Method of purifying graphite

Abstract

The present invention relates to a method of purifying graphite, comprising: an alkaline treatment step of dry-mixing a graphite material and a metal hydroxide, and heat-treating same in an inert gas atmosphere; and a step of acid-treating the alkali-treated graphite material.

Description

Graphite purification method

[0001] The present invention relates to the purification of graphite, and more particularly, to a method for purifying graphite.

[0002] Lithium secondary batteries generally consist of a positive electrode containing positive active material, a negative electrode containing negative active material, a separator, and an electrolyte, and charge and discharge are performed by intercalation and deintercalation of lithium ions. The lithium secondary batteries have the advantages of high energy density, high electromotive force, and high capacity, and are therefore applied in various fields.

[0003] In particular, graphite is widely used as an anode active material, which constitutes the anode, and the graphite is mainly made up of natural graphite and artificial graphite. Natural graphite is a type of carbon element that exists in a form extracted from fossil fuels such as coal or petroleum, and has a structure and characteristics that are natural in nature, with a high degree of crystallinity and very low residue content. In addition, natural graphite has very high electrical conductivity, and is utilized as an anode material for battery materials such as secondary batteries.

[0004] The above natural graphite is extracted from graphite minerals, extracted as flake graphite through a beneficiation process, spheroidized the extracted flake graphite to produce spherical graphite, refined spherical graphite is produced through high-purity processing, and the refined spherical graphite is coated to produce a cathode material.

[0005] At this time, research is actively being conducted on controlling various conditions in the method of purifying spherical graphite.

[0006] According to one embodiment of the present invention, a method for purifying graphite capable of increasing the purity of graphite is provided.

[0007] According to one embodiment of the present invention, a method for purifying graphite having high purity and simple processing steps is provided.

[0008] A method for purifying graphite according to one embodiment of the present invention may include a base treatment step of mixing a graphite material and a metal hydroxide and heat-treating them in an inert gas atmosphere, and an acid treatment step of the base-treated graphite material. In one embodiment, the flow rate of the gas in the inert gas atmosphere is 0.1 to 3.2 L / min / L. f It could be.

[0009] In one embodiment, the base treatment step of heat treatment in an inert gas atmosphere may be performed at 300 to 600° C. In one embodiment, the base treatment step of heat treatment in an inert gas atmosphere may be performed for 1.0 hour or more.

[0010] In one embodiment, the inert gas atmosphere may include at least one of nitrogen (N2), helium (He), or argon (Ar) gas. In the base treatment step, the graphite material and the metal hydroxide may be dry or wet mixed.

[0011] In one embodiment, the base treatment step of dry mixing and heat treating the graphite material and the metal hydroxide may include a first washing and filtering step of washing and filtering the heated mixture. In one embodiment, in the base treatment step of dry mixing and heat treating the graphite material and the metal hydroxide, the content ratio of the metal hydroxide to the graphite material may be 10 to 60 by weight.

[0012] In one embodiment, the step of acid-treating the base-treated graphite material may be performed at a temperature range of room temperature to 95° C. In one embodiment, the step of acid-treating the base-treated graphite material may be performed with at least one acid selected from the group consisting of hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, and boric acid.

[0013] In one embodiment, the step of acid-treating the base-treated graphite material may include a second washing and filtration step of washing and filtering the acid-leached resultant. In one embodiment, the second washing and filtration step may be performed at a temperature ranging from room temperature to 60° C. for 5 to 60 minutes.

[0014] According to another embodiment of the present invention, a method for purifying graphite may include a base treatment step of mixing a graphite material and a metal hydroxide and heat-treating the mixture, and an acid treatment step of treating the base-treated graphite material with an acid solution of 0.3 to 1.5 mol / L prepared by adding an acid solution to 2.0 to 5.0 times the amount of water (H2O) of the graphite material.

[0015] In one embodiment, the purified graphite may have silicon (Si) content of 300 ppm or less based on 100 wt%. In one embodiment, in the acid treatment step, the acid solution may have a pH of 2 or less. In one embodiment, the acid treatment step may be performed at a temperature ranging from room temperature to 95°C.

[0016] According to another embodiment of the present invention, a method for purifying graphite includes a base treatment step of mixing a graphite material and a metal hydroxide and heat-treating them, an acid treatment step of the base-treated graphite material, and a first washing and filtering step after mixing the graphite material and the metal hydroxide and heat-treating them, wherein the first washing and filtering step may be performed at a stirring speed of 100 to 500 rpm. In one embodiment, the contents of Si, Al, and Fe in the impurities in the washing and filtering steps may satisfy the following equation 1.

[0017] <Formula 1>

[0018] ([Al]+[Si]) / [Fe] < 6.0

[0019] (In the above formula 1, [Al], [Si], and [Fe] represent the ppm contents of Al, Si, and Fe in the impurities)

[0020] According to one embodiment of the present invention, a method for purifying graphite provides a method for purifying graphite capable of increasing the purity of graphite by controlling heat treatment conditions in a base treatment step.

[0021] According to another embodiment of the present invention, a method for purifying graphite provides a method for purifying graphite having an excellent purification effect by controlling acid treatment conditions in the acid treatment step.

[0022] According to another embodiment of the present invention, a method for purifying graphite is provided that increases the efficiency of washing and the purity of graphite by controlling conditions during washing treatment.

[0023] Figure 1 illustrates a flow chart of a method for purifying graphite according to one embodiment of the present invention.

[0024] The terms first, second, and third, etc., are used to describe, but are not limited to, various parts, components, regions, layers, and / or sections. These terms are used only to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Accordingly, a first part, component, region, layer, or section described below may be referred to as a second part, component, region, layer, or section without departing from the scope of the present invention.

