Carbon black dispersion, and secondary battery electrode composition, electrode film, and secondary battery using the same.

Abstract

To provide a carbon black dispersion, a carbon black resin composition and composite slurry having high concentration and high dispersibility in order to give an electrode film having high adhesion and conductivity, and also to provide a nonaqueous electrolyte secondary battery having excellent rate properties and cycle characteristics.SOLUTION: A carbon black dispersion contains carbon black, carboxymethyl cellulose or a salt thereof and water. The carboxymethyl cellulose or a salt thereof has a weight average molecular weight of 10,000-150,000 and a degree of etherification of 0.5-0.9. The product (X×Y) of a complex modulus X(Pa) and a phase angle Y(°) of the carbon black dispersion is 100 or more and 1,500 or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a carbon black dispersion, and a composition for a secondary battery electrode, an electrode film, and a secondary battery using the same. [Background technology]

[0002] Because the capacity of lithium-ion secondary batteries is highly dependent on the cathode and anode active materials, various materials have been actively researched. However, the charge capacities of all active materials currently in practical use are close to the theoretical value, and improvement is nearing its limit. Therefore, since increasing the amount of active material packed into the battery simply increases capacity, attempts have been made to reduce the amount of conductive material and binder added, which do not directly contribute to capacity. Of these, conductive material forms conductive paths within the battery and connects active material particles, thereby preventing the conductive paths from being broken due to the expansion and contraction of the active material. To maintain performance with a small amount of conductive material added, it is effective to form an efficient conductive network using a conductive material dispersion (Patent Document 1).

[0003] Examples of conductive materials that have been used include carbon black, ketjen black, graphene, fine carbon materials, etc. Among these, when a conductive material with a large specific surface area is used, a conductive network can be efficiently formed with a small amount, and the amount of conductive material contained in the positive and negative electrodes of a lithium-ion secondary battery can be reduced. For example, in a negative electrode containing graphite and silicon, the following issues have been addressed: reducing electrode resistance, improving the load resistance of the battery, improving the electrode strength, and improving the electrode expansion and contraction properties. In addition, from the perspectives of reducing environmental impact and reducing costs, there is a growing demand for conductive material dispersions that use water as a dispersion medium, but carbon-based conductive materials are highly hydrophobic, making them difficult to disperse in water.

[0004] In addition, Patent Document 2 proposes a conductive material dispersion liquid using carboxymethyl cellulose with an average degree of polymerization of 500 or more and 2500 or less, but in order to achieve a viscosity suitable for coating, dispersion is carried out using a bead mill, which has the problem of reducing the structure of the conductive material. 2 / g or more and 300m 2 / g or less of carbon black has been proposed, but a large amount of dispersant was required to prepare a conductive material dispersion with excellent dispersion stability. Patent Document 4 proposes an aqueous conductive material dispersion using ethyl cellulose as a dispersant, but it was difficult to contain a conductive material at a high concentration in the dispersion in order to prepare a conductive material dispersion with excellent dispersibility. Dispersions with low concentrations of conductive materials have problems such as reduced design freedom when mixing materials such as active materials and binders, and high transportation costs per solid content of conductive material. Therefore, there is a demand for dispersing conductive materials with high specific surface areas at high concentrations. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-162877 [Patent Document 2] Japanese Patent Application Publication No. 2017-10822 [Patent Document 3] Japanese Patent Application Laid-Open No. 2017-84682 [Patent Document 4] Japanese Patent Application Laid-Open No. 2011-70908 Summary of the Invention [Problem to be solved by the invention]

[0006] Furthermore, the inventors' investigations have revealed that it is difficult to obtain a high concentration and good dispersion state for active materials such as silicon-based active materials and lithium iron phosphate that have been microparticulated and coated on the surface with a carbon film using water as a dispersion medium for the same reasons as for the conductive materials described above. Therefore, it has been found that it is difficult to obtain a particularly good dispersion state when various active materials, and in particular active materials such as silicon-based active materials and lithium iron phosphate that have been microparticulated and coated on the surface with a carbon film, are combined with carbon black, and as a result, it is also difficult to obtain a secondary battery with excellent rate characteristics and cycle characteristics.

[0007] The present invention provides a carbon black dispersion, a carbon black resin composition, and a composite slurry having a high concentration and high dispersibility to obtain an electrode film with high adhesion and conductivity. More specifically, the present invention provides a nonaqueous electrolyte secondary battery having excellent rate and cycle characteristics. [Means for solving the problem]

[0008] The inventors have conducted extensive research and found that by dispersing carboxymethyl cellulose or its salt having a specific weight-average molecular weight and degree of etherification with carbon black so that the product (X × Y) of the complex modulus X (Pa) and the phase angle Y (°) is 100 to 1,500, the carbon black can be well dispersed in water and a large structure can be maintained, maintaining a good conductive network, thereby improving the rate and cycle characteristics of secondary batteries.

[0009] That is, the present invention includes the following embodiments. A carbon black dispersion containing carbon black, carboxymethyl cellulose or a salt thereof, and water, The carboxymethyl cellulose or its salt has a weight average molecular weight of 10,000 to 150,000 and a degree of etherification of 0.5 to 0.9, the product (X×Y) of the complex elastic modulus X (Pa) and the phase angle Y (°) of the carbon black dispersion is 100 or more and 1,500 or less; Carbon black dispersion.

[0010] The carbon black has a BET specific surface area of ​​30 to 1500 m 2 / g of the carbon black dispersion.

[0011] The carbon black dispersion, wherein the carbon black has a pH of 7 to 10.5.

[0012] The carbon black dispersion has a complex modulus of 50 Pa or less and a phase angle of 10° or more.

[0013] The carbon black dispersion further contains polyacrylic acid.

[0014] The carbon black dispersion described above, wherein the median diameter is 0.1 μm or more and 2.0 μm or less.

[0015] The carbon black dispersion, wherein the TI value of the dispersion is 1.5 to 5.0.

[0016] The carbon black dispersion, wherein a coating film of the carbon black dispersion has a gloss measured at 60° of 5 to 120.

[0017] The carbon black dispersion has a pH of 7.0 to 10.5.

[0018] A composition for a secondary battery electrode comprising the carbon black dispersion.

[0019] An electrode film comprising a coating film of the secondary battery electrode composition.

[0020] A secondary battery comprising the electrode film.

[0021] 14. The method for producing a carbon black dispersion according to claim 1, comprising a step of dispersing the carbon black at a pressure of 60 to 120 MPa using a high-pressure homogenizer to adjust the median diameter to 2.0 μm or less. [Effects of the Invention]

[0022] According to an embodiment of the present invention, it is possible to provide a carbon black dispersion having a high concentration and high dispersibility, a composition for a secondary battery electrode, an electrode film that can improve the output and cycle life of a secondary battery, and a secondary battery having high output and good cycle life. DETAILED DESCRIPTION OF THE INVENTION

[0023] Hereinafter, carbon black, carboxymethyl cellulose and its salt, carbon black dispersion, secondary battery electrode composition, electrode film, secondary battery, and other embodiments of the present invention will be described in detail. The present invention is not limited to the following embodiments, and the present invention also includes embodiments that are implemented within the scope of the present invention.

[0024] In this specification, carbon black may be abbreviated as "CB." Carboxymethyl cellulose may be abbreviated as "CMC." In this specification, carbon black dispersion may be simply referred to as "dispersion."

[0025] <Carbon black> As the CB used in the present invention, various commercially available acetylene black, furnace black, hollow CB, channel black, thermal black, Ketjen black, etc. can be used. Conventionally used carbon black that has been subjected to oxidation treatment and graphitized CB can also be used. Among these, acetylene black, furnace black, and Ketjen black are preferred, and furnace black is more preferred.

[0026] The average primary particle size of CB is preferably 0.01 to 1 μm, particularly preferably 0.01 to 0.2 μm, and more preferably 0.01 to 0.1 μm. The average primary particle size here refers to the arithmetic mean particle size measured with an electron microscope, and this physical property value is generally used to represent the physical characteristics of CB.

[0027] Other known physical properties that represent the physical characteristics of CB include the BET specific surface area and pH. The BET specific surface area is the specific surface area measured by the BET method using nitrogen adsorption. This BET specific surface area corresponds to the surface area of ​​the CB, and the larger the BET specific surface area, the greater the amount of dispersant required. The pH changes depending on the functional groups on the CB surface and the impurities contained therein.

