WO2022097683A1

WO2022097683A1 - Copolymer, binder for non-aqueous secondary battery electrode, and slurry for non-aqueous secondary battery electrode

Info

Publication number: WO2022097683A1
Application number: PCT/JP2021/040613
Authority: WO
Inventors: 勇汰川原; 亮介池端; 秀雄堀越; 充花▲崎▼
Original assignee: 昭和電工株式会社
Priority date: 2020-11-04
Filing date: 2021-11-04
Publication date: 2022-05-12
Also published as: KR20230101828A; JPWO2022097683A1; CN116547328A

Abstract

Provided are: a copolymer which has less generation of coarse grains and effectively improved peel strength from a current collector of an electrode active material layer, and thus can contribute to a reduction in the internal resistance of a battery and excellent cycle characteristics; a binder for a non-aqueous secondary battery electrode; and a slurry for a non-aqueous secondary battery electrode. A copolymer according to the present invention includes a first structural unit to a third structural unit which are respectively derived from monomers (a1)-(a3). The monomer (a1) is composed of a nonionic compound having an ethylenically unsaturated bond, the monomer (a2) has an ethylenically unsaturated bond and an anionic functional group, and the monomer (a3) has 31st to 33rd structural units represented by formulae (1)-(3). 1.0-30 parts by mass of the second structural unit and 0.010-70 parts by mass of the third structural unit are included with respect to 100 parts by mass of the first structural unit.

Description

Copolymers, binders for non-aqueous secondary battery electrodes, and slurries for non-aqueous secondary battery electrodes

The present invention relates to a copolymer, a binder for a non-aqueous secondary battery electrode, and a slurry for a non-aqueous secondary battery electrode.
This application claims priority based on Japanese Patent Application No. 2020-184544 filed in Japan on November 4, 2020, the contents of which are incorporated herein by reference.

The non-aqueous secondary battery includes, for example, a positive electrode using a metal oxide or the like as an active material, a negative electrode using a carbon material such as graphite as an active material, and an electrolytic solution. A non-aqueous secondary battery is a secondary battery in which ions move between a positive electrode and a negative electrode to charge and discharge the battery.

A typical example is a lithium ion secondary battery as a non-aqueous secondary battery. Non-aqueous secondary batteries are used as power sources for notebook computers, mobile phones, power tools, and electronic / communication devices in terms of miniaturization and weight reduction. Recently, it has also been used for electric vehicles and hybrid vehicles from the viewpoint of application to environmental vehicles. Under these circumstances, there is a strong demand for higher output, higher capacity, longer life, etc. of non-aqueous secondary batteries.

The binder used for the positive electrode and the negative electrode has a role of binding the active material to each other and a role of binding the active material and the current collector. Water dispersion binders are being developed to improve the capacity of non-aqueous secondary batteries and protect the working environment. For example, a styrene-butadiene rubber (SBR) -based aqueous dispersion using carboxymethyl cellulose (CMC) as a thickener is known.

Patent Document 1 describes a method for polymerizing ethylene oxide with an alkylene oxide other than ethylene oxide, an alkyl glycidyl ether, an allyl glycidyl ether, or a combination thereof. It is described that the composition containing the copolymer obtained by polymerization can be used as a binder material in a battery electrode containing electroactive particles.

In Patent Document 2, a copolymer obtained from a (meth) acrylic acid ester and a vinyl monomer having an acid component, a polyoxyethylene alkyl ether derivative, polyoxyethylene-polyoxypropylene condensate, and polyoxyethylene- Described is a secondary battery negative electrode comprising an electrode layer containing at least one selected from the group consisting of polyoxypropylene alkyl ether derivatives.

Special Table 2012-517519 Gazette Japanese Unexamined Patent Publication No. 2014-239070

However, in the components described in Patent Documents 1 and 2, when used as a binder for electrodes, there is room for improving the peel strength of the electrode active material layer with respect to the current collector, and the internal resistance is reduced when the battery is manufactured. There is room for.

The present invention is a copolymer and non-aqueous secondary battery that can effectively improve the peel strength of the electrode active material layer with respect to the current collector in a non-aqueous secondary battery, and contribute to the reduction of the internal resistance of the battery and the improvement of the cycle characteristics. It is an object of the present invention to provide a binder for a battery electrode and a slurry for a non-aqueous secondary battery electrode.

In order to solve the above problems, the present invention is as follows [1] to [15].
[1] A polymer of a compound having an ethylenically unsaturated bond.
A first structural unit derived from the monomer (a1) and a second structural unit derived from the monomer (a2).
It has a third structural unit derived from the monomer (a3); or a first structural unit derived from the monomer (a1) and a second structural unit derived from the monomer (a2). , A third structural unit derived from the monomer (a3) and a fourth structural unit derived from the internal cross-linking agent (a4).
The monomer (a1) has an ethylenically unsaturated bond, has neither a hydroxy group nor a cyano group, has no polyoxyalkylene structure, and has a plurality of independent ethylenically unsaturated bonds. It is a nonionic compound that does not
The monomer (a2) is a compound having an ethylenically unsaturated bond and an anionic functional group, and has neither a polyoxyalkylene structure nor a plurality of independent ethylenically unsaturated bonds.
The monomer (a3) has a 31st structural unit represented by the following formula (1), a 32nd structural unit represented by the following formula (2), and a 33rd structural unit represented by the following formula (3). With structural units,
The second structural unit is included in an amount of 1.0 part by mass or more and 30 parts by mass or less with respect to 100 parts by mass of the first structural unit.
The third structural unit is contained in an amount of 0.010 parts by mass or more and 70 parts by mass or less with respect to 100 parts by mass of the first structural unit.
The content of the fourth structural unit with respect to 100 parts by mass of the first structural unit is 0 parts by mass or more and 20 parts by mass or less.
The internal cross-linking agent (a4) does not correspond to the monomer (a3), has a plurality of independent ethylenically unsaturated bonds, and has the monomer (a1), the monomer (a2), and the like. A copolymer characterized by being a compound capable of forming a crosslinked structure in radical polymerization of a monomer containing the monomer (a3).

(In the formula (2), R ¹ is an alkyl group having 1 or more and 6 or less carbon atoms which may have a branch.)

(In formula (3), R ² is a functional group having an ethylenically unsaturated bond.)
[2] The monomer (a3) is
With respect to the total amount of the 31st structural unit, the 32nd structural unit, and the 33rd structural unit.
The 31st structural unit contains 5.0 mol% or more and 98 mol% or less.
The 32nd structural unit contains 0.30 mol% or more and 90 mol% or less.
The copolymer according to [1], which contains the 33rd structural unit in an amount of 0.30 mol% or more and 10 mol% or less.
[3] The copolymer according to [1] or [2], wherein the monomer (a3) has a plurality of independent ethylenically unsaturated bonds in one molecule.
[4] In the above formula (3), R ² is composed of a vinyloxy group, an allyloxy group, a (meth) acryloyl group, a (meth) acryloyloxy group, and -OCH ₂ -CH ₂ -CH ₂ = CH ₂ . The copolymer according to any one of [1] to [3], which has at least one selected.
[5] In the formula (3), R ² is a copolymer according to any one of [1] to [4] represented by the following formula (4).

(In the formula (4), R ²¹ is an alkylene group having 1 to 5 carbon atoms which may have a branch, and R ²² is a vinyloxy group, an allyloxy group, a (meth) acryloyl group, and a (meth) acryloyloxy. It is one functional group selected from the group consisting of groups.)
[6] The monomer (a3) has a first block composed of the 31st structural unit, a second block composed of the 32nd structural unit, and a third block composed of the 33rd structural unit [1]. The copolymer according to any one of [5].
[7] The monomer (a3) contains 90% by mass or more of the 31st structural unit, the 32nd structural unit, and the 33rd structural unit in the total structural units [1] to [6]. The copolymer according to any one of.
[8] The copolymer according to any one of [1] to [7], wherein the monomer (a1) does not have a polar functional group.
[9] The copolymer according to any one of [1] to [8], wherein the monomer (a2) is a compound having at least one of a carboxy group and a sulfo group.
[10] The copolymer according to any one of [1] to [9], which contains the first structural unit, the second structural unit, and the third structural unit in a total amount of 80% by mass or more.
[11] The copolymer according to any one of [1] to [10], wherein the content of the fourth structural unit with respect to 100 parts by mass of the first structural unit is 0.050 parts by mass or more.
[12] A binder composition for a non-aqueous secondary battery electrode in which the copolymer according to any one of [1] to [11] is dispersed in an aqueous medium.
[13] A binder for a non-aqueous secondary battery electrode containing the copolymer according to any one of [1] to [11].
[14] The binder according to [13], the electrode active material, and the aqueous medium are included.
The binder and the electrode active material are dispersed in an aqueous medium, and the binder is dispersed in the aqueous medium.
The aqueous medium is a slurry for a non-aqueous secondary battery electrode, which is one medium selected from the group consisting of water, a hydrophilic solvent, and a mixture containing water and a hydrophilic solvent.
[15] A non-aqueous secondary battery electrode containing the binder according to [13].

According to the present invention, in a non-aqueous secondary battery, the peeling strength of the electrode active material layer with respect to the current collector can be effectively improved, and the internal resistance of the battery can be reduced and the cycle characteristics can be improved. A binder for a secondary battery electrode and a slurry for a non-aqueous secondary battery electrode can be provided.

Hereinafter, as embodiments of the present invention, a copolymer, a binder for a non-aqueous secondary battery electrode, a binder composition for a non-aqueous secondary battery electrode, a slurry for a non-aqueous secondary battery electrode, a non-aqueous secondary battery electrode, and A non-aqueous secondary battery will be described.

"(Meta) acrylic" is a general term for acrylic and methacrylic, and "(meth) acrylate" is a general term for acrylate and methacrylate.

The "nonvolatile component" is a component remaining after weighing 1 g of the composition in an aluminum dish having a diameter of 5 cm and drying at 105 ° C. for 1 hour while circulating air in a dryer at 1 atm (1013 hPa). The form of the composition includes, but is not limited to, a solution, a dispersion, and a slurry. The "nonvolatile content concentration" is the mass ratio (mass%) of the non-volatile content after drying under the above conditions with respect to the mass (1 g) of the composition before drying.

