Battery pack

Abstract

A battery pack comprising: a housing; a secondary battery accommodated in the housing; and a fire extinguishing film disposed in the housing and containing a fire extinguishing agent. When thermal runaway of the secondary battery is caused in the battery pack, a value calculated by the following formula (1) is 550 or less. (C1-V1) / A1 ･･･ (1) (In this formula, C1 represents the capacity (unit: cm3) of the housing, V1 represents the volume (unit: cm3) of the secondary battery, and A1 represents the mass (unit: g) of the fire extinguishing agent reacted due to ignition of the secondary battery.)

Description

Battery pack

[0001] The present disclosure relates to a battery pack.

[0002] In recent years, technological advances have made our lives more comfortable. However, a large amount of energy is required to create this comfort. High levels of safety are required in the handling of energy in a variety of situations, such as when large amounts of energy are densely packed, stored, transported, and used.

[0003] Taking automobiles as an example, there is a risk of ignition and fire when mining fossil fuels, refining gasoline from fossil fuels, transporting gasoline, and burning gasoline in the engine.

[0004] Taking electronics as an example, there is a similar risk of fire when electrical energy is transferred through power lines, when electrical energy is regulated in substations or transformers, when electrical energy is used in electrical equipment in homes or factories, or when electrical energy is temporarily stored in batteries.

[0005] Lithium-ion batteries, a typical secondary battery, are known to short-circuit and cause fires when overcharged or subjected to strong external impacts. When a lithium-ion battery shorts or experiences thermal runaway, it releases a large amount of flammable gas, which can cause a serious fire. Therefore, in recent years, functional materials have been installed in modules containing secondary batteries for the purpose of fire suppression.

[0006] For example, Patent Document 1 discloses an electricity storage module including a flame-retardant heat-insulating sheet, and Patent Document 2 discloses a battery module characterized by the placement of a fire-extinguishing sheet at a specific position.

[0007] JP 2019-147357 A JP 2022-145344 A

[0008] However, although the power storage module of Patent Document 1 can prevent the spread of fire, it cannot extinguish flames that occur in the battery cells, nor can it prevent the spread of fire caused by ignition of high-temperature gas.

[0009] Furthermore, in the battery module of Patent Document 2, if a cell catches fire, a large amount of high-temperature flammable gas is released from inside the battery module. Therefore, the released fire extinguishing agent is pushed out of the battery module in an extremely short time. As a result, there is a possibility that the fire will not be fully extinguished.

[0010] The present disclosure has been made in consideration of the above circumstances, and provides a battery pack that has excellent fire extinguishing performance in the event of a fire occurring in a secondary battery.

[0011] The present disclosure provides the following battery pack: [1] A battery pack comprising: a housing; a secondary battery housed in the housing; and a fire-extinguishing film containing a fire-extinguishing agent, disposed in the housing, wherein, when thermal runaway occurs in the secondary battery, the value calculated by the following formula (1) is 550 or less: (C1-V1) / A1 (1) [where C1 is the volume of the housing (unit: cm ３ ), and V1 is the volume of the secondary battery (unit: cm ３), and A1 represents the mass (unit: g) of the fire-extinguishing agent that reacts due to the ignition of the secondary battery.] [2] The battery pack according to [1], wherein the fire-extinguishing film has a laminated structure including a substrate and a fire-extinguishing agent layer, and the fire-extinguishing agent layer contains a fire-extinguishing agent and a binder resin. [3] The battery pack according to [1] or [2], wherein the fire-extinguishing agent contains potassium citrate and potassium chlorate. [4] The battery pack according to any one of [1] to [3], wherein the housing has an opening that connects the inside of the housing to the outside of the housing. [5] The battery pack according to [4], wherein the fire-extinguishing film is provided in a position that covers at least a part of the opening. [6] The battery pack according to [4] or [5], wherein the opening is formed in a position that satisfies the condition expressed by the following inequality (a): L1>L2...(a) [wherein L1 represents the shortest distance from the opening to the positive electrode of the secondary battery, and L2 represents the shortest distance from the opening to the negative electrode of the secondary battery. [7] The battery pack according to any one of [1] to [6], wherein the fire-extinguishing film is disposed at a position that satisfies the condition expressed by the following inequality (b): L3<L4 (b) [where L3 represents the shortest distance from the fire-extinguishing film to the positive electrode of the secondary battery, and L4 represents the shortest distance from the fire-extinguishing film to the negative electrode of the secondary battery.] [8] The battery pack according to any one of [1] to [7], wherein the casing has a fragile part that breaks under external pressure to form an opening. [9] In formula (1), V1 is 45 cm ３ More than 9000cm ３

[10] In formula (1), C1-V1 is 100 cm ３ More than 50000cm ３ The battery pack according to any one of [1] to [9] below.

[0012] According to the present disclosure, a battery pack is provided that has excellent fire extinguishing performance in the event of a fire occurring in a secondary battery.

[0013] FIG. 1 is a perspective view schematically showing a battery pack according to one embodiment. FIG. 2 is a cross-sectional view taken along a line a-a in FIG. 1. FIG. 3 is a cross-sectional view taken along a line b-b in FIG. 1. FIG. 4 is a cross-sectional view schematically showing an example of a fire extinguishing film. FIG. 5 is a plan view schematically showing an example of a fire extinguishing film. FIG. 6 is a cross-sectional view schematically showing the fire extinguishing film taken along line II-II in FIG. 5. FIG. 7 is a cross-sectional view schematically showing a battery pack according to another embodiment. FIG. 8 is a plan view schematically showing the surface of the fire extinguishing agent layer on the secondary battery side after a fire extinguishing test.

