Preparation method for modified natural graphite, graphite material and battery cell

Abstract

Provided in the present application are a preparation method for modified natural graphite, a graphite material and a battery cell. The preparation method comprises: sequentially subjecting natural graphite to a carbonization treatment and an oxidation treatment, so as to obtain modified natural graphite, wherein the oxidation treatment comprises: feeding the natural graphite into a heating furnace to perform a heating treatment, and simultaneously introducing a reaction gas into the heating furnace to perform modification. The present application can effectively improve the high-temperature storage performance of natural graphite by means of a carbonization treatment and an oxidation treatment.

Description

A preparation method of modified natural graphite, graphite material and battery core

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on December 13, 2023, with application number 2023117200502. The entire contents of the above application are incorporated by reference into this application. Technical Field

[0002] The present application relates to the technical field of graphite preparation, and in particular to a preparation method of modified natural graphite, a graphite material and a battery cell. Background Art

[0003] Due to the rapid development of lithium-ion batteries, natural graphite has become widely used as an inexpensive raw material. However, the presence of numerous impurities and defects in natural graphite limits its application in lithium-ion battery anodes. To meet the requirements of various application scenarios, the high-temperature storage performance of lithium batteries has become increasingly important. Furthermore, given the timeliness of product development, high-temperature accelerated decay is often used to simulate the long-term service life of batteries. Therefore, improving the high-temperature storage performance of lithium batteries is crucial.

[0004] Due to its material properties, natural flake graphite contains more defects and impurities than synthetic graphite. These impurities and defects are more likely to react with the electrolyte during high-temperature storage, consuming the electrolyte and generating a large amount of byproducts that deposit on the surface of the negative electrode graphite, causing battery performance degradation. To effectively utilize natural graphite in lithium batteries, it must undergo purification, coating, modification, and graphitization. Currently, except for graphitized natural graphite, which has fewer defects and impurities, graphite treated by other methods still has a significant gap compared to synthetic graphite. Technical issues

[0005] Graphitization treatment can reduce the overall defectivity of the material, and high-temperature treatment can also burn off most impurities. However, due to the relatively long processing cycle and high cost of graphitization, the application of natural graphite is limited and it has no competitive advantage over artificial graphite.

[0006] The present application provides a preparation method of modified natural graphite, a graphite material, and a battery cell. Without wasting a large amount of energy on graphitization treatment, the high-temperature storage performance of natural graphite can be effectively improved through carbonization + oxidation treatment. Technical Solutions

[0007] In a first aspect, the present application provides a method for preparing modified natural graphite, the preparation method comprising:

[0008] The natural graphite is subjected to carbonization treatment and oxidation treatment in sequence to obtain modified natural graphite.

[0009] The oxidation treatment includes: sending natural graphite into a heating furnace for heating treatment, and simultaneously introducing reaction gas into the heating furnace for modification.

[0010] In a second aspect, the present application provides a graphite material, which is prepared using the preparation method described in the first aspect.

[0011] In a third aspect, the present application provides a battery cell, which includes the graphite material described in the second aspect. Beneficial effects

[0012] Compared with the related art, the beneficial effects of this application are:

[0013] The present application provides a preparation method for modified natural graphite, a graphite material, and a battery cell with simple process and low cost. The natural graphite is modified by carbonization + oxidation treatment, which increases the oxygen-containing functional groups on the graphite surface and forms -COOLi, -OLi, or -C-OLi during electrode formation, thereby establishing a structural connection between the lithium salt component and the boundary carbon atoms at the graphite level, greatly enhancing the high-temperature stability; at the same time, the oxidation treatment is also beneficial for removing carbon chains, carbon free atoms, and other heteroatoms (defects) in the graphite, reducing the overall defects of the graphite, and helping to reduce the degree of side reactions during high-temperature storage, effectively improving the high-temperature storage performance of natural graphite.

