Method for refining graphite

Abstract

The present invention relates to a method for refining graphite, and may include a base treatment step of dry mixing a graphite material and a metal hydroxide and heat treating them, and a step of acid treating the base-treated graphite material.

Description

Technical Field

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

Background Art

[0002] A lithium secondary battery generally consists of a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, a separator, and an electrolyte, and is charged and discharged by the insertion and extraction (Intercalation-Deintercalation) of lithium ions. The lithium secondary battery has the advantages of high energy density, high electromotive force, and high capacity, and is therefore applied in various fields.

[0003] In particular, graphite is widely used as the negative electrode active material in the configuration of the negative electrode, and natural graphite and artificial graphite are mainly used as the graphite. In the case of the natural graphite, it is one of the carbon elements existing in the form extracted from fossil fuels such as coal and oil, has the structure and properties of natural nature as it is, has high crystallinity and very low residue content. In addition, the natural graphite has very high electrical conductivity and is utilized as a negative electrode material for battery materials such as secondary batteries.

[0004] The natural graphite is extracted from graphite minerals, extracted as flaky graphite through a beneficiation process, the extracted flaky graphite is spheroidized to produce spherical graphite, purified spherical graphite is produced through purification, and the purified spherical graphite is coated to produce a negative electrode material. At this time, a wet process is utilized as a method for purifying spherical graphite. When utilizing the wet process, there are problems that the stages of washing and filtering the liquid are excessively numerous, the processing stage is long, and it is complicated.

Summary of the Invention

Problems to be Solved by the Invention

[0005] According to one embodiment of the present invention, a method for purifying graphite is provided that results in high-purity graphite and has a simple processing step. [Means for solving the problem]

[0006] A graphite purification method according to one embodiment of the present invention may include a base treatment step of dry mixing a graphite material and a metal hydroxide and heat treating the mixture, and an acid treatment step of the base-treated graphite material. In one embodiment, the particle size of the metal hydroxide may be 1 to 100 μm or less.

[0007] In one embodiment, the process may further include a step of grinding the metal hydroxide before the step of dry mixing the graphite material and the metal hydroxide. 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 filtration step of washing and filtering the heated mixture.

[0008] In one embodiment, in the base treatment step in which the graphite material and metal hydroxide are dry-mixed and heat-treated, the content ratio of the metal hydroxide to the graphite material can be 10 to 60. In one embodiment, in the base treatment step in which the graphite material and metal hydroxide are dry-mixed and heat-treated, the mixture can be heated to a temperature in the range of 400 to 600°C.

[0009] In one embodiment, two to twenty times the amount of water used in the first washing and filtration step can be used in the base-treated graphite material. The first washing and filtration step can be carried out in a temperature range of room temperature to 60°C.

[0010] In one embodiment, the first washing and filtration step may include washing the base-treated graphite material for 5 to 60 minutes. In one embodiment, the acid treatment step of the base-treated graphite material may be carried out in a temperature range of room temperature to 95°C.

[0011] In one embodiment, the step of acid-treating the base-treated graphite material may be carried out with at least one acid from hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, and boric acid. In one embodiment, the step of acid-treating the base-treated graphite material includes a second washing and filtering step of washing and filtering the acid-leached result with water, the second washing and filtering step may use 2 to 5 times the volume of water of the acid-treated result.

[0012] In one embodiment, the second washing and filtration step may be carried out for 5 to 60 minutes at a temperature range of room temperature to 60°C. In one embodiment, the concentration of the diluted acid used in the step of acid-treating the base-treated graphite material may be 0.1 to 3.0 mol / L. [Effects of the Invention]

[0013] A graphite purification method according to one embodiment of the present invention provides a graphite purification method with high graphite purity and simple processing steps, by dry mixing with solid sodium hydroxide. [Brief explanation of the drawing]

[0014] [Figure 1] A flowchart of a graphite refining method according to one embodiment of the present invention is shown. [Figure 2] A photograph of graphite refined using one embodiment of the present invention is shown. [Figure 3] An electron microscope image of graphite purified by one embodiment of the present invention is shown. [Modes for carrying out the invention]

[0015] The terms first, second, and third are used to describe various parts, components, regions, layers, and / or sections, but are not limited to these. These terms are used solely to distinguish one part, component, region, layer, or section from other parts, components, regions, layers, or sections. Accordingly, the first part, component, region, layer, or section described below may be referred to as the second part, component, region, layer, or section without departing from the scope of the invention.