[0014] Preferred embodiments of the present disclosure will be described in detail below. However, the present disclosure is not limited to the following embodiments. In the drawings, the same or corresponding parts are designated by the same reference numerals, and redundant explanations will be omitted.

[0015] [Battery Pack] First Embodiment A battery pack according to a first embodiment will now be described. Fig. 1 is a perspective view schematically showing a battery pack according to this embodiment. Fig. 2 is a cross-sectional view taken along a line a-a in Fig. 1. Fig. 3 is a cross-sectional view taken along a line bb in Fig. 1.

[0016] 1 to 3 includes a housing 10, a secondary battery 15 housed in the housing 10, and a fire-extinguishing film 20 disposed within the housing. The housing 10 has an opening 10a that connects the inside of the housing 10 to the outside of the housing 10. The battery pack 100 has a value calculated by the following formula (1) of 550 or less: (C1-V1) / A1 (1) [where C1 is the volume of the housing (unit: cm ３ ), and V1 is the volume of the secondary battery (unit: cm ３ ), and A1 represents the mass (unit: g) of the fire extinguishing agent that reacted due to the ignition of the secondary battery.]

[0017] The value calculated by the above formula (1) is preferably 450 or less, more preferably 300 or less, even more preferably 250 or less, and particularly preferably 200 or less. This tends to further improve fire extinguishing performance. The value calculated by the above formula (1) is preferably 0 or more, more preferably 5 or more, and even more preferably 10 or more. This tends to provide an appropriate spatial volume within the battery pack, which allows the fire extinguishing agent to be contained within the battery pack and improves fire extinguishing performance.

[0018] In formula (1), when the housing has an opening, the volume of the housing is the volume calculated as if the housing did not have the opening. The volume is calculated based on the internal dimensions of the housing. When the secondary battery has an exterior, the volume of the secondary battery in formula (1) is the volume of the exterior. The volume is calculated based on the external dimensions of the exterior. Items other than the secondary battery and the fire extinguishing film may or may not be housed inside the housing. The volume of the items other than the secondary battery and the fire extinguishing film may be 30% by volume or less, 20% by volume or less, 10% by volume or less, 5% by volume or less, 3% by volume or less, or 1% by volume or less, based on C1-V1 in formula (1).

[0019] The battery pack 100 can be suitably used in, for example, various vehicles such as automobiles, bicycles, agricultural machinery, and aircraft, electronic devices such as notebook computers and mobile phones, and other consumer devices that use secondary batteries.

[0020] In the above formula (1), C1 is 50 cm ３ Above, 500cm ３ or more, or 1500 cm ３ C1 may be 600,000 cm or more. ３ Below, 100000cm ３ or less than 10,000 cm ３ It may be the following:

[0021] When the battery pack is for an automobile, C1 in the above formula (1) is 10000 cm ３ More than 50000cm ３ or more, or 100,000 cm ３ C1 may be 600,000 cm or more.３ Below, 450000cm ３ or less, or 300,000 cm ３ It may be the following:

[0022] When the battery pack is for a bicycle, C1 in the above formula (1) is 500 cm ３ Above, 1000cm ３ or more, or 1300 cm ３ C1 may be 3000 cm or more. ３ Below, 2500cm ３ or less than 1500 cm ３ It may be the following:

[0023] In the above formula (1), V1 is 45 cm ３ Above, 450cm ３ or more, or 1400 cm ３ V1 may be 540000 cm or more. ３ Below, 90000cm ３ or less, or 9000 cm ３ It may be the following:

[0024] When the battery pack is for an automobile, V1 in the above formula (1) is 9000 cm ３ Above, 45000cm ３ or more, or 90,000 cm ３ V1 may be 540000 cm or more. ３ Below, 400000cm ３ or less, or 270,000 cm ３ It may be the following:

[0025] When the battery pack is for a bicycle, V1 in the above formula (1) is 1200 cm ３ Above, 900cm ３ or more, or 400 cm ３ V1 may be 2700 cm or more. ３ Below, 2200cm ３ or less than 1300 cm ３ It may be the following:

[0026] In the above formula (1), C1-V1 is 10 cm ３ Above, 100cm ３ or more, or 1000 cm ３C1-V1 may be 200,000 cm ３ Below, 100000cm ３ or less, or 50,000 cm ３ It may be the following:

[0027] When the battery pack is for an automobile, C1-V1 in the above formula (1) is 3000 cm ３ Above, 5000cm ３ or more, or 10,000 cm ３ C1-V1 may be 180000 cm ３ Below, 90000cm ３ or less, or 30,000 cm ３ It may be the following:

[0028] When the battery pack is for a bicycle, C1-V1 in the above formula (1) is 50 cm ３ Above, 200cm ３ or more, or 400 cm ３ C1-V1 may be 1000 cm ３ Below, 500cm ３ or less than 200 cm ３ It may be the following:

[0029] In the above formula (1), A1 may be 3 g or more, 30 g or more, or 70 g or more. A1 may be 6000 g or less, 3000 g or less, or 600 g or less.

[0030] When the battery pack is for use in an automobile, A1 in the above formula (1) may be 8 g or more, 30 g or more, or 80 g or more, and A1 may be 6000 g or less, 3000 g or less, or 600 g or less.