"Ethylene unsaturated bond" refers to an ethylenically unsaturated bond having radical polymerization unless otherwise specified.

In the polymer of a compound having an ethylenically unsaturated bond, the structural unit derived from the compound having a certain ethylenically unsaturated bond is the chemical structure of the portion other than the ethylenically unsaturated bond of the compound and its in the polymer. It is assumed that the chemical structure of the part other than the part corresponding to the ethylenically unsaturated bond of the structural unit is the same. For example, the structural unit derived from sodium acrylate has a -CH ₂ CH (COONa)-structure in the polymer.

Further, for a compound having a plurality of independent ethylenically unsaturated bonds, an ethylenically unsaturated bond may remain as a structural unit of the polymer. A plurality of independent ethylenically unsaturated bonds are a plurality of ethylenically unsaturated bonds that do not form conjugated diene with each other. For example, the structural unit derived from divinylbenzene may have a structure having no ethylenically unsaturated bond (a form in which a portion corresponding to any ethylenically unsaturated bond is incorporated into a polymer chain), or one ethylene. A structure having a sex-unsaturated bond (a form in which only the portion corresponding to one ethylenically unsaturated bond is incorporated into the polymer chain) may be used.

Furthermore, if the chemical structure of the monomer does not correspond to the chemical structure of the polymer, such as chemical reaction of the part other than the chain corresponding to the ethylenically unsaturated bond after polymerization, the chemical structure after polymerization is used as a reference. .. For example, when vinyl acetate is polymerized and then saponified, it is not a structural unit derived from vinyl acetate but a structural unit derived from vinyl alcohol in consideration of the chemical structure of the polymer.

<1. Copolymer (P)>
In the present embodiment, the copolymer (P) is a copolymer for a non-aqueous secondary battery electrode binder. The copolymer (P) is a polymer of a compound having an ethylenically unsaturated bond. The copolymer (P) has a first structural unit derived from the monomer (a1), a second structural unit derived from the monomer (a2), and a third structure derived from the monomer (a3). It has a unit and. The copolymer (P) may further have a fourth structural unit derived from the internal cross-linking agent (a4). The copolymer (P) can be used as another monomer (a5) which does not correspond to any of the monomer (a1), the monomer (a2), the monomer (a3) and the internal cross-linking agent (a4). It may contain the structural unit from which it is derived. Details of each monomer and internal cross-linking agent will be described below.

<1-1. Monomer (a1)>
The monomer (a1) has an ethylenically unsaturated bond, does not have a polyoxyalkylene structure, and does not have a plurality of independent ethylenically unsaturated bonds. Nonionic (anionic functional group and cationic functional group). It is a compound (which does not have any of the above). "No polyoxyalkylene structure" means an alkylene group sandwiched between two ether bonds (a bond represented by -C-OC _x -OC- (x is an integer of 1 or more)). Say you don't have.

The monomer (a1) has neither a hydroxy group nor a cyano group. The monomer (a1) preferably has no polar functional group. The monomer (a1) may contain only one kind of compound, or may contain two or more kinds of compounds. The monomer (a1) is preferably at least one of a (meth) acrylic acid ester having no polar functional group and an aromatic vinyl compound, and more preferably containing both. The (meth) acrylic acid ester having no polar functional group more preferably contains a (meth) acrylic acid alkyl ester. The total content of the (meth) acrylic acid alkyl ester and the aromatic vinyl compound in the monomer (a1) is more preferably 80% by mass or more, further preferably 90% by mass or more, and 100% by mass. Is most preferable.

Further, regarding the composition of the monomer (a1), in order to adjust the glass transition point of the copolymer (P) or to adjust the polymerization rate according to the molecular design, within the range specified in the present invention. It is preferable to appropriately adjust the preferred compound and the amount thereof.

Examples of the (meth) acrylic acid alkyl ester include methyl (meth) acrylic acid, ethyl (meth) acrylic acid, n-propyl (meth) acrylic acid, isopropyl (meth) acrylic acid, and n-butyl (meth) acrylic acid. , (Meta) tert-butyl acrylate, (meth) cyclohexyl acrylate, (meth) 2-ethylhexyl acrylate, isobornyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate and the like. ..

Here, the aromatic vinyl compound does not contain a (meth) acryloyl group. Examples of the aromatic vinyl compound include styrene, t-butylstyrene, α-methylstyrene, p-methylstyrene, 1,1-diphenylethylene and the like. When the monomer (a1) contains an aromatic vinyl compound, the monomer (a1) more preferably contains at least one of styrene and α-methylstyrene, and further preferably contains styrene.

The monomer (a1) may contain a plurality of ethylenically unsaturated bonds forming conjugated diene with each other. Examples of the compound having a plurality of ethylenically unsaturated bonds forming conjugated diene with each other include 1,3-butadiene, 1,3-pentadiene and the like.

[1-2. Monomer (a2)]
The monomer (a2) is a compound having an ethylenically unsaturated bond and an anionic functional group. The monomer (a2) has neither a polyoxyalkylene structure nor a plurality of independent ethylenically unsaturated bonds. Examples of the anionic functional group include a carboxy group, a sulfo group, a phosphoric acid group and the like. The monomer (a2) preferably contains a compound having at least one of a carboxy group and a sulfo group, and more preferably contains a compound having a carboxy group.

The monomer (a2) may contain only one kind of compound, or may contain two or more kinds of compounds. The monomer (a2) may contain a compound having a plurality of the same kind of anionic functional groups in one molecule. That is, the copolymer (P) may contain a plurality of anionic functional groups of the same type in one structural unit. The monomer (a2) may contain a compound having two or more different anionic functional groups in one molecule. That is, the copolymer (P) may contain two or more different anionic functional groups in one structural unit. Further, the monomer (a2) may contain two or more kinds of compounds containing different anionic functional groups. That is, the copolymer (P) may contain two or more structural units containing different anionic functional groups.

Examples of the monomer (a2) include unsaturated monocarboxylic acids such as (meth) acrylic acid and crotonic acid; unsaturated dicarboxylic acids such as maleic acid, fumaric acid and itaconic acid; half esters of unsaturated dicarboxylic acids; parastyrene. Examples include sulfonic acid. Among these, the monomer (a2) preferably contains at least one of (meth) acrylic acid and itaconic acid.

At least a part of the structural unit derived from the monomer (a2) may form a salt with a basic substance. Here, examples of the monomer (a2) forming the salt include sodium (meth) acrylate, sodium parastyrene sulfonate, and the like.

The monomer (a2) preferably contains at least one of a sulfonic acid having an ethylenically unsaturated bond and a salt thereof, and more preferably contains a sulfonic acid salt having an ethylenically unsaturated bond. The sulfonic acid preferably contains an aromatic vinyl compound having a sulfo group, and more preferably contains parastyrene sulfonic acid. The sulfonate preferably contains a salt of an aromatic vinyl compound having a sulfo group, more preferably contains a parastyrene sulfonate, and even more preferably contains sodium parastyrene sulfonate. This is because the generation of coarse particles can be suppressed in the binder composition.

[1-3. Monomer (a3)]
The monomer (a3) has a 31st structural unit represented by the following formula (1), a 32nd structural unit represented by the following formula (2), and a 33rd structural unit represented by the following formula (3). A compound containing a unit. The monomer (a3) preferably has a plurality of ethylenically unsaturated bonds in one molecule. The monomer (a3) may contain only one kind of compound, or may contain two or more kinds of compounds.

In the monomer (a3), when describing the structure of the structural unit, the terminal structure is not considered unless otherwise specified. For example, the content of a certain structural unit in the monomer (a3) is the content of the structural unit in the structure excluding the terminal structure unless otherwise specified. Further, when the monomer (a3) is composed of a certain structural unit, it may contain a terminal structure in addition to the structural unit. Here, the terminal structure in the monomer (a3) is on the molecular terminal side of the ether bond closest to the molecular end, and is not included in any of the structures of the following formulas (1) to (3). It is a structure. Further, the terminal structure does not include the structures represented by the following formulas (1) to (3).

In the formula (2), R ¹ is an alkyl group having 1 or more and 6 or less carbon atoms which may have a branch. R ¹ preferably has 4 or less carbon atoms, more preferably 2 or less carbon atoms, and even more preferably a methyl group.

In formula (3), R ² is a group having an ethylenically unsaturated bond. ^R2 is a vinyloxy group (-OCH ₂ = CH ₂ ), an allyloxy group (-OCH ₂ -CH ₂ = CH ₂ ), a (meth) acryloyl group, a (meth) acryloyloxy group, and -OCH ₂ -CH _2- . It is preferable to have at least one selected from the group consisting of CH ₂ = CH ₂ , and at least one selected from the group consisting of an allyloxy group, a (meth) acryloyl group, and a (meth) acryloyloxy group. It is more preferable to have it, and it is further preferable to have an allyloxy group. The number of ethylenically unsaturated bonds contained in one 33rd structural unit is preferably one.

The structure of ^R2 is preferably represented by the following formula (4).

In formula (4), R ²¹ is an alkylene group having 1 to 5 carbon atoms which may have a branch, and R ²² is a vinyloxy group, an allyloxy group, a (meth) acryloyl group, a (meth) acryloyloxy group, and-. OCH ₂ -CH ₂ -CH ₂ = CH ₂ is any one of them.

In the formula (4), R ²¹ is preferably an alkylene group having 1 or 2 carbon atoms, and more preferably a methylene group. In the formula (4), R ²² is more preferably any one of an allyloxy group, a (meth) acryloyl group, and a (meth) acryloyloxy group, and even more preferably an allyloxy group.

By adjusting the content of each of the 31st structural unit, the 32nd structural unit, and the 33rd structural unit in the monomer (a3), the hydrophilicity of the monomer (a3) is adjusted to an appropriate range. The hydrophilicity of the copolymer (P) can be controlled. For example, if the content of the 31st structural unit in the monomer (a3) is increased, the hydrophilicity of the copolymer (P) is improved, and if the content of the 31st structural unit is decreased, the copolymer (P) is used. The hydrophilicity of is reduced.

