Positive electrode composition, positive electrode, battery, method for manufacturing coating liquid for forming positive electrode, method for manufacturing positive electrode, and method for manufacturing battery

Abstract

This positive electrode composition contains carbon black, carbon nanotubes, a binder, and an active material. When the carbon black has been divided into first primary aggregates having an X value higher than 1.7, second primary aggregates having a Y value of 1.2 or lower, third primary aggregates having a Z value of 2.0 or lower, and fourth primary aggregates having an X value of 1.7 or lower, a Y value higher than 1.2, and a Z value higher than 2.0, the total number of the second and third primary aggregates accounts for 22% or more.　Drawing_references_to_be_translated:<sp / > <sp / >

Description

Technical Field

[0001] The present invention relates to a positive electrode composition, a positive electrode, a battery, a method for producing a coating liquid for forming a positive electrode, a method for producing a positive electrode, and a method for producing a battery.

Background Art

[0002] Due to the increasing environmental and energy problems, the development of technologies for realizing a low-carbon society with reduced dependence on fossil fuels has been actively carried out. Such technological developments include the development of low-emission vehicles such as hybrid electric vehicles and electric vehicles, the development of natural energy power generation and storage systems such as solar power generation and wind power generation, and the development of next-generation power grids that efficiently supply power and reduce power transmission losses. etc., covering a wide range.

[0003] One of the key devices required in common for these technologies is a battery, and for such a battery, a high energy density for miniaturizing the system is required. In addition, high output characteristics are required to enable stable power supply regardless of the operating environment temperature. Furthermore, good cycle characteristics that can withstand long-term use are also required. Therefore, there has been a rapid shift from conventional lead-acid batteries, nickel-cadmium batteries, and nickel-metal hydride batteries to lithium-ion secondary batteries having higher energy density, output characteristics, and cycle characteristics.

[0004] Conventionally, the positive electrode of a lithium-ion secondary battery has been manufactured by coating a positive electrode paste containing a positive electrode active material, a conductive material, and a binder (also referred to as a binder) on a current collector. As the positive electrode active material, lithium-containing composite oxides such as lithium cobaltate and lithium manganate have been used. In addition, since the positive electrode active material has poor conductivity, a conductive material such as carbon black has been added to the positive electrode paste for the purpose of imparting conductivity (for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0005] Patent Document 1 Japanese Patent Application Laid-Open No. 2008-227481 Summary of the Invention Problems to be Solved by the Invention

[0006] In recent years, further performance improvements have been demanded in batteries such as lithium-ion secondary batteries.

[0007] An object of the present invention is to provide a positive electrode composition capable of realizing a battery having a small internal resistance and excellent discharge rate characteristics and cycle characteristics. Another object of the present invention is to provide a method for producing a coating liquid for forming a positive electrode capable of realizing a battery having a small internal resistance and excellent discharge rate characteristics and cycle characteristics. Another object of the present invention is to provide a positive electrode capable of realizing a battery having a small internal resistance and excellent discharge rate characteristics and cycle characteristics and a method for producing the same. Furthermore, an object of the present invention is to provide a battery including the positive electrode and a method for producing the same. Means for Solving the Problems

[0008] The present invention relates to, for example, the following <1> to <7>. <1> containing carbon black, carbon nanotubes, a binder, and an active material, the carbon nanotubes having an average diameter of 5 to 15 nm, When the carbon black is classified into a first primary aggregate in which the X value obtained by the following formula (X) exceeds 1.7, a second primary aggregate in which the X value is 1.7 or less and the Y value obtained by the following formula (Y) is 1.2 or less, a third primary aggregate in which the X value is 1.7 or less, the Y value exceeds 1.2, and the Z value obtained by the following formula (Z) is 2.0 or less, and a fourth primary aggregate in which the X value is 1.7 or less, the Y value exceeds 1.2, and the Z value exceeds 2.0, the number ratio of the total number of the second primary aggregate and the third primary aggregate to the total number of the first primary aggregate, the second primary aggregate, the third primary aggregate, and the fourth primary aggregate is 22% or more, a positive electrode composition. X = L / W (X) Y = P 2 / 4πA (Y) Z = (L×W) / A (Z) [In the formula, in the two-dimensional projection image of the primary aggregate by a transmission electron microscope, the Feret diameter in the short axis direction of the primary aggregate is W (μm), the Feret diameter in the long axis direction of the primary aggregate is L (μm), the perimeter of the primary aggregate is P (μm), and the projected area of the primary aggregate is A (μm 2 ).] <2> The ratio of the average diameter to the BET specific surface area of the carbon nanotube (average diameter / BET specific surface area) is 0.01 to 0.1 nm / (m 2 / g), the positive electrode composition according to <1>. <3> A positive electrode including a composite material layer made of the positive electrode composition according to <1> or <2>. <4> A battery including the positive electrode according to <3>. <5> A mixing step of mixing carbon black and a first liquid medium to obtain a first agent containing the carbon black and the first liquid medium, A coating liquid forming step of mixing the first agent, a second agent containing carbon nanotubes and a second liquid medium, a third agent containing a binder and a third liquid medium, and an active material to form a coating liquid for forming a positive electrode, including, The carbon nanotube has an average diameter of 5 to 15 nm, When the carbon black is classified into a first primary aggregate in which the X value obtained by the following formula (X) exceeds 1.7, a second primary aggregate in which the X value is 1.7 or less and the Y value obtained by the following formula (Y) is 1.2 or less, a third primary aggregate in which the X value is 1.7 or less, the Y value exceeds 1.2, and the Z value obtained by the following formula (Z) is 2.0 or less, and a fourth primary aggregate in which the X value is 1.7 or less, the Y value exceeds 1.2, and the Z value exceeds 2.0, the number ratio of the total number of the second primary aggregate and the third primary aggregate to the total number of the first primary aggregate, the second primary aggregate, the third primary aggregate, and the fourth primary aggregate is 22% or more. A method for producing a coating liquid for forming a positive electrode. X = L / W (X) Y = P 2 / 4πA (Y) Z = (L×W) / A (Z) [In the formula, in the two-dimensional projection image of the primary aggregate by a transmission electron microscope, the Feret diameter in the short axis direction of the primary aggregate is W (μm), the Feret diameter in the long axis direction of the primary aggregate is L (μm), the perimeter of the primary aggregate is P (μm), and the projected area of the primary aggregate is A (μm 2 2).] <6> A method for producing a positive electrode, including a positive electrode forming step of applying a coating liquid for forming a positive electrode produced by the production method according to <5> onto a current collector to form a composite material layer composed of a positive electrode composition containing the carbon black, the carbon nanotube, the binder, and the active material on the current collector, and obtaining a positive electrode including the current collector and the composite material layer. <7> A method for producing a battery, including a positive electrode forming step of applying a coating liquid for forming a positive electrode produced by the production method according to <5> onto a current collector to form a composite material layer composed of a positive electrode composition containing the carbon black, the carbon nanotube, the binder, and the active material on the current collector, and obtaining a positive electrode including the current collector and the composite material layer.

Advantages of the Invention

[0009] According to the present invention, there is provided a positive electrode composition capable of realizing a battery having a small internal resistance and excellent discharge rate characteristics and cycle characteristics. Further, according to the present invention, there is provided a method for producing a coating liquid for forming a positive electrode capable of realizing a battery having a small internal resistance and excellent discharge rate characteristics and cycle characteristics. Further, according to the present invention, there is provided a positive electrode capable of realizing a battery having a small internal resistance and excellent discharge rate characteristics and cycle characteristics and a method for manufacturing the same. Furthermore, according to the present invention, there are provided a battery including the positive electrode and a method for manufacturing the same.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0011] Hereinafter, preferred embodiments of the present invention will be described in detail. In this specification, carbon black may be abbreviated as "CB" and carbon nanotube may be abbreviated as "CNT". Further, in this specification, the tilde symbol "~" is a symbol used to indicate a numerical range including the numerical values described before and after it. Specifically, the description "X~Y" (both X and Y are numerical values) indicates "X or more and Y or less".

[0012] <Carbon Black> The carbon black of the present embodiment is divided into a first primary aggregate in which the X value obtained by formula (X) exceeds 1.7, a second primary aggregate in which the X value is 1.7 or less and the Y value obtained by formula (Y) is 1.2 or less, a third primary aggregate in which the X value is 1.7 or less, the Y value exceeds 1.2, and the Z value obtained by formula (Z) is 2.0 or less, and a fourth primary aggregate in which the X value is 1.7 or less, the Y value exceeds 1.2, and the Z value exceeds 2.0. When classified in this way, the carbon black is such that the number ratio of the total number (N2 + N3) of the second and third primary aggregates to the total number (N1 + N2 + N3 + N4) of the first, second, third, and fourth primary aggregates is 22% or more. X = L / W (X) Y = P 2 / 4πA (Y) Z = (L×W) / A (Z)

[0013] In formulas (X), (Y), and (Z), in the two-dimensional projection image of the primary aggregate obtained by a transmission electron microscope, the Feret diameter (short diameter) in the short axis direction of the primary aggregate is W (μm), the Feret diameter (long diameter) in the long axis direction of the primary aggregate is L (μm), the perimeter of the primary aggregate is P (μm), and the projected area of the primary aggregate is A (μm 2 )

[0014] FIG. 1 is a schematic diagram for explaining the two-dimensional projection image of the primary aggregate. The width of the rectangle circumscribing the primary aggregate is W (μm), the length of the rectangle circumscribing the primary aggregate is L (μm), the perimeter of the primary aggregate is P (μm), and the projected area of the primary aggregate is A (μm 2 )

[0015] The first primary aggregate is a primary aggregate in which the X value of formula (X) exceeds 1.7. Here, the X value of formula (X) indicates the aspect ratio of the primary aggregate, and the larger the difference between the long diameter and the short diameter, the larger the X value. Since the X value of the first primary aggregate exceeds 1.7, it can be said that the first primary aggregate has a shape close to a linear shape.

[0016] The second primary aggregate is a primary aggregate in which the X value of formula (X) is 1.7 or less and the Y value of formula (Y) is 1.2 or less. Here, the Y value of formula (Y) is an index of the complexity of the primary aggregate, and it can be said that the closer the Y value is to 1, the closer the shape is to a perfect circle. Since the second primary aggregate has an X value of 1.7 or less and a Y value of 1.2 or less, it can be said to be a primary aggregate having a shape close to an ellipsoid of revolution.

[0017] The third primary aggregate is a primary aggregate in which the X value of formula (X) is 1.7 or less, the Y value of formula (Y) exceeds 1.2, and the Z value of formula (Z) is 2.0 or less. Here, the Z value of formula (Z) is the ratio of the area (L×W) of the rectangle circumscribing the projection diagram of the primary aggregate to the projected area (A) of the primary aggregate. It can be said that the larger the Z value, the more branched the primary aggregate is. Since the third primary aggregate has an X value of 1.7 or less, a Y value exceeding 1.2, and a Z value of 2.0 or less, it can be said to be a primary aggregate having a shape close to an ellipsoid.

[0018] The fourth primary aggregate is a primary aggregate in which the X value of formula (X) is 1.7 or less, the Y value of formula (Y) exceeds 1.2, and the Z value of formula (Z) exceeds 2.0. Since the fourth primary aggregate has an X value of 1.7 or less, a Y value exceeding 1.2, and a Z value exceeding 2.0, it can be said to be a highly branched dendritic primary aggregate.

[0019] According to the findings of the present inventors, the second and third primary aggregates having a shape close to an ellipsoid of revolution or an ellipsoid are less likely to cause an increase in the viscosity of the slurry due to the entanglement of the primary aggregates as compared with the first and fourth primary aggregates. Since the carbon black of the present embodiment has a proportion of the total number of the second and third primary aggregates of 22% or more (preferably 23%), it has excellent dispersibility and can form a slurry with a low viscosity.

[0020] The first primary aggregate and the fourth primary aggregate are advantageous for the formation of a conductive path, and from the viewpoint of excellent performance as a conductive agent, it is desirable that the first primary aggregate and the fourth primary aggregate be present in a predetermined amount or more. For this reason, the number ratio of the total number (N2 + N3) of the second primary aggregate and the third primary aggregate to the total number (N1 + N2 + N3 + N4) of the first primary aggregate, the second primary aggregate, the third primary aggregate, and the fourth primary aggregate may be, for example, 50% or less, preferably 45% or less, more preferably 40% or less, and still more preferably 35% or less. That is, the number ratio of the total number (N2 + N3) of the second primary aggregate and the third primary aggregate to the total number (N1 + N2 + N3 + N4) of the first primary aggregate, the second primary aggregate, the third primary aggregate, and the fourth primary aggregate may be, for example, 22 to 50%, 22 to 45%, 22 to 40%, 22 to 35%, 23 to 50%, 23 to 45%, 23 to 40%, or 23 to 35%.

