WO2018092675A1

WO2018092675A1 - Vinylidene fluoride copolymer, binder composition, electrode mix, electrode, and nonaqueous-electrolyte secondary battery

Info

Publication number: WO2018092675A1
Application number: PCT/JP2017/040407
Authority: WO
Inventors: 勇樹堺; 壮哉土肥; 絵美菅原
Original assignee: 株式会社クレハ
Priority date: 2016-11-15
Filing date: 2017-11-09
Publication date: 2018-05-24

Abstract

Provided is a vinylidene fluoride copolymer which has sufficient adhesiveness to current collectors and gives electrode mixes inhibited from gelling. The vinylidene fluoride copolymer according to the present invention is a copolymer of vinylidene fluoride, chlorotrifluoroethylene, and a compound represented by formula (1) and/or a compound represented by formula (2).

Description

Vinylidene fluoride copolymer, binder composition, electrode mixture, electrode, and nonaqueous electrolyte secondary battery

The present invention relates to a vinylidene fluoride copolymer, a binder composition, an electrode mixture, an electrode, and a nonaqueous electrolyte secondary battery.

In recent years, the development of electronic technology has been remarkable, and advanced functions of small portable devices are progressing. For this reason, power sources used for these are required to be smaller and lighter, that is, to have higher energy density. As batteries having a high energy density, nonaqueous electrolyte secondary batteries represented by lithium ion secondary batteries and the like are widely used.

Nonaqueous electrolyte secondary batteries are also used in hybrid vehicles combining secondary batteries and engines, and electric vehicles powered by secondary batteries, from the viewpoint of global environmental problems and energy saving. Applications are expanding.

The electrode for a non-aqueous electrolyte secondary battery has a structure having a current collector and an electrode mixture layer formed on the current collector. The electrode mixture layer is generally applied on a current collector in a slurry state in which an electrode mixture containing an electrode active material, a conductive assistant, and a binder composition is dispersed in an appropriate solvent or dispersion medium. It is formed by volatilizing the medium. As the positive electrode active material (electrode active material), lithium cobaltate has been mainly used. In recent years, lithium nickel composite oxide, lithium iron phosphate, and the like are also known as the positive electrode active material depending on the application.

When using lithium nickel composite oxide as the positive electrode active material, if polyvinylidene fluoride (PVDF) is used as the binder composition, the electrode mixture tends to thicken during storage, and in some cases gels. Have.

Therefore, several vinylidene fluoride copolymers have been developed for the purpose of suppressing the gelation of the electrode mixture (for example, Patent Document 1). Patent Document 1 discloses that a copolymer containing vinylidene fluoride and chlorotrifluoroethylene is used as the vinylidene fluoride polymer.

Japanese Patent Publication “JP 11-195419 A (published July 21, 1999)”

However, as disclosed in Patent Document 1, when preparing an electrode mixture using a vinylidene fluoride polymer and a positive electrode active material, a high nickel-based high nickel content as the positive electrode active material is used. When an electrode mixture is prepared using a positive electrode active material, gelation is suppressed, but there is a problem that adhesiveness is lowered.

The present invention has been made in view of the above-described problems of the prior art, and an object thereof is to provide a binder composition that has sufficient adhesiveness and suppresses gelation of an electrode mixture. .

In order to solve the above problems, a vinylidene fluoride copolymer according to the present invention is a copolymer of a first monomer component, a second monomer component, and a third monomer component. A vinylidene fluoride copolymer, wherein the first monomer component is vinylidene fluoride, the second monomer component is chlorotrifluoroethylene, and the third monomer. The component is at least one of a compound represented by the following formula (1) and a compound represented by the following formula (2).

(In the formula ^(1), R 1, ^{R 2} and ^{R 3} are each independently a hydrogen atom, a fluorine atom, a chlorine atom or an alkyl group having 1 to 3 carbon atoms.)

(In the formula ^(2), R 4, ^{R 5} and ^{R 6} are each independently a hydrogen atom, a fluorine atom, a chlorine atom or an alkyl group having a carbon number of 1 ~ 3, X is the main chain atoms of 2 to 10 and an atomic group having a molecular weight of 500 or less and containing at least one heteroatom selected from an oxygen atom and a nitrogen atom.)

According to the present invention, it is possible to provide a vinylidene fluoride copolymer that has sufficient adhesiveness and suppresses gelation of an electrode mixture.

It is sectional drawing of the electrode in the nonaqueous electrolyte secondary battery in this embodiment. It is a disassembled perspective view of the nonaqueous electrolyte secondary battery in this embodiment.

An embodiment of the vinylidene fluoride copolymer according to the present invention will be described in detail below.

[Vinylidene fluoride copolymer]
The vinylidene fluoride copolymer according to the present embodiment includes a vinylidene fluoride as a first monomer component, chlorotrifluoroethylene (hereinafter referred to as CTFE) as a second monomer component, 3 is a ternary copolymer of at least one of the compound represented by the following formula (1) and the compound represented by the following formula (2) (hereinafter referred to as an acrylic acid derivative) which is a monomer component of 3. .

R ¹ , R ² and R ³ in the formula (1) are each independently a hydrogen atom, a fluorine atom, a chlorine atom or an alkyl group having 1 to 3 carbon atoms. Examples of the alkyl group having 1 to 3 carbon atoms include a methyl group, an ethyl group, a propyl group, and an isopropyl group. Among these, R ¹ is preferably a hydrogen atom or a methyl group, and more preferably a hydrogen atom. R ² is preferably a hydrogen atom or a methyl group, and more preferably a hydrogen atom. R ³ is preferably a hydrogen atom, a fluorine atom, or a methyl group, more preferably a hydrogen atom or a methyl group, and even more preferably a hydrogen atom.

