Flameproof sheet, method for manufacturing same, and battery pack

Abstract

Provided is a flameproof sheet composed of a combination of a heat insulating material and an elastic body, in which there is no problem of powder falling from the heat insulating material, the elastic body is hardly broken, a hole is hardly opened, and the elastic body can be made thin. The flameproof sheet (1) has a heat insulating sheet (50), and an elastic coating (60) comprising a foam of a thermosetting resin. The elastic coating (60) covers the entire heat insulating sheet (50) without having a joint part.

Description

Flame-retardant sheet, its manufacturing method, and battery pack

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

[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 as well.

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

[0005] In addition, battery cells repeatedly expand and contract during charging and discharging, even during normal use other than when thermal runaway occurs, and so elastic bodies are sometimes used in combination to accommodate this. The elastic body also has the effect of increasing adhesion to the battery cells. For example, Patent Document 1 describes an insulator 13, as shown in Figure 5, that includes a foam sheet 11 made of thermoplastic resin, an insulating sheet 12 provided inside the foam sheet 11, and a heat-sealed portion 15.

[0006] International Patent Publication No. 2021 / 079601

[0007] The insulator 13 in Patent Document 1 is bag-shaped with incisions 14 formed along the edge of a foam sheet 11, and an insulating sheet 12 is inserted into the bag and housed therein, with a heat-sealed section 15 formed and sealed at the opening made by the incision 14. The insulating sheet 12 is a fiber sheet impregnated with silica gel, and the heat-sealed section 15 is formed and sealed to prevent the silica gel from falling off (powdering). However, because the heat-sealed section 15 is formed by applying heat to the overlapping portion of the two upper and lower foam sheets 11 shown in the figure, stress remains in the heat-sealed section 15, which may cause it to peel off when subjected to external force.

[0008] Furthermore, since the heat insulating sheet 12 is inserted through the slits 14 in the foam sheet 11, tension is easily applied to the portion of the foam sheet 11 that slides against the edge of the heat insulating sheet 12, which may result in damage. Furthermore, when the heat insulating sheet 12 is inserted, the foam sheet is partially stretched, and tensile stress remains in the stretched portion. Thus, the foam sheet 11 may be subject to tearing or holes due to the manufacturing process.

[0009] In a battery pack, it is desirable to make the volume of components other than the battery cells as small as possible, and in a heat insulating material with an elastic portion, the entire battery pack can be made smaller by reducing the thickness of the elastic portion and increasing the elastic modulus. However, as the thickness of the elastic portion is reduced, the risk of tearing or holes increases.

[0010] As described above, in the thermal insulator 13 of Patent Document 1, there is a risk of breakage or hole formation in the foam sheet 11, and the thinner the sheet, the more likely this breakage or hole formation occurs. In addition, tensile stress is generated in the heat-sealed portion 15 from both sides, so a sufficient width must be ensured, which makes it difficult to achieve compactness in the thermal insulator 13. Furthermore, because the thermal insulator sheet 12 is inserted by making cuts in the foam sheet 11, if there are air bubbles that reach a depth of more than half the thickness from the surface of the foam sheet 11 before the cuts are made, only a very thin portion of the surface will remain after the cuts, making the sheet more susceptible to breakage or hole formation.

[0011] Therefore, the present invention aims to provide a fireproof sheet which is made by combining a heat insulating material and an elastic body, which does not have the problem of powder falling off from the heat insulating material, in which the elastic body is hard to tear and hard to develop holes, and in which the elastic body can be made thin.

[0012] The above object of the present invention is achieved by the following configuration [1] relating to a flame-retardant sheet.

[0013] [1] A flame-retardant sheet comprising a heat insulating sheet and an elastic covering made of a foamed thermosetting resin, wherein the elastic covering covers the entire heat insulating sheet without any joints.

[0014] Furthermore, preferred embodiments of the present invention relating to the flame retardant sheet relate to the following [2] to [8].

