JP2023182565A - Polymer, electrode for lithium ion secondary battery, and the lithium ion secondary battery - Google Patents

Abstract

To provide a polymer or the like that exhibits an excellent adhesive property and a cycle characteristic.SOLUTION: A polymer is for a binder for a lithium ion secondary battery, includes: a unit U1 derived from a (meth) acrylic single functional monomer M1; a unit U2 derived from a (meth) acrylic acid monomer M2; and a unit U3 derived from a monomer M3 optionally copolymerizable with the M1 and M2. A weight average of a MAX_EStateIndex (ave_MAX_EStateIndex) calculated by a RDkit(Release 2020.09.1) in response to the M1, M2, and M3 is 9.8 or more and 10.6 or less.SELECTED DRAWING: None

Description

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

Conventionally, the method for producing electrodes used in electrochemical devices such as lithium-ion secondary batteries involves applying a liquid composition containing an electrode active material with binders, thickeners, etc. on the surface of a current collector. For example, an electrode layer may be formed on the current collector by drying the current collector. In particular, it has been proposed to use graphite-based materials, silicon-based materials, or tin-based materials as negative electrode active materials for lithium-ion secondary batteries; Expansion and contraction occur, which tends to cause deformation of the electrode layer and isolation of the active material. Specifically, since the active material expands during charging and contracts during discharge, a force acts between the active materials to separate them during contraction, and the bond between the active materials and the conductive network are severed. Due to such a phenomenon, the cycle life of batteries tends to decrease, and in the prior art, various studies have been made from the viewpoint of the performance of binder materials. For example, in Patent Document 1, it is proposed to use a slurry for a negative electrode of a lithium ion secondary battery containing a binder containing 0.1 to 15% by weight of polymerized units of an ethylenically unsaturated carboxylic acid monomer and a predetermined material. ing.

International Publication No. 2011/037142

According to Patent Document 1, the adhesion strength inside the active material layer and the adhesion strength between the active material layer and the current collector, that is, the adhesion strength of the electrode, are improved, and furthermore, the expansion and contraction of the alloy-based active material is reduced by the carbon-based active material. It is said that it is possible to obtain a battery with less deterioration in life because it is relaxed by the substance and the internal resistance of the negative electrode is reduced. However, according to studies by the present inventors, it has been found that the technique described in Patent Document 1 still has room for improvement from the viewpoints of adhesiveness and cycle characteristics.

The present invention has been made in view of the problems of the above-mentioned prior art, and an object of the present invention is to provide a polymer etc. that exhibits excellent adhesiveness and cycle characteristics.

As a result of intensive research, the present inventors have found that the above problems can be solved by using a polymer having a predetermined composition and/or satisfying predetermined parameters, and have completed the present invention.

That is, the present invention includes the following aspects.
[1]
A polymer for a binder for lithium ion secondary batteries,
A unit U1 derived from a (meth)acrylic monofunctional monomer M1,
A unit U2 derived from (meth)acrylic acid monomer M2,
Optionally, a unit U3 derived from a monomer M3 copolymerizable with M1 and M2,
has
A polymer whose weight average value (ave_MAX_EStateIndex) of MAX_EStateIndex calculated by RDkit (Release 2020.09.1) for M1, M2, and M3 is 9.8 or more and 10.6 or less.
[2]
The polymer according to [1], wherein the weight average value of Chi3n (ave_Chi3n) calculated by the RDkit (Release 2020.09.1) is 1.2 or more and 2.6 or less.
[3]
The polymer according to [1] or [2], wherein the weight average value of EState_VSA10 (ave_EState_VSA10) calculated by the RDkit (Release 2020.09.1) is 4.6 or more and 8.9 or less.
[4]
The polymer according to any one of [1] to [3], wherein M1 includes a (meth)acrylic monofunctional monomer M1' represented by formula (1).
(In formula (1), R1 represents an organic group having 6 to 18 carbon atoms, and R2 represents a hydrogen atom or a methyl group.)
[5]
The polymer according to any one of [1] to [3], wherein M1 is at least one selected from the group consisting of nonyl acrylate, isodecyl acrylate, dodecyl acrylate, and ethoxyethoxyethyl acrylate.
[6]
A polymer for a binder for lithium ion secondary batteries,
A unit U1 derived from a (meth)acrylic monofunctional monomer M1,
A unit U2 derived from (meth)acrylic acid monomer M2,
Optionally, a unit U3 derived from a monomer M3 copolymerizable with M1 and M2,
has
The M1 includes at least one selected from the group consisting of nonyl (meth)acrylate, isodecyl (meth)acrylate, dodecyl (meth)acrylate, and ethoxyethoxyethyl (meth)acrylate,
In all units of the polymer, the content of U1 is 90% by mass or less, the content of U2 is 5% by mass or more and 40% by mass or less, and the content of U3 is 0. A polymer having a content of % by mass or more and 20% by mass or less.
[7]
The polymer according to [6], wherein M2 contains at least one selected from the group consisting of acrylic acid, methacrylic acid, and 2-acryloyloxyethyl-succinic acid.
[8]
The polymer according to [6] or [7], wherein the content of U1 in all units of the polymer is 40% by mass or more and 90% by mass or less.
[10]
The polymer according to any one of [1] to [9], wherein the polymer is a particulate polymer.
[11]
an active material;
The polymer according to any one of [1] to [10],
Electrodes for lithium ion secondary batteries, including:
[12]
A lithium ion secondary battery comprising the lithium ion secondary battery electrode according to [11].

According to the present invention, it is possible to provide a polymer etc. that exhibits excellent adhesiveness and cycle characteristics.

Hereinafter, an embodiment of the present invention (hereinafter also referred to as "this embodiment") will be described in detail. Note that the present invention is not limited to the following embodiment, and can be implemented with various modifications within the scope of the gist. In this specification, "(meth)acrylic" and "(meth)acrylate" are used to include both "methacrylic and acrylic" and "methacrylate and acrylate."

