Insulation sheets, battery packs

Abstract

The present invention provides an insulating sheet with excellent heat insulation properties and winding processability; and a battery pack equipped with the insulating sheet. [Solution] The heat insulating sheet of the present invention contains inorganic fibers, diatomaceous earth, and sepiolite. The diatomaceous earth content is 30% by mass or more relative to the total amount of inorganic fibers, diatomaceous earth, and sepiolite. The total content of diatomaceous earth and sepiolite is 50 to 90% by mass relative to the total amount of inorganic fibers, diatomaceous earth, and sepiolite, and the heat mass reduction rate when the heat insulating sheet is heated at 450°C for 2 hours is 20% by mass or less.

Description

Technical Field

[0001] The present invention relates to a heat insulation sheet and a battery pack.

Background Art

[0002] High-output and high-capacity rechargeable batteries such as lithium-ion batteries are widely used in mobile devices, tools, automobiles, railways, aircraft, etc. In high-output and high-capacity rechargeable batteries, if a short circuit occurs due to damage or internal impurities, internal energy is instantaneously released as heat. As a result, the deterioration of the battery is accelerated and it may also catch fire. For example, in applications such as automobiles that require a high-capacity power storage, high voltage and high output are required. Therefore, a battery pack (sometimes called a battery pack or an assembly) in which adjacent single cells are packed so that a large number of single cells are stacked is often used. In such a battery pack, there is a concern that a defect in one single cell may affect adjacent single cells. Therefore, in order to prevent a defect in one single cell from affecting adjacent single cells, it has been proposed to dispose a non-combustible heat insulation sheet between the single cells (for example, Patent Documents 1 and 2).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] In addition to excellent heat insulation properties, the heat insulation sheet is also required to be wound up in a roll with a diameter as small as possible (winding processability) in consideration of convenience during transportation and productivity. The present invention provides a heat insulating sheet with excellent heat insulating properties and winding processability; and a battery pack equipped with the heat insulating sheet. [Means for solving the problem]

[0005] The inventors attempted to manufacture a flame-retardant heat-insulating sheet that is excellent in heat insulation and winding processability, as well as in shape conformability that can follow shape changes caused by ignition or heat generation of a single cell, by papermaking a slurry containing inorganic fibers, diatomaceous earth, and sepiolite. However, the slurry containing these materials had high film-forming ability, and water could not escape from between the fibers during papermaking, making it difficult to form a wet web. Furthermore, in the case of heat-insulating sheets obtained from wet webs made from this slurry, powder could fall from the surface of the sheet, resulting in insufficient surface strength and tensile strength. The powder that fell from the sheet could reduce workability during transport and could cause malfunctions or failures if it adhered to production equipment. Therefore, the inventors diligently investigated the mixing ratio of inorganic fibers, diatomaceous earth, and sepiolite, and after resolving these problems, discovered that an insulating sheet with excellent heat insulation properties and winding processability could be obtained, thus completing the present invention.

[0006] The present invention has the following aspects. [1] An insulating sheet comprising inorganic fibers, diatomaceous earth, and sepiolite; wherein the diatomaceous earth content is 30% by mass or more relative to the total amount of the inorganic fibers, diatomaceous earth, and sepiolite; the total content of the diatomaceous earth and sepiolite is 50 to 90% by mass relative to the total amount of the inorganic fibers, diatomaceous earth, and sepiolite; and the thermal mass loss rate when the insulating sheet is heated at 450°C for 2 hours is 20% by mass or less. [2] The thermal insulation sheet according to [1], wherein the mass ratio of diatomaceous earth to sepiolite is 50 / 50 or more. [3] The thermal insulation sheet according to [1] or [2], wherein the fiber diameter of the inorganic fiber is 3 to 13 μm. [4] The basis weight of the insulation sheet is 20 to 500 g / m².2 The insulating sheet according to any one of [1] to [4], wherein the thickness of the insulating sheet is 0.05 to 3 mm. [5] A battery pack comprising: a plurality of stacked single cells; an insulating sheet inserted between the plurality of single cells; and at least one of the insulating sheets being an insulating sheet according to any of [1] to [4]. [Effects of the Invention]

[0007] According to the present invention, an insulating sheet with excellent heat insulation properties and winding processability is provided; and a battery pack equipped with the insulating sheet is provided. [Brief explanation of the drawing]

[0008] [Figure 1] This is a diagram showing an example of a battery pack configuration. [Modes for carrying out the invention]

[0009] In this specification, the "~" symbol indicating a numerical range means that the numbers before and after it are included as the lower and upper limits, respectively. The lower and upper limits of the numerical ranges disclosed herein can be combined in any way to create new numerical ranges.

