JP2013178926A - Positive electrode mixture for nonaqueous secondary battery - Google Patents

Abstract

Provided is a positive electrode mixture for a non-aqueous secondary battery that can suppress corrosion of a current collector even when it contains a highly basic positive electrode active material, and that does not thicken over time and has good storage stability. To do.
A positive electrode active material (a), a fluorine-containing copolymer (f) having a polymer unit based on tetrafluoroethylene and a polymer unit based on propylene, a water-soluble thickener (c), and an aqueous medium, A positive electrode mixture for non-aqueous secondary batteries, wherein the pH is 6 or more and less than 10.
[Selection figure] None

Description

  The present invention relates to a positive electrode mixture for a non-aqueous secondary battery and a method for producing the same, a method for producing a positive electrode for a non-aqueous secondary battery using the positive electrode mixture, and a non-aqueous two produced using the positive electrode mixture. The present invention relates to a non-aqueous secondary battery including a positive electrode for a secondary battery.

  In recent years, electronic devices have made remarkable progress, and portable electronic devices have been rapidly reduced in size and weight. Therefore, high energy density is required so that these batteries as power sources can be reduced in size and weight. In particular, lithium ion secondary batteries are attracting attention as non-aqueous secondary batteries.

  A lithium ion secondary battery is comprised from members, such as a positive electrode and a negative electrode, a non-aqueous electrolyte, and a separator. Among these, for example, a positive electrode active material and a conductive material are dispersed in an organic solvent or water together with a binder to prepare a positive electrode mixture, which is applied to the surface of a current collector, and volatilizes the solvent or the dispersion medium. It is obtained by fixing the positive electrode active material on the surface of the electric body. If the binder cannot fix a sufficient amount of battery active material to the electrode, a battery with a large initial capacity cannot be obtained, and the battery active material may fall off from the current collector due to repeated charge and discharge, etc. Will decline.

  As a positive electrode mixture, an organic solvent-based positive electrode mixture or an aqueous positive electrode mixture can be obtained by using an organic solvent-based binder or an aqueous binder. The positive electrode mixture using an aqueous binder has recently attracted particular attention because it can improve the environmental load and the working environment.

As an aqueous binder, latex of polytetrafluoroethylene or styrene-butadiene copolymer rubber produced by an emulsion polymerization method is known (for example, Patent Document 1).
However, polytetrafluoroethylene has poor adhesion to the current collector, and when an external force such as a winding process is applied, the electrode surface peels off from the metal foil as the current collector, or when used as a battery, There is a problem that stability in a long-term charge / discharge cycle is lowered.
In addition, styrene-butadiene copolymer rubber is a rubber polymer, so it has better flexibility and adhesion than polyvinylidene fluoride and polytetrafluoroethylene, but the polymer has poor oxidation resistance, and in particular increases the charging voltage. In this case, the charge / discharge resistance is not sufficient.

On the other hand, as for the positive electrode active material, lithium cobaltate has been widely used, but various developments are being promoted from the viewpoint of battery characteristics, safety, and cost. In particular, the so-called ternary positive electrode active material, which has reduced cobalt as much as possible and replaced it with nickel, manganese, etc. to realize increased capacity, has attracted attention as a positive electrode material for next-generation lithium ion batteries.
However, since the positive electrode active material containing nickel has high basicity, the basicity of the positive electrode mixture is increased, corroding the surface of the current collector made of aluminum foil, and hydrogen at the interface between the aluminum foil and the positive electrode active material. As a result, gas was generated, resulting in problems such as poor adhesion to the current collector and loss of electrode surface smoothness.

  In Patent Document 2, when the pH of the aqueous positive electrode mixture is lowered to 9 or less, the stability of the acrylic particulate polymer (positive electrode binder) contained in the aqueous positive electrode mixture is reduced. It has been shown that when the pH is adjusted in the range of 10 or more and 12 or less, the stability of the positive electrode mixture can be achieved while suppressing the corrosion of the current collector.

International Publication No. 2010/074293 JP 2011-76981 A

However, according to the study by the present inventors, in the method described in Patent Document 2, even if the pH of the aqueous positive electrode mixture to be applied is adjusted to 10 or more and 12 or less, coating is performed to increase the electrode density. It was found that when the thickness is increased, the drying time becomes longer, and as a result, corrosion of the current collector cannot be suppressed. Therefore, it has been found that even if the drying temperature is increased in order to shorten the drying time and increase the productivity at the time of manufacturing the electrode, the corrosion reaction is accelerated, and the corrosion of the current collector cannot be suppressed.
In addition, when the pH of the positive electrode mixture is less than 10, such corrosion is reduced, but aggregation of the particulate polymer occurs, and the positive electrode mixture is likely to thicken with time, which may impair storage stability. I found out.

  The object of the present invention is to suppress the corrosion of the current collector even when it contains a highly basic positive electrode active material, and it is difficult to increase the viscosity over time and has a good storage stability. Agent, method for producing the same, method for producing a positive electrode for a non-aqueous secondary battery using the positive electrode mixture, and a non-aqueous secondary provided with a positive electrode for a non-aqueous secondary battery produced using the positive electrode mixture To provide a battery.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors use the fluorine-containing copolymer (f) as a positive electrode binder, so that it is difficult to increase the viscosity even if the pH of the aqueous positive electrode mixture is less than 10. In addition, the present inventors have found that a positive electrode mixture that can suppress corrosion of a current collector and is excellent in storage stability can be obtained even when a highly basic electrode active material is contained. The present invention has been completed.

That is, the present invention includes the following [1] to [8].
[1] A pH containing a positive electrode active material (a), a fluorocopolymer (f) having a polymer unit based on tetrafluoroethylene and a polymer unit based on propylene, a water-soluble thickener (c), and an aqueous medium, Is a positive electrode mixture for a non-aqueous secondary battery, wherein the positive electrode mixture is 6 or more and less than 10.

[2] The positive electrode mixture for nonaqueous secondary batteries according to [1], further comprising a pH adjuster.
[3] The positive electrode active material is selected from the group consisting of a lithium nickel composite oxide (X) represented by the following formula (1) and a lithium nickel cobalt composite oxide (Y) represented by the formula (2): The positive electrode mixture for nonaqueous secondary batteries according to [1] or [2], which is a seed or more.
LiNi _x M _(1-x) O ₂ (1)
(In the formula, M is at least one selected from the group consisting of Al, B, Sn, Mn and Nb, and x is 0.1 ≦ x ≦ 1.)
LiNi _x Co _y M _(1-xy) O ₂ (2)
(In the formula, M is at least one selected from the group consisting of Al, B, Sn, Mn and Nb, x is 0.1 ≦ x ≦ 0.9, and y is 0.1 ≦ y ≦ 0.9. Is)

[4] A method for producing a positive electrode mixture for a non-aqueous secondary battery according to any one of [1] to [3], wherein the positive electrode active material (a), a polymer unit based on tetrafluoroethylene, and A step of mixing the aqueous dispersion (b) in which the fluorine-containing copolymer (f) having polymer units based on propylene is dispersed in an aqueous medium, and the water-soluble thickener (c), The aqueous medium in the body (b) is water alone or a mixture of water and a water-soluble organic solvent, and the content of the water-soluble organic solvent in the mixture is less than 1 part by mass with respect to 100 parts by mass of water. The manufacturing method of the positive mix for non-aqueous secondary batteries which is.
[5] The aqueous dispersion (b) containing the fluorine-containing copolymer contains particles of the fluorine-containing copolymer (f) and an anionic emulsifier in an aqueous medium, and contains the anionic emulsifier. The method for producing a positive electrode mixture for a non-aqueous secondary battery according to [4], wherein the amount is 1.5 to 5.0 parts by mass with respect to 100 parts by mass of the fluorine-containing copolymer (f). .

