WO2019220676A1

WO2019220676A1 - Electrode mixture, electrode mixture production method, electrode structure, electrode structure production method, and secondary battery

Info

Publication number: WO2019220676A1
Application number: PCT/JP2018/047007
Authority: WO
Inventors: 民人五十嵐; 健太青木; 正太小林; 佐藤　宏
Original assignee: 株式会社クレハ
Priority date: 2018-05-15
Filing date: 2018-12-20
Publication date: 2019-11-21
Also published as: CN112005406A; JP7017468B2; CN112005406B; KR102561871B1; KR20210002633A; JP2019200894A

Abstract

Provided is an electrode mixture that is capable of minimizing gelling thereof in a slurry form. The electrode mixture according to the present invention comprises an electrode active material and a binder composition, wherein the binder composition comprises a copolymer between vinylidene fluoride and a monomer represented by formula (1), the electrode active material comprises a lithium metal oxide represented by Li1+xMO2, and, when water is used to extract the lithium metal oxide, the pH of said water is 11.3 or higher.

Description

Electrode mixture, method for producing electrode mixture, electrode structure, method for producing electrode structure, and secondary battery

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 advanced functions of small portable devices have progressed, and power sources used for these devices are required to be small and light (high energy density). As a battery having a high energy density, a nonaqueous electrolyte secondary battery represented by a lithium ion secondary battery or the like is widely used.

The electrode of the lithium ion secondary battery can be obtained, for example, as follows. First, a binder (binder) is mixed with an electrode active material and a powdered electrode material such as a conductive auxiliary agent added as necessary, and dissolved or dispersed in an appropriate solvent to form a slurry electrode mixture (hereinafter, (Also referred to as electrode mixture slurry). Subsequently, an electrode of a lithium ion secondary battery can be obtained by applying the obtained electrode mixture slurry on a current collector and evaporating the solvent to form a structure retained as an electrode mixture layer. .

As a technique for increasing the energy density in a lithium ion secondary battery, a technique for increasing the charge / discharge capacity of the positive electrode active material itself in the electrode is used. As a technique for increasing the charge / discharge capacity of the positive electrode active material, for example, it is known to use a nickel-containing compound 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 is increased, there is a problem that the electrode mixture slurry is easily gelled.

Therefore, an electrode mixture for the purpose of suppressing gelation of the electrode mixture slurry has been developed so far. As an example of such an electrode mixture, there is 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. Known (Patent Document 1). Also proposed is a lithium-containing composite oxide with a specific composition containing nickel as the positive electrode active material, and a polyvinylidene fluoride and vinylidene fluoride-chlorotrifluoroethylene copolymer as the positive electrode binder. (For example, Patent Document 2).

International Publication No. 2010/074041 Japanese Published Patent Gazette, Japanese Patent Laid-Open No. 2014-7088

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

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

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

(Wherein R ¹ , R ² and R ³ are each independently a hydrogen atom, a chlorine atom, a fluorine atom, an alkyl group having 1 to 6 carbon atoms or a fluorine-substituted alkyl group having 1 to 6 carbon atoms.)
Containing 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 including Ni or Ni and two or more elements including Ni. Includes 55 mol% or more of Ni.)
The pH of the water when the lithium metal oxide is extracted with water is greater than 11.3.

In addition, in order to solve the above problems, the method for producing an electrode mixture according to the present invention includes vinylidene fluoride and the following formula (1):

(Wherein R ¹ , R ² and R ³ are each independently a hydrogen atom, a chlorine atom, a fluorine atom, an alkyl group having 1 to 6 carbon atoms or a fluorine-substituted alkyl group having 1 to 6 carbon atoms.)
A step of kneading a copolymer with a monomer represented by: and an 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 including Ni or Ni and two or more elements including Ni. Includes 55 mol% or more of Ni.)
The lithium metal oxide has a configuration in which the pH of the water when extracted with water is greater than 11.3.