[0015] [2] The flame-retardant sheet according to [1], characterized in that the average thickness of the elastic coating covering the main surface of the heat insulating sheet is 0.01 to 10 mm. [3] The flame-retardant sheet according to [1] or [2], characterized in that the average width of the frame region of the elastic coating located outside the end surface of the heat insulating sheet is 0.1 to 2 mm. [4] The flame-retardant sheet according to any one of [1] to [3], characterized in that the elastic coating contains a silicone resin. [5] The flame-retardant sheet according to any one of [1] to [4], characterized in that the elastic coating contains a flame retardant. [6] The flame-retardant sheet according to any one of [1] to [5], characterized in that the heat insulating sheet contains ceramic particles. [7] The flame-retardant sheet according to [6], characterized in that the ceramic particles contain one or more particles selected from metal oxide particles, inorganic hydrates, thermally expandable inorganic materials, and hydrous porous bodies. [8] The flame-retardant sheet according to any one of [1] to [7], characterized in that the elastic coating has a compressibility of 40 to 99% when compressed at 2 MPa.

[0016] The above object of the present invention is achieved by the following configuration [9] relating to a method for producing a flame-retardant sheet.

[0017] [9] A method for producing a flame-retardant sheet according to any one of [1] to [8], comprising: a covering step of covering a heat insulating sheet with an elastic coating raw material containing a thermosetting resin precursor and a foaming agent; a foaming step of foaming the elastic coating raw material while the heat insulating sheet is covered with the elastic coating raw material; and a curing step of curing the foamed elastic coating raw material.

[0018] Furthermore, preferred embodiments of the present invention relating to a method for producing a flame-retardant sheet relate to the following

[10] to

[15] .

[0019]

[10] A method for manufacturing a flame-retardant sheet according to [9], comprising: a first step including: a first covering step of covering one side of the heat insulating sheet with the elastic covering raw material; a first foaming step of foaming the elastic covering raw material while the heat insulating sheet is covered with the elastic covering raw material; and a first curing step of foaming and then curing the elastic covering raw material; and a second step including: a second covering step of covering the other side of the heat insulating sheet obtained in the first step, one side of which is covered with an elastic covering, with the elastic covering raw material; a second foaming step of foaming the elastic covering raw material while the heat insulating sheet is covered with the elastic covering raw material; and a second curing step of foaming and then curing the elastic covering raw material.

[11] The method for producing a fire-resistant sheet according to

[10] , wherein in the first step, the first covering step is carried out by injecting the elastic covering raw material into a first molding frame with the heat insulating sheet housed inside the first molding frame, followed by the first foaming step and the first curing step inside the first molding frame; and in the second step, the second covering step is carried out by injecting the elastic covering raw material into a second molding frame with the heat insulating sheet housed upside down after the first step, followed by the second foaming step and the second curing step inside the second molding frame.

[12] The method for producing a fire-resistant sheet according to any one of [9] to

[11] , wherein the thermosetting resin precursor contains a silicone-based raw material.

[13] The method for producing a fire-resistant sheet according to any one of [9] to

[12] , wherein the elastic covering raw material contains a flame retardant.

[14] The method for producing a fire-resistant sheet according to any one of [9] to

[13] , wherein the heat insulating sheet contains ceramic particles.

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

[14] , characterized in that the ceramic particles contain one or more selected from metal oxide particles, inorganic hydrates, thermally expandable inorganic materials, and hydrous porous bodies.

[0020] The above object of the present invention is achieved by the following configuration

[16] relating to a battery pack.

[0021]

[16] A battery pack characterized in that the fireproof sheet according to any one of [1] to [8] is inserted between battery cells, and the battery cells are connected in series or in parallel.

[0022] The flame-retardant sheet of the present invention is a heat insulating sheet entirely covered with an elastic coating, eliminating the problem of powder falling off from the fire-retardant sheet. Furthermore, when covering with the heat insulating sheet, the elastic coating raw material is first covered with the heat insulating sheet, and then the elastic coating raw material is foamed and cured. Therefore, there are no joints such as heat-sealed joints in the elastic coating, and the heat insulating sheet is directly bonded without an adhesive layer or the like. Therefore, the joints do not peel off due to external forces such as heat or vibration, as occurs when heat is fused or an adhesive is used.

