Positive electrode composition, coating liquid for forming positive electrode, positive electrode, battery, conductive material, slurry, method for producing coating liquid for forming positive electrode, and method for producing positive electrode

Abstract

To provide a positive electrode composition capable of implementing a battery having excellent cycle characteristics.SOLUTION: A positive electrode composition includes an active material, a binder, and a conductive material, and the conductive material includes carbon black (A) having an average primary particle diameter of 17 nm or more and 30 nm or less, first carbon nanotubes (B) having an average diameter of 2 nm or more and 15 nm or less, and second carbon nanotubes (C) having an average diameter of 0.5 nm or more and less than 2 nm.SELECTED DRAWING: None

Description

Technical Field

[0001] The present disclosure relates to a positive electrode composition, a coating liquid for forming a positive electrode, a positive electrode, a battery, a conductive material, a slurry, a method for manufacturing a coating liquid for forming a positive electrode, and a method for manufacturing a positive electrode.

Background Art

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

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

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

Prior Art Documents

Patent Documents

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

[0006] In recent years, further performance improvement has been demanded in batteries such as lithium ion secondary batteries.

[0007] One object of the present disclosure is to provide a positive electrode composition capable of realizing a battery having excellent cycle characteristics. Another object of the present disclosure is to provide a coating liquid for forming a positive electrode capable of realizing a battery having excellent cycle characteristics. Another object of the present disclosure is to provide a positive electrode capable of realizing a battery having excellent cycle characteristics. Another object of the present disclosure is to provide a battery having excellent cycle characteristics. Another object of the present disclosure is to provide a conductive material and a slurry containing the conductive material capable of realizing a battery having excellent cycle characteristics. Further, one object of the present disclosure is to provide a method for manufacturing a coating liquid for forming a positive electrode that can be easily manufactured, and a method for manufacturing a positive electrode that can be easily manufactured. Means for Solving the Problems

[0008] The present disclosure relates to, for example, the following [1] to

[16] . [1] comprising an active material, a binder, and a conductive material, wherein the conductive material is carbon black (A) having an average primary particle diameter of 17 nm or more and 30 nm or less, a first carbon nanotube (B) having an average diameter of 2 nm or more and 15 nm or less, a second carbon nanotube (C) having an average diameter of 0.5 nm or more and less than 2 nm, and a positive electrode composition. [2] The positive electrode composition according to [1], wherein the carbon black (A) is selected from the group consisting of furnace black, acetylene black, and ketjen black. [3] The BET specific surface area of the carbon black (A) is 100 m 2 / g or more and 900 m 2 / g or less, and the positive electrode composition according to [1] or [2]. [4] The content of the carbon black (A) is 30% by mass or more and 90% by mass or less based on the total amount of the conductive material, and the positive electrode composition according to any one of [1] to [3]. [5] The peak ratio (D / G) of the D band and the G band in the Raman spectrum of the first carbon nanotube (B) is 0.1 or more and 1.5 or less, and the positive electrode composition according to any one of [1] to [4]. [6] The peak ratio (D / G) of the D band and the G band in the Raman spectrum of the first carbon nanotube (B) is 0.3 or more and 1.4 or less, and the positive electrode composition according to any one of [1] to [5]. [7] The content of the first carbon nanotube (B) is 5% by mass or more and 50% by mass or less based on the total amount of the conductive material, and the positive electrode composition according to any one of [1] to [6]. [8] The content of the second carbon nanotube (C) is 1% by mass or more and 45% by mass or less based on the total amount of the conductive material, and the positive electrode composition according to any one of [1] to [7]. [9] A coating liquid for forming a positive electrode, comprising the positive electrode composition according to any one of [1] to [8] and a dispersion medium.

[10] A positive electrode comprising the positive electrode composition according to any one of [1] to [8].

[11] A battery comprising the positive electrode according to

[10] .

[12] Carbon black (A) having an average primary particle diameter of 17 nm or more and 30 nm or less, and The first carbon nanotube (B) having an average diameter of 2 nm or more and 15 nm or less, and A second carbon nanotube (C) having an average diameter of 0.5 nm or more and less than 2 nm, and A conductive material containing the same.

[13] A slurry containing the conductive material according to

[12] and a dispersion medium.

[14] A mixing step of mixing an active material, a binder, a conductive material, and a dispersion medium, The conductive material includes carbon black (A) having an average primary particle diameter of 17 nm or more and 30 nm or less, a first carbon nanotube (B) having an average diameter of 2 nm or more and 15 nm or less, and a second carbon nanotube (C) having an average diameter of 0.5 nm or more and less than 2 nm. A method for producing a coating liquid for forming a positive electrode.

[15] The mixing step is a step of mixing the active material, a binder solution containing the binder, a slurry (A) containing the carbon black (A), a slurry (B) containing the first carbon nanotube (B), and a slurry (C) containing the second carbon nanotube (C). The production method according to

[14] .

[16] A method for producing a positive electrode, comprising a step of applying a coating liquid for forming a positive electrode produced by the production method according to

[14] or

[15] onto a current collector to form a composite material layer containing the active material, the binder, and the conductive material on the current collector. [Effects of the Invention]

[0009] According to the present disclosure, a positive electrode composition capable of realizing a battery having excellent cycle characteristics is provided. Further, according to the present disclosure, a coating liquid for forming a positive electrode capable of realizing a battery having excellent cycle characteristics is provided. Further, according to the present disclosure, a positive electrode capable of realizing a battery having excellent cycle characteristics is provided. Further, according to the present disclosure, a battery having excellent cycle characteristics is provided. Further, according to the present disclosure, a conductive material capable of realizing a battery having excellent cycle characteristics and a slurry containing the conductive material are provided. Furthermore, according to the present disclosure, a method for producing a coating liquid for forming a positive electrode that can easily produce the above-described coating liquid for forming a positive electrode, and a method for producing a positive electrode that can easily produce the above-described positive electrode are provided.

Best Mode for Carrying Out the Invention

[0010] Hereinafter, preferred embodiments of the present disclosure will be described in detail. In this specification, carbon black may be abbreviated as "CB", and carbon nanotube may be abbreviated as "CNT". Further, in this specification, the tilde symbol "~" is a symbol used to indicate a numerical range including the numerical values described before and after it. Specifically, "X~Y" (both X and Y are numerical values) indicates "X or more and Y or less".

[0011] (Positive Electrode Composition) The positive electrode composition of this embodiment contains an active material, a binder, and a conductive material. In this embodiment, the conductive material includes carbon black (A) having an average primary particle diameter of 17 nm or more and 30 nm or less, first carbon nanotubes (B) having an average diameter of 2 nm or more and 15 nm or less, and second carbon nanotubes (C) having an average diameter of 0.5 nm or more and less than 2 nm.

[0012] The positive electrode composition of this embodiment may be a material constituting the composite layer in the positive electrode. By using a positive electrode provided with a composite layer composed of the positive electrode composition of this embodiment, a battery excellent in cycle characteristics can be realized.

