A fast-charging artificial graphite negative electrode active material and preparation and application thereof

Abstract

The present application belongs to the technical field of lithium secondary battery, and particularly relates to a fast-charging artificial graphite negative electrode active material, which comprises a graphitized carbon core, a graphene intermediate layer covering the core, and an amorphous shell layer with local graphitization covering the intermediate layer; the graphitized carbon core has micropore and mesopore structures, and comprises a soft carbon graphitized carbon matrix and coke-based graphite particles inlaid in the matrix. The present application also provides preparation of the material and application of the material in lithium secondary batteries. The material has excellent lithium adaptability, excellent capacity and fast-charging performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium battery electrode materials, and particularly relates to a graphite negative electrode material. BACKGROUND

[0002] Lithium ion battery is a typical representative of a new type of green rechargeable battery system, and has a wide application in many fields due to its excellent use performance. The comprehensive performance of the negative electrode material of the lithium ion battery is the key to realize long cycle life and high energy density. Graphite material is the key to realize commercialization of the lithium ion battery due to its low delithiation potential, high theoretical lithium intercalation capacity, good cycle stability and good reversibility. And the current commercialized negative electrode material of the lithium ion battery is mainly artificial graphite. The compaction density of the artificial graphite material is generally low, and the electronic conductivity thereof is lower than that of natural graphite, so the fast charging performance is not good. The method of adopting multi-stage particle coating reported on the current market also has the problem of limited electronic and ionic transmission between primary particles. Therefore, it is necessary to develop a new preparation process to obtain high-compaction artificial graphite negative electrode material with high capacity and fast charging performance. SUMMARY

[0003] In view of the problem that the fast charging performance of the existing graphite material is not ideal, the first object of the application is to provide a fast charging artificial graphite negative electrode active material, which aims to obtain a lithium ion battery artificial graphite negative electrode material with high capacity, fast charging and high compaction.

[0004] The second object of the application is to provide a preparation method of the fast charging artificial graphite negative electrode active material, which aims to prepare a material with high tap density and high fast charging performance.

[0005] The third object of the application is to provide an application of the fast charging artificial graphite negative electrode active material in a lithium secondary battery, a negative electrode thereof and a negative electrode material.

[0006] The fourth object of the application is to provide a lithium secondary battery, a negative electrode thereof and a negative electrode material comprising the fast charging artificial graphite negative electrode active material.

[0007] A fast charging artificial graphite negative electrode active material comprises a graphitized carbon core, a graphene intermediate layer coating the core, and an amorphous shell layer with local graphitization coating the intermediate layer.

[0008] The graphitized carbon core has a microporous and mesoporous structure, and comprises a soft carbon graphitized carbon matrix and coke-based graphite particles inlaid in the matrix.

[0009] The application provides a brand-new graphite negative electrode active material, which has a double-carbon structure, takes a soft carbon graphitized carbon matrix and coke-based graphite particles inlaid in the matrix as a core, and coats a graphene layer on the surface of the core to form a primary carbon-coated structure, and further coats a locally graphitized amorphous shell layer on the surface of the shell.

[0010] In the application, the combination of the soft carbon-coke composite graphitized core and the graphene-local graphitization amorphous double-carbon structure is the key to synergistically improving the performance of the material, in particular the fast-charging performance.

[0011] As a preferred, the graphene intermediate layer is a thin-layer graphene layer with a pore structure.

[0012] Preferably, the fast-charging artificial graphite negative electrode active material has a tap density of not less than 1.0 g / cm3, preferably 1.6-2 g / cm3.

[0013] Preferably, the size of the graphitized carbon core is 8-18 μm; the thickness of the graphene intermediate layer is 1-8 nm; and the thickness of the amorphous shell layer is 0.1-2 μm.

[0014] The application further provides a preparation method of the fast-charging artificial graphite negative electrode active material.

[0015] Step (1):

[0016] The coke raw material primary particles and the soft carbon raw material A are mixed and granulated to obtain secondary particles; the secondary particles are subjected to thermal modification in an atmosphere containing gaseous water; and the modified material is prepared; wherein the temperature of the thermal modification is 300-600 ℃.

[0017] Step (2):

[0018] The modified material obtained in step (1) and graphene oxide are coated to obtain a primary coating precursor.

