Carbon black, slurry, and lithium-ion secondary battery

Abstract

Carbon black, having a specific surface area of 150 m 2 / g or more and 400 m 2 / g or less, a hydrochloric acid absorption amount of 30 mL / 5 g or more, and when preparing a 3 mass% slurry using N-methyl-2-pyrrolidone as a dispersion medium, the slurry viscosity at 25 °C and a shear rate of 10 s ‑1 is 200 mPa·s or more and 1200 mPa·s or less.

Description

Technical Field

[0001] The present invention relates to carbon black, a slurry, and a lithium ion secondary battery. Background Art

[0002] Lithium ion secondary batteries are widely used as power sources for small electronic devices such as smartphones and tablet computers. A lithium ion secondary battery generally includes an electrode, a separator, and an electrolyte. For the electrode, a composite material layer is formed by coating a composite material slurry obtained by dispersing an active material, a conductive agent, an adhesive, etc. in a dispersion medium on a current collector metal plate and drying it.

[0003] As the conductive agent, for example, carbon black is used (for example, Patent Document 1).

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2014-193986 Summary of the Invention

[0007] Problems to be Solved by the Invention

[0008] An object of the present invention is to provide carbon black useful for manufacturing a lithium ion secondary battery having excellent discharge rate characteristics and cycle characteristics. Another object of the present invention is to provide a slurry useful for forming an electrode of a lithium ion secondary battery. Further, an object of the present invention is to provide a lithium ion secondary battery having excellent discharge rate characteristics and cycle characteristics.

[0009] Means for Solving the Problems

[0010] The inventors of the present application conducted intensive studies to solve the above problems, and as a result, found that by using carbon black having a high specific surface area, a hydrochloric acid absorption amount, and a low slurry viscosity to form an electrode, a lithium ion secondary battery having excellent discharge rate characteristics and cycle characteristics can be formed.

[0011] That is, the present invention for solving the above problems is as follows.

[0012] (1) Carbon black having a specific surface area of 150 m 2 / g or more and 400 m 2 / g or less, a hydrochloric acid absorption amount of 30 mL / 5 g or more, and when a 3 mass% slurry is prepared using N-methyl-2-pyrrolidone as a dispersion medium, the slurry viscosity at 25°C and a shear rate of 10 s -1 is 200 mPa·s or more and 1200 mPa·s or less.

[0013] (2) The carbon black described in (1), wherein the DBP absorption of the carbon black is 200 mL / 100 g or more and 350 mL / 100 g or less.

[0014] (3) The carbon black described in (1) or (2), wherein the ash content of the carbon black is 0.02 mass% or less.

[0015] (4) The carbon black described in any one of (1) to (3), wherein the iron content is less than 2000 mass ppb.

[0016] (5) A slurry comprising the carbon black described in any one of (1) to (4) and a dispersion medium.

[0017] (6) The slurry described in (5), wherein the viscosity of the slurry at 25 °C and a shear rate of 10 s -1 is 200 mPa·s or more and 1200 mPa·s or less.

[0018] (7) A lithium ion secondary battery comprising a positive electrode, a negative electrode, and a separator, wherein at least one of the positive electrode and the negative electrode contains the carbon black described in any one of (1) to (4).

[0019] Effects of the Invention

[0020] According to the present invention, carbon black useful for manufacturing a lithium ion secondary battery having excellent discharge rate characteristics and cycle characteristics can be provided. In addition, according to the present invention, a slurry useful for forming an electrode of a lithium ion secondary battery can be provided. Furthermore, according to the present invention, a lithium ion secondary battery having excellent discharge rate characteristics and cycle characteristics can be provided. Detailed Embodiments

[0021] Hereinafter, preferred embodiments of the present invention will be described in detail. It should be noted that the present invention is not limited to the embodiments described below. It should be noted that in this specification, unless otherwise specified, the numerical range represented by "~" means a range that is "more than" the numerical value on the left and "less than" the numerical value on the right. For example, "A~B" means A or more and B or less.

[0022] <Carbon Black>

[0023] The carbon black of the present embodiment has a specific surface area of 150 m 2 / g or more and 400 m 2 / g or less. This specific surface area is higher than that of the carbon black conventionally used as a conductive agent for lithium ion secondary batteries. The conductivity imparting ability of the carbon black having such a high specific surface area is increased due to the percolation effect in the matrix, and thus it is effective as a conductive agent.

[0024] It should be noted that the specific surface area is measured by the A method flow method (thermal conductivity measurement method) of JIS K6217-2:2017.

[0025] If the specific surface area of the carbon black is less than 150 m 2 / g, the number of contact points with the active material in the composite material layer becomes small, and sufficient conductivity may not be exhibited. From the viewpoint of further improving the conductivity imparting ability, the specific surface area of the carbon black is preferably 160 m 2 / g or more, more preferably 180 m 2 / g or more, and further preferably 200 m 2 / g or more. That is, the specific surface area of the carbon black can be, for example, 150 to 400 m 2 / g, 160 to 400 m 2 / g, 180 to 400 m 2 / g or 200 to 400 m 2 / g. In addition, if the specific surface area of the carbon black exceeds 400 m 2 / g, the dispersion in the slurry becomes significantly difficult, and a portion with poor conductivity locally appears in the electrode, and sometimes the battery characteristics deteriorate. The specific surface area of the carbon black can be increased by reducing the particle size of the primary particles, making them hollow, or making the particle surface porous.

