JP6365181B2 - 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 method for producing secondary battery - Google Patents

Description

  The present invention relates to a conductive material paste for a secondary battery electrode, 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 such as 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.

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. An electrode mixture layer, for example, a positive electrode mixture layer, is usually formed by applying a positive electrode slurry obtained by dispersing or dissolving a positive electrode active material, a conductive material, a binder, or the like in a dispersion medium on a current collector and drying it. It is formed by binding a positive electrode active material and a conductive material with a binder.
Therefore, attempts have been made to improve the slurry for electrodes in order to achieve further improvement in performance of the secondary battery. Specifically, a technique using a plurality of types of binders as a binder to be blended in the electrode slurry has been reported (for example, see 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. Has been proposed to improve the performance of the electrode and improve the energy density and cycle characteristics of the secondary battery through 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, a secondary battery is prepared 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. There are reports on techniques for improving various performances (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 fluoropolymer, 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.

  Furthermore, in Patent Document 4, a conductive material paste containing a conductive material and a binder is prepared, and after the obtained conductive material paste is diluted with a solvent, 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, in order to improve electrical characteristics such as output characteristics in a low temperature environment, the secondary battery not only secures ionic conductivity in the secondary battery but also reduces DC resistance (corresponding to IV resistance). There is a demand for sufficiently reducing internal resistance. Here, particularly in a low temperature environment, since the direct current resistance is large, for example, a large voltage drop occurs at the time of discharge, and the operating voltage is quickly reached, so that a sufficient battery capacity cannot be obtained. Therefore, it is particularly important to reduce the direct current resistance at low temperatures.
However, the conventional technology described above cannot provide a secondary battery having a sufficiently low DC resistance at low temperatures. In addition, the conductive material paste and the electrode slurry obtained by using the above-described conventional technology aggregate the conductive material over time, and the electrical property of the secondary battery obtained by using the conductive material paste and the electrode slurry. The characteristics may be impaired. In industrial production of secondary batteries, long-term transport and long-term storage in the state of conductive material paste and electrode slurry is inevitable, ensuring the stability of conductive material paste and electrode slurry over time. Is also very important.
Therefore, the above conventional technology still has room for improvement in terms of reducing the DC resistance at low temperatures of the obtained secondary battery while ensuring the temporal stability of the conductive material paste and the electrode slurry.

Therefore, an object of the present invention is to provide a conductive material paste for a secondary battery electrode that is excellent in stability over time and can sufficiently reduce the direct current resistance of a secondary battery at a low temperature.
Another object of the present invention is to provide a slurry for a secondary battery positive electrode that is excellent in stability over time and can sufficiently reduce the direct current resistance of a secondary battery at a low temperature.
Furthermore, the present invention provides a method for producing a positive electrode for a secondary battery capable of producing a positive electrode capable of sufficiently reducing the direct current resistance at a low temperature of the secondary battery, and a method for producing the positive electrode for the secondary battery. An object of the present invention is to provide a secondary battery including the positive electrode.

  The present inventor has intensively studied for the purpose of solving the above problems. And this inventor is the conductive material paste in which the amount of adsorption to the conductive material includes at least two binders each having a specific range, and the TI value indicating thixotropy is controlled within the specific range, It has been found that the stability over time is excellent, and that the use of the conductive material paste can suppress the DC resistance of the secondary battery at a low temperature, and the present invention has been completed.

That is, this invention aims at solving the said subject advantageously, and the electrically conductive material paste for secondary battery electrodes of this invention contains a electrically conductive material, a 1st binder, a 2nd binder, and a solvent. And the adsorption amount of the first binder to the conductive material is 110 mg / g or more and 1000 mg / g or less, and the adsorption amount of the second binder to the conductive material is 0 mg / g or more and less than 110 g / g. And the TI value (ratio of the viscosity at 6 rpm to the viscosity at 60 rpm) is 1.0 or more and 6.0 or less. As described above, two binders each having an adsorption amount on the conductive material of 110 mg / g or more and 1000 mg / g or less and 0 mg / g or more and less than 100 mg / g are included, and the TI value is 1.0 to 6 The conductive material paste for secondary battery electrodes within the range of 0.0 is excellent in stability over time, and by using the conductive material paste, a secondary battery having a sufficiently low DC resistance at a low temperature can be produced. it can.
The “adsorption amount of the first binder to the conductive material”, the “adsorption amount of the second binder to the conductive material”, and the “TI value of the conductive material paste” were measured by the methods described in this specification. Can be calculated.

Here, it is preferable that the conductive material paste for a secondary battery electrode of the present invention has a viscosity at 60 rpm of 500 mPa · s or more and 10,000 mPa · s or less. When the viscosity of the conductive material paste at 60 rpm is in the range of 500 to 10,000 mPa · s, the temporal stability of the conductive material paste and the electrode slurry containing the conductive material paste can be further improved.
The “viscosity of the conductive material paste at 60 rpm” is measured with a single cylindrical rotational viscometer (B-type viscometer), and can be specifically measured by the method described in this specification.

  In the conductive material paste for a secondary battery electrode of the present invention, the first binder includes at least one of an alkylene structural unit and a (meth) acrylic acid ester monomer unit, and further includes a nitrile group-containing monomer. The unit is preferably contained in an amount of 2% by mass to 50% by mass. If the first binder includes an alkylene structural unit and / or a (meth) acrylic acid ester monomer unit, and further includes a nitrile group-containing monomer unit in an amount of 2 to 50% by mass, the conductive material paste and the conductive material paste The temporal stability of the electrode slurry can be further improved. In addition, the direct current resistance of the secondary battery at a low temperature can be further reduced, and the high-temperature storage characteristics can be further improved.

  Furthermore, in the conductive material paste for a secondary battery electrode of the present invention, the ratio of the amount of the first binder in the total amount of the first binder and the second binder is 10% by mass or more and 50% by mass or less. It is preferable that If the first binder is 10 to 50% by mass in the total of the first binder and the second binder, both the solid content concentration and the viscosity of the obtained electrode slurry are suitable, It becomes possible to ensure a good balance between the coating property of the slurry on the current collector and the drying efficiency. Moreover, the temporal stability of the conductive material paste and the electrode slurry containing the conductive material paste can be further improved, and the DC resistance of the secondary battery at a low temperature can be further reduced.

  In addition, the conductive material paste for secondary battery electrodes of the present invention preferably has a TI value of 2.0 or more and 3.0 or less. When the TI value of the conductive material paste is in the range of 2.0 to 3.0, the temporal stability of the conductive material paste and the electrode slurry containing the conductive material paste can be further improved. In addition, the DC resistance of the secondary battery at a low temperature can be further reduced.

