JP2021008089A - Thermal runaway inhibition fire-resistive sheet - Google Patents

Abstract

To provide a thermal runaway inhibition fire-resistive sheet with excellent flexibility which is designed to prevent a fire spread to an adjacent lithium ion battery if one cell is subjected to thermal runaway to cause a fire.SOLUTION: A thermal runaway inhibition fire-resistive sheet includes a base material including a glass fiber, a heat-resistant fiber and a binder fiber, and an inorganic particle layer.SELECTED DRAWING: None

Description

The present invention relates to a thermal runaway suppression refractory sheet that suppresses thermal runaway of adjacent elementary batteries and prevents the spread of fire when one elementary battery runs away due to thermal runaway in a battery pack including a plurality of elementary batteries and ignites.

In recent years, with the diversification of electronic devices, there is a demand for a battery pack having a high capacity, a high voltage, a high output, and high safety, or a battery pack including a plurality of batteries. These elementary batteries include cylindrical, square, and pouch types. In order to provide highly safe elementary batteries and battery packs, the elementary batteries and battery packs are equipped with PTC elements to prevent the temperature from rising. There are known technologies equipped with various protective means such as equipment, a thermal fuse, and a protection circuit that senses the internal pressure of a battery and shuts off the current. Further, there is also known a technique in which a battery pack is provided with a control circuit for controlling charging / discharging of the elementary battery so that the elementary battery does not enter an abnormal state (for example, a thermal runaway state).

However, even if the protective means and the control circuit as described above are provided, when the elementary battery is placed under abnormal conditions, the elementary battery may cause thermal runaway due to various causes. When thermal runaway occurs, the temperature of the elementary battery rises sharply to 300 ° C. or higher, and in some cases 400 ° C. or higher, and high-temperature flammable gas may be ejected from the inside. In the worst case, it may ignite and the housing of the battery pack containing the elementary battery may be damaged or melted.

As a technique for preventing such thermal runaway, Patent Document 1 provides a heat insulating sheet in which silica xerogel is supported in the space of the glass fiber sheet and the outer peripheral portion of the fiber sheet is covered with a dense resin layer to fix the silica xerogel. It is disclosed. Although this heat insulating sheet can be used for square or pouch-type elementary electrons, it has a problem that it cannot be used for a cylindrical elementary battery because it is inflexible. Further, although the heat insulating property is excellent, since the silica xerogel is fixed by the resin layer, there is a problem that the fire resistance is inferior when the temperature of the elementary battery exceeds 300 ° C.

Further, in Patent Document 2, it contains at least one of a mineral powder and a flame retardant, starts an endothermic reaction at 100 to 1000 ° C., and is selected from the group consisting of phase change, expansion, foaming and hardening accordingly. A thermal runaway prevention sheet that causes at least one type of structural change is disclosed. This sheet uses aluminum foil laminated glass cloth as a base material, and a resin composition containing mineral powder and a flame retardant is supplied to a uniaxial extruder and extruded to form a heat-absorbing material sheet. By obtaining a fire-resistant heat-insulating sheet and further pressing the obtained heat-absorbing material sheet and fire-resistant heat-insulating sheet to obtain a heat-runaway prevention sheet, there is a problem that the productivity is very low and the cost is high. Although it can be used for square or pouch type elementary batteries, there is a problem that it cannot be used for cylindrical elementary batteries due to its inflexibility.

International Publication No. 2018/110055 Pamphlet Japanese Unexamined Patent Publication No. 2018-20606

An object of the present invention is that in a battery pack including a plurality of lithium-ion batteries, thermal runaway that can prevent the spread of fire to adjacent lithium-ion batteries when one battery runs away and ignites. An object of the present invention is to provide a thermal runaway suppression fireproof sheet having excellent fire resistance and flexibility as a suppression fireproof sheet.

As a result of diligent research to solve the above problems, the following inventions were found.

(1) A thermal runaway refractory sheet containing a base material containing glass fibers, heat-resistant fibers, and binder fibers, and an inorganic particle layer.

(2) The thermal runaway suppression refractory sheet according to (1) above, wherein the content of heat-resistant fibers is 10% by mass or more and 50% by mass or less with respect to all the fiber components contained in the base material.