[0016] The technical terms used herein are for the sole purpose of referring to specific embodiments and are not intended to limit the invention. The singular form used herein also includes plural forms unless the wording explicitly indicates otherwise. The meaning of “including” as used in this specification embodies a particular characteristic, area, integer, stage, operation, element, and / or component, and does not exclude the presence or addition of other characteristics, areas, integers, stages, operations, elements, and / or components.

[0017] When we say that one part is "on top of" another part, it means that it is either directly above the other part, or that another part may be in between them. In contrast, when we say that one part is "directly above" another part, it means that no other part is in between them.

[0018] Unless otherwise defined, all terms used herein, including technical and scientific terms, have the same meaning as those generally understood by a person of ordinary skill in the art to which this invention pertains. Terms defined in commonly used dictionaries are further interpreted to have the meaning consistent with the relevant technical literature and the present disclosures, and are not interpreted in their ideal or highly formal sense unless otherwise defined.

[0019] Embodiments of the present invention will be described in detail below. However, these are presented as examples only and the present invention is not limited thereto, and is defined solely within the scope of the claims described later.

[0020] FIG. 1 shows a flowchart of a method for purifying graphite according to an embodiment of the present invention.

[0021] Referring to FIG. 1, the method for purifying graphite of the present invention includes a base treatment step (S100) of dry-mixing a graphite material and a metal hydroxide and performing heat treatment, and a step (S200) of acid-treating the base-treated graphite material. Specifically, the method for manufacturing purified graphite of the present invention removes the impurity content in graphite to manufacture highly purified graphite.

[0022] The base treatment step (S100) of dry-mixing a graphite material and a metal hydroxide and performing heat treatment may include a step of preparing a graphite material and a metal hydroxide, a step of dry-mixing the graphite material and the metal hydroxide, and a step of heat-treating a mixture in which the graphite material and the metal hydroxide are mixed.

[0023] In the step of preparing the graphite material and the metal hydroxide, the graphite material relates to powdered graphite and may be, for example, manufactured through steps of pulverizing, rounding, homogenizing, and purifying earthy graphite, flaky graphite, etc.

[0024] The metal hydroxide may be, for example, sodium hydroxide (NaOH). Specifically, the metal hydroxide is in a solid state and may be in the form of fine powder.

[0025] In one embodiment, before the step of dry-mixing the graphite material and the metal hydroxide, a step of pulverizing the metal hydroxide may further be included. The step of pulverizing can crush the solid metal hydroxide into a powder form. Specifically, the pulverizing may include a process of applying physical or mechanical force to the solid metal hydroxide to crush the solid metal hydroxide or finely crush it into powder. The pulverizing can be performed using various types of pulverizers, such as a blade-type pulverizer.

[0026] In one embodiment, the step of grinding the metal hydroxide includes a step of classifying the metal hydroxide after grinding. The step of classifying the metal hydroxide may be carried out so 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 classification using the size of the sieve.

[0027] If the solid metal hydroxide exceeds the upper limit of the range described above, there is a problem of reduced purification effect and aggregation and hardening of the material after heat treatment. If the solid sodium hydroxide exceeds the lower limit of the range described above, there is a problem of reduced grinding yield and aggregation due to moisture.

[0028] The step of mixing the graphite material and the metal hydroxide may be a step of dry mixing the graphite material and the pulverized metal hydroxide in a predetermined ratio. The ratio of the metal hydroxide content 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 100:15 to 100:50, specifically 100:17 to 100:30.

[0029] If the content of the metal hydroxide in the graphite material falls outside the upper limit of the range described above, there is a problem that the sample obtained after heat treatment will solidify and become hard. If the content of the solid sodium hydroxide (NaOH) in the graphite material falls outside the lower limit of the range described above, there is a problem that the graphite refining effect will decrease.

[0030] In one embodiment, the step of mixing the graphite material and the metal hydroxide can be carried out using at least one of a ribbon mixer, V-mixer, screw mixer, ball mill, hammer mill, and a stirring mill, planetary mixer, or roller mixer. Since the graphite material and the metal hydroxide are dry-mixed, this can be carried out using at least one of the mixers such as the ribbon mixer, V-mixer, screw mixer, ball mill, hammer mill, and a stirring mill, planetary mixer, or roller mixer, using the aforementioned mixers offers advantages in terms of energy efficiency compared to mixing a substance with viscosity such as a slurry.

[0031] For example, a substance with viscosity, such as a slurry, may be formed when a graphite material is mixed with a metal hydroxide in an aqueous solution. Mixing such a substance with viscosity, such as a slurry, presents a problem in terms of energy efficiency compared to the dry mixing method of the present invention.

