Binder for lithium-ion battery positive electrode, slurry for forming lithium-ion battery positive electrode mixture layer, positive electrode for lithium-ion battery, and lithium-ion battery

Abstract

A binder for a lithium-ion battery positive electrode according to the present invention binds a positive electrode active material, a conductive auxiliary agent, and a current collector in the lithium-ion battery, and contains a chelate group-containing polymer compound and a flexible polymer.

Description

Binder for lithium ion battery positive electrode, slurry for forming lithium ion battery positive electrode composite layer, positive electrode for lithium ion battery, and lithium ion battery

[0001] The present disclosure relates to a binder for a lithium ion battery positive electrode, a slurry for forming a lithium ion battery positive electrode composite layer, a lithium ion battery positive electrode, and a lithium ion battery.

[0002] Lithium-ion batteries have been widely used in recent years as power sources for electrical devices, etc. Furthermore, their use has recently expanded to include power sources for electric vehicles, and there is a demand for improved performance, such as higher capacity, higher output, and improved cycle life, as well as high safety.

[0003] The electrode of a lithium-ion battery has a structure in which a porous body composed mainly of a powdered active material, a conductive additive, and a binder is layered and bound on a current collector. Therefore, it is known that the performance of the electrode is significantly affected not only by the properties of the active material but also by the type of binder.

[0004] Conventionally, polyvinylidene fluoride (PVDF) has been the mainstream binder for positive electrodes. However, because it has been used in conjunction with organic solvents such as N-methylpyrrolidone during electrode production, it has had drawbacks such as the need for detoxification equipment in the slurry preparation process and electrode sheet application process, and the need for solvent recovery equipment in the electrode sheet drying process, which increases the amount of ancillary equipment required for electrode production and leads to higher costs, and the cost of purchasing and recovering organic solvents increases, resulting in higher running costs.

[0005] On the other hand, as aqueous binders that can be dispersed and dissolved in water without using organic solvents, the use of polyvinyl alcohol and methyl cellulose (see, for example, Patent Document 1), the use of xanthan gum (see, for example, Patent Document 2), the use of starch-type polysaccharides such as amylose and aminopectin (see, for example, Patent Documents 3 and 4), and the use of alginic acid or alginic acid derivatives (see, for example, Patent Documents 5 to 9) have been disclosed. Note that binders obtained using aqueous emulsions are preferred because they do not require decontamination equipment during electrode sheet production and also improve the working environment.

[0006] The positive electrode active material is LiMn ２ O ４ , LiNi ０．５ Mn １．５ O ４ , LiNi ０．５ Mn ０．３ Co ０．２ O ２ , LiNi ０．３３ Mn ０．３３ Co ０．３３ O ２ , LiNi ０．８ Mn ０．１ Co ０．１ O ２ However, it was known that manganese and nickel in the active material of these lithium composite oxides dissolve and ionize during charge and discharge, depositing and building up on the negative electrode, resulting in a deterioration in cycle characteristics and rate performance.

[0007] JP 53-41732 A JP 2003-68292 A JP 2008-27904 A International Publication No. 2012 / 133120 JP 10-92415 A JP 2001-15114 A JP 2014-96238 A JP 2014-195018 A JP 2015-191862 A

[0008] The present disclosure aims to provide a binder for a lithium-ion battery positive electrode that is highly flexible (bendable), less susceptible to cracking during winding, and easy to work with during electrode fabrication, and that can suppress the precipitation and deposition of manganese from the positive electrode active material onto the negative electrode active material, thereby enabling the fabrication of a battery that can extend its cycle life; a slurry for forming a positive electrode composite layer for a lithium-ion battery, which is provided with the binder; and a lithium-ion battery positive electrode and a lithium-ion battery that are provided with the binder. In other words, the present disclosure aims to provide a binder for a lithium-ion battery positive electrode that is highly flexible, less susceptible to cracking during electrode fabrication, and that can enable the fabrication of a battery with an extended cycle life, as well as a slurry for forming a positive electrode composite layer for a lithium-ion battery, a positive electrode for a lithium-ion battery, and a lithium-ion battery that use the binder.

[0009] In the present disclosure, it has been found that the above object can be achieved by using a chelating group-containing polymer compound and a flexible polymer as a binder.

[0010] That is, each aspect of the present invention is as set forth in the claims, and the gist of the present disclosure is as follows.

[0011] [1] A binder for a positive electrode of a lithium ion battery, which binds a positive electrode active material, a conductive additive, and a current collector in a lithium ion battery, the binder comprising a chelate group-containing polymer compound and a flexible polymer.

[0012] [2] The binder according to the above [1], wherein in the chelate group-containing polymer compound, the chelate group is bonded to the polymer compound via a covalent bond and / or an ionic bond. (In other words, the binder according to the above [1], wherein in the chelate group-containing polymer compound, the chelate group is bonded to the polymer compound via at least one bond selected from the group consisting of a covalent bond and an ionic bond.) [3] The binder for a lithium ion battery positive electrode according to the above [1] or [2], wherein the flexible polymer is at least one selected from the group consisting of polyvinylidene fluoride and copolymers thereof, and polymers containing an aromatic vinyl monomer and an aliphatic conjugated diene monomer.

[0013] [4] The binder for a lithium ion battery positive electrode according to any one of the above [1] to [3], wherein the flexible polymer is a dried product of an aqueous emulsion (obtained by drying an aqueous emulsion).

[0014] [5] A slurry for forming a lithium ion battery positive electrode composite layer, the slurry comprising a positive electrode active material, a conductive additive, a chelating group-containing polymer compound, a flexible polymer, and water, and the slurry is for forming a positive electrode composite layer comprising the binder for a lithium ion battery positive electrode according to any one of [1] to [4] above.

[0015] [6] A positive electrode for a lithium ion battery, comprising the binder for a lithium ion battery positive electrode according to any one of [1] to [4] above.

[0016] [7] A lithium ion battery having the positive electrode for a lithium ion battery according to [6] above.

[0017] [8] A method for producing a composition (mixture) that can be used to produce the binder for a lithium ion battery positive electrode according to any one of [1] to [4] above, comprising adding and mixing a flexible polymer in the form of an aqueous polymer emulsion to a chelate group-containing polymer compound.

[0018] The present inventors speculate as follows as to why the above object is achieved by the binder for a lithium-ion battery positive electrode according to one embodiment of the present disclosure.

[0019] That is, by using a chelating group-containing polymer compound as a binder, the chelating group captures manganese ions and nickel ions eluted from the positive electrode active material near the positive electrode. This suppresses the deposition and accumulation of manganese on the negative electrode active material. As a result, excellent charge / discharge characteristics and a long cycle life can be achieved. On the other hand, by using a flexible polymer (more preferably a dried aqueous polymer emulsion) as a binder, the adhesion of the positive electrode mixture layer to the current collector is improved, and peeling of the positive electrode mixture layer is suppressed even when the positive electrode mixture layer is applied thickly. Furthermore, since flexibility is imparted to the positive electrode, cracking during winding can be suppressed. Because cracking during winding can be suppressed in this way, by using the binder for a lithium-ion battery positive electrode according to one embodiment of the present disclosure, it is possible to efficiently manufacture the positive electrode by applying a winding process during positive electrode production, thereby improving the workability during positive electrode fabrication.

[0020] According to the present disclosure, it is possible to provide a binder for a lithium-ion battery positive electrode that is highly flexible (bendable), unlikely to crack when wound, has excellent workability when fabricating an electrode, and can suppress the precipitation and deposition of manganese from the positive electrode active material to the negative electrode active material, thereby enabling the fabrication of a battery that can extend the cycle life; a slurry for forming a lithium-ion battery positive electrode composite layer for forming a positive electrode composite layer that includes the binder; and a lithium-ion battery positive electrode and a lithium-ion battery that include the binder.

[0021] In other words, the present disclosure makes it possible to provide a binder for a lithium-ion battery positive electrode and a slurry for forming a lithium-ion battery positive electrode composite layer that are excellent in workability during positive electrode fabrication, are highly flexible, are less susceptible to cracking, and enable the fabrication of an electrode with an extended cycle life.Furthermore, by using the binder and a slurry, it becomes possible to provide a lithium-ion battery positive electrode and a lithium-ion battery with an extended cycle life.

[0022] The present disclosure will be described in detail below with reference to preferred embodiments. The present disclosure includes any combination of the configurations disclosed in this specification and any combination of the numerical values ​​disclosed in this specification.

[0023] A binder for a lithium ion battery positive electrode according to one embodiment of the present disclosure includes a chelate group-containing polymer compound.

[0024] A chelating group refers to a ligand having multiple coordination sites and is a functional group capable of forming a chelate with a polyvalent metal ion. Suitable chelating groups include aminocarboxylic acid chelating groups, aminophosphonic acid chelating groups, and polyamine chelating groups. Examples of aminocarboxylic acid chelating functional groups include iminodiacetic acid, nitrilotriacetic acid, N,N-bis(2-hydroxyethyl)glycine, hydroxyethyliminodiacetic acid, ethylenediaminetriacetic acid, ethylenediaminetetraacetic acid, 1,2-bis(2-aminophenoxy)ethanetetraacetic acid, 1,2-diaminocyclohexanetetraacetic acid, diethylenetriaminepentaacetic acid, (2-hydroxyethyl)ethylenediaminetriacetic acid, bis(2-aminoethyl)ethyleneglycoltetraacetic acid, and triethylenetriaminehexaacetic acid. Suitable aminocarboxylic acid chelating functional groups include at least one selected from the groups listed above. Examples of aminophosphonic acid-based chelating groups include aminomethylphosphonic acid groups and nitrilotris(methylphosphonic acid) groups. At least one selected from the groups exemplified herein can be suitably used as such aminophosphonic acid-based chelating groups. Examples of polyamine-based chelating groups include polyethyleneimine groups, polyamidoamine dendrimer groups, and tetrakis(2-pyridylmethyl)ethylenediamine groups. At least one selected from the groups exemplified herein can be suitably used as such polyamine-based chelating groups. When the chelating group contains carboxylic acid or phosphonic acid, it is preferable for these acidic functional groups to be in the form of a monovalent salt, such as an alkali metal salt or ammonium salt, rather than in the proton form, since this facilitates ion exchange with heavy metal ions.