[0010] <Insulation sheet> The heat insulating sheet of the present invention comprises inorganic fibers, diatomaceous earth, and sepiolite. The heat insulating sheet of the present invention may further contain other components as optional components, insofar as they do not impair the effects of the invention.

[0011] (Inorganic fibers) Examples of the inorganic fibers include glass fibers, carbon fibers, glass wool, rock wool, molten rock fibers such as basalt fibers, ceramic fibers such as alumina fibers, and silicon carbide fibers. Among them, glass fibers and ceramic fibers are preferred. Glass fibers are more preferred because they are inexpensive, have no conductivity, and cause less wear of the cutting blade when cutting the sheet. The inorganic fibers may be used alone or in combination of two or more kinds.

[0012] Examples of the glass fibers include, in addition to general E-glass, high-strength S-glass and acid-resistant C-glass. From the viewpoint of cost, inexpensive E-glass is preferred. The cross-sectional shape of the glass fibers is not particularly limited. For example, circular and flat shapes can be mentioned. When using glass fibers as the inorganic fibers, the glass fibers may be used alone or in combination of two or more kinds.

[0013] The fiber diameter of the inorganic fibers is preferably 3 to 13 μm, more preferably 4 to 10 μm, and even more preferably 5 to 8 μm. When the fiber diameter of the inorganic fibers is equal to or greater than the lower limit value within the above numerical range, it is easy to ensure the force for maintaining the voids between the fibers. Therefore, it is easy to avoid the voids between the fibers being crushed by the capillary force of the adsorbed water due to moisture absorption and water absorption. In addition, it is also easy to avoid the overall thickness of the heat insulation sheet decreasing due to the compression force between the single cells. Therefore, it is possible to suppress the decrease in heat insulation performance due to the decrease in thickness. In addition, it is easy to avoid an increase in the contact points between the fibers and an increase in the heat transfer rate. The fiber diameter is a value calculated as the average value of 100 fibers measured by microscopic observation of the fiber lengths of 100 fibers.

[0014] In addition, according to the World Health Organization (WHO), "WHO inhalable fibers" refer to fibrous substances that are inhaled into the body through respiration and reach the lungs, with a length exceeding 5 μm, a diameter less than 3 μm, and an aspect ratio exceeding 3. Using WHO inhalable fibers raises concerns about health effects and there are also restrictions on their use. Therefore, the fiber diameter of the inorganic fibers is preferably 3 μm or more.

[0015] When the fiber diameter of the inorganic fiber is below the upper limit within the above numerical range, the gaps between the inorganic fibers become narrow, making it difficult for convection within the gaps and the passage of gas to occur, and it becomes easier to obtain a heat insulation effect. Also, since it is easy to secure the contact points and entanglement points between the inorganic fibers, the tensile strength of the entire heat insulation sheet increases, making it easier to handle. In addition, the skin irritation does not become too strong, and it is easy to suppress fluffing and powder dropping during cutting. Also, since the gaps between the fibers do not become excessively large, it is easy to avoid the passage of heated air and the occurrence of convection within the gaps.

[0016] As the inorganic fiber, an inorganic fiber with a fiber diameter of 3 to 13 μm and an inorganic fiber with a fiber diameter exceeding 13 μm may be used in combination. By using a combination of inorganic fibers with different fiber diameters, while obtaining the effect of improving the heat insulation effect and the surface smoothing effect by narrowing the gaps between the inorganic fibers, and the effect of improving the tensile strength by securing the contact points and entanglement points between the inorganic fibers, it may be possible to ensure the thickness of the heat insulation sheet and maintain the gaps between the fibers.

