JP7400193B2 - Energy storage device - Google Patents

Description

The present invention relates to an electricity storage device.

2. Description of the Related Art Electricity storage devices including active materials capable of occluding and releasing alkali metal ions are widely used because they exhibit excellent properties such as high operating voltage and excellent energy density. In order to improve the safety of power storage devices, many studies have been made and numerous tests have been conducted on power storage devices. For example, regarding power storage devices for vehicles, nail penetration tests and crush tests that simulate internal short circuits of the power storage device, and tests in which the power storage device is heated from the outside, assuming that the vehicle in which it is installed will be involved in a fire or traffic accident, are conducted. A heating test is being conducted to simulate this. Furthermore, when an internal short circuit occurs in an electrical storage device or when the electrical storage device is heated, the possibility of the electrical storage device catching fire may be a problem. Then, when a power storage device ignites, a technique for extinguishing the ignited power storage device has been proposed. For example, Patent Document 1 describes a technique for extinguishing a power storage device that has caught fire by disposing a fire extinguishing agent around the power storage device.

Special Publication No. 2013-541131

However, even if the technique described in Patent Document 1 is used, there is a possibility that an ignited electricity storage device cannot be easily extinguished. For example, even if a fire extinguishing agent is placed around multiple electricity storage devices whose electrolyte solvent is an organic solvent that easily evaporates at high temperatures, the high temperature electricity storage devices will ignite and the temperature of the electricity storage devices will further increase. If the organic solvent contained in the electricity storage device vaporizes and diffuses into the surroundings, and further ignites the vaporized organic solvent, a plurality of electricity storage devices may ignite in a chain reaction. When the electricity storage devices ignite in a chain manner like this, it becomes difficult to extinguish the fire, so even if the technique described in Patent Document 1 is used, there is a possibility that the fire cannot be extinguished easily.

The present invention was devised in view of these points, and an object of the present invention is to provide a highly flame-retardant electricity storage device.

In order to solve the above problems, the electricity storage device according to the present invention takes the following measures. First, a first aspect of the present invention provides a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, a separator sandwiched between the positive electrode and the negative electrode and made of cellulose, and the positive electrode and the negative electrode. an electrolytic solution containing an alkali metal ion and in contact with the electrolytic solution, and a sealing body that contacts the electrolytic solution inside and seals the electrolytic solution, and at least one of the positive electrode active material and the negative electrode active material. is an electricity storage device capable of occluding and releasing alkali metal ions, wherein the electrolytic solution contains a carbonate-based organic solvent and an imide-based lithium salt, and the RED value based on the Hansen solubility parameter for the electrolytic solution is less than 1. , and a fire extinguishing agent that exhibits a flame retardant function is provided in the internal space of the sealed body, and the fire extinguishing agent is an ether-type nonionic surfactant (excluding halogen-based surfactants). and the concentration of the electrolytic solution is 0.1% by mass or more and 1% by mass or less.

Next, a second invention of the present invention is the electricity storage device according to the first invention, wherein the extinguishing agent is electrochemically stable within the operating potential range of the positive electrode at a predetermined temperature or lower, Moreover, the electricity storage device is electrochemically stable within the operating potential range of the negative electrode.

Next, a third invention of the present invention is an electricity storage device according to the first or second invention , which is a lithium ion capacitor.

According to the first invention, in the electricity storage device, the extinguishing agent is provided in the internal space of the sealed body. Therefore, the fire retardant function of the fire extinguisher to make the electricity storage device flame retardant can be exerted not from the outside of the sealing body but from inside the sealing body, so that the fire extinguisher can reliably improve the flame retardance of the electricity storage device.

According to the second invention, the extinguishing agent is electrochemically stable within the operating potential range of the positive electrode and electrochemically stable within the operating potential range of the negative electrode at a predetermined temperature or lower. Therefore, the extinguishing agent can be considered stable. Therefore, the fire extinguisher stably increases the flame retardancy of the power storage device over time, and does not have a large effect on the charging and discharging process of the power storage device.

According to the third invention, the electricity storage device is a lithium ion capacitor. Generally, a single lithium metal is used in the pre-doping step included in the manufacturing method of a lithium ion capacitor. Usually, a pre-doping process is performed so that no single lithium metal remains in the lithium ion capacitor. However, in order to ensure the safety of lithium ion capacitors, in the unlikely event that a single piece of lithium metal remains inside the lithium ion capacitor, an internal short circuit occurs in the lithium ion capacitor, or the lithium ion capacitor becomes heated. At times, the possibility of ignition of lithium ion capacitors is a problem. Even in such a case, in the lithium ion capacitor of the present invention, the possibility of ignition is suppressed because a fire extinguishing agent that exhibits a flame retardant function is provided in the internal space of the sealed body. Further, it is no longer necessary to spend time on the pre-doping process to prevent metal lithium from precipitating, as in the past, and the time for the pre-doping process can be shortened.

FIG. 1 is a schematic exploded perspective view of a power storage device according to a first embodiment. FIG. 1 is a perspective view of a power storage device according to a first embodiment. 3 is a schematic diagram of a cross section taken along line III in the electricity storage device of FIG. 2. FIG. FIG. 3 is a diagram illustrating an example of the appearance of a positive electrode plate in the first embodiment. FIG. 5 is a sectional view taken along the line VV in the positive electrode plate of FIG. 4; FIG. 3 is a diagram illustrating an example of the appearance of a negative electrode plate in the first embodiment. 7 is a sectional view taken along line VII-VII of the negative electrode plate in FIG. 6. FIG. FIG. 2 is a diagram illustrating the positional relationship among a positive plate of a positive electrode, a negative plate of a negative electrode, a separator, an electrolyte, and a fire extinguisher in the first embodiment.

[First embodiment (FIGS. 1 to 8)]
EMBODIMENT OF THE INVENTION Below, the form for implementing this invention is demonstrated using a lithium ion capacitor as an example of an electrical storage device using drawings. As shown in the exploded perspective view of FIG. 1, the lithium ion capacitor 1 of this embodiment includes a plurality of plate-shaped positive electrode plates 11 and a plurality of plate-shaped negative electrode plates 21, which are arranged alternately. Laminated. Each positive electrode plate 11 includes an electrode terminal connection portion 12b that protrudes in one direction. Furthermore, each negative electrode plate 21 also includes an electrode terminal connection part 22b that protrudes in the same direction as the direction in which the electrode terminal connection part 12b of the positive electrode plate 11 projects. As shown in FIG. 1, the direction in which the electrode terminal connection portions 12b of the positive electrode plate 11 protrude is the X-axis direction, the direction in which they are stacked is the Z-axis direction, and the direction perpendicular to the X-axis and the Z-axis is the Y-axis. direction. These X, Y, and Z axes are orthogonal to each other. In all the figures in which the X-axis, Y-axis, and Z-axis are shown, these axes indicate the same direction, and in the following description, descriptions regarding directions may be based on these axes. Note that in this embodiment and the embodiments described below, illustrations and detailed descriptions of incidental structures will be omitted.

