Carbon composite active material-based material and method for producing same, electrode and method for producing same, and secondary battery

Abstract

This carbon composite active material-based material includes an electrode active material and a graphene material, and has an angle of repose of 20-45°.

Description

Carbon composite active material and manufacturing method thereof, electrode and manufacturing method thereof, and secondary battery

[0001] The present disclosure relates to a carbon composite active material and a method for producing the same, an electrode and a method for producing the same, and a secondary battery.

[0002] With the trend toward smaller and lighter electronic materials and the advancement of hybrid and electric vehicles (HEVs) and electric vehicles (EVs), there is a demand for smaller and larger-capacity secondary batteries, which are the driving sources for these vehicles. Among secondary batteries, various technological developments are being conducted for lithium-ion secondary batteries, which have the advantages of high voltage and high energy density.

[0003] Patent Document 1 discloses a technique for using a composite as a positive electrode active material for a lithium-ion secondary battery, which is formed by adhering a large number of particles of a carbon material (such as acetylene black) as a conductive additive to the surface of a phosphoric acid compound, and which has a specific surface area per unit mass of the positive electrode active material of a predetermined value or more. While phosphoric acid compounds have advantages such as high safety, they have the problem of low electronic conductivity. However, it has been reported that the composite increases the contact area between the positive electrode active material and the conductive additive, thereby improving electronic conductivity.

[0004] However, acetylene black is a bulky particle with an average particle size of several tens to several hundreds of nanometers, and contact with the active material is point contact with high contact resistance. In an active material layer where the active material and the conductive additive are connected by point contact, it is difficult to form a network for electronic conduction, resulting in low electronic conductivity. To improve electronic conductivity, it is necessary to increase the amount of conductive additive to increase the number of contact points. However, increasing the amount of conductive additive reduces the ratio of the active material in the electrode, which leads to a problem of reducing the discharge capacity of a secondary battery using the electrode.

[0005] Patent Literature 2 discloses a technique of using graphene as a conductive additive contained in a positive electrode active material layer. In a positive electrode active material layer using graphene as a conductive additive, graphene particles are connected to each other through surface contact, forming an electron conduction network. An active material layer having conductive paths connected through surface contact has high electron conductivity.

[0006] JP 2002-110162 A JP 2020-21745 A

[0007] In recent years, there has been a demand for further improvement in the battery capacity of secondary batteries, but sufficient battery capacity has not yet been achieved with either of the techniques disclosed in Patent Documents 1 and 2. The present disclosure has been made in view of the above-described circumstances, and aims to provide a carbon composite active material capable of improving battery capacity, and to provide related techniques.

[0008] To achieve the above object, the present disclosure provides the following means.

[0009] <Carbon composite active material> [1] A carbon composite active material comprising an electrode active material and a graphene material, and having an angle of repose of 20° to 45°. [2] The carbon composite active material of [1], wherein the graphene material forms a surface layer that covers at least a part of the surface of the electrode active material, and the coverage of the surface layer is 10% or more. [3] The carbon composite active material of [1], wherein the graphene material comprises an anionic functional group and a counter cation of the anionic functional group at an end, and the peak intensity ratio (I Ｄ / I Ｇ) is 0.50 or less. [4] The carbon composite active material of any of [1] to [3], wherein a content ratio of the graphene material to the electrode active material is 0.1 to 2.4 in mass ratio. [5] The carbon composite active material of any of [1] to [4], wherein a ratio (DG / DA) of a planar size DG of the graphene material to a particle size DA of the electrode active material is 0.002 to 3.000. [6] The carbon composite active material of any of [2] to [5], wherein the surface layer contains the graphene material and a binder. [7] The carbon composite active material of any of [1] to [6], wherein the electrode active material is a positive electrode active material. [8] The carbon composite active material of [7], wherein the positive electrode active material is a lithium-containing composite oxide. <Secondary battery> [9] A secondary battery comprising an electrode formed using a slurry containing the carbon composite active material according to any one of [1] to [8]. <Method for producing a carbon composite active material>

[10] A method for producing a carbon composite active material in which the surface of an electrode active material is coated with a graphene material, the method comprising the steps of fluidizing the electrode active material in a tumbling fluidized bed granulator and spraying a solution containing the graphene material into the tumbling fluidized bed granulator, wherein the carbon composite active material has an angle of repose of 20° to 45°.

[11] A method for producing a carbon composite active material according to

[10] , in which the spraying is carried out under the following conditions: Solution concentration (mass %): 1 to 10 Spray rate (g / sec): 2 to 4 Spray time (min): 5 to 180

[12] A method for producing a carbon composite active material according to

[11] , the method comprising the steps of calcining the granules obtained in the spraying step under the following conditions. Firing atmosphere: nitrogen Firing temperature (°C): 200 to 350°C Firing time (hours): 24 to 48 hours

[13] The method for producing a carbon composite active material according to any one of

[10] to

[12] , wherein the graphene material has a surface layer that covers at least a part of the surface of the electrode active material, and the coverage of the surface layer is 10% or more.

[14] The graphene material contains an anionic functional group and a counter cation of the anionic functional group at an end, and the peak intensity ratio (I Ｄ / I Ｇ) is 0.50 or less.

[0010] According to the present disclosure, the battery capacity of a secondary battery can be improved.

[0011] 1 is a graph showing the results of measuring powder resistivity.

[0023] FIG. 1 is a schematic diagram of a tumbling fluidized bed granulation apparatus. The image of an electrode active material observed at 4000x magnification using a JEOL JEM-ARM200F NEOARM atomic resolution analytical electron microscope (TEM) was processed using image analysis software TEM Control System (TEMCON). The image of a carbon composite active material according to an embodiment of the present disclosure observed at 4000x magnification using a JEOL JEM-ARM200F NEOARM atomic resolution analytical electron microscope (TEM) was processed using image analysis software Digital Micrograph. The image of a carbon composite active material according to an embodiment of the present disclosure observed at 4000x magnification using a JEOL JEM-ARM200F NEOARM atomic resolution analytical electron microscope (TEM) was processed using image analysis software Digital Micrograph. The image of a tumbling fluidized bed granulation apparatus. ...

[0012] The present disclosure will be described in detail below with reference to one embodiment. In this specification, the expression "XX to YY" means "XX or more and YY or less." Furthermore, in this specification, for numerical ranges (e.g., ranges of content, etc.), lower and upper limits described in stages can be independently combined. Furthermore, in the numerical ranges described in this specification, the upper or lower limit of the numerical range may be replaced with a value shown in an example.

[0013] [Carbon Composite Active Material] The carbon composite active material of the present disclosure includes an electrode active material and a graphene material, and has an angle of repose of 20° to 45°. The angle of repose may be 20° to 40°, or may be 20° to 30°.

[0014] Here, the "angle of repose" refers to the angle between the slope of the mound of a carbon composite active material and a horizontal plane when the carbon composite active material is dropped from a certain height and forms a stable mound on the horizontal plane without spontaneously collapsing. The smoother the surface of the carbon composite active material, the higher the fluidity and the smaller the angle of repose. The angle of repose can also be measured using a known instrument for measuring powder properties. For example, the angle of repose can be measured using a powder tester manufactured by Hosokawa Micron Corporation.