Since the refractory sheet for suppressing thermal runaway of the present invention uses a base material containing glass fibers, heat-resistant fibers, and binder fibers, the permeability of the coating liquid for forming the inorganic particle layer to the base material and the permeability of the inorganic particle layer in the base material Excellent retention. Further, it is possible to increase the flexibility while maintaining the fire resistance of the thermal runaway suppression refractory sheet, and to achieve the effect of being able to wrap the outer circumference of the cylindrical elementary battery.

In the present invention, the thermal runaway suppression refractory sheet is a sheet containing a base material containing glass fibers, heat-resistant fibers, and binder fibers, and an inorganic particle layer.

Examples of glass fibers in the present invention include chopped strands, glass wool, and glass flakes. Any glass fiber may be used as long as it is hard to break and has the ability to form a base material. The fiber diameter of the glass fiber is preferably 1 to 18 μm, more preferably 3 to 15 μm, and even more preferably 5 to 12 μm. If the fiber diameter is less than 1 μm, the glass fiber may fall off from the base material during papermaking because it is too thin, resulting in insufficient strength and thickness. If the fiber diameter exceeds 18 μm, the glass fiber becomes too thick, the gap between the base materials becomes large, the workability is inferior, and the workability is hindered, making it difficult to use. May become.

The fiber length of the glass fiber in the present invention is preferably 1 to 30 mm, more preferably 3 to 15 mm, and even more preferably 5 to 12 mm. If the fiber length is less than 1 mm, the strength may be insufficient, and if the fiber length exceeds 30 mm, the texture of the base material may be deteriorated and the quality may vary.

The content of the glass fiber in the present invention is preferably 40 to 80% by mass, more preferably 45 to 75% by mass, and 50 to 70% of the total fiber components contained in the base material. It is more preferably by mass%. If the content is less than 40% by mass, fire resistance and dimensional stability may be deteriorated, and if the content exceeds 80% by mass, flexibility may not be exhibited.

The heat-resistant fibers in the present invention include total aromatic polyamide, total aromatic polyester, polyimide, polyamideimide, polyetheretherketone, polyphenylene sulfide, polybenzoimidazole, poly-p-phenylene benzobisthiazole, and poly-p-phenylene benzo. Fibers made of heat-resistant resins such as bisoxazole, polysulfoneamide, polyetherimide, and polytetrafluoroethylene are used. The heat-resistant fiber preferably has a critical oxygen index (LOI) of 20 or more.

The fiber diameter of the heat-resistant fiber is preferably 5 to 25 μm, more preferably 7 to 20 μm, and even more preferably 9 to 16 μm. When the fiber diameter is less than 5 μm, the flexibility of the base material is improved, but the price of the fiber may be very high, and the retention of the inorganic particle layer is improved, so that the inorganic particles are used as the base material. Since it becomes easier to fill the voids in the sheet, the flexibility of the sheet may decrease. When the fiber diameter exceeds 25 μm, the heat-resistant fiber becomes too thick, the gap between the base materials becomes large, the retention of the inorganic particle layer is lowered, and the fire resistance may be lowered. Further, since the heat-resistant fiber itself becomes more rigid, the flexibility of the base material may decrease.

The fiber length of the heat-resistant fiber in the present invention is preferably 3 to 20 mm, more preferably 5 to 15 mm, and even more preferably 6 to 10 mm. If the fiber length is less than 3 mm, the strength may be insufficient, and if the fiber length exceeds 20 mm, the texture of the base material may be deteriorated and the quality may vary.

The heat-resistant fiber content in the present invention is preferably 10 to 50% by mass, more preferably 15 to 45% by mass, and 20 to 40% by mass with respect to the total fiber components contained in the base material. It is more preferably by mass%. If the content is less than 10% by mass, sufficient flexibility may not be obtained, and if the content exceeds 50% by mass, fire resistance and dimensional stability may be deteriorated.

As the binder fiber of the present invention, a wet-heat adhesive binder fiber or a heat-sealing binder fiber can be used. The moist heat-adhesive binder fiber refers to a fiber that flows from the fiber state at a certain temperature or is easily deformed to exhibit an adhesive function in a wet state. Specifically, it is a thermoplastic fiber that can be softened with hot water (for example, about 80 to 120 ° C.) and self-adhesive or adheres to other fibers. For example, polyvinyl-based fibers (polyvinylpyrrolidone, polyvinyl ether, polyvinyl). Alcohol-based, polyvinyl acetal, etc.), Cellulose-based fibers (C1-3 alkyl cellulose such as methyl cellulose, hydroxy C1-3 alkyl cellulose such as hydroxymethyl cellulose, carboxy C1-3 alkyl cellulose such as carboxymethyl cellulose, or salts thereof), modification Fibers made of vinyl copolymer (polyvinyl monomer such as isobutylene, styrene, ethylene, vinyl ether and unsaturated carboxylic acid such as maleic anhydride, or a copolymer of an anhydride thereof, or a salt thereof, etc. ) And so on. As the moist heat-adhesive binder fiber used in the present invention, polyvinyl-based fibers are preferable, polyvinyl alcohol (PVA) -based fibers are more preferable, the base material strength is higher, and a film is easily formed between the fibers, and inorganic particles. Is easier to hold between the fibers.