[0021] The number ratio (N1) of the first primary aggregate is not particularly limited, but may be, for example, 25% or more, 30% or more, or 35% or more with respect to the total number (N1 + N2 + N3 + N4) of the first primary aggregate, the second primary aggregate, the third primary aggregate, and the fourth primary aggregate. Further, the number ratio (N1) of the first primary aggregate may be, for example, 70% or less, 65% or less, or 60% or less with respect to the total number (N1 + N2 + N3 + N4) of the first primary aggregate, the second primary aggregate, the third primary aggregate, and the fourth primary aggregate. That is, the number ratio (N1) of the first primary aggregate is not particularly limited, but may be, for example, 25 to 70%, 25 to 65%, 25 to 60%, 30 to 70%, 30 to 65%, 30 to 60%, 35 to 70%, 35 to 65%, or 35 to 60% with respect to the total number (N1 + N2 + N3 + N4) of the first primary aggregate, the second primary aggregate, the third primary aggregate, and the fourth primary aggregate.

[0022] The proportion (N2) of the number of the second primary aggregates is not particularly limited, but may be, for example, 1% or more, 2% or more, or 3% or more with respect to the total number (N1 + N2 + N3 + N4) of the first primary aggregates, the second primary aggregates, the third primary aggregates, and the fourth primary aggregates. Further, the proportion (N2) of the number of the second primary aggregates may be, for example, 20% or less, 10% or less, or 8% or less with respect to the total number (N1 + N2 + N3 + N4) of the first primary aggregates, the second primary aggregates, the third primary aggregates, and the fourth primary aggregates. That is, the proportion (N2) of the number of the second primary aggregates may be, for example, 1 to 20%, 1 to 10%, 1 to 8%, 2 to 20%, 2 to 10%, 2 to 8%, 3 to 20%, 3 to 10%, or 3 to 8% with respect to the total number (N1 + N2 + N3 + N4) of the first primary aggregates, the second primary aggregates, the third primary aggregates, and the fourth primary aggregates.

[0023] The proportion (N3) of the number of the third primary aggregates is not particularly limited, but may be, for example, 5% or more, 10% or more, or 15% or more with respect to the total number (N1 + N2 + N3 + N4) of the first primary aggregates, the second primary aggregates, the third primary aggregates, and the fourth primary aggregates. Further, the proportion (N3) of the number of the third primary aggregates may be, for example, 55% or less, 50% or less, or 45% or less with respect to the total number (N1 + N2 + N3 + N4) of the first primary aggregates, the second primary aggregates, the third primary aggregates, and the fourth primary aggregates. That is, the proportion (N3) of the number of the third primary aggregates may be, for example, 5 to 55%, 5 to 50%, 5 to 45%, 10 to 55%, 10 to 50%, 10 to 45%, 15 to 55%, 15 to 50%, or 15 to 45% with respect to the total number (N1 + N2 + N3 + N4) of the first primary aggregates, the second primary aggregates, the third primary aggregates, and the fourth primary aggregates.

[0024] The number ratio (N4) of the fourth primary aggregate is not particularly limited, but may be, for example, 5% or more, 10% or more, or 15% or more with respect to the total number (N1 + N2 + N3 + N4) of the first primary aggregate, the second primary aggregate, the third primary aggregate, and the fourth primary aggregate. Further, the number ratio (N4) of the fourth primary aggregate may be, for example, 45% or less, 40% or less, or 35% or less with respect to the total number (N1 + N2 + N3 + N4) of the first primary aggregate, the second primary aggregate, the third primary aggregate, and the fourth primary aggregate. That is, the number ratio (N4) of the fourth primary aggregate may be, for example, 5 to 45%, 5 to 40%, 5 to 35%, 10 to 45%, 10 to 40%, 10 to 35%, 15 to 45%, 15 to 40%, or 15 to 35% with respect to the total number (N1 + N2 + N3 + N4) of the first primary aggregate, the second primary aggregate, the third primary aggregate, and the fourth primary aggregate.

[0025] In this specification, the photographing of the two-dimensional projection image of the primary aggregate by a transmission electron microscope and the image analysis can be performed by the following method. First, carbon black is dispersed in chloroform at an ultrasonic output of 90 W for 10 minutes to loosen it from the secondary aggregate to the primary aggregate. This is scooped up on a collodion membrane mesh and photographed with a transmission electron microscope at a magnification of 2000 times. Next, the Feret diameter W (μm) in the short-axis direction, the Feret diameter L (μm) in the long-axis direction, the perimeter P (μm), and the projected area A (μm 2 ) of 100 or more randomly selected carbon black primary aggregates from the photographed two-dimensional projection image are measured using the image analysis software "Image-Pro Plus 6.2J (manufactured by Media Cybernetics)". Specifically, after subjecting the two-dimensional projection image to a filter process (median filter. Option 7×7. Number of times: 3), the luminance range is manually extracted according to the primary aggregate. Select "Size (width)", "Size (length)", "Perimeter", and "Area" from the measurement items and measure. Note that the primary aggregates, scale bars, and background noise on the edge of the two-dimensional projection image are excluded from the measurement.

[0026] Carbon black varies greatly in the shape of primary aggregates and the like due to differences in the heat history during synthesis (e.g., heat history resulting from thermal decomposition and combustion reactions of fuel oil, thermal decomposition and combustion reactions of raw materials, quenching with a cooling medium, and reaction termination), differences in the collision frequency of primary particles, and the like.

[0027] The specific surface area of the carbon black of this embodiment may be, for example, 130 m 2 / g or more. From the perspective of further improving the conductivity imparting ability, the specific surface area of the carbon black is preferably 140 m 2 / g or more, more preferably 150 m 2 / g or more, and still more preferably 160 m 2 / g or more. The specific surface area of the carbon black can be increased by reducing the particle size of primary particles, hollowing, making the particle surface porous, and the like.

[0028] Also, the specific surface area of the carbon black of this embodiment may be, for example, 500 m 2 / g or less. From the perspective of further improving the dispersibility, the specific surface area of the carbon black is preferably 450 m 2 / g or less, and more preferably 400 m 2 / g or less. That is, the specific surface area of the carbon black of this embodiment is, for example, 130 to 500 m 2 / g, 130 to 450 m 2 / g, 130 to 400 m 2 / g, 140 to 500 m 2 / g, 140 to 450 m 2 / g, 140 to 400 m 2 / g, 150 to 500 m 2 / g, 150 to 450 m 2 / g, 150 to 400 m 2 / g, 160 to 500 m 2 / g, 160 to 450 m 2 / g or 160 to 400 m 2 / g may also be acceptable.

[0029] In addition, in this specification, the specific surface area is measured according to Method A (thermal conductivity measurement method) of the flow method in JIS K6217-2:2017.

[0030] The DBP absorption amount of the carbon black of this embodiment may be, for example, 150 mL / 100 g or more, preferably 160 mL / 100 g or more, more preferably 165 mL / 100 g or more. Also, the DBP absorption amount of the carbon black of this embodiment is, for example, 300 mL / 100 g or less, more preferably 285 mL / 100 g or less. That is, the DBP absorption amount of the carbon black of this embodiment may be, for example, 150 to 300 mL / 100 g, 150 to 285 / 100 g, 160 to 300 mL / 100 g, 160 to 285 / 100 g, 165 to 300 mL / 100 g, or 165 to 285 / 100 g.

[0031] The DBP absorption amount is an index for evaluating the ability of carbon black particles and the voids formed by primary aggregates to absorb dibutyl phthalate (DBP). In carbon black with well-developed primary aggregates, the number of neck parts formed by the fusion of primary particles and the voids formed between particles increases, so the DBP absorption amount increases. When the DBP absorption amount is large, the ability to impart conductivity in the electrode tends to increase due to the development of primary aggregates, and it also tends to easily follow the volume change of the active material accompanying the charge and discharge of the battery, and the battery characteristics such as cycle characteristics tend to be more improved. Also, when the DBP absorption amount is small, it is possible to avoid the binder in the composite layer being trapped in the primary aggregates of the carbon black, and it tends to be easier to maintain good adhesion with the active material and the current collector.

[0032] In this specification, the DBP absorption amount indicates the value obtained by converting the value measured by the method described in Method B of JIS K6221 to a value equivalent to JIS K6217-4:2008 according to the following formula (a). DBP absorption amount = (A - 10.974) / 0.7833…(a) [In the formula, A indicates the value of the DBP absorption amount measured by the method described in Method B of JIS K6221.]

[0033] The average primary particle diameter of the carbon black of this embodiment may be less than, for example, 35 nm, preferably less than 30 nm, and more preferably less than 25 nm. The average primary particle diameter of the carbon black of this embodiment may be, for example, 1 nm or more.

[0034] Conventionally, carbon black used as a conductive agent in a lithium-ion secondary battery has been difficult to form a slurry when the average primary particle diameter is small (for example, less than 30 nm). However, the carbon black of this embodiment can easily form a low-viscosity slurry even when the average primary particle diameter is small (for example, less than 30 nm). By being able to use carbon black with a small particle size in this way, high conductivity can be exhibited even when the blending ratio in the composite material layer is low.

[0035] The average primary particle diameter of carbon black can be obtained by measuring the primary particle diameters of 100 or more carbon blacks randomly selected from a 50,000-fold magnified image of a transmission electron microscope (TEM) and calculating the average value. The primary particles of carbon black have an aspect ratio that is small and a shape close to a perfect sphere, but they are not perfect spheres. Therefore, in this embodiment, the maximum value among the line segments connecting two points on the outer periphery of the primary particle in the TEM image is defined as the primary particle diameter of the carbon black.

[0036] The ash content of the carbon black of this embodiment may be, for example, 0.05 mass% or less, preferably 0.03 mass% or less, and more preferably 0.02 mass% or less. The ash content can be measured according to JIS K1469:2003 and can be reduced, for example, by classifying carbon black using a device such as a dry cyclone.

[0037] The iron content of the carbon black of this embodiment may be, for example, less than 2500 mass ppb, preferably less than 2300 mass ppb, and more preferably less than 2000 mass ppb. The iron content can be reduced, for example, by bringing the carbon black into contact with a magnet.

[0038] The iron content of carbon black can be pretreated by an acid decomposition method in accordance with JIS K0116:2014 and measured by high-frequency inductively coupled plasma mass spectrometry. Specifically, it can be measured by the following method. First, 1 g of carbon black is precisely weighed into a quartz beaker and heated in an electric furnace at 800 °C for 3 hours in an air atmosphere. Next, 10 mL of a mixed acid (70% by mass hydrochloric acid, 30% by mass nitric acid) and 10 mL or more of ultrapure water are added to the residue, and the mixture is heated and dissolved on a hot plate at 200 °C for 1 hour. After cooling, the solution diluted and adjusted to 25 mL with ultrapure water is measured with a high-frequency inductively coupled plasma mass spectrometer (Agilent 8800 manufactured by Agilent).

[0039] When the ash content and iron content of carbon black are low, in the kneading process, the mixing of foreign substances such as metals and ceramics due to damage to the equipment can be more significantly suppressed. In addition, a decrease in conductivity within the electrode due to the mixing of ash, insulating foreign substances, etc. can also be suppressed. Therefore, carbon black with a low ash content and iron content can be suitably used in lithium-ion secondary batteries that require high safety.

[0040] The method for producing the carbon black of the present embodiment is not particularly limited. For example, a raw material such as a hydrocarbon is supplied from a nozzle installed in the upstream part of a reactor, carbon black is produced by a thermal decomposition reaction and / or a combustion reaction, and it can be collected from a bag filter directly connected to the downstream part of the reactor.

[0041] The raw material to be used is not particularly limited, and gaseous hydrocarbons such as acetylene, methane, ethane, propane, ethylene, propylene, butadiene, and oil-based hydrocarbons such as toluene, benzene, xylene, gasoline, kerosene, light oil, and heavy oil can be used. Among them, it is preferable to use acetylene with few impurities. Acetylene has a larger heat of decomposition than other raw materials and can increase the temperature inside the reactor. Therefore, the nucleation of carbon black becomes more dominant than the particle growth by an addition reaction, and the primary particle size of carbon black can be reduced.

[0042] In addition to the raw material serving as the carbon source, it is preferable to supply oxygen, carbon dioxide, hydrogen, nitrogen, steam, etc. to the reactor. Gases other than these raw materials promote gas stirring in the reactor and increase the frequency of collisions and fusion between primary particles of carbon black generated from the raw materials. Therefore, by using gases other than the raw materials, primary aggregates of carbon black tend to develop and the DBP absorption amount tends to increase. As the gas other than the raw materials, it is preferable to use oxygen. When oxygen is used, a part of the raw material burns and the temperature in the reactor rises, making it easier to obtain carbon black with a small particle size and a high specific surface area. As the gas other than the raw materials, a plurality of gases can also be used. The supply location of the gas other than the raw materials is preferably the upstream part of the reactor, and it is preferably supplied from a nozzle separate from the raw materials. This enables efficient stirring of the raw materials also supplied from the upstream part, making it easier for primary aggregates to develop.

[0043] In addition, as a result of intensive studies to control the shape of the primary aggregates, the present inventors have found that supplying a gas other than the raw materials to the reactor from a direction orthogonal to the flow of the raw material gas is effective for the production of carbon black in this embodiment. In this method, compared with the conventional case of supplying the raw material gas and the gas other than the raw materials in parallel, a rotating action acts on the generated carbon black, and it is considered that primary aggregates having a shape closer to a rotating ellipsoid or an ellipsoid are more likely to be formed than linear or branched primary aggregates. It has also been found that the ejection speed of the gas other than the raw materials into the reactor affects the shape of the primary aggregates.

