Mixed carbon black and electrode slurry

Abstract

To provide carbon black capable of improving compound dispersibility by simply forming electrode slurry used for a secondary battery, etc., into high viscosity to enhance shear stress, and electrode slurry simply formed into high viscosity and capable of improving compound dispersibility by enhancing shear stress.SOLUTION: Mixed carbon black is obtained by mixing two kinds of carbon black of first carbon black and second carbon black having different specific surface areas. The second carbon black is porous carbon black; the specific surface area of the first carbon black is smaller than the specific surface area of the second porous carbon black; when setting the specific surface area of the first carbon black to N2SA(1) m2 / g and setting the specific surface area of the second carbon black to N2SA(2) m2 / g, a value calculated by the following formula (I) is 120-350 m2 / g; and (N2SA(2)-N2SA (1)) in the following formula (I) is 140-650 m2 / g.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to carbon black and electrode slurry, which are useful for use as electrodes in secondary batteries. [Background technology]

[0002] In recent years, secondary batteries have been used in a very wide range of fields and industries, including electric vehicles and mobile phones. Along with this expansion, the demand for higher energy density, higher power density, and faster charging / discharging speeds has also increased, and various materials are being actively developed to meet these requirements. One area of ​​focus is electrode slurries containing various conductive materials and other compounds, which are applied to current collector foils. One of the challenges is to improve the dispersibility of these compounds within the slurry. Improving dispersibility enhances the efficiency of conductive path formation and improves the performance of the final product, the secondary battery. As a countermeasure, one idea is to increase the viscosity of the slurry and raise the shear stress to break up the aggregation of each compound and improve dispersibility.

[0003] Various studies have been conducted to increase the viscosity of slurries, and countermeasures have typically been taken by increasing the solid content ratio of the slurry, using a high-viscosity type of binder itself, improving the carbon black concentration by adding a dispersant, and making improvements to the manufacturing process such as the compounding method (Patent Document 1). However, the solid content ratio is closely related to the formulation and cannot be easily changed. In particular, the amount of binder added has limited flexibility in terms of solubility and other factors, making it difficult to adjust. In addition, simply increasing the concentration leads to a loss of fluidity, worsening handling before transferring the slurry to a stirring container. Furthermore, the manufacturing techniques and other aspects are naturally limited by the available conditions, and in some cases, specialized equipment such as other mixers may be required, so it cannot be said that it is easily applicable. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-21632 [Overview of the project] [Problems that the invention aims to solve]

[0005] The present invention aims to solve the problems of the above-mentioned prior art and to provide a carbon black that can easily increase the viscosity of electrode slurries used in secondary batteries and the like, thereby improving the dispersibility of the compound by increasing the shear stress, and an electrode slurry that can be easily increased in viscosity and improve the dispersibility of the compound by increasing the shear stress. [Means for solving the problem]

[0006] As a result of diligent research, the inventors have found that the above problem can be solved by using a combination of ordinary carbon black and porous carbon black, and by setting the relationship between the degree of porosity of the porous carbon black and the mixing ratio within a specific range. When porous carbon black is used, the proportion of micropores in the carbon black as a whole increases, but since the solvent does not enter the micropores during slurry formation, the overall density decreases and the centrifugal force during stirring weakens. This adversely affects the dispersibility of carbon black, inhibits the formation of conductive paths, and consequently degrades the performance of the battery. For this reason, conventional attempts have not been made to use porous carbon black to increase viscosity and improve dispersibility. Therefore, in conventional technology, there are no examples of achieving high viscosity of slurry while maintaining the properties of a conductive material by arbitrarily controlling and defining within an appropriate range the mixing ratio of carbon black as a compound, particularly ordinary carbon black and porous carbon black, and the degree of porosity of porous carbon black. Furthermore, the present invention presents the optimal conditions and achieves remarkable effects that cannot be achieved with conventional methods.

[0007] In other words, the present invention is defined by the following: [1] A mixed carbon black obtained by mixing two types of carbon black, a first carbon black and a second carbon black, which have different specific surface areas, wherein the second carbon black is porous carbon black, the specific surface area of ​​the first carbon black is smaller than the specific surface area of ​​the second porous carbon black, and the specific surface area of ​​the first carbon black is N2SA(1)m 2 / g, the specific surface area of ​​the second carbon black is N2SA(2)m 2 When expressed as / g, the value calculated by the following formula (I) is between 120 and 350m 2 / g, and in the following equation (I), (N2SA(2)-N2SA(1)) is 140-650m 2 Mixed carbon black at / g

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[0008] According to the present invention, it is possible to efficiently improve the viscosity of an electrode slurry used for an electrode of a secondary battery or the like, and it is possible to provide carbon black that can easily increase the viscosity of the electrode slurry. Further, according to the present invention, it is possible to provide an electrode slurry used for an electrode of a secondary battery or the like that can easily increase the viscosity. Since the carbon black and the electrode slurry of the present invention can increase the viscosity, the dispersion of the blend can be improved by increasing the shear stress, so that the battery performance can be improved.