[Polymer]
The polymer according to the first aspect of the present embodiment (hereinafter also referred to as "first polymer") is a (meth)acrylic monofunctional polymer for a binder for lithium ion secondary batteries. A unit U1 derived from the monomer M1 (hereinafter also simply referred to as "M1"), a unit U2 derived from the (meth)acrylic acid monomer M2 (hereinafter also simply referred to as "M2"), and optionally, the above-mentioned M1 and a unit U3 derived from a monomer M3 copolymerizable with M2 (hereinafter also simply referred to as "M3"), and for the M1, M2, and M3, RDkit (Release 2020.09.1) The weighted average value of MAX_EStateIndex (ave_MAX_EStateIndex) calculated by is 9.8 or more and 10.6 or less. Since the first polymer is configured as described above, it can exhibit excellent adhesiveness and cycle characteristics.
The polymer according to the second aspect of the present embodiment (hereinafter also referred to as "second polymer") is a (meth)acrylic monofunctional polymer for a binder for lithium ion secondary batteries. It has a unit U1 derived from a monomer M1 and a unit U2 derived from a (meth)acrylic acid monomer M2, and the M1 is nonyl (meth)acrylate, isodecyl (meth)acrylate, dodecyl (meth)acrylate, and ethoxy. The polymer contains at least one member selected from the group consisting of ethoxyethyl (meth)acrylate, and the content of U1 is 90% by mass or less in all units of the polymer. The second polymer configured as described above can also exhibit excellent adhesiveness and cycle characteristics.
In addition, in this specification, unless otherwise specified, the following explanation regarding the polymer shall relate to both the first polymer and the second polymer. Moreover, the "polymer of this embodiment" will be explained as including the first polymer and the second polymer.

(ave_MAX_EStateIndex)
In the first polymer, the weight average value of MAX_EStateIndex (ave_MAX_EStateIndex) calculated by RDkit (Release 2020.09.1) for M1, M2, and M3 is 9.8 or more and 10.6 or less.
ave_MAX_EStateIndex is a parameter given as a weighted average value of the two-dimensional descriptor "MAX_EStateIndex" calculated for each of the monomers M1 to M3 constituting the polymer. The weight average value indicates the value expressed by the weight ratio of the monomers constituting the polymer, which is the descriptor obtained for each of the monomers M1 to M3 constituting the polymer, and is shown below. "Polymerization average value" has the same meaning. For example, if a polymer has one type of unit U1 (descriptor value of M1 = a1), one type of unit U2 (descriptor value of M2 = a2), and one type of unit U3 (descriptor value of M3) = a3) and the mass ratio is w1:w2:w3, the weight average value is given by "(a1 x w1 + a2 x w2 + a3 x w3)/(w1 + w2 + w3)". Here, a descriptor (molecular descriptor) is a characteristic quantity such as a molecule characteristic converted into a number. The two-dimensional descriptor referred to here is a topological descriptor, and is also called a topological index or connectivity index. A topological descriptor is a value calculated as an invariant to the graph structure, considering the molecular structure of a compound as a graph structure.
In this embodiment, descriptor calculation is performed by RDkit (Release 2020.09.1). RDkit is a typical open source library used in the field of chemoinformatics, which handles compound information on computers, and can be handled with python. In this embodiment, the version of RDkit is "Release 2020.09.1", and the numerical value calculated from this is used. For specific instructions on how to operate RDkit (Release 2020.09.1), you can also refer to the following URL (https://github.com/rdkit/neo4j-rdkit/issues/11).
Specifically, MAX_EStateIndex can be said to be a descriptor that expresses the electron distribution of atoms in the compound to be calculated, and it is implemented in the Chem.EState module in RDkit (Release 2020.09.1), so This allows calculation.
More specifically, MAX_EStateIndex can be calculated as follows. First, Estate is a numerical value that is calculated for a certain atom i in a molecule and expresses the electron distribution of that atom, and is hereinafter referred to as S _i . Si can be calculated using Formula 1 below.
(Here, Ii is the roughly approximated electronegativity of atom i, which is determined by the atomic species, and ΔIi is a perturbation term that takes into account the influence of atom j other than atom i, expressed by the following formula 2.)
(Here I _j is the electronegativity of atom j other than i, and r _ij is the distance between atom i and atom j.)
MAX_EStateIndex is a parameter calculated as the maximum value of the Estate calculated for each atom in the molecule as described above.
The value of MAX_EStateIndex tends to increase as the molecular size increases, and the value of MAX_EStateIndex tends to increase when the molecular chain is branched than when the molecular chain is linear. It is presumed that if the electron distribution is wide, a sufficient contact area with the electrode constituents such as the active material can be secured, and as a result, adhesiveness tends to improve. On the other hand, if ave_MAX_EStateIndex is too large, it is thought that a structure with no expansion (excessively few branches) is suggested as a polymer molecule. The present inventors have repeatedly studied the design of polymers from the above-mentioned viewpoints, and have found that a polymer designed to have an ave_MAX_EStateIndex value of 9.8 or more and 10.6 or less has excellent adhesion. It has been found that this material has excellent durability and cycle characteristics.
From the same viewpoint as above, ave_MAX_EStateIndex of the first polymer is 9.8 or more and 10.6 or less.
Further, from the same viewpoint as above, the ave_MAX_EStateIndex of the second polymer is preferably 9.8 or more and 10.6 or less.
ave_MAX_EStateIndex can be adjusted within the above range by, for example, calculating MAX_EStateIndex for each monomer constituting the polymer and then adjusting the blending ratio of each monomer.

