Positive electrode composition, positive electrode, and method for manufacturing a positive electrode

Abstract

To provide a positive electrode composition that enables the production of lithium-ion secondary batteries with low internal resistance and excellent discharge rate characteristics and cycle characteristics. [Solution] A positive electrode composition containing carbon black, carbon nanotubes, an active material, a binder, and a liquid medium, wherein the solid content concentration is 60 to 85% by mass, and the ratio of viscosity V2 at a shear rate of 1 (1 / sec) at 25°C to viscosity V1 at a shear rate of 0.01 (1 / sec) at 25°C (V2 / V1) is 0.02 or more and 0.2 or less.

Description

[Technical Field]

[0001] The present invention relates to a positive electrode composition, a positive electrode, and a method for manufacturing a positive electrode. [Background technology]

[0002] Due to the growing environmental and energy concerns, there is a surge in the development of technologies aimed at realizing a low-carbon society that reduces reliance on fossil fuels. Such technological developments are diverse and include the development of low-emission vehicles such as hybrid electric vehicles and electric vehicles, the development of renewable energy power generation and storage systems such as solar and wind power generation, and the development of next-generation power grids that efficiently supply electricity and reduce transmission losses.

[0003] One of the key devices required for these technologies is the battery, and such batteries need high energy density to miniaturize the system. They also need high output characteristics to enable stable power supply regardless of ambient temperature. Furthermore, they need good cycle characteristics to withstand long-term use. For these reasons, there is a rapid shift from conventional lead-acid batteries, nickel-cadmium batteries, and nickel-metal hydride batteries to lithium-ion secondary batteries, which have higher energy density, output characteristics, and cycle characteristics.

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

[0005] [Patent Document 1] Japanese Patent Publication No. 2008-227481 [Overview of the project] [Problems that the invention aims to solve]

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

[0007] The present invention aims to provide a positive electrode composition that can produce a lithium-ion secondary battery with low internal resistance and excellent discharge rate characteristics and cycle characteristics. Furthermore, the present invention aims to provide a positive electrode that can produce a lithium-ion secondary battery with low internal resistance and excellent discharge rate characteristics and cycle characteristics, and to provide a method for manufacturing a positive electrode. [Means for solving the problem]

[0008] The present invention, for example, the following <1> ~ <8> Regarding. <1> A positive electrode composition comprising carbon black, carbon nanotubes, an active material, a binder, and a liquid medium, wherein the solid content concentration is 60 to 85% by mass, and the ratio of viscosity V2 at a shear rate of 1 (1 / sec) at 25°C to viscosity V1 at a shear rate of 0.01 (1 / sec) at 25°C (V2 / V1) is 0.02 or more and 0.2 or less. <2> The BET specific surface area of ​​the carbon black is 100-500 m². 2 / g <1> The positive electrode composition described above. <3> The ratio of the content (mass%) of carbon nanotubes to the total content (mass%) of carbon black and carbon nanotubes is 0.07 to 0.85. <1> or <2> The positive electrode composition described above. <4> The solid content concentration is 65-80% by mass. <1> ~ <3> A positive electrode composition as described in any of the following. <5> The aforementioned carbon black is 100-400m 2 It has a BET specific surface area of ​​1 / g and a crystallite size (Lc) of 15-26 Å. <1> ~ <4> A positive electrode composition as described in any of the following. <6> The carbon nanotubes have an average diameter of 5 to 15 nm. <1> ~ <5> A positive electrode composition as described in any of the following. <7> <1> ~ <6> A method for producing a positive electrode, comprising the step of applying a positive electrode composition according to any one of the above items onto a current collector to form a composite layer on the current collector containing the carbon black, the carbon nanotubes, the binder, and the active material. <8> A positive electrode comprising a composite layer containing carbon black, carbon nanotubes, a binder, and an active material, wherein the total content of the carbon black and carbon nanotubes is 0.3 to 2.5% by mass based on the total amount of the composite layer, and the composite layer has a surface in which the black ratio is 50 to 80% when the image obtained by binarizing the image obtained by observing it with a scanning electron microscope at a magnification of 1000x is processed. <9> <8> A battery having the positive electrode described above. [Effects of the Invention]

[0009] The present invention provides a positive electrode composition that can produce a lithium-ion secondary battery with low internal resistance and excellent discharge rate characteristics and cycle characteristics. Furthermore, the present invention provides a positive electrode that can produce a lithium-ion secondary battery with low internal resistance and excellent discharge rate characteristics and cycle characteristics. Moreover, the present invention provides a method for manufacturing a positive electrode. [Brief explanation of the drawing]

[0010] [Figure 1] (a) is a figure showing an example of a scanning electron microscope image of the positive electrode used in the example, and (b) is a figure showing an example of a scanning electron microscope image of the positive electrode used in the comparative example. [Modes for carrying out the invention]

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

[0012] The positive electrode composition of this embodiment contains carbon black, carbon nanotubes, an active material, a binder, and a liquid medium. The positive electrode composition of this embodiment is a dispersion for forming a positive electrode, and can also be called a positive electrode forming composition, a positive electrode forming dispersion, or a positive electrode forming coating.

[0013] In the positive electrode composition of this embodiment, the solid content concentration is 60 to 85% by mass. Furthermore, in the positive electrode composition of this embodiment, the ratio of viscosity V2 at a shear rate of 1 (1 / sec) at 25°C to viscosity V1 at a shear rate of 0.01 (1 / sec) at 25°C (V2 / V1) is 0.02 or more and 0.2 or less.

[0014] The positive electrode composition of this embodiment enables the realization of a lithium-ion secondary battery with low internal resistance and excellent discharge rate characteristics and cycle characteristics.

[0015] In this embodiment, carbon black and carbon nanotubes function as conductive materials. The basic role of conductive materials is to impart conductivity to active materials that have poor conductivity. In addition, in lithium-ion secondary batteries, the active materials expand and contract as they undergo repeated charging and discharging, causing the contact points between the active materials to gradually be lost. Conductive materials also play a role in connecting the active materials that have lost their contact points, thereby preventing the loss of conductivity.

[0016] According to the inventors' findings, when the above ratio (V2 / V1) is within the above range, it is considered that the conductive materials, carbon black and carbon nanotubes, are dispersed in a suitable dispersion state in the positive electrode composition. If the dispersion of the conductive material is poor, the active material and the conductive material cannot make sufficient contact, making it difficult to form conductive paths, and resulting in a problem where the performance of the active material cannot be fully utilized. As a result, areas with poor conductivity appear locally within the positive electrode, so the active material is not fully utilized, the discharge capacity decreases, and the battery life is shortened. In contrast, in the positive electrode composition of this embodiment, the conductive material is dispersed in a suitable dispersion state, so the above problem does not occur, and it is considered that excellent discharge rate characteristics and cycle characteristics are achieved.

[0017] The above ratio (V2 / V1) may be 0.03 or more, or may be 0.05 or more. Further, the above ratio (V2 / V1) may be 0.18 or less, 0.16 or less, 0.14 or less, 0.12 or less, or may be 0.10 or less. That is, the above ratio (V2 / V1) may be, for example, 0.02 to 0.2, 0.02 to 0.18, 0.02 to 0.16, 0.02 to 0.14, 0.02 to 0.12, 0.02 to 0.10, 0.03 to 0.2, 0.03 to 0.18, 0.03 to 0.16, 0.03 to 0.14, 0.03 to 0.12, 0.03 to 0.10, 0.05 to 0.2, 0.05 to 0.18, 0.05 to 0.16, 0.05 to 0.14, 0.05 to 0.12, or 0.05 to 0.10.

[0018] The carbon black may be carbon black used as a general conductive material for batteries, and may be acetylene black, furnace black, channel black, or the like. From the viewpoint of excellent purity and easy obtaining of excellent battery characteristics, the carbon black is preferably acetylene black.

[0019] The BET specific surface area of the carbon black is preferably 100 m 2 / g or more. When the BET specific surface area of the carbon black is 100 m 2 / g or more, the electrical contact with the active material and the conductive material increases, and the effect of imparting conductivity becomes better, so that more excellent battery characteristics can be obtained. From the viewpoint of making the internal resistance smaller and the viewpoint of more excellent discharge rate characteristics and cycle characteristics, the BET specific surface area of the carbon black is preferably 120 m 2 / g or more, more preferably 140 m 2 / g or more, still more preferably 160 m 2 / g or more, and 180 m 2 / g or more, 200 m 2 / g or more, or 220 m 2It may be greater than or equal to / g. Note that the ratio (V2 / V1) tends to decrease when the BET specific surface area of ​​carbon black is large. From the viewpoint of easily obtaining a positive electrode composition with a ratio (V2 / V1) of 0.2 or less, it is preferable that the BET specific surface area of ​​carbon black be within the above range.

[0020] Furthermore, the BET specific surface area of ​​carbon black is 500m². 2 It is preferable that the BET specific surface area of ​​the carbon black is 500 m² or less. 2 When the amount is less than / g, the interaction between the liquid medium and the conductive material, and the interaction between conductive materials themselves, becomes smaller, making it easier to uniformly disperse in the active material. This makes it easier to form conductive paths, resulting in better battery characteristics. From the viewpoint of reducing internal resistance and improving discharge rate characteristics and cycle characteristics, the BET specific surface area of ​​carbon black is preferably 450m². 2 / g or less, more preferably 400m 2 It is less than / g and 350m 2 / g or less, 300m 2 / g or less or 250m 2 It may be less than or equal to / g. Note that the ratio (V2 / V1) tends to increase when the BET specific surface area of ​​carbon black is small. From the viewpoint of easily obtaining a positive electrode composition with a ratio (V2 / V1) of 0.02 or higher, it is preferable that the BET specific surface area of ​​carbon black be within the above range. In other words, the BET specific surface area of ​​carbon black is, for example, 100-500 m². 2 / g, 100~450m 2 / g, 100-400m 2 / g, 100-350m 2 / g, 100-300m 2 / g, 100-250m 2 / g, 120~500m 2 / g, 120~450m 2 / g, 120~400m 2 / g, 120-350m 2 / g, 120-300m 2 / g, 120-250m 2 / g, 140~500m2 / g, 140~450m 2 / g, 140~400m 2 / g, 140-350m 2 / g, 140-300m 2 / g, 140-250m 2 / g, 160~500m 2 / g, 160~450m 2 / g, 160~400m 2 / g, 160~350m 2 / g, 160~300m 2 / g, 160-250m 2 / g, 180~500m 2 / g, 180~450m 2 / g, 180~400m 2 / g, 180~350m 2 / g, 180-300m 2 / g, 180-250m 2 / g, 200-500m 2 / g, 200~450m 2 / g, 200-400m 2 / g, 200-350m 2 / g, 200-300m 2 / g, 200-250m 2 / g, 220-500m 2 / g, 220~450m 2 / g, 220~400m 2 / g, 220-350m 2 / g, 220-300m 2 / g or 220-250m 2 / g is also acceptable.

[0021] The BET specific surface area of ​​carbon black can be measured using the static volumetric method in accordance with JIS Z8830, with nitrogen as the adsorbate.

[0022] The crystallite size (Lc) of the carbon black is preferably 15 Å or larger. A crystallite size (Lc) of 15 Å or larger allows π electrons to move more easily through the crystal layer, making it easier to form conductive pathways that carry electrons flowing from the current collector to the active material, resulting in superior battery characteristics. The crystallite size (Lc) of the carbon black may also be 16 Å or larger, 18 Å or larger, or 20 Å or larger.

[0023] Furthermore, the crystallite size (Lc) of the carbon black is preferably 26 Å or less. A crystallite size (Lc) of 26 Å or less makes the particle shape of the carbon black more rounded, which reduces interparticle interactions and makes it easier to disperse more uniformly in the active material. This makes it easier to form conductive paths and obtain better battery characteristics. From the viewpoint of reducing internal resistance and improving discharge rate characteristics and cycle characteristics, the crystallite size (Lc) of the carbon black is preferably 24 Å or less, but it may also be 22 Å or less or 20 Å or less. In other words, the crystallite size (Lc) of carbon black may be, for example, 15-26 Å, 15-24 Å, 15-22 Å, 15-20 Å, 16-26 Å, 16-24 Å, 16-22 Å, 16-20 Å, 18-26 Å, 18-24 Å, 18-22 Å, 18-20 Å, 20-26 Å, 20-24 Å, or 20-22 Å.

[0024] The crystallite size (Lc) of carbon black is measured in accordance with JIS R7651. Note that the crystallite size (Lc) of carbon black refers to the crystallite size in the c-axis direction of the carbon black crystal layer.

[0025] The average primary particle size of the carbon black is preferably 15 nm or larger. A carbon black average primary particle size of 15 nm or larger reduces the interaction between the liquid medium and the conductive material, as well as the interaction between conductive materials themselves. This makes it easier to disperse the carbon black more uniformly in the active material, facilitates the formation of conductive pathways, and ultimately leads to better battery characteristics. The average primary particle size of the carbon black is preferably 16 nm or larger, more preferably 17 nm or larger, and may also be 18 nm or larger, 19 nm or larger, or 20 nm or larger.