[6] A step of applying the positive electrode mixture for a non-aqueous secondary battery according to any one of [1] to [3] onto a current collector made of metal; A method for producing a positive electrode for a non-aqueous secondary battery, further comprising a step of drying the positive electrode mixture for a non-aqueous secondary battery to remove the aqueous medium.
[7] A step of producing a positive electrode mixture for a non-aqueous secondary battery by the production method according to [4] or [5], and collecting the obtained positive electrode mixture for a non-aqueous secondary battery from a metal A method for producing a positive electrode for a non-aqueous secondary battery, comprising: a step of applying on a body; and a step of drying the positive electrode mixture for a non-aqueous secondary battery applied on the current collector to remove an aqueous medium. .

[8] A non-aqueous secondary battery comprising a positive electrode for a secondary battery, a negative electrode, an electrolytic solution, and a separator produced by the production method according to any one of [6] or [7].

According to the present invention, even when a highly basic positive electrode active material is contained, corrosion of the current collector can be suppressed, and the positive electrode composite for a non-aqueous secondary battery that does not thicken over time and has good storage stability can be obtained. An agent is obtained.
ADVANTAGE OF THE INVENTION According to this invention, even when a highly basic positive electrode active material is used, the positive electrode for non-aqueous secondary batteries by which corrosion of a collector is suppressed and a non-aqueous secondary battery provided with the same are obtained.

<Positive electrode mixture for non-aqueous secondary battery>
The positive electrode mixture for non-aqueous secondary batteries of the present invention (hereinafter sometimes simply referred to as positive electrode mixture) has a positive electrode active material (a), a polymer unit based on tetrafluoroethylene, and a polymer unit based on propylene. A fluorine-containing copolymer (f), a water-soluble thickener (c), and an aqueous medium are included. Hereinafter, each component will be described.

[Positive electrode active material (a)]
The positive electrode active material (a) used by this invention is not specifically limited, A well-known positive electrode active material can be used. For example, lithium nickel composite oxide (X) represented by the following formula (1), lithium nickel cobalt composite oxide (Y) represented by formula (2), and composite oxide (Z) represented by formula (3) Is mentioned. As the positive electrode active material (a), one type may be used, or two or more types may be used in combination.

(Lithium nickel composite oxide (X))
LiNi _x M _(1-x) O ₂ (1)
In the formula, M is at least one selected from the group consisting of Al, B, Sn, Mn and Nb, and x is 0.1 ≦ x ≦ 1.
(Lithium nickel cobalt composite oxide (Y))
LiNi _x Co _y M _(1-xy) O ₂ (2)
In the formula, M is at least one selected from the group consisting of Al, B, Sn, Mn, and Nb, x is 0.1 ≦ x ≦ 0.9, and y is 0.1 ≦ y ≦ 0.9. is there.
Specific examples of the lithium nickel composite oxide represented by the formula (1) include LiNi _0.5 Mn _0.5 O ₂ , LiNi _0.75 Mn _0.25 O ₂ , and LiNi _0.25 Mn _0.75 O. ₂ and the like.
Specifically, as the lithium nickel cobalt composite oxide represented by the formula (2), for example, LiNi _0.8 Co _0.2 O ₂ , LiNi _0.7 Co _0.3 O ₂ , LiNi _0.5 Co _0.5 O ₂ , LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiNi _0.5 Co _0.2 Mn _0.3 O ₂ , LiNi _0.5 Co _0.3 Mn _0.2 O ₂ , LiNi _{0 .75} Co _0.15 Al _0.1 O _{2 and the} like.
In particular, LiNi _0.7 Co _0.3 O ₂ , LiNi _0.5 Co _0.5 O ₂ , LiNi _0.5 Co _0.2 Mn _0.3 O ₂ , LiNi having high capacity density and high stability A lithium nickel cobalt manganese composite oxide such as _1/3 Co _1/3 Mn _1/3 O ₂ is preferable.

(Composite oxide (Z))
_{Li (Li x Mn y Me '} z) O p F q ··· (3)
In the formula, Me ′ is at least one selected from Co, Ni, Cr, Fe, Al, Ti, Zr and Mg, and 0.09 <x <0.3, y> 0, z> 0, 1 .9 <p <2.1, 0 ≦ q ≦ 0.1, 0.4 ≦ y / (y + z) ≦ 0.8, x + y + z = 1, 1.2 <(1 + x) / (y + z).
In the composite oxide (Z) represented by the formula (3), the proportion of Li exceeds 1.2 times mol with respect to the total of Mn and Me ′. Further, the formula (3) is also characterized in that it is a compound containing a specific amount of Mn, and the ratio of Mn to the total amount of Mn and Me ′ is preferably 0.4 to 0.8, and preferably 0.55 to 0.75. More preferred. When Mn is in the above range, the discharge capacity becomes high.
Here, q represents the ratio of F, but q is 0 when F does not exist. P is a value determined according to x, y, z, and q, and is 1.9 to 2.1.

  In the compound represented by the formula (3), the composition ratio of the Li element with respect to the total molar amount of the transition metal element is preferably 1.25 ≦ (1 + x) / (y + z) ≦ 1.75, and 1.35 ≦ ( 1 + x) / (y + z) ≦ 1.65 is more preferable, and 1.40 ≦ (1 + x) / (y + z) ≦ 1.55 is particularly preferable. When the composition ratio is in the above range, a positive electrode material having a high discharge capacity per unit mass can be obtained when a high charging voltage of 4.6 V or higher is applied.

Among the compounds represented by the formula (3), a compound represented by the following formula (3 ′) is more preferable.
_{Li (Li x Mn y Ni v} Co w) O p ··· (3 ')
In the formula, 0.09 <x <0.3, 0.36 <y <0.73, 0 <v <0.32, 0 <w <0.32, 1.9 <p <2.1, x + y + v + w = 1.
In the formula (3 ′), the composition ratio of the Li element with respect to the sum of the Mn, Ni, and Co elements is 1.2 <(1 + x) / (y + v + w) <1.8. 1.35 <(1 + x) / (y + v + w) <1.65 is preferable, and 1.45 <(1 + x) / (y + v + w) <1.55 is more preferable.

As a compound represented by the formula (3 ′), Li (Li _0.16 Ni _0.17 Co _0.08 Mn _0.59 ) O ₂ , Li (Li _0.17 Ni _0.17 Co _0.17 Mn _0.49 ) O ₂ , Li (Li _0.17 Ni _0.21 Co _0.08 Mn _0.54 ) O ₂ , Li (Li _0.17 Ni _0.14 Co _0.14 Mn _0.55 ) O ₂ , Li (Li _0.18 Ni _0.12 Co _0.12 Mn _0.58 ) O ₂ , Li (Li _0.18 Ni _0.16 Co _0.12 Mn _0.54 ) O ₂ , Li (Li _{0. 20} Ni _0.12 Co _0.08 Mn _0.60 ) O ₂ , Li (Li _0.20 Ni _0.16 Co _0.08 Mn _0.56 ) O ₂ , Li (Li _0.20 Ni _0.13 Co _0.13 Mn _0.54 ) O ₂ is particularly preferred.

The compound represented by the above formula (3) preferably has a layered rock salt type crystal structure (space group R-3m). In addition, since the ratio of Li element to transition metal element is high, XRD (X-ray diffraction) measurement using CuKα ray as an X-ray source has a peak in a range of 2θ = 20 to 25 °, similarly to layered Li ₂ MnO _3. Is observed.