[0028] The BET specific surface area of ​​CB is 30 to 1500 m 2 / g is preferred, and 30 to 1000m 2 / g is more preferable, and 100 to 300m 2 / g is particularly preferred. 2 By using CB with a BET specific surface area of ​​100 to 300 m / g or more, there will be many electrical contacts, making it easier to obtain good electronic conductivity. 2 / g of carbon black makes it easier to obtain a CB dispersion that has both good dispersibility and good electronic conductivity, making it suitable as a CB dispersion for secondary batteries.

[0029] The pH of the CB (that is, the value as a surface property of the CB before preparing the CB dispersion of the present invention) is preferably 5-10, and more preferably 6-9.

[0030] <Carboxymethylcellulose or its salt> Carboxymethyl cellulose (CMC) or its salts are anionic water-soluble polymers obtained from cellulose. The weight-average molecular weight of CMC is preferably 10,000 or more. It is also preferably 150,000 or less, more preferably 100,000 or less, even more preferably 70,000 or less, even more preferably 60,000 or less, and particularly preferably 30,000 or less. By setting the weight-average molecular weight within the above range, the intermolecular forces between CMC and CB and between CMC and water are well balanced, allowing for good dispersion and maintenance. The degree of etherification of CMC is also preferably 0.5 or more, more preferably 0.6 or more. It is also preferably 0.9 or less, more preferably 0.8 or less. Setting the degree of etherification within the above range allows for appropriate affinity for water and CB. Furthermore, when used in secondary batteries, problems such as dissolving the dispersant in the electrolyte in the battery and increasing the viscosity of the electrolyte can be prevented.

[0031] The method for producing CMC or its salts is not particularly limited, and CMC or its salts can be produced by a general method for producing CMC or its salts. That is, CMC or its salts can be produced by performing a mercerization reaction in which cellulose is reacted with an alkali, followed by adding an etherifying agent to the resulting alkali cellulose and performing an etherification reaction. For example, CMC or its salts can be produced by performing a mercerization reaction using a mixed solvent containing water and an organic solvent, adding monochloroacetic acid to perform an etherification reaction, neutralizing the excess alkali with an acid, removing the mixed solvent, washing, drying, and then pulverizing the resulting product. The molecular weight of the cellulose raw material can be reduced by extending the reaction time of the mercerization reaction.

[0032] The weight-average molecular weight of CMC, calculated as pullulan, is preferably 10,000 or more, more preferably 15,000 or more. It is also preferably 100,000 or less, more preferably 60,000 or less, and even more preferably 30,000 or less. Having a moderate weight-average molecular weight improves adsorption to CB and the stability of the dispersion. If the weight-average molecular weight is below the above range, hygroscopicity increases, and film strength tends to decrease. If the weight-average molecular weight exceeds the above range, viscosity increases due to hydrogen bonding in the aqueous solution, reducing the ease of CB preparation and machine storage stability. If the weight-average molecular weight exceeds the above range, when using a disperser in which the dispersion liquid passes through a narrow channel, such as a nozzle-type high-pressure homogenizer, it becomes difficult to transport the liquid through the narrow channel, resulting in reduced dispersion efficiency.

[0033] Since many commercially available CMCs have a molecular weight higher than the above-mentioned preferred range, they can be used after being hydrolyzed in an acidic aqueous solution to lower the molecular weight. The CMC to be hydrolyzed preferably has a weight-average molecular weight of more than 60,000 and not more than 500,000. If the weight-average molecular weight exceeds 500,000, the hydrolysis reaction takes a long time, and a large amount of oxidative decomposition products of CMC are generated, making purification difficult. The hydrolysis reaction in an acidic aqueous solution can be carried out in a short time by heating and pressurizing. The molecular weight of CMC can be controlled by adjusting the reaction time, temperature, and pH. The reaction can also be stopped by cooling and neutralizing with an alkali to a pH of 7 or higher. Generally available acids and bases can be used.

[0034] The content of CMC or its salt is preferably 3% by mass or more, more preferably 5% by mass or more, based on the mass of CB. It is also preferably 50% by mass or less, more preferably 25% by mass or less, and even more preferably 15% by mass or less. By adjusting the content within the above range, CB can be maintained in a good and stable state without impairing the conductivity when used in a secondary battery electrode. Furthermore, from the viewpoints of coating processability and storage stability, a CMC with a higher molecular weight than the CMC used in the dispersion may be added. When a high-molecular-weight CMC is added, it is preferable to add it after producing the CB dispersion or at the end of the dispersion process. Adding it from the early stage of dispersion can result in problems such as an excessively high viscosity of the dispersion medium, which reduces the stirring efficiency, or a change in the adsorption equilibrium with respect to CB, which reduces the dispersibility.

[0035] <Dispersion medium> The dispersion medium is water, and may optionally contain a water-soluble solvent, such as alcohols such as ethanol, propanol, butanol, methyl cellosolve, butyl cellosolve, and propylene glycol monomethyl ether, and N-methyl-2-pyrrolidone (NMP).

[0036] <Carbon black dispersion> The carbon black dispersion of the present invention contains at least carbon black (CB), carbon monoxide (CMC) or a salt thereof, and water. The carbon black dispersion of the present invention may optionally contain additives such as dispersants, wetting agents, antifoaming agents, surfactants, pH adjusters, wetting and penetrating agents, antioxidants, preservatives, antifungal agents, and leveling agents, as well as water-soluble dispersion media, conductive materials other than carbon black, and polymeric components other than carbon monoxide (CMC), as long as they do not impair the objectives of the present invention. These additives may be added at any time, such as before, during, or after dispersion preparation. Polyacrylic acid is preferably used as the pH adjuster. Polyacrylic acid of any polymerization degree may be used, and it may also be used as a copolymer with any monomer. It may be produced by a commonly known synthesis method, or a commercially available product may be purchased and used.

[0037] The molecular weight of the polyacrylic acid used as the pH adjuster is not particularly limited, but the weight average molecular weight is preferably 5,000 to 100,000, and more preferably 10,000 to 50,000.

[0038] It is preferable to use polyacrylic acid as a pH adjuster that has not been neutralized. Neutralization of the carboxyl groups in polyacrylic acid causes counterion condensation, significantly increasing the viscosity of the aqueous solution. This increase in aqueous solution viscosity not only worsens the handleability of the carbon black dispersion, but also causes the water content during the electrode composition preparation process (described below) to remain, albeit in trace amounts, even after the drying process, potentially affecting the performance of the secondary battery.

[0039] The pH of the CB dispersion is preferably 7.0 to 10.5, and more preferably 9.0 to 10.5. If the pH is below this range, the CB dispersion is likely to gel. If the pH is above this range, problems such as corrosion of various raw materials and exterior materials in the battery or gelation of the binder are likely to occur. The pH can be measured using a common pH meter.

[0040] The dispersibility of CB in CB dispersions can be evaluated by measuring the complex modulus and phase angle using dynamic viscoelasticity measurements. The complex modulus indicates the hardness of the CB dispersion, and decreases with better CB dispersibility and lower viscosity. However, if the CB structure is large, the complex modulus may be high even when the CB is uniformly and stably dissolved in the medium due to the structural viscosity of the CB itself. Furthermore, the phase angle indicates the phase shift of the stress wave when the strain applied to the CB dispersion is a sine wave, i.e., the ease of flow of the dispersion. A purely elastic material will produce a sine wave in phase with the applied strain, resulting in a phase angle of 0°. On the other hand, a purely viscous material will produce a stress wave that is 90° ahead. Typical viscoelasticity measurement samples produce a sine wave with a phase angle greater than 0° but less than 90°. If the CB dispersion has good dispersibility, the phase angle approaches 90°, which is the phase angle for a purely viscous material. However, similar to the complex elastic modulus, if the conductive material itself has structural viscosity, the phase angle may be a low value even if the conductive material is dissolved uniformly and stably in the medium.

[0041] The complex modulus of the CB dispersion is preferably 50 Pa or less, more preferably less than 20 Pa, more preferably 10 Pa or less, and even more preferably 5 Pa or less. The complex modulus of the CB dispersion is preferably 0.01 Pa or more, more preferably 0.1 Pa or more, and even more preferably 0.5 Pa or more. The phase angle of the CB dispersion is preferably 5° or more, more preferably 10° or more, even more preferably 20° or more, and particularly preferably 30° or more. The phase angle of the CB dispersion is preferably 90° or less, more preferably 80° or less, and even more preferably 75° or less. The complex modulus and phase angle can be measured by the methods described in the examples.

