Flame-retardant material and battery pack using the same

Abstract

The flame-retardant material comprises an inorganic fiber nonwoven fabric and a thickness-reducing agent impregnated into the inorganic fiber nonwoven fabric. The inorganic fiber nonwoven fabric is held in a compressed state in the thickness direction by the thickness-reducing agent. Upon the disappearance of the thickness-reducing agent, the inorganic fiber nonwoven fabric returns to a thickness of 60% or more of its thickness before the thickness-reducing agent was impregnated.

Description

[Technical Field]

[0001] This disclosure relates to a flame-retardant material and a battery pack using the same. Regarding. [Background technology]

[0002] Electric vehicles and hybrid vehicles are equipped with a battery pack (also called a battery module) in which multiple battery cells (also called battery cells) are connected to each other, which serves as the power source for the electric motor that drives the vehicle.

[0003] High-capacity, high-output lithium-ion secondary batteries are primarily used in vehicles, and these batteries are susceptible to ignition due to collisions, battery degradation, or thermal runaway caused by abnormal charging. Extinguishing a fire in a battery cell that has experienced thermal runaway is difficult, and to prevent a chain reaction of thermal runaway and protect occupants, it is necessary to install flame-retardant material in the battery pack. The flame-retardant material must have thermal insulation properties to prevent the spread of fire due to heat diffusion outside the battery pack. A thicker flame-retardant material is better for high thermal insulation. On the other hand, due to space constraints, the flame-retardant material installed in the battery pack must be as thin as possible. As it is thinner, the thermal insulation properties of the flame-retardant material are reduced, resulting in a trade-off between thermal insulation and ease of installation.

[0004] Patent Document 1 discloses an inorganic fiber composite material that comprises a sheet-like inorganic fiber molded body and has a particle impact resistant layer on at least one side of the inorganic fiber molded body, and is characterized by having a specific particle impact resistant property.

[0005] Patent Document 2 discloses a heat transfer suppression sheet comprising at least one of a first inorganic fiber having a glass transition temperature of 800°C or less and a first inorganic particle having a glass transition temperature of 800°C or less, a second inorganic fiber having a glass transition temperature of 1000°C or more, a second inorganic particle having a glass transition temperature of 800°C or more, and an organic binder.

[0006] Patent Document 3 discloses a laminate comprising a layer (A) in which a thermoplastic resin composition (X) and inorganic fibers (Y) are integrated, and a layer (B) having a higher thermoelectric coefficient in the thickness direction than layer (A), wherein the thermoplastic resin composition (X) comprises a thermoplastic resin (a) and a thermally expandable flame retardant (b1). [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] International release 2024 / 034628 [Patent Document 2] International release 2023 / 127904 [Patent Document 3] International release 2024 / 085233 [Overview of the project] [Problems that the invention aims to solve]

[0008] For the inorganic fiber composite material described in Patent Document 1 to have sufficient thermal insulation performance, the weight of the inorganic fiber molded body must be increased, which increases the thickness of the inorganic fiber molded body. A larger thickness of the inorganic fiber molded body leads to poor mounting capabilities.

[0009] Patent document 2 describes a technique for processing a heat transfer suppression sheet into a thin sheet by combining inorganic fibers in an inorganic fiber molded body with an inorganic binder or resin. However, since the inorganic binder does not disappear when heated, even when the inorganic fiber molded body is heated, the restraining force of the inorganic fibers by the inorganic binder does not decrease, and the inorganic fiber molded body maintains its thinness. When the thickness of the inorganic fiber molded body is thin, the heat insulation performance decreases.

[0010] In the technology described in Patent Document 3, a thermally expandable substance contained in a molded body comprising a thermoplastic resin composition (X) and inorganic fibers (Y) expands during flame suppression, increasing its thickness and providing an insulating effect. However, from the standpoint of the dispersion of the thermally expandable substance and expansion control, it is difficult to reliably and uniformly increase the thickness of the molded body.

[0011] One of the problems to be solved in the present disclosure is to provide a flame shield having mountability and heat insulation properties, and a battery pack having such a flame shield.

Means for Solving the Problems

[0012] The present disclosure includes, for example, the subject matter described below.