The average particle diameter (D50) of the positive electrode active material is preferably 0.1 to 50 μm, and more preferably 1 to 20 μm, from the viewpoint of improving battery characteristics such as charge / discharge capacity and cycle characteristics.
Here, the average particle size (D50) is a particle size distribution at a point where the cumulative curve is 50% in a cumulative curve obtained by obtaining a particle size distribution on a volume basis and setting the total volume to 100%. It means% diameter. The particle size distribution is obtained from a frequency distribution and a cumulative volume distribution curve measured with a laser scattering particle size distribution measuring apparatus. The particle size is measured by sufficiently dispersing the powder in an aqueous medium by ultrasonic treatment or the like and measuring the particle size distribution (for example, a laser diffraction / scattering particle size distribution measuring device Partica LA-950VII manufactured by HORIBA, etc.). Used).

Examples of positive electrode active materials other than (X), (Y), and (Z) include LiCoO ₂ , LiMn ₂ O ₄ , LiMnO ₂ , LiFePO ₄ , and LiMnPO ₄ .
Moreover, it is preferable that the sum total of the positive electrode active material contained in said (X), (Y), (Z) among 100 mass parts of positive electrode active material (a) is 50 mass parts or more, and 70 mass parts or more. Is more preferably 99 parts by mass or more, and particularly preferably 100 parts by mass.

The present invention is particularly useful when the positive electrode mixture exhibits strong basicity when the positive electrode active material (a) is contained in the positive electrode mixture. Examples of the positive electrode active material (a) exhibiting basicity include the lithium nickel composite oxide (X) and the lithium nickel cobalt composite oxide (Y).
That is, in the present invention, the positive electrode active material (a) is composed of the lithium nickel composite oxide (X) represented by the above formula (1) and the lithium nickel cobalt composite oxide (Y) represented by the formula (2). It is particularly preferable that it is one or more selected from the group.

[Fluorine-containing copolymer (f)]
The fluorine-containing copolymer (f) has a polymer unit based on tetrafluoroethylene and a polymer unit based on propylene. By having such a polymerized unit, the coating property to the current collector is good, the positive electrode active materials are excellent, and the adhesion between the positive electrode active material and the current collector is excellent, and the electrode swells with respect to the electrolytic solution. The effect of being small and good is obtained.
The fluorine-containing copolymer (f) has a polymer unit based on tetrafluoroethylene and a polymer unit based on propylene, but is within the range that does not impair the function of the fluorine-containing copolymer (f), and is optionally tetrafluoroethylene. You may have other polymerization units other than the polymerization unit based on ethylene, and the polymerization unit based on propylene. Examples of the monomer that forms other polymerized units include fluorine-containing monomers and hydrocarbon monomers.

As fluorine-containing monomers, fluorine-containing olefins such as vinylidene fluoride, hexafluoropropylene, chlorotrifluoroethylene, and perfluorobutylethylene, fluorine-containing vinyl ethers such as perfluoropropyl vinyl ether, perfluoromethyl vinyl ether, and the like should be used. Can do.
Examples of the hydrocarbon monomer include α-olefins such as ethylene and 1-butene, vinyl ethers such as ethyl vinyl ether, butyl vinyl ether and hydroxybutyl vinyl ether, and vinyl esters such as vinyl acetate and vinyl benzoate.

  Since the fluorine-containing copolymer (f) has good alkali resistance, oxidation resistance, electrolytic solution swellability, adhesion, and flexibility, only from a polymer unit based on tetrafluoroethylene and a polymer unit based on propylene. The fluorine-containing copolymer is more preferable.

The composition of the fluorinated copolymer (f) is such that the ratio of polymer units based on tetrafluoroethylene / polymer units based on polymer units based on propylene is in the range of 30/70 to 85/15 (mol%). It is preferably 40/60 to 70/30, more preferably 50/50 to 60/40. Within this composition ratio range, it is possible to obtain an electrode having excellent storage stability, good coating properties, low swelling of the electrolyte solution with respect to the solvent at high temperatures, and good adhesion between the current collector and the electrode. .
Further, when the fluorinated copolymer (f) has the other polymerized units, the content of the other polymerized units is 10 mol in all the polymerized units contained in the fluorinated copolymer (f). % Or less, more preferably 5 mol% or less, and particularly preferably 1 mol% or less.

The Mooney viscosity of the fluorinated copolymer in the present invention is preferably 5 to 200, more preferably 10 to 170, and most preferably 20 to 100.
Mooney viscosity is measured according to JIS K6300 using an L-shaped rotor with a diameter of 38.1 mm and a thickness of 5.54 mm, at 100 ° C., with a preheating time of 1 minute and a rotor rotation time of 10 minutes. It is a measure of the molecular weight of polymer materials such as rubber. Moreover, it shows that it is a high molecular weight indirectly, so that a value is large. When the Mooney viscosity is in the range of 5 to 200, when used as a binder for an electricity storage device, good adhesion (binding property) and excellent flexibility are easily obtained at the same time.
As the fluorine-containing copolymer (f), one type of fluorine-containing copolymer may be used, or two or more types of copolymers having different polymerization unit compositions may be used in combination.

  The content of the fluorinated copolymer (f) in the positive electrode mixture is preferably 0.1 to 20 parts by mass, more preferably 1 to 10 parts by mass, particularly preferably 1 to 1 part by mass with respect to 100 parts by mass of the positive electrode active material. 8 parts by mass. When the content of the fluorinated copolymer (f) is within this range, the adhesion is improved while suppressing an increase in resistance inside the electrode as much as possible.

In the positive electrode mixture, the fluorine-containing copolymer (f) is preferably dispersed as particles having an average particle diameter of 10 to 500 nm. The lower limit of the average particle diameter is more preferably 20 nm or more, further preferably 30 nm or more, and most preferably 50 nm or more. Further, the upper limit of the average particle diameter is more preferably 300 nm or less, further preferably 200 nm or less, still more preferably 150 nm or less, and most preferably 100 nm or less.
When the average particle size is in the above range, the fluorine-containing copolymer (f) does not cover the entire surface of the positive electrode active material densely, the internal resistance is lowered, and the fluorine-containing copolymer (f ) Binding force is difficult to decrease.
In addition, the average particle diameter of the particle | grains of a fluorine-containing copolymer (f) can be measured with a dynamic light-scattering method using the laser zeta electrometer ELS-8000 by an Otsuka Electronics company.

[Other polymers]
The positive electrode mixture of the present invention may contain other polymers in addition to the fluorine-containing copolymer (f). Examples of other polymers include polyethylene oxide (PEO), polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), and tetrafluoroethylene-hexafluoropropylene copolymer (FEP). ), Fluororesins such as ethylene-tetrafluoroethylene copolymer (ETFE), polyethylene, polypropylene, aramid resin, polyamide, polyimide, polyamideimide, polyacrylonitrile, polyacrylic acid, polyacrylic acid methyl ester, polyacrylic acid Ethyl ester, polyacrylic acid hexyl ester, polymethacrylic acid, polymethacrylic acid methyl ester, polymethacrylic acid ethyl ester, polymethacrylic acid hexyl ester, poly (vinyl acetate) , Polyvinylpyrrolidone, polyether, polyether sulfone, hexafluoropolypropylene, styrene-butadiene rubber.

  The content of the other polymer is preferably 0.1 to 50 parts by mass, and more preferably 0.1 to 30 parts by mass with respect to 100 parts by mass of the fluoropolymer (f). If the content of the other polymer is within this range, the adhesion may be improved without impairing the characteristics of the positive electrode mixture of the present invention.

[Water-soluble thickener (c)]
The water-soluble thickener (c) used in the present invention is not particularly limited as long as it is a polymer that dissolves in water at 25 ° C. and exhibits viscosity. Specifically, carboxymethylcellulose, methylcellulose, and hydroxypropylcellulose. Cellulose polymers such as and their ammonium salts and alkali metal salts, poly (meth) acrylic acid, and their ammonium salts and alkali metal salts, polyvinyl alcohol, polyethylene oxide, polyvinyl pyrrolidone, acrylic acid or acrylic acid salts and vinyl alcohol A copolymer of maleic anhydride or a complete or partial saponified product of maleic anhydride or a copolymer of fumaric acid and vinyl acetate, modified polyvinyl alcohol, modified polyacrylic acid, polyethylene glycol, polycarboxylic acid, ethylene- Alkenyl alcohol copolymer, water-soluble polymers such as vinyl acetate polymers.