[0042] The complex modulus and phase angle of a CB dispersion are determined by the dispersibility of CB in the CB dispersion, the entanglement of CB, CMC, and other resin components, and the influence of their intermolecular forces. Therefore, when the complex modulus X (Pa) and phase angle Y (°) are within the above-mentioned preferred ranges and the product (X × Y) is between 100 and 1,500, a CB dispersion with excellent dispersion stability can be obtained. Furthermore, an excellent conductive network can be formed, resulting in an electrode film with excellent conductivity. Furthermore, CMC with a weight-average molecular weight of 10,000 to 150,000 and a degree of etherification of 0.5 to 0.9 has low viscoelasticity by itself. However, when the product (X × Y) of the complex modulus X (Pa) and phase angle Y (°) is between 100 and 1,500, it can function as a thickener or binder in electrode compositions for secondary batteries, improving electrode strength and battery performance. Furthermore, a complex modulus of 50 Pa or less and a phase angle of 15° or more are more preferable. It is not enough for the CB dispersion to simply have low viscosity and good (apparent) dispersibility; it is particularly effective to judge the dispersion state by combining the complex modulus and phase angle with conventional indices such as viscosity.

[0043] The dispersibility of CB in a CB dispersion can also be evaluated by the median diameter (μm) determined using a laser diffraction / scattering particle size distribution analyzer. The median diameter (μm) determined using a laser diffraction / scattering particle size distribution analyzer can estimate the particle size of CB aggregate particles based on the scattered light intensity distribution by the particles. The median diameter (μm) is preferably 0.1 to 2.0, and more preferably 0.15 to 1.5. By setting the median diameter within the above range, a CB dispersion in an appropriate dispersion state can be obtained. If the median diameter exceeds the above range, aggregated CB will be present, and if the median diameter is below the above range, many finely cut CBs will be generated, which may make it difficult to form an efficient conductive network. The median diameter can be measured using the method described in the Examples.

[0044] The dispersibility of CB in a CB dispersion can also be evaluated by measuring the gloss (i.e., the intensity of reflected light at an angle of 60° relative to the incident angle) of a coating film obtained by coating a smooth glass substrate, baking, and drying. For example, 1 mL of the CB dispersion is dropped onto a smooth glass substrate, coated at 2 cm / sec using a No. 7 bar coater, baked in a hot air oven at 140°C for 10 minutes, and allowed to cool. The gloss at 60° can be measured using a gloss meter (BYK Gardner Micro Gross 60° gloss meter) at three randomly selected locations on the coating surface, excluding the edges, and the average value measured once is used to determine the gloss at 60°. The better the dispersibility of light incident on the coating film, the smoother the coating surface will be, resulting in a higher gloss. Conversely, the worse the dispersibility, the lower the gloss will be due to light scattering caused by the unevenness of the coating surface. The gloss at 60° can be measured using the method described in the Examples. A gloss of 5 or more is preferred, 50 or more is more preferred, 60 or more is even more preferred, and 70 or more is particularly preferred. Furthermore, it is preferably 120 or less, and more preferably 110 or less. By setting it within this range, a CB dispersion in an appropriately dispersed state can be obtained. If it is below this range, CBs in an aggregated state will exist, and if it is above this range, many CBs with small structures will be produced, making it difficult to form an efficient conductive network.

[0045] The TI value of a CB dispersion can be calculated by dividing the viscosity (mPa·s) at 60 rpm measured with a Brookfield viscometer by the viscosity (mPa·s) at 6 rpm. A TI value of 1.5 or greater and 5.0 or less is preferable. The higher the TI value, the greater the structural viscosity due to the entanglement of CB, CMC, and other resin components, or their intermolecular forces, and the lower the TI value, the smaller the structural viscosity. By keeping the TI value within the above range, it is possible to suppress the entanglement of CB, CMC, and other resin components while allowing these intermolecular forces to act appropriately.

[0046] <Distribution method> The CB dispersion of the present invention is preferably produced by, for example, dispersing CB, CMC or a salt thereof, and water using a dispersing device to finely disperse them. The dispersion treatment can be a multi-stage treatment of two or more steps by arbitrarily adjusting the timing of addition of the materials used.

[0047] Examples of dispersion devices include kneaders, two-roll mills, three-roll mills, planetary mixers, ball mills, horizontal sand mills, vertical sand mills, annular bead mills, attritors, high-shear mixers, high-pressure homogenizers, and ultrasonic homogenizers. From the viewpoint of promoting wetting of the CB and dissolving coarse particles, it is particularly preferable to use a high-shear mixer in the initial dispersion step, followed by a high-pressure homogenizer to disperse the CB while maintaining its structure length. The pressure when using a high-pressure homogenizer is preferably 60 to 150 MPa, more preferably 60 to 120 MPa.

[0048] Dispersion methods using a dispersing device include batch dispersion, pass dispersion, and circulation dispersion. Any of these methods may be used, or two or more methods may be combined. Batch dispersion is a method in which dispersion is performed using only the dispersing device itself, without using piping or the like. Because it is easy to handle, it is preferred for small-scale production. Pass dispersion is a dispersion method in which the dispersing device itself is equipped with a tank that supplies the dispersion liquid via piping and a tank that receives the dispersion liquid, and the dispersion passes through the dispersing device itself. Furthermore, circulation dispersion is a method in which the dispersion liquid that has passed through the dispersing device itself is returned to the tank that supplies the dispersion liquid and dispersed while circulating. In both methods, the longer the processing time, the more the dispersion progresses; therefore, the pass or circulation can be repeated until the desired dispersion state is achieved, and the processing volume can be increased by changing the tank size or processing time. Pass dispersion is preferred over circulation dispersion because it is easier to achieve a uniform dispersion state. Circulation dispersion is preferred over pass dispersion because the operation and manufacturing equipment are simpler. In the dispersion step, the disintegration of agglomerated particles, the loosening of CB, wetting, stabilization, etc. proceed sequentially or simultaneously, and the final dispersion state differs depending on how these steps proceed, so it is preferable to control the dispersion state in each dispersion step by using various evaluation methods. For example, it can be controlled by the methods described in the Examples.

[0049] <Composition for secondary battery electrodes> The composition for a secondary battery electrode of the present invention contains at least the CB dispersion liquid, and may contain a binder resin, and may further contain any optional components. The composition for a secondary battery electrode contains water, and may optionally contain the water-soluble solvent exemplified as the dispersion medium.

[0050] <Binder resin> When the secondary battery electrode composition further contains a binder resin, there are no particular limitations on the binder resin, as long as it is typically used as a binder resin in paints, and it can be appropriately selected depending on the purpose. Furthermore, the binder resin used in the secondary battery electrode composition is a resin that can bond between substances such as active materials, CB, and other conductive materials, and in this specification, it may be a CMC that differs in molecular weight, degree of etherification, etc. from the CMC contained in the CB dispersion of the present invention. Examples of binder resins used in secondary battery electrode compositions include polymers or copolymers containing ethylene, propylene, vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylic acid esters, methacrylic acid, methacrylic acid esters, acrylonitrile, styrene, vinyl butyral, vinyl acetal, and vinyl pyrrolidone as structural units; polyurethane resins, polyester resins, phenolic resins, epoxy resins, phenoxy resins, urea resins, melamine resins, alkyd resins, acrylic resins, formaldehyde resins, silicone resins, and fluororesins; cellulose resins; elastomers such as styrene-butadiene rubber and fluororubber; and conductive resins such as polyaniline and polyacetylene. Modified resins, mixtures, and copolymers of these resins are also acceptable. Among these, when used as a binder resin for a positive electrode, polymers or copolymers containing fluorine atoms in the molecule, such as polyvinylidene fluoride, polyvinyl fluoride, and tetrafluoroethylene, are preferred from the viewpoint of structural integrity. Furthermore, when used as a binder resin for the negative electrode, CMC with good adhesion (however, CMC with a different molecular weight, degree of etherification, etc. from the CMC contained in the CB dispersion of the present invention), styrene butadiene rubber, polyacrylic acid, etc. are preferred.