  Moreover, this invention aims to solve the said subject advantageously, The slurry for secondary battery positive electrodes of this invention is the electrically conductive material paste for any of the above-mentioned secondary battery electrodes, and positive electrode active material. It is characterized by including. A secondary battery positive electrode slurry containing any of the above-described conductive material pastes for secondary battery electrodes is excellent in stability over time, and a secondary battery having sufficiently low DC resistance at low temperatures by using the conductive material paste. Can be manufactured.

  Furthermore, the present invention aims to advantageously solve the above-mentioned problems, and the method for producing a positive electrode for a secondary battery according to the present invention comprises the above-described slurry for a secondary battery positive electrode at least as a current collector. It is characterized by including a step of applying to one surface and drying to form a positive electrode mixture layer. If a positive electrode mixture layer is formed from the above-mentioned slurry for secondary battery positive electrode, a positive electrode capable of sufficiently reducing the direct current resistance at low temperature of the secondary battery can be produced.

  In addition, the secondary battery of the present invention is a secondary battery having a positive electrode, a negative electrode, a separator, and an electrolyte solution, wherein the positive electrode is manufactured by the above-described method for manufacturing a positive electrode for a secondary battery. It is a positive electrode. A secondary battery including a secondary battery positive electrode manufactured by the above-described method for manufacturing a secondary battery positive electrode has sufficiently low DC resistance at a low temperature and is excellent in electrical characteristics such as output characteristics.

ADVANTAGE OF THE INVENTION According to this invention, the electrically conductive material paste for secondary battery electrodes which is excellent in temporal stability and can fully reduce the direct current resistance in the low temperature of a secondary battery can be provided.
In addition, according to the present invention, it is possible to provide a slurry for a secondary battery electrode that has excellent temporal stability and can sufficiently reduce the direct current resistance of a secondary battery at a low temperature.
Furthermore, according to this invention, the manufacturing method of the positive electrode for secondary batteries which can manufacture the positive electrode which can fully reduce the direct current resistance at the low temperature of a secondary battery, and the manufacturing method of the said positive electrode for secondary batteries A secondary battery including the positive electrode manufactured in (1) 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 slurry for secondary battery positive electrodes of this invention is formed using the electrically conductive material paste for secondary battery electrodes of this invention. In addition, the method for producing a positive electrode for a secondary battery of the present invention is characterized in that a positive electrode mixture layer is formed from the slurry for a secondary battery positive electrode of the present invention. Moreover, 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 a conductive material, a binder component including a first binder and a second binder, and a solvent, and the adsorption amount of the first binder to the conductive material is 110 mg. / G or more and 1000 mg / g or less, the adsorption amount of the second binder to the conductive material is 0 mg / g or more and less than 110 mg / g, and the TI value is 1.0 or more and 6.0 or less. It is characterized by that.
As described above, the conductive material paste containing at least two types of binders having different adsorption capacities to the conductive material as the binder component and having a TI value within a specific range has excellent temporal stability and the conductive material paste. It is possible to sufficiently reduce the direct current resistance at a low temperature of a secondary battery including an electrode formed by using.

<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, preferably 1500 m ² / g or less, more preferably 1000 m ² / g or less. If the specific surface area of the conductive material is 10 m ² / g or more, the adsorption amount of each binder to the conductive material can be easily adjusted, and the binder (especially the first binder) is less than 1500 m ² / g. ) Can be prevented from being deteriorated due to excessive adsorption.
In the present specification, the “specific surface area of a conductive material” is a BET specific surface area by a nitrogen adsorption method, and can be measured in accordance with ASTM D3037-81.

<Binder component>
The binder component 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 component contained in the electrode mixture layer is detached from the electrode mixture layer. It is a component that can be retained so that it does not. In general, the binder component 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, the positive electrode active material and the conductive material, Alternatively, the conductive materials are bound together to prevent the positive electrode active material and the like from dropping from the current collector.
The conductive material paste of the present invention contains at least a first binder and a second binder as binder components. In addition, binder components other than a 1st binder and a 2nd binder may be contained in the electrically conductive material paste.

[First binder]
The first binder favorably disperses the conductive material by adsorbing well to the conductive material, contributes to the improvement of the temporal stability of the conductive material paste, and in addition promotes the formation of a good conductive path. It is a component (polymer) that can reduce the direct current resistance of a secondary battery at a low temperature and improve electrical characteristics in a high temperature environment such as high temperature storage characteristics.

[[First Binder Composition]]
The composition of the first binder is not particularly limited, but the first binder preferably includes at least one of an alkylene structural unit and a (meth) acrylic acid ester monomer unit. Moreover, it is preferable that a 1st binder contains a nitrile group containing monomer unit.
In the present specification, “including an alkylene structural unit” means “repeating composed of only 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.

When the first binder includes an alkylene structural unit and / or a (meth) acrylic acid ester monomer unit, adsorbability of the first binder to the conductive material is ensured. Therefore, the aggregation of the conductive material is suppressed, the direct current resistance at a low temperature of the secondary battery is reduced, and the temporal stability of the conductive material paste can be improved. In addition, the oxidation resistance of the first binder is improved by including an alkylene structural unit and / or a (meth) acrylic acid ester monomer unit. And the good dispersion state of the conductive material in the electrode mixture layer and the excellent oxidation resistance combine to improve the high-temperature storage characteristics of a secondary battery comprising an electrode formed using the conductive material paste of the present invention. be able to.
The first binder contains a nitrile group-containing monomer unit, which improves the stability of the conductive material paste over time, reduces the DC resistance of the secondary battery at low temperatures, and improves high-temperature storage characteristics. Can be made.

The first binder 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. In particular, when both the alkylene structural unit and the (meth) acrylic acid ester monomer unit are included, the stability of the conductive material paste over time can be improved, and in addition, the conductive material paste was used. This is because the DC resistance of the secondary battery at a low temperature can be reduced and the high-temperature storage characteristics can be improved.
Hereinafter, the alkylene structural unit, (meth) acrylic acid ester monomer unit, nitrile group-containing monomer unit and other monomer units contained in the first binder will be described in detail.

-Alkylene structural unit-
The alkylene structural unit may be linear or branched, but from the viewpoint of improving the temporal stability of the conductive material paste, the alkylene structural unit is linear, that is, a linear alkylene structural unit. Preferably there is.
The method for introducing the alkylene structural unit into the first binder 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) The method of preparing a polymer from the monomer composition containing a 1-olefin monomer is mentioned. Among these, the method (1) is preferable because the production of the first binder 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 is a unit (1,3-butadiene hydride unit).
Moreover, as a 1-olefin monomer, ethylene, propylene, 1-butene etc. are mentioned, for example.
These conjugated diene monomers and 1-olefin monomers can be used alone or in combination of two or more.

