Graphite composite negative electrode material and preparation method and application thereof

Abstract

The invention provides a graphite composite negative electrode material and a preparation method and application thereof. The graphite composite negative electrode material has a hierarchical pore structure. The first pore structure is a nano-pore with the average pore size of 2-50nm, the second pore structure is a nano-pore with the average pore size of less than 2nm, and the third pore structure is a micron-pore with the average pore size of more than 0.1 mu m. The graphite composite negative electrode material comprises graphitized particles and a carbon coating layer coating the graphitized particles. The preparation raw materials comprise 70-100 parts of a carbon skeleton material, 7-10 parts of an asphalt binder, 2-3 parts of conductive carbon black and 2-5 parts of a co-carbonization coating agent. The carbon framework material comprises petroleum coke tail powder, needle coke and porous hard carbon. The co-carbonization coating agent comprises carbide of a mixture of PET micro powder and coal tar. And the material of the carbon coating layer comprises a co-carbonization coating agent. The graphite composite negative electrode material is compounded by multiple pore structures, has good coating performance, and can effectively inhibit volume expansion of the material and decomposition reaction with electrolyte, so that a secondary battery has relatively long cycle life and first coulombic efficiency.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of material preparation, and particularly relates to a graphite composite negative electrode material and a preparation method and application thereof. BACKGROUND

[0002] In the field of energy storage, especially in the secondary battery technology such as lithium ion batteries, the negative active material as a key component directly affects the core indicators such as the energy density, cycle life, charge-discharge efficiency and safety of the secondary battery. Among the traditional negative active materials, the graphite-based negative electrode material occupies a dominant position in the commercial lithium ion battery due to its suitable lithium intercalation potential, good electronic conductivity and relatively stable cycle performance. However, with the increasing demand for battery performance in the energy storage market, the traditional graphite negative electrode material gradually exposes many shortcomings and is difficult to meet the growing demand for high performance.

[0003] In terms of raw materials, the traditional graphite negative electrode material has a high degree of dependence on high-purity graphite powder in the preparation process. The preparation process of high-purity graphite powder is complex and needs to go through multiple purification processes, which not only leads to high production costs, but also produces a large amount of industrial waste in the production process, causing certain pressure on the environment. At the same time, with the increasing shortage of graphite resources, the supply stability of high-purity graphite powder also faces challenges, further limiting the large-scale industrial application of traditional graphite negative electrode materials.

[0004] From the relationship between material structure and performance, the traditional graphite negative electrode material has some inherent defects in the cycle process. On the one hand, the structure of the graphite material is relatively simple, lacking effective lithium ion storage channels and buffer spaces. In the battery charge and discharge process, the repeated intercalation and extraction of lithium ions will cause the periodic change of the volume of graphite particles, generating a large volume change stress. After long-term cycling, this stress accumulation is easy to cause the crushing and pulverization of graphite particles, and then leads to the blockage of electrode pores and the shedding of active materials, which makes the battery capacity rapidly decay and the cycle life greatly reduce. On the other hand, the interface stability between the graphite material and the electrolyte is poor. In the first charge and discharge process of the battery, the electrolyte will undergo a reduction decomposition reaction on the surface of the graphite, forming a layer of solid electrolyte interface (SEI) film. However, the SEI film on the surface of the traditional graphite negative electrode material is easy to break and regenerate during the cycle process, leading to the continuous consumption of electrolyte, not only reducing the charge-discharge efficiency of the battery, but also further aggravating the decay of the battery capacity, affecting the safety and cycle life of the battery.

[0005] In order to improve the performance of traditional graphite negative electrode materials, researchers have tried various methods, such as surface modification of graphite, doping other elements or compounding with other materials. But these methods often have some limitations. For example, although some surface modification methods can improve the interface stability of graphite materials to some extent, the modification effect is not durable enough, and performance decline will still occur during long-term cycling. While element doping can improve the electronic structure and ion transport performance of graphite materials, it may introduce new impurity phases, thereby affecting the crystallinity and stability of the electrochemical performance of the material. In addition, the preparation process of some composite materials is complex, the cost is high, and it is difficult to realize large-scale industrial production.

[0006] In summary, the existing traditional graphite negative electrode materials have deficiencies in raw material cost, structural performance and modification method, etc. Therefore, it is urgent to develop a new type of long-life graphite composite negative electrode material for energy storage and its preparation method and application to solve the above problems and meet the demand of the energy storage market for high-performance battery materials. SUMMARY

[0007] In view of the problems existing in the above-mentioned graphite composite negative electrode material, the purpose of the present application is to provide a graphite composite negative electrode material and its preparation method and application. This graphite composite negative electrode material has a composite of multiple pore structures and good coating performance, can effectively inhibit the volume expansion of the material and the decomposition reaction with the electrolyte, so that the secondary battery has a high cycle life and a high initial coulomb efficiency.

[0008] To achieve the above-mentioned purpose, the first aspect of the present application provides a graphite composite negative electrode material with a hierarchical pore structure, the hierarchical pore structure includes a first pore structure, a second pore structure and a third pore structure, the first pore structure is a nanopore and the average pore size is 2-50 nm, the second pore structure is a nanopore and the average pore size is less than 2 nm, the third pore structure is a micropore and the average pore size is greater than 0.1 μm, including graphitized particles and a carbon coating layer coating the graphitized particles, the preparation raw materials include 70-100 parts by weight of carbon skeleton material, 7-10 parts by weight of pitch binder, 2-3 parts by weight of conductive carbon black and 2-5 parts by weight of co-carbonized coating agent, the carbon skeleton material includes petroleum coke tail powder, needle coke and porous hard carbon, the co-carbonized coating agent includes carbonates of PET micro powder and coal tar mixture, and the material of the carbon coating layer includes co-carbonized coating agent.

[0009] The graphite composite negative electrode material of the present application has at least the following technical effects.

[0010] (1) The petroleum coke tail powder is used as a part of carbon skeleton material to replace, which can reduce solid waste from the source and reduce raw material cost. The carbonized product of the mixture of PET micro powder and coal tar is used as coating material to complete recycling and value amplification, so as to reduce cost, and has the advantages of green label and large-scale production.

[0011] (2) The carbonized product of the mixture of PET micro powder and coal tar is used as coating material, which has high contact density with graphitized particles, can form a protective film on the surface of the graphitized particles, can slow down the interface reaction between electrolyte and graphite composite negative electrode material, improve the interface stability, inhibit the excessive growth of electrolyte decomposition products (such as SEI film), reduce the risk of electrode pore blockage and active material shedding, thereby greatly improving the cycle life and safety of the battery.

[0012] (3) The petroleum coke tail powder, needle coke and porous hard carbon are used as carbon skeleton material, and the pitch binder can bond the petroleum coke tail powder, needle coke and porous hard carbon into a whole particle, and then the conductive particles are dispersed in it, so that the graphite composite negative electrode material with multi-phase structure can be prepared, which can effectively inhibit the volume expansion of the material and the decomposition reaction with electrolyte, so that the secondary battery has high cycle life and high initial coulomb efficiency. The porous properties of porous hard carbon provide additional storage channels and buffer space for lithium ions, which helps to disperse the volume change stress in the cycle process.

[0013] (4) The present application selects specific raw materials to form a hierarchical pore structure with nano-pores with an average pore size of 2-50 nm, nano-pores with an average pore size of less than 2 nm, and micropores with an average pore size of more than 0.1 μm. This hierarchical pore structure can greatly benefit the buffering and ion transmission, so that the graphite composite negative electrode material used as the negative electrode material of the secondary battery can make the battery have better cycle performance and initial coulomb efficiency.

[0014] As a technical solution of the present application, the carbon skeleton material further comprises natural flake graphite.

[0015] As a technical solution of the present application, the carbon skeleton material comprises petroleum coke tail powder, needle coke, natural flake graphite and porous hard carbon, and the weight ratio of the four is 10-15:45-55:10-15:5-15.

