Graphite negative electrode material and preparation method thereof, lithium ion battery and electric equipment

Abstract

The invention provides a graphite negative electrode material and a preparation method thereof, a lithium ion battery and electric equipment, and relates to the technical field of new energy. According to the preparation method, the raw material asphalt is subjected to low-temperature oxidation, so that volatile components are reduced, asphaltene is increased, the compactness of an amorphous carbon layer on the surface of carbonized graphite is improved, the proportion of active groups in the amorphous carbon layer with relatively low crystallinity is relatively small, the interaction with electrolyte is relatively small, and the first efficiency and cycle performance of the material are further improved. A rich oxygen-containing functional group structure is generated by performing high-temperature oxidation on the graphite aggregate, so that the carbon layer spacing on the graphite surface is effectively increased, and the ion transmission sites and the transmission rate of lithium ions entering the carbon layer are further improved. The oxidized asphalt and graphite are subjected to mixed carbonization treatment, a compact amorphous carbon layer of the asphalt on the surface of the graphite provides rich active sites for lithium ions, and in cooperation with a rapid lithium ion transmission rate provided by an expanded carbon layer structure in the graphite, the excellent rapid charging performance of a negative electrode product is ensured.

Description

Technical Field

[0001] This application relates to the field of new energy technologies, and particularly to a graphite anode material, a preparation method thereof, a lithium-ion battery, and an electrical device. Background Art

[0002] In recent years, the power performance and cruising range of electric vehicles have been comparable to those of traditional internal combustion engine vehicles. However, compared with the fast refueling of fuel, the high time cost of charging electric vehicles limits their application scenarios, especially in the field of commercial vehicles that pursue timeliness. Therefore, solving the fast charging problem is a threshold that must be overcome in the development of electric vehicles and is also the focus of lithium-ion battery technology research and development.

[0003] The anode material is an important factor affecting the cycle life and fast charging performance of lithium-ion batteries. Usually, small particle aggregates are used for secondary granulation to improve the rate performance of the anode material. However, due to the release of light components during carbonization of low softening point asphalt, a large number of micro-mesopores are formed on the surface of graphite, resulting in more irreversible capacity loss; and the smaller layer spacing of conventional artificial graphite aggregates also limits the fast charging performance of lithium-ion batteries. Summary of the Invention

[0004] The purpose of this application is to provide a graphite anode material, a preparation method thereof, a lithium-ion battery, and an electrical device, aiming to solve the problem that the existing graphite anode material cannot improve the cycle life and fast charging performance of lithium-ion batteries.

[0005] To achieve the above purpose, this application provides a preparation method of a graphite anode material, including:

[0006] Subjecting graphite aggregates to a first oxidation heat treatment to obtain modified graphite;

[0007] Subjecting the crushed asphalt raw material to a second oxidation heat treatment to obtain modified asphalt;

[0008] Mixing the modified graphite and the modified asphalt to obtain a mixture;

[0009] Subjecting the mixture to a heat treatment to obtain granulated material;

[0010] Subjecting the granulated material to a carbonization treatment and screening to obtain the graphite anode material.

[0011] In some embodiments, compressed air is respectively introduced during the first oxidation heat treatment and the second oxidation heat treatment, and the flow rate of the compressed air is 10 - 20 L / min.

[0012] In some embodiments, the graphite aggregates are obtained by graphitizing the crushed coke raw material and satisfy at least one of the following conditions:

[0013] A. The particle size of the crushed coke raw material satisfies: Dv10 is 4.0 - 7.0 μm, Dv50 is 9 - 11 μm, and Dv90 is 19.0 - 24.0 μm;

[0014] B. The temperature of the graphitization treatment is 3000 - 3200 °C;

[0015] C. The time of the graphitization treatment is 10 - 20 h;

[0016] D. The graphitization degree of the graphite aggregate is 92% - 98%;

[0017] E. The particle size of the graphite aggregate satisfies: Dv10 is 3.0 - 6.0 μm, Dv50 is 8.5 - 10 μm, and Dv90 is 18.0 - 22.0 μm.

[0018] In some embodiments, at least one of the following conditions is satisfied:

[0019] A. The temperature of the first oxidation heat treatment is 450 - 600 °C;

[0020] B. The heating rate of the first oxidation heat treatment is not higher than 5 °C / min;

[0021] C. The holding time of the first oxidation heat treatment is 2 - 5 h.

[0022] In some embodiments, at least one of the following conditions is satisfied:

[0023] A. The particle size Dv50 of the crushed asphalt raw material is 3 - 5 μm;

[0024] B. The temperature of the second oxidation heat treatment is 140 - 200 °C;

[0025] C. The heating rate of the second oxidation heat treatment is not higher than 5 °C / min;

[0026] D. The holding time of the second oxidation heat treatment is 2 - 5 h.

