Insulation sheets, battery packs

Abstract

To provide a heat-insulating sheet that features superior heat insulation and winding processability, and a battery pack that includes the heat-insulating sheet.SOLUTION: A heat-insulating sheet includes wollastonite, sepiolite, inorganic fibers and binder. In the heat-insulating sheet, the inorganic fiber content is 10 mass% or more relative to 100 mass% of the heat-insulating sheet. The total content of wollastonite and sepiolite is 48 mass% or more relative to 100 mass% of the heat-insulating sheet. The mass ratio of sepiolite to wollastonite in the heat-insulating sheet is 0.1 or more and 5.0 or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to a heat insulating sheet and a battery pack. [Background technology]

[0002] High-power, high-capacity rechargeable batteries, such as lithium-ion batteries, are widely used in mobile devices, tools, automobiles, railways, aircraft, and other applications. In high-power, high-capacity rechargeable batteries, if a short circuit occurs due to damage or internal impurities, the internal energy is instantaneously released as heat. As a result, battery degradation accelerates, and in some cases, ignition may occur. For example, applications requiring high-capacity energy storage, such as automobiles, demand high voltage and high output. Therefore, battery packs (sometimes called assemblies) are often used, where multiple individual cells are packed together in a stacked fashion. In such battery packs, there is a concern that a malfunction in one cell could affect adjacent cells. Therefore, in order to prevent a malfunction in one cell from affecting adjacent cells, it has been proposed to place a non-flammable heat-insulating sheet between cells (for example, Patent Documents 1 and 2). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] International Publication No. 2020 / 129274 [Patent Document 2] Japanese Patent Publication No. 2006-310274 [Overview of the project] [Problems that the invention aims to solve]

[0004] In addition to excellent heat insulation properties, insulation sheets also need to be able to be rolled up into the smallest possible diameter (winding processability) for ease of transport 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 excellent 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, a binder, wollastonite, and β-type sepiolite. However, in the case of thermal insulation sheets obtained from wet webs made by papermaking using slurries containing these materials, powder sometimes falls off the surface of the sheet, resulting in insufficient surface strength and insufficient tensile strength. The powder that falls off the sheet can reduce workability during transport and can also cause malfunctions and defects by adhering to production equipment. Therefore, the inventors diligently investigated the blending ratio of inorganic fibers, binder, wollastonite, and β-type 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 wollastonite, sepiolite, and inorganic fibers; wherein the content of the inorganic fibers is 10% by mass or more relative to 100% by mass of the insulating sheet; the total content of the wollastonite and sepiolite is 48% by mass or more relative to 100% by mass of the insulating sheet; and the mass ratio of the sepiolite to the wollastonite is 0.1 or more and 5.0 or less. [2] The thermal insulation sheet according to [1], wherein the average length of the wollastonite is 5 to 100 μm, the average diameter of the wollastonite is 1 to 30 μm, and the aspect ratio of the wollastonite is 3 to 100. [3] The heat insulating sheet according to [1] or [2], wherein the content of organic components in the heat insulating sheet is 8% by mass or less relative to the total mass of the heat insulating sheet. [4] The basis weight of the insulation sheet is 20 to 500 g / m². 2 The insulating sheet is one of the items described in [1] to [3]. [5] The insulating sheet according to any one of [1] to [4], wherein the thickness of the insulating sheet is 0.1 to 3 mm. [6] The air permeability of the heat insulating sheet is 50 cc / cm 2 An insulating sheet described in any of [1] to [5], which is less than or equal to / sec. [7] 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 one of [1] to [6]. [8] The battery pack according to [7], wherein an insulating sheet is also placed on the outside of the outermost cell among the plurality of cells stacked in the layer. [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 thermal insulation sheet of the present invention comprises wollastonite, sepiolite, inorganic fibers, and a binder. The heat insulation sheet of the present invention may further contain other components other than inorganic fibers, wollastonite, sepiolite and binder as optional components as long as the effects of the invention are not impaired.

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

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

[0013] The fiber diameter of the inorganic fiber is preferably 3 to 13 μm, more preferably 4 to 12 μm, and even more preferably 5 to 10 μm. When the fiber diameter of the inorganic fiber is not less 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, when the sheet absorbs moisture or water, it is easy to avoid the voids between the fibers being collapsed by the capillary force of the adsorbed water. Also, it is 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 sheet thickness. Also, it is easy to avoid the increase in the contact points between the fibers and the increase in the thermal conductivity.