[0023] Furthermore, no parts for forming joints are required, which allows for more compact fire-retardant sheets. Furthermore, the elastic covering has no sliding contact with the heat-insulating sheet, so there is no risk of it tearing or developing holes. The elastic covering is made of a thermosetting resin foam, so it does not creep or deform even when heated, allowing it to be made thinner. This, combined with the absence of joints, contributes to more compact fire-retardant sheets.

[0024] The battery pack of the present invention, in which the insulating sheet of the present invention is disposed between the battery cells, can more reliably prevent fire from spreading to the outside even if thermal runaway occurs, and can smoothly follow the expansion and contraction of the battery cells during normal charging and discharging. Furthermore, the elastic coating is not prone to tearing or holes and can be made thin, which, combined with the absence of joints, allows for the battery pack to be made more compact.

[0025] Fig. 1 is a cross-sectional view showing an example of a flame-retardant sheet of the present invention. Fig. 2 is a process diagram showing an example of a method for manufacturing a flame-retardant sheet of the present invention, showing a first step. Fig. 3 is a process diagram showing an example of a method for manufacturing a flame-retardant sheet of the present invention, showing a second step performed subsequent to the first step. Fig. 4 is a cross-sectional view showing an embodiment of a battery pack of the present invention. Fig. 5 is a cross-sectional view showing a heat insulator of Patent Document 1.

[0026] 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.

[0027] [Flame-Retardant Sheet] As shown in the cross-sectional view of FIG. 1 , the flame-retardant sheet 1 of this embodiment is a heat insulating sheet 50 entirely covered with an elastic covering 60 .

[0028] <Elastic coating 60> The elastic coating 60 is made of a thermosetting resin foam, and therefore countless closed cells 65 made of air or foaming gas are dispersed throughout the elastic coating 60. Since the cells of a foam are closed and the gas is not released to the outside, even if the gas is compressed when an external force is applied, the repulsive force of the gas allows the foam to easily return to its original shape, thereby maintaining its elasticity. On the other hand, with an open-cell structure, the gas is released when an external force is applied, and the only stress is the force causing the resin to return to its original shape, resulting in a weaker elasticity.

[0029] The foam does not need to have any pores penetrating the elastic coating to prevent powder from falling off, and it is not necessary for all of the foam to be closed cells. There is nothing to prevent some of the cells present in the thermosetting resin from being interconnected.

[0030] Furthermore, since the thermosetting resin is crosslinked, it is less likely to be thermally deformed when heated, and is less likely to develop holes or break due to thermal fatigue.

[0031] Furthermore, the elastic covering 60 does not have a heat-sealed portion (reference numeral 15 in FIG. 5) like that in Patent Document 1, or a "joint" like that bonded using an adhesive. Therefore, there is no problem of peeling originating from the joint. Furthermore, there is no need for a portion to form a joint, making the flameproof sheet 1 more compact, which in turn contributes to a more compact battery pack. Note that heat-sealed portions like those in Patent Document 1 destroy any bubbles that have formed and form a layer (joint) with different mechanical properties from the surrounding area, which can easily become a starting point for stress generation.

[0032] As shown in FIG. 1 , the average width (D1) of the frame region located outside the end surface 50 a of the insulating sheet 50, which corresponds to the conventional joint, can be thinned, preferably to 2 mm or less. When the average width (D1) of the frame region located outside the end surface of the insulating sheet is 2 mm or less, the area without the insulating sheet between battery cells can be reduced, thereby preventing the spread of flames to adjacent battery cells in the event of thermal runaway. Furthermore, the average width (D1) is preferably 0.01 mm or more. When the average width (D1) of the frame region located outside the end surface 50 a of the insulating sheet 50 is 0.01 mm or more, sufficient thickness can be ensured for the closed cells 65, completely covering the insulating sheet 50 and preventing particle generation from the insulating sheet 50.

