Coating liquid for forming electrode

Abstract

The purpose of the present invention is to provide a carbon nanotube dispersion liquid having excellent dispersibility. [Solution] A carbon nanotube dispersion liquid which is characterized by containing at least carbon nanotubes, oxidized cellulose nanofibers, and water, and which is characterized in that the oxidized cellulose nanofibers having a fiber length of 50-250 nm account for 85% or more of the oxidized cellulose nanofibers.

Description

Technical Field

[0001] The present invention relates to a coating liquid for electrode formation which is a raw material for manufacturing electrodes of lithium ion batteries. Background Art

[0002] With the popularity of electric vehicles, the miniaturization, lightness and high performance of portable devices such as mobile phones and notebook personal computers, there is a demand for secondary batteries with high energy density and high capacity of the secondary batteries. In this context, lithium-ion secondary batteries using non-aqueous electrolytes are used in many devices due to their high energy density and high voltage.

[0003] The following research has been conducted: By using carbon nanotube dispersions in the negative electrode materials and positive electrode materials used in these lithium-ion secondary batteries, good conductive performance can be achieved, electrode resistance can be reduced, and a conductive network can be effectively formed with a small amount. Recently, carbon nanotube dispersions using cellulose nanofibers as dispersants have also been known.

[0004] For example, in Patent Document 1, in order to provide a carbon nanotube dispersion that suppresses the aggregation of carbon nanotubes and shows high dispersion stability, a carbon nanotube dispersion comprising carbon nanotubes, cellulose nanofibers and a dispersion medium is disclosed, wherein the aforementioned cellulose nanofibers are fine cellulose fibers having a maximum fiber diameter of not more than 1000 nm and a number average fiber diameter of not less than 2 nm and not more than 150 nm, a portion of the hydroxyl groups of the fine cellulose fibers are substituted by at least one functional group selected from the group consisting of a carboxyl group and an aldehyde group, and the fine cellulose fibers have a cellulose I type crystal structure, etc.

[0005] Patent Document 2 discloses a nanomaterial composition characterized by comprising a dispersion medium, and cellulose nanofibers and carbon nanotubes dispersed in the dispersion medium in order to provide a nanomaterial composition capable of improving the surface hardness of a molded body.

[0006] In addition, in Patent Document 3, in order to provide a composition containing a dispersion stabilizer for an electrode coating liquid in a storage device, a dispersant for an electrode coating liquid of a storage device and an electrode coating dispersion are disclosed, wherein the composition has excellent dispersion stability of an electrode active material and a conductive material and can produce a uniform electrode even when a dispersion device with weak shear force is used; the dispersant for the electrode coating liquid contains cellulose fibers that meet the following conditions: (a) the number average width of the short side is 2 to 200 nm, (b) the aspect ratio is 7.5 or more and 250 or less, (c) it has cellulose I type crystals and the degree of crystallinity is 70% or more and 95% or less; the electrode coating dispersion is (d) a dispersion having anionic functional groups, (e) the anionic functional groups are carboxyl groups and the content thereof is 1.2 to 2.5 mmol / g.

[0007] Furthermore, in Patent Document 4, in order to provide an electrode binder composition that can obtain an electrode showing high durability even when an active material with a large volume change is used, an electrode for a storage device made using the same, and a storage device having the electrode for a storage device, an electrode binder composition, etc. are disclosed, characterized in that it contains: (A) at least one or two or more polymer components selected from the group consisting of fluorine-based polymers, butadiene-based polymers and thermoplastic elastomers; (B) fibrous nanocarbon materials having an average fiber diameter of not less than 0.5 nm and not more than 20 nm and a fiber length of not less than 0.5 μm and not more than 1 mm; (C) cellulose material; (D) nanocellulose fibers; and (E) water, the mass ratio of the above (A) to (B) being (A) / (B)=60 / 40 to 98 / 2.

[0008] Patent document 5 discloses a dispersion liquid comprising: a dispersion medium, metal-containing oxidized cellulose nanofibers containing a metal other than sodium in the form of a salt, and a single-layer nanotube. As oxidized cellulose nanofibers, carboxylated cellulose nanofibers obtained by TEMPO oxidation are described, but their properties are not described. TEMPO oxidation of cellulose nanofibers is usually achieved by allowing the oxidation reaction to proceed as completely as possible.

[0009] Furthermore, in the "Results Report of the Project Performance Evaluation of Products Using Effective Cellulose Nanofibers in 2011 (Project Extraction for the Practical Application of Lithium-ion Batteries for Idle Stop Vehicles Using Cellulose Nanofibers) in the Commissioned Business for the Effective Utilization of Cellulose Nanofibers in 2011 (Commissioned Business of the Ministry of the Environment in 2011), March 16, 2011: Dai-ichi Kogyo Seiyaku Co., Ltd.", which has become non-patent document 1, it is recorded that by applying cellulose nanofibers to the manufacture of electrodes for lithium-ion batteries, the positive electrode coating liquid can be made aqueous, and it was found that the battery deterioration associated with charging and discharging was greatly improved. In addition, the improvement of the discharge capacity retention rate during cycling is recorded.

[0010] However, in the carbon nanotube dispersions of Patent Documents 1 to 5 and Non-Patent Document 1, there are still problems such as the decrease in dispersibility over time and difficulty in achieving high stability and conductivity. In particular, there are problems such as the time-consuming dispersion process to prevent insufficient dispersion when mixing cellulose nanofibers, and the increase in the resistance value of the battery due to the inclusion of a large amount of binding material (binder) to improve the durability of the battery. Further improvements are urgently desired.

[0011] Prior art literature

[0012] Patent Literature

[0013] Patent Document 1: Japanese Patent Application Publication No. 2017-206412 (patent claims, examples, etc.)

[0014] Patent Document 2: Japanese Patent Application Publication No. 2020-019924 (patent claims, examples, etc.)

[0015] Patent Document 3: Japanese Patent Application Publication No. 2010-254546 (patent claims, examples, etc.)

[0016] Patent Document 4: Japanese Patent Application Publication No. 2007-169120 (patent claims, examples, etc.)

[0017] Patent Document 5: Japanese Patent Application Publication No. 2021-57271 (patent claims, examples, etc.)

[0018] Non-patent document 1: Report on the results of the project "Identification of issues toward the practical application of lithium-ion batteries for stop-start vehicles using cellulose nanofibers" in the project commissioned by the Ministry of the Environment in 2011 (2011), March 16, 2011, Daiichi Kogyo Seiyaku Co., Ltd. Summary of the invention

[0019] Problem that the invention aims to solve

[0020] The present invention is made to solve the above-mentioned conventional problems, etc., and aims to provide a carbon nanotube dispersion liquid with excellent dispersibility. In particular, the present invention aims to provide a means for solving the problems that when carbon nanotubes are dispersed in a dispersion medium such as water, carbon nanotubes aggregate and are not dispersed sufficiently, or that a long time is required for the dispersion process to be completely dispersed.