[0014] In addition, according to the World Health Organization (WHO), "WHO inhalable fibers" are fibrous materials that are inhaled into the body through respiration and reach the lungs, with a length greater than 5 μm, a diameter of less than 3 μm, and an aspect ratio greater than 3. The use of WHO inhalable fibers raises concerns about health effects and is subject to usage restrictions. Therefore, it is desirable for inorganic fibers to have a diameter of 3 μm or more.

[0015] When the fiber diameter of inorganic fibers is below the upper limit of the aforementioned numerical range, the voids between inorganic fibers become narrower, making it difficult for convection and gas to pass through the voids to occur, thus making it easier to obtain an insulating effect. Because it is easier to secure contact points and entanglement points between inorganic fibers, the tensile strength of the entire insulating sheet increases. This improves handling and makes it easier to suppress fuzzing and powder shedding during cutting. This also helps to prevent increased skin irritation. Furthermore, because the voids between fibers do not become excessively large, it is easier to avoid the passage of heated air and the occurrence of convection within the voids. The fiber length of inorganic fibers is calculated by measuring the fiber length of 100 fibers under a microscope and taking the average value of 100 fibers.

[0016] As inorganic fibers, inorganic fibers with a fiber diameter of 3 to 13 μm and inorganic fibers with a fiber diameter greater than 13 μm may be used in combination. By using a combination of inorganic fibers with different fiber diameters, it may be possible to achieve improved heat insulation and surface smoothing effects by narrowing the gaps between inorganic fibers, as well as improved tensile strength by ensuring contact points and entanglement points between inorganic fibers, while maintaining the thickness of the insulation sheet and preserving the gaps between 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. If the fiber length of the inorganic fibers is greater than or equal to the lower limit of the aforementioned numerical range, it is easier to ensure mechanical strength during the sheet manufacturing process. If the fiber length of the inorganic fibers is less than or equal to the upper limit of the aforementioned numerical range, there is no binding due to twisting of the fibers, and it is easier to maintain a good texture (uniformity of thickness and fiber density). The fiber diameter of the inorganic fibers is calculated as the average value of 100 fibers.

[0018] The heat insulating sheet may contain organic fibers as needed. Examples of organic fibers include polyolefin fibers, nylon fibers, rayon fibers, polyvinyl chloride fibers, acrylic fibers, polyester fibers, polyurethane fibers, poly(p-phenylene)benzobisoxazole fibers, polyamide-imide fibers, polyimide fibers, polyarylate fibers, polyetherimide fibers, vinylon fibers, polycarbonate fibers, ethylene-vinyl acetate fibers, polyphenylene sulfide fibers, polyethylene terephthalate fibers, polybutylene terephthalate fibers, polyethylene naphthalate fibers, and aramid fibers, among other chemical fibers. By supporting a filler containing calcium silicate hydrate and hydrated magnesium silicate on an insulating sheet, the heat shielding properties, handling properties, toughness, and flexibility can be improved.

[0019] Calcium silicate hydrate crystals have a plate-like or needle-like microstructure, and many voids are formed within the crystal. These voids suppress heat conduction, resulting in heat retention and insulation properties. In addition, the evaporation of crystalline hydrate during heating slows down the temperature rise due to the heat of vaporization.

[0020] Calcium silicate board is one of the representative non-combustible building materials. Calcium silicate board is produced by mixing siliceous and calcareous raw materials with reinforcing materials such as fibers, adding water, and then hydrothermally synthesizing calcium silicate hydrate in an autoclave. The board is typically manufactured in thicknesses of 5mm to 15mm. Before the hydrothermal synthesis process, the board is formed into a flat sheet. The general process involves either cutting the sheet obtained through papermaking or pouring the fluid material into a mold. After autoclaving, while some products retain some flexibility, the board is fundamentally rigid. Therefore, production must be batch-based, making continuous operation difficult.

[0021] By supporting fine particulate crystalline calcium silicate hydrate during the manufacturing process of nonwoven fabrics, a more flexible and windable heat-resistant calcium silicate material can be obtained, contributing to improved productivity.

[0022] Examples of crystalline calcium silicate hydrates include fossilagite, gyrolite, hillebrandite, tobermorite, truscotite, wollastonite, zonolite, or mixtures thereof.