[0025] In addition, such a chelating group is preferably at least one of an aminocarboxylic acid-based chelating group, an aminophosphonic acid-based chelating group, and alkali metal salts thereof.Furthermore, from the viewpoint of enabling more efficient introduction of a large number of chelating groups, such a chelating group is preferably at least one selected from the group consisting of an iminodiacetic acid group, an ethylenediaminetetraacetic acid group, a nitrilotris(methylphosphonic acid) group, a nitrilotriacetic acid group, an ethylenediaminetriacetic acid group, an aminomethylphosphonic acid group, and alkali metal salts thereof, more preferably at least one selected from the group consisting of an iminodiacetic acid group, an ethylenediaminetetraacetic acid group, a nitrilotris(methylphosphonic acid) group, and alkali metal salts thereof, and particularly preferably at least one selected from the group consisting of a disodium iminodiacetic acid group, a tetrasodium ethylenediaminetetraacetic acid group, and a nitrilotris(trisodium methylphosphonic acid) group.

[0026] The amount of chelate groups contained in the chelate group-containing polymer compound is 0.2 mmol / g or more and 6 mmol / g or less, preferably 0.5 mmol / g or more and 5 mmol / g or less. A chelate group content within this range is preferable because it allows for rapid capture of heavy metal ions and a sufficient amount of captured heavy metal ions. The content of such chelate groups is not particularly limited, and may be determined appropriately depending on the type of chelate group. For example, when the chelate group contains a nitrogen element, such as an aminocarboxylic acid-based chelate group or an aminophosphonic acid-based chelate group, and the polymer compound portion (the polymer portion into which the chelate group is introduced) has a structure that does not contain a nitrogen element, a method may be adopted in which elemental analysis is performed on the chelate group-containing polymer compound to determine the nitrogen atom content ratio, and the molar amount of the chelate group content is calculated from the content. The method of elemental analysis referred to here is not particularly limited, but for example, a MICRO CORDER JM10 manufactured by J Science Co., Ltd. is used as a measuring device to completely combust a sample under an oxygen atmosphere, and the CO generated is analyzed. ２ , H ２ O, N２ A method can be employed in which the amount of each element is determined by measuring the amount of each element with a thermal conductivity detector.

[0027] The polymer compound into which the chelate group is introduced (the compound constituting the polymer compound portion excluding the chelate group in the chelate group-containing polymer compound) is not particularly limited. Examples of polymer compounds into which the chelate group is introduced include vinyl polymers, polyamides, polyesters, polyurethanes, polysaccharides, and cellulose. The polymer compound is preferably water-soluble at the time the chelate group is introduced, and is therefore preferably hydrophilic. Furthermore, as such a polymer compound (the polymer compound portion in the chelate group-containing polymer compound), polysaccharides are more preferred, with at least one of acidic polysaccharides and basic polysaccharides being even more preferred, and at least one selected from the group consisting of alginic acid, sulfated alginic acid, and salts thereof being particularly preferred, with alginic acid being the most preferred.

[0028] The molecular weight of the chelating group-containing polymer compound is preferably 10,000 to 1,000,000, more preferably 50,000 to 1,000,000, in terms of weight average molecular weight. A weight average molecular weight within this range is preferable because it ensures sufficient mechanical strength and allows the viscosity during electrode coating to be adjusted to a range that does not affect workability. The "weight average molecular weight" of the chelating group-containing polymer compound can be measured using a Tosoh HLC-8320 GPC measuring device, a TSKgel GMPXL column, a pH 8.0, 0.1 mol / L phosphate buffer solution as the eluent, and polyethylene glycol as the standard sample at a flow rate of 1 mL / min.

[0029] The term "chelate group-containing polymeric compound" as used herein refers to a polymeric compound in which a chelate group is bonded to the polymeric compound via a covalent bond and / or an ionic bond. In other words, the term "chelate group-containing polymeric compound" as used herein refers to a polymeric compound in which a chelate group is bonded to the polymeric compound via at least one bond selected from the group consisting of a covalent bond and an ionic bond.

[0030] When the chelating group is bonded to the polymer compound via a covalent bond, an example of the structure is shown in the following general formula (1).

[0031] PS-X-A-CL (1) (In the formula, PS represents an acidic polysaccharide or a basic polysaccharide. X represents a group represented by -O- or -N(R)-, where R represents a hydrogen atom or a hydrocarbon group having 1 to 6 carbon atoms. A represents an organic group having 3 to 30 carbon atoms, and CL represents an organic group having 1 to 30 carbon atoms and containing a chelating group.) In general formula (1), PS represents an acidic polysaccharide or a basic polysaccharide. Acidic polysaccharides refer to polysaccharides containing functional groups that exhibit acidity, such as carboxyl groups and sulfate groups. Examples of acidic polysaccharides include at least one selected from the group consisting of carboxymethylcellulose, gellan gum, alginic acid, sulfated alginic acid, carrageenan, xanthan gum, chondroitin sulfate, heparin, hyaluronic acid, pectinic acid, gum arabic, agar, tragacanth gum, and salts thereof. Furthermore, acidic polysaccharides may be mixed with neutral polysaccharides or other water-soluble polymers to the extent that the amount of chelating groups introduced is not significantly reduced. Among these acidic polysaccharides, at least one selected from the group consisting of alginic acid, sulfated alginic acid, and salts thereof is preferred due to its excellent oxidation resistance and high mechanical strength. Alginic acid is composed of mannuronic acid and guluronic acid. The ratio of mannuronic acid to guluronic acid, which are the components of alginic acid, is arbitrary. In this embodiment, the alginic acid may be either alginic acid with a high mannuronic acid ratio, which produces a flexible gel, or alginic acid with a high guluronic acid ratio, which produces a rigid gel. On the other hand, basic polysaccharides refer to polysaccharides containing functional groups exhibiting basicity, such as amino groups. An example of a basic polysaccharide is chitosan.

[0032] Furthermore, sulfated polysaccharides in which sulfate groups have been introduced into the above polysaccharides are also suitable for use as PS in general formula (1). The sulfate group, both in its basic salt and neutral salt, is a strongly acidic cation exchange group capable of ion exchange. Therefore, the "sulfate group" referred to here may be in the form of a basic salt or a neutral salt. The sulfate group is introduced at the site of a hydroxyl group contained in the polysaccharide structure, and the hydrogen of the hydroxyl group is -SO ３ The sulfate groups are introduced by substitution with H. The amount of sulfate groups introduced into the polysaccharide is preferably 0.5 to 5.0 mmol / g. When the amount of sulfate groups introduced is within the above range, oxidation resistance is improved while maintaining the amount of chelating groups introduced, which is preferable.

[0033] In general formula (1), X represents a group represented by -O- or -N(R)-, and R represents a hydrogen atom or a hydrocarbon group having 1 to 6 carbon atoms. Examples of the hydrocarbon group having 1 to 6 carbon atoms include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a sec-butyl group, a tert-butyl group, an isobutyl group, an n-pentyl group, a sec-pentyl group, a tert-pentyl group, an isopentyl group, a neopentyl group, a 3-pentyl group, a cyclopentyl group, an n-hexyl group, an isohexyl group, a sec-hexyl group, a tert-hexyl group, a neohexyl group, a 2-methylpentyl group, a 3-methylpentyl group, a 1,2-dimethylbutyl group, a 2,2-dimethylbutyl group, a 1-ethylbutyl group, a 2-ethylbutyl group, and a cyclohexyl group. As the hydrocarbon group having 1 to 6 carbon atoms, at least one selected from the group consisting of these exemplified groups can be suitably used.

[0034] In general formula (1), A is an organic group having 3 to 30 carbon atoms, and divalent hydrocarbon groups such as propylene, butylene, and phenylene groups, as well as groups in which a hydroxyl group or the like has been introduced into such hydrocarbon groups, are preferably used. Examples of organic groups that can be used as A in formula (1) include 2-hydroxypropylene, 2,2-bis[4-(hydroxypropyloxy)phenyl]propane, 1,2-bis(2-hydroxypropyloxy)ethyl, and 1,3-bis(2-hydroxypropyloxy)benzene. Note that the term "organic group" as used in the present disclosure refers to divalent hydrocarbon groups such as those described above, as well as groups containing heteroatoms such as oxygen, nitrogen, phosphorus, and sulfur as constituent atoms in addition to carbon and hydrogen.

[0035] CL in general formula (1) may contain a chelating group, and may have 1 to 30 carbon atoms and may contain heteroatoms such as oxygen, nitrogen, phosphorus, sulfur, etc. in addition to carbon and hydrogen. CL may consist solely of the chelating group, or may have bound to it a hydrocarbon group such as a methyl group, an ethyl group, or a phenyl group, an ester group such as an acetate ester, an ether group such as an ethyl ether, an amide group such as a benzoic acid amide, or a sulfonate ester group such as a toluenesulfonate ester.

[0036] When the chelating group is bonded to the polymer compound via a covalent bond, a polymer compound having a structure represented by the following general formula (2) in which the chelating group is introduced into a graft chain is also suitably used in the binder of one embodiment of the present disclosure.

[0037]

[0038] (In the formula, PS and X have the same meanings as PS and X in the general formula (1). B represents a vinyl monomer residue containing a chelating group and having 4 to 30 carbon atoms, D represents a vinyl monomer residue containing no chelating group and having 4 to 30 carbon atoms, and l and m each independently represent an integer of 10 to 500.) In the general formula (2), the chelate group is introduced into the graft polymer chain and is bonded to the acidic polysaccharide or basic polysaccharide via a covalent bond. Examples of the chelate group include the same as the chelate group in the chelate group-containing polymer compound of the general formula (1). Examples of the vinyl monomer residue having a chelate group represented by B in the general formula (2) include a reaction product of an epoxy group and an amino group in a vinyl monomer residue having an epoxy group, such as glycidyl methacrylate, and an amino group in a compound having a chelate group. Furthermore, examples of the vinyl monomer residue having 4 to 30 carbon atoms and not containing a chelating group, represented by D in general formula (2), include not only vinyl monomer residues in which the epoxy group remains intact in the vinyl monomer residue having an epoxy group, such as glycidyl methacrylate, and vinyl monomer residues that have been hydrolyzed and ring-opened, but also vinyl monomer residues that do not contain an epoxy group.

[0039] Whether the chelating group is bound to the polymer compound via a covalent bond can be confirmed, for example, by measuring the weight increase before and after the introduction of the chelating group.