[0026] The hydrochloric acid absorption amount of the carbon black of this embodiment is 30 mL / 5 g or more. The hydrochloric acid absorption amount is the amount of hydrochloric acid that can be held in the voids formed by the particle surface, structure, and aggregates (secondary aggregation of the structure) of the carbon black, and is an index for evaluating the development degree of the structure and aggregates. Here, the structure of the carbon black refers to the structure formed by the connection of primary particles. The structure of the carbon black develops in a complex intertwined shape as the particle size of the primary particles decreases. The hydrochloric acid absorption amount can be measured according to JIS K1469:2003. Specifically, hydrochloric acid is added little by little to 5 g of carbon black placed in an Erlenmeyer flask and vibrated and mixed, and the amount of hydrochloric acid required to form a single lump is measured to obtain it.

[0027] In addition, the slurry viscosity of the carbon black of the present embodiment is not less than 200 mPa·s and not more than 1200 mPa·s. It should be noted that, in this specification, the slurry viscosity of carbon black refers to the viscosity of the slurry obtained by dispersing carbon black at 3% by mass using N-methyl-2-pyrrolidone as a dispersion medium. More specifically, 3% by mass of carbon black and 97% by mass of N-methyl-2-pyrrolidone as a dispersion medium are kneaded at a rotation speed of 2000 rpm for 30 minutes using a rotation-revolution type mixer ("Thinky Mixer ARV-310 (Japanese: あわとり炼太郎 ARV-310") manufactured by Thinky Co., Ltd.) to obtain a slurry, and the viscosity of the slurry at 25°C is measured using a viscoelasticity measuring machine ("MCR102" manufactured by Anton Paar Co., Ltd.), using The cone plate with an angle of 3° and a gap of 1 mm) makes the shear rate increase from 0.01s -1 Change to 100s -1 To measure, find the shear rate 10s -1 The viscosity under the conditions of 25°C and shear rate of 10s -1 The viscosity under the given conditions was taken as the slurry viscosity of carbon black.

[0028] The inventors of the present application have conducted in-depth research to solve the above-mentioned problems, and found that when carbon black with a high specific surface area is used to form an electrode of a lithium ion secondary battery, the hydrochloric acid absorption and slurry viscosity greatly affect the discharge rate characteristics and cycle characteristics of the obtained lithium ion secondary battery. That is, in this embodiment, by making the specific surface area, hydrochloric acid absorption and slurry viscosity of the carbon black within the above range, a lithium secondary battery with excellent discharge rate characteristics and cycle characteristics can be achieved.

[0029] For carbon black, the structure and the degree of development of agglomerates vary greatly depending on the thermal history during synthesis (for example, thermal decomposition and combustion reaction of fuel oil, thermal decomposition and combustion reaction of raw materials, thermal history caused by quenching and reaction cessation caused by cooling medium, etc.), the collision frequency of primary particles, etc. In addition, when carbon black is used as a conductive agent, the structure of carbon black affects the conductivity and slurry viscosity. If the structure is developed, although a conductive path in a layer of high-efficiency electrodes can be formed, if the dispersion state is poor, this effect cannot be fully exerted.

[0030] The carbon black of the present embodiment has a hydrochloric acid absorption of 30 mL / 5 g or more and has a structure in which the structure and agglomerates are fully developed. Therefore, the carbon black of the present embodiment can efficiently form a conductive path in an electrode.

[0031] In addition, the slurry viscosity of the carbon black in this embodiment is 200 mPa·s or more and 1200 mPa·s or less. Therefore, it is possible to form a slurry for electrode formation in which the carbon black is uniformly dispersed. By forming an electrode from this slurry for electrode formation, the carbon black is uniformly dispersed in the electrode, local reduction in conductivity, reduction in the discharge capacity of the battery, etc. are suppressed, and high capacity of the lithium-ion secondary battery is achieved. It should be noted that if the slurry viscosity is too high, strong shearing is applied during kneading with the active material, so that the structure of the carbon black may be damaged, resulting in a decrease in conductivity and foreign matter mixing due to wear of the device. On the other hand, if the slurry viscosity is too low, sedimentation of the carbon black is likely to occur in the slurry, and it may be difficult to maintain uniformity.

[0032] In the carbon black of this embodiment, from the viewpoint of more significantly obtaining the above effects, the hydrochloric acid absorption amount is preferably 31 mL / 5 g or more, more preferably 33 mL / 5 g or more, and still more preferably 35 mL / 5 g or more.

[0033] In the carbon black of this embodiment, if the hydrochloric acid absorption amount increases significantly, the slurry viscosity increases due to excessive development of the structure. Therefore, the hydrochloric acid absorption amount of the carbon black in this embodiment is limited to a range that makes the slurry viscosity 1200 mPa·s or less. In other words, for the carbon black of this embodiment, the upper limit of the hydrochloric acid absorption amount can be specified by the slurry viscosity.

[0034] For the carbon black of this embodiment, the hydrochloric acid absorption amount only needs to make the slurry viscosity in the above range. For example, it can be 60 mL / 5 g or less, 55 mL / 5 g or less, or 50 mL / 5 g or more. That is, for the carbon black of this embodiment, the hydrochloric acid absorption amount can be, for example, 30 to 60 mL / 5 g, 30 to 55 mL / 5 g, 30 to 50 mL / 5 g, 31 to 60 mL / 5 g, 31 to 55 mL / 5 g, 31 to 50 mL / 5 g, 33 to 60 mL / 5 g, 33 to 55 mL / 5 g, 33 to 50 mL / 5 g, 35 to 60 mL / 5 g, 35 to 55 mL / 5 g, or 35 to 50 mL / 5 g.

