WO2015098116A1

WO2015098116A1 - Conductive material paste for secondary battery electrode, method for producing slurry for secondary battery cathode, method for producing secondary battery cathode, and secondary battery

Info

Publication number: WO2015098116A1
Application number: PCT/JP2014/006464
Authority: WO
Inventors: 真弓福峯; 高橋　直樹; 麻貴片桐
Original assignee: 日本ゼオン株式会社
Priority date: 2013-12-27
Filing date: 2014-12-25
Publication date: 2015-07-02
Also published as: CN105814718A; CN105814718B; KR20160102404A; KR102393257B1

Abstract

The objective of the present invention is to provide a conductive material paste that is for a secondary battery electrode and that can form an electrode having superior electrical potential stability and superior dispersion stability. The conductive material paste for a secondary battery electrode contains a conductive material and a binder (A), the binder (A) contains an alkylene structural unit and/or a (meth)acrylate ester monomer unit, and the binder adsorption amount of the conductive material is 100-600 mg/g inclusive.

Description

Conductive material paste for secondary battery electrode, method for producing slurry for secondary battery positive electrode, method for producing positive electrode for secondary battery, and secondary battery

The present invention relates to a conductive paste for a secondary battery electrode, a method for producing a slurry for a secondary battery positive electrode, a method for producing a positive electrode for a secondary battery, and a secondary battery.

Secondary batteries, especially lithium ion secondary batteries, are small and light, have high energy density, and can be repeatedly charged and discharged, and are used in a wide range of applications. In particular, in recent years, lithium ion secondary batteries have attracted attention as an energy source for electric vehicles (EV) and hybrid electric vehicles (HEV), and higher performance is required. Therefore, in recent years, improvement of battery members such as electrodes has been studied for the purpose of further improving the performance of secondary batteries such as lithium ion secondary batteries. Specifically, in order to improve the performance of the secondary battery, it has been studied to improve the electrical characteristics by improving battery members such as electrodes.

Here, for example, an electrode for a lithium ion secondary battery usually includes a current collector and an electrode mixture layer formed on the current collector. The electrode mixture layer, for example, the positive electrode mixture layer is usually formed by dispersing a positive electrode slurry as an electrode slurry on a current collector, in which a positive electrode active material, a conductive material, a binder, and the like are dispersed or dissolved in a dispersion medium. It is formed by applying and drying and binding a positive electrode active material, a conductive material, and the like with a binder.
In general, the composition of the electrode slurry and the manufacturing process thereof affect the properties of the obtained electrode slurry. And the property of the slurry for electrodes influences the electrical property of a secondary battery provided with the electrode compound-material layer formed using this slurry for electrodes.
Thus, attempts have been made to improve the slurry for electrodes in order to achieve further improvement in performance of the secondary battery (see, for example, Patent Document 1).

In Patent Document 1, a mixture of a fluorine-based polymer and nitrile rubber or hydrogenated nitrile rubber is used as a binder to be blended in an electrode slurry for forming an electrode mixture layer, and nitrile rubber or hydrogenated nitrile rubber is used. It has been proposed to improve the performance of the electrode and improve the energy density and cycle characteristics of the secondary battery by a synergistic effect of having high adhesiveness and bonding of the fluoropolymer in the fiber state. Yes.

On the other hand, attempts have been made to further improve the performance of secondary batteries by changing the manufacturing procedure of the slurry for electrodes. Specifically, by preparing a conductive material paste in which a binder and a conductive material are dissolved or dispersed in a solvent, and using an electrode slurry obtained by combining the conductive material paste and the positive electrode active material, Techniques for improving various performances of batteries have been reported (see, for example, Patent Documents 2 to 4).
In Patent Document 2, when preparing a slurry for a positive electrode containing a mixture of a fluorinated polymer and a hydrogenated nitrile rubber as a binder, an organic solvent solution of the fluorinated polymer, a hydrogenated nitrile rubber, and a conductive material are previously added. After mixing to obtain a conductive material paste, the conductive material paste and the positive electrode active material are mixed to prepare a positive electrode slurry, thereby improving the performance of the positive electrode and reducing the battery capacity in large current discharge. It has been proposed to provide fewer secondary batteries.

In Patent Document 3, a lithium-containing transition metal oxide as a positive electrode active material, a first binder A such as a fluorine-based polymer and a paste A containing a dispersion medium, carbon black as a conductive material, hydrogenated nitrile rubber, and the like The second binder B and the paste B (conductive material paste) containing the dispersion medium are prepared, and the positive electrode slurry obtained by mixing the paste A and the paste B is used for forming the positive electrode. It has been proposed that a hydrogenated nitrile rubber having a low affinity with a fluorine-based polymer is disposed on the surface to suppress aggregation of the conductive material due to the fluorine-based polymer.

Further, in Patent Document 4, a conductive material paste containing a conductive material and a binder is prepared, and the obtained conductive material paste is diluted with a solvent, and then a lithium-transition metal composite oxide as a positive electrode active material is added and stirred. Thus, by preparing the positive electrode slurry, it is possible to improve the dispersibility of the conductive material in the positive electrode mixture layer and increase the fine pores through which the electrolyte can permeate, thereby ensuring the ionic conductivity of the positive electrode. Proposed.

Japanese Patent Laid-Open No. 9-63590 Japanese Patent No. 4502311 Japanese Patent No. 3585122 JP 2001-238331 A

Here, the secondary battery is not only required to improve the low temperature characteristics by further reducing the internal resistance and ensure high output, but also, for example, the above-described electric vehicle (EV) or hybrid electric vehicle (HEV). It is required to ensure high-temperature storage characteristics and high-temperature cycle characteristics in order to fully exhibit its performance even in a high-temperature environment such as In order to improve the electrical characteristics of such a secondary battery, it is necessary to ensure durability (potential stability) with respect to voltage application of the electrode while ensuring conductivity in the electrode. Furthermore, when manufacturing a battery industrially, the dispersion stability of the electrode slurry and the conductive material paste used for preparing the electrode slurry is also very important.
However, even if the technique of Patent Document 1 is used, sufficient potential stability of the electrode cannot be obtained. Further, even if the technique using the conductive material paste in the above Patent Documents 2 to 4 is used, sufficient potential stability of the electrode is not obtained, and in addition, the dispersion stability of the conductive material paste is satisfactory. It wasn't.
Therefore, the above conventional technology still has room for improvement in terms of improving the potential stability of the electrode while improving the dispersion stability of the conductive material paste, and exhibiting excellent electrical characteristics in the secondary battery. there were.

Then, an object of this invention is to provide the electrically conductive material paste for secondary battery electrodes which can form the electrode which is excellent in dispersion stability and excellent in electric potential stability.
Moreover, an object of this invention is to provide the manufacturing method of the slurry for secondary battery positive electrodes which can improve the electrical property and can improve the performance of a secondary battery.
Furthermore, an object of this invention is to provide the manufacturing method of the positive electrode for secondary batteries which can improve the electrical property and can improve the performance of a secondary battery.
In addition, an object of the present invention is to provide a secondary battery having excellent electrical characteristics.

The present inventors have intensively studied for the purpose of solving the above-mentioned problems and found the following points.

First, the present inventors have excellent dispersion stability when a conductive material paste containing a binder having a specific repeating unit and the amount of the binder adsorbed on the conductive material is controlled within a predetermined range. I found out. In addition, by using the conductive material paste for the preparation of secondary battery electrode slurry (especially positive electrode slurry), in the electrode formed from the electrode slurry, the oxidation of the binder is suppressed and the potential stability is improved. It has been found that electrical characteristics such as high temperature storage characteristics can be enhanced.

Second, the present inventors have formed the above conventional electrode slurry from an electrode slurry because the binder and the conductive material are sufficiently kneaded with a relatively high solid content. There is a possibility that a good conductive network may not be formed between the conductive materials due to excessive dispersion of the conductive material in the electrode mixture layer, and a secondary where the conductive network between the conductive materials is insufficient. It was further found that the battery may not be able to suppress capacity deterioration due to internal resistance, particularly capacity deterioration at low temperatures.
Accordingly, the present inventors have repeatedly studied and have come up with the idea of forming a good conductive network between conductive materials by adjusting the manufacturing conditions and the like of electrode slurry (especially positive electrode slurry). The inventors further studied and prepared a slurry for an electrode by mixing the solid content concentration of the conductive material paste containing the binder containing the specific repeating unit and the conductive material within a predetermined range. And / or by producing a slurry for a secondary battery electrode by a specific manufacturing process using a binder containing the specific repeating unit described above, it is possible to form a good conductive network between conductive materials, It has been found that the internal resistance of the secondary battery manufactured using the obtained secondary battery electrode slurry is reduced, and the high-temperature cycle characteristics and low-temperature characteristics are improved.

Based on the newly found findings as described above, the present inventors have completed the present invention.

That is, this invention aims to solve the above-mentioned problems advantageously, and the conductive material paste for a secondary battery electrode of the present invention contains a conductive material and a binder A, and the binder A is an alkylene. It includes at least one of a structural unit and a (meth) acrylic acid ester monomer unit, and the binder adsorption amount of the conductive material is 100 mg / g or more and 600 mg / g or less. Thus, the secondary battery containing the binder A containing the alkylene structural unit and / or the (meth) acrylic acid ester monomer unit, and the binder adsorption amount of the conductive material is 100 mg / g or more and 600 mg / g or less. The electrode conductive material paste has excellent dispersion stability, and an electrode having excellent potential stability can be produced by using the conductive material paste. In addition, the electrode obtained using the conductive material paste can exhibit excellent electrical characteristics for the secondary battery.
The “binder adsorption amount of the conductive material” can be measured by the method described in this specification.

Here, in the conductive material paste for a secondary battery electrode of the present invention, the binder A preferably includes an alkylene structural unit. When the binder A contains an alkylene structural unit, the dispersion stability of the conductive material paste and the potential stability of the electrode can be further improved, and the electrical characteristics of the secondary battery can be further enhanced. Because.

In the conductive material paste for secondary battery electrodes of the present invention, it is preferable that the binder A includes both an alkylene structural unit and a (meth) acrylate monomer unit. If the binder A includes both an alkylene structural unit and a (meth) acrylic acid ester monomer unit, the dispersion stability of the conductive material paste and the potential stability of the electrode can be further improved. This is because the electrical characteristics of the battery can be further enhanced.

In the conductive material paste for secondary battery electrodes of the present invention, it is preferable that the binder A further contains 2% by mass to 50% by mass of a nitrile group-containing monomer unit. If the binder A contains a nitrile group-containing monomer unit in the range of 2% by mass to 50% by mass, the dispersion stability of the conductive material paste and the potential stability of the electrode can be further improved. Moreover, it is because the electrical property of a secondary battery can be improved further while improving the stability with respect to the electrolyte solution of the positive electrode for secondary batteries manufactured using the electrically conductive material paste.

Furthermore, the conductive material paste for a secondary battery electrode of the present invention preferably has a viscosity of 1000 mPa · s or more and 10,000 mPa · s or less. Thus, the dispersion stability of the conductive material paste can be made excellent by setting the viscosity of the conductive material paste to 1000 mPa · s or more and 10,000 mPa · s or less.
In the present specification, the viscosity of the conductive material paste can be measured with a single cylindrical rotational viscometer (25 ° C., rotational speed = 60 rpm, spindle shape: 4) according to JIS Z 8803: 1991.

In addition, the conductive material paste for a secondary battery electrode of the present invention preferably has a solid content concentration of 5% by mass or more and 15% by mass or less. Thus, if the solid content concentration of the conductive material paste is 5% by mass or more and 15% by mass or less, the conductive material is well dispersed in the obtained electrode mixture layer, and the electrical characteristics of the secondary battery are further enhanced. Because it can.
In the present specification, the conductive material is “dispersed well” means that the conductive material is appropriately dispersed without excessively dispersing or aggregating in the electrode mixture layer. It refers to a state where each other can form a conductive network.

Moreover, this invention aims at solving the said subject advantageously, The manufacturing method of the slurry for secondary battery positive electrodes of this invention uses the electrically conductive paste for any of the above-mentioned secondary battery electrodes. It includes a step (X) of preparing, and a step (Y) of mixing the conductive material paste for a secondary battery electrode and a positive electrode active material. The secondary battery positive electrode slurry obtained by using any one of the above-described conductive pastes for secondary battery electrodes is excellent in dispersion stability, and if the positive electrode slurry is used, a positive electrode excellent in potential stability is produced. Thus, the secondary battery can exhibit excellent electrical characteristics.

Here, in the method for producing a slurry for a secondary battery positive electrode of the present invention, the step (X) mixes and premixes the conductive material and the first binder component containing the binder A as a main component. A first step (X-1) for obtaining a paste; and adding a second binder component containing a fluorine-based polymer as a main component to the premixed paste to obtain the conductive material paste for a secondary battery electrode Second step (X-2) to be obtained. This is because if the positive electrode slurry is prepared using the conductive material paste through the first step and the second step, the electrical characteristics of the secondary battery can be further enhanced.
In addition, in this specification, "it contains as a main component" shows containing in the ratio of 50 mass% or more in conversion of solid content.

Moreover, this invention aims at solving the said subject advantageously, The manufacturing method of the positive electrode for secondary batteries of this invention was obtained by the manufacturing method of the slurry for secondary battery positive electrodes mentioned above. The method includes a step of applying a slurry for a secondary battery positive electrode to at least one surface of a current collector and drying to form a positive electrode mixture layer. If the positive electrode mixture layer is formed from the above-described slurry for the secondary battery positive electrode, a positive electrode having excellent potential stability can be produced, and the positive electrode can exhibit excellent electrical characteristics in the secondary battery. .

Moreover, this invention aims at solving the said subject advantageously, The secondary battery of this invention is a secondary battery which has a positive electrode, a negative electrode, a separator, and electrolyte solution, Comprising: The said positive electrode is A secondary battery positive electrode manufactured by the above-described method for manufacturing a secondary battery positive electrode. A secondary battery provided with the positive electrode for secondary batteries manufactured by the manufacturing method of the positive electrode for secondary batteries mentioned above is excellent in an electrical property.

ADVANTAGE OF THE INVENTION According to this invention, the electrically conductive material paste for secondary battery electrodes which can form the electrode which is excellent in dispersion stability and is excellent in electric potential stability can be provided.
Moreover, according to this invention, the manufacturing method of the slurry for secondary battery positive electrodes which can improve an electrical characteristic and can improve the performance of a secondary battery can be provided.
Furthermore, according to this invention, the manufacturing method of the positive electrode for secondary batteries which can improve an electrical characteristic and can improve the performance of a secondary battery can be provided.
In addition, according to the present invention, a secondary battery having excellent electrical characteristics can be provided.

Hereinafter, embodiments of the present invention will be described in detail.
Here, the conductive material paste for a secondary battery electrode of the present invention is used as a material for producing a slurry for a secondary battery electrode, preferably a slurry for a secondary battery positive electrode. And the manufacturing method of the slurry for secondary battery positive electrodes of this invention manufactures the slurry for secondary battery positive electrodes used for formation of the positive electrode of a secondary battery using the electrically conductive material paste for secondary battery electrodes of this invention. Used when In addition, the method for producing a positive electrode for a secondary battery according to the present invention is characterized in that a positive electrode mixture layer is formed from the slurry for a secondary battery positive electrode produced by using the method for producing a slurry for a secondary battery positive electrode according to the present invention. And The secondary battery of the present invention is characterized by using a positive electrode manufactured by the method for manufacturing a positive electrode for a secondary battery of the present invention.

(Conductive material paste for secondary battery electrode)
The conductive material paste of the present invention comprises at least a conductive material and a binder A, and the binder A includes at least one of an alkylene structural unit and a (meth) acrylic acid ester monomer unit. The binder adsorption amount of the conductive material is 100 mg / g or more and 600 mg / g or less.
Thus, the conductive material paste containing at least the binder A containing an alkylene structural unit and / or a (meth) acrylic acid ester monomer unit as a binder, and the binder adsorption amount of the conductive material is within a specific range, If the conductive material paste is excellent in dispersion stability, an electrode having excellent potential stability can be produced, and the secondary battery can exhibit excellent electrical characteristics.
In the present specification, “including an alkylene structural unit” means “a repeating structure composed only of an alkylene structure represented by the general formula —C _n H _2n — [where n is an integer of 2 or more] in a polymer. It means "unit is included".
Further, in the present specification, “including a monomer unit” means “a repeating unit derived from a monomer is contained in a polymer obtained using the monomer”.
In the present specification, “(meth) acryl” means acryl and / or methacryl.

