the adhesive are not particularly limited; solvent-based, solvent-free, and water-based adhesives can all be used.

[0073] For example, in this invention, it is preferable to form a bag-shaped body by manufacturing the laminated film into a bag shape. As this laminated film, it is preferable to have a film formed by laminating a metal foil and a resin film. An example is a three-layer laminated film consisting of an outer resin film, a metal foil, and an inner resin film. Specifically, it is suitable to use a bag formed by sealing a resin film with an aluminum vapor-deposited layer on the outside with a polyurethane laminated adhesive layer; a bag formed by sealing a three-layer laminated film with a nylon film on the outside, an aluminum foil in the center, and a modified polypropylene adhesive layer on the inside with a polyurethane laminated adhesive layer; or a bag formed by sealing a laminated film with a PET layer, an aluminum layer, and a polyethylene layer with a polyurethane laminated adhesive layer. Examples include the AB series of gas-barrier aluminum bags (manufactured by Mitsubishi Gas Chemical Co., Ltd.) and the Lamizip AL type (manufactured by Seisaku Nippon Co., Ltd.).

[0074] The higher the melting temperature (e.g., 120~140°C) of the adhesive used to seal the opening of the bag in this embodiment or the heat-sealing area, the higher the strength and the more likely it is to withstand internal pressure.

[0075] The water vapor permeability of the sheet material constituting the bag body in this embodiment is ([g / (m)) 2 The preferred value is 50g / (m²) (24h). 2 ·24h or less, more preferably 10g / (m 2 ·24h or less, further preferably 5g / (m 2 ·24h and below.

[0076] If the water vapor permeability of the sheet material constituting the bag is 50 g / (m²) 2 A range of 24h or less can prevent moisture inside the bag from leaking out, which is preferred from the viewpoint of preventing the decrease in heat absorption performance caused by years.

[0077] The water vapor transmission rate (g / (m)) in this specification 2 The 24h result was measured according to the JIS K7129 standard at an environment of 40°C and 90% relative humidity.

[0078] (This refers to the dissolution of more than 1g of water-soluble inorganic powder (hereinafter also referred to as water-soluble inorganic powder) in 100g of water at 20℃.)

[0079] The endothermic material of this embodiment contains water-soluble inorganic powder. Furthermore, more than 1 g of this water-soluble inorganic powder dissolves in 100 g of water at 20°C. Moreover, this water-soluble inorganic powder exhibits hydrophilicity, thus readily dissolving in aqueous solvents and readily existing uniformly within the contents. As a result, in temperature ranges exceeding the thermal runaway temperature (e.g., around 1000°C), the water-soluble inorganic powder readily forms a homogeneous porous mass, effectively functioning as a thermal insulator.

[0080] Furthermore, if water-soluble inorganic powder and aqueous solvent are present in the contents of the endothermic body, a synergistic effect of heat absorption with the aqueous solvent is observed, enabling continuous heat absorption at endothermic temperatures different from those of the aqueous solvent. Moreover, even when the endothermic body is exposed to high temperatures, the water-soluble inorganic powder can remain porous (for example, see below). Figure 5 (See the photograph in Figure 6). As a result, it exhibits excellent heat insulation and fireproofing effects. Therefore, the heat absorber containing water-soluble inorganic powder mainly functions as a heat absorber in the 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 above the thermal runaway temperature (e.g., around 1000°C), the water-soluble inorganic powder becomes a porous body as a whole, and therefore can also function as a heat absorber. As a result, when the heat absorber of this embodiment is arranged between the individual cells of a battery stack in which multiple individual cells are stacked, the thermal influence on adjacent individual cells can be isolated or suppressed.

[0081] For example, in the event of thermal runaway, the heat absorbers between individual cells are compressed due to cell expansion, resulting in extremely small distances between the cells and making it difficult to exhibit effective thermal insulation performance. However, if water-soluble inorganic powder is included as the content of the heat absorber in this embodiment, the powder sintersulates under high temperatures due to thermal runaway or similar conditions, forming a porous body with a certain strength, thereby increasing its compressive strength. This allows the distance between the individual cells to remain constant, thus maintaining effective thermal insulation and effectively suppressing chain reactions such as explosions between individual cells.

[0082] The water-soluble inorganic powder of this embodiment dissolves in an aqueous solvent. Therefore, because it readily dissolves in aqueous solvents, the water-soluble inorganic powder is easily and uniformly distributed within the contents. It should be noted that "water-soluble" in this specification means that it dissolves at least 1g per 100g of water at 20°C. Therefore, the water-soluble inorganic powder of this embodiment can be an inorganic powder that dissolves at least 1g per 100g of water at 20°C.

[0083] The solubility of the water-soluble inorganic powder in this embodiment is 1 g or more relative to 100 g of water at 20°C. From the viewpoint of the stability, dispersibility, and sinterability of the water-soluble inorganic powder in the endothermic body using high-temperature heating, the solubility of the above-mentioned water-soluble inorganic powder (relative to 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, further 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.

[0084] The solubility of water-soluble inorganic powder relative to 100g of water at 20°C can be appropriately recombined with the above upper and lower limits.

[0085] If the solubility of the water-soluble inorganic powder at 20°C is within the above range, the solubility can be ensured. Therefore, since the water-soluble inorganic powder is uniformly dissolved or dispersed relative to the aqueous solvent, a homogeneous porous body is easily formed during sintering.

[0086] The solubility of the water-soluble inorganic powder in this embodiment is preferably 10g or more relative to 100g of water at 60°C. The solubility of the water-soluble inorganic powder (relative to 100g of water at 60°C) is preferably 10g or more and 150g or less, more preferably 15g or more and 120g or less, even more preferably 20g or more and 100g or less, even more preferably 25g or more and 80g or less, even more preferably 30g or more and 60g or less, and particularly preferably 35g or more.

[0087] The solubility of water-soluble inorganic powders relative to 100g of water at 60℃ can be appropriately recombined with the aforementioned upper and lower limits.

[0088] The solubility of the water-soluble inorganic powder in this embodiment is preferably 15g or more relative to 100g of water at 80°C. The solubility of the water-soluble inorganic powder (relative to 100g of water at 80°C) is preferably 15g or more and 160g or less, more preferably 20g or more and 120g or less, even more preferably 25g or more and 100g or less, even more preferably 30g or more and 80g or less, and particularly preferably 35g or more and 60g or less.

[0089] The solubility of water-soluble inorganic powders relative to 100g of water at 80℃ can be appropriately recombined with the above upper and lower limits.

[0090] The solubility of the water-soluble inorganic powder in this embodiment is preferably 15g or more relative to 100g of water at 100°C. The solubility of the water-soluble inorganic powder (relative to 100g of water at 100°C) can be, for example, set to 15g or more and 170g or less, preferably 20g or more and 130g or less, more preferably 25g or more and 100g or less, further preferably 30g or more and 80g or less, and particularly preferably 35g or more and 60g or less.

[0091] The solubility of water-soluble inorganic powder relative to 100g of water at 100℃ can be appropriately recombined with the above upper and lower limits.

[0092] The preferred solubility of the water-soluble inorganic powder in this embodiment is 1g or more and 90g or less relative to 100g of water at 20°C, more preferably 5g or more and 90g or less, 5g or more and 100g or less relative to 100g of water at 40°C, 10g or more and 150g or less relative to 100g of water at 60°C, 15g or more and 160g or less relative to 100g of water at 80°C, and 15g or more and 170g or less relative to 100g of water at 100°C.

[0093] If the solubility of water-soluble inorganic powders at various temperatures falls within the above-mentioned range, it is preferable from the viewpoint of achieving suitable heat absorption and pressure resistance.

[0094] The solubility of water-soluble inorganic powder relative to 100g of water at 20°C can be appropriately recombined with the aforementioned upper and lower limits.

[0095] The method for determining solubility in this specification is as follows.

[0096] After weighing a specified amount of the water-soluble inorganic powder to be tested into a glass bottle, 100g of pure water (pH=7) was added to the bottle. The mixture was stirred at 80 rpm for 24 hours on a mixing rotor at 1 atmosphere and temperatures of 20°C, 40°C, 60°C, 80°C, and 100°C to prepare a mixed solution. Then, the transmittance of the mixture after 24 hours of stirring was measured under the following conditions. In this case, the amount of water-soluble inorganic powder dissolved was varied during the transmittance measurement, and the upper limit (g) at which the transmittance reached 99% was taken as the solubility of the water-soluble inorganic powder in water.

[0097] <Transmittance Measurement Conditions>

[0098] Dynamic light scattering (DLS) measurement

[0099] Apparatus: Otsuka Electronics DLS Measurement Apparatus DLS-8000

[0100] Laser wavelength and output power: 488nm / 100mW

[0101] Sample chamber: NMR tube

[0102] The water-soluble inorganic powder in this embodiment is preferably a solid at room temperature. Furthermore, in the heat absorber of this embodiment, the bag body is preferably filled with an aqueous solution containing an aqueous solvent and the water-soluble inorganic powder as the contents of the heat absorber.

[0103] By filling the above-mentioned endothermic body 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, so the water-soluble inorganic powder is uniformly present in the contents, resulting in the formation of a homogeneous porous body.

[0104] The transmittance of the above-mentioned aqueous solution is preferably 99% or higher, and more preferably 99.5% or higher.

[0105] The heat absorption of the above-mentioned water-soluble inorganic powder (= heat absorption 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, there is no particular limitation on the upper limit of the heat absorption of the above-mentioned water-soluble inorganic powder, but it is preferably 4000 J / g or less.

[0106] The heat absorption of the aforementioned 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 absorption of the aforementioned water-soluble inorganic powder can be appropriately reconfigured.

[0107] If the heat absorption of the aforementioned water-soluble inorganic powder is within the above-mentioned range, the heat absorption effect is improved, thus exhibiting a synergistic effect with the heat absorption of the aqueous solvent, making it easier to suppress ignition. The upper and lower limits of the above-mentioned content can be appropriately combined.

[0108] It should be noted that the heat absorption of water-soluble inorganic powders, as described in Example 1, can be measured using a differential scanning calorimeter (DSC).