[0044] In conventional carbon black production, a cooling medium such as water may be fed from the downstream part of the reactor to stop the thermal decomposition and combustion reactions of the raw materials. However, no effect on the development of primary aggregates is observed, and on the other hand, there is a risk that the characteristics may vary greatly due to a rapid temperature change. Therefore, in this embodiment, it is preferable not to feed the cooling medium from the downstream part of the reactor.

[0045] The carbon black of the present embodiment is not limited to the carbon black directly obtained by the production in the reactor as described above. For example, it can also be obtained by pulverizing the obtained carbon black or by mixing carbon blacks produced under different conditions.

[0046] <First agent> The first agent of the present embodiment is a mixture of the above carbon black and a liquid medium. The first agent of the present embodiment can also be referred to as a slurry containing carbon black and a liquid medium.

[0047] The first agent of the present embodiment may further contain a dispersant that assists in the dispersion of carbon black in the liquid medium. That is, the first agent of the present embodiment may be a mixture of the above carbon black, liquid medium, and dispersant.

[0048] Examples of the liquid medium include water, N-methyl-2-pyrrolidone, cyclohexane, methyl ethyl ketone, methyl isobutyl ketone, and the like. Among these, from the viewpoint of dispersibility, N-methyl-2-pyrrolidone is preferable. N-methyl-2-pyrrolidone may be abbreviated as "NMP".

[0049] The dispersant may be any component having a function of assisting the dispersion of the conductive material (carbon black) in the liquid medium.

[0050] Examples of the dispersant include polymer-type dispersants and low-molecular-type dispersants. From the viewpoint of the long-term dispersion stability of the conductive material (carbon black), polymer-type dispersants are preferable.

[0051] The dispersant may be, for example, a dispersant selected from the group consisting of polyvinyl alcohol, polyvinyl pyrrolidone, polyvinyl butyral, carboxymethyl cellulose and its salts, polyvinyl acetal, polyvinyl acetate, polyvinyl amine, and polyvinyl formal.

[0052] The content of the dispersant in the first agent may be, for example, 1 part by mass or more with respect to 100 parts by mass of carbon black, and from the viewpoint of enhancing the dispersibility of carbon black, it may be 2 parts by mass or more, 3 parts by mass or more, 4 parts by mass or more, or 5 parts by mass or more. Further, the content of the dispersant in the first agent may be, for example, 50 parts by mass or less with respect to 100 parts by mass of carbon black, and from the viewpoint of suppressing the decrease in conductivity due to the insulating dispersant, it may be 45 parts by mass or less, 40 parts by mass or less, 35 parts by mass or less, 30 parts by mass or less, 25 parts by mass or less, or 20 parts by mass or less. That is, the content of the dispersant in the first agent may be, for example, 1 to 50 parts by mass, 1 to 45 parts by mass, 1 to 40 parts by mass, 1 to 35 parts by mass, 1 to 30 parts by mass, 1 to 25 parts by mass, 1 to 20 parts by mass, 2 to 50 parts by mass, 2 to 45 parts by mass, 2 to 40 parts by mass, 2 to 35 parts by mass, 2 to 30 parts by mass, 2 to 25 parts by mass, 2 to 20 parts by mass, 3 to 50 parts by mass, 3 to 45 parts by mass, 3 to 40 parts by mass, 3 to 35 parts by mass, 3 to 30 parts by mass, 3 to 25 parts by mass, 3 to 20 parts by mass, 4 to 50 parts by mass, 4 to 45 parts by mass, 4 to 40 parts by mass, 4 to 35 parts by mass, 4 to 30 parts by mass, 4 to 25 parts by mass, 4 to 20 parts by mass, 5 to 50 parts by mass, 5 to 45 parts by mass, 5 to 40 parts by mass, 5 to 35 parts by mass, 5 to 30 parts by mass, 5 to 25 parts by mass, or 5 to 20 parts by mass with respect to 100 parts by mass of carbon black.

[0053] The solid content concentration of the first agent is not particularly limited, and may be, for example, 1% by mass or more, and may also be 2% by mass or more, 3% by mass or more, 4% by mass or more, or 5% by mass or more. Further, the solid content concentration of the first agent may be, for example, 25% by mass or less, and may also be 23% by mass or less, 20% by mass or less, 18% by mass or less, or 15% by mass or less. That is, the solid content concentration of the first agent may be, for example, 1 to 25% by mass, 1 to 23% by mass, 1 to 20% by mass, 1 to 18% by mass, 1 to 15% by mass, 2 to 25% by mass, 2 to 23% by mass, 2 to 20% by mass, 2 to 18% by mass, 2 to 15% by mass, 3 to 25% by mass, 3 to 23% by mass, 3 to 20% by mass, 3 to 18% by mass, 3 to 15% by mass, 4 to 25% by mass, 4 to 23% by mass, 4 to 20% by mass, 4 to 18% by mass, 4 to 15% by mass, 5 to 25% by mass, 5 to 23% by mass, 5 to 20% by mass, 5 to 18% by mass, or 5 to 15% by mass.

[0054] If the viscosity of the first agent is too high, strong shear is applied during kneading with the active material, so that the primary aggregates of carbon black may be broken and the conductivity may decrease, or foreign matter may be mixed in due to wear of the device. On the other hand, if the viscosity of the first agent is too low, sedimentation of carbon black is likely to occur in the first agent, and it may be difficult to maintain uniformity. In the present embodiment, since the slurry viscosity can be lowered by using the above-mentioned carbon black, the destruction of the primary aggregates of carbon black is significantly suppressed, and the excellent conductivity-imparting ability can be maintained. In addition, the mixing of foreign matter due to wear of the equipment is significantly suppressed. That is, in the present embodiment, the blending ratio of the active material in the composite material layer can be increased without impairing the viscosity characteristics and conductivity of the slurry, and high capacity of a battery such as a lithium ion secondary battery can be achieved.

[0055] From the viewpoint of obtaining the above effects more significantly, the viscosity of the first agent (at 25°C, shear rate 10s -1 ) may be, for example, 100 mPa·s or more, and may also be 200 mPa·s or more. Further, from the viewpoint of obtaining the above effects more significantly, the viscosity of the first agent (at 25°C, shear rate 10s -1 ) may be, for example, 1500 mPa·s or less, and may also be 1200 mPa·s or less. That is, the viscosity of the first agent (at 25°C, shear rate 10s -1 ) may be, for example, 100 to 1500 mPa·s, 100 to 1200 mPa·s, 200 to 1500 mPa·s, or 200 to 1200 mPa·s.

[0056] <Carbon Nanotube> The carbon nanotubes of this embodiment have an average diameter of 5 to 15 nm.

[0057] When the average diameter of the carbon nanotubes is 5 nm or more, the interaction between the solvent and the conductive material and between the conductive materials becomes small, so that it becomes easy to uniformly disperse in the active material, and thus it becomes easy to form a conductive path, and excellent battery characteristics are more easily obtained. When the average diameter of the carbon nanotubes is 15 nm or less, the electrical contact with the active material and the conductive material increases, the effect of imparting conductivity becomes good, and excellent battery characteristics are more easily obtained.

[0058] The average diameter of the carbon nanotubes means the average value of the diameters measured based on the images when observing the carbon nanotubes with a transmission electron microscope (TEM). Specifically, using a transmission electron microscope JEM-2000FX (manufactured by JEOL Ltd.), 10 images of the carbon nanotubes are taken at a magnification of 200,000 times, and the diameters of 100 randomly extracted carbon nanotubes in the obtained images are measured by image analysis and arithmetically averaged.

[0059] The average diameter of the carbon nanotubes may be 14 nm or less, 13 nm or less, 12 nm or less, 11 nm or less, 10 nm or less, 9 nm or less, 8 nm or less, or 7 nm or less from the viewpoint of making the internal resistance smaller and from the viewpoint of more excellent discharge rate characteristics and cycle characteristics. That is, the average diameter of the carbon nanotubes may be, for example, 5 to 15 nm, 5 to 14 nm, 5 to 13 nm, 5 to 12 nm, 5 to 11 nm, 5 to 10 nm, 5 to 9 nm, 5 to 8 nm, or 5 to 7 nm.

[0060] The BET specific surface area of the carbon nanotubes is preferably 170 to 320 m 2 / g. When the BET specific surface area of the carbon nanotubes is 170 m 2By being 320 m 2 / g or more, the number of electrical contacts with the active material and the conductive material increases, and the effect of imparting conductivity becomes good, so that excellent battery characteristics can be more easily obtained. The BET specific surface area of the carbon nanotube is 320 m

[0061] The BET specific surface area of the carbon nanotube can be measured by the static volumetric method in accordance with JIS Z8830 using nitrogen as the adsorbate.

[0062] The BET specific surface area of the carbon nanotube is 180 m 2 / g or more, 190 m 2 / g or more, 200 m 2 / g or more, 210 m 2 / g or more, 220 m 2 / g or more, 230 m 2 / g or more, 240 m 2 / g or more, 250 m 2 / g or more, 260 m 2 / g or more, 270 m 2 / g or more, 280 m 2 / g or more or 290 m 2 / g or more may also be acceptable. Also, the BET specific surface area of the carbon nanotube is 310 m 2 / g or less may also be acceptable. That is, the BET specific surface area of the carbon nanotube is, for example, 170 to 320 m 2 / g, 180 to 320 m 2 / g, 190 to 320 m 2 / g, 200 to 320 m 2 / g, 210 to 320 m 2 / g, 220 to 320 m 2 / g, 230 to 320 m 2 / g, 240 to 320 m 2 / g, 250 - 320 m 2 / g, 260 - 320 m 2 / g, 270 - 320 m 2 / g, 280 - 320 m 2 / g, 290 - 320 m 2 / g, 170 - 310 m 2 / g, 180 - 310 m 2 / g, 190 - 310 m 2 / g, 200 - 310 m 2 / g, 210 - 310 m 2 / g, 220 - 310 m 2 / g, 230 - 310 m 2 / g, 240 - 310 m 2 / g, 250 - 310 m 2 / g, 260 - 310 m 2 / g, 270 - 310 m 2 / g, 280 - 310 m 2 / g or 290 - 310 m 2 It may be / g.

[0063] The ratio of the average diameter of carbon nanotubes to the BET specific surface area of carbon black (average diameter / BET specific surface area) is preferably 0.01 - 0.1 nm / (m 2 / g). The above ratio (average diameter / BET specific surface area) is the value obtained by dividing the average diameter of carbon nanotubes by the BET specific surface area of carbon nanotubes. When the ratio (average diameter / BET specific surface area) is 0.01 nm / (m 2 / g) or more, the entanglement between carbon nanotubes decreases, and it becomes easier to disperse uniformly in the active material, so it is easier to form a conductive path, and excellent battery characteristics are more easily obtained. When the ratio (average diameter / BET specific surface area) is 0.1 nm / (m 2 / g) or less, the number of carbon nanotubes per unit weight increases, and electricity can flow efficiently through the entire active material, so excellent battery characteristics can be obtained.

[0064] The ratio (average diameter / BET specific surface area) is 0.09 nm / (m from the viewpoint of making the internal resistance smaller, and from the viewpoint of more excellent discharge rate characteristics and cycle characteristics 2 / g) or less, 0.08 nm / (m 2 / g) or less, 0.07 nm / (m 2 / g) or less, 0.06 nm / (m 2 / g) or less, 0.05 nm / (m 2 / g) or less, 0.04 nm / (m 2 / g) or less, or 0.03 nm / (m 2 / g) or less may be sufficient. That is, the ratio (average diameter / BET specific surface area) is, for example, 0.01 to 0.1 nm, 0.01 to 0.09 nm / (m 2 / g), 0.01 to 0.08 nm / (m 2 / g), 0.01 to 0.07 nm / (m 2 / g), 0.01 to 0.06 nm / (m 2 / g), 0.01 to 0.05 nm / (m 2 / g), 0.01 to 0.04 nm / (m 2 / g), or 0.01 to 0.03 nm / (m 2 / g) may be sufficient.

[0065] The above carbon nanotubes can be produced by a conventionally known method for producing carbon nanotubes. For example, a powdered catalyst in which iron is supported on magnesia (magnesium oxide) is present over the entire horizontal cross-sectional direction of the reactor in a vertical reactor, methane is circulated vertically in the reactor, and after bringing methane into contact with the above catalyst at 500 to 1200 °C, the obtained product (unoxidized carbon nanotubes) can be produced by subjecting them to an oxidation treatment. By the above method for producing carbon nanotubes, carbon nanotubes having an average diameter of 5 to 15 nm and composed of several graphene layers can be obtained.