[0023] Among these, wollastonite is preferred. Wollastonite is mainly produced as a natural mineral, and because its crystals take the form of needle-like or elongated columnar shapes with a high aspect ratio, it can provide both reinforcing effect and flexibility when bonded to fibers, etc., within the paper on which it is supported. Wollastonite can be used from various sources, both domestically and internationally. Furthermore, wollastonite may be used alone or in combination of two or more types.

[0024] The average length of wollastonite is preferably 5 to 100 μm, more preferably 7 to 90 μm, and even more preferably 10 to 80 μm. If the average length of wollastonite is above the lower limit of the above numerical range, it can produce a sufficient reinforcing effect when bonded to fibers. If the average length of wollastonite is below the upper limit of the above numerical range, it can produce sufficient flexibility. The average length of wollastonite is the average value obtained by averaging the lengths of 100 wollastonite particles in a 200x magnification planar photograph taken using an electron microscope. The wollastonite used for measurement is that which is located on the diagonal of the observation range of the electron microscope image.

[0025] The average diameter of wollastonite is preferably 1 to 30 μm, more preferably 2 to 28 μm, and even more preferably 3 to 25 μm. If the average diameter of wollastonite is above the lower limit of the above numerical range, a sufficient number of contact points are formed between the fibers and the wollastonite, making it easier to obtain strength. If the average diameter of wollastonite is below the upper limit of the above numerical range, it is easier to balance flexibility and strength. The average diameter of wollastonite is the average value obtained by considering the width as the diameter for 100 wollastonite in a planar image taken with an electron microscope at a magnification of 200x. As the wollastonite to be used for measurement, wollastonite located on the diagonal of the observation range of the electron microscope image is used.

[0026] The aspect ratio (average length / average diameter) of wollastonite is preferably 3 to 100, more preferably 4 to 90, and even more preferably 5 to 80. If the aspect ratio of wollastonite is above the lower limit of the above numerical range, it is easier to obtain strength due to confounding. If the aspect ratio of wollastonite is below the upper limit of the above numerical range, it is easier to balance flexibility and strength.

[0027] By incorporating hydrated magnesium silicate in a predetermined ratio into the filler in addition to wollastonite, the necessary heat shielding, handling properties, toughness, and flexibility can be achieved. Because the binding force between the fine needle-shaped particles of hydrated magnesium silicate is stronger than that of wollastonite, it densely fills the paper sheet in which it is supported. As a result, the sheet-like heat-resistant material exhibits high shielding against gases while simultaneously increasing its mechanical strength. This reduces the contribution of gas heat transfer, improving heat shielding performance, as well as improving handling properties and flexibility, thus improving winding during papermaking.

[0028] When a heat-insulating sheet-like material is placed between individual cells to form a battery pack, the compressive force between the cells reduces the overall thickness of the heat-insulating sheet, leading to a decrease in thermal insulation. However, adding a filler can suppress this thickness reduction and prevent an increase in thermal conductivity. This effect is further enhanced by the mechanical strength-enhancing effect of hydrated magnesium silicate. However, as the amount of filler increases, the effect of increased thermal conductivity due to solid heat transfer by the filler itself becomes significant, and the thermal conductivity of hydrated magnesium silicate is slightly higher than that of wollastonite. Therefore, depending on the addition rate, it can result in a decrease in heat shielding performance.

[0029] Examples of hydrated magnesium silicate include sepiolite, atabulgite, kaolinite, smectite, montmorillonite, sericite, illite, gluconite, chlorite, talc, or mixtures thereof. In particular, the hydrated magnesium silicate preferably contains at least one selected from the group consisting of sepiolite and atabulgite. Such hydrated magnesium silicate has particularly high binding strength and easily provides mechanical strength.

[0030] 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.

[0031] Sepiolite is classified into α-type and β-type sepiolite based on its origin. α-type sepiolite is formed by hydrothermal activity under high temperature and pressure. α-type sepiolite has a relatively high degree of crystallinity and exhibits a distinct fibrous morphology 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.

[0032] Wollastonite and β-type sepiolite are preferred because they contain relatively low amounts of crystalline silica such as quartz (impurity content), which is undesirable from a safety standpoint for the human body. In particular, it is desirable to select and use materials from sources with a low crystalline silica content. Furthermore, since crystalline silica accelerates the wear of cutting tools when cutting sheets (sheet-shaped heat-resistant materials), a lower crystalline silica content is preferable.

[0033] 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.

