JP7800121B2 - Method for producing resin composition for secondary battery electrodes - Google Patents

Description

The present invention relates to a method for producing a resin composition for secondary batteries.

Lithium-ion secondary batteries are widely used as batteries for electric vehicles, portable devices, and other devices. As the performance of electric vehicles and portable devices improves, demand for lithium-ion secondary batteries with higher capacity, higher output, and smaller size and lighter weight is increasing year by year.

The electrodes of a lithium-ion secondary battery are a positive electrode in which an electrode mixture consisting of a positive electrode active material containing lithium ions, a conductive material, a binder, etc. is fixed to the surface of a metal foil current collector, and a negative electrode in which an electrode mixture consisting of a negative electrode active material into which lithium ions can be inserted and removed, a conductive material, a binder, etc. is fixed to the surface of a metal foil current collector.
The capacity of a lithium-ion secondary battery depends on the cathode and anode active materials, which are the main materials, and the capacity can be increased by increasing the amount of electrode active material packed in the electrode film. Therefore, attempts have been made to increase the capacity of batteries by increasing the packing density of the active material while maintaining electrical conductivity and binding properties.

On the other hand, lithium-ion secondary batteries also face serious problems, such as battery performance degradation due to the reduction and precipitation of metal components on the negative electrode, as well as excessive heat generation and fires due to short circuits. Causes of performance degradation and short circuits due to metal components include (1) the inclusion of metal impurities from the manufacturing process (e.g., those derived from stainless steel used in transportation piping) and from raw materials such as conductive materials and resins (dispersants and binders); (2) metal ions contained in the positive electrode, current collector, battery container, etc., leaching into the electrolyte and then being reduced and precipitated on the negative electrode; and (3) metal ions leaching from the positive electrode active material due to positive electrode deterioration, which are then reduced and precipitated on the negative electrode. This can lead to serious accidents, particularly in applications involving larger batteries, such as automotive applications, so there is an increasing need to strictly prevent or eliminate the inclusion of metal particles.

Patent Document 1 proposes a method for removing particulate metal components from resin compositions for secondary batteries using magnetic force, although the purpose is different. However, while this method makes it possible to recover magnetic metals such as iron even if they are mixed in, it is problematic in that non-magnetic metals such as copper are difficult to remove after being mixed in.

When non-magnetic metal impurities such as copper are present, various additives have been investigated to prevent the elution of metal ions into the electrolyte and the deposition of foreign matter on the negative electrode. Patent Document 2 proposes an alkaline battery in which a chelating agent such as EDTA is blended into the positive electrode mixture. This invention attempts to prevent elution by adding a chelating agent to the positive electrode mixture, even if the copper, a metal impurity in the positive electrode mixture, is ionized, by complexing the copper ions. However, because the chelating agent diffuses through the electrolyte and captures the ionized active material by forming a chelate, problems arise such as a decrease in the capacity of the active material and an accompanying decrease in discharge capacity, making this invention insufficient.

International Publication No. 2010/032784 JP 2008-21497 A

In light of the above, the objective of the present invention is to produce a resin composition for secondary batteries that can achieve excellent battery characteristics without degrading battery performance due to short circuits or the like even when metallic foreign matter such as copper is mixed in.

As a result of extensive research to solve the above-mentioned problems, the inventors discovered that by oxidizing metallic foreign matter in a resin composition for secondary batteries, it is possible to realize a battery with excellent battery performance that does not suffer from performance degradation due to short circuits or the like even when metallic foreign matter is mixed in, leading to the creation of the present invention.

The present invention provides a method for producing a resin composition for a secondary battery, comprising:
The present invention relates to a method for producing a resin composition for a secondary battery, which comprises a step of oxidizing a metal component contained in the resin composition for a secondary battery.

The present invention relates to a method for producing a resin composition for secondary batteries, in which the step of oxidizing the metal component is a step of contacting the resin composition for secondary batteries with oxygen gas.

The present invention relates to the method for producing a resin composition for a secondary battery, wherein the flow rate of the oxygen gas blown in is 20 NL/h or more per 1 m ³ of the resin composition for a secondary battery.

The present invention relates to a method for producing the resin composition for secondary batteries, which further contains a conductive material.

The present invention relates to a method for producing the resin composition for secondary batteries, which further contains an inorganic acid and/or an inorganic base.

The present invention relates to a method for producing a slurry composition for secondary battery electrodes, which contains a resin composition for secondary batteries obtained by the above-mentioned production method and an electrode active material.

The present invention relates to a method for producing an electrode film by applying a slurry composition for secondary battery electrodes obtained by the above-mentioned production method.

The present invention relates to a method for manufacturing a battery electrode, in which the electrode film obtained by the above manufacturing method is formed on an electrode substrate.

The present invention relates to a method for manufacturing a lithium-ion secondary battery using a battery electrode obtained by the above-mentioned manufacturing method.

The present invention provides a resin composition for secondary batteries that can achieve excellent battery characteristics without degrading battery performance due to short circuits or the like even when metallic foreign matter such as copper is mixed in.

FIG. 1 shows one embodiment of a production line (production line (A)) for a binder composition for a secondary battery. FIG. 2 shows one embodiment of a production line (production line (B)) for a binder composition for a secondary battery. FIG. 3 shows an embodiment of a production line (production line (C)) for a binder composition for a secondary battery.

The present invention will be described in detail below. In this specification, "N-methyl-2-pyrrolidone" may be abbreviated as "NMP," "positive electrode active material or negative electrode active material" may be abbreviated as "electrode active material" or "active material," and "battery composition containing active material and resin" may be abbreviated as "battery composite slurry," "composite slurry," or "composite composition."

<Resin composition for secondary batteries>
The resin composition for a secondary battery in the present invention contains a polymer and a dispersion medium (solvent). That is, the resin composition for a secondary battery contains at least a polymer and a dispersion medium (solvent), and may further contain any component that can be blended into a secondary battery electrode, such as a conductive material, a base, or an acid.

<Polymer>
The polymer in the present invention is not particularly limited, and may be a commercially available product or a synthetic product, and may be used alone or in combination of two or more kinds. The polymer is preferably contained mainly as a dispersant for suitably dispersing the conductive material or electrode active material.
Although not particularly limited, examples of polymers that function favorably in N-methyl-2-pyrrolidone (NMP) solvent include polyvinylpyrrolidone, polyvinyl acetal, polyvinyl alcohol, and hydrogenated nitrile rubber. Examples of polymers that function favorably in water include carboxymethyl cellulose and acrylic acid.

When dispersing a carbon-based conductive material using a polymer, adding a sufficient amount of polymer to the carbon-based conductive material enables it to be uniformly dispersed in the dispersion medium (solvent). When the amount of carbon-based conductive material contained in the resin composition for secondary batteries is taken as 100% by mass, the total amount of polymer used to disperse the carbon-based conductive material is preferably 1% by mass or more and 200% by mass or less. Blending polymers at this ratio enables the resin composition for secondary batteries to exhibit good conductivity. Polymers are non-conductive components, and when considering their use in lithium-ion secondary batteries, they generally have low electrochemical stability and low resistance to non-aqueous electrolytes. Therefore, if the blending ratio of polymer is 200% by mass or more, even if initial properties are good, these properties may deteriorate over time. It is desirable to blend the polymer in as small an amount as possible within the range that allows for favorable dispersion of the carbon-based conductive material.

The content of the polymer contained in the resin composition for secondary batteries is preferably 0.05% by mass or more, and more preferably 0.1% by mass or more, based on the mass of the resin composition for secondary batteries (the mass of the resin composition for secondary batteries being 100% by mass). It is also preferably 30% by mass or less, and more preferably 20% by mass or less. By keeping the content of the polymer contained in the resin composition for secondary batteries within the above range, sedimentation and gelation can be prevented, which is useful from the perspective of storage stability. It is also preferable to appropriately adjust the content of the polymer so as to obtain a resin composition for secondary batteries that exhibits appropriate viscosity, taking into account factors such as affinity to the dispersion medium and the ease of use in the dispersion treatment process for the conductive material.

