JP2015061046A - Power storage device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power storage device having small initial electrostatic capacity, allowing suppression of gas generation, and having small initial direct current resistance.SOLUTION: In a power storage device having a positive electrode, a negative electrode, an electrolyte, and an electrolyte comprising a lithium phosphate coat, the negative electrode has a negative electrode active material consisting of a carbon material forming a core and a carbon material for coating with low crystallinity coating the surface of the carbon material, and the electrolyte comprises a phosphazene compound and an ionic compound composed of a cation below and an anion below. Cation: organic onium cation or alkali metal cation. Anion: carboxylic acid anion, boron anion, anion represented by the formula (1), or anion represented by the formula (2).

Description

  The present invention relates to an electricity storage device that can increase initial capacitance, suppress generation of gas, and have low initial DC resistance.

  Conventionally, an electricity storage device has been regarded as a problem in that it generates heat or ignites while it is repeatedly charged and discharged. For this reason, for example, as disclosed in Patent Document 1, a nonaqueous battery has been proposed in which flame retardant properties are provided and battery performance is improved by adding a cyclic phosphazene compound and salts to the battery electrolyte. Further, Patent Document 2 proposes a lithium ion capacitor that prevents ignition of an electrolyte or ignition in overcharge by adding a specific amount of a cyclic phosphazene compound even in a high temperature environment.

  However, when the electricity storage device as described above is stored in a high temperature environment, gas may be generated depending on conditions, and the cell may swell. This was because the electrolytic solution decomposed on the negative electrode.

  Therefore, in Patent Document 3, a negative electrode active material is used in order to suppress a decrease in battery capacity and battery swelling when a charge / discharge cycle is repeated, and to suppress an increase in battery thickness even when charged and discharged at a low temperature. As a non-aqueous electrolyte secondary battery using a coated graphite in which the entire surface of graphite is coated with a coating carbon material having lower crystallinity than graphite and using an electrolyte containing unsaturated sultone and diol sulfonic acid is disclosed. Has been.

  However, in an electricity storage device such as a capacitor, even if an electrolyte containing unsaturated sultone is used as in Patent Document 3, if charge / discharge is repeated many times, a high capacity retention rate cannot be obtained, It has been difficult to sufficiently suppress the generation of gas.

JP 2009-129541 A JP 2011-204822 A JP 2007-173014 A

  An object of the present invention is to provide an electricity storage device that has a high initial capacitance, can suppress gas generation, and has a low initial DC resistance.

（Ｒ^１、Ｒ^２は、それぞれ独立に、炭素数１〜１２を有する、アルキル基、アルコキシ基、ハロゲン化アルキル基、又はハロゲンである。）

（Ｒ^３は、炭素数１〜１２を有する、アルキル基、アルコキシ基、ハロゲン化アルキル基、又はハロゲンである。） The gist of the present invention is as follows.
(1) In an electricity storage device having a positive electrode, a negative electrode, an electrolytic solution, and an electrolytic solution containing a lithium phosphate coating,
The negative electrode has a negative electrode active material composed of a carbon material that forms a core and a low-crystallizing carbon material that covers the surface of the carbon material,
The said electrolyte solution contains the ionic compound comprised from the phosphazene compound and the following cation and the following anion, The electrical storage device characterized by the above-mentioned.
Cation: Organic onium cation or alkali metal cation.
Anion: Carboxylic acid anion, boron anion, anion represented by formula (1) or anion represented by formula (2).

(R ¹ and R ² are each independently an alkyl group, an alkoxy group, a halogenated alkyl group, or a halogen having 1 to 12 carbon atoms.)

(R ³ is an alkyl group, alkoxy group, halogenated alkyl group, or halogen having 1 to 12 carbon atoms.)

(2) The organic onium cation is an organic quaternary ammonium ion, organic phosphonium ion, substituted or unsubstituted piperidinium ion, substituted or unsubstituted piperazinium ion, substituted or unsubstituted pyrrolidinium ion, and substituted or At least one selected from the group consisting of unsubstituted imidazolium ions,
The alkali metal cation is at least one selected from the group consisting of lithium ions, potassium ions, and sodium ions;
The carboxylate anion is at least one selected from the group consisting of R ⁴ COO— (R ⁴ is an alkyl group having 1 to 10 carbon atoms, an aryl group, or an alkylaryl group) and an oxalate ion. ,
The boron anion is at least one selected from the group consisting of borate ions, tetrafluoroborate ions, and bis (oxalato) borate ions,
The anion of the formula (1) is at least one selected from the group consisting of bis (trifluoromethanesulfonyl) amide ion and bis (fluorosulfonyl) amide ion, and the anion of the formula (2) is bis ( The electricity storage device according to (1), which is a fluorosulfone) amide ion.

（Ｒ^５〜Ｒ^１０は、それぞれ独立に、炭素数１〜１２を有するアルキル基、アルケニル基、アルコキシル基アシル基若しくはアリール基（但し、水素原子の一部若しくは全部がハロゲン原子で置換されていてもよく、また、炭素−炭素結合間に−Ｏ−、−ＣＯＯ−及びＯＣＯ−からなる群から選ばれる少なくとも一種を有する基を有してもいてもよい。）、水素原子、又はハロゲン原子である。） (3) The electricity storage device according to (1) or (2), wherein the phosphazene compound is a compound represented by the following formula (3).

(R ^{5 to} R ¹⁰ are each independently an alkyl group, alkenyl group, alkoxyl acyl group or aryl group having 1 to 12 carbon atoms (provided that some or all of the hydrogen atoms are substituted with halogen atoms) And may have a group having at least one selected from the group consisting of —O—, —COO—, and OCO— between carbon-carbon bonds), a hydrogen atom, or a halogen atom. is there.)

(4) The electricity storage device according to any one of (1) to (3), wherein a content ratio of the phosphazene compound in the electrolytic solution is 0.1 to 10% by mass.
(5) The electricity storage device according to any one of (1) to (4), wherein the content of the ionic compound is 0.005 to 5% by mass.
(6) The electricity storage device according to any one of (1) to (5), wherein the carbon material forming the core is graphite and the coating carbon material is pitch or tar.

