JP6759589B2 - Conductive composition for electrochemical element, composition for electrochemical element electrode, current collector with adhesive layer and electrode for electrochemical element - Google Patents

Description

The present invention relates to a conductive composition for an electrochemical element having excellent coatability, a composition for an electrode of an electrochemical element obtained by using this conductive composition for an electrochemical element, a current collector with an adhesive layer, and electricity. It relates to electrodes for chemical elements.

Demand for electrochemical elements, especially lithium-ion batteries, which are small in size, lightweight, have high energy density, and can be repeatedly charged and discharged, is rapidly expanding by taking advantage of their characteristics. Further, since the electrochemical element represented by the lithium ion battery has a large energy density and output density, it is expected to be used in a large-scale application such as a vehicle from a small-sized application of a mobile phone or a notebook personal computer. Therefore, these electrochemical devices are required to be further improved such as lower resistance, higher capacity, higher withstand voltage, mechanical properties, and improvement of cycle life with the expansion and development of applications.

Electrochemical devices can increase the operating voltage and energy density by using an organic electrolytic solution, but on the other hand, there is a problem that the internal resistance is large due to the high viscosity of the electrolytic solution.

In order to reduce the internal resistance, it has been proposed to provide a conductive adhesive layer between the electrode composition layer and the current collector (see, for example, Patent Document 1). In Patent Document 1, a conductive adhesive layer is formed by using a conductive composition for an electrochemical element containing a conductive carbon, a water-soluble polymer, a particulate binder, and a dispersion medium.

International Publication No. 2014/05/1043

By the way, the conductive composition is required to have an appropriately low viscosity in consideration of the coatability on the current collector. For that purpose, for example, it is necessary to suppress the aggregation of conductive carbon. Here, when the conductive carbon aggregates, the resistance of the conductive adhesive layer obtained by using the conductive composition increases, so that the obtained battery may be inferior in output characteristics.

An object of the present invention is to obtain a conductive composition for an electrochemical element, which is excellent in coatability on a current collector and has good output characteristics and cycle characteristics of the obtained electrochemical element, and a conductive composition for this electrochemical element. It is an object of the present invention to provide a composition for an electrochemical element electrode, a current collector with an adhesive layer, and an electrode for an electrochemical element.

As a result of diligent studies, the present inventor has found that the above object can be achieved by using an aqueous solution of a chitosan compound having a specific viscosity and a particulate copolymer having a specific surface acid amount in combination, and completed the present invention. I came to do it.
That is, according to the present invention
(1) A chitosan compound having a viscosity of 1 mPa · s or more and 500 mPa · s or less of an aqueous solution dissolved in a 0.5% acetic acid aqueous solution so as to be 0.5% by mass, and a surface acid amount of 0.1 mmol / g or more. A conductive composition for an electrochemical element, which comprises a particulate copolymer and a conductive material.
(2) The conductive composition for an electrochemical device according to (1), wherein the electrolytic solution swelling degree of the particulate copolymer is 100% or more and 500% or less.
(3) The conductive composition for an electrochemical element according to (1) or (2), wherein the value obtained by dividing the mass of the chitosan compound by the mass of the particulate copolymer is 0.1 or more and 10 or less.
(4) The particulate copolymer contains an aromatic vinyl monomer unit and a (meth) acrylic acid ester monomer unit, and the aromatic vinyl monomer unit and (meth) contained in the particulate copolymer. ) For the electrochemical element according to any one of (1) to (3), wherein the content ratio of the aromatic vinyl monomer unit to the total amount of the acrylic acid ester monomer unit is 10% by mass or more and 70% by mass or less. Conductive composition,
(5) The particulate copolymer contains an aromatic vinyl monomer unit and a (meth) acrylic acid ester monomer unit, and the aromatic vinyl monomer unit and (meth) contained in the particulate copolymer. ) The electricity according to any one of (1) to (4), wherein the content ratio of the (meth) acrylic acid ester monomer unit to the total amount of the acrylic acid ester monomer unit is 30% by mass or more and 90% by mass or less. Conductive composition for chemical elements,
(6) A composition for an electrochemical device electrode, which comprises the conductive composition for an electrochemical device according to any one of (1) to (5) and contains an electrode active material.
(7) A current collector with an adhesive layer, which has a conductive adhesive layer on the current collector using the conductive composition for an electrochemical element according to any one of (1) to (5).
(8) An electrode for an electrochemical element, which has an electrode composition layer containing an electrode active material on the conductive adhesive layer of the current collector with an adhesive layer according to (7), is provided.

According to the present invention, a conductive composition for an electrochemical element, which is excellent in coatability to a current collector and has good output characteristics and cycle characteristics of the obtained electrochemical element, and a conductive composition for this electrochemical element can be obtained. The composition for an electrochemical element electrode, a current collector with an adhesive layer, and an electrode for an electrochemical element are provided.

In calculating the surface acid amount of the particulate copolymer, it is the graph which plotted the electric conductivity (mS) with respect to the cumulative amount (mmol) of added hydrochloric acid.

Hereinafter, the present invention will be described in more detail including embodiments. The conductive composition for an electrochemical element of the present invention (hereinafter, may be simply referred to as "conductive composition") is an aqueous solution dissolved in a 0.5% aqueous acetic acid solution so as to be 0.5% by mass. Includes a chitosan compound having a viscosity of 1 mPa · s or more and 500 mPa · s or less, a particulate copolymer having a surface acid amount of 0.1 mmol / g or more, and a conductive material.

(Chitosan compound)
The conductive composition for an electrochemical element of the present invention contains a chitosan compound having a viscosity of 1 mPa · s or more and 500 mPa · s or less of an aqueous solution dissolved in a 0.5% acetic acid aqueous solution so as to be 0.5% by mass. ..

In the conductive composition for an electrochemical element of the present invention, the chitosan compound functions as a viscosity modifier by being dissolved in a dispersion medium such as water, and is applied onto a current collector using the conductive composition. When a coating film composed of a conductive adhesive layer (hereinafter, may be simply referred to as "coating film") is formed by drying, it is formed on a binder and a coating film that prevent detachment of coating film components. It can also function as a component for improving the adhesion with the electrode composition layer to be formed.

Examples of the chitosan compound used in the conductive composition for an electrochemical element of the present invention include chitosan obtained by deacetylating chitin and a derivative thereof (chitosan derivative). Further, the chitosan compound may be in the form of a salt such as a sodium salt. Here, examples of the chitosan derivative include those in which at least a part of hydrogen atoms of a plurality of hydroxyl groups and / or amino groups existing in chitosan are replaced with other structures. Examples of such chitosan derivatives include those described in JP-A-2009-277660, JP-A-2015-5474, and JP-A-2013-229110.

Among these chitosan compounds, it is necessary to use a water-soluble chitosan compound in the present invention. The term "water-soluble" means that the chitosan compound does not pass through the screen with respect to the mass (equivalent to solid content) of the added chitosan compound when the evaluation sample containing the chitosan compound and water passes through the 250 mesh screen. It means that the ratio of the mass (corresponding to the solid content) of the residue remaining on the screen is 50% by mass or less. Further, when the above conditions are satisfied, it is said that "the chitosan compound is dissolved in water" in the present invention. Here, the above-mentioned evaluation sample is a mixture obtained by adding 1 part by mass (equivalent to solid content) of a chitosan compound per 100 parts by mass of ion-exchanged water and stirring the mixture in a temperature range of 20 ° C. or higher and 70 ° C. or lower. Moreover, it is adjusted to at least one of the conditions within the range of pH 5 or more and 7 or less (a HCl aqueous solution is used for pH adjustment). Even if the evaluation sample is in an emulsion state in which it separates into two phases when left to stand, the chitosan compound is defined to be water-soluble if the above definition is satisfied.
When the chitosan compound is water-insoluble, the coatability of the slurry-like conductive composition (hereinafter, may be simply referred to as “slurry”) is impaired, and the peel strength of the electrode and the lithium ion secondary battery are impaired. There is a problem that the output characteristics and cycle characteristics of the are deteriorated.

The viscosity of the aqueous solution of the chitosan compound used in the present invention dissolved in a 0.5% acetic acid aqueous solution so as to be 0.5% by mass is 1 mPa · from the viewpoint of obtaining a slurry having good coatability and dispersibility. It is s or more and 500 mPa · s or less, preferably 5 mPa · s or more and 300 mPa · s or less, and more preferably 10 mPa · s or more and 100 mPa · s or less. If the viscosity is too high, the viscosity of the slurry will increase and the coatability will decrease. On the contrary, if the viscosity is too low, the dispersibility of the slurry is lowered and the resistance value of the obtained coating film is increased.

The content ratio of the chitosan compound in the conductive composition for an electrochemical element is preferably 2% by mass or more and 50% by mass or less, more preferably 3% by mass or more and 40% by mass or less, and particularly preferably 4% by mass or more and 30% by mass or less. It is as follows.