[0015] The graphene material may form a surface layer that covers at least a portion of the surface of the electrode active material. The coverage of the surface layer may be 10% or more, 15% or more, or 20% or more. Here, "coverage" refers to the degree of coverage area relative to the particles of the electrode active material. The coverage can be calculated, for example, by using a field emission scanning electron microscope (FE-SEM, SU8600, manufactured by Hitachi High-Technologies Corporation) to observe the particles in the backscattered electron image TD observation mode (accelerating voltage: 1.5 kV during observation, observation magnification: 3500x), and then using image processing software ImageJ (National Institutes of Health, USA) to clarify the difference between the electrode active material (white) and the coated graphene (black) using threshold processing, and then measuring the coverage area, thereby calculating the coverage relative to the total area.

[0016] An electrode active material that does not have the surface layer made of the graphene material has an uneven surface as shown in Fig. 1. On the other hand, a carbon composite active material in which the surface layer made of the graphene material is formed on the surface of the electrode active material has a highly smooth surface as shown in Fig. 2.

[0017] 3, the carbon composite active material having the surface layer of the graphene material formed on the surface of the electrode active material has a lower powder resistivity than an electrode active material not having the surface layer of the graphene material. The powder resistivity may be less than 7 Ω cm, less than 5 Ω cm, or less than 2 Ω cm.

[0018] Here, "powder resistivity" is a parameter that represents the conductivity of a material itself. Powder resistivity is the volume resistivity of the powder and is different from the resistivity of the pole pieces. Powder resistivity can be measured, for example, using a powder resistivity measurement system (MCP-PD51) and a low-resistivity powder probe (MCP-PD511) manufactured by Nitto Seiko Analytech Co., Ltd., using a constant current four-probe method. Specifically, for example, a powder sample is uniformly mixed and filled into a dedicated measurement cell. A pressure of up to 20 kN is applied to the powder sample in stages using the built-in load cell. An appropriate probe (ring probe or four-probe probe) is selected based on JIS K7194:1994, and a current is applied through the probe to calculate the volume resistivity of the powder.

[0019] In an electrode using a carbon composite active material in which the surface layer made of the graphene material is formed on the surface of the electrode active material, the electronic conductivity is improved, so that the blending ratio of the conductive additive in the electrode components can be reduced, and the blending amount of the active material can be increased, thereby improving the battery capacity. The mechanism by which the electronic conductivity is improved is presumed to be that the conductive additive, which is the graphene material, is present so as to coat the surface of the electrode active material, and therefore the conductive additive is efficiently utilized when electrons move within the electrode.

[0020] The content of the graphene material in the carbon composite active material may be 0.1 to 2.4 mass%, 0.6 to 2.4 mass%, or 1.0 to 2.4 mass%. When the content of the graphene material is 0.1 mass% or more, the highly conductive graphene material uniformly coats the surface of the active material, allowing the blending ratio of conventional conductive additives in the electrode components to be reduced. As a result, the amount of conductive additive used can be reduced, allowing the blending amount of the active material to be increased. This improves the total capacity of the battery. By limiting the content of the graphene material to 2.4 mass% or less, material costs can be optimized. In other words, by setting the content of the graphene material within the above range, maximum electrode performance can be achieved with the minimum amount of graphene used.

[0021] The content of graphene material can be determined from the difference between the carbon content (mass%) in the carbon composite active material and the carbon content (mass%) in the electrode active material. The carbon content can be determined, for example, by heating a solid sample at high temperature in a high-frequency induction furnace, causing a reaction of the carbon components in the sample to gasify as carbon dioxide, introducing the gas into an infrared detector, detecting the absorbance of the carbon dioxide molecules with the infrared detector, calculating the carbon dioxide concentration from the absorbance, and then calculating the carbon dioxide concentration data.

[0022] In the carbon composite active material, the content ratio of the graphene material to the electrode active material may be, in mass ratio, 0.01 to 0.3, 0.01 to 0.17, or 0.01 to 0.06.

[0023] When the carbon composite active material contains a binder, the content of the binder in the carbon composite active material may be 0.01 to 0.7% by mass, 0.01 to 0.25% by mass, or 0.01 to 0.06% by mass. A binder content of 0.01% by mass or more can prevent exfoliation of the graphene material, thereby avoiding a decrease in conductivity and stability due to exfoliation of the graphene material. A binder content of 0.7% by mass or less can prevent a decrease in the reactive surface area of ​​the electrode active material, thereby avoiding a decrease in the diffusion efficiency of lithium ions and the electrolyte due to a decrease in the reactive surface area of ​​the electrode active material. In other words, by setting the binder content within the above range, electrode performance can be improved without deteriorating battery characteristics.

[0024] When the carbon composite active substance contains a binder, the content ratio of the graphene material to the binder, in mass ratio, may be 3 to 40, 15 to 40, or 25 to 40. When the content ratio is within the above range, the high electronic conductivity of graphene can be utilized, the electrode structure can be stabilized by interaction with the binder, and the internal resistance can be reduced by improving the migration paths of electrons and lithium ions.

[0025] In the obtained carbon composite active material, the ratio (DG / DA) of the planar size DG of the graphene material to the particle size DA of the electrode active material may be 0.002 to 3.000, 0.003 to 0.400, or 0.020 to 0.100. When DG / DA is 3.000 or less, the graphene material can be easily coated on the surfaces of the electrode active material particles, and when DG / DA is 0.002 or more, the internal resistance (electron / lithium ion transfer resistance) of a secondary battery using an electrode formed with the carbon composite active material is reduced, and electronic conductivity is improved.

[0026] The planar size DG of the graphene material refers to the planar size, i.e., the long side of the plate-like graphene material. Specifically, it can be measured by the method described in the Examples.

[0027] The particle size DA of the electrode active material refers to the average of the longest and shortest diameters of the electrode active material particles, and can be measured by the method described in the Examples.

[0028] <Graphene Material> The graphene material contained in the surface layer of the carbon composite active material may be a graphene material obtained by introducing a modifying group into a base material graphene. Specifically, the graphene material contains an anionic functional group and a counter cation of the anionic functional group at its terminal, and has a peak at 1300 to 1400 cm in a Raman spectrum. －１ The D band peak intensity I in the range Ｄ and 1550-1650 cm －１ The G-band peak intensity I in the range Ｇ The peak intensity ratio (I Ｄ / I Ｇ ) may be 0.50 or less.

[0029] Graphene materials may have some structural defects from the viewpoint of improving ionic conductivity. When a graphene material contains structural defects, ions can move through the structural defects, thereby improving ionic conductivity. On the other hand, if the graphene material has too many structural defects, it will have low conductivity. Structural defects in graphene materials can be measured by Raman spectroscopy. The D band is a peak derived from defects in the graphene material, and the G band is a peak derived from the graphite structure of the graphene material. In a perfect graphite crystal, I is originally Ｄ However, as the symmetry of the graphite structure is lost, the peak of I Ｄ As the peaks become more intense and the graphene material has more structural defects, the peak intensity ratio (I Ｄ / I Ｇ In a graphene material containing an anionic functional group and a counter cation of the anionic functional group at its terminal, the peak intensity ratio (I Ｄ / I Ｇ By using a graphene material having a peak intensity ratio (I) of 0.50 or less as a conductive additive, it is possible to achieve both ionic conductivity and electrical conductivity. Ｄ / I Ｇ The lower limit of the peak intensity ratio (I) is not limited, but from the viewpoint of current manufacturing technology, it may be 0.10 or more. Ｄ / I Ｇ ) may be 0.10 to 0.50, 0.11 to 0.40, or 0.12 to 0.30. All of the peak intensity ratios are measured using a solid-state laser as the excitation laser at an excitation wavelength of 514.79 nm. In Raman spectroscopy, graphene powder has a peak intensity of 1570 cm －１ Nearby and 1345cm －１ It has a peak near

[0030] (Graphene) In the present disclosure, graphene refers to a one-atom-thick sp ２ It refers to a flake-like sheet material in which sheets of bonded carbon atoms (single-layer graphene) are stacked together, and the number of layers in the stack may be less than 100, less than 50, or less than 20.

