Graphite negative electrode material and preparation method and application thereof

Abstract

The application provides a graphite negative electrode material and a preparation method and application thereof. The graphite negative electrode material is a core-shell structure with graphite as the core and modified carbon material as the shell. The preparation raw material of the modified carbon material comprises a base material and a modifier. The modifier is a modifier containing N element and / or P element. The mass percentage content of the modifier in the modified carbon material is 5-50%. The mass percentage content of the modified carbon material in the graphite negative electrode material is 0.5-8%. First, the base material and the modifier are modified to obtain a coating agent. Then, the coating agent and the graphite are heat-treated to obtain the graphite negative electrode material. The graphite negative electrode material provided by the application has high specific capacity and good fast charging performance, and is suitable for use as a negative electrode material of a fast charging lithium ion battery.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, specifically relating to a graphite anode material, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries have wide applications in the new energy field. Graphite, as the negative electrode material in lithium-ion batteries, has a stable voltage platform and long-cycle stability, making it the most widely used negative electrode material. The lithium storage mechanism of graphite mainly relies on the process of lithium ions intercalating and deintercalating between graphite layers. Its theoretical capacity is 372 mAh / g, making it the preferred negative electrode material for producing high-energy-density cells. With the large-scale and widespread application of electric vehicles and electronic devices in people's lives, the energy consumption patterns of society are undergoing tremendous changes. In this transformation, in addition to high energy density, lithium-ion batteries, as energy storage devices, also require increasingly higher fast-charging performance. This necessitates that batteries be able to charge in a shorter time, mainly by constructing rapid particle transport channels on the surface of graphite materials to improve their fast-charging performance. For example, etchants can be used to construct ion porosity channels on the surface of graphite materials, or coating agents can be used to improve ion diffusion on the graphite surface.

[0003] CN109748587A discloses a high-capacity fast-charging graphite anode material and its preparation method. In this technical solution, components A and B are sequentially subjected to raw material pretreatment, asphalt mixing, composite reaction, crushing, graphitization, and modified carbonization processes to ultimately prepare an anode material with a secondary particle core and double-layer coating. Component A is easily graphitized coke or highly crystalline graphite, and component B is difficult-to-graphitize coke or hard carbon. The modifier used in the modified carbonization process is one or more of petroleum asphalt or coal tar, coal tar, petroleum residue oil, petroleum slurry, liquid asphalt, phenolic resin, epoxy resin, furan resin, toluene, methane, and acetylene, with a residual carbon value of 10%-70% and a softening point of 40-300℃. Although the anode material prepared by this technical solution has a high capacity, its preparation process is relatively complex.

[0004] CN105024043A discloses a fast-charging graphite lithium-ion battery anode material and its preparation method. The preparation method includes the following steps: (1) mixing, heating and kneading, and pulverizing a mixture containing natural graphite and asphalt; wherein, the average particle size D of the natural graphite is... 50The particle size is 5-10 μm, and the mass ratio of the natural graphite to the asphalt is 50:50-90:10; (2) under inert gas protection, heat treatment is carried out at 300-700℃; (3) graphitization. In this technical solution, natural graphite and asphalt are selected as raw materials for preparing negative electrode materials. However, during the graphitization process, the surface of the particles of natural graphite and asphalt becomes highly ordered after graphitization, which will have a negative impact on the fast charging performance of lithium-ion batteries.

[0005] CN108328614A discloses a graphite anode material for fast-charging lithium-ion batteries and its preparation method. The preparation method includes the following steps: S1, pulverizing a carbon-based material and then sieving and classifying it to obtain primary particles; wherein, the primary particles have a density of D... 50 The initial particle size is 12-20 μm. The resulting primary particles are mixed with asphalt to obtain powder. S2. The powder is kneaded to obtain a kneaded material. S3. The kneaded material is pulverized and then carbonized in an inert atmosphere to obtain carbonized material. S4. The carbonized material is pulverized, sieved, graphitized, demagnetized, and then sieved to obtain graphite anode material for fast-charging lithium-ion batteries. During the carbonization process, the asphalt exhibits anisotropic structural characteristics, affecting the diffusion of lithium ions on the surface of the graphite anode material, thus affecting the rate performance of the material.

