Carbon black dispersion composition for storage battery, mixed paste for forming positive electrode, positive electrode for forming lithium ion secondary battery, and lithium ion secondary battery

Abstract

The present invention relates to a carbon black dispersion composition for a storage battery, a mixed paste for forming a positive electrode, a positive electrode for forming a lithium ion secondary battery, and a lithium ion secondary battery. In a carbon black dispersion composition containing carbon black, methylcellulose, and N-methyl-2-pyrrolidone, the polydispersity index of the methylcellulose is 1.9 or less as determined on the basis of absolute molecular weight measurement by SEC-MALS, and the viscosity of a 2 wt% aqueous solution at 20 DEG C is 3-30 mPa.s. The composition in which the carbon black is uniformly dispersed and the initial dispersed state (i.e., the composition has storage stability) can be obtained without excessive labor force and / or time.

Description

Technical Field

[0001] The present invention relates to a carbon black dispersion composition for a storage battery, a mixed paste for forming a positive electrode, a positive electrode for forming a lithium ion secondary battery, and a lithium ion secondary battery. Background Art

[0002] Lithium-ion secondary batteries are characterized by high energy density. They have expanded their market driven by the widespread use of mobile terminals such as mobile phones and laptops. They mark a significant improvement in performance. Recently, in order to build a sustainable society, there is an increasing drive for vehicle electrification and efficient operation of energy storage systems. Under these circumstances, it is expected that the lithium-ion secondary battery market will expand.

[0003] The positive electrode of a lithium-ion secondary battery mainly comprises an active material, a conductive agent, a binder and a current collector. Since the capacity of a lithium-ion secondary battery is mainly determined by the amount of active material, it is preferred to minimize the amount of conductive agent and components other than active material to develop a high-capacity battery. Conductive agents that impart high conductivity even when added in small amounts are tailored to have a larger specific surface area and a higher structure. However, conductive agents with a large surface area and a high structure are more condensed, making it difficult to achieve uniform dispersion. This can cause uneven positions of conductive paths within the electrode, thereby increasing internal resistance, and can also cause uneven load distribution, thereby shortening battery life.

[0004] Then, as a means of forming a uniformly dispersed electrode while preventing the conductive agent from agglomerating, a common practice now is to uniformly disperse the conductive agent in a dispersion medium (usually an organic solvent) in advance with the help of a polymer dispersant to form a conductive agent dispersion, and to mix the conductive agent dispersion with the positive electrode active material and the binder to form a positive electrode mixed slurry.

[0005] The conductive agent dispersion must satisfy the following requirements: the conductive agent is dispersed uniformly and effectively, and the dispersion state of the conductive agent and the viscosity of the dispersion remain unchanged or stable throughout the storage period from the preparation of the dispersion to the preparation of the electrode mix slurry.

[0006] If the conductive agent agglomerates due to poor dispersibility, the dispersion viscosity increases. Then, the positive electrode mixture slurry prepared from the dispersion has lower coating properties and cannot form a flat coating of the mixture. As a result, the distribution of the conductive path within the electrode becomes uneven, resulting in degradation of electrode performance.

[0007] The dispersion storage stability reflects the change of the dispersion state of the conductive agent over time. Therefore, the great change of the dispersion state during storage aggravates the change of the quality of the manufactured positive electrode.

[0008] Most commonly, carbon black is used as a conductive agent. As a means of improving the dispersibility and storage stability of a dispersion using carbon black as a conductive agent, for example, a dispersion to which an acidic compound such as carboxylic acid is added as an additional additive is known from Patent Document 1: JP-A 2016-046188.

[0009] As a means for improving the dispersion of a conductive agent without using an additional additive, a dispersion whose dispersibility and storage stability are improved by controlling its viscosity within a specific range is known from Patent Document 2: JP-A 2020-021632.

[0010] Citation List

[0011] Patent Document 1: JP-A 2016-046188

[0012] Patent Document 2: JP-A 2020-021632 Summary of the invention

[0013] Although Patent Document 1 does not describe the mechanism by which the acidic compound acts on the dispersibility of carbon black, it is estimated that the dispersibility of carbon black is enhanced by controlling the pH environment on the surface of carbon black particles. However, since there is a concern that the acidic compound may cause chemical modification of the electrode mixture, it is not desirable to add the acidic compound to the carbon black dispersion.

[0014] In the method of Patent Document 2, it is necessary to continue the dispersion process until the dispersion reaches the desired viscosity characteristics. This generally requires more labor and time, making it difficult to meet the current demands of the storage battery market for production cost savings and increased production.

[0015] The object of the present invention is to provide a carbon black dispersion composition for a battery, which contains N-methyl-2-pyrrolidone as a dispersion medium, is capable of improving the dispersibility of carbon black, maintaining the dispersed state immediately after the dispersion step, and achieving storage stability without requiring additional labor and time; a mixed paste for forming a positive electrode; a positive electrode for forming a lithium ion secondary battery; and a lithium ion secondary battery using the carbon black dispersion composition.

[0016] The inventor tried to select a dispersant from a variety of polymers that could improve the dispersibility of carbon black in N-methyl-2-pyrrolidone (NMP) and the storage stability of the dispersion. During the research work, the inventor paid attention to cellulose derivatives and conducted repeated trial and error experiments on the application of various cellulose derivatives.

[0017] Unexpectedly, when methylcellulose having a polydispersity index of 1.9 or less as determined based on absolute molecular weight measurement by size exclusion chromatography (SEC) combined with multi-angle light scattering (MALS) and a viscosity of 3-30 mPa·s in a 2 wt % aqueous solution at 20° C. was selected as a dispersant among a variety of cellulose derivatives, the dispersibility and storage stability of carbon black were significantly improved. The present invention was formed based on this finding.

[0018] In one aspect, the present invention provides a carbon black dispersion composition for a battery, comprising carbon black, methylcellulose and N-methyl-2-pyrrolidone, wherein the methylcellulose has a polydispersity index of less than 1.9 determined based on absolute molecular weight measurement by size exclusion chromatography (SEC) combined with multi-angle light scattering (MALS), and a viscosity of 2 wt % aqueous solution at 20° C. of 3-30 mPa·s.

[0019] In a preferred embodiment, the carbon black is present in an amount of 5-20% by weight of the composition.

[0020] In a preferred embodiment, the BET specific surface area of ​​the carbon black is 30-1500 m 2 / g.

[0021] In a preferred embodiment, 1 to 20 parts by weight of methyl cellulose is present relative to 100 parts by weight of carbon black.