The viscosity of the resin composition for secondary batteries is not particularly limited, but it is preferable that the viscosity at 60 rpm using a Brookfield viscometer be in the range of 5 to 10,000 mPa·s. By keeping the viscosity of the resin composition for secondary batteries within this range, workability during production is improved. It also helps prevent blockages in the production line.

The polymer may also contain components other than the dispersant components described above, primarily components that function as binders. Binders are resins that can bond together substances such as electrode active materials and conductive materials in the electrode film. Examples include polymers or copolymers containing structural units such as ethylene, propylene, vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylic acid esters, methacrylic acid, methacrylic acid esters, acrylonitrile, styrene, vinyl butyral, vinyl acetal, and vinyl pyrrolidone; resins such as polyurethane resins, polyester resins, phenolic resins, epoxy resins, phenoxy resins, urea resins, melamine resins, alkyd resins, acrylic resins, formaldehyde resins, silicone resins, and fluororesins; cellulose resins such as carboxymethyl cellulose; rubbers such as styrene-butadiene rubber and fluororubber; and conductive resins such as polyaniline and polyacetylene. Modified versions, mixtures, or copolymers of these materials are also acceptable. Among these, when used as a binder for a positive electrode film, polymers or copolymers containing fluorine atoms in the molecule, such as polyvinylidene fluoride, polyvinyl fluoride, and tetrafluoroethylene, are preferred in terms of durability. When used as a binder for a negative electrode film, styrene butadiene rubber and polyacrylic acid, which have good adhesion, are preferred.

The weight-average molecular weight of the binder is preferably 10,000 to 2,000,000, more preferably 100,000 to 1,000,000, and even more preferably 200,000 to 1,000,000.

<Dispersion medium (solvent)>
The dispersion medium (solvent) in the present invention is not particularly limited, but examples thereof include alcohols, glycols, cellosolves, aminoalcohols, amines, ketones, carboxylic acid amides, phosphoric acid amides, sulfoxides, carboxylic acid esters, phosphoric acid esters, ethers, nitriles, and water. A mixed solvent consisting of two or more of these may also be used. Among these, N-methyl-2-pyrrolidone (NMP) and water are often used in the production of electrodes for lithium-ion secondary batteries.

<Metallic components (metallic foreign matter)>
The metal component (metal foreign matter) in the present invention will be described. The state of the metal component is not particularly limited, and may be a metal, its oxide, or an alloy such as brass or bronze. A typical metal component is copper. The route of contamination of the metal component is also not particularly limited. Examples include contamination from raw materials (conductive materials or polymers) constituting the resin composition for secondary batteries, and contamination during the composition preparation process, such as charging or mixing. Carbon-based conductive materials such as carbon black and carbon nanotubes may contain large amounts of metal components derived from their manufacturing process (as manufacturing equipment or catalysts). The present invention is preferably applicable when the resin composition for secondary batteries contains 10 ppb or more of a metal component based on its mass. The effects of the present invention can be enjoyed regardless of the amount of metal component contained, although the effects vary.

<Step of oxidizing metal components>
The present invention includes a step of oxidizing a metal component contained in a resin composition for a secondary battery. The step of oxidizing the metal component is not particularly limited. Examples include electrochemical methods and chemical treatment methods using additives such as acids and bases. Among these, a method of contacting with oxygen gas is preferred, and a method of blowing oxygen gas into a resin composition for a secondary battery while stirring the resin composition to cause gas-liquid mixing is preferred.

While there are no particular limitations on the method for stirring the resin composition for secondary batteries, a disperser (stirring blade) or similar is typically used. Various types of stirrers, including propeller and turbine types, are available, provided they can uniformly stir the resin composition for secondary batteries. The stirring speed is preferably 0.5 m/s or higher, and is determined by appropriately adjusting the size and rotation speed of the stirring blade. A stirring speed of 0.5 m/s or higher is preferred because it ensures sufficient gas-liquid mixing of the resin composition for secondary batteries and oxygen gas. The upper limit of the stirring speed is not particularly limited and may be set appropriately within the range permitted by the actual operating process. The conditions for sufficient gas-liquid mixing of the resin composition for secondary batteries and oxygen gas cannot be uniquely determined, but they can be set by appropriately adjusting the viscosity of the resin composition for secondary batteries, production scale, and tank volume, as well as the size and rotation speed of the stirring blade, the shape of the stirring blade, and the distance from the tank bottom, so as to achieve the objectives of the present invention.

The method for injecting oxygen (air) gas is not particularly limited, but production lines such as those shown in Figures 1 to 3 are possible. Figure 1 shows a case in which oxygen (air) gas is directly injected from the top of a tank containing a resin composition for secondary batteries. Figure 2 shows a case in which a static mixer is attached to the tank via piping, and oxygen (air) gas is directly injected into the resin composition for secondary batteries in the tank while the resin composition for secondary batteries in the tank is circulated by a pump. Figure 3 shows a case in which a bubbler is installed at the bottom of the tank, and oxygen (air) gas is directly injected into the resin composition for secondary batteries in the tank. The size, length, diameter, etc. of the gas inlet piping can be set so as to achieve the objectives of the present invention, taking into account the production scale of the resin composition for secondary batteries and the capacity of the tank.

A static mixer is a stationary mixer with no driving means. It contains around 6 to 10 guides (baffle plates) called elements arranged in a spiral. The fluid flowing inside flows along the twisted surfaces of the elements, creating turbulence, which disperses oxygen (air) gas at high speed and breaks it into small bubbles, facilitating its dispersion and dissolution into the dispersion medium. For example, Noritake Company Limited sells a variety of gas-liquid mixing types, which can be selected and used depending on the pipe diameter, circulating gas flow rate, scale, etc.

In the present invention, the flow rate of oxygen gas blown in is preferably 20 NL/hour (hereinafter referred to as "h") or more per 1 ^m3 of resin composition for secondary batteries. It is preferably 100 NL/h or more, and more preferably 300 NL/h or more. When compressed air is used as a substitute for oxygen gas, it is calculated from the proportion of oxygen in air (about 20%) and is preferably 100 NL/h or more per 1 ^m3 . Similarly, the preferred range is 500 NL/h or more, and more preferably 1500 NL/h or more.

NL (normal liter) refers to the academic volume of a gas measured under conditions of atmospheric pressure 0.1013 MPa (1 atmosphere), temperature 0°C, and relative humidity 0%. When calculating the volume under actual use (production) conditions, it is possible to make an approximate calculation using the ideal gas equation of state. For example, the volume of a gas at atmospheric pressure 0.1013 MPa (1 atmosphere) and temperature 25°C is approximately 1.080 L.

<Conductive material (carbon-based conductive material)>
The resin composition for a secondary battery may further contain a conductive material. The conductive material in the present invention is a carbon-based conductive material. The carbon-based conductive material is not particularly limited as long as it is a carbon material having conductivity, and graphite, carbon black, carbon nanotubes, carbon nanofibers, carbon fibers, fullerenes, etc. can be used alone or in combination of two or more types. The conductive material is a substance (material) different from the electrode active material described below.

Various types of carbon black can be used, including commercially available acetylene black, furnace black, hollow carbon black, channel black, thermal black, and ketjen black. Furthermore, carbon black may be neutral, acidic, or basic, and oxidation-treated carbon black or graphitized carbon black may also be used.

Carbon nanotubes (CNTs) include single-walled carbon nanotubes, multi-walled carbon nanotubes, and nanotubes in the form of planar graphite rolled into a cylinder, and these may be mixed. Single-walled carbon nanotubes have a structure in which one layer of graphite is rolled up. Multi-walled carbon nanotubes have a structure in which two or more layers of graphite are rolled up. Furthermore, the sidewalls of carbon nanotubes do not have to have a graphite structure. For example, carbon nanotubes with sidewalls having an amorphous structure are also considered carbon nanotubes in this specification.

