Binder for electrode, slurry for electrode, electrode for lib, and lithium ion secondary battery

Abstract

To provide a binder for an electrode capable of improving cycle characteristics.SOLUTION: A binder for an electrode is a binder for an electrode, which contains a polymer having structural units (1) to (4) as repeating units, has a weight average molecular weight of 520,000 to 1,100,000, and has a creep displacement of 8% or more and 14% or less as determined by a nanoindentation test according to ISO14577-1. The repeating unit (1) is represented by the following formula (1).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to an electrode binder, an electrode slurry, an electrode for a LIB, and a lithium-ion secondary battery. [Background technology]

[0002] The components of lithium-ion secondary batteries (LIBs), such as electrodes and electrolytes, have a significant impact on battery performance. The electrodes, which are components, contain binders that bind the electrodes to the current collectors, and the binder also plays a decisive role in determining the performance of LIBs.

[0003] However, electrodes using silicon materials as the electrode active material undergo large volume changes during charge and discharge. As a result, the electrode itself is destroyed by repeated charge and discharge, resulting in a decrease in charge and discharge capacity and poor cycle characteristics. To prevent this, various binders have been investigated.

[0004] For example, Patent Document 1 discloses a binder for LIBs in which components containing monomer units derived from acrylic acid and monomer units derived from a specific compound are crosslinked with a specific crosslinking agent. Patent Document 2 also discloses a binder for LIB anodes containing a (meth)acrylic copolymer containing (aminoalkyl-alkoxysilane)-(meth)acrylic acid units as repeating units. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2015 / 163302 [Patent Document 2] Patent Publication No. 2021-063946 Summary of the Invention [Problem to be solved by the invention]

[0006] However, with the demand for higher performance LIBs, further improvements in cycle characteristics are required. An object of the present disclosure is to provide at least one of an electrode binder that can improve the cycle characteristics of LIBs and an electrode slurry containing the same. [Means for solving the problem]

[0007] In the present disclosure, electrode binders containing (meth)acrylic polymers have been investigated, focusing on the weight-average molecular weight and creep displacement. As a result, it has been found that the above-mentioned object can be achieved by controlling the weight-average molecular weight and creep displacement within specific ranges. That is, the present invention is as described in the claims, and the gist of the present disclosure is as follows.

[0008] [1] A polymer having a constitutional unit represented by formula (1), a constitutional unit represented by formula (2), a constitutional unit represented by formula (3), and a constitutional unit represented by formula (4) as repeating units, An electrode binder having a weight average molecular weight of 520,000 to 1,100,000 and a creep displacement of 8% or more and 14% or less as determined by a nanoindentation test in accordance with ISO14577-1.

[0009] [ka]

[0010] [ka] However, in formula (1) and formula (2), R 1 , R 2 each independently represents a hydrogen atom or a methyl group; M represents Na, K, or Li; n and m represent the number of repetitions, and n / m is greater than 0 and not greater than 0.25.

[0011] [ka] However, in formula (3), R 3 is a hydrogen atom, R 4 is a methylene group, an ethylene group, a propylene group, or a butylene group, l is the number of repetitions, and m / l is 0.8 or more and less than 4.0.

[0012] [ka] In equation (4), R 5 represents a hydrogen atom or a methyl group, L represents -O- or -NH-, R 6 is an alkylene group having 1 to 10 carbon atoms, -R 9 -OR 10 -, or -R 11 -NH-R 12 - represents a group represented by R 7 represents an alkyl group having 1 to 6 carbon atoms or an alkoxy group having 1 to 6 carbon atoms, and R 8 represents an alkyl group having 1 to 6 carbon atoms, and R 9 represents an alkylene group having 1 to 5 carbon atoms which may be substituted with a hydroxy group, and R 10 , R 11 , R 12 each independently represents an alkylene group having 2 to 5 carbon atoms, p represents the number of repetitions, and p / m is 0.001 or more and 0.1 or less.

[0013] [2] With respect to 100 mol% of the electrode binder, The structural unit represented by formula (1) is more than 0 mol% and 8 mol% or less, The structural unit represented by formula (2) is 48 mol% or more and 70 mol% or less, and The electrode binder according to the above [1], which contains the constitutional unit represented by formula (3) in a range of 23 mol % to 45 mol %.

[0014] [3] With respect to 100 mol% of the electrode binder, The electrode binder according to the above [1] or [2], which contains the constitutional unit represented by formula (4) in an amount of 0.1 mol % or more and 3.5 mol % or less. [4]R1 and R 2

[0023] The electrode binder according to any one of [1] to [3] above, wherein is a hydrogen atom.

[0015] [5] A slurry for an electrode, comprising an electrode active material, a solvent, and the electrode binder according to any one of [1] to [4] above.

[0016] [6] A LIB electrode comprising the electrode binder according to any one of [1] to [4] above.

[0017] [7] A lithium ion secondary battery comprising the LIB electrode according to [6] above. [Effects of the Invention]

[0018] According to the present disclosure, it is possible to provide at least one of an electrode binder that can improve the cycle characteristics of a LIB and an electrode slurry containing the same. DETAILED DESCRIPTION OF THE INVENTION

[0019] The present disclosure will be described below with reference to an example of an embodiment. The present disclosure includes any combination of the configurations and parameters disclosed herein, and also includes any combination of upper and lower limits of the ranges disclosed herein. In this specification, the symbol "to" includes both the upper and lower limits.

[0020] <Electrode binder> The electrode binder of this embodiment contains a polymer having, as repeating units, a structural unit represented by formula (1) and a structural unit represented by formula (2) (hereinafter also referred to as "structural unit (1)" and "structural unit (2)", respectively). That is, the electrode binder of this embodiment is an electrode binder containing a (meth)acrylic polymer. In this specification, (meth)acrylic acid means at least one of acrylic acid and methacrylic acid, and (meth)acrylate means at least one of acrylate and methacrylate.

[0021] [ka]

[0022] [ka] In formula (1) and formula (2), R 1 , R 2 each independently represents a hydrogen atom or a methyl group, and M represents Na, K, or Li. Furthermore, n and m represent the number of repetitions, and n / m is more than 0 and 0.25 or less, and more preferably 0.04 or more and 0.16 or less.

[0023] The electrode binder of the present embodiment contains a polymer having the structural unit (1) and the structural unit (2), and when formed into an electrode slurry, not only is the dispersibility of the electrode active material improved, but the adhesive strength between the electrode active material and the current collector is also improved.

[0024] The weight-average molecular weight (hereinafter also referred to as "Mw") of the electrode binder of this embodiment is 520,000 to 1,100,000, preferably 550,000 to 1,050,000, and more preferably 600,000 to 1,000,000. An electrode containing an electrode binder with an Mw of less than 520,000 as a binder is prone to electrode destruction due to cohesive failure. On the other hand, an electrode binder with an Mw of more than 1,100,000 cannot wet the electrode active material and the fine irregularities on the current collector surface. Therefore, an electrode containing such an electrode binder as a binder has low adhesive strength and is prone to electrode destruction due to adhesive failure.