[0031] The average particle size of graphene is not particularly limited, but in one embodiment, from the viewpoint of dispersibility, it may be 0.5 to 15 μm, 1.0 to 10 μm, or 1.5 to 5 μm. In the present disclosure, the average particle size of graphene refers to the particle size (D50) at which the cumulative number in the particle size distribution is 50%. The average particle size of graphene can be measured using a laser diffraction particle size distribution meter (for example, MT3300EXII, manufactured by Microtrackbell Corporation).

[0032] Graphene having the above average particle size can be obtained by pulverizing a carbon material having a particle size of 1 to 700 μm using a known pulverizer. The carbon material may have a particle size of 3 to 500 μm, 5 to 300 μm, or 10 to 200 μm. Examples of known pulverizers include dry pulverizers such as a ball mill, planetary mill, stirring mill, bead mill, jet mill, hammer mill, and high-speed stirrer, and may also be a ball mill, planetary mill, stirring mill, or bead mill that uses media. From the viewpoint of improving productivity, it is preferable that the rotation speed for stirring is high and the stirring time is short.

[0033] The carbon atom content in graphene is not particularly limited and may be 95 mass % or more, 99 mass % or more, or 100 mass %. The impurity substance content in graphene is not particularly limited and may be 5 mass % or less, 1 mass % or less, or 0 mass %.

[0034] From the viewpoint of dispersibility, the thickness of graphene may be 0.3 to 60.0 nm, 0.3 to 30.0 nm, or 0.6 to 12.0 nm. The "thickness" referred to here refers to the thickness of one layer in the case of a single layer, and refers to the thickness of the entire layer in the case of a multilayer. The thickness of graphene can be measured using, for example, an atomic force microscope.

[0035] (Modifying Group) In graphene materials, the modifying group introduced into the base graphene consists of an anionic functional group and a counter cation of the anionic functional group. It is inferred that the anionic functional group binds to the edge of the graphene particle, and the counter cation is attracted around the negatively charged graphene.

[0036] As described below, during the production of graphene material, the grinding of graphite is promoted, and radicals are generated on the fracture surfaces of the graphite during grinding. It is believed that the counter anions of the water-soluble salt bond to graphene through a weak acid liberation reaction between the radicals generated on the fracture surfaces of the graphite and a weak acid. The bond may be a covalent bond, an ionic bond, or a coordinate bond. Alternatively, a component of the water-soluble salt may be physically adsorbed to the carbon material.

[0037] The mechanical energy generated during the crushing promotes the reaction between radicals generated on the fracture surfaces of the graphite and weak acid salts (e.g., lithium acetate), resulting in bonding.

[0038] When a solvent is added to a graphene material in which a modifying group has been introduced to the graphene, the counter cation dissociates in the solvent, and an electrostatic repulsion acts on the graphene to which the anionic functional group is bonded. As a result, the graphene material has good dispersibility when dispersed in a solvent and is resistant to re-aggregation.

[0039] By bonding an anionic modification group to graphene, the graphene has the characteristic of being highly negatively charged in the dispersion liquid. As the amount of negative charge increases, the dispersibility index, which will be described later, increases. General-purpose graphene (for example, a commercially available product: graphene nanoplate (manufactured by XG Science, product name: R10)) and crushed products of graphite alone have a small amount of negative charge, and van der Waals forces become dominant, so they aggregate and the dispersibility index decreases.

[0040] The anionic functional group constituting the modifying group may be at least one selected from the group consisting of a carboxy group, a carbonate group, a sulfonic acid group, and a phosphate group, or may be a carboxy group or a carbonate group, from the viewpoint of the dissociation property of the counter cation of the anionic functional group.

[0041] From the viewpoint of ionization tendency, the counter cation constituting the modifying group may be at least one selected from the group consisting of potassium ion, sodium ion, lithium ion, barium ion, calcium ion, magnesium ion, rubidium ion, and ammonium ion, or may be a potassium ion, a lithium ion, or a sodium ion.

[0042] When the modifying group is composed of an anionic functional group and a counter cation of the anionic functional group, the concentration of the counter cation contained in the graphene material may be 50 to 15,000 ppm by mass, 50 to 13,000 ppm by mass, 50 to 10,000 ppm by mass, 50 to 5,000 ppm by mass, or 100 to 5,000 ppm by mass. When the concentration of the counter cation is 50 ppm by mass or more, the dispersibility of the graphene material in the solvent can be further improved. When the concentration is 15,000 ppm by mass or less, the electrostatic repulsive force acting on the graphene material in the solvent becomes stronger, and the graphene material can better maintain its dispersed state in the solvent. The concentration of counter cations contained in the graphene material can be measured by ICP-OES (Inductively Coupled Plasma Optical Emission Spectrometry) or ICP-MS (Inductively Coupled Plasma Mass Spectrometry). Specifically, it can be measured by the method described in the examples.

[0043] (pH) The pH (25°C) of a dispersion obtained by dispersing a graphene material (concentration: 0.3% by mass) in a mixed solvent containing deionized water and 2-propanol in a volume ratio of 6:4 may be 5.1 to 8.1, 5.5 to 8.0, or 6.0 to 7.9. When the pH of a graphene material having a modifying group consisting of an anionic functional group and a counter cation of the anionic functional group is within the above range, the counter cation is easily dissociated in the solvent, and the anionic functional group is easily charged. As a result, electrostatic repulsion acts on the graphene to which the anionic functional group is bonded, thereby further improving the dispersibility of the graphene material in the solvent and making it less likely to re-aggregate. The pH can be adjusted within the above range by appropriately adjusting the properties of the graphene, the type of water-soluble salt, the compounding ratio of graphene to the water-soluble salt, and the mixing and grinding conditions.

[0044] (Particle size) In a volume-based particle size cumulative distribution measured by a laser diffraction scattering method, the cumulative 50% particle size (D50) from the small particle side of the graphene material may be 0.5 to 15.0 μm. When the particle size D50 is 0.5 μm or more, the crystallinity of the graphene material is more easily maintained and dispersibility is improved. When the particle size (D50) is 15.0 μm or less, the crystallinity of the graphene material is maintained and dispersibility is further improved. The particle size (D50) may be 1.0 to 10.0 μm, or 1.5 to 5.0 μm.

[0045] (Dispersion Index) The graphene material may have a dispersion index of 20 to 70% as calculated by the following <Equation 1>: <Equation 1> Dispersion Index (X) [%] = [(Absorbance) / (Absorbance Coefficient × Cell Thickness) / (Initial Concentration)] × 100 (In Equation 1, the absorbance coefficient is 3200 (L / g m), the cell thickness is 0.0001 (m), and the initial concentration is the solids concentration when the graphene material is dispersed in a mixed solvent of water and 2-propanol (IPA) in a volume ratio of water:IPA = 6:4, and is 3 (g / L).)

