JP2015207708A - Binder for lithium ion capacitor electrodes, electrode for lithium ion capacitors, and lithium ion capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a binder for lithium ion capacitor electrodes, which keeps a binding property that a binder is required to have and is superior oxidation resistant.SOLUTION: A binder for lithium ion capacitor electrodes comprises a copolymer having, as monomer units, an ethylenic unsaturated monomer having a cycloalkyl group, and other monomers copolymerizable with the ethylenic unsaturated monomer having a cycloalkyl group.

Description

  The present invention relates to a binder for forming an electrode of a lithium ion capacitor (hereinafter also referred to as “LIC”), an electrode for a lithium ion capacitor using the binder, and a lithium ion capacitor used for producing the electrode. The present invention relates to a slurry for use and a lithium ion capacitor including the electrode.

  In recent years, with the drastic rise in oil prices due to political instability in oil-producing countries and the tightening of carbon dioxide gas emission regulations, the movement to review the lifestyle and industrial structure depending on oil has been rapidly activated on a global scale. Yes. One of the most notable examples is the development of a hybrid vehicle powered by an engine and a motor. The hybrid vehicle assists the driving force by supplying power to the motor from the power source during acceleration, and collects the power generated by the regeneration of the motor during deceleration. Vehicle acceleration and power recovery efficiency improve as the current that can flow through the circuit instantaneously increases. Therefore, it is desirable that the hybrid vehicle power supply not only has a large amount of electric power (energy density) stored per unit volume, but also has a large amount of electric power (input / output density) that can be charged and discharged per unit time. In other words, it is desirable that the capacity and operating voltage are large and the internal resistance is small. Furthermore, it is also an important requirement that the characteristic deterioration due to repeated charge / discharge is small and that the risk of ignition / explosion is small. Currently, secondary batteries such as nickel metal hydride batteries and lithium ion batteries (hereinafter referred to as “LIB”) and electric double layer capacitors (hereinafter referred to as “EDLC”) are practically used as power sources for hybrid vehicles. It has become. However, LIB has problems in power density, durability, and safety, and EDLC has problems in energy density. Therefore, there is a demand for a new power storage element that satisfies these requirements in a high level with a good balance.

  The LIC is a so-called hybrid capacitor in which a charge / discharge mechanism between the positive electrode and the negative electrode is different. At the time of charge / discharge, adsorption / desorption of ions to / from the activated carbon surface occurs in the positive electrode, as in EDLC. On the other hand, in the negative electrode, similar to LIB, oxidation / reduction of the carbon material accompanied by insertion / release of lithium ions occurs. Thus, LIC that uses both EDLC and LIB charging / discharging mechanisms is superior to EDLC in energy density and superior in power density, durability, and safety to LIB. As expected.

  In general, an electrode used in the power storage element as described above is obtained by supporting an active material related to an electrochemical reaction on a metal foil called a current collector in a layer thickness of a micron order. The active material layer includes an organic polymer called a binder in order to bind the powdered active materials to each other and the active material and the current collector. In such an electrode, a slurry obtained by dispersing or dissolving a binder in water or an organic solvent and mixing an active material and, if necessary, a conductive aid such as carbon black, is applied onto a current collector. And then dried. Therefore, the binder is required to give a slurry that can be easily dispersed or dissolved in water or an organic solvent and stably applied. Furthermore, after water and solvent are removed, the binder is resistant to swelling and corrosion caused by the electrolyte, ensuring electrical communication between the active material and the current collector, and reducing the internal resistance of the storage element. It is required to be kept small over a long period of time.

The resistance to the electrolyte required for the binder differs between LIC and EDLC. Generally, lithium hexafluorophosphate (LiPF ₆ ) is used as a supporting salt in the LIC electrolyte. LiPF ₆ is easily decomposed by heat to produce phosphorus pentafluoride (PF ₅ ). The produced PF ₅ further reacts with a small amount of water present in the electrolyte to produce highly corrosive hydrofluoric acid (HF). Therefore, the LIC binder is required to have high resistance to HF. This is a significant difference from EDLC that uses alkylammonium tetrafluoroborate as the supporting electrolyte.

  In addition to these requirements, the positive electrode binder is particularly required to have high resistance to electrochemical oxidation. Therefore, a fluorine-based polymer typified by polyvinylidene fluoride (hereinafter referred to as “PVDF”) is used as a positive electrode binder. However, the fluorine-based polymer has a smaller surface energy than other organic polymers, and there is a problem in the binding property that the binder should originally have. Furthermore, since fluorine-based polymers can only be dissolved in polar organic solvents having a relatively high boiling point, it requires a large amount of energy and a long time to dry the slurry, and additional equipment is required for solvent recovery and explosion protection. There are problems such as what you need. Accordingly, studies have been made on binders using water as a solvent or dispersion medium as described below.

  Patent Document 1 proposes a technique using a latex in which an acrylate copolymer and a fluorine-containing vinyl compound copolymer are alloyed. Patent Document 2 proposes a technique using an acrylic ester latex obtained by copolymerizing a monomer containing a cyano group.

Japanese Patent No. 5163919 Japanese Patent No. 5195157

In Patent Documents 1 and 2, a charge / discharge test is performed at a positive electrode potential of less than 4.0 V. In order to increase the energy density of the LIC, it is necessary to increase the positive electrode potential. However, acrylic ester copolymers are considered to be unsuitable as positive electrode binders at higher potentials because they are less resistant to oxidation than fluoropolymers.
The present invention has been made in view of such a current situation, and an object thereof is a lithium ion capacitor electrode binder and a lithium ion capacitor excellent in oxidation resistance while maintaining the binding property that the binder should have. An electrode and a lithium ion capacitor are provided.

As a result of intensive studies to achieve the above object, the present inventors have found that the above object can be achieved by using a copolymer containing an ethylenically unsaturated monomer having a cycloalkyl group as a binder. The present invention has been reached.
That is, the present invention is as follows.
[1] A copolymer having, as monomer units, an ethylenically unsaturated monomer having a cycloalkyl group and another monomer copolymerizable with the ethylenically unsaturated monomer having a cycloalkyl group. The binder for lithium ion capacitor electrodes containing a polymer.
[2] The copolymer is obtained by combining the ethylenically unsaturated monomer having 25 to 50% by mass of the cycloalkyl group with respect to 100% by mass of the copolymer and the other monomer. The binder for lithium ion capacitor electrodes according to [1], which is a copolymer having a monomer unit.
[3] The other monomer includes a (meth) acrylate monomer composed of an alkyl group having 4 or more carbon atoms and a (meth) acryloyloxy group,
The total content of the ethylenically unsaturated monomer having a cycloalkyl group and the (meth) acrylic acid ester monomer is 50 to 99.9% by mass with respect to 100% by mass of the copolymer. The binder for lithium ion capacitor electrodes as set forth in [1] or [2].
[4] The lithium according to [3], wherein the (meth) acrylic acid ester monomer includes a (meth) acrylic acid ester monomer composed of an alkyl group having 6 or more carbon atoms and a (meth) acryloyloxy group. Binder for ion capacitor electrodes.
[5] The binder for a lithium ion capacitor electrode according to any one of [1] to [4], wherein the other monomer includes an ethylenically unsaturated monomer having an amide group.
[6] The binder for a lithium ion capacitor electrode according to any one of [1] to [5], wherein the other monomer includes an ethylenically unsaturated monomer having a carboxyl group.
[7] The binder for a lithium ion capacitor electrode according to any one of [1] to [6], wherein the other monomer includes an ethylenically unsaturated monomer having a hydroxyl group.
[8] The binder for a lithium ion capacitor electrode according to any one of [1] to [7], wherein the other monomer includes a crosslinkable monomer.
[9] The binder for lithium ion capacitor electrodes according to any one of [1] to [8], wherein the ethylenically unsaturated monomer having a cycloalkyl group is cyclohexyl acrylate or cyclohexyl methacrylate.
[10] The binder for a lithium ion capacitor electrode according to any one of [1] to [9], wherein the copolymer includes a copolymer produced by emulsion polymerization.
[11] A slurry for a lithium ion capacitor containing an active material and the binder for a lithium ion capacitor electrode according to any one of [1] to [10].
[12] An electrode for a lithium ion capacitor comprising an active material layer obtained by applying the slurry for a lithium ion capacitor according to [11] on the surface of a current collector.
[13] A lithium ion capacitor comprising the electrode for a lithium ion capacitor according to [12].

  ADVANTAGE OF THE INVENTION According to this invention, the binder for lithium ion capacitor electrodes, the electrode for lithium ion capacitors, and the lithium ion capacitor which were excellent also in oxidation resistance can be provided, maintaining the binding property which a binder should have.

(A) is sectional drawing of the plane direction which shows typically the one aspect | mode of the lithium ion capacitor which concerns on this invention. (B) is sectional drawing of the thickness direction which shows typically the one aspect | mode of the lithium ion capacitor which concerns on this invention.

  Hereinafter, an embodiment for carrying out the present invention (hereinafter abbreviated as “this embodiment”) will be described in detail with reference to the drawings as necessary. The present invention is not limited to the following embodiment, and can be implemented with various modifications within the scope of the gist. In the present specification, “(meth) acryl” means “acryl” and “methacryl” corresponding thereto, “(meth) acrylate” means “acrylate” and “methacrylate” corresponding thereto, “(Meth) acryloyl” means “acryloyl” and its corresponding “methacryloyl”.