The shape of the carbon nanotubes is not limited. Examples of such shapes include needles, cylindrical tubes, fishbone shapes (fishbone or cup stacked shapes), playing cards (platelets), and coil shapes. In this embodiment, the shape of the carbon nanotubes is preferably needles or cylindrical tubes. The carbon nanotubes may have a single shape or a combination of two or more shapes.

Examples of carbon nanotube forms include graphite whiskers, filamentous carbon, graphite fibers, ultrafine carbon tubes, carbon tubes, carbon fibrils, carbon microtubes, and carbon nanofibers. Carbon nanotubes may have any of these forms alone or a combination of two or more of them.

The carbon purity of the carbon-based conductive material can be determined by standard CHN elemental analysis and is expressed as the carbon atom content (mass %) in the carbon-based conductive material. Based on the mass of the carbon-based conductive material (taking the mass of the carbon-based conductive material as 100 mass %), the carbon purity is preferably 90 mass % or more, more preferably 95 mass % or more, and even more preferably 98 mass % or more. By keeping the carbon purity within the above range, problems such as the formation of dendrites due to impurities and short circuits can be prevented when the material is used in a secondary battery.

The amount of metal contained in the carbon-based conductive material is preferably less than 10% by mass, more preferably less than 5% by mass, and even more preferably less than 2% by mass, based on 100% by mass of the carbon-based conductive material. In particular, metals contained in carbon nanotubes include metals and metal oxides used as catalysts when synthesizing carbon nanotubes. Specific examples include metals such as iron, cobalt, nickel, aluminum, magnesium, silica, manganese, and molybdenum, as well as metal oxides and composite oxides of these.

Furthermore, the carbon-based conductive material may contain 50 ppm or less, more specifically 20 ppm or less, of iron metal element in the catalyst used in the manufacturing process. By significantly reducing the iron content as an impurity remaining in the carbon-based conductive material in this way, superior conductivity can be exhibited without the risk of side reactions in the electrode. The content of metal impurities remaining in the conductive material can be analyzed using inductively coupled plasma (ICP). Furthermore, the carbon-based conductive material does not necessarily need to contain iron metal element.

The BET specific surface area of the carbonaceous conductive material is preferably 20 to 1,000 ^{m 2} /g, and more preferably 30 to 500 m ² /g.

The content of the carbon-based conductive material contained in the resin composition for secondary batteries is preferably 0.1% by mass or more, and more preferably 0.5% by mass or more, based on the mass of the resin composition for secondary batteries (the mass of the resin composition for secondary batteries being 100% by mass). It is also preferably 30% by mass or less, and more preferably 25% by mass or less. By keeping the content of the conductive material contained in the resin composition for secondary batteries within the above range, the conductive material can be maintained in a good and stable state without sedimentation or gelation. It is also preferable to appropriately adjust the content of the conductive material so as to obtain a resin composition for secondary batteries that exhibits an appropriate viscosity, taking into account the specific surface area of the conductive material, its affinity for the dispersion medium, etc.

The method for dispersing the carbon-based conductive material is not particularly limited, but examples include methods using various dispersing means such as a disperser, homogenizer, Silverson mixer, kneader, two-roll mill, three-roll mill, ball mill, horizontal sand mill, vertical sand mill, annular bead mill, attritor, planetary mixer, or high-pressure homogenizer.

<Inorganic Acids and Inorganic Bases>
The resin composition for a secondary battery may further contain an inorganic acid and/or an inorganic base. The inorganic acid in the present invention refers to an acid derived from an inorganic compound, and is not particularly limited, but examples thereof include oxo acids such as nitric acid, phosphoric acid, sulfuric acid, and boric acid, and hydroacids such as hydrochloric acid, hydrocyanic acid, and hexafluorophosphoric acid. Examples of inorganic bases include chlorides, hydroxides, carbonates, nitrates, sulfates, phosphates, tungstates, vanadates, molybdates, niobates, and borates of alkali metals or alkaline earth metals; and ammonium hydroxide. The metal contained in the inorganic base may be a transition metal.

The amount of inorganic acid and inorganic base used is preferably 0.001% by mass or more, and more preferably 0.005% by mass or more, based on the mass of the resin composition for secondary batteries. Furthermore, the amount of inorganic acid and inorganic base used is preferably 20% by mass or less, and more preferably 15% by mass or less, based on the mass of the resin composition for secondary batteries.

<Slurry composition for secondary battery electrode>
The slurry composition for a secondary battery electrode contains at least the secondary battery resin composition and an electrode active material. In other words, the slurry composition for a secondary battery electrode contains at least a polymer, a dispersion medium, and an electrode active material, and may further contain optional components such as a conductive material, a base, an acid, and a binder. In this specification, the "slurry composition for a secondary battery electrode" may also be referred to as a "composite slurry" or "slurry for an electrode film."

Electrode active materials are materials that form the basis of battery reactions. Electrode active materials are divided into positive electrode active materials and negative electrode active materials based on their electromotive force.

The positive electrode active material is not particularly limited, but may be a material capable of reversibly doping or intercalating lithium ions. Examples include metal compounds such as metal oxides and metal sulfides. Specifically, examples include inorganic compounds such as oxides of transition metals such as Fe, Co, Ni, and Mn, composite oxides with lithium, and transition metal sulfides. Specifically, examples include transition metal oxide powders such as MnO, V ₂ O ₅ , V ₆ O ₁₃ , and TiO ₂ ; composite oxide powders of lithium and transition metals such as layered lithium nickel oxide, lithium cobalt oxide, lithium manganate, and spinel-structured lithium manganate; lithium iron phosphate-based materials, which are phosphate compounds with an olivine structure; and transition metal sulfide powders such as TiS ₂ and FeS. The positive electrode active material is preferably a material containing at least Ni. One or more positive electrode active materials can be used in combination.

The negative electrode active material may be a material capable of reversibly doping or intercalating lithium ions. Examples include alloys such as metal Li and its alloys, such _{as tin alloys, silicon alloys, and lead alloys; metal oxides such as LiXFe2O3 , LiXFe3O4 , and LiXWO2} (where x is a number in the range of 0<x< ₁ ), _lithium titanate, lithium vanadate, and lithium silicate; conductive polymers such as polyacetylene and poly-p-phenylene; carbonaceous powders such as artificial graphite and natural graphite, including highly graphitized carbon materials; and carbon materials such as resin-baked carbon materials. The negative electrode active material may be used alone or in combination.

The polymer content in the slurry composition for secondary battery electrodes is preferably 0.01 to 10 mass% and more preferably 0.05 to 5 mass% based on the mass of the electrode active material (the mass of the electrode active material being 100 mass%).

The content of the conductive material in the slurry composition for secondary battery electrodes is preferably 0.01 to 10 mass%, more preferably 0.02 to 5 mass%, and even more preferably 0.03 to 3 mass%, based on the mass of the electrode active material (the mass of the electrode active material being 100 mass%).

When the slurry composition for secondary battery electrodes contains a binder, the content of the binder in the slurry composition for secondary battery electrodes is preferably 0.1 to 30 mass%, more preferably 0.5 to 20 mass%, and even more preferably 1 to 10 mass%, based on the mass of the electrode active material (the mass of the electrode active material being 100 mass%).

The solid content in the slurry composition for secondary battery electrodes of the present invention is preferably 30 to 90 mass%, more preferably 30 to 80 mass%, and even more preferably 40 to 75 mass%, based on the mass of the slurry composition for secondary battery electrodes (the mass of the slurry composition for secondary battery electrodes being 100 mass%).

Slurry compositions for secondary battery electrodes can be prepared by a variety of conventional methods. Examples include a method in which an electrode active material is added to a resin composition for secondary batteries (since the polymer also functions as a binder, a slurry composition for secondary battery electrodes can be obtained without adding a binder); a method in which a binder is added to a resin composition for secondary batteries, and then an electrode active material is added; and a method in which an electrode active material is added to a resin composition for secondary batteries, and then a binder is added.