Although it does not specifically limit as a compound shown by Formula (1), For example, acrylic acid, methacrylic acid, tiglic acid, crotonic acid, etc. are mentioned. In this specification, acrylic acid and methacrylic acid are collectively referred to as (meth) acrylic acid.

In the formula ^{^{(2), R 4, R}} 5, and ^{R 6} are each independently a hydrogen atom, a fluorine atom, a chlorine atom or an alkyl group having 1 to 3 carbon atoms. Examples of the alkyl group having 1 to 3 carbon atoms include a methyl group, an ethyl group, a propyl group, and an isopropyl group. Among these, R ⁴ is preferably a hydrogen atom or a methyl group, and more preferably a hydrogen atom. R ⁵ is preferably a hydrogen atom or a methyl group, and more preferably a hydrogen atom. R ⁶ is preferably a hydrogen atom, a fluorine atom, or a methyl group, and more preferably a hydrogen atom.

The main chain constituting X in the compound represented by the formula (2) has 2 to 10 atoms, preferably 2 to 8 atoms, and more preferably 2 to 7. Examples of the atoms constituting the main chain include carbon atoms. The number of hydrogen atoms is not included in the number of atoms in the main chain. The number of atoms in the main chain refers to the carboxyl group described on the right side of X in the formula (2) and the group (R ₄ R ₅ C═CR ₆ —CO—) described on the left side of X. It means the number of atoms in the skeleton part of the chain connected by the smallest number of atoms. X may be branched by including a functional group as a side chain. One or more side chains may be included in X.

The molecular weight of the atomic group of X is 500 or less, preferably 300 or less, and more preferably 200 or less. The lower limit of the molecular weight in the case of an atomic group is not particularly limited, but may be 30.

X contains at least one heteroatom selected from an oxygen atom and a nitrogen atom. Moreover, the above-described atomic group only needs to include at least one heteroatom and may include a plurality of heteroatoms. From the viewpoint of copolymerization with vinylidene fluoride, the heteroatom is preferably an oxygen atom. In addition, the hetero atom may be contained in both the main chain and the side chain of the atomic group, or may be contained in only one of them.

Although it does not specifically limit as a compound shown by Formula (2), For example, carboxyethyl acrylate, succinic acid mono ((meth) acryloyloxyethyl), succinic acid mono ((meth) acryloyloxypropyl), and phthalic acid Mono ((meth) acryloyloxyethyl).

As the structural unit of the third monomer component, only a structural unit corresponding to one of the compound represented by the formula (1) and the compound represented by the formula (2) may be included, or a plurality of structural units may be included. A plurality of types of structural units corresponding to each of the types of compounds may be included.

The proportion of the vinylidene fluoride constituent unit in the vinylidene fluoride copolymer is preferably 90 mol% or more, more preferably 93 mol% or more, and even more preferably 95 mol% or more. The proportion of the constituent units of CTFE in the vinylidene fluoride copolymer is preferably 0.1 mol% or more and 5 mol% or less, more preferably 0.3 mol% or more and 4 mol% or less. More preferably, it is 0.5 mol% or more and 3 mol% or less. The proportion of the structural unit of the acrylic acid derivative in the vinylidene fluoride copolymer is preferably 0.1 mol% or more and 5 mol% or less, and preferably 0.1 mol% or more and 3 mol% or less. More preferably, it is 0.2 mol% or more and 2 mol% or less. In particular, when the proportion of the constituent units of CTFE is in the above-described range, in the binder composition containing the present copolymer, the binder composition can be prevented from expanding, and the battery performance can be prevented from deteriorating.

By using the vinylidene fluoride copolymer according to the present embodiment for the binder composition, it is possible to obtain a binder composition that can suppress gelation of the electrode mixture layer while maintaining the peel strength.

[Method for producing vinylidene fluoride copolymer]
The method for producing a vinylidene fluoride copolymer includes a polymerization step of copolymerizing vinylidene fluoride, CTFE, and an acrylic acid derivative to obtain a vinylidene fluoride copolymer.

The amount of CTFE used for the polymerization is preferably 0.1 parts by mass or more and 10 parts by mass or less, and 0.3 parts by mass or more and 7 parts by mass or less when the total amount of vinylidene fluoride is 100 parts by mass. More preferably, it is more preferably 0.5 parts by mass or more and 5 parts by mass or less. The amount of the acrylic acid derivative used for the polymerization is preferably 0.1 parts by mass or more and 5 parts by mass or less, and 0.1 parts by mass or more and 3 parts by mass when the total amount of the monomers is 100 parts by mass. The amount is more preferably at most 0.2 parts by mass, even more preferably at least 0.2 parts by mass and at most 2 parts by mass. The above monomers may be supplied to the polymerization system during the polymerization as required.

The polymerization method in the polymerization step is not particularly limited, and a conventionally known polymerization method can be used. Examples of the polymerization method include suspension polymerization, emulsion polymerization, and solution polymerization. Among them, aqueous suspension polymerization and emulsion polymerization are preferable from the viewpoint of ease of post-treatment, and aqueous suspension polymerization is particularly preferable. preferable. Further, depending on the polymerization method, a dispersion medium, a suspending agent and a polymerization initiator can be appropriately used.

The dispersion medium is not particularly limited and a conventionally known medium can be used, but water is preferably used as the dispersion medium.

The mass ratio between the total amount of monomers and the dispersion medium during copolymerization is preferably 1: 1 to 1:10, and more preferably 1: 2 to 1: 5.