<1. Overall structure of lithium ion capacitor 1 (Figures 1 to 3)>
As shown in FIG. 1, the lithium ion capacitor 1 includes a plurality of positive electrode plates 11, a plurality of negative electrode plates 21, a plurality of separators 30, an electrolytic solution 40, and a laminate member 60. The lithium ion capacitor 1 also includes an enclosure 50 (not shown in FIG. 1), which will be described later. Here, as shown in FIG. 1, the positive electrode plates 11 and the negative electrode plates 21 are alternately stacked, and a separator 30 is sandwiched between the positive electrode plates 11 and the negative electrode plates 21, respectively. The electrolytic solution 40 is wrapped in two laminate members 60 (sealed bodies) together with a portion of the plurality of positive electrode plates 11, a portion of the plurality of negative electrode plates 21, and a plurality of separators 30, which are laminated in this way. It's sealed. Thereby, the electrolytic solution 40 is in contact with the positive electrode 10 and the negative electrode 20, and the laminate member 60 (sealed body) is in contact with the electrolytic solution 40. As will be described later, the electrolytic solution 40 contains a fire extinguisher, and the fire extinguisher can improve the flame retardance of the lithium ion capacitor 1.

The electrode terminal connecting portions 12b of the plurality of positive electrode plates 11 protrude in the same direction and are electrically connected to the positive electrode terminal 14. The conductor members constituting the positive terminal side, such as the positive terminal 14 and the plurality of positive plates 11 connected thereto, can be collectively referred to as the positive electrode 10. Similarly, the electrode terminal connection portions 22b of the plurality of negative electrode plates 21 and the negative electrode terminal 24 are electrically connected, and the negative electrode terminal 24 and the plurality of negative electrode plates 21 connected thereto constitute the negative electrode terminal side. The conductor members can be collectively referred to as the negative electrode 20. The lithium ion capacitor 1 has the above-described structure inside, and its appearance is shown in FIG. 2. FIG. 3 schematically shows a III-III cross section of the lithium ion capacitor 1 shown in FIG. In FIG. 3, each member within the lithium ion capacitor 1 is illustrated with a space provided therebetween for the sake of clarity. However, in reality, the positive electrode plate 11, the negative electrode plate 21, and the separator 30 are stacked with almost no gaps. Further, as shown in FIG. 3, a long sheet-like material is wound to surround a portion of the plurality of positive electrode plates 11, a portion of the plurality of negative electrode plates 21, and a plurality of separators 30, which are stacked. An enclosure 50 is provided.

<2. About each part of lithium ion capacitor 1 (Fig. 1, Fig. 3 to Fig. 7)>
<2-1. Regarding the positive electrode plate 11 (Fig. 1, Fig. 3 to Fig. 5)>
As the positive electrode plate 11, a conventional positive electrode plate of a lithium ion capacitor can be used. That is, the positive electrode plate 11 includes a thin plate-shaped current collector 12 and a positive electrode active material layer 13 coated on the current collector 12. The current collector 12 is a metal foil in which a plurality of holes 12c penetrating in the Z direction are formed (see FIG. 5), and includes a rectangular current collecting portion 12a (see FIG. 4) and one end of the current collecting portion 12a (see FIG. In example No. 4, the electrode terminal connecting portion 12b protruding from the left end of the upper side is integrally formed. Although a plurality of holes 12c are formed in the current collecting part 12a (see FIG. 5), the electrode terminal connecting part 12b does not have to have the same plurality of holes as the holes 12c of the current collecting part 12a. It may well be formed. The width of the electrode terminal connecting portion 12b in the Y-axis direction shown in FIGS. 1 and 4 can be changed as appropriate, and may be set to the same width as the current collecting portion 12a, for example. Furthermore, although the positive electrode active material layer 13 is coated on both sides of the current collector 12a, it may be coated on either one side. Here, since the plurality of holes 12c are formed in the current collecting section 12a, cations and anions of the electrolytic solution 40 can pass through the current collecting section 12a.

For the current collector 12, for example, a metal foil made of aluminum, stainless steel, copper, or nickel can be used. The cathode active material layer 13 includes a cathode active material having a large specific surface area and high conductivity, a conductive agent for increasing the electrical conductivity of the cathode active material layer 13, and binding and aggregation of the cathode active material. It contains a binder that binds the current collecting part 12a of the electric body 12, and may further contain other components such as a thickener. As the positive electrode active material, activated carbon, carbon nanotubes, polyacene, etc. can be used, for example. As the conductive aid, for example, Ketjen black, acetylene black, graphite fine particles, or graphite fine fibers can be used. As the thickener, for example, carboxymethyl cellulose [CMC] can be used.

The binder is used to bind the materials that make up the positive electrode. The binder is mainly composed of a polymer which is an adhesive component. The polymer is selected from polyvinylidene fluoride, styrene-butadiene rubber [SBR], polyacrylic acid, and the like. Here, in order to install the lithium ion capacitor 1 in the passenger compartment of an automobile, heat resistance in a high temperature environment of 85° C. is required. Therefore, it is preferable that the polymer has a RED value (relative energy difference) greater than 1 based on the Hansen solubility parameter (HSP) for the electrolytic solution 40. This is because a polymer having a RED value greater than 1 with respect to the electrolytic solution 40 does not dissolve in the electrolytic solution 40, so that even if the lithium ion capacitor 1 is used for a long time in a high-temperature environment of 85° C., the rate of increase in internal resistance is small. Such polymers include polyacrylic acid. Polyacrylic acid here is a broad concept that includes not only unneutralized polyacrylic acid but also neutralized salts and crosslinked polyacrylic acids. Polyacrylic acid may be used alone or in combination of two or more. Water or an organic solvent can be used as a solvent for dissolving the polymer. A water-based binder that uses water as a solvent is preferable because it can reduce the environmental load during the manufacturing process. Polyacrylic acid is also suitable in that it can form an aqueous binder using water as a solvent. Note that a detailed explanation of the RED value based on the Hansen solubility parameter will be given later.

The binder is preferably added in an amount of 1 to 10% by mass based on the positive electrode active material. If it is less than 1% by mass, the binding force tends to be insufficient. On the other hand, if it exceeds 10% by mass, it may cause an increase in internal resistance.

<2-2. Regarding the negative electrode plate 21 (Fig. 1, Fig. 3, Fig. 6, Fig. 7)>
As the negative electrode plate 21, a conventional negative electrode plate of a lithium ion capacitor can be used. The negative electrode plate 21 has roughly the same structure as the positive electrode plate 11 described above, and includes a thin plate-shaped current collector 22 and a negative electrode active material layer 23. The negative electrode plate 21, unlike the positive electrode plate 11, includes a negative electrode active material of the negative electrode active material layer 23 that is capable of intercalating and releasing lithium ions Li ⁺ . As will be described later, the negative electrode active material is adsorbed with lithium ions Li ⁺ (so-called pre-doped) during manufacture.