[0025] In the present embodiment, Mw can be determined as a PEO / PEG equivalent value measured by gel permeation chromatography (GPC, for example, HLC-8320GPC, manufactured by Tosoh Corporation) under the following conditions. Column: TSKgel guardcolumn PW XL (6.0mmI.D.×4cm)+TSKgel G6000PW XL +TSKgel G4000PW XL +TSKgel G2500PW XL (7.8mmI.D.×30cm each) Detector: RI detector polarity(+) Eluent: 0.2M phosphate buffer (pH 7.0) / acetonitrile = 9 / 1 Flow rate: 1.0mL / min Injection volume: 100μL Column temperature: 40℃

[0026] The electrode binder of this embodiment has a creep displacement (hereinafter simply referred to as "creep displacement") determined by a nanoindentation test in accordance with ISO 14577-1 of 8% to 14%, preferably 9% to 14%, and more preferably 10% to 14%. If the creep displacement is less than 8%, the volume change of the current collector cannot keep up with the volume change of the electrode active material that occurs during charge and discharge. As a result, the electrode active material peels off from the current collector, making adhesion failure more likely. On the other hand, if the creep displacement exceeds 14%, the electrode itself deforms due to the volume change of the electrode active material that occurs during charge and discharge, making the electrode more likely to break.

[0027] In this embodiment, the creep displacement is determined by a nanoindentation test in accordance with ISO14577-1. A specific example of the nanoindentation test is a nanoindentation test using a drift test method under the following conditions. Measurement temperature: 25℃ Maximum load: 20mN Maximum load holding time: 5000ms Time to reach maximum load: 10s Push speed: 2mN / s

[0028] The creep displacement can be calculated from the creep strain obtained by the nanoindentation test using the following formula: Creep displacement (%) = {(h2-h1) / h1} x 100 In the above formula, h1 is the creep strain (μm) when the maximum load is reached, and h2 is the maximum value of creep strain (μm) during the maximum load holding time.

[0029] The measurement sample may be an electrode binder in the form of a 50 μm-thick cast film formed on copper foil, and a general nanoindenter (e.g., ENT-5, manufactured by ELIONIX) and a measuring indenter (shape: Berkovich) may be used as the measurement device.

[0030] Here, the main causes of electrode destruction are thought to be cohesive failure, which occurs when the electrode binder itself is destroyed, and adhesive failure, which occurs at the interface between the electrode binder and the electrode active material or current collector. Cohesive failure is electrode destruction caused by the electrode binder itself being destroyed and the electrode active material peeling off from the current collector. Adhesive failure is electrode destruction caused by peeling off at the interface between the electrode binder and the electrode active material or current collector.

[0031] As described above, the Mw and creep displacement of the electrode binder of this embodiment are both important components for preventing electrode destruction. When the electrode binder of this embodiment contains the above-described polymer and simultaneously satisfies the Mw and creep displacement requirements, the cycle characteristics are improved when the binder is used in a LIB.

[0032] The polymer preferably further has a structural unit represented by formula (3) (hereinafter also referred to as "structural unit (3)") as a repeating unit.

[0033] [ka] In equation (3), R 3 represents a hydrogen atom or a methyl group, and R 4 represents an alkylene group having 1 to 6 carbon atoms. Furthermore, l represents the number of repetitions, and m / l is 0.8 or more and less than 4.0, and preferably m / l is 1.06 or more and 3.1 or less. R 4 is, for example, a methylene group, an ethylene group, a propylene group or a butylene group, with an ethylene group being preferred. When the polymer contains the structural unit (3), the electrode binder of this embodiment improves its binding ability to the electrode active material and current collector, thereby further suppressing the occurrence of adhesive failure. In addition, the glass transition temperature (Tg) is lowered, improving flexibility in low-temperature environments, which in turn reduces the cohesive force of the electrode binder itself and further suppresses the occurrence of cohesive failure.

[0034] The electrode binder of this embodiment may contain the structural unit (1) in an amount of more than 0 mol%, 0.1 mol% or more, or 2 mol% or more, or 8 mol% or less, or 5 mol% or less, based on 100 mol% of the electrode binder of this embodiment. The electrode binder of this embodiment preferably contains the structural unit (1) in an amount of more than 0 mol% and 8 mol% or less, more preferably 0.1 mol% or more and 5 mol% or less, and even more preferably 2 mol% or more and 5 mol% or less.

[0035] The electrode binder of this embodiment may contain 48 mol% or more, 50 mol% or more, or 55 mol% or more of the structural unit (2) relative to 100 mol% of the electrode binder of this embodiment. The electrode binder of this embodiment preferably contains 48 mol% or more and 70 mol% or less of the structural unit (2), more preferably 50 mol% or more and 65 mol% or less of the structural unit (2), and even more preferably 55 mol% or more and 65 mol% or less of the structural unit (2).

[0036] The electrode binder of this embodiment may contain 23 mol% or more, 25 mol% or more, or 30 mol% or more of the structural unit (3), and may contain 45 mol% or less, or 40 mol% or less, based on 100 mol% of the electrode binder of this embodiment. The electrode binder of this embodiment preferably contains 23 mol% or more and 45 mol% or less of the structural unit (3), more preferably 25 mol% or more and 45 mol% or less of the structural unit (3), and even more preferably 30 mol% or more and 40 mol% or less of the structural unit (3).

[0037] The electrode binder of this embodiment may also be composed of the above-described polymer, in which case the total of the structural units (1) to (3) is 100 mol%. The electrode binder of this embodiment may also contain components other than the structural units (1) to (3). Therefore, the total of the structural units (1) to (3) may be 100 mol% or less, and may even be less than 100 mol%. The total of the structural units (1) to (3) is preferably greater than 71 mol%, more preferably greater than 85 mol%, and even more preferably greater than 93 mol%. The total of the structural units (1) to (3) is preferably greater than 71 mol% but less than 100 mol%, more preferably greater than 85 mol% but less than 100 mol%, and even more preferably greater than 93 mol% but less than 100 mol%.

[0038] By having each constituent unit in such a ratio, the viscosity of the electrode slurry is optimized. As a result, the electrode binder can wet even the fine irregularities on the electrode active material and current collector surfaces. This not only improves the adhesive strength between the electrode active material and the electrode binder, but also improves the dispersion stability of the electrode slurry, making it easier to form an electrode in which the electrode active material and the electrode binder are more uniformly dispersed. As a result, the occurrence of cohesive failure and adhesive failure is further suppressed.

[0039] The polymer preferably further has a structural unit represented by formula (4) (hereinafter also referred to as "structural unit (4)") as a repeating unit.