In suspension polymerization using water as a dispersion medium, a suspending agent is used. There is no limitation in particular as a suspending agent, A conventionally well-known thing can be used. Examples of the suspending agent include methyl cellulose, methoxylated methyl cellulose, propoxylated methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, polyvinyl alcohol, polyethylene oxide, and gelatin.

The addition amount of the suspending agent is preferably 0.005 to 1.0 part by mass, and 0.01 to 0.5 part by mass, when the total amount of monomers used for copolymerization is 100 parts by mass. More preferably.

The polymerization initiator is not particularly limited, and conventionally known polymerization initiators can be used. Examples of the polymerization initiator include diisopropyl peroxydicarbonate, dinormalpropyl peroxydicarbonate, dinormalheptafluoropropyl peroxydicarbonate, isobutyryl peroxide, di (chlorofluoroacyl) peroxide, and di (perfluoroacyl) peroxide. Examples thereof include oxide and t-butyl peroxypivalate.

The addition amount of the polymerization initiator is preferably 0.05 to 5 parts by mass, more preferably 0.15 to 2 parts by mass, when the total amount of monomers used for copolymerization is 100 parts by mass. .

In suspension polymerization, a chain transfer agent may be used to adjust the degree of polymerization of the resulting vinylidene fluoride copolymer. Examples of the chain transfer agent include ethyl acetate, methyl acetate, diethyl carbonate, acetone, ethanol, n-propanol, acetaldehyde, propyl aldehyde, ethyl propionate, and carbon tetrachloride.

When a chain transfer agent is used, the addition amount of the chain transfer agent is preferably 0.05 to 5 parts by mass, and 0.1 to 3 parts, with the total amount of monomers used for copolymerization being 100 parts by mass. More preferably, it is part by mass.

Further, a buffer solution may be used as necessary. The buffer that can be used is not particularly limited, and conventionally known buffers can be used. Examples of the buffer include citrate buffer, phosphate buffer, citrate phosphate buffer, acetate buffer, borate buffer, and Tris buffer. When the buffer solution is used, the amount of the buffering agent constituting the buffer solution is preferably 0.01 to 5 parts by mass, with the total amount of all monomers used for copolymerization being 100 parts by mass, It is preferably ˜3 parts by mass.

The polymerization temperature T is suitably selected according to the 10-hour half-life temperature _{T 10} of the polymerization initiator, usually selected in the range of _{_{T 10 -25 ℃ ≦ T ≦ T}} 10 + 25 ℃. For example, t- butyl peroxypivalate _{T 10} is 54.6 ° C. (see NOF Corporation Product Catalog). Therefore, in the polymerization using t-butylperoxypivalate as a polymerization initiator, the polymerization temperature T is appropriately selected within the range of 29.6 ° C. ≦ T ≦ 79.6 ° C. Further, for example, _{T 10} of diisopropyl peroxydicarbonate is 40.5 ° C. (see NOF Corporation Product Catalog). Therefore, in the polymerization using diisopropyl peroxydicarbonate as a polymerization initiator, the polymerization temperature T is appropriately selected within the range of 15.5 ° C. ≦ T ≦ 65.5 ° C.

The pressure during the polymerization is usually under pressure, preferably 2.0 to 15.0 MPa-G.

The polymerization time is not particularly limited, but is preferably 100 hours or less in consideration of productivity and the like.

(Binder composition)
The binder composition according to this embodiment is a composition used for binding an electrode active material to a current collector in an electrode in which an electrode mixture layer containing the electrode active material is formed on the current collector. is there. The binder composition according to the present embodiment includes the vinylidene fluoride copolymer according to the present embodiment.

The binder composition according to the present embodiment is not particularly limited as long as it includes the vinylidene fluoride copolymer according to the present embodiment, and there are two or more types of vinylidene fluoride copolymers according to the present embodiment having different compositions. It may be in a mixed form. Moreover, unless the effect calculated | required by the binder composition which concerns on this embodiment is impaired, the other polymer may be included. Examples of other polymers that can be included in the binder composition include polyacrylonitrile, poly (vinyl alcohol) acrylate, and copolymers thereof. When another polymer is included, the content of the other polymer is preferably 50 wt% or less, more preferably 40 wt% or less, and more preferably 30 wt% or less with respect to the vinylidene fluoride copolymer. More preferably.

The inherent viscosity of the vinylidene fluoride copolymer according to this embodiment is not particularly limited, but is preferably 0.5 dl / g or more and 5 dl / g or less, and is 1.0 dl / g or more and 4 dl / g or less. Is more preferably 1.5 dl / g or more and 3.5 dl / g or less. When the inherent viscosity is 0.5 dl / g or more, the adhesiveness of the binder composition becomes better. Further, when the inherent viscosity is 5 dl / g or less, the decrease in the solid content of the slurry is further suppressed, and the productivity becomes better.

The binder composition according to the present embodiment may contain a solvent in addition to the vinylidene fluoride copolymer. The solvent may be a non-aqueous solvent or water. Examples of the non-aqueous solvent include N-methyl-2-pyrrolidone (NMP), N, N-dimethylformamide, N, N-dimethylacetamide, dimethyl sulfoxide, hexamethylphosphoric triamide, 1,4-dioxane, tetrahydrofuran, Examples thereof include tetramethyl urea, triethyl phosphate, trimethyl phosphate, acetone, methyl ethyl ketone, and tetrahydropyran. These nonaqueous solvents may be used alone or as a mixed solvent in which two or more kinds are mixed.

