Flame-retardant sheet, manufacturing method of the same, and assembled battery

Abstract

To provide a flame-retardant sheet which is formed by combining a heat insulation sheet with an elastic material and enables easy and quick adjustment of characteristics of the flame-retardant sheet even if demands for the characteristics frequently change.SOLUTION: A flame-retardant sheet 1 includes: a heat insulation sheet 50 having a first major surface 51 and a second major surface 52 which are orthogonal to a thickness direction; a first elastic material 61 disposed on the first major surface 51 side of the heat insulation sheet 50; and a second elastic material 62 disposed on the second major surface 52 side of the heat insulation sheet 50. The first elastic material 61 and the second elastic material 62 have characteristics different from each other.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a fireproof sheet, a method for manufacturing the same, and a battery pack including the fireproof sheet. [Background technology]

[0002] In recent years, from the viewpoint of environmental protection, active development has been made of electric vehicles, hybrid vehicles, and the like that are driven by electric motors. These electric vehicles, hybrid vehicles, and the like are equipped with assembled batteries in which multiple battery cells are connected in series or parallel to serve as the power source for the driving electric motor.

[0003] The battery cells mainly used are lithium-ion secondary batteries, which have higher capacity and higher output than lead-acid batteries, nickel-metal hydride batteries, etc. If a battery cell experiences thermal runaway, where it suddenly rises in temperature and continues to generate heat due to an internal short circuit or overcharging, the heat from the battery cell experiencing thermal runaway may propagate to other adjacent battery cells, causing thermal runaway in those cells.

[0004] A common method for suppressing the transfer of heat from a battery cell that has experienced thermal runaway as described above is to place a fireproof sheet (also called a "heat transfer suppression sheet") between the battery cells.

[0005] Furthermore, battery cells repeatedly expand and contract during charging and discharging even during normal use, not just when thermal runaway occurs. To accommodate this expansion and contraction, a heat insulating sheet and an elastic body are sometimes used in combination. The elastic body also has the effect of improving adhesion to the battery cell. For example, Patent Document 1 describes an insulator that includes a foam sheet made of thermoplastic resin, a heat insulating sheet provided inside the foam sheet, and a heat-sealed portion. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Patent Publication No. 2021 / 079601 Summary of the Invention [Problem to be solved by the invention]

[0007] Elastic bodies, including foam sheets, have various properties, and the compression characteristics of a fire-resistant sheet manufactured by combining a heat insulating sheet with an elastic body are greatly affected by the properties of the elastic body. Recently, there have been increasing demands for the properties of the fire-resistant sheet as a whole. Specifically, there is a demand for the sheet to exhibit a specific range of stress at a certain compression rate.

[0008] However, adjusting the properties of the elastic body by considering the material, foaming ratio, hardness of the rubber, etc. to meet the above requirements would require a significant amount of time and cost. Furthermore, the required properties change frequently, and various design changes are made, so the elastic body must be remade each time, which is an extremely difficult task.

[0009] Even with the heat insulating material described in Patent Document 1, it is thought that it would take time and cost to produce a foam sheet used in a fireproof sheet having the desired properties.

[0010] The present invention has been made in consideration of such problems, and aims to provide a flame-retardant sheet which is made by combining a heat insulating sheet and an elastic material, and whose properties can be quickly and easily adjusted even when requirements for the properties of the flame-retardant sheet change frequently, a method for manufacturing the flame-retardant sheet which can easily manufacture the flame-retardant sheet, and a battery pack which includes the flame-retardant sheet. [Means for solving the problem]

[0011] The above object of the present invention is achieved by the following configuration [1] relating to a flame-retardant sheet.

[0012] [1] A heat insulating sheet having a first main surface and a second main surface perpendicular to the thickness direction; a first elastic material disposed on the first main surface side of the heat insulating sheet; A flame-retardant sheet having a second elastic material arranged on the second main surface side of the heat-insulating sheet, A fireproof sheet, characterized in that the first elastic material and the second elastic material have different properties.

[0013] Furthermore, preferred embodiments of the present invention relating to the flame-retardant sheet relate to the following [2] to

[11] .

[0014] [2] The flame-retardant sheet according to [1], characterized in that at least one of the material, porosity, and thickness of the first elastic material is different from that of the second elastic material. [3] The flame-retardant sheet according to [1], characterized in that the first elastic material and the second elastic material have different stress-strain curves. [4] The flame-retardant sheet according to [3], characterized in that the stress of the first elastic material is 0.2 MPa or more when the compression rate in the thickness direction is 10%, and the maximum compression rate of the second elastic material is 70% or more. [5] The heat insulating sheet has an end surface connecting the first main surface and the second main surface, The flame-retardant sheet described in [1] is characterized in that at least one of the first elastic material and the second elastic material covers the end surface of the insulating sheet, and the first elastic material and the second elastic material are joined together. [6] The flame-retardant sheet described in [5], characterized in that the average film thickness of the first elastic material and the second elastic material in the region facing the end face of the insulating sheet is 0.01 mm or more and 2 mm or less. [7] The flame-retardant sheet described in [1], characterized in that the average film thickness of the first elastic material and the second elastic material in the areas facing the first main surface and the second main surface of the insulating sheet is 0.01 mm or more and 10 mm or less. [8] The flame-retardant sheet according to [1], characterized in that the first elastic material and the second elastic material each contain at least one selected from silicone resin, phenolic resin, epoxy resin, melamine resin, urea resin, unsaturated polyester resin, alkyd resin, urethane resin, and thermosetting polyimide resin. [9] The flame-retardant sheet according to [1], wherein both the first elastic material and the second elastic material contain a flame retardant.

[10] The flame-retardant sheet according to [1], characterized in that the heat insulating sheet contains ceramic particles.

[11] The flame-retardant sheet according to

[10] , characterized in that the ceramic particles contain at least one type of particles selected from metal oxide particles, inorganic hydrates, thermally expandable inorganic materials, and hydrous porous bodies.

[0015] The above object of the present invention is achieved by the following configuration

[12] relating to a method for producing a flame-retardant sheet.

[0016]

[12] A method for producing a flame-retardant sheet according to any one of [1] to

[11] , a data acquisition step of acquiring characteristic data of each of a plurality of elastic materials in advance; A method for manufacturing a fire-retardant sheet, characterized by comprising a selection process for selecting the first elastic material and the second elastic material, which have different properties from each other, from the plurality of elastic materials based on the characteristic data so that the fire-retardant sheet after manufacture has predetermined properties.

[0017] Furthermore, preferred embodiments of the present invention relating to a method for producing a flameproof sheet relate to the following

[13] to

[22] .