[0013] Item 1. An inorganic fiber nonwoven fabric, and a thickness inhibitor impregnated in the inorganic fiber nonwoven fabric, wherein the inorganic fiber nonwoven fabric is held in a state of being compressed in the thickness direction by the thickness inhibitor, and the inorganic fiber nonwoven fabric restores to a thickness of 60% or more of the thickness before the thickness inhibitor is impregnated due to the disappearance of the thickness inhibitor, a flame shield.

[0014] Item 2. The flame shield according to Item 1, wherein the inorganic fiber nonwoven fabric is a needle blanket containing alumina / silica fiber. Item 3. The flame shield according to Item 1, wherein the thickness inhibitor contains a thermoplastic resin.

[0015] Item 4. The flame shield according to Item 3, wherein the thickness inhibitor contains a flame retardant. Item 5. [[ID=XXX]] The flame shield according to Item 1, wherein the basis weight of the inorganic fiber nonwoven fabric is in the range of 400 to 1400 g / m 2 .

[0016] Item 6. [[ID=4XXX]] The flame shield according to Item 1, wherein the GBD of the inorganic fiber nonwoven fabric in the compressed state is 0.47 g / cm 3 or less.

[0017] Item 7. A battery pack having a plurality of battery cells, a battery case housing the plurality of battery cells, and a flame shield according to any one of Items 1 to 6 housed in the battery case.

Brief Description of the Drawings

[0018] [Figure 1] This is a perspective view of the flame-retardant material according to the embodiment. [Figure 2] This is a schematic diagram of a battery pack according to an embodiment. [Figure 3] This graph shows the flame temperature during heating with a burner and the temperature change over time of a SUS plate using samples of each flame-shielding material. [Figure 4] Figure 3 shows a graph illustrating the temperature change over time of a SUS plate when using samples of each flame-retardant material. [Modes for carrying out the invention]

[0019] In this specification, the singular form includes both singular and plural forms unless otherwise explicitly stated herein or the context clearly contradicts it.

[0020] In this specification, "includes" is a concept that also includes "substantially consists only of" and "consists only of."

[0021] In the numerical ranges described stepwise in this specification, the upper or lower limit of a numerical range in one step can be arbitrarily combined with the upper or lower limit of a numerical range in another step. Furthermore, in the numerical ranges described in this specification, the upper or lower limit of a numerical range may be replaced with values ​​shown in the examples or values ​​that can be uniquely derived from the examples. Moreover, in this specification, numbers connected by "~" mean a numerical range that includes the numbers before and after "~" as the lower and upper limits.

[0022] The embodiments included in this disclosure will be described further below. The embodiments described below are examples of typical embodiments of this disclosure and do not limit the scope of the invention.

[0023] This disclosure provides a flame-retardant comprising an inorganic fiber nonwoven fabric and a thickness-reducing agent impregnated into the inorganic fiber nonwoven fabric, wherein the inorganic fiber nonwoven fabric is held in a compressed state in the thickness direction by the thickness-reducing agent, and the inorganic fiber nonwoven fabric recovers to a thickness of 60% or more of its thickness before impregnation with the thickness-reducing agent upon the disappearance of the thickness-reducing agent.

[0024] Inorganic fiber nonwoven fabric Inorganic fiber nonwoven fabrics are sheet-like fiber aggregates having a predetermined thickness, and include, for example, inorganic fiber blankets (also called "blankets") or papermaking mats. Because inorganic fiber nonwoven fabrics have elasticity (cushioning properties), when compressed, they generate a rebound force to restore them to their original thickness.

[0025] The inorganic fiber nonwoven fabric is preferably a needle blanket. The needle blanket is an inorganic fiber nonwoven fabric that has undergone a needleing treatment. Needling treatment not only results in a strong inorganic fiber nonwoven fabric in which the inorganic fibers constituting the inorganic fiber nonwoven fabric are intertwined, but also allows for adjustment of the thickness of the inorganic fiber nonwoven fabric.

[0026] If the inorganic fiber nonwoven fabric is a needle blanket, it has multiple needle marks, i.e., multiple recesses. The needle marks may be through holes that penetrate in the thickness direction of the inorganic fiber nonwoven fabric, or they may be non-through holes that do not penetrate.

