Composition for non-aqueous secondary battery positive electrode, slurry for non-aqueous secondary battery positive electrode, positive electrode for non-aqueous secondary battery, and non-aqueous secondary battery

Abstract

To provide a composition for a nonaqueous secondary battery positive electrode, which suppresses occurrence of electrode corrosion by preventing temporal pH increase in slurry for a positive electrode, and can improve adhesion and charge / discharge endurance characteristics of a positive electrode for a nonaqueous secondary battery.SOLUTION: A composition for a nonaqueous secondary battery positive electrode according to the present invention contains a polymer (A), a polysaccharide (B) in which at least a part of a hydroxyl group is protected with a protecting group, and a liquid medium (C). When the total of repeating units that are included in the polymer (A) is 100 mass%, the polymer (A) contains 0.1-10 mass% of repeating units (a1) derived from an unsaturated carboxylic acid.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a composition for a non-aqueous secondary battery cathode, a slurry for a non-aqueous secondary battery cathode, a cathode for a non-aqueous secondary battery, and a non-aqueous secondary battery.

Background Art

[0002] In recent years, as a power source for driving electronic devices, a power storage device having a high voltage and a high energy density has been demanded. As such a power storage device, a lithium ion battery, a lithium ion capacitor, etc. are expected.

[0003] An electrode used in such a power storage device is manufactured by applying and drying a composition (slurry for a power storage device electrode) containing an active material and a polymer functioning as a binder on the surface of a current collector. The characteristics required for the polymer used as a binder include the binding ability between the active materials, the adhesion ability between the active material and the current collector, the abrasion resistance in the process of winding the electrode, and the resistance to powder falling, such that fine powder of the active material does not fall off from the coated and dried composition coating film (hereinafter, also referred to as the "active material layer") even by subsequent cutting. By such a binder material exhibiting good adhesion and reducing the internal resistance of the battery caused by the binder material, good charge and discharge characteristics can be imparted to the power storage device.

[0004] It should be noted that, empirically, it has been clarified that the binding ability between the above-mentioned active materials, the adhesion ability between the active material and the current collector, and the resistance to powder falling are almost in a proportional relationship in terms of the quality of performance. Therefore, in this specification, these may sometimes be represented using the term "adhesion" including the above.

[0005] Recently, in order to produce an electrochemical device excellent in capacity and charge-discharge cycle characteristics, the use of a cathode active material having high reactivity with water has been studied. And when manufacturing a slurry for a cathode containing a cathode active material and a binder, the use of an aqueous binder has been studied for the purpose of cost reduction, safety improvement, and environmental load reduction.

[0006] Under these circumstances, various binder materials have been proposed to solve the various problems associated with positive electrode slurries (see, for example, Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] International Publication No. 2020 / 095466 [Patent Document 2] Japanese Patent Application Publication No. 2019-194944 Summary of the Invention [Problem to be solved by the invention]

[0008] However, when a positive electrode slurry containing the binder material disclosed in Patent Documents 1 and 2 is used, the water in the positive electrode slurry reacts with the positive electrode active material to generate hydroxide ions (OH - ) and these hydroxide ions can corrode the electrode. Furthermore, the positive electrodes produced using such positive electrode slurries are insufficient in terms of adhesion and charge / discharge durability, and further improvements are needed.

[0009] Some embodiments of the present invention prevent the pH of the positive electrode slurry from increasing over time, thereby improving the electrode's The present invention provides a composition for a non-aqueous secondary battery positive electrode that can suppress the occurrence of corrosion and improve the adhesion and charge / discharge durability of the positive electrode for the non-aqueous secondary battery. Furthermore, some aspects of the present invention provide a slurry for a non-aqueous secondary battery positive electrode that can suppress the occurrence of electrode corrosion by preventing an increase in pH over time and improve the adhesion and charge / discharge durability of the positive electrode for the non-aqueous secondary battery. Furthermore, some aspects of the present invention provide a non-aqueous secondary battery positive electrode that can suppress corrosion and improve the adhesion and charge / discharge durability. Furthermore, some aspects of the present invention provide a non-aqueous secondary battery with excellent charge / discharge durability.

Means for Solving the Problems

[0010] The present invention has been made to solve at least a part of the above problems and can be realized in any of the following aspects.

[0011] One aspect of the composition for a non-aqueous secondary battery cathode according to the present invention is containing a polymer (A), a polysaccharide (B) in which at least a part of the hydroxyl groups is protected by a protecting group, and a liquid medium (C), when the total of the repeating units contained in the polymer (A) is 100% by mass, the polymer (A) contains 0.1 to 10% by mass of a repeating unit (a1) derived from an unsaturated carboxylic acid.

[0012] In one aspect of the composition for a non-aqueous secondary battery cathode, the polysaccharide (B) may have a structure derived from cellulose or alginic acid.

[0013] In any aspect of the composition for a non-aqueous secondary battery cathode, the protecting group of the polysaccharide (B) may be deprotected by the action of a base.

[0014] In any aspect of the composition for a non-aqueous secondary battery cathode, the protecting group of the polysaccharide (B) may be an acyl group.

[0015] In any aspect of the composition for a non-aqueous secondary battery cathode, the polymer (A) may further contain 45 to 99% by mass of a repeating unit (a2) derived from an unsaturated carboxylic acid ester.

[0016] In any aspect of the composition for a non-aqueous secondary battery cathode, the polymer (A) may further contain 0.1 to 30% by mass of a repeating unit (a3) derived from an aromatic vinyl compound.

[0017] In any aspect of the composition for non-aqueous secondary battery cathode, When the polymer (A) is immersed in a solvent composed of propylene carbonate and diethyl carbonate at a volume fraction of 1:1 under the conditions of 70 °C for 24 hours, the swelling ratio may be 130% by mass or more and 350% by mass or less.

[0018] In any aspect of the composition for non-aqueous secondary battery cathode, For the polymer (A), when differential scanning calorimetry (DSC) is performed in accordance with JIS K7121, an endothermic peak may be observed in the temperature range of -50 °C to 50 °C.

[0019] In any aspect of the composition for non-aqueous secondary battery cathode, The polymer (A) is polymer particles, The number average particle diameter of the polymer particles may be 50 nm or more and 500 nm or less.

[0020] In any aspect of the composition for non-aqueous secondary battery cathode, The surface acid amount of the polymer particles may be 0.05 mmol / g or more and 6 mmol / g or less.

[0021] In any aspect of the composition for non-aqueous secondary battery cathode, The liquid medium (C) may be water.

[0022] One aspect of the slurry for non-aqueous secondary battery cathode according to the present invention is It contains the composition for non-aqueous secondary battery cathode in any of the above aspects and an active material.

[0023] One aspect of the positive electrode for non-aqueous secondary battery according to the present invention is It includes a current collector and an active material layer formed by applying and drying the slurry for non-aqueous secondary battery cathode in the above aspect on the surface of the current collector.

[0024] One aspect of the non-aqueous secondary battery according to the present invention is It includes a positive electrode for a non-aqueous secondary battery according to the above aspect.

Advantages of the Invention

[0025] According to the composition for a positive electrode of a non-aqueous secondary battery according to the present invention, by preventing the pH of the positive electrode slurry from rising over time, the occurrence of corrosion of the electrode is suppressed, and a positive electrode for a non-aqueous secondary battery excellent in adhesion and charge-discharge durability characteristics can be manufactured.

Embodiments for Carrying Out the Invention

[0026] Hereinafter, preferred embodiments according to the present invention will be described in detail. It should be understood that the present invention is not limited only to the embodiments described below, and includes various modifications implemented within the scope without changing the gist of the present invention.

[0027] In this specification, “(meth)acrylic acid~” is a concept including both “acrylic acid~” and “methacrylic acid~”. Also, “~(meth)acrylate” is a concept including both “~acrylate” and “~methacrylate”.

[0028] In this specification, “polysaccharide” means a carbohydrate containing monosaccharide units integrally bonded by glycosidic bonds. In the polysaccharide, a part of the hydrogen atoms of the hydroxyl groups of the monosaccharide units may be substituted with groups other than the protecting groups described later.

[0029] 1. Composition for Positive Electrode of Non-Aqueous Secondary Battery The composition for a positive electrode of a non-aqueous secondary battery according to an embodiment of the present invention contains a polymer (A), a polysaccharide (B) in which at least a part of the hydroxyl groups is protected by a protecting group (hereinafter, also simply referred to as “polysaccharide (B)”), and a liquid medium (C). When the total of the repeating units contained in the polymer (A) is 100% by mass, the polymer (A) contains 0.1 to 10% by mass of repeating units (a1) derived from an unsaturated carboxylic acid. Hereinafter, each component contained in the composition for a positive electrode of a non-aqueous secondary battery according to this embodiment will be described in detail.

[0030] 1.1. Polymer (A) The composition for a non-aqueous secondary battery positive electrode according to this embodiment contains a polymer (A). When the total of the repeating units contained in the polymer (A) is 100% by mass, the polymer (A) contains 0.1 to 10% by mass of a repeating unit (a1) derived from an unsaturated carboxylic acid (hereinafter also simply referred to as "repeating unit (a1)"). In addition to the repeating unit (a1), the polymer (A) may contain a repeating unit derived from another monomer copolymerizable therewith.

[0031] The polymer (A) contained in the composition for a non-aqueous secondary battery positive electrode according to this embodiment may be in the form of a latex dispersed in the liquid medium (C) or may be in a state dissolved in the liquid medium (C), but it is preferably in the form of a latex dispersed in the liquid medium (C). When the polymer (A) is in the form of a latex dispersed in the liquid medium (C), the stability of the slurry for a non-aqueous secondary battery positive electrode (hereinafter also referred to as "positive electrode slurry") prepared by mixing with the active material is good, and the coatability of the positive electrode slurry on the current collector is good, which is preferable.

[0032] Hereinafter, the repeating units constituting the polymer (A), the physical properties of the polymer (A), and the production method will be described in this order.

[0033] 1.1.1. Repeating units constituting the polymer (A) 1.1.1.1. Repeating unit (a1) derived from an unsaturated carboxylic acid The polymer (A) contains a repeating unit (a1) derived from an unsaturated carboxylic acid. The content ratio of the repeating unit (a1) derived from an unsaturated carboxylic acid is 0.1 to 10% by mass based on 100% by mass of the total repeating units contained in the polymer (A). The lower limit of the content ratio of the repeating unit (a1) is preferably 0.2% by mass, more preferably 0.5% by mass. The upper limit of the content ratio of the repeating unit (a1) is preferably 9% by mass, more preferably 8% by mass. When the polymer (A) contains the repeating unit (a1) within the above range, the dispersion stability of the polymer (A) during the preparation of the positive electrode slurry is excellent, and thus aggregates are less likely to occur. In addition, an increase in the slurry viscosity over time can also be suppressed.

[0034] The unsaturated carboxylic acid is not particularly limited, and examples thereof include monocarboxylic acids and dicarboxylic acids (including anhydrides) such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, and itaconic acid, and one or more selected from these can be used. As the unsaturated carboxylic acid, it is preferable to use one or more selected from acrylic acid, methacrylic acid, and itaconic acid.