  The binder for lithium ion capacitor electrodes of the present embodiment (hereinafter also simply referred to as “binder”) includes a copolymer having an ethylenically unsaturated monomer (A) having a cycloalkyl group as a monomer unit. It is a waste. Further, the electrode for a lithium ion capacitor (hereinafter also simply referred to as “electrode”) of the present embodiment includes a current collector, an active material, and the binder. Furthermore, the slurry for lithium ion capacitors of the present embodiment (hereinafter also simply referred to as “slurry”) contains an active material and the binder. Here, the “ethylenically unsaturated monomer” means a monomer having one or more ethylenically unsaturated bonds in the molecule.

(binder)
The binder of this embodiment contains the copolymer which has the ethylenically unsaturated monomer (A) which has a cycloalkyl group as a monomer unit. The ethylenically unsaturated monomer (A) having a cycloalkyl group is not particularly limited, and examples thereof include those having a cycloalkyl group and one ethylenically unsaturated bond. More specifically, the monomer (A) is a (meth) acrylic acid ester having a cycloalkyl group, such as cyclohexyl acrylate, cyclohexyl methacrylate, isobornyl acrylate, isobornyl methacrylate, adamantyl acrylate, adamantyl methacrylate and the like. From the viewpoint of more effectively and reliably solving the problems according to the present invention, these are preferable. The monomer (A) is more preferably a (meth) acrylic acid ester monomer composed of a cycloalkyl group and a (meth) acryloyloxy group. 4-8 are preferable, as for the number of the carbon atoms which comprise the alicyclic ring of a cycloalkyl group, 6 and 7 are more preferable, and 6 is especially preferable. Further, the cycloalkyl group may or may not have a substituent. Examples of the substituent include a methyl group and a tertiary butyl group. Among the monomers (A), cyclohexyl acrylate and cyclohexyl methacrylate are preferable in terms of good copolymerizability with other monomers. These are used singly or in combination of two or more.

  In order to improve various qualities and physical properties, the copolymer has other monomer (B) copolymerizable with the monomer (A) as a monomer unit. The other monomer (B) is a monomer different from the monomer (A).

  Examples of the other monomer (B) include an ethylenically unsaturated monomer (b1) having an amide group, an ethylenically unsaturated monomer (b2) having a carboxyl group, and an ethylenically unsaturated monomer having a hydroxyl group. Saturated monomer (b3), crosslinkable monomer (b4), (meth) acrylic acid ester monomer (b5), ethylenically unsaturated monomer having cyano group, ethylenically unsaturated monomer having aromatic group Examples thereof include saturated monomers and other ethylenically unsaturated monomers. Another monomer (B) is used individually by 1 type or in combination of 2 or more types. Further, the other monomer (B) may belong to two or more of the above monomers at the same time. That is, the other monomer (B) is an ethylenically unsaturated monomer having two or more groups selected from the group consisting of a carboxyl group, an amide group, a hydroxyl group, a cyano group, and an aromatic group. Alternatively, it may be a crosslinkable monomer having two or more groups selected from the group consisting of a carboxyl group, an amide group, a hydroxyl group, a cyano group and an aromatic group together with an ethylenically unsaturated bond.

  Especially, from a viewpoint of the intensity | strength improvement of an electrode, it is preferable that another monomer (B) contains the ethylenically unsaturated monomer (b1) which has an amide group. Although it does not specifically limit as ethylenically unsaturated monomer (b1) which has an amide group, For example, acrylamide, methacrylamide, N, N-methylenebisacrylamide, diacetone acrylamide, diacetone methacrylamide, maleic acid amide, Maleimide is mentioned. These are used singly or in combination of two or more. Of these, acrylamide and methacrylamide are preferable. By using acrylamide and / or methacrylamide, the strength of the electrode tends to be further improved.

  From the viewpoint of improving the strength of the electrode, the other monomer (B) preferably contains an ethylenically unsaturated monomer (b2) having a carboxyl group. Examples of the ethylenically unsaturated monomer (b2) having a carboxyl group include monocarboxylic acid monomers such as acrylic acid, methacrylic acid, itaconic acid half ester, maleic acid half ester, and fumaric acid half ester. And dicarboxylic acid monomers such as itaconic acid, fumaric acid and maleic acid. These are used singly or in combination of two or more. Among these, from the same viewpoint, acrylic acid, methacrylic acid and itaconic acid are preferable, and acrylic acid and methacrylic acid are more preferable. Furthermore, methacrylic acid is still more preferable from the viewpoint of dispersion stability of the slurry.

  Further, from the viewpoint of improving the dispersion stability of the slurry and the polymerization stability of the copolymer, the other monomer (B) preferably contains an ethylenically unsaturated monomer (b3) having a hydroxyl group. Examples of the ethylenically unsaturated monomer (b3) having a hydroxyl group include hydroxyl groups such as hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, polyethylene glycol acrylate and polyethylene glycol methacrylate (meta ) Acrylates. These are used singly or in combination of two or more. Of these, hydroxyethyl acrylate and hydroxyethyl methacrylate are preferred. The use of hydroxyethyl acrylate and / or hydroxyethyl methacrylate tends to improve the dispersion stability of the slurry and the polymerization stability of the copolymer.

  Further, from the viewpoint of making the insoluble content in the electrolytic solution to an appropriate amount, the other monomer (B) preferably contains a crosslinkable monomer (b4). The crosslinkable monomer (b4) is not particularly limited. For example, a monomer having two or more radical polymerizable double bonds, a functional group that gives a self-crosslinking structure during or after polymerization. The monomer which has. These are used singly or in combination of two or more.

  Examples of the monomer having two or more radical polymerizable double bonds include divinylbenzene and polyfunctional (meth) acrylate. Of these, polyfunctional (meth) acrylate is preferable from the viewpoint of maintaining the strength of the electrode.

  The polyfunctional (meth) acrylate may be a bifunctional (meth) acrylate, a trifunctional (meth) acrylate, or a tetrafunctional (meth) acrylate. For example, polyoxyethylene diacrylate, polyoxyethylene dimethacrylate, poly Oxypropylene diacrylate, polyoxypropylene dimethacrylate, neopentyl glycol diacrylate, neopentyl glycol dimethacrylate, butanediol diacrylate, butanediol dimethacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, pentaerythritol tetraacrylate, And pentaerythritol tetramethacrylate. These are used singly or in combination of two or more. Of these, trimethylolpropane triacrylate and trimethylolpropane trimethacrylate are preferable from the same viewpoint as described above.

  Examples of the monomer having a functional group that gives a self-crosslinking structure during or after polymerization include, for example, an ethylenically unsaturated monomer having an epoxy group, an ethylenic monomer having a methylol group, and an ethylene having an alkoxymethyl group And an ethylenically unsaturated monomer having a hydrolyzable silyl group. These are used singly or in combination of two or more.

  Examples of the ethylenically unsaturated monomer having an epoxy group include glycidyl acrylate, glycidyl methacrylate, allyl glycidyl ether, methyl glycidyl acrylate, and methyl glycidyl methacrylate. These are used singly or in combination of two or more. Of these, glycidyl methacrylate is preferred.

  Examples of the ethylenically unsaturated monomer having a methylol group include N-methylol acrylamide, N-methylol methacrylamide, dimethylol acrylamide, and dimethylol methacrylamide. These are used singly or in combination of two or more.

  Examples of the ethylenically unsaturated monomer having an alkoxymethyl group include N-methoxymethyl acrylamide, N-methoxymethyl methacrylamide, N-butoxymethyl acrylamide, and N-butoxymethyl methacrylamide. These are used singly or in combination of two or more.

  Examples of the ethylenically unsaturated monomer having a hydrolyzable silyl group include vinyl silane, γ-acryloxypropyltrimethoxysilane, γ-acryloxypropyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, and γ. -Methacryloxypropyltriethoxysilane. These are used singly or in combination of two or more.

  Among the crosslinkable monomers (b4), polyfunctional (meth) acrylate is particularly preferable from the viewpoint of maintaining the strength of the electrode.

  Moreover, it is preferable that another monomer (B) contains the (meth) acrylic acid ester monomer (b5) from a viewpoint of making the oxidation resistance of the binder containing this copolymer favorable. The (meth) acrylic acid ester monomer (b5) is a monomer different from the monomers (b1) to (b4). Examples of the (meth) acrylic acid ester monomer (b5) include (meth) acrylic acid ester having one ethylenically unsaturated bond, and more specifically, methyl acrylate, ethyl acrylate, propyl acrylate. , Isopropyl acrylate, butyl acrylate, isobutyl acrylate, t-butyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl acrylate, butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate , N-hexyl methacrylate, 2-ethylhexyl methacrylate, (meth) aldehyde having an alkyl group such as lauryl methacrylate Relate (more preferably (meth) acrylate comprising an alkyl group and a (meth) acryloyloxy group), (meth) acrylate (more preferably aromatic ring) having an aromatic ring such as benzyl acrylate, phenyl acrylate, benzyl methacrylate, phenyl methacrylate And (meth) acrylates comprising (meth) acryloyloxy groups. Among these, from the viewpoint of suppressing the swelling of the copolymer with respect to the electrolytic solution, a (meth) acrylic acid ester monomer composed of an alkyl group having 4 or more carbon atoms and a (meth) acryloyloxy group is preferable, A (meth) acrylic acid ester monomer composed of 6 or more alkyl groups and a (meth) acryloyloxy group is more preferred. More specifically, methyl methacrylate, butyl acrylate, butyl methacrylate and 2-ethylhexyl acrylate are preferable, butyl acrylate, butyl methacrylate and 2-ethylhexyl acrylate are more preferable, and 2-ethylhexyl acrylate is still more preferable. Furthermore, in these, the (meth) acrylic acid ester monomer which consists of a C10 or less alkyl group and a (meth) acryloyloxy group is preferable from a viewpoint of the oxidation resistance improvement of a binder. These (meth) acrylic acid ester monomers (b5) are used singly or in combination of two or more.