[0026] Furthermore, the average primary particle diameter of the carbon black is preferably 30 nm or less. A carbon black average primary particle diameter of 30 nm or less increases the number of electrical contact points with the active material and conductive material, resulting in a better conductivity-imparting effect and thus making it easier to obtain superior battery characteristics. From the viewpoint of further reducing internal resistance and achieving superior discharge rate and cycle characteristics, the average primary particle diameter of the carbon black is preferably 28 nm or less, but may also be 26 nm or less, 24 nm or less, 22 nm or less, or 20 nm or less. In other words, the average primary particle size of carbon black is, for example, 15-30nm, 15-28nm, 15-26nm, 15-24nm, 15-22nm, 15-20nm, 16-30nm, 16-28nm, 16-26nm, 16-24nm, 16-22nm, 16-20nm, 17-30nm, 17-28nm, 17-26nm, 17-24nm, 17- 22nm, 17-20nm, 18-30nm, 18-28nm, 18-26nm, 18-24nm, 18-22nm, 18-20nm, 19-30nm, 19-28nm, 19-26nm, 19-24nm, 19-22nm, 19-20nm, 20-30nm, 20-28nm, 20-26nm, 20-24nm, or 20-22nm may also be used.

[0027] The average primary particle diameter of carbon black refers to the average value of the equivalent circle diameter measured from images of carbon black observed with a transmission electron microscope (TEM). Specifically, it is obtained by using a JEM-2000FX transmission electron microscope (manufactured by JEOL Ltd.), taking 10 images of carbon black at a magnification of 100,000x, and then measuring the equivalent circle diameter of 200 randomly selected primary particles of carbon black from the resulting images using image analysis, and then taking the arithmetic mean.

[0028] When the peak area of ​​the peak with mass number m / z 57 detected by the thermal desorption gas analysis method of carbon black is denoted as S1, and the peak area of ​​the peak with mass number m / z 128 is denoted as S2, the ratio of peak area S2 to peak area S1 (S2 / S1) is preferably between 0.2 and 1.9. The ratio (S2 / S1) indicates the proportion of organic components adsorbed on the surface of the carbon black. When the ratio (S2 / S1) is 1.9 or less, the amount of organic components adsorbed on the surface of the carbon black is sufficiently small, and the decrease in conductivity caused by the organic components trapping π electrons is significantly suppressed. Furthermore, when the ratio (S2 / S1) is 0.2 or more, the organic components adsorbed on the surface of the carbon black act as a dispersant, improving dispersibility in the liquid medium, and thus further reducing the slurry viscosity. The peak area S1 of the peak with mass number m / z 57 and the peak area S2 of the peak with mass number m / z 128 can be measured by generated gas mass spectrometry (EGA-MS). For example, carbon black is placed in a gas chromatograph-mass spectrometer equipped with a pyrolysis apparatus, held at 50°C for 5 minutes in a He flow at atmospheric pressure, then heated to 800°C at 80°C / min, and the peak area S1 of the peak with mass number m / z 57 and the peak area S2 of the peak with mass number m / z 128 can be measured by performing mass spectrometry on the components desorbed by the heating.

[0029] The ratio (S2 / S1) may be 1.5 or less, 1.0 or less, 0.8 or less, 0.6 or less, 0.5 or less, 0.4 or less, or 0.3 or less, from the viewpoint of reducing internal resistance and improving discharge rate characteristics and cycle characteristics. Alternatively, the ratio (S2 / S1) may be 0.25 or greater, or 0.3 or greater. That is, the ratio (S2 / S1) may be, for example, 0.2~1.9, 0.2~1.5, 0.2~1.0, 0.2~0.8, 0.2~0.6, 0.2~0.5, 0.2~0.4, 0.2~0.3, 0.25~1.9, 0.25~1.5, 0.25~1.0, 0.25~0.8, 0.25~0.6, 0.25~0.5, 0.25~0.4, 0.25~0.3, 0.3~1.9, 0.3~1.5, 0.3~1.0, 0.3~0.8, 0.3~0.6, 0.3~0.5, or 0.3~0.4.

[0030] The volume resistivity of carbon black may be 0.30 Ω·cm or less or 0.25 Ω·cm or less, from the viewpoint of excellent conductivity. The volume resistivity of carbon black is measured, for example, under compression under a load of 7.5 MPa.

[0031] The ash content and moisture content of the carbon black are not particularly limited. The ash content of the carbon black may be, for example, 0.04% by mass or less, and the moisture content of the carbon black may be, for example, 0.10% by mass or less.

[0032] The method for producing carbon black is not particularly limited. For example, carbon black may be produced by a manufacturing method that includes a synthesis step of treating a raw material gas containing hydrocarbons in a cylindrical decomposition furnace to obtain carbon black, and a purification step of removing magnetic foreign matter from the carbon black obtained in the synthesis step using a magnet.

[0033] In the synthesis process, the raw material gas is treated in a cylindrical cracking furnace. The cylindrical cracking furnace may, for example, include a pyrolysis section for carrying out the thermal decomposition reaction of hydrocarbons and a maturation section for modifying the pyrolysis reaction products. The cylindrical cracking furnace may further include a supply port for supplying the raw material gas to the pyrolysis section and a recovery port for recovering the carbon black produced from the maturation section.

[0034] In the pyrolysis section, it is preferable that the supplied raw material gas remains at a temperature of 1900°C or higher for 30 to 150 seconds. A residence time of 30 seconds or more ensures that the pyrolysis reaction is completed and that carbon aerosols are formed through the development of a chain structure. Furthermore, a residence time of 150 seconds or less suppresses the aggregation of carbon aerosols, making it easier to remove magnetic foreign matter in the high-purity process and thus easier to obtain high-purity carbon black.

[0035] In the maturation section, it is preferable that the pyrolysis reaction products supplied from the pyrolysis section remain at a temperature of 1700°C or higher for 20 to 90 seconds. A residence time of 20 seconds or more for the pyrolysis reaction products promotes the modification of carbon aerosols and the development of aggregates, making it easier to obtain higher quality carbon black. On the other hand, a residence time of 90 seconds or less for the pyrolysis reaction products suppresses the aggregation of carbon aerosols, making it easier to remove magnetic foreign matter in the high-purity process and making it easier to obtain high-purity carbon black.

[0036] The residence times in the pyrolysis section and the maturation section can be appropriately adjusted by controlling the linear velocity of the flowing gas. It is preferable that the residence time in the maturation section be shorter than that in the pyrolysis section. That is, it is preferable that the linear velocity of the gas in the maturation section be faster than that in the pyrolysis section.

[0037] In this embodiment, the raw material gas preferably contains acetylene as a carbon source. The carbon source (e.g., acetylene) content in the raw material gas is, for example, 10% by volume or more, preferably 20% by volume or more, more preferably 30% by volume or more, and may be 100% by volume. The content of each component in the raw material gas is expressed as a volume ratio based on the volume at 100°C and 1 atmosphere.

[0038] The raw material gas may further contain other hydrocarbons besides the carbon source (e.g., acetylene). Examples of other hydrocarbons include methane, ethane, propane, ethylene, propylene, butadiene, benzene, toluene, xylene, gasoline, kerosene, light oil, and heavy oil. By adding these other hydrocarbons, the reaction temperature can be changed to increase or decrease the specific surface area of ​​the carbon black. The other hydrocarbons are preferably selected from the group consisting of aromatic hydrocarbons such as benzene and toluene, and unsaturated hydrocarbons such as ethylene and propylene.

[0039] When the raw material gas contains acetylene and other hydrocarbons, the content of the other hydrocarbons is, for example, 0.1 to 99 parts by volume, preferably 0.2 to 50 parts by volume, and more preferably 0.3 to 30 parts by volume, per 100 parts by volume of acetylene. In other words, the content of other hydrocarbons may be, for example, 0.1 to 99 parts by volume, 0.1 to 50 parts by volume, 0.1 to 30 parts by volume, 0.2 to 99 parts by volume, 0.2 to 50 parts by volume, 0.2 to 30 parts by volume, 0.3 to 99 parts by volume, 0.3 to 50 parts by volume, or 0.3 to 30 parts by volume, relative to 100 parts by volume of acetylene.

[0040] The raw material gas may further contain water vapor, oxygen, hydrogen, carbon dioxide, etc. It is preferable to use high-purity gases with a purity of 99.9% or higher. Using such high-purity gases tends to facilitate the production of carbon black with fewer magnetic impurities and stable BET specific surface area and oil absorption.

[0041] The water vapor content may be, for example, 0 to 80 parts by volume, preferably 0.1 to 70 parts by volume, more preferably 1 to 60 parts by volume, and even more preferably 3 to 55 parts by volume, relative to 100 parts by volume of the carbon source (e.g., acetylene) in the raw material gas. When the water vapor content is within the above range, the BET specific surface area of ​​the carbon black tends to increase. In other words, the water vapor content may be, for example, 0 to 80 parts by volume, 0 to 70 parts by volume, 0 to 60 parts by volume, 0 to 55 parts by volume, 0.1 to 80 parts by volume, 0.1 to 70 parts by volume, 0.1 to 60 parts by volume, 0.1 to 55 parts by volume, 1 to 80 parts by volume, 1 to 70 parts by volume, 1 to 60 parts by volume, 1 to 55 parts by volume, 3 to 80 parts by volume, 3 to 70 parts by volume, 3 to 60 parts by volume, or 3 to 55 parts by volume, relative to 100 parts by volume of the carbon source (e.g., acetylene) in the raw material gas.

[0042] In the synthesis process, it is preferable to supply oxygen gas to the pyrolysis section along with the raw material gas, and it is even more preferable to supply oxygen gas to the pyrolysis section by injecting oxygen gas from around the supply port to which the raw material gas is supplied.

[0043] A cylindrical cracking furnace preferably has an oxygen gas injection port near the raw material gas supply port, and more preferably has a plurality of injection ports arranged at equal intervals surrounding the supply port. The number of injection ports is preferably 3 or more, more preferably 3 to 8.

[0044] Furthermore, the cylindrical decomposition furnace may be equipped with a nozzle having a multi-tube structure (e.g., a double-tube structure, a triple-tube structure, etc.) that has a raw material gas supply port and an injection port for injecting oxygen gas from around it. In the case of a double-tube structure, for example, the raw material gas may be injected from the gap on the inner cylinder side and the oxygen gas from the gap on the outer cylinder side. In the case of a triple-tube structure consisting of an inner tube, a middle tube, and an outer tube, for example, the oxygen gas may be injected from the gap formed by the outer wall of the middle tube and the inner wall of the outer tube, and the raw material gas may be injected from the remaining gap.

[0045] The amount of oxygen gas injected is not particularly limited, provided that the carbon black production yield is not considered. Carbon black can be produced even if more oxygen gas is injected than necessary. The amount of oxygen gas injected may be, for example, 0 to 300, 0 to 250, 0 to 220, or 0 to 200 parts per 100 parts per volume of carbon source (e.g., acetylene) in the raw material gas, preferably 0.1 to 190 parts, more preferably 0.5 to 180 parts, and even more preferably 1 to 160 parts. When the amount of oxygen gas injected increases, the BET specific surface area of ​​the carbon black and the above ratio (S1 / S2) tend to increase, and when the amount of oxygen gas injected decreases, the primary particle size of the carbon black tends to increase. In other words, the amount of oxygen gas injected is, for example, 0-300 parts by volume, 0-250 parts by volume, 0-220 parts by volume, 0-200 parts by volume, 0-190 parts by volume, 0-180 parts by volume, 0-160 parts by volume, 0.1-300 parts by volume, 0.1-250 parts by volume, 0.1-220 parts by volume, 0.1-200 parts by volume, 0.1-190 parts by volume, 0 The volume may be 1 to 180 parts, 0.1 to 160 parts, 0.5 to 300 parts, 0.5 to 250 parts, 0.5 to 220 parts, 0.5 to 200 parts, 0.5 to 190 parts, 0.5 to 180 parts, 0.5 to 160 parts, 1 to 300 parts, 1 to 250 parts, 1 to 220 parts, 1 to 200 parts, 1 to 190 parts, 1 to 180 parts, or 1 to 160 parts.

[0046] In the synthesis process, the primary particle size, BET specific surface area, and crystallite size (Lc) of the resulting carbon black can be adjusted, for example, by adjusting the addition rate of hydrocarbons other than acetylene, the amount of oxygen gas injected, etc.

[0047] The high-purity process is a process of removing magnetic foreign matter from the carbon black obtained in the synthesis process using a magnet. The high-purity process may be a process of removing magnetic foreign matter from the carbon black obtained in the synthesis process by bringing it into contact with a magnet or by placing it near a magnet (for example, by passing it near a magnet).

[0048] The maximum surface magnetic flux density of the magnet is not particularly limited, but may be, for example, 700 mT or more, preferably 1000 mT or more, and more preferably 1200 mT or more. This allows fine magnetic foreign matter attached to the carbon black to be more strongly attracted, making it easier to obtain carbon black with a lower nickel content. The upper limit of the maximum surface magnetic flux density of the magnet is not particularly limited, and may be, for example, 1400 mT or less. In other words, the maximum surface magnetic flux density of the magnet may be, for example, 700-1400 mT, 1000-1400 mT, or 1200-1400 mT.