[0006] Therefore, how to provide a fast-charging graphite anode material with high capacity and good rate performance has become an urgent technical problem to be solved. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a graphite anode material, its preparation method, and its applications. This invention designs the core-shell components and their content in the graphite anode material and further selects modifiers containing N and / or P elements to prepare a graphite anode material with excellent electrochemical properties and fast-charging performance. The graphite anode material provided by this invention is suitable for preparing fast-charging lithium-ion batteries.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a graphite anode material, wherein the graphite anode material has a core-shell structure;

[0010] The core of the shell-core structure is graphite, and the shell is a modified carbon material;

[0011] The raw materials for preparing the modified carbon material include a base material and a modifier;

[0012] The modifier is a modifier containing N and / or P elements;

[0013] The modifier has a mass percentage content of 5% to 50% in the modified carbon material;

[0014] The modified carbon material has a mass percentage of 0.5% to 8% in the graphite anode material.

[0015] In this invention, by designing the core-shell components and their content in the graphite anode material, and further selecting modifiers containing N and / or P elements, the wetting characteristics of the electrolyte on the material surface can be effectively increased through the modification of the substrate material by specific modifiers. This increases the diffusion rate of lithium ions on the surface of the graphite anode material and enhances the fast-charging performance of the graphite anode material. As a result, a graphite anode material with excellent electrochemical characteristics and fast-charging performance is prepared, and the prepared graphite anode material is suitable for preparing fast-charging lithium-ion batteries.

[0016] In this invention, by controlling the content of the modifier in the modified carbon material within a specific range, the prepared graphite anode material exhibits high capacity characteristics and good fast-charging performance. If the content of the modifier in the modified carbon material is low, the modification effect of the modifier on the substrate material is poor, resulting in a low content of N and / or P heteroatoms in the final prepared graphite anode material, leading to a low specific capacity. Conversely, if the content of the modifier in the modified carbon material is high, the modified carbon material cannot construct a microporous structure on the graphite surface, resulting in an excessively large specific surface area and a low initial coulombic efficiency in the final prepared graphite anode material.

[0017] In this invention, the mass percentage of the modifier in the modified carbon material can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or 50%.

[0018] The mass percentage of the modified carbon material in the graphite anode material can be 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, or 8%.

[0019] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The purpose and beneficial effects of the present invention can be better achieved and realized through the following preferred technical solutions.

[0020] As a preferred technical solution of the present invention, the D of the graphite 50 The particle size is 5 to 20 μm, for example, it can be 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm or 20 μm, etc.

[0021] Preferably, the modifier is selected from any one or a combination of at least two of melamine, melamine resin, dicyandiamide, thiourea, cyanamide, phytic acid, phosphoric acid, P2O5, ammonium chloride, or ammonium carbonate.

[0022] Preferably, the base material is selected from bitumen and / or tar.

[0023] It should be noted that the present invention does not impose any special restrictions on asphalt and tar. For example, the asphalt may be selected from one or a combination of at least two of low-temperature asphalt, medium-temperature asphalt, or high-temperature asphalt.

[0024] In a second aspect, the present invention provides a method for preparing a graphite anode material as described in the first aspect, comprising the following steps:

[0025] (1) Modify the base material and the modifier to obtain the coating agent;

[0026] (2) Heat-treat the coating agent and graphite obtained in step (1) to obtain the graphite anode material.

[0027] In this invention, a coating agent is obtained by modifying the substrate material using a modifier. The coating agent and graphite are then subjected to heat treatment. On the one hand, the functional groups contained in the modifier in the coating agent undergo a partial cross-linking reaction with the active groups in the substrate material, thereby achieving the doping of heteroatoms such as N and P in the graphite anode material. On the other hand, the substrate material and the modifier are carbonized through heat treatment to obtain a modified carbon material. Finally, a graphite anode material with a microporous structure on the surface, with graphite as the core and modified carbon material as the shell, is constructed.

[0028] As a preferred technical solution of the present invention, the modification treatment method in step (1) is to perform modification treatment by a high-temperature stirring device.

[0029] It should be noted that there are no special limitations on high-temperature stirring equipment in this invention. Exemplary examples include, but are not limited to, any one or at least a combination of two of the following: kneading pot, open mill, internal mixer, stirring tank, high-temperature stirring reactor, or twin-screw extruder.