Embodiments for Carrying Out the Invention

[0009] Hereinafter, the present invention will be described in detail. The mixed carbon black of the present invention is a mixed carbon black obtained by mixing two types of carbon black, a first carbon black and a second carbon black, having different specific surface areas. The second carbon black is porous carbon black, and the specific surface area of the first carbon black is smaller than the specific surface area of the second carbon black. When the specific surface area of the first carbon black is N2SA(1) m 2 / g and the specific surface area of the second carbon black is N2SA(2) m 2 / g, the value calculated by the following formula (I) is 120 to 350 m 2 / g, and (N2SA(2) - N2SA(1)) in the following formula (I) is 140 to 650 m 2 / g.

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[0010] The first carbon black and the second carbon black in the present invention are not particularly limited in terms of their type, production method, etc. For example, those produced by production methods such as the oil furnace method, acetylene decomposition method, thermal method, channel method, etc. can be used. Also, their particle size, shape, etc. are not particularly limited as long as they can be used for electrodes. The second carbon black in the present invention can be obtained, for example, by subjecting the carbon black produced by the above production method to an activation treatment of contacting with water vapor, carbon dioxide gas, etc. at high temperature to make it porous. The activation treatment can include generally performed treatments on carbon black. In relation to the first carbon black, as long as the second carbon black satisfying the conditions of formula (I) is obtained, its conditions, etc. are not particularly limited.

[0011] Formula (I) is an index representing the dispersibility in the slurry system of carbon black, and is a value obtained from (N2SA(2) - N2SA(1)) (hereinafter, also referred to as "ΔN2SA") described below and the blending ratio of the first carbon black and the second carbon black. Here, the blending ratio is the ratio of the mass of the second carbon black to the total mass of the first carbon black and the second carbon black. N2SA(1) and N2SA(2) in formula (I) are the specific surface areas per unit mass measured by the method described in JIS K6217-7:2013, and the unit is m 2 / g. In the present invention, the value calculated by formula (I) is 120 to 350 m 2 / g. When the value calculated by formula (I) is less than 120, the difference in specific surface area between the first carbon black and the second porous carbon black is insufficient or the ratio of the second porous carbon black is too low, so it does not contribute to the improvement of the viscosity of the slurry when mixed with the binder to prepare a slurry. When the value calculated by formula (I) exceeds 350, the specific surface area of the second porous carbon black is too large or the blending ratio of the second porous carbon black is too high, so the binder thickens too much, significantly hindering the productivity of the slurry and the workability in the subsequent manufacturing process.

[0012] In equation (I), (N2SA(2)-N2SA(1)) is an index representing the porosity of the carbon black surface, and is a value obtained from the difference in specific surface area between the second carbon black and the first carbon black. In this invention, (N2SA(2)-N2SA(1)) is 140-650 m 2 The value is / g. If it is less than 140, the pore development is insufficient and does not contribute to improving the viscosity of the binder, and if it is greater than 650, the pore development is excessive, which also increases the viscosity of the binder excessively and significantly hinders manufacturability. The mixed carbon black in the present invention may contain carbon black other than the first carbon black and the second carbon black, to the extent that it does not hinder the effects of the present invention. In this case, the total amount of the first carbon black and the second carbon black in the total carbon black is preferably 70 to 100% by mass, more preferably 80 to 100% by mass, and even more preferably 90 to 100% by mass.

[0013] The electrode slurry of the present invention comprises a first carbon black and a second carbon black with different specific surface areas and a binder, wherein the second carbon black is porous carbon black, the specific surface area of ​​the first carbon black is smaller than the specific surface area of ​​the second carbon black, and the specific surface area of ​​the first carbon black is N2SA(1)m 2 / g, the specific surface area of ​​the second carbon black is N2SA(2)m 2 When expressed as / g, the value calculated by the following formula (I) is between 120 and 350m 2 / g, and in the following equation (I), (N2SA(2)-N2SA(1)) is 140-650m 2 It is / g.

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[0014] The first carbon black and second carbon black used in the electrode slurry of the present invention are the same as those described above for the mixed carbon black of the present invention. In the electrode slurry of the present invention, the first carbon black and second carbon black may be mixed and added to the binder, or they may be added to the binder separately. The binder in the electrode slurry of the present invention is not particularly limited as long as it is used in electrode slurries for secondary batteries and the like, and examples of binders include polyvinylidene fluoride, polyimide, SBR (styrene-butadiene rubber), and polyacrylic acid. Other components used in electrode slurries, such as active materials, conductive additives, and viscosity modifiers, may be added to the electrode slurry of the present invention, and other carbon blacks other than the first carbon black and second carbon black of the present invention may be added as long as they do not hinder the effects of the present invention. When other carbon blacks are added, the total amount of the first carbon black and second carbon black in the total amount of carbon black is preferably 70 to 100% by mass, more preferably 80 to 100% by mass, and even more preferably 90 to 100% by mass. The electrode slurry of the present invention can be manufactured by adding the first carbon black and the second carbon black of the present invention, as well as other components as needed, to a binder and stirring and mixing. [Examples]

[0015] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited in any way by these examples.

