JP7017468B2 - Electrode mixture, method for manufacturing electrode mixture, electrode structure, method for manufacturing electrode structure and secondary battery - Google Patents

Description

The present invention relates to an electrode mixture, and more particularly to an electrode mixture for a lithium ion secondary battery.

In recent years, the development of electronic technology has been remarkable, and the functions of small mobile devices have become more sophisticated, and the power sources used for these devices are required to be smaller and lighter (higher energy density). As a battery having a high energy density, a non-aqueous electrolyte secondary battery represented by a lithium ion secondary battery or the like is widely used.

For the electrodes of a lithium ion secondary battery, for example, a binder (binder) is mixed with a powdered electrode material such as an electrode active material and a conductive auxiliary agent added as needed, and the binder is dissolved or dispersed in an appropriate solvent. It is obtained by applying a obtained slurry-like electrode mixture (hereinafter, also referred to as an electrode mixture slurry) on a current collector and volatilizing the solvent to form a structure held as an electrode mixture layer.

As a method for increasing the energy density in a lithium ion secondary battery, a method for increasing the charge / discharge capacity of the positive electrode active material itself in the electrode is used. As a method for increasing the charge / discharge capacity of the positive electrode active material, for example, it is known that a nickel-containing compound is used as the positive electrode active material. Further, it is known that the discharge capacity can be improved by using an electrode active material having a high nickel ratio.

However, when the nickel ratio in the electrode active material increases, there is a problem that the electrode mixture slurry tends to gel.

Therefore, an electrode mixture has been developed for the purpose of suppressing gelation of the electrode mixture slurry. As an example of such an electrode mixture, a negative electrode mixture for a non-aqueous electrolyte secondary battery containing a polar group-containing vinylidene fluoride polymer, a chlorine atom-containing vinylidene fluoride polymer, an electrode active material and an organic solvent is used. It is known (Patent Document 1). It is also proposed to use a lithium-containing composite oxide having a specific composition containing nickel as the positive electrode active material and to contain polyvinylidene fluoride and vinylidene fluoride-chlorotrifluoroethylene copolymer as the binder of the positive electrode. (For example, Patent Document 2).

International Publication No. 2010/074041 Japanese Unexamined Patent Publication No. 2014-7088

In both of the techniques described in Patent Documents 1 and 2, a vinylidene fluoride polymer containing a chlorine atom is used as the binder composition. Although chlorine compounds are chemically stable, they have a large impact on the environmental load such as dioxins if they are not properly treated. Therefore, in recent years, various industries have been required to design materials that do not contain chlorine atoms, and lithium ion secondary batteries are also required to have materials that do not contain chlorine atoms.

Therefore, the present invention has been made in view of the above problems, and an object thereof is to provide a novel electrode mixture in which gelation of a slurry is suppressed even when an electrode active material having a high nickel content is used. To do.

The electrode mixture according to the present invention contains an electrode active material provided on the current collector and a binder composition for binding the electrode active material to the current collector in order to solve the above problems. death,
The binder composition contains vinylidene fluoride and the following formula (1).

(In the formula, R ¹ , R ² and R ³ are independently hydrogen atom, chlorine atom, fluorine atom, alkyl group having 1 to 6 carbon atoms or fluorine-substituted alkyl group having 1 to 6 carbon atoms, respectively.)
Contains a copolymer with a monomer represented by
The electrode active material has the following formula (2).
Li _{1 + x} MO ₂ ... (2)
(X is a number satisfying −0.15 <X ≦ 0.15. M is a group of two or more elements containing Ni or Ni, and is a group of two or more elements containing Ni. Contains 55 mol% or more of Ni.)
It contains a lithium metal oxide represented by, and has a configuration in which the pH of the water when the lithium metal oxide is extracted with water is higher than 11.3.

Further, in order to solve the above-mentioned problems, the method for producing an electrode mixture according to the present invention uses vinylidene fluoride and the following formula (1).

(In the formula, R ¹ , R ² and R ³ are independently hydrogen atom, chlorine atom, fluorine atom, alkyl group having 1 to 6 carbon atoms or fluorine-substituted alkyl group having 1 to 6 carbon atoms, respectively.)
Including the step of kneading the copolymer with the monomer represented by, and the electrode active material.
The electrode active material has the following formula (2).
Li _{1 + x} MO ₂ ... (2)
(X is a number satisfying −0.15 <X ≦ 0.15. M is a group of two or more elements containing Ni or Ni, and is a group of two or more elements containing Ni. Contains 55 mol% or more of Ni.)
The lithium metal oxide contains the lithium metal oxide represented by (1), and the lithium metal oxide has a structure in which the pH of the water when extracted with water is higher than 11.3.

Further, one aspect of the electrode structure according to the present invention includes a current collector and an electrode mixture layer provided on the current collector in order to solve the above-mentioned problems. The layer has a structure of being a layer formed by using the above-mentioned electrode mixture.

Further, another aspect of the electrode structure according to the present invention includes a current collector and an electrode mixture layer provided on the current collector in order to solve the above problems.
The electrode mixture layer is a layer containing a binder composition and an electrode active material, and the binder composition contains vinylidene fluoride and the following formula (1).

(In the formula, R ¹ , R ² and R ³ are independently hydrogen atom, chlorine atom, fluorine atom, alkyl group having 1 to 6 carbon atoms or fluorine-substituted alkyl group having 1 to 6 carbon atoms, respectively.)
The electrode active material contains a copolymer with a monomer represented by the following formula (2).
Li _{1 + x} MO ₂ ... (2)
(X is a number satisfying −0.15 <X ≦ 0.15. M is a group of two or more elements containing Ni or Ni, and is a group of two or more elements containing Ni. Contains 55 mol% or more of Ni.)
It contains a lithium metal oxide represented by 1 and has a configuration in which the pH of the water when the electrode mixture layer is extracted with water is higher than 11.3.