[0049] The high-purity process may involve removing magnetic impurities from the carbon black so that the nickel content is 50 ppb or less (preferably 40 ppb or less, more preferably 30 ppb or less, and even more preferably 20 ppb or less). There is no particular lower limit to the nickel content, but the nickel content in the carbon black may be, for example, 1 ppb or more, and from the viewpoint of cost and productivity, it may be 10 ppb or more, or even 15 ppb or more. In other words, the nickel content in the carbon black after the high-purity process may be, for example, 1-50 ppb, 1-40 ppb, 1-30 ppb, 1-20 ppb, 10-50 ppb, 10-40 ppb, 10-30 ppb, 10-20 ppb, 15-50 ppb, 15-40 ppb, 15-30 ppb, or 15-20 ppb.

[0050] The carbon black content (C1) may be, for example, 0.01% by mass or more, 0.05% by mass or more, 0.1% by mass or more, 0.2% by mass or more, 0.3% by mass or more, 0.4% by mass or more, or 0.5% by mass or more, based on the total mass of solids in the positive electrode composition. The carbon black content (C1) may be, for example, 10% by mass or less, 7% by mass or less, 5% by mass or less, 4% by mass or less, 3% by mass or less, or 2% by mass or less, based on the total mass of solids in the positive electrode composition. In other words, the carbon black content (C1) is based on the total mass of solids in the positive electrode composition, for example, 0.01-10% by mass, 0.01-7% by mass, 0.01-5% by mass, 0.01-4% by mass, 0.01-3% by mass, 0.01-2% by mass, 0.05-10% by mass, 0.05-7% by mass, 0.05-5% by mass, 0.05-4% by mass, 0.05-3% by mass, 0.05-2% by mass, 0.1-10% by mass, 0.1-7% by mass, 0.1-5% by mass, 0.1-4% by mass, 0.1-3% by mass, 0.1-2% by mass, 0. 2-10 mass%, 0.2-7 mass%, 0.2-5 mass%, 0.2-4 mass%, 0.2-3 mass%, 0.2-2 mass%, 0.3-10 mass%, 0.3-7 mass%, 0.3-5 mass%, 0.3-4 mass%, 0.3-3 mass%, 0.3-2 mass%, 0.4-1 It may be 0% by mass, 0.4-7% by mass, 0.4-5% by mass, 0.4-4% by mass, 0.4-3% by mass, 0.4-2% by mass, 0.5-10% by mass, 0.5-7% by mass, 0.5-5% by mass, 0.5-4% by mass, 0.5-3% by mass or 0.5-2% by mass.

[0051] Carbon nanotubes have an average diameter of 5-15 nm, and the ratio of the average diameter to the BET specific surface area (average diameter / BET specific surface area) is 0.01-0.068 nm / (m²). 2 Carbon nanotubes with a specific surface area of ​​0.01-0.068 nm / (m²) are preferred. The average diameter of the carbon nanotubes is small, between 5 and 15 nm, and the ratio of the average diameter to the specific surface area of ​​0.01 to 0.068 nm / (m²) is also preferred. 2 If ( / g), more conductive paths can be formed in the positive electrode.

[0052] The average diameter of the carbon nanotubes is preferably 5 nm or larger. An average diameter of 5 nm or larger reduces the interaction between the liquid medium and the conductive material, as well as the interaction between the conductive materials themselves, making them more uniformly dispersed in the active material. This facilitates the formation of conductive pathways, resulting in superior battery characteristics. The average diameter of the carbon nanotubes may also be 6 nm or larger.

[0053] Furthermore, the average diameter of the carbon nanotubes is preferably 15 nm or less. An average diameter of 15 nm or less increases the number of electrical contact points between the active material and the conductive material, resulting in a better conductivity and easier acquisition of superior battery characteristics. From the viewpoint of further reducing internal resistance and achieving superior discharge rate and cycle characteristics, the average diameter of the carbon nanotubes is preferably 12 nm or less, more preferably 10 nm or less, and may also be 9 nm or less, 8 nm or less, or 7 nm or less. In other words, the average diameter of the carbon nanotubes may be 5-15 nm, 5-12 nm, 5-10 nm, 5-9 nm, 5-8 nm, 5-7 nm, 6-15 nm, 6-12 nm, 6-10 nm, 6-9 nm, 6-8 nm, or 6-7 nm.

[0054] The average diameter of a carbon nanotube refers to the average diameter measured based on images of carbon nanotubes observed with a transmission electron microscope (TEM). Specifically, it is obtained by using a JEM-2000FX transmission electron microscope (manufactured by JEOL Ltd.), taking 10 images of carbon nanotubes at a magnification of 200,000x, and then measuring the diameters of 100 randomly selected carbon nanotubes from the resulting images using image analysis, and then taking the arithmetic mean.

[0055] The BET specific surface area of ​​carbon nanotubes is 170-320 m². 2 It is preferable that the BET specific surface area of ​​the carbon nanotube is 170 m². 2 Having a BET specific surface area of ​​320 m² or more increases the number of electrical contact points with the active material and conductive material, resulting in a better conductivity-imparting effect and making it easier to obtain superior battery characteristics. 2 Having a BET specific surface area of ​​less than / g allows for more uniform dispersion of carbon nanotubes, facilitates the formation of conductive pathways, and makes it easier to obtain better battery characteristics. The BET specific surface area of ​​carbon nanotubes can be measured using the static capacity method in accordance with JIS Z8830, with nitrogen used as the adsorbate.

[0056] From the perspective of reducing internal resistance and achieving superior discharge rate and cycle characteristics, the BET specific surface area of ​​carbon nanotubes is 180m. 2 / g or more, 200m 2 / g or more, 230m 2 / g or more, 250m 2 / g or more, 280m 2 / g or more, or 300m 2 It may be 300 m² or more. From the viewpoint of reducing internal resistance and improving discharge rate characteristics and cycle characteristics, the BET specific surface area of ​​carbon nanotubes should be 300 m². 2 It may be less than or equal to / g. In other words, the BET specific surface area of ​​carbon nanotubes is, for example, 170-320 m². 2 / g, 170-300m 2 / g, 180~320m 2 / g, 180-300m 2 / g, 200-320m 2 / g, 200-300m 2 / g, 230~320m 2 / g, 230-300m 2 / g, 250~320m 2 / g, 250~300m 2 / g, 280~320m 2 / g, 280-300m 2 / g or 300-320m 2 / g is also acceptable.

[0057] The ratio of the average diameter to the BET specific surface area of ​​carbon nanotubes (average diameter / BET specific surface area) is 0.01 to 0.068 nm / (m²). 2 It is preferable that the ratio (average diameter / BET specific surface area) is 0.01 nm / (m²). The above ratio (average diameter / BET specific surface area) is the value obtained by dividing the average diameter of the carbon nanotube by the BET specific surface area of ​​the carbon nanotube. 2By being as described above, the entanglement between carbon nanotubes is reduced, and it becomes easier to disperse uniformly in the active material. As a result, it becomes easier to form a conductive path, and more excellent battery characteristics can be obtained. The ratio (average diameter / BET specific surface area) is 0.068 nm / (m 2 / g) or less, the number of carbon nanotubes per unit weight increases, and since electricity can flow more efficiently through the entire active material, more excellent battery characteristics can be obtained.

[0058] The ratio (average diameter / BET specific surface area) may be 0.06 nm / (m 2 / g) or less, 0.04 nm / (m 2 / g) or less, 0.03 nm / (m 2 [[ID= twelfth]] / g) or less, or 0.02 nm / (m 2 / g) or less from the viewpoint of making the internal resistance smaller and from the viewpoint of more excellent discharge rate characteristics and cycle characteristics. The ratio (average diameter / BET specific surface area) may be 0.02 nm / (m 2 / g) or more 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 ratio (average diameter / BET specific surface area) is, for example, 0.01 to 0.068 nm / (m 2 / g), 0.01 to 0.06 nm / (m 2 / g), 0.01 to 0.04 nm / (m 2 / g), 0.01 to 0.03 nm / (m 2 / g), 0.01 to 0.02 nm / (m 2 / g), 0.02 to 0.068 nm / (m 2 / g), 0.02 to 0.06 nm / (m 2 / g), 0.02 to 0.04 nm / (m 2 / g) or 0.02 to 0.03 nm / (m 2 / g).

[0059] The manufacturing method of the carbon nanotubes is not particularly limited. The carbon nanotubes may be, for example, those manufactured by a conventionally known manufacturing method of carbon nanotubes.

[0060] Carbon nanotubes can be produced, for example, by placing a powdered catalyst consisting of iron supported on magnesia (magnesium oxide) across the entire horizontal cross-section of a vertical reactor, flowing methane vertically through the reactor, contacting the methane with the catalyst at 500-1200°C, and then oxidizing the resulting product (unoxidized carbon nanotubes). By this method of producing carbon nanotubes, it is possible to obtain nanotubes consisting of several layers of graphene, with an average diameter of 5-15 nm and a BET specific surface area of ​​160-300 nm. 2 Carbon nanotubes are easily obtained in quantities of / g.

[0061] The oxidation treatment of the above product may be, for example, a calcination treatment. The temperature of the calcination treatment is not particularly limited and may be, for example, 300 to 1000°C. Since the temperature of the calcination treatment is affected by the atmospheric gas, it is preferable to perform the calcination 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 a calcination treatment of the product, one method is to calcine under air within a range of ±50°C from the combustion peak temperature of the carbon nanotubes before oxidation treatment. However, if the oxygen concentration is higher than that of the atmosphere, calcination should be performed in a temperature range lower than the calcination peak temperature, and if the oxygen concentration is lower than that of the atmosphere, a temperature range higher than the calcination peak temperature should be selected. In particular, when calcining carbon nanotubes before oxidation treatment under air, it is preferable to perform the calcination treatment within a range of ±15°C from the combustion peak temperature of the carbon nanotubes before oxidation treatment.

[0062] The oxidation treatment of the above product may be carried out with hydrogen peroxide, mixed acid, nitric acid, etc. For example, a method of treating the above product with hydrogen peroxide involves mixing the above product in 34.5% hydrogen peroxide solution to a concentration of 0.01 to 10% by mass, and reacting it at a temperature of 0 to 100°C for 0.5 to 48 hours. Alternatively, a method of treating the above product with mixed acid involves mixing the above product in a mixed solution of concentrated sulfuric acid and concentrated nitric acid (concentrated sulfuric acid:concentrated nitric acid = 3:1) to a concentration of 0.01 to 10% by mass, and reacting it at a temperature of 0 to 100°C for 0.5 to 48 hours. 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 depending on the amount of single-walled carbon nanotubes in the above product. One method for treating the above product with nitric acid is to mix the above product with nitric acid at a concentration of 40-80% by mass so that it is present in a concentration of 0.01-10% by mass, and to react it at a temperature of 60-150°C for 0.5-48 hours.

[0063] By performing an oxidation treatment on the above product, impurities such as amorphous carbon and single-walled carbon nanotubes with low heat resistance can be selectively removed, improving the purity of several graphene layers, especially 2 to 5 layers of carbon nanotubes. At the same time, the oxidation treatment of the product adds functional groups to the surface of the carbon nanotubes, improving their affinity with the dispersion medium and additives, and thus improving their dispersibility. Among the above oxidation treatments, treatment using nitric acid is preferred.

[0064] The above oxidation treatment may be performed immediately after obtaining the carbon nanotubes before oxidation, or after another purification treatment. For example, when using iron / magnesia as a catalyst, the oxidation treatment may be performed after purification with an acid such as hydrochloric acid to remove the catalyst, or the oxidation treatment may be performed after purification to remove the catalyst.

[0065] The carbon nanotube content (C2) may be, for example, 0.01% by mass or more, based on the total mass of solids in the positive electrode composition. From the viewpoint of lowering the internal resistance of the battery and improving the discharge rate characteristics and cycle characteristics, it may be 0.03% by mass or more, 0.05% by mass or more, 0.07% by mass or more, 0.1% by mass or more, or 0.2% by mass or more. Furthermore, the carbon nanotube content (C2) may be, for example, 5% by mass or less, based on the total mass of solids in the positive electrode composition, and may be 3% by mass or less, 2% by mass or less, 1% by mass or less, 0.9% by mass or less, 0.8% by mass or less, or 0.7% by mass or less. In other words, the carbon nanotube content (C2) is based on the total mass of solids in the cathode composition, for example, 0.01-5% by mass, 0.01-3% by mass, 0.01-2% by mass, 0.01-1% by mass, 0.01-0.9% by mass, 0.01-0.8% by mass, 0.01-0.7% by mass, 0.03-5% by mass, 0.03-3% by mass, 0.03-2% by mass, 0.03-1% by mass, 0.03-0.9% by mass, 0.03-0.8% by mass, 0.03-0.7% by mass, 0.05-5% by mass, 0.05-3% by mass, 0.05-2% by mass, 0.05-1% by mass, and 0.05-0.9% by mass. Mass%, 0.05-0.8 mass%, 0.05-0.7 mass%, 0.07-5 mass%, 0.07-3 mass%, 0.07-2 mass%, 0.07-1 mass%, 0.07-0.9 mass%, 0.07-0.8 mass%, 0.07-0.7 mass%, 0.1-5 mass%, 0.1-3 mass%, 0.1 ~2% by mass, 0.1-1% by mass, 0.1-0.9% by mass, 0.1-0.8% by mass, 0.1-0.7% by mass, 0.2-5% by mass, 0.2-3% by mass, 0.2-2% by mass, 0.2-1% by mass, 0.2-0.9% by mass, 0.2-0.8% by mass or 0.2-0.7% by mass.