The heat-bondable binder fiber is a fiber that exhibits an adhesive function by heat-sealing when the paper is dried. Examples of the heat-sealing binder fiber include core-sheath type, eccentric type, side-by-side type, sea island type, orange type, multiple bimetal type composite fiber, single fiber and the like, and in particular, core-sheath type heat-sealing property. It preferably contains binder fibers. The core-sheath type heat-sealing binder fiber is suitable for softening and melting only the sheath portion to bond the fibers to each other while maintaining the fiber shape of the core portion. The resin components constituting the core and sheath of the core-sheath type heat-sealing fiber are not particularly limited, and any resin having fiber-forming ability may be used. Specific examples of the heat-sealing binder fiber include polypropylene single fiber, polyethylene single fiber, low melting point polyester single fiber, composite fiber of a combination of polypropylene (core) and polyethylene (sheath), polypropylene (core) and ethylene. Examples thereof include composite fibers of a combination of vinyl alcohol (sheath), composite fibers of a combination of high melting point polypropylene (core) and low melting point polypropylene (sheath), and the like.

The fineness of the binder fiber used in the present invention is preferably 0.1 to 5.6 decitex, more preferably 0.6 to 3.3 decitex, and 0.8 to 2.2 decitex. Is even more preferable. If it is less than 0.1 decitex, the fiber itself becomes very expensive and the substrate may become dense and thin. On the other hand, when it exceeds 5.6 decitex, the number of contacts with the glass fiber is reduced, and it may be difficult to maintain the strength in a wet state. In addition, a uniform texture may not be obtained.

The fiber length of the binder fiber used in the present invention is preferably 1 to 15 mm, more preferably 2 to 10 mm, and even more preferably 3 to 5 mm. If it is less than 1 mm, it may come off from the papermaking wire during papermaking, and sufficient strength may not be obtained. On the other hand, if it exceeds 15 mm, entanglement or the like may occur when it is dispersed in water, and a uniform texture may not be obtained.

As the binder fibers used in the present invention, each binder fiber may be used alone or in combination. The content of the binder fiber is preferably 4% by mass or more and 30% by mass or less, more preferably 6% by mass or more and 25% by mass or less, and 8% by mass, based on the total fiber components contained in the base material. It is more preferably% or more and 20% by mass or less. If the amount of the binder fiber is less than 4% by mass, the strength of the base material is lowered, and the paper may be cut off when the inorganic particles are applied, or the glass fiber may fall off. On the other hand, when the content of the binder fiber exceeds 30% by mass, the releasability from the dryer may deteriorate when the base material is made by the wet papermaking method, and when the inorganic particles are applied, the material may deteriorate. The permeability to the base material may decrease, and the fire resistance of the thermal runaway suppression fireproof sheet may deteriorate.

In the present invention, in addition to glass fibers, heat-resistant fibers, and binder fibers, various fibers can be blended, if necessary, as long as the performance is not impaired. As a result, the number of voids can be further increased, and the retention of inorganic particles and the strength of the thermal runaway-suppressing refractory sheet can be improved. Such fibers are mainly fibrous having very finely divided portions in the direction parallel to the fiber axis, and at least a part of the fibrillated cellulose fibers having a fiber diameter of 1 μm or less, rayon, cupra, lyocell. Recycled fibers such as fibers, semi-synthetic fibers such as acetate, triacetate, and promix, polyolefin-based, polyamide-based, polyacrylic, vinylon-based, vinylidene, polyvinyl chloride, polyester-based, benzoate, polyclar, phenol, melamine, furan, Inorganic fibers such as urea, aniline, unsaturated polyester, fluorine, silicone, synthetic resin fibers such as derivatives thereof, metal fibers, carbon fibers, alumina, silica, ceramics, and rock fibers can be added. The synthetic resin fiber may be a fiber made of a single resin (single fiber), or may be a composite fiber made of two or more kinds of resins. Further, the synthetic resin fiber contained in the thermal runaway suppression refractory sheet of the present invention may be used alone or in combination of two or more.