[0021] Solutions for solving problems

[0022] The present inventors have conducted intensive studies on the above-mentioned problems and have found that the above-mentioned target carbon nanotube dispersion can be obtained by using a carbon nanotube dispersion containing at least carbon nanotubes, oxidized cellulose nanofibers having specific physical properties, and water, thereby completing the present invention.

[0023] That is, the coating liquid of the present invention is a coating liquid for forming an electrode layer, characterized in that it is a carbon nanotube-dispersed coating liquid containing at least carbon nanotubes, oxidized cellulose nanofibers, an active material, a binder and water.

[0024] The peak derived from C=O in the infrared spectrum of oxidized cellulose nanofibers (1610 cm -1 The height of the peak (1062cm -1The peak height ratio (C=O / CO) of the peak at or near the C=O source (1610 cm -1 The height of the peak (3340 cm -1 The peak height ratio (C=O / OH) at a height near 1.50 (C=O / OH) is 1.35 or less.

[0025] Another invention is the aforementioned coating solution, wherein the oxidized cellulose nanofibers have a fiber length of 50 to 250 nm accounting for 85% or more.

[0026] In addition, another invention is the above-mentioned coating liquid, which has structural recovery properties.

[0027] The structural recovery of the coating liquid of the present invention can be confirmed by showing the recovery of viscosity when the coating liquid exhibits thixotropy. In particular, the structural recovery is shown by increasing the shear rate from 2.2 s to 1.5 s in the viscosity measurement using a rotational viscometer. -1 Reciprocating change to 1000s -1 In the viscosity measurement diagram at the time of , the ratio of the gradient of the reverse path to the gradient of the forward path is 0.75 or more.

[0028] The coating liquid of the present invention preferably contains synthetic rubber as a binder.

[0029] By using the coating liquid of the present invention, an electrode composition used for an electrode for a lithium battery can be suitably produced.

[0030] It is known that carboxylated oxidized cellulose nanofibers can be obtained by subjecting cellulose nanofibers to TEMPO oxidation, but this is usually achieved by allowing the TEMPO oxidation reaction to proceed as completely as possible. The oxidized cellulose nanofibers are not controlled to have specific physical properties by adjusting the TEMPO oxidation reaction. On the other hand, in the present invention, it is important that the TEMPO oxidation reaction of the cellulose nanofibers is not completely carried out so that the oxidized cellulose nanofibers have various specific physical properties.

[0031] Effects of the Invention

[0032] According to the present invention, there is provided a coating liquid for forming an electrode layer, which can obtain a homogeneous film having a predetermined conductivity with good coating properties.

[0033] The objects and effects of the present invention are particularly achieved and obtained by using the constituent elements and combinations indicated in the claims. Both the above general description and the following detailed description are exemplary and illustrative and do not limit the present invention described in the patent claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1In the viscosity measurement of the coating liquid of the present invention, the shear rate of the disk of the rotational viscometer is increased from 2.2 s -1 Reciprocating change to 1000s -1 The upper line represents the positive path from left to right, and the lower line represents the reverse path from right to left. DETAILED DESCRIPTION

[0035] The following is a detailed description of the embodiments of the present invention. However, it should be noted that the scope of protection of the present invention is not limited to the embodiments described in detail below, but covers the inventions described in the patent claims and their equivalents. In addition, the present invention can be implemented based on the contents disclosed in this specification and the technical common sense in the field (including design matters and known matters).

[0036] 〈Carbon Nanotube Dispersion Liquid〉

[0037] The carbon nanotube dispersion of the present invention is characterized by containing at least carbon nanotubes, specific oxidized cellulose nanofibers and water.

[0038] The oxidized cellulose nanofiber (CeNF) of the present invention is suitably used as a dispersant for a carbon nanotube dispersion.

[0039] 〈Carbon Nanotube (CNT)〉

[0040] The carbon nanotubes (CNTs) used in the present invention are not particularly limited as long as they have a shape in which one surface of graphite is essentially rolled into a tube. Single-layer CNTs in which one surface of graphite is rolled into a single layer can be used, and multilayer CNTs in which two or three or more layers are rolled into multiple layers can also be used.

[0041] In addition, examples of carbon nanotube forms include graphite whiskers, filamentous carbon, graphite fibers, ultrafine carbon tubes, carbon tubes, carbon fibrils, carbon microtubes, and carbon nanofibers, but are not limited to these and may be any one of these or a combination of two or more (hereinafter referred to as "at least one").

[0042] Furthermore, from the viewpoints of the viscosity, conductivity and stability of the dispersion, the average outer diameter of the carbon nanotubes is preferably 1 nm to 90 nm, more preferably 3 nm to 30 nm, and even more preferably 3 nm to 15 nm.

[0043] In the present invention, the average outer diameter of the carbon nanotubes refers to the arithmetic mean of a sufficient number of n outer shapes measured using an image at a magnification of 100,000 or more using a transmission electron microscope.

[0044] The purity of the carbon nanotubes used in the present invention is preferably 90 to 100 mass %, particularly preferably 95 to 100 mass %. The purity of the carbon nanotubes is calculated based on the amount of impurities, with ash measured in accordance with JIS K 1469 and JIS K 6218 as impurities.

[0045] Specific examples of carbon nanotubes (CNTs) that can be used include NC7000 (average outer diameter 10 nm) manufactured by Nanocyl, Baytubes C150P (average outer diameter 11 nm) manufactured by Bayer, FloTube9000 (average outer diameter 19 nm), FloTube7320 (average outer diameter 9 nm), FloTube7010 (average outer diameter 9 nm), FloTube6810 (average outer diameter 8 nm), FloTube6120 (average outer diameter 8 nm), FloTube6100 (average outer diameter 8 nm), FloTube2020 (average outer diameter 4 nm) manufactured by Cnano, MEIJOeDIPS EC2.0 (average outer diameter 2.0 nm) manufactured by MEIJO NANO CARBON, KORBON-A7 (average outer diameter 1.2 nm) manufactured by KOATSU GAS KOGYO CO., LTD., NFT-7 (average outer diameter 30 nm), KOATSU At least one of NFT-15 (average outer diameter 30 nm) manufactured by GAS KOGYO CO., LTD., and the like.

[0046] The content of these carbon nanotubes (CNT) can be appropriately set according to the application, and is not particularly limited.

[0047] For example, when used in a conductive paste, an electrode paste for a secondary battery, an electrode for a secondary battery, etc., its content is preferably 0.1 to 15.0% by mass, more preferably 0.1 to 10.0% by mass, more preferably 0.5 to 8.0% by mass, relative to the total amount of the dispersion, from the perspective of achieving both high stability and conductive performance and the viscosity when the dispersion is prepared. It is ideal to set it to 1.0 to 6.0% by mass, and particularly to set it to 2.0 to 5.0% by mass.

