Energy storage device structure

Abstract

To provide a power storage device structure capable of reducing a risk of ignition at the time of abnormality such as breakage or overcharge of a power storage device, in particular, a power storage device stack in which a plurality of power storage devices are stacked.SOLUTION: The power storage device includes a power storage device and a casing that encloses the power storage device with a gap, and has a structure in which a foam molded body of a thermally depolymerizable polymer is disposed in the gap between the power storage device and the casing.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a power storage device structure that envelopes a power storage device such as a lithium-ion battery, a lithium-ion capacitor, or an electric double-layer capacitor, and particularly relates to a power storage device structure capable of reducing the risk of ignition during abnormal conditions such as when the power storage device is damaged or overcharged.

Background Art

[0002] In recent years, as a power source for high-output portable devices and electric vehicles, power storage devices such as secondary batteries, lithium-ion capacitors, and electric double-layer capacitors, which house a power storage device using a non-aqueous electrolyte in a casing, have been used.

[0003] Such power storage devices usually have a defined upper limit voltage and are controlled so as not to exceed the upper limit voltage in combination with an appropriate protection circuit. However, when the protection circuit malfunctions and exceeds the upper limit voltage, when charging and discharging are repeated, or when a short circuit occurs due to external factors, the power storage device falls into an overcharged state, and the electrolyte reacts with the electrode material and gas is generated, and the internal pressure rises due to this generated gas. This generated gas may contain flammable gases such as electrolyte, methane, carbon monoxide, ethylene, ethane, and propane, and when released outside the power storage device, there is a risk of ignition or explosion.

[0004] In recent years, in power storage devices such as lithium-ion capacitors and electric double-layer capacitors, higher output and larger capacity have been demanded, and the opportunity to use a large current in a single power storage device or a module configuration in which a plurality of power storage devices are stacked has increased. For example, in a module in which a plurality of power storage devices are stacked, when one power storage device falls into an overcharged state, even after gas is released together with the electrolyte, the other power storage devices may continue to function, and thus a large current may continue to flow. Therefore, it may be severely overheated due to a short circuit, and the risk of ignition or explosion as described above increases.

[0005] As a technology to prevent such energy storage devices from catching fire, for example, a method has been proposed in which gas generated inside the lithium-ion battery is absorbed by a flammable gas absorbent to prevent the battery from rupturing (Patent Documents 1, 2).

[0006] On the other hand, a method has been proposed to reduce 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 lithium-ion battery by placing a fire extinguishing agent inside the battery (Patent Document 3). Furthermore, a method has been proposed to prevent ignition caused by gas generated from lithium-ion batteries by placing a non-flammable gas, an aqueous solvent, or a porous material in which a non-flammable solvent is adsorbed in the pores and on the surface inside the lithium-ion battery (Patent Document 4). [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2001-155790 [Patent Document 2] Japanese Patent Publication No. 2003-077549 [Patent Document 3] Japanese Patent Publication No. 2010-287488 [Patent Document 4] Japanese Patent Publication No. 2013-187089 [Overview of the project] [Problems that the invention aims to solve]

[0008] However, in the event of electrical abnormalities or thermal runaway, a large amount of gas is instantaneously generated. Therefore, methods of placing gas adsorbents inside energy storage devices, as described in Patent Documents 1 and 2, are insufficient in terms of both gas adsorption amount and gas adsorption rate for the limited space of an energy storage device, and thus cannot completely suppress gas ejection from the energy storage device. Furthermore, as described in Patent Documents 3 and 4, methods of placing fire extinguishing agents or materials that adsorb non-combustible gases or aqueous solvents or non-combustible solvents inside an energy storage device to lower the internal temperature of a lithium-ion battery have the problem that if the amount of gas adsorbed is insufficient, the effect will not be fully realized, and gas ejection cannot be completely suppressed.

