Carbon black, slurry, coating liquid for forming positive electrode, positive electrode composition, positive electrode, and battery

Abstract

Provided is carbon black capable of achieving low electrode plate resistance even when added in small amounts.　With this carbon black, the BET specific surface area is 500 m2 / g to 1200 m2 / g, the average primary particle diameter Dp is 16 nm to 25 nm, and the structure length Dagg is 180 nm or more.

Description

Carbon black, slurry, coating liquid for forming a positive electrode, positive electrode composition, positive electrode, and battery

[0001] The present disclosure relates to carbon black, a slurry, a coating liquid for forming a positive electrode, a positive electrode composition, a positive electrode, and a battery.

[0002] In response to growing environmental and energy issues, there has been active development of technologies aimed at realizing a low-carbon society that reduces dependence on fossil fuels. Such technological development is wide-ranging, and includes the development of low-pollution vehicles such as hybrid electric vehicles and electric vehicles, natural energy generation and storage systems such as solar and wind power generation, and next-generation power transmission networks that supply electricity efficiently and reduce transmission losses.

[0003] Batteries are one of the key devices required for these technologies, and they are required to have high energy density to enable system miniaturization. They also need high output characteristics to enable stable power supply regardless of the ambient temperature. They also need good cycle characteristics to withstand long-term use. Therefore, conventional lead-acid batteries, nickel-cadmium batteries, and nickel-metal hydride batteries are rapidly being replaced by lithium-ion secondary batteries, which have higher energy density, output characteristics, and cycle characteristics.

[0004] Conventionally, the positive electrode of a lithium-ion secondary battery is manufactured by coating a current collector with a positive electrode paste containing a positive electrode active material, a conductive material, and a binder. Lithium-containing composite oxides such as lithium cobalt oxide and lithium manganese oxide have been used as the positive electrode active material. Furthermore, because the positive electrode active material has poor electrical conductivity, a conductive material such as carbon black has been added to the positive electrode paste to impart electrical conductivity (see, for example, Patent Document 1).

[0005] JP 2008-227481 A

[0006] In recent years, there has been a demand for further improvements in the performance of lithium-ion secondary batteries.

[0007] Increasing the content of the positive electrode active material in the positive electrode of a lithium-ion secondary battery can be considered as a way to improve the battery capacity. However, increasing the content of the positive electrode active material reduces the content of the conductive material, which can make it difficult to ensure sufficient conductivity.

[0008] The present disclosure aims to provide a carbon black that can achieve low plate resistance even with a small additive amount. The present disclosure also aims to provide a slurry, a coating liquid for forming a positive electrode, and a positive electrode composition that contain the carbon black and are useful for forming a positive electrode of a lithium-ion secondary battery. The present disclosure also aims to provide a positive electrode and a battery that contain the carbon black.

[0009] The present disclosure relates to, for example, the following [1] to [8]. [1] A BET specific surface area of ​​500 m ２ / g or more 1400m ２ / g or less, average primary particle diameter D ｐ is 16 nm or more and 25 nm or less, and the structure length D ａｇｇ [2] A slurry comprising the carbon black according to [1] and a liquid medium. [3] A coating liquid for forming a positive electrode comprising the carbon black according to [1], an active material, a binder, and a liquid medium. [4] The coating liquid for forming a positive electrode according to [3], in which the carbon black content is less than 1 mass% based on the total amount of solids. [5] A positive electrode composition comprising the carbon black according to [1], an active material, and a binder. [6] The positive electrode composition according to [5], in which the carbon black content is less than 1 mass%. [7] A positive electrode comprising a current collector and a composite layer disposed on the current collector, wherein the composite layer comprises the positive electrode composition according to [5] or [6]. [8] A battery comprising the positive electrode according to [7].

[0010] The present disclosure provides carbon black that can achieve low electrode plate resistance even with a small additive amount. The present disclosure also provides a slurry, a coating liquid for forming a positive electrode, and a positive electrode composition that contain the carbon black and are useful for forming a positive electrode of a lithium-ion secondary battery. The present disclosure also provides a positive electrode and a battery that contain the carbon black.

[0011] Preferred embodiments of the present disclosure will be described in detail below.

[0012] (Carbon Black) The carbon black of this embodiment is 500 m ２ / g or more 1400m ２ / g or less BET specific surface area, and an average primary particle diameter D of 16 nm or more and 25 nm or less ｐ , and a structure length (average aggregate diameter) D of 180 nm or more ａｇｇ It has.

[0013] The carbon black of the present embodiment has a large specific surface area and an average primary particle diameter D ｐ is small, and the structure length D ａｇｇ Because the carbon black has a long length, it can easily penetrate between particles of the active material and easily entangle with the particles of the active material to form a suitable conductive path. Therefore, the carbon black of this embodiment can achieve low electrode plate resistance even when added in a small amount (for example, when the content in the positive electrode composition is less than 1 mass %).

[0014] The BET specific surface area of ​​carbon black is 500m ２ / g or more, and from the viewpoint of easily obtaining a lower electrode plate resistance, 600m ２ / g or more, 700m ２ / g or more, or 800m ２ The BET specific surface area of ​​the carbon black may be 1400 m / g or more. ２ / g or less, and from the viewpoint of being easily dispersed more uniformly around the positive electrode active material, ２ / g or less, 1200m ２ / g or less, or 1100m ２ / g or less.

[0015] The BET specific surface area of ​​carbon black is measured using nitrogen as an adsorbate by a method in accordance with JIS Z8830.