[0046] When the dispersion index is 20% or more, the graphene material has good dispersibility, and when it is 70% or less, the interparticle distance between graphene materials is maintained and aggregation can be reduced. The dispersion index may be 25 to 65%, or may be 30 to 60%. The dispersion index can be set within the above range by appropriately adjusting the average particle size of the carbon material as the base material, the water-soluble salt concentration, the pH of the solvent, and the conductivity of the solvent.

[0047] The larger the absolute value of the zeta potential of the graphene material, the stronger the electrostatic repulsion between the graphene materials, resulting in more stable dispersibility. From the viewpoint of further enhancing the dispersibility of the graphene material, the absolute value of the zeta potential of the graphene material may be 30 to 60 mV, 30 to 55 mV, or 30 to 50 mV.

[0048] (Method for Producing Graphene Material) The graphene material contains an anionic functional group at an end and a counter cation of the anionic functional group, and has a peak at 1300 to 1400 cm in a Raman spectrum. －１ The D band peak intensity I in the range Ｄ and 1550-1650 cm －１ The G-band peak intensity I in the range Ｇ The peak intensity ratio (I Ｄ / I Ｇ In the case of a graphene material having a ρ of 0.50 or less, examples of a manufacturing method thereof include a method in which a water-soluble salt is added to graphite, the resulting mixture is mixed in a dry state, and the resulting mixture is washed with water. Anions liberated from the water-soluble salt bond with graphene and are incorporated into the graphene, thereby facilitating the exfoliation and pulverization of the graphene. Note that in the present disclosure, "pulverization" is not limited to crushing or disintegration for downsizing the graphite used as a raw material, but also includes the purpose of simply breaking down the agglomerations of graphene.

[0049] The graphene described above can be used. The water-soluble salt is not particularly limited as long as it is a salt that is soluble in water. Specific examples of the water-soluble salt include tripotassium citrate, potassium tartrate, potassium acetate, potassium glutamate, potassium carbonate, and tripotassium phosphate. Further examples include salts in which the potassium in these water-soluble salts is replaced with sodium, lithium, barium, calcium, magnesium, rubidium, and ammonium, respectively. The water-soluble salt may be used alone or in combination of two or more.

[0050] The blending amount of the water-soluble salt may be 1 to 500 parts by mass, 10 to 400 parts by mass, or 100 to 300 parts by mass relative to 100 parts by mass of the carbon material. When the blending amount of the water-soluble salt is 1 part by mass or more, dispersibility in a solvent is improved by the generation of a graphene material, and when it is 500 parts by mass or less, reaction and adsorption of an excess of the water-soluble salt can be reduced.

[0051] The environmental conditions for mixing and pulverizing the water-soluble salt and graphene are not particularly limited. The pulverization may be performed under similar environmental conditions to those used for the pulverization described above, such as room temperature (25°C) in air, a nitrogen atmosphere, or an inert gas environment such as argon. Furthermore, the pulverization may be performed at a high or low temperature, or under a pressurized or reduced pressure environment, as necessary. The pulverization apparatus and examples thereof are as described above, and known apparatuses can be used without limitation. Examples of suitable pulverization apparatuses include dry pulverization apparatuses such as a ball mill, a bead mill, a jet mill, a hammer mill, and a high-speed agitator. The processing conditions may be adjusted appropriately depending on the type of carbon material, particle size, and the like.

[0052] After mixing the water-soluble salt and graphene, the resulting mixture is washed with water. This removes excess water-soluble salt. The amount of water added during the water washing is not particularly limited, as long as it is an amount sufficient to obtain a suspension. Heating may be performed as necessary. For example, water is added in an amount 10 to 10,000 times the total mass of the water-soluble salt and the carbon material, and the mixture is mixed and stirred. The number of water washings may be, for example, 2 to 10 times, or 2 to 8 times. The water washing conditions may be appropriately set depending on the types of graphene and water-soluble salt used, etc.

[0053] After washing with water, a filter may be used for filtration. The optimum pore size of the filter is selected depending on the application of the obtained graphene material. The obtained graphene material may be dried and extracted as a powder, or it may be dispersed in a liquid or used as a paste. Drying can be performed by any method. For example, the graphene material can be dried by spray drying.

[0054] <Binder> The surface layer of the carbon composite active material according to the present disclosure may contain a binder. The binder serves to bind the electrode active material and the graphene material, and may contain at least one binder selected from the group consisting of fluororesin, olefin resin, vinyl resin, polyamide, polyimide, polyether, polysaccharide, and rubber. For example, the material may be a fluororesin such as poly(vinyldifluoroethylene) (PVDF), poly(vinyldifluoroethylene-co-hexafluoropropylene) (PVDF-HFP), poly(tetrafluoroethylene) (PTFE), or ethylene tetrafluoroethylene (ETFE); an olefin resin such as polyethylene (PE) or polypropylene (PP); a vinyl resin such as polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), polyacrylic acid (PAA), or lithium polyacrylic acid (LiPAA); a polyamide (PA); a polyimide (PI); a polyether such as poly(ethylene) oxide (PEO); a polysaccharide such as cellulose, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, or regenerated cellulose; or a rubber such as fluororubber, styrene-butadiene rubber (SBR), ethylene propylene diene rubber (EPDM), or sulfonated EPDM.

[0055] <Electrode Active Material> In the carbon composite active material of the present disclosure, the electrode active material may be a positive electrode active material or a negative electrode active material.

[0056] (Positive Electrode Active Material) The positive electrode active material may be a lithium-containing composite oxide having at least one crystal structure selected from the group consisting of an olivine type, a layered rock salt type, and a spinel type.

[0057] The lithium-containing composite oxide having an olivine structure is represented by the general formula LiMPO ４ (M is one or more of Fe(II), Mn(II), Co(II), and Ni(II)). ４ Representative examples include LiFePO ４ , LiNiPO ４ , LiCoPO ４ , LiMnPO ４ , LiFe ａ Ni ｂ P.O. ４ , LiFe ａ Co ｂ P.O. ４ , LiFe ａ Mn ｂ P.O. ４ , LiNi ａ Co ｂ P.O. ４ , LiNi ａ Mn ｂ P.O. ４ (a+b is 1 or less, 0<a<1, 0<b<1), LiFe ｃ Ni ｄ Co ｅ P.O. ４ , LiFe ｃ Ni ｄ Mn ｅ P.O. ４ , LiNi ｃ Co ｄ Mn ｅ P.O. ４ (c+d+e is 1 or less, 0<c<1, 0<d<1, 0<e<1), LiFe ｆ Ni ｇ Co ｈ Mn ｉ P.O. ４ (f+g+h+i is 1 or less, 0<f<1, 0<g<1, 0<h<1, 0<i<1), etc.

[0058] The lithium-containing composite oxide having a layered rock salt crystal structure is lithium cobalt oxide (LiCoO ２ ), LiNiO ２ , LiMnO ２ , Li ２ MnO ３ , LiNi ０．８ Co０．２ O ２ NiCo-based alloys (general formula: LiNi ｘ Co １－ｘ O ２ (0<x<1)), LiNi ０．５ Mn ０．５ O ２ NiMn-based alloys (general formula: LiNi ｘ Mn １－ｘ O ２ (0<x<1)), LiNi １／３ Mn １／３ Co １／３ O ２ NiMnCo-based alloys (also called NMC) such as LiNi ｘ Mn ｙ Co １－ｘ－ｙ O ２ (x>0, y>0, x+y<1)) ０．８ Co ０．１５ Al ０．０５ ) O ２ , Li ２ MnO ３ -LiMO ２ (M=Co, Ni, Mn) or the like may also be used.