According to the electrode mixture according to the present invention, it is possible to provide a novel electrode mixture in which gelation of the slurry during storage is suppressed even when an electrode active material having a high nickel content is used.

It is sectional drawing of the electrode structure which concerns on one Embodiment of this invention. It is an exploded perspective view of the secondary battery which concerns on one Embodiment of this invention.

The electrode mixture according to the present invention and one embodiment of its use will be described.

[Electrode combination]
The electrode mixture according to the present embodiment contains an electrode active material provided on the current collector and a binder composition for binding the electrode active material to the current collector. The binder composition contains a specific vinylidene fluoride copolymer. Further, the electrode active material contains a lithium metal oxide represented by the following formula (2).
Li _{1 + x} MO ₂ ... (2)
(X is a number satisfying −0.15 <X ≦ 0.15. M is a group of two or more elements containing Ni or Ni, and is a group of two or more elements containing Ni. Contains 55 mol% or more of Ni.)
The pH of water when the lithium metal oxide is extracted with water is higher than 11.3.

(Binder composition)
The binder composition in the present embodiment is used as a binder for binding the electrode active material onto the current collector. The binder composition contains a vinylidene fluoride copolymer which is a copolymer of vinylidene fluoride and a monomer represented by the following formula (1).

In the formula (1), R ¹ , R ² and R ³ are independently hydrogen atoms, chlorine atoms, fluorine atoms, alkyl groups having 1 to 6 carbon atoms or fluorine-substituted alkyl groups having carbon atoms 1 to 6, respectively. Considering the influence on the environmental load, a hydrogen atom or an alkyl group having 1 to 6 carbon atoms is preferable. Further, from the viewpoint of the polymerization reaction, R ¹ , R ² or R ³ is desired to be a substituent having a small steric hindrance, and hydrogen or an alkyl group having 1 to 3 carbon atoms is preferable, and hydrogen or a methyl group is preferable. More preferred.

The vinylidene fluoride copolymer in the present embodiment preferably has a structural unit derived from the monomer represented by the formula (1) of 0.40 to 10.00 mol%, preferably 0.50 to 7.00 mol. % Is more preferable, and 0.60 to 4.00 mol% is particularly preferable. Further, it is preferable to have 90.0 to 99.6 mol%, more preferably 93.0 to 99.5 mol%, and 96.0 to 99.5 mol% of the constituent units derived from vinylidene fluoride. Especially preferable. When the constituent unit derived from the monomer represented by the formula (1) is 0.40 mol% or more, it occupies in the electrode mixture slurry of the constituent unit derived from the monomer represented by the formula (1). The ratio does not become too small, and the effect of suppressing gelation of the electrode mixture slurry can be obtained. Further, when the structural unit derived from the monomer represented by the formula (1) is 10.00 mol% or less, the viscosity of the electrode mixture slurry does not become too high, and it becomes difficult to apply the electrode mixture slurry. It can be prevented from becoming. In particular, by using the vinylidene fluoride copolymer of the present embodiment, it is possible to obtain the effect of suppressing gelation of the electrode mixture slurry even when it is stored for a longer period of time.

The amount of vinylidene fluoride unit of the vinylidene fluoride copolymer and the amount of the monomer unit represented by the formula ( ¹ ) can be determined by 1H NMR spectrum of the copolymer or neutralization titration. can.

The vinylidene fluoride copolymer in the present embodiment may have components of vinylidene fluoride and a monomer other than the monomer represented by the formula (1). For example, a fluorine-based monomer copolymerizable with vinylidene fluoride, a hydrocarbon-based monomer such as ethylene and propylene, or a monomer copolymerizable with the formula (1) can be mentioned. Examples of the fluorine-based monomer copolymerizable with vinylidene fluoride include vinyl fluoride, trifluoroethylene, tetrafluoroethylene, chlorotrifluoroethylene, hexafluoropropylene, perfluoroalkyl vinyl ether typified by perfluoromethyl vinyl ether and the like. be able to. Examples of the monomer copolymerizable with the formula (1) include (meth) acrylic acid and an alkyl (meth) acrylate compound typified by methyl (meth) acrylate. The other monomer may be used alone or in combination of two or more.

When the vinylidene fluoride copolymer has the above-mentioned other monomers, it is preferable to have 0.01 to 10 mol% of the other monomer units.

The vinylidene fluoride copolymer in the present embodiment can be obtained by polymerizing vinylidene fluoride and the monomer represented by the formula (1) by a conventionally known method. The polymerization method is not particularly limited, and examples thereof include suspension polymerization, emulsion polymerization, and solution polymerization. Among these, the polymerization method is preferably aqueous suspension polymerization or emulsion polymerization because of the ease of post-treatment and the like. Further, the vinylidene fluoride used for the polymerization and the monomer represented by the formula (1) are already well-known compounds, and general commercial products may be used.

The vinylidene fluoride copolymer in the present embodiment has a weight average molecular weight in the range of 50,000 to 1.5 million as measured by GPC (gel permeation chromatography).

The intrinsic viscosity η _i of the vinylidene fluoride copolymer in the present embodiment is preferably 0.5 dl / g to 5.0 dl / g, and more preferably 1.0 dl / g to 4.5 dl / g. It is preferably 1.5 dl / g to 4.0 dl / g, and more preferably 1.5 dl / g to 4.0 dl / g. When the intrinsic viscosity is within the above range, the deterioration of productivity due to the decrease in the solid content of the electrode mixture slurry can be prevented, and the electrode can be easily manufactured without causing uneven thickness of the electrode when the electrode mixture is applied. Preferred in terms of points. The intrinsic viscosity η _i can be obtained by dissolving 80 mg of the polymer in 20 ml of N, N-dimethylformamide and using a Ubbelohde viscometer in a constant temperature bath at 30 ° C. by the following formula.

