Fire-resistant sheet, method for manufacturing the same, and battery

Abstract

To obtain a laminated fire-resistant sheet that maintains the flexibility of the sponge sheets, maintains high adhesive strength between sponge sheets, reduces environmental and human health burdens, and lowers manufacturing costs. [Solution] The present invention relates to a fire-spread prevention sheet 15, which is positioned between multiple heat sources to prevent the spread of fire between them, and is formed by laminating multiple porous sheets 1 without an adhesive layer between them, with the porous sheets 1 being chemically bonded to each other on their opposing surfaces, as well as a method for manufacturing the same and a battery.

Description

Technical Field

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[0001] The present invention relates to a flame retardant sheet, a method for manufacturing the same, and a battery.

Background Art

[0002] Currently, around the world, there is an active movement to gradually convert conventional gasoline or diesel vehicles to electric vehicles for the purpose of reducing the burden on the global environment. In particular, in addition to European countries such as France, the Netherlands, and Germany, the spread of electric vehicles is also progressing in China. The spread of electric vehicles requires high-performance batteries.

[0003] Conventionally, as an automobile battery, one in which a plurality of battery cells (also simply referred to as "cells") are arranged and mounted in a housing is known. The container of the cell expands when it overheats during discharge and / or charging. When the cells expand, there is a risk of abnormal overheating and even ignition due to the cells coming into contact with each other and the chain transmission of heat. To address such problems, for example, a method of providing a flame retardant sheet between a plurality of cells is known (see Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Prior to the present invention, the inventor developed a porous resin or rubber sheet, so-called sponge sheet, as a flame retardant sheet. There are still points to be improved in the flame retardant sheet. Hereinafter, the points to be improved will be described in detail.

[0006] Figure 7 shows the changes in the sponge sheet of a currently used lithium-ion battery cell when it is not expanded (also called the normal state) and when it is expanded (7A), and the changes in the sponge sheet of a future solid-state battery cell when it is not expanded (also called the normal state) and when it is expanded (7B). Figure 8 shows the manufacturing process of a laminated sponge sheet developed by the inventors of this applicant prior to the present invention.

[0007] In the case of a battery equipped with multiple lithium-ion batteries, the thickness of the sponge sheet 115 sandwiched between cells (lithium-ion batteries) 123a, 123a is approximately 4 mm. On the other hand, in the case of a battery equipped with multiple solid-state batteries, the cell (solid-state battery) 123b expands more significantly, so the thickness of the sponge sheet 115 sandwiched between cells 123b, 123b is expected to exceed 4 mm when considering this expansion. Generally, it is difficult to mold a single sponge sheet that has uniform elasticity throughout its surface. In particular, in the case of solid-state batteries, which may expand more than existing lithium-ion batteries, more uniform elasticity is required within the sheet surface.

[0008] To meet these demands, the inventors of the present applicant, prior to the present invention, molded thin sponge sheets (also called porous sheets) having uniform elasticity in the plane, and manufactured a laminated sponge sheet composed of multiple sponge sheets by interposing an adhesive between opposing sponge sheets. The manufacturing process of the laminated sponge sheet will be briefly described below with reference to Figure 8. First, two sponge sheets (in the example in Figure 8, silicone rubber sponge sheets) 100,100 were prepared, and the sponge sheets 100,100 were laminated with an adhesive 105 in between. Next, another sponge sheet 100 was laminated to the previously obtained laminate via the adhesive 105. After repeating this lamination process, the laminated sponge sheet 115 was completed by heating.

[0009] The problem here lies in the presence of adhesive 105 or the adhesive layer after it has hardened. When adhesive 105 is used, the flexibility of the sponge sheet 100 may decrease as the adhesive 105 hardens. In addition, the adhesive layer tends to deteriorate over time, reducing its adhesive strength. Furthermore, some adhesives 105 contain harmful chemicals, posing a risk of adverse effects on the environment and health. Moreover, the use of adhesive 105 requires additional materials and processes, increasing the manufacturing cost of the final product. Some adhesives 105 cannot be used in high-temperature environments. There is a demand in the market for fire-resistant sheets that address these issues. Furthermore, developing such a fire-resistant sheet will also contribute to achieving the applicant's Sustainable Development Goal of "ensuring access to affordable, reliable, sustainable, and modern energy for all."