[0027] <Material> The inorganic fibers constituting the inorganic fiber nonwoven fabric are not particularly limited, and for example, ceramic fibers, biosoluble fibers (alkali earth silicate fibers), rock wool, basalt fibers, potassium titanate fibers, calcium silicate fibers, glass fibers, etc., can be used. Examples of ceramic fibers include silica, alumina, alumina / silica, zirconia containing these, spinel, titania, and calcia, either as single fibers or composite fibers. Among these, the inorganic fibers are preferably alumina / silica fibers, and particularly preferably crystalline alumina / silica fibers. When the inorganic fibers are alumina / silica fibers, the composition ratio (mass ratio) of alumina / silica is preferably in the range of 60 / 40 to 98 / 2, more preferably in the range of 65 / 35 to 95 / 5, and preferably in the range of 70 / 30 to 80 / 20.

[0028] <Average fiber length> The inorganic fibers have an average fiber length of preferably 1.0 mm or more, more preferably 2.0 mm or more, and even more preferably 3.0 mm or more. The upper limit is not particularly limited, but preferably 3.0 × 10⁻⁶. 3 mm or less, more preferably 1.0 × 10 3 The length is less than or equal to mm. Note that the average fiber length of inorganic fibers is the average value of 300 fibers measured under a microscope.

[0029] <Average fiber diameter> The average fiber diameter of the inorganic fibers is preferably 3 μm to 15 μm, and particularly preferably 5 μm to 10 μm. The average fiber diameter is the average value of 100 fibers measured under a microscope.

[0030] <Basic weight> The basis weight (mass per unit area) of the inorganic fiber nonwoven fabric is preferably 1400 g / m². 2 The following applies: By keeping the basis weight within the above range, the thickness of the inorganic fiber nonwoven fabric can be reduced, making it possible to manufacture a flame-retardant material with improved mountability. Such a flame-retardant material can be fitted into limited spaces, such as above or between battery cells.

[0031] Also, the lower limit of the basis weight of the inorganic fiber non-woven fabric is not particularly limited, but is preferably 400 g / m 2 or more. If the basis weight is within the above range, a flame shielding material with improved flame shielding performance (especially heat insulation) can be manufactured in terms of the amount of fibers per unit area, that is, the thickness.

[0032] In terms of achieving both the mounting property and heat insulation of the flame shielding material, the basis weight of the inorganic fiber non-woven fabric is preferably 400 to 1400 g / m 2 or more.

[0033] <Bulk density> The bulk density of the inorganic fiber non-woven fabric is preferably 0.100 g / cm 3 or more, more preferably 0.125 g / cm 3 or more, and particularly preferably 0.130 g / cm 3 or more.

[0034] Also, the upper limit of the bulk density is not particularly limited, but is preferably 0.200 g / cm 3 or less, more preferably 0.190 g / cm 3 or less, and particularly preferably 0.180 g / cm 3 or less.

[0035]

[0036] If the bulk density is within the above range, since the amount of fibers per unit volume is sufficient, a flame shielding material with improved flame shielding performance (especially heat insulation performance) can be manufactured. <Thickness> The thickness of the inorganic fiber non-woven fabric is preferably 3.00 mm to 10.0 mm.

[0037] The thickness of the inorganic fiber non-woven fabric can be measured, for example, by the measurement method shown in the following examples.

[0038] The inorganic fiber non-woven fabric can be manufactured, for example, by the method disclosed in paragraphs

[0043] to

[0064] of International Publication No. 2024 / 034628.

[0039] Thickness inhibitor The thickness-reducing agent is impregnated into the inorganic fiber nonwoven fabric, restraining the inorganic fibers within the nonwoven fabric and acting to suppress the thickness of the inorganic fiber nonwoven fabric, i.e., the thickness of the flame-retardant material. Examples of thickness-reducing agents include, but are not limited to, thermoplastic resins, flame retardants, or both.

[0040] The thickness inhibitor preferably contains a thermoplastic resin. Since the thermoplastic resin melts upon heating, it restrains the inorganic fibers in the inorganic fiber nonwoven fabric under normal conditions, but releases them from restraint during heating such as thermal runaway, allowing the flame-retardant material to expand or recover. Compared to inorganic binders that do not disappear or soften upon heating, the thermoplastic resin has the advantage of allowing the flame-retardant material to expand or recover.

[0041] The thickness-reducing agent is preferably a thermoplastic resin with low viscosity when impregnated into the inorganic fibers constituting the inorganic fiber nonwoven fabric. By using a thermoplastic resin with such properties, the thermoplastic resin can be impregnated more uniformly into the entire inorganic fiber nonwoven fabric.