[0109] The preferred thermal decomposition initiation temperature of the water-soluble inorganic powder in this embodiment is 80°C or higher and 800°C or lower, more preferably 90°C or higher and 500°C or lower, even more preferably 100°C or higher and 350°C or lower, and even more preferably 110°C or higher and 150°C or lower. By keeping the thermal decomposition initiation temperature of the water-soluble inorganic powder within the above range, the water-soluble inorganic powder decomposes rapidly, making it easier to suppress ignition. The upper and lower limits of the above thermal decomposition initiation temperature can be appropriately rearranged.

[0110] It should be noted that the thermal decomposition onset temperature can be determined using a differential scanning calorimeter (DSC).

[0111] The shape of the water-soluble inorganic powder in this embodiment is not particularly limited, and examples include powder, granules, crystals, or plates. Furthermore, as the water-soluble inorganic powder in this embodiment, a water-soluble inorganic powder with endothermic effect is preferred, and preferred forms of the water-soluble inorganic powder include porous powders, solid particles, or hollow particles.

[0112] The water-soluble inorganic powder can take any shape and form as long as it dissolves in an aqueous solvent. When the water-soluble inorganic powder is in powder or particle form, the average particle size 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 is easily dispersed in the system.

[0113] It should be noted that the above average particle size can be the median particle size (D50) measured using a laser diffraction / scattering particle size distribution measuring device.

[0114] The material of the water-soluble inorganic powder in this embodiment is preferably composed of a water-soluble inorganic salt. Moreover, the water-soluble inorganic salt is preferably one or more compounds composed of a combination of inorganic cations and organic / inorganic anions.

[0115] Examples of inorganic cations include alkali metal ions, alkaline earth metal ions, aluminum ions, zinc ions, silver ions, copper(I) ions, and copper(II) ions, preferably one or more selected from the group consisting of potassium ions, calcium ions, magnesium ions, and aluminum ions.

[0116] The organic / inorganic anion is preferably selected from one or more of the following: oxygen ions, sulfate ions, halide ions (chloride ions, fluoride ions, bromide ions, etc.), nitrate ions, carbonate ions, acetate ions, and phosphate ions.

[0117] 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 it to exhibit excellent solubility in aqueous solvents.

[0118] It should be noted that water-soluble inorganic powders, before mixing with aqueous solvents, can be either anhydrous or hydrated as long as they exhibit the desired solubility described above. It should also be noted that hydrates of water-soluble inorganic powders inside the bag are usually present in anhydrous form.

[0119] The water-soluble inorganic powder or the aforementioned water-soluble inorganic salts in this embodiment are preferably chlorides such as sodium chloride, potassium chloride, and ammonium chloride; sulfates such as sodium sulfate, potassium sulfate, magnesium sulfate, aluminum sulfate, and alum; carbonates such as sodium bicarbonate, sodium sesquicarbonate, sodium carbonate, potassium carbonate, potassium sesquicarbonate, and ammonium carbonate; nitrates such as sodium nitrate, potassium nitrate, and calcium nitrate; phosphates such as sodium phosphate, sodium dihydrogen phosphate, dipotassium hydrogen phosphate, and sodium polyphosphate; acetates such as zinc acetate, sodium acetate, potassium acetate, copper acetate (I), or copper acetate (II); oxides such as chromium oxide, barium oxide, and boric acid oxide; and their hydrates. Among the above, magnesium sulfate or magnesium sulfate heptahydrate is particularly preferred.

[0120] The water-soluble inorganic powder of this embodiment can be used alone as exemplified above, or multiple types can be used.

[0121] The content of water-soluble inorganic powder in this embodiment can be 1 to 90% by mass relative to the total amount (100% by mass) of the contents of the heat absorber, or 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.

[0122] If the content of the water-soluble inorganic powder is within the above range, the endothermic body will easily sinter and form a homogeneous porous body when exposed to high heat. 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 of the water-soluble inorganic powder.

[0123] The upper and lower limits of the content of the aforementioned water-soluble inorganic powders can be appropriately reconfigured.

[0124] In this embodiment, it is preferable that the contents of the heat absorber change into a porous material when heated to 120°C or higher. The temperature at which this change occurs 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.

[0125] If the heat absorber is exposed to high temperatures due to combustion or other reasons, the aqueous solvent will evaporate. However, since it can form a porous body made of water-soluble inorganic powder through sintering, it can exhibit heat insulation and fireproofing effects on components adjacent to the heat absorber (such as battery cells).

[0126] In particular, when two or more heat absorbers of this embodiment are sandwiched between a component (e.g., a battery cell) or surrounding the component, it is considered difficult for heat from the component to leak to the outside. For example, it is believed that when the component is exposed to high heat, the water-soluble inorganic powder inside the heat absorber forms a sintered porous body, and the porous body acts as a so-called fireproof wall, thus exhibiting excellent heat insulation and fireproofing effects. Therefore, if the heat absorber of this embodiment is arranged in a secondary battery module such as a stacked battery described later, it is possible to suppress, prevent, or delay chain explosions by suppressing heat transfer to other individual cells.

[0127] (Aqueous solvent)

[0128] The heat absorber of this embodiment contains an aqueous solvent as its contents. Therefore, heat absorption can be achieved by utilizing the latent heat of vaporization of the aqueous solvent within the bag, particularly water, which has a higher latent heat of vaporization than typical hydrates. Furthermore, due to the absorption of sensible heat by the aqueous solvent, temperature stabilization is possible even at room temperature. On the other hand, when the heat absorber is exposed to high temperatures due to combustion or other reasons, the aqueous solvent evaporates, but the water-soluble inorganic powder may form a sintered porous body. Therefore, it can provide heat insulation and fireproofing effects for components adjacent to the heat absorber.

[0129] The aqueous solvent in this embodiment only needs to contain water as the main component, meaning water or a solvent with water as the main component. Therefore, the aqueous solvent includes mixed solvents with solvents other than water, and aqueous solutions containing salts (e.g., buffer solutions, electrolyte solutions). It should be noted that "containing water as the main component" in this specification means that the aqueous solvent contains 45% or more water by mass relative to the total aqueous solvent. In addition, purified water, pure water, ultrapure water, or distilled water can be used as water without particular restrictions.

[0130] 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, acetic acid-sodium acetate, citrate-disodium hydrogen phosphate, sodium dihydrogen phosphate-disodium hydrogen phosphate, glycine-sodium hydroxide, and sodium carbonate-sodium bicarbonate. Additionally, good buffer solutions such as HEPES or MOPS can be used as aqueous solvents.

[0131] Other solvents besides water that constitute the mixed solvent include organic solvents (such as lower alcohols, lower ketones, etc.) that can be mixed uniformly with water, or low-volatility solvents used as antifreeze.

[0132] In this embodiment, the water content in the aqueous solvent is preferably 50% to 100% by mass relative to the total aqueous solvent content, more preferably 80% to 100% by mass, more preferably 90% to 100% by mass, and particularly preferably 95% to 100% by mass.

[0133] The preferred range of water content in the aforementioned aqueous solvents can be achieved by appropriately combining the upper and lower limits mentioned above.

[0134] In this embodiment, the content of the aqueous solvent relative to the total amount (100% by mass) of the contents of the heat absorber is preferably 10% by mass or more and 95% by mass or less, more preferably 20% by mass or more and 90% by mass or less, even more preferably 30% by mass or more and 80% by mass or less, and particularly preferably 50% by mass or more and 70% by mass or less.

[0135] The preferred range of the content of the above-mentioned aqueous solvents can be appropriately reorganized from the upper and lower limits mentioned above.

[0136] When the content of the aqueous solvent is within the above range, the heat absorption, heat insulation and pressure resistance are better, and it can be transformed into a heat insulation material in the high temperature region.

[0137] The above describes the bag body, water-soluble inorganic powder, and aqueous solvent, which are essential components of this disclosure. Hereinafter, inorganic fibers, antifreeze agents, and additives of any component of this invention will be described.

[0138] The contents of the heat absorber in this embodiment may contain one or more of the following: inorganic fibers and antifreeze.

[0139] (Inorganic fibers)

[0140] The inorganic fibers in this embodiment are either fibrous aggregates formed by intertwined fibers of inorganic materials or porous bodies made of inorganic materials. As a foaming nucleating agent, they facilitate the formation of porous bodies from water-soluble inorganic powders. Furthermore, when water-soluble inorganic powders are transformed into porous bodies, porous composites containing both the inorganic fibers and the water-soluble inorganic powders can be formed. Thus, for example, if the temperature exceeds the thermal runaway temperature, it is easy to form a thermally insulating wall with the desired mechanical strength.

[0141] Specifically, the inorganic fibers can be woven fabrics (glass cloth or silica cloth), nonwoven fabrics (glass fiber or ceramic fiber), and cotton-like materials (including not only glass wool, asbestos and ceramic wool, but also sponge-like materials (sponge body)).

[0142] The heat resistance of the inorganic fiber in this embodiment is preferably 300°C or higher, more preferably 700°C or higher, and even more preferably 1200°C or higher.

[0143] The heat resistance refers to the temperature at which the volume change (in the thickness direction) of the test specimen is -20% when the temperature changes from 100°C to 200-700°C and is maintained at each temperature for 30 minutes.

[0144] In this embodiment, when the inorganic fiber is a porous body having at least one of specific air permeability resistance, specific porosity, specific tortuosity, or specific porosity, the absorber as a whole tends to form a relatively stable porous body even from the high-temperature region (critical temperature (e.g., 150°C) to the temperature range exceeding the thermal runaway temperature (e.g., around 1000°C)), thus showing a tendency to function as a thermal insulator. In particular, if the inorganic fiber has a specific porosity, it can become an even better thermal insulator by combining it with water-soluble inorganic powder.

[0145] Porosity

[0146] 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, even more preferably 70% or more and 99.3% or less, and particularly preferably 90% or more and 99% or less.

[0147] In this specification, the average porosity of the inorganic fiber is a value derived from the bulk density and true density described later, and is based on the volume density occupied by the inorganic fiber. Furthermore, the bulk density is a volume density that also includes the voids contained within the inorganic fiber. In contrast, the true density is a volume density based on the material volume occupied by the inorganic fiber.

