Fireproof sheet for lithium ion battery case

Abstract

To provide a fireproof sheet for a lithium ion battery case, capable of coping with reduction in weight and size, and exhibiting excellent properties with respect to heat insulation and heat resistance against a high-temperature heat source such as flame, and impact resistance against ejecta even in the case where flame or neighboring cells of the high-temperature occur like the case where a lithium ion battery is in a thermal runaway, and / or where objects such as debris due to burst of the battery is scattered at a high-speed.SOLUTION: In a fireproof sheet for a lithium ion battery case, having a base material, and a matrix resin, a thickness of the fireproof sheet for the lithium ion battery case is 3 mm or less, the base material is nonwoven fabric of an inorganic fiber, the matrix resin is formed from a phenol resin, a content amount of the matrix resin is 50 to 80 weight% based on the whole fireproof sheet for the lithium ion battery case.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a refractory sheet for a lithium ion battery case.

Background Art

[0002] A lithium ion battery (hereinafter sometimes referred to as "lithium ion battery" or "LIB") has a high energy density and is widely used as a power source for portable electronic devices such as digital cameras, mobile phones, and notebook personal computers. In recent years, in order to address global warming, lithium ion secondary batteries are being adopted as all or part of the energy source in the fields of transportation such as automobiles and railways, which conventionally used fossil fuels as the energy source.

[0003] On the other hand, since a flammable organic electrolyte is currently used for LIB, for example, it is known that when a short circuit of the electrode occurs for some reason, thermal runaway occurs in which the temperature rises rapidly. When thermal runaway occurs and it becomes uncontrollable, there is a risk that the battery will rupture and its fragments will scatter, or a high-temperature flame will occur. In addition, when LIB is composed of a plurality of cells such as a battery module, if thermal runaway occurs in one cell, there is a possibility that it will spread to other adjacent cells and cause thermal runaway. Therefore, even when thermal runaway occurs in LIB and the battery ruptures or catches fire, it is required to suppress the spread of fire and the scattering of fragments.

[0004] As a countermeasure, Patent Document 1 proposes a thermal runaway suppression refractory sheet that can prevent the spread of fire to other adjacent single cells when one cell of LIB thermally runs away and catches fire. This refractory sheet includes a base material containing glass fiber, heat-resistant fiber, and binder fiber and an inorganic particle layer, and the retention of the inorganic particle layer is ensured by the base material containing three specific fiber types, and it is said that the fire resistance of the inorganic particle layer and the effect of suppressing the thermal shrinkage of the sheet can be obtained.

[0005] Patent Document 2 describes a fiber-reinforced plastic in which a phenolic resin is supported on a base fabric woven from mineral fiber yarns, and the mineral fiber is contained at a ratio exceeding 65% by mass and less than 85% by mass. This fiber-reinforced plastic is excellent in flame retardancy and is described as being applicable to members arranged in the engine room of an automobile, such as a battery case (container) and a battery cover (lid).

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] According to the fireproof sheet described in Patent Document 1, it is considered that it is possible to some extent to prevent the spread of fire to other adjacent single cells in a LIB, but the heat insulation and heat resistance when in contact with a high-temperature flame or an adjacent cell that has become high-temperature due to the thermal runaway of the LIB are not necessarily high, and there is room for improvement. The fiber-reinforced plastic described in Patent Document 2 is considered to have a certain degree of flame retardancy, but it cannot necessarily be said that it is sufficient to cope with the thermal runaway of the LIB, and there is room for improvement especially in terms of heat insulation and heat resistance when in contact with a high-temperature heat source. In addition, not only in portable electronic devices but also in transportation equipment, there is a demand for dealing with the weight reduction and miniaturization of lithium-ion batteries. However, the fiber-reinforced plastic described in Patent Document 2 has a high content of mineral fiber, and there is also room for improvement in dealing with weight reduction.

[0008] Therefore, an object of the present invention is to provide a refractory sheet for a lithium-ion battery case that has good heat insulation and heat resistance against high-temperature heat sources such as flames and impact resistance against ejected objects even when a lithium-ion battery undergoes thermal runaway, resulting in high-temperature flames or adjacent cells, or when objects such as fragments due to battery rupture scatter at high speed, and is capable of corresponding to weight reduction and miniaturization.

Means for Solving the Problems

[0009] In order to solve the above-mentioned problems, the present inventor conducted intensive studies. As a result, it was found that by using a non-woven fabric of inorganic fibers as a base material and combining it with a matrix resin composed of the base material and a phenolic resin to form a refractory sheet with a predetermined thickness, and setting the content of the matrix resin to 50 to 80% by weight based on the entire refractory sheet, the above-mentioned problems can be solved. The present invention includes the following [1] to [6].