In the present invention, the thickness of the thermal runaway suppression refractory sheet is preferably 0.1 to 0.8 mm, more preferably 0.2 to 0.6 mm, and more preferably 0.3 to 0.5 mm. Is even more preferable. When the thickness of the base material is within the above range, the base material in the present invention can easily maintain the tensile strength required in the papermaking process and the coating process, so that the base material can be made in each process including the papermaking property. Workability is not impaired. If the thickness of the base material exceeds 0.8 mm, the rigidity of the base material becomes too strong, so that the flexibility of the thermal runaway suppression refractory sheet may decrease. If the thickness of the base material is less than 0.1 mm, the voids in the base material become large, making it difficult to apply the material, and the fire resistance of the thermal runaway-suppressing refractory sheet may decrease.

The density of the base material in the present invention is preferably 0.07 g / cm ³ or more, and more preferably 0.10 g / cm ³ or more. Further, it is preferably 0.20 g / cm ³ or less, more preferably 0.18 g / cm ³ or less. If the density is less than 0.07 g / cm ³ , the strength of the base material becomes too weak and there is a risk of damage during handling or coating of the base material, and if it exceeds 0.20 g / cm ³ , the base material The rigidity of the fireproof sheet may become too high, and the flexibility of the thermal runaway suppression refractory sheet may decrease.

The base material in the present invention is preferably a wet non-woven fabric produced by a wet papermaking method. In the wet papermaking method, fibers are dispersed in water to form a uniform papermaking slurry, and the papermaking slurry is squeezed with a papermaking machine to produce a wet non-woven fabric. Examples of the paper machine include a circular net paper machine, a long net paper machine, an inclined paper machine, an inclined short net paper machine, and a combination machine thereof. Further, it can be manufactured by a paper machine having a plurality of head boxes and stacking wet papers on a wire. In addition to the fiber raw material, a dispersant, a paper strength enhancer, a thickener, an inorganic filler, an organic filler, an antifoaming agent and the like can be appropriately added to the papermaking slurry, if necessary. The solid content concentration of the papermaking slurry is preferably about 5 to 0.001% by mass. This papermaking slurry is further diluted to a predetermined concentration before making a paper. Then, the paper-made wet paper web is nipated with a press roll or the like, and then a dryer is used to melt the binder fibers to develop the strength. It is preferable to use a Yankee dryer as the dryer because the dried surface becomes smooth and a surface with less unevenness can be formed. In addition, as auxiliary drying, there is no problem even if a heating device such as a hot air dryer, a heating roll, or an infrared heater is used together. The drying temperature at this time is preferably a temperature at which the moisture of the wet paper web can be sufficiently removed and the strength can be exhibited by the binder fibers.

In the present invention, the inorganic particle layer is a layer containing inorganic particles, and more preferably contains a binder. By filling the voids of the base material with this inorganic particle layer, the effects of fire resistance and suppression of heat shrinkage of the sheet can be obtained. Inorganic particles include aluminum hydroxide, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, dihydrate plaster, calcium aluminated, clay, kaolin, calcined kaolin, calcium carbonate, magnesium carbonate, barium carbonate, talc, etc. Inorganic particles with good water dispersibility such as titanium dioxide can be used.

Among the inorganic particles, aluminum hydroxide oxide, clay, kaolin, calcined kaolin, and carbonate-based inorganic particles are preferable because the inorganic particles solidify when hit by a flame and can prevent the inorganic particles from falling off from the sheet. Further, aluminum hydroxide oxide, clay, kaolin, and calcined kaolin are more preferable because they are excellent in dimensional stabilization and can maintain sheet strength even when they are held at a high temperature.

In the present invention, the particle size of the inorganic particles is preferably 0.08 μm or more and 2.00 μm or less, and more preferably 0.30 μm or more and 1.50 μm or less. If the particle size exceeds 2.00 μm, the fire resistance of the thermal runaway suppression refractory sheet may deteriorate, or the dimensional stability of the thermal runaway suppression refractory sheet when exposed to a high temperature may deteriorate. On the other hand, when the particle size is less than 0.08 μm, the inorganic particles tend to thicken when dispersed and are difficult to disperse, and when coated on the base material, the inorganic particles easily fall off from the base material. It is necessary to increase the amount of binder to prevent it from falling off. The particle size referred to in the present invention is an average value of 20 particles obtained by converting the area of the inorganic particles obtained from the SEM photograph of the inorganic particles into a diameter as a perfect circle.