[0016] Average primary particle diameter D of carbon black ｐThe average primary particle diameter D of the carbon black is 16 nm or more, and from the viewpoint of increasing the number of electrical contacts with the active material and the current collector and easily achieving a good conductivity-imparting effect, the average primary particle diameter D of the carbon black may be 16.5 nm or more, 17 nm or more, or 17.5 nm or more. ｐ is 25 nm or less, and from the viewpoint of reducing the interparticle interaction between carbon black particles and making it easier to obtain better dispersibility, it may be 24 nm or less, 22 nm or less, or 20 nm or less.

[0017] Average primary particle diameter D of carbon black ｐ is the average value of the equivalent circle diameters measured based on photographs taken with a transmission electron microscope. Specifically, ten images were taken at 100,000 magnifications using a transmission electron microscope JEM-2000FX (manufactured by JEOL Ltd.), and the equivalent circle diameters of 200 or more randomly selected primary particles were determined by image analysis, and the values ​​were then taken as the arithmetic mean.

[0018] Carbon black structure length D ａｇｇ In order to easily obtain a lower electrode plate resistance, the structure length D of the carbon black may be 190 nm or more, 200 nm or more, 210 nm or more, or 220 nm or more. ａｇｇ The particle size may be, for example, 900 nm or less, and from the viewpoint of reducing the interparticle interaction between carbon black particles and making it easier to obtain better dispersibility, the particle size may be 800 nm or less, 700 nm or less, or 600 nm or less.

[0019] The carbon black structure is defined as the structure (aggregate) of carbon black primary particles that are fused at contact points and cannot be easily separated by shear. ａｇｇ indicates the average particle size of the structure.

[0020] Carbon black structure length D ａｇｇ is calculated from SEM image analysis according to ISO 9276-6 using the imaging technique described in ASTM D3849-14a.

[0021] In carbon black, the average primary particle diameter D ｐ Structure length D ａｇｇ Ratio D ａｇｇ / D ｐ The ratio D may be, for example, 8 or more, and from the viewpoint of facilitating the formation of a network structure between the conductive materials, may be 9 or more, 10 or more, or 11 or more. ａｇｇ / D ｐ may be, for example, 30 or less, and from the viewpoint of reducing the interparticle interaction between carbon black particles and making it easier to obtain better dispersibility, may be 25 or less, 20 or less, or 15 or less.

[0022] The carbon black may be, for example, acetylene black, furnace black, channel black, etc., and from the viewpoint of obtaining the above-mentioned effects more significantly, acetylene black may be used.

[0023] Carbon black may be produced, for example, by the following method.

[0024] (Method for Producing Carbon Black) The method for producing carbon black according to the present embodiment may include, for example, a first step of reacting a raw material gas in a reactor to obtain a precursor of carbon black, and a second step of activating the precursor obtained in the first step to obtain carbon black.

[0025] In the first step, carbon black is formed by a thermal decomposition reaction and / or a combustion reaction of a raw material gas. In the second step, the carbon black (precursor) obtained in the first step is subjected to an activation treatment to increase the specific surface area, thereby forming the carbon black of the present embodiment.

[0026] The first step may be carried out, for example, by supplying a raw material gas from a nozzle installed at the top of a vertical reactor and collecting carbon nanotubes with a bag filter directly connected to the bottom of the reactor.

[0027] In the first step, the raw material gas may be, for example, acetylene gas.

[0028] In the first step, an oxygen-containing gas may be supplied to the reactor, and the oxygen-containing gas may be air, oxygen gas, or the like.

[0029] In the first step, water vapor may be supplied into the reactor. In particular, when acetylene gas is used as the raw material gas, supplying water vapor tends to cause incomplete combustion of the acetylene gas, resulting in a higher specific surface area. Furthermore, if the amount of water vapor supplied is too large, the formation of a structure due to fusion of carbon black particles may be inhibited. However, by adjusting the amount of water vapor supplied, the structure length D ａｇｇ That is, when the amount of water vapor is increased, the BET specific surface area of ​​the carbon black tends to increase, and when the amount of water vapor is decreased, the structure length D ａｇｇ tends to be larger.

[0030] The ratio (volume ratio) of the amount of water vapor supplied to the amount of raw material gas supplied may be, for example, 0 to 80 parts by volume, preferably 0.1 to 70 parts by volume, more preferably 1 to 60 parts by volume, and even more preferably 3 to 55 parts by volume, per 100 parts by volume of the carbon source (e.g., acetylene) in the raw material gas. When the content of water vapor gas is within the above range, the BET specific surface area of ​​the carbon black tends to be larger.

[0031] In the first step, a hydrocarbon gas other than the raw material gas may be further supplied to the reactor. Examples of the hydrocarbon gas include methane, ethane, propane, ethylene, propylene, butadiene, benzene, toluene, xylene, gasoline, kerosene, light oil, and heavy oil. The addition of such a hydrocarbon gas can change the reaction temperature and thereby increase or decrease the specific surface area of ​​the carbon black.

[0032] The activation treatment in the second step may be, for example, a dry method using an oxidizing gas such as air or ozone, or water vapor, or a wet method using an aqueous solution containing an oxidizing agent.

[0033] An example of a dry method is to contact carbon black with an oxidizing gas or water vapor (preferably uniformly while stirring the carbon black) in a horizontal furnace maintained at a temperature of 500 to 1000° C. Another example of a dry method is to spray carbon black from the top of a vertical furnace maintained in an oxidizing gas atmosphere at a temperature of 500 to 800° C.