[0042] The thermoplastic resin is not particularly limited, but examples include polyamide, polyurethane, ethylene vinyl acetate (EVA), phenoxy resin, polyolefin, polycarbonate, polyvinyl chloride (PVC), and combinations of two or more of these. For example, polyamide is preferred from the viewpoint of heat resistance and strength, while polyolefin (e.g., polyethylene, polypropylene) is preferred from the viewpoint of cost and moldability.

[0043] Flame retardants prevent or suppress the spread of fire and improve the heat insulation properties of the flame-blocking material. Thickness-reducing agents may or may not contain flame retardants, but preferably they do. Flame retardants are broadly classified into halogen-based flame retardants and non-halogen-based flame retardants, and non-halogen-based flame retardants are preferred. Examples of non-halogen-based flame retardants include phosphorus-based flame retardants (phosphate esters, ammonium polyphosphate, etc.), metal hydroxides (magnesium hydroxide, etc.), and polytetrafluoroethylene.

[0044] The amount of thickness-reducing agent in the flame-retardant material (or the total amount if there are two or more types of thickness-reducing agents) is not particularly limited, but is, for example, 60 to 300% by mass relative to the mass of the inorganic fiber nonwoven fabric. The content of thermoplastic resin in the flame-retardant material (or the total amount if there are two or more types of thermoplastic resin) is not particularly limited, but is, for example, 60 to 250% by mass relative to the mass of the inorganic fiber nonwoven fabric. The amount of flame retardant (or the total amount if there are two or more types of flame retardants) in the flame-retardant material is not particularly limited, but is, for example, 0 to 150% by mass relative to the mass of the inorganic fiber nonwoven fabric. If the flame-retardant material contains a flame retardant, the amount of flame retardant in the flame-retardant material is preferably 15 to 150% by mass relative to the mass of the inorganic fiber nonwoven fabric.

[0045] Flameproof material The flame-retardant material of this disclosure comprises an inorganic fiber nonwoven fabric and a thickness-reducing agent impregnated into the inorganic fiber nonwoven fabric. The inorganic fiber nonwoven fabric portion of the flame-retardant material will return to a thickness of 60% or more of its thickness before the thickness-reducing agent was impregnated, due to the disappearance of the thickness-reducing agent.

[0046] For the inorganic fiber nonwoven fabric to restore to the desired thickness when the thickness-reducing agent disappears, it is necessary that the inorganic fibers of the inorganic fiber nonwoven fabric do not collapse during restoration (i.e., the inorganic fibers of the inorganic fiber nonwoven fabric do not collapse during compression), thereby maintaining the resilience of the inorganic fiber nonwoven fabric. When inorganic fibers collapse, they cannot maintain their fibrous state and become powdered.

[0047] Even if only a portion of the thickness-reducing agent disappears, the flame-retardant material will recover once the constraint on the inorganic fibers by the thickness-reducing agent is released. Therefore, the disappearance can be complete or partial.

[0048] In a preferred embodiment, the disappearance of the thickness inhibitor means that the mass of the thermoplastic resin contained in the flame-retardant after heating is 60% or less of the mass of the thermoplastic resin contained in the flame-retardant before heating.

[0049] The thickness of the flame-retardant material is preferably 0.50 mm to 15.0 mm, and more preferably 1.00 mm to 3.00 mm for housing inside the battery pack or between battery cells.

[0050] The thickness of the flame-retardant material can be measured, for example, by the measurement method shown in the following example.

[0051] <Recovery Rate> The ratio of the thickness of the flame-retardant (or the inorganic fiber nonwoven fabric in the flame-retardant, hereinafter the same) after the thickness-reducing agent has disappeared to the thickness of the inorganic fiber nonwoven fabric before impregnation with the thickness-reducing agent is referred to as the recovery rate.

[0052] The recovery rate can also be easily measured by measuring the thickness of the inorganic fiber nonwoven fabric before impregnation with the thickness-reducing agent and the thickness of another flame-retardant of the same type after the thickness-reducing agent has disappeared, and calculating the ratio between them.

[0053] For example, in one embodiment, the thickness of the flame-retardant after the thickness-reducing agent has disappeared is the thickness of the flame-retardant after heating it at 1000°C for 1 hour.