[0013] The reason why the above effects are achieved by the positive electrode composition of this embodiment is considered as follows. The positive electrode composition of this embodiment combines carbon black having a spherical structure and carbon nanotubes having a fibrous structure. Due to these combinations, it is considered that the positive electrode composition of this embodiment has improved followability with respect to the expansion and contraction of the positive electrode active material accompanying charge and discharge of the battery. Further, the positive electrode composition of this embodiment contains two types of carbon nanotubes having different diameters. As a result, the above-mentioned followability is further improved, and even when the charge and discharge of the battery are repeated, the conductive network in the positive electrode is easily maintained well, and thus it is considered that a battery excellent in cycle characteristics can be realized.

[0014] Hereinafter, each component of the positive electrode composition of the present embodiment will be described in detail.

[0015] <Conductive material> The positive electrode composition of the present embodiment contains carbon black (A) as a conductive material. The average primary particle diameter of the carbon black (A) is 17 nm or more and 30 nm or less.

[0016] When the average primary particle diameter of the carbon black (A) is 17 nm or more, the conductive network formed in the positive electrode is likely to develop. Also, when the average primary particle diameter of the carbon black (A) is 30 nm or less, the conductive network formed in the positive electrode is likely to develop. From the viewpoint of obtaining this effect more remarkably, the average primary particle diameter of the carbon black (A) may be 27 nm or less, or may be 25 nm or less.

[0017] In this specification, the average primary particle diameter of the carbon black (A) can be obtained by measuring the primary particle diameters of 100 or more carbon blacks randomly selected from a 50,000-fold magnified image of a transmission electron microscope (TEM) and calculating the average value. The primary particles of carbon black have a small aspect ratio and are nearly spherical in shape, but are not perfect spheres. Therefore, in this specification, the maximum of the line segments connecting two points on the outer periphery of the primary particle in the TEM image is taken as the primary particle diameter of the carbon black.

[0018] The carbon black (A) may be selected from the group consisting of, for example, acetylene black, furnace black, and ketjen black, and is preferably acetylene black.

[0019] The BET specific surface area of the carbon black (A) may be, for example, 100 m 2 / g or more, 110 m 2 / g or more, 120 m 2 / g or more, or 130 m 2 / g or more. Thereby, the conductive network formed in the positive electrode tends to develop more. The BET specific surface area of the carbon black (A) is, for example, 900 m 2It may be below / g, 890 m 2 / g or less, 880 m 2 / g or less, or 870 m 2 It may also be below / g. As a result, the conductive network formed in the positive electrode tends to be more developed.

[0020] In addition, in this specification, the BET specific surface area of carbon black (A) is a value measured by the static volumetric method in accordance with JIS Z8830 using nitrogen as the adsorbate.

[0021] The content of carbon black (A) may be, for example, 30% by mass or more based on the total amount of the conductive material. From the viewpoint of further improving the cycle characteristics, it may be 35% by mass or more, 40% by mass or more, 45% by mass or more, 50% by mass or more, 55% by mass or more, 60% by mass or more, or 65% by mass or more. Also, the content of carbon black (A) may be, for example, 90% by mass or less based on the total amount of the conductive material. From the viewpoint of further improving the cycle characteristics, it may be 85% by mass or less, 80% by mass or less, or 75% by mass or less.

[0022] The positive electrode composition of this embodiment further contains first carbon nanotubes (B) as a conductive material. The average diameter of the first carbon nanotubes (B) is 2 nm or more and 15 nm or less.

[0023] The average diameter of the first carbon nanotubes (B) may be 3 nm or more, 4 nm or more, or 5 nm or more from the viewpoint that the conductive network in the positive electrode is more likely to be developed. Also, the average diameter of the first carbon nanotubes (B) may be 13 nm or less, 11 nm or less, or 10 nm or less from the viewpoint that the conductive network in the positive electrode is more likely to be developed.

[0024] In addition, in this specification, the average diameter of the carbon nanotube means the average value of the diameters measured based on an image obtained when observing the carbon nanotube with a transmission electron microscope (TEM). Specifically, using a transmission electron microscope JEM-2000FX (manufactured by JEOL Ltd.), 10 images of the carbon nanotube are taken at a magnification of 200,000 times, and the diameters of 100 randomly extracted carbon nanotubes in the obtained images are measured by image analysis and arithmetically averaged.

[0025] The first carbon nanotube (B) may be a multi-walled carbon nanotube (MWCNT). The multi-walled carbon nanotube may be a carbon nanotube having a structure in which three or more graphene sheets are stacked coaxially in a tubular shape.

[0026] In the carbon nanotube, the peak ratio (D / G) of the D band and the G band in the Raman spectrum can be an index for evaluating the crystallinity of the carbon nanotube. The peak ratio (D / G) of the first carbon nanotube (B) may be, for example, 0.1 or more, and from the viewpoint of further improving the conductivity, it may be 0.2 or more, 0.3 or more, 0.4 or more, 0.5 or more, or 0.6 or more. Also, the peak ratio (D / G) of the first carbon nanotube (B) may be, for example, 1.5 or less, and from the viewpoint of further improving the conductivity, it may be 1.4 or less, 1.3 or less, 1.2 or less, 1.1 or less, 1.0 or less, or 0.9 or less.

[0027] In addition, in this specification, the Raman spectrum of the carbon nanotube measured using a microscopic laser Raman system (manufactured by Thermo Fisher Scientific, product name "Nicolet Almega XR") includes a G band (1600 cm -1 near) and a D band (1350 cm -1A vibration mode called the "near" mode is observed. The G band is a vibration mode derived from the hexagonal lattice structure of graphite, which is the cylindrical surface of the carbon nanotube, and the D band is a vibration mode derived from amorphous regions. The lower the peak intensity ratio (D / G ratio) of this D band to the G band, the higher the crystallinity of the carbon nanotube can be evaluated.

[0028] As the first carbon nanotube (B), a commercially available product may be used. For example, Flotube6000, Flotube7000 (both manufactured by Cnano Technology Ltd, MWCNT), etc. can be used as the first carbon nanotube (B).

[0029] The content of the first carbon nanotube (B) may be, for example, 5% by mass or more based on the total amount of the conductive material, and from the viewpoint of further improving the cycle characteristics, it may be 10% by mass or more, 15% by mass or more, 18% by mass or more, 20% by mass or more, or 22% by mass or more. Also, the content of the first carbon nanotube (B) may be, for example, 50% by mass or less based on the total amount of the conductive material, and from the viewpoint of further improving the cycle characteristics, it may be 45% by mass or less, 40% by mass or less, 35% by mass or less, 30% by mass or less, or 28% by mass or less.

[0030] The positive electrode composition of this embodiment further includes a second carbon nanotube (C) as a conductive material. The average diameter of the second carbon nanotube (C) is 0.5 nm or more and less than 2 nm.

[0031] The average diameter of the second carbon nanotube (C) may be 0.6 nm or more, or 0.7 nm or more from the viewpoint that the conductive network in the positive electrode is more likely to develop. Also, the average diameter of the second carbon black (C) may be 1.7 nm or less, 1.5 nm or less, 1.3 nm or less, 1.1 nm or less, or 1.0 nm or less from the viewpoint that the conductive network in the positive electrode is more likely to develop.

[0032] The second carbon nanotube (C) may be a single-walled carbon nanotube (SWCNT) or a double-walled carbon nanotube (DWCNT). The single-walled carbon nanotube may be a carbon nanotube having a tubular structure composed of a graphene sheet, and the double-walled carbon nanotube may be a carbon nanotube having a structure in which two layers of graphene sheets are stacked coaxially in a tubular shape.