[0019] Step (3):

[0020] The primary coating precursor is subjected to pre-carbonization and graphitization treatment, and then is placed in an aqueous solution for quenching treatment while hot to prepare a graphitized material.

[0021] Step (4):

[0022] The graphitization material, a catalytic aid and the carbon raw material B are mixed, formed and subjected to a two-stage carbonization treatment to obtain the fast-charging artificial graphite negative electrode active material.

[0023] The two-stage carbonization treatment process comprises a first-stage carbonization process under a protective atmosphere and a second-stage carbonization process under negative pressure.

[0024] The present application researches and finds that the coke raw material-soft carbon raw material A is innovatively preheated and modified in the atmosphere of gaseous water, and is further combined with the graphene oxide coating, the quenching after graphitization and the local graphitization outer layer construction process, so that the micro-pores and structures can be adjusted and the material surface can be functionally modified, thereby improving the matching ability between the particles and the layers, reducing the particle and layer impedance, improving the tap density, improving the ion and electron transmission network and path, and thus the electrochemical performance of the prepared material can be improved, especially the capacity and fast-charging stability.

[0025] In the present application, the coke raw material is at least one of petroleum coke and needle coke.

[0026] Preferably, the particle size of the primary particles is 5-10 mu m.

[0027] Preferably, the soft carbon raw material A is at least one of pitch, petroleum coke and needle coke.

[0028] In the present application, the coke raw material and the soft carbon raw material A are combined and further combined with subsequent processes, which can unexpectedly achieve synergy, obtain better particle and layer matching, further improve the embedding and de-embedding of lithium ions, improve the lithium storage performance, and further help to construct a short layer transmission network, thereby improving the capacity and fast-charging performance.

[0029] Preferably, the weight ratio of the coke raw material to the soft carbon raw material A is 100:1-10, and further preferably 100:5-8.

[0030] In the present application, the coke raw material and the soft carbon raw material A are jointly heat-modified in gaseous water, which helps to adjust the microstructure and functionalize the surface, thereby helping to improve the interaction between the particles and the layers and the ion and electron transmission path, and improve the fast-charging performance.

[0031] In the present application, the heat modification atmosphere can be pure gaseous water or a mixture of gaseous water and a protective atmosphere such as nitrogen or inert gas.

[0032] The present application researches and finds that controlling the heat modification problem helps to further combine with other processes to improve the capacity and fast-charging performance of the prepared material.

[0033] In the present application, the temperature of the thermal modification is preferably 350-600℃.

[0034] Preferably, the time of the thermal modification is 0.5-2h, preferably 1-1.5h.

[0035] In the present application, the modified material is coated with graphene oxide, which can realize functional adaptation, reduce hierarchical impedance, improve ion and electron transmission network, and improve capacity and fast charging performance.

[0036] Preferably, in step (2), the graphene oxide is coated on the surface of the modified material by a spheroidization coating method.

[0037] In the present application, in step (2), the weight ratio of the modified material to graphene oxide is 100:1-10; preferably 100:2-8. Considering performance and cost, it is further preferred to be 100:2-4.

[0038] In the present application, the pre-carbonization and graphitization are carried out in a protective atmosphere.

[0039] Preferably, the protective atmosphere is at least one of nitrogen, hydrogen, argon or helium.

[0040] Preferably, the temperature of the pre-carbonization is 950-1250℃, preferably 1000-1050℃, and the preferred time is 4-10h, further preferably 4-6h.

[0041] Preferably, the temperature of the graphitization is 2800-3200℃, preferably 3000-3100℃; and the preferred time is 8-18h, preferably 9-12h.

[0042] In the present application, the graphene-coated graphitized particles are subjected to quenching treatment in an aqueous solution, which helps to regulate the surface structure and functional modification, facilitates the subsequent coating of amorphous carbon layer of local graphitization, and reduces the hierarchical impedance and improves the fast charging performance.

[0043] In the present application, after graphitization treatment, the temperature of the graphitized raw material is cooled to 1200-1600℃ and then placed in an aqueous solution for quenching.

[0044] In the present application, the aqueous solution can be a pure aqueous solution, or a solution containing other trace ions, a mixed solution of water and water-soluble organic solvent, preferably a mixed solution of water and ethanol, wherein the volume ratio of water to ethanol is 100:10-100. The present application also found that quenching in a mixed solution of water-soluble organic solvent medium helps to further adjust the physical and chemical structure, improves the adaptability of lithium, and further improves the capacity and fast charging performance of the material.