[0025] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the present invention. As used herein, the singular forms "singular" and "comprising" include plural forms as well, unless the context clearly dictates otherwise. The word "comprising" as used herein specifies a particular feature, region, integer, step, operation, element, and / or component, but does not exclude the presence or addition of other features, regions, integers, steps, operations, elements, and / or components.

[0026] When a part is referred to as being "on" or "over" another part, it can be directly on or over the other part, or there may be other parts intervening. Conversely, when a part is referred to as being "directly on" another part, there are no other parts intervening.

[0027] Although not defined otherwise, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention pertains. Terms defined in commonly used dictionaries are further interpreted to have meanings consistent with the relevant technical literature and the present disclosure, and are not to be construed as ideal or overly formal unless otherwise defined.

[0028] Hereinafter, embodiments of the present invention will be described in detail. However, these are presented as examples and the present invention is not limited thereto, and the present invention is defined solely by the scope of the claims set forth below.

[0029] Figure 1 illustrates a flow chart of a method for purifying graphite according to one embodiment of the present invention.

[0030] Referring to Figure 1, the method for purifying graphite of the present invention includes a base treatment step (S100) of mixing a graphite material and a metal hydroxide and heat-treating it, and a step (S200) of acid-treating the base-treated graphite material. Specifically, the method for producing purified graphite of the present invention removes impurities in graphite to produce high-purity purified graphite.

[0031] The base treatment step (S100) of mixing and heat-treating graphite material and metal hydroxide may be, for example, a step for removing impurities from the graphite material extracted from ore. Specifically, the graphite material may contain impurities such as silicon, magnesium, or aluminum, and the graphite material may be reacted in a state where it can be easily removed by base treatment using the metal hydroxide.

[0032] The base treatment step (S100) of mixing and heat-treating a graphite material and a metal hydroxide may include a step of preparing a graphite material and a metal hydroxide, a step of mixing the graphite material and the metal hydroxide, and a step of heat-treating a mixture of the graphite material and the metal hydroxide.

[0033] In the step of preparing the above graphite material and metal hydroxide, the graphite material may be, for example, at least one of earthy graphite or flaky graphite. The metal hydroxide may be, for example, sodium hydroxide (NaOH). Specifically, the metal hydroxide may be in a liquid or solid state, and if the metal hydroxide is in a liquid state, it may be liquid sodium hydroxide. If the metal hydroxide is in a solid state, it may be finely divided sodium hydroxide powder.

[0034] In one embodiment, when the metal hydroxide is in a solid state, the method may further include a step of crushing the metal hydroxide prior to the step of mixing the graphite material and the metal hydroxide. The crushing step may be a step of crushing the solid metal hydroxide into a powder form. Specifically, the crushing may include a process of crushing or finely crushing the solid metal hydroxide into powder by applying physical or mechanical force to the solid metal hydroxide. The crushing may be performed using various types of crushers, such as, for example, a blade-type crusher.

[0035] In one embodiment, the step of crushing the metal hydroxide includes the step of crushing and then classifying the metal hydroxide. The step of classifying the metal hydroxide may be performed such that the particle size of the solid sodium hydroxide is 150 μm or less, specifically 1 to 100 μm, and more specifically 5 to 70 μm. The particle size may be derived by performing classification according to the size of a sieve.

[0036] If the solid metal hydroxide exceeds the upper limit of the aforementioned range, there are problems such as a decrease in purification effect and the material coagulating and hardening after heat treatment. If the solid sodium hydroxide exceeds the lower limit of the aforementioned range, there are problems such as a decrease in grinding yield and coagulation due to moisture.

[0037] The step of mixing the graphite material and the metal hydroxide may be a step of mixing the graphite material and the metal hydroxide at a predetermined ratio. The content ratio of the metal hydroxide to the graphite material may be 5 to 50. Specifically, the ratio may be 10 to 45. More specifically, the weight ratio of the graphite material to the metal hydroxide may be mixed at a ratio of 100:15 to 100:50, specifically, 100:17 to 100:30. When the metal hydroxide is in a liquid state, the weight of the metal hydroxide may be the weight of the solid content.

[0038] If the content of the metal hydroxide in the graphite material exceeds the upper limit of the aforementioned range, there is a problem in that the sample obtained after heat treatment clumps and hardens. If the content of the sodium hydroxide (NaOH) in the graphite material exceeds the lower limit of the aforementioned range, there is a problem in that the purification effect of the graphite is reduced.

[0039] In one embodiment, the step of mixing the graphite material and the metal hydroxide is to mix the metal hydroxide in a solid or liquid state, and may be performed by at least one of a ribbon mixer, a V-mixer, a screw mixer, a ball mill, a hammer mill, and a stirring mill, a reciprocating mixer, and a roller mixer. As the graphite material and the metal hydroxide are dry mixed, the mixing may be performed by at least one of a ribbon mixer, a V-mixer, a screw mixer, a ball mill, the hammer mill, and a stirring mill, a reciprocating mixer, and a roller mixer. When the metal hydroxide is in a liquid state, a viscous material such as a slurry may be mixed, and when the metal hydroxide is in a solid state, the mixing may be performed using a mixer.

[0040] In the step of mixing the graphite material and the metal hydroxide, the step of heat-treating the mixture may be performed in an inert gas atmosphere. The inert gas atmosphere may include, for example, at least one of nitrogen (N2), helium (He), or argon (Ar) gas. By heat-treating the mixture in the inert gas atmosphere, there is an advantage in that the purification effect of the graphite is improved and loss of the product due to oxidation reaction can be prevented. If the heat-treating step is not performed in an inert atmosphere, oxygen in the atmosphere may react with graphite to induce an oxidation or combustion reaction, which may result in loss of the product.

[0041] In one embodiment, the partial pressure of nitrogen in the inert gas atmosphere may be 98 to 100 vol%. Specifically, the partial pressure of nitrogen may be 99.0 to 99.9999 vol%.