In the present invention, the inorganic particle layer can contain a binder. As the binder, various organic polymers can be used. Examples are vinyl chloride copolymer, vinyl acetate copolymer, styrene-butadiene copolymer elastomer (styrene butadiene rubber), acrylonitrile-butadiene copolymer elastomer, (meth) acrylic acid ester polymer elastomer, styrene-. (Meta) Acrylic acid ester polymer Various organic polymers such as elastomer and polyvinylidene fluoride polymer can be used.

In the present invention, the content of the binder contained in the inorganic particle layer is preferably 2% by mass or more and 100% by mass or less, and 5% by mass or more and 50% by mass or less, based on the total amount of the inorganic particles. More preferably, it is 10% by mass or more and 30% by mass or less. If the amount of the binder is less than 2% by mass, the inorganic particles may easily fall off from the base material. Further, when the amount of the binder exceeds 100% by mass, the fire resistance may be lowered, the coatability of the inorganic particles may be deteriorated, or the flexibility of the sheet may be impaired.

The medium for preparing the coating liquid for forming the inorganic particle layer is not particularly limited as long as it can uniformly dissolve or disperse the binder and the inorganic particles. For example, aromatic hydrocarbons such as toluene, ethers such as tetrahydrofuran, ketones such as methyl ethyl ketone, alcohols such as isopropyl alcohol, N-methyl-2-pyrrolidone (NMP), dimethylacetamide, dimethylformamide, dimethyl sulfoxide, etc. Water or the like can be used as needed. The medium used is preferably a medium that does not expand the base material or a medium that does not dissolve the base material.

The content of the inorganic particle layer is a value calculated by "absolute dry coating amount of the inorganic particle layer (g / m ² ) / substrate basis weight (g / m ² ) x 100", and is 90% by mass or more. Is preferable, 100% by mass or more is more preferable, and 130% by mass or more is further preferable. When the content of the inorganic particle layer is 90% by mass or more with respect to the base material, there is almost no melting or damage of the sheet even when the thermal runaway suppression refractory sheet is exposed to flame. The higher the content of the inorganic particle layer, the higher the fire resistance and heat insulation. On the other hand, the content of the inorganic particle layer is preferably 200% by mass or less, more preferably 180% by mass or less, and further preferably 160% by mass or less. If it exceeds 200% by mass, the voids of the base material may be filled and the flexibility may decrease.

Various coating devices can be used as devices for coating the inorganic particles on the base material in order to form the inorganic particle layer. For example, impregnation of 2 roll size press, gate roll coater, gravure coater, die coater, lip coater, blade coater, curtain coater, air knife coater, rod coater, kiss touch coater, dip coater, etc., or various coaters by coating equipment. Can be used, but is not limited to this.

In the present invention, in addition to the inorganic particles and the binder, the inorganic particle layer contains various dispersants such as polyacrylic acid and sodium carboxymethyl cellulose, and hydroxyethyl cellulose, sodium carboxymethyl cellulose, and polyethylene in order to increase the liquid stability of the coating liquid. Various additives such as various thickeners such as oxides, various water-retaining agents, various wetting agents, preservatives, and antifoaming agents can be added as needed. In general, a non-aqueous coating liquid using an organic solvent as a medium has a low surface tension, and a water-based coating liquid using water as a medium has a high surface tension. Since the base material used in the present invention has high acceptability of the coating liquid, both the non-aqueous coating liquid and the water-based coating liquid can be applied without any problem, but in the present invention, only water is used as the medium. It is preferable to use the water-based coating solution used.

The present invention will be described below with reference to examples, but the present invention is not limited to these examples. In the examples, the percentages (%) and parts are all based on mass unless otherwise specified. The coating amount is the dry coating amount.