(7) The ionic compound according to any one of (1) to (6), wherein the ionic compound is R ⁴ COOLi (R ⁴ is alkyl having 1 to 10 carbon atoms) or lithium oxalate. Power storage device.
(8) The ionic compound is composed of a substituted or unsubstituted pyrrolidinium ion and at least one selected from the group consisting of bis (trifluoromethanesulfonyl) amide ion and bis (fluorosulfonyl) amide ion. The electrical storage device of any one of said (1)-(7).

(9) The electricity storage according to any one of (1) to (8), wherein a content of the phosphazene compound in the electrolytic solution is 5 to 1000 times (mass basis) of a content of the ionic compound. device.
(10) The lithium phosphate, device according to any one of a LiPF ₆ (1) to (9).
(11) The electricity storage device according to any one of (1) to (10), wherein the electricity storage device is a lithium ion capacitor.

  According to the present invention, since the composite carbon material is used for the negative electrode and the electrolytic solution contains the phosphazene compound and the specific ionic compound, the initial capacitance is increased, and the generation of gas can be suppressed. In addition, an electricity storage device having a low initial DC resistance can be obtained.

Hereinafter, the electricity storage device of the present invention will be described by taking, for example, a case where it is implemented as a lithium ion capacitor.
The lithium ion capacitor according to the present invention basically has an electrode unit in which the positive electrode and the negative electrode are alternately stacked via a separator or further wound in an outer container. As the outer container, a container having a cylindrical shape, a square shape, a laminate shape, or the like can be appropriately used, and is not particularly limited.

  In this specification, “dope” means occlusion, adsorption, or insertion, and broadly refers to a phenomenon in which at least one of lithium ions and anions enters the positive electrode active material, or a phenomenon in which lithium ions enter the negative electrode active material. . In addition, “de-doping” means desorption and release, and refers to a phenomenon in which lithium ions or anions are desorbed from the positive electrode active material, or a phenomenon in which lithium ions are desorbed from the negative electrode active material.

  As a method of previously doping lithium ions into at least one of the negative electrode and the positive electrode, for example, a lithium ion source such as metallic lithium is disposed in the capacitor cell as a lithium electrode, and at least one of the negative electrode and the positive electrode and a lithium ion source A method of doping lithium ions by electrochemical contact is used.

In the lithium ion capacitor of the present invention, it is possible to uniformly dope lithium ions into at least one of the negative electrode and the positive electrode also by locally disposing the lithium electrode in the cell and bringing it into electrochemical contact.
Therefore, even when a large-capacity cell in which the positive electrode and the negative electrode are stacked or further wound is formed, at least one of the negative electrode and the positive electrode can be smoothly and uniformly doped with lithium ions.

[Current collector]
Each of the positive electrode and the negative electrode is provided with a positive electrode current collector and a negative electrode current collector (hereinafter collectively referred to as a current collector) that receive and distribute electricity. The current collector is preferably formed with a through-hole penetrating the front and back surfaces. The shape, number, etc. of the through holes in the current collector are not particularly limited, and lithium ions electrochemically supplied from a lithium electrode arranged to face at least one of the positive electrode and the negative electrode, and lithium ions in the electrolyte solution It can set so that it can move between the front and back of an electrode, without interrupted | blocked by each electrical power collector.

Even if the current collector has a through-hole formed by etching or the like, such as an electrolytic etching foil, the through-hole can be formed by mechanical driving or other mechanical processing such as punching metal or expanded metal. May be formed. The diameter of the through hole of the current collector is, for example, 0.1 μm to 100 μm, preferably 0.5 to 80 μm, and particularly preferably 1 to 50 μm.
Further, the porosity of the current collector is preferably 20 to 80%, more preferably 30 to 70%.

As a material constituting the current collector, a material generally used for a lithium battery can be used. For example, aluminum, stainless steel, or the like can be used as the material constituting the positive electrode current collector, while stainless steel, copper, nickel, or the like can be used as the material constituting the negative electrode current collector.
Although the thickness of a collector is not specifically limited, Usually, what is necessary is just 2-100 micrometers, 5-80 micrometers is preferable and 10-50 micrometers is especially preferable.

[Positive electrode active material]
The positive electrode is configured by forming a positive electrode active material layer on one surface or both surfaces of a positive electrode current collector.
As the positive electrode active material, a material capable of reversibly adsorbing and desorbing at least one kind of anion such as lithium ion and tetrafluoroborate is used. Specific examples thereof include activated carbon powder. The activated carbon powder preferably has a volume average particle diameter D50 of 2 μm or more, more preferably 2 to 50 μm, and particularly preferably 2 to 20 μm. Furthermore, the activated carbon powder preferably has an average pore size of 10 nm or less, and preferably has a specific surface area of 600 to 3000 m ² / g, more preferably 1300 to 2500 m ² / g.

[Negative electrode active material]
The negative electrode is configured by forming a negative electrode active material layer on one surface or both surfaces of a negative electrode current collector.
The negative electrode active material is a composite carbon containing a carbon material that forms a core and a coating carbon material that covers at least a part of the core among materials that can be reversibly doped and dedoped with lithium ions. Material is used.
This composite carbon material is, for example, at least part of the surface of graphite-based particles such as natural graphite, artificial graphite, hard carbon, coke, etc., which is a carbon material forming the core, preferably the entire surface is pitch, tar, hard It is manufactured by coating with a coating carbon material having different crystallinity from the core, such as carbon, coke, mesocarbon microbeads (MCMB) fired at 1500 ° C. or less, and mesophase pitch carbon fiber (MCF). These composite carbon materials may be used alone or in combination of two or more.