[0027] In some embodiments, at least one of the following conditions is satisfied:

[0028] A. The mass ratio of the modified graphite to the modified asphalt is 100:(2 - 5);

[0029] B. The mixing time is not less than 1 h;

[0030] C. The heating rate of the heat treatment is not higher than 10 °C / min;

[0031] D. The heat treatment includes a first stage and a second stage. The temperature in the first stage is 400 - 500 °C and the time is 2 h; the temperature in the second stage is 650 - 750 °C and the time is 2 h;

[0032] E. During the heat treatment, N 2 , N 2 is introduced at a flow rate of not less than 5 L / min;

[0033] F. The particle size of the granulated material meets the requirements: Dv10 is 6.0 - 9.0 μm, Dv50 is 12 - 15 μm, and Dv90 is 23.0 - 27.0 μm.

[0034] In some embodiments, at least one of the following conditions is satisfied:

[0035] A. The temperature of the carbonization treatment is 1100 - 1200 °C;

[0036] B. The time of the carbonization treatment is not less than 12 h;

[0037] C. The heating rate of the carbonization treatment is not higher than 2 °C / min;

[0038] D. During the carbonization treatment, N 2 , N 2 is introduced at a flow rate of not less than 5 L / min;

[0039] E. The particle size of the graphite anode material meets the requirements: Dv10 is 6.0 - 8.0 μm, Dv50 is 12 - 14.0 μm, and Dv90 is 22.0 - 25.0 μm.

[0040] This application also provides a graphite anode material prepared by the above - mentioned preparation method of the graphite anode material.

[0041] This application also provides a lithium - ion battery including the above - mentioned graphite anode material.

[0042] This application also provides an electrical device including the above - mentioned lithium - ion battery.

[0043] Compared with the prior art, the beneficial effects of this application include:

[0044] The preparation method of the graphite anode material provided by this application conducts low-temperature oxidation on the raw asphalt and utilizes the non-fusion treatment of low-temperature oxidation to change the internal molecular structure of the asphalt. The oxidation reaction will destroy the blending state inside the asphalt, thereby reducing the components of small asphalt molecules (saturates and aromatics), relatively increasing the content of polar components (resins and asphaltenes), and at the same time, the oxidation process can also increase the adhesion of the asphalt, not only increasing the adhesion between the asphalt and graphite and improving the granulation strength; moreover, the reduction of volatile matter and the increase of asphaltenes also improve the compactness of the amorphous carbon layer on the surface of graphite after carbonization. At the same time, the low-temperature oxidation process will consume the relatively active polar functional groups inside the asphalt and generate relatively stable oxygen-containing functional group structures, and the interaction between such structures and the electrolyte is relatively small, thereby improving the initial efficiency and cycle performance of the material.

[0045] In addition, by conducting high-temperature oxidation treatment on the graphite aggregate, oxygen atoms in the air oxidize the carbon layer on the surface of graphite under high-temperature conditions. During the oxidation process, carbon atoms on the surface of graphite combine with oxygen atoms to generate rich oxygen-containing functional group structures (such as -OH, -COOH, etc.), which can effectively increase the carbon layer spacing on the surface of graphite, thereby improving the ion transport sites and transport rate for lithium ions to enter the interior of the carbon layer.

[0046] Furthermore, by conducting mixed carbonization treatment on the oxidized asphalt and graphite, the rich oxygen-containing functional groups in the asphalt and the oxygen-containing functional groups on the surface of graphite undergo cross-linking and bonding, so that the asphalt is more tightly bonded to the surface of graphite. The dense amorphous carbon layer of asphalt on the surface of graphite provides rich active sites for lithium ions, and together with the fast lithium ion transport rate provided by the expanded carbon layer structure inside the graphite, it ensures excellent fast charging performance of the anode product.

[0047] The graphite anode material, lithium-ion battery, and electrical equipment provided by this application have high initial efficiency, good cycle performance, and excellent fast charging performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] In order to more clearly illustrate the technical solutions of the embodiments of this application, the following will briefly introduce the drawings required to be used in the embodiments. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as limiting the scope of this application.

[0049] Figure 1 It is a schematic flow chart of the preparation method of the graphite anode material of this application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0050] As used herein, the terms:

[0051] "Prepared by" is synonymous with "comprising". As used herein, the terms "comprising", "including", "having", "containing" or any other variation thereof are intended to cover non-exclusive inclusion. For example, a composition, step, method, article or apparatus that comprises the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article or apparatus.

[0052] The conjunctive "consisting of" excludes any unrecited element, step or component. If used in a claim, this phrase renders the claim closed, so that it does not include materials other than those described, except for conventional impurities associated therewith. When the phrase "consisting of" appears in a clause of the claim body rather than immediately following the subject, it only limits the elements described in that clause; other elements are not excluded from the claim as a whole.