[0045] The temperature of the aqueous solution is not particularly required, and for example, can be less than or equal to 100°C.

[0046] In the present application, the catalytic aid is a catalytic graphitization catalyst;

[0047] Preferably, the catalytic aid is a compound of at least one of nickel and cobalt.

[0048] Preferably, the catalytic aid is nickel nitrate, cobalt nitrate, nickel hydroxide, cobalt hydroxide, nickel oxide, cobalt oxide, nickel oxalate, etc.

[0049] Preferably, the carbon raw material B is at least one of pitch, polypropylene, polypyrrole, glucose, etc.

[0050] Preferably, the mass ratio of the graphitization material, the catalytic aid, and the soft carbon raw material B is 100:1-5:2-8, and further can be 100:2-3:4-6.

[0051] In the present application, the graphitization material, the catalytic aid, and the soft carbon raw material B are mixed and then molded, and then subjected to subsequent two-stage carbonization treatment. In the present application, the molding can be performed based on the existing means.

[0052] The first-stage carbonization treatment is performed under a protective atmosphere, for example, at least one of nitrogen, hydrogen, argon, or helium. The pressure during the treatment process is normal pressure or positive pressure.

[0053] Preferably, the temperature of the first-stage carbonization treatment is 600-700°C, and the time is 2-4 hours.

[0054] The negative pressure of the second-stage carbonization is 2-20 Pa, the temperature is 900-1250°C, preferably 1000-1100°C, and the time is 2-5 hours, preferably 3-4 hours.

[0055] Preferably, after the second-stage carbonization treatment, the fast-charging artificial graphite negative electrode active material is obtained through magnetic removal and crushing treatment.

[0056] One preferred method for preparing a fast-charging and high-density artificial graphite negative electrode according to the present application includes the following steps:

[0057] Step (1):

[0058] The petroleum coke (or needle coke) with a particle size of 5-10 μm is mixed with pitch to obtain secondary particles with a particle size of 10-20 μm through fusion granulation.

[0059] The mass ratio of the petroleum coke (or needle coke) to pitch is 100:2-8.

[0060] Step (2):

[0061] The secondary particles are placed in a tube furnace for thermal modification in gaseous water to obtain modified material;

[0062] The temperature of the thermal modification is 300-600℃, and the time is 0.5-2h.

[0063] Step (3):

[0064] The modified material and graphene oxide are placed in a spheroidizing machine for spheroidization coating;

[0065] The ratio of the modified material to graphene oxide is 100:2-8.

[0066] Step (4):

[0067] The spheroidization coated material is pre-carbonized and graphitized, and after graphitization cooling to 1200-1600℃, it is placed in an aqueous solution for quenching while hot;

[0068] The pre-carbonization atmosphere is a protective atmosphere, such as one or more of nitrogen, hydrogen, argon or helium, the pre-carbonization temperature is 950-1250℃, and the time is 4-10h;

[0069] Step (5):

[0070] The obtained graphite material, catalytic aid and pitch are mixed uniformly according to a certain ratio and then pressed into shape;

[0071] The mass ratio of the graphite material to the catalytic aid is 100:1-5, and the mass ratio of the graphite material to the pitch is 100:2-8. The catalytic aid is an organic or inorganic salt or oxide of nickel or cobalt, such as nickel nitrate, cobalt nitrate, nickel hydroxide, cobalt hydroxide, nickel oxide, cobalt oxide, nickel oxalate, etc. The pressing is a pressing into shape in an isostatic press with a pressure of 50-300MPa.

[0072] Step (6):

[0073] After the pressed and shaped material is subjected to two-stage heat treatment under normal pressure and negative pressure, it is subjected to conventional depolymerization, demagnetization and screening to obtain the artificial graphite negative electrode material with fast charging and high compaction.

[0074] The two-stage heat treatment under normal pressure and negative pressure is to place the pressed and shaped block in an atmosphere furnace, heat it to 600-700℃ at a heating rate of 2-10℃ / min and keep it at this temperature for 2-4h, then vacuumize the system to a negative pressure of 2-20Pa, keep the pressure unchanged, continue to heat it to 900-1250℃ and keep it at this temperature for 2-4h.