[0059] The lithium-containing composite oxide having a spinel-type crystal structure is LiMn ２ O ４ , Li １＋ｘ Mn ２－ｘ O ４ , Li(MnAl) ２ O ４ , LiMn １．５ Ni ０．５ O ４ may be.

[0060] The positive electrode active material is represented by the general formula Li （２－ｊ） MSiO ４ (M is one or more of Fe(II), Mn(II), Co(II), and Ni(II), and 0≦j≦2) may be a composite oxide represented by the general formula Li （２－ｊ） MSiO ４ Representative examples include Li （２－ｊ） FeSiO ４ , Li （２－ｊ） NiSiO ４ , Li （２－ｊ） CoSiO４ , Li （２－ｊ） MnSiO ４ , Li （２－ｊ） Fe ｋ Ni ｌ SiO ４ , Li （２－ｊ） Fe ｋ Co ｌ SiO ４ , Li （２－ｊ） Fe ｋ Mn ｌ SiO ４ , Li （２－ｊ） Ni ｋ Co ｌ SiO ４ , Li （２－ｊ） Ni ｋ Mn ｌ SiO ４ (k+l is 1 or less, 0<k<1, 0<l<1), Li （２－ｊ） Fe ｍ Ni ｎ Co ｑ SiO ４ , Li （２－ｊ） Fe ｍ Ni ｎ Mn ｑ SiO ４ , Li （２－ｊ） Ni ｍ Co ｎ Mn ｑ SiO ４ (m+n+q is 1 or less, 0<m<1, 0<n<1, 0<q<1), Li （２－ｊ） Fe ｒ Ni ｓ Co ｔ Mn ｕ SiO ４ (r+s+t+u is 1 or less, 0<r<1, 0<s<1, 0<t<1, 0<u<1), etc.

[0061] (Negative electrode active material) The negative electrode active material may be a carbon material such as natural graphite, artificial graphite, mesocarbon microbeads, mesocarbon fiber (MCF), cokes, glassy carbon, or a fired organic compound; a silicon-containing material SiOx (0≦x<2), a metal capable of combining with lithium such as Sn or aluminum, an alloy thereof, a composite material of such a metal and a carbon material, or lithium titanate (Li ４ Ti ５ O１２ ), SnO ２ The negative electrode active material may be at least one selected from the group consisting of graphite, SiOx (0≦x<2), and lithium titanate.

[0062] The shape of the active material is not particularly limited, and examples thereof include spherical, non-spherical, scale-like, and plate-like shapes. The active material may also be hollow particles having a void in the center. When the active material is in the form of particles, the average particle size may be 1 nm or more and 100 μm or less, 100 nm or more and 50 μm or less, or 1000 nm or more and 25 μm or less. The average particle size in the present disclosure refers to the particle diameter D50 at which the cumulative number of particles in the particle size distribution reaches 50%, and can be measured using a laser diffraction particle size distribution analyzer.

[0063] <Combining electrode active material and graphene material>

[0064] The electrode active material and the graphene material may be composited by a method including a spraying step of fluidizing the electrode active material in a tumbling fluidized bed granulator and spraying a solution containing the graphene material into the tumbling fluidized bed granulator. The carbon composite active material produced by this method contains the electrode active material and the graphene material and has an angle of repose of 20° to 40°.

[0065] The tumbling fluidized bed granulator may be a tumbling fluidized bed granulator as shown in Fig. 4. Examples of the tumbling fluidized bed granulator include Multiplex manufactured by Powrex Corporation and Flowcoater manufactured by Freund Corporation.

[0066] The solution can be sprayed onto active material particles flowing in a tumbling fluidized bed granulator. By supplying dry air, inert gas, or atmospheric air at a constant temperature, the solution adheres uniformly to the particle surfaces while drying proceeds. This simultaneous spraying and drying process efficiently coats the active material particle surfaces with graphene, improving structural stability in the subsequent firing process.

[0067] The spraying speed of the solution can be appropriately set depending on the environment of the apparatus used (size of the apparatus, set temperature, etc.), the amount of active material particles, etc. For example, in the initial stage, spraying may be started at a low speed to prevent aggregation of the active material particles due to adhesion of the solution, and then the speed may be adjusted stepwise while checking the uniformity of the particle surfaces.

[0068] The spray rate may be increased while the supply rate of the gas used for drying is increased. The timing for increasing the supply rate of the gas may be the same as the timing for increasing the spray rate, or may be different from the timing for increasing the spray rate.

[0069] The temperature during spraying may be any temperature that allows volatile components such as the solvent and hydration water to volatilize from the solution. For example, the temperature may be 120°C or higher, 140°C or higher, or 160°C or higher. Furthermore, the temperature may be 220°C or lower, 200°C or lower, or 180°C or lower so as to ensure complete removal of the volatile components while avoiding damage to the active material particles and graphene.

[0070] The atmosphere during spraying is not particularly limited, and an environment that can maintain the chemical stability of the active material particles and the solution is recommended. Specifically, the atmosphere may be substantially inert to the active material particles and the solution, a dry air atmosphere, or the air atmosphere.

[0071] The spraying time can be appropriately set taking into consideration the size of the device used, the amount of coating liquid to be supplied, and the like.

[0072] In one embodiment, when the tumbling fluidized bed granulator is a Multiplex manufactured by Powrex Corporation, the spraying may be carried out under the following conditions: Solution concentration (mass%): 1 to 10 Spray rate (g / sec): 2 to 4 Spray time (min): 5 to 180

[0073] The method may include a calcination step in which the granules obtained in the spraying step are calcined to form a carbon composite active material. The granules obtained in the spraying step can be subjected to a subsequent calcination step to form a carbon composite active material. In this calcination step, graphene is firmly bonded to the surface of the active material particles, improving electrical conductivity and structural stability.

[0074] The baking device may be, for example, a muffle furnace or a hot plate, but is not limited to these.

[0075] The firing conditions are not particularly limited and can be set appropriately taking into consideration the firing apparatus, the type of graphene material, and the like.

[0076] In one embodiment, when the firing device is an explosion-proof dryer, the spraying may be carried out under the following conditions: firing atmosphere: nitrogen firing temperature (°C): 200 to 350°C firing time (hours): 24 to 48 hours

[0077] [Electrode] The electrode of the present disclosure can be formed using a slurry containing a carbon composite active material having the above-described angle of repose. The configuration and manufacturing method of the electrode are not particularly limited and may follow a known form. The carbon composite active material may include, in addition to the carbon composite active material having the above-described angle of repose, a carbon composite active material obtained by mechanically attaching a graphene material to the surface of an electrode active material. "Mechanically attaching" refers to repeatedly applying shear or compressive force to a mixture of the materials to bond them together. This refers to compounding by a so-called mechanical compounding method. The specific method of mechanical compounding is not particularly limited, and may be performed by a known compounding method. Either dry compounding or wet compounding may be used. For example, a binder may be added and dispersed in a water / IPA solution containing isopropyl alcohol and water, and then a graphene material may be added and ultrasonically dispersed, followed by centrifugation to prepare a graphene dispersion. An active material may be mixed with the graphene dispersion, suction filtered, and then dried to obtain a carbon composite active material.