  Examples of the ethylenically unsaturated monomer having a cyano group include acrylonitrile and methacrylonitrile. Examples of the ethylenically unsaturated monomer having an aromatic group include styrene, vinyl toluene, and α-methyl styrene. Of these, styrene is preferable.

  The content of the ethylenically unsaturated monomer (A) having a cycloalkyl group in the copolymer is preferably 25 to 50% by mass with respect to 100% by mass of the copolymer. The lower limit is more preferably 30% by mass, and still more preferably 35% by mass. It is preferable that the content ratio of the ethylenically unsaturated monomer (A) having a cycloalkyl group is within the above range because the oxidation resistance of the binder is improved. The content of the ethylenically unsaturated monomer (A) having a cycloalkyl group is preferably 50% by mass or less because the strength of the electrode can be maintained. In other words, the content of the other monomer (B) in the copolymer is preferably 75 to 50% by mass with respect to 100% by mass of the copolymer. The upper limit value is more preferably 70% by mass, still more preferably 65% by mass.

  The total content of the monomer (A) and the (meth) acrylic acid ester monomer (b5) in the copolymer is preferably 50 to 99.9% by mass with respect to 100% by mass of the copolymer. More preferably, it is 60-99.9 mass%, More preferably, it is 70-99.9 mass%, Still more preferably, it is 80-99.9 mass%. When the total content of these monomers (A) and (b5) is within the above range, the oxidation resistance of the copolymer becomes better. In this case, the monomer (A) is more preferably a (meth) acrylic acid ester monomer having a cycloalkyl group. The (meth) acrylic acid ester monomer (b5) is preferably a (meth) acrylic acid ester monomer composed of an alkyl group having 4 or more carbon atoms and a (meth) acryloyloxy group, and has 6 or more carbon atoms. A (meth) acrylic acid ester monomer comprising an alkyl group and a (meth) acryloyloxy group is more preferred. Furthermore, a (meth) acrylic acid ester monomer composed of an alkyl group having 10 or less carbon atoms and a (meth) acryloyloxy group is more preferable.

  When the other monomer (B) contains an ethylenically unsaturated monomer (b1) having an amide group, the content of the ethylenically unsaturated monomer (b1) having an amide group in the copolymer is: Preferably it is 0.1-10 mass% with respect to 100 mass% of copolymers, More preferably, it is 2-10 mass%. If the content of the ethylenically unsaturated monomer (b1) having an amide group is 0.1% by mass or more, the strength of the electrode tends to be further improved, and if it is 10% by mass or less, the copolymer There is a tendency that the polymerization stability at the time of preparing is improved.

  When the other monomer (B) contains an ethylenically unsaturated monomer (b2) having a carboxyl group, the content ratio of the ethylenically unsaturated monomer (b2) having a carboxyl group in the copolymer is: Preferably it is 0.1-5 mass% with respect to 100 mass% of copolymers, More preferably, it is 1.5-5 mass%. When the content ratio of the ethylenically unsaturated monomer having a carboxyl group is 0.1% by mass or more, the strength of the electrode tends to be improved, and when it is 5% by mass or less, the polymerization stability is good. There is a tendency.

  When the other monomer (B) contains an ethylenically unsaturated monomer (b3) having a hydroxyl group, the content ratio of the ethylenically unsaturated monomer (b3) having a hydroxyl group in the copolymer is: Preferably it is 0.1-10 mass% with respect to 100 mass% of copolymers, More preferably, it is 1-10 mass%. When the content ratio of the ethylenically unsaturated monomer (b3) having a hydroxyl group is within the above range, the dispersion stability of the slurry and the polymerization stability of the copolymer tend to be further improved.

  When the other monomer (B) contains the crosslinkable monomer (b4), the content of the crosslinkable monomer (b4) in the copolymer is preferably 100% by mass of the copolymer. It is 0.01-10 mass%, More preferably, it is 0.1-7.5 mass%, More preferably, it is 0.1-5 mass%. When the content of the crosslinkable monomer (b4) is 0.01% by mass or more, the electrolytic solution resistance is further improved, and when it is 5% by mass or less, the strength of the electrode can be maintained.

  The glass transition temperature (hereinafter also referred to as “Tg”) of the copolymer is not particularly limited, but may be −50 ° C. or higher, preferably 50 ° C. or lower, more preferably −30 ° C. to 20 ° C. It exists in the tendency for the intensity | strength of an electrode to improve that Tg of a copolymer is -30 degreeC-20 degreeC.

  Here, the glass transition temperature is determined from a DSC curve obtained by differential scanning calorimetry (DSC). Specifically, it is determined by the intersection of a straight line obtained by extending the base line on the low temperature side in the DSC curve to the high temperature side and the tangent at the inflection point of the stepped change portion of the glass transition.

  “Glass transition” refers to a change in calorific value associated with a change in the state of the polymer that is a test piece in DSC on the endothermic side. Such a change in heat quantity is observed as a step-like change shape in the DSC curve. The “step change” refers to a portion of the DSC curve until the curve moves away from the previous low-temperature base line to a new high-temperature base line. Note that a combination of a step change and a peak is also included in the step change.

  Further, the “inflection point” indicates a point at which the gradient of the DSC curve of the step-like change portion is maximized. Further, in the step-like change portion, when the upper side is the heat generation side, it can also be expressed as a point where the upward convex curve changes to the downward convex curve. “Peak” indicates a portion of the DSC curve from when the curve leaves the low-temperature side baseline until it returns to the same baseline again. “Baseline” refers to a DSC curve in a temperature region where no transition or reaction occurs in the test piece.

  The copolymer is obtained, for example, by a usual emulsion polymerization method. There is no restriction | limiting in particular regarding the method of emulsion polymerization, A conventionally well-known method can be used. For example, in a dispersion system containing the above-mentioned monomer, surfactant, radical polymerization initiator, and other additive components used as necessary in an aqueous medium as a basic composition component, each of the above monomers. A copolymer is obtained by polymerizing the monomer composition. In the polymerization, the composition of the monomer composition to be supplied is made constant throughout the entire polymerization process, or the morphological composition change of the particles of the resin dispersion to be produced is changed sequentially or continuously in the polymerization process. Various methods can be used as necessary, such as a method of giving When the copolymer is obtained by emulsion polymerization, for example, it may be in the form of an aqueous dispersion (latex) containing water and a particulate copolymer dispersed in the water.

  The surfactant is a compound having at least one or more hydrophilic groups and one or more lipophilic groups in one molecule. Examples of the surfactant include non-reactive alkyl sulfate, polyoxyethylene alkyl ether sulfate, alkyl benzene sulfonate, alkyl naphthalene sulfonate, alkyl sulfosuccinate, alkyl diphenyl ether disulfonate, naphthalene sulfone. Anionic interfaces such as acid formalin condensate, polyoxyethylene polycyclic phenyl ether sulfate, polyoxyethylene distyrenated phenyl ether sulfate, fatty acid salt, alkyl phosphate, polyoxyethylene alkylphenyl ether sulfate Activators and non-reactive polyoxyethylene alkyl ethers, polyoxyalkylene alkyl ethers, polyoxyethylene polycyclic phenyl ethers, polyoxyethylene disty Phenyl ether, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene sorbitol fatty acid ester, glycerin fatty acid ester, polyoxyethylene fatty acid ester, polyoxyethylene alkylamine, alkylalkanolamide, polyoxyethylene alkylphenyl ether, etc. Nonionic surfactants. In addition to these, a so-called reactive surfactant in which an ethylenic double bond is introduced into the chemical structural formula of a surfactant having a hydrophilic group and a lipophilic group may be used.

  Examples of the anionic surfactant in the reactive surfactant include an ethylenically unsaturated monomer having a sulfonic acid group, a sulfonate group or a sulfate ester group and a salt thereof, and a sulfonic acid group, or A compound having a group (ammonium sulfonate group or alkali metal sulfonate group) which is an ammonium salt or an alkali metal salt thereof is preferable. Specifically, for example, alkylallylsulfosuccinate (for example, Eleminol (trademark) JS-20 manufactured by Sanyo Chemical Co., Ltd., Latemuru (trademark; manufactured by Kao Corporation), S-120, S-180A, S- 180), polyoxyethylene alkylpropenyl phenyl ether sulfate ester salt (for example, Aqualon (trademark; the same shall apply hereinafter) HS-10 manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), α- [1- [ (Allyloxy) methyl] -2- (nonylphenoxy) ethyl] -ω-polyoxyethylene sulfate ester salt (for example, ADEKA Corporation soap (trademark; the same shall apply hereinafter) SE-10N manufactured by ADEKA Corporation), ammonium. = Α-sulfonato-ω-1- (allyloxymethyl) alkyloxypolyoxyethylene (eg, Aquaron KH-10 manufactured by Ichi Kogyo Seiyaku Co., Ltd.), styrene sulfonate (for example, Spinomer (trademark) NaSS manufactured by Tosoh Organic Chemical Co., Ltd.), α- [2-[(allyloxy)- 1- (alkyloxymethyl) ethyl] -ω-polyoxyethylene sulfate ester salt (for example, Adeka Soap SR-10 manufactured by ADEKA Corporation), polyoxyethylene polyoxybutylene (3-methyl-3- Butenyl) ether sulfate (for example, LATEMUL PD-104 manufactured by Kao Corporation) may be mentioned.

