Power storage device structure

Abstract

A power storage device structure according to the present invention comprises a power storage device and a casing that encloses the power storage device with a gap therebetween, and has a structure in which a thermally-depolymerizable polymer foam-molded body is disposed in the gap between the power storage device and the casing. Such a power storage device structure makes it possible to reduce the risk of ignition when an abnormality occurs, such as damage to or overcharging of the power storage device, or in particular, a power storage device stack in which a plurality of the power storage devices are stacked.

Description

Electricity storage device structure

[0001] The present invention relates to an electricity storage device structure that encapsulates an electricity storage device such as a lithium ion battery, a lithium ion capacitor, or an electric double layer capacitor, and in particular to an electricity storage device structure that can reduce the risk of fire in the event of an abnormality such as damage to the electricity storage device or overcharging.

[0002] In recent years, electricity storage devices such as secondary batteries, lithium ion capacitors, and electric double layer capacitors, each of which has an electricity storage device using a non-aqueous electrolyte housed in a casing, have been used as power sources for high-output portable devices, electric vehicles, and the like.

[0003] Such energy storage devices typically have a set upper voltage limit, and are controlled to not exceed the upper voltage limit by combining them with an appropriate protection circuit. However, if the protection circuit malfunctions and the upper voltage limit is exceeded, if charging and discharging are repeated, or if a short circuit occurs due to an external factor, the energy storage device falls into an overcharged state, and the electrolyte reacts with the electrode material, etc., generating gas, which increases the internal pressure. This generated gas may contain flammable gases such as the electrolyte, methane, carbon monoxide, ethylene, ethane, and propane, and may pose a risk of fire or explosion if released outside the energy storage device.

[0004] In recent years, there has been a demand for higher output and larger capacity in electricity storage devices such as lithium-ion capacitors and electric double-layer capacitors, and opportunities to use large currents in individual electricity storage devices or in modules in which multiple electricity storage devices are stacked are increasing. For example, in a module in which multiple electricity storage devices are stacked, if one electricity storage device falls into an overcharged state, even after gas is released together with the electrolyte, the other electricity storage devices may continue to function and continue to flow a large current. This may result in severe overheating due to a short circuit, increasing the risk of fire or explosion as described above.

[0005] As a technology for preventing ignition of such an electricity storage device, for example, a method has been proposed in which gas generated inside a lithium ion battery is absorbed by a flammable gas absorbent material to prevent the battery from exploding (Patent Documents 1 and 2).

[0006] On the other hand, a method has been proposed in which a fire extinguishing agent is placed inside a lithium-ion battery to lower the temperature of the gas released to the outside when the safety valve opens due to an increase in internal pressure caused by gas generation inside the battery (Patent Document 3).Furthermore, a method has been proposed in which a porous material having a non-flammable gas, an aqueous solvent, or a non-flammable solvent adsorbed in the pores and on the surface is placed inside the lithium-ion battery to prevent fires caused by gas generated from the lithium-ion battery (Patent Document 4).

[0007] JP 2001-155790 A JP 2003-077549 A JP 2010-287488 A JP 2013-187089 A

[0008] However, because a large amount of gas is instantaneously generated during an electrical abnormality or thermal runaway, the method of disposing a gas adsorbent in an electricity storage device as described in Patent Documents 1 and 2 has the problem that both the gas adsorption amount and gas adsorption speed are insufficient for the limited space of an electricity storage device, and gas emission from the electricity storage device cannot be completely suppressed. Also, as described in Patent Documents 3 and 4, the method of disposing a fire extinguishing agent or a material that adsorbs a non-flammable gas or an aqueous solvent or a non-flammable solvent in the pores and surface of a porous material in an electricity storage device to lower the temperature inside the lithium ion battery has the problem that if the gas adsorption amount is insufficient, the effect is not fully exerted and gas emission cannot be completely suppressed.

[0009] The present invention has been made in consideration of the above-mentioned problems, and aims to provide an electricity storage device structure that can reduce the risk of fire in the event of an abnormality such as damage or overcharging of an electricity storage device, particularly an electricity storage device stack in which multiple electricity storage devices are stacked.

[0010] In order to solve the above problems, the present invention provides an electricity storage device structure comprising an electricity storage device and a casing that encases the electricity storage device with a gap therebetween, in which a foamed molded body of a thermally depolymerizable polymer is disposed in the gap between the electricity storage device and the casing (Invention 1).