[0035] From the viewpoint of more significantly obtaining the above effects, the slurry viscosity of the carbon black in this embodiment is preferably 230 mPa·s or more, more preferably 250 mPa·s or more. In addition, from the viewpoint of more significantly obtaining the above effects, the slurry viscosity of the carbon black in this embodiment is preferably 1170 mPa·s or less, more preferably 1150 mPa·s or less. It should be noted that the slurry viscosity of the carbon black can be appropriately adjusted by the average primary particle diameter of the carbon black, the surface properties of the carbon black, the shape of the structure of the carbon black, etc. That is, the slurry viscosity of the carbon black in this embodiment can be, for example, 200 to 1200 mPa·s, 200 to 1170 mPa·s, 200 to 1150 mPa·s, 230 to 1200 mPa·s, 230 to 1170 mPa·s, 230 to 1150 mPa·s, 250 to 1200 mPa·s, 250 to 1170 mPa·s, or 250 to 1150 mPa·s.

[0036] The DBP absorption of the carbon black in this embodiment can be, for example, 180 mL / 100 g or more, preferably 190 mL / 100 g or more, and more preferably 200 mL / 100 g or more. In addition, the DBP absorption of the carbon black in this embodiment is, for example, 370 mL / 100 g or less, and more preferably 350 mL / 100 g or less. That is, the DBP absorption of the carbon black in this embodiment can be, for example, 180 to 370 mL / 100 g, 180 to 350 mL / 100 g, 190 to 370 mL / 100 g, 190 to 350 mL / 100 g, 200 to 370 mL / 100 g, or 200 to 350 mL / 100 g.

[0037] The DBP absorption is an index for evaluating the ability to absorb dibutyl phthalate (DBP) in the voids formed on the particle surface and structure of the carbon black. In this specification, the DBP absorption represents the value obtained by converting the value measured by the method described in Method B of JIS K6221 into a value equivalent to JIS K6217-4:2008 using the following formula (a).

[0038] DBP absorption = (A - 10.974) / 0.7833…(a)

[0039] [In the formula, A represents the value of the DBP absorption measured by the method described in Method B of JIS K6221.]

[0040] In carbon black with a developed structure, there are more voids formed between particles and at the necks where primary particles are fused, so the DBP absorption amount increases. It should be noted that the hydrochloric acid absorption amount evaluates the surface, structure, and the degree of development of aggregates of primary particles. However, for the DBP absorption amount, a stronger external force than that in the measurement of the hydrochloric acid absorption amount is applied during measurement. Therefore, the aggregates are crushed, and the degree of development of the surface and structure of primary particles can be evaluated.

[0041] If the DBP absorption amount is too small, sometimes the ability to impart conductivity in the electrode may be low due to insufficient development of the structure. In addition, sometimes the volume change of the active material occurring during charge and discharge of the lithium-ion secondary battery cannot be buffered, and battery characteristics such as cycle characteristics deteriorate. If the DBP absorption amount is too large, sometimes the binder in the composite material layer is trapped by the structure of the carbon black, and the adhesion to the active material and the current collector decreases, resulting in a decrease in battery characteristics.

[0042] The average primary particle diameter of the carbon black of this embodiment can be, for example, less than 35 nm, preferably less than 30 nm, and more preferably less than 25 nm. By using carbon black with a small particle diameter, high conductivity can be exhibited even when the blending ratio of carbon black in the composite material layer is low. The average primary particle diameter of the carbon black can be, for example, 1 nm or more, can be 5 nm or more, and can also be 10 nm or more. That is, the average primary particle diameter of the carbon black can be, for example, 1 nm or more and less than 35 nm, 1 nm or more and less than 30 nm, 1 nm or more and less than 25 nm, 5 nm or more and less than 35 nm, 5 nm or more and less than 30 nm, 5 nm or more and less than 25 nm, 10 nm or more and less than 35 nm, 10 nm or more and less than 30 nm, or 10 nm or more and less than 25 nm.

[0043] The average primary particle diameter of the carbon black can be obtained by the following method: Measure 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 calculate the average value. The primary particles of the carbon black are in a shape close to a perfect sphere with a small aspect ratio, but not a perfect sphere. Therefore, in this embodiment, the maximum length of the line segment connecting two peripheral points of the primary particles in the TEM image is used as the primary particle diameter of the carbon black.

[0044] The ash content of the carbon black of this embodiment can be, for example, 0.05 mass% or less, preferably 0.03 mass% or less, and more preferably 0.02 mass% or less. The ash content can be measured according to JIS K1469:2003. For example, it can be reduced by classifying the carbon black using a device such as a dry cyclone separator.

[0045] The iron content of the carbon black of this embodiment can be, for example, less than 2500 mass ppb, preferably less than 2300 mass ppb, and more preferably less than 2000 mass ppb. The iron content can be reduced, for example, by bringing the carbon black into contact with a magnet.