The current collector 22 is a metal foil in which a plurality of holes 22c penetrating in the Z direction are formed (see FIG. 7), and includes a rectangular current collecting portion 22a and one end of the current collecting portion 22a (in the example of FIG. 6, An electrode terminal connecting portion 22b protruding outward from the right end of the upper side is integrally formed. Note that although a plurality of holes 22c are formed in the current collecting section 22a (see FIG. 7), the plurality of holes similar to the holes 22c of the current collecting section 22a are not formed in the electrode terminal connecting section 22b. may also be formed. Further, although the negative electrode active material layer 23 is coated on both sides of the current collector 22a, it may be coated on either one side. Here, like the positive electrode plate 11 described above, the current collecting section 22a is formed with a plurality of holes 22c, so that the cations and anions of the electrolytic solution 40 can pass through the current collecting section 22a. Further, as shown in FIG. 1, the electrode terminal connection portion 12b of the positive electrode plate 11 and the electrode terminal connection portion 22b of the negative electrode plate 21 are provided at positions spaced apart from each other in the surface direction of the negative electrode plate so that they do not overlap. It is being Here, the width of the electrode terminal connection part 22b in the Y-axis direction shown in FIGS. 1 and 6 can be changed as appropriate, and may be made the same width as the current collector part 22a, for example.

Similar to the current collector 12 of the positive electrode plate 11, the current collector 22 can be made of, for example, a metal foil made of aluminum, stainless steel, or copper. The negative electrode active material layer 23 includes a negative electrode active material capable of adsorbing and desorbing lithium ions Li ⁺ , and a binder that binds the negative electrode active material and binds the negative electrode active material and the current collecting portion 22 a of the current collector 22 . Other components such as a conductive additive and a thickener for increasing the electrical conductivity of the negative electrode active material layer 23 may also be included. For example, graphite can be used as the negative electrode active material. As the conductive aid, binder, and thickener, the same substances as those for the positive electrode plate 11 described above can be used. That is, for example, Ketjen black, acetylene black, graphite fine particles, and graphite fine fibers can be used as the conductive aid. As the binder, for example, polyvinylidene fluoride, styrene-butadiene rubber [SBR], or polyacrylic acid can be used. As the thickener, for example, carboxymethyl cellulose [CMC] can be used.

<2-3. Regarding the separator 30 (Fig. 1, Fig. 3)>
As shown in FIG. 1, the separator 30 is made of a porous material that isolates the positive electrode plate 11 and the negative electrode plate 21 and allows the cations and anions of the electrolytic solution 40 to pass through, and has a rectangular sheet shape. is formed. The vertical and horizontal lengths of the separator 30 are set longer than the length of the current collecting part 12a of the current collector 12 of the positive electrode plate 11 and the length of the current collecting part 22a of the current collector 22 of the negative electrode plate 21. (See Figures 1, 4, and 6). As the separator 30, a conventional lithium ion capacitor separator can be used, and for example, paper made of viscose rayon, natural cellulose, etc., nonwoven fabric of polyethylene, polypropylene, etc. can be used.

<2-4. About the electrolyte 40>
The electrolytic solution 40 is a solution obtained by adding a fire extinguisher to the electrolytic solution of a conventional lithium ion capacitor. That is, the electrolytic solution 40 includes an organic solvent (non-aqueous solvent), an electrolyte, and a fire extinguisher. An additive may be added to the electrolytic solution 40 as appropriate, and examples of the additive include vinylene carbonate [VC].

As organic solvents, carbonate-based organic solvents, nitrile-based organic solvents, lactone-based organic solvents, ether-based organic solvents, alcohol-based organic solvents, ester-based organic solvents, amide-based organic solvents, sulfone-based organic solvents, ketone-based organic solvents, aromatic Examples include group organic solvents. The solvents can be used alone or in a mixture of two or more at an appropriate composition ratio. When the lithium ion capacitor 1 is to have heat resistance of 85° C. or higher, it is preferable that the organic solvent also has heat resistance. Here, as carbonate-based organic solvents, cyclic carbonates such as ethylene carbonate [EC], propylene carbonate [PC], and fluoroethylene carbonate [FEC], ethyl methyl carbonate [EMC], diethyl carbonate [DEC], dimethyl carbonate [DMC], etc. Examples include chain carbonates.

Various types of chain carbonates can be used as the chain carbonate, but in order to provide the lithium ion capacitor 1 with heat resistance of 85°C or higher, dimethyl carbonate [DMC], which has a low boiling point and poor heat resistance, is not used. It is preferable. That is, when dimethyl carbonate [DMC] is contained in the organic solvent, dimethyl carbonate [DMC] thermally decomposes to diethyl carbonate [DEC], and the decomposition byproducts at that time cause an increase in internal resistance and deterioration of heat resistance. (Note that this speculation does not limit the present invention). Considering the possibility that the lithium ion capacitor 1 will be used in a high-temperature environment, ethyl methyl carbonate [EMC], which has a relatively high boiling point and low viscosity, and diethyl carbonate [DEC], which has a higher boiling point, are recommended as chain carbonates. It is preferable to use From the viewpoint of improving heat resistance, it is more preferable to use a mixture of ethyl methyl carbonate [EMC] and diethyl carbonate [DEC]. Note that the ratio of ethyl methyl carbonate [EMC] and diethyl carbonate [DEC] in the organic solvent is not particularly limited, but can be set, for example, in the range of EMC:DEC=2:1 to 1:2.

Further, various cyclic carbonates can be used as the cyclic carbonate, but from the viewpoint of improving the oxidation resistance of the electrolyte, ethylene carbonate [EC], which has the ability to generate a protective film called an SEI (Solid Electrolyte Interface) film, is used. It is preferable. When using a mixture of ethylene carbonate [EC] and another cyclic carbonate (for example, propylene carbonate [PC]) as the cyclic carbonate, ethylene carbonate [EC] is mixed with another cyclic carbonate (for example, propylene carbonate [PC]). ) is preferably included. By containing a relatively large amount of ethylene carbonate [EC] in this way, its SEI film forming ability is suitably exhibited, and after ethylene carbonate [EC] is reductively decomposed, an SEI film is formed on the negative electrode surface, and the electrolyte is no longer directly exposed to the potential of lithium (Li).

Examples of nitrile organic solvents include acetonitrile, acrylonitrile, adiponitrile, valeronitrile, and isobutyronitrile. Examples of lactone-based organic solvents include γ-butyrolactone and γ-valerolactone. Examples of ether organic solvents include cyclic ethers such as tetrahydrofuran and dioxane, and chain ethers such as 1,2-dimethoxyethane, dimethyl ether and triglyme. Examples of alcohol-based organic solvents include ethyl alcohol and ethylene glycol. Examples of ester-based organic solvents include phosphoric acid esters such as methyl acetate, propyl acetate, and trimethyl phosphate, sulfuric acid esters such as dimethyl sulfate, and sulfite esters such as dimethyl sulfite. Examples of amide organic solvents include N-methyl-2-pyrrolidone and ethylenediamine. Examples of sulfone-based organic solvents include chain sulfones such as dimethylsulfone and cyclic sulfones such as 3-sulfolene. Examples of the ketone organic solvent include methyl ethyl ketone, and examples of the aromatic organic solvent include toluene. The above-mentioned various organic solvents other than carbonate-based organic solvents are preferably used in combination with a cyclic carbonate, and particularly preferably used in combination with ethylene carbonate [EC] which can form an SEI film.