[Electrode mixture]
The electrode mixture according to the present embodiment includes the binder composition and the electrode active material according to the present embodiment. In addition, the electrode mixture which concerns on this embodiment may further contain the nonaqueous solvent, the conductive support agent, and another component. The electrode mixture is in the form of a slurry, and the viscosity of the electrode mixture can be adjusted to a desired viscosity by adjusting the amount of the non-aqueous solvent. An electrode mixture layer can be formed by applying this electrode mixture to a current collector and volatilizing the solvent.

The electrode mixture according to the present embodiment can suppress gelation by including the binder composition described above. The suppression of gelation can be determined by confirming the change in slurry viscosity.

(Electrode active material)
The electrode active material used in the electrode mixture in the present embodiment contains a lithium-based composite metal oxide. In the present embodiment, the electrode active material may contain, for example, impurities and additives in addition to the lithium-based composite metal oxide. Further, the types of impurities and additives contained in the electrode active material are not particularly limited.

Examples of the lithium-based composite metal oxide include a compound represented by the general formula LiMO ₂ or spinel type LiMn ₂ O ₄ . Here, M consists of at least one kind of metal element, and preferably contains at least one kind of transition metals such as Co, Ni, Fe, Mn, Cr and V. Preferred examples of the lithium-based composite metal oxide include LiCoO ₂ , LiNiO ₂ , LiNi _x Co _y O ₂ , LiNi _x Co _y N _Z O ₂ (N represents one of Mn and Al), or a spinel type LiMn ₂ O ₄ is preferable. Among these, LiNi _x Co _y O ₂ (0 <x ≦ 1, 0 <y ≦ 1) binary lithium-based composite metal oxide or LiNi _x Co _y N _Z O ₂ (0 <x ≦ 1, 0 < A ternary lithium-based composite metal oxide satisfying y ≦ 1, 0 <z ≦ 1) is particularly preferably used because of its high charge / discharge potential and excellent cycle characteristics.

The composition of the ternary lithium-based composite metal oxide of LiNi _x Co _y N _z O ₂ is not particularly limited. For example, Li _1.0 Ni _0.3 Co _0.3 Mn _0.3 O ₂ (NCM111 _{_{_{_{), Li 1.0 Ni 0.5 Co 0.2}}}} Mn 0.3 O 2 (NCM523), Li 1.0 Ni 0.8 Co 0.1 Mn 0.1 O 2 (NCM811), Li 1.0 A composition of Ni _0.8 Co _0.1 Al _0.1 O ₂ (NCA811) can be used. Among them, a composition having a Ni content in M of 50 mol% or more is preferable, and a composition of 60 mol% or more is more preferable.

Generally, when an electrode active material having a high Ni ratio is included, the electrode mixture tends to thicken. However, by using the binder composition in the present embodiment, thickening of the electrode mixture can be suppressed even when an electrode active material having a high Ni ratio is used.

In the lithium-based composite metal oxide, when the ratio of Ni is increased, alkali such as lithium hydroxide and lithium carbonate is likely to be mixed as an impurity during the synthesis of the composite metal oxide. Therefore, when a lithium-based composite metal oxide having a high Ni ratio is used as the electrode active material, the pH of water tends to increase when the electrode active material is dispersed in water.

An electrode that is a lithium-based composite metal oxide having a pH of 10.5 or more, 11.0 or more, or 11.5 or more when dispersed in water by using the binder composition in the present embodiment Even if an active material is used, thickening of the electrode mixture can be suppressed. Therefore, as the lithium-based composite metal oxide used together with the binder composition in the present embodiment, the lithium-based composite having a water pH of 10.5 or more, 11.0 or more, or 11.5 or more when dispersed in water. Metal oxides can be suitably used. In this specification and the like, “pH of water when lithium composite metal oxide is dispersed in water” or “pH of lithium composite metal oxide” is defined in JIS K 5101-17-2. This means the pH of water when extracted by room temperature extraction.

In addition, the electrode active material in this embodiment may contain multiple types of electrode active materials. For example, a plurality of LiNi _x Co _y Mn _Z O ₂ having different composition ratios of x, y, and z may be included, and LiNi _x Co _y Mn _Z O ₂ and LiNi _x Co _y Al _z O ₂ are used. A plurality of electrode active materials having different compositions may be included.

(Conductive aid)
As the conductive assistant, graphites such as natural graphite and artificial graphite, carbons such as acetylene black, ketjen black, channel black and furnace black, carbon materials such as carbon fibers, and carbon nanotubes are preferably used. In addition, conductive fibers such as metal fibers, metal powders, conductive metal oxides, and organic conductive materials can also be used.

(Other components of electrode mixture)
The electrode mixture in this embodiment may contain components other than the above-described components. Examples of other components include pigment dispersants such as polyvinyl pyrrolidone.

(Slurry viscosity)
The slurry viscosity of the electrode mixture is usually 2000 to 50000 mPa · s, preferably 3000 to 30000 mPa · s, and more preferably 3000 to 20000 mPa · s.

When the slurry viscosity is 2000 mPa · s or more, unevenness of the thickness of the electrode mixture layer can be suppressed when the electrode mixture is applied to the current collector, and the productivity becomes better. Moreover, when the slurry viscosity is 50000 mPa · s or less, the electrode mixture can be easily applied to the current collector, and the electrode can be easily produced.

[Method for producing electrode mixture]
The electrode mixture may be produced by mixing the electrode active material and the binder composition so as to form a uniform slurry, and the order of mixing is not particularly limited. Moreover, when a binder composition contains a solvent, you may add an electrode active material etc. before adding a solvent to a binder composition.