[0075] In the prior art, the soft carbon material is usually coated with pitch carbon and then graphitized. Although the graphitization process can convert the soft carbon material into a crystalline state, the electronic transfer kinetics is poor and the ion transfer path is long during the electrochemical reaction, so the rate performance of the artificial graphite is poor. In addition, although the use of secondary particles has been reported to improve the rate performance of the material, the particles are relatively loose, resulting in low tap density. Therefore, the preparation method provided by the present application innovatively pre-modifies the primary particles of petroleum coke or needle coke and the soft carbon raw material A under gaseous water to control the structure and functional modification, improve the structure and adaptability of the components, and reduce the particle impedance. Furthermore, the primary coating of graphene oxide, the water quenching after graphitization, and the secondary coating of local graphitized amorphous carbon are further combined to improve the adaptability of the components and structure of the particles and layers, reduce the impedance of the particles and layers, improve the tap density, improve the ion and electron transfer network, and improve the electrochemical performance of the material.

[0076] The artificial graphite negative electrode material prepared by the preparation method has a multi-core-double-shell structure, and from the inside out, it is a multi-core, an outer shell 1 (an intermediate layer), and an outer shell 2 (an outer layer). The multi-core is a graphitized carbon particle with a pore structure, which includes a soft carbon graphitized carbon substrate and coke-based graphitized carbon anchored in the substrate. The outer shell 1 is few-layer graphene with a pore structure, and the outer shell 2 is a pitch carbon outer layer with a local graphitization structure. The present application finds that the artificial graphite negative electrode material has the advantages of high tap density, excellent rate performance, high first efficiency, and good cycle stability.

[0077] The present application also provides an application of the artificial graphite negative electrode material prepared by the preparation method, which is used as a negative active material of a lithium secondary battery.

[0078] Preferably, the application is used as a negative active material, which is used to be compounded with a conductive agent and a binder to prepare a negative electrode material. The conductive agent and the binder are both materials known in the industry.

[0079] Further preferably, the application is to use the negative electrode material on the surface of a negative current collector to prepare a negative electrode. The present application can be prepared by using conventional methods, such as coating the negative electrode material on the current collector to form the negative electrode. The current collector is any material known in the industry.

[0080] More preferably, the application is to assemble the negative electrode and the positive electrode, the separator, and the electrolyte into a lithium secondary battery.

[0081] In the present application, the lithium secondary battery is a lithium ion battery.

[0082] The application further provides a lithium secondary battery negative electrode material, which comprises a negative electrode active material, a conductive agent and a binder, wherein the negative electrode active material comprises the fast-charging artificial graphite negative electrode active material.

[0083] Preferably, the content of the negative electrode active material is 70-95 wt%.

[0084] Preferably, the lithium secondary battery is a lithium ion battery.

[0085] The application further provides a lithium secondary battery negative electrode, which comprises a current collector and a negative electrode material, wherein the negative electrode material comprises the negative electrode material.

[0086] The application further provides a lithium secondary battery, which comprises the negative electrode.

[0087] The lithium secondary battery is a lithium ion battery.

[0088] The application has the following beneficial effects:

[0089] (1) The application provides a brand-new graphite negative electrode active material, which has a double-carbon coating structure, takes a soft carbon graphitized carbon matrix and a pyrolytic graphite particle embedded in the matrix as a core, coats a graphene layer on the surface of the core to form a primary carbon coating structure, and further coats a locally graphitized amorphous shell layer on the surface of the outer shell. The application finds that the combined control of the special core-primary shell and secondary shell structure and composition can unexpectedly achieve synergy, can significantly improve the combination ability between materials and levels, improve the tap density, reduce the material impedance, improve the electronic and ionic transmission channels, and is helpful to synergistically improve the performance of the material, especially the fast-charging stability of the material.

[0090] (2) The application provides a method capable of successfully preparing the special structure and making the prepared material have excellent electrochemical performance, which innovatively pre-modifies a pyrolytic raw material-soft carbon raw material A in a gaseous water atmosphere, further combines the graphene coating, quenching after graphitization and local graphitization outer layer construction process, can synergistically adjust the micro-pores and structure, and can functionalize and modify the surface of the material, so as to improve the adaptability between particles and layers, reduce the particle and level impedance, improve the tap density, improve the ionic and electronic transmission network and path, so as to synergistically improve the electrochemical performance of the prepared material, especially the capacity and fast-charging stability.