η _i = (1 / C) ・ ln (η / η ₀ )
In the above formula, η is the viscosity of the polymer solution, η ₀ is the viscosity of the solvent N, N-dimethylformamide, and C is 0.4 g / dl.

The binder composition according to the present embodiment may contain other vinylidene fluoride-based polymers as long as the desired effects are not impaired. Other vinylidene fluoride-based polymers that can be included in the binder composition include vinylidene fluoride homopolymers and vinylidene fluoride copolymers of vinylidene fluoride and other monomers copolymerizable with vinylidene fluoride. Coalescence is mentioned. The other monomer here is a monomer not included in the monomer represented by the above formula (1). Examples of such other monomers include a fluorine-based monomer copolymerizable with vinylidene fluoride described above, a hydrocarbon-based monomer such as ethylene and propylene, and an alkyl (meth) acrylate compound. Be done. Further, the other monomer may be a polar group-containing compound. Examples of the polar group-containing compound include compounds containing a carboxyl group, an epoxy group, a sulfonic acid group, and the like, and among them, a compound containing a carboxyl group is preferable. Specific examples thereof include 2-carboxyethyl acrylate, 2-carboxyethyl methacrylate, acryloyloxyethyl acrylic acid, and acryloyloxypropyl succinic acid.

When other vinylidene fluoride-based polymers are contained, the proportion of the vinylidene fluoride copolymer containing the structural unit derived from the monomer represented by the formula (1) in the entire polymer contained in the binder composition. Is preferably 10% by weight or more, and more preferably 30% by weight or more. Further, the content of the structural unit derived from the monomer represented by the formula (1) in the entire polymer contained in the binder composition is preferably 0.10 mol% or more, preferably 0.20 mol% or more. It is more preferable that there is, and it is further preferable that it is 0.30 mol% or more. The content of the vinylidene fluoride copolymer containing the structural unit derived from the monomer represented by the formula (1) in the binder composition, and the single amount represented by the formula (1) in the binder composition. By setting the content of the structural unit derived from the body within the above range, the effect of suppressing gelation of the electrode mixture slurry can be suitably obtained.

Further, the binder composition according to the present embodiment has been developed in consideration of the load on the environment so that gelation of the electrode mixture slurry is suppressed even if a polymer containing no chlorine atom is used. Is. Therefore, the amount of chlorine in the binder composition in the present embodiment is preferably small, specifically, preferably 1000 ppm or less, more preferably 500 ppm or less, and particularly preferably 300 ppm.

The amount of chlorine in the binder composition conforms to JIS K 7229, the binder composition is burned in an oxygen atmosphere in a flask, the generated combustion gas is absorbed by an absorption liquid, and this liquid is subjected to an ion chromatograph to perform a calibration curve. The chlorine concentration can be calculated by the method.

(Electrode active material)
The electrode active material in the present embodiment contains a lithium metal oxide represented by the following formula (2).
Li _{1 + x} MO ₂ ... (2)
In the formula (2), X is a number satisfying −0.15 <X ≦ 0.15.

M is a group of two or more elements containing Ni or Ni. When M is a group of two or more elements containing Ni, examples of the elements other than Ni contained in M include Co, Mn, Ti, Cr, Fe, Cu, Zn, Al, Ge, Sn, and the like. Examples thereof include Mg, Ag, Ta, Nb, B, P, Zr, Ca, Sr and Ba. Of these, Co, Mn and Al are preferable. When M is a group of two or more kinds of elements containing Ni, the element other than Ni contained in M may be only one kind of these or two or more kinds. It is preferable that the lithium metal oxide contains Ni in that the capacity of the secondary battery can be increased by increasing the capacity density. Further, it is preferable that the lithium metal oxide contains Co or the like in addition to Ni in that the crystal structure change in the charge / discharge process is suppressed and stable cycle characteristics are exhibited.

Ni in the lithium metal oxide represented by the formula (2) is a component that contributes to capacity improvement in the electrode active material. Therefore, when M is a group of two or more elements containing Ni, the proportion of Ni is preferably 55 mol% or more, preferably 60 mol% or more, when the total number of elements constituting M is 100 mol%. Is preferable, and 70 mol% or more is more preferable.

As a particularly preferable lithium metal oxide in the present embodiment, for example, the following formula (3)
LiNi _Y1 N1 _Y2 O ₂ ... (3)
(In the formula, N1 represents Co or Mn, and 0.55 ≦ Y1 <1, 0 <Y2 <0.55.)
Binary lithium metal oxide represented by or the following formula (4)
LiNi _Y1 Co _Y2 N2 _Y3 O ₂ ... (4)
(In the formula, N2 represents Mn or Al, 0.55 ≦ Y1 <1, 0 <Y2 <0.55, 0 <Y3 <0.55, and Y1 / (Y1 + Y2 + Y3) ≧ 0.55. There is a ternary lithium metal oxide represented by).

The ternary lithium metal oxide is particularly preferably used as the electrode active material in the present embodiment because it has a high charging potential and excellent cycle characteristics.

The composition of the binary lithium metal oxide in the present embodiment is not particularly limited, and examples thereof include Li _1.0 Ni _0.8 Co _0.2 O ₂ .

The composition of the ternary lithium metal oxide in the present embodiment is not particularly limited, and examples thereof include Li _1.00 Ni _0.6 Co _0.2 Mn _0.2 O ₂ (NCM622). , Li _1.00 Ni _0.83 Co _0.12 Mn _0.05 O ₂ (NCM811), and Li _1.00 Ni _0.85 Co _0.15 Al _0.05 O ₂ (NCA811). ..