[0010] [1] In a refractory sheet for a lithium-ion battery case including a base material and a matrix resin, the thickness of the refractory sheet for the lithium-ion battery case is 3 mm or less, the base material is a non-woven fabric of inorganic fibers, the matrix resin is composed of a phenolic resin, and the content of the matrix resin is 50 to 80% by weight based on the entire refractory sheet for the lithium-ion battery case. [2] The refractory sheet for a lithium-ion battery case according to the above item [1], wherein the single fibers of the inorganic fibers are coated with the matrix resin. [3] The refractory sheet for a lithium-ion battery case according to the above item [1] or [2], wherein the average fiber spacing between the single fibers of the inorganic fibers in the matrix resin is 10 μm or more. [4] The refractory sheet for a lithium-ion battery case according to the above item [1] or [2], wherein the temperature of the anti-flame surface when a 1200°C flame is applied indirectly to one surface of the refractory sheet for 10 seconds is 400°C or less. [5] The base material has a plurality of non-woven fabrics made of inorganic fibers, The refractory sheet for a lithium-ion battery case according to the preceding item [1] or [2], comprising a laminate of a plurality of the non-woven fabrics and a matrix resin. [6] The refractory sheet for a lithium-ion battery case according to the preceding item [1] or [2], which is a cured product of a prepreg obtained by impregnating the non-woven fabric with a matrix resin.

[0011] In addition, in the embodiment of the preceding item [1], each configuration in the preceding items [2] to [6] can be arbitrarily combined and applied.

Effects of the Invention

[0012] According to the present invention, even when a high-temperature flame or an adjacent cell occurs, for example, when a lithium-ion battery undergoes thermal runaway, or when an object such as a fragment due to battery rupture scatters at high speed, the heat insulation and heat resistance against a high-temperature heat source such as a flame and the impact resistance against ejected matter are good, and a refractory sheet for a lithium-ion battery case capable of coping with weight reduction and miniaturization can be provided.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Figure 15

Figure 16

Figure 17

Figure 18

Figure 19

Figure 20

Figure 21

Embodiments for Carrying Out the Invention

[0014] The refractory sheet for a lithium-ion battery case according to an embodiment of the present invention (hereinafter, may be simply referred to as "refractory sheet") includes a base material and a matrix resin. The base material is a non-woven fabric of inorganic fibers. The matrix resin is made of a phenolic resin. The content of the matrix resin is 50 to 80% by weight based on the whole refractory sheet. The thickness of the refractory sheet is 3 mm or less.

[0015] Thus, due to the high content rate of the matrix resin made of phenolic resin in the whole refractory sheet, it is considered that many parts where each single fiber of the inorganic fibers constituting the non-woven fabric is covered with the matrix resin account for a large proportion. Therefore, for example, when the LIB runs away, the inorganic fibers are protected by the matrix resin from a high-temperature heat source, and it is considered that the high-temperature rise of the refractory sheet caused by the inorganic fibers having a higher thermal conductivity than the matrix resin is suppressed and the heat insulation property is improved.

[0016] In addition, the phenolic resin constituting the matrix resin generates decomposition gas when exposed to high temperature. That is, when the refractory sheet is exposed to high temperature, the phenolic resin decomposes and decomposition gas is generated, resulting in the formation of a large number of voids having a size of 100 μm or more in a predetermined cross-section in the matrix resin. And, combined with the above-described action and effect of the matrix resin contained in the refractory sheet at a high content rate, it is considered that the heat insulation property of the refractory sheet is further improved by these voids.

[0017] Furthermore, it is considered that the binding force between single fibers in the nonwoven fabric is smaller compared to that in woven fabrics and the like. Therefore, for example, when high-speed flying objects such as ejecta from a runaway LIB collide with the refractory sheet, the single fibers coated with the matrix resin can easily deform along with the deformation of the entire refractory sheet while maintaining a certain binding force to the matrix resin within the matrix resin as a whole nonwoven fabric. As a result, even when subjected to the impact of the aforementioned flying objects, it is possible to absorb the impact in the vicinity including the collision point of the flying object or the entire nonwoven fabric as the base material, and it is considered that the impact resistance is improved.

[0018] From the above, it is considered that even with a thickness of 3 mm or less, excellent impact absorbency against, for example, ejecta from a runaway LIB and excellent heat insulation against a high-temperature heat source such as a flame can be exhibited.

[0019] Furthermore, since the matrix resin is made of a phenolic resin, the heat loss against a particularly high-temperature flame is small. Coupled with the mechanism of action for improving the aforementioned heat insulation and impact resistance, the decrease in strength is suppressed even at high temperatures, that is, it is considered that the heat resistance is also improved.

[0020] The inorganic fibers constituting the nonwoven fabric, which is a base material usable in the embodiments of the present invention, are not particularly limited and may be either natural inorganic fibers or artificial inorganic fibers. However, from the viewpoint of ease of obtaining the nonwoven fabric, artificial inorganic fibers are preferred, and artificial mineral fibers are more preferred. Examples of artificial mineral fibers include glass fibers, basalt fibers, ceramic fibers, rock wool, slag wool, polycrystalline fibers, non-bio-persistent fibers, alumina fibers, silica fibers, silicon carbide fibers, boron silicate fibers, and the like. The inorganic fibers may be used alone or in combination of two or more. From the viewpoint of cost, glass fibers are preferred as artificial mineral fibers. Examples of glass fibers include E glass fibers, S glass fibers, R glass fibers, ECR glass fibers, C glass fibers, AR glass fibers, and the like. Among these, E glass fibers are preferred from the viewpoints of cost and availability of a wide variety of types.

[0021] The form of the inorganic fibers used for the nonwoven fabric is not particularly limited, and those generally used in the production of nonwoven fabrics can be used. For example, monofilaments (single fibers), or multifilaments or spun yarns that are bundles of single fibers can be mentioned. Also, the fiber diameter of the single fibers of the inorganic fibers and the thickness of the multifilaments and spun yarns can be appropriately determined in consideration of the impregnability of the matrix resin, the strength of the nonwoven fabric base material, and the working efficiency in the resin impregnation process. The length of the inorganic fibers is not particularly limited, but from the viewpoint of ease of obtaining the base material, 1 to 100 mm is preferred.