(Particulate copolymer)
The conductive composition for an electrochemical device of the present invention contains a particulate copolymer having a surface acid amount of 0.1 mmol / g or more. Examples of the particulate copolymer used in the present invention include aromatic vinyl monomer units, (meth) acrylic acid ester monomer units, aliphatic conjugated diene monomer units, and acidic group-containing monomer units. Examples thereof include those containing an aromatic vinyl monomer unit, a (meth) acrylic acid ester monomer unit, and an acidic group-containing monomer unit.

(Aromatic vinyl monomer)
Examples of the aromatic vinyl monomer capable of forming an aromatic vinyl monomer unit include styrene, α-methylstyrene, vinyltoluene, divinylbenzene and the like. Among these, styrene is preferable from the viewpoint of increasing the mechanical strength of the coating film. Further, these may be used alone or in combination of two or more.

The content ratio of the aromatic vinyl monomer unit to the total amount of the aromatic vinyl monomer unit and the (meth) acrylic acid ester monomer unit contained in the particulate copolymer used in the present invention is the coating film. From the viewpoint of improving adhesion and suppressing swelling during immersion in the electrolytic solution, it is preferably 10% by mass or more and 70% by mass or less, more preferably 20% by mass or more and 60% by mass or less, and particularly preferably 30% by mass or more and 50% by mass. % Or less. When the content ratio of the aromatic vinyl monomer unit is not more than the upper limit of the above range, the phenomenon that the strength and adhesion of the coating film are excessively lowered can be suppressed. Further, when the content ratio is equal to or higher than the lower limit of the above range, the adhesion between the coating film and the current collector is excessively lowered due to swelling, and the coating film and the electrode composition layer are swelled. It is possible to suppress the phenomenon that the adhesion of the material is excessively lowered.

((Meta) acrylic acid ester monomer)
Examples of the (meth) acrylic acid ester monomer capable of forming a (meth) acrylic acid ester monomer unit include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, and t-butyl acrylate. Acrylic acid alkyl esters such as isobutyl acrylate, n-pentyl acrylate, isopentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate, stearyl acrylate; Methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, isobutyl methacrylate, n-pentyl methacrylate, isopentyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, Alkyl methacrylates such as nonyl methacrylate, decyl methacrylate, lauryl methacrylate, n-tetradecyl methacrylate, stearyl methacrylate, and glycidyl methacrylate; and the like. Among these, 2-ethylhexyl acrylate is preferable from the viewpoint of imparting sufficient flexibility and adhesion to the coating film. Further, these may be used alone or in combination of two or more.
In the present invention, "(meth) acrylic" means acrylic or methacrylic.

The content ratio of the (meth) acrylic acid ester monomer unit to the total amount of the aromatic vinyl monomer unit and the (meth) acrylic acid ester monomer unit contained in the particulate copolymer used in the present invention is. From the viewpoint of improving the adhesion of the coating film and suppressing swelling during immersion in the electrolytic solution, it is preferably 30% by mass or more and 90% by mass or less, more preferably 40% by mass or more and 80% by mass or less, and particularly preferably 50% by mass. It is 70% by mass or less. When the content ratio of the (meth) acrylic acid ester monomer unit is not more than the upper limit of the above range, the adhesion between the coating film and the current collector is excessively lowered due to swelling, or due to swelling. It is possible to suppress the phenomenon that the adhesion between the coating film and the electrode composition layer is excessively lowered. Further, when the content ratio is not more than the lower limit value in the above range, the phenomenon that the strength and adhesion of the coating film are excessively lowered can be suppressed.

(Aliphatic conjugated diene monomer)
Examples of the aliphatic conjugated diene monomer capable of forming an aliphatic conjugated diene monomer unit include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, Examples include 2-chloro-1,3-butadiene, substituted linear conjugated pentadienes, substituted and side chain conjugated hexadienes and the like. Of these, 1,3-butadiene is preferable. Further, these may be used alone or in combination of two or more.

(Acid group-containing monomer)
Examples of the acidic group-containing monomer capable of forming an acidic group-containing monomer unit include a monomer having a carboxylic acid group, a monomer having a sulfonic acid group, and a monomer having a phosphoric acid group. Can be mentioned. In the present invention, the monomer having an acidic group is included in the acidic group-containing monomer even when it has a functional group (for example, an amide group or a hydroxyl group) other than the acidic group. To do.

Examples of the monomer having a carboxylic acid group include monocarboxylic acid and dicarboxylic acid. Examples of the monocarboxylic acid include acrylic acid, methacrylic acid, crotonic acid and the like. Examples of the dicarboxylic acid include maleic acid, fumaric acid, itaconic acid and the like.

Examples of the monomer having a sulfonic acid group include vinyl sulfonic acid, methyl vinyl sulfonic acid, (meth) allyl sulfonic acid, ethyl (meth) acrylic acid-2-sulfonate, and 2-acrylamide-2-methyl propane sulfone. Acids, 3-allyloxy-2-hydroxypropanesulfonic acid and the like can be mentioned. In addition, in this invention, "(meth) allyl" means allyl and / or allyl.

Examples of the monomer having a phosphate group include -2- (meth) acryloyloxyethyl phosphate, methyl-2- (meth) acryloyloxyethyl phosphate, ethyl phosphate- (meth) acryloyloxyethyl and the like. Can be mentioned. In addition, in this invention, "(meth) acryloyl" means acryloyl and / or methacryloyl.

Among these, as the acidic group-containing monomer, a monomer having a carboxylic acid group is preferable, acrylic acid, methacrylic acid, itaconic acid, and maleic acid are more preferable, and itaconic acid is particularly preferable. In addition, one type of acidic group-containing monomer may be used alone, or two or more types may be used in combination. For example, as the acidic group-containing monomer, a monomer having a carboxylic acid and a monomer having a sulfonic acid group can be used in combination.

The content ratio of the acidic group-containing monomer unit to all the monomer units constituting the particulate copolymer used in the present invention is from the viewpoint of enhancing the bondability between the current collector and the conductive adhesive layer, and the conductivity. From the viewpoint of enhancing the bondability between the sex adhesive layer and the electrode composition layer, it is preferably 1 to 5% by mass, more preferably 1.5 to 4.5% by mass, and particularly preferably 2 to 4% by mass. .. When the content ratio of the acidic group-containing monomer unit is not more than the upper limit of the above range, the bondability between the current collector and the conductive adhesive layer becomes excessively weak, and the conductive adhesive It is possible to suppress the phenomenon that the bondability between the layer and the electrode composition layer becomes excessively weak. On the contrary, if it is equal to or more than the lower limit of the above range, the bondability between the current collector and the conductive adhesive layer becomes excessively weak, and the bond between the conductive adhesive layer and the electrode composition layer It is possible to suppress the phenomenon that the adhesiveness becomes excessively weak.

(Amount of surface acid)
The amount of surface acid of the particulate copolymer used in the present invention is 0.1 mmol / g or more, preferably 0.15 mmol / g or more, more preferably 0.15 mmol / g or more, from the viewpoint of obtaining a slurry having good stability and coatability. It is 0.2 mmol / g or more, preferably 0.5 mmol / g or less. If the amount of surface acid is too small, the stability of the obtained slurry is lowered and the coatability is lowered.

In the present invention, the surface acid amount of the particulate copolymer means the surface acid amount per 1 g of the solid content of the particulate copolymer. Here, the surface acid amount of the particulate copolymer can be calculated by the following method.

First, an aqueous dispersion (solid content concentration 4%) containing a particulate copolymer is prepared. 50 g of the aqueous dispersion containing the particulate copolymer is placed in a glass container having a capacity of 150 mL washed with distilled water, set in a solution conductivity meter (COM-2000, manufactured by Hiranuma Sangyo), and stirred. The stirring is continued until the addition of hydrochloric acid, which will be described later, is completed.
A 0.1N aqueous sodium hydroxide solution is added to the aqueous dispersion containing the particulate copolymer so that the electrical conductivity of the aqueous dispersion containing the particulate copolymer is 2.5 to 3.0 mS. To do. Then, after 5 minutes have passed, the electric conductivity is measured. This value is taken as the electrical conductivity at the start of measurement.

Further, 0.5 mL of 0.1N hydrochloric acid is added to the aqueous dispersion containing the particulate copolymer, and the electric conductivity is measured after 30 seconds. Then, 0.5 mL of 0.1N hydrochloric acid is added again, and the electric conductivity is measured after 30 seconds. This operation is repeated at intervals of 30 seconds until the electric conductivity of the aqueous dispersion containing the particulate copolymer becomes equal to or higher than the electric conductivity at the start of measurement.