[0148] The average porosity (%) can be calculated using the following formula (1) based on the following bulk density ρf and true density ρr.

[0149] Average porosity (%) = ((1 / ρf) - (1 / ρr)) / (1 / ρf) × 100 ··· Equation (1)

[0150] <Bulk Density>

[0151] In this embodiment, the bulk density ρf of the inorganic fiber is preferably 0.020 g / cm³. 3 Above and 1g / cm 3 The following is more preferably 0.022 g / cm³. 3 Above and 0.5g / cm 3 The following is a further preferred value: 0.024 g / cm³ 3 Above and 0.1g / cm 3 The following is particularly preferred: 0.026 g / cm³ 3 Above and 0.07g / cm 3 the following.

[0152] After determining the size of the inorganic fiber and calculating its bulk volume V, the mass M of the inorganic fiber is determined using a precision balance. The bulk density of the inorganic fiber can be calculated using the following formula (2) based on the obtained mass M and bulk volume V.

[0153] Bulk density ρf (g / cm³) 3 =M / V…Equation (2)

[0154] True density

[0155] In this embodiment, the true density ρr of the inorganic fiber is preferably 0.5 g / cm³. 3 Above and 10g / cm 3 The following is more preferably 1 g / cm³ 3 Above and 7g / cm 3 The following is a further preferred value: 1.5 g / cm³ 3 Above and 5g / cm 3 The following is particularly preferred: 2g / cm 3 Above and 3g / cm 3 the following.

[0156] There are no particular limitations on the method for determining the true density ρr of inorganic fibers. It can be calculated using a flotation method with a mixture of n-heptane, carbon tetrachloride, and dibromoethane. Specifically, first, a sample of inorganic fiber of appropriate size is placed in a co-stoppered test tube. Next, a suitable mixture of the three solvents is added to the test tube, which is then immersed in a constant temperature bath at 30°C. When the sample floats, n-heptane, representing the lower density, is added. Conversely, when the sample sinks, ethylene dibromide, representing the higher density, is added. This operation is repeated until the sample floats in the liquid. Finally, the density of the mixed solvent is determined using a Cap-Lussac hydrometer flask.

[0157] Composition of Inorganic Fibers

[0158] Examples of inorganic materials constituting the inorganic fiber of this embodiment, or inorganic materials contained in the inorganic fiber, include elements selected from the group consisting of silicon, titanium, barium, zirconium, zinc, calcium, magnesium, cerium, aluminum, indium, tin, and lanthanum, individual oxides or composite oxides of the above elements, individual sulfides or composite sulfides of the above elements, and individual phosphate compounds or composite phosphate compounds of the above elements, with silicon, titanium, zirconium, magnesium, aluminum, indium, tin, and their individual or composite oxides being preferred.

[0159] Specifically, the inorganic materials constituting the aforementioned inorganic fibers include glass, white sand, silica, silica gel, alumina, clay, ceramics, bentonite, perovskite compounds (strontium titanate), talc, mica, wollastonite, potassium titanate, calcium oxide, alkaline magnesium sulfate, sepiolite, calcareous silica, pearlite, zeolite, apatite, hydroxyapatite, kaolinite, montmorillonite, acid clay, diatomaceous earth, basalt, wet silica, dry silica, aerogel, mica, and vermiculite, etc.

[0160] <Shape of Inorganic Material Fibers>

[0161] The shape of the inorganic fiber in this embodiment can be selected from filamentous, fibrous, fiber bundle, fiber aggregate, cotton-like, woven, or nonwoven fabric. Furthermore, "woven fabric" in this specification refers to textiles or woven fabrics.

[0162] When the inorganic fiber in this embodiment is a fabric, known weaving methods such as plain weave, twill weave, satin weave, tatami weave, gauze weave, and curtain weave can be appropriately used as the weaving method. Among these weaving methods, it is preferable to use a weaving method in which the resistance to fluid passage (e.g., the air resistance described later) passing through each (hole) space formed by the intersection of the warp and weft threads is within a specified range. From these viewpoints, plain weave, twill weave, satin weave, gauze weave, and tatami weave are preferred.

[0163] In this embodiment, when the inorganic fiber is a woven fabric, the weaving method for this fabric includes warp knitting (longitudinal knitting such as lace knitting, Raschel knitting, Trico warp knitting, Van Dyck knitting), weft knitting (transverse knitting such as warp knitting, cross knitting, plain knitting, rib knitting, tube knitting, single-sided knitting, double-sided knitting, terry knitting, jacquard knitting), and other known knitting methods. Among these methods, it is preferable to use a knitting method where the resistance to fluid flow through the connecting holes (e.g., the ventilation resistance described later) is within a specified range. Furthermore, various knitting machines such as warp knitting machines, cross knitting machines, circular knitting machines, and Raschel knitting machines can be used as the knitting machine.

[0164] In this embodiment, when the inorganic fiber is a woven fabric, there are no particular limitations on the woven yarn used. The fineness is preferably 50 dtex or more and 8000 dtex or less, more preferably 100 dtex or more and 3000 dtex or less. Furthermore, there are no limitations on the twisting method of the woven yarn; it can be dry twisting, wet twisting (dampening), or a combination thereof. Furthermore, there are no particular limitations on the twisting direction; it can be right-hand twist, left-hand twist, or a combination thereof. Moreover, the woven yarn used in this embodiment can also be false-twist yarn or filament yarn, or yarn processed using the POY-DTY method or the PTY (Producers Textured Yarn) method.

[0165] It should be noted that the conditions for using the braided yarn described above can be appropriately selected based on the intended use or the type of aqueous solvent. Furthermore, the material of the braided yarn refers to the materials constituting inorganic fibers or the inorganic materials contained within those inorganic fibers.

[0166] The BET specific surface area of ​​inorganic fibers can range from 0.3 to 5000 m². 2 / g, or 10~2000m 2 / g, and can also be 30~1600m 2 / g.

[0167] Regarding the method for determining the BET specific surface area of ​​the aforementioned inorganic fibers, a specific surface area meter (manufactured by Microtrac BEL Co., Ltd., BELSORP-mini) was used. The surface area of ​​each 1g sample, determined by the amount of nitrogen adsorbed based on the BET method, was taken as the specific surface area (m²). 2 Calculated using / g).

[0168] In this embodiment, when the inorganic fibers are composed of a nonwoven fabric, the average fiber diameter of all the fibers constituting the nonwoven fabric (fibers made from the inorganic material of the raw material) is preferably 1 to 100 μm, more preferably 2 to 10 μm. If the average fiber diameter of the fibers constituting the nonwoven fabric is within the above range, it is easy to ensure the desired porosity, and therefore preferred. The average fiber diameter can be determined by observing it under a microscope or by image analysis results obtained using a fiber length measuring device (e.g., KAJAANI Fiber Lab.).

[0169] Furthermore, when the inorganic fibers in this embodiment are composed of nonwoven fabric, the average fiber length of all fibers (raw material fibers) constituting the nonwoven fabric is preferably 3 mm or more and 200 mm or less, more preferably 5 mm or more and 100 mm or less, and even more preferably 10 mm or more and 50 mm or less. If the average fiber length of all fibers constituting the nonwoven fabric is within the above range, and the average fiber diameter of the fibers constituting the nonwoven fabric is within the above range, it is easy to ensure the desired porosity, and therefore preferred. The average fiber length can be determined by microscopic observation or by image analysis results from a fiber length measuring device (e.g., KAJAANI Fiber Lab.).

[0170] In this embodiment, when the inorganic fibers are formed from a cotton-like body, the average fiber length of all the fibers (raw material fibers) constituting the cotton-like body is preferably 0.5 μm or more and 50 μm or less, more preferably 0.8 μm or more and 32 μm or less, and even more preferably 1 μm or more and 25 μm or less. If the average fiber length of all the fibers constituting the cotton-like body is within the above-mentioned range, and the average fiber diameter of the fibers constituting the cotton-like body is within the above-mentioned range, it is easy to ensure the desired porosity, and therefore preferred. The average fiber length can be determined by microscopic observation or by image analysis results from a fiber length measuring device (e.g., KAJAANI Fiber Lab.).

[0171] Furthermore, in this specification, cotton-like body is also a type of nonwoven fabric, and a shape other than cloth-like (or flat) is defined as cotton-like body, which retains the state of fibers.

[0172] <Preferred Methods for Inorganic Fibers>

[0173] The preferred inorganic fibers used in this embodiment are glass cloth, ceramic wool, asbestos, and glass wool.

[0174] In this embodiment, the content of inorganic fiber relative to the total amount (100% by mass) of the contents of the heat absorber is preferably 0% by mass or more and 50% by mass or less, more preferably 1% by mass or more and 30% by mass or less, even more preferably 1% by mass or more and 10% by mass or less, more preferably 1% by mass or more and 5% by mass or less, and particularly preferably 1% by mass or more and 3% by mass or less.

[0175] The preferred range of the content of the aforementioned inorganic fibers can be appropriately reorganized from the aforementioned upper and lower limits.

[0176] If the content of inorganic fibers is within the above range, it has better heat absorption and pressure resistance, and in high-temperature areas, the heat absorption effect can be changed into a heat insulation effect.

[0177] Antifreeze

[0178] In this embodiment, since the effect of suppressing temperature drop below the freezing point can be improved, antifreeze can be added to the aqueous solvent or contents as needed. In particular, by adding antifreeze to the contents of the heat absorber, high buffering capacity can be maintained over a wide temperature range.

[0179] The antifreeze in this embodiment can be an inorganic antifreeze or an organic antifreeze. Furthermore, the antifreeze can be in liquid, powder, or solid form.

[0180] As the antifreeze agent for this inorganic system, chlorides such as sodium chloride, calcium chloride, or magnesium chloride (including magnesium chloride hexahydrate and other hydrates) are preferred.

[0181] On the other hand, as an organic antifreeze, salts of organic acids, low-volatility substances (low-volatility solvents or urea) are preferred, and salts of organic acids or low-volatility solvents are more preferred.

[0182] As salts (including hydrates) of the aforementioned organic acids, salts of sodium, potassium, magnesium, or ammonium, such as formic acid, propionic acid, or succinic acid, are preferred. Examples include disodium succinate (including hydrates such as disodium succinate hexahydrate) or sodium propionate.