[0033] The peak ratio (D / G) of the second carbon nanotube (C) may be, for example, less than 0.3, and from the viewpoint of further improving conductivity, it may be less than 0.2 or less than 0.1. Also, the peak ratio (D / G) of the second carbon nanotube (C) may be, for example, 0.01 or more, and from the viewpoint of further improving conductivity, it may be 0.02 or more, 0.03 or more, 0.04 or more, or 0.05 or more.

[0034] As the second carbon nanotube (C), commercially available products may be used. As the second carbon nanotube (C), for example, Signis CG300 (manufactured by CHASM, SWCNT), etc. can be used.

[0035] The content of the second carbon nanotube (C) may be, for example, 1% by mass or more based on the total amount of the conductive material, and from the viewpoint of further improving cycle characteristics, it may be 3% by mass or more, 5% by mass or more, 10% by mass or more, 15% by mass or more, 18% by mass or more, 20% by mass or more, or 22% by mass or more. Also, the content of the first carbon nanotube (C) may be, for example, 45% by mass or less based on the total amount of the conductive material, and from the viewpoint of further improving cycle characteristics, it may be 40% by mass or less, 35% by mass or less, 30% by mass or less, 28% by mass or less, or 25% by mass or less.

[0036] The positive electrode composition of this embodiment may further contain, as a conductive material, other components (D) other than carbon black (A), the first carbon nanotube (B), and the second carbon nanotube (C).

[0037] Examples of the component (D) include graphene, graphite, and porous carbon.

[0038] The content of component (D) may be, for example, less than 50% by mass based on the total amount of the conductive material, and from the viewpoint of obtaining the above-mentioned effect by the combined use of carbon black (A), the first carbon nanotube (B) and the second carbon nanotube (C) more significantly, it may be 40% by mass or less, 30% by mass or less, 20% by mass or less, 10% by mass or less, 5% by mass or less, 3% by mass or less, or 1% by mass or less, or it may be 0% by mass. That is, the total content of carbon black (A), the first carbon nanotube (B) and the second carbon nanotube (C) may be, for example, more than 50% by mass based on the total amount of the conductive material, and from the viewpoint of obtaining the above-mentioned effect by the combined use of carbon black (A), the first carbon nanotube (B) and the second carbon nanotube (C) more significantly, it may be 60% by mass or more, 70% by mass or more, 80% by mass or more, 90% by mass or more, 95% by mass or more, 97% by mass or more, or 99% by mass or more, or it may be 100% by mass.

[0039] The content of the conductive material may be, for example, 0.05% by mass or more based on the total amount of the positive electrode composition, and from the viewpoint of more easily developing the conductive network, may be 0.1% by mass or more, 0.3% by mass or more, or 0.5% by mass or more. The content of the conductive material may be, for example, 10% by mass or less based on the total amount of the positive electrode composition, and from the viewpoint of sufficiently forming the conductive network, may be 5% by mass or less, 3% by mass or less, or 1% by mass or less.

[0040] <Active material> The positive electrode composition of the present embodiment includes an active material. The active material may be any material capable of reversibly absorbing and releasing cations. The active material may also be referred to as a positive electrode active material.

[0041] The active material is not particularly limited, and for example, known active materials used in lithium ion secondary batteries can be used without particular limitation. Examples of the active material include lithium cobaltate, lithium nickelate, lithium manganate, lithium nickel manganese cobaltate, lithium iron phosphate, and the like.

[0042] The active material may be, for example, a lithium-containing composite oxide containing manganese with a volume resistivity of 1×10 4 Ω·cm or more, or a lithium-containing polyanion compound. Examples of the lithium-containing composite oxide containing manganese include lithium manganates such as LiMnO2, LiMnO3, LiMn2O3, Li 1+x Mn 2-x O4 (where x = 0 to 0.33); lithium manganates such as LiMn x Ni y Co z O2 (where x + y + z = 1, 0 ≦ y < 1, 0 ≦ z < 1, 0 ≦ x < 1), Li 1+x Mn 2-x-y M y O4 (where x = 0 to 0.33, y = 0 to 1.0, 2 - x - y > 0), LiMn 2-x M x O2 (where x = 0.01 to 0.1), Li2Mn3MO8, and composite oxides containing one or more transition metal elements. Examples of the lithium-containing polyanion compound include polyanion compounds such as LiFePO4, LiMnPO4, and Li2MPO4F (where M is at least one metal selected from Co, Ni, Fe, Cr, and Zn). M in each composition formula is at least one selected from the group consisting of Fe, Co, Ni, Al, Cu, Mg, Cr, Zn, and Ta.

[0043] The average particle diameter (D 50 ) of the active material may be 20 μm or less or 10 μm or less from the viewpoint of easily obtaining a battery with sufficiently excellent binding properties between the conductive material and the binder and more excellent cycle characteristics. The average particle diameter (D 50 ) of the active material can be measured by the laser light scattering method. The average particle diameter (D 50 ) of the active material may be, for example, 1 μm or more.

[0044] The content of the active material may be, for example, 80% by mass or more based on the total amount of the positive electrode composition, and from the viewpoint of further improving the battery capacity, it may be 85% by mass or more, 90% by mass or more, or 95% by mass or more. Also, the content of the active material may be, for example, 99.9% by mass or less based on the total amount of the positive electrode composition, and from the viewpoint of sufficiently obtaining the battery capacity and more easily obtaining the above-described effects by the conductive material, it may be 99% by mass or less, 98% by mass or less, or 97% by mass or less.

[0045] <Binder The binder may be any material that can bind the active material and the conductive material and maintain the shape of the composite layer.

[0046] Examples of the binder include polyvinylidene fluoride, polytetrafluoroethylene, styrene-butadiene copolymer, and (meth)acrylate copolymer. The polymer structure of the binder may be, for example, a random copolymer, an alternating copolymer, a graft copolymer, a block copolymer, etc. From the viewpoint of excellent withstand voltage properties, polyvinylidene fluoride is preferred as the binder.

[0047] The content of the binder may be, for example, 0.5% by mass or more based on the total amount of the positive electrode composition, and from the viewpoint of better binding properties, it may be 1% by mass or more, 1.5% by mass or more, or 2% by mass or more. Also, the content of the binder may be, for example, 10% by mass or less based on the total amount of the positive electrode composition, and from the viewpoint of further improving the battery capacity, it may be 8% by mass or less, 6% by mass or less, or 4% by mass or less.

[0048] The positive electrode composition of the present embodiment may further contain a dispersant as a component other than the active material, the binder, and the conductive material.

[0049] <Dispersant The dispersant is a component having a function of assisting the dispersion of the conductive material in the dispersion medium. When the positive electrode composition is manufactured using a slurry in which the conductive material is dispersed in the dispersion medium, the dispersant may be contained in the positive electrode composition.

[0050] Examples of the dispersant include polymer dispersants and low-molecular dispersants. From the viewpoint of long-term dispersion stability of the conductive material, polymer dispersants are preferred. The dispersant may be, for example, a dispersant selected from the group consisting of polyvinyl alcohol, polyvinylpyrrolidone, polyvinyl butyral, carboxymethyl cellulose and its salts, polyvinyl acetal, polyvinyl acetate, polyvinylamine, and polyvinyl formal.