[0018]

[13] A method for manufacturing a flame-retardant sheet as described in

[12] , characterized in that it includes, after the selection process, an arrangement process of arranging the first elastic material selected in the selection process so as to face the first main surface of the insulating sheet, and arranging the second elastic material selected in the selection process so as to face the second main surface of the insulating sheet.

[14] After the selection step, a first covering step is performed to cover the first main surface of the heat insulating sheet with a first liquid foaming raw material for producing the first elastic material selected in the selection step. a second covering step of covering the second main surface of the heat insulating sheet with a second liquid foaming raw material for producing the second elastic material selected in the selection step; a first foaming and curing step of foaming and curing the first liquid foaming raw material to obtain the first elastic material selected in the selection step;

[13] The method for producing a fireproof sheet according to

[12] , further comprising a second foaming and curing step of foaming and curing the second liquid foaming raw material to obtain the second elastic material selected in the selection step.

[15] In the first covering step, the first liquid foaming raw material is injected into a first molding frame with the heat insulating sheet accommodated therein, and then the first foaming and curing step is carried out inside the first molding frame;

[14] The method for producing a fire-retardant sheet according to

[14] , characterized in that in the second covering step, the heat insulating sheet after the first foaming and curing step is placed inside a second molding frame with the front and back sides inverted, and the second liquid foaming raw material is injected into the second molding frame, and the second foaming and curing step is subsequently carried out inside the second molding frame.

[16] The method for producing a fireproof sheet according to

[14] , characterized in that the first liquid foaming raw material and the second liquid foaming raw material both contain a thermosetting resin precursor and a foaming agent.

[17] The method for producing a flame-retardant sheet according to

[16] , characterized in that the thermosetting resin precursor contains at least one selected from silicone-based raw materials, phenol-based raw materials, epoxy-based raw materials, melamine-based raw materials, urea-based raw materials, unsaturated polyester-based raw materials, alkyd-based raw materials, urethane-based raw materials, and thermosetting polyimide-based raw materials.

[18] The method for manufacturing a fire-retardant sheet according to

[16] , wherein the first liquid foaming raw material and the second liquid foaming raw material contain a flame retardant.

[19] After the selection process, a first foaming material sheet preparation process is performed to prepare a first foaming material sheet for producing the first elastic material selected in the selection process so that the first foaming material sheet has a size larger than the first main surface of the heat insulating sheet. a second foaming material sheet preparation step of preparing a second foaming material sheet for producing the second elastic material selected in the selection step so that the second foaming material sheet has a size larger than the second main surface of the heat insulating sheet; a foaming material sheet arranging step of arranging the first foaming material sheet so as to face the first main surface of the heat insulating sheet and arranging the second foaming material sheet so as to face the second main surface of the heat insulating sheet; a compression joining step of overlapping and compressing and joining the first foaming material sheet and the second foaming material sheet at an end surface side connecting the first main surface and the second main surface of the heat insulating sheet;

[13] The method for manufacturing a fire-retardant sheet according to

[12] , characterized by comprising a foaming and curing step of foaming and curing the first foam raw material sheet and the second foam raw material sheet to obtain the first elastic material and the second elastic material selected in the selection step.

[20] The method for manufacturing a flame-retardant sheet described in

[19] , characterized in that the first foaming raw material sheet and the second foaming raw material sheet both contain a thermosetting resin precursor and a foaming agent or a foaming accelerator.

[21] The method for producing a flame-retardant sheet according to

[20] , characterized in that the thermosetting resin precursor contains at least one selected from silicone-based raw materials, phenol-based raw materials, epoxy-based raw materials, melamine-based raw materials, urea-based raw materials, unsaturated polyester-based raw materials, alkyd-based raw materials, urethane-based raw materials, and thermosetting polyimide-based raw materials.

[22] The method for manufacturing a flame-retardant sheet according to

[19] , wherein both the first foaming material sheet and the second foaming material sheet contain a flame retardant.

[0019] The above object of the present invention is achieved by the following configuration

[23] relating to a battery pack.

[0020]

[23] A battery pack comprising a plurality of battery cells and the flame-retardant sheet according to any one of [1] to

[11] , wherein the plurality of battery cells are connected in series or in parallel. [Effects of the Invention]

[0021] The flame-retardant sheet of the present invention has a first elastic material arranged on the first main surface side of the insulating sheet and a second elastic material arranged on the second main surface side of the insulating sheet that have different properties.Therefore, even if requirements for the properties of the flame-retardant sheet change frequently, the above requirements can be easily met simply by selecting the optimal combination from various elastic materials.

[0022] Furthermore, according to the method for manufacturing a fire-retardant sheet of the present invention, a fire-retardant sheet having the desired properties can be easily obtained simply by selecting the optimal combination from various elastic materials. This eliminates the need to repeatedly prototype the elastic materials according to requirements, thereby increasing manufacturing efficiency and reducing manufacturing costs.

[0023] The battery pack of the present invention includes the heat insulating sheet of the present invention, which can more reliably prevent the spread of fire to the outside even if thermal runaway occurs. Furthermore, because the fireproof sheet is manufactured by selecting a combination of elastic materials with desired properties, it can smoothly follow the expansion and contraction of the battery cells, resulting in excellent battery performance. [Brief explanation of the drawings]

[0024] [Figure 1] FIG. 1 is a schematic cross-sectional view showing a flame-resistant sheet according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a graph showing SS curves of various elastic materials. [Figure 3] FIG. 3 is a schematic cross-sectional view showing a flameproof sheet according to a second embodiment of the present invention. [Figure 4] FIG. 4 is a schematic cross-sectional view showing a fireproof sheet according to a third embodiment of the present invention. [Figure 5]5(A) to 5(C) are schematic diagrams showing the order of steps in a method for producing a flame-resistant sheet according to a second embodiment of the present invention. [Figure 6] 6(A) to 6(C) are diagrams showing a method for producing a fireproof sheet according to a second embodiment of the present invention, and are schematic diagrams showing the steps subsequent to those of FIG. 5(C) in the order of steps. [Figure 7] 7(A) and 7(B) are schematic diagrams showing the order of steps in a method for producing a fireproof sheet according to a third embodiment of the present invention. [Figure 8] FIG. 8 is a schematic diagram showing a battery pack according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0025] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments described below, and can be implemented with any modifications within the scope of the gist of the present invention.

