Positive electrode composition, coating solution for positive electrode formation, positive electrode, battery, conductive material, slurry, method for manufacturing coating solution for positive electrode formation, and method for manufacturing positive electrode

Abstract

A positive electrode composition including an active material, a binder, and a conductive material, wherein the conductive material includes carbon black (A) having an average primary particle size of 17-30 nm, first carbon nanotubes (B) having a peak ratio (D / G) of D-band to G-band in a Raman spectrum of 0.3-1.4, and second carbon nanotubes (C) having a peak ratio (D / G) of D-band to G-band in a Raman spectrum of less than 0.3.

Description

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

[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 producing a coating liquid for forming a positive electrode, and a method for producing a positive electrode.

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

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

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

[0005] JP 2008-227481 A

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

[0007] An object of the present disclosure is to provide a positive electrode composition capable of realizing a battery with excellent cycle characteristics. Another object of the present disclosure is to provide a positive electrode-forming coating liquid capable of realizing a battery with excellent cycle characteristics. Another object of the present disclosure is to provide a positive electrode capable of realizing a battery with excellent cycle characteristics. Another object of the present disclosure is to provide a battery with excellent cycle characteristics. Another object of the present disclosure is to provide a conductive material capable of realizing a battery with excellent cycle characteristics, and a slurry containing the conductive material. Another object of the present disclosure is to provide a method for producing a positive electrode-forming coating liquid capable of easily producing the above-mentioned positive electrode-forming coating liquid, and a method for producing a positive electrode capable of easily producing the above-mentioned positive electrode.

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

[14] . [1] A positive electrode composition comprising an active material, a binder, and a conductive material, wherein the conductive material comprises: carbon black (A) having an average primary particle diameter of 17 nm to 30 nm; first carbon nanotubes (B) having a peak ratio (D / G) of D band to G band in a Raman spectrum of 0.3 to 1.4; and second carbon nanotubes (C) having a peak ratio (D / G) of D band to G band in a Raman spectrum of less than 0.3. [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] A positive electrode composition according to [1], wherein the carbon black (A) has a BET specific surface area of ​​100 m ２ / g or more 900m ２ / g or less. [4] The positive electrode composition according to any one of [1] to [3], 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 any one of [1] to [4], wherein the content of the first carbon nanotubes (B) is 5% by mass or more and 50% by mass or less, based on the total amount of the conductive material. [6] The positive electrode composition according to any one of [1] to [5], wherein the content of the second carbon nanotubes (C) is 1% by mass or more and 45% by mass or less, based on the total amount of the conductive material. [7] A coating liquid for forming a positive electrode, comprising the positive electrode composition according to any one of [1] to [6] and a dispersion medium. [8] A positive electrode comprising the positive electrode composition according to any one of [1] to [6]. [9] A battery comprising the positive electrode according to [8].

[10] A conductive material comprising: carbon black (A) having an average primary particle size of 17 nm or more and 30 nm or less; first carbon nanotubes (B) having a peak ratio (D / G) of D band to G band in Raman spectrum of 0.3 or more and 1.4 or less; and second carbon nanotubes (C) having a peak ratio (D / G) of D band to G band in Raman spectrum of less than 0.3.

[11] A slurry comprising the conductive material according to

[10] and a dispersion medium.

[12] A method for producing a coating liquid for forming a positive electrode, comprising: a mixing step of mixing an active material, a binder, a conductive material, and a dispersion medium, wherein the conductive material comprises carbon black (A) having an average primary particle diameter of 17 nm to 30 nm, first carbon nanotubes (B) having a peak ratio (D / G) of D band to G band in Raman spectrum of 0.3 to 1.4, and second carbon nanotubes (C) having a peak ratio (D / G) of D band to G band in Raman spectrum of less than 0.3.

[13] The production method according to

[12] , wherein 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).

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

[12] or

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

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

[0010] Preferred embodiments of the present disclosure will be described in detail below. In this specification, carbon black may be abbreviated as "CB" and carbon nanotubes may be abbreviated as "CNT." In this specification, the tilde symbol "~" is used to indicate a numerical range that includes the numerical values ​​before and after it. Specifically, "X~Y" (X and Y are both numerical values) indicates "X or greater and Y or less."

[0011] (Positive Electrode Composition) The positive electrode composition of this embodiment includes 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 to 30 nm, first carbon nanotubes (B) having a peak ratio (D / G) of D band to G band in a Raman spectrum of 0.3 to 1.4, and second carbon nanotubes (C) having a peak ratio (D / G) of D band to G band in a Raman spectrum of less than 0.3.

[0012] The positive electrode composition of the present embodiment may be a material constituting a composite layer in a positive electrode. By using a positive electrode including a composite layer made of the positive electrode composition of the present embodiment, a battery with excellent cycle characteristics is realized.

[0013] The reason why the positive electrode composition of this embodiment exhibits the above-mentioned effects is believed to be as follows. The positive electrode composition of this embodiment combines carbon black having a spherical structure with carbon nanotubes having a fibrous structure. This combination is believed to improve the positive electrode composition of this embodiment's ability to follow the expansion and contraction of the positive electrode active material that accompanies the charge and discharge of the battery. In addition, the positive electrode composition of this embodiment contains two types of carbon nanotubes with different peak ratios (D / G). This further improves the above-mentioned followability, making it easier to maintain the conductive network in the positive electrode well even after repeated charge and discharge of the battery, which is believed to result in a battery with excellent cycle characteristics.

[0014] Each component of the positive electrode composition of this embodiment will be described in detail below.

[0015] <Conductive Material> The positive electrode composition of this 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, a conductive network formed in the positive electrode is likely to develop. Furthermore, when the average primary particle diameter of the carbon black (A) is 30 nm or less, a conductive network formed in the positive electrode is likely to develop. To achieve this effect more significantly, the average primary particle diameter of the carbon black (A) may be 27 nm or less, or 25 nm or less. That is, the average primary particle diameter of the carbon black (A) may be, for example, 17 to 30 nm, 17 to 27 nm, or 17 to 25 nm.

[0017] In this specification, the average primary particle size of carbon black (A) can be determined by measuring the primary particle sizes of 100 or more carbon black particles randomly selected from a 50,000x magnification image taken with a transmission electron microscope (TEM) and calculating the average value. Primary particles of carbon black have a small aspect ratio and are close to being spherical, but are not completely spherical. Therefore, in this specification, the primary particle size of carbon black is defined as the largest line segment connecting two points on the periphery of a primary particle in a TEM image.