[0046] The iron content of the carbon black can be pretreated by an acid decomposition method in accordance with JIS K0116:2014 and determined by inductively coupled plasma mass spectrometry. Specifically, it can be determined by the following method. First, 1 g of carbon black is accurately weighed in a quartz beaker and heated at 800 °C for 3 hours using an electric furnace in an air atmosphere. Then, 10 mL of a mixed acid (70 mass% hydrochloric acid, 30 mass% nitric acid) and 10 mL or more of ultrapure water are added to the residue, and the mixture is heated and dissolved at 200 °C for 1 hour on a hot plate. After cooling, the solution diluted with ultrapure water to a volume of 25 mL is measured using an inductively coupled plasma mass spectrometry apparatus (Agilent 8800 manufactured by Agilent).

[0047] If the ash content and iron content of the carbon black of this embodiment are low, then in the kneading process, it is possible to more significantly suppress the incorporation of foreign substances such as metals and ceramics caused by damage to the equipment, etc. In addition, it is also possible to suppress a decrease in the conductivity inside the electrode caused by the incorporation of ash, insulating foreign substances, etc. Therefore, the carbon black of this embodiment with a low ash content and iron content can be preferably used for lithium ion secondary batteries that require high safety.

[0048] The manufacturing method of the carbon black of this embodiment is not particularly limited. For example, a raw material such as a hydrocarbon can be supplied from a nozzle provided in the upstream part of the reaction furnace, carbon black can be manufactured by a thermal decomposition reaction and / or a combustion reaction, and collected by a bag filter directly connected to the downstream part of the reaction furnace.

[0049] The raw materials used are not particularly limited, and gaseous hydrocarbons such as acetylene, methane, ethane, propane, ethylene, propylene, and butadiene, and oily hydrocarbons such as toluene, benzene, xylene, gasoline, kerosene, light oil, and heavy oil can be used. Among them, acetylene with few impurities is preferably used. The heat of decomposition of acetylene is larger than that of other raw materials, and the temperature in the reaction furnace can be increased. Therefore, the nucleation of carbon black is dominant over the particle growth caused by the addition reaction, and the primary particle size of carbon black can be reduced. In addition, the inventors of the present application conducted in-depth research to control the hydrochloric acid absorption amount of carbon black, and as a result, it was found that it is effective to use a variety of raw materials and supply them to the reaction furnace after heating the raw materials. In the conventional production method, carbon black generated through the high-temperature part of the reaction furnace and carbon black generated through the low-temperature part are mixed and present, and the deviation in characteristics is also large. However, by using a variety of raw materials, the temperature in the reaction furnace becomes uniform, and the reaction processes of thermal decomposition and combustion passed through also become uniform. Therefore, it is considered that the structure and aggregates of carbon black are likely to develop. In addition, it is also considered that by heating the raw materials, the timing of the generation of primary particles of carbon black becomes earlier, the collision frequency between primary particles increases, and the development of the structure and aggregates is promoted. The various raw materials are preferably mixed before being supplied to the reaction furnace. In the case of using oily hydrocarbons, it is preferably gasified by heating and then supplied. The heating method is not particularly limited. For example, the tank and the transfer pipe can be heated by heat exchange with a heat medium.

[0050] In addition, it is preferable to separately supply oxygen, hydrogen, nitrogen, water vapor, etc. to the reaction furnace relative to the raw materials that become the carbon source. Gases other than these raw materials promote gas stirring in the reaction furnace and increase the frequency of collision and fusion between primary particles of carbon black generated from the raw materials. Therefore, by using gases other than the raw materials, there is a tendency for the structure of carbon black to develop and the DBP absorption amount to increase. As the gas other than the raw materials, oxygen is preferably used. If oxygen is used, a part of the raw materials burns, the temperature in the reaction furnace becomes higher, and it is easy to obtain carbon black with a small particle size and a high specific surface area. As the gas other than the raw materials, a variety of gases can also be used. The supply position of the gas other than the raw materials is preferably the upstream part of the reaction furnace, and it is preferably supplied from a nozzle different from the raw materials. Thus, the stirring of the raw materials supplied from the upstream part also occurs efficiently, and the structure becomes easy to develop.

[0051] In the conventional carbon black production, in consideration of the stop of the thermal decomposition and combustion reactions of the raw materials, a cooling medium such as water is sometimes fed from the downstream part of the reaction furnace, but no effect of structure development is found. Therefore, in the present embodiment, it is preferable not to feed a cooling medium from the downstream part of the reaction furnace.

[0052] <Slurry>

[0053] The slurry of the present embodiment contains the carbon black of the present embodiment and a dispersion medium.

[0054] If the viscosity of the slurry is too high, strong shearing is applied during kneading with the active material. Therefore, sometimes the structure of the carbon black is damaged and the conductivity decreases, and foreign matter is mixed in due to wear of the equipment. On the other hand, if the viscosity of the slurry is too low, sedimentation of the carbon black sometimes easily occurs in the slurry, making it difficult to maintain uniformity. In the present embodiment, since the above carbon black is used, the viscosity of the slurry can be reduced. Therefore, the destruction of the carbon black structure is significantly suppressed, and the excellent conductivity imparting ability can be maintained. In addition, the mixing of foreign matter due to wear of the equipment is significantly suppressed. That is, in the present embodiment, the mixing ratio of the active material in the composite material layer can be increased without impairing the viscosity characteristics and conductivity of the slurry, and high capacity of the lithium ion secondary battery can be achieved.