  And the content rate of the alkylene structural unit in said 1st binder is 30 mass when all the repeating units (total of a monomer unit and a structural unit) in a 1st binder are 100 mass%. % Or more is 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 first binder within the above range, the temporal stability of the conductive material paste is improved. In addition, the conductive material is well dispersed in the electrode mixture layer of the electrode formed using the conductive material paste, and the direct current resistance at low temperature can be reduced. In addition, the high temperature storage characteristics of the secondary battery are improved. be able to.

  In addition, when the content rate of the alkylene structural unit in the first binder is less than 30% by mass, the solubility of the first binder in a solvent such as N-methylpyrrolidone (NMP) becomes excessively high, and as a result. The first binder cannot be stably adsorbed to the conductive material and dissociates in the solvent, so that the temporal stability is lowered. In addition, there is a possibility that the high-temperature storage characteristics of secondary batteries manufactured using them will be reduced by reducing the amount of adsorption to the conductive material. On the other hand, when the content ratio of the alkylene structural unit in the first binder exceeds 98% by mass, the solubility of the first binder particularly in a solvent such as NMP becomes excessively low. In the secondary battery electrode slurry, there is a bias in the dispersion of the conductive material, which may increase the low-temperature direct current resistance of the secondary battery manufactured using them, and may decrease the high-temperature storage characteristics.

-(Meth) acrylate 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 methacrylate 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 temporal stability of the conductive material paste, the (meth) acrylic acid ester monomer has an alkyl group having 4 to 10 carbon atoms bonded to a non-carbonyl oxygen atom. Of these, preferred are alkyl acrylates of which n-butyl acrylate and 2-ethylhexyl acrylate are preferred, and n-butyl acrylate is more preferred.
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 said 1st binder is 10 mass% or more and 40 mass% when all the repeating units in a 1st binder are 100 mass%. The following is preferable. By making the content ratio of the (meth) acrylic acid ester monomer unit in the first binder within the above-mentioned range, the solubility of the first binder in a solvent such as NMP is secured, and the resulting conductivity is obtained. The stability with time of the material paste is improved. Further, the stability of the first binder in the electrolytic solution is ensured, and in particular, the high-temperature storage characteristics of the secondary battery can be improved.

  In addition, when the content rate of the (meth) acrylic acid ester monomer unit in the first binder is less than 10% by mass, the strength of the electrode mixture layer formed using the conductive material paste is reduced, and the amount of the electrolyte mixture with respect to the electrolytic solution is reduced. The degree of swelling increases and the peel strength decreases. Therefore, there is a possibility that the high-temperature storage characteristics of a secondary battery provided with such an electrode will be deteriorated. On the other hand, when the content ratio of the (meth) acrylic acid ester monomer unit in the first binder exceeds 40% by mass, the solubility of the first binder particularly in a solvent such as NMP is lowered. In the conductive material paste and the electrode slurry, there is a possibility that the conductive material is unevenly dispersed, and the stability with time thereof may be impaired. Therefore, the electrodes formed using them are inferior in uniformity, and there is a risk that the DC resistance at a low temperature of a secondary battery equipped with the electrodes will increase and the high-temperature storage characteristics will deteriorate.

-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 first binder 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 first binder is preferably 2% by mass or more, when the total repeating unit in the first binder is 100% by mass, preferably 10% by mass. The above is more preferable, 12% by mass or more is further preferable, 50% by mass or less is preferable, 40% by mass or less is more preferable, 35% by mass or less is further preferable, and 25% by mass or less is particularly preferable. By setting the content ratio of the nitrile group-containing monomer unit in the first binder within the above range, the temporal stability of the conductive material paste is improved. In addition, the conductive material is well dispersed in the electrode mixture layer of the electrode formed using the conductive material paste, and the direct current resistance at low temperature can be reduced. In addition, the high temperature storage characteristics of the secondary battery are improved. be able to.

  In addition, when the content ratio of the nitrile group-containing monomer unit in the first binder exceeds 50% by mass, the first binder is easily dissolved in the electrolytic solution and cannot be stably adsorbed to the conductive material. Dissociation in the solvent reduces the temporal stability. And there exists a possibility that the DC resistance in the low temperature of a secondary battery may rise, and the high temperature storage characteristic of a secondary battery may fall. Furthermore, the adsorption capacity of the first binder with respect to the conductive material is lowered, and it becomes difficult to adjust the adsorption amount of the conductive material to the first binder. On the other hand, when the ratio of the nitrile group-containing monomer unit in the first binder is less than 2% by mass, the solubility of the first binder in a solvent such as NMP is particularly lowered, and the conductive material paste and the two There is a possibility that the dispersibility of the conductive material in the slurry for the secondary battery electrode may decrease. And there exists a possibility that the direct current resistance in the low temperature of a secondary battery provided with the electrode manufactured using them may rise, and a high temperature storage characteristic may fall.

-Other monomer units-
The 1st binder may contain other monomer units other than the alkylene structural unit mentioned above, a (meth) acrylic acid ester monomer unit, and a nitrile group containing monomer unit. Examples of other monomer units include hydrophilic group-containing monomer units and aromatic vinyl monomer units derived from aromatic vinyl monomers such as styrene.

Here, as the hydrophilic group-containing monomer capable of forming a hydrophilic group-containing monomer unit, a monomer having a carboxylic acid group, a monomer having a sulfonic acid group, a single monomer having a phosphate group And monomers having a hydroxyl group can be used.
Specific examples of these monomers include those described in International Publication No. 2013/080989.
In the present invention, the above-mentioned (meth) acrylic acid ester monomer and nitrile group-containing monomer do not include a carboxylic acid group, a sulfonic acid group, a phosphoric acid group and a hydroxyl group.

  Here, in particular, the hydrophilic group-containing monomer such as a monomer having a carboxylic acid group can contribute to the improvement of the production stability of the first binder, while the hydrophilic group-containing monomer unit is the first. When included in the binder, the dispersibility of the conductive material of the first binder may be impaired. Therefore, from the viewpoint of securing the temporal stability of the conductive material paste, the content ratio of the hydrophilic group-containing monomer unit in the first binder is 100% by mass of all repeating units in the first binder. In some cases, it is preferably less than 0.05% by mass (substantially free), more preferably 0% by mass.

[[Adsorption amount of first binder to conductive material]]
Here, the adsorption amount of the first binder to the conductive material (first binder adsorption amount) needs to be 110 mg / g or more and 1000 mg / g or less, preferably 100 mg / g or more, more preferably 150 mg / g. g or more, more preferably 200 mg / g or more, preferably 600 mg / g or less, more preferably 400 mg / g or less. When the first binder adsorption amount is less than 110 mg / g, the conductive material agglomerates, the stability of the conductive material paste cannot be ensured over time, and the secondary battery obtained using the conductive material paste has a direct current at low temperature. Resistance increases and high temperature storage characteristics decrease. On the other hand, when the first binder adsorption amount exceeds 1000 mg / g, the first binder as an insulator is excessively adsorbed on the conductive material, and the secondary battery obtained using the conductive material paste at low temperature DC resistance increases and high temperature storage characteristics decrease.