[0035] 1.1.1.2. Other repeating units In addition to the repeating unit (a1), the polymer (A) may contain a repeating unit derived from another monomer copolymerizable therewith. Examples of such a repeating unit include a repeating unit (a2) derived from an unsaturated carboxylic acid ester (hereinafter also simply referred to as "repeating unit (a2)"), a repeating unit (a3) derived from an aromatic vinyl compound (hereinafter also simply referred to as "repeating unit (a3)"), a repeating unit (a4) derived from an α,β-unsaturated nitrile compound (hereinafter also simply referred to as "repeating unit (a4)"), a repeating unit (a5) derived from (meth)acrylamide (hereinafter also simply referred to as "repeating unit (a5)"), a repeating unit (a6) derived from a compound having a sulfonic acid group (hereinafter also simply referred to as "repeating unit (a6)"), a repeating unit derived from a cationic monomer, and the like.

[0036] <Repeating unit (a2) derived from an unsaturated carboxylic acid ester> Polymer (A) may contain a repeating unit (a2) derived from an unsaturated carboxylic acid ester. The content ratio of the repeating unit (a2) is preferably 45 to 99% by mass when the total of the repeating units contained in the polymer (A) is 100% by mass. The lower limit of the content ratio of the repeating unit (a2) is more preferably 46% by mass, and particularly preferably 47% by mass. The upper limit of the content ratio of the repeating unit (a2) is more preferably 98% by mass, and particularly preferably 97% by mass. When the polymer (A) contains the repeating unit (a2) within the above range, the affinity between the polymer (A) and the electrolytic solution becomes better, and in a non-aqueous secondary battery, the increase in internal resistance due to the polymer (A) becoming an electric resistance component can be suppressed. Further, it is possible to effectively suppress the decrease in the binding property between the positive electrode active material layer and the current collector due to the polymer (A) excessively absorbing the electrolytic solution. Substance layer and the current collector can be effectively suppressed.

[0037] Among unsaturated carboxylic acid esters, (meth)acrylic acid esters can preferably be used. Specific examples of (meth)acrylic acid esters include, for example, methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, n-amyl (meth)acrylate, isoamyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, allyl (meth)acrylate, 2-hydroxymethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 5-hydroxypentyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, glycerin mono(meth)acrylate, glycerin di(meth)acrylate, etc. One or more selected from these can be used. Among these, one or more selected from methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, cyclohexyl (meth)acrylate, ethylene glycol di(meth)acrylate, and 2-hydroxyethyl (meth)acrylate are preferable, and methyl (meth)acrylate is particularly preferable.

[0038] <Repeating unit (a3) derived from an aromatic vinyl compound> The polymer (A) may contain a repeating unit (a3) derived from an aromatic vinyl compound. The content ratio of the repeating unit (a3) derived from the aromatic vinyl compound is preferably 0.1 to 30% by mass when the total of the repeating units contained in the polymer (A) is 100% by mass. The lower limit of the content ratio of the repeating unit (a3) is more preferably 0.2% by mass, and particularly preferably 0.5% by mass. The upper limit of the content ratio of the repeating unit (a3) is more preferably 27% by mass, and particularly preferably 25% by mass. By containing the polymer (A) with the repeating unit (a3) within the above range, the fusion of the polymers (A) dispersed in the active material layer can be suppressed, and the permeability of the electrolyte can be improved. Therefore, a non-aqueous secondary battery showing good charge-discharge cycle characteristics may be obtained. Further, since it shows good adhesion to ternary lithium nickel cobalt manganese oxide (hereinafter also referred to as "NMC"), lithium nickel oxide (hereinafter also referred to as "NCA"), etc. used as the active material, a positive electrode for a non-aqueous secondary battery excellent in adhesion may be obtained.

[0039] The aromatic vinyl compound is not particularly limited, and examples thereof include styrene, α-methylstyrene, p-methylstyrene, vinyltoluene, chlorostyrene, divinylbenzene, etc., and one or more selected from these can be used.

[0040] <Repeating unit (a4) derived from an α,β-unsaturated nitrile compound> The polymer (A) may contain a repeating unit (a4) derived from an α,β-unsaturated nitrile compound. The content ratio of the repeating unit (a4) is preferably 0 to 60% by mass when the total of the repeating units contained in the polymer (A) is 100% by mass. The lower limit of the content ratio of the repeating unit (a4) is more preferably 0.5% by mass, and particularly preferably 1% by mass. The upper limit of the content ratio of the repeating unit (a4) is more preferably 55% by mass, and particularly preferably 50% by mass. By containing the repeating unit (a4) in the above range in the polymer (A), it becomes possible to reduce the dissolution of the polymer (A) in the electrolytic solution, and in some cases, it is possible to suppress a decrease in adhesion due to the electrolytic solution. Further, in some cases, it is possible to suppress an increase in the internal resistance due to the dissolved polymer component becoming an electric resistance component in the non-aqueous secondary battery. When the dissolved polymer component becomes an electric resistance component in the non-aqueous secondary battery, the increase in the internal resistance can be suppressed in some cases.

[0041] The α,β-unsaturated nitrile compound is not particularly limited, and examples thereof include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethylacrylonitrile, vinylidene cyanide, etc., and one or more selected from these can be used. Among these, one or more selected from the group consisting of acrylonitrile and methacrylonitrile are preferable, and acrylonitrile is particularly preferable.

[0042] <(Repeating unit (a5) derived from (meth)acrylamide)> The polymer (A) may contain a repeating unit (a5) derived from (meth)acrylamide. The content ratio of the repeating unit (a5) is preferably 0 to 10% by mass when the total of the repeating units contained in the polymer (A) is 100% by mass. The lower limit of the content ratio of the repeating unit (a5) is more preferably 1% by mass, and particularly preferably 2% by mass. The upper limit of the content ratio of the repeating unit (a5) is more preferably 8% by mass, and particularly preferably 5% by mass. When the polymer (A) contains the repeating unit (a5) within the above range, the dispersibility of the active material in the slurry may be good. Also, the flexibility of the obtained active material layer may be appropriate, and the adhesion between the current collector and the active material layer may be improved. Furthermore, since the binding ability between active materials such as NMC and NCA can be enhanced, an active material layer with better flexibility and adhesion to the current collector may be obtained.

[0043] (Meth)acrylamide is not particularly limited, and examples thereof include acrylamide, methacrylamide, N-isopropylacrylamide, N,N-dimethylacrylamide, N,N-dimethylmethacrylamide, N,N-diethylacrylamide, N,N-diethylmethacrylamide, N,N-dimethylaminopropylacrylamide, N,N-dimethylaminopropylmethacrylamide, N-methylolacrylamide, N-methylolmethacrylamide, diacetoneacrylamide, maleic acid amide, acrylamide tert-butyl sulfonic acid, etc. One or more selected from these can be used.

[0044] (Repeating unit (a6) derived from a compound having a sulfonic acid group) The polymer (A) may contain a repeating unit (a6) derived from a compound having a sulfonic acid group. The content ratio of the repeating unit (a6) is preferably 0 to 10% by mass when the total of the repeating units contained in the polymer (A) is 100% by mass. The lower limit of the content ratio of the repeating unit (a6) is more preferably 0.5% by mass, and particularly preferably 1% by mass. The upper limit of the content ratio of the repeating unit (a6) is more preferably 8% by mass, and particularly preferably 5% by mass.

[0045] The compound having a sulfonic acid group is not particularly limited, and examples thereof include compounds such as vinyl sulfonic acid, styrene sulfonic acid, allyl sulfonic acid, sulfoethyl (meth) acrylate, sulfopropyl (meth) acrylate, sulfobutyl (meth) acrylate, 2-acrylamido-2-methylpropane sulfonic acid, 2-hydroxy-3-acrylamidopropane sulfonic acid, 3-allyloxy-2-hydroxypropane sulfonic acid, and alkali salts thereof. One or more selected from these can be used.

[0046] <Repeating unit derived from cationic monomer> The polymer (A) may contain a repeating unit derived from a cationic monomer. The cationic monomer is not particularly limited, but is preferably at least one monomer selected from the group consisting of secondary amine (salt), tertiary amine (salt), and quaternary ammonium salt. Specific examples of these cationic monomers are not particularly limited, but include (meth) 2-(Dimethylamino)ethyl acrylate, methyl chloride quaternary salt of dimethylaminoethyl (meth)acrylate, 2-(Diethylamino)ethyl (meth)acrylate, 3-(Dimethylamino)propyl (meth)acrylate, 3-(Diethylamino)propyl (meth)acrylate, 4-(Dimethylamino)phenyl (meth)acrylate, 2-[(3,5-Dimethylpyrazolyl)carbonylamino]ethyl (meth)acrylate, 2-(0-[1’-Methylpropylideneamino]carboxamido)ethyl (meth)acrylate, 2-(1-Aziridinyl)ethyl (meth)acrylate, methacryloylcholine chloride, tris(2-acryloyloxyethyl) isocyanurate, 2-Vinylpyridine, quinacrine red, 1,2-di(2-pyridyl)ethylene, 4’-Hydrazino-2-stilbazoles dihydrochloride hydrate, 4-(4-Dimethylaminostyryl)quinoline, 1-Vinylimidazole, diallylamine, diallylamine hydrochloride, triallylamine, diallyldimethylammonium chloride, dichloramide, N-Allylbenzylamine, N-Allylaniline, 2,4-Diamino-6-diallylamino-1,3,5-triazine, N-trans-Cinnamyl-N-methyl-(1-naphthylmethyl)amine hydrochloride, trans-N-(6,6-Dimethyl-2-hepten-4-ynyl)-N-methyl-1-naphthylmethylamine hydrochloride, etc. may be mentioned, and one or more selected from these can be used.

[0047] 1.1.2. Physical properties of polymer (A) 1.1.2.1. Glass transition temperature (Tg) The polymer (A) preferably has an endothermic peak in the temperature range of -50°C to 50°C when measured by differential scanning calorimetry (DSC) in accordance with JIS K7121. The lower limit of the temperature of this endothermic peak (i.e., the glass transition temperature (Tg)) is more preferably -48°C, and particularly preferably -45°C. The upper limit of Tg is more preferably 48°C, and particularly preferably 45°C. When the polymer (A) has only one endothermic peak in the DSC analysis and the peak temperature is within the above range, the polymer (A) exhibits good adhesion and can impart better flexibility and adhesiveness to the active material layer, which is preferable.

[0048] 1.1.2.2. Swelling ratio When the polymer (A) is immersed in a solvent composed of propylene carbonate and diethyl carbonate at a volume fraction of 1:1 under the conditions of 70°C for 24 hours, the swelling ratio is preferably 130% by mass or more and 350% by mass or less. The lower limit of the swelling ratio is more preferably 150% by mass, and particularly preferably 170% by mass. The upper limit of the swelling ratio is more preferably 320% by mass, and particularly preferably 300% by mass. When the swelling ratio is within the above range, the polymer (A) can swell moderately with respect to the electrolyte solution. As a result, the solvated lithium ions can easily reach the active material, reducing the internal resistance of the electrode and realizing better charge-discharge cycle characteristics. Also, with a swelling ratio within the above range, no large volume change occurs, so the adhesion is also excellent. The swelling ratio of the polymer (A) can be measured by the method described in the examples below.