[0034] The filler may further contain organic compounds. Specifically, the filler preferably contains, for example, a fluororesin, a silicone resin, or a silane coupling agent for the purpose of imparting water resistance. Among these, the silane coupling agent can link the hydrated magnesium silicate particles together, thereby further increasing the mechanical strength (film strength) of the coating. As a result, it is easier to suppress powder fallout when cutting the sheet-like heat-resistant material. In addition, the linking of the hydrated magnesium silicate particles via the silane coupling agent can also be expected to enhance the water resistance of the coating. The silane coupling agent may be present only on the outermost surface of the sheet, or it may be present within the sheet. Examples of silane coupling agents that can be used include silane compounds having vinyl, epoxy, methacryloxy, or amino groups as functional groups. These silane coupling agents have high hydrophobicity. Therefore, the water resistance of the sheet can be further improved, and it is easier to avoid the sheet absorbing moisture or water, which can clog the voids between inorganic fibers.

[0035] (binder) A binder may be included to facilitate the papermaking process and increase the mechanical strength of the produced paper by binding inorganic or organic fibers together. The binder should be binding, heat-resistant, and have low corrosive properties to batteries, electrodes, and wiring. The binder may be an inorganic binder (excluding sepiolite and wollastonite) or an organic binder. Examples of inorganic binders include various inorganic cements, various types of glass, as well as hydrated magnesium silicate, colloidal silica, silica sol, and alumina sol. On the other hand, examples of organic binders include various thermosetting resins and various thermoplastic resins. Examples of organic binder forms include powders, particles, fibers, emulsions, solutions, and varnishes. Specific examples of organic binders include polyethylene resin, polyvinyl chloride resin, (meth)acrylic acid ester resin, styrene-acrylic acid ester copolymer, vinyl acetate resin, vinyl acetate-(meth)acrylic acid ester copolymer, ethylene-vinyl acetate copolymer, polyester resin, polyvinyl alcohol (PVA), ethylene-vinyl alcohol copolymer, styrene-butadiene rubber (SBR), nitrile rubber (NBR), phenolic resin, epoxy resin, melamine resin, urea resin, unsaturated polyester resin, polyurethane resin, thermosetting polyimide resin, and the like. Inorganic binders and organic binders may be used individually or in combination of two or more types.

[0036] 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.

[0037] The more organic binder is added, the higher the mechanical strength of the sheet (sheet-type heat-resistant material). However, if a large amount of organic binder is included, the thermal shrinkage rate of the sheet increases, which tends to reduce its heat resistance. Also, when the sheet-type heat-resistant material is heated, the organic binder may generate heat or decompose gases due to oxidation. Therefore, the amount of organic binder in the sheet should be as low as possible.

[0038] In addition to the organic binder component added to the raw material slurry for manufacturing nonwoven fabrics, a liquid containing the aforementioned organic binder component may be applied (external coating) to the nonwoven fabric carrying the filler obtained in the previous process by methods such as spray coating, curtain coating, impregnation coating, bar coating, roll coating, or blade coating. The nonwoven fabric to be externally coated may be a dried nonwoven fabric after drying or a wet web before drying. External coating of the organic binder can increase the flexibility of the sheet and further improve winding properties. It can also better prevent the shedding of filler and fibers from the sheet surface. However, similar to the organic binder added to the raw material slurry, if the sheet-like heat-resistant material is heated, the organic binder may generate heat due to oxidation or produce decomposition gases.

[0039] (optional ingredient) The heat insulating sheet may contain, as needed, additives such as crosslinking agents, silane coupling agents, antioxidants, light stabilizers, UV absorbers, thickeners, nucleating agents, neutralizing agents, lubricants, anti-blocking agents, dispersants, flow improvers, release agents, flame retardants, foaming agents, colorants, wetting agents, viscous agents, yield improvers, paper strength improvers, water filter agents, pH adjusters, defoamers, preservatives, and pitch control agents, as well as fillers such as calcium silicate, calcium carbonate, silica aerosol, fumed silica, kaolinite, smectite, montmorillonite, sericite, illite, gluconite, chlorite, talc, plastic pigments, hollow glass beads, and shirasu balloons.

[0040] Other clay minerals besides β-type sepiolite include, for example, kaolinite, smectite, montmorillonite, sericite, illite, gluconite, chlorite, α-type sepiolite, and talc. Examples of fillers include calcium silicate and calcium carbonate.