[0054] <GBD flame-retardant material> The GBD (compression density) of the flame-retardant material disclosed herein is not particularly limited, but if it is too high, there is a high possibility that crushing will occur in the inorganic fibers when the flame-retardant material is restored by heating (i.e., crushing will occur in the inorganic fibers of the inorganic fiber nonwoven fabric during compression). For this reason, the GBD of the flame-retardant material is preferably 0.47 g / cm³. 3 The following applies. The lower limit of GBD is not particularly limited, but for example, 0.13 g / cm³ 3 That's all.

[0055] The GBD of flame-retardant materials is calculated by dividing the basis weight of the inorganic fiber nonwoven fabric by its thickness when compressed. In one embodiment, the flame-retardant material of the present disclosure has a thickness of 1.5 times or more after the thickness-reducing agent has disappeared compared to the thickness before the thickness-reducing agent disappeared. In a further embodiment, the flame-retardant material of the present disclosure has a thickness of 1.00 mm to 3.00 mm before the thickness-reducing agent has disappeared, a thickness exceeding 3.00 mm after the thickness-reducing agent has disappeared, and a thickness of 1.5 times or more compared to the thickness before the thickness-reducing agent has disappeared. Such a flame-retardant material has mountability and heat insulation properties and is suitable for use in battery cells.

[0056] In one embodiment of the flame-blocking material of this disclosure, a fire-resistant layer made of an inorganic material may be laminated on at least one side of an inorganic fiber nonwoven fabric impregnated with a thickness-reducing agent. The fire-resistant layer may be a particle impact-resistant layer described in International Publication 2024 / 034628. By providing a fire-resistant layer, the flame-blocking performance (particularly particle impact resistance and fire resistance) is improved.

[0057] The fire-resistant layer may be integrated with the inorganic fiber nonwoven fabric using a thickness-reducing agent, or it may be bonded with an adhesive or the like.

[0058] Manufacturing method of flame-retardant materials The method for manufacturing the flame-retardant material of this disclosure includes an impregnation step of impregnating an inorganic fiber nonwoven fabric with a thickness-reducing agent, and a solidification step after the impregnation step of maintaining a thickness-reduced state by cooling, drying, or chemically reacting the inorganic fiber nonwoven fabric impregnated with the thickness-reducing agent. The inorganic fiber nonwoven fabric and the thickness-reducing agent have been described above and will not be described further.

[0059] The method for impregnating an inorganic fiber nonwoven fabric with a thickness-reducing agent is not particularly limited as long as it can impregnate the inorganic fiber nonwoven fabric with the thickness-reducing agent. Examples include a method of permeating the inorganic fiber nonwoven fabric with a thickness-reducing agent melted by heating, a method of coating the inorganic fiber nonwoven fabric with a liquid containing the thickness-reducing agent, and a method of injecting the inorganic fiber nonwoven fabric with a liquid containing the thickness-reducing agent. The liquid containing the thickness-reducing agent is, for example, a solvent in which the thickness-reducing agent is dissolved or a dispersion medium in which the thickness-reducing agent is dispersed.

[0060] 1. Impregnation process The impregnation process using the melted thickness inhibitor includes a heating step and a pressurizing step. The heating step may be performed before the pressurizing step or simultaneously with the pressurizing step. The heating temperature in the heating step is not particularly limited as long as it is greater than the melting point of the thickness inhibitor. In the pressurizing step, the inorganic fiber nonwoven fabric is pressurized so that it is compressed in the thickness direction compared to the inorganic fiber nonwoven fabric before pressurizing.

[0061] In one example, an inorganic fiber nonwoven fabric, in contact with a solid thickness inhibitor (e.g., a sheet, film, powder, or pellet containing a thermoplastic resin), is sandwiched between molds. During the heating stage, the thickness inhibitor is melted, and during the subsequent pressurizing stage, the melted thickness inhibitor is impregnated into the inorganic fiber nonwoven fabric. In another example, an inorganic fiber nonwoven fabric, in contact with a solid thickness inhibitor (e.g., a sheet or film containing a thermoplastic resin), is sandwiched between molds and heated under pressure, i.e., heating and pressurizing are performed simultaneously, to impregnate the inorganic fiber nonwoven fabric with the melted thickness inhibitor. In the impregnation step, the solid thickness inhibitor may be in contact with only one side of the inorganic fiber nonwoven fabric, or it may be in contact with both sides of the inorganic fiber nonwoven fabric. In this specification, "film" refers to a thin film with a thickness of less than 250 μm. "Sheet" refers to a plate-like member with a thickness of 250 μm or more. "Powder" refers to a powder with a diameter of less than 1 mm. "Pellet" refers to a granular member with a diameter of 1 mm or more.