[0031] When the battery pack is for a bicycle, in the above formula (1), A1 may be 1 g or more, 3 g or more, or 5 g or more, and A1 may be 45 g or less, 25 g or less, or 15 g or less.

[0032] The thermal runaway of the secondary battery may be caused by a nail penetration test. That is, in the above formula (1), A1 may be the mass of the fire extinguishing agent that reacted in the nail penetration test. The nail penetration test is performed, for example, as follows.

[0033] (Nail penetration test) In a room with a temperature of 25±5°C and humidity of 30-80%, a nail is driven from the outside of the housing towards the secondary battery inside. The nail used must have a sufficiently sharp tip (stainless steel, N65 nail with a length of 65 mm and a body diameter of approximately 3.05 mm). The nail penetration speed is 40 mm / sec. The nail is driven so as to penetrate the secondary battery. If the battery pack has multiple cells, the nail is driven so as to penetrate one of the cells.

[0034] The housing, secondary battery, and fire-extinguishing film that constitute the battery pack according to this embodiment will be described in detail below.

[0035] <Housing> The housing 10 may be made of either resin or metal. Examples of metals include stainless steel (SUS), aluminum, iron, and high-tensile steel. Examples of resins include polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS), ABS resin, AS resin, polyethylene terephthalate (PET), acrylic resin (PMMA), polycarbonate (PC), polyamide (PA), acetal resin (POM), polybutylene terephthalate (PBT), phenolic resin, and epoxy resin. From the viewpoint of heat resistance, it is preferable that one or more flame retardants be added to these resins. Examples of flame retardants include halogen-based flame retardants, phosphorus-based flame retardants, inorganic flame retardants, nitrogen-based flame retardants, and silicone-based flame retardants.

[0036] The shape of the housing 10 is not particularly limited, but examples thereof include a cube, a rectangular parallelepiped, and a cylinder.

[0037] The housing 10 has only one opening 10a that connects the interior to the exterior. With only one opening 10a, the extinguishing agent released from the fire extinguishing film 20 is retained and can more easily hit the flames released from the opening 10a, compared to when there are two or more openings. This tends to give the battery pack 100 even better fire extinguishing performance.

[0038] The shape of the opening 10a is not particularly limited, but may be, for example, a rectangle with a width of 0.5 to 200 mm and a height of 0.5 to 200 mm, or a circle with a diameter of 1 to 30 mm. A safety valve may be provided at the opening so that when the internal pressure of the housing 10 increases, gas can be released through the safety valve to reduce the pressure.

[0039] The position where the opening 10a is provided is not particularly limited, but it is preferable that the opening be formed at a position that satisfies the condition expressed by the following inequality (a): L1>L2 (a) (where L1 represents the shortest distance from the opening to the positive electrode of the secondary battery, and L2 represents the shortest distance from the opening to the negative electrode of the secondary battery).

[0040] According to the inventors' investigations, a flame from a secondary battery is likely to be emitted from the positive electrode side of the secondary battery. By selectively forming an opening at a position that satisfies the condition expressed by inequality (a), it is possible to prevent a flame from the secondary battery from spraying out of the battery pack.

[0041] Although an example of the housing 10 has been described above, the housing is not limited to the above example. For example, in addition to the opening 10a, the housing may have an opening on a surface opposite to the surface on which the opening 10a is provided. In other words, the housing may have two or more openings.

[0042] <Secondary Battery> The secondary battery may include one cell or multiple cells. Although three secondary battery cells are illustrated in Fig. 2, the number of secondary battery cells is not limited to this. There are no particular limitations on the connection between the secondary battery cells, and they may be connected in series or in parallel.

[0043] The shape of the secondary battery cell is not particularly limited, and examples thereof include a cylindrical shape, a square shape, and a pouch shape. When the secondary battery has multiple cells, the shapes of the cells may be the same or different.

[0044] Examples of secondary batteries include lead-acid batteries, lithium-ion batteries, nickel-metal hydride batteries, and nickel-cadmium batteries. The secondary battery is preferably a lithium-ion battery because of its large capacity. The orientation of the secondary battery does not matter, whether it is upside-down or left-right. The secondary battery may or may not have an exterior case.

[0045] The capacity of the secondary battery housed in the housing (if there are multiple cells, the total capacity of each cell) may be 5.0 Ah or more, 50 Ah or more, or 100 Ah or more, and may be 10,000 Ah or less, 5,000 Ah or less, or 1,000 Ah or less.

[0046] The capacity of each cell may be 1.5 Ah or more, 5 Ah or more, or 10 Ah or more, and may be 120 Ah or less, 50 Ah or less, or 20 Ah or less.

[0047] <Fire-extinguishing film> In this embodiment, the fire-extinguishing film 20 is disposed on the inner wall of the top surface of the housing 10 and on the inner wall of the side surface facing the positive electrode 15p of the secondary battery. The positions at which the fire-extinguishing film is disposed are not limited to these positions and can be adjusted as appropriate depending on the arrangement of the secondary battery 15. The fire-extinguishing film 20 may be disposed, for example, on the inner wall of another side surface or the inner wall of the bottom surface of the housing 10. The fire-extinguishing film 20 may be disposed in one location or in two or more locations.