[0014] Still other aspects will become apparent upon reading and understanding the accompanying drawings and detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] FIG1 is a Raman spectrum of the modified natural graphite obtained in Example 1, Comparative Example 1 and Comparative Example 2 of the present application. Modes for Carrying Out the Invention

[0016] In a first aspect, the present application provides a method for preparing modified natural graphite, the preparation method comprising:

[0017] The natural graphite is subjected to carbonization treatment and oxidation treatment in sequence to obtain modified natural graphite.

[0018] The oxidation treatment includes: sending natural graphite into a heating furnace for heating treatment, and simultaneously introducing reaction gas into the heating furnace for modification.

[0019] The preparation method of modified natural graphite provided in the present application is simple in process and low in cost. Natural graphite is modified by carbonization + oxidation treatment, which increases oxygen-containing functional groups (-COOH, -OH, -C=O, etc.) on the graphite surface. These oxygen-containing functional groups form -COOLi, -OLi or -C-OLi during electrode formation, thereby establishing a structural connection between the lithium salt component and the boundary carbon atoms at the graphite level, greatly enhancing the high-temperature stability; at the same time, the oxidation treatment is also beneficial for removing carbon chains, carbon free atoms and other heteroatoms (defects) in the graphite, reducing the overall defects of the graphite, and helping to reduce the degree of side reactions during high-temperature storage, effectively improving the high-temperature storage performance of natural graphite.

[0020] As an optional technical solution of the present application, the temperature of the heat treatment is 350~800℃, for example, it can be 350℃, 380℃, 400℃, 430℃, 450℃, 480℃, 500℃, 550℃, 580℃, 600℃, 650℃, 680℃, 700℃, 720℃, 750℃, 780℃ or 800℃, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0021] This application controls the heating temperature of the oxidation treatment within the above range. Too high a temperature may easily cause safety accidents and damage to operators and equipment; too low a temperature may increase the oxidation time and easily cause insufficient oxidation.

[0022] Optionally, the heating treatment time is 1 to 5 hours, for example, it can be 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours or 5 hours, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0023] The present application controls the heating treatment time within the above range. When the heating treatment time is too long, the production efficiency will be reduced; when the heating treatment time is too short, the defect of insufficient oxidation will easily occur.

[0024] As an optional technical solution of the present application, the reaction gas includes any one of nitrogen, chlorine, oxygen, air and carbon dioxide, or a combination of at least two of them.

[0025] As an optional technical solution of the present application, the preparation method further includes: adjusting the introduction rate of the reaction gas by regulating the pressure in the heating furnace.

[0026] Optionally, the pressure in the heating furnace is 3~8kPa, for example, it can be 3kPa, 3.5kPa, 4kPa, 4.5kPa, 5kPa, 5.5kPa, 6kPa, 6.5kPa, 7kPa, 7.5kPa or 8kPa, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0027] The present application adjusts the pressure in the heating furnace so that the introduction rate of the reaction gas is kept within a suitable range, avoiding waste of resources caused by an excessively high introduction rate, and at the same time preventing insufficient oxidation caused by an excessively low introduction rate.

[0028] Optionally, the heating furnace includes a horizontal carbonization furnace.

[0029] Optionally, the natural graphite is fed into a heating furnace for heating, and after the temperature is raised to the heating treatment temperature, a reaction gas is introduced into the heating furnace for modification.

[0030] As an optional technical solution of the present application, the temperature of the carbonization treatment is 1000~1200℃, for example, it can be 1000℃, 1020℃, 1050℃, 1080℃, 1100℃, 1120℃, 1140℃, 1150℃, 1180℃ or 1200℃, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0031] Optionally, the carbonization treatment time is 3 to 10 hours, for example, it can be 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours, 6.5 hours, 7 hours, 8 hours, 9 hours, 9.5 hours or 10 hours, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0032] Optionally, the carbonization treatment is performed under a protective atmosphere.

[0033] The protective atmosphere in this application includes but is not limited to nitrogen.

[0034] As an optional technical solution of the present application, the preparation method further includes: sequentially shaping, crushing and purifying the flake graphite and / or spherical graphite to obtain the natural graphite.