The obtained electrical conductivity data is displayed on a graph with the electrical conductivity (unit "mS") on the vertical axis (Y coordinate axis) and the cumulative amount of added hydrochloric acid (unit "mmol") on the horizontal axis (X coordinate axis). Plot. As a result, a hydrochloric acid amount-electrical conductivity curve having three inflection points is obtained as shown in FIG. Let the X coordinates of the three inflection points be P1, P2, and P3, respectively, in ascending order of value. Approximate straight lines L1, L2, and L3 are obtained by the least squares method for the data in the three categories in which the X coordinate is from zero to coordinate P1, from coordinate P1 to coordinate P2, and from coordinate P2 to coordinate P3, respectively. .. Let A1 (mmol) be the X coordinate of the intersection of the approximate straight line L1 and the approximate straight line L2, and A2 (mmol) be the X coordinate of the intersection of the approximate straight line L2 and the approximate straight line L3.
The amount of surface acid per 1 g of the particulate copolymer is given as a value (mmol / g) converted to hydrochloric acid according to the following formula (a).
Amount of surface acid per 1 g of particulate copolymer = A2-A1 ... (a)

The amount of surface acid of the particulate copolymer can be controlled by, for example, changing the types and proportions of the monomer units constituting the particulate copolymer and the polymerization method.
More specifically, for example, the amount of surface acid can be efficiently controlled by adjusting the type and ratio of the acidic group-containing monomer unit. Normally, when an acidic group-containing monomer having a large difference in reactivity compared to other monomers (itaconic acid, etc.) is used, the acidic group-containing monomer is present on the surface of the particulate copolymer. Since it becomes easy to copolymerize with, the amount of surface acid tends to increase.

(Electrolytic solution swelling degree)
The degree of swelling of the electrolytic solution of the particulate copolymer used in the present invention is preferably 100% from the viewpoint of not increasing the resistance value of the coating film and maintaining the adhesion between the coating film and the electrode composition layer. It is 500% or more, more preferably 100% or more and 300% or less, and particularly preferably 100% or more and 150% or less. When the degree of swelling of the electrolytic solution of the particle copolymer is not more than the upper limit of the above range, the resistance value of the coating film is excessively increased, and the adhesion between the coating film and the electrode composition layer is deteriorated. It is possible to suppress the phenomenon of excessive decrease.

Here, the degree of swelling of the electrolytic solution of the particulate copolymer refers to the degree of swelling when the film obtained by drying the aqueous dispersion of the particulate copolymer is immersed in a specific electrolytic solution. The degree of swelling of the electrolytic solution of the particulate copolymer can be calculated by the following method.
An aqueous dispersion containing a particulate copolymer is prepared, and the aqueous dispersion is dried at room temperature to form a film having a thickness of 0.2 to 0.5 mm. This film is punched into a circle of 10 mmφ, and the mass (mass before immersion A) is measured. A mixture of film pieces after mass measurement mixed with an electrolytic solution at a temperature of 60 ° C. (ethylene carbonate (EC) and ethyl methyl carbonate (EMC) so that the mass ratio at 20 ° C. is EC: EMC = 3: 7). Immerse in a solvent (a solution in which LiPF ₆ is dissolved at a concentration of 1.0 mol / L). After 72 hours, the soaked film is pulled up, the electrolytic solution is wiped off with a towel paper, and the mass (mass B after soaking) is measured immediately. The mass change is calculated according to the following formula, and this is taken as the degree of swelling of the electrolytic solution.
Electrolyte swelling degree (%) = (B / A) x 100

Among the components contained in the conductive composition for an electrochemical element of the present invention, the value obtained by dividing the mass of the chitosan compound by the mass of the particulate copolymer is from the viewpoint of improving the dispersibility of the conductive material and the coating film. From the viewpoint of improving the adhesion of the above, it is preferably 0.1 or more and 10 or less, more preferably 0.2 or more and 9 or less, and particularly preferably 0.3 or more and 8 or less. When this value is not more than the upper limit of the above range, the phenomenon that the viscosity of the slurry increases and the coatability is excessively lowered can be suppressed. Further, when this value is not more than the lower limit value in the above range, the phenomenon that the dispersibility of the conductive material is lowered and the resistance value of the coating film is excessively increased can be suppressed.

(Production of Particulate Copolymer)
The method for producing the particulate copolymer is not particularly limited, but as described above, it can be obtained by emulsion polymerization of a monomer mixture containing a monomer constituting a polymer compound. The method of emulsion polymerization is not particularly limited, and a conventionally known emulsion polymerization method may be adopted.

Examples of the polymerization initiator used for emulsification polymerization include inorganic peroxides such as sodium persulfate, potassium persulfate, ammonium persulfate, potassium perphosphate, and hydrogen peroxide; t-butyl peroxide, cumene hydroperoxide, and the like. p-menthan hydroperoxide, di-t-butyl peroxide, t-butylcumyl peroxide, acetyl peroxide, isobutyryl peroxide, octanoyl peroxide, benzoyl peroxide, 3,5,5-trimethylhexanoylper Organic peroxides such as oxides and t-butylperoxyisobutyrate; azo compounds such as azobisisobutyronitrile, azobis-2,4-dimethylvaleronitrile, azobiscyclohexanecarbonitrile, methyl azobisisobutyrate, etc. Be done.

Among these, inorganic peroxides can be preferably used. These polymerization initiators can be used alone or in combination of two or more. In addition, the peroxide initiator can also be used as a redox-based polymerization initiator in combination with a reducing agent such as sodium bisulfite. The amount of the polymerization initiator used is preferably 0.05 to 5 parts by mass, more preferably 0.1 to 2 parts by mass, based on 100 parts by mass of the total amount of the monomer mixture used for the polymerization.

It is preferable to further use an anionic surfactant during emulsion polymerization. Polymerization stability can be improved by using an anionic surfactant.

As the anionic surfactant, conventionally known ones in emulsion polymerization can be used. Specific examples of anionic surfactants include sodium lauryl sulfate, ammonium lauryl sulfate, sodium dodecyl sulfate, ammonium dodecyl sulfate, sodium octyl sulfate, sodium decyl sulfate, sodium tetradecyl sulfate, sodium hexadecyl sulfate, sodium octadecyl sulfate, and the like. Sulfate esters of higher alcohols; alkylbenzene sulfonates such as sodium dodecylbenzene sulfonate, sodium laurylbenzene sulfonate, sodium hexadecylbenzene sulfonate; fats such as sodium lauryl sulfonate, sodium dodecyl sulfonate, sodium tetradecyl sulfonate Group sulfonates; and the like.

The amount of the anionic surfactant used is preferably 0.5 to 10 parts by mass, and more preferably 1 to 5 parts by mass with respect to 100 parts by mass of the monomer mixture. When the amount used is small, the particle size of the obtained particles tends to be large, and when the amount used is large, the particle size tends to be small. Further, in addition to the anionic surfactant, a nonionic surfactant, a cationic surfactant, an amphoteric surfactant and the like can be used in combination.

Further, during emulsion polymerization, various additives such as pH adjusters such as sodium hydroxide and ammonia; dispersants, chelating agents, oxygen scavengers, builders, and seed latex for adjusting particle size can be appropriately used. .. Emulsion polymerization using seed latex is particularly preferable. The seed latex is a dispersion of fine particles that is the core of the reaction during emulsion polymerization. The particle size of the fine particles is often 100 nm or less. The fine particles are not particularly limited, and a general-purpose polymer such as an acrylic polymer is used. According to the seed polymerization method, a particulate copolymer having a relatively uniform particle size can be obtained.

The polymerization temperature at the time of carrying out the polymerization reaction is not particularly limited, but is usually 0 to 100 ° C, preferably 40 to 80 ° C. Emulsion polymerization is carried out in such a temperature range, and the polymerization reaction is stopped by adding a polymerization terminator or cooling the polymerization system at a predetermined polymerization conversion rate. The polymerization conversion rate at which the polymerization reaction is stopped is preferably 93% by mass or more, more preferably 95% by mass or more.

After terminating the polymerization reaction, if desired, the unreacted monomer is removed, the pH and solid content concentration are adjusted, and the particulate copolymer is obtained in a form (latex) dispersed in a dispersion medium. Then, if necessary, the dispersion medium may be replaced, or the dispersion medium may be evaporated to obtain a particulate binder in the form of a powder.

Known dispersants, thickeners, antiaging agents, defoaming agents, preservatives, antibacterial agents, blister inhibitors, pH adjusters, etc. are added to the obtained dispersion of the particulate copolymer as necessary. can do.

(Conductive material)
The conductive composition for an electrochemical device of the present invention contains a conductive material. The conductive material preferably contains carbon black, graphite, carbon nanotubes, graphene and the like, more preferably carbon black, graphite and carbon nanotubes, and particularly preferably carbon black and graphite. Since the conductivity is improved by using a mixture of carbon black and graphite as the conductive material, it is preferable to use a mixture of these. These conductive materials can be used alone or in combination of two or more.