Example 1
<Preparation of base material>
60 parts of glass fiber (trade name: ECS06I-33G, manufactured by Nippon Denki Glass Co., Ltd., fiber diameter 10 μm x fiber length 6 mm), PVA binder fiber (trade name: VPB107, manufactured by Kuraray Co., Ltd., 1.1) as a binder fiber 10 parts of decitex x 3 mm, moist heat adhesive binder fiber) and 30 parts of 2.2 decitex x 6 mm polyetherimide fiber as heat resistant fibers were dispersed in water with a pulper to make a uniform concentration of 0.5%. A papermaking slurry is prepared, a wet paper web is obtained using a circular net paper machine, and dried with a Yankee dryer having a surface temperature of 140 ° C. to prepare a base material having a basis weight of 50.2 g / m ² and a thickness of 0.306 mm. did.

<Preparation of coating liquid for forming inorganic particle layer>
Sufficiently mix 100 parts of kaolin (trade name: NU clay, manufactured by BASF CORPORATION) and 0.5 part of a special carboxylic acid type polymer activator (trade name: Poise (registered trademark) 520, manufactured by Kao Corporation) in water. Stir, then mix and stir 20 parts of vinyl chloride emulsion (trade name: Viniblanc (registered trademark) 278, manufactured by Nissin Chemical Industry Co., Ltd.) (solid content concentration 43%), and solid content concentration 38%. A coating solution was prepared.

<Preparation of thermal runaway suppression fireproof sheet>
The base material was impregnated with a coating liquid by a size press and dried with an air dryer at 125 ° C., and the absolute dry coating amount was 55.0 g / m ² , the content of the inorganic particle layer was 110%, and the total basis weight was 105. A thermal runaway suppression fireproof sheet having a thickness of ² g / m ² and a thickness of 0.385 mm was prepared.

Example 2
The glass fiber used in Example 1 was 40 parts, the binder fiber used in Example 1 was 10 parts, and the heat-resistant fiber used in Example 1 was 50 parts. In the same manner as in Example 1, the basis weight was 50. A substrate having a thickness of 9 g / m ² and a thickness of 0.320 mm was prepared. Then, this base material was impregnated with the coating solution used in Example 1 by a size press, dried, and the absolute dry coating amount was 57.0 g / m ² , the content of the inorganic particle layer was 112%, and the total basis weight. A thermal runaway suppression fireproof sheet having a thickness of 107.9 g / m ² and a thickness of 0.407 mm was prepared.

Example 3
The glass fiber used in Example 1 was 80 parts, the binder fiber used in Example 1 was 10 parts, and the heat-resistant fiber used in Example 1 was 10 parts. In the same manner as in Example 1, the basis weight was 50. A substrate having a thickness of 5 g / m ² and a thickness of 0.306 mm was prepared. Then, this base material was impregnated with the coating solution used in Example 1 by a size press, dried, and the absolute dry coating amount was 52.0 g / m ² , the content of the inorganic particle layer was 103%, and the total basis weight. A thermal runaway suppression fireproof sheet having a thickness of 102.6 g / m ² and a thickness of 0.366 mm was prepared.

Example 4
The glass fiber used in Example 1 was 38 parts, the binder fiber used in Example 1 was 10 parts, and the heat-resistant fiber used in Example 1 was 52 parts. In the same manner as in Example 1, the basis weight was 50. A substrate having a thickness of 1 g / m ² and a thickness of 0.330 mm was prepared. Then, this base material was impregnated with the coating solution used in Example 1 by a size press, dried, and the absolute dry coating amount was 60.0 g / m ² , the content of the inorganic particle layer was 120%, and the total basis weight. A thermal runaway suppression fireproof sheet having a thickness of 110.1 g / m ² and a thickness of 0.420 mm was prepared.

Example 5
The glass fiber used in Example 1 was 81 parts, the binder fiber used in Example 1 was 10 parts, and the heat-resistant fiber used in Example 1 was 9 parts, and the basis weight was 50 in the same manner as in Example 1. A substrate having a thickness of 4 g / m ² and a thickness of 0.302 mm was prepared. Then, this base material was impregnated with the coating solution used in Example 1 by a size press, dried, and the absolute dry coating amount was 51.5 g / m ² , the content of the inorganic particle layer was 102%, and the total basis weight. A thermal runaway suppression fireproof sheet having a thickness of 101.9 g / m ² and a thickness of 0.362 mm was prepared.