The electrolyte uses a lithium salt of Li ions, which are positive ions, and anions. Examples of electrolytes include lithium perchlorate [LiClO ₄ ], lithium hexafluorophosphate [LiPF ₆ ], lithium tetrafluoroborate [LiBF ₄ ], lithium bis(fluorosulfonyl)imide [LiN(FSO ₂ ) ₂ , LiFSI]. ], lithium bis(trifluoromethanesulfonyl)imide [LiN(SO ₂ CF ₃ ) ₂ , LiTFSI], lithium bis(pentafluoroethanesulfonyl)imide [LiN(SO ₂ CF ₂ CF ₃ ) ₂ , LiBETI] may be used. , these lithium salts may be used alone or in combination of two or more. In particular, imide-based lithium salts such as lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, and lithium bis(pentafluoroethanesulfonyl)imide (lithium having -SO ₂ -N-SO ₂ - as a partial structure) Salt) is preferable because it has heat resistance of 85° C. or higher. When an imide-based lithium salt is used as an electrolyte, the capacity retention rate of the lithium ion capacitor 1 can be kept high for a long time even in a high temperature environment of 85°C.

The concentration of the electrolyte in the electrolytic solution 40 is preferably 0.5 to 10.0 mol/L. From the viewpoint of appropriate viscosity and ionic conductivity of the electrolytic solution 40, the concentration of the electrolyte in the electrolytic solution 40 is more preferably 0.5 to 2.0 mol/L. If the concentration of the electrolyte is less than 0.5 mol/L, the ionic conductivity of the electrolytic solution 40 will be too low due to a decrease in the concentration of ions dissociated from the electrolyte, which is not preferable. Furthermore, if the concentration of the electrolyte is higher than 10.0 mol/L, the ionic conductivity of the electrolytic solution 40 will be too low due to an increase in the viscosity of the electrolytic solution 40, which is not preferable.

The extinguishing agent exhibits a flame retardant function, has a RED value of less than 1 based on the Hansen solubility parameter in the electrolytic solution 40, is electrochemically stable within the operating potential range of the positive electrode plate 11 at a predetermined temperature or below, and , is electrochemically stable within the operating potential range of the negative electrode plate 21. Here, the extinguishing agent is dissolved in the electrolytic solution 40 because the RED value based on the Hansen solubility parameter (HSP) for the electrolytic solution 40 is smaller than 1. The Hansen solubility parameter was published by Charles M. Hansen and is known as an index of solubility that indicates how much a certain substance dissolves in a certain substance. For example, water and oil generally do not mix together, but this is because their ``properties'' are different. In the Hansen solubility parameter, three items, a dispersion term D, a polarity term P, and a hydrogen bond term H, are numerically expressed for each substance as "properties" of a substance related to solubility. Here, the dispersion term D is a value representing the magnitude of van der Waals force, the polarity term P is a value representing the magnitude of dipole moment, and the hydrogen bond term H is a value representing the magnitude of hydrogen bond. The basic idea will be explained below. Therefore, a description of how the hydrogen bond term H is divided into donor property and acceptor property will be omitted.

The Hansen solubility parameters (D, P, H) are plotted in a three-dimensional orthogonal coordinate system (Hansen space, HSP space) to study solubility. For example, the Hansen solubility parameters of solution A and solid B can be plotted at two coordinates (coordinate A, coordinate B) corresponding to solution A and solid B, respectively, on Hansen space. It can be assumed that the shorter the distance Ra (HSP distance, Ra) between coordinates A and B, the easier it is for solid B to dissolve in solution A because solution A and solid B have similar "properties" mentioned above. can. On the contrary, it can be considered that the longer this distance Ra is, the more difficult it is for solid B to dissolve in solution A, since solution A and solid B have "properties" that are not similar to each other.

Further, with respect to the solution A, the distance Ra that is the boundary between a substance that dissolves and a substance that does not dissolve is defined as an interaction radius R0. Therefore, regarding solution A and solid B, if the distance Ra is smaller than the interaction radius R0 (Ra<R0), it can be considered that solid B dissolves in solution A. On the other hand, if this Ra is larger than the interaction radius R0 (R0<Ra), it can be considered that solid B is not dissolved in solution A. Furthermore, the value obtained by dividing the distance Ra by the interaction radius R0 is set as the RED value (=Ra/Ro). Then, when the RED value is smaller than 1 (RED=Ra/Ro<1), Ra<R0 and it can be considered that the solid B is dissolved in the solution A. On the other hand, when the RED value is larger than 1 (RED=Ra/Ro>1), R0<Ra, and it can be considered that solid B does not dissolve in solution A. In this way, based on the RED values regarding solution A and solid B, it can be determined whether solid B is soluble in solution A or not.

Here, in this embodiment, the solution A corresponds to the electrolytic solution 40, and the solid B corresponds to the extinguishing agent. The extinguishing agent dissolves in the electrolyte 40 because the RED value based on the Hansen solubility parameter for the electrolyte 40 is less than 1. Conversely, a fire extinguisher that is easily soluble in the electrolyte 40 to the extent that the RED value based on the Hansen solubility parameter for the electrolyte 40 is smaller than 1 can also be considered to have a RED value smaller than 1 based on the Hansen solubility parameter. .

The Hansen solubility parameter and the interaction radius R0 can be calculated using the chemical structures and composition ratios of the components and experimental results. In that case, it can be determined using the software HSPiP (Hansen Solubility Parameters in Practice: Windows (registered trademark) software for efficiently handling HSP) developed by Hansen et al. This software HSPiP is available as of March 5, 2018 from http://www.hansen-solubility.com/. Furthermore, the Hansen solubility parameters (D, P, H) can be calculated even in the case of a mixed solvent in which a plurality of solvents are mixed.

The extinguishing agent exhibits a flame retardant function, has a RED value of less than 1 based on the Hansen solubility parameter in the electrolytic solution 40, is electrochemically stable within the operating potential range of the positive electrode plate 11 at a predetermined temperature or below, and A known extinguishing agent that is electrochemically stable within the operating potential range of the negative electrode plate 21 can be used. Here, the flame retardant function of the extinguishing agent means that when the temperature of the lithium ion capacitor 1 reaches a predetermined temperature or higher and a part of the lithium ion capacitor 1 starts to ignite, the extinguishing effect works to suppress the ignition. This is a function to Examples of such extinguishing agents include nonionic surfactants. Since the nonionic surfactant has lipophilicity, the RED value based on the Hansen solubility parameter is smaller than 1 with respect to the electrolytic solution 40, which is an organic solvent. Further, the nonionic surfactant is electrochemically stable within the operating potential range of the positive electrode plate 11 and electrochemically stable within the operating potential range of the negative electrode plate 21 at a predetermined temperature or lower. Furthermore, as will be described later, the anions of the electrolytic solution 40 and ions such as lithium ions Li ⁺ are involved in the charging and discharging of the lithium ion capacitor 1, but since the nonionic surfactant does not dissociate into ions, the lithium ions It is not involved in charging and discharging the capacitor 1.