[0016] As a technical solution of the present application, the petroleum coke tail powder is obtained by purifying the tail powder of the raw material for producing medium coke.

[0017] As a technical solution of the present application, the purification comprises impurity removal by acid immersion, alkali washing and neutralization, and drying in sequence.

[0018] As a technical solution of the present application, the Dv50 of the graphite composite negative electrode material is 18-30 μm.

[0019] As a technical scheme of the present application, the tap density of the graphite composite negative electrode material is 1.00-1.25 g / cm 3 .

[0020] As a technical scheme of the present application, the specific surface area of the graphite composite negative electrode material is 2.1-5.5 m 2 / g.

[0021] As a technical scheme of the present application, the d002 of the graphite composite negative electrode material is 0.33-0.34 nm.

[0022] As a technical scheme of the present application, the thickness of the carbon coating layer is 10-20 nm.

[0023] As a technical scheme of the present application, the Dv50 of the needle coke is 15-35 μm.

[0024] As a technical scheme of the present application, the Dv50 of the petroleum coke tail powder is 1-10 μm, and the carbon content is >95%.

[0025] As a technical scheme of the present application, the viscosity of the pitch binder is 1000-1200 Pa·s, and the softening point is 75-100℃.

[0026] As a technical scheme of the present application, the Dv50 of the natural flake graphite is 10-25 μm, and the carbon content is >99%.

[0027] As a technical scheme of the present application, the specific surface area of the porous hard carbon is 50-150 m 2 / g, the pore size is 2-10 nm, the pore volume is 0.20-0.45 cm 3 / g, and the porosity is 35-55%.

[0028] As a technical scheme of the present application, the Dv50 of the conductive carbon black is 40-60 nm.

[0029] As a technical scheme of the present application, the Dv50 of the PET micro powder is 20-50 μm.

[0030] As a technical scheme of the present application, the softening point of the coal tar is 90-110℃.

[0031] As a technical scheme of the present application, the weight ratio of the PET micro powder to the coal tar is 1-3:7-9.

[0032] As a technical scheme of the present application, the volume ratios of the first pore structure, the second pore structure and the third pore structure in the hierarchical pore structure are 45-50%, 30-40% and 15-25%, respectively.

[0033] The second aspect of the present application provides a preparation method of the graphite composite negative electrode material, comprising the steps of: S1, adding pitch binder and conductive carbon black to a carbon skeleton material, stirring to obtain a mixed prebody, the carbon skeleton material comprising petroleum coke tail powder, needle coke and porous hard carbon; S2, wet granulating the mixed prebody to obtain spherical granules by sieving; S3, carbonizing the spherical granules in an inert atmosphere to obtain carbonized particles; S4, graphitizing the carbonized particles in an inert atmosphere to obtain graphitized particles; S5, blending the graphitized particles with a co-carbonization coating agent comprising a carbonized product of a mixture of PET micro powder and coal tar, and performing carbon coating by heat treatment in an inert atmosphere.

[0034] The formation mechanism of the graphite composite negative electrode material of the present application is as follows.

[0035] (1) The needle coke as a "skeleton carbon source" provides a high crystallinity precursor, which is easy to form an ordered layered carbon (graphite phase) in the high-temperature graphitization step, thereby ensuring the electronic conductivity and structural density (volume energy density basis) of the material. The particles of the needle coke are generally larger, which can complementarily fill the small particle size of the petroleum coke tail powder, improve the particle size distribution and reduce large voids, and the high crystallization tendency of the needle coke can also "pull" the surrounding low-order carbon (after modification of the tail powder) to a more ordered structure in the graphitization stage of the preparation of the graphite composite negative electrode material, so as to improve the overall crystallinity of the material.

[0036] (2) In the wet granulation stage, the pitch binder acts as a granulation binder during wet granulation, which can improve the spheroidization and particle shape uniformity of the granules. The pitch binder flows / soaks into the gaps between the petroleum coke tail powder, needle coke and porous hard carbon.

[0037] (3) In the carbonization stage, the pitch binder forms a carbon connection layer after decomposition and carbonization, which is a continuous carbon bridge with a protective or transitional effect, so that the originally dispersed small petroleum coke tail powder can be tightly mechanically and carbonically combined with the needle coke and porous hard carbon, which can reduce the interface contact resistance and increase the overall mechanical strength. The petroleum coke tail powder, needle coke and porous hard carbon are bonded into a whole particle, and the pore structure of the hard carbon is embedded on the surface of the skeleton. The protective / transitional layer, the tightly bonded whole particle and the pore structure on the surface of the skeleton form a composite structure of "dense conductive matrix + pore buffer phase" at the particle scale.

[0038] In the composite structure, the accumulation gap between particles of petroleum coke tail powder, needle coke, and porous hard carbon, the pore structure of hard carbon itself, the pore structure on the surface of the skeleton, the micro-cracks or micro-gaps caused by thermal shrinkage and the difference in thermal expansion coefficient of different components, and the nanoscale gaps caused by co-carbonization coating agent / interface shrinkage are combined to form a multi-level pore structure, which greatly helps to buffer and ion transmission.

[0039] In addition, a low content of conductive carbon black as a micro-scale conductive filler can significantly improve the electronic connectivity of the particle surface and the inter-particle, reduce the contact resistance, and help to establish a stable conductive network immediately after low-temperature carbonization. And after the carbonization of the asphalt binder, the electric carbon black is embedded as a "conductive bone point", together with the high crystalline conductive path of the needle coke, to jointly build a continuous electronic path from the particle interior to the inter-particle, and to jointly form a "skeleton-bonding-conductive" three-phase interpenetrating structure.

[0040] (4) During the graphitization / coating stage, the needle coke provides an ordered domain for easy graphitization, the PET powder and the coal tar co-carbonization coating agent and the carbon phase of the petroleum coke tail powder are rearranged and crystallized with the needle coke at high temperature, and the conductive carbon black maintains electronic connectivity at the microscale, so that the overall performance of the material is improved. It is not a simple addition of substances, but a synergistic evolution of material phase and interface driven by process.

[0041] As a technical solution of the present application, the Dv50 of the spherical granules is 10-20 μm.

[0042] As a technical solution of the present application, the carbonization temperature is 500-600℃, the heating rate is 1-10℃ / min, and the time is 1-2h.

[0043] As a technical solution of the present application, the graphitization temperature is 2700-3000℃, the heating rate is 1-10℃ / min, and the time is 5-8h.

[0044] As a technical solution of the present application, the heat treatment temperature is 800-1000℃, the heating rate is 1-10℃ / min, and the time is 1-2h.

[0045] As a technical solution of the present application, the inert atmosphere in step S3, step S4 and step S5 is independently selected from nitrogen, helium, neon or argon, and the flow rate of the inert atmosphere is 120-220 mL / min.

[0046] As a technical solution of the present application, the wet granulation includes mixing the mixed pre-bodies and water, then adding them into a granulator, and then spheroidizing and screening.

[0047] As a technical scheme of the present application, the carbonization to the pitch binder pyrolysis forms a carbon connecting layer with a thickness of 50-100 nm.

[0048] As a technical scheme of the present application, the interplanar spacing of the graphitized particles is ≤0.336 nm, and the content of graphite is >95 wt.%.

[0049] As a technical scheme of the present application, the step S5 is followed by post-treatment, which comprises cooling to 600-780℃, heat treatment for 0.5-2.0 h, and then sieving.

[0050] As a technical scheme of the present application, the preparation of the co-carbonized coating agent comprises: swelling the PET micro-powder in an ethanol aqueous solution, adding the coal tar for kneading to obtain a slurry, spray drying the slurry to obtain spherical precursors, oxidizing the spherical precursors, and then carbonizing, grinding, and sieving.

[0051] The third aspect of the present application provides an application of the aforementioned graphite composite negative electrode material as a negative electrode active material in a negative electrode. BRIEF DESCRIPTION OF DRAWINGS

[0052] Figure 1 TEM image of the graphite composite negative electrode material prepared in Example 1.

