Purification method for natural flake graphite, purified graphite and lithium-ion battery

Abstract

Provided in the present application are a purification method for natural flake graphite, purified graphite and a lithium-ion battery. The purification method comprises: heating natural flake graphite in an atmosphere of reaction gases, wherein the reaction gases comprise a combination of at least two of nitrogen, chlorine, CO2, CO or helium. In the present application, by heating natural flake graphite in an atmosphere of the reaction gases to achieve purification, under the synergistic effect of at least two gases of nitrogen, chlorine, CO2, CO and helium, the content of impurity elements and magnetic substances in natural flake graphite can be reduced, thereby ensuring the purity of graphite; in addition, the purification method of the present invention has simple steps, a relatively low energy consumption and cost, and relatively low pollution.

Description

Method for purifying natural flake graphite, purified graphite and lithium-ion battery

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on December 13, 2023, with application number 2023117198945. The entire contents of the above application are incorporated by reference into this application.

[0002] Technical Field

[0003] The present application relates to the field of battery technology, and in particular to a method for purifying natural flake graphite, purified graphite, and a lithium-ion battery.

[0004] Background Art

[0005] Due to the rapid development of lithium-ion batteries, natural flake graphite has become a widely used, inexpensive raw material. However, the numerous impurities and defects in natural flake graphite limit its application in lithium-ion battery anodes. Natural flake graphite often contains metallic impurities such as Fe, Cr, Ni, and Zn. These metallic impurities are also components of magnetic materials, making natural flake graphite magnetic and unsuitable for use. To meet the increasingly stringent material requirements of the lithium battery industry, the content of metallic impurities and magnetic materials in graphite needs to be controlled to the part-per-billion level. Therefore, natural flake graphite needs to be purified.

[0006] Technical issues

[0007] Existing methods for purifying natural flake graphite primarily include: ① flotation purification; ② pickling and high-temperature treatment. Large-scale graphite plants typically use a combination of pickling and high-temperature treatment to purify graphite, but this method consumes a lot of energy and generates significant pollution, increasing graphite production costs.

[0008] Therefore, there is an urgent need for a purification method that can reduce energy consumption and cost and reduce pollution.

[0009] This application provides a method for purifying natural flake graphite, purified graphite, and a lithium-ion battery. This method purifies natural flake graphite by heating it in an atmosphere of a reactive gas. Through the synergistic effect of at least two gases selected from nitrogen, chlorine, CO₂, CO, and helium, the content of impurity elements and magnetic substances in the natural flake graphite is reduced, thereby ensuring the purity of the graphite. Furthermore, this method has a simple process, low energy consumption and cost, and is less polluting.

[0010] Technical Solutions

[0011] In a first aspect, the present application provides a method for purifying natural flake graphite, the purification method comprising:

[0012] The natural flake graphite is heated in an atmosphere of a reaction gas;

[0013] The reaction gas includes a combination of at least two of nitrogen (N2), chlorine (Cl2), CO2, CO or helium.

[0014] In a second aspect, the present application provides a purified graphite, which is prepared using the purification method described in the first aspect.

[0015] In a third aspect, the present application provides a lithium-ion battery, wherein the negative electrode of the lithium-ion battery includes the purified graphite described in the second aspect.

[0016] Beneficial effects

[0017] Compared with the related art, the beneficial effects of this application are:

[0018] The present application provides a method for purifying natural flake graphite, which is purified by heating the natural flake graphite in an atmosphere of a reaction gas, wherein the reaction gas includes a combination of at least two of nitrogen, chlorine, CO2, CO or helium. Under heating conditions, nitrogen, chlorine, CO2, CO and helium can react with metallic impurity elements in the natural flake graphite, lowering the boiling point of the impurity compounds, thereby enabling the impurity compounds to be separated from the graphite under high-temperature heating, reducing the content of metallic impurities and magnetic substances, and thus under the synergistic effect of at least two of the above-mentioned gases, the content of impurity elements and magnetic substances in the natural flake graphite can be reduced, thereby ensuring the purity of the graphite; while the heating step can also enhance the degree of graphitization of the material, increase the crystallinity of graphite and reduce the defects of graphite crystals. The purification method of the present application has a simple process, low energy consumption and cost, and less pollution, greatly optimizing the purification process and timeliness.

