Composite powder, manufacturing method of composite powder, and manufacturing method of dry electrode

Abstract

To provide a composite powder containing an active material and carbon black and having low volume resistivity when pressed.SOLUTION: In a composite powder of an active material and carbon black, the carbon black has a BET specific surface area of 200 m2 / g or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a composite powder, a method for manufacturing the composite powder, and a method for manufacturing a dry electrode. [Background technology]

[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 miniaturize the systems. They also need high output characteristics to enable stable power supply regardless of the ambient temperature. Furthermore, 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 binding material (also called a binder) to form a composite layer. 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 conductivity, a conductive material such as carbon black has been added to the positive electrode paste to impart conductivity (e.g., Patent Document 1).

[0005] However, in conventional methods, when the solvent contained in the positive electrode paste is evaporated, defects such as pinholes and cracks may occur in the composite layer, or the uniformity of the composite layer may be impaired due to differences in the solvent flow rate between the inside and outside of the composite layer. For this reason, in recent years, methods for producing dry electrodes without using solvents have been investigated. For example, Patent Document 2 discloses a method for producing an electrode powder, including: (a) producing a mixture containing an active material, a conductive material, and a binder; (b) kneading the mixture at a temperature ranging from 70°C to 200°C under a pressure equal to or higher than atmospheric pressure to produce a mixture mass in order to fiberize the binder; and (c) pulverizing the mixture mass to obtain an electrode powder (see, for example, Patent Document 2). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-227481 [Patent Document 2] Japanese Patent Application Publication No. 2023-547117 Summary of the Invention [Problem to be solved by the invention]

[0007] The present disclosure aims to provide a composite powder containing an active material and carbon black and having low volume resistivity under pressure, as well as a method for producing the composite powder and a method for producing a dry electrode using the composite powder. [Means for solving the problem]

[0008] The present disclosure relates to, for example, the following [1] to [8]. [1] It is a composite powder of an active material and carbon black, The BET specific surface area of ​​the carbon black is 200m 2 / g or more. [2] The composite powder according to [1], wherein the carbon black content is 0.1 mass % or more and 5 mass % or less based on the total amount of the composite powder. [3] The composite powder according to [1] or [2], wherein the carbon black has an average primary particle size of 15 nm or more and 50 nm or less. [4] The composite powder according to any one of [1] to [3], which is for forming a dry electrode. [5] Active material and 200m 2 and carbon black having a BET specific surface area of ​​1 / 2 g or more, to obtain a composite powder. [6] The method according to [5], wherein the amount of the carbon black is 0.1% by mass or more and 5% by mass or less based on the total amount of the composite powder. [7] The method according to [5] or [6], wherein the dry mixing is performed using an acoustic mixer. [8] A step of mixing the composite powder according to any one of [1] to [4] with a binder to obtain a dry electrode-forming material; a step of providing a composite layer formed by molding the dry electrode-forming material on a current collector to obtain a dry electrode including the current collector and the composite layer; A method for manufacturing a dry electrode, comprising: [Effects of the Invention]

[0009] The present disclosure provides a composite powder containing an active material and carbon black and having low volume resistivity under pressure. The present disclosure also provides a method for producing the composite powder and a method for producing a dry electrode using the composite powder. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram showing the results of observation of the composite powder of Example 1-1 with a tabletop SEM. [Figure 2] FIG. 2 is a diagram showing the results of observation of the composite powder of Example 1-4 by a benchtop SEM. [Figure 3] FIG. 3 is a diagram showing the results of observation of the composite powder of Comparative Example 1-1 with a benchtop SEM. [Figure 4] FIG. 4 is a diagram showing the results of observation of the composite powder of Comparative Example 1-2 with a benchtop SEM. [Figure 5] FIG. 5 is a diagram showing the results of observation of the composite powder of Comparative Example 1-3 by a benchtop SEM. DETAILED DESCRIPTION OF THE INVENTION

[0011] Preferred embodiments of the present disclosure will be described in detail below.