[0066] The total content of carbon black and carbon nanotubes (C1+C2) may be, for example, 0.5% by mass or more, based on the total mass of solids in the positive electrode composition. From the viewpoint of lowering the internal resistance of the battery and improving the discharge rate characteristics and cycle characteristics, it may be 0.75% by mass or more, 1.0% by mass or more, or 2.0% by mass or more. Furthermore, the total content of carbon black and carbon nanotubes (C1+C2) may be, for example, 5.0% by mass or less, based on the total mass of solids in the positive electrode composition. From the viewpoint of improving the dispersibility of conductive materials in the positive electrode composition, it may be 4.5% by mass or less, 3.5% by mass or less, or 3.0% by mass or less. In other words, the total content of carbon black and carbon nanotubes (C1+C2) may be, for example, 0.5-5.0% by mass, 0.5-4.5% by mass, 0.5-3.5% by mass, 0.5-3.0% by mass, 0.75-5.0% by mass, 0.75-4.5% by mass, 0.75-3.5% by mass, 0.75-3.0% by mass, 1.0-5.0% by mass, 1.0-4.5% by mass, 1.0-3.5% by mass, 1.0-3.0% by mass, 2.0-5.0% by mass, 2.0-4.5% by mass, 2.0-3.5% by mass, or 2.0-3.0% by mass, based on the total mass of solids in the positive electrode composition.

[0067] The ratio of the carbon nanotube content (C2) to the total carbon black and carbon nanotube content (C1+C2) (C2 / (C1+C2)) may be, for example, 0.06 or higher, and may be 0.07 or higher, 0.1 or higher, or 0.3 or higher from the viewpoint of lowering the internal resistance of the battery and improving the discharge rate characteristics and cycle characteristics. Note that when the above ratio (C2 / (C1+C2)) is large, the above ratio (V2 / V1) tends to be small. From the viewpoint of making it easier to obtain a positive electrode composition with a ratio (V2 / V1) of 0.2 or less, it is preferable that the above ratio (C2 / (C1+C2)) is within the above range.

[0068] Furthermore, the ratio of the carbon nanotube content (C2) to the total carbon black and carbon nanotube content (C1+C2) (C2 / (C1+C2)) may be, for example, 0.87 or less, and from the viewpoint of improving the dispersibility of the conductive material in the positive electrode composition, it may be 0.85 or less, 0.82 or less, 0.8 or less, or 0.7 or less. Note that when the above ratio (C2 / (C1+C2)) is small, the above ratio (V2 / V1) tends to be large. From the viewpoint of easily obtaining a positive electrode composition with a above ratio (V2 / V1) of 0.02 or more, it is preferable that the above ratio (C2 / (C1+C2)) is within the above range. In other words, the ratio of the carbon nanotube content (C2) to the total carbon black and carbon nanotube content (C1+C2) (C2 / (C1+C2)) may be, for example, 0.06~0.87, 0.06~0.85, 0.06~0.82, 0.06~0.8, 0.06~0.7, 0.07~0.87, 0.07~0.85, 0.07~0.82, 0.07~0.8, 0.07~0.7, 0.1~0.87, 0.1~0.85, 0.1~0.82, 0.1~0.8, 0.1~0.7, 0.3~0.87, 0.3~0.85, 0.3~0.82, 0.3~0.8, or 0.3~0.7.

[0069] The active material can be any substance capable of reversibly intercalating and deintercalating cations. The active material can also be called the positive electrode active material. The active material has, for example, a volume resistivity of 1 × 10⁻⁶. 4 This may be a lithium-containing composite oxide or lithium-containing polyanionic compound containing manganese of Ω·cm or more. Examples of manganese-containing lithium-containing composite oxides include LiMnO2, LiMnO3, LiMn2O3, Li 1+x Mn 2-x Lithium manganese oxide such as O4 (where x = 0 to 0.33); LiMn x Ni y Co z O2 (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-xy > 0), LiMn 2-x Mx Examples of composite oxides containing one or more transition metal elements include O2 (where x = 0.01 to 0.1) and Li2Mn3MO8. Examples of lithium-containing polyanionic compounds include LiFePO4, LiMnPO4, and Li2MPO4F (where M is at least one metal selected from Co, Ni, Fe, Cr, and Zn). In each compositional formula, M is at least one selected from the group consisting of Fe, Co, Ni, Al, Cu, Mg, Cr, Zn, and Ta.

[0070] Average particle size of the active material (D 50 The average particle size of the active material (D) may be 20 μm or less or 10 μm or less, from the viewpoint of obtaining a battery with sufficiently excellent bonding properties between the conductive material and the binder and which has superior cycle characteristics. 50 The average particle size (D) of the active material may be 100 nm or larger. 50 ) can be measured by laser light scattering.

[0071] The active material content may be, for example, 80% by mass or more, based on the total mass of solids in the positive electrode composition, and preferably 85% by mass or more, but may also be 87% by mass or more, 90% by mass or more, 92% by mass or more, or 95% by mass, based on the total mass of solids in the positive electrode composition. In other words, the content of the active material may be, for example, 80-99.9% by mass, 80-99.5% by mass, 80-99% by mass, 80-98% by mass, 85-99.9% by mass, 85-99.5% by mass, 85-99% by mass, 85-98% by mass, 87-99.9% by mass, 87-99.5% by mass, 87-99% by mass, 87-98% by mass, 90-99.9% by mass, 90-99.5% by mass, 90-99% by mass, 90-98% by mass, 92-99.9% by mass, 92-99.5% by mass, 92-99% by mass, 92-98% by mass, 95-99.9% by mass, 95-99.5% by mass, 95-99% by mass, or 95-98% by mass, based on the total mass of solids in the positive electrode composition.

[0072] Examples of binders include polyvinylidene fluoride, polytetrafluoroethylene, styrene-butadiene copolymer, and (meth)acrylic acid ester copolymer. The polymer structure of the binder may be, for example, random copolymer, alternating copolymer, graft copolymer, block copolymer, etc. From the viewpoint of excellent dielectric strength, polyvinylidene fluoride is preferred as the binder.

[0073] The binder content may be, for example, 0.3% by mass or more based on the total mass of solids in the positive electrode composition, and may be 0.5% by mass or more, 1.0% by mass or more, or 1.5% by mass or more from the viewpoint of further improving the bonding properties of the positive electrode plate and improving the cycle characteristics. The binder content may be, for example, 5.0% by mass or less based on the total mass of solids in the positive electrode composition, and may be 4.5% by mass or less, 4.0% by mass or less, or 3.5% by mass or less from the viewpoint of further reducing the resistance of the positive electrode plate and further improving the discharge rate characteristics. In other words, the binder content may be, for example, 0.3-5.0% by mass, 0.3-4.5% by mass, 0.3-4.0% by mass, 0.3-3.5% by mass, 0.5-5.0% by mass, 0.5-4.5% by mass, 0.5-4.0% by mass, 0.5-3.5% by mass, 1.0-5.0% by mass, 1.0-4.5% by mass, 1.0-4.0% by mass, 1.0-3.5% by mass, 1.5-5.0% by mass, 1.5-4.5% by mass, 1.5-4.0% by mass, or 1.5-3.5% by mass, based on the total mass of solids in the positive electrode composition.

[0074] Examples of liquid media include water, N-methyl-2-pyrrolidone (hereinafter also referred to as "NMP"), cyclohexane, methyl ethyl ketone, and methyl isobutyl ketone. Of these, N-methyl-2-pyrrolidone is preferred from the viewpoint of dispersibility.

[0075] The content of the liquid medium is not particularly limited and may be changed as appropriate so that the solid content concentration of the positive electrode composition is within a desired range.

[0076] The solid content concentration of the positive electrode composition is, for example, 63% by mass or more. From the viewpoint of shortening the drying time of the liquid medium when manufacturing the positive electrode, and from the viewpoint of 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. Note that when the solid content concentration of the positive electrode composition is high, the above ratio (V2 / V1) tends to decrease. From the viewpoint of easily obtaining a positive electrode composition with the above ratio (V2 / V1) of 0.2 or less, it is preferable that the solid content concentration of the positive electrode composition be within the above range.

[0077] Furthermore, the solid content concentration of the positive electrode composition is, for example, 82% by mass or less. From the viewpoint of being able to make the coating film smooth when manufacturing the positive electrode, and from the viewpoint of being able to reduce variations in the internal resistance of the battery, it may be 80% by mass or less, 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. Note that when the solid content concentration of the positive electrode composition is low, the above ratio (V2 / V1) tends to increase. From the viewpoint of easily obtaining a positive electrode composition with the above ratio (V2 / V1) of 0.02 or more, it is preferable that the solid content concentration of the positive electrode composition is within the above range. That is, the solid content concentration of the positive electrode composition is, for example, 63-82% by mass, 63-80% by mass, 63-78% by mass, 63-76% by mass, 63-74% by mass, 63-7% by mass. 2% by mass, 63-70% by mass, 65-82% by mass, 65-80% by mass, 65-78% by mass, 65-76% by mass, 65-74% by mass, 65-72% by mass, 65 ~70% by mass, 66-82% by mass, 66-80% by mass, 66-78% by mass, 66-76% by mass, 66-74% by mass, 66-72% by mass, 66-70% by mass, It may be 67-82% by mass, 67-80% by mass, 67-78% by mass, 67-76% by mass, 67-74% by mass, 67-72% by mass, or 67-70% by mass.

[0078] The viscosity V1 of the positive electrode composition at a shear rate of 0.01 (1 / sec) at 25°C is, for example, 900 Pa·s or less. From the viewpoint of ensuring a smooth coating film without irregularities when manufacturing the positive electrode, and reducing entanglement between conductive materials, thus minimizing variations in the internal resistance of the battery, it may be 800 Pa·s or less, 600 Pa·s or less, or 500 Pa·s or less. Alternatively, the viscosity V1 of the positive electrode composition at a shear rate of 0.01 (1 / sec) at 25°C is, for example, 50 Pa·s or more. From the viewpoint of ensuring a smooth coating film without dripping when manufacturing the positive electrode, and suppressing migration of conductive materials when drying the liquid medium, it may be 100 Pa·s or more, 150 Pa·s or more, or 300 Pa·s or more. That is, the viscosity V1 of the positive electrode composition at a shear rate of 0.01 (1 / sec) at 25°C may be, for example, 50-900 Pa·s, 50-800 Pa·s, 50-600 Pa·s, 50-500 Pa·s, 100-900 Pa·s, 100-800 Pa·s, 100-600 Pa·s, 100-500 Pa·s, 150-900 Pa·s, 150-800 Pa·s, 150-600 Pa·s, 150-500 Pa·s, 300-900 Pa·s, 300-800 Pa·s, 300-600 Pa·s, or 300-500 Pa·s.

[0079] The viscosity V2 of the positive electrode composition at a shear rate of 1 (1 / sec) at 25°C is, for example, 30 Pa·s or less, and may be 20 Pa·s or less, 15 Pa·s or less, or 10 Pa·s or less, from the viewpoint of being able to produce a smooth coating film without irregularities when manufacturing the positive electrode, and from the viewpoint of being able to improve the dispersibility of the conductive material. Alternatively, the viscosity V2 of the positive electrode composition at a shear rate of 1 (1 / sec) at 25°C is, for example, 0.5 Pa·s or more, and may be 1 Pa·s or more, 3 Pa·s or more, or 5 Pa·s or more, from the viewpoint of being able to produce a smooth coating film without dripping when manufacturing the positive electrode, and from the viewpoint of being able to suppress the migration of the conductive material when drying the liquid medium. That is, the viscosity V2 of the positive electrode composition at a shear rate of 1 (1 / sec) at 25°C may be, for example, 0.5-30 Pa·s, 0.5-20 Pa·s, 0.5-15 Pa·s, 0.5-10 Pa·s, 1-30 Pa·s, 1-20 Pa·s, 1-15 Pa·s, 1-10 Pa·s, 3-30 Pa·s, 3-20 Pa·s, 3-15 Pa·s, 3-10 Pa·s, 5-30 Pa·s, 5-20 Pa·s, 5-15 Pa·s, or 5-10 Pa·s.

[0080] (Method for manufacturing the positive electrode composition) The method for manufacturing the positive electrode composition of this embodiment is not particularly limited, but from the viewpoint of easily obtaining a positive electrode composition in which the above ratio (V2 / V1) is within a suitable range, the following manufacturing method is preferred.

[0081] The method for producing the positive electrode composition of this embodiment involves mixing a first agent containing a binder and a first liquid medium, a second agent containing carbon black and a second liquid medium, a third agent containing carbon nanotubes and a third liquid medium, and an active material in a predetermined order to obtain the positive electrode composition.

[0082] According to the method for producing the positive electrode composition of this embodiment, the above ratio (V2 / V1) tends to fall within a suitable range compared to the case where carbon black, carbon nanotubes, binder, and active material are mixed simultaneously, making it easier to obtain a positive electrode composition that can achieve excellent discharge rate characteristics and cycle characteristics.