[0010] The present invention aims to resolve or reduce the problems caused by the presence of the aforementioned adhesive, that is, to obtain a laminated fire-resistant sheet that can maintain the flexibility of the sponge sheet, maintain high adhesive strength between sponge sheets, reduce the burden on the environment and human body, and reduce manufacturing costs. [Means for solving the problem]

[0011] (1) A fire spread prevention sheet according to one embodiment for achieving the above objective is a sheet that is placed at least between multiple heat sources and is capable of preventing the spread of fire between the heat sources, Multiple porous sheets are laminated without an adhesive layer in between. The porous sheets are chemically bonded to each other at their opposing surfaces. (2) In a fire-spread prevention sheet according to another embodiment, preferably the porous sheet may be a silicone sponge sheet. (3) In a fire-spread prevention sheet according to another embodiment, preferably the porous sheet may contain a filler with higher heat resistance. (4) A method for manufacturing a fire-spread prevention sheet according to one embodiment for achieving the above objective is a method for manufacturing a sheet that is placed at least between a plurality of heat sources and is capable of preventing the spread of fire between the heat sources, A step of applying a surface modification treatment to at least one of the two surfaces in the thickness direction of the porous sheet that bond the porous sheets together, A step of laminating the porous sheets with the surfaces that have undergone the surface modification treatment facing each other, The process involves heating and compressing the porous sheets after lamination, Includes. (5) In a method for manufacturing a fire-spread prevention sheet according to another embodiment, the step of applying the surface modification treatment may be a plasma treatment step in which the surface free energy of the porous sheet is 15 mN / m or more. (6) A battery according to one embodiment for achieving the above objective comprises a plurality of cells in a housing, and at least one of the above-described fire-spread prevention sheets is provided between the cells and between the cells and the housing. (7) In a battery according to another embodiment, the cell may be an all-solid-state battery. [Effects of the Invention]

[0012] According to the present invention, it is possible to obtain a laminated fire-preventive sheet that can maintain the flexibility of the sponge sheets, maintain high adhesive strength between sponge sheets, reduce the burden on the environment and human body, and reduce manufacturing costs. [Brief explanation of the drawing]

[0013] [Figure 1] Figure 1 shows a diagram illustrating a fire-spread prevention sheet and its manufacturing process according to one embodiment. [Figure 2] Figure 2 shows a longitudinal cross-sectional view of a battery according to one embodiment and an enlarged view of a fire-prevention sheet installed inside the battery. [Figure 3] Figure 3 shows a stress-strain curve graph illustrating the relationship between strain and stress in a fire-spread prevention sheet composed of a single porous sheet. [Figure 4] Figure 4 shows a graph of a stress-strain curve representing the relationship between the strain and stress of a fire-retardant sheet obtained by laminating seven porous sheets without an adhesive. [Figure 5] Figure 5 shows a diagram for explaining a preferable characteristic region, taking the graph of Figure 4 as an example. [Figure 6] Figure 6 shows a graph obtained by adding, to the curve of Figure 4, a stress-strain curve representing the relationship between the strain and stress of a fire-retardant sheet obtained by laminating seven porous sheets with an adhesive applied between the sheets for comparison. [Figure 7] Figure 7 shows the change (7A) of a sponge sheet when a cell of a currently used lithium-ion battery is not expanded (also referred to as normal time) and when it is expanded, and the change (7B) of a sponge sheet when a cell of an all-solid-state battery to be put into practical use in the future is not expanded (also referred to as normal time) and when it is expanded. [Figure 8] Figure 8 shows a manufacturing process of a laminated sponge sheet developed by the inventors of the present applicant prior to the present invention.

Mode for Carrying Out the Invention

[0014] Next, embodiments of the present invention will be described with reference to the drawings. Note that the embodiments described below do not limit the invention according to the claims, and not all of the elements and combinations thereof described in the embodiments are essential for the solution means of the present invention.

[0015] 1. Fire-retardant sheet and method for manufacturing the same First, a fire-retardant sheet and a method for manufacturing the same according to an embodiment will be described.