The content of the water-soluble thickener (c) in the positive electrode mixture is preferably 0.01 to 10 parts by mass, more preferably 0.05 to 5 parts by mass, particularly preferably 100 parts by mass of the positive electrode active material. Is 0.1 to 2 parts by mass. When the content ratio of the water-soluble thickener is within the above range, a positive electrode mixture with excellent dispersibility of active materials and the like in the positive electrode mixture and high stability can be obtained, and a smooth electrode can be obtained. Excellent battery characteristics can be exhibited.
The viscosity of the positive electrode mixture is preferably from 100 to 10000 mPa · s, more preferably from 500 to 5000 mPa · s, and particularly preferably from 1000 to 3000 mPa · s because of excellent coating properties.

[Aqueous medium]
The aqueous medium in the positive electrode mixture essentially contains water, and may contain a water-soluble organic solvent that can be mixed with water in any proportion in addition to water. As such a water-soluble organic solvent, alcohols such as methanol, ethanol, propanol, isopropanol, n-butanol, and t-butanol are preferable. The smaller the content of the water-soluble organic solvent is, the more preferable, and zero is particularly preferable.
When the aqueous medium is a mixture of water and a water-soluble organic solvent, the content of the water-soluble organic solvent is preferably less than 1% by mass, more preferably 0.1% by mass or less, and most preferably zero. When the content of the water-soluble organic solvent is within this range, aggregation is unlikely to occur in the positive electrode mixture, and good binding properties are easily obtained.
The content ratio of the aqueous medium in the positive electrode mixture is preferably 1 to 900 parts by mass, more preferably 5 to 300 parts by mass, and particularly preferably 10 to 50 parts by mass with respect to 100 parts by mass of the positive electrode active material. When the content of the aqueous medium is within the above range, the dispersibility of each component is good and the coating property is excellent.

[PH adjuster]
The pH of the positive electrode mixture of the present invention is 6 or more and less than 10, preferably 7 to 10, more preferably 8 to 10, and particularly preferably 9 to 10. By setting the pH of the positive electrode mixture within the above range, the current collector can be prevented from corroding even when a highly basic electrode active material is contained without affecting the battery characteristics of the positive electrode active material.

The positive electrode mixture can contain a pH adjuster as necessary. By adding a pH adjuster, the pH of the positive electrode mixture can be easily adjusted.
Although the kind of pH adjuster is not specifically limited, It is preferable that it is a water-soluble substance which shows acidity. Either strong acid or weak acid can be used. Further, it may be an inorganic acid or an organic acid.
Specific examples of the inorganic acid include hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid and the like. Sulfuric acid is preferred. Examples of the organic acid include organic compounds having an acid group such as a carboxylic acid group, a phosphoric acid group, and a sulfonic acid group. In particular, an organic compound having a carboxylic acid group is preferably used. Specific examples of the compound having a carboxylic acid group include acetic acid, oxalic acid, succinic acid, citric acid, phthalic acid, maleic acid, succinic anhydride, phthalic anhydride, maleic anhydride and the like.
The addition amount of the pH adjuster is preferably in the range of 0.1 parts by mass or more and 1 part by mass or less with respect to 100 parts by mass of the positive electrode mixture.

[Conductive material]
The positive electrode mixture may contain a conductive material as necessary. By using the conductive material, the electrical contact between the electrode active materials can be improved, the electrical resistance in the active material layer can be lowered, and the discharge rate characteristics of the non-aqueous secondary battery can be improved.
Examples of the conductive material include conductive carbon such as acetylene black, ketjen black, carbon black, graphite, vapor grown carbon fiber, and carbon nanotube.
When using an electrically conductive material, 0.1-30 mass parts is preferable with respect to 100 mass parts of positive electrode active materials (a), and, as for content of the electrically conductive material in a positive electrode mixture, 1-10 mass parts is more preferable. When the positive electrode material mixture contains a conductive material with a content in this range, the effect of reducing electrical resistance is greatly improved with the addition of a small amount of conductive material.

<Method for producing positive electrode mixture for non-aqueous secondary battery>
The positive electrode mixture of the present invention includes a positive electrode active material (a), a fluorine-containing copolymer (f) having a polymer unit based on tetrafluoroethylene and a polymer unit based on propylene, a water-soluble thickener (c), and an aqueous medium , And if necessary, a conductive material and a pH adjuster are mixed uniformly.
The fluorine-containing copolymer (f) is an aqueous dispersion (b) in which the fluorine-containing copolymer (f) is dispersed in an aqueous medium in advance (hereinafter sometimes simply referred to as an aqueous dispersion (b)). It is preferable that the aqueous dispersion (b) is mixed with other components.
That is, in the method for producing a positive electrode mixture of the present invention, a positive electrode active material (a), a fluorine-containing copolymer (f) having a polymer unit based on tetrafluoroethylene and a polymer unit based on propylene are dispersed in an aqueous medium. And a step of mixing the aqueous dispersion (b) and the water-soluble thickener (c). Furthermore, it is preferable to add and mix an aqueous medium. If necessary, a conductive material, a pH adjuster, etc. are added and mixed.

[Aqueous dispersion (b) in which fluorine-containing copolymer (f) is dispersed in an aqueous medium]
The aqueous medium in the aqueous dispersion (b) essentially contains water, and may contain a water-soluble organic solvent that can be mixed with water in any proportion in addition to water. As such a water-soluble organic solvent, alcohols such as methanol, ethanol, propanol, isopropanol, n-butanol, and t-butanol are preferable. The smaller the content of the water-soluble organic solvent is, the more preferable, and zero is particularly preferable.
When the aqueous medium is a mixture of water and a water-soluble organic solvent, the content of the water-soluble organic solvent is preferably less than 1% by mass, more preferably 0.1% by mass or less, and most preferably zero. When the content of the water-soluble organic solvent is within this range, the fluorinated copolymer (f) hardly aggregates in the aqueous dispersion (b), and good binding properties are obtained when used in the positive electrode mixture. Easy to obtain.
The component composition of the aqueous medium in the aqueous dispersion (b) and the component composition of the aqueous medium in the positive electrode mixture may be the same or different.

  The concentration of the fluorinated copolymer (f) in the aqueous dispersion (b) is preferably 5 to 60% by mass, more preferably 10 to 50% by mass, and particularly preferably 15 to 35% by mass. When the concentration of the fluorinated copolymer is within this range, excellent dispersion stability of the fluorinated copolymer (f) in the aqueous dispersion (b) can be easily obtained.

When the aqueous dispersion (b) is a latex (emulsion) containing particles of the fluorinated copolymer (f) and an anionic emulsifier in an aqueous medium, the aqueous dispersion (b) has excellent stability, When this aqueous dispersion (b) is used for a positive electrode mixture, it is preferable because excellent charge / discharge characteristics can be obtained.
Known anionic emulsifiers can be used. Specific examples include hydrocarbon emulsifiers (sodium lauryl sulfate, sodium dodecylbenzenesulfonate, etc.), fluorine-containing alkyl carboxylates (ammonium perfluorooctanoate, ammonium perfluorohexanoate, etc.), represented by the following formula (I). And the like (hereinafter also referred to as compound (I)).
F (CF ₂ ) _p O (CF (X) CF ₂ O) _q CF (X) COOA (A)
In the formula, X represents a fluorine atom or a C 1-3 perfluoroalkyl group, A represents a hydrogen atom, an alkali metal, or NH ₄ , p represents an integer of 1 to 10, and q represents Represents an integer of 0 to 3;
Examples of compound (I) include the following compounds.