[0183] In addition, examples of low-volatility substances include urea or low-volatility solvents (e.g., polyols). Examples of such low-volatility solvents include ethylene glycol, diethylene glycol, glycerol, dipropylene glycol, propylene glycol, butyrolactone, N,N-dimethylformamide, glycerol, 1,3-propanediol, glycol ethers, glycol monoethers, 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.

[0184] As a low-volatility solvent in this embodiment, a more preferable option is a solvent with a volatility of less than 1 cm³ in an open system at 60°C and 1 atmosphere. 2 • Less than 0.1g (0.1g / cm³) within 1 hour 2 The organic solvent used should be 0.05 g or less (hr·60℃·1 atm or less), and even more preferably 0.01 g or less. Specifically, from the viewpoint of preferring solvents that are easily miscible with water, glycerol (0.001 g or less / cm³) is preferred. 2 •hr •60℃ •1atm), diglycerides (less than 0.001g / cm³) 2 •hr •60℃ •1atm), ethylene glycol (less than 0.01g / cm³) 2 •hr •60℃ •1atm), propylene glycol (less than 0.001g / cm³) 2•hr •60℃ •1atm), polyethylene glycol (less than 0.001g / cm³) 2 Polyols such as glycerol and diglycerol (·hr·60℃·1atm) are preferred. These low-volatility solvents can be used alone or in combination of two or more.

[0185] The contents of the heat absorber in this embodiment contain a low-volatility solvent, particularly a polyol, thereby suppressing or preventing the evaporation of aqueous solvents, or suppressing the decrease in buffering capacity at low temperatures (improving the antifreeze effect).

[0186] When using a low-volatility solvent as any component, the mass ratio (aqueous solvent / low-volatility solvent) of the contents of the heat absorber in 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.

[0187] In this embodiment, the antifreeze content relative to the total amount (100% by mass) of the contents of the heat absorber can be set to 0% by mass or more and 70% by mass or less, preferably 5% by mass or more and 60% by mass or less, more preferably 10% by mass or more and 50% by mass or less, further preferably 15% by mass or more and 35% by mass or less, and particularly preferably 20% by mass or more and 30% by mass or less. The preferred range of the antifreeze content can be appropriately rearranged from the aforementioned upper and lower limits. Furthermore, if the antifreeze content is within the above range, it is difficult to freeze even at -20°C, thus enabling the battery to be used over a wide temperature range.

[0188] (additive)

[0189] The contents or dispersion (a) of the heat absorber in this embodiment may, as needed, contain ultraviolet absorbers, antioxidants, organic solvents, inorganic fillers other than the aforementioned water-swellable clay minerals, viscosity modifiers such as thickeners, crosslinking agents, flame retardants, and various other additives. These additives are arbitrary components, and when using them, it is preferable to use them in proportions that do not impair the effects of this disclosure and correspond to the purpose of each additive. This proportion is not fixed, but the content of each additive relative to the total mass of the aqueous solvent and various additives used in this disclosure is preferably 0% by mass or more and 50% by mass or less, more preferably 10% by mass or more and 40% by mass or less.

[0190] Examples of ultraviolet absorbers mentioned above include triazine derivatives such as 2-[4-{(2-hydroxy-3-dodecyloxypropyl)oxy}-2-hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine, 2-[4-{(2-hydroxy-3-tetrazoloxypropyl)oxy}-2-hydroxyphenyl]-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine, 2-(2'-xanthonylcarboxyl-5'-methylphenyl)benzotriazole, 2-(2'-o-nitrobenzyloxy-5'-methylphenyl)benzotriazole, 2-xanthonylcarboxyl-4-dodecyloxybenzophenone, and 2-o-nitrobenzyloxy-4-dodecyloxybenzophenone. These ultraviolet absorbers can be used alone or in combination of two or more.

[0191] Examples of such antioxidants include "Sumilizer BBM-S" and "Sumilizer GA-80" manufactured by Sumitomo Chemical Co., Ltd.

[0192] Examples of organic solvents mentioned above include aromatic hydrocarbons such as toluene and xylene; glycols such as ethylene glycol and propylene glycol; polyether glycols as their polymers; cellosols; carbitols; and aliphatic alcohols, represented by methanol. These organic solvents can be used alone or in combination of two or more.

[0193] Examples of inorganic filler materials mentioned above include fused silica, crystalline silica, alumina, silicon nitride, and aluminum hydroxide.

[0194] Examples of viscosity modifiers such as thickeners include 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 esters, and petroleum resin-based thickeners.

[0195] Examples of crosslinking agents include isocyanate-based, epoxy-based, aziridine-based, polyvalent metal salt-based, metal chelate-based, keto-hydrazide-based, oxazoline-based, carbodiimide-based, silane-based, and glycidyl (alkoxy)epoxysilane-based crosslinking agents.

[0196] Examples of flame retardants include: red phosphorus, monoammonium phosphate, diammonium phosphate, triammonium phosphate, ammonium polyphosphate, and other inorganic phosphorus compounds such as ammonium phosphate and phosphoramide; phosphate ester compounds; phosphonic acid compounds, phosphonic acid compounds, phosphine oxide compounds, orthophosphine compounds, organic nitrogen- and phosphorus-containing compounds, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, 10-(2,5-dihydrooxyphenyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxide, 10-(2,7- Cyclic organophosphorus compounds such as dihydronaphthyl-10H-9-oxa-10-phosphaphenanthrene-10-oxide, and their derivatives obtained by reacting them with compounds such as epoxy resin and phenolic resin; nitrogen-based flame retardants such as triazine compounds, cyanuric acid compounds, isocyanuric acid compounds, and phenothiazine; organosilicon-based flame retardants such as silicone oil, silicone rubber, and organosilicon resin; and inorganic flame retardants such as metal hydroxides, metal oxides, metal carbonate compounds, metal powders, boron compounds, and low-melting-point glasses. These flame retardants can be used alone or in combination of two or more. Furthermore, when using these flame retardants, the preferred concentration is 0.1 to 20% by mass relative to the entire contents of the endothermic body or the entire dispersion (a).

[0197] (Manufacturing method of heat absorber)

[0198] As an example of the method for manufacturing the heat absorber in this embodiment, it preferably includes the following steps: filling the opening of the bag with an aqueous solvent, a water-soluble inorganic powder, and one or more of the group consisting of inorganic fibers and additives as needed; and sealing the bag by sealing the opening of the bag.

[0199] The above-mentioned aqueous solvent, the above-mentioned water-soluble inorganic powder, and one or more of the group consisting of inorganic fibers and additives selected as needed can be filled from the opening of the bag body, or the mixed solution (1) formed by impregnating or dispersing the water-soluble inorganic powder and the inorganic fibers and additives selected as needed in the above-mentioned aqueous solvent can be prepared in advance and then filled from the opening of the bag body.

[0200] The above-mentioned mixed solution (1) preferably contains the above-mentioned aqueous solvent and the above-mentioned water-soluble inorganic powder, wherein it preferably contains the above-mentioned aqueous solvent, the above-mentioned water-soluble inorganic powder, and one or more of the group consisting of inorganic fibers and additives as needed.

[0201] The mixed solution (1) preferably contains, relative to the total amount (100% by mass) of the mixed solution (1), 0-50% by mass of inorganic fiber, 10-95% by mass of aqueous solvent, 0-50% by mass of antifreeze, 5%-90% by mass of water-soluble inorganic powder (containing water in the case of hydrate), and 0-10% by mass of additives. More preferably, it contains 0%-30% by mass of inorganic fiber, 10-95% by mass of aqueous solvent, 0-50% by mass of antifreeze, 5%-70% by mass of water-soluble inorganic powder (containing water in the case of hydrate), and 0-10% by mass of additives. More preferably, it contains 1-12% by mass of inorganic fiber, 20-94% by mass of aqueous solvent, 0-25% by mass of antifreeze, 5%-50% by mass of water-soluble inorganic powder (containing water in the case of hydrate), and 0-50% by mass of additives.

[0202] The amount of “water-soluble inorganic powder (containing water in the case of hydrate)” relative to the total amount (100% by mass) of the above mixed solution (1) refers to the amount of the mixture. Therefore, when the above water-soluble inorganic powder is a hydrate, the amount of water-soluble inorganic powder (containing water in the case of hydrate) includes the amount of water contained in the above water-soluble inorganic powder as a hydrate.

[0203] A preferred heat absorber in this embodiment may be a heat absorber comprising a bag body and contents of the bag body, including inorganic fibers (e.g., 4-9% by mass of rock wool relative to the total amount of the contents), an aqueous solvent (e.g., 20-60% by mass of water relative to the total amount of the contents), and a water-soluble inorganic powder (e.g., 10-50% by mass of magnesium sulfate relative to the total amount of the contents). This provides a heat absorber with superior heat absorption and pressure resistance, and capable of changing from a heat absorption effect to a heat insulation effect in high-temperature regions.

[0204] In this embodiment, the total content of aqueous solvents and water-soluble inorganic powders contained in the contents of the bag is preferably 79 to 100% by mass, more preferably 91 to 99.5% by mass, further preferably 94 to 99% by mass, and even more preferably 96 to 99.4% by mass, relative to the total amount of the contents of the bag.

[0205] In this embodiment, the total content of aqueous solvent, inorganic fiber and water-soluble inorganic powder contained in the contents of the bag is preferably 80 to 100% by mass, more preferably 92 to 99.5% by mass, further preferably 93 to 99.4% by mass, and even more preferably 96 to 99.1% by mass, relative to the total amount of the contents of the bag.

[0206] In this embodiment, relative to the total amount (100% by mass) of the contents of the bag, the total content of the aqueous solvent, inorganic fiber, water-soluble inorganic powder, antifreeze and additive contained in the contents of the bag is preferably 83 to 100% by mass, more preferably 94 to 99.8% by mass, further preferably more than 95% by mass and less than 99.6% by mass, and even more preferably more than 96% by mass and less than 99.5% by mass.

[0207] The upper and lower limits of the above total content can be appropriately reorganized.