[0053] When an equivalent, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper preferred values and lower preferred values, this should be understood to specifically disclose all ranges formed by any pairing of any upper range limit or preferred value with any lower range limit or preferred value, whether or not the ranges are separately disclosed. For example, when the range "1 to 5" is disclosed, the described range should be interpreted to include the ranges "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", "1 to 3 and 5", etc. When a numerical range is described herein, unless otherwise stated, the range is intended to include its end values and all integers and fractions within the range.

[0054] In these examples, unless otherwise specified, the parts and percentages are by mass.

[0055] "Parts by mass" refers to the basic measurement unit representing the mass ratio relationship of multiple components. 1 part can represent any unit mass, such as 1 g or 2.689 g, etc. If we say that the mass part of component A is a parts and the mass part of component B is b parts, it means the mass ratio of component A to component B is a:b. Or, it means the mass of component A is aK and the mass of component B is bK (K is any number representing a multiple factor). It should not be misunderstood that, different from the number of mass parts, the sum of the mass parts of all components is not limited to 100 parts.

[0056] "And / or" is used to indicate that either or both of the stated circumstances may occur. For example, A and / or B includes (A and B) and (A or B).

[0057] In addition, the terms "first" and "second" are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present invention, "a plurality of" means two or more, unless otherwise specifically defined.

[0058] The present application provides a method for preparing a graphite anode material. Please refer to Figure 1 , including:

[0059] S100: Subject the graphite aggregate to a first oxidation heat treatment to obtain modified graphite.

[0060] S200: Subject the crushed asphalt raw material to a second oxidation heat treatment to obtain modified asphalt.

[0061] S300: Mix the modified graphite and the modified asphalt to obtain a mixture.

[0062] S400: Subject the mixture to a heat treatment to obtain a granulated material.

[0063] S500: Subject the granulated material to a carbonization treatment and screen to obtain the graphite anode material.

[0064] In the method for preparing the graphite anode material provided by the present application, by performing low-temperature oxidation on the raw asphalt and using the non-fusion treatment of low-temperature oxidation, the internal molecular structure of the asphalt is changed. The oxidation reaction will destroy the blending state inside the asphalt, thereby reducing the components of small asphalt molecules (saturates and aromatics) and relatively increasing the content of polar components (resins and asphaltenes). At the same time, the oxidation process can also increase the adhesiveness of the asphalt, not only increasing the adhesion between the asphalt and the graphite and improving the granulation strength; and the reduction of volatile matter and the increase of asphaltenes also improve the compactness of the amorphous carbon layer on the surface of the graphite after carbonization. At the same time, the low-temperature oxidation process will consume the relatively active polar functional groups inside the asphalt and generate a relatively stable oxygen-containing functional group structure. The interaction between such a structure and the electrolyte is small, thereby improving the first efficiency and cycle performance of the material.

[0065] In addition, by performing high-temperature oxidation treatment on the graphite aggregate, oxygen atoms in the air oxidize the carbon layer on the surface of the graphite under high-temperature conditions. During the oxidation process, the carbon atoms on the surface of the graphite combine with the oxygen atoms to generate a rich oxygen-containing functional group structure (such as -OH, -COOH, etc.), which can effectively increase the carbon layer spacing on the surface of the graphite, thereby improving the ion transport sites and transport rate for lithium ions to enter the interior of the carbon layer.

[0066] Furthermore, through the hybrid carbonization treatment of the oxidized pitch and graphite, the abundant oxygen-containing functional groups in the pitch and those on the surface of the graphite undergo cross-linking and bonding, enabling the pitch to bind more closely to the surface of the graphite. The dense amorphous carbon layer of the pitch on the graphite surface provides abundant active sites for lithium ions. Collaborating with the enhanced lithium ion transport rate provided by the expanded carbon layer structure inside the graphite, it ensures excellent fast charging performance of the negative electrode product.

[0067] In some embodiments, compressed air is introduced respectively during the first oxidation heat treatment in step S100 and the second oxidation heat treatment in step S200. The flow rate of the compressed air is 10 - 20 L / min, for example, it can be 10 L / min, 15 L / min, 20 L / min, or any value between 10 - 20 L / min.

[0068] Different flow rates of compressed air have different catalytic intensities for the modification reactions of graphite and pitch. By changing the flow rate of compressed air, the components and softening point of the pitch can be changed, further affecting the compactness of the amorphous carbon layer after carbonization; and the flow rate of compressed air can also affect the oxidation degree of the graphite surface layer. These additional oxygen atoms can escape during the carbonization process, further increasing the layer spacing between the graphite carbon layers and forming pores on the graphite surface, thereby improving the fast charging performance and initial efficiency and other electrochemical properties of the negative electrode product.