[0030] Preferably, the temperature of the modification treatment is 100 to 300°C, for example, it can be 100°C, 120°C, 140°C, 160°C, 180°C, 200°C, 220°C, 240°C, 260°C, 280°C or 300°C.

[0031] Preferably, the stirring rate of the high-temperature stirring device is 100-800 rpm, for example, it can be 100 rpm, 150 rpm, 200 rpm, 250 rpm, 300 rpm, 350 rpm, 400 rpm, 450 rpm, 500 rpm, 550 rpm, 600 rpm, 650 rpm, 700 rpm, 750 rpm or 800 rpm, etc.

[0032] As a preferred technical solution of the present invention, the modification process in step (1) further includes a pretreatment step.

[0033] Preferably, the pretreatment method involves mixing the base material and the modifier evenly.

[0034] Preferably, after the modification process described in step (1) is completed, a post-processing step is also included.

[0035] Preferably, the post-processing method involves crushing the coating agent.

[0036] Preferably, the coating agent has a D 50 The particle size is 2 to 15 μm, for example, it can be 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm or 15 μm, etc.

[0037] As a preferred embodiment of the present invention, the heat treatment includes a first heat treatment and a second heat treatment.

[0038] In this invention, by performing a first heat treatment operation on the coating agent and graphite obtained in step (1), the coating agent can be uniformly coated on the surface of the graphite material, and the functional groups contained in the modifier undergo a partial cross-linking reaction with the active groups in the substrate material. At the same time, heteroatoms such as N or P react with the active sites on the graphite material, thus preparing a graphite anode material doped with heteroatoms such as N and P.

[0039] In this invention, during the second heat treatment process, the coating agent gradually decomposes and carbonizes on the graphite surface to obtain a modified carbon material, which further forms a graphite anode material with a modified carbon material as the shell, graphite as the core, and a microporous structure on the surface. The presence of the microporous structure is beneficial for the rapid transport of lithium ions, improving the fast-charging performance of the anode material. The doping of heteroatoms such as N and P can increase the adsorption sites for lithium ions, thereby enhancing the lithium storage properties of the material and increasing the specific capacity of the graphite anode material. At the same time, the introduction of atoms such as N and P can also enhance the wettability of the electrolyte to the graphite anode material, enabling rapid transport of lithium ions on the surface of the graphite anode material, and can suppress uneven deposition of lithium ions, thereby improving the electrochemical performance of the lithium-ion battery.

[0040] Preferably, the temperature of the first heat treatment is 400 to 600°C, for example, it can be 400°C, 420°C, 440°C, 460°C, 480°C, 500°C, 520°C, 540°C, 560°C, 580°C or 600°C.

[0041] Preferably, the heating rate of the first heat treatment is 1 to 10 °C / min, for example, it can be 1 °C / min, 2 °C / min, 3 °C / min, 4 °C / min, 5 °C / min, 6 °C / min, 7 °C / min, 8 °C / min, 9 °C / min or 10 °C / min, etc.

[0042] Preferably, the first heat treatment time is 4 to 12 hours, for example, it can be 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours or 12 hours.

[0043] Preferably, the first heat treatment is performed in the presence of an inert gas.

[0044] As a preferred embodiment of the present invention, the temperature of the second heat treatment is 900 to 1200°C, for example, it can be 900°C, 930°C, 950°C, 970°C, 1000°C, 1020°C, 1050°C, 1080°C, 1100°C, 1120°C, 1150°C, 1170°C or 1200°C, etc.

[0045] Preferably, the heating rate of the second heat treatment is 1 to 10 °C / min, for example, it can be 1 °C / min, 2 °C / min, 3 °C / min, 4 °C / min, 5 °C / min, 6 °C / min, 7 °C / min, 8 °C / min, 9 °C / min or 10 °C / min, etc.

[0046] Preferably, the second heat treatment time is 4 to 12 hours, for example, it can be 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours or 12 hours.

[0047] Preferably, the second heat treatment is performed in the presence of an inert gas.

[0048] It should be noted that the first heat treatment and the second heat treatment in this invention are both carried out in the presence of an inert gas. This invention does not have any special limitations on the inert gas, which includes, but is not limited to, nitrogen and / or argon.