[0033] Because the elastic covering 60 is shaped to fit the outer surface of the heat insulating sheet 50, there is no deformation or tension that occurs when the heat insulating sheet 50 is inserted, as in Patent Document 1, and there is no risk of tearing, particularly at the edge portions, due to sliding contact with the heat insulating sheet 50. Furthermore, by reducing the average film thickness (D2) of the portion in contact with the main surface 50b of the heat insulating sheet 50 and the average width (D1) of the frame region located outside the end surface 50a of the heat insulating sheet 50, this, in combination with the flame retardant sheet 1, makes the battery pack more compact, and increases the capacity per volume of the entire battery pack.

[0034] It is also preferable that the elastic covering 60 and the heat insulating sheet 50 are integrally joined together. If they are integrally joined together, even if a difference in size occurs between the heat insulating sheet 50 and the elastic covering 60 due to a difference in thermal expansion or expansion / contraction, local tension is not generated in the elastic covering 60 around the edge of the heat insulating sheet 50.

[0035] The average thickness (D2) of the portion of the heat insulating sheet 50 in contact with the main surface 50b is preferably 0.01 mm or more. If the average thickness (D2) is 0.01 mm or more, powder falling off can be prevented. It is even more preferable that the average thickness (D2) of the portion of the heat insulating sheet 50 in contact with the main surface 50b is 0.5 mm or more. If the average thickness (D2) is 0.5 mm or more, appropriate elasticity can be imparted, and further, since the size can be made sufficiently larger than the size of the closed cells 65, powder falling off can be prevented.

[0036] Furthermore, the average thickness (D2) of the portion of the insulating sheet 50 in contact with the main surface 50b is preferably 10 mm or less. If the average thickness (D2) is 10 mm or less, the battery pack can be made more compact, and the capacity per volume of the entire battery pack can be increased. The average thickness (D2) of the portion covering the main surface 50b of the insulating sheet 50 is measured as the distance between the main surface 50b of the insulating sheet 50 and the surface of the elastic coating 60 in an uncompressed state.

[0037] There are no restrictions on the thermosetting resin that serves as the base material for the elastic covering 60, and well-known thermosetting resins such as phenolic resin, epoxy resin, melamine resin, urea resin, unsaturated polyester resin, alkyd resin, silicone resin, urethane resin, and thermosetting polyimide resin can be used, but silicone resin is preferred. Silicone resin ceramicizes at high temperatures and does not disappear, protecting the fireproof sheet 1 in the event of thermal runaway in the battery cells.

[0038] A foaming agent is used to foam the thermosetting resin, but there are no limitations on the foaming agent, and known foaming agents can be used, such as 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. There are no limitations on the amount of foaming agent, but a range of 1 to 5 mass % is appropriate, based on the total amount including the thermosetting resin.

[0039] The elastic coating 60 preferably contains a flame retardant to enhance its own fire resistance. The flame retardant is not limited, and known flame retardants can be used, such as red phosphorus, guanidine phosphate compounds, polyphosphate compounds such as ammonium polyphosphate, organic boron compounds, boric acid, boron oxide, boric acid esters, metaboric acid, and other boron compounds, aluminum oxide, aluminum hydroxide, boehmite, dolomide, hydrotalcite, calcium hydroxide, basic magnesium carbonate, zirconium hydroxide, and tin oxide, and halogen compounds. By appropriately adjusting the amount of flame retardant, standards such as UL94V-0 can be met. The elastic coating 60 may further contain additives such as plasticizers, surface treatment agents, fillers, heat resistance agents, and adhesion promoters. 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.

[0040] Furthermore, to enhance the heat resistance of the elastic coating 60, for example, iron oxide, cerium oxide, titanium oxide, or a rare earth compound may be used, and to impart flame retardancy, a flame retardant such as titanium oxide, carbon black, or aluminum hydroxide may be used. Furthermore, an organometallic compound or the like may be used as an adhesion promoter.