[0017] The fiber length of the inorganic fiber is preferably 1 to 25 mm, more preferably 3 to 20 mm, and even more preferably 5 to 15 mm. When the fiber length of the inorganic fiber is at least the lower limit within the above numerical range, it is easy to ensure the strength during the sheet manufacturing process. When the fiber length of the inorganic fiber is below the upper limit within the above numerical range, there is no occurrence of bundling due to the twisting of the fibers, and it is easy to maintain a good texture (uniformity of thickness and fiber density). The fiber length is a value calculated as the average value of 100 fibers measured by microscopic observation of the fiber lengths of 100 fibers.

[0018] (Diatomaceous earth, Sepiolite) Diatomaceous earth is a porous natural substance mainly composed of silica deposited by diatoms. Diatomaceous earth can be used from various production areas regardless of domestic or foreign production areas. Also, diatomaceous earth may be used alone or in combination of two or more kinds.

[0019] Sepiolite is a type of naturally occurring clay mineral. It is a hydrated magnesium silicate with a unique chain-like particle structure. Sepiolite can be sourced from various locations, both domestically and internationally. Furthermore, sepiolite can be used alone or in combination of two or more types.

[0020] Among sepiolites, it is preferable to select and use β-type sepiolite. Sepiolites are classified into α-type and β-type sepiolite based on their origin. α-type sepiolite is formed by hydrothermal action under high temperature and pressure. α-type sepiolite has a relatively high degree of crystallinity and exhibits a distinct fibrous form with long fibers. α-type sepiolite is sometimes called mountain bark. β-type sepiolite is formed by sedimentation on shallow seabeds and lakebeds. β-type sepiolite has a relatively low degree of crystallinity. β-type sepiolite can take the form of short fibers, massive particles, or clay-like material. β-type sepiolite is more preferable because it contains relatively little crystalline silica (impurity content), which is undesirable from a safety standpoint for the human body.

[0021] Among β-type sepiolites, it is desirable to select and use sepiolite from a source with a low crystalline silica content. Since crystalline silica accelerates the wear of cutting tools when cutting sheets, a lower crystalline silica content is preferable.

[0022] The crystalline silica content can be quantified by comparing the peak intensity of crystalline silica with that of a standard sample using X-ray powder diffraction. The crystalline silica content in the heat insulating sheet is preferably 1% by mass or less, more preferably 0.5% by mass or less, and even more preferably 0.2% by mass or less.

[0023] (optional ingredient) Insulation sheets containing a binder as an optional component are also useful. The binder is used to bind the inorganic fibers together. A suitable binder is one that has binding properties, heat resistance, and low corrosiveness to batteries, electrodes, and wiring. The binder can be either an inorganic binder (excluding sepiolite and diatomaceous earth) or an organic binder. Examples of inorganic binders include various types of inorganic cements and various types of glass. Examples of organic binders include heat-fusible resin powders, heat-fusible resin fibers, resin emulsions, resin solutions, thermosetting resins, and thermoplastic resins. Inorganic binders and organic binders may be used individually or in combination of two or more types.

[0024] Among these, polyvinyl alcohol fibers (PVA fibers) are preferably used due to their excellent binding properties relative to the amount added and their low heat generation. Acrylic resin emulsions are also suitable from the viewpoint of water resistance. Core-sheath type binder fibers, in which the outer layer is made of a low-melting-point resin and the inner layer is made of a high-melting-point resin, are also suitable. In the case of core-sheath type binder fibers, the binder content is calculated as the total amount of resin in the core and the sheath. In addition, para-aramid fibers, aramid pulp, crystalline polyester, liquid crystalline polyester, wood-derived pulp, and grass-derived pulp, which do not have melt-bonding properties but have a high ability to finely fibrillate and entangle, can also be used as organic binders.

[0025] Other optional components include, for example, clay minerals other than sepiolite, fillers other than diatomaceous earth (excluding clay minerals), dispersants, thickeners, flocculants, paper strength improvers, and yield improvers. Other ingredients may be used individually or in combination of two or more.

[0026] Other clay minerals besides sepiolite include, for example, kaolinite, smectite, montmorillonite, sericite, illite, gluconite, chlorite, alpha-type sepiolite, and talc. Other fillers besides diatomaceous earth include, for example, calcium silicate, calcium carbonate, silica aerosol, fumed silica, talc, plastic pigments, hollow glass beads, and shirasu balloons.