[0012] (composite powder) The composite powder of this embodiment is a composite powder of an active material and carbon black. In the composite powder of this embodiment, the BET specific surface area of ​​the carbon black is 200 m 2 / g or more.

[0013] In the composite powder of this embodiment, the carbon black with a large specific surface area is uniformly attached to the active material, which is thought to efficiently form conductive paths between the active materials, thereby achieving low volume resistivity during pressure molding. Furthermore, while the composite layer that constitutes the positive electrode of a lithium-ion secondary battery contains an active material, a conductive material, and a binder, the composite powder of this embodiment can be said to be a premix of the active material and the conductive material (carbon black). By pre-producing the composite powder of this embodiment, the conductive material, carbon black, is uniformly distributed on the surface of the active material, which is expected to improve the properties of the resulting electrode compared to when the active material, conductive material, and binder are simultaneously mixed.

[0014] The active material may be a powdered active material or an active material powder. The active material may be a positive electrode active material.

[0015] The active material (positive electrode active material) is not particularly limited as long as it is a material that can reversibly store and release cations. 4The lithium-containing composite oxide containing manganese may have a resistivity of Ω·cm or more, or may be a lithium-containing polyanion compound. Examples of the lithium-containing composite oxide containing manganese include LiMnO2, LiMnO3, LiMn2O3, and Li 1+x Mn 2-x Lithium manganese oxide such as O4 (where x = 0 to 0.33); LiMn x Ni y Co z O2 (x+y+z=1, 0≦y<1, 0≦z<1, 0≦x<1), Li 1+x Mn 2-x-y M y O4 (where x = 0 to 0.33, y = 0 to 1.0, 2-xy>0), LiMn 2-x M x Examples of the lithium-containing polyanion compounds include polyanion compounds such as LiFePO4, LiMnPO4, and Li2MPO4F (where M is at least one metal selected from Co, Ni, Fe, Cr, and Zn). In each composition formula, M is at least one metal selected from the group consisting of Fe, Co, Ni, Al, Cu, Mg, Cr, Zn, and Ta.

[0016] The average particle size of the active material may be, for example, 3 μm or more, and from the viewpoint of facilitating packing of the active material and increasing the composite density, may be 5 μm or more, 10 μm or more, or 20 μm or more. The average particle size of the active material may be, for example, 45 μm or less, and from the viewpoint of increasing the number of active material particles per weight and further improving ion diffusibility, may be 40 μm or less, 35 μm or less, or 30 μm or less.

[0017] In this specification, the average particle size of the active material is the average particle size (D 50 ) is shown.

[0018] Carbon black can also be referred to as powdered carbon black or carbon black powder.

[0019] The carbon black may be, for example, acetylene black, furnace black, channel black, etc., and from the viewpoint of obtaining the above-mentioned effects more significantly, acetylene black may be used.

[0020] The BET specific surface area of ​​carbon black is 200m 2 / g or more, and from the viewpoint of obtaining the above-mentioned effect more significantly, 300m 2 / g or more, 400m 2 / g or more, 500m 2 / g or more, 600m 2 / g or more, or 700m 2 The BET specific surface area of ​​the carbon black may be, for example, 2000 m / g or more. 2 / g or less, and from the viewpoint of reducing the interaction between the conductive materials and improving the dispersibility, 1500 m 2 / g or less, 1400m 2 / g or less, or 1300m 2 / g or less.

[0021] The BET specific surface area of ​​carbon black is a value measured by the static volume method in accordance with JIS Z 8830 using nitrogen as the adsorbate.

[0022] The average primary particle size of the carbon black may be, for example, 15 nm or more, and from the viewpoint of facilitating dispersion of the conductive material in the mixed powder, may be 16 nm or more, 17 nm or more, or 18 nm or more. The average primary particle size of the carbon black may be, for example, 50 nm or less, 40 nm or less, 30 nm or less, or 20 nm or less.