The nonionic surfactant used as a fire extinguisher is not particularly limited, but at least one selected from the group consisting of ether type, ester type, and ester/ether type can be used. These nonionic surfactants can be used at a concentration of 0.1% by mass or more and 1% by mass or less based on the electrolytic solution 40. If the concentration of the nonionic surfactant in the electrolytic solution 40 is less than 0.1% by mass, it is not preferable because the flame retardant function will not be sufficiently exhibited. Furthermore, if the concentration of the nonionic surfactant in the electrolytic solution 40 exceeds 1% by mass, this is not preferable because it may adversely affect the charge/discharge characteristics of the lithium ion capacitor 1. In order to exhibit a good flame retardant function, it is more preferable that the concentration of the nonionic surfactant in the electrolytic solution 40 is 0.5% by mass or more and 1% by mass or less.

As the ether type nonionic surfactant, for example, polyoxyethylene alkyl ether, polyoxyethylene alkylphenyl ether, polyoxyethylene polyoxypropylene glycol, polyalkylene alkyl ether, etc. can be used. As the ester type nonionic surfactant, for example, glycerin fatty acid ester, sorbitan fatty acid ester, sucrose fatty acid ester, etc. can be used. As the ester/ether type nonionic surfactant, for example, fatty acid polyethylene glycol, fatty acid polyoxyethylene sorbitan, etc. can be used.

<2-5. Regarding the enclosure 50 (Fig. 3)>
The enclosure 50 is formed into a porous elongated sheet. As shown in FIG. 3, the enclosure 50 is wound so as to surround the outer periphery of the plurality of positive electrode plates 11 of the positive electrode 10, the plurality of negative electrode plates 21 of the negative electrode 20, and the plurality of separators 30, which are stacked. There is. The material of the envelope 50 can be the same as the separator of a conventional lithium ion capacitor, similar to the separator 30 described above. As the material of the enclosure 50, for example, paper such as viscose rayon or natural cellulose, nonwoven fabric such as polyethylene or polypropylene, etc. can be used.

<2-6. Regarding the laminate member 60 (Fig. 1, Fig. 3)>
As shown in FIG. 3, the laminate member 60 includes a core sheet 61, an outer sheet 62, and an inner sheet 63. An outer sheet 62 is bonded to the outer surface of the core sheet 61, and an inner sheet 63 is bonded to the inner surface of the core sheet 61. For example, the core sheet 61 may be an aluminum foil, the outer sheet 62 may be a resin sheet such as nylon PET film, and the inner sheet 63 may be a resin sheet such as polypropylene.

<3. Regarding the charging and discharging process of lithium ion capacitor 1 (Figure 3, Figure 8)>
As described above, the current collecting portion 12a of the current collector 12 of the positive electrode plate 11 is provided with a plurality of holes 12c penetrating in the Z direction, and the current collecting portion 22a of the current collector 22 of the negative electrode plate 21 also penetrates in the Z direction. By providing the plurality of holes 22c, anions and cations of the electrolytic solution 40 can pass through the current collector 12a of the positive electrode plate 11 and the current collector 22a of the negative electrode plate 21. Further, the separator 30 is also configured to allow cations and anions of the electrolytic solution 40 to pass therethrough. FIG. 8 schematically shows the positional relationship among the positive plate 11 of the positive electrode 10, the negative plate 21 of the negative electrode 20, the separator 30, and the electrolyte 40 of the lithium ion capacitor 1. As shown in FIG. 8, the lithium ion capacitor 1 has a configuration in which a positive electrode plate 11 and a negative electrode plate 21 face each other with a separator 30 in between. The lithium ion capacitor 1 forms an electric double layer on the surface of the positive electrode plate 11 with the positive electrode active material and anions of the electrolyte, and on the negative electrode plate 21, lithium ions Li ⁺ are adsorbed and desorbed to the negative electrode active material. Perform charging and discharging. Furthermore, when manufacturing the lithium ion capacitor 1, lithium ions Li ⁺ are adsorbed onto the negative electrode active material of the negative electrode plate 21 (pre-doping). By adsorbing lithium ions Li ⁺ to the negative electrode active material, the potential difference between the positive electrode plate 11 and the negative electrode plate 21 increases, and the energy density of the electric double layer formed on the positive electrode plate 11 can be increased. . As a result, the lithium ion capacitor 1 has a large capacity and high output.

<4. About the effect of fire extinguishing agent>
Generally, manufacturing a lithium ion capacitor includes a pre-doping process, and in this pre-doping process, lithium ions Li ⁺ are adsorbed onto the negative electrode active material of the negative electrode plate 21 . In general, a single lithium metal is used in the pre-doping step included in the manufacturing method of a lithium ion capacitor. Usually, a pre-doping process is performed so that no single lithium metal remains in the lithium ion capacitor. However, in order to ensure the safety of lithium ion capacitors, in the unlikely event that a single piece of lithium metal remains inside the lithium ion capacitor, an internal short circuit occurs in the lithium ion capacitor, or the lithium ion capacitor becomes heated. At times, the possibility of ignition of lithium ion capacitors is a problem. Even in such a case, in the lithium ion capacitor 1 of the present embodiment, the fire extinguishing agent that exhibits a flame retardant function is provided in the internal space of the laminate member 60 (sealed body), so there is no possibility of ignition. suppressed. Further, it is no longer necessary to spend time on the pre-doping process to prevent metal lithium from precipitating, as in the past, and the time for the pre-doping process can be shortened.

Further, in the lithium ion capacitor 1 (power storage device), a fire extinguishing agent is provided in the internal space of the laminate member 60 (sealed body). Therefore, the fire retardant function of making the lithium ion capacitor 1 (electricity storage device) flame retardant by the fire extinguisher can be exerted not from the outside of the laminate member 60 (sealing body) but from inside the laminate member 60 (sealing body). It is possible to reliably improve the flame retardancy of (electricity storage device).

Moreover, the extinguishing agent is electrochemically stable within the operating potential range of the positive electrode 10 and within the operating potential range of the negative electrode 20 at a predetermined temperature or lower. Therefore, the extinguishing agent can be considered stable. Therefore, the fire extinguisher stably increases the flame retardance of the lithium ion capacitor 1 (power storage device) over time, and does not have a large effect on the charging and discharging process of the lithium ion capacitor 1 (power storage device).