Carbon black is a spherical aggregate in which several layers of graphitic carbon microcrystals are gathered to form a disordered layer structure. Specifically, acetylene black, ketjen black, other furnace black, channel black, thermal lamp black, etc. Can be exemplified. As the conductive material, only a single carbon black can be used alone, or a plurality of different types of carbon black can be used in combination.

The content ratio of carbon black in the conductive composition for an electrochemical element is preferably 3% by mass or more and 40% by mass or less, and further, from the viewpoint of maintaining good conductivity and obtaining a slurry having a viscosity suitable for high-speed coating. It is preferably 5% by mass or more and 30% by mass or less, and particularly preferably 7% by mass or more and 20% by mass or less. When the content ratio of carbon black is not more than the upper limit of the above range, it is possible to suppress the phenomenon that the viscosity becomes excessively high and it becomes difficult to produce a slurry. On the contrary, when the content ratio of carbon black is not more than the lower limit value in the above range, the phenomenon that the conductivity is excessively lowered can be suppressed.

(Wet material)
The conductive composition for an electrochemical device of the present invention preferably contains a wetting material. As the wetting material, it is preferable to use a polyamide polymer, a polyester polymer, or the like from the viewpoint of enhancing the wettability of the conductive composition with respect to the current collector and from the viewpoint of being able to uniformly coat the current collector.

（上記一般式（１）中、Ｒは、２、４、６あるいは８個のカルボン酸アミド基によって割りこまれた炭素数６〜１５０の脂肪族あるいは脂肪族と芳香族との両者を含む炭化水素基、炭素数２〜６０の脂肪族炭化水素基または炭素数６〜２０の芳香族炭化水素基、または２〜７５個の酸素原子（−Ｏ−）によって割りこまれた炭素数４〜１５０の脂肪族炭化水素基、Ｒ’は水素原子、炭素数１〜４のアルキル基または−Ｚ’−（Ｑ）ｙ−（ＯＨ）ｘ、ｘは１〜３、ｙは０または１、Ｚは炭素数２〜６のアルキレン基、Ｚ’は炭素数２〜６のＺと同じまたは異なるアルキレン基、ＱはＺおよび（または）Ｚ′に−Ｏ−またはカルボキシル基を介して連結されており、０〜９９個の酸素原子および（または）カルボン酸エステル基によって割りこまれている炭素数２〜２００の脂肪族炭化水素基、ｎは２〜３である。） (Polyamide polymer)
As the polyamide polymer, it is preferable to use one represented by the following general formula (1).

(In the above general formula (1), R is an aliphatic having 6 to 150 carbon atoms interrupted by 2, 4, 6 or 8 carboxylic acid amide groups, or a carbide containing both an aliphatic and an aromatic group. Hydrogen group, aliphatic hydrocarbon group having 2 to 60 carbon atoms or aromatic hydrocarbon group having 6 to 20 carbon atoms, or 4 to 150 carbon atoms interrupted by 2 to 75 oxygen atoms (-O-). An aliphatic hydrocarbon group, R'is a hydrogen atom, an alkyl group having 1 to 4 carbon atoms or -Z'-(Q) y- (OH) x, x is 1-3, y is 0 or 1, Z is 0 or 1. An alkylene group having 2 to 6 carbon atoms, Z'is the same or different alkylene group as Z having 2 to 6 carbon atoms, Q is linked to Z and / or Z'via an -O- or a carboxyl group. An aliphatic hydrocarbon group having 2 to 200 carbon atoms, which is interrupted by 0 to 99 oxygen atoms and / or a carboxylic acid ester group, n is 2 to 3).

（上記一般式（２）中、Ｒ^１が、分子当たり１〜３個のヒドロキシル基を有する化合物の有機ラジカル、又はシリコン原子に結合しない１〜３個のヒドロキシル基を有するポリシロキサンのラジカルであり、Ｒ^２が、二価の直鎖又は分枝脂肪酸又はシクロ脂肪酸ラジカルであり、ｘが２〜８、ｎが１０〜５００、且つｍが１〜３である。） (Polyester polymer)
As the polyester polymer, it is preferable to use one represented by the following general formula (2).

(In the above general formula (2), R ¹ is an organic radical of a compound having 1 to 3 hydroxyl groups per molecule, or a radical of a polysiloxane having 1 to 3 hydroxyl groups not bonded to a silicon atom. , R ² is a divalent linear or branched fatty acid or cyclo fatty acid radical, x is 2 to 8, n is 10 to 500, and m is 1 to 3.)

The content ratio of the wetting material in the conductive composition for an electrochemical element is preferably 0.1 from the viewpoint of enhancing the wettability of the conductive composition with respect to the current collector and from the viewpoint of being able to uniformly coat the current collector. It is ~ 3% by mass, more preferably 0.2 to 2% by mass, and particularly preferably 0.3 to 1% by mass. When the content ratio of the wet material is not more than the upper limit value in the above range, the phenomenon that the resistance value of the coating film made of the conductive adhesive layer is excessively increased can be suppressed. On the contrary, when the content ratio of the wetting material is not more than the lower limit of the above range, the phenomenon that the wettability is excessively lowered and uniform coating becomes difficult can be suppressed.

(Dispersant)
The conductive composition for an electrochemical device of the present invention preferably contains a dispersant. Examples of the dispersant include anionic surfactants, cationic surfactants, amphoteric surfactants, and polymer-based surfactants. Specifically, β-naphthalene sulfonic acid formarin condensate sodium salt (for example, Demol NL: manufactured by Kao Co., Ltd.), alkylbenzyldimethylammonium chloride (for example, Sanizole C: manufactured by Kao Co., Ltd.), lauryldimethylamine oxide (for example, manufactured by Kao Co., Ltd.). , Anchtor 20N: manufactured by Kao Co., Ltd.), polyoxyethylene distyrene phenyl ether (for example, Emulgen A-60: manufactured by Kao Co., Ltd.), β-naphthalene sulfonic acid formarin condensate sodium salt, and polyoxy. Ethylene distyrene phenyl ether is preferable, and β-naphthalene sulfonic acid formarin condensate sodium salt is more preferable.

The content ratio of the dispersant in the conductive composition for an electrochemical element is preferably 0.5 to 5% by mass, more preferably 0.8 to 3.5% by mass, from the viewpoint that carbon black is easily dispersed in water. %, Especially preferably 1.1 to 2% by mass. When the content ratio of the dispersant is not more than the upper limit value in the above range, the phenomenon that the resistance value of the coating film composed of the conductive adhesive layer is excessively increased can be suppressed. On the contrary, when the content ratio of the dispersant is not more than the lower limit of the above range, the phenomenon that carbon black is excessively difficult to disperse in water can be suppressed.

(Dispersion medium and other components)
The conductive composition for an electrochemical element of the present invention is a slurry-like composition in which the above-mentioned chitosan compound, particulate copolymer, conductive material, wetting material, and dispersant are dispersed in a dispersion medium. Here, as the dispersion medium, water and various organic solvents such as NMP, toluene, xylene, and acetone can be used without particular limitation as long as each of the above components can be uniformly dispersed and the dispersed state can be maintained stably. Among them, it is preferable to use water or NMP, and it is more preferable to use water.

The content ratio of the dispersion medium in the conductive composition for an electrochemical element is preferably 60 to 90% by mass, more preferably 65 to 85% by mass, and particularly preferably 68 to 85 from the viewpoint of obtaining a viscosity suitable for coating. It is mass%.

Additives such as preservatives can be further added to the conductive composition for an electrochemical device of the present invention, if necessary.
Specific examples of the preservative include 2-methyl-4-isothiazolin-3-one (hereinafter, may be referred to as "MIT") and 1,2-benz-4-isothiazolin-3-one (hereinafter, referred to as "MIT"). (Sometimes referred to as “BIT”) and the like. These isothiazolin-based compounds can be used alone or in combination of two or more. As the isothiazolin-based compound, it is more preferable to use MIT and BIT in combination.

(Conductive composition for electrochemical device)
The conductive composition for an electrochemical device of the present invention is in the form of a slurry, and its viscosity is preferably 200 mPa · s or less, more preferably 150 mPa · s or less, and particularly preferably 150 mPa · s or less, from the viewpoint of obtaining good coatability. It is 100 mPa · s or less. The viscosity is a value measured at 25 ° C. and a rotation speed of 60 rpm using a B-type viscometer.

The pH of the conductive composition for an electrochemical element of the present invention is 6 to 10, preferably 6.5 to 9.7, from the viewpoint of obtaining a low resistance electrode without corroding the current collector. More preferably, it is 7 to 9.5.

