JP7676803B2 - Binder composition for battery electrodes and its manufacturing method, composition for producing battery electrodes and its manufacturing method, electrode, and battery - Google Patents

Description

The present invention relates to a binder composition for battery electrodes and a method for producing the same, a composition for producing battery electrodes and a method for producing the same, an electrode, and a battery.

Various types of battery storage devices, such as nickel-metal hydride secondary batteries, lithium-ion secondary batteries, and electric double-layer capacitors, have been put to practical use. Electrodes used in these batteries may be produced by applying a composition containing an active material and a binder to a current collector and drying the composition. For example, in lithium-ion secondary batteries, a water-based binder containing styrene butadiene rubber (SBR) latex and carboxymethyl cellulose (CMC) is used as the binder in the composition that forms the negative electrode in a layered form.

There is an increasing demand for improved energy density, reliability, and durability in various secondary batteries. For example, graphite is generally used as an active material for the negative electrode of a lithium-ion secondary battery, but as the battery is repeatedly used, layers in the electrode peel off or fall off, resulting in a problem of battery performance degradation, such as a decrease in battery capacity and deterioration in cycle characteristics (durability). In order to suppress such a decrease in battery performance, studies have been conducted to improve battery performance by firmly binding active materials together (binding property), reducing the size of active materials to relieve stress associated with swelling and shrinkage, and devising additives for the electrolyte.
In addition, a secondary battery electrode may be obtained by applying a composition for forming a battery electrode (hereinafter also referred to as "electrode slurry") containing an active material and a binder to the surface of an electrode current collector and drying the composition. In this case, it is advantageous to increase the active material concentration in the electrode slurry from the viewpoint of increasing the drying efficiency of the electrode slurry and improving the productivity of the electrode. However, as the active material concentration is increased, the solid content concentration of the electrode slurry also increases, making it difficult to ensure good coatability. Conventionally, in aqueous slurries, carboxymethyl cellulose has been used as a binder that stabilizes the dispersion of the active material and imparts good coatability (see, for example, Patent Document 1).

It is also known to use cellulose fibers as a material for making electrodes.
For example, Patent Document 2 discloses a thickener/stabilizer for an electrode coating solution for an electricity storage device, which contains cellulose having a number average width of the short width of 2 to 1000 nm. The thickener/stabilizer is said to have excellent dispersion stability for the electrode active material, does not cause a decrease in viscosity due to stirring shear force during the dispersion process, and has excellent binding properties and electrolyte resistance.
Patent Document 3 discloses a binder composition for secondary battery electrodes that contains cellulose fibers and a particulate polymer such as SBR. The composition is said to suppress migration of the particulate polymer, to ensure uniform distribution of the particulate polymer in the resulting electrode mixture layer, and to provide excellent adhesion strength between the electrode active material layer and the current collector.
Patent Document 4 discloses a composition for battery electrodes, which is characterized by containing an active material, a fibrous polysaccharide having a carboxyl group, and a dispersion medium. The composition for battery electrodes is said to improve the degree of freedom in the composition design of battery electrodes, to be excellent in productivity, and to have excellent cycle characteristics as well as excellent output characteristics.

JP 2011-192610 A JP 2015-125920 A International Publication No. 2015/107896 JP 2014-86285 A

The slurry of Patent Document 1 contains carboxymethylcellulose, which disperses and stabilizes the active material and provides good coating properties, but there is a problem in further improving the performance of the battery obtained from the slurry, particularly in terms of increasing the binding properties.

In the thickener/stabilizer for electrode coating fluid of an electricity storage device of Patent Document 2, cellulose having a number average width of 2 to 1000 nm in the short width is used, which may be cellulose fiber obtained by mechanically defibrating pulp (hereinafter also referred to as mechanically defibrated cellulose fiber) or cellulose fiber obtained by defibrating oxidized cellulose obtained by oxidation with TEMPO, an N-oxyl compound (hereinafter also referred to as TEMPO oxidized cellulose fiber). The thickener/stabilizer for electrode coating fluid of an electricity storage device of Patent Document 2 is said to be capable of imparting binding properties, but the above-mentioned cellulose fiber is thought to have a structure that is widely spread in water, and even a small amount of addition significantly increases the viscosity, making it difficult to apply the electrode coating fluid during electrode production.
In the binder composition for secondary battery electrodes of Patent Document 3, mechanically defibrated cellulose fibers such as BinFi-s (registered trademark) and Celish (registered trademark) are used as the cellulose fibers. In the composition for battery electrodes of Patent Document 4, TEMPO oxidized cellulose fibers are used as the fibrous polysaccharide having a carboxy group. As described above, such cellulose fibers cause a large increase in viscosity even when added in small amounts, and there are problems with coatability.

As described above, when carboxymethyl cellulose, mechanically defibrated cellulose fibers, or TEMPO oxidized cellulose fibers are used as electrode binders, it is difficult to achieve both coatability and binding properties.

The present invention was made in consideration of the above circumstances, and aims to provide a composition for producing battery electrodes that has good coating properties, and also to provide an electrode binder composition that has excellent binding properties.

As a result of intensive research, the inventors discovered that nanocellulose derived from an oxide obtained by oxidizing raw cellulose with hypochlorous acid or its salt provides a composition for producing battery electrodes with excellent coating properties and excellent binding properties, which led to the completion of the present invention.

According to the present invention, the following means are provided.
[1]
A binder composition for a battery electrode comprising nanocellulose,
The nanocellulose comprises an oxide of a cellulosic raw material with hypochlorous acid or a salt thereof, and is substantially free of N-oxyl compounds;
Binder composition for battery electrodes.
[2]
The carboxyl group content of the nanocellulose is 0.2 mmol / g or more and 2.0 mmol / g or less,
The binder composition for a battery electrode according to [1].
[3]
The average fiber length of the nanocellulose is 50 nm or more and 700 nm or less.
The binder composition for a battery electrode according to [1] or [2].
[4]
Contains a particulate polymer and/or a polymer having a carboxy group or a salt thereof,
The binder composition for a battery electrode according to any one of [1] to [3].
[5]
the polymer having a carboxy group contains a structural unit derived from a crosslinkable monomer,
the content of the structural unit derived from the crosslinkable monomer is 0.1 parts by mass or more and 2.0 parts by mass or less with respect to 100 parts by mass of the total amount of the monomer units constituting the polymer having a carboxy group;
The binder composition for a battery electrode according to [4].
[6]
the polymer having a carboxy group is neutralized to a degree of neutralization of 80 to 100 mol %, and then the particle size measured in an aqueous medium is 0.1 μm or more and 5.0 μm or less in terms of volume-based median size;
The binder composition for a battery electrode according to [4] or [5].
[7]
A composition for producing a battery electrode, comprising the battery electrode binder composition according to any one of [1] to [6].
[8]
An electrode produced using the composition for producing a battery electrode according to [7].
[9]
A battery comprising the electrode according to [8].
[10]
A method for producing a binder composition for a battery electrode comprising nanocellulose, comprising:
The method includes obtaining the binder composition for battery electrodes by stirring a mixture containing oxidized cellulose and a material other than nanocellulose of the binder composition for battery electrodes,
The method for producing the oxidized cellulose comprises an oxidation product of a cellulosic raw material with hypochlorous acid or a salt thereof, and is substantially free of N-oxyl compounds.
[11]
A method for producing a binder composition for a battery electrode comprising nanocellulose, comprising:
obtaining said battery electrode binder composition by stirring oxidized cellulose and continuously adding materials other than nanocellulose of said battery electrode binder composition;
The method for producing the oxidized cellulose comprises an oxidation product of a cellulosic raw material with hypochlorous acid or a salt thereof, and is substantially free of N-oxyl compounds.
[12]
A method for producing a composition for producing a battery electrode containing nanocellulose, comprising:
The method includes a step of obtaining the composition for producing a battery electrode by stirring a mixture containing oxidized cellulose and a material other than nanocellulose of the composition for producing a battery electrode,
The method for producing the oxidized cellulose comprises an oxidation product of a cellulosic raw material with hypochlorous acid or a salt thereof, and is substantially free of N-oxyl compounds.
[13]
A method for producing a composition for producing a battery electrode containing nanocellulose, comprising:
The method includes a step of obtaining the composition for preparing a battery electrode by stirring the oxidized cellulose and continuously adding materials other than nanocellulose of the composition for preparing a battery electrode,
The method for producing the oxidized cellulose comprises an oxidation product of a cellulosic raw material with hypochlorous acid or a salt thereof, and is substantially free of N-oxyl compounds.

The binder composition for battery electrodes of the present invention provides a composition for producing battery electrodes with excellent coating properties. The binder composition for battery electrodes of the present invention can also provide an electrode layer with excellent binding properties. The binder composition for battery electrodes of the present invention can also provide an electrode and a battery.

[Battery electrode binder composition]
The binder composition for battery electrodes (hereinafter, also simply referred to as the binder composition) of the present invention contains nanocellulose. The nanocellulose contained in the binder composition of the present invention is nanocellulose that contains an oxide of a cellulose-based raw material with hypochlorous acid or a salt thereof and is substantially free of N-oxyl compounds.

By using the nanocellulose of the present disclosure as a binder, a composition for producing a battery electrode having excellent coating properties and excellent binding properties can be obtained. Although the reason why this is the case is unclear, it is generally believed to be as follows.
Nanocellulose is obtained through defibration, and defibration proceeds by breaking hydrogen bonds between cellulose microfibrils. In the oxidation treatment using hypochlorous acid or its salt, the degree of polymerization of microfibrils decreases as the oxidation progresses (i.e., the cellulose molecular chains are shortened). This decrease in the degree of polymerization is unlikely to occur only by mechanical defibration. In addition, when oxidized with hypochlorous acid or its salt, the degree of polymerization is more likely to decrease with an increase in the degree of oxidation compared to, for example, the TEMPO oxidation method. For this reason, the number of hydrogen bonds to be broken by defibration in each microfibril due to the oxidation treatment is small, and the amount of carboxyl groups increases as the oxidation progresses, which strengthens the repulsive force between the microfibrils and improves the dispersion stability of the obtained nanocellulose. It is believed that the dispersion stability can suppress the increase in viscosity, thereby improving the coatability.
In addition, the carboxyl group contained in the nanocellulose of the present invention has a structure in which at least two of the hydroxyl groups of the glucopyranose ring are oxidized when viewed in glucopyranose units, as described below, and the primary hydroxyl group at the C6 position is not oxidized and is considered to exist as a hydroxyl group as it is. On the other hand, in the nanocellulose obtained by the TEMPO oxidation method, the primary hydroxyl group at the C6 position of the glucopyranose ring is oxidized. As described above, it is considered that the nanocellulose used in the present invention can maintain the hydroxymethyl group structure at the C6 position and can increase the amount of primary hydroxyl groups. It is considered that the above hydroxymethyl group is likely to form an interaction and enhance the binding property.
Usually, when trying to increase binding properties, for example, the fluidity of the components in the composition, such as the coating liquid, decreases and the viscosity tends to increase. However, the nanocellulose in the present invention has excellent viscosity stability while maintaining binding properties, and is thought to be able to impart coatability to the composition for producing battery electrodes.