[0019] Still other aspects will become apparent upon reading and understanding the accompanying drawings and detailed description.

[0020] BRIEF DESCRIPTION OF THE DRAWINGS

[0021] FIG1 is a schematic flow chart of a method for purifying natural flake graphite provided in an embodiment of the present application.

[0022] FIG2 is a schematic flow chart of a conventional method for purifying natural flake graphite.

[0023] DETAILED DESCRIPTION

[0024] In a first aspect, the present application provides a method for purifying natural flake graphite, the purification method comprising:

[0025] The natural flake graphite is heated in an atmosphere of a reaction gas;

[0026] The reaction gas includes a combination of at least two of nitrogen (N2), chlorine (Cl2), CO2, CO or helium.

[0027] The present application provides a method for purifying natural flake graphite, which is purified by heating the natural flake graphite in an atmosphere of a reaction gas, wherein the reaction gas includes a combination of at least two of nitrogen, chlorine, CO2, CO or helium. Under heating conditions, nitrogen, chlorine, CO2, CO and helium can react with metallic impurity elements in the natural flake graphite, lowering the boiling point of the impurity compounds, thereby enabling the impurity compounds to be separated from the graphite under high-temperature heating, reducing the content of metallic impurities and magnetic substances, and thus under the synergistic effect of at least two of the above-mentioned gases, the content of impurity elements and magnetic substances in the natural flake graphite can be reduced, thereby ensuring the purity of the graphite; while the heating step can also enhance the degree of graphitization of the material, increase the crystallinity of graphite and reduce the defects of graphite crystals. The purification method of the present application has a simple process, low energy consumption and cost, and less pollution, greatly optimizing the purification process and timeliness.

[0028] In the present application, typical non-limiting combinations of the reaction gases include: a combination of nitrogen and chlorine, a combination of CO2 and CO, a combination of CO2 and chlorine, and a combination of CO2 and helium.

[0029] Optionally, after the heating, a screening and demagnetization step is performed.

[0030] Optionally, the reaction gas is a combination of CO2 and nitrogen or a combination of CO2 and chlorine.

[0031] In the present application, a combination of CO2 and nitrogen or a combination of CO2 and chlorine is used as the reaction gas. The reaction efficiency of the gas with the metal impurities is the highest and the production cost is also low.

[0032] Optionally, the flow rate of the reaction gas is 1-20 L / min, for example, it can be 1 L / min, 2 L / min, 3 L / min, 4 L / min, 5 L / min, 6 L / min, 7 L / min, 8 L / min, 9 L / min, 10 L / min, 11 L / min, 12 L / min, 13 L / min, 14 L / min, 15 L / min, 16 L / min, 17 L / min, 18 L / min, 19 L / min or 20 L / min, etc., but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable, and 3-18 L / min can be selected.

[0033] Optionally, when the reaction gas is a combination of CO2 and nitrogen, the flow rates of CO2 and nitrogen are independently 5-8 L / min, for example, 5 L / min, 6 L / min, 7 L / min or 8 L / min, etc., but are not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0034] In this application, if the flow rate of CO2 and nitrogen is too small, the metal impurities will not react fully with the gas, resulting in low efficiency; if the flow rate of CO2 and nitrogen is too large, it will cause gas waste and increase production costs.