By adjusting the content of each of the 31st structural unit, the 32nd structural unit, and the 33rd structural unit in the monomer (a3), the crystallinity of the monomer (a3) is adjusted to an appropriate range. The crystallinity of the copolymer (P) can be controlled. For example, if the content of the 31st structural unit in the monomer (a3) is increased, the crystallinity of the copolymer (P) is improved, and if the content of the 31st structural unit is decreased, the copolymer (P) is used. Crystallinity is reduced.

By adjusting the content of the 33rd structural unit in the monomer (a3), the crosslink density of the copolymer (P) can be adjusted, and the electrode activity containing the copolymer (P) as an electrode binder is possible. The flexibility and strength of the material layer can be controlled. For example, if the content of the 33rd structural unit in the monomer (a3) is increased, the crosslink density of the copolymer (P) is increased, and the strength of the electrode active material layer can be further improved. On the other hand, if the content of the 33rd structural unit is reduced, the crosslink density of the copolymer (P) is lowered, and the flexibility of the electrode active material layer can be further improved.

Hereinafter, the relationship between the contents of these structural units contained in the monomer (a3) will be described.

In the monomer (a3), the content of the 31st structural unit with respect to the total amount of the 31st structural unit, the 32nd structural unit, and the 33rd structural unit is preferably 5.0 mol% or more, preferably 18 mol. % Or more, more preferably 25 mol% or more.

In the monomer (a3), the content of the 31st structural unit with respect to the total amount of the 31st structural unit, the 32nd structural unit, and the 33rd structural unit is preferably 98 mol% or less, preferably 97 mol% or less. Is more preferable.

In the monomer (a3), the content of the 32nd structural unit with respect to the total amount of the 31st structural unit, the 32nd structural unit, and the 33rd structural unit is preferably 0.30 mol% or more, and 0. It is more preferably 50 mol% or more, and further preferably 0.70 mol% or more.

In the monomer (a3), the content of the 32nd structural unit with respect to the total amount of the 31st structural unit, the 32nd structural unit, and the 33rd structural unit is preferably 90 mol% or less, preferably 80 mol% or less. It is more preferable that it is 75 mol% or less, and it is further preferable that it is 75 mol% or less.

In the monomer (a3), the content of the 33rd structural unit with respect to the total amount of the 31st structural unit, the 32nd structural unit, and the 33rd structural unit is preferably 0.30 mol% or more, and 0. It is more preferably 50 mol% or more, and further preferably 0.70 mol% or more.

In the monomer (a3), the content of the 33rd structural unit with respect to the total amount of the 31st structural unit, the 32nd structural unit, and the 33rd structural unit is preferably 10 mol% or less, preferably 6.0 mol. % Or less, more preferably 4.5 mol% or less.

The monomer (a3) may contain a structural unit that does not fall under any of the 31st structural unit, the 32nd structural unit, and the 33rd structural unit. However, the total content of the 31st structural unit, the 32nd structural unit, and the 33rd structural unit in the monomer (a3) is preferably 90% by mass or more, preferably 95% by mass. The above is more preferable, 98% by mass is further preferable, and 100% by mass is most preferable. Here, the structural unit constituting the monomer (a3) does not include the terminal structure (definition is as described above). The same applies to the monomer (a31) according to the first form and the monomer (a32) according to the second form described below.

Examples of the monomer (a3) include the following two preferable forms having different hydrophilicity. Hereinafter, these forms will be described as the monomer (a31) according to the first form and the monomer (a32) according to the second form. The monomer (a32) according to the second form is more hydrophilic than the monomer (a31) according to the first form.

In the monomer (a31) according to the first embodiment, the content of the 31st structural unit with respect to the total amount of the 31st structural unit, the 32nd structural unit, and the 33rd structural unit is 5.0 mol% or more. It is preferably 18 mol% or more, more preferably 25 mol% or more, and even more preferably 25 mol% or more.

In the monomer (a31) according to the first embodiment, the content of the 31st structural unit with respect to the total amount of the 31st structural unit, the 32nd structural unit, and the 33rd structural unit may be 50 mol% or less. It is preferably 40 mol% or less, more preferably 40 mol% or less.

In the monomer (a31) according to the first embodiment, the content of the 32nd structural unit with respect to the total amount of the 31st structural unit, the 32nd structural unit, and the 33rd structural unit may be 40 mol% or more. It is more preferably 50 mol% or more, and even more preferably 60 mol% or more.

In the monomer (a31) according to the first embodiment, the content of the 32nd structural unit with respect to the total amount of the 31st structural unit, the 32nd structural unit, and the 33rd structural unit may be 90 mol% or less. It is more preferably 80 mol% or less, still more preferably 75 mol% or less.

In the monomer (a31) according to the first embodiment, the content of the 33rd structural unit with respect to the total amount of the 31st structural unit, the 32nd structural unit, and the 33rd structural unit is 0.30 mol% or more. It is preferably 0.50 mol% or more, more preferably 0.70 mol% or more, and even more preferably 0.70 mol% or more.

In the monomer (a31) according to the first embodiment, the content of the 33rd structural unit with respect to the total amount of the 31st structural unit, the 32nd structural unit, and the 33rd structural unit may be 10 mol% or less. It is more preferably 6.0 mol% or less, still more preferably 4.5 mol% or less.

In the monomer (a32) according to the second embodiment, the content of the 31st structural unit with respect to the total amount of the 31st structural unit, the 32nd structural unit, and the 33rd structural unit may be 70 mol% or more. It is more preferably 80 mol% or more, and even more preferably 90 mol% or more.

In the monomer (a32) according to the second embodiment, the content of the 31st structural unit with respect to the total amount of the 31st structural unit, the 32nd structural unit, and the 33rd structural unit may be 98 mol% or less. It is preferably 97 mol% or less, and more preferably 97 mol% or less.

In the monomer (a3) according to the second embodiment, the content of the 32nd structural unit with respect to the total amount of the 31st structural unit, the 32nd structural unit, and the 33rd structural unit is 0.30 mol% or more. It is preferably 0.50 mol% or more, more preferably 0.70 mol% or more, and even more preferably 0.70 mol% or more.

In the monomer (a32) according to the second embodiment, the content of the 32nd structural unit with respect to the total amount of the 31st structural unit, the 32nd structural unit, and the 33rd structural unit may be 20 mol% or less. It is more preferably 15 mol% or less, still more preferably 10 mol% or less.

In the monomer (a32) according to the second embodiment, the content of the 33rd structural unit with respect to the total amount of the 31st structural unit, the 32nd structural unit, and the 33rd structural unit is 0.30 mol% or more. It is preferably 0.50 mol% or more, more preferably 0.70 mol% or more, and even more preferably 0.70 mol% or more.

In the monomer (a32) according to the second embodiment, the content of the 33rd structural unit with respect to the total amount of the 31st structural unit, the 32nd structural unit, and the 33rd structural unit may be 10 mol% or less. It is more preferably 6.0 mol% or less, still more preferably 4.5 mol% or less.

The monomer (a3) is preferably a block copolymer having a first block composed of the 31st structural unit, a second block composed of the 32nd structural unit, and a third block composed of the 33rd structural unit. It is more preferable that the monomer (a3) is a ternary block copolymer composed of a first block, a second block, and a third block (however, the terminal structure may be included as defined above). The monomer (a3) is a ternary in which the first block, the second block, and the third block are arranged in that order (that is, the second block exists between the first block and the third block). It is more preferably a block copolymer.

The preferred range of the weight average molecular weight of the monomer (a3) depends on the presence or absence of water solubility of the monomer (a3). When the monomer (a3) can be dissolved in a 0.1 M NaNO ₃ aqueous solution to prepare an aqueous solution containing 0.1% by mass of the monomer (a3), the weight average of the monomer (a3) The molecular weight is a pullulan-converted value measured by an aqueous GPC under the conditions shown below.

[Water-based GPC]
GPC device: GPC-101 (manufactured by Showa Denko KK))
Solvent: 0.1M NaNO ₃ aqueous solution Sample column: Shodex Volume Ohpak SB-806 HQ (8.0 mm ID x 300 mm) x 2
Reference column: Shodex Colon Ohpak SB-800 RL (8.0 mm ID x 300 mm) x 2
Column temperature: 40 ° C
Sample concentration: 0.1% by mass
Detector: RI-71S (manufactured by Shimadzu Corporation)
Flow rate: 1 ml / min
Molecular weight standard: Pullulan (P-5, P-10, P-20, P-50, P-100, P-200, P-400, P-800, P-1300, P-2500 (manufactured by Showa Denko KK) )))

In this case, the weight average molecular weight M _w (pullulan equivalent value) of the monomer (a3) is preferably 10,000 or more, more preferably 30,000 or more, and further preferably 50,000 or more. This is because the strength of the electrode is improved. Further, in this case, the weight average molecular weight M _w (pullulan equivalent value) of the monomer (a3) is preferably 300,000 or less, more preferably 200,000 or less, and further preferably 120,000 or less. This is because the dispersibility of the solid content in the electrode slurry described later is improved.

When it is impossible to dissolve the monomer (a3) in a 0.1 M NaNO ₃ aqueous solution to prepare an aqueous solution containing 0.1% by mass of the monomer (a3), the monomer (a3) is used. The weight average molecular weight of is a polystyrene-equivalent value measured by a solvent-based GPC under the following conditions.

[Solvent-based GPC]
GPC device: Waters GPC System e2695
Solvent: Tetrahydrofuran Column: SHODEX KF-806L x 2, SHODEX KF-G (manufactured by Showa Denko KK) Column temperature: 40 ° C.
Column temperature: 40 ° C
Sample concentration: 0.2% by mass
Detector: Waters 2414RI
Flow rate: 0.65 mL / min
Molecular weight standard: Polystyrene (Shodex Polystyrene STANDARD SL-105, SM-105 (manufactured by Showa Denko KK))

In this case, the weight average molecular weight M _w (polystyrene conversion value) of the monomer (a3) is preferably 10,000 or more, more preferably 20,000 or more, and further preferably 30,000 or more. This is because the strength of the electrode is improved. Further, in this case, the weight average molecular weight M _w (polystyrene equivalent value) of the monomer (a3) is preferably 200,000 or less, more preferably 150,000 or less, and further preferably 80,000 or less. This is because the dispersibility of the solid content in the electrode slurry described later is improved.