Further, the electrode active material in the present embodiment may contain a plurality of different types of lithium metal oxides, and may contain, for example, a plurality of LiNi _Y1 Co _Y2 Mn _Y3 O ₂ having different compositions, or LiNi _Y1 . Co _Y2 Mn _Y3 O ₂ and LiNi _Y1 Co _Y2 Al _Y3 O ₂ may be contained.

Further, as the lithium metal oxide in the present embodiment, 49 g of ultrapure water is added to 1 g of the lithium metal oxide, and the mixture is stirred for 10 minutes, and then the pH of the water is 11.3 when the pH of the water is measured. It exceeds. The upper limit of the pH of the water is not particularly limited. Generally, an alkaline substance is attached to the electrode active material added to the electrode mixture, and when the amount thereof is large, the obtained electrode mixture slurry tends to gel. The higher the nickel content in the electrode active material, the more alkaline substances adhere to it. That is, the pH when extracted with water becomes high. Therefore, if a lithium metal oxide having a large nickel content is used as the electrode active material in order to increase the discharge capacity, the electrode mixture slurry tends to gel. In the electrode mixture of the present embodiment, gelation of the electrode mixture slurry is suppressed even when such an electrode active material is used.

In the present embodiment, the electrode active material may contain, for example, impurities and additives in addition to the lithium metal oxide represented by the formula (2). Further, the types of impurities and additives contained in the electrode active material are not particularly limited.

(solvent)
The electrode mixture in the present embodiment may contain a solvent. The solvent may be water or a non-aqueous solvent. Examples of the non-aqueous solvent include N-methyl-2-pyrrolidone (NMP), dimethylformamide, N-dimethylformamide, N, N-dimethylacetamide, dimethylsulfoxide, N, N-dimethylsulfoxide, hexamethylphosphoamide, and the like. Examples thereof include dioxane, tetrahydrofuran, tetramethylurea, triethyl phosphate, trimethyl phosphate, acetone, cyclohexane, methyl ethyl ketone, and tetrahydrofuran. These solvents may be contained alone or in combination of two or more in the electrode mixture. The solvent may be added to the binder composition or may be added separately from the binder composition.

(Other ingredients)
The electrode mixture in the present embodiment may contain other components, if necessary. Examples of other components include conductive auxiliaries and pigment dispersants.

The conductive auxiliary agent is added for the purpose of improving the conductivity of the electrode mixture layer formed by using the electrode mixture. Examples of the conductive auxiliary agent include natural graphite (scaly graphite, etc.), artificial graphite, graphite fine powder, graphite such as graphite fiber, carbon black such as acetylene black, ketjen black, channel black, furnace black, and carbon. Examples include carbon materials such as fibers and carbon nanonucleotides. Further, conductive fibers such as metal fibers such as Ni and Al, metal powders, conductive metal oxides, organic conductive materials and the like can also be mentioned.

Moreover, as a pigment dispersant, for example, polyvinylpyrrolidone and the like can be mentioned.

In the present embodiment, the above-mentioned other components are 0 to 10 parts by weight, preferably 0 to 5 parts by weight, based on 100 parts by weight of the electrode mixture.

As described above, since the electrode mixture of the present embodiment uses a vinylidene fluoride copolymer that does not contain chlorine atoms, the burden on the environment is reduced. In addition, even when an electrode active material having a high nickel content is used, gelation of the electrode mixture slurry can be suppressed. In particular, gelation of the electrode mixture slurry is suppressed even when stored for a relatively long time. Further, according to the electrode mixture of the present embodiment, it is possible to prevent the solid content of the electrode active material or the like from settling and accumulating during the storage period. By suppressing the sedimentation during the storage period, it is possible to prevent the solid content concentration from changing, and thereby it is possible to prevent the viscosity of the electrode mixture from increasing. As a result, it is possible to prevent the handleability when manufacturing the electrode structure from being lowered.

(Manufacturing method of electrode mixture)
The electrode mixture in the present embodiment is obtained by kneading a vinylidene fluoride copolymer obtained by copolymerizing vinylidene fluoride with a monomer represented by the formula (1) and an electrode active material. Can be manufactured. In the production of the electrode mixture, the solvent and other components may be kneaded, if necessary, and the method is not particularly limited. Further, the order of adding various components at the time of kneading is not particularly limited. Further, when adding a solvent, the electrode active material and the solvent may be stirred and mixed first, and then the vinylidene fluoride copolymer may be added.

The electrode mixture in the present embodiment is produced by using as the lithium metal oxide contained in the electrode active material, a lithium metal oxide having a pH of water higher than 11.3 when extracted with water. Is to be done.

(Slurry viscosity of electrode mixture)
When the electrode mixture of the present invention is used, the extent to which gelation of the electrode mixture slurry can be suppressed can be determined by the slurry viscosity of the electrode mixture. In the present specification, "gelling" means, for example, when the electrode mixture slurry is stored at 40 ° C. in a nitrogen atmosphere for 96 hours, and then the electrode mixture slurry is stirred for 30 seconds using a mixer. , The electrode mixture slurry does not form a uniform paste, and the slurry viscosity cannot be measured due to the presence of solid matter. The solid substance refers to a solid substance that remains on the upper part of the mesh after the slurry is passed through a mesh having a mesh size of 2.36 mm and left for 1 hour. The mixer is not particularly limited, and for example, Awatori Rentaro ARE310 (rotational rotation 800 rpm, revolution 2000 rpm) manufactured by Shinky Co., Ltd. can be used.

[Electrode structure]
Subsequently, an embodiment of the electrode structure formed by using the electrode mixture of the present embodiment will be described with reference to FIG. 1. FIG. 1 is a cross-sectional view of an electrode structure according to an embodiment of the present invention.

As shown in FIG. 1, the electrode structure 10 has a current collector 11, and electrode mixture layers 12a and 12b.