[0066] The oxidation treatment of the above product may be, for example, a firing treatment. The temperature of the firing treatment is not particularly limited and may be, for example, 300 to 1000 °C. Since the temperature of the firing treatment is affected by the atmospheric gas, it is preferable to perform the firing treatment at a relatively low temperature when the oxygen concentration is high and at a relatively high temperature when the oxygen concentration is low. Specifically, as the firing treatment of the product, a method of firing within the range of ±50 °C of the combustion peak temperature of the carbon nanotubes before the oxidation treatment in the air can be mentioned. However, when the oxygen concentration is higher than that of the air, firing is performed in a temperature range lower than the combustion peak temperature, and when the oxygen concentration is lower than that of the air, a temperature range higher than the combustion peak temperature is selected. In particular, when performing the firing treatment of the carbon nanotubes before the oxidation treatment in the air, it is preferable to perform it within the range of ±15 °C of the combustion peak temperature of the carbon nanotubes before the oxidation treatment.

[0067] The oxidation treatment of the above product may also be treatment with hydrogen peroxide, mixed acid, nitric acid, etc. As a method of treating the above product with hydrogen peroxide, for example, a method of mixing the above product into 34.5% hydrogen peroxide water so as to be 0.01 to 10% by mass and reacting at a temperature of 0 to 100 °C for 0.5 to 48 hours can be mentioned. Further, as a method of treating the above product with mixed acid, for example, a method of mixing the above product into a mixed solution of concentrated sulfuric acid and concentrated nitric acid (concentrated sulfuric acid: concentrated nitric acid = 3:1) so as to be 0.01 to 10% by mass and reacting at a temperature of 0 to 100 °C for 0.5 to 48 hours can be mentioned. The mixing ratio of the mixed acid (concentrated sulfuric acid: concentrated nitric acid) can be adjusted within the range of 1:10 to 10:1 according to the amount of single-walled carbon nanotubes in the above product. As a method of treating the above product with nitric acid, for example, a method of mixing the above product into nitric acid with a concentration of 40 to 80% by mass so as to be 0.01 to 10% by mass and reacting at a temperature of 60 to 150 °C for 0.5 to 48 hours can be mentioned.

[0068] By performing an oxidation treatment on the above product, impurities such as amorphous carbon in the product and single-walled carbon nanotubes with low heat resistance can be selectively removed, and the purity of the few-layer graphene layers, particularly the 2 to 5-layer carbon nanotubes, can be improved. At the same time, by performing an oxidation treatment on the product, functional groups are added to the surface of the carbon nanotubes, so the affinity with the liquid medium and the dispersant is improved, and the dispersibility is improved. Among the above oxidation treatments, treatment with nitric acid is preferred.

[0069] The above oxidation treatment may be performed immediately after obtaining the carbon nanotubes before the oxidation treatment, or may be performed after another purification treatment. For example, when using iron / magnesia as a catalyst, a purification treatment may be performed with an acid such as hydrochloric acid to remove the catalyst before the oxidation treatment, and then the oxidation treatment may be performed, or a purification treatment may be performed for catalyst removal after the oxidation treatment.

[0070] <Second agent> The second agent of this embodiment is a mixture of the above carbon nanotubes and a liquid medium. The second agent of this embodiment can also be said to be a slurry containing carbon nanotubes and a liquid medium.

[0071] The second agent of this embodiment may further contain a dispersant that assists in the dispersion of the carbon nanotubes in the liquid medium. That is, the second agent of this embodiment may be a mixture of the above carbon nanotubes, a liquid medium, and a dispersant.

[0072] Examples of the liquid medium include water, N-methyl-2-pyrrolidone, cyclohexane, methyl ethyl ketone, methyl isobutyl ketone, etc. Among these, from the viewpoint of dispersibility, N-methyl-2-pyrrolidone is preferred.

[0073] The dispersant may be any component having a function of assisting the dispersion of the conductive material (carbon nanotubes) in the liquid medium.

[0074] Examples of the dispersant include a polymer dispersant and a low-molecular dispersant. From the perspective of long-term dispersion stability of the conductive material (carbon nanotube), a polymer dispersant is preferred.

[0075] The dispersant may be, for example, a dispersant selected from the group consisting of polyvinyl alcohol, polyvinyl pyrrolidone, polyvinyl butyral, carboxymethyl cellulose and its salts, polyvinyl acetal, polyvinyl acetate, polyvinylamine, and polyvinyl formal.

[0076] The content of the dispersant in the second agent may be, for example, 1 part by mass or more with respect to 100 parts by mass of the carbon nanotubes. From the perspective of enhancing the dispersibility of the carbon nanotubes, it may be 5 parts by mass or more, 10 parts by mass or more, 15 parts by mass or more, or 20 parts by mass or more. Also, the content of the dispersant in the second agent may be, for example, 50 parts by mass or less with respect to 100 parts by mass of the carbon nanotubes. From the perspective of suppressing the decrease in conductivity due to the insulating dispersant, it may be 45 parts by mass or less or 40 parts by mass or less. That is, the content of the dispersant in the second agent may be, for example, 1 to 50 parts by mass, 1 to 45 parts by mass, 1 to 40 parts by mass, 5 to 50 parts by mass, 5 to 45 parts by mass, 5 to 40 parts by mass, 10 to 50 parts by mass, 10 to 45 parts by mass, 10 to 40 parts by mass, 15 to 50 parts by mass, 15 to 45 parts by mass, 15 to 40 parts by mass, 20 to 50 parts by mass, 20 to 45 parts by mass, or 20 to 40 parts by mass with respect to 100 parts by mass of the carbon nanotubes.

[0077] The solid content concentration of the second agent is not particularly limited and may be, for example, 0.1 mass% or more, and may also be 1 mass% or more, 2 mass% or more, or 3 mass% or more. Also, the solid content concentration of the second agent may be, for example, 10 mass% or less, and may also be 9 mass% or less, 8 mass% or less, or 7 mass% or less. That is, the solid content concentration of the second agent may be, for example, 0.1 to 10% by mass, 0.1 to 9% by mass, 0.1 to 8% by mass, 0.1 to 7% by mass, 1 to 10% by mass, 1 to 9% by mass, 1 to 8% by mass, 1 to 7% by mass, 2 to 10% by mass, 2 to 9% by mass, 2 to 8% by mass, 2 to 7% by mass, 3 to 10% by mass, 3 to 9% by mass, 3 to 8% by mass, or 3 to 7% by mass.

[0078] If the viscosity of the second agent is too high, strong shear is applied during kneading with the active material, so that the primary aggregates of the carbon black to be mixed together may be broken and the conductivity may decrease, or foreign matter may be mixed in due to wear of the device. On the other hand, if the viscosity of the second agent is too low, sedimentation of the carbon nanotubes in the second agent is likely to occur, and it may be difficult to maintain uniformity. That is, in the present embodiment, when the second agent has the following suitable viscosity, the above-described effects are more significantly exhibited.

[0079] From the viewpoint of more significantly obtaining the above effects, the viscosity of the second agent (at 25°C, shear rate 10 s -1 ) may be, for example, 10 mPa·s or more, and may also be 50 mPa·s or more. Further, from the viewpoint of more significantly obtaining the above effects, the viscosity of the second agent (at 25°C, shear rate 10 s -1 ) may be, for example, 1000 mPa·s or less, and may also be 500 mPa·s or less. That is, the viscosity of the second agent (at 25°C, shear rate 10 s -1 ) may be, for example, 10 to 1000 mPa·s, 10 to 500 mPa·s, 50 to 1000 mPa·s, or 50 to 500 mPa·s.

[0080] <Third agent> The third agent contains a binder and a liquid medium. The third agent can also be said to be a mixture of a binder and a liquid medium.

[0081] Examples of the binder include polyvinylidene fluoride, polytetrafluoroethylene, styrene-butadiene copolymer, and (meth)acrylate copolymer. The structure of the polymer of the binder may be, for example, a random copolymer, an alternating copolymer, a graft copolymer, a block copolymer, or the like. From the viewpoint of excellent withstand voltage properties, polyvinylidene fluoride is preferable as the binder.

[0082] Examples of the liquid medium include water, N-methyl-2-pyrrolidone, cyclohexane, methyl ethyl ketone, methyl isobutyl ketone, and the like. Among these, N-methyl-2-pyrrolidone is preferable from the viewpoint of dispersibility.

[0083] <Active material> The active material may be any substance that can reversibly occlude and release cations. The active material can also be referred to as a positive electrode active material.

[0084] The active material is not particularly limited, and for example, known active materials used in lithium-ion secondary batteries can be used without particular limitation. Examples of the active material include lithium cobaltate, lithium nickelate, lithium manganate, lithium nickel manganese cobaltate, lithium iron phosphate, and the like.

[0085] The active material may be, for example, a lithium-containing composite oxide containing manganese with a volume resistivity of 1×10 4 Ω·cm or more, or a lithium-containing polyanion compound. Examples of the lithium-containing composite oxide containing manganese include lithium manganates such as LiMnO2, LiMnO3, LiMn2O3, Li 1+x Mn 2-x O4 (where x = 0 to 0.33); LiMn x Ni y Co z O2 (where x + y + z = 1, 0 ≦ y < 1, 0 ≦ z < 1, 0 ≦ x < 1), Li 1+x Mn 2-x-y M y O4 (where x = 0 to 0.33, y = 0 to 1.0, 2 - x - y > 0), LiMn 2-x M xComposite oxides containing one or more transition metal elements such as O2 (where x = 0.01 to 0.1), Li2Mn3MO8, etc. are included. Examples of the lithium-containing polyanion compound include polyanion compounds such as LiFePO4, LiMnPO4, Li2MPO4F (where M is at least one metal selected from Co, Ni, Fe, Cr, Zn). M in each composition formula is at least one selected from the group consisting of Fe, Co, Ni, Al, Cu, Mg, Cr, Zn, Ta.

[0086] The average particle diameter (D 50 ) may be 20 μm or less or 10 μm or less from the viewpoint that a battery with sufficiently excellent binding property between the conductive material and the binder and more excellent cycle characteristics can be easily obtained. The average particle diameter (D 50 ) can be measured by the laser light scattering method. The average particle diameter (D 50 ) may be, for example, 1 μm or more.

[0087] <Coating liquid for forming positive electrode> The coating liquid for forming the positive electrode of this embodiment may be a coating liquid containing carbon black, carbon nanotubes, a binder, an active material, and a liquid medium. The coating liquid for forming the positive electrode may further contain a dispersant (dispersant for conductive material).

[0088] In the coating liquid for forming the positive electrode of this embodiment, the same ones as those described above can be exemplified for carbon black, carbon nanotubes, the binder, the active material, the dispersant, and the liquid medium.

[0089] The coating liquid for forming the positive electrode of this embodiment may be, for example, produced by the following production method.

[0090] The manufacturing method of the coating liquid for forming a positive electrode according to this embodiment includes a mixing step of mixing the above carbon black and the first liquid medium to obtain a first agent containing the carbon black and the first liquid medium, and a coating liquid forming step of mixing the first agent, a second agent containing carbon nanotubes and a second liquid medium, a third agent containing a binder and a third liquid medium, and an active material to form a coating liquid for forming a positive electrode.

[0091] In the manufacturing method of the coating liquid for forming a positive electrode according to this embodiment, examples of the first agent, the second agent, the third agent, and the active material can be the same as those described above.

[0092] In the mixing step, the method of mixing the carbon black and the first liquid medium is not particularly limited, and it may be carried out by a known method (for example, stirring and mixing using a ball mill, a sand mill, a twin-screw kneader, a rotating and revolving stirrer, a planetary mixer, a disperser mixer, etc.).

[0093] In the coating liquid forming step, the method of mixing the first agent, the second agent, the third agent, and the active material is not particularly limited, and it may be carried out by a known method (for example, stirring and mixing using a ball mill, a sand mill, a twin-screw kneader, a rotating and revolving stirrer, a planetary mixer, a disperser mixer, etc.). The first agent, the second agent, the third agent, and the active material may be mixed simultaneously or sequentially. For example, after mixing the first agent, the second agent, and the third agent, the active material may be mixed, or the first agent and the third agent may be mixed, then the second agent may be mixed, and finally the active material may be mixed.