[0048] When the content of the carbon nanotubes (CNT) is 0.1% by mass or more, sufficient conductivity can be ensured, whereas when the content is 15.0% by mass or less, stability of the dispersion and good conductivity can be ensured.

[0049] 〈Oxidized cellulose nanofiber (CeNF)〉

[0050] The oxidized cellulose nanofiber (CeNF) of the present invention is used as a dispersant for a carbon nanotube dispersion liquid and is an oxidized cellulose nanofiber satisfying the following characteristics.

[0051] As oxidized cellulose nanofibers, the hydroxyl group at the 6th position of the glucose unit is preferably selectively oxidized to have a carboxylic acid group (COOH). The carboxylic acid group may also be neutralized to form a carboxylate group (COOX, where X represents a cation that forms a salt with a carboxylic acid). The fact that oxidized cellulose is formed by selectively oxidizing the hydroxyl group at the 6th position of the glucose unit can be, for example, 13 It should be noted that the oxidized cellulose nanofibers may have an aldehyde group or a ketone group together with a carboxylic acid group and / or a carboxylate group, but preferably do not substantially have an aldehyde group or a ketone group.

[0052] In the oxidized cellulose nanofibers used, since a certain amount of alcoholic hydroxyl groups remain, the molecules can form stronger hydrogen bonds with each other, thereby obtaining structural recovery. In addition, when the composition is applied, the viscosity decreases during the coating process, making it easy to apply evenly, and the viscosity recovers after coating, and a uniform state can be maintained thereafter. In addition, since the viscosity recovers (becomes higher) after coating, the material is not easy to aggregate and becomes less likely to warp when drying. The alcoholic hydroxyl groups are detected by infrared spectroscopy.

[0053] The peak derived from C=O in the infrared spectrum (1610 cm -1 The height of the peak (1062cm -1 The peak height ratio (C=O / CO) of the peak at or near the C=O source (1610 cm -1 The height of the peak (3340 cm -1 The peak height ratio (C=O / OH) at a height near 1.50 (C=O / OH) is 1.35 or less.

[0054] When the peak height ratio (C=O / CO) is 0.70 or less, or the peak height ratio (C=O / OH) is 1.35 or less, the TEMPO-oxidized cellulose can be used as cellulose having good dispersibility of carbon nanotubes.

[0055] On the other hand, when the peak height ratio (C=O / CO) exceeds 0.70 or the peak height ratio (C=O / OH) exceeds 1.35, oxidation excessively proceeds, which adversely affects the dispersibility of carbon nanotubes.

[0056] The peak height ratio (C=O / CO) is preferably 0.25 or more and 0.70 or less, or the peak height ratio (C=O / OH) is more preferably 0.45 or more and 1.35 or less.

[0057] In the present invention, it is preferred that the peak height ratio (C=O / CO) is 0.70 or less, or the peak height ratio (C=O / OH) is 1.35 or less. During analysis, peaks may be affected by noise due to impurities from the material, but any one of the peak height ratios may be satisfied.

[0058] From the viewpoint of the dispersibility of carbon nanotubes, it is further preferred that the peak height ratio (C=O / CO) is 0.70 or less and the peak height ratio (C=O / OH) is 1.35 or less.

[0059] In order to make the above-mentioned peak height ratio (C=O / CO) less than 0.70, or the above-mentioned peak height ratio (C=O / OH) less than 1.35, during the subsequent production, the amount of carboxyl groups can be controlled by adjusting the addition amount of the co-oxidant used in the oxidation process of the cellulose fiber and the reaction time.

[0060] The infrared spectrum of the oxidized cellulose nanofibers can be measured using an infrared spectrometer. In the present invention, the oxidized cellulose nanofibers are irradiated with infrared rays, the infrared absorption intensities of the functional groups at characteristic wavelengths are measured, and the ratios of the absorption intensities are compared as peak height ratios.

[0061] It is preferred that 85% or more of the oxidized cellulose nanofibers blended in the coating liquid have a fiber length of 50 nm to 250 nm, and more preferably 30% or more of the oxidized cellulose nanofibers have a fiber length of 100 nm to 150 nm.

[0062] The number average fiber length L of the oxidized cellulose nanofibers blended in the carbon nanotube dispersion is 100 nm to 150 nm, and the ratio of the length-weighted average fiber length L1 to the number average fiber length L (L1 / L) is preferably 1.0 to 1.4.

[0063] The fiber length of the oxidized cellulose nanofibers can be measured by a transmission electron microscope (TEM). From the TEM image, for example, a histogram of the fiber length of the oxidized cellulose nanofibers is prepared at a scale of 50 nm, and the proportion of fibers with a fiber length in the range of 50 nm to 250 nm or in the range of 100 nm to 150 nm is calculated, thereby evaluating the distribution of the fiber length. In addition, from the above-mentioned histogram of fiber length, the number average fiber length L and the length weighted average fiber length Ll, as well as the ratio of the length weighted average fiber length Ll to the number average fiber length L (Ll / L) can be calculated.

[0064] When the fiber length of the oxidized cellulose nanofibers is within the above range, the dispersibility of the carbon nanotubes is good. Although the mechanism is not clear, it is presumed that this is related to the permeability of the oxidized cellulose nanofibers into the carbon nanotubes.

[0065] The carboxylic acid content of the oxidized cellulose nanofibers (hereinafter referred to as the carboxyl content) is preferably adjusted to 0.5 mmol / g to 3.0 mmol / g relative to the absolute dry mass of the cellulose nanofibers. When the carboxyl content is within the above range, the dispersibility when the coating liquid is used to prepare the electrode material coating liquid becomes good.

[0066] The amount of carboxyl groups in the oxidized cellulose nanofibers is measured, for example, by preparing 60 mL of a 0.5-1% by mass slurry from a cellulose sample whose dry mass is accurately weighed, adjusting the pH to about 2.5 with a 0.1 M hydrochloric acid aqueous solution, and then dropping a 0.05 M sodium hydroxide aqueous solution to measure the conductivity. The measurement is continued until the pH reaches about 11. The amount of carboxyl groups can be calculated from the amount of sodium hydroxide (V) consumed in the neutralization stage of the weak acid in which the change in conductivity is moderate, according to the following formula (2).

[0067] Carboxyl group content (mmol / g) = V (mL) × [0.05 / cellulose mass] (2)

[0068] As will be described later, the amount of carboxyl groups can be adjusted by controlling factors such as the amount of the co-oxidant added and the reaction time used in the oxidation step of the cellulose fibers.