(ave_Chi3n)
In the polymer of this embodiment, the weight average value of Chi3n (ave_Chi3n) calculated by RDkit (Release 2020.09.1) for the monomers constituting the polymer is 1.3 or more and 2. It is preferably 6 or less.
Chi3n can be said to be a descriptor expressing the atomic connectivity in the compound to be calculated, that is, it represents the bonding state of valence electrons. In RDkit (Release 2020.09.1), it is implemented in the Chem.EState module, so it can be calculated using this.
More specifically, Chi3n can be calculated as follows.
First, let the valence of a certain vertex be δ ^v , and calculate it using Equation 3 below.
(Here, Z ^v is the number of valence electrons, h is the number of bonded hydrogen atoms, and k is any natural number. In other words, δ is the number of bonds an atom that makes up the skeleton of a molecule has with other atoms. δ of the k-th atom in the molecular skeleton is expressed as δ _k , and δ _k indicates how many bonds there are in the k-th skeleton atom. δ ^v _k is the number of bonds in the k-th skeleton atom. It is the number of bonds of the k-th atom constituting the k-th atom, taking into account the valence. _{h k} means the number of hydrogen atoms bonded to the k-th atom, and the result of equation 3 is the number of hydrogen atoms bonded to the k-th atom. (matches the number of atoms other than hydrogen)
Next, subgraph connection term c is determined. c is calculated from all fragment types except for hydrogen atoms, and is calculated using the following formula 4 using the order m. Here, the order m is a positive integer starting from 0, and represents the number of atoms to be focused on at the same time. In other words, the order m is the dimension of the graph starting from 0. In other words, when m=0, it means focusing on one atom. Moreover, when m=3, it means that attention is paid to 4 atoms (when the arrangement of 4 atoms is regarded as 4 vertices, the number of edges obtained by connecting these is 3).
Furthermore, χ in the case of m=3 can be calculated using the following equation 5.
(Here, A means the number of atoms, excluding hydrogen atoms.)
The value of Chi3n tends to increase as the molecular size increases, and the value of Chi3n tends to increase when the molecular chain is branched than when the molecular chain is linear.
From the above viewpoint, ave_Chi3n is preferably 1.8 or more and 2.6 or less, more preferably 1.8 or more and 2.5 or less.
ave_Chi3n can be adjusted within the above range by, for example, calculating Chi3n for each monomer constituting the polymer and adjusting the blending ratio of each monomer.

(ave_EState_VSA10)
In the polymer of this embodiment, the weight average value of EState_VSA10 (ave_EState_VSA10) calculated by RDkit (Release 2020.09.1) for the monomers constituting the polymer is 4.6 or more and 8. It is preferably 9 or less.
EState_VSA10 can be said to be a descriptor that expresses the surface area (van der Waals surface area) of the compound to be calculated, and it is implemented in the Chem.EState module in RDkit (Release 2020.09.1), so this It can be calculated.
More specifically, Estate_VSA10 can be calculated as follows. That is, as described above, Estate can be calculated using Equations 1 and 2 above. Estate_VSA10 is a parameter that calculates Estate for each atom in the molecule, and is calculated as the total value of the van der Waals surface areas of atoms whose value is 9.17 or more and less than 15.00.
The value of EState_VSA10 tends to increase as the molecular size increases, and the value of EState_VSA10 tends to increase when the molecular chain is branched than when the molecular chain is linear.
From the above viewpoint, ave_EState_VSA10 is preferably 4.6 or more and 8.9 or less, more preferably 4.6 or more and 8.6 or less.
ave_EState_VSA10 can be adjusted within the above range by, for example, calculating EState_VSA10 for each monomer constituting the polymer and then adjusting the blending ratio of each monomer.

The descriptors (MAX_EStateIndex, Chi3n, and EState_VSA10) in this embodiment are all described in the document "Electrotopological State Indices for Atom Types: A Novel Combination of Electronic, Topological, and Valence State Information" (J. Chem. Inf. Comput. Sci. 1995, 35, 1039.).

(Unit U1)
The polymer of this embodiment has a unit U1 derived from a (meth)acrylic monofunctional monomer M1. M1 is a monomer having a structure derived from acrylic acid or methacrylic acid, and is distinguished from the (meth)acrylic acid monomer M2 described later in that it is monofunctional and does not have a carboxyl group. As used herein, "monofunctional" means a compound having only one acryloyl group or methacryloyl group in the molecule.
M1 is not particularly limited, but for example, methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, i-propyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, n-amyl (meth)acrylate, i-amyl (meth)acrylate, hexyl (meth)acrylate, 2-hexyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl acrylate, n-nonyl ( meth)acrylate, i-nonyl(meth)acrylate, n-decyl(meth)acrylate, i-decyl(meth)acrylate, dodecyl(meth)acrylate, hydroxymethyl(meth)acrylate, hydroxyethyl(meth)acrylate, ethoxyethoxy Ethyl (meth)acrylate (2-(2-ethoxyethoxy)ethyl (meth)acrylate), aminoethyl acrylate, dimethylaminoethyl acrylate, diethylaminoethyl acrylate, acrylamide, methacrylamide, glycidylmethacrylamide, N,N -butoxymethylacrylamide and the like.
These may be used alone or in combination of two or more.

From the viewpoint of adhesiveness and cycle characteristics, M1 preferably contains a (meth)acrylic monofunctional monomer M1' represented by formula (1) (hereinafter also simply referred to as "M1'").
(In formula (1), R1 represents an organic group having 6 to 18 carbon atoms, and R2 represents a hydrogen atom or a methyl group.)

R1 in formula (1) is not particularly limited, but includes, for example, an alkyl group having 6 to 18 carbon atoms or an alkoxy group having 6 to 18 carbon atoms.
Examples of the alkyl group having 6 to 18 carbon atoms include, but are not limited to, hexyl, heptyl, octyl, nonyl, decyl, dodecyl, and the like.
The alkoxy group having 6 to 18 carbon atoms is not particularly limited, but examples include ethoxyethoxyethyl group, methoxypolyethylene glycol group (monofunctional methoxypolyethylene glycol acrylate (commercially available products, such as Shin Nakamura Chemical Co., Ltd.) "AM-90G" etc.) from which the acryloyl group has been removed), phenoxydiethylene glycol group (phenoxydiethylene glycol acrylate (commercially available products include, for example, "AMP-20GY" manufactured by Shin-Nakamura Chemical Co., Ltd.) to an acryloyl group) ), acryloyl group from ethoxylated o-phenylphenol (ethoxylated o-phenylphenol acrylate (commercially available products include, for example, "A-LEN-10" manufactured by Shin-Nakamura Chemical Co., Ltd.) ), etc.
These may be used alone or in combination of two or more.
From the viewpoint of adhesiveness and cycle characteristics, M1' is preferably at least one selected from the group consisting of nonyl acrylate, isodecyl acrylate, dodecyl acrylate, and ethoxyethoxyethyl acrylate.

In the second polymer, M1 includes at least one selected from the group consisting of nonyl (meth)acrylate, isodecyl (meth)acrylate, dodecyl (meth)acrylate, and ethoxyethoxyethyl (meth)acrylate. By including such a unit derived from M1, the second polymer exhibits excellent adhesiveness and cycle characteristics.