Moreover, in order to solve the above problems, an aspect of the electrode structure according to the present invention includes a current collector and an electrode mixture layer provided on the current collector. The layer has a configuration that is a layer formed 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-described problems.
The electrode mixture layer is a layer containing a binder composition and an electrode active material, and the binder composition includes vinylidene fluoride and the following formula (1):

(Wherein R ¹ , R ² and R ³ are each independently a hydrogen atom, a chlorine atom, a fluorine atom, an alkyl group having 1 to 6 carbon atoms or a fluorine-substituted alkyl group having 1 to 6 carbon atoms.)
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 including Ni or Ni and two or more elements including Ni. Includes 55 mol% or more of Ni.)
And the pH of the water when the electrode mixture layer is extracted with water is greater than 11.3.

The electrode mixture according to the present invention can 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. 1 is an exploded perspective view of a secondary battery according to an embodiment of the present invention.

The electrode mixture according to the present invention and an embodiment thereof will be described. In the present specification, “to” is used to mean that the numerical values described before and after it are included as a lower limit value and an upper limit value.

[Electrode mixture]
The electrode mixture according to the present embodiment comprises an electrode active material provided on a 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. The electrode active material includes 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 Ni or two or more element groups including Ni, and two or more element groups including Ni. In this case, Ni contains 55 mol% or more.) 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 an electrode active material onto a current collector. The binder composition contains a vinylidene fluoride copolymer that 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 each independently a hydrogen atom, a chlorine atom, a fluorine atom, an alkyl group having 1 to 6 carbon atoms or a fluorine-substituted alkyl group having 1 to 6 carbon atoms. 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 desirably a substituent having a small steric hindrance, preferably hydrogen or an alkyl group having 1 to 3 carbon atoms, and preferably hydrogen or a methyl group. More preferred.

In the vinylidene fluoride copolymer in the present embodiment, the structural unit derived from the monomer represented by the formula (1) is preferably 0.40 to 10.00 mol%, and 0.50 to 7.00 mol. % Is more preferable, and 0.60 to 4.00 mol% is particularly preferable. In addition, the structural unit derived from vinylidene fluoride is preferably 90.0 to 99.6 mol%, more preferably 93.0 to 99.5 mol%, and 96.0 to 99.5 mol%. Particularly preferred. When the structural 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 structural unit derived from the monomer represented by the formula (1). The ratio does not become too small, and the effect of suppressing the gelation of the electrode mixture slurry can be obtained. Moreover, 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. Can be prevented. In particular, by using the vinylidene fluoride copolymer of the present embodiment, it is possible to obtain an effect of suppressing gelation of the electrode mixture slurry even when stored for a longer time.

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

The vinylidene fluoride copolymer in the present embodiment may have components of monomers other than vinylidene fluoride and the monomer represented by the formula (1). Examples thereof include a fluorine monomer copolymerizable with vinylidene fluoride or a hydrocarbon monomer such as ethylene and propylene, or a monomer copolymerizable with the formula (1). Examples of the fluorine-based monomer copolymerizable with vinylidene fluoride include perfluoroalkyl vinyl ethers typified by vinyl fluoride, trifluoroethylene, tetrafluoroethylene, chlorotrifluoroethylene, hexafluoropropylene, and perfluoromethyl vinyl ether. be able to. Examples of the monomer copolymerizable with the formula (1) include (meth) acrylic acid and alkyl (meth) acrylates represented by methyl (meth) acrylate. In addition, another monomer may be used individually by 1 type and may use 2 or more types.

When the vinylidene fluoride copolymer has the other monomer described above, it preferably has another monomer unit of 0.01 to 10 mol%.

The vinylidene fluoride copolymer in the present embodiment can be obtained by polymerizing vinylidene fluoride and a monomer represented by the formula (1) by a conventionally known method. Although it does not specifically limit about the polymerization method, For example, methods, such as suspension polymerization, emulsion polymerization, and solution polymerization, can be mentioned. Among these, the polymerization method is preferably aqueous suspension polymerization or emulsion polymerization in view of ease of post-treatment. The vinylidene fluoride and the monomer represented by the formula (1) used for the polymerization 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 determined by measurement by GPC (gel permeation chromatography) in the range of 50,000 to 1,500,000.