[0062] 2.Solidification process In the solidification process using the melted thickness inhibitor, the melted thickness inhibitor is solidified by cooling. The cooling method is not particularly limited as long as it can cool the thickness inhibitor impregnated into the inorganic fiber nonwoven fabric, and examples include air cooling, water cooling, oil cooling, etc.

[0063] The cooling temperature is appropriately selected according to the cooling method and the type of thickness inhibitor, and should be a temperature at which the thickness inhibitor impregnated into the inorganic fiber nonwoven fabric solidifies. In the cooling process, the inorganic fiber nonwoven fabric is sandwiched between molds to maintain its compressed state while being cooled under predetermined conditions. The mold used in the cooling process may be the same as the mold used in the impregnation process, or it may be different. As a result, the inorganic fiber nonwoven fabric is held in a state compressed in the thickness direction by the thickness inhibitor, and the flame-retardant material of this disclosure is obtained.

[0064] In the solidification process using a solvent in which the thickness-reducing agent is dissolved or a dispersion medium in which the thickness-reducing agent is dispersed, solidification is achieved by drying the solvent or by a chemical reaction.

[0065] By selecting the viscosity of the thickness-reducing agent or the liquid containing it when impregnating the inorganic fibers constituting the inorganic fiber nonwoven fabric, and the degree of compression of the inorganic fiber nonwoven fabric, a person skilled in the art can easily manufacture a flame-retardant material in which the thickness of the inorganic fiber nonwoven fabric is suppressed under normal conditions, and when the thickness-reducing agent disappears, the inorganic fiber nonwoven fabric is restored to a thickness of 60% or more of the thickness before impregnation with the thickness-reducing agent.

[0066] In this embodiment, when the inorganic fiber nonwoven fabric is cut, the impregnation process may be performed before the cutting process or after the cutting process. The cutting process may be performed before the solidification process or after the solidification process.

[0067] Purpose The flame-retardant material disclosed herein can be used in a variety of applications, including as a flame-retardant material for battery packs. If a battery pack using the flame-retardant material disclosed herein is installed in electric mobility devices such as electric vehicles, hybrid vehicles, electric motorcycles, ships, and railways, even if the battery overheats and ignites, the high thermal insulation performance can prevent the initial spread of the fire.

[0068] Figure 1 is a perspective view of a sheet-like flame-retardant material 10 as an embodiment.

[0069] Figure 2 is a cross-sectional view of a battery pack 100 having a plurality of battery cells 20, a battery case 30 housing the plurality of battery cells 20, and the flame-retardant material 10 shown in Figure 1 housed inside the battery case 30. The battery case 30 may also be called a housing. The battery cells 20 may be cylindrical, rectangular, or pouch-type, but rectangular cells with high electrical density are preferred.

[0070] The flame-retardant material 10 may be placed on the entire or partial surface of the inner wall of the battery case 30. For example, the battery case 30 comprises a cover, i.e., an upper member 30a, and a housing, a lower member 30b, and the flame-retardant material 10 can be attached to the inner surface of the upper member 30a of the battery case 30 for use. In one embodiment, the flame-retardant material 10 is attached to the inner surface of the upper member 30a of the battery case 30 at a certain distance from the battery cells 20. Even if thermal runaway occurs in one of the battery cells 20, the flame-retardant material 10 suppresses the transfer of heat to the upper member 30a of the battery case 30. As a result, ignition from the battery case 30 is suppressed, and when the battery pack 100 is installed in an automobile or the like, occupants can be protected from flames.

[0071] The flame-shielding material 10 may be placed, for example, between adjacent battery cells 20. In one embodiment, the flame-shielding material 10 is placed in contact with one or both of adjacent battery cells 20. To suppress thermal runaway of the battery cells 20, a laminated structure may be used in which the battery cells 20 are sandwiched between a pair of flame-shielding materials 10. Even if thermal runaway occurs in a battery cell 20, the flame-shielding material 10 suppresses the transfer of heat to other adjacent battery cells 20.

[0072] All patent applications and disclosures cited herein are incorporated herein by reference in their entirety.