[0034] The wet method can be carried out by, for example, adding carbon black (precursor) to an aqueous solution containing an oxidizing agent, treating the mixture at 50 to 120° C. for 5 to 30 hours, and then washing and drying. Examples of the oxidizing agent that can be used include hydrogen peroxide, inorganic acids such as hydrochloric acid, sulfuric acid, and nitric acid, and salts such as sodium hypochlorite and potassium dichromate.

[0035] When the activation treatment conditions are made stricter, the BET specific surface area of ​​the carbon black becomes larger, and the average primary particle diameter D ｐ becomes smaller, and the structure length D ａｇｇ tends to be shorter.

[0036] In this embodiment, the BET specific surface area and average primary particle diameter D ｐ , and structure length D ａｇｇ may be adjusted by controlling the shape of the reactor in the first step, the temperature distribution inside the reactor, etc., or by supplying water vapor into the reactor, or by adjusting the activation treatment conditions in the second step.

[0037] (Slurry) The slurry of the present embodiment contains the carbon black of the above embodiment and a liquid medium. The slurry of the present embodiment may further contain a dispersant.

[0038] The slurry of this embodiment can be suitably used as a raw material for forming a coating liquid for forming a positive electrode by mixing it with an active material and a binder.

[0039] The content of carbon black in the slurry is not particularly limited, and may be, for example, 1% by mass or more, 3% by mass or more, 5% by mass or more, or 7% by mass or more. A high carbon black content makes it easier to prepare a coating liquid for forming a positive electrode with a high solids concentration. Furthermore, the content of carbon black in the slurry may be, for example, 30% by mass or less, 25% by mass or less, 20% by mass or less, or 15% by mass or less. A low carbon black content makes it easier to prepare a coating liquid for forming a positive electrode with a low viscosity. A low viscosity coating liquid for forming a positive electrode makes it easier to obtain a uniform electrode.

[0040] The liquid medium may be any liquid medium capable of dispersing carbon black. Examples of liquid media include water, N-methyl-2-pyrrolidone, cyclohexane, methyl ethyl ketone, and methyl isobutyl ketone. Of these, N-methyl-2-pyrrolidone is preferred from the viewpoint of easy dispersibility of carbon black. In this specification, N-methyl-2-pyrrolidone may be abbreviated as "NMP."

[0041] The dispersant may be any component that has the function of assisting the dispersion of carbon black in a liquid medium. The dispersant may also be referred to as a dispersant for dispersing carbon black in a liquid medium, a dispersant for carbon black, or the like.

[0042] Examples of the dispersant include polymeric dispersants and low molecular weight dispersants, and from the viewpoint of long-term dispersion stability of carbon black, polymeric dispersants are preferred.

[0043] The polymer dispersant may be any polymer that functions as a dispersant. Examples of polymer dispersants include vinyl polymers having polar groups, carboxymethyl cellulose, and salts thereof. Such polymer dispersants are preferred because they have high affinity with both carbon black and the liquid medium and have excellent functionality as a dispersant.

[0044] Examples of polar groups include hydroxyl groups, acetyl groups, amino groups, amide groups, acetal groups, oxycarbonyl groups, and nitrile groups. The vinyl polymer preferably has at least one polar group selected from the group consisting of hydroxyl groups, acetyl groups, amino groups, and oxycarbonyl groups, and more preferably has a hydroxyl group. The hydroxyl group is preferred from the viewpoints of excellent voltage resistance and resistance to decomposition even after repeated charge and discharge.

[0045] Examples of vinyl polymers having a polar group include polyvinyl alcohol, polyvinyl acetal (e.g., polyvinyl butyral, polyvinyl formal, etc.), polyvinyl pyrrolidone, polyvinyl amine, polyvinyl acetate, polyacrylonitrile, etc. Among these, polyvinyl alcohol and polyvinyl pyrrolidone are preferred from the viewpoints of high solubility in NMP and high adsorption to carbon black, and polyvinyl alcohol is more preferred from the viewpoints of excellent voltage resistance and having hydroxy groups that are not easily decomposed even after repeated charge and discharge.

[0046] The content of the dispersant in the slurry may be, for example, 1 part by mass or more, 3 parts by mass or more, 5 parts by mass or more, or 7 parts by mass or more, relative to 100 parts by mass of carbon black. A high content of the dispersant tends to make it easier for the carbon black to be dispersed more uniformly, and to make it easier to obtain better battery characteristics. The content of the dispersant in the slurry may be, for example, 30 parts by mass or less, 25 parts by mass or less, 20 parts by mass or less, or 15 parts by mass or less, relative to 100 parts by mass of carbon black. A low content of the dispersant tends to reduce the insulating component in the positive electrode composition, making it easier to obtain lower electrode plate resistance.

[0047] The slurry of the present embodiment may further contain components other than the carbon black, the liquid medium, and the dispersant, such as carbon nanotubes, graphite, graphene, a binder, a dispersion stabilizer, and a defoaming agent.

[0048] The content of other components may be, for example, 50 parts by mass or less, 45 parts by mass or less, 40 parts by mass or less, or 35 parts by mass or less, relative to 100 parts by mass of carbon black, or may be 0% by mass.

[0049] The slurry of this embodiment can be produced by mixing carbon black with a liquid medium (and further with a dispersant, if necessary).

[0050] The mixing method is not limited, and may be carried out by a known method (for example, stirring and mixing using a bead mill, ball mill, sand mill, twin-screw kneader, planetary mixer, disper mixer, etc.). These methods and devices may also be used in appropriate combination.