The binder composition for battery electrodes in the present invention refers to a composition used as a binder in battery electrodes. Here, the binder refers to a component that has the effect of binding components constituting a battery electrode, for example, components constituting an electrode such as an active material, to each other, or an electrode layer containing components such as an active material to a current collector of the electrode. The properties of the binder composition of the present invention are not particularly limited, and may be liquid or solid. The binder composition of the present invention may be in the form of an aqueous dispersion containing nanocellulose.

<Nanocellulose>
The nanocellulose in the present invention is a nano-sized oxidized cellulose obtained by oxidizing a cellulosic raw material with hypochlorous acid or a salt thereof. Here, the oxidized cellulose can also be said to be an oxide of the cellulosic raw material. The nanocellulose in the present invention includes an oxide of the cellulosic raw material with hypochlorous acid or a salt thereof.
The main component of plants is cellulose, and cellulose molecules bundled together are called cellulose microfibrils. The cellulose in cellulose-based raw materials is also contained in the form of cellulose microfibrils. Nanocellulose in the present invention is a general term for cellulose that has been nanosized, and includes fine cellulose fibers and cellulose nanocrystals. Fine cellulose fibers are also called cellulose nanofibers (also written as CNF).
The nanocellulose of the present invention contains a carboxyl group, and the carboxyl group may be in the H type (-COOH) or in the salt type. The type of salt is not particularly limited, and examples thereof include alkali metal salts such as lithium, sodium, and potassium; alkaline earth metal salts such as calcium salts and barium salts; other metal salts such as magnesium salts and aluminum salts; ammonium salts, and organic amine salts. Among these, alkali metal salts are preferred, and lithium salts are preferred from the viewpoint of obtaining a battery with low resistance.

The nanocellulose of the present invention is obtained by oxidizing a cellulose-based raw material with hypochlorous acid or a salt thereof, and N-oxyl compounds such as TEMPO are not used in this oxidation. Therefore, the nanocellulose of the present invention does not substantially contain N-oxyl compounds. Therefore, the impact of N-oxyl compounds on the environment and human body of nanocellulose is sufficiently reduced, and it is highly safe. Here, in this specification, nanocellulose "substantially does not contain N-oxyl compounds" means that no N-oxyl compounds are used in producing oxidized cellulose, or the content of nitrogen derived from N-oxyl compounds in oxidized cellulose is 2.0 ppm or less as an increase from a cellulose-based raw material such as raw pulp. The amount of N-oxyl compounds in oxidized cellulose is preferably 1.0 ppm or less as an increase from a cellulose-based raw material such as raw pulp. The content of N-oxyl compounds can be measured by known means. One known means is a method using a total nitrogen trace analyzer. Specifically, the nitrogen components derived from N-oxyl compounds in oxidized cellulose can be measured as the amount of nitrogen using a total nitrogen trace analyzer (e.g., Mitsubishi Chemical Analytech Co., Ltd., device name: TN-2100H, etc.).

(Amount of carboxyl group)
The amount of carboxy groups in the nanocellulose and oxidized cellulose in the present invention is preferably 0.20 mmol/g or more and less than 2.0 mmol/g. When the amount of carboxy groups is 0.20 mmol/g or more, sufficient easy defibration properties can be imparted to the oxidized cellulose. As a result, even when the defibration treatment is performed under mild conditions, a composition for producing a battery electrode with a stabilized dispersion can be obtained, and it is believed that the coatability can be further improved. On the other hand, when the amount of carboxy groups is less than 2.0 mmol/g, excessive decomposition of cellulose during the defibration treatment can be suppressed, and nanocellulose with a low ratio of particulate cellulose and uniform quality can be obtained. This is believed to improve the dispersibility of nanocellulose and further increase the binding property. From this viewpoint, the amount of carboxy groups in the nanocellulose and oxidized cellulose in the present invention is more preferably 0.5 mmol/g or more, even more preferably 0.6 mmol/g or more, and even more preferably 0.65 mmol/g or more. The upper limit of the amount of carboxy groups is more preferably 1 mmol/g or less, even more preferably 0.9 mmol/g, and even more preferably 0.8 mmol/g or less.

The amount of carboxy groups (mmol/g) is a value calculated using the following formula from the amount of sodium hydroxide (a) consumed in the neutralization stage of weak acid, where the change in electrical conductivity is gradual, after adding a 0.1 M aqueous hydrochloric acid solution to an aqueous solution obtained by mixing oxidized cellulose with water to adjust the pH to 2.5, and then dropping a 0.05 N aqueous sodium hydroxide solution and measuring the electrical conductivity until the pH reaches 11.0. Details are given in accordance with the method described in the Examples below. The amount of carboxy groups can be adjusted by changing the reaction time, reaction temperature, pH of the reaction solution, etc. of the oxidation reaction.
Amount of carboxyl group=a (ml)×0.05/mass of oxidized cellulose (g)

The oxidized cellulose can be obtained, for example, by oxidizing a cellulosic raw material under conditions in which the available chlorine concentration of hypochlorous acid or a salt thereof in the reaction system is relatively high (e.g., 14% by mass to 43% by mass). The oxidized cellulose can also be produced by appropriately controlling reaction conditions such as the available chlorine concentration, the pH during the reaction, and the reaction temperature. The oxidized cellulose thus obtained preferably has a structure in which at least two of the hydroxyl groups of the glucopyranose ring constituting the cellulose are oxidized, and more specifically, preferably has a structure in which the hydroxyl groups at the second and third positions of the glucopyranose ring are oxidized and carboxyl groups are introduced. The positions of the carboxyl groups in the glucopyranose ring of the oxidized cellulose can be analyzed by solid-state ^13C -NMR spectroscopy.

The nanocellulose of the present invention is an aggregate of individual fibers. When the nanocellulose of the present invention contains carboxylated CNF, it is sufficient that it contains at least one carboxylated CNF, and it is preferable that the carboxylated CNF is the main component. Here, "carboxylated CNF is the main component" means that the proportion of carboxylated CNF in the total amount of CNF is more than 50% by mass, preferably more than 70% by mass, and more preferably more than 80% by mass. The upper limit of the above proportion is 100% by mass, but it may be 98% by mass or 95% by mass.

The average fiber length of the nanocellulose in the present invention is preferably 50 nm or more and 700 nm or less. When the average fiber length exceeds 700 nm, the slurry containing nanocellulose tends to thicken. In addition, when the average fiber length is less than 50 nm, the viscosity characteristic of CNF is difficult to be expressed, and the cellulose cannot bind the active materials together, so that the binding property is reduced. In addition, by having an average fiber length of 50 nm or more and 700 nm or less, it is possible to suppress the increase in viscosity of the binder composition or the composition for preparing a battery electrode, and obtain a composition for preparing a battery electrode that is dispersed and stabilized, and it is believed that the coatability can be further improved and good binding property can be imparted.
The average fiber width of the nanocellulose in the present invention is not particularly limited, but is preferably 2.0 nm to 5.0 nm. By having an average fiber width of 2.0 nm to 5.0 nm, it is possible to suppress an increase in the viscosity of the binder composition or the composition for preparing a battery electrode, obtain a composition for preparing a battery electrode that is dispersed and stabilized, and further improve the coatability.

From the viewpoint of further improving the coatability, the average fiber length is more preferably in the range of 50 nm or more and 550 nm or less, even more preferably in the range of 50 nm or more and 500 nm or less, and even more preferably in the range of 50 nm or more and 400 nm or less.
From the viewpoint of further improving the coatability, the average fiber width is more preferably in the range of 2.0 nm or more and 4.5 nm or less, and even more preferably in the range of 2.5 nm or more and 4.0 nm or less.

In the nanocellulose of the present invention, the aspect ratio (average fiber length/average fiber width), which is the ratio of the average fiber width to the average fiber length, is preferably 20 or more and 200 or less.
It is believed that the dispersibility of nanocellulose can be improved and the binding property can be further increased by having an aspect ratio of 200 or less. From this viewpoint, the aspect ratio is more preferably 190 or less, and further preferably 180 or less.
On the other hand, if the aspect ratio is too low, i.e., if the shape of the nanocellulose is a thick rod rather than a long and thin fiber, aggregation occurs due to uneven distribution, and dispersibility tends to decrease. Therefore, the aspect ratio is preferably 20 or more, more preferably 30 or more, and even more preferably 40 or more.

The average fiber width and average fiber length are calculated by mixing nanocellulose and water so that the nanocellulose concentration is approximately 1 to 10 ppm, naturally drying the sufficiently diluted cellulose water dispersion on a mica substrate, observing the shape of the nanocellulose using a scanning probe microscope, randomly selecting any number of fibers from the obtained image, and setting the cross-sectional height of the shape image = fiber width and the circumference ÷ 2 = fiber length. Image processing software can be used to calculate such average fiber width and average fiber length. In this case, the image processing conditions are arbitrary, but even for the same image, the calculated values may differ depending on the conditions. The range of value differences due to conditions is preferably within ±100 nm for the average fiber length. The range of value differences due to conditions is preferably within ±10 nm for the average fiber width. For more detailed measurement methods, follow the method described in the examples below.

(Method for producing nanocellulose)
In the present invention, the nanocellulose may be a commercially available product or may be prepared by the user.
The method for producing nanocellulose of the present invention will be described. Nanocellulose in the present invention can be produced, for example, by a method including a step A of oxidizing a cellulose-based raw material with hypochlorous acid or a salt thereof to obtain oxidized cellulose, and, if necessary, a step B of defibrating the oxidized cellulose.

(Step A: Production of oxidized cellulose)
The cellulosic raw material is not particularly limited as long as it is a material mainly composed of cellulose, and examples thereof include pulp, natural cellulose, regenerated cellulose, and fine cellulose obtained by depolymerizing cellulose by mechanical treatment. As the cellulosic raw material, commercially available products such as crystalline cellulose made from pulp can be used as they are. In addition, unused biomass containing a large amount of cellulose components, such as soybean pulp pulp, may be used as the raw material. In addition, the cellulosic raw material may be treated in advance with an appropriate concentration of alkali in order to facilitate the penetration of the oxidizing agent used into the raw pulp.