[0027] (composition ratio) The diatomaceous earth content is 30% by mass or more relative to the total amount of inorganic fibers, diatomaceous earth, and sepiolite (hereinafter referred to as "total amount (T)"), preferably 30 to 85% by mass, more preferably 35 to 80% by mass, and even more preferably 40 to 70% by mass. If the diatomaceous earth content is above the lower limit of the above numerical range, it is easier to obtain an insulating sheet with excellent heat insulation properties and winding processability. If the diatomaceous earth content is below the upper limit of the above numerical range, it is easier to obtain an insulating sheet with excellent surface strength and tensile strength.

[0028] The total content of diatomaceous earth and sepiolite is 50 to 90% by mass of the total amount (T), preferably 60 to 90% by mass, more preferably 65 to 90% by mass, and even more preferably 70 to 85% by mass. If the total content of diatomaceous earth and sepiolite is above the lower limit of the above numerical range, it is easier to obtain an insulating sheet with excellent heat insulation properties. If the total content of diatomaceous earth and sepiolite is below the upper limit of the above numerical range, it is easier to form a wet web during papermaking.

[0029] The mass ratio of diatomaceous earth to sepiolite is 50 / 50 or higher, preferably 50 / 50 to 90 / 10, more preferably 55 / 45 to 90 / 10, and even more preferably 70 / 30 to 80 / 20. If the mass ratio is above the lower limit of the numerical range, it is easier to obtain an insulating sheet with excellent heat insulation properties and winding processability. If the mass ratio is below the upper limit of the numerical range, it is easier to obtain an insulating sheet with excellent surface strength and tensile strength.

[0030] (Composition of the insulation sheet) The proportion of inorganic fibers is preferably 5 to 50% by mass, more preferably 10 to 40% by mass, and even more preferably 10 to 35% by mass, based on the total mass of the heat insulating sheet. If the proportion of inorganic fibers is above the lower limit of the above numerical range, it is easier to form a wet web during papermaking. If the proportion of inorganic fibers is below the upper limit of the above numerical range, it is easier to obtain a heat insulating sheet with excellent heat insulating properties and winding processability.

[0031] The proportion of diatomaceous earth is preferably 35 to 85% by mass, more preferably 40 to 80% by mass, and even more preferably 45 to 75% by mass, relative to the total mass of the insulation sheet. If the proportion of diatomaceous earth is above the lower limit of the above numerical range, an insulation sheet with excellent heat insulation properties and winding processability is likely to be obtained. If the proportion of diatomaceous earth is below the upper limit of the above numerical range, an insulation sheet with excellent surface strength and tensile strength is likely to be obtained.

[0032] The proportion of sepiolite is preferably 5 to 45% by mass, more preferably 10 to 35% by mass, and even more preferably 15 to 25% by mass, relative to the total mass of the heat insulating sheet. When the proportion of sepiolite is above the lower limit of the above numerical range, it is easier to obtain a heat insulating sheet with excellent heat insulating properties, surface strength, and tensile strength. When the proportion of sepiolite is below the upper limit of the above numerical range, it is easier to obtain a heat insulating sheet with excellent winding processability and easier formation of a wet web during papermaking.

[0033] The total amount (T) is preferably 90 to 100% by mass of the total mass of the heat insulating sheet, more preferably 93 to 100% by mass, and even more preferably 95 to 100% by mass. If the total amount (T) is above the lower limit of the above numerical range, it is easier to obtain a heat insulating sheet with excellent heat insulating properties and heat resistance. If the total amount (T) is below the upper limit of the above numerical range, the properties of other components are more likely to be expressed if the heat insulating sheet contains other components.

[0034] (Properties of the heat-insulating sheet) When the heat insulation sheet is heated at 450°C for 2 hours, the thermal mass reduction rate is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less. When the thermal mass reduction rate is below the upper limit of the above numerical range, the heat insulation sheet has excellent heat resistance, the amount of smoke generated by the ignition of a single cell is reduced, and the changes in shape and properties due to thermal degradation are reduced. From the standpoint of heat resistance, a lower thermal mass loss is preferable, and there is no particular lower limit to it. However, considering that an insulating sheet is obtained by bonding inorganic fibers, it is thought to be, for example, around 0.1 mass%. The thermal mass reduction rate of the insulation sheet is a value obtained by the method described in the examples below.