[0051] The content of the dispersant may be, for example, 100 parts by mass or less with respect to 100 parts by mass of the conductive material. From the viewpoint of suppressing the decrease in conductivity due to the dispersant, it may be 80 parts by mass or less, 60 parts by mass or less, or 40 parts by mass or less. When the positive electrode composition of the present embodiment contains a dispersant, the content of the dispersant may be, for example, 5 parts by mass or more with respect to 100 parts by mass of the conductive material. From the viewpoint of further improving the dispersibility of the conductive material, it may be 10 parts by mass or more, 15 parts by mass or more, or 20 parts by mass or more.

[0052] The content of the dispersant may be, for example, 10% by mass or less based on the total amount of the positive electrode composition. From the viewpoint of suppressing the decrease in conductivity due to the dispersant, it may be 5% by mass or less, 3% by mass or less, or 1% by mass or less. When the positive electrode composition of the present embodiment contains a dispersant, the content of the dispersant may be, for example, 0.05% by mass or more based on the total amount of the positive electrode composition. From the viewpoint of further improving the dispersibility of the conductive material, it may be 0.1% by mass or more, 0.3% by mass or more, or 0.5% by mass or more.

[0053] The positive electrode composition of the present embodiment may further contain other components other than the active material, the binder, the conductive material, and the dispersant.

[0054] Examples of the other components include wetting agents and defoaming agents.

[0055] The content of other components may be, for example, 5% by mass or less, 3% by mass or less, 2% by mass or less, 1% by mass or less, 0.5% by mass or less, 0.3% by mass or less, 0.2% by mass or less, or 0.1% by mass or less, based on the total amount of the positive electrode composition, and may even be 0% by mass. That is, the total content of the active material, binder, and conductive material (which may be the total content of the active material, binder, conductive material, and dispersant) may be, for example, 95% by mass or more, 97% by mass or more, 98% by mass or more, 99% by mass or more, 99.5% by mass or more, 99.7% by mass or more, 99.8% by mass or more, or 99.9% by mass or more, based on the total amount of the positive electrode composition, and may even be 100% by mass.

[0056] The positive electrode composition of this embodiment may be a material that constitutes the composite material layer in the positive electrode. That is, the positive electrode composition of this embodiment may be formed in a layered shape.

[0057] The positive electrode composition of this embodiment may be formed, for example, by applying and drying the coating liquid for positive electrode formation described later.

[0058] (Coating liquid for positive electrode formation) The coating liquid for positive electrode formation of this embodiment contains an active material, a binder, a conductive material, and a dispersion medium. Further, the coating liquid for positive electrode formation of this embodiment may further contain a dispersant.

[0059] The active material, binder, conductive material, and dispersant in the coating liquid for positive electrode formation of this embodiment may be the same as the active material, binder, conductive material, and dispersant in the above-described positive electrode composition, respectively. That is, the coating liquid for positive electrode formation of this embodiment can also be said to be a coating liquid containing the above-described positive electrode composition and a dispersion medium.

[0060] The contents of the active material, binder, conductive material, and dispersant in the coating liquid for positive electrode formation of this embodiment (based on the total amount of the solid content in the coating liquid for positive electrode formation) may be the same as the contents of the active material, binder, conductive material, and dispersant in the above-described positive electrode composition (based on the total amount of the positive electrode composition), respectively.

[0061] The dispersion medium may be any dispersion medium capable of dispersing each component in the coating liquid. Examples of the dispersion medium include water, N-methyl-2-pyrrolidone, cyclohexane, methyl ethyl ketone, methyl isobutyl ketone, and the like. Among these, from the viewpoint of excellent dispersibility, N-methyl-2-pyrrolidone is preferable.

[0062] The content of the dispersion medium is not particularly limited, and it may be within a range where sufficient coatability of the coating liquid for forming the positive electrode can be obtained. The content of the dispersion medium may be, for example, 10% by mass or more, 20% by mass or more, 30% by mass or more, or 40% by mass or more based on the total amount of the coating liquid for forming the positive electrode. Also, the content of the dispersion medium may be, for example, 90% by mass or less, 80% by mass or less, 70% by mass or less, or 60% by mass or less based on the total amount of the coating liquid for forming the positive electrode.

[0063] The coating liquid for forming the positive electrode of the present embodiment can form a composite layer composed of the above-described positive electrode composition by coating and drying. Here, drying refers to an operation of removing at least a part of the dispersion medium from the coating film obtained by coating the coating liquid for forming the positive electrode.

[0064] The method for applying the coating liquid for forming the positive electrode of the present embodiment is not particularly limited, and it may be appropriately selected from known coating methods (coating means, coating apparatus). Examples of the coating method include a die coating method, a dip coating method, a roll coating method, a doctor coating method, a knife coating method, a spray coating method, a gravure coating method, a screen printing method, and an electrostatic coating method.

[0065] The drying method of the coating film is not particularly limited, and it may be appropriately selected from known drying methods (drying means, drying apparatus). Examples of the drying method include a method of vaporizing at least a part of the dispersion medium by heating and / or reducing the pressure. The drying method may be, for example, air drying, heat drying, vacuum drying, or a drying method using a dryer such as a blowing dryer, a warm air dryer, an infrared heater, or a far-infrared heater.

[0066] The coating liquid for forming the positive electrode of the present embodiment may be applied onto a current collector and dried. Thereby, a composite layer made of the positive electrode composition is formed on the current collector, and a positive electrode including the current collector and the composite layer is obtained.

[0067] The coating liquid for forming the positive electrode of the present embodiment can be obtained by dispersing each component in the above-described positive electrode composition in a dispersion medium. The coating liquid for forming the positive electrode of the present embodiment may be manufactured, for example, by the following manufacturing method.

[0068] <Manufacturing Method of Coating Liquid for Forming Positive Electrode> The manufacturing method of the coating liquid for forming the positive electrode may include a mixing step of mixing each component in the above-described positive electrode composition and a dispersion medium.

[0069] The mixing step may be a step of dispersing each component in the dispersion medium at once, or may be a step of dispersing each component in the dispersion medium and then mixing them.

[0070] The mixing step may be, for example, a step of mixing an active material, a binder solution containing a binder, a slurry (A) containing carbon black (A), a slurry (B) containing a first carbon nanotube (B), and a slurry (C) containing a second carbon nanotube (C). According to such a mixing step, a coating liquid in which each component is uniformly dispersed can be easily obtained, and destruction of the conductive material due to stirring during mixing can be suppressed.

[0071] The binder solution contains a binder and a dispersion medium. The dispersion medium in the binder solution can be appropriately selected from the above-described dispersion media. The dispersion medium in the binder solution may be the same as the dispersion media in the slurry (A), the slurry (B), and the slurry (C).

[0072] The content of the dispersion medium in the binder solution is not particularly limited as long as the binder can be sufficiently dissolved. The content of the dispersion medium in the binder solution may be, for example, 60% by mass or more, 70% by mass or more, 80% by mass or more, or 90% by mass or more based on the total amount of the binder solution. Also, the content of the dispersion medium in the binder solution may be, for example, 99.9% by mass or less, 99% by mass or less, 98% by mass or less, or 97% by mass or less based on the total amount of the binder solution.