  Examples of the nonionic surfactant in the reactive surfactant include α- [1-[(allyloxy) methyl] -2- (nonylphenoxy) ethyl] -ω-hydroxypolyoxyethylene (for example, Adeka Soap NE-20, NE-30, NE-40 manufactured by ADEKA Co., Ltd.), polyoxyethylene alkylpropenyl phenyl ether (for example, Aqualon RN-10, RN-20, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) RN-30 and RN-50), α- [2-[(allyloxy) -1- (alkyloxymethyl) ethyl] -ω-hydroxypolyoxyethylene (for example, Adeka Soap ER manufactured by ADEKA Corporation) -10)), polyoxyethylene polyoxybutylene (3-methyl-3-butenyl) A Le (for example, Kao Corp. LATEMUL PD-420.) And the like.

  Among the above-mentioned various surfactants, reactive surfactants are preferable, anionic reactive surfactants are more preferable, and reactive surfactants having a sulfonic acid group are more preferable. The surfactant is preferably used in an amount of 0.1 to 5 parts by mass with respect to 100 parts by mass of the monomer composition. Surfactant is used individually by 1 type or in combination of 2 or more types.

  The radical polymerization initiator is one that initiates addition polymerization of monomers by radical decomposition with heat or a reducing substance, and any of inorganic initiators and organic initiators can be used. As the radical polymerization initiator, a water-soluble or oil-soluble polymerization initiator can be used. Examples of the water-soluble polymerization initiator include peroxodisulfates, peroxides, water-soluble azobis compounds, and peroxide-reducing agent redox systems. Examples of the peroxodisulfate include potassium peroxodisulfate (KPS), sodium peroxodisulfate (NPS), and ammonium peroxodisulfate (APS). Examples of the peroxide include hydrogen peroxide, t- Examples thereof include butyl hydroperoxide, t-butyl peroxymaleic acid, succinic acid peroxide, and benzoyl peroxide. Examples of water-soluble azobis compounds include 2,2-azobis (N-hydroxyethylisobutyramide), 2 And 2-azobis (2-amidinopropane) dichloride and 4,4-azobis (4-cyanopentanoic acid). Examples of the redox system of the peroxide-reducing agent include sodium peroxide and sodium peroxide. Sulfooxylate formaldehyde, sodium bisulfite, sodium thiosulfate Um, sodium hydroxymethanesulfinic acid, L- ascorbic acid, and its salts, cuprous salts, and include those that combine one or more reducing agents such as ferrous salts.

  The radical polymerization initiator is preferably used in an amount of 0.05 to 2 parts by mass with respect to 100 parts by mass of the monomer composition. A radical polymerization initiator is used individually by 1 type or in combination of 2 or more types.

  A monomer composition containing an ethylenically unsaturated monomer (A) having a cycloalkyl group and another monomer (B) is emulsion-polymerized, and the polymer particles are dispersed in a solvent (water). In the case of forming the obtained dispersion, the solid content of the obtained dispersion is preferably 20% by mass to 70% by mass.

  The dispersion is preferably adjusted to have a pH in the range of 5 to 12 in order to maintain long-term dispersion stability. For pH adjustment, amines such as ammonia, sodium hydroxide, potassium hydroxide, and dimethylaminoethanol are preferably used, and pH is more preferably adjusted with ammonia (water) or sodium hydroxide.

  The aqueous dispersion of the present embodiment preferably contains a copolymer obtained by copolymerizing the monomer composition containing the specific monomer as particles dispersed in water (copolymer particles). . In addition to water and the copolymer, the aqueous dispersion may contain a solvent such as methanol, ethanol, isopropyl alcohol, a dispersant, a lubricant, a thickener, a bactericide, and the like.

  The average particle diameter of the copolymer particles is preferably 30 to 500 nm, more preferably 30 to 300 nm, still more preferably 30 to 200 nm, and particularly preferably 30 to 100 nm. Setting the average particle size of the copolymer particles to 30 nm or more is preferable from the viewpoint of reliably achieving the preparation of the aqueous dispersion. Moreover, it is preferable from the viewpoint of ensuring the dispersion stability of the aqueous dispersion that the average particle diameter of the copolymer particles is 300 nm or less. The average particle diameter of the copolymer particles can be measured according to the method described in the following examples.

  In addition, it can be confirmed by pyrolysis gas chromatography that the copolymer has an ethylenically unsaturated monomer having a cycloalkyl group as a monomer unit. More specifically, a homopolymer of an ethylenically unsaturated monomer having a cycloalkyl group is measured by pyrolysis gas chromatography, and the retention time of the pyrolyzate is determined in advance. Next, when the copolymer is measured under the same conditions by pyrolysis gas chromatography and has a peak of pyrolyzate at the same retention time, the ethylenic group having a cycloalkyl group as the monomer unit of the copolymer It can be estimated that it has an unsaturated monomer. Moreover, the ratio of the ethylenically unsaturated monomer which has a cycloalkyl group in the monomer unit which a copolymer has by making the homopolymer of the ethylenically unsaturated monomer which has a cycloalkyl group into an internal standard Is also possible.

(slurry)
The slurry of this embodiment contains an active material and the binder. The slurry is a dispersion used to form an active material layer on the current collector after being applied onto the current collector and then dried. This slurry preferably contains at least the binder and the active material, and further contains water. Moreover, you may contain at least any one of a conductive support agent, a thickener, and a non-aqueous solvent other than these as needed.

[Active material]
In the slurry for forming the positive electrode of LIC, examples of the active material include porous carbon. These are used singly or in combination of two or more. In these, activated carbon can be used suitably from a viewpoint of exhibiting the function as an active material more effectively. The carbon material used as a raw material for activated carbon is not particularly limited as long as it is a carbon source that is usually used as a raw material for activated carbon. For example, plant raw materials such as wood, wood flour and coconut shells; petroleum pitch and coke And various synthetic resins such as phenol resin, furan resin, vinyl chloride resin, vinyl acetate resin, melamine resin, urea resin and resorcinol resin.

  Examples of the method for carbonizing these raw materials or the heating method during the activation treatment include known methods such as a fixed bed method, a moving bed method, a fluidized bed method, a slurry method, and a rotary kiln method. As the atmosphere during heating, an inert gas such as nitrogen, carbon dioxide, helium, or argon, or a gas mixed with another gas containing these inert gases as a main component is used. The conditions for carbonization are generally conditions of firing for about 0.5 to 10 hours in a temperature range of 400 to 800 ° C.

  Examples of the activation method of the carbonized product include a gas activation method in which baking is performed using an activation gas such as water vapor, carbon dioxide, and oxygen, and an alkali activation method in which heat treatment is performed after mixing with an alkali compound. Among these, the alkali activation method is preferable from the viewpoint of producing activated carbon having a high specific surface area.

The average particle diameter of the activated carbon is preferably 1 to 20 μm, more preferably 2 to 15 μm, from the viewpoint of further improving the dispersion stability in the slurry and the viewpoint of further increasing the peel strength of the electrode. This average particle diameter is measured according to the method described in the Examples. Further, from the viewpoint of further increasing the capacity, it is desirable to further develop the micropores (pores having a pore diameter of less than 2 nm) of activated carbon to further increase the specific surface area. Furthermore, from the viewpoint of reducing the resistance, it is desirable to develop the mesopores (pores having a pore diameter of 2 nm or more and less than 50 nm) to accelerate the movement of ions in the pores. On the other hand, from the viewpoint of further increasing the electrode density, it is desirable to moderately suppress the development of pores. From the viewpoint of satisfying these conflicting requirements well-balanced, the specific surface area of the activated carbon is preferable to be 1000~3000m ² · g ^-1, more preferably a 1500~2500m ² · g ^-1. Moreover, the mesopore volume of the activated carbon preferable to be 0.05~0.40cc · g ^-1, more preferably a 0.10~0.30cc · g ^-1. Further, micropore volume of activated carbon preferable to be 0.20~1.00cc · g ^-1, more preferably a 0.40~0.80cc · g ^-1. Furthermore, the ratio of the mesopore volume to the micropore volume of activated carbon (mesopore volume / micropore volume) is preferably 0.1 to 0.5, and more preferably 0.2 to 0.4. Moreover, the average pore diameter of activated carbon is preferably 1.0 to 3.0 nm, and more preferably 1.5 to 2.5 nm. Specific surface area, mesopore volume, micropore volume and average pore diameter are measured by the methods described in the Examples.

  The content ratio of the active material, particularly activated carbon, is preferably 5 to 35% by mass and more preferably based on the total amount of the slurry from the viewpoint of enhancing dispersibility in the slurry and from the viewpoint of more effectively exerting the function. Is 7 to 30% by mass, more preferably 10 to 25% by mass.