[0053] Figure 2 TEM image of the graphite composite negative electrode material prepared in Comparative Example 2.

[0054] Figure 3 TEM image of the graphite composite negative electrode material prepared in Example 1 after being cycled in a battery.

[0055] Figure 4 TEM image of the graphite composite negative electrode material prepared in Comparative Example 2 after being cycled in a battery. DETAILED DESCRIPTION

[0056] The graphite composite negative electrode material of the present application can be used alone or mixed with other negative electrode active materials (such as natural graphite, artificial graphite, soft carbon, and / or hard carbon, etc.). The graphite composite negative electrode material can be applied in a secondary battery, which comprises a positive electrode active material and a negative electrode active material. The positive electrode active material comprises at least one of lithium cobaltate-based positive electrode materials, lithium iron phosphate-based positive electrode materials, lithium nickel cobalt manganese acid-based positive electrode materials, and lithium nickel cobalt aluminum acid-based positive electrode materials.

[0057] The Dv50 of the graphite composite negative electrode material of the present application is 18-30 μm, for example, but not limited to, 18 μm, 20 μm, 22 μm, 24 μm, 26 μm, 28 μm, 30 μm. The tap density of the graphite composite negative electrode material is 1.00-1.25 g / cm 3 , for example, but not limited to, 1.00 g / cm 3 , 1.03 g / cm 3 , 1.05 g / cm 3 , 1.10 g / cm 3 , 1.13 g / cm 3 , 1.15 g / cm 3 , 1.20 g / cm 3 , 1.23 g / cm 3 , 1.25 g / cm 3 . The BET of the graphite composite negative electrode material is 2.1-5.5 m 2 / g, for example, but not limited to, 2.1 m 2 / g, 2.2 m 2 / g, 2.3 m 2 / g, 2.4 m 2 / g, 2.5 m 2 / g, 2.6 m 2 / g, 2.7 m 2 / g, 2.8 m 2 / g, 2.9 m 2 / g, 3.0 m 2 / g, 3.1 m 2 / g, 3.5 m 2 / g, 3.8 m 2 / g, 4.0 m 2 / g, 4.5 m 2 / g, 5.0 m 2 / g, 5.5 m 2 / g. The d002 of the graphite composite negative electrode material is 0.33-0.34 nm, for example, but not limited to, 0.330 nm, 0.331 nm, 0.332 nm, 0.333 nm, 0.334 nm, 0.335 nm, 0.336 nm, 0.337 nm, 0.338 nm, 0.339 nm, 0.340 nm.

[0058] The graphite composite negative electrode material of the present application comprises graphitized particles and a carbon coating layer covering the graphitized particles. The thickness of the carbon coating layer is 10-20 nm, and as an example, the thickness can be but is not limited to 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, 15 nm, 16 nm, 17 nm, 18 nm, 19 nm, 20 nm. The graphite composite negative electrode material has a hierarchical pore structure, which comprises a first pore structure, a second pore structure and a third pore structure, the first pore structure is a nanopore with an average pore diameter of 2-50 nm, the second pore structure is a nanopore with an average pore diameter of less than 2 nm, and the third pore structure is a micropore with an average pore diameter of greater than 0.1 μm. The volume proportions of the first pore structure, the second pore structure and the third pore structure in the hierarchical pore structure are 45-50%, 30-40% and 15-25%, respectively.

[0059] The preparation raw materials of the graphite composite negative electrode material of the present application comprise, in parts by weight, 70-100 parts of carbon skeleton material, 7-10 parts of pitch binder, 2-3 parts of conductive carbon black and 2-5 parts of co-carbonization coating agent.

[0060] The weight fraction of the carbon skeleton material can be, but is not limited to, 70 parts, 75 parts, 80 parts, 85 parts, 90 parts, 95 parts, 100 parts. The carbon skeleton material includes petroleum coke tail powder, needle coke and porous hard carbon. As a technical solution, the carbon skeleton material also includes natural flake graphite. If the carbon skeleton material includes petroleum coke tail powder, needle coke, natural flake graphite and porous hard carbon, the weight ratio of the four can be 10-15:45-55:10-15:5-15. As an example, the weight ratio can be, but is not limited to, 10:45:10:5, 10:50:10:5, 10:55:10:5, 10:50:15:5, 10:50:15:10, 10:50:15:15, 13:45:10:5, 13:50:10:5, 13:55:10:5, 13:50:15:5, 13:50:15:10, 13:50:15:15, 15:45:10:5, 15:50:10:5, 15:55:10:5, 15:50:15:5, 15:50:15:10, 15:50:15:15. The petroleum coke tail powder is obtained by purifying the tail powder of the raw material for producing medium coke, which includes impurity removal by acid immersion, alkali washing and neutralization and drying in sequence. As an example, the tail powder of the raw material for producing medium coke can be soaked in 1M hydrochloric acid at 80°C for 1h to remove soluble metal impurities, then treated with 1M hydrofluoric acid at 50°C for 0.5h to remove silicon and aluminum impurities, and finally neutralized with 0.1M sodium hydroxide, washed with deionized water until the pH is about 7, and dried at 100°C for 2h to obtain the petroleum coke tail powder. The Dv50 of the needle coke is 15-35μm. The Dv50 of the petroleum coke tail powder is 1-10μm, and the carbon content is >95%. The Dv50 of the natural flake graphite is 10-25μm, and the carbon content is >99%. The specific surface area of the porous hard carbon is 50-150m 2 / g, the pore size is 2-10nm, the pore volume is 0.20-0.45cm 3 / g, and the porosity is 35-55%. The low specific surface area of the porous hard carbon can ensure that enough lithium ions can enter while controlling the growth of the SEI area, balancing the first coulombic efficiency and the cycle stability. The moderate pore volume and porosity can ensure good wettability and ion transport of the electrolyte while maintaining a high tap density, so as to balance the energy density and cycle stability.

[0061] Among them, the stacking voids between the particles of the petroleum coke tail powder, the needle coke and the porous hard carbon after carbonization are macroscopic fluid / electrolyte wetting channels, which produce microcracks or microgaps under the action of thermal shrinkage of carbonization or graphitization and the difference in thermal expansion coefficient of different components. The channels and microcracks or microgaps form a third pore structure of the micropore level. The pore structure of the porous hard carbon itself can constitute a first pore structure.

[0062] The asphalt binder can be, but is not limited to, 7 parts, 8 parts, 9 parts, 10 parts. The viscosity of the asphalt binder is 1000-1200 Pa·s, and the softening point is 75-100 DEG C. The asphalt binder can be coal tar binder, petroleum asphalt binder, etc. The asphalt binder is decomposed and carbonized to form a carbon connecting layer and generate a nanoscale gap at the interface, which can constitute a second pore structure.

[0063] The conductive carbon black can be, but is not limited to, 2.0 parts, 2.1 parts, 2.2 parts, 2.3 parts, 2.4 parts, 2.5 parts, 2.6 parts, 2.7 parts, 2.8 parts, 2.9 parts, 3.0 parts. The Dv50 of the conductive carbon black is 40-60 nm, and as an example, the Dv50 can be, but is not limited to, 40 nm, 42 nm, 44 nm, 46 nm, 48 nm, 50 nm, 52 nm, 54 nm, 56 nm, 58 nm, 60 nm.

[0064] The co-carbonization coating agent can be, but is not limited to, 2 parts, 3 parts, 4 parts, 5 parts. The co-carbonization coating agent includes a carbonide of a PET micro powder and a coal tar mixture. The Dv50 of the PET micro powder is 20-50 μm, and as an example, can be, but is not limited to, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm. The PET micro powder can be obtained by crushing recycled PET bottles. The softening point of the coal tar is 90-110 DEG C, and as an example, can be, but is not limited to, 90 DEG C, 92 DEG C, 94 DEG C, 96 DEG C, 98 DEG C, 100 DEG C, 102 DEG C, 104 DEG C, 106 DEG C, 108 DEG C, 110 DEG C. The weight ratio of the PET micro powder and the coal tar is 1-3:7-9, and as an example, the weight ratio can be, but is not limited to, 1:7, 1:8, 1:9, 2:7, 2:8, 2:9, 3:7, 3:8, 3:9, and the viscosity of the system is controllable and the residual carbon is 70 wt.% or more. The co-carbonization coating agent forms a carbon coating layer.