F (CF ₂ ) ₂ OCF ₂ CF ₂ OCF ₂ COONH ₄ ,
F (CF ₂ ) ₂ O (CF ₂ CF ₂ O) ₂ CF ₂ COONH ₄ ,
F (CF ₂ ) ₃ O (CF (CF ₃ ) CF ₂ O) ₂ CF (CF ₃ ) COONH ₄ ,
F (CF ₂ ) ₃ OCF ₂ CF ₂ OCF ₂ COONH ₄ ,
F (CF ₂ ) ₃ O (CF ₂ CF ₂ O) ₂ CF ₂ COONH ₄ ,
F (CF ₂ ) ₄ OCF ₂ CF ₂ OCF ₂ COONH ₄ ,
F (CF ₂ ) ₄ O (CF ₂ CF ₂ O) ₂ CF ₂ COONH ₄ ,
F (CF ₂ ) ₂ OCF (CF ₃ ) CF ₂ OCF (CF ₃ ) COONH ₄ ,
F (CF ₂ ) ₂ OCF ₂ CF ₂ OCF ₂ COONa,
F (CF ₂ ) ₂ O (CF ₂ CF ₂ O) ₂ CF ₂ COONa,
F (CF ₂ ) ₃ OCF ₂ CF ₂ OCF ₂ COONa,
F (CF ₂ ) ₃ O (CF ₂ CF ₂ O) ₂ CF ₂ COONa,
F (CF ₂ ) ₄ OCF ₂ CF ₂ OCF ₂ COONa,
F (CF ₂ ) ₄ O (CF ₂ CF ₂ O) ₂ CF ₂ COONa and the like.

Of these, sodium lauryl sulfate is particularly preferable because of excellent dispersion stability of latex. An anionic emulsifier may be used individually by 1 type, and may be used in combination of 2 or more type.
The content of the anionic emulsifier in the aqueous dispersion (b) is preferably 1.5 to 5.0 parts by mass, and 1.5 to 3.8 parts by mass with respect to 100 parts by mass of the fluorinated copolymer. More preferred is 1.7 to 3.2 parts by mass. When the content of the anionic emulsifier is within this range, the stability of the aqueous dispersion (b) is excellent, and excellent charge / discharge characteristics are easily obtained when the aqueous dispersion (b) is used in the positive electrode mixture. .

When the fluorine-containing copolymer (f) in the aqueous dispersion (b) is in the form of particles, the average particle size is the same as the average particle size of the fluorine-containing copolymer (f) in the positive electrode mixture described above. It is.
The average particle size of the fluorinated copolymer (f) in the aqueous dispersion (b) can be adjusted by known methods such as the type and amount of emulsifier added in the polymerization step. Specifically, when the amount of the emulsifier added is increased, the average particle size tends to decrease.

The fluorine-containing copolymer (f) can be produced by a known method such as suspension polymerization, emulsion polymerization, or solution polymerization. The fluoropolymer (f) obtained by polymerization may be in any state of a dispersion dispersed in an aqueous medium such as water or a solution dissolved in a solvent. Among these, the dispersion dispersed in the aqueous medium in that the homodispersibility of the fluoropolymer (f) is good and the liquid obtained by polymerization can be used as the aqueous dispersion (b) as it is. In particular, a latex (milky emulsion) state in which particles are dispersed in an aqueous medium is preferable. Such a latex-containing fluorine-containing copolymer (f) can be easily obtained by synthesizing the fluorine-containing copolymer (f) by an emulsion polymerization method.
Further, a dispersion obtained by purifying the fluorine-containing copolymer (f) obtained by arbitrary polymerization to a solid state and re-dispersing the solid in an aqueous medium is also used as the aqueous dispersion (b) in the present invention. be able to.

  When employing an emulsion polymerization method or a suspension polymerization method as a method for producing the fluorinated copolymer (f), an emulsifier or a dispersant may be used. As the emulsifier or dispersant, those used in usual emulsion polymerization method, suspension polymerization method and the like can be used. As the emulsifier or dispersant, an ionic emulsifier is preferable from the viewpoint of excellent mechanical and chemical stability of the obtained liquid (an aqueous dispersion in which the fluorinated copolymer (f) is dispersed). An emulsifier is more preferable.

  When the dispersion of the fluorinated copolymer obtained by polymerization is used as it is as the aqueous dispersion (b), an emulsifier is further added to the aqueous dispersion of the fluorinated copolymer after the emulsion polymerization step. May be. That is, it is preferable to add an emulsifier after adding an emulsifier in the emulsion polymerization step of the fluorinated copolymer to obtain an aqueous dispersion of the fluorinated copolymer. The emulsifier added to the aqueous dispersion of the fluorinated copolymer after the emulsion polymerization step may be the same as the emulsifier used in the emulsion polymerization step or may be different.

In the method for producing the positive electrode mixture of the present invention, the mixing method and the mixing order are not particularly limited. For example, to the mixture of the water-soluble thickener (c) and the aqueous medium (aqueous solution of the water-soluble thickener (c)), the positive electrode active material (a), and other components such as a conductive material, if necessary, Furthermore, after adding and mixing an aqueous medium additionally, the method of adding and mixing the aqueous dispersion (b) containing a fluorine-containing copolymer (f) can be used.
The step of adjusting the pH of the positive electrode mixture may be performed anywhere during the production of the positive electrode mixture, but after adjusting the positive electrode mixture to a predetermined solid content concentration, it may be adjusted by adding a pH adjuster. preferable. Moreover, you may add the pH adjuster previously to the aqueous dispersion (b) containing a fluorine-containing copolymer (f), or the aqueous solution of a water-soluble thickener (c).

  The mixer used for mixing is not particularly limited as long as it is an apparatus capable of uniformly mixing the above components, a planetary mixer, a blade type agitator such as a kneader, a single or twin screw extruder, a ball mill, Bead mills, roll mills, Henschel mixers, rotating / revolving mixers, etc. can be used. Among these, a bead mill, a planetary mixer, a rotation / revolution mixer, and the like are preferable because high concentration dispersion is possible, and a rotation / revolution mixer is particularly preferable.

<Method for producing positive electrode for non-aqueous secondary battery>
The method for producing a positive electrode for a non-aqueous secondary battery according to the present invention comprises a step of applying the positive electrode mixture of the present invention on a current collector made of a metal, and the positive electrode mixture applied on the current collector. Drying to remove the aqueous medium.
Or the process of apply | coating the positive mix obtained with the manufacturing method of the positive mix of this invention on the collector which consists of metals, and drying the said positive mix applied on the said collector Removing the aqueous medium.

The current collector is not particularly limited as long as it is made of a conductive material, but generally includes metal foils such as aluminum, nickel, stainless steel, copper, metal nets, metal porous bodies, and the like. Aluminum is particularly preferable.
The thickness of the current collector is preferably 1 to 100 μm. If it is less than 1 μm, the durability of the battery is insufficient and the reliability of the battery may be lowered. On the other hand, if it exceeds 100 μm, the mass of the battery increases.

As a method for applying the positive electrode mixture to the current collector, various application methods may be mentioned. For example, the method of apply | coating with application tools, such as a doctor blade, etc. are mentioned. The coating temperature is not particularly limited, but usually a temperature around room temperature is preferable.
The thickness of the coating layer of the positive electrode mixture is preferably 0.5 to 2000 μm, more preferably 10 to 1000 μm, and particularly preferably 50 to 500 μm in terms of the thickness after drying.