[0049] 1.1.2.3. Number average particle diameter When the polymer (A) is in the form of particles, the number-average particle diameter of the particles is preferably 50 nm or more and 500 nm or less. The lower limit of the number-average particle diameter is more preferably 60 nm, and particularly preferably 70 nm. The upper limit of the number-average particle diameter is more preferably 450 nm, and particularly preferably 400 nm. When the number-average particle diameter of the particles of the polymer (A) is within the above range, the particles of the polymer (A) are likely to adsorb on the surface of the active material, so that the particles of the polymer (A) can follow and move as the active material moves. As a result, migration can be suppressed, and thus deterioration of electrical characteristics may be reduced. The number-average particle diameter of the polymer (A) can be measured by the method described in the examples below.

[0050] 1.1.2.4. Surface acid amount When the polymer (A) is in the form of particles, the surface acid amount of the particles is preferably 0.05 mmol / g or more and 6 mmol / g or less. The lower limit of the surface acid amount is more preferably 0.06 mmol / g, and particularly preferably 0.07 mmol / g. The upper limit of the surface acid amount is more preferably 5.8 mmol / g, and particularly preferably 5.5 mmol / g. When the surface acid amount of the particles of the polymer (A) is within the above range, a stable and homogeneous slurry can be prepared. When an active material layer is prepared using such a homogeneous slurry, an active material layer in which the active material and the particles of the polymer (A) are uniformly dispersed and the thickness variation is small can be obtained. As a result, the variation in charge-discharge characteristics within the electrode can be suppressed, and thus a non-aqueous secondary battery exhibiting good charge-discharge characteristics can be obtained.

[0051] 1.1.3. Method for producing polymer (A) The method for producing the polymer (A) is not particularly limited. For example, it can be carried out by an emulsion polymerization method in the presence of a known emulsifier (surfactant), chain transfer agent, polymerization initiator, etc. As the emulsifier (surfactant), chain transfer agent, and polymerization initiator, the compounds described in Japanese Patent No. 5999399 and the like can be used.

[0052] The emulsion polymerization method for synthesizing the polymer (A) may be carried out by one-stage polymerization or may be carried out by multi-stage polymerization of two or more stages.

[0053] When the polymer (A) is synthesized by one-stage polymerization, the above monomer mixture can be subjected to emulsion polymerization in the presence of a suitable emulsifier, chain transfer agent, polymerization initiator, etc., preferably at 40 to 80 ° C, preferably for 4 to 36 hours.

[0054] When the polymer (A) is synthesized by two-stage polymerization, it is preferable to set the polymerization of each stage as follows.

[0055] The usage ratio of the monomer used in the first-stage polymerization is preferably in the range of 20 to 100% by mass, more preferably in the range of 25 to 100% by mass, based on the total mass of the monomers (the total mass of the monomer used in the first-stage polymerization and the monomer used in the second-stage polymerization). By carrying out the first-stage polymerization with such a usage ratio of the monomer, polymer (A) particles excellent in dispersion stability and hardly generating aggregates can be obtained, and the viscosity increase over time of the composition for the non-aqueous secondary battery positive electrode can also be suppressed, which is preferable.

[0056] The type and usage ratio of the monomer used in the second-stage polymerization may be the same as or different from the type and usage ratio of the monomer used in the first-stage polymerization.

[0057] From the viewpoint of the dispersibility of the obtained polymer (A) particles, the polymerization conditions for each stage are preferably as follows. · First-stage polymerization; preferably a temperature of 40 to 80 ° C: preferably a polymerization time of 2 to 36 hours: preferably a polymerization conversion rate of 50% by mass or more, more preferably 60% by mass or more. · Second-stage polymerization; preferably a temperature of 40 to 80 ° C; preferably a polymerization time of 2 to 18 hours.

[0058] By setting the total solid concentration in emulsion polymerization to 50% by mass or less, the polymerization reaction can proceed with good dispersion stability of the particles of the resulting polymer (A). This total solid concentration is preferably 48% by mass or less, more preferably 45% by mass or less.

[0059] Even when the synthesis of the polymer (A) is carried out as a one-stage polymerization or a two-stage polymerization method, after the completion of emulsion polymerization, it is preferable to adjust the pH to about 5 to 10, preferably 6 to 9.5, more preferably 6.5 to 9 by adding a neutralizing agent to the polymerization mixture. The neutralizing agent used here is not particularly limited, and examples include metal hydroxides such as sodium hydroxide and potassium hydroxide; ammonia and the like. By setting the pH within the above range, the stability of the polymer (A) becomes good. After the neutralization treatment, by concentrating the polymerization mixture, the solid content concentration can be increased while maintaining good stability of the polymer (A).

[0060] 1.1.4. Content ratio of polymer (A) In the composition for a non-aqueous secondary battery positive electrode according to this embodiment, the content ratio of the polymer (A) is preferably 10 to 90% by mass, more preferably 25 to 85% by mass, and particularly preferably 50 to 80% by mass in 100% by mass of the polymer component. Here, the polymer component includes the polymer (A), the polysaccharide (B) described later, polymers other than the polymer (A), thickeners, and the like.

[0061] 1.2. Polysaccharide (B) The composition for a non-aqueous secondary battery cathode according to this embodiment contains a polysaccharide (B) in which at least a part of the hydroxyl groups is protected by a protecting group. When a liquid medium mainly composed of water is used to prepare the cathode slurry, there is a problem that water reacts with the cathode active material to generate hydroxide ions, and the pH shifts to the basic side, causing corrosion of the electrode. The composition for a non-aqueous secondary battery cathode according to this embodiment contains the polysaccharide (B), and the protecting group of the polysaccharide (B) captures hydroxide ions that are bases and is deprotected, thereby consuming the hydroxide ions in the system and preventing the pH of the cathode slurry from rising over time. Thereby, the occurrence of electrode corrosion can be effectively suppressed.

[0062] The polysaccharide constituting the polysaccharide (B) is not particularly limited as long as it is a carbohydrate having a structure in which two or more monosaccharides are bonded via a glycosidic bond. Examples of the monosaccharide include sugars composed only of carbon atoms, hydrogen atoms, and oxygen atoms such as glucose, mannose, xylose, galactose, mannose, and fucose; amino sugars such as N-acetylglucosamine and N-acetylgalactosamine; and sugar acids such as saccharic acid, mannuronic acid, and glucuronic acid. The polysaccharide may be composed of only one type of the monosaccharides or may be composed of two or more types of the monosaccharides. Examples of the polysaccharide composed of only one type of the monosaccharides include amylose, cellulose, curdlan, and chitin. Examples of the polysaccharide composed of two or more types of the monosaccharides include agarose, hyaluronic acid, and alginic acid.

[0063] In the polysaccharide, a part of the hydrogen atoms of the hydroxyl groups contained in the polysaccharide may be substituted with a group (R 1 ) other than the protecting group described later. Examples of R 1 include an alkyl group such as a methyl group and an ethyl group; a hydroxyalkyl group such as a 2-hydroxyethyl group; a carboxyalkyl group such as a carboxymethyl group; a glyceryl group, an alkylglyceryl group, and the like. Examples of R 1Examples of the polysaccharide having it include methylcellulose, methyl glyceryl cellulose, carboxymethyl cellulose, and the like.

[0064] When the polysaccharide has a carboxy group in the molecule, some or all of the hydrogen atoms constituting the carboxy group may be substituted with metal ions. Examples of the metal ions include alkali metal ions, alkaline earth metal ions, ions of elements located in Groups 3 to 12 of the periodic table, and aluminum ions.

[0065] The weight average molecular weight (Mw) of the polysaccharide is preferably from 10,000 to 4,000,000, more preferably from 100,000 to 3,000,000, still more preferably from 300,000 to 2,000,000 in order to appropriately maintain the slurry viscosity.

[0066] The protecting group of the polysaccharide (B) is not particularly limited as long as it is a group that can be used as a protecting group for a hydroxyl group, but it is preferably one that is hydrolyzed and deprotected by the action of a base. Examples of such protecting groups include arylmethyl groups such as benzyl group and 4-methoxybenzyl group; trihydrocarbylsilyl groups such as trimethylsilyl group and tert-butyldimethylsilyl group; acyl groups such as acetyl group and benzoyl group. Among these, an acyl group is preferable in order to facilitate the introduction into the polysaccharide.

[0067] ​Examples of the acyl group include aliphatic acyl groups and aromatic acyl groups. The aliphatic acyl group may be linear or branched, and a linear structure is preferred in order to improve both solubility in organic solvents and water solubility. Also, the aliphatic acyl group may be saturated or unsaturated, and a saturated structure is preferred in order to improve oxidation resistance. The number of carbon atoms of the aliphatic acyl group is preferably 2 to 20, more preferably 2 to 15, and even more preferably 2 to 10 in order to improve both solubility in organic solvents and water solubility. The aliphatic hydrocarbon group in the aliphatic acyl group may have heteroatoms such as oxygen, nitrogen, sulfur, fluorine, chlorine, bromine, and silicon. Specific examples of the aliphatic acyl group include acyl groups derived from fatty acids such as acetic acid, propionic acid, and pivalic acid. Also, the aromatic acyl group is not particularly limited as long as it is an acyl group derived from an aromatic carboxylic acid. The number of carbon atoms of the aromatic acyl group is preferably 6 to 20, more preferably 6 to 15, and even more preferably 6 to 10 in order to improve both solubility in organic solvents and water solubility. The aromatic hydrocarbon group in the aromatic acyl group may have heteroatoms such as oxygen, nitrogen, sulfur, fluorine, chlorine, bromine, and silicon. Specific examples of the aromatic acyl group include acyl groups derived from aromatic carboxylic acids such as benzoic acid, 4-methoxybenzoic acid, naphthalene-1-carboxylic acid, and naphthalene-2-carboxylic acid.

[0068] The polysaccharide (B) is not particularly limited as long as it is a compound in which at least some of the hydrogen atoms of the hydroxyl groups of the polysaccharide are substituted with the protecting group, and any combination can be selected from the polysaccharide and the protecting group. Also, the protecting group may be used alone or a combination of two or more kinds may be selected.

[0069] The substitution ratio of the hydroxyl groups of polysaccharide (B) by a protecting group (hereinafter also referred to as "substitution ratio of hydroxyl groups") is preferably 30 mol% or more, more preferably 45 mol% or more, and particularly preferably 65 mol% or more in order to suppress the increase in slurry pH. And in order to simplify the synthesis, it is preferably 99 mol% or less, more preferably 98 mol% or less, and particularly preferably 97 mol% or less. The substitution ratio of hydroxyl groups can be calculated using gas chromatography, and specifically, it can be calculated by the method described in the examples.