<Conductive material>
The conductive material is, for example, for ensuring electrical contact between the positive electrode active materials in the positive electrode mixture layer. And as a electrically conductive material used for the electrically conductive material paste of this invention, a well-known electrically conductive material can be used, without being specifically limited. Specifically, as the conductive material, acetylene black, ketjen black (registered trademark), furnace black, graphite, carbon fiber, carbon flake, carbon ultrashort fiber (for example, carbon nanotube, vapor grown carbon fiber, etc.), etc. Conductive carbon materials: various metal fibers, foils and the like can be used. Among these, from the viewpoint of sufficiently improving the rate characteristics while maintaining the battery capacity of the secondary battery, it is preferable to use acetylene black, ketjen black, or furnace black as the conductive material.

The specific surface area of the conductive material is preferably 10 m ² / g or more, more preferably 50 m ² / g or more, further preferably 65 m ² / g or more, preferably 1500 m ² / g or less, more preferably 1000 m ² / g Hereinafter, it is more preferably 500 m ² / g or less. If the specific surface area of the conductive material is 10 m ² / g or more, the amount of binder adsorbed on the conductive material is easy to adjust, and if it is 1500 m ² / g or less, the conductive due to excessive adsorption of the binder as an insulator. Sexual deterioration can be suppressed.
In the present specification, the “specific surface area of the conductive material” is a BET specific surface area by a nitrogen adsorption method, and can be measured in accordance with ASTM D3037-81.

<Binder A>
Binder A is an electrode manufactured by forming an electrode mixture layer on a current collector with an electrode slurry containing the conductive material paste of the present invention, and the components contained in the electrode mixture layer are detached from the electrode mixture layer. It is a component that can be retained so as not to be present. In general, the binder in the electrode mixture layer, for example, the positive electrode mixture layer, when immersed in the electrolytic solution absorbs the electrolytic solution and swells, while the positive electrode active materials are in contact with each other, the positive electrode active material and the conductive material, or The conductive materials are bound to each other to prevent the positive electrode active material and the like from dropping from the current collector.

And the binder A used for the electrically conductive material paste of this invention needs to contain at least one of an alkylene structural unit and a (meth) acrylic acid ester monomer unit. The binder A may optionally contain other monomer units other than the alkylene structural unit and the (meth) acrylate monomer unit.
Thus, the binder A contains an alkylene structural unit and / or a (meth) acrylic acid ester monomer unit, so that the adsorbing ability of the binder A to the conductive material is ensured, and the aggregation of the conductive material is suppressed and the conductive material is suppressed. The dispersion stability of the paste can be improved. And since the electrode slurry containing such a conductive material paste is also excellent in dispersion stability, the conductive material is well dispersed in the electrode mixture layer formed from the electrode slurry. In addition, the binder A containing an alkylene structural unit and a (meth) acrylic acid ester monomer unit has excellent oxidation resistance, and ensures the potential stability of an electrode prepared using an electrode slurry containing a conductive material paste. Can do. And while the favorable dispersion state of the conductive material in the electrode mixture layer and the oxidation resistance of the binder A are combined, the internal resistance of the secondary battery including the electrode formed using the conductive material paste of the present invention is reduced. In addition, the secondary battery can be improved in low temperature characteristics, high temperature cycle characteristics and high temperature storage characteristics, and excellent in electrical characteristics.

The binder A used in the conductive material paste of the present invention preferably includes at least an alkylene structural unit, and more preferably includes both an alkylene structural unit and a (meth) acrylic acid ester monomer unit. When the alkylene structural unit is included and when both the alkylene structural unit and the (meth) acrylate monomer unit are included, the dispersion stability of the conductive material paste and the potential stability of the electrode are further improved. This is because the electrical characteristics of a secondary battery including an electrode manufactured using a conductive material paste can be improved.

[Alkylene structural unit]
The alkylene structural unit may be linear or branched, but from the viewpoint of improving the dispersion stability of the conductive material paste and the potential stability of the electrode, the alkylene structural unit is linear. It is preferably a linear alkylene structural unit.
The method for introducing the alkylene structural unit into the binder A is not particularly limited. For example, the following methods (1) and (2):
(1) A method of preparing a polymer from a monomer composition containing a conjugated diene monomer and converting the conjugated diene monomer unit to an alkylene structural unit by hydrogenating the polymer (2) Examples thereof include a method for preparing a polymer from a monomer composition containing a 1-olefin monomer. Among these, the method (1) is preferable because the production of the binder A is easy.

Here, examples of the conjugated diene monomer include conjugated diene compounds having 4 or more carbon atoms such as 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, and 1,3-pentadiene. It is done. Of these, 1,3-butadiene is preferred. That is, the alkylene structural unit is preferably a structural unit (conjugated diene hydride unit) obtained by hydrogenating a conjugated diene monomer unit, and a structure obtained by hydrogenating a 1,3-butadiene monomer unit. More preferred are units (1,3-butadiene hydride units).
Examples of the 1-olefin monomer include ethylene, propylene, 1-butene and the like.
These conjugated diene monomers and 1-olefin monomers can be used singly or in combination of two or more.

The content ratio of the alkylene structural unit in the binder A is preferably 30% by mass or more when all repeating units (total of monomer units and structural units) in the binder A are 100% by mass. 50 mass% or more is more preferable, 98 mass% or less is preferable, and 80 mass% or less is more preferable. By setting the content ratio of the alkylene structural unit in the binder A within the above range, the dispersion stability of the conductive material paste is improved by suppressing the sedimentation of the conductive material in the conductive material paste, and in addition, the electrode Is ensured. Furthermore, in the electrode mixture layer formed using the slurry for the secondary battery positive electrode obtained from the conductive material paste, the conductive material is well dispersed and the conductive network is well formed. The electrical characteristics of the secondary battery having the layer are improved.

When the content ratio of the alkylene structural unit in the binder A is less than 30% by mass, the solubility of the binder A in a solvent such as N-methylpyrrolidone (NMP) becomes excessively high. As a result, the binder A becomes conductive. Dispersion stability declines by not being able to adsorb | suck stably to a material but dissociating in a solvent. In addition, since the adsorption amount to the conductive material is reduced, the internal resistance of the secondary battery manufactured using them is increased, and the low temperature characteristics, the high temperature storage characteristics, and the high temperature cycle characteristics may be decreased. On the other hand, when the content ratio of the alkylene structural unit in the binder A exceeds 98% by mass, the solubility of the binder A particularly in a solvent such as NMP becomes excessively low. As a result, for the conductive material paste and the secondary battery electrode There is a bias in dispersion of the conductive material in the slurry, the internal resistance of the secondary battery manufactured using them increases, and there is a risk that the low temperature characteristics, the high temperature storage characteristics and the high temperature cycle characteristics will deteriorate.

[(Meth) acrylic acid ester monomer unit]
Examples of the (meth) acrylate monomer that can form a (meth) acrylate monomer unit include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, Alkyl acrylates 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 meta Relate, t-butyl methacrylate, isobutyl methacrylate, n-pentyl methacrylate, isopentyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, lauryl methacrylate, n-tetradecyl methacrylate, stearyl methacrylate Methacrylic acid alkyl esters such as glycidyl methacrylate; and the like. Among these, from the viewpoint of improving the dispersion stability of the conductive material paste and the dispersibility of the conductive material in the electrode mixture layer, the (meth) acrylic acid ester monomer is a non-carbonyl oxygen. Acrylic acid alkyl ester having 4 to 10 carbon atoms in the alkyl group bonded to the atom is preferable, and specifically, ethyl acrylate, n-butyl acrylate and 2-ethylhexyl acrylate are preferable, and n-butyl acrylate is more preferable. preferable.
These can be used alone or in combination of two or more.

And the content rate of the (meth) acrylic acid ester monomer unit in the said binder A shall be 10 mass% or more and 40 mass% or less, when all the repeating units in the binder A are 100 mass%. Is preferred. By making the content ratio of the (meth) acrylic acid ester monomer unit in the binder A 40% by mass or less, particularly the solubility of the binder A in a solvent such as NMP is improved, and the conductive material paste is dispersed. Stability can be further improved. Furthermore, the content ratio of the (meth) acrylic acid ester monomer unit in the binder A is 10% by mass or more, thereby improving the stability of the electrode mixture layer formed using the conductive material paste with respect to the electrolytic solution. The high temperature storage characteristic and high temperature cycling characteristic of the secondary battery manufactured using the electrically conductive material paste can be improved.

In addition, when the content rate of the (meth) acrylic acid ester monomer unit in the binder A is less than 10% by mass, the strength of the electrode mixture layer formed using the conductive material paste is lowered, and the degree of swelling with respect to the electrolytic solution Increases and peel strength decreases. Therefore, there is a possibility that the high-temperature storage characteristics and high-temperature cycle characteristics of a secondary battery provided with such electrodes will deteriorate. On the other hand, when the content ratio of the (meth) acrylic acid ester monomer unit in the binder A exceeds 40% by mass, the solubility of the binder A particularly in a solvent such as NMP is lowered. As a result, the conductive material paste and In the slurry for secondary battery electrodes, the dispersion of the conductive material may be biased, and the dispersion stability thereof may be impaired. Therefore, the electrodes formed using them are inferior in uniformity, the internal resistance of the secondary battery including the electrodes is increased, and the low temperature characteristics, the high temperature storage characteristics, and the high temperature cycle characteristics may be decreased.

[Other monomer units]
The binder A may contain other monomer units in addition to the above-described alkylene structural unit and (meth) acrylic acid ester monomer unit. Such other monomer units include nitrile group-containing monomer units, hydrophilic group-containing monomer units, crosslinkable monomer units, aromatic vinyl monomer units, ethylenically unsaturated carboxylic acids. Examples thereof include an amide monomer unit and a fluorine-containing monomer unit.
And it is preferable that the binder A contains a nitrile group containing monomer unit. On the other hand, it is preferable that the binder A does not substantially contain a hydrophilic group-containing monomer unit.

[[Nitrile group-containing monomer unit]]
Examples of the nitrile group-containing monomer that can form a nitrile group-containing monomer unit include α, β-ethylenically unsaturated nitrile monomers. The α, β-ethylenically unsaturated nitrile monomer is not particularly limited as long as it is an α, β-ethylenically unsaturated compound having a nitrile group. For example, acrylonitrile; α-chloroacrylonitrile, α-bromo Α-halogenoacrylonitrile such as acrylonitrile; α-alkylacrylonitrile such as methacrylonitrile and α-ethylacrylonitrile; and the like. Among these, from the viewpoint of increasing the binding force of the binder A and increasing the mechanical strength of the electrode, the nitrile group-containing monomer is preferably acrylonitrile and methacrylonitrile, and more preferably acrylonitrile.
These can be used alone or in combination of two or more.

The content ratio of the nitrile group-containing monomer unit in the binder A is preferably 2% by mass or more and more preferably 10% by mass or more when the total repeating unit in the binder A is 100% by mass. 12 mass% or more is particularly preferable, 50 mass% or less is preferable, 40 mass% or less is more preferable, 35 mass% or less is even more preferable, 30 mass% or less is particularly preferable, and 25 mass% or less is most preferable. By making the content ratio of the nitrile group-containing monomer unit in the binder A within the above range, the conductive material is well dispersed in the electrode mixture layer of the electrode formed using the conductive material paste of the present invention. The internal resistance of the secondary battery having such a positive electrode mixture layer is lowered. Furthermore, the stability of the electrode with respect to the electrolytic solution is improved, and the low-temperature characteristics, high-temperature storage characteristics, and high-temperature cycle characteristics of the secondary battery can be improved. In particular, by setting the nitrile group-containing monomer to 35% by mass or less, the content ratio of the alkylene structural unit and / or the (meth) acrylic acid ester monomer unit can be sufficiently ensured. Can be improved.

In addition, when the content ratio of the nitrile group-containing monomer unit in the binder A exceeds 40% by mass, the binder A is easily dissolved in the electrolytic solution and cannot be stably adsorbed to the conductive material and dissociates in the solvent. As a result, the dispersion stability decreases. As a result, the high-temperature storage characteristics and high-temperature cycle characteristics of the secondary battery may be degraded. Moreover, the adsorption capacity of the binder A with respect to the conductive material is lowered, and it becomes difficult to adjust the binder adsorption amount of the conductive material. On the other hand, when the ratio of the nitrile group-containing monomer unit in the binder A is less than 2% by mass, the solubility of the binder A in a solvent such as NMP is particularly reduced, and the conductive material paste and the secondary battery electrode are used. There is a possibility that the dispersibility of the conductive material in the slurry may be lowered. Therefore, the internal resistance of the secondary battery including the electrode manufactured using them is increased, and the low temperature characteristics, the high temperature storage characteristics, and the high temperature cycle characteristics may be deteriorated.

[[Hydrophilic group-containing monomer unit]]
Examples of the hydrophilic group-containing monomer that can form a hydrophilic group-containing monomer unit include a monomer having a carboxylic acid group, a monomer having a sulfonic acid group, a monomer having a phosphate group, and a hydroxyl group A monomer having can be used.

Examples of the monomer having a carboxylic acid group include monocarboxylic acids and derivatives thereof, dicarboxylic acids and acid anhydrides, and derivatives thereof.
Examples of monocarboxylic acids include acrylic acid, methacrylic acid, and crotonic acid.
Examples of monocarboxylic acid derivatives include 2-ethylacrylic acid, isocrotonic acid, α-acetoxyacrylic acid, β-trans-aryloxyacrylic acid, α-chloro-β-E-methoxyacrylic acid, β-diaminoacrylic acid, and the like. Can be mentioned.
Examples of the dicarboxylic acid include maleic acid, fumaric acid, itaconic acid and the like.
Dicarboxylic acid derivatives include methylmaleic acid, dimethylmaleic acid, phenylmaleic acid, chloromaleic acid, dichloromaleic acid, fluoromaleic acid, methylallyl maleate, diphenyl maleate, nonyl maleate, decyl maleate, dodecyl maleate And maleate esters such as octadecyl maleate and fluoroalkyl maleate.
Examples of the acid anhydride of dicarboxylic acid include maleic anhydride, acrylic anhydride, methyl maleic anhydride, and dimethyl maleic anhydride.
Moreover, as a compound which has a carboxylic acid group, the acid anhydride which produces | generates a carboxyl group by hydrolysis can also be used.
In addition, monoethyl maleate, diethyl maleate, monobutyl maleate, dibutyl maleate, monoethyl fumarate, diethyl fumarate, monobutyl fumarate, dibutyl fumarate, monocyclohexyl fumarate, dicyclohexyl fumarate, monoethyl itaconate, diethyl itaconate Also included are monoesters and diesters of α, β-ethylenically unsaturated polyvalent carboxylic acids such as monobutyl itaconate and dibutyl itaconate.

Examples of monomers having a sulfonic acid group include vinyl sulfonic acid, methyl vinyl sulfonic acid, (meth) allyl sulfonic acid, styrene sulfonic acid, (meth) acrylic acid-2-ethyl sulfonate, 2-acrylamido-2-methyl. Examples thereof include propanesulfonic acid and 3-allyloxy-2-hydroxypropanesulfonic acid.
In the present specification, “(meth) allyl” means allyl and / or methallyl.
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. .
In the present specification, “(meth) acryloyl” means acryloyl and / or methacryloyl.

Examples of the monomer having a hydroxyl group include those described in International Publication No. 2013/088099.