[0009] The present invention has been made in view of the above problems, and aims to provide an energy storage device structure that can reduce the risk of fire occurring in the event of abnormalities such as damage or overcharging of an energy storage device, particularly an energy storage device stack comprising multiple stacked energy storage devices. [Means for solving the problem]

[0010] To solve the above problems, the present invention provides an energy storage device structure comprising an energy storage device and a casing that encloses the energy storage device with a void, wherein a foamed molded body of a thermodepolymer is arranged in the void between the energy storage device and the casing (Invention 1).

[0011] According to this invention (Invention 1), by placing a foamed molded body of a thermodepolymer that decomposes into monomers upon heating in the space of the casing surrounding the energy storage device, rather than inside the energy storage device itself, the risk of fire spreading outside the casing in the event of ignition inside the energy storage device can be reduced.

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

[0013] According to this invention (Invention 2), it is possible to effectively prevent the spread of fire to the outside when ignition occurs in the energy storage device due to a non-aqueous electrolyte.

[0014] In the above invention (Invention 1), it is preferable that the foamed molded article of the pyropolymer contains 10% by weight or more of the pyropolymer portion (Invention 3).

[0015] According to this invention (Invention 3), it is possible to effectively prevent the spread of fire to the outside when ignition occurs inside the energy storage device.

[0016] In the above invention (Invention 1), it is preferable that the foamed molded article of the pyropolymer is a foamed molded article 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 effectively prevent the spread of fire to the outside when ignition occurs inside the energy storage device.

[0018] In the above invention (Invention 1), it is preferable that the foamed molded article of the pyropolymerizable polymer is in the form of a sheet or a plate (Invention 5).

[0019] According to this invention (Invention 5), by making it in the form of a sheet or plate, it can be attached inside the casing, inserted into gaps, and the installation variations can be increased, and it can be made easy to handle.

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

[0021] According to such an invention (Inventions 6 and 7), by disposing a sheet-like or plate-like foamed molded body having a predetermined thickness and weight in the gap between the power storage device and the casing, it is possible to suitably exhibit the effect of preventing the spread of fire to the outside when ignition occurs in the power storage device.

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

[0023] In a power storage device stack in which a plurality of power storage devices are stacked, even when one power storage device falls into an overcharged state, the other power storage devices continue to function and thus a large current continues to flow, so it becomes extremely overheated and the combustible gas is likely to reach a temperature above the ignition temperature. At this time, according to such an invention (Invention 8), even if a combustible gas jets out from the power storage device and flows out into the space of the casing, since the material of the present invention affects the combustible gas, the risk of the fire spreading outside the casing can be significantly reduced, so it can be particularly suitably applied to the power storage device stack.

Effect of the Invention

[0024] In the present invention, by disposing a foamed molded body of a thermally depolymerizable polymer in the gap between the power storage device and the casing, due to the mechanism in which the thermally depolymerizable polymer thermally decomposes to generate monomers by high-temperature ejecta or ejected gas released from the power storage device due to a short circuit or the like of the power storage device, the risk of ignition of the power storage device structure can be significantly reduced. Moreover, since the thermally depolymerizable polymer is converted into monomers by heat, no combustion residue or the like remains in the casing.

Mode for Carrying Out the Invention

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

[0026] [Power Storage Device Structure] The energy storage device structure of this embodiment consists of an energy storage device and a casing that encloses the energy storage device with a gap between them, and has a structure in which a foamed molded body of a thermodepolymer is placed in the gap between the energy storage device and the casing.

[0027] (Energy storage device) In this embodiment, there are no particular restrictions on the energy storage device, and either a primary battery or a secondary battery can be used, but a secondary battery is preferred. There are no particular restrictions on the type of secondary battery, and for example, lithium-ion batteries, lithium-ion polymer batteries, all-solid-state batteries, lead-acid batteries, nickel-metal hydride batteries, nickel-cadmium batteries, nickel-iron batteries, nickel-zinc batteries, silver oxide-zinc batteries, metal-air batteries, polyvalent cation batteries, capacitors, etc., can be used. Among these, those using a non-aqueous electrolyte can be suitably used. Among these secondary batteries, lithium-ion batteries, lithium-ion polymer batteries, lithium-ion capacitors, all-solid-state batteries, etc., can be suitably used as suitable applications for the battery material of the present invention.