[0069] In some embodiments, the graphite aggregate in step S100 is obtained by graphitizing the crushed coke raw material, and the particle size of the used crushed coke raw material satisfies: Dv10 is 4.0 - 7.0 μm, for example, it can be 4.0 μm, 5.0 μm, 6.0 μm, 7.0 μm, or any value between 4.0 - 7.0 μm; Dv50 is 9.0 - 11.0 μm, for example, it can be 9.0 μm, 10.0 μm, 11.0 μm, or any value between 9.0 - 11.0 μm; Dv90 is 19.0 - 24.0 μm, for example, it can be 19.0 μm, 20.0 μm, 21.0 μm, 22.0 μm, 23.0 μm, 24.0 μm, or any value between 19.0 - 24.0 μm.

[0070] In some embodiments, the temperature of the graphitization treatment is 3000 - 3200 °C, for example, it can be 3000 °C, 3050 °C, 3100 °C, 3150 °C, 3200 °C, or any value between 3000 - 3200 °C; the time of the graphitization treatment is 10 - 20 h, for example, it can be 10 h, 12 h, 15 h, 17 h, 19 h, 20 h, or any value between 10 - 20 h.

[0071] In some embodiments, the graphitization degree of the graphite aggregate in step S100 is 92% to 98%, for example, it can be 92%, 93%, 94%, 95%, 96%, 97%, 98% or any value between 92% and 98%; the particle size of the graphite aggregate satisfies: Dv10 is 3.0 to 6.0 μm, Dv50 is 8.5 to 10 μm, and Dv90 is 18.0 to 22.0 μm.

[0072] In some embodiments, the temperature of the first oxidation heat treatment in step S100 is 450 to 600 °C, for example, it can be 450 °C, 500 °C, 550 °C, 600 °C or any value between 450 and 600 °C.

[0073] In some embodiments, the heating rate of the first oxidation heat treatment in step S100 is not higher than 5 °C / min, for example, it can be 1 °C / min, 2 °C / min, 3 °C / min, 4 °C / min, 5 °C / min or any value between not higher than 5 °C / min; the holding time of the first oxidation heat treatment is 2 to 5 h, for example, it can be 2 h, 3 h, 4 h, 5 h or any value between 2 and 5 h.

[0074] In some embodiments, the Dv50 of the particle size of the crushed asphalt raw material used in step S200 is 3 to 5 μm, for example, it can be 3 μm, 4 μm, 5 μm or any value between 3 and 5 μm.

[0075] In some embodiments, the temperature of the second oxidation heat treatment in step S200 is 140 to 200 °C, for example, it can be 140 °C, 150 °C, 160 °C, 170 °C, 180 °C, 190 °C, 200 °C or any value between 140 and 200 °C.

[0076] In some embodiments, the heating rate of the second oxidation heat treatment in step S200 is not higher than 5 °C / min, for example, it can be 1 °C / min, 2 °C / min, 3 °C / min, 4 °C / min, 5 °C / min or any value between not higher than 5 °C / min; the holding time of the second oxidation heat treatment is 2 to 5 h, for example, it can be 2 h, 3 h, 4 h, 5 h or any value between 2 and 5 h.

[0077] In some embodiments, the mass ratio of the modified graphite to the modified asphalt in step S300 is 100:(2 to 5), for example, it can be 100:2, 100:3, 100:4, 100:5 or any value between 100:(2 to 5), and the mixing time is 1 h.

[0078] In some embodiments, the heating rate of the heat treatment in step S400 is not higher than 10 °C / min. For example, it can be 2 °C / min, 3 °C / min, 4 °C / min, 5 °C / min, 6 °C / min, 7 °C / min, 8 °C / min, 9 °C / min, 10 °C / min, or any value between not higher than 10 °C / min.

[0079] In some embodiments, the heat treatment in step S400 includes a first stage and a second stage. The temperature of the first stage is 400 - 500 °C. For example, it can be 400 °C, 450 °C, 500 °C, or any value between 400 - 500 °C, and the time is 2 h. The temperature of the second stage is 650 - 750 °C. For example, it can be 650 °C, 700 °C, 750 °C, or any value between 650 - 750 °C, and the time is 2 h.

[0080] In some embodiments, during the heat treatment process of step S400, N 2 , N 2 is introduced at a flow rate not higher than 5 L / min. The particle size of the obtained granulated material satisfies: Dv10 is 6.0 - 9.0 μm, Dv50 is 12 - 15 μm, and Dv90 is 23.0 - 27.0 μm.

[0081] In some embodiments, the temperature of the carbonization treatment in step S500 is 1100 - 1200 °C. For example, it can be 1100 °C, 1150 °C, 1200 °C.