In this specification, (meth) acrylic acid ester monomer and nitrile group-containing monomer which can constitute binder A, crosslinkable monomer, aromatic vinyl monomer, and ethylenic unsaturation described later The carboxylic acid amide monomer and the fluorine-containing monomer do not contain a carboxylic acid group, a sulfonic acid group, a phosphoric acid group, or a hydroxyl group.
Here, in particular, a hydrophilic group-containing monomer such as a monomer having a carboxylic acid group can contribute to an improvement in the production stability of the binder A, while a hydrophilic group-containing monomer unit is included in the binder A. In addition, the dispersibility of the conductive material included in the binder A may be impaired. Therefore, from the viewpoint of ensuring the dispersion stability of the conductive material paste, the content ratio of the hydrophilic group-containing monomer unit in the binder A is 0 when the total repeating unit in the binder A is 100% by mass. Less than 0.05 mass% (substantially free) is preferable, and 0 mass% is more preferable.

[[Crosslinkable monomer unit]]
The crosslinkable monomer that can form a crosslinkable monomer unit includes an epoxy group-containing monomer, a carbon-carbon double bond and an epoxy group-containing monomer, a halogen atom and an epoxy group. A monomer containing an oxetanyl group, a monomer containing an oxazoline group, a polyfunctional monomer having two or more olefinic double bonds, and the like.

[[Aromatic vinyl monomer units]]
Examples of the aromatic vinyl monomer that can form an aromatic vinyl monomer unit include styrene, α-methylstyrene, pt-butylstyrene, vinyltoluene, and chlorostyrene.

[[Ethylenically unsaturated carboxylic acid amide monomer unit]]
Examples of the ethylenically unsaturated carboxylic acid amide monomer that can form an ethylenically unsaturated carboxylic acid amide monomer unit include acrylamide, methacrylamide, N, N-dimethylacrylamide, and the like.

[[Fluorine-containing monomer unit]]
As the fluorine-containing monomer that can form a fluorine-containing monomer unit, the same monomer as the fluorine-containing monomer that can form a fluorine-based polymer described later can be used. In addition, when the binder A contains a fluorine-containing unit, the ratio of the fluorine-containing unit is less than 70% when the total repeating unit of the binder A is 100% by weight.

[Method for preparing binder A]
The method for producing the binder A is not particularly limited. For example, a polymer is obtained by polymerizing a monomer composition containing the above-mentioned monomers, and optionally prepared by hydrogenating the obtained polymer. can do.
Here, the content ratio of each monomer in the monomer composition in the present specification can be determined according to the content ratio of each monomer unit and structural unit (repeating unit) in the binder A.
The polymerization mode is not particularly limited, and any method such as a solution polymerization method, a suspension polymerization method, a bulk polymerization method, and an emulsion polymerization method can be used. In each polymerization method, known emulsifiers and polymerization initiators can be used as necessary.
The hydrogenation method is not particularly limited, and a general method using a catalyst (for example, see International Publication No. 2012/165120, International Publication No. 2013/088099 and Japanese Patent Application Laid-Open No. 2013-8485) may be used. it can.
The iodine value of the hydrogenated polymer is preferably 60 mg / 100 mg or less, more preferably 30 mg / 100 mg or less, and particularly preferably 20 mg / 100 mg or less. Further, the lower limit is preferably 3 mg / 100 mg or more, and more preferably 8 mg / 100 mg or more. The iodine value is obtained by measuring the iodine value of a dried polymer obtained by coagulating 100 g of an aqueous dispersion of a polymer with 1 liter of methanol and then vacuum drying at 60 ° C. for 12 hours according to JIS K6235 (2006). Can be obtained.

The binder A is used in the state of a dispersion liquid or a dissolved solution dispersed in a dispersion medium. The dispersion medium of the binder A is not particularly limited as long as the binder A can be uniformly dispersed or dissolved, and water or an organic solvent can be used, and an organic solvent is preferably used. In addition, as an organic solvent, it does not specifically limit, The organic solvent used as a solvent of the electrically conductive material paste mentioned later can be used.

[Binder A content]
The blending amount of the binder A in the conductive material paste is preferably 20 parts by mass or more, more preferably 50 parts by mass or more, preferably 200 parts by mass or less, more preferably 150 parts by mass or less, per 100 parts by mass of the conductive material. It is. When the blending amount of the binder A in the conductive material paste is within the above range, the dispersion stability of the conductive material paste becomes good.

<Other binders>
In addition to the binder A described above, the conductive material paste of the present invention may contain another binder different from the binder A (hereinafter referred to as the binder B). Similarly to the binder A, the binder B, for example, is held in a positive electrode produced by forming a positive electrode mixture layer on a current collector so that components contained in the positive electrode mixture layer are not detached from the positive electrode mixture layer.
Here, as the binder B, it is preferable to use a fluoropolymer. This is because, as will be described later, by using a fluorine-based polymer, the temporal stability of the secondary battery positive electrode slurry can be further improved.

[Fluoropolymer]
The fluorine polymer is a polymer containing a fluorine-containing monomer unit. Specifically, as the fluorine-based polymer, a homopolymer or copolymer of one or more kinds of fluorine-containing monomers, one or more kinds of fluorine-containing monomers and a monomer not containing fluorine (hereinafter referred to as “fluorine-containing monomers”) And a copolymer with “fluorine-free monomer”).
In addition, the ratio of the fluorine-containing monomer unit in a fluorine-type polymer is 70 mass% or more normally, Preferably it is 80 mass% or more. Moreover, the ratio of the fluorine-free monomer unit in the fluoropolymer is usually 30% by mass or less, preferably 20% by mass or less.

Here, examples of the fluorine-containing monomer that can form a fluorine-containing monomer unit include vinylidene fluoride, tetrafluoroethylene, hexafluoropropylene, vinyl trifluoride chloride, vinyl fluoride, and perfluoroalkyl vinyl ether. It is done. Among these, as the fluorine-containing monomer, vinylidene fluoride is preferable.

Examples of the fluorine-free monomer that can form a fluorine-free monomer unit include a fluorine-free monomer copolymerizable with the fluorine-containing monomer, such as ethylene, propylene, and 1-butene. 1-olefin; aromatic vinyl compounds such as styrene, α-methylstyrene, pt-butylstyrene, vinyltoluene, chlorostyrene; unsaturated nitrile compounds such as (meth) acrylonitrile; methyl (meth) acrylate, ( (Meth) acrylic acid ester compounds such as (meth) butyl acrylate and (meth) acrylic acid 2-ethylhexyl; (meth) acrylamides such as (meth) acrylamide, N-methylol (meth) acrylamide and N-butoxymethyl (meth) acrylamide Acrylamide compounds; (meth) acrylic acid, itaconic acid, fumaric acid, crotonic acid Vinyl compounds containing carboxyl groups such as maleic acid; epoxy group-containing unsaturated compounds such as allyl glycidyl ether and glycidyl (meth) acrylate; amino such as dimethylaminoethyl (meth) acrylate and diethylaminoethyl (meth) acrylate Group-containing unsaturated compounds; sulfonic acid group-containing unsaturated compounds such as styrene sulfonic acid, vinyl sulfonic acid and (meth) allyl sulfonic acid; sulfate group-containing unsaturated compounds such as 3-allyloxy-2-hydroxypropanesulfuric acid; And phosphate group-containing unsaturated compounds such as acrylic acid-3-chloro-2-propyl phosphate and 3-allyloxy-2-hydroxypropane phosphoric acid.

The fluorine-based polymer is preferably a polymer using vinylidene fluoride as the fluorine-containing monomer and a polymer using vinyl fluoride as the fluorine-containing monomer, and vinylidene fluoride as the fluorine-containing monomer. A polymer using is more preferable.
Specifically, as the fluoropolymer, a homopolymer of vinylidene fluoride (polyvinylidene fluoride), a copolymer of vinylidene fluoride and hexafluoropropylene, and polyvinyl fluoride are preferable, and polyvinylidene fluoride is more preferable. .
In addition, the fluoropolymer mentioned above may be used individually by 1 type, and may use 2 or more types together.

Here, the weight average molecular weight in terms of polystyrene by gel permeation chromatography of the fluoropolymer is preferably 100,000 to 2,000,000, more preferably 200,000 to 1,500,000, and particularly Preferably, it is 400,000 to 1,000,000.
By setting the weight average molecular weight of the fluoropolymer within the above range, detachment (powder off) from the electrode mixture layer such as the electrode active material or the conductive material is suppressed, and the viscosity of the conductive material paste can be easily adjusted. Become.

Further, the glass transition temperature (Tg) of the fluoropolymer is preferably 0 ° C. or lower, more preferably −20 ° C. or lower, and particularly preferably −30 ° C. or lower. The lower limit of the Tg of the fluoropolymer is not particularly limited, but is preferably −50 ° C. or higher, more preferably −40 ° C. or higher. When the Tg of the fluoropolymer is in the above range, detachment (powder off) from the electrode mixture layer such as an electrode active material or a conductive material can be suppressed. In addition, Tg of a fluorine-type polymer can be adjusted by changing the kind of monomer used for superposition | polymerization. Tg can be measured in accordance with JIS K7121; 1987 using a differential scanning calorimeter.

The melting point (Tm) of the fluoropolymer is preferably 190 ° C. or lower, more preferably 150 to 180 ° C., and further preferably 160 to 170 ° C. When the Tm of the fluoropolymer is in the above range, an electrode excellent in flexibility and adhesion strength can be obtained. In addition, Tm of a fluoropolymer can be adjusted by changing the kind of monomer used for superposition | polymerization or controlling superposition | polymerization temperature. In addition, Tm can be measured based on JIS K7121; 1987 using a differential scanning calorimeter.

Here, the method for producing the above-described fluoropolymer is not particularly limited, and any method such as a solution polymerization method, a suspension polymerization method, a bulk polymerization method, and an emulsion polymerization method can be used.
As the polymerization method, addition polymerization such as ionic polymerization, radical polymerization, living radical polymerization and the like can be used. Moreover, as a polymerization initiator, a known polymerization initiator can be used.

The fluoropolymer is used in a state of a dispersion liquid or a dissolved solution dispersed in a dispersion medium. The dispersion medium of the fluorine-based polymer is not particularly limited as long as the fluorine-based polymer can be uniformly dispersed or dissolved, and water or an organic solvent can be used, and an organic solvent is preferably used. In addition, as an organic solvent, it does not specifically limit, The organic solvent used as a solvent of the electrically conductive material paste mentioned later can be used.

[Binder B content]
The blending amount of the binder B such as a fluoropolymer is preferably 10% by mass or less based on the blending amount of the binder A so that the binder A is suitably attached to the conductive material and the dispersion stability of the conductive material paste is improved. , More preferably 5% by mass or less, particularly preferably 0% by mass. That is, the conductive material paste preferably does not contain a binder B other than the binder A, such as a fluoropolymer, from the viewpoint of ensuring the dispersion stability of the conductive material paste.
On the other hand, the fluorine-based polymer has an advantage while there is a possibility that the dispersion stability of the conductive material paste may be lowered as described above. Specifically, the fluorine-based polymer can suppress the precipitation of the positive electrode active material having a relatively heavy specific gravity in the slurry for the positive electrode of the secondary battery, in the slurry for the positive electrode. Stability over time can be improved.
As described above, from the viewpoint of securing the temporal stability of the obtained secondary battery positive electrode slurry, the conductive material paste may contain a fluorine-based polymer. In such a case, the blending amount of the fluoropolymer in the conductive material paste is preferably 50% by weight or more, based on 100% by weight of the total solid content of the binder (binder resin) in the conductive material paste, and 80% by weight. % Or more is more preferable. Moreover, in the slurry for secondary battery positive electrode described later, the blending amount of the fluoropolymer is preferably 1 part by mass or more, more preferably 2 parts by mass or more per 100 parts by mass of the positive electrode active material. It is preferably 5 parts by mass or less, and more preferably 4 parts by mass or less.
If the blending amount of the fluoropolymer is within such a range, it is possible to suppress the precipitation of the positive active material having a relatively high specific gravity in the secondary battery positive electrode slurry, and the secondary battery positive electrode slurry is stable over time. This is because the performance can be improved.

Similarly, from the viewpoint of improving the temporal stability of the secondary battery positive electrode slurry, the blending amount of the binder A in the conductive material paste is the solid content of all the binders (binder resin) in the conductive material paste. As 100 mass%, it is preferable that it is 10 mass% or more, It is more preferable that it is 15 mass% or more, It is preferable that it is 70 mass% or less, It is more preferable that it is 50 mass% or less.
Which of the conductive material paste and the positive electrode slurry is selected as the addition destination of the fluoropolymer may be appropriately determined according to the mode of implementation.

<Solvent>
The conductive material paste preferably contains a solvent. Here, as a solvent mix | blended with an electrically conductive material paste, the organic solvent which has the polarity which can melt | dissolve the binder A mentioned above can be used, for example.
Specifically, as the organic solvent, acetonitrile, N-methylpyrrolidone, acetylpyridine, cyclopentanone, N, N-dimethylacetamide, dimethylformamide, dimethyl sulfoxide, methylformamide, methyl ethyl ketone, furfural, ethylenediamine, or the like may be used. it can. Among these, N-methylpyrrolidone (NMP) is most preferable as the organic solvent from the viewpoints of ease of handling, safety, and ease of synthesis.
In addition, these organic solvents may be used independently and may mix and use 2 or more types.

<Other ingredients>
In addition to the above components, for example, components such as a viscosity modifier, a reinforcing material, an antioxidant, and an electrolytic solution additive having a function of suppressing the decomposition of the electrolytic solution may be mixed in the conductive material paste. As these other components, known ones can be used.

<Binder adsorption amount of conductive material>
In the conductive material paste, the binder adsorption amount of the conductive material needs to be 100 mg / g or more and 600 mg / g or less, preferably 150 mg / g or more, more preferably 170 mg / g or more, It is still more preferably 200 mg / g or more, particularly preferably 250 mg / g or more, preferably 400 mg / g or less, and more preferably 390 mg / g or less. When the binder adsorption amount of the conductive material is less than 100 mg / g, the conductive material aggregates and the dispersion stability of the conductive material paste cannot be ensured, and the interior of the secondary battery including the electrode obtained using the conductive material paste Resistance increases, and low temperature characteristics, high temperature storage characteristics, and high temperature cycle characteristics decrease. On the other hand, when the binder adsorption amount of the conductive material is more than 600 mg / g, the conductive material becomes excessively adsorbed with the binder as an insulator, and the inside of the secondary battery including the electrode obtained using the conductive material paste Resistance increases, and low temperature characteristics, high temperature storage characteristics, and high temperature cycle characteristics decrease.

The binder adsorption amount of the conductive material can be calculated by the following method.
First, if necessary, a solvent is further added to the conductive material paste to adjust the solid content concentration (for example, 1% by mass) that can be easily centrifuged. In addition, since the binder once adsorbed to the conductive material is difficult to desorb from the conductive material, the influence on the measured value of the binder adsorption amount due to the adjustment of the solid content concentration can be ignored.
Next, the conductive material paste or the diluted solution thereof is subjected to a centrifugal separation process until the supernatant and the precipitate are separated using a centrifuge, and the precipitate is collected. The precipitate is dried under conditions where the solvent is vaporized but the binder is not thermally decomposed until there is no change in weight, and the solvent remaining in the precipitate is removed to obtain a dried product (mainly composed of a binder and a conductive material). obtain. The drying may be performed under reduced pressure.
The obtained dried product is gradually heated to a temperature at which the binder is sufficiently decomposed and vaporized using a thermobalance (for example, heated to 500 ° C. at a heating rate of 10 ° C./min in a nitrogen atmosphere) in the dried product. Remove the binder.
The binder adsorption amount of the conductive material can be calculated from the following formula, assuming that the weight before heat treatment (dried material) by this thermobalance is W1 (g) and the weight W2 (g) after heat treatment.
Binder adsorption amount of conductive material (mg / g) = {(W1-W2) × 1000} / W2

Here, “the binder adsorption amount of the conductive material” measured as described above is a value correlated with the amount of the total binder adsorbed per 1 g of the conductive material. The binder adsorption amount of the conductive material is the composition of the binder A, the composition of the binder B other than the binder A, the specific surface area of the conductive material, the blending amount of the binder with respect to the conductive material, the viscosity of the conductive material paste, the solid content concentration, and It can be controlled by the preparation method.
Specifically, for example, by increasing the ratio of the nitrile group-containing monomer in the binder A, the binder adsorption amount of the conductive material can be reduced. Moreover, the binder adsorption amount of the conductive material can be reduced by using a polymer having a low adsorption capacity for the conductive material, for example, the binder B made of polyvinylidene fluoride. Furthermore, the binder adsorption amount of the conductive material can be increased by increasing the specific surface area of the conductive material and the blending amount of the binder with respect to the conductive material.