[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) is, for example, 100 m ２ / g or more, ２ / g or more, 120m ２ / g or more, or 130m ２ / g or more. This tends to further develop the conductive network formed in the positive electrode. The BET specific surface area of ​​the carbon black (A) is, for example, 900 m ２ / g or less, and ２ / g or less, 880m ２ / g or less, or 870m ２ / g or less. This allows the conductive network formed in the positive electrode to develop more. That is, the BET specific surface area of ​​the carbon black (A) may be, for example, 100 to 900 m ２ / g, 100-890m ２ / g, 100-880m ２ / g, 100-870m ２ / g, 110-900m ２ / g, 110-890m ２ / g, 110-880m ２ / g, 110-870m ２ / g, 120-900m ２ / g, 120-890m ２ / g, 120-880m ２ / g, 120-870m ２ / g, 130-900m ２ / g, 130-890m ２ / g, 130-880m ２ / g, or 130 to 870 m ２ / g.

[0020] In this specification, the BET specific surface area of ​​carbon black (A) is a value measured by the static volume 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, and from the viewpoint of further improving 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. Furthermore, the content of carbon black (A) may be, for example, 90% 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 85% by mass or less, 80% by mass or less, or 75% by mass or less. That is, the content of carbon black (A) is, for example, 30 to 90 mass%, 30 to 85 mass%, 30 to 80 mass%, 30 to 75 mass%, 35 to 90 mass%, 35 to 85 mass%, 35 to 80 mass%, 35 to 75 mass%, 40 to 90 mass%, 40 to 85 mass%, 40 to 80 mass%, 40 to 75 mass%, 45 to 90 mass%, 45 to 85 mass%, 45 to 80 mass%, 45 to 85 mass%, 45 to 80 mass%, 45 to 9 ... Mass%, 45-75% by mass, 50-90% by mass, 50-85% by mass, 50-80% by mass, 50-75% by mass, 55-90% by mass, 55-85% by mass, 55-80% by mass, 55-75% by mass %, 60-90% by weight, 60-85% by weight, 60-80% by weight, 60-75% by weight, 65-90% by weight, 65-85% by weight, 65-80% by weight, or 65-75% by weight.

[0022] The positive electrode composition of this embodiment further contains first carbon nanotubes (B) as a conductive material. In the first carbon nanotubes (B), the peak ratio (D / G) of the D band to the G band in the Raman spectrum is 0.3 to 1.4.

[0023] In carbon nanotubes, 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 nanotubes. The peak ratio (D / G) of the first carbon nanotube (B) is 0.3 or more, and from the viewpoint of more easily developing a conductive network in the positive electrode, it may be 0.4 or more, 0.5 or more, or 0.6 or more. The peak ratio (D / G) of the first carbon nanotube (B) is 1.4 or less, and from the viewpoint of more easily developing a conductive network in the positive electrode, it may be 1.3 or less, 1.2 or less, 1.1 or less, 1.0 or less, or 0.9 or less. That is, the peak ratio (D / G) of the first carbon nanotube (B) may be, for example, 0.3 to 1.4, 0.3 to 1.3, 0.3 to 1.2, 0.3 to 1.1, 0.3 to 1.0, 0.3 to 0.9, 0.4 to 1.4, 0.4 to 1.3, 0.4 to 1.2, 0.4 to 1.1, 0.4 to 1.0, 0.4 to 0.9, 0.5 to 1.4, 0.5 to 1.3, 0.5 to 1.2, 0.5 to 1.1, 0.5 to 1.0, 0.5 to 0.9, 0.6 to 1.4, 0.6 to 1.3, 0.6 to 1.2, 0.6 to 1.1, 0.6 to 1.0, or 0.6 to 0.9.

[0024] In this specification, the Raman spectrum of carbon nanotubes measured using a microscopic laser Raman system (manufactured by Thermo Fisher Scientific, product name "Nicolet Almega XR") includes the G band (1600 cm －１ around 1350 cm －１ A vibration mode called the G band (near the G band) 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 the amorphous part. The lower the peak intensity ratio of the D band to the G band (D / G ratio), the more crystalline the carbon nanotube can be evaluated to be.

[0025] The average diameter of the first carbon nanotubes (B) may be, for example, 2 nm or more, and from the viewpoint of more easily developing a conductive network in the positive electrode, it may be 3 nm or more, 4 nm or more, or 5 nm or more. The average diameter of the first carbon nanotubes (B) may be, for example, 15 nm or less, and from the viewpoint of more easily developing a conductive network in the positive electrode, it may be 13 nm or less, 11 nm or less, or 10 nm or less. That is, the average diameter of the first carbon nanotubes (B) may be, for example, 2 to 15 nm, 2 to 13 nm, 2 to 11 nm, 2 to 10 nm, 3 to 15 nm, 3 to 13 nm, 3 to 11 nm, 3 to 10 nm, 4 to 15 nm, 4 to 13 nm, 4 to 11 nm, 4 to 10 nm, 5 to 15 nm, 5 to 13 nm, 5 to 11 nm, or 5 to 10 nm.

[0026] In this specification, the average diameter of carbon nanotubes refers to the average value of diameters measured based on images of carbon nanotubes observed with a transmission electron microscope (TEM). Specifically, the average diameter is obtained by taking 10 images of carbon nanotubes at a magnification of 200,000 using a transmission electron microscope JEM-2000FX (manufactured by JEOL Ltd.), measuring the diameters of 100 carbon nanotubes randomly selected from the obtained images by image analysis, and calculating the arithmetic mean.

[0027] 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 in the shape of a coaxial tube.

[0028] As the first carbon nanotube (B), a commercially available product may be used, such as Flotube 6000 or Flotube 7000 (both manufactured by Cnano Technology Ltd., MWCNT).

[0029] The content of the first carbon nanotubes (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, 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. Furthermore, the content of the first carbon nanotubes (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, 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. That is, the content of the first carbon nanotubes (B) is, for example, 5 to 50 mass%, 5 to 45 mass%, 5 to 40 mass%, 5 to 35 mass%, 5 to 30 mass%, 5 to 28 mass%, 10 to 50 mass%, 10 to 45 mass%, 10 to 40 mass%, 10 to 35 mass%, 10 to 30 mass%, 10 to 28 mass%, 15 to 50 mass%, 15 to 45 mass%, 15 to 40 mass%, 15 to 35 mass%, 15 to 30 mass%, Mass%, 15-28 mass%, 18-50 mass%, 18-45 mass%, 18-40 mass%, 18-35 mass%, 18-30 mass%, 18-28 mass%, 20-50 mass%, 20-45 mass%, 20-40 mass% %, 20-35% by weight, 20-30% by weight, 20-28% by weight, 22-50% by weight, 22-45% by weight, 22-40% by weight, 22-35% by weight, 22-30% by weight, or 22-28% by weight.