  In the above composite carbon material, the presence or absence of coating with a carbon material having different crystallinity from the core on the particle surface can be confirmed by measurement of Raman spectrum, XRD, or the like. The covering structure can be confirmed by cutting a part of the particles with a focused ion beam (FIB) and observing the cross section with a transmission electron microscope (TEM).

Graphite, which is a preferred carbon material forming the core, has an average interplanar spacing (d002) of (002) plane of 3.357 mm by X-ray wide angle diffraction method, and 1355 cm with respect to a peak near 1580 cm ⁻¹ by argon laser Raman. The intensity ratio of peaks in the vicinity of ⁻¹ (I1355 / I1580) is, for example, 0.25, and graphite having crystallite sizes Lc and La determined by X-ray diffraction of 100 nm or more can be suitably used. In the composite carbon material, the intensity ratio of the peak near 1355 cm ^{−1 to} the peak near 1580 cm ⁻¹ by argon laser Raman is, for example, 1.03.

  The coating amount of the coating carbon material in the composite carbon material is preferably 5 to 200% by mass, and more preferably 10 to 100% by mass. Here, the coating amount of the coating carbon material in the composite carbon material is a value obtained by (mass of coating carbon material in composite carbon material / mass of graphite in composite carbon material) × 100 (mass%). When the coating amount of the coating carbon material is too small, the active sites of graphite with high crystallinity are likely to be exposed on the surface of the composite carbon material, so that reductive decomposition of the electrolyte proceeds when charging and discharging are repeated. A large amount of gas is likely to be generated. On the other hand, when the coating amount of the carbon material for coating is excessive, carbon with low crystallinity excessively covers the surface, making it difficult for lithium ions to intercalate. Electrolytic transfer resistance with the liquid increases, and the resistance of the electricity storage device increases.

  As a preferable production method of the composite carbon material, for example, 100 to 50 parts by mass of fine particle graphite powder having a volume average particle diameter D50 of preferably 1 to 3 μm, and 10 to 50 mass of low crystallinity pitch or tar. Mix the parts with a kneader. The resulting mixture is fired under a nitrogen atmosphere by keeping the temperature preferably at 800 to 1200 ° C., preferably for 1 to 72 hours. The obtained fired product has a volume average particle size D50 value of preferably 1 to 5 μm, a chemical vapor deposition method using toluene gas as a carbon raw material, and the surface of graphite particles with respect to the mass of natural graphite. For example, the method etc. which coat | cover with 5-30 mass% carbon material with low crystallinity are mentioned.

As the negative electrode active material, a powdery material is used as in the case of the positive electrode active material. A negative electrode active material having a volume average particle diameter D50 of less than 0.1 μm is difficult to produce. On the other hand, with a negative electrode active material having a volume average particle diameter D50 exceeding 5 μm, it may be difficult to obtain a lithium ion capacitor having a sufficiently low internal resistance. The negative electrode active material preferably has a specific surface area of 0.1 to 2000 m ² / g, more preferably 0.1 to 600 m ² / g.

  In the present invention, a composite carbon material is used for the negative electrode active material, and an electricity storage device in which initial DC-IR is small and gas generation is suppressed is obtained. When the composite carbon material is not used, the reduction reaction of the electrolytic solution proceeds on the surface of the graphite particles, and it is difficult to form a high-quality SEI film on the negative electrode active material, the initial DC-IR becomes large, and the surface of the negative electrode active material is increased. Since a high-quality SEI film is unlikely to exist, the electrolytic solution tends to be reduced and decomposed to easily generate gas.

[Active material layer]
The positive electrode active material or the negative electrode active material is preferably formed on the current collector by applying a slurry containing these active materials and a binder, or by depositing the positive electrode active material or the negative electrode active material. It can be formed as a positive electrode active material layer or a negative electrode active material layer. The thickness of the positive electrode active material layer and the negative electrode active material layer is usually 1 to 100 μm, preferably 1 to 80 μm, more preferably 2 to 70 μm.

[Binder]
In the case where the positive electrode having the positive electrode active material and the negative electrode having the negative electrode active material as described above are prepared using the positive electrode active material or the slurry containing the negative electrode active material and the binder, the slurry is the positive electrode active material or the negative electrode active material. It is prepared by adding a substance, a binder, and a conductive material, carboxymethylcellulose (CMC) (including carboxymethylcellulose salt) and the like, which are used as necessary, to water or an organic solvent and mixing them.
And a positive electrode or a negative electrode can be produced by apply | coating the obtained slurry to a collector, or shape | molding a slurry in a sheet form and sticking to a collector.

In the production of the positive electrode or the negative electrode, examples of the binder include a rubber-based binder such as SBR, a fluorine-containing resin such as polytetrafluoroethylene and polyvinylidene fluoride, a thermoplastic resin such as polypropylene and polyethylene, and an acrylic resin. Etc. can be used.
Examples of the conductive material include carbon black such as acetylene black and ketjen black, graphite, and metal powder.
The amount of each of the binder and the conductive material added varies depending on the electric conductivity of the positive electrode active material or negative electrode active material used, the shape of the electrode to be produced, etc. It is preferable that it is 2-40 mass%.

[Separator]
As a separator in the lithium ion capacitor according to the present invention, it is preferable to use a material having an air permeability measured by a method in accordance with JIS P8117 within a range of 1 to 200 sec. As such a separator, for example, a nonwoven fabric or a microporous membrane made of polyethylene, polypropylene, polyester, cellulose, polyolefin, cellulose / rayon, or the like can be used as appropriate. From the viewpoint of cycle characteristics and electrolyte solution impregnation, it is particularly preferable to use a film obtained by applying silica to polyethylene. Moreover, the thickness of a separator is 5-100 micrometers, for example, and 10-50 micrometers is preferable.

[Electrolyte]
In the lithium ion capacitor according to the present invention, a non-protonic organic solvent electrolyte solution of a lithium salt containing an unsaturated sultone and a phosphazene compound is used as the electrolytic solution. Below, each component in electrolyte solution is demonstrated.