[0049] As a preferred technical solution of the present invention, step (2) further includes a pretreatment step before the heat treatment.

[0050] Preferably, the pretreatment method is to mix the coating agent obtained in step (1) and graphite evenly.

[0051] It should be noted that the present invention does not impose any special restrictions on the operation of mixing the coating agent and graphite obtained in step (1) evenly. Exemplary examples include, but are not limited to, using any one or at least a combination of two of the following: a VC mixer, a gravity-free mixer, or a ball mill to mix the coating agent and graphite.

[0052] As a preferred embodiment of the present invention, the preparation method specifically includes the following steps:

[0053] (1) After the base material and modifier are mixed evenly, the mixture is modified by a high-temperature stirring device at 100-300℃ and a stirring rate of 100-800rpm, and then crushed to obtain D. 50 Coating agents with a particle size of 2–15 μm;

[0054] (2) After the coating agent and graphite obtained in step (1) are mixed evenly, the first heat treatment is carried out at 400-600℃ for 4-12 hours in an inert atmosphere, and then the temperature is raised to 900-1200℃ for a second heat treatment for 4-12 hours to obtain the graphite anode material. The heating rate of the first heat treatment is 1-10℃ / min, and the heating rate of the second heat treatment is 1-10℃ / min.

[0055] Thirdly, the present invention provides an application of the graphite anode material as described in the first aspect in lithium-ion batteries.

[0056] Compared with the prior art, the present invention has the following beneficial effects:

[0057] This invention designs the core-shell composition and content of graphite anode materials and prepares graphite anode materials containing heteroatoms such as N and P and having a microporous structure on the surface through a specific preparation method. The modified carbon material of the graphite anode material has a mass percentage content of N and / or P elements of 3.2% to 16.8%, and the specific surface area of ​​the prepared graphite anode material is 1.44 to 1.92 m2 / g. At the same time, the prepared graphite anode material has good electrical performance, with a capacity of 353.1 to 355.3 mAh / g, an initial coulombic efficiency of 92.5% to 93.2%, and a rate performance of 31.2% to 35.6%. Attached Figure Description

[0058] Figure 1 This is a SEM image of the graphite anode material prepared in Example 1. Detailed Implementation

[0059] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments are merely illustrative of the present invention and should not be construed as limiting the invention.

[0060] Example 1

[0061] This embodiment provides a graphite anode material and its preparation method, and its SEM image is shown below. Figure 1 As shown, the graphite anode material has a core-shell structure;

[0062] The core of the shell-core structure is graphite, and the shell is a modified carbon material;

[0063] The raw materials for preparing the modified carbon material include a substrate material and melamine;

[0064] The modifier has a mass percentage of 25% in the modified carbon material;

[0065] The modified carbon material has a mass percentage of 5% in the graphite anode material.

[0066] The preparation method of the above-mentioned graphite anode material is as follows:

[0067] (1) After the asphalt and melamine are mixed evenly, they are modified and crushed by a twin-screw extruder at 200°C and a stirring rate of 400 rpm to obtain D. 50 Coating agent with a particle size of 10 μm;

[0068] (2) After the coating agent and graphite obtained in step (1) are mixed evenly, the first heat treatment is carried out at 500°C for 8 hours in an argon atmosphere, and then the temperature is raised to 1000°C for a second heat treatment for 10 hours to obtain the graphite anode material, wherein the heating rate of the first heat treatment is 5°C / min and the heating rate of the second heat treatment is 5°C / min.

[0069] The microstructure of the graphite anode material provided in Example 1 was characterized using a scanning electron microscope (model SU81510), such as... Figure 1 As shown, by Figure 1 It can be seen that the carbon-coated graphite composite material with a uniform coating layer was prepared in Example 1.

[0070] Example 2

[0071] This embodiment provides a graphite anode material and its preparation method, wherein the graphite anode material has a core-shell structure;

[0072] The core of the shell-core structure is graphite, and the shell is a modified carbon material;

[0073] The raw materials for preparing the modified carbon material include a substrate material and melamine resin;

[0074] The modifier has a mass percentage of 5% in the modified carbon material;

[0075] The modified carbon material has a mass percentage of 8% in the graphite anode material.