[0051] (Positive Electrode Forming Coating Liquid) The positive electrode forming coating liquid of this embodiment contains the carbon black of the above embodiment, a liquid medium, an active material, and a binder. The positive electrode forming coating liquid of this embodiment may further contain a dispersant.

[0052] The positive electrode-forming coating liquid of this embodiment can be applied to a current collector and dried to form a composite layer on the current collector. The current collector and the composite layer disposed on the current collector can be suitably used as a positive electrode, particularly as a positive electrode for a lithium-ion secondary battery.

[0053] In the coating liquid for forming a positive electrode of this embodiment, examples of the liquid medium and dispersant are the same as those mentioned above.

[0054] The active material (positive electrode active material) is not particularly limited as long as it is a material that can reversibly absorb and release cations. ４ The lithium-containing composite oxide may be a lithium-containing composite oxide containing manganese having a resistivity of Ω cm or more, or a lithium-containing polyanion compound. Examples of the lithium-containing composite oxide containing manganese include LiMnO ２ , LiMnO ３ , LiMn ２ O ３ , Li １＋ｘ Mn ２－ｘ O ４ Lithium manganate such as LiMn (where x = 0 to 0.33); ｘ Niｙ Co ｚ O ２ (However, x+y+z=1, 0≦y<1, 0≦z<1, 0≦x<1), Li １＋ｘ Mn ２－ｘ－ｙ M ｙ O ４ (where x = 0 to 0.33, y = 0 to 1.0, 2-x-y > 0), LiMn ２－ｘ M ｘ O ２ (where x = 0.01 to 0.1), Li ２ Mn ３ MO ８ Examples of lithium-containing polyanion compounds include composite oxides containing one or more transition metal elements such as LiFePO ４ , LiMnPO ４ , Li ２ MPO ４ Examples of suitable anionic compounds include polyanionic compounds such as F (wherein M is at least one metal selected from Co, Ni, Fe, Cr, and Zn), in which M in each composition formula is at least one metal selected from the group consisting of Fe, Co, Ni, Al, Cu, Mg, Cr, Zn, and Ta.

[0055] The average particle diameter of the active material (D ５０ ) may be, for example, 3 μm or more, and from the viewpoint of more significantly obtaining the above-mentioned effects of carbon black, it may be 5 μm or more, 10 μm or more, or 20 μm or more. ５０ ) may be, for example, 45 μm or less, and from the viewpoint of more significantly obtaining the above-mentioned effects of carbon black, it may be 40 μm or less, 35 μm or less, or 30 μm or less.

[0056] The average particle diameter of the active material (D ５０ ) is measured by laser light scattering.

[0057] Examples of binders include polyvinylidene fluoride, polytetrafluoroethylene, styrene-butadiene copolymer, (meth)acrylic acid ester copolymer, etc. The polymer structure of the binder may be, for example, a random copolymer, an alternating copolymer, a graft copolymer, a block copolymer, etc. As the binder, polyvinylidene fluoride is preferred from the viewpoint of excellent voltage resistance.

[0058] The carbon black content in the positive electrode-forming coating liquid may be, for example, 0.01% by mass or more, based on the total amount of solids, and from the viewpoint of obtaining lower plate resistance, it may be 0.05% by mass or more, 0.1% by mass or more, 0.3% by mass or more, or 0.5% by mass or more. Furthermore, the carbon black content in the positive electrode-forming coating liquid may be, for example, 10% by mass or less, 5% by mass or less, 3% by mass or less, or 1% by mass or less, based on the total amount of solids, and from the viewpoint of achieving sufficiently low plate resistance with a low addition amount, it may be less than 1% by mass, 0.9% by mass or less, or 0.8% by mass or less.

[0059] The content of the active material in the positive electrode-forming coating liquid may be, for example, 80% by mass or more, 85% by mass or more, 90% by mass or more, 95% by mass or more, 97% by mass or more, or 98% by mass or more, based on the total amount of solids. In this embodiment, since the above-mentioned carbon black is used, even if the amount of carbon black added is reduced and the content of the active material is increased, a sufficiently low electrode plate resistance is achieved. The content of the active material in the positive electrode-forming coating liquid may be, for example, 99.9% by mass or more, based on the total amount of solids, and may be 99.7% by mass or less, 99.5% by mass or less, 99.3% by mass or less, or 99% by mass or less.

[0060] The content of the binder in the positive electrode-forming coating liquid may be, for example, 0.1% by mass or more based on the total amount of solids, and from the viewpoint of further improving the binding property of the composite layer and further improving battery performance, it may be 0.2% by mass or more, 0.3% by mass or more, 0.4% by mass or more, or 0.5% by mass or more. Furthermore, the content of the binder in the positive electrode-forming coating liquid may be, for example, 10% by mass or less based on the total amount of solids, and from the viewpoint of more easily obtaining a lower electrode plate resistance, it may be 5% by mass or less, 4% by mass or less, 3% by mass or less, 2% by mass or less, or 1.5% by mass or less.

[0061] When the positive electrode-forming coating liquid contains a dispersant, the content of the dispersant in the positive electrode-forming coating liquid may be, for example, 1 part by mass or more, or may be 3 parts by mass or more, 5 parts by mass or more, or 7 parts by mass or more, relative to 100 parts by mass of carbon black. Furthermore, the content of the dispersant in the positive electrode-forming coating liquid may be, for example, 30 parts by mass or less, or may be 25 parts by mass or less, 20 parts by mass or less, or 15 parts by mass or less, relative to 100 parts by mass of carbon black.