[0208] (Preferred method for heat absorber)

[0209] The heat absorber in this embodiment preferably exhibits high buffering capacity and / or excellent pressure resistance during heating. The preferred embodiments are described in detail below.

[0210] Highly buffered heat absorber

[0211] The preferred heat absorber of this embodiment has a bag and contents filled in the bag, the contents comprising an aqueous solvent (preferably water) and a water-soluble inorganic powder (preferably magnesium sulfate), exhibiting high buffering capacity. More preferably, the heat absorber exhibiting high buffering capacity has a bag, an aqueous solvent (preferably water), a water-soluble inorganic powder (preferably magnesium sulfate), and inorganic fibers (preferably ceramic cotton) contained as the contents filled in the bag.

[0212] In this specification, the heat absorber with high buffering capacity will also be referred to as a heat absorber with high buffering capacity.

[0213] This high cushioning capacity refers to excellent cushioning performance. When inorganic fibers are used as the contents of the bag, a tendency to exhibit high cushioning capacity is observed.

[0214] Furthermore, the term "high buffering capacity" specifically refers to a buffering capacity (%) preferably expressed by the following formula (I) of 90% or more, more preferably 93% or more. By exhibiting such a buffering capacity of 90% or more, it is easier to follow short-term deformations such as expansion and contraction caused by the charging and discharging of the battery cell. In addition, the upper limit of the above-mentioned high buffering capacity can be 100%.

[0215] [Number 2]

[0216] "Bufferability (%) = h" a / h b ×100 Formula (I)

[0217] (In the above formula (I), h) a The height (mm) of the pressed portion after the surface of the highly buffered heat absorber is pressed in at 1 MPa for 60 seconds, the pressure is released, and 5 minutes have passed.b This indicates the height (in mm) reached 60 seconds before the surface of the highly buffered heat absorber was pressed in at 1 MPa.

[0218] In the heat absorber of this embodiment, where buffering capacity is important, it is preferable that not only is the buffering capacity (%) expressed by formula (I) 90% or more, but the content of antifreeze is also controlled to be below a specified value. That is, where buffering capacity is important, the content of antifreeze relative to the total amount of contents is preferably 40% by mass or less, more preferably 30% by mass or less, further preferably 20% by mass or less, even more preferably 12% by mass or less, even more preferably 9% by mass or less, even more preferably 6% by mass or less, and particularly preferably substantially non-existent (0.5% by mass or less).

[0219] Furthermore, in the heat absorber of this embodiment, when buffering is important, the lower limit of the total amount of aqueous solvent, inorganic fiber, water-soluble inorganic powder and antifreeze contained in the contents relative to the total amount of the contents of the heat absorber (100% by mass) is preferably more than 30% by mass, more preferably 50% by mass or more, further 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.

[0220] 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 above contents is preferably 100% by mass or less, more preferably 50% by mass or less, relative to the total amount of the contents of the heat absorber (100% by mass).

[0221] It is believed that if the combined amount of inorganic fibers, aqueous solvents, and water-soluble inorganic powders increases relative to the total amount of contents, the inorganic fibers and water-soluble inorganic powders enhance the elasticity of the contents, thus exhibiting high buffering capacity.

[0222] High-pressure resistant heat absorber

[0223] The preferred heat absorber in this embodiment is a heat absorber with excellent pressure resistance during heating, which has a bag body and contents filled in the bag body, the contents comprising an aqueous solvent (preferably water) and a water-soluble inorganic powder (preferably magnesium sulfate). More preferably, it is a heat absorber with excellent pressure resistance during heating, which has a bag body and contents filled in the bag body, the contents comprising an aqueous solvent (preferably water), a water-soluble inorganic powder and inorganic fibers.

[0224] In this specification, the heat absorber with excellent pressure resistance during heating is also referred to as a high-pressure-resistant heat absorber. This high-pressure-resistant heat absorber tends to exhibit excellent pressure resistance when heated at high temperatures (e.g., above 800°C) due to thermal runaway of the battery.

[0225] The display of pressure resistance during heating refers to the high pressure resistance exhibited by the heat absorber when heated.

[0226] Therefore, a preferred embodiment of the high-pressure-resistant heat absorber is a high-pressure-resistant heat absorber comprising a bag body capable of holding contents, an aqueous solvent, a water-soluble inorganic powder, and inorganic fibers, wherein the inorganic fibers and the water-soluble inorganic powder are filled into the contents as a composite. In this case, the water-soluble inorganic powder exhibits excellent solubility in water, thus allowing for uniform dispersion or dissolution as the contents.

[0227] It is believed that if inorganic fibers and water-soluble inorganic powders coexist, a foamed film will temporarily form during thermal runaway, and this foamed film will thus play a role in enhancing dispersion. Furthermore, it is believed that by having inorganic fibers and water-soluble inorganic powders coexist, the inorganic fibers carry the water-soluble inorganic powders, and the inorganic fibers enhance the dispersibility of the water-soluble inorganic powders, thus achieving a synergistic effect of high pressure resistance.

[0228] In detail, the high-pressure-resistant heat absorber of this embodiment heats the aqueous solvent (water component) within the heat absorber to exhibit an endothermic effect, forming a foam film while evaporating. By reducing the amount of aqueous solvent, voids are created between the inorganic fibers, improving the thermal insulation performance. Furthermore, during the evaporation of the aqueous solvent, water-soluble inorganic powder precipitates and is supported on the inorganic fibers. When the water-soluble inorganic powder is a hydrate, the water component retained as a hydrate also evaporates while exhibiting an endothermic effect as heating continues. At this time, the water-soluble inorganic powder can be uniformly dispersed or dissolved in the aqueous solvent, thereby preventing the water-soluble inorganic powder from being biasedly supported within the inorganic fibers.

[0229] As overheating progresses, the water-soluble inorganic powder loaded onto the inorganic fibers sinters, firmly reinforcing the mesh structure of the inorganic fibers. Furthermore, the formation of a porous body within the inorganic fibers by the inorganic powder further improves thermal insulation. As described above, the dispersed presence of the water-soluble inorganic powder enables the reinforcement of the mesh structure and the formation of a porous body throughout the entire region of the inorganic fibers. Therefore, the high-pressure-resistant heat absorber of this embodiment can achieve a synergistic effect of thermal insulation and high pressure resistance. It should be noted that this uniform dispersion means, for example, that when the composite as the contents is removed, the difference in concentration (mass %) of the water-soluble inorganic powder present at both ends of a portion approximately 3 mm from the end of the composite can be within ±15%.

[0230] Furthermore, the phrase "exhibiting high pressure resistance upon heating" specifically refers to the following: after heating the absorber to a predetermined temperature on the side opposite to the heating surface, the thickness change rate (%) expressed by the following formula (II) is preferably 70% or more, more preferably 75% or more, further preferably 85% or more, and particularly preferably 90% or more. By exhibiting the aforementioned thickness change rate of 70% or more, excellent pressure resistance is achieved, thus effectively suppressing and preventing chain explosions between individual cells. It should be noted that the upper limit of the aforementioned thickness change rate can be 100%.

[0231] [Number 3]

[0232] Equation (II):

[0233] "Thickness change rate (%) = (Thickness of the heat absorber after being pressed at 0.5 MPa for 60 seconds on the surface of the heated high-pressure-resistant heat absorber) / (Thickness of the heat absorber before being pressed at 0.5 MPa for 60 seconds on the surface of the heated high-pressure-resistant heat absorber) × 100"

[0234] In the above formula (II), "the thickness of the heat absorber after pressing the surface of the heated high-pressure-resistant heat absorber with 0.5 MPa for 60 seconds" refers to the average thickness of the heat absorber (arithmetic mean of the thicknesses at any 5 locations) after pressing the surface of the high-pressure-resistant heat absorber after heating to a specified temperature or above, preferably after pressing the surface of the high-pressure-resistant heat absorber after heating under the following heating conditions with 0.5 MPa for 60 seconds (within approximately 20 minutes immediately after pressing).

[0235] Similarly, in the above formula (II), "the thickness of the heat absorber before the surface of the heated high-pressure-resistant heat absorber is pressed with 0.5 MPa for 60 seconds" is the average thickness of the heat absorber before the surface of the heated high-pressure-resistant heat absorber is pressed with 0.5 MPa for 60 seconds after one surface of the high-pressure-resistant heat absorber is heated to a specified temperature or above, preferably under the following heating conditions, and then pressed with 0.5 MPa for 60 seconds.

[0236] Heating conditions:

[0237] "Utilizing radiant heat at 50kW / m 2 After the heat is heated to the temperature of the side (back side) of the heat absorber opposite to the heating surface, the heat absorber is allowed to dissipate heat at room temperature (22~28℃) and naturally cool down until the surface temperature of the heat absorber becomes room temperature (22~28℃). The thickness change rate (%) before and after heating is calculated.

[0238] In addition, the heating surface of the absorber is pressurized at 0.5 MPa for 60 seconds.

[0239] In the above heating conditions, the "specified temperature" refers to the temperature at which the heat absorber can become a porous body, and can be set according to the operating environment of the heat absorber, the required explosion resistance, and the anticipated thermal runaway initiation temperature. For example, the "specified temperature" can be set to 240°C (or higher), preferably 200°C (or higher), more preferably 180°C (or higher), further preferably 160°C (or higher), even more preferably 150°C (or higher), and particularly preferably 120°C (or higher). For example, if the heat absorber, when heated to 150°C on the side opposite to the heating surface (the side directly in contact with radiant heat), has a thickness change rate (%) of at least a specified value, then the heat absorber can achieve a thickness change rate of at least a specified value even in a temperature range of 150°C or higher.

[0240] In the case of prioritizing high pressure resistance, the contents of the heat absorber in this embodiment preferably contain inorganic fibers, aqueous solvents, and water-soluble inorganic powders.

[0241] [Secondary Battery Module]

[0242] There are no particular limitations on the type of secondary battery that can be equipped with the heat absorber of this embodiment. 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-zinc oxide batteries, metal-air batteries, multivalent cation batteries, capacitors, and capacitors. Among these, lithium-ion batteries are a preferred application.