〔electrode〕
The electrode according to the present embodiment has a configuration in which a layer formed from the electrode mixture according to the present embodiment is provided on a current collector. Below, with reference to FIG. 1, the structure of the electrode which concerns on this embodiment is demonstrated. FIG. 1 is a cross-sectional view of an electrode 10 in the present embodiment.

As shown in FIG. 1, the electrode 10 has a current collector 11 and electrode mixture layers 12 a and 12 b, and electrode mixture layers 12 a and 12 b are formed on the current collector 11. The current collector 11 is a base material for the electrode 10 and is a terminal for taking out electricity. Examples of the material of the current collector 11 include iron, stainless steel, steel, copper, 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. When the size of the electrode 10 is small, the thickness of the current collector 11 may be 5 to 20 μm.

The

electrode mixture layers

12a and 12b are layers obtained by applying the electrode mixture according to the present embodiment to the current collector 11 and drying it. The method for applying the electrode mixture is not particularly limited as long as it is a conventionally known method, and examples thereof include a method using a bar coater, a die coater or a comma coater.

The drying temperature for forming the

electrode mixture layers

12a and 12b is preferably 50 to 170 ° C. The thickness of the

electrode mixture layers

12a and 12b is preferably 10 to 1000 μm.

In FIG. 1, the electrode 10 has electrode mixture layers 12 a and 12 b formed on both surfaces of the current collector 11. However, the present invention is not limited to this, and any one surface of the current collector 11. The electrode mixture layer may be formed only on the surface.

The thickness of the electrode mixture layer is usually 20 to 250 μm, preferably 20 to 150 μm. The basis weight of the mixture layer is usually 20 to 700 g / m ² , preferably 30 to 500 g / m ² .

The electrode according to this embodiment has sufficient adhesiveness because it uses the above-described binder composition.

[Nonaqueous electrolyte secondary battery]
The nonaqueous electrolyte secondary battery according to this embodiment will be described below with reference to FIG. FIG. 2 is an exploded perspective view of the nonaqueous electrolyte secondary battery.

As shown in FIG. 2, the nonaqueous electrolyte secondary battery 100 has a positive electrode 1, a negative electrode 2, a separator 3, and a metal casing 5. Specifically, in the nonaqueous electrolyte secondary battery 100, a power generation element in which a laminated body in which a separator 3 is disposed between a positive electrode 1 and a negative electrode 2 is spirally wound is housed in a metal casing 5. Structure. Here, the positive electrode 1 or the negative electrode 2 is the same as the electrode 10 in FIG. As the separator 3, a known material such as a porous film of a polymer material such as polypropylene and polyethylene can be used.

In FIG. 2, the nonaqueous electrolyte secondary battery 100 is illustrated as a cylindrical battery, but the nonaqueous electrolyte secondary battery 100 in the present embodiment is not limited to this, and a coin shape, a square shape, It may be a paper battery.

(Summary)
The vinylidene fluoride copolymer according to one embodiment of the present invention is a fluoride that is a copolymer of a first monomer component, a second monomer component, and a third monomer component. A vinylidene copolymer, wherein the first monomer component is vinylidene fluoride, the second monomer component is chlorotrifluoroethylene, and the third monomer component is represented by the following formula: It is a vinylidene fluoride copolymer characterized by being at least one of a compound represented by (1) and a compound represented by the following formula (2).

(In Formula (1), R ¹ , R ² and R ³ are each independently a hydrogen atom, a fluorine atom, a chlorine atom or an alkyl group having 1 to 3 carbon atoms.)

(In the formula (2), R ⁴ , R ⁵ and R ⁶ are each independently a hydrogen atom, a fluorine atom, a chlorine atom or an alkyl group having 1 to 3 carbon atoms, and X is a main chain having 2 to 2 atoms. 10 and an atomic group having a molecular weight of 500 or less and containing at least one heteroatom selected from an oxygen atom and a nitrogen atom.)
In the vinylidene fluoride copolymer according to the present invention, the third monomer component is preferably (meth) acrylic acid.

In the vinylidene fluoride copolymer according to an embodiment of the present invention, the third monomer component is carboxyethyl acrylate, succinic acid mono ((meth) acryloyloxyethyl), succinic acid mono (( It is preferably at least one selected from (meth) acryloyloxypropyl) and mono ((meth) acryloyloxyethyl) phthalate.

Moreover, the vinylidene fluoride copolymer according to an embodiment of the present invention is the vinylidene fluoride copolymer, wherein the constituent unit of the third monomer component is 0.1 mol% or more and 5 mol% or less. It is preferable that

In addition, a binder composition according to an embodiment of the present invention is a binder composition used for binding an electrode active material to a current collector, and includes the above-mentioned vinylidene fluoride copolymer. It is.

In the binder composition according to an embodiment of the present invention, the electrode active material contains a lithium-based composite metal oxide, and the water has a pH of 10 when the lithium-based composite metal oxide is dispersed in water. .5 or more is preferably used.

In the binder composition according to an embodiment of the present invention, the electrode active material is represented by the general formula LiMO ₂ (M is composed of at least one metal element and contains 50 mol% or more of nickel). It is preferably used when it contains a lithium-based composite metal oxide.

In addition, an electrode mixture including a binder composition and an electrode active material according to an embodiment of the present invention is also included in the present invention.

Furthermore, the present invention also includes an electrode provided on a current collector with a layer formed from an electrode mixture according to an embodiment of the present invention, and a nonaqueous electrolyte secondary battery including the electrode.