[0022] In another aspect, the present invention provides a mixed paste for forming a positive electrode, which comprises the above-mentioned carbon black dispersion composition, a positive electrode active material and a binder.

[0023] In another aspect, the present invention provides a positive electrode for forming a lithium ion secondary battery, which includes a current collector and a positive electrode mixture layer formed on the current collector by applying the mixed paste to the current collector and drying it.

[0024] In another aspect, the present invention provides a lithium ion secondary battery comprising the above-mentioned positive electrode, negative electrode, electrolyte and separator.

[0025] Advantageous Effects of the Invention

[0026] The carbon black dispersion composition for a battery according to the present invention can improve the dispersibility and storage stability of carbon black. By using the carbon black dispersion composition, it is expected to reduce the scrap rate and production cost in the lithium ion secondary battery manufacturing process. DETAILED DESCRIPTION OF THE INVENTION

[0028] In this disclosure, N-methyl-2-pyrrolidone is often abbreviated as NMP.

[0029] [Carbon black dispersion composition]

[0030] The carbon black dispersion composition for batteries is described in detail below.

[0031] The present invention provides a carbon black dispersion composition for a battery, comprising carbon black, methyl cellulose and N-methyl-2-pyrrolidone (NMP). The methyl cellulose has a polydispersity index of 1.9 or less determined based on absolute molecular weight measurement by size exclusion chromatography (SEC) combined with multi-angle light scattering (MALS), and a viscosity of 3-30 mPa·s in a 2 wt % aqueous solution at 20° C.

[0032] <Carbon Black>

[0033] Carbon black is added as a conductive agent to improve the conductivity of an electrode (particularly a positive electrode in the case of a lithium ion secondary battery) made from a carbon black dispersion composition. Examples of carbon black are acetylene black, furnace black, thermal black, and Ketjen black. Among them, acetylene black is preferred in terms of conductivity and dispersibility.

[0034] Considering the dispersibility of carbon black in NMP and the conductivity to be imparted to the positive electrode, the BET specific surface area of ​​carbon black (i.e., the specific surface area measured by the BET method) is preferably 30-1500 m 2 / g, more preferably 40-600m 2 / g, even more preferably 50-300m 2 / g.

[0035] Considering the fluidity and handling of the dispersion composition, the content of carbon black is preferably 5-20 weight % of the composition, more preferably 9-19 weight %. In other words, the content of carbon black is preferably 5-20 weight % relative to 100 weight % of the total carbon black dispersion composition (preferably the total of carbon black, methyl cellulose and NMP), more preferably 9-19 weight %.

[0036] Another carbon material such as carbon nanotubes, graphene or graphite can also be mixed with carbon black as a conductive agent. When other carbon materials are additionally mixed, their amount is preferably 5-20 parts by weight, more preferably 9-19 parts by weight relative to 100 parts by weight of the total carbon black dispersion composition (preferably the total of carbon black, methylcellulose and NMP).

[0037] <Methylcellulose>

[0038] Methyl cellulose is used as a dispersant to improve the dispersibility of carbon black.

[0039] The methoxyl substitution degree (DS) of methylcellulose is preferably in the range of 1.60 to 2.10, more preferably 1.70 to 2.00. The DS of the methoxyl group can be measured by the methylcellulose DS analysis method prescribed in the Japanese Pharmacopoeia 18th edition (the same applies hereinafter).

[0040] The viscosity of a 2 wt % aqueous solution of methyl cellulose at 20° C. should be 3.0-30.0 mPa·s, preferably 3.5-20.0 mPa·s, from the viewpoint of the dispersibility and storage stability of carbon black. The viscosity of a 2 wt % aqueous solution at 20° C. is the result of measuring the viscosity of a 2 wt % aqueous solution of methyl cellulose at 20° C. using an Ubbelohde viscometer in accordance with JIS K2283-1993 (the same applies hereinafter).

[0041] The polydispersity index of methylcellulose determined based on the absolute molecular weight measurement of size exclusion chromatography (SEC) combined with multi-angle light scattering (MALS) is less than 1.9, preferably 1.0-1.80, and more preferably 1.40-1.80. The polydispersity index is defined as the ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn), and represents the distribution of molecular weights. The smaller the value of Mw / Mn, the narrower the molecular weight distribution, and the larger the value of Mw / Mn, the wider the molecular weight distribution. Mw and Mn can be measured by absolute molecular weight measurement of size exclusion chromatography (SEC) combined with multi-angle light scattering (MALS) (see Tablets & Capsules, 14-20, July 2007). Here, "polydispersity index" refers to Mw / Mn determined based on the absolute molecular weight measurement of SEC combined with MALS.

[0042] Considering the dispersibility of carbon black and the electrical properties of the electrode made of the carbon black dispersion composition, the amount of methylcellulose added is preferably 1-20 parts by weight, more preferably 3-15 parts by weight, relative to 100 parts by weight of carbon black in the carbon black dispersion composition. Considering the dispersibility of carbon black and the electrical properties of the electrode made of the carbon black dispersion composition, the content of methylcellulose is preferably 0.05-4% by weight of the carbon black dispersion composition, more preferably 0.15-3% by weight. In other words, relative to 100 parts by weight of the total carbon black dispersion composition (preferably the total of carbon black, methylcellulose and NMP), the content of methylcellulose is preferably 0.05-4% by weight, more preferably 0.15-3% by weight.

[0043] The method for preparing methyl cellulose is not particularly limited as long as the polydispersity index of methyl cellulose is 1.9 or less and the viscosity of a 2 wt % aqueous solution at 20° C. is 3-30 mPa·s. For example, methyl cellulose can be prepared by a method (hereinafter referred to as “method 1 for preparing methyl cellulose”) comprising at least a step (S11) of contacting pulp with an alkali metal hydroxide solution to form alkali cellulose, a step (S12) of supplying oxygen to the alkali cellulose for depolymerization treatment, a step (S13) of subjecting the depolymerized alkali cellulose to an etherification reaction with a methylating agent to form a reaction product, a step (S14) of washing the reaction product to obtain washed methyl cellulose, and a step (S15) of drying and grinding the washed methyl cellulose. Alternatively, methylcellulose can be prepared by a method (hereinafter referred to as "method 2 for preparing methylcellulose") comprising at least step (S21) of contacting pulp with an alkali metal hydroxide solution to form alkali cellulose, step (S22) of subjecting the alkali cellulose to an etherification reaction with a methylating agent to form a reaction product (i.e., the etherification reaction is carried out by adding a methylating agent without carrying out a depolymerization treatment of supplying oxygen to the alkali cellulose as carried out in method 1 for preparing methylcellulose), step (S23) of washing the reaction product to obtain washed methylcellulose, step (S24) of drying and grinding the washed methylcellulose to form methylcellulose before depolymerization, step (S25) of subjecting the methylcellulose (before depolymerization) to a depolymerization treatment with an acid to form depolymerized methylcellulose, and step (S26) of subjecting the depolymerized methylcellulose to a dialysis treatment. The above exemplary method is described in detail below.