The step of drying the positive electrode mixture applied on the current collector can be performed using various dryers. For example, a heat dryer using hot air or hot air, a heating vacuum dryer, a dryer using irradiation with far infrared rays or an electron beam, and the like can be given. Among these, a heat dryer or a heat-type vacuum dryer is preferable.
The higher the drying temperature, the shorter the drying time and the better the productivity. In the case where the positive electrode mixture contains a highly basic positive electrode active material, the higher the drying temperature and the longer the drying time, the more likely the corrosion of the current collector tends to occur.
In the present invention, the drying temperature is usually preferably from room temperature (for example, 25 ° C.) to 200 ° C., and particularly from 50 to 150 ° C., preferably from 70 ° C. to 150 ° C. until the residual moisture becomes less than 5% in order to increase productivity. It is preferable to perform vacuum drying at 100 ° C. to 200 ° C. after drying using a heat dryer.
The drying time is not particularly limited, but is preferably 30 minutes or more in total, and more preferably 2 hours or more.

Thus, after apply | coating a positive mix and drying and removing an aqueous medium, you may shape | mold to desired thickness with a press as needed. Such pressing is preferred in that the porosity of the electrode can be lowered.
As a pressing method, a mold press, a roll press or the like can be used.

The non-aqueous secondary battery of the present invention includes the positive electrode for a non-aqueous secondary battery of the present invention, and further includes a negative electrode, a separator, and a non-aqueous electrolyte solution. As the negative electrode, a commonly used negative electrode can be used, and a negative electrode mixture composed of lithium metal, a lithium alloy such as a lithium aluminum alloy, a negative electrode active material, and a binder is held in a negative electrode current collector. And the negative electrode.
The type of the negative electrode active material is not particularly limited, and examples thereof include high-molecular carbides such as coke, graphite, mesophase pitch spherules, phenol resin, and polyparaphenylene; and carbonaceous materials such as vapor-phase-generated carbon fiber and carbon fiber. It is done. In addition, metals such as Si, Sn, Sb, Al, Zn, and W that can be alloyed with lithium are also included. An electrode active material having a conductive material attached to the surface by a mechanical modification method can also be used.

<Non-aqueous secondary battery>
The non-aqueous secondary battery of this invention is equipped with the positive electrode for secondary batteries manufactured by the manufacturing method of the positive electrode for non-aqueous secondary batteries of this invention, a negative electrode, electrolyte solution, and a separator. A known structure can be adopted as the structure of the secondary battery.
The positive electrode for a non-aqueous secondary battery obtained in the present invention can be used for batteries having any shape such as a cylindrical shape, a sheet shape, and a square shape. A non-aqueous secondary battery in which a separator is provided between the positive electrode and the negative electrode and these are accommodated in a case together with a non-aqueous electrolyte is highly reliable even at high temperatures.

  As the separator, a microporous polymer film is used, and the material is nylon resin, polyester resin, cellulose acetate resin, nitrocellulose resin, polysulfone resin, polyacrylonitrile resin, polyvinylidene fluoride resin, tetrafluoroethylene resin. , Tetrafluoroethylene-ethylene copolymer resin, polypropylene resin, polyethylene resin and the like.

Examples of the non-aqueous electrolyte include aprotic organic solvents such as propylene carbonate, ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, γ-butyrolactone, and diethoxyethane. Examples of the electrolyte include lithium salts such as LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAsF ₅ , CF ₃ SO ₃ Li, and (CF ₃ SO ₂ ) ₂ NLi.

According to the present invention, when the fluorine-containing copolymer (f) is used as a binder for the positive electrode active material, and the pH of the positive electrode mixture is set to a specific range of less than 10, a highly basic electrode active material is contained. Can suppress corrosion of the current collector, the positive electrode mixture is hard to thicken, has excellent storage stability, and is excellent in the adhesion between the positive electrode mixture and the current collector and the charge / discharge characteristics of the battery. A positive electrode mixture is obtained.
As described above, the excellent adhesion between the positive electrode mixture and the current collector and the excellent charge / discharge characteristics of the battery can be obtained by suppressing the corrosion of the current collector due to the positive electrode mixture. This is thought to be because an increase in electrical resistance between the electric body and the positive electrode active material can be suppressed. Further, the fluorine-containing copolymer (f) is extremely stable against changes in pH, and the storage stability of the electrode mixture is increased, so that the fluorine-containing copolymer (f) in the positive electrode becomes more uniform. It is thought to be dispersed.

Examples of the present invention will be described below. However, the following examples are illustrative of the present invention and the present invention is not limited thereto.
Measurement and evaluation in Examples and Comparative Examples were performed by the following methods.

(1) pH of positive electrode mixture
The pH of the obtained positive electrode mixture was measured at 25 ° C. with a pH meter (product name: HM-20P) manufactured by Toa DKK Corporation.

(2) Viscosity of positive electrode mixture (storage stability)
The obtained positive electrode mixture was measured at 25 ° C. using a conical plate type rotational viscometer (manufactured by Toki Sangyo Co., Ltd., product name: RE215H) at 1 ° 34 ′ × R24 rotor, rotation speed: 1.0 rpm. went. Immediately after the preparation of the positive electrode mixture, it was measured for one day at 25 ° C. and after 7 days at 25 ° C. The smaller the increase in viscosity after storage compared to the viscosity immediately after creation, the better the storage stability of the positive electrode mixture.

(3) Peel strength (adhesion)
A positive electrode obtained by applying a positive electrode mixture on a current collector and drying was cut into a strip shape having a width of 2 cm and a length of 10 cm, and fixed with the coating surface of the positive electrode mixture facing up. Cellophane tape (trade name, manufactured by Nichiban Co., Ltd.) is applied to the coating surface of the positive electrode mixture, and the strength (N) when the tape is peeled off at 90 ° C. from the coating surface at a speed of 10 mm / min. Was measured 5 times, and the average value was taken as the peel strength. It shows that it is excellent in adhesiveness (binding property), so that this value is large.

(4) Confirmation of corrosion of current collector A positive electrode mixture was applied on the current collector, and the surface of the positive electrode after drying was visually observed to determine the corrosivity of the current collector. When aluminum of the current collector comes into contact with the positive electrode mixture, if hydrogen gas is generated at the interface with the positive electrode mixture, irregularities due to foaming are generated on the surface of the positive electrode. The case where such unevenness was not recognized was regarded as “no corrosion”, and the case where unevenness was observed as “corrosion”.

(5) Capacity retention (charge / discharge characteristics)
The coin-type non-aqueous electrolyte secondary battery was charged at a constant current corresponding to 0.5 C at 25 ° C. up to 4.5 V (the voltage represents a voltage with respect to lithium), and further, the current value was 0. Charging was performed until the temperature reached 02C, and thereafter, a cycle of discharging to 3V with a constant current corresponding to 0.5C was performed. The capacity retention rate (unit:%) of the discharge capacity at the 50th cycle relative to the discharge capacity at the time of the first cycle discharge was determined and used as an index for the charge / discharge measurement of the battery. The higher the capacity retention rate, the better.
Note that 1 C represents a current value for discharging the reference capacity of the battery in one hour, and 0.5 C represents a half current value.