[0030] The positive electrode composition of this embodiment further contains second carbon nanotubes (C) as a conductive material. In the second carbon nanotubes (C), the peak ratio (D / G) of the D band to the G band in the Raman spectrum is less than 0.3.

[0031] The peak ratio (D / G) of the second carbon nanotubes (C) is less than 0.3, and from the viewpoint of further improving the conductivity, it may be less than 0.2 or less than 0.1. The peak ratio (D / G) of the second carbon nanotubes (C) may be, for example, 0.01 or more, and from the viewpoint of further improving the conductivity, it may be 0.02 or more, 0.03 or more, 0.04 or more, or 0.05 or more. That is, the peak ratio (D / G) of the second carbon nanotube (C) may be 0.02 or more and less than 0.3, 0.02 or more and less than 0.2, 0.02 or more and less than 0.1, 0.03 or more and less than 0.3, 0.03 or more and less than 0.2, 0.03 or more and less than 0.1, 0.04 or more and less than 0.3, 0.04 or more and less than 0.2, 0.04 or more and less than 0.1, 0.05 or more and less than 0.3, 0.05 or more and less than 0.2, or 0.05 or more and less than 0.1.

[0032] The average diameter of the second carbon nanotubes (C) may be, for example, 0.5 nm or more, and from the viewpoint of more easily developing a conductive network in the positive electrode, may be 0.6 nm or more, or 0.7 nm or more. The average diameter of the second carbon black (C) may be, for example, less than 2 nm, and from the viewpoint of more easily developing a conductive network in the positive electrode, 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. That is, the average diameter of the second carbon nanotubes (C) may be, for example, 0.5 nm or more and less than 2 nm, 0.5 to 1.7 nm, 0.5 to 1.5 nm, 0.5 to 1.3 nm, 0.5 to 1.1 nm, 0.5 to 1.0 nm, 0.6 nm or more and less than 2 nm, 0.6 to 1.7 nm, 0.6 to 1.5 nm, 0.6 to 1.3 nm, 0.6 to 1.1 nm, 0.6 to 1.0 nm, 0.7 nm or more and less than 2 nm, 0.7 to 1.7 nm, 0.7 to 1.5 nm, 0.7 to 1.3 nm, 0.7 to 1.1 nm, or 0.7 to 1.0 nm.

[0033] 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 made of graphene sheets, and the double-walled carbon nanotube may be a carbon nanotube having a structure in which two layers of graphene sheets are stacked in a coaxial tubular shape.

[0034] The second carbon nanotubes (C) may be commercially available products, such as Signis CG300 (manufactured by CHASM, SWCNT).

[0035] The content of the second carbon nanotubes (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 the cycle characteristics, 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. The content of the first carbon nanotubes (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 the cycle characteristics, 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. That is, the content of the second carbon nanotubes (C) is, for example, 1 to 45 mass%, 1 to 40 mass%, 1 to 35 mass%, 1 to 30 mass%, 1 to 28 mass%, 1 to 25 mass%, 3 to 45 mass%, 3 to 40 mass%, 3 to 35 mass%, 3 to 30 mass%, 3 to 28 mass%, 3 to 25 mass%, 5 to 45 mass%, 5 to 40 mass%, 5 to 35 mass%, 5 to 30 mass%, 5 to 28 mass%, 5 to 25 mass%, 10 to 45 mass%, 10 to 40 mass%, 10 to 35 mass%, 10 to 30 mass%, 10 to 28 mass%, 10 ... ~25% by mass, 15-45% by mass, 15-40% by mass, 15-35% by mass, 15-30% by mass, 15-28% by mass, 15-25% by mass, 18-45% by mass, 18-40% by mass, 18-35% by mass, 18-30% by mass, 18-28% by mass, 18-25% by mass, 2 It may be 0-45% by mass, 20-40% by mass, 20-35% by mass, 20-30% by mass, 20-28% by mass, 20-25% by mass, 22-45% by mass, 22-40% by mass, 22-35% by mass, 22-30% by mass, 22-28% by mass, or 22-25% by mass.

[0036] The positive electrode composition of this embodiment may further contain, as a conductive material, another component (D) other than the carbon black (A), the first carbon nanotubes (B), and the second carbon nanotubes (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 more significantly obtaining the above-mentioned effects of the combined use of carbon black (A), the first carbon nanotubes (B), and the second carbon nanotubes (C), 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, 1% by mass or less, or 0% by mass. That is, the total content of carbon black (A), the first carbon nanotubes (B), and the second carbon nanotubes (C) may be, for example, more than 50% by mass based on the total amount of the conductive material, and from the viewpoint of more significantly obtaining the above-mentioned effects of the combined use of carbon black (A), the first carbon nanotubes (B), and the second carbon nanotubes (C), 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, 99% by mass or more, or even 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 a 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 a conductive network, may be 5% by mass or less, 3% by mass or less, or 1% by mass or less. That is, the content of the conductive material may be, for example, 0.05 to 10 mass%, 0.05 to 5 mass%, 0.05 to 3 mass%, 0.05 to 1 mass%, 0.1 to 10 mass%, 0.1 to 5 mass%, 0.1 to 3 mass%, 0.1 to 1 mass%, 0.3 to 10 mass%, 0.3 to 5 mass%, 0.3 to 3 mass%, 0.3 to 1 mass%, 0.5 to 10 mass%, 0.5 to 5 mass%, 0.5 to 3 mass%, or 0.5 to 1 mass%, based on the total amount of the positive electrode composition.

[0040] <Active Material> The positive electrode composition of this embodiment contains an active material. The active material may be any material that can reversibly store and release cations. The active material may also be referred to as a positive electrode active material.

[0041] The active material is not particularly limited, and any known active material used in lithium ion secondary batteries can be used without particular limitation, such as lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel-manganese-cobalt oxide, and lithium iron phosphate.