The adsorption amount of the first binder to the conductive material can be calculated by the following method.
A conductive material, a solution obtained by dissolving the same amount of the first binder as the conductive material (solid content equivalent amount) in a solvent (such as NMP), and an appropriate amount of solvent as necessary are stirred with a disper (3000 rpm, 60 minutes) to prepare a conductive material paste for adsorption amount measurement with a solid content concentration of 10% by mass. Thereafter, if necessary, a solvent is further added to the conductive material paste for measuring the amount of adsorption to adjust the solid content concentration (for example, 1% by mass) that can be easily centrifuged. Since the first binder once adsorbed on the conductive material is difficult to be detached from the conductive material, the influence on the measured value of the first binder adsorption amount by adjusting the solid content concentration can be ignored.
Next, the conductive paste for measuring the adsorption amount or the diluted solution thereof is subjected to a centrifugal separation process using a centrifugal separator until the supernatant and the precipitate are separated, and the precipitate is collected. The precipitate is dried under conditions where the solvent is vaporized but the first binder is not thermally decomposed until there is no change in mass, the solvent remaining in the precipitate is removed, and the dried product (mainly the first binder + A conductive material). The drying may be performed under reduced pressure.
The obtained dried product is gradually heated to a temperature at which the first 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), The first binder in the dried product is removed.
Calculate the amount of adsorption of the first binder to the conductive material from the following formula, assuming that the mass before heat treatment (dry matter) by this thermobalance is W1 (g) and the mass after heat treatment W2 (g). Can do.
First binder adsorption amount (mg / g) = {(W1-W2) × 1000} / W2

Here, the “first binder adsorption amount” measured as described above is a value correlated with the amount of the first binder adsorbed per 1 g of the conductive material in the conductive material paste of the present invention. The first binder adsorption amount can be controlled by the composition of the first binder, the specific surface area of the conductive material, and the like.
Specifically, for example, the first binder adsorption amount can be reduced by increasing the ratio of the nitrile group-containing monomer in the first binder. Further, the amount of the first binder adsorbed can be increased by controlling the proportion of the alkylene structural unit in the first binder within the above-mentioned preferable range. Furthermore, the first binder adsorption amount can be increased by increasing the specific surface area of the conductive material.

[[First Binder Preparation Method]]
Although the manufacturing method of a 1st binder is not specifically limited, For example, the monomer composition containing the monomer mentioned above is superposed | polymerized, a polymer is obtained, and the obtained polymer is hydrogenated arbitrarily. Can be prepared.
Here, in the present invention, the content ratio of each monomer in the monomer composition can be determined according to the content ratio of each monomer unit and structural unit (repeating unit) in the first binder.
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 JP2013-8485A) 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.

[[Blend amount of first binder]]
The amount of the first binder 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 per 100 parts by mass of the conductive material. Or less. When the blending amount of the first binder in the conductive material paste is within the above-described range, the temporal stability of the conductive material paste becomes good.

[Second binder]
The second binder is a component (polymer) having a lower adsorbing ability to the conductive material than the first binder. Such a second binder is inferior in the function of dispersing and stabilizing the conductive material because of its low adsorbing ability to the conductive material, while being able to sufficiently impart viscosity to the electrode slurry, an electrode having a high specific gravity. A component such as an active material can be prevented from settling in the electrode slurry. As a result, uneven distribution of the electrode active material or the like in the electrode mixture layer can be suppressed.

[[Composition of the second binder]]
The composition of the second binder is not particularly limited, and examples of the second binder include a fluorine-based polymer containing a fluorine-containing monomer unit.
Hereinafter, the composition of the second binder will be described using a fluoropolymer as an example. 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 that does not contain fluorine. (Hereinafter referred to as “fluorine-free monomer”).
The ratio of the fluorine-containing monomer unit in the fluoropolymer is usually 70% by mass or more, preferably 80% by mass or more when the total monomer units in the fluoropolymer is 100% by mass. is there. The proportion of the fluorine-free monomer unit in the fluoropolymer is usually 30% by mass or less, preferably 20% by mass or less, based on 100% by mass of all monomer units in the fluoropolymer. It is.

-Fluorine-containing monomer-
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.

-Fluorine-free monomer-
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) 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 oleic 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; ) Phosphoric acid group-containing unsaturated compounds such as acrylic acid-3-chloro-2-phosphate and 3-allyloxy-2-hydroxypropanephosphoric acid.

-Suitable fluoropolymer-
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.

-Preparation method of fluoropolymer-
And the fluoropolymer as a 2nd binder is manufactured by superposing | polymerizing the monomer composition containing the monomer mentioned above in an aqueous solvent, for example. In addition, the content rate of each monomer in a monomer composition can be defined according to the content rate of the desired monomer unit (repeating unit) in a fluoropolymer.
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. As the polymerization reaction, any reaction such as ionic polymerization, radical polymerization, and living radical polymerization can be used. In the polymerization, known emulsifiers and polymerization initiators can be used as necessary.

[[Viscosity of second binder]]
Here, the viscosity at 60 rpm of the 8% by mass NMP solution of the second binder is preferably 1000 mPa · s or more, and preferably 4000 mPa · s or more. If a second binder having a viscosity of 8 m% NMP solution at 60 rpm of 1000 mPa · s or more is blended in the conductive material paste, the viscosity of the resulting electrode slurry is sufficiently secured, and particularly the electrode active material, etc. The dispersion stability of a component having a large specific gravity can be improved. In addition, the upper limit of the viscosity at 60 rpm of the 8% by mass NMP solution of the second binder is not particularly limited, but the amount of solvent required for dilution during preparation of the slurry for the electrode is reduced, and the drying time during electrode production is From the viewpoint of shortening, it is usually 100,000 mPa · s or less.
Here, the viscosity at 60 rpm of the 8 mass% NMP solution of the second binder can be controlled by the molecular weight of the polymer constituting the second binder, the ratio of the crosslinkable monomer units, and the like. Specifically, for example, the molecular weight of the polymer constituting the second binder is increased, or a large amount of crosslinkable monomers such as allyl glycidyl ether and glycidyl (meth) acrylate are used in the polymerization of the polymer. By using it, the viscosity at 60 rpm of the 8 mass% NMP solution of the second binder can be increased.
The “viscosity of the second binder 8 mass% NMP solution at 60 rpm” can be measured by the same method as “the viscosity of the conductive material paste at 60 rpm” described later.