[0069] The above-mentioned oxidized cellulose nanofibers can be obtained by the following production method, which includes the following steps: an oxidation reaction step (1), using natural cellulose fibers as a raw material, an N-oxyl compound as an oxidation catalyst, and allowing a co-oxidant to act in water, thereby oxidizing the natural cellulose fibers to obtain a reaction product; a purification step (2), removing impurities to obtain a reaction product impregnated with water; and a dispersion step (3), dispersing the reaction product impregnated with water in a solvent.

[0070] (1) Oxidation reaction process

[0071] After dispersing natural cellulose fibers and N-oxyl compounds in water (dispersion medium), a co-oxidant is added to start the reaction. During the reaction, a 0.5M sodium hydroxide aqueous solution is added dropwise to maintain the pH at 10 to 11 while adding the co-oxidant. Here, the co-oxidant is not a substance that directly oxidizes the hydroxyl groups of cellulose, but refers to a substance that oxidizes the N-oxyl compound used as an oxidation catalyst.

[0072] The above-mentioned natural cellulose fibers refer to purified cellulose fibers isolated from the biosynthetic system of cellulose such as gel produced by plants, animals, and bacteria. More specifically, non-wood pulps such as cotton pulps such as coniferous wood pulp, broadleaf wood pulp, cotton lint, and cotton lint, straw pulp, and bagasse pulp, bacterial cellulose fibers (BC), cellulose fibers isolated from sea squirts, and cellulose fibers isolated from seaweed can be listed. These can be used alone or in combination of two or more. Among these, non-wood pulps such as cotton pulps such as coniferous wood pulp, broadleaf wood pulp, cotton lint, and cotton lint, straw pulp, and bagasse pulp are preferred.

[0073] The above-mentioned natural cellulose fibers are preferably subjected to treatments such as beating to increase the surface area, because the reaction efficiency can be improved and the productivity can be improved. In addition, as the above-mentioned natural cellulose fibers, if they are used without drying (never dried) after separation and purification, the microfibril bundles are in a state where swelling easily occurs, so the reaction efficiency can be improved and the number average fiber diameter after the micronization treatment can be reduced, so it is preferred.

[0074] As the cellulose raw material, particularly preferred are: regenerated cellulose obtained by dissolving cellulose in a certain solvent such as a cuprammonium solution, a morpholine derivative, etc. and then spinning the resulting cellulose; and fine cellulose obtained by depolymerizing the cellulose by subjecting the above-mentioned cellulose raw material to hydrolysis, alkali hydrolysis, enzymatic hydrolysis, blasting treatment, mechanical treatment such as a vibration ball mill, etc.

[0075] The dispersion medium of the natural cellulose fibers in the above reaction is water, and the concentration of the natural cellulose fibers in the reaction aqueous solution can be any concentration as long as it is a concentration that allows the reagent (natural cellulose fibers) to be fully diffused. Generally, it is about 5% or less relative to the mass of the reaction aqueous solution, but the reaction concentration can be increased by using a device with a strong mechanical stirring force.

[0076] In addition, as the above-mentioned N-oxyl compound, for example, a compound having a nitroxide free radical which is generally used as an oxidation catalyst can be cited. The above-mentioned N-oxyl compound is preferably a water-soluble compound, among which a piperidine nitroxide free radical is preferred, and 2,2,6,6-tetramethylpiperidinyloxy free radical (TEMPO) or 4-acetamide-TEMPO is particularly preferred. There is no particular limitation on the addition of the above-mentioned N-oxyl compound as long as it is a catalytic amount that can oxidize the cellulose that will become the raw material. For example, relative to 1g of absolute dry cellulose, 0.01 to 10mmol is preferred, 0.02 to 1mmol is more preferred, and 0.05 to 0.5mmol is further preferred. In addition, it is preferably about 0.1 to 4mmol / L relative to the reaction system.

[0077] As the above-mentioned co-oxidant, for example, hypohalous acid or its salt, halous acid or its salt, perhalogen acid or its salt, hydrogen peroxide, organic peracid, etc. can be listed. These can be used alone or in combination of two or more. Among them, alkali metal hypohalites such as sodium hypochlorite and sodium hypobromite are preferred. In addition, when using the above-mentioned sodium hypochlorite, from the aspect of reaction speed, it is preferred to react in the presence of alkali metal bromide such as sodium bromide. The addition amount of the above-mentioned alkali metal bromide is about 1 to 40 times the molar amount, preferably about 10 to 20 times the molar amount relative to the above-mentioned N-oxyl compound.

[0078] The pH of the reaction aqueous solution is preferably maintained in the range of about 8 to 11. The temperature of the aqueous solution is selected from the range of about 4 to 40°C. In order to obtain the desired amount of carboxyl groups, etc., the degree of oxidation is controlled by the amount of co-oxidant added and the reaction time. The reaction time in the oxidation reaction can be appropriately set according to the degree of oxidation, and is usually 0.5 to 6 hours, for example, about 1 to 4 hours. In addition, the oxidation reaction can be carried out in two stages. For example, after the first stage reaction is completed, the oxidized cellulose obtained by filtration and separation is oxidized again under the same or different reaction conditions, thereby enabling efficient oxidation without being inhibited by the reaction caused by the salt produced as a by-product in the first stage reaction.

[0079] In addition to these, by controlling the amount of co-oxidant added and the pH of the reaction aqueous solution, the degree of oxidation and hydrolysis of the cellulose molecules can be controlled, and various properties of the oxidized cellulose nanofibers can be arbitrarily set. TEMPO oxidation of cellulose nanofibers is usually achieved by allowing the oxidation reaction to proceed as completely as possible. However, it is important in the present invention not to excessively perform TEMPO oxidation so that the oxidized cellulose nanofibers have the aforementioned specific various physical properties.

[0080] (2) Purification process

[0081] Next, purification is performed for the purpose of removing unreacted co-oxidants (such as hypochlorous acid), various by-products, etc. The reaction product fibers are usually not dispersed into nanofiber units at this stage, so a high-purity (99% by mass or more) dispersion of the reaction product fibers and water can be prepared by repeating the usual purification method, i.e., water washing and filtration.

[0082] The purification method in the above purification step may be any device as long as it can achieve the above purpose, such as a method using centrifugal dehydration (for example, a continuous decanter). The solid content (cellulose fiber) concentration of the aqueous dispersion of the reaction product fibers thus obtained in the extruded state is in the range of about 10% to 50% by mass. Considering the subsequent dispersion step, if the solid content concentration is higher than 50% by mass, extremely high energy is required for dispersion, which is not preferred.