[0065] The preparation method of the graphite composite negative electrode material of the present application comprises the following steps.

[0066] S1, adding an asphalt binder and a conductive carbon black to a carbon skeleton material to obtain a mixed prebody by stirring, wherein the carbon skeleton material includes petroleum coke tail powder, needle coke and porous hard carbon.

[0067] S2, wet granulation of the mixed prebody to obtain a spherical granule by sieving.

[0068] S3, carbonization of the spherical granule in an inert atmosphere to obtain a carbonized particle.

[0069] S4, graphitization of the carbonized particle in an inert atmosphere to obtain a graphitized particle.

[0070] S5, blending the graphitized particles with the co-carbonization coating agent and heat treating in an inert atmosphere to perform carbon coating.

[0071] The wet granulation of step S2 includes mixing the mixed pre-bodies and water, then adding into a granulator, and then spheroidizing and screening to obtain spherical granules with Dv50 of 10-20 μm. Water is added and stirred to mix to have a certain low viscosity to facilitate entering the granulator for wet granulation, but the viscosity cannot be too low, and the integrity and strength of the granules during granulation need to be ensured.

[0072] The spheroidizing rotation speed, the screening times and the mesh can be determined according to the situation, but the spherical granules with Dv50 of 10-20 μm need to be obtained.

[0073] The carbonization temperature of step S3 is 500-600°C, and as an example, the temperature can be but is not limited to 500°C, 510°C, 520°C, 530°C, 540°C, 550°C, 560°C, 570°C, 580°C, 590°C, 600°C. The heating rate is 1-10°C / min, and as an example, the heating rate can be but is not limited to 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, 10°C / min. The carbonization time is 1-2h, and as an example, the time can be but is not limited to 1h, 2h. The inert atmosphere in carbonization is selected from nitrogen, helium, neon or argon, and the flow rate of the inert atmosphere is 120-220 mL / min, and as an example, can be but is not limited to 120 mL / min, 140 mL / min, 160 mL / min, 180 mL / min, 200 mL / min, 220 mL / min. The carbonization of step S3 makes the pitch binder completely pyrolyze, and forms a carbon connecting layer with a thickness of 50-100 nm. By controlling the amount of pitch binder and the carbonization temperature and time, the thickness of the carbon connecting layer can be accurately controlled to facilitate the subsequent formation of a dense coating layer and connection with the micro / nano pores to form a second pore structure.

[0074] The temperature of the graphitization in step S4 is 2700-3000°C, and as examples, the temperature can be but is not limited to 2700°C, 2750°C, 2800°C, 2850°C, 2900°C, 2950°C, 3000°C. The temperature rising rate is 1-10°C / min, and as examples, the temperature rising rate can be but is not limited to 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, 10°C / min. The time is 5-8h, and as examples, the time can be but is not limited to 5h, 6h, 7h, 8h. The inert atmosphere in the graphitization is selected from nitrogen, helium, neon or argon, and the flow rate of the inert atmosphere is 120-220mL / min, and as examples, can be but is not limited to 120mL / min, 140mL / min, 160mL / min, 180mL / min, 200mL / min, 220mL / min. The interplanar spacing of the obtained graphitized particles after graphitization is ≤0.336nm, and the content of graphite is >95wt.%.

[0075] In step S5, the co-carbonized coating agent includes carbonates of the mixture of PET micro powder and coal tar. The weight ratio of the PET micro powder and the coal tar is 1-3:7-9, and as examples, the weight ratio can be but is not limited to 1:7, 1:8, 1:9, 2:7, 2:8, 2:9, 3:7, 3:8, 3:9, and the viscosity of the system can be controlled and the residual carbon can be up to 70wt.% or more by using this weight ratio. The preparation of the co-carbonized coating agent includes: swelling the PET micro powder in an ethanol aqueous solution, adding the coal tar to knead to obtain a slurry, spray drying the slurry to obtain spherical precursors, oxidizing and then carbonizing the spherical precursors, grinding and sieving. In the preparation of the co-carbonized coating agent, the PET micro powder is swelled to destroy the crystal and activate the hydroxyl group, and then the ester exchange occurs between the PET oligomer and the aromatic ring of the coal tar tar during the kneading process to obtain a homogeneous slurry, which is instantaneously solidified into spherical precursors during spray drying, and the spherical precursors are oxidized in air to further crosslink the system, and then carbonized to obtain a co-carbonized coating agent with high crosslinking degree.

[0076] The temperature of the heat treatment is 800-1000℃, and as an example, the temperature can be but is not limited to 800℃, 820℃, 850℃, 870℃, 900℃, 920℃, 950℃, 970℃, 1000℃. The heating rate is 1-10℃ / min, and as an example, the heating rate can be but is not limited to 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, 10℃ / min. The time is 1-2h, and as an example, the time can be but is not limited to 1.0h, 1.5h, 2.0h. The inert atmosphere in the heat treatment is selected from nitrogen, helium, neon or argon, and the flow rate of the inert atmosphere is 120-220mL / min, and as an example, can be but is not limited to 120mL / min, 140mL / min, 160mL / min, 180mL / min, 200mL / min, 220mL / min. During the heat treatment, the glassy carbon left after the carbonization of the PET micro-powder and the coal tar can first penetrate into the micro-cracks, step sites and micropores on the surface of the graphite / carbon, and shrinkage occurs during the carbonization process. This shrinkage will “nail” the carbon film into the pits on the surface of the substrate, achieving mechanical-physical interlocking rather than just surface adhesion. The volume of the co-carbonized coating agent shrinks (shrinks), and this process generates inward shrinkage stress and presses the co-carbonized coating agent to the surface of the graphitized particles, thereby improving the contact tightness.

[0077] After step S5, post-treatment is further included, which comprises reducing the temperature to 600-780℃, and then performing heat treatment for 0.5-2.0h, and then screening, and further heat treatment to stabilize the structure of the coating layer. As an example, the reduced temperature can be but is not limited to 600℃, 620℃, 640℃, 660℃, 680℃, 700℃, 720℃, 740℃, 760℃, 780℃.

[0078] In order to better illustrate the purpose, technical scheme and beneficial effects of the present application, the present application will be further described below in combination with specific examples. It should be noted that the following implementation of the method is a further explanation and description of the present application, and should not be regarded as a limitation of the present application.

[0079] Example 1 This example is a graphite composite negative electrode material. The raw materials for preparing the graphite composite negative electrode material include, in parts by weight, 15 parts of petroleum coke tail powder (Dv50 is 5μm, carbon content is >95%), 50 parts of needle coke (Dv50 is 20μm), 15 parts of natural flake graphite (Dv50 is 15μm, carbon content is >99%), 5 parts of hard carbon (made of coconut shell, BET is 80m 2 / g, pore size is 5nm, pore volume is 0.35cm 3 / g, porosity of 45%), 8 parts of pitch binder (viscosity of 1052 Pa·s, softening degree of 85℃), 3 parts of conductive carbon black (C65, Dv50 of 50 nm) and 4 parts of co-carbonized coating agent.

[0080] The preparation of the petroleum coke tailings is as follows: 100 g of coke raw material tailings and 1 L of 1 M HCl are added to a glass reaction kettle with a stirring device, and stirring is performed at 80℃ for 6 h (rotation speed of 200 rpm) to remove soluble metal impurities; the solid is filtered out and washed with deionized water until the pH is 7, and then transferred to another reaction kettle, 1 M HF solution is added, and stirring is performed at 50℃ for 3 h to remove insoluble impurities such as silicon and aluminum; then 0.1 M NaOH solution is used for neutralization, and finally washed with deionized water until neutral; the powder is placed in a vacuum oven and dried at 100℃ for 2 h to obtain purified tailings. A small amount of the purified tailings is taken for XRF determination (such as PANalytical Axios), and the metal impurity content is reduced to <0.1 wt.%.