[0083] The method for manufacturing the positive electrode composition of this embodiment may be, for example, the first embodiment or the second embodiment described below.

[0084] In a first embodiment, a method for producing a positive electrode composition includes a first step of mixing a first agent containing a binder and a first liquid medium, a second agent containing carbon black and a second liquid medium, and a third agent containing carbon nanotubes and a third liquid medium to obtain a mixture, and a second step of mixing the mixture with an active material to obtain a positive electrode composition.

[0085] According to the first embodiment, compared to the case where carbon black, carbon nanotubes, binder, and active material are mixed simultaneously, the above ratio (V2 / V1) tends to fall within a suitable range, making it easier to obtain a cathode composition capable of achieving excellent discharge rate characteristics and cycle characteristics. One reason why the above effect is achieved by the manufacturing method of the first embodiment is that in the first step, the interaction between the binder and carbon black creates a dispersion state that is less prone to aggregation and less prone to entanglement with carbon nanotubes, thereby suppressing non-uniformity caused by the aggregation of carbon black or entanglement between carbon black and carbon nanotubes.

[0086] The first step of the first embodiment is to obtain a mixture by mixing a first agent containing a binder and a first liquid medium, a second agent containing carbon black and a second liquid medium, and a third agent containing carbon nanotubes and a third liquid medium.

[0087] In the first step of the first embodiment, the method of mixing the first agent, the second agent, and the third agent is not particularly limited and may be carried out by known methods (for example, stirring and mixing using a ball mill, sand mill, twin-screw kneader, orbital agitator, planetary mixer, disper mixer, etc.). The first step of the first embodiment may be, for example, a step of putting the first agent, the second agent, and the third agent into a mixing container and stirring to obtain a mixed liquid.

[0088] The second step of the first embodiment is to mix the mixture obtained in the first step with the active material to obtain a positive electrode composition.

[0089] In the second step of the first embodiment, the method for mixing the mixed liquid and the active material is not particularly limited and may be carried out by known methods (for example, stirring and mixing using a ball mill, sand mill, twin-screw kneader, orbital agitator, planetary mixer, disper mixer, etc.). The second step of the first embodiment may be, for example, a step of adding the active material to a mixing container containing the mixed liquid and then stirring to obtain a positive electrode composition.

[0090] In a second embodiment, a method for producing a positive electrode composition includes: a first step of mixing a first agent containing a binder and a first liquid medium with a second agent containing carbon black and a second liquid medium to obtain a first mixture; a second step of mixing the first mixture with a third agent containing carbon nanotubes and a third liquid medium to obtain a second mixture; and a third step of mixing the second mixture with an active material to obtain a positive electrode composition.

[0091] According to the second embodiment, compared to the case where carbon black, carbon nanotubes, binder, and active material are mixed simultaneously, the above ratio (V2 / V1) tends to fall within a suitable range, making it easier to obtain a cathode composition capable of achieving excellent discharge rate characteristics and cycle characteristics. The reason why the above effect is achieved by the manufacturing method of the first embodiment is that, in the first step, the interaction between the binder and carbon black creates a dispersion state that is less prone to aggregation and less prone to entanglement with carbon nanotubes, thereby suppressing non-uniformity of the electrode structure caused by the aggregation of carbon black or entanglement between carbon black and carbon nanotubes.

[0092] The first step of the second embodiment is to mix a first agent containing a binder and a first liquid medium with a second agent containing carbon black and a second liquid medium to obtain a first mixture.

[0093] In the first step of the second embodiment, the method of mixing the first agent and the second agent is not particularly limited and may be carried out by known methods (for example, stirring and mixing using a ball mill, sand mill, twin-screw kneader, orbital agitator, planetary mixer, disper mixer, etc.). The first step of the second embodiment may be, for example, a step of putting the first agent and the second agent into a mixing container and stirring to obtain the first mixture.

[0094] The second step of the second embodiment is to mix the first mixture obtained in the first step with a third agent containing carbon nanotubes and a third liquid medium to obtain a second mixture.

[0095] In the second step of the second embodiment, the method of mixing the first mixture and the third agent is not particularly limited and may be carried out by known methods (for example, stirring and mixing using a ball mill, sand mill, twin-screw kneader, orbital agitator, planetary mixer, disper mixer, etc.). The second step of the second embodiment may be, for example, a step of adding the third agent to a mixing container containing the first mixture, and then stirring to obtain the second mixture.

[0096] The third step of the second embodiment is to mix the second mixture obtained in the second step with the active material to obtain a positive electrode composition.

[0097] In the third step of the second embodiment, the method for mixing the second mixture and the active material is not particularly limited and may be carried out by known methods (for example, stirring and mixing using a ball mill, sand mill, twin-screw kneader, orbital agitator, planetary mixer, disper mixer, etc.). The third step of the second embodiment may be, for example, a step of adding the active material to a mixing container containing the second mixture and then stirring to obtain the positive electrode composition.

[0098] The first, second, and third agents used in the manufacturing method of the positive electrode composition of this embodiment will be described in detail below.

[0099] The first agent comprises a binder and a first liquid medium.

[0100] The first liquid medium is not particularly limited as long as it can dissolve the binder and is compatible with the second and third liquid mediums. Examples of the first liquid medium include water, N-methyl-2-pyrrolidone, cyclohexane, methyl ethyl ketone, and methyl isobutyl ketone, among which N-methyl-2-pyrrolidone is preferred from the viewpoint of solubility.

[0101] The content of the first liquid medium in the first agent is not particularly limited, as long as it is within a range that can dissolve the binder, and may be appropriately changed so that the solid content concentration of the positive electrode composition is within a desired range.

[0102] The solid content concentration of the first component is not particularly limited and may be, for example, 1.0% by mass or more, 2.0% by mass or more, 3.0% by mass or more, or 4.0% by mass or more. Furthermore, the solid content concentration of the first component may be, for example, 11.0% by mass or less, 10.0% by mass or less, or 9.0% by mass or less. In other words, the solid content concentration of the first agent may be, for example, 1.0-11.0% by mass, 1.0-10.0% by mass, 1.0-9.0% by mass, 2.0-11.0% by mass, 2.0-10.0% by mass, 2.0-9.0% by mass, 3.0-11.0% by mass, 3.0-10.0% by mass, 3.0-9.0% by mass, 4.0-11.0% by mass, 4.0-10.0% by mass, or 4.0-9.0% by mass.

[0103] The first agent may further contain components other than the binder and the first liquid medium. For example, the first agent may further contain polyvinylpyrrolidone, polyvinylimidazole, polyethylene glycol, polyvinyl alcohol, polyvinyl butyral, carboxymethylcellulose, acetylcellulose, or carboxylic acid-modified (meth)acrylic acid ester copolymer.

[0104] The second agent comprises carbon black and a second liquid medium.

[0105] The carbon black content in the second agent is not particularly limited and may be changed as appropriate so that the carbon black content in the cathode composition is within a desired range.

[0106] The second liquid medium is not particularly limited as long as it can disperse carbon black and is compatible with the first and third liquid mediums. Examples of the second liquid medium include water, N-methyl-2-pyrrolidone, cyclohexane, methyl ethyl ketone, and methyl isobutyl ketone. Of these, N-methyl-2-pyrrolidone is preferred from the viewpoint of easy dispersibility of carbon black. The second liquid medium may be the same as or different from the first and third liquid mediums, but it is preferable that they be the same.

[0107] The content of the second liquid medium in the second agent is not particularly limited, as long as it is within a range that allows for the dispersion of carbon black, and may be appropriately changed so that the solid content concentration of the positive electrode composition is within a desired range.

[0108] The solid content concentration of the second agent is not particularly limited and may be, for example, 1.5% by mass or more, 2.5% by mass or more, 3.5% by mass or more, or 5.0% by mass or more. Furthermore, the solid content concentration of the second agent may be, for example, 25.0% by mass or less, 22.0% by mass or less, 20.0% by mass or less, or 18.0% by mass or less. In other words, the solid content concentration of the second agent may be, for example, 1.5-25.0% by mass, 1.5-22.0% by mass, 1.5-20.0% by mass, 1.5-18.0% by mass, 2.5-25.0% by mass, 2.5-22.0% by mass, 2.5-20.0% by mass, 2.5-18.0% by mass, 3.5-25.0% by mass, 3.5-22.0% by mass, 3.5-20.0% by mass, 3.5-18.0% by mass, 5.0-25.0% by mass, 5.0-22.0% by mass, 5.0-20.0% by mass, or 5.0-18.0% by mass.

[0109] The second agent may further contain components other than carbon black and the second liquid medium. For example, the second agent may further contain polyvinylpyrrolidone, polyvinylimidazole, polyethylene glycol, polyvinyl alcohol, polyvinyl butyral, carboxymethylcellulose, acetylcellulose, or carboxylic acid-modified (meth)acrylic acid ester copolymer.

[0110] The third agent comprises carbon nanotubes and a third liquid medium.

[0111] The carbon nanotube content in the third agent is not particularly limited and may be changed as appropriate so that the carbon nanotube content in the cathode composition is within a desired range.

[0112] The third liquid medium is not particularly limited as long as it can disperse carbon nanotubes and is compatible with the first and second liquid mediums. Examples of the third liquid medium include water, N-methyl-2-pyrrolidone, cyclohexane, methyl ethyl ketone, and methyl isobutyl ketone. Of these, N-methyl-2-pyrrolidone is preferred from the viewpoint of easy dispersibility of carbon nanotubes. The third liquid medium may be the same as or different from the first and second liquid mediums, but it is preferable that it be the same.

[0113] The content of the third liquid medium in the third agent is not particularly limited, as long as it is within a range in which carbon nanotubes can be dispersed, and may be appropriately changed so that the solid content concentration of the cathode composition is within a desired range.

[0114] The solid content concentration of the third agent is not particularly limited and may be, for example, 0.2% by mass or more, 0.8% by mass or more, 1.5% by mass or more, or 2.5% by mass or more. Furthermore, the solid content concentration of the third agent may be, for example, 15.0% by mass or less, 12.5% ​​by mass or less, 10.0% by mass or less, or 7.5% by mass or less. In other words, the solid content concentration of the third agent may be, for example, 0.2-15.0% by mass, 0.2-12.5% ​​by mass, 0.2-10.0% by mass, 0.2-7.5% by mass, 0.8-15.0% by mass, 0.8-12.5% ​​by mass, 0.8-10.0% by mass, 0.8-7.5% by mass, 1.5-15.0% by mass, 1.5-12.5% ​​by mass, 1.5-10.0% by mass, 1.5-7.5% by mass, 2.5-15.0% by mass, 2.5-12.5% ​​by mass, 2.5-10.0% by mass, or 2.5-7.5% by mass.

[0115] The third agent may further contain components other than carbon nanotubes and the third liquid medium. For example, the third agent may further contain polyvinylpyrrolidone, polyvinylimidazole, polyethylene glycol, polyvinyl alcohol, polyvinyl butyral, carboxymethylcellulose, acetylcellulose, or carboxylic acid-modified (meth)acrylic acid ester copolymer.

[0116] (Method of manufacturing the positive electrode) The method for manufacturing the positive electrode of this embodiment includes a forming step of applying the above-described positive electrode composition onto a current collector to form a composite layer on the current collector containing carbon black, carbon nanotubes, a binder, and an active material.

[0117] In the formation process, the positive electrode composition is applied to the current collector to form an asphalt layer on the current collector. The asphalt layer is a layer containing the solid components of the positive electrode composition (at least carbon black, carbon nanotubes, binder, and active material), and may be a layer obtained by removing at least a portion of the liquid medium from the positive electrode composition.

[0118] The current collector is not particularly limited, and known current collectors can be used without any particular restrictions. For example, metal foil (metals such as gold, silver, copper, platinum, aluminum, iron, nickel, chromium, manganese, lead, tungsten, and titanium, and alloys mainly composed of any one of these) can be used as the current collector. Among these, it is preferable to use aluminum for the positive electrode and copper for the negative electrode. The current collector is generally provided in the form of foil, but is not limited to this, and perforated foil and mesh-type current collectors can also be used.

[0119] The method for applying the positive electrode composition onto the current collector is not particularly limited and may include, for example, die coating, dip coating, roll coating, doctor coating, knife coating, spray coating, gravure coating, screen printing, and electrostatic coating.

[0120] The amount of positive electrode composition applied is not particularly limited and may be adjusted as appropriate so that the thickness of the composite layer is within a desired range.

[0121] The composite layer may be formed by removing at least a portion of the liquid medium from the coating film of the positive electrode composition formed on the current collector. The method for removing the liquid medium is not particularly limited, and examples of methods for removing at least a portion of the liquid medium by vaporizing it through heating and / or reduced pressure include standing drying, forced-air drying, hot-air drying, infrared heating, far-infrared heating, etc.

[0122] The positive electrode manufacturing method of this embodiment may further include a pressurizing step in which the composite layer formed in the forming step and the current collector are pressed in the stacking direction. The pressurizing step can bring the composite layer and the current collector into close contact.

[0123] The pressurizing method used in the pressurizing process is not particularly limited and may include methods such as roll pressing, die pressing, and calendering.