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 described later, various binder compositions according to the present invention were prepared, and the slurry viscosity was measured for those immediately after preparation of the electrode mixture and 7 days after preparation of the electrode mixture. Moreover, the electrode was manufactured using the binder composition which concerns on this invention, and the peeling test was done using it. Before describing specific examples, a method for calculating inherent viscosity and a method for measuring slurry viscosity are described below.

(Inherent viscosity η _i )
Inherent viscosity (η _i ) indicates logarithmic viscosity. In this embodiment, 80 mg of vinylidene fluoride copolymer is dissolved in 20 ml of N, N-dimethylformamide and placed in a thermostatic bath at 30 ° C. It can be calculated from the following equation according to JIS K6721 using an Ubbelohde viscometer.

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

(Slurry viscosity)
The slurry viscosity in this example is the mixture viscosity of the electrode mixture. The slurry viscosity was measured for viscosity when subjected using E type viscometer (Toki Sangyo Co., Ltd. "RE80 type"), a measurement temperature 25 ° C., 300 seconds shear at a shear rate of 2s ^-1.

Example 1
[Preparation of binder composition]
In an autoclave with an internal volume of 2 liters, 1000 g of ion-exchanged water as a dispersion medium, 0.22 g of Metroles SM-100 (manufactured by Shin-Etsu Chemical Co., Ltd.) as a cellulose-based suspending agent, 50 wt% diisopropyl peroxydicarbonate as a polymerization initiator 2.6 g of HFE-347pc-f solution, 413 g of vinylidene fluoride, and 17 g of CTFE were charged, and the temperature was raised to 28 ° C. over 1 hour. While maintaining the temperature at 28 ° C., 108 g of a 2 wt% aqueous mono (acryloyloxypropyl) succinate solution was added over 10 hours after 5 hours from the start of temperature increase. The polymerization was stopped when the internal pressure in the reaction vessel reached 1.6 MPa-G, and was carried out for 32 hours from the start of temperature increase.

After completion of the polymerization, the polymer slurry was heat treated at 95 ° C. for 60 minutes, dehydrated, washed with water, and further dried at 80 ° C. for 20 hours to obtain a polymer powder. The yield of the obtained polymer was 91%, and the inherent viscosity η _i was 2.08 dl / g. Hereinafter, the obtained polymer powder was used as a binder composition.

[Production of electrode mixture]
As an electrode active material, nickel cobalt aluminum ternary lithium-based composite metal oxide (specific surface area 0.17 m ² / g, average particle size D ₅₀ 15 μm, pH 12.2) 100 parts by weight, carbon black (manufactured by TIMCAL, Super-P 2 parts by weight and 1 part by weight of the binder composition were added to N-methyl-2-pyrrolidone and kneaded to prepare a slurry-like positive electrode mixture. The addition amount of N-methyl-2-pyrrolidone is appropriately adjusted according to the inherent viscosity of the vinylidene fluoride copolymer, and the viscosity of the mixture is 25 ° C. using an E-type viscometer, with a shear rate of 2 s. When the measurement was performed at ⁻¹ , the pressure was adjusted to 3000 to 20000 mPa · s.

[Manufacture of electrodes]
The obtained electrode mixture was applied to a 15 μm-thick aluminum foil as a current collector with a bar coater, and dried at 110 ° C. for 30 minutes in a nitrogen atmosphere using a thermostatic bath. An electrode having a mixture weight per unit area of 300 g / m ² was produced.

(Example 2)
Instead of adding 50 wt% diisopropylperoxydicarbonate-HFE-347pc-f solution to 3.0 g and adding 2 wt% aqueous solution of mono (acryloyloxypropyl) succinate, 5.5 hours after the start of temperature increase A binder composition was obtained in the same manner as in Example 1 except that 86 g of a 5 wt% aqueous mono (acryloyloxypropyl) succinate solution was added over 19.2 hours. The yield of the obtained polymer was 93%, and the inherent viscosity η _i was 2.62 dl / g. The electrode mixture and the electrode were produced by the same method as in Example 1.

(Example 3)
Instead of adding 2 wt% aqueous mono (acryloyloxypropyl) succinate to 962 g of ion-exchanged water, 143 g of 3 wt% aqueous mono (acryloyloxypropyl) succinate was added over 20 hours. Except for the above, a binder composition was obtained in the same manner as in Example 2. The yield of the obtained polymer was 90%, and the inherent viscosity η _i was 2.40 dl / g. The electrode mixture and the electrode were produced by the same method as in Example 1.

(Comparative Example 1)
[Production of first vinylidene fluoride copolymer]
In an autoclave having an internal volume of 2 liters, 1020 g of ion-exchanged water as a dispersion medium, 0.22 g of Metroles SM-100 (manufactured by Shin-Etsu Chemical Co., Ltd.) as a cellulose-based suspending agent, 50 wt% diisopropyl peroxydicarbonate as a polymerization initiator An HFE-347pc-f solution (3.0 g), vinylidene fluoride (426 g), ethyl acetate (3.05 g) and succinic acid mono (acryloyloxypropyl) (0.96 g) were charged, and the temperature was raised to 26 ° C. over 1 hour. While maintaining the temperature at 26 ° C., 83 g of a 5 wt% mono (acryloyloxypropyl) succinate aqueous solution was added over 16.4 hours after 2.5 hours from the start of the temperature increase. When the internal pressure in the reaction vessel decreased by 0.2 MPa, the temperature was raised to 40 ° C. over 3 hours. The polymerization was stopped when the internal pressure in the reaction vessel reached 1.47 MPa-G, and was carried out for 27 hours from the start of temperature increase.