[0078] For example, in one embodiment, a positive electrode for a lithium secondary battery can be produced by mixing a carbon composite active material having the angle of repose described above, a conductive additive, a binder, and a solvent in an appropriate ratio to prepare a slurry, uniformly applying the slurry onto a positive electrode current collector, drying the slurry, and then pressing the slurry.

[0079] Examples of conductive additives that can be used include carbon materials such as Ketjen black, metal materials such as Al, and conductive oxides. These materials complement the conductivity of the electrode by combining with the carbon composite active material, improving the efficiency of electron conduction from the current collector to the active material. Examples of binders that can be used include polyvinylidene fluoride, acrylic resins, polytetrafluoroethylene resins, and rubber-based resins, which effectively bind the carbon composite active material and conductive additives together, ensuring long-term stability of the electrode structure.

[0080] The solvent may be N-methylpyrrolidone, water, ethanol, or a mixture thereof. The positive electrode current collector may be a thin metal film containing mainly aluminum. The thickness of the positive electrode current collector is not particularly limited, but may be, for example, 5 to 50 μm.

[0081] The method for applying the slurry onto the current collector is not particularly limited, and examples thereof include a doctor blade method, a dipping method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, brush coating, etc. The amount of the slurry to be applied is not particularly limited, and can be appropriately set depending on the desired thickness of the electrode mixture layer, etc.

[0082] The method for drying the slurry on the current collector is not particularly limited, and examples thereof include drying with warm air, hot air, or low-humidity air, vacuum drying, and drying by irradiation with (far) infrared rays, electron beams, or the like. Drying conditions can be set appropriately, and the drying temperature may be 50 to 250°C, or 80 to 200°C. The drying time is not particularly limited, and is usually within a range of 10 to 60 minutes. The electrode may be stabilized by pressing after drying. Examples of pressing methods include die pressing and calendar pressing, but are not limited thereto.

[0083] In one embodiment, when the pressing device is an air-hydro type heating roll, the pressing may be performed under the following conditions: Pressing pressure: 50 to 300 MPa Pressing speed: 0.5 to 2 m / min Pressing temperature: room temperature to 150° C. Pressing gap: 30 μm to 200 μm

[0084] [Secondary Battery] The secondary battery of the present disclosure includes the above-described electrode. That is, in the secondary battery of the present disclosure, at least one of the positive electrode and the negative electrode is the electrode of the present disclosure. The secondary battery of the present disclosure has a high discharge capacity. When one of the positive electrode and the negative electrode is the electrode of the present disclosure and the other is not the electrode of the present disclosure, the other electrode is not particularly limited, and any electrode can be used.

[0085] The secondary battery of the present disclosure particularly includes a lithium ion secondary battery, but can also be applied to next-generation batteries such as sodium ion batteries, lithium sulfur batteries, and solid-state batteries.

[0086] The secondary battery of the present disclosure may include an electrolyte layer in addition to the electrodes described above. The secondary battery of the present disclosure is, for example, stacked such that the positive electrode and the negative electrode face each other via the electrolyte layer. The electrolyte layer may be composed of an electrolytic solution or a solid electrolyte. When the electrolyte layer is an electrolytic solution, it may be a nonaqueous electrolytic solution obtained by dissolving an electrolyte salt in a nonaqueous solvent. Examples of non-aqueous solvents include ethylene carbonate, fluoroethylene carbonate, chloroethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, cyclopentanone, cyclohexylbenzene, sulfolane, propane sultone, 3-methyl sulfolane, 2,4-dimethyl sulfolane, 3-methyl-1,3-oxazolidin-2-one, γ-butyrolactone, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, butyl methyl carbonate, ethyl propyl carbonate, butyl ethyl carbonate, dipropyl carbonate, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, methyl acetate, ethyl acetate, trimethyl phosphate, and triethyl phosphate. These may be used alone or in combination of two or more. Examples of electrolyte salts include lithium salts. The lithium salt is not particularly limited as long as it dissolves in a non-aqueous solvent and exhibits high ionic conductivity, and can be appropriately selected depending on the purpose. For example, lithium hexafluorophosphate (LiPF ６ ), lithium tetrafluoroborate (LiBF４ ) etc.

[0087] The concentration of the electrolyte salt is not particularly limited and can be appropriately selected depending on the purpose. From the viewpoints of lithium ion mobility and viscosity, the concentration may be 0.5 to 3.0 mol / L or 0.8 to 1.5 mol / L in the non-aqueous solvent.

[0088] (Separator) A separator is provided between the positive and negative electrodes to prevent short-circuiting between them. Examples of separator materials include paper (e.g., kraft paper, vinylon-blended paper, synthetic pulp-blended paper), cellophane, polyolefin nonwoven fabrics (e.g., polyethylene graft membranes, polypropylene melt-blown nonwoven fabrics), polyamide nonwoven fabrics, glass fiber nonwoven fabrics, and micropore membranes. The size of the separator is not particularly limited as long as it can be used in electrochemical devices. The thickness of the separator may be adjusted appropriately to ensure uniform ion movement between the positive and negative electrodes. For example, a separator thickness of approximately 20 to 40 μm can be designed to achieve both low internal resistance and high energy density. The separator may have a single-layer structure or a laminated structure. Note that the separator can be omitted when a solid electrolyte is used.

[0089] The present disclosure will now be described in detail with reference to examples, but the present disclosure is not limited to these examples.

[0090] <Preparation of Positive Electrode> The positive electrode active material, conductive additive, and binder were blended in a blending ratio (positive electrode active material: conductive additive: binder) of 97:2:1 (unit: wt%) and mixed using a rotation / revolution mixer (manufactured by Thinky Corporation, product name "Awatori Rentaro") under the conditions of "rotation speed 2000 rpm / min, rotation time 2 minutes." Next, a solvent was added, and the mixture was mixed using a high-speed agitator (Filmix) under the conditions of "slurry charge amount 200 g, peripheral speed 20 m / s, operating time 30 min" while adjusting the amount of solvent until a uniform paste was formed. The solvent content was 87% by mass relative to the total amount of binder and solvent. Next, the resulting slurry (hereinafter also referred to as "positive electrode paste") was applied to the surface of a current collector made of aluminum foil. The application method used was a doctor blade method, and an electrode layer of uniform thickness (82 μm) was formed. The current collector on which the electrode layer was formed was then dried at 85°C for 24 hours to completely volatilize the solvent. An air-hydro heating roll was then used to apply a pressure of 150 MPa to increase the density of the electrode, thereby obtaining a high-performance electrode that can be used as a positive electrode material for secondary batteries.