[0081] The preparation of the co-carbonized coating agent is as follows: the recycled PET bottle is crushed to Dv50 of 30-40 μm, swelled in 1 wt.% ethanol-water solution at 80℃ for 30 min; and the softening point of the coal tar is 95±3℃, which is added into a 150℃ kneader at a weight ratio of 2:8 to shear for 20 min to obtain a slurry; the slurry is spray dried at 180℃ (nitrogen protection), and instantaneously solidified into spherical precursors with Dv50 of 10-15 μm; the spherical precursors are oxidized (heated at 250℃ for 1 h in air atmosphere); and then carbonized at 1000℃ for 4 h under nitrogen atmosphere at a heating rate of 3℃ / min; and sieved with a 325 mesh screen after airflow milling to Dv50 of 5-10 μm.

[0082] The preparation method of the graphite composite negative electrode material of the embodiment includes the following steps.

[0083] S1, in a double-shaft mortar mixer, petroleum coke tailings, needle coke, natural flake graphite, hard carbon, pitch binder, and conductive carbon black are dry mixed at a rotation speed of 100 rpm for 10 min, distilled water is slowly added (total amount is 10% of the weight of the previous powder), and stirring is continued for 30 min until a viscous and uniform slurry is formed, which is a mixed prebody.

[0084] S2, the mixed prebody is sent into a Φ300 mm drum granulator (rotation speed of 20 r / min), and after spheroidization for 30 min, it is sieved through two-stage vibration screens of 40 μm and 10 μm to retain spherical granules with Dv50 of 10-20 μm. The Dv50 of the spherical granules is measured by a laser particle size analyzer (Malvern Mastersizer 3000) to be 12 μm, the span is about 1.2, and the tap density test gives a tap density of 0.85 g / cm 3 .

[0085] S3, the spherical granules were placed in a tube furnace, high-purity nitrogen was introduced (flow rate was 200 mL / min), and the temperature was raised to 550℃ at a rate of 10℃ / min and maintained for 1.5 h, and then reduced to room temperature at a rate of 5℃ / min, to obtain carbonized particles. TEM (JEOL JEM-2100) was used to determine that the carbon connecting layer formed was about 60 nm, and the specific surface area measured by BET was 5.2 m 2 / g.

[0086] S4, the carbonized particles were loaded into a graphitization resistance furnace, and the temperature was raised to 2800℃ at a rate of 8℃ / min under a high-purity argon atmosphere and maintained for 6 h, and then reduced to room temperature at a rate of 3℃ / min, to obtain graphitized particles. XRD (CuKα, Bruker D8 Advance) was used to test the (002) peak position of the graphitized particles 2θ≈26.60°, and the calculation d-spacing≈0.3359 nm (d=λ / 2sinθ), the crystallinity >96%, and the Raman spectrum (Renishaw inVia) ID / IG≈0.12.

[0087] S5, the graphitized particles and the co-carbonization coating agent were mixed and transferred into a tube furnace (nitrogen atmosphere, flow rate was 150 mL / min), and the temperature was raised to 900℃ at a rate of 5℃ / min and maintained for 1 h, and then treated at 700℃ under a nitrogen atmosphere for 0.5 h, and then cooled to room temperature, and then sieved.

[0088] The prepared graphite composite negative electrode material was characterized by TEM (JEOL JEM-2100), and the results are shown in Figure 1 , and it can be seen that the material surface shows a uniform carbon layer. Figure 1

[0089] Example 2 This example is a graphite composite negative electrode material. The preparation raw materials of the graphite composite negative electrode material include, in parts by weight, 13 parts of petroleum coke tail powder (Dv50 is 10 μm, carbon content >95%), 50 parts of needle coke (Dv50 is 30 μm), 10 parts of natural flake graphite (Dv50 is 15 μm, carbon content >99%), 10 parts of hard carbon (made of coconut shell, BET is 80 m 2 / g, pore size is 5 nm, pore volume is 0.35 cm 3 / g, porosity is 45%), 10 parts of pitch binder (viscosity is 1090 Pa·s, softening degree is 90℃), 2 parts of conductive carbon black (C65, Dv50 is 50 nm), and 5 parts of co-carbonization coating agent.

[0090] ​The petroleum coke tail powder is prepared as follows: 100 g of coke raw material tail powder and 1.5 L of 1M HCl are added into a glass reaction kettle with a stirring device, and stirring is performed at 70°C for 5 h (rotation speed is 250 rpm) to remove soluble metal impurities; the solid is filtered out, washed with deionized water until the pH is 7, transferred to another reaction kettle, 1M HF solution is added, and stirring is performed at 60°C for 4 h to remove insoluble impurities such as silicon and aluminum; then, 0.1M NaOH solution is used for neutralization, and finally, deionized water is used for washing until neutral; the powder is placed in a vacuum oven and dried at 100°C for 3 h to obtain the purified tail powder. A small amount of the purified tail powder is taken for XRF determination (such as PANalytical Axios), and the content of metal impurities is reduced to <0.1 wt.%.

[0091] The preparation of the co-carbonized coating agent is as follows: the recycled PET bottle is crushed to Dv50 of 20-30 μm, swelled in 1 wt.% ethanol-water solution at 80°C for 45 min; and the softening point of the coal tar is 100±3°C, which is added into a 150°C kneader at a weight ratio of 1:9 to shear for 30 min to obtain a slurry; the slurry is spray dried at 180°C (nitrogen protection), and instantaneously solidified into spherical precursors with Dv50 of 10-15 μm; the spherical precursors are oxidized (heated at 250°C for 1 h in an air atmosphere); and then carbonized at 900°C for 2 h under a nitrogen atmosphere at a rate of 5°C / min; and sieved with a 325 mesh screen.

[0092] The preparation method of the graphite composite negative electrode material of the embodiment includes the following steps.

[0093] S1, in a double-shaft mortar mixer, petroleum coke tail powder, needle coke, natural flake graphite, hard carbon, pitch binder, and conductive carbon black are dry mixed at a rotation speed of 100 rpm for 10 min, distilled water (total amount is 10% of the weight of the previous powder) is slowly added dropwise, and stirring is continued for 30 min until a viscous and uniform slurry is formed, which is a mixed prebody.

[0094] S2, the mixed prebody is sent into a Φ300 mm drum granulator (rotation speed is 25 r / min), and spheroidization is performed for 30 min, and then sieved through two-stage vibration screens of 50 μm and 20 μm, and the spherical granules with Dv50 of 15-25 μm are retained. The Dv50 of the spherical granules is 15 μm, the span is about 1.3, and the tap density test obtains a tap density of 0.83 g / cm 3 .

[0095] S3, the spherical granules were placed in a tube furnace, high-purity nitrogen was introduced (flow rate was 200 mL / min), and the temperature was raised to 600℃ at a rate of 5℃ / min and maintained for 1.0 h, then reduced to room temperature at a rate of 4℃ / min, to obtain carbonized particles. TEM (JEOL JEM-2100) was used to measure that the formed carbon connecting layer was about 65 nm, and the BET specific surface area was 5.1 m 2 / g.

[0096] S4, the carbonized particles were loaded into a graphitization resistance furnace, and the temperature was raised to 3000℃ at a rate of 5℃ / min under high-purity argon atmosphere and maintained for 7 h, then reduced to room temperature at a rate of 3℃ / min, to obtain graphitized particles. XRD (CuKα, Bruker D8 Advance) was used to test that the (002) peak position of the graphitized particles was 2θ≈26.60°, the calculated d-spacing was≈0.3357 nm (d=λ / 2sinθ), the crystallinity was >96%, and the Raman spectrum (Renishaw inVia) ID / IG≈0.12.