[0041] In terms of the physical properties of the elastic coating 60, a compression ratio of 40% or more when compressed at 2 MPa is preferable to ensure and maintain sufficient elastic properties. The compression ratio when compressed at 2 MPa is obtained by measuring the thickness when a pressure of 2 MPa is applied, with the initial thickness of the flame-retardant sheet 1 (at 0 MPa) set to 100%. A compression ratio of 40% or more when compressed at 2 MPa ensures sufficient compressibility for the entire flame-retardant sheet 1, even when using an insulating sheet with poor compressibility, thereby expanding design flexibility. An upper limit of the compression ratio is preferably 99%. When the compression ratio is 99%, sufficient repulsion force is ensured when multiple battery cells are arranged to form a stack, ensuring reliable fixation of the battery cells. An upper limit of the compression ratio is more preferably 80%. When the compression ratio is 80%, the proportion of closed cells can be increased, ensuring sufficient strength of the cell walls.

[0042] <Thermal Insulation Sheet 50> While there are no limitations on the type of thermal insulation sheet 50, it is preferable for the sheet to contain ceramic particles due to its high thermal insulation performance. Examples of ceramic particles that can be used 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 be in 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. Examples of nanoparticles that can be used include silica nanoparticles such as wet silica, dry silica, and aerogel.

[0043] Below are preferred examples of formulations containing ceramic particles.

[0044] (Fibrous Material) The heat insulating sheet 50 contains ceramic particles and 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. The inclusion of the fibrous material can improve the mechanical strength of the heat insulating sheet 50 and its ability to hold the ceramic particles. Specific examples of inorganic fibers include ceramic fibers such as silica fiber, alumina fiber, alumina silicate fiber, zirconia fiber, carbon fiber, soluble fiber, refractory ceramic fiber, aerogel composite, magnesium silicate fiber, alkaline earth silicate fiber, 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, and mullite fiber; and natural mineral fibers such as wollastonite as mineral fibers other than those mentioned above.

[0045] Furthermore, fibers with a melting point exceeding 1000°C are suitable for use because they do not melt or soften and can maintain their shape even if thermal runaway occurs in the battery cell. 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, and even more preferable to use fibers with a melting point exceeding 1000°C. As the organic fiber, for example, at least one selected from polyvinyl alcohol (PVA) fibers, polyethylene fibers, nylon fibers, polyurethane fibers, and ethylene-vinyl alcohol copolymer fibers can be used. When organic fibers are used, they are less likely to break even when bent, making it possible to obtain a heat insulating sheet that is resistant to deformation and less likely to flake off.

[0046] (Other Compounding Materials) In addition to the above-mentioned fibrous material and ceramic particles, the heat insulating sheet 50 may contain additives such as a resin binder, a pH adjuster, and a flocculant.

[0047] Resin Binder The fibrous material can also be bound by a resin binder. There are no particular limitations on the resin binder, as long as it has a glass transition point lower than that of the fibrous material described below. For example, a resin binder 9 containing at least one resin selected from styrene-butadiene resin, acrylic resin, silicon-acrylic resin, and styrene resin can be used.

[0048] 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 9 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.

[0049] 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.

[0050] (Method for manufacturing the heat insulating sheet 50) The heat insulating sheet 50 can be manufactured by a papermaking method. That is, the materials for forming the heat insulating sheet 50, such as ceramic particles, fibrous material, and other compounding materials, are dispersed in water, and the dispersion is dehydrated, molded, and dried to produce the sheet.

[0051] Alternatively, the heat insulating sheet 50 may be produced by a dry method, in which the ceramic particles, fibrous material, and other ingredients that form the heat insulating sheet 50 are placed in an appropriate mixer, thoroughly dispersed, and pre-molded.

[0052] [Method for manufacturing the flame-retardant sheet 1] To manufacture the flame-retardant sheet 1, the following steps are sequentially performed: a covering step in which the heat insulating sheet 50 is covered with an elastic coating raw material containing a thermosetting resin precursor, a foaming agent, and, if necessary, a flame retardant; a foaming step in which the elastic coating raw material is foamed while the heat insulating sheet 50 is covered with the elastic coating raw material; and a curing step in which the foamed elastic coating raw material is cured. Because the elastic coating raw material is foamed and cured in the presence of the heat insulating sheet, the elastic coating 60 and the heat insulating sheet can be integrally bonded.