[0022] As the nonwoven fabric constituting the base material, those obtained by various conventional manufacturing methods can be used. For example, a web (also referred to as a fleece) obtained by a conventional method can be used as it is, or a web in which the fibers are bonded by a conventional method as needed can be used. Examples of the web manufacturing method include a dry method, a wet method (wet papermaking method), a spunbond method, a meltblown method, an airlaid method, and the like. Examples of the fiber bonding method of the web include a chemical bond method, a thermal bond method, a needle punch method, a hydroentangling method, a stitch bond method, and the like. Among these, from the viewpoint of achieving better integration with the matrix resin, a nonwoven fabric in which the fibers of the web are bonded by the needle punch method is preferable. In the case of such a nonwoven fabric by needle punching, compared with other nonwoven fabrics and woven fabrics, the matrix resin is easily impregnated, and the inorganic fibers are intertwined at pinpoint, so that almost the entire surface of the single fiber of the inorganic fiber is in contact with the matrix resin, and it is considered that the reinforcing effect of the inorganic fiber is maximally exerted.

[0023] The thickness of the nonwoven fabric as the base material may be such that the thickness of the refractory sheet is 3 mm or less, and can be appropriately determined according to the characteristics of the refractory sheet, the thickness, the number of layers of the base material, and the like. From the viewpoint of uniformly impregnating the nonwoven fabric base material with the matrix resin, the thickness as the raw nonwoven fabric is preferably 10 mm or less. Also, from the viewpoint of reducing the number of layers in the case of laminating, 1 mm or more is preferable.

[0024] The basis weight of the base material (nonwoven fabric) can be appropriately determined in consideration of the impregnability of the matrix resin and the like. For example, it can be 20 to 3000 g / m 2 From the viewpoints of tensile strength and maintaining uniformity when impregnating the resin of the refractory sheet, 100 to 1000 g / m 2 is preferable.

[0025] The nonwoven fabric constituting the base material or the inorganic fibers constituting the nonwoven fabric may be surface-treated or untreated. Examples of surface treatment include silane coupling treatment, titanium coupling treatment, plasma coating treatment, etc. from the viewpoint of improving the adhesion to the matrix resin and further enhancing the reinforcing effect, and coating treatment with inorganic particles, etc. from the viewpoint of improving fire resistance. When coating the surface with inorganic particles, for example, as described in JP-A-2021-96935, it can be constituted by a layer containing inorganic particles and an inorganic binder. Examples of inorganic particles include silicon oxides such as amorphous silica, alumina such as α-alumina and γ-alumina; alumina hydrates such as boehmite; aluminum oxides and their hydrates such as diaspore and gypsum, alumina-silica composite oxides, clay minerals such as kaolin, fired kaolin, talc, natural mica, synthetic mica, barium titanate, magnesium hydroxide, calcium hydroxide, dihydrate gypsum, and calcium aluminoxide, calcium carbonate, magnesium carbonate, barium carbonate, titanium dioxide, etc.

[0026] The number of layers of the base material can be appropriately determined according to the characteristics, thickness, etc. of the refractory sheet, and it may be a single layer or a multi-layer of two or more layers. When laminating, from the viewpoint of the processability of the molded body, the number of layers is preferably 2 to 10. The nonwoven fabrics used for laminating may be the same, or nonwoven fabrics with different fiber diameters, thicknesses, basis weights, etc. may be combined. In addition to nonwoven fabrics, woven or knitted fabrics of inorganic fibers may be further combined as the base material. Also, when forming a refractory sheet using a prepreg as described later, a cloth such as a nonwoven fabric, a woven fabric, or a knitted fabric may be laminated on one or both surfaces of the prepreg to form a refractory sheet, or the cloth may be provided on one or both surfaces of the laminate of the prepreg to form a refractory sheet.

[0027] The matrix resin in the refractory sheet is made of a phenolic resin. Since the matrix resin is made of a phenolic resin, impregnation between the single fibers constituting the base material (non-woven fabric) is good, and the content rate of the matrix resin in the refractory sheet can be easily set to a high content rate within a predetermined range, and appropriate heat insulation, heat resistance, and impact resistance based on the properties of the phenolic resin can be imparted to the flame. For example, since the phenolic resin has a high char residue rate after combustion, a refractory sheet excellent in the performance of maintaining the product shape can be provided even after the refractory sheet is exposed to high heat. In addition, the phenolic resin is easily available and advantageous in terms of cost.

[0028] The matrix resin is preferably a phenolic resin, but may further contain other curable resins. Alternatively, the phenolic resin may be replaced with other curable resins. Examples of such other curable resins include thermosetting polyimide, melamine resin, urea resin, silicone resin, furan resin, benzoxazine resin, and the like. The other curable resins may be used alone or in combination of two or more. The content rate of the phenolic resin is preferably 50% by mass or more in the whole matrix resin.

