Spherical Natural Graphite, Negative Electrode Active Material for Secondary Battery and the Fabrication Method Thereof

Abstract

Spherical natural graphite according to the initiation of the first step has a cumulative number of particles at a size of 50 nm of 8.0% or less relative to the total number of 100% in the number cumulative particle size distribution based on the dynamic light scattering method according to the following conditions: (Condition) A mixture is prepared by mixing 2 g of octylphenol ethoxylate with 100 g of distilled water, 0.15 g of the spherical natural graphite is added to 100 ml of the prepared mixture, and the mixture is stirred by applying ultrasound at 200 W for 10 minutes, then centrifuged at 4000 rpm. 1 ml of the supernatant obtained is collected and analyzed by the dynamic light scattering method at 25 ℃.

Description

Technology Field

[0001] The present invention relates to spherical natural graphite, a negative electrode material for a secondary battery containing the same, and a method for manufacturing the same. More specifically, it relates to spherical natural graphite from which fine particles have been removed, a negative electrode material for a lithium secondary battery containing the same, and a method for manufacturing the same. Background Technology

[0002] As the market for electronic devices such as mobile phones, laptops, and PCs grows, the market for lithium-ion batteries, their power source, is also expanding rapidly. Furthermore, as interest in environmental issues grows and the demand for eco-friendly vehicles like electric cars increases, there is a growing trend of research into lithium-ion batteries capable of meeting various applications.

[0003] Among the components of a lithium secondary battery, the negative electrode active material stores lithium ions during charging and plays an important role in improving charging speed and determining battery capacity.

[0004] Natural graphite, a representative cathode active material, has high cost competitiveness and a higher capacity than artificial graphite, but it has the problem of large irreversible reactions due to exposed edge surfaces, reduced output characteristics due to the limited lithium ion diffusion path caused by the uniaxial orientation of the graphene layer, and low electrode density because it is easy to orient in a planar shape on the current collector.

[0005] To address these problems, technology is being developed to process natural graphite into a spherical shape through mechanical processing and to form a carbon coating layer on the surface of the spherical natural graphite. The technology for sphericalizing natural graphite through mechanical processing involves sphericalizing natural graphite by applying mechanical forces, such as impact compression, friction, and shear force. During the mechanical processing of natural graphite, ultrafine particles are inevitably generated. When these ultrafine particles adhere to the spherical natural graphite, the exposure of the edge surface increases significantly, which degrades the quality of the spherical natural graphite. However, to date, sphericalization technology for natural graphite has focused only on improving sphericity, reducing porosity, and enhancing crystallographic isotropy, while research aimed at controlling the ultrafine particles adhered to the spherical natural graphite is practically lacking. Prior art literature

[0006] Republic of Korea Published Patent No. 10-2021-0115461 The problem to be solved

[0007] According to one embodiment of the present invention, spherical natural graphite with controlled ultrafine particles can be provided.

[0008] According to another embodiment of the present invention, a cathode material comprising spherical natural graphite with controlled ultrafine particles may be provided.

[0009] According to another embodiment of the present invention, a method for manufacturing spherical natural graphite with controlled ultrafine particles may be provided.

[0010] The problems of the present invention are not limited to those described above. A person skilled in the art to which the present invention pertains will have no difficulty understanding additional problems of the present invention from the overall contents of this specification. means of solving the problem

[0011] In a number cumulative particle size distribution based on a dynamic light scattering method according to one embodiment of the present invention, the cumulative number of particles at a size of 50 nm is 8.0% or less relative to the total number of 100%.

[0012] Condition: A mixture was prepared by mixing 2 g of octylphenol ethoxylate with 100 g of distilled water, 0.15 g of the spherical natural graphite was added to 100 ml of the prepared mixture and stirred by applying ultrasound at 200 W for 10 minutes, then centrifuged at 4000 rpm. 1 ml of the obtained supernatant was collected and analyzed by the dynamic light scattering method at 25 ℃.

[0013] In one specific example, the cumulative number may be 5.0% or less.

[0014] In one embodiment, the cumulative number of particles at a size of 100 nm in the cumulative number particle size distribution may be 5.0% or less.

[0015] In one embodiment, the m of the spherical natural graphite 2 The BET specific surface area in units of / g is the cumulative volume-based median diameter D of the spherical natural graphite in units of μm. 50 The ratio divided by may be 0.40 or less.

[0016] In one embodiment, the degree of sphericity of the spherical natural graphite may be 0.85 to 0.95.

[0017] In one embodiment, the impurity content of the spherical natural graphite may be 500 ppm or less.

[0018] In one embodiment, the cumulative volume-based median diameter D of the spherical natural graphite 50 It can be 10 to 25 μm.

[0019] The present invention includes a negative electrode material for a lithium secondary battery containing the aforementioned spherical natural graphite.

[0020] The present invention comprises a negative electrode material for a lithium secondary battery comprising the aforementioned spherical natural graphite and a surface layer covering part to all of the surface of the spherical natural graphite.

[0021] In one embodiment, the surface layer may comprise amorphous carbon, graphitic carbon, graphene, carbon nanotubes, silicon-based materials, metal oxides, mixtures thereof, or composites thereof.

[0022] A method for manufacturing spherical natural graphite according to one embodiment of the present invention comprises: a sphericalization step of obtaining spherical natural graphite using mechanical processing; and a cleaning step of cleaning the spherical natural graphite with a cleaning solution containing a surfactant.

[0023] In one embodiment, the washing step may be performed in a base-acid purification process that purifies spherical natural graphite using a basic substance and an acidic substance, respectively.

[0024] In one embodiment, the washing step may be performed during the rinsing process after acid treatment of the base-acid purification process.

[0025] In one embodiment, the washing step may be performed during the washing process after the base treatment of the base-acid purification process.

[0026] In one embodiment, the surfactant-containing cleaning solution may be an aqueous cleaning solution.

[0027] In one embodiment, mechanical energy, thermal energy, or energy including mechanical energy and thermal energy may be applied during the cleaning process.

[0028] In one embodiment, the surfactant may include a non-ionic surfactant, an anionic surfactant, or a mixture thereof. Effects of the invention

[0029] In the spherical natural graphite according to one embodiment, surface-bound ultrafine particles are removed, thereby preventing edge surface exposure and increased specific surface area due to ultrafine particles.

[0030] The various and beneficial advantages and effects of the present invention are not limited to those described above and will be more easily understood in the process of explaining specific embodiments of the present invention. Brief explanation of the drawing

[0031] Figure 1 is a scanning electron microscope image showing the surface of spherical natural graphite produced by mechanical processing, and FIG. 2 is a scanning electron microscope image showing the surface of spherical natural graphite prepared according to one embodiment, and Figure 3 is a scanning electron microscope image showing the surface of ultrasonically treated natural graphite prepared according to one comparative example. Figure 4 is a diagram showing the number cumulative particle size distribution obtained by analyzing spherical natural graphite manufactured according to one embodiment using a dynamic light scattering method under specified conditions. Specific details for implementing the invention

[0032] Preferred embodiments of the present invention will be described below with reference to the attached drawings. However, embodiments of the present invention may be modified in various other forms, and the scope of the present invention is not limited to the embodiments described below.

[0033] In addition, embodiments of the present invention are provided to more completely explain the present invention to those with average knowledge in the relevant technical field.

[0034] In drawings, the shapes and sizes of elements may be exaggerated for clearer explanation.

[0035] In describing the embodiments of the present invention, if it is determined that a detailed description of known technology related to the present invention may unnecessarily obscure the essence of the present invention, such detailed description will be omitted. Furthermore, the terms described below are defined considering their functions in the present invention, and these may vary depending on the intentions or conventions of the user or operator. Therefore, such definitions should be based on the content throughout this specification. The terms used in the detailed description are merely for describing the embodiments of the present invention and should not be limited in any way. Unless explicitly stated otherwise, expressions in the singular form include the meaning of the plural form.