[[Adsorption amount of second binder to conductive material]]
Here, the adsorption amount of the second binder to the conductive material (second binder adsorption amount) needs to be 0 mg / g or more and less than 110 mg / g, preferably 100 mg / g or less, more preferably 80 mg / g. g or less, more preferably 50 mg / g or less, particularly preferably 40 mg / g or less. When the second binder adsorption amount is 110 mg / g or more, there is a possibility that the surface of the conductive material may be completely covered with the binder component which is an insulator in combination with the first binder. For this reason, the DC resistance of the secondary battery at a low temperature increases, and the ionic conductivity decreases.

  And the adsorption amount of the second binder to the conductive material can be calculated by the same method as the first binder adsorption amount.

Here, the “second binder adsorption amount” measured as described above is a value correlated with the amount of the second binder adsorbed per 1 g of the conductive material in the conductive material paste of the present invention. The second binder adsorption amount can be controlled by the composition of the second binder, the specific surface area of the conductive material, and the like.
Specifically, for example, the second binder adsorption amount can be decreased by increasing the ratio of the nitrile group-containing monomer in the second binder. Furthermore, the second binder adsorption amount can be increased by increasing the specific surface area of the conductive material.

[[Binder content of second binder]]
The blending amount of the second binder in the conductive material paste is preferably 100 parts by weight or more, more preferably 300 parts by weight or more, preferably 700 parts by weight or less, more preferably 500 parts by weight per 100 parts by weight of the conductive material. Or less. When the blending amount of the second binder in the conductive material paste is within the above-described range, the DC resistance at a low temperature of the secondary battery can be reduced and the high-temperature storage characteristics can be improved.

[Amount ratio of the first binder and the second binder]
Further, the proportion of the amount of the first binder in the total amount of the first binder and the second binder in the conductive material paste is preferably 10% by mass or more, and more preferably 15% by mass or more. Preferably, it is preferably 50% by mass or less, and more preferably 30% by mass or less. If the ratio of the amount of the first binder in the total amount of the first binder and the second binder is within the above range, the conductive material is stable over time while the slurry for the electrode is set to an appropriate solid concentration and viscosity. The direct current resistance at the low temperature of the secondary battery can be reduced.

<Solvent>
As a solvent mix | blended with an electrically conductive material paste, the organic solvent which has the polarity which can melt | dissolve the 1st binder mentioned above and the 2nd binder, for example can be used.
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 easy 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.

<Method for preparing conductive paste>
The method for preparing the conductive material paste by mixing the above-mentioned conductive material, first binder, second binder, solvent and any other components is not particularly limited. In preparing the conductive material paste, these components may be mixed together or sequentially mixed, but it is preferable to premix the conductive material and the first binder and then mix the second binder. By mixing the conductive material and the first binder prior to the second binder, the first binder is favorably adsorbed to the conductive material, ensuring the stability of the conductive material over time, and the TI of the conductive material paste. The value can be lowered and within a suitable range.
The mixing method is not particularly limited, and for example, a general mixing apparatus such as a disper, a mill, or a kneader can be used. Taking the case of using a disper as an example, the mixing conditions in each mixing step can be appropriately set within a range of, for example, a rotational speed of 2000 rpm to 5000 rpm and a stirring time of 5 minutes to 60 minutes.

<Viscosity of conductive paste>
The conductive material paste preferably has a viscosity at 60 rpm of 500 mPa · s or more, more preferably 1000 mPa · s or more, preferably 10,000 mPa · s or less, and more preferably 8000 mPa · s or less. Preferably, it is 5000 mPa · s or less. When the viscosity of the conductive material paste is within the above range, the temporal stability of the conductive material paste is good.
The viscosity of the conductive material paste at 60 rpm (rotation speed) can be measured with a single cylindrical rotational viscometer (25 ° C., spindle shape: 4) according to JIS Z8803: 1991.
Here, the viscosity at 60 rpm 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, and the types of the first binder and the second binder.

<TI value of conductive material paste>
The conductive material paste is 6 rpm measured by the same method as the viscosity at 60 rpm except that only the rotation speed is changed with respect to the viscosity at 60 rpm measured by the above method using a single cylindrical rotational viscometer. The viscosity ratio (TI value) must be 1.0 or more and 6.0 or less, preferably 2.0 or more, more preferably 5.0 or less, and 3.0 or less. It is more preferable that When the TI value of the conductive material paste is out of the above range, the temporal stability of the conductive material paste cannot be ensured, and the DC resistance of the secondary battery at a low temperature increases.

<Solid content concentration of conductive material paste>
The conductive material paste has a solid content concentration of preferably 5% by mass or more, more preferably 10% by mass or more, and preferably 50% by mass or less.
By setting the solid content concentration of the conductive material paste within the above range, the conductive material is favorably dispersed in the electrode mixture layer, and the DC resistance at a low temperature of the secondary battery can be reduced.
When the solid content concentration of the conductive material paste exceeds 50% by mass, it is difficult to obtain excellent dispersibility of the conductive material, and agglomerates tend to remain in the paste, and the direct current resistance at low temperature of the secondary battery increases. There is a fear. On the other hand, when the solid content concentration of the conductive material paste is less than 5% by mass, the conductive material in the conductive material paste is precipitated, which may impair the temporal stability of the conductive material paste.

(Slurry for secondary battery positive electrode)
The slurry for secondary battery positive electrode of the present invention includes the above-described conductive material paste for secondary battery electrode and 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 by using a positive electrode formed from the positive electrode slurry, the direct current resistance at a low temperature of the secondary battery is sufficient. Can be lowered.

<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.

<Other ingredients>
The secondary battery positive electrode slurry may contain, in addition to the above components, those listed as the other components in the section “Secondary battery electrode conductive material paste”.
Moreover, the slurry for secondary battery positive electrodes may contain the solvent arbitrarily added at the time of preparation of the said slurry other than the said component. In addition, as a solvent to add, the thing similar to the solvent which can be used for preparation of an electrically conductive material paste can be used.