[Specific example of monomer (a3)]
The monomer (a3) is preferably, for example, a ternary block copolymer represented by the following formula (5).

In the formula (5), n: m: l = 5.0 to 98: 0.30 to 90: 0.30 to 4.5, n: m: l = 18 to 97: 0.50 to 80: 0. It is preferably 50 to 6.0, and more preferably n: m: l = 25 to 97: 0.70 to 75: 0.80 to 4.5. The preferred range of weight average molecular weight is as described above.

The first form of the compound represented by the above formula (5) is n: m: l = 5.0 to 50:40 to 90: 0.30 to 4.5 in the above formula (5). , N: m: l = 18-40: 50-80: 0.50-6, preferably n: m: l = 25-40: 60-75: 0.80-4.5. Is more preferable. When it is impossible to prepare an aqueous solution containing 0.1% by mass of the compound according to the first embodiment by dissolving it in a 0.1 M NaNO ₃ aqueous solution, the weight average molecular weight is 10,000 to 200,000 in terms of polystyrene, and 20,000 to 20,000. It is preferably 150,000, more preferably 30,000 to 80,000.

A specific example of the first embodiment includes a compound (a3-1) having n: m: l = 30: 69: 1.0 and Mw = 50,000 in the formula (5).

The second form of the compound represented by the above formula (5) is a compound represented by the above formula (5), and in the formula (5), n: m: l = 70 to 98: 0. .30 to 20: 0.30 to 10, preferably n: m: l = 80 to 97: 0.50 to 15: 0.50 to 6.0, and n: m: l = 90 to It is more preferable that 97: 0.70 to 10: 0.80 to 4.5 and Mw = 50,000 to 80,000. When it is possible to prepare an aqueous solution containing 0.1% by mass of the compound according to the second embodiment by dissolving it in a 0.1 M NaNO ₃ aqueous solution, the weight average molecular weight is 10,000 to 300,000 in terms of pullulan, and 30,000 to 200,000. It is preferably 50,000 to 120,000, and more preferably 50,000 to 120,000.

Specific examples of the second embodiment include the compound (a3-2) having n: m: l = 93: 6.0: 1.0 and Mw = 80,000 in the formula (5), and n: m. : L = 96: 1.0: 3.0, Mw = 80,000, and the compound (a3-3).

[Method for synthesizing monomer (a3)]
The method for synthesizing the monomer (a3) is not particularly limited, but can be obtained, for example, by ring-opening polymerization of the epoxide using an acid catalyst.

[1-4. Internal cross-linking agent (a4)]
The internal cross-linking agent (a4) does not correspond to the monomer (a3), has a plurality of independent ethylenically unsaturated bonds, and contains the monomers (a1), (a2), and (a3). It is a compound capable of forming a crosslinked structure in radical polymerization of a monomer. Examples of such a compound include divinylbenzene, ethylene glycol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, 2-hydroxy-3-acryloyloxypropyl methacrylate and the like.

[1-5. Other monomers (a5)]
The other monomer (a5) does not correspond to any of the monomers (a1) to (a4). The other monomer (a5) is a compound having an ethylenically unsaturated bond and a polar functional group, a surfactant having an ethylenically unsaturated bond (hereinafter, may be referred to as “polymerizable surfactant”), and the like. Examples thereof include compounds having an ethylenically unsaturated bond and a function as a silane coupling agent, but the present invention is not limited thereto.

The polar functional group preferably contains at least one of a hydroxy group and a cyano group. Examples of the monomer having an ethylenically unsaturated bond and a polar functional group include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl acrylate, and (meth) acrylonitrile. The copolymer (P) preferably contains a structural unit derived from an ethylenically unsaturated bond and a compound containing a hydroxy group, and more preferably has a structural unit derived from a (meth) acrylate having a hydroxy group. It is more preferable to contain a structural unit derived from 2-hydroxyethyl (meth) acrylate.

Examples of the polymerizable surfactant include compounds having an ethylenically unsaturated bond and having a function as a surfactant, and examples thereof include compounds represented by the following chemical formulas (6) to (9). ..

In formula (6), R ³ is preferably an alkyl group, and p is preferably an integer of 10 to 40. It is more preferable that R ³ has 10 to 40 carbon atoms, and it is further preferable that R ³ is a linear unsubstituted alkyl group having 10 to 40 carbon atoms.

In formula (7), R ⁴ is preferably an alkyl group, and q is preferably an integer of 10 to 12. It is more preferable that R ⁴ has 10 to 40 carbon atoms, and it is further preferable that R ⁴ is a linear unsubstituted alkyl group having 10 to 40 carbon atoms.

In formula (8), R ⁵ is preferably an alkyl group, and M ¹ is preferably NH ₄ or Na. It is more preferable that R ⁵ has 10 to 40 carbon atoms, and it is further preferable that R ⁵ is a linear unsubstituted alkyl group having 10 to 40 carbon atoms.

In formula (9), R ⁶ is preferably an alkyl group, and M ² is preferably NH ₄ or Na. It is more preferable that R ⁶ has 10 to 40 carbon atoms, and it is further preferable that R ⁶ is a linear unsubstituted alkyl group having 10 to 40 carbon atoms.

Examples of the compound having an ethylenically unsaturated bond and functioning as a silane coupling agent include vinyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, vinyltriethoxysilane, and γ-methacryloxypropyltriethoxysilane. And so on.

[1-6. Content of each structural unit in the copolymer (P)]
In the copolymer (P), the content of the second structural unit derived from the monomer (a2) is 1.0 part by mass or more with respect to 100 parts by mass of the first structural unit derived from the monomer (a1). It is preferably 1.5 parts by mass or more, and more preferably 3.0 parts by mass or more. This is because the mechanical stability of the copolymer (P) is improved. This is also because the peel strength of the electrode active material layer containing the copolymer (P) as an electrode binder is improved.

In the copolymer (P), the content of the second structural unit derived from the monomer (a2) is 30 parts by mass or less with respect to 100 parts by mass of the first structural unit derived from the monomer (a1). , 15 parts by mass or less, more preferably 7.5 parts by mass or less. This is to suppress gelation of the copolymer (P). This is also because the mechanical stability of the copolymer (P) is improved.

In the copolymer (P), the content of the third structural unit derived from the monomer (a3) is 0.010 parts by mass or more with respect to 100 parts by mass of the first structural unit derived from the monomer (a1). It is preferably 0.030 parts by mass or more, more preferably 0.15 parts by mass or more, and further preferably 0.65 parts by mass or more. This is because the peel strength of the electrode active material layer containing the copolymer (P) as the electrode binder is improved. Further, it is possible to reduce the DCR of the battery using the electrode containing the copolymer (P) as the electrode binder in the electrode active material layer.

In the copolymer (P), the content of the third structural unit derived from the monomer (a3) is 70 parts by mass or less with respect to 100 parts by mass of the first structural unit derived from the monomer (a1). , 40 parts by mass or less, more preferably 35 parts by mass or less. This is because the polymerization stability in radical polymerization is improved and the generation of coarse particles of the copolymer (P) is suppressed. This is also to suppress gelation of the copolymer (P).

The mass ratio of the first structural unit, the second structural unit, and the third structural unit to the copolymer (P) is preferably 80% by mass or more in total, and more preferably 85% by mass or more. , 90% by mass or more is more preferable. This is because the effect obtained by the present invention is further enhanced by increasing the content of these structural units.

When the copolymer (P) contains a fourth structural unit derived from the internal cross-linking agent (a4), the internal cross-linking agent (a4) is used with respect to 100 parts by mass of the first structural unit derived from the monomer (a1). The content of the derived fourth structural unit is preferably 0.050 parts by mass or more, more preferably 0.075 parts by mass or more, and further preferably 0.50 parts by mass or more. This is because the deterioration of the copolymer (P) can be suppressed, and the discharge capacity retention rate of the battery using the electrode containing the copolymer (P) as the electrode binder in the electrode active material layer can be improved.

When the copolymer (P) contains a structural unit derived from the internal cross-linking agent (a4), it is derived from the internal cross-linking agent (a4) with respect to 100 parts by mass of the first structural unit derived from the monomer (a1). The content of the fourth structural unit is 20 parts by mass or less, preferably 7.5 parts by mass or less, and more preferably 2.5 parts by mass or less. This is to suppress gelation of the copolymer (P).

[1-7. Glass transition point of copolymer (P)]
The glass transition point Tg of the copolymer (P) is obtained as a temperature differential of DSC by performing DSC measurement in a nitrogen gas atmosphere at a heating rate of 10 ° C./min using EXSTAR DSC / SS7020 manufactured by Hitachi High-Tech Science. The peak top temperature of the DDSC chart.

The glass transition point Tg of the copolymer (P) is preferably −30 ° C. or higher, more preferably −10 ° C. or higher, and even more preferably 0 ° C. or higher. This is because the cycle characteristics of the non-aqueous secondary battery using the copolymer (P) as the electrode binder are improved.

The glass transition point Tg of the copolymer (P) is preferably 100 ° C. or lower, more preferably 50 ° C. or lower, and even more preferably 30 ° C. or lower. This is because the adhesion of the electrode active material layer containing the copolymer (P) as the electrode binder to the current collector foil is improved.