[0083] (3) Dispersion process (micronization process)

[0084] The reaction product (water dispersion) impregnated with water obtained in the above-mentioned purification process is dispersed in a dispersion medium for dispersion treatment. The viscosity rises with the treatment, and a dispersion of cellulose fibers processed by micronization can be obtained. It should be noted that, since the length direction of the cellulose fibers will be cut off simultaneously with the micronization of the cellulose fibers, the aspect ratio of the cellulose fibers can be arbitrarily set by controlling the degree of micronization treatment (for example, the processing shear force, processing pressure, processing times, processing time, etc. of the dispersion machine). Then, the above-mentioned cellulose fibers can be dried as needed. As the drying method of the dispersion of the above-mentioned cellulose fibers, for example, when the dispersion medium is water, spray drying, freeze drying, vacuum drying, etc. can be used. When the dispersion medium is a mixed solution of water and an organic solvent, a drying method based on a drum dryer, a spray drying method based on a spray dryer, etc. can be used. It should be noted that the dispersion of the above-mentioned cellulose fibers can also be used in the state of a dispersion without drying.

[0085] As the disperser used in the above-mentioned dispersion process, by using a homogenizer under high-speed rotation, a high-pressure homogenizer, an ultra-high-pressure homogenizer, an ultrasonic dispersion processor, a stirrer, a disc refiner, a cone refiner (ConicalRefiner), a double disc refiner, a grinder, etc., which have a strong beating ability, more effective and highly miniaturized can be achieved, which is preferred in terms of being able to economically obtain an aqueous lubricant composition. It should be noted that as the above-mentioned disperser, for example, a screw mixer, a paddle mixer, a dispersing mixer, a turbine mixer, a disperser, a propeller mixer, a kneader, a stirrer, a homogenizer, an ultrasonic homogenizer, a colloid mill, a pebble mill, a bead mill, etc. can be used. In addition, two or more dispersers can also be used in combination.

[0086] (4) Reduction process

[0087] In the present invention, it is preferred that the oxidized cellulose nanofibers be further subjected to a reduction reaction after the above-mentioned oxidation reaction step. Specifically, the fine oxidized cellulose fibers after the oxidation reaction are dispersed in purified water, the pH of the aqueous dispersion is adjusted to about 10, and a reduction reaction is performed using various reducing agents. As the reducing agent used in the present invention, a common reducing agent can be used, but LiBH is preferably used. 4 , NaBH 3 CN, NaBH 4 Among them, NaBH is preferred from the perspective of cost and availability. 4 .

[0088] The amount of the reducing agent is preferably in the range of 0.1 to 4% by weight, particularly preferably in the range of 1 to 3% by weight, based on the dry weight of the oxidized cellulose nanofibers. The reaction is usually carried out at room temperature or a temperature slightly higher than room temperature for 10 minutes to 10 hours, preferably for 30 minutes to 2 hours.

[0089] Through the above-mentioned reduction step, the aldehyde groups and ketone groups contained in the oxidized cellulose nanofibers can be converted into hydroxyl groups.

[0090] In addition, oxidized cellulose nanofibers in which the peak height ratio (C=O / CO) or (C=O / OH) in the infrared spectroscopic spectrum is within a specific range, or the fiber length is within a specific range can be obtained by selecting the raw materials, the amount of co-oxidant added during the oxidation of the cellulose nanofibers in the manufacturing method, controlling the reaction time, controlling the defibration time, etc.

[0091] The oxidized cellulose nanofibers satisfying the various characteristics of the present invention can be produced by adopting the above-mentioned means / methods, etc., and commercially available products having various characteristics can be used.

[0092] In the present invention, the content of the oxidized cellulose nanofibers contained in the coating liquid can be appropriately set according to the intended use.

[0093] For example, when used in a conductive paste, an electrode paste for a secondary battery, an electrode for a secondary battery, etc., the content of the oxidized cellulose nanofibers contained in the coating liquid is preferably 0.1 to 2 mass %, more preferably 0.1 to 1.5 mass %, more preferably 0.1 to 1 mass %, and particularly preferably 0.1 to 0.8 mass % relative to the mass of the active substance, from the perspective of achieving both high stability and conductive performance and the viscosity when preparing the dispersion.

[0094] By setting the content of oxidized cellulose nanofibers to 0.1 mass % or more relative to the active material, sufficient dispersibility of the coating liquid and cycle characteristics as a battery can be ensured, while by setting it to 2 mass % or less, stability of the dispersion liquid and good conductivity can be ensured.

[0095] The dispersion medium (the balance of the dispersion) in the coating liquid of the present invention is water (eg, purified water, distilled water, pure water, ultrapure water, tap water, ion-exchanged water, etc.), and a water-soluble solvent may be used in addition to water.

[0096] Examples of the water-soluble solvent that can be used include ethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, dipropylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butylene glycol, 2,3-butylene glycol, 1,3-butylene glycol, 1,4-butylene glycol, 1,2-pentanediol, 1,5-pentanediol, 2,5-hexanediol, 3-methyl-1,3-butylene glycol, 2-methyl-2,4-pentanediol, 3- At least one of alkylene glycols such as methyl-1,3,5-pentanetriol and 1,2,3-hexanetriol, polyalkylene glycols such as polyethylene glycol and polypropylene glycol, glycerols such as glycerol, dipropylene glycol and tripropylene glycol, lower alkyl ethers of glycols such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monomethyl ether and diethylene glycol mono-n-butyl ether, N-methyl-2-pyrrolidone and 1,3-dimethyl-2-imidazolidinone.

[0097] Furthermore, water-soluble solvents such as amides such as dimethylformamide and dimethylacetamide and ketones such as acetone may be mixed.

[0098] The content of these water-soluble solvents varies depending on the solid content of the dispersion, and is preferably 0.1 to 7% by mass relative to the total amount of the coating liquid. From the perspective of improving the miscibility of the slurry and storage stability, it is more preferably less than 10% by mass, and even more preferably 0.1 to 5% by mass.

[0099] From the perspective of storage stability and preventing the growth of bacteria, the coating liquid of the present invention preferably contains a preservative. In addition, additives may be added according to the purpose. For example, as a thickener, sodium carboxymethyl cellulose, an anti-settling agent, a wetting agent, an emulsifier, an anti-drip agent, a defoamer, a leveling agent, a plasticizer, etc. may be listed.

[0100] The coating liquid of the present invention preferably has structural recovery. The structural recovery refers to the thixotropy of viscosity recovery. Specifically, it is preferred that the coating liquid has thixotropy and the structural recovery ratio is 0.75 or more.

[0101] As a thixotropic property, a rotational viscometer was used to increase the shear rate from 2.2 s -1 Change to 1000s -1 When the measured viscosity decreases, preferably 1000s -1 The viscosity is 2.2s -1 0.2 to 15% of the viscosity below.

[0102] The structural recovery ratio is obtained by increasing the shear rate from 2.2 s to 1.5 s in the viscosity measurement using a rotational viscometer. -1 Reciprocating change to 1000s -1 The ratio of the gradient of the reverse path to the gradient of the forward path in the viscosity measurement diagram when the viscosity is measured is preferably 0.75 or more.