[0011] According to this invention (Invention 1), by placing a foamed molded body of a thermally depolymerizable polymer that decomposes into monomers when heated in the space of the casing that encases the electricity storage device, rather than inside the electricity storage device, it is possible to reduce the risk of fire spreading outside the casing in the event of a fire occurring inside the electricity storage device.

[0012] In the above invention (invention 1), it is preferable that the electricity storage device uses a non-aqueous electrolyte (invention 2).

[0013] According to this invention (Invention 2), it is possible to preferably exert the effect of preventing the fire from spreading to the outside when a fire occurs inside the electricity storage device due to the non-aqueous electrolyte.

[0014] In the above invention (Invention 1), it is preferable that the foamed molded article of the thermally depolymerizable polymer contains a thermally depolymerizable polymer portion in an amount of 10% by weight or more of the total weight (Invention 3).

[0015] According to this invention (Invention 3), it is possible to preferably exert the effect of preventing the fire from spreading to the outside when a fire occurs inside the electricity storage device.

[0016] In the above invention (Invention 1), the foamed molded product of the thermally depolymerizable polymer is preferably a foamed molded product of a polymer (homopolymer or copolymer of two or more components) using one or more of methyl methacrylate (MMA), α-methylstyrene (AMS), and tetrafluoroethylene (TFE) as monomer components (Invention 4).

[0017] According to this invention (Invention 4), it is possible to preferably exert the effect of preventing the fire from spreading to the outside when a fire occurs inside the electricity storage device.

[0018] In the above invention (Invention 1), the foamed molded product of the thermally depolymerizable polymer is preferably in the form of a sheet or plate (Invention 5).

[0019] According to this invention (Invention 5), by making it in a sheet or plate shape, it can be attached inside a casing or inserted into a gap, allowing for a wide variety of installation options and making it easy to handle.

[0020] In the above invention (Invention 5), the sheet-like or plate-like foamed molded article preferably has a thickness of 1 mm to 100 mm (Invention 6). In particular, in the above invention (Invention 6), the sheet-like or plate-like foamed molded article preferably has a density of 18 g to 20 g / L (Invention 7).

[0021] According to such inventions (Inventions 6 and 7), by placing a sheet-like or plate-like foamed molded body of a predetermined thickness and weight in the gap between the electricity storage device and the casing, it is possible to effectively prevent the fire from spreading to the outside in the event of a fire occurring inside the electricity storage device.

[0022] In the above inventions (Inventions 1 to 7), a plurality of the electricity storage devices may be stacked (Invention 8).

[0023] In an electricity storage device stack in which multiple electricity storage devices are stacked, even if one electricity storage device falls into an overcharged state, the other electricity storage devices continue to function and a large current continues to flow, causing severe overheating and making it easy for flammable gas to exceed its ignition temperature.In this case, according to this invention (Invention 8), even if flammable gas is ejected from the electricity storage device and flows into the space in the casing, the material of the present invention has an effect on the flammable gas, thereby significantly reducing the risk of the fire spreading outside the casing, making it particularly suitable for application to electricity storage device stacks.

[0024] The present invention significantly reduces the risk of fire in an electricity storage device structure by disposing a foamed molded body of a thermally depolymerizable polymer in the gap between the electricity storage device and the casing, due to a mechanism in which the thermally depolymerizable polymer is thermally decomposed to generate monomers by high-temperature ejecta or gas emitted from the electricity storage device due to a short circuit, etc. Moreover, because the thermally depolymerizable polymer is converted into monomers by heat, no combustion residues or the like remain in the casing.

[0025] The electricity storage device structure of the present invention will be described in detail below based on the following embodiments.

[0026] [Electricity storage device structure] The electricity storage device structure of this embodiment comprises an electricity storage device and a casing that encases the electricity storage device with a gap therebetween, and has a structure in which a foamed molded body of a thermally depolymerizable polymer is disposed in the gap between the electricity storage device and the casing.

[0027] (Electricity Storage Device) In this embodiment, the electric storage device is not particularly limited, and either a primary battery or a secondary battery can be used, but a secondary battery is preferred. The type of this secondary battery is not particularly limited, and for example, a lithium ion battery, a lithium ion polymer battery, an all-solid-state battery, a lead acid battery, a nickel-metal hydride battery, a nickel-cadmium battery, a nickel-iron battery, a nickel-zinc battery, a silver oxide-zinc battery, a metal-air battery, a polyvalent cation battery, a condenser, a capacitor, etc. can be used. Among these, those using a nonaqueous electrolyte can be preferably used. Among these secondary batteries, lithium ion batteries, lithium ion polymer batteries, lithium ion capacitors, all-solid-state batteries, etc. can be preferably used as suitable applications of the battery material of the present invention.