[0040] On the other hand, when a chelating group is bonded to a polymer compound via an ionic bond, an example of such a structure is one in which a polymer compound having an anionic functional group and a chelating group-containing compound having a cationic functional group (for example, a compound having an amino group and a chelating group) are bonded by an ionic bond. Examples of anionic functional groups include a carboxyl group, a sulfonic acid group, a phosphate group, and a phenolic hydroxyl group. Specific examples of polymer compounds having an anionic functional group include poly(acrylic acid), poly(methacrylic acid), poly(itaconic acid), poly(maleic acid), ethylene-maleic acid copolymer, isobutene-maleic acid copolymer, methyl vinyl ether-maleic acid copolymer, styrene-maleic acid copolymer, poly(fumaric acid), poly(vinyl sulfonic acid), poly(styrene sulfonic acid), poly(2-sulfoethyl methacrylate), poly(2-sulfoethyl acrylate), poly(3-sulfopropyl methacrylate), and poly(3-sulfopropyl methacrylate). Examples of suitable binders include vinyl polymers composed of poly(4-sulfobutyl methacrylate), poly(4-sulfobutyl acrylate), poly(2-acrylamido-2-methylpropanesulfonic acid), poly(2-methacrylamido-2-methylpropanesulfonic acid), and copolymers thereof; and acidic polysaccharides such as carboxymethyl cellulose, gellan gum, alginic acid, sulfated alginic acid, carrageenan, xanthan gum, chondroitin sulfate, heparin, hyaluronic acid, pectinic acid, gum arabic, agar, and tragacanth gum. These polymers may be copolymerized with other monomers as long as the oxidation resistance and reduction resistance are acceptable. Among these polymer compounds, acidic polysaccharides with high oxidation resistance are preferably used as binders for positive electrodes, with alginic acid and sulfated alginic acid being more preferred. On the other hand, poly(acrylic acid), poly(styrenesulfonic acid), and copolymers thereof, alginic acid, and sulfated alginic acid, which have excellent reduction resistance, are preferably used as binders for negative electrodes.

[0041] On the other hand, examples of chelating group-containing compounds having a cationic functional group include chelating group-containing compounds containing an ammonium group, a phosphonium group, a sulfonium group, or the like. Specific examples of such compounds include iminodiacetic acid, nitrilotriacetic acid, ethylenediaminetetraacetic acid, N,N-bis(2-hydroxyethyl)glycine, 1,2-diaminocyclohexanetetraacetic acid, diethylenetriaminepentaacetic acid, N-(2-hydroxyethyl)ethylenediaminetriacetic acid, bis(2-aminoethyl)ethyleneglycoltetraacetic acid, bis(2-aminophenyl)ethyleneglycoltetraacetic acid, N-(2-hydroxyethyl)iminodiacetic acid, tetrakis(2-pyridylmethyl)ethylenediamine, triethylenetetraminehexaacetic acid, aminomethylphosphonic acid, aminoethylphosphonic acid, aminopropylphosphonic acid, nitrilotris(methylphosphonic acid), and salts thereof. The acetate group and phosphonic acid group in the above compounds are preferably in the form of a monovalent salt, such as an alkali metal salt or an ammonium salt, rather than in the proton form, because they are more easily ion-exchanged with heavy metal ions.

[0042] The fact that the chelating group is bonded to the polymer compound via an ionic bond can be confirmed, for example, by FT-IR measurement. When the presence or absence of the bond of the chelating group is confirmed by FT-IR measurement, for example, when the chelating group-containing polymer compound is a compound obtained by reacting hydrogen ion type alginic acid with iminodiacetic acid disodium salt, the hydrogen ion type alginic acid as the raw material has a peak at 1740 cm －１ In the compound into which the iminodiacetic acid disodium salt was introduced after the reaction (the chelate group-containing polymer compound after the reaction), an absorption due to the stretching vibration of the carbonyl of the carboxylic acid was observed at 1740 cm －１ The absorption of 1600 cm derived from iminodiacetic acid disodium salt disappeared, and a new absorption －１Since the absorption due to the stretching vibration of the carbonyl of the carboxylate salt can be confirmed, the presence or absence of the bond (ionic bond) of the chelate group introduced into the chelate group-containing polymer compound can be confirmed by measuring the change in the absorption wavelength. Note that the FT-IR measurement method may also employ a method in which the FT-IR spectrum is measured by the ATR method using a Fourier transform infrared spectrophotometer (FT-IR) (SPECTRUM ONE, manufactured by PerkinElmer) as the measuring device.

[0043] Methods for producing such chelate group-containing polymeric compounds include, but are not limited to, contacting a polymeric compound having an anionic functional group (preferably at least one of carboxyl, sulfonic acid, and sulfate groups) with an acid to convert the anionic functional group to a hydrogen ion form, followed by contacting the polymeric compound with a chelate group-containing compound having a cationic functional group (e.g., a compound having an amino group and a chelate group) to introduce the chelate group into the anionic polymer, thereby obtaining a chelate group-containing polymeric compound. Another method for producing chelate group-containing polymeric compounds includes reacting an acidic polysaccharide and / or a basic polysaccharide with epihalohydrin and / or a polyfunctional epoxy compound having 2 to 6 epoxy groups, followed by reaction with a chelate group-containing compound having a cationic functional group (e.g., a compound having an amino group and a chelate group) to introduce the chelate group into the acidic polysaccharide or basic polysaccharide via a covalent bond, thereby obtaining a chelate group-containing polymeric compound. Examples of the epihalohydrin that can be used include epichlorohydrin, epibromohydrin, epiiodohydrin, and mixtures thereof. Examples of the polyfunctional epoxy compound having 2 to 6 epoxy groups include bisphenol A diglycidyl ether, bisphenol F diglycidyl ether, resorcinol diglycidyl ether, ethylene glycol diglycidyl ether, glycerin triglycidyl ether, and 1,3-bis(oxiran-2-ylmethoxy)-2,2-bis[(oxiran-2-ylmethoxy)methyl]propane.

[0044] A binder for a lithium-ion battery positive electrode according to one aspect of the present disclosure includes a flexible polymer.

[0045] The flexible polymer in such a binder is preferably a polymer (a dried product of an aqueous emulsion) obtained by using a polymer dispersed as an emulsion in an aqueous medium (a water-based polymer emulsion). That is, from the viewpoint of improving binding properties, the flexible polymer is preferably a dried product of an aqueous emulsion (obtained by drying an aqueous emulsion). Note that the flexible polymer may also be obtained by utilizing a solution obtained by dissolving a polymer in water.

[0046] The flexible polymer is not particularly limited, but since one of the purposes of adding it is to impart flexibility to the positive electrode, it is preferable that the polymer be highly flexible.

[0047] Specific examples of flexible polymers include fluororesins such as polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, perfluoromethyl vinyl ether-tetrafluoroethylene copolymer, polytetrafluoroethylene, and fluororubber, and hydrocarbon elastomers such as styrene-butadiene copolymer and ethylene-propylene copolymer, with preferred examples being polymers containing an aromatic vinyl monomer and an aliphatic conjugated diene monomer such as polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, and styrene-butadiene copolymer. Another suitable example of the flexible polymer is a metal salt of polyacrylic acid. Furthermore, the flexible polymer is preferably at least one of a metal salt of polyacrylic acid, polyvinylidene fluoride and its copolymer, and a polymer containing an aromatic vinyl monomer and an aliphatic conjugated diene monomer, more preferably at least one of polyvinylidene fluoride and its copolymer, and a polymer containing an aromatic vinyl monomer and an aliphatic conjugated diene monomer, and even more preferably at least one of polyvinylidene fluoride and its copolymer, and a copolymer containing at least a styrene monomer and a butadiene monomer. This makes a positive electrode produced using the binder for a lithium-ion battery positive electrode according to one embodiment of the present disclosure more flexible.

[0048] The molecular weight of the flexible polymer is 50,000 to 2,000,000, preferably 100,000 to 1,000,000 in weight average molecular weight. A weight average molecular weight within this range is preferable because it ensures flexibility and sufficient mechanical strength. The "weight average molecular weight" of the flexible polymer can be measured using GPC as the measuring device, selecting a solvent that dissolves the polymer as the eluent, and using polyethylene glycol as the standard sample.

[0049] The term "aqueous" in aqueous polymer emulsion refers to a medium whose main component is water, and may contain organic compounds other than water, such as alcohols, ethers, esters, amines, and amides, as long as they are soluble in water. The emulsion in aqueous polymer emulsion refers to a dispersion medium in which fine particles are dispersed, with the size of the fine particles being on the order of several tens to several hundreds of nanometers. The dispersion state of the polymer in the emulsion may be confirmed by the presence or absence of sedimentation from a stationary state.

[0050] When an aqueous emulsion (hereinafter sometimes referred to as "aqueous polymer emulsion") is used to incorporate a flexible polymer into a binder, the proportion (content) of the flexible polymer component in the emulsion is preferably 20% by mass to 60% by mass (more preferably 30% by mass to 50% by mass). There are no particular restrictions on the method for preparing such an aqueous emulsion, and known methods can be used as appropriate. Alternatively, a commercially available product may be used as such an aqueous polymer emulsion.

[0051] The binder for lithium ion battery positive electrodes comprises a chelating group-containing polymer compound and a flexible polymer (preferably a dried aqueous polymer emulsion), and the weight ratio thereof is preferably chelating group-containing polymer compound:flexible polymer (preferably a dried aqueous polymer emulsion (mass of solids in the emulsion))=50 to 90:10 to 50 (more preferably 60 to 80:20 to 40).

[0052] The content (blending amount) of the binder according to one embodiment of the present disclosure is preferably 1 to 20 mass % and more preferably 3 to 10 mass % based on the total amount of the active material, binder, and conductive additive.

[0053] In addition, a mixture (composition) of a chelate group-containing polymer compound and a flexible polymer can be prepared by adding a flexible polymer in the form of an aqueous polymer emulsion to a chelate group-containing polymer compound and mixing them together. The resulting mixture (composition) can be used to efficiently prepare a slurry, a positive electrode, and a lithium ion battery, which will be described later.

[0054] The binder according to one embodiment of the present disclosure is highly flexible and can follow the volume change of the electrode during charge and discharge, preventing cracking of the electrode due to the volume change, peeling and detachment of the active material, and destruction of the conductive channel. Furthermore, the binder according to one embodiment of the present disclosure has excellent performance as a binder for lithium-ion battery electrodes, such as excellent ionic conductivity due to excellent affinity with the electrolyte, and excellent oxidation resistance and reduction resistance, which ensures the stability of the electrode.