A preferred method for preparing a slurry composition for secondary battery electrodes is to add a binder to a resin composition for secondary batteries, then add an electrode active material and perform a dispersion treatment. The dispersion device used for dispersion is not particularly limited. The dispersion means mentioned in the description of the dispersion method for carbon-based conductive materials can be used to obtain a slurry composition for secondary battery electrodes. Alternatively, an electrode active material may be added to a resin composition for secondary batteries without adding a binder, and then a dispersion treatment may be performed.

<Electrode film>
The electrode film includes a film formed using the slurry composition for a secondary battery electrode film, and may further include a current collector. For example, the electrode film can be obtained by applying the slurry composition for a secondary battery electrode film onto a current collector and drying it, and includes the current collector and a film. In this specification, the "film formed using the slurry composition for a secondary battery electrode film" may be referred to as an "electrode mixture layer."

The material and shape of the current collector used to form the electrode film are not particularly limited, and can be selected appropriately to suit various types of secondary batteries. Examples of current collector materials include metals or alloys such as aluminum, copper, nickel, titanium, and stainless steel. Furthermore, while flat foil is generally used as the shape, current collectors with a roughened surface, perforated foil current collectors, and mesh-shaped current collectors can also be used.

The method for applying the secondary battery electrode slurry composition to the current collector is not particularly limited, and any known method can be used. Specific examples include die coating, dip coating, roll coating, doctor coating, knife coating, spray coating, gravure coating, screen printing, and electrostatic painting. Drying methods include, but are not limited to, leaving the composition to dry, or drying using a blower dryer, warm air dryer, infrared heater, or far-infrared heater.

After coating, a rolling process using a lithographic press, calendar roll, or the like may be performed. The thickness of the formed film is, for example, from 1 μm to 500 μm, and preferably from 10 μm to 300 μm.

<Nonaqueous electrolyte secondary battery>
The nonaqueous electrolyte secondary battery includes a positive electrode, a negative electrode, and an electrolyte, and at least one selected from the group consisting of the positive electrode and the negative electrode includes the electrode film.

For example, an electrode film can be used as the positive electrode, which is prepared by applying an electrode slurry composition for secondary batteries containing a positive electrode active material onto a current collector and then drying it.

For example, an electrode film can be used as the negative electrode, which is prepared by applying an electrode slurry composition for secondary batteries containing a negative electrode active material onto a current collector and then drying it.

The electrolyte may be any of various conventionally known electrolytes capable of transferring ions. Examples include, but _{are not limited} to, _{lithium salts such as LiBF4, LiClO4, LiPF6, LiAsF6, LiSbF6, LiCF3SO3, Li(CF3SO2)2N, LiC4F9SO3, Li(CF3SO2)3C , LiI , LiBr , LiCl , LiAlCl , LiHF2 , LiSCN} , or _LiBPh4 (wherein Ph is a phenyl group). The electrolyte is preferably dissolved in a non-aqueous solvent and used as an electrolytic solution.

Non-aqueous solvents include, but are not limited to, carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate; lactones such as gamma-butyrolactone, gamma-valerolactone, and gamma-octanoic lactone; glymes such as tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,2-methoxyethane, 1,2-ethoxyethane, and 1,2-dibutoxyethane; esters such as methyl formate, methyl acetate, and methyl propionate; sulfoxides such as dimethyl sulfoxide and sulfolane; and nitriles such as acetonitrile. These solvents may be used alone or in combination.

Non-aqueous electrolyte secondary batteries preferably include a separator. Examples of separators include, but are not limited to, polyethylene nonwoven fabric, polypropylene nonwoven fabric, polyamide nonwoven fabric, and nonwoven fabrics that have been hydrophilically treated.

The structure of the nonaqueous electrolyte secondary battery of this embodiment is not particularly limited, but typically comprises a positive electrode, a negative electrode, and a separator, if necessary, and can be in a variety of shapes depending on the intended use, such as a paper type, a cylindrical type, a button type, or a laminated type.

The present invention will be explained in more detail below with reference to examples. The present invention is not limited to the following examples, provided that the gist of the invention is not exceeded. Unless otherwise specified, "parts" means "parts by mass" and "%" means "% by mass."

<Conductive material>
Carbon black: Acetylene black HS-100 (manufactured by Denka Co., Ltd.) with a specific surface area of 39 m ² /g calculated from the nitrogen adsorption amount using the S-BET equation, hereinafter abbreviated as "CB".
Carbon nanotubes: Multi-walled carbon nanotubes 100T (manufactured by Kumho Petrochemical Co., Ltd.), fiber diameter 10 to 15 μm, hereinafter abbreviated as "CNT."

<Polymer>
Polyvinylpyrrolidone: K30 (manufactured by Nippon Shokubai Co., Ltd.), hereinafter abbreviated as PVP.
Hydrogenated nitrile rubber: Zpole® 2000L (manufactured by Zeon Corporation), hereinafter abbreviated as HNBR.
Carboxymethyl cellulose: Sunrose (R) 0F01MC (manufactured by Nippon Paper Industries Co., Ltd.), hereinafter abbreviated as CMC.

<Inorganic Acids and Inorganic Bases>
Sodium hydroxide, granular (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), hereinafter abbreviated as NaOH.
Hydrochloric acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) Hereinafter abbreviated as HCl.

<Binder>
Polyvinylidene fluoride: KF Polymer W7300 (manufactured by Kureha Corporation), weight-average molecular weight of approximately 1,000,000. Hereinafter abbreviated as PVDF.
Styrene butadiene rubber (hereinafter abbreviated as SBR) emulsion solution: TRD2001 (manufactured by JSR Corporation), solid content 48%

<Others>
Copper powder: Fujifilm Wako Pure Chemical Industries, Ltd., D50 75 μm, purity 99.9%
Copper oxide: Kishida Chemical Co., Ltd., D50 150 μm (100 mesh)

<Electrode active material>
LiNi _1/3 Mn _1/3 Co _1/3 O ₂ : Positive electrode active material, lithium nickel manganese cobalt oxide. Average primary particle diameter determined by observation with an electron microscope was 5.5 μm, and specific surface area determined by the S-BET equation from the nitrogen adsorption amount was 0.62 m ² /g. hereinafter abbreviated as “NCM.”
Artificial graphite: negative electrode active material, CGB-20 (manufactured by Nippon Graphite Industries Co., Ltd.), average particle size 12 μm, hereinafter abbreviated as "graphite".

<Method for measuring metal ion and atom content in raw materials>
The conductive material, polymer, and binder used in the examples were pretreated by acid decomposition in accordance with Japanese Industrial Standard JIS K 0116; 2014, and the contents of iron and copper ions and atoms were measured by ICP atomic emission spectrometry. It is thought that using these as raw materials may result in the inclusion of metal foreign matter in the composition.
CB: Iron 0 ppm (below detection limit), Copper 0 ppm (below detection limit)
CNT: Iron 9976 ppm, Copper 1.6 ppm
PVP: Iron 13 ppm, Copper 0 ppm (below detection limit)
CMC: Iron 0.9 ppm, Copper 0 ppm (below detection limit)
・HNBR: Iron 28 ppm, Copper 0 ppm (below detection limit)
PVDF: Iron 32 ppm, Copper 0.9 ppm

Hereinafter, one embodiment of a production line for a resin composition for a secondary battery of the present invention will be described with reference to the drawings.
FIG. 1 shows an example of a production line in which oxygen (air) gas is introduced from the top of a tank and the resin composition for secondary batteries and the oxygen (air) gas in the tank are mixed into a gas-liquid mixture by dispersing.
FIG. 2 shows an example of a production line in which a static mixer is attached to a tank via piping, and oxygen (air) gas is directly introduced into the composition while circulating the resin composition for a secondary battery in the tank with a pump, thereby performing gas-liquid mixing.
FIG. 3 shows an example of a production line in which a bubbler is installed at the bottom of a tank, and oxygen (air) gas is directly introduced into the resin composition for a secondary battery in the tank while being stirred with a disperser to mix the gas and liquid.
The sizes of the components such as tanks and pipes that make up each production line are adjusted according to the scale of production.