<Method for preparing slurry for secondary battery positive electrode>
In obtaining the slurry for the secondary battery positive electrode by mixing the above-described positive electrode active material and optionally other components and an additional solvent with respect to the conductive material paste, there is no particular limitation on the mixing method, for example, A general mixing apparatus such as a disper, a mill, or a kneader can be used. For example, when using a disper, it is preferable to stir at 2000 rpm or more and 5000 rpm or less for 20 minutes or more and 600 minutes or less.
The positive electrode active material is not mixed at the same time as the conductive material and the binder component, but after the conductive material paste is prepared, it is added to the conductive material paste and mixed when preparing the slurry for the secondary battery positive electrode. The deterioration of the temporal stability of the secondary battery positive electrode slurry can be suppressed. Moreover, the dispersion state of the conductive material is made more uniform than when produced by batch mixing, and the difference in viscosity and concentration between production batches can be kept small. Therefore, it becomes easy to produce the slurry for electrodes of the same viscosity and solid content industrially.
In addition, from the viewpoint of ensuring the coatability on the current collector, the viscosity of the slurry for the secondary battery positive electrode at 60 rpm is preferably 1500 mPa · s or more and 10,000 mPa · s or less, and the solid content concentration is 50 mass. % Or more and 90% by mass or less is preferable. The “viscosity of secondary battery positive electrode slurry at 60 rpm” can be measured by the same method as “the viscosity of the conductive material paste at 60 rpm”.
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 manufacturing method of the positive electrode for secondary batteries of this invention includes the process of apply | coating the slurry for secondary battery positive electrodes of this invention to at least one surface of a collector, and drying, and forming a positive mix 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. And 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, the positive electrode mixture layer is formed using the slurry for secondary battery positive electrode of the present invention described above, so if the positive electrode for secondary battery is used, The direct current resistance at a low temperature of the secondary battery can be sufficiently reduced.

<Application 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 on 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. Can be obtained.

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. And since the secondary battery of this invention uses the positive electrode manufactured by the manufacturing method of the positive electrode for secondary batteries of this invention, DC resistance in low temperature is low enough, and it is excellent in electrical characteristics, such as an output characteristic. . 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.
In addition, the density | concentration of the electrolyte in electrolyte solution can be adjusted suitably, for example, it is preferable to set it as 0.5-15 mass%, it is more preferable to set it as 2-13 mass%, and it shall be 5-10 mass%. Is more preferable. Further, known additives such as fluoroethylene carbonate and ethyl methyl sulfone may be added to the electrolytic solution.

<Separator>
As a separator, it does not specifically limit, For example, the thing of Unexamined-Japanese-Patent No. 2012-204303 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 the examples and comparative examples, the viscosity and TI value of the conductive material paste, the adsorption amount of the first binder to the conductive material and the adsorption amount of the second binder to the conductive material, the temporal stability of the conductive material paste, and two The direct current resistance and high-temperature storage characteristics of the secondary battery at low temperatures were evaluated using the following methods, respectively.

<Viscosity and TI value of conductive material paste>
The viscosity (X) at a rotational speed of 6 rpm and the viscosity (Y) at 60 rpm of the conductive material paste are measured by a single cylindrical rotational viscometer (25 ° C., spindle shape: 4) according to JIS Z8803: 1991, respectively. did. And TI value was computed by the formula of TI = X / Y.
<Adsorption amount of the first binder to the conductive material>
A conductive material (acetylene black (Denka black powder: Denki Kagaku Kogyo, specific surface area 68 m ² / g, average particle size 35 nm) and the same amount of the first binder as the conductive material (solid content equivalent amount) are dissolved in NMP. Then, an appropriate amount of NMP was added to a disper and then stirred (3000 rpm, 60 minutes) to prepare a conductive material paste 1 for adsorption amount measurement with a solid content concentration of 10% by mass. NMP was added to the material paste 1 so that the solid content concentration was 1% by mass, and a diluted solution 1 was obtained.
The diluted solution 1 was centrifuged for 10 minutes at a rotational speed of 10,000 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 mass 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 mass W1 (g) before the heat treatment (dried material) by the thermobalance, From the mass W2 (g), the first binder adsorption amount was calculated by the following formula.
First binder adsorption amount (mg / g) = {(W1-W2) × 1000} / W2
<Adsorption amount of second binder to conductive material>
Conductive material (acetylene black (Denka black powder: Denki Kagaku Kogyo, specific surface area 68 m ² / g, average particle size 35 nm) and the same amount of the conductive material as the conductive material (solid content equivalent amount) are dissolved in NMP. Then, an appropriate amount of NMP was added to a disper and then stirred (3000 rpm, 60 minutes) to prepare a conductive material paste 2 for adsorption amount measurement with a solid content concentration of 10% by mass. NMP was added to the material paste 2 so that the solid content concentration was 1% by mass, and a diluted solution 2 was obtained.
The diluted solution 2 was centrifuged for 10 minutes at a rotation 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 mass change due to drying.
The dried product was heated to 500 ° C. in a nitrogen atmosphere at a heating rate of 10 ° C./min using a thermobalance, and the mass W3 (g) before the heat treatment (dried material) by the thermobalance, From the mass W4 (g), the second binder adsorption amount was calculated by the following formula.
Second binder adsorption amount (mg / g) = {(W3-W4) × 1000} / W4
<Stability of conductive material paste over time>
The conductive material paste was left in a 15 mL glass bottle for 2 weeks. 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 (primary particle diameter) of the conductive material when the binder is not adsorbed), the smaller the cohesiveness and the better the temporal stability of the conductive material paste. Indicates that
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 size D50 is 15 μm or more <DC resistance of secondary battery at low temperature>
The secondary battery is charged to 50% of SOC (State Of Charge, depth of charge) at 1C (C is a numerical value represented by rated capacity (mA) / 1h (hour)) in an atmosphere of −10 ° C. Centering on 50% of the battery, charging is performed for 15 seconds and discharging for 15 seconds at 0.5C, 1.0C, 1.5C, and 2.0C, respectively, and after 0.1 second in each case (charging side and discharging side) The battery voltage was plotted against the current value, and 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. The smaller the IV resistance value, the lower the internal resistance and the lower the DC resistance at low temperatures.
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 15Ω or less D: IV resistance is more than 15Ω <High temperature storage characteristics of secondary battery>
First, the secondary battery was charged to a cell voltage of 4.2 V by a constant current method of 0.2 C in an atmosphere of 25 ° C., then discharged to 3.0 V, and the electric capacity before storage was measured. Next, the secondary battery was charged to a cell voltage of 4.2 V by a constant current method of 0.2 C in an atmosphere of 25 ° C. The charged battery was stored in a constant temperature bath at 60 ° C. for 4 weeks (high temperature storage). After storage at a high temperature, the battery was discharged to 3 V by a constant current method of 0.2 C, charged to 4.2 V again by a constant current method of 0.2 C, and then discharged to 3 V, and the electric capacity after storage was measured. The ratio of the electric capacity after storage and the electric capacity before storage measured in advance (= (recovered electric capacity after storage / electric capacity before storage) × 100) (%) is obtained for 5 cells, and the average is obtained. The charge / discharge capacity retention rate was evaluated based on the following criteria. It shows that it is excellent in the high temperature storage characteristic, so that the value of charge / discharge capacity retention is large.
A: Charge / discharge capacity retention is 85% or more B: Charge / discharge capacity retention is 80% or more and less than 85% C: Charge / discharge capacity retention is 75% or more and less than 80% D: Charge / discharge capacity retention is 70% or more Less than 75% E: Charge / discharge capacity retention is less than 70%

Example 1
<Preparation of first binder>
In an autoclave equipped with a stirrer, 240 parts of ion-exchanged water, 2.5 parts of sodium alkylbenzene sulfonate 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 put in this order, the inside of the bottle is replaced with nitrogen, and then 45 parts of 1,3-butadiene (BD) as a conjugated diene monomer (above BA, AN, BD monomer composition) 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 and added 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 made into 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 A first binder NMP solution was obtained. The adsorption amount of the obtained first binder to the conductive material was measured. The results are shown in Table 1.