(Content of unit U1)
In the second polymer, from the viewpoint of adhesion and cycle characteristics, the content of the unit U1 is 90% by mass or less in the total units of the polymer (relative to 100% by mass of all structural units of the polymer). . In the second polymer, M1 contains at least one member selected from the group consisting of nonyl (meth)acrylate, isodecyl (meth)acrylate, dodecyl (meth)acrylate, and ethoxyethoxyethyl (meth)acrylate. In addition, by setting the content of unit U1 to 90% by mass or less, it is possible to increase the content of U2 to 5% by mass or more, which provides excellent adhesiveness while maintaining the stability of the material. and can exhibit cycle characteristics. From the same viewpoint as above, in the second polymer, the content of the unit U1 is preferably 40% by mass or more and 90% by mass or less, more preferably 60% by mass or more and 85% by mass or less.

In addition, from the viewpoint of adhesion and cycle characteristics, the content of the unit U1 in the first polymer is 90% by mass or less in all units of the polymer (relative to 100% by mass of all constituent units of the polymer). It is preferably 40% by mass or more and 90% by mass or less, and even more preferably 60% by mass or more and 85% by mass or less.

(Unit U2)
The polymer of this embodiment has a unit U2 derived from a (meth)acrylic acid monomer M2 (hereinafter also simply referred to as "M2"). M2 is a monomer having a structure derived from acrylic acid or methacrylic acid, and has at least one carboxyl group.
Examples of M2 include, but are not limited to, acrylic acid, methacrylic acid, fumaric acid, itaconic acid, glutaconic acid, mono(2-acryloyloxyethyl) succinate, vinylbenzoic acid, and the like. These monomers may be salts.
These may be used alone or in combination of two or more.
Among the above, from the viewpoint of adhesiveness and cycle characteristics, M2 is preferably mono(2-acryloyloxyethyl) succinate or methacrylic acid.

(Content of unit U2)
In the second polymer, from the viewpoint of adhesion and cycle characteristics, the content of the unit U2 is 5% by mass or more and 40% by mass in all units of the polymer (relative to 100% by mass of all constituent units of the polymer). % or less. By setting the content of U2 to 5% by mass or more, excellent adhesiveness and cycle characteristics can be exhibited while maintaining the stability of the material. By setting the content of U2 to 40% by mass or less, the content of U1 can be ensured, and therefore excellent adhesiveness and cycle characteristics can be exhibited.
From the same viewpoint as above, in the second polymer, the content of the unit U2 is 10% by mass or more and 40% by mass or less in all units of the polymer (relative to 100% by mass of all structural units of the polymer). It is preferable that More preferably, it is 11% by mass or more and 40% by mass or less. However, the content of the unit U2 can be 5% by mass, 10% by mass, 11% by mass, 20% by mass, 30% by mass, or 40% by mass, and between any two of these values. may be within the range of
Moreover, in this embodiment, from the viewpoint of adhesiveness and storage stability, it is particularly preferable that the content of the unit U2 in the second polymer is 11% by mass or more and 20% by mass or less.

In addition, from the viewpoint of adhesion and cycle characteristics, the content of the unit U2 in the first polymer is 5% by mass or more in the total units of the polymer (relative to 100% by mass of all constituent units of the polymer). It is preferably 40% by mass or less, more preferably 10% by mass or more and 40% by mass or less. However, the content of the unit U2 in the first polymer can be any of 5% by mass, 10% by mass, 20% by mass, 30% by mass, and 40% by mass, and any of these values It may be within a range between the two.

(Unit U3)
The first polymer optionally has units U3 derived from monomer M3 copolymerizable with M1 and M2. M3 does not correspond to M1 and M2, and is not particularly limited as long as it can be copolymerized with M1 and M2.
M3 is not particularly limited, but includes, for example, (meth)acrylic polyfunctional monomers such as 1,9-nonanediol diacrylate, styrene, α-methylstyrene, p-methylstyrene, vinyltoluene, chlorostyrene, and divinylbenzene. and vinyl cyanide compounds such as acrylonitrile, methacrylonitrile, and α-chloroacrylonitrile.
These may be used alone or in combination of two or more.
The second polymer may also have a unit U3 derived from a monomer M3 copolymerizable with M1 and M2, and in that case, M3 may be used alone from the above-mentioned types. Often, two or more types may be used in combination.

(Content of unit U3)
In this embodiment, from the viewpoint of adhesiveness and cycle characteristics, the content of the unit U3 is 0% by mass or more and 20% by mass or less in all units of the polymer (relative to 100% by mass of all structural units of the polymer). It is preferably 0.1% by mass or more and 14% by mass or less, and still more preferably 5% by mass or more and 10% by mass or less.

In this embodiment, from the viewpoint of adhesiveness and cycle characteristics, the content of U1 is 40% by mass or more and 90% by mass or less, and the content of U2 is 5% by mass or more in all units of the polymer. It is preferable that the content of U3 is 40% by mass or less, and the content of U3 is 0% by mass or more and 20% by mass or less.

The content of each monomer (that is, the content of U1 to U3) can be specified as the charging ratio of each monomer, but for example, it can be specified by analyzing the polymer as shown below. You can also do it.
By subjecting a polymer to pyrolysis gas chromatography, it is possible to identify the monomer composition of the polymer. Next, by measuring the pH and estimating the degree of neutralization from the composition, the salt content range of each monomer unit can be estimated.

The Tg of the polymer of this embodiment is not particularly limited, but from the viewpoint of adhesiveness, it is preferably -60°C or more and 80°C or less. When Tg is 80° C. or less, it tends to be possible to prevent a reduction in the contact area with irregularities on the surface of the adherend due to excessive hardness and difficulty in deformation. Further, when Tg is -60°C or higher, depending on the monomer composition, the strength as a binder is prevented from becoming excessively low, and the shape tends to be easily maintained even after bonding.
From the same viewpoint as above, the Tg of the polymer of this embodiment is more preferably -40°C or more and 40°C or less.
Tg can be measured based on the method described in Examples below.
Furthermore, Tg can be adjusted within the above-mentioned range based on, for example, the type of each monomer constituting the polymer, the content of units U1 to U3, and the like.

[Polymer form]
The form of the polymer of this embodiment is not particularly limited, and can take any form. The arbitrary form may be, for example, a liquid polymer or a particulate polymer. In this embodiment, when the form of the polymer is a particulate polymer, the molecular weight tends to be large, and as a result, the cycle characteristics tend to be further improved.