[0070] The weight-average molecular weight of polysaccharide (B) is preferably 100,000 or more, more preferably 120,000 or more, still more preferably 200,000 or more, even more preferably 300,000 or more, and particularly preferably 500,000 or more in order to appropriately maintain the slurry viscosity. And from the same viewpoint, it is preferably 5,000,000 or less, more preferably 4,000,000 or less, still more preferably 3,000,000 or less, even more preferably 2,000,000 or less. From the same viewpoint, the weight-average molecular weight is preferably from 100,000 to 5,000,000, more preferably from 120,000 to 4,000,000, still more preferably from 200,000 to 4,000,000, even more preferably from 300,000 to 3,000,000, and even more preferably from 500,000 to 2,000,000.

[0071] Polysaccharide (B) can be produced by reacting the polysaccharide with a compound capable of introducing the protecting group. When the protecting group is an acyl group, it can be produced by reacting the polysaccharide with an acid halide having a linear or branched alkyl group or alkenyl group, or an aryl group to substitute (acylate) the hydrogen atom of the hydroxyl group of the polysaccharide.

[0072] The content ratio of polysaccharide (B) in the non-aqueous secondary battery positive electrode composition according to this embodiment is preferably 10 to 90% by mass, more preferably 15 to 80% by mass, and particularly preferably 20 to 70% by mass when the polymer component is 100% by mass. Here, the polymer component includes the polymer (A), the polysaccharide (B), polymers other than the polymer (A) described later, thickeners, and the like.

[0073] 1.3. Liquid medium (C) The composition for a non-aqueous secondary battery cathode according to this embodiment contains a liquid medium (C). As the liquid medium (C), an aqueous medium containing water is preferable, and water is more preferable. The aqueous medium can contain a non-aqueous medium other than water. Examples of this non-aqueous medium include amide compounds, hydrocarbons, alcohols, ketones, esters, amine compounds, lactones, sulfoxides, sulfone compounds, etc., and one or more selected from these can be used. By using an aqueous medium as the liquid medium (C) in the composition for a non-aqueous secondary battery cathode according to this embodiment, the degree of adverse impact on the environment is reduced, and the safety for handling workers is also increased.

[0074] The content ratio of the non-aqueous medium contained in the aqueous medium is preferably 10% by mass or less, more preferably 5% by mass or less, and particularly preferably substantially not contained in 100% by mass of the aqueous medium. Here, "substantially not contained" means to the extent that a non-aqueous medium is not intentionally added as the liquid medium (C), and it may include non-aqueous media unavoidably mixed in when preparing the composition for a non-aqueous secondary battery cathode.

[0075] 1.4. Other Additives The composition for a non-aqueous secondary battery cathode according to this embodiment can contain additives other than the above-described components as necessary. Examples of such additives include polymers other than the polymer (A), preservatives, thickeners, etc.

[0076] 1.4.1. Polymers Other than Polymer (A) The composition for a non-aqueous secondary battery cathode according to this embodiment may contain a polymer other than the polymer (A). Such polymers are not particularly limited, but include acrylic polymers containing unsaturated carboxylic acid esters or derivatives thereof as constitutional units, fluorine-based polymers such as PVDF (polyvinylidene fluoride), etc. These polymers may be used alone or in combination of two or more. By containing these polymers, flexibility and adhesion may be further improved.

[0077] 1.4.2. Antiseptic The composition for non-aqueous secondary battery positive electrode according to this embodiment may contain an antiseptic. By containing an antiseptic, when the composition for non-aqueous secondary battery positive electrode is stored, it may be possible to suppress the growth of bacteria, mold, etc. and the generation of foreign matters. Specific examples of the antiseptic include the compounds described in Japanese Patent No. 5477610 and the like.

[0078] 1.4.3. Thickener The composition for non-aqueous secondary battery positive electrode according to this embodiment may contain a thickener. By containing a thickener, the coating property of the slurry, the charge and discharge characteristics of the obtained non-aqueous secondary battery, etc. may be further improved.

[0079] Specific examples of the thickener include, for example, cellulose compounds such as carboxymethyl cellulose, methyl cellulose, hydroxypropyl cellulose; poly(meth)acrylic acid; ammonium salts or alkali metal salts of the cellulose compounds or the poly(meth)acrylic acid; polyvinyl alcohol-based (co)polymers such as polyvinyl alcohol, modified polyvinyl alcohol, ethylene-vinyl alcohol copolymer; and water-soluble polymers such as saponified products of copolymers of unsaturated carboxylic acids such as (meth)acrylic acid, maleic acid, fumaric acid and vinyl esters. Among these, alkali metal salts of carboxymethyl cellulose, alkali metal salts of poly(meth)acrylic acid, etc. are preferable.

[0080] Examples of commercially available products of these thickeners include alkali metal salts of carboxymethyl cellulose such as CMC1120, CMC1150, CMC2200, CMC2280, CMC2450 (all manufactured by Daicel Corporation).

[0081] When the composition for non-aqueous secondary battery cathode according to this embodiment contains a thickener, the content ratio of the thickener is preferably 5% by mass or less, more preferably 0.1 - 4% by mass, based on 100% by mass of the total solid content of the composition for non-aqueous secondary battery cathode.

[0082] 1.5. pH of the composition for non-aqueous secondary battery cathode The pH of the composition for non-aqueous secondary battery cathode according to this embodiment is preferably 5.0 - 10.5, more preferably 6.0 - 10.0, and particularly preferably 6.5 - 9.5. If the pH is within the above range, it is possible to suppress the occurrence of problems such as insufficient leveling property and liquid dripping, and it becomes easy to manufacture a non-aqueous secondary battery cathode that achieves both good electrical characteristics and adhesion.

[0083] As used in this specification, "pH" refers to the physical property measured as follows. At 25°C, it is the value measured in accordance with JIS Z8802:2011 using a pH meter with a glass electrode calibrated with neutral phosphate standard solution and borate standard solution as pH standard solutions. Examples of such pH meters include "HM-7J" manufactured by Toa DKK Corporation and "D-51" manufactured by Horiba, Ltd.

[0084] It should be noted that although it is not denied that the pH of the composition for non-aqueous secondary battery cathode is affected by the monomer composition constituting the polymer (A), it is added that it is not determined only by the monomer composition. That is, generally, even with the same monomer composition, it is known that the pH of the composition for non-aqueous secondary battery cathode changes depending on polymerization conditions and the like, and the examples in this specification only show one example of this.

[0085] For example, even with the same monomer composition, when all the unsaturated carboxylic acid is charged into the polymerization reaction solution from the beginning and then other monomers are sequentially added, and when monomers other than the unsaturated carboxylic acid are charged into the polymerization reaction solution and the unsaturated carboxylic acid is finally added, the amount of carboxy groups derived from the unsaturated carboxylic acid exposed on the surface of the resulting polymer is different. Thus, it is considered that even just changing the order of adding monomers in the polymerization method can cause a significant difference in the pH of the composition for the non-aqueous secondary battery positive electrode.

[0086] 2. Slurry for Non-aqueous Secondary Battery Positive Electrode The slurry for a non-aqueous secondary battery positive electrode according to one embodiment of the present invention contains the above-described composition for a non-aqueous secondary battery positive electrode and an active material. The above-described composition for a non-aqueous secondary battery positive electrode is used as a material for producing a positive electrode (active material layer) for a non-aqueous secondary battery that improves the binding ability between active materials, the adhesion ability between the active material and the current collector, and the resistance to powder falling. The positive electrode for a non-aqueous secondary battery is manufactured by applying the above-described slurry for a non-aqueous secondary battery positive electrode onto the surface of a current collector and then drying it to form an active material layer on the surface of the current collector.

[0087] Generally, the slurry for a non-aqueous secondary battery positive electrode often contains a binder component such as an SBR-based copolymer and a thickener such as carboxymethyl cellulose in order to improve the adhesion. On the other hand, the slurry for a non-aqueous secondary battery positive electrode according to the present embodiment can improve the flexibility and adhesion even when it contains only the polymer (A) described above as the polymer component. Of course, the slurry for a non-aqueous secondary battery positive electrode according to the present embodiment may further contain a polymer other than the polymer (A) or a thickener in order to further improve the adhesion.

[0088] Hereinafter, the components included in the slurry for a non-aqueous secondary battery positive electrode according to the present embodiment will be described.

[0089] 2.1. Composition for Non-aqueous Secondary Battery Positive Electrode The composition for a non-aqueous secondary battery positive electrode has been described above, so the description will be omitted.

[0090] The content ratio of the polymer component in the slurry for the non-aqueous secondary battery cathode according to this embodiment is preferably 1 to 8 parts by mass, more preferably 1 to 7 parts by mass, and particularly preferably 1.5 to 6 parts by mass with respect to 100 parts by mass of the active material. When the content ratio of the polymer component is within the above range, the dispersibility of the active material in the slurry becomes good, and the coatability of the slurry is also excellent. Here, the polymer component includes polymer (A), polysaccharide (B), polymers other than polymer (A), thickeners, and the like.

[0091] 2.2. Active Material Examples of the active material used in the slurry for the non-aqueous secondary battery cathode according to this embodiment include oxides containing lithium atoms, lead compounds, tin compounds, arsenic compounds, antimony compounds, aluminum compounds, conductive polymers such as polyacene, A X B Y O Z (However, A is an alkali metal or a transition metal, B is at least one selected from transition metals such as cobalt, nickel, aluminum, tin, manganese, etc., O represents an oxygen atom, and X, Y, and Z are numbers in the ranges of 1.10 > X > 0.05, 4.00 > Y > 0.85, and 5.00 > Z > 1.5, respectively), and composite metal oxides represented thereby, and other metal oxides, etc. are mentioned. Specific examples thereof include the compounds described in Japanese Patent No. 5999399 and the like.

[0092] Examples of the oxide containing a lithium atom include one or more selected from lithium atom-containing oxides (olivine-type lithium-containing phosphate compounds) represented by the following general formula (1) and having an olivine-type crystal structure.

[0093] Li 1-x M x (AO4) ·····(1) (In formula (1), M is an ion of at least one metal selected from the group consisting of Mg, Ti, V, Nb, Ta, Cr, Mn, Fe, Co, Ni, Cu, Zn, Al, Ga, Ge, and Sn, A is at least one selected from the group consisting of Si, S, P, and V, and x is a number satisfying the relationship of 0 < x < 1.) In addition, the value of x in the general formula (1) is selected so that the valence of the entire general formula (1) becomes 0 valence according to the valences of M and A.

[0094] Examples of the olivine-type lithium-containing phosphate compound include LiFePO4, LiCoPO4, LiMnPO4, Li 0.90 Ti 0.05 Nb 0.05 Fe 0.30 Co 0.30 Mn 0.30 PO4 and the like. Among these, LiFePO4 (lithium iron phosphate) is particularly preferable because the iron compound used as a raw material is easily available and inexpensive.

[0095] The average particle diameter of the olivine-type lithium-containing phosphate compound is preferably in the range of 1 to 30 μm, more preferably in the range of 1 to 25 μm, and particularly preferably in the range of 1 to 20 μm.

[0096] In addition, the active material layer may contain the active materials exemplified below. For example, conductive polymers such as polyacene; A X B Y O Z (However, A is an alkali metal or a transition metal, B is at least one selected from transition metals such as cobalt, nickel, aluminum, tin, manganese, etc., O represents an oxygen atom, and X, Y, and Z are each 1.10 > X > 0.05, 4.00 > Y > 0 .85, 5.00 > Z > 1.5), composite metal oxides represented by the above, and other metal oxides and the like.