<2. Method for synthesizing copolymer (P)>
The copolymer (P) can be obtained by copolymerizing a monomer containing the monomers (a1) to (a3). As the monomer, an internal cross-linking agent (a4) and another monomer (a5) may be copolymerized, if necessary. Here, the monomers used for synthesizing the copolymer (P) may be collectively referred to as the monomer (a). Examples of the polymerization method include emulsion polymerization of the monomer (a) in the aqueous medium (b). Other components used in the synthesis of the copolymer (P) by emulsion polymerization include, for example, a non-polymerizable surfactant (c), a basic substance (d), a radical polymerization initiator (e), and the like. Examples thereof include a chain transfer agent (f). Hereinafter, these components necessary for the synthesis of the copolymer (P) or may be used as needed, and the emulsion polymerization method will be described, but the monomer (a) will be described as described above. Therefore, it will not be described below.

[2-1. Aqueous medium (b)]
The aqueous medium (b) is water, a hydrophilic solvent, or a mixture thereof. Examples of the hydrophilic solvent include methanol, ethanol, isopropyl alcohol, N-methylpyrrolidone and the like. From the viewpoint of polymerization stability, the aqueous medium (b) is preferably water. As the aqueous medium (b), a water to which a hydrophilic solvent is added may be used as long as the polymerization stability is not impaired.

[2-2. Non-polymerizable Surfactant (c)]
In the emulsion polymerization of the monomer (a), a non-polymerizable surfactant (c) may be used. The surfactant (c) can improve the dispersion stability of the dispersion liquid (emulsion) during and / or after the polymerization. As the surfactant (c), it is preferable to use an anionic surfactant or a nonionic surfactant.

Examples of the anionic surfactant include alkylbenzene sulfonates, alkyl sulfates, polyoxyethylene alkyl ether sulfates, and fatty acid salts.

Examples of the nonionic surfactant include polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, polyoxyethylene polycyclic phenyl ether, polyoxyalkylene alkyl ether, sorbitan fatty acid ester, and polyoxyethylene sorbitan fatty acid ester.

The above-mentioned surfactant may be used alone or in combination of two or more.

[2-3. Basic substance (d)]
When the monomer (a) is emulsion-polymerized in the aqueous medium (b), the basic substance (d) may be added. By adding the basic substance (d), the acidic component contained in the monomer (a) can be neutralized and the pH can be adjusted. By adjusting the pH, the mechanical stability and chemical stability of the dispersion during and / or after emulsion polymerization can be improved.

The pH of the dispersion liquid at 23 ° C. may be appropriately adjusted depending on the specifications of the electrodes, the conditions for preparing the slurry described later, and the like, and is not limited, but is preferably 1.5 to 10, preferably 6.0 to 9. It is more preferably 0, and even more preferably 5.0 to 9.0. This is to suppress the sedimentation of the active material in the electrode slurry described later.

Examples of the basic substance (d) include ammonia, triethylamine, sodium hydroxide, lithium hydroxide and the like. These basic substances (d) may be used alone or in combination of two or more.

[2-4. Radical Polymerization Initiator (e)]
The radical polymerization initiator (e) used in the emulsion polymerization is not particularly limited, and known ones can be used. Examples of the radical polymerization initiator include persulfates such as ammonium persulfate and potassium persulfate; hydrogen peroxide; azo compounds; organic peroxides such as t-butylhydroperoxide, tert-butylperoxybenzoate and cumenehydroperoxide. Examples include oxides. Of these, persulfates and organic peroxides are preferable. In the present embodiment, a radical polymerization initiator and a reducing agent such as sodium bisulfite, longalit, and ascorbic acid may be used in combination during emulsion polymerization for redox polymerization.

The amount of the radical polymerization initiator added is preferably 0.10 part by mass or more, and more preferably 0.80 part by mass or more with respect to 100 parts by mass of the monomer (a). This is because the conversion rate of the monomer (a) to the copolymer (P) at the time of polymerization can be increased. The amount of the radical polymerization initiator added is preferably 3.0 parts by mass or less, and more preferably 2.0 parts by mass or less with respect to 100 parts by mass of the monomer (a). This is because the molecular weight of the copolymer (P) can be increased and the swelling rate of the electrode active material layer with respect to the electrolytic solution can be reduced.

[2-5. Chain transfer agent (f)]
The chain transfer agent (f) is used to adjust the molecular weight of the copolymer (P) in emulsion polymerization. Examples of the chain transfer agent (f) include n-dodecyl mercaptan, tert-dodecyl mercaptan, n-butyl mercaptan, 2-ethylhexylthioglycolate, 2-mercaptoethanol, β-mercaptopropionic acid, methyl alcohol, and n-propyl alcohol. Examples thereof include isopropyl alcohol, t-butyl alcohol and benzyl alcohol.

[2-6. Emulsification polymerization method]
Examples of the emulsion polymerization method include a method of emulsion polymerization while continuously supplying each component used for emulsion polymerization. The temperature of the emulsion polymerization is not particularly limited, but is, for example, 30 to 90 ° C, preferably 50 to 85 ° C, and even more preferably 55 to 80 ° C. Emulsion polymerization is preferably carried out with stirring. Further, it is preferable that the monomer (a) and the radical polymerization initiator are continuously supplied so as to be uniform in the reaction vessel.

<3. Binder for non-aqueous secondary battery electrodes ＞
The binder for a non-aqueous secondary battery electrode (or a non-aqueous secondary battery electrode binder; hereinafter, may be referred to as an “electrode binder”) according to the present embodiment contains the copolymer (P) described above. .. The electrode binder may contain other components, and may contain, for example, a polymer other than the copolymer (P), a surfactant, or the like.

Here, the electrode binder is composed of a component that remains without volatilizing in a process involving heating in the battery manufacturing process described later. Specifically, the components constituting the electrode binder remained after weighing 1 g of the mixture containing the electrode binder in an aluminum dish having a diameter of 5 cm and drying at 105 ° C. for 1 hour while circulating air in a dryer at atmospheric pressure. It is an ingredient.

The content of the copolymer (P) in the electrode binder is preferably 80% by mass or more, more preferably 90% by mass or more, further preferably 95% by mass or more, and 98% by mass. The above is more preferable. This is to increase the contribution of the copolymer (P) to the desired effect of the present invention.

<4. Binder composition for non-aqueous secondary battery electrodes>
In the binder composition for a non-aqueous secondary battery electrode of the present embodiment (hereinafter, may be referred to as a binder composition), the copolymer (P) is dispersed in the aqueous medium (B). In addition to these components, the binder composition may contain, for example, the above-mentioned components used in the synthesis of the copolymer (P). The binder composition may be a dispersion obtained by a method for synthesizing the copolymer (P), or may be obtained by dispersing the copolymer (P) obtained by a method other than emulsion polymerization in an aqueous medium (B). The dispersion may be obtained, or may be a dispersion obtained by another method.

[4-1. Aqueous medium (B)]
The aqueous medium (B) is water, a hydrophilic solvent, or a mixture thereof. Examples of hydrophilic solvents are as mentioned in the description of the aqueous medium (b) in the synthesis of the copolymer (P). The aqueous medium (B) may be the same as or different from the aqueous medium (b) used for the synthesis of the copolymer (P).

As the aqueous medium (B), the aqueous medium (b) used for the synthesis of the copolymer (P) may be used as it is, or the aqueous medium (b) may be configured by adding an aqueous solvent, or the copolymer (P) may be used. ) May be replaced with a new aqueous solvent after the synthesis of the aqueous medium (b). Here, the aqueous solvent to be added or replaced may have the same composition as the solvent used for the synthesis of the copolymer (P), or may have a different composition.

[4-2. Non-volatile content concentration of binder composition]
The non-volatile content concentration of the binder composition is preferably 20% by mass or more, more preferably 25% by mass or more, and further preferably 30% by mass or more. This is to increase the amount of the active ingredient contained in the binder composition. The non-volatile content concentration of the binder composition can be adjusted by the amount of the aqueous medium (B).

The non-volatile content concentration of the binder composition is preferably 80% by mass or less, more preferably 70% by mass or less, and further preferably 60% by mass or less. This is to suppress an increase in the viscosity of the binder composition and facilitate the production of a slurry described later.

<5. Slurry for non-aqueous secondary battery electrodes ＞
Next, a slurry for a non-aqueous secondary battery electrode (hereinafter, may be referred to as an “electrode slurry”) will be described in detail. The electrode slurry has a structure in which the copolymer (P) and the electrode active material are dispersed in an aqueous medium. In addition to these components, the electrode slurry may contain a thickener, a conductive auxiliary agent, the above-mentioned components used for synthesizing the copolymer (P), and the like.

[5-1. Content of copolymer (P)]
The content of the copolymer (P) is preferably 0.50 part by mass or more, and more preferably 1.0 part by mass or more with respect to 100 parts by mass of the electrode active material. This is to fully exhibit the effect of the copolymer (P).

The content of the copolymer (P) is preferably 5.0 parts by mass or less, more preferably 4.0 parts by mass or less, and 3.0 parts by mass with respect to 100 parts by mass of the electrode active material. More preferably, it is less than or equal to a portion. This is to increase the content of the electrode active material in the electrode active material layer produced by using the electrode slurry.

[5-2. Electrode active material]
The electrode active material is a material capable of inserting / desorbing ions such as lithium ions that serve as charge carriers. The ion serving as a charge carrier is preferably an alkali metal ion, more preferably a lithium ion, a sodium ion, or a potassium ion, and even more preferably a lithium ion.

When the electrode is a negative electrode, the electrode active material, that is, the negative electrode active material preferably contains at least one of a carbon material, a material containing silicon, and a material containing titanium. Examples of the carbon material used as the electrode active material include coke such as petroleum coke, pitch coke, and coal coke, carbonized organic polymer, artificial graphite, and graphite such as natural graphite. Examples of the material containing silicon include a simple substance of silicon and a silicon compound such as silicon oxide. Examples of the material containing titanium include lithium titanate and the like. These materials may be used alone, or may be mixed or combined.

The negative electrode active material preferably contains at least one of a carbon material and a material containing silicon, and more preferably contains a carbon material. This is because the copolymer (P) has a very large effect of improving the binding property between the electrode active materials and between the electrode active material and the current collector.