Examples of hypochlorous acid or its salts used in the oxidation of cellulosic raw materials include hypochlorous acid water, sodium hypochlorite, potassium hypochlorite, calcium hypochlorite, and ammonium hypochlorite. Among these, sodium hypochlorite is preferred from the viewpoint of ease of handling.

One method for producing oxidized cellulose by oxidation of a cellulosic raw material is to mix the cellulosic raw material with a reaction liquid containing hypochlorous acid or a salt thereof. The solvent contained in the reaction liquid is preferably water, as it is easy to handle and unlikely to cause side reactions. The effective chlorine concentration of hypochlorous acid or a salt thereof in the reaction liquid is preferably 7 to 43% by mass, and more preferably 14 to 43% by mass. When the effective chlorine concentration of the reaction liquid is within the above range, the amount of carboxyl groups in the oxidized cellulose can be sufficiently increased, and the oxidized cellulose can be easily defibrated.

From the viewpoint of sufficiently increasing the amount of carboxy groups in the oxidized cellulose, the effective chlorine concentration of the reaction liquid is more preferably 15% by mass or more, even more preferably 18% by mass or more, and even more preferably 20% by mass or more. Furthermore, from the viewpoint of suppressing excessive decomposition of cellulose during defibration, the effective chlorine concentration of the reaction liquid is more preferably 40% by mass or less, and even more preferably 38% by mass or less. The range of the effective chlorine concentration of the reaction liquid can be an appropriate combination of the above-mentioned lower and upper limits. The range of the effective chlorine concentration is more preferably 16 to 43% by mass, and even more preferably 18 to 40% by mass.

The effective chlorine concentration of hypochlorous acid or its salt is defined as follows. Hypochlorous acid is a weak acid that exists as an aqueous solution, and hypochlorite is a compound in which hydrogen of hypochlorous acid is replaced by other cations. For example, sodium hypochlorite, which is a hypochlorite, exists in a solvent (preferably in an aqueous solution), so the concentration is measured as the effective chlorine amount in the solution, not the concentration of sodium hypochlorite. Here, for the effective chlorine of sodium hypochlorite, the oxidizing power of the divalent oxygen atom generated by the decomposition of sodium hypochlorite corresponds to the two atomic equivalents of monovalent chlorine, so that the bonded chlorine atom of sodium hypochlorite (NaClO) has the same oxidizing power as two atoms of unbonded chlorine (Cl ₂ ), and the effective chlorine is 2×(chlorine in NaClO). As a specific procedure for measurement, first, the sample is precisely weighed, water, potassium iodide and acetic acid are added, and the sample is left to stand, and the liberated iodine is titrated with a sodium thiosulfate solution using a starch aqueous solution as an indicator to measure the effective chlorine concentration.

The oxidation reaction of the cellulosic raw material with hypochlorous acid or a salt thereof is preferably carried out while adjusting the pH to the range of 5.0 to 14.0. In this range, the oxidation reaction of the cellulosic raw material can be sufficiently progressed, and the amount of carboxyl groups in the oxidized cellulose can be sufficiently increased. This makes it possible to easily defibrate the oxidized cellulose. The pH of the reaction system is more preferably 7.0 or higher, and even more preferably 8.0 or higher. The upper limit of the pH of the reaction system is more preferably 13.5 or lower, and even more preferably 13.0 or lower. The pH range of the reaction system is more preferably 7.0 to 14.0, and even more preferably 8.0 to 13.5.

The method for producing oxidized cellulose will be further explained below using an example in which sodium hypochlorite is used as hypochlorous acid or its salt.

When oxidizing a cellulosic raw material using sodium hypochlorite, the reaction liquid is preferably an aqueous sodium hypochlorite solution. Methods for adjusting the effective chlorine concentration of an aqueous sodium hypochlorite solution to a desired concentration (e.g., a target concentration: 7% by mass to 43% by mass) include concentrating an aqueous sodium hypochlorite solution having an effective chlorine concentration lower than the target concentration, diluting an aqueous sodium hypochlorite solution having an effective chlorine concentration higher than the target concentration, and dissolving sodium hypochlorite crystals (e.g., sodium hypochlorite pentahydrate) in a solvent. Among these, adjusting the effective chlorine concentration as an oxidizing agent by diluting an aqueous sodium hypochlorite solution or dissolving sodium hypochlorite crystals in a solvent is preferable because it causes less self-decomposition (i.e., less reduction in effective chlorine concentration) and makes it easy to adjust the effective chlorine concentration.

In order to efficiently proceed with the oxidation reaction of the cellulosic raw material, it is preferable to carry out the oxidation reaction while stirring the mixture of the cellulosic raw material and the aqueous sodium hypochlorite solution. Examples of the stirring method include a magnetic stirrer, a stirring rod, a stirrer with stirring blades (three-one motor), a homomixer, a dispersion type mixer, a homogenizer, and external circulation stirring. Among these, a method using one or more of shear type stirrers such as a homomixer and a homogenizer, a stirrer with stirring blades, and a dispersion type mixer is preferable in terms of the smooth progress of the oxidation reaction of the cellulosic raw material, and a method using a stirrer with stirring blades is particularly preferable. When a stirrer with stirring blades is used, a device equipped with known stirring blades such as a propeller blade, a paddle blade, or a turbine blade can be used as the stirrer. In addition, when a stirrer with stirring blades is used, it is preferable to stir at a rotation speed of 50 to 300 rpm.

The reaction temperature in the oxidation reaction is preferably 15°C to 100°C, and more preferably 20°C to 90°C. During the reaction, the pH of the reaction system decreases as carboxyl groups are generated in the cellulosic raw material by the oxidation reaction. For this reason, from the viewpoint of efficiently proceeding with the oxidation reaction, it is preferable to add an alkaline agent (e.g., sodium hydroxide, etc.) or an acid (e.g., hydrochloric acid, etc.) to the reaction system to adjust the pH of the reaction system to the above-mentioned preferred range. The reaction time of the oxidation reaction can be set according to the degree of progress of the oxidation, but is preferably about 15 minutes to 50 hours. When the pH of the reaction system is to be 10 or more, it is preferable to set the reaction temperature to 30°C or more and/or the reaction time to 30 minutes or more.

The solution containing the oxidized cellulose obtained by the above reaction can be subjected to a known isolation process such as filtration, and further purified as necessary to obtain oxidized cellulose as an oxide of the cellulose-based raw material with hypochlorous acid or a salt thereof. The solution containing the oxidized cellulose obtained by the above reaction may be subjected directly to a defibration process.

(Step B: defibration treatment)
The nanocellulose of the present invention can be obtained by defibrating the oxidized cellulose obtained above to produce nano-sized particles. Methods for defibrating oxidized cellulose include a method using weak stirring with a magnetic stirrer or the like, and a method using mechanical defibration. Mechanical defibration is preferred for defibrating oxidized cellulose, since it allows sufficient defibration of oxidized cellulose and can shorten the defibration time.

Mechanical fiberization methods include, for example, methods using various mixing and stirring devices such as a screw mixer, a paddle mixer, a disperser mixer, a turbine mixer, a homo mixer under high speed rotation, a high pressure homogenizer, an ultra-high pressure homogenizer, a double cylindrical homogenizer, an ultrasonic homogenizer, a water current collision type disperser, a beater, a disk type refiner, a conical type refiner, a double disk type refiner, a grinder, a single-shaft or multi-shaft kneader, a planetary centrifugal mixer, and a vibration type mixer. By using these devices alone or in combination of two or more types, and treating the oxidized cellulose preferably in a dispersion medium, it is possible to nanoize the oxidized cellulose and produce nanocellulose.

For the defibration of oxidized cellulose, a method using an ultra-high pressure homogenizer can be preferably used, since it can produce nanocellulose with a more advanced defibration. When applying defibration processing using an ultra-high pressure homogenizer, the pressure during the defibration processing is preferably 100 MPa or more, more preferably 120 MPa or more, and even more preferably 150 MPa or more. The number of times of defibration processing is not particularly limited, but from the viewpoint of sufficiently progressing defibration, it is preferably two or more times, more preferably three or more times. In addition, the above-mentioned oxidized cellulose can be sufficiently defibrated by gentle stirring using a planetary stirrer, a vibration type stirrer, or the like. Examples of vibration type stirrers include a vortex mixer (touch mixer). In other words, with the above-mentioned oxidized cellulose, homogenized nanocellulose can be obtained even when defibration processing is performed under gentle defibration conditions.

The defibration process is preferably carried out in a state where the oxidized cellulose is mixed with a dispersion medium. There are no particular limitations on the dispersion medium, and it can be selected appropriately depending on the purpose. Specific examples of dispersion media include water, alcohols, ethers, ketones, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethylsulfoxide. As the solvent, one of these may be used alone, or two or more may be used in combination.

Among the dispersion media, examples of alcohols include methanol, ethanol, isopropanol, isobutanol, sec-butyl alcohol, tert-butyl alcohol, methyl cellosolve, ethylene glycol, and glycerin. Examples of ethers include ethylene glycol dimethyl ether, 1,4-dioxane, and tetrahydrofuran. Examples of ketones include acetone and methyl ethyl ketone.
By using an organic solvent as a dispersion medium during the defibration treatment, it becomes easier to isolate oxidized cellulose and the nanocellulose obtained by defibrating it.

The nanocellulose in the present invention preferably satisfies the following zeta potential and light transmittance.

(Zeta potential)
The nanocellulose in the present invention preferably has a zeta potential of -30 mV or less. When the zeta potential is -30 mV or less (i.e., the absolute value is 30 mV or more), the repulsion between microfibrils is sufficient, and nanocellulose with a high surface charge density is easily produced during mechanical defibration. This improves the dispersibility of nanocellulose, and tends to have excellent viscosity stability when made into a slurry. As a result, when a composition for producing a battery electrode containing the nanocellulose of the present invention is obtained, it tends to be possible to achieve a better balance between coatability and binding properties.
When the zeta potential is -100 mV or higher (i.e., the absolute value is 100 mV or lower), oxidative scission in the fiber direction that accompanies the progression of oxidation tends to be suppressed, making it possible to obtain nanocellulose of uniform size, and the nanocellulose tends to be uniformly dispersed in the binder composition or the composition for producing battery electrodes, resulting in higher binding properties.