[0040] [ka] In equation (4), R 5 represents a hydrogen atom or a methyl group, L represents -O- or -NH-, and is preferably -NH-, and R 6 is an alkylene group having 1 to 10 carbon atoms, -R 9 -OR 10 -, or -R 11 -NH-R 12 - represents a group represented by R 7 represents an alkyl group having 1 to 6 carbon atoms or an alkoxy group having 1 to 6 carbon atoms, and R 8 represents an alkyl group having 1 to 6 carbon atoms, and R 9 represents an alkylene group having 1 to 5 carbon atoms which may be substituted with a hydroxy group, and R 10 , R 11 , R 12 each independently represents an alkylene group having 2 to 5 carbon atoms. Furthermore, p represents the number of repetitions, and p / m is 0.001 or more and 0.1 or less, and preferably p / m is 0.003 or more and less than 0.08.

[0041] By including a polymer having the structural unit (4) in the electrode binder of this embodiment, when the binder is made into an electrode slurry, the binder has improved adhesion to the electrode active material and current collector, thereby further suppressing the occurrence of adhesive failure. R 6 Examples of the alkylene group having 1 to 10 carbon atoms include a methylene group, an ethylene group, a propylene group, and a butylene group, with a propylene group being preferred. R 7 Examples of the alkyl group having 1 to 6 carbon atoms include a methyl group, an ethyl group, a propyl group, and a butyl group, and a methyl group is preferred. R 7 Examples of the alkoxy group having 1 to 6 carbon atoms include a methoxy group, an ethoxy group, a propoxy group, and a butoxy group, with a methoxy group or an ethoxy group being preferred, and an ethoxy group being more preferred. R 8is, for example, a methyl group, an ethyl group, a propyl group, or a butyl group, with a methyl group or an ethyl group being preferred, and an ethyl group being more preferred. R 9 is, for example, a methylene group, an ethylene group, a propylene group or a butylene group, with a propylene group being preferred. R 10 is, for example, a methylene group, an ethylene group, a propylene group or a butylene group, with a propylene group being preferred. R 11 is, for example, a methylene group, an ethylene group, a propylene group or a butylene group, with a propylene group being preferred. R 12 is, for example, a methylene group, an ethylene group, a propylene group or a butylene group, with a propylene group being preferred.

[0042] The electrode binder of this embodiment preferably contains the structural unit (4) in a range of 0.1 mol% to 3.5 mol% based on 100 mol% of the electrode binder of this embodiment. If the structural unit (4) is contained in a range of 0.1 mol% to 3.5 mol%, dispersibility in the electrode slurry state is improved, allowing the structural unit (4) to be present at the interface between the current collector foil and the active material particles in the electrode mixture layer, thereby improving adhesion between the electrode mixture layer and the current collector foil. The electrode binder of this embodiment preferably contains the structural unit (4) in a range of 0.1 mol% to 3 mol%, more preferably in a range of 0.1 mol% to 2 mol%, and even more preferably in a range of 0.2 mol% to 1.5 mol%.

[0043] The electrode binder of this embodiment may also be composed of the above-described polymer. In this case, the total of the structural units (1) to (4) is 100 mol%. The electrode binder of this embodiment may also contain components other than the structural units (1) to (4). Therefore, the total of the structural units (1) to (4) may be 100 mol% or less, and may even be less than 100 mol%. The total of the structural units (1) to (4) is preferably greater than 71.1 mol%, more preferably greater than 85 mol%, and even more preferably greater than 93 mol%. The total of the structural units (1) to (4) is preferably greater than 71.1 mol% but less than 100 mol%, more preferably greater than 85 mol% but less than 100 mol%, and even more preferably greater than 93 mol% but less than 100 mol%.

[0044] The electrode binder of this embodiment may contain, in addition to the structural units (1) to (4), structural units (1) to (4) having a crosslinked structure. The inclusion of the structural units (1) to (4) in a crosslinked state improves the strength of the electrode binder itself and its adhesiveness to the electrode active material and current collector. As a result, the occurrence of cohesive failure and adhesive failure is further suppressed.

[0045] The crosslinked structure is a structure in which at least two of the structural units (1) to (4) are chemically bonded by crosslinking with a crosslinkable monomer. The method for forming the crosslinked structure may be any method that forms a chemical bond between two or more of the structural units (1) to (4) via the crosslinkable monomer. For example, such a method may involve polymerizing the monomers of the structural units (1) to (4) in the presence of the crosslinkable monomer, and polymerizing a composition containing the crosslinkable monomer and the monomers of the structural units (1) to (4).

[0046] The crosslinkable monomer is not particularly limited as long as it is a monomer having a structure that can chemically bond at least two of the structural units (1) to (4) by crosslinking.

[0047] The crosslinkable monomer may be, for example, a monomer having an ethylenically unsaturated bond. Examples of the monomer having an ethylenically unsaturated bond include one or more selected from the group consisting of (poly)ethylene glycol di(meth)acrylate, (poly)propylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, 2-(dimethylamino)ethyl (meth)acrylate, and pentaerythritol tetra(meth)acrylate. The crosslinkable monomer may also be a (meth)acrylic acid derivative having an alkoxysilyl group, obtained by modifying (meth)acrylic acid with a silane coupling agent, for example.

[0048] Examples of the silane coupling agent include one or more selected from the group consisting of 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, N-2(aminoethyl)3-aminopropyltrimethoxysilane, N-2(aminoethyl)3-aminopropyltriethoxysilane, N-phenyl-3-aminopropyltrimethoxysilane, 3-aminopropylmethyldimethoxysilane, 3-aminopropylmethyldiethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, and 3-glycidoxypropyltriethoxysilane, and 3-aminopropyl One or more selected from the group consisting of trimethoxysilane, 3-aminopropyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, N-2(aminoethyl)3-aminopropyltrimethoxysilane, N-2(aminoethyl)3-aminopropyltriethoxysilane, 3-aminopropylmethyldimethoxysilane, 3-aminopropylmethyldiethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, and 3-glycidoxypropyltriethoxysilane are preferred, and at least one of 3-aminopropyltriethoxysilane and 3-glycidoxypropyltrimethoxysilane is more preferred.

[0049] The crosslinkable monomer increases the cohesive strength of the electrode binder while decreasing its flexibility. To maintain flexibility, the amount of the crosslinkable monomer added is preferably 7 mol % or less, more preferably 1 mol % or less, and even more preferably 0 mol % to 7 mol %, more than 0 mol % to 7 mol %, or more than 0 mol % to 1 mol % relative to 100 mol % of the electrode binder.

[0050] When the electrode binder of this embodiment is made of a polymer, the polymer may be considered to be 100 mol %. On the other hand, when the electrode binder of this embodiment contains a crosslinked structure, the total of the polymer and the crosslinked structure may be considered to be 100 mol %.

[0051] The electrode binder of this embodiment can be used as a binder for secondary battery electrodes and further as a binder for LIB electrodes. The electrode binder of this embodiment can be used as at least one of a positive electrode binder and a negative electrode binder, and is preferably used as a negative electrode binder, and more preferably used as a LIB negative electrode binder.