[0097] S5, the graphitized particles and co-carbonization coating agent were mixed and transferred into a tube furnace (nitrogen atmosphere, flow rate was 180 mL / min), the temperature was raised to 950℃ at a rate of 5℃ / min and maintained for 1 h, then treated at 700℃ under argon atmosphere for 0.5 h, cooled to room temperature, and sieved.

[0098] Example 3 This example is a kind of graphite composite negative material. The preparation raw materials of the graphite composite negative material include 12 parts of petroleum coke tail powder (Dv50 is 8 μm, carbon content is >95%), 51 parts of needle coke (Dv50 is 20 μm), 13 parts of natural flake graphite (Dv50 is 25 μm, carbon content is >99%), 8 parts of hard carbon (made of coconut shell, BET is 100 m 2 / g, pore size is 10 nm, pore volume is 0.30 cm 3 / g, porosity is 30%), 9 parts of pitch binder (viscosity is 1200 Pa·s, softening degree is 85℃), 2 parts of conductive carbon black (C65, Dv50 is 60 nm) and 5 parts of co-carbonization coating agent, all by weight.

[0099] The preparation of the petroleum coke tailings is as follows: 100 g of coke raw material tailings and 1 L of 1 M HC1 are added to a glass reaction kettle with a stirring device, and stirred at 90°C for 5 h (rotational speed of 250 rpm) to remove soluble metal impurities; the solid is filtered out, washed with deionized water until the pH is 7, transferred to another reaction kettle, 1 M HF solution is added, and stirred at 65°C for 2 h to remove insoluble impurities such as silicon and aluminum; then neutralized with 0.1 M NaOH solution, and finally washed with deionized water until neutral; the powder is placed in a vacuum oven and dried at 90°C for 3 h to obtain purified tailings. A small amount of the purified tailings is taken for XRF determination (such as PANalytical Axios), and the content of metal impurities is reduced to <0.1 wt.%.

[0100] The preparation of the co-carbonized coating agent is as follows: the recycled PET bottles are crushed to a Dv50 of 30-40 μm, swelled in a 2 wt.% ethanol-water solution at 85°C for 30 min; and the coal tar with a softening point of 95±3°C is added to a 130°C kneader at a weight ratio of 2:7 and sheared for 30 min to obtain a slurry; the slurry is spray dried at 180°C (under nitrogen protection), instantaneously solidified into spherical precursors with a Dv50 of 10-15 μm; the spherical precursors are oxidized (heated at 250°C for 1 h under air atmosphere); and then carbonized at 900°C for 5 h under nitrogen atmosphere at a heating rate of 4°C / min; and sieved with a 325 mesh sieve while the Dv50 is 5-10 μm.

[0101] The preparation method of the graphite composite negative electrode material of the embodiment includes the following steps.

[0102] S1, in a double-shaft mortar mixer, the petroleum coke tailings, needle coke, natural flake graphite, hard carbon, pitch binder, and conductive carbon black are dry mixed at a rotational speed of 150 rpm for 8 min, distilled water is slowly added (total amount is 8% of the weight of the previous powder), and stirring is continued for 20 min until a viscous and uniform slurry is formed, which is a mixed prebody.

[0103] S2, the mixed prebody is fed into a Φ300 mm drum granulator (rotational speed of 20 r / min), and spheroidized for 20 min, then sieved through two-stage vibration sieves of 40 μm and 10 μm, and the spherical granules with a Dv50 of 10-20 μm are retained. The Dv50 of the spherical granules is 13 μm, the span is about 1.2, and the tap density test shows that the tap density is 0.84 g / cm 3 .

[0104] S3, the spherical granules were placed in a tube furnace, high-purity nitrogen was introduced (flow rate was 200 mL / min), and the temperature was raised to 500℃ at a rate of 10℃ / min and maintained for 1.0 h, then reduced to room temperature at a rate of 5℃ / min, to obtain carbonized particles. TEM (JEOL JEM-2100) was used to measure that the carbon connecting layer formed was about 62 nm, and the BET specific surface area was 5.1 m 2 / g.

[0105] S4, the carbonized particles were loaded into a graphitization resistance furnace, and the temperature was raised to 3000℃ at a rate of 8℃ / min under a high-purity argon atmosphere and maintained for 5 h, then reduced to room temperature at a rate of 3℃ / min, to obtain graphitized particles. XRD (CuKα, Bruker D8 Advance) was used to test the (002) peak position of the graphitized particles 2θ≈26.60°, the calculation d-spacing≈0.3357 nm (d=λ / 2sinθ), the crystallinity >96%, and the Raman spectrum (Renishaw inVia) ID / IG≈0.12.

[0106] S5, the graphitized particles and co-carbonization coating agent were mixed and transferred into a tube furnace (argon atmosphere, flow rate was 180 mL / min), the temperature was raised to 950℃ at a rate of 8℃ / min and maintained for 2 h, then treated at 650℃ under an argon atmosphere for 2.0 h, cooled to room temperature, and sieved.

[0107] Example 4 This example is a kind of graphite composite negative material. The preparation raw materials of graphite composite negative material include 10 parts of petroleum coke tail powder (Dv50 is 5 μm, carbon content >95%), 55 parts of needle coke (Dv50 is 20 μm), 15 parts of hard carbon (coconut shell, BET is 80 m 2 / g, pore size is 5 nm, pore volume is 0.35 cm 3 / g, porosity is 45%), 10 parts of pitch binder (viscosity is 1052 Pa·s, softening degree is 85℃), 2 parts of conductive carbon black (C65, Dv50 is 50 nm) and 3 parts of co-carbonization coating agent, by weight.

[0108] The petroleum coke tailings are prepared by adding 100 g of coke raw material tailings and 1 L of 1 M HC1 into a glass reactor with a stirring device, stirring at 90 °C for 5 h (rotation speed of 200 rpm) to remove soluble metal impurities; filtering out the solid, washing with deionized water until the pH is 7, transferring to another reactor, adding 1 M HF solution, stirring at 60 °C for 2 h to remove insoluble impurities such as silicon and aluminum; then neutralizing with 0.1 M NaOH solution, and finally washing with deionized water until neutral; placing the powder in a vacuum oven, drying at 100 °C for 3 h to obtain purified tailings. A small amount of purified tailings is taken for XRF determination (such as PANalytical Axios), and the metal impurity content is reduced to <0.1 wt.%.

[0109] The preparation of the co-carbonized coating agent is as follows: the recycled PET bottle is crushed to Dv50 of 30-40 μm, swelled in a 3 wt.% ethanol-water solution at 80 °C for 30 min; and the softening point of the coal tar is 95±3 °C, which is added into a 140 °C kneader at a weight ratio of 2:9 to shear for 30 min to obtain a slurry; the slurry is spray dried at 180 °C (nitrogen protection), and instantaneously solidified into spherical precursors with Dv50 of 10-15 μm; the spherical precursors are oxidized (heated at 200 °C for 2 h in an air atmosphere); and then carbonized at 950 °C for 6 h at a rate of 5 °C / min in a nitrogen atmosphere; and sieved with a 325 mesh sieve while the Dv50 is 5-10 μm.

[0110] The preparation method of the graphite composite negative electrode material of the embodiment includes the following steps.

[0111] S1, in a double-shaft mortar mixer, the petroleum coke tailings, needle coke, hard carbon, pitch binder, and conductive carbon black are dry mixed at a rotation speed of 80 rpm for 20 min, distilled water is slowly added (total amount is 10% of the weight of the previous powder), and stirring is continued for 45 min until a viscous and uniform slurry is formed, which is a mixed prebody.

[0112] S2, the mixed prebody is sent into a Φ300 mm drum granulator (rotation speed is 35 r / min), and spheroidization is performed for 20 min, then sieved through two-stage vibration sieves of 40 μm and 10 μm, and the spherical granules with Dv50 of 10-20 μm are retained. The Dv50 of the spherical granules is 14 μm, the span is about 1.1, and the tap density test shows that the tap density is about 0.86 g / cm 3 .