[0062] The solids concentration of the positive electrode-forming coating liquid is not particularly limited, and may be any solids concentration that allows the formation of a composite layer, i.e., a viscosity that allows coating onto a current collector. The solids concentration of the positive electrode-forming coating liquid may be, for example, 40% by mass or more, 50% by mass or more, 60% by mass or more, or 70% by mass or more. The solids concentration of the positive electrode-forming coating liquid may be, for example, 95% by mass or less, 90% by mass or less, 85% by mass or less, or 80% by mass or less.

[0063] The solid content of the coating liquid for forming a positive electrode may be, for example, the remainder after removing the liquid medium from the coating liquid for forming a positive electrode, and includes carbon black, an active material, and a binder.

[0064] The coating liquid for forming a positive electrode of this embodiment may be prepared by, for example, mixing the slurry of the above embodiment, a binder-containing solution, and an active material, or by mixing the slurry of the above embodiment with the binder-containing solution and then further mixing the active material. Furthermore, the viscosity may be adjusted by adding a liquid medium after mixing the active material.

[0065] The binder-containing solution may contain a binder and a solvent, and examples of the solvent include the same liquid medium as in the slurry of the above embodiment.

[0066] The solids concentration of the binder-containing solution is not particularly limited and may be, for example, 0.3% by mass or more, and from the viewpoint of further improving the binding strength of the positive electrode plate and further improving the cycle characteristics, it may be 0.5% by mass or more, 1.0% by mass or more, or 1.5% by mass or more. The binder content may be, for example, 5.0% by mass or less based on the total mass of the solids in the positive electrode composition, and from the viewpoint of further reducing the resistance of the positive electrode plate and further improving the discharge rate characteristics, it may be 4.5% by mass or less, 4.0% by mass or less, or 3.5% by mass or less.

[0067] (Positive Electrode Composition) The positive electrode composition of this embodiment contains the carbon black of the above embodiment, an active material, and a binder. The positive electrode composition of this embodiment may further contain a dispersant.

[0068] The positive electrode composition of the present embodiment may be a composition constituting a composite layer disposed on a current collector. A positive electrode including a composite layer made of the positive electrode composition of the present embodiment can be suitably used as a positive electrode for a lithium-ion secondary battery.

[0069] In the positive electrode composition of this embodiment, examples of the active material, binder, and dispersant are the same as those described above.

[0070] The content of carbon black in the positive electrode composition may be, for example, 0.01% by mass or more, and from the viewpoint of obtaining lower electrode plate resistance, it may be 0.05% by mass or more, 0.1% by mass or more, 0.3% by mass or more, or 0.5% by mass or more. Furthermore, the content of carbon black in the positive electrode composition may be, for example, 10% by mass or less, 5% by mass or less, 3% by mass or less, or 1% by mass or less, and from the viewpoint of achieving sufficiently low electrode plate resistance with a small addition amount, it may be less than 1% by mass, 0.9% by mass or less, or 0.8% by mass or less.

[0071] The content of the active material in the positive electrode composition may be, for example, 80% by mass or more, 85% by mass or more, 90% by mass or more, 95% by mass or more, 97% by mass or more, or 98% by mass or more. In this embodiment, since the above-mentioned carbon black is used, even if the amount of carbon black added is reduced and the content of the active material is increased, a sufficiently low electrode plate resistance is achieved. The content of the active material in the positive electrode composition may be, for example, 99.9% by mass or more, 99.7% by mass or less, 99.5% by mass or less, 99.3% by mass or less, or 99% by mass or less.

[0072] The content of the binder in the positive electrode composition may be, for example, 0.1% by mass or more, and from the viewpoint of further improving the binding property of the composite layer and further improving battery performance, it may be 0.2% by mass or more, 0.3% by mass or more, 0.4% by mass or more, or 0.5% by mass or more. Furthermore, the content of the binder in the positive electrode composition may be, for example, 10% by mass or less, and from the viewpoint of more easily obtaining a lower electrode plate resistance, it may be 5% by mass or less, 4% by mass or less, 3% by mass or less, 2% by mass or less, or 1.5% by mass or less.

[0073] When the positive electrode composition contains a dispersant, the content of the dispersant in the positive electrode composition may be, for example, 1 part by mass or more, 3 parts by mass or more, 5 parts by mass or more, or 7 parts by mass or more relative to 100 parts by mass of carbon black. Furthermore, the content of the dispersant in the positive electrode composition may be, for example, 30 parts by mass or less, 25 parts by mass or less, 20 parts by mass or less, or 15 parts by mass or less relative to 100 parts by mass of carbon black.

[0074] (Positive Electrode) The positive electrode of this embodiment includes a current collector and a mixture layer. The mixture layer includes the carbon black of the above embodiment.

[0075] The composite layer may include the positive electrode composition of the above embodiment, or may be made of the positive electrode composition of the above embodiment. Furthermore, the composite layer may be formed by applying and drying the positive electrode-forming coating liquid of the above embodiment, or may include the solid content of the positive electrode-forming coating liquid of the above embodiment.

[0076] The positive electrode of this embodiment may be manufactured, for example, by forming a composite layer on a current collector using a positive electrode-forming coating liquid. The composite layer can be formed, for example, by applying the positive electrode-forming coating liquid to a current collector, drying it, and, if necessary, pressing, cutting, or the like.