[Second embodiment]
Next, a power storage device (not shown) according to a second embodiment will be described. This embodiment will also be described using a lithium ion capacitor as an example of a power storage device. Note that, in this embodiment, parts having substantially the same configuration and function as those of the lithium ion capacitor 1 described in the first embodiment are given the same reference numerals, and a description thereof will be omitted.

<1. Structure of lithium ion capacitor 2>
In the first embodiment described above, the extinguishing agent was dissolved in the electrolytic solution 40. However, the extinguishing agent only needs to be provided in the internal space of the laminate member 60 (sealed body). The extinguishing agent (not shown) used in the lithium ion capacitor 2 (not shown) of this embodiment has a RED value of less than 1 based on the Hansen solubility parameter in the electrolytic solution 40, and at a predetermined temperature or lower, the extinguishing agent (not shown) It is electrochemically unstable within at least one of the operating potential range of the negative electrode plate 21 and the operating potential range of the negative electrode plate 21 . Further, as the extinguishing agent, a fire extinguishing agent having the same components as the extinguishing agent of the first embodiment can also be used. The extinguishing agent is sealed in one or more hollow extinguishing agent containers (not shown). The extinguishing agent storage container is formed so as not to dissolve in the electrolyte 40, and is configured to leak the extinguishing agent to the outside at a temperature higher than a release temperature which is a predetermined temperature below the ignition point of a single lithium metal (alkali metal). has been done. When the lithium ion capacitor 2 is heated and the temperature of the fire extinguishing agent storage container becomes equal to or higher than the release temperature, the fire extinguishing agent is released from the fire extinguishing agent storage container to the outside, allowing the fire extinguishing agent to exhibit a flame retardant function. Here, as described above, the flame retardant function of the extinguishing agent is a function that suppresses ignition by exerting an extinguishing effect when a part of the lithium ion capacitor 2 starts to ignite.

For example, the extinguishing agent storage container may be configured to melt at a release temperature set below the ignition point of lithium metal, or may be configured to melt at a release temperature set below the ignition point of lithium metal, or may be configured to melt due to an increase in internal pressure due to volumetric expansion of the contents containing the extinguishing agent. It may be configured to be damaged. For example, the extinguishing agent storage container may be configured to seal an inert gas such as carbon dioxide, nitrogen, or argon together with the extinguishing agent, and to release the extinguishing agent to the outside at a temperature equal to or higher than the release temperature. Here, the configuration of the extinguishing agent storage container, such as the shape and material, and the amount of inert gas sealed in the extinguishing agent storage container are determined so that when the extinguishing agent storage container reaches a predetermined release temperature or higher, the inert gas is released. Appropriate settings are made so that the extinguishing agent can exert its flame retardant function by expanding and cracking the extinguishing agent storage container, causing the extinguishing agent to leak out from the extinguishing agent storage container together with the inert gas. Further, the fire extinguishing agent may be any fire extinguisher as long as it has a flame retardant function to prevent ignition as described above. The extinguishing agent may be configured to generate an inert gas such as nitrogen, argon, carbon dioxide, etc. and release the extinguishing agent to the outside of the extinguishing agent storage container at a temperature equal to or higher than the release temperature, for example, a configuration that generates these inert gases. , a metal occlusion structure in which the inert gas is released from a metal that has previously occluded the inert gas, and a compressed gas structure in which the inert gas is released by thermal expansion of the compressed gas. These configurations provide higher environmental safety than extinguishing agents based on halogen and phosphorus flame retardants. Furthermore, if the above configuration is configured to emit an inert gas other than carbon dioxide, the safety for humans will be higher.

Although not shown, the extinguishing agent storage container can be provided in the same space as the space in which the electrolytic solution 40 is stored inside the laminate member 60, and its size and shape can be set as appropriate. Further, depending on the size of the extinguishing agent storage container, it can be mixed with the electrolyte 40. The extinguishing agent storage container can be, for example, a spherical microcapsule with a diameter of several hundred nanometers to several millimeters. In addition, the fire extinguishing agent storage container is shaped like a spheroid, with a longitudinal length of several millimeters to several centimeters and a maximum width perpendicular to the longitudinal direction of several hundred nanometers to several millimeters. It can be shaped like a polygonal column or a polygonal column. Further, the extinguishing agent storage container can also be shaped into a disc having a diameter of several millimeters to several centimeters and a thickness of several hundred nanometers to several millimeters. In addition, the fire extinguishing agent storage container can also be formed into a thin plate having a side length of about several millimeters to several centimeters and a thickness of about several hundred nanometers to several millimeters.

<2. About the charging and discharging process of lithium ion capacitor 2>
The configurations of the positive electrode 10, negative electrode 20, and separator 30 are the same between the lithium ion capacitor 2 of this embodiment and the lithium ion capacitor 1 of the first embodiment (see FIG. 3). Therefore, in the lithium ion capacitor 2 of the present embodiment, the positional relationship between the positive plate 11 of the positive electrode 10, the negative plate 21 of the negative electrode 20, the separator 30, and the electrolyte 40 is different from that of the first embodiment. This is similar to the lithium ion capacitor 1 (see FIG. 8). Therefore, in the lithium ion capacitor 2, like the lithium ion capacitor 1, an electric double layer is formed on the surface of the positive electrode plate 11 by the positive electrode active material and the anions of the electrolytic solution 40, and on the negative electrode plate 21, the negative electrode active material Charging and discharging is performed by adsorbing and desorbing lithium ions Li ⁺ .

<3. Regarding fire extinguishing agent for lithium ion capacitor 2>
In the lithium ion capacitor 2 of this embodiment, similar to the lithium ion capacitor 1 of the first embodiment described above, the extinguishing agent has a large effect on the charging and discharging process of the lithium ion capacitor 2 (electricity storage device). There is no. Here, the extinguishing agent is sealed in the extinguishing agent storage container at a temperature below a predetermined temperature below the ignition point of lithium metal (a predetermined temperature below the ignition point of a single alkali metal corresponding to the alkali metal ion). It remains in good condition. Therefore, the extinguishing agent does not dissolve in the electrolytic solution 40 below this predetermined temperature, and is more reliably stable. Therefore, the fire extinguisher stably increases the flame retardancy of the lithium ion capacitor 2 (power storage device) over time, and does not have a large effect on the charging and discharging process of the lithium ion capacitor 2 (power storage device).

[Other embodiments]
As other embodiments, for example, in the first and second embodiments, the lithium ion capacitor 1 and the lithium ion capacitor 2 are provided with the enclosure 50, but may not be provided with an enclosure. Further, although the extinguishing agent storage container of the lithium ion capacitor 2 of the second embodiment is hollow, it is provided in the internal space of the laminate member 60 (sealing body) and configured to seal the extinguishing agent. It is fine as long as it is something. For example, the outer periphery of a sheet that dissolves at a temperature below the ignition point of lithium metal (a single alkali metal corresponding to an alkali metal ion) and that does not dissolve in the electrolytic solution 40 is removed from the electrolytic solution of the inner sheet 63 of the laminate member 60. 40, and a fire extinguishing agent can be placed between this sheet and the inner sheet 63. In this case, this sheet and the inner sheet 63 constitute a fire extinguishing agent storage container.