[0035] The basis weight of the insulation sheet is 20-500 g / m². 2 Preferably, 50-400 g / m² 2 More preferably, 80-350 g / m 2 This is even more preferable. If the basis weight of the insulation sheet is above the lower limit of the aforementioned numerical range, the insulation performance of the insulation sheet tends to improve. If the basis weight of the insulation sheet is below the upper limit of the aforementioned numerical range, the winding processability of the insulation sheet tends to improve. The basis weight of the insulation sheet is determined by the method described in the examples below.

[0036] The thickness of the heat insulating sheet is preferably 0.05 to 3.00 mm, more preferably 0.07 to 2.50 mm, and even more preferably 0.10 to 2.00 mm. If the thickness of the heat insulating sheet is above the lower limit of the above numerical range, the heat insulating properties of the heat insulating sheet tend to improve. If the thickness of the heat insulating sheet is below the upper limit of the above numerical range, it is easier to make the battery pack to which the heat insulating sheet is applied thinner. The thickness of the insulation sheet is determined by the method described in the examples below.

[0037] The air permeability of the insulation sheet is 50 cc / cm². 2 Preferably less than / sec, and 40cc / cm³ 2 Less than / sec is more preferable, 20cc / cm³ 2A value of less than / sec is even more preferable. When the air permeability of the insulation sheet is below the above upper limit, the heat shielding performance of the insulation sheet tends to improve. From the viewpoint of heat shielding, the lower the air permeability of the insulation sheet, the better. The lower limit is not particularly limited, but considering the physical limits derived from the shape of the material and the practical thickness, for example, 0.01 cc / cm 2 It is estimated to be around / sec. The air permeability of the insulation sheet is a value determined by the method described in the examples below.

[0038] The thermal insulation temperature T of the thermal insulation sheet is preferably 400°C or lower, and more preferably 395°C or lower. If the thermal insulation temperature T of the thermal insulation sheet is below the upper limit within the above numerical range, the thermal insulation sheet can be said to have excellent thermal insulation properties. The lower the thermal insulation temperature T of the thermal insulation sheet, the better. The adiabatic temperature T of the insulation sheet is the value (T1, T2) obtained by the method described in the examples below.

[0039] The tensile strength of the thermal insulation sheet is preferably 10 N / 30 mm or higher, more preferably 15 N / 30 mm or higher, and even more preferably 20 N / 30 mm or higher. If the ash content of the thermal insulation sheet is above the lower limit, it can be said that the thermal insulation sheet has excellent strength. The higher the tensile strength of the thermal insulation sheet, the better. There is no particular upper limit, but considering the physical limits derived from the material and the practical thickness, it is considered to be, for example, around 200 N / 30 mm. The tensile strength of the heat-insulating sheet is determined by the method described in the examples below.

[0040] (Manufacturing method) Insulating sheets can be manufactured, for example, by forming a wet web by papermaking a slurry containing at least inorganic fibers, diatomaceous earth, and sepiolite, and then drying the wet web. In insulating sheets obtained by this wet method, diatomaceous earth and sepiolite can be incorporated internally into the insulating sheet. Therefore, diatomaceous earth and sepiolite can be uniformly dispersed in the voids between inorganic fibers and on the fiber surface. As a result, when applied to a battery pack, the insulating sheet can follow the shape changes due to ignition and thermal expansion, and an insulating sheet with excellent shape-following properties can be obtained.

[0041] The slurry may contain additional optional components as needed. Examples of optional components of the slurry include dispersants, liquid retainers, viscosity modifiers, pH adjusters, and packing agents. If the slurry contains a heat-melt type binder, inorganic fibers in the wet web can be bonded by the thermal bonding method. If the slurry does not contain a heat-melt type binder, the wet web can be formed by entangling the fibers through methods such as adding fibrillated fibers, adding fine fibers, needle punching, or water jet entanglement.

[0042] Various types of paper machines can be used when wet-processing slurry paper. Examples of such paper machines include cylinder paper machines, inclined paper machines, long-screen paper machines, and short-screen paper machines. Multilayer papermaking may be performed by combining the same or different types of these paper machines.