[0051] The content of the binder resin used in the composition for a secondary battery electrode is preferably 0.5 to 30 mass %, more preferably 0.5 to 25 mass %, of the nonvolatile content of the composition for a secondary battery electrode.

[0052] The secondary battery electrode composition may contain a positive electrode active material or a negative electrode active material. In this specification, the positive electrode active material and the negative electrode active material may be simply referred to as "active material." Active material refers to a material that is the basis of a battery reaction. Active materials are classified into positive electrode active materials and negative electrode active materials based on their electromotive force. In this specification, a secondary battery electrode composition containing a positive electrode active material or a negative electrode active material may be referred to as a "positive electrode composite composition," a "negative electrode composite composition," or simply a "composite composition," respectively. The composite composition is preferably in a slurry form to improve uniformity and processability. The composite composition contains at least the CB dispersion and an active material, or at least the CB dispersion, a binder resin, and an active material.

[0053] <Cathode active material> The positive electrode active material is not particularly limited. For example, for secondary battery applications, metal compounds such as metal oxides and metal sulfides that can reversibly dope or intercalate lithium ions can be used. For example, lithium manganese composite oxides (e.g., Li x Mn2O4 or LixMnO2), lithium nickel composite oxides (e.g., Li x NiO2), lithium cobalt composite oxide (Li x CoO2), lithium nickel cobalt composite oxide (e.g., Li x Ni 1-y Co y O2), lithium manganese cobalt composite oxide (e.g., Li x Mn y Co 1-y O2), lithium nickel manganese cobalt composite oxide (e.g., Li x Ni y Co z Mn 1-y-z O2), spinel-type lithium manganese nickel composite oxide (e.g., Li x Mn 2-y Ni y O4), lithium phosphate powder with an olivine structure (e.g., Li x FePO4, Li x Fe 1-y Mn yPO4, Li x such as CoPO4), manganese oxide, iron oxide, copper oxide, nickel oxide, vanadium oxides (e.g., V2O5, V6O 13 ), transition metal oxide powders such as titanium oxide, iron sulfate (Fe2(SO4)3), transition metal sulfide powders such as TiS2 and FeS, etc. However, x, y, and z are numbers, where 0 < x < 1, 0 < y < 1, 0 < z < 1, and 0 < y + z < 1. These cathode active materials can also be used alone or in combination of one or more.

[0054] <Anode active material> The anode active material is not particularly limited. For example, it can be metal Li capable of reversibly doping or intercalating lithium ions, or its alloy, tin alloy, silicon alloy anode, Li X TiO2, Li X Fe2O3, Li X Fe3O4, Li X Metal oxide systems such as WO2, conductive polymers such as polyacetylene and poly-p-phenylene, artificial graphite such as highly graphitized carbon materials, or carbonaceous powders such as natural graphite, and resin-fired carbon materials can be used. However, x is a number, where 0 < x < 1. These anode active materials can also be used alone or in combination of one or more. In particular, when using a silicon alloy anode, although the theoretical capacity is large, the volume expansion is extremely large. Therefore, it is preferably used in combination with artificial graphite such as highly graphitized carbon materials, or carbonaceous powders such as natural graphite, and resin-fired carbon materials, etc.

[0055] The content of CB in the composite composition is preferably 0.01% by mass or more, more preferably 0.02% by mass or more, and even more preferably 0.03% by mass or more, based on the mass of the active material (taking the mass of the active material as 100% by mass). Also, it is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less.

[0056] The content of the dispersant in the composite composition is preferably 0.01% by mass or more, more preferably 0.02% by mass or more, based on the mass of the active material (the mass of the active material being 100% by mass), and is preferably 10% by mass or less, more preferably 5% by mass or less.

[0057] When the composite composition contains a binder resin, the content of the binder resin in the composite composition is preferably 0.5% by mass or more, more preferably 0.5% by mass or more, based on the mass of the active material (the mass of the active material being 100% by mass), and is preferably 30% by mass or less, more preferably 25% by mass or less, and even more preferably 20% by mass or less.

[0058] The solid content of the composite composition is preferably 30% by mass or more, more preferably 40% by mass or more, based on the mass of the composite composition (the mass of the composite composition being 100% by mass), and is preferably 90% by mass or less, more preferably 80% by mass or less.

[0059] The composite composition can be prepared by various conventional methods. Examples include a method of adding an active material to a CB dispersion; a method of adding an active material to a CB dispersion and then adding a binder resin; and a method of adding a binder resin to a CB dispersion and then adding an active material. A preferred method of preparing the composite composition is to add a binder resin to the CB dispersion and then add and disperse the active material. The dispersion device used for dispersion is not particularly limited. The composite composition can be prepared using the dispersion means described above for the CB dispersion. Therefore, a composite composition may be prepared by adding and dispersing an electrode active material to a CB dispersion without adding a binder resin.

[0060] <Electrode film> The electrode film includes at least one selected from the group consisting of a film formed using the CB dispersion and a film formed using the composition for a secondary battery electrode. The electrode film may further include a current collector. The electrode film can be obtained, for example, by applying the composition for a secondary battery electrode onto a current collector and drying it, and includes a current collector and a film. An electrode film formed using a positive electrode mixture composition can be used as a positive electrode. An electrode film formed using a negative electrode mixture composition can be used as a negative electrode. In this specification, a film formed using a composition for a secondary battery electrode containing an active material may be referred to as an "electrode mixture layer."

[0061] The material and shape of the current collector used to form the electrode film are not particularly limited and can be appropriately selected from those suitable for various secondary batteries. Examples of current collector materials include conductive metals or alloys such as aluminum, copper, nickel, titanium, and stainless steel. While flat foils are generally used, current collectors with roughened surfaces, perforated foil current collectors, and mesh current collectors can also be used. The thickness of the current collector is preferably about 0.5 to 30 μm.

[0062] The method for applying the CB dispersion or the secondary battery electrode composition to the current collector is not particularly limited, and any known method can be used. Specific examples include die coating, dip coating, roll coating, doctor coating, knife coating, spray coating, gravure coating, screen printing, and electrostatic painting. Drying methods include, but are not limited to, leaving the coating to dry or drying using a blower dryer, warm air dryer, infrared heater, far-infrared heater, or the like.

[0063] After coating, the coating may be rolled using a lithographic press, a calender roll, etc. The thickness of the formed film is, for example, from 1 μm to 500 μm, and preferably from 10 μm to 300 μm.

[0064] A film formed using the CB dispersion or the composition for a secondary battery electrode can also be used as a base layer for the electrode mixture layer in order to improve the adhesion between the electrode mixture layer and a current collector or to improve the conductivity of the electrode film.

[0065] <Secondary battery> The secondary battery includes a positive electrode, a negative electrode, and an electrolyte, and at least one selected from the group consisting of the positive electrode and the negative electrode includes the electrode film.

[0066] Various conventionally known electrolytes capable of ion mobility can be used. Examples include, but are not limited to, lithium salts such as LiBF, LiClO, LiPF, LiAsF, LiSbF, LiCFSO, Li(CFSO)N, LiCFSO, Li(CFSO)C, LiI, LiBr, LiCl, LiAlCl, LiHF, LiSCN, or LiBPh (where Ph is a phenyl group). The electrolyte is preferably dissolved in a non-aqueous solvent and used as an electrolytic solution.

[0067] The non-aqueous solvent is not particularly limited, but examples thereof include carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate; lactones such as γ-butyrolactone, γ-valerolactone, and γ-octanoic lactone; glymes such as tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,2-methoxyethane, 1,2-ethoxyethane, and 1,2-dibutoxyethane; esters such as methyl formate, methyl acetate, and methyl propionate; sulfoxides such as dimethyl sulfoxide and sulfolane; and nitriles such as acetonitrile. These solvents may be used alone or in combination.

[0068] The non-aqueous electrolyte secondary battery preferably includes a separator, such as, but not limited to, polyethylene nonwoven fabric, polypropylene nonwoven fabric, polyamide nonwoven fabric, and nonwoven fabrics obtained by subjecting these to hydrophilic treatment.

[0069] The structure of the nonaqueous electrolyte secondary battery of the present embodiment is not particularly limited, but typically includes a positive electrode, a negative electrode, and a separator that is provided as needed, and can be in various shapes depending on the purpose of use, such as a paper type, a cylindrical type, a button type, or a laminated type. [Example]

[0070] The present invention will be described in more detail below with reference to examples. The present invention is not limited to the following examples as long as it does not depart from the gist of the invention. Unless otherwise specified, "parts" means "parts by mass" and "%" means "% by mass".