[0035] Optionally, the purification treatment includes acid-base purification or hydrofluoric acid purification.

[0036] Optionally, the particle size D of the natural graphite 50It is 6 to 10 μm, for example, it can be 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm or 10 μm, but is not limited to the listed values. Other unlisted values ​​within the numerical range are also applicable.

[0037] Optionally, the fixed carbon content of the natural graphite is 99.6% to 99.9%, for example, it can be 99.6%, 99.62%, 99.65%, 99.7%, 99.73%, 99.75%, 99.78%, 99.8%, 99.83%, 99.85%, 99.88% or 99.9%, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0038] It should be noted that the hydrofluoric acid purification method includes: soaking treatment with a mixed acid of HCl and HF, the volume ratio of HCl to HF in the mixed acid is (0.9~1.3):1, the temperature of the mixed acid is 60~75°C, and the soaking treatment time is 12~24h.

[0039] The acid-base purification comprises: an immersion treatment using an acid solution, an alkaline solution, and an oxidant. The acid solution comprises any one of sulfuric acid, hydrochloric acid, hydrofluoric acid, and phosphoric acid, or a combination of at least two thereof; the alkaline solution comprises any one of sodium hydroxide, potassium hydroxide, and calcium hydroxide, or a combination of at least two thereof; and the oxidant comprises any one of hydrogen peroxide, peracetic acid, chlorine, chlorine dioxide, and perchloric acid, or a combination of at least two thereof. The immersion treatment lasts for 10 to 18 hours.

[0040] As an optional technical solution of the present application, the preparation method further includes: cooling to room temperature after completing the oxidation treatment, and screening and demagnetizing the natural graphite in sequence to obtain the modified natural graphite.

[0041] For example, the preparation method of modified natural graphite provided in this application specifically includes the following steps:

[0042] S1: The flake graphite and / or spherical graphite are shaped, crushed and purified in sequence to obtain a particle size of D 50 Natural graphite of 6~10μm;

[0043] S2 carbonizes the natural graphite in step S1 under a protective atmosphere at a temperature of 1000-1200° C. for 3-10 hours;

[0044] S3: placing the carbonized natural graphite in a heating furnace, heating the furnace to 350-800° C., then introducing a reaction gas, and heating for 1-5 hours. During this period, the pressure in the heating furnace is adjusted to 3-8 kPa, thereby adjusting the introduction rate of the reaction gas. The reaction gas used includes any one of nitrogen, chlorine, oxygen, air, and carbon dioxide, or a combination of at least two thereof;

[0045] After the oxidation treatment is completed in step S4, the mixture is cooled to room temperature, and the natural graphite is screened and demagnetized in sequence to obtain modified natural graphite.

[0046] Among them, this application provides two solutions for the purification process in step S1:

[0047] (1) The flake graphite and / or spherical graphite is soaked in a mixed acid of HCl and HF for 12 to 24 hours, wherein the volume ratio of HCl to HF in the mixed acid is (0.9 to 1.3):1, and the temperature of the mixed acid is 60 to 75°C.

[0048] (2) The flake graphite and / or spherical graphite is impregnated for 10 to 18 hours using an acid solution, an alkaline solution and an oxidant, wherein the acid solution includes any one of sulfuric acid, hydrochloric acid, hydrofluoric acid and phosphoric acid or a combination of at least two of them; the alkaline solution includes any one of sodium hydroxide, potassium hydroxide and calcium hydroxide or a combination of at least two of them; the oxidant includes any one of hydrogen peroxide, peracetic acid, chlorine, chlorine dioxide and perchloric acid or a combination of at least two of them.

[0049] This application modifies natural graphite through a carbonization and oxidation process, increasing the number of oxygen-containing functional groups on the graphite surface, thereby strengthening the bonding strength with the SEI (Solid Electrolyte Interface) membrane and enhancing the stability of the SEI membrane during high-temperature storage. At the same time, the defectivity and oxygen atom content of the graphite are regulated by changing the type of gas introduced, the gas rate, the oxidation temperature, and the oxidation time. Compared with traditional graphitization treatment methods, this application significantly saves preparation costs and reduces carbon emissions.