[0055] From the viewpoint of more significantly obtaining the above effects, the slurry viscosity (25 °C, shear rate 10 s -1 ) is preferably 100 mPa·s or more, more preferably 200 mPa·s or more. Thereby, sedimentation of the carbon black is suppressed. The uniformity of the slurry is improved. In addition, from the viewpoint of more significantly obtaining the above effects, the slurry viscosity (25 °C, shear rate 10 s -1 ) is preferably 1500 mPa·s or less, more preferably 1200 mPa·s or less. That is, the slurry viscosity (25 °C, shear rate 10 s -1 ) can be, for example, 100 to 1500 Pa·s, 100 to 1200 Pa·s, 200 to 1500 Pa·s, or 200 to 1200 Pa·s.

[0056] The dispersion medium is not particularly limited, and for example, N-methyl-2-pyrrolidone, ethanol, ethyl acetate, etc. can be used.

[0057] Within the range that does not impair the conductivity imparting ability and dispersibility of the carbon black of the present embodiment, the slurry of the present embodiment may also contain other carbon blacks, graphite, carbon nanotubes, carbon nanofibers, etc.

[0058] The slurry of the present embodiment may also contain additives such as active materials and dispersants.

[0059] In the slurry of the present embodiment, the content of the carbon black of the present embodiment can be, for example, 0.5% by mass or more, preferably 1% by mass or more. In addition, in the slurry of the present embodiment, the content of the carbon black of the present embodiment can be, for example, 50% by mass or less, preferably 20% by mass or less. That is, in the slurry of the present embodiment, the content of the carbon black of the present embodiment can be, for example, 0.5 to 50% by mass, 0.5 to 20% by mass, 1 to 50% by mass, or 1 to 20% by mass.

[0060] The method for producing the slurry of the present embodiment is not particularly limited. For example, it can be produced by kneading each component using general devices such as a mixer, a kneader, a disperser, a mill, and an automatic revolution type rotating device.

[0061] The slurry of the present embodiment can preferably be used as a slurry for forming an electrode of a lithium ion secondary battery. The slurry for forming an electrode can be a slurry for forming a positive electrode or a slurry for forming a negative electrode.

[0062] When the slurry of the present embodiment is a slurry for forming an electrode, the slurry of the present embodiment may contain an active material, a conductive agent, and a dispersion medium. In this case, the slurry contains the carbon black of the present embodiment as the conductive agent.

[0063] The content of the conductive agent in the slurry for forming an electrode can be, for example, 0.01% by mass or more, preferably 0.05% by mass or more, and more preferably 0.08% by mass or more. In addition, the content of the conductive agent in the slurry for forming an electrode can be, for example, 20% by mass or less, preferably 15% by mass or less, and more preferably 10% by mass or less. That is, the content of the conductive agent in the slurry for forming an electrode can be, for example, 0.01 to 20% by mass, 0.01 to 15% by mass, 0.01 to 10% by mass, 0.05 to 20% by mass, 0.05 to 15% by mass, 0.05 to 10% by mass, 0.08 to 20% by mass, 0.08 to 15% by mass, or 0.08 to 10% by mass.

[0064] The slurry for forming an electrode may further contain a conductive agent other than carbon black. Examples of the conductive agent other than carbon black include graphite, carbon nanotubes, and carbon nanofibers.

[0065] In the slurry for forming an electrode, the proportion of carbon black in the conductive agent can be, for example, 50% by mass or more, preferably 70% by mass or more, more preferably 90% by mass or more, and can also be 100%.

[0066] The active material is not particularly limited, and known active materials for lithium ion secondary batteries can be used without particular limitation. Examples of the positive electrode active material include lithium cobaltate, lithium nickelate, lithium manganate, lithium nickel manganese cobaltate, and lithium iron phosphate. Examples of the negative electrode active material include natural graphite, artificial graphite, graphite, activated carbon, coke, needle coke, sulfurized coke, mesophase carbon microbeads, carbon fiber, and pyrolytic carbon.

[0067] The paste for forming an electrode may further contain a binder. The binder is not particularly limited, and known binders for lithium ion secondary batteries can be used without particular limitation. Examples of the binder include polyethylene, nitrile rubber, polybutadiene, butyl rubber, polystyrene, styrene-butadiene rubber, polysulfide rubber, nitrocellulose, carboxymethyl cellulose, polyvinyl alcohol, tetrafluoroethylene resin, polyvinylidene fluoride, polyvinylidene chloride fluoride, and the like.

[0068] The method for forming an electrode using the paste for forming an electrode is not particularly limited. For example, by coating the paste for forming an electrode on a current collector and drying it, an electrode including a current collector and a composite material layer can be formed.

[0069] The current collector is not particularly limited. For example, metal foils such as gold, silver, copper, platinum, aluminum, iron, nickel, chromium, manganese, lead, tungsten, titanium, and alloys mainly composed of them are used. For example, an aluminum foil is preferably used as the positive electrode current collector, and a copper foil is preferably used as the negative electrode current collector.

[0070] <Lithium Ion Secondary Battery>

[0071] The lithium ion secondary battery of the present embodiment includes a positive electrode, a negative electrode, and a separator. In addition, at least one of the positive electrode and the negative electrode of the lithium ion secondary battery of the present embodiment contains the carbon black of the present embodiment. At least one of the positive electrode and the negative electrode of the lithium ion secondary battery of the present embodiment may also be formed of the above-described paste for forming an electrode, and at least one of the positive electrode and the negative electrode may also include a composite material layer formed on a current collector by the above-described paste for forming an electrode.