[0055] Furthermore, a chelating group is introduced into the binder according to one embodiment of the present disclosure, and this chelating group captures manganese ions and the like eluted from the positive electrode active material near the positive electrode and / or negative electrode, thereby suppressing precipitation and deposition on the negative electrode active material, thereby achieving excellent charge / discharge characteristics and a long cycle life.

[0056] The binder for a lithium-ion battery positive electrode according to one embodiment of the present disclosure may contain a chelate group-containing polymer compound and a flexible polymer, and may further contain other components in addition to these components. Thus, the binder for a lithium-ion battery positive electrode according to one embodiment of the present disclosure may contain other components in addition to the chelate group-containing polymer compound and the flexible polymer. These other components are not particularly limited, and known components (such as known binders) that are usable in binders in the field of lithium-ion batteries may be used as appropriate. Suitable examples of such other components include silane coupling agents and inorganic components (e.g., colloidal silica, heavy phosphate, and alumina sol).

[0057] In the present disclosure, the positive electrode active material is not particularly limited as long as it is capable of inserting and extracting lithium ions, and examples thereof include CuO, Cu ２ O, MnO ２ , MoO ３ , V ２ O ５ , CrO ３ , Fe ２ O ３ , Ni ２ O ３ , CoO ３ transition metal oxides such as Li Ｘ CoO２ , Li Ｘ NiO ２ , Li Ｘ MnO ２ , Li Ｘ Mn ２ O ４ , LiNi Ｘ Co （１－Ｘ） O ２ , LiNi Ｘ Mn （２－Ｘ） O ４ , LiMn ａ Ni ｂ Co ｃ O ２ (a+b+c=1), LiFePO ４ As described above, the positive electrode active material may be, for example, at least one of the transition metal oxides and the lithium composite oxides. Here, the transition metal oxides include CuO, Cu ２ O, MnO ２ , MoO ３ , V ２ O ５ , CrO ３ , Fe ２ O ３ , Ni ２ O ３ , and CoO ３ Preferably, the lithium composite oxide is at least one selected from the group consisting of: Ｘ CoO ２ , Li Ｘ NiO ２ , Li Ｘ MnO ２ , Li Ｘ Mn ２ O ４ , LiNi Ｘ Co （１－Ｘ） O ２ , LiNi Ｘ Mn （２－Ｘ） O ４ , LiMn ａ Ni ｂ Co ｃ O ２ (a+b+c=1), and LiFePO ４Among these, the positive electrode active material is more preferably a composite oxide of lithium and at least one transition metal selected from transition metals such as Co, Ni, and Mn. A specific example of a preferred positive electrode active material is LiCoO ２ , LiNiO ２ , LiMnO ２ , LiMn ２ O ４ , LiNi Ｘ Co （１－Ｘ） O ２ , LiNi Ｘ Mn （２－Ｘ） O ４ and LiMn ａ Ni ｂ Co ｃ O ２ (a+b+c=1) These lithium composite oxides may be doped with a small amount of elements such as fluorine, boron, Al, Cr, Zr, Mo, and Fe, or the particle surfaces of the lithium composite oxides may be doped with carbon, MgO, Al, or the like. ２ O ３ , SiO ２ As described above, the lithium composite oxide may be a positive electrode active material that has been surface-treated with at least one element selected from the group consisting of fluorine, boron, Al, Cr, Zr, Mo, and Fe. ２ O ３ and SiO ２ Alternatively, a surface-treated product may be used which has been surface-treated with at least one selected from the group consisting of:

[0058] In the present disclosure, the negative electrode active material is not particularly limited as long as it is capable of inserting and extracting lithium ions. Examples of the negative electrode active material include natural graphite, artificial graphite, graphite, mesocarbon microbeads (MCMB), tin and / or tin alloys, tin oxide, silicon and / or silicon alloys, and silicon oxide. When the negative electrode active material is an alloy, the negative electrode active material may contain a material that alloys with lithium. Examples of the material that alloys with lithium include one or more selected from the group consisting of germanium, tin, lead, zinc, magnesium, sodium, aluminum, gallium, and indium, as well as alloys thereof.

[0059] When these active materials are in particulate form, the average particle size is not particularly limited, but is preferably 5 μm or more and 20 μm or less.

[0060] The conductive additive contained in the electrode is not particularly limited, and any electronically conductive material that does not adversely affect the battery characteristics can be used. Specific examples of conductive additives include conductive carbon such as ketjen black and acetylene black, natural graphite, artificial graphite, carbon whiskers, carbon nanotubes (CNT), and carbon fiber powder, as well as metal powders and fibers such as Cu, Fe, Ag, Ni, Pd, Au, Pt, In, and W, and conductive metal oxides such as indium oxide and tin oxide. As described above, at least one selected from the group consisting of conductive carbon, carbon materials, metal powders, metal fibers, and conductive metal oxides can be suitably used as the conductive additive. Among these, at least one selected from the group consisting of conductive carbon and carbon materials is more preferred, as it can provide higher conductivity with a small amount of use. At least one selected from the group consisting of ketjen black, carbon nanotubes, and acetylene black is even more preferred. Furthermore, since such a conductive additive is more effective in forming a conductive path, it is preferable to use a combination of conductive carbon and carbon nanotubes (CNTs). The amount of the conductive additive to be added is preferably 1 to 30% by mass relative to the active material.

[0061] The lithium-ion battery positive electrode composite layer forming slurry according to one embodiment of the present disclosure is a slurry for forming a lithium-ion battery positive electrode composite layer comprising the binder. The slurry contains a positive electrode active material, a conductive additive, a chelating group-containing polymer compound, a flexible polymer, and water. The slurry may optionally contain a viscosity modifier such as carboxymethyl cellulose or a pH modifier such as an acid or alkali. The solids concentration of the slurry is not particularly limited, but is preferably 20 to 80% by mass, taking into consideration the viscosity of the slurry, the dispersibility of the solids, the load on the drying process, and other factors. Furthermore, the solids ratio in the slurry is preferably 70 to 98:1 to 30:1 to 20 (more preferably 90 to 98:1 to 5:1 to 5) by mass. There are also no particular limitations on the method for producing the slurry. Examples of methods for producing the above-mentioned slurry include a method in which a chelating group-containing polymer compound, a flexible polymer, an active material, and a conductive additive are mixed in water, dispersed, and / or dissolved to produce a slurry; a method in which a chelating group-containing polymer compound and a flexible polymer are first dissolved and / or dispersed in water, and then the active material and the conductive additive are added to an aqueous solution or dispersion of the chelating group-containing polymer compound and the flexible polymer and mixed to produce a slurry; and a method in which an active material and a conductive additive are first mixed, and then mixed with an aqueous solution or dispersion of the binder components. There are also no particular restrictions on the mixer used to produce the slurry; for example, a mortar, a roll mill, a ball mill, a screw mill, a vibration mill, a homogenizer, or a planetary mixer can be used. In these methods for producing a slurry, it is preferable to use an aqueous emulsion of a flexible polymer when introducing the flexible polymer into the slurry. In this way, preparing a slurry using an aqueous emulsion of a flexible polymer tends to enable the production of electrodes with higher flexibility.

[0062] A lithium-ion battery positive electrode according to one embodiment of the present disclosure includes the binder. The lithium-ion battery positive electrode comprises a current collector and an electrode mixture layer (cathode mixture layer) obtained by applying the slurry onto the current collector and drying it. The thickness of the electrode mixture layer (cathode mixture layer) comprising the active material, binder, and conductive additive is preferably 10 to 200 μm. To form an electrode mixture layer of this thickness on the current collector, the basis weight of the electrode mixture layer (cathode mixture layer) should be 4 to 25 mg / cm. ２ It is recommended to set it to .

[0063] The current collector may be any conductor as long as the surface in contact with the electrode mixture layer (positive electrode mixture layer) exhibits electrical conductivity, and examples thereof include conductors formed from metals such as copper, gold, aluminum, titanium, nickel, stainless steel, or alloys thereof, conductive metal oxides such as indium oxide or tin oxide, and conductive materials such as conductive carbon. There are no particular restrictions on the shape of the current collector, and shapes such as foil, film, sheet, net, expanded metal, punched metal, and foam can be used. There are also no particular restrictions on the thickness of the current collector, and it is preferably about 1 to 100 μm.

[0064] There are no particular limitations on the manufacturing method of a positive electrode for a lithium ion battery, and it can be manufactured by applying the above-mentioned slurry to a current collector and drying it. There are also no particular limitations on the method of applying the slurry, and methods such as slit coating, die coating, roll coating, dip coating, blade coating, knife coating, and wire bar coating can be used. There are also no particular limitations on the drying method and conditions, and a typical hot air circulation dryer, reduced pressure dryer, infrared dryer, or microwave heating dryer can be used. When heating is performed during drying, there are no limitations on the heating temperature, and the electrode can be heated and dried at, for example, 50 to 150°C. Furthermore, the porous structure can be made uniform by pressing the electrode during or after drying.

[0065] When a flexible polymer in the form of an aqueous polymer emulsion is used in preparing the slurry, the slurry is applied to a current collector and dried to produce a positive electrode composite layer, whereby the flexible polymer in the binder in the positive electrode for a lithium ion battery can be made to consist of a dried aqueous emulsion. By making the flexible polymer in the binder consist of a dried aqueous emulsion, it becomes possible to impart higher flexibility to the positive electrode, and there is a tendency that it becomes possible to more effectively suppress the occurrence of defective products in the winding process during battery production.

[0066] A lithium-ion battery (lithium-ion secondary battery; LIB) according to one embodiment of the present disclosure includes the above-described lithium-ion battery positive electrode. By using the above-described lithium-ion battery positive electrode, a high-performance lithium-ion battery can be provided, achieving excellent charge / discharge characteristics and a long cycle life. Lithium-ion batteries generally consist of a positive electrode, a negative electrode, a separator, a non-aqueous electrolyte, and the like. The positive electrode is formed by binding the above-described positive electrode active material together with the above-described conductive additive to a positive electrode current collector with a binder, and has a structure in which a positive electrode composite layer composed of the positive electrode active material, binder, and conductive additive is formed on the current collector. The negative electrode has a similar structure to the positive electrode, and is formed by binding the above-described negative electrode active material and the above-described conductive additive to a negative electrode current collector with a binder. The separator is typically a porous film such as polyolefin, and is sandwiched between the positive and negative electrodes to provide a shutdown function in the event of thermal runaway of the battery. The non-aqueous electrolyte is LiPF ４ The battery is made by dissolving an electrolyte salt such as ammonium hydroxide in an organic solvent such as cyclic carbonate. The inside of the battery is filled with a non-aqueous electrolyte, and lithium ions move from the positive electrode to the negative electrode during charging and from the negative electrode to the positive electrode during discharging.