[0048] Although there are no particular limitations on the position where the fire extinguishing film is disposed, it is preferable that the fire extinguishing film be disposed at a position that satisfies the condition expressed by the following inequality (b): L3<L4 (b) [where L3 represents the shortest distance from the fire extinguishing film to the positive electrode of the secondary battery, and L4 represents the shortest distance from the fire extinguishing film to the negative electrode of the secondary battery]

[0049] Since it is expected that a flame from a secondary battery will likely escape from the positive electrode side of the secondary battery, selectively forming a fire-extinguishing film at a position that satisfies the condition expressed by inequality (b) can effectively extinguish a flame escaping from the secondary battery. When multiple fire-extinguishing films are arranged within the housing, L3 in inequality (b) indicates the shortest distance from the fire-extinguishing film closest to the positive electrode of the secondary battery to the positive electrode of the secondary battery. Also, when multiple fire-extinguishing films are arranged within the housing, L4 in inequality (b) indicates the shortest distance from the fire-extinguishing film closest to the negative electrode of the secondary battery to the negative electrode of the secondary battery.

[0050] The fire extinguishing film is preferably positioned to cover at least a portion of the opening, thereby effectively extinguishing a flame emitted from the secondary battery. The area of ​​the opening that is covered by the fire extinguishing film may be 50 area% or more, 60 area% or more, 70 area% or more, 80 area% or more, 90 area% or more, or 100 area% of the area of ​​the opening.

[0051] Fig. 4 is a schematic cross-sectional view showing an example of a fire extinguishing film. As shown in Fig. 4, the fire extinguishing film 20 has a laminated structure including a substrate 21 and a fire extinguishing agent layer 22. Each layer of the fire extinguishing film 20 will be described in detail below.

[0052] (Substrate) Resins can be selected as the material for the substrate 21, taking into account that the temperature of a flame is generally about 700°C to 900°C. Examples of resins include polyolefins (LLDPE, PP, COP, CPP, etc.), polyesters (PET, etc.), fluororesins (PTFE, ETFE, EFEP, PFA, FEP, PCTFE, etc.), PVC, PVA, acrylic resins, epoxy resins, polyamides, and polyimides. These resins can be perforated by heat. Furthermore, selecting a transparent material makes it easier to visually inspect the fire extinguishing film and determine when it needs to be replaced. The substrate may contain a fire extinguishing agent, as described below.

[0053] The thickness and breaking strength of the substrate can be appropriately selected depending on the amount of heat, impact, allowable space, etc., at the time of fire outbreak. For example, a thick substrate can provide strength and rigidity, and can achieve a highly flat form, making handling easier. Furthermore, a thin substrate allows the fire extinguishing film to be placed in a narrow space, and holes can be made in a short time, thereby shortening the time it takes to start extinguishing a fire. The thickness of the substrate can be, for example, 4.5 to 100 μm, and may be 12 to 50 μm. The substrate may also be a laminate of multiple substrates.

[0054] (Fire-extinguishing agent layer) The fire-extinguishing agent layer preferably contains a fire-extinguishing agent and a binder resin that fixes the fire-extinguishing agent.

[0055] As the extinguishing agent, those having the four elements of fire extinguishing (removal action, cooling action, suffocation action, and negative catalytic action) can be used appropriately depending on the fire to be extinguished. Examples of the extinguishing agent include potassium salts, sodium salts, and ammonium salts, and potassium citrate, which is a potassium salt, is particularly preferred from the viewpoint of fire extinguishing performance. Furthermore, the extinguishing agent preferably contains an oxidizing agent to promote the reaction of the agent, and potassium chlorate is particularly preferred from the viewpoint of oxidizing performance.

[0056] The content of the fire extinguishing agent may be 60% by mass or more, 90% by mass or more, or even 100% by mass, based on the total amount of the fire extinguishing agent layer, which tends to make the battery pack 100 more likely to exhibit excellent fire extinguishing performance.

[0057] Thermoplastic resins and thermosetting resins can be used as the binder resin. Examples of the thermoplastic resin include polyolefin resins such as polypropylene resins, polyethylene resins, poly(1-)butene resins, and polypentene resins, polystyrene resins, acrylonitrile-butadiene-styrene resins, methyl methacrylate-butadiene-styrene resins, ethylene-vinyl acetate resins, ethylene-propylene resins, polycarbonate resins, polyphenylene ether resins, acrylic resins, polyamide resins, polyvinyl chloride resins, polyvinyl alcohol (PVA), and polyvinyl butyral (PVB).

[0058] Examples of thermosetting resins include rubbers such as natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), 1,2-polybutadiene rubber (1,2-BR), styrene-butadiene rubber (SBR), chloroprene rubber (CR), nitrile rubber (NBR), butyl rubber (IIR), ethylene-propylene rubber (EPR, EPDM), chlorosulfonated polyethylene (CSM), acrylic rubber (ACM, ANM), epichlorohydrin rubber (CO, ECO), multi-vulcanized rubber (T), silicone rubber (Q), fluororubber (FKM, FZ), and urethane rubber (U); polyurethane resins, phenolic resins, epoxy resins, and polyvinyl ether (PMVE)-maleic anhydride resins.

[0059] The binder resin is preferably a polyurethane resin, and more preferably an ether-based urethane resin, which tends to provide even better fire extinguishing performance.

[0060] The content of the binder resin may be 30% by mass or less, 15% by mass or less, or 13% by mass or less, based on the total amount of the fire-extinguishing agent layer.