[Non-prototronic organic solvent electrolyte]
Examples of the aprotic organic solvent constituting the electrolyte include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), diethyl carbonate ( Chain carbonates such as DEC), methylpropyl carbonate (MPC), and methylbutyl carbonate (MBC) can be used. You may use the mixed solvent which mixed 2 or more types of these. In particular, it is preferable to use a mixture of a cyclic carbonate and a chain carbonate because an electrolytic solution having a low viscosity, a high degree of dissociation, and a high ionic conductivity can be obtained.

  Further, the non-protonic organic solvent constituting the electrolytic solution is an organic solvent other than cyclic carbonate and chain carbonate, for example, cyclic ester such as γ-butyrolactone, cyclic sulfone such as sulfolane, cyclic ether such as dioxolane, ethyl propionate, and the like. A chain ether such as a chain carboxylic acid ester such as dimethoxyethane may be contained.

  The ratio of the cyclic carbonate and the chain carbonate in the aprotic organic solvent is expressed by mass ratio, and the cyclic carbonate: chain carbonate is preferably 5:95 to 80:20, more preferably 10:90. ~ 70: 30. By using an aprotic organic solvent containing cyclic carbonate and chain carbonate at such a ratio, the increase in the viscosity of the electrolyte can be suppressed and the degree of dissociation of the electrolyte can be increased. The conductivity of the electrolytic solution can be increased, and the solubility of the electrolyte can be further increased.

[Lithium phosphate]
A specific example of the lithium phosphate in the electrolytic solution is LiPF ₆ , which is preferable because it has high ionic conductivity and low resistance. The concentration of the lithium salt in the electrolytic solution is preferably 0.1 mol / L or more, more preferably 0.5 to 1.5 mol / L, because low internal resistance is obtained.

[Phosphazene compounds]
As the phosphazene compound contained in the electrolytic solution, it is preferable to use a compound represented by the following formula (1).

In the above formula (3), R ^{5 to} R ¹⁰ are each independently an alkyl group, alkenyl group, alkoxyl group acyl group or aryl group having 1 to 12 carbon atoms, preferably 1 to 10 Part or all may be substituted with a halogen atom, and may have a group having at least one selected from the group consisting of —O—, —COO— and OCO— between carbon-carbon bonds. Or a hydrogen atom or a halogen atom. In the above, the halogen atom is preferably a fluorine atom.

Specific examples of groups other than hydrogen atoms and halogen atoms among R ^{5 to} R ¹⁰ in the above formula (3) include methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group, heptyl group, octyl group. A group having 1 to 12 carbon atoms such as a group, nonyl group, decyl group and the like, and a group in which part or all of the hydrogen atoms are substituted with fluorine atoms; methoxy group, ethoxy group, propoxy group, butoxy group, pentoxy group, A C1-C12 alkoxyl group such as hexyloxy group, heptyloxy group, octyloxy group and the like, and a group in which some or all of the hydrogen atoms are substituted by fluorine atoms; methoxymethyl group, ethoxymethyl group, propoxymethyl group , Butoxymethyl group, methoxyethyl group, ethoxyethyl group, propoxyethyl group, methoxypropyl group, ethoxypropyl group, A C1-C10 alkoxyalkyl group such as a loxypropyl group and a group in which some or all of the hydrogen atoms are substituted with fluorine atoms; a vinyl group, a 1-propenyl group, a 2-propenyl group, and a 1-butenyl group 1-pentenyl group, 3-butenyl group, 3-pentenyl group, 2-fluoroethenyl group, 2,2-difluoroethenyl group, 1,2,2-trifluoroethenyl group, 4,4-difluoro-3 -Alkenyl groups such as butenyl group, 3,3-difluoro-2-propenyl group, 5,5-difluoro-4-pentenyl group; carboxyl group; formyl group, acetyl group, propionyl group, butyryl group, isobutyryl group, valeryl group An aryl group such as a phenyl group and a group in which some or all of the hydrogen atoms are substituted with fluorine atoms; an aryl group such as a phenoxy group Shi group and the like.

Specific examples of the most preferred phosphazene compounds are one or more compounds represented by the following formula.

  By containing such a phosphazene compound in the electrolytic solution, the flame retardancy of the electrolytic solution can be improved. This is because the phosphazene compound has the property of capturing oxygen necessary for the electrolyte to burn from its structure, and this property can be used to control the thermal runaway reaction of the lithium ion capacitor. .

  And, when both the ionic compound and the phosphazene compound are contained in the electrolytic solution, it is possible to suppress the decrease in the capacity of the lithium ion capacitor even when charging and discharging are repeated many times. It becomes possible to suppress gas generation accompanying decomposition. Furthermore, the initial value of the direct current resistance (hereinafter also referred to as DC-IR) can be reduced, and the direct current resistance value can be kept low even when charging and discharging are repeated many times. .

  The ratio of the phosphazene compound in the electrolytic solution is preferably 0.1 to 10% by mass, and more preferably 0.5 to 8% by mass. When the content ratio of the phosphazene compound is too small, there is a possibility that the effect due to the inclusion of the phosphazene compound becomes difficult to express. On the other hand, when the content ratio of the phosphazene compound is excessive, the resistance value may be increased because the polarity of the phosphazene compound is low.

式（１）において、Ｒ^１、Ｒ^２は、それぞれ独立に、炭素数１〜１２を有する、アルキル基、アルコキシ基又はハロゲン化アルキル基である。 [Ionic compounds]
As an ionic compound contained in the electrolytic solution, the cation is an organic onium cation or an alkali metal cation, and the anion is a carboxylate anion, a boron anion, an anion represented by the following formula (1), or the following formula (2). An anion represented, and at least one selected from the cations and anions.

In Formula (1), R ¹ and R ² are each independently an alkyl group, an alkoxy group, or a halogenated alkyl group having 1 to 12 carbon atoms.

式（２）において、Ｒ^３は、炭素数１〜１２を有する、アルキル基、アルコキシ基、又はハロゲン化アルキル基である。

In Formula (2), R ³ is an alkyl group, an alkoxy group, or a halogenated alkyl group having 1 to 12 carbon atoms.