[0072] Since the carbon black of the present embodiment is used in the lithium ion secondary battery of the present embodiment, it has a high capacity. In addition, by using the above-described paste for forming an electrode, a battery excellent in discharge rate characteristics and cycle characteristics can be obtained.

[0073] In the lithium ion secondary battery of the present embodiment, it is preferable that the positive electrode contains the carbon black of the present embodiment. In addition, in the lithium ion secondary battery of the present embodiment, it is preferable that the positive electrode is formed of the above-described paste for forming an electrode, and more preferably, the positive electrode includes a composite material layer formed on a current collector by the above-described paste for forming an electrode.

[0074] In the lithium ion secondary battery of the present embodiment, the configuration other than the electrode containing the carbon black of the present embodiment may be the same as that of a known lithium ion secondary battery.

[0075] The separator is not particularly limited, and known separators can be used without particular limitation as separators for lithium ion secondary batteries. Examples of the separator include synthetic resins such as polyethylene and polypropylene. From the viewpoint of good electrolyte retention, the separator is preferably a porous membrane.

[0076] The lithium ion secondary battery of the present embodiment may include an electrode group in which a positive electrode and a negative electrode are laminated or wound with a separator interposed therebetween.

[0077] For the lithium ion secondary battery of the present embodiment, it is sufficient to immerse the positive electrode, the negative electrode, and the separator in an electrolytic solution.

[0078] The electrolytic solution is not particularly limited, and for example, it may be a non-aqueous electrolytic solution containing a lithium salt. Examples of the non-aqueous solvent in the non-aqueous electrolytic solution containing a lithium salt include ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate. In addition, examples of the lithium salt that can be dissolved in the non-aqueous solvent include lithium hexafluorophosphate, lithium tetrafluoroborate, and lithium trifluoromethanesulfonate.

[0079] The lithium ion secondary battery of the present embodiment may also use an ion conductive polymer or the like as an electrolyte.

[0080] As described above, the preferred embodiments of the present invention have been described, but the present invention is not limited to the above-described embodiments.

[0081] For example, one aspect of the present invention may be a method for evaluating carbon black having a specific surface area of 150 m 2 / g or more and 400 m 2 / g or less. The evaluation method may include: a step of measuring the hydrochloric acid absorption amount and the slurry viscosity; and an evaluation step of evaluating the carbon black using the hydrochloric acid absorption amount and the slurry viscosity.

[0082] The evaluation step may also be a screening step of screening carbon black having a hydrochloric acid absorption amount of 30 mL / 5 g or more and a slurry viscosity of 200 mPa·s or more and 1200 mPa·s or less. In this case, the above evaluation method can also be referred to as a method for screening carbon black.

[0083] Examples

[0084] Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to these examples.

[0085] (Example 1)

[0086] <Manufacture of carbon black>

[0087] Acetylene as a raw material was supplied at 12 Nm 3 / h from a nozzle provided in the upstream portion of a carbon black reaction furnace (furnace length 6 m, furnace diameter 0.65 m), toluene was supplied at 32 kg / h, and 20 Nm 3 / h is used to supply oxygen as a gas other than the raw material to produce carbon black, and the oxygen is captured by a bag filter installed in the downstream part of the reactor. Then, it is passed through a dry cyclone separator device and a magnet for iron removal and recovered in a tank. It should be noted that acetylene, toluene and oxygen are supplied to the reactor after being heated to 115°C. The following physical properties of the obtained carbon black are measured. The evaluation results are shown in Table 1.

[0088] (1) Specific surface area

[0089] The thermal conductivity was measured according to the A method flow method (thermal conductivity measurement method) of JIS K6217-2:2017.

[0090] (2) Hydrochloric acid absorption: measured in accordance with JIS K1469-4:2003.

[0091] (3) DBP absorption: The value measured by the method described in Method B of JIS K6221 was converted into a value equivalent to JIS K6217-4:2008 using the above formula (a).

[0092] (4) Average primary particle size: The primary particle sizes of 100 or more carbon black particles randomly selected from a 50,000-times-magnification image of a transmission electron microscope were measured, and the average value was calculated.

[0093] (5) Ash content: measured in accordance with JIS K1469:2003.

[0094] (6) Iron content: The iron content was measured by high-frequency inductively coupled plasma mass spectrometry after pretreatment by an acid decomposition method in accordance with JIS K0116:2014.

[0095] <Preparation of slurry>

[0096] 3 parts by mass of carbon black and 97 parts by mass of N-methyl-2-pyrrolidone (manufactured by Kanto Chemical Co., Ltd.) as a dispersion medium were kneaded at a rotation speed of 2000 rpm for 30 minutes using a rotary mixer ("Thinky Mixer ARV-310" manufactured by Thinky Co., Ltd.) to prepare a carbon black slurry. A viscoelasticity tester ("MCR102" manufactured by Anton Paar Co., Ltd., The viscosity of the slurry at 25°C was evaluated by using a cone plate with an angle of 3° and a gap of 1 mm. The shear rate was changed from 0.01 s -1 Change to 100s -1 And measure and find the shear rate 10s -1 The results are shown in Table 2.