[0053] It is preferable that the viscosity of the thermosetting resin precursor in the elastic coating raw material is high, as low viscosity tends to cause coarsening of the closed cells 65. For example, in the case of silicone resin, it is preferable to adjust the temperature and the component ratio of the elastic coating raw material so that the viscosity is 10 to 1000 Pa s.

[0054] Methods for covering the insulating sheet 50 with the elastic coating material include dipping and insert molding. The dipping method is effective when forming a relatively thin elastic coating on the surface of the insulating sheet, while the insert molding method is effective when forming a relatively thick elastic coating. The dipping method involves immersing the insulating sheet 50 in a storage container of liquid elastic coating material and then lifting it out. After lifting, the elastic coating material is then heated to the foaming temperature of the foaming agent to foam and harden it. This results in a fire-retardant sheet 1 in which the entire insulating sheet 50 is covered with a continuous elastic coating 60 without any joints such as heat-sealed joints.

[0055] The above series of steps can also be carried out by an "insert molding method." For example, this can be carried out in a two-step process as shown in Figures 2 and 3. Figure 2 is a process diagram showing the first step, and Figure 3 is a process diagram showing the second step.

[0056] (First Step) In the first step, as shown in FIG. 2(A), a 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. 2(B), an elastic coating raw material 80 is poured into the gap between the heat insulating sheet 50 and the frame 75A. Then, as shown in FIG. 2(C), the frame 75A and the elastic coating raw material 80 are covered with a release paper 70B to seal, foam, and harden. After hardening, the release papers 70A and 70B are peeled off, and the product is subjected to the second step described below. At this time, to ensure a consistent thickness of the elastic coating 60A and a consistent width of the frame region, 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 they may be provided at the edge of the heat insulating sheet 50 for positioning. Furthermore, if the base has a recess, the heat insulating sheet 50 can be placed in the recess and the release paper 70A can be laid around the heat insulating sheet 50, allowing the heat insulating sheet 50 to be positioned accurately at the desired position.

[0057] (Second Step) In the second step, as shown in FIG. 3(D), the single-sided covering 55 obtained in the first step, with one main surface and one end surface covered with the elastic covering 60A, is turned upside down and placed on the release paper 70C of the frame 75B. The height of the frame 75B is set to be greater than the thickness of the single-sided covering 55. Next, as shown in FIG. 3(E), the elastic covering raw material 80 is poured into the gap between the single-sided covering 55 and the frame 75B. Then, as shown in FIG. 3(F), the frame 75B and the elastic covering raw material 80 are covered with the release paper 70D, sealed, foamed, and cured. After curing, the release papers 70C and 70D are peeled off to obtain the flame-retardant sheet 1 shown in FIG. 1. Since the elastic covering is formed in the second step following the first step, the entire insulating sheet 50 can be covered without any joints. In addition, because the elastic covering 60 is formed by foaming around the heat insulating sheet 50, tension is less likely to remain at the edges of the heat insulating sheet 50, making it less likely to tear or develop holes. Furthermore, because the elastic covering raw material is foamed and then hardened, crosslinking makes it less likely to undergo creep deformation and less likely to tear or develop holes due to thermal fatigue.

[0058] [Battery Module (Battery Assembly)] As shown in Fig. 4, the battery assembly 100 has a plurality of battery cells 110 housed in a battery case 120. In this embodiment, the above-described fireproof sheet 1 is disposed between the battery cells 110. The battery cells 110 are connected in series or in parallel by bus bars (not shown).

[0059] Although various embodiments have been described above with reference to the drawings, it goes without saying that the present invention is not limited to such examples. It is clear that a person skilled in the art can conceive of various modifications or alterations within the scope of the claims, and it is understood that these also naturally fall within the technical scope of the present invention. Furthermore, the components of the above-described embodiments may be combined in any manner without departing from the spirit of the invention.

