WO2025007998A1 - Purification method for natural flake graphite, purified graphite and lithium-ion battery - Google Patents

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

A method for purifying natural flake graphite, purified graphite and lithium ion battery

This application claims the priority of 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.

Technical Field

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.

Background Art

Due to the rapid development of lithium-ion batteries, natural flake graphite is used in large quantities as a low-cost raw material, but the large amount of impurities and defects in natural flake graphite limit its application in the negative electrode of lithium-ion batteries. Natural flake graphite usually contains metal impurity elements, such as Fe, Cr, Ni and Zn, and the above-mentioned metal impurity elements are magnetic material components, which makes natural flake graphite magnetic and not conducive to use. In order to meet the increasingly stringent material requirements of the lithium battery industry, the content of metal impurity elements and magnetic substances in graphite needs to be controlled at the ppb level. Therefore, natural flake graphite needs to be purified.

Technical issues

The existing methods for purifying natural flake graphite mainly include: ① flotation purification method; ② pickling and high temperature treatment. Generally, large-scale graphite factories usually use a combination of pickling and high temperature treatment to purify graphite, but this method consumes a lot of energy and produces a lot of pollution, which increases the production cost of graphite.

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

The present application provides a method for purifying natural flake graphite, purified graphite and a lithium-ion battery. The present application purifies natural flake graphite by heating it in an atmosphere of reaction gas, and under the synergistic effect of at least two gases among nitrogen, chlorine, _CO2 , CO and helium, the content of impurity elements and magnetic substances in the natural flake graphite can be reduced to ensure the purity of the graphite; and the purification method of the present application has simple procedures, low energy consumption and cost, and less pollution.

Technical Solutions

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

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

The reaction gas includes a combination of at least two of nitrogen (N ₂ ), chlorine (Cl ₂ ), CO ₂ , CO or helium.

In a second aspect, the present application provides a purified graphite, wherein the purified graphite is prepared by the purification method described in the first aspect.

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.

Beneficial Effects

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

The present application provides a method for purifying natural flake graphite, wherein the natural flake graphite is purified by heating it in an atmosphere of a reaction gas, wherein the reaction gas includes a combination of at least two of nitrogen, chlorine, CO ₂ , CO or helium. Under the heating condition, nitrogen, chlorine, CO ₂ , CO and helium can react with metal impurity elements in the natural flake graphite to reduce the boiling point of the impurity compound, so that the impurity compound can be separated from the graphite under high temperature heating, and the content of metal impurities and magnetic substances can be reduced. Therefore, under the synergistic effect of at least two of the above gases, the content of impurity elements and magnetic substances in the natural flake graphite can be reduced to ensure the purity of the graphite; at the same time, the heating step can also improve the graphitization degree of the material, increase the crystallinity of the graphite and reduce the defects of the graphite crystals. The purification method of the present application has a simple process, low energy consumption and cost, and less pollution, which greatly optimizes the purification process and timeliness.

Other aspects will be apparent upon reading and understanding the drawings and detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

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

FIG. 2 is a schematic flow diagram of a conventional method for purifying natural flake graphite.

DETAILED DESCRIPTION

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

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

The reaction gas includes a combination of at least two of nitrogen (N ₂ ), chlorine (Cl ₂ ), CO ₂ , CO or helium.

The present application provides a method for purifying natural flake graphite, wherein the natural flake graphite is purified by heating it in an atmosphere of a reaction gas, wherein the reaction gas includes a combination of at least two of nitrogen, chlorine, CO ₂ , CO or helium. Under the heating condition, nitrogen, chlorine, CO ₂ , CO and helium can react with metal impurity elements in the natural flake graphite to reduce the boiling point of the impurity compound, so that the impurity compound can be separated from the graphite under high temperature heating, and the content of metal impurities and magnetic substances can be reduced. Therefore, under the synergistic effect of at least two of the above gases, the content of impurity elements and magnetic substances in the natural flake graphite can be reduced to ensure the purity of the graphite; at the same time, the heating step can also improve the graphitization degree of the material, increase the crystallinity of the graphite and reduce the defects of the graphite crystals. The purification method of the present application has a simple process, low energy consumption and cost, and less pollution, which greatly optimizes the purification process and timeliness.