The inherent viscosity η _i of the vinylidene fluoride copolymer in the present embodiment is preferably 0.5 dl / g to 5.0 dl / g, more preferably 1.0 dl / g to 4.5 dl / g. Preferably, it is 1.5 dl / g to 4.0 dl / g. If the inherent viscosity is within the above range, the deterioration of productivity due to a decrease in the electrode mixture slurry solid content is prevented, and the electrode can be easily produced without causing unevenness of the electrode thickness when the electrode mixture is applied. It is preferable in that it can be performed. The inherent viscosity η _i can be obtained from the following equation by dissolving 80 mg of the polymer in 20 ml of N, N-dimethylformamide and using an Ubbelohde viscometer in a constant temperature bath at 30 ° C.

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 N, N-dimethylformamide as a solvent, and C is 0.4 g / dl.

The binder composition according to the present embodiment may contain another vinylidene fluoride polymer as long as the required effect is not impaired. Other vinylidene fluoride-based polymers that can be included in the binder composition include vinylidene fluoride homopolymers, and fluoropolymers obtained by polymerizing vinylidene fluoride and other monomers copolymerizable with vinylidene fluoride. And vinylidene chloride copolymer. In addition, the other monomer here is a monomer not included in the monomer represented by the above formula (1). Examples of such other monomers include fluorine monomers copolymerizable with the above-mentioned vinylidene fluoride, hydrocarbon monomers such as ethylene and propylene, and alkyl (meth) acrylate compounds. It is done. Moreover, as another monomer, a polar group containing compound may be sufficient. As a polar group containing compound, the compound containing a carboxyl group, an epoxy group, or a sulfonic acid group etc. is mentioned, for example, It is preferable that it is a compound containing a carboxyl group especially. Specific examples include 2-carboxyethyl acrylate, 2-carboxyethyl methacrylate, acryloyloxyethyl acrylic acid, and acryloyloxypropyl succinic acid.

When other vinylidene fluoride polymer is included, the proportion of the vinylidene fluoride copolymer containing the structural unit derived from the monomer represented by 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 whole polymer contained in the binder composition is preferably 0.10 mol% or more, and 0.20 mol% or more. More preferably, it is more preferably 0.30 mol% or more. Content of the vinylidene fluoride copolymer containing the structural unit derived from the monomer represented by Formula (1) in the binder composition, and the single amount represented by Formula (1) in the binder composition By making content of the structural unit derived from a body into said range, the effect which suppresses gelatinization of an electrode mixture slurry can be acquired suitably.

In addition, the binder composition according to the present embodiment has been developed so that gelation of the electrode mixture slurry is suppressed even when a polymer that does not contain chlorine atoms is used in consideration of environmental load. It is. Therefore, it is desirable that the amount of chlorine in the binder composition in this embodiment is small, specifically, it is preferably 1000 ppm or less, more preferably 500 ppm or less, and particularly preferably 300 ppm.

The amount of chlorine in the binder composition is in accordance with JIS K 7229. The binder composition is burned in an oxygen atmosphere in the flask, and the generated combustion gas is absorbed into the absorption liquid. It can be obtained by calculating the chlorine concentration by the method.

(Electrode active material)
The electrode active material in the present embodiment includes 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 Ni or two or more element groups including Ni. When M is a group of two or more elements including Ni, examples of elements other than Ni included in M include, for example, Co, Mn, Ti, Cr, Fe, Cu, Zn, Al, Ge, Sn, Examples thereof include Mg, Ag, Ta, Nb, B, P, Zr, Ca, Sr and Ba. Of these, Co, Mn and Al are preferable. In the case where M is a group of two or more elements including Ni, the element other than Ni included in M may be only one of these, or two or more. 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 further contains Co or the like in addition to Ni in that stable cycle characteristics are exhibited by suppressing changes in the crystal structure during the charge / discharge process.

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

As a particularly preferable lithium metal oxide in the present embodiment, for example, the following formula (3)
LiNi _Y1 N1 _Y2 O ₂ (3)
(Wherein N1 represents Co or Mn, and 0.55 ≦ Y1 <1, 0 <Y2 <0.55), or a binary lithium metal oxide represented by the following formula (4)
LiNi _Y1 Co _Y2 N2 _Y3 O ₂ (4)
(Wherein 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 an electrode active material in this embodiment because it has a high charge 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 .