[0067] The non-aqueous electrolyte is not particularly limited, and known materials can be used. The non-aqueous electrolyte is a solution of an electrolyte salt dissolved in an organic solvent. The electrolyte salt is CF ３ SO ３ Li, (CF ３ SO ２ ) ２ NLi, (CF ３ SO ２) ２ CLi, LiBF ４ , LiB(C ６ H ８ ) ４ , LiPF ４ , LiClO ４ , LiAsF ６ , LiCl, and LiBr are examples of organic solvents that can dissolve the electrolyte salt. Examples of organic solvents that can dissolve the electrolyte salt include ethylene carbonate, vinylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, tetrahydrofuran, 1,4-dioxane, anisole, diethyl ether, sulfolane, methyl sulfolane, acetonitrile, propionitrile, butyronitrile, valeronitrile, benzonitrile, dimethylformamide, dimethyl sulfoxide, trimethyl phosphate, and triethyl phosphate. The concentration of the electrolyte salt in the nonaqueous electrolyte solution can be selected from the range of preferably 0.1 to 5 mol / L, and more preferably 0.5 to 3 mol / L.

[0068] There are no particular restrictions on the separator, and any known separator can be used. Examples of the separator include a polyethylene microporous membrane, a polypropylene microporous membrane, a laminated membrane of a polyethylene microporous membrane and a polypropylene microporous membrane, and a nonwoven fabric made of polyester fiber, aramid fiber, glass fiber, or the like.

[0069] Hereinafter, embodiments of the present disclosure will be described in more detail based on examples, but the embodiments of the present disclosure are not limited to these examples.

[0070] <Production of Chelate Group-Containing Polymer Compound> (Reference Example 1) Production of Alginic Acid with Iminodiacetate Disodium Group Introduced by Ionic Bond (Chelate Group-Containing Alginic Acid) 1.0 g (5.7 mmol as monosaccharide units) of hydrogen ion-form alginic acid (Kimika Corporation, trade name Kimika Acid G) was added little by little to 100 ml of pure water while stirring to prepare a white, paste-like uniform dispersion. Next, 1.1 g (5.7 mmol) of iminodiacetate disodium monohydrate (Fujifilm Wako Pure Chemical Industries, Ltd.) was added directly to the alginic acid dispersion and stirred. The dispersion gradually became transparent with the addition, and after the addition was completed, it became a transparent, viscous aqueous solution. This aqueous solution was stirred at room temperature for 1 hour and then added dropwise to 4 L of acetone to produce a precipitate. The resulting precipitate was collected by filtration, washed with acetone, and then isolated by drying under reduced pressure. The isolated yield was 1.9 g, the nitrogen content determined by elemental analysis was 3.7% by mass, and the chelating group content calculated from the nitrogen content was 2.6 mmol / g, indicating that the alginic acid was readily soluble in water. Furthermore, to confirm that the chelating group had been introduced into the alginic acid, the FT-IR spectra were compared before and after the reaction. The hydrogen ion form of alginic acid before the reaction had a peak at 1740 cm －１ After the reaction, the absorption due to the carbonyl stretching vibration of the carboxylic acid was observed at 1740 cm －１ The absorption at 1620 cm －１ A new absorption due to the carbonyl stretching vibration of the carboxylate salt was observed. This indicates that alginic acid and iminodiacetic acid are bonded via an ionic bond. Next, the molecular weight of the chelating group-containing polymer compound was measured by aqueous GPC. The weight-average molecular weight was 320,000.

[0071] The nitrogen content of the resulting chelate group-containing polymer compound (chelate polymer) was determined by elemental analysis using a MICRO CORDER JM10 manufactured by J Science Co., Ltd., by completely combusting the sample in an oxygen atmosphere and measuring the amount of CO produced. ２ , H ２ O, N ２A method of measuring the molecular weight using a thermal conductivity detector was adopted. Furthermore, FT-IR spectra of the chelating group-containing polymeric compounds were measured using a Fourier transform infrared spectrophotometer (FT-IR) (SPECTRUM ONE, manufactured by PerkinElmer) as the measuring device, and measurements were made by the ATR method. Furthermore, aqueous GPC measurements of the chelating group-containing polymeric compounds were made using a Tosoh HLC-8320GPC measuring device, a TSKgel GMPXL column, a column temperature set at 40°C, a pH 8.0, 0.1 mol / L phosphate buffer solution as the eluent, and a flow rate of 1 mL / min. Polyethylene glycol was used as the standard sample, and conditions for molecular weight conversion in terms of polyethylene glycol were adopted, thereby determining the weight-average molecular weight of the chelating group-containing polymeric compounds.

[0072] Reference Example 2: Production of alginic acid with tetrasodium ethylenediaminetetraacetate groups introduced by ionic bonds (chelate group-containing alginic acid) Alginic acid with chelate groups introduced by ionic bonds (chelate group-containing polymeric compound: chelate polymer) was produced in the same manner as in Reference Example 1, except that tetrasodium ethylenediaminetetraacetate tetrahydrate was used in place of disodium iminodiacetate monohydrate in an equal molar ratio. The properties of the resulting chelate group-containing polymeric compound were confirmed in the same manner as in Reference Example 1, and the chelate group content calculated from the nitrogen content was 3.8 mmol / g, and the weight average molecular weight measured using aqueous GPC was 370,000.

[0073] (Reference Example 3) Production of alginic acid (chelate group-containing alginic acid) into which tetrasodium ethylenediaminetetraacetate groups have been introduced by ionic bonds. Instead of hydrogen ion alginic acid (manufactured by Kimika Co., Ltd., trade name Kimika Acid G), 1 g of hydrogen ion alginic acid with a weight average molecular weight of 960,000, produced in-house from sodium alginate (manufactured by Qingdao Ju Dayang Algae Industry Group Co., Ltd., weight average molecular weight 1,300,000), was used. In the same manner as in Reference Example 2, an alginic acid (chelate group-containing polymer compound: chelate polymer) into which tetrasodium ethylenediaminetetraacetate has been introduced by ionic bonds was produced. The properties of the resulting chelate group-containing polymer compound were confirmed in the same manner as in Reference Example 1. The chelate group content calculated from the nitrogen content was 4.7 mmol / g, and the weight average molecular weight measured using aqueous GPC was 920,000. (Reference Example 4) Production of alginic acid (chelate group-containing alginic acid) into which nitrilotris (trisodium methylphosphonate) groups have been introduced by ionic bonds. Instead of tetrasodium ethylenediaminetetraacetate tetrahydrate, nitrilotris (trisodium methylphosphonate) was used in the same molar ratio as in Reference Example 3, except that an alginic acid (chelate group-containing polymer compound: chelate polymer) into which chelate groups have been introduced by ionic bonds was produced. The properties of the obtained chelate group-containing polymer compound were confirmed in the same manner as in Reference Example 1. The chelate group content calculated from the nitrogen content was 1.2 mmol / g, and the weight average molecular weight measured using aqueous GPC was 900,000.

[0074] Reference Example 5: Production of alginic acid (chelating group-containing alginic acid) with covalently bonded iminodiacetate disodium groups. 0.50 g (2.5 mmol as monosaccharide units) of sodium alginate (manufactured by Qingdao Ju Dayang Algae Industry Group Co., Ltd., weight average molecular weight 1,300,000) was added in small amounts to 50 ml of pure water while stirring to prepare a viscous, uniform aqueous solution. Next, 0.10 g (2.5 mmol) of sodium hydroxide (manufactured by Tokyo Chemical Industry Co., Ltd.) was added to the aqueous solution and dissolved. 3.10 g (50 mmol) of epichlorohydrin (manufactured by Tokyo Chemical Industry Co., Ltd.) was then added and reacted at 20 ° C. for 6 hours. The aqueous solution after the reaction was then added dropwise to 2 L of ethanol to form a precipitate. The precipitate was then recovered by filtration, washed with ethanol, and dried under reduced pressure to isolate the reaction intermediate. The isolated yield was 0.43 g, and the reaction intermediate was readily soluble in water. It should be noted that such a reaction intermediate is formed by the reaction between sodium alginate and epichlorohydrin, and it is clear that an epoxy group has been introduced into the reaction product.

[0075] Next, 0.30 g of the reaction intermediate was weighed and dissolved in 100 ml of pure water to obtain an aqueous solution. Next, 8.4 g (43 mmol) of iminodiacetic acid disodium monohydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added to the aqueous solution, dissolved, and reacted at 80 ° C. for 2 hours. The aqueous solution after the reaction was then purified using an ultrafiltration membrane (manufactured by Nippon Pall, molecular weight cutoff: 1000) to remove excess iminodiacetic acid from the aqueous solution. The purified aqueous solution was then dropped into acetone to precipitate the polymer, and the precipitate was collected by filtration and dried under reduced pressure to isolate the reaction product (chelate group-containing polymer: chelate polymer). The isolated yield of the obtained chelate group-containing polymer was 0.33 g and it was soluble in water. Furthermore, the properties of the obtained chelate group-containing polymer were confirmed in the same manner as in Reference Example 1. The weight-average molecular weight measured using aqueous GPC was 420,000, and the iminodiacetic acid group content calculated from the nitrogen content was 1.8 mmol / g.

[0076] <Evaluation of Heavy Metal Ion Trapping Ability> (Reference Example 6) In order to evaluate the heavy metal ion trapping ability of the chelate group-containing polymer compound (chelate polymer) obtained in Reference Example 1, the following measurement was carried out. 0.1 g of the chelate polymer was dissolved in 20 ml of pure water, and lithium manganate (LiMn ２ O ４ 1.9 g of LMO (prototype manufactured in-house, average particle size: 10 μm, hereinafter abbreviated as LMO) was added to prepare a slurry. The obtained slurry was concentrated using an evaporator and then dried under reduced pressure at 80°C to remove water, obtaining a mixture of chelating polymer and LMO. 1.0 g was taken from the mixture, placed in a Teflon (registered trademark) container, dried under reduced pressure at 120°C for 4 hours, and then sealed. The sealed Teflon (registered trademark) container was opened in a glove box, and LiPF was dissolved in an electrolyte (Kishida Chemical Co., Ltd., ethylene carbonate: dimethyl carbonate = 1:2 mixed solvent) and added. ６ After adding 15 ml of a solution in which 1 mol / L of LMO was dissolved, the container was sealed again and heated at 85°C for 4 hours. After heating was completed, the Teflon (registered trademark) container was opened in a glove box and filtered using a syringe filter, and the filtrate was collected. The obtained filtrate was subjected to acid decomposition, and manganese ions were quantified by ICP-MS. The manganese ion concentration was found to be less than 1 ppm by mass, confirming that the manganese ions eluted from the LMO by heating had been captured by the chelating polymer.