[0042] If the partial pressure of the nitrogen exceeds the upper limit of the aforementioned range, the nitrogen production yield decreases, leading to a decrease in economic feasibility. If the partial pressure of the nitrogen exceeds the lower limit of the aforementioned range, the graphite purification effect decreases, and there are problems of product loss and quality deterioration due to oxidation or combustion reactions.

[0043] In one embodiment, the flow rate of the inert gas atmosphere is 0.1 L / min / L. f 3.2 L / min / L f It can be. Specifically, the flow rate is 0.2 L / min / L. f 2.4 L / min / L f It can be. Here L f refers to the internal volume of the furnace and accordingly L / min / L f refers to the flow rate of gas per 1 L of volume in the furnace (L / min).

[0044] If the flow rate of the above gas exceeds the upper limit of the above-mentioned range, a cooling effect is induced due to the temperature difference between the gas and the heat treatment furnace, which may result in insufficient attainment of the target heat treatment temperature or excessive power consumption due to heat loss. If the flow rate of the above-mentioned gas exceeds the lower limit of the above-mentioned range, there may be problems with a reduction in the graphite purification effect due to insufficient maintenance of the atmosphere and product loss due to oxidation.

[0045] In the step of mixing the above graphite material and the metal hydroxide, the step of heat-treating the mixture may include heating the mixture at a temperature in the range of 300 to 600°C. Specifically, the mixture may be heated at a temperature in the range of 400 to 600°C, and more specifically, at a temperature in the range of 440 to 560°C. By satisfying the above temperature range, there is an advantage in that the metal hydroxide melts, thereby increasing the reaction efficiency. If the temperature range is exceeded, there is a problem in that a side reaction occurs, thereby reducing the reaction efficiency.

[0046] In one embodiment, the step of heating the mixture may be performed for 30 minutes to 1.0 hour or more. Specifically, the step of heating the mixture may be performed for 1.0 hour or more. More specifically, the step of heating the mixture may be performed for 1 hour to 8 hours. It may be performed for a time of 4.0 hours or more and 16 hours or less. As the step of heating the mixture is performed within the temperature and time ranges described above, the impurities in the graphite material and the metal hydroxide may react appropriately.

[0047] In one embodiment, after the base treatment step, a first washing and filtering step for washing the heated mixture may be included. In one embodiment, the first washing and filtering step for washing and filtering the heated mixture is a step for washing and filtering the heated mixture using a liquid, such as water. The first washing and filtering step may facilitate the removal of impurities, such as silicon, magnesium, or aluminum, that have been readily reacted to be dissolved in water by the above-described base treatment.

[0048] In one embodiment, the first washing and filtering step may be, for example, immersing the heated mixture in hot water. Specifically, the first washing and filtering step may be performed by washing and filtering the heated mixture in a washing neutral step.

[0049] In one embodiment, the amount of water used in the first washing and filtering step may be 2 to 50 times, specifically 3 to 50 times, more specifically 5 to 30 times, and even more specifically 15 to 25 times the amount of the base-treated graphite material, specifically the heat-treated product. By using the water in the first washing and filtering step, there is an advantage in that the washing and filtering of the graphite material is easy. If necessary, heated water may be used to increase the purification efficiency. By performing the first washing and filtering step under the conditions described above, the purification efficiency of the graphite can be increased.

[0050] In one embodiment, the first washing and filtering step may include a step of adjusting the content of Si, Al, and Fe in the impurities so that it satisfies the following equation 1.

[0051] <Formula 1>

[0052] ([Al]+[Si]) / [Fe] < 6.0

[0053]

[0054] (In the above formula 1, [Al], [Si], and [Fe] represent the ppm contents of Al, Si, and Fe in the impurities)

[0055]

[0056] By satisfying the above formula 1, there is an advantage in that the content of Si and Al is reduced, thereby improving the washing efficiency. The above formula 1 may be 6.0 or less. Specifically, the above formula 1 may be 2.5 or less, and more specifically, 0.25 to 1.00.

[0057] When the above formula 1 exceeds the upper limit, there is a problem that the Si and Al contents increase excessively, and when the above formula 1 exceeds the lower limit, there is a problem that the content of impurities in the ash increases as Fe increases excessively.

[0058] In one embodiment, the first washing and filtering step may be performed at a stirring speed of 100 to 500 rpm. Specifically, the stirring speed may be performed at 200 to 300 rpm.

[0059] If the above stirring speed exceeds the upper limit, there is a problem of excessive energy consumption. If the above stirring speed exceeds the lower limit, there is a problem of reduced ash purification effect.

[0060] In one embodiment, the first washing and filtering step may be performed at a temperature range of 40 to 95° C. Specifically, the temperature may be 60 to 85° C.

[0061] If the temperature exceeds the upper limit, excessive energy consumption leads to reduced economic efficiency and accelerated evaporation, which reduces the purification effect. If the temperature exceeds the lower limit, the purification effect is reduced.

[0062] The acid treatment step (S200) of the base-treated graphite material may be a step of subjecting the washed and filtered result to acid leaching. The acid treatment step of the base-treated graphite material may be a step for removing impurities such as iron (Fe) that were not removed through the above-described base treatment step.

[0063] In one embodiment, the step of acid-treating the base-treated graphite material may be a step of leaching the resultant product after washing and filtering with an acid solution, for example, a diluted substance including water and an acid solution. For example, the acid solution may be included in water (H2O) in an amount of 2.0 to 5.0 times that of the graphite material to have a concentration of 0.1 to 3.0 mol / L. Specifically, the acid solution may be acid-treated in water (H2O) in an amount of 2.0 to 5.0 times that of the graphite material to have a concentration of 0.2 to 2.0 mol / L, more specifically, 0.3 to 1.5 mol / L, more specifically, 0.3 to 1.2 mol / L, and even more specifically, 0.5 to 0.8 mol / L. For example, at least one of hydrochloric acid, nitric acid, phosphoric acid, boric acid, and sulfuric acid may be used as the acid solution.