Example 6
60 parts of the glass fiber used in Example 1 was used as a binder fiber, the core part was polyethylene terephthalate (melting point: 255 ° C.), and the sheath part was an amorphous copolymer polyester (copolymer of polyethylene terephthalate and polyethylene isophthalate). , Melting point: 110 ° C.), 10 parts of core-sheath type polyester composite fiber having a fiber diameter of 11 μm, fiber length of 5 mm, and a core / sheath volume ratio of 50/50, and 30 heat-resistant fibers used in Example 1. A base material having a basis weight of 50.8 g / m ² and a thickness of 0.317 mm was prepared in the same manner as in Example 1. Then, this base material was impregnated with the coating solution used in Example 1 by a size press, dried, and the absolute dry coating amount was 52.0 g / m ² , the content of the inorganic particle layer was 102%, and the total basis weight. A thermal runaway suppression fireproof sheet having a thickness of 102.8 g / m ² and a thickness of 0.379 mm was prepared.

Example 7
The glass fiber used in Example 1 was 60 parts, the binder fiber used in Example 1 was 10 parts, and the heat-resistant fiber was 1.7 decitex × 6 mm para-aromatic polyamide fiber 30 parts. A substrate having a basis weight of 50.3 g / m ² and a thickness of 0.305 mm was prepared in the same manner as in the above. Then, this base material was impregnated with the coating liquid used in Example 1 by a size press, dried, and the absolute dry coating amount was 56.0 g / m ² , the content of the inorganic particle layer was 111%, and the total basis weight. A thermal runaway suppression fireproof sheet having a thickness of 106.3 g / m ² and a thickness of 0.387 mm was prepared.

Example 8
60 parts of the glass fiber used in Example 1, 10 parts of the binder fiber used in Example 1, 30 parts of 1.3 decitex × 5 mm polyphenylene sulfide fiber as heat-resistant fibers, and the same method as in Example 1. A base material having a basis weight of 50.3 g / m ² and a thickness of 0.301 mm was prepared. Then, this base material was impregnated with the coating liquid used in Example 1 by a size press, dried, and the absolute dry coating amount was 59.0 g / m ² , the content of the inorganic particle layer was 117%, and the total basis weight. A thermal runaway suppression fireproof sheet having a thickness of 109.3 g / m ² and a thickness of 0.396 mm was prepared.

Comparative Example 1
90 parts of the glass fiber used in Example 1 and 10 parts of the binder fiber used in Example 1 were used, and a substrate having a basis weight of 49.7 g / m ² and a thickness of 0.299 mm was used in the same manner as in Example 1. Was produced. Then, this base material was impregnated with the coating solution used in Example 1 by a size press, dried, and the absolute dry coating amount was 50.3 g / m ² , the content of the inorganic particle layer was 101%, and the total basis weight. A thermal runaway suppression refractory sheet having a thickness of 100.0 g / m ² and a thickness of 0.352 mm was prepared.

Comparative Example 2
10 parts of the binder fiber used in Example 1 and 90 parts of the heat-resistant fiber used in Example 1 were used, and a substrate having a basis weight of 50.9 g / m ² and a thickness of 0.344 mm was used in the same manner as in Example 1. Was produced. Then, this base material was impregnated with the coating liquid used in Example 1 by a size press, dried, and the absolute dry coating amount was 68.0 g / m ² , the content of the inorganic particle layer was 134%, and the total basis weight. A thermal runaway suppression refractory sheet having a thickness of 118.9 g / m ² and a thickness of 0.459 mm was prepared.

The following physical properties were measured and evaluated for the base material for the thermal runaway suppression refractory sheet and the thermal runaway suppression refractory sheet of Examples and Comparative Examples, and the results are shown in Table 1.

<Basis weight of base material, basis weight of fireproof sheet for suppressing thermal runaway, and coating amount of inorganic particle layer>
In accordance with JIS P8124: 2011, the basis weight of the base material and the basis weight of the thermal runaway suppression refractory sheet were measured. The coating amount of the inorganic particle layer was calculated by subtracting the basis weight of the base material from the basis weight of the thermal runaway suppression refractory sheet.

<Thickness of base material and thermal runaway suppression fireproof sheet>
The thickness under 5N load was measured using an outer micrometer specified in JIS B7502: 2016.

<Fire resistance>
To evaluate the fire resistance of the thermal runaway suppression refractory sheet, three test pieces with a size of 100 mm in the width direction and 100 mm in the flow direction were cut out from each sheet, and a burner (trade name: Lab Burner APTL, Co., Ltd.) was placed in the center of each test piece. A flame of Phoenix Dent) was applied for 5 minutes. After that, the surface of the thermal runaway suppression refractory sheet on the side exposed to the flame was visually observed and evaluated according to the following evaluation criteria. The flame temperature of the burner was 1100 ° C.

