JP6207219B2 - Carbon black and battery electrode using the same - Google Patents

Description

  The present invention relates to carbon black.

  In recent years, carbon black is often used in lithium ion secondary batteries and fuel cells. Specifically, a lithium ion secondary battery is used as a conductive agent for a positive electrode and a negative electrode, and as a catalyst carrier in a fuel cell. The general structure of a lithium ion secondary battery is that an ion is interposed between a positive electrode in which a positive electrode active material and a conductive agent solution are coated on an aluminum foil, and a negative electrode in which a solution such as a carbon material is coated on a copper foil. It is configured by sandwiching a movable porous insulating film and filling the whole with an electrolytic solution. Carbon black used as a conductive agent is required to have a high specific surface area, high crystallinity, and high dispersion for its purpose (improvement of conductivity of the positive electrode active material). The cell structure of a fuel cell has a structure in which a gas diffusion layer, a catalyst layer, and an electrolyte membrane are sandwiched between separators provided with gas flow paths. The catalyst layer is composed of carbon black on which catalyst metal particles (often platinum is used) are supported, and the catalyst metal particles are supported on the carbon black surface in a highly dispersed manner. Here, the term “supported” refers to a state in which another particle is attached to the carbon black surface by a chemical bond or a physical bond. Since the source gas such as hydrogen and oxygen is activated by contact with the catalyst metal particles to generate water, the reaction efficiency is higher when the catalyst metal particles in the catalyst layer are supported in a highly dispersed state. On the contrary, when the catalyst metal particles are supported on the carbon black with low dispersion, that is, the catalyst metal particles are aggregated and supported, the contact area between the raw material gas and the catalyst metal particles is reduced, and the reaction efficiency is lowered.

  For the above reasons, carbon black preferably has a high specific surface area. Although furnace black was initially used, furnace black has low crystallinity and contains impurities derived from raw materials, such as sulfur, chlorine, potassium, lead, sodium, and calcium, on the order of several tens of ppm to several percent. In many cases, these impurities have caused a decrease in battery performance.

Therefore, it is conceivable to use acetylene black, which has much less impurities than furnace black, but the specific surface area of normal acetylene black is 30 to ²⁰⁰ m ² / g, and the supported area compared to furnace black with a high specific surface area. The catalyst metal particles are agglomerated and supported, and cannot be supported in a highly dispersed state. Therefore, it is necessary to increase the specific surface area of acetylene black. A specific surface area of acetylene black can be increased by oxidizing the surface of acetylene black with air, oxygen or the like at a temperature of 500 ° C. or higher (Patent Document 1). The acetylene black having a high specific surface area as described above is used as a catalyst carrier, but there are agglomerated particles in which acetylene blacks are partly aggregated.

  As the battery manufacturing technology has been improved in recent years, as a result of the progress of thinning, there has been a demand for reducing the above-mentioned aggregated particles. When the aggregated particles are present, protrusions due to the aggregated particles are formed on the coating surface of the positive electrode or the catalyst layer, and charge concentration occurs in the vicinity thereof, which causes the battery life to be shortened. In acetylene black, a bonded body of primary particles called a structure is developed in a branch shape, and it is necessary to loosen the entanglement between the structures to reduce the aggregated particles, but it is not easy.

  As a technique for reducing carbon black aggregated particles, the carbon black and ion exchange resin are mixed with a solvent to form a slurry, and this is made into an external shearing machine (bead mill, ball mill, three rolls, etc.) and an internal shearing machine (ultrasonic homogenizer, Crushing using a jet mill or the like has been proposed (Patent Document 2). In addition, methods have been proposed in which the carbon black itself is pulverized with various pulverization apparatuses (jet mill, planetary mill, etc.) in the form of powder (Patent Documents 3 and 4). However, acetylene black used in this application not only has a structure developed more than that of general carbon black, but also has a high specific surface area, so that there is a limit to crushing by post-treatment.

JP-A-61-66759 JP 2005-216661 A JP-A-2005-41967 JP 2006-274189 A

  An object of the present invention is to provide a carbon black having a high specific surface area, high crystallinity, and low agglomeration.