[0044] [Methylcellulose Preparation Method 1]

[0045] First, the methyl cellulose preparation method 1 is described.

[0046] The step (S11) is to contact the pulp with an alkali metal hydroxide solution to form alkali cellulose.

[0047] Examples of pulp include cellulose pulp such as wood pulp and cotton linter pulp.

[0048] The solids in the pulp contain cellulose as the main component, and small amounts of organic matter such as low-polymerization cellulose, hemicellulose, lignin and resin, and inorganic matter such as Si and Fe components. Since the content of low-polymerization cellulose in commercial pulp obtained by digestion and bleaching of wood is very low, the cellulose content of the solids in the pulp is considered to be substantially equal to the content of α-cellulose.

[0049] Solids in pulp can be calculated from the dry matter content measured according to the test method for determining dry matter content of pulp of JIS P8203: 1998. The dry matter content in weight % is determined by drying a sample at 105±2°C until its weight is constant and calculating the ratio of the dry weight to the initial weight.

[0050] In view of reducing the polydispersity index (Mw / Mn) of methylcellulose, the intrinsic viscosity (polymerization index) of pulp is preferably less than 800 ml / g, more preferably less than 600 ml / g. The lower limit of the intrinsic viscosity is preferably 200 ml / g. It is worth noting that the intrinsic viscosity can be measured by the viscosity measurement method of JIS P8215.

[0051] Examples of the alkali metal hydroxide solution include aqueous solutions of alkali metal hydroxides such as sodium hydroxide and potassium hydroxide.

[0052] The alkali metal hydroxide solution preferably has an alkali metal hydroxide concentration of 10 to 60% by weight from the viewpoints of economy and ease of handling.

[0053] The amount of the alkali metal hydroxide solution can be appropriately set according to the DS of the methoxyl groups in the methylcellulose and the alkali metal hydroxide concentration of the alkali metal hydroxide solution. Preferably, the amount of the alkali metal hydroxide solution is such that 0.01-2.0 parts by weight, more preferably 0.5-1.5 parts by weight of alkali metal hydroxide is provided per unit weight part (i.e., 1.00 parts by weight) of pulp.

[0054] The pulp is contacted with an alkali metal hydroxide solution in a reactor, such as an internally stirred tank reactor.

[0055] The step (S12) is to supply oxygen to the alkali cellulose to perform a depolymerization treatment to obtain depolymerized alkali cellulose.

[0056] For example, oxygen may be supplied by passing air through the reactor.

[0057] After the addition of the alkali metal hydroxide solution is completed in step (11), oxygen supply may be performed continuously or discontinuously. By supplying oxygen at the end of the addition of the alkali metal hydroxide solution, the alkali metal hydroxide solution is evenly distributed on the pulp, so that the depolymerization reaction using oxygen can occur evenly.

[0058] Although the precise mechanism is unclear, the uniform depolymerization reaction using oxygen ensures minimal changes in molecular weight and a low polydispersity index (Mw / Mn).

[0059] The temperature of the depolymerization reaction using oxygen is preferably in the range of 30-85°C, more preferably 30-80°C, from the viewpoint of reducing the polydispersity index (Mw / Mn) of methylcellulose.

[0060] The time of the depolymerization reaction with oxygen is preferably in the range of 10 minutes to 2 hours, although the time can be appropriately set depending on the viscosity of a 2 wt % aqueous solution of methylcellulose at 20° C. and the reaction temperature.

[0061] Step (S13) is to subject the depolymerized alkali cellulose to an etherification reaction with a methylating agent to form a reaction product.

[0062] A typical methylating agent is methyl chloride. The amount of the methylating agent used is preferably 0.5 to 3.0 parts by weight relative to 1.0 part by weight of pulp, although the amount can be appropriately set according to the DS of methyl cellulose.

[0063] For the etherification reaction, the temperature is preferably 40-100° C., and the time is preferably 1-5 hours.

[0064] Step (S14) is to wash the reaction product to obtain washed methyl cellulose.

[0065] Water is usually used for washing. The water temperature is preferably 85-100° C. In view of the removal of impurities and easy adjustment of the water content in the subsequent steps, the washed methylcellulose preferably has a water content of 25-95% by weight. The water content of the washed methylcellulose can be measured by the drying loss test of the Japanese Pharmacopoeia 18th edition.

[0066] Step (S15) is to dry and grind the washed methyl cellulose to obtain the desired methyl cellulose.

[0067] There is no particular limitation on the equipment that can be used in the drying step as long as the desired water content can be achieved. An example is a blower dryer. There is no particular limitation on the equipment that can be used in the grinding step as long as the methylcellulose can be ground. Examples are impact mills and ball mills.

[0068] [Methylcellulose preparation method 2]

[0069] Next, methylcellulose production method 2 is described.

[0070] In the methylcellulose production method 2, the same steps as those in the methylcellulose production method 1 are performed until the step of drying and grinding the washed methylcellulose (to produce methylcellulose before depolymerization), except that the etherification reaction is performed after the step of forming the alkali cellulose without performing the depolymerization treatment with oxygen. That is, the method 2 includes a step (S21) similar to the step (S11), a step (S22) of adding a methylating agent to the alkali cellulose to perform an etherification reaction, a step (S23) similar to the step (S14), and a step (S24) similar to the step (S15).

[0071] The next step (S25) is to depolymerize methyl cellulose (before depolymerization) with an acid to form depolymerized methyl cellulose.

[0072] The depolymerization treatment with an acid can be carried out by standard techniques. For example, hydrogen halides such as hydrogen chloride can be used as the acid. The acid can be used in the form of an aqueous solution. For example, hydrogen chloride can be used in the form of an aqueous solution of hydrogen chloride, i.e., hydrochloric acid. The aqueous solution of hydrogen chloride preferably has a hydrogen chloride concentration of 1-45% by weight.

[0073] The amount of the acid is preferably 0.04-1 part by weight relative to 100 parts by weight of methyl cellulose before depolymerization. For the depolymerization treatment with an acid, the temperature is preferably 40-85 °C and the time is preferably 0.1-4 hours.