Further, the composition of the ternary lithium metal oxide in the present embodiment is not particularly limited, and for example, 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). .

Furthermore, the electrode active material in the present embodiment may include a plurality of different types of lithium metal oxides. For example, the electrode active material may include 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} and may contain.

Furthermore, the lithium metal oxide in the present embodiment is prepared by adding 49 g of ultrapure water to 1 g of lithium metal oxide, stirring for 10 minutes, and then measuring the pH of the water to 11.3. Is more than The upper limit value of the pH of the water is not particularly limited. Generally, an alkaline substance adheres to the electrode active material added to the electrode mixture, and when the amount increases, the resulting electrode mixture slurry tends to gel. And the more the nickel content in the electrode active material, the more alkaline material that adheres. That is, the pH when extracted with water increases. Therefore, if a lithium metal oxide having a high nickel content is used as an electrode active material in order to increase the discharge capacity, the electrode mixture slurry is likely 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 this embodiment, the electrode active material may contain, for example, impurities and additives in addition to the lithium metal oxide represented by the formula (2). Also, 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, dimethyl sulfoxide, N, N-dimethyl sulfoxide, hexamethylphosphoamide, Examples include dioxane, tetrahydrofuran, tetramethylurea, triethyl phosphate, trimethyl phosphate, acetone, cyclohexane, methyl ethyl ketone, and tetrahydrofuran. One or more of these solvents may be contained 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 as necessary. Examples of other components include a conductive aid and a pigment dispersant.

The conductive auxiliary agent is added for the purpose of improving the conductivity of the electrode mixture layer formed using the electrode mixture. Examples of the conductive assistant include graphites such as natural graphite (eg, scaly graphite), artificial graphite, graphite fine powder and graphite fiber, carbon blacks such as acetylene black, ketjen black, channel black and furnace black, carbon Examples include fibers and carbon materials such as carbon nano-nanotubes. In addition, conductive fibers such as metal fibers such as Ni and Al, metal powders, conductive metal oxides, and organic conductive materials are also included.

In addition, examples of the pigment dispersant include polyvinyl pyrrolidone.

In the present embodiment, the other components described above are 0 to 10 parts by weight, preferably 0 to 5 parts by weight with respect to 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, gelation of the electrode mixture slurry can be suppressed even when an electrode active material having a high nickel content is used. In particular, gelation of the electrode mixture slurry is suppressed even when stored for a relatively long time. Furthermore, according to the electrode mixture of this embodiment, it can suppress that solid content, such as an electrode active material, settles and accumulates during a storage period. By suppressing sedimentation during the storage period, it is possible to prevent the solid content concentration from changing, thereby preventing an increase in the viscosity of the electrode mixture. As a result, it is possible to prevent the handling property when the electrode structure is manufactured from being lowered.

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

The electrode mixture in the present embodiment is manufactured by using a lithium metal oxide whose pH when extracted with water is greater than 11.3 as the lithium metal oxide contained in the electrode active material. It is what is done.

(Slurry viscosity of electrode mixture)
The degree to which gelation of the electrode mixture slurry can be suppressed when the electrode mixture of the present invention is used can be determined by the slurry viscosity of the electrode mixture. In this specification, “gelation” 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 become a uniform paste, and a solid is present, so that the slurry viscosity cannot be measured. In addition, a solid substance refers to the thing which passes a slurry through a mesh with an opening of 2.36 mm, and is left on the mesh after being left for 1 hour. Further, the mixer is not particularly limited, and for example, Shintaro Awatori Nertaro ARE310 (autorotation 800 rpm, revolution 2000 rpm) manufactured by Shinky Co., Ltd. can be used.

(Electrode structure)
Subsequently, an embodiment of an electrode structure formed using the electrode mixture of the present embodiment will be described with reference to FIG. 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 includes a current collector 11 and

electrode mixture layers

12a and 12b.

The current collector 11 is a base material for the electrode structure 10 and is a terminal for taking out 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 a foil or a net. In the present embodiment, the current collector 11 is preferably an aluminum foil.

The thickness of the current collector 11 is preferably 5 to 100 μm, and more 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 μm to 250 μm, and still more preferably 20 μm to 150 μm.