[0077] The current collector is not particularly limited, and known current collectors can be used without any particular limitation. For example, metal foils (metals such as gold, silver, copper, platinum, aluminum, iron, nickel, chromium, manganese, lead, tungsten, and titanium, and alloys containing any one of these as the main component) are used as current collectors. Among these, it is preferable to use aluminum for the positive electrode and copper for the negative electrode. Current collectors are generally provided in the form of foils, but are not limited thereto, and perforated foil and mesh-shaped current collectors can also be used.

[0078] The method for applying the coating liquid for forming a positive electrode onto the current collector is not particularly limited, and may be, for example, a die coating method, a dip coating method, a roll coating method, a doctor coating method, a knife coating method, a spray coating method, a gravure coating method, a screen printing method, or an electrostatic coating method.

[0079] The amount of the coating liquid for forming a positive electrode to be applied is not particularly limited, and may be adjusted appropriately so that the thickness of the composite layer falls within a desired range.

[0080] The composite layer may be formed by removing at least a portion of the liquid medium from a coating film of the positive electrode-forming coating liquid formed on the current collector. The method for removing the liquid medium is not particularly limited, and examples of the method for removing the liquid medium include leaving it to dry, using a blower dryer, a hot air dryer, an infrared heater, and a far-infrared heater, and the like, as methods for vaporizing and removing at least a portion of the liquid medium by heating and / or reducing pressure.

[0081] In manufacturing the positive electrode of this embodiment, a pressurizing step may be performed in which the composite layer and the current collector are pressed in the stacking direction. The pressurizing step can improve the adhesion between the composite layer and the current collector.

[0082] The pressing method in the pressing step is not particularly limited, and may be, for example, a roll press, a mold press, a calendar press, or the like.

[0083] The thickness of the composite layer in the positive electrode is not particularly limited and may be, for example, 50 μm or more, and from the viewpoint of increasing the capacity of the battery, it is preferably 55 μm or more, more preferably 60 μm or more, and may be 65 μm or more or 70 μm or more. Furthermore, the thickness of the composite layer in the positive electrode may be, for example, 150 μm or less, and from the viewpoint of further improving the discharge rate characteristics, it is preferably 140 μm or less, more preferably 130 μm or less, and may be 120 μm or less or 110 μm or less.

[0084] The positive electrode of this embodiment can be suitably used as a positive electrode for a battery, particularly a secondary battery (lithium ion secondary battery).

[0085] (Battery) The battery of this embodiment includes the positive electrode of the above embodiment. The battery of this embodiment may be a secondary battery or a lithium ion secondary battery.

[0086] In the battery of this embodiment, the configuration other than the positive electrode may be the same as that of a known battery.

[0087] The uses of the battery of the present embodiment are not particularly limited, and the battery can be used in a wide range of fields, for example, portable AV devices such as digital cameras, video cameras, portable audio players, and portable LCD televisions, portable information terminals such as notebook personal computers, smartphones, and mobile PCs, as well as portable game devices, power tools, electric bicycles, hybrid vehicles, electric vehicles, and power storage systems.

[0088] Although the preferred embodiments of the present disclosure have been described above, the present disclosure is not limited to the above embodiments.

[0089] For example, one aspect of the present disclosure is a sintered body having a BET specific surface area of ​​500 m ２ / g or more 1200m ２ / g or less, average primary particle diameter D ｐ For carbon black having a structure length D of 16 nm or more and 25 nm or less, ａｇｇ A measurement step of measuring the structure length D ａｇｇ The present invention may relate to a method for evaluating or sorting carbon black, in which carbon black is evaluated or sorted based on the above.

[0090] According to such an evaluation method or selection method, it is possible to easily evaluate or select carbon black that can achieve low electrode plate resistance even with a small amount added.

[0091] The present disclosure will be described in more detail below with reference to examples, but the present disclosure is not limited to these examples.

[0092] Example 1 (1) Preparation of Carbon Black A-1 (Manufacturing of Carbon Black) Carbon black A-1 was manufactured by the following method. Acetylene, a raw material, was injected at 12 Nm from a nozzle installed upstream of a carbon black reactor (furnace length 6 m, furnace diameter 0.65 m). ３ / h, toluene 32 kg / h, oxygen 20 Nm ３ / h to produce carbon black, which was then collected in a bag filter installed downstream of the reactor. The carbon black was then passed through a dry cyclone device and an iron-removing magnet and collected in a tank. The acetylene, toluene, and oxygen were heated to 115°C before being supplied to the reactor to produce carbon black. The carbon black obtained had a BET specific surface area of ​​301 m. ２ / g, average primary particle diameter D ｐ The carbon black thus obtained was subjected to activation treatment in a kiln furnace under a nitrogen atmosphere at a temperature of 900°C with a water vapor amount of 18 mL / min for 2 hours to obtain carbon black A-1.

[0093] The obtained carbon black A-1 was measured for its BET specific surface area and average primary particle diameter D ｐ , and structure length D ａｇｇ The results are shown in Table 1.

[0094] (Measurement of BET Specific Surface Area) The BET specific surface area of ​​carbon black A-1 was measured in accordance with JIS K6217-2 using "Macsorb 1201" (manufactured by MOUNTECH Co., Ltd.).

[0095] (Average primary particle diameter D ｐ Measurement of the average primary particle diameter D of carbon black A-1 ｐwas determined by measuring the primary particle diameters of 100 or more carbon black particles randomly selected from a 50,000x magnification image taken by a transmission electron microscope (TEM) and calculating the average value. The primary particles of Carbon Black A-1 have a small aspect ratio and are close to being spherical, but are not completely spherical. Therefore, in this embodiment, the largest line segment connecting two points on the periphery of a primary particle in the TEM image was used as the primary particle diameter of the carbon black.