[0071] (Method for measuring weight average molecular weight (Mw)) The weight-average molecular weight (Mw) of the produced carboxymethylcellulose sodium salt was measured by gel permeation chromatography (GPC) equipped with an RI detector under the following conditions. The molecular weight is a pullulan-equivalent value. Measurement sample: 0.1% by mass aqueous solution Device: HLC-8320GPC (Tosoh) Eluent: 0.1M NaCl aqueous solution Column: TSKgel SuperMultiporePW-M (Tosoh) Flow rate: 1.0mL / min Temperature: 25℃ Injection volume: 100μl

[0072] (Method for measuring the degree of etherification) 0.6 g of carboxymethylcellulose sodium salt was dried at 105°C for 4 hours. The mass of the dried product was accurately weighed, then wrapped in filter paper and incinerated in a porcelain crucible. The incinerated product was transferred to a 500 ml beaker, and 250 ml of water and 35 ml of 0.05 mol / l aqueous sulfuric acid solution were added and boiled for 30 minutes. After cooling, the excess acid was back-titrated with a 0.1 mol / l aqueous potassium hydroxide solution. Phenolphthalein was used as an indicator. The degree of etherification was calculated using the measurement results according to the following formula (1). (Degree of etherification) = 162 × A / (10000-80A) (Equation 1) A = (af-bf1) / weight of dry matter (g) A: The amount (ml) of 0.05 mol / l sulfuric acid solution consumed by the combined alkali in 1 g of sample a: Amount (ml) of 0.05 mol / l sulfuric acid solution used f: Potency of 0.05 mol / l sulfuric acid aqueous solution b: Titration volume (ml) of 0.1 mol / L potassium hydroxide solution f1: Potency of 0.1 mol / L potassium hydroxide solution

[0073] (Preparation of Carboxymethylcellulose Sodium Salt) (Production Example 1) 10 parts by mass of low-density pulp pulverized in a household mixer was placed in the tank of a planetary mixer (Hibis Dispermix 3D-2, manufactured by Primix). Next, 90 parts by mass of a 15% by mass sodium hydroxide / IPA / aqueous solution (IPA:water mass ratio 80:20) was added to the tank and stirred at 40 °C for 150 minutes to carry out a mercerization reaction, obtaining alkali cellulose. Next, 10 parts by mass of monochloroacetic acid was dissolved in 6 parts by mass of the above IPA / aqueous solution, adjusted to 25 °C, and the alkali cellulose was added over 60 minutes while maintaining the temperature at 35 °C. The temperature was then raised to 80 °C over 30 minutes, and an etherification reaction was carried out at 80 °C for 50 minutes. Subsequently, the mixture was neutralized with 50% by mass of acetic acid to a pH of 7.0.

[0074] The solid component of the neutralized product was separated using a Buchner funnel and then washed on the Buchner funnel with a 70% by mass aqueous methanol solution to remove the by-products sodium chloride, sodium glycolate, and sodium acetate. The product was transferred to a stainless steel square tray, dried in a hot air oven at 90°C for 4 hours, and pulverized to obtain carboxymethylcellulose sodium salt (CMC1). The weight-average molecular weight and degree of etherification of the obtained carboxymethylcellulose sodium salt are shown in Table 1.

[0075] (Manufacturing Examples 2 and 3) Carboxymethyl cellulose sodium salts (CMC2, CMC3) were obtained in the same manner as in Production Example 1, except that the reaction times in the mercerization step and the etherification step were changed to the times shown in Table 1. The weight average molecular weights and degrees of etherification of the obtained carboxymethyl cellulose sodium salts were as shown in Table 1.

[0076] [Table 1]

[0077] (CB specific surface area measurement method) 0.1 g of CB was weighed using an electronic balance (Sartorius, MSA225S100DI) and then dried at 110°C for 15 minutes while degassing. Thereafter, the specific surface area (m ) of the CB was measured using a fully automatic specific surface area measuring device (MOUNTECH, HM-model 1208). 2 / g) was measured.

[0078] (Method for measuring the average primary particle size of CB) Approximately 1 / 4 of a spatula of CB was collected, attached to the surface of a sample holder substrate with carbon tape, and observed using an SEM. Multiple photographs were taken so that multiple CB particles were included in the field of view, and the particle diameters of 100 randomly selected CB particles were measured. The average value was taken as the average primary particle diameter (nm) of CB.

[0079] (Method for measuring dispersed particle size) The dispersed particle size was determined using a grind gauge with a maximum groove depth of 300 μm, according to the determination method in accordance with JIS K5600-2-5.

[0080] (Gloss measurement method) The sample for gloss measurement was prepared by dropping 1 mL of the CB dispersion onto a smooth glass substrate, coating it with a No. 7 bar coater at 2 cm / sec, baking it in a hot air oven at 140°C for 10 minutes, and allowing it to cool. The coating area was approximately 10 cm x 10 cm. Using a gloss meter (BYK Gardner micro gloss 60° gloss meter), three locations on the coating surface, excluding the edges, were randomly selected, and measurements were taken once each, with the average value taken as the gloss at 60°.

[0081] (Method for measuring the median particle size of CB dispersion liquid) The median diameter was measured using a particle size distribution analyzer (Partical LA-960V2, manufactured by HORIBA). The circulation / ultrasonic operating conditions were: circulation speed: 3, ultrasonic intensity: 7, ultrasonic time: 1 minute, stirring speed: 1, and stirring mode: continuous. During air removal, ultrasonic operation was performed with an ultrasonic intensity of 7 and an ultrasonic time of 5 seconds. The refractive index of water was 1.333, and the refractive index of the carbon material was 1.92. Measurements were performed after diluting the measurement sample so that the transmittance of the red laser diode was 60-80%, and the particle size was measured by volume.

[0082] (Method for measuring viscosity of CB dispersion) The viscosity of the CB dispersion was measured using a Brookfield viscometer (Toki Sangyo "BL") at 25°C. After thoroughly stirring the dispersion with a spatula, the measurement was immediately performed at a rotor speed of 6 rpm, followed by another measurement at 60 rpm. The lower the viscosity, the better the dispersibility, and the higher the viscosity, the worse the dispersibility. Dispersions that showed clear separation or sedimentation were considered to have poor dispersibility. The TI value was calculated by dividing the viscosity (mPa·s) at 60 rpm by the viscosity (mPa·s) at 6 rpm. A CB dispersion with a viscosity of less than 500 mPa·s was considered excellent; between 500 and 2,000 mPa·s, good; between 2,000 and 10,000 mPa·s, poor; and a viscosity of 10,000 mPa·s or greater, indicating very poor sedimentation or separation.

[0083] (Measurement of complex modulus and phase angle of CB dispersion) The complex modulus X and phase angle Y of the CB dispersion were evaluated by dynamic viscoelasticity measurements using a rheometer (RheoStress1 rotational rheometer, Thermo Fisher Scientific) with a 35 mm diameter, 2° cone angle, at 25°C, a frequency of 1 Hz, and a strain rate range of 0.01% to 5%. The smaller the complex modulus, the better the dispersibility; the larger the complex modulus, the worse the dispersibility. The larger the phase angle, the better the dispersibility; the smaller the phase angle, the worse the dispersibility. The product (X × Y) of the complex modulus X (Pa) and the phase angle Y (°) was calculated. The complex modulus X of the CB dispersion was considered best when it was between 0.5 and 10 Pa, excellent when it was between 10 Pa and 15 Pa·s, good when it was between 15 Pa and 20 Pa, fair when it was between 20 Pa and 50 Pa, and poor when it was above 50 Pa. The phase angle Y of the CB dispersion is best when it is 35° or more and 75° or less, excellent when it is 25° or more and less than 35°, good when it is 15° or more and less than 25°, fair when it is 10° or more and less than 15°, and poor when it is less than 10°.

[0084] (Method for measuring pH of CB dispersion) The pH of the CB dispersion was measured at 25°C using a benchtop pH meter (Seven Compact S220 Expert Pro, Mettler-Toledo).