[0028] As the above non-aqueous electrolyte, for example, a mixed solution of cyclic carbonates such as propylene carbonate (PC) and ethylene carbonate (EC) and chain carbonates such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) can be used. Furthermore, the above non-aqueous electrolyte may, if necessary, contain a dissolved lithium salt such as lithium hexafluoride phosphate as the electrolyte. For example, a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a 1:1:1 ratio, or a mixture of propylene carbonate (PC), ethylene carbonate (EC), and diethyl carbonate (DEC) in a 1:1:1 ratio to which 1 mol / L of lithium hexafluoride phosphate can be added can be used.

[0029] The energy storage devices described above may also be in the form of an energy storage device stack consisting of multiple devices stacked on top of each other. An energy storage device stack is particularly suitable because, even if one energy storage device enters an overcharge state, the other energy storage devices continue to function and supply a large current, making it easier for the temperature to exceed the ignition temperature when flammable gas is generated due to the non-aqueous electrolyte.

[0030] (Casing) In this embodiment, the casing is not particularly limited as long as it can enclose the energy storage device (energy storage device stack) with an air gap, and includes cases for housing energy storage devices (energy storage device stacks) such as battery cases, and housings for equipment that uses energy storage devices (energy storage device stacks). The material of this casing is not limited to synthetic resin, metal, etc.

[0031] (Flame-resistant material) In this embodiment, a foamed molded body of a thermopolymerizable polymer is placed in the gap between the energy storage device and the casing as the fire prevention material.

[0032] (Thermolytic polymer) In this embodiment, a thermally depolymerizable polymer is a polymer that has the property of depolymerizing into monomers by heat or light, and leaves no residue when heated. Examples of the above thermally depolymerizable polymer include a polymer (homopolymer or polymer with two or more components) that uses one or more of methyl methacrylate (MMA), α-methylstyrene (AMS), and tetrafluoroethylene (TFE) as monomer components as a base polymer. 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 be used, and furthermore, a polymer obtained by polymerizing these with other monomer components (monomers such as styrene) added during polymerization may also be used. Such thermally depolymerizable polymers can significantly reduce the risk of fire in energy storage device structures due to a mechanism in which they thermally decompose and generate monomers when exposed to high-temperature ejected materials or gases released from energy storage devices due to short circuits or other issues.

[0033] (Foam molded articles of pyrolytic polymers) In this embodiment, the foamed molded article of the above-mentioned pyropolymerizable 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 Japanese Patent Application Publication No. 2007-314774).

[0034] The foamed molded article of the above-mentioned pyromreparable polymer may contain any suitable additives as needed. Examples of such additives include crosslinking agents, tackifiers, plasticizers (e.g., trimellitic acid ester plasticizers, pyromellitic acid ester plasticizers, etc.), pigments, dyes, fillers, antioxidants, conductive materials, antistatic agents, ultraviolet absorbers, light stabilizers, release modifiers, softeners, surfactants, flame retardants, antioxidants, and the like. It is also possible to add known fire extinguishing agent components to the foamed molded article, or to use known fire extinguishing agents sandwiched between the foamed molded articles.

[0035] In this embodiment, there are no particular restrictions on the shape of the foamed molded body placed in the gap between the energy storage device and the casing. However, considering ease of handling when installing it in the gap between the energy storage device and the casing, it is preferable to have a sheet or plate shape. By making the fire-preventive material a sheet or plate, it is possible to attach it to the inside of the casing, insert it into gaps, and have a wide variety of installation options. In the case of a sheet or plate-shaped foamed molded body, a thickness of 1 mm to 100 mm, and particularly 10 mm to 80 mm, is preferable in terms of handling and cost-effectiveness. Furthermore, the density of the foamed molded body, especially the sheet or plate-shaped foamed molded body, is preferably about 18 g to 20 g / L.