The present invention employs the following means in order to solve the above problems.
(1) Carbon black having a specific surface area of 300 to 1100 m ² / g, a crystal layer thickness (Lc) of 25 to 100 mm, and a maximum diameter of aggregated particles of 20 μm or less.
(2) The carbon black as described in (1) above, having a bulk density of 0.010 to 0.030 g / cm ³ .
(3) The carbon black as described in (1) or (2) above, which has a dispersity of 20 μm or less by a tube gauge specified in JIS K 5600-2-5.
(4) A battery electrode using the carbon black according to any one of (1) to (3).

The carbon black of the present invention has a high specific surface area and a high crystal, and when used as a battery material, higher performance can be obtained than before. In addition, since aggregated particles are reduced, high dispersion is possible when mixed with water, alcohol, or other solvents, and a uniform flat surface can be obtained without special consideration during coating. Since it can be made thinner than the conventional one and the number of stacked layers can be increased, the battery performance is improved.

The carbon black of the present invention has a specific surface area of 300 to 1100 m ² / g. If it is less than 300 m < ² > / g, it cannot fully disperse | distribute in an electrode slurry or a catalyst loading process etc., and a desired performance cannot be obtained. When it exceeds 1100 m ² / g, it is difficult to soak in the chemical solution in the above-mentioned process, and desired performance cannot be obtained. The crystal layer thickness (Lc) measured by X-ray diffraction is 25 to 100 mm. If it is less than 25%, the crystallinity is insufficient and the conductivity cannot be sufficiently provided. If it exceeds 100 mm, the primary particle size becomes too large and high dispersion cannot be maintained.

  In the carbon black of the present invention, the maximum diameter of the aggregated particles is 20 μm or less. When aggregated particles having a size of 20 μm or more are present, the surface smoothness cannot be maintained by the aggregated particles at the time of coating, and the density of electric charges is generated in the concavo-convex portions, resulting in deterioration of battery characteristics.

  The carbon black of the present invention is preferably a carbon black having a dispersity of 20 μm or less by a tube gauge specified in JIS K 5600-2-5. The average agglomerated particle size can be measured with a tube gauge, but is preferably 20 μm or less.

  As an example of the method for producing carbon black of the present invention, a raw material (acetylene, benzene, etc.) is first subjected to incomplete combustion reaction in a reaction furnace to produce carbon black having a high specific surface area. This carbon black having a high specific surface area can be produced by containing moisture and then oxidizing it using an oxidizing gas such as air or ozone.

The carbon black synthesized in the process of paragraph (0014) is the carbon black raw material powder of the present invention, and the aggregated particles are reduced as compared with the conventional carbon black, but since it remains, a ball mill, a vibration mill, A step of reducing aggregated particles using a jet mill or the like is necessary. In particular, when a jet mill is used, aggregated particles can be more effectively reduced. Of the physical properties of the raw material powder used for the process of reducing the aggregated particles, the specific surface area and bulk density must be within the scope of the claims of the present invention. When the specific surface area is less than 300 m ² / g, the specific surface area is further lowered by this treatment, and sufficient performance cannot be obtained. When the specific surface area exceeds 1100 m ² / g, the effect of reducing aggregation by this step becomes insufficient. When the thickness of the crystalline phase is less than 25 mm, the thickness of the crystalline phase is greatly reduced by crushing, and the battery performance is lowered. When it exceeds 100%, the effect of reducing aggregation by this step becomes insufficient. Furthermore, when the thickness of the crystal phase is in the range of 25 to 65 mm, it is preferable because a decrease in the thickness of the crystal phase after the treatment can be suppressed.

Examples 1-10, Comparative Examples 1-6
Acetylene gas and oxygen gas are mixed and sprayed from a nozzle installed at the top of a carbon black production furnace (furnace total length 5 m, furnace diameter 0.5 m), and acetylene black is obtained by utilizing the thermal decomposition and combustion reaction of acetylene. Manufactured. Thereafter, acetylene black was collected from a bag filter directly connected to the lower part of the furnace. 500 g of the collected acetylene black was hydrated with a constant temperature and humidity device having a temperature of 30 ° C. and a humidity of 50% until the mass reached a steady state. After that, it was put into an electric furnace heated to 700 ° C., and while maintaining the pressure in the furnace at 0.1 kPa, air was introduced at 30 L / hour and oxidation treatment was performed for 1 hour to obtain a high specific surface area, high crystal And high dispersion treatment. This acetylene black was processed with a jet mill under the conditions of a pulverization pressure of 0.3 MPa.