[0036] In this description, expressions such as “include” or “equipped” are intended to refer to certain characteristics, numbers, steps, actions, elements, parts or combinations thereof, and should not be interpreted to exclude the existence or possibility of one or more other characteristics, numbers, steps, actions, elements, parts or combinations thereof other than those described.

[0037] Unless otherwise specifically defined in the specification of the present invention, % units mean weight %.

[0038] In this specification, terms such as 'top', 'upper', 'upper surface', 'lower', 'lower', 'lower surface', 'side', etc. are based on the drawings and may actually vary depending on the direction in which the elements or components are arranged.

[0039] Additionally, throughout the specification, when it is said that one part is 'connected' to another part, this includes not only cases where they are 'directly connected,' but also cases where they are 'indirectly connected' with other elements in between.

[0040] The present invention will be described in detail below through each embodiment or example of the invention. It should be noted that each embodiment or example described in this specification is not limited to a single embodiment or example, but may also be combined with other embodiments or examples. Accordingly, the citation of claims in the patent claims is merely an example of an embodiment, and the technical concept of the present invention should not be interpreted as being limited only to a combination with the cited claims; rather, combinations with various claims are also included within the scope of the technical concept of the present invention.

[0041] In the course of conducting research on a technology for spheroidizing natural graphite through mechanical processing, the inventors noted that the ultrafine particles of natural graphite generated during mechanical processing are very strongly bound to the final obtained spheroidized natural graphite, and significantly increase the specific surface area and surface-exposed edges of the spheroidized natural graphite.

[0042] As a result of conducting various studies to remove ultrafine particles bound to spherical natural graphite, it was discovered that the bound ultrafine particles are effectively removed with the help of surfactants. Furthermore, it was found that removing the bound ultrafine particles using surfactants during the purification process also enhances the purification effect, leading to the filing of the present invention.

[0043] Method for manufacturing spherical natural graphite

[0044] A method for producing spherical natural graphite according to one disclosure, based on the aforementioned discovery, comprises: a sphericalization step of obtaining spherical natural graphite using mechanical processing; and a cleaning step of cleaning the spherical natural graphite with a cleaning solution containing a surfactant.

[0045] Spheroidization stage

[0046] The spheroidization step may include a step of spheroidizing natural graphite particles through mechanical processing to obtain spheroidized natural graphite.

[0047] Natural graphite particles may include natural graphite particles having an anisotropic shape, natural graphite particles that have been sphericalized through separate (preceded) mechanical processing, or a mixture thereof.

[0048] In natural graphite particles having an anisotropic shape, the anisotropic shape may refer to a shape in which the aspect ratio, calculated by dividing the longest length (e.g., lx) by the shortest length (e.g., lz) among the three mutually orthogonal axes (x, y, z) with the center of the particle as the origin, is 2 or greater, specifically 3 or greater. In this case, lx, ly, and lz can be experimentally measured through image observation, including conventional scanning electron microscopy. Representative examples of anisotropic shapes include plate shapes and / or flake shapes. Practical examples of natural graphite particles having an anisotropic shape include, but are not limited to, flake-like natural graphite, which is the subject of mechanical processing and can be easily and densely interlocked, folded, and / or assembled.

[0049] The primary spheroidized natural graphite particles may be natural graphite particles that have already been spheroidized through separate (preceded) mechanical processing. By re-spheroidizing these primary spheroidized natural graphite particles through mechanical processing, crystallographic isotropy, tissue density, and sphericity can be improved. In this case, the spheroidization step may correspond to the re-spheroidization step.

[0050] Mechanical processing may refer to a process of mechanically adjusting the shape of natural graphite into a spherical shape by applying mechanical force to it.

[0051] Mechanical processing is sufficient if performed by methods commonly known for spheroidizing natural graphite in the field of secondary batteries. Representative examples of mechanical processing include, but are not limited to, Air Classifying milling, Spheronizing milling, Grinding milling, Mechanofusion milling, Planetary milling, Hybridization milling, Shape milling, and High Speed ​​milling.

[0052] Mechanical processing can be performed under conditions commonly used for spheroidizing natural graphite in the secondary battery field, for example, at a rotational speed of 500 to 4000 rpm, and for 5 to 60 minutes, but is not limited thereto.

[0053] After obtaining spherical natural graphite through a sphericalization step, a classification step may be further performed to remove fine and / or coarse particles through classification such as air stream classification and / or sieving classification if necessary.

[0054] Cleaning step

[0055] The cleaning step may include a step of cleaning spherical natural graphite with a cleaning solution containing a surfactant.

[0056] Fine particles bound to spherical natural graphite can have a size of tens to hundreds of nanometers; the smaller the size of the fine particles, the more strongly they are bound to the natural graphite. Due to this strong binding force, smaller fine particles (hereinafter referred to as ultrafine particles) are difficult to remove through air-friction-related methods such as air classification, water washing, or ultrasonic cleaning.

[0057] However, ultrafine particles bound to spherical natural graphite can be removed through a simple process of mixing and stirring spherical natural graphite with a surfactant-containing cleaning solution and then separating and recovering the natural graphite.

[0058] In this case, ultrafine particles may refer to natural graphite with a diameter in the size range of 1 nm to 100 nm, substantially natural graphite with a size range of 1 nm to 50 nm, more substantially natural graphite with a size range of 1 nm to 30 nm, and more substantially natural graphite with a size range of 3 nm to 25 nm.

[0059] The cleaning solution may include a surfactant and a solvent in which the surfactant is dissolved, and the solvent may include a polar solvent. Examples of polar solvents include water, C1-C3 lower alcohols, and acetone, but are not limited thereto. However, it is advantageous for the polar solvent to be water, which is commercially beneficial, harmless to the environment, and allows the spherical natural graphite to receive greater drag from the fluid within the cleaning solution during stirring. In this case, the water may include deionized water or distilled water.

[0060] Surfactants may include nonionic surfactants, anionic surfactants, or mixtures thereof.

[0061] Nonionic surfactants may include alkyl ether surfactants, alkanolamide surfactants, glyceryl ester surfactants, polysorbate surfactants, or mixtures thereof. Representative examples of alkyl ether surfactants include octylphenol ethoxylate, polyoxyethylene lauryl ether, nonoxynol-9, and polyethylene-polypropylene glycol ether. Representative examples of alkanolamide surfactants include coco diethanolamide, lauramide diethanolamide, oleamide diethanolamide, and myristamide diethanolamide. Representative examples of glyceryl ester surfactants include glyceryl stearate, glyceryl laurate, glyceryl oleate, and glyceryl palmitate. Representative examples of polysorbate surfactants include polysorbate 20, polysorbate 40, polysorbate 60, polysorbate 80, and polysorbate 85. Anionic surfactants may be substances in which the hydrophilic portion is a carboxylate, sulfate salt, or sulfonate salt, and the hydrophobic portion is a C10-20 alkyl group, a C10-20 alkenyl group, or a C12-20 alkylaryl group, and representative examples include sodium laureth sulfate, sodium lauryl ether sulfate, sodium (C14-C16)olefin sulfonate, sodium dodecyl benzene sulfonate, and sodium stearate.However, nonionic surfactants and anionic surfactants are not limited to the aforementioned materials; any surfactant material known to improve the dispersibility of graphite in an aqueous medium or used to improve the dispersibility of graphite is sufficient. However, considering the use of secondary battery anode materials, it is advantageous to use nonionic surfactants in order to firmly prevent contamination by unwanted elements originating from surfactants in the cleaning solution. However, even if surfactants that pose a risk of contamination are used, contamination by surfactants can be prevented if surfactant components that may remain on the graphite are removed through rinsing with water or the like after the cleaning step using the cleaning solution.