<Production line (A) of resin composition for secondary batteries>
The production line (A) for producing a resin composition for a secondary battery shown in FIG. 1 will be described in detail.
The production line (A) includes a tank for dissolving/storing/preparing the resin composition for secondary batteries shown in 1A, and a disper (stirring blade) 2A for stirring the resin composition for secondary batteries in the tank. A pipe 31A for introducing oxygen (air) gas is connected to the top of the tank, and by introducing oxygen (air) gas while stirring the resin composition for secondary batteries in the tank, gas-liquid mixing becomes possible.

<Production line (B) of resin composition for secondary batteries>
The production line (B) for the resin composition for secondary batteries shown in FIG. 2 will be described in detail.
The production line (B) includes a tank for dissolving/storing/preparing the resin composition for secondary batteries shown in 1B, and a disper (stirring blade) 2B for stirring the resin composition for secondary batteries in the tank, and is connected from the bottom of the tank to a pipe 31B via a valve 5. The pipe 31B is connected to a circulation pump 6, and the end of the pump outlet pipe 32B is connected to an oxygen (air) gas inlet 7 and a static mixer 8, and the end of the static mixer 8 is connected to a pipe 33B at the top of the tank 1B. This allows oxygen (air) gas to be directly introduced into the resin composition for secondary batteries while circulating and stirring, thereby enabling gas-liquid mixing.

<Production line (C) of resin composition for secondary battery>
The production line (C) for the resin composition for secondary batteries shown in FIG. 3 will be described in detail.
The production line (C) is equipped with a tank for dissolving/storing/preparing the resin composition for secondary batteries shown in 1C, a disper (stirring blade) 2C for stirring the resin composition for secondary batteries in the tank, and a bubbler at the bottom of the tank. These enable gas-liquid mixing by circulating and stirring while bubbling oxygen (air) gas directly into the resin composition for secondary batteries.

<Evaluation of the Oxidation Effect of Metal Impurities in Resin Compositions for Secondary Batteries>
Regarding the oxidation effect of introducing oxygen (air) gas into the resin composition for secondary batteries and mixing the gas and liquid,
(1) Amount of magnetically attracted material in a resin composition for a secondary battery (2) Linear sweep voltammetry measurement (hereinafter referred to as LSV measurement) of a resin composition for a secondary battery to which copper powder has been intentionally added
(3) Evaluation was performed by LSV measurement using the filtration residue of the resin composition for secondary batteries.
In the evaluation of (1), the amount of magnetic material in the composition can be confirmed by filtering the resin composition for secondary batteries with a magnetic filter, recovering and weighing the magnetic material. If the magnetic metal (such as iron) in the composition is oxidized, it loses its magnetism, and the amount of magnetic material decreases. On the other hand, the effect of oxidation cannot be confirmed for metals that are not inherently magnetic, such as copper. In the evaluation of (2), when copper, a typical example of a metal that is not magnetic as described above, is intentionally added to the resin composition for secondary batteries, the effect of oxidation on the added copper is confirmed. In the evaluation of (3), the effect of oxidation on non-magnetic metals derived from conductive materials, polymers, and binders in the resin composition for secondary batteries is confirmed.

LSV measurement is a technique in which the electrode potential is swept over a specific range, the corresponding reaction current is measured, and various electrochemical information is analyzed. This measurement allows quantitative confirmation of the reaction volume from the current amount, and the reaction rate from the slope. For example, when copper is present in the positive electrode and lithium foil is used as the negative electrode, the oxidation-reduction potential of copper is approximately 3.4 V based on the standard electrode potential. This means that electron transfer associated with the copper dissolution reaction occurs at voltages of approximately 3.4 V or higher. The rise of the reaction current in LSV measurement indicates the reaction onset potential, while the reaction current amount and slope indicate the ease of copper dissolution. If the surface of a copper particle is chemically converted to copper oxide due to oxidation, the dissolution of copper ions is suppressed, and the reaction onset potential in LSV measurement shifts to a higher voltage.

<(1) Evaluation of the amount of magnetic particles in a resin composition for a secondary battery>
[Example 1]
A resin composition for a secondary battery was produced using production line (A). 540 kg of NMP was charged into a tank, and while stirring with a disperser, the NMP in the tank was heated to a temperature of 60°C. 60 kg of PVP was then added as a polymer, and stirring with a disperser was continued until the polymer was completely dissolved, yielding a 10% PVP-NMP solution.
Subsequently, dry air containing 20% oxygen was introduced from the piping at the top of the tank at a flow rate of 1500 NL/h (300 NL/h as oxygen content) while the 10% PVP-NMP solution in the tank was stirred with a disperser for an additional 8 hours to perform gas-liquid mixing, thereby obtaining a resin composition for a secondary battery (composition 1).
The obtained resin composition for secondary batteries was filtered through a magnetic filter (manufactured by Tok Engineering) at room temperature and a magnetic flux density of 12,000 gauss. After filtration, a small amount of magnetic granular metal particles was observed adhering to the magnetic filter. These metal particles were recovered and weighed to be 3.4 mg.

[Examples 2 to 7]
Resin compositions for secondary batteries were produced in the same manner as in Example 1, except that the amount of polymer, concentration, amount of solvent, dry air flow rate, and temperature inside the tank were changed as shown in Table 1. Thereafter, magnetic filtration was carried out in the same manner as in Example 1, and the magnetic deposits were recovered and weighed. The results are shown in Table 1.

[Example 8]
A resin composition for a secondary battery was produced using production line (B). 540 kg of NMP was charged into a tank, and while stirring with a disperser, the NMP in the tank was heated to a temperature of 60°C. 60 kg of PVP was then added as a polymer, and stirring with a disperser was continued until it was completely dissolved, yielding a 10% PVP-NMP solution.
Next, the valve at the bottom of the tank was opened and the circulation pump was driven to circulate the solution through the tank, pump, static mixer, and tank (return) in that order, and then dry air containing 20% oxygen was introduced through the oxygen (air) gas inlet at a flow rate of 1500 NL/h (300 NL/h as oxygen content). The introduced dry air flows together with the solution, and after gas-liquid mixing is performed in the static mixer, gas-liquid mixing is further performed in the tank by disper stirring.
The above circulation stirring was carried out for 8 hours to obtain a resin composition for secondary batteries (composition 8). The obtained resin composition for secondary batteries was passed through a magnetic filter and subjected to magnetic filter filtration in the same manner as in Example 1. The magnetic deposits were recovered and weighed, which was 1.6 mg. The results are shown in Table 1.

[Example 9]
A resin composition for secondary batteries was produced using production line (C). 540 kg of NMP was added to a tank, and while stirring with a disperser, the temperature of the NMP in the tank was heated to 60 ° C. Thereafter, 60 kg of PVP was added as a polymer, and stirring with a disperser was continued until completely dissolved, resulting in a 10% PVP-NMP solution. Subsequently, dry air containing 20% oxygen was introduced from a bubbler at the bottom of the tank at a flow rate of 1500 NL / h (oxygen content: 300 NL / h), while stirring with a disperser for an additional 8 hours, and gas-liquid mixing was performed to obtain a resin composition for secondary batteries (composition 9).
The obtained resin composition for a secondary battery was subjected to magnetic filter filtration in the same manner as in Example 1, and the magnetic deposit was recovered and weighed to be 2.3 mg. The results are shown in Table 1.

[Example 10]
A resin composition for a secondary battery (composition 10) was produced in the same manner as in Example 9, except that the polymer type was changed to HNBR. Thereafter, magnetic filtration was carried out in the same manner as in Example 1, and the magnetic deposit was recovered and weighed, yielding 3.1 mg. The results are shown in Table 1.