The electrode mixture layer in this embodiment is formed using the electrode mixture described above. Therefore, when the electrode mixture layer in this embodiment is extracted at room temperature (25 ° C.) by the extraction method specified in JIS K 5101-16-2, the pH of the water exceeds 11.3. ing. Specifically, the pH is measured by the same method as the above-described method for measuring the pH of a lithium metal oxide, except that the electrode mixture layer is peeled off from the current collector foil and used as a sample. It is.

In the electrode structure 10, the electrode mixture layers 12 a and 12 b are formed on the upper and lower surfaces of the current collector 11 as shown in FIG. 1, but the present invention is not limited to this. What has the electrode mixture layer formed in any one surface, ie, the electrode structure in which any one of the

electrode mixture layers

12a and 12b was formed may be sufficient.

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

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 and dried. By making it, it can obtain by passing through the process of forming a coating film in the collector 11 surface, and the process of heat-processing a coating film.

As a method for applying the electrode mixture slurry, a known method can be used, and a method using a bar coater, a die coater, a comma coater (registered trademark), or the like can be given.

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 addition, although this embodiment demonstrated the method of forming an electrode mixture layer by apply | coating an electrode mixture slurry to the upper and lower surfaces of the electrical power collector 11, the manufacturing method of the electrode structure of this embodiment is to this. Without limitation, the electrode mixture may be applied to at least one surface of the current collector.

[Secondary battery]
The secondary battery of the present embodiment is a nonaqueous electrolyte secondary battery including the electrode structure of the present embodiment. The secondary battery of this 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 generating element in which a separator 3 is disposed 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 film of a polymer material such as polypropylene and polyethylene may be used. In addition, as the members used in the secondary battery 100, those normally 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 may be 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 a current collector and a binder composition for binding the electrode active material to the current collector. Contains a copolymer of vinylidene fluoride and the monomer represented by the above formula (1), and 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 including Ni or Ni and two or more elements including Ni. Includes 55 mol% or more of Ni.)
The pH of the water when the lithium metal oxide is extracted with water is greater than 11.3.

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

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

Further, in one aspect of the electrode mixture of the present invention, the binder composition includes a vinylidene fluoride 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 includes a step of kneading a copolymer of vinylidene fluoride, a monomer represented by the above formula (1), and an electrode active material, The active material contains a lithium metal oxide represented by the above formula (2), and the pH of the lithium metal oxide when extracted with water is greater than 11.3.

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 electrode mixture described above. It is a layer formed.

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 includes a binder composition and an electrode active layer. The binder composition contains a copolymer of vinylidene fluoride and a monomer represented by the above formula (1), and the electrode active material has the above formula ( The lithium metal oxide represented by 2) is included, and the pH of the water when the electrode mixture layer is extracted with water is greater than 11.3.

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

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

Examples will be shown below, and the 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 in detail. Further, the present invention is not limited to the above-described embodiments, and various modifications can be made within the scope shown in the claims, and the present invention is also applied to the embodiments obtained by appropriately combining the disclosed technical means. It is included in the technical scope of the invention. Moreover, all the literatures described in this specification are used as reference.

As shown below, an electrode mixture and an electrode structure were prepared using various binder compositions, and a confirmation test of viscosity change and solid content concentration change of the electrode mixture slurry was performed. Prior to the description of specific examples, each method of measurement of pH of lithium metal oxide, calculation of slurry viscosity, and 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 water when the lithium metal oxide was extracted with water at room temperature (25 ° C.). The extraction of lithium metal oxide into water was performed by the extraction method defined in JIS K 5101-16-2. Specifically, the lithium metal oxide is put into ultrapure water 50 times the weight of the lithium metal oxide, and stirred with a magnetic stirrer at a rotation speed of 600 rpm for 10 minutes. The pH was measured using a pH meter MODEL: F-21 manufactured by Seisakusho.

(Calculation of inherent viscosity η _i )
In order to calculate the inherent 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. And inherent viscosity (eta) _i was calculated | required by the following formula using the said viscosity (eta).