[0036] Furthermore, these fire-preventing materials can also be used with materials that provide cooling effects through heat transfer and absorption, suppression of combustion radical reactions, and flame-extinguishing effects that destabilize flames on the surface of the adsorbent, in response to ejected materials and gases from energy storage devices.

[0037] The fire-preventing materials described above may be used individually or in combination of two or more materials.

[0038] The energy storage device structure of the present invention has been described above. However, the present invention only requires that a foamed molded body of a thermodepolymer be placed in the gap between the energy storage device (energy storage device stack) and the casing, and there are no particular restrictions on the size, shape, etc. of the energy storage device (energy storage device stack). Therefore, it can be applied to a wide range of energy storage devices (energy storage device stacks), from smartphones and batteries to automotive applications. [Examples]

[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. [Manufacturing of foamed molded articles of pyrolytic polymers] In this embodiment, the foamed molded article of the pyropolymerizable polymer was manufactured by the following method based on the method described in Japanese Patent Application Publication No. 2007-314774.

[0040] A volume of 1 m³ with a stirring device 3In the autoclave, 430 kg of deionized water, 0.4 kg of tricalcium phosphate (manufactured by Taihei Chemical Industry Co., Ltd.) as a suspension agent, 70 g of disodium dodecyldiphenyl ethersulfonate (manufactured by Kao Corporation: Perex SSH 50% aqueous solution) as a surfactant, and 0.65 kg of sodium acetate as an electrolyte were added. Next, 1.5 kg of benzoyl peroxide (manufactured by Nippon Oil & Fats Co., Ltd.: Niper BW, water-diluted powder) and 0.4 kg of t-butyl peroxy-2-ethylhexyl monocarbonate (manufactured by Nippon Oil & Fats Co., Ltd.: Perbutyl E) were dissolved as polymerization initiators, 3.1 kg of liquid paraffin (manufactured by MORESCO Corporation: Moresco White P60, average carbon number 20) as a networking agent, and 0.6 kg of α-methylstyrene dimer (manufactured by Nippon Oil & Fats Co., Ltd.: Nofmer MSD) as a chain transfer agent in 233 kg of methyl methacrylate, 56 kg of styrene, and 22 kg of α-methylstyrene. This mixture was then added to an autoclave while stirring at 110 rpm. After purging the autoclave with nitrogen, heating was started and the temperature was raised to 80°C over 1.5 hours. During the heating process 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, held at 115°C for 5 hours, and then cooled to 30°C over approximately 6 hours. During the heating process from 80°C to 115°C, when the temperature reached 110°C, 37 kg of pentane (a mixture of 80% n-pentane and 20% isopentane) was added to the autoclave over approximately 60 minutes as a blowing agent. After adding the blowing agent, the stirring speed was reduced to 90 rpm. After cooling, the contents were removed, nitric acid was added to dissolve the tricalcium phosphate adhering to the surface of the foamed acrylic resin particles, then dewatered and washed using a centrifuge, and moisture adhering to the surface was removed using an air-flow dryer to obtain foamed acrylic resin particles with an average particle size of approximately 0.8 mm. The obtained foamed acrylic resin particles were sieved to separate particles with a diameter of 0.5 to 1.2 mm. To 100 parts by weight of these foamed acrylic resin particles, 0.015 parts by weight of N,N-bis(2-hydroxyethyl)alkylamine, an antistatic agent, was added, and the mixture was 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 foamed acrylic resin particles were heated in a pressurized batch foaming machine (Daisen Kogyo Co., Ltd.: DYH850) by supplying steam to maintain an internal pressure of 0.01 MPa (gauge pressure) within the foaming machine, and the steam pressure was maintained for approximately 80 seconds until the bulk density was approximately 20 kg / m³. 3 Foamed particles of acrylic resin were obtained.