[0074] After the depolymerization treatment with an acid, the acid can be removed, for example, by evacuating the reactor. If necessary, the acid can be neutralized by adding sodium bicarbonate or the like.

[0075] Step (S26) is to perform dialysis treatment on the depolymerized methyl cellulose to obtain the desired methyl cellulose.

[0076] The dialysis treatment can be carried out as follows: Dissolve the depolymerized methyl cellulose in deionized water to form an aqueous solution, load the aqueous solution into a dialysis tube, immerse the loaded tube in deionized water, and after immersion, dry the contents in the tube to precipitate the methyl cellulose.

[0077] The dialysis tube preferably has a cut-off molecular weight of 10,000-20,000, more preferably 12,000-14,000. As long as dialysis can be carried out, the length and diameter of the tube are not particularly limited.

[0078] The immersion time is preferably 30 minutes to 5 days, more preferably 1-3 days. The volume of deionized water in which the tube is immersed is preferably at least 50 times the volume of the aqueous solution in the tube.

[0079] The drying technique is not particularly limited. For example, drying is carried out by pouring the aqueous solution from the tube into a bucket and placing the bucket in a blow dryer. The precipitated methyl cellulose obtained by drying can be further ground. For example, grinding can be carried out using a forced mill.

[0080] In this way, methyl cellulose with a polydispersity index of 1.9 or less and a viscosity of 3-30 mPa·s in a 2% by weight aqueous solution at 20 °C is obtained.

[0081] <N-methyl-2-pyrrolidone>

[0082] N-methyl-2-pyrrolidone (NMP) is a typical organic solvent used in the production of positive electrodes of lithium ion batteries. In the carbon black dispersion composition of the present invention, NMP is added as a dispersion medium for carbon black.

[0083] Although the content of NMP is not particularly limited, from the viewpoint of operation, the content of NMP is preferably 75-95% by weight, more preferably 81-91% by weight, of the carbon black dispersion composition. In other words, the content of NMP is preferably 75-95 parts by weight, more preferably 81-91 parts by weight, relative to 100 parts by weight of the total carbon black dispersion composition (preferably the total of carbon black, methyl cellulose and NMP).

[0084] From the aspect of enhancing the affinity of various components (i.e., the components of the carbon black dispersion composition and the mixed paste for forming the positive electrode), at least one type of another solvent can be used. Examples of solvents other than NMP include water, N-ethyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, N,N-dimethylpropionamide, N,N-diethylacetamide and 4-acetylmorpholine. In the practice of the present invention, NMP is preferably used alone as a solvent.

[0085] <Other components>

[0086] The carbon black dispersion composition of the present invention may contain other components as long as they do not impair the purpose of the present invention, the dispersibility of the composition and the performance of the electrode formed therefrom. Suitable other components include surfactants, defoamers, pH adjusters and viscosity adjusters.

[0087] As long as the aforementioned components are uniformly mixed and the carbon black is dispersed, the method for preparing the carbon black dispersion composition of the present invention is not particularly limited. For example, the composition is prepared by the step of dispersing carbon black, methylcellulose and NMP using a disperser. An exemplary dispersion step includes premixing carbon black and methylcellulose as powder materials, and dispersing the premix in NMP. Another exemplary dispersion step includes dissolving a dispersant in a solvent (usually NMP) and mixing the solution with carbon black.

[0088] Examples of the disperser include a homogenizer, a homodisperser, a planetary mixer, a coating conditioner, a bead mill, and a thin film cyclone high-speed mixer.

[0089] In order to improve the dispersibility of carbon black, the dispersing step can be carried out stepwise using multiple dispersers. In one example, the powder material (e.g., carbon black, dispersant, and hindered phenol) and the dispersion medium (NMP) are uniformly mixed using a homogeneous disperser or a planetary mixer, and then the carbon black in the form of particles is dispersed therein using a bead mill or a thin film cyclone high-speed mixer.

[0090] [Mixed paste for forming positive electrode]

[0091] Another embodiment of the present invention is a mixed paste for forming a positive electrode, which includes the above-mentioned carbon black dispersion composition, a positive electrode active material and a binder, and the paste is used for manufacturing a positive electrode for forming a lithium ion secondary battery.

[0092] There is no particular limitation on the positive electrode active material, as long as it is commonly used in the positive electrode of a lithium ion secondary battery. It includes lithium-containing transition metal oxides, and some of these transition metal oxides in which transition metal elements are replaced by different elements. Examples of transition metal oxides include lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, ternary (NCM) active materials and NCA active materials. Unlike oxide-based active materials, it is also possible to use materials that are prepared by introducing polyvalent anions such as phosphate ions (PO 3 3- ) or silicate ions (SiO 4 4- ) A polyanionic positive electrode active material that makes the transition metal more ionic. Examples of polyanionic active materials include lithium iron phosphate and lithium iron silicate.

[0093] The amount of the positive electrode active material is preferably 35-80% by weight of the mixed paste, more preferably 40-70% by weight. In other words, the amount of the positive electrode active material is preferably 35-80 parts by weight, more preferably 40-70 parts by weight relative to 100 parts by weight of the mixed paste. If the amount of the positive electrode active material is less than 35% by weight, the battery constructed therefrom may have a low energy density. If the amount of the active material exceeds 80% by weight, the mixed paste for forming the positive electrode may become too hard to apply the paste to the current collector.

[0094] From the durability of the positive electrode mixed layer, it is preferred to use a fluorinated polymer as a binder. Suitable polymers include polyvinylidene fluoride, polyvinyl fluoride and tetrafluoroethylene. In addition, from the adhesiveness and coating properties of the mixed paste, the polymer used as a binder preferably has an Mw of 200000-1200000, more preferably 600000-1000000. It is worth noting that the Mw of the polymer as a binder can be measured by any well-known method such as gel permeation chromatography.

[0095] The amount of the binder is preferably 0.3-10 weight % of the mixed paste, more preferably 0.5-6 weight %. In other words, the amount of the binder is preferably 0.3-10 weight parts relative to 100 weight parts of the mixed paste, more preferably 0.5-6 weight parts. If the amount of the binder is less than 0.3 weight %, the strength of the positive electrode mixed layer is so poor that the mixed layer may separate or crack. If the amount of the binder exceeds 10 weight %, the internal resistance of the electrode may increase.

[0096] The mixed paste for forming the positive electrode can be prepared by mixing the carbon black dispersion composition, the positive electrode active material and the binder. As the mixer, the disperser exemplified in the above-mentioned method for preparing the carbon black dispersion composition can be used.