[0016] [Manufacturing of porous carbon black (second type of carbon black)] Untreated carbon black (N2SA: 54m) 2 / g, STSA: 54m 2100g of (1g) was placed in a cylindrical kiln with an inner diameter of 10cm and a length of 20cm, and steam activation treatment was performed at 850°C under the treatment conditions shown in Table 1 to produce carbon blacks CB-A to CB-E. The physicochemical properties of the obtained porous carbon blacks CB-A to CB-E and untreated carbon black are shown in Table 2.

[0017] [Table 1]

[0018] [Table 2]

[0019] The characteristics shown in Table 2 above were measured using the following method. [Specific surface area (Specific surface area for nitrogen adsorption)] The specific surface area in Table 2 is the specific surface area per unit mass (m²). 2 The values ​​were per g and measured according to the method described in JIS K6217-7:2013. [ΔN2SA] This is the difference between the specific surface area of ​​each porous carbon black (CB-A to CB-E) after activation treatment and the specific surface area of ​​untreated carbon black.

[0020] Using the carbon blacks listed in Table 2, electrode slurries were prepared and evaluated according to the following procedure. The viscosity measurement results are shown in Table 3. [Electrode slurry preparation method] Mixed carbon blacks for Examples 1-3 and Comparative Examples 1-5 were prepared by mixing untreated carbon black with each porous carbon black. The prepared mixed carbon blacks were weighed into a stirring vessel so that the mass ratio of mixed carbon black to binder was 1:5, and stirred at 2000 rpm / 20 min using a self-rotating stirrer (Thinky "Awatori Rentaro ARV-310"). The binder used was KF polymer L#1120 (Kureha PVdF / NMP solution), which is commonly used. The resulting slurry was used as a viscosity measurement sample.

[0021] [Table 3]

[0022] [Table 4]

[0023] "The value of equation (I)" The "value of formula (I)" in Tables 3 and 4 above is the value calculated using formula (I) in the present invention, with untreated carbon black as the first carbon black and its specific surface area being N2SA(1), and each porous carbon black as the second carbon black and its specific surface area being N2SA(2).

[0024] "Viscosity (Index)" The "Viscosity (Index)" in Tables 3 and 4 above is calculated by measuring the viscosity of the slurry using the method described below, and setting the reference example as 100 to determine the viscosity index for each slurry. [Viscosity measurement method] A cone-plate rotational viscometer (HAAKE "Visco Tester VT550") was used. The temperature was controlled to 25°C in a constant temperature bath, and the viscosity was measured using a predetermined amount of slurry at a rotational speed of 1 rpm.

[0025] As is clear from the evaluation results in Table 3, the electrode slurry prepared using the mixed carbon black of the present invention showed higher viscosity compared to the electrode slurry using the mixed carbon black of the comparative example and the electrode slurry using the untreated carbon black of the reference example. Therefore, the shear stress of the electrode slurry improved, and the dispersibility of the compound improved, leading to improved conductivity. This contributes to improved battery performance. [Industrial applicability]

[0026] The mixed carbon black of the present invention can be suitably used as a conductive material for electrode slurries in secondary batteries and the like, and the electrode slurry of the present invention can be suitably used as an electrode slurry in secondary batteries and the like.

Claims

【Request Item 1】 A mixed carbon black comprising two types of carbon black, a first carbon black and a second carbon black, having different specific surface areas, wherein the second carbon black is a porous carbon black that has been activated and made porous, and the first carbon black is an unactivated carbon black, the specific surface area of ​​the first carbon black is smaller than the specific surface area of ​​the second porous carbon black, and the specific surface area of ​​the first carbon black is N2SA(1)m ２ / g, the specific surface area of ​​the second carbon black is N2SA(2)m ２ When expressed as / g, the value calculated by the following formula (I) is between 120 and 350m ２ / g, and in the following equation (I), (N2SA(2) - N2SA(1)) is between 140 and 650 m ２ Mixed carbon black for secondary battery electrodes, rated at / g. [Math 1] 【Request Item 2】 The material comprises a first carbon black and a second carbon black with different specific surface areas and a binder, wherein the second carbon black is a porous carbon black that has been activated and made porous, and the first carbon black is an unactivated carbon black, the specific surface area of ​​the first carbon black is smaller than the specific surface area of ​​the second carbon black, and the specific surface area of ​​the first carbon black is N2SA(1)m ２ / g, the specific surface area of ​​the second carbon black is N2SA(2)m ２ When expressed as / g, the value calculated by the following formula (I) is between 120 and 350m ２ / g, and in the following equation (I), (N2SA(2) - N2SA(1)) is between 140 and 650 m ２ A slurry for secondary battery electrodes, which is / g. [Math 2]

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