[0103] More specifically, in the viscosity measurement using a rotational viscometer, the shear rate of the coating liquid was increased from 2.2 s to 1.5 s by increasing the rotational speed of the rotational viscometer. -1 Change to 1000s -1 The viscosity change when the shear rate is 0.05 is plotted in a double logarithmic curve graph to obtain a shear rate-viscosity graph (hereinafter referred to as a graph). Then, the ratio of the gradient of the reverse path to the gradient of the forward path is calculated. The greater the ratio of the gradient of the reverse path to the gradient of the forward path, that is, the closer the viscosity of the reverse path is to the viscosity of the forward path, the greater the structural recovery.

[0104] The coating liquid used is particularly preferably such that the shear rate is from 2.2s -1 Change to 1000s -1 The ratio of the gradient of the reverse path to the gradient of the forward path in the viscosity at the time of 0.75 or more is preferably set. -1 Change to 1000s -1 The ratio of the gradient of the reverse path to the gradient of the forward path in the viscosity is 0.75 or more means that: in the figure, the gradient of the forward path is set to X, and the gradient of the reverse path is set to Y, and the gradient ratio (X / Y) is 0.75 or more. The ratio of the gradient of the reverse path to the gradient of the forward path is more preferably 0.75 or more and 1.00 or less.

[0105] If the ratio of the gradient of the reverse path to the gradient of the forward path is 0.75 or more, the viscosity can be reduced during coating by stirring during coating, making it easy to apply the coating evenly. In addition, since the viscosity is restored after coating, the coating thickness is unlikely to change until the coating is dried, and warping and uneven coating of the coating are unlikely to occur.

[0106] Oxidized cellulose nanofibers having a structural recovery ratio, i.e., the ratio of the gradient of the reverse path to the gradient of the forward path, of 0.75 or more can be obtained by selecting raw materials, adding the amount of co-oxidant during the oxidation reaction of the cellulose nanofibers, controlling the reaction time, controlling the defibration time, etc. during their production.

[0107] The coating liquid of the present invention can be produced by, for example, adding at least carbon nanotubes, oxidized cellulose nanofibers having the above-mentioned characteristics, water, flat graphite, a water-soluble solvent, a preservative, etc., stirring and mixing, and then performing a dispersion step to obtain the coating liquid.

[0108] The dispersion treatment of the above-mentioned dispersion can be carried out using, for example, mixers such as ultrasonic dispersers, dispersers, homomixers, rotation and revolution mixers, Henschel mixers, planetary mixers, (high-pressure) homogenizers, paint conditioners, colloid mills, bead mills, cone mills, ball mills, sand mills, attritors, pearl mills, annular gap ball mills and other media-type dispersers, wet jet mills, thin film rotary high-speed mixers and other media-free dispersers, and roller mills and other dispersing devices, but are not limited to these.

[0109] As a preferable dispersion apparatus, a thin film rotating high-speed mixer, a bead mill, etc. are preferable from the viewpoint of stability and dispersion efficiency.

[0110] In addition, in order to obtain the fluidity required for handling, the coating liquid of the present invention preferably has a viscosity (mPa·s) of 5 to 700, more preferably 5 to 200, measured at 25° C. with a rotor (1°34′×R24 mm) rotating at 10 rpm using an E-type rotational viscometer [TV-25 manufactured by Toki Sangyo Co., Ltd.].

[0111] The coating liquid of the present invention can be used for an electrode layer forming coating liquid (hereinafter also referred to as electrode slurry) suitable for manufacturing an electrode (positive electrode or negative electrode) of a lithium ion secondary battery. When coating is performed to form an electrode, the carbon nanotubes and active materials that become conductive materials are uniformly dispersed, and the dispersion stability becomes excellent. Moreover, it becomes an electrode composition suitable for manufacturing battery electrodes such as high-efficiency lithium ion batteries without adversely affecting the resistance value of the electrode itself. The electrode layer obtained by the electrode layer forming coating liquid highly maintains the cycle characteristics and self-discharge characteristics, and can take into account high stability and conductivity, and will not affect the Li + The in and out of plasma and the decrease in electrode resistance have adverse effects.

[0112] 〈Positive electrode slurry〉

[0113] The positive electrode slurry is the coating liquid of the present invention containing a positive electrode active material.

[0114] As the positive electrode active material that can be used, any common positive electrode active material (active material that allows lithium ions to reversibly enter and exit) that can be used for the positive electrode of a lithium ion battery can be used without particular limitation.

[0115] For example, composite oxides of lithium and transition metals such as lithium-nickel composite oxides, lithium-cobalt composite oxides, lithium-manganese composite oxides, lithium-nickel-manganese composite oxides, lithium-nickel-cobalt composite oxides, lithium-nickel-aluminum composite oxides, lithium-nickel-cobalt-aluminum composite oxides, lithium-nickel-manganese-cobalt composite oxides, lithium-nickel-manganese-aluminum composite oxides, lithium-nickel-cobalt-manganese-aluminum composite oxides, and lithium-nickel-cobalt-manganese-aluminum composite oxides, TiS 2 , FeS, MoS 2 Transition metal sulfides, MnO, V 2 O 5 、V 6 O 13 、TiO 2 Transition metal oxides such as quartz, olivine-type lithium phosphorus oxides, etc. Olivine-type lithium phosphorus oxides, for example, contain at least one element selected from the group consisting of Mn, Cr, Co, Cu, Ni, V, Mo, Ti, Zn, Al, Ga, Mg, B, Nb and Fe and contain lithium, phosphorus and oxygen. In order to improve the properties of these compounds, some elements may be partially replaced by other elements.

[0116] As a preferred positive electrode active material, a lithium-nickel composite oxide is used. More preferably, the lithium-nickel composite oxide is of the formula: LiNi X M1 Y M2 Z O 2 The lithium-nickel composite oxide represented by (M1 and M2 are at least one metal element selected from the group consisting of Al, B, alkali metals, alkaline earth metals, and transition metals, 0.8≤X≤1.0, 0≤Y≤0.2, and 0≤Z≤0.2) is ideal.

[0117] These positive electrode active materials may be used alone or in combination of two or more.

[0118] In the positive electrode slurry of the present invention, the content of the positive electrode active material is preferably 50 to 70 mass %, more preferably 50 to 63 mass % based on the total amount of the positive electrode slurry in order to ensure battery capacity and fluidity of the slurry.

[0119] The content of the carbon nanotubes is preferably 0.5 to 10% by mass, more preferably 0.5 to 7% by mass, based on the total amount of the positive electrode slurry in terms of solid content.