[0064] When the content of the above acid solution is excessive, there is a problem that Na2SiO3 is easily dissolved in water as a water-soluble substance during the heat treatment process, but reacts with acid and precipitates as H2SiO3 salt. The precipitate increases the Si content and, at the same time, increases the ash content.

[0065] In one embodiment, in the acid treatment step, the acid solution may have a pH of 2 or less. Specifically, the acid solution may have a pH of 0.3 to 1.4.

[0066] In the acid treatment step, if the pH of the acid solution exceeds the upper limit, there is a problem of increased impurity content. In the acid treatment step, if the pH of the acid solution exceeds the lower limit, the use of high-concentration acid causes environmental pollution, poses safety issues, and is uneconomical.

[0067] In one embodiment, the step (S200) of acid-treating the base-treated graphite material may be performed at a temperature range of 60 to 100°C. Specifically, the temperature range may be performed at a temperature range of 70 to 90°C. In one embodiment, the step (S200) of acid-treating the base-treated graphite material may be performed at a time range of 5 to 60 minutes, specifically, 25 to 45 minutes.

[0068] As acid leaching is performed within the above temperature and time range, the reactivity in acid leaching is increased, so that impurities can be easily removed. If the temperature and time range are exceeded, there is a problem that the reactivity in acid leaching is reduced, making it difficult to obtain high-purity graphite. In addition, if the leaching time is long, the purification effect is excellent, but considering the economic aspect, the above-mentioned range is preferable. In one embodiment, the step (S200) of acid-treating a base-treated graphite material may further include a second washing and filtering step of washing and filtering the acid-treated result. The acid treatment, specifically, the second washing and filtering step of washing and filtering the acid-leached result, may include filtering the result of acid leaching at room temperature and washing with water. The second washing and filtering step can further remove impurities that were not removed in the acid treatment step, thereby obtaining more purified graphite.

[0069] In one embodiment, the second washing and filtering step is a step of washing and filtering the heated mixture using a liquid, such as water. The washing and filtering step may, for example, involve immersing the heated mixture in hot water. Specifically, the washing and filtering step may be performed in a neutral washing step.

[0070] In one embodiment, the second washing and filtering step may be performed at least twice to produce purified graphite. By performing the second washing and filtering step multiple times, the content of impurities can be more easily removed. The additional washing and filtering step may refer to the first washing and filtering step described above, as long as it does not contradict the first washing and filtering step.

[0071] Specifically, when using water, the process can be performed at room temperature for 5 to 60 minutes using 2 to 5 times the volume of water (H2O). Elevated water can also be used to increase purification efficiency, if necessary. By performing the washing and filtration steps under the aforementioned conditions, the purification efficiency of graphite can be increased.

[0072] The purified graphite, which is purified through a base treatment step (S100) of mixing the above graphite material and metal hydroxide and heat-treating it, and a step (S200) of acid-treating the base-treated graphite material, may have an ash content (Ash) of 0.06 wt% or less, specifically 0.05 wt% or less, and more specifically 0.04 wt% or less.

[0073] The graphite purified by the graphite purification method of the present invention may have an ash content of 0.06 wt% or less, specifically 0.05 wt% or less, and more specifically 0.04 wt% or less, in wt%. When the ash content satisfies the above-mentioned range, high-purity graphite can be obtained.

[0074] In one embodiment, the purified graphite may have a silicon (Si) content of 300 ppm or less, based on 100 wt% of the graphite material. Specifically, the silicon content may be 150 ppm or less, and more specifically, 69.5 ppm or less. The silicon content may increase when the acid concentration increases during acid washing, and as the acid concentration increases, the ash content (Ash) may increase.

[0075] In one embodiment, the refined graphite may have a potassium content of 15 ppm or less, by weight. Specifically, the aluminum content may be 12 ppm or less, and more specifically, 5.0 ppm or less.

[0076] By ensuring that the silicon and aluminum contents are within the aforementioned ranges, high-purity, refined graphite with fewer impurities can be obtained. If the silicon and aluminum contents exceed the aforementioned ranges, the refining efficiency deteriorates, and the capacity and efficiency of the graphite decrease when applied as a secondary battery anode material.

[0077] In one embodiment, the refined graphite may comprise, by weight ppm, no more than 80 ppm of Fe. Specifically, the Fe may comprise no more than 70 ppm, and more specifically, no more than 60 ppm.

[0078] If the content of Fe exceeds the above-mentioned range, the purification efficiency decreases, and thus, there is a problem of reduced capacity and efficiency when applied as a secondary battery negative electrode material.

[0079]

[0080] Hereinafter, preferred embodiments and comparative examples of the present invention are described. However, the following examples are only preferred embodiments of the present invention, and the present invention is not limited to the following examples.

[0081] Graphite purification method

[0082] Experimental Example 1: <Changes in Ash Content According to Heat Treatment Atmosphere>

[0083] Experimental Example 1-1 - N2 gas atmosphere

[0084] A liquid sodium hydroxide (NaOH) aqueous solution (45%) and spherical graphite with an average particle diameter (D50) of 16 ㎛ were mixed at a weight ratio of 30:100 based on solid content using a planetary mixer at 5 RPM for 0.5 hours. The mixed mixture was then placed in a box-shaped furnace and heat-treated at 300°C for 4 hours under a nitrogen gas atmosphere with a partial pressure of 99.999%.

[0085] Afterwards, the heat-treated mixture was washed with graphite: distilled water = 1:5 at 40°C and vacuum filtered using filter paper and a Buchner funnel.

[0086] Afterwards, the material that had undergone washing and filtration was subjected to acid leaching with hydrochloric acid at a concentration of 0.61 mol / L in water three times the amount of graphite material for 35 minutes at a temperature range of 80°C.