[0029] The phenolic resin that can be used as the matrix resin may be a reaction product of phenols and aldehydes, and known ones can be adopted. The phenols are not particularly limited, and examples include alkylphenols (such as cresol and xylenol), polyhydric phenols (such as resorcin), phenylphenol, aminophenol, and the like. Also, the aldehydes are not particularly limited, and examples include formaldehyde, paraformaldehyde, acetaldehyde, furfural, and the like. Further, the phenolic resin may be either a resol type or a novolak type. A modified phenolic resin may also be used. From the viewpoint of ease of impregnation into the base material, a resol type phenolic resin is preferable. The phenolic resin may be used alone or in combination of two or more.

[0030] Examples of novolak-type phenolic resins include cresol novolak resins and bisphenol A-type novolak resins. Examples of resol-type phenolic resins include methylol-type resol resins, dimethylene ether-type resol resins, and the like. Examples of modified phenolic resins include arylalkylene-type phenolic resins, and more specifically, phenol-aralkyl resins and the like.

[0031] The phenolic resin may optionally contain a curing agent. For example, in the case of novolak-type phenolic resins or arylalkylene-type phenolic resins, hexamethylenetetramine can usually be preferably used.

[0032] The matrix resin may optionally contain, in addition to the aforementioned curing agent for phenolic resins, a curing agent applicable thereto when containing a resin other than the phenolic resin, and other additives. Examples of such additives include flame retardants, inorganic fillers, ultraviolet absorbers, antioxidants, dyes, pigments, foaming agents, and the like.

[0033] The flame retardant is not particularly limited, and examples thereof include brominated flame retardants, phosphorus-based flame retardants, hydrated metal compound-based flame retardants, silicone-based flame retardants, nitrogen-containing compounds, hindered amine compounds, organometallic compounds, and aromatic enamels. These may be used alone or in combination of two or more.

[0034] The inorganic filler is not particularly limited, and examples thereof include silica such as fused crushed silica, fused spherical silica, crystalline silica, secondary aggregated silica, and fine powder silica, metal compounds such as alumina, silicon nitride, aluminum nitride, boron nitride, titanium oxide, silicon carbide, aluminum hydroxide, magnesium hydroxide, and titanium white, inorganic minerals such as glass bubbles, kaolin clay, talc, mica, calcium carbonate, wollastonite, montmorillonite, smectite, bentonite, and sepiolite, and the like. These may be used alone or in combination of two or more.

[0035] The phenolic resin and other resins that make up the matrix resin can be prepared according to established methods, but commercially available ones can also be used.

[0036] The refractory sheet includes the base material and a matrix resin composed of the phenolic resin. The matrix resin is in a state of impregnating the base material. By setting the content rate of the matrix resin in the refractory sheet to a high content rate within a predetermined range, in many parts of the nonwoven fabric serving as the base material, the matrix resin is in a state of impregnating between the single fibers of the inorganic fibers constituting the nonwoven fabric. That is, it is considered that many parts of the single fibers of the inorganic fibers constituting the nonwoven fabric are covered with the matrix resin. Further, as the impregnated state, it is preferable that each single fiber of the inorganic fibers is covered with the matrix resin in the entire nonwoven fabric by the matrix resin impregnating between the single fibers. Whether or not the single fiber is covered with the matrix resin can be confirmed by observing a microscopic image of a cross section in the thickness direction at a predetermined position of the refractory sheet. The position of the cross section to be observed may be one place, but it is preferably performed at two or more places.

[0037] Also, the degree of impregnation of the matrix resin between the single fibers can be indicated by the fiber-to-fiber distance of the single fibers in the above-mentioned microscopic image. Here, the fiber-to-fiber distance means the length of a line segment connecting the closest contact points of the surfaces of each single fiber and the surface of the single fiber adjacent to the single fiber in the above-mentioned microscopic image. This fiber-to-fiber distance is preferably, for example, the average value of the fiber-to-fiber distances of each single fiber in the entire cross-sectional observation image of the above-mentioned microscopic image, that is, the average fiber-to-fiber distance. When the position of the cross section to be observed is two or more places, it is preferable to use the average value of the average fiber-to-fiber distances as the average fiber-to-fiber distance. And when the average fiber-to-fiber distance is 10 μm or more, substantially the entire single fibers in the nonwoven fabric are covered with the matrix resin, and it is preferable in terms of excellent heat insulation, heat resistance, and impact resistance. In addition, from the viewpoint of the fiber reinforcement efficiency, the average fiber-to-fiber distance is preferably 50 μm or less. This average fiber-to-fiber distance can be calculated by the method described in the column of the examples described later.

[0038] The refractory sheet may be any one provided with the base material and a matrix resin made of the phenolic resin, but it is preferably a cured product of a prepreg in which the base material is impregnated with the matrix resin. This cured product can be manufactured, for example, using a prepreg obtained by a wet method as follows, but is not limited thereto, and can also be manufactured using a prepreg obtained by a hot melt method or spray coating.

[0039] First, a matrix resin, additives added as necessary, and a solvent are mixed to prepare a varnish of the matrix resin. The solvent applicable to the varnish is not particularly limited, and those used for preparing this type of varnish can be used. For example, water, organic solvents, etc. can be mentioned. As the organic solvent, it may be water-soluble or water-insoluble, but a water-soluble organic solvent is preferred. Examples of the water-soluble organic solvent include monohydric alcohols having 1 to 3 carbon atoms, acetone, and cyclic ethers such as tetrahydrofuran.