[0097] Examples of the composite metal oxide include lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, ternary nickel cobalt manganese lithium oxide, and the like.

[0098] When a liquid medium mainly composed of water is used to prepare the positive electrode slurry, there is a problem that the charge and discharge characteristics are inferior. The positive electrode active material is known to have high reactivity with water, and it is considered that one of the factors is that the hydroxide ions generated by the reaction between the positive electrode active material and water corrode the positive electrode surface.

[0099] However, the positive electrode for a non-aqueous secondary battery produced using the slurry for a non-aqueous secondary battery positive electrode according to this embodiment can exhibit good charge and discharge characteristics without the above problems even when a liquid medium mainly composed of water is used as the liquid medium of the positive electrode slurry. The reason for this is considered to be that the protecting group of the polysaccharide (B) reacts with the hydroxide ions generated by the reaction between the positive electrode active material and water and is deprotected, so that the hydroxide ions in the system are consumed and the corrosion of the positive electrode surface can be suppressed.

[0100] The shape of the active material is preferably particulate. The average particle diameter of the active material is preferably 0.1 to 100 μm, more preferably 1 to 20 μm. Here, the average particle diameter of the active material refers to the volume average particle diameter calculated from the particle size distribution measured using a particle size distribution measuring device based on the laser diffraction method as the measurement principle. Examples of such a laser diffraction type particle size distribution measuring device include HORIBA LA-300 series and HORIBA LA-920 series (both manufactured by Horiba, Ltd.).

[0101] The usage ratio of the active material is preferably such that the content ratio of the polymer (A) to 100 parts by mass of the active material is 0.5 to 8 parts by mass, more preferably 1 to 6 parts by mass, and particularly preferably 2 to 4 parts by mass. By setting the usage ratio in this way, an electrode having excellent adhesion, low electrode resistance, and excellent charge and discharge characteristics can be manufactured.

[0102] 2.3. Other components In the slurry for the non-aqueous secondary battery cathode according to this embodiment, other components may be added as necessary in addition to the components described above. Examples of such components include polymers other than polymer (A), thickeners, liquid media, conductivity-imparting agents, pH adjusters, corrosion inhibitors, cellulose fibers, and the like. As the polymer other than polymer (A) and the thickener, they can be appropriately selected from the compounds exemplified in the section of "1.4. Other Additives" and used in the same purpose and content ratio.

[0103] <Liquid medium> In the slurry for the non-aqueous secondary battery cathode according to this embodiment, in addition to the carry-in from the composition for the non-aqueous secondary battery cathode, a liquid medium may be further added. The added liquid medium may be of the same type or different from the liquid medium (C) contained in the composition for the non-aqueous secondary battery cathode, but it is preferably selected from the liquid media exemplified in the section of "1.3. Liquid Medium (C)" and used.

[0104] The content ratio of the liquid medium (including the carry-in from the composition for the non-aqueous secondary battery cathode) in the slurry for the non-aqueous secondary battery cathode according to this embodiment is preferably such that the solid content concentration in the slurry (the ratio of the total mass of the components other than the liquid medium in the slurry to the total mass of the slurry. The same shall apply hereinafter.) is 30 to 85% by mass, and more preferably 40 to 80% by mass. It is more preferable to be in this ratio.

[0105] <Conductivity-imparting agent> In the slurry for the non-aqueous secondary battery cathode according to this embodiment, a conductivity-imparting agent may be further added for the purpose of imparting conductivity and buffering the volume change of the active material due to the ingress and egress of lithium ions.

[0106] Specific examples of the conductivity-imparting agent include carbons such as activated carbon, acetylene black, ketjen black, furnace black, graphite, carbon fiber, fullerene, and carbon nanotube. Among these, acetylene black or carbon nanotube can be preferably used. The content ratio of the conductivity-imparting agent is preferably 20 parts by mass or less, more preferably 1 to 15 parts by mass, and particularly preferably 2 to 10 parts by mass with respect to 100 parts by mass of the active material.

[0107] <pH Adjusting Agent / Corrosion Inhibitor> For the slurry for non-aqueous secondary battery positive electrode according to this embodiment, a pH adjusting agent or a corrosion inhibitor or both may be further added for the purpose of suppressing the corrosion of the current collector according to the type of the active material.

[0108] Examples of the pH adjusting agent include hydrochloric acid, phosphoric acid, sulfuric acid, acetic acid, formic acid, ammonium phosphate, ammonium sulfate, ammonium acetate, ammonium formate, ammonium chloride, sodium hydroxide, potassium hydroxide, etc. Among these, sulfuric acid, ammonium sulfate, sodium hydroxide, and potassium hydroxide are preferable. Also, it can be selected and used from among the neutralizing agents described in the method for producing the polymer (A).

[0109] Examples of the corrosion inhibitor include ammonium metavanadate, sodium metavanadate, potassium metavanadate, ammonium metatungstate, sodium metatungstate, potassium metatungstate, ammonium paratungstate, sodium paratungstate, potassium paratungstate, ammonium molybdate, sodium molybdate, potassium molybdate, etc. Among these, ammonium paratungstate, ammonium metavanadate, sodium metavanadate, potassium metavanadate, and ammonium molybdate are preferable.

[0110] <Cellulose Fiber> Cellulose fibers may be further added to the slurry for the non-aqueous secondary battery positive electrode according to this embodiment. By adding cellulose fibers, the adhesion of the active material to the current collector may be improved. It is considered that the fibrous cellulose fibers can prevent the active material from falling off and improve the adhesion to the current collector by fibrously binding adjacent active materials by wire adhesion or wire contact.

[0111] The average fiber length of the cellulose fibers can be selected from a wide range of 0.1 to 1000 μm. For example, it is preferably 1 to 750 μm, more preferably 1.3 to 500 μm, still more preferably 1.4 to 250 μm, and particularly preferably 1.8 to 25 μm. If the average fiber length is within the above range, the surface smoothness (coating film uniformity) is good, and the adhesion of the active material to the current collector may be improved.

[0112] The fiber length of the cellulose fibers may be uniform, and the coefficient of variation of the fiber length ([standard deviation of fiber length / average fiber length] × 100) is, for example, preferably 0.1 to 100, more preferably 0.5 to 50, and particularly preferably 1 to 30. The maximum fiber length of the cellulose fibers is, for example, preferably 500 μm or less, more preferably 300 μm or less, still more preferably is 200 μm or less, even more preferably 100 μm or less, and particularly preferably 50 μm or less.

[0113] When the average fiber length of the cellulose fibers is 5 times or less the average thickness of the active material layer, it is advantageous because the surface smoothness (coating film uniformity) and the adhesion of the active material to the current collector are further improved. The average fiber length of the cellulose fibers is preferably 0.01 to 5 times, more preferably 0.02 to 3 times, and particularly preferably 0.03 to 2 times the average thickness of the active material layer.

[0114] The average fiber diameter of the cellulose fiber is preferably from 1 nm to 10 μm, more preferably from 5 nm to 2.5 μm, still more preferably from 20 nm to 700 nm, and particularly preferably from 30 nm to 200 nm. When the average fiber diameter is within the above range, the occupied volume of the fiber does not become too large, and the filling density of the active material may be increased. Therefore, the cellulose fiber is preferably a cellulose nanofiber having a nanometer-sized average fiber diameter (for example, a cellulose nanofiber having an average fiber diameter of 10 nm to 500 nm, preferably about 25 nm to 250 nm).

[0115] The fiber diameter of the cellulose fiber is also uniform, and the coefficient of variation of the fiber diameter ([standard deviation of fiber diameter / average fiber diameter] × 100) is preferably from 1 to 80, more preferably from 5 to 60, and particularly preferably from 10 to 50. The maximum fiber diameter of the cellulose fiber is preferably 30 μm or less, more preferably 5 μm or less, and particularly preferably 1 μm or less.

[0116] The ratio of the average fiber length to the average fiber diameter (aspect ratio) of the cellulose fiber is, for example, preferably from 10 to 5000, more preferably from 20 to 3000, and particularly preferably from 50 to 2000. When the aspect ratio is within the above range, the adhesion of the active material to the current collector is good, and the surface smoothness (coating film uniformity) of the electrode may be good without weakening the breaking strength of the fiber.

[0117] In the present invention, the average fiber length, the standard deviation of the fiber length distribution, the maximum fiber length, the average fiber diameter, the standard deviation of the fiber diameter distribution, and the maximum fiber diameter may be values calculated from fibers (n = about 20) measured based on electron micrographs.

[0118] The material of the cellulose fiber only needs to be formed of a polysaccharide having a β-1,4-glucan structure. Examples of the cellulose fiber include cellulose fibers derived from higher plants (e.g., wood fibers (such as wood pulp from conifers, broad-leaved trees, etc.), bamboo fibers, sugarcane fibers, seed hair fibers (e.g., cotton linter, bombax cotton, kapok, etc.), bast fibers (e.g., hemp, mulberry, kozo, etc.), leaf fibers (e.g., manila hemp, New Zealand hemp, etc.) and other natural cellulose fibers (pulp fibers)), cellulose fibers derived from animals (e.g., sea squirt cellulose, etc.), cellulose fibers derived from bacteria (e.g., cellulose contained in nata de coco, etc.), and chemically synthesized cellulose fibers (e.g., rayon, cellulose esters (such as cellulose acetate), cellulose ethers (e.g., hydroxyalkyl celluloses such as hydroxyethyl cellulose (HEC), hydroxypropyl cellulose, alkyl celluloses such as methyl cellulose, ethyl cellulose, and other cellulose derivatives)). These cellulose fibers may be used alone or in combination of two or more.

[0119] Among these cellulose fibers, cellulose fibers derived from pulp such as cellulose fibers derived from higher plants, for example, wood fibers (such as wood pulp from conifers, broad-leaved trees, etc.) and seed hair fibers (such as cotton linter pulp), are preferred because it is easy to prepare nanofibers having an appropriate aspect ratio.

[0120] The method for producing the cellulose fiber is not particularly limited, and a conventional method, for example, the methods described in Japanese Patent Publication No. 60-19921, Japanese Patent Application Laid-Open No. 2011-26760, Japanese Patent Application Laid-Open No. 2012-25833, Japanese Patent Application Laid-Open No. 2012-36517, Japanese Patent Application Laid-Open No. 2012-36518, Japanese Patent Application Laid-Open No. 2014-181421, etc., may be used according to the desired fiber length and fiber diameter.

[0121] 2.4. Method for Preparing Slurry for Non-aqueous Secondary Battery Cathode The slurry for the non-aqueous secondary battery positive electrode according to this embodiment may be manufactured by any method as long as it contains the above-described composition for the non-aqueous secondary battery positive electrode and the active material. From the viewpoint of manufacturing a slurry having better dispersibility and stability more efficiently and inexpensively, it is preferable to add the active material and optional additive components used as necessary to the composition for the non-aqueous secondary battery positive electrode and mix them. Specific manufacturing methods include, for example, the methods described in Japanese Patent No. 6544150 and the like.