[0243] The secondary battery module capable of carrying the heat absorber of this embodiment is, for example, a secondary battery mounted on a mobile body such as a vehicle or an aircraft (especially a drone), and has multiple battery cells and a housing that houses the multiple battery cells.

[0244] The battery cell (or battery unit) constituting the above-mentioned secondary battery module can be, for example, a battery unit consisting of a battery outer packaging film as the outer packaging material, and a battery element having at least a positive electrode material layer, a negative electrode material layer, a separator, a positive current collector, and a negative current collector sealed inside the outer packaging material.

[0245] The following uses Figure 1 A secondary battery module capable of carrying the heat absorber of this embodiment will be described. Figure 1 A cross-sectional view of a stacked battery 20, exemplified as a secondary battery, is shown. Furthermore, secondary batteries capable of incorporating the heat absorber of this embodiment are not limited to, for example... Figure 1The stacked battery 20 has a flat shape as shown. The secondary battery capable of carrying the heat absorber of this embodiment can be, for example, cylindrical like a wound secondary battery, or the cylindrical secondary battery can be deformed into a rectangular flat shape.

[0246] In this embodiment, the stacked battery 20 has a structure in which a flat, generally rectangular battery element 10, which substantially undergoes a charge-discharge reaction, is sealed inside battery outer packaging materials 18a and 18b. The battery element 10 has a structure in which a positive electrode, an electrolyte layer (or separator) 14, and a negative electrode are stacked. The positive electrode has a structure in which a positive electrode material layer 11 containing a positive electrode active material is disposed on both sides of the positive electrode current collector 12. The negative electrode has a structure in which a negative electrode material layer 16 containing a negative electrode active material is disposed on both sides of the 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 opposite each other with the electrolyte layer 14 in between, and the positive electrode, electrolyte layer 14, and negative electrode are stacked sequentially. Thus, adjacent positive electrodes, electrolyte layers 14, and negative electrodes form a single battery cell. Figure 1 The stacked battery 20 shown has a structure formed by stacking multiple such individual cells and connecting them in parallel. In addition, an activated carbon layer 19 is provided, which adsorbs components from the positive electrode active material caused by the melting and sublimation of the positive electrode active material when the battery is exposed to high temperature.

[0247] In addition, such as Figure 1 As shown, the positive current collector 12 and the negative current collector 17 are respectively equipped with a positive terminal 13 and a negative terminal 15 that conduct electricity between the positive and negative electrodes, and have a structure in which they are led out to the outside of the battery outer packaging materials 18a and 18b by being clamped by the ends of the battery outer packaging materials 18a and 18b. The positive terminal 13 and the negative terminal 15 can be mounted to the positive current collector 12 and the negative current collector 17 of each electrode by welding or other means, as needed, via positive leads and negative leads (not shown).

[0248] The battery outer packaging materials 18a and 18b use laminated films, and the sealing layers formed on the surfaces of the battery outer packaging films 18a and 18b are typically heat-sealed together. In addition, there are areas on the periphery of the battery outer packaging materials 18a and 18b where the sealing layers are sealed together by heat sealing.

[0249] Next, use Figure 2 The secondary battery module equipped with the heat absorber of this embodiment will be described. Figure 2 It is a general indication that will Figure 1 A 3D view of the disassembled secondary battery module. Figure 2The battery element 10 shown has the following structure: a positive electrode formed on a positive current collector 12 (such as aluminum foil) having a positive terminal 13 and a negative electrode disposed on a negative current collector 17 (such as metal foil) having a negative terminal 15 are stacked opposite each other with a separator 14 containing an electrolyte in between. Then, multiple battery elements 10 are stacked and sealed with battery outer packaging materials 18a, 18b (such as aluminum laminate outer packaging). In this embodiment, the heat absorber 1 is arranged to contact the negative current collector 17. The heat absorber 1 can be configured to contact not only the negative current collector 17 but also the positive current collector 12. Therefore, the secondary battery module on which the heat absorber 1 is mounted on the battery element 10 has one or more stacked bodies. The stacked bodies are formed by sequentially stacking a positive electrode formed on a positive current collector 12 (aluminum foil, etc.) having a positive terminal 13, a separator 14 containing an electrolyte, and a negative electrode disposed on a negative current collector 17 (metal foil, etc.) having a negative terminal 15. One or more heat absorbers 1 can be configured to abut against the positive current collector 12 and / or the negative current collector 17, but not against the separator 14.

[0250] It should be noted that when using solid electrolytes or gel electrolytes as electrolytes, they can also be configured to replace the diaphragm 14 and place these electrolytes between the electrodes.

[0251] On the other hand, the aqueous solvent in the contents of the heat absorber in this embodiment does not come into direct contact with the battery element 10. Therefore, the preferred heat absorber for a secondary battery in this embodiment is one in which the bag is filled with an aqueous solvent, water-soluble inorganic powder and inorganic fibers, but the aqueous solvent in the contents of the bag does not come into direct contact with the battery element 10. More preferably, the contents of the bag as a heat absorber for a secondary battery do not contain the aforementioned battery element 10.

[0252] The secondary battery module disclosed herein can also hold the heat absorber 1 of this embodiment between multiple housings (not shown) or multiple adjacent battery elements 10 (or also referred to as battery cells) housed within battery outer packaging films 18a, 18b. Furthermore, the aforementioned housings can be formed, for example, of aluminum, iron, or metal materials containing them, or resin materials such as polyphenylene sulfide. If formed of a resin material, it can contribute to the lightweighting of the secondary battery module.

[0253] The heat absorber 1 can be clamped between multiple battery elements 10, for example, by adhesives, welding (ultrasonic welding, high-frequency welding, thermal welding), bonding agents, etc.

[0254] According to this structure, the heat absorber 1 sandwiched between the battery elements 10 absorbs the heat generated during secondary battery charging, thereby suppressing rapid temperature rises in the battery elements 10 and preventing potential degradation or fires. Since the heat absorber 1 is sandwiched between the battery elements 10, it can suppress temperature fluctuations between the battery elements 10 through thermal insulation, and further acts as a buffer material for volume changes caused by the expansion of the battery elements 10, easily mitigating the rise in internal pressure of the secondary battery module. On the other hand, when the battery elements 10 experience thermal runaway due to overheating, the water-soluble inorganic powder within the heat absorber 1 sinters and transforms into a hard, plate-like porous body, thus increasing its pressure resistance and decreasing its thermal conductivity. Therefore, the heat absorber 1 can maintain a fixed distance between individual cells, effectively maintaining thermal insulation and controlling thermal conductivity, effectively suppressing chain explosions of the battery elements 10.

[0255] In addition, in the secondary battery module, the heat absorber of this embodiment can also be disposed in the housing or battery outer packaging film that houses multiple battery elements (battery cells).

[0256] Example

[0257] The present invention will now be specifically described through examples and comparative examples. However, the present invention is not limited to the examples listed below.

[0258] (1) Determination of endothermic onset temperature, endothermic peak temperature, and amount of heat absorbed

[0259] For the heat absorbers prepared in this embodiment and the comparative example, the heat absorption start temperature and the heat absorption peak temperature were measured as follows.

[0260] Using a differential scanning calorimeter (DSC; DSC-7020, manufactured by Hitachi High Technology Co., Ltd.), under a nitrogen atmosphere, the temperature was increased from 20°C to 350°C at a rate of 1°C / min. The temperature at which the straight line obtained by extending the baseline of the DSC measurement curve from the low-temperature side to the high-temperature side intersects the tangent line drawn from the curve on the low-temperature side of the endothermic peak accompanied by evaporation at the point of maximum slope is taken as the endothermic onset temperature (°C). The point where the DSC measurement curve differs most from the baseline is taken as the endothermic peak temperature (°C). Furthermore, the heat of heat (J / g or mJ / mg) is obtained by dividing the integral value of the endothermic peak relative to the baseline of the DSC measurement curve by the mass of the water-soluble inorganic powder used in the measurement.

[0261] (2) Evaluation of buffering capacity

[0262] The buffering capacity of the absorbers prepared in this embodiment and the comparative example was evaluated using the following methods. Specifically, at room temperature (23°C), the absorber, with dimensions of 100 mm (length) × 100 mm (width) × 4.8 mm (height), was placed in a Tensilon universal testing machine (Orientec Corporation "RTE-1210") equipped with a 7 mm φ indentation fixture, and an indentation test was performed. In this indentation test, the surface of the absorber was pressed in at 1 MPa for 60 seconds, and then the pressure was released. The height (mm) h of the indented portion of the surface was measured after 5 minutes. a The height (mm) of the absorber surface pressed into the ground at 1 MPa for 60 seconds. b Observe the cushioning (or recovery) of the following formula (I) and evaluate it according to the following criteria. It should be noted that the above-mentioned indentation test is carried out at two indentation points on the surface of the heat absorber. The height (or thickness) is measured at each point, and the cushioning (%) is calculated by the following formula (I). The average values ​​are shown in Table 1.

[0263] Equation (I): Buffering capacity (%) = h a / h b ×100

[0264] (Evaluation criteria for buffering capacity)

[0265] Set "Restore more than 90% of the original height" to "◎".

[0266] Set "Restore more than 80% of the original height" to "0".

[0267] Set "Restore more than 70% of the original height" to "△".

[0268] Set "Restores less than 70% of the original height or cannot be measured" to "×".

[0269] (3) Heating experiment using a cone calorimeter

[0270] According to JIS A 1316 standard, use Figure 4 The cone calorimeter 30 shown (manufactured by Toyo Seiki Co., Ltd.) directly heats the absorber prepared in this embodiment and comparative example using radiant heat. More specifically, the cone calorimeter 30 is based on the principle that the relationship between the heat generated during combustion and the amount of oxygen consumed is independent of the type of organic material, with 1 kg of oxygen producing 13.1 MJ. By measuring the oxygen concentration and flow rate in the combustion exhaust gas, the heat generation rate and total calorific value are calculated using the oxygen consumption method. The absorber 1 is placed at the top of the support 32 as the test body, and a radiant heat is generated from the cone 31 at a rate of 50 kW / m². 2The heat is applied to the heat exchanger. Then, using thermocouple 33, which serves as the back surface of the heat exchanger 1, the temperature change on the back surface of the heat exchanger 1 is measured up to 200°C. In addition, along with the temperature change, the presence or absence of combustion is also observed.