[0052] <Method for manufacturing electrode binder> The electrode binder of this embodiment can be produced, for example, by a polymerization step of polymerizing a composition in which at least a monomer having the structural unit (1) and a monomer having the structural unit (2) are dissolved in an aqueous medium at a temperature of 50°C or higher and 100°C or lower in the presence of a radical polymerization initiator.

[0053] Examples of the monomer having the structural unit (1) include at least one of acrylic acid and methacrylic acid, and acrylic acid is preferred.

[0054] Examples of the monomer having the structural unit (2) include one or more selected from the group consisting of sodium acrylate, sodium methacrylate, potassium acrylate, potassium methacrylate, lithium acrylate, and lithium methacrylate, and sodium acrylate is preferred. The monomer of the structural unit (2) may be a monomer of the structural unit (1) modified with an alkali metal compound.

[0055] The aqueous medium may be water or a mixed solvent of water and a water-soluble organic solvent, preferably water. The water-soluble organic solvent may be, for example, one or more selected from the group consisting of lower alcohols, amides, ketones, and ethers.

[0056] Preferred water-soluble organic solvents include one or more selected from the group consisting of methanol, ethanol, 1-propanol, 2-propanol (isopropanol), 1-butanol, 2-butanol, t-butanol, dimethylformamide, acetone, and 1,4-dioxane, and further include at least one of ethanol and 2-propanol (isopropanol), and further include ethanol.

[0057] The composition to be subjected to the polymerization step may contain a monomer having the structural unit (3) dissolved therein. Examples of the monomer having the structural unit (3) include one or more selected from the group consisting of 2-hydroxymethyl acrylate, 2-hydroxymethyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, 2-hydroxybutyl acrylate, and 2-hydroxybutyl methacrylate, and 2-hydroxyethyl acrylate is preferred.

[0058] The composition to be subjected to the polymerization step may have a silane coupling agent dissolved therein. The silane coupling agent reacts with a monomer having the structural unit (1) to form a monomer having the structural unit (4). Examples of the silane coupling agent include one or more selected from the group consisting of 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, N-2(aminoethyl)3-aminopropyltrimethoxysilane, N-2(aminoethyl)3-aminopropyltriethoxysilane, N-phenyl-3-aminopropyltrimethoxysilane, 3-aminopropylmethyldimethoxysilane, 3-aminopropylmethyldiethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, and 3-glycidoxypropyltriethoxysilane. 3-aminopropyltrimethoxysilane is particularly preferred.

[0043] One or more selected from the group consisting of N-(2-aminoethyl)-3-aminopropyltriethoxysilane, 3-aminopropyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, N-2(aminoethyl)-3-aminopropyltriethoxysilane, 3-aminopropylmethyldimethoxysilane, 3-aminopropylmethyldiethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, and 3-glycidoxypropyltriethoxysilane are preferred, 3-aminopropyltriethoxysilane or 3-glycidoxypropyltrimethoxysilane is more preferred, and 3-aminopropyltriethoxysilane is even more preferred.

[0059] The radical polymerization initiator may be at least one selected from the group consisting of persulfates such as potassium persulfate, azos such as azobisisobutyronitrile, and peroxides such as benzoyl peroxide, with potassium persulfate being preferred.

[0060] The polymerization temperature in the polymerization step is 50°C or higher and 100°C or lower, preferably 60°C or higher and 90°C or lower.

[0061] A preferred polymerization method in the polymerization step is to dropwise add a mixed solution of at least a monomer having the structural unit (1), a monomer having the structural unit (2), an aqueous medium, and a radical polymerization initiator to water heated to the polymerization temperature, thereby allowing the polymerization reaction to proceed stably and producing a polymer having a uniform composition.

[0062] The polymerization time in the polymerization step may be from 1 hour to 24 hours, and is preferably from 3 hours to 15 hours.

[0063] <Slurry for electrodes> The electrode slurry of the present embodiment may be a slurry containing the electrode binder of the present embodiment, or may further be a slurry containing the electrode binder of the present embodiment, an electrode active material, and an aqueous medium, and is preferably a slurry containing the electrode binder of the present embodiment, an electrode active material, a conductive assistant, and an aqueous medium.

[0064] The content of the electrode binder in the electrode slurry of this embodiment is preferably 1% by mass or more and 12% by mass or less, or 2% by mass or more and 8% by mass or less, expressed as the content of the electrode binder relative to the total mass (hereinafter also referred to as "solid content") of the electrode binder, electrode active material, and conductive assistant in the electrode slurry.

[0065] By ensuring that the content of the electrode binder in the electrode slurry is within the above range, the content of the electrode active material is such that the battery capacity can be ensured. Furthermore, the adhesive strength between the electrode active material and the current collector is improved. This makes it difficult for the electrode active material to peel off from the current collector, further improving the cycle characteristics.

[0066] The electrode active material contained in the electrode slurry of this embodiment may be either a positive electrode active material or a negative electrode active material, preferably a negative electrode active material, and more preferably a negative electrode active material containing a silicon material. Since the negative electrode active material containing a silicon material undergoes a large volume change during charge and discharge, the electrode binder of this embodiment is particularly effective in improving cycle characteristics.

[0067] Examples of the negative electrode active material containing a silicon material include a negative electrode active material containing at least one of Si and a Si alloy (hereinafter collectively referred to as "Si compound") and a carbon material.

[0068] A Si alloy is a metal composed of Si and elements other than Si. Examples of elements contained in a Si alloy other than Si include elements of groups 2 to 15 of the periodic table.

[0069] The carbon material may be, for example, one or more selected from the group consisting of graphite, natural graphite, and artificial graphite.

[0070] The negative electrode active material preferably has an average particle size (D50) of 1 μm or more and 40 μm or less. The particle size (D50) of the Si compound contained in the negative electrode active material is preferably 0.01 μm or more and 5 μm or less, more preferably 0.01 μm or more and 1 μm or less, and even more preferably 0.05 μm or more and 0.6 μm or less. The particle size (D50) is the volume average particle size measured with a laser particle size analyzer. By having the particle size of the Si compound within the above range, the decrease in the initial capacity and initial efficiency of the battery due to surface oxidation of the Si compound is further suppressed. In addition, the decrease in cycle characteristics due to the expansion and destruction of the Si compound due to the insertion of lithium ions during charging is further suppressed.

[0071] The content of the Si compound in the negative electrode active material is preferably 10% by mass or more and 80% by mass or less, and more preferably 15% by mass or more and 50% by mass or less.

[0072] By ensuring that the content of the Si compound is within the above range, the capacity and cycle characteristics of the battery are further optimized when the battery is fabricated.

[0073] The cathode active material contained in the electrode slurry of this embodiment is more preferably a cathode active material having an average particle size (D50) of 5 μm or less. A cathode active material having an average particle size (D50) of 5 μm or less is easily peeled off from the current collector foil during electrode formation, and the electrode binder of this embodiment is highly effective in improving peel strength.

[0074] The positive electrode active material may have at least one of a spinel structure and an olivine structure.

[0075] The positive electrode active material having a spinel structure is an oxide containing Li and Mn. Elements contained therein other than Li, Mn, and O include elements of Groups 2 to 15 of the periodic table.