[0094] The content of carbon black in the coating liquid for forming the positive electrode may be, for example, 5 parts by mass or more with respect to a total of 100 parts by mass of carbon black and carbon nanotubes, and from the viewpoints of making the internal resistance smaller and having more excellent discharge rate characteristics and cycle characteristics, it may be 10 parts by mass or more, 15 parts by mass or more, 20 parts by mass or more, 25 parts by mass or more, 30 parts by mass or more, 35 parts by mass or more, 40 parts by mass or more, 45 parts by mass or more, 50 parts by mass or more, 55 parts by mass or more, 60 parts by mass or more, or 65 parts by mass or more. Further, the content of carbon black in the coating liquid for forming the positive electrode may be, for example, 99 parts by mass or less with respect to a total of 100 parts by mass of carbon black and carbon nanotubes, and from the viewpoints of making the internal resistance smaller and having more excellent discharge rate characteristics and cycle characteristics, it may be 95 parts by mass or less, 90 parts by mass or less, 85 parts by mass or less, 80 parts by mass or less, or 75 parts by mass or less. That is, the content of carbon black in the coating liquid for forming the positive electrode may be, for example, 5 to 99 parts by mass, 5 to 95 parts by mass, 5 to 90 parts by mass, 5 to 85 parts by mass, 5 to 80 parts by mass, 5 to 75 parts by mass, 10 to 99 parts by mass, 10 to 95 parts by mass, 10 to 90 parts by mass, 10 to 85 parts by mass, 10 to 80 parts by mass, 10 to 75 parts by mass, 15 to 99 parts by mass, 15 to 95 parts by mass, 15 to 90 parts by mass, 15 to 85 parts by mass, 15 to 80 parts by mass, 15 to 75 parts by mass, 20 to 99 parts by mass, 20 to 95 parts by mass, 20 to 90 parts by mass, 20 to 85 parts by mass, 20 to 80 parts by mass, 20 to 75 parts by mass, 25 to 99 parts by mass, 25 to 95 parts by mass, 25 to 90 parts by mass, 25 to 85 parts by mass, 25 to 80 parts by mass, 25 to 75 parts by mass, 30 to 99 parts by mass, 30 to 95 parts by mass, 30 to 90 parts by mass, 30 to 85 parts by mass, 30 to 80 parts by mass, 30 to 75 parts by mass, 35 to 99 parts by mass, 35 to 95 parts by mass, 35 to 90 parts by mass, 35 to 85 parts by mass, 35 to 80 parts by mass, 35 to 75 parts by mass, 40 to 99 parts by mass, 40 to 95 parts by mass, 40 to 90 parts by mass, 40 to 85 parts by mass, 40 to 80 parts by mass, 40 to 75 parts by mass, 45 to 99 parts by mass, 45 to 95 parts by mass, 45 to 90 parts by mass, 45 to 85 parts by mass, 45 to 80 parts by mass, 45 to 75 parts by mass, 50 to 99 parts by mass, 50 to 95 parts by mass, 50 to 90 parts by mass, 50 to 85 parts by mass, 50 to 80 parts by mass, 50 to 75 parts by mass, 55 to 99 parts by mass, 55 to 95 parts by mass, 55 to 90 parts by mass, 55 to 85 parts by mass, 55 to 80 parts by mass, 55 to 75 parts by mass, 60 to 99 parts by mass, 60 to 95 parts by mass, 60 to 90 parts by mass, 60 to 85 parts by mass, 60 to 80 parts by mass, 60 to 75 parts by mass, 65 to 99 parts by mass, 65 to 95 parts by mass, 65 to 90 parts by mass, 65 to 85 parts by mass, 65 to 80 parts by mass or 65 to 75 parts by mass with respect to a total of 100 parts by mass of carbon black and carbon nanotubes.

[0095] The content of carbon nanotubes in the coating liquid for forming the positive electrode may be, for example, 1 part by mass or more with respect to a total of 100 parts by mass of carbon black and carbon nanotubes, and may be 5 parts by mass or more, 10 parts by mass or more, 15 parts by mass or more, 20 parts by mass or more, or 25 parts by mass or more from the viewpoint of further reducing the internal resistance and from the viewpoint of more excellent discharge rate characteristics and cycle characteristics. Further, the content of carbon nanotubes in the coating liquid for forming the positive electrode may be, for example, 90 parts by mass or less, 85 parts by mass or less, 80 parts by mass or less, 75 parts by mass or less, 70 parts by mass or less, 65 parts by mass or less, 60 parts by mass or less, 55 parts by mass or less, 50 parts by mass or less, 45 parts by mass or less, 40 parts by mass or more, or 35 parts by mass or less with respect to a total of 100 parts by mass of carbon black and carbon nanotubes. That is, the content of the carbon nanotubes in the coating liquid for forming the positive electrode may be, for example, 1 to 90 parts by mass, 1 to 85 parts by mass, 1 to 80 parts by mass, 1 to 75 parts by mass, 1 to 70 parts by mass, 1 to 65 parts by mass, 1 to 60 parts by mass, 1 to 55 parts by mass, 1 to 50 parts by mass, 1 to 45 parts by mass, 1 to 40 parts by mass, 1 to 35 parts by mass, 5 to 90 parts by mass, 5 to 85 parts by mass, 5 to 80 parts by mass, 5 to 75 parts by mass, 5 to 70 parts by mass, 5 to 65 parts by mass, 5 to 60 parts by mass, 5 to 55 parts by mass, 5 to 50 parts by mass, 5 to 45 parts by mass, 5 to 40 parts by mass, 5 to 35 parts by mass, 10 to 90 parts by mass, 10 to 85 parts by mass, 10 to 80 parts by mass, 10 to 75 parts by mass, 10 to 70 parts by mass, 10 to 65 parts by mass, 10 to 60 parts by mass, 10 to 55 parts by mass, 10 to 50 parts by mass, 10 to 45 parts by mass, 10 to 40 parts by mass, 10 to 35 parts by mass, 15 to 90 parts by mass, 15 to 85 parts by mass, 15 to 80 parts by mass, 15 to 75 parts by mass, 15 to 70 parts by mass, 15 to 65 parts by mass, 15 to 60 parts by mass, 15 to 55 parts by mass, 15 to 50 parts by mass, 15 to 45 parts by mass, 15 to 40 parts by mass, 15 to 35 parts by mass, 20 to 90 parts by mass, 20 to 85 parts by mass, 20 to 80 parts by mass, 20 to 75 parts by mass, 20 to 70 parts by mass, 20 to 65 parts by mass, 20 to 60 parts by mass, 20 to 55 parts by mass, 20 to 50 parts by mass, 20 to 45 parts by mass, 20 to 40 parts by mass, 20 to 35 parts by mass, 25 to 90 parts by mass, 25 to 85 parts by mass, 25 to 80 parts by mass, 25 to 75 parts by mass, 25 to 70 parts by mass, 25 to 65 parts by mass, 25 to 60 parts by mass, 25 to 55 parts by mass, 25 to 50 parts by mass, 25 to 45 parts by mass, 25 to 40 parts by mass or 25 to 35 parts by mass with respect to a total of 100 parts by mass of the carbon black and the carbon nanotubes.

[0096] The total content of carbon nanotubes and carbon black in the coating liquid for forming the positive electrode may be, for example, 0.1% by mass or more based on the total mass of the solid content in the coating liquid for forming the positive electrode. From the viewpoint of making the internal resistance smaller and from the viewpoint of more excellent discharge rate characteristics and cycle characteristics, it may be 0.3% by mass or more, 0.5% by mass or more, 0.7% by mass or more, or 0.9% by mass or more. Further, the total content of carbon nanotubes and carbon black in the coating liquid for forming the positive electrode may be, for example, 5% by mass or less based on the total mass of the solid content in the coating liquid for forming the positive electrode. From the viewpoint of making the internal resistance smaller and from the viewpoint of more excellent discharge rate characteristics and cycle characteristics, it may be 4% by mass or less, 3% by mass or less, 2% by mass or less, or 1.5% by mass or less. That is, the total content of carbon nanotubes and carbon black in the coating liquid for forming the positive electrode may be, for example, 0.1 to 5% by mass, 0.1 to 4% by mass, 0.1 to 3% by mass, 0.1 to 2% by mass, 0.1 to 1.5% by mass, 0.3 to 5% by mass, 0.3 to 4% by mass, 0.3 to 3% by mass, 0.3 to 2% by mass, 0.3 to 1.5% by mass, 0.5 to 5% by mass, 0.5 to 4% by mass, 0.5 to 3% by mass, 0.5 to 2% by mass, 0.5 to 1.5% by mass, 0.7 to 5% by mass, 0.7 to 4% by mass, 0.7 to 3% by mass, 0.7 to 2% by mass, 0.7 to 1.5% by mass, 0.9 to 5% by mass, 0.9 to 4% by mass, 0.9 to 3% by mass, 0.9 to 2% by mass, or 0.9 to 1.5% by mass based on the total mass of the solid content in the coating liquid for forming the positive electrode.

[0097] The content of the binder in the coating liquid for forming the positive electrode may be, for example, 0.1% by mass or more based on the total mass of the solid content in the coating liquid for forming the positive electrode. From the viewpoint of making the internal resistance smaller and from the viewpoint of more excellent discharge rate characteristics and cycle characteristics, it may be 0.5% by mass or more, 1% by mass or more, or 1.5% by mass or more. Further, the content of the binder in the coating liquid for forming the positive electrode may be, for example, 10% by mass or less based on the total mass of the solid content in the coating liquid for forming the positive electrode. From the viewpoint of making the internal resistance smaller and from the viewpoint of more excellent discharge rate characteristics and cycle characteristics, it may be 9% by mass or less, 8% by mass or less, 7% by mass or less, 6% by mass or less, 5% by mass or less, 4% by mass or less, or 3% by mass or less. That is, the content of the binder in the coating liquid for positive electrode formation may be, for example, 0.1 to 10% by mass, 0.1 to 9% by mass, 0.1 to 8% by mass, 0.1 to 7% by mass, 0.1 to 6% by mass, 0.1 to 5% by mass, 0.1 to 4% by mass, 0.1 to 3% by mass, 0.5 to 10% by mass, 0.5 to 9% by mass, 0.5 to 8% by mass, 0.5 to 7% by mass, 0.5 to 6% by mass, 0.5 to 5% by mass, 0.5 to 4% by mass, 0.5 to 3% by mass, 1 to 10% by mass, 1 to 9% by mass, 1 to 8% by mass, 1 to 7% by mass, 1 to 6% by mass, 1 to 5% by mass, 1 to 4% by mass, 1 to 3% by mass, 1.5 to 10% by mass, 1.5 to 9% by mass, 1.5 to 8% by mass, 1.5 to 7% by mass, 1.5 to 6% by mass, 1.5 to 5% by mass, 1.5 to 4% by mass or 1.5 to 3% by mass, based on the total mass of the solid content in the coating liquid for positive electrode formation.

[0098] The content of the active material in the coating liquid for positive electrode formation may be, for example, 90% by mass or more, and from the viewpoint of more excellent discharge rate characteristics and cycle characteristics, it may be 92% by mass or more, 94% by mass or more, or 96% by mass or more, based on the total mass of the solid content in the coating liquid for positive electrode formation. Further, the content of the active material in the coating liquid for positive electrode formation may be, for example, 99.5% by mass or less, and from the viewpoint of making the internal resistance smaller, it may be 99% by mass or less or 98% by mass or less. That is, the content of the active material in the coating liquid for positive electrode formation may be, for example, 90 to 99.5% by mass, 90 to 99% by mass, 90 to 98% by mass, 92 to 99.5% by mass, 92 to 99% by mass, 92 to 98% by mass, 94 to 99.5% by mass, 94 to 99% by mass, 94 to 98% by mass, 96 to 99.5% by mass, 96 to 99% by mass or 96 to 98% by mass, based on the total mass of the solid content in the coating liquid for positive electrode formation.

[0099] The content of the dispersant in the coating liquid for positive electrode formation may be, for example, 0.05% by mass or more, and may be 0.1% by mass or more or 0.15% by mass or more, based on the total mass of the solid content in the coating liquid for positive electrode formation. Further, the content of the dispersant in the coating liquid for positive electrode formation may be, for example, 0.8% by mass or less, and may be 0.5% by mass or less or 0.2% by mass or less. That is, the content of the dispersant in the coating liquid for forming the positive electrode may be, for example, 0.05 to 0.8% by mass, 0.05 to 0.5% by mass, 0.05 to 0.2% by mass, 0.1 to 0.8% by mass, 0.1 to 0.5% by mass, 0.1 to 0.2% by mass, 0.15 to 0.8% by mass, 0.15 to 0.5% by mass, or 0.15 to 0.2% by mass based on the total mass of the solid content in the coating liquid for forming the positive electrode.

[0100] The solid content concentration of the coating liquid for forming the positive electrode may be, for example, 63% by mass or more. From the viewpoint of shortening the time for drying the liquid medium when manufacturing the positive electrode and the viewpoint of further suppressing the migration of the conductive material when drying the liquid medium, it may be 65% by mass or more, 66% by mass or more, or 67% by mass or more. Also, the solid content concentration of the coating liquid for forming the positive electrode may be, for example, 80% by mass or less. From the viewpoint of making the coating film smoother when manufacturing the positive electrode and the viewpoint of further reducing the variation in the internal resistance of the battery, it may be 78% by mass or less, 76% by mass or less, 74% by mass or less, 72% by mass or less, or 70% by mass or less. That is, the solid content concentration of the coating liquid for forming the positive electrode may be, for example, 63 to 80% by mass, 63 to 78% by mass, 63 to 76% by mass, 63 to 74% by mass, 63 to 72% by mass, 63 to 70% by mass, 65 to 80% by mass, 65 to 78% by mass, 65 to 76% by mass, 65 to 74% by mass, 65 to 72% by mass, 65 to 70% by mass, 66 to 80% by mass, 66 to 78% by mass, 66 to 76% by mass, 66 to 74% by mass, 66 to 72% by mass, 66 to 70% by mass, 67 to 80% by mass, 67 to 78% by mass, 67 to 76% by mass, 67 to 74% by mass, 67 to 72% by mass, or 67 to 70% by mass.