[0073] Slurry (A) contains carbon black (A) and a dispersion medium. Slurry (A) may further contain a dispersant. The dispersion medium in Slurry (A) can be appropriately selected from the above-mentioned dispersion media. The dispersion medium of Slurry (A) may be the same as the dispersion media in the binder solution, Slurry (B), and Slurry (C).

[0074] The content of the dispersion medium in Slurry (A) is not particularly limited as long as carbon black (A) can be sufficiently dispersed. The content of the dispersion medium in Slurry (A) may be, for example, 60% by mass or more, 70% by mass or more, 80% by mass or more, or 90% by mass or more based on the total amount of Slurry (A). Also, the content of the dispersion medium in Slurry (A) may be, for example, 99.9% by mass or less, 99% by mass or less, 98% by mass or less, or 97% by mass or less based on the total amount of Slurry (A).

[0075] When Slurry (A) contains a dispersant, the content of the dispersant may be, for example, 5 parts by mass or more, 10 parts by mass or more, 15 parts by mass or more, or 20 parts by mass or more with respect to 100 parts by mass of carbon black (A). Also, the content of the dispersant may be, for example, 100 parts by mass or less, 90 parts by mass or less, 80 parts by mass or less, or 70 parts by mass or less with respect to 100 parts by mass of carbon black (A).

[0076] Slurry (B) contains the first carbon nanotube (B) and a dispersion medium. Slurry (B) may further contain a dispersant. The dispersion medium in Slurry (B) can be appropriately selected from the above-mentioned dispersion media. The dispersion medium of Slurry (B) may be the same as the dispersion media in the binder solution, Slurry (A) and Slurry (C).

[0077] The content of the dispersion medium in Slurry (B) is not particularly limited as long as the first carbon nanotube (B) is sufficiently dispersed. The content of the dispersion medium in Slurry (B) may be, for example, 60% by mass or more, 70% by mass or more, 80% by mass or more, or 90% by mass or more based on the total amount of Slurry (B). Also, the content of the dispersion medium in Slurry (B) may be, for example, 99.9% by mass or less, 99% by mass or less, 98% by mass or less, or 97% by mass or less based on the total amount of Slurry (B).

[0078] When Slurry (B) contains a dispersant, the content of the dispersant may be, for example, 5 parts by mass or more, 10 parts by mass or more, 15 parts by mass or more, or 20 parts by mass or more with respect to 100 parts by mass of the first carbon nanotube (B). Also, the content of the dispersant may be, for example, 100 parts by mass or less, 90 parts by mass or less, 80 parts by mass or less, or 70 parts by mass or less with respect to 100 parts by mass of the first carbon nanotube (B).

[0079] Slurry (C) contains the second carbon nanotube (C) and a dispersion medium. Slurry (C) may further contain a dispersant. The dispersion medium in Slurry (C) can be appropriately selected from the above-mentioned dispersion media. The dispersion medium of Slurry (C) may be the same as the dispersion media in the binder solution, Slurry (A) and Slurry (B).

[0080] The content of the dispersion medium in the slurry (C) is not particularly limited, and any amount may be used as long as the second carbon nanotube (C) is sufficiently dispersed. The content of the dispersion medium in the slurry (C) may be, for example, 60% by mass or more, 70% by mass or more, 80% by mass or more, or 90% by mass or more based on the total amount of the slurry (C). Also, the content of the dispersion medium in the slurry (C) may be, for example, 99.9% by mass or less, 99% by mass or less, 98% by mass or less, or 97% by mass or less based on the total amount of the slurry (C).

[0081] When the slurry (C) contains a dispersant, the content of the dispersant may be, for example, 5 parts by mass or more, 10 parts by mass or more, 15 parts by mass or more, or 20 parts by mass or more with respect to 100 parts by mass of the second carbon nanotube (C). Also, the content of the dispersant may be, for example, 100 parts by mass or less, 90 parts by mass or less, 80 parts by mass or less, or 70 parts by mass or less with respect to 100 parts by mass of the second carbon nanotube (C).

[0082] The mixing method in the mixing step is not particularly limited, and may be appropriately selected from known mixing methods (mixing means, mixing devices).

[0083] (Positive electrode) The positive electrode of this embodiment contains the above-described positive electrode composition. The positive electrode of this embodiment may include, for example, a composite layer composed of the positive electrode composition and a current collector. The composite layer may be disposed (laminated) on the current collector.

[0084] The current collector is not particularly limited, and a known current collector can be used without particular limitation. As the current collector, for example, a metal foil (metals such as gold, silver, copper, platinum, aluminum, iron, nickel, chromium, manganese, lead, tungsten, and titanium, and alloys having any one of these as a main component) is used. The current collector is generally provided in the form of a foil, but is not limited thereto, and perforated foil-shaped and mesh-shaped current collectors can also be used.

[0085] The composite material layer may contain the above-described positive electrode composition or may be composed of the above-described positive electrode composition.

[0086] The thickness of the composite material layer may be, for example, 20 μm or more, and from the viewpoint of further improving conductivity, it may be 30 μm or more, 40 μm or more, or 50 μm or more. Also, the thickness of the composite material layer may be, for example, 100 μm or less, and from the viewpoint of further improving conductivity, it may be 90 μm or less, 80 μm or less, or 70 μm or less.

[0087] The positive electrode of the present embodiment may be manufactured, for example, by a manufacturing method (manufacturing method of a positive electrode) including a composite material layer forming step of applying the above-described coating liquid for positive electrode formation onto a current collector and drying it to form a composite material layer on the current collector.

[0088] The manufacturing method of the positive electrode may further include a pressing step of pressing the composite material layer formed in the composite material layer forming step and the current collector in the stacking direction. The pressing method in the pressing step is not particularly limited, and may be, for example, a method such as roll pressing, die pressing, or calendar pressing.

[0089] The manufacturing method of the positive electrode may further include a drying step of removing moisture from the composite material layer after the pressing step. In the drying step, for example, residual moisture in the composite material layer may be removed by vacuum drying.

[0090] The positive electrode of the present embodiment can be suitably used as a positive electrode of a battery, particularly a secondary battery (for example, a lithium ion secondary battery).

[0091] (Battery) The battery of the present embodiment includes the above-described positive electrode. The battery of the present embodiment may be a secondary battery or may be a lithium ion secondary battery. Since the battery of the present embodiment includes the above-described positive electrode, it tends to have excellent cycle characteristics.

[0092] In the battery of the present embodiment, the configuration other than the positive electrode may be the same as that of a known battery. The method for manufacturing the battery of the present embodiment is not particularly limited, and it can be manufactured in the same manner as the manufacturing method of a known battery, except for using the above-described positive electrode.

[0093] The battery of the present embodiment may include, for example, the above-described positive electrode, a negative electrode, and a separator.

[0094] The separator is not particularly limited, and for example, a separator known as a separator for a lithium-ion secondary battery can be used without particular limitation. Examples of the separator include synthetic resins such as polyethylene and polypropylene. The separator is preferably a porous film because it has good electrolyte retention properties.

[0095] The negative electrode is not particularly limited, and for example, a negative electrode known as a negative electrode for a lithium-ion secondary battery can be used without particular limitation. The negative electrode may include, for example, a negative electrode composite material layer containing a negative electrode active material and a binder, and a negative electrode current collector.