(Manufacturing method of conductive composition for electrochemical device)
The method for producing the conductive composition is not particularly limited, and any means may be used as long as it can be dispersed in the above-mentioned dispersion medium. For example, first, a dispersant, a wetting material, a chitosan compound, a dispersion of a particulate copolymer, and any component to be added as necessary are collectively added to the dispersion medium, and the mixture is uniformly stirred, and then the conductive material is added. Then, it is preferable that the raw material composition is obtained by performing preliminary dispersion by stirring, and then the raw material composition is subjected to a high-pressure dispersion treatment using a high-pressure disperser.

Here, the rotation speed at the time of performing preliminary dispersion is usually 500 to 3000 rpm, preferably 700 to 1800 rpm, and more preferably 1000 to 1500 rpm from the viewpoint of obtaining good dispersibility.

Further, the high-pressure disperser is a device that makes the raw material composition high-pressure and ejects it from a narrow gap such as a nozzle, and is not particularly limited as long as it can loosen the aggregation of carbon black, but Nanovaita (C-ES008, Yoshida Kikai Kogyo) It is preferable to use (manufactured by Co., Ltd.). The pressure when performing the high-pressure dispersion treatment is usually 20 to 150 MPa, preferably 30 to 110 MPa, and more preferably 40 to 70 MPa from the viewpoint of obtaining good dispersibility.

(Current collector with adhesive layer)
The current collector with an adhesive layer of the present invention has a conductive adhesive layer obtained from the above-mentioned conductive composition for an electrochemical element on the current collector.

The material of the current collector is, for example, a metal, carbon, a conductive polymer, or the like, and a metal is preferably used. As the metal for the current collector, aluminum, platinum, nickel, tantalum, titanium, stainless steel, copper, other alloys and the like are usually used. Among these, copper, aluminum or an aluminum alloy is preferably used from the viewpoint of conductivity and withstand voltage.
The thickness of the current collector is 5 to 100 μm, preferably 8 to 70 μm, and particularly preferably 10 to 50 μm.

The method for forming the conductive adhesive layer is not particularly limited. For example, it is formed on the current collector by a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, a die coating method, a brush coating, or the like. Further, after forming the conductive adhesive layer on the release paper, this may be transferred to the current collector.

Examples of the method for drying the conductive adhesive layer include drying with warm air, hot air, and low humidity air, vacuum drying, and drying with irradiation with (far) infrared rays or electron beams. Of these, a drying method using hot air and a drying method using far-infrared irradiation are preferable. The drying temperature and drying time are preferably a temperature and a time during which the solvent in the conductive composition coated on the current collector can be completely removed, and the drying temperature is usually 50 to 300 ° C., preferably 80 to 250 ° C. The drying time is usually 2 hours or less, preferably 5 seconds to 30 minutes.

The thickness of the conductive adhesive layer is 0.5 to 5 μm, preferably 0.5 to 4 μm, from the viewpoint of obtaining an electrode having good adhesion to the electrode composition layer described later and low resistance. Particularly preferably, it is 0.5 to 3 μm.

The conductive adhesive layer has a composition corresponding to the solid content composition of the conductive composition for an electrochemical element, and contains a chitosan compound, a particulate copolymer, a conductive material, a wetting material, and a dispersant.

(Electrodes for electrochemical devices)
The electrode for an electrochemical element of the present invention has an electrode composition layer containing an electrode active material on the conductive adhesive layer of the current collector with the adhesive layer. The electrode composition layer is composed of an electrode active material, an electrode binder, an electrode conductive material used as necessary, and the like, and is prepared from an electrode slurry containing these components.

(Electrode active material)
The electrode active material may be a negative electrode active material or a positive electrode active material. The electrode active material is a substance that transfers electrons in the battery. Hereinafter, a case where the electrode for an electrochemical device of the present invention is used in a lithium ion secondary battery will be described.
The positive electrode active material is a compound capable of occluding and releasing lithium ions. Positive electrode active materials are roughly classified into those composed of inorganic compounds and those composed of organic compounds.

Examples of the positive electrode active material composed of an inorganic compound include a transition metal oxide, a composite oxide of lithium and a transition metal, and a transition metal sulfide. Fe, Co, Ni, Mn and the like are used as the transition metal. Specific examples of the inorganic compounds used in the positive electrode active material include lithium-containing composite metal oxides such as LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiFePO ₄ , and LiFeVO ₄ ; TiS ₂ , TiS ₃ , non- Transition metal sulfides such as crystalline MoS ₂ ; transition metal oxides such as Cu ₂ V ₂ O ₃ , amorphous V ₂ O-P ₂ O ₅ , MoO ₃ , V ₂ O ₅ , V ₆ O ₁₃ Be done. These compounds may be partially elementally substituted.

Examples of the positive electrode active material composed of an organic compound include polyaniline, polypyrrole, polyacene, a disulfide compound, a polysulfide compound, and an N-fluoropyridinium salt. The positive electrode active material may be a mixture of the above-mentioned inorganic compound and organic compound.

Examples of the negative electrode active material include allotropes of carbon such as graphite and coke. The negative electrode active material composed of the allotrope of carbon can also be used in the form of a mixture with a metal, a metal salt, an oxide, or the like, or a covering body. Examples of the negative electrode active material include oxides such as silicon, tin, zinc, manganese, iron and nickel, sulfates, metallic lithium, lithium alloys such as Li-Al, Li-Bi-Cd and Li-Sn-Cd. Lithium transition metal nitride, silicone and the like can be used.

The volume average particle size of the electrode active material is usually 0.01 to 100 μm, preferably 0.05 to 50 μm, and more preferably 0.1 to 20 μm for both the positive electrode active material and the negative electrode active material. These electrode active materials can be used alone or in combination of two or more.

(Binder for electrodes)
The electrode binder is not particularly limited as long as it is a compound capable of binding the electrode active material and the electrode conductive material to each other.

The amount of the electrode binder is such that the electrode composition layer and the conductive adhesive layer can be sufficiently adhered to each other, the capacity of the lithium ion battery can be increased, and the internal resistance can be reduced. It is usually in the range of 0.1 to 50 parts by mass, preferably 0.5 to 20 parts by mass, and more preferably 1 to 10 parts by mass with respect to 100 parts by mass of the substance.

(Conductive material for electrodes)
The conductive material for electrodes used as needed is made of particulate carbon allotrope, which has conductivity and does not have pores capable of forming an electric double layer, and specifically, furnace black and acetylene. Examples include black and conductive carbon blacks such as Ketjen Black (registered trademark of Akzonobel Chemicals Veslotenfen Note Shap). Among these, acetylene black and furnace black are preferable.

(Electrode composition layer)
The electrode composition layer is provided on the conductive adhesive layer, but the method for forming the electrode composition layer is not limited. The electrode slurry contains an electrode active material and an electrode binder as essential components, and if necessary, an electrode conductive material, a dispersant, and other additives can be blended. Specific examples of the dispersant include cellulosic polymers such as polyvinylidene fluoride, polytetrafluoroethylene, carboxymethyl cellulose, methyl cellulose, ethyl cellulose and hydroxypropyl cellulose, and ammonium salts or alkali metal salts thereof; poly (meth) acrylic acid. Poly (meth) acrylates such as sodium; polyvinyl alcohol, modified polyvinyl alcohol, polyethylene oxide, polyvinylpyrrolidone, polycarboxylic acid, oxidized starch, starch phosphate, casein, various modified starches and the like. These dispersants can be used alone or in combination of two or more. The amount of these dispersants is not particularly limited, but is usually 0.1 to 10 parts by mass, preferably 0.5 to 5 parts by mass, and more preferably 0 parts by mass with respect to 100 parts by mass of the electrode active material. It is in the range of 8 to 2 parts by mass.

When forming the electrode composition layer, the paste-like electrode slurry (positive electrode slurry or negative electrode slurry) is an essential component of the electrode active material and the electrode binder, and an electrode conductive material and dispersion used as necessary. The agent and additive can be produced by kneading with water or an organic solvent such as N-methyl-2-pyrrolidone or tetrahydrofuran.

The solvent used to obtain the electrode slurry is not particularly limited, but when the above-mentioned dispersant is used, a solvent capable of dissolving the dispersant is preferably used. Specifically, water is usually used, but an organic solvent may be used, or a mixed solvent of water and an organic solvent may be used. Examples of the organic solvent include alkyl alcohols such as methyl alcohol, ethyl alcohol and propyl alcohol; alkyl ketones such as acetone and methyl ethyl ketone; ethers such as tetrahydrofuran, dioxane and jigglime; diethylformamide, dimethylacetamide and N-methyl- Examples thereof include amides such as 2-pyrrolidone and dimethylimidazolidinone; sulfur-based solvents such as dimethylsulfoxide and sulfolane; and the like. Among these, alcohols are preferable as the organic solvent. As the electrode slurry, an aqueous slurry using water as a dispersion medium is preferable from the viewpoint of easy drying of the electrode composition layer and excellent load on the environment. When water and an organic solvent having a boiling point lower than that of water are used in combination, the drying rate can be increased during drying. In addition, the dispersibility of the binder for electrodes or the solubility of the dispersant changes depending on the amount or type of the organic solvent used in combination with water. As a result, the viscosity and fluidity of the electrode slurry can be adjusted, and the production efficiency can be improved.