[Ionic compound-cation]
Organic onium cations include organic quaternary ammonium ions, organic phosphonium ions, substituted or unsubstituted piperidinium ions, substituted or unsubstituted piperazinium ions, substituted or unsubstituted pyrrolidinium ions, or substituted or unsubstituted ions. Examples include imidazolium ions.

  The organic quaternary ammonium ion and the organic phosphonium ion are a group selected from a hydrocarbon group having 1 to 15 carbon atoms, an alkoxy group, an alkoxycarbonyl group, an acyl group, and an acyloxy group, or a part of hydrogen atoms of these groups. You may have a substituent substituted by halogen.

  Substituted or unsubstituted piperidinium ion, substituted or unsubstituted piperazinium ion, substituted or unsubstituted pyrrolidinium ion, and substituted or unsubstituted imidazolium ion are a hydrocarbon group having 1 to 15 carbon atoms, alkoxy A group selected from a group, an alkoxycarbonyl group, an acyl group, and an acyloxy group, or a part of hydrogen atoms of these groups may be substituted with a halogen.

Examples of the substituent constituting the organic onium cation include an alkyl group, an alkenyl group, and an aryl group as the hydrocarbon group having 1 to 15 carbon atoms.
Examples of the alkyl group include an alkyl group having 1 to 15 carbon atoms, and an alkyl group having 1 to 10 carbon atoms is preferable. Examples of the alkyl group include linear and branched alkyl groups. Specifically, methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, tert. -Butyl group, n-pentyl group, n-hexyl group, n-heptyl group, n-octyl group, n-nonyl group, n-decanyl group and the like can be mentioned.

Examples of the alkenyl group include alkenyl groups having 1 to 15 carbon atoms, and alkenyl groups having 1 to 10 carbon atoms are preferable. Specific examples include a vinyl group, a propenyl group, and a 3-butenyl group.
Examples of the aryl group include aryl groups having 6 to 15 carbon atoms, and specific examples include phenyl, tolyl, naphthyl, and the like.

  Examples of the alkoxy group of the substituent constituting the organic onium cation include a methoxy group, an ethoxy group, a propoxy group, a butoxy group, a t-butoxy group, a pentyloxy group, a hexyloxy group, an isopropoxy group, and an isobutoxy group. A methoxy group and an ethoxy group are preferable.

Examples of the alkoxycarbonyl group as a substituent constituting the organic onium cation include a methoxycarbonyl group, an ethoxycarbonyl group, and a propoxycarbonyl group.
Examples of the acyl group include an acetyl group, a propionyl group, a butyryl group, a valeryl group, and a caproyl group.
Examples of the acyloxy group of the substituent constituting the organic onium cation include a formyloxy group and an acetyloxy group.
Specifically, as the cation, lithium ion, pyrrolidinium ion, and the like are preferable from the viewpoint of forming a film having good properties with low DC-IR.

[Ionic compounds-anions]
Examples of the anion constituting the ionic compound include R ⁴ COO— (R ⁴ is an alkyl group having 1 to 10 carbon atoms, an aryl group, or an alkylaryl group), a carboxylic acid anion such as an oxalate ion; Boron anions such as acid ion, tetrafluoroborate ion and bis (oxalato) borate ion; anions represented by formula (1) such as bis (trifluoromethanesulfonyl) amide ion and bis (fluorosulfonyl) amide ion; bis ( And anions represented by the formula (2) such as fluorosulfone) amide ion.

R ⁴ COO— includes formate ion, acetate ion, propionate ion, butanoic acid ion, pentanoic acid ion, hexanoic acid ion, heptanoic acid ion, octanoic acid ion, nonanoic acid ion, decanoic acid ion, dodecanoic acid ion, etc. Can be mentioned.
The alkyl group having 1 to 10 carbon atoms R ^4, or the aryl group can be the equivalent of groups described above (described substituent constituting the organic onium cation).
Examples of the alkylaryl group include groups in which the above-described aryl group having 6 to 15 carbon atoms is substituted with the above-described alkyl group having 1 to 8 carbon atoms (substituent constituting the organic onium cation).

As the alkyl group and alkoxy group of R ^{1 to} R ^3, the same groups as those described above (substituents constituting the organic onium cation) can be used.
Examples of the halogen for R ^{1 to} R ³ include F, Cl, Br, and I.
Examples of the halogenated alkyl group for R ^{1 to} R ³ include a trifluoromethyl group and a pentafluoroethyl group.

  As the anion, specifically, acetate ion, oxalate ion, bis (trifluoromethanesulfone) amide ion and the like are preferable from the viewpoint of forming a good film with low DC-IR.

  As the ionic compound, lithium acetate, lithium oxalate, or 1-butyl-1-methylpyrrolidinium bis (trifluoromethanesulfone) amide is preferable from the viewpoint of forming a good film with low DC-IR.

0.005-5 mass% is preferable and, as for content of the ionic compound in electrolyte solution, 0.01-5 mass% is more preferable. When the content falls within this range, a sufficient amount of film can be formed, and a sufficiently low DC-IR film can be formed.
In addition, it is preferable that content of the said phosphazene compound in electrolyte solution is 5-1000 times (mass standard) of content of this ionic compound, 5-500 times is more preferable, and it is 5-200 times. Is more preferable.

[Other additives]
In addition to the ionic compound and the phosphazene compound, other additives may be contained in the electrolytic solution.
Specific examples of other additives include compounds represented by the following formula (4).