[0091] (3) The main raw materials and materials are widely available and low in cost, the mixing, fusion granulation, heat treatment and graphitization process is simple and easy to control, and the process is easy to realize large-scale production and has good practical prospect. BRIEF DESCRIPTION OF DRAWINGS

[0092] SEM image of the material obtained in step (2) of Example 1. Figure 1

[0093] SEM image of the material obtained in step (4) of Example 1. Figure 2

[0094] Figure 3 SEM image of the final material obtained in Example 1.

[0095] SEM image of the final material obtained in Example 1. Figure 4 TEM image of the final material obtained in Example 1. DETAILED DESCRIPTION

[0096] The following examples illustrate the specific steps of the present application, and it should be understood that these examples are merely illustrative of the present application and are not intended to limit the scope of the present application in any way. Various processes and methods not described in detail in the present application are conventional methods known in the art.

[0097] In the following cases, the particle size refers to the D50 particle size unless otherwise specified.

[0098] Example 1

[0099] Step (1): 8 μm needle coke and pitch were mixed in a mass ratio of 100:5 and then placed in a fusion for treatment to obtain secondary particles with a particle size of 18 μm;

[0100] Step (2): The secondary particles were placed in a tube furnace, the tube furnace was heated to 350°C (marked as T1), and then gaseous water was introduced for 1 h, and then the material was naturally cooled and dried;

[0101] Step (3): The material prepared in step (2) was mixed with graphene oxide in a mass ratio of 100:2, and then placed in a spheroidizing machine for spheroidizing and coating;

[0102] Step (4): The spheroidized and coated material was placed in an atmosphere furnace and heated to 1000°C (marked as T2) at 5°C / min under argon protection and held for 5 h, and then cooled to room temperature; the obtained material was then subjected to graphitization at a temperature of 3050°C (marked as T3) for 10 h, and then naturally cooled to 1500°C (marked as T4), and then the material was placed in water for rapid cooling, and then subjected to solid-liquid separation and drying to obtain a graphitized material (also referred to as a graphite material);

[0103] Step (5): The obtained graphite material, nickel oxalate, and pitch were mixed in a mass ratio of 100:2:5, and then pressed into a compact in an isostatic press at a pressure of 150 MPa to obtain an isostatic compact;

[0104] ​​​Step (6): The isostatic pressing block was placed in a vacuum atmosphere furnace, and heated to 600℃ (marked as T5) at 5℃ / min under argon protection, and kept for 2h. Then the system was vacuumized to a negative pressure of 2Pa, and kept the pressure unchanged, and continued to heat to 1050℃ (marked as T6) and kept for 4h. After natural cooling to room temperature, the obtained material was depolymerized, demagnetized, and sieved to obtain the artificial graphite negative electrode material with fast charging and high compaction.

[0105] According to GB / T 24533-2009, the graphite electrode was used as the working electrode, lithium metal as the negative electrode, 1 mol / L LiPF6 in EC / EMC (volume ratio 1:1) as the electrolyte, and PE-PP composite film as the separator to assemble CR2025 button cells in an argon-filled dry glove box. The electrochemical performance was detected at room temperature in the voltage range of 0.001-2.0V.

[0106] Example 2

[0107] Compared with Example 1, the only difference was that the mass ratio of needle coke to pitch used in step (1) was 100:8.

[0108] Example 3

[0109] Compared with Example 1, the only difference was that in step (2), the temperature of T1 was controlled at 600℃.

[0110] Example 4

[0111] Compared with Example 1, the only difference was that in step (3), the mass ratio of the material prepared in step (2) to graphene oxide was controlled at 100:8.

[0112] Example 5

[0113] Compared with Example 1, the only difference was that in step (4), the material after graphitization treatment for 10h was naturally cooled to 1200℃, and then placed in normal temperature water while hot for quenching.

[0114] Example 6

[0115] Compared with Example 1, the only difference was that in step (5), an equal weight of cobalt nitrate was used to replace the nickel oxalate.

[0116] Example 7

[0117] Compared with Example 1, the only difference was that in step (4), the quenching medium was 20v% ethanol aqueous solution, and other operations and parameters were the same as Example 1.