When the electrode is a positive electrode, the electrode active material, that is, the positive electrode active material, uses a substance having a higher standard electrode potential than the negative electrode active material. As the positive electrode active material, a lithium composite oxide containing nickel such as a Ni—Co—Mn-based lithium composite oxide, a Ni—Mn—Al based lithium composite oxide, and a Ni—Co—Al based lithium composite oxide. , Lithium cobalt oxide (LiCoO ₂ ), spinel-type lithium manganate (LiMn ₂ O ₄ ), olivine-type lithium iron phosphate, _TiS ₂ , MnO ₂ , MoO ₃ , V2 O ₅ , and the like. As the positive electrode active material, these substances may be used alone or in combination of two or more.

[5-3. Thickener]
Examples of the thickener include celluloses such as carboxymethyl cellulose (CMC), hydroxyethyl cellulose and hydroxypropyl cellulose, ammonium salts of celluloses, alkali metal salts of celluloses, polyvinyl alcohol, polyvinylpyrrolidone and the like. The thickener preferably contains at least one of carboxymethyl cellulose, an ammonium salt of carboxymethyl cellulose, and an alkali metal salt of carboxymethyl cellulose. This is because the electrode active material is easily dispersed in the electrode slurry.

The content of the thickener in the electrode slurry is preferably 0.50 part by mass or more, and more preferably 0.80 part by mass or more with respect to 100 parts by mass of the electrode active material. This is to improve the bondability between the electrode active materials and between the electrode active material and the current collector in the electrode active material layer produced by using the electrode slurry.

The content of the thickener in the electrode slurry is preferably 3.0 parts by mass or less, more preferably 2.0 parts by mass or less, and 1.5 parts by mass with respect to 100 parts by mass of the electrode active material. The following is more preferable. This is because the coatability of the electrode slurry is improved.

[5-4. Aqueous medium]
The aqueous medium is water, a hydrophilic solvent, or a mixture thereof. Examples of hydrophilic solvents are as mentioned in the description of the aqueous medium (b) in the synthesis of the copolymer (P). The aqueous medium contained in the electrode slurry may be the same as or different from the aqueous medium (B) contained in the binder composition or the aqueous medium (b) used for synthesizing the copolymer (P).

[5-5. Conductive aid]
As the conductive auxiliary agent, it is preferable to use carbon black, carbon fiber or the like. Examples of carbon black include furnace black, acetylene black, denka black (registered trademark) (manufactured by Denka Co., Ltd.), and Ketjen black (registered trademark) (manufactured by Ketjen Black International Co., Ltd.). Examples of the carbon fiber include carbon nanotubes and carbon nanofibers, and examples of the carbon nanotube include VGCF (registered trademark, manufactured by Showa Denko Co., Ltd.), which is a vapor phase carbon fiber.

[5-6. Properties of electrode slurry]
The non-volatile content concentration of the electrode slurry is preferably 20% by mass or more, more preferably 30% by mass or more, and further preferably 40% by mass or more. This is because the concentration of the active ingredient in the electrode slurry becomes high, and a sufficient amount of the electrode active material layer can be formed with a small amount of the electrode slurry. The non-volatile content concentration of the electrode slurry can be adjusted by adjusting the amount of the aqueous medium in the electrode slurry.

The non-volatile content concentration of the electrode slurry is preferably 85% by mass or less, more preferably 75% by mass or less, and further preferably 65% by mass or less. This is to maintain good coatability of the electrode slurry.

The viscosity of the electrode slurry is preferably 20000 mPa · s or less, more preferably 10,000 mPa · s or less, and further preferably 5000 mPa · s or less. This is because the applicability of the electrode slurry to the current collector is improved and the productivity of the electrodes is improved. The viscosity of the electrode slurry is greatly affected by the non-volatile content concentration of the electrode slurry and the type and amount of the thickener.

The pH of the electrode slurry at 23 ° C. may be appropriately adjusted depending on the specifications of the electrode, the production conditions, and the like, and is not limited, but is preferably 2.0 to 10, and more preferably 4.0 to 9.0. , More preferably 6.0 to 9.0. This is to improve the durability of the battery manufactured by using the electrode slurry.

[5-7. Method of manufacturing electrode slurry]
As a method for preparing the electrode slurry in the present embodiment, a binder composition, an electrode active material, a thickener if necessary, an aqueous medium if necessary, and a conductive auxiliary agent if necessary are required. A method of mixing with other components may be mentioned depending on the above, but the method is not limited to this. The order of the components to be added is not particularly limited and may be appropriately determined. Examples of the mixing method include a method using a mixing device such as a stirring type, a rotary type, and a shaking type.

<6. Non-aqueous secondary battery electrode ＞
The non-aqueous secondary battery electrode (hereinafter, may be referred to as “electrode”) according to the present embodiment includes a current collector and an electrode active material layer formed on the current collector. Examples of the shape of the electrode include a laminated body and a wound body, but the shape is not particularly limited. Further, the range of forming the electrode active material layer on the current collector is not particularly limited, and it may be formed on the entire surface of the current collector or may be formed on a part of the surface of the current collector. When the current collector is in the shape of a plate, foil, or the like, the electrode active material layer may be formed on both sides of the current collector, or may be formed on only one side.

[6-1. Current collector]
The current collector is preferably a metal sheet having a thickness of 0.001 mm or more and 0.5 mm or less, and examples of the metal include iron, copper, aluminum, nickel, and stainless steel. When the non-aqueous secondary battery electrode is the negative electrode of the lithium ion secondary battery, the current collector is preferably a copper foil.

[6-2. Electrode active material layer]
The electrode active material layer according to the present embodiment includes an electrode binder and an electrode active material. The electrode active material layer may contain a conductive auxiliary agent, a thickener and the like. The components listed here are as described above.

[6-3. Electrode manufacturing method]
As a method for manufacturing an electrode, for example, an electrode slurry is applied onto a current collector, dried to form an electrode active material layer, and then cut into an appropriate size.

The method of applying the electrode slurry onto the current collector is not particularly limited, but for example, the reverse roll method, the direct roll method, the doctor blade method, the knife method, the extrusion method, the curtain method, the gravure method, the bar method, and the dip method. Law, squeeze method, etc. can be mentioned. Among these, the doctor blade method, the knife method, or the extrusion method is preferably used in consideration of various physical properties such as the viscosity of the electrode slurry and the drying property. This is because it is possible to obtain an electrode active material layer having a smooth surface and a small variation in thickness.

The electrode slurry may be applied to only one side of the current collector or may be applied to both sides. When the electrode slurry is applied to both sides of the current collector, it may be applied sequentially on one side at a time or on both sides at the same time. Further, the electrode slurry may be continuously applied to the current collector or may be applied intermittently. The coating amount of the electrode slurry can be appropriately determined according to the design capacity of the battery, the composition of the electrode slurry, and the like. The coating amount of the electrode slurry depends on the properties of the electrode slurry, but is preferably 13 mg / cm ² or less (when coated on both sides, the coating amount per one side). This is because the occurrence of cracks on the electrode surface can be suppressed in the process of drying the electrode slurry.

By drying the electrode slurry applied on the current collector, an electrode active material layer is formed on the current collector. The method for drying the electrode slurry is not particularly limited, and for example, hot air, reduced pressure or vacuum environment, (far) infrared rays, and low temperature air can be used alone or in combination. The drying temperature and drying time of the electrode slurry can be appropriately adjusted depending on the concentration of non-volatile components in the electrode slurry, the amount of coating on the current collector, and the like. The drying temperature is preferably 40 ° C. or higher and 350 ° C. or lower, and more preferably 60 ° C. or higher and 100 ° C. or lower from the viewpoint of productivity. The drying time is preferably 1 minute or more and 30 minutes or less.

The electrode sheet on which the electrode active material layer is formed on the current collector may be cut in order to obtain an appropriate size and shape as an electrode. The method for cutting the electrode sheet is not particularly limited, but for example, a slit, a laser, a wire cut, a cutter, a Thomson, or the like can be used.

The electrode sheet may be pressed as needed before or after cutting the electrode sheet. As a result, the electrode active material is firmly bound to the current collector, and the electrode can be made thinner, so that the non-aqueous battery can be miniaturized. As a pressing method, a general method can be used, and it is particularly preferable to use a die pressing method or a roll pressing method. In the case of the die pressing method, the pressing pressure is not particularly limited, but is preferably 0.5 t / cm ² or more and 5 t / cm ² or less. In the case of the roll press method, the linear pressure is not particularly limited, but is preferably 0.5 t / cm or more and 5 t / cm or less. This is to suppress the insertion of charge carriers such as lithium ions into the electrode active material and the decrease in the desorption capacity while obtaining the above effects by the press.

<7. Non-water-based secondary battery ＞
A lithium ion secondary battery will be described as a preferred example of the non-aqueous secondary battery according to the present embodiment, but the battery configuration is not limited to that described here. The non-aqueous secondary battery according to the present embodiment has a positive electrode, a negative electrode, an electrolytic solution, and, if necessary, components such as a separator, housed in an exterior body, and is one of a positive electrode and a negative electrode. Alternatively, the electrodes produced by the above method are used for both. In the non-aqueous secondary battery according to the present embodiment, at least one of the positive electrode and the negative electrode contains the copolymer (P) in the electrode binder, but it is preferable that at least the negative electrode contains the copolymer (P).

[7-1. Electrolyte]
As the electrolytic solution, a non-aqueous liquid having ionic conductivity is used. Examples of the electrolytic solution include a solution in which an electrolyte is dissolved in an organic solvent, an ionic liquid, and the like, and the former is preferable. This is because a non-aqueous battery having a low manufacturing cost and a low internal resistance can be obtained.

As the electrolyte, an alkali metal salt can be used and can be appropriately selected depending on the type of the electrode active material and the like. Examples of the electrolyte include LiClO ₄ , LiBF ₆ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₆ , LiB ₁₀ Cl ₁₀ , _LiAlCl ₄ , LiCl, LiBr, LiB (C2H ₅ ). ₄ , CF ₃ SO ₃ Li, CH ₃ SO ₃ Li, LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, lithium aliphatic carboxylate and the like can be mentioned. Further, other alkali metal salts can also be used as the electrolyte.