[0043] (Mechanism of action) In the heat insulating sheet of the present invention described above, the diatomaceous earth content is 30% by mass or more of the total amount (T). Therefore, the winding processability of the heat insulating sheet is improved. In the heat insulating sheet of the present invention, the diatomaceous earth content is 30% by mass or more of the total amount (T), and the combined content of diatomaceous earth and sepiolite is 50% by mass or more of the total amount (T). Therefore, the heat insulating properties of the heat insulating sheet are improved. The heat insulating sheet of the present invention contains sepiolite. Therefore, the heat insulating sheet has good surface strength and tensile strength.

[0044] <Battery pack> The heat insulating sheet of the present invention can be applied to various industrial applications where heat insulation between objects is required. For example, the heat insulating sheet of the present invention can be suitably applied to battery packs and can be suitably used as a heat insulating sheet for battery packs. The battery pack comprises a plurality of stacked single cells and an insulating sheet inserted between the plurality of single cells. At least one of the insulating sheets is the insulating sheet of the present invention described above.

[0045] Figure 1 is a diagram showing the configuration of a battery pack 50 according to one embodiment. As shown in Figure 1, in the battery pack 50, an insulating sheet 10 is inserted between each of the multiple laminated single cells 20. In addition, an insulating sheet 10 is also placed on the outside of the bottommost and topmost laminated single cells 20 (the laminated single cells 20 stacked in the outermost layer). The battery pack 50 is housed in a metal casing or the like to form a battery pack.

[0046] The laminated cell 20 can be any type of laminated cell in which the electrode group and electrolyte are housed within a laminate film. Various types of laminated cells can be used. As shown in Figure 1, the positive electrode tab 21 and the negative electrode tab 22 are located outside the laminate film. The heat insulating sheet 10 is inserted between each laminate cell 20 so as to block the entire surface, but the positive electrode tab 21 and the negative electrode tab 22 are led out to the outside of the heat insulating sheet 10.

[0047] In the battery pack 50, an insulating sheet 10 is inserted between each laminated cell 20. Therefore, even if a malfunction such as overheating occurs in one laminated cell 20, it is possible to prevent or delay the adverse effect of that malfunction on adjacent laminated cells 20. Furthermore, even if a malfunction such as overheating occurs in the bottom or top layer of laminated single cell 20, it is possible to prevent or delay the adverse effect of that malfunction on other battery packs.

[0048] In the battery pack 50, for the sake of explanation, the individual cells are shown as laminated single cells 20, but the individual cells are not limited to laminated single cells. The individual cells may be, for example, single cells in which an electrode group and electrolyte are housed in a metal case. However, laminated single cells are susceptible to heat. Therefore, from the viewpoint of making better use of the effects of the present invention, laminated single cells are preferred.

[0049] In the battery pack 50, for the sake of explanation, all of the multiple heat insulating sheets are the heat insulating sheets of the present invention, but the configuration of the battery pack is not limited to that illustrated in Figure 1. That is, all of the multiple heat insulating sheets may be the heat insulating sheets of the present invention, as in the battery pack 50, or some of the multiple heat insulating sheets may be other heat insulating sheets other than the heat insulating sheets of the present invention. However, using the heat-insulating sheet of the present invention has the advantage of being relatively inexpensive, easy to work with, and having superior heat insulation properties.

[0050] Multiple layers of insulating sheets may be inserted between each laminated cell 20. When multiple sheets are layered, only the insulating sheets of the present invention may be layered, only other insulating sheets may be layered, or the insulating sheets of the present invention may be layered with other insulating sheets. From the viewpoint of suppressing the overall thickness of the battery pack 50, it is preferable to insert only one insulating sheet, and if multiple sheets are to be stacked, it is preferable to stack two insulating sheets. [Examples]

[0051] The present invention will be specifically described below with reference to examples, but the present invention is not limited to the following description.

[0052] <Raw materials> The raw materials used in each example are listed below. (Inorganic fibers) • Glass fiber: E glass fiber with a fiber diameter of 6 μm and a fiber length of 6 mm. • Ceramic fiber: Ceramic fiber with a fiber diameter of 3 μm and a fiber length of 6 mm.