[0101] <Positive electrode> The positive electrode of this embodiment includes a composite layer made of a positive electrode composition and a current collector.

[0102] The positive electrode composition may be a composition containing the solid content of the coating liquid for forming the positive electrode, and may be obtained by removing at least a part of the liquid medium from the coating liquid for forming the positive electrode. That is, the positive electrode composition may be a composition containing carbon black, carbon nanotubes, a binder, and an active material. The positive electrode composition may further contain a dispersant.

[0103] The content of carbon black in the positive electrode composition may be, for example, 5 parts by mass or more with respect to a total of 100 parts by mass of carbon black and carbon nanotubes, and from the viewpoints of making the internal resistance smaller and having more excellent discharge rate characteristics and cycle characteristics, it may be 10 parts by mass or more, 15 parts by mass or more, 20 parts by mass or more, 25 parts by mass or more, 30 parts by mass or more, 35 parts by mass or more, 40 parts by mass or more, 45 parts by mass or more, 50 parts by mass or more, 55 parts by mass or more, 60 parts by mass or more, or 65 parts by mass or more. Also, the content of carbon black in the positive electrode composition may be, for example, 99 parts by mass or less with respect to a total of 100 parts by mass of carbon black and carbon nanotubes, and from the viewpoints of making the internal resistance smaller and having more excellent discharge rate characteristics and cycle characteristics, it may be 95 parts by mass or less, 90 parts by mass or less, 85 parts by mass or less, 80 parts by mass or less, or 75 parts by mass or less. That is, the content of carbon black in the positive electrode composition may be, for example, 5 to 99 parts by mass, 5 to 95 parts by mass, 5 to 90 parts by mass, 5 to 85 parts by mass, 5 to 80 parts by mass, 5 to 75 parts by mass, 10 to 99 parts by mass, 10 to 95 parts by mass, 10 to 90 parts by mass, 10 to 85 parts by mass, 10 to 80 parts by mass, 10 to 75 parts by mass, 15 to 99 parts by mass, 15 to 95 parts by mass, 15 to 90 parts by mass, 15 to 85 parts by mass, 15 to 80 parts by mass, 15 to 75 parts by mass, 20 to 99 parts by mass, 20 to 95 parts by mass, 20 to 90 parts by mass, 20 to 85 parts by mass, 20 to 80 parts by mass, 20 to 75 parts by mass, 25 to 99 parts by mass, 25 to 95 parts by mass, 25 to 90 parts by mass, 25 to 85 parts by mass, 25 to 80 parts by mass, 25 to 75 parts by mass, 30 to 99 parts by mass, 30 to 95 parts by mass, 30 to 90 parts by mass, 30 to 85 parts by mass, 30 to 80 parts by mass, 30 to 75 parts by mass, 35 to 99 parts by mass, 35 to 95 parts by mass, 35 to 90 parts by mass, 35 to 85 parts by mass, 35 to 80 parts by mass, 35 to 75 parts by mass, 40 to 99 parts by mass, 40 to 95 parts by mass, 40 to 90 parts by mass, 40 to 85 parts by mass, 40 to 80 parts by mass, 40 to 75 parts by mass, 45 to 99 parts by mass, 45 to 95 parts by mass, 45 to 90 parts by mass, 45 to 85 parts by mass, 45 to 80 parts by mass, 45 to 75 parts by mass, 50 to 99 parts by mass, 50 to 95 parts by mass, 50 to 90 parts by mass, 50 to 85 parts by mass, 50 to 80 parts by mass, 50 to 75 parts by mass, 55 to 99 parts by mass, 55 to 95 parts by mass, 55 to 90 parts by mass, 55 to 85 parts by mass, 55 to 80 parts by mass, 55 to 75 parts by mass, 60 to 99 parts by mass, 60 to 95 parts by mass, 60 to 90 parts by mass, 60 to 85 parts by mass, 60 to 80 parts by mass, 60 to 75 parts by mass, 65 to 99 parts by mass, 65 to 95 parts by mass, 65 to 90 parts by mass, 65 to 85 parts by mass, 65 to 80 parts by mass or 65 to 75 parts by mass with respect to a total of 100 parts by mass of carbon black and carbon nanotubes.

[0104] The content of carbon nanotubes in the positive electrode composition may be, for example, 1 part by mass or more with respect to a total of 100 parts by mass of carbon black and carbon nanotubes, and from the viewpoint of making the internal resistance smaller and from the viewpoint of more excellent discharge rate characteristics and cycle characteristics, it may be 5 parts by mass or more, 10 parts by mass or more, 15 parts by mass or more, 20 parts by mass or more, or 25 parts by mass or more. Further, the content of carbon nanotubes in the positive electrode composition may be, for example, 90 parts by mass or less, 85 parts by mass or less, 80 parts by mass or less, 75 parts by mass or less, 70 parts by mass or less, 65 parts by mass or less, 60 parts by mass or less, 55 parts by mass or less, 50 parts by mass or less, 45 parts by mass or less, 40 parts by mass or more, or 35 parts by mass or less with respect to a total of 100 parts by mass of carbon black and carbon nanotubes. That is, the content of the carbon nanotubes in the positive electrode composition may be, for example, 1 to 90 parts by mass, 1 to 85 parts by mass, 1 to 80 parts by mass, 1 to 75 parts by mass, 1 to 70 parts by mass, 1 to 65 parts by mass, 1 to 60 parts by mass, 1 to 55 parts by mass, 1 to 50 parts by mass, 1 to 45 parts by mass, 1 to 40 parts by mass, 1 to 35 parts by mass, 5 to 90 parts by mass, 5 to 85 parts by mass, 5 to 80 parts by mass, 5 to 75 parts by mass, 5 to 70 parts by mass, 5 to 65 parts by mass, 5 to 60 parts by mass, 5 to 55 parts by mass, 5 to 50 parts by mass, 5 to 45 parts by mass, 5 to 40 parts by mass, 5 to 35 parts by mass, 10 to 90 parts by mass, 10 to 85 parts by mass, 10 to 80 parts by mass, 10 to 75 parts by mass, 10 to 70 parts by mass, 10 to 65 parts by mass, 10 to 60 parts by mass, 10 to 55 parts by mass, 10 to 50 parts by mass, 10 to 45 parts by mass, 10 to 40 parts by mass, 10 to 35 parts by mass, 15 to 90 parts by mass, 15 to 85 parts by mass, 15 to 80 parts by mass, 15 to 75 parts by mass, 15 to 70 parts by mass, 15 to 65 parts by mass, 15 to 60 parts by mass, 15 to 55 parts by mass, 15 to 50 parts by mass, 15 to 45 parts by mass, 15 to 40 parts by mass, 15 to 35 parts by mass, 20 to 90 parts by mass, 20 to 85 parts by mass, 20 to 80 parts by mass, 20 to 75 parts by mass, 20 to 70 parts by mass, 20 to 65 parts by mass, 20 to 60 parts by mass, 20 to 55 parts by mass, 20 to 50 parts by mass, 20 to 45 parts by mass, 20 to 40 parts by mass, 20 to 35 parts by mass, 25 to 90 parts by mass, 25 to 85 parts by mass, 25 to 80 parts by mass, 25 to 75 parts by mass, 25 to 70 parts by mass, 25 to 65 parts by mass, 25 to 60 parts by mass, 25 to 55 parts by mass, 25 to 50 parts by mass, 25 to 45 parts by mass, 25 to 40 parts by mass or 25 to 35 parts by mass with respect to a total of 100 parts by mass of the carbon black and the carbon nanotubes.

[0105] The total content of carbon nanotubes and carbon black in the positive electrode composition may be, for example, 0.1% by mass or more based on the total mass of the positive electrode composition, and from the viewpoint of making the internal resistance smaller and from the viewpoint of more excellent discharge rate characteristics and cycle characteristics, it may be 0.3% by mass or more, 0.5% by mass or more, 0.7% by mass or more, or 0.9% by mass or more. Further, the total content of carbon nanotubes and carbon black in the positive electrode composition may be, for example, 5% by mass or less based on the total mass of the positive electrode composition, and from the viewpoint of making the internal resistance smaller and from the viewpoint of more excellent discharge rate characteristics and cycle characteristics, it may be 4% by mass or less, 3% by mass or less, 2% by mass or less, or 1.5% by mass or less. That is, the total content of carbon nanotubes and carbon black in the positive electrode composition may be, for example, 0.1 to 5% by mass, 0.1 to 4% by mass, 0.1 to 3% by mass, 0.1 to 2% by mass, 0.1 to 1.5% by mass, 0.3 to 5% by mass, 0.3 to 4% by mass, 0.3 to 3% by mass, 0.3 to 2% by mass, 0.3 to 1.5% by mass, 0.5 to 5% by mass, 0.5 to 4% by mass, 0.5 to 3% by mass, 0.5 to 2% by mass, 0.5 to 1.5% by mass, 0.7 to 5% by mass, 0.7 to 4% by mass, 0.7 to 3% by mass, 0.7 to 2% by mass, 0.7 to 1.5% by mass, 0.9 to 5% by mass, 0.9 to 4% by mass, 0.9 to 3% by mass, 0.9 to 2% by mass, or 0.9 to 1.5% by mass based on the total mass of the positive electrode composition.

[0106] The content of the binder in the positive electrode composition may be, for example, 0.1% by mass or more based on the total mass of the positive electrode composition, and from the viewpoint of making the internal resistance smaller and from the viewpoint of more excellent discharge rate characteristics and cycle characteristics, it may be 0.5% by mass or more, 1% by mass or more, or 1.5% by mass or more. Further, the content of the binder in the positive electrode composition may be, for example, 10% by mass or less based on the total mass of the positive electrode composition, and from the viewpoint of making the internal resistance smaller and from the viewpoint of more excellent discharge rate characteristics and cycle characteristics, it may be 9% by mass or less, 8% by mass or less, 7% by mass or less, 6% by mass or less, 5% by mass or less, 4% by mass or less, or 3% by mass or less. That is, the content of the binder in the positive electrode composition may be, for example, 0.1 to 10% by mass, 0.1 to 9% by mass, 0.1 to 8% by mass, 0.1 to 7% by mass, 0.1 to 6% by mass, 0.1 to 5% by mass, 0.1 to 4% by mass, 0.1 to 3% by mass, 0.5 to 10% by mass, 0.5 to 9% by mass, 0.5 to 8% by mass, 0.5 to 7% by mass, 0.5 to 6% by mass, 0.5 to 5% by mass, 0.5 to 4% by mass, 0.5 to 3% by mass, 1 to 10% by mass, 1 to 9% by mass, 1 to 8% by mass, 1 to 7% by mass, 1 to 6% by mass, 1 to 5% by mass, 1 to 4% by mass, 1 to 3% by mass, 1.5 to 10% by mass, 1.5 to 9% by mass, 1.5 to 8% by mass, 1.5 to 7% by mass, 1.5 to 6% by mass, 1.5 to 5% by mass, 1.5 to 4% by mass, or 1.5 to 3% by mass, based on the total mass of the positive electrode composition.

[0107] The content of the active material in the positive electrode composition may be, for example, 90% by mass or more, and from the viewpoint of more excellent discharge rate characteristics and cycle characteristics, it may be 91% by mass or more, 92% by mass or more, 93% by mass or more, 94% by mass or more, or 95% by mass or more, based on the total mass of the positive electrode composition. Further, the content of the active material in the positive electrode composition may be, for example, 99.5% by mass or less, and from the viewpoint of making the internal resistance smaller, it may be 99% by mass or less or 98% by mass or less. That is, the content of the active material in the positive electrode composition may be, for example, 90 to 99.5% by mass, 90 to 99% by mass, 90 to 98% by mass, 91 to 99.5% by mass, 91 to 99% by mass, 91 to 98% by mass, 92 to 99.5% by mass, 92 to 99% by mass, 92 to 98% by mass, 93 to 99.5% by mass, 93 to 99% by mass, 93 to 98% by mass, 94 to 99.5% by mass, 94 to 99% by mass, 94 to 98% by mass, 95 to 99.5% by mass, 95 to 99% by mass, or 95 to 98% by mass, based on the total mass of the positive electrode composition.

[0108] The content of the dispersant in the positive electrode composition may be, for example, 0.05% by mass or more, 0.1% by mass or more, or 0.15% by mass or more based on the total mass of the positive electrode composition. Also, the content of the dispersant in the positive electrode composition may be, for example, 0.8% by mass or less, 0.5% by mass or less, or 0.2% by mass or less based on the total mass of the positive electrode composition. That is, the content of the dispersant in the positive electrode composition may be, for example, 0.05 to 0.8% by mass, 0.05 to 0.5% by mass, 0.05 to 0.2% by mass, 0.1 to 0.8% by mass, 0.1 to 0.5% by mass, 0.1 to 0.2% by mass, 0.15 to 0.8% by mass, 0.15 to 0.5% by mass, or 0.15 to 0.2% by mass based on the total mass of the positive electrode composition.