[0016] Figure 1 shows a diagram for explaining a fire-retardant sheet and a manufacturing process thereof according to an embodiment.

[0017] (1) Configuration of the fire-retardant sheet The fire-spread prevention sheet 15 according to this embodiment is a sheet that is placed at least between multiple heat sources and is capable of preventing the spread of fire between heat sources. Heat sources include not only cells mounted inside a battery, but also heat-generating elements other than cells, such as electronic components on a circuit board. Furthermore, preventing the spread of fire is interpreted broadly to include reducing the spread of fire. The fire-spread prevention sheet 15 is laminated by interposing multiple porous sheets 1 without an adhesive layer between them. The porous sheets 1 are chemically bonded to each other on their opposing surfaces. The porous sheets 1 may also be referred to as sponge sheets or foamed sheets.

[0018] The fire-spread prevention sheet 15 is not a single porous sheet, but a laminate of two or more porous sheets 1. This is because forming sheets with a smaller thickness results in more uniform elastic function within the plane. The thickness of the porous sheet 1 is preferably 1 to 5 mm, more preferably 1.5 to 4.5 mm, and even more preferably 1.8 to 2.5 mm. The thickness of the fire-spread prevention sheet 15 is preferably 8 to 20 mm, more preferably 10 to 16 mm, and even more preferably 13 to 15 mm. The number of porous sheets 1 constituting the fire-spread prevention sheet 15 is preferably 2 to 12, more preferably 4 to 10, and even more preferably 6 to 8.

[0019] The main material of the porous sheet 1 is a resin or rubber that is elastically flexible, easily shrinking and recovering to its original shape. The main material is not particularly restricted, but preferably a resin or rubber that is highly flexible and heat-resistant. Examples of resins include polypropylene, polyvinylidene fluoride, polyamide, polycarbonate, polyphenylene sulfide, polyimide, polyetherimide, polytetrafluoroethylene, polyamideimide, phenolic resin, allyl resin, epoxy resin, furan resin, and silicone resin. Examples of rubbers include silicone rubber, acrylic rubber, urethane rubber, styrene rubber, butyl rubber, ethylene propylene rubber, and fluororubber, with silicone rubber being a more preferred example. The porous sheet 1 is preferably a silicone sponge sheet. The porous sheet 1 may be fully cured or semi-cured. The semi-cured porous sheet 1 may be fully cured by heating. The air present inside the pores of the porous sheet 1 contributes to enhancing the heat insulation and elastic deformability of the fire-preventing sheet 15. The volume of pores in the porous sheet 1 is preferably 20 / 100 to 97 / 100, more preferably 40 / 100 to 90 / 100.

[0020] The porous sheet 1 may contain a filler with higher heat resistance than the main material (resin or rubber) constituting the sheet. The form of the filler is not particularly limited and may be, for example, granular, needle-shaped, plate-shaped, or fibrous. Examples of fillers include ceramics, carbon materials (however, materials with high electrical insulation properties are preferred), and / or resins. Examples of ceramics include alumina, silica, mullite, cordierite, steatite, forsterite, titania, zirconia, talc, mica, silicon carbide, and silicon nitride. Examples of carbon materials include natural or artificial diamonds. Examples of resins include polyphenylene sulfide and polyetheretherketone, which are materials different from the main material of the porous sheet 1. The spherical diameter of the filler is preferably 0.01 to 100 μm, more preferably 1 to 50 μm, and even more preferably 5 to 30 μm. The filler content in the porous sheet 1 (including the filler) is preferably 2 to 60% by mass, more preferably 5 to 50% by mass, and even more preferably 10 to 40% by mass.

[0021] (2) Method for manufacturing fire-resistant sheets The method for manufacturing a fire-spread prevention sheet according to this embodiment is a method for manufacturing a sheet that is placed between multiple heat sources and is capable of preventing the spread of fire between heat sources, and includes the steps of: (a) applying a surface modification treatment to at least the surfaces of both sides in the thickness direction of the porous sheet 1 that are bonded together; (b) laminating the porous sheets 1 with the surfaces that have been treated with the surface modification treatment facing each other; and (c) heating and compressing the porous sheets 1 after lamination. Each step will be described below.