<Preparation 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 diameter 35 nm) as a conductive material, and the NMP solution of the first binder obtained as described above were mixed with solid content. An equivalent amount of 0.6 part and an appropriate amount of NMP were stirred with a disper (3000 rpm, 10 minutes), and then PVDF (“KF Polymer # 7200” manufactured by Kureha Corporation, 8) as a second binder. NMP solution having a viscosity of 60% by mass of 6000 mPa · s) and 2.4 parts of solid content equivalent amount, and an appropriate amount of NMP so that the solid content concentration of the conductive material paste is 10% by mass. The mixture was stirred with a disper (3000 rpm, 10 minutes) to prepare a conductive material paste. In addition, the adsorption amount of the second binder to the conductive material was separately measured. The results are shown in Table 1.
And the viscosity (6 rpm, 60 rpm) and TI value of the obtained electrically conductive material paste, and temporal stability were evaluated. The results are shown in Table 1.

<Preparation of secondary battery positive electrode slurry and production of positive electrode>
100 parts of a ternary active material (LiNi _0.5 Co _0.2 Mn _0.3 O ₂ ) (average particle diameter: 10 μm) having a layered structure as a positive electrode active material and an appropriate amount of NMP as a solvent are added to the conductive material paste described above. The mixture was stirred with a disper (3000 rpm, 20 minutes) to prepare a positive electrode slurry. The amount of NMP added was adjusted so that the viscosity of the resulting positive electrode slurry at 60 rpm was in the range of 4000 to 5000 mPa · s.

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.

<Preparation of negative electrode slurry and production of 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” manufactured 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 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 liquid 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, which is a current collector, with 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. Further, the negative electrode obtained above was cut into a square of 4.2 cm × 4.2 cm, and this was placed 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 DC resistance at low temperature and high temperature storage characteristics. The results are shown in Table 1.

(Example 2)
A first binder was produced in the same manner as in Example 1 except that 49 parts of BD, 27 parts of BA, and 24 parts of AN were used as the monomer composition for producing the first binder. Except having used the said 1st binder, it carried out similarly to Example 1, and manufactured the electrically conductive material paste, the slurry for positive electrodes, the positive electrode, the negative electrode, and the secondary battery. And the amount of adsorption of the first binder to the conductive material, the amount of adsorption of the second binder to the conductive material, the viscosity of the conductive material paste, the TI value, the stability over time, and the DC resistance at low temperature of the secondary battery And the high temperature storage characteristics were evaluated. The results are shown in Table 1.

(Example 3)
As the monomer composition used for the production of the first binder, the first binder was produced in the same manner as in Example 1 except that 56 parts of BD, 44 parts of AN were used, and BA was not used. did. And except having used the said 1st binder, it carried out similarly to Example 1, and manufactured the electrically conductive material paste, the slurry for positive electrodes, the positive electrode, the negative electrode, and the secondary battery. And the amount of adsorption of the first binder to the conductive material, the amount of adsorption of the second binder to the conductive material, the viscosity of the conductive material paste, the TI value, the stability over time, and the DC resistance at low temperature of the secondary battery And the high temperature storage characteristics were evaluated. The results are shown in Table 1.

Example 4
As a monomer composition used for the production of the first binder, BA as a (meth) acrylic acid ester monomer, 82 parts and 3 parts of glycidyl methacrylate (GMA), and 15 parts of AN, respectively, and BD A first binder was produced in the same manner as in Example 1 except that no hydrogenation reaction was performed. Except having used the said 1st binder, it carried out similarly to Example 1, and manufactured the electrically conductive material paste, the slurry for positive electrodes, the positive electrode, the negative electrode, and the secondary battery. And the amount of adsorption of the first binder to the conductive material, the amount of adsorption of the second binder to the conductive material, the viscosity of the conductive material paste, the TI value, the stability over time, and the DC resistance at low temperature of the secondary battery And the high temperature storage characteristics were evaluated. The results are shown in Table 1.

(Example 5)
A conductive material paste was manufactured in the same manner as in Example 1 except that the NMP solution of the second binder (PVDF) was added simultaneously with the addition of the NMP solution of the first binder when the conductive material paste was manufactured. A positive electrode slurry, a positive electrode, a negative electrode, and a secondary battery were produced in the same manner as in Example 1 except that the conductive material paste was used. And the amount of adsorption of the first binder to the conductive material, the amount of adsorption of the second binder to the conductive material, the viscosity of the conductive material paste, the TI value, the stability over time, and the DC resistance at low temperature of the secondary battery And the high temperature storage characteristics were evaluated. The results are shown in Table 1.

(Example 6)
The conductive material paste was manufactured in the same manner as in Example 1 except that the timing of adding the NMP solution of the first binder and the timing of adding the NMP solution of the second binder (PVDF) were changed during the manufacturing of the conductive material paste. did. A positive electrode slurry, a positive electrode, a negative electrode, and a secondary battery were produced in the same manner as in Example 1 except that the conductive material paste was used. And the amount of adsorption of the first binder to the conductive material, the amount of adsorption of the second binder to the conductive material, the viscosity of the conductive material paste, the TI value, the stability over time, and the DC resistance at low temperature of the secondary battery And the high temperature storage characteristics were evaluated. The results are shown in Table 1.

(Example 7)
A first binder was produced in the same manner as in Example 1 except that 55 parts of BD, 20 parts of BA, and 25 parts of AN were used as the monomer composition used for producing the first binder. Except having used the said 1st binder, it carried out similarly to Example 1, and manufactured the electrically conductive material paste, the slurry for positive electrodes, the positive electrode, the negative electrode, and the secondary battery. And the amount of adsorption of the first binder to the conductive material, the amount of adsorption of the second binder to the conductive material, the viscosity of the conductive material paste, the TI value, the stability over time, and the DC resistance at low temperature of the secondary battery And the high temperature storage characteristics were evaluated. The results are shown in Table 1.