〔water〕
The slurry of this embodiment can further contain water. Compared with high-boiling organic solvents commonly used in slurries (for example, N-methylpyrrolidone (hereinafter referred to as “NMP”)), water has a higher evaporation rate and is produced by shortening the drying time. There is also an effect of improving the property and suppressing the migration of particles. Also, water is preferable to organic solvents from the viewpoint of reducing environmental burden, ensuring worker safety, and reducing management costs. The content ratio of water is preferably 90% by mass or less, more preferably 60 to 90% by mass, and further preferably 70 to 85% by mass with respect to the total amount of the slurry.

[Conductive aid]
As the conductive auxiliary agent, for example, a highly conductive carbon material can be used. Examples of the highly conductive carbon material include natural graphite, artificial graphite, furnace black, acetylene black, vapor grown carbon fiber, carbon nanofiber, and carbon nanotube. Among these, furnace black and acetylene black are preferable. A conductive support agent is used individually by 1 type or in combination of 2 or more types. The content ratio of the conductive assistant is preferably 8% by mass or less, more preferably 1 to 6% by mass, and further preferably 1 to 3% by mass with respect to the total amount of the slurry.

[Thickener]
The slurry of this embodiment can contain a thickener for the purpose of improving the dispersibility of the active material and the coating properties of the slurry. Examples of the thickener include cellulose compounds such as carboxymethylcellulose, methylcellulose and hydroxypropylcellulose; ammonium salts or alkali metal salts of the cellulose compounds; polycarboxylic acids such as polymethacrylic acid and modified polymethacrylic acid; Alkali metal salts; Vinyl alcohol (co) polymers such as polyvinyl alcohol, modified polyvinyl alcohol and ethylene-vinyl alcohol copolymers; Copolymerization of unsaturated carboxylic acids such as methacrylic acid, maleic acid and fumaric acid with vinyl esters Water-soluble polymers such as a saponified product of coalesced are listed. A thickener is used individually by 1 type or in combination of 2 or more types. Among these, particularly preferable thickeners include, for example, alkali metal salts of carboxymethyl cellulose and alkali metal salts of polymethacrylic acid. As a commercial item of the alkali metal salt of carboxymethylcellulose, Tokyo Chemical Industry Co., Ltd. C0603 is mentioned, for example. The content of the thickener is preferably 5.0% by mass or less, more preferably 0.1 to 3.0% by mass, and further 0.1 to 1.5% by mass with respect to the total amount of the slurry. % Is preferred.

[Non-aqueous solvent]
The slurry of this embodiment can contain a non-aqueous solvent for the purpose of improving the wettability of the active material with water and the coating properties of the slurry. Examples of the non-aqueous solvent include amide compounds such as NMP, N, N-dimethylformamide and N, N-dimethylacetamide; higher alcohols such as 2-ethyl-1-hexanol, 1-nonanol and lauryl alcohol.

[Preferred embodiment of slurry]
The slurry preferably contains the binder of this embodiment in a proportion of 0.1 to 3.0% by mass in terms of solid content with respect to the total amount of the slurry, and is 0.3 to 2.5% by mass. It is more preferable to contain in the ratio. Thereby, it is possible to more effectively suppress the falling off of the active material layer.

  The slurry is prepared by mixing the binder of this embodiment with the active material as described above, water, and other materials added as necessary. As a means for mixing them, for example, a known mixing apparatus such as a homodisper, a ball mill, a roll mill, and a homogenizer can be used. Mixing is preferably performed under reduced pressure. Thereby, the formation of bubbles in the obtained active material layer can be more effectively suppressed.

(electrode)
The electrode in the present embodiment includes a current collector and an active material layer formed through a step of applying the slurry onto the surface of the current collector and drying it. After drying of the applied slurry, preferably press working may be performed.

[Current collector]
The material of the current collector is not particularly limited as long as it is an electroconductive material that is unlikely to deteriorate due to elution or reaction in the electrolyte solution in the LIC including the current collector. Suitable materials include, for example, aluminum, titanium and stainless steel when the current collector is provided on the positive electrode of the LIC. The current collector may be a metal foil or a structure (such as a foam) in which an electrode can be formed in a metal gap. The metal foil may be a normal metal foil having no through hole, or a metal foil having a through hole such as an expanded metal or a punching metal. The thickness of the current collector is not particularly limited as long as the shape and strength of the electrode can be sufficiently maintained, but for example, 1 to 100 μm is preferable from the viewpoint of reduction in resistance, strength, and improvement in capacity per unit volume. Moreover, it is preferable to provide the layer (anchor layer) which consists of a carbon material on the surface of metal foil from a viewpoint of resistance reduction and a binding improvement with an active material layer. The thickness of the anchor layer is preferably 10 μm or less.

[Formation of active material layer]
An active material layer is formed through the process of apply | coating the above-mentioned slurry on the surface of the said electrical power collector, and drying. Examples of the method for applying the slurry on the surface of the current collector include a doctor blade method, a reverse roll method, a gravure method, and an air knife method.

  The slurry is preferably dried in a temperature range of 20 to 250 ° C., more preferably 50 to 150 ° C., preferably 1 to 130 minutes, more preferably 5 to 60 minutes.

  The dried coating film is preferably subjected to press working. Examples of the means for performing press working include a roll press machine, a calendar press machine, and a hot press machine. The press working conditions are appropriately set in consideration of the type of apparatus to be used and the desired thickness and density of the active material layer.

The thickness and density of the active material layer vary depending on the application. The active material layer provided in the positive electrode of the LIC preferably has a thickness per side of 20 to 100 μm and a density of 0.3 to 0.7 g · cm ⁻³ . The active material layer may be formed only on one side of the current collector, or may be formed on both sides.

  In addition, the content ratio of the binder, active material, conductive additive and thickener in the active material layer may be the same as the preferable content ratio of each material in the slurry based on the total amount excluding volatile components such as water. That's fine. Specifically, based on the total amount of the active material layer (the same applies hereinafter in this paragraph), the binder content is preferably 15% by mass or less, and more preferably 2 to 12% by mass. Further, the content ratio of the active material is preferably 95% by mass or less, more preferably 75 to 90% by mass, and further preferably 80 to 88% by mass. The content ratio of the conductive assistant is preferably 15% by mass or less, more preferably 3 to 12% by mass, and further preferably 5 to 10% by mass. The content of the thickener is preferably 10% by mass or less, more preferably 1 to 8% by mass, and further preferably 2 to 6% by mass.

(Lithium ion capacitor)
An example of the LIC of this embodiment is shown in FIG. FIG. 1 is a cross-sectional view schematically showing the LIC. (A) is sectional drawing seen from the lamination direction of each layer with which the electrode body of LIC is equipped, (b) is sectional drawing seen from the direction orthogonal to the lamination direction of each layer. In this LIC, the positive electrode terminal 1 and the negative electrode terminal 2 are led out from one side of the electrode body 4. As another mode (not shown), a mode in which the positive electrode terminal 1 and the negative electrode terminal 2 are led out from two opposing sides of the electrode body 4 can be cited. The latter embodiment is suitable for applications in which a larger current flows because the electrode terminals can be widely used.

  The LIC includes a positive electrode in which a positive electrode active material layer 6 is formed on the surface of a positive electrode current collector 5, and a negative electrode in which a negative electrode active material layer 9 is formed on the surface of a negative electrode current collector 8. The electrode body 4 is formed by alternately laminating so as to face the negative electrode active material layer 9 across the separator 7, the positive electrode terminal 1 is connected to the positive electrode current collector 5, and the negative electrode terminal 2 is connected to the negative electrode current collector. Connected to the body 8, the electrode body 4 is accommodated in the exterior body 3, an electrolyte (not shown) is injected into the exterior body 3, and the ends of the positive electrode terminal 1 and the negative electrode terminal 2 are connected to the exterior body. 3 is formed by sealing the peripheral edge of the exterior body 3 in a state of being pulled out to the outside.

  Here, the positive electrode is the electrode of the present embodiment described above. The electrode body is formed by laminating the positive electrode, the separator 7 and the negative electrode. The LIC of this embodiment is obtained by housing the electrode body together with a non-aqueous electrolyte containing a lithium salt in an exterior body.

[Licium anode]
As the negative electrode active material of LIC, a material capable of reversibly occluding and releasing lithium ions is preferably used. Examples of such a negative electrode active material include carbon materials such as graphite, coke, carbon fiber, activated carbon, and composite porous carbon material, and a mixture of two or more of these carbon materials.

  The material of the negative electrode current collector is not particularly limited as long as it is a material that does not easily deteriorate due to elution or reaction in the electrolyte solution in the LIC including the negative electrode current collector. For example, a metal such as copper, iron, and stainless steel Is mentioned. In the negative electrode of LIC, it is preferable to use copper as a negative electrode current collector from the viewpoint of electrochemical stability and conductivity. As the negative electrode current collector, one having a structure in which an electrode can be formed in a metal foil or a metal gap can be used. The metal foil may be a normal metal foil having no through hole, or a metal foil having a through hole such as an expanded metal or a punching metal. Further, the thickness of the negative electrode current collector is not particularly limited as long as the shape and strength of the negative electrode can be sufficiently maintained, but for example, 1 to 100 μm is preferable.