[0082] In some embodiments, the time of the carbonization treatment in step S500 is not less than 10 h; the heating rate of the carbonization treatment is not higher than 2 °C / min; during the carbonization treatment process, N 2 , N 2 is introduced at a flow rate not less than 10 L / min. The particle size of the obtained graphite anode material satisfies: Dv10 is 6.0 - 8.0 μm, Dv50 is 12 - 14.0 μm, and Dv90 is 22.0 - 25.0 μm.

[0083] This application also provides a graphite anode material, which is prepared by the preparation method of the above-mentioned graphite anode material.

[0084] This application also provides a lithium-ion battery, including the above-mentioned graphite anode material.

[0085] This application also provides an electrical equipment, including the above-mentioned lithium-ion battery.

[0086] The graphite anode material, lithium-ion battery, and electrical equipment provided by this application have high initial efficiency, good cycle performance, and excellent fast charging performance.

[0087] The implementation solutions of the present application will be described in detail below in conjunction with specific embodiments. However, those skilled in the art will understand that the following embodiments are only used to illustrate the present application and should not be regarded as limiting the scope of the present application. For those conditions not specified in the embodiments, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. For the reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0088] Example 1

[0089] The preparation method of the graphite anode material in Example 1 includes the following steps:

[0090] Step 1: In a pulverizing device, the calcined needle coke is pulverized to obtain a powder. The particle size of the powder is controlled such that Dv10 is 4.0 - 5.0 μm, Dv50 is 9 - 10 μm, and Dv90 is 19.0 - 21.0 μm. The pulverized material is subjected to shaping treatment, and the shaped powder is mixed evenly.

[0091] Step 2: Under nitrogen protection, the mixed powder is graphitized. The graphitization temperature is 3000 °C, and the graphitization time is 12 h to obtain graphite aggregate.

[0092] Step 3: The graphitized material is sieved. The mesh number of the sieve is 250 meshes to remove the massive substances formed by rapid coking at high temperature during the graphitization process.

[0093] Step 4: The graphitized aggregate and the asphalt raw material after sieving are subjected to oxidation modification treatment.

[0094] Among them, the preparation method of the modified graphite: The graphite aggregate (Dv50: 8.5 - 10 μm) is added to a horizontal rotary kiln, compressed air is introduced at a speed of 10 L / min, the temperature is raised to 500 °C at a heating rate of 4 °C / min, and the reaction is carried out for 2 h to obtain the modified graphite.

[0095] Among them, the preparation method of the modified asphalt: The asphalt raw material (Dv50: 3 - 4 μm) is added to a horizontal rotary kiln, compressed air is introduced at a speed of 10 L / min, the temperature is raised to 180 °C at a heating rate of 3 °C / min, and the reaction is carried out for 2 h to obtain the modified asphalt.

[0096] Step 5: The modified graphite and the modified asphalt after sieving are fully mixed according to a mass ratio of 100:3 and mixed for 1 h to make the asphalt evenly distributed in the sieved material, thereby obtaining a mixed material.

[0097] Step 6: Heat-treat the mixture, which includes two stages. The temperature in the first stage is 450°C and the time is 2 h; the temperature in the second stage is 700°C and the time is 2 h. This treatment process is carried out under the condition of stirring in a vertical kettle, and the stirring speed is 15 rpm / min to obtain granulated material.

[0098] Step 7: Under nitrogen protection, carbonize the granulated material, heat it up to 1100°C at a heating rate of 2°C / min, and keep it at 1100°C for 12 h. Finally, carry out screening treatment, and the screening and demagnetization treatment time is 2 h to remove large particle materials after carbonization treatment, and the graphite anode material of Example 1 is prepared.

[0099] The differences between Example 1-10 and Comparative Example 1-15 are shown in Table 1. Others are the same as Example 1. Among them, the unit of air flow is L / mim, the unit of temperature is °C, and the unit of time is h. The graphite anode materials of Example 2-10 and Comparative Example 1-15 are prepared respectively.

[0100] Table 1 Differences in graphite anode materials of each example and comparative example

[0101]

[0102]

[0103]

[0104] Among them, the specific steps of Comparative Example 1 and Comparative Example 2 are as follows.

[0105] Comparative Example 1

[0106] The preparation method of the graphite anode material of Comparative Example 1 includes the following steps:

[0107] Step 1: In a pulverizing device, pulverize the calcined needle coke to obtain a powder, and control the particle size of the powder so that Dv10 is 4.0 - 5.0 μm, Dv50 is 9 - 10 μm, and Dv90 is 19.0 - 21.0 μm; carry out shaping treatment on the pulverized material, and mix the shaped powder evenly.