Tables 1 and 2 show the physical properties of the acetylene black raw material powder and the physical properties of the acetylene black-treated powder obtained by processing the raw material powder. In addition, the physical property of the following item was measured as a physical property.
(1) Specific surface area: Measured according to JIS K 6217-2.
(2) Bulk density: Measured according to JIS K 5101-12-2: 2004.
(3) Thickness of the crystal phase: An X-ray diffraction apparatus D8ADVANCE manufactured by Bruker, Inc. was measured, and an X-ray diffraction image of 15 ° to 35 ° of the obtained acetylene black was measured. (Lc) was determined.
(4) Aggregated particle size: As a pretreatment, 0.1 g of acetylene black was added to 10 mL of a 0.5% aqueous solution of sodium hexamethylphosphate, and a dispersion treatment was performed at 150 W for 3 minutes using an ultrasonic water bath. Then, it measured using the flow type particle shape measuring apparatus FPIA-3000 (made by Malvern). The measurement mode was LFP, the count was a quantitative count, the objective lens was 10 times, and a particle image of the sample was taken and analyzed by a computer to determine the particle diameter.
(5) Tub gauge dispersity: As a pretreatment, 0.1 g of acetylene black and 30 g of dibutyl phthalate were put in a centrifugal sedimentation tube, and mixed under a condition of 2000 rpm for 1 minute using a homogenizer (BM-2 manufactured by Nippon Seiki). Then, according to JIS K 5600-2-5, the particle size of the tube was measured with a grind gauge (50 μm or 25 μm groove).

From Table 1, the acetylene black obtained by the Example of this invention has a high specific surface area, high crystallinity, a small aggregated particle diameter, and excellent dispersibility. In particular, by using acetylene black having a specific surface area of 300 to 800 m ² / g and a crystal phase thickness of 25 to 65 mm as a raw material, the agglomerated particles can be reduced while maintaining the specific surface area and crystal phase thickness after treatment. And dispersibility can be improved.

  Electrodes were produced using the acetylene blacks of Examples 8 to 10 and Comparative Example 6, and the number of aggregates (convex portions generated on the coated surface) recognized on the surface was compared. The method for producing the electrode is shown below. Cobalt lithium oxide was used as the positive electrode material, and polyvinylidene fluoride (Kufa Chemical Co., Ltd., KF polymer solution) was used as the binder. A positive electrode mixture (slurry) was prepared by adding and kneading N-methylpyrrolidone (manufactured by Aldrich) as a dispersion solvent. The positive electrode mixture slurry was applied to an aluminum foil to a thickness of 20 μm using a bar coater, and then dried to produce an electrode.

The surface smoothness of the fabricated electrode was evaluated by observing 10 fields of 100 μm square using each SEM and evaluating the number of projections formed on the coated surface. As a result, Example 8 had an average of 0.5, Example 9 had an average of 0.7, Example 10 had an average of 1.3, and Comparative Example 6 had an average of 15.
Since Comparative Example 1 has a specific surface area that is too low and Comparative Example 3 has an excessively thin crystal phase thickness, it is unsuitable for use in an electrode.

The carbon black of the present invention can be used as a battery material or a catalyst carrier.

Claims (4)

An acetylene black having a specific surface area of 300 to 1100 m ² / g, a crystal layer thickness (Lc) of 25 to 100 mm, and a maximum diameter of aggregated particles of 20 μm or less. The acetylene black according to claim 1, wherein the bulk density is from 0.010 to 0.030 g / cm ³ . The acetylene black according to claim 1 or 2, wherein the degree of dispersion by a tube gauge specified in JIS K 5600-2-5 is 20 µm or less. The battery electrode using the acetylene black as described in any one of Claim 1 to 3.