The current collector 11 is a base material of the electrode structure 10 and is a terminal for extracting electricity. Examples of the material of the current collector 11 include iron, stainless steel, steel, aluminum, nickel, and titanium. The shape of the current collector 11 is preferably foil or net. In the present embodiment, the current collector 11 is preferably made of aluminum foil.

The thickness of the current collector 11 is preferably 5 to 100 μm, and preferably 5 to 20 μm.

The electrode mixture layers 12a and 12b are layers made of the electrode mixture of the present embodiment. The thickness of the electrode mixture layers 12a and 12b is 10 μm to 1000 μm, more preferably 20 to 250 μm, and even more preferably 20 to 150 μm.

The electrode mixture layer in the present embodiment is formed by using the above-mentioned electrode mixture. Therefore, the pH of the water of the electrode mixture layer in the present embodiment also exceeds 11.3 when extracted at room temperature (25 ° C.) by the extraction method specified in JIS K 5101-16.2. ing. Specifically, the pH is measured by the same method as the above-mentioned lithium metal oxide pH measuring method except that the electrode mixture layer is peeled off from the current collecting foil and used as a sample. Is.

As shown in FIG. 1, the electrode structure 10 has electrode mixture layers 12a and 12b formed on the upper and lower surfaces of the current collector 11, but the electrode structure 10 is not limited to this, and the current collector 11 is not limited to these. It may be a structure in which an electrode mixture layer is formed on one of the surfaces, that is, an electrode structure in which either one of the electrode mixture layers 12a and 12b is formed.

The electrode structure 10 can be used, for example, as a positive electrode of a lithium secondary battery.

Next, a method for manufacturing the electrode structure will be described.

In the electrode structure 10 of the present embodiment, a slurry-like electrode mixture (electrode mixture slurry) containing a vinylidene fluoride copolymer, a lithium metal oxide, and a solvent is applied to the surface of the current collector 11. It can be obtained by going through a step of forming a coating film on the surface of the current collector 11 and a step of applying a heat treatment to the coating film.

As a method for applying the electrode mixture slurry, a known method can be used, and examples thereof include a bar coater, a die coater, and a comma coater.

The drying temperature for drying the electrode mixture slurry applied to the upper and lower surfaces of the current collector 11 can be 50 to 170 ° C, preferably 50 to 150 ° C.

In the present embodiment, the method of forming the electrode mixture layer by applying the electrode mixture slurry to the upper and lower surfaces of the current collector 11 has been described, but the method of manufacturing the electrode structure of the present embodiment is based on this. The electrode mixture may be applied to at least one surface of the current collector without limitation.

[Secondary battery]
The secondary battery of the present embodiment is a non-aqueous electrolyte secondary battery including the electrode structure of the present embodiment. The secondary battery of the present embodiment will be described with reference to FIG. FIG. 2 is an exploded perspective view of the secondary battery according to the present embodiment.

As shown in FIG. 2, the secondary battery 100 has a structure in which a power generation element in which a separator 3 is arranged and laminated between a positive electrode 1 and a negative electrode 2 and wound in a spiral shape is housed in a metal casing 5. .. The positive electrode 1 corresponds to the electrode structure 10 in FIG.

As the separator 3, a known material such as a porous membrane of a polymer substance such as polypropylene or polyethylene may be used. In addition, as the member used in the secondary battery 100, those usually used in this field can be appropriately used.

The secondary battery 100 is a cylindrical battery, but of course, the secondary battery 100 in the present invention is not limited to this, and is, for example, a secondary battery having another shape such as a coin shape, a square shape, or a paper shape. There may be.

〔summary〕
As described above, the electrode mixture of the present invention contains an electrode active material provided on the current collector and a binder composition for binding the electrode active material to the current collector, and is a binder composition. Contains a copolymer of vinylidene fluoride and a monomer represented by the above formula (1), and the electrode active material is the following formula (2).
Li _{1 + x} MO ₂ ... (2)
(X is a number satisfying −0.15 <X ≦ 0.15. M is a group of two or more elements containing Ni or Ni, and is a group of two or more elements containing Ni. Contains 55 mol% or more of Ni.)
It contains the lithium metal oxide represented by, and the pH of the water when the lithium metal oxide is extracted with water is higher than 11.3.

Further, in the electrode mixture of the present invention, the amount of chlorine in the binder composition is preferably 1000 ppm or less.

Further, in the electrode mixture of the present invention, it is preferable that the constituent unit derived from the monomer represented by the above formula (1) in the above copolymer is 0.40 mol% or more.

Further, in one aspect of the electrode mixture of the present invention, the binder composition contains a vinylidene fluoride-based polymer different from the copolymer.

Further, the electrode mixture of the present invention preferably contains a solvent.

The method for producing an electrode mixture according to the present invention comprises a step of kneading a copolymer of vinylidene fluoride, a monomer represented by the above formula (1), and an electrode active material, and the above electrode. The active material contains a lithium metal oxide represented by the above formula (2), and the lithium metal oxide has a pH higher than 11.3 when extracted with water.

One aspect of the electrode structure according to the present invention includes a current collector and an electrode mixture layer provided on the current collector, and the electrode mixture layer uses the above-mentioned electrode mixture. It is a layer formed by.

Another aspect of the electrode structure according to the present invention includes a current collector and an electrode mixture layer provided on the current collector, and the electrode mixture layer is a binder composition and an electrode activity. It is a layer containing a substance, the binder composition contains a copolymer of vinylidene fluoride and a monomer represented by the above formula (1), and the above electrode active material is the above formula ( It contains the lithium metal oxide represented by 2), and the pH of the water when the electrode mixture layer is extracted with water is higher than 11.3.