[0087] Afterwards, the acid-leached material was washed and filtered at room temperature for 40 minutes with graphite:distilled water in a ratio of 1:2 to produce purified graphite.

[0088]

[0089] Experimental Example 1-2 - Air Atmosphere

[0090] The same procedure as Experimental Example 1 was followed, except that a mixture of liquid sodium hydroxide and spherical graphite was heat-treated in an air atmosphere.

[0091]

[0092] Table 1 below shows the ash content according to the heat treatment atmosphere.

[0093] Ash (wt%) Heat treatment conditions After heat treatment in the high alkali treatment stage After acid treatment stage Atmosphere temperature [℃] Experimental example 1-11.550.21N2(99.999%) Partial pressure 300 Example Experimental example 1-22.711.90Air 300 Comparative example

[0094] Referring to Table 1 above, it can be confirmed that heat treatment in a nitrogen atmosphere can reduce the ash content rather than an air atmosphere during heat treatment.

[0095]

[0096] <Changes in ash content according to heat treatment temperature>

[0097] Experimental examples 1_1_1 to 1_1_6

[0098] Experimental examples 1_1_1 to 1_1_6 show the change in ash content after base treatment when temperature was controlled among the heat treatment conditions, as shown in Table 2 below, and other than the temperature conditions, the remaining conditions were performed in the same manner as Experimental example 1.

[0099]

[0100] Experimental examples 1_2_1 to 1_2_2

[0101] Experimental examples 1_2_1 to 1_2_2 show the change in ash content when temperature was controlled among the heat treatment conditions, as shown in Table 2 below, and other than the temperature conditions, the remaining conditions were performed in the same manner as Experimental example 2.

[0102]

[0103] Ash (wt%) Heat treatment conditions Remarks Atmosphere temperature [℃] Experimental example 1_1_11.69 N2 (99.999%) Partial pressure 200 Comparative example Experimental example 1_1_20.21 N2 (99.999%) Partial pressure 300 Example Experimental example 1_1_30.14 N2 (99.999%) Partial pressure 400 Example Experimental example 1_1_40.03 N2 (99.999%) Partial pressure 500 Example Experimental example 1_1_50.31 N2 (99.999%) Partial pressure 600 Example Experimental example 1_1_64.23 N2 (99.999%) Partial pressure 700 Comparative example Experimental example 1_2_12.12 Air 200 Comparative example Experimental example 1_2_21.90 Air 300 Comparative example

[0104] Examining Table 2 above, it was confirmed that when the temperature is excessively low or high, the ash content after acid treatment becomes excessively high. Furthermore, it was confirmed that the ash content at 300°C in a nitrogen atmosphere was lower than in an air atmosphere. Furthermore, at temperatures above 400°C, oxidation and combustion reactions between oxygen and graphite can occur, making experiments impossible in an air atmosphere.

[0105]

[0106] <Changes in ash content according to heat treatment time>

[0107] Experimental examples 1_3_1 to 1_3_3

[0108] Experimental examples 1_3_1 to 1_3_3 show the change in ash content when temperature was controlled among the heat treatment conditions as shown in Table 3 below, and other than the temperature conditions and time, the remaining conditions were performed in the same manner as Experimental example 1.

[0109]

[0110] Ash (wt%) Heat treatment conditions Note Atmosphere Temperature [℃] Time [h] Experimental example 1_3_10.06N 299.999% Partial pressure 5000.5 Comparative example Experimental example 1_3_20.04N 299.999% Partial pressure 5001.0 Example Experimental example 1_3_30.03N 299.999% Partial pressure 5004.0 Example

[0111] Looking at Table 3 above, it was confirmed that the shorter the heat treatment time, the higher the ash content. As such, it was confirmed that the ash content decreased when the heat treatment was performed for more than 1 hour under a nitrogen atmosphere under the heat treatment conditions.

[0112] <Changes in ash content according to flow rate>

[0113] Solid sodium hydroxide (NaOH) beads were ground with a blade-type grinder for 5 minutes. The ground NaOH beads were sieved through a 38 μm sieve to obtain solid sodium hydroxide (NaOH) powder of 38 μm or less. The spherical graphite having an average particle diameter (D50) of 16 μm and the sieved solid NaOH powder of 38 μm or less were mixed at a mixing ratio of 100:30 at 100 RPM for 0.5 hours. The mixed mixture was then heat-treated at 500°C for 4 hours in a box-type furnace.

[0114] Afterwards, the heat-treated mixture was washed with graphite: distilled water = 1:5 at 40°C and vacuum filtered using filter paper and a Buchner funnel.

[0115] Afterwards, the material that had been washed and filtered was subjected to acid leaching with hydrochloric acid having a concentration of 0.61 for 35 minutes at a temperature range of 80°C.

[0116] Afterwards, the acid-leached material was washed and filtered at room temperature for 40 minutes with graphite:distilled water in a ratio of 1:2 to produce purified graphite.

[0117]

[0118] Experimental examples 1_4_1 to 1_4_3

[0119] In an experimental example on the change in ash content according to the aforementioned flow rate, the nitrogen flow rate was controlled as shown in Table 4 below to confirm the ash content.

[0120] Ash (wt%) Heat treatment conditions Note Atmosphere flow rate [L / min / L f ]Temperature [℃]Time [h]Graphite:NaOHExperimental Example 1_4_10.06N2 99.999% partial pressure 0.15004100:30 Comparative example Experimental example 1_4_20.01N2 99.999% partial pressure 0.85004100:30 Example Experimental Example 1_4_30.04N2 99.999% partial pressure 2.45004100:30 Example

[0121] Looking at Table 4 above, it was confirmed that when the flow rate of nitrogen gas was 0.8 [L / min / Lf] or more, the ash content was 0.04 (wt%) or less. When the flow rate of nitrogen gas was outside the range of the present invention, it was confirmed that the ash content was high.