[0124] The thickness of the composite layer in the positive electrode is not particularly limited and may be, for example, 50 μm or more. From the viewpoint of increasing the battery capacity, it is preferably 55 μm or more, more preferably 60 μm or more, and may be 65 μm or more or 70 μm or more. Furthermore, the thickness of the composite layer in the positive electrode may be, for example, 150 μm or less. 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. In other words, the thickness of the composite layer in the positive electrode may be, for example, 50-150 μm, 50-140 μm, 50-130 μm, 50-120 μm, 50-110 μm, 55-150 μm, 55-140 μm, 55-130 μm, 55-120 μm, 55-110 μm, 60-150 μm, 60-140 μm, 60-130 μm, 60-120 μm, 60-110 μm, 65-150 μm, 65-140 μm, 65-130 μm, 65-120 μm, 65-110 μm, 70-150 μm, 70-140 μm, 70-130 μm, 70-120 μm, or 70-110 μm.

[0125] The positive electrode manufactured by the manufacturing method of this embodiment can be suitably used as the positive electrode of a battery, particularly a secondary battery (lithium-ion secondary battery).

[0126] (positive electrode) The positive electrode in this embodiment may be a positive electrode manufactured by the manufacturing method described above.

[0127] The positive electrode in this embodiment may be, for example, one of the following positive electrodes.

[0128] A preferred embodiment of the positive electrode is a positive electrode comprising a composite layer containing carbon black, carbon nanotubes, a binder, and an active material.

[0129] In the positive electrode of this embodiment, the total content of carbon black and carbon nanotubes is 0.3 to 2.5% by mass based on the total amount of the composite layer. Furthermore, in the positive electrode of this embodiment, the composite layer has a surface in which the black ratio is 50 to 80% when the image obtained by observing with a scanning electron microscope at a magnification of 1000x is binarized.

[0130] When the black ratio is 50% or more, there is a sufficient amount of conductive material to transport electrons to the positive electrode active material, allowing the positive electrode active material to react uniformly. Furthermore, when the black ratio is 80% or less, the contact resistance between conductive materials does not increase, and the internal resistance of the battery can be kept low. In other words, when the black ratio is between 50% and 80%, there is a sufficient amount of conductive material to transport electrons to the positive electrode active material, and the contact resistance between conductive materials is low, so a highly efficient conductive path is formed, the positive electrode active material is fully utilized even when a large current is flowed, a high discharge rate characteristic is obtained, and the ability to follow the expansion and contraction of the positive electrode active material when repeated charging and discharging is improved, resulting in a high cycle characteristic. The black ratio is preferably 55% or more, and more preferably 58% or more. The black ratio is preferably 75% or less, and more preferably 70% or less. In other words, the above black ratio may be, for example, 50-80%, 50-75%, 50-70%, 55-80%, 55-75%, 55-70%, 58-80%, 58-75%, or 58-70%.

[0131] Observation of the composite layer using a scanning electron microscope is performed using the following method. The composite layer is cut into a 1cm x 1cm square and fixed to a sample stage covered with carbon tape. Next, the sample stage is attached to a scanning electron microscope (JEOL Ltd., JSM-7900F), and a secondary electron image is observed at an acceleration voltage of 1kV and an observation magnification of 1000x. The obtained secondary electron image is binarized using the following method.

[0132] The binarization process is performed using the following method. The secondary electron image is loaded into image analysis software (ImageJ), the threshold is set to 100, and the ratio of white to black areas is calculated using binarization.

[0133] The preferred range for the content of each component in the positive electrode of this embodiment may be the same as the content (based on the total amount of solids) in the positive electrode composition described above.

[0134] The positive electrode of this embodiment can be suitably used as the positive electrode of a battery, particularly a secondary battery (lithium-ion secondary battery).

[0135] The battery in this embodiment (preferably a secondary battery, more preferably a lithium-ion secondary battery) comprises a positive electrode manufactured by the manufacturing method described above. In the battery of this embodiment, the components other than the positive electrode may be the same as those of known batteries.

[0136] The battery in this embodiment is not particularly limited in its applications and can be used in a wide range of fields, such as portable AV equipment including digital cameras, video cameras, portable audio players, portable LCD TVs, portable information terminals such as notebook computers, smartphones, and mobile PCs, as well as portable game devices, power tools, electric bicycles, hybrid vehicles, electric vehicles, and power storage systems.

[0137] Although preferred embodiments of the present invention have been described above, the present invention is not limited to the above embodiments. [Examples]

[0138] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0139] <Example 1> (Carbon Black) Acetylene, the raw material, is injected at a rate of 12 Nm³ from a nozzle installed in the upstream section of the carbon black reactor (furnace length 6m, furnace diameter 0.65m). 3 / h, toluene 32 kg / h, oxygen 22 Nm³ 3 Carbon black was produced by supplying a certain amount of water per hour and collected in a bag filter installed downstream of the reactor. It was then collected in a tank after passing through a dry cyclone and an iron-removing magnet. Acetylene, toluene, and oxygen were heated to 115°C before being supplied to the reactor to obtain carbon black A. The obtained carbon black A had a BET specific surface area of ​​240 m². 2 The average primary particle size was 20 nm, and the crystallite size (Lc) was 16 Å.

[0140] (Carbon black dispersion) Carbon black A, NMP as a dispersion medium, and polyvinyl alcohol (Denka Co., Ltd., Poval DR-1137, degree of saponification 86.5 mol%, average degree of polymerization 500) were prepared. 1.0% by mass of polyvinyl alcohol and 10.0% by mass of carbon black A were added to 89.0% by mass of NMP and stirred for 120 minutes in a planetary mixer (Primix Co., Ltd., Hibis Dispers Mix 3D-5 type) to prepare a slurry containing carbon black A. The obtained slurry was placed into a bead mill (Ashizawa Finetech Co., Ltd., Mugen Flow MGF2-ZA) equipped with zirconia beads (diameter 0.5 mm) and dispersed. After dispersion, the zirconia beads were removed by filtration to obtain a carbon black dispersion.

[0141] (Carbon nanotube dispersion) Carbon nanotubes (CNano, "Flotube6000", average diameter 6nm, BET specific surface area 300m²) 2A slurry containing carbon nanotubes was prepared by adding 1.0% by mass of polyvinylpyrrolidone and 4.0% by mass of carbon nanotubes to 95.0% by mass of NMP and stirring for 120 minutes in a planetary mixer (Hybis Dispersmix 3D-5, manufactured by Primix). The slurry was then placed into a bead mill (Mugen Flow MGF2-ZA, manufactured by Ashizawa Finetech Co., Ltd.) equipped with zirconia beads (0.5 mm in diameter) and dispersed. After dispersion, the zirconia beads were removed by filtration to obtain a carbon nanotube dispersion.

[0142] (Manufacturing of positive electrode composition) As an active material, average particle size D 50 We prepared 12 μm lithium nickel manganese cobalt oxide (manufactured by Beijing Dangsheng Co., Ltd., "ME6A"). As the first step, polyvinylidene fluoride NMP solution (Kureha Corporation, "L#7208"), carbon black dispersion, and carbon nanotube dispersion were weighed into a poly container in the following proportions: 0.7 parts by mass of carbon black, 0.3 parts by mass of carbon nanotube, and 2 parts by mass of binder. The mixture was then mixed for 5 minutes at a rotational speed of 2000 rpm using a rotational mixer (Thinky Co., Ltd., Awatori Rentaro ARV-310) to obtain a mixed solution. In the second step, 97 parts by mass of active material and NMP solution were added to the mixture obtained in the first step to adjust the total solid content concentration to 69% by mass. The mixture was then mixed for 5 minutes at a rotational speed of 2000 rpm using a rotational mixer (Awatori Rentaro ARV-310, manufactured by Thinky Co., Ltd.) to obtain the cathode composition.

[0143] (Viscosity measurement of positive electrode composition) The viscosity of the obtained positive electrode composition was evaluated using a rotary rheometer as described in JIS K7244-10. Specifically, using a rotary rheometer (Anton Paar, MCR302), 1 g of the positive electrode composition was applied to a disk at 25°C, and the shear rate was set to 100 sec. -1from 0.01 sec -1 Measurements were taken while varying the value up to a shear rate of 0.01 sec. -1 Shear rate 1 sec for viscosity -1 The viscosity ratio was calculated for the shear rate of 0.01 sec in this example. -1 Shear rate 1 sec for viscosity -1 The viscosity ratio was 0.064.

[0144] (Manufacturing of positive electrodes) A positive electrode composition was deposited onto one side of a 15 μm thick aluminum foil (manufactured by UACJ) using an applicator to create a laminate. The laminate was then placed in a dryer and pre-dried at 105°C for 1 hour to completely remove NMP. Next, the dried laminate was pressed in a roll press at a linear pressure of 200 kg / cm to adjust the total thickness of the laminate to 80 μm. Finally, it was vacuum-dried at 170°C for 3 hours to completely remove residual moisture, obtaining a positive electrode comprising a current collector and an asphalt layer.

[0145] (Scanning electron microscope observation and image analysis of the positive electrode) The obtained positive electrode was cut into a 1cm x 1cm square and fixed to a sample stage covered with carbon tape. The sample stage was attached to a scanning electron microscope (JEOL Ltd., JSM-7900F), and a secondary electron image was observed at an acceleration voltage of 1kV and an observation magnification of 1000x. The obtained secondary electron image was loaded into image analysis software (ImageJ), the threshold was set to 100, and the ratio of white to black areas was calculated by binarization processing. In this example, the ratio of black areas was 59%.

[0146] (Manufacturing of negative electrodes) Pure water (manufactured by Kanto Chemical Co., Ltd.) was prepared as the solvent, artificial graphite (manufactured by Hitachi Chemical Co., Ltd., "MAG-D") as the negative electrode active material, styrene-butadiene rubber (manufactured by Nippon Zeon Co., Ltd., "BM-400B", hereinafter referred to as SBR) as the binder, and carboxymethylcellulose (manufactured by Daicel Corporation, "D2200", hereinafter referred to as CMC) as the dispersant. Next, CMC was weighed to 1% by mass in solid content and artificial graphite to 97% by mass in solid content and mixed. Pure water was added to this mixture and mixed until homogeneous using a rotation-and-revolution type mixer (manufactured by Thinky Co., Ltd., Awatori Rentaro ARV-310) to obtain a mixture. Next, SBR was weighed to 2% by mass in solid content and added to the obtained mixture and mixed until homogeneous using a rotation-and-revolution type mixer (manufactured by Thinky Co., Ltd., Awatori Rentaro ARV-310) to obtain a negative electrode composition. Next, the negative electrode composition was deposited onto a 10 μm thick copper foil (manufactured by UACJ) using an applicator to create a laminate, which was then left to stand 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 / cm to adjust the total thickness of the laminate to 60 μm. Finally, it was vacuum-dried at 120°C for 3 hours to completely remove residual moisture, obtaining a negative electrode comprising a current collector and an asphalt layer.

[0147] (Battery manufacturing) In a dry room controlled to a dew point of -50°C or lower, the fabricated positive electrode was processed to 40 x 40 mm and the fabricated negative electrode to 44 x 44 mm. Then, an aluminum tab was welded to the positive electrode and a nickel tab to the negative electrode. The composite coating surfaces of the positive and negative electrodes were positioned facing each other in the center, and a 45 x 45 mm polyolefin microporous membrane was placed between the positive and negative electrodes. Next, a sheet-like outer covering cut and processed to a 70 x 140 mm square was folded in half along the center of its long side. Then, the outer covering was positioned so that the aluminum tab for the positive electrode and the nickel tab for the negative electrode were exposed to the outside of the outer covering, and the laminate of the positive electrode / polyolefin microporous membrane / negative electrode was sandwiched between the folded outer covering. Next, using a heat sealer, two sides of the outer casing, including the side where the aluminum tab for the positive electrode and the nickel tab for the negative electrode are exposed, were heat-fused together. Then, 2 g of electrolyte (a solution containing ethylene carbonate / diethyl carbonate = 1 / 2 (volume ratio) and 1 M LiPF6 solution, manufactured by Kishida Chemical Co., Ltd.) was poured into the unfused side to allow the electrolyte to thoroughly permeate the positive electrode, negative electrode, and polyolefin microporous membrane. Finally, the remaining side of the outer casing was heat-fused together using a vacuum heat sealer while reducing the internal pressure to obtain a lithium-ion secondary battery.

[0148] (Battery evaluation) [Internal resistance] The fabricated battery was charged at 25°C under constant current and voltage conditions, limited to 4.3V and 0.2C, and then discharged to 3.0V with a constant current of 0.2C. Next, it underwent 5 charge / discharge cycles under the same conditions, and then charged to a depth of charge of 50%. Afterward, impedance measurements were performed at a frequency range of 10MHz to 0.001Hz and an oscillating voltage of 5mV to determine the internal resistance. The results of the internal resistance measurements are shown in Table 1.