The zeta potential of the nanocellulose in the present invention is preferably -35 mV or less, more preferably -40 mV or less, and even more preferably -50 mV or less. The lower limit of the zeta potential is preferably -70 mV or more, more preferably -65 mV or more, and even more preferably -60 mV or more. The range of the zeta potential can be appropriately combined with the above-mentioned lower and upper limits.
In this specification, the zeta potential is a value measured at pH 8.0 and 20°C for a cellulose aqueous dispersion obtained by mixing nanocellulose and water to a nanocellulose concentration of 0.1% by mass.
Specifically, it can be measured according to the following method.
Pure water is added to the aqueous dispersion of nanocellulose to dilute it to a nanocellulose concentration of 0.1%. A 0.05 mol/L aqueous solution of sodium hydroxide is added to the diluted aqueous dispersion of nanocellulose to adjust the pH to 8.0, and the zeta potential is measured at 20°C using a zeta potential measuring device such as an Otsuka Electronics Zeta Potential Meter (ELSZ-1000).

(light transmittance)
The nanocellulose in the present invention has few aggregates, and the nanocellulose dispersion dispersed in the dispersion medium has little light scattering of fine cellulose fibers, and tends to show high light transmittance. Specifically, the nanocellulose in the present invention preferably has a light transmittance of 95% or more in a mixed liquid mixed with water to a solid content concentration of 0.1% by mass. The light transmittance is more preferably 96% or more, and even more preferably 97% or more. The light transmittance is a value at a wavelength of 660 nm measured by a spectrophotometer. The light transmittance can also be measured using an aqueous dispersion containing nanocellulose.
Specifically, it can be measured according to the following method.
An aqueous dispersion of nanocellulose is placed in a 10 mm thick quartz cell, and the light transmittance at a wavelength of 660 nm is measured using a spectrophotometer such as the JASCO V-550.

The zeta potential and light transmittance of nanocellulose can be adjusted by adjusting the reaction time, reaction temperature, stirring conditions, etc. of the oxidation reaction. Specifically, as the reaction time is lengthened and/or the reaction temperature is raised, oxidation of the surface of the cellulose microfibrils in the cellulose-based raw material progresses, and the average fiber width tends to become smaller due to stronger repulsion between fibrils caused by electrostatic repulsion and osmotic pressure. In addition, the zeta potential tends to be increased by setting one or more of the reaction time, reaction temperature, and stirring conditions of the oxidation to the side that advances the oxidation more (i.e., the side that increases the degree of oxidation) (for example, by lengthening the reaction time).

As described above, the nanocellulose in the present invention is obtained via oxidized cellulose. Here, the degree of polymerization of the oxidized cellulose used in the present invention is preferably 600 or less. If the degree of polymerization of oxidized cellulose exceeds 600, it tends to require a large amount of energy for defibration, and sufficient easy defibration cannot be achieved, which tends to lead to a decrease in the viscosity stability and dispersibility of nanocellulose, and ultimately to a decrease in coatability and binding ability. In addition, if the degree of polymerization of oxidized cellulose exceeds 600, there will be a lot of oxidized cellulose that is insufficiently defibrated, and when this is finely defibrated to form nanocellulose and dispersed in a dispersion medium, light scattering and the like will increase, and transparency may decrease. From the viewpoint of easy defibration, no lower limit is particularly set for the degree of polymerization of oxidized cellulose. However, if the degree of polymerization of oxidized cellulose is less than 50, the proportion of cellulose that is particulate rather than fibrous will increase, and the effect of nanocellulose may decrease. From the above viewpoint, the degree of polymerization of oxidized cellulose is preferably in the range of 50 to 600.

The degree of polymerization of the oxidized cellulose is more preferably 580 or less, even more preferably 560 or less, still more preferably 550 or less, even more preferably 500 or less, and even more preferably 450 or less. From the viewpoint of improving the viscosity stability and coatability of the slurry, the lower limit of the degree of polymerization is more preferably 80 or more, even more preferably 90 or more, even more preferably 100 or more, even more preferably 110 or more, and even more preferably 120 or more. A preferred range of the degree of polymerization can be determined by appropriately combining the above-mentioned upper and lower limits.
The degree of polymerization of oxidized cellulose is the average degree of polymerization (viscosity average degree of polymerization) measured by a viscosity method, the details of which are as follows:
Oxidized cellulose was added to an aqueous solution of sodium borohydride adjusted to pH 10, and reduction treatment was carried out at 25°C for 5 hours. The amount of sodium borohydride was 0.1 g per 1 g of oxidized cellulose. After reduction treatment, solid-liquid separation was performed by suction filtration, washing with water, and the obtained oxidized cellulose fiber was freeze-dried. 0.04 g of dried oxidized cellulose fiber was added to 10 ml of pure water and stirred for 2 minutes, and then 10 ml of 1 M copper ethylenediamine solution was added to dissolve. Then, the flow time of the blank solution and the flow time of the cellulose solution were measured at 25°C using a capillary viscometer. The relative viscosity (η r ), specific viscosity (η _sp ), and intrinsic viscosity ([η]) were calculated in sequence from the flow time of the blank solution (t0), the flow time of the cellulose solution ( _t ), and the concentration of oxidized cellulose fiber (c [g/ml]) according to the following formula, and the degree of polymerization (DP) of oxidized cellulose was calculated from the viscosity measurement formula.
η _r =η/η ₀ =t/t0
η _sp ＝η _r －１
[η]=η _sp /(100×c(1+0.28η _sp ))
DP = 175 × [η]

The degree of polymerization of oxidized cellulose can be adjusted by changing the reaction time, reaction temperature, pH, and effective chlorine concentration of hypochlorous acid or its salt during the oxidation reaction. Specifically, since the degree of polymerization tends to decrease as the degree of oxidation increases, a method for decreasing the degree of polymerization can be, for example, increasing the reaction time and/or reaction temperature of the oxidation. As another method, the degree of polymerization of oxidized cellulose can be adjusted by the stirring conditions of the reaction system during the oxidation reaction. For example, under conditions in which the reaction system is sufficiently homogenized using a stirring blade or the like, the oxidation reaction proceeds smoothly and the degree of polymerization tends to decrease. On the other hand, under conditions in which the reaction system is likely to be insufficiently stirred, such as stirring with a stirrer, the reaction tends to become non-uniform, making it difficult to sufficiently reduce the degree of polymerization of oxidized cellulose. The degree of polymerization of oxidized cellulose also tends to vary depending on the selection of the raw cellulose. For this reason, the degree of polymerization of oxidized cellulose can also be adjusted by selecting the cellulosic raw material.

<Other binder components>
The binder composition of the present invention may contain other binder components other than the nanocellulose. The other binder components are not particularly limited as long as they are generally used when binding materials such as the active material of a battery electrode to a current collector. In addition, the other binder components may be appropriately selected depending on the types of active materials, current collectors, etc. Suitable examples of the other binder components include particulate polymers and polymers having carboxy groups or salts thereof. These binder components may be contained alone or in combination of two or more types.

(Particulate polymer)
Examples of the particulate polymer include latexes such as aromatic vinyl monomer/aliphatic conjugated diene monomer latex, acrylic latex, and polyvinylidene fluoride latex. These particulate polymers may be commercially available products, or may be produced by polymerizing the monomers constituting these latexes by a known method. These latexes may be used alone or in combination of two or more.

Aromatic vinyl monomers in the aromatic vinyl monomer/aliphatic conjugated diene monomer latex include, for example, styrene, α-methylstyrene, vinyltoluene, divinylbenzene, etc., and one or more of these can be used. Aliphatic conjugated diene monomers include, for example, butadiene compounds such as 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, etc., and one or more of these can be used.

As the latex of aromatic vinyl monomer/aliphatic conjugated diene monomer, styrene/butadiene latex (hereinafter also referred to as SBR) is preferred. The styrene/butadiene latex refers to an aqueous dispersion of a copolymer having a structural unit derived from an aromatic vinyl monomer such as styrene and a structural unit derived from the butadiene compound.
The structural unit derived from the aromatic vinyl monomer in the copolymer may be, for example, in the range of 20 to 60% by mass, or may be in the range of 30 to 50% by mass, from the viewpoint of binding property.
The structural unit derived from the aliphatic conjugated diene monomer in the copolymer may be, for example, in the range of 30 to 70 mass %, or may be in the range of 40 to 60 mass %, from the viewpoint of improving the binding property of the binder and the flexibility of the obtained electrode.

In addition to the above-mentioned monomers, the styrene/butadiene-based latex may contain, as other monomers, nitrile group-containing monomers such as (meth)acrylonitrile, and carboxy group-containing monomers such as (meth)acrylic acid, itanconic acid, and maleic acid as copolymerization monomers in order to further improve performance such as binding property.
The content of the structural units derived from the other monomers in the copolymer may be, for example, in the range of 0 to 30% by mass, or may be in the range of 0 to 20% by mass.

(Polymer having a carboxy group or a salt thereof)
The polymer having a carboxy group or its salt (hereinafter, simply referred to as a polymer) contains a structural unit derived from a monomer having a carboxy group. An example of the monomer having a carboxy group is an ethylenically unsaturated carboxylic acid monomer. The polymer having a carboxy group or its salt may be a commercially available product, or may be produced by polymerizing a monomer constituting the polymer, such as an ethylenically unsaturated carboxylic acid monomer, by a known method.
The structural unit derived from a monomer having a carboxyl group can be introduced into a polymer by polymerizing a monomer containing an ethylenically unsaturated carboxylic acid monomer. In addition, it can also be obtained by (co)polymerizing a (meth)acrylic acid ester monomer and then hydrolyzing it. In addition, it can also be a method of polymerizing (meth)acrylamide and (meth)acrylonitrile, etc., and then treating them with a strong alkali, or a method of reacting a polymer having a hydroxyl group with an acid anhydride.

Examples of ethylenically unsaturated carboxylic acid monomers include (meth)acrylic acid, itaconic acid, crotonic acid, maleic acid, and fumaric acid; (meth)acrylamidoalkyl carboxylic acids such as (meth)acrylamidohexanoic acid and (meth)acrylamidododecanoic acid; and ethylenically unsaturated monomers having a carboxy group such as monohydroxyethyl succinate (meth)acrylate, ω-carboxy-caprolactone mono(meth)acrylate, and β-carboxyethyl (meth)acrylate, or (partially) alkali-neutralized products thereof. One of these may be used alone, or two or more may be used in combination. Among the above, from the viewpoint of obtaining a polymer having a long primary chain length due to a high polymerization rate and further increasing the binding strength of the binder, a compound having an acryloyl group as a polymerizable functional group is preferable, and acrylic acid is more preferable. When acrylic acid is used as the ethylenically unsaturated carboxylic acid monomer, a polymer having a high carboxy group content can be obtained.