[0062] The cleaning solution may contain 0.1 g to 3.0 g, specifically 0.1 g to 2.5 g, more specifically 0.5 g to 2.0 g, and even more specifically 0.5 g to 1.5 g of surfactant per 1 L of solvent. The concentration of surfactant in the aforementioned cleaning solution is such that fine particles (including ultrafine particles) attached to spherical natural graphite are removed smoothly and effectively, while preventing commercial viability from being compromised by excessive use of surfactant.

[0063] In the cleaning step, the amount of mixture between the spherical natural graphite and the cleaning solution is sufficient if it allows the spherical natural graphite to be dispersed as individual particles within the cleaning solution. As a practical example, a cleaning solution of at least twice the weight of the spherical natural graphite may be mixed. As a more practical example, the weight M of the spherical natural graphite SNG Based on 2 M SNG to 50 M SNG The weight of, more specifically 2 M SNG to 20 M SNG Weight of, 2 M SNG to 10 M SNG A cleaning solution of the weight of spherical natural graphite may be mixed, but is not necessarily limited thereto.

[0064] Energy may be applied to a mixture of spherical natural graphite and a cleaning solution. The applied energy may include mechanical energy, thermal energy, or mechanical and thermal energy.

[0065] Examples of the application of mechanical energy include stirring using a mixer or milling machine stirrer, and / or the application of vibration including ultrasound. As a practical example, stirring may be performed at 100 to 1000 rpm, specifically at 200 to 500 rpm for 10 to 60 minutes, but is not necessarily limited thereto.

[0066] When thermal energy is applied, the mixture may be heated to a temperature of 30 to 90°C, 30 to 70°C, or 30 to 50°C. However, it goes without saying that the cleaning step can be performed at room temperature (25°C ± 5°C) without artificial thermal energy being applied from the outside.

[0067] After the step of mixing and stirring natural graphite and a cleaning solution is performed, the step of separating and recovering the cleaned natural graphite from the mixture may be performed.

[0068] Separation and recovery can be achieved by using solid / liquid separation methods commonly used to separate and recover particles from a mixture of liquid and particulate phases. For example, separation and recovery can be performed by vacuum filtration, filtration using a filter, or filtration by centrifugation. In the case of vacuum filtration or filtration using a filter, water can be added to the cake during or at the end of filtration to prevent the removed fine particles from remaining in the cake. Alternatively, the cake obtained by filtration can be mixed with water, and then additionally washed to separate and recover natural graphite can be performed to remove any fine particles that may remain in the cake. The separated and recovered natural graphite can be dried using vacuum drying or oven drying, and a crushing process can be further performed to break down the particles clumped together in the cake into individual particles.

[0069] Merging into subsequent processes

[0070] The cleaning step can be performed as a standalone process with spherical natural graphite as the treatment target. Alternatively, the cleaning step may be merged into a subsequent process after the sphericalization of natural graphite is performed, so that cleaning can be carried out during the subsequent process.

[0071] A purification process can be cited as a representative subsequent process in the spheroidization technology of natural graphite. The following provides an example in which a washing step is incorporated into the purification process, but this is merely one advantageous example. A washing step may be incorporated into any subsequent process performed on spheroidized natural graphite. In this case, incorporation includes cases where the washing originally performed in the subsequent process is replaced with washing using a washing solution, or cases where washing using a washing solution is additionally introduced during the subsequent process even if washing was not originally performed in the subsequent process.

[0072] The washing step can be combined with a base-acid purification process that purifies spherical natural graphite using a basic substance and an acidic substance, respectively.

[0073] Specifically, the base-acid purification process (hereinafter collectively referred to as the purification step) may include a step of base-treating spherical natural graphite with a basic substance (base treatment) and a step of acid-treating the base-treated spherical natural graphite with an acidic substance (acid treatment).

[0074] More specifically, the base treatment may include the step of mixing (dry mixing) a basic material, which is a solid metal hydroxide, with spherical natural graphite to be purified, and heat treating it.

[0075] The metal hydroxide may include sodium hydroxide, but is not necessarily limited thereto. The solid metal hydroxide may have an average particle size of 150 μm or less, specifically 1 to 100 μm, 5 to 70 μm, or 5 to 50 μm. When mixed, the weight ratio of spherical natural graphite to metal hydroxide may be at the level of 1:0.1 to 0.6. By using the aforementioned particle size and mixing weight ratio of the metal hydroxide, it is possible to improve the purification efficiency of the spherical natural graphite while preventing the product obtained after heat treatment from aggregating or hardening.

[0076] The heat treatment of the mixture of metal hydroxide and spherical natural graphite can be performed at 300 to 600°C, specifically 400 to 600°C, more specifically 440 to 560°C for 30 minutes to 10 hours so as to exhibit improved purification reaction efficiency by melting the metal hydroxide. This heat treatment may be performed in an inert atmosphere (such as nitrogen, argon, helium, or a mixture thereof).

[0077] After base treatment with a metal hydroxide, acid treatment may be performed. Impurities that are not removed by base treatment (e.g., Fe, etc.) can be removed by acid treatment.

[0078] Acid treatment can be performed by leaching heat-treated graphite with an acidic solution. For example, the acid treatment step can be performed with an acidic solution having a concentration of 0.1 to 3.0 mol / L. The acid used for acid treatment may be hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, boric acid, or a mixture thereof. Acid treatment can be performed at room temperature to 95°C, specifically at 45 to 95°C, more specifically at 60 to 90°C for 5 to 60 minutes.

[0079] In the purification process, a step (washing process) is performed to wash the product obtained by the base treatment after the aforementioned base treatment, and to wash the product obtained by the acid treatment after the acid treatment. This washing is intended to remove reacted impurities that are easily soluble in water and to remove bases or acids remaining in the spherical natural graphite. Additionally, this washing can be repeated if necessary until the pH reaches neutral.

[0080] The washing step can be incorporated into the washing process of a base-acid purification process that purifies spherical natural graphite using a basic substance and an acidic substance, respectively.

[0081] In detail, the washing step may be performed during the rinsing process following acid treatment in the purification process. In this case, the manufacturing method according to one embodiment may include a spheroidization step of obtaining spheroidized natural graphite using mechanical processing, a step of base treatment of the spheroidized natural graphite with a basic substance, a rinsing step of washing the product obtained by base treatment with water, a step of acid treatment of the washed spheroidized natural graphite with an acidic substance, and a washing step of washing the product obtained by acid treatment (acid-treated spheroidized natural graphite) with a washing solution containing a surfactant. At this time, it goes without saying that the method may further include a step of washing the product obtained by acid treatment or the product generated in the washing step with water before and / or after the washing step.

[0082] In detail, the washing step may be performed during the washing process following the base treatment of the purification process. In this case, the manufacturing method according to one embodiment may include a spheroidization step of obtaining spheroidized natural graphite using mechanical processing, a base treatment step of the spheroidized natural graphite with a basic substance, a washing step of washing the product obtained by the base treatment (base-treated spheroidized natural graphite) with a washing solution containing a surfactant, a step of acid treatment of the product generated in the washing step with an acidic substance, and a washing step of washing the product obtained by the acid treatment with water. At this time, it goes without saying that the method may further include a step of washing the product obtained by the base treatment or the product generated in the washing step with water immediately before and / or immediately after the washing step performed after the base treatment.

[0083] In one advantageous example, the washing step can be combined with the rinsing process performed after the base treatment of the base-acid purification process. In this case, due to the synergistic effect resulting from the combination of the two processes, fine particles bound to the natural graphite can be removed more effectively, while the purity of the natural graphite can be further improved.