[0026] [Flame-retardant sheet] [First embodiment] FIG. 1 is a schematic cross-sectional view showing a flame-retardant sheet according to a first embodiment of the present invention. As shown in FIG. 1, the flame-retardant sheet 1 includes a heat insulating sheet 50, a first elastic member 61, and a second elastic member 62. The heat insulating sheet 50 has a first main surface 51 and a second main surface 52 that are perpendicular to the thickness direction of the heat insulating sheet 50, and an end surface 53 that connects the first main surface 51 and the second main surface 52. The first elastic member 61 is disposed on the first main surface 51 side of the heat insulating sheet 50 that is perpendicular to the thickness direction, so as to face the first main surface 51. The second elastic member 62 is disposed on the second main surface 52 side of the heat insulating sheet 50 that is perpendicular to the thickness direction, so as to face the second main surface 52. The first elastic member 61 and the second elastic member 62 have different properties. The first elastic member 61, the second elastic member 62, and the heat insulating sheet 50 are described in detail below.

[0027] <First elastic material, second elastic material> For example, it is desirable for the fire-resistant sheet 1 interposed between battery cells (described later) to maintain a minimum compressibility required to hold the battery cells in place while not exerting too much repulsive force on the battery cells when they expand. Specifically, it is desirable for the fire-resistant sheet to have a certain degree of hardness when pressure is applied to the fire-resistant sheet up to a certain range, and to become flexible when pressure exceeds this range. Therefore, to approach such an ideal fire-resistant sheet, it is required that the fire-resistant sheet 1 exhibit various stress-strain curves (SS curves) depending on the application and the state of the battery cells.

[0028] Fig. 2 is a graph showing the SS curves of various elastic materials. As shown in Fig. 2, elastic materials A to F each have a different SS curve. Specifically, elastic materials A to F all contain silicone resin, and differ from one another in terms of expansion ratio (porosity), type of filler added, molecular weight of the resin, etc. Therefore, by selecting a first elastic material 61 and a second elastic material 62 from elastic materials A to F according to the required properties of the flame-retardant sheet and adjusting their thicknesses, the properties of the entire flame-retardant sheet 1 can be made closer to the ideal SS curve.

[0029] The first elastic material 61 and the second elastic material 62 are preferably made of a thermosetting resin foam. Hereinafter, unless a distinction is needed, the first elastic material and the second elastic material may be simply referred to as elastic materials. Elastic materials made of a thermosetting resin foam have numerous closed cells 65 composed of air or foaming gas dispersed throughout, providing excellent thermal insulation. Furthermore, as described above, by adjusting the porosity by changing the expansion ratio, it is possible to manufacture first elastic materials 61 and second elastic materials 62 with different properties. Furthermore, because thermosetting resins are crosslinked, they are resistant to thermal deformation even when heated, providing excellent strength. Furthermore, as shown in FIG. 1, closed cells prevent gas from being released to the outside. Therefore, even if the gas is compressed when an external force is applied, the gas repulsive force allows the material to easily return to its original shape, maintaining its elasticity.

[0030] Furthermore, if the elastic material has a large number of interconnected open-cell structures, and these open cells are connected to the outside of the elastic material, gas will be released when external force is applied. As a result, the only stress is the force that causes the resin to return to its original shape, weakening the elastic force of the elastic material. Therefore, it is preferable to use a thermosetting resin foam with countless closed cells 65 dispersed therein as the elastic material, and it is even more preferable to use a material that contains silicone resin.

[0031] The air bubbles inside the elastic material do not all need to be isolated, and some of the air bubbles may be interconnected. However, it is preferable that there are no air bubbles that penetrate through the elastic material in the thickness direction, which makes it possible to suppress powder falling from the first main surface 51 and second main surface 52 of the heat insulating sheet 50 and maintain heat insulating properties, for example.

[0032] The thermosetting resin, which is one of the materials constituting the elastic material, is not particularly limited, and may be any known thermosetting resin, such as phenolic resin, epoxy resin, melamine resin, urea resin, unsaturated polyester resin, alkyd resin, silicone resin, urethane resin, or thermosetting polyimide resin. Of these thermosetting resins, silicone resin ceramicizes at high temperatures and does not disappear, thus protecting the fireproof sheet 1 in the event of thermal runaway in the battery cell. Therefore, it is preferable that both the first elastic material 61 and the second elastic material 62 contain silicone resin as the thermosetting resin.

[0033] Furthermore, the elastic material preferably contains a flame retardant to enhance its own fire resistance. The flame retardant contained in the elastic material is not particularly limited, and examples thereof include known flame retardants such as red phosphorus, guanidine phosphate compounds, polyphosphate compounds such as ammonium polyphosphate, organic boron compounds, boric acid, boron oxide, boric acid esters, and metaboric acid, metal compounds such as aluminum oxide, aluminum hydroxide, boehmite, dolomide, hydrotalcite, calcium hydroxide, basic magnesium carbonate, zirconium hydroxide, and tin oxide, halogen compounds, platinum compounds, titanium oxide, carbon, metal carbonates, and iron oxide. By appropriately adjusting the amount of flame retardant added, standards such as UL94V-0 can be met.

[0034] The elastic material may further contain additives such as plasticizers, surface treatment agents, fillers, heat resistance agents, adhesion promoters, etc. Examples of fillers that can be used include silica particles such as dry silica, wet silica, and crystalline silica, calcium carbonate, talc, and diatomaceous earth. These fillers can increase the strength and hardness of the elastic coating. When using these fillers, a plasticizer such as polyorganosiloxane or an organosiloxane oligomer may be used, and a silicon-based surface treatment agent such as silane, silazane or a silane coupling agent may be used as a surface treatment agent to strengthen the adhesive strength of the filler surface.

[0035] Furthermore, in order to enhance the heat resistance of the elastic material, the elastic material may contain, for example, iron oxide, cerium oxide, titanium oxide, or a rare earth compound, and in order to impart flame retardancy, the elastic material may contain a flame retardant such as titanium oxide, carbon black, aluminum hydroxide, etc. Furthermore, the elastic material may contain an organometallic compound or the like as an adhesion promoter.

[0036] Furthermore, the film thicknesses of the first elastic member 61 and the second elastic member 62 in the regions facing the first principal surface 51 and the second principal surface 52 of the insulating sheet 50 are not particularly limited, but it is preferable that the main surface-side average film thickness (D2) in these regions be 10 mm or less. A main surface-side average film thickness (D2) of 10 mm or less allows the battery pack to be more compact, thereby increasing the overall battery pack capacity per volume. The main surface-side film thicknesses of the first elastic member 61 and the second elastic member 62 in the regions facing the first principal surface 51 and the second principal surface 52 of the insulating sheet 50 are measured in an uncompressed state, measuring the distance between the first principal surface 51 and the surface of the first elastic member 61, and the distance between the second principal surface 52 and the surface of the second elastic member 62. The main surface-side average film thickness (D2) may be the average of film thicknesses measured at any five locations on each of the first principal surface 51 side and the second principal surface 52 side.