The content of the structural unit derived from the monomer having a carboxy group is not particularly limited, and may be in the range of more than 0% by mass and not more than 100% by mass relative to the total structural units of the polymer having a carboxy group, and may be in the range of 10% by mass or more and 100% by mass or less. By containing the structural unit derived from the monomer having a carboxy group in such a range, excellent adhesion to the current collector can be easily ensured. The lower limit of the content may be 20% by mass or more, 30% by mass or more, or 40% by mass or more. The upper limit of the content may be 99% by mass or less, 95% by mass or less, 90% by mass or less, or 80% by mass or less.

The polymer having a carboxy group can contain, in addition to the structural units derived from the monomer having a carboxy group, structural units derived from other ethylenically unsaturated monomers copolymerizable therewith (hereinafter also referred to as other structural units). Examples of the other structural units include structural units derived from ethylenically unsaturated monomer compounds having anionic groups other than carboxy groups, such as sulfonic acid groups and phosphoric acid groups, and nonionic ethylenically unsaturated monomers.
These structural units can be introduced by copolymerizing an ethylenically unsaturated monomer compound having an anionic group other than a carboxy group, such as a sulfonic acid group or a phosphoric acid group, or a monomer containing a nonionic ethylenically unsaturated monomer.
The ratio of the other structural units can be in the range of 0% by mass or more and less than 100% by mass, and may be in the range of 1% by mass or more and 60% by mass or less, based on the total structural units of the polymer having a carboxy group.

The polymer having a carboxy group may be in the form of a salt in which some or all of the carboxy groups contained in the polymer are neutralized. The type of salt is not particularly limited, but examples include alkali metal salts such as lithium, sodium, and potassium; alkaline earth metal salts such as calcium salts and barium salts; other metal salts such as magnesium salts and aluminum salts; ammonium salts and organic amine salts. Among these, alkali metal salts and magnesium salts are preferred from the viewpoint of being less likely to adversely affect the battery characteristics, and alkali metal salts are more preferred. Among these, lithium salts are particularly preferred from the viewpoint of obtaining a battery with low resistance.

The polymer having a carboxy group preferably contains a structural unit derived from a crosslinkable monomer. When the polymer having a carboxy group has a crosslinked structure, the binder composition containing the crosslinked polymer or a salt thereof tends to have a higher binding strength.
The content of the structural unit derived from the crosslinkable monomer is preferably 0.1 parts by mass or more and 2.0 parts by mass or less based on 100 parts by mass of the total amount of the monomer units constituting the polymer having a carboxy group.

Examples of crosslinkable monomers include polyfunctional polymerizable monomers having two or more polymerizable unsaturated groups, and monomers having self-crosslinkable crosslinkable functional groups such as hydrolyzable silyl groups.

The above-mentioned polyfunctional polymerizable monomer refers to a compound having two or more polymerizable functional groups, such as (meth)acryloyl groups and alkenyl groups, in the molecule, and examples thereof include polyfunctional (meth)acrylate compounds, polyfunctional alkenyl compounds, and compounds having both (meth)acryloyl groups and alkenyl groups. These compounds may be used alone or in combination of two or more. Among these, polyfunctional alkenyl compounds are preferred from the viewpoint of easily obtaining a uniform crosslinked structure, and polyfunctional allyl ether compounds having multiple allyl ether groups in the molecule are more preferred.

Examples of polyfunctional (meth)acrylate compounds include di(meth)acrylates of dihydric alcohols such as ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, polyethylene glycol di(meth)acrylate, and polypropylene glycol di(meth)acrylate; tri(meth)acrylates of trihydric or higher polyhydric alcohols such as trimethylolpropane tri(meth)acrylate, tri(meth)acrylate of trimethylolpropane ethylene oxide modified product, glycerin tri(meth)acrylate, pentaerythritol tri(meth)acrylate, and pentaerythritol tetra(meth)acrylate; and poly(meth)acrylates such as tetra(meth)acrylate; and bisamides such as methylene bisacrylamide and hydroxyethylene bisacrylamide.

Examples of polyfunctional alkenyl compounds include polyfunctional allyl ether compounds such as trimethylolpropane diallyl ether, trimethylolpropane triallyl ether, pentaerythritol diallyl ether, pentaerythritol triallyl ether, tetraallyloxyethane, and polyallyl saccharose; polyfunctional allyl compounds such as diallyl phthalate; and polyfunctional vinyl compounds such as divinylbenzene.

Examples of compounds having both a (meth)acryloyl group and an alkenyl group include allyl (meth)acrylate, isopropenyl (meth)acrylate, butenyl (meth)acrylate, pentenyl (meth)acrylate, and 2-(2-vinyloxyethoxy)ethyl (meth)acrylate.

Examples of the monomer having a self-crosslinkable crosslinking functional group include a hydrolyzable silyl group-containing vinyl monomer, N-methylol (meth)acrylamide, and N-methoxyalkyl (meth)acrylate. These compounds can be used alone or in combination of two or more.

In the binder composition or the composition for producing a battery electrode of the present invention, the polymer having a carboxy group is preferably present as particles. The polymer having a carboxy group is preferably dispersed as particles in the binder composition or the composition for producing a battery electrode.
The polymer having a carboxy group is preferably neutralized to a degree of neutralization of 80 to 100 mol % and then dispersed in water, and the particle size (also referred to as water-swollen particle size) is preferably in the range of 0.1 μm to 5.0 μm in volume-based median size. The degree of neutralization is preferably based on the carboxy group possessed by the polymer. The particle size is more preferably in the range of 0.1 μm to 5.0 μm, and even more preferably in the range of 0.5 μm to 3.0 μm. If the particle size is in the range of 0.1 μm to 5.0 μm, the particles are uniformly present at a suitable size in the composition of the present invention, and therefore the composition of the present invention tends to be highly stable and exhibit better binding properties.
The particle size of the polymer having a carboxy group when dried (dry particle size) is preferably in the range of 0.03 μm or more and 3 μm or less in terms of volume-based median size.

The polymer having a carboxy group is preferably used in the form of a salt in which an acid group such as a carboxy group derived from an ethylenically unsaturated carboxylic acid monomer is neutralized so that the degree of neutralization is 20 mol% or more in the binder composition or the composition for preparing a battery electrode of the present invention. The degree of neutralization is more preferably 50 mol% or more, even more preferably 70 mol% or more, even more preferably 75 mol% or more, even more preferably 80 mol% or more, and even more preferably 85 mol% or more. The upper limit of the degree of neutralization is 100 mol%, and may be 98 mol% or 95 mol%. The range of the degree of neutralization can be appropriately combined with the above lower limit and upper limit. When the degree of neutralization is 20 mol% or more, the water swelling property becomes good and the dispersion stabilization effect tends to be easily obtained.
In this specification, the neutralization degree can be calculated from the charge amount of the monomer having an acid group such as a carboxyl group and the neutralizing agent used for neutralization. The neutralization degree can be confirmed by IR measurement of the powder after drying treatment of the crosslinked polymer or its salt at 80° C. for 3 hours under reduced pressure conditions, and the intensity ratio of the peak derived from the C=O group of the carboxylic acid to the peak derived from the C=O group of the carboxylate salt. More specifically, the neutralization degree can be measured by the method described in the Examples.

(Method for producing polymer having carboxy group)
For the polymer having a carboxyl group, known polymerization methods such as solution polymerization, precipitation polymerization, suspension polymerization, and emulsion polymerization can be used, and from the viewpoint of productivity, precipitation polymerization and suspension polymerization (reverse phase suspension polymerization) are preferred. From the viewpoint of obtaining better performance in terms of binding property, etc., heterogeneous polymerization methods such as precipitation polymerization, suspension polymerization, and emulsion polymerization are preferred, and among them, precipitation polymerization is more preferred.
Precipitation polymerization is a method for producing a polymer by carrying out a polymerization reaction in a solvent that dissolves the raw material unsaturated monomer but does not substantially dissolve the resulting polymer. As the polymerization proceeds, the polymer particles become larger through aggregation and growth, and a dispersion of polymer particles is obtained in which primary particles of several tens to several hundreds of nm are secondary aggregated to several μm to several tens of μm. A dispersion stabilizer may be used to control the particle size of the polymer.

In the case of precipitation polymerization, the polymerization solvent may be selected from water and various organic solvents, taking into consideration the type of monomer to be used. In order to obtain a polymer having a longer primary chain length, it is preferable to use a solvent having a small chain transfer constant. Specific polymerization solvents include water-soluble solvents such as methanol, t-butyl alcohol, acetone, methyl ethyl ketone, acetonitrile, and tetrahydrofuran, as well as benzene, ethyl acetate, dichloroethane, n-hexane, cyclohexane, and n-heptane, and one of these may be used alone or two or more of them may be used in combination. Alternatively, these may be used as a mixed solvent with water. In the present invention, the water-soluble solvent refers to a solvent having a solubility in water of more than 10 g/100 ml at 20° C.
Of the above, methyl ethyl ketone and acetonitrile are preferred because the precipitated polymer microparticles are less likely to undergo secondary aggregation (or even if secondary aggregation does occur, the particles are easily dissolved in an aqueous medium), a polymer having a small chain transfer constant and a large degree of polymerization (primary chain length) can be obtained, and the operation during neutralization is easy.
In addition, in the polymerization of highly hydrophilic ethylenically unsaturated carboxylic acid monomers such as acrylic acid, the polymerization rate is increased when a highly polar solvent is added, and it becomes easier to obtain a polymer having a long primary chain length. As such a highly polar solvent, water and methanol are preferably used, and among them, water is preferred because it has a large effect of increasing the polymerization rate.

As the polymerization initiator, a known polymerization initiator such as an azo compound, an organic peroxide, or an inorganic peroxide can be used, but there is no particular limitation.
The preferred amount of the polymerization initiator used is usually 0.001 to 2 parts by mass, may be 0.005 to 1 part by mass, or may be 0.01 to 0.1 part by mass, when the total amount of the monomer components used is 100 parts by mass.

The polymerization temperature varies depending on conditions such as the type and concentration of the monomers used, but is preferably 0 to 100° C., more preferably 20 to 80° C. The polymerization temperature may be constant or may vary during the polymerization reaction. The polymerization time is preferably 1 minute to 20 hours, more preferably 1 hour to 10 hours.
After the polymerization, a base may be appropriately added to neutralize the reaction.