[0084] The present invention includes spherical natural graphite produced by the aforementioned manufacturing method.

[0085] Method for manufacturing cathode material

[0086] The present invention comprises a cathode material comprising spherical natural graphite produced by the aforementioned manufacturing method.

[0087] Spherical natural graphite can be used as a negative electrode material for secondary batteries. That is, spherical natural graphite can be used as a negative electrode material for secondary batteries in a state where the bare surface of the spherical natural graphite is exposed.

[0088] In contrast, spherical natural graphite can be used as a negative electrode material for secondary batteries in a state where at least a portion of the surface of the spherical natural graphite is covered with a heterogeneous material (a material other than spherical natural graphite).

[0089] Accordingly, the present invention includes a method for manufacturing a negative electrode material for a secondary battery, and the method for manufacturing a negative electrode material for a secondary battery includes all the contents described above in the method for manufacturing spherical natural graphite.

[0090] A method for manufacturing a negative electrode material for a secondary battery according to one embodiment may include the step of obtaining spherical natural graphite according to the method for manufacturing spherical natural graphite described above, and further may include the step of forming a heterogeneous material to cover at least a portion of the surface of the spherical natural graphite.

[0091] The heterogeneous material is sufficient if it is a material known to be used for coating spherical natural graphite in the field of secondary batteries. Representative examples of heterogeneous materials include amorphous carbon, graphitic carbon, graphene, carbon nanotubes, silicon-based materials, metal oxides, mixtures thereof, or composites thereof. In this case, representative examples of silicon-based materials include metallic silicon, silicon oxide, silicon carbide, complex oxides of silicon and alkali to alkaline earth metals, mixtures thereof, or composites thereof. Representative examples of metal oxides include lithium titanium oxide, iron oxide, titanium oxide, aluminum oxide, chromium oxide, zinc oxide, copper oxide, magnesium oxide, zirconium oxide, molybdenum oxide, vanadium oxide, niobium oxide, manganese oxide, vanadium oxide, cobalt oxide, nickel oxide, tantalum oxide, mixtures thereof, or composites thereof.

[0092] The method of coating the aforementioned heterogeneous material onto spherical natural graphite is sufficient if it is a known method used for coating the material, taking into account the specific material. Examples include, but are not limited to, vapor deposition methods including CVD (chemical vapor deposition) or PVD (physical vapor deposition), deposition methods using liquid-phase reduction, bonding methods using mechanical force such as milling, electroplating methods, and methods of coating a solid or liquid precursor and then converting the precursor into a target material.

[0093] Hereinafter, a method for forming amorphous carbon, which is most typically used as a heterogeneous material covering part or all of the surface of spherical natural graphite, is described in more detail; however, the cathode material provided in the present invention should not be interpreted as being limited to a cathode material in which an amorphous carbon layer is formed on spherical natural graphite.

[0094] Amorphous carbon formation

[0095] The step of forming a heterogeneous material may include the step of mixing and heating spherical natural graphite with a carbon precursor. The carbon precursor may be one or more selected from the group consisting of isotropic pitch, anisotropic pitch, heavy oil, light oil, polyvinyl alcohol (PVA), polyvinyl chloride (PVC), sucrose, phenol resin, furan resin, furfuryl alcohol, polyacrylonitrile, cellulose, styrene, polyimide, epoxy resin, and glucose, but is not limited thereto.

[0096] The mixing of spherical natural graphite and a carbon precursor may be mechanical mixing. For example, mechanical mixing may be one or more selected from the group consisting of ball milling, mechanofusion milling, shaker milling, planetary milling, atritor milling, shape milling, nauta milling, nobilta milling, high speed mixing, paddle mixing, ribbon mixing, Henschel mixing, corn type mixing, homo mixing, and a stirrer, but is not limited thereto. If necessary, mechanical mixing may be performed with a solvent for dissolving the carbon precursor mixed together, and independently thereof, mechanical mixing may be performed with the carbon precursor in a state where it has been melted or softened by heating. At this time, heating may include frictional heat during mechanical mixing.

[0097] When mixing, the mixing ratio of the carbon precursor mixed with the spherical natural graphite may be any amount sufficient to form a surface layer that stably covers the surface of the spherical natural graphite. As a specific example, the weight ratio of spherical natural graphite to carbon precursor may be 100:0.1 to 20, specifically 100:1 to 15, but is not limited thereto.

[0098] After mixing of spherical natural graphite and a carbon precursor, a heat treatment to carbonize the carbon precursor in an inert atmosphere may be performed. The inert atmosphere may be a nitrogen, argon, helium, or a mixed gas atmosphere, and the carbonization heat treatment may be performed at 600 to 1500°C, but is not limited thereto.

[0099] Spherical natural graphite

[0100] In the number cumulative particle size distribution based on the dynamic light scattering method according to the following conditions, the cumulative number of particles at size 50 nm is 8.0% or less relative to the total number of 100% of the spherical natural graphite according to the onset of the day.

[0101] Condition: A mixture was prepared by mixing 2 g of octylphenol ethoxylate with 100 g of distilled water, 0.15 g of the spherical natural graphite was added to 100 ml of the prepared mixture and stirred by applying ultrasound at 200 W for 10 minutes, then centrifuged at 4000 rpm. 1 ml of the obtained supernatant was collected and analyzed by the dynamic light scattering method at 25 ℃.

[0102] The aforementioned condition is a condition that allows for the direct detection of the amount of fine particles (including ultrafine particles) present bound to spherical natural graphite according to one embodiment.

[0103] As is well known, the size of spherical natural graphite used as a negative electrode material for secondary batteries is at the level of several micrometers to tens of micrometers. Accordingly, even if the particle size distribution of natural graphite, whose shape has been adjusted to a spherical form by mechanical processing, is analyzed in the presence of octylphenol ethoxylate under certain conditions, ultrafine particles at the level of several to tens of nanometers cannot be significantly detected by the volume cumulative particle size distribution. Furthermore, even if analyzed by the number cumulative particle size distribution, ultrafine particles cannot be significantly and quantitatively detected in a state where the spherical natural graphite and fine particles detached from the natural graphite coexist.

[0104] Accordingly, when the natural graphite to be analyzed is treated by a method equivalent to the aforementioned washing step and then centrifuged to obtain the supernatant, and the particle size of the solids contained in the supernatant is analyzed by a dynamic light scattering method to obtain the number cumulative particle size distribution, the fine particles bound to the natural graphite to be analyzed can be detected reliably and reproducibly.

[0105] The cumulative number particle size distribution is a particle size distribution in which the number of particles up to a given size is accumulated from the smaller particle size side to the larger particle size side, and is a particle size distribution plotted as the cumulative number by particle size. In this case, 'relative to 100% of the total number' means that the number is accumulated with the total number of particles contributing to the particle size distribution set to 100%. Specifically, 'relative to 100% of the total number' refers to the ratio of the number of particles up to that size to the total number of particles.

[0106] In the number cumulative particle size distribution based on the dynamic light scattering method according to conditions, the cumulative number at the 50 nm size is an indicator indicating the content of ultrafine particles having a size of 50 nm or less that are bound to spherical natural graphite.