[0077] Reference Example 7 A slurry was prepared by adding 0.05 g of the chelate polymer obtained in Reference Example 1, 0.05 g of a 48% by mass styrene-butadiene copolymer emulsion (aqueous emulsion, solvent: water, weight average molecular weight of the styrene-butadiene copolymer (SBR) in the emulsion: 120,000; hereinafter, this emulsion will be referred to as "SBR emulsion") as solids, and 1.9 g of LMO to 20 ml of pure water. The obtained slurry was concentrated using an evaporator and then dried under reduced pressure at 80°C to remove water, and the manganese ion concentration was measured in the same manner as in Reference Example 6, except that a mixture of the chelate polymer, SBR, and LMO was obtained. As a result, the manganese ion concentration was less than 1 ppm by mass, confirming that even when used in combination with the SBR emulsion, manganese ions eluted from the LMO upon heating were captured by the chelate polymer.

[0078] Reference Example 8 The manganese ion concentration was measured in the same manner as in Reference Example 7, except that the SBR emulsion was changed to a 30 mass% polyvinylidene fluoride emulsion (aqueous emulsion, solvent: water, weight average molecular weight of polyvinylidene fluoride emulsion (PVDF) in the emulsion: 1,000,000; hereinafter, this emulsion is referred to as "PVDF emulsion"). As a result, the manganese ion concentration was less than 1 ppm by mass, and it was confirmed that even when used in combination with the PVDF emulsion, manganese ions eluted from the LMO by heating were captured by the chelating polymer.

[0079] The LMO, SBR emulsion, and PVDF emulsion used in the following reference examples and working examples are the same as the LMO used in reference example 6, the SBR emulsion used in reference example 7, and the PVDF emulsion used in reference example 8, respectively.

[0080] Reference Example 9 The manganese ion concentration was measured in the same manner as in Reference Example 6, except that the alginic acid to which ethylenediaminetetraacetic acid tetrasodium groups had been introduced by ionic bonds, produced in Reference Example 2, was used instead of the chelate group-containing polymer compound (chelate polymer) obtained in Reference Example 1. As a result, the manganese ion concentration was less than 1 ppm by mass.

[0081] Reference Example 10 The manganese ion concentration was measured in the same manner as in Reference Example 7, except that the alginic acid produced in Reference Example 2 to which tetrasodium ethylenediaminetetraacetate groups had been introduced by ionic bonds was used instead of the chelate group-containing polymer compound (chelate polymer) obtained in Reference Example 1. As a result, the manganese ion concentration was less than 1 ppm by mass, and it was confirmed that, even when used in combination with an SBR emulsion, manganese ions eluted from LMO by heating were captured by the chelate polymer obtained in Reference Example 2.

[0082] Reference Example 11 The manganese ion concentration was measured in the same manner as in Reference Example 8, except that the alginic acid produced in Reference Example 2 to which tetrasodium ethylenediaminetetraacetate groups had been introduced by ionic bonds was used instead of the chelate group-containing polymer compound (chelate polymer) obtained in Reference Example 1. As a result, the manganese ion concentration was less than 1 ppm by mass, and it was confirmed that, even when used in combination with a PVDF emulsion, manganese ions eluted from LMO by heating were captured by the chelate polymer obtained in Reference Example 2.

[0083] Reference Example 12 The manganese ion concentration was measured in the same manner as in Reference Example 6, except that the alginic acid to which ethylenediaminetetraacetic acid tetrasodium groups had been introduced by ionic bonds, produced in Reference Example 3, was used instead of the chelate group-containing polymer compound (chelate polymer) obtained in Reference Example 1. As a result, the manganese ion concentration was less than 1 ppm by mass.

[0084] Reference Example 13 The manganese ion concentration was measured in the same manner as in Reference Example 7, except that the alginic acid produced in Reference Example 3 to which tetrasodium ethylenediaminetetraacetate groups had been introduced by ionic bonds was used instead of the chelate group-containing polymer compound (chelate polymer) obtained in Reference Example 1. As a result, the manganese ion concentration was less than 1 ppm by mass, and it was confirmed that, even when used in combination with an SBR emulsion, manganese ions eluted from LMO by heating were captured by the chelate polymer obtained in Reference Example 3.

[0085] Reference Example 14 The manganese ion concentration was measured in the same manner as in Reference Example 8, except that the alginic acid produced in Reference Example 3 to which ethylenediaminetetraacetic acid tetrasodium groups had been introduced by ionic bonds was used instead of the chelate group-containing polymer compound (chelate polymer) obtained in Reference Example 1. As a result, the manganese ion concentration was less than 1 ppm, and it was confirmed that, even when used in combination with a PVDF emulsion, manganese ions eluted from LMO by heating were captured by the chelate polymer obtained in Reference Example 3.

[0086] Reference Example 15 The manganese ion concentration was measured in the same manner as in Reference Example 6, except that the alginic acid to which nitrilotris(trisodium methylphosphonate) groups had been introduced by ionic bonds, produced in Reference Example 4, was used instead of the chelate group-containing polymer compound (chelate polymer) obtained in Reference Example 1. As a result, the manganese ion concentration was less than 1 ppm by mass.

[0087] Reference Example 16 The manganese ion concentration was measured in the same manner as in Reference Example 7, except that the alginic acid to which nitrilotris(trisodium methylphosphonate) groups had been introduced by ionic bonds, produced in Reference Example 4, was used instead of the chelate group-containing polymer compound (chelate polymer) obtained in Reference Example 1. As a result, the manganese ion concentration was less than 1 ppm by mass, and it was confirmed that, even when used in combination with an SBR emulsion, manganese ions eluted from LMO by heating were captured by the chelate polymer obtained in Reference Example 4.

[0088] Reference Example 17 The manganese ion concentration was measured in the same manner as in Reference Example 8, except that the alginic acid to which nitrilotris(trisodium methylphosphonate) groups had been introduced by ionic bonds, produced in Reference Example 4, was used instead of the chelate group-containing polymer compound (chelate polymer) obtained in Reference Example 1. As a result, the manganese ion concentration was less than 1 ppm by mass, and it was confirmed that, even when used in combination with a PVDF emulsion, manganese ions eluted from LMO by heating were captured by the chelate polymer obtained in Reference Example 4.

[0089] Reference Example 18 The manganese ion concentration was measured in the same manner as in Reference Example 6, except that the alginic acid to which iminodiacetate disodium groups had been introduced via covalent bonds, produced in Reference Example 5, was used instead of the chelate group-containing polymer compound (chelate polymer) obtained in Reference Example 1. As a result, the manganese ion concentration was less than 1 ppm by mass.

[0090] Reference Example 19 The manganese ion concentration was measured in the same manner as in Reference Example 7, except that the alginic acid to which iminodiacetate disodium groups had been introduced via covalent bonds, produced in Reference Example 5, was used instead of the chelate group-containing polymer compound (chelate polymer) obtained in Reference Example 1. As a result, the manganese ion concentration was less than 1 ppm by mass, and it was confirmed that, even when used in combination with an SBR emulsion, manganese ions eluted from LMO by heating were captured by the chelate polymer obtained in Reference Example 5.

[0091] Reference Example 20 The manganese ion concentration was measured in the same manner as in Reference Example 8, except that the alginic acid to which iminodiacetate disodium groups had been introduced via covalent bonds, produced in Reference Example 5, was used instead of the chelate group-containing polymer compound (chelate polymer) obtained in Reference Example 1. As a result, the manganese ion concentration was less than 1 ppm by mass, and it was confirmed that, even when used in combination with a PVDF emulsion, manganese ions eluted from LMO by heating were captured by the chelate polymer obtained in Reference Example 5.

[0092] Reference Example 21 First, an aqueous solution of sodium polyacrylate with a weight-average molecular weight of 510,000 and a concentration of 13% by mass was prepared. Then, the manganese ion concentration was measured in the same manner as in Reference Example 14, except that the aqueous sodium polyacrylate solution was used instead of the PVDF emulsion. As a result, the manganese ion concentration was found to be less than 1 ppm, confirming that even when used in combination with sodium polyacrylate, manganese ions eluted from LMO by heating were captured by the chelating polymer obtained in Reference Example 3.

[0093] <Production of Positive Electrode> Example 1 A positive electrode slurry was prepared from the following materials, and a positive electrode was produced. Positive electrode active material: LMO 94 parts by mass Conductive additive: acetylene black (AB) (Li-400 manufactured by Denka Co., Ltd.) 2.5 parts by mass Binder: chelate group-containing alginic acid (Reference Example 1) 3 parts by mass SBR 0.5 parts by mass 94 parts by mass of LMO, 3 parts by mass of the chelate group-containing alginic acid produced in Reference Example 1, and 2.5 parts by mass of AB were added, and stirred with a planetary mixer while adding water. When the stirred mixture became a slurry, 0.5 parts by mass of SBR emulsion (as SBR solids content) was added, and the mixture was stirred again with a planetary mixer to prepare a positive electrode slurry. This slurry was applied to a 12 μm thick aluminum foil using a film applicator, dried at 80° C. for 24 hours under nitrogen and atmospheric pressure, and then further dried at 120° C. for 4 hours under reduced pressure to prepare a positive electrode. The resulting positive electrode was then compressed using a roll press. In this way, a positive electrode having a positive electrode composite layer formed on the aluminum foil was obtained. The basis weight was 17.3 mg / cm. ２ It was.

[0094] (Example 2) A positive electrode was produced in the same manner as in Example 1, except that the emulsion was changed from SBR emulsion to PVDF emulsion. In this way, a positive electrode was produced in the same manner as in Example 1, except that PVDF emulsion was used instead of SBR emulsion. The basis weight was 16.4 mg / cm ２ It was.