<Viscosity of conductive paste>
The conductive material paste preferably has a viscosity of 1000 mPa · s or more, more preferably 3000 mPa · s or more, particularly preferably 4000 mPa · s or more, and preferably 10,000 mPa · s or less, and 8000 mPa · s. It is more preferably s or less, and particularly preferably 6000 mPa · s or less. When the viscosity of the conductive material paste is within the above range, the dispersion stability of the conductive material paste is good.
Here, the viscosity of the conductive material paste can be adjusted by the amount of the solvent added during mixing, the solid content concentration of the conductive material paste, the type and molecular weight of the binder, and the like.
In addition, when the upper limit of the viscosity of the conductive material paste exceeds 10,000 mPa · s, it can be dispersed only by using only a part of the mixing device, the dispersibility of the conductive material is inferior, and further, the conductive material paste is used. There is a possibility that the electric resistance of the formed electrode mixture layer is increased. On the other hand, when the lower limit value of the conductive material paste is less than 1000 mPa · s, the dispersion stability of the conductive material paste may be impaired.

<Solid content concentration of conductive material paste>
The conductive material paste preferably has a solid content concentration of 5% by mass or more, more preferably 8% by mass or more, preferably 15% by mass or less, and more preferably 12% by mass or less. In particular, the solid content concentration of the conductive material paste is preferably within the above range from the start of mixing to the end of mixing when preparing the conductive material paste.
By setting the solid content concentration of the conductive material paste within the above range, the conductive material is well dispersed in the electrode mixture layer, and the internal resistance of the secondary battery is reduced. Cycle characteristics can be improved.
When the solid content concentration of the conductive material paste exceeds 15% by mass, the dispersion stability of the conductive material paste may be impaired, and the electric resistance of the obtained electrode may be increased. On the other hand, when the solid content concentration of the conductive material paste is less than 5% by mass, the conductive material is precipitated in the conductive material paste, and the dispersion stability of the conductive material paste may be impaired.
In addition, even in the secondary battery positive electrode slurry after the positive electrode active material is added to the paste, the concentration of the positive electrode slurry becomes too low, and sedimentation may occur.

<Method for preparing conductive paste>
There are no particular restrictions on the mixing method for obtaining the conductive material paste by mixing the above-mentioned conductive material and binder A and, if necessary, binder B, solvent and other components. For example, disper, mill, kneader, etc. The following general mixing apparatus can be used. For example, when using a disper, it is preferable to stir at 2000 rpm or more and 5000 rpm or less, preferably 5 minutes or more, more preferably 10 minutes or more, and preferably 60 minutes or less.
Further, the conductive material paste may be prepared by employing the steps (X-1) and (X-2) described later in the section “Method for producing slurry for secondary battery positive electrode”.

(Slurry for secondary battery positive electrode)
By using the secondary battery electrode paste of the present invention described above, a secondary battery positive electrode slurry can be produced. The slurry for the secondary battery positive electrode includes the above-described conductive material paste for the secondary battery electrode and the positive electrode active material, and more specifically includes at least the conductive material, the binder A, and the positive electrode active material.
Thus, the secondary battery positive electrode slurry containing the conductive material paste described above is excellent in stability over time, and a positive electrode excellent in potential stability can be produced by using the positive electrode slurry. In addition, the positive electrode formed from the positive electrode slurry can reduce the internal resistance of the secondary battery, and can improve the low temperature characteristics, high temperature cycle characteristics, and high temperature storage characteristics. The characteristics can be exhibited.

<Positive electrode active material>
As a positive electrode active material mix | blended with the slurry for secondary battery positive electrodes, it is not specifically limited, A known positive electrode active material can be used.
For example, a positive electrode active material used for a lithium ion secondary battery is not particularly limited, and lithium-containing cobalt oxide (LiCoO ₂ ), lithium manganate (LiMn ₂ O ₄ ), lithium-containing nickel oxide (LiNiO _2). ), Lithium-containing composite oxide of Co—Ni—Mn, lithium-containing composite oxide of Ni—Mn—Al, lithium-containing composite oxide of Ni—Co—Al, olivine type lithium iron phosphate (LiFePO ₄ ), olivine Type lithium manganese phosphate (LiMnPO ₄ ), Li _{1 + x} Mn _2−x O ₄ (0 <X <2), an excess lithium spinel compound, Li [Ni _0.17 Li _0.2 Co _0.07 Mn _0.56 ] O ₂ , LiNi _0.5 Mn _1.5 O _{4 and the} like.

Among the above, from the viewpoint of improving the battery capacity of the lithium ion secondary battery, lithium-containing cobalt oxide (LiCoO ₂ ), lithium-containing nickel oxide (LiNiO ₂ ), and Co—Ni—Mn are used as the positive electrode active material. It is preferable to use lithium-containing composite oxide, Ni—Co—Al lithium-containing composite oxide, Li [Ni _0.17 Li _0.2 Co _0.07 Mn _0.56 ] O ₂ or LiNi _0.5 Mn _1.5 O ₄ .
In addition, the compounding quantity and particle size of a positive electrode active material are not specifically limited, It can be made to be the same as that of the positive electrode active material used conventionally.

Further, the blending ratio of the positive electrode active material and the conductive material is not particularly limited, but the blending amount of the conductive material is preferably 1 part by mass or more per 100 parts by mass of the positive electrode active material, and is 2 parts by mass or more. Is more preferably 3 parts by mass or more, preferably 10 parts by mass or less, more preferably 5 parts by mass or less, and particularly preferably 4 parts by mass or less. When the amount of the conductive material is too small, sufficient electrical contact between the positive electrode active materials cannot be ensured, the internal resistance of the secondary battery increases, and the low temperature characteristics cannot be sufficiently improved. There is. On the other hand, when the amount of the conductive material is too large, the stability of the secondary battery positive electrode slurry may deteriorate with time, and the density of the positive electrode mixture layer in the secondary battery positive electrode may decrease. There is a possibility that the capacity cannot be increased sufficiently.

<Other ingredients>
The slurry for secondary battery positive electrode may contain the components mentioned in the section of “conductive material paste for secondary battery electrode” in addition to the conductive material, binder A, and positive electrode active material.

(Method for producing secondary battery positive electrode slurry)
And the slurry for secondary battery positive electrodes mentioned above is the process (Y) which prepares the electrically conductive material paste for secondary battery electrodes, and the process (Y) which mixes the electrically conductive material paste for secondary battery electrodes, and a positive electrode active material, for example. And a slurry for a secondary battery positive electrode according to the present invention.
Thus, after preparing the conductive material paste in the step (X), the positive electrode slurry prepared by mixing the conductive material paste and the positive electrode active material in the step (Y) is formed when the positive electrode mixture layer is formed. The dispersion of the conductive material is at an appropriate level. Therefore, if a positive electrode is produced using the positive electrode slurry, a good conductive network can be formed between the conductive materials, and capacity deterioration due to internal resistance can be suppressed. As a result, the electrical characteristics of the secondary battery produced using the secondary battery positive electrode slurry can be improved.

<Process (X)>
In step (X), a conductive material paste is prepared. Here, as a method for preparing the conductive material paste, the method described above in “Preparation Method of Conductive Material Paste” can be used. In particular, when the fluoropolymer is included in the conductive material paste, (X) is a first step (X-1) in which a conductive material and a first binder component containing binder A as a main component are mixed to obtain a premixed paste; It is preferable to include a second step (X-2) of adding a second binder component containing a polymer as a main component to obtain the conductive material paste for a secondary battery electrode.
As described above, the pre-mixed paste obtained by mixing the first binder component containing the binder A as a main component and the conductive material in the first step (X-1) with respect to the second step ( In X-2), a second binder component containing a fluorine-based polymer as a main component is added to obtain a conductive material paste, so that the conductive material is contained in the secondary battery positive electrode slurry obtained through the step (Y) described later. The material is properly dispersed. Therefore, if a positive electrode is manufactured using the slurry for a secondary battery positive electrode, a better conductive network can be formed between the conductive materials, and in particular, capacity deterioration at a low temperature can be suppressed. And the electrical characteristic of the secondary battery manufactured using the slurry for secondary battery positive electrodes can further be improved.

[First step (X-1)]
In the first step (X-1) of the step (X), the conductive material and the first binder component containing the binder A as a main component are mixed in a solvent as necessary, and a premixed paste Get.
In addition, as long as the 1st binder component contains the binder A as a main component, binders (binder resin) other than the binder A may be included.

[[Binder A ratio]]
The ratio of the binder A in the first binder component blended in the first step (X-1) is the solid content of the binder (binder resin) constituting the first binder component contained in the premixed paste. When the amount is 100% by mass, it is necessary to be 50% by mass or more, preferably 70% by mass or more, and more preferably 80% by mass or more. Most preferably, the ratio of binder A in the first binder component is 100% by mass. By making the compounding quantity of the binder A in a 1st binder component into the said range, the binder A fully adsorb | sucks to a electrically conductive material, and the dispersion stability of a premix paste and a electrically conductive material paste improves. And the secondary battery manufactured using this pre-mixing paste and conductive material paste is excellent in electrical characteristics (low temperature characteristics, cycle characteristics, etc.).
In addition, it does not specifically limit as binders other than the binder A which can be used as a binder which comprises a 1st binder component, A well-known binder, the fluorine-type polymer mentioned above, etc. are mentioned.

Further, when the amount of the conductive material in the premixed paste is 100% by mass, the blending amount of the binder A in the premixed paste is preferably 5% by mass or more, and more preferably 15% by mass or more. 100 wt% or less, and more preferably 50 wt% or less, the binder A content within the above range, the binder A is sufficiently adsorbed to the conductive material, the premixed paste Dispersion stability is improved. And the secondary battery manufactured using this pre-mixed paste is excellent in electrical characteristics (low temperature characteristics, high temperature cycle characteristics, etc.).

[[Blend amount of first binder component]]
In the above-described embodiment, the first binder component and the second binder component are added in the first step (X-1) and the second step (X-2), respectively. The total amount of the first binder component and the second binder component is 1 part by mass or more and 5 parts by mass when the amount of the positive electrode active material added in the step (Y) described later is 100 parts by mass. Part or less, preferably 2 parts by mass or more and 4 parts by mass or less. This is because if the amount of the binder is too small, the strength of the positive electrode is impaired, and if it is too large, the resistance of the positive electrode becomes too high.
And the compounding ratio of the 1st binder component with respect to the total compounding quantity of a 1st binder component and a 2nd binder component is 10 mass parts or more by making the total compounding quantity of these binder components into 100 mass parts. 90 parts by mass or less is preferable.

[[Solvent and other ingredients]]
As the solvent that can be used in the first step (X-1), for example, an organic solvent having a polarity capable of dissolving the binder A described above in the section of “conductive material paste for secondary battery electrode” can be used. .
In addition, in the first step (X-1), in addition to the above components, for example, a component such as a viscosity modifier, a reinforcing material, an antioxidant, an electrolytic solution additive having a function of suppressing decomposition of the electrolytic solution, and the like. You may mix. As these other components, known ones can be used.

[[Mixing method]]
In the first step (X-1), the conductive material and the first binder component described above, and optionally the solvent and other components are mixed in the first step (X-1) to obtain a premixed paste. For example, a general mixing device such as a disper, a mill, or a kneader can be used.
In addition, when using binder (binding resin) other than binder A and binder A as a 1st binder component, binder A and binders other than binder A may mix with a electrically conductive material after premixing. Alternatively, the conductive material may be mixed without premixing.
The solvent in which the binder A is dispersed may be used as it is, or a solvent may be added separately.

The viscosity of the premixed paste obtained in the first step (X-1) is a viscosity that can be mixed by the general mixing method as described above, and the viscosity range of the conductive material paste is within the above range. The viscosity is not particularly limited as long as the viscosity can be set as follows.

[Second step]
In the second step (X-2) in the step (X), a conductive material paste is prepared by adding a second binder component containing a fluoropolymer as a main component to the premixed paste prepared in the first step. Get.
The second binder component may contain a binder (binder resin) other than the fluoropolymer as long as it contains the fluoropolymer as a main component.

[[Ratio of fluoropolymer]]
The proportion of the fluoropolymer in the second binder component to be blended in the second step is 50% by mass or more, where the solid content of the binder (binder resin) constituting the second binder is 100% by mass. It is necessary to be 80% by mass or more. Most preferably, the ratio of the fluoropolymer in the second binder component is 100% by mass. The blending amount of the fluoropolymer in the second binder component is within the above range, and the first binder component is adsorbed on the conductive material by adding the fluoropolymer in such a ratio in the second step. It is possible to improve the stability of the conductive material paste without hindering the operation.
The binder other than the fluoropolymer that can be used as the binder constituting the second binder component is not particularly limited, and examples thereof include a known binder and the above-described binder A.

[[Blend amount of second binder component]]
The blending ratio of the second binder component to the total blending amount of the first binder component and the second binder component is the total blending amount of the binder (binder resin) from the viewpoint of the stability of the positive electrode slurry. As 100 mass parts, 50 mass parts or more and 90 mass parts or less are preferable.

[[Solvent and other ingredients]]
In the second step (X-2), a solvent may be added. Usable solvents include the same solvents as those described above with respect to the first step (X-1). Such a solvent may be, for example, an organic solvent having a polarity capable of dissolving the above-described second binder component.
In the second step (X-2), in addition to the above components, the conductive material paste is added with, for example, a viscosity modifier, a reinforcing material, an antioxidant, and an electrolytic solution having a function of suppressing decomposition of the electrolytic solution. You may mix components, such as an agent. As these other components, known ones can be used.

[[Mixing method]]
In the second step (X-2), the second binder component is added to the premixed paste to obtain a conductive material paste, and there is no particular limitation on the mixing method. For example, disper, mill, kneader A general mixing apparatus such as can be used. For example, when a disper is used, it is preferable to stir at 2000 rpm to 5000 rpm for 20 minutes to 120 minutes.
In the second step (X-2), by adding and mixing the second binder component to the premixed paste obtained by mixing the conductive material and the first binder component in advance, A plurality of types of binders (binder resins) having different properties can be mixed, and the positive electrode active material added in the step (Y) described later can be favorably dispersed in the positive electrode slurry. Thereby, the battery capacity of the secondary battery can be increased.

<Process (Y)>
In step (Y), the conductive material paste prepared in step (X), the positive electrode active material described above, and, in some cases, a solvent and other components are mixed.

[[Solvent and other ingredients]]
As the solvent, the same solvents as those described above with respect to the first step (X-1) and the second step (X-2) in the step (X) can be used.
In the step (Y), the slurry for the secondary battery positive electrode includes, for example, a viscosity modifier, a reinforcing material, an antioxidant, and an electrolytic solution additive having a function of suppressing decomposition of the electrolytic solution in addition to the above components. The components may be mixed. As these other components, known ones can be used.

[[Mixing method]]
In the step (Y), when the conductive material paste and the positive electrode active material are mixed to obtain the positive electrode slurry, the mixing method is not particularly limited, and for example, a general mixing device such as a disper, mill, kneader or the like is used. be able to. For example, when a disper is used, it is preferable to stir at 2000 rpm to 5000 rpm for 20 minutes to 120 minutes.