[0053] (binder) • Core-sheath PET fiber: Core-sheath heat-sealed polyester fiber with a fiber diameter of 14 μm and a fiber length of 5 mm (manufactured by Teijin Fibers, core melting point 260°C, sheath bonding temperature 110°C) • PVA fiber: Polyvinyl alcohol fiber with a fiber diameter of 11 μm and a fiber length of 3 mm (manufactured by Kuraray Co., Ltd., bonding temperature 60°C)

[0054] <Example 1> Samples were prepared by adjusting the basis weight to achieve a thickness of 500 μm with the composition shown in Table 1. First, E glass fibers, core-sheath PET fibers, and PVA fibers were mixed and dispersed in water to obtain a 0.4 mass% fiber slurry. Separately, a mixture of diatomaceous earth and sepiolite was dispersed in water, and 1.8 parts by mass of aluminum sulfate, an amphoteric polyacrylamide resin-based yield improver (manufactured by Arakawa Chemical Industries, Ltd.), and 0.6 parts by mass of anionic polyacrylamide resin-based polymer flocculant (manufactured by MT Aquapolymer Co., Ltd.) were sequentially added and stirred to obtain a final filler slurry of 0.4% by mass. The raw material slurry, obtained by mixing and stirring the fiber slurry and filler slurry described above, was fed into a hand-made sheet-making machine, and wet papermaking was performed to obtain a wet web. After that, the wet web was dewatered by suction, and then dried in a 180°C hot air dryer to obtain an insulating sheet (25cm x 25cm).

[0055] <Examples 2-7, Comparative Examples 1-3> The thermal insulation sheets for each example were manufactured using the same method and conditions as in Example 1, except that the slurry composition and the type of inorganic fiber were changed as shown in Tables 1 and 2. However, in Example 3, ceramic fibers were used instead of glass fibers. In addition, no thermal insulation sheet was obtained with the slurry composition of Comparative Example 3.

[0056] <Comparative Example 4> We prepared commercially available aerogel-impregnated glass paper (manufactured by Panasonic, 1000 μm thick).

[0057] <Measurement methods, evaluation methods> (Basic weight) The basis weight of the insulation sheets in each example was measured according to the method specified in JIS P 8124:2011.

[0058] (Thickness, density) For each example of insulation sheet, the thickness was measured in accordance with JIS P 8118:1998, and the pressure between the pressurized surfaces was set to 50 kPa. The density was calculated by dividing the basis weight by the thickness.

[0059] (Air permeability) The air permeability of the insulation sheets in each example was measured according to Method A (Fragile method) specified in JIS L 1096:2010.

[0060] (Winding processability) The winding processability was evaluated based on the winding diameter. The winding diameter for each example of the heat-insulating sheet was measured as follows: A sample of 200 mm in length and 30 mm in width was cut from the sheet, and this was wound onto cylinders of different diameters in order from the largest diameter. The smallest winding diameter that could be wound without cracking, folding, or wrinkling the sheet surface was defined as the winding diameter. The winding diameter was evaluated according to the following criteria. A: The maximum winding diameter is less than 65 mm. B: The winding diameter is between 65 mm and 110 mm. C: The maximum winding diameter is over 110 mm.

[0061] (Surface strength) Surface strength was evaluated based on the amount of powder shedding. The amount of powder shedding for each example of insulation sheet was measured as follows: A 50mm length of 15mm wide cellophane tape was cut and placed with the adhesive side facing the sheet surface. The index and middle fingers were held together and rubbed back and forth three times without applying force to ensure adhesion. The cellophane tape was peeled off the sheet and stuck to black drawing paper, and the condition of the powder and fibers adhered to the cellophane tape was visually checked.

[0062] Surface strength was evaluated according to the following criteria. A: Adhesion to powder or fiber cellophane tape is barely observed. B: A small amount of adhesion to powder or fiber cellophane tape is observed, but it is within acceptable limits. C: Excessive adhesion to powder or fiber cellophane tape is observed.

[0063] (Tensile strength) The tensile strength of each example of the heat-insulating sheet was measured as follows: A sample measuring 240 mm in length and 15 mm in width was cut from the sheet and, in accordance with JIS P8113, was set to a test length of 180 mm on a tensile testing machine (model name: RTC-1210A, manufactured by Orientec Co., Ltd.) at 23°C and 50% RH, and the tensile strength was measured.

[0064] The tensile strength was evaluated according to the following criteria. A: The tensile strength is 15 N / 30 mm or more. B: Tensile strength is 10 N / 30 mm or more and less than 15 N / 30 mm. C: Tensile strength is less than 10 N / 30 mm.