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 2 s ⁻¹ using an E-type viscometer RE-550 MODEL: R, RC-550 manufactured by Toki Sangyo Co., Ltd. The viscosity was measured by waiting 60 seconds after the slurry was charged into the measuring apparatus and then rotating the rotor. The value after 300 seconds from the start of rotation of the rotor was taken as the initial slurry viscosity. The slurry viscosity after being allowed to stand for a predetermined time (24 hours or 120 hours) in a nitrogen atmosphere at 25 ° C. was measured and used as the slurry viscosity after storage.

(Measurement of solid content concentration change)
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 in an environment of 25 ° C. and 20% RH for 24 hours. After storage, an electrode mixture slurry having a height of 1 cm from the bottom of the tube was collected, weighed in an aluminum cup, 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. It was calculated lower solids concentration (NV _A) from the weight before and after drying obtained here. The ratio of the lower solid content concentration (NV _A ) to the initial solid content concentration (NV _B ) of the charged electrode mixture slurry (NV _A / NV _B ) was calculated as an index. This indicates that the larger the value of NV _A / NV _B, the easier the electrode active material sinks and accumulates in the lower part of the container during storage.

(Constitutional unit amount of vinylidene fluoride and comonomer)
The ¹ H NMR spectrum of the polymer powder was determined under the following conditions.

Apparatus: manufactured by Bruker. AVANCE AC 400FT NMR spectrum meter Measurement conditions Frequency: 400 MHz
Measuring solvent: DMSO-d6
Measurement temperature: 25 ° C
The amount of the structural unit derived from the 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 intensity of signals mainly derived from comonomer and 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 a comonomer, the amount of the structural unit containing a structure derived from acrylic acid in the polymer is neutralized with a sodium hydroxide aqueous solution of 0.03 mol / l. Determined by More specifically, a solution to be titrated was prepared by dissolving 0.3 g of a polymer in 9.7 g of acetone at about 80 ° C. and then adding 3 g of pure water. As an indicator, phenolphthalein was used, and neutralization titration was performed using a 0.03 mol / l aqueous sodium hydroxide solution at room temperature.

[Example 1]
(Preparation of binder composition)
Into an autoclave with an internal volume of 2 liters, each amount of 900 g of ion exchange water, 0.4 g of hydroxypropyl methylcellulose, 2 g of butyl peroxypivalate, 396 g of vinylidene fluoride, and 0.2 g of an initial addition amount of acrylic acid was charged to 50 ° C. Heated. A 1% by weight aqueous acrylic acid solution containing acrylic acid was continuously fed 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). A total of 4 g of acrylic acid was added, including the amount added initially.

(Preparation of electrode mixture)
Carbon black (SP: SuperP (registered trademark) 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, and powder mixing was performed. On the other hand, a vinylidene fluoride copolymer (VDF / AA) was dissolved in N-methyl-2pyrrolidone (hereinafter referred to as NMP) to prepare a 5 wt% vinylidene fluoride solution. 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. The mixture was added and primary kneading was performed at 2000 rpm for 2 minutes. Then, 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 measurement of the viscosity change of the slurry. And secondary kneading at 2000 rpm for 3 minutes to obtain an electrode mixture. The weight ratio of the electrode active material, carbon black, and vinylidene fluoride copolymer in the obtained electrode mixture was 100: 2: 1 in this order when measuring the solid content concentration change, and this ratio was measured when measuring the viscosity change of the slurry. In order, it is 100: 2: 2. Table 1 shows the composition of the electrode mixture.

(Production 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 heat-dried at 110 ° C. for 30 minutes and further at 130 ° C. for 2 hours. An electrode structure of approximately 200 g / m ² was produced.

(Measurement of slurry viscosity change and solid content concentration change)
The obtained electrode mixture was measured for slurry viscosity and solid content concentration change. The results are shown in Table 2.

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

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

A vinylidene fluoride copolymer (VDF / APS) was prepared as follows. In an autoclave having an internal volume of 2 liters, 1096 g of ion-exchanged water, 0.2 g of Metroze 90SH-100 (manufactured by Shin-Etsu Chemical Co., Ltd.), 2.2 g of a 50 wt% diisopropyl peroxydicarbonate-fluorocarbon 225 cb, 426 g of vinylidene fluoride, and Each amount of 0.2 g of initial addition amount of acryloyloxypropyl succinic acid was charged, and the temperature was raised to 26 ° C. over 1 hour. Thereafter, the temperature was maintained at 26 ° C., and a 6 wt% acryloyloxypropyl succinic acid aqueous solution 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 of 4 g of acryloyloxypropyl succinic acid was added, including the amount added initially.