[0122]

[0123] Experimental Example 2: <Ash content change according to acid type>

[0124] Experimental Example 2_1 - Hydrochloric acid

[0125] Liquid sodium hydroxide (NaOH) (solid content: 98%) and spherical graphite with an average particle diameter (D50) of 16 ㎛ were mixed at a mixing ratio of 30:100 at 100 RPM for 0.5 hour. The mixed mixture was then heat-treated at 500°C for 4 hours.

[0126] Afterwards, the heat-treated mixture was washed with graphite: distilled water = 1:5 at 40°C and vacuum filtered.

[0127] Afterwards, the washed and filtered material was subjected to acid leaching at a temperature of 80°C for 35 minutes by adding 35% hydrochloric acid in a volume of 0.186 times that of the graphite material to water three times that of the graphite material. Specifically, 600 g of water and 37.2 g of 35% hydrochloric acid were added to 200 g of graphite.

[0128] Afterwards, the acid-leached material was washed and filtered at room temperature for 40 minutes with graphite:distilled water in a ratio of 1:2 to produce purified graphite.

[0129]

[0130] Experimental Example 2_2 - Nitric Acid

[0131] The same procedure as Example 1 was followed, except that hydrochloric acid was replaced with nitric acid. In the acid leaching step, the amount of nitric acid added was measured to have the same molar concentration as in Example 1.

[0132]

[0133] Experiment 2_3 - Sulfuric acid

[0134] The same procedure as Example 2_1 was followed, except that hydrochloric acid was replaced with sulfuric acid. The amount of nitric acid added in the acid leaching step was measured to have the same molar concentration as in Example 1.

[0135] Table 5 below shows the ash content when different types of acids are used in the acid leaching process, such as hydrochloric acid, nitric acid, and sulfuric acid.

[0136]

[0137] Acid treatment conditionsAsh(wt%)Acid typeGraphite material[parts by weight]Water content[parts by weight]Acid solution concentration[mol / L]Raw material----3.95Experimental example 2_1Hydroxychloric acid130.610.03Experimental example 2_2Nitric acid130.610.04Experimental example 2_3Sulfuric acid130.610.05

[0138] Looking at Table 5 above, it can be seen that the ash content is somewhat different depending on the type of acid used under acid treatment conditions including the same acid solution concentration conditions, and the ash content was confirmed to be low at 0.05 wt% or less for all of hydrochloric acid, nitric acid, and sulfuric acid, but it was confirmed that the ash content was the lowest for hydrochloric acid.

[0139]

[0140] <Ash content change according to acid concentration>

[0141] Experimental examples 2_4_1 to 2_4_5

[0142] In Example 2_1, the concentration of hydrochloric acid was adjusted as shown in Table 6 below, but the remaining conditions were the same.

[0143]

[0144] Experimental examples 2_5_1 to 2_5_3

[0145] In Example 2, the remaining conditions were performed the same except that the concentration of nitric acid was adjusted as shown in Table 6 below.

[0146]

[0147] Experimental examples 2_6_1 to 2_6_3

[0148] In Example 3, the remaining conditions were performed the same except that the concentration of sulfuric acid was adjusted as shown in Table 6 below.

[0149]

[0150] Acid treatment conditionsAsh(wt%)Acid typeGraphite material[parts by weight]Water content[parts by weight]Acid solution concentration[mol / L]RemarkExperimental example 2_4_1Hydroxychloric acid130.15251 / 4 times the basic concentration0.11Experimental example 2_4_2Hydroxychloric acid130.3051 / 2 times the basic concentration0.07Experimental example 2_4_3Hydroxychloric acid130.611 / 2 times the basic concentration0.03Experimental example 2_4_4Hydroxychloric acid131.222 / 2 times the basic concentration0.02Experimental example 2_4_5Hydroxychloric acid132.444 / 4 times the basic concentration0.03Experimental example 2_5_1Nitric acid130.3051 / 2 times the basic concentration0.05Experimental example 2_5_2Nitric acid130.611 / 2 times the basic concentration0.04Experimental example 2_5_3Nitric acid131.221 / 2 times the basic concentration0.04Experimental example 2_5_3Nitric acid131.221 / 2 times the basic concentration0.03Experimental example 2_5_1Nitric acid130.3051 / 2 times the basic concentration0.05Experimental example 2_5_2Nitric acid130.611 / 2 times the basic concentration0.04Experimental example 2_5_3Nitric acid131.221 / 2 times the basic concentration 2x the concentration 0.11 Experimental example 2_6_1 Sulfuric acid 130.305 1 / 2 the base concentration 0.09 Experimental example 2_6_2 Sulfuric acid 130.61 Base concentration 0.05 Experimental example 2_6_3 Sulfuric acid 131.22 2x the base concentration 0.10

[0151] Looking at Table 6 above, it can be seen that in the case of hydrochloric acid, nitric acid, and sulfuric acid, when the acid concentration becomes excessively high or excessively low, the ash content increases. Acid leaching was performed in water with hydrochloric acid at a concentration of 0.61 mol / L for 35 minutes at a temperature range of 80°C.

[0152] When the concentration of hydrochloric acid and nitric acid is high, the contents of impurity elements in the ash, such as iron (Fe), magnesium (Mg), potassium (K), and calcium (Ca), decrease, while the content of silicon (Si) shows an increasing trend after the appropriate concentration is reached. This is believed to be because the presence of an excess acid during the acid treatment process precipitates Si salts, which are insoluble in water, increasing the ash and Si contents of the purified graphite.

[0153]

[0154] Experimental Example 3: <Condition Control of Washing and Filtration Steps>

[0155] Experimental Example 3_1_1 - Mechanical stirrer

[0156] A liquid sodium hydroxide (NaOH) aqueous solution (45%) and spherical graphite having an average particle diameter (D50) of 16 ㎛ were mixed at a weight ratio of 30:100 based on solid content using a planetary mixer at 5 rpm for 0.5 hour. The mixed mixture was then heat-treated at 500°C for 4 hours.