[0108] Step 2: Under nitrogen protection, graphitize the mixed powder, the graphitization temperature is 3000°C, and the graphitization time is 12 h to obtain graphite aggregate.

[0109] Step 3: Screen the material after graphitization treatment, the mesh number of the sieve is 250 meshes, and remove the massive materials that quickly coke at high temperature during graphitization.

[0110] Step 4: The screened graphite and asphalt are fully mixed in a mass ratio of 100:3 for 1 hour to make the asphalt evenly distributed in the screened material to obtain a mixture.

[0111] Step 5: The mixed material is heat treated in two stages, the first stage is at 450°C for 2 hours, and the second stage is at 700°C for 2 hours. The treatment process is carried out in a vertical kettle with stirring at a speed of 15 rpm / min to obtain granulated material.

[0112] Step 6: Under nitrogen protection, the granulated material was carbonized, heated to 1100°C at a heating rate of 2°C / min, and kept at 1100°C for 12 hours. Finally, screening was performed, and the screening and demagnetization time was 2 hours to remove the large particles after carbonization treatment, and the graphite negative electrode material of Comparative Example 1 was obtained.

[0113] Comparative Example 2

[0114] The preparation method of the graphite negative electrode material of Comparative Example 2 comprises the following steps:

[0115] Step 1: In a pulverizing device, the calcined needle coke is pulverized to obtain a powder, and the particle size of the powder is controlled within the range of 4.0-5.0 μm for Dv10, 9-10 μm for Dv50, and 19.0-21.0 μm for Dv90; the pulverized material is shaped, and the shaped powder is mixed evenly.

[0116] Step 2: Under nitrogen protection, the mixed powder is graphitized at a graphitization temperature of 3000° C. for 12 h to obtain graphite aggregate.

[0117] Step 3: The graphitized material is screened with a mesh size of 250 to remove the lumps that are rapidly coked during the graphitization process at high temperature.

[0118] Step 4: The screened graphite and asphalt are fully mixed in a mass ratio of 100:4 for 1 hour to make the asphalt evenly distributed in the screened material to obtain a mixture.

[0119] Step 5: subjecting the screened graphite aggregate and asphalt raw materials to oxidation modification.

[0120] Graphite aggregate (Dv50: 8.5-10 μm) and asphalt raw material (Dv50: 3-4 μm) are added into a horizontal rotary kiln, compressed air is introduced at a rate of 20 L / min, the temperature is increased to 450°C at a rate of 4°C / min, and the reaction is carried out for 3 hours to obtain a mixture of modified graphite and asphalt.

[0121] Step 6: Heat-treat the mixture, which includes two stages. The temperature in the first stage is 500 °C and the time is 2 h; the temperature in the second stage is 650 °C and the time is 2 h. This treatment process is carried out under the condition of stirring in a vertical kettle, and the stirring speed is 15 rpm / min to obtain granulated material.

[0122] Step 7: Under nitrogen protection, carbonize the granulated material, heat it up to 1100 °C at a heating rate of 2 °C / min, and keep it at 1100 °C for 12 h. Finally, perform screening treatment. The screening and demagnetization treatment time is 2 h to remove large particle materials after carbonization treatment, and the graphite anode material of Comparative Example 2 is prepared.

[0123] Performance test of anode material:

[0124] 1. Electrochemical performance test

[0125] Adopt the half-cell test method to test the performance of the anode materials in the examples and comparative examples on the Blue Electric battery test system.

[0126] Anode slurry ratio: graphite: CMC: SP: SBR = 95:1.5:1.5:2. Coat the slurry on the copper foil, and put the coated electrode sheet into a vacuum drying oven at 110 °C for vacuum drying for 4 h for standby. The electrolyte is 1 mol / L LiPF6 + EC:DEC:DM = 1:1:1 (volume ratio), the metal lithium sheet is the counter electrode, and the polypropylene microporous membrane is the separator to assemble the battery.

[0127] Charge and discharge regime: First, stand still for 2 h, discharge: from 0.1C to 0.09C, 0.08C, 0.07C... 0.02C to 0.001V; stand still for 15 min; charge: from 0.1C to 1.5V; stand still for 15 min.

[0128] 2. Particle size test

[0129] Adopt the Malvern 3000 laser particle size analyzer to conduct wet tests on the particle sizes of the materials in the examples and comparative examples.

[0130] 3. Scanning electron microscope test

[0131] Adopt the SU3900 scanning electron microscope of Hitachi High-Technologies Corporation, Japan to observe the morphologies of the materials in the examples and comparative examples.

[0132] 4. Tap density test

[0133] The graphite placed in a glass graduated cylinder vibrates 3000 times in a Quantachrome tap density tester. Calculate the volume after vibration through its descending depth, and then divide the weight of the graphite by its volume after vibration to obtain the tap density.