[0040] Next, after impregnating the base material with this varnish, it is dried / solidified to obtain a prepreg in which the base material is impregnated with the matrix resin. By drying, volatile components such as the solvent are vaporized and solid components such as the matrix resin are solidified. The impregnation rate (RC) of the matrix resin with respect to the base material is not particularly limited, but is preferably 50 to 90% based on the solid content. This impregnation rate can be controlled, for example, by adjusting the roll interval when passing the varnish-impregnated base material between two rolls.

[0041] Next, the prepreg is heat-treated to cure the prepolymer of the matrix resin, thereby obtaining a refractory sheet as a cured product of the prepreg. When forming a laminate of the matrix resin and a non-woven fabric which is a plurality of base materials, by laminating and heat-treating the obtained plurality of prepregs, a laminate of the matrix resin and the base material, that is, a refractory sheet is obtained as a laminated cured product of the prepregs. Note that the above heat treatment may be performed under pressure. When performing the heat treatment under pressure, for example, it can be molded using a heatable press machine. When molding into a predetermined shape, it can be molded using a press machine with a corresponding mold.

[0042] From the viewpoints of impact resistance and heat insulation, the content of the matrix resin in the refractory sheet is preferably 50 to 80% by weight.

[0043] From the viewpoints of weight reduction and miniaturization of the LIB case, the thickness of the refractory sheet is 3 mm or less, and from the viewpoints of impact resistance, heat insulation, and heat resistance, it is preferably 0.2 mm or more.

[0044] The refractory sheet is configured as described above, so that it has good heat resistance and impact resistance, and is particularly excellent in heat insulation, and is suitable for use as an LIB case.

[0045] When the refractory sheet is used for an LIB case, it may be provided on the inner wall surface of the case that houses the LIB, or may be provided between the cells of the LIB. The refractory sheet can be made into an arbitrary shape according to the shape of the inner wall surface of the LIB case and the arrangement of the cells of the LIB in this way. And even when the LIB undergoes thermal runaway and the battery ruptures or catches fire, the refractory sheet can suppress the spread of fire outside the case and the scattering of fragments. When it is provided between the cells of the LIB, it is possible to suppress the spread of fire to adjacent cells.

Examples

[0046] Hereinafter, embodiments of the present invention will be described in detail based on examples.

[0047] (Example 1) 50 parts by weight of a resol-type phenol resin and 50 parts by weight of methanol were mixed to prepare a phenol resin varnish. Using nonwoven fabric 1 having the characteristics shown in Table 1 as a base material, after immersing nonwoven fabric 1 in the varnish, the varnish was passed between squeezing rolls to impregnate nonwoven fabric 1 with the varnish. Then, it was dried at room temperature for 24 hours or more to obtain a prepreg. The prepreg was cut into a size of 250 mm × 300 mm, and this was subjected to a heat and pressure treatment at 160°C, 5 MPa, and 10 min using a press machine without installing a spacer between the press platens to obtain a molded body (refractory sheet) which is a cured product of a single layer (single-layer base material) of the prepreg. The characteristics of the obtained molded body were measured, and the results are shown in Table 2. Also, evaluations described later were performed using the obtained molded body.

[0048] (Example 2) A molded body (refractory sheet) which is a cured product of a single layer (single-layer base material) of a prepreg having a smaller apparent specific gravity and a larger fiber distance than Example 1 was obtained in the same manner as in Example 1 except that a spacer having a thickness of 2.4 mm was installed between the press platens during the heat and pressure treatment and the heat and pressure treatment was performed at 160°C for 10 min. The characteristics of the obtained molded body were measured, and the results are shown in Table 2. Also, evaluations described later were performed using the obtained molded body.

[0049] (Example 3) A prepreg was obtained in the same manner as in Example 1 except that nonwoven fabric 2 having the characteristics shown in Table 1 was used as the base material. The prepreg was cut into a size of 250 mm × 300 mm and stacked in 4 layers, and a molded body (refractory sheet) which is a cured product of 4 layers (4-layer base material) of the prepreg was obtained by performing a heat and pressure treatment at 160°C, 5 MPa, and 10 min using a press machine without installing a spacer between the press platens. The characteristics of the obtained molded body were measured, and the results are shown in Table 2. Also, evaluations described later were performed using the obtained molded body.

[0050] (Comparative Example 1) A molded article (refractory sheet), which is a cured product of a single layer (single-layer base material) of a prepreg with a low resin content, was obtained in the same manner as in Example 1, except that 20 parts by weight of a resol-type phenol resin and 80 parts by weight of methanol were mixed to prepare a phenol resin varnish. The properties of the obtained molded article were measured, and the results are shown in Table 2. Also, the evaluation described later was performed using the obtained molded article.

[0051] (Comparative Example 2) A prepreg was prepared in the same manner as in Example 1 using a fabric having the properties shown in Table 1 as the base material. A molded article (refractory sheet), which is a cured product of three layers (three-layer base material) of the prepreg, was obtained in the same manner as in Example 1, except that three layers of the prepreg were stacked. The properties of the obtained molded article were measured, and the results are shown in Table 2. Also, the evaluation described later was performed using the obtained molded article.