[0065] (thermal mass reduction rate) The thermal mass loss rate for each example of insulation sheet was measured as follows: The sample was dried at 105°C for 2 hours, cooled in a desiccator, and the oven-dry weight was measured. The same sample was heated at 450°C for 2 hours, cooled in a desiccator, and the post-heating weight was measured. The thermal mass loss was measured from the difference between the post-heating weight and the oven-drying weight.

[0066] (Temperature T1 after thermal compression at 500°C for 10 minutes, thickness 500 μm, thickness 1000 μm) Thermal insulation performance was evaluated based on the temperature T after 10 minutes at 500°C following thermal compression. For each example of thermal insulation sheet, the temperature T after 10 minutes at 500°C following thermal compression was measured as follows. 80mm x 100mm samples were cut from the sheet, and samples of one, two, and three layers were obtained. After measuring the thickness, the samples were compressed at 200°C and 2MPa for 15 minutes, and then cooled while maintaining the compression. The compressed samples were placed on a 500°C hot plate and held at a pressure of 1kPa for 10 minutes, after which the temperature of the side not in contact with the hot plate was measured using a contact thermometer. Measurements were taken for the one-layer, two-layer, and three-layer compressed samples, and regression curves were obtained between the thickness before heating and compression and the temperature reached after 10 minutes. Using these regression curves, the temperature T1 after heating at 500°C for 10 minutes, corresponding to a thickness of 500μm before heating and compression, and the temperature T2 after heating at 500°C for 10 minutes, corresponding to a thickness of 1000μm before heating and compression, were obtained.

[0067] T1 equivalent to 500 μm was evaluated according to the following criteria. A: T1 is less than 395°C. B:T1 is between 395°C and 400°C. C:T1 is over 400℃.

[0068] T2 equivalent to 1000 μm was evaluated according to the following criteria. A: T2 is less than 372°C. B:T2 is between 372°C and 377°C. C:T2 is over 377°C.

[0069] <Result> The measurement and evaluation results for each example are shown in Tables 1 and 2. The evaluation results are indicated in parentheses in each column, along with the measurement results, using either A, B, or C.

[0070] [Table 1]

[0071] [Table 2]

[0072] Examples 1 to 7 yielded thermal insulation sheets with excellent thermal insulation properties and winding processability. In contrast, Comparative Example 1 had insufficient winding processability. Comparative Example 2 had insufficient winding processability, surface strength, tensile strength, and thermal insulation properties. In Comparative Example 3, strong bonding between fibers during papermaking prevented water from escaping from the wet web, resulting in the failure to obtain a thermal insulation sheet. [Industrial applicability]

[0073] According to the present invention, an insulating sheet with excellent heat insulation properties and winding processability is provided; and a battery pack equipped with the insulating sheet is provided. [Explanation of Symbols]

[0074] 10...Insulation sheet, 20...Laminated single cell, 21...Positive electrode tab, 22...Negative electrode tab, 50...Battery pack.

Claims

1. This is an insulating sheet containing inorganic fibers, diatomaceous earth, and sepiolite. The diatomaceous earth content is 30% by mass or more relative to the total amount of the inorganic fibers, the diatomaceous earth, and the sepiolite. The total content of diatomaceous earth and sepiolite is 50 to 90% by mass relative to the total amount of inorganic fibers, diatomaceous earth, and sepiolite. An insulating sheet in which the thermal mass loss rate when the insulating sheet is heated at 450°C for 2 hours is 20% by mass or less.

2. The heat insulating sheet according to claim 1, wherein the mass ratio of diatomaceous earth to sepiolite is 50 / 50 or more.

3. The heat insulating sheet according to claim 1, wherein the fiber diameter of the inorganic fiber is 3 to 13 μm.

4. The basis weight of the aforementioned insulation sheet is 20 to 500 g / m². ２ The heat insulating sheet according to claim 1, wherein the thickness of the heat insulating sheet is 0.05 to 3 mm.

5. Multiple stacked single cells, An insulating sheet inserted between the aforementioned multiple single cells, Equipped with, A battery pack in which at least one of the aforementioned heat insulating sheets is a heat insulating sheet according to any one of claims 1 to 4.

Images