In this way, by mixing the positive electrode active material not in the step (X) but in the step (Y), in the step (X), a good network between the conductive materials is formed, and in the secondary battery positive electrode slurry. Dispersibility of the positive electrode active material can be improved. Note that the step (Y) does not affect the network between the conductive materials formed as a result of the step (X).
Further, by mixing the positive electrode active material in the step (Y) instead of the step (X), it is possible to prevent the decrease in the binder adsorption amount of the conductive material due to the binder A preferentially adsorbing to the positive electrode active material, The deterioration of the stability with time of the battery positive electrode slurry can be suppressed.
Then, by mixing with the positive electrode active material in a state where the binder (particularly binder A) is pre-adsorbed to the conductive material, the conductive material is coordinated via the binder in the vicinity of the positive electrode active material during the dispersion process. Thus, electrical characteristics such as low temperature characteristics of the obtained secondary battery are improved.
When the step (X) includes the first step (X-1) and the second step (X-2), the conductive material obtained in the second step (X-2) In the paste, since binders (binder resins) having different properties are uniformly mixed in advance, the time-dependent stability of the positive electrode slurry is improved by mixing the positive electrode active material in the step (Y).

In addition, from the viewpoint of ensuring applicability on the current collector, the viscosity of the secondary battery positive electrode slurry is preferably 1500 mPa · s or more and 10,000 mPa · s or less, and the solid content concentration is 50% by mass or more and 90% or less. It is preferable that it is below mass%. The viscosity of the secondary battery positive electrode slurry can be measured by the same method as that of the conductive material paste.
The ratio between the amount of conductive material paste (corresponding to solid content) and the amount of positive electrode active material can be adjusted as appropriate.

(Method for producing positive electrode for secondary battery)
The secondary battery positive electrode manufacturing method of the present invention is obtained by applying the secondary battery positive electrode slurry obtained by the secondary battery positive electrode slurry manufacturing method of the present invention to at least one surface of the current collector and drying. And forming a positive electrode mixture layer. More specifically, the manufacturing method includes a step of applying the slurry for a secondary battery positive electrode to at least one surface of the current collector (application step), and a secondary battery applied to at least one surface of the current collector. A step of drying the positive electrode slurry to form a positive electrode mixture layer on the current collector (drying step).

In the positive electrode for secondary battery manufactured in this way, since the positive electrode mixture layer is formed using the slurry for secondary battery positive electrode described above, if the positive electrode for secondary battery is used, the secondary battery The internal resistance of the battery can be reduced, and the low temperature characteristics, high temperature storage characteristics, and high temperature cycle characteristics can be improved, and excellent electrical characteristics can be exhibited in the secondary battery.

[Coating process]
A method for applying the slurry for a secondary battery positive electrode on the current collector is not particularly limited, and a known method can be used. Specifically, as a coating method, 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, or the like can be used. At this time, the secondary battery positive electrode slurry may be applied to only one side of the current collector, or may be applied to both sides. The thickness of the slurry film on the current collector after application and before drying can be appropriately set according to the thickness of the positive electrode mixture layer obtained by drying.

Here, as the current collector to which the slurry for the secondary battery positive electrode is applied, an electrically conductive and electrochemically durable material is used. Specifically, a current collector made of aluminum or an aluminum alloy can be used as the current collector. At this time, aluminum and an aluminum alloy may be used in combination, or different types of aluminum alloys may be used in combination. Aluminum and aluminum alloys are excellent current collector materials because they have heat resistance and are electrochemically stable.

[Drying process]
A method for drying the slurry for the secondary battery positive electrode on the current collector is not particularly limited, and a known method can be used. For example, drying with hot air, hot air, low-humidity air, vacuum drying, infrared rays, electron beam, etc. And a drying method by irradiation. By drying the slurry for the secondary battery positive electrode on the current collector in this way, a positive electrode mixture layer is formed on the current collector, and a positive electrode for a secondary battery comprising the current collector and the positive electrode mixture layer is provided. Obtainable.

Note that after the drying step, the positive electrode mixture layer may be subjected to pressure treatment using a die press or a roll press. By the pressure treatment, the adhesion between the positive electrode mixture layer and the current collector can be improved.
Furthermore, when the positive electrode mixture layer contains a curable polymer, the polymer is preferably cured after the positive electrode mixture layer is formed.

(Secondary battery)
The secondary battery of the present invention includes a positive electrode, a negative electrode, a separator, and an electrolytic solution, and the positive electrode for a secondary battery obtained by the method for producing a positive electrode for a secondary battery of the present invention is used as the positive electrode. It is. Since the secondary battery of the present invention uses the positive electrode manufactured by the method for manufacturing the positive electrode for secondary battery of the present invention, the internal resistance is reduced, and the low temperature characteristics, high temperature storage characteristics, and high temperature cycle characteristics are reduced. Excellent and high performance. Hereinafter, a lithium ion secondary battery will be described in detail as an example of the secondary battery of the present invention.

<Negative electrode>
As the negative electrode of the secondary battery, a known negative electrode used as a negative electrode for a secondary battery can be used. Specifically, as the negative electrode, for example, a negative electrode made of a thin plate of metallic lithium or a negative electrode formed by forming a negative electrode mixture layer on a current collector can be used.
In addition, as a collector, what consists of metal materials, such as iron, copper, aluminum, nickel, stainless steel, titanium, a tantalum, gold | metal | money, platinum, can be used. As the negative electrode mixture layer, a layer containing a negative electrode active material and a binder can be used. Furthermore, the binder is not particularly limited, and any known material can be used.

<Electrolyte>
As the electrolytic solution, an organic electrolytic solution in which a supporting electrolyte is dissolved in an organic solvent is usually used. For example, a lithium salt is used as the supporting electrolyte. Examples of the lithium salt include 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 NLi , (CF ₃ SO ₂ ) ₂ NLi, (C ₂ F ₅ SO ₂ ) NLi, and the like. Of these, LiPF ₆ , LiClO ₄ , and CF ₃ SO ₃ Li are preferable, and LiPF ₆ is particularly preferable because it is easily dissolved in a solvent and exhibits a high degree of dissociation. In addition, electrolyte may be used individually by 1 type and may be used combining two or more types by arbitrary ratios. Usually, the lithium ion conductivity tends to increase as the supporting electrolyte having a higher degree of dissociation is used, so that the lithium ion conductivity can be adjusted depending on the type of the supporting electrolyte.

The organic solvent used in the electrolytic solution is not particularly limited as long as it can dissolve the supporting electrolyte. For example, dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), Carbonates such as butylene carbonate (BC) and methyl ethyl carbonate (EMC); esters such as γ-butyrolactone and methyl formate; ethers such as 1,2-dimethoxyethane and tetrahydrofuran; sulfur-containing compounds such as sulfolane and dimethyl sulfoxide Etc. are preferably used. Moreover, you may use the liquid mixture of these solvents. Among them, it is preferable to use carbonates because they have a high dielectric constant and a wide stable potential region, and it is more preferable to use a mixture of ethylene carbonate and ethyl methyl carbonate.
The concentration of the electrolyte in the electrolytic solution can be adjusted as appropriate. For example, it is preferably 0.5 to 15% by mass, more preferably 2 to 13% by mass, and 5 to 10% by mass. Is more preferable. Further, known additives such as fluoroethylene carbonate and ethyl methyl sulfone may be added to the electrolytic solution.

<Separator>
The separator is not particularly limited, and for example, those described in JP 2012-204303 A can be used. Among these, since the film thickness of the entire separator can be reduced, and the ratio of the electrode active material in the secondary battery can be increased, and the capacity per volume can be increased. A microporous film made of a resin such as polyethylene, polypropylene, polybutene, or polyvinyl chloride is preferable.

<Method for producing secondary battery>
The secondary battery of the present invention includes, for example, a positive electrode and a negative electrode that are overlapped with a separator, wound in accordance with the battery shape as necessary, folded into a battery container, and electrolyzed in the battery container. It can be manufactured by injecting and sealing the liquid. In order to prevent an increase in pressure inside the secondary battery, overcharge / discharge, and the like, a fuse, an overcurrent prevention element such as a PTC element, an expanded metal, a lead plate, and the like may be provided as necessary. The shape of the secondary battery may be any of, for example, a coin shape, a button shape, a sheet shape, a cylindrical shape, a square shape, and a flat shape.

EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited to these Examples. In the following description, “%” and “part” representing amounts are based on mass unless otherwise specified.
In Examples and Comparative Examples, the binder adsorption amount of the conductive material, the dispersion stability of the conductive material paste, the potential stability of the conductive material paste, the temporal stability of the slurry for the secondary battery positive electrode, and the internal resistance of the secondary battery, the low temperature Characteristics, high temperature cycle characteristics and high temperature storage characteristics were evaluated using the following methods.

<Binder adsorption amount of conductive material>
NMP was added to the conductive material paste so that the solid content concentration was 1% by mass to obtain a diluted solution.
This diluted solution was centrifuged for 10 minutes at a rotational speed of 1000 rpm using a centrifuge. The obtained precipitate was dried in a vacuum dryer at 150 ° C. for 3 hours to obtain a dried product. At this time, it was confirmed that there was no weight change due to drying.
This dried product was heated to 500 ° C. in a nitrogen atmosphere at a heating rate of 10 ° C./min using a thermobalance, and the weight W1 (g) before the heat treatment (dry product) by the thermobalance was measured. From the weight W2 (g), the binder adsorption amount of the conductive material was calculated by the following formula.
Binder adsorption amount of conductive material (mg / g) = {(W1-W2) × 1000} / W2
<Dispersion stability of conductive material paste [Evaluation Method 1]>
The conductive material paste was allowed to stand in a 15 mL glass bottle for one week. And the dispersion particle diameter of the particle | grains in the electrically conductive material paste after standing was measured using the laser diffraction type particle size distribution measuring apparatus, the volume average particle diameter D50 was calculated | required, and the dispersibility was judged on the following reference | standard. The smaller the volume average particle diameter D50 (that is, the closer to the average particle diameter of the conductive material in the state where the binder is not adsorbed), the smaller the cohesiveness and the better the dispersion stability of the conductive material paste.
A: Volume average particle diameter D50 is less than 2 μm B: Volume average particle diameter D50 is from 2 μm to less than 5 μm C: Volume average particle diameter D50 is from 5 μm to less than 10 μm D: Volume average particle diameter D50 is from 10 μm to less than 15 μm E: Volume average Particle diameter D50 is 15 μm or more <Dispersion stability of conductive material paste [Evaluation method 2]>
The conductive material paste was put to a height of 5 cm in a glass test tube having an inner diameter of 8 mm, and allowed to stand for one week. And when the supernatant liquid was confirmed during standing, the number of days of standing until the supernatant liquid was confirmed was recorded. The longer the standing time until the supernatant liquid is confirmed, the better the dispersion stability, and the conductive material paste in which the supernatant liquid is not confirmed during standing is particularly excellent in the dispersion stability.
<Potential stability of conductive paste>
The conductive material paste is applied on an aluminum foil (thickness 20 μm) as a current collector with a comma coater so that the weight per unit area after drying is 10 mg / cm ² , 20 minutes at 90 ° C., 20 minutes at 120 ° C. After drying, heat treatment was further performed at 60 ° C. for 10 hours to obtain a laminate A having a conductive material coating film on the current collector.
This laminate A is cut into a circle having a diameter of 12 mm, and a circular polypropylene porous film (diameter 18 mm, thickness 25 μm), metallic lithium (diameter 14 mm), and expanded are formed on the cut-out laminate A on the conductive material coating film side. Metals were laminated in this order to obtain a laminate B. This laminate B was accommodated in a stainless steel coin-type outer container (diameter 20 mm, height 1.8 mm, stainless steel thickness 0.25 mm) provided with polypropylene packing. In this container, an electrolytic solution (a solution obtained by dissolving LiPF ₆ at a concentration of 1 mol / L in a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (EC / EMC = 3/7 by weight)) Was injected so that no air remained. After injecting the electrolyte, a 0.2 mm thick stainless steel cap is placed on the outer container via a polypropylene packing, and the battery can is sealed to produce a coin cell having a diameter of 20 mm and a thickness of about 2 mm. did.
A voltage of 4.4 V was applied to the obtained coin cell for 10 hours in an atmosphere at 25 ° C. The current density per unit mass (mA / g) of the conductive material flowing after 10 hours was determined and used as the oxidation current density. As the oxidation current density is smaller, the oxidation reaction of the binder when a voltage is applied is suppressed, that is, the potential stability of the electrode using the conductive material paste is excellent.
A: Oxidation current density of less than 0.2 mA / g B: Oxidation current density of 0.2 mA / g or more and less than 0.3 mA / g C: Oxidation current density of 0.3 mA / g or more and less than 0.4 mA / g D: Oxidation current density is 0.4 mA / g or more and less than 0.5 mA / g E: Oxidation current density is 0.5 mA / g or more

<Stability of secondary battery positive electrode slurry over time>
According to JIS Z 8803: 1991, the viscosity of the slurry for positive electrode was measured with a single cylindrical rotational viscometer (25 ° C., rotational speed = 60 rpm, spindle shape: 4), and a value of 1 minute was obtained after the measurement was started. The slurry viscosity was A. Moreover, the slurry viscosity B 1 day after preparation of the positive electrode slurry was measured. The viscosity change rate of the positive electrode slurry was calculated as follows and evaluated according to the following criteria. It shows that it is excellent in slurry stability, so that a viscosity change rate is low.
Viscosity change rate (%) = {(BA) / A} × 100
A: Viscosity change rate is less than 10% B: Viscosity change rate is 10% or more and less than 20% C: Viscosity change rate is 20% or more and less than 50% D: Viscosity change rate is 50% or more and less than 100% E: Viscosity change rate Is over 100%

<Internal resistance of secondary battery>
In order to evaluate the internal resistance of the secondary battery, the IV resistance was measured as follows. After charging to 50% of SOC (State Of Charge: Depth of Charge) at 1C (C is a numerical value expressed by rated capacity (mA) / 1h (hour)) in a 25 ° C atmosphere, focusing on 50% of SOC Charging for 20 seconds and discharging for 20 seconds at 0.5C, 1.0C, 1.5C, and 2.0C, respectively, and the battery voltage after 20 seconds in each case (charging side and discharging side) with respect to the current value The slope was obtained as IV resistance (Ω) (IV resistance during charging and IV resistance during discharging). The obtained IV resistance value (Ω) was evaluated according to the following criteria. It shows that internal resistance is so small that the value of IV resistance is small.
A: IV resistance is 2Ω or less B: IV resistance is more than 2Ω, 2.3Ω or less C: IV resistance is more than 2.3Ω, 2.5Ω or less D: IV resistance is more than 2.5Ω, 3.0Ω or less E: IV resistance is 3 More than 0Ω <Low-temperature characteristics of secondary battery>
In order to evaluate the low temperature characteristics of the secondary battery, the IV resistance was measured as follows. After charging to 50% of SOC (State Of Charge: Charging Depth) at 1C (C is a numerical value expressed by rated capacity (mA) / 1h (hours)) at -10 ° C atmosphere, centering on 50% of SOC As a result, charging for 15 seconds and discharging for 15 seconds at 0.5C, 1.0C, 1.5C, and 2.0C, respectively, and the battery voltage after 15 seconds in each case (charging side and discharging side) as current values The slope was determined as IV resistance (Ω) (IV resistance during charging and IV resistance during discharging). The obtained IV resistance value (Ω) was evaluated according to the following criteria. The smaller the IV resistance value, the lower the internal resistance, especially at low temperatures, and the better the low temperature characteristics.
A: IV resistance is 10Ω or less B: IV resistance is more than 10Ω and 12Ω or less C: IV resistance is more than 12Ω and less than 15Ω D: IV resistance is more than 15Ω and less than 20Ω E: IV resistance is more than 20Ω <high temperature cycle characteristics of secondary battery [ Evaluation method 1] >>
The secondary battery was charged to 4.2 V by a constant current method of 0.5 C in an atmosphere of 45 ° C., and charging / discharging to discharge to 3.0 V was repeated 200 cycles. Charge / discharge capacity retention represented by the ratio of the electric capacity at the end of 200 cycles to the electric capacity at the end of 5 cycles (= (electric capacity at the end of 200 cycles / electric capacity at the end of 5 cycles) × 100) (%) The rate was determined. It shows that it is excellent in high temperature cycling characteristics, so that this value is large. The obtained value (%) was evaluated according to the following criteria.
A: Charge / discharge capacity retention is 95% or more B: Charge / discharge capacity retention is 90% or more and less than 95% C: Charge / discharge capacity retention is 85% or more and less than 90% D: Charge / discharge capacity retention is 80% or more Less than 85% E: Charge / discharge capacity retention is less than 80% <High-temperature cycle characteristics of secondary battery [Evaluation Method 2]>
Charging / discharging which charged the 5-cell secondary battery to 4.2V by the constant-current method of 1.0C in 45 degreeC atmosphere, and discharged to 3.0V was repeated 100 cycles. Charge / discharge capacity retention represented by the ratio of the electric capacity at the end of 100 cycles to the electric capacity at the end of 5 cycles (= (electric capacity at the end of 100 cycles / electric capacity at the end of 5 cycles) × 100) (%) The rate was determined. It shows that it is excellent in high temperature cycling characteristics, so that this value is large. The obtained value (%) was evaluated according to the following criteria.
A: Charge / discharge capacity retention is 95% or more B: Charge / discharge capacity retention is 90% or more and less than 95% C: Charge / discharge capacity retention is 85% or more and less than 90% D: Charge / discharge capacity retention is 80% or more Less than 85% E: Charge / discharge capacity retention is less than 80% <High temperature storage characteristics of secondary battery>
The secondary battery was charged to a cell voltage of 4.2 V by a constant current method of 0.5 C in an atmosphere of 25 ° C., then discharged to 3.0 V, and an initial discharge capacity C ₀ was measured. Thereafter, the battery was charged to a cell voltage of 4.2 V by a constant current method of 0.5 C in a 25 ° C. atmosphere, and stored for 4 weeks (high temperature storage) in a 60 ° C. atmosphere. After high temperature storage, under 25 ° C. atmosphere to measure the residual capacity C ₁ after high-temperature storage was discharged to a constant current method 3.0V of 0.5 C. And capacity retention ratio (DELTA) Cs was computed according to the following formula. It shows that it is excellent in high temperature storage characteristics, so that (triangle | delta) Cs is large.
ΔCs (%) = (C ₁ / C ₀ ) × 100

-Experiment 1
In Experiment 1, the influence of the conductive material paste adsorption amount in the conductive material paste and the composition of the binder A on the dispersion stability and potential stability of the conductive material paste was examined.