[0097] <Battery production>

[0098] 40 parts by mass of a carbon black slurry (1.2 parts by mass of carbon black and 38.8 parts by mass of N-methyl-2-pyrrolidone), LiNi 0.5 Mn 0.3 Co 0.2 O2 (“TX10” manufactured by Umicore) 96.8 parts by mass, polyvinylidene fluoride (“HSV900” manufactured by Arkema) 2 parts by mass as a binder, polyvinyl alcohol (“B05” manufactured by Denka) 0.1 part by mass as a dispersant, and N-methyl-2-pyrrolidone (manufactured by Kanto Chemical Co., Inc.) 10 parts by mass as a dispersion medium were kneaded for 10 minutes at a rotation speed of 2000 rpm using a planetary mixer (“Thinky Mixer ARV-310” manufactured by Thinky Corporation) to prepare a composite material slurry for positive electrode formation. The obtained composite material slurry for positive electrode formation was coated on an aluminum foil (manufactured by UACJ Corporation) with a thickness of 15 μm using a coater and pre-dried at 105°C for 1 hour. Then, it was pressed using a roll press at a linear pressure of 200 kg / cm2 to prepare it such that the total thickness of the aluminum foil and the coated film became 80 μm. In order to remove volatile components, it was vacuum dried at 170°C for 3 hours to fabricate a positive electrode.

[0099] 97 parts by mass of artificial graphite (“MAG-D” manufactured by Hitachi Chemical Co., Ltd.) as a negative electrode active material, 2 parts by mass of styrene-butadiene rubber (“BM-400B” manufactured by Nippon Zeon Co., Ltd.) as a binder, and 1 part by mass of carboxymethyl cellulose (“D2200” manufactured by Daicel Corporation) as a dispersant were weighed, pure water was added, and they were mixed using a planetary mixer (manufactured by Thinky Corporation, Thinky Mixer ARV-310) to prepare a composite material slurry for negative electrode formation. The obtained composite material slurry for negative electrode formation was coated on a copper foil (manufactured by UACJ Corporation) with a thickness of 10 μm using a coater and pre-dried at 60°C for 1 hour. Then, it was pressed using a roll press at a linear pressure of 100 kg / cm2 to prepare it such that the total thickness of the copper foil and the coated film became 40 μm. In order to completely remove moisture, it was vacuum dried at 120°C for 3 hours to fabricate a negative electrode.

[0100] The above positive electrode was processed into 40 × 40 mm, and the above negative electrode was processed into 44 × 44 mm. A polyolefin microporous membrane as a separator was disposed between the two electrodes to fabricate a battery. As the electrolyte, a solution obtained by dissolving 1 mol / L of lithium hexafluorophosphate (manufactured by Stella Chemifa) in a solution obtained by mixing ethylene carbonate (manufactured by Aldrich) / dimethyl carbonate (manufactured by Aldrich) at a volume ratio of 1 / 1 was used.

[0101] As a discharge test of the battery, the fabricated battery was charged at a constant current and constant voltage of 4.35 V with a 0.2C limit at 25°C, and then discharged at a constant current of 0.2C to 3.0 V. Then, the discharge current was changed to 0.2C, 0.5C, 1C, 2C, and 3C, and the discharge capacity with respect to each discharge current was measured. The capacity retention rate at 3C discharge relative to 0.2C discharge was calculated and evaluated as the discharge rate characteristic. In addition, the fabricated battery was charged at a constant current and constant voltage of 4.35 V with a 1C limit at 25°C, and then discharged at a constant current of 1C to 3.0 V. Then, the above charge and discharge were repeated 500 cycles, and the discharge capacity was measured. The capacity retention rate at 500-cycle discharge relative to 1-cycle discharge was calculated and evaluated as the cycle characteristic. The measurement results are shown in Table 2.

[0102] (Examples 2 to 4)

[0103] The oxygen supply amount was changed to 21 Nm 3 / h (Example 2), 22 Nm 3 / h (Example 3) or 24 Nm 3 / h (Example 4). Except for this, carbon black was produced and evaluated in the same manner as in Example 1. The results are shown in Table 1. In addition, using the obtained carbon black, slurries and batteries were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0104] (Example 5)

[0105] The temperature at the time of toluene supply was changed to 100°C, and the oxygen supply amount was changed to 21 Nm 3 / h. Except for this, carbon black was produced and evaluated in the same manner as in Example 1. The results are shown in Table 1. In addition, using the obtained carbon black, slurries and batteries were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0106] (Example 6)

[0107] The temperature at the time of acetylene supply was changed to 85°C and the temperature at the time of toluene supply was changed to 100°C, and the oxygen supply amount was changed to 21 Nm 3 / h. Except for this, carbon black was produced and evaluated in the same manner as in Example 1. The results are shown in Table 1. In addition, using the obtained carbon black, slurries and batteries were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0108] (Example 7)

[0109] The temperature at the time of acetylene supply was changed to 85°C and the temperature at the time of toluene supply was changed to 85°C, and the oxygen supply amount was changed to 21 Nm 3 / h. Except for this, carbon black was produced and evaluated in the same manner as in Example 1. The results are shown in Table 1. In addition, using the obtained carbon black, slurry and battery were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0110] (Example 8)

[0111] The supply amount of acetylene was changed to 11 Nm 3 / h, the supply amount of toluene was changed to 30 kg / h, and the supply amount of oxygen was changed to 19 Nm 3 / h. Except for this, carbon black was produced and evaluated in the same manner as in Example 1. The results are shown in Table 1. In addition, using the obtained carbon black, slurry and battery were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0112] (Example 9)