[0061] The binder resin may contain a curing agent component. Furthermore, from the viewpoint of property stability, the binder resin may contain optional additives such as a surfactant, a silane coupling agent, and an antiblocking agent.

[0062] The fire extinguishing agent layer 22 may contain components other than the fire extinguishing agent and the binder resin. Examples of the other components include a curing agent. In addition, from the viewpoint of property stability, examples of the other components include a surfactant, a silane coupling agent, and an antiblocking agent.

[0063] The fire extinguishing agent layer 22 may be formed by molding a composition containing a fire extinguishing agent and a binder resin. The composition may further contain a liquid medium in addition to the fire extinguishing agent and the binder resin.

[0064] Examples of the liquid medium include organic solvents. Examples of the organic solvent include water-soluble solvents, such as alcohols such as methanol, ethanol, isopropyl alcohol, and n-propyl alcohol; ketones such as acetone and methyl ethyl ketone; glycols such as ethylene glycol and diethylene glycol; and glycol ethers such as N-methylpyrrolidone (NMP), tetrahydrofuran, and butyl cellosolve. In view of the deliquescent properties of the organic salt and inorganic salt, the liquid medium may be an alcohol-based solvent, specifically ethanol.

[0065] The fire-extinguishing agent layer 22 is formed, for example, by applying the composition to the substrate 21 to form a coating film and then drying the coating film. The coating can be performed by a wet coating method. Examples of the wet coating method include gravure coating, comma coating, dip coating, curtain coating, spin coating, sponge roll coating, and die coating.

[0066] The fire extinguishing agent layer may be composed of a single layer, or may be composed of multiple layers with different compositions.

[0067] Although an example of the fire extinguishing film has been described above, the fire extinguishing film is not limited to the above example. For example, the fire extinguishing film may further include an adhesive layer on the surface of the substrate 21 opposite to the fire extinguishing agent layer 22.

[0068] (Adhesive Layer) The adhesive layer may be made of any known adhesive material, such as an acrylic adhesive, a urethane adhesive, a silicone adhesive, or a rubber adhesive. The thickness of the adhesive layer is preferably 1 μm to 100 μm.

[0069] (Packaging Material) The substrate 21 and the fire-extinguishing agent layer 22 may be enclosed in a packaging material 24. FIG. 5 is a plan view schematically showing an example of a fire-extinguishing film. FIG. 6 is a schematic cross-sectional view of the fire-extinguishing film shown in FIG. 5 taken along line II-II. The fire-extinguishing film 20 has a peripheral edge portion 20a. As shown in FIG. 6, the packaging material 24 has a resin film 24a, a water vapor barrier layer 24b, and an adhesive layer 24c. The peripheral edge portion 20a is formed by a sealing portion formed by the adhesive layers 24c of a pair of packaging materials 24. Each layer of the packaging material 24 will be described in detail below.

[0070] Examples of materials for the resin film 24a include polyolefin resin, polyester resin, fluororesin, vinyl resin, acrylic resin, epoxy resin, polyamide, polyimide, urethane resin, styrene-based resin, polycarbonate, ketone resin, sulfone-based resin, and cellulose-based resin.

[0071] Examples of the water vapor barrier layer 24b include inorganic metal oxide vapor-deposited layers such as an alumina vapor-deposited layer and a silica vapor-deposited layer, and metal foils such as aluminum foil. When the water vapor barrier layer is a metal oxide vapor-deposited layer, the metal oxide vapor-deposited layer may be disposed on the main surface of the resin film facing the fire extinguishing agent layer.

[0072] The water vapor permeability of the packaging material 24 is 2×10 ２ g / m ２ / day or less, and ２ g / m ２ The water vapor transmission rate is measured in accordance with JIS K 7129 under conditions of 40°C and 90% RH.

[0073] Examples of materials for the adhesive layer 24c include heat sealing materials, adhesives, and pressure sensitive adhesives.

[0074] The peripheral edge 20a is formed by a sealed portion. The sealed portion prevents the fire extinguishing agent layer 22 from coming into contact with air, thereby preventing deterioration of the stability of the fire extinguishing agent layer 22. When the adhesive layer 24c has heat-sealing properties, the sealed portion may be formed by heat fusion.

[0075] The adhesive strength between the packaging materials 24 at the sealed portion may be 5 N / 15 mm or more, or from the viewpoint of stably enclosing the fire extinguishing agent layer, may be 7 N / 15 mm or more, or may be 10 N / 15 mm or more. The adhesive strength can be varied by adjusting the resin layer, the adhesive, the heat sealing conditions (heat sealing temperature, pressure, and time), etc.

[0076] The adhesive strength between packaging materials 24 is measured as follows. That is, a sample is prepared in which a pair of packaging materials 24 are bonded together. The sealed portion of this sample is cut into a width of 15 mm, and T-peel is performed at a peel rate of 300 mm / min using a tensile tester placed in an environment of room temperature of 23°C in accordance with JIS K6854-3. The average strength from the start of peeling until the sealed portions of the packaging materials 24 are separated is taken as the adhesive strength between the packaging materials 24.

[0077] Although the packaging material shown in Fig. 6 includes a water vapor barrier layer, the packaging material does not necessarily have to include a water vapor barrier layer. Although the fire extinguishing film shown in Fig. 6 includes a substrate, the fire extinguishing film does not necessarily have to include a substrate.