[0028] The non-aqueous electrolyte may be, for example, a mixed solution of a cyclic carbonate such as propylene carbonate (PC) or ethylene carbonate (EC) with a chain carbonate such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), or diethyl carbonate (DEC). Furthermore, the non-aqueous electrolyte may contain a lithium salt such as lithium hexafluorophosphate dissolved therein as needed. For example, a mixed solution obtained by mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a ratio of 1:1:1, or a mixed solution obtained by mixing propylene carbonate (PC), ethylene carbonate (EC), and diethyl carbonate (DEC) in a ratio of 1:1:1 to which 1 mol / L of lithium hexafluorophosphate has been added, may be used.

[0029] The above-described electricity storage device may be in the form of an electricity storage device stack in which a plurality of such devices are stacked. An electricity storage device stack is particularly suitable because, even if one electricity storage device falls into an overcharged state, the other electricity storage devices continue to function and a large current continues to flow, and therefore, when flammable gas is generated due to the non-aqueous electrolyte, the temperature is likely to exceed the ignition temperature.

[0030] (Casing) In this embodiment, the casing is not particularly limited as long as it can enclose the above-mentioned electricity storage device (electricity storage device stack) with a gap therebetween, and examples thereof include a storage case for the electricity storage device (electricity storage device stack), such as a battery case, a housing for a device that uses the electricity storage device (electricity storage device stack), etc. The material of this casing is not limited, and it can be made of synthetic resin, metal, or the like.

[0031] (Ignition Prevention Material) In this embodiment, a foam molded body of a thermally depolymerizable polymer is disposed as the ignition prevention material disposed in the gap between the electricity storage device and the casing.

[0032] (Thermal Depolymerizable Polymer) In this embodiment, the thermal depolymerizable polymer refers to a polymer that has depolymerization properties in which a polymer is decomposed into monomers by heat or light and leaves no residue when heated. Examples of the thermal depolymerizable polymer include thermal depolymerizable polymers whose base polymer is a polymer (homopolymer or polymer of two or more components) using one or more of methyl methacrylate (MMA), α-methylstyrene (AMS), and tetrafluoroethylene (TFE) as monomer components. Among these, a polymer using methyl methacrylate (MMA) and α-methylstyrene (AMS) as monomer components is preferred, or a polymer composed of methyl methacrylate (MMA):α-methylstyrene (AMS) in a molar ratio of 5:95 to 95:5 may also be used. Furthermore, a polymer obtained by blending other monomer components (monomers such as styrene) during polymerization of these polymers may also be used. Such thermally depolymerizable polymers can significantly reduce the risk of fire in the energy storage device structure, due to the mechanism in which they undergo thermal decomposition to generate monomers due to high-temperature ejecta and gas emitted from the energy storage device due to a short circuit or other reason.

[0033] (Foamed Molded Product of Thermally Depolymerizable Polymer) In this embodiment, the foamed molded product of the thermally depolymerizable polymer can be produced using one or more of methyl methacrylate (MMA), α-methylstyrene (AMS), and tetrafluoroethylene (TFE) as monomer components using a known method (for example, the method described in JP 2007-314774 A).

[0034] The foamed molded article of the thermally depolymerizable polymer may contain any suitable additives as needed. Examples of the additives include crosslinkers, tackifiers, plasticizers (e.g., trimellitic ester-based plasticizers, pyromellitic ester-based plasticizers, etc.), pigments, dyes, fillers, antioxidants, conductive materials, antistatic agents, UV absorbers, light stabilizers, release agents, softeners, surfactants, flame retardants, and antioxidants. Known fire extinguishing agent components can also be added to the foamed molded article, or known fire extinguishing agents can be sandwiched between the foamed molded article and used.

[0035] In this embodiment, there are no particular limitations on the shape of the foam molded article to be placed in the gap between the electricity storage device and the casing, but a sheet or plate shape is preferred in consideration of ease of handling when placing it in the gap between the electricity storage device and the casing. By making the fire prevention material into a sheet or plate shape, it is possible to provide a wide variety of installation options, such as pasting it inside the casing or inserting it into a gap. In the case of a sheet or plate-shaped foam molded article, a thickness of 1 mm to 100 mm, particularly 10 mm to 80 mm, is preferred in terms of ease of handling and profitability. Furthermore, the density of the foam molded article, particularly a sheet or plate-shaped foam molded article, is preferably about 18 g to 20 g / L.