[Binder composition]
The polymer of this embodiment is used as a binder for lithium ion secondary batteries. That is, the binder composition of this embodiment contains the polymer of this embodiment. The binder composition of this embodiment is not particularly limited as long as it contains the polymer of this embodiment as a binder component, and can contain various optional components. The optional component is not particularly limited, and may be, for example, a positive electrode active material or a negative electrode active material.

(Other optional ingredients)
Optional components that may be included in the binder composition of this embodiment may include an isothiazoline compound. In that case, the content of the isothiazoline compound is preferably 0.0001% by mass or more and 1.0% by mass or less with respect to 100% by mass of the binder composition of the present embodiment. When the above range is satisfied, hysteretic viscosity behavior with respect to shear force can be suppressed, and more stable coating properties tend to be exhibited. The isothiazoline compound is not particularly limited, and various known compounds can be used, such as 2-methyl-4-isothiazolin-3-one, 5-chloro-2-methyl-4-isothiazolin-3-one, 1 , 2-benzisothiazolin-3-one, 2-n-octyl 4-isothiazolin-3-one, 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one, 2-ethyl-4-isothiazoline -3-one, 4,5-dichloro-2-cyclohexyl-4-isothiazolin-3-one, 5-chloro-2-ethyl-4-isothiazolin-3-one, 5-chloro-2-t-octyl-4 -Isothiazolin-3-one, 4-chloro-2-n-octyl-4-isothiazolin-3-one, 5-chloro-2-n-octyl-4-isothiazolin-3-one, N-n-butyl-1 , 2-benzisothiazolin-3-one, N-butylbenzisothiazolin-3-one, N-methylbenzisothiazolin-3-one, N-ethylbenzisothiazolin-3-one, N-propylbenzisothiazolin-3-one, N-isobutylbenzisothiazolin-3-one, N-pentylbenzisothiazolin-3-one, N-isopentylbenzisothiazolin-3-one, N-hexylbenzisothiazolin-3-one, N-allylbenzisothiazolin-3-one , N-(2-butenyl)benzisothiazolin-3-one, and the like. Among these, 2-methyl-4-isothiazolin-3-one is preferred.
In addition, the binder composition of this embodiment can include an antifoaming agent as an optional component.
Examples of antifoaming agents include mineral oil-based, silicone-based, acrylic-based, and polyether-based antifoaming agents. When it contains an antifoaming agent, it tends to have better defoaming properties.
In this case, the types and blending ratios of optional components are not particularly limited.

[Method for producing polymer or binder composition]
The method for producing the polymer of this embodiment or the composition for an electrode binder for secondary batteries is not particularly limited, but for example, it may be produced by preparing a system containing the monomers described above and polymerizing it by a conventional method. be able to. Conditions such as stirring speed, polymerization temperature, reaction (polymerization) time, etc. during production are not particularly limited as long as the polymer or binder composition of this embodiment can be obtained. In this embodiment, an azo polymerization initiator, a peroxide polymerization initiator, a photopolymerization initiator, etc. that have good compatibility with each monomer and solvent are selected according to the monomers and solvent used. It can be selected as appropriate. Further, in order to increase the molecular weight Mw, it is preferable to carry out the reaction at a low temperature of about +40 to +70°C, and accordingly, it is preferable to use a polymerization initiator with a short half-life of 10 hours for practical purposes.

[Lithium ion secondary battery electrode and lithium ion secondary battery]
With the binder composition of this embodiment, an electrode for a lithium ion secondary battery can be manufactured, and a lithium ion secondary battery including the electrode for a lithium ion secondary battery can be manufactured. In other words, the lithium ion secondary battery of this embodiment includes the lithium ion secondary battery electrode of this embodiment, and the lithium ion secondary battery electrode includes an active material and the polymer of this embodiment. That is, the lithium ion secondary battery of this embodiment can be specified as containing the binder composition of this embodiment or the polymer of this embodiment.
The configuration of the lithium ion secondary battery of this embodiment is not particularly limited, but typical constituent members include a negative electrode, a negative electrode current collector, a positive electrode, a positive electrode current collector, a separator, and an electrolytic solution. The lithium ion secondary battery of this embodiment may be one in which at least one of the electrodes (negative electrode and positive electrode) is obtained using the binder composition of this embodiment. Whether each member contains the binder composition of this embodiment can be specified by whether or not the active material and the polymer of this embodiment are contained in the electrode.

When manufacturing a negative electrode using a binder composition, the negative electrode active material that can be used is not particularly limited, but includes, for example, a silicon-based active material and a tin-based active material in addition to a carbon-based active material.
Examples of carbon-based active materials include, but are not limited to, graphite, carbon fiber, coke, hard carbon, mesocarbon microbeads (MCMB), fired furfuryl alcohol resin (PFA), and conductive polymers (poly-p -phenylene, etc.).
Examples of silicon-based active materials include, but are not limited to, silicon, SiO _x (0.01≦x<2), alloys of silicon and transition metals, and the like.
Examples of the tin-based active material include, but are not limited to, Sn, SnOx (0<x<2), an alloy of tin and a transition metal, and the like.

When manufacturing a positive electrode for a secondary battery using a binder composition, the positive electrode active material that can be used is not particularly limited, but includes, for example, a lithium-containing composite oxide, a transition metal oxide, a transition metal fluoride, a transition metal sulfide, etc. can be mentioned.
Examples of the lithium-containing composite oxide include, but are not limited to, LiCoO ₂ , LiMnO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiXCoYSnZO ₂ , LiFePO ₄ , LiXCoYSnZO ₂ and the like.
Examples of transition metal oxides include, but are not limited to, MnO ₂ , MoO ₃ , V ₂ O ₅ , V ₆ O ₁₃ , Fe ₂ O ₃ , Fe ₃ O ₄ and the like.
Examples of the transition metal fluoride include, but are not limited to, CuF ₂ and NiF ₂ .
Examples of transition metal sulfides include, but are not limited to, TiS ₂ , TiS ₃ , MoS ₃ , and FeS ₂ .