[0050] In a second aspect, the present application provides a graphite material, which is prepared using the preparation method described in the first aspect.

[0051] As an optional technical solution of the present application, the total number of atoms on the surface of the graphite material is 100%, and the oxygen atom content is 2.85~4.53%, for example, it can be 2.85%, 2.86%, 2.90%, 2.92%, 2.95%, 2.96%, 3%, 3.22%, 3.47%, 3.50%, 3.60%, 3.70%, 3.80%, 3.83%, 4%, 4.10%, 4.12%, 4.23%, 4.30%, 4.42%, 4.5% or 4.53%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0052] In a third aspect, the present application provides a battery cell, which includes the graphite material described in the second aspect.

[0053] In the present application, the surface of the graphite material has a large number of oxygen-containing functional groups, which form -COOLi, -OLi, and -C-OLi during electrode formation, so that the lithium salt component of the SEI film on the electrode surface establishes a connection with the boundary carbon atoms on the graphite surface, increasing the bonding force with the SEI film and greatly enhancing the stability of the SEI film.

[0054] 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 space limitations and for the sake of simplicity, this application no longer exhaustively lists the specific point values ​​included in the range.

[0055] The technical solution of the present application will be further explained below with reference to the accompanying drawings and through specific implementation methods.

[0056] Example 1

[0057] This embodiment provides a method for preparing modified natural graphite, which specifically includes the following steps:

[0058] (1) The flake graphite is shaped, crushed and purified in turn to obtain a particle size D 50 8μm natural graphite, wherein the purification treatment adopts acid and alkali purification;

[0059] (2) Carbonizing the natural graphite in step (1) under a protective atmosphere at a temperature of 1100° C. for 6 h;

[0060] (3) The carbonized natural graphite is placed in a heating furnace, the temperature of the heating furnace is raised to 680°C, and then the reaction gas is introduced and heated for 3 hours. During this period, the pressure in the heating furnace is adjusted to 6 kPa, and the reaction gas used is a mixture of oxygen and air;

[0061] (4) After the oxidation treatment is completed, the natural graphite is cooled to room temperature, and the natural graphite is screened and demagnetized in sequence to obtain modified natural graphite.

[0062] Example 2

[0063] This embodiment provides a method for preparing modified natural graphite, which specifically includes the following steps:

[0064] (1) The flake graphite is shaped, crushed and purified in turn to obtain a particle size D 50 6μm natural graphite, wherein the purification treatment is carried out using hydrofluoric acid;

[0065] (2) carbonizing the natural graphite in step (1) under a protective atmosphere at a temperature of 1150° C. for 4 h;

[0066] (3) The carbonized natural graphite is placed in a heating furnace, the temperature of the heating furnace is raised to 350°C, and then the reaction gas is introduced and heated for 4 hours. During this period, the pressure in the heating furnace is adjusted to 4 kPa, and the reaction gas used is a mixture of oxygen and air;

[0067] (4) After the oxidation treatment is completed, the natural graphite is cooled to room temperature, and the natural graphite is screened and demagnetized in sequence to obtain modified natural graphite.

[0068] Example 3

[0069] This embodiment provides a method for preparing modified natural graphite, which specifically includes the following steps:

[0070] (1) The flake graphite is shaped, crushed and purified in turn to obtain a particle size D 50 10μm natural graphite, wherein the purification treatment is carried out using hydrofluoric acid;

[0071] (2) carbonizing the natural graphite in step (1) under a protective atmosphere at a temperature of 1200° C. for 8 h;

[0072] (3) The carbonized natural graphite is placed in a heating furnace, the temperature of the heating furnace is raised to 800°C, and then the reaction gas is introduced and heated for 5 hours. During this period, the pressure in the heating furnace is adjusted to 4 kPa, and the reaction gas used is a mixture of carbon dioxide and air;

[0073] (4) After the oxidation treatment is completed, the natural graphite is cooled to room temperature, and the natural graphite is screened and demagnetized in sequence to obtain modified natural graphite.