[0042] The active material has a volume resistivity of, for example, 1×10 ４ The lithium-containing composite oxide may be a lithium-containing composite oxide containing manganese having a resistivity of Ω cm or more, or a lithium-containing polyanion compound. Examples of the lithium-containing composite oxide containing manganese include LiMnO ２ , LiMnO ３ , LiMn ２ O ３ , Li １＋ｘ Mn ２－ｘ O ４ Lithium manganate such as LiMn (where x = 0 to 0.33); ｘ Ni ｙ Co ｚ O ２ (However, x+y+z=1, 0≦y<1, 0≦z<1, 0≦x<1), Li １＋ｘ Mn ２－ｘ－ｙ M ｙ O ４ (where x = 0 to 0.33, y = 0 to 1.0, 2-x-y > 0), LiMn ２－ｘ M ｘ O ２ (where x = 0.01 to 0.1), Li ２ Mn ３ MO ８ Examples of lithium-containing polyanion compounds include composite oxides containing one or more transition metal elements such as LiFePO ４ , LiMnPO ４ , Li ２ MPO ４ Examples of suitable anionic compounds include polyanionic compounds such as F (wherein M is at least one metal selected from Co, Ni, Fe, Cr, and Zn), in which M in each composition formula is at least one metal selected from the group consisting of Fe, Co, Ni, Al, Cu, Mg, Cr, Zn, and Ta.

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

[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. Furthermore, 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 obtaining a sufficient battery capacity and more significantly achieving the above-mentioned effects of the conductive material, it may be 99% by mass or less, 98% by mass or less, or 97% by mass or less. That is, the content of the active material may be, for example, 80 to 99.9 mass%, 80 to 99 mass%, 80 to 98 mass%, 80 to 97 mass%, 85 to 99.9 mass%, 85 to 99 mass%, 85 to 98 mass%, 85 to 97 mass%, 90 to 99.9 mass%, 90 to 99 mass%, 90 to 98 mass%, 90 to 97 mass%, 95 to 99.9 mass%, 95 to 99 mass%, 95 to 98 mass%, or 95 to 97 mass%, based on the total amount of the positive electrode composition.

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

[0046] 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, a random copolymer, an alternating copolymer, a graft copolymer, or a block copolymer. As the binder, polyvinylidene fluoride is preferred from the viewpoint of excellent voltage resistance.

[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. From the viewpoint of improving binding, it may be 1% by mass or more, 1.5% by mass or more, or 2% by mass or more. Furthermore, the content of the binder may be, for example, 10% by mass or less based on the total amount of the positive electrode composition. From the viewpoint of further improving battery capacity, it may be 8% by mass or less, 6% by mass or less, or 4% by mass or less. That is, the content of the binder may be, for example, 0.5 to 10% by mass, 0.5 to 8% by mass, 0.5 to 6% by mass, 0.5 to 4% by mass, 1 to 10% by mass, 1 to 8% by mass, 1 to 6% by mass, 1 to 4% by mass, 1.5 to 10% by mass, 1.5 to 8% by mass, 1.5 to 6% by mass, 1.5 to 4% by mass, 2 to 10% by mass, 2 to 8% by mass, 2 to 6% by mass, or 2 to 4% by mass based on the total amount of the positive electrode composition.

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

[0049] <Dispersant> The dispersant is a component that has a function of assisting dispersion of the conductive material in the dispersion medium. When a positive electrode composition is produced 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 polymeric dispersants and low molecular weight dispersants, and from the viewpoint of long-term dispersion stability of the conductive material, polymeric 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 relative to 100 parts by mass of the conductive material, and from the viewpoint of suppressing a decrease in conductivity due to the dispersant, 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 relative to 100 parts by mass of the conductive material, and from the viewpoint of further improving the dispersibility of the conductive material, may be 10 parts by mass or more, 15 parts by mass or more, or 20 parts by mass or more. That is, the content of the dispersant may be, for example, 5 to 100 parts by mass, 5 to 80 parts by mass, 5 to 60 parts by mass, 5 to 40 parts by mass, 10 to 100 parts by mass, 10 to 80 parts by mass, 10 to 60 parts by mass, 10 to 40 parts by mass, 15 to 100 parts by mass, 15 to 80 parts by mass, 15 to 60 parts by mass, 15 to 40 parts by mass, 20 to 100 parts by mass, 20 to 80 parts by mass, 20 to 60 parts by mass, or 20 to 40 parts by mass, relative to 100 parts by mass of the conductive material.

[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, and from the viewpoint of suppressing a decrease in conductivity due to the dispersant, may be 5% by mass or less, 3% by mass or less, or 1% by mass or less. When the positive electrode composition of this 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, and from the viewpoint of further improving the dispersibility of the conductive material, may be 0.1% by mass or more, 0.3% by mass or more, or 0.5% by mass or more. That is, the content of the dispersant may be, for example, 0.05 to 10 mass%, 0.05 to 5 mass%, 0.05 to 3 mass%, 0.05 to 1 mass%, 0.1 to 10 mass%, 0.1 to 5 mass%, 0.1 to 3 mass%, 0.1 to 1 mass%, 0.3 to 10 mass%, 0.3 to 5 mass%, 0.3 to 3 mass%, 0.3 to 1 mass%, 0.5 to 10 mass%, 0.5 to 5 mass%, 0.5 to 3 mass%, or 0.5 to 1 mass%, based on the total amount of the positive electrode composition.

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

[0054] Other ingredients include, for example, wetting agents, defoaming agents, and the like.

[0055] The content of the 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. 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, or 99.9% by mass or more, based on the total amount of the positive electrode composition, or may be 100% by mass.

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

[0057] The positive electrode composition of this embodiment may be formed, for example, by applying a positive electrode-forming coating liquid described below and drying it.

[0058] (Positive Electrode Forming Coating Liquid) The positive electrode forming coating liquid of this embodiment contains an active material, a binder, a conductive material, and a dispersion medium. The positive electrode forming coating liquid of this embodiment may further contain a dispersant.

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

[0060] The contents of the active material, binder, conductive material, and dispersant in the coating liquid for forming a positive electrode of the present embodiment (based on the total amount of solids in the coating liquid for forming a positive electrode) 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 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, and methyl isobutyl ketone. Of these, N-methyl-2-pyrrolidone is preferred from the viewpoint of excellent dispersibility.