After completion of the polymerization, the polymer slurry was heat treated at 95 ° C. for 60 minutes, dehydrated, washed with water, and further dried at 80 ° C. for 20 hours to obtain a first vinylidene fluoride copolymer. The yield of the obtained polymer was 92%, and the inherent viscosity η _i was 1.82 dl / g.

[Production of Second Vinylidene Fluoride Copolymer]
In an autoclave with an internal volume of 2 liters, 1100 g of ion-exchanged water as a dispersion medium, 0.22 g of Metroles SM-100 (manufactured by Shin-Etsu Chemical Co., Ltd.) as a cellulose-based suspending agent, 50 wt% diisopropyl peroxydicarbonate as a polymerization initiator 2.6 g of HFE-347pc-f solution, 413 g of vinylidene fluoride, 17.2 g of CTFE, 0.43 g of disodium dihydrogen pyrophosphate and 0.43 g of tetrasodium pyrophosphate were charged and heated to 28 ° C. over 1 hour. The temperature was maintained at 28 ° C., and the polymerization was stopped 21 hours after the start of temperature increase. After the completion of the polymerization, the polymer slurry was heat treated at 95 ° C. for 60 minutes, dehydrated, washed with water, and further dried at 80 ° C. for 20 hours to obtain a second vinylidene fluoride copolymer. The yield of the obtained polymer was 90%, and the inherent viscosity η _i was 2.05 dl / g.

[Preparation of binder composition]
The 1st vinylidene fluoride and the 2nd vinylidene fluoride were mixed so that it might become 1: 1 by weight ratio, and the binder composition was obtained.

The electrode mixture and the electrode were produced by the same method as in Example 1.

(Comparative Example 2)
[Production of first vinylidene fluoride copolymer]
In an autoclave having an internal volume of 2 liters, 1020 g of ion-exchanged water as a dispersion medium, 0.22 g of Metroles SM-100 (manufactured by Shin-Etsu Chemical Co., Ltd.) as a cellulose-based suspending agent, 50 wt% diisopropyl peroxydicarbonate as a polymerization initiator A solution of 2.2 g of HFE-347pc-f, 426 g of vinylidene fluoride, 1.55 g of ethyl acetate and 0.22 g of mono (acryloyloxypropyl) succinate was charged, and the temperature was raised to 26 ° C. over 1 hour. The temperature was maintained at 26 ° C., and 82 g of a 5 wt% aqueous solution of mono (acryloyloxypropyl) succinate was added over 16 hours after 2.5 hours from the start of temperature increase. When the internal pressure in the reaction vessel decreased by 0.2 MPa, the temperature was raised to 40 ° C. over 3 hours. The polymerization was stopped when the internal pressure in the reaction vessel reached 1.51 MPa-G, and was carried out for 28 hours from the start of temperature increase.

After completion of the polymerization, the polymer slurry was heat treated at 95 ° C. for 60 minutes, dehydrated, washed with water, and further dried at 80 ° C. for 20 hours to obtain a first vinylidene fluoride copolymer. The yield of the obtained polymer was 92%, and the inherent viscosity η _i was 2.50 dl / g.

[Production of Second Vinylidene Fluoride Copolymer]
In an autoclave having an internal volume of 2 liters, 1225 g of ion-exchanged water as a dispersion medium, 0.22 g of Metroles SM-100 (manufactured by Shin-Etsu Chemical Co., Ltd.) as a suspending agent, and 50 wt% diisopropyl peroxydicarbonate as a polymerization initiator 8.6 g of HFE-347pc-f solution, 267 g of vinylidene fluoride, 16.3 g of CTFE, 0.43 g of disodium dihydrogen pyrophosphate and 0.43 g of tetrasodium pyrophosphate were charged and heated to 26 ° C. over 1 hour. The temperature was maintained at 28 ° C., and the polymerization was stopped 6.7 hours after the start of temperature increase. After the completion of the polymerization, the polymer slurry is heat treated at 50 ° C. for 90 minutes, dehydrated, washed with water, further dried at 60 ° C. for 20 hours, and further dried at 50 ° C. for 8 hours under vacuum. A vinylidene fluoride copolymer was obtained. The yield of the obtained polymer was 82%, and the inherent viscosity η _i was 2.10 dl / g.

[Preparation of binder composition]
A first vinylidene fluoride and a second vinylidene fluoride described below were mixed at a weight ratio of 1: 1 to obtain a binder composition.

(Comparative Example 3)
[Production of first vinylidene fluoride copolymer]
In an autoclave having an internal volume of 2 liters, 1064 g of ion-exchanged water as a dispersion medium, 0.22 g of Metroles SM-100 (manufactured by Shin-Etsu Chemical Co., Ltd.) as a cellulose-based suspending agent, 50 wt% diisopropyl peroxydicarbonate as a polymerization initiator An HFE-347pc-f solution (2.2 g), vinylidene fluoride (426 g), ethyl acetate (1.55 g) and succinic acid mono (acryloyloxyethyl) (0.22 g) were charged, and the temperature was raised to 26 ° C. over 1 hour. The temperature was maintained at 26 ° C., and after 3 hours from the start of temperature increase, 41 g of a 10% aqueous solution of mono (acryloyloxyethyl) succinate was added over 16 hours. When the internal pressure in the reaction vessel decreased by 0.2 MPa, the temperature was raised to 40 ° C. over 3 hours. The polymerization was stopped when the internal pressure in the reaction vessel reached 1.51 MPa-G, and was carried out for 28 hours from the start of temperature increase.