The method for producing an electrode structure according to the present invention includes a step of forming a coating film on the surface of the current collector by applying the above-mentioned electrode mixture on the surface of the current collector and drying it, and heat treatment on the above-mentioned coating film. Includes the process of applying.

The secondary battery according to the present invention includes the above-mentioned electrode structure.

Examples are shown below, and embodiments of the present invention will be described in more detail. Of course, the present invention is not limited to the following examples, and it goes without saying that various aspects are possible for details. Further, the present invention is not limited to the above-described embodiment, and various modifications can be made within the scope of the claims, and the present invention also relates to an embodiment obtained by appropriately combining the disclosed technical means. It is included in the technical scope of the invention. In addition, all of the documents described in this specification are incorporated by reference.

As shown below, an electrode mixture and an electrode structure were prepared using various binder compositions, and a confirmation test was conducted to confirm changes in viscosity and solid content concentration of the electrode mixture slurry. Prior to the description of specific examples, each method of measuring the pH of the lithium metal oxide, calculating the slurry viscosity, and the solid content concentration change test will be described.

(PH measurement of lithium metal oxide)
The pH of the lithium metal oxide as the electrode active material was the pH of the water when the lithium metal oxide was extracted with water at room temperature (25 ° C.). The lithium metal oxide was extracted into water by the extraction method specified in JIS K 5101-16.2. Specifically, lithium metal oxide is put into ultrapure water 50 times the weight of lithium metal oxide, stirred with a magnetic stirrer at a rotation speed of 600 rpm for 10 minutes, and the solution is mixed with Horiba Co., Ltd. The pH was measured using a pH meter MODEL: F-21 manufactured by Mfg. Co., Ltd.

(Calculation of intrinsic viscosity η _i )
In order to calculate the intrinsic viscosity η _i , a polymer solution was prepared by dissolving 80 mg of the polymer in 20 ml of N, N-dimethylformamide. The viscosity η of this polymer solution was measured using a Ubbelohde viscometer in a constant temperature bath at 30 ° C. Then, the intrinsic viscosity η _i was obtained by the following formula using the viscosity η.

η _i = (1 / C) · ln (η / η ₀ )
In the above formula, η is the viscosity of the polymer solution, η ₀ is the viscosity of the solvent N, N-dimethylformamide, and C is 0.4 g / dl.

(Measurement of slurry viscosity)
The slurry viscosity of the electrode mixture was measured at 25 ° C. and a shear rate of 2s ^-1 using an E-type viscometer RE-550 MODEL: R, RC-550 manufactured by Toki Sangyo Co., Ltd. The viscosity was measured by charging the slurry into the measuring device, waiting for 60 seconds, and then rotating the rotor. Further, the value 300 seconds after the start of rotation of the rotor was taken as the initial slurry viscosity. The slurry viscosity after being left at 25 ° C. and a nitrogen atmosphere for a predetermined time (24 hours or 120 hours) was measured and used as the slurry viscosity after storage.

(Measurement of change in solid content concentration)
The prepared electrode mixture slurry was poured into a polypropylene tube (φ12 × 75 mm) to a height of 5 cm from the bottom of the tube, and stored for 24 hours in a 25 ° C. and 20% RH environment. After storage, an electrode mixture slurry having a height of 1 cm from the bottom of the tube was collected, placed in an aluminum cup and weighed, and the weight of the collected electrode mixture slurry was measured. The aluminum cup was heated at 110 ° C. for 2 hours to remove the solvent, and then weighed to measure the solid content of the collected electrode mixture slurry. The lower solid content concentration ( _NVA ) was calculated from the weight before and after drying obtained here. The ratio ( _{NVA / NV B )} of the lower solid content concentration (NV _A ) to the initial solid content concentration (NV _B ) of the charged electrode mixture slurry was calculated as an index. The larger the value of NV _A / NV _B , the easier it is for the electrode active material to sink and deposit in the lower part of the container during storage.

(Amount of constituent units of vinylidene fluoride and comonomer)
The ¹ H NMR spectrum of the polymer powder was determined under the following conditions.

Equipment: Made by Bruker. AVANCE AC 400FT NMR spectrum meter Measurement conditions Frequency: 400MHz
Measuring solvent: DMSO-d6
Measurement temperature: 25 ° C
The amount of the structural unit derived from vinylidene fluoride of the polymer and the amount of the structural unit derived from the comonomer were calculated from the ¹ H NMR spectrum. Specifically, it was calculated based on the integrated intensities of the signals mainly derived from comonomer and the signals observed at 2.24 ppm and 2.87 ppm mainly derived from vinylidene fluoride.

When a comonomer having a structure derived from acrylic acid is used as the comonomer, neutralization titration using a sodium hydroxide aqueous solution of 0.03 mol / l in the amount of the structural unit containing the structure derived from acrylic acid in the polymer is performed. Asked by. More specifically, 0.3 g of the polymer was dissolved in 9.7 g of acetone at about 80 ° C., and then 3 g of pure water was added to prepare a titration solution. Phenolphthalein was used as an indicator, and neutralization titration was performed using a 0.03 mol / l sodium hydroxide aqueous solution at room temperature.

[Example 1]
(Preparation of binder composition)
In an autoclave with a content of 2 liters, 900 g of ion-exchanged water, 0.4 g of hydroxypropylmethylcellulose, 2 g of butylperoxypivalate, 396 g of vinylidene fluoride, and 0.2 g of the initial addition amount of acrylic acid were charged and heated to 50 ° C. Heated. A 1 wt% acrylic acid aqueous solution containing acrylic acid was continuously supplied to the reaction vessel under the condition that the pressure was kept constant during the polymerization. The obtained polymer slurry was dehydrated and dried to obtain a vinylidene fluoride copolymer (VDF / AA). Acrylic acid was added in a total amount of 4 g, including the amount initially added.