[0073] The following examples are for illustrative purposes only and are not intended to limit the technical scope of the present invention in any way. Unless otherwise specified, reagents may be commercially available or obtained or prepared by methods commonly used in the art or by procedures in known literature. [Examples]

[0074] 1. Manufacturing of flame-retardant materials Examples 1-4, Comparative Examples 1, 3 On top of the mold, from bottom to top, are a resin film and a blanket made of alumina / silica fiber nonwoven fabric (manufactured by Maftec Co., Ltd., 600g / m²). 2 A laminate was prepared by laminating PA6I film (polyamide resin film, each 250mm x 250mm), and a mold was placed on top of the laminate as a pressing plate. Next, the mold was placed on a hot / cold press and heated. After confirming that the mold had risen to the predetermined temperature, pressure was applied from above to compress each laminate to a predetermined thickness (for example, the target thickness during molding in Table 1). At this time, the compression allowance was controlled with spacers to ensure that it was compressed to the predetermined thickness. After holding it in the compressed state for 10 minutes, it was cooled to room temperature for about 20 minutes, and the compressed molded product was removed from the mold to complete the flame-shielding materials according to Examples 1 to 4 and Comparative Examples 1 and 3. Example 5 In the above manufacturing methods for the flame-retardant materials in Examples 1-4 and Comparative Example 1, alumina / silica fiber nonwoven fabric was used in the same manner, and as a thickness-reducing agent, pellets (PNAH5, Novacell Co., Ltd.) made by compounding a non-halogenated flame retardant with polypropylene (PP) were used.

[0075] Comparative Example 2 Blanket made of alumina / silica fiber nonwoven fabric (manufactured by Maftec Co., Ltd., 432g / m²) 2 A blanket measuring 300 mm x 300 mm was immersed in alumina sol with a solid content concentration of 9.6% by mass, so that the alumina sol impregnated the entire blanket. This blanket was sandwiched between compression jigs made of perforated metal and compressed to a predetermined thickness of 2.0 mm, adjusted with spacers. The molded product was then placed in a dryer and dried at 120°C for 10 hours to complete the flame-retardant material according to Comparative Example 2.

[0076] The thickness of the flame-retardant after drying was 2.38 mm, and the amount of inorganic binder impregnated was 76.1% by mass.

[0077] 2. Various Tests (1) Measurement of the blanket thickness before impregnation First, the thickness of the blankets in Examples 1-5 and Comparative Examples 1-3 before impregnation was measured. This thickness was calculated as the average of the measured values ​​at six arbitrarily selected points on each blanket. (2) Measurement of the thickness of the flame-retardant material before resin removal Next, the thickness of each flame-retardant material (100 mm x 180 mm) in Examples 1-5 and Comparative Examples 1-3, before resin removal, was measured. This thickness was calculated as the average of the measured values ​​at six arbitrarily selected points for each flame-retardant material. (3) Measurement of GBD Next, the GBD (g / cm³) of each flame-retardant material in Examples 1-5 and Comparative Examples 1-3. 3 The GBD was measured. As mentioned above, this GBD is calculated by dividing the basis weight of each blanket by the thickness when compressed (thickness of the flame-retardant material before resin removal). (4) Mass ratio of thickness inhibitor to inorganic fiber mass The mass ratio of the thickness inhibitor to the inorganic fiber mass is calculated by dividing the mass of the thickness inhibitor (total of resin component and flame retardant) by the inorganic fiber mass. (5) Removal of resin components Next, each flame-retardant material from Examples 1-5 and Comparative Examples 1-2 was heated at 1000°C for 1 hour to remove the resin component. Then, the thickness of each flame-retardant material (100mm x 180mm) from Examples 1-5 and Comparative Examples 1-2 after the removal of the resin component (after restoration) was measured. The calculation of this thickness was the same as the measurement of the thickness of the flame-retardant material described above. Furthermore, the condition of each flame-retardant after the removal of resin components was evaluated. Specifically, the presence or absence of pulverization of alumina / silica fibers in the flame-retardant after the removal of resin components, and the presence or absence of warp threads in the flame-retardant after the removal of resin components were qualitatively evaluated. The presence or absence of pulverization was evaluated by visual observation and by whether or not the alumina / silica fibers crumbled when touched by hand. The presence or absence of warp threads was evaluated as present if visible warp threads were present in the flame-retardant after the removal of resin components, and absent if no visible warp threads were present. (6) Calculation of the recovery rate Furthermore, the recovery rate (%) was calculated as the ratio of the thickness (mm) of the flame-retardant material after removal of the resin component to the thickness (mm) of the blanket before resin impregnation. (7) Thermal insulation performance evaluation test Next, the blanket was placed on top of a SUS plate (1.00 mm) with the blanket facing downwards, and the center of the blanket was heated from below with a burner to evaluate the thermal insulation performance of the flame-retardant material after resin removal (restoration). In the thermal insulation evaluation, a pass was given if the temperature of the SUS plate 5 minutes after the start of heating was below 300°C, and a fail was given if it was above this temperature. Since 300°C is the approximate temperature at which toxic gases are generated from the coating agent of the battery pack, the pass / fail criterion for the thermal insulation evaluation test was set at 300°C. Furthermore, the temperature of the center of the upper SUS plate was measured during heating with a burner (Figure 3).