[0023] The average primary particle diameter of carbon black was determined by taking 10 images at 100,000 magnification using a transmission electron microscope JEM-2000FX (manufactured by JEOL Ltd.), determining the circle-equivalent diameter of at least 200 randomly selected primary particles through image analysis, and then calculating the arithmetic mean of these values.

[0024] The oil absorption of the carbon black may be, for example, 300 mL / 100 g or more, and from the viewpoint of increasing the number of electrical contacts with the active material and obtaining a better conductive path, may be 325 mL / 100 g or more, 350 mL / 100 g or more, or 375 mL / 100 g or more. The oil absorption of the carbon black may be, for example, 500 mL / 100 g or less, and from the viewpoint of facilitating dispersion of the conductive material in the mixed powder, may be 475 mL / 100 g or less, 450 mL / 100 g or less, or 425 mL / 100 g or less.

[0025] The oil absorption amount in this specification is an index for evaluating the ability of carbon black to absorb dibutyl phthalate (DBP) into the voids formed by the particle surface and structure, and is a value measured by the method described in JIS K6217-4:2008.

[0026] The carbon black content may be, for example, 0.1% by mass or more based on the total amount of the composite powder, and from the viewpoint of increasing the number of electrical contacts with the active material and obtaining a better conductive path, it may be 0.3% by mass or more, 0.5% by mass or more, or 0.7% by mass or more. The carbon black content may be, for example, 5% by mass or less based on the total amount of the composite powder, and from the viewpoint of increasing the proportion of the active material in the composite and increasing the battery capacity, it may be 4% by mass or less, 3% by mass or less, or 2% by mass or less.

[0027] The carbon black content may be, for example, 0.1 parts by mass or more relative to 100 parts by mass of active material, and from the viewpoint of increasing the number of electrical contacts with the active material and obtaining a better conductive path, it may be 0.3 parts by mass or more, 0.5 parts by mass or more, or 0.7 parts by mass or more. The carbon black content may be, for example, 5 parts by mass or less relative to 100 parts by mass of active material, and from the viewpoint of increasing the proportion of active material in the composite and increasing battery capacity, it may be 4 parts by mass or less, 3 parts by mass or less, or 2 parts by mass or less.

[0028] The composite powder may further contain components other than the active material and carbon black. Examples of the other components include metal materials (e.g., copper, nickel, etc.), carbon materials (e.g., amorphous carbon, etc.), and organic materials (e.g., polymer compounds, etc.). Examples of amorphous carbon include graphite, graphene, needle coke, carbon nanotubes, fullerene, and VGCF. Examples of polymer compounds include polyvinyl alcohol, polyvinylpyrrolidone, polyvinyl butyral, carboxymethyl cellulose and its salts, polyvinyl acetal, polyvinyl acetate, polyvinylamine, and polyvinyl formal.

[0029] The content of other components may be, for example, 3 mass% or less, 2 mass% or less, 1 mass% or less, 0.5 mass% or less, or 0.1 mass% or less, based on the total amount of the composite powder, or may be 0 mass%.

[0030] The composite powder of this embodiment can be produced, for example, by the following production method.

[0031] (Method for manufacturing composite powder) The method for producing the composite powder of this embodiment is to mix an active material and 200 ml 2 The method includes a mixing step of dry-mixing the composite powder with carbon black having a BET specific surface area of ​​1 / 2 g or more to obtain a composite powder.

[0032] In the manufacturing method of this embodiment, examples of the active material and carbon black are the same as those described above.

[0033] The amount of carbon black mixed in the mixing step may be, for example, 0.1% by mass or more based on the total amount of powder mixed in the mixing step, and from the viewpoint of increasing the number of electrical contacts with the active material and obtaining a better conductive path, may be 0.3% by mass or more, 0.5% by mass or more, or 0.7% by mass or more. The amount of carbon black mixed in the mixing step may be, for example, 5% by mass or less based on the total amount of powder mixed in the mixing step, and from the viewpoint of increasing the proportion of active material in the composite and increasing battery capacity, may be 4% by mass or less, 3% by mass or less, or 2% by mass or less.