[0118] Comparative Example 1

[0119] Compared with Example 1, the only difference is that in step 2, the holding stage is not in a gaseous water atmosphere, but in pure nitrogen. The difference is that step (2) is: the above secondary particles are placed in a tube furnace, and the tube furnace is heated to 350℃ under nitrogen and held for 1h, and then naturally cooled and dried; other processes and steps are the same as Example 1.

[0120] Comparative Example 2

[0121] Compared with Example 1, the only difference is that in step (3), the added graphene oxide is 0. Other operations and parameters are the same as Example 1.

[0122] Comparative Example 3

[0123] Compared with Example 1, the only difference is that in step (4), after graphitization, the material is not quenched in water, but is naturally cooled to room temperature in the furnace. The difference is that step (4) is: the spheroidized coated material is placed in an atmosphere furnace under argon protection, and heated to 1000℃ at a rate of 5℃ / min and held for 5h, and then cooled to room temperature; the obtained material is then subjected to graphitization operation, the graphitization temperature is 3050℃, and the graphitization treatment time is 10h, and then naturally cooled to room temperature.

[0124] Other operations and parameters are the same as Example 1.

[0125] Comparative Example 4

[0126] Compared with Example 1, the only difference is that in step (5), no nickel oxalate is added. Other operations and parameters are the same as Example 1.

[0127] Comparative Example 5

[0128] Compared with Example 1, the only difference is that in step (6), T6 is not held under negative pressure, but is treated under Ar atmosphere. The difference is that step (6) is: the isostatic pressing block is placed in a vacuum atmosphere furnace under argon protection, and heated to 600℃ at a rate of 5℃ / min and held for 2h, then heated to 1050℃ and held for 4h, and then naturally cooled to room temperature.

[0129] Comparative Example 6

[0130] Compared with Example 1, the raw material used in step (1) is needle coke, and other steps are the same.

[0131] Comparative Example 7

[0132] Compared with Example 1, the raw material used in step (1) is pitch, and other steps are the same.

[0133] Comparative Example 8

[0134] Compared with Example 1, the step of step (2) is replaced by: the secondary particles obtained in step (1) are mixed with 10% potassium hydroxide and then placed in a tube furnace, the tube furnace is heated to 350℃ and kept for 1h, and then naturally cooled and dried. Other process steps and parameters are the same as those in Example 1.

[0135] Comparative Example 9

[0136] Compared with Example 1, the only difference is that the treatment temperature of step (2) is 650℃, and the other steps are the same.

[0137] Comparative Example 10

[0138] Compared with Example 1, the only difference is that in step (3), equal weight of natural flake graphite is used to replace the graphene oxide. The difference in step (3) is: the material prepared in step (2) is mixed with natural flake graphite at a mass ratio of 100:2, and then placed in a spheroidizing machine for spheroidizing and coating operation.

[0139] Comparative Example 11

[0140] Compared with Example 1, the difference is that step (3) does not use graphene oxide, but uses super-conductive carbon (SP). The difference in step (3) is: the material prepared in step (2) is mixed with super-conductive carbon (SP) at a mass ratio of 100:2, and then placed in a spheroidizing machine for spheroidizing and coating operation.

[0141] Comparative Example 12

[0142] Compared with Example 1, the only difference is that the quenching medium used in step (4) is liquid nitrogen. Step (4) is as follows:

[0143] Step (4): the spheroidized and coated material is placed in an atmosphere furnace, heated to 1000℃ at 5℃ / min under argon protection and kept for 5h, then cooled to room temperature; then the obtained material is subjected to graphitization operation, the graphitization temperature is 3050℃, the graphitization treatment time is 10h, then the material is placed in liquid nitrogen for rapid cooling when the material is naturally cooled to 1500℃, and then the material is subjected to solid-liquid separation, drying of the material;

[0144] The test results of the materials obtained in the above examples and comparative examples are as follows:

[0145]

[0146] In summary, the combination of the innovative use of the focus raw material and the carbon source, the gaseous water heat treatment, the encapsulation of graphene oxide, the pre-carbonization-graphitization quenching treatment, and the subsequent local catalytic graphitized carbon coating process can achieve synergy, can significantly improve the compatibility between the particles and the levels of the material, improve the tap density, improve the electrochemical performance, and especially help to improve the fast charging performance.