[0062] The content of the dispersion medium is not particularly limited as long as it is within a range that allows sufficient coatability of the positive electrode-forming coating liquid to 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 positive electrode-forming coating liquid. Furthermore, 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 positive electrode-forming coating liquid. That is, the content of the dispersion medium may be, for example, 10 to 90 mass%, 10 to 80 mass%, 10 to 70 mass%, 10 to 60 mass%, 20 to 90 mass%, 20 to 80 mass%, 20 to 70 mass%, 20 to 60 mass%, 30 to 90 mass%, 30 to 80 mass%, 30 to 70 mass%, 30 to 60 mass%, 40 to 90 mass%, 40 to 80 mass%, 40 to 70 mass%, or 40 to 60 mass%, based on the total amount of the positive electrode-forming coating liquid.

[0063] The positive electrode-forming coating liquid of this embodiment can form a composite layer composed of the above-mentioned 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 positive electrode-forming coating liquid.

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

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

[0066] The coating liquid for forming a positive electrode of the present embodiment may be applied to, for example, a current collector and dried, thereby forming a composite layer made of the positive electrode composition on the current collector, thereby obtaining a positive electrode including the current collector and the composite layer.

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

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

[0069] The mixing step may be a step in which each component is dispersed in a dispersion medium at once, or a step in which each component is dispersed in a dispersion medium separately and then mixed.

[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 first carbon nanotubes (B), and a slurry (C) containing second carbon nanotubes (C). Such a mixing step makes it easy to obtain a coating liquid in which each component is uniformly dispersed, and can prevent damage to the conductive material due to stirring during mixing.

[0071] The binder solution contains a binder and a dispersion medium. The dispersion medium in the binder solution can be appropriately selected from the dispersion media described above. The dispersion medium in the binder solution may be the same as the dispersion medium 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 is 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. Furthermore, 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. That is, the content of the dispersion medium in the binder solution may be, for example, 60 to 99.9 mass%, 60 to 99 mass%, 60 to 98 mass%, 60 to 97 mass%, 70 to 99.9 mass%, 70 to 99 mass%, 70 to 98 mass%, 70 to 97 mass%, 80 to 99.9 mass%, 80 to 99 mass%, 80 to 98 mass%, 80 to 97 mass%, 90 to 99.9 mass%, 90 to 99 mass%, 90 to 98 mass%, or 90 to 97 mass% based on the total amount of the binder solution.

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

[0074] The content of the dispersion medium in the slurry (A) is not particularly limited, as long as the carbon black (A) is sufficiently dispersed. The content of the dispersion medium in the 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 the slurry (A). Furthermore, the content of the dispersion medium in the 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 the slurry (A). That is, the content of the dispersion medium in the slurry (A) is, for example, 60 to 99.9 mass%, 60 to 99 mass%, 60 to 98 mass%, 60 to 97 mass%, 70 to 99.9 mass%, 70 to 99 mass%, 70 to 98 mass%, 70 to 97 mass%, 80 to 99.9 mass%, 80 to 99 mass%, 80 to 98 mass%, 80 to 97 mass%, 90 to 99.9 mass%, 90 to 99 mass%, 90 to 98 mass%, or 90 to 97 mass%, based on the total amount of the slurry (A).

[0075] When the 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, per 100 parts by mass of the carbon black (A). 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, per 100 parts by mass of the carbon black (A). That is, when the slurry (A) contains a dispersant, the content of the dispersant may be, for example, 5 to 100 parts by mass, 5 to 90 parts by mass, 5 to 80 parts by mass, 5 to 70 parts by mass, 10 to 100 parts by mass, 10 to 90 parts by mass, 10 to 80 parts by mass, 10 to 70 parts by mass, 15 to 100 parts by mass, 15 to 90 parts by mass, 15 to 80 parts by mass, 15 to 70 parts by mass, 20 to 100 parts by mass, 20 to 90 parts by mass, 20 to 80 parts by mass, or 20 to 70 parts by mass, relative to 100 parts by mass of the carbon black (A).

[0076] The slurry (B) contains the first carbon nanotubes (B) and a dispersion medium. The slurry (B) may further contain a dispersant. The dispersion medium in the slurry (B) may be appropriately selected from the dispersion media described above. The dispersion medium in the slurry (B) may be the same as the dispersion medium in the binder solution, the slurry (A), and the slurry (C).

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

[0078] When the 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, relative to 100 parts by mass of the first carbon nanotubes (B). Moreover, 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, relative to 100 parts by mass of the first carbon nanotubes (B). That is, when the slurry (B) contains a dispersant, the content of the dispersant may be, for example, 5 to 100 parts by mass, 5 to 90 parts by mass, 5 to 80 parts by mass, 5 to 70 parts by mass, 10 to 100 parts by mass, 10 to 90 parts by mass, 10 to 80 parts by mass, 10 to 70 parts by mass, 15 to 100 parts by mass, 15 to 90 parts by mass, 15 to 80 parts by mass, 15 to 70 parts by mass, 20 to 100 parts by mass, 20 to 90 parts by mass, 20 to 80 parts by mass, or 20 to 70 parts by mass, relative to 100 parts by mass of the first carbon nanotubes (B).

[0079] The slurry (C) contains the second carbon nanotubes (C) and a dispersion medium. The slurry (C) may further contain a dispersant. The dispersion medium in the slurry (C) may be appropriately selected from the dispersion media described above. The dispersion medium in the slurry (C) may be the same as the dispersion medium in the binder solution, the slurry (A), and the slurry (B).