[0113] S3, the spherical granules were placed in a tube furnace, high-purity nitrogen was introduced (flow rate was 180 mL / min), and the temperature was raised to 600℃ at a rate of 8℃ / min and maintained for 1.0 h, and then reduced to room temperature at a rate of 3℃ / min, to obtain carbonized particles. TEM (JEOL JEM-2100) was used to measure that the carbon connecting layer formed was about 65 nm, and the specific surface area measured by BET was about 5.1 m 2 / g.

[0114] S4, the carbonized particles were loaded into a graphitization resistance furnace, and the temperature was raised to 2700℃ at a rate of 8℃ / min under a high-purity argon atmosphere and maintained for 8 h, and then reduced to room temperature at a rate of 4℃ / min, to obtain graphitized particles. XRD (CuKα, Bruker D8 Advance) was used to test the (002) peak position of the graphitized particles 2θ≈26.60°, the calculation d-spacing≈0.3358 nm (d=λ / 2sinθ), the crystallinity >96%, and the Raman spectrum (Renishaw inVia) ID / IG≈0.12.

[0115] S5, the graphitized particles and co-carbonization coating agent were mixed and transferred into a tube furnace (nitrogen atmosphere, flow rate was 120 mL / min), and the temperature was raised to 1000℃ at a rate of 8℃ / min and maintained for 2 h, and then treated at 650℃ under a nitrogen atmosphere for 1.0 h, and then cooled to room temperature, and then sieved.

[0116] Comparative Example 1 Natural flake graphite (Dv50 was 15 μm, carbon content >99%) was used as the negative electrode material.

[0117] Comparative Example 2 This comparative example was a graphite composite negative electrode material. The preparation raw materials of the graphite composite negative electrode material included, in parts by weight, 15 parts of petroleum coke tail powder (Dv50 was 5 μm, carbon content >95%), 50 parts of needle coke (Dv50 was 20 μm), 15 parts of natural flake graphite (Dv50 was 15 μm, carbon content >99%), 5 parts of hard carbon (made of coconut shell, BET was 80 m 2 / g, pore size was 5 nm, pore volume was 0.35 cm 3 / g, porosity was 45%), 8 parts of pitch binder (viscosity was 1052 Pa·s, softening degree was 85℃), 3 parts of conductive carbon black (C65, Dv50 was 50 nm), and 4 parts of 10 wt.% phenolic resin / methanol solution.

[0118] The petroleum coke tailings are prepared as follows: 100 g of coke raw material tailings and 1 L of 1 M HCl are added to a glass reaction kettle with a stirring device, and stirred at 80°C for 6 h (rotation speed of 200 rpm) to remove soluble metal impurities; the solid is filtered out, washed with deionized water until the pH is 7, transferred to another reaction kettle, 1 M HF solution is added, and stirred at 50°C for 3 h to remove insoluble impurities such as silicon and aluminum; then neutralized with 0.1 M NaOH solution, and finally washed with deionized water until neutral; the powder is placed in a vacuum oven and dried at 100°C for 2 h to obtain purified tailings. A small amount of the purified tailings is taken for XRF determination (such as PANalytical Axios), and the metal impurity content is reduced to <0.1 wt.%.

[0119] The preparation method of the graphite composite negative electrode material of the present comparative example comprises the following steps.

[0120] S1, in a double-shaft mortar mixer, petroleum coke tailings, needle coke, natural flake graphite, hard carbon, pitch binder, and conductive carbon black are dry mixed at a rotation speed of 100 rpm for 10 min, distilled water (total amount of 10% of the weight of the previous powder) is slowly added dropwise, and stirring is continued for 30 min until a viscous and uniform slurry is formed, which is a mixed prebody.

[0121] S2, the mixed prebody is sent to a Φ300 mm drum granulator (rotation speed of 20 r / min), and spheroidized for 30 min, then sieved through two-stage vibration sieves of 40 μm and 10 μm, and the spherical granules with Dv50 of 10-20 μm are retained. The Dv50 of the spherical granules is measured by a laser particle size analyzer (Malvern Mastersizer 3000) to be 12 μm, the span is about 1.2, and the tap density test shows that the tap density is 0.85 g / cm 3 .

[0122] S3, the spherical granules are placed in a tube furnace, high-purity nitrogen gas is introduced (flow rate of 200 mL / min), the temperature is raised to 550°C at a rate of 10°C / min and maintained for 1.5 h, and then reduced to room temperature at a rate of 5°C / min to obtain carbonized particles. TEM (JEOL JEM-2100) is used to measure that the carbon connecting layer formed is about 60 nm, and the BET specific surface area is 5.2 m 2 / g.

[0123] S4, the carbonized particles were loaded into a graphitization resistance furnace, and were raised to 2800°C at a rate of 8°C / min under a high-purity argon atmosphere and maintained for 6 h, and then were lowered to room temperature at a rate of 3°C / min, to obtain graphitized particles. The graphitized particles were tested by XRD (CuKa, Bruker D8 Advance) to have a (002) peak position 2theta ≈ 26.60°, and a calculated d-spacing ≈ 0.3359 nm (d = λ / 2sintheta), a crystallinity > 96%, and a Raman spectrum (Renishaw inVia) ID / IG ≈ 0.12.

[0124] S5, the graphitized particles were immersed in a phenolic resin / methanol solution, stirred at room temperature for 0.8 h, filtered, and placed in a vacuum drying oven to remove the solvent for 30 min, transferred to a tube furnace (nitrogen atmosphere, flow rate 150 mL / min), raised to 900°C at a rate of 5°C / min and maintained for 1 h, and then treated at 700°C under a nitrogen atmosphere for 0.5 h, cooled to room temperature, and sieved.

[0125] The prepared graphite composite negative electrode material was characterized by TEM (JEOL JEM-2100), and the results are shown in FIG. 2, and it can be seen from FIG. 2 that the coating layer formed on the surface of the material is not uniform. Figure 2 Figure 2 The prepared graphite composite negative electrode material was characterized by TEM (JEOL JEM-2100), and the results are shown in FIG. 2, and it can be seen from FIG. 2 that the coating layer formed on the surface of the material is not uniform.

[0126] Comparative Example 3 The graphite composite negative electrode material of this comparative example was prepared from the following raw materials, by weight fraction: 80 parts of natural flake graphite (Dv50 15 pm, carbon content > 99%), 5 parts of hard carbon (made from coconut shells, BET 80 m 2 / g, pore size 5 nm, pore volume 0.35 cm 3 / g, porosity 45%), 8 parts of pitch binder (viscosity 1052 Pa·s, softening point 85°C), 3 parts of conductive carbon black (C65, Dv50 50 nm), and 4 parts of co-carbonized coating agent.

[0127] The co-carbonized coating agent was prepared as follows: recycled PET bottles were crushed to Dv50 30-40 pm, swelled in a 1 wt.% ethanol-water solution at 80°C for 30 min, and coal tar with a softening point of 95±3°C was added at a weight ratio of 2:8 into a 150°C kneader and sheared for 20 min to obtain a slurry; the slurry was spray dried (nitrogen protection) at 180°C, instantaneously solidified into spherical precursors with Dv50 10-15 pm; the spherical precursors were oxidized (heated at 250°C for 1 h under an air atmosphere); and then carbonized at 1000°C for 4 h under a nitrogen atmosphere at a rate of 3°C / min; and the Dv50 was 5-10 pm using an air flow mill, and sieved using a 325 mesh sieve.

[0128] ​The preparation method of the graphite composite negative electrode material of the present comparative example comprises the following steps.

[0129] S1, in a double-shaft mortar mixer, dry mix natural flake graphite, hard carbon, pitch binder, and conductive carbon black at a rotation speed of 100 rpm for 10 min, slowly drop distilled water (total amount is 10% of the weight of the previous powder), continue to stir for 30 min, until a viscous uniform slurry is formed, which is a mixed prebody.