[0041] (Composition of the insulation sheet) The proportion of inorganic fibers is 10% by mass or more of the total mass of the heat insulating sheet, preferably 10 to 52% by mass, more preferably 13 to 51% by mass, and even more preferably 15 to 50% by mass. 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 surface strength, tensile strength, and heat insulating properties.

[0042] The total content of wollastonite and β-type sepiolite is 48% by mass or more of the total mass of the heat insulating sheet, preferably 48-90% by mass, more preferably 49-87% by mass, and even more preferably 50-85% by mass. If the proportion of wollastonite 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 winding processability. If the proportion of wollastonite is below the upper limit of the above numerical range, it is easier to avoid a decrease in heat shielding properties due to increased solid heat transfer.

[0043] The mass ratio of wollastonite to β-type sepiolite in the thermal insulation sheet is 0.1 to 5.0, preferably 0.15 to 4.5, more preferably 0.2 to 4.0, and even more preferably 0.25 to 3.5. If the mass ratio is above the lower limit of the numerical range, a thermal insulation sheet with excellent tensile strength is likely to be obtained. If the mass ratio is below the upper limit of the numerical range, a thermal insulation sheet with excellent heat shielding properties is likely to be obtained.

[0044] The total amount (T) is preferably 80 to 100% by mass of the total mass of the heat insulating sheet, more preferably 90 to 100%, even more preferably 95 to 100%, and most preferably 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 winding processability. 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.

[0045] (Properties of the heat-insulating sheet) The content of organic components in the heat insulating sheet is preferably 8% by mass or less, more preferably 7% by mass or less, and even more preferably 5% by mass or less, relative to the total mass of the heat insulating sheet. When the content of organic components is below the upper limit within the above numerical range, the heat insulating sheet has excellent heat resistance, the amount of smoke generated when a single cell ignites is reduced, and the changes in shape and properties due to thermal degradation are reduced. From the standpoint of heat resistance, the lower the organic component content, the better. While there is no particular lower limit, considering that inorganic fibers are bonded to obtain an insulating sheet, it is thought to be, for example, around 0.1% by mass.

[0046] The basis weight of the insulation sheet is 20-500 g / m². 2 Preferably, 30-400 g / m² 2 More preferably, 40-350 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.

[0047] The thickness of the heat insulating sheet is preferably 0.1 to 3 mm, more preferably 0.15 to 2.5 mm, and even more preferably 0.2 to 2 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.

[0048] The air permeability of the insulation sheet is 50 cc / cm². 2 Preferably less than / sec, and 30cc / cm³ 2 Less than / sec is more preferable, 20cc / cm³ 2It is more preferable that it is below / sec. When the air permeability of the heat insulating sheet is below the above upper limit value, the heat shielding property of the heat insulating sheet is likely to be improved. From the viewpoint of heat shielding property, the lower the air permeability of the heat insulating sheet, the better. The lower limit value is not particularly limited. However, considering the physical limit derived from the shape of the material and the practical thickness, for example, it is considered to be about 0.01 cc / cm 2 / sec. The air permeability of the heat insulating sheet is a value obtained by the method described in the examples below.

[0049] The tensile strength of the heat insulating sheet is preferably 12 N / 15 mm or more, more preferably 14 N / 15 mm or more, and even more preferably 15 N / 15 mm or more. When the ash content of the heat insulating sheet is above the above lower limit value, it can be said that the heat insulating sheet has excellent strength. The higher the tensile strength of the heat insulating sheet, the better. The upper limit value is not particularly limited. However, considering the physical limit derived from the material and the practical thickness, for example, it is considered to be about 100 N / 15 mm. The tensile strength of the heat insulating sheet is a value obtained by the method described in the examples below.

[0050] (Manufacturing method) The heat insulating sheet can be manufactured, for example, by papermaking a slurry containing at least inorganic fiber, wollastonite, β-type sepiolite, and a binder to form a wet web, and then drying the wet web. In the heat insulating sheet obtained by the wet method in this way, wollastonite and β-type sepiolite can be added and contained in the heat insulating sheet. Therefore, wollastonite and β-type sepiolite can be uniformly dispersed in the voids between inorganic fibers and on the fiber surface. As a result, when applied to a laminated battery, a heat insulating sheet that can follow the shape change due to ignition or thermal expansion and has excellent shape followability can be obtained.