[0036] Furthermore, these ignition prevention materials can also be used by adding materials that have a cooling effect through heat transfer and absorption against ejected materials and gases from the electricity storage device, an effect of suppressing combustion radical reactions, and an extinguishing effect that makes flames on the surface of the adsorbent unstable.

[0037] The above-mentioned fire prevention materials may be used alone or in combination of two or more materials.

[0038] The electricity storage device structure of the present invention has been described above, but the present invention is not particularly limited in size or shape of the electricity storage device (electricity storage device stack) as long as a foam molded article of a thermally depolymerizable polymer is disposed in the space between the electricity storage device (electricity storage device stack) and the casing. Therefore, the present invention is applicable to electricity storage devices (electricity storage device stacks) of a wide range of sizes, from smartphones and storage batteries to in-vehicle devices.

[0039] The present invention will be described in more detail based on the following specific examples, but the present invention is not limited to the following examples. [Production of foamed molded article of thermally depolymerizable polymer] In these examples, a foamed molded article of a thermally depolymerizable polymer was produced by the following method based on the method described in JP 2007-314774 A.

[0040] The internal volume is 1 m with a stirring device. ３Into an autoclave, 430 kg of deionized water, 0.4 kg of tribasic calcium phosphate (manufactured by Taihei Chemical Industry Co., Ltd.) as a suspending agent, 70 g of disodium dodecyl diphenyl ether sulfonate (manufactured by Kao Corporation: Pelex SSH 50% aqueous solution) as a surfactant, and 0.65 kg of sodium acetate as an electrolyte were charged. Next, 1.5 kg of benzoyl peroxide (Niper BW, water-dilutable powder product, manufactured by NOF Corporation) as a polymerization initiator, 0.4 kg of t-butylperoxy-2-ethylhexyl monocarbonate (Perbutyl E, manufactured by NOF Corporation), 3.1 kg of liquid paraffin (Moresco White P60, average carbon number 20, manufactured by MORESCO Corporation) as a network former, and 0.6 kg of α-methylstyrene dimer (Nofmer MSD, manufactured by NOF Corporation) as a chain transfer agent were dissolved in 233 kg of methyl methacrylate, 56 kg of styrene, and 22 kg of α-methylstyrene, and the solution was charged into an autoclave while stirring at 110 rpm. After replacing the atmosphere inside the autoclave with nitrogen, the temperature was raised to 80°C over one and a half hours. During the temperature increase to 80°C, when the temperature reached 60°C, 0.8 kg of a 0.02% aqueous solution of potassium persulfate was added as a suspension aid. After reaching 80°C, the temperature was further increased to 115°C over 6 hours, maintained at 115°C for 5 hours, and then cooled to 30°C over approximately 6 hours. While increasing the temperature from 80°C to 115°C, 37 kg of pentane (a mixture of 80% n-pentane and 20% isopentane) was added to the autoclave over approximately 60 minutes when the temperature reached 110°C. After the addition of the blowing agent, the stirring speed was reduced to 90 rpm. After cooling, the contents were removed, and nitric acid was added to dissolve the tribasic calcium phosphate adhering to the surface of the expandable acrylic resin particles. The contents were then dehydrated and washed in a centrifuge, and the moisture adhering to the surface was removed using an airflow dryer, yielding expandable acrylic resin particles with an average particle size of approximately 0.8 mm. The resulting expandable acrylic resin particles were sieved to separate particles with diameters of 0.5 to 1.2 mm. To 100 parts by weight of these expandable acrylic resin particles, 0.015 parts by weight of N,N-bis(2-hydroxyethyl)alkylamine as an antistatic agent was added, and the particles were further coated with a mixture of 0.2 parts by weight of zinc stearate and 0.1 parts by weight of glycerin monostearate.12.5 kg of the obtained expandable acrylic resin particles were heated in a pressure batch expansion machine (DYH850, manufactured by Daisen Kogyo Co., Ltd.) by supplying steam so that the pressure inside the expansion machine became 0.01 MPa (gauge pressure), and the steam pressure was maintained for about 80 seconds to make the bulk density about 20 kg / m. ３ As a result, foamed acrylic resin particles were obtained.