[0085] (Method for evaluating the stability of CB dispersion) The storage stability was evaluated by measuring the viscosity of the dispersion after storing it at 50° C. for 7 days in the same manner as for the initial viscosity. Judgment criteria ◎:Equivalent to initial condition (excellent) ○: Viscosity changed slightly (good) △: Viscosity has increased but gelation has not occurred (acceptable) ×: Gelled or solids settled (poor)

[0086] (Preparation of CB dispersion) (Example 1-A1) 93.7 parts by mass of ion-exchanged water was added to a stainless steel container, and while stirring with a disperser, 1.5 parts by mass of APP-84 (CMC) was added and dissolved. Next, 8.0 parts by mass of LITX200 (CB) was added while stirring with a disperser. A high-shear mixer (L5M-A, Silverson) equipped with a square-hole high-shear screen was used for batch dispersion at 8,600 rpm until the mixture was uniform and the dispersion particle size measured with a grind gauge was 200 μm or less. At this time, the dispersion particle size measured with a grind gauge was 150 μm. The dispersion liquid was then fed from the stainless steel container via piping to a high-pressure homogenizer (Starburst Lab HJP-17007, Sugino Machine) for circulation dispersion. Dispersion was performed using a single nozzle chamber with a nozzle diameter of 0.25 mm and a pressure of 100 MPa. The dispersion liquid was dispersed until the viscosity at 60 rpm, measured using a Brookfield viscometer (TOKI SANGYO, VISCOMETER, MODEL: BL), reached 3,000 mPa·s or less. Then, while stirring with a disperser, 1.0 parts by mass of LITX200 was added to the stainless steel container, and a circulation dispersion process was again performed using a high-pressure homogenizer. After circulation dispersion using the high-pressure homogenizer until the viscosity reached 3,000 mPa·s or less, LITX200 was added to the stainless steel container while stirring with a disperser. This process was repeated a total of seven times (a total amount of LITX200 added was 15.0 parts by mass). Subsequently, five passes of dispersion were performed using the high-pressure homogenizer, yielding a CB dispersion containing 15.0 parts by mass of CB (CB dispersion A1).

[0087] (Examples 1-A2 and 1-A3) CB dispersions (CB dispersions A2 and A3) were obtained in the same manner as in Example 1-A1, except that the number of pass-type dispersions was changed to 10 and 20, respectively.

[0088] (Examples 1-A4 to 1-A13, 1-A15 to 1A18) Except for changing the materials, composition ratios, and number of pass-type dispersions shown in Table 3, CB dispersions (CB dispersions A4 to A13, A15 to A18) were obtained in the same manner as in Example 1-1A.

[0089] (Example 1-A14) The CB dispersion obtained in Example 1-A11 (CB dispersion A11) was placed in a stainless steel container, and while stirring with a disperser, 0.004 parts by mass of PAA was added to obtain a CB dispersion containing 15.0 parts by mass of CB (CB dispersion A14). The pH of CB dispersion A12 was 7.15.

[0090] (Example 1-A19) The CB dispersion liquid (CB dispersion liquid A3) obtained in Example 1-A3 was placed in a stainless steel container, diluted with ion-exchanged water to a CB concentration of 10.0 parts by mass, and stirred with a disperser for 10 minutes to obtain a CB dispersion liquid (CB dispersion liquid A19).

[0091] (Example 1-A20) The CB dispersion obtained in Example 1-A13 (CB dispersion A13) was placed in a stainless steel container, diluted with ion-exchanged water to a CB concentration of 6.0 parts by mass, and stirred for 10 minutes with a disper to obtain a CB dispersion (CB dispersion A20).

[0092] (Comparative examples 1-a1~1-a2, 1-a5~1-a8) CB dispersions (CB dispersions a1 to a2, a5 to a8) were obtained in the same manner as in Example 1-1A, except that the materials, composition ratios, and number of pass-type dispersions were changed as shown in Table 4.

[0093] (Comparative example 1-a3) A dispersion study of a CB dispersion (CB dispersion a3) was carried out in the same manner as in Example 1-1A, except that 15.0 parts by mass of CB was added from the beginning and no additional addition (circulation dispersion) was performed. However, during the first pass dispersion, the liquid significantly increased in viscosity and lost its fluidity, making it impossible to send the liquid to the high-pressure homogenizer, and a dispersion could not be produced.

[0094] (Comparative example 1-a4) A CB dispersion (CB dispersion a4) was obtained in the same manner as in Example 1-1A, except that the CB concentration at the start of the circulation dispersion was changed to 3.0 parts by mass, and the materials, composition ratio, and number of pass-type dispersions were changed as shown in Table 4.

[0095] (Comparative example 1-a9) A dispersion study of a CB dispersion (CB dispersion a9) was carried out in the same manner as in Example 1-1A, except that the materials and composition ratios were changed as shown in Table 4. However, because the viscosity of the dispersion during circulation dispersion was high and the fluidity was poor, even when additional CB was added, it did not mix with the dispersion, and a CB dispersion (CB dispersion a9) could not be produced.

[0096] (Comparative Example 1-b1) A glass bottle (M-140, manufactured by Kashiwa Glass Co., Ltd.) was charged with 15 parts by mass of LITX200 (CB), 1.5 parts by mass of APP-84 (CMC), 83.5 parts by mass of ion-exchanged water, and 140 parts by mass of zirconia beads (bead diameter 1.0 mmφ), and the mixture was subjected to a dispersion treatment for 6 hours using a paint conditioner manufactured by Red Devil. The zirconia beads were then separated to obtain a CB dispersion (CB dispersion b1).

[0097] (Comparative example 1-b2) A CB dispersion (CB dispersion b2) was obtained in the same manner as in Comparative Example 1-b1, except that the composition ratio was changed as shown in Table 4.

[0098] LITX200: Furnace black (manufactured by Cabot, average primary particle diameter 22 nm, specific surface area 150 m 2 / g) LITX300: Furnace black (manufactured by Cabot, average primary particle diameter 23 nm, specific surface area 140 m 2 / g) 3230B: Furnace black (Mitsubishi Carbon Black, average primary particle diameter 23 nm, specific surface area 220 m 2 / g) EC-300J: Ketjenblack (manufactured by Lion Specialty Chemicals, average primary particle diameter 40 nm, specific surface area 800 m 2 / g) HS-100: Denka Black HS-100 (manufactured by Denka, acetylene black, average primary particle diameter 48 nm, specific surface area 39 m 2 / g) FX-35: Denka Black FX-35 (manufactured by Denka, acetylene black, average primary particle diameter 23 nm, specific surface area 133 m 2 / g) APP-84: Carboxymethylcellulose sodium salt, Nippon Paper Industries Co., Ltd., Sunrose A APP-84 F01MC: Carboxymethylcellulose sodium salt, Nippon Paper Industries Co., Ltd., Sunrose F F01MC A02SH: Carboxymethylcellulose sodium salt, Nippon Paper Industries Co., Ltd., Sunrose A A02SH F10MC: Carboxymethylcellulose sodium salt, Nippon Paper Industries Co., Ltd., Sunrose F F10MC F30MC: Carboxymethylcellulose sodium salt, Nippon Paper Industries Co., Ltd., Sunrose F F30MC MAC500LC: Carboxymethylcellulose sodium salt, Nippon Paper Industries, Sunrose special type MAC500LC Cellogen 5A: Carboxymethylcellulose sodium salt, manufactured by Daiichi Kogyo Seiyaku Cellogen 6A: Carboxymethylcellulose sodium salt, manufactured by Daiichi Kogyo Seiyaku PAA: Polyacrylic acid, manufactured by Wako Pure Chemical Industries, average molecular weight 25,000

[0099] The weight-average molecular weight and degree of etherification of the carboxymethyl cellulose or its salt used in the Examples and Comparative Examples are shown in Table 2. The weight-average molecular weight and degree of etherification were calculated using the same measurement methods as in the Production Examples.

[0100] [Table 2]

[0101] [Table 3]

[0102] [Table 4]

[0103] (Preparation of negative electrode mixture composition and negative electrode) (Example 2-A1) Capacity 150cm 3 The CB dispersion (CB dispersion A1), MAC500LC (CMC), and water were added to the plastic container and stirred at 2,000 rpm for 30 seconds using a centrifugal mixer (Thinky's Awatori Rentaro, ARE-310). Then, artificial graphite and silicon were added as negative electrode active materials, and the mixture was stirred at 2,000 rpm for 150 seconds using the centrifugal mixer. SBR was then added, and the mixture was stirred at 2,000 rpm for 30 seconds using the centrifugal mixer to obtain a negative electrode composite composition. The nonvolatile content of the negative electrode composite composition was 48% by mass. The nonvolatile content ratio of artificial graphite:silicon:CB:CMC (MAC500LC):SBR in the nonvolatile content of the negative electrode composite composition was 87:10:0.5:1:1.5.