[0120] The positive electrode slurry of the present invention contains carbon nanotubes and a positive electrode active material, and may contain a solid electrolyte such as a sulfide solid electrolyte, an oxide solid electrolyte, a dry polymer electrolyte, a gel polymer electrolyte, or a quasi-solid electrolyte as necessary.

[0121] 〈Negative electrode slurry〉

[0122] The negative electrode slurry is the coating liquid of the present invention containing a negative electrode active material.

[0123] The negative electrode active material that can be used is not particularly limited. In addition to graphite, as long as it is not conductive, for example, metal oxide active material particles, silicon active material particles, and particularly metal oxide negative electrode active material particles can be used.

[0124] As the metal oxide-based negative electrode active material particles, for example, titanium oxide can be used. As the titanium oxide, there is no particular limitation as long as it can absorb and release lithium, for example, spinel lithium titanate, ramsdellite lithium titanate, titanium-containing metal composite oxides, titanium dioxide (TiO2) having a monoclinic crystal structure can be used. 2 (B)), and anatase titanium dioxide, etc.

[0125] Examples of spinel lithium titanate include Li 4 +xTi 5 O 12 (x varies in the range of -1≤x≤3 depending on the charge and discharge reaction) etc. Examples of ramsdellite-type lithium titanate include Li 2 +yTi 3 O 7 (y varies within the range of -1≤y≤3 depending on the charge and discharge reaction). 2 (B) and anatase-type titanium dioxide, for example Li 1 +zTiO 2 (z changes within the range of -1≤z≤0 depending on the charge and discharge reaction) etc.

[0126] Examples of the titanium-containing metal composite oxide include metal composite oxides containing Ti and at least one element selected from the group consisting of P, V, Sn, Cu, Ni, and Fe. Examples of the metal composite oxides containing Ti and at least one element selected from the group consisting of P, V, Sn, Cu, Ni, and Fe include TiO 2 -P 2 O 5 、TiO 2 -V 2 O 5 、TiO 2 -P 2 O 5 -SnO 2 、TiO 2 -P 2 O 5 -MeO (Me is at least one element selected from the group consisting of Cu, Ni and Fe) and the like.

[0127] Such a metal composite oxide preferably has low crystallinity and has a microstructure in which a crystalline phase and an amorphous phase coexist, or an amorphous phase exists alone. The microstructure can further improve the cycle performance.

[0128] In the negative electrode slurry of the present invention, the content of the negative electrode active material is preferably 30 to 60% by mass, more preferably 35 to 55% by mass based on the total amount of the negative electrode slurry, from the perspective of ensuring battery capacity and fluidity of the slurry.

[0129] The content of the carbon nanotubes is preferably 0.5 to 10% by mass, more preferably 0.5 to 7% by mass, based on the total amount of the negative electrode slurry in terms of solid content.

[0130] The negative electrode slurry of the present invention may contain a negative electrode active material in the carbon nanotube dispersion having the above constitution, and may contain a solid electrolyte such as a sulfide solid electrolyte, an oxide solid electrolyte, a dry polymer electrolyte, a gel polymer electrolyte, or a quasi-solid electrolyte as required.

[0131] By using the above-mentioned positive electrode slurry and negative electrode slurry, an electrode for secondary batteries can be obtained.

[0132] It is preferred that the positive electrode slurry and the negative electrode slurry further contain a binding material (binder).

[0133] As the adhesive material that can be used, for example, fluororesins such as polyimide resin, polyvinylidene fluoride (PVdF), polytetrafluoroethylene, tetrafluoroethylene / hexafluoropropylene / vinylidene fluoride copolymer, hexafluoropropylene / vinylidene fluoride copolymer, tetrafluoroethylene / perfluorovinyl ether copolymer, polyolefin resins such as polyethylene and polypropylene, polyvinyl pyrrolidone, polyvinyl alcohol, styrene-butadiene rubber (SBR), acrylic resins, etc. can be listed. These adhesive materials can also be used by mixing two or more.

[0134] The amount of these binders is preferably 0.2 to 3.0 mass %, more preferably 0.5 to 2.5 mass % based on the total amount of each electrode slurry for the secondary battery from the viewpoint of adhesion to the collector foil, battery capacity after batteryization, and charge and discharge characteristics.

[0135] In the slurry for electrode, the dissolution of the binder, especially the binder component, may be inhibited and precipitation may occur. However, the slurry for electrode of the present invention does not inhibit the dissolution of the binder.

[0136] Furthermore, various solvents may be added to the above-mentioned electrode slurries. As solvents, for example, water (purified water, ion exchange water, distilled water, ultrapure water, etc.), aromatic solvents, alcohols, polyols, ether solvents, glycol ether solvents, ester solvents, amine solvents, amide solvents, heterocyclic solvents, sulfoxide solvents, sulfone solvents, etc. may be listed. These solvents may be used alone or in combination of two or more.

[0137] The amount of these solvents is preferably 0.5 to 80% by mass, more preferably 1 to 70% by mass, based on the total amount of each electrode slurry for secondary batteries, in order to adjust the viscosity to a suitable level when coating each electrode slurry.

[0138] Furthermore, in each of the above-mentioned electrode slurries, in addition to the above-mentioned graphite dispersion for battery electrodes, each active material, and a binder, a leveling agent, a solid electrolyte material, and the like may be appropriately blended within a range that does not impair the effects of the present invention.

[0139] The slurry for each electrode of the secondary battery thus constituted can be prepared by mixing the carbon nanotube dispersion, each active material for the positive electrode or negative electrode of the secondary battery, a binder, a solvent, etc., using, for example, a twin-screw kneading machine.

[0140] The obtained slurry for each electrode for the secondary battery is applied to a collector as a conductive component of the lithium ion secondary battery and dried to obtain a specified positive electrode and negative electrode for the lithium ion secondary battery. In the present invention, a slurry for each electrode for the secondary battery and an electrode for the secondary battery that can withstand long-term repeated charge and discharge can be obtained.

[0141] Example

[0142] Examples 1 to 3, Comparative Example 1

[0143] The present invention will be described below by way of examples, but the present invention is not limited to these examples.

[0144] As oxidized cellulose nanofibers (CeNF), the following CeNF-1 and CeNF-2 were used.

[0145] (Method for measuring fiber length)

[0146] The fiber length of the oxidized cellulose nanofibers was measured from an image obtained by a transmission electron microscope (manufactured by Hitachi High-Tech Corporation, H-7650; TEM), and the ratio of the number of 50 nm to 250 nm or 100 nm to 150 nm to the total number was calculated. The number n was set to 100. In addition, the number average fiber length L and the length weighted average fiber length Ll were obtained from the distribution, and the ratio of the length weighted average fiber length Ll to the number average fiber length L (Ll / L) was calculated.

[0147] The measurement results of the fiber length of the used oxidized cellulose nanofibers are as follows.