[0095] (Example 3) The electrode was thickly coated to a basis weight of 28.2 mg / cm ２ A positive electrode was produced in the same manner as in Example 2, except that the weight per unit area of ​​the electrode mixture layer was 28.2 mg / cm ２ A positive electrode was produced in the same manner as in Example 2, except that the slurry was applied thickly so that the thickness of the positive electrode was as follows:

[0096] (Example 4) A positive electrode was prepared in the same manner as in Example 1, except that the amount of SBR solid content was changed to 1 part by mass and the amount of AB was changed to 2 parts by mass. That is, a positive electrode was prepared in the same manner as in Example 1, except that the amount of SBR emulsion used, converted to SBR solid content, was changed to 1 part by mass and the amount of AB used was changed to 2 parts by mass. The basis weight was 19.7 mg / cm ２ It was.

[0097] (Example 5) A positive electrode was produced in the same manner as in Example 4, except that the emulsion was changed from SBR emulsion to PVDF emulsion. In this way, a positive electrode was produced in the same manner as in Example 1, except that PVDF emulsion was used instead of SBR emulsion. The basis weight was 19.2 mg / cm ２ It was.

[0098] Example 6 A positive electrode slurry having the following composition was prepared from the following materials, and a positive electrode was produced. Positive electrode active material: LMO 95 parts by mass Conductive additive: acetylene black (AB) (Li-400 manufactured by Denka Co., Ltd.) 1 part by mass Carbon nanotubes (CNT) 1 part by mass Binder: chelate group-containing alginic acid (Reference Example 1) 2 parts by mass SBR 1 part by mass First, 95 parts by mass of LMO, 2 parts by mass of the chelate group-containing alginic acid produced in Reference Example 1, 1 part by mass of AB, and 1 part by mass of CNT were added to a planetary mixer, and then these were stirred with the planetary mixer while adding water. By such stirring, when the stirred product became a slurry, 1 part by mass of SBR emulsion was added to the stirred product in terms of SBR solids content, and the mixture was again stirred with the planetary mixer to prepare a positive electrode slurry. Next, the obtained positive electrode slurry was applied to a 12 μm thick aluminum foil using a film applicator, and the coating film was dried at 80° C. for 24 hours under normal pressure in a nitrogen atmosphere, and then further dried under reduced pressure at 120° C. for 4 hours. The resulting laminate of the aluminum foil and the dried coating film was then compressed using a roll press to obtain a positive electrode. In this way, a positive electrode was prepared in which a positive electrode composite layer was formed on the aluminum foil. The basis weight of the positive electrode composite layer was 20.1 mg / cm.２ It was.

[0099] Example 7 A positive electrode was fabricated in the same manner as in Example 4, except that the type of emulsion was changed from SBR emulsion to PVDF emulsion. The basis weight of the positive electrode mixture layer was 20.7 mg / cm ２ It was.

[0100] (Comparative Example 1) A positive electrode was produced in the same manner as in Example 1 using 94 parts by mass of LMO, 3 parts by mass of AB, and 3 parts by mass of chelate-containing alginic acid (Reference Example 1). That is, a positive electrode was produced in the same manner as in Example 1, except that the SBR emulsion was not used and the amounts of LMO, AB, and chelate-containing alginic acid (Reference Example 1) used were changed to 94 parts by mass of LMO, 3 parts by mass of AB, and 3 parts by mass of chelate-containing alginic acid (Reference Example 1), respectively. The basis weight of the positive electrode composite layer was 16.8 mg / cm ２ It was.

[0101] [Method for Evaluating Characteristics of Positive Electrode] Hereinafter, a method for evaluating the characteristics of the positive electrodes obtained in each example will be described.

[0102] <Confirmation of Appearance of Positive Electrode> The appearance (electrode appearance) of the positive electrodes manufactured in each Example was visually inspected to confirm the presence or absence of cracks on the surface of the manufactured positive electrode. The results are shown in Table 1. Regarding the results of such visual inspection, in the table, those in which no cracks were observed on the appearance are marked with "A," and those in which cracks were observed on the appearance are marked with "B."

[0103] <Confirmation of crack occurrence due to positive electrode curl> The positive electrodes of Examples 1 to 7 and Comparative Example 1 were wound around metal rods with diameters of 10 mm, 8 mm, 6 mm, 4 mm, and 2 mm, and the presence or absence of crack occurrence was confirmed. The obtained results (results of the winding test) are shown in Table 1. Note that, with regard to the results of such measurements, those in which no cracks occurred are marked with "A" and those in which cracks occurred are marked with "B".

[0104] <Measurement of Peel Strength> 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 an adherend tape (single-sided tape: manufactured by Nitto Denko Corporation, polyester adhesive tape No. 31B) was attached to the other side of the double-sided tape (however, a 1 cm long range from the end of the adherend tape was left floating). Next, the positive electrodes prepared in each example were cut to a width of 15 mm and a length of 8 cm and attached so that the positive electrode composite layer surface of the positive electrode was adhered to the adhesive surface of the adherend tape. At this time, the electrode was not attached to the 1 cm long range from the end of the adherend tape, and this range was left floating, and the positive electrode was attached to the adherend tape. Then, a PET film was attached to the 1 cm long section from the end where the positive electrode was not attached, to provide a tensile allowance. In this way, a test specimen was prepared in which the positive electrode composite layer portion was firmly adhered to the adherend tape.

[0105] The obtained test specimen was then fixed to a tensile tester (Tensilon RTG-1210, manufactured by A&D Co., Ltd.), and the tensile portion of the test specimen was pulled at a peel rate of 100 mm / min to perform a 180° peel. 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 results are shown in Table 1. It should be noted that a peel strength of 5 mN / mm or more measured in this manner can be said to have excellent adhesiveness.

[0106] <Measurement of Electrode Penetration Resistance> Two electrodes for measurement samples in each example were prepared in the same manner as in Examples 6 and 7, except that the coating method of the positive electrode slurry was changed so that a continuous 1 cm square coated and uncoated area was present. The coated portions of the two electrodes were then overlapped, and a load was applied to the overlapped portion. A tester was then applied to the uncoated portion of each electrode to measure the resistance. This resistance was determined as the electrode penetration resistance of the positive electrodes obtained in Examples 6 and 7. The results are shown in Table 1. It should be noted that a penetration resistance measured in this manner of, for example, 40 Ω or less can be considered to be sufficient for use as a positive electrode in a lithium battery. On the other hand, the lower the value of this penetration resistance, the more excellent the input / output characteristics of the positive electrode can be evaluated. From this perspective, a penetration resistance of 10 Ω or less can be evaluated as having a higher level of input / output characteristics that are particularly suitable for use as a positive electrode in a lithium battery. Furthermore, a penetration resistance of 3 Ω or less can be evaluated as exhibiting even better input / output characteristics.

[0107]

[0108] As shown in Table 1, in a test (winding test) to confirm crack occurrence due to positive electrode curl, no cracks were observed in the positive electrodes of Examples 1 to 7 even when wound around a metal rod with a diameter of 2 mm. In the positive electrode of Comparative Example 1, cracks were visible when wound around a metal rod with a diameter of 6 mm or less. From these results, it can be understood that the use of an emulsion (aqueous emulsion) containing a flexible polymer in combination with a chelate group-containing polymer compound improved the adhesion of the positive electrode mixture layer to the current collector, suppressing peeling of the positive electrode mixture layer even when the positive electrode mixture layer was applied thickly, thereby suppressing crack occurrence. It can also be understood that the flexibility imparted to the positive electrode prevented crack occurrence during winding.

[0109] The results shown in Table 1 indicate that the electrodes (positive electrodes) produced in Examples 1 to 7 have electrode composite layers with excellent flexibility (flexibility) and adhesiveness, and are less likely to crack during winding. Furthermore, these results clearly demonstrate that electrodes can be efficiently manufactured using a winding process during production, and that the slurry used during positive electrode production can also improve workability during electrode fabrication. Furthermore, in the results of the evaluation of the heavy metal ion capture ability of the chelating polymer shown in Reference Examples 6 to 8, the measured manganese ion concentration in the system containing the chelating group-containing alginic acid produced in Reference Example 1 was all less than 1 ppm by mass. Therefore, it is clear that the precipitation and deposition of manganese from the positive electrode active material to the negative electrode active material can be suppressed in the positive electrode active material using the chelating group-containing alginic acid produced in Reference Example 1. These results clearly demonstrate that the electrodes produced in each Example can impart excellent charge / discharge characteristics to batteries using the electrodes and extend the cycle life of the batteries.

[0110] In the examples and the like described below, the various evaluation methods described in the above section [Method for evaluating positive electrode characteristics] were employed to evaluate the characteristics of the obtained positive electrodes, and the evaluation results are described in each example and table.

[0111] Example 8 A positive electrode was fabricated in the same manner as in Example 6, except that 2.5 parts by mass of the chelate group-containing alginic acid obtained in Reference Example 2 was used instead of 2 parts by mass of the chelate group-containing alginic acid produced in Reference Example 1, and the amount of AB used was changed from 1 part by mass to 0.5 parts by mass. The basis weight of the positive electrode composite layer was 26.6 mg / cm ２ The thickness of the positive electrode mixture layer was 110 μm, the peel strength was 13 mN / mm, and the electrode penetration resistance was 16 Ω. Furthermore, visual inspection revealed no cracks on the electrode exterior, and no cracks occurred in the winding test.

[0112] Example 9 A positive electrode was fabricated in the same manner as in Example 8, except that the type of emulsion was changed from SBR emulsion to PVDF emulsion. The basis weight of the positive electrode mixture layer was 25.3 mg / cm ２The thickness of the positive electrode mixture layer was 114 μm, the peel strength was 7 mN / mm, and the electrode penetration resistance was 9 Ω. Furthermore, visual inspection revealed no cracks on the electrode exterior, and no cracks occurred in the winding test.