[0035] Optionally, the particle size D50 of the natural flake graphite is 7-20 μm, for example, it can be 7 μm, 8 μm, 10 μm, 12 μm, 14 μm, 16 μm, 18 μm or 20 μm, etc., but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0036] Optionally, the heating temperature is 800-3200°C, for example, it can be 800°C, 900°C, 1000°C, 1100°C, 1200°C, 1500°C, 1800°C, 2000°C, 2100°C, 2200°C, 2300°C, 2500°C, 2600°C, 2800°C, 2900°C, 2950°C, 3000°C, 3050°C, 3100°C, 3150°C or 3200°C, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0037] Optionally, the heating time is 5-56h, for example, it can be 5h, 10h, 15h, 20h, 25h, 30h, 35h, 40h, 45h, 48h, 50h, 52h, 55h or 56h, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0038] Optionally, the heating includes one-stage heating and two-stage heating performed sequentially.

[0039] In the present application, a first stage of heating is performed to allow the natural flake graphite to fully contact and mix with the reaction gas in advance; and a second stage of heating is performed to allow the metal impurity elements to fully react with the reaction gas to generate compounds that are separated from the graphite.

[0040] Optionally, the temperature of the heating stage is 800-1200°C, for example, it can be 800°C, 900°C, 1000°C, 1100°C or 1200°C; the time of the heating stage is 2-8h, for example, it can be 2h, 3h, 4h, 5h, 6h, 7h or 8h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0041] Optionally, the temperature of the second stage heating is 2800-3100°C, for example, it can be 2800°C, 2900°C, 2950°C, 3000°C, 3050°C or 3100°C; the time of the second stage heating is 5-48h, for example, it can be 5h, 10h, 15h, 20h, 25h, 30h, 35h, 40h, 45h or 48h, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0042] As an optional technical solution of this application, the purification method specifically includes:

[0043] The natural flake graphite with a particle size D50 of 7-20 μm is shaped, placed in a container, and a reaction gas is introduced into the container. The container is then heated at a temperature of 800-1200°C for 2-8 hours, and then heated at a temperature of 2800-3100°C for 5-48 hours. The product is then sieved and demagnetized to complete the purification.

[0044] The reaction gas includes a combination of at least two of nitrogen, chlorine, CO2, CO or helium.

[0045] In a second aspect, the present application provides a purified graphite, which is prepared using the purification method described in the first aspect.

[0046] In a third aspect, the present application provides a lithium-ion battery, wherein the negative electrode of the lithium-ion battery includes the purified graphite described in the second aspect.

[0047] The numerical range described in this application includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to limited space and for the sake of simplicity, this application no longer exhaustively lists the specific point values ​​included in the range.

[0048] The technical solution of this application is further explained below through specific implementation methods.

[0049] In one embodiment, the present application provides a method for purifying natural flake graphite, the process of which is shown in FIG1 , comprising the following steps:

[0050] The natural flake graphite is shaped, then heated in an atmosphere of reaction gas, and then sieved and demagnetized to complete the purification.

[0051] Compared with the traditional method for purifying natural flake graphite (the process is shown in Figure 2), which includes the following steps: shaping the natural flake graphite, then pickling the shaped natural flake graphite, and then performing high-temperature treatment and screening for demagnetization; the method for purifying natural flake graphite provided in this application can not only achieve purification, but also has a simple process, low energy consumption and cost, and less pollution.

[0052] Example 1

[0053] This embodiment provides a method for purifying natural flake graphite, comprising the following steps:

[0054] Natural flake graphite with a particle size D50 of 10 μm is shaped, placed in a container, and reaction gas is introduced into the container. The reaction gas is a combination of CO2 and N2, the flow rate of CO2 is 5 L / min, and the flow rate of N2 is 5 L / min. Then, it is heated at 800°C for 5 hours for the first stage, and then heated at 2800°C for 48 hours for the second stage. After cooling, the graphite sample is obtained by screening and demagnetization.

[0055] Examples 2-25 and Comparative Examples 1-2 are based on Example 1 with parameter changes. The specific changed parameters are detailed in Table 1.