[0109] The positive electrode of this embodiment may be manufactured by a manufacturing method including a positive electrode forming step of applying the above-described coating liquid for positive electrode formation onto a current collector to form a composite material layer made of the positive electrode composition on the current collector.

[0110] The current collector is not particularly limited, and known current collectors can be used without particular limitation. As the current collector, for example, a metal foil (metals such as gold, silver, copper, platinum, aluminum, iron, nickel, chromium, manganese, lead, tungsten, and titanium, and alloys having any one of these as a main component) is used. The current collector is generally provided in the form of a foil, but is not limited thereto, and perforated foil-shaped and mesh-shaped current collectors can also be used.

[0111] The method for applying the coating liquid for positive electrode formation onto the current collector is not particularly limited, and may be, for example, methods such as 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, and an electrostatic coating method.

[0112] The coating amount of the coating liquid for positive electrode formation is not particularly limited, and may be appropriately adjusted so that the thickness of the composite material layer is within a desired range.

[0113] The composite material layer may be formed by removing at least a part of the liquid medium from a coating film of a coating liquid for forming a positive electrode formed on a current collector. The method for removing the liquid medium is not particularly limited. For example, as a method of vaporizing and removing at least a part of the liquid medium by heating and / or reducing the pressure, methods such as natural drying, a blow dryer, a hot air dryer, an infrared heater, and a far-infrared heater can be mentioned.

[0114] The method for manufacturing the positive electrode of the present embodiment may further include a pressing step of pressing the composite material layer and the current collector formed in the positive electrode forming step in the stacking direction. By the pressing step, the composite material layer and the current collector can be brought into close contact with each other.

[0115] The pressing method in the pressing step is not particularly limited, and for example, methods such as roll pressing, die pressing, and calendar pressing may be used.

[0116] The thickness of the composite material layer in the positive electrode is not particularly limited, and for example, it may be 50 μm or more. 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. Further, the thickness of the composite material layer in the positive electrode may be, for example, 150 μm or less. 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. That is, the thickness of the composite material layer in the positive electrode may be, for example, 50 to 150 μm, 50 to 140 μm, 50 to 130 μm, 50 to 120 μm, 50 to 110 μm, 55 to 150 μm, 55 to 140 μm, 55 to 130 μm, 55 to 120 μm, 55 to 110 μm, 60 to 150 μm, 60 to 140 μm, 60 to 130 μm, 60 to 120 μm, 60 to 110 μm, 65 to 150 μm, 65 to 140 μm, 65 to 130 μm, 65 to 120 μm, 65 to 110 μm, 70 to 150 μm, 70 to 140 μm, 70 to 130 μm, 70 to 120 μm, or 70 to 110 μm.

[0117] The positive electrode of the present embodiment can be suitably used as a positive electrode of a battery, particularly a secondary battery (lithium ion secondary battery).

[0118] <Battery> The battery of the present embodiment (preferably a secondary battery, more preferably a lithium-ion secondary battery) includes a positive electrode manufactured by the above-described manufacturing method. In the battery of the present embodiment, the configuration other than the positive electrode may be the same as that of a known battery. The manufacturing method of the battery in the present embodiment is not particularly limited, and may be the same as the manufacturing method of a conventionally known battery except that the positive electrode manufactured by the above-described manufacturing method is used.

[0119] Since the battery of the present embodiment includes a positive electrode using the carbon black of the present embodiment, it has a small internal resistance and excellent discharge rate characteristics and cycle characteristics.

[0120] The battery of the present embodiment may include, for example, a positive electrode, a negative electrode, and a separator.

[0121] The separator is not particularly limited, and a separator known as a separator for a lithium-ion secondary battery can be used without particular limitation. Examples of the separator include synthetic resins such as polyethylene and polypropylene. The separator is preferably a porous film because it has good electrolyte retention.

[0122] The battery of the present embodiment may include an electrode group in which a positive electrode and a negative electrode are laminated or wound with a separator interposed therebetween.

[0123] In the battery of the present embodiment, the positive electrode, the negative electrode, and the separator may be immersed in an electrolyte.

[0124] The electrolyte is not particularly limited and may be, for example, a non-aqueous electrolyte containing a lithium salt. Examples of the non-aqueous solvent in the non-aqueous electrolyte containing a lithium salt include ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, and the like. Examples of the lithium salt that can be dissolved in the non-aqueous solvent include lithium hexafluorophosphate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, and the like. The battery of the present embodiment may use an ion-conductive polymer or the like as an electrolyte.

[0125] The negative electrode in the battery of the present embodiment may include a negative electrode composite layer formed by coating a negative electrode composite material containing a negative electrode active material and a binder on a negative electrode current collector, similar to the negative electrode used in a general lithium-ion secondary battery, and a negative electrode current collector.

[0126] The use of the battery in the present embodiment is not particularly limited, and it can be used, for example, in a wide range of fields such as portable AV devices such as digital cameras, video cameras, portable audio players, and portable liquid crystal televisions, portable information terminals such as notebook computers, smartphones, and mobile PCs, and other portable game devices, power tools, electric bicycles, hybrid vehicles, electric vehicles, and power storage systems.

[0127] As described above, the preferred embodiments of the present invention have been described, but the present invention is not limited to the above embodiments.

[0128] For example, one aspect of the present invention may be a method for manufacturing a coating liquid for forming a positive electrode, a method for manufacturing a positive electrode, or a method for manufacturing a battery, which includes an image acquisition step of acquiring a two-dimensional projection image of primary aggregates of carbon black by a transmission electron microscope, and from the two-dimensional projection image, obtaining the number of the first primary aggregate, the second primary aggregate, the third primary aggregate, and the fourth primary aggregate respectively, and obtaining the number ratio of the total number of the second primary aggregate and the third primary aggregate to the total number of the first primary aggregate, the second primary aggregate, the third primary aggregate, and the fourth primary aggregate, and a selection step of selecting carbon black in which the number ratio is 22% or more. That is, the above-described method for manufacturing a coating liquid for forming a positive electrode, a method for manufacturing a positive electrode, and a method for manufacturing a battery may further include the above image acquisition step and selection step.

Example

[0129] Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to these examples.

[0130] (Production Example A1: Production of Carbon Black (A1)) Acetylene (110°C) as a raw material gas was supplied at 20 Nm 3 / h from a nozzle installed in the upstream part of a cylindrical reactor (diameter 1 m, length 7 m), and oxygen (25°C) as a gas other than the raw material was supplied at 12 Nm 3 / h from a nozzle installed in a direction orthogonal to the raw material gas to produce carbon black, which was collected by a bag filter installed in the downstream part of the reactor. Thereafter, it was passed through a dry cyclone device and a magnet for iron removal and recovered in a tank. The nozzle diameter was adjusted so that the ejection speed of the raw material gas into the reactor was 5 m / s and the ejection speed of the gas other than the raw material was 8 m / s.

[0131] (Production Examples A2 to A5: Production of Carbon Blacks (A2) to (A5)) Carbon black was produced in the same manner as in Production Example A1 except that the supply amount and ejection speed of oxygen (25°C) were changed as shown in Table 1.

[0132] (Production Example X1: Production of Carbon Black (X1)) Carbon black was produced in the same manner as in Production Example A1, except that the supply amount and ejection rate of oxygen (at 25°C) were changed as shown in Table 1.

[0133] (Production Example X2: Production of Carbon Black (X2)) Carbon black was produced in the same manner as in Production Example A1, except that oxygen (at 25°C) was supplied parallel to the supply direction of the raw material gas.

[0134] [Table 1]

[0135] The following measurements were carried out on the carbon blacks obtained in Production Examples A1 to A5 and X1 to X2. The results are shown in Table 2. (1) Specific surface area It was measured according to Method A (thermal conductivity measurement method) of the flow method of JIS K6217-2:2017. (2) DBP absorption The DBP absorption is the value measured by the method described in Method B of JIS K6221, converted to a value equivalent to JIS K6217-4:2008 by the following formula (a). DBP absorption = (A - 10.974) / 0.7833…(a) [In the formula, A represents the value of the DBP absorption measured by the method described in Method B of JIS K6221.]

[0136] Next, the carbon blacks obtained in Production Examples A1 to A5 and X1 to X2 were dispersed in chloroform at an ultrasonic output of 90 W for 10 minutes to loosen the secondary aggregates into primary aggregates, which were scooped up with a collodion membrane mesh and photographed at a magnification of 2000 times using a transmission electron microscope.

[0137] The obtained two-dimensional projection image was subjected to filter processing (median filter, option 7×7, number of times: 3) using image analysis software "Image-Pro Plus 6.2J (manufactured by Media Cybernetics)". After that, the luminance range was manually extracted according to the primary aggregates. "Size (width)", "Size (length)", "Perimeter length", and "Area" were selected from the measurement items, and the Feret diameter W (μm) in the short-axis direction, the Feret diameter L (μm) in the long-axis direction, the perimeter length P (μm), and the projected area A (μm 2 ) of 100 or more randomly selected primary aggregates were measured. The primary aggregates, scale bars, and background noise on the edge of the image were excluded. Based on formula (X), formula (Y), and formula (Z), the primary aggregates were classified into the first primary aggregate, the second primary aggregate, the third primary aggregate, and the fourth primary aggregate, and the respective number ratios were calculated. The results are shown in Table 2.

[0138] Note that FIG. 2 is a diagram showing a two-dimensional projection image of the primary aggregates of carbon black (A3) of Production Example A3 by a transmission electron microscope.

[0139]

Table 2

[0140] (Example 1) <Production of the coating liquid for forming the positive electrode> Carbon black (A1) of Production Example A1, N-methyl-2-pyrrolidone (manufactured by Kanto Chemical Co., Inc.) as a dispersion medium, and polyvinyl alcohol (manufactured by Denka Co., Ltd., Poval B05) as a dispersant were prepared. 10 parts by mass of carbon black (A1) and 1 part by mass of polyvinyl alcohol were added to 89 parts by mass of NMP, and the mixture was stirred for 120 minutes using a planetary mixer (manufactured by Primix Co., Ltd., Highbis Dispermix 3D-5 type) to obtain a slurry (the first agent). Next, with an average diameter of 6 nm and a BET specific surface area of 300 m 2 / g, carbon nanotubes with a BET specific surface area of 0.02 (manufactured by CNano, "Flotube6000") were prepared. 1.0 mass% of polyvinylpyrrolidone (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., "Pitcol K-90") and 4.0 mass% of carbon nanotubes were added to 95.0 mass% of NMP, and the mixture was stirred for 120 minutes using a planetary mixer (manufactured by Primix Corporation, High Bis Dispermix 3D-5 type) to prepare a slurry containing carbon nanotubes. The obtained slurry was charged into a bead mill (manufactured by Asazawa Fine Tech Co., Ltd., Mugen Flow MGF2-ZA) equipped with zirconia beads (diameter 0.5 mm), and dispersion treatment was performed. After the dispersion treatment, the zirconia beads were removed by filtration to obtain a slurry (secondary agent). Next, an NMP solution of polyvinylidene fluoride (manufactured by Kureha Corporation, "L#7208", tertiary agent) as a binder, nickel manganese cobalt lithium oxide with an average particle diameter D 50 of 10 μm (manufactured by Beijing Easpring Material Technology Co., Ltd., "ME6E") as an active material, and NMP as a dispersion medium were prepared. The first agent, the second agent, the third agent, and the active material were mixed so that, based on the total amount of solids, the active material was 97.0 mass%, carbon black was 0.7 mass%, carbon nanotubes were 0.3 mass%, and the binder was 2.0 mass%. NMP was added until a coatable viscosity was achieved, and the mixture was uniformly mixed using a planetary mixer (manufactured by Shinchi Co., Ltd., Awatori Rentaro ARV-310) to obtain a coating solution for positive electrode formation.

[0141] <Manufacture of Positive Electrode> The coating solution for positive electrode formation was coated on one side of an aluminum foil (manufactured by UACJ Corporation) with a thickness of 15 μm using an applicator, left standing in a dryer, and pre-dried at 105 °C for 1 hour to completely remove NMP and form a composite layer. Next, it was pressed using a roll press at a linear pressure of 200 kg / cm² to adjust the total thickness of the laminate to 80 μm. Then, it was vacuum dried at 170 °C for 3 hours to completely remove residual moisture, and a positive electrode comprising a current collector and a composite layer was obtained.

[0142] <Manufacture of Negative Electrode> Pure water (manufactured by Kanto Chemical Co., Inc.) 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, respectively. Next, 1 part by mass of CMC and 97 parts by mass of artificial graphite were weighed and mixed. Pure water was added to this mixture, and using a planetary mixer (manufactured by Shinchi Co., Ltd., Awatori Rentaro ARV-310), it was mixed until uniform to obtain a mixture. Next, 2 parts by mass of SBR was weighed and added to the obtained mixture, and using a planetary mixer (manufactured by Shinchi Co., Ltd., Awatori Rentaro ARV-310), it was mixed until uniform to obtain a coating liquid for forming a negative electrode. Next, the coating liquid for forming a negative electrode was coated on a copper foil (manufactured by UACJ Corporation) with a thickness of 10 μm using an applicator, and left standing in a dryer and pre-dried at 60°C for 1 hour. Next, it was pressed with a roll press at a linear pressure of 50 kg / cm² so that the total thickness of the laminate became 60 μm. Next, it was vacuum dried at 120°C for 3 hours to completely remove the residual moisture, and a negative electrode having a current collector and a composite material layer was obtained.