[0080] The content of the dispersion medium in the slurry (C) is not particularly limited, as long as the second carbon nanotubes (C) are sufficiently dispersed. The content of the dispersion medium in the slurry (C) may be, for example, 60 mass% or more, 70 mass% or more, 80 mass% or more, or 90 mass% or more, based on the total amount of the slurry (C). Furthermore, the content of the dispersion medium in the slurry (C) may be, for example, 99.9 mass% or less, 99 mass% or less, 98 mass% or less, or 97 mass% or less, based on the total amount of the slurry (C). That is, the content of the dispersion medium in the slurry (C) is, for example, 60 to 99.9 mass%, 60 to 99 mass%, 60 to 98 mass%, 60 to 97 mass%, 70 to 99.9 mass%, 70 to 99 mass%, 70 to 98 mass%, 70 to 97 mass%, 80 to 99.9 mass%, 80 to 99 mass%, 80 to 98 mass%, 80 to 97 mass%, 90 to 99.9 mass%, 90 to 99 mass%, 90 to 98 mass%, or 90 to 97 mass%, 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, relative to 100 parts by mass of the second carbon nanotubes (C). Furthermore, 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, relative to 100 parts by mass of the second carbon nanotubes (C). That is, when the slurry (C) contains a dispersant, the content of the dispersant may be, for example, 5 to 100 parts by mass, 5 to 90 parts by mass, 5 to 80 parts by mass, 5 to 70 parts by mass, 10 to 100 parts by mass, 10 to 90 parts by mass, 10 to 80 parts by mass, 10 to 70 parts by mass, 15 to 100 parts by mass, 15 to 90 parts by mass, 15 to 80 parts by mass, 15 to 70 parts by mass, 20 to 100 parts by mass, 20 to 90 parts by mass, 20 to 80 parts by mass, or 20 to 70 parts by mass, per 100 parts by mass of the second carbon nanotubes (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 includes the above-described positive electrode composition. The positive electrode of this embodiment may include, for example, a composite layer made 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 known current collectors can be used without any particular limitation. For example, metal foils (metals such as gold, silver, copper, platinum, aluminum, iron, nickel, chromium, manganese, lead, tungsten, and titanium, and alloys containing any one of these as a main component) are used as current collectors. Current collectors are generally provided in the form of foils, but are not limited thereto, and perforated foil and mesh current collectors can also be used.

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

[0086] The thickness of the composite 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. Furthermore, the thickness of the composite 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. That is, the thickness of the composite layer may be, for example, 20 to 100 μm, 20 to 90 μm, 20 to 80 μm, 20 to 70 μm, 30 to 100 μm, 30 to 90 μm, 30 to 80 μm, 30 to 70 μm, 40 to 100 μm, 40 to 90 μm, 40 to 80 μm, 40 to 70 μm, 50 to 100 μm, 50 to 90 μm, 50 to 80 μm, or 50 to 70 μm.

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

[0088] The method for producing a positive electrode may further include a pressurizing step of pressing the composite layer formed in the composite layer forming step and the current collector in the stacking direction. The pressurizing method in the pressurizing step is not particularly limited, and may be, for example, a roll press, a mold press, a calendar press, or the like.

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

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

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

[0092] The battery of this embodiment may have the same configuration as known batteries except for the positive electrode. The method for producing the battery of this embodiment is not particularly limited, and the battery may be produced by the same method as known batteries except for using the above-described positive electrode.

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

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

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

[0096] The battery of this embodiment may include, for example, an electrode group in which a positive electrode and a negative electrode are stacked or wound with a separator interposed therebetween.

[0097] In the battery of this embodiment, for example, the positive electrode, the negative electrode, and the separator may be immersed in the electrolyte solution.

[0098] The electrolyte is not particularly limited and may be, for example, a non-aqueous electrolyte containing a lithium salt. Examples of non-aqueous solvents in non-aqueous electrolytes containing a lithium salt include ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, and methyl ethyl carbonate. Examples of lithium salts that can be dissolved in non-aqueous solvents include lithium hexafluorophosphate, lithium borotetrafluoride, and lithium trifluoromethanesulfonate. The battery of this embodiment may also use an ion-conducting polymer or the like as the electrolyte.

[0099] The uses of the battery of the present embodiment are not particularly limited, and the battery can be used in a wide range of fields, for example, portable AV devices such as digital cameras, video cameras, portable audio players, and portable LCD televisions, portable information terminals such as notebook personal computers, smartphones, and mobile PCs, as well as portable game devices, power tools, electric bicycles, hybrid vehicles, electric vehicles, and power storage systems.

[0100] Although the preferred embodiments of the present disclosure have been described above, 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), first carbon nanotubes (B), and second carbon nanotubes (C). Another aspect of the present disclosure relates to a slurry including the conductive material and a dispersion medium. With 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 include the same dispersion medium as 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 mass % or more, 70 mass % or more, 80 mass % or more, or 90 mass % or more, based on the total amount of the slurry. Furthermore, the content of the dispersion medium in the slurry may be, for example, 99.9 mass % or less, 99 mass % or less, 98 mass % or less, or 97 mass % or less, based on the total amount of the slurry (C). That is, the content of the dispersion medium in the slurry is, for example, 60 to 99.9 mass%, 60 to 99 mass%, 60 to 98 mass%, 60 to 97 mass%, 70 to 99.9 mass%, 70 to 99 mass%, 70 to 98 mass%, 70 to 97 mass%, 80 to 99.9 mass%, 80 to 99 mass%, 80 to 98 mass%, 80 to 97 mass%, 90 to 99.9 mass%, 90 to 99 mass%, 90 to 98 mass%, or 90 to 97 mass%, based on the total amount of the slurry.

[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 relative to 100 parts by mass of the conductive material. Furthermore, 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 relative to 100 parts by mass of the conductive material. That is, when the slurry contains a dispersant, the content of the dispersant may be, for example, 5 to 100 parts by mass, 5 to 90 parts by mass, 5 to 80 parts by mass, 5 to 70 parts by mass, 10 to 100 parts by mass, 10 to 90 parts by mass, 10 to 80 parts by mass, 10 to 70 parts by mass, 15 to 100 parts by mass, 15 to 90 parts by mass, 15 to 80 parts by mass, 15 to 70 parts by mass, 20 to 100 parts by mass, 20 to 90 parts by mass, 20 to 80 parts by mass, or 20 to 70 parts by mass, relative to 100 parts by mass of the conductive material.

[0105] The slurry may further contain other components in addition to the conductive material and the dispersant, such as a wetting agent and a defoaming agent.

[0106] The conductive material and the slurry can be used, for example, to produce the coating liquid for forming a positive electrode described above. The conductive material and the slurry can also be used for applications such as a coating liquid for forming a negative electrode and a coating liquid for a carbon-coated current collector.

[0107] Hereinafter, one embodiment of the present disclosure will be described in more detail with reference to 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]

[0110] (Preparation of Carbon Nanotubes) Carbon nanotubes (B-1), (B-2), (Y-1), and (Y-2) shown in Table 2 were prepared. Carbon nanotubes (C-1) shown in Table 3 were also prepared. In the table, MWCNT means multi-walled carbon nanotubes, and SWCNT means single-walled carbon nanotubes.