Claims

1. A fast-charging artificial graphite negative electrode active material, characterized in that: It includes a graphitized carbon core, a graphene middle layer covering the core, and an amorphous shell layer with localized graphitization covering the middle layer; The graphitized carbon core has a microporous and mesoporous structure and comprises a soft carbon graphitized carbon matrix and coke-based graphite particles embedded in the matrix; The fast-charging artificial graphite negative electrode active material is prepared by the following steps: Step (1): Primary particles of coke raw material and soft carbon raw material A are mixed and granulated to obtain secondary particles; the secondary particles are thermally modified in an atmosphere containing gaseous water to obtain a modified material; wherein the thermal modification temperature is 300-600°C; Step (2): The modified material obtained in step (1) and graphene oxide are subjected to a spheroidization coating method, and the graphene oxide is coated on the surface of the modified material to obtain a primary coating precursor; Step (3): The primary coating precursor is pre-carbonized and graphitized, and then placed in an aqueous solution while hot for rapid cooling to obtain a graphitized material; wherein the pre-carbonization temperature is 950-1250°C, and the graphitization temperature is 2800-3200°C; Step (4): The graphitized material, the catalyst promoter and the carbon raw material B are mixed, formed, and subjected to a two-stage carbonization treatment to obtain the fast-charging artificial graphite negative electrode active material; The two-stage carbonization process includes a first carbonization process under a protective atmosphere and a second carbonization process under negative pressure; The temperature of the first carbonization treatment is 600~700℃; the temperature of the second carbonization treatment is 900~1250℃.

2. The fast-charging artificial graphite negative electrode active material according to claim 1, characterized in that The graphene intermediate layer is a thin graphene layer with a pore structure; The fast-charging artificial graphite negative electrode active material has a tap density of not less than 1.0 g / cm 3 ; The size of the graphitized carbon core is 8~18μm; the thickness of the graphene middle layer is 1~8nm; and the thickness of the amorphous shell is 0.1~2μm.

3. A method for preparing the fast-charging artificial graphite negative electrode active material according to claim 1 or 2, characterized in that the steps include: Step (1): Primary particles of coke raw material and soft carbon raw material A are mixed and granulated to obtain secondary particles; the secondary particles are thermally modified in an atmosphere containing gaseous water to obtain a modified material; wherein the thermal modification temperature is 300-600°C; Step (2): The modified material obtained in step (1) and graphene oxide are subjected to a spheroidization coating method, and the graphene oxide is coated on the surface of the modified material to obtain a primary coating precursor; Step (3): The primary coating precursor is pre-carbonized and graphitized, and then placed in an aqueous solution while hot for rapid cooling to obtain a graphitized material; wherein the pre-carbonization temperature is 950-1250°C, and the graphitization temperature is 2800-3200°C; Step (4): The graphitized material, the catalyst promoter and the carbon raw material B are mixed, formed, and subjected to a two-stage carbonization treatment to obtain the fast-charging artificial graphite negative electrode active material; The two-stage carbonization process includes a first carbonization process under a protective atmosphere and a second carbonization process under negative pressure; The temperature of the first carbonization treatment is 600~700℃; the temperature of the second carbonization treatment is 900~1250℃.

4. The method for preparing the fast-charging artificial graphite negative electrode active material according to claim 3, wherein: The coke raw material is at least one of petroleum coke and needle coke.

5. The method for preparing the fast-charging artificial graphite negative electrode active material according to claim 3, wherein: The particle size of the primary particles is 5-10 μm.

6. The method for preparing the fast-charging artificial graphite negative electrode active material according to claim 3, wherein: The soft carbon raw material A is at least one of asphalt, petroleum coke and needle coke.

7. The method for preparing the fast-charging artificial graphite negative electrode active material according to claim 3, wherein: The weight ratio of the coke raw material to the soft carbon raw material A is 100:1~10.

8. The method for preparing the fast-charging artificial graphite negative electrode active material according to claim 3, wherein: The weight ratio of the coke raw material to the soft carbon raw material A is 100:5~8.

9. The method for preparing a fast-charging artificial graphite negative electrode active material according to claim 3, wherein: The thermal modification time is 0.5 to 2 hours.

10. The method for preparing a fast-charging artificial graphite negative electrode active material according to claim 3, wherein: In step (2), the weight ratio of the modified material to graphene oxide is 100:1~10.

11. The method for preparing a fast-charging artificial graphite negative electrode active material according to claim 10, wherein: In step (2), the weight ratio of the modified material to graphene oxide is 100:2~8.