[0076] The positive electrode active material having an olivine structure is a phosphate oxide containing Li and contains at least one of Fe and Mn. Elements contained therein other than Li, Mn, Fe, P, and O can include elements of Groups 2 to 15 of the periodic table.

[0077] The average particle size (D50) of the positive electrode active material is preferably 5 μm or less. The average particle size (D50) of the positive electrode active material is preferably 0.01 μm or more and 5 μm or less, more preferably 0.01 μm or more and 1 μm or less, and even more preferably 0.05 μm or more and 0.6 μm or less. The particle size (D50) is the volume average particle size measured with a laser particle size distribution analyzer. By having the average particle size of the positive electrode active material within the above range, the electrode resistance can be further reduced when the material is used as an electrode.

[0078] The aqueous medium contained in the electrode slurry may be, for example, one or more selected from the group consisting of water, 2-propanol (isopropyl alcohol), N-methylpyrrolidone, and dimethylformamide, with water being preferred.

[0079] Examples of the conductive additive include one or more conductive carbons selected from the group consisting of acetylene black, ketjen black, carbon black, vapor-grown carbon fiber, and carbon nanotubes, with acetylene black being preferred. Carbon powders such as graphite, and fibers or foils of various metals may also be used. The content of the conductive additive relative to the solid content in the electrode slurry is preferably 0.5% by mass to 10% by mass, more preferably 1% by mass to 5% by mass.

[0080] The electrode slurry may be produced by a production method including a mixing step of mixing the electrode binder of this embodiment, the electrode active material, and the aqueous medium, and optionally a conductive additive. The mixing may be performed by a known mixing method, and may be performed using one or more machines selected from the group consisting of a stirrer, a mixer, a kneader, and a kneader.

[0081] The slurry obtained in the mixing step is used as the electrode slurry of this embodiment, and is applied to a current collector and dried to obtain an electrode containing the current collector.

[0082] An electrode including the electrode binder of this embodiment can be used as an electrode for a LIB. Furthermore, a LIB including an electrode containing the electrode binder of this embodiment can be used in various portable electronic devices. Examples of portable electronic devices that can be used include notebook personal computers, notebook word processors, palmtop (pocket) personal computers, mobile phones, portable fax machines, portable printers, headphone stereos, video cameras, portable televisions, portable CD players, portable MDs, electric shavers, electronic organizers, transceivers, power tools, radios, tape recorders, digital cameras, portable copiers, and portable game consoles. Furthermore, a LIB including an electrode containing the electrode binder can also be used as a secondary battery in electric vehicles, hybrid vehicles, vending machines, electric carts, load leveling energy storage systems, home energy storage devices, distributed energy storage systems (built into stationary electrical appliances), emergency power supply systems, and the like. [Example]

[0083] The present disclosure will be described in more detail below with reference to examples, but the present disclosure is not limited to these examples.

[0084] (Measurement of weight average molecular weight (Mw)) The Mw of the electrode binder was measured by gel permeation chromatography (GPC, Tosoh Corporation, HLC-8320GPC) under the following conditions, and calculated as a PEO / PEG equivalent value. Column: TSKgel guardcolumn PW XL (6.0mmI.D.×4cm)+TSKgel G6000PW XL +TSKgel G4000PW XL +TSKgel G2500PW XL (7.8mmI.D.×30cm each) Detector: RI detector polarity(+) Eluent: 0.2M phosphate buffer (pH 7.0) / acetonitrile = 9 / 1 Flow rate: 1.0mL / min Injection volume: 100μL Column temperature: 40℃

[0085] (Creep displacement measurement) The creep displacement was determined by a nanoindentation test in accordance with ISO 14577-1. Specifically, a nanoindenter (device name: ENT-5, ELIONIX Co., Ltd.) and a measuring indenter (shape: Berkovich) were used as the measuring device, and the creep strain of the sample was measured by the drift test method under the following conditions: Measurement temperature: 25℃ Maximum load: 20mN Maximum load holding time: 5000ms Time to reach maximum load: 10s Push speed: 2mN / s The creep strain thus obtained was used to calculate the creep displacement according to the following formula: Creep displacement (%) = {(h2-h1) / h1} x 100 In the above formula, h1 is the creep strain (μm) when the maximum load is reached, and h2 is the maximum value of the creep strain (μm) during the maximum load holding time. The measurement sample was prepared by forming the electrode binder on a copper foil as a cast film with a thickness of 50 μm.

[0086] [Example 1] A reactor equipped with a stirrer, thermometer, condenser, nitrogen gas inlet, and dropping device was charged with 300.0 g of water and heated to 75°C. A mixture consisting of 2.6 g of acrylic acid, 64.6 g of sodium acrylate, 48.4 g of 2-hydroxyethyl acrylate, 0.3 g of potassium persulfate, and 300.0 g of water was added dropwise to the reactor with stirring over 3 hours. After the addition was completed, the mixture was allowed to polymerize at the same temperature for 6 hours. In other words, the polymerization time was 9 hours. After polymerization was complete, the mixture was cooled to 50°C and diluted with 175.9 g of water to obtain a polymer having the structural units (1), (2), and (3) as repeating units, R 1 is a hydrogen atom, R 2 is a hydrogen atom, R 3 is a hydrogen atom, R 4 was an ethylene group, n / m was 0.05, and m / l was 1.65, and the content of structural unit (1) was 3.1 mol %, the content of structural unit (2) was 60.3 mol %, and the content of structural unit (3) was 36.6 mol %, and this polymer was used as the electrode binder of this example. The Mw of the electrode binder in this example was 820,000.

[0087] [Example 2] A reactor equipped with a stirrer, thermometer, condenser, nitrogen gas inlet, and dropping device was charged with 300.0 g of water and heated to 75°C. A mixture consisting of 2.6 g of acrylic acid, 64.6 g of sodium acrylate, 48.4 g of 2-hydroxyethyl acrylate, 7.9 g of 3-aminopropyltriethoxysilane, 0.3 g of potassium persulfate, and 300.0 g of water was added dropwise with stirring over 3 hours. After the addition was completed, polymerization was carried out at the same temperature for 6 hours. In other words, the polymerization time was 9 hours. After polymerization was complete, the mixture was cooled to 50°C and diluted with 228.8 g of water to obtain a polymer having the structural units (1), (2), (3), and (4) as repeating units, R 1 is a hydrogen atom, R 2 is a hydrogen atom, R 3 is a hydrogen atom, R 4 is an ethylene group, R 5 is a hydrogen atom, R 6is a propylene group, R 7 is an ethoxy group, R 8 was an ethyl group, L was -NH-, n / m was 0.002, m / l was 1.65, and p / m was 0.05, and the content of structural unit (1) was 0.1 mol %, the content of structural unit (2) was 60.3 mol %, the content of structural unit (3) was 36.5 mol %, and the content of structural unit (4) was 3.1 mol %, and this polymer was used as the electrode binder of this example. The Mw of the electrode binder in this example was 740,000.