[0113] The supply amount of acetylene was changed to 13 Nm 3 / h, the supply amount of toluene was changed to 35 kg / h, and the supply amount of oxygen was changed to 26 Nm 3 / h. Except for this, carbon black was produced and evaluated in the same manner as in Example 1. The results are shown in Table 1. In addition, using the obtained carbon black, slurry and battery were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0114] (Example 10)

[0115] Instead of acetylene, 12 Nm 3 / h of ethylene was heated to 115 °C and supplied, and the supply amount of oxygen was changed to 22 Nm 3 / h. Except for this, carbon black was produced and evaluated in the same manner as in Example 1. The results are shown in Table 1. In addition, using the obtained carbon black, slurry and battery were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0116] (Example 11)

[0117] Instead of toluene, 32 kg / h of benzene was heated to 115 °C and supplied, and the supply amount of oxygen was changed to 21 Nm 3 / h. Except for this, carbon black was produced and evaluated in the same manner as in Example 1. The results are shown in Table 1. In addition, using the obtained carbon black, slurry and battery were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0118] (Comparative Example 1)

[0119] Instead of oxygen, 21 Nm 3The hydrogen at 115°C was heated and supplied at a rate of / h. Except for this, carbon black was produced and evaluated in the same manner as in Example 1. The results are shown in Table 1. Additionally, using the obtained carbon black, slurries and batteries were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0120] (Comparative Example 2)

[0121] The supply rate of acetylene was changed to 11 Nm 3 / h, the supply rate of toluene was changed to 30 kg / h, and the supply rate of oxygen was changed to 24 Nm 3 / h. Except for this, carbon black was produced and evaluated in the same manner as in Example 1. The results are shown in Table 1. Additionally, using the obtained carbon black, slurries and batteries were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0122] (Example 12)

[0123] The carbon black obtained in Comparative Example 1 was oxidized in an electric furnace heated to 720°C to obtain carbon black. The obtained carbon black was evaluated in the same manner as in Example 1. The results are shown in Table 1. Additionally, using the obtained carbon black, slurries and batteries were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0124] (Example 13)

[0125] The supply rate of oxygen was changed to 21 Nm 3 / h, and the classification conditions of the dry cyclone separator device were changed to adjust the ash content. Except for this, carbon black was produced and evaluated in the same manner as in Example 1. The results are shown in Table 1. Additionally, using the obtained carbon black, slurries and batteries were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0126] (Example 14)

[0127] The supply rate of oxygen was changed to 21 Nm 3 / h, and the magnetic flux density conditions of the iron removal magnet were changed to adjust the iron content. Except for this, carbon black was produced and evaluated in the same manner as in Example 1. The results are shown in Table 1. Additionally, using the obtained carbon black, slurries and batteries were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0128] (Comparative Example 3)

[0129] The supply rate of acetylene was changed to 38 Nm 3 / h, toluene was not supplied, and the supply rate of oxygen was changed to 10 Nm 3 / h. Other than this, carbon black was produced and evaluated in the same manner as in Example 1. The results are shown in Table 1. Further, using the obtained carbon black, slurries and batteries were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0130] (Comparative Example 4)

[0131] The supply amount of oxygen was changed to 22 Nm 3 / h, and the temperatures at the time of supplying acetylene, the temperature at the time of supplying toluene, and the temperature at the time of supplying oxygen were all changed to 25°C. Other than this, carbon black was produced and evaluated in the same manner as in Example 1. The results are shown in Table 1. Further, using the obtained carbon black, slurries and batteries were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0132] [Table 1]

[0133]

[0134] [Table 2]

[0135]

[0136] As shown in Table 1, it was confirmed that excellent battery characteristics were achieved when using the carbon black of the examples, and high-performance lithium-ion secondary batteries could be obtained with good productivity from the carbon black of the present invention.

[0137] Industrial Applicability

[0138] The carbon black of the present invention can be preferably used for slurries for lithium-ion secondary battery electrodes and lithium-ion secondary batteries.

Claims

1. Carbon black, having a specific surface area of 150 m 2 / g or more and 400 m 2 / g or less, The hydrochloric acid absorption amount is 30 mL / 5 g or more, When preparing a 3% by mass slurry with N-methyl-2-pyrrolidone as the dispersion medium, the viscosity of the slurry at 25 °C and a shear rate of 10 s -1 is 200 mPa·s or more and 1200 mPa·s or less.

2. The carbon black according to claim 1, wherein, the DBP absorption amount of the carbon black is 200 mL / 100 g or more and 350 mL / 100 g or less.

3. The carbon black according to claim 1 or 2, wherein, The ash content of the carbon black is 0.02 mass% or less.

4. The carbon black according to any one of claims 1 to 3, wherein The content of iron is less than 2000 mass ppb.

5. A slurry, which comprises the carbon black according to any one of claims 1 to 4 and a dispersion medium.

6. The slurry according to claim 5, wherein, The viscosity of the slurry at 25°C and a shear rate of 10 s -1 is 200 mPa·s or more and 1200 mPa·s or less.

7. A lithium ion secondary battery, which includes a positive electrode, a negative electrode and a separator, and at least one of the positive electrode and the negative electrode contains the carbon black according to any one of claims 1 to 4.

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