The organic solvent that dissolves the electrolyte is not particularly limited, and is, for example, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), dimethyl carbonate (DMC), and fluoroethylene carbonate. (FEC), carbonic acid ester compounds such as vinylene carbonate (VC); nitrile compounds such as acetonitrile; carboxylic acid esters such as ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate and the like. These organic solvents may be used alone or in combination of two or more. Above all, it is preferable to use a combination of a linear carbonate solvent. Examples of the linear carbonate-based solvent include diethyl carbonate, dimethyl carbonate, and ethylmethyl carbonate.

[7-2. Exterior]
As the exterior body, for example, a laminated material of an aluminum foil and a resin film can be appropriately used, but the exterior body is not limited to this. The shape of the battery may be any shape such as a coin type, a button type, a sheet type, a cylindrical type, a square type, and a flat type.

In the following examples, as an example of the configuration of the present invention, a negative electrode of a lithium ion secondary battery and a lithium ion secondary battery are manufactured, and the negative electrode of the lithium ion secondary battery and the lithium ion secondary battery according to the comparative example are used. By comparison, the effect of the present invention is confirmed. The present invention is not limited thereto. Unless otherwise specified, the water used in the following Examples and Comparative Examples is ion-exchanged water.

<1. Synthesis of copolymer (P) and preparation of binder composition>
In each Example and each Comparative Example, the monomer (a), the surfactant (c), and the chain transfer agent (f) are mixed with water as an aqueous medium (b) in the amounts shown in Tables 1 and 2. , An emulsified monomeric emulsion was prepared. As the acrylic acid, an 80% by mass aqueous solution is used, and the amount of acrylic acid shown in the table is the amount of acrylic acid contained in the aqueous solution. Further, the amount of water added here was adjusted to 360 parts by mass in total with the amount of water contained in the acrylic acid aqueous solution.

Regarding the monomer (a3), the composition of the compound (a3-1), the compound (a3-2), and the compound (a3-3) in Tables 1 and 2 is as follows.

The compound (a3-1), the compound (a3-2), and the compound (a3-3) are all a block composed of a structural unit (10), a block composed of a structural unit (11), and a structural unit (12). The blocks consisting of are ternary block copolymers arranged in this order. The structures of the structural units (10), (11), and (12) are as shown below. The compound (a3-1) contains 30 mol% of the structural unit (10), 69 mol% of the structural unit (11), and 1.0 mol% of the structural unit (12), and has a polystyrene-equivalent weight average molecular weight of 50,000. be. The compound (a3-2) contains 93 mol% of the structural unit (10), 6.0 mol% of the structural unit (11), and 1.0 mol% of the structural unit (12), and has a weight average molecular weight in terms of pullulan. It is 80,000. The compound (a3-3) contains 96 mol% of the structural unit (10), 1.0 mol% of the structural unit (11), and 3.0 mol% of the structural unit (12), and has a weight average molecular weight in terms of pullulan. It is 80,000.

169 parts by mass of water was placed in a separable flask having a cooling tube, a thermometer, a stirrer, and a dropping funnel, and the temperature was raised to 75 ° C. In this separable flask, the above-mentioned monomer emulsion and an aqueous solution prepared by dissolving 2.2 parts by mass of potassium persulfate as a polymerization initiator (e1) in 48 parts by mass of water are stirred at 80 ° C. for 4 hours. While dropping, it was emulsion-polymerized. After dropping the monomeric emulsion and the aqueous potassium persulfate solution, the mixture in the separable flask was stirred at 80 ° C. for 60 minutes.

Next, 0.81 parts by mass of tert-butylperoxybenzoate (Kayabutyl B manufactured by Kayaku Akzo Corporation) and 0.52 parts by mass of ascorbic acid as the polymerization initiator (e2) were added to 8.1 parts by mass of water. The dissolved aqueous solution was added. Next, as a polymerization initiator (e3), an aqueous solution prepared by dissolving 2.3 parts by mass of tert-butyl hydroperoxide (Kayabutyl H-70 manufactured by Kayaku Akzo Corporation) in 15 parts by mass of water and Longalit 2.3. An aqueous solution in which a mass portion was dissolved in 15 parts by mass of water was stirred for 60 minutes while being added dropwise to carry out polymerization. Then, an aqueous emulsion of the copolymer (P) according to the example and an aqueous emulsion of the polymer (CP) according to the comparative example were obtained.

The obtained aqueous emulsion was cooled to room temperature. Then, in order to neutralize the aqueous emulsion, 19 parts by mass of 25% by mass of ammonia water and 155 parts by mass of water were added to the separable flask, and the binder composition containing the copolymer (P) according to the examples was added. , And a binder composition containing the polymer (CP) according to the examples were obtained. The amount of ammonia shown in Tables 1 and 2 indicates the amount of ammonia contained in the aqueous ammonia.

Tables 1 and 2 show the total amount of water used in the copolymer (P) synthesis step and the polymer (CP) synthesis step. The amount of water shown in Tables 1 and 2 includes not only water added alone but also water contained in the aqueous acrylic acid solution and aqueous ammonia, and water added together with a polymerization initiator and the like.

<2. Evaluation of copolymer (P), polymer (CP) and binder composition>
The binder compositions obtained in Examples and Comparative Examples, and the physical properties and performance evaluation of the batteries obtained using these binder compositions were carried out by the following methods. The evaluation results are shown in Tables 1 and 2.

[2-1. Glass transition point Tg of copolymer (P) and polymer (CP)]
The binder composition was cast on a polyethylene sheet, dried at 50 ° C. for 5 hours, and then vacuum dried at 50 ° C. for 1 hour under 98 kPa conditions to obtain a film having a thickness of 0.5 mm.
The obtained film was cut into 2 mm × 2 mm, sealed in an aluminum pan, and DSC measurement was performed using EXSTAR DSC / SS7020 manufactured by Hitachi High-Tech Science Co., Ltd. at a heating rate of 10 ° C./min in a nitrogen gas atmosphere. The peak top temperature of the DDSC chart obtained as the temperature differential of DSC was measured, and this temperature was defined as the glass transition point Tg (° C.) of the copolymer (P) and the polymer (CP). The measurement temperature range was −40 ° C. to 200 ° C.

[2-2. Non-volatile content concentration]
1 g of the binder composition was weighed on an aluminum dish having a diameter of 5 cm, dried at 105 ° C. for 1 hour at 1 atm (1013 hPa) while circulating air in a dryer, and the mass of the remaining components was measured. The mass ratio (mass%) of the above-mentioned components remaining after drying with respect to the mass (1 g) of the binder composition before drying was calculated as the non-volatile content concentration.

[2-3. Coarse grain amount]
The binder composition was sieved by 1 L using a wire mesh having a 300 mesh opening, and then the wire mesh was washed with ion-exchanged water to remove the liquid residue of the binder composition. The mass of the wire mesh after washing was measured at 1 atm (1013 hPa) and dried at 105 ° C. for 1 hour while circulating air in the dryer. The difference between the mass of the wire mesh after drying and the mass of the wire mesh used alone was calculated as the coarse grain amount (g / L).

<3. Evaluation of electrode and battery performance>
Using the binder compositions prepared in each Example and Comparative Example, a negative electrode and a lithium ion secondary battery were prepared and evaluated.

[3-1. Battery production]
[3-1-1. Fabrication of positive electrode]
_N _- _N- _{_} 50 parts by mass of methylpyrrolidone was added and further mixed to prepare a positive electrode slurry.

The positive electrode slurry was applied to both sides of an aluminum foil (positive electrode current collector) having a thickness of 15 μm by the direct roll method. The amount of the positive electrode slurry applied to the positive electrode current collector was adjusted so that the thickness after the roll press treatment described later was 125 μm per side.

The positive electrode slurry applied on the positive electrode current collector was dried at 120 ° C. for 5 minutes and pressed by a roll press (manufactured by Thunk Metal Co., Ltd., press load 5 tons, roll width 7 cm) to form a positive electrode active material layer. A positive electrode sheet was obtained. The obtained positive electrode sheet was cut out to a size of 50 mm × 40 mm, and a conductive tab was attached to prepare a positive electrode.

[3-1-2. Fabrication of negative electrode]
100 parts by mass of artificial graphite (G49, manufactured by Esai Shiho Technology Co., Ltd.) as the negative electrode active material, and 3.9 parts by mass of the binder composition prepared in each Example and Comparative Example (1.5 parts by mass as a non-volatile content). , And CMC (Carboxymethyl Cellulose-Sodium Salt, Sunrose (registered trademark) MAC500LC manufactured by Nippon Paper Chemicals Co., Ltd.) are mixed in an amount of 62 parts by mass, and 28 parts by mass of water is added to prepare a negative slurry. Obtained.

Negative electrode slurry was applied to both sides of a copper foil (negative electrode current collector) having a thickness of 10 μm by the direct roll method. The amount of the negative electrode slurry applied to the negative electrode current collector was adjusted so that the thickness after the roll press treatment described later was 170 μm per side.

The negative electrode slurry applied on the negative electrode current collector is dried at 90 ° C. for 10 minutes, pressed by a roll press (manufactured by Thunk Metal, press load 8 t, roll width 7 cm), and the negative electrode active material layer is placed on the current collector. Was formed to obtain a negative electrode sheet. The obtained negative electrode sheet was cut out to a size of 52 mm × 42 mm, and a conductive tab was attached to prepare a negative electrode.

[3-1-3. Battery production]
An aluminum-laminated exterior body (battery pack) with a separator (made of polyethylene, 25 μm) made of a polyolefin-based porous film interposed between the positive electrode and the negative electrode so that the positive electrode active material layer and the negative electrode active material layer face each other. ). An electrolytic solution was injected into the exterior body, vacuum impregnated, and packed with a vacuum heat sealer to prepare a lithium ion secondary battery for evaluation. The electrolytic solution is a solution 99 in which LiPF ₆ is dissolved at 1.0 mol / L in a mixed solvent of ethylene carbonate (EC) / ethylmethyl carbonate (EMC) / diethyl carbonate (DEC) = 30/50/20 (volume ratio). It was prepared by mixing 1 part by mass of vinylene carbonate with 1 part by mass.