[0096] (Structure length D ａｇｇ Measurement of carbon black structure length D ａｇｇ was calculated from SEM image analysis according to ISO 9276-6 using the imaging technique described in ASTM D3849-14a.

[0097]

[0098] (Preparation of Carbon Black Slurry) Carbon black A-1, N-methyl-2-pyrrolidone (referred to as NMP) as a dispersion medium, and polyvinyl alcohol (Poval B05, manufactured by Denka Co., Ltd.) as a dispersant were prepared. 1.0% by mass of polyvinyl alcohol and 11.0% by mass of carbon black A-1 were added to 89.0% by mass of NMP, and the mixture was stirred for 120 minutes using a planetary mixer (Hivis Dispermix 3D-5, manufactured by Primix Corporation) to obtain a slurry. The resulting slurry was then placed in a bead mill (Mugen Flow MGF2-ZA, manufactured by Ashizawa Finetech Co., Ltd.) equipped with zirconia beads (diameter 0.5 mm) and subjected to a dispersion treatment. After the dispersion treatment, the zirconia beads were removed by filtration to obtain a slurry of carbon black A-1 (first slurry).

[0099] (2) Preparation and Evaluation of Positive Electrode Positive electrodes were prepared by the following method. (Preparation of Positive Electrode-Forming Coating Liquid) ５０A conductive material slurry using lithium nickel manganese cobalt oxide (manufactured by Beijing Dangsheng Co., Ltd., "ME6E") having a particle size of 10 μm, carbon black A as a conductive material, an NMP solution of polyvinylidene fluoride as a binder, and NMP as a dispersion medium were prepared, and these were added to a container so as to have a solid content composition as shown in Table 1, and mixed until uniform using a planetary centrifugal mixer (manufactured by Thinky Corporation, Awatori Rentaro ARV-310), to obtain a coating liquid for forming a positive electrode.

[0100] (Preparation of Positive Electrode) The prepared positive electrode-forming coating liquid was applied to one side of a 15 μm thick aluminum foil (manufactured by UACJ Corporation) using an applicator, and then placed in a dryer and pre-dried at 105 ° C for one hour to completely remove the NMP solvent. Next, the aluminum foil was pressed with a roll press at a linear pressure of 200 kg / cm to form a composite layer on the aluminum foil. The amount of positive electrode-forming coating liquid applied was such that the total thickness of the aluminum foil and the composite layer was 80 μm. Next, to completely remove residual moisture, the positive electrode was vacuum-dried at 170 ° C for 3 hours to obtain a positive electrode. The electrode plate resistance of the obtained positive electrode was measured using the following method. The results are shown in Table 2.

[0101] (Measurement of electrode plate resistance) An electrode resistance measuring device (manufactured by Hioki E.E. Corporation, product name: RM2610) was used, and the operation mode was: potential measurement + calculation, potential measurement: contact check - threshold 1.0. ７ The measurement was performed under the conditions of Ω and Auto range. The electrode plate resistance was the sum of the interface resistance between the positive electrode composite layer and the aluminum current collector and the composite resistance of the positive electrode composite layer. The voltage range was measured within a range where the resistance value did not overload.

[0102] (3) Preparation and Evaluation of Battery A battery for evaluation was prepared by the following method. (Preparation of Negative Electrode) Pure water (manufactured by Kanto Chemical Co., Ltd.) was used as the solvent, artificial graphite (manufactured by Hitachi Chemical Co., Ltd., "MAG-D") was used as the negative electrode active material, styrene butadiene rubber (manufactured by Nippon Zeon Co., Ltd., "BM-400B", hereinafter referred to as SBR) was used as the binder, and carboxymethyl cellulose (manufactured by Daicel Corporation, "D2200", hereinafter referred to as CMC) was used as the dispersant. Next, CMC was weighed and mixed so that the solid content was 1 mass % and the solid content was 97 mass %, and pure water was added to this mixture, and the mixture was mixed until uniform using a planetary centrifugal mixer (manufactured by Thinky Corporation, Awatori Rentaro ARV-310). Furthermore, SBR was weighed out so that the solid content was 2% by mass, added to the above mixture, and mixed until uniform using a planetary centrifugal mixer (Thinky Corporation, Awatori Rentaro ARV-310) to obtain a negative electrode slurry. Next, the negative electrode slurry was formed into a film on a 10 μm thick copper foil (manufactured by UACJ Corporation) using an applicator, and then placed in a dryer and pre-dried at 60 ° C. for one hour. Next, it was pressed with a roll press at a linear pressure of 50 kg / cm, and the thickness of the coating film containing the copper foil was adjusted to 60 μm. In order to completely remove residual moisture, it was vacuum dried at 120 ° C. for 3 hours to obtain a negative electrode.