[0148] *CeNF-1: 90% of fibers are 50nm to 250nm in length, 35% of fibers are 100nm to 150nm in length, the ratio of the length-weighted average fiber length Ll to the number-average fiber length Ll / L 1.3

[0149] *CeNF-2: 60% of fibers with a fiber length of 50nm to 250nm, 13% of fibers with a fiber length of 100nm to 150nm, the ratio of the length-weighted average fiber length Ll to the number-average fiber length Ll / L 1.6

[0150] (The peak derived from C=O in the infrared spectrum (1610 cm -1 The height of the peak (1062cm -1 The peak height ratio (C=O / CO) and the peak derived from C=O (1610 cm -1 The height of the peak (3340 cm -1 Method for measuring the peak height ratio (C=O / OH) of the peaks at the vicinity of

[0151] The naturally dried cellulose nanofibers were measured for infrared spectra using an infrared spectrometer (Nicolet iZ10 manufactured by Thermo Scientific Inc.) The maximum absorption at a wavelength characteristic of each functional group in the obtained infrared spectrum was defined as a peak, and the ratio of the respective absorption ratios was defined as a peak height ratio.

[0152] *CeNF-1: peak height ratio (C=O / CO) 0.61, peak height ratio (C=O / OH) 1.16

[0153] *CeNF-2: peak height ratio (C=O / CO) 0.72, peak height ratio (C=O / OH) 1.39

[0154] [Preparation of Carbon Nanotube Dispersion]

[0155] Specified amounts of carbon nanotubes, flat graphite (J-SP-α, manufactured by Nippon Graphite Co., Ltd.) and the aforementioned oxidized cellulose nanofibers CeNF-1 or CeNF-2 were added to distilled water, and stirred using a dispersing device (a bead mill using φ1.0 mm zirconium oxide beads; the peripheral speed was set to 10 m / s) to obtain a carbon nanotube dispersion.

[0156] [Preparation of coating liquid for forming electrode layer]

[0157] Active material, conductive auxiliary material, dispersant and preservative were added to the carbon nanotube dispersion obtained above, and dispersed by a dispersing device (bead mill using zirconia beads of φ1.0 mm; peripheral speed was set to 10 m / s). The obtained dispersion was further transferred to a planetary mixer, a rubber component as a binding material was added, the revolution speed was set to 10 rpm, and the composition was kneaded for 120 minutes to obtain a coating liquid for electrode layer formation. Lithium titanium oxide was used as the active material. Graphite was used as the conductive auxiliary material. Carboxymethyl cellulose was used as the dispersing aid. An organic nitrogen-sulfur compound was used as the preservative. Styrene-butadiene rubber (SBR) was used as the binding material. The compounding composition is shown in Table 1.

[0158] (Method for measuring viscosity gradient ratio (reverse path / forward path))

[0159] The viscosity gradient ratio (reverse path / forward path) of the obtained coating liquid was measured as follows.

[0160] A rotational viscometer (MCR-102 manufactured by Anton Paar) was used for the coating liquid, and the shear rate was gradually increased from 0.1 s to 1.5 s over 30 seconds by increasing the rotation speed. -1 Increase to 1000s -1 . Shear speed reaches 1000s -1 When the shear rate is increased from 1000 s to -1 Reduced to 0.1s -1 The measurement results are plotted on a graph with the horizontal axis set to shear velocity (s -1 ), the vertical axis is set to viscosity (cP·s) in a double logarithmic curve, and we get Figure 1 Such a viscosity measurement graph.

[0161] In the viscosity measurement graph, a straight line is used to connect the shear rate from 2.2s -1 Increase to 1000s -1 The gradient is calculated by connecting the two ends of the shear rate from 1000s to -1 Reduced to 2.2s -1The gradient was calculated at both ends of the reverse path (reverse path). In addition, the ratio of the gradient of the reverse path to the gradient of the forward path was calculated as the structural recovery ratio of the coating solution for forming an electrode layer containing the respective oxidized cellulose nanofibers (CeNF).

[0162] *CeNF-1: structural recovery ratio 0.88

[0163] *CeNF-2: structural recovery ratio 0.59

[0164] (Evaluation of coating liquid for electrode layer formation)

[0165] The obtained electrode layer forming coating liquid was applied to one surface of a PET film (Lumirror #100-T60, TORAY) using an applicator with a gap of 50 μm, and then dried at 80° C. to obtain an electrode layer film.

[0166] The obtained film was visually evaluated for its weight stability (thickness unevenness) and warping. The case where no thickness unevenness or warping was observed was marked as ○, where slightly observed was marked as △, and where significantly observed was marked as ×.

[0167] The resistance value was measured as sheet resistance using a device consisting of four probes with a probe interval of 10 mm and a measuring instrument (HiTESTER 3227 manufactured by Hioki Electric Co., Ltd.) When the sheet resistance was 1.0 kΩ / □ or less, it was confirmed that the conductivity was excellent.

[0168] The obtained electrode layer-forming coating liquid was filtered through a mesh with a mesh size of 50 μm. A case where no insoluble matter was observed on the mesh was rated as ○, and a case where insoluble matter was observed was rated as ×. The main component of the insoluble matter was the SBR rubber blended as a binder.

[0169] Table 1 shows these evaluation results.

[0170] [Table 1]

[0171] (parts by weight)

[0172]

[0173] As is clear from the evaluation results in Table 1, the film obtained using the electrode layer forming coating solution within the scope of the present invention has both excellent coating properties and conductivity without impairing the prescribed properties. In contrast, the film obtained using the coating solution of Comparative Example 1 lacks uniformity.

[0174] Industrial Applicability

[0175] The coating liquid of the present invention can be used for the preparation of a composition for an electrode (positive electrode or negative electrode) of a lithium ion secondary battery, and the like.

Claims

1. A coating liquid for forming an electrode layer, It is characterized in that The carbon nanotube dispersion coating liquid contains at least carbon nanotubes, oxidized cellulose nanofibers, an active substance, a binder and water. The C=O-derived 1610 cm-1 spectroscopy of oxidized cellulose nanofibers -1 The peak height near 1062cm -1 The peak height ratio C=O / CO near the peak height is 0.70 or less, or the peak height of 1610 cm derived from C=O is -1 The peak height near 3340 cm -1 The peak height ratio C=O / OH of the peak heights in the vicinity is 1.35 or less.

2. The coating liquid according to claim 1, in, Among the oxidized cellulose nanofibers, those with a fiber length of 50 to 250 nm account for more than 85%. The coating liquid according to claim 1 , which has structural recovery properties.

4. The coating liquid according to claim 1, It is characterized in that It has thixotropy and a structural recovery ratio of 0.75 or more.

5. The coating liquid according to claim 1, in, The bonding material is synthetic rubber. 6 . A composition for an electrode produced using the coating liquid according to claim 1 .

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