Regarding the amount of solvent used when preparing the electrode slurry, the solid content concentration of the slurry is usually 1 to 90% by mass, preferably 5 to 85% by mass, more preferably from the viewpoint of uniformly dispersing each component. The amount is in the range of 10 to 80% by mass.

The method or procedure for dispersing or dissolving the electrode active material, the electrode binder, and the electrode conductive material, the dispersant, and the additive used as needed in the solvent is not particularly limited, and for example, the electrode active material in the solvent. Method of adding and mixing electrode binder, electrode conductive material, dispersant and additive; after dissolving the dispersant in the solvent, add the electrode binder dispersed in the solvent and mix, and finally the electrode active material. And a method of adding and mixing the electrode conductive material; the electrode active material and the electrode conductive material are added to and mixed with the electrode binder dispersed in the solvent, and the dispersant dissolved in the solvent is added to this mixture. And the method of mixing. Examples of the mixing means include mixing equipment such as a ball mill, a sand mill, a bead mill, a pigment disperser, a grinder, an ultrasonic disperser, a homogenizer, a homomixer, and a planetary mixer. Mixing is usually carried out in the range of room temperature to 80 ° C. for 10 minutes to several hours.

The viscosity of the electrode slurry is usually 10 to 100,000 mPa · s, preferably 30 to 50,000 mPa · s, and more preferably 50 to 20,000 mPa · s at room temperature from the viewpoint of increasing productivity. The range.

The method of applying the electrode slurry onto the conductive adhesive layer is not particularly limited. For example, a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, a brush coating method and the like can be mentioned. The coating thickness of the slurry is appropriately set according to the thickness of the target electrode composition layer.

Examples of the drying method include drying with warm air, hot air, and low humidity air, vacuum drying, and drying with irradiation with (far) infrared rays or electron beams. Above all, the drying method by irradiation with far infrared rays is preferable. The drying temperature and the drying time are preferably a temperature and a time during which the solvent in the slurry applied to the current collector can be completely removed, and the drying temperature is 100 to 300 ° C., preferably 120 to 250 ° C. The drying time is usually 5 minutes to 100 hours, preferably 10 minutes to 20 hours.

The density of the electrode composition layer is not particularly limited, but is usually 0.30 to 10 g / cm ³ , preferably 0.35 to 8.0 g / cm ³ , and more preferably 0.40 to 6.0 g / cm ^3. Is. The thickness of the electrode composition layer is not particularly limited, but is usually 5 to 1000 μm, preferably 20 to 500 μm, and more preferably 30 to 300 μm.

(Electrochemical element)
Examples of the usage mode of the electrode for the electrochemical element include a lithium ion secondary battery, an electric double layer capacitor, a lithium ion capacitor, a sodium battery, a magnesium battery, and the like, and a lithium ion secondary battery using the above electrode is preferable. is there. For example, a lithium ion secondary battery is composed of the electrodes for an electrochemical element, a separator, and an electrolytic solution.

(Separator)
The separator is not particularly limited as long as it can insulate between the electrodes for the electrochemical element and allow cations and anions to pass through. Specifically, (a) a porous separator having pores, (b) a porous separator having a polymer coat layer formed on one or both sides, or (c) a porous resin coat layer containing an inorganic ceramic powder. Examples thereof include a porous separator in which is formed. Non-limiting examples of these are solids such as polypropylene-based, polyethylene-based, polyolefin-based, or aramid-based porous separators, polyvinylidene fluoride, polyethylene oxide, polyacrylonitrile, or polyvinylidene fluoride hexafluoropropylene copolymers. Use a polymer film for a polymer electrolyte or a gel-like polymer electrolyte, a separator coated with a gelled polymer coat layer, or a separator coated with an inorganic filler or a porous film layer made of a dispersant for the inorganic filler. be able to. The separators are arranged between the electrodes for the electrochemical device so that the pair of electrode composition layers face each other, and the device is obtained. The thickness of the separator is appropriately selected depending on the intended use, but is usually 1 to 100 μm, preferably 10 to 80 μm, and more preferably 15 to 60 μm.

(Electrolytic solution)
The electrolytic solution is not particularly limited, and for example, one in which a lithium salt is dissolved as a supporting electrolyte in a non-aqueous solvent can be used. Lithium salts include, for example, LiPF ₆ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAlCl ₄ , LiClO ₄ , CF ₃ SO ₃ Li, C ₄ F ₉ SO ₃ Li, CF ₃ COOLi, (CF ₃ CO) ₂ N Li. , (CF ₃ SO ₂ ) ₂ NLi, (C ₂ F ₅ SO ₂ ) NLi and other lithium salts. In particular, LiPF ₆ , LiClO ₄ , and CF ₃ SO ₃ Li, which are easily soluble in a solvent and show a high degree of dissociation, are preferably used. These can be used alone or in combination of two or more. The amount of the supporting electrolyte is usually 1% by mass or more, preferably 5% by mass or more, and usually 30% by mass or less, preferably 20% by mass or less, based on the electrolytic solution. If the amount of supporting electrolyte is too small or too large, the ionic conductivity will decrease and the charging and discharging characteristics of the battery will deteriorate.

The solvent used in the electrolytic solution is not particularly limited as long as it dissolves the supporting electrolyte, but is usually dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butylene. Alkyl carbonates such as carbonate (BC) and methyl ethyl carbonate (MEC); esters such as γ-butyrolactone, methyl formate, ethers such as 1,2-dimethoxyethane, and tetrahydrofuran; sulfolane, and dimethyl sulfoxide. Sulfur-containing compounds; are used. In particular, dimethyl carbonate, ethylene carbonate, propylene carbonate, diethyl carbonate, and methyl ethyl carbonate are preferable because high ionic conductivity can be easily obtained and the operating temperature range is wide. These can be used alone or in combination of two or more. It is also possible to use an electrolytic solution containing an additive. Further, as the additive, a carbonate-based compound such as vinylene carbonate (VC) is preferable.

As an electrolytic solution other than the above, polyethylene oxide, a polymer electrolyte such as polyacrylonitrile gel polymer electrolyte and impregnated with the electrolytic solution, lithium _{sulfide, LiI, Li 3 N, Li} 2 S-P 2 S such as ₅ glass ceramic Inorganic solid electrolytes can be mentioned.

A secondary battery is obtained by stacking a negative electrode and a positive electrode via a separator, winding or folding the secondary battery according to the shape of the battery, putting it in a battery container, injecting an electrolytic solution into the battery container, and sealing the battery. Further, if necessary, an expanded metal, an overcurrent prevention element such as a fuse or a PTC element, a lead plate, or the like can be inserted to prevent the pressure inside the battery from rising and overcharge / discharge. The shape of the battery may be any of a laminated cell type, a coin type, a button type, a sheet type, a cylindrical type, a square type, a flat type and the like.

According to the conductive composition for an electrochemical element of the present invention, the coatability to a current collector is excellent, and the output characteristics and cycle characteristics of the obtained electrochemical element are good.
Further, in the present invention, the conductive composition obtained by using the chitosan compound whose viscosity is controlled in an appropriate range and the particulate copolymer whose surface acid amount is controlled in an appropriate range is conductive. The dispersibility of the conductive carbon is good, and the conductive adhesive layer obtained by using this conductive composition has excellent strength and electrolytic solution resistance, and the electrode composition formed on the conductive adhesive layer. Excellent adhesion to the layer.

In the above-described embodiment, the configuration for forming the conductive adhesive layer using the conductive composition for an electrochemical element of the present invention has been described, but the conductive composition for an electrochemical element and the electrode of the present invention have been described. A composition (carbon paste) for an electrochemical element electrode containing an active material (preferably a positive electrode active material) may be prepared. In this case, the electrode can be obtained by applying and drying this composition for an electrochemical device electrode on a current collector. Further, an electrochemical device including the electrode, the separator and the electrolytic solution can be manufactured. Here, when a lithium ion secondary battery as an electrochemical element is manufactured, the above-mentioned electrode active material, current collector, separator, and electrolytic solution can be used.

Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited to these examples. Each characteristic is evaluated by the following method. Unless otherwise specified, "parts" and "%" in this embodiment are "parts by mass" and "% by mass", respectively.
The degree of swelling of the electrolytic solution and the amount of surface acid of the particulate copolymer were calculated and measured by the above-mentioned methods.