[0088] [Example 3] A reactor equipped with a stirrer, thermometer, condenser, nitrogen gas inlet, and dropping device was charged with 300.0 g of water and heated to 75°C. A mixture consisting of 2.6 g of acrylic acid, 64.6 g of sodium acrylate, 48.4 g of 2-hydroxyethyl acrylate, 1.5 g of 3-aminopropyltriethoxysilane, 0.3 g of potassium persulfate, and 300.0 g of water was added dropwise with stirring over 3 hours. After the addition was completed, polymerization was carried out at the same temperature for 6 hours. In other words, the polymerization time was 9 hours. After polymerization was complete, the mixture was cooled to 50°C and diluted with 185.9 g of water to obtain a polymer having the structural units (1), (2), (3), and (4) as repeating units, R 1 is a hydrogen atom, R 2 is a hydrogen atom, R 3 is a hydrogen atom, R 4 is an ethylene group, R 5 is a hydrogen atom, R 6 is a propylene group, R 7 is an ethoxy group, R 8 was an ethyl group, L was -NH-, n / m was 0.04, m / l was 1.64, and p / m was 0.01, and the content of structural unit (1) was 2.6 mol%, the content of structural unit (2) was 60.2 mol%, the content of structural unit (3) was 36.6 mol%, and the content of structural unit (4) was 0.6 mol%, and this polymer was used as the electrode binder of this example. The Mw of the electrode binder in this example was 980,000.

[0089] [Example 4] A reactor equipped with a stirrer, thermometer, condenser, nitrogen gas inlet, and dropping device was charged with 300.0 g of water and heated to 75°C. A mixture consisting of 2.6 g of acrylic acid, 64.6 g of sodium acrylate, 48.4 g of 2-hydroxyethyl acrylate, 1.0 g of 3-aminopropyltriethoxysilane, 0.3 g of potassium persulfate, and 300.0 g of water was added dropwise with stirring over 3 hours. After the addition was completed, polymerization was carried out at the same temperature for 6 hours. In other words, the polymerization time was 9 hours. After polymerization was complete, the mixture was cooled to 50°C and diluted with 182.5 g of water to obtain a polymer having the structural units (1), (2), (3), and (4) as repeating units, R 1 is a hydrogen atom, R 2 is a hydrogen atom, R 3 is a hydrogen atom, R 4 is an ethylene group, R 5 is a hydrogen atom, R 6 is a propylene group, R 7 is an ethoxy group, R 8 was an ethyl group, L was -NH-, n / m was 0.05, m / l was 1.64, and p / m was 0.01, and the content of structural unit (1) was 2.8 mol%, the content of structural unit (2) was 60.2 mol%, the content of structural unit (3) was 36.6 mol%, and the content of structural unit (4) was 0.4 mol%, and this polymer was used as the electrode binder of this example.

[0090] [Example 5] A reactor equipped with a stirrer, thermometer, condenser, nitrogen gas inlet, and dropping device was charged with 300.0 g of water and heated to 75°C. A mixture consisting of 2.6 g of acrylic acid, 64.6 g of sodium acrylate, 48.4 g of 2-hydroxyethyl acrylate, 0.5 g of 3-aminopropyltriethoxysilane, 0.3 g of potassium persulfate, and 300.0 g of water was added dropwise with stirring over 3 hours. After the addition was completed, polymerization was carried out at the same temperature for 6 hours. In other words, the polymerization time was 9 hours. After polymerization was complete, the mixture was cooled to 50°C and diluted with 179.2 g of water to obtain a polymer having the structural units (1), (2), (3), and (4) as repeating units, R 1 is a hydrogen atom, R 2 is a hydrogen atom, R 3 is a hydrogen atom, R 4 is an ethylene group, R 5 is a hydrogen atom, R 6 is a propylene group, R 7 is an ethoxy group, R 8 was an ethyl group, L was -NH-, n / m was 0.05, m / l was 1.64, and p / m was 0.003, and the content of structural unit (1) was 3.0 mol%, the content of structural unit (2) was 60.2 mol%, the content of structural unit (3) was 36.6 mol%, and the content of structural unit (4) was 0.2 mol%, and this polymer was used as the electrode binder of this example.

[0091] [Example 6] A reactor equipped with a stirrer, thermometer, condenser, nitrogen gas inlet, and dropping device was charged with 300.0 g of water and heated to 75°C. A mixture consisting of 2.6 g of acrylic acid, 64.3 g of sodium acrylate, 48.2 g of 2-hydroxyethyl acrylate, 0.5 g of 3-aminopropyltriethoxysilane, 0.5 g of 2-(dimethylamino)ethyl methacrylate, 0.3 g of potassium persulfate, and 300.0 g of water was added dropwise with stirring over 3 hours. After the addition was completed, polymerization was carried out at the same temperature for 6 hours. In other words, the polymerization time was 9 hours. After polymerization was complete, the mixture was cooled to 50°C and diluted with 178.6 g of water to obtain a polymer having the structural units (1), (2), (3), and (4) as repeating units, R 1 is a hydrogen atom, R 2 is a hydrogen atom, R 3 is a hydrogen atom, R 4 is an ethylene group, R 5 is a hydrogen atom, R 6 is a propylene group, R 7 is an ethoxy group, R 8was an ethyl group, L was -NH-, n / m was 0.05, m / l was 1.65, and p / m was 0.003, and the content of structural unit (1) was 3.0 mol%, the content of structural unit (2) was 60.2 mol%, the content of structural unit (3) was 36.4 mol%, and the content of structural unit (4) was 0.2 mol%, and this polymer was used as the electrode binder of this example.

[0092] [Example 7] A reactor equipped with a stirrer, thermometer, condenser, nitrogen gas inlet, and dropping device was charged with 300.0 g of water and heated to 75°C. A mixture consisting of 2.5 g of acrylic acid, 64.0 g of sodium acrylate, 47.9 g of 2-hydroxyethyl acrylate, 1.0 g of polyethylene glycol diacrylate, 0.4 g of potassium persulfate, and 300.0 g of water was added dropwise with stirring over 3 hours. After the addition was completed, polymerization was carried out at the same temperature for 6 hours. In other words, the polymerization time was 9 hours. After polymerization was complete, the mixture was cooled to 50°C and diluted with 206.2 g of water to obtain a polymer having the structural units (1), (2), and (3) as repeating units, R 1 is a hydrogen atom, R 2 is a hydrogen atom, R 3 is a hydrogen atom, R 4 was an ethylene group, n / m was 0.05, and m / l was 1.65, and the content of structural unit (1) was 3.1 mol %, the content of structural unit (2) was 60.0 mol %, and the content of structural unit (3) was 36.3 mol %, and this polymer was used as the electrode binder of this example.