[Production Example 1: Production of aqueous dispersion (b1) containing fluorine-containing copolymer (f1)]
After degassing the inside of a 3200 mL stainless steel pressure-resistant reactor equipped with a stirring anchor blade, 1700 g of ion-exchange water, 39 g of disodium hydrogen phosphate 12 hydrate, 0.0 g sodium hydroxide, 9 g sodium lauryl sulfate, 4.4 g ammonium persulfate were added.
Next, at 75 ° C., a monomer mixed gas of ethylene tetrafluoride (hereinafter referred to as TFE) / propylene (hereinafter referred to as P) = 88/12 (molar ratio) was used, and the internal pressure of the reactor was 2 Press-fitted to 50 MPaG. The anchor blade was rotated at 300 rpm to initiate the polymerization reaction.
As the polymerization proceeds, the pressure in the reactor decreases. When the internal pressure of the reactor drops to 2.49 MPaG, the monomer mixed gas of TFE / P = 56/44 (molar ratio) is self-pressured. And the internal pressure of the reactor was increased to 2.51 MPaG. This was repeated, and the internal pressure of the reactor was maintained at 2.49 to 2.51 MPaG, and the polymerization reaction was continued. When the total amount of the TFE / P monomer mixed gas injected reaches 900 g, the internal temperature of the reactor is cooled to 10 ° C., the polymerization reaction is stopped, and the latex of the fluorine-containing copolymer (f1) An aqueous dispersion (b1) containing a fluorinated copolymer (f1) was obtained. The polymerization time was 8 hours.
The solid content in the obtained aqueous dispersion (b1) was 34% by mass, and the content of the emulsifier (sodium lauryl sulfate) was 1.0 part by mass with respect to 100 parts by mass of the fluorinated copolymer. It was. The average particle diameter of the fine particles comprising the fluorinated copolymer (f1) was 80 nm.
The copolymer composition of the fluorinated copolymer (f1) was a repeating unit based on TFE / a repeating unit based on P = 56/44 (molar ratio). The Mooney viscosity of the fluorinated copolymer (f1) was 80. The concentration of the fluorinated copolymer (f1) in the aqueous dispersion (b1) was 33% by mass.

[Production Example 2: Production of aqueous dispersion (b2) containing fluorine-containing copolymer (f2)]
An aqueous dispersion (b2) containing a fluorinated copolymer (f2) was obtained in the same manner as in Production Example 1, except that the amount of sodium lauryl sulfate was 13.5 g.
The solid content in the obtained aqueous dispersion (b2) was 34% by mass, and the content of the emulsifier (sodium lauryl sulfate) was 1.5 parts by mass with respect to 100 parts by mass of the fluorinated copolymer. It was. The average particle size of the fine particles comprising the fluorinated copolymer (f2) was 60 nm.
The copolymer composition of the fluorinated copolymer (f2) was a repeating unit based on TFE / a repeating unit based on P = 56/44 (molar ratio). The Mooney viscosity of the fluorinated copolymer (f2) was 70. The concentration of the fluorinated copolymer (f2) in the aqueous dispersion (b2) was 33% by mass.

[Production Example 3: Production of aqueous dispersion (b3) containing fluorine-containing copolymer (f1)]
To 100 g of the aqueous dispersion (b1) containing the fluorinated copolymer (f1) obtained in Production Example 1, 2.5 g of a 20% by mass aqueous solution of sodium lauryl sulfate was added and stirred to obtain a fluorinated copolymer. An aqueous dispersion (b3) containing (f1) was obtained.
The content of the emulsifier (sodium lauryl sulfate) in the obtained aqueous dispersion (b3) was 2.5 parts by mass with respect to 100 parts by mass of the fluorinated copolymer. The concentration of the fluorinated copolymer (f1) in the aqueous dispersion (b3) was 32% by mass.

[Example 1]
95 parts by mass of LiNi _0.5 Co _0.2 Mn _0.3 O _{2 having} an average particle size of 10 μm as a positive electrode active material in 25 parts by mass of a 2% by mass aqueous solution of sodium carboxymethylcellulose as a water-soluble thickener (c) Then, 2.5 parts by mass of acetylene black was mixed, water was added and stirred so that the solid content concentration became 75% by mass. Subsequently, the aqueous dispersion (b1) containing the fluorinated copolymer (f1) obtained in Production Example 1 was added so that the fluorinated copolymer would be 2.5 parts by mass and uniformly stirred. Then, 1.8 parts by mass of a 10% by mass sulfuric acid aqueous solution was added as a pH adjuster to obtain a positive electrode mixture 1.
The pH of the positive electrode mixture 1 was 9.7. The obtained positive electrode mixture 1 was applied to a 15 μm thick aluminum foil (current collector) with a roughened surface so that the thickness after drying with a doctor blade was 120 μm, and then dried with hot air at 80 ° C. It was put into the machine and dried for 30 minutes. After confirming that the water | moisture content in an electrode was 1%, it dried for 2 hours with the 150 degreeC vacuum dryer, and obtained the electrode (positive electrode 1). The moisture in the electrode after drying was 10 ppm. The moisture in the electrode was measured using a Karl Fischer moisture meter.

The obtained positive electrode 1 was cut into a circle having a diameter of 18 mm, and a lithium metal foil having the same area and a polyethylene separator were laminated in a 2016 type coin cell in the order of the lithium metal foil, the separator, and the positive electrode to obtain a battery element. A coin-type nonaqueous electrolyte secondary battery 1 was manufactured by adding a nonaqueous electrolyte solution of ethylmethyl carbonate-ethylene carbonate (volume ratio of 1: 1) of 1M-LiPF ₆ and sealing it.
Measurement and evaluation were performed for the above (1) to (5). The results are shown in Table 1.

[Example 2]
Instead of the aqueous dispersion (b1) containing the fluorinated copolymer (f1) obtained in Production Example 1, an aqueous dispersion (b2) containing the fluorinated copolymer (f2) obtained in Production Example 2 A positive electrode mixture 2 was obtained in the same manner as in Example 1 except that. The pH of the positive electrode mixture was 9.7. Thereafter, a positive electrode 2 was prepared in the same manner as in Example 1 and measured and evaluated. The results are shown in Table 1.

[Example 3]
A positive electrode mixture 3 was obtained in the same manner as in Example 2 except that the addition amount of the 10% by mass sulfuric acid aqueous solution was changed to 3 parts by mass. The pH of the positive electrode mixture was 8.4. Thereafter, the positive electrode 3 was prepared in the same manner as in Example 1 and measured and evaluated. The results are shown in Table 1.

[Example 4]
A positive electrode mixture 4 was obtained in the same manner as in Example 2 except that the addition amount of the 10% by mass sulfuric acid aqueous solution was changed to 7 parts by mass. The pH of the positive electrode mixture 4 was 6.6. Thereafter, the positive electrode 4 was prepared in the same manner as in Example 1 and measured and evaluated. The results are shown in Table 1.

[Example 5]
A positive electrode mixture 5 was obtained in the same manner as in Example 2 except that 3 parts by mass of a 10% by mass aqueous maleic anhydride solution was used instead of the 10% by mass sulfuric acid aqueous solution as a pH adjuster. The pH of the positive electrode mixture was 9.5. Thereafter, the positive electrode 5 was prepared in the same manner as in Example 1 and measured and evaluated. The results are shown in Table 1.

[Example 6]
Instead of the aqueous dispersion (b1) containing the fluorinated copolymer (f1) obtained in Production Example 1, an aqueous dispersion (b3) containing the fluorinated copolymer (f1) obtained in Production Example 3 A positive electrode mixture 6 was obtained in the same manner as in Example 1 except that. The pH of the positive electrode mixture was 9.8. Thereafter, a positive electrode 6 was prepared in the same manner as in Example 1 and measured and evaluated. The results are shown in Table 1.

[Example 7]
Example except that LiMn ₂ O ₄ having an average particle diameter of 10 μm was used in place of LiNi _0.5 Co _0.2 Mn _0.3 O ₂ as a positive electrode active material, and no 10 mass% sulfuric acid aqueous solution was added. In the same manner as in Example 2, a positive electrode mixture 7 was obtained. The pH of the positive electrode mixture 7 was 7.0. Thereafter, a positive electrode 7 was prepared in the same manner as in Example 1 and measured and evaluated. The results are shown in Table 1.

[Comparative Example 1]
A positive electrode mixture 8 was obtained in the same manner as in Example 2 except that the 10% by mass sulfuric acid aqueous solution was changed to 0.9 parts by mass. The pH of the positive electrode mixture 8 was 10.5. Thereafter, a positive electrode 8 was prepared in the same manner as in Example 1 and measured and evaluated. The results are shown in Table 1.