[0157] Afterwards, the base-treated material was washed and filtered using a mechanical stirrer with a stirring speed of 250 rpm and a motor output of 75 W at room temperature for 40 minutes in a ratio of graphite:distilled water of 1:2 to produce purified graphite.

[0158] Afterwards, the heat-treated mixture was washed with water at a ratio of graphite [wt%]: distilled water [wt%] = 1:5 at 40°C and vacuum filtered.

[0159] Afterwards, the material that had undergone washing and filtration was subjected to acid leaching with hydrochloric acid at a concentration of 0.61 mol / L in water three times the amount of graphite material for 35 minutes at a temperature range of 80°C.

[0160]

[0161] Experimental Example 3_1_2 - Magnetic stirrer

[0162] The washing and filtration steps performed immediately after the heat treatment step in the base step were performed in the same manner as Experimental Example 1_1, except that a magnetic stirrer with a stirring speed of 250 rpm and a motor output of 1 W was used instead of a mechanical stirrer.

[0163] Table 7 below shows the impurity content when a mechanical stirrer and a magnetic stirrer were used in the washing and filtration steps.

[0164] Washing and filtration stage conditions Impurity content [ppm] Formula 1 Device Stirring speed [rpm] AlCaFeKMgSi [Al]+[Si] / Fe Experimental example 1 Mechanical Stirrer 2 50 3 55 4 52 2 8 0.57 Experimental example 2 Magnetic stirrer 2 50 1 7 6 1 3 5 8 6 7 6.46

[0165] Looking at Table 7 above, it was confirmed that when a mechanical stirrer is used in the washing and filtration step, specifically, in the washing and filtration step immediately after the heat treatment step during the base treatment step, purified graphite with low Al and Si content can be obtained.

[0166]

[0167] <Experimental examples 3_2_1 to 3_2_4: Stirring speed>

[0168] Table 8 below shows the change in ash content after acid treatment according to the stirring rpm in the washing and filtration steps immediately after the heat treatment step.

[0169] Specifically, solid sodium hydroxide (NaOH) beads were ground for 5 minutes using a blade-type grinder. The ground NaOH beads were sieved through a 38 μm sieve to obtain solid sodium hydroxide (NaOH) powder having a size of 38 μm or less.

[0170] Spherical graphite having an average particle size (D50) of 16 ㎛ and solid NaOH powder having a particle size of 38 ㎛ or less, which was sorted and filtered, were mixed at a mixing ratio of 100:30 at 100 rpm for 0.5 hour. The mixed mixture was then heat-treated at 500°C for 4 hours.

[0171] Afterwards, the heat-treated mixture was washed with water under the conditions of graphite: distilled water = 1:5, 40°C and stirring rpm below, and vacuum filtration was performed using filter paper and a Buchner funnel.

[0172] Afterwards, the material that had been washed and filtered was subjected to acid leaching with hydrochloric acid having a concentration of 0.61 for 35 minutes at a temperature range of 80°C.

[0173] Afterwards, the acid-leached material was washed and filtered at room temperature for 40 minutes with graphite:distilled water in a ratio of 1:2 to produce purified graphite.

[0174] Stirring rpmAsh(%)Experimental example 2_1500.07Experimental example 2_21000.04Experimental example 2_32500.01Experimental example 2_45000.03

[0175] Looking at Table 8 above, it can be seen that the purification efficiency is high and the amount of residual ash is low within the optimal stirring speed range of 100 to 500 rpm of the present invention. Conversely, at speeds below 100 rpm, the purification effect is reduced. Above 500 rpm, excessive energy consumption is a problem.

[0176]

[0177] <Experimental examples 3_3_1 to 3_3_3: Washing temperature>

[0178] Table 9 below shows the change in ash content after acid treatment according to the washing temperature in the washing and filtration steps immediately following the heat treatment step. The remaining steps were performed in the same manner as in Experimental Example 1_1 described above.

[0179] Specifically, solid sodium hydroxide (NaOH) beads were ground with a blade-type grinder for 5 minutes to obtain solid sodium hydroxide (NaOH) powder.

[0180] Spherical graphite having an average particle size (D50) of 16 ㎛ and solid NaOH powder having a particle size of 38 ㎛ or less, which was filtered through sorting, were mixed at a mixing ratio of 100:30 at 100 RPM for 0.5 hour. The mixed mixture was then heat-treated at 500°C for 4 hours.

[0181] Afterwards, the heat-treated mixture was washed under the conditions of graphite: distilled water = 1:5, 40°C, and a stirring speed of 250 rpm, and the washing was performed at the washing temperature shown in Table 3 below, and vacuum filtration was performed using filter paper and a Buchner funnel.

[0182] Afterwards, the material that had been washed and filtered was subjected to acid leaching with hydrochloric acid having a concentration of 0.61 for 35 minutes at a temperature range of 80°C.

[0183] Afterwards, the acid-leached material was washed and filtered at room temperature for 40 minutes with graphite:distilled water in a ratio of 1:2 to produce purified graphite.

[0184] Temperature [℃] Ash (%) Experimental example 3_3_1400.04 Experimental example 3_3_2600.03 Experimental example 3_3_3850.02

[0185] Looking at Table 9 above, it can be seen that the higher the temperature during washing, the better the purification effect. If the temperature is lower than the lower limit in Table 3, the purification effect is low. If the temperature is higher than the upper limit, excessive energy consumption reduces economic efficiency, and evaporation is accelerated, which can reduce the purification effect.

[0186]

[0187] <Experimental examples 3_4_1 to 3_4_5: Washing temperature>

[0188] Table 10 below shows the change in ash content according to the amount of distilled water added to graphite during the washing and filtration steps immediately following the heat treatment step. The remaining steps were performed in the same manner as in Experimental Example 1_1 described above.