In formula (4), M is a transition metal or any one of Group 13 to Group 15 elements, Aa + is a metal ion or an organic onium cation, a is an integer of 1 to 3, and b is 1 An integer of ˜3, p = b / a, q is an integer of 1 to 4, n is an integer of 1 to 8, and m is 0 or 1.
R ¹¹ is a halogen atom, and R ¹² is an alkylene group having 2 to 10 carbon atoms, a halogenated alkylene group, or an arylene group or halogenated arylene group having 6 to 20 carbon atoms (both are substituted or heteroatoms). And q R ^{12 s} may be bonded to each other). X ¹ and X ² are each independently a hetero atom or NR ¹³ (R ¹³ is a hydrogen atom, an alkyl group or halogenated alkyl group having 1 to 10 carbon atoms, or an aryl group or halogenated aryl having 6 to 20 carbon atoms) Group (all may contain substituents or heteroatoms).

Examples of the transition metal as M include Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn. Examples of Group 13 elements include B, Al, Ga, In, and Tl. Examples of Group 14 elements include C, Si, Ge, Sn, and Pb.
Examples of the Group 15 element include N, P, As, Sb, and Bi.
Aa + includes a metal ion or an organic onium cation, and examples thereof include those equivalent to those described above.

In R ¹¹ , examples of the halogen atom include fluorine, chlorine, boron, iodine and the like.
Examples of the alkylene group for R ¹² include an ethylene group, a propylene group, a butylene group, a pentylene group, a hexylene group, a heptylene group, an octylene group, a nonylene group, and a decylene group.
Examples of the halogenated alkylene group for R ¹² include those in which the halogen atom described above is substituted with at least part of the hydrogen atoms of the aforementioned alkylene group.

Examples of the arylene group for R ¹² include a phenylene group, a tolylene group, a biphenylene group, and a naphthylene group.
Examples of the halogenated arylene group for R ¹² include those in which the halogen atom described above is substituted with at least a part of the hydrogen atoms of the arylene group described above.
In X ¹ and X ² , examples of the hetero atom include oxygen, nitrogen, sulfur and the like.
As the alkyl group for R ¹³ , those equivalent to the groups described above (explained with the substituents constituting the organic onium cation) can be used.

As the halogenated alkyl group for R ^13, a group equivalent to R ¹ and R ² can be used.
As the aryl group for R ¹³ , those equivalent to the groups described above (explained with the substituents constituting the organic onium cation) can be used.
Examples of the halogenated aryl group for R ¹³ include a group in which at least a part of the hydrogen atom of the aryl group described above (explained by the substituent constituting the organic onium cation) is substituted with fluorine, chlorine, bromine, or iodine. .

As the other additive in the present invention, a compound in which M is B or P in the formula (4) is particularly preferable, lithium bis (oxalato) borate (the following formula (4-1)), and difluoro (oxalato). More preferably, it is at least one selected from the group consisting of lithium borate (formula (4-2) below). In particular, lithium bis (oxalato) borate represented by the above formula (4-1) is preferable.

  The content of other additives in the electrolyte is 0 to 5% by mass. However, if the content of other additives exceeds 5% by mass, the film becomes thick and DC-IR increases, which is not preferable. .

[Structure of lithium ion capacitor]
As a structure of the lithium ion capacitor according to the present invention, a winding-type, plate-shaped or sheet-like positive electrode and negative electrode in which a belt-like positive electrode and a negative electrode are wound via a separator are laminated in three or more layers via a separator. A laminated type, and a film type in which units having such a laminated structure are enclosed in an exterior film.
The structures of these lithium ion capacitors are known, for example, from Japanese Patent Application Laid-Open No. 2004-266091, and can be configured similarly to those capacitors.

  As mentioned above, although the case where it implemented as a lithium ion capacitor was mentioned as an example about the electrical storage device of this invention, the electrical storage device of this invention is not limited to a lithium ion capacitor, It applies to another capacitor or a secondary battery. It is possible.

  EXAMPLES Hereinafter, although this invention is demonstrated further more concretely based on an Example, this invention is not restrict | limited by these Examples. “Parts” and “%” in Examples and Comparative Examples are based on mass unless otherwise specified.

[Example 1]
(1) Fabrication of positive electrode Conductive paint on both sides of aluminum expanded metal (made by Nippon Metal Industry Co., Ltd.) having a porosity of 47% and a thickness of 38 μm, which is a positive electrode current collector precursor, both sides of a vertical die system By using a coating machine, applying a double-sided coating with a coating width of 130 mm and a coating speed of 8 m / min, setting the target value of the coating thickness on both sides to 20 μm, and then drying under reduced pressure A conductive layer was formed on the front and back surfaces of the positive electrode current collector precursor.

  Next, on the conductive layers formed on the front and back surfaces of the positive electrode current collector precursor, a slurry containing activated carbon as a positive electrode active material was applied at a coating speed of 8 m / min using a vertical die type double-side coating machine. The electrode layer was formed on the conductive layer by applying a double-sided coating by setting the target value of the coating thickness of both surfaces to 150 μm depending on the coating conditions, and then drying under reduced pressure.

  The material obtained by laminating the conductive layer and the electrode layer on a part of the positive electrode current collector precursor thus obtained is referred to as a portion where the conductive layer and the electrode layer are laminated (hereinafter, the positive electrode is also referred to as a coating part). .) Is 98 mm × 126 mm, and a portion where no layer is formed (hereinafter, also referred to as an uncoated portion of the positive electrode) is cut to a size of 98 mm × 141 mm so that it becomes 98 mm × 15 mm. A positive electrode having electrode layers formed on both sides of the positive electrode current collector was produced.

(2) Production of negative electrode Value of volume average particle diameter D50 which is a negative electrode active material on both surfaces of copper expanded metal (manufactured by Nippon Metal Industry Co., Ltd.) having a porosity of 57% and a thickness of 32 μm which is a negative electrode current collector precursor. Is a slurry containing a composite carbon material coated with a carbon material for coating of 4 μm, using a vertical die type double-side coating machine, with a coating width of 130 mm and a coating speed of 8 m / min, After setting the target value of the coating thickness on both sides to 80 μm and applying both sides, the electrode layer was formed on the front and back surfaces of the negative electrode current collector precursor by drying under reduced pressure.