The binder composition of the present invention can be produced by blending the above-mentioned nanocellulose or oxidized cellulose with other binder components such as a particulate polymer, a polymer having a carboxyl group or a salt thereof, as necessary. The binder composition of the present invention preferably contains water.
As described above, oxidized cellulose can be used in the production of the binder composition. The oxidized cellulose is defibrated in the composition by a dispersing or kneading operation during production to become nanocellulose. Specifically, nanocellulose can be obtained by blending the oxidized cellulose with materials other than the oxidized cellulose of the binder composition and defibrating the mixture by stirring such as dispersing or kneading, or by the user of the oxidized cellulose defibrating it into nano-size. The stirring can be performed by the above-mentioned (Step B: defibration treatment).
One of the present inventions is a method for producing a binder composition using as a material oxidized cellulose that contains an oxide of a cellulose-based raw material with hypochlorous acid or a salt thereof and that is substantially free of N-oxyl compounds, specifically, a method for producing a binder composition for battery electrodes that contains nanocellulose, the method comprising the step of obtaining the binder composition for battery electrodes by stirring a mixture containing oxidized cellulose and a material of the binder composition for battery electrodes other than nanocellulose. Another of the present inventions is a method for producing a binder composition for battery electrodes that contains nanocellulose, the method comprising the step of obtaining the binder composition for battery electrodes by stirring oxidized cellulose and continuously adding a material of the binder composition for battery electrodes other than nanocellulose.
Here, the aspects of the nanocellulose, oxidized cellulose, and binder composition for battery electrodes are as described above. The material other than nanocellulose in the binder composition for battery electrodes is any material other than nanocellulose that can be contained in the binder composition for battery electrodes, and examples thereof include, but are not limited to, the other binder components and dispersion mediums described above.
In addition, in this specification, "adding materials continuously" means that the refining of oxidized cellulose by stirring and the addition of the materials are carried out in a series. Specific embodiments in which stirring and addition are carried out in a series include, for example, an embodiment in which the refining of oxidized cellulose by stirring and the addition of the materials are carried out in a one-pot operation; an embodiment in which the materials are added simultaneously while stirring the oxidized cellulose; and the like, but are not limited to these.

<Composition for producing battery electrodes>
The composition for producing a battery electrode of the present invention includes the binder composition of the present invention. The composition for producing a battery electrode of the present invention is a material composition for obtaining a battery electrode, and is suitably used for producing a mixture layer of a battery electrode. When used for producing a mixture layer, the composition for producing a battery electrode of the present invention is also called a composition for a battery electrode mixture layer.
The composition for producing a battery electrode of the present invention preferably contains, in addition to the binder composition of the present invention, electrode materials such as components constituting a battery electrode and components for forming an electrode. The composition for a battery electrode mixture layer preferably contains components constituting a mixture layer and components for forming a mixture layer, and preferably contains an active material and water in addition to the binder composition.

The amount of the binder composition of the present invention used in the composition for producing a battery electrode of the present invention may be usually 0.1% by mass or more and 20% by mass or less, or may be 0.2% by mass or more and 10% by mass or less, or may be 0.3% by mass or more and 8% by mass or less, based on the total amount of the active material. If the amount of the binder used is 0.1% by mass or more, sufficient binding properties can be obtained. In addition, the dispersion stability of the active material, etc. can be ensured, and a uniform mixture layer tends to be formed. If the amount of the binder used is 20% by mass or less, the electrode mixture layer composition does not become highly viscous, and the coatability to the current collector can be ensured. As a result, a mixture layer having a uniform and smooth surface can be formed.

The active material used in the present invention may be a positive electrode active material or a negative electrode active material.
As the positive electrode active material, lithium salt of transition metal oxide can be used, for example, layered rock salt type and spinel type lithium-containing metal oxide can be used. Specific compounds of layered rock salt type positive electrode active material include lithium cobalt oxide, lithium nickel oxide, and ternary system NCM {Li (Nix, Coy, Mnz), x + y + z = 1} and NCA {Li (Ni1-a-bCoaAlb)}. In addition, as a spinel type positive electrode active material, lithium manganate can be used. In addition to oxides, phosphates, silicates, sulfur, etc. are used, and phosphates include olivine type lithium iron phosphate, etc. As the positive electrode active material, one of the above may be used alone, or two or more may be combined and used as a mixture or composite. A conductive assistant may be added to the positive electrode active material. As the conductive assistant, carbon-based materials such as carbon black, carbon nanotubes, carbon fibers, graphite fine powder, and carbon fibers can be used. The conductive assistant may be used alone or in combination of two or more kinds.

Examples of negative electrode active materials include carbon-based materials, lithium metal, lithium alloys, and metal oxides. One or more of these can be used in combination. Among these, active materials made of carbon-based materials such as natural graphite, artificial graphite, hard carbon, and soft carbon (hereinafter also referred to as "carbon-based active materials") are preferred, and graphite such as natural graphite and artificial graphite, and hard carbon are more preferred. In the case of graphite, spherical graphite is preferably used from the viewpoint of battery performance, and the preferred range of particle size is, for example, 1 to 20 μm, and also, for example, 5 to 15 μm. In order to increase the energy density, metals or metal oxides that can occlude lithium, such as silicon and tin, can also be used as negative electrode active materials.

The composition for producing a battery electrode of the present invention can be in the form of a slurry. When the composition for producing a battery electrode of the present invention is in the form of a slurry, the amount of active material used is usually in the range of 10 to 75% by mass, and may be in the range of 30 to 65% by mass, based on the total amount of the composition.

The composition for producing battery electrodes preferably contains water as a medium. In order to adjust the properties and drying properties of the composition, the composition may be mixed with lower alcohols such as methanol and ethanol, carbonates such as ethylene carbonate, ketones such as acetone, tetrahydrofuran, N-methylpyrrolidone, or other water-soluble organic solvents. The proportion of water in the mixed medium is usually 50% by mass or more, and may be 70% by mass or more.

When the composition for producing a battery electrode is made into a coatable slurry state, the content of the water-containing medium in the entire composition is usually in the range of 25 to 90 mass %, and may be 35 to 70 mass %, from the viewpoints of the coatability of the slurry, the energy cost required for drying, and productivity.

The composition for producing a battery electrode of the present invention is obtained by mixing the components of the composition. The method of mixing each component is not particularly limited, and a known method can be adopted, but a method of mixing each component such as a binder composition, an active material, and a conductive assistant with a dispersion medium such as water and dispersing and kneading is preferred. When the composition for producing a battery electrode is obtained in a slurry state, it is preferable to finish it into a slurry without poor dispersion or aggregation.
As a mixing means, known mixers such as a planetary mixer, a thin film swirling mixer, and a planetary mixer can be used, but it is preferable to use a thin film swirling mixer because a good dispersion state can be obtained in a short time. In addition, when using a thin film swirling mixer, it is preferable to perform preliminary dispersion in advance using a stirrer such as a disperser.
From the viewpoint of coatability, the viscosity of the slurry may be in the range of 500 to 10,000 mPa·s as Brookfield viscosity at 60 rpm.
When the composition for preparing a battery electrode is obtained in a wet powder state, it is preferable to knead each component such as the binder composition, the active material, the conductive assistant, etc., to a uniform state without unevenness in concentration using a Henschel mixer, a blender, a planetary mixer, a twin-screw kneader, or the like.

When producing the composition for producing a battery electrode of the present invention, oxidized cellulose before being made into the nanocellulose of the present invention (i.e., before being nano-sized) can be used as a material. During production, the oxidized cellulose is defibrated in the composition by a dispersing or kneading operation to become nanocellulose. Specifically, nanocellulose can be obtained by blending the oxidized cellulose with other materials of the composition for producing a battery electrode, defibrating the mixture by a dispersing or kneading operation, or by the user of the oxidized cellulose defibrating and nano-sizing it himself. The dispersing or kneading operation can be performed by the above-mentioned (Step B: defibration treatment).
One of the present inventions is a method for producing a composition for producing a battery electrode using, as a material, oxidized cellulose that contains an oxide of a cellulose-based raw material by hypochlorous acid or a salt thereof and that is substantially free of N-oxyl compounds, specifically, a method for producing a composition for producing a battery electrode that contains nanocellulose, the method comprising the step of obtaining the composition for producing a battery electrode by stirring a mixture containing oxidized cellulose and a material of the composition for producing a battery electrode other than nanocellulose. Another of the present inventions is a method for producing a composition for producing a battery electrode that contains nanocellulose, the method comprising the step of obtaining the composition for producing a battery electrode by stirring oxidized cellulose and continuously adding a material of the composition for producing a battery electrode other than nanocellulose.
Here, the aspects of the nanocellulose, oxidized cellulose, and battery electrode preparation composition are as described above. The material other than nanocellulose in the battery electrode preparation composition is any material other than nanocellulose that can be contained in the battery electrode preparation composition, such as the other binder components, dispersion medium, and components constituting the battery electrode (specifically, active materials, etc.) and components for forming the electrode (specifically, water, etc.) described above, but is not limited thereto.

The battery electrode preparation composition of the present invention contains the binder composition of the present invention. When the binder composition contains two or more binder components, each binder component may be mixed during the production of the battery electrode preparation composition, or a mixture of each binder component may be mixed in advance.

<Electrodes, batteries>
The battery electrode of the present invention is not particularly limited as long as it is produced using the composition for producing a battery electrode of the present invention, but it is preferable that the electrode has a mixture layer formed from the composition for producing a battery electrode of the present invention on the surface of a current collector such as copper or aluminum. The mixture layer can be formed by applying the composition for producing a battery electrode of the present invention to the surface of the current collector and then drying and removing the medium such as water. The method for applying the composition is not particularly limited, and known methods such as a doctor blade method, a dip method, a roll coating method, a comma coating method, a curtain coating method, a gravure coating method, and an extrusion method can be adopted. In addition, the drying can be performed by known methods such as hot air blowing, reduced pressure, (far) infrared rays, and microwave irradiation.
Usually, the mixture layer obtained after drying is subjected to a compression treatment using a mold press, a roll press, or the like. Compression brings the active material and the binder into close contact with each other, and improves the strength of the mixture layer and its adhesion to the current collector. The thickness of the mixture layer can be adjusted by compression to, for example, about 30 to 80% of the thickness before compression, and the thickness of the mixture layer after compression is generally about 4 to 200 μm.

A battery can be produced by providing the battery electrode of the present invention with a separator and an electrolyte. The battery in the present invention is preferably a secondary battery. The electrolyte may be in a liquid state or a gel state.
The separator is disposed between the positive and negative electrodes of the battery, and serves to prevent short circuits caused by contact between the electrodes and to retain the electrolyte to ensure ionic conductivity. The separator is preferably a film-like insulating microporous membrane having good ion permeability and mechanical strength. Specific examples of the material that can be used include polyolefins such as polyethylene and polypropylene, and polytetrafluoroethylene.