[0022] (a) A process of applying surface modification treatment. In this embodiment, the surface modification treatment is preferably plasma treatment. The plasma treatment will be described in detail below. Plasma treatment is a method of surface modification that activates the treated surface. Plasma treatment is not particularly limited and examples include atmospheric pressure plasma treatment performed under atmospheric pressure and vacuum plasma treatment performed under reduced pressure. Examples of atmospheric pressure plasma treatment include gas irradiation type and discharge treatment type. Gas irradiation type plasma treatment refers to a treatment performed using ionized gas after supplying argon gas, oxygen gas, etc., to create a plasma state. Discharge treatment type plasma treatment refers to a treatment performed using ionized gas after applying a high voltage between electrodes to ionize gas in the air. The plasma treatment performed in this embodiment is preferably atmospheric pressure plasma treatment, and more preferably gas irradiation type plasma treatment. The gas used during plasma treatment is preferably argon, oxygen, nitrogen, or a mixed gas of any combination thereof. Plasma treatment is performed on at least the surfaces (two bonding surfaces) of two porous sheets 1 that are bonded to each other. In this embodiment, the plasma treatment is not limited to the adhesive surface, but is performed on both sides in the thickness direction of the porous sheet 1. Alternatively, the plasma treatment may be performed on the entire surface of the porous sheet 1. Preferred conditions for the plasma treatment are as follows: In this embodiment, the plasma treatment can be performed under conditions where the surface free energy of the sponge sheet is preferably 15 mN / m or more, more preferably 25 mN / m or more, and even more preferably 35 mN / m or more.

[0023] (a) The process of applying surface modification treatment may be a process other than plasma treatment, for example, a so-called dry treatment process such as excimer treatment, corona treatment, or electron beam irradiation. Excimer treatment refers to a surface treatment that is carried out by decomposing oxygen in the air with ultraviolet light having a short wavelength of 200 nm or less (called excimer light or excimer UV light), which generates ozone and reactive oxygen species. Corona treatment refers to a surface treatment that is carried out by electrons emitted by corona discharge irradiation colliding with molecules such as oxygen in the atmosphere, exciting, dissociating, and ionizing the collided molecules. Electron beam irradiation refers to a treatment that directly modifies the surface of the object to be modified by irradiating it with an electron beam.

[0024] (b) Lamination process This process involves bonding multiple porous sheets 1, after surface modification treatment, in the thickness direction to form a laminate 10. In this process, lamination using adhesives, as in conventional methods, is not performed.

[0025] (c) process of heating and compressing This step involves heating the laminate 10 to obtain a cured body in which the porous sheet 1 is completely integrated. This step involves pressing the laminate 10 in the thickness direction in addition to heating. The heating temperature is preferably 80 to 180°C, more preferably 100 to 160°C, and even more preferably 120 to 150°C. The pressing pressure is preferably 40 to 120 kPa, more preferably 50 to 110 kPa, and even more preferably 60 to 100 kPa.

[0026] 2. Battery Next, a battery according to one embodiment will be described.

[0027] Figure 2 shows a longitudinal cross-sectional view of a battery according to one embodiment and an enlarged view of a fire-prevention sheet installed inside the battery.

[0028] The battery 20 according to this embodiment is, for example, a battery for an electric vehicle, and comprises a plurality of cells 23 arranged in a row. In this embodiment, there are 9 cells 23, but there may be 2 to 8 or 10 or more. The cells 23 are secondary batteries, preferably lithium-ion batteries, and more preferably all-solid-state batteries. The battery 20 comprises a bottomed housing 21 that opens on one side. The cells 23 are arranged inside 22 of the housing 21. Preferably, the plurality of cells 23 are compressed from both sides of the housing 21 using screws or the like, so that they are in close contact with each other (not shown). The cells 20 are arranged inside the housing 21 with a fire-prevention sheet 15 sandwiched between adjacent cells 23. The fire-prevention sheet 15 is also placed between the inner wall of the housing 21 and the cells 23. However, it is not necessary to place the fire-prevention sheet 15 between the inner wall of the housing 21 and the cells 23. As described above, the battery 20 according to this embodiment includes a plurality of cells 23 inside the housing 21, and fire-spread prevention sheets 15 are provided between the cells 23 and between the cells 23 and the housing 21, at least between the cells 23.