Example 1-1
<Preparation of binder A1>
In an autoclave equipped with a stirrer, 240 parts of ion-exchanged water, 2.5 parts of sodium alkylbenzenesulfonate as an emulsifier, 35 parts of n-butyl acrylate (BA) as a (meth) acrylate monomer, a nitrile group-containing monomer 20 parts of acrylonitrile (AN) are added in this order, and the inside of the bottle is replaced with nitrogen. Then, 45 parts of 1,3-butadiene (BD) as a conjugated diene monomer (monomer composition of BA, AN, and BD) And 0.25 parts of ammonium persulfate as a polymerization initiator and polymerization reaction at a reaction temperature of 40 ° C. to give a conjugated diene monomer unit, a (meth) acrylate monomer unit and a nitrile A polymer comprising a group-containing monomer unit was obtained. The polymerization conversion rate was 85%.

400 ml (total solid content 48 grams) of a solution obtained by adding ion-exchanged water to the obtained polymer to adjust the total solid content concentration to 12% by mass was charged into a 1 liter autoclave equipped with a stirrer. After removing dissolved oxygen in the solution by flowing nitrogen gas for 10 minutes, as a hydrogenation reaction catalyst, 75 mg of palladium acetate was dissolved in 180 mL of ion-exchanged water added with 4-fold molar nitric acid with respect to palladium (Pd). And added. After the inside of the system was replaced with hydrogen gas twice, the content of the autoclave was heated to 50 ° C. while being pressurized with hydrogen gas to 3 MPa, and subjected to hydrogenation reaction (first stage hydrogenation reaction) for 6 hours. .

Next, the autoclave was returned to atmospheric pressure, and 25 mg of palladium acetate was dissolved in 60 ml of ion-exchanged water added with 4-fold mol of nitric acid with respect to Pd as a hydrogenation reaction catalyst. After the system was replaced twice with hydrogen gas, the contents of the autoclave were heated to 50 ° C. under pressure with hydrogen gas up to 3 MPa and subjected to hydrogenation reaction (second stage hydrogenation reaction) for 6 hours. .

Thereafter, the contents were returned to room temperature, the inside of the system was changed to a nitrogen atmosphere, and then concentrated using an evaporator until the solid concentration was 40% to obtain a binder aqueous dispersion. Further, 320 parts of NMP is added to 100 parts of this binder aqueous dispersion, water is evaporated under reduced pressure, and a polymer containing an alkylene structural unit, a (meth) acrylate monomer unit and a nitrile group-containing monomer unit An NMP solution of binder A1 was obtained.

<Manufacture of conductive material paste>
3.0 parts of acetylene black (Denka black powder: Denki Kagaku Kogyo, specific surface area 68 m ² / g, average particle size 35 nm) as a conductive material, and an NMP solution of binder A1 obtained as described above corresponding to solid content Then, 3.0 parts (100 parts per 100 parts of the conductive material) and an appropriate amount of NMP are stirred with a disper (3000 rpm, 10 minutes), and then the solid content concentration of the conductive material paste is 10% by mass. An appropriate amount of NMP was added and stirred with a disper (3000 rpm, 10 minutes) to prepare a conductive material paste. In the obtained conductive material paste, the binder adsorption amount of the conductive material was 375 mg / g, and the viscosity was 5500 mPa · s. Dispersion stability [Evaluation Method 1] and potential stability of the conductive material paste were evaluated using the produced conductive material paste. The results are shown in Table 1.

Example 1-2
Binder A2 was produced in the same manner as in Example 1-1 except that 49 parts of BD, 27 parts of BA, and 24 parts of AN were used as the monomer composition during the production of the binder. Then, a conductive material paste having a solid content concentration of 10% was produced in the same manner as in Example 1-1 except that binder A2 was used instead of binder A1. The obtained conductive material paste had a binder adsorption amount of 390 mg / g and a viscosity of 4000 mPa · s. Dispersion stability [Evaluation Method 1] and potential stability of the obtained conductive material paste were evaluated. The results are shown in Table 1.

(Example 1-3)
Binder A3 was produced in the same manner as in Example 1-1 except that 30 parts of BD, 30 parts of BA, and 40 parts of AN were used as the monomer composition during the production of the binder. A conductive material paste having a solid content concentration of 10% was produced in the same manner as in Example 1-1, except that binder A3 was used instead of binder A1. The obtained conductive material paste had a binder adsorption amount of 250 mg / g and a viscosity of 7000 mPa · s. Dispersion stability [Evaluation Method 1] and potential stability of the obtained conductive material paste were evaluated. The results are shown in Table 1.

(Example 1-4)
At the time of manufacturing the binder, except that 30 parts of BD, 25 parts of BA, 40 parts of AN, and 5 parts of monobutyl maleate (MBM) as a hydrophilic group-containing monomer were used as the monomer composition. Binder A4 was produced in the same manner as Example 1-1. Then, a conductive material paste having a solid content concentration of 10% was produced in the same manner as in Example 1-1 except that binder A4 was used instead of binder A1. The obtained conductive material paste had a binder adsorption amount of 170 mg / g and a viscosity of 6000 mPa · s. Dispersion stability [Evaluation Method 1] and potential stability of the obtained conductive material paste were evaluated. The results are shown in Table 1.

(Example 1-5)
Binder A5 was produced in the same manner as in Example 1-1, except that 56 parts of BD and 44 parts of AN were used as the monomer composition during the production of the binder, and that BA was not used. A conductive material paste having a solid content concentration of 10% was produced in the same manner as in Example 1-1, except that binder A5 was used instead of binder A1. The obtained conductive material paste had a binder adsorption amount of 150 mg / g and a viscosity of 3000 mPa · s. Dispersion stability [Evaluation Method 1] and potential stability of the obtained conductive material paste were evaluated. The results are shown in Table 1.

(Example 1-6)
In a reactor equipped with a stirrer, 70 parts of ion exchange water, 0.2 part of sodium dodecylbenzenesulfonate and 0.3 part of potassium persulfate were respectively supplied, the gas phase part was replaced with nitrogen gas, and the temperature was changed to 60 ° C. The temperature rose. Meanwhile, in a separate container, 50 parts of ion-exchanged water, 0.5 part of sodium dodecylbenzenesulfonate, 82 parts of BA, 15 parts of AN, 3 parts of methacrylic acid (MAA) (above, monomer composition with BA, AN, MAA) To obtain a mixture. This mixture was continuously added to the reactor over 4 hours for polymerization. During the addition, the reaction was carried out at 60 ° C. After completion of the addition, the reaction was further completed by stirring at 70 ° C. for 3 hours. The polymerization conversion rate was 99%. After cooling the obtained polymerization reaction liquid to 25 ° C., ammonia water was added to adjust the pH to 7, and then steam was introduced to remove unreacted monomers to obtain a 40% aqueous dispersion. In addition, NMP (320 parts) was added to 100 parts of this aqueous dispersion, and water was evaporated under reduced pressure to obtain a (meth) acrylate monomer unit, a nitrile group-containing monomer unit, and a hydrophilic group-containing monomer unit. An NMP solution of binder A6 made of a polymer containing was obtained.
A conductive material paste having a solid content concentration of 10% was produced in the same manner as in Example 1-1, except that binder A6 was used instead of binder A1. The obtained conductive material paste had a binder adsorption amount of 115 mg / g and a viscosity of 7500 mPa · s. Dispersion stability [Evaluation Method 1] and potential stability of the obtained conductive material paste were evaluated. The results are shown in Table 1.

(Comparative Example 1-1)
At the time of producing the conductive material paste, the NMP solution of binder A1 was changed to 0.6 part in solid equivalent, and the NMP solution of PVdF (KF Polymer # 7200, manufactured by Kureha Co., Ltd.) was 0.6 in solid equivalent. A conductive material paste having a solid content concentration of 10% was produced in the same manner as in Example 1-1 except that a part of the conductive material paste was used. In the obtained conductive material paste, the binder adsorption amount of the conductive material was 37 mg / g, and the viscosity of the conductive material paste was 9400 mPa · s. Dispersion stability [Evaluation Method 1] and potential stability of the obtained conductive material paste were evaluated. The results are shown in Table 1.

(Comparative Example 1-2)
Binder A7 was produced in the same manner as in Example 1-6, except that 2-ethylhexyl acrylate (2-HEA) was used instead of BA during the production of the binder. Then, a conductive material paste having a solid content concentration of 10% was manufactured in the same manner as in Example 1-1 except that binder A7 was used instead of binder A1. The obtained conductive material paste had a binder adsorption amount of 80 mg / g and a viscosity of 8500 mPa · s. Dispersion stability [Evaluation Method 1] and potential stability of the obtained conductive material paste were evaluated. The results are shown in Table 1.

In Tables 1 and 2, “◯” in the column of the structural unit of the binder and each monomer unit means that the binder includes the structural unit or the monomer unit, and “−” indicates the binder. Means that the structural unit or monomer unit is not included.

From Table 1, it can be seen that in Examples 1-1 to 1-6, a conductive material paste capable of forming a positive electrode having excellent dispersion stability and potential stability is obtained.
On the other hand, from Table 1, in Comparative Example 1-1, PVdF containing neither an alkylene structural unit nor a (meth) acrylic acid ester monomer unit is used as a binder. Since it is small, it turns out that it is inferior to the dispersion stability and electric potential stability of electrically conductive material paste. In Comparative Example 1-2, the binder A7 containing a (meth) acrylic acid ester monomer unit is used, but the value of the binder adsorption amount of the conductive material is small, and the dispersion stability and potential stability of the conductive material paste. It turns out that it is inferior to.

Here, from Examples 1-1 to 1-6, the binder adsorption amount of the conductive material can be controlled by changing the composition of the binder, which improves the dispersion stability and potential stability of the conductive material paste. I can understand. More specifically, based on a comparison between Examples 1-1 to 1-4 and Examples 1-5 and 1-6, a binder containing both an alkylene structural unit and a (meth) acrylate monomer unit is used. As a result, it was found that the dispersion stability and potential stability of the conductive material paste were further improved as compared with the case where a binder containing only one of them was used. From the comparison of Example 1-4, by using a binder that does not contain a hydrophilic group-containing monomer unit, compared with the case where a binder that contains a hydrophilic group-containing monomer unit is used, the conductive material paste is dispersed. It can be seen that the stability is further improved.

-Experiment 2-
Furthermore, in order to confirm that the high-temperature storage characteristics of the secondary battery produced using the conductive material paste were improved, the following comparative experiment was performed.

Example 2-1
<Production of secondary battery positive electrode slurry and positive electrode>
100 parts of a ternary active material (LiNi _0.5 Co _0.2 Mn _0.3 O ₂ ) (average particle size: 10 μm) having a layered structure as a positive electrode active material in the conductive material paste (including binder A6) of Example 1-6 Then, an appropriate amount of NMP was added as a solvent and stirred with a disper (3000 rpm, 20 minutes) to prepare a positive electrode slurry. The amount of NMP added was adjusted so that the solid content concentration of the positive electrode slurry was 65% by mass.

An aluminum foil with a thickness of 20 μm was prepared as a current collector. The positive electrode slurry obtained as described above was applied onto an aluminum foil with a comma coater so that the basis weight after drying was 20 mg / cm ² , dried at 90 ° C. for 20 minutes, and 120 ° C. for 20 minutes, A positive electrode raw material was obtained by heat treatment at 10 ° C. for 10 hours. This positive electrode original fabric was rolled by a roll press to produce a positive electrode comprising a positive electrode mixture layer having a density of 3.2 g / cm ³ and an aluminum foil. The positive electrode had a thickness of 70 μm.

<Manufacture of slurry for negative electrode and negative electrode>
In a planetary mixer with a disper, 100 parts of artificial graphite (volume average particle size: 24.5 μm) having a specific surface area of 4 m ² / g as a negative electrode active material, and a 1% aqueous solution of carboxymethyl cellulose as a dispersant (Daiichi Kogyo Seiyaku Co., Ltd.) 1 part of “BSH-12” produced by the company was added in an amount corresponding to the solid content, adjusted to a solid content concentration of 55% with ion-exchanged water, and then mixed at 25 ° C. for 60 minutes. Next, the solid content concentration was adjusted to 52% with ion-exchanged water. Thereafter, the mixture was further mixed at 25 ° C. for 15 minutes to obtain a mixed solution.

Into the mixed solution obtained as described above, 1.0 part of a 40% aqueous dispersion of a styrene-butadiene copolymer (with a glass transition temperature of −15 ° C.) in an amount corresponding to a solid content, and ion-exchanged water are added. The final solid content concentration was adjusted to 50%, and the mixture was further mixed for 10 minutes. This was defoamed under reduced pressure to obtain a slurry for a negative electrode having good fluidity.

The slurry for the negative electrode was applied on a copper foil having a thickness of 20 μm as a current collector by a comma coater so that the film thickness after drying was about 150 μm and dried. This drying was performed by conveying the copper foil in an oven at 60 ° C. at a speed of 0.5 m / min for 2 minutes. Then, the negative electrode original fabric was obtained by heat-processing at 120 degreeC for 2 minute (s). This negative electrode original fabric was rolled with a roll press to obtain a negative electrode having a negative electrode mixture layer with a thickness of 80 μm.

<Preparation of separator>
A single-layer polypropylene separator (width 65 mm, length 500 mm, thickness 25 μm, produced by a dry method, porosity 55%) was cut into a 5 cm × 5 cm square.