[0032] In the step of dry mixing the graphite material and the metal hydroxide, the heat treatment step can involve heating the mixture to a temperature in the range of 400 to 600°C. Specifically, the mixture can be heated to a temperature in the range of 440 to 560°C. By keeping within this temperature range, the metal hydroxide melts, which has the advantage of increasing the reaction efficiency. If the temperature is outside this range, side reactions occur, leading to a decrease in reaction efficiency.

[0033] In one embodiment, the step of heating the mixture may be carried out for 30 minutes to 10 hours. Specifically, the step of heating the mixture may be carried out for 1 to 8 hours. By carrying out the step of heating the mixture within the aforementioned temperature and time range, the impurities in the graphite material and the metal hydroxide can react appropriately.

[0034] In one embodiment, the base treatment step may be followed by a first washing and filtration step in which the heated mixture is washed.

[0035] In one embodiment, a first washing and filtering step involves washing and filtering a heated mixture using a liquid such as water. The first washing and filtering step can be performed by immersing the heated mixture in, for example, hot water. Specifically, the first washing and filtering step may involve washing and filtering the heated mixture in a washing neutral step.

[0036] In one embodiment, in the first washing and filtration stage, two to twenty times the amount of water as the base-treated graphite material, specifically the heat-treated product, can be used. Using the water in the first washing and filtration stage has the advantage of facilitating the washing and filtration of the graphite material.

[0037] The step of acid-treating the base-treated graphite material (S200) may be a step of applying the washed and filtered results to acid leaching. The step of acid-treating the base-treated graphite material may be a step of leaching the washed and filtered results with an acidic solution, such as water and a diluted substance containing the acidic solution. For example, the acidic solution may be contained in 2.0 to 5.0 times the amount of water (H2O) of the graphite material to a concentration of 0.1 to 3.0 mol / L. For example, at least one of hydrochloric acid, nitric acid, phosphoric acid, boric acid, and sulfuric acid can be used as the acidic solution.

[0038] In one embodiment, the step of acid-treating the base-treated graphite material (S200) may be carried out in a temperature range of 60 to 100°C. Specifically, the temperature range may be 70 to 90°C. In one embodiment, the step of acid-treating the base-treated graphite material (S200) may be carried out in a time range of 5 to 60 minutes, specifically 25 to 45 minutes.

[0039] By performing acid leaching within the aforementioned temperature and time range, the reactivity during acid leaching is increased, allowing for easier removal of impurities. If the temperature and time range is outside of this range, the reactivity during acid leaching decreases, making it impossible to obtain high-purity graphite. While longer leaching times result in superior purification, the aforementioned range is preferable from an economic standpoint.

[0040] In one embodiment, the step of acid-treating the base-treated graphite material (S200) may further include a second washing and filtration step of washing and filtering the acid-treated result with water. The acid treatment, specifically the second washing and filtration step of washing and filtering the acid-leached result with water, may include filtering the acid-leached result at room temperature and washing with water. Specifically, when water is used, it may be carried out at room temperature for 5 to 60 minutes using 2 to 5 times the amount of H2O. If necessary, heated water may be used to increase the purification efficiency. By performing the washing and filtration step under the above conditions, the purification efficiency of graphite can be increased.

[0041] The graphite refined through a base treatment step (S100) in which the graphite material and metal hydroxide are dry-mixed and heat-treated, and a step (S200) in which the base-treated graphite material is acid-treated, may have an ash content of 0.04 wt% or less, specifically 0.03 wt%, and more specifically 0.01 wt% or less.

[0042] Thus, the graphite purification method of the present invention simplifies the overall process by using solid sodium hydroxide and can purify high-purity graphite.

[0043] The graphite refined by the graphite refining method of the present invention may have an ash content of 0.04 wt% or less by weight, specifically 0.03 wt% or less, and more specifically 0.01 wt% or less. High-purity graphite can be obtained by satisfying the aforementioned range for the ash content. In one embodiment, the refined graphite may have a silicon content of 60 ppm or less by weight. Specifically, the silicon content may be 57 ppm or less, and more specifically 30 ppm or less. In one embodiment, the refined graphite may have an aluminum content of 15 ppm or less by weight. Specifically, the aluminum content may be 12 ppm or less, and more specifically 5 ppm or less.

[0044] By ensuring that the silicon and aluminum content meets the aforementioned ranges, it is possible to obtain highly purified graphite with fewer impurities. [Examples]

[0045] The following describes preferred embodiments and comparative examples of the present invention. However, the following embodiments are merely preferred embodiments of the present invention, and the present invention is not limited to these embodiments.