[0097] When preparing the mixed paste for forming the positive electrode, a solvent may be added from the perspective of viscosity adjustment. As the solvent, various solvents exemplified by the above-mentioned carbon black dispersion composition may be used, including NMP. The amount of the solvent (NMP) (i.e., the total amount of NMP and additional NMP in the carbon black dispersion composition) is preferably 10-70% by weight, more preferably 20-60% by weight, of the mixed paste for forming the positive electrode.

[0098] The order in which the components are introduced in the mixing step is not particularly limited. All components may be added at once. The mixing step may be performed in stages by premixing the binder, the positive electrode active material, and the solvent, adding the carbon black dispersion composition to the premix, and then further mixing. From the perspective of preventing foreign particles such as undissolved lumps from entering the mixed paste, it is recommended to dissolve the binder in the solvent in advance to form a solution, and then add it in the form of a solution.

[0099] The mixed paste for forming the positive electrode is suitable for manufacturing the positive electrode of a lithium ion secondary battery. Specifically, the mixed paste is applied to a current collector to any desired thickness to form a coating, the coating is dried, and the dried coating is processed into a positive electrode mixed layer to manufacture the positive electrode for forming a lithium ion secondary battery.

[0100] As the current collector, a film or foil of a metal or alloy such as iron, stainless steel, copper, aluminum and nickel is used. Aluminum is particularly preferred from the perspective of the potential stability of the positive electrode. In order to reduce the interface resistance, the current collector may be surface treated, such as carbon coating.

[0101] Examples of coaters for coating the mixed paste for forming the positive electrode include blade coaters, comma coaters, die coaters, and gravure coaters, but are not limited thereto. In order to improve the resistance of the positive electrode and the adhesion of the mixed layer, the mixed paste or the dry coating of the mixed paste applied to the current collector can be rolled using a roller press or the like.

[0102] The coating thickness of the mixed paste is preferably 50-1000 μm, more preferably 100-500 μm.

[0103] The applied mixed paste coating is dried in a drying oven at a drying temperature and time of preferably 50-180° C. and 0.5-1200 minutes, more preferably 60-140° C. and 1-600 minutes.

[0104] In this way, a positive electrode for forming a lithium ion secondary battery is obtained, which includes a current collector and a mixed layer in the form of a mixed paste dry film. The thickness of the positive electrode mixed layer is preferably 10-800 μm, more preferably 30-400 μm.

[0105] [Lithium-ion secondary battery]

[0106] The lithium ion secondary battery is defined as comprising a positive electrode carrying the mixed layer of the present invention, a negative electrode, a separator and an electrolyte. The separator is interposed between the positive electrode and the negative electrode in a closed state and is impregnated with an electrolyte.

[0107] The negative electrode has a negative electrode mixture layer on one or both surfaces of a negative electrode current collector.

[0108] Like the positive electrode current collector, the negative electrode current collector is a film or foil of a metal or alloy, preferably copper foil or nickel foil from the perspective of the potential stability of the negative electrode.

[0109] The negative electrode mixed layer contains one or more materials capable of occluding and releasing lithium ions, and optionally a binder, a conductive agent, and a dispersant for the negative electrode.

[0110] The negative electrode active material is not particularly limited as long as it is generally used as a negative electrode active material for lithium ion secondary batteries. Examples include natural graphite, synthetic graphite, oxide-based negative electrode materials such as lithium titanium oxide, and silicon-based negative electrode materials such as nanosilicon, silicon alloys, and silicon monoxide.

[0111] The negative electrode binder may be at least one of a polymer and a synthetic rubber. Suitable polymers include polyvinylidene fluoride, polyimide, polyamide-imide, aromatic polyamide, polyacrylic acid, lithium polyacrylate, and sodium carboxymethyl cellulose. Suitable synthetic rubbers include styrene butadiene rubber, fluororubber, and ethylene propylene diene rubber.

[0112] The negative electrode conductive agent is at least one carbon material selected from acetylene black, Ketjen black, graphite, carbon nanotubes and carbon nanofibers.

[0113] The negative electrode dispersant is at least one selected from, for example, methyl cellulose, hydroxypropyl methyl cellulose, ethyl cellulose, sodium carboxymethyl cellulose, polyvinyl alcohol, polyvinyl pyrrolidone, and polyurethane.

[0114] The separator is used to provide electronic insulation between the positive electrode and the negative electrode, thereby preventing the current short circuit caused by the contact between the positive electrode and the negative electrode, and allowing lithium ions to pass when impregnated with an electrolyte. The separator is formed of a porous film of a synthetic resin or ceramic, and may have a multilayer structure in which two or more porous films are stacked on each other. Suitable synthetic resins include polytetrafluoroethylene, polypropylene, and polyethylene. Alumina is a typical ceramic.

[0115] The electrolyte is a material used to mediate ion conduction between the positive electrode and the negative electrode. For example, the electrolyte is prepared by dissolving a lithium salt such as lithium hexafluorophosphate in a non-aqueous solvent, which is a mixture of ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and propylene carbonate. In order to improve stability and safety and reduce resistance, any desired additives may be added to the electrolyte.

[0116] As described above, the carbon black dispersion composition of the present invention is improved in the dispersibility and storage stability of carbon black. Using this carbon black dispersion composition, the scrap rate and production cost in the manufacturing process of lithium ion secondary batteries can be reduced. Example

[0117] Embodiments of the invention are shown below by way of illustration and not limitation.

[0118] It is noted that the BET surface area is a specific surface area measured by the BET method. The viscosity of a 2 wt % aqueous solution of methylcellulose at 20° C. is measured using an Ubbelohde viscometer according to JIS K2283-1993. As used herein, wt % is wt % and pbw is parts by weight.

[0119] The polydispersity index (Mw / Mn) is measured by the following method.

[0120] <Measurement of Polydispersity Index (Mw / Mn)>

[0121] Molecular weight was measured using a GPC-MALS system. The system included a pump (LC-20AD, Shimadzu Corp.), a degasser (DGU-20A3R, Shimadzu Corp.), an autosampler (SIL-20A, Shimadzu Corp.), a column oven (CTO-20A, Shimadzu Corp.), a guard column (SB-G, Shoko Science Co., Ltd.), a size exclusion column (OHpakSB-806HQ, Shoko Science Co., Ltd.), an 18-angle light scattering instrument (DAWN M3220, Wyatt Technologies), and a differential refractometer (Optilab M1520, Wyatt Technologies).