[Example 11]
A resin composition for a secondary battery (composition 10) was produced in the same manner as in Example 9, except that the polymer type was changed to CMC, the solvent was changed to water, the polymer concentration was changed to 5%, and the temperature in the tank was changed to 40°C. Thereafter, magnetic filtration was carried out in the same manner as in Example 1, and the magnetic deposit was recovered and weighed, which was 0.7 mg. The results are shown in Table 1.

[Comparative Examples 1 to 3]
Except for not introducing oxygen gas, a resin composition for a secondary battery was produced as described in Table 1. Thereafter, magnetic filtration was performed, and the magnetic deposits were recovered and weighed. The results are shown in Table 1.

[Example 12]
The production of a resin composition for secondary batteries was carried out using the production line (C). 534 kg of NMP was added to the tank, and while stirring with a disperser, the temperature of the NMP in the tank was heated to 60 ° C. Thereafter, 60 kg of HNBR was added as a polymer, and stirring with a disperser was continued until completely dissolved, resulting in a 10% concentration HNBR-NMP solution. Subsequently, while stirring with a disperser, 6 kg of NaOH was slowly added as an inorganic base, and then dry air containing 20% oxygen was introduced from the bubbler at the bottom of the tank at a flow rate of 1500 NL / h (oxygen content, 300 NL / h), and the mixture was stirred with a disperser for an additional 8 hours, resulting in gas-liquid mixing. A resin composition for secondary batteries (composition 12) containing an inorganic base was obtained.
The obtained resin composition for a secondary battery was subjected to magnetic filter filtration in the same manner as in Example 1, and the magnetic deposit was recovered and weighed to be 1.2 mg. The results are shown in Table 1.

[Example 13]
The production of a resin composition for secondary batteries was carried out using the production line (C). 558 kg of water was added to the tank, and while stirring with a disperser, the temperature of the water in the tank was heated to 40 ° C. Then, 30 kg of CMC was added as a polymer, and the disperser stirring was continued until completely dissolved, resulting in a 5% CMC aqueous solution. Next, while stirring with a disperser, 12 kg of HCl was slowly added as an inorganic acid, and then dry air containing 20% oxygen was introduced from the bubbler at the bottom of the tank at a flow rate of 1500 NL / h (oxygen content, 300 NL / h), and the disperser stirring was continued for an additional 8 hours, and gas-liquid mixing was performed to obtain a resin composition for secondary batteries (composition 13) containing an inorganic acid.
The obtained resin composition for a secondary battery was subjected to magnetic filter filtration in the same manner as in Example 1, and the magnetic deposit was recovered and weighed to be 0.2 mg. The results are shown in Table 1.

[Comparative Examples 4 and 5]
A resin composition for a secondary battery containing an inorganic acid or an inorganic base was produced as shown in Table 1, except that oxygen gas was not introduced. Then, magnetic filtration was performed, and the magnetic deposits were recovered and weighed. The results are shown in Table 1.

[Example 14]
According to the composition shown in Table 2, NMP was added to a stainless steel tank, and while stirring with a disperser, PVP was added to dissolve and adjusted to a predetermined concentration. Next, CNT was added while stirring with a disperser, and a batch dispersion process was performed using a high-shear mixer (manufactured by SILVERSON) equipped with a square-hole high-shear screen until the particle size on the grind gauge was 250 μm or less. Next, the dispersion liquid was supplied from the stainless steel tank to a high-pressure homogenizer (Starburst 10, manufactured by Sugino Machine) via piping, and additional dispersion processing was performed. The additional dispersion processing used a single nozzle chamber, and 45 passes were performed at a nozzle diameter of 0.25 mm and a pressure of 100 MPa to obtain 60 kg of a resin composition for secondary batteries (composition 12) containing a conductive material.
The obtained resin composition for a secondary battery (composition 14) was subjected to gas-liquid mixing on production line (B) at a dry air flow rate of 1500 NL/h (300 NL/h as oxygen content) for 8 hours at a temperature of 40° C. Finally, magnetic filter filtration was carried out, and the magnetic deposit was recovered and its weight was measured, which was 15.3 mg.

[Example 15]
A resin composition for secondary batteries was produced according to the composition shown in Table 2. Ion-exchanged water was added to a stainless steel tank, and while stirring with a disperser, CMC was added to dissolve the mixture and adjusted to a predetermined concentration. Subsequently, CB was added while stirring with a disperser, and a batch dispersion process was performed using a high-shear mixer (manufactured by SILVERSON) equipped with a square-hole high-shear screen until the particle size measured on a grind gauge reached 250 μm or less. Next, the dispersion liquid was supplied from the stainless steel tank via piping to a bead mill (Dyno Mill MULTI LAB, manufactured by Shinmaru Enterprises) filled with 1.00 mm diameter zirconia beads, and additional dispersion processing was performed. The additional dispersion processing was continued until the particle size measured on a grind gauge of the dispersion liquid reached 20 μm or less. After the viscosity decreased and sufficient fluidity was confirmed, dispersion was terminated, and 60 kg of a resin composition for secondary batteries (composition 15) containing a conductive material was obtained.
Ta.
The obtained resin composition for a secondary battery containing a conductive material (composition 15) was subjected to gas-liquid mixing on production line (B) at a dry air flow rate of 1500 NL/h (300 NL/h as oxygen content) for 8 hours at a temperature of 40° C. Finally, magnetic filter filtration was carried out, and the magnetic deposit was recovered and its weight was measured, which was 0.9 mg.

[Example 16]
A resin composition for a secondary battery was produced according to the composition shown in Table 2. NMP was added to a stainless steel tank, and while stirring with a disperser, PVP was added to dissolve the mixture and adjusted to a predetermined concentration. Next, CB and PVDF powders (PVP:PVDF mass ratio 1:5) were simultaneously added while stirring with a disperser, and a batch dispersion process was performed using a high shear mixer (manufactured by SILVERSON) equipped with a square-hole high shear screen until the particle size measured on a grind gauge was 20 μm or less, thereby obtaining a resin composition for a secondary battery (composition 16).
60 kg of the obtained resin composition for a secondary battery (composition 16) was subjected to gas-liquid mixing on production line (B) at a dry air flow rate of 1500 NL/h (300 NL/h as oxygen content) for 8 hours at a temperature of 45° C. Finally, magnetic filter filtration was carried out, and the magnetic deposit was recovered and its weight was measured, which was 10.4 mg.

[Comparative Example 6]
A resin composition for a secondary battery was produced in the same manner as in Example 14, except that dry air was not introduced. Then, magnetic filtration was performed, and the magnetic deposit was recovered and weighed, which was 172 mg. The results are shown in Table 2.

[Comparative Example 7]
A resin composition for a secondary battery was produced in the same manner as in Example 15, except that dry air was not introduced. Then, magnetic filtration was performed, and the magnetic deposit was recovered and weighed, which was 12.8 mg. The results are shown in Table 2.

[Comparative Example 8]
A resin composition for a secondary battery was produced in the same manner as in Example 16, except that dry air was not introduced. Then, magnetic filtration was performed, and the magnetic deposit was recovered and weighed, which was 90.2 mg. The results are shown in Table 2.

In the evaluation results of the amount of magnetically attracted material in Table 1, when focusing on the difference between the presence and absence of oxygen (air) gas introduction in the same system (for example, Example 1 and Comparative Example 1, or Example 10 and Comparative Example 2), it can be seen that the introduction of oxygen (air) gas significantly reduces the amount of magnetically attracted material. This is presumably because the introduction of oxygen (air) gas oxidizes the magnetic metal components in the system, making them unreactive to the magnetic filter. Focusing on the effect of oxidation, the results of Examples 1 and 2 show that a higher temperature in the tank and the results of Examples 1 and 5 to 7 show that a greater amount of oxygen (air) gas introduced results in a higher oxidation effect. Furthermore, the results of Examples 1, 8, and 9 show that high effects can be obtained by directly introducing oxygen (air) gas into the resin composition for secondary batteries. These significant effects are obtained regardless of the type of solvent, polymer type, or concentration. Focusing on the effects of inorganic acids and inorganic bases, the results of Examples 10 and 12 and the results of Examples 11 and 13 confirm that the amount of magnetically attracted material is reduced. In addition, taking into account the results of Comparative Examples 4 and 5, it is clear that the effect of simply treating with an inorganic acid and an inorganic base without introducing oxygen (air) gas is small.
From Table 2, it can be seen that the same oxidation effect is obtained even in the resin composition for a secondary battery containing a conductive material and a binder.