(Preparation of electrode mixture)
Carbon black (SP: SuperP® manufactured by Timcal Japan, average particle size: 40 nm, specific surface area: 60 m ² / g) was added to NCA811 as an electrode active material as a conductive auxiliary agent, and powder mixing was performed. On the other hand, the vinylidene fluoride copolymer (VDF / AA) was dissolved in N-methyl-2pyrrolidone (hereinafter, NMP) to prepare a vinylidene fluoride solution having a concentration of 5% by mass. To the mixture of NCA811 and carbon black, the vinylidene fluoride solution was added in two portions and kneaded. Specifically, the vinylidene fluoride solution was prepared so that the solid content concentration was 84.2% by weight in the measurement of the solid content concentration change, and the solid content concentration was 81.5% by weight in the measurement of the viscosity change of the slurry. It was added and the primary kneading was carried out at 2000 rpm for 2 minutes. Next, the remaining vinylidene fluoride solution is added so that the solid content concentration is 72.0% by weight in the measurement of the solid content concentration change, and the solid content concentration is 75% by weight in the viscosity change measurement of the slurry. Then, the electrode mixture was obtained by performing secondary kneading at 2000 rpm for 3 minutes. The weight ratios of the electrode active material, carbon black, and vinylidene fluoride copolymer in the obtained electrode mixture are in this order in the measurement of solid content concentration change, 100: 2: 1, and this in the measurement of slurry viscosity change. In order, it is 100: 2: 2. The composition of the electrode mixture is shown in Table 1.

(Preparation of electrode structure)
The obtained electrode mixture was applied on an aluminum foil having a thickness of 15 μm with a bar coater, and this was heated and dried at 110 ° C. for 30 minutes and then at 130 ° C. for 2 hours to determine the amount of the electrode mixture in a dry state. An electrode structure of about 200 g / m ² was prepared.

(Measurement of change in slurry viscosity and change in solid content concentration)
With respect to the obtained electrode mixture, changes in slurry viscosity and solid content concentration were measured. The results are shown in Table 2.

[Example 2]
Vinylidene fluoride copolymer (VDF / AA), vinylidene fluoride copolymer (VDF / AA) which is a copolymer of vinylidene fluoride and acrylic acid, vinylidene fluoride and acryloyloxypropylsuccinic acid An electrode mixture was prepared in the same manner as in Example 1 except that the blend was changed to a blend with vinylidene fluoride copolymer (VDF / APS), which is a copolymer of the above, to prepare an electrode structure. The weight ratio of the vinylidene fluoride copolymer (VDF / AA) to the vinylidene fluoride copolymer (VDF / APS) is 5: 5.

As the vinylidene fluoride copolymer (VDF / AA) in this example, the same one as the vinylidene fluoride copolymer (VDF / AA) in Example 1 was used.

The vinylidene fluoride copolymer (VDF / APS) was prepared as follows. In an autoclave with a content of 2 liters, 1096 g of ion-exchanged water, 0.2 g of Metrose 90SH-100 (manufactured by Shin-Etsu Chemical Co., Ltd.), 2.2 g of 50 wt% diisopropylperoxydicarbonate-fluorocarbon 225 kb solution, 426 g of vinylidene fluoride, and Each amount of 0.2 g of the initial addition amount of acryloyloxypropyl succinic acid was charged, and the temperature was raised to 26 ° C. in 1 hour. Then, the temperature was maintained at 26 ° C., and a 6 wt% aqueous solution of acryloyloxypropylsuccinic acid was gradually added at a rate of 0.5 g / min. The obtained polymer slurry was dehydrated and dried to obtain a vinylidene fluoride copolymer (VDF / APS). A total amount of 4 g of acryloyloxypropylsuccinic acid was added, including the amount initially added.

With respect to the obtained electrode mixture, changes in slurry viscosity and solid content concentration were measured. The results are shown in Table 2.

[Example 3]
Examples except that the vinylidene fluoride copolymer (VDF / AA) was changed to a blend of the vinylidene fluoride copolymer (VDF / AA) of Example 1 and the vinylidene fluoride homopolymer (PVDF). An electrode mixture was prepared in the same manner as in 1, and an electrode structure was prepared. As the vinylidene fluoride homopolymer (PVDF), KF # 7200 manufactured by Kureha Corporation was used. The weight ratio of the vinylidene fluoride copolymer (VDF / AA) to the vinylidene fluoride homopolymer (PVDF) is 5: 5.

With respect to the obtained electrode mixture, changes in slurry viscosity and solid content concentration were measured. The results are shown in Table 2.

[Comparative Example 1]
An electrode mixture was prepared in the same manner as in Example 1 except that the vinylidene fluoride copolymer (VDF / AA) was changed to the vinylidene fluoride copolymer (VDF / APS) of Example 2, and the electrode structure was prepared. The body was made.

With respect to the obtained electrode mixture, changes in slurry viscosity and solid content concentration were measured. The results are shown in Table 2.

[Comparative Example 2]
The vinylidene fluoride copolymer (VDF / AA) was changed to the vinylidene fluoride copolymer (VDF / APS) of Example 2, and the electrode active material was Li _1.00 Ni _0.52 Co _0.20 Mn ₀ . An electrode mixture was prepared in the same manner as in Example 1 except that it was changed to _.30 O ₂ (NCM523), and an electrode structure was prepared.

The slurry viscosity of the obtained electrode mixture was measured. The results are shown in Table 2.

[Comparative Example 3]
The vinylidene fluoride copolymer (VDF / AA) is the vinylidene fluoride copolymer (VDF / APS) of Example 2, and the vinylidene fluoride copolymer which is a copolymer of vinylidene fluoride and chlorotrifluoroethylene. An electrode mixture was prepared in the same manner as in Example 1 except that the blend was changed to a blend (VDF / CTFE), and an electrode structure was prepared. The weight ratio of the vinylidene fluoride copolymer (VDF / APS) to the vinylidene fluoride copolymer (VDF / CTFE) is 5: 5.