  A negative electrode active material layer can contain a conductive support agent and a binder other than a negative electrode active material as needed. The kind in particular of conductive support agent is not restrict | limited, Acetylene black, ketjen black, and a vapor growth carbon fiber are illustrated. As for the content rate of a conductive support agent, 0-30 mass% is preferable with respect to the whole quantity of a negative electrode active material, for example. The binder is not particularly limited, and examples thereof include PVDF, polytetrafluoroethylene, and styrene-butadiene copolymer. The content ratio of the binder is preferably 3 to 20% by mass with respect to the total amount of the negative electrode active material, for example. Each material in a negative electrode active material layer is used individually by 1 type or in combination of 2 or more types, respectively.

  The negative electrode may have a negative electrode active material layer formed on only one side of the current collector, or may be formed on both sides. The thickness of the negative electrode active material layer is preferably in the range of 20 to 100 μm per side, for example.

  The negative electrode can be manufactured by a method similar to a known electrode forming method in LIB. For example, a slurry in which a negative electrode active material, a conductive additive and a binder are dispersed in a solvent is applied onto the surface of the current collector, dried, and pressed as necessary. Further, without using a solvent, the active material, the conductive auxiliary agent and the binder can be dry-mixed, press-molded into a thin film, and then attached to the current collector using a conductive adhesive or the like.

  The negative electrode of the LIC of this embodiment is preferably doped with lithium ions in advance. This dope amount is preferably in the range of 30 to 100% of lithium ions that can be occluded by the negative electrode active material, and more preferably in the range of 40 to 80%. By pre-doping the negative electrode active material with lithium ions, the negative electrode potential is lowered, the cell voltage is increased when combined with the positive electrode, and the available capacity of the positive electrode is increased. High energy density can be obtained.

  The method of previously doping the negative electrode with lithium ions is not particularly limited in the present embodiment, and a known method can be used. For example, after forming a negative electrode active material into an electrode, using the negative electrode as a working electrode and metallic lithium as a counter electrode, an electrochemical cell combining non-aqueous electrolyte is produced and electrochemically doped with lithium ions A method is mentioned. It is also possible to dope lithium ions into the negative electrode by pressing a metal lithium foil on the negative electrode and immersing it in a non-aqueous electrolyte.

[Other elements of lithium ion capacitor]
In the LIC of this embodiment, the molded positive electrode and negative electrode are inserted into an exterior body formed from a metal can or a laminate film as an electrode body laminated or wound around via a separator.

  The LIC separator is not particularly limited, and those provided in a conventional LIC can also be used. Further, a polyethylene microporous film or polypropylene microporous film that can be provided in LIB, or a cellulose nonwoven paper that can be provided in EDLC can also be used.

  The thickness of the separator is preferably 10 to 50 μm. If the thickness is 10 μm or more, it is excellent in suppressing self-discharge due to an internal micro short circuit, while if the thickness is 50 μm or less, the energy density and input / output characteristics of the LIC are further improved.

  In the electrode body, one end of the positive electrode terminal is electrically connected to the positive electrode, and one end of the negative electrode terminal is electrically connected to the negative electrode. Specifically, the positive electrode terminal is electrically connected to a region where the positive electrode active material layer of the positive electrode current collector is not formed, and the negative electrode terminal is electrically connected to a region where the negative electrode active material layer of the negative electrode current collector is not formed. In the LIC of the present embodiment, it is preferable that the material of the positive electrode terminal is aluminum and the material of the negative electrode terminal is copper plated with nickel.

  The electrode terminal generally has a substantially rectangular shape, and one end of the electrode terminal is electrically connected to the current collector of the electrode, and the other end is an external load (when discharging) or a power source (when charging) during use. And electrically connected. Resin such as polypropylene is used in the central part of the electrode terminal, which becomes the sealing part of the laminate film outer package, in order to prevent a short circuit between the electrode terminal and the metal foil constituting the laminate film and to improve the sealing hermeticity. It is preferable that the made film is affixed.

  For example, an ultrasonic welding method is generally used as an electrical connection method between the electrode and the electrode terminal, but resistance welding or laser welding may be used, and the method is not particularly limited.

  As a metal can used as an exterior body, the thing made from aluminum is preferable. Moreover, the laminated film used as an exterior body is preferably a film in which a metal foil and a resin film are laminated, and an example of a three-layer structure composed of an outer layer resin film / metal foil / inner layer resin film is exemplified. The outer layer resin film is for preventing the metal foil from being damaged by contact or the like, and the material is preferably a resin such as nylon or polyester. The metal foil is for preventing the permeation of moisture or gas, and foils such as copper, aluminum and stainless steel are preferable. The inner layer resin film protects the metal foil from the electrolyte contained therein and melts and seals it at the time of heat sealing. The material is preferably polyolefin or acid-modified polyolefin.

  In the present embodiment, the solvent of the non-aqueous electrolyte solution contained in the LIC includes, for example, a cyclic carbonate represented by ethylene carbonate and propylene carbonate, a chain carbonate represented by diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate. Examples include esters, lactones such as γ-butyrolactone, and mixed solvents thereof.

The electrolyte dissolved in the electrolytic solution contained in the lithium ion capacitor needs to be a lithium salt. In addition, the tetraalkylammonium salt normally contained in EDLC cannot be contained in a lithium ion capacitor. Preferred lithium salts include, for example, LiBF ₄ , LiPF ₆ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiN (SO ₂ CF ₃ ) (SO ₂ C ₂ F ₅ ), and LiN (SO ₂ CF ₃ ) (SO ₂ C ₂ F ₄ H), and mixed salts thereof. The electrolyte concentration in the nonaqueous electrolytic solution is preferably in the range of 0.5 to 2.0 mol·L ⁻¹ . When the electrolyte concentration is 0.5 mol·L ⁻¹ or more, the supply of ions is further hardly insufficient, and the capacity of the LIC is further increased. On the other hand, if the electrolyte concentration is 2.0 mol·L ⁻¹ or less, the salt can be further prevented from being precipitated in the electrolyte solution or the viscosity of the electrolyte solution being too high. Therefore, it is possible to more effectively prevent the conductivity from being lowered and the output characteristics from being lowered.

  According to this embodiment, the potential of the positive electrode of the lithium ion capacitor can be made higher than before, and as a result, a lithium ion capacitor with higher energy density can be provided. Further, a binder for a lithium ion capacitor electrode excellent in oxidation resistance while maintaining the binding property that the binder should have, an electrode for a lithium ion capacitor comprising the binder, and a slurry for a lithium ion capacitor for forming the electrode And a lithium ion capacitor provided with the said electrode can be provided.

  The LIC of this embodiment is suitably used as a power source for a hybrid vehicle that requires high energy density and excellent durability, for example.

  EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated in detail, this invention is not limited at all by the Example.

[Measuring method]
(1) Solid content About 1 g of the obtained aqueous dispersion of the copolymer was precisely weighed on an aluminum dish, and the mass of the aqueous dispersion weighed at this time was defined as (a) g. It was dried for 1 hour with a hot air dryer at 130 ° C., and the dry mass of the dried copolymer was (b) g. The solid content was calculated by the following formula.
Solid content = (b) / (a) × 100 [%]

(2) Average particle diameter of copolymer particles 50% particle diameter (nm) was measured using a particle diameter measuring apparatus by a light scattering method (manufactured by LEED & NORTHRUP, trade name “MICROTRAC UPA150”) to obtain an average particle diameter. .

(3) Glass transition temperature of copolymer An appropriate amount of an aqueous dispersion (solid content = 38 to 42% by mass, pH = 9.0) containing the copolymer is placed in an aluminum dish and heated in a 130 ° C. hot air dryer. Dried for minutes. About 17 mg of the dried film after drying was packed in an aluminum container for measurement, and a DSC curve and a DDSC curve in a nitrogen atmosphere were obtained with a DSC measuring apparatus (manufactured by Shimadzu Corporation, model number: DSC6220). Measurement conditions were as follows.
(First stage temperature rise program)
Starting at 70 ° C., the temperature was increased at a rate of 15 ° C. per minute. After reaching 110 ° C., the temperature was maintained for 5 minutes.
(Second stage temperature drop program)
The temperature was lowered from 110 ° C. at a rate of 30 ° C. per minute. After reaching −50 ° C., the temperature was maintained for 4 minutes.
(Third-stage temperature rising program)
The temperature was raised from -50 ° C to 130 ° C at a rate of 15 ° C per minute. A DSC curve and a DDSC curve were obtained during the third stage of temperature increase.
The intersection of the straight line obtained by extending the base line in the obtained DSC curve to the high temperature side and the tangent at the inflection point was defined as the glass transition temperature (Tg).