[0034] The amount of carbon black mixed in the mixing step may be, for example, 0.1 parts by mass or more relative to 100 parts by mass of active material, and from the viewpoint of increasing the number of electrical contacts with the active material and obtaining a better conductive path, it may be 0.3 parts by mass or more, 0.5 parts by mass or more, or 0.7 parts by mass or more. The amount of carbon black mixed in the mixing step may be, for example, 5 parts by mass or less relative to 100 parts by mass of active material, and from the viewpoint of increasing the proportion of active material in the composite and increasing battery capacity, it may be 4 parts by mass or less, 3 parts by mass or less, or 2 parts by mass or less.

[0035] Dry mixing refers to a method of directly mixing powders together without using a liquid medium. In the mixing step, the dry mixing method may be appropriately selected from known dry mixing methods.

[0036] From the viewpoint of suppressing crushing of the active material and carbon black during mixing and achieving the above-mentioned effects more significantly, it is preferable that the dry mixing be performed using an acoustic mixer. The conditions for mixing using an acoustic mixer are not particularly limited, and for example, the vibration acceleration may be 10 G to 100 G, or may be 30 G to 80 G. Furthermore, the vibration time may be, for example, 1 minute to 90 minutes, or may be 1 minute to 30 minutes.

[0037] The composite powder of the present embodiment has a low volume resistivity when pressed, and therefore can be suitably used as a material for forming a dry electrode. For example, a material for forming a dry electrode can be obtained by mixing the composite powder of the present embodiment with a binder.

[0038] (Dry electrode manufacturing method) The method for producing a dry electrode of this embodiment includes a step (i) of mixing the above-mentioned composite powder with a binder to obtain a dry-electrode-forming material, and a step (ii) of providing a composite layer formed by molding the dry-electrode-forming material on a current collector to obtain a dry electrode including the current collector and the composite layer.

[0039] In the manufacturing method of this embodiment, a composite powder of a mixture of an active material and carbon black is prepared in advance, and the mixed powder is mixed with a binder to obtain a dry electrode-forming material. Therefore, in the manufacturing method of this embodiment, the conductive carbon black is uniformly distributed on the surface of the active material, and it is expected that the characteristics of the resulting electrode will be improved compared to when the active material, conductive material, and binder are mixed simultaneously.

[0040] In step (i), the method for mixing the composite powder and the binder is not particularly limited, but dry mixing is preferred in order to maintain the relationship between the active material and the carbon black in the composite powder.

[0041] The dry mixing method is not particularly limited, and may be appropriately selected from known dry mixing methods.

[0042] Examples of binders include polyvinylidene fluoride, polytetrafluoroethylene, styrene-butadiene copolymer, (meth)acrylic acid ester copolymer, etc. The polymer structure of the binder may be, for example, a random copolymer, an alternating copolymer, a graft copolymer, a block copolymer, etc. As the binder, polytetrafluoroethylene is preferred from the viewpoint of excellent voltage resistance.

[0043] In step (i), the amount of binder mixed may be, for example, 0.5 parts by mass or more relative to 100 parts by mass of the composite powder, and may be 0.75 parts by mass or more, 1 part by mass or more, or 1.25 parts by mass or more from the viewpoint that the active material is more firmly held in the composite layer, the mechanical strength of the composite layer is further improved, and battery performance such as cycle characteristics is more likely to be improved. Also, in step (i), the amount of binder mixed may be, for example, 5 parts by mass or less relative to 100 parts by mass of the composite powder, and may be 3 parts by mass or less, 2 parts by mass or less, or 1 part by mass or less from the viewpoint that the proportions of active material and carbon black in the composite are increased and better battery capacity and conductivity are more likely to be obtained.

[0044] In the step (ii), the mixture layer is formed by molding a dry electrode-forming material, and contains an active material, carbon black, and a binder.

[0045] The current collector is not particularly limited, and known current collectors can be used without any particular limitations. Examples of current collectors include 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). At least one side of the metal foil may be coated with a conductive primer. The conductive primer may contain, for example, a conductive material (e.g., a carbon material) and a binder.