[0096] The battery of the present embodiment may include, for example, an electrode group in which a positive electrode and a negative electrode are laminated or wound via a separator.

[0097] The battery of the present embodiment may have, for example, the positive electrode, the negative electrode, and the separator immersed in an electrolyte solution.

[0098] The electrolyte solution is not particularly limited, and for example, it may be a non-aqueous electrolyte solution containing a lithium salt. Examples of the non-aqueous solvent in the non-aqueous electrolyte solution containing a lithium salt include ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, and methyl ethyl carbonate. Examples of the lithium salt that can be dissolved in the non-aqueous solvent include lithium hexafluorophosphate, lithium tetrafluoroborate, and lithium trifluoromethanesulfonate. Further, the battery of the present embodiment may use an ion-conductive polymer or the like as an electrolyte.

[0099] The applications of the battery of this embodiment are not particularly limited. For example, it can be used in a wide range of fields such as portable AV devices such as digital cameras, video cameras, portable audio players, and portable liquid crystal televisions, portable information terminals such as notebook computers, smart phones, and mobile PCs, and other portable game devices, power tools, electric bicycles, hybrid automobiles, electric automobiles, and power storage systems.

[0100] As described above, the preferred embodiments of the present disclosure have been described, but the present disclosure is not limited to the above embodiments.

[0101] (Conductive material, slurry) For example, one aspect of the present disclosure relates to a conductive material including carbon black (A), a first carbon nanotube (B), and a second carbon nanotube (C). Another aspect of the present disclosure relates to a slurry including the conductive material and a dispersion medium. According to such a conductive material and slurry, the above-described positive electrode composition can be easily obtained.

[0102] Examples of the dispersion medium in the slurry can be the same as those in the coating liquid for forming the positive electrode described above.

[0103] The content of the dispersion medium in the slurry is not particularly limited as long as the conductive material is sufficiently dispersed. The content of the dispersion medium in the slurry may be, for example, 60% by mass or more, 70% by mass or more, 80% by mass or more, or 90% by mass or more based on the total amount of the slurry. Also, the content of the dispersion medium in the slurry may be, for example, 99.9% by mass or less, 99% by mass or less, 98% by mass or less, or 97% by mass or less based on the total amount of the slurry (C).

[0104] The slurry may further contain a dispersant. When the slurry contains a dispersant, the content of the dispersant may be, for example, 5 parts by mass or more, 10 parts by mass or more, 15 parts by mass or more, or 20 parts by mass or more with respect to 100 parts by mass of the conductive material. Also, the content of the dispersant may be, for example, 100 parts by mass or less, 90 parts by mass or less, 80 parts by mass or less, or 70 parts by mass or less with respect to 100 parts by mass of the conductive material.

[0105] The slurry may further contain other components other than the conductive material and the dispersant. Examples of the other components include a wetting agent, a defoaming agent, and the like.

[0106] The conductive material and the slurry can be used, for example, in the production of the above-described coating liquid for positive electrode formation. Also, the conductive material and the slurry can be used in applications such as a coating liquid for negative electrode formation and a coating liquid for a carbon-coated current collector.

Examples

[0107] Hereinafter, one aspect of the present disclosure will be described in more detail by way of examples, but the present disclosure is not limited to these examples.

[0108] (Preparation of Carbon Black) Carbon blacks (A-1) to (A-3) and (X-1) to (X-3) shown in Table 1 were prepared. In the table, AB means acetylene black, FB means furnace black, and KB means ketjen black.

[0109]

Table 1

[0110] (Preparation of Carbon Nanotubes) Carbon nanotubes (B-1) to (B-4) shown in Table 2 were prepared. Also, carbon nanotube (C-1) shown in Table 3 was prepared. In the tables, MWCNT means multi-walled carbon nanotube, and SWCNT means single-walled carbon nanotube.

[0111]

Table 2

[0112]

Table 3

[0113] (Preparation of Carbon Black Slurry) N-methyl-2-pyrrolidone (hereinafter referred to as NMP) was prepared as a dispersion medium, and polyvinyl alcohol (manufactured by Denka Co., Ltd., Poval B05) was prepared as a dispersant. 1.0 mass% of polyvinyl alcohol and 10.0 mass% of carbon black (any one of carbon blacks (A-1) to (A-3) and (X-1) to (X-3) in Table 1) were added to 89.0 mass% of NMP, and stirred with a planetary mixer (manufactured by Primix Corporation, Highvis Dispermic 3D-5 type) for 120 minutes to obtain a slurry. Next, the obtained slurry was charged into a bead mill (manufactured by Asazawa Fine Tech Co., Ltd., Mugunflow MGF2-ZA) equipped with zirconia beads (diameter 0.5 mm), and a dispersion treatment was performed. After the dispersion treatment, the zirconia beads were removed by filtration to prepare a carbon black slurry.

[0114] (Preparation of Carbon Nanotube Slurry) N-methyl-2-pyrrolidone (hereinafter referred to as NMP) was prepared as a dispersion medium, and polyvinyl alcohol (manufactured by Denka Co., Ltd., Poval B05) was prepared as a dispersant. 0.4% by mass of polyvinyl alcohol and 0.4% by mass of carbon nanotubes (any one of carbon nanotubes (B-1) to (B-4) in Table 2 and carbon nanotubes (C-1) in Table 3) were added to 99.2% by mass of NMP, and the mixture was stirred with a planetary mixer (manufactured by Primix Corporation, High-Speed Dispermix 3D-5 type) for 120 minutes to obtain a slurry. Next, the obtained slurry was charged into a bead mill (manufactured by Asazawa Fine Tech Co., Ltd., Mugunflow MGF2-ZA) equipped with zirconia beads (diameter 0.5 mm), and a dispersion treatment was performed. After the dispersion treatment, the zirconia beads were removed by filtration to prepare a slurry of carbon nanotubes.

[0115] <Example 1-1> (1) Preparation of Coating Liquid for Positive Electrode Formation Slurries of carbon black (A-1), carbon nanotubes (B-1), and carbon nanotubes (C-1) were prepared by the above method. Also, lithium nickel manganese cobalt oxide (manufactured by Beijing Easpring Material Technology Co., Ltd., "ME6E") with an average particle diameter D 50 of 10 μm was used as the active material, an NMP solution of polyvinylidene fluoride (manufactured by Solvey Co., Ltd., "Solef5130") was used as the binder, and NMP was prepared as the dispersion medium. In terms of solid ratio conversion, the amounts of each raw material were adjusted so that the active material was 97.55% by mass, the conductive material was 1.0% by mass (0.7% by mass of carbon black (A-1), 0.25% by mass of carbon nanotubes (B-1), and 0.05% by mass of carbon nanotubes (C-1)), the binder was 1.3% by mass, and the dispersant was 0.15% by mass. NMP was added until the viscosity became suitable for coating, and the mixture was uniformly mixed using a rotation-revolution mixer (manufactured by Shinchi Co., Ltd., Awatori Renkatarou ARV-310) to obtain a coating liquid for positive electrode formation.