[0052] (Comparative Example 3) Instead of the phenol resin, 68.1 parts by weight of an epoxy resin (manufactured by DIC Corporation, EPICLON 1051-75M), 1.84 parts by weight of a curing agent (manufactured by Tokyo Chemical Industry Co., Ltd., dicyandiamide), 0.06 parts by weight of a curing accelerator (manufactured by Shikoku Kasei Co., Ltd., imidazole-based Curezol C11Z), and 30.0 parts by weight of acetone were mixed, and a molded article, which is a cured product of a single layer (single-layer base material) of a prepreg, was obtained in the same manner as in Example 1 using the epoxy resin varnish. In the same manner as in Example 1, the properties of the obtained molded article were measured and evaluated.

[0053] (Measurement of Properties of Molded Article) (Measurement of Thickness of Molded Article) The thickness of the obtained molded article was measured at four locations using a micrometer (manufactured by Mitutoyo Corporation, outside micrometer M220-15 (101-227)), and the average value was taken as the thickness of the molded article. The results are shown in Table 2.

[0054] (Measurement of Resin Content of Molded Article) The weights were measured using the base material (fabric) as a raw material, the prepregs and molded articles prepared in each Example and Comparative Example, and the resin content (RC) was calculated from the following formula. The results are shown in Table 2. Resin content (RC) = (M1 - S1 - B1) / (M1 - S1) × 100 (%) M1: In a molded body obtained by laminating and hot-pressing a 250 mm × 300 mm prepreg, the weight including the resin burr that has melted and flowed out S1: The weight of the resin burr that has flowed out from the 250 mm × 300 mm molded body obtained by hot-pressing B1: The total weight of the 250 mm × 300 mm raw material base materials of the number of laminations of the molded body

[0055] <Measurement of average fiber spacing> (1) Preparation of observation sample A 30 mm × 30 mm test piece was cut out from the obtained molded body, embedded in an epoxy resin (manufactured by Mitsui Chemicals, Inc., Zero Mer S), cut in the thickness direction of the molded body, and the cut surface was polished using a polishing machine (manufactured by Mitsui Chemicals, Inc., Sample Polisher KIRIME 300) to prepare an observation sample with a polished surface for observation. The polishing conditions are as follows. Water-resistant abrasive papers with grit sizes #80, #320, and #2000 were used, and wet polishing was performed at a rotational speed of 100 rpm for 3 minutes each in this order of grit sizes, and then buff polishing was performed at a rotational speed of 100 rpm for 10 minutes using an alumina slurry (particle size 3 μm). (2) Microscopic observation Regarding the polished surface for observation of the test piece of the obtained observation sample, using a scanning electron microscope (manufactured by Hitachi High-Technologies Corporation, S-3400N), the impregnation state of the resin between single fibers was observed for the image in the cross-sectional direction of the single fiber of the inorganic fiber. The observation conditions were an acceleration voltage of 15 kV, a backscattered electron composite image, and a magnification of 300 times. (3) Image processing Regarding the imaging obtained by microscopic observation, binarization processing was performed using an automatic image processing and analysis device (manufactured by Nireco Corporation, LUZEX AP), and the fiber spacing between adjacent single fibers in the cross-sectional image in the cross-sectional direction of the inorganic fiber was measured using the software equipped with the device, and the average value thereof was obtained as the average single fiber spacing. The representative images used for calculating the average fiber spacing in Examples 1 to 3 and Comparative Examples 1 to 3 are shown in FIGS. 1 to 6. For calculating the average fiber spacing, the entire images in FIGS. 1 to 6 (excluding the parts where the measurement conditions and scales are described) were taken as the objects of calculation. In the images in FIGS. 1 to 6, the white parts are the single fibers of the inorganic fibers, and the black parts are the matrix resins. The calculation results are shown in Table 2. The measurement was performed on cross-sections at three different locations to calculate each average fiber spacing, and their average value was shown in Table 2 as the average fiber spacing.

[0056] <Apparent density> A test piece with a size of 50 mm × 50 mm was cut out from the obtained molded body, and the apparent density was measured. The cut surface of the test piece was smoothed with #1000 water-resistant abrasive paper. The volume V of the test piece was determined from the values measured for the length, width, and thickness of the test piece with a digital caliper. Next, the mass M of the cut-out test piece was precisely weighed with an electronic balance. The above operations were repeated three times, and the volume V and mass M were measured for each of the three test pieces, and the density D = (M / V) (kg / m 3 ) was calculated, and the average value thereof was taken as the apparent density.