[3-2. Evaluation of electrodes and batteries]
[3-2-1. Peeling strength of negative electrode active material layer (electrode performance)]
The peel strength of the negative electrode active material layer with respect to the current collector was measured as follows. The negative electrode sheet after pressing in the above negative electrode manufacturing step was cut into a size of 25 mm × 100 mm and used as a test piece. Using double-sided tape (NITTO TAPE (registered trademark) No. 5, manufactured by Nitto Denko KK) with the negative electrode active material layer on the test piece and a SUS plate with a width of 50 mm and a length of 200 mm, the center of the test piece and the center of the SUS plate. It was pasted so that it matches. The double-sided tape was attached so as to cover the entire range of the test piece.

After leaving the test piece and the SUS plate bonded together for 10 minutes, the negative electrode active material layer was peeled off by 20 mm in the length direction from one end of the test piece, and the test piece on the copper foil side was folded back 180 ° to this portion ( The copper foil side of the part of the test piece from which the negative electrode active material layer was peeled off) was grasped by the chuck on the upper side of the testing machine. Further, one end of the SUS plate from which the negative electrode active material layer was peeled off was grasped by the lower chuck. In that state, the copper foil was peeled off from the test piece at a speed of 100 ± 10 mm / min, and a graph of peeling length (mm) -peeling force (mN) was obtained. In the obtained graph, the average value (mN) of the peeling force at the peeling length of 10 to 45 mm was calculated, and the value obtained by dividing the average value of the peeling force by the width of the test piece of 25 mm was the peeling strength (mN / mN /) of the negative electrode active material layer. mm). In each of the Examples and Comparative Examples, peeling between the double-sided tape and the SUS plate and interfacial peeling between the double-sided tape and the negative electrode active material layer did not occur during the test.

[3-2-2. Cycle capacity retention rate under high temperature (battery performance)]
The cycle capacity retention rate of the battery under high temperature was repeated in the following steps (i) to (iv) under the condition of 45 ° C. Here, one cycle of a series of operations (i) to (iv) is defined as one cycle.
(I) Charge with a current of 1 C until the voltage reaches 4.2 V (constant current (CC) charge).
(Ii) Charge at a voltage of 4.2 V until the current reaches 0.05 C (constant voltage (CV) charge). (Iii) Let stand for 30 minutes.
(Iv) Discharge with a current of 1 C until the voltage reaches 2.75 V (constant current (CC) discharge).

The time integral value of the current in the steps (i) and (ii) is the charge capacity, and the time integral value of the current in the step (iv) is the discharge capacity. The discharge capacity in the first cycle and the discharge capacity in the 100th cycle were measured. 100 × (discharge capacity in the 100th cycle) / (discharge capacity in the first cycle) [%] was calculated as the cycle capacity retention rate under high temperature of the battery, and is shown in Tables 1 and 2.

[3-2-3. Internal resistance (DCR)]
The internal resistance (DCR (Ω)) test of the battery was carried out under the condition of 25 ° C. by the following procedure. A constant current charge of 0.2 C was performed from the rest potential to 3.6 V, and the charged state was set to 50% of the initial capacity (SOC 50%). Then, discharge was performed for 60 seconds at each current value of 0.2C, 0.5C, 1C and 2C. The DCR (Ω) at 50% SOC was determined from the relationship between these four types of current values (values per second) and voltage. The results are shown in Tables 1 and 2.

<4. Evaluation result>
Looking at the evaluation results of each example, since the amount of coarse particles in the binder composition is small in each of the examples, the copolymer (P) according to these examples can suppress the generation of coarse particles. I understand. In the evaluation of the electrodes, it can be seen that the electrodes according to any of the examples have high peel strength of the negative electrode active material layer. In the evaluation of the batteries, the batteries according to any of the embodiments have low internal resistance and high discharge capacity retention rate (excellent cycle characteristics).

In Comparative Example 1, a polymer derived from the monomer (a3) and having no third structural unit was synthesized. The peel strength of the negative electrode active material layer was low in the electrode manufactured by using the polymer according to Comparative Example 1 as the electrode binder, and the internal resistance of the battery manufactured by using this electrode was high.

In Comparative Example 2, a polymer containing an excess of a third structural unit derived from the monomer (a3) was synthesized, but gelation progressed, and an electrode and a battery using this polymer as an electrode binder could be produced. There wasn't.

In Comparative Example 3, a polymer containing no second structural unit derived from the monomer (a2) was synthesized. In the electrode prepared by using the polymer according to Comparative Example 3 as an electrode binder, the peel strength of the negative electrode active material layer was low.

In Comparative Example 4, a polymer containing an excess of the second structural unit derived from the monomer (a2) was synthesized, but gelation progressed, and an electrode and a battery using this polymer as an electrode binder could be produced. There wasn't.

In Comparative Example 5, a polymer containing an excess of the fourth structural unit derived from the internal cross-linking agent (a4) was synthesized, but gelation progressed, and an electrode and a battery using this polymer as an electrode binder could be produced. There wasn't.

As can be seen from the above results, according to the copolymer (P) having the configuration according to the present invention, the peel strength of the electrode active material layer with respect to the current collector is effectively improved in the non-aqueous secondary battery, and the battery It can contribute to the reduction of internal resistance and the improvement of cycle characteristics.

Claims

A polymer of a compound having an ethylenically unsaturated bond.
It has a first structural unit derived from the monomer (a1), a second structural unit derived from the monomer (a2), and a third structural unit derived from the monomer (a3); or , A first structural unit derived from the monomer (a1), a second structural unit derived from the monomer (a2), a third structural unit derived from the monomer (a3), and an internal cross-linking agent ( It has a fourth structural unit derived from a4), and
The monomer (a1) has an ethylenically unsaturated bond, has neither a hydroxy group nor a cyano group, has no polyoxyalkylene structure, and has a plurality of independent ethylenically unsaturated bonds. It is a nonionic compound that does not
The monomer (a2) is a compound having an ethylenically unsaturated bond and an anionic functional group, and has neither a polyoxyalkylene structure nor a plurality of independent ethylenically unsaturated bonds.
The monomer (a3) has a 31st structural unit represented by the following formula (1), a 32nd structural unit represented by the following formula (2), and a 33rd structural unit represented by the following formula (3). With structural units,
The second structural unit is included in an amount of 1.0 part by mass or more and 30 parts by mass or less with respect to 100 parts by mass of the first structural unit.
The third structural unit is contained in an amount of 0.010 parts by mass or more and 70 parts by mass or less with respect to 100 parts by mass of the first structural unit.
The content of the fourth structural unit with respect to 100 parts by mass of the first structural unit is 0 parts by mass or more and 20 parts by mass or less.
The internal cross-linking agent (a4) does not correspond to the monomer (a3), has a plurality of independent ethylenically unsaturated bonds, and has the monomer (a1), the monomer (a2), and the like. A copolymer characterized by being a compound capable of forming a crosslinked structure in radical polymerization of a monomer containing the monomer (a3).

(In the formula (2), R 1 is an alkyl group having 1 or more and 6 or less carbon atoms which may have a branch.)

(In formula (3), R 2 is a functional group having an ethylenically unsaturated bond.)
The monomer (a3) is
With respect to the total amount of the 31st structural unit, the 32nd structural unit, and the 33rd structural unit.
The 31st structural unit contains 5.0 mol% or more and 98 mol% or less.
The 32nd structural unit contains 0.30 mol% or more and 90 mol% or less.
The copolymer according to claim 1, which contains the 33rd structural unit in an amount of 0.30 mol% or more and 10 mol% or less.
The copolymer according to claim 1 or 2, wherein the monomer (a3) has a plurality of independent ethylenically unsaturated bonds in one molecule.
In the formula (3), R 2 is at least selected from the group consisting of a vinyloxy group, an allyloxy group, a (meth) acryloyl group, a (meth) acryloyloxy group, and -OCH 2 -CH 2 -CH 2 = CH 2 . The copolymer according to any one of claims 1 to 3, which has any one.
In the formula (3), R 2 is the copolymer according to any one of claims 1 to 4 represented by the following formula (4).

(In the formula (4), R 21 is an alkylene group having 1 to 5 carbon atoms which may have a branch, and R 22 is a vinyloxy group, an allyloxy group, a (meth) acryloyl group, and a (meth) acryloyloxy. It is one functional group selected from the group consisting of groups.)
The monomer (a3) has a first block made of the 31st structural unit, a second block made of the 32nd structural unit, and a third block made of the 33rd structural unit. The copolymer according to any one item.
One of claims 1 to 6, wherein the monomer (a3) contains 90% by mass or more in total of the 31st structural unit, the 32nd structural unit, and the 33rd structural unit in all the structural units. The copolymer according to.
The copolymer according to any one of claims 1 to 7, wherein the monomer (a1) does not have a polar functional group.
The copolymer according to any one of claims 1 to 8, wherein the monomer (a2) is a compound having at least one of a carboxy group and a sulfo group.
The copolymer according to any one of claims 1 to 9, which contains the first structural unit, the second structural unit, and the third structural unit in a total amount of 80% by mass or more.
The copolymer according to any one of claims 1 to 10, wherein the content of the fourth structural unit is 0.050 parts by mass or more with respect to 100 parts by mass of the first structural unit.
A binder composition for a non-aqueous secondary battery electrode in which the copolymer according to any one of claims 1 to 11 is dispersed in an aqueous medium.
A binder for a non-aqueous secondary battery electrode containing the copolymer according to any one of claims 1 to 11.
The binder according to claim 13, the electrode active material, and the aqueous medium are included.
The binder and the electrode active material are dispersed in an aqueous medium, and the binder is dispersed in the aqueous medium.
The aqueous medium is a slurry for a non-aqueous secondary battery electrode, which is one medium selected from the group consisting of water, a hydrophilic solvent, and a mixture containing water and a hydrophilic solvent.
A non-aqueous secondary battery electrode containing the binder according to claim 13.