[0056] Table 1

[0057]

[0058] Performance Testing

[0059] The graphite samples provided in the above embodiments and comparative examples were subjected to ICP testing to detect the content of metallic impurity elements and magnetic substances therein.

[0060] The test results are shown in Table 2.

[0061] Table 2

[0062]

[0063] analyze:

[0064] It can be seen from the data results of Examples 1-20 that by adopting the purification method of the present application, the content of impurity elements and magnetic substances in the obtained graphite sample is low, and the purification effect is better.

[0065] It can be seen from the data results of Examples 10 and 21-22 that if the temperature of the second-stage heating is too low, the content of impurity elements and magnetic substances in the sample will be higher; if the temperature of the second-stage heating is too high, although the purification effect is better, it will lead to increased energy consumption and increased costs.

[0066] It can be seen from the data results of Example 10 and Example 23 that if only one-stage heating is used, the reaction between the gas and the metal elements in the graphite is insufficient, and the content of metal impurities and magnetic substances in the product is relatively high.

[0067] It can be seen from the data results of Example 10 and Examples 24-25 that if the flow rate of CO2 and N2 is too small, the reaction gas will not react completely with the metal impurities in the graphite; if the flow rate of CO2 and N2 is too large, the content of metal impurities and magnetic substances in the product will not be significantly reduced, but the production cost will increase.

[0068] It can be seen from the data results of Example 10 and Comparative Examples 1-2 that if only one gas is used as the reaction gas, the content of metal impurities and magnetic substances will increase slightly. It is possible that some metal elements have higher reaction activity with specific gases, and the impurity removal effect of mixing multiple gases is better.

Claims

1. A method for purifying natural flake graphite, comprising: The natural flake graphite is heated in an atmosphere of a reaction gas; Wherein, the reaction gas includes a combination of at least two of nitrogen, chlorine, CO2, CO or helium.

2. The purification method according to claim 1, wherein The reaction gas is a combination of CO2 and nitrogen or a combination of CO2 and chlorine.

3. The purification method according to claim 1 or 2, wherein: The flow rate of the reaction gas is 1-20 L / min.

4. The purification method according to claim 3, wherein: The flow rate of the reaction gas is 3-18 L / min.

5. The purification method according to any one of claims 1 to 4, wherein: When the reaction gas is a combination of CO 2 and nitrogen, the flow rates of CO 2 and nitrogen are independently 5-8 L / min.

6. The purification method according to any one of claims 1 to 5, wherein: The particle size D50 of the natural flake graphite is 7-20 μm.

7. The purification method according to any one of claims 1 to 6, wherein: The heating temperature is 800-3200°C.

8. The purification method according to any one of claims 1 to 7, wherein: The heating time is 5-56h.

9. The purification method according to any one of claims 1 to 8, wherein: The heating includes one-stage heating and two-stage heating performed sequentially.

10. The purification method according to claim 9, wherein: The temperature of the first stage heating is 800-1200° C.; the time of the first stage heating is 2-8 hours.

11. The purification method according to claim 9 or 10, wherein: The temperature of the second stage heating is 2800-3100° C.; the time of the second stage heating is 5-48 hours.

12. The purification method according to any one of claims 1 to 11, wherein: The purification method specifically comprises: The natural flake graphite with a particle size D50 of 7-20 μm is shaped, the shaped natural flake graphite is placed in a container, and a reaction gas is introduced into the container, and then heated at a temperature of 800-1200° C. for 2-8 hours, and then heated at a temperature of 2800-3100° C. for 5-48 hours, and then sieved and demagnetized to complete the purification; Wherein, the reaction gas includes a combination of at least two of nitrogen, chlorine, CO2, CO or helium.

13. A purified graphite, wherein: The purified graphite is prepared by the purification method described in any one of claims 1 to 12.

14. A lithium ion battery, wherein: The negative electrode of the lithium-ion battery comprises the purified graphite according to claim 13.

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