<Manufacture of secondary batteries>
An aluminum packaging exterior was prepared as the battery exterior. The positive electrode obtained above was cut into a 4 cm × 4 cm square and arranged so that the current collector-side surface was in contact with the aluminum packaging exterior. The square separator obtained above was disposed on the surface of the positive electrode mixture layer of the positive electrode. Furthermore, the negative electrode obtained above was cut into a square of 4.2 cm × 4.2 cm, and this was arranged on the separator so that the surface on the negative electrode mixture layer side faces the separator. Further, vinylene carbonate (VC) containing 1.5%, was charged with LiPF ₆ solution having a concentration of 1.0 M. The solvent of this LiPF ₆ solution is a mixed solvent (EC / EMC = 3/7 (volume ratio)) of ethylene carbonate (EC) and ethyl methyl carbonate (EMC). Furthermore, in order to seal the opening of the aluminum packaging material, heat sealing at 150 ° C. was performed to close the aluminum exterior, and a lithium ion secondary battery was manufactured. The obtained lithium ion secondary battery was evaluated for high-temperature storage characteristics. The results are shown in Table 2.

(Comparative Example 2-1)
Without passing through the conductive material paste, 3.0 parts of acetylene black (Denka black powder: Denki Kagaku, specific surface area 68 m ² / g, average particle size 35 nm) as the conductive material, and NMP solution of binder A6 corresponding to the solid content In addition, add 100 parts of a ternary active material (LiNi _0.5 Co _0.2 Mn _0.3 O ₂ ) having a layered structure as a positive electrode active material and an appropriate amount of NMP as a solvent, and stir with a disper. (3000 rpm, 60 minutes), a slurry for positive electrode was prepared. The amount of NMP added was adjusted so that the solid content concentration of the positive electrode slurry was 65% by mass. A positive electrode and a secondary battery were produced in the same manner as in Example 2-1, except that this positive electrode slurry was used, and the high-temperature storage characteristics of the secondary battery were evaluated. The results are shown in Table 2.

Table 2 shows that the secondary battery of Example 2-1 including the positive electrode formed using the conductive material paste of the present invention is obtained by mixing the conductive material, the binder, and the positive electrode active material all together without passing through the conductive material paste. It can be seen that it has excellent high-temperature storage characteristics as compared with the secondary battery of Comparative Example 2-1, which comprises a positive electrode formed from the prepared positive electrode slurry.

-Experiment 3
In Experiment 3, the solid content concentration of the conductive material paste, the composition of the binder A, the blending ratio of the binder A and the binder B, the manufacturing method of the positive electrode slurry, and the like were determined. The effects on stability and the internal resistance and high-temperature cycle characteristics of the secondary battery were investigated.

Example 3-1
<Manufacture of binder A8>
Except that the amount of AN used as a nitrile group-containing monomer was changed to 18.6 parts and the amount of BD used as a conjugated diene monomer was changed to 46.4 parts, the same as in Example 1-1, A polymer comprising a conjugated diene monomer unit, a (meth) acrylate monomer unit, and a nitrile group-containing monomer unit was obtained. The polymerization conversion was 85%, and the iodine value was 280 mg / 100 mg.
In addition, the measurement procedure of iodine value is as follows. First, 100 g of an aqueous dispersion of a polymer was coagulated with 1 liter of methanol and then vacuum-dried at 60 ° C. for 12 hours. The iodine value of the obtained dried polymer was measured according to JIS K6235 (2006).

The resulting polymer was subjected to a first stage hydrogenation reaction in the same manner as in Example 1-1. At this time, the iodine value of the polymer was 35 mg / 100 mg.

Subsequently, a second stage hydrogenation reaction was performed in the same manner as in Example 1-1.

Thereafter, the contents were returned to room temperature, the inside of the system was changed to a nitrogen atmosphere, and then concentrated using an evaporator until the solid concentration was 40% to obtain a binder aqueous dispersion. Further, 320 parts of NMP is added to 100 parts of this binder aqueous dispersion, water is evaporated under reduced pressure, and a polymer containing an alkylene structural unit, a (meth) acrylate monomer unit and a nitrile group-containing monomer unit An NMP solution of binder A8 was obtained.

<Manufacture of conductive material paste>
3.0 parts of acetylene black (Denka black powder: Denki Kagaku Kogyo, specific surface area 68 m ² / g, average particle size 35 nm) as a conductive material, and an NMP solution of binder A8 obtained as described above corresponding to solid content Then, 0.6 part and an appropriate amount of NMP are stirred with a disper (3000 rpm, 10 minutes), and then PVdF (KF polymer # 7200, manufactured by Kureha Co., Ltd.) is used as binder B in a solid equivalent amount). An appropriate amount of NMP was added to 2.4 parts and the solid content concentration of the conductive material paste was 10% by mass, and stirred with a disper (3000 rpm, 10 minutes) to prepare a conductive material paste. The binder amount of the conductive material of the obtained conductive material paste was 200 mg / g, and the viscosity was 5000 mPa · s. The dispersion stability [Evaluation Method 2] of the conductive material paste was evaluated using the produced conductive material paste. The results are shown in Table 3.

<Production of secondary battery positive electrode slurry and positive electrode>
In the conductive material paste obtained as described above, 100 parts of a ternary active material (LiNi _0.5 Co _0.2 Mn _0.3 O ₂ ) (average particle size: 10 μm) having a layered structure as a positive electrode active material and an appropriate amount as a solvent Of NMP was added and stirred with a disper (3000 rpm, 20 minutes) to prepare a positive electrode slurry. The amount of NMP added was adjusted so that the solid content concentration of the positive electrode slurry was 65% by mass. Using the prepared positive electrode slurry, the temporal stability of the slurry was evaluated. The results are shown in Table 3.

A positive electrode composed of a positive electrode mixture layer having a density of 3.2 g / cm ³ and an aluminum foil was produced in the same manner as in Example 2-1, except that the positive electrode slurry obtained above was used. The positive electrode had a thickness of 70 μm.

<Manufacture of slurry for negative electrode and negative electrode>
In the same manner as in Example 2-1, a negative electrode slurry was prepared, and a negative electrode having a negative electrode mixture layer having a thickness of 80 μm was obtained.

<Preparation of separator>
A separator was prepared in the same manner as in Example 2-1.

<Manufacture of secondary batteries>
A lithium ion secondary battery was produced in the same manner as in Example 2-1, except that the positive electrode obtained above was used.
The obtained lithium ion secondary battery was evaluated for internal resistance and high-temperature cycle characteristics [Evaluation Method 1]. The results are shown in Table 3.

(Example 3-2)
A conductive material paste was manufactured in the same manner as in Example 3-1, except that the blending ratio of the binder A8 and the binder B was changed as shown in Table 3 when the conductive material paste was manufactured. The binder amount of the conductive material of the obtained conductive material paste was 190 mg / g, and the viscosity was 7000 mPa · s. Except for using such a conductive material paste, a positive electrode slurry, a positive electrode, and a secondary battery were produced in the same manner as in Example 3-1, and evaluation was performed on each evaluation item. The results are shown in Table 3.

(Example 3-3)
A conductive material paste was manufactured in the same manner as in Example 3-1, except that the blending ratio of the binder A8 and the binder B was changed as shown in Table 3 when the conductive material paste was manufactured. The binder amount of the conductive material of the obtained conductive material paste was 250 mg / g, and the viscosity was 3000 mPa · s. Except for using such a conductive material paste, a positive electrode slurry, a positive electrode, and a secondary battery were produced in the same manner as in Example 3-1, and evaluation was performed on each evaluation item. The results are shown in Table 3.

(Example 3-4)
A conductive material paste was manufactured in the same manner as in Example 3-1, except that the solid content concentration was 13% and the blending ratio of binder A8 and binder B was changed as shown in Table 3 when the conductive material paste was manufactured. The binder amount of the conductive material of the obtained conductive material paste was 270 mg / g, and the viscosity was 7500 mPa · s. Except for using such a conductive material paste, a positive electrode slurry, a positive electrode, and a secondary battery were produced in the same manner as in Example 3-1, and evaluation was performed on each evaluation item. The results are shown in Table 3.

(Example 3-5)
At the time of production of the conductive material paste, first, acetylene black (DENKA BLACK powder: Denki Kagaku Kogyo, specific surface area 68 m ² / g, average particle size 35 nm) 3.0 parts as a conductive material, and PVdF (KF polymer) as a binder B # 7200 (manufactured by Kureha Co., Ltd.) was 2.4 parts by solid equivalent, and an appropriate amount of NMP solution was stirred with a disper (3000 rpm, 10 minutes). Thereafter, an NMP solution of binder A8 is added in an amount of NMP corresponding to the solid content (solid content concentration 8.0% by mass) and the solid content concentration is 7% by mass, and stirred with a disper. (3000 rpm, 10 minutes) to prepare a conductive material paste. The binder amount of the conductive material of the obtained conductive material paste was 170 mg / g, and the viscosity was 2000 mPa · s. A positive electrode slurry, a positive electrode, and a secondary battery were prepared in the same manner as in Example 3-1, except that the conductive material paste thus obtained was used, and each evaluation item was evaluated. The results are shown in Table 3. In addition, when the dispersion stability [Evaluation Method 2] of the obtained conductive material paste was evaluated, sedimentation was confirmed on the fifth day, but the secondary battery used for evaluation of internal resistance and high-temperature cycle characteristics was The conductive material paste on the day of preparation was used.
In addition, by mixing the binder B and the conductive material first, and then mixing the binder A8, the binder A8 having a relatively high dispersibility becomes difficult to be adsorbed to the conductive material, so that the dispersibility of the conductive material is lowered. At the same time, the viscosity of the conductive material paste becomes relatively high.

(Example 3-6)
As binder A, binder A9 produced as follows was used. In the production of binder A9, n-butyl acrylate (BA) as a (meth) acrylic acid ester monomer is not blended, 37 parts of acrylonitrile (AN) as a nitrile group-containing monomer, and as a conjugated diene monomer A binder A9 was obtained in the same manner as in Example 3-1, except that 63 parts of 1,3-butadiene (BD) was used. The density | concentration of the NMP solution of obtained binder A9 was 12 mass%.
A conductive material paste was prepared in the same manner as in Example 3-1, except that the solid content concentration was 13% by mass during the production of the conductive material paste and the obtained binder A9 was used. The amount of binder adsorbed on the conductive material of the obtained conductive material paste was 130 mg / g, and the viscosity was 5000 mPa · s. A positive electrode slurry, a positive electrode, and a secondary battery were prepared in the same manner as in Example 3-1, except that the conductive material paste obtained as described above was used, and each evaluation item was evaluated. The results are shown in Table 3.

(Example 3-7)
<Manufacture of binder A10>
In an autoclave equipped with a stirrer, 300 parts of ion exchange water, 82 parts of n-butyl acrylate and 3.0 parts of methacrylic acid as a (meth) acrylic acid ester monomer, 15 parts of acrylonitrile as a nitrile group-containing monomer, and molecular weight 0.05 part of t-dodecyl mercaptan as a regulator and 0.3 part of potassium persulfate as a polymerization initiator were added and stirred sufficiently, followed by polymerization by heating to 70 ° C. to obtain an aqueous dispersion. The polymerization conversion rate determined from the solid content concentration was approximately 99%. 320 parts of NMP was added to 100 parts of this latex, and water was evaporated under reduced pressure to obtain Binder A10. The density | concentration of the NMP solution of obtained binder A10 was 12 mass%.

A conductive material paste was prepared in the same manner as in Example 3-1, except that the binder A10 obtained as described above was used. The conductive material of the obtained conductive material paste had a binder adsorption amount of 105 mg / g and a viscosity of 9300 mPa · s. A positive electrode slurry, a positive electrode, and a secondary battery were prepared in the same manner as in Example 3-1, except that the conductive material paste obtained as described above was used, and each evaluation item was evaluated. The results are shown in Table 3.

(Example 3-8)
<Manufacture of binder A11>
In an autoclave equipped with a stirrer, 300 parts of ion-exchanged water, 72 parts of n-butyl acrylate as a (meth) acrylic acid ester monomer and 3.0 parts of methacrylic acid, 25 parts of acrylonitrile as a nitrile group-containing monomer, and molecular weight 0.05 part of t-dodecyl mercaptan as a regulator and 0.3 part of potassium persulfate as a polymerization initiator were added and stirred sufficiently, followed by polymerization by heating to 70 ° C. to obtain an aqueous dispersion. The polymerization conversion rate determined from the solid content concentration was approximately 99%. 320 parts of NMP was added to 100 parts of this latex, and water was evaporated under reduced pressure to obtain a binder A11. The density | concentration of the NMP solution of obtained binder A11 was 12 mass%.

A conductive material paste was prepared in the same manner as in Example 3-1, except that the binder A11 obtained as described above was used. The binder amount of the conductive material of the obtained conductive material paste was 103 mg / g, and the viscosity was 9150 mPa · s. A positive electrode slurry, a positive electrode, and a secondary battery were prepared in the same manner as in Example 3-1, except that the conductive material paste obtained as described above was used, and each evaluation item was evaluated. The results are shown in Table 3.

(Example 3-9)
Example 3 except that the amount of the binder A8 was changed to 0.8 part, the binder B, PVdF, 3.2 parts, and the conductive material, acetylene black, 2.0 parts at the time of producing the conductive material paste. In the same manner as in No. 1, a conductive material paste, a positive electrode slurry, a positive electrode, and a secondary battery were prepared, and evaluation was performed on each evaluation item. The binder amount of the conductive material of the obtained conductive material paste was 240 mg / g, and the viscosity was 5000 mPa · s.

(Comparative Example 3-1)
A conductive material paste was produced in the same manner as in Example 3-1, except that the binder A9 produced in the same manner as in Example 3-6 was used and the solid content concentration was changed to 3% during the production of the conductive material paste. The binder adsorption amount of the conductive material of the obtained conductive material paste was 50 mg / g, and the viscosity was lower than the detection lower limit of the apparatus. Evaluation was made for each evaluation item in the same manner as in Example 3-1, except that the conductive material paste thus obtained was used. The conductive material paste settled in 3 days, and the internal resistance of the secondary battery was reduced. Further, the high-temperature cycle characteristics [Evaluation Method 1] could not be evaluated. The results are shown in Table 3.

(Comparative Example 3-2)
Binder A9 produced in the same manner as in Example 3-6, 0.6 part, PVdF (KF Polymer # 7200, manufactured by Kureha Co., Ltd.) as binder B, 2.4 parts corresponding to the solid content, and conductive material Of acetylene black (Denka black powder: Denki Kagaku Kogyo, specific surface area 68 m ² / g, average particle size 35 nm) and ternary active material (LiNi _0.5 Co _0.2 Mn _0.3 O ₂ ) (average particle size: 10 parts) and an appropriate amount of NMP as a solvent were stirred with a planetary mixer (3000 rpm, 40 minutes) to prepare a positive electrode slurry. The solid content concentration of the obtained slurry was the same as in Example 3-1.

A positive electrode and a secondary battery were produced in the same manner as in Example 3-1, except that the positive electrode slurry obtained as described above was used, and each evaluation item was evaluated. The results are shown in Table 3.

(Comparative Example 3-3)
Conductive material paste was prepared in the same manner as in Example 3-1, except that binder A was not used at the time of production of the conductive material paste, 3 parts by mass of PVdF was used as binder B, and the solid concentration was 7%. Manufactured. The binder amount of the conductive material of the obtained conductive material paste was 37 mg / g, and the viscosity was 8000 mPa · s. Except for using such a conductive material paste, a positive electrode slurry, a positive electrode, and a secondary battery were produced in the same manner as in Example 3-1, and evaluation was performed on each evaluation item. The results are shown in Table 3.

In Tables 3 and 4, “-” in the column “Binder adsorption amount of conductive material” means that a conductive material paste is not prepared.