[0107] As described above, the spherical natural graphite according to one embodiment may have a cumulative number of particles at a size of 50 nm in a number cumulative particle size distribution based on a dynamic light scattering method according to the conditions described above, and specifically, may be 7.0% or less to 0% or more, 6.0% or less to 0% or more, 5.0% or less to 0% or more, 4.0% or less to 0% or more, 3.0% or less to 0% or more, 2.0% or less to 0% or more, 1.5% or less to 0% or more, 1.0% or less to 0% or more, 0.5% or less to 0% or more, 0.4% or less to 0% or more, 0.3% or less to 0% or more, 0.2% or less to 0% or more, 0.1% or less to 0% or more, or 0%. In this case, 0% is 0% in a practical sense, and 0% in a practical sense means that the value of the cumulative number at a size of 50 nm corresponds to a value within the error range that inevitably occurs during dynamic light scattering measurement.

[0108] In the number cumulative particle size distribution based on the dynamic light scattering method according to conditions, the cumulative number at the 100 nm size is an indicator indicating the content of fine particles smaller than 100 nm that are bound to spherical natural graphite and the amount of fine spherical natural graphite or fine natural graphite fragments contained in the spherical natural graphite (particle group).

[0109] According to one embodiment, the spherical natural graphite may have a cumulative number of particles at a size of 100 nm in a number cumulative particle size distribution based on a dynamic light scattering method according to the conditions described above, and specifically, it may be 4.0% or less to 0% or more, 3.5% or less to 0% or more, 3.0% or less to 0% or more, 2.5% or less to 0% or more, 2.0% or less to 0% or more, 1.5% or less to 0% or more, 1.0% or less to 0% or more, 0.5% or less to 0% or more, 0.1% or less to 0% or more, or 0%.

[0110] The main factors contributing to the high specific surface area in spherical natural graphite produced by mechanical processing are the increase in specific surface area caused by internal pores present within the spherical natural graphite and the increase in specific surface area caused by ultrafine particles bound to the spherical natural graphite.

[0111] Spherical natural graphite according to one embodiment may have a significantly low specific surface area as there is substantially no ultrafine particle bonded to the natural graphite that is inevitably spherical by mechanical processing.

[0112] Specifically, spherical natural graphite according to one embodiment is m 2 BET specific surface area in / g based on cumulative volume in μm median diameter D 50 Ratio divided by (BET specific surface area / D 50 ) may be 0.40 or less, specifically 0.10 to 0.40, more specifically 0.13 to 0.35, even more specifically 0.13 to 0.30, and even more specifically 0.13 to 2.70. For reference, spherical natural graphite produced by mechanical processing has a BET specific surface area / D 50 It exhibits a high specific surface area of ​​0.50, and even after undergoing purification processes through base-acid treatment or ultrasonic cleaning, the BET specific surface area / D 50 It exhibits a high specific surface area of ​​approximately 0.45.

[0113] In one embodiment, the cumulative volume-based median diameter (D) of spherical natural graphite 50 ) can be a size advantageous for the application of the cathode material, and substantially, the median diameter (D 50 )silver It may be 10 to 25 μm, specifically 10 to 20 μm, more specifically 12 to 18 μm, but is not necessarily limited thereto.

[0114] In one embodiment, the degree of sphericity of the spherical natural graphite may be 0.85 to 0.95, specifically 0.87 to 0.94, more specifically 0.89 to 0.94, and more specifically 0.90 to 0.94, but is not necessarily limited thereto. In this case, the 'spherical' of the spherical natural graphite may be interpreted as a shape having a degree of sphericity of 0.85 or higher.

[0115] In one embodiment, the spherical natural graphite may be a particulate form (secondary particulate form) in which natural graphite fragments are organized and assembled. Specifically, the spherical natural graphite may be a particle in which natural graphite fragments are organized, folded, and / or assembled. In detail, the spherical natural graphite may be a natural graphite particle in which natural graphite fragments are organized and assembled in a cabbage shape, organized, folded, and / or assembled randomly, or organized and assembled in a combined form of cabbage shape and random shape. In this case, an example of a combined form may be a form in which the central region of the particle is randomly assembled and the surface region is organized in a cabbage shape.

[0116] In terms of manufacturing method, spherical natural graphite may be particles in which natural graphite fragments are joined, folded, and / or assembled by mechanical processing. That is, spherical natural graphite may be natural graphite in which a mechanical force is applied (mechanically processed) to natural graphite having an anisotropic shape, such as flakes, so that natural graphite fragments originating from natural graphite having an anisotropic shape are folded, bent, joined, and / or assembled, and the shape is mechanically adjusted to be spherical.

[0117] In one embodiment, the impurity concentration of the spherical natural graphite may be 500 ppm or less, specifically 400 ppm or less, more specifically 300 ppm or less, and even more specifically 200 ppm or less, and substantially 50 ppm or more, more substantially 80 ppm or more. Here, ppm refers to atomic ppm, and the group of elements belonging to the impurities may be zirconium, aluminum, calcium, cobalt, chromium, copper, iron, magnesium, manganese, nickel, sulfur, and silicon. Spherical natural graphite satisfying the aforementioned cumulative number at the 50 nm size and satisfying the aforementioned impurity concentration may refer to spherical natural graphite in a purified state from which fine particles, including ultrafine particles, have been removed. However, the spherical natural graphite provided by the present invention should not be interpreted as being limited only to spherical natural graphite in a purified state from which fine particles have been removed.

[0118] cathode material

[0119] The present invention includes a negative electrode material for a secondary battery containing the aforementioned spherical natural graphite.

[0120] A cathode material according to one embodiment may include spherical natural graphite with a bare surface exposed.

[0121] A cathode material according to one embodiment may include spherical natural graphite and a surface layer that partially or entirely covers the surface of the spherical natural graphite. In this case, the surface layer may include a material different from the spherical natural graphite (a heterogeneous material). That is, it may include spherical natural graphite and a heterogeneous material that partially or entirely covers the surface of the spherical natural graphite.

[0122] To elaborate further, the cathode material may comprise a core of spherical natural graphite and a shell of a heterogeneous material. The shell of the heterogeneous material may have a structure of a single shell of a single heterogeneous material, a single shell in which two or more heterogeneous materials are mixed, or a multilayer shell in which each of two or more heterogeneous materials forms a different shell. Such a shell of the heterogeneous material may form the surface of the cathode material.

[0123] Heterogeneous materials may include amorphous carbon, graphitic carbon, graphene, carbon nanotubes, silicon-based materials, metal oxides, mixtures thereof, or composites thereof. Silicon-based materials may include metallic silicon, silicon oxide, silicon carbide, composite oxides of silicon and alkali to alkaline earth metals, mixtures thereof, or composites thereof. Metal oxides may include lithium titanium oxide, iron oxide, titanium oxide, aluminum oxide, chromium oxide, zinc oxide, copper oxide, magnesium oxide, zirconium oxide, molybdenum oxide, vanadium oxide, niobium oxide, manganese oxide, vanadium oxide, cobalt oxide, nickel oxide, tantalum oxide, mixtures thereof, or composites thereof.

[0124] In one embodiment, the thickness of the shell of the heterogeneous material (thickness of the surface layer) may be 1 to 50 nm, but is not necessarily limited thereto.

[0125] As a practical example, the shell (surface layer) of the heterogeneous material may be a carbon shell (carbon layer), and the carbon shell (carbon layer) may be an amorphous carbon shell (amorphous carbon layer).

[0126] In one embodiment, the negative electrode material for a secondary battery may be a negative electrode material for a lithium secondary battery. The lithium secondary battery may be a lithium-ion battery, a lithium-ion polymer battery, or a lithium-polymer battery based on the type of separator and electrolyte, and may be cylindrical, prismatic, coin-type, or pouch-type based on the shape, but is not limited thereto.

[0127] The present invention includes a negative electrode for a lithium secondary battery comprising the aforementioned negative electrode material.

[0128] The negative electrode may include a current collector; a negative electrode active material layer located on at least one surface of the current collector and containing the aforementioned negative electrode material, and if necessary, the negative electrode active material layer may further include a binder, a conductive material, and / or a negative electrode active material different from the aforementioned negative electrode material that are typically used in the negative electrode of a secondary battery.