[0122] 3. Positive Electrode for Non-Aqueous Secondary Battery The positive electrode for a non-aqueous secondary battery according to an embodiment of the present invention includes a current collector and an active material layer formed by applying and drying the above-described slurry for the non-aqueous secondary battery positive electrode on the surface of the current collector. Such a positive electrode for a non-aqueous secondary battery can be manufactured by applying the above-described slurry for the non-aqueous secondary battery positive electrode on the surface of a current collector such as a metal foil to form a coating film, and then drying the coating film to form an active material layer. The positive electrode for a non-aqueous secondary battery manufactured in this way has an active material layer containing the above-described polymer (A), polysaccharide (B), active material, and optional components added as necessary bound to the surface of the current collector. Therefore, the occurrence of corrosion on the electrode surface is suppressed, the adhesion is excellent, and the charge and discharge durability characteristics of the power storage device can be improved.

[0123] The current collector is not particularly limited as long as it is made of a conductive material. However, when the positive electrode for a non-aqueous secondary battery is used in a lithium-ion secondary battery, for example, a current collector made of a metal such as iron, copper, aluminum, nickel, stainless steel, etc. can be used. In particular, a current collector made of aluminum or copper is preferable.

[0124] When the positive electrode for a non-aqueous secondary battery is used in a nickel-metal hydride secondary battery, for example, a current collector made of punched metal, expanded metal, wire mesh, foam metal, sintered body of network metal fibers, metal-plated resin plate, etc. can be used.

[0125] The shape and thickness of the current collector are not particularly limited. For example, a sheet-like current collector with a thickness of about 0.001 to 0.5 mm is preferable. When applying the slurry for the non-aqueous secondary battery positive electrode to the surface of the current collector, the application method is not particularly limited. As the application method, for example, the doctor blade method, dip method, reverse roll method, direct roll method, gravure method, extrusion method, dipping method, brush coating method, etc. can be appropriately used.

[0126] The coating amount of the slurry for the non-aqueous secondary battery positive electrode is not particularly limited. The coating amount that results in a thickness of the positive electrode active material layer of 0.005 to 5 mm after applying the slurry for the non-aqueous secondary battery positive electrode and removing the liquid medium (a concept that includes both water and an optionally used non-aqueous medium) is preferable, and a coating amount that results in a thickness of 0.01 to 2 mm is more preferable.

[0127] When the thickness of the positive electrode active material layer is within the above range, the electrolyte can be efficiently infiltrated into the positive electrode active material layer. As a result, the transfer of metal ions accompanying charge and discharge between the positive electrode active material and the electrolyte in the positive electrode active material layer can be easily performed, so that the internal resistance of the positive electrode can be further reduced.

[0128] Also, when the thickness of the positive electrode active material layer is within the above range, even when the positive electrode is processed by folding or winding, etc., the adhesion between the positive electrode active material layer and the current collector is good, and the positive electrode active material layer is difficult to peel off from the current collector. That is, a non-aqueous secondary battery positive electrode rich in flexibility can be obtained.

[0129] The drying method of the coating film formed by applying the slurry for the non-aqueous secondary battery positive electrode (the method for removing water and an optionally used non-aqueous medium) is not particularly limited. For example, drying with warm air, hot air, low-humidity air; vacuum drying; drying by irradiation with (far) infrared rays, electron beams, etc. can be used.

[0130] When drying a coating film formed by applying a slurry for a non-aqueous secondary battery positive electrode, the drying rate can be appropriately set so that the liquid medium can be removed as quickly as possible under conditions such as no cracks in the positive electrode active material layer due to stress concentration or no peeling of the positive electrode active material layer from the current collector.

[0131] After drying a coating film formed by applying a slurry for a non-aqueous secondary battery positive electrode, by pressing the positive electrode for a non-aqueous secondary battery, it is preferable to increase the density of the positive electrode active material layer and adjust the density and porosity in the positive electrode active material layer to the ranges shown below.

[0132] The density of the positive electrode active material layer after pressing is preferably 2.2~3.6 g / cm 3 and more preferably 2.3~3.5 g / cm 3 even more preferably 2.4~3.4 g / cm 3 still more preferably 2.5~3.3 g / cm 3 and particularly preferably 2.5~3.3 g / cm. If the density of the positive electrode active material layer is within the above range, a positive electrode for a non-aqueous secondary battery with good adhesion between the current collector and the positive electrode active material layer, excellent powder falling property, and excellent electrical characteristics can be obtained.

[0133] The porosity of the positive electrode active material layer after pressing is preferably 10~50%, more preferably 15~45%, and particularly preferably 20~40%. If the porosity of the positive electrode active material layer is within the above range, a positive electrode for a non-aqueous secondary battery with good adhesion between the current collector and the positive electrode active material layer, excellent powder falling property, and excellent electrical characteristics can be obtained.

[0134] Also, if the porosity of the positive electrode active material layer is within the above range, the electrolyte can be sufficiently infiltrated into the positive electrode active material layer, and the surface of the positive electrode active material and the electrolyte can be sufficiently contacted. As a result, the transfer of lithium ions between the positive electrode active material and the electrolyte becomes easy, and good charge and discharge characteristics can be exhibited.

[0135] Examples of the pressing method include methods such as die pressing and roll pressing. The pressing conditions can be appropriately set according to the type of pressing equipment used, the desired values of the porosity and density of the positive electrode active material layer, and the like. The pressing conditions can be easily set by a few preliminary experiments by those skilled in the art.

[0136] When using the roll pressing method, the pressing conditions can be, for example, as follows. · Linear pressure of the roll press: 0.1 to 10 (t / cm), preferably 0.5 to 5 (t / cm). · Roll temperature: 20 to 100 °C. · Feeding speed of the positive electrode for non-aqueous secondary battery (rotation speed of the roll): 0.5 to 50 m / min, preferably 1 to 30 m / min.

[0137] 4. Non-aqueous secondary battery The non-aqueous secondary battery according to an embodiment of the present invention includes the above-described positive electrode for non-aqueous secondary battery, and further contains, for example, an electrolytic solution and includes components such as a separator and a negative electrode for non-aqueous secondary battery.

[0138] As a specific manufacturing method, for example, a negative electrode for non-aqueous secondary battery and a positive electrode for non-aqueous secondary battery are overlapped via a separator, and this is wound, folded, etc. according to the shape of the battery and placed in a battery container, and an electrolytic solution is injected into the battery container and sealed. The shape of the battery can be appropriately set, such as coin type, button type, sheet type, cylindrical type, rectangular type, flat type, etc.

[0139] The electrolytic solution is a solution in which an electrolyte is dissolved in a suitable solvent. The electrolytic solution may be liquid or gel-like. The electrolytic solution may be selected from known electrolytic solutions used for non-aqueous secondary batteries according to the type of the positive electrode active material so as to effectively exhibit the function as a non-aqueous secondary battery.

[0140] As the electrolyte, it can be appropriately selected from electrolytes known in the technical field of non-aqueous secondary batteries. When the non-aqueous secondary battery is a lithium-ion secondary battery, as the electrolyte, a conventionally known lithium salt can be appropriately selected and used. Specific examples thereof include LiClO4, LiBF4, LiPF6, LiCF3CO2, LiAsF6, LiSbF6, LiB 10 Cl 10 , LiAlCl4, LiCl, LiBr, LiB(C2H5)4, LiCF3SO3, LiCH3SO3, LiC4F9SO3, Li(CF3SO2)2N, lithium lower fatty acid carboxylate, and the like.

[0141] The solvent contained in the electrolytic solution is not particularly limited. Examples of the solvent include carbonate compounds such as propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate; lactone compounds such as γ-butyrolactone; ether compounds such as trimethoxymethane, 1,2-dimethoxyethane, diethyl ether, 2-ethoxyethane, tetrahydrofuran, and 2-methyltetrahydrofuran; and sulfoxide compounds such as dimethyl sulfoxide. One or more selected from these can be mentioned. The concentration of the electrolyte in the electrolytic solution is preferably 0.5 to 3.0 mol / L, more preferably 0.7 to 2.0 mol / L.

[0142] The negative electrode included in the non-aqueous secondary battery according to this embodiment includes, for example, a current collector and a negative electrode active material layer formed on the surface thereof. The negative electrode active material layer contains a negative electrode active material. The negative electrode can be manufactured, for example, by applying and drying a negative electrode slurry used for manufacturing a negative electrode containing a negative electrode active material on the surface of a current collector to form a negative electrode active material layer.

[0143] The negative electrode active material is not particularly limited, and an appropriate negative electrode active material can be appropriately selected according to the type of the target non-aqueous secondary battery. Examples of the negative electrode active material include carbon materials, silicon materials, oxides containing lithium atoms, lead compounds, tin compounds, arsenic compounds, antimony compounds, aluminum compounds, and the like.

[0144] Examples of the carbon material include those known as negative electrode active materials such as amorphous carbon, graphite, natural graphite, mesocarbon microbeads (MCMB), pitch-based carbon fibers, and the like.

[0145] Examples of the silicon material include those known as negative electrode active materials such as elemental silicon, silicon oxide, and silicon alloy. When a silicon material is used as the active material, it is preferable to use in combination an active material other than the silicon material, and since the volume change associated with the occlusion and release of lithium is small, it is preferable to use in combination a carbon material.

[0146] In addition to the negative electrode active material, the slurry for the negative electrode can contain other polymers, thickeners, liquid media, conductivity-imparting agents, pH adjusters, corrosion inhibitors, cellulose fibers, etc. described in the section of "2.3. Other Components".

[0147] 5. Examples Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to these examples. "Parts" and "%" in the polymerization examples, synthesis examples, examples, and comparative examples are based on mass unless otherwise specified. In this specification, the polymer (A) obtained in Polymerization Example 1 is referred to as "Polymer (A-1)", and similarly, the polymer (A) obtained in Polymerization Example 2 is referred to as "Polymer (A-2)", and so on.

[0148] 5.1. Polymerization Examples and Physical Property Evaluations of Polymer (A) 5.1.1. Polymerization Examples of Polymer (A) <Polymerization Example 1> ​Into an autoclave equipped with a stirrer and capable of temperature adjustment, 200 parts by mass of water, 0.9 part by mass of sodium dodecylbenzenesulfonate, 1.0 part by mass of potassium persulfate, 0.5 part by mass of sodium bisulfite, 0.2 part by mass of α-methylstyrene dimer, 0.2 part by mass of dodecyl mercaptan, and the monomer components shown in the column of "Polymerization Example 1" in Table 1 were charged all at once, heated to 70 °C, and subjected to a polymerization reaction for 2 hours. Thereafter, the residual monomer was treated by steam distillation and concentrated under reduced pressure to 50% solids content to obtain an aqueous dispersion containing 50% of polymer (A-1). The polymer (A-1) was dispersed in the form of particles in the aqueous medium.

[0149] <Polymerization Examples 2 to 13> The reaction was carried out in the same manner as in Polymerization Example 1 except that the charged monomer components were changed to the monomers shown in Table 1 to obtain polymers (A-2) to (A-13).