[0134] 5. Specific surface area test

[0135] The adsorption isotherm of nitrogen on graphite within a certain temperature and pressure range was measured using a Beijing Jingwei Gaobo specific surface area tester, and then the specific surface area and pore size distribution of the material were calculated.

[0136] The physical and chemical parameters and electrochemical performance parameters of the graphite anode materials in each example and comparative example are shown in Table 2.

[0137] Table 2 Physical and chemical parameters and electrochemical performance of the graphite anode materials in each example and comparative example

[0138]

[0139]

[0140] As shown in Table 1 and Table 2 above, within the preferred range of this application, eight groups of example experiments were conducted. Powders with similar particle sizes after sieving were selected to reduce the influence of external errors, and eight groups of electrochemical performance tests were carried out. Among the eight groups of examples, Examples 1 and 4 had relatively better performance.

[0141] The difference between Comparative Example 1 and the above-mentioned examples is that after mixing asphalt and graphite, no oxidation modification was carried out, and granulation and carbonization were directly carried out. Therefore, in this case, the interlayer spacing of graphite did not change; and the fast charging performance has a positive correlation with the graphite layer spacing, so the final electrochemical performance of this group of comparative examples is not good.

[0142] The difference between Comparative Example 2 and the above-mentioned examples is that after mixing asphalt and graphite, they were jointly subjected to oxidation modification. To meet the conditions for the oxidation of both raw materials, a high-temperature oxidation method was used for this experiment. However, asphalt is extremely easy to melt and undergo thermal polymerization reaction at high temperature. Therefore, in this case, asphalt has been coated on the surface of graphite in advance during the process of softening and denaturing, which will affect the final oxygen content and the full removal of oxygen atoms of the oxidized graphite during the subsequent heat treatment process, and thus affect the electrochemical performance of the graphite product.

[0143] The differences between Comparative Examples 3 and 4 and the above-mentioned examples are that raw material oxidation modification temperature parameters outside the scope of the conditions of this application were used. For graphite and asphalt materials, the lower oxidation modification temperature in Comparative Example 4 could not meet the oxidation requirements of the two materials. Although graphite can be oxidized at a higher oxidation modification temperature, it will increase the cost additionally, and asphalt materials are extremely easy to polymerize and denature at high temperature as mentioned above. Therefore, although graphite and asphalt were oxidized at high temperature in Comparative Example 3, the raw materials were over-oxidized and even denatured, which will ultimately affect the product performance.

[0144] The differences between Comparative Examples 6 and 5 and the above-mentioned groups of Examples lie in the adjustment of the addition amount of oxidized asphalt. It is known that the oxidized asphalt finally needs to coat the surface of graphite and improve the interfacial state of graphite. If the asphalt addition amount is at a low level as in Comparative Example 5, the surface defects of graphite cannot be fully improved, and the performance of the final product is poor; while when the asphalt addition amount is too high as in Comparative Example 6, not only will the cost be wasted, but also the difficulty of lithium ion insertion and extraction from the negative electrode surface will be increased.

[0145] The differences between Comparative Examples 7 and 8 and the above-mentioned groups of Examples lie in the use of final carbonization treatment temperature parameters outside the scope of the conditions of this application. Although oxygen atoms will escape at different carbonization temperatures, the low carbonization temperature in Comparative Example 7 cannot completely remove the impurities of graphite and asphalt, while the high carbonization temperature in Comparative Example 8 will cause over-sintering, affecting the pore structure on the surface of graphite. These changes will all affect the final performance of the finished negative electrode. At the same time, it can be seen from the electrochemical performance that the combination of fully oxidized graphite and asphalt materials is beneficial to the improvement of the rate performance of the final carbonized product.

[0146] The differences between Comparative Examples 9, 10 and 11 and the above two groups of Examples lie in the use of pre-carbonization heat treatment temperature parameters outside the scope of the conditions of this application. In order to enable the asphalt to be fully softened, melted and completed the coating process, a heat treatment process needs to be added before carbonization. At the heat treatment temperature above 700 °C in Comparative Example 9, the asphalt is extremely prone to coking and thus does not have fluidity and viscosity, and cannot complete the task of uniformly coating graphite; while the lower heat treatment temperature in Comparative Example 10 cannot completely melt the asphalt to have a fluidity similar to water; the one-stage heat preservation program in Comparative Example 11 ignores the softening process of the asphalt, and at the same time the one-stage heat preservation will also cause the rapid coking and denaturation of the asphalt, thereby affecting the product performance.