[0041] The resulting foamed beads were placed in an aging silo and aged at room temperature for one day. A block molding machine (VS-2000-5VMC, manufactured by Daisen Kogyo Co., Ltd.) was used to mold the foamed beads into a block. The mold dimensions were 2.0 m long x 1.0 m wide x 0.5 m thick, and heating and demolding were controlled using a pressure gauge attached to the center of the 2.0 m x 1.0 m surface of the mold. Steam was supplied into the mold to heat the foamed acrylic resin beads filled in the mold until the foaming pressure reached a maximum of 0.098 MPa. The mold was then water-cooled for three seconds. The pressure inside the mold cavity was then reduced to -0.06 MPa (gauge pressure). This reduced pressure was maintained until the pressure gauge reached 0.00 MPa (gauge pressure). The mold was then opened, and a block-shaped foamed molded product was removed. The resulting foamed molded product had a density of approximately 19 g / L.

[0042] [Overcharge Test] (Comparative Example 1) A PP resin container (inner diameter: 80 mm wide x 105 mm long x 34 mm deep, resin thickness: 2 mm, the electrode side of an aluminum-laminated lithium-ion battery was placed on the 80 mm wide side of the PP resin container, and five 10 mm diameter holes were drilled on the 80 mm wide side of the PP resin container, leaving an open top) was prepared as a container for an electricity storage device. A 1500 mAh aluminum-laminated lithium-ion battery (35 mm wide, 75 mm long) with a positive electrode ternary system was placed inside the PP resin container, and a 4 mm thick PP resin plate was placed over the battery and the periphery of the lid was sealed tightly with heat-resistant tape, so that any ejection from the lithium-ion battery due to overcharge would be released only through the five holes.

[0043] A PP resin container intended for the casing container (inner diameter: 98 mm wide x 148 mm long x 48 mm deep, resin thickness: 2 mm, container with an open top and five 10 mm diameter holes drilled on the 98 mm wide side (a container with holes drilled on the opposite side to the holes in the PP resin container intended for the above-mentioned electricity storage device container)) was placed outside the PP resin container intended for the electricity storage device container, and wiring was provided so that the battery could be overcharged.A 4 mm thick PP resin plate was then placed over the container to cover the lid, and the edges of the lid were sealed using heat-resistant tape so that there were no gaps, thereby completing an electricity storage device structure so that any ejection from the battery in the event of overcharge would be released only through the five holes.

[0044] When this electricity storage device structure was overcharged at 15 V and 7.5 A, the battery was destroyed after about 19 minutes, and violent fire was observed on the outside of the casing.

[0045] (Example 1) In the electricity storage device structure used in Comparative Example 1, a plate-shaped molded product (thickness 3 mm, density 19 g / L) of the foamed acrylic resin obtained above as a foamed molded product of a thermally depolymerizable polymer was attached to the upper surface of the inner side of a PP resin plate of an upper cover of a PP resin container assumed to be a casing by 0.011 m. ２ The resulting assembly was attached with double-sided tape to form a power storage device structure.

[0046] When this electricity storage device structure was overcharged under the same conditions as in Comparative Example 1, that is, at 15 V and 7.5 A, the battery was destroyed after about 19 minutes, but no fire was observed outside the casing.

Claims

1. An electricity storage device structure comprising an electricity storage device and a casing that encases the electricity storage device with a gap therebetween, in which a foamed molded body of a thermally depolymerizable polymer is disposed in the gap between the electricity storage device and the casing.

2. The electricity storage device structure according to claim 1, wherein the electricity storage device uses a non-aqueous electrolyte.

3. The electric storage device structure according to claim 1, wherein the thermally depolymerizable polymer foam contains a thermally depolymerizable polymer portion in an amount of 10% by weight or more of the entire foam.

4. The energy storage device structure according to claim 1, wherein the foamed molded product of the thermally depolymerizable polymer is a foamed molded product of a polymer (homopolymer or copolymer of two or more components) using one or more of methyl methacrylate (MMA), α-methylstyrene (AMS), and tetrafluoroethylene (TFE) as monomer components.

5. The electricity storage device structure according to claim 1, wherein the foamed molded product of the thermally depolymerizable polymer is in the form of a sheet or plate.

6. The electricity storage device structure according to claim 5, wherein the sheet-like or plate-like foam molded article has a thickness of 1 mm to 100 mm.

7. The electricity storage device structure according to claim 6, wherein the density of the sheet-like or plate-like foamed molded article is 18 g to 20 g / L.

8. The electricity storage device structure according to any one of claims 1 to 7, wherein a plurality of the electricity storage devices are stacked.