[0122] Before measurement, methylcellulose (MC) prepared as follows was metered into a 50 mL screw bottle. 20 mL of 0.1 M sodium nitrate (NaNO 3) buffer. MC was dissolved by stirring at room temperature for 1 hour, and completely dissolved by further stirring for 1 hour under ice cooling. The solution was then allowed to stand at room temperature for 30 minutes until the solution returned to room temperature. The concentration of the solution varies with the viscosity of a 2 wt % aqueous solution of MC at 20°C. When the viscosity is 3 mPa·s to less than 6 mPa·s, the solution is prepared to have a concentration of 0.30 wt %, and when the viscosity is 6 mPa·s to 30 mPa·s, the solution is prepared to have a concentration of 0.20 wt %. The solution thus prepared was filtered through a membrane filter with a pore size of 0.45 μm (DIMIC-13CP, Advantec Co., Ltd.). By adding 2 mL of 0.1 M sodium nitrate (NaNO 3 ) buffer was added to 5 mg of pullulan (P50, Shoko Science Co., Ltd.) to dissolve the pullulan, and the solution was filtered through a membrane filter with a pore size of 0.20 μm (DIMIC-13CP, Advantec Co., Ltd.) to prepare a reference material.

[0123] Use 0.1 M sodium nitrate (NaNO 3 ) buffer as the mobile phase, the molecular weight of the MC solution and the pullulan solution as a reference was measured under the following conditions: flow rate 1.0 mL / min, column temperature 40°C, differential refractometer temperature 25°C, injection volume 200 μL, measurement time 20 minutes. At the end of the measurement, the analysis was performed using the analysis software ASTRA 7.3.2 version as follows. It is worth noting that the dn / dc value of MC is 0.139 mL / g.

[0124] The peak range was selected from the light scattering chromatogram and detectors 5-16 of the light scattering instrument were used. The molecular weight was calculated by AUTOFitting using extrapolation (once). In this way, the polydispersity index (Mw / Mn) was obtained. The polydispersity index measurement data of MC was normalized with reference to the measurement data of pullulan.

[0125] <Preparation of methylcellulose>

[0126] [Synthesis Example 1]

[0127] Preparation of MC-1

[0128] Wood pulp with an intrinsic viscosity of 370 ml / g was ground into powder slurry using a grinder. Of this powder slurry, a portion of 6.0 kg of cellulose content corresponding to the solids in the pulp was supplied to a jacketed, internally stirred pressure-resistant reactor. Vacuuming and nitrogen purging were performed until oxygen in the reactor was completely removed.

[0129] Under stirring, 13.54 kg of a 49 wt% sodium hydroxide aqueous solution was added to the reactor over 20 minutes. While the reactor was maintained at an internal temperature of 80° C., air was passed through the reactor at a rate of 10 NL / min for about 38 minutes. At the end of the air supply, stirring was continued until 40 minutes had passed from the start of the air supply. At the end of the air supply, vacuuming and nitrogen purging were performed until oxygen in the reactor was completely removed.

[0130] After adding 2.4 kg of dimethyl ether and 10.9 kg of methyl chloride to the reactor, the reaction was carried out at 60-90° C. for 110 minutes. At the end of the reaction, the reaction solution was washed with water to a water content of 85 wt %. It was dried using a blower dryer to a water content of 2 wt %. The block was crushed using an impact mill (Victory Mill) to obtain methylcellulose 1 (MC-1).

[0131] The viscosity of a 2 wt % aqueous solution of MC-1 at 20° C. was 15 mPa·s, the DS of the methoxy group was 1.8, and the polydispersity index (Mw / Mn) was 1.52.

[0132] [Synthesis Example 2]

[0133] Preparation of MC-2

[0134] Wood pulp with an intrinsic viscosity of 700 ml / g was ground into powder slurry using a grinder. Of this powder slurry, a portion of 6.0 kg of cellulose content corresponding to the solids in the pulp was supplied to a jacketed, internally stirred pressure-resistant reactor. Vacuuming and nitrogen purging were performed until oxygen in the reactor was completely removed.

[0135] Under stirring, 13.43 kg of a 49 wt% aqueous sodium hydroxide solution was added to the reactor over 20 minutes.

[0136] 2.4 kg of dimethyl ether and 10.0 kg of methyl chloride were added to the reactor. The reaction was carried out at 60-90° C. for 110 minutes. At the end of the reaction, the reaction solution was washed with water to a water content of 85% by weight. It was dried using a blow dryer to a water content of 2% by weight. The block was crushed using an impact mill (Victory Mill) to obtain powdered methylcellulose.

[0137] Then, 10.5 wt% hydrochloric acid was sprayed onto the methylcellulose powder so that the amount of hydrogen chloride was 0.15 wt% relative to 100 wt% of the methylcellulose. The methylcellulose sprayed with hydrochloric acid was subjected to a depolymerization reaction for 70 minutes in a rotary glass reactor at a jacket temperature of 80°C.

[0138] The jacket temperature was maintained at 80°C, and the glass reactor was maintained under a reduced pressure of 40 mmHg for 30 minutes to volatilize hydrogen chloride and water from the reactor.

[0139] Sodium bicarbonate in an amount equivalent to 1 / 2 mol per mol of hydrogen chloride added was added to the methylcellulose in the reactor to neutralize the methylcellulose, thereby obtaining methylcellulose 2 (MC-2).

[0140] The viscosity of a 2 wt % aqueous solution of MC-2 at 20° C. was 15 mPa·s, the DS of the methoxy group was 1.8, and the polydispersity index (Mw / Mn) was 2.17.

[0141] [Synthesis Example 3]

[0142] Preparation of MC-3

[0143] Methylcellulose 3 (MC-3) was obtained by following the same procedure as MC-2 except that the hydrochloric acid concentration was 14 wt %, the jacket temperature was 95° C., and the time was 25 minutes in the depolymerization reaction.

[0144] The viscosity of a 2 wt % aqueous solution of MC-3 at 20° C. was 15 mPa·s, the DS of the methoxy group was 1.8, and the polydispersity index (Mw / Mn) was 6.74.

[0145] [Synthesis Example 4]

[0146] Preparation of MC-4

[0147] Powdered methyl cellulose was obtained as in Synthesis Example 2 through the etherification reaction step of alkali cellulose with a methylating agent, the washing step, and the drying / pulverizing step.

[0148] Then, 14 wt% hydrochloric acid was sprayed onto the methylcellulose powder so that the amount of hydrogen chloride was 0.30 wt% relative to 100 wt% of the methylcellulose. The methylcellulose sprayed with hydrochloric acid was subjected to a depolymerization reaction for 70 minutes in a rotary glass reactor at a jacket temperature of 80°C.