The electrolyte may be a known one that is generally used depending on the type of active material. In the lithium ion secondary battery, specific solvents include cyclic carbonates with high dielectric constant and high electrolyte dissolving ability such as propylene carbonate and ethylene carbonate, and chain carbonates with low viscosity such as ethyl methyl carbonate, dimethyl carbonate and diethyl carbonate, which may be used alone or as a mixed solvent. The electrolyte is used by dissolving lithium salts such as LiPF ₆ , LiSbF ₆ , LiBF ₄ , LiClO ₄ and LiAlO ₄ in these solvents. In the nickel-hydrogen secondary battery, an aqueous potassium hydroxide solution may be used as the electrolyte. The secondary battery is obtained by storing a positive electrode plate and a negative electrode plate separated by a separator in a spiral or stacked structure in a case or the like.

The present invention will be specifically described below based on examples. Note that the present invention is not limited to these examples. Note that, in the following, "parts" and "%" mean parts by mass and % by mass unless otherwise specified.
The physical properties of nanocellulose and oxidized cellulose were measured as follows.

<Method of measuring fiber length and fiber width>
Pure water was added to the aqueous dispersion of fine cellulose fibers obtained above, and the concentration of fine cellulose fibers in the CNF aqueous dispersion was adjusted to 5 ppm. The CNF aqueous dispersion after the concentration adjustment was naturally dried on a mica substrate, and the shape of the fine cellulose fibers was observed in AC mode using a scanning probe microscope "MFP-3D infinity" manufactured by Oxford Asylum.
The fiber length was analyzed by binarizing the obtained image using the image processing software "ImageJ". For 100 or more fibers, the number average fiber length was calculated as fiber length = "perimeter" ÷ 2.
The average fiber width was calculated using the software attached to the "MFP-3D infinity" for 50 or more fibers, and the number average fiber width [nm] was calculated as the cross-sectional height of the shape image = fiber width.

<Measurement of Carboxy Group Amount>
To 60 ml of an oxidized cellulose aqueous dispersion in which the concentration of oxidized cellulose had been adjusted to 0.5% by mass, a 0.1 M aqueous hydrochloric acid solution was added to adjust the pH to 2.5, and then a 0.05 N aqueous sodium hydroxide solution was added dropwise and the electrical conductivity was measured until the pH reached 11.0. The amount of carboxy groups (mmol/g) was calculated using the following formula from the amount of sodium hydroxide (a) consumed in the neutralization stage of the weak acid, in which the change in electrical conductivity was gradual.
Amount of carboxyl group = a (ml) x 0.05 / mass of oxidized cellulose fiber (g)

<Production of Carboxy Group-Containing Polymer Salt>
For the polymerization, a reactor equipped with a stirring blade, a thermometer, a reflux condenser and a nitrogen inlet tube was used.
Into the reactor, 567 parts of acetonitrile, 100.0 parts of acrylic acid (hereinafter referred to as "AA"), 0.9 parts of trimethylolpropane diallyl ether (manufactured by Daiso Co., Ltd., trade name "Neoallyl T-20"), and triethylamine equivalent to 1.0 mol% relative to the AA were charged. After the inside of the reactor was sufficiently replaced with nitrogen, the inside temperature was raised to 55°C by heating. After confirming that the inside temperature was stable at 55°C, 0.040 parts of 2,2'-azobis(2,4-dimethylvaleronitrile) (manufactured by Wako Pure Chemical Industries, Ltd., trade name "V-65") was added as a polymerization initiator, and the reaction solution became cloudy, so this point was determined to be the polymerization initiation point. The monomer concentration was calculated to be 15.0%. Cooling of the reaction solution was started 12 hours after the polymerization initiation point, and after the internal temperature had dropped to 25°C, 52.4 parts of lithium hydroxide monohydrate (hereinafter referred to as " _LiOH.H2O ") powder was added. After the addition, stirring was continued for 12 hours at room temperature to obtain a polymerization reaction solution in the form of a slurry in which particles of PAA crosslinked polymer salt (Li salt, neutralization degree 90 mol%) were dispersed in the medium. The reaction rate of AA was calculated to be 97.3% at 12 hours after the polymerization initiation.

The obtained polymerization reaction solution was centrifuged to settle the polymer particles, and the supernatant was removed. The precipitate was then redispersed in acetonitrile of the same weight as the polymerization reaction solution, and the washing operation of settling the polymer particles by centrifugation and removing the supernatant was repeated twice. The precipitate was collected and dried at 80°C for 3 hours under reduced pressure conditions to remove the volatile matter, thereby obtaining a powder of PAA crosslinked polymer salt. Since the PAA crosslinked polymer salt is hygroscopic, it was sealed and stored in a container with water vapor barrier properties. The powder of PAA crosslinked polymer salt was subjected to IR measurement, and the degree of neutralization was calculated from the intensity ratio of the peak derived from the C=O group of the carboxylic acid and the peak derived from the C=O of the carboxylic acid Li, which was 90 mol%, equal to the calculated value from the charge.

<Measurement of particle size in aqueous medium (water-swollen particle size)>
0.25 g of the PAA crosslinked polymer salt powder and 49.75 g of ion-exchanged water were weighed into a 100 cc container and set in a rotation/revolution type mixer (Thinky Corporation, Awatori Rentaro AR-250). Next, stirring (rotation speed 2000 rpm/revolution speed 800 rpm, 7 minutes) and degassing (rotation speed 2200 rpm/revolution speed 60 rpm, 1 minute) were performed to prepare a hydrogel in which the crosslinked polymer salt was swollen in water.
Next, the particle size distribution of the hydrogel was measured using a laser diffraction/scattering particle size distribution meter (Microtrack MT-3300EXII, manufactured by Microtrack Bell) using ion-exchanged water as a dispersion medium. When an excess amount of dispersion medium was circulated relative to the hydrogel and an amount of hydrogel was added to obtain an appropriate scattered light intensity, the measured particle size distribution shape stabilized after a few minutes. As soon as stability was confirmed, the particle size distribution was measured and the volume-based median diameter (D50) was measured as a representative value of the particle diameter, resulting in a particle diameter of 1.7 μm in the aqueous medium.

Example 1
<Production of nanocellulose>
As a cellulose-based raw material, softwood pulp (Sigma-Aldrich Corporation, NIST RM 8495, bleached kraft pulp) was cut with scissors into 5 mm squares and mechanically defibrated into a cotton-like form by processing at 25,000 rpm for 1 minute in a "Wonder Blender WB-1" manufactured by Osaka Chemical Co., Ltd.
In a beaker, 350 g of sodium hypochlorite pentahydrate crystals with an effective chlorine concentration of 42% by mass were placed, and pure water was added and stirred to adjust the effective chlorine concentration to 21% by mass. 35% by mass hydrochloric acid was added thereto and stirred to obtain an aqueous sodium hypochlorite solution with a pH of 11.
The aqueous sodium hypochlorite solution was heated to 30° C. in a thermostatic water bath while being stirred at 200 rpm using a propeller-type stirring blade in a stirrer manufactured by Shinto Scientific Co., Ltd. (Three-One Motor, BL600), and then 50 g of the above-mentioned cellulosic raw material was added.
After supplying the cellulosic raw material, the mixture was kept at 30° C. in the same thermostatic water bath, and the pH during the reaction was adjusted to 11 by adding 48% by mass sodium hydroxide, and the mixture was stirred under the same conditions for 30 minutes using a stirrer.
After completion of the reaction, the product was subjected to solid-liquid separation by suction filtration using a PTFE mesh filter having an opening of 134 μm, and the obtained oxidized cellulose was washed with pure water.
Pure water was added to the oxidized cellulose to prepare a 5% dispersion, which was then processed five times at 200 MPa with an ultra-high pressure homogenizer "Starburst Lab" manufactured by Sugino Machine Co., Ltd. to obtain nanocellulose as an aqueous dispersion. This nanocellulose is designated as nanocellulose A.
In the ultra-high pressure homogenizer, the oxidized cellulose aqueous dispersion was circulated through the built-in ultra-high pressure defibrating section to advance defibration. One pass was counted as one liquid passing through the defibrating section.

The available chlorine concentration in the aqueous sodium hypochlorite solution was measured by the following method.
(Measurement of available chlorine concentration in sodium hypochlorite aqueous solution)
0.582g of the aqueous solution of sodium hypochlorite pentahydrate crystals added to pure water was precisely measured, 50mL of pure water was added, 2g of potassium iodide and 10mL of acetic acid were added, and the solution was immediately sealed and left in the dark for 15 minutes. After leaving the solution for 15 minutes, the liberated iodine was titrated with 0.1mol/L sodium thiosulfate solution (solution factor 1.000) (indicator starch test solution), and the titration amount was 34.55mL. A blank test was separately performed to correct the amount, and 1mL of 0.1mol/L sodium thiosulfate solution was equivalent to 3.545mgCl, so the effective chlorine concentration in the aqueous sodium hypochlorite solution was 21% by mass.

<Preparation of electrode composition>
As a binder, a mixture of nanocellulose A, PAA crosslinked polymer salt, and styrene butadiene rubber (SBR)-based latex was used.
As the active material, natural graphite (manufactured by Nippon Graphite Co., Ltd., product name "CGB-10") was used.
The solid content of the composition for preparing an electrode was 43% by mass. The mixture was thoroughly mixed in advance with water as a diluting solvent to give a mass ratio of natural graphite: PAA crosslinked polymer salt: SBR: nanocellulose A = 100: 1.5: 1.5: 1.5 (solid content). The mixture was then dispersed for 15 seconds using a thin film rotary mixer (FM-56-30, manufactured by Primix Corporation) at a peripheral speed of 20 m/sec to give a slurry-like composition for preparing an electrode (hereinafter also referred to as "electrode slurry").
The obtained electrode slurry was used to prepare an electrode, which was then evaluated. The specific procedure and evaluation method are described below.

Example 2
Nanocellulose B was produced under the same conditions as in Example 1, except that 10 passes were performed in the <Production of nanocellulose> of Example 1. Thereafter, a slurry for an electrode was obtained in the same manner as in Example 1 <Production of composition for producing an electrode>.

Example 3
Nanocellulose C was produced under the same conditions as in Example 1, except that 15 passes were performed in <Production of nanocellulose> in Example 1. Thereafter, a slurry for an electrode was obtained in the same manner as in <Production of composition for producing an electrode> in Example 1.