[0029] The fire-spread prevention sheet 15 is compressed between the cells 23 when the cells 23 are set in the housing 21, and even if this compression is repeated many times, it elastically deforms in the thickness direction and easily recovers to its original thickness. Furthermore, the fire-spread prevention sheet 15 is compressed in the thickness direction when it is stored in the housing 21 while compressed between the cells 23, and is further compressed when the cells 23 heat up and expand during charging and / or discharging of the battery 20. The fire-spread prevention sheet 15 is a sheet made by laminating porous sheets 1 that are thinner than the sheet 15 without adhesive. Therefore, the in-plane elasticity of the fire-spread prevention sheet 15 is extremely uniform. The absence of adhesive also contributes to maintaining the flexibility of the porous sheets 1. Therefore, even if the cells 23 expand significantly, the fire-spread prevention sheet 15 can contract significantly in accordance with that expansion. When the cells 23 are lithium-ion batteries, the expansion rate of the cells 23 is around 2%. On the other hand, when cell 23 is an all-solid-state battery, the expansion rate of cell 23 is around 20%. For this reason, the highly flexible and easily shrinkable fire-resistant sheet 15 is particularly preferable in a battery 20 equipped with an all-solid-state battery as cell 23. Since the fire-resistant sheet 15 does not have the risk of deterioration of the adhesive layer over time, the adhesive strength between the porous sheets 1 can be maintained at a high level. In addition, since no adhesive is used in the fire-resistant sheet 15, the burden on the environment and human body caused by harmful components contained in adhesives can be reduced. Furthermore, by not using adhesive, the manufacturing cost of the fire-resistant sheet 15 can be reduced. Since the fire-resistant sheet 15 is constructed by laminating porous sheets 1, it can exhibit high heat insulation properties, reducing heat conduction between adjacent cells 23 and the risk of fire spreading.

[0030] 3. Evaluation of the characteristics of fire-spread prevention sheets Next, we will show the characteristics evaluation of the fire-spread prevention sheet according to this embodiment.

[0031] Figure 3 shows a stress-strain curve graph representing the relationship between strain and stress of a fire-spread prevention sheet composed of a single porous sheet. Figure 4 shows a stress-strain curve graph representing the relationship between strain and stress of a fire-spread prevention sheet made by laminating seven porous sheets without adhesive. Figure 5 shows a diagram illustrating the preferred characteristic region using the graph in Figure 4 as an example. Figure 6 shows a graph in addition to the curve in Figure 4, adding a stress-strain curve representing the relationship between strain and stress of a fire-spread prevention sheet made by laminating seven porous sheets with adhesive applied between the sheets, for comparison. The curves in Figures 3 to 6 are reciprocal curves showing the change in strain when a load is applied in the thickness direction of the sheet, and the change in strain when the load is reduced from the point where the load is maximum.

[0032] The preferred characteristics of the fire-spread prevention sheet 15 are as follows. The minimum load condition described below is the normal or non-expanding state of the fire-spread prevention sheet 15. The maximum load condition is the state when the fire-spread prevention sheet 15 is expanded and compressed. When the cells 23 expand, it is preferable that the amount of stress the fire-spread prevention sheet 15 can receive from the cells 23 and deform is large. "The strain at the maximum load (3 MPa to 5 MPa) should be close to 100%." "The difference in strain between the maximum load (3 MPa to 5 MPa) and the minimum load (0.2 MPa to 1.5 MPa) is large."

[0033] The fire-spread prevention sheet 15 shown in Figure 3 is a single-layer porous sheet 1. The fire-spread prevention sheet 15 shown in Figure 4 is a laminated sheet formed by bonding seven porous sheets 1 together by applying atmospheric pressure plasma treatment to the surfaces between the sheets. The atmospheric pressure plasma conditions are: velocity: 150 mm / s, voltage: 280 V, and frequency: 23 kHz. The fire-spread prevention sheet 15 shown in Figure 6 is a laminated sheet formed by bonding seven porous sheets 1 together by applying adhesive between the sheets. The adhesive is: This is a silicone-based adhesive (product number: KE-1800T-A / B) manufactured by Shin-Etsu Chemical Co., Ltd. The thickness of the adhesive layer is 10-30 μm.