[0149] The jacket temperature was maintained at 80°C, and the reactor was maintained under a reduced pressure of 40 mmHg for 30 minutes to volatilize hydrogen chloride and water from the reactor.

[0150] Sodium bicarbonate in an amount equivalent to 1 / 2 mol per mol of hydrogen chloride was added to the methylcellulose in the reactor to neutralize the methylcellulose.

[0151] The neutralized methylcellulose was dissolved in deionized water to form a 2 wt% aqueous solution, which was loaded into a dialysis tube (molecular weight cutoff 12000-14000, diameter 28.6 mm). The tube containing the solution was immersed in deionized water and then dialyzed for 2 days. After the board is laid in a metal bucket, the solution is poured from the tube into the bucket. The bucket is placed in a desiccator and the solution is dried at 100°C for 2 hours, leaving a methylcellulose film.

[0152] The film was cut and pulverized using a forced mill to obtain powdered methylcellulose 4 (MC-4).

[0153] The viscosity of a 2 wt % aqueous solution of MC-4 at 20° C. was 4 mPa·s, the DS of the methoxy group was 1.8, and the polydispersity index (Mw / Mn) was 1.71.

[0154] [Synthesis Example 5]

[0155] Preparation of MC-5

[0156] Methylcellulose 5 (MC-5) was obtained by following the procedure of Synthesis Example 4 except that the dialysis treatment was omitted after the depolymerization reaction and neutralization with hydrochloric acid.

[0157] The viscosity of a 2 wt % aqueous solution of MC-5 at 20° C. was 4 mPa·s, the DS of the methoxy group was 1.8, and the polydispersity index (Mw / Mn) was 1.99.

[0158] <Test Sample>

[0159] Various materials used in the carbon black dispersion compositions of Examples and Comparative Examples are shown below.

[0160] Carbon Black:

[0161] Acetylene black: DENKA BLACK Li-435 (hereinafter referred to as Li-435, manufactured by Denka Co., Ltd., BET surface area 136 m 2 / g)

[0162] Acetylene black: DENKA BLACK Li-100 (hereinafter referred to as Li-100, manufactured by Denka Co., Ltd., BET surface area 68 m 2 / g)

[0163] Furnace black: VULCAN XC72 (hereinafter referred to as VXC72, manufactured by Cabot Corp., BET surface area 237 m 2 / g)

[0164] Dispersants:

[0165] ·Methylcellulose 1 (MC-1): 2 wt% aqueous solution viscosity (20°C) 15 mPa·s, methoxy DS 1.8, polydispersity index (Mw / Mn) 1.52

[0166] ·Methylcellulose 2 (MC-2): 2 wt% aqueous solution viscosity (20°C) 15 mPa·s, methoxy DS 1.8, Mw / Mn 2.17

[0167] ·Methylcellulose 3 (MC-3): 2 wt% aqueous solution viscosity (20°C) 15 mPa·s, methoxy DS 1.8, Mw / Mn 6.74

[0168] ·Methylcellulose 4 (MC-4): 2 wt% aqueous solution viscosity (20°C) 4 mPa·s, methoxy DS 1.8, Mw / Mn 1.71

[0169] ·Methylcellulose 5 (MC-5): 2 wt% aqueous solution viscosity (20°C) 4 mPa·s, methoxy DS 1.8, Mw / Mn 1.99

[0170] <Preparation of Carbon Black Dispersion Composition>

[0171] [Example 1]

[0172] The carbon black dispersion composition for secondary batteries was prepared by the following procedure.

[0173] 2.6 g of acetylene black (Li-435) as carbon black and 0.208 g of methylcellulose 1 (MC-1) as a dispersant were mixed in powder form (8 parts by weight of MC-1 relative to 100 parts by weight of carbon black). 12.0 g of NMP was added to the mixture, which was pre-mixed at 2000 rpm for 5 minutes using a deaerator mixer (ARV-310, Thinky Co., Ltd.). Thereafter, 3.8 g of NMP was added to the mixer and mixing continued for 5 minutes. The dispersion was further stirred at 12500 rpm for 1 minute using a thin film rotary system dispersing mixer (Filmix 30-L, manufactured by Primix Co., Ltd.) to obtain a carbon black dispersion composition.

[0174] [Comparative Example 1]

[0175] A carbon black dispersion composition was obtained by the same procedure as in Example 1, except that methylcellulose 2 (MC-2) was used instead of MC-1.

[0176] [Comparative Example 2]

[0177] A carbon black dispersion composition was obtained by the same procedure as in Example 1, except that methylcellulose 3 (MC-3) was used instead of MC-1.

[0178] [Example 2]

[0179] 2.6 g of acetylene black (Li-435) as carbon black and 0.286 g of methylcellulose 4 (MC-4) as a dispersant were mixed in powder form (11 parts by weight of MC-4 relative to 100 parts by weight of carbon black). 12.0 g of NMP was added to the mixture, which was pre-mixed at 2000 rpm for 5 minutes using a deaerator mixer (ARV-310, Thinky Co., Ltd.). Thereafter, 3.7 g of NMP was added to the mixer and mixing continued for 5 minutes. The dispersion was further stirred at 12500 rpm for 1 minute using a thin film rotary system dispersing mixer (Filmix 30-L, manufactured by Primix Co., Ltd.) to obtain a carbon black dispersion composition.

[0180] [Comparative Example 3]

[0181] A carbon black dispersion composition was obtained by the same procedure as in Example 2, except that methylcellulose 5 (MC-5) was used instead of MC-4.

[0182] [Example 3]

[0183] 3.3 g of acetylene black (Li-100) as carbon black and 0.116 g of methylcellulose 1 (MC-1) as a dispersant were mixed in powder form (3.5 parts by weight of MC-1 relative to 100 parts by weight of carbon black). 11.0 g of NMP was added to the mixture, which was pre-mixed at 2000 rpm for 5 minutes using a deaerator mixer (ARV-310, Thinky Co., Ltd.). Thereafter, 3.9 g of NMP was added to the mixer and mixing continued for 5 minutes. The dispersion was further stirred at 12500 rpm for 1 minute using a thin film rotary system dispersing mixer (Filmix 30-L, Primix Co., Ltd.) to obtain a carbon black dispersion composition.

[0184] [Comparative Example 4]

[0185] A carbon black dispersion composition was obtained by the same procedure as in Example 3, except that methylcellulose 2 (MC-2) was used instead of MC-1.