[Lithium ion secondary battery electrode or lithium ion secondary battery manufacturing method]
The method for producing the electrode for a lithium ion secondary battery or the lithium ion secondary battery of this embodiment is not particularly limited, but may include mixing the binder composition of this embodiment, an active material, and optionally a thickener etc. Examples include applying a liquid composition to a current collector, heating it, and drying it to form a corresponding electrode, making the positive and negative electrodes face each other with a separator in between, and injecting an electrolyte and sealing. . Examples of the negative electrode current collector include, but are not limited to, copper foil, and examples of the positive electrode current collector include, but are not limited to, aluminum foil. The electrolytic solution is not particularly limited, but includes, for example, those obtained by dissolving an electrolyte such as LiClO ₄ , LiBF ₄ , LiPF ₆ in an organic solvent. Examples of organic solvents include, but are not limited to, ethers, ketones, lactones, nitriles, amines, amides, carbonates, chlorinated hydrocarbons, and representative examples include tetrahydrofuran and acetonitrile. , butyronitrile, propylene carbonate, ethylene carbonate, diethyl carbonate, etc., which may be used singly or as a mixture of two or more.

The coating method is not particularly limited, but any coater head such as a reverse roll coater, comma bar coater, gravure coater, or air knife coater can be used. The drying method is not particularly limited, and for example, drying by leaving, blow drying, hot air drying, infrared heating, far infrared heating, etc. can be used. The drying temperature is not particularly limited, but may be, for example, 60°C to 150°C.

The present embodiment will be described in more detail with reference to examples below, but the present embodiment is not limited to these examples in any way.

[Example 1]
100 parts by mass of ion-exchanged water was placed in a reactor, and the temperature was raised to 70° C. and maintained while stirring. To this, 0.5 parts by mass of sodium persulfate (NPS) and 0.5 parts by mass of sodium dodecyl sulfate (SDS) were added, and stirring was continued.
Next, 40 parts by mass of dodecyl acrylate (DA), 120 parts by mass of nonyl acrylate (NAA), 10 parts by mass of methacrylic acid (MAA), 20 parts by mass of mono-2-acryloyloxyethyl succinate (MAES), An emulsion was obtained by mixing and stirring 10 parts by mass of 1,9-nonanediol diacrylate (19ND), 1.0 parts by mass of SDS, and 200 parts by mass of ion-exchanged water. The obtained emulsion was dropped into the reactor over 2 hours, and stirring was continued while maintaining the internal temperature at 70°C. After the dropwise addition was completed, the temperature was maintained at 70° C. for another 2 hours to complete the polymerization.
After the polymerization was completed, 0.05 parts by mass of methylisothiazoline was added as an additive to 100 parts by mass of the solid content, and then filtration was performed using #200 mesh. Finally, a sodium hydroxide aqueous solution and ion-exchanged water were added to neutralize and adjust the pH to 7 and solid content to 30% by mass, thereby obtaining a binder composition containing a polymer. A portion of the binder composition before being neutralized was subjected to the storage stability evaluation described below.

[Calculation of MAX_EStateIndex, Chi3n, EState_VSA10, etc.]
MAX_EStateIndex, Chi3n and EState_VSA10 were calculated based on the chemical structural formula of the monomer used to manufacture the polymer. That is, each monomer was converted to SMILES notation (SMILES linear notation), and calculation processing was performed using RDkit (Release 2020.09.1).
As a result, the MAX_EStateIndex of DA, NAA, MAA, MAES, and 19ND used in Example 1 was calculated to be 10.7, 10.6, 9.6, 10.8, and 10.7, respectively.
Moreover, Chi3n of DA, NAA, MAA, MAES, and 19ND used in Example 1 was calculated to be 2.9, 2.2, 0.4, 1.3, and 2.6, respectively.
Furthermore, EState_VSA10 of DA, NAA, MAA, MAES, and 19ND used in Example 1 was calculated to be 4.8, 4.8, 4.8, 14.4, and 9.6, respectively.
Next, from the mass ratio of each monomer to the total amount of DA, NAA, MAA, MAES and 19ND and the MAX_EStateIndex value of each monomer, the weight average value of MAX_EStateIndex of the polymer obtained in Example 1 (ave_MAX_EStateIndex) was calculated. That is, ave_MAX_EStateIndex of the polymer in Example 1 was calculated as 10.6 from (20×10.7+60×10.6+5×9.6+10×10.8+5×10.7)/100.
Similarly to the above, when the weight average value of Chi3n (ave_Chi3n) and the weight average value of EState_VSA10 (ave_EState_VSA10) were calculated, they were calculated to be 2.2 and 6.0, respectively.
Following the above, the calculation results of MAX_EStateIndex, Chi3n and EState_VSA10 of each monomer obtained in each example are also shown in Table 1, and based on the monomer ratio of each example, the weight average value of MAX_EStateIndex (ave_MAX_EStateIndex), The results of calculating the weight average value of Chi3n (ave_Chi3n) and the weight average value of EState_VSA10 (ave_EState_VSA10) are shown in Table 2 below.

In Table 1 above, each monomer is abbreviated as follows.
DA: Dodecyl acrylate IDAA: Isodecyl acrylate NAA: Nonyl acrylate CBA: 2-[2-(ethyloxy)ethyloxy]ethyl acrylate ST: Styrene BD: Butadiene MAA: Methacrylic acid AA: Acrylic acid MAES: 2-Acryloyloxy Ethyl-succinic acid 19ND: 1,9-nonanediol diacrylate

[Tg measurement]
An appropriate amount of the polymer-containing binder composition obtained in Example 1 was placed in an aluminum dish and dried in a hot air dryer at 130°C for 30 minutes.
Approximately 17 mg of the dried film was packed into an aluminum container for measurement, and a DSC curve and a DDSC curve were obtained in a nitrogen atmosphere using a DSC measurement device (manufactured by Shimadzu Corporation, model number: DSC6220). Note that the measurements were performed using the following program.
(1st stage heating program)
The temperature was raised at a rate of 30°C per minute from the room temperature at the time of measurement. After reaching 220°C, it was maintained for 1 minute.
(Second stage temperature reduction program)
The temperature was lowered from 220°C at a rate of 30°C per minute. After reaching -50°C, it was maintained for 1 minute.
(3rd stage temperature increase program)
The temperature was raised from -50°C to 220°C at a rate of 15°C per minute. DSC and DDSC data were acquired during this third stage of temperature rise.
The intersection of the straight line extending the baseline of the obtained DSC curve toward the high temperature side and the tangent at the inflection point was defined as the glass transition temperature (Tg). Tg was measured in the same manner for the following Examples and Comparative Examples.