(4) Swelling degree of copolymer with respect to electrolyte solution The aqueous dispersion containing the copolymer was allowed to stand in an oven at 130 ° C. for 1 hour and dried. The copolymer film obtained by drying was cut to 0.5 g. The cut sample was put into a 50 mL vial together with 10 g of a mixed solvent of ethylene carbonate: diethyl carbonate = 2: 3 (mass ratio), and the mixed solvent was infiltrated for one day. Next, the sample was taken out from the vial, washed with the above mixed solvent, and the mass (Wa: g) was measured. Thereafter, the sample was allowed to stand in an oven at 150 ° C. for 1 hour, then the mass was measured (Wb: g), and the degree of swelling of the copolymer with respect to the electrolytic solution was calculated by the following formula.
Swelling degree of copolymer to electrolyte (times) = (Wa−Wb) ÷ (Wb)

(Preparation of binder)
[Synthesis Example 1]
In a reaction vessel equipped with a stirrer, reflux condenser, dropping tank and thermometer, 70.4 parts by mass of ion-exchanged water and “AQUALON KH1025” as an emulsifier (registered trademark, 25% aqueous solution manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) 0.5 part by mass and 0.5 part by mass of “ADEKA rear soap SR1025” (registered trademark, 25% aqueous solution manufactured by ADEKA Corporation) were added. Next, the temperature inside the reaction vessel was raised to 80 ° C., and 7.5 parts by mass of a 2% aqueous solution of ammonium persulfate was added while maintaining the temperature at 80 ° C. Five minutes after the completion of the addition of the ammonium persulfate aqueous solution, the emulsion was dropped from the dropping tank into the reaction vessel over 150 minutes. The emulsion is cyclohexyl methacrylate (“CHMA” in the table) as an ethylenically unsaturated monomer (A) having a cycloalkyl group (in the table, expressed as “monomer (A)”, the same shall apply hereinafter). The same shall apply hereinafter. 35.0 parts by mass, ethylenically unsaturated monomer (b1) having an amide group (in the table, indicated as “monomer (b1)”, the same shall apply hereinafter) acrylamide (table In the middle, expressed as “AM.” The same applies hereinafter.) 5.0 parts by mass, ethylenically unsaturated monomer (b2) having a carboxyl group (in the table, expressed as “monomer (b2)”) methacryl 0.1 parts by mass of an acid (in the table, expressed as “MAA”, the same applies hereinafter), acrylic acid (in the table, expressed as “AA”, the same applies hereinafter), 0.1 part by mass, an ethylenic group having a hydroxyl group Saturated monomer (b3) (denoted as “monomer (b3)” in the table) The same shall apply hereinafter.) 2-hydroxyethyl methacrylate (in the table, expressed as “2HEMA”; the same shall apply hereinafter) 2.0 parts by mass, crosslinkable monomer (b4) (in the table, “monomer (b4)” The same shall apply hereinafter.) Trimethylolpropane triacrylate (A-TMPT, trade name of Shin-Nakamura Chemical Co., Ltd., indicated as “A-TMPT” in the table, the same shall apply hereinafter.) 0.7 parts by mass, glycidyl Methacrylate (in the table, expressed as “GMA”, the same applies hereinafter) 2.8 parts by mass, (meth) acrylic acid ester monomer (b5) other than the above (in the table, expressed as “monomer (b5)”) The same shall apply hereinafter.) Methyl methacrylate (denoted as “MMA” in the table, the same shall apply hereinafter) 2.3 parts by mass, butyl acrylate (in the table, indicated as “BA”, the same shall apply hereinafter) 1.0 part by mass, Butyl methacrylate (table , “BMA”, the same shall apply hereinafter.) 1.0 part by mass, 2-ethylhexyl acrylate (in the table, indicated as “2EHA”, the same shall apply hereinafter) 50.0 parts by mass, “AQUALON KH1025” (registered trademark) as an emulsifier , Daiichi Kogyo Seiyaku Co., Ltd., 25% aqueous solution) 3.0 parts by mass, “ADEKA rear soap SR1025” (registered trademark, ADEKA Corporation 25% aqueous solution) 3.0 parts by mass, sodium p-styrenesulfonate (table) In the middle, it is expressed as “NaSS”. The same applies hereinafter.) A mixture of 0.05 part by mass, 7.5 part by mass of a 2% aqueous solution of ammonium persulfate, and 52.0 parts by mass of ion-exchanged water was mixed with a homomixer for 5 minutes. Produced.

  After completion of dropping of the emulsion, the temperature inside the reaction vessel was maintained at 80 ° C. for 90 minutes, and then cooled to room temperature. The obtained emulsion was adjusted to pH = 9.0 with an aqueous ammonium hydroxide solution (25% aqueous solution) to obtain an aqueous dispersion having a concentration of 40% (aqueous dispersion A1). About the copolymer in obtained water dispersion A1, Tg, an average particle diameter, and the swelling degree with respect to electrolyte solution were measured with the said method. The obtained results are shown in Table 1.

[Synthesis Examples 2 to 27]
In the same manner as in Synthesis Example 1, except that the types and blending ratios of the raw materials were changed as shown in Tables 1 to 4 and the amount of the emulsifier used in the reaction vessel was adjusted to adjust the particle size. Aqueous dispersions A2 to A27 were obtained. In the table, “SZ6030” means γ-methacryloxypropyltrimethoxysilane (trade name, manufactured by Dow Corning Toray), which is one kind of the crosslinkable monomer (b4). About the copolymer in obtained water dispersion A2-A27, the swelling degree with respect to Tg, a particle diameter, and electrolyte solution was measured with the said method. The obtained results are shown in Tables 1 to 4. In the table, the composition of raw materials is expressed in parts by mass.

[Example of binder]
The aqueous dispersions A1 to A25 were used as they were as the aqueous dispersions containing the binders B1 to B25 of the examples.

[Comparative example of binder]
The aqueous dispersions A26 to A27 were used as they were as the aqueous dispersion containing the binders C1 to C2 of the comparative example.

<Example of electrode>
(Preparation of positive electrode)
Commercially available coconut shell activated carbon was used as the positive electrode active material. The average particle size measured using a laser diffraction particle size distribution measuring apparatus (Shimadzu Corporation, product name “SALD-200V ER”) was 5.8 μm. The nitrogen adsorption / desorption isotherm was measured using an automatic gas adsorption tester (manufactured by Quantachrome Co. Ltd., product name “AUTOSORB-1 AS-1-MP”). Based on the adsorption / desorption isotherm, the specific surface area determined by the BET one-point method was 1780 m ² · g ⁻¹ . Further, the mesopore volume and the micropore volume were determined by applying the BJH method and the MP method to the desorption isotherm and the adsorption isotherm, respectively. As a result, the mesopore volume was 0.198 cc · g ⁻¹ , the micropore volume was 0.695 cc · g ⁻¹ , and the ratio of the mesopore volume to the micropore volume (mesopore volume / micropore volume) was 0.29. Met. The average pore diameter determined from the BET specific surface area and the total pore volume was 2.12 nm.

18.5 parts by mass of the activated carbon, 1.4 parts by mass of carbon black (manufactured by Lion Corporation, Ketjen Black ECP600JD (product name)), sodium carboxymethylcellulose (manufactured by Tokyo Chemical Industry Co., Ltd., C0603 (product name) )) And 0.77.4 parts by mass of water, 77.4 parts by mass of water, and a mechanical stirrer were used to obtain a mixture. Next, this mixture was stirred using a thin film swirl type high speed mixer (manufactured by PRIMIX, product name “Filmix 56-50”). To this was added 2.0 parts by mass (40% solids) of the binder B1 and stirred to prepare a slurry. The viscosity of the obtained slurry was measured at 25 ° C. and 10 rpm using a B-type viscometer (manufactured by Toki Sangyo Co., Ltd., product name “TVE-35H”). From the result of the viscosity, the quality of the dispersion stability of the slurry was evaluated based on the following criteria. The lower the viscosity, the better the dispersion stability of the slurry and the better the coating stability.
<Evaluation criteria>
Viscosity: less than 1500 mPa · s… ◎
Viscosity: 1500 mPa · s or more and less than 3000 mPa · s… ○
Viscosity 3000 mPa · s or more… △

  The slurry was applied to one side of an aluminum foil (thickness: 15 μm) as a current collector using an applicator. Next, the applied slurry was dried by heating at 60 ° C. for 10 minutes and at 100 ° C. for 20 minutes. The dried coating film was pressed at room temperature using a roll press machine to obtain a positive electrode E1 having an active material layer thickness of 55 μm.

(Positive electrode peeling test)
The peel test of the positive electrode was performed according to JIS K 6854-3. An electrode having a cellophane tape attached to the active material layer side was cut into a width of 25 mm and a length of 150 mm. Cellophane tape and current collector aluminum foil are held by the upper and lower chucks of a small desktop testing machine (manufactured by Shimadzu Corporation, model number: EZ-S) and pulled at a pulling speed of 50 mm · min ⁻¹ . The load-displacement curve was measured. The average peel load was obtained by dividing the integrated value in the displacement range of 25 to 65 mm in the load-displacement curve by the displacement range of 40 mm. The peel load per unit width obtained by dividing the average peel load by the sample width of 25 mm was defined as peel strength. From the measured peel strength, the quality of the electrode binding was evaluated based on the following criteria.
<Evaluation criteria>
Peel strength: 2.0 N / m or more ... ◎
Peel strength: 1.5 N / m or more and less than 2.0 N / m ... ○
Peel strength: 1.0 N / m or more and less than 1.5 N / m ... △
Peel strength: less than 1.0 N / m ... ×

(Preparation of negative electrode)
Activated carbon covered with pitch-derived carbon, which is a negative electrode active material, was produced by the following method. 150 g of activated carbon which is the same as the positive electrode active material is placed in a stainless steel mesh basket and placed on a stainless steel bat containing 270 g of coal-based pitch (softening point: 50 ° C.). × 300 mm × 300 mm), and the inside of the furnace was replaced with a nitrogen atmosphere. Next, the temperature in the furnace was raised to 600 ° C. over 8 hours, kept at the same temperature for 4 hours, and then allowed to cool to 60 ° C. The obtained composite porous material was taken out of the furnace and its pore structure was measured in the same manner as the positive electrode active material. As a result, the BET specific surface area was 262 m ² · g ⁻¹ and the mesopore volume was 0.179 cc · g ^−1. The micropore volume was 0.084 cc · g ⁻¹ , and the ratio of the mesopore volume to the micropore volume was 2.13.