The obtained electrode mixture was measured for slurry viscosity and solid content concentration change. The results are shown in Table 2.

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

[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 an electrode structure was prepared. The body was made.

[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 the material was changed to _.30 O ₂ (NCM523).

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

[Comparative Example 3]
The vinylidene fluoride copolymer (VDF / AA) was converted into the vinylidene fluoride copolymer (VDF / APS) of Example 2 and 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). The weight ratio of the vinylidene fluoride copolymer (VDF / APS) and the vinylidene fluoride copolymer (VDF / CTFE) is 5: 5.

A vinylidene fluoride copolymer (VDF / CTFE) was prepared as follows. An autoclave with an internal volume of 2 liters was charged with 1040 g of ion-exchanged water, 0.4 g of methylcellulose, 1.6 g of diisopropyl peroxydicarbonate, 2 g of ethyl acetate, g372 of vinylidene fluoride and 28 g of chlorotrifluoroethylene and suspended at 28 ° C. Polymerization was performed. After the polymerization is completed, 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). It was.

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

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 time was suppressed in the electrode mixture using vinylidene fluoride copolymer (VDF / AA). It was done.

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

DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Negative electrode 3 Separator 5 Metal casing 10 Electrode structure 11

Current collector

12a, 12b Electrode mixture layer

Claims

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 includes vinylidene fluoride and the following formula (1):

(Wherein R 1 , R 2 and R 3 are each independently a hydrogen atom, a chlorine atom, a fluorine atom, an alkyl group having 1 to 6 carbon atoms or a fluorine-substituted alkyl group having 1 to 6 carbon atoms.)
Containing 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 including Ni or Ni and two or more elements including Ni. Includes 55 mol% or more of Ni.)
A lithium metal oxide represented by
An electrode mixture, wherein the pH of the lithium metal oxide when extracted with water is greater than 11.3.
The electrode mixture according to claim 1, wherein the amount of chlorine in the binder composition is 1000 ppm or less.
The electrode mixture according to claim 1 or 2, wherein the constituent unit derived from the monomer represented by the formula (1) in the copolymer is 0.40 mol% or more.
The electrode mixture according to any one of claims 1 to 3, wherein the binder composition contains a vinylidene fluoride polymer different from the copolymer.
The electrode mixture according to any one of claims 1 to 4, comprising a solvent.
Vinylidene fluoride and the following formula (1)

(Wherein R 1 , R 2 and R 3 are each independently a hydrogen atom, a chlorine atom, a fluorine atom, an alkyl group having 1 to 6 carbon atoms or a fluorine-substituted alkyl group having 1 to 6 carbon atoms.)
A step of kneading a copolymer with a monomer represented by: and an 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 including Ni or Ni and two or more elements including Ni. Includes 55 mol% or more of Ni.)
A lithium metal oxide represented by
The method for producing an electrode mixture, wherein the lithium metal oxide has a pH higher than 11.3 when extracted with water.
A current collector, and an electrode mixture layer provided on the current collector,
6. The electrode structure according to claim 1, wherein the electrode mixture layer is a layer formed using the electrode mixture according to any one of claims 1 to 5.
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,
The binder composition includes vinylidene fluoride and the following formula (1):

(Wherein R 1 , R 2 and R 3 are each independently a hydrogen atom, a chlorine atom, a fluorine atom, an alkyl group having 1 to 6 carbon atoms or a fluorine-substituted alkyl group having 1 to 6 carbon atoms.)
Containing 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 including Ni or Ni and two or more elements including Ni. Includes 55 mol% or more of Ni.)
A lithium metal oxide represented by
An electrode structure, wherein the pH of the water when the electrode mixture layer is extracted with water is greater than 11.3.
Forming a coating film on the current collector surface by applying the electrode mixture according to claim 5 to the current collector surface and drying;
And a step of heat-treating the coating film.
A secondary battery comprising the electrode structure according to claim 7 or 8.