[Storage stability of binder composition before neutralization]
800 g of the binder composition before neutralization was placed in a 1 L plastic bottle and left in a constant temperature bath at 40° C. for 30 days. After 30 days, the plastic bottle was turned upside down and the presence or absence of sediment at the bottom of the plastic bottle was visually evaluated. An evaluation of △ or higher was considered to be a pass.
○: There is no precipitate △: There is precipitate, but the precipitate disappears after being turned upside down 5 times ×: The precipitate does not disappear

[Examples 2 to 16 and Comparative Example 2]
In each example, a binder composition containing a polymer was prepared in the same manner as in Example 1, except that the type of monomer component and the blending amount of the monomer component in Example 1 were changed as shown in Table 2. Prepared.

[Comparative example 1]
150 parts by mass of ion-exchanged water and 0.5 parts by mass of SDS were placed in a pressure-resistant reactor, and the temperature was raised to 80° C. and maintained while stirring.
Next, an initiator solution containing 0.5 parts by mass of NPS dissolved in 10 parts by mass of ion-exchanged water was added.
Furthermore, 110 parts by mass of butadiene, 82 parts by mass of styrene, 8 parts by mass of acrylic acid, 0.1 parts by mass of t-dodecyl mercaptan, 100 parts by mass of ion-exchanged water, and 0.5 parts by mass of SDS were mixed and stirred to form an emulsion. was prepared and added to the pressure reactor over a period of 2 hours following the initiator solution. After the addition was completed, the temperature was maintained at 85° C. for another 2 hours to complete the polymerization.
After the polymerization was completed, 0.05 parts by mass of methylisothiazoline was added as an additive to 100 parts by mass of the solid content, and then filtration was performed using #200 mesh. Finally, a sodium hydroxide aqueous solution and ion-exchanged water were added to adjust the pH to 7 and the solid content to be 40% by weight, thereby obtaining a binder composition containing a polymer.

[Comparative example 3]
A reactor was charged with 200 parts by mass of acetonitrile, 100 parts by mass of ion-exchanged water, 50 parts by mass of methacrylic acid (MAA), and 0.1 part by mass of pentaerythritol triallyl ether. After raising the liquid temperature to 60° C., 0.05 part by mass of V-65 (2,2′-azobis(2,4-dimethylvaleronitrile)) was added as a polymerization initiator. The polymerization reaction was continued while maintaining the internal temperature at 60°C, and cooling of the reaction solution was started 8 hours after the addition of the initiator. After the internal temperature had decreased to 25°C, lithium hydroxide/monohydrate was added. Then, 20 parts by mass of a powder of the compound was added. After the addition, stirring was continued at 25° C. for 10 hours to obtain a binder composition containing the polymer. The binder composition had a solids content of 19.1% and a pH of 9.5.

[Comparative example 4]
A reactor was charged with 200 parts by mass of acetonitrile, 100 parts by mass of ion-exchanged water, 50 parts by mass of acrylic acid (AA), and 0.1 part by mass of pentaerythritol triallyl ether. After raising the liquid temperature to 60°C, 0.05 parts by mass of V-65 was added as a polymerization initiator. The polymerization reaction was continued while maintaining the internal temperature at 60°C, and cooling of the reaction solution was started 8 hours after the addition of the initiator. After the internal temperature had decreased to 25°C, lithium hydroxide/monohydrate was added. Then, 20 parts by mass of a powder of the compound was added. After the addition, stirring was continued at 25° C. for 10 hours to obtain a binder composition containing the polymer. The binder composition had a solids content of 19.1% and a pH of 8.9.

<Preparation of coating liquid for negative electrode>
[Examples 1 to 15 and Comparative Examples 1 to 4]
To 2.0 parts by mass of the solid content of the obtained binder composition, 1.0 parts by mass of carboxymethyl cellulose (CMC) as a thickener component and 2.0 parts of acetylene black as a conductive additive were added as solid content. Parts by mass and 95.0 parts by mass of natural graphite as a negative electrode active material were added, ion-exchanged water was added thereto so that the solid content was 70% by mass, and kneading was performed for 10 minutes by mechanical stirring. Furthermore, while continuing kneading, ion-exchanged water was added to adjust the solid content to 55% by mass, thereby obtaining a negative electrode coating liquid.

[Example 16]
To 3.0 parts by mass of the solid content of the obtained binder composition, 1.0 parts by mass of carboxymethyl cellulose as a thickener component, 2.0 parts by mass of acetylene black as a conductive agent, and further a negative electrode active material were added. 82.0 parts by mass of natural graphite and 10.0 parts by mass of SiOx (0.8<x<1.1) were added as substances, and ion-exchanged water was added thereto so that the solid content was 70%, followed by mechanical stirring. Kneading was carried out for 10 minutes. Furthermore, while continuing kneading, ion-exchanged water was added to adjust the solid content to 55% by mass, thereby obtaining a negative electrode coating liquid.

<Preparation of negative electrode>
The above negative electrode coating solution was applied to one side of a copper foil using a die coater so that the thickness after drying was 60 μm, and then the coating film was dried at 60° C. for 60 minutes. After further drying at 120° C. for 3 minutes, a negative electrode was obtained by compression molding using a roll press machine.

<Preparation of coating liquid for positive electrode>
[Examples 1 to 14, 16 and Comparative Examples 1 to 4]
As a binder, PVDF-HFP (poly(vinylidene fluoride-co-hexafluoropropylene)) resin was dissolved in N-methylpyrrolidone (NMP) to prepare a PVDF-HFP solution. To 4.0 parts by mass of the solid content of the PVDF-HFP solution, 2.0 parts by mass of acetylene black as a conductive aid and 94 parts by mass of lithium cobalt oxide (LCO) as a positive electrode active material were added, and by mechanical stirring. Kneading was carried out for 10 minutes. Further, while continuing kneading, NMP was added to adjust the solid content to 60% by mass, thereby obtaining a positive electrode coating liquid.

[Example 15]
To 4.0 parts by mass of the solid content of the obtained binder resin for lithium ion batteries, 2.0 parts by mass of acetylene black was added as a conductive aid, and 94 parts by mass of lithium cobalt oxide (LCO) was added as a positive electrode active material. , Kneading was carried out for 10 minutes by mechanical stirring. Further, while continuing kneading, ion-exchanged water was added to adjust the solid content to 65% by mass, thereby obtaining a positive electrode coating liquid.