[0149] [Discharge rate characteristics (rate capacity maintenance rate)] The fabricated batteries were charged at 25°C under constant current and voltage conditions of 4.3V and 0.2C limit, and then discharged to 3.0V with a constant current of 0.2C. Next, they were recharged again under constant current and voltage conditions of 4.3V and 0.2C limit, and then discharged to 3.0V with a constant current of 0.2C, and the discharge capacity at this time was measured. Subsequently, the recharge conditions were set to constant current and voltage of 4.3V and 0.2C limit, while the discharge current was gradually changed to 0.5C, 1C, 2C, and 3C. The recharge and discharge cycles were repeated, and the discharge capacity for each discharge current was measured. As an indicator of the battery's discharge rate characteristics, the capacity retention rate at 3C discharge compared to 0.2C discharge was calculated as the rate capacity retention rate. The calculation results of the rate capacity retention rate are shown in Table 1.

[0150] [Cycle characteristics (cycle capacity maintenance rate)] The fabricated batteries were charged at 25°C with a constant current and voltage limit of 4.3V and 1C, and then discharged to 3.0V with a constant current of 1C. The above charge-discharge cycle was repeated 500 times, and the discharge capacity in each cycle was measured. As an indicator of the battery's cycle characteristics, the cycle capacity retention rate was calculated as the capacity retention rate after 500 cycles relative to the capacity retention rate after 1 cycle. The results of the cycle capacity retention rate calculation are shown in Table 1.

[0151] <Example 2> A carbon black dispersion, carbon nanotube dispersion, binder, and active material were prepared in the same manner as in Example 1. As the first step, a polyvinylidene fluoride NMP solution (manufactured by Kureha Corporation, "L#7208") and a carbon black dispersion were weighed into a plastic container so that the carbon black was 0.7 parts by mass and the binder was 2 parts by mass. The mixture was then mixed for 5 minutes at a rotational speed of 2000 rpm using a rotational mixer (manufactured by Thinky Corporation, Awatori Rentaro ARV-310) to obtain the first mixed solution. In the second step, a carbon nanotube dispersion was added to the first mixture so that it contained 0.3 parts by mass of carbon nanotubes. The mixture was then mixed for 5 minutes at a rotational speed of 2000 rpm using a rotational mixer (Awatori Rentaro ARV-310, manufactured by Thinky Co., Ltd.) to obtain a second mixture. In the third step, 97 parts by mass of active material and NMP solution were added to the second mixture to adjust the total solid content concentration to 69% by mass. The mixture was then mixed for 5 minutes at a rotational speed of 2000 rpm using a rotational mixer (Awatori Rentaro ARV-310, manufactured by Thinky Co., Ltd.) to obtain the cathode composition. Using the obtained positive electrode composition, the viscosity of the positive electrode composition was measured in the same manner as in Example 1, followed by the manufacture of the positive electrode. After scanning electron microscope observation and image analysis of the positive electrode, a battery was manufactured and evaluated. The results are shown in Table 1.

[0152] <Example 3> A carbon black dispersion, carbon nanotube dispersion, binder, and active material were prepared in the same manner as in Example 1. As the first step, polyvinylidene fluoride NMP solution (Kureha Corporation, "L#7208"), carbon black dispersion, and carbon nanotube dispersion were weighed into a poly container in the following proportions: 0.8 parts by mass of carbon black, 0.2 parts by mass of carbon nanotube, and 2 parts by mass of binder. The mixture was then mixed for 5 minutes at a rotational speed of 2000 rpm using a rotational mixer (Thinky Co., Ltd., Awatori Rentaro ARV-310) to obtain a mixed solution. In the second step, 97 parts by mass of active material and NMP solution were added to the mixture obtained in the first step to adjust the total solid content concentration to 69% by mass. The mixture was then mixed for 5 minutes at a rotational speed of 2000 rpm using a rotational mixer (Awatori Rentaro ARV-310, manufactured by Thinky Co., Ltd.) to obtain the cathode composition. Using the obtained positive electrode composition, the viscosity of the positive electrode composition was measured in the same manner as in Example 1, followed by the manufacture of the positive electrode. After scanning electron microscope observation and image analysis of the positive electrode, a battery was manufactured and evaluated. The results are shown in Table 1.

[0153] <Example 4> A carbon black dispersion, carbon nanotube dispersion, binder, and active material were prepared in the same manner as in Example 1. As the first step, polyvinylidene fluoride NMP solution (Kureha Corporation, "L#7208"), carbon black dispersion, and carbon nanotube dispersion were weighed into a poly container in the following proportions: 0.2 parts by mass of carbon black, 0.8 parts by mass of carbon nanotube, and 2 parts by mass of binder. The mixture was then mixed for 5 minutes at a rotational speed of 2000 rpm using a rotational mixer (Thinky Co., Ltd., Awatori Rentaro ARV-310) to obtain a mixed solution. In the second step, 97 parts by mass of active material and NMP solution were added to the mixture obtained in the first step to adjust the total solid content concentration to 65% by mass. The mixture was then mixed for 5 minutes at a rotational speed of 2000 rpm using a rotational mixer (Awatori Rentaro ARV-310, manufactured by Thinky Co., Ltd.) to obtain the cathode composition. Using the obtained positive electrode composition, the viscosity of the positive electrode composition was measured in the same manner as in Example 1, followed by the manufacture of the positive electrode. After scanning electron microscope observation and image analysis of the positive electrode, a battery was manufactured and evaluated. The results are shown in Table 1.

[0154] <Example 5> A carbon black dispersion, carbon nanotube dispersion, binder, and active material were prepared in the same manner as in Example 1. As the first step, polyvinylidene fluoride NMP solution (Kureha Corporation, "L#7208"), carbon black dispersion, and carbon nanotube dispersion were weighed into a poly container in the following proportions: 0.9 parts by mass of carbon black, 0.1 parts by mass of carbon nanotube, and 2 parts by mass of binder. The mixture was then mixed for 5 minutes at a rotational speed of 2000 rpm using a rotational mixer (Thinky Co., Ltd., Awatori Rentaro ARV-310) to obtain a mixed solution. In the second step, 97 parts by mass of active material and NMP solution were added to the mixture obtained in the first step to adjust the total solid content concentration to 73% by mass. The mixture was then mixed for 5 minutes at a rotational speed of 2000 rpm using a rotational mixer (Awatori Rentaro ARV-310, manufactured by Thinky Co., Ltd.) to obtain the cathode composition. Using the obtained positive electrode composition, the viscosity of the positive electrode composition was measured in the same manner as in Example 1, followed by the manufacture of the positive electrode. After scanning electron microscopy observation and image analysis of the positive electrode, a battery was manufactured and evaluated. The results are shown in Table 2.

[0155] <Example 6> A carbon black dispersion, carbon nanotube dispersion, binder, and active material were prepared in the same manner as in Example 1. As the first step, polyvinylidene fluoride NMP solution (Kureha Corporation, "L#7208"), carbon black dispersion, and carbon nanotube dispersion were weighed into a poly container in the following proportions: 1.4 parts by mass of carbon black, 0.6 parts by mass of carbon nanotube, and 2 parts by mass of binder. The mixture was then mixed for 5 minutes at a rotational speed of 2000 rpm using a rotational mixer (Thinky Co., Ltd., Awatori Rentaro ARV-310) to obtain a mixed solution. In the second step, 96 parts by mass of active material and NMP solution were added to the mixture obtained in the first step to adjust the total solid content concentration to 65% by mass. The mixture was then mixed for 5 minutes at a rotational speed of 2000 rpm using a rotational mixer (Awatori Rentaro ARV-310, manufactured by Thinky Co., Ltd.) to obtain the cathode composition. Using the obtained positive electrode composition, the viscosity of the positive electrode composition was measured in the same manner as in Example 1, followed by the manufacture of the positive electrode. After scanning electron microscopy observation and image analysis of the positive electrode, a battery was manufactured and evaluated. The results are shown in Table 2.

[0156] <Example 7> (Carbon Black) Acetylene, the raw material, is injected at a rate of 12 Nm³ from a nozzle installed in the upstream section of the carbon black reactor (furnace length 6m, furnace diameter 0.65m). 3 / h, toluene 32 kg / h, oxygen 19 Nm³ 3Carbon black was produced by supplying a certain amount of fuel per hour and collected in a bag filter installed downstream of the reactor. It was then collected in a tank after passing through a dry cyclone and an iron-removing magnet. Acetylene, toluene, and oxygen were heated to 115°C before being supplied to the reactor to obtain carbon black B. The resulting carbon black B had a BET specific surface area of ​​178 m². 2 The average primary particle size was 22 nm, and the crystallite size (Lc) was 17 Å.

[0157] (Carbon black dispersion) Carbon black B, NMP as a dispersion medium, and polyvinyl alcohol (Denka Co., Ltd., Poval DR-1137, saponification degree 86.5 mol%, average degree of polymerization 500) were prepared. 1.0% by mass of polyvinyl alcohol and 10.0% by mass of carbon black B were added to 89.0% by mass of NMP and stirred for 120 minutes in a planetary mixer (Primix Co., Ltd., Hibis Disperser Mix 3D-5 type) to prepare a slurry containing carbon black B. The obtained slurry was placed into a bead mill (Ashizawa Finetech Co., Ltd., Mugen Flow MGF2-ZA) equipped with zirconia beads (diameter 0.5 mm) and dispersed. After dispersion, the zirconia beads were removed by filtration to obtain a carbon black dispersion.

[0158] Except for changing the carbon black dispersion using carbon black A from that used in Example 1 to that using carbon black B, the same carbon nanotube dispersion, binder, and active material as in Example 1 were prepared. As the first step, polyvinylidene fluoride NMP solution (Kureha Corporation, "L#7208"), carbon black dispersion, and carbon nanotube dispersion were weighed into a poly container in the following proportions: 0.7 parts by mass of carbon black, 0.3 parts by mass of carbon nanotube, and 2 parts by mass of binder. The mixture was then mixed for 5 minutes at a rotational speed of 2000 rpm using a rotational mixer (Thinky Co., Ltd., Awatori Rentaro ARV-310) to obtain a mixed solution. In the second step, 97 parts by mass of active material and NMP solution were added to the mixture obtained in the first step to adjust the total solid content concentration to 78% by mass. The mixture was then mixed for 5 minutes at a rotational speed of 2000 rpm using a rotational mixer (Awatori Rentaro ARV-310, manufactured by Thinky Co., Ltd.) to obtain the cathode composition. Using the obtained positive electrode composition, the viscosity of the positive electrode composition was measured in the same manner as in Example 1, followed by the manufacture of the positive electrode. After scanning electron microscopy observation and image analysis of the positive electrode, a battery was manufactured and evaluated. The results are shown in Table 2.

[0159] <Example 8> (Carbon Black) Acetylene, the raw material, is injected at a rate of 12 Nm³ from a nozzle installed in the upstream section of the carbon black reactor (furnace length 6m, furnace diameter 0.65m). 3 / h, toluene 32 kg / h, oxygen 26 Nm³ 3 Carbon black was produced by supplying a certain amount of water per hour and collected in a bag filter installed downstream of the reactor. It was then collected in a tank after passing through a dry cyclone and an iron-removing magnet. Acetylene, toluene, and oxygen were heated to 115°C before being supplied to the reactor to obtain carbon black C. The obtained carbon black C had a BET specific surface area of ​​370 m². 2 The average primary particle size was 18 nm, and the crystallite size (Lc) was 20 Å.

[0160] (Carbon black dispersion) Carbon black C, NMP as a dispersion medium, and polyvinyl alcohol (Denka Co., Ltd., Poval DR-1137, degree of saponification 86.5 mol%, average degree of polymerization 500) were prepared. 1.0% by mass of polyvinyl alcohol and 10.0% by mass of carbon black C were added to 89.0% by mass of NMP and stirred for 120 minutes in a planetary mixer (Primix Co., Ltd., Hibis Dispers Mix 3D-5 type) to prepare a slurry containing carbon black C. The obtained slurry was placed into a bead mill (Ashizawa Finetech Co., Ltd., Mugen Flow MGF2-ZA) equipped with zirconia beads (diameter 0.5 mm) and dispersed. After dispersion, the zirconia beads were removed by filtration to obtain a carbon black dispersion.

[0161] Except for changing the carbon black dispersion using carbon black A from that used in Example 1 to that using carbon black C, the same carbon nanotube dispersion, binder, and active material as in Example 1 were prepared. As the first step, polyvinylidene fluoride NMP solution (Kureha Corporation, "L#7208"), carbon black dispersion, and carbon nanotube dispersion were weighed into a poly container in the following proportions: 0.7 parts by mass of carbon black, 0.3 parts by mass of carbon nanotube, and 2 parts by mass of binder. The mixture was then mixed for 5 minutes at a rotational speed of 2000 rpm using a rotational mixer (Thinky Co., Ltd., Awatori Rentaro ARV-310) to obtain a mixed solution. In the second step, 97 parts by mass of active material and NMP solution were added to the mixture obtained in the first step to adjust the total solid content concentration to 78% by mass. The mixture was then mixed for 5 minutes at a rotational speed of 2000 rpm using a rotational mixer (Awatori Rentaro ARV-310, manufactured by Thinky Co., Ltd.) to obtain the cathode composition. Using the obtained positive electrode composition, the viscosity of the positive electrode composition was measured in the same manner as in Example 1, followed by the manufacture of the positive electrode. After scanning electron microscopy observation and image analysis of the positive electrode, a battery was manufactured and evaluated. The results are shown in Table 2.