[0051] The slurry may further contain optional components as needed. Examples of the optional components of the slurry include a dispersant, a liquid retention agent, a viscosity modifier, a pH modifier, and a filler. 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.

[0052] 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.

[0053] (Mechanism of action) In the heat insulating sheet of the present invention described above, the inorganic fiber content is 10% by mass or more relative to the heat insulating sheet, the total content of wollastonite and β-type sepiolite is 48% by mass or more relative to the heat insulating sheet, and the mass ratio of β-type sepiolite to wollastonite in the heat insulating sheet is 0.1 or more and 5.0 or less. Therefore, the heat insulating sheet has excellent heat insulating properties and winding processability, as well as good surface strength and tensile strength.

[0054] <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.

[0055] Figure 1 is a diagram of 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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 more flexible, thus having higher resistance to pressure failure and making it easier to maintain heat insulation when the battery is damaged.

[0060] 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]

[0061] The present invention will be specifically described below with reference to examples, but the present invention is not limited to the following description.

[0062] <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.

[0063] (Organic fibers) • PET fiber: PET fiber with a fiber diameter of 12 μm and a fiber length of 5 mm.

[0064] (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 binder fibers: Polyvinyl alcohol binder with a fiber diameter of 11 μm and a fiber length of 3 mm (manufactured by Kuraray, dissolution temperature in water of 60°C)

[0065] <Example 1> A mixture was obtained by mixing glass fibers, core-sheath PET fibers, and PVA binder fibers in the composition ratios shown in Table 1. The mixture was then dispersed in water to obtain a fiber slurry with a final concentration of 0.4% by mass. A mixture was obtained by mixing wollastonite and β-type sepiolite separately in the composition ratios shown in Table 1. This mixture was then dispersed in water to obtain a filler slurry. To this filler slurry, 3 parts aluminum sulfate relative to solids, 0.5 parts by mass of an amphoteric polyacrylamide resin-based yield improver (manufactured by Arakawa Chemical Industries) relative to solids, and 0.2 parts by mass of anionic polyacrylamide resin-based polymer flocculant (manufactured by MT Aquapolymer) relative to solids were sequentially added and stirred to form filler flocs. The final concentration was adjusted to 0.4% by mass. The above fiber slurry was mixed with a filler slurry that had formed flocs in a mass ratio (fiber slurry:filler slurry = 41.6:58.4) to obtain a raw material slurry with a concentration of 0.4 mass%. This raw material slurry was wet-processed using a manual sheet-making machine to obtain a wet web in which E-glass fibers were randomly arranged, and a filler consisting of 49.4 parts wollastonite and 9 parts β-type sepiolite per 41.6 parts fibers (of which 40 parts E-glass fibers) was incorporated into the paper structure. After dewatering this wet web by suction, it was dried in a hot air dryer at 180°C to obtain a basis weight of 186.3 g / m². 2 , 52m thick 3 I obtained an insulating sheet (25cm x 25cm).

[0066] <Examples 2-7, Comparative Examples 1-3> The ratios of glass fiber, PET fiber, core-sheath PET fiber, and PVA fiber, as well as the ratios of wollastonite and β-type sepiolite, were changed as shown in Table 1, and thermal insulation sheets with the basis weight, thickness, and density shown in Table 1 were manufactured using the same method as in Example 1.

[0067] <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.

[0068] (thickness) For each example of the 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.

[0069] (density) For each example of the insulation sheet, the density was obtained by dividing the basis weight obtained in the previous section by the thickness.

[0070] (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.) in a 23°C 50% RH environment, and the tensile strength was measured. The obtained tensile strength was evaluated according to the following criteria.

[0071] A: The tensile strength is 15 N / 15 mm or more. B: Tensile strength is 12 N / 15 mm or more and less than 15 N / 15 mm. C: Tensile strength is less than 12 N / 15 mm.

[0072] (Surface strength) The surface strength of each insulation sheet was evaluated 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 any powder or fibers adhering to the cellophane tape was visually checked.

[0073] 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.

[0074] (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 measuring 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 diameter to which the sheet could be wound without cracking, folding, or wrinkling the sheet surface was defined as the winding diameter.

[0075] The winding diameter was evaluated according to the following criteria. A: The maximum winding diameter is less than 60 mm. B: The maximum winding diameter is 60 mm or more and less than 80 mm. C: The maximum winding diameter is 80 mm or more.