[0111]

[0112]

[0113] (Preparation of Carbon Black Slurry) N-methyl-2-pyrrolidone (hereinafter referred to as NMP) was prepared as a dispersion medium, and polyvinyl alcohol (Poval B05, manufactured by Denka Co., Ltd.) was prepared as a dispersant. 1.0% by mass of polyvinyl alcohol and 10.0% by mass of carbon black (any of carbon blacks (A-1) to (A-3) and (X-1) to (X-3) in Table 1) were added to 89.0% by mass of NMP, and the mixture was stirred for 120 minutes using a planetary mixer (Hivis Dispermix 3D-5, manufactured by Primix Corporation) to obtain a slurry. The resulting slurry was then placed in a bead mill (Mugen Flow MGF2-ZA, manufactured by Ashizawa Finetech Co., Ltd.) equipped with zirconia beads (0.5 mm diameter) and subjected to a dispersion treatment. After the dispersion treatment, the zirconia beads were removed by filtration to produce 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 (Poval B05, manufactured by Denka Co., Ltd.) was prepared as a dispersant. 0.4% by mass of polyvinyl alcohol and 0.4% by mass of carbon nanotubes (any of carbon nanotubes (B-1), (B-2), (Y-1), and (Y-2) in Table 2 and carbon nanotube (C-1) in Table 3) were added to 99.2% by mass of NMP, and the mixture was stirred for 120 minutes using a planetary mixer (Hivis Dispermix 3D-5, manufactured by Primix Corporation) to obtain a slurry. The obtained slurry was then placed in a bead mill (Mugen Flow MGF2-ZA, manufactured by Ashizawa Finetech Co., Ltd.) equipped with zirconia beads (diameter 0.5 mm) and subjected to a dispersion treatment. After the dispersion treatment, the zirconia beads were removed by filtration to produce a carbon nanotube slurry.

[0115] Example 1-1 (1) Preparation of coating liquid for forming positive electrode A slurry of carbon black (A-1), a slurry of carbon nanotubes (B-1), and a slurry of carbon nanotubes (C-1) were prepared by the method described above. ５０A 10 μm diameter nickel manganese cobalt oxide lithium (Beijing Dangsheng Co., Ltd., "ME6E"), an NMP solution of polyvinylidene fluoride as a binder (Solvey Co., Ltd., "Solef5130"), and NMP as a dispersion medium were prepared. The amount of each raw material was adjusted to 97.55% by mass, 1.0% by mass (carbon black (A-1) 0.7% by mass, carbon nanotubes (B-1) 0.25% by mass, carbon nanotubes (C-1) 0.05% by mass), 1.3% by mass, and 0.15% by mass of the binder, and NMP was added until a coatable viscosity was achieved, and the mixture was mixed until uniform using a planetary mixer (Thinky Corporation, Awatori Rentaro ARV-310) to obtain a coating liquid for forming a positive electrode.

[0116] (2) Production of Positive Electrode The positive electrode-forming coating solution prepared in (1) above was applied to one side of a 15 μm thick aluminum foil (manufactured by UACJ Corporation) using an applicator to form a laminate, which was then placed in a dryer and pre-dried at 105 ° C for 1 hour to completely remove the NMP. Next, the dried laminate was pressed with a roll press at a linear pressure of 200 kg / cm so that the overall thickness of the laminate became 80 μm. Next, it was vacuum dried at 170 ° C for 3 hours to completely remove residual moisture, and a positive electrode comprising a current collector and a composite layer was obtained.

[0117] (3) Production of negative electrode Pure water (manufactured by Kanto Chemical Co., Ltd.) as a solvent, artificial graphite (manufactured by Hitachi Chemical Co., Ltd., "MAG-D") as a negative electrode active material, styrene butadiene rubber (manufactured by Nippon Zeon Co., Ltd., "BM-400B", hereinafter referred to as SBR) as a binder, and carboxymethyl cellulose (manufactured by Daicel Corporation, "D2200", hereinafter referred to as CMC) as a dispersant were prepared. Next, CMC was weighed and mixed so that it was 1% by mass in solids content and 97% by mass in solids content, and pure water was added to this mixture, and a rotation-revolution mixer (manufactured by Thinky Corporation, Awatori Rentaro ARV-310) was used to mix until uniform. Next, SBR was weighed so that it was 2% by mass in solids content, and added to the obtained mixture, and a rotation-revolution mixer (manufactured by Thinky Corporation, Awatori Rentaro ARV-310) was used to mix until uniform, and a coating liquid for forming a negative electrode was obtained. Next, the negative electrode-forming coating liquid was applied to a 10 μm-thick copper foil (manufactured by UACJ Corporation) using an applicator to prepare a laminate, which was then placed in a dryer and pre-dried at 60° C. for 1 hour. Next, the laminate was pressed with a roll press at a linear pressure of 50 kg / cm so that the overall thickness of the laminate became 60 μm. Next, the laminate was vacuum-dried at 120° C. for 3 hours to completely remove residual moisture, thereby obtaining a negative electrode including a current collector and a composite layer.

[0118] (4) Battery Production In a dry room controlled to a dew point of -50°C or less, the positive electrode was processed to 40 x 40 mm, and the negative electrode was processed to 44 x 44 mm. An aluminum tab was then welded to the positive electrode, and a nickel tab was welded to the negative electrode. The composite-coated surfaces of the positive and negative electrodes were arranged facing each other in the center, and a polyolefin microporous membrane processed to 45 x 45 mm was placed between the positive and negative electrodes. Next, a sheet-like exterior cut and processed to a 70 x 140 mm square was folded in half at the center of the long side. Next, the exterior was positioned so that the aluminum tab for the positive electrode and the nickel tab for the negative electrode were exposed to the outside of the exterior, and the positive electrode / polyolefin microporous membrane / negative electrode laminate was sandwiched between the folded exterior. Next, using a heat sealer, two sides including the side where the aluminum tab for the positive electrode and the nickel tab for the negative electrode of the exterior were exposed were heat-sealed, and then 2 g of electrolyte (Kishida Chemical, ethylene carbonate / diethyl carbonate = 1 / 2 (volume ratio) and 1 M LiPF ６The remaining side of the exterior was heat-sealed using a vacuum heat sealer while reducing the internal pressure to obtain a lithium-ion secondary battery.