20.9 parts by mass of composite porous material, 2.1 parts by mass of acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd., trade name “DENKA BLACK”), and an NMP solution of PVDF (concentration of 5% by mass) 41.5 parts by mass of Kureha, trade name “KF polymer # 9305”) and 35.5 parts by mass of NMP were mixed to obtain a slurry. Next, the obtained slurry was applied to one side of a copper foil having a thickness of 15 μm, dried, and pressed to obtain a negative electrode having an active material layer thickness of 60 μm. This negative electrode was electrochemically doped with lithium ions corresponding to 760 mAh · g ⁻¹ per unit mass of the composite porous material using a lithium metal foil.

(Assembling LIC)
And two positive electrode cut to a size of 4 cm ^2, the pre-negative one size lithium ions doped 4.41Cm ² as described above, a thickness of 30μm cellulose nonwoven fabric separator (Nippon Kodoshi (strain ), Model number: TF4535). This laminate was inserted into an exterior body formed from a laminate film, an electrolyte was injected to seal the exterior body, and an LIC was assembled. As an electrolytic solution, a solution obtained by dissolving LiPF ₆ at a concentration of ¹ mol·L ⁻¹ in a solvent in which ethylene carbonate and ethyl methyl carbonate are mixed in a volume ratio of 1: 4 (trade name “manufactured by Toyama Pharmaceutical Co., Ltd., trade name“ LIPASTE-E4MEC-PF1 ") was used.

(Charge / discharge characteristics evaluation)
The manufactured LIC was charged with a constant current up to 4.0 V at a current value of 1.5 C, and then subjected to constant voltage charging for applying a constant voltage of 4.0 V for 2 hours. Subsequently, the battery was discharged to 2.0 V at a current value of 300C. Based on the direct current resistance obtained from the initial voltage drop during discharge, the quality of the charge / discharge characteristics was evaluated based on the following criteria.
<Evaluation criteria>
DC resistance: less than 0.80 ohm ... S
DC resistance: 0.80 ohm or more and less than 0.90 ohm ... A
DC resistance: 0.90 ohm or more and less than 1.00 ohm ... B
DC resistance: 1.00 ohm or more ... C

(Impedance measurement)
The impedance of the manufactured LIC was measured using a frequency response analyzer (Solatron, model 1253). Impedance was measured by applying AC voltage modulation in the range of a voltage amplitude of 5 mV and a frequency of 20 kHz to 0.1 Hz to a LIC to which a bias voltage of 4.0 V was applied. From the value of the real number component (initial Z ′) of the impedance at a frequency of 0.1 Hz, the quality of the impedance characteristics was evaluated based on the following criteria.
<Evaluation criteria>
Initial Z ': Less than 0.75 ohm ... S
Initial Z ′: 0.75 ohm or more and less than 0.85 ohm ... A
Initial Z ': 0.85 ohm or more and less than 0.95 ohm ... B
Initial Z ': 0.95 ohm or more ... C

(Oxidation resistance evaluation)
The oxidation resistance of the positive electrode was evaluated by a float test in which a constant voltage was continuously applied for a predetermined time. The LIC was placed in a constant temperature bath at 60 ° C., charged at a constant current of up to 4.2 V at a current value of 1.5 C, and then subjected to constant voltage charging for applying a constant voltage of 4.2 V for 24 hours. Then, after taking out LIC from a thermostat and cooling to room temperature, impedance was measured like the said "impedance measurement". In this measurement, the real component of the impedance at a frequency of 0.1 Hz is “post-test Z ′”, and the oxidation resistance is determined from the ratio of the post-test Z ′ to the initial Z ′ (resistance ratio) based on the following criteria: evaluated.
<Evaluation criteria>
Resistance ratio: 130% or more and less than 150% ... ◎
Resistance ratio: 150% or more and less than 170%… ○
Resistance ratio: 170% or more and less than 185%… △

<Examples E2-E25>
In the above “preparation of positive electrode”, except that the binders listed in Tables 1 to 3 were used, a positive electrode was produced in the same manner as the production of the positive electrode E1, and LIC was produced to evaluate the characteristics. The evaluation results are shown in Tables 5-7.

<Comparative Examples F1, F2>
In the above “preparation of positive electrode”, a positive electrode was produced in the same manner as the production of positive electrode E1, except that binders C1 and C2 shown in Table 4 were used as binders. The evaluation results are shown in Table 8.

<Comparative Example F3>
12.3 parts by mass of the activated carbon, 1.0 part by mass of the carbon black, 30.6 parts by mass of an NMP solution of PVDF having the concentration of 5% by mass, polyvinylpyrrolidone (manufactured by Tokyo Chemical Industry Co., Ltd. : P0473) was mixed with 0.5 parts by mass, NMP was 55.6 parts by mass, and a mechanical stirrer was mixed and stirred. Next, the obtained mixture was stirred using the thin film swirl type high speed mixer to obtain a slurry. The obtained slurry was applied to one side of a 15 μm thick aluminum foil provided with an anchor layer using an applicator. The applied slurry was dried by heating at 100 ° C. for 10 minutes and at 150 ° C. for 20 minutes. The coating film obtained by drying was pressed at room temperature using a roll press machine to obtain a positive electrode F3 having an active material layer thickness of 55 μm.
LIC was manufactured and various characteristics were evaluated in the same manner as in Example 1 except that the positive electrode F3 was used instead of the positive electrode E1. The evaluation results are shown in Table 8.

  As can be seen from Tables 5 to 8, when the electrodes (positive electrodes) E1 to E25 according to the examples are used, the oxidation resistance superior to the case where the electrodes (positive electrodes) F1 to F2 according to the comparative examples are used. Is shown. Further, when the electrodes E1 to E25 are used, the oxidation resistance equivalent to that when the electrode (positive electrode) F3 according to the comparative example using the fluorine-based polymer is used as the binder is exhibited, and at the same time, higher. It was found to exhibit peel strength.

  The lithium ion capacitor of the present invention has industrial applicability, for example, as a power source for a hybrid vehicle that requires high energy density and excellent durability.

  DESCRIPTION OF SYMBOLS 1 ... Positive electrode terminal, 2 ... Negative electrode terminal, 3 ... Exterior body, 4 ... Electrode body, 5 ... Positive electrode collector, 6 ... Positive electrode active material layer, 7 ... Separator, 8 ... Negative electrode collector, 9 ... Negative electrode active material layer.

Claims (13)

  A copolymer having, as monomer units, an ethylenically unsaturated monomer having a cycloalkyl group and another monomer copolymerizable with the ethylenically unsaturated monomer having the cycloalkyl group. Including a binder for a lithium ion capacitor electrode.   The copolymer comprises a monomer unit of 25 to 50% by mass of the ethylenically unsaturated monomer having the cycloalkyl group with respect to 100% by mass of the copolymer, and the other monomer. The binder for lithium ion capacitor electrodes according to claim 1, wherein the binder is a copolymer. The other monomer includes a (meth) acrylic acid ester monomer composed of an alkyl group having 4 or more carbon atoms and a (meth) acryloyloxy group,
The total content of the ethylenically unsaturated monomer having a cycloalkyl group and the (meth) acrylic acid ester monomer is 50 to 99.9% by mass with respect to 100% by mass of the copolymer. The binder for lithium ion capacitor electrodes according to claim 1 or 2.   The lithium ion capacitor electrode according to claim 3, wherein the (meth) acrylic acid ester monomer includes a (meth) acrylic acid ester monomer composed of an alkyl group having 6 or more carbon atoms and a (meth) acryloyloxy group. Binder.   The binder for lithium ion capacitor electrodes according to any one of claims 1 to 4, wherein the other monomer includes an ethylenically unsaturated monomer having an amide group.   The binder for lithium ion capacitor electrodes according to any one of claims 1 to 5, wherein the other monomer includes an ethylenically unsaturated monomer having a carboxyl group.   The binder for lithium ion capacitor electrodes according to claim 1, wherein the other monomer includes an ethylenically unsaturated monomer having a hydroxyl group.   The binder for lithium ion capacitor electrodes according to claim 1, wherein the other monomer includes a crosslinkable monomer.   The binder for lithium ion capacitor electrodes according to any one of claims 1 to 8, wherein the ethylenically unsaturated monomer having a cycloalkyl group is cyclohexyl acrylate or cyclohexyl methacrylate.   The binder for lithium ion capacitor electrodes according to any one of claims 1 to 9, wherein the copolymer includes a copolymer produced by emulsion polymerization.   The slurry for lithium ion capacitors containing an active material and the binder for lithium ion capacitor electrodes of any one of Claims 1-10.   The electrode for lithium ion capacitors provided with the active material layer obtained by apply | coating the slurry for lithium ion capacitors of Claim 11 on the surface of an electrical power collector.   A lithium ion capacitor comprising the lithium ion capacitor electrode according to claim 12.

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