[0091] (Preparation Example 1 - Preparation of Comparative Positive Electrode-1 Using Acetylene Black as a Conductive Aid) Comparative positive electrode-1 was prepared by the method described above in <Preparation of Positive Electrode> using the following as the positive electrode active material, binder, conductive aid, and solvent. Positive electrode active material: lithium nickel oxide, manufactured by JFE Mineral Co., Ltd., average particle diameter D50: 10 μm. Conductive aid: acetylene black (hereinafter, AB), manufactured by Denka Co., Ltd., specific surface area: 68 m ２ / g, average particle size 35 nm Binder: polyvinylidene fluoride (hereinafter referred to as PVDF), manufactured by Kureha Corporation Solvent: N-methyl-2-pyrrolidone (hereinafter referred to as NMP)

[0092] (Preparation Example 2 - Preparation of Comparative Positive Electrode-2 Using Acetylene Black and Carbon Nanotubes as Conductive Aids) Comparative positive electrode-2 was prepared in the same manner as in Preparation Example 1, except that AB and carbon nanotubes (hereinafter, CNT) were used as conductive aids in a blending ratio of 1:1, and the blending ratio of the positive electrode paste (positive electrode active material: conductive aid (AB): conductive aid (CNT): PVDF) was 97:1:1:1 (unit: wt%). The following CNT was used. Conductive aid: CNT, manufactured by Resonac Inc., SSA: 15m ２ / g, outer diameter: 150 nm, length: 4 μm

[0093] (Preparation Example 3 - Preparation of Comparative Positive Electrode-3 Using Graphene as a Conductive Aid) Comparative positive electrode-3 was prepared in the same manner as in Preparation Example 1, except that graphene was used as the conductive aid and the compounding ratio of the positive electrode paste (positive electrode active material: conductive aid (graphene): PVDF) was 97:2:1 (unit: wt %). The following graphene was used. Conductive aid: graphene, manufactured by Graphene Supermarket, specific surface area 600 m ２ / g, flake size 10 μm, thickness 1 nm or less, O / C 0.02

[0094] (Preparation Example 4—Preparation of Comparative Positive Electrode-4 Using Graphene Material Having Modified Groups) <Preparation of "Graphene Material Having Modified Groups"> 4 g of natural graphite (ACB-50, manufactured by Nippon Graphite Industries Co., Ltd., average particle size 350 μm) and 8 g of potassium L-glutamate were weighed out in a nitrogen atmosphere at room temperature (25°C) and pulverized for 40 minutes using a planetary ball mill (manufactured by Fritsch, model: P-6, ball diameter 10 mm, rotation speed 540 rpm). The mixture was then washed with deionized water, filtered, and dried at 60°C to obtain a "graphene material having modified groups." 0.3 g of the resulting graphene material was added to 100 mL of a mixed solvent of deionized water and 2-propanol (IPA) (volume ratio: 60 / 40), and ultrasonicated for 3 minutes using an ultrasonic homogenizer (UH-600S, manufactured by SMT Corporation) with a tip size of 26 mmφ to obtain a dispersion. The resulting dispersion was sprayed onto a mica plate to prepare a measurement sample. The measurement sample was observed using an atomic force microscope (Hitachi High-Tech Corporation, Model: AFM5300E) to measure the thickness of the graphene material. As a result, it was confirmed that the thickness was 0.99 nm, the number of graphene layers was equivalent to three or less, and that natural graphite had exfoliated between the layers to form graphene. The resulting graphene material was placed in a platinum crucible, incinerated, and dissolved in a hydrochloric acid solution by alkali fusion. This was diluted with ultrapure water, and the target cation was quantitatively analyzed using an ICP optical emission spectrometer (Analytik Jena, Model: PQ9000 Elite). As a result, it was confirmed that the counter cation, potassium, was contained at 2200 ppm by mass. <Preparation of Comparative Positive Electrode-4> A comparative positive electrode-4 was prepared in the same manner as in Preparation Example 1, except that the “graphene material having a modified group” was used as the conductive additive, and the compounding ratio of the positive electrode paste (positive electrode active material:conductive additive (graphene material having a modified group):PVDF) was set to 97:2:1 (unit: wt %).

[0095] (Preparation Example 5 - Preparation of Comparative Positive Electrode-5 Without Using Conductive Aid) Comparative positive electrode-5 was prepared in the same manner as in Preparation Example 1, except that no conductive aid was used and the compounding ratio of the positive electrode paste (positive electrode active material:PVDF) was 99:1 (unit: wt %).

[0096] (Preparation Example 6 - Preparation of Comparative Positive Electrode-6 Using Carbon Composite Active Material-1) <Preparation of Carbon Composite Active Material-1> 0.02 g of a binder (carboxymethyl cellulose (CMC)) was added to 100 g of a water / IPA solution consisting of isopropyl alcohol (hereinafter, IPA) and water (water:IPA=60:40 (unit: wt%)), and the mixture was stirred using a magnetic stirrer at 60°C for 6 hours to fully dissolve the binder. Next, a conductive additive (graphene powder, manufactured by Graphene Supermarket, specific surface area 250 m) was added. 2 0.65 g of a graphene dispersion (0.5 μm / g, average particle size 0.5 μm) was added to the mixture, and the mixture was dispersed using an ultrasonic disperser under the conditions of "frequency 80 kHz, dispersion time 3 minutes x 3 times," followed by centrifugation (2000 rpm, 10 minutes) to prepare a graphene dispersion. Next, 150 g of a positive electrode active material (lithium nickel oxide, manufactured by JFE Mineral Co., Ltd., average particle size D50: 10 μm) was mixed with the graphene dispersion, and the mixture was suction filtered and dried (80°C, 10 hours) to obtain carbon composite active material material-1. The graphene material content in carbon composite active material material-1 was 0.26 mass %, and the binder content was 0.01 mass %. <Preparation of Comparative Positive Electrode-6> A comparative positive electrode-6 was prepared in the same manner as in Preparation Example 1, except that the composite active material-1 was used as the positive electrode active material and the conductive additive, and the compounding ratio of the positive electrode paste (positive electrode active material:conductive additive (graphene):PVDF) was set to 97:2:1 (unit: wt %).

[0097] (Preparation Example 7 - Preparation of Comparative Positive Electrode-7 Using Carbon Composite Active Material-2) <Preparation of Carbon Composite Active Material-2> 1 g of a conductive additive (acetylene black, manufactured by Denka Co., Ltd.) was dissolved in 100 g of a water / IPA solution (water:IPA=60:40 (unit: wt %)) to prepare a coating solution. Next, using a tumbling fluidized granulation coating device (manufactured by Powrex Corporation, MP-01), the coating solution was sprayed onto 1 kg of a positive electrode active material (lithium nickel oxide, manufactured by JFE Mineral Co., Ltd., average particle size D50: 10 μm), causing the solution to adhere to the surfaces of the positive electrode active material particles. The operating conditions of the coating device were as follows: nitrogen was used as the intake gas, the intake temperature was 140°C, and the intake air volume was 0.4 m ３The spraying speed was 3.0 g / min, the rotor rotation speed was 400 rpm, and the spray rate was 3.0 g / min. After spraying, the resulting coated powder was collected and calcined in air at 200°C for 5 hours, and then re-pulverized in an agate mortar (target particle size distribution D50: 10 μm) to obtain a composite active material material-2 in which acetylene black and a positive electrode active material were combined. <Preparation of Comparative Positive Electrode-7> Comparative positive electrode-7 was prepared in the same manner as in Preparation Example 1, except that composite active material material-2 was used as the positive electrode active material and conductive additive, and the compounding ratio of the positive electrode paste (positive electrode active material:conductive additive (AB):PVDF) was 97:2:1 (unit: wt%).

[0098] (Preparation Example 8 — Preparation of Positive Electrode-1 Using Carbon Composite Active Material-3) <Preparation of Carbon Composite Active Material-3> Composite active material-3 was obtained in the same manner as <Preparation of Carbon Composite Active Material-1>, except that the “graphene material having a modified group” was used as the conductive additive instead of the graphene powder. <Preparation of Positive Electrode-1> Positive electrode-1 was prepared in the same manner as in Preparation Example 1, except that composite active material-3 was used as the positive electrode active material and the conductive additive, and the compounding ratio of the positive electrode paste (positive electrode active material:conductive additive (graphene material having a modified group):PVDF) was 97:2:1 (unit: wt %).