[0119] (5) Battery Evaluation (5-1) Evaluation of Internal Resistance The fabricated batteries were charged at a constant current and constant voltage of 4.3 V at 25°C with a limit of 0.2 C, and then discharged to 3.0 V at a constant current of 0.2 C. Next, after five charge / discharge cycles under the same conditions, the batteries were charged to a charge depth of 50%. Subsequently, impedance measurements were performed at a frequency range of 1.5 MHz to 0.01 Hz and an oscillating voltage of 5 mV to measure the internal resistance. The results are shown in Table 4.

[0120] (5-2) Evaluation of Cycle Characteristics The prepared battery was charged at a constant current and constant voltage of 4.3 V at 25°C with a limit of 1 C, and then discharged to 3.0 V at a constant current of 1 C. The above charge and discharge cycle was repeated 500 times, and the discharge capacity at each cycle was measured. As an index of the cycle characteristics of the battery, the capacity retention rate after 500 cycles relative 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 Preparation of a coating liquid for forming a positive electrode, production of a positive electrode, production of a negative electrode, production of a battery, and 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 nanotubes (B-1), and carbon nanotubes (C-1) was changed from 70:25:5 to 65:20:15. The results are shown in Table 4.

[0122] Example 1-3 Preparation of a coating liquid for forming a positive electrode, production of a positive electrode, production of a negative electrode, production of a battery, and 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 nanotubes (B-1), and carbon nanotubes (C-1) was changed from 70:25:5 to 40:30:30. The results are shown in Table 4.

[0123] Example 1-4 Preparation of a coating liquid for forming a positive electrode, production of a positive electrode, production of a negative electrode, production of a battery, and 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 nanotubes (B-1), and carbon nanotubes (C-1) was changed from 70:25:5 to 80:17:3. The results are shown in Table 4.

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

[0126] <Comparative Example 1-3> Preparation of a coating liquid for forming a positive electrode, production of a positive electrode, production of a negative electrode, production of a battery, and evaluation of the battery were carried out in the same manner as in Example 1-1, except that the carbon nanotubes (C-1) were not used and the content ratio of carbon black (A-1), carbon nanotubes (B-1), and carbon nanotubes (C-1) was changed from 70:25:5 to 70:30:0. The results are shown in Table 5.

[0127] <Comparative Example 1-4> Preparation of a coating liquid for forming a positive electrode, production of a positive electrode, production of a negative electrode, production of a battery, and evaluation of the battery were carried out in the same manner as in Example 1-1, except that carbon nanotubes (B-1) were not used and the content ratio of carbon black (A-1), carbon nanotubes (B-1), and carbon nanotubes (C-1) was changed from 70:25:5 to 70:0:30. The results are shown in Table 5.

[0128] Comparative Example 1-5 Preparation of a coating liquid for forming a positive electrode, production of a positive electrode, production of a negative electrode, production of a battery, and evaluation of the battery were carried out in the same manner as in Example 1-1, except that carbon black (A-1) was not used and the content ratio of carbon black (A-1) to carbon nanotubes (B-1) to carbon nanotubes (C-1) was changed from 70:25:5 to 0:95:5. The results are shown in Table 5.

[0129]

[0130]

[0131] Example 2-1 Preparation of a coating liquid for forming a positive electrode, production of a positive electrode, production of a negative electrode, production of a battery, and evaluation of the battery were carried out in the same manner as in Example 1-1, except that carbon black (A-1) was changed to carbon black (A-2). The results are shown in Table 6.

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

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

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

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

[0136]

[0137]

[0138] Example 3-1 Preparation of a coating liquid for forming a positive electrode, production of a positive electrode, production of a negative electrode, production of a battery, and evaluation of the battery were carried out in the same manner as in Example 1-1, except that the carbon nanotubes (B-1) were changed to carbon nanotubes (B-2). The results are shown in Table 8.

[0139] <Comparative Example 3-1> Preparation of a coating liquid for forming a positive electrode, production of a positive electrode, production of a negative electrode, production of a battery, and evaluation of the battery were carried out in the same manner as in Example 1-1, except that the carbon nanotube (B-1) was changed to the carbon nanotube (Y-1). The results are shown in Table 8.

[0140] <Comparative Example 3-2> Preparation of a coating liquid for forming a positive electrode, production of a positive electrode, production of a negative electrode, production of a battery, and evaluation of the battery were carried out in the same manner as in Example 1-1, except that the carbon nanotube (B-1) was changed to the carbon nanotube (Y-2). The results are shown in Table 8.

[0141]

[0142] In Tables 4 to 8, "primary particle size (nm)" indicates the average primary particle size (nm) of the carbon black, and "(A) / (B) / (C)" indicates the mass ratio of the carbon black (A), the first carbon nanotubes (B), and the second carbon nanotubes (C).

[0143] From the above results, it was confirmed that the battery produced using the positive electrode composition according to the above embodiment has a low internal resistance and excellent cycle characteristics.

Claims

1. A positive electrode composition comprising a living material, a binder, and a conductive material, wherein 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 a peak ratio (D / G) of the D band and the G band in the Raman spectrum of 0.3 or more and 1.4 or less, and a second carbon nanotube (C) having a peak ratio (D / G) of the D band and the G band in the Raman spectrum of less than 0.

3.

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. 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 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.

6. 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.

7. A coating liquid for forming a positive electrode, comprising the positive electrode composition according to any one of claims 1 to 6 and a dispersion medium.

8. A positive electrode comprising the positive electrode composition according to any one of claims 1 to 6.

9. A battery comprising the positive electrode according to claim 8.

10. A conductive material comprising 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 a peak ratio (D / G) of the D band and the G band in the Raman spectrum of 0.3 or more and 1.4 or less, and a second carbon nanotube (C) having a peak ratio (D / G) of the D band and the G band in the Raman spectrum of less than 0.

3.

11. A slurry comprising the conductive material according to claim 10 and a dispersion medium.

12. A method for manufacturing a coating liquid for forming a positive electrode, comprising a mixing step of mixing a living material, a binder, a conductive material, and a dispersion medium, wherein 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 a peak ratio (D / G) of the D band and the G band in a Raman spectrum of 0.3 or more and 1.4 or less, and a second carbon nanotube (C) having a peak ratio (D / G) of the D band and the G band in a Raman spectrum of less than 0.

3.

13. The manufacturing method according to claim 12, wherein the mixing step is a step of mixing the living 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).

14. A method for manufacturing a positive electrode, comprising a step of applying the coating liquid for forming a positive electrode manufactured by the manufacturing method according to claim 12 or 13 onto a current collector to form a composite material layer including the living material, the binder, and the conductive material on the current collector.

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