[0076] The preparation method of the above-mentioned graphite anode material is as follows:

[0077] (1) After the asphalt and melamine resin are mixed evenly, they are modified and crushed in an internal mixer at 100°C and 100 rpm to obtain D. 50 Coating agent with a particle size of 15 μm;

[0078] (2) After the coating agent and graphite obtained in step (1) are mixed evenly, the first heat treatment is carried out at 400°C for 12 hours in a nitrogen atmosphere, and then the temperature is raised to 1200°C for a second heat treatment for 4 hours to obtain the graphite anode material. The heating rate of the first heat treatment is 1°C / min and the heating rate of the second heat treatment is 10°C / min.

[0079] Example 3

[0080] This embodiment provides a graphite anode material and its preparation method, wherein the graphite anode material has a core-shell structure;

[0081] The core of the shell-core structure is graphite, and the shell is a modified carbon material;

[0082] The raw materials for preparing the modified carbon material include a base material and thiourea;

[0083] The modifier has a mass percentage of 50% in the modified carbon material;

[0084] The modified carbon material has a mass percentage of 2% in the graphite anode material.

[0085] The preparation method of the above-mentioned graphite anode material is as follows:

[0086] (1) After the tar and thiourea are mixed evenly, they are modified and crushed in a two-roll mill at 300°C and a stirring speed of 800 rpm to obtain D. 50 Coating agent with a particle size of 2 μm;

[0087] (2) After the coating agent and graphite obtained in step (1) are mixed evenly, the first heat treatment is carried out at 600°C for 4 hours in an argon atmosphere, and then the temperature is raised to 900°C for a second heat treatment for 12 hours to obtain the graphite anode material. The heating rate of the first heat treatment is 10°C / min, and the heating rate of the second heat treatment is 1°C / min.

[0088] Example 4

[0089] This embodiment provides a graphite anode material and its preparation method, wherein the graphite anode material has a core-shell structure;

[0090] The core of the shell-core structure is graphite, and the shell is a modified carbon material;

[0091] The raw materials for preparing the modified carbon material include a base material and phytic acid;

[0092] The modifier has a mass percentage content of 15% in the modified carbon material;

[0093] The modified carbon material has a mass percentage of 0.5% in the graphite anode material.

[0094] The preparation method of the above-mentioned graphite anode material is as follows:

[0095] (1) After the asphalt and phytic acid are mixed evenly, they are extruded and crushed in a high-temperature stirred reactor at 250°C and a stirring rate of 600 rpm to obtain D. 50 Coating agent with a particle size of 7 μm;

[0096] (2) After the coating agent obtained in step (1) is mixed evenly with graphite, the first heat treatment is carried out at 450°C for 6 hours in an argon atmosphere, and then the temperature is raised to 1100°C for 8 hours to obtain the graphite anode material. The heating rate of the first heat treatment is 7°C / min, and the heating rate of the second heat treatment is 4°C / min.

[0097] Example 5

[0098] This embodiment provides a graphite anode material and its preparation method. The only difference from Embodiment 1 is that the modifier has a mass percentage content of 5% in the modified carbon material; other conditions are the same as in Embodiment 1.

[0099] Example 6

[0100] This embodiment provides a graphite anode material and its preparation method. The only difference from Embodiment 1 is that the modifier has a mass percentage content of 50% in the modified carbon material; other conditions are the same as in Embodiment 1.

[0101] Example 7

[0102] This embodiment provides a graphite anode material and its preparation method. The only difference from Embodiment 1 is that the preparation method of the graphite anode material does not involve a first heat treatment, while the other conditions are the same as in Embodiment 1.

[0103] Comparative Example 1

[0104] This comparative example provides a graphite anode material and its preparation method. The only difference from Example 1 is that the modifier has a mass percentage content of 2% in the modified carbon material; other conditions are the same as in Example 1.

[0105] Comparative Example 2

[0106] This comparative example provides a graphite anode material and its preparation method. The only difference from Example 1 is that the modifier has a mass percentage content of 60% in the modified carbon material; other conditions are the same as in Example 1.

[0107] Comparative Example 3

[0108] This comparative example provides a graphite anode material and its preparation method. The only difference from Example 1 is that the raw material components of the graphite anode material do not contain modifiers, and the other conditions are the same as in Example 1.