[0057] (Evaluation of the molded body (refractory sheet)) <Heat insulation property (1)> Using the flame irradiation test apparatus 1 schematically shown in Fig. 7, the heat insulation properties (heat insulation property (1)) of the molded bodies obtained in Examples 1 to 3 and Comparative Examples 1 to 3 against a high-temperature flame were evaluated. The test apparatus 1 shown in Fig. 7 has a gas burner 2 and a fixing jig 5 schematically shown in Fig. 8, and a test piece 4 of the molded body is fixed to the fixing jig 5. As shown in Figs. 7 and 8, the fixing jig 5 has a test piece 4 (35 mm × 50 mm × each thickness) installed between a flame-facing side fixing plate 6 (70 mm × 40 mm × 12 mm) and a counter-flame-facing side fixing plate 9 (70 mm × 40 mm × 8 mm) facing the former, and the two fixing plates 6 and 9 are tightened with four sets of bolts 14 and nuts 15 provided at the four corners to grip and fix the test piece 4 between the two fixing plates 6 and 9. In order to directly apply the flame 3 irradiated from the gas burner 2 to the flame-facing side surface of the test piece 4, a through hole 7 (φ20 mm) through which the flame-facing side and the counter-flame-facing side of the fixing plate 6 communicate is provided. Further, in order to measure the temperature of the flame-facing side surface of the test piece 4 with a flame-facing side K thermocouple 12, a temperature measuring through hole 8 (φ3.5 mm) through which the wall surface forming the through hole 7 and the side surface of the fixing plate 6 communicate is provided. Similarly to the flame-facing side fixing plate 6, the counter-flame-facing side fixing plate 9 is provided with a through hole 10 (φ16 mm) provided concentrically with the through hole 7 and a temperature measuring through hole 11 (φ3.5 mm) for installing a counter-flame-facing side K thermocouple 13. The counter-flame-facing side K thermocouple 13 measures the temperature of the counter-flame-facing side surface of the test piece 4. The materials of the fixing plates 6 and 9 are S45C. The distance between the flame outlet of the gas burner 2 and the center of the through hole 7 on the flame-facing side surface of the flame-facing side fixing plate 6 is 100 mm as shown in Fig. 7. The gas burner used was a Coleman Japan Co., Ltd. Sword Gas 206 Auto (liquefied butane / liquefied propane), and the gas volume was maximized. For the evaluation of the heat insulation property, using the test apparatus 1 shown in Figs. 7 and 8, the flame was irradiated for 10 seconds, and the temperature on the flame-facing side and the temperature on the counter-flame-facing side of the test piece 4 during irradiation were measured. When the temperature on the counter-flame-facing side was 400°C or lower, it was evaluated that the heat insulation property (1) was good. For the test pieces after heating, in the same manner as in the case of "measurement of average fiber spacing", observation samples were prepared, microscopic observation was carried out, and their cross-sections were photographed to confirm the presence or absence of void generation. Each imaging is shown in FIGS. 9 to 14. The magnification under the observation conditions of the electron microscope was 50 times. In the imaging of FIGS. 9 to 14, the white part is the single fiber of the inorganic fiber, and the gray part is the matrix resin. Also, in the imaging of FIGS. 9 to 11, 13, and 14, the long and thin black part is the void. Regarding FIG. 13, long and thin voids are formed within the portion surrounded by the ellipse.

[0058] <Heat insulation property (2)> In order to evaluate the heat insulation property (heat insulation property (2)) of the molded bodies obtained in Examples 1 to 3 and Comparative Examples 1 to 3 against a high-temperature heat source in contact other than the flame, the following tests were conducted. First, a 50 mm × 50 mm test sample was cut out from each molded body, and a K thermocouple was fixed to the center of one surface thereof with a glass cloth tape (manufactured by 3M Japan Ltd.). With the surface attached with the thermocouple facing upward, each test sample was placed on a hot plate (manufactured by MSA Factory Co., Ltd., high-temperature hot plate PA8010) heated to 500°C so that the unattached surface was in contact. The temperatures 10 seconds and 30 seconds after installation were measured, and when the temperature 10 seconds after installation was 100°C or lower and the temperature 30 seconds after installation was 200°C or lower, the heat insulation property (2) was evaluated as good. Also, in the same manner as in the test of "heat insulation property (1)", the presence or absence of void generation was confirmed. Representative images 5 minutes after installation are shown in FIGS. 15 to 20. In the imaging of FIGS. 15 to 20, the white part is the single fiber of the inorganic fiber, and the gray part is the matrix resin. Also, in the imaging of FIGS. 15 to 17, 19, and 20, the long and thin black part is the void. Regarding FIG. 19, long and thin voids are formed within the portion surrounded by the ellipse.

[0059] <Heat resistance> After the evaluation test of the aforementioned "heat insulation property" was completed and for each test piece that had not been tested, the breaking strength of the test piece was measured using an autograph (Autograph AG-Xplus, manufactured by Shimadzu Corporation) equipped with the measuring jig 20 schematically shown in Fig. 21. The measuring jig 20 schematically shown in Fig. 21 has a movable-side pushing tool 21 and a fixed-side receiving jig 23. In the movable-side pushing tool 21, the hemispherical portion of a steel ball 22 with a diameter of φ10 mm protrudes toward the fixed-side receiving jig 23. The fixed-side receiving jig 23 has a fixed base 24 and a ring-shaped test piece fixture 25 (outer diameter 70 mm × inner diameter 30 mm) having a through hole 26 fixed to the movable-side pushing tool 21 side. On the movable-side pushing tool 21 side of the test piece fixture 25, a ring-shaped flat surface for installing the test piece 4 is provided. The measurement of the breaking strength was performed as follows using the measuring jig 20 shown in Fig. 21. First, the test piece 4 was installed on the movable-side pushing tool 21 side of the test piece fixture 25 of the fixed-side receiving jig 23. When using the test piece after the evaluation test, it was installed so that the center of the flame irradiation portion generally coincided with the center of the through hole 26. Next, the movable-side pushing tool 21 was operated toward the fixed-side receiving jig 23 at a speed of 10 mm / min (in the direction of the arrow in Fig. 21(b)), the steel ball with a diameter of φ10 mm was pressed against the test piece 4 at a speed of 10 mm / min, and the test force at the time of fracture was measured respectively. From the measurement results of both, the strength change rate represented by the following formula was calculated, and when the change rate was 20% or less, it was evaluated that the heat resistance was good. Strength change rate (%) = (1 - test force after the heat insulation test / test force of the untested specimen) × 100