12. The method for preparing a fast-charging artificial graphite negative electrode active material according to claim 10, wherein: In step (2), the weight ratio of the modified material to graphene oxide is 100:2~4.

13. The method for preparing a fast-charging artificial graphite negative electrode active material according to claim 3, wherein: Pre-carbonization and graphitization are carried out in a protective atmosphere.

14. The method for preparing a fast-charging artificial graphite negative electrode active material according to claim 13, wherein: The protective atmosphere is at least one of nitrogen, hydrogen, argon or helium.

15. The method for preparing a fast-charging artificial graphite negative electrode active material according to claim 3, wherein: The pre-carbonization time is 4~10h.

16. The method for preparing a fast-charging artificial graphite negative electrode active material according to claim 3, wherein: The graphitization time is 8~18h.

17. The method for preparing a fast-charging artificial graphite negative electrode active material according to claim 3, wherein: After the graphitization treatment, the temperature of the graphitized raw material is cooled to 1200-1600°C and then rapidly cooled in water while still hot.

18. The method for preparing a fast-charging artificial graphite negative electrode active material according to claim 3, wherein: The catalyst promoter is a catalytic graphitization catalyst.

19. The method for preparing a fast-charging artificial graphite negative electrode active material according to claim 18, wherein: The catalyst promoter is a compound of at least one element selected from nickel and cobalt.

20. The method for preparing a fast-charging artificial graphite negative electrode active material according to claim 19, wherein: The catalyst promoter is at least one of nickel nitrate, cobalt nitrate, nickel hydroxide, cobalt hydroxide, nickel oxide, cobalt oxide and nickel oxalate.

21. The method for preparing a fast-charging artificial graphite negative electrode active material according to claim 3, wherein: The carbon raw material B is at least one of pitch, polypropylene, polypyrrole, and glucose.

22. The method for preparing a fast-charging artificial graphite negative electrode active material according to claim 3, wherein: The mass ratio of the graphitized material, the catalyst aid, and the carbon raw material B is 100:1~5:2~8.

23. The method for preparing a fast-charging artificial graphite negative electrode active material according to claim 3, wherein: The first carbonization treatment takes 2 to 4 hours.

24. The method for preparing a fast-charging artificial graphite negative electrode active material according to claim 3, wherein: The negative pressure of the second carbonization stage is 2~20Pa, and the time of the second carbonization stage is 2~4h.

25. The method for preparing a fast-charging artificial graphite negative electrode active material according to claim 3, wherein: After the second-stage carbonization treatment, the fast-charging artificial graphite negative electrode active material is obtained through demagnetization and pulverization treatment.

26. A use of the fast-charging artificial graphite negative electrode active material according to any one of claims 1 to 2 or the fast-charging artificial graphite negative electrode active material prepared by the preparation method according to any one of claims 3 to 25, characterized in that: It is used as a negative electrode active material for lithium secondary batteries.

27. The use according to claim 26, characterized in that Used as negative electrode active material, used to be compounded with conductive agents and binders to prepare negative electrode materials.

28. The use according to claim 27, characterized in that The negative electrode material is placed on the surface of the negative electrode current collector to prepare the negative electrode.

29. The use according to claim 28, characterized in that The negative electrode, the positive electrode, the separator and the electrolyte are assembled into a lithium secondary battery.

30. The use according to claim 29, characterized in that The lithium secondary battery is a lithium ion battery.

31. A negative electrode material for a lithium secondary battery, comprising a negative electrode active material, a conductive agent and a binder, characterized in that: The negative electrode active material comprises the fast-charging artificial graphite negative electrode active material according to any one of claims 1 to 2 or the fast-charging artificial graphite negative electrode active material prepared by the preparation method according to any one of claims 3 to 25.

32. The negative electrode material for a lithium secondary battery according to claim 31, wherein The content of the negative electrode active material is 70-95wt%.

33. The negative electrode material for a lithium secondary battery according to claim 31 or 32, wherein: The lithium secondary battery is a lithium ion battery.

34. A negative electrode for a lithium secondary battery, comprising a current collector and a negative electrode material, characterized in that: The negative electrode material comprises the negative electrode material according to any one of claims 31 to 33.

35. A lithium secondary battery, characterized in that: Comprising the negative electrode according to claim 34.

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