[0037] On the other hand, it is preferable that the main surface side average film thickness (D2) of each of the first elastic material 61 and the second elastic material 62 in the regions facing the first main surface 51 and the second main surface 52 of the heat insulating sheet 50 is 0.01 mm or more. If the main surface side average film thickness (D2) is 0.01 mm or more, it is possible to obtain the effect of suppressing the falling off (powder shedding) of particles and the like contained in the heat insulating sheet 50. Furthermore, from the viewpoints of imparting appropriate elasticity and improving the effect of suppressing powder shedding, it is more preferable that the main surface side average film thickness (D2) be 0.5 mm or more.

[0038] Incidentally, by making the film thickness of the first elastic material 61 and the second elastic material 62 different from each other, it is possible to impart different properties to the first elastic material 61 and the second elastic material 62.

[0039] In this embodiment, the elastic materials can be grouped based on their properties, with relatively hard elastic materials being group α and relatively soft elastic materials being group β. In this case, it is preferable that one elastic material (first elastic material 61) be selected from group α, and the other elastic material (second elastic material 62) be selected from group β. As examples of groups α and β, elastic materials whose stress when the compressibility in the thickness direction is 10% is 0.2 MPa or more can be group α, and elastic materials whose stress is less than 0.2 MPa can be group β. Furthermore, elastic materials whose maximum compressibility is less than 70% can be group α, and elastic materials whose maximum compressibility is 70% or more can be group β. In this way, by using first elastic material 61 and second elastic material 62 with different properties and further adjusting the thickness of each elastic material, a fireproof sheet with desired properties can be easily obtained.

[0040] The stress at a compression rate of 10% refers to the stress when pressure is applied to an elastic material in the thickness direction and the thickness decreases by 10% compared to the initial thickness of the elastic material (0 MPa). In other words, an elastic material with a stress of 0.2 MPa or more at a compression rate of 10% is made of a relatively hard material. Furthermore, the maximum compression rate refers to the rate of thickness reduction compared to the initial thickness of the elastic material (0 MPa) at the point when pressure is applied to the elastic material in the thickness direction and the thickness no longer changes. In other words, an elastic material with a maximum compression rate of 70% or more is made of a relatively soft material.

[0041] In addition to the SS curve, the properties of the first elastic material 61 and the second elastic material 62 include various other properties such as hardness and elastic modulus. In this embodiment, the first elastic material 61 and the second elastic material 62 having different values ​​for these various properties are combined, so that a fireproof sheet having the desired properties can be obtained.

[0042] <Thermal insulation sheet> In this embodiment, the heat insulating sheet 50 is not particularly limited, but preferably has excellent heat insulating properties. Examples of materials that are preferably contained in the heat insulating sheet 50 are described below.

[0043] (ceramic particles) The heat insulating sheet 50 can achieve excellent heat insulation by including ceramic particles. Examples of ceramic particles include metal oxide particles such as silica, titania, alumina, and magnesia; inorganic hydrates such as aluminum hydroxide, magnesium hydroxide, calcium hydroxide, zinc hydroxide, iron hydroxide, and manganese hydroxide; thermally expandable inorganic materials such as vermiculite, bentonite, mica, and perlite; and hydrous porous materials such as zeolite, kaolinite, montmorillonite, acid clay, and diatomaceous earth. The ceramic particles can take the form of ordinary powders with an average particle size of approximately 1 to 100 μm, as well as spherical or nearly spherical nanoparticles with an average particle size of 1 μm or less, and hollow particles such as shirasu balloons, silica balloons, fly ash balloons, perlite balloons, and glass balloons. These particles can be used alone or in combination. As the nanoparticles, silica nanoparticles such as wet silica, dry silica, and aerogel can be used.

[0044] (fibrous materials) The heat insulating sheet 50 preferably contains a fibrous material for holding the ceramic particles. The fibrous material is not particularly limited as long as it can hold the ceramic particles with high thermal insulation properties, and organic fibers, inorganic fibers, etc. can be used. By including a fibrous material, the mechanical strength of the heat insulating sheet 50 and its ability to hold the ceramic particles can be improved.

[0045] Specific examples of inorganic fibers include silica fibers, alumina fibers, alumina silicate fibers, zirconia fibers, carbon fibers, soluble fibers, refractory ceramic fibers, aerogel composite materials, magnesium silicate fibers, alkaline earth silicate fibers, Ceramic fibers such as potassium titanate fiber, silicon carbide fiber, and potassium titanate whisker fiber; glass fibers such as glass fiber, glass wool, and slag wool; rock wool; Basalt fiber, mullite fiber, and other mineral fibers such as wollastonite and other natural mineral fibers can be used. Among the above fibers, it is more preferable to use ceramic fibers such as silica fibers, alumina fibers, and alumina silicate fibers, as well as natural mineral fibers. Furthermore, if the melting point of the fibrous material exceeds 1000°C, it will not melt or soften and will be able to maintain its shape even if thermal runaway occurs in the battery cell. Therefore, it is more preferable that the heat insulating sheet 50 contain a fibrous material with a melting point exceeding 1000°C.

[0046] The organic fiber may be at least one selected from the group consisting of polyvinyl alcohol (PVA) fiber, polyethylene fiber, nylon fiber, polyurethane fiber, and ethylene-vinyl alcohol copolymer fiber. When organic fiber is used, it is difficult to break even when bent, so that a heat insulating sheet that is resistant to deformation and powder shedding can be obtained.

[0047] (Other compounding materials) In addition to the ceramic particles and fibrous material, the heat insulating sheet 50 may contain additives such as a resin binder, a pH adjuster, and a flocculant.

[0048] If the heat insulating sheet 50 contains a resin binder as an additive, the other materials contained in the heat insulating sheet 50 can also be bound by the resin binder. There are no particular restrictions on the resin binder, as long as it has a glass transition point lower than that of the fibrous material. For example, a resin binder containing at least one resin selected from styrene-butadiene resin, acrylic resin, silicone-acrylic resin, and styrene resin can be used.

[0049] The glass transition point of the resin binder is not particularly specified, but is preferably -10°C or higher. If the glass transition point of the resin binder is room temperature or higher, the strength of the heat insulating sheet 50 can be further improved when a heat insulating material containing the resin binder is used at room temperature. Therefore, the glass transition point of the resin binder is more preferably 20°C or higher, even more preferably 30°C or higher, even more preferably 50°C or higher, and particularly preferably 60°C or higher.

[0050] When the heat insulating sheet 50 contains a resin binder, the content of the resin binder is preferably 0.5% by mass or more, and more preferably 1% by mass or more, relative to the total mass of the heat insulating sheet 50. Also, it is preferably 20% by mass or less, and more preferably 10% by mass or less.