(Example 8)
Other than using 42 parts of BD, 30 parts of BA, 20 parts of AN, and 8 parts of methacrylic acid (MAA) as a hydrophilic group-containing monomer as the monomer composition used for the production of the first binder Produced a first binder in the same manner as in Example 1. Except having used the said 1st binder, it carried out similarly to Example 1, and manufactured the electrically conductive material paste, the slurry for positive electrodes, the positive electrode, the negative electrode, and the secondary battery. And the amount of adsorption of the first binder to the conductive material, the amount of adsorption of the second binder to the conductive material, the viscosity of the conductive material paste, the TI value, the stability over time, and the DC resistance at low temperature of the secondary battery And the high temperature storage characteristics were evaluated. The results are shown in Table 1.

(Comparative Example 1)
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 a ternary active material (LiNi _0.5 Co having a layered structure as a positive electrode active material) 100 parts of _0.2 Mn _0.3 O ₂ ) (average particle size: 10 μm) were powder-mixed (20 rpm, 10 minutes) with a planetary mixer to obtain a powder mixture. In the powder mixture, an NMP solution of the first binder produced in the same manner as in Example 1 was 0.6 parts corresponding to the solid content, and PVDF (“KF polymer # manufactured by Kureha Co., Ltd.) as the second binder was used. 7200 ", an NMP solution of 8% mass solution at 60 rpm viscosity of 6000 mPa · s), 2.4 parts of solid content equivalent amount, and an appropriate amount of NMP are added and mixed with a planetary mixer (60 rpm, 1 Time). While mixing, NMP was further added to prepare a positive electrode slurry having a viscosity at 60 rpm in the range of 4000 to 5000 mPa · s.
A positive electrode, a negative electrode, and a secondary battery were produced in the same manner as in Example 1 except that the above positive electrode slurry was used. And the direct-current resistance at low temperature and the high-temperature storage characteristic of the secondary battery were evaluated. The results are shown in Table 1.

(Comparative Example 2)
A conductive material paste was manufactured in the same manner as in Example 1 except that the NMP solution of the first binder was not added when the conductive material paste was manufactured. A positive electrode slurry, a positive electrode, a negative electrode, and a secondary battery were produced in the same manner as in Example 1 except that the conductive material paste was used. And the amount of adsorption of the first binder to the conductive material, the amount of adsorption of the second binder to the conductive material, the viscosity of the conductive material paste, the TI value, the stability over time, and the DC resistance at low temperature of the secondary battery And the high temperature storage characteristics were evaluated. The results are shown in Table 1.

  In Table 1, “◯” in the column of the structural unit of the first binder and each monomer unit means that the first binder includes the structural unit or monomer unit, and “−”. Means that the first binder does not contain the structural unit or monomer unit.

From Examples 1 to 8 and Comparative Examples 1 and 2 in Table 1, the amount of adsorption to the conductive material includes the first binder and the second binder each within a specific range, and the TI value is within a specific range. It can be seen that the conductive material paste is excellent in stability over time, and if the conductive material paste is used, the direct current resistance of the secondary battery at a low temperature can be sufficiently lowered and the high-temperature storage characteristics can be improved.
Further, from Examples 1 to 4, 7 and 8 in Table 1, the composition of the first binder is changed, and the first binder adsorption amount and the TI value are changed, whereby the temporal stability of the conductive material and the secondary battery are changed. It can be seen that the high-temperature storage characteristics of the secondary battery can be further improved, and the DC resistance of the secondary battery at a low temperature can be further reduced.
And from Examples 1, 5, and 6 in Table 1, the order of addition of the first binder and the second binder can be changed, and the TI value can be changed to further improve the temporal stability of the conductive material. It can be seen that the DC resistance of the secondary battery at a low temperature can be further reduced.

ADVANTAGE OF THE INVENTION According to this invention, the electrically conductive material paste for secondary battery electrodes which is excellent in temporal stability and can fully reduce the direct current resistance in the low temperature of a secondary battery can be provided.
In addition, according to the present invention, it is possible to provide a secondary battery positive electrode slurry that is excellent in stability over time and can sufficiently reduce the direct current resistance of a secondary battery at a low temperature.
Furthermore, according to this invention, the manufacturing method of the positive electrode for secondary batteries which can manufacture the positive electrode which can fully reduce the direct current resistance at the low temperature of a secondary battery, and the manufacturing method of the said positive electrode for secondary batteries A secondary battery including the positive electrode manufactured in (1) can be provided.

Claims (7)

Including a conductive material, a first binder, a second binder and a solvent;
The conductive material is a conductive carbon material having a specific surface area of 10 m ² / g or more and 1500 m ² / g or less,
The solvent is an organic solvent having a polarity capable of dissolving the first binder and the second binder,
The first binder includes at least one of an alkylene structural unit and a (meth) acrylic acid ester monomer unit, and the content ratio of the nitrile group-containing monomer unit in the first binder is 2% by mass or more and 50%. The content ratio of the hydrophilic group-containing monomer unit in the first binder is less than 0.05% by mass,
The second binder contains 70 mass% or more of fluorine-containing monomer units,
The amount of adsorption of the first binder to the conductive material is 110 mg / g or more and 1000 mg / g or less,
The amount of adsorption of the second binder to the conductive material is 0 mg / g or more and less than 110 mg / g,
The blending amount of the first binder per 100 parts by mass of the conductive material is 20 parts by mass or more and 200 parts by mass or less,
And the electrically conductive material paste for secondary battery electrodes whose TI value (ratio of the viscosity in 6 rpm with respect to the viscosity in 60 rpm) is 1.0 or more and 6.0 or less.   The conductive material paste for a secondary battery electrode according to claim 1, wherein the viscosity at 60 rpm is 500 mPa · s or more and 10,000 mPa · s or less. The secondary battery electrode according to claim 1 or 2 , wherein a ratio of the amount of the first binder in the total amount of the first binder and the second binder is 10% by mass or more and 50% by mass or less. Conductive material paste. The electrically conductive material paste for secondary battery electrodes in any one of Claims 1-3 whose said TI value is 2.0-3.0. A secondary battery electrode conductive material paste according to any one of claims 1 to 4 comprising the step of adding a positive electrode active material, method for producing the slurry for a secondary battery positive electrode. A process for obtaining a secondary battery positive electrode slurry by the method for producing a secondary battery positive electrode slurry according to claim 5 , and applying the secondary battery positive electrode slurry to at least one surface of a current collector, The manufacturing method of the positive electrode for secondary batteries including the process of drying and forming a positive mix layer. A method for producing a secondary battery having a positive electrode, a negative electrode, a separator, and an electrolyte solution ,
The method for manufacturing a secondary battery according to claim 6, comprising a step of manufacturing the positive electrode.