[0116] (2) Manufacture of Positive Electrode The coating liquid for positive electrode preparation prepared in the above (1) was formed into a film on one side of an aluminum foil (manufactured by UACJ Corporation) with a thickness of 15 μm using an applicator to produce a laminate, which was left standing in a dryer and pre-dried at 105°C for 1 hour to completely remove NMP. Next, the dried laminate was pressed with a roll press at a linear pressure of 200 kg / cm so that the total thickness of the laminate became 80 μm. Then, it was vacuum dried at 170°C for 3 hours to completely remove residual moisture, and a positive electrode comprising a current collector and a composite material layer was obtained.

[0117] (3) Manufacture of negative electrode Pure water (manufactured by Kanto Chemical Co., Inc.) was used as the solvent, artificial graphite (manufactured by Hitachi Chemical Co., Ltd., "MAG-D") was used as the negative electrode active material, styrene-butadiene rubber (manufactured by Nippon Zeon Co., Ltd., "BM-400B", hereinafter referred to as SBR) was used as the binder, and carboxymethyl cellulose (manufactured by Daicel Corporation, "D2200", hereinafter referred to as CMC) was used as the dispersant. Next, they were weighed and mixed so that CMC was 1 mass% in solid content and artificial graphite was 97 mass% in solid content. Pure water was added to this mixture, and it was mixed using a planetary mixer (manufactured by Shin-Kei Co., Ltd., Awatori Rentaro ARV-310) until it became uniform to obtain a mixture. Next, it was weighed so that SBR was 2 mass% in solid content, added to the obtained mixture, and mixed using a planetary mixer (manufactured by Shin-Kei Co., Ltd., Awatori Rentaro ARV-310) until it became uniform to obtain a coating liquid for negative electrode formation. Next, the coating liquid for negative electrode formation was applied on a copper foil (manufactured by UACJ Corporation) with a thickness of 10 μm using an applicator to produce a laminate, which was left standing in a dryer and pre-dried at 60°C for 1 hour. Next, it was pressed with a roll press at a linear pressure of 50 kg / cm so that the total thickness of the laminate became 60 μm. Then, it was vacuum dried at 120°C for 3 hours to completely remove residual moisture, and a negative electrode comprising a current collector and a composite material layer was obtained.

[0118] (4) Manufacture of battery In a dry room controlled to a dew point of -50°C or lower, after processing the positive electrode to 40×40 mm and the negative electrode to 44×44 mm, an aluminum tab was welded to the positive electrode and a nickel tab was welded to the negative electrode, respectively. The coated surfaces of the positive and negative electrodes were made to face each other at the center, and a polyolefin microporous membrane processed to 45×45 mm was placed between the positive and negative electrodes. Next, a sheet-shaped exterior cut and processed to 70×140 mm square was folded in half at the center of the long side. Then, while arranging the exterior such that the aluminum tab for the positive electrode and the nickel tab for the negative electrode were exposed outside the exterior, the laminate of the positive electrode / polyolefin microporous membrane / negative electrode was sandwiched by the folded exterior. Next, using a heat sealer, two sides including the sides where the aluminum tab for the positive electrode and the nickel tab for the negative electrode of the exterior were exposed were heat-sealed. Then, from one side that was not heat-sealed, 2 g of an electrolyte solution (a solution containing ethylene carbonate / diethyl carbonate = 1 / 2 (volume ratio) and 1 M LiPF6 solution manufactured by Kishida Chemical Co., Ltd.) was injected. After allowing the electrolyte solution to thoroughly penetrate the positive electrode, negative electrode, and polyolefin microporous membrane, the remaining side of the exterior was heat-sealed while reducing the internal pressure with a vacuum heat sealer to obtain a lithium-ion secondary battery.

[0119] (5) Evaluation of the battery (5-1) Evaluation of the internal resistance The fabricated battery was charged at a constant current and constant voltage of 4.3 V with a 0.2C limit at 25°C, and then discharged at a constant current of 0.2C to 3.0 V. Next, after charging / discharging 5 cycles under the same conditions, it was charged to a 50% state of charge. Then, impedance measurement was performed at a vibration voltage of 5 mV in the frequency range of 1.5 MHz to 0.01 Hz to measure the internal resistance. The results are shown in Table 4.

[0120] (5-2) Evaluation of the cycle characteristics The fabricated battery was charged at a constant current and constant voltage of 4.3 V with a 1C limit at 25°C, and then discharged at a constant current of 1C to 3.0 V. The above charging and discharging were repeated 500 cycles, and the discharge capacity in each cycle was measured. As an index of the cycle characteristics of the battery, the capacity retention rate after 500 cycles with respect to the capacity retention rate after 1 cycle was calculated as the cycle capacity retention rate. The results are shown in Table 4.

[0121] <Example 1-2> The preparation of the coating liquid for forming the positive electrode, the production of the positive electrode, the production of the negative electrode, the production of the battery, and the evaluation of the battery were carried out in the same manner as in Example 1-1, except that the content ratio of carbon black (A-1), carbon nanotube (B-1), and carbon nanotube (C-1) was changed from 70:25:5 to 65:20:15. The results are shown in Table 4.

[0122] <Example 1-3> The preparation of the coating liquid for forming the positive electrode, the production of the positive electrode, the production of the negative electrode, the production of the battery, and the evaluation of the battery were carried out in the same manner as in Example 1-1, except that the content ratio of carbon black (A-1), carbon nanotube (B-1), and carbon nanotube (C-1) was changed from 70:25:5 to 40:30:30. The results are shown in Table 4.

[0123] <Example 1-4> The preparation of the coating liquid for forming the positive electrode, the production of the positive electrode, the production of the negative electrode, the production of the battery, and the evaluation of the battery were carried out in the same manner as in Example 1-1, except that the content ratio of carbon black (A-1), carbon nanotube (B-1), and carbon nanotube (C-1) was changed from 70:25:5 to 80:17:3. The results are shown in Table 4.

[0124] <Comparative Example 1-1> The preparation of the coating liquid for forming the positive electrode, the production of the positive electrode, the production of the negative electrode, the production of the battery, and the evaluation of the battery were carried out in the same manner as in Example 1-1, except that only carbon black (A-1) was used as the conductive material. The results are shown in Table 5.

[0125] <Comparative Example 1-2> The preparation of the coating liquid for forming the positive electrode, the production of the positive electrode, the production of the negative electrode, the production of the battery, and the evaluation of the battery were carried out in the same manner as in Example 1-1, except that only carbon nanotube (B-1) was used as the conductive material. The results are shown in Table 5.

[0126] <Comparative Example 1-3> Except for not using carbon nanotube (C-1) and changing the content ratio of carbon black (A-1), carbon nanotube (B-1), and carbon nanotube (C-1) from 70:25:5 to 70:30:0, the preparation of the coating liquid for positive electrode formation, the production of the positive electrode, the production of the negative electrode, the production of the battery, and the evaluation of the battery were carried out in the same manner as in Example 1-1. The results are shown in Table 5.

[0127] <Comparative Example 1-4> Except for not using carbon nanotube (B-1) and changing the content ratio of carbon black (A-1), carbon nanotube (B-1), and carbon nanotube (C-1) from 70:25:5 to 70:0:30, the preparation of the coating liquid for positive electrode formation, the production of the positive electrode, the production of the negative electrode, the production of the battery, and the evaluation of the battery were carried out in the same manner as in Example 1-1. The results are shown in Table 5.