[0093] [Example 8] A reactor equipped with a stirrer, thermometer, condenser, nitrogen gas inlet, and dropping device was charged with 300.0 g of water and heated to 75°C. A mixture consisting of 2.6 g of acrylic acid, 64.6 g of sodium acrylate, 48.4 g of 2-hydroxyethyl acrylate, 0.3 g of potassium persulfate, and 300.0 g of water was added dropwise to the reactor over a period of 3 hours with stirring. After the addition was complete, 0.5 g of 3-glycidoxypropyltrimethoxysilane was added and the mixture was polymerized at the same temperature for 6 hours. This resulted in a polymerization time of 9 hours. After polymerization was complete, the mixture was cooled to 50°C and diluted with 199.2 g of water to obtain a polymer having the structural units (1), (2), (3), and (4) as repeating units, R 1 is a hydrogen atom, R 2 is a hydrogen atom, R 3 is a hydrogen atom, R 4 is an ethylene group, R 5 is a hydrogen atom, R 6 Ga-R 9 -OR 10 -, a group represented by R 7 is a methoxy group, R 8 is a methyl group, R 9 is a hydroxyethylene group, R 10 was a propylene group, L was -O-, n / m was 0.05, m / l was 1.65, and p / m was 0.003, and the content of structural unit (1) was 3.0 mol %, the content of structural unit (2) was 60.3 mol %, the content of structural unit (3) was 36.5 mol %, and the content of structural unit (4) was 0.2 mol %, and this polymer was used as the electrode binder of this example. The Mw of the electrode binder in this example was 780,000.

[0094] [Example 9] A reactor equipped with a stirrer, thermometer, condenser, nitrogen gas inlet, and dropping device was charged with 300.0 g of water and heated to 75°C. A mixture consisting of 2.6 g of acrylic acid, 64.3 g of sodium acrylate, 48.2 g of 2-hydroxyethyl acrylate, 0.5 g of 2-(dimethylamino)ethyl methacrylate, 0.3 g of potassium persulfate, and 300.0 g of water was added dropwise with stirring over 3 hours. After the addition was complete, 0.5 g of 3-glycidoxypropyltrimethoxysilane was added and the mixture was polymerized at the same temperature for 6 hours. The polymerization time was 9 hours. After polymerization was complete, the mixture was cooled to 50°C and diluted with 178.6 g of water to obtain a polymer having the structural units (1), (2), (3), and (4) as repeating units, R 1 is a hydrogen atom, R 2 is a hydrogen atom, R 3 is a hydrogen atom, R 4 is an ethylene group, R 5 is a hydrogen atom, R 6 Ga-R 9 -OR 10 -, a group represented by R 7 is a methoxy group, R 8 is a methyl group, R 9 is a hydroxyethylene group, R 10 was a propylene group, L was -O-, n / m was 0.05, m / l was 1.65, and p / m was 0.005, and the content of structural unit (1) was 3.0 mol %, the content of structural unit (2) was 60.1 mol %, the content of structural unit (3) was 36.5 mol %, and the content of structural unit (4) was 0.3 mol %, and this polymer was used as the electrode binder of this example. The Mw of the electrode binder in this example was 770,000.

[0095] [Example 10] A reactor equipped with a stirrer, thermometer, condenser, nitrogen gas inlet, and dropping device was charged with 300.0 g of water and heated to 75°C. A mixture consisting of 2.6 g of acrylic acid, 64.6 g of sodium acrylate, 48.4 g of 2-hydroxyethyl acrylate, 7.9 g of 3-aminopropyltriethoxysilane, 0.3 g of potassium persulfate, and 300.0 g of water was added dropwise with stirring over 3 hours. After the addition was completed, polymerization was carried out at the same temperature for 12 hours. In other words, the polymerization time was 15 hours. After polymerization was complete, the mixture was cooled to 50°C and diluted with 228.8 g of water to obtain a polymer having the structural units (1), (2), (3), and (4) as repeating units, R 1 is a hydrogen atom, R 2 is a hydrogen atom, R 3 is a hydrogen atom, R 4 is an ethylene group, R 5 is a hydrogen atom, R 6 is a propylene group, R 7 is an ethoxy group, R 8 A polymer was obtained in which n / m was an ethyl group, L was -NH-, n / m was 0.002, m / l was 1.65, and p / m was 0.05. The polymer also contained 0.1 mol% of structural unit (1), 60.3 mol% of structural unit (2), 36.5 mol% of structural unit (3), and 3.1 mol% of structural unit (4). These polymers were mixed with the electrode binder of Example 3 in a ratio of 44.3:55.7 mass% to produce the electrode binder of this example. The n / m was 0.02, m / l was 1.64, and p / m was 0.03. The content of structural unit (1) was 1.7 mol%, the content of structural unit (2) was 60.2 mol%, the content of structural unit (3) was 36.6 mol%, and the content of structural unit (4) was 1.5 mol%.

[0096] [Comparative Example 1] A reactor equipped with a stirrer, thermometer, condenser, nitrogen gas inlet, and dropping device was charged with 200.0 g of water and heated to 75°C. A mixture of 100.0 g of acrylic acid, 1.2 g of potassium persulfate, and 250.0 g of water was added dropwise to the reactor with stirring over 3 hours. After the addition was completed, the mixture was polymerized at the same temperature for 6 hours. In other words, the polymerization time was 9 hours. After the polymerization was completed, the mixture was cooled to 50°C and neutralized with an aqueous solution of 33.3 g of sodium hydroxide dissolved in 341.3 g of water to obtain a copolymer having the structural units (1) and (2) as repeating units, R 1 is a hydrogen atom, R 2 was a hydrogen atom, n / m was 0.67, and the content of structural unit (1) was 39.8 mol % and the content of structural unit (2) was 60.2 mol %, and this polymer was used as the electrode binder of this comparative example. The Mw of the electrode binder of this comparative example was 510,000.

[0097] [Table 1]

[0098] [Table 2]

[0099] (Preparation of electrode slurry) The electrode binders of the Examples and Comparative Examples were weighed out and mixed to give a mixture of 7 mass %, 92.5 mass % of a negative electrode active material obtained by mixing a SiOC negative electrode active material and graphite at a mass ratio of 20:80, and 0.5 mass % of a conductive additive (acetylene black). To the mixture was added water in an amount 1.05 times the mass of the mixture, and the mixture was mixed for 10 minutes using a planetary centrifugal mixer to prepare an electrode slurry.

[0100] (Evaluation of battery characteristics) The prepared electrode slurry was applied using an applicator at a solid content of 3 mg / cm 2The mixture was applied to a 15 μm thick copper foil so that the thickness was 15 μm, and then dried in a stationary dryer at 110°C for 0.5 hours. After drying, the foil was punched out into a circle with a diameter of 14 mm, and heat-treated in vacuum at 110°C for 3 hours to obtain a negative electrode for a LIB.