Furthermore, in the first and second embodiments, the lithium ion capacitor 1 and the lithium ion capacitor 2 are stacked cells in which the positive electrode plate 11, the negative electrode plate 21, and the separator 30 are laminated, but the elongated positive electrode and the separator 30 are laminated. , it is possible to form a wound cell in which a long negative electrode and a long separator are wound.

In the above description of the first and second embodiments, the lithium ion capacitor 1 and the lithium ion capacitor 2 have been described as examples of power storage devices, but the invention is not limited to lithium ion capacitors, and materials that can occlude alkali metal ions can also be used. It is applicable to various power storage devices used. Examples of the alkali metal include lithium, which has a standard electrode potential of -3.045V, sodium, which has a standard electrode potential of -2.714V, and potassium, which has a standard electrode potential of -2.925V. Electricity storage devices using these alkali metals include a carbon material in the negative electrode, an alkali metal oxide, etc. in the positive electrode so that the standard electrode potential difference is relatively large. Specific examples thereof include various power storage devices such as lithium ion secondary batteries, lithium polymer secondary batteries, sodium ion secondary batteries, potassium ion secondary batteries, and all-solid-state batteries. Even in secondary batteries that use alkali metals other than lithium ion capacitors, alkali metal dendrites are generated due to long-term use, which can cause short circuits and fires. Therefore, the technology of the present disclosure can suppress ignition and maintain safety in various power storage devices that utilize alkali metal ions.

The power storage device of the present invention is not limited to the structure, configuration, appearance, shape, etc. described in the above embodiments, and various changes, additions, and deletions can be made without changing the gist of the present invention. It is.

[Example]
The present invention will be explained in more detail below with reference to Examples and Comparative Examples, but the present invention is not limited to the scope of these Examples.

<Creation of lithium ion capacitor>
[Creation of positive electrode]
First, 88 parts by mass of activated carbon powder as a positive electrode active material, 6 parts by mass of polyacrylic acid (sodium neutralized salt of polyacrylic acid) as a binder, 15 parts by mass of acetylene black as a conductive agent, and 345 parts by mass of water as a solvent. A positive electrode slurry A containing a positive electrode active material was prepared using the following method.

Positive electrode slurry A using polyacrylic acid as a binder was prepared according to the following procedure.
(1) All the materials and water were mixed in mixer a (Awatori Rentaro ARE-310, manufactured by Thinky Co., Ltd.) to prepare a press slurry.
(2) The press slurry obtained in (1) was further mixed in mixer b (Filmix 40-L manufactured by Primix Co., Ltd.) to prepare an intermediate slurry.
(3) The intermediate slurry obtained in (2) was mixed again using mixer a to prepare positive electrode slurry A.

Next, using an aluminum foil (porous foil) with a thickness of 15 μm as a current collector foil, positive electrode slurry A was applied to each current collector foil and dried to create a positive electrode A. The coating amount of positive electrode slurry A was adjusted so that the mass of activated carbon after drying was 3 mg/cm ² . A blade coater or a die coater was used to apply the positive electrode slurry A to the current collector foil.

[Creation of negative electrode]
First, 95 parts by mass of graphite as a negative electrode active material, 1 part by mass of SBR as a binder, 1 part by mass of CMC as a thickener, and 100 parts by mass of water as a solvent were mixed, and a slurry for a negative electrode was prepared according to the following procedure. .
(1) A press slurry was prepared by mixing the materials excluding the binder and water in a mixer a.
(2) The press slurry obtained in (1) was further mixed in mixer b to prepare an intermediate slurry.
(3) A binder was added to the intermediate slurry obtained in (2) and mixed in mixer a to prepare a negative electrode slurry.

Next, using a copper foil (porous foil) with a thickness of 10 μm as a current collector foil, a negative electrode slurry was applied to the current collector foil and dried to create a negative electrode. The amount of the negative electrode slurry applied was adjusted so that the mass of graphite after drying was 3 mg/cm ² . A blade coater was used to apply the negative electrode slurry to the current collector foil.

[Preparation of electrolyte]
1 mol/L of lithium bis(fluorosulfonylimide) (LiFSI) was added to a mixed solvent of 30 vol% ethylene carbonate (EC), 30 vol% dimethyl carbonate (DMC) and 40 vol% ethyl methyl carbonate (EMC), and electrolyte I was added. Prepared. Further, polyoxyethylene alkyl ether was added to the electrolytic solution I in an amount of 0.5% by mass to prepare an electrolytic solution IA. The RED value of polyoxyethylene alkyl ether based on the Hansen solubility parameter in electrolyte I was calculated and was found to be 0.86. In addition, 1 mol/L of lithium bis(fluorosulfonylimide) (LiFSI) was added to a mixed solvent of 30 vol% ethylene carbonate (EC), 30 vol% dimethyl carbonate (DMC), and 40 vol% ethyl methyl carbonate (EMC) to form an electrolytic solution. IB was prepared.

[Assembly of lithium ion capacitor]
Lithium ion capacitors of Example 1 and Comparative Example 1 were manufactured in the following procedure.
(1) Punch out the positive and negative electrodes to form a rectangle with a size of 60 mm x 40 mm, leave a 40 mm x 40 mm coating film, peel off the coating film in a 20 mm x 40 mm area on one end of the long side, and then create a current collection tab. was installed.
(2) A laminate was prepared by making the coating parts of the positive and negative electrodes face each other with a cellulose separator having a thickness of 20 μm interposed therebetween.
(3) The laminate produced in (2) and metallic lithium foil for lithium pre-doping are surrounded by a 20 μm thick cellulose enclosure, enclosed in aluminum laminate foil, injected with electrolyte, and sealed. A lithium ion capacitor was fabricated.
Note that electrolytic solution IA was used for the lithium ion capacitor of Example 1, and electrolytic solution IB was used for the lithium ion capacitor of Comparative Example 1.

<Internal resistance>
In a lithium ion capacitor, after performing lithium pre-doping, charging/discharging, and aging, the internal resistance is measured at room temperature (25°C) with a cutoff voltage of 2.2 to 3.8V and a measurement current of 10C. The resistance ratio was determined. The internal resistance ratio was 98.1% in Example 1, with Comparative Example 1 being 100%. There was no significant difference in internal resistance between Example 1 and Comparative Example 1, and the fire extinguisher did not deteriorate the performance of the capacitor.

<Nail penetration test>
A nail was inserted into the lithium ion capacitor, and the presence or absence of ignition was observed, and the surface temperature was measured. A 3 mm diameter nail was inserted into the lithium ion capacitor at a speed of 80 mm/sec. The position where the nail was inserted is the position where two diagonal lines intersect on a large surface parallel to the height direction of the lithium ion capacitor. The temperature at a position 10 mm away from the current collection tab side from the nail insertion point was measured for one hour from the nail insertion point.