[0051] (Method of manufacturing heat insulating sheet) Methods for producing the heat insulating sheet 50 include a wet method (papermaking method) and a dry method. When using the papermaking method, the ceramic particles, fibrous material, and other compounding materials that form the heat insulating sheet 50 are dispersed in water, and the dispersion is dehydrated, molded, and dried to produce the heat insulating sheet 50. When using the dry method, the ceramic particles, fibrous material, and other compounding materials that form the heat insulating sheet 50 are placed in an appropriate mixer, thoroughly dispersed, and then pressurized and heated in a predetermined mold to produce the heat insulating sheet 50.

[0052] Second Embodiment FIG. 3 is a schematic cross-sectional view showing a flame-retardant sheet according to a second embodiment of the present invention. In the second embodiment shown in FIG. 3, the same components as those in the first embodiment are designated by the same reference numerals, and detailed descriptions thereof will be omitted or simplified. As shown in FIG. 3, the flame-retardant sheet 2 includes a heat insulating sheet 50, a first elastic member 61 disposed on the first main surface 51 side of the heat insulating sheet 50, and a second elastic member 62 disposed on the second main surface 52 side. The heat insulating sheet 50 has an end surface 53 connecting the first main surface 51 and the second main surface, and the second elastic member 62 covers the surface of the heat insulating sheet 50 continuously from the second main surface 52 side to the end surface 53. The first elastic member 61 and the second elastic member 62 are bonded together, and the heat insulating sheet 50 is completely covered by the first elastic member 61 and the second elastic member 62.

[0053] The flame-retardant sheet 2 according to the second embodiment configured as described above can achieve the same effects as those of the first embodiment. Furthermore, in the second embodiment, the end surface 53 of the insulating sheet 50 is covered by the second elastic material 62, and the surface of the insulating sheet 50 is not exposed. This prevents particles and other components contained in the insulating sheet 50 from falling off. Furthermore, in this embodiment, the second elastic material 62 is shaped along the second main surface 52 and the end surface 53 of the insulating sheet 50, thereby closely adhering the insulating sheet 50 to the first elastic material 61 and the second elastic material 62. Therefore, even if dimensional differences occur between the insulating sheet 50 and the first elastic material 61 and the second elastic material 62 due to differences in thermal expansion or expansion / contraction, localized tension and deformation in the first elastic material 61 and the second elastic material 62 can be suppressed. As a result, slippage and peeling between the insulating sheet 50 and the first elastic material 61 and the second elastic material 62 can be prevented, thereby suppressing breakage.

[0054] 3, the second elastic material 62 is shaped along the second main surface 52 and the edge surface 53 of the heat insulating sheet 50, but the present invention is not limited to this configuration. Either the first elastic material 61 or the second elastic material 62 may be configured to cover the edge surface 53 of the heat insulating sheet 50, or both may extend toward the edge surface 53 to cover it, and the first elastic material 61 and the second elastic material 62 may be joined near the center of the heat insulating sheet 50 in the thickness direction.

[0055] The film thicknesses of the first elastic material 61 and the second elastic material 62 in the region facing the edge surface 53 of the heat insulating sheet 50 are not particularly limited, but it is preferable that the average edge surface thickness (D1) in these regions is 2 mm or less. If the average edge surface thickness (D1) is 2 mm or less, the area between the battery cells where the heat insulating sheet 50 is not present can be reduced, thereby preventing flames from spreading to adjacent battery cells in the event of thermal runaway. Note that the edge surface thickness is measured in an uncompressed state, measuring the distance between the edge surface 53 of the heat insulating sheet 50 and the edge surface of the flame-retardant sheet 2. The average edge surface thickness can be the average of film thicknesses measured at any five locations.

[0056] On the other hand, if the average film thickness (D1) of the end face side of the first elastic material 61 and the second elastic material 62 in the area facing the end face 53 of the insulating sheet 50 is 0.01 mm or more, the effect of preventing powder from falling off from the insulating sheet 50 can be obtained.

[0057] Furthermore, in this embodiment, if the properties of the first elastic material 61 and the second elastic material 62 can be controlled so that the fireproof sheet has the desired properties, it is preferable that the first elastic material 61 and the second elastic material 62 are thin. By reducing the film thickness of both materials, the fireproof sheet and the battery pack can be made more compact, and the capacity per volume of the entire battery pack can be increased.

[0058] Third Embodiment Fig. 4 is a schematic cross-sectional view showing a flame-retardant sheet according to a third embodiment of the present invention. In the third embodiment shown in Fig. 4, the same parts as those in the second embodiment are given the same reference numerals, and detailed description thereof will be omitted or simplified. In the flame-retardant sheet 3, as in the second embodiment, a part of the end surface 53 is covered with a first elastic material 61 and a second elastic material 62. Furthermore, the first elastic material 61 and the second elastic material 62 are overlapped and joined to each other near the end surface 53, forming an ear portion 63.

[0059] The third embodiment configured in this manner can also achieve the same effects as the first and second embodiments. Furthermore, in this embodiment, since the heat insulating sheet 50 has the ears 63 on the end face 53 side, for example, when the fire-retardant sheet 3 is transported with the end face 53 facing up or down, the ears 63 can absorb impacts on the fire-retardant sheet 3. Therefore, the first elastic material 61 and the second elastic material 62 are not damaged or peeled off, and the fire-retardant sheet 3 can be held in good condition.

[0060] [Fireproof sheet manufacturing method] [First embodiment] A method for manufacturing the fireproof sheet 1 according to this embodiment will be described in detail below with reference to FIGS.

[0061] <Manufacturing process of elastic material for acquiring characteristic data> A raw material for an elastic material containing a thermosetting resin precursor, a foaming agent or foaming accelerator, and optionally a flame retardant, etc., is placed in a mold, and the raw material is heated to foam and harden, thereby producing a plurality of elastic materials with different properties. Methods for producing elastic materials with various properties include adjusting the viscosity and molecular weight of the thermosetting resin precursor contained in the raw material, the amount of foaming agent or foaming accelerator, the amount of additives, and the foaming and hardening conditions.

[0062] <Data acquisition process> The characteristic data of each of the above multiple elastic materials is obtained. If the objective is to manufacture a fireproof sheet with a desired SS curve, the SS curves of multiple elastic materials (elastic materials A to F) are measured as shown in Figure 2.

[0063] <Selection process> Next, based on the characteristic data acquired in the data acquisition step, elastic materials having different characteristics are selected from the plurality of elastic materials so that the manufactured flame-retardant sheet 1 has predetermined characteristics, and these are designated as the first elastic material 61 and the second elastic material 62. For example, from elastic materials A to F, elastic material A is selected as the first elastic material 61, and elastic material E is selected as the second elastic material 62. Elastic materials with different film thicknesses may be prepared in advance and their respective characteristic data may be acquired, or the film thicknesses of the first elastic material 61 and the second elastic material 62 may be adjusted after selecting them.