[0074] Example 4

[0075] This embodiment provides a method for preparing modified natural graphite, which specifically includes the following steps:

[0076] (1) The spherical graphite is shaped, crushed and purified in turn to obtain a particle size D50 7μm natural graphite, which is purified by hydrofluoric acid;

[0077] (2) carbonizing the natural graphite in step (1) under a protective atmosphere at a temperature of 1050° C. for 10 h;

[0078] (3) The carbonized natural graphite is placed in a heating furnace, the temperature of the heating furnace is raised to 700°C, and then the reaction gas is introduced and heated for 2 hours. During this period, the pressure in the heating furnace is adjusted to 4 kPa, and the reaction gas used is air;

[0079] (4) After the oxidation treatment is completed, the natural graphite is cooled to room temperature, and the natural graphite is screened and demagnetized in sequence to obtain modified natural graphite.

[0080] Example 5

[0081] This embodiment provides a method for preparing modified natural graphite, which specifically includes the following steps:

[0082] (1) The mixed raw materials of flake graphite and spherical graphite are shaped, crushed and purified in turn to obtain particle size D 50 9μm natural graphite, which is purified by hydrofluoric acid;

[0083] (2) carbonizing the natural graphite in step (1) under a protective atmosphere at a temperature of 1200° C. for 3 h;

[0084] (3) The carbonized natural graphite is placed in a heating furnace, the temperature of the heating furnace is raised to 500°C, and then the reaction gas is introduced and heated for 2 hours. During this period, the pressure in the heating furnace is adjusted to 5 kPa, and the reaction gas used is a mixture of oxygen and air;

[0085] (4) After the oxidation treatment is completed, the natural graphite is cooled to room temperature, and the natural graphite is screened and demagnetized in sequence to obtain modified natural graphite.

[0086] Example 6

[0087] This embodiment provides a method for preparing modified natural graphite, which specifically includes the following steps:

[0088] (1) The flake graphite is shaped, crushed and purified in turn to obtain a particle size D 50 8μm natural graphite, wherein the purification treatment adopts hydrofluoric acid purification;

[0089] (2) carbonizing the natural graphite in step (1) under a protective atmosphere at a temperature of 1150° C. for 5 h;

[0090] (3) The carbonized natural graphite is placed in a heating furnace, the temperature of the heating furnace is raised to 450°C, and then the reaction gas is introduced and heated for 3 hours. During this period, the pressure in the heating furnace is adjusted to 8 kPa, and the reaction gas used is a mixture of oxygen and air;

[0091] (4) After the oxidation treatment is completed, the natural graphite is cooled to room temperature, and the natural graphite is screened and demagnetized in sequence to obtain modified natural graphite.

[0092] Example 7

[0093] This embodiment provides a method for preparing modified natural graphite, which differs from Example 1 in that the reaction gas used in step (3) is oxygen, and the remaining operating steps and process parameters are the same as those in Example 1.

[0094] Example 8

[0095] This embodiment provides a method for preparing modified natural graphite, which differs from Example 1 in that the reaction gas used in step (3) is CO2, and the remaining operating steps and process parameters are the same as those in Example 1.

[0096] Example 9

[0097] This embodiment provides a method for preparing modified natural graphite, which differs from Example 1 in that: in step (3), the heating furnace is heated to 300°C for modification, and the remaining operating steps and process parameters are the same as those in Example 1.

[0098] Example 10

[0099] This embodiment provides a method for preparing modified natural graphite, which differs from Example 1 in that: in step (3), the heating furnace is heated to 850° C. for modification, and the remaining operating steps and process parameters are the same as those in Example 1.

[0100] Example 11

[0101] This embodiment provides a method for preparing modified natural graphite, which differs from Example 1 in that the pressure in the heating furnace in step (3) is 2 kPa, and the remaining operating steps and process parameters are the same as those in Example 1.