<Preparation of positive electrode>
Using the above coating solution for positive electrode, apply it to one side of aluminum foil with a die coater, adjusting the coating weight so that the capacity ratio is positive electrode / negative electrode = 1.0 / 1.1 with respect to the negative electrode. After that, the coating film was dried at 90° C. for 60 minutes. After further drying at 120° C. for 30 minutes, compression molding was performed using a roll press machine.

(electrode peel strength)
A test piece with a width of 2 cm and a length of 12 cm was cut out from the negative electrode obtained in Examples 1 to 14, 16 and Comparative Examples 1 to 4, or the positive electrode obtained in Example 15, and the current collector side of this test piece was cut out. The surface was attached to an aluminum plate with double-sided tape. In accordance with JIS Z 1522, a tape with a width of 18 mm (trade name "Cello Tape (registered trademark)" (manufactured by Nichiban)) was pasted on the electrode layer side of the test piece, and the tape was applied at a speed of 100 mm/min in a 180° direction. The strength when peeled was measured six times, and the average value (N/18 mm) was calculated as the peel strength. The larger this value is, the higher the adhesive strength between the current collector and the electrode layer is, and it can be evaluated that the electrode layer is difficult to peel off from the current collector. Specifically, the peel strength was evaluated based on the following criteria. A rating of B or higher was considered a pass.
A: 40N/m or more B: 30N/m or more and less than 40N/m C: 20N/m or more and less than 30N/m D: Less than 20N/m

(Cycle test)
A secondary battery was manufactured by the following method for a cycle test. For the evaluation, 2032-type coin batteries were fabricated at each level N=10. The positive and negative electrodes prepared in each example were placed facing each other, a separator (porous polyethylene membrane) was inserted between the electrodes, and LiPF ₆ was dissolved in ethylene carbonate: diethyl carbonate = 1:1 to a concentration of 1 mol/L. A battery for evaluation of a positive electrode or a negative electrode was prepared using the obtained electrolyte as an electrolyte.
For evaluation, first, the following initial charge/discharge test was conducted.
The evaluation battery was charged at a current of 0.1 C to 4.0 V (from approximately 0 V) in a 25° C. environment. After resting for 30 minutes, the battery was discharged to 3.0V at a current of 0.1C in an environment of 25°C. The procedure up to this point was used as an initial charge/discharge test.
After the above initial charge/discharge test, a cycle test was conducted using the following procedure. Constant current charging was performed at a current of 1.0 C to 4.2 V in an environment of 45° C., and after a 10 minute rest, the battery was discharged to 3.0 V at a current of 1.0 C. This charging and discharging was regarded as one cycle, and 500 cycles were performed, and the ratio of the discharge capacity at the 500th cycle to the discharge capacity at the 1st cycle was defined as the capacity retention rate, and the evaluation was made according to the following criteria. The larger this value is, the smaller the decrease in capacity due to repeated charging and discharging is.
The maximum and minimum values of N=10 were excluded, and the other average values were taken as the results for that level. The results were evaluated based on the following criteria. A rating of B or higher was considered a pass.
A: Capacity retention rate is 90% or more B: Capacity retention rate is 80% or more and less than 90% C: Capacity retention rate is 70% or more and less than 80% D: Capacity retention rate is less than 70%

Table 2 also shows the results of evaluating Examples 1 to 16 and Comparative Examples 1 to 4 as described above.

Note that a blank column in the monomer composition in Table 2 means that the corresponding monomer component was not blended.

Claims (12)

A polymer for a binder for lithium ion secondary batteries,
A unit U1 derived from a (meth)acrylic monofunctional monomer M1,
A unit U2 derived from (meth)acrylic acid monomer M2,
Optionally, a unit U3 derived from a monomer M3 copolymerizable with M1 and M2,
has
A polymer whose weight average value (ave_MAX_EStateIndex) of MAX_EStateIndex calculated by RDkit (Release 2020.09.1) for M1, M2, and M3 is 9.8 or more and 10.6 or less. The polymer according to claim 1, wherein the weight average value of Chi3n (ave_Chi3n) calculated by the RDkit (Release 2020.09.1) is 1.2 or more and 2.6 or less. The polymer according to claim 1, wherein the weight average value of EState_VSA10 (ave_EState_VSA10) calculated by the RDkit (Release 2020.09.1) is 4.6 or more and 8.9 or less. The polymer according to claim 1, wherein the M1 includes a (meth)acrylic monofunctional monomer M1' represented by formula (1).
(In formula (1), R1 represents an organic group having 6 to 18 carbon atoms, and R2 represents a hydrogen atom or a methyl group.) The polymer according to claim 1, wherein the M1 is at least one selected from the group consisting of nonyl acrylate, isodecyl acrylate, dodecyl acrylate, and ethoxyethoxyethyl acrylate. A polymer for a binder for lithium ion secondary batteries,
A unit U1 derived from a (meth)acrylic monofunctional monomer M1,
A unit U2 derived from (meth)acrylic acid monomer M2,
Optionally, a unit U3 derived from a monomer M3 copolymerizable with M1 and M2,
has
The M1 includes at least one selected from the group consisting of nonyl (meth)acrylate, isodecyl (meth)acrylate, dodecyl (meth)acrylate, and ethoxyethoxyethyl (meth)acrylate,
In all units of the polymer, the content of U1 is 90% by mass or less, the content of U2 is 5% by mass or more and 40% by mass or less, and the content of U3 is 0. A polymer having a content of % by mass or more and 20% by mass or less. The polymer according to claim 6, wherein the M2 contains at least one selected from the group consisting of acrylic acid, methacrylic acid, and 2-acryloyloxyethyl-succinic acid. The polymer according to claim 6, wherein the content of U1 in all units of the polymer is 40% by mass or more and 90% by mass or less. The polymer of claim 1, wherein the polymer is a particulate polymer. 7. The polymer of claim 6, wherein the polymer is a particulate polymer. an active material;
The polymer according to any one of claims 1 to 10,
Electrodes for lithium ion secondary batteries, including: A lithium ion secondary battery comprising the lithium ion secondary battery electrode according to claim 11.