[0064] <Placement process> After the selection step, the first elastic material 61 selected in the selection step is arranged so as to face the first main surface 51 of the heat insulating sheet 50, and the second elastic material 62 selected in the selection step is arranged so as to face the second main surface 52 of the heat insulating sheet 50. There are no particular restrictions on the method for fixing the heat insulating sheet 50 to the first elastic material 61 and the second elastic material 62. For example, the two can be fixed in a stacked state by bonding them together with an adhesive or the like, wrapping them in a heat-compressible resin film, using a fixing jig, or the like.

[0065] According to the above manufacturing method, the characteristic data of each of the multiple elastic materials is acquired in advance in the data acquisition process, so the desired flame-retardant sheet can be obtained simply by selecting the optimal combination of elastic materials based on the required flame-retardant sheet characteristics. Specifically, when elastic materials A and E shown in Figure 2 are manufactured with the same thickness, the SS curve of the resulting flame-retardant material can be calculated to show the curve shown by the thick solid line in Figure 2. In this way, there is no need to repeatedly prototype the elastic materials, and a flame-retardant sheet with the desired characteristics can be easily manufactured at low cost.

[0066] Second Embodiment Next, a method for manufacturing a flame-retardant sheet 2 according to this embodiment will be described below with reference to Figures 3, 5, and 6. Figures 5(A) to 5(C) and Figures 6(A) to 6(C) are schematic diagrams showing the process sequence of a method for manufacturing a flame-retardant sheet according to a second embodiment of the present invention. In the manufacturing method according to the second embodiment, the same components as those in the first embodiment are given the same reference numerals, and detailed descriptions thereof will be omitted or simplified. Furthermore, the "manufacturing process of an elastic material for characteristic data acquisition," "data acquisition process," and "selection process" in the first embodiment are also the same in the second embodiment, so the process after the selection process will be described here.

[0067] <First coating process> After the selection step, as shown in FIG. 5(A), a frame (first molding frame) 75A is attached onto a release paper 70A, and the heat insulating sheet 50 is placed on the release paper 70A. The height of the frame 75A is set to be greater than the thickness of the heat insulating sheet 50. Next, as shown in FIG. 5(B), with the heat insulating sheet 50 housed inside the frame 75A, a first liquid foaming raw material 81 is injected into the gap between the heat insulating sheet 50 and the frame 75A. The first liquid foaming raw material 81 is a raw material for producing the first elastic material 61 selected in the selection step.

[0068] In the first covering step, to make the thickness of the first elastic material 61 and the width of the frame region constant, positioning pins may be used or the base may have positioning recesses. For example, positioning pins may be provided so as to penetrate the release paper 70A and pierce the heat insulating sheet 50, or may be provided at the edge of the heat insulating sheet 50 to determine position. Furthermore, if the base has recesses, the heat insulating sheet 50 can be placed in the recesses and the release paper 70A laid around the heat insulating sheet 50, thereby allowing the heat insulating sheet 50 to be positioned accurately in the desired position.

[0069] <First foaming and curing process> 5(C), the frame 75A and the first liquid foaming raw material 81 are covered and sealed with a release paper 70B, and following the first covering step, the first liquid foaming raw material 81 is foamed and cured inside the frame 75A to form the first elastic material 61. After curing, the release papers 70A and 70B are peeled off, and the material is subjected to the second covering step described below. In the first foaming and curing step, the conditions for foaming and curing the first liquid foaming raw material 81 and the thickness of the first elastic material 61 are also adjusted so that the elastic material selected in the selection step is obtained.

[0070] <Second coating process> After the first foaming and curing step, as shown in FIG. 6(D), the single-sided covering body 55 after the first foaming and curing step, in which the first main surface 51 and end surface 53 of the heat insulating sheet 50 are covered with the first elastic material 61, is turned upside down and placed on the release paper 70C of a frame (second molding frame) 75B. The height of the frame 75B is preferably greater than the thickness of the single-sided covering body 55. Thereafter, as shown in FIG. 6(E), with the single-sided covering body 55 housed in the frame 75B, a second liquid foaming raw material 82 is injected into the gap between the single-sided covering body 55 and the frame 75B.

[0071] <Second foaming and curing process> Thereafter, as shown in Figure 6(F), the frame 75B and the second liquid foaming raw material 82 are covered and sealed with release paper 70D, and following the second covering step, the second liquid foaming raw material 82 is foamed and cured to form the second elastic material 62. After curing, the release papers 70C and 70D are peeled off to obtain the flame-retardant sheet 2 as shown in Figure 3. In the second foaming and curing step, the conditions for foaming and curing the second liquid foaming raw material 82 and the thickness of the second elastic material 62 to be formed are taken into consideration, and adjustments are made so that the elastic material selected in the selection step is obtained.

[0072] According to the manufacturing method of the second embodiment, after the first elastic material 61 is formed, the second liquid foaming raw material 82 is injected so as to contact the first elastic material 61 to form the second elastic material 62. This allows for a strong bond between the first elastic material 61 and the second elastic material 62, and allows the entire heat insulating sheet 50 to be covered with the first elastic material 61 and the second elastic material 62 with high adhesion. Furthermore, since the first elastic material 61 and the second elastic material 62 are formed by foaming and curing around the heat insulating sheet 50, tension is less likely to remain at the edge of the heat insulating sheet 50, making it less likely to tear or develop holes. Furthermore, if the first liquid foaming raw material 81 and the second liquid foaming raw material 82 contain a thermosetting resin precursor, the thermosetting resin precursor crosslinks during the first foaming and curing process and the second foaming and curing process. This allows for the production of a first elastic material 61 and a second elastic material 62 that are less susceptible to creep deformation and tearing or development of holes due to thermal fatigue.

[0073] Third Embodiment Next, a method for manufacturing a flame-retardant sheet 3 according to this embodiment will be described below with reference to Figs. 4 and 7. Figs. 7(A) and 7(B) are schematic diagrams showing the process sequence of a method for manufacturing a flame-retardant sheet according to a third embodiment of the present invention. In the manufacturing method according to the third embodiment, the same components as those in the first embodiment are given the same reference numerals, and detailed descriptions thereof will be omitted or simplified. Furthermore, the "manufacturing process of an elastic material for characteristic data acquisition," "data acquisition process," and "selection process" in the first embodiment are also the same in the third embodiment, so the description will begin with the process after the selection process.