[0102] Example 12

[0103] This embodiment provides a method for preparing modified natural graphite, which differs from Example 1 in that the pressure in the heating furnace in step (3) is 9 kPa, and the remaining operating steps and process parameters are the same as those in Example 1.

[0104] Example 13

[0105] This embodiment provides a method for preparing modified natural graphite, which differs from Example 1 in that the heating treatment in step (3) is 0.5 h, and the remaining operating steps and process parameters are the same as those in Example 1.

[0106] Example 14

[0107] This embodiment provides a method for preparing modified natural graphite, which differs from Example 1 in that the heating treatment in step (3) is 5.5 h, and the remaining operating steps and process parameters are the same as those in Example 1.

[0108] Comparative Example 1

[0109] This comparative example provides a method for preparing modified natural graphite, which specifically comprises the following steps:

[0110] (1) The flake graphite is shaped, crushed and purified in turn to obtain a particle size D 50 8μm natural graphite, wherein the purification treatment adopts acid and alkali purification;

[0111] (2) Carbonizing the natural graphite in step (1) under a protective atmosphere at a temperature of 1100° C. for 6 h;

[0112] (3) After the carbonization treatment is completed, the natural graphite is screened and demagnetized in sequence to obtain modified natural graphite.

[0113] Comparative Example 2

[0114] This comparative example provides a method for preparing modified natural graphite, which specifically comprises the following steps:

[0115] (1) The flake graphite is shaped, crushed and purified in turn to obtain a particle size D 50 8μm natural graphite, wherein the purification treatment adopts acid and alkali purification;

[0116] (2) graphitizing the natural graphite in step (1) under a protective atmosphere at a temperature of 2800° C. for 36 h;

[0117] (3) After the carbonization treatment is completed, the natural graphite is screened and demagnetized in sequence to obtain modified natural graphite.

[0118] The present application tests the surface oxygen atom content (measured by X-ray photoelectron spectroscopy XPS) and defectivity (measured by Raman spectroscopy) of the modified natural graphites obtained in Examples 1 to 14 and Comparative Examples 1 and 2. The results are shown in Table 1 and Figure 1.

[0119] In this application, the modified natural graphites obtained in Examples 1 to 14 and Comparative Examples 1 and 2 were made into battery cells, and their performance during high-temperature storage (85°C, 25 days) was tested. The results are shown in Table 1.

[0120] The battery cell's positive electrode utilizes a nickel-cobalt-manganese ternary cathode material, the negative electrode is made from the aforementioned modified natural graphite, and the separator is an alumina ceramic separator. The positive electrode sheet, separator, and negative electrode sheet are placed in this order from top to bottom, assembled by winding, and then injected with electrolyte, packaged, and aged to form the battery cell.

[0121] Table 1

[0122]

[0123] It can be seen from the contents of Table 1 that the modified natural graphites obtained in Examples 1 to 14 have a high surface oxygen atom content, a low defect degree, and maintain a high capacity at high temperatures, and have good high-temperature storage performance.

[0124] Compared with Example 1 in which a mixed gas is used as the reaction gas, the oxygen atom content on the surface of the modified natural graphite in Examples 7 and 8 is reduced. This is mainly because Examples 7 and 8 only use a single reaction gas to modify the natural graphite, which weakens the oxidation effect and reduces the generation of oxygen-containing functional groups.

[0125] Compared with Example 1, the oxidation temperature in Example 9 is too low, resulting in incomplete oxidation, which reduces the surface oxygen atom content and thus causes the capacity retention rate of the battery cell to decrease; in addition, the oxygen atom content on the surface of the modified natural graphite in Example 10 is relatively small compared with that in Example 1, but the production cost increases due to the increase in oxidation temperature.

[0126] It is not difficult to see from Examples 1, 11 and 12 that when the pressure in the heating furnace is too high or too low, it will affect the oxidation effect, resulting in a decrease in the oxygen atom content on the graphite surface, and further causing the capacity retention rate of the battery cell at high temperature to be reduced.