[0034] The porous sheet 1 that makes up each of the fire-spread prevention sheets 15 in Figures 3 to 6 is, in all cases, a rectangular parallelepiped silicone sponge sheet with dimensions of 50 mm in width, 50 mm in length, and 2 mm in thickness. The volume ratio of pores to the total volume of the sheet is 55-65%.

[0035] A fire-spread prevention sheet 15, formed by bonding seven porous sheets 1 together without adhesive, exhibited greater strain at the maximum load (3 MPa to 5 MPa). In this fire-spread prevention sheet 15, the strain at the maximum load (3 MPa to 5 MPa) reached 60 to 65%, which was a larger difference compared to the strain at the minimum load (0.2 MPa to 1.5 MPa) compared to a fire-spread prevention sheet 15 made of a single layer of porous sheet 1 (see Figures 3 to 5).

[0036] Furthermore, as shown in Figure 6, when comparing the differences in the characteristics of the fire-spread prevention sheet 15 with and without adhesive, the fire-spread prevention sheet 15 made by bonding seven porous sheets 1 without adhesive showed greater strain at the maximum load (3 MPa to 5 MPa) and a larger difference in strain between the maximum load (3 MPa to 5 MPa) and the minimum load (0.2 MPa to 1.5 MPa) compared to the fire-spread prevention sheet 15 made by bonding and laminating the same number of porous sheets 1 with adhesive.

[0037] From the above results, it was found that a fire-spread prevention sheet 15, which is made by bonding and laminating multiple porous sheets 1 without adhesive, exhibits favorable characteristics compared to a fire-spread prevention sheet 15 made of a single porous sheet 1 or a fire-spread prevention sheet 15 made by bonding and laminating multiple porous sheets 1 with adhesive, namely, "strain at the maximum load (3 MPa to 5 MPa) is close to 100%" and "the difference in strain between the maximum load (3 MPa to 5 MPa) and the minimum load (0.2 MPa to 1.5 MPa) is large." [Industrial applicability]

[0038] This invention can be used as a sheet that can be compressed and deformed in response to the expansion of a heat source. [Explanation of Symbols]

[0039] 1...Porous sheet (e.g., silicone sponge sheet), 10...Laminate, 15...Fire-proof sheet, 20...Battery, 21...Housing, 23...Cell (an example of a heat source, including lithium-ion batteries or all-solid-state batteries).

Claims

1. A sheet that is placed at least between multiple heat sources and is capable of preventing the spread of fire between the heat sources, Multiple porous sheets are laminated without an adhesive layer in between. A fire-spread prevention sheet characterized in that the porous sheets are chemically bonded to each other on their opposing surfaces.

2. The fire-spread prevention sheet according to claim 1, characterized in that the porous sheet is a silicone sponge sheet.

3. The fire-spread prevention sheet according to claim 1, characterized in that the porous sheet contains a filler with higher heat resistance.

4. A method for manufacturing a sheet that is placed at least between multiple heat sources and is capable of preventing the spread of fire between the heat sources, A step of applying a surface modification treatment to at least one of the two surfaces in the thickness direction of the porous sheet that bond the porous sheets together, A step of laminating the porous sheets with the surfaces that have undergone the surface modification treatment facing each other, The process involves heating and compressing the porous sheets after lamination, A method for manufacturing a fire-spread prevention sheet, characterized by including the following:

5. The method for manufacturing a fire-spread prevention sheet according to claim 4, characterized in that the step of applying the surface modification treatment is a plasma treatment step in which the surface free energy of the porous sheet is 15 mN / m or more.

6. In a battery that has multiple cells inside the casing, A battery characterized in that it is provided with a fire-spread prevention sheet according to any one of claims 1 to 3 between the cells and between the cells and the housing, at least between the cells.

7. The battery according to claim 6, characterized in that the cell is an all-solid-state battery.

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