[0271] (4) Evaluation of the pressure resistance of the test specimens after heating test

[0272] For the absorbers prepared in this embodiment and the comparative example, after heating experiments using the cone calorimeter described above, their pressure resistance was evaluated using the following methods. Specifically, at room temperature (23°C), a pressing test was performed in a Tensilon universal testing machine (Orientec Corporation "RTE-1210") equipped with a 7mmφ pressing clamp. The pressing test measured the amount of pressure applied when pressed at 0.5 MPa for 60 seconds (=when pressurized). The thickness change rate during pressurization was calculated from this amount of pressure using the following formula (II), and the results were evaluated according to the following criteria. It should be noted that the pressing test was performed at two points on the surface of the absorber after the heating experiment using the cone calorimeter described above. The height (or thickness) was measured at each point, and the thickness change rate was calculated using the following formula (II). The average values ​​of these values ​​are shown in Table 1.

[0273] Formula (II): Thickness change rate (%) = (Thickness of the heat absorber after pressing the surface of the heated heat absorber with 0.5 MPa for 60 seconds) / (Thickness of the heat absorber before pressing the surface of the heated heat absorber with 0.5 MPa for 60 seconds) × 100

[0274] (Evaluation criteria for thickness change rate)

[0275] Set the range of thickness variation rate from 70% to 100% as “◎”.

[0276] Set the range of thickness variation rate from 40% to 69% to "0".

[0277] Set the thickness variation rate to the range of 0~39% or the case where it cannot be measured to "×".

[0278] It should be noted that the pressure resistance is best when the thickness change rate is in the range of 70-100%.

[0279] Excellent pressure resistance is achieved when the indentation amount (= the amount of flattening) is low.

[0280] Furthermore, in Example 1, during the heating experiment using the aforementioned cone calorimeter, the back surface of the absorber 1 was allowed to reach temperatures of 150°C, 160°C, 170°C, 180°C, and 240°C, and then allowed to cool naturally until the surface temperature of the absorber reached room temperature. The thickness change rate (%) before and after heating at each temperature was calculated. The results are recorded in Table 2 below.

[0281] (5) Methods for determining average porosity, true density and bulk density

[0282] The average porosity of the inorganic fiber is calculated using the following formula (1) based on the bulk density ρf and true density ρr determined by the following method.

[0283] Average porosity (%) = ((1 / ρf) - (1 / ρr)) / (1 / ρf) × 100 ·· Equation (1)

[0284] <Determination of True Density>

[0285] Inorganic fibers removed from the contents of the absorber, or inorganic fibers sealed in the bag, are thoroughly washed with distilled water and dried overnight. Then, the dried inorganic fibers are placed in a co-stoppered test tube, and a suitable mixture of three solvents is added to the test tube, immersing it in a constant temperature bath at 30°C. When the inorganic fibers float, heptane (a low-density solvent) is added. Conversely, when the inorganic fibers sink, dibromoethylene (a high-density solvent) is added. This process is repeated until the inorganic fibers are floating in the liquid, and the density of the mixed solvent is determined using a Cap-Lussac specific gravity flask.

[0286] <Determination of Bulk Density>

[0287] After thoroughly washing with distilled water and drying overnight, the inorganic fibers removed from the contents of the absorber or sealed in the bag are measured and their bulk volume V is calculated. Then, the mass M of the inorganic fibers is measured using a precision balance. Based on the obtained mass M and bulk volume V, the bulk density of the inorganic fibers is calculated using the following formula (2).

[0288] Bulk density ρf (g / cm³) 3 =M / V…Equation (2)

[0289] (2) Raw materials used

[0290] Water-soluble inorganic powders

[0291] The water-soluble inorganic powders used in the examples and comparative examples are described below.

[0292] • Magnesium sulfate heptahydrate: (Product name "Magnesium Sulfate Heptahydrate Grade 1", manufactured by Kanto Chemical Co., Ltd., solubility in 100g of water at 20℃ (g / 100g): 71g)

[0293] • 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)

[0294] Sodium acetate: (Product name "Sodium Acetate Grade 1", manufactured by Kanto Chemical Co., Ltd., solubility in 100g of water at 20°C (g / 100g): 46.5g)

[0295] • 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)

[0296] It should be noted that the solubility of the above hydrates in anhydrous form is as described below.

[0297] • Solubility of anhydrous magnesium sulfate in 100g of water at 20℃ (g / 100g): 30g

[0298] • Solubility of anhydrous calcium sulfate in 100g of water at 20℃ (g / 100g): 0.2g

[0299] It should be noted that within the bag of the heat absorber, magnesium sulfate heptahydrate exists in anhydrous form, while calcium sulfate dihydrate exists in hydrate form.

[0300] <Bag>

[0301] The water vapor permeability (g / (m) of the aluminum bag used in Examples 1-4 described below) was confirmed. 2 ·24h)]) is 50g / (m 2 ·24h and below.

[0302] (3) Examples and Comparative Examples

[0303] <Example 1>

[0304] 32 parts by mass of magnesium sulfate heptahydrate (including the amount of water in the hydrate) and 60 parts by mass of pure water were mixed to prepare an aqueous solution (1) containing water-soluble inorganic powder. Then, 92 parts by mass of the above aqueous solution (1) containing water-soluble inorganic powder and 8 parts by mass of ceramic cotton (average porosity 96.9%, true density 3, bulk density 0.093) were inserted into a container made of an aluminum bag (a gas barrier bag manufactured by Mitsubishi Gas Chemical Co., Ltd., with a thickness of 0.094 mm, composed of PET, aluminum foil and polyethylene laminated together) with a length of 116 mm and a width of 116 mm.

[0305] Next, the aluminum bag was filled with the aqueous solution (1) containing the water-soluble inorganic powder. After the injection port was heat-sealed, the aluminum bag was placed flat between 4.8 mm thick gap materials, and a flat plate was placed on top. The mixture was left to stand at 20°C for 10 minutes to produce a sheet-like heat absorber (1) with a thickness of 4.8 mm. Then, the heat absorber (1) was evaluated according to the steps described in the evaluation section above. The results are shown in Table 1 and... Figure 3 .

[0306] In addition, the heat absorber (1) prepared in Example 1 was heated to 200°C according to the temperature of the back side of the test body using a cone calorimeter. The result confirmed that the heat absorber (1) prepared in Example 1 changed into a porous body at a temperature above 150°C. Figure 5 (a) shows a cross-sectional photograph of the endothermic body (1) that has changed into a porous material.

[0307] <Example 2>

[0308] 27 parts by mass of sodium acetate and 64 parts by mass of pure water were mixed to prepare an aqueous solution (2) containing water-soluble inorganic powder. Then, 91 parts by mass of the above aqueous solution (2) containing water-soluble inorganic powder and 9 parts by mass of ceramic cotton (average porosity 96.8%, true density 3, bulk density 0.096) were inserted into a container made of an aluminum bag (a gas barrier bag manufactured by Mitsubishi Gas Chemical Co., Ltd., with a thickness of 0.094 mm, made of PET, aluminum foil and polyethylene laminated together) with a length of 116 mm and a width of 116 mm.

[0309] Next, the aluminum bag was filled with the aqueous solution (2) containing the water-soluble inorganic powder. After the injection port was heat-sealed, the aluminum bag was placed flat between 4.8 mm thick interlayer materials, and a flat plate was placed on top. The mixture was then left to stand at 20°C for 10 minutes to produce a sheet-like heat absorber (2) with a thickness of 4.8 mm. The heat absorber (2) was then evaluated according to the steps described in the evaluation section above. The results are shown in Table 1 and... Figure 3 .

[0310] In addition, the heat absorber (1) prepared in Example 2 was heated to 200°C using a cone calorimeter, and the results showed that the heat absorber (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 absorber (2) that has changed into a porous material.

[0311] <Example 3>

[0312] 35 parts by mass of magnesium sulfate heptahydrate (including the amount of water in the hydrate) and 65 parts by mass of pure water were mixed to prepare an aqueous solution (3) containing water-soluble inorganic powder. Then, 100 parts by mass of the above aqueous solution (3) containing water-soluble inorganic powder were inserted into a container made of an aluminum bag (a 0.094 mm thick "gas barrier bag" manufactured by Mitsubishi Gas Chemical Co., Ltd., made of PET, aluminum foil and polyethylene laminated together) with a length of 116 mm and a width of 116 mm.

[0313] Next, the aluminum bag was filled with the aqueous solution (3) containing the water-soluble inorganic powder. After the injection port was sealed by heat sealing, the aluminum bag was placed flat between 4.8 mm thick gap materials, and a flat plate was placed on it. The plate was then left to stand at 20°C for 10 minutes to produce a sheet-like heat absorber (3) with a thickness of 4.8 mm. Then, the heat absorber (3) was evaluated according to the steps described in the evaluation column above. The results are shown in Table 1 and Figure 3 .

[0314] In addition, the absorber (3) prepared in Example 3 was heated to 200°C using a cone calorimeter, and the results confirmed that the absorber (3) prepared in Example 3 at temperatures above 180°C also changed into a porous body in the same way as the absorbers in Examples 1 and 2.

[0315] <Example 4>

[0316] 25 parts by mass of anhydrous magnesium sulfate (including the amount of water in the hydrate) and 75 parts by mass of pure water were mixed to prepare an aqueous solution (4) containing water-soluble inorganic powder. Then, 100 parts by mass of the above aqueous solution (4) containing water-soluble inorganic powder were inserted into a container made of an aluminum bag (a 0.094 mm thick "gas barrier bag" manufactured by Mitsubishi Gas Chemical Co., Ltd., made of PET, aluminum foil and polyethylene laminated together) with a length of 116 mm and a width of 116 mm.

[0317] Next, the aluminum bag was filled with the aqueous solution (4) containing the water-soluble inorganic powder. After the injection port was heat-sealed, the aluminum bag was placed flat between 4.8 mm thick gap materials, and a flat plate was placed on it. The mixture was then left to stand at 20°C for 10 minutes to produce a sheet-like heat absorber (4) with a thickness of 4.8 mm. Then, the heat absorber (4) was evaluated according to the steps described in the evaluation section above. As a result, the evaluation results for heat absorption, melting temperature, heat absorption start temperature, heat absorption peak temperature, pressure resistance, and buffering properties were all the same as those in Example 2.