<(2) LSV Measurement of Resin Composition for Secondary Battery with Intentionally Added Copper Powder>
[Example 17]
A resin composition for secondary batteries was produced using production line (A). NMP was added to a tank, and while stirring with a disperser, the temperature of the NMP in the tank was heated to 60 ° C. Thereafter, PVP was added as a polymer, and stirring with a disperser was continued until completely dissolved, resulting in a 10% PVP-NMP solution. Subsequently, copper powder was added to a concentration of 500 ppm, and then dry air containing 20% oxygen was introduced from the piping at the top of the tank at a flow rate of 1500 NL / h (oxygen content: 300 NL / h), while the 10% PVP-NMP solution in the tank was stirred with a disperser for an additional 8 hours, and gas-liquid mixing was performed to obtain a resin composition for secondary batteries (composition 17) containing copper powder.

(LSV Measurement of Resin Composition for Secondary Battery Obtained in Example 17)
First, 12 g of a resin composition for secondary batteries (composition 17) containing 500 ppm copper powder was weighed into a 300 ml polypropylene cup, followed by 164 g of NMP. While stirring with a high-shear mixer (manufactured by Silverson) equipped with a square-hole high-shear screen, 19.2 g of CB and 4.8 g of PVDF were simultaneously added as conductive materials, and a batch dispersion process was performed until the particle size measured with a grind gauge reached 20 μm or less. The prepared conductive paste was applied to a 20 μm-thick aluminum foil using a doctor blade, then heated and dried at 120 ° C under reduced pressure. This was then punched out to a radius of 9 mm to form a working electrode. A metallic lithium foil (0.15 mm thick) was used as the counter electrode, and a separator (20 μm thick, 50% by volume porosity) made of a porous polypropylene film was inserted and laminated between the working electrode and the counter electrode, and a non-aqueous electrolyte (a non-aqueous electrolyte obtained by dissolving LiPF ₆ at a concentration of 1 M in a mixed solvent of ethylene carbonate and diethyl carbonate in a volume ratio of 1:1) was filled to assemble a bipolar sealed metal cell (Hosen HS Flat Cell). The cell was assembled in an argon gas-substituted glove box.

The LSV measurement was carried out under the following conditions.
・Sweep start potential: 3.0V (vsLi/Li ⁺ )
Sweep end potential: 4.3 V (vs. Li/Li ⁺ )
・Sweep speed: 10mV/min.
・Measurement temperature: 25℃
The copper oxidation-reduction onset potential, which is an index of the ease of copper elution, was determined as the potential at which the current density reached 20 μA/cm ² from the start of the potential sweep.
When the test battery constructed under the above conditions was evaluated, no current due to the copper oxidation-reduction reaction was measured. This is thought to be because the added copper was oxidized by the introduction of oxygen (air) gas. Note that copper contained in CB was not detected in this measurement.

[Comparative Example 9]
A resin composition for a secondary battery and then a test battery were constructed in the same manner as in Example 17, except that dry air was not introduced. Evaluation was performed by LSV measurement, and the oxidation-reduction potential was found to be about 3.4 V. A short circuit occurred during potential sweep. This is thought to be due to copper particles eluting from the positive electrode side due to potential sweep and then being reduced and generated on the negative electrode side.

[Production Example 1]
A resin composition for a secondary battery and then a test battery were constructed in the same manner as in Example 17, except that copper oxide was added instead of copper, and evaluation was performed by LSV measurement. No current derived from the oxidation-reduction reaction of copper was measured. This result is consistent with the result of Example 17, in which no current derived from the oxidation-reduction reaction of copper was measured, and indicates that if copper is oxidized, no current is measured.

<(3) LSV Measurement Using Filtration Residue of Resin Composition for Secondary Battery>
[Example 18]
First, according to the composition of Example 14 shown in Table 2, NMP was charged into a stainless steel tank, and while stirring with a disperser, PVP was added to dissolve and adjust to a predetermined concentration. Next, CNT was added while stirring with a disperser, and a batch dispersion process was performed using a high-shear mixer (manufactured by Silverson) equipped with a square-hole high-shear screen until the particle size measured on a grind gauge reached 250 μm or less. Next, the dispersion liquid was supplied from the stainless steel tank to a high-pressure homogenizer (Starburst 10, manufactured by Sugino Machine) via piping, and an additional dispersion process was performed. The additional dispersion process used a single nozzle chamber, and 45 passes of dispersion process were performed at a nozzle diameter of 0.25 mm and a pressure of 100 MPa to obtain a resin composition for secondary batteries (composition 18) containing a conductive material.
60 kg of the obtained resin composition for secondary batteries (composition 18) was mixed with gas and liquid at a temperature of 40°C for 8 hours at a dry air flow rate of 1500 NL/h (oxygen content: 300 NL/h) on production line (B). Subsequently, magnetic filter filtration was performed to remove magnetic foreign matter. Subsequently, after diluting 10 times with NMP, the mixture was filtered through a 25 μm mesh to recover residual solids containing non-magnetic metal foreign matter such as copper. The resulting residue was washed with NMP and dried under reduced pressure at 40°C to obtain 30 mg of residual solids containing non-magnetic metal foreign matter such as copper. The obtained non-magnetic metal foreign matter is presumed to be non-magnetic metal foreign matter that was mixed into the resin composition for secondary batteries (composition 18) mainly due to the CNT and PVP in the resin composition, the production line, etc.

(LSV Measurement Using Filtration Residue of Resin Composition for Secondary Battery Obtained in Example 18)
CB and PVDF were used as conductive materials, weighed to a CB:PVDF ratio of 8:2. The residual solid material containing the non-magnetic metal described above was added at a ratio of 1% to CB, and the mixture was dispersed in NMP solvent to prepare a conductive paste. The prepared conductive paste was applied to a 20 μm thick aluminum foil using a doctor blade, then heated and dried at 120 ° C under reduced pressure, and punched into a 9 mm radius to form a working electrode. A lithium metal foil (0.15 mm thick) was used as the counter electrode, and a separator (20 μm thick, porosity 50% by volume) made of porous polypropylene film was inserted and laminated between the working electrode and the counter electrode. A non-aqueous electrolyte (a non-aqueous electrolyte prepared by dissolving _LiPF6 at a concentration of 1 M in a mixed solvent of ethylene carbonate and diethyl carbonate at a volume ratio of 1:1) was filled to form a bipolar sealed metal cell (Hosen HS Flat Cell). The cell was assembled in an argon-purged glove box. The constructed test battery was evaluated by LSV measurement in the same manner as in Example 17, but no current resulting from the oxidation-reduction reaction of copper was measured, which is thought to be because the added residual solid had already been oxidized by the introduction of oxygen (air) gas.

[Comparative Example 10]
A resin composition for a secondary battery and then a test battery were constructed in the same manner as in Example 18, except that dry air was not introduced, and evaluated by LSV measurement. The oxidation-reduction potential was about 3.4 V, and a short circuit occurred during potential sweep. This is thought to be because copper particles contained in the residual solid matter were eluted on the positive electrode side by potential sweep and then reduced and generated on the negative electrode side.