[0099] (Preparation Example 9 — Preparation of Positive Electrode-2 Using Carbon Composite Active Material-4) <Preparation of Carbon Composite Active Material-4> Composite active material-4 was obtained in the same manner as <Preparation of Carbon Composite Active Material-2>, except that the graphene powder (manufactured by Graphene Supermarket) was used instead of the acetylene black as the conductive additive. <Preparation of Positive Electrode-2> Positive electrode-2 was prepared in the same manner as in Preparation Example 1, except that composite active material-4 was used as the positive electrode active material and the conductive additive, and the compounding ratio of the positive electrode paste (positive electrode active material:conductive additive (graphene):PVDF) was 97:2:1 (unit: wt %).

[0100] (Preparation Example 10 — Preparation of Positive Electrode-3 Using Carbon Composite Active Material-5) <Preparation of Carbon Composite Active Material-5> Composite active material-5 was obtained in the same manner as <Preparation of Carbon Composite Active Material-2>, except that the "graphene material having a modified group" was used instead of the acetylene black as the conductive additive. <Preparation of Positive Electrode-3> Positive electrode-3 was prepared in the same manner as in Preparation Example 1, except that composite active material-5 was used as the positive electrode active material and the conductive additive, and the compounding ratio of the positive electrode paste (positive electrode active material:conductive additive (graphene material having a modified group):PVDF) was 97:2:1 (unit: wt %).

[0101] (Preparation Example 11 — Preparation of Positive Electrode-4 Using Carbon Composite Active Material-6) <Preparation of Carbon Composite Active Material-6> Composite active material-6 was obtained in the same manner as <Preparation of Carbon Composite Active Material-2>, except that the "graphene material having a modified group" was used instead of the acetylene black as the conductive additive. <Preparation of Positive Electrode-4> Positive electrode-4 was prepared in the same manner as in Preparation Example 1, except that composite active material-6 was used as the positive electrode active material and the conductive additive, and the compounding ratio of the positive electrode paste (positive electrode active material: conductive additive (graphene material having a modified group): conductive additive (AB): conductive additive (CNT): PVDF) was 95:2:1:1:1 (unit: wt %).

[0102] <Angle of repose> The angle of repose of carbon composite active material materials-1 to 6 and the positive electrode active material was measured. The angle of repose was measured by the injection method using a powder flow meter (manufactured by Furukawa Co., Ltd., in accordance with JIS R9301-2-2:1999). 20 g of each of carbon composite active material materials-1 to 6 and the positive electrode active material was weighed out, and a sulfide-based inorganic solid electrolyte material was supplied from a φ4 mm (discharge hole diameter) orifice at the bottom of a funnel (inclination angle 60°) in a circular manner along the funnel wall circumference to be deposited in a conical shape. The angle of repose α between the generatrix of the cone and the bottom was measured. α = arctan [2h / (D-d)] h: height of the cone (distance between the substrate and the tip of the funnel nozzle) (mm) D: average value of the diameters in four directions (mm) d: diameter of the funnel nozzle (mm) Here, the distance from the discharge hole of the funnel to the disc was 25 mm.

[0103] <Powder Resistivity> The powder resistance of carbon composite active material materials-1 to 6 and the positive electrode active material was measured. The powder resistance was measured using a powder resistance measurement system MCP-PD51 and a low resistance probe for powder MCP-PD511 manufactured by Nitto Seiko Analytech Co., Ltd., and the volume resistivity (powder resistance) of the powder was calculated using a constant current application type four-probe method based on JIS K7194:1994. The measurement results are shown in Table 1.

[0104] <Electronic Conductivity> The electronic conductivity (25°C) of Positive Electrodes-1 to 4 (Examples 1 to 4) and Comparative Positive Electrodes-1 to 7 (Comparative Examples 1 to 7) was measured. The electronic conductivity was measured using an electrode resistance measurement system (RM2611 manufactured by Nippon Denkei Co., Ltd.). The volume resistivity of the current collecting foil used in the measurement was 2.5 × 10 ?８ The measurement results are shown in Table 1.

[0105]

[0106] It was confirmed that the use of the carbon composite active material of the present disclosure (Examples 1 to 4) improved electronic conductivity. The use of a carbon composite active material with excellent electronic conductivity made it possible to reduce the blending ratio of the conductive additive and increase the blending ratio of the active material compared to conventional techniques. Increasing the blending ratio of the active material leads to improved battery capacity.

[0107] The carbon composite active material of the present disclosure is suitable for use as an electrode for a secondary battery in fields where further improvement in battery capacity is required, and is particularly suitable for use in next-generation mobility such as electric vehicles (EVs) and drones, where the weight of the battery accounts for a large proportion of the vehicle's weight and where weight reduction and long-term flight times are required.

Claims

1. A carbon composite active material comprising an electrode active material and a graphene material, and having an angle of repose of 20° to 45°.

2. The carbon composite active material according to claim 1, wherein the graphene material forms a surface layer that covers at least a portion of the surface of the electrode active material, and the coverage of the surface layer is 10% or more.

3. The graphene material contains an anionic functional group and a counter cation of the anionic functional group at its terminal, and the peak intensity ratio (I Ｄ / I Ｇ 3. The carbon composite active material according to claim 1, wherein the value of σ is 0.50 or less.

4. The carbon composite active material according to claim 1 or 2, wherein the content ratio of the graphene material to the electrode active material is 0.1 to 2.4 by mass.

5. The carbon composite active material according to claim 1 or 2, wherein the ratio (DG / DA) of the planar size DG of the graphene material to the particle size DA of the electrode active material is 0.002 to 3.

000.

6. The carbon composite active material according to claim 2, wherein the surface layer comprises the graphene material and a binder.

7. The carbon composite active material according to claim 1 or 2, wherein the electrode active material is a positive electrode active material.

8. The carbon composite active material according to claim 7, wherein the positive electrode active material is a lithium-containing composite oxide.

9. A secondary battery having an electrode formed using a slurry containing the carbon composite active material according to claim 1 or 2.

10. A method for producing a carbon composite active material in which the surface of an electrode active material is coated with a graphene material, the method comprising a spraying step of fluidizing the electrode active material in a tumbling fluidized bed granulator and spraying a solution containing the graphene material into the tumbling fluidized bed granulator, wherein the carbon composite active material has an angle of repose of 20° to 45°.

11. The method for producing a carbon composite active material according to claim 10, wherein the spraying is carried out under the following conditions: solution concentration (mass %): 1 to 10, spraying rate (g / sec): 2 to 4, spraying time (min): 5 to 180.

12. The method for producing a carbon composite active material according to claim 11, further comprising a calcining step of calcining the granules obtained in the spraying step under the following conditions: calcination atmosphere: nitrogen, calcination temperature (°C): 200 to 350°C, calcination time (hours): 24 to 48 hours.

13. The method for producing a carbon composite active material according to claim 10, wherein the graphene material has a surface layer that covers at least a portion of the surface of the electrode active material, and the coverage of the surface layer is 10% or more.

14. The graphene material contains an anionic functional group and a counter cation of the anionic functional group at its terminal, and the peak intensity ratio (I Ｄ / I Ｇ 11. The method for producing a carbon composite active material according to claim 10, wherein the value of σ is 0.50 or less.

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