[0078] Second Embodiment A battery pack according to a second embodiment will now be described. Fig. 7 is a cross-sectional view schematically showing a battery pack 200 according to this embodiment. The battery pack 200 differs from the battery pack 100 in that, instead of an opening, the battery pack 200 has a fragile portion 10b that breaks when subjected to external pressure to form an opening. In other respects, the battery pack 200 may be similar to the battery pack 100 according to the first embodiment.

[0079] The fragile portion 15b may be thinner than the other portions of the housing and break when subjected to external pressure. The thickness of the fragile portion 15b may be, for example, 30% or less, 20% or less, 10% or less, or 5% or less of the thickness of the other portions of the housing. The fragile portion 15b may be a door that opens when subjected to external pressure.

[0080] The housing 10 has one fragile portion 10b. Compared to a housing with two or more openings, the single fragile portion 10b allows the extinguishing agent released from the fire extinguishing film 20 to remain and more easily hit the flames released from the fragile portion 10b. This tends to give the battery pack 200 even better fire extinguishing performance.

[0081] Although the embodiments of the present disclosure have been described in detail above, the present disclosure is not limited to the above embodiments.

[0082] The present disclosure will be explained in more detail by the following examples, but the present disclosure is not limited to these examples.

[0083] [Example 1] <Preparation of fire extinguishing film> Potassium chlorate (KClO ３ A fire extinguishing agent was prepared by crushing ammonium nitrate and tripotassium citrate in an agate mortar to an average particle size D50 of 12 μm or less. This fire extinguishing agent was mixed with various materials in the following blending ratios to obtain a composition for forming a fire extinguishing agent layer.

[0084] Tripotassium citrate and potassium chlorate mixture: 87.4 parts by mass; Ether-based urethane resin solution (a solution obtained by dissolving 100 parts by mass of ether-based polyurethane resin in 210 parts by mass of isopropyl alcohol): 39.4 parts by mass; Ethanol: 87 parts by mass

[0085] A polyethylene terephthalate (PET) film was prepared as a substrate. The fire extinguishing agent layer-forming composition was applied to the PET film using an applicator to form a coating film. The coating film was dried in an oven at 75°C for 7 minutes. This resulted in a laminate in which a fire extinguishing agent layer (thickness: 150 μm) was formed on the substrate. The laminate was enclosed in a packaging material (layer structure: polyethylene terephthalate resin film / silica vapor deposition layer (water vapor barrier layer) / linear low-density polyethylene resin (adhesive layer)) to obtain a fire extinguishing film.

[0086] <Preparation of Housing Member> A member for forming a housing having six opposing faces open was prepared. Specifically, two 2.0 mm thick stainless steel plates were prepared. Each stainless steel plate was bent 90° at two locations to obtain a pair of U-shaped members. The pair of U-shaped members was screwed together to obtain a member (inner dimensions: 93 mm × 184 mm × 50 mm) having six opposing faces open.

[0087] <Secondary Battery> A battery box (size: 75 mm x 170 mm x 90 mm) with 7 x 4 battery storage holes in a staggered arrangement was prepared as the exterior. Twenty-eight cylindrical lithium-ion batteries (single cell, ternary type, rated voltage 3.7 V, capacity 3600 mAh, diameter 18 mm, 18650 type) were housed in the battery box to obtain a secondary battery with an exterior. The secondary batteries were housed in a plastic bag and placed inside the housing-forming member. The volume of the battery box was 1147.5 cm. ３ It was.

[0088] <Battery pack> Three pieces of fire-extinguishing film were attached to the top surface and the side surface facing the positive electrode of the lithium-ion battery of a housing-forming member. A glass plate was placed on each of the two open surfaces of the housing-forming member. A slit (opening 10a, size: width 83 mm × height 10 mm) was formed between the top surface of the housing-forming member and the glass plate. This resulted in a housing (rectangular shape, internal dimensions: 89 mm × 184 mm × 100 mm, volume: 1637.6 cm) with two openings, consisting of a rectangular parallelepiped member and a glass plate. ３ ) was obtained. This also resulted in a battery pack including a housing, a secondary battery, and a fire-extinguishing film. The fire-extinguishing film was positioned so as to satisfy the condition expressed by the above inequality (b).

[0089] <Fire Extinguishing Test> A nail penetration test was conducted indoors at a temperature of 25±5°C and humidity of 30-80%. Specifically, a nail was driven from the outside of the housing toward the lithium-ion battery inside. A sufficiently sharp nail (stainless steel, 65 mm long, approximately 3.05 mm diameter) was used. The nail penetration speed was 40 mm / sec. The nail penetration depth into the lithium-ion battery was 18 mm or more. That is, the nail penetrated the housing, the fire-extinguishing film attached to the top surface, and one lithium-ion battery. The nail was driven in a radial direction (through the outer diameter of the lithium-ion battery) perpendicular to the central axis of the lithium-ion battery. This caused thermal runaway in the lithium-ion battery, resulting in the battery ignition. The fire-extinguishing agent in the fire-extinguishing film was then checked for reaction and fire extinguishing ability, and the results were evaluated according to the following criteria. The results are shown in Table 1.

[0090] (Criteria) A: Fire was extinguished B: Fire was not extinguished

[0091] The order of fire extinguishing time was also checked in each example described later. The results are shown in Table 1. The group that extinguished the fire in the shortest time (extinguishing time: 0.6 seconds or less) was given a grade of "1," the group that extinguished the fire in the next shortest time (extinguishing time: more than 0.6 seconds but 1 second or less) was given a grade of "2," and the group that extinguished the fire in the longest time (extinguishing time: more than 1 second) was given a grade of "3."