◯: There are no holes, cracks or melting in the thermal runaway suppression refractory sheet.
Δ: Slight melting or dents can be seen on the surface of the refractory sheet that suppresses thermal runaway when exposed to flames.
X: There are holes or cracks in the thermal runaway suppression fireproof sheet.

<Shape retention after fire resistance test>
The shape of the test piece used for the evaluation of the fire resistance test was evaluated by visual evaluation according to the following criteria.

◯: The surface of the test piece is horizontal and there is no unevenness or curl.
Δ: Slight unevenness occurred on the surface of the test piece.
X: The surface of the test piece was greatly deformed, and curls and irregularities were observed.

<Flexibility of thermal runaway suppression fireproof sheet>
To evaluate the flexibility of the thermal runaway suppression refractory sheet, three test pieces with a size of 70 mm in the width direction and 120 mm in the flow direction were cut out from each thermal runaway suppression refractory sheet, wound around a stainless rod having a diameter of 18 mm and a length of 100 mm, and the sheets were wound. The condition of was evaluated by the following criteria by visual evaluation.

Here, the reason why the stainless rod having a diameter of 18 mm is used is to confirm whether or not it can be wound around the outer circumference of the 18650 series cylindrical battery having a diameter of 18 mm and a length of 65 mm, which is most used as a cylindrical battery.

◯: There were no cracks in the sheet, and it was possible to wind it around the stainless steel rod without any gaps.
Δ: There were no cracks in the sheet, but a slight gap was observed with respect to the outer circumference of the stainless steel rod.
X: A crack was generated in the sheet, or a large gap was generated on the outer circumference of the stainless steel rod.

As shown in Table 1, the thermal runaway suppression refractory sheets produced in Examples 1 to 8 include a base material containing glass fibers, heat-resistant fibers, and binder fibers, and an inorganic particle layer. The thermal runaway suppression refractory sheets of Examples 1 to 8 were excellent in fire resistance, shape retention after the heat resistance test, and flexibility.

Comparing Examples 1 to 5, the flexibility of the thermal runaway suppression refractory sheet tends to improve as the blending ratio of the heat-resistant fibers increases, and the heat-resistant fiber content of Example 5 is less than 10% by mass. The thermal runaway suppression refractory sheet of Examples 1 to 4 having a heat-resistant fiber content of 10% by mass or more was more flexible than the thermal runaway suppression refractory sheet. On the other hand, the thermal runaway suppression refractory of Examples 1 to 3 and 5 having a heat resistant fiber content of 50% by mass or less is higher than that of the thermal runaway suppression fireproof sheet of Example 4 in which the heat-resistant fiber content exceeds 50% by mass. The sheet was superior in shape retention after the fire resistance test. Therefore, it was found that the content of the heat-resistant fiber is preferably 10 to 50% by mass from the viewpoint of flexibility and shape retention after the fire resistance test.

From Example 6, it was found that even if a core-sheath type heat-sealing binder fiber is used as the binder fiber, there is no problem in fire resistance, shape retention after the fire resistance test, and flexibility.

Comparing Example 1 with Examples 7 and 8, it was found that whichever heat-resistant fiber was used, it was excellent in fire resistance, shape maintenance characteristics after the fire resistance test, and flexibility.

Since the thermal runaway suppression refractory sheet of Comparative Example 1 does not contain heat-resistant fibers, it lacks flexibility, and even if the basis weight of the base material is reduced to around 50 g / m ² , it cannot be neatly wound around a stainless steel rod having a diameter of 18 mm. It was found that it cannot be used for a cylindrical elementary battery having a diameter of at least 18 mm or less.

The thermal runaway suppression refractory sheet of Comparative Example 2 is a base material containing only heat-resistant fibers and binder fibers, and although it is excellent in flexibility, its fire resistance and shape retention after the fire resistance test are deteriorated.

The thermal runaway suppression refractory sheet of the present invention can be suitably used for a plurality of lithium ion elementary batteries, particularly a battery pack equipped with a cylindrical elementary battery.

Claims (2)

A fire-resistant sheet for suppressing thermal runaway, which comprises a base material containing glass fibers, heat-resistant fibers, and binder fibers, and an inorganic particle layer. The thermal runaway suppression refractory sheet according to claim 1, wherein the content of heat-resistant fibers is 10% by mass or more and 50% by mass or less with respect to all the fiber components contained in the base material.