[0143] (Manufacture of battery) In a dry room controlled to a dew point of -50°C or lower, the fabricated positive electrode was processed to 40×40 mm, and the fabricated negative electrode was processed to 44×44 mm. Then, an aluminum tab was welded to the positive electrode and a nickel tab was welded to the negative electrode. The composite material layers of the positive and negative electrodes were opposed to each other at the center, and a polyolefin microporous membrane processed to 45×45 mm was placed between the positive and negative electrodes. Next, a sheet-shaped exterior cut and processed into a 70×140 mm square was folded in half at the center of the long side. Then, while arranging the exterior so that the aluminum tab for the positive electrode and the nickel tab for the negative electrode were exposed outside the exterior, the laminate of the positive electrode / polyolefin microporous membrane / negative electrode was sandwiched by the folded exterior. Next, using a heat sealer, two sides including the sides where the aluminum tab for the positive electrode and the nickel tab for the negative electrode of the exterior were exposed were heat-sealed. Then, from one side that was not heat-sealed, 2 g of an electrolytic solution (a solution containing ethylene carbonate / diethyl carbonate = 1 / 2 (volume ratio) and 1 M LiPF6 solution manufactured by Kishida Chemical Co., Ltd.) was injected. After allowing the electrolytic solution to fully penetrate into the positive electrode, negative electrode, and polyolefin microporous membrane, the remaining side of the exterior was heat-sealed while reducing the internal pressure with a vacuum heat sealer to obtain a lithium-ion secondary battery.

[0144] (Evaluation of the battery) [Internal resistance] The fabricated battery was charged at a constant current and constant voltage of 4.3 V and 0.2C limit at 25°C, and then discharged at a constant current of 0.2C to 3.0 V. Then, after charging / discharging 5 cycles under the same conditions, it was charged so that the depth of charge became 50%. Thereafter, impedance measurement was performed at a frequency range of 10 MHz to 0.001 Hz and a vibration voltage of 5 mV to measure the internal resistance. The results are shown in Table 3.

[0145] [Discharge rate characteristics (rate capacity retention rate)] The fabricated battery was charged at a constant current and constant voltage with a limit of 4.3V and 0.2C at 25°C, and then discharged at a constant current of 0.2C until 3.0V. Subsequently, it was restored and charged again at a constant current and constant voltage with a limit of 4.3V and 0.2C, and then discharged at a constant current of 0.2C until 3.0V, and the discharge capacity at this time was measured. Next, the restoration charging conditions were set to a constant current and constant voltage with a limit of 4.3V and 0.2C for charging, while the discharge current was changed stepwise to 0.5C, 1C, 2C, and 3C, and the restoration charging and discharging were repeated to measure the discharge capacity for each discharge current. As an index of the discharge rate characteristics of the battery, the capacity retention rate at 3C discharge with respect to the discharge at 0.2C was calculated as the rate capacity retention rate. The results are shown in Table 3.

[0146] [Cycle characteristics (cycle capacity retention rate)] The fabricated battery was charged at a constant current and constant voltage with a limit of 4.3V and 1C at 25°C, and then discharged at a constant current of 1C until 3.0V. The above charge and discharge were repeated 500 cycles, and the discharge capacity in each cycle was measured. As an index of the cycle characteristics of the battery, the capacity retention rate after 500 cycles with respect to the capacity retention rate after 1 cycle was calculated as the cycle capacity retention rate. The results are shown in Table 3.

[0147] <Example 2> A battery was fabricated and evaluated in the same manner as in Example 1, except that the carbon black (A1) in Example 1 was changed to carbon black (A2).

[0148] <Example 3> A battery was fabricated and evaluated in the same manner as in Example 1, except that the carbon nanotube in Example 1 was changed to a carbon nanotube (manufactured by CNano, "Flotube7000") with an average diameter of 9nm, a BET specific surface area of 250m 2 / g, and an average diameter / BET specific surface area of 0.036.

[0149] <Example 4> A battery was fabricated and evaluated in the same manner as in Example 1, except that the carbon black (A1) in Example 1 was changed to carbon black (A5).

[0150] <Example 5> A battery was fabricated and evaluated in the same manner as in Example 1, except that the carbon black (A1) in Example 1 was changed to carbon black (A3).

[0151] <Example 6> The carbon nanotubes in Example 1 were changed to carbon nanotubes (manufactured by CNano, "Flotube9000") with an average diameter of 12 nm, a BET specific surface area of 180 m 2 / g, and an average diameter / BET specific surface area of 0.067. A battery was fabricated and evaluated in the same manner as in Example 1.

[0152] <Example 7> A battery was fabricated and evaluated in the same manner as in Example 1, except that the amounts of the first agent and the second agent were changed so that the content of carbon black in the coating liquid for forming the positive electrode was 0.5% by mass based on the total mass of the solid content, and the content of carbon nanotubes in the coating liquid for forming the positive electrode was 0.5% by mass based on the total mass of the solid content.

[0153] <Example 8> A battery was fabricated and evaluated in the same manner as in Example 1, except that the amounts of the first agent and the second agent were changed so that the content of carbon black in the coating liquid for forming the positive electrode was 0.9% by mass based on the total mass of the solid content, and the content of carbon nanotubes in the coating liquid for forming the positive electrode was 0.1% by mass based on the total mass of the solid content.

[0154] <Example 9> A battery was fabricated and evaluated in the same manner as in Example 1, except that the carbon black (A1) in Example 1 was changed to carbon black (A4).

[0155] <Example 10> The active material in Example 1 had an average particle diameter D 50It was changed to lithium cobaltate (manufactured by Yumicore Co., Ltd., "KD-20") with a particle size of 20 μm, and the amount of the first agent and the second agent was changed so that the content of carbon black in the coating liquid for forming the positive electrode was 0.9% by mass based on the total mass of the solid content, and the content of carbon nanotubes in the coating liquid for forming the positive electrode was 0.1% by mass based on the total mass of the solid content. Except for this, a battery was fabricated and evaluated in the same manner as in Example 1.

[0156] <Example 11> The carbon black (A1) in Example 1 was changed to carbon black (A2), and the carbon nanotubes were changed to carbon nanotubes (manufactured by CNano Co., Ltd., "Flotube7000") with an average diameter of 9 nm, a BET specific surface area of 250 m 2 / g, and an average diameter / BET specific surface area of 0.036. The amount of the first agent and the second agent was changed so that the content of carbon black in the coating liquid for forming the positive electrode was 0.1% by mass based on the total mass of the solid content, and the content of carbon nanotubes in the coating liquid for forming the positive electrode was 0.9% by mass based on the total mass of the solid content. Except for this, a battery was fabricated and evaluated in the same manner as in Example 1.

[0157] <Comparative Example 1> The carbon black (A1) in Example 1 was changed to carbon black (A3), no carbon nanotubes were used, and the amount of the first agent was changed so that the content of carbon black in the coating liquid for forming the positive electrode was 1% by mass based on the total mass of the solid content. Except for this, a battery was fabricated and evaluated in the same manner as in Example 1.

[0158] <Comparative Example 2> The carbon nanotubes in Example 1 were changed to carbon nanotubes (manufactured by CNano Co., Ltd., "Flotube7000") with an average diameter of 9 nm, a BET specific surface area of 250 m 2 / g, and an average diameter / BET specific surface area of 0.036. No carbon black was used, and the amount of the second agent was changed so that the content of carbon nanotubes in the coating liquid for forming the positive electrode was 1% by mass based on the total mass of the solid content. Except for this, a battery was fabricated and evaluated in the same manner as in Example 1.

[0159] <Comparative Example 3> The carbon nanotubes of Example 1 were changed to carbon nanotubes with an average diameter of 32 nm, a BET specific surface area of 110 m 2 / g, and an average diameter / BET specific surface area of 0.29 (manufactured by Tokyo Chemical Industry Co., Ltd., "MWNT"). A battery was fabricated and evaluated in the same manner as in Example 1, except for this change.

[0160] <Comparative Example 4> The carbon nanotubes of Example 1 were changed to carbon nanotubes with an average diameter of 2.5 nm, a BET specific surface area of 740 m 2 / g, and an average diameter / BET specific surface area of 0.003 (manufactured by Sigma-Aldrich Co., LLC, "SignisFW100"). Also, the amount of the first agent and the second agent was changed so that the content of carbon black in the coating liquid for forming the positive electrode was 0.9% by mass based on the total mass of the solid content, and the content of carbon nanotubes in the coating liquid for forming the positive electrode was 0.1% by mass based on the total mass of the solid content. A battery was fabricated and evaluated in the same manner as in Example 1, except for these changes.

[0161] <Comparative Example 5> A battery was fabricated and evaluated in the same manner as in Example 1, except that the carbon black (A1) of Example 1 was changed to carbon black (X1).

[0162] <Comparative Example 6> A battery was fabricated and evaluated in the same manner as in Example 1, except that the carbon black (A1) of Example 1 was changed to carbon black (X2).

[0163]

Table 3

Claims

1. A positive electrode composition containing carbon black, carbon nanotubes, a binder, and an active material, wherein the carbon nanotubes have an average diameter of 5 to 15 nm, when the carbon black is classified into a first primary aggregate having an X value obtained by the following formula (X) exceeding 1.7, a second primary aggregate having the X value of 1.7 or less and a Y value obtained by the following formula (Y) of 1.2 or less, a third primary aggregate having the X value of 1.7 or less, the Y value exceeding 1.2, and a Z value obtained by the following formula (Z) of 2.0 or less, and a fourth primary aggregate having the X value of 1.7 or less, the Y value exceeding 1.2, and the Z value exceeding 2.0, the number ratio of the total number of the second primary aggregate and the third primary aggregate to the total number of the first primary aggregate, the second primary aggregate, the third primary aggregate and the fourth primary aggregate is 22% or more. X = L / W (X) Y = P ２ / 4πA(Y) Z = (L × W) / A (Z) [wherein, in the two-dimensional projection image of the primary aggregate obtained by a transmission electron microscope, the Feret diameter in the short axis direction of the primary aggregate is W (μm), the Feret diameter in the long axis direction of the primary aggregate is L (μm), the perimeter of the primary aggregate is P (μm), and the projected area of the primary aggregate is A (μm ２ 2).]

2. The ratio of the average diameter to the BET specific surface area of the carbon nanotube (average diameter / BET specific surface area) is 0.01 to 0.1 nm / (m ２ / g), and the positive electrode composition according to claim 1.

3. A positive electrode including a composite material layer made of the positive electrode composition according to Claim 1 or 2.

4. A battery including the positive electrode according to Claim 3.

5. A mixing step of mixing carbon black and a first liquid medium to obtain a first agent containing the carbon black and the first liquid medium, a coating liquid forming step of mixing the first agent, a second agent containing carbon nanotubes and a second liquid medium, a third agent containing a binder and a third liquid medium, and an active material to form a coating liquid for forming a positive electrode, wherein the carbon nanotubes have an average diameter of 5 to 15 nm, when the carbon black is classified into a first primary aggregate having an X value obtained by the following formula (X) exceeding 1.7, a second primary aggregate having the X value of 1.7 or less and a Y value obtained by the following formula (Y) of 1.2 or less, a third primary aggregate having the X value of 1.7 or less, the Y value exceeding 1.2, and a Z value obtained by the following formula (Z) of 2.0 or less, and a fourth primary aggregate having the X value of 1.7 or less, the Y value exceeding 1.2, and the Z value exceeding 2.0, the number ratio of the total number of the second primary aggregate and the third primary aggregate to the total number of the first primary aggregate, the second primary aggregate, the third primary aggregate and the fourth primary aggregate is 22% or more. A method for manufacturing a coating liquid for forming a positive electrode. X = L / W (X) Y = P ２ / 4πA(Y) Z = (L × W) / A (Z) [wherein, in the two-dimensional projection image of the primary aggregate obtained by a transmission electron microscope, the Feret diameter in the short axis direction of the primary aggregate is W (μm), the Feret diameter in the long axis direction of the primary aggregate is L (μm), the perimeter of the primary aggregate is P (μm), and the projected area of the primary aggregate is A (μm ２ ).] Claim 6 A method for manufacturing a positive electrode, comprising a positive electrode forming step of applying a coating liquid for forming a positive electrode manufactured by the manufacturing method according to claim 5 onto a current collector to form a composite material layer made of a positive electrode composition containing the carbon black, the carbon nanotube, the binder, and the active material on the current collector, and obtaining a positive electrode including the current collector and the composite material layer. Claim 7 A method for manufacturing a battery, comprising a positive electrode forming step of applying a coating liquid for forming a positive electrode manufactured by the manufacturing method according to claim 5 onto a current collector to form a composite material layer made of a positive electrode composition containing the carbon black, the carbon nanotube, the binder, and the active material on the current collector, and obtaining a positive electrode including the current collector and the composite material layer.

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