[0092] <Value calculated by the following formula (1)> After the fire extinguishing test, the area of ​​the main surface of the fire extinguishing film consumed by fire extinguishing was measured. Specifically, the area of ​​the region (reaction region) that reacted due to ignition on the surface of the fire extinguishing agent layer facing the secondary battery was measured. FIG. 8 is a plan view schematically showing the surface of the fire extinguishing agent layer facing the secondary battery after the fire extinguishing test. The fire extinguishing agent layer 22 shown in FIG. 8 has a black region R1. The black region R1 is the region (reaction region) where the fire extinguishing agent layer 22 reacted due to ignition of the secondary battery. The reaction region was composed of a central portion where a cavity was formed due to the ejection of the fire extinguishing agent and a peripheral portion where the fire extinguishing agent had turned black due to soot. The proportion of the area consumed by fire extinguishing to the area of ​​the main surface of the fire extinguishing film was calculated. Specifically, the proportion of the area of ​​the reaction region on the surface of the fire extinguishing agent layer facing the secondary battery was calculated. The mass of the reacted fire extinguishing agent was calculated by multiplying the mass of the fire extinguishing agent contained in the fire extinguishing film before the fire extinguishing by the area proportion. The mass (unit: g) of the fire extinguishing agent that reacted with each of the multiple fire extinguishing films placed inside the housing was determined, and these were summed to calculate the mass (unit: g) of the fire extinguishing agent that reacted with the ignition in the battery pack of this example. ３ ), secondary battery (battery box) volume (1147.5 cm ３ The value was calculated from the mass of the fire extinguishing agent reacted by ignition using the following formula (1). The results are shown in Table 1.

[0093] (C1-V1) / A1 (1) [wherein C1 is the volume of the housing (unit: cm ３ ), and V1 is the volume of the secondary battery (unit: cm ３ ), and A1 represents the mass (unit: g) of the fire extinguishing agent that reacted due to the ignition of the lithium ion battery.

[0094] [Example 2] A battery pack was obtained in the same manner as in Example 1, except that one fire extinguishing film was attached to each of the top surface and the side surface facing the positive electrode of the lithium ion battery of the housing-forming member. A fire extinguishing test was carried out using the obtained battery pack in the same manner as in Example 1, and the value calculated by the above formula (1) was obtained.

[0095] [Example 3] A fire extinguishing film was obtained in the same manner as in Example 2, except that a packaging material (layer structure: polyethylene terephthalate resin layer / aluminum foil / linear low-density polyethylene resin layer) was used as the packaging material. A battery pack was obtained using the obtained fire extinguishing film in the same manner as in Example 2. A fire extinguishing test was carried out using the obtained battery pack in the same manner as in Example 2, and the value calculated by the above formula (1) was obtained.

[0096] Example 4 A fire extinguishing agent was mixed with various materials in the following blending ratios to obtain compositions for forming first and second fire extinguishing agent layers.

[0097] (First fire extinguishing agent layer forming composition) Tripotassium citrate and potassium chlorate mixture 87.4 parts by mass Ether-based urethane resin solution (solution obtained by dissolving 100 parts by mass of ether-based polyurethane resin in 210 parts by mass of isopropyl alcohol) 39.4 parts by mass Ethanol 87 parts by mass (Second fire extinguishing agent layer forming composition) Tripotassium citrate and potassium chlorate mixture 87.4 parts by mass Ether-based urethane resin solution 15.1 parts by mass Silane coupling agent 7.8 parts by mass Ethanol 87 parts by mass

[0098] A polyethylene terephthalate (PET) film was prepared as a substrate. A first fire extinguishing agent layer-forming composition was applied to the PET film using an applicator to form a coating film. The coating film was dried in an oven at 75°C for 7 minutes. This resulted in a first fire extinguishing agent layer (thickness: 150 μm) being formed on the substrate. A second fire extinguishing agent layer-forming composition was applied to the first fire extinguishing agent layer using an applicator to form a coating film. The coating film was dried in an oven at 75°C for 7 minutes. This resulted in a laminate in which a second fire extinguishing agent layer (thickness: 100 μm) was formed on the first fire extinguishing agent layer. The laminate was enclosed in a packaging material (layer structure: polyethylene terephthalate resin layer / water vapor barrier layer / linear low-density polyethylene resin layer) to obtain a fire extinguishing film.

[0099] A battery pack was obtained using the obtained fire extinguishing film in the same manner as in Example 2. A fire extinguishing test was performed using the obtained battery pack in the same manner as in Example 2, and the value calculated by the above formula (1) was obtained. The mass of the extinguishing agent that reacted due to ignition was calculated as follows. That is, the area of ​​the region that reacted due to ignition (reaction region) on the surface of the first extinguishing agent layer facing the secondary battery was measured. The proportion of the area of ​​the reaction region on the surface of the first extinguishing agent layer facing the secondary battery was calculated. The mass of the extinguishing agent that reacted in the first extinguishing agent layer was calculated by multiplying the mass of the extinguishing agent contained in the first extinguishing agent layer by the area proportion. The area of ​​the region that reacted due to ignition (reaction region) on the surface of the second extinguishing agent layer facing the secondary battery was measured. The proportion of the area of ​​the reaction region on the surface of the second extinguishing agent layer facing the secondary battery was calculated. The mass of the extinguishing agent that reacted in the second extinguishing agent layer was calculated by multiplying the mass of the extinguishing agent contained in the second extinguishing agent layer by the area proportion. The total mass of the extinguishing agent that reacted in the first and second extinguishing agent layers was taken as the mass (unit: g) of the extinguishing agent that reacted due to ignition in the battery pack of this example.