[0186] [Comparative Example 5]

[0187] A carbon black dispersion composition was obtained by the same procedure as in Example 3, except that methylcellulose 3 (MC-3) was used instead of MC-1.

[0188] [Example 4]

[0189] 2.5 g of furnace black (VXC72) as carbon black and 0.325 g of methylcellulose 1 (MC-1) as a dispersant were mixed in powder form (13 parts by weight of MC-1 relative to 100 parts by weight of carbon black). 10.0 g of NMP was added to the mixture, which was pre-mixed at 2000 rpm for 5 minutes using a deaerator mixer (ARV-310, Thinky Co., Ltd.). Thereafter, 6.4 g of NMP was added to the mixer and mixing continued for 5 minutes. The dispersion was further stirred at 12500 rpm for 1 minute using a thin film rotary system dispersing mixer (Filmix 30-L, Primix Co., Ltd.) to obtain a carbon black dispersion composition.

[0190] [Comparative Example 6]

[0191] A carbon black dispersion composition was obtained by the same procedure as in Example 4, except that methylcellulose 3 (MC-3) was used instead of MC-1.

[0192] <Evaluation method>

[0193] The dispersibility of the carbon black dispersion composition thus obtained was evaluated by a rotational rheometer. Specifically, the shear viscosity was measured at a set temperature of 20°C and a shear rate of 10m / s using a rotational rheometer (MCR702, Anton Paar GmbH) and a cone plate as a measuring fixture. The lower the shear viscosity, the better the dispersibility of the carbon black. Here, when the initial viscosity is 600mPa·s or less, the carbon black is judged to have satisfactory dispersibility. When the hardness of the slurry causes overload or the viscosity behavior cannot be measured normally when the carbon black dispersion composition is sandwiched between the cone plates for shear viscosity measurement, the sample is rated as "unmeasurable (×)".

[0194] The storage stability of the carbon black dispersion composition was evaluated by measuring the shear viscosity of the composition after static storage at 35°C for 1 week and calculating the change in the shear viscosity after storage from the initial shear viscosity (measured immediately after dispersion). The smaller the viscosity change, the better the storage stability of the dispersion. When the shear viscosity after storage is within ±20% of the initial shear viscosity, the composition is evaluated to have satisfactory storage stability.

[0195] The results are shown in Table 1.

[0196] Table 1

[0197]

[0198] *1: “×” indicates unmeasurable

[0199] *2: MC stands for methylcellulose

[0200] *3: Viscosity of a 2 wt% aqueous solution at 20°C

[0201] *4: Amount of MC per 100 pbw of carbon black

[0202] It can be seen from Example 1 that the carbon black dispersion composition using methyl cellulose with a polydispersity index of less than 1.9 as a dispersant is superior to Comparative Examples 1 and 2 using methyl cellulose with a polydispersity index exceeding 1.9 in terms of carbon black dispersibility and storage stability.

[0203] From the results of Examples 2 to 4 and Comparative Examples 3 to 6, it can be seen that the carbon black dispersion composition using methyl cellulose having a polydispersity index of 1.9 or less as a dispersant is improved in carbon black dispersibility and storage stability.

[0204] <Preparation of mixed paste for forming positive electrode>

[0205] Using the carbon black dispersion composition of Examples 1 to 4, a mixed paste for forming a positive electrode was prepared by the following procedure.

[0206] 7.1 g of the carbon black dispersion composition of Example 1 and 14.3 g of NMP solution (concentration 7 wt%) of polyvinylidene fluoride (Mw 630000) were loaded into a mixing container and kneaded at 2000 rpm for 2 minutes using a deaerator (ARV-310, Thinky Co., Ltd.). 48.0 g of ternary positive electrode active material (NCM622) and 7.6 g of NMP were added to the premix. The mixture was kneaded at 2000 rpm for 3 minutes using a deaerator to obtain a mixed paste for forming a positive electrode with a solid concentration of 65 wt%.

[0207] By the same procedure as above, mixed pastes for forming a positive electrode were prepared from the carbon black dispersion compositions of Examples 2 to 4. All mixed pastes for forming a positive electrode could be uniformly dispersed and efficiently coated.

[0208] <Preparation of positive electrode for forming a lithium ion secondary battery>

[0209] Using the mixed paste for forming a positive electrode, a positive electrode for a lithium ion secondary battery was prepared by the following procedure.

[0210] The mixed paste for forming the positive electrode was coated on a current collector in the form of 20 μm thick and 14 mm wide aluminum foil and dried using an electrode coater / dryer (LiB-W140, Clean Technology Inc.). The coating / drying conditions included a coating thickness of 180 μm, a conveying speed of 0.2 m / min, a drying furnace length of 50 cm, and a drying furnace internal temperature of 115-125°C.

[0211] Then, using a table roller press (SA-602, Tester Industry Co., Ltd.), the dry coating obtained by the coating / drying step was rolled together with the current collector at a line pressure of 200 kg / cm to obtain a positive electrode for a lithium ion secondary battery. A positive electrode for a lithium ion secondary battery can generally be prepared from any mixed paste for forming a positive electrode.

[0212] Although the present invention has been illustrated and described in typical embodiments, it is not intended to be limited to the details shown. Various other embodiments, additions and modifications may be conceived by those skilled in the art. As long as the effects and benefits of the present invention can be achieved, all of these embodiments fall within the spirit and scope of the present invention.

Claims

1. A carbon black dispersion composition for a battery, comprising carbon black, methyl cellulose, and N-methyl-2-pyrrolidone, wherein The methylcellulose has a polydispersity index of 1.9 or less based on absolute molecular weight measurement by size exclusion chromatography (SEC) combined with multi-angle light scattering (MALS), and a viscosity of 3-30 mPa·s in a 2 wt % aqueous solution at 20° C.

2. The carbon black dispersion composition according to claim 1, wherein the content of carbon black is 5-20% by weight of the composition.

3. The carbon black dispersion composition according to claim 1, wherein the BET specific surface area of ​​the carbon black is 30-1500 m 2 / g.

4. The carbon black dispersion composition according to claim 1, wherein 1 to 20 parts by weight of methyl cellulose is present relative to 100 parts by weight of carbon black.

5. A mixed paste for forming a positive electrode, comprising the carbon black dispersion composition according to any one of claims 1 to 4, a positive electrode active material and a binder.

6. A positive electrode for forming a lithium ion secondary battery, comprising a current collector and a positive electrode mixed layer formed on the current collector by coating the mixed paste of claim 5 on the current collector and drying it. 7 . A lithium ion secondary battery comprising the positive electrode according to claim 6 , a negative electrode, an electrolyte and a separator.

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