Example 4
Nanocellulose D was produced under the same conditions as in Example 1, except that 20 passes were performed in the <Production of nanocellulose> of Example 1. Thereafter, a slurry for an electrode was obtained in the same manner as in Example 1 <Production of composition for producing an electrode>.

Example 5
The oxidation reaction was carried out under the same conditions as in Example 1 <Production of nanocellulose>, except that the reaction time was 120 minutes.
After the reaction was completed, an aqueous sodium sulfite solution was added to the excess sodium hypochlorite to stop the reaction, and then hydrochloric acid was added to adjust the pH to 2.5 to convert the carboxyl groups to -COOH type (H type). The resulting oxidized cellulose aqueous dispersion was subjected to solid-liquid separation and washing. Specifically, the process of centrifugation (1000G, 10 minutes), removing the supernatant by decantation, adding an amount of pure water equivalent to the amount removed, stirring thoroughly with a spoon to make it uniform, and then centrifuging again was repeated six times in total to recover purified oxidized cellulose. Thereafter, sodium hydroxide was added in an amount approximately equivalent to the amount of the introduced carboxyl groups to convert the carboxyl groups back to -COONa type (Na type). The oxidized cellulose aqueous dispersion was adjusted to 1% by mass by adding pure water, and then defibrated with a homomixer (10,000 rpm, 10 minutes) to obtain nanocellulose as an aqueous dispersion. This nanocellulose was designated as nanocellulose E.
Thereafter, a slurry for an electrode was obtained in the same manner as in <Preparation of composition for preparing electrode> in Example 1.

Example 6
The purified oxidized cellulose reverted to the Na form obtained in Example 5 was used. That is, a slurry for an electrode was obtained in the same manner as in Example 1 <Preparation of a composition for preparing an electrode> except that the above oxidized cellulose was used instead of nanocellulose A.

Example 7
Nanocellulose G was produced under the same conditions as in Example 5, except that potassium hydroxide was used instead of sodium hydroxide to convert the carboxyl group to -COOK type (K type).
Thereafter, a slurry for an electrode was obtained in the same manner as in <Preparation of composition for preparing electrode> in Example 1.

Example 8
Nanocellulose H was produced under the same conditions as in Example 5, except that lithium hydroxide was used instead of sodium hydroxide to convert the carboxyl group to the -COOLi type (Li type).
Thereafter, a slurry for an electrode was obtained in the same manner as in <Preparation of composition for preparing electrode> in Example 1.

Comparative Example 1
<Production of nanocellulose>
As the cellulosic raw material, cotton-like softwood pulp obtained from the same raw material and under the same mechanical processing conditions as in Example 1 was prepared.
0.16 g of TEMPO and 1.0 g of sodium bromide were placed in a beaker, and purified water was added and stirred to prepare an aqueous solution, to which 10.0 g of the mechanically defibrated softwood kraft pulp was added.
The above-mentioned aqueous solution is heated to 25°C in a thermostatic water bath while stirring with a stirrer, then 0.1M sodium hydroxide is added and stirred to obtain an aqueous solution of pH 10.0.Add 25.8g of an aqueous solution of sodium hypochlorite with an effective chlorine concentration of 13.2% by mass, and while keeping the solution at 25°C in the same thermostatic water bath, adjust the pH during reaction to 10.0 while adding 0.1M sodium hydroxide, and stir with a stirrer for 120 minutes.
After completion of the reaction, the product was subjected to solid-liquid separation by suction filtration using a PTFE mesh filter having an opening of 134 μm, and the obtained oxidized cellulose was washed with pure water.
Pure water was added to the oxidized cellulose to prepare a 0.5% dispersion, which was then processed at 200 MPa and 30 passes using a super-high pressure homogenizer "Starburst Lab" manufactured by Sugino Machine Co., Ltd. to obtain an aqueous dispersion of nanocellulose. This was heated and concentrated in an evaporator as necessary before use. This nanocellulose was designated as nanocellulose I.
<Preparation of electrode composition>
Thereafter, a slurry for an electrode was obtained in the same manner as in <Preparation of composition for preparing electrode> in Example 1.

Comparative Example 2
As a cellulose-based raw material, cotton-like softwood pulp obtained under the same raw material and mechanical processing conditions as in Example 1 was added to water to obtain a 0.5% aqueous dispersion, which was pre-defibrated at 1500 rpm for 10 passes using a fine grinder (Supermasscolloider) manufactured by Masuko Sangyo. The dispersion was then processed at 200 MPa for 40 passes using an ultra-high pressure homogenizer "Starburst Lab" manufactured by Sugino Machine Co., Ltd. to obtain a CNF aqueous dispersion. This was heated and concentrated in an evaporator as necessary before use. This nanocellulose was designated as nanocellulose J.
Thereafter, a slurry for an electrode was obtained in the same manner as in <Preparation of composition for preparing electrode> in Example 1.

Comparative Example 3
This was produced under the same conditions as in Production Example 9, except that it was treated in the "Starburst Lab" at 200 MPa for three passes.
Thereafter, a slurry for an electrode was obtained in the same manner as in <Preparation of composition for preparing electrode> in Example 1.

The electrode slurries of Examples 1 to 8 and Comparative Examples 1 to 3 were evaluated. In addition, electrodes were produced using the electrode slurries of Examples 1 to 8 and Comparative Examples 1 to 3, and the electrodes were evaluated. The specific procedures and evaluation methods are described below.

<Measurement of Viscosity of Electrode Slurry>
The obtained electrode slurry was subjected to measurement of the slurry viscosity at a shear rate of 60 s ⁻¹ using a rheometer (Physica MCR301) manufactured by Anton Paar, with a CP25-5 cone plate (diameter 25 mm, cone angle 5°).

<Evaluation of Coating Properties of Electrode Slurry>
The obtained electrode slurry was applied to a copper foil (thickness: 20 μm, manufactured by Furukawa Electric Co., Ltd.) using a variable applicator, and dried at 60° C. for 2 minutes, and then further dried at 150° C. for 5 minutes to form a mixture layer. After drying, the thickness of the mixture layer was measured using a Digimatic Indicator ID-H0560 manufactured by Mitutoyo Corporation to evaluate the coatability. The evaluation criteria were as follows:
⊚: The variation in film thickness was 0 μm or more and 4 μm or less in a 200 ^cm2 coating film.
A: The variation in film thickness was more than 4 μm and not more than 9 μm in an area of 200 ^cm2 of coating film.
×: The variation in film thickness exceeds 9 μm in 200 ^cm2 of the coating film

<90° peel strength (bonding strength)>
The mixture layer obtained above was rolled to a thickness of 80 μm and a packing density of 1.6 g/cm ³ to obtain a negative electrode plate. The negative electrode plate was cut into strips of 25 mm width, and the mixture layer surface of the sample was attached to a double-sided tape fixed to a horizontal surface to prepare a peel test sample. The test sample was dried at 60 ° C. under reduced pressure overnight, and then a tensile tester (ORIENTEC Co., Ltd. Tensilon universal testing material machine RTE-1210) was used to perform 90 ° peeling at a measurement temperature of 25 ° C. and a tensile speed of 50 mm / min to measure the peel strength between the mixture layer and the copper foil.

The evaluation results of the electrode slurries and mixture layers of Examples 1 to 8 and Comparative Examples 1 to 3 are shown in Table 1.

The battery electrode binder composition of the present invention has industrial applicability in the fields of battery electrodes and batteries, particularly in the fields of secondary battery electrodes and batteries.

Claims (13)

A binder composition for a battery electrode comprising nanocellulose,
The nanocellulose has a structure in which the hydroxyl groups at the second and third positions of the glucopyranose ring are oxidized to introduce a carboxyl group, and a hydroxyl group is present at the sixth position .
Binder composition for battery electrodes. The carboxyl group content of the nanocellulose is 0.2 mmol / g or more and 2.0 mmol / g or less,
The battery electrode binder composition according to claim 1 . The average fiber length of the nanocellulose is 50 nm or more and 700 nm or less.
The binder composition for battery electrodes according to claim 1 or 2. Contains a particulate polymer and/or a polymer having a carboxy group or a salt thereof,
The binder composition for battery electrodes according to any one of claims 1 to 3. the polymer having a carboxy group contains a structural unit derived from a crosslinkable monomer,
the content of the structural unit derived from the crosslinkable monomer is 0.1 parts by mass or more and 2.0 parts by mass or less with respect to 100 parts by mass of the total amount of the monomer units constituting the polymer having a carboxy group;
The battery electrode binder composition according to claim 4 . the polymer having a carboxy group is neutralized to a degree of neutralization of 80 to 100 mol %, and then the particle size measured in an aqueous medium is 0.1 μm or more and 5.0 μm or less in terms of volume-based median size;
The binder composition for battery electrodes according to claim 4 or 5. A composition for producing a battery electrode, comprising the battery electrode binder composition according to any one of claims 1 to 6. An electrode made using the composition for making a battery electrode according to claim 7. A battery comprising the electrode according to claim 8. A method for producing a binder composition for a battery electrode comprising nanocellulose, comprising:
The method includes obtaining the binder composition for battery electrodes by stirring a mixture containing oxidized cellulose and a material other than nanocellulose of the binder composition for battery electrodes,
The oxidized cellulose has a structure in which the hydroxyl groups at the second and third positions of the glucopyranose ring are oxidized to introduce a carboxyl group, and a hydroxyl group is present at the sixth position . A method for producing a binder composition for a battery electrode comprising nanocellulose, comprising:
obtaining said battery electrode binder composition by stirring oxidized cellulose and continuously adding materials other than nanocellulose of said battery electrode binder composition;
The oxidized cellulose has a structure in which the hydroxyl groups at the second and third positions of the glucopyranose ring are oxidized to introduce a carboxyl group, and a hydroxyl group is present at the sixth position . A method for producing a composition for producing a battery electrode containing nanocellulose, comprising:
The method includes obtaining the composition for producing a battery electrode by stirring a mixture containing oxidized cellulose and a material other than nanocellulose of the composition for producing a battery electrode,
The oxidized cellulose has a structure in which the hydroxyl groups at the second and third positions of the glucopyranose ring are oxidized to introduce a carboxyl group, and a hydroxyl group is present at the sixth position . A method for producing a composition for producing a battery electrode containing nanocellulose, comprising:
The method includes a step of obtaining the composition for preparing a battery electrode by stirring the oxidized cellulose and continuously adding materials other than nanocellulose of the composition for preparing a battery electrode,
The oxidized cellulose has a structure in which the hydroxyl groups at the second and third positions of the glucopyranose ring are oxidized to introduce a carboxyl group, and a hydroxyl group is present at the sixth position .