[0129] The present invention includes a lithium secondary battery comprising the aforementioned negative electrode.

[0130] A lithium secondary battery may include a positive electrode comprising a positive current collector and a positive active material layer located on at least one surface of the positive current collector, the aforementioned negative electrode; a separator interposed between the positive electrode and the negative electrode; and an electrolyte that conducts lithium ions.

[0131] The positive electrode current collector, negative electrode current collector, positive active material or composition of the positive active material layer, separator, and electrolyte solvent or electrolyte salt or electrolyte salt concentration, etc., may be materials or compositions that are conventionally adopted in lithium secondary batteries.

[0132] The present invention will be described in detail below through examples. However, it should be noted that the examples described below are intended only to illustrate and embody the present invention and are not intended to limit the scope of the present invention. This is because the scope of the present invention is determined by the matters described in the claims and matters reasonably inferred therefrom. The physical properties or measurement results presented in the claims and detailed description are based on the analysis method described below.

[0133] Analysis method

[0134] (D 50 )

[0135] 0.01 g of the analyte was suspended in ethanol, and the prepared suspension was sonicated for 1 minute. Subsequently, the cumulative volumetric particle size distribution of the analyte was measured using a laser diffraction particle size distribution analyzer (Microtrac S3500). From the cumulative volumetric particle size distribution, D 50 The median diameter (D) of the substance to be analyzed was calculated. At this time, the median diameter of the substance to be analyzed (D 50 ) refers to the diameter at the position where the cumulative volume is 50% in the cumulative volume particle size distribution.

[0136] (Sphericality)

[0137] Sphericity was measured by ultrasonically dispersing 0.01 g of the analyte in 5 mL of ethanol and using a particle shape analyzer (Flowcam 8100, Fluid Imaging Technologies) commonly used for particle shape analysis. The sphericity of a substance refers to the average value of the sphericity. That is, the sphericity of a substance is a statistical average value obtained by obtaining the sphericity of each particle and averaging the obtained sphericity values.

[0138] (BET specific surface area)

[0139] After performing pretreatment by drying the analyte at a vacuum of 0.1 Torr or less and a temperature of 300°C for 1 hour, the BET specific surface area (m²) was calculated using the BET method from the nitrogen adsorption isotherm of the pretreated analyte. 2 / g) was calculated. The nitrogen adsorption-desorption isotherm was measured using a specific surface area measuring device (ASAP 2400, Micromeritics) with a specific surface area measuring device (ASAP 2400, Micromeritics) at a temperature of 77K using liquid nitrogen as the adsorbed nitrogen gas and a relative pressure (P / P0) measurement precision of 0.05.

[0140] (Dynamic light scattering-based cumulative particle size distribution)

[0141] Octylphenol ethoxylate (C) in 100 g of distilled water 14 H 22 O(C2H4O) nA mixture was prepared by mixing 2 g of n=9~10, 647 g / mol), 0.15 g of the analyte was added to 100 ml of the prepared mixture, and the mixture was stirred by applying ultrasound (Bathsonic ultrasonic disperser) at 200 W for 10 minutes. Then, 25 ml of the stirred solution was placed in a conical tube and centrifuged at 4000 rpm to obtain the supernatant. 1 ml of the obtained supernatant was collected and analyzed by the dynamic light scattering method at 25 ℃.

[0142] Specifically, the supernatant was analyzed using a dynamic light scattering particle size distribution measuring device (Malvern Instruments LTD. Zetasizer Nano ZSP) to obtain the number cumulative particle size distribution. The measurement conditions for dynamic light scattering were a measurement temperature of 25°C, a solvent refractive index of 1.330, and a solvent viscosity (cP) of 0.8872, and the time variation of scattering intensity was analyzed using the cumulant method.

[0143] (Impurity content)

[0144] 5g of the substance to be analyzed was oxidized at 1000℃ for 12 hours, and then 1g of a flux mixture of sodium carbonate and boric acid in a mass ratio of 3:1 was added to the oxidized substance and heated to 950℃ for melting treatment. Subsequently, the melted substance was placed in a beaker containing a solution of ultrapure water and an aqueous hydrochloric acid solution (35–40 wt%) mixed in a volume ratio of 1:1, and heated at 290℃ for 5 minutes to dissolve it. The solution in which the substance was dissolved was analyzed for each element using inductively coupled plasma spectroscopy (ICP-OES).

[0145] (Manufacturing Example)

[0146] Spherical flaky natural graphite was sphericalized using a spheroidization device. Specifically, D 50 This 21.1 μm flake-shaped natural graphite raw material is fed into a spheroidization device and processed at 1900 rpm for 15 minutes, after which ultrafine and coarse particles are removed through air stream classification and sieve classification, D 50Spherical natural graphite (raw material) with a diameter of 14.9 μm was manufactured.

[0147] (Example 1)

[0148] To remove ultrafine particles present in the spherical natural graphite (raw material) prepared in the preparation example, octylphenol ethoxylate (C) at a concentration of 0.96 g / L 14 H 22 O(C2H4O) n Distilled water in which , n=9~10, derived from TRITON X-100) was dissolved was used as the cleaning solution.

[0149] Spherical natural graphite (raw material) : Spherical natural graphite and washing solution were mixed such that the weight ratio of the washing solution was 1:15, and after stirring at 350 rpm for 40 minutes at room temperature, spherical natural graphite with ultrafine particles removed was prepared by separating solid and liquid by centrifugation (3000 rpm).

[0150] (Example 2)

[0151] In Example 1, spherical natural graphite with ultrafine particles removed was prepared in the same manner as in Example 1, except that a mixture of spherical natural graphite (raw material) and a washing solution was stirred at a temperature of 40°C instead of room temperature, and solid / liquid separation was performed by vacuum filtration using a filter instead of centrifugation.

[0152] (Example 3)

[0153] A graphite mixture was prepared by mixing spherical natural graphite (raw material) prepared in the preparation example and sodium hydroxide powder (average particle size about 10 μm) in a weight ratio of 1:0.3. The prepared graphite mixture was heat-treated at 480°C for 4 hours in a nitrogen atmosphere.

[0154] Subsequently, octylphenol ethoxylate (C) at a concentration of 0.58 g / L 14 H 22 O(C2H4O) nDistilled water in which , n=9~10) was dissolved was used as a washing solution, and the mixture was mixed such that the weight ratio of the heat-treated graphite mixture to the washing solution was 1:5. After stirring at 40°C at 350 rpm for 35 minutes, solid / liquid separation was performed by vacuum filtration using a filter to obtain spherical natural graphite with ultrafine particles removed.

[0155] (Example 4)

[0156] A graphite mixture was prepared by mixing spherical natural graphite (raw material) prepared in the preparation example and sodium hydroxide powder (average particle size about 10 μm) in a weight ratio of 1:0.3. The prepared graphite mixture was heat-treated at 480°C for 4 hours in a nitrogen atmosphere.

[0157] Subsequently, the heat-treated graphite mixture was mixed with distilled water in a weight ratio of 1:5 and stirred at 350 rpm for 40 minutes at 40°C, and then solid / liquid separation was performed by vacuum filtration using a filter to obtain the heat-treated graphite.

[0158] Acid leaching of heat-treated graphite was performed using hydrochloric acid at a concentration of 0.61 mol / L at 80°C for 35 minutes.

[0159] Subsequently, octylphenol ethoxylate (C) at a concentration of 1.4 g / L 14 H 22 O(C2H4O) n Distilled water in which , n=9~10) was dissolved was used as a washing solution, and the mixture was mixed such that the weight ratio of acid-leached graphite to washing solution was 1:2. After stirring at 350 rpm for 35 minutes at room temperature, solid / liquid separation was performed by vacuum filtration using a filter to obtain spherical natural graphite with ultrafine particles removed.