[0060] <Penetration resistance of flying objects> Test pieces (100 mm × 100 mm × each thickness) of the molded bodies obtained in Examples 1 to 3 and Comparative Examples 1 to 3 were placed on a hot plate (high-temperature hot plate PA8010, manufactured by MSA Factory Co., Ltd.) heated to 500°C for 5 minutes for heat treatment. Immediately after the heat treatment was completed, a blast test was performed as follows. The test piece immediately after heating was placed on one open end face of a steel square pipe (with an outer dimension of 100 mm square, an inner dimension of 90 mm square, and a height of 100 mm) that is open at both ends in the height direction, such that the four sides of the test piece coincide with the four sides of the open end face of the square pipe. A blast test was conducted using a blast processing machine (manufactured by Koji Tekko Co., Ltd., Asco Blast Machine Model BA-2) under the following conditions, and the penetration time until the test piece penetrated was measured. When the penetration time was 50 seconds or more, it was evaluated that the resistance to spatter penetration, i.e., the impact resistance, was good. Set discharge pressure: 0.5 MPa Discharge orifice diameter: φ5 mm Distance from the discharge orifice: 3 mm above the test piece in the vertical direction Discharged material: special steel (polygonal particles, size: 125 - 425 μm)

[0061]

Table 1

[0062]

Table 2

[0063]

Table 3

[0064] As shown in Table 3, it can be seen that the refractory sheets of Examples 1 to 3 are all good in heat insulation (1), (2), heat resistance, and resistance to penetration of flying objects. In particular, the temperature on the flame contact surface exposed to a high-temperature flame was 1254 to 1325 °C, while on the non-flame contact surface on the opposite side with a thickness of only 1.9 to 2.6 mm, it was 234 to 247 °C. Also, even when in contact with a hot plate heated to 500 °C, on the non-contact surface opposite to the contact surface, it reached 65 to 88 °C after 10 seconds and 149 to 180 °C after 30 seconds, indicating that the heat insulation is extremely excellent. Further, as shown in FIGS. 9 to 11 and 15 to 17, it is considered that the heat insulation is further improved due to the formation of voids when the refractory sheets of Examples 1 to 3 are in contact with a high-temperature heat source. In Example 2, as shown in FIG. 2, the formation of voids with a diameter of 20 to 50 μm was observed inside the molded body, and it is considered that the voids contribute to showing higher heat insulation in both heat insulation (1) and heat insulation (2) than in Example 1. On the other hand, Comparative Example 1 with a low content of the matrix resin does not meet the evaluation criteria for all of heat insulation (1), (2), heat resistance, and resistance to penetration of flying objects. Comparative Example 2 with a fabric as the base material meets the evaluation criteria for heat insulation (1), but does not meet the evaluation criteria for heat insulation (2), heat resistance, and resistance to penetration of flying objects. Comparative Example 3 with an epoxy resin as the matrix resin and no phenolic resin does not meet the evaluation criteria for heat insulation (2) and heat resistance although it meets the evaluation criteria for heat insulation (1) and resistance to penetration of flying objects. Therefore, it can be seen that the refractory sheet according to the embodiment of the present invention has particularly excellent heat insulation characteristics and is suitable for use as an LIB case.

Explanation of Signs

[0065] 1 Flame irradiation test apparatus 2 Gas burner 3 Flame 4 Test piece 5, 20 Fixing jig 6 Flame contact side fixing plate 7, 10, 26 Through hole 8, 11 Temperature measurement through hole 9 Non-flame contact side fixing plate 12 Flame contact side K thermocouple 13 Non-flame contact side K thermocouple 14 bolts 15 nuts 21 movable side pusher 22 steel balls 23 jig 24 fixed table 25 test piece fixture

Claims

1. In a refractory sheet for a lithium-ion battery case comprising a base material and a matrix resin, the thickness of the refractory sheet for the lithium-ion battery case is 3 mm or less, the base material is a non-woven fabric of inorganic fibers, the matrix resin is made of a phenolic resin, and the content of the matrix resin is 50 to 80% by weight based on the entire refractory sheet for the lithium-ion battery case. A refractory sheet for a lithium-ion battery case.

2. The refractory sheet for a lithium-ion battery case according to claim 1, wherein the single fibers of the inorganic fibers are coated with the matrix resin.

3. The refractory sheet for a lithium-ion battery case according to claim 1 or 2, wherein the average fiber spacing between the single fibers of the inorganic fibers in the matrix resin is 10 μm or more.

4. The refractory sheet for a lithium-ion battery case according to claim 1 or 2, wherein the temperature of the anti-flame surface when a flame at 1200 °C is applied to one surface of the refractory sheet for 10 seconds is 400 °C or less.

5. the base material has a plurality of non-woven fabrics of inorganic fibers, The refractory sheet for a lithium-ion battery case according to claim 1 or 2, comprising a laminate of the plurality of non-woven fabrics and a matrix resin.

6. The refractory sheet for a lithium-ion battery case according to claim 1 or 2, which is a cured product of a prepreg impregnated with a matrix resin in the non-woven fabric.

Images