[0103] (Battery Fabrication) In a dry room controlled at a dew point of -50°C or less, the positive electrode was processed to 40 x 40 mm, and the negative electrode was processed to 44 x 44 mm. An aluminum tab was then welded to the positive electrode and a nickel tab was welded to the negative electrode. The composite-coated surfaces of the positive electrode and negative electrode were arranged to face each other in the center, and a polyolefin microporous film processed to 45 x 45 mm was placed between the positive electrode and negative electrode. Next, a sheet-shaped exterior cut and processed to a 70 x 140 mm square was folded in half at the center of the long side. Next, the exterior was positioned so that the aluminum tab for the positive electrode and the nickel tab for the negative electrode were exposed to the outside of the exterior, and the positive electrode-polyolefin microporous film-negative electrode laminate was sandwiched between the folded exterior. Next, using a heat sealer, two sides of the exterior, including the side where the aluminum tab for the positive electrode and the nickel tab for the negative electrode were exposed, were heat-sealed, and then 2 g of electrolyte (Kishida Chemical, ethylene carbonate / diethyl carbonate = 1 / 2 (volume ratio) + 1 M LiPF ６A solution (hereinafter referred to as the electrolyte solution) was poured into the battery and allowed to fully penetrate the positive electrode, negative electrode, and polyolefin microporous membrane. The remaining side of the exterior was then heat-sealed using a vacuum heat sealer while reducing the internal pressure to obtain a battery. The resulting battery was evaluated using the following methods. The results are shown in Table 2.

[0104] (Battery Evaluation) The fabricated battery was charged at a constant current and constant voltage of 4.3 V at 25°C with a limit of 0.2 C, and then discharged to 3.0 V at a constant current of 0.2 C. Next, after five charge / discharge cycles under the same conditions, the battery was charged to a charge depth of 50%. Then, impedance measurements were performed at a frequency range of 10 MHz to 0.001 Hz and an oscillating voltage of 5 mV to evaluate the internal resistance.

[0105] (4) Changes in Composition The compositions of carbon black (referred to as the conductive material in the table), active material, and binder in the coating liquid for forming a positive electrode were changed as shown in Table 2, and positive electrodes and batteries were fabricated and evaluated in the same manner as in (2) and (3) above. The results are shown in Table 2.

[0106]

[0107] Example 2 (1) Preparation of Carbon Black A-2 Carbon black A-2 was produced in the same manner as in Example 1, except that the amount of steam in the activation treatment conditions for the carbon black was changed to 9 ml / min. The BET specific surface area and average primary particle diameter D ｐ , and structure length D ａｇｇ The results are shown in Table 3.

[0108]

[0109] (2) Preparation and Evaluation of Positive Electrode and Electrode Except for using carbon black A-2 instead of carbon black A-1, a positive electrode and an electrode were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 4.

[0110]

[0111] Example 3 (1) Preparation of Carbon Black A-3 Carbon black A-3 was produced in the same manner as in Example 1, except that the activation time in the carbon black activation treatment conditions was changed to 5 hours. The BET specific surface area and average primary particle diameter D ｐ , and structure length D ａｇｇ The results are shown in Table 5.

[0112]

[0113] (2) Preparation and Evaluation of Positive Electrode and Electrode Except for using Carbon Black A-3 instead of Carbon Black A-1, a positive electrode and an electrode were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 6.

[0114]

[0115] Example 4 (1) Preparation of Carbon Black A-4 Carbon black A-4 was produced in the same manner as in Example 1, except that the activation treatment conditions for carbon black were changed to 5 hours and the amount of steam was changed to 27 ml / min.

[0116] The obtained carbon black A-4 was measured for the BET specific surface area and the average primary particle diameter D ｐ , and structure length D ａｇｇ The results are shown in Table 7.

[0117]

[0118] (2) Preparation and Evaluation of Positive Electrode and Electrode Except for using Carbon Black A-4 instead of Carbon Black A-1, a positive electrode and an electrode were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 8.

[0119]

[0120] Comparative Example 1 (1) Preparation of Carbon Black B-1 Carbon black B-1 having the properties shown in Table 9 was prepared.

[0121]

[0122] (2) Preparation and Evaluation of Positive Electrode and Electrode Except for using carbon black B-1 instead of carbon black A-1, a positive electrode and an electrode were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 10.

[0123]

[0124] Comparative Example 2 (1) Preparation of Carbon Black B-2 Carbon black B-2 having the properties shown in Table 11 was prepared.

[0125]

[0126] (2) Preparation and Evaluation of Positive Electrode and Electrode Except for using carbon black B-2 instead of carbon black A-1, a positive electrode and an electrode were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 12.

[0127]

[0128] Comparative Example 3 (1) Preparation of Carbon Black B-3 Carbon black B-3 having the properties shown in Table 13 was prepared.

[0129]

[0130] (2) Preparation and Evaluation of Positive Electrode and Electrode Except for using carbon black B-3 instead of carbon black A-1, a positive electrode and an electrode were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 14.

[0131]

[0132] As described above, in the low-addition compositions in which the amount of carbon black added was less than 1 mass %, Examples 1 to 4 yielded positive electrodes with lower plate resistance than Comparative Examples 1 to 3.

Claims

1. BET specific surface area is 500m ２ / g or more 1400m ２ / g or less, average primary particle diameter D ｐ is 16 nm or more and 25 nm or less, and the structure length D ａｇｇ Carbon black having a particle size of 180 nm or more.

2. A slurry comprising the carbon black of claim 1 and a liquid medium.

3. A coating liquid for forming a positive electrode, comprising the carbon black according to claim 1, an active material, a binder, and a liquid medium.

4. The coating liquid for forming a positive electrode according to claim 3, wherein the content of the carbon black is less than 1 mass % based on the total amount of solids.

5. A positive electrode composition comprising the carbon black of claim 1, an active material, and a binder.

6. The positive electrode composition according to claim 5, wherein the carbon black content is less than 1% by mass.

7. A positive electrode comprising a current collector and a composite layer disposed on the current collector, wherein the composite layer comprises the positive electrode composition according to claim 5 or 6.

8. A battery comprising the positive electrode of claim 7.

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