[0160] (Example 5)

[0161] A graphite mixture was prepared by mixing spherical natural graphite (raw material) prepared in the preparation example and sodium hydroxide powder (average particle size about 10 μm) in a weight ratio of 1:0.3. The prepared graphite mixture was heat-treated at 480°C for 4 hours in a nitrogen atmosphere.

[0162] Subsequently, octylphenol ethoxylate (C) at a concentration of 0.58 g / L 14 H 22 O(C2H4O) n Distilled water in which , n=9~10) was dissolved was used as a washing solution, and the mixture was mixed such that the weight ratio of the heat-treated graphite mixture to the washing solution was 1:5. After stirring at 40°C at 350 rpm for 40 minutes, solid / liquid separation was performed by vacuum filtration using a filter to obtain spherical natural graphite with ultrafine particles removed.

[0163] Acid leaching of spherical natural graphite with ultrafine particles removed was performed using hydrochloric acid at a concentration of 0.61 mol / L at 80°C for 35 minutes.

[0164] Afterwards, the acid-leached graphite was washed with distilled water (weight ratio of acid-leached graphite to distilled water = 1:2) at room temperature for 40 minutes, and vacuum filtration was performed to produce purified spherical natural graphite with ultrafine particles removed.

[0165] (Example 6)

[0166] In Example 1, octylphenol ethoxylate (C) at a concentration of 0.14 g / L 14 H 22 O(C2H4O) n Spherical natural graphite with ultrafine particles removed was prepared in the same manner as in Example 1, except that distilled water in which , n=9~10) was dissolved was used as the cleaning solution.

[0167] (Example 7)

[0168] In Example 1, octylphenol ethoxylate (C) at a concentration of 2.8 g / L 14 H 22 O(C2H4O) nSpherical natural graphite with ultrafine particles removed was prepared in the same manner as in Example 1, except that distilled water in which , n=9~10) was dissolved was used as the cleaning solution.

[0169] (Example 8)

[0170] Spherical natural graphite with ultrafine particles removed was prepared in the same manner as in Example 1, except that distilled water in which polyethylene sorbitan monooleate (derived from TWIN 80) was dissolved at a concentration of 1.4 g / L was used as the cleaning solution.

[0171] (Example 9)

[0172] Spherical natural graphite with ultrafine removed was prepared in the same manner as in Example 1, except that distilled water in which glyceryl laurate was dissolved at a concentration of 1.4 g / L was used as the cleaning solution.

[0173] (Example 10)

[0174] In Example 1, sodium lauryl ether sulfate (SLES, C) at a concentration of 1.4 g / L was used. 24 H 50 Spherical natural graphite with ultrafine particles removed was prepared in the same manner as in Example 1, except that distilled water in which Na2O5S was dissolved was used as the cleaning solution.

[0175] (Example 11)

[0176] In Example 1, sodium stearate (sodium octadecanate, C) at a concentration of 1.4 g / L 18 H 35 Spherical natural graphite with ultrafine particles removed was prepared in the same manner as in Example 1, except that distilled water in which NaO2) was dissolved was used as the cleaning solution.

[0177] (Example 12)

[0178] 100 parts by weight of spherical natural graphite prepared in Example 5 and 5 parts by weight of petroleum-based pitch with a softening point of 250°C were mixed with a stirrer for 10 minutes, and then the mixture was heat-treated at 1200°C for 5 hours to produce spherical natural graphite coated with amorphous carbon.

[0179] (Comparative Example 1)

[0180] Spherical natural graphite prepared in the preparation example was mixed with ethanol in a weight ratio of 1:10, then ultrasonically washed for 10 minutes, and the cleaned spherical natural graphite was recovered by centrifugation (3000 Rpm).

[0181] (Comparative Example 2)

[0182] A graphite mixture was prepared by mixing spherical natural graphite (raw material) prepared in the preparation example and sodium hydroxide powder (average particle size about 10 μm) in a weight ratio of 1:0.3. The prepared graphite mixture was heat-treated at 480°C for 4 hours in a nitrogen atmosphere.

[0183] Subsequently, the heat-treated graphite mixture was mixed with distilled water in a weight ratio of 1:5 and stirred at 350 rpm for 40 minutes at 40°C, and then solid / liquid separation was performed through vacuum filtration using a filter to obtain washed graphite.

[0184] Acid leaching of washed graphite was performed using hydrochloric acid at a concentration of 0.61 mol / L at 80°C for 35 minutes.

[0185] Afterwards, the acid-leached graphite was washed with distilled water (weight ratio of acid-leached graphite to distilled water = 1:2) at room temperature for 40 minutes, and filtered to produce purified natural graphite.

[0186] Figure 1 is a scanning electron microscope image of spherical natural graphite (raw material in the example) prepared in the preparation example. In Figure 1, some of the ultrafine particles bound to the surface of the spherical natural graphite are additionally shown as black circles.

[0187] As can be seen from the observation results in Fig. 1, in the case of natural graphite sphericalized by mechanical processing, ultrafine particles of the natural graphite are generated by the mechanical force applied to the sphericalized natural graphite, and it can be seen that sphericalized natural graphite with these ultrafine particles bound is produced. Furthermore, as specified in the manufacturing example, the produced sphericalized natural graphite is graphite from which ultrafine particle removal has already been performed through air stream classification. The result in Fig. 1 implies that the ultrafine particles bound to the sphericalized natural graphite are not removed by air drag.

[0188] Figure 2 is a scanning electron microscope image of the spherical natural graphite prepared in Example 1. As shown in the observation results of Figure 2, it can be seen that ultrafine particles bound to the spherical natural graphite during mechanical processing are removed by simply washing the spherical natural graphite with an aqueous solution containing a surfactant, and spherical natural graphite with a clean surface is obtained.

[0189] Figure 3 is a scanning electron microscope image of natural graphite prepared in Comparative Example 1. In Figure 3, some of the ultrafine particles bound to the surface of the ultrasonically treated natural graphite are additionally shown as black circles.

[0190] As can be seen from Figure 3, even when cleaning based on the cavitation phenomenon of ultrasound is performed, it can be seen that a large amount of ultrafine particles bound to spherical natural graphite remain.

[0191] Figure 4 illustrates the number cumulative particle size distribution of the supernatant analyzed by the dynamic light scattering method according to the aforementioned conditions, and shows the results for the spherical natural graphite prepared in Example 1, the spherical natural graphite prepared in Example 5, and the spherical natural graphite prepared in the preparation example.

[0192] Specifically, the number cumulative particle size distribution of Fig. 4 is the result of analyzing the subject to analysis under the aforementioned conditions, by mixing and stirring the subject to analysis with a liquid equivalent to a cleaning solution containing a surfactant, then taking the supernatant by centrifugation and analyzing the solid content within the supernatant. The supernatant obtained under the conditions contains ultrafine particles detached from the subject to analysis, and accordingly, the number cumulative particle size distribution of the supernatant measured by the laser diffraction method under the conditions directly corresponds to the number cumulative particle size distribution of natural graphite ultrafine particles attached to the subject to analysis. That is, the number cumulative particle size distribution of Fig. 4 is not the particle size distribution of spherical natural graphite, but rather the result representing the particle size distribution of ultrafine particles that were detached by the treatment under the aforementioned conditions and separated and recovered by centrifugation under the conditions.