[0104] The obtained negative electrode composite composition was applied to a copper foil having a thickness of 20 μm using an applicator, and the coating was dried in an electric oven at 120°C ± 5°C for 25 minutes to prepare an electrode film. The electrode film was then rolled using a roll press (Thank Metal, 3 ton hydraulic roll press) to obtain a negative electrode (negative electrode A1). The weight per unit area of ​​the composite layer was 10 mg / cm. 2 The density of the composite layer after the rolling treatment was 1.6 g / cc.

[0105] Silicon: Silicon monoxide (Osaka Titanium Technology Co., Ltd., SILICON MONOOXIDE SiO 1.3C 5μm, non-volatile content 100%) Artificial graphite: CGB-20 (Nippon Graphite Industries, 100% non-volatile content) MAC500LC: Carboxymethylcellulose sodium salt, Sunrose special type MAC500LC (Nippon Paper Industries, non-volatile content 100%) SBR: Styrene butadiene rubber TRD2001 (JSR, non-volatile content 48%)

[0106] (Examples 2-A2 to 2-A20, Comparative Examples 2-a1 to 2-a8, 2-b1 to 2-b2) Negative electrodes A2 to A20, a1 to a8, and b1 to b2 were obtained in the same manner as in Example 2-A1, except that the CB dispersion was changed to each of the CB dispersions shown in Table 5 (CB dispersions A2 to A20, a1 to a8, a1 to a8, and b1 to b2).

[0107] (Method for evaluating the conductivity of the negative electrode) The surface resistivity (Ω / □) of the composite layer of the obtained negative electrode was measured using a Mitsubishi Chemical Analytech Loresta GP MCP-T610. After measurement, the surface resistivity was multiplied by the thickness of the composite layer to obtain the volume resistivity (Ω·cm) of the negative electrode. The thickness of the composite layer was measured at three points in the electrode using a film thickness meter (NIKON DIGIMICRO MH-15M), and the copper foil film thickness was subtracted from the average value to obtain the volume resistivity (Ω·cm) of the negative electrode. Judgment criteria ◎: Less than 0.3Ω·cm (excellent) ○: 0.3Ω·cm or more and less than 0.5Ω·cm (good) ×: 0.5Ω·cm or more (defective)

[0108] (Method for evaluating adhesion of negative electrode) The resulting negative electrode was cut into two 90mm x 20mm rectangles with the coating direction as the long axis. Peel strength was measured using a desktop tensile tester (Strograph E3, manufactured by Toyo Seiki Seisakusho) using a 180° peel test method. Specifically, a 100mm x 30mm double-sided tape (No. 5000NS, manufactured by Nitoms) was attached to a stainless steel plate, and the composite layer side of the fabricated negative electrode was attached to the other side of the double-sided tape to form a test sample. Next, the test sample was fixed vertically with the short sides of the rectangle facing up and down. The copper foil was peeled off by pulling the ends from bottom to top at a constant speed (50mm / min). The average stress value during this process was recorded as the peel strength. Judgment criteria ◎: 0.25N / cm or more (excellent) ○: 0.1N / cm or more and less than 0.25N / cm (good) ×: Less than 0.1N / cm (poor)

[0109] [Table 5]

[0110] All of the negative electrodes using the CB dispersion of the present invention had good conductivity and adhesion. This is thought to be because the dispersant was able to act effectively by satisfying the constituent requirements of the present invention.

[0111] (Preparation of Positive Electrode Mixture Composition and Positive Electrode) (Example 3-A1) Capacity 150cm 3 The CB dispersion (CB dispersion A1), MAC500LC, and water were added to the plastic container and stirred at 2,000 rpm for 30 seconds using a planetary centrifugal mixer (Thinky's Awatori Rentaro, ARE-310). LFP was then added as the positive electrode active material, and the mixture was stirred at 2,000 rpm for 150 seconds using a planetary centrifugal mixer (Thinky's Awatori Rentaro, ARE-310). PTFE was then added, and the mixture was stirred at 2,000 rpm for 30 seconds using a planetary centrifugal mixer (Thinky's Awatori Rentaro, ARE-310) to obtain a positive electrode composite composition. The nonvolatile content of the positive electrode composite composition was 75% by mass. The nonvolatile content ratio of LFP:conductive material:PTFE:MAC500LC in the nonvolatile content of the positive electrode composite composition was 97:0.5:1:1.5.

[0112] The positive electrode composite composition was applied to a 20 μm thick aluminum foil using an applicator, and then dried in an electric oven at 120°C ± 5°C for 25 minutes to prepare an electrode film. The electrode film was then rolled using a roll press (Thank Metal, 3 ton hydraulic roll press) to obtain a positive electrode (positive electrode 1). The weight per unit area of ​​the composite layer was 20 mg / cm. 2 The density of the composite layer after the rolling treatment was 2.1 g / cc.

[0113] LFP: Lithium iron phosphate HED (trademark) LFP-400 (BASF, 100% non-volatile content) PTFE: Polytetrafluoroethylene Polyflon PTFE D-210C (manufactured by Daikin, non-volatile content 60%) MAC500LC: Carboxymethylcellulose sodium salt, Sunrose special type MAC500LC (Nippon Paper Industries, non-volatile content 100%)

[0114] (Examples 3-A2 to 3-A20, Comparative Examples 3-a1 to 3-a8, 3-b1 to 3-b2) Positive electrodes A2 to A20, positive electrodes a1 to a8, and positive electrodes b1 to b2 were obtained in the same manner as in Example 3-A1, except that the CB dispersion was changed to each of the CB dispersions shown in Table 6 (CB dispersions A2 to A20, CB dispersions a1 to a8, dispersions a1 to a8, and CB dispersions b1 to b2).

[0115] (Method for evaluating the conductivity of the positive electrode) The conductivity of the obtained positive electrode was evaluated in the same manner as for the negative electrode, except that aluminum foil was used instead of copper foil. Judgment criteria ◎: Less than 10Ω·cm (excellent) ○: 10Ω·cm or more and less than 20Ω·cm (good) ×: 20Ω·cm or more (defective)

[0116] (Method for evaluating adhesion of positive electrode) The adhesion of the obtained positive electrode was evaluated in the same manner as for the negative electrode, except that aluminum foil was used instead of copper foil. Judgment criteria ◎: 0.5N / cm or more (excellent) ○: 0.3N / cm or more and less than 0.5N / cm (good) ×: Less than 0.3N / cm (poor)

[0117] [Table 6]

[0118] All of the positive electrodes using the CB dispersion of the present invention had good conductivity and adhesion. As with the negative electrodes, this is thought to be because the dispersant was able to function effectively by satisfying the constituent requirements of the present invention.

[0119] (Preparation of standard positive electrode) As a positive electrode active material, 92 parts by mass of LFP (HED™ LFP-400, manufactured by BASF, 100% non-volatile content), 4 parts by mass of acetylene black (Denka Black™ HS-100, manufactured by Denka, 100% non-volatile content), and 1.6 parts by mass of MAC500LC (carboxymethylcellulose sodium salt, Sunrose Special Type MAC500L, manufactured by Nippon Paper Industries, 100% non-volatile content) were added to a 150 ml plastic container and mixed with a spatula until the powder was uniform. Then, 25 parts by mass of water was added, and the mixture was stirred at 2,000 rpm for 30 seconds using a planetary centrifugal mixer (Thinky Awatori Rentaro, ARE-310). The mixture in the plastic container was then mixed with a spatula until uniform, and 4 parts by mass of PTFE (manufactured by Daikin, 60% non-volatile content) was added using the planetary centrifugal mixer and stirred at 2,000 rpm for 30 seconds. After that, 11.2 parts by mass of water was added, and the mixture was stirred at 2,000 rpm for 30 seconds using the planetary centrifugal mixer. Finally, the mixture was stirred at 3,000 rpm for 10 minutes using a high-speed mixer to obtain a standard positive electrode composite composition. The nonvolatile content of the standard positive electrode composite composition was 79% by mass.