[0078] 3.Results and discussion The results are shown in Table 1.

[0079] The flame-blocking materials in Examples 1-5 and Comparative Examples 1-2 had a thickness before resin removal within ±0.5 mm of the target thickness during molding, and were within a highly mountable thickness range of 1.00 mm to 3.00 mm. On the other hand, the flame-blocking material in Comparative Example 3 had a low mass ratio of thickness-reducing agent to inorganic fiber mass, resulting in insufficient thickness reduction to 3.35 mm compared to the target thickness of 2 mm during molding, and thus undesirable mountability could not be achieved. Furthermore, in the flame-retardant materials of Examples 1 to 5, although the resin component had disappeared after resin removal, the alumina / silica fibers had not been powdered, and the warp threads remained, suggesting that the structure and function of the flame-retardant material were maintained. As a result, the recovery rates of the flame-retardant materials in Examples 1, 2, 3, 4, and 5 were 69%, 87%, 88%, 88%, and 80%, respectively. On the other hand, in the flame-retardant material of Comparative Example 1, the alumina / silica fibers had been powdered, and the warp threads were absent, suggesting that the structure and function of the flame-retardant material had deteriorated. As a result, the recovery rate of the flame-retardant material of Comparative Example 1 was 59%. In the flame-retardant material of Comparative Example 2, although the alumina / silica fibers had not been powdered, the alumina sol (inorganic binder) maintained the constraint of the alumina / silica fibers, resulting in a low recovery rate. The flame-retardant materials of Examples 1 to 5, whose structure and function were maintained, showed a higher recovery rate compared to the flame-retardant materials of Comparative Examples 1 and 2.

[0080] As shown in Figure 4, when using the flame-retardant materials of Examples 1 to 4, the temperature of the SUS plate remained below 300°C even 5 minutes after heating with a burner, confirming that it had higher thermal insulation properties compared to the flame-retardant sheet of Comparative Example 2. Note that the flame-retardant sheet of Comparative Example 1 could not be overlaid on the SUS plate because the alumina / silica fibers had been powdered.

[0081] [Table 1] [Explanation of Symbols]

[0082] 10...Flame-retardant material, 20...Battery cell, 30...Battery case, 100...Battery pack.

Claims

1. Inorganic fiber nonwoven fabric and The inorganic fiber nonwoven fabric comprises a thickness-reducing agent impregnated with the inorganic fiber nonwoven fabric, The inorganic fiber nonwoven fabric is held in a state compressed in the thickness direction by the thickness-reducing agent, The inorganic fiber nonwoven fabric is a flame-retardant material that, upon the disappearance of the thickness-reducing agent, restores to a thickness of 60% or more of the thickness before the thickness-reducing agent was impregnated.

2. The flame-retardant material according to claim 1, wherein the inorganic fiber nonwoven fabric is a needle blanket containing alumina / silica fibers.

3. The flame-shielding material according to claim 1, wherein the thickness-reducing agent comprises a thermoplastic resin.

4. The flame-retardant material according to claim 3, wherein the thickness-reducing agent comprises a flame retardant.

5. The basis weight of the inorganic fiber nonwoven fabric is 400 to 1400 g / m². ２ The flame-retardant material according to claim 1, which is within the range.

6. The GBD of the inorganic fiber nonwoven fabric in a compressed state is 0.47 g / cm³. ３ The flame-retardant material according to claim 1, which is as follows:

7. A battery pack comprising: a plurality of battery cells; a battery case housing the plurality of battery cells; and a flame-retardant material according to any one of claims 1 to 6 housed within the battery case.

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