[0046] Method for refining graphite Example 1 Solid sodium hydroxide (NaOH) beads were pulverized for 5 minutes using a blade-type pulverizer. The pulverized NaOH beads were classified using a 75 μm sieve to obtain solid sodium hydroxide (NaOH) powder with particles of 75 μm or less.

[0047] Spheroidal graphite with an average particle size (D50) of 16 μm and solid NaOH powder with a particle size of 75 μm or less, which had been classified and filtered, were mixed in a 100:30 ratio at 100 RPM for 0.5 hours. The mixture was then heat-treated at 500°C for 4 hours.

[0048] Subsequently, the heat-treated mixture was washed with graphite:distilled water in a 1:5 ratio at 40°C, and then vacuum filtered using filter paper and a Buchner funnel.

[0049] Subsequently, the material, after being washed with water and filtered, was subjected to acid leaching with 0.61 mol / L hydrochloric acid for 35 minutes at a temperature range of 80°C.

[0050] Subsequently, the acid-leached substance was washed with graphite and distilled water in a 1:2 ratio at room temperature for 40 minutes, followed by filtration to produce purified graphite.

[0051] Example 2 Solid sodium hydroxide (NaOH) beads were pulverized in a blade-type pulverizer for 5 minutes. The procedure was the same as in Example 1, except that the pulverized sodium hydroxide (NaOH) beads were classified using a 38 μm sieve to obtain solid sodium hydroxide (NaOH) powder with a particle size of 38 μm or less.

[0052] Example 3 The procedure was the same as in Example 2, except that the mixing ratio of graphite to NaOH powder was 100:23.

[0053] Example 4 The procedure was the same as in Example 2, except that the mixing ratio of graphite to NaOH powder was 100:17.

[0054] Comparative Example 1 - Wet method A liquid NaOH aqueous solution (45%) containing spheroidal graphite with an average particle size (D50) of 16 μm was slurry-mixed in a planetary mixer in a weight ratio of graphite:45% NaOH aqueous solution = 100:66. The mixed mixture was then heat-treated at 500°C for 4 hours.

[0055] Subsequently, the heat-treated mixture was washed with water and filtered under the conditions of graphite:distilled water = 1:5, 40°C, for 10 minutes.

[0056] Subsequently, the material, after being washed with water and filtered, was subjected to acid leaching with 0.61 mol / L hydrochloric acid for 35 minutes at a temperature of 80°C. Then, the acid-leached material was washed with water and filtered at room temperature for 40 minutes to produce purified graphite. Next, a base treatment was performed with graphite:distilled water:NaOH aqueous solution (45%) = 5:15:1 (wt%) at 80°C for 120 minutes. Following this, an additional washing and filtration was performed with graphite:distilled water in a ratio of 1:5 at 80°C for 30 minutes, followed by a secondary acid treatment with graphite:distilled water in a ratio of 1:3 at 80°C for 35 minutes. Finally, purified graphite was produced by washing with water and filtering with graphite:distilled water in a ratio of 2:9 at 80°C for 30 minutes.

[0057] Comparative Example 2 The procedure was carried out in the same manner as in Example 1, except that solid NaOH beads (Beads) with an average particle size (D50) of 0.9 mm were mixed with spheroidal graphite without crushing.

[0058] Comparative Example 3 The procedure was carried out in the same manner as in Example 1, except that the crushed NaOH beads were classified using a 150 μm sieve to obtain solid NaOH powder with particles of 150 μm or less.

[0059] Comparative Example 4 The procedure was carried out in the same manner as in Example 1, except that the crushed NaOH beads were classified using a 38 μm sieve to obtain solid NaOH powder of 38 μm or less, and the mixing ratio of graphite to NaOH powder was 100:60.

[0060] Comparative Example 5 The procedure was carried out in the same manner as in Example 1, except that the crushed NaOH beads were classified using a 38 μm sieve to obtain solid NaOH powder of 38 μm or less, and the mixing ratio of graphite to solid NaOH powder was 100:10.

[0061] Evaluation Example 1: Evaluation Example for High-Purity Processing of Spheroidal Graphite Table 1 below shows the properties of graphite refined according to Examples 1-4 and Comparative Examples 1-5 described above.

[0062] Ash (wt%) was determined by drying 5g of the sample at 150°C for 5 hours, then placing it in a crucible and heating it in a box furnace to 950°C at a rate of 10°C per minute for 12 hours. The weight of the resulting material was then measured by dividing it by the weight of the initial sample.