[0128] <Comparative Example 1-5> Except for not using carbon black (A-1) and changing the content ratio of carbon black (A-1), carbon nanotube (B-1), and carbon nanotube (C-1) from 70:25:5 to 0:95:5, the preparation of the coating liquid for positive electrode formation, the production of the positive electrode, the production of the negative electrode, the production of the battery, and the evaluation of the battery were carried out in the same manner as in Example 1-1. The results are shown in Table 5.

[0129]

Table 4

[0130]

Table 5

[0131] <Example 2-1> Except for changing carbon black (A-1) to carbon black (A-2), the preparation of the coating liquid for positive electrode formation, the production of the positive electrode, the production of the negative electrode, the production of the battery, and the evaluation of the battery were carried out in the same manner as in Example 1-1. The results are shown in Table 6.

[0132] <Example 2-2> Except that carbon black (A-1) was changed to carbon black (A-3) and the content ratio of carbon black (A-3), carbon nanotube (B-1), and carbon nanotube (C-1) was set to 45:30:25, the preparation of the coating liquid for positive electrode formation, the production of the positive electrode, the production of the negative electrode, the production of the battery, and the evaluation of the battery were carried out in the same manner as in Example 1-1. The results are shown in Table 6.

[0133] <Comparative Example 2-1> Except that carbon black (A-1) was changed to carbon black (X-1), the preparation of the coating liquid for positive electrode formation, the production of the positive electrode, the production of the negative electrode, the production of the battery, and the evaluation of the battery were carried out in the same manner as in Example 1-1. The results are shown in Table 7.

[0134] <Comparative Example 2-2> Except that carbon black (A-1) was changed to carbon black (X-2), the preparation of the coating liquid for positive electrode formation, the production of the positive electrode, the production of the negative electrode, the production of the battery, and the evaluation of the battery were carried out in the same manner as in Example 1-1. The results are shown in Table 7.

[0135] <Comparative Example 2-3> Except that carbon black (A-1) was changed to carbon black (X-3), the preparation of the coating liquid for positive electrode formation, the production of the positive electrode, the production of the negative electrode, the production of the battery, and the evaluation of the battery were carried out in the same manner as in Example 1-1. The results are shown in Table 7.

[0136]

Table 6

[0137]

Table 7

[0138] <Example 3-1> Except for changing carbon nanotube (B-1) to carbon nanotube (B-2), the preparation of the coating liquid for positive electrode formation, the production of positive electrode, the production of negative electrode, the production of battery, and the evaluation of battery were carried out in the same manner as in Example 1-1. The results are shown in Table 8.

[0139] <Example 3-2> Except for changing carbon nanotube (B-1) to carbon nanotube (B-3), the preparation of the coating liquid for positive electrode formation, the production of positive electrode, the production of negative electrode, the production of battery, and the evaluation of battery were carried out in the same manner as in Example 1-1. The results are shown in Table 8.

[0140] <Example 3-3> Except for changing carbon nanotube (B-1) to carbon nanotube (B-4), the preparation of the coating liquid for positive electrode formation, the production of positive electrode, the production of negative electrode, the production of battery, and the evaluation of battery were carried out in the same manner as in Example 1-1. The results are shown in Table 9.

[0141] <Comparative Example 3-1> Except for changing carbon nanotube (B-1) to carbon nanotube (B-4), not using carbon nanotube (C-1), and changing the content ratio of carbon black (A-1) to carbon nanotube (B-4) to 70:30, the preparation of the coating liquid for positive electrode formation, the production of positive electrode, the production of negative electrode, the production of battery, and the evaluation of battery were carried out in the same manner as in Example 1-1. The results are shown in Table 9.

[0142]

Table 8

[0143]

Table 9

[0144] In Tables 4 to 9, "primary particle diameter (nm)" indicates the average primary particle diameter (nm) of carbon black. Also, "(A) / (B) / (C)" indicates the mass ratio of carbon black (A), the first carbon nanotube (B), and the second carbon nanotube (C).

[0145] From the above results, it was confirmed that the battery produced using the positive electrode composition according to the above-described embodiment has a small internal resistance and excellent cycle characteristics.

Claims

1. comprising an active material, a binder, and a conductive material, wherein the conductive material is carbon black (A) having an average primary particle diameter of 17 nm or more and 30 nm or less, a first carbon nanotube (B) having an average diameter of 2 nm or more and 15 nm or less, and a second carbon nanotube (C) having an average diameter of 0.5 nm or more and less than 2 nm, and is a positive electrode composition.

2. The positive electrode composition according to claim 1, wherein the carbon black (A) is selected from the group consisting of furnace black, acetylene black, and ketjen black.

3. The BET specific surface area of the carbon black (A) is 100 m ２ / g or more and 900 m ２ / g or less, and the positive electrode composition according to claim 1.

4. The positive electrode composition according to claim 1, wherein the content of the carbon black (A) is 30% by mass or more and 90% by mass or less based on the total amount of the conductive material.

5. The positive electrode composition according to claim 1, wherein the peak ratio (D / G) of the D band and the G band in the Raman spectrum of the first carbon nanotube (B) is 0.1 or more and 1.5 or less.

6. The positive electrode composition according to claim 1, wherein the peak ratio (D / G) of the D band and the G band in the Raman spectrum of the first carbon nanotube (B) is 0.3 or more and 1.4 or less.

7. The positive electrode composition according to claim 1, wherein the content of the first carbon nanotube (B) is 5% by mass or more and 50% by mass or less based on the total amount of the conductive material.

8. The positive electrode composition according to claim 1, wherein the content of the second carbon nanotube (C) is 1% by mass or more and 45% by mass or less based on the total amount of the conductive material.

9. A coating liquid for forming a positive electrode, comprising the positive electrode composition according to any one of claims 1 to 8 and a dispersion medium.

10. A positive electrode comprising the positive electrode composition according to any one of claims 1 to 8.

11. A battery comprising the positive electrode according to claim 10.

12. carbon black (A) having an average primary particle diameter of 17 nm or more and 30 nm or less, a first carbon nanotube (B) having an average diameter of 2 nm or more and 15 nm or less, and a second carbon nanotube (C) having an average diameter of 0.5 nm or more and less than 2 nm, and is a conductive material.

13. A slurry comprising the conductive material according to claim 12 and a dispersion medium.

14. comprising a mixing step of mixing an active material, a binder, a conductive material, and a dispersion medium, The conductive material includes carbon black (A) having an average primary particle diameter of 17 nm or more and 30 nm or less, first carbon nanotubes (B) having an average diameter of 2 nm or more and 15 nm or less, and second carbon nanotubes (C) having an average diameter of 0.5 nm or more and less than 2 nm. A method for manufacturing a coating liquid for forming a positive electrode.

15. The mixing step is a step of mixing the active material, a binder solution containing the binder, a slurry (A) containing the carbon black (A), a slurry (B) containing the first carbon nanotubes (B), and a slurry (C) containing the second carbon nanotubes (C). The manufacturing method according to claim 14.

16. A method for manufacturing a positive electrode, comprising a step of applying a coating liquid for forming a positive electrode manufactured by the manufacturing method according to claim 14 or 15 onto a current collector to form a composite layer containing the active material, the binder, and the conductive material on the current collector.

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