[0318] <Comparative Example 1>

[0319] As Comparative Example 1, a commercially available material, "Xiaomei Corporation's silica aerogel pad material, thickness 4.8 mm (measured), thermal conductivity: 0.012~0.018 W / m·K," was used as the comparative sheet (C1). It should be noted that the silica aerogel pad material of Comparative Example 1 has a nominal thickness of 3 mm. Then, the comparative sheet (C1) was evaluated according to the steps described in the evaluation section above. The results are shown in Table 1 and... Figure 3 .

[0320] It should be noted that the material "Silica Aerogel Mat Material manufactured by Xiaomei Company" in Comparative Example 1 does not actually have heat absorption capacity. Therefore, it is recorded as "substantially has no heat absorption capacity" in the items of "Heat absorption start temperature (°C), heat absorption peak temperature (°C), and heat absorption (J / g or mJ / mg)" in the table. In addition, although the bulk density of the material used in Comparative Example 1 can be measured, the true density cannot be determined. Therefore, it is recorded as "unmeasurable" in the items of true density and average porosity in the table.

[0321] <Comparative Example 2>

[0322] An aluminum bag (Mitsubishi Gas Chemical Co., Ltd. "Gas Barrier Bag", 0.094 mm thick, constructed by laminating PET, aluminum foil, and polyethylene) was prepared as a bag-shaped body 116 mm long × 116 mm wide. Next, 33 parts by mass of pure water and 67 parts by mass of calcium sulfate dihydrate (including the amount of water in the hydrate) as inorganic powder were filled into the bag-shaped body of the aluminum bag. After heat-sealing the injection port, the bag-shaped body of the aluminum bag was laid flat between 4.8 mm thick gap materials, and a flat plate was placed on it. The mixture was left to stand at 20°C for 10 minutes to produce a 4.8 mm thick sheet for comparison (C2). Then, the obtained comparative sheet (C2) was evaluated according to the steps described in the evaluation section above. The results are shown in Table 1 and... Figure 3 .

[0323] It should be noted that in the system of Comparative Example 2, since the DSC of the liquid could not be measured, data on the heat endothermic (J / g or mJ / mg) could not be obtained. Therefore, the value of 1170 J / g, calculated based on the literature value of 2257 J / g approximation of 2000 J / g (100°C), is recorded in the table.

[0324] (Specifically, the approximate heat absorption of water is 2000 J / g × 33% + the heat absorption of calcium sulfate (measured value) is 762 J / g × 67% = 1170 J / g)

[0325] <Comparative Example 3>

[0326] 91 parts by weight of pure water and 9 parts by weight of ceramic cotton (average porosity 96.9%, true density 3, bulk density 0.092) were inserted into a container made of an aluminum bag (a gas barrier bag manufactured by Mitsubishi Gas Chemical Co., Ltd., with a thickness of 0.094 mm, composed of PET, aluminum foil and polyethylene layers) that was made into a bag shape with a length of 116 mm and a width of 116 mm.

[0327] Next, the aluminum bag was filled with the aforementioned pure water and ceramic cotton. After heat-sealing the injection port, the aluminum bag was placed flat between 4.8 mm thick gap materials, and a flat plate was placed on top. The mixture was then left to stand at 20°C for 10 minutes to produce a 4.8 mm thick comparative sheet (C3). The comparative sheet (C3) was then evaluated according to the steps described in the evaluation section above. The results are shown in Table 1 and... Figure 3 .

[0328] <Comparative Example 4>

[0329] A dispersion (1) was prepared by mixing 27 parts by mass of aluminum hydroxide (solubility in 100g water at 20°C is 0.0001g) and 64 parts by mass of pure water. Then, 91 parts by mass of the above dispersion (1) and 9 parts by mass of ceramic cotton (average porosity 96.8%, true density 3, bulk density 0.096) were inserted into a container made of an aluminum bag (a 0.094mm thick "gas barrier bag" manufactured by Mitsubishi Gas Chemical Co., Ltd., composed of PET, aluminum foil and polyethylene laminated together) in the shape of a bag with a length of 116mm and a width of 116mm.

[0330] Next, the aluminum bag was filled with the dispersion (1) described above, and the injection port was sealed by heat sealing. The aluminum bag was then placed flat between 4.8 mm thick gap materials, and a flat plate was placed on top. The mixture was left to stand at 20°C for 10 minutes to produce a 4.8 mm thick comparative sheet (C4). Then, the comparative sheet (C4) was evaluated according to the steps described in the evaluation column above. The results are shown in Table 1 and... Figure 3 .

[0331] It should be noted that, for Examples 1 and 3, the "content of water-soluble inorganic powder (mass%)" in "contents (amount during preparation)" in Table 1 represents the content in the hydrate state, the "content of water-soluble inorganic powder (mass%)" in "contents (inside the bag)" represents the content in the state where water has been removed from the hydrate (anhydrous), and the "content of aqueous solvent (mass%)" represents the content of water removed from the hydrate of the water-soluble inorganic powder in the aqueous solvent content during preparation.

[0332] Furthermore, regarding Comparative Examples 2 and 4, the "content of water-soluble inorganic powder (mass %)" in "Contents (amount added during preparation)" and the "content of water-soluble inorganic powder (mass %)" in "Contents (inside the bag)" in Table 1 represent the content (mass %) of non-water-soluble inorganic powder. In Comparative Example 2, the "content of water-soluble inorganic powder (mass %)" in "Contents (inside the bag)" represents the content of water, which also includes hydrates, and the "content of aqueous solvent (mass %)" is the same as the content of aqueous solvent during preparation.

[0333] [Table 1]

[0334]

[0335] [Table 2]

[0336]

[0337] Based on the above experimental results, the heat absorber of this embodiment functions as a porous body due to the filling contents and the bag as a whole. Therefore, even with rising battery temperature over time, sufficient heat absorption, pressure resistance, and the transformation from heat absorber to heat insulator were confirmed. Heat absorbers using non-water-soluble inorganic powders (Comparative Examples 2 and 4) showed particularly poor pressure resistance compared to heat absorbers containing water-soluble inorganic powders. It should be noted that the content values ​​of the contents in Table 1 are expressed by rounding to the nearest decimal.

[0338] in addition, Figure 3 The graphs show the results of cone calorimeter tests on 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. Figure 3 The vertical axis represents temperature (°C), and the horizontal axis represents elapsed time (seconds). Therefore, Figure 3 (1)~(3) and (C1), (C3), (C4) in the examples and comparative examples correspond to the heat absorbers (1)~(3) and the comparative sheets (C1), (C3), (C4) in the examples and comparative examples.

[0339] from Figure 3 The experimental results confirmed that, compared with the heat absorber of the comparative example, the heat absorbers (1) to (3) prepared in Examples 1 to 3 have a higher heat absorption capacity, thus delaying the time until the temperature of the heat absorber reaches 200°C.

[0340] [Explanation of reference numerals in the attached figures]

[0341] 1. Heat absorber; 10. Battery element; 11. Positive electrode 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, 18b. Battery outer packaging material; 19. Activated carbon layer; 20. Stacked battery; 30. Cone calorimeter; 31. Cone (heater); 32. Stainless steel bracket; 33. Aluminum foil cover; 34. Thermocouple; 35. Stainless steel bracket; 36. Ceramic wool (large); 37. Ceramic wool (small).

[0342] This application claims priority to three Japanese patent applications filed on July 3, 2023 (Japanese Patent Application No. 2023-109644), December 25, 2023 (Japanese Patent Application No. 2023-218613), and December 25, 2023 (Japanese Patent Application No. 2023-218614), the contents of which are incorporated herein by reference.

Claims

1. A heat-absorbing body having: a bag body capable of filling a content, and a water-based solvent and a water-soluble inorganic powder of which 1 g or more is dissolved in 100 g of water at 20°C being filled in the bag body as the content. The water-soluble inorganic powder has a solubility of 5 g / 100 g or more in water at 20°C in terms of g. The content further contains one or two or more selected from the group consisting of an anti-freezing agent and an inorganic fiber.

2. The heat-absorbing body according to claim 1, wherein The water-soluble inorganic powder is one or two or more selected from the group consisting of a chloride, a sulfate, a carbonate, a nitrate, a phosphate, an acetate, an alkali metal oxide, and an alkaline earth metal oxide.

3. The heat-absorbing body according to claim 1 or 2, wherein A water solution containing the water-based solvent and the water-soluble inorganic powder is filled in the content, and the content of the water-soluble inorganic powder in the water solution is 5 to 80 mass% relative to the total amount of the water solution.

4. The heat-absorbing body according to claim 1 or 2, wherein The content changes to a porous body when the content is heated to 120°C or more.

5. The heat-absorbing body according to claim 1 or 2, wherein The thickness change rate of the following formula (I) is 70% or more, 6. The heat-absorbing body according to claim 1 or 2, wherein [Num 1] 7. The heat-absorbing body according to claim 1 or 2, wherein Thickness change rate (%) = (thickness of the heat-absorbing body after being pressed at 0.5 MPa for 60 seconds on the surface of the heat-absorbing body heated under the following heating condition) / (thickness of the heat-absorbing body before being pressed at 0.5 MPa for 60 seconds on the surface of the heat-absorbing body heated under the following heating condition) x 100 Heating condition: The heat-absorbing body according to claim 1 or 2 is provided. The heat-absorbing body is sandwiched between battery cells. The heat of 50 kW / m 2 After the temperature of the back surface of the heat-absorbing body opposite to the heating surface is raised to a predetermined temperature by the radiant heat, the heat-absorbing body is cooled at room temperature, and the temperature of the surface of the heat-absorbing body is naturally cooled to room temperature. The thickness change rate in % before and after heating is calculated. In addition, the heating surface of the heat-absorbing body is pressed at 0.5 MPa for 60 seconds.

8. A secondary battery module characterized by comprising: ​ 9. The secondary battery module according to claim 1 or 2, wherein ​

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