[0109] Comparative Example 4

[0110] This comparative example provides a graphite anode material and its preparation method. The only difference from Example 1 is that the modifier is replaced with phenolic resin, while the other conditions are the same as in Example 1.

[0111] The performance of the graphite anode materials provided in the above embodiments and comparative examples was tested using the following methods:

[0112] (1) Mass percentage of N and / or P elements in modified carbon materials: The nitrogen content in the material was tested using an oxygen and nitrogen element analyzer (ON330 oxygen and nitrogen analyzer), and the phosphorus content in the material was tested using an inductively coupled plasma atomic emission spectrometer (ICAP7200). The sum of the mass percentage of nitrogen and phosphorus was recorded as a; the mass of the modified carbon material was recorded as b.

[0113] The mass percentage of N and / or P elements in modified carbon materials = a / b × 100%;

[0114] (2) Specific surface area: The specific surface area of ​​the graphite anode materials provided in the above examples and comparative examples was tested using a fully automatic nitrogen adsorption-desorption specific surface area analyzer (3H-2000III type).

[0115] (3) Capacity and initial coulombic efficiency: The graphite anode material provided in the above examples and comparative examples was mixed uniformly with SBR, CMC, and SP in a ratio of 94.5:2.5:1.5:1.5, coated onto copper foil, and then dried, rolled, and cut to prepare an electrode sheet with a diameter of 12 mm. This electrode sheet was then assembled with a lithium metal sheet to form a coin cell. The electrolyte was LBC3008A, and the separator was a PP separator. The capacity and initial coulombic efficiency of the coin cell were tested using a blue dot tester at a rate of 0.1C and a charge / discharge voltage of 0.05–2.0V.

[0116] (4) Rate performance: The capacity of the above button cells at 2C and 0.2C rates was tested using a blue dot tester. The rate performance is the ratio of the capacity measured at 2C and 0.2C.

[0117] The characterization of the graphite anode materials provided in the above embodiments and comparative examples is shown in Table 1:

[0118] Table 1

[0119]

[0120]

[0121] As shown in Table 1, this invention, through the design of the core-shell composition and content of graphite anode materials and the preparation of a graphite anode material using a specific method, yields a graphite anode material containing heteroatoms such as N and P and possessing a microporous structure on its surface. Furthermore, the mass percentage of N and / or P elements in the modified carbon material of the graphite anode material ranges from 3.2% to 16.8%, and the specific surface area of ​​the prepared graphite anode material is 1.44 to 1.92 m². 2 / g; the graphite anode material prepared at the same time has good electrical performance, with a capacity of 353.1-355.3 mAh / g, an initial coulombic efficiency of 92.5-93.2%, and a rate performance of 31.2-35.6%.

[0122] Compared with Example 1, if the first heat treatment (Example 7) is not performed during the preparation of the graphite anode material, the rate performance of the prepared graphite anode material is worse by 28.3%.

[0123] Compared to Example 1, if the amount of modifier used is small (Comparative Example 1), the mass percentage of N and / or P elements in the prepared graphite anode material is lower at 1.2%, and the rate performance is poorer at 26.3%. If the amount of modifier used is large (Comparative Example 2), although the mass percentage of N and / or P elements in the prepared graphite anode material is higher at 20.8%, the specific surface area is larger at 2.89 m². 2 / g, the initial coulombic efficiency is relatively low. Therefore, it can be seen that by controlling the content of the modifier within a specific range, the graphite anode material prepared in this invention has a higher mass percentage content of N and / or P elements and better rate performance.

[0124] Compared to Example 1, if the raw material components for preparing the graphite anode material do not contain a modifier (Comparative Example 3), the specific surface area of ​​the prepared graphite anode material is smaller, at 1.33 m². 2 / g, the rate performance is poor at 25.1%; if the modifier does not contain N and / or P elements (Comparative Example 4), the rate performance of the prepared graphite anode material is also poor. Therefore, this invention improves the electrical properties of the graphite anode material by using a modifier containing N and / or P elements to modify the substrate material.

[0125] In summary, this invention designs the core-shell composition and content of graphite anode materials and prepares graphite anode materials containing heteroatoms such as N and P and having a microporous structure on the surface through a specific preparation method. The prepared graphite anode materials have good electrical properties.