[0060] This application is based on a Japanese patent application (Patent Application No. 2023-141218) filed on August 31, 2023, the contents of which are incorporated herein by reference.

[0061] REFERENCE SIGNS LIST 1 Flame retardant sheet (heat transfer suppression sheet) 50 Heat insulating sheet 50a End surface 50b Main surface 55 One-sided covering body 60, 60A Elastic covering 65 Closed cells 70A, 70B, 70C, 70D Release paper 75A, 75B Frame 80 Elastic covering raw material 100 Assembled battery 110 Battery cell 120 Battery case

Claims

1. A flame-retardant sheet comprising an insulating sheet and an elastic covering made of a thermosetting resin foam, the elastic covering covering the entire insulating sheet without any joints.

2. A flame-retardant sheet as described in claim 1, characterized in that the average thickness of the elastic coating covering the main surface of the heat-insulating sheet is 0.01 to 10 mm.

3. A fire-retardant sheet as described in claim 1, characterized in that the average width of the frame region of the elastic covering located outside the end face of the heat insulating sheet is 0.01 to 2 mm.

4. The fireproof sheet according to claim 1, characterized in that the elastic coating contains a silicone resin.

5. The fireproof sheet according to claim 1, characterized in that the elastic covering contains a fire retardant.

6. The fireproof sheet according to claim 1, characterized in that the heat insulating sheet contains ceramic particles.

7. The flame-retardant sheet according to claim 6, characterized in that the ceramic particles contain one or more particles selected from metal oxide particles, inorganic hydrates, thermally expandable inorganic materials and water-containing porous bodies.

8. The fireproof sheet according to claim 1, characterized in that the elastic coating has a compression rate of 40 to 99% when compressed at 2 MPa.

9. A method for producing a fire-retardant sheet according to any one of claims 1 to 8, comprising: a covering step of covering an insulating sheet with an elastic coating raw material containing a thermosetting resin precursor and a foaming agent; a foaming step of foaming the elastic coating raw material while the insulating sheet is covered with the elastic coating raw material; and a curing step of curing the foamed elastic coating raw material.

10. A method for producing a flame-retardant sheet as claimed in claim 9, comprising a first step having: a first covering step of covering one side of the insulation sheet with the elastic covering raw material; a first foaming step of foaming the elastic covering raw material while the insulation sheet is covered with the elastic covering raw material; and a first curing step of foaming and then curing the elastic covering raw material; and a second step having: a second covering step of covering the other side of the insulation sheet obtained in the first step, one side of which is covered with an elastic covering, with the elastic covering raw material; a second foaming step of foaming the elastic covering raw material while the insulation sheet is covered with the elastic covering raw material; and a second curing step of foaming and then curing the elastic covering raw material.

11. A method for manufacturing a fire-retardant sheet as described in claim 10, characterized in that in the first step, the first covering step is carried out by injecting the elastic covering raw material with the insulation sheet contained inside a first molding frame, and then the first foaming step and the first hardening step are carried out inside the first molding frame, and in the second step, the second covering step is carried out by injecting the elastic covering raw material with the insulation sheet after the first step contained inside a second molding frame with the front and back sides inverted, and then the second foaming step and the second hardening step are carried out inside the second molding frame.

12. The method for producing a fireproof sheet according to claim 9, characterized in that the thermosetting resin precursor contains a silicone-based raw material.

13. The method for producing a fire-retardant sheet according to claim 9, characterized in that the elastic coating raw material contains a fire retardant.

14. The method for producing a fireproof sheet according to claim 9, wherein the heat insulating sheet contains ceramic particles.

15. The method for manufacturing a fire-retardant sheet as described in claim 14, characterized in that the ceramic particles contain one or more selected from metal oxide particles, inorganic hydrates, thermally expandable inorganic materials and water-containing porous bodies.

16. A battery pack comprising: a fireproof sheet according to any one of claims 1 to 8 interposed between battery cells; and the battery cells are connected in series or parallel.

Images