The polymerization was stopped after the addition of the mono (acryloyloxyethyl) succinate aqueous solution. After completion of the polymerization, the polymer slurry was heat treated at 95 ° C. for 60 minutes, dehydrated, washed with water, and further dried at 80 ° C. for 20 hours to obtain a first vinylidene fluoride copolymer. The yield of the obtained polymer was 59%, and the inherent viscosity η _i was 2.60 dl / g.

[Production of Second Vinylidene Fluoride Copolymer]
The second vinylidene fluoride copolymer was produced by the same method as in Comparative Example 1.

(Comparative Example 4)
[Preparation of binder composition]
In an autoclave with an internal volume of 2 liters, 1092 g of ion-exchanged water as a dispersion medium, 0.42 g of Metroles SM-100 (manufactured by Shin-Etsu Chemical Co., Ltd.) as a cellulose-based suspending agent, 50 wt% diisopropyl peroxydicarbonate as a polymerization initiator 2.9 g of HFE-347pc-f solution, 412 g of vinylidene fluoride, and 2.94 g of monomethyl maleate were charged, and the temperature was raised to 28 ° C. over 1 hour.

Next, polymerization was carried out for 54 hours while maintaining the temperature at 28 ° C. After completion of the polymerization, the polymer slurry was heat treated at 95 ° C. for 60 minutes, dehydrated, washed with water, and further dried at 80 ° C. for 20 hours to obtain a binder composition. The yield of the obtained polymer was 85%, and the inherent viscosity η _i was 2.28 dl / g. The electrode mixture and the electrode were produced by the same method as in Example 1.

(Comparative Example 5)
[Preparation of binder composition]
The binder composition was prepared in the same manner as the second vinylidene fluoride production method of Comparative Example 1. The electrode mixture and the electrode were produced by the same method as in Example 1.

[Slurry viscosity]
The slurry viscosity of each electrode mixture obtained in Examples 1 to 3 and Comparative Examples 1 to 5 was evaluated. The slurry viscosity is measured immediately after preparing the electrode mixture and after holding the electrode mixture for 7 days in an atmosphere of 40 ° C., and the slurry viscosity after holding the electrode mixture for 7 days in an atmosphere of 40 ° C. is prepared. The value divided by the slurry viscosity immediately after the process was defined as the slurry viscosity change rate.

[Peel strength]
The peel strength between the aluminum foil and the electrode mixture layer in the electrodes obtained in Examples 1 to 3 and Comparative Examples 1 to 5 was evaluated. Specifically, the upper surface of the electrode formed by coating was bonded to a plastic thick plate (made of acrylic resin, thickness 5 mm), and evaluated by performing a 90 ° peel test in accordance with JIS K6854.

Table 1 shows the results of the rate of change in slurry viscosity and the peel strength in each example and each comparative example.

As shown in Table 1, in Examples 1 to 3, the increase in slurry viscosity was suppressed compared to Comparative Examples 1 to 4, and the peel strength was sufficient compared to Comparative Example 5. It was confirmed.

According to the present invention, it is possible to obtain a binder composition that suppresses gelation of the electrode mixture while having sufficient adhesiveness with the current collector.

DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Negative electrode 3 Separator 5 Metal casing 10 Electrode 11 Current collector 12a Electrode mixture layer 12b Electrode mixture layer 100 Battery

Claims

A vinylidene fluoride copolymer which is a copolymer of a first monomer component, a second monomer component, and a third monomer component,
The first monomer component is vinylidene fluoride;
The second monomer component is chlorotrifluoroethylene;
The vinylidene fluoride copolymer, wherein the third monomer component is at least one of a compound represented by the following formula (1) and a compound represented by the following formula (2).

(In Formula (1), R 1 , R 2 and R 3 are each independently a hydrogen atom, a fluorine atom, a chlorine atom or an alkyl group having 1 to 3 carbon atoms.)

(In the formula (2), R 4 , R 5 and R 6 are each independently a hydrogen atom, a fluorine atom, a chlorine atom or an alkyl group having 1 to 3 carbon atoms, and X is a main chain having 2 to 2 atoms. 10 and an atomic group having a molecular weight of 500 or less and containing at least one heteroatom selected from an oxygen atom and a nitrogen atom.)
The vinylidene fluoride copolymer according to claim 1, wherein the compound represented by the formula (1) is (meth) acrylic acid.
The third monomer component includes carboxyethyl acrylate, succinic acid mono ((meth) acryloyloxyethyl), succinic acid mono ((meth) acryloyloxypropyl), and phthalic acid mono ((meth) acryloyloxy). The vinylidene fluoride copolymer according to claim 1, wherein the copolymer is at least one selected from ethyl).
4. The vinylidene fluoride copolymer according to claim 1, wherein the constituent unit of the third monomer component is 0.1 mol% or more and 5 mol% or less. 5. The vinylidene fluoride copolymer as described.
A binder composition used for binding an electrode active material to a current collector,
A binder composition comprising the vinylidene fluoride copolymer according to any one of claims 1 to 4.
6. The electrode active material includes a lithium-based composite metal oxide, and the pH of the water when the lithium-based composite metal oxide is dispersed in water is 10.5 or more. Binder composition.
The electrode active material includes a lithium-based composite metal oxide represented by a general formula LiMO 2 (M is composed of at least one metal element and contains 50 mol% or more of nickel). Item 7. The binder composition according to Item 5 or 6.
An electrode mixture comprising the binder composition according to any one of claims 5 to 7 and the electrode active material.
An electrode comprising a layer formed from the electrode mixture according to claim 8 on a current collector.
A non-aqueous electrolyte secondary battery comprising the electrode according to claim 9.