(Colability of conductive composition)
Using a gravure coater (μCoater350TM, manufactured by Yasui Seiki Co., Ltd.), a slurry-like conductive composition was applied onto an aluminum current collector foil at a speed of 5 m / min. The surface of the conductive adhesive layer formed on the aluminum current collector foil was observed, and the occurrence rate of uncoated parts on the aluminum current collector foil was determined. The incidence of uncoated parts was evaluated according to the following criteria, and the results are shown in Table 1. It is shown that the smaller the occurrence rate of uncoated parts, the better the coatability.
A: Uncoated part is 0% or more and less than 1% B: Uncoated part is 1% or more and less than 5% C: Uncoated part is 5% or more and less than 10% D: Uncoated part is 10% or more

(Output characteristics of lithium-ion secondary battery)
Using the laminated cells prepared in Examples and Comparative Examples, the cells were charged at 25 ° C. with a constant current of 0.1 C to a charging depth (SOC) of 50%, and the voltage V1 was measured. Then, it was discharged at 25 ° C. at a constant current of 5C for 10 seconds, and the voltage V2 was measured. From these measurement results, the voltage drop ΔV = V1-V2 was calculated. The calculated voltage drop ΔV was evaluated according to the following criteria, and the results are shown in Table 1. The smaller the value of the voltage drop ΔV, the better the output characteristics.
A: Voltage drop ΔV is 100 mV or more and less than 150 mV B: Voltage drop ΔV is 150 mV or more and less than 200 mV C: Voltage drop ΔV is 200 mV or more and less than 250 mV D: Voltage drop ΔV is 250 mV or more and less than 300 mV

(Cycle characteristics of lithium-ion secondary battery)
The lithium ion secondary batteries prepared in Examples and Comparative Examples were allowed to stand for 24 hours in an environment of 25 ° C. Then, in an environment of 25 ° C., the initial capacitance C0 was measured by performing a charge / discharge operation of charging to 4.2 V at a rate of 1.0 C and discharging to 3.0 V. Further, this lithium ion secondary battery was repeatedly charged and discharged 200 times (200 cycles) in the same manner as described above in an environment of 60 ° C., and the capacity C1 after 200 cycles was measured. The cycle characteristic (high temperature cycle characteristic) was evaluated by calculating the capacity retention rate ΔC represented by ΔC = (C1 / C0) × 100 (%) according to the following criteria. The higher the value of the capacity retention rate ΔC, the better the cycle characteristics.
A: Capacity retention rate ΔC is 85% or more B: Capacity retention rate ΔC is 80% or more and less than 85% C: Capacity retention rate ΔC is 75% or more and less than 80% D: Capacity retention rate ΔC is less than 75%

(Measurement of viscosity of chitosan solution)
An aqueous solution consisting of 0.5% chitosan and 0.5% acetic acid used in each Example and each Comparative Example was prepared, and the viscosity thereof was measured by a Brookfield Digital Viscometer (hereinafter, may be referred to as "B-type viscometer"). Measured using LVDV-IIPro. The value 60 seconds after the start of the measurement was taken as the measured value of the viscosity of the chitosan solution, and the unit was shown as mPa · s. The measurement conditions were a temperature of 25 ° C., a rotation speed of 60 rpm, and a spindle shape of 4.

(Example 1)
(Production of Particulate Copolymer)
63.4 parts of 2 ethylhexyl acrylate, 2.5 parts of itaconic acid, 34.1 parts of styrene, 2 parts of ammonium lauryl sulfate (anionic surfactant), and ion-exchanged water in a stainless steel pressure reactor equipped with a stirrer. 108 parts were added and stirred. Then, after raising the temperature in the reactor to 60 ° C., 10 parts of a 4% potassium persulfate aqueous solution was added to start the polymerization reaction. Then, the polymerization reaction was allowed to proceed, and when the polymerization conversion rate reached 70%, the reaction temperature was raised to 70 ° C. While maintaining the reaction temperature at 70 ° C., the polymerization reaction was continued until the polymerization conversion rate reached 97%. The reaction system was cooled to room temperature, the polymerization reaction was stopped, and the pressure was reduced to remove unreacted monomers. Ion-exchanged water was added to adjust the solid content concentration to 45% and the pH of the dispersion to 7.5 to obtain a dispersion of the particulate copolymer. The pH of the dispersion was adjusted by adding a 10% aqueous ammonia solution. The volume average particle diameter of the obtained particulate copolymer was about 300 nm, the amount of surface acid was 0.2 mmol / g, and the degree of swelling of the electrolytic solution was 120%.

(Manufacturing of conductive composition)
1.5 parts of anionic surfactant (Demor NL, manufactured by Kao) as a dispersant in ion-exchanged water, 0.5 part of polyester polymer (DISPERBYK-2010, manufactured by BYK) as a wetting material, and chitosan with a viscosity of 50 mPa · s. Aqueous solution (an aqueous solution containing 0.5% of chitosan 50 (manufactured by Wako Pure Chemical Industries, Ltd.) and 0.5% of acetic acid) (In the following examples and comparative examples, the chitosan aqueous solution contains acetic acid in addition to the chitosan compound. (Including 5%) is equivalent to 2 parts of chitosan solid content, 4 parts of the particulate copolymer (styrene / acrylic acid polymer) obtained above is equivalent to solid content, and an aqueous solution of inchazoline compound (ACTICIDE) as an antiseptic. (Registered Trademark), MBS (2-methyl-4-isothiazolin-3-one (MIT) / 1,2-benz-4-isothiazolin-3-one (BIT) = 50/50 5% aqueous solution), Saw. (Made in Japan) was added in an amount equivalent to 0.1 part of a solid content, and the mixture was stirred at 1000 rpm for 10 minutes. After confirming that the mixture was uniformly agitated, a carbon material (5 parts of carbon black (Denka Black, manufactured by Denka Kagaku Kogyo Co., Ltd.) and 15 parts of graphite) was added as a conductive material for preliminary dispersion. The mixture was stirred at 1200 rpm for 10 minutes using a dispar. After that, the temperature of the raw material composition was cooled to 20 ° C., a nanovaita (C-ES008, manufactured by Yoshida Kikai Kogyo Co., Ltd.) was used as a high-pressure disperser, a cross-type nozzle having a nozzle diameter of 400 μm was used, and the condition was 50 MPa. The high-pressure dispersion treatment was carried out twice to prepare a conductive composition. The solid content concentration of the obtained conductive composition was 25% by mass. The value obtained by dividing the mass of chitosan contained in the obtained conductive composition by the mass of the particulate copolymer was 0.5.

(Formation of conductive adhesive layer)
The obtained conductive composition was applied to one side of the aluminum current collector foil at a speed of 5 m / min using a gravure coater (μCoater350TM, manufactured by Yasui Seiki). A conductive adhesive layer having a thickness of about 1 μm was formed at a drying temperature of 100 ° C.

(Preparation of electrodes)
As an electrode active material for the positive electrode, 94 parts of lithium-containing nickel-manganese-cobalt composite oxide having a volume average particle diameter of 20 μm is used, and as a binder for the positive electrode, a 9.0% aqueous solution of polyvinylidene fluoride (HSV900, manufactured by Kynar) is equivalent to the solid content. A slurry was prepared by adding 3 parts of acetylene black (Denka Black powder, manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive material for electrodes, and N-methylpyrrolidone as a solvent. Kneading was repeated using a kneader (Kentaro, manufactured by Shinky Co., Ltd.) while gradually adding N-methylpyrrolidone to reduce the solid content concentration. Finally, the total solid content concentration was reduced to 55% to obtain a viscosity suitable for coating, and a slurry for a positive electrode was obtained. The positive electrode slurry was applied to the surface of the current collector at an electrode forming rate of 20 m / min on the aluminum current collector on which the conductive adhesive layer was formed, and the temperature was 80 ° C. for 20 minutes and then 120 ° C. for 20 minutes. After drying, it was cut out to a size of 4.0 cm × 3.8 cm to form a positive electrode composition layer having a thickness of 100 μm on one side. Then, it was rolled by a roll press to obtain a positive electrode plate having a thickness of 50 μm.

On the other hand, 100 parts of graphite (KS-6, manufactured by Timcal) having a volume average particle diameter of 3.7 μm was used as the electrode active material of the negative electrode, and a 1.5% aqueous solution of carboxymethyl cellulose (MAC350HC, Nippon Paper Chemical Co., Ltd.) was used as the dispersant. 1 part equivalent to solid content, 40% aqueous dispersion of diene polymer with glass transition temperature of -48 ° C and number average particle size of 0.18 μm as a binder for negative electrode, 1 part equivalent to solid content , And ion-exchanged water were mixed using a planetary mixer so that the total solid content concentration was 50%, and a slurry for a negative electrode was prepared having a viscosity suitable for coating. This negative electrode slurry is applied to one side of a copper foil having a thickness of 18 μm using an applicator so that the film thickness after drying is about 100 μm, dried at 50 ° C. for 20 minutes, and then heat-treated at 110 ° C. for 20 minutes. The negative electrode composition layer was formed. Then, it was rolled by a roll press to obtain a negative electrode plate having a thickness of 50 μm.