[0126] The applicant declares that the detailed process flow of this invention is illustrated by the above embodiments, but this invention is not limited to the above detailed process flow, that is, it does not mean that this invention must rely on the above detailed process flow to be implemented. Those skilled in the art should understand that any improvements to this invention, equivalent substitutions of raw materials for the product of this invention, addition of auxiliary components, and selection of specific methods, etc., all fall within the protection scope and disclosure scope of this invention.

Claims

1. A method for producing a graphite negative electrode material, characterized by, The preparation method comprises the following steps: (1) modifying the base material and the modifier to obtain a coating agent; (2) heat treating the coating agent obtained in step (1) and the graphite to obtain the graphite negative electrode material; The heat treatment comprises a first heat treatment and a second heat treatment; The modifier is selected from any one or a combination of at least two of melamine, melamine resin, dicyandiamide, thiourea, cyanamide or phytic acid; The base material is selected from asphalt and / or tar; The temperature of the first heat treatment is 400-600°C, and the time of the first heat treatment is 4-12 h; The temperature of the second heat treatment is 900-1200°C, and the time of the second heat treatment is 4-12 h; The graphite negative electrode material has a core-shell structure; The core of the core-shell structure is graphite, and the shell is a modified carbon material; The raw material for preparing the modified carbon material comprises the base material and the modifier; The modifier is a modifier containing N and / or P elements; The mass percentage of the modifier in the modified carbon material is 5%-50%; The mass percentage of the modified carbon material in the graphite negative electrode material is 0.5%-8%.

2. The production method according to claim 1, characterized by, The D 50 The particle diameter is 5 to 20 μm.

3. The preparation method according to claim 1, characterized in that, The method of the modification treatment in step (1) is modification treatment by a high-temperature stirring device.

4. The preparation method according to claim 1, characterized in that, The temperature of the modification treatment is 100-300°C.

5. The preparation method according to claim 3, characterized in that, The stirring rate of the high-temperature stirring device is 100-800 rpm.

6. The method of claim 1, wherein, Step (1) further comprises a pretreatment step before the modification treatment.

7. The production method according to claim 6, characterized by, The method of the pretreatment is mixing the base material and the modifier uniformly.

8. The method of claim 1, wherein, Step (1) further comprises a post-treatment step after the modification treatment.

9. The production method according to claim 8, characterized by, The method of the post-treatment is crushing the coating agent.

10. The method of claim 9, wherein, The D50 of the broken coated agent is 2 to 15 μm. 50 The particle size is 2 to 15 μm.

11. The method of claim 1, wherein, The temperature rising rate of the first heat treatment is 1-10°C / min.

12. The method of claim 1, wherein, The first heat treatment is performed in the presence of an inert gas.

13. The method of claim 1, wherein, The temperature rising rate of the second heat treatment is 1-10°C / min.

14. The method of claim 1, wherein, The second heat treatment is performed in the presence of an inert gas.

15. The method of claim 1, wherein, Step (2) further comprises a pretreatment step before the heat treatment.

16. The method of claim 15, wherein, The method of the pretreatment is mixing the coating agent obtained in step (1) and the graphite uniformly.

17. The method of claim 1, wherein, The preparation method specifically comprises the following steps: (1) After the base material and the modifier are mixed uniformly, the modified treatment is carried out in a high-temperature stirring equipment under the conditions of 100-300°C and a stirring rate of 100-800 rpm, and then crushing is carried out to obtain D 50 The coating agent has a particle size of 2-15 μm. (2) mixing the coating agent obtained in step (1) and the graphite uniformly, then performing a first heat treatment at 400-600°C for 4-12 h in an inert atmosphere, and then performing a second heat treatment at 900-1200°C for 4-12 h after temperature rising, to obtain the graphite negative electrode material, wherein the temperature rising rate of the first heat treatment is 1-10°C / min, and the temperature rising rate of the second heat treatment is 1-10°C / min; The modifier is selected from any one or a combination of at least two of melamine, melamine resin, dicyandiamide, thiourea, cyanamide or phytic acid; The base material is selected from asphalt and / or tar.

18. Application of the graphite negative electrode material prepared by the preparation method in any one of claims 1-17 in a lithium ion battery.

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