[0046] The current collector is preferably made of aluminum for the positive electrode and copper for the negative electrode. The current collector is generally provided in the form of a foil, but is not limited thereto, and perforated foil and mesh current collectors can also be used.

[0047] Step (ii) may include, for example, step (ii-1) of molding a dry electrode-forming material to obtain a composite film, and step (ii-2) of laminating the composite film onto a current collector to obtain a dry electrode.

[0048] In the step (ii-1), the method for forming the composite film is not particularly limited and may be appropriately selected from known film forming methods, such as calendaring and extrusion molding.

[0049] Step (ii-2) may be performed, for example, by rolling the composite film to a predetermined thickness and adhering it onto a current collector, thereby forming a dry electrode including a composite layer of a predetermined thickness and a current collector.

[0050] The thickness of the composite layer is not particularly limited and may be, for example, 10 μm or more, 20 μm or more, or 30 μm or more, or may be, for example, 1 mm or less, 500 μm or less, or 450 μm or less.

[0051] The dry electrode produced by the production method of this embodiment can be suitably used as a positive electrode for a battery, particularly as a positive electrode for a lithium ion secondary battery.

[0052] Although the preferred embodiments of the present disclosure have been described above, the present disclosure is not limited to the above embodiments. [Example]

[0053] The present disclosure will be described in more detail below with reference to examples, but the present disclosure is not limited to these examples.

[0054] (Example 1-1) (1) Preparation of materials LiNi as the active material 0.6 Mn 0.2 Co 0.2 O2 (manufactured by Tosho Technology Co., Ltd.) is a conductive material with a BET specific surface area of ​​823m 2 / g of carbon black (manufactured by Denka Company Ltd.) was prepared. The average primary particle size, BET specific surface area, and oil absorption of the carbon black were measured by the following methods. The average particle size of the active material was also measured by the following method. The results are shown in Table 1.

[0055] (Measurement of the average primary particle size of carbon black) The average primary particle diameter of carbon black was determined by taking 10 images at 100,000 magnification using a transmission electron microscope JEM-2000FX (manufactured by JEOL Ltd.), determining the circle-equivalent diameter of at least 200 randomly selected primary particles through image analysis, and then calculating the arithmetic mean of these values.

[0056] (Measurement of BET specific surface area of ​​carbon black) The BET specific surface area of ​​the carbon black was measured by the static volume method in accordance with JIS Z 8830 using nitrogen as the adsorbate.

[0057] (Measurement of oil absorption of carbon black) The oil absorption of carbon black is a value measured by the method described in JIS K6217-4:2008.

[0058] (2) Preparation and evaluation of composite powder The active material and carbon black were weighed out so that the active material and carbon black were 99% by mass and 1% by mass, respectively (1.01 parts by mass of carbon black per 100 parts by mass of active material), and then filled into a 20 mL plastic container. The container was placed in a low-frequency resonant acoustic mixer (LabRAM II, manufactured by Resodyn Acoustic Mixers) and treated for 30 minutes under a vibration acceleration of 50 G to obtain a composite powder. Observation of the composite powder using a benchtop SEM JCM-6000Plus (manufactured by JEOL Ltd.) confirmed that the carbon black was uniformly adhered to the active material. Figure 1 shows the results of benchtop SEM observation of the composite powder of Example 1-1. The volume resistivity of the obtained composite powder was measured using the following method.

[0059] (Volume resistivity measurement) The measurement equipment used was a powder resistivity measurement system (product name: MCP-PD51, manufactured by Nitto Seiko Analytech Co., Ltd.) equipped with a resistivity meter (product name: Loresta GP, manufactured by Mitsubishi Chemical Analytech Co., Ltd.). 3.5 g of the composite powder was filled into a measurement container and pressurized with 7.5 kN to measure the volume resistivity. The measurement conditions were a four-point probe, electrode spacing of 3 mm, electrode radius of 0.7 mm, and sample radius of 10 mm.