The fluorovinylidene copolymer (VDF / CTFE) was prepared as follows. 1040 g of ion-exchanged water, 0.4 g of methyl cellulose, 1.6 g of diisopropyl peroxydicarbonate, 2 g of ethyl acetate, 372 g of vinylidene fluoride, and 28 g of chlorotrifluoroethylene are charged in an autoclave having a content of 2 liters and suspended at 28 ° C. Polymerization was performed. After completion of the polymerization, the polymer slurry is dehydrated, the dehydrated polymer slurry is washed with water, the polymer slurry is dehydrated again, and then dried at 80 ° C. for 20 hours to obtain a vinylidene fluoride copolymer (VDF / CTFE). rice field.

The slurry viscosity of the obtained electrode mixture was measured. The results are shown in Table 2.

As shown in Table 2, in the electrode mixture using vinylidene fluoride copolymer (VDF / AA) in the binder composition part, the increase in the viscosity of the electrode mixture slurry is suppressed even after storage for 5 days. Was being done. On the other hand, in the electrode mixture using vinylidene fluoride copolymer (VDF / APS) in the binder composition part, the increase in the viscosity of the electrode mixture slurry was suppressed if it was stored for a short period (1 day). , An increase in slurry viscosity was observed when stored for a longer period (5 days).

In addition, when the same electrode active material (NCA811) was used, it was observed that the change in solid content concentration after storage for a certain period of time was suppressed in the electrode mixture using vinylidene fluoride copolymer (VDF / AA). Was done.

The present invention can be used for a lithium ion secondary battery.

1 Positive electrode 2 Negative electrode 3 Separator 5 Metal casing 10 Electrode structure 11 Current collectors 12a, 12b Electrode mixture layer

Claims (9)

It contains an electrode active material provided on the current collector and a binder composition for binding the electrode active material to the current collector.
The binder composition contains vinylidene fluoride and the following formula (1).

(In the formula, R ¹ , R ² and R ³ are independently hydrogen atom, chlorine atom, fluorine atom, alkyl group having 1 to 6 carbon atoms or fluorine-substituted alkyl group having 1 to 6 carbon atoms, respectively.)
Contains a copolymer with the monomer represented by
The amount of chlorine in the binder composition is 1000 ppm or less, and the amount of chlorine is 1000 ppm or less.
The electrode active material has the following formula (2).
Li _{1 + x} MO ₂ ... (2)
(X is a number satisfying −0.15 <X ≦ 0.15. M is a group of two or more elements containing Ni or Ni, and is a group of two or more elements containing Ni. Contains 55 mol% or more of Ni.)
Contains lithium metal oxides represented by
An electrode mixture characterized in that the pH of the water when the lithium metal oxide is extracted with water is higher than 11.3 (excluding the electrode mixture containing a boric acid ester) . The electrode mixture according to claim 1, wherein the constituent unit derived from the monomer represented by the above formula (1) in the above copolymer is 0.40 mol% or more. The electrode mixture according to claim 1 or 2, wherein the binder composition contains a vinylidene fluoride-based polymer different from the copolymer. The electrode mixture according to any one of claims 1 to 3, which contains a solvent. The method for producing an electrode mixture according to any one of claims 1 to 4.
Vinylidene fluoride and the following formula (1)

(In the formula, R ¹ , R ² and R ³ are independently hydrogen atom, chlorine atom, fluorine atom, alkyl group having 1 to 6 carbon atoms or fluorine-substituted alkyl group having 1 to 6 carbon atoms, respectively.)
Including the step of kneading the copolymer with the monomer represented by, and the electrode active material.
The electrode active material has the following formula (2).
Li _{1 + x} MO ₂ ... (2)
(X is a number satisfying −0.15 <X ≦ 0.15. M is a group of two or more elements containing Ni or Ni, and is a group of two or more elements containing Ni. Contains 55 mol% or more of Ni.)
Contains lithium metal oxides represented by
The lithium metal oxide is a method for producing an electrode mixture, characterized in that the pH of the water when extracted with water is higher than 11.3. It is provided with a current collector and an electrode mixture layer provided on the current collector.
The electrode mixture layer is an electrode structure which is a layer formed by using the electrode mixture according to any one of claims 1 to 4. It is provided with a current collector and an electrode mixture layer provided on the current collector.
The electrode mixture layer is a layer containing a binder composition and an electrode active material (however, excluding an electrode mixture layer containing a boric acid ester) .
The binder composition contains vinylidene fluoride and the following formula (1).

(In the formula, R ¹ , R ² and R ³ are independently hydrogen atom, chlorine atom, fluorine atom, alkyl group having 1 to 6 carbon atoms or fluorine-substituted alkyl group having 1 to 6 carbon atoms, respectively.)
Contains a copolymer with a monomer represented by
The amount of chlorine in the binder composition is 1000 ppm or less, and the amount of chlorine is 1000 ppm or less.
The electrode active material has the following formula (2).
Li _{1 + x} MO ₂ ... (2)
(X is a number satisfying −0.15 <X ≦ 0.15. M is a group of two or more elements containing Ni or Ni, and is a group of two or more elements containing Ni. Contains 55 mol% or more of Ni.)
Contains lithium metal oxides represented by
An electrode structure characterized in that the pH of the water when the electrode mixture layer is extracted with water is higher than 11.3. A step of forming a coating film on the surface of the current collector by applying the electrode mixture according to claim 4 to the surface of the current collector and drying the mixture.
A method for manufacturing an electrode structure, which comprises a step of applying a heat treatment to the coating film. A secondary battery comprising the electrode structure according to claim 6 or 7.

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