As a result of the nail penetration test, Example 1 had a maximum surface temperature of 198° C. and did not catch fire. In Comparative Example 1, the maximum surface temperature was 332° C., and the lithium ion capacitor exploded immediately after being pierced with a nail. The lithium ion capacitor of Example 1 was able to fully exhibit the flame retardant function by incorporating a fire extinguisher. In addition, in Example 1, there was no ignition even when the maximum surface temperature reached 198°C. We were able to confirm that the product does not ignite and remains safe even when exposed to test and crush test conditions (such as car accidents).

<Creation of other lithium ion capacitors>
In order to examine the high-temperature durability of lithium ion capacitors, a plurality of lithium ion capacitors with different binders and electrolytes were created using the following procedure. Incidentally, since the basic production method is the same as that of the first embodiment, only the differences will be described below.

[Creation of positive electrode]
Positive electrode slurries B and C containing positive electrode active materials were prepared with the compositions shown in Table 1 below. Carboxymethyl cellulose (CMC) was used as a thickener. In Table 1, SBR indicates styrene-butadiene rubber, "part" indicates parts by mass, and "%" indicates mass %.

Positive electrode slurries B and C using acrylic ester or SBR as a binder were prepared according to the following procedure.
(1) A press slurry was prepared by mixing the materials excluding the binder and water in a mixer a.
(2) The press slurry obtained in (1) was further mixed in mixer b to prepare an intermediate slurry.
(3) A binder was added to the intermediate slurry obtained in (2) and mixed in mixer a to prepare positive electrode slurry B or C.

Next, positive electrode slurry B was applied to each current collector foil and dried to create positive electrode B. The current collector foil is an aluminum foil (porous foil) with a thickness of 15 μm. The amount of positive electrode slurry B applied was adjusted so that the mass of activated carbon after drying was 3 mg/cm ² . A blade coater or a die coater was used to apply the positive electrode slurry B to the current collector foil. Similarly, positive electrode C was created using positive electrode slurry C.

[Preparation of electrolyte]
Lithium hexafluorophosphate (LiPF6) was added to a mixed solvent of 30 vol% ethylene carbonate (EC), 30 vol% dimethyl carbonate (DMC) and 40 vol% ethyl methyl carbonate (EMC), and 0.0% polyoxyethylene alkyl ether was added. Electrolyte solution P was prepared by adding 5% by mass. In addition, lithium bis(fluorosulfonylimide) ( An electrolytic solution I2 was prepared by adding 1 mol/L of LiFSI) and further adding polyoxyethylene alkyl ether to a concentration of 0.5% by mass.

[Assembly of lithium ion capacitor]
A lithium ion capacitor was fabricated using the combinations of positive electrodes and electrolytes shown in Table 2 below. Table 2 also shows the RED value of the polymer constituting the binder with respect to the electrolytic solution for each combination.

[Measurement of initial performance]
In the lithium ion capacitors of Examples 1 to 5, after performing lithium pre-doping, charging/discharging, and aging, the internal resistance was measured at room temperature (25°C) with a cutoff voltage of 2.2 to 3.8 V and a measurement current of 10 C. and the discharge capacity were measured, and the results were taken as the initial performance.

[Durability test (85℃ float test)]
The lithium ion capacitors of Examples 1 to 5, which were connected to an external power source and maintained at a voltage of 3.8 V, were left in a constant temperature bath at 85°C. The standing time corresponds to a 3.8V float time at 85°C. After a predetermined period of time, the lithium ion capacitor was taken out from the thermostatic chamber, returned to room temperature, and then the internal resistance and discharge capacity were measured under the same conditions as the initial performance measurement above, and the capacity retention rate (initial discharge capacity was taken as 100%) was determined. The percentage of discharge capacity at that time) and the rate of increase in internal resistance (rate of increase in internal resistance from initial performance) were calculated. The results are shown in Table 3.

As shown in Table 3, when left in a high-temperature environment of 85°C, the capacity retention rate was halved in a short time in Example 5, which used an electrolyte containing lithium fluorophosphate, which is not an imide-based lithium salt. On the other hand, in Examples 1 to 4 in which an electrolytic solution containing an imide-based lithium salt was used as the electrolyte, the capacity retention rate was maintained high for a long time. However, it has become clear that even when an electrolytic solution containing an imide-based lithium salt is used as the electrolyte, there is a difference in the internal resistance increase rate depending on the composition of the binder of the positive electrode. Therefore, when comparing the RED values (see Table 2) of the polymer constituting the binder of the positive electrode with respect to the electrolyte, it was found that in Example 3 using an acrylic ester and Example 4 using SBR, the RED value was 1 or less. It was found that the rate of increase in internal resistance was high. On the other hand, in Examples 1 and 2, an electrolytic solution containing an imide-based lithium salt is used as the electrolyte, and polyacrylic acid having a RED value of greater than 1 with respect to the electrolytic solution is used as the polymer constituting the binder of the positive electrode. . In this case, it is clear that the polymer that makes up the binder of the positive electrode is difficult to dissolve in the electrolyte, and that the capacity retention rate is maintained high even when left in a high-temperature environment of 85 degrees Celsius, and the rate of increase in internal resistance can be kept small. became.

1, 2 Lithium ion capacitor 10 Positive electrode 11 Positive electrode plate 12 Current collector 12a Current collector part 12b Electrode terminal connection part 12c Hole 13 Positive electrode active material layer 14 Positive electrode terminal 20 Negative electrode 21 Negative electrode plate 22 Current collector 22a Current collector part 22b Electrode terminal Connection part 22c Hole 23 Negative electrode active material layer 24 Negative electrode terminal 30 Separator 40 Electrolyte 50 Enveloping body 60 Laminate member (sealing body)
61 Core sheet 62 Outer sheet 63 Inner sheet

Claims (3)

a positive electrode comprising a positive electrode active material; a negative electrode comprising a negative electrode active material; a separator sandwiched between the positive electrode and the negative electrode and made of cellulose; and an electrolytic solution in contact with the positive electrode and the negative electrode and containing alkali metal ions. and a sealing body that contacts the electrolytic solution on the inside and seals the electrolytic solution, wherein at least one of the positive electrode active material and the negative electrode active material is capable of occluding and releasing alkali metal ions. It is a power storage device,
The electrolytic solution contains a carbonate-based organic solvent and an imide-based lithium salt,
A fire extinguishing agent having a RED value based on the Hansen solubility parameter in the electrolytic solution smaller than 1 and exhibiting a flame retardant function, provided in the internal space of the sealing body,
The extinguishing agent is an ether-type nonionic surfactant (excluding halogen-based surfactants) , and the concentration of the extinguishing agent is 0.1% by mass or more and 1% by mass or less with respect to the electrolytic solution. . The electricity storage device according to claim 1,
The extinguishing agent is electrochemically stable within the operating potential range of the positive electrode and electrochemically stable within the operating potential range of the negative electrode at a predetermined temperature or lower. The electricity storage device according to claim 1 or 2,
A power storage device that is a lithium ion capacitor.

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