  The material in which the electrode layer is formed on a part of the current collector precursor thus obtained is 100 mm × 128 mm in the part where the electrode layer is formed (hereinafter also referred to as the coating part for the negative electrode), By cutting into a size of 100 × 143 mm so that a portion where the electrode layer is not formed (hereinafter, also referred to as an uncoated portion of the negative electrode) is 100 mm × 15 mm, both sides of the negative electrode current collector are formed. A negative electrode on which an electrode layer was formed was produced.

The composite carbon material used here was produced as follows.
A mixture in which 50 parts by mass of a pitch, which is a precursor of a coating carbon material, is mixed with 100 parts by mass of fine particle graphite powder having a volume average particle diameter D50 of 2.5 μm with a kneader in a nitrogen atmosphere. The temperature was raised at a rate of ° C./min, and firing was carried out at a temperature of 1000 ° C. for 6 hours. The obtained fired product was pulverized to a volume average particle size D50 value of 4 μm to prepare a composite carbon material. The coating amount of the coating carbon material in this composite carbon material is 50% by mass.

(3) Production of Separator A separator (hereinafter referred to as Separator A) is cut by cutting a cellulose / rayon composite film having a thickness of 50 μm and an air permeability of 100 sec so that the vertical and horizontal widths are 102 mm × 130 mm. Produced.

(4) Production of Lithium Ion Capacitor Element First, 10 positive electrodes, 11 negative electrodes, and 22 separators are prepared, and the positive electrode and the negative electrode are overlapped with each other, but the respective uncoated portions are opposite to each other. In a state of being aligned so as not to overlap each other, the separator, the negative electrode, the separator, and the positive electrode were stacked in this order. By fixing the four sides of this stack with tape, an electrode laminate unit was produced.
Next, a lithium foil having a thickness of 100 μm is cut and bonded to a copper mesh having a thickness of 40 μm to produce a lithium ion supply member, and the lithium ion supply member is disposed on the upper side of the electrode stacking unit so as to face the negative electrode. did.

  And for the positive electrode made of aluminum having a width of 50 mm, a length of 50 mm, and a thickness of 0.2 mm, a sealant film is heat-sealed in advance to the uncoated portion of each of the 10 positive electrodes in the produced electrode laminate unit. The power tabs were stacked and welded. On the other hand, each of the 11 negative electrodes of the electrode laminate unit is made of copper having a width of 50 mm, a length of 50 mm, and a thickness of 0.2 mm, in which a sealant film is heat-sealed in advance to the seal portion on each of the uncoated portions and the lithium ion supply member A lithium ion capacitor element was prepared by overlapping and welding the negative electrode power supply tab.

(5) Production of Lithium Ion Capacitor Next, a polypropylene layer, an aluminum layer, and a nylon layer are laminated, and the dimensions are 125 mm (vertical width) × 160 mm (horizontal width) × 0.15 mm (thickness), and 105 mm ( One exterior film that has been subjected to drawing processing of (vertical width) × 145 mm (horizontal width), and a polypropylene layer, an aluminum layer, and a nylon layer are laminated, and the dimensions are 125 mm (vertical width) × 160 mm (horizontal width) × 0. The other exterior film of 15 mm (thickness) was produced.

  Next, at the position that becomes the housing part on the other exterior film, the lithium ion capacitor element is arranged so that each of the positive electrode terminal and the negative electrode terminal protrudes outward from the end of the other exterior film, One exterior film is overlaid on the lithium ion capacitor element, and three sides (including two sides from which the positive electrode terminal and the negative electrode terminal protrude) are heat-sealed at the outer peripheral edge of one exterior film and the other exterior film. did.

On the other hand, using a mixed solvent of ethylene carbonate, propylene carbonate, and diethyl carbonate (3: 1: 4 by volume), the additive is represented by the above formula (3-1) with respect to 100 mass% of the total mass of the electrolytic solution. The electrolyte solution was adjusted so that the concentration of lithium acetate (ionic compound) was 0.01% by mass and LiPF ₆ was 1.2 mol / L with respect to 5% by mass of the phosphazene compound and 100% by mass of the total electrolyte solution. Prepared.

Subsequently, after inject | pouring the said electrolyte solution between one exterior film and the other exterior film, the remaining one side in the outer periphery part of one exterior film and the other exterior film was heat-seal | fused.
As described above, three laminated exterior lithium ion capacitors (hereinafter also referred to as cells) were produced.

[Examples 2 to 5 and Comparative Examples 1 to 4]
A cell was produced in the same manner as in Example 1 except that the content of the phosphazene compound and the content of the ionic compound were changed to the contents shown in Table 1 in the preparation of the electrolytic solution.
In the table, “-” indicates that the corresponding component was not added.

[Examples 6 to 8]
In the preparation of the electrolytic solution, in addition to the phosphazene compound and the ionic compound, it was carried out except that the compound 2 represented by the formula (4-1) was added as the other additive in the content described in Table 1. Three cells were produced in the same manner as in Example 1.

[Comparative Example 5]
Three cells were prepared in the same manner as in Example 1 except that graphite was used as the negative electrode active material in the preparation of the electrolytic solution.

[Initial capacitance measurement of cell and initial DC-IR (direct current resistance) measurement test]
For the cells according to Examples 1 to 8 and Comparative Examples 1 to 5, the initial capacitance (F) and the initial DC-IR (mΩ) of the cell were subjected to CC discharge using a charge / discharge device manufactured by Nippon Denki Co., Ltd. The value according to was measured. The initial capacitance [F] of the two cells according to each of the examples and the comparative examples with respect to the case where the average value of the initial capacitance [F] of the two cells according to the example 1 is 100%. The result of the relative value with the average value is shown in Table 1. Moreover, with respect to the average value of initial DC-IR [mΩ] of two cells according to Example 1, the average value of initial DC-IR [mΩ] of two cells according to each Example and each Comparative Example The results of relative values are shown in Table 1.