In the present application, typical non-limiting combinations of the reaction gases include: a combination of nitrogen and chlorine, a combination of CO ₂ and CO, a combination of CO ₂ and chlorine, and a combination of CO ₂ and helium, etc.

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

Optionally, the reaction gas is a combination of CO ₂ and nitrogen or a combination of CO ₂ and chlorine.

In the present application, a combination of _CO2 and nitrogen or a combination of _CO2 and chlorine is used as the reaction gas, and the gas has the highest reaction efficiency with the metal impurities and the production cost is also low.

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, but is not limited to the listed values, other unlisted values within the numerical range are also applicable, which can be selected as 3-18 L/min.

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 the numerical range are also applicable.

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 lead to gas waste and increase production costs.

Optionally, the particle size D50 of the natural flake graphite is 7-20 μm, for example, 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 the numerical range are also applicable.

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.

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, but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.

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

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 and separate from the graphite.

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, etc.; the time of the heating stage is 2-8h, for example, it can be 2h, 3h, 4h, 5h, 6h, 7h or 8h, etc., but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.

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 the numerical range are also applicable.

As an optional technical solution of the present application, the purification method specifically includes:

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;

The reaction gas includes a combination of at least two of nitrogen, chlorine, CO ₂ , CO or helium.

In a second aspect, the present application provides a purified graphite, wherein the purified graphite is prepared by the purification method described in the first aspect.

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.

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 brevity, this application no longer exhaustively lists the specific point values included in the range.

The technical solution of the present application is further illustrated below through specific implementation methods.

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:

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

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 acid washing the shaped natural flake graphite, and then high-temperature treatment and screening for demagnetization; the method for purifying natural flake graphite provided in the present application can not only achieve purification, but also has a simple process, low energy consumption and cost, and less pollution.

Example 1

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

Natural flake graphite with a particle size D50 of 10 μm was shaped and placed in a container. Reaction gas was introduced into the container. The reaction gas was a combination of CO ₂ and N _2. The flow rate of CO ₂ was 5 L/min and the flow rate of N ₂ was 5 L/min. Then, it was heated at 800°C for 5 h for the first stage and then heated at 2800°C for 48 h for the second stage. After cooling, the graphite sample was sieved and demagnetized to obtain the graphite sample.

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.

Table 1

Performance Testing

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

The test results are shown in Table 2.

Table 2

analyze:

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.

It can be seen from the data results of Example 10 and Examples 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.

It can be seen from the data results of Example 10 and Example 23 that if only one-stage heating is used, the gas will not react fully with the metal elements in the graphite, and the content of metal impurities and magnetic substances in the product will be high.

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.

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 (14)

A method for purifying natural flake graphite, comprising: The natural flake graphite is heated in an atmosphere of a reaction gas; The reaction gas includes a combination of at least two of nitrogen, chlorine, CO ₂ , CO or helium. 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. The purification method according to claim 1 or 2, wherein the flow rate of the reaction gas is 1-20 L/min. The purification method according to claim 3, wherein the flow rate of the reaction gas is 3-18 L/min. The purification method according to any one of claims 1 to 4, wherein when the reaction gas is a combination of _CO2 and nitrogen, the flow rates of _CO2 and nitrogen are independently 5-8 L/min. The purification method according to any one of claims 1 to 5, wherein the particle size D50 of the natural flake graphite is 7 to 20 μm. The purification method according to any one of claims 1 to 6, wherein the heating temperature is 800-3200°C. The purification method according to any one of claims 1 to 7, wherein the heating time is 5 to 56 hours. The purification method according to any one of claims 1 to 8, wherein the heating comprises a first-stage heating and a second-stage heating performed sequentially. The purification method according to claim 9, wherein the temperature of the heating stage is 800-1200° C. and the time of the heating stage is 2-8 h. The purification method according to claim 9 or 10, wherein the temperature of the second stage heating is 2800-3100°C; and the time of the second stage heating is 5-48h. 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; The reaction gas includes a combination of at least two of nitrogen, chlorine, CO ₂ , CO or helium. A purified graphite, wherein the purified graphite is prepared by the purification method according to any one of claims 1 to 12. A lithium-ion battery, wherein the negative electrode of the lithium-ion battery comprises the purified graphite according to claim 13.