[0113]

[0114] Example 10 A positive electrode slurry having the following composition was prepared from the following materials, and a positive electrode was produced. Positive electrode active material: LMO 95 parts by mass Conductive additive: acetylene black (AB) (Li-400 manufactured by Denka Co., Ltd.) 0.5 parts by mass Carbon nanotubes (CNT) 1 part by mass Binder: chelate group-containing alginic acid (Reference Example 3) 2.5 parts by mass SBR 1 part by mass First, 95 parts by mass of LMO, 2.5 parts by mass of the chelate group-containing alginic acid produced in Reference Example 3, 0.5 parts by mass of AB, and 1 part by mass of CNT were added to a planetary mixer, and then these were stirred with the planetary mixer while adding water. By such stirring, when the stirred product became a slurry, 1 part by mass of SBR emulsion was added to the stirred product in terms of SBR solids content, and the mixture was again stirred with the planetary mixer to prepare a positive electrode slurry. Next, the obtained slurry was applied to a 12 μm thick aluminum foil using a film applicator, and the coating film was dried at 80° C. for 24 hours under normal pressure in a nitrogen atmosphere, and then further dried under reduced pressure at 120° C. for 4 hours. The laminate of the aluminum foil and the dried coating film was then compressed using a roll press to obtain a positive electrode. In this way, a positive electrode was prepared in which a positive electrode composite layer was formed on the aluminum foil. The basis weight of the positive electrode composite layer was 28.9 mg / cm. ２ The thickness of the positive electrode mixture layer was 110 μm, the peel strength was 17 mN / mm, and the electrode penetration resistance was 19.5 Ω. Visual inspection revealed no cracks on the electrode exterior, and no cracks occurred in the winding test.

[0115] Example 11 A positive electrode was produced in the same manner as in Example 10, except that the amount of the chelating group-containing alginic acid produced in Reference Example 3 was changed to 2 parts by mass, the amount of SBR used in terms of solid content was changed to 0.5 parts by mass, and the amount of CNT used was changed to 2 parts by mass. The basis weight of the positive electrode composite layer was 32.3 mg / cm ２ The thickness of the positive electrode mixture layer was 135 μm, the peel strength was 6 mN / mm, and the electrode penetration resistance was 2.5 Ω. Visual inspection revealed no cracks on the electrode exterior, and no cracks occurred in the winding test.

[0116] Example 12 A positive electrode was fabricated in the same manner as in Example 10, except that the amount of the chelating group-containing alginic acid produced in Reference Example 3 was changed to 1.5 parts by mass, the amount of AB was changed to 1 part by mass, and the amount of CNT was changed to 1.5 parts by mass. The basis weight of the positive electrode composite layer was 27.7 mg / cm ２ The thickness of the positive electrode mixture layer was 128 μm, the peel strength was 12 mN / mm, and the electrode penetration resistance was 3.5 Ω. Furthermore, visual inspection revealed no cracks on the electrode exterior, and no cracks occurred in the winding test.

[0117] Example 13 A positive electrode was fabricated in the same manner as in Example 10, except that the amount of the chelating group-containing alginic acid produced in Reference Example 3 was changed to 1 part by mass, the amount of AB was changed to 1.5 parts by mass, and the amount of CNT was changed to 1.5 parts by mass. The basis weight of the positive electrode composite layer was 28.3 mg / cm ２ The thickness of the positive electrode mixture layer was 114 μm, the peel strength was 7 mN / mm, and the electrode penetration resistance was 1.5 Ω. Furthermore, visual inspection revealed no cracks on the electrode exterior, and no cracks occurred in the winding test.

[0118] Example 14 A positive electrode was fabricated in the same manner as in Example 10, except that the type of emulsion was changed from SBR emulsion to PVDF emulsion. The basis weight of the positive electrode mixture layer was 27.7 mg / cm ２The thickness of the positive electrode mixture layer was 120 μm, the peel strength was 10 mN / mm, and the electrode penetration resistance was 35 Ω. Furthermore, visual inspection revealed no cracks on the electrode exterior, and no cracks occurred in the winding test.

[0119] Example 15 A positive electrode was fabricated in the same manner as in Example 14, except that the amount of PVDF used was changed to 0.5 parts by mass in terms of solid content, and the amount of CNT used was changed to 1.5 parts by mass. The basis weight of the positive electrode mixture layer was 30.8 mg / cm ２ The thickness of the positive electrode mixture layer was 137 μm, the peel strength was 6 mN / mm, and the electrode penetration resistance was 5.5 Ω. Furthermore, visual inspection revealed no cracks on the electrode exterior, and no cracks occurred in the winding test.

[0120]

[0121] Example 16 A positive electrode was produced in the same manner as in Example 10, except that the chelate group-containing alginic acid produced in Reference Example 4 was used instead of the chelate group-containing alginic acid produced in Reference Example 3. The basis weight of the positive electrode mixture layer was 29.0 mg / cm ２ The thickness of the positive electrode mixture layer was 110 μm, the peel strength was 15 mN / mm, and the electrode penetration resistance was 11.1 Ω. Furthermore, visual inspection revealed no cracks on the electrode exterior, and no cracks occurred in the winding test.

[0122] Example 17 A positive electrode was fabricated in the same manner as in Example 16, except that the type of emulsion was changed from SBR emulsion to PVDF emulsion. The basis weight of the positive electrode mixture layer was 26.2 mg / cm ２ The thickness of the positive electrode mixture layer was 114 μm, the peel strength was 9 mN / mm, and the electrode penetration resistance was 7.8 Ω. Furthermore, visual inspection revealed no cracks on the electrode exterior, and no cracks occurred in the winding test.

[0123]

[0124] Example 18 A positive electrode was produced in the same manner as in Example 10, except that the chelate group-containing alginic acid produced in Reference Example 5 was used instead of the chelate group-containing alginic acid produced in Reference Example 3. The basis weight of the positive electrode mixture layer was 28.8 mg / cm ２ The thickness of the positive electrode mixture layer was 122 μm, the peel strength was 16 mN / mm, and the electrode penetration resistance was 17 Ω. Furthermore, visual inspection revealed no cracks on the electrode exterior, and no cracks occurred in the winding test.

[0125] Example 19 A positive electrode was produced in the same manner as in Example 18, except that the type of emulsion was changed from SBR emulsion to PVDF emulsion. The basis weight of the positive electrode mixture layer was 28.4 mg / cm ２ The thickness of the positive electrode mixture layer was 108 μm, the peel strength was 12 mN / mm, and the electrode penetration resistance was 8.6 Ω. Furthermore, visual inspection revealed no cracks on the electrode exterior, and no cracks occurred in the winding test.

[0126] Comparative Example 2 A positive electrode was produced in the same manner as in Example 18, except that the amount of the chelating group-containing alginic acid produced in Reference Example 5 was changed to 3 parts by mass, no SBR emulsion was used, and the amount of AB was changed to 1 part by mass. The basis weight of the positive electrode composite layer was 29.2 mg / cm ２ The thickness of the positive electrode composite layer was 130 μm, the peel strength was 2 mN / mm, and the electrode penetration resistance was 7 Ω. Furthermore, although no cracks were observed on the electrode exterior by visual inspection, cracks occurred during a 4 mm diameter winding test.

[0127]

[0128] (Example 20) A positive electrode was fabricated in the same manner as in Example 10, except that the sodium polyacrylate aqueous solution prepared in Reference Example 21 (a sodium polyacrylate aqueous solution containing sodium polyacrylate having a weight-average molecular weight of 510,000 and a concentration of 13 mass %) was used instead of the SBR emulsion. The basis weight of the positive electrode composite layer was 24.7 mg / cm ２The thickness of the positive electrode mixture layer was 83 μm, the peel strength was 9 mN / mm, and the electrode penetration resistance was 4.4 Ω. Visual inspection revealed no cracks on the electrode exterior, and no cracks occurred in the winding test.

[0129] Example 21 A positive electrode was produced in the same manner as in Example 20, except that the amount of the chelating group-containing alginic acid produced in Reference Example 3 was changed to 1.5 parts by mass. The basis weight of the positive electrode mixture layer was 23.0 mg / cm ２ The thickness of the positive electrode mixture layer was 81 μm, the peel strength was 9 mN / mm, and the electrode penetration resistance was 1.3 Ω. Furthermore, visual inspection revealed no cracks on the exterior of the electrode, and no cracks occurred in the winding test either.

[0130]

[0131] As is clear from the results shown in Tables 2 to 6, none of the electrodes (positive electrodes) obtained in Examples 10 to 21 were found to have cracks in the winding test, indicating that they are highly flexible (flexible) and are less likely to crack when wound, providing excellent workability during electrode production. Furthermore, the chelate group-containing alginic acid (chelate polymer) used in Examples 10 to 21 and produced in Reference Examples 2 to 5 was used in the evaluation of the heavy metal ion capture ability of the chelate polymer shown in Reference Examples 9 to 21. The manganese ion concentration measurement results were all less than 1 mass ppm. Therefore, it is clear that the use of these chelate polymers can suppress the deposition and accumulation of manganese from the positive electrode active material to the negative electrode active material. From these results, it can be seen that the electrodes produced in Examples 10 to 21 can impart excellent charge / discharge characteristics to batteries using them, and can also extend the cycle life of the battery.

[0132] As described above, the present disclosure provides a binder for a lithium-ion battery positive electrode and a slurry for forming a lithium-ion battery positive electrode composite layer that are easy to work with during electrode fabrication and enable the fabrication of a battery with an extended cycle life. Furthermore, by using the binder and a slurry, it is possible to provide a lithium-ion battery positive electrode and a lithium-ion battery that have excellent charge-discharge characteristics and an extended cycle life.

Claims

1. A binder for a positive electrode of a lithium ion battery, which binds a positive electrode active material, a conductive additive, and a current collector in a lithium ion battery, the binder comprising a chelating group-containing polymer compound and a flexible polymer.

2. The binder for a positive electrode of a lithium ion battery according to claim 1, wherein in the chelate group-containing polymer compound, the chelate group is bonded to the polymer compound via a covalent bond and / or an ionic bond.

3. The binder for a lithium ion battery positive electrode according to claim 1, wherein the flexible polymer is at least one selected from the group consisting of polyvinylidene fluoride and its copolymers, and polymers containing an aromatic vinyl monomer and an aliphatic conjugated diene monomer.

4. The binder for a lithium ion battery positive electrode according to claim 1, wherein the flexible polymer is a dried product of a water-based emulsion.

5. A slurry for forming a positive electrode mixture layer for a lithium ion battery, the slurry comprising a positive electrode active material, a conductive assistant, a chelating group-containing polymer compound, a flexible polymer, and water, and the binder for a lithium ion battery positive electrode according to claim 1.

6. A positive electrode for a lithium ion battery comprising the binder for a lithium ion battery positive electrode according to claim 1.

7. A lithium ion battery comprising the positive electrode for a lithium ion battery according to claim 6.

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