The measurement conditions are described below.
(Measurement condition)
Temperature: 25 ° C
Voltage range: 3.8 to 2.2V
Current value: 10A

[High temperature load test]
Using one cell according to Examples 1 to 10 and Comparative Examples 1 to 5, performing a high temperature load test under the following conditions, and measuring the volume of the cell before and after the test, the gas generation state inside the cell was examined. It was. Table 1 shows the volume ratio of the volume of one cell according to each example and each comparative example to the volume value of one cell according to example 1 after the high temperature load test.

(Test conditions)
Test equipment: DC power supply device (PW8-3AQP) manufactured by TEXIO, Yamato Scientific thermostat (DKN812)
Test temperature: 60 ° C
Test voltage: 3.8V
Test time: 100 hours

(Cell volume measurement method)
A state in which a container containing water (density 1 g / cm ³ ) was placed on a balance was set as a wind body 0, and the cells before and after the test were hung with a wire whose volume was negligible, and the weight was measured by immersing the cell in the container. .
The weight of the cell that had changed after the test was converted to a volume and used as the gas generation volume (Archimedes principle).

About each of the cell which concerns on Examples 1-5, compared with the cell which concerns on Comparative Examples 1-3, there was little generation amount of gas. Moreover, compared with the cell which concerns on Comparative Examples 2-3, DC-IR showed the low value.
About each of the cell which concerns on Examples 6-8, there was little generation amount of gas compared with the cell which concerns on Comparative Examples 1-3.
About each of the cells according to Example 9, since the amount of compound 1 added was small, the amount of gas generated was slightly larger than that of the cells according to Examples 1 to 8, but according to Comparative Examples 1 to 3. Compared with the cell, DC-IR showed a low value.
For each of the cells according to Example 10, since the amount of Compound 1 added was large, the DC-IR was higher compared to the cells according to Examples 1 to 8, but the cells according to Comparative Examples 1 to 5 In comparison, the DC-IR showed a low value.

About each of the cell which concerns on the comparative example 1, since the phosphazene compound was not added, compared with the cell which concerns on Examples 1-8, there was much generation amount of gas.
In each of the cells according to Comparative Example 2, since no ionic compound was added, the DC-IR was higher than that of the cell according to Example 1, and the amount of gas generated was particularly large.
Since each of the cells according to Comparative Example 3 used graphite as the negative electrode active material, the DC-IR was higher than that of the cell according to Example 1, and the amount of gas generated was particularly large.

  The electricity storage device of the present invention can be widely applied to lithium ion capacitors, other capacitors, or secondary batteries.

Claims (11)

In an electricity storage device having a positive electrode, a negative electrode, an electrolytic solution, and an electrolytic solution containing a lithium phosphate coating,
The negative electrode has a negative electrode active material composed of a carbon material forming a core and a coating carbon material covering the surface of the carbon material,
The said electrolyte solution contains the ionic compound comprised from the phosphazene compound and the following cation and the following anion, The electrical storage device characterized by the above-mentioned.
Cation: Organic onium cation or alkali metal cation.
Anion: Carboxylic acid anion, boron anion, anion represented by formula (1) or anion represented by formula (2).

(R ¹ and R ² are each independently an alkyl group, an alkoxy group, a halogenated alkyl group, or a halogen having 1 to 12 carbon atoms.)

(R ³ is an alkyl group, alkoxy group, halogenated alkyl group, or halogen having 1 to 12 carbon atoms.) The organic onium cation is an organic quaternary ammonium ion, organic phosphonium ion, substituted or unsubstituted piperidinium ion, substituted or unsubstituted piperazinium ion, substituted or unsubstituted pyrrolidinium ion, and substituted or unsubstituted. At least one selected from the group consisting of imidazolium ions,
The alkali metal cation is at least one selected from the group consisting of lithium ions, potassium ions, and sodium ions;
The carboxylate anion is at least one selected from the group consisting of R ⁴ COO— (R ⁴ is an alkyl group having 1 to 10 carbon atoms, an aryl group, or an alkylaryl group) and an oxalate ion. ,
The boron anion is at least one selected from the group consisting of borate ions, tetrafluoroborate ions, and bis (oxalato) borate ions,
The anion of the formula (1) is at least one selected from the group consisting of bis (trifluoromethanesulfonyl) amide ion and bis (fluorosulfonyl) amide ion, and the anion of the formula (2) is bis ( The electricity storage device according to claim 1, which is a fluorosulfone) amide ion. The electricity storage device according to claim 1 or 2, wherein the phosphazene compound is a compound represented by the following formula (3).

(R ^{5 to} R ¹⁰ are each independently an alkyl group, alkenyl group, alkoxyl acyl group or aryl group having 1 to 12 carbon atoms (provided that some or all of the hydrogen atoms are substituted with halogen atoms) And may have a group having at least one selected from the group consisting of —O—, —COO—, and OCO— between carbon-carbon bonds), a hydrogen atom, or a halogen atom. is there.)   4. The electricity storage device according to claim 1, wherein a content of the phosphazene compound in the electrolytic solution is 0.1 to 10% by mass.   5. The electricity storage device according to claim 1, wherein the content of the ionic compound is 0.005 to 5 mass%.   The electrical storage device according to any one of claims 1 to 5, wherein the carbon material forming the core is graphite, and the carbon material for coating is pitch or tar. The electricity storage device according to claim 1, wherein the ionic compound is R ⁴ COOLi (R ⁴ is alkyl having 1 to 10 carbon atoms) or lithium oxalate.   The ionic compound is composed of a substituted or unsubstituted pyrrolidinium ion and at least one selected from the group consisting of bis (trifluoromethanesulfonyl) imide ion and bis (fluorosulfonyl) imide ion. The electricity storage device according to any one of the above.   The power storage device according to claim 1, wherein a content of the phosphazene compound in the electrolytic solution is 5 to 1000 times (mass basis) of a content of the ionic compound. The electricity storage device according to claim 1, wherein the lithium phosphate is LiPF ₆ .   It is a lithium ion capacitor, The electrical storage device of any one of Claims 1-19.