[0127] It is not difficult to see from Table 1 that compared with Example 1, Example 13 has a too short heating treatment time, resulting in only partial oxidation of the natural graphite, which reduces the oxygen atom content on the surface of the material and causes a decrease in the high-temperature performance of the battery cell; while Example 14 has a too long heating time, which increases the production cost.

[0128] It can be seen from Example 1 and Comparative Example 1 that the oxygen atom content on the surface of the modified natural graphite in Example 1 is higher, the surface defect degree is lower, and the capacity retention rate and capacity recovery rate of the battery cell are both increased. This is mainly because Example 1 oxidizes the carbonized natural graphite, thereby increasing the number of oxygen-containing functional groups on the graphite surface. During the battery cell formation stage, a connection can be formed between the graphite and the lithium salt, thereby improving the stability of the battery cell at high temperature and effectively reducing the surface defect degree of the graphite.

[0129] Example 1 adopts a modification method of carbonization + oxidation treatment. Compared with the high-temperature graphitization method adopted in Comparative Example 2, Example 1 can increase the oxygen atom content on the graphite surface and reduce the surface defect degree. In addition, the heating treatment temperature is much lower than the graphitization temperature, which greatly reduces the production cost.

[0130] The present application can obtain natural graphite with excellent high-temperature storage performance through carbonization + oxidation treatment without using a high-energy graphitization process, and optimize the high-temperature storage performance of natural graphite by adjusting parameters such as the air flow rate, gas type, temperature, and time.

Claims

1. A method for preparing modified natural graphite, include: Carrying out carbonization treatment and oxidation treatment on natural graphite in sequence to obtain modified natural graphite; The oxidation treatment comprises: sending natural graphite into a heating furnace for heating treatment, and simultaneously introducing reaction gas into the heating furnace for modification.

2. The preparation method according to claim 1, in, The temperature of the heating treatment is 350-800°C.

3. The preparation method according to claim 1 or 2, in, The heating time is 1 to 5 hours.

4. The preparation method according to any one of claims 1 to 3, in, The reaction gas includes any one of nitrogen, chlorine, oxygen, air and carbon dioxide, or a combination of at least two of them.

5. The preparation method according to any one of claims 1 to 4, in, The preparation method further comprises: adjusting the introduction rate of the reaction gas by adjusting the pressure in the heating furnace; Optionally, the pressure in the heating furnace is 3-8 kPa; Optionally, the heating furnace includes a horizontal carbonization furnace; Optionally, the natural graphite is fed into a heating furnace to be heated, and after the temperature is raised to the heating treatment temperature, a reaction gas is introduced into the heating furnace to perform modification.

6. The preparation method according to any one of claims 1 to 5, in, The temperature of the carbonization treatment is 1000-1200°C; Optionally, the carbonization treatment time is 3 to 10 hours.

7. The preparation method according to any one of claims 1 to 6, in, The carbonization treatment is carried out under a protective atmosphere.

8. The preparation method according to any one of claims 1 to 7, in, The preparation method further comprises: sequentially performing shaping, crushing and purification treatments on flake graphite and / or spherical graphite to obtain the natural graphite.

9. The preparation method according to claim 8, in, The purification treatment includes acid-base purification or hydrofluoric acid purification.

10. The preparation method according to claim 8 or 9, in, The particle size D of the natural graphite 50 6~10μm.

11. The preparation method according to any one of claims 8 to 10, in, The fixed carbon content of the natural graphite is 99.6-99.9%.

12. The preparation method according to any one of claims 1 to 11, in, The preparation method further comprises: cooling to room temperature after the oxidation treatment is completed, and screening and demagnetizing the natural graphite in sequence to obtain the modified natural graphite.

13. A graphite material, in, The graphite material is prepared by the preparation method described in any one of claims 1 to 12.

14. The graphite material according to claim 13, in, The total number of atoms on the surface of the graphite material is 100%, and the oxygen atom content is 2.85-4.53%.

15. A battery cell, in, The battery core comprises the graphite material according to claim 13 or 14.

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