(Battery manufacturing)
Using the positive electrode, the negative electrode, and the separator, a laminated laminated cell-shaped lithium ion battery was produced. As the electrolytic solution, LiPF ₆ was dissolved at a concentration of 1.0 mol / liter in a solvent obtained by adding 2.0% of vinylene carbonate to a mixture of ethylene carbonate and ethyl methyl carbonate at a mass ratio of 3: 7 and mixing them. I used the one that was made to.

(Example 2)
The conductive composition was produced in the same manner as in Example 1 except that the type of chitosan compound used was changed to chitosan 5 (manufactured by Wako Pure Chemical Industries, Ltd.) and an aqueous chitosan solution having a viscosity of 5 mPa · s was used. It was. Except for using this conductive composition, electrodes and batteries were produced in the same manner as in Example 1.

(Example 3)
The conductive composition was produced in the same manner as in Example 1 except that the type of chitosan compound used was changed to chitosan 500 (manufactured by Wako Pure Chemical Industries, Ltd.) and an aqueous chitosan solution having a viscosity of 500 mPa · s was used. It was. Except for using this conductive composition, electrodes and batteries were produced in the same manner as in Example 1.

(Example 4)
A particulate copolymer was produced in the same manner as in Example 1 except that the amount of 2 ethylhexyl acrylate was changed to 63.7 parts, the amount of itaconic acid was changed to 2 parts, and the amount of styrene was changed to 34.3 parts. .. The volume average particle diameter of the obtained particulate copolymer was about 300 nm, the amount of surface acid was 0.15 mmol / g, and the degree of swelling of the electrolytic solution was 120%. A conductive composition was produced in the same manner as in Example 1 except that this particulate copolymer was used. Further, except that this conductive composition was used, electrodes and batteries were produced in the same manner as in Example 1.

(Example 5)
A particulate copolymer was produced in the same manner as in Example 1 except that the amount of 2 ethylhexyl acrylate was changed to 64 parts, the amount of itaconic acid was changed to 1.5 parts, and the amount of styrene was changed to 34.5 parts. .. The volume average particle diameter of the obtained particulate copolymer was about 300 nm, the amount of surface acid was 0.1 mmol / g, and the degree of swelling of the electrolytic solution was 120%. A conductive composition was produced in the same manner as in Example 1 except that this particulate copolymer was used. Further, except that this conductive composition was used, electrodes and batteries were produced in the same manner as in Example 1.

(Example 6)
A particulate copolymer was produced in the same manner as in Example 1 except that the amount of 2 ethylhexyl acrylate was changed to 73.1 parts and the amount of styrene was changed to 24.4 parts. The volume average particle size of the obtained particulate copolymer was about 300 nm, the amount of surface acid was 0.2 mmol / g, and the degree of swelling of the electrolytic solution was 150%. A conductive composition was produced in the same manner as in Example 1 except that this particulate copolymer was used. Further, except that this conductive composition was used, electrodes and batteries were produced in the same manner as in Example 1.

(Example 7)
A conductive composition was produced in the same manner as in Example 6 except that 0.4 part of a chitosan aqueous solution having a viscosity of 50 mPa · s was used, which was equivalent to the solid content of chitosan. The value obtained by dividing the mass of chitosan contained in the obtained conductive composition by the mass of the particulate copolymer was 0.1. Except for using this conductive composition, electrodes and batteries were produced in the same manner as in Example 1.

(Example 8)
A particulate copolymer was produced in the same manner as in Example 1 except that the amount of 2-ethylhexyl acrylate was changed to 82.9 parts and the amount of styrene was changed to 14.6 parts. The volume average particle diameter of the obtained particulate copolymer was about 300 nm, the amount of surface acid was 0.2 mmol / g, and the degree of swelling of the electrolytic solution was 180%. A conductive composition was produced in the same manner as in Example 1 except that this particulate copolymer was used. Further, except that this conductive composition was used, electrodes and batteries were produced in the same manner as in Example 1.

(Comparative Example 1)
The particulate copolymer was produced in the same manner as in Example 1 except that the amount of 2 ethylhexyl acrylate was changed to 64.7 parts, the amount of itaconic acid was changed to 0.5 parts, and the amount of styrene was changed to 34.8 parts. went. The volume average particle diameter of the obtained particulate copolymer was about 300 nm, the amount of surface acid was 0.05 mmol / g, and the degree of swelling of the electrolytic solution was 120%. A conductive composition was produced in the same manner as in Example 1 except that this particulate copolymer was used. Further, except that this conductive composition was used, electrodes and batteries were produced in the same manner as in Example 1.

(Comparative Example 2)
The conductive composition was produced in the same manner as in Example 1 except that an aqueous chitosan solution having a viscosity of 0.5 mPa · s was used in the production of the conductive composition. Except for using this conductive composition, electrodes and batteries were produced in the same manner as in Example 1.
The chitosan aqueous solution having a viscosity of 0.5 mPa · s is a nanovaita (C-ES008, Yoshida) using an aqueous solution containing 0.5% of chitosan 5 (manufactured by Wako Pure Chemical Industries, Ltd.) and 0.5% of acetic acid as a high-pressure disperser. It was obtained by performing a high-pressure dispersion treatment three times under the condition of 200 MPa using a cross-type nozzle having a nozzle diameter of 400 μm using a machine manufactured by Kikai Kogyo Co., Ltd.

(Comparative Example 3)
Examples except that an aqueous chitosan solution having a viscosity of 1000 mPa · s (an aqueous solution containing 0.5% of Daichitosan H (manufactured by Dainichiseika Kogyo) and 0.5% of acetic acid) was used in the production of the conductive composition. The conductive composition was produced in the same manner as in 1. Except for using this conductive composition, electrodes and batteries were produced in the same manner as in Example 1.

As shown in Table 1, a chitosan compound having a viscosity of 1 mPa · s or more and 500 mPa · s or less dissolved in a 0.5% acetic acid aqueous solution so as to be 0.5% by mass, and a surface acid amount of 0. A conductive composition for an electrochemical element containing a particulate copolymer having a concentration of 1 mmol / g or more and a conductive material is excellent in coatability. Further, when the conductive adhesive layer is formed by using this conductive composition for an electrochemical device, the obtained battery is excellent in output characteristics and cycle characteristics.

Claims (6)

A chitosan compound having a viscosity of 1 mPa · s or more and 500 mPa · s or less of an aqueous solution dissolved in a 0.5% acetic acid aqueous solution so as to be 0.5% by mass.
It comprises an aromatic vinyl monomer unit, a (meth) acrylic acid ester monomer unit and an acidic group-containing monomer unit.
Electrolyte swelling it ((after dipping mass B / dipping mass before A) × 100) is der than 500% 100% or more, the after dipping mass B, the temperature 60 ° C. of the electrolyte (ethylene carbonate (EC) In a mixed solvent prepared by mixing and ethyl methyl carbonate (EMC) at a mass ratio of EC: EMC = 3: 7 at 20 ° C., in which LiPF ₆ is dissolved at a concentration of 1.0 mol / L). pulling up the immersed film after 72 hours, Ri mass der which wipe off the electrolyte was measured immediately with a towel paper one,
Particulate copolymer having a surface acid amount of 0.1 mmol / g or more and
Including conductive material
A conductive composition for an electrochemical element in which the value obtained by dividing the mass of the chitosan compound by the mass of the particulate copolymer is 0.1 or more and 10 or less. The content ratio of the aromatic vinyl monomer unit to the total amount of the aromatic vinyl monomer unit and the (meth) acrylic acid ester monomer unit contained in the particulate copolymer is 10% by mass or more and 70% by mass or less. The conductive composition for an electrochemical element according to claim 1. The content ratio of the (meth) acrylic acid ester monomer unit to the total amount of the aromatic vinyl monomer unit and the (meth) acrylic acid ester monomer unit contained in the particulate copolymer is 30% by mass or more and 90. The conductive composition for an electrochemical element according to claim 1 or 2, which has a mass% or less. A composition for an electrochemical element electrode, comprising the conductive composition for an electrochemical element according to any one of claims 1 to 3, and containing an electrode active material. A current collector with an adhesive layer, which has a conductive adhesive layer on the current collector using the conductive composition for an electrochemical element according to any one of claims 1 to 3. An electrode for an electrochemical element, which has an electrode composition layer containing an electrode active material on the conductive adhesive layer of the current collector with an adhesive layer according to claim 5.

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