[0074] <First foaming raw material sheet manufacturing process> After the selection step, a first foaming raw material sheet 91 is prepared so as to be larger in size than the first main surface 51 of the heat insulating sheet 50. The first foaming raw material sheet 91 is a raw material sheet for preparing the first elastic material selected in the selection step, and such a raw material sheet is called, for example, millable silicone rubber. The first foaming raw material sheet 91 can be prepared by kneading a thermosetting resin precursor, a foaming agent or foaming accelerator, a crosslinking agent, etc. at a low temperature and molding the mixture into a sheet. At this point, no foaming or crosslinking has occurred inside the first foaming raw material sheet 91, and the first foaming raw material sheet 91 is in a soft state.

[0075] <Second foaming raw material sheet manufacturing process> In addition, the second foam raw material sheet 92 is prepared so as to have a size larger than the second main surface 52 of the heat insulating sheet 50. The second foam raw material sheet 92 is a raw material sheet for preparing the second elastic material selected in the above selection step. The manufacturing method of the second foam raw material sheet 92 is the same as that of the above first foam raw material sheet 91.

[0076] <Foaming material sheet placement process> 7(A), a first foaming raw material sheet 91 is placed so as to face the first main surface 51 of the heat insulating sheet 50, and a second foaming raw material sheet 92 is placed so as to face the second main surface 52 of the heat insulating sheet 50. At this time, the first foaming raw material sheet 91 and the second foaming raw material sheet 92 are placed so as to protrude from the edge surface 53 of the heat insulating sheet 50.

[0077] <Compression joining process> Then, as shown in Figure 7(B), the first foaming material sheet 91 and the second foaming material sheet 92 are overlapped on the end surface 53 side of the heat insulating sheet 50 so that they face each other, and pressure is applied in the direction of the arrow to compress and bond the two together.

[0078] <Foaming and curing process> Thereafter, the first foaming raw material sheet 91 and the second foaming raw material sheet 92 are foamed and cured, thereby obtaining the first elastic material 61 and the second elastic material 62 selected in the selection step, as shown in Fig. 4, and the fireproof sheet 3 can be manufactured.

[0079] According to the manufacturing method of the third embodiment, although the first foaming raw material sheet 91 and the second foaming raw material sheet 92 are made of different materials, they are compressed and bonded together, and then foamed and cured, so they can be bonded together with high bonding strength. Also, as described above, it is possible to easily form the ear portions 63 that have the effect of absorbing shock when transporting the fireproof sheet. Furthermore, since the first foaming raw material sheet 91 and the second foaming raw material sheet 92 are foamed and cured simultaneously, the foaming and curing conditions for both sheets in this process are the same, but since two foaming raw material sheets can be foamed and cured simultaneously in a single process, the manufacturing process can be simplified.

[0080] The raw materials used in the first to third embodiments of the present invention will be described below.

[0081] (thermosetting resin precursor) The thermosetting resin precursor is contained in the first liquid foaming raw material 81, the second liquid foaming raw material 82, the first foaming raw material sheet 91, and the second foaming raw material sheet 92. In the foaming and curing process, the thermosetting resin precursor crosslinks, thereby improving heat resistance and strength. As the thermosetting resin precursor, a precursor of a known thermosetting resin such as the silicone resin, phenolic resin, epoxy resin, melamine resin, urea resin, unsaturated polyester resin, alkyd resin, urethane resin, or thermosetting polyimide resin listed above as the thermosetting resin, i.e., a raw material before curing (at least one selected from silicone-based raw materials, phenol-based raw materials, epoxy-based raw materials, melamine-based raw materials, urea-based raw materials, unsaturated polyester-based raw materials, alkyd-based raw materials, urethane-based raw materials, and thermosetting polyimide-based raw materials), can be used, and it is preferable to use a pre-cured silicone.

[0082] (Foaming agents and foaming accelerators) The raw materials for the elastic material (first liquid foaming raw material 81 and second liquid foaming raw material 82) preferably contain a foaming agent or foaming accelerator for forming pores (bubbles) in the elastic material. The foaming agent used in the present invention is one that foams itself. The type of foaming agent is not particularly limited. Examples of the foaming agent include hydrocarbons, halogenated hydrocarbons such as halogenated saturated hydrocarbons and halogenated unsaturated hydrocarbons, low-boiling gases such as nitrogen, argon, carbon dioxide, and air, chemical foaming agents such as sodium bicarbonate, sodium carbonate, calcium carbonate, magnesium carbonate, azodicarboxylic acid amide, azobisisobutyronitrile, barium azodicarboxylate, N,N'-dinitrosopentamethylenetetramine, p,p'-oxybisbenzenesulfonylhydrazide, and trihydrazinotriazine, and porous solid materials. The amount of foaming agent is not limited, but is preferably 0.1 to 5% by mass based on the total amount of the thermosetting resin precursor and foaming agent used to produce the liquid foaming raw material or foaming raw material sheet.

[0083] The foaming accelerator refers to a catalyst or the like that generates hydrogen or the like as a by-product when a precursor of a thermosetting resin is cured, and examples thereof include platinum catalysts, aminoxy catalysts, organotin catalysts, etc. The raw material of the elastic material may contain either a foaming agent or a foaming accelerator, or may contain both.

[0084] (Flame retardant) The flame retardant material is the same as that explained in the "Flame Retardant Sheet" section above.

[0085] [Battery module (assembled battery)] FIG. 8 is a schematic diagram showing a battery pack according to an embodiment of the present invention. As shown in FIG. 8, the battery pack 100 includes multiple battery cells 20a, 20b, and 20c housed in a battery case 30. The battery cells 20a, 20b, and 20c are connected in series or in parallel by bus bars (not shown). In this embodiment, fire-retardant sheets 1 are disposed between the battery cells 20a, 20b, and 20c. However, the fire-retardant sheets 1 can be disposed not only between the battery cells but also between the battery cells 20a, 20b, and 20c and the battery case 30. Although FIG. 8 shows fire-retardant sheets 1 disposed between the battery cells 20a, 20b, and 20c, fire-retardant sheets 2 and 3 can also be used in the present invention. Furthermore, various fire-retardant sheets can be used without departing from the spirit and scope of the present invention.

[0086] In a battery pack configured in this manner, a fireproof sheet with desired characteristics can be easily manufactured by taking into consideration the pressure applied to the battery cells 20a, 20b, and 20c, the repulsive force when the battery cells 20a, 20b, and 20c expand, etc. Therefore, a battery pack with excellent performance can be obtained. [Explanation of symbols]

[0087] 1,2,3 Fireproof sheet 20a, 20b, 20c battery cells 30 Battery case 50 Heat insulation sheet 51 First main surface 52 Second main surface 53 End face 61 First elastic material 62 Second elastic material 63 Ears 81 First liquid foaming material 82 Second liquid foaming raw material 91 First foaming material sheet 92 Second foam material sheet 100 battery packs

Claims

1. A heat insulating sheet having a first main surface and a second main surface perpendicular to the thickness direction; a first elastic material disposed on the first main surface side of the heat insulating sheet; A flame-retardant sheet having a second elastic material arranged on the second main surface side of the heat-insulating sheet, A fireproof sheet, characterized in that the first elastic material and the second elastic material have different properties from each other.