[0189] Specifically, solid sodium hydroxide (NaOH) beads were ground with a blade-type grinder for 5 minutes to obtain solid sodium hydroxide (NaOH) powder.

[0190] Spherical graphite having an average particle size (D50) of 16 ㎛ and solid NaOH powder having a particle size of 38 ㎛ or less, which was filtered through sorting, were mixed at a mixing ratio of 100:30 at 100 RPM for 0.5 hour. The mixed mixture was then heat-treated at 500°C for 4 hours.

[0191] Afterwards, the heat-treated mixture was washed with water under the conditions of graphite: distilled water = 1:5, 40°C, and a stirring speed of 250 rpm, and the washing was performed at the washing temperature shown in Table 10 below, and vacuum filtration was performed using filter paper and a Buchner funnel.

[0192] Afterwards, the material that had been washed and filtered was subjected to acid leaching with hydrochloric acid having a concentration of 0.61 for 35 minutes at a temperature range of 80°C.

[0193] Afterwards, the acid-leached material was washed with graphite:distilled water at a ratio of Table 10 below at room temperature for 40 minutes and filtered to produce purified graphite.

[0194] Graphite [wt%]: Distilled water [wt%] Ash (%)Measured after heat treatment in the base treatment stepMeasured after base treatment and acid treatmentExperimental example 3_4_11:31.400.06Experimental example 3_4_21:51.360.04Experimental example 3_4_31:101.350.04Experimental example 3_4_41:201.240.03Experimental example 3_4_51:500.720.06

[0195] Looking at Table 10 above, it can be confirmed that the residual ash content is excellent because the ratio of distilled water to graphite satisfies the range of the present invention. It was confirmed that when the ratio of distilled water to graphite exceeds the lower limit of the present invention, the purification efficiency is significantly reduced. When the ratio of distilled water to graphite exceeds the upper limit, there is the problem of excessive energy and water consumption, which is uneconomical.

[0196] Although the preferred embodiments have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements made by those skilled in the art using the basic concepts defined in the following claims also fall within the scope of the present invention.

Claims

1. Base treatment step of mixing graphite material and metal hydroxide and heat treating in an inert gas atmosphere; and A method for purifying graphite, comprising a step of acid-treating the base-treated graphite material.

2. In paragraph 1, A method for purifying graphite in an inert gas atmosphere at a gas flow rate of 0.1 to 3.2 L / min / Lf.

3. In paragraph 1, A method for purifying graphite, wherein the base treatment step of heat treatment in an inert gas atmosphere is performed at 300 to 600°C.

4. In paragraph 1, A method for purifying graphite, wherein the base treatment step of heat treatment in an inert gas atmosphere is performed for 1.0 hour or more.

5. In paragraph 1, A method for purifying graphite, wherein the inert gas atmosphere comprises at least one of nitrogen (N2), helium (He), or argon (Ar) gases.

6. In paragraph 1, In the above base treatment step, A method for purifying graphite by dry or wet mixing the above graphite material and the above metal hydroxide.

7. In paragraph 1, A method for purifying graphite, wherein the base treatment step of dry mixing and heat treating the above graphite material and metal hydroxide includes a first washing and filtering step of washing and filtering the heated mixture.

8. In paragraph 1, A method for purifying graphite, wherein in a base treatment step of dry mixing and heat treating the graphite material and the metal hydroxide, the content ratio of the metal hydroxide to the graphite material is 10 to 60 by weight.

9. In paragraph 7, A method for purifying graphite using water 2 to 20 times the amount of the base-treated graphite material in the first washing and filtration step.

10. In paragraph 7, A method for purifying graphite, wherein the first washing and filtering step is performed at a temperature range of room temperature to 60°C.

11. In paragraph 1, A method for purifying graphite, wherein the step of acid-treating the base-treated graphite material is performed at a temperature range of room temperature to 95°C.

12. In paragraph 1, A method for purifying graphite, wherein the step of treating the base-treated graphite material with acid is performed with at least one acid selected from the group consisting of hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, and boric acid.

13. In paragraph 1, A method for purifying graphite, wherein the step of treating the base-treated graphite material with acid includes a second washing and filtering step of washing and filtering the acid-leached resultant.

14. In paragraph 13, A method for purifying graphite, wherein the second washing and filtering step is performed at a temperature range of room temperature to 60°C for 5 to 60 minutes.

15. Base treatment step of mixing graphite material and metal hydroxide and heat treatment, and A method for purifying graphite, comprising a step of acid-treating the base-treated graphite material with an acid solution of 0.3 to 1.5 mol / L prepared by adding an acid solution to 2.0 to 5.0 times the amount of water (H2O) of the graphite material.

16. In paragraph 15, A method for purifying graphite, wherein the purified graphite has silicon (Si) of 300 ppm or less based on 100 wt%.

17. In paragraph 15, A method for purifying graphite in which, in the acid treatment step, the acid solution has a pH of 2 or less.

18. In paragraph 15, A method for purifying graphite, wherein the above acid treatment step is performed at a temperature range of room temperature to 95°C.

19. Base treatment step of mixing graphite material and metal hydroxide and heat treating; A step of acid-treating the above base-treated graphite material; and The above base treatment step includes a step of mixing the graphite material and the metal hydroxide, heat treating them, and then performing a first washing and filtering step. A method for purifying graphite, wherein the first washing and filtering step is performed at a stirring speed of 100 to 500 rpm.

20. In paragraph 19, A method for purifying graphite, wherein the contents of Si, Al, and Fe in the impurities in the first washing and filtration step satisfy the following equation 1. <Formula 1> ([Al]+[Si]) / [Fe] < 6.0 (In the above formula 1, [Al], [Si], and [Fe] represent the ppm contents of Al, Si, and Fe in the impurities)

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