[0076] (Air permeability) For each example of insulation sheet, the air permeability was measured according to Method A (Fragile method) specified in JIS L 1096:2010 and evaluated according to the following criteria. A: Air permeability is 20 cc / cm² 2 It is less than / sec. B: Air permeability is 20 cc / cm² 2 / sec super 50cc / cm 2 It is less than / sec. C: Air permeability of 50 cc / cm² 2 It is over / sec.

[0077] (Heat-shielding properties) The heat-shielding properties of each example's insulation sheet were evaluated using the following procedure. An 80mm x 100mm sample was cut from the sheet, its thickness was measured as in the previous step, and then it was compressed at 200°C and 2MPa for 15 minutes, after which it was cooled while maintaining the compression. Similarly, two and three layers of the same cut sample were stacked, their thickness measured in the same manner, and then heated and compressed. The compressed sample described above was placed on a 500°C hot plate and held for 10 minutes under a pressure of 1 kPa. The temperature of the top surface of the sample, i.e., the temperature of the surface opposite to the side in contact with the hot plate, was then measured using a contact thermometer. Using the same procedure, measurements were taken for samples compressed with two layers and three layers, respectively, and regression curves were obtained between the thickness before heating and compression and the temperature reached on the opposite side after heating at 500°C for 10 minutes. Using these regression curves, the temperatures reached on the opposite side after heating at 500°C for 10 minutes, corresponding to thicknesses of 500 μm, 1000 μm, and 1500 μm before heating and compression, were obtained. These values ​​were evaluated according to the following evaluation criteria.

[0078] Temperature T1 reached on the opposite side after heating at 500°C for 10 minutes, equivalent to a thickness of 500 μm before heating and compression. A: T1 is less than 400℃. B:T1 is between 400°C and 405°C. C:T1 is 405°C or higher.

[0079] Temperature T2 reached on the opposite side after heating at 500°C for 10 minutes, equivalent to a thickness of 1000 μm before heating and compression. A: T2 is less than 365°C. B:T2 is between 365°C and 370°C. C:T2 is 370°C or higher.

[0080] Temperature T3 reached on the opposite side after heating at 500°C for 10 minutes, equivalent to a thickness of 1500 μm before heating and compression. A: T3 is less than 345°C. B:T3 is between 345°C and 350°C. C:T3 is 350°C or higher.

[0081] <Result> Table 1 shows the measurement and evaluation results for each example.

[0082] [Table 1]

[0083] Examples 1 to 7 yielded thermal insulation sheets with excellent heat insulation properties and winding processability, and the surface strength and tensile strength of the thermal insulation sheets were also good. In contrast, Comparative Example 1 had insufficient tensile strength. Comparative Example 2 had insufficient surface strength, tensile strength, and thermal insulation properties. Comparative Example 3 had insufficient tensile strength, winding processability, and thermal insulation properties. [Industrial applicability]

[0084] 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]

[0085] 10...Insulation sheet, 20...Laminated single cell, 21...Positive electrode tab, 22...Negative electrode tab, 50...Battery pack.

Claims

1. It is an insulating sheet, It contains wollastonite, sepiolite, and inorganic fibers. The inorganic fiber content is 10% by mass or more relative to 100% by mass of the heat insulating sheet. The total content of wollastonite and sepiolite is 48% by mass or more relative to 100% by mass of the heat insulating sheet. An insulating sheet in which the mass ratio of sepiolite to wollastonite is 0.1 or more and 5.0 or less.

2. The thermal insulation sheet according to claim 1, wherein the average length of the wollastonite is 5 to 100 μm, the average diameter of the wollastonite is 1 to 30 μm, and the aspect ratio of the wollastonite is 3 to 100.

3. The heat insulating sheet according to claim 1, wherein the content of organic components in the heat insulating sheet is 8% by mass or less relative to the total mass of the heat insulating sheet.

4. The basis weight of the aforementioned insulation sheet is 20 to 500 g / m². ２ The heat insulating sheet according to claim 1.

5. The heat insulating sheet according to claim 1, wherein the thickness of the heat insulating sheet is 0.1 to 3 mm.

6. The air permeability of the aforementioned insulation sheet is 50 cc / cm². ２ The heat insulating sheet according to claim 1, wherein the value is less than or equal to / sec.

7. 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 6.

8. The battery pack according to claim 7, wherein an insulating sheet is also placed on the outside of the single cell that is stacked in the outermost layer among the plurality of single cells.

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