[0150] 5.1.2. Physical Property Evaluation of Polymer (A) For the polymers (A-1) to (A-13) obtained above, the glass transition temperature (Tg), swelling ratio, pH, number average particle diameter, and surface acid amount were measured. In the measurement of pH, average particle diameter, and surface acid amount, the aqueous dispersion of polymer (A) was used as the measurement sample. The results are shown in Table 1.

[0151] <Glass Transition Temperature (Tg)> The polymer (A) obtained above was dried at room temperature, and the glass transition temperature (Tg) was measured by a differential scanning calorimeter (DSC, DSC204F1 Phoenix manufactured by NETZSCH) in accordance with JIS K7121.

[0152] <Swelling Ratio> The polymer (A) obtained above was dried in a thermostatic bath at 85°C for 24 hours to prepare a film. 1 g of this film was immersed in 20 mL of a mixed solution composed of propylene carbonate (PC) and diethyl carbonate (DEC) (PC / DEC = 1 / 1 (volume ratio), hereinafter this mixed solution is referred to as "PC / DEC"), and shaken at 70°C for 24 hours. Next, after filtering through a 300-mesh wire mesh to separate the insoluble matter, the weight (Y (g)) of the residue obtained by evaporating and removing the PC / DEC of the dissolved matter was measured. Also, after removing the PC / DEC adhering to the surface of the insoluble matter (film) separated by the above filtration by absorbing it with paper, the weight (Z (g)) of the insoluble matter (film) was measured. The swelling ratio of the polymer (A) was determined from the following formula. Swelling ratio (mass%) = (Z / (1 - Y)) × 100

[0153] <ph> Regarding the aqueous dispersion of the polymer (A) obtained above, the pH at 25 °C was measured using a pH meter (manufactured by Horiba, Ltd.).

[0154] <Number average particle diameter> A latex obtained by diluting the aqueous dispersion of the polymer (A) obtained above to 0.1 wt% was dropped one drop onto a collodion support film with a pipette, and further, one drop of a 0.02 wt% osmium tetroxide solution was dropped onto the collodion support film with a pipette and air-dried for 12 hours to prepare a sample. The sample thus prepared was observed at a magnification of 10K using a transmission electron microscope (TEM, manufactured by Hitachi High-Technologies Corporation, model number "H-7650"), and image analysis was performed using the program of HITACHI EMIP, and the number average particle diameter of 50 randomly selected particles of the polymer (A) was calculated.

[0155] <Surface acid amount> The surface acid amount of the particles of the polymer (A) obtained above was measured as follows. First, it was confirmed that the burette of the potentiometric titration apparatus (manufactured by Kyoto Electronics Industry Co., Ltd., model "AT-510") and the reagent bottle above the main body were filled with 0.005 mol / L sulfuric acid, and it was confirmed that the conductivity of ultrapure water was 2 μS or less. Next, for degassing the burette, purging was performed, and further, the bubbles at the nozzle were removed. Then, approximately 1 g of the polymer (A) obtained above in terms of solid content was collected in a 300 mL beaker, and its sample weight was recorded. After adding ultrapure water and diluting to 200 mL, a 1 mol / L aqueous sodium hydroxide solution was dropped. When the end point was reached, it was stirred for about 30 seconds, and it was confirmed that the conductivity had stabilized. The RESET button of the measurement program was pressed to set it in the measurement standby state. The START button of the measurement program was pressed to start the measurement with 0.005 mol / L sulfuric acid. Since it automatically ends and the file is saved when the end point is reached, the obtained curve was analyzed, and the surface acid amount was determined from the following formula using the amount of sulfuric acid used. Surface acid amount (mmol / g) = Amount of acid used in the carboxylic acid region on the particle surface [mL] × Acid concentration [mol / L] × Degree of ionization / Sample weight [g] / 1000

[0156]

Table 1

[0157] The abbreviations of each component in Table 1 have the following meanings respectively. <Unsaturated carboxylic acid> ·TA: Itaconic acid ·AA: Acrylic acid ·MAA: Methacrylic acid <Unsaturated carboxylic acid ester> ·MMA: Methyl methacrylate ·BA: Butyl acrylate ·2EHA: 2-Ethylhexyl acrylate ·CHMA: Cyclohexyl methacrylate ·EDMA: Ethylene glycol dimethacrylate ·EA: Ethyl acrylate ·AMA: Allyl methacrylate ·HEMA: 2-Hydroxyethyl methacrylate ·HEA: 2-Hydroxyethyl acrylate <Aromatic vinyl compound> ·ST: Styrene ·DVB: Divinylbenzene <α,β-Unsaturated nitrile compound> ·AN: Acrylonitrile <(Meth)acrylamide> ·AAM: Acrylamide ·MAM: Methacrylamide <Compound having a sulfonic acid group> ·NASS: Sodium styrene sulfonate

[0158] 5.2. Synthesis example of polysaccharide (B) <Synthesis example 1> In a four-neck separable flask equipped with a stirrer, Dimroth condenser, and thermometer, 10 g of carboxymethyl cellulose (manufactured by Daicel Corporation, trade name "CMC2200") was dissolved in 720 g of chloroform. 100 g of pyridine and 0.35 g of 4-dimethylaminopyridine were added, and the temperature was raised to 50 °C. 55 g of acetyl chloride was added over 30 minutes, and the reaction was carried out at 50 °C for 15 hours. After washing with ethanol and drying, about 13 g of light yellow odorless carboxymethyl cellulose acetate ester (B-1) was obtained. The hydroxyl group protection rate of the obtained compound was 95%, and the weight average molecular weight was 900,000.

[0159] <Synthesis Example 2> Synthesis Example 1 was carried out in the same manner as in Synthesis Example 1 except that 100 g of benzoyl chloride was used instead of 55 g of acetyl chloride, and about 13 g of light yellow odorless carboxymethyl cellulose benzoate ester (B-2) was obtained. The hydroxyl group protection rate of the obtained compound was 60%, and the weight average molecular weight was 900,000.

[0160] <Synthesis Example 3> Synthesis Example 1 was carried out in the same manner as in Synthesis Example 1 except that 84 g of pivaloyl chloride was used instead of 55 g of acetyl chloride, and about 13 g of light yellow odorless carboxymethyl cellulose pivalate ester (B-3) was obtained. The hydroxyl group protection rate of the obtained compound was 25%, and the weight average molecular weight was 900,000.

[0161] <Synthesis Example 4> Synthesis Example 1 was carried out in the same manner as in Synthesis Example 1 except that 10 g of sodium alginate (manufactured by Fujifilm Wako Pure Chemical Corporation, trade name "Sodium Alginate 80 - 120") was used instead of 10 g of carboxymethyl cellulose (manufactured by Daicel Corporation, trade name "CMC2200"), and about 13 g of light yellow odorless alginic acid acetate ester (B-4) was obtained. The hydroxyl group protection rate of the obtained compound was 95%, and the weight average molecular weight was 900,000.

[0162] <Synthesis Example 5> In Synthesis Example 2, the procedure of Synthesis Example 1 was repeated except that 10 g of sodium alginate (manufactured by Fujifilm Wako Pure Chemical Corporation, product name "Sodium Alginate 80 - 120") was used instead of 10 g of carboxymethyl cellulose (manufactured by Daicel Corporation, product name "CMC2200"), and approximately 13 g of light yellow, odorless benzoic acid alginate (B-5) was obtained. The hydroxyl group protection rate of the resulting compound was 60%, and the weight average molecular weight was 900,000.

[0163] <Synthesis Example 6> In Synthesis Example 3, the procedure of Synthesis Example 1 was repeated except that 10 g of sodium alginate (manufactured by Fujifilm Wako Pure Chemical Corporation, product name "Sodium Alginate 80 - 120") was used instead of 10 g of carboxymethyl cellulose (manufactured by Daicel Corporation, product name "CMC2200"), and approximately 13 g of light yellow, odorless pivalic acid alginate (B-6) was obtained. The hydroxyl group protection rate of the resulting compound was 12%, and the weight average molecular weight was 900,000.

[0164] <Measurement of substitution rate (hydroxyl group protection rate)> To 0.2 g of polysaccharide (B), 20 g of toluene and 6 g of 0.5 N sodium hydroxide ethanol solution were added, and the mixture was heated and stirred at 100 °C for 7 hours to cleave the ester bond. 1 g of the solution was measured, neutralized by adding 1 g of phosphoric acid ethanol solution, and then the solution was filtered through a filter. The hydroxyl group protection rate was calculated by quantifying the amount of carboxylic acid contained in the solution by gas chromatography.

[0165] 5.3. Example 1 5.3.1. Preparation and Physical Property Evaluation of Slurry for Non-aqueous Secondary Battery Cathode <Preparation of Slurry for Non-aqueous Secondary Battery Cathode> To a two-axis planetary mixer (manufactured by Primix Corporation, trade name "TK Hibiscus Mix 2P-03"), 2 parts by mass of polymer (A-1) (in terms of solid content, added as an aqueous dispersion of the polymer (A-1) obtained above), 1.5 parts by mass of polysaccharide (B-4), 100 parts by mass of NMC622 (trade name "ME-8A", manufactured by Beijing Easpring Material Technology Co., Ltd.) as a positive electrode active material, 5 parts by mass of acetylene black, 1 part by mass of a thickener (trade name "CMC2200", manufactured by Daicel Corporation), and 20 parts by mass of water were added, and stirring was carried out at 60 rpm for 1 hour. Further, the NMC622 is an example of a positive electrode active material.

[0166] Thereafter, stirring was continued for another 1 hour to obtain a paste. After adding water to the obtained paste to adjust the solid content concentration to 70%, using a stirring and defoaming machine (manufactured by Shin-Kee Co., Ltd., trade name "Awatori Ren-taro"), stirring was carried out at 200 rpm for 2 minutes, at 1,800 rpm for 5 minutes, and further at 1,800 rpm for 1.5 minutes under vacuum (about 5.0×10 3 Pa) to prepare a positive electrode slurry. This positive electrode slurry has the composition shown in the column of "Example 1" in Table 2.

[0167] <pH Evaluation> The non-aqueous secondary battery positive electrode slurry obtained above was left standing at 25°C for 4 days. When the pH at 25°C at 1 day and 4 days later was measured with a pH meter (manufactured by Horiba, Ltd.), they were 8.9 and 9.8, respectively. The evaluation results are shown in Table 2.

[0168] 5.3.2. Fabrication and Physical Property Evaluation of Positive Electrode for Non-aqueous Secondary Battery <Fabrication of Positive Electrode for Non-aqueous Secondary Battery> On the surface of a current collector made of an aluminum foil with a thickness of 20 μm, the non-aqueous secondary battery positive electrode slurry prepared as described above was uniformly coated by the doctor blade method so that the film thickness after drying would be 100 μm, and dried at 120°C for 20 minutes. Thereafter, by pressing using a roll press machine so that the density of the formed film (positive electrode active material layer) would be 3.0 g / cm 3 a positive electrode for a non-aqueous secondary battery was obtained.