[0147] The differences between Comparative Examples 12 to 15 and the above-mentioned groups of Examples lie in the adjustment of the compressed air volume and oxidation reaction time of oxidized asphalt and graphite. For Comparative Examples 13 and 14, a lower air flow rate and a shorter oxidation reaction time will surely not be able to obtain qualified modified graphite and asphalt; while Comparative Examples 12 and 15 use a higher air flow rate and a long time of oxidation to obtain modified materials. In such cases, the raw materials are over-oxidized. Even if the performance of the final product meets the standards, the production cost will be greatly increased.

[0148] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the various embodiments of the present application.

[0149] In addition, those skilled in the art can understand that although some of the embodiments herein include certain features included in other embodiments rather than other features, the combination of the features of different embodiments means that it is within the scope of the present application and forms different embodiments. For example, in the claims above, any one of the claimed embodiments can be used in any combination. The information disclosed in this background art section is only intended to deepen the understanding of the overall background art of the present application, and should not be regarded as an admission or any form of implication that this information constitutes the prior art known to those skilled in the art.

Claims

1. A method for preparing a graphite negative electrode material, characterized in that: include: The graphite aggregate is subjected to a first oxidation heat treatment to obtain modified graphite; The crushed asphalt raw material is subjected to a second oxidation heat treatment to obtain modified asphalt; Mixing the modified graphite and the modified asphalt to obtain a mixture; The mixed material is subjected to heat treatment to obtain granulated material; The granulated material is carbonized and sieved to obtain the graphite negative electrode material.

2. The method for preparing a graphite negative electrode material according to claim 1, characterized in that: Compressed air is introduced during the first oxidation heat treatment and the second oxidation heat treatment, respectively, and the flow rate of the compressed air is 10 to 20 L / min.

3. The method for preparing a graphite negative electrode material according to claim 1, characterized in that: The graphite aggregate is obtained by graphitizing the crushed coke raw material and meets at least one of the following conditions: A. The particle size of the crushed coke raw material meets the following requirements: Dv10 is 4.0-7.0 μm, Dv50 is 9-11 μm, and Dv90 is 19.0-24.0 μm; B. The temperature of the graphitization treatment is 3000-3200°C; C. The graphitization treatment time is 10 to 20 hours; D. The graphitization degree of the graphite aggregate is 92% to 98%; E. The particle size of the graphite aggregate meets the following requirements: Dv10 is 3.0-6.0 μm, Dv50 is 8.5-10 μm, and Dv90 is 18.0-22.0 μm.

4. The method for preparing a graphite negative electrode material according to claim 1, characterized in that: At least one of the following conditions is met: A. The temperature of the first oxidation heat treatment is 450-600°C; B. The heating rate of the first oxidation heat treatment is not higher than 5°C / min; C. The holding time of the first oxidation heat treatment is 2 to 5 hours.

5. The method for preparing a graphite negative electrode material according to claim 1, characterized in that: At least one of the following conditions is met: A. The particle size Dv50 of the crushed asphalt raw material is 3 to 5 um; B. The temperature of the second oxidation heat treatment is 140-200°C; C. The heating rate of the second oxidation heat treatment is not higher than 5°C / min; D. The holding time of the second oxidation heat treatment is 2 to 5 hours.

6. The method for preparing a graphite negative electrode material according to claim 1, characterized in that: At least one of the following conditions is met: A. The mass ratio of the modified graphite to the modified asphalt is 100:(2-5); B. The mixing time is not less than 1 hour; C. The heating rate of the heat treatment is not higher than 10°C / min; D. The heat treatment includes a first stage and a second stage, wherein the temperature of the first stage is 400-500°C and the time is 2h; the temperature of the second stage is 650-750°C and the time is 2h; E. N2 is introduced during the heat treatment process, and the N2 flow rate is not less than 5L / min; F. The particle size of the granulated material meets the following requirements: Dv10 is 6.0-9.0 μm, Dv50 is 12-15 μm, and Dv90 is 23.0-27.0 μm.

7. The method for preparing a graphite negative electrode material according to claim 1, characterized in that: At least one of the following conditions is met: A. The temperature of the carbonization treatment is 1100-1200°C; B. The carbonization treatment time is not less than 10 hours; C. The heating rate of the carbonization treatment is not higher than 2°C / min; D. N2 is introduced during the carbonization process, and the N2 flow rate is not less than 5L / min; E. The particle size of the graphite negative electrode material meets the following requirements: Dv10 is 6.0-8.0 μm, Dv50 is 12-14.0 μm, and Dv90 is 22.0-25.0 μm.

8. A graphite negative electrode material, characterized in that: The graphite negative electrode material is prepared by the method for preparing the graphite negative electrode material according to any one of claims 1 to 7.

9. A lithium ion battery, characterized in that: Comprising the graphite negative electrode material as described in claim 8.

10. An electrical device, characterized in that: Includes the lithium ion battery as claimed in claim 9.

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