[0193] In Figure 4, results of 100 nm or larger are due to fine spherical natural graphite particles that are partially included in the supernatant under centrifugation conditions or natural graphite particles that are not completely removed by air classification, and results of 100 nm or smaller, specifically in the size range of 1 nm to 50 nm, are due to ultrafine particles detached from the graphite that is the subject of analysis.

[0194] As can be explicitly seen from the number cumulative particle size distribution in Fig. 4, in the case of the spherical natural graphite produced in the preparation example, it can be seen that a large amount of ultrafine particles having a size of 5 to 20 nm are bound together.

[0195] On the other hand, as shown in the result of Example 1 of Fig. 4, by a simple process of simply washing with a cleaning solution containing a surfactant and separating and recovering the washed graphite, it can be seen that the ultrafine particles bound to the spherical natural graphite (raw material) are substantially all removed and have a number cumulative particle size distribution of 0% in the size range of 1 nm to 50 nm.

[0196] In addition, through the results of Example 1 and Example 5 of FIG. 4, it can be seen that the process of removing bound ultrafine particles by the cleaning solution does not necessarily have to be performed through a separate, independent cleaning process.

[0197] That is, the result of Example 5 in Fig. 4 shows that in a subsequent process performed after spheroidization by mechanical processing of natural graphite, if the subsequent process includes a washing step, simply changing the water in the washing step to an aqueous solution containing a surfactant results in an ultrafine removal effect equivalent to or superior to a separate, independent cleaning process.

[0198] Table 1 shows the BET specific surface area (m²) of graphite prepared in Preparation Example, Example 1, Example 5, Comparative Example 1, and Comparative Example 2. 2 This is a table summarizing / g).

[0199] (Table 1)

[0200]

[0201] The specific surface area results in Table 1 directly demonstrate the effect of ultrafine particles bound to spherical natural graphite on the specific surface area. As the spherical natural graphite prepared in the preparation example has a large amount of extremely fine ultrafine particles ranging in size from several nm to tens of nm bound to it, 7.2 m 2 It can be seen that it exhibits a very high specific surface area reaching / g.

[0202] In addition, as can be seen from the BET specific surface area results of Comparative Examples 1 and 2, it can be confirmed that ultrafine particles bound to graphite are substantially hardly removed through ultrasonic cleaning or base-acid purification processes, and these BET specific surface area results are consistent with scanning electron microscope observation results.

[0203] On the other hand, when spherical natural graphite is cleaned with a cleaning solution containing a surfactant, it can be seen that the specific surface area of ​​the spherical natural graphite is significantly reduced to 68% of the level. Furthermore, while most ultrafine particles are removed by the cleaning process alone (Example 1), it can be seen that when the cleaning process is combined with the purification process (Example 5), more strongly bound ultrafine particles are also removed, resulting in a lower specific surface area. At this time, the specific surface area of ​​the purified spherical natural graphite obtained when the cleaning process is combined with the base purification process (Example 5) and when the cleaning process is combined with the acid purification process (Example 4) was substantially similar to each other.

[0204] Table 2 is a table summarizing the cumulative number (%) at 50 nm size and the cumulative number (%) at 100 nm size in the number cumulative particle size distribution of the supernatant analyzed according to the aforementioned conditions.

[0205] (Table 2)

[0206]

[0207] As can be seen from Table 2, it can be seen that ultrafine particles bound to spherical natural graphite are effectively removed by non-ionic or anionic surfactants. Furthermore, it can be seen that ultrafine particles are most effectively removed when a washing process is introduced during the rinsing process performed after base treatment in the base-acid purification process, followed by acid treatment. Additionally, although it has a slight effect on the content of fine particles with a size of 100 nm or larger, it can be seen that ultrafine particles detached from spherical natural graphite by surfactants are completely separated and removed even if the solid / liquid separation method is changed.

[0208] In order to determine the effect on the purification of spherical natural graphite when cleaning with a surfactant is combined with the purification process, an analysis of impurity components was performed using ICP-OES on the spherical natural graphite prepared in Example 5 and the purified graphite prepared by the simple purification process of Comparative Example 2.

[0209] When examining the impurity content of Zr, Al, Ca, Co, Cr, Cu, Fe, Mg, Mn, Ni, S, and Si remaining in the graphite, the purified graphite of Comparative Example 2 contained 133.5 ppm of impurities, and the spherical natural graphite of Example 5 contained 119.9 ppm of impurities. Through this, it can be seen that during the purification process, particularly when fine particles are removed after base treatment and acid treatment is performed, fine particles bound to the graphite are removed and impurity removal is achieved more effectively.

[0210] The present invention is not limited to the embodiments described above but can be manufactured in various different forms, and those skilled in the art will understand that the invention can be implemented in other specific forms without altering the technical concept or essential features of the invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

Claims

Claim 1 Spherical natural graphite having a cumulative number of particles at a size of 50 nm of 8.0% or less relative to 100% of the total number in a number cumulative particle size distribution based on a dynamic light scattering method according to the following conditions: (Condition) A mixture was prepared by mixing 2 g of octylphenol ethoxylate with 100 g of distilled water, 0.15 g of the spherical natural graphite was added to 100 ml of the prepared mixture, and the mixture was stirred by applying ultrasound at 200 W for 10 minutes, followed by centrifugation at 4000 rpm. 1 ml of the supernatant obtained was collected and analyzed by a dynamic light scattering method at 25 ℃. Claim 2 In claim 1, spherical natural graphite having an accumulated number of 5.0% or less. Claim 3 In claim 2, spherical natural graphite having a cumulative number of 100 nm particles in the cumulative number distribution of the above-mentioned number of particles of 5.0% or less. Claim 4 In Article 1, m 2 BET specific surface area in / g based on cumulative volume in μm median diameter D 50 Spherical natural graphite with a ratio divided by 0.40 or less. Claim 5 In claim 1, spherical natural graphite having a degree of sphericity of 0.85 to 0.

95. Claim 6 In claim 1, spherical natural graphite having an impurity content of 500 ppm or less. Claim 7 In claim 1, the cumulative volume-based median diameter D 50 Spherical natural graphite with a thickness of 10 to 25 μm. Claim 8 A negative electrode material for a lithium secondary battery containing spherical natural graphite according to any one of claims 1 to 7. Claim 9 A negative electrode material for a lithium secondary battery comprising spherical natural graphite according to any one of claims 1 to 7 and a surface layer covering part to all of the surface of said spherical natural graphite. Claim 10 In claim 9, the surface layer comprises amorphous carbon, graphitic carbon, graphene, carbon nanotubes, silicon-based materials, metal oxides, mixtures thereof, or composites thereof, for a negative electrode material for a lithium secondary battery. Claim 11 A method for producing spherical natural graphite, comprising: a spherical step of obtaining spherical natural graphite using mechanical processing; and a cleaning step of cleaning the spherical natural graphite with a cleaning solution containing a surfactant. Claim 12 A method for producing spherical natural graphite according to claim 11, wherein the washing step is performed in a base-acid purification process that purifies spherical natural graphite using a basic substance and an acidic substance, respectively. Claim 13 A method for producing spherical natural graphite, wherein, in claim 12, the washing step is performed during the washing process after acid treatment of the base-acid purification process. Claim 14 A method for producing spherical natural graphite, wherein the washing step is performed during the washing process after the base treatment of the base-acid purification process in claim 12. Claim 15 A method for manufacturing spherical natural graphite, wherein the surfactant-containing cleaning solution is a water-based cleaning solution in claim 11. Claim 16 A method for manufacturing spherical natural graphite according to claim 11, wherein mechanical energy, thermal energy, or energy including mechanical energy and thermal energy is applied during the cleaning process. Claim 17 A method for producing spherical natural graphite according to claim 11, wherein the surfactant comprises a non-ionic surfactant, an anionic surfactant, or a mixture thereof.

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