[0100] Example 5 Two 1.5 mm thick stainless steel plates were prepared. Each stainless steel plate was bent 90° at two locations to obtain a pair of U-shaped members. The pair of U-shaped members were fastened together with screws to obtain a first member (inner dimensions: 80 mm × 80 mm × 40 mm) having six rectangular parallelepiped faces, each of which had openings on one pair of opposing faces.

[0101] The battery pack 100 shown in Figures 1 to 3 was obtained. Specifically, three cylindrical lithium ion batteries (single cell, ternary type, rated voltage 3.7 V, capacity 3600 mAh) were prepared. The total volume of the three lithium ion batteries was 49.6 cm. ３Three lithium-ion batteries were placed inside the first member. Fire-extinguishing films were attached to the top surface of the first member and the side of the first member facing the positive electrodes of the lithium-ion batteries. Transparent acrylic plates were placed on each of the two open surfaces of the first member. The installation position of the acrylic plate was adjusted on one of the two open surfaces of the first member to form a slit (opening 10a, size: width 74 mm × height 10 mm) between the top surface of the first member and the acrylic plate. This resulted in a housing (rectangular shape, internal dimensions: 80 mm × 80 mm × 40 mm) with one opening, consisting of a rectangular member and an acrylic plate. This also resulted in a battery pack comprising the housing, secondary batteries, and fire-extinguishing films. A fire-extinguishing test was conducted using the obtained battery pack in the same manner as in Example 1, and the value calculated using the above formula (1) was obtained.

[0102] [Comparative Example 1] A fire extinguishing film and a battery pack were obtained in the same manner as in Example 2, except that a composition for forming a fire extinguishing agent layer obtained by mixing a fire extinguishing agent and various materials in the following compounding ratio was used. A fire extinguishing test was carried out using the obtained battery pack in the same manner as in Example 2, and the value calculated by the above formula (1) was obtained.

[0103] Tripotassium citrate and potassium chlorate mixture: 87.4 parts by mass Polyvinyl butyral resin solution: 52.5 parts by mass (a resin solution prepared by dissolving 100 parts by mass of polyvinyl butyral resin in 910 parts by mass of a mixture of ethanol and isopropyl alcohol) Silane coupling agent: 2.9 parts by mass Epoxy resin: 3.9 parts by mass Ethanol: 87 parts by mass

[0104] For each example battery pack, L1 and L2 in the above inequality (a) are shown in Table 1. L3 and L4 in the above inequality (b) are shown in Table 1. L3 is the shortest distance from the fire-extinguishing film closest to the positive electrode to the positive electrode among the multiple fire-extinguishing films. L4 is the shortest distance from the fire-extinguishing film closest to the negative electrode to the negative electrode among the multiple fire-extinguishing films.

[0105]

[0106] 10...housing, 10a...opening, 10b...fragile portion, 15...secondary battery, 20...fire-extinguishing film, 100, 200...battery pack

Claims

1. A battery pack comprising: a housing; a secondary battery housed in the housing; and a fire extinguishing film containing a fire extinguishing agent disposed in the housing, wherein when thermal runaway occurs in the secondary battery, the value calculated by the following formula (1) is 550 or less: (C1-V1) / A1 (1) [where C1 is the volume of the housing (unit: cm ３ ), and V1 is the volume of the secondary battery (unit: cm ３ ), and A1 represents the mass (unit: g) of the fire extinguishing agent that reacted due to the ignition of the secondary battery.

2. The battery pack according to claim 1, wherein the fire-extinguishing film has a laminated structure comprising a substrate and a fire-extinguishing agent layer, and the fire-extinguishing agent layer contains the fire-extinguishing agent and a binder resin.

3. The battery pack according to claim 1 or 2, wherein the fire extinguishing agent contains potassium citrate and potassium chlorate.

4. The battery pack according to claim 1 or 2, wherein the housing has an opening that connects the inside of the housing to the outside of the housing.

5. The battery pack according to claim 4, wherein the fire-extinguishing film is disposed in a position that covers at least a portion of the opening.

6. The battery pack according to claim 4, wherein the opening is formed at a position that satisfies the condition expressed by the following inequality (a): L1>L2 (a) [where L1 represents the shortest distance from the opening to the positive electrode of the secondary battery, and L2 represents the shortest distance from the opening to the negative electrode of the secondary battery] 7. The battery pack according to claim 1 or 2, wherein the fire-extinguishing film is disposed at a position that satisfies the condition expressed by the following inequality (b): L3<L4 (b) [where L3 represents the shortest distance from the fire-extinguishing film to the positive electrode of the secondary battery, and L4 represents the shortest distance from the fire-extinguishing film to the negative electrode of the secondary battery] 8. The battery pack according to claim 1 or 2, wherein the housing has a weak part that breaks when subjected to external pressure to form an opening.

9. In the formula (1), V1 is 45 cm ３ More than 9000cm ３ 3. The battery pack according to claim 1, wherein:

10. In the formula (1), C1-V1 is 100 cm ３ More than 50000cm ３ 3. The battery pack according to claim 1, wherein:

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