[0162] <Comparative Example 1> A carbon black dispersion, carbon nanotube dispersion, binder, and active material were prepared in the same manner as in Example 1. A polyvinylidene fluoride NMP solution (manufactured by Kureha Corporation, "L#7208"), a carbon black dispersion, a carbon nanotube dispersion, and an active material were weighed into a poly container in the following proportions: 0.7 parts by mass of carbon black, 0.3 parts by mass of carbon nanotubes, 2 parts by mass of the binder, and 97 parts by mass of the active material. The mixture was then mixed for 5 minutes at a rotational speed of 2000 rpm using a rotational mixer (manufactured by Thinky Co., Ltd., Awatori Rentaro ARV-310) to obtain a cathode composition. Using the obtained positive electrode composition, the viscosity of the positive electrode composition was measured in the same manner as in Example 1, followed by the manufacture of the positive electrode. After scanning electron microscopy observation and image analysis of the positive electrode, a battery was manufactured and evaluated. The results are shown in Table 3.

[0163] <Comparative Example 2> A carbon black dispersion, carbon nanotube dispersion, binder, and active material were prepared in the same manner as in Example 1. As the first step, polyvinylidene fluoride NMP solution (Kureha Corporation, "L#7208"), carbon black dispersion, and carbon nanotube dispersion were weighed into a poly container in the following proportions: 0.1 parts by mass of carbon black, 0.9 parts by mass of carbon nanotube, and 2 parts by mass of binder. The mixture was then mixed for 5 minutes at a rotational speed of 2000 rpm using a rotational mixer (Thinky Co., Ltd., Awatori Rentaro ARV-310) to obtain a mixed solution. In the second step, 97 parts by mass of active material and NMP solution were added to the mixture obtained in the first step to adjust the total solid content concentration to 69% by mass. The mixture was then mixed for 5 minutes at a rotational speed of 2000 rpm using a rotational mixer (Awatori Rentaro ARV-310, manufactured by Thinky Co., Ltd.) to obtain the cathode composition. Using the obtained positive electrode composition, the viscosity of the positive electrode composition was measured in the same manner as in Example 1, followed by the manufacture of the positive electrode. After scanning electron microscopy observation and image analysis of the positive electrode, a battery was manufactured and evaluated. The results are shown in Table 3.

[0164] <Comparative Example 3> A carbon black dispersion, carbon nanotube dispersion, binder, and active material were prepared in the same manner as in Example 1. As the first step, polyvinylidene fluoride NMP solution (Kureha Corporation, "L#7208"), carbon black dispersion, and carbon nanotube dispersion were weighed into a poly container in the following proportions: 0.95 parts by mass of carbon black, 0.05 parts by mass of carbon nanotube, and 2 parts by mass of binder. The mixture was then mixed for 5 minutes at a rotational speed of 2000 rpm using a rotational mixer (Thinky Co., Ltd., Awatori Rentaro ARV-310) to obtain a mixed solution. In the second step, 97 parts by mass of active material and NMP solution were added to the mixture obtained in the first step to adjust the total solid content concentration to 71% by mass. The mixture was then mixed for 5 minutes at a rotational speed of 2000 rpm using a rotational mixer (Awatori Rentaro ARV-310, manufactured by Thinky Co., Ltd.) to obtain the cathode composition. Using the obtained positive electrode composition, the viscosity of the positive electrode composition was measured in the same manner as in Example 1, followed by the manufacture of the positive electrode. After scanning electron microscopy observation and image analysis of the positive electrode, a battery was manufactured and evaluated. The results are shown in Table 3.

[0165] <Comparative Example 4> (Carbon black dispersion) As carbon black, the BET specific surface area is 87 m². 2Carbon black (Cabot Corporation, "LiTX-HP") with a mean primary particle size of 25 nm and a crystallite size (Lc) of 23 Å was prepared as the dispersion medium, NMP was used, and polyvinyl alcohol (Denka Corporation, Poval DR-1137, degree of saponification 86.5 mol%, average degree of polymerization 500) was used as the dispersant. 1.0 mass% polyvinyl alcohol and 10.0 mass% LiTX-HP were added to 89.0 mass% NMP and stirred for 120 minutes in a planetary mixer (Primix Corporation, Hibis Dispers Mix 3D-5) to prepare a slurry containing LiTX-HP. The obtained slurry was placed in a bead mill (Ashizawa Finetech Corporation, Mugen Flow MGF2-ZA) equipped with zirconia beads (diameter 0.5 mm) and dispersed. After dispersion, the zirconia beads were removed by filtration to obtain a carbon black dispersion.

[0166] Except for changing the carbon black dispersion using carbon black A in Example 1 to a carbon black dispersion using LiTX-HP, the same carbon nanotube dispersion, binder, and active material as in Example 1 were prepared. As the first step, polyvinylidene fluoride NMP solution (Kureha Corporation, "L#7208"), carbon black dispersion, and carbon nanotube dispersion were weighed into a poly container in the following proportions: 0.7 parts by mass of carbon black, 0.3 parts by mass of carbon nanotube, and 2 parts by mass of binder. The mixture was then mixed for 5 minutes at a rotational speed of 2000 rpm using a rotational mixer (Thinky Co., Ltd., Awatori Rentaro ARV-310) to obtain a mixed solution. In the second step, 97 parts by mass of active material and NMP solution were added to the mixture obtained in the first step to adjust the total solid content concentration to 70% by mass. The mixture was then mixed for 5 minutes at a rotational speed of 2000 rpm using a rotational mixer (Awatori Rentaro ARV-310, manufactured by Thinky Co., Ltd.) to obtain the cathode composition. Using the obtained positive electrode composition, the viscosity of the positive electrode composition was measured in the same manner as in Example 1, followed by the manufacture of the positive electrode. After scanning electron microscopy observation and image analysis of the positive electrode, a battery was manufactured and evaluated. The results are shown in Table 3.

[0167] <Comparative Example 5> (Carbon black dispersion) As carbon black, the BET specific surface area is 820 m². 2 Carbon black (Lion Corporation, "ECP") with an average primary particle size of 40 nm and a crystallite size (Lc) of 16 Å was prepared as the dispersion medium, NMP was used, and polyvinyl alcohol (Denka Corporation, Poval DR-1137, degree of saponification 86.5 mol%, average degree of polymerization 500) was used as the dispersant. 1.0 mass% polyvinyl alcohol and 10.0 mass% ECP were added to 89.0 mass% NMP and stirred for 120 minutes in a planetary mixer (Primix Corporation, Hibis Dispers Mix 3D-5 type) to prepare a slurry containing ECP. The obtained slurry was placed in a bead mill (Ashizawa Finetech Corporation, Mugen Flow MGF2-ZA) equipped with zirconia beads (diameter 0.5 mm) and dispersed. After dispersion, the zirconia beads were removed by filtration to obtain a carbon black dispersion.

[0168] Except for changing the carbon black dispersion using carbon black A in Example 1 to a carbon black dispersion using ECP, the same carbon nanotube dispersion, binder, and active material as in Example 1 were prepared. As the first step, polyvinylidene fluoride NMP solution (Kureha Corporation, "L#7208"), carbon black dispersion, and carbon nanotube dispersion were weighed into a poly container in the following proportions: 0.7 parts by mass of carbon black, 0.3 parts by mass of carbon nanotube, and 2 parts by mass of binder. The mixture was then mixed for 5 minutes at a rotational speed of 2000 rpm using a rotational mixer (Thinky Co., Ltd., Awatori Rentaro ARV-310) to obtain a mixed solution. In the second step, 97 parts by mass of active material and NMP solution were added to the mixture obtained in the first step to adjust the total solid content concentration to 66% by mass. The mixture was then mixed for 5 minutes at a rotational speed of 2000 rpm using a rotational mixer (Awatori Rentaro ARV-310, manufactured by Thinky Co., Ltd.) to obtain the cathode composition. Using the obtained positive electrode composition, the viscosity of the positive electrode composition was measured in the same manner as in Example 1, followed by the manufacture of the positive electrode. After scanning electron microscopy observation and image analysis of the positive electrode, a battery was manufactured and evaluated. The results are shown in Table 4.

[0169] <Comparative Example 6> A carbon black dispersion, carbon nanotube dispersion, binder, and active material were prepared in the same manner as in Example 1. As the first step, polyvinylidene fluoride NMP solution (Kureha Corporation, "L#7208"), carbon black dispersion, and carbon nanotube dispersion were weighed into a poly container in the following proportions: 0.7 parts by mass of carbon black, 0.3 parts by mass of carbon nanotube, and 2 parts by mass of binder. The mixture was then mixed for 5 minutes at a rotational speed of 2000 rpm using a rotational mixer (Thinky Co., Ltd., Awatori Rentaro ARV-310) to obtain a mixed solution. In the second step, 97 parts by mass of active material and NMP solution were added to the mixture obtained in the first step to adjust the total solid content concentration to 62% by mass. The mixture was then mixed for 5 minutes at a rotational speed of 2000 rpm using a rotational mixer (Awatori Rentaro ARV-310, manufactured by Thinky Co., Ltd.) to obtain the cathode composition. Using the obtained positive electrode composition, the viscosity of the positive electrode composition was measured in the same manner as in Example 1, followed by the manufacture of the positive electrode. After scanning electron microscopy observation and image analysis of the positive electrode, a battery was manufactured and evaluated. The results are shown in Table 4.

[0170] <Comparative Example 7> A carbon black dispersion, carbon nanotube dispersion, binder, and active material were prepared in the same manner as in Example 1. As the first step, polyvinylidene fluoride NMP solution (Kureha Corporation, "L#7208"), carbon black dispersion, and carbon nanotube dispersion were weighed into a poly container in the following proportions: 0.7 parts by mass of carbon black, 0.3 parts by mass of carbon nanotube, and 2 parts by mass of binder. The mixture was then mixed for 5 minutes at a rotational speed of 2000 rpm using a rotational mixer (Thinky Co., Ltd., Awatori Rentaro ARV-310) to obtain a mixed solution. In the second step, 97 parts by mass of active material and NMP solution were added to the mixture obtained in the first step to adjust the total solid content concentration to 83% by mass. The mixture was then mixed for 5 minutes at a rotational speed of 2000 rpm using a rotational mixer (Awatori Rentaro ARV-310, manufactured by Thinky Co., Ltd.) to obtain the cathode composition. Using the obtained positive electrode composition, the viscosity of the positive electrode composition was measured in the same manner as in Example 1, followed by the manufacture of the positive electrode. After scanning electron microscopy observation and image analysis of the positive electrode, a battery was manufactured and evaluated. The results are shown in Table 4.

[0171] [Table 1]

[0172] [Table 2]

[0173] [Table 3]

[0174] [Table 4]

[0175] In the table, CB represents carbon black, and CNT represents carbon nanotube. Also, in the table, C 1 +C 2 The values ​​represent the total content of carbon black and carbon nanotubes, the ratio (C2 / (C1+C2)) represents the ratio of the carbon nanotube content to the total content of carbon black and carbon nanotubes, and the ratio (V2 / V1) represents the ratio of the viscosity at a shear rate of 1 (1 / sec) at 25°C to the viscosity at a shear rate of 0.01 (1 / sec) at 25°C.

[0176] Figure 1(a) shows an example of a scanning electron microscope image of the positive electrode used in the example, and Figure 1(b) shows an example of a scanning electron microscope image of the positive electrode used in the comparative example.

Claims

1. A positive electrode composition containing carbon black, carbon nanotubes, an active material, a binder, and a liquid medium, The solid content concentration is 60-85% by mass. Viscosity V at a shear rate of 0.01 (1 / sec) at 25°C １ Viscosity V at a shear rate of 1 (1 / sec) at 25°C ２ The ratio (V ２ / V １ A positive electrode composition in which the ratio is 0.02 or more and 0.2 or less.

2. The BET specific surface area of ​​the carbon black is 100 to 500 m². ２ The positive electrode composition according to claim 1, wherein the value is / g.

3. The positive electrode composition according to claim 1, wherein the ratio of the content (mass%) of carbon nanotubes to the total content (mass%) of carbon black and carbon nanotubes is 0.07 to 0.

85.

4. The positive electrode composition according to claim 1, wherein the solid content concentration is 65 to 80% by mass.

5. The carbon black is 100 to 400 m ２ The positive electrode composition according to claim 1, having a BET specific surface area of ​​1 / g and a crystallite size (Lc) of 15 to 26 Å.

6. The cathode composition according to claim 1, wherein the carbon nanotubes have an average diameter of 5 to 15 nm.

7. A method for producing a positive electrode, comprising the step of applying the positive electrode composition according to any one of claims 1 to 6 onto a current collector to form a composite layer on the current collector containing the carbon black, the carbon nanotubes, the binder, and the active material.

8. A positive electrode comprising a composite layer containing carbon black, carbon nanotubes, a binder, and an active material, The total content of the carbon black and carbon nanotubes is 0.3 to 2.5% by mass based on the total amount of the composite layer. The composite layer has a surface in which the black ratio is 50-80% when the image obtained by observing it with a scanning electron microscope at a magnification of 1000x is binarized.

9. A battery comprising the positive electrode described in claim 8.

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