[0169] <Evaluation of Adhesion Strength> On the surface of the positive electrode for non-aqueous secondary batteries obtained above, using a knife, ten cuts were made vertically and horizontally at 2 mm intervals from the positive electrode active material layer to the depth reaching the current collector, creating a grid of cuts. An adhesive tape with a width of 18 mm (manufactured by Nichiban Co., Ltd., trade name "Cellotape" (registered trademark), specified in JIS Z1522) was attached to these cuts and immediately peeled off, and the degree of active material dropout was visually evaluated. The evaluation criteria are as follows. The evaluation results are shown in Table 2. (Evaluation Criteria) · 5 points: The number of dropouts from the active material layer is 0. · 4 points: The number of dropouts from the active material layer is 1 - 5. · 3 points: The number of dropouts from the active material layer is 6 - 20. · 2 points: The number of dropouts from the active material layer is 21 - 40. · 1 point: The number of dropouts from the active material layer is 41 or more.

[0170] 5.3.3. Fabrication and Physical Property Evaluation of Non-aqueous Secondary Batteries <Fabrication of Negative Electrode for Non-aqueous Secondary Batteries> Into a biaxial planetary mixer (manufactured by Primix Corporation, trade name "TK High Vis Mix 2P-03"), 1 part by mass (in terms of solid content) of a thickening agent (trade name "CMC2200", manufactured by Daicel Corporation), 100 parts by mass (in terms of solid content) of graphite as the negative electrode active material, and 68 parts by mass of water were charged, and stirring was carried out at 60 rpm for 1 hour.

[0171] Next, an amount corresponding to 2 parts by mass (in terms of solid content) of SBR (trade name "TRD105A", manufactured by JSR Corporation) was added, and stirring was continued for another 1 hour to obtain a paste. Water was added to the obtained paste, and after adjusting the solid content to 50%, using a stirring and defoaming machine (manufactured by Shin Key Co., Ltd., trade name "Foam Removing Rintaro"), stirring and mixing were carried out at 200 rpm for 2 minutes, 1800 rpm for 5 minutes, and further at 1800 rpm for 1.5 minutes under vacuum to prepare a slurry for the negative electrode of non-aqueous secondary batteries.

[0172] Next, the non-aqueous secondary battery negative electrode slurry prepared as described above was uniformly coated on the surface of a current collector made of a copper foil with a thickness of 20 μm by the doctor blade method so that the film thickness after drying would be 80 μm, and then dried at 120°C for 20 minutes. Thereafter, the formed film (negative electrode active material layer) was press-processed using a roll press machine so that the density would be 1.6 g / cm 3 to obtain a negative electrode for a non-aqueous secondary battery.

[0173] <Assembly of Lithium-Ion Battery> In a glove box purged with Ar so that the dew point would be -80°C or lower, a negative electrode for a non-aqueous secondary battery obtained above, which was punched and formed into a circle with a diameter of 15.95 mm, was placed on a two-pole coin cell (manufactured by Takizawa Co., Ltd., trade name "HS Flat Cell").

[0174] Next, a separator made of a porous polypropylene film punched into a circle with a diameter of 24 mm (manufactured by Celgard LLC, trade name "Celgard #2400") was placed on top of the negative electrode for a non-aqueous secondary battery.

[0175] Furthermore, after injecting 500 μL of electrolyte so that no air would enter, a positive electrode for a non-aqueous secondary battery obtained above, which was punched and formed into a circle with a diameter of 16.16 mm, was placed on top of the separator, and the outer body of the two-pole coin cell was closed and sealed with a screw to assemble a lithium-ion battery cell (an example of a non-aqueous secondary battery). The electrolyte used here is a solution in which LiPF6 is dissolved at a concentration of 1 mol / L in a solvent of ethylene carbonate / ethyl methyl carbonate = 1 / 1 (mass ratio).

[0176] <Evaluation of Cycle Characteristics> Regarding the lithium-ion battery manufactured above, charging was started at a constant current (1.0C) in a thermostatic bath adjusted to 45°C. When the voltage reached 4.2V, charging was continued at a constant voltage (4.2V). When the current value reached 0.01C, charging was completed (cut-off). Thereafter, discharging was started at a constant current (1.0C), and when the voltage reached 3.0V, discharging was completed (cut-off), and the discharge capacity of the first cycle was calculated. In this way, 200 charge-discharge cycles were repeated. The capacity retention rate was calculated by the following formula and evaluated according to the following criteria. The evaluation results are shown in Table 2. Capacity retention rate (%) = (Discharge capacity of the 200th cycle) / (Discharge capacity of the first cycle) (Evaluation criteria) · 5 points: Capacity retention rate is 95% or more. · 4 points: Capacity retention rate is 90% or more and less than 95%. · 3 points: Capacity retention rate is 85% or more and less than 90%. · 2 points: Capacity retention rate is 80% or more and less than 85%. · 1 point: Capacity retention rate is 75% or more and less than 80%. · 0 points: Capacity retention rate is less than 75%.

[0177] 5.4. Examples 2 to 13, Comparative Examples 1 to 6 In the section of "5.3.1. Preparation and Physical Property Evaluation of Slurry for Non-aqueous Secondary Battery Cathode" above, except that the types and amounts of the components used were the same as those described in Table 2 or Table 3, slurries for non-aqueous secondary battery cathodes were obtained in the same manner and pH evaluation was performed. Except for using the slurries for non-aqueous secondary battery cathodes thus obtained, non-aqueous secondary battery cathodes and non-aqueous secondary batteries were produced in the same manner as in Example 1 above and evaluated in the same manner as in Example 1 above.

[0178] 5.5. Evaluation results Table 2 and Table 3 show the compositions of the slurries for non-aqueous secondary battery cathodes used in Examples 1 to 13 and Comparative Examples 1 to 6, and the evaluation results for each. The numerical values representing the polymer (A), polysaccharide (B), and other components shown in Table 2 or Table 3 represent parts by mass, respectively.

[0179]

Table 2

[0180]

Table 3

[0181] In addition, the following products were used for the other components in Table 2 and Table 3, respectively. <Other components> · CMC: Trade name "CMC2200", manufactured by Daicel Corporation, sodium carboxymethyl cellulose · Sodium alginate: Trade name "Sodium alginate 80 - 120", manufactured by Fujifilm Wako Pure Chemical Corporation

[0182] As is clear from Table 2 to Table 3 above, the non-aqueous secondary battery positive electrode slurries prepared using the non-aqueous secondary battery positive electrode compositions shown in Examples 1 to 13 and Comparative Examples 1 to 4 were able to suppress the pH to 10.2 after 4 days. The reason is considered as follows. Since water is used as the liquid medium, water reacts with the positive electrode active material to generate hydroxide ions, and the pH easily shifts to the basic side over time. However, the non-aqueous secondary battery positive electrode compositions of Examples 1 to 13 and Comparative Examples 1 to 4 contain polysaccharide (B). It is considered that the protective group of polysaccharide (B) captures hydroxide ions, which are bases, and is deprotected, thereby consuming the hydroxide ions in the system and suppressing the change in pH of the positive electrode slurry over time. As a result, it is presumed that the occurrence of corrosion of the positive electrode for non-aqueous secondary batteries could be effectively suppressed.

[0183] Moreover, it can be understood that the non-aqueous secondary battery positive electrode slurry prepared using the non-aqueous secondary battery positive electrode composition shown in Examples 1 to 13 can preferably bind the active materials together by using a polymer (A) containing 0.1 to 10% by mass of a repeating unit (a1) derived from an unsaturated carboxylic acid and a polysaccharide (B) in combination. In addition, the non-aqueous secondary battery positive electrode slurry prepared using the non-aqueous secondary battery positive electrode composition shown in Examples 1 to 13 has good binding properties, and the occurrence of corrosion of the positive electrode for non-aqueous secondary batteries is suppressed and a low resistance can be achieved. Therefore, it is presumed that good charge-discharge durability characteristics are exhibited.

[0184] The present invention is not limited to the above-described embodiments, and various modifications are possible. The present invention includes configurations that are substantially the same as the configurations described in the embodiments (for example, configurations having the same functions, methods, and results, or configurations having the same purposes and effects). The present invention also includes configurations in which non-essential parts of the configurations described in the above embodiments are replaced with other configurations. Furthermore, the present invention also includes configurations that exhibit the same operational effects as the configurations described in the above embodiments or configurations that can achieve the same purpose. Furthermore, the present invention also includes configurations in which known techniques are added to the configurations described in the above embodiments.< / ph>

Claims

1. A composition for a non-aqueous secondary battery positive electrode, comprising a polymer (A), a polysaccharide (B) in which at least a part of hydroxyl groups is protected by a protecting group, and a liquid medium (C). When the total of the repeating units contained in the polymer (A) is 100% by mass, the polymer (A) contains 0.1 to 10% by mass of repeating units (a1) derived from an unsaturated carboxylic acid.

2. The composition for a non-aqueous secondary battery positive electrode according to Claim 1, wherein the polysaccharide (B) has a structure derived from cellulose or alginic acid.

3. The composition for a non-aqueous secondary battery positive electrode according to Claim 1 or Claim 2, wherein the protecting group of the polysaccharide (B) is deprotected by the action of a base.

4. The composition for a non-aqueous secondary battery positive electrode according to any one of Claims 1 to 3, wherein the protecting group of the polysaccharide (B) is an acyl group.

5. The composition for a non-aqueous secondary battery positive electrode according to any one of Claims 1 to 4, wherein the polymer (A) further contains 45 to 99% by mass of repeating units (a2) derived from an unsaturated carboxylic acid ester.

6. The composition for a non-aqueous secondary battery positive electrode according to any one of Claims 1 to 5, wherein the polymer (A) further contains 0.1 to 30% by mass of repeating units (a3) derived from an aromatic vinyl compound.

7. The composition for a non-aqueous secondary battery positive electrode according to any one of Claims 1 to 6, wherein when the polymer (A) is immersed in a solvent composed of propylene carbonate and diethyl carbonate at a volume fraction of 1:1 under the conditions of 70°C for 24 hours, the swelling ratio is 130% by mass or more and 350% by mass or less.

8. The composition for a non-aqueous secondary battery positive electrode according to any one of Claims 1 to 7, wherein when differential scanning calorimetry (DSC) is performed on the polymer (A) in accordance with JIS K7121, an endothermic peak is observed in the temperature range of -50°C to 50°C.

9. The polymer (A) is polymer particles, The composition for a non-aqueous secondary battery positive electrode according to any one of Claims 1 to 8, wherein the number average particle diameter of the polymer particles is 50 nm or more and 500 nm or less.

10. The composition for a non-aqueous secondary battery positive electrode according to Claim 9, wherein the surface acid amount of the polymer particles is 0.05 mmol / g or more and 6 mmol / g or less.

11. The composition for a non-aqueous secondary battery positive electrode according to any one of Claims 1 to 10, wherein the liquid medium (C) is water.

12. A slurry for a non-aqueous secondary battery positive electrode, comprising the composition for a non-aqueous secondary battery positive electrode according to any one of Claims 1 to 11 and an active material.

13. A positive electrode for a non-aqueous secondary battery, comprising a current collector and an active material layer formed by applying and drying the slurry for a non-aqueous secondary battery positive electrode according to Claim 12 on the surface of the current collector.

14. A non-aqueous secondary battery comprising the positive electrode for a non-aqueous secondary battery according to Claim 13.

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