[0060] (Examples 1-2 to 1-4) (1) Preparation of materials The same active material as in Example 1-1 was prepared as the active material. Carbon black (manufactured by Denka Co., Ltd.) having the properties shown in Table 1 was prepared as the conductive material. (2) Preparation and evaluation of composite powder Except for changing the carbon black, composite powders were produced and evaluated in the same manner as in Example 1-1. The results are shown in Table 1. Note that Figure 2 shows the results of observation of the composite powder of Example 1-4 with a benchtop SEM.

[0061] (Comparative Examples 1-1 to 1-5) (1) Preparation of materials The same active material as in Example 1-1 was prepared as the active material. Carbon black (manufactured by Denka Co., Ltd.) having the properties shown in Table 1 was prepared as the conductive material. (2) Preparation and evaluation of composite powder Except for changing the carbon black, composite powders were produced and evaluated in the same manner as in Example 1-1. The results are shown in Table 1. FIG. 3 shows the results of observation of the composite powder of Comparative Example 1-1 using a benchtop SEM. FIG. 4 shows the results of observation of the composite powder of Comparative Example 1-2 using a benchtop SEM. FIG. 5 shows the results of observation of the composite powder of Comparative Example 1-3 using a benchtop SEM.

[0062] [Table 1]

[0063] Example 2-1 The composite powder was prepared and evaluated in the same manner as in Example 1-1, except that the active material was weighed out to be 98 mass % and the carbon black was weighed out to be 2 mass % (2.04 mass parts of carbon black per 100 mass parts of active material). The results are shown in Table 2.

[0064] (Examples 2-2 to 2-4) A composite powder was produced and evaluated in the same manner as in Example 2-1, except that the carbon black was changed to carbon black having the properties shown in Table 2. The results are shown in Table 2.

[0065] (Comparative Examples 2-1 to 2-4) A composite powder was produced and evaluated in the same manner as in Example 2-1, except that the carbon black was changed to carbon black having the properties shown in Table 2. The results are shown in Table 2.

[0066] [Table 2]

[0067] Example 3-1 The composite powder was prepared and evaluated in the same manner as in Example 1-1, except that the active material was weighed out to be 97 mass % and the carbon black was weighed out to be 3 mass % (3.09 mass parts of carbon black per 100 mass parts of active material). The results are shown in Table 3.

[0068] (Examples 3-2 to 3-4) A composite powder was produced and evaluated in the same manner as in Example 3-1, except that the carbon black was changed to carbon black having the properties shown in Table 3. The results are shown in Table 3.

[0069] (Comparative Examples 3-1 to 3-3) A composite powder was produced and evaluated in the same manner as in Example 3-1, except that the carbon black was changed to carbon black having the properties shown in Table 3. The results are shown in Table 3.

[0070]

Table 3

Claims

1. It is a composite powder of an active material and carbon black, The BET specific surface area of ​​the carbon black is 200 m ２ / g or more.

2. The composite powder according to claim 1, wherein the content of the carbon black is 0.1 mass % or more and 5 mass % or less based on the total amount of the composite powder.

3. 2. The composite powder according to claim 1, wherein the average primary particle size of the carbon black is 15 nm or more and 50 nm or less.

4. The composite powder according to claim 1, which is used for forming a dry electrode.

5. Active material and 200m ２ and carbon black having a BET specific surface area of ​​1 / 2 g or more, to obtain a composite powder.

6. The method according to claim 5 , wherein the amount of the carbon black is 0.1% by mass or more and 5% by mass or less based on the total amount of the composite powder.

7. The method of claim 5, wherein the dry mixing is performed using an acoustic mixer.

8. A step of mixing the composite powder according to any one of claims 1 to 4 with a binder to obtain a dry electrode-forming material; a step of providing a composite layer formed by molding the dry electrode-forming material on a current collector to obtain a dry electrode including the current collector and the composite layer; A method for manufacturing a dry electrode, comprising:

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