[0120] The standard positive electrode composite composition was applied to a 20 μm thick aluminum foil current collector using an applicator, and then dried in an electric oven at 120°C ± 5°C for 25 minutes to obtain a coating weight per unit area of ​​the electrode of 20 mg / cm. 2 Further, a rolling treatment was carried out using a roll press (Thank Metal, 3 ton hydraulic roll press) to adjust the density of the composite layer to 2.1 g / cm. 3 A standard positive electrode was fabricated.

[0121] (Preparation of standard negative electrode) A 150 ml plastic container was charged with 0.5 parts by weight of acetylene black (Denka Black® HS-100, manufactured by Denka), 1 part by weight of MAC500LC (carboxymethylcellulose sodium salt, Sunrose Special Type MAC500L, manufactured by Nippon Paper Industries Co., Ltd., 100% nonvolatile content), and 98.4 parts by weight of water, and then stirred at 2,000 rpm for 30 seconds using a planetary centrifugal mixer (Thinky's Awatori Rentaro, ARE-310). Furthermore, 87 parts by weight of artificial graphite (CGB-20, manufactured by Nippon Graphite Industries Co., Ltd.) and 10 parts by weight of silicon were added as active materials, and the mixture was stirred at 2,000 rpm for 150 seconds using a planetary centrifugal mixer (Thinky's Awatori Rentaro, ARE-310). Next, 3.1 parts by mass of SBR (TRD2001, manufactured by JSR) was added, and the mixture was stirred at 2,000 rpm for 30 seconds using a planetary centrifugal mixer (Thinky's Awatori Rentaro, ARE-310) to obtain a standard negative electrode composite composition with a non-volatile content of 50% by mass.

[0122] The standard negative electrode composite composition was applied to a 20 μm thick copper foil current collector using an applicator, and then dried in an electric oven at 80°C ± 5°C for 25 minutes to obtain an electrode with a coating weight per unit area of ​​10 mg / cm. 2 Further, a rolling process was carried out using a roll press (Thank Metal, 3 ton hydraulic roll press) to adjust the density of the composite layer to 1.6 g / cm. 3 A standard negative electrode was fabricated.

[0123] (Examples 4-A1 to 4-A20, Comparative Examples 4-a1 to 4-a8, 4-b1 to 4-b2) (Examples 5-A1 to 5-A20, Comparative Examples 5-a1 to 5-a8, 5-b1 to 5-b2) (Secondary battery production) The negative and positive electrodes listed in Tables 7 and 8 were punched out to 50 mm x 45 mm and 45 mm x 40 mm, respectively, and the separator (porous polypropylene film) inserted between them was inserted into an aluminum laminate bag and dried in an electric oven at 70 °C for 1 hour. Then, in a glove box filled with argon gas, 2 mL of electrolyte (a nonaqueous electrolyte prepared by mixing ethylene carbonate, dimethyl carbonate, and diethyl carbonate in a volume ratio of 1:1:1, adding 1 part by mass of vinylene carbonate per 100 parts by mass as an additive, and dissolving LiPF6 at a concentration of 1 M) was poured into the bag, and the aluminum laminate was sealed to prepare secondary batteries.

[0124] (Method for evaluating rate characteristics of secondary batteries) The resulting secondary battery was placed in a thermostatic chamber at 25°C and subjected to charge / discharge measurements using a charge / discharge device (Hokuto Denko, SM-8). The battery was charged at a constant current / constant voltage of 10 mA (0.2 C) with a charge cutoff voltage of 4.3 V (cutoff current: 1 mA (0.02 C)), followed by a constant current discharge at a discharge current of 10 mA (0.2 C) with a charge cutoff voltage of 4.3 V (cutoff current: 1 mA 0.02 C). This procedure was repeated three times, followed by a constant current / constant voltage charge at a charge current of 10 mA (0.2 C) with a charge cutoff voltage of 4.3 V (cutoff current: 1 mA 0.02 C). The battery was then discharged at constant currents of 0.2 C and 3 C until the discharge cutoff voltage reached 3.0 V, and the discharge capacities were calculated. The rate characteristics can be expressed as the ratio of the 0.2 C discharge capacity to the 3 C discharge capacity, using the following formula: (Formula 1) Rate characteristic = 3C discharge capacity / 3rd 0.2C discharge capacity × 100 (%) Judgment criteria ◎: 80% or more (excellent) ○: 60% or more but less than 80% (good) ×: Less than 60% (defective)

[0125] (Method for evaluating cycle characteristics of secondary batteries) The resulting secondary battery was placed in a thermostatic chamber at 25°C and subjected to charge / discharge measurements using a charge / discharge device (Hokuto Denko, SM-8). Constant-current, constant-voltage charging (cutoff current 2.5 mA (0.05 C)) was performed at a charge current of 25 mA (0.5 C) with a charge cutoff voltage of 4.3 V, followed by constant-current discharging at a discharge current of 25 mA (0.5 C) with a discharge cutoff voltage of 3 V. This procedure was repeated 200 times. The cycle characteristics can be expressed as the ratio of the 3rd 0.5 C discharge capacity to the 200th 0.5 C discharge capacity at 25°C, using the following formula: (Formula 2) Cycle characteristics = 3rd 0.5C discharge capacity / 200th 0.5C discharge capacity × 100 (%) Judgment criteria ◎: 85% or more (excellent) ○: 80% or more but less than 85% (good) ×: Less than 80% (poor)

[0126] [Table 7]

[0127] [Table 8]

[0128] In the above examples using the dispersion of the present invention, nonaqueous electrolyte secondary batteries having superior cycle characteristics compared to the comparative examples were obtained. Therefore, it is clear that the present invention can provide a nonaqueous electrolyte secondary battery having cycle characteristics that are difficult to achieve with conventional CB dispersions.

Claims

1. A carbon black dispersion containing carbon black, carboxymethyl cellulose or a salt thereof, and water, The carboxymethyl cellulose or its salt has a weight average molecular weight of 10,000 to 100,000 and a degree of etherification of 0.5 to 0.9, the content of the carboxymethyl cellulose or a salt thereof is 3% by mass or more and 50% by mass or less based on the mass of the carbon black, the product (X×Y) of the complex modulus X (Pa) and the phase angle Y (°), as measured in dynamic viscoelasticity of the carbon black dispersion at 25°C, a frequency of 1 Hz, and a strain rate in the range of 0.01% to 5%, is 100 or more and 1,500 or less; Carbon black dispersion.

2. The BET specific surface area of ​​the carbon black is 30 to 1500 m 2 2. The carbon black dispersion of claim 1, wherein the carbon black dispersion has a molecular weight of 1000 or more.

3. 3. The carbon black dispersion according to claim 1, wherein the pH is from 7.0 to 10.

5.

4. 4. The carbon black dispersion according to claim 1, wherein the carbon black dispersion has a complex modulus of 50 Pa or less and a phase angle of 10° or more.

5. The carbon black dispersion according to claim 1 , further comprising polyacrylic acid.

6. The carbon black dispersion according to any one of claims 1 to 5, wherein the median diameter is 0.1 µm or more and 2.0 µm or less.

7. 7. The carbon black dispersion according to claim 1, wherein the dispersion has a TI value of 1.5 to 5.

0.

8. 8. The carbon black dispersion according to claim 1, wherein a coating of the carbon black dispersion has a gloss measured at 60° of 5 to 120.

9. A composition for a secondary battery electrode, comprising the carbon black dispersion according to any one of claims 1 to 8.

10. An electrode film comprising a coating film of the composition for a secondary battery electrode according to claim 9.

11. A secondary battery comprising the electrode film according to claim 10.

12. A method for producing a carbon black dispersion containing carbon black, carboxymethyl cellulose or a salt thereof, and water, comprising: the carbon black dispersion is dispersed using a high-pressure homogenizer so that the product (X × Y) of the complex modulus X (Pa) and the phase angle Y (°), as measured at 25°C, a frequency of 1 Hz, and a strain rate in the range of 0.01% to 5%, is 100 or more and 1,500 or less; The carboxymethyl cellulose or its salt has a weight average molecular weight of 10,000 to 100,000 and a degree of etherification of 0.5 to 0.9, the content of the carboxymethyl cellulose or a salt thereof is 3% by mass or more and 50% by mass or less based on the mass of the carbon black; Method for producing carbon black dispersion.

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