[0063] [Table 1]

[0064] Referring to Table 1 above, a comparison of Examples 1-4 and Comparative Example 1 confirms that using solid sodium hydroxide powder allows for higher purity purification than using an aqueous sodium hydroxide solution. A comparison of Examples 1-4 and Comparative Example 2 shows that even when using solid sodium hydroxide, the purification effect is significantly reduced when the particle size is large without pulverization. A comparison of Examples 1-4 and Comparative Example 3 shows that even when using pulverized solid sodium hydroxide, the purification effect is reduced when the particle size is large. In the case of Comparative Example 4, the purification effect was high when the particle size of sodium hydroxide was sufficiently reduced to 38 μm or less, but it was confirmed that the amount added was excessively large compared to graphite, causing the material to solidify and harden after heat treatment. In such cases, sample recovery becomes difficult, and the efficiency of subsequent washing, filtration, and acid leaching is significantly reduced.

[0065] In Comparative Example 5, the mixing ratio of sodium hydroxide was reduced to 100:10, resulting in a graphite material:sodium hydroxide ratio that was insufficient, significantly lowering the purification efficiency.

[0066] [Table 2]

[0067] Referring to Table 2 above, a comparison of Examples 1 and 2 with Comparative Examples 1 and 2 confirmed that when using fine sodium hydroxide powder obtained by grinding solid sodium hydroxide powder, the overall impurity content, such as Al, Si, Mg, and Fe, was lower, at levels similar to or lower than when using existing liquid sodium hydroxide. This confirmed that the process can be simplified compared to existing processes, and the purity of graphite can be increased.

[0068] Figure 2 is a photograph of graphite purified by the graphite purification method of the present invention.

[0069] Referring to Figure 2, it can be confirmed that, according to Example 1 of the present invention, the purified graphite has low hardness after heat treatment, is easy to crush, and easy to discharge, demonstrating excellent processability.

[0070] Figure 3 is an electron microscope image of graphite purified by the graphite purification method of the present invention.

[0071] Referring to Figure 3, it was confirmed that the graphite refined according to Example 2 of the present invention retained the shape of the spheroidal graphite before refinement without any damage.

[0072] Although preferred embodiments have been described in detail above, the scope of the present invention is not limited thereto. Various modifications and improvements by those skilled in the art, utilizing the basic concepts defined in the following claims, also fall within the scope of the present invention.

Claims

1. A base treatment step in which graphite material and metal hydroxide are dry-mixed and heat-treated, and A method for purifying graphite, comprising the step of treating the base-treated graphite material with acid.

2. The method for purifying graphite according to claim 1, wherein the particle size of the metal hydroxide is 1 to 100 μm or less.

3. Before the step of dry mixing the graphite material and metal hydroxide, The method for purifying graphite according to claim 1, further comprising the step of grinding the metal hydroxide.

4. The method for purifying graphite according to claim 1, wherein the base treatment step of dry mixing the graphite material and metal hydroxide and heat treating it comprises a first washing and filtering step of washing and filtering the heated mixture.

5. The method for purifying graphite according to claim 1, wherein in the base treatment step of dry mixing the graphite material and the metal hydroxide and heat treating it, the content ratio of the metal hydroxide to the graphite material is 10 to 60.

6. The method for purifying graphite according to claim 1, wherein in the base treatment step of dry mixing the graphite material and the metal hydroxide and heat treating the mixture, the mixture is heated to a temperature in the range of 400 to 600°C.

7. The method for purifying graphite according to claim 4, wherein in the first washing and filtration step, two to twenty times the amount of water used is used for the base-treated graphite material.

8. The method for purifying graphite according to claim 4, wherein the first washing and filtration step is performed in a temperature range of room temperature to 60°C.

9. The method for purifying graphite according to claim 4, wherein the first washing and filtration step includes washing the base-treated graphite material for 5 to 60 minutes.

10. The method for purifying graphite according to claim 1, wherein the step of acid-treating the base-treated graphite material is carried out in a temperature range of room temperature to 95°C.

11. The method for purifying graphite according to claim 1, wherein the step of acid-treating the base-treated graphite material is carried out with at least one acid selected from hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, and boric acid.

12. The method for purifying graphite according to claim 1, wherein the step of acid-treating the base-treated graphite material includes a second washing and filtering step of washing and filtering the acid-leached result with water.

13. The method for purifying graphite according to claim 12, wherein the second washing and filtration step uses two to five times the amount of water as the acid-treated result.

14. The method for purifying graphite according to claim 12, wherein the second washing and filtration step is performed for 5 to 60 minutes in a temperature range of room temperature to 60°C.

15. The method for purifying graphite according to claim 1, wherein the concentration of the diluted acid used in the step of acid-treating the base-treated graphite material is 0.1 to 3.0 mol / L.

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