2. The fireproof sheet according to claim 1, wherein the first elastic material is different from the second elastic material in at least one selected from the material, porosity, and thickness.

3. The fireproof sheet according to claim 1, wherein the first elastic material and the second elastic material have different stress-strain curves.

4. The fire-retardant sheet according to claim 3, characterized in that the first elastic material has a stress of 0.2 MPa or more when the compression rate in the thickness direction is 10%, and the second elastic material has a maximum compression rate of 70% or more.

5. the heat insulating sheet has an end surface connecting the first main surface and the second main surface, The flame-retardant sheet according to claim 1, characterized in that at least one of the first elastic material and the second elastic material covers an end surface of the insulating sheet, and the first elastic material and the second elastic material are joined together.

6. The flame-retardant sheet according to claim 5, wherein the average film thickness of the first elastic material and the second elastic material in the region facing the end face of the heat insulating sheet is 0.01 mm or more and 2 mm or less.

7. The flame-retardant sheet according to claim 1, characterized in that the average film thickness of the first elastic material and the second elastic material in the areas facing the first main surface and the second main surface of the insulation sheet is 0.01 mm or more and 10 mm or less.

8. The flame-retardant sheet according to claim 1, characterized in that both the first elastic material and the second elastic material contain at least one selected from silicone resin, phenolic resin, epoxy resin, melamine resin, urea resin, unsaturated polyester resin, alkyd resin, urethane resin, and thermosetting polyimide resin.

9. The fireproof sheet according to claim 1, wherein both the first elastic material and the second elastic material contain a fire retardant.

10. The fireproof sheet according to claim 1, wherein the heat insulating sheet contains ceramic particles.

11. The fireproof sheet according to claim 10, wherein the ceramic particles include at least one type of particles selected from the group consisting of metal oxide particles, inorganic hydrates, thermally expandable inorganic materials, and hydrous porous bodies.

12. A method for producing a flame-retardant sheet according to any one of claims 1 to 11, a data acquisition step of acquiring characteristic data of each of a plurality of elastic materials in advance; A method for manufacturing a fire-retardant sheet, characterized by comprising a selection process for selecting the first elastic material and the second elastic material, which have different properties from each other, from the plurality of elastic materials based on the characteristic data so that the fire-retardant sheet after manufacture has predetermined properties.

13. 13. A method for manufacturing a fire-retardant sheet as described in claim 12, characterized in that it comprises, after the selection process, an arrangement process of arranging the first elastic material selected in the selection process so as to face the first main surface of the insulation sheet, and arranging the second elastic material selected in the selection process so as to face the second main surface of the insulation sheet.

14. After the selection step, a first covering step of covering the first main surface of the heat insulating sheet with a first liquid foaming raw material for producing the first elastic material selected in the selection step; a second covering step of covering the second main surface of the heat insulating sheet with a second liquid foaming raw material for producing the second elastic material selected in the selection step; a first foaming and curing step of foaming and curing the first liquid foaming raw material to obtain the first elastic material selected in the selection step; 13. The method for manufacturing a fireproof sheet according to claim 12, further comprising a second foaming and curing step of foaming and curing the second liquid foaming raw material to obtain the second elastic material selected in the selection step.

15. In the first covering step, the first liquid foaming raw material is injected into a first molding frame with the heat insulating sheet accommodated therein, and then the first foaming and curing step is carried out inside the first molding frame; 15. The method for manufacturing a fire-retardant sheet according to claim 14, characterized in that in the second covering step, the second liquid foaming raw material is injected into a second molding frame while the insulating sheet after the first foaming / curing step is placed upside down inside the second molding frame, and then the second foaming / curing step is carried out inside the second molding frame.

16. The method for manufacturing a fireproof sheet according to claim 14, wherein the first liquid foaming raw material and the second liquid foaming raw material each contain a thermosetting resin precursor, and a foaming agent or a foaming accelerator.

17. 17. The method for producing a fire-retardant sheet according to claim 16, wherein the thermosetting resin precursor contains at least one selected from the group consisting of a silicone-based raw material, a phenol-based raw material, an epoxy-based raw material, a melamine-based raw material, a urea-based raw material, an unsaturated polyester-based raw material, an alkyd-based raw material, a urethane-based raw material, and a thermosetting polyimide-based raw material.

18. The method for manufacturing a fireproof sheet according to claim 16, wherein the first liquid foaming raw material and the second liquid foaming raw material contain a fire retardant.

19. a first foaming material sheet preparation step of preparing a first foaming material sheet for producing the first elastic material selected in the selection step so that the first foaming material sheet has a size larger than the first main surface of the heat insulating sheet, after the selection step; a second foaming material sheet preparation step of preparing a second foaming material sheet for producing the second elastic material selected in the selection step so that the second foaming material sheet has a size larger than the second main surface of the heat insulating sheet; a foaming material sheet arranging step of arranging the first foaming material sheet so as to face the first main surface of the heat insulating sheet and arranging the second foaming material sheet so as to face the second main surface of the heat insulating sheet; a compression joining step of overlapping and compressing the first foaming material sheet and the second foaming material sheet at an end surface side connecting the first main surface and the second main surface of the heat insulating sheet; The method for manufacturing a fireproof sheet according to claim 12, further comprising a foaming and curing step of foaming and curing the first foam raw material sheet and the second foam raw material sheet to obtain the first elastic material and the second elastic material selected in the selection step.

20. The method for manufacturing a fireproof sheet according to claim 19, wherein the first foaming raw material sheet and the second foaming raw material sheet each contain a thermosetting resin precursor, and a foaming agent or a foaming accelerator.

21. 21. The method for producing a fire-retardant sheet according to claim 20, wherein the thermosetting resin precursor contains at least one selected from the group consisting of silicone-based raw materials, phenol-based raw materials, epoxy-based raw materials, melamine-based raw materials, urea-based raw materials, unsaturated polyester-based raw materials, alkyd-based raw materials, urethane-based raw materials, and thermosetting polyimide-based raw materials.

22. The method for manufacturing a fireproof sheet according to claim 19, wherein both the first foaming material sheet and the second foaming material sheet contain a fire retardant.

23. An assembled battery comprising a plurality of battery cells and the flame retardant sheet according to any one of claims 1 to 11, the plurality of battery cells being connected in series or in parallel.

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