[0101] (Preparation of half-cell for evaluation) A half-cell consisting of a coin cell with a lithium metal counter electrode was fabricated for the evaluation battery. The evaluation half-cell was fabricated in a glove box by stacking the negative electrode, a 19-mm diameter polypropylene separator, a 19-mm diameter glass filter, a gasket, a 16-mm diameter x 0.6-mm thick lithium metal, a stainless steel metal plate, a stainless steel washer, and the coin cell lid in that order within a CR2032-type coin cell case (20 mm diameter, 3.2 mm thickness), and then screwing the lid on. The negative electrode, separator, and glass filter were immersed in an electrolyte solution before stacking and were wetted with the electrolyte. The electrolyte solution used was a 1:1 mixture of ethylene carbonate and diethyl carbonate in a volume ratio, containing 1.2 mol / L LiPF6 and 2% by volume of fluoroethylene carbonate.

[0102] (Cycle test) The half evaluation cell was placed in a thermostatic chamber at 25°C and subjected to a cycle test by charging and discharging. Charging was performed at a constant current of 0.6 mA up to 0.01 V, followed by a constant voltage of 0.01 V until the current value reached 0.01 mA. Discharging was performed at a constant current of 0.6 mA down to a voltage of 1.5 V. The charge / discharge cycle was repeated under the above conditions, and the ratio of the discharge capacity (mAh / g) after 50 charge / discharge cycles to the initial discharge capacity (mAh / g) was calculated as the capacity retention rate (%), which was used as the cycle performance. The evaluation results are shown in Tables 3 and 4.

[0103] (Preparation of positive electrode slurry) A mixture was obtained by weighing and mixing 3 mass % of the electrode binder of each of the Examples and Comparative Examples, 93 mass % of the positive electrode active material having an olivine structure and an average particle size (D50) of 1.4 μm, and 4 mass % of the conductive additive (acetylene black). To this mixture was added water in an amount 0.5 times the mass of the mixture, and the mixture was mixed for 10 minutes using a rotation-revolution mixer. The same amount of water was further added, and the mixture was mixed with a spatula. Finally, the mixture was mixed for 5 minutes using a rotation-revolution mixer to prepare a positive electrode slurry.

[0104] (Evaluation of positive electrode characteristics) The prepared positive electrode slurry was applied using an applicator at a solid content of 15 mg / cm 2 The mixture was applied to a 20 μm thick aluminum foil so that the thickness of the coating was 1.8 g / cc, dried in a stationary dryer at 100°C for 5 minutes, and then further dried in a vacuum at 100°C for 12 hours. After that, pressure was applied in the thickness direction of the electrode using a roll press (manufactured by Thank Metals Co., Ltd.) to process the electrode to a density of 1.8 g / cc, thereby obtaining a positive electrode for a LIB.

[0105] (Peel strength measurement) The peel strength was determined by a tensile test using a tensile tester (Tensilon RTG-1210, manufactured by A&D Co., Ltd.) under the following conditions: Measurement temperature: 25℃ Tensile speed: 100 mm / min One side of a 20 mm wide double-sided tape (manufactured by Nichiban Co., Ltd., product name: Nicetack) was attached to a 1.5 mm thick polycarbonate substrate, and the non-adhesive side of a substrate tape (single-sided tape: Nitto Denko Corporation, polyester adhesive tape No. 31B) was attached to the other side of the double-sided tape (however, a 1 cm long area from the edge of the substrate tape was left floating). Next, a positive electrode cut to a width of 15 mm and a length of 8 cm was attached so that the positive electrode composite layer surface of the positive electrode adhered to the adhesive surface of the substrate tape. At this time, the electrode was not attached to the 1 cm long area from the edge of the substrate tape, and this area was left floating, and the positive electrode was attached to the substrate tape. Then, a PET film was attached to the 1 cm long area from the edge where the positive electrode was not attached to serve as a pulling allowance. In this way, a test specimen was prepared in which the positive electrode composite layer portion was firmly adhered to the substrate tape. The obtained test specimen was fixed to a tensile tester, and the tensile portion of the test specimen was pulled at a peel rate of 100 mm / min to perform 180° peeling. The tensile strength was measured at 10 mm, 20 mm, 30 mm, and 40 mm from the start of peeling, and the average value was calculated as the peel strength. The peel strengths are shown in Tables 3 and 4. The peel strength of Example 10 was 7 mN / mm.

[0106] [Table 3]

[0107] [Table 3] The evaluation results in Tables 3 and 4 show that the electrode binder and electrode slurry of this embodiment make it possible to produce a LIB that exhibits excellent cycle characteristics. This application is based on a Japanese patent application (Patent Application No. 2024-021814) filed on February 16, 2024, the entire contents of which are incorporated herein by reference. In addition, all references cited herein are incorporated herein in their entirety.

Claims

1. The polymer includes a repeating unit represented by formula (1), a repeating unit represented by formula (2), a repeating unit represented by formula (3), and a repeating unit represented by formula (4), An electrode binder having a weight average molecular weight of 520,000 to 1,100,000 and a creep displacement of 8% or more and 14% or less as determined by a nanoindentation test in accordance with ISO 14577-1. 【Chemistry 1】 【Chemistry 2】 However, in formula (1) and formula (2), R １ , R ２ each independently represents a hydrogen atom or a methyl group; M represents Na, K, or Li; n and m represent the number of repetitions, and n / m is greater than 0 and not greater than 0.

25. 【Transformation 3】 However, in formula (3), R ３ is a hydrogen atom, R ４ represents a methylene group, an ethylene group, a propylene group, or a butylene group; l represents the number of repetitions; and m / l is 0.8 or more and less than 4.

0. 【Chemistry 4】 In formula (4), R ５ represents a hydrogen atom or a methyl group, L represents —O— or —NH—, R ６ represents an alkylene group having 1 to 10 carbon atoms, -R ９ -O-R １０ a group represented by - or -R １１ -NH-R １２ represents a group represented by -, and R ７ represents an alkyl group having 1 to 6 carbon atoms or an alkoxy group having 1 to 6 carbon atoms, and R ８ represents an alkyl group having 1 to 6 carbon atoms, and R ９ represents an alkylene group having 1 to 5 carbon atoms which may be substituted with a hydroxy group, R １０ , R １１ , R １２ each independently represents an alkylene group having 2 to 5 carbon atoms, p represents the number of repetitions, and p / m is 0.001 or more and 0.1 or less.

2. With respect to 100 mol% of the electrode binder, The structural unit represented by formula (1) is more than 0 mol % and 8 mol % or less, The structural unit represented by formula (2) is 48 mol % or more and 70 mol % or less, and 2. The electrode binder according to claim 1, which contains the structural unit represented by formula (3) in a range of 23 mol % to 45 mol %.

3. With respect to 100 mol% of the electrode binder, 3. The electrode binder according to claim 1, which contains the structural unit represented by formula (4) in an amount of 0.1 mol % to 3.5 mol %.

4. R １ and R ２ The electrode binder according to claim 1 or 2, wherein is a hydrogen atom.

5. An electrode slurry comprising an electrode active material, a solvent, and the electrode binder according to claim 1 or 2.

6. An electrode for LIB, comprising the electrode binder according to claim 1 or 2.

7. A lithium ion secondary battery comprising the LIB electrode according to claim 6.

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