From Table 3, the conductive material paste of Examples 3-1 to 3-9, the slurry for secondary battery positive electrode, and the secondary battery are the conductive material paste of Comparative Examples 3-1 to 3-3, slurry for secondary battery positive electrode It can be seen that the internal resistance is low and the high-temperature cycle characteristics are good as compared with the secondary battery.
In particular, by adjusting the solid content concentration and viscosity of the conductive material paste from Examples 3-1 to 3-5 in Table 3, the aging stability of the secondary battery positive electrode slurry is improved, and the interior of the secondary battery is increased. It can be seen that the resistance can be reduced and the high-temperature cycle characteristics can be improved.
Further, from Examples 3-1 and 3-6 to 3-8 in Table 3, by adjusting the blending ratio of the three types of monomer units blended in the binder A, the dispersion stability of the conductive material paste and the secondary It can be seen that the time stability of the battery positive electrode slurry can be increased, the internal resistance of the secondary battery can be decreased, and the high-temperature cycle characteristics can be improved. In Example 3-6, since acrylonitrile was not blended in binder A, the cycle characteristics of the secondary battery positive electrode were relatively low, and the viscosity of the conductive paste was relatively high. It can be seen that the internal resistance of the secondary battery positive electrode is relatively high.
Further, from Example 3-1 and Comparative Example 3-2 in Table 3, the conductive material, the binder, and the positive electrode active material are mixed together, resulting in insufficient dispersion of the conductive material in the slurry. It can be seen that not only the cycle characteristics but also the time stability of the slurry was deteriorated.

-Experiment 4
In Experiment 4, the preparation method of the conductive material paste, the solid content concentration and viscosity, the composition of the binder A, the production method of the slurry for the positive electrode, etc., the dispersion stability of the conductive material paste, the low temperature characteristics and the high temperature cycle of the secondary battery The effect on characteristics was examined.

Example 4-1
<Manufacture of binder A8>
In the same manner as in Example 3-1, an NMP solution of binder A8 was obtained.

<Premix paste production>
3.0 parts of acetylene black (Denka black powder: Denki Kagaku Kogyo, specific surface area 68 m ² / g, average particle diameter 35 nm) as a conductive material, and NMP solution of the binder A8 as a first binder component corresponding to a solid content 0.6 parts (solid content concentration 8.0% by mass) and an appropriate amount of NMP such that the solid content concentration of the premixed paste becomes 10% by mass is stirred with a disper (3000 rpm, 10 minutes) and premixed. A paste was obtained. As shown in Table 4, the blending ratio of binder A8 to acetylene black, which is a conductive material, in the premixed paste was 20% when the blending amount of the conductive material was 100%. Further, the blending ratio of the binder A8 was 100% when the solid content of the total binder resin of the first binder component contained in the premix paste was 100%.

<Manufacture of conductive material paste>
Thereafter, 2.4 parts of a fluoropolymer composed of PVdF (KF polymer # 7200, manufactured by Kureha Co., Ltd.) as the second binder component is equivalent to the solid content, and the solid content concentration of the conductive material paste is 10% by mass. A suitable amount of NMP was added so that the mixture was stirred with a disper (3000 rpm, 10 minutes) to prepare a conductive material paste. In addition, as shown in Table 4, the blending ratio of the fluoropolymer when the solid content of all the binder resins (first binder component and second binder component) contained in the conductive material paste is 100% Was 80%. The binder amount of the conductive material of the obtained conductive material paste was 200 mg / g, and the viscosity was 5000 mPa · s. The dispersion stability [Evaluation Method 1] of the conductive material paste was evaluated using the produced conductive material paste. The results are shown in Table 4.

<Production of secondary battery positive electrode slurry and positive electrode>
In the conductive material paste obtained as described above, 100 parts of a ternary active material (LiNi _0.5 Co _0.2 Mn _0.3 O ₂ ) (average particle size: 10 μm) having a layered structure as a positive electrode active material and an appropriate amount as a solvent Of NMP was added and stirred with a disper (3000 rpm, 20 minutes) to prepare a positive electrode slurry.

<Manufacture of secondary batteries>
A lithium ion secondary battery was produced in the same manner as in Example 2-1, except that the positive electrode obtained above was used.
The obtained lithium ion secondary battery was evaluated for high-temperature cycle characteristics [Evaluation Method 2] and low-temperature characteristics. The results are shown in Table 4.

(Example 4-2)
Binder A8 blending ratio when binder A8 and fluoropolymer (PVdF) are used as the first binder component at the time of manufacturing the premixed paste, and the solid content of the first binder component is 100% Was prepared in the same manner as in Example 4-1, except that the blending ratio of the fluoropolymer was changed to 70% (0.42 parts) and the blending ratio of the fluoropolymer was changed to 30% (0.18 parts). The blending ratio of the binder A8 to the acetylene black as the conductive material in the premixed paste at this time was 14% when the blending amount of the conductive material was 100%.
Then, as a second binder component, 0.18 part of binder A8 corresponding to the solid content and 2.22 parts of fluoropolymer (PVdF) corresponding to the solid content are added to the obtained premixed paste. A conductive material paste was prepared in the same manner as in Example 4-1, except for the above. The binder amount of the conductive material of the obtained conductive material paste was 192 mg / g, and the viscosity was 6000 mPa · s. Then, a positive electrode slurry, a positive electrode, and a secondary battery were produced in the same manner as in Example 4-1, except that such a conductive material paste was used, and each evaluation item was evaluated. The results are shown in Table 4.

(Example 4-3)
Binder A8 blending ratio when binder A8 and fluoropolymer (PVdF) are used as the first binder component at the time of manufacturing the premixed paste, and the solid content of the first binder component is 100% Was mixed in the same manner as in Example 4-1, except that the blending ratio of the fluoropolymer was changed to 50% (0.3 part). Note that the blending ratio of the binder A8 to the acetylene black as the conductive material in the premixed paste at this time was 10% when the blending amount of the conductive material was 100%.
Then, with respect to the obtained premixed paste, as a second binder, the first binder resin A1 is 0.3 parts corresponding to the solid content, and the second binder resin (PVdF) is equivalent to the solid content 2. A conductive material paste was prepared in the same manner as in Example 4-1, except that 1 part was added. The binder amount of the conductive material of the obtained conductive material paste was 185 mg / g, and the viscosity was 7000 mPa · s. Then, a positive electrode slurry, a positive electrode, and a secondary battery were produced in the same manner as in Example 4-1, except that such a conductive material paste was used, and each evaluation item was evaluated. The results are shown in Table 4.

(Example 4-4)
In preparing a conductive material paste using a pre-mixed paste manufactured in the same manner as in Example 4-1, NMP was added so that the solid content concentration of the conductive material paste was 14% by mass, and a planetary mixer was used. Stirred (60 rpm, 60 minutes). The binder amount of the conductive material of the obtained conductive material paste was 190 mg / g, and the viscosity was 9000 mPa · s. Then, a positive electrode slurry, a positive electrode, and a secondary battery were produced in the same manner as in Example 4-1, except that such a conductive material paste was used, and each evaluation item was evaluated. The results are shown in Table 4.

(Example 4-5)
In preparing a conductive material paste using a premixed paste produced in the same manner as in Example 4-1, NMP was added so that the solid content concentration of the conductive material paste was 7% by mass, and Example 4-1. And stirred under the same conditions. The binder amount of the conductive material of the obtained conductive material paste was 175 mg / g, and the viscosity was 2500 mPa · s. Then, a positive electrode slurry, a positive electrode, and a secondary battery were produced in the same manner as in Example 4-1, except that such a conductive material paste was used, and each evaluation item was evaluated. The results are shown in Table 4.

(Example 4-6)
At the time of manufacturing the premixed paste, the blending ratio of the binder A8 to the acetylene black as the conductive material in the premixed paste is 5% (0.15 when 3 parts as the blended amount of the conductive material is 100%) Part). Further, an appropriate amount of NMP was added so that the solid content concentration of the premixed paste was 12% by mass. A premixed paste was obtained in the same manner as in Example 4-1. Example 4-1 except that 0.45 part of binder A8 and 2.4 parts of a fluoropolymer (PVdF) were added as a second binder component to the premixed paste obtained. Thus, a conductive material paste was obtained. The binder amount of the conductive material of the obtained conductive material paste was 102 mg / g, and the viscosity was 8000 mPa · s. Then, a positive electrode slurry, a positive electrode, and a secondary battery were produced in the same manner as in Example 4-1, except that such a conductive material paste was used, and each evaluation item was evaluated. The results are shown in Table 4.

(Example 4-7)
At the time of manufacturing the premixed paste, the blending ratio of the binder A8 to the acetylene black that is the conductive material in the premixed paste is 50% (1.5% when 3 parts that is the blended amount of the conductive material is 100%). Part). Further, an appropriate amount of NMP was added so that the solid content concentration of the premixed paste was 8% by mass. Others were the same as in Example 1, and a premixed paste was obtained. A conductive material paste was obtained in the same manner as in Example 4-1, except that 1.5 parts of a fluoropolymer (PVdF) was added as a second binder component to the obtained premixed paste. The conductive material of the obtained conductive material paste had a binder adsorption amount of 290 mg / g and a viscosity of 3500 mPa · s. Then, a positive electrode slurry, a positive electrode, and a secondary battery were produced in the same manner as in Example 4-1, except that such a conductive material paste was used, and each evaluation item was evaluated. The results are shown in Table 4.

(Example 4-8)
<Manufacture of binder A9>
In the same manner as in Example 3-6, an NMP solution of binder A9 was obtained.

<Manufacture of premixed paste and conductive material paste>
A premixed paste 1 and a conductive material paste were produced in the same manner as in Example 4-1, except that the binder A9 obtained as described above was used. The binder amount of the conductive material of the obtained conductive material paste was 130 mg / g, and the viscosity was 4000 mPa · s. Then, a positive electrode slurry, a positive electrode, and a secondary battery were produced in the same manner as in Example 4-1, except that such a conductive material paste was used, and each evaluation item was evaluated. The results are shown in Table 4.

(Example 4-9)
<Manufacture of binder A10>
In the same manner as in Example 3-7, an NMP solution of binder A10 was obtained.

<Manufacture of premixed paste and conductive material paste>
A premixed paste and 2 were produced in the same manner as in Example 4-1, except that the binder A10 obtained as described above was used. The binder amount of the conductive material of the obtained conductive material paste was 105 mg / g, and the viscosity was 8000 mPa · s. Then, a positive electrode slurry, a positive electrode, and a secondary battery were produced in the same manner as in Example 4-1, except that such a conductive material paste was used, and each evaluation item was evaluated. The results are shown in Table 4.

(Comparative Example 4-1)
A conductive material paste was produced in the same manner as in Comparative Example 3-3. The binder amount of the conductive material of the obtained conductive material paste was 37 mg / g, and the viscosity was 8000 mPa · s. Then, a positive electrode slurry, a positive electrode, and a secondary battery were produced in the same manner as in Example 4-1, except that such a conductive material paste was used, and each evaluation item was evaluated. The results are shown in Table 4.

(Comparative Example 4-2)
0.6 parts of the above-mentioned binder A9, acetylene black (DENKA BLACK powder: Denki Kagaku Kogyo, specific surface area 68 m ² / g, average particle diameter 35 nm) as a conductive material, 3.0 parts, and solid content concentration of the premix paste Was stirred with a disper (3000 rpm, 10 minutes) to obtain a premixed paste. In addition, the binder adsorption amount of the conductive material in this premixed paste was less than 100 mg / g.
In addition to the premixed paste, a ternary system having a layered structure as a positive electrode active material and 2.4 parts of a fluorine-based polymer made of PVdF (KF polymer # 7200, manufactured by Kureha Co., Ltd.) corresponding to the solid content. 100 parts of active material (LiNi _0.5 Co _0.2 Mn _0.3 O ₂ ) (average particle size: 10 μm) and an appropriate amount of NMP were stirred to obtain a positive electrode active material paste.
These premixed paste and positive electrode active material paste were mixed to obtain a positive electrode slurry.
Using the obtained slurry for positive electrode, a positive electrode and a secondary battery were prepared, and each evaluation item was evaluated. The results are shown in Table 4.

In Table 4, the terms * 1 to * 3 mean the following contents.
* 1: Mixing ratio when the solid content of the first binder component in the premixed paste is 100% * 2: Mixing ratio when the conductive material content in the premixed paste is 100% * 3 : Mixing ratio when the solid content of all binders in the conductive material paste is 100%

From Table 4, the conductive material paste of Examples 4-1 to 4-9, the slurry for secondary battery positive electrode, and the secondary battery are the conductive material paste of Comparative Examples 4-1 to 4-2, slurry for secondary battery positive electrode It can be seen that the dispersion stability of the conductive material paste is excellent as compared with the secondary battery, and the high-temperature cycle characteristics and low-temperature characteristics of the secondary battery are good.
In particular, from Examples 4-1 to 4-3 in Table 4, the conductive material paste was dispersed by adjusting the blending ratio of binder A in the first binder component of the premixed paste and the viscosity of the conductive material paste. It can be seen that the stability and low temperature characteristics of the secondary battery can be improved.
Also, from Examples 4-1 and 4-4 to 4-5 in Table 4, by adjusting the viscosity and solid content concentration of the conductive material paste, the dispersion stability of the conductive material paste and the low-temperature characteristics of the secondary battery and It can be seen that the high-temperature cycle characteristics can be improved.
Further, from Examples 4-1 and 4-6 to 4-7 in Table 4, the binder A having a specific property is blended mainly in the first step (X-1) of the step (X), and the blending thereof. It can be seen that by adjusting the amount, the dispersion stability of the conductive material paste and the low-temperature characteristics and high-temperature cycle characteristics of the secondary battery can be improved.
Further, from Examples 4-1 and 4-8 to 4-9 in Table 4, the dispersion stability of the conductive material paste is improved by adjusting the composition of the binder A, and the high-temperature cycle characteristics of the secondary battery and It can be seen that the low temperature characteristics can be improved.
Further, from Example 4-1 in Table 4 and Comparative Example 4-1 using only PVdF as the first binder component, the content of binder A in the first binder component is If it is insufficient, it can be seen that the low temperature characteristics and the high temperature cycle characteristics deteriorate. Further, from Example 4-1 and Comparative Example 4-2 in Table 4, the process (X) (first process (X-1) and second process (X-2)) and process (Y) were performed. If the slurry for the positive electrode is manufactured without the conductive material paste being sufficiently dispersible in the conductive material paste, the dispersion stability of the conductive material paste and the low-temperature characteristics and high-temperature cycle characteristics of the secondary battery may be deteriorated. I understand that.

Claims

Containing conductive material and binder A,
The binder A includes at least one of an alkylene structural unit and a (meth) acrylic acid ester monomer unit,
The binder adsorption amount of the conductive material is 100 mg / g or more and 600 mg / g or less,
Conductive material paste for secondary battery electrodes.
The conductive material paste for a secondary battery electrode according to claim 1, wherein the binder A includes an alkylene structural unit.
The conductive material paste for a secondary battery electrode according to claim 1, wherein the binder A includes both an alkylene structural unit and a (meth) acrylic acid ester monomer unit.
The conductive material paste for a secondary battery electrode according to any one of claims 1 to 3, wherein the binder A further contains 2% by mass to 50% by mass of a nitrile group-containing monomer unit.
The conductive material paste for a secondary battery electrode according to any one of claims 1 to 4, having a viscosity of 1000 mPa · s to 10,000 mPa · s.
The conductive material paste for a secondary battery electrode according to any one of claims 1 to 5, wherein the solid content concentration is 5% by mass or more and 15% by mass or less.
A step (X) of preparing a conductive material paste for a secondary battery electrode according to any one of claims 1 to 6;
The manufacturing method of the slurry for secondary battery positive electrodes including the process (Y) of mixing the said electrically conductive material paste for secondary battery electrodes, and a positive electrode active material.
The step (X)
A first step (X-1) of mixing the conductive material and a first binder component containing the binder A as a main component to obtain a premixed paste;
A second step (X-2) of obtaining a conductive material paste for a secondary battery electrode by adding a second binder component containing a fluorine-based polymer as a main component to the premixed paste;
The manufacturing method of the slurry for secondary battery positive electrodes of Claim 7 containing these.
The secondary battery positive electrode slurry obtained by the manufacturing method according to claim 7 or 8 is applied to at least one surface of the current collector and dried to form a positive electrode mixture layer. A method for producing a positive electrode for a battery.
A secondary battery having a positive electrode, a negative electrode, a separator and an electrolyte,
A secondary battery, wherein the positive electrode is a positive electrode for a secondary battery manufactured by the method for manufacturing a positive electrode for a secondary battery according to claim 9.