[0041] The obtained foamed particles were placed in a maturation silo and matured at room temperature for one day. Block molding was then performed using a block molding machine (Daisen Kogyo Co., Ltd.: VS-2000-5VMC). The mold dimensions were 2.0m (length) x 1.0m (width) x 0.5m (thickness). Heating and demolding control were performed using a surface pressure gauge installed in the center of the 2.0m x 1.0m surface of the mold. Heating steam was supplied into the mold to heat the foamed acrylic resin particles until the foaming pressure reached a maximum surface pressure of 0.098MPa. After that, water cooling was performed for 3 seconds, and then the pressure inside the mold cavity was reduced to -0.06MPa (gauge pressure). The reduced pressure state was maintained until the surface pressure gauge read 0.00MPa (gauge pressure), after which the mold was opened and the block-shaped foamed molded body was removed. The density of the obtained foamed molded body was approximately 19g / L.

[0042] [Overcharge test] (Comparative Example 1) A PP resin container (internal dimensions: 80mm wide x 105mm long x 34mm deep, resin thickness 2mm, with the electrode side of an aluminum laminate lithium-ion battery positioned on the 80mm wide side of the PP resin container, and with five 10mm diameter holes on the 80mm wide side of the container, resulting in an open top) was prepared for use as a container for an energy storage device. A 1500mAh aluminum laminate lithium-ion battery (35mm wide x 75mm long) with a positive electrode ternary system was placed inside this PP resin container, and a 4mm thick PP resin plate was used as a lid. The edges of the lid were sealed with heat-resistant tape to ensure there were no gaps, and the device was configured so that any ejection from the lithium-ion battery due to overcharging would only be released through the five holes.

[0043] A PP resin container, intended as the container for this energy storage device, is placed outside a PP resin container intended as the container for the casing (internal dimensions: 98mm wide x 148mm long x 48mm deep, resin thickness 2mm, with five 10mm diameter holes on the 98mm side and an open top (the holes are drilled on the opposite side from the holes in the PP resin container intended as the container for the energy storage device)). Wiring is done to allow the battery to overcharge, and a 4mm thick PP resin plate is placed over it to cover it. Heat-resistant tape is used to seal the edges of the cover so that there are no gaps, and any ejected battery material during overcharging is released only through the five holes, thus creating an energy storage device structure.

[0044] When this energy storage device structure was subjected to overcharging at 15V, 7.5A, the battery was destroyed after approximately 19 minutes, and a violent fire was observed outside the casing.

[0045] (Example 1) In the energy storage device structure used in Comparative Example 1, a plate-shaped molded body (3 mm thick, 19 g / L density) of the acrylic resin foam molded body obtained above was used as a foam molded body of a thermodepolymer, and 0.011 m was applied to the upper inner surface of the PP resin plate of the lid of a PP resin container, which is intended to be a casing. 2 The device was then attached using double-sided tape to form a power storage device structure.

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

Claims

1. A power storage device structure comprising a power storage device and a casing that encloses the power storage device with a void, wherein a foamed molded body of a thermodepolymer is placed in the void between the power storage device and the casing. The foamed molded article of the pyropolymer is in the form of a sheet or a plate. The aforementioned sheet-like or plate-like foamed molded body has a thickness of 1 mm to 100 mm. A power storage device structure wherein the density of the sheet-like or plate-like foamed molded body is 18 g to 20 g / L.

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

3. The energy storage device structure according to claim 1, wherein the foamed molded article of the thermally depolymerizable polymer contains 10% by weight or more of the thermally depolymerizable polymer portion.

4. The energy storage device structure according to claim 1, wherein the foamed molded article of the thermally depolymerizable polymer is a foamed molded article 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 energy storage device structure according to any one of claims 1 to 4, wherein a plurality of the aforementioned energy storage devices are stacked.