Example 19: Preparation of positive electrode composite slurry and positive electrode film
The following describes an example of producing an electrode mixture slurry using the resin composition for a secondary battery produced according to the present invention, and an electrode coated with the slurry.
In a 150 mL plastic container, 1.08 g of CB was added as a conductive material, 0.54 g of the resin composition for secondary batteries (composition 1) produced in Example 1 (PVP solids content 0.054 g; CB ratio 5%), and 9 g of an 8 mass% PVDF solution (PVDF solids content 0.72 g) was added, and then stirred at 2,000 rpm for 30 seconds using a rotation and revolution mixer (Thinky Corporation, Awatori Rentaro, ARE-310). Next, 34.2 g of NMC was added as an electrode active material, and the mixture was stirred at 2,000 rpm for 20 minutes using a rotation and revolution mixer. Thereafter, 5.18 g of NMP was added, and the mixture was stirred at 2,000 rpm for 30 seconds using a rotation and revolution mixer to obtain a positive electrode composite slurry with a solids content of approximately 72%.

The positive electrode composite slurry was applied to a 20 μm thick aluminum foil current collector using an applicator and dried in an electric oven at 120°C ± 5°C for 25 minutes to produce an electrode. The applicator gap was adjusted sequentially to achieve a coating weight per unit area of 20 mg/ ^cm² . The resulting electrode was then rolled using a roll press (Thank Metal Co., Ltd., 3 ton hydraulic roll press) to produce a positive electrode film with a positive electrode composite layer density of 3.1 g/ ^cm³ .

Example 20: Preparation of negative electrode composite slurry and negative electrode film
In a 150 mL plastic container, 0.6 g of the resin composition for secondary batteries prepared in Example 15 (containing 0.12 g of CB; HS-100 as a conductive material), 0.24 g of CMC, and 25.14 g of water were added, and then the mixture was stirred for 30 seconds at 2,000 rpm using a rotation and revolution mixer. 23.28 g of artificial graphite was added as a negative electrode active material, and the mixture was stirred for 150 seconds at 2,000 rpm using a rotation and revolution mixer. Subsequently, 0.75 g of SBR emulsion solution (containing 0.36 g of SBR as solids) was added, and the mixture was stirred for 30 seconds at 2,000 rpm using a rotation and revolution mixer, to obtain a negative electrode composite slurry with a solids content of approximately 48%. The solid content ratio of the negative electrode active material:conductive material:CMC:SBR in the negative electrode mixture slurry was 97:0.5:1:1.5.

The negative electrode composite slurry was applied to a 20 μm thick copper foil current collector using an applicator, and then dried in an electric oven at 80°C ± 5°C for 25 minutes to produce an electrode. The applicator gap was adjusted sequentially so that the coating weight per unit area was 10 mg/ ^cm² . Further, a rolling process was performed using a roll press (Thank Metal Co., Ltd., 3 ton hydraulic roll press) to produce a negative electrode with a negative electrode composite layer density of 1.6 g/ ^cm³ .

Example 21: Fabrication of non-aqueous electrolyte secondary battery
The positive electrode membrane of Example 19 and the negative electrode membrane of Example 20 were punched out to 50 mm x 45 mm and 45 mm x 40 mm, respectively, and the separator (porous polypropylene film) inserted between them was inserted into an aluminum laminate bag and dried in an electric oven at 70 ° C. for 1 hour. Subsequently, 2 mL of electrolyte was poured into a glove box filled with argon gas, and the aluminum laminate bag was sealed to prepare a battery. The electrolyte was a non-aqueous electrolyte prepared by mixing ethylene carbonate, dimethyl carbonate, and diethyl carbonate in a 1:1:1 (volume ratio) mixed solvent, and further adding 1 part of VC (vinylene carbonate) to 100 parts of the electrolyte solution as an additive, followed by dissolving _LiPF6 at a concentration of 1 M.

<Evaluation of rate characteristics of non-aqueous electrolyte secondary batteries>
The nonaqueous electrolyte secondary battery was placed in a thermostatic chamber at 25°C and subjected to charge/discharge measurements using a charge/discharge device (SM-8, manufactured by Hokuto Denko Corporation). A constant-current, constant-voltage charge (cutoff current 1 mA (0.02 C)) was performed at a charge current of 10 mA (0.2 C) with a charge cutoff voltage of 4.3 V, followed by a constant-current discharge at a discharge current of 10 mA (0.2 C) with a discharge cutoff voltage of 3 V. This operation was repeated three times, followed by a constant-current, constant-voltage charge (cutoff current 1 mA (0.02 C)) at a charge current of 10 mA (0.2 C) with a charge cutoff voltage of 4.3 V, followed by constant-current discharge at discharge currents of 0.2 C and 3 C until the discharge cutoff voltage reached 3.0 V, and the discharge capacity was calculated for each. The rate characteristic can be expressed as the ratio of the 0.2 C discharge capacity to the 3 C discharge capacity, using the following equation:

(Formula 1)
Rate characteristic = 3C discharge capacity / third 0.2C discharge capacity × 100 (%)

As a result, the rate characteristics of the fabricated battery were 80% or more, which was an excellent result.

<Method for Evaluating Cycle Characteristics of Non-Aqueous Electrolyte Secondary Batteries>
The nonaqueous electrolyte secondary battery was placed in a thermostatic chamber at 25°C, and charge/discharge measurements were performed using a charge/discharge device (SM-8, manufactured by Hokuto Denko Corporation). Constant-current, constant-voltage charging (cutoff current 2.5 mA (0.05 C)) was performed at a charge current of 25 mA (0.5 C) with a charge cut-off voltage of 4.3 V, followed by constant-current discharging at a discharge current of 25 mA (0.5 C) with a discharge cut-off voltage of 3 V. This operation was repeated 200 times. The cycle characteristics can be expressed as the ratio of the third 0.5 C discharge capacity to the 200th 0.5 C discharge capacity at 25°C, using the following equation:

(Formula 2)
Cycle characteristics = 3rd 0.5C discharge capacity / 200th 0.5C discharge capacity × 100 (%)

As a result, the cycle characteristics of the produced battery were 85% or more, which was an excellent result.

As described above, it has been confirmed that batteries with excellent rate characteristics and cycle characteristics can be manufactured by using the resin composition for secondary batteries obtained by the manufacturing method of the present invention.

The present invention has been described with reference to the embodiments, but the present invention is not limited to the above. Various modifications that would be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention.

1A, 1B, 1C: Tanks 2A, 2B, 2C: Disperser (agitating blades)
5: Valve 6: Circulation pump 7: Oxygen (air) inlet 8: Static mixer 9: Bubbler 31A, 31B, 31C, 32B, 33B: Pipe 40: Gas cylinder

Claims (10)

A method for producing a resin composition for a secondary battery electrode , comprising:
a step of oxidizing a metal component contained in the resin composition for a secondary battery electrode ,
The internal temperature of the step of oxidizing the metal component is 40°C or higher,
A method for producing a resin composition for a secondary battery electrode , which does not include adding an electrode active material . 2. The method for producing a resin composition for a secondary battery electrode according to claim 1, wherein the step of oxidizing the metal component is a step of contacting the resin composition for a secondary battery electrode with oxygen gas. The method for producing a resin composition for a secondary battery electrode according to claim 2 , wherein a static mixer is used in the step of contacting the oxygen gas. 4. The method for producing a resin composition for a secondary battery electrode according to claim 2, wherein the flow rate of the oxygen gas blown in is 20 NL/h or more per 1 ^m <3> of the resin composition for a secondary battery electrode . The method for producing a resin composition for a secondary battery electrode according to any one of claims 1 to 4 , further comprising a conductive material. The method for producing a resin composition for a secondary battery electrode according to any one of claims 1 to 5 , further comprising an inorganic acid and/or an inorganic base. A method for producing a slurry composition for a secondary battery electrode , comprising adding an electrode active material to the resin composition for a secondary battery electrode obtained by the production method according to any one of claims 1 to 6 . A method for producing an electrode film, comprising coating a slurry composition for a secondary battery electrode obtained by the method according to claim 7 . A method for producing a battery electrode, comprising forming an electrode film obtained by the method according to claim 8 on an electrode substrate. A method for producing a lithium ion secondary battery using a battery electrode obtained by the method of claim 9 .