[Comparative Example 2]
A positive electrode mixture 9 was obtained in the same manner as in Example 2 except that 10 parts by mass of a 10% by mass sulfuric acid aqueous solution was used. The pH of the positive electrode mixture 9 was 5.5. Thereafter, a positive electrode 9 was prepared in the same manner as in Example 1 and measured and evaluated. The results are shown in Table 1.

[Comparative Example 3]
Instead of the aqueous dispersion (b2) containing the fluorinated copolymer (f2) obtained in Production Example 2, an acrylic rubber latex composed of acrylonitrile-2-ethylhexyl acrylate (solid content: 40% by mass) was used. In the same manner as in Example 3, a positive electrode mixture 10 was obtained. The pH of the positive electrode mixture 10 was 8.2. Thereafter, a positive electrode 10 was prepared in the same manner as in Example 1, and measurement and evaluation were performed. The results are shown in Table 1.
In the positive electrode mixture 10, the viscosity was remarkably increased, and the aggregation of the polymer, which was considered to be the aggregation of latex, was visually observed. The viscosity after 1 day of storage could not be measured.

[Comparative Example 4]
Example 4 and Example 4 were added except that a polytetrafluoroethylene aqueous dispersion having a solid content of 50% by mass was added instead of the aqueous dispersion (b2) containing the fluorinated copolymer (f2) obtained in Production Example 2. Similarly, the positive electrode mixture 11 was obtained. The pH of the positive electrode mixture 11 was 6.4. Thereafter, a positive electrode 11 was prepared in the same manner as in Example 1, and measurement and evaluation were performed. The results are shown in Table 1.

[Comparative Example 5]
Instead of the aqueous dispersion (b2) containing the fluorinated copolymer (f2) obtained in Production Example 2, an acrylic rubber latex composed of acrylonitrile-2-ethylhexyl acrylate (solid content: 40% by mass) was used. In the same manner as in Example 5, a positive electrode mixture 12 was obtained. The pH of the positive electrode mixture 12 was 9.5. Thereafter, a positive electrode 12 was prepared in the same manner as in Example 1 and measured and evaluated. The results are shown in Table 1.

[Comparative Example 6]
A positive electrode mixture 13 was obtained in the same manner as in Example 2 except that 10% by mass sulfuric acid aqueous solution was not added. The pH of the positive electrode mixture 13 was 11.8. Thereafter, a positive electrode 13 was prepared in the same manner as in Example 1 and measured and evaluated. The results are shown in Table 1.

As shown in the results of Table 1, as a binder, the fluorine-containing copolymer (f) according to the present invention was used, and the pH of the positive electrode mixture for non-aqueous secondary batteries applied to the current collector was 6-10. In Examples 1 to 7, it is possible to obtain an electrode that is excellent in storage stability of the positive electrode mixture, does not corrode the current collector even at a relatively high drying temperature, and has excellent adhesion, and is a non-aqueous secondary battery. As a result, good charge / discharge characteristics can be obtained.
Further, when Example 1 and Example 3 are compared, Example 3 in which the content of the emulsifier (sodium lauryl sulfate) in the aqueous dispersion (b3) containing the fluorine-containing copolymer (f1) is larger is higher in the positive electrode composite. Excellent in storage stability, adhesion and charge / discharge characteristics of the agent.

On the other hand, even when the fluorine-containing copolymer (f) according to the present invention is used as a binder, the positive electrode mixture (Comparative Examples 1 and 6) having a pH exceeding 10 shows corrosion of the current collector, and the resulting electrode. Has poor adhesion, and the charge / discharge characteristics of the battery are also poor. Moreover, there exists a tendency for a viscosity to fall during preservation | save of a positive mix, and the viscosity after 7-day storage is low compared with another example.
Further, even when the fluorine-containing copolymer (f) according to the present invention is used as a binder, the positive electrode mixture having a pH lower than 6 (Comparative Example 2) has excellent current collector corrosion and electrode adhesion. However, it is inferior to the charging / discharging characteristic of a battery. This is presumably because the positive electrode active material was deteriorated because the amount of acid added was excessive.

In Comparative Examples 3 and 5 using acrylic rubber instead of the fluorine-containing copolymer (f) according to the present invention as a binder, and Comparative Example 4 using polytetrafluoroethylene, the pH of the positive electrode mixture As a result, the stability of the positive electrode mixture was significantly lowered, resulting in poor electrode adhesion and battery charge / discharge characteristics.
In Comparative Examples 3 to 5, the electrode adhesion and the charge / discharge characteristics of the battery are inferior because the dispersion stability of acrylic rubber (Comparative Examples 3 and 5) or polytetrafluoroethylene (Comparative Example 4) deteriorates over time. This is probably because the acrylic rubber and polytetrafluoroethylene in the positive electrode are likely to be unevenly distributed.

Claims (8)

  A positive electrode active material (a), a fluorine-containing copolymer (f) having a polymer unit based on tetrafluoroethylene and a polymer unit based on propylene, a water-soluble thickener (c), and an aqueous medium, and having a pH of 6 or more A positive electrode mixture for a non-aqueous secondary battery, wherein the positive electrode mixture is less than 10.   Furthermore, the positive mix for non-aqueous secondary batteries of Claim 1 containing a pH adjuster. The positive electrode active material is at least one selected from the group consisting of a lithium nickel composite oxide (X) represented by the following formula (1) and a lithium nickel cobalt composite oxide (Y) represented by the formula (2) The positive electrode mixture for non-aqueous secondary batteries according to claim 1 or 2.
LiNi _x M _(1-x) O ₂ (1)
(In the formula, M is at least one selected from the group consisting of Al, B, Sn, Mn and Nb, and x is 0.1 ≦ x ≦ 1.)
LiNi _x Co _y M _(1-xy) O ₂ (2)
(In the formula, M is at least one selected from the group consisting of Al, B, Sn, Mn and Nb, x is 0.1 ≦ x ≦ 0.9, and y is 0.1 ≦ y ≦ 0.9. .) A method for producing a positive electrode mixture for a non-aqueous secondary battery according to any one of claims 1 to 3,
A positive electrode active material (a), an aqueous dispersion (b) in which a fluorine-containing copolymer (f) having a polymer unit based on tetrafluoroethylene and a polymer unit based on propylene is dispersed in an aqueous medium, and water-soluble thickening Mixing the agent (c),
The aqueous medium in the aqueous dispersion (b) is water alone or a mixture comprising water and a water-soluble organic solvent, and the content of the water-soluble organic solvent in the mixture is 1 with respect to 100 parts by mass of water. The manufacturing method of the positive mix for nonaqueous secondary batteries which is less than a mass part.   The aqueous dispersion (b) containing the fluorinated copolymer contains particles of the fluorinated copolymer (f) and an anionic emulsifier in an aqueous medium, and the content of the anionic emulsifier is The manufacturing method of the positive mix for non-aqueous secondary batteries of Claim 4 which is 1.5-5.0 mass parts with respect to 100 mass parts of the said fluorocopolymer (f).   The process of apply | coating the positive mix for non-aqueous secondary batteries as described in any one of Claims 1-3 on the electrical power collector which consists of metals, The said non-aqueous secondary apply | coated on the said electrical power collector The manufacturing method of the positive electrode for non-aqueous secondary batteries which has the process of drying the positive electrode mixture for secondary batteries, and removing an aqueous medium. A step of producing a positive electrode mixture for a non-aqueous secondary battery by the production method according to claim 4,
Applying the obtained positive electrode mixture for a non-aqueous secondary battery onto a current collector made of metal;
The manufacturing method of the positive electrode for non-aqueous secondary batteries which has the process of drying the said positive electrode mixture for non-aqueous secondary batteries apply | coated on the said electrical power collector, and removing an aqueous medium.   A non-aqueous secondary battery comprising a positive electrode for a secondary battery, a negative electrode, an electrolytic solution, and a separator manufactured by the manufacturing method according to claim 6.