[0130] S2, the mixed prebody is sent to a Φ300mm drum granulator (rotation speed is 20r / min), after spheroidization for 30 min, it is sieved through two levels of 40μm and 10μm vibrating screens, and the spherical granules with Dv50 of 10-20μm are retained. The Dv50 of the spherical granules is measured by a laser particle size analyzer (Malvern Mastersizer 3000) to be 12μm, the span is about 1.2, and the tap density test obtains a tap density of 0.85g / cm 3 .

[0131] S3, the spherical granules are placed in a tube furnace, high-purity nitrogen gas is introduced (flow rate is 200mL / min), the temperature is raised to 550℃ at a rate of 10℃ / min and maintained for 1.5h, then reduced to room temperature at a rate of 5℃ / min, and carbonized granules are obtained. The TEM (JEOL JEM-2100) is used to measure that the carbon connecting layer formed is about 60nm, and the BET measures that the specific surface area is 5.2m 2 / g.

[0132] S4, the carbonized granules are loaded into a graphitization resistance furnace, under a high-purity argon gas atmosphere, the temperature is raised to 2800℃ at a rate of 8℃ / min and maintained for 6h, then reduced to room temperature at a rate of 3℃ / min, and graphitized granules are obtained. The XRD (CuKα, Bruker D8 Advance) is used to test that the (002) peak position of the graphitized granules is 2θ≈26.60°, the d-spacing is calculated to be≈0.3359nm (d=λ / 2sinθ), the crystallinity is >96%, and the Raman spectrum (Renishaw inVia) ID / IG≈0.12.

[0133] S5, the graphitized granules and co-carbonization coating agent are mixed and transferred into a tube furnace (nitrogen atmosphere, flow rate is 150mL / min), the temperature is raised to 900℃ at a rate of 5℃ / min and maintained for 1h, then treated at 700℃ under a nitrogen atmosphere for 0.5h, cooled to room temperature, and sieved.

[0134] Comparative Example 4 This comparative example is a graphite composite anode material. By weight, the raw materials for preparing the graphite composite anode material include 15 parts petroleum coke tail powder (Dv50 of 5 μm, carbon content >95%), 50 parts needle coke (Dv50 of 20 μm), 20 parts natural flake graphite (Dv50 of 15 μm, carbon content >99%), 8 parts asphalt binder (viscosity 1052 Pa·s, softening degree 85℃), 3 parts conductive carbon black (C65, Dv50 of 50 nm), and 4 parts co-carbonization coating agent.

[0135] The preparation of petroleum coke tail powder is as follows: 100g of coke tail powder and 1L of 1M HCl are added to a glass reactor equipped with a stirrer. The mixture is stirred at 80℃ for 6 hours (200rpm) to remove soluble metal impurities. The solid is filtered out, washed with deionized water until pH 7, and transferred to another reactor. 1M HF solution is added, and the mixture is stirred at 50℃ for 3 hours to remove sparingly soluble impurities such as silicon and aluminum. The mixture is then neutralized with 0.1M NaOH solution and finally rinsed with deionized water until neutral. The powder is placed in a vacuum oven and dried at 100℃ for 2 hours to obtain purified tail powder. A small amount of the purified tail powder is subjected to XRF analysis (such as PANalytical Axios), and its metal impurity content is reduced to <0.1wt.%.

[0136] The co-carbonization coating agent was prepared as follows: recycled PET bottles were crushed to a Dv50 of 30-40 μm and swollen in a 1 wt.% ethanol-water solution at 80°C for 30 min; coal tar with a softening point of 95±3°C was added together with the PET bottles at a weight ratio of 2:8 and sheared in a kneader at 150°C for 20 min to obtain a slurry; the slurry was spray-dried at 180°C (under nitrogen protection) and instantly solidified into a spherical precursor with a Dv50 of 10-15 μm; the spherical precursor was oxidized (heated at 250°C for 1 h in air); then carbonized at 1000°C for 4 h in a nitrogen atmosphere at a rate of 3°C / min; the mixture was then milled with an air jet mill to a Dv50 of 5-10 μm and sieved using a 325 mesh sieve.

[0137] The preparation method of the graphite composite anode material in this comparative example includes the following steps.

[0138] S1. In a twin-shaft mortar mixer, dry mix petroleum coke tail powder, needle coke, natural flake graphite, asphalt binder, and conductive carbon black at 100 rpm for 10 minutes. Slowly add distilled water (total amount is 10% of the weight of the powdered materials) and continue stirring for 30 minutes until a viscous and uniform slurry is formed, which is the premixed mixture.

[0139] S2, the mixed pre-bodies were fed into a Φ300 mm drum granulator (rotating speed was 20 r / min), and after spheroidization for 30 min, the spherical granules with Dv50 of 10-20 μm were screened through two-stage vibration screens of 40 μm and 10 μm. The Dv50 of the spherical granules was 12 μm, the span was about 1.2, and the tap density was 0.85 g / cm 3 .

[0140] S3, the spherical granules were placed in a tube furnace, high-purity nitrogen was introduced (flow rate was 200 mL / min), and the temperature was raised to 550 ℃ at a rate of 10 ℃ / min and maintained for 1.5 h, and then reduced to room temperature at a rate of 5 ℃ / min, to obtain carbonized particles. The carbon connecting layer formed was about 60 nm, as determined by TEM (JEOL JEM-2100), and the specific surface area was 5.2 m 2 / g, as determined by BET.

[0141] S4, the carbonized particles were loaded into a graphitization resistance furnace, and under a high-purity argon atmosphere, the temperature was raised to 2800 ℃ at a rate of 8 ℃ / min and maintained for 6 h, and then reduced to room temperature at a rate of 3 ℃ / min, to obtain graphitized particles. The (002) peak position of the graphitized particles was 2θ≈26.60°, as determined by XRD (CuKα, Bruker D8 Advance), the d-spacing was calculated to be ≈0.3359 nm (d=λ / 2sinθ), the crystallinity was >96%, and the Raman spectrum (Renishaw inVia) ID / IG≈0.12.

[0142] S5, the graphitized particles and the co-carbonization coating agent were mixed and transferred into a tube furnace (nitrogen atmosphere, flow rate was 150 mL / min), and the temperature was raised to 900 ℃ at a rate of 5 ℃ / min and maintained for 1 h, and then treated at 700 ℃ under a nitrogen atmosphere for 0.5 h, and then cooled to room temperature, and then screened.

[0143] Comparative Example 5 This comparative example was a graphite composite negative electrode material. The raw materials for preparing the graphite composite negative electrode material included, by weight fraction, 15 parts of petroleum coke tail powder (Dv50 was 5 μm, carbon content was >95%), 50 parts of needle coke (Dv50 was 20 μm), 15 parts of natural flake graphite (Dv50 was 15 μm, carbon content was >99%), 5 parts of hard carbon (made of coconut shells, BET was 80 m 2 / g, pore size was 5 nm, pore volume was 0.35 cm 3 / g, porosity was 45%), 3 parts of conductive carbon black (C65, Dv50 was 50 nm), and 4 parts of co-carbonization coating agent.

[0144] The petroleum coke tailings are prepared by adding 100 g of coke raw material tailings and 1 L of 1 M HC1 into a glass reactor with stirring device, stirring at 80 °C for 6 h (rotation speed of 200 rpm) to remove soluble metal impurities; filtering out the solid, washing with deionized water until the pH is 7, transferring to another reactor, adding 1 M HF solution, stirring at 50 °C for 3 h to remove insoluble impurities such as silicon and aluminum; then neutralizing with 0.1 M NaOH solution, and finally washing with deionized water until neutral; placing the powder in a vacuum oven, drying at 100 °C for 2 h to obtain purified tailings. A small amount of purified tailings is taken for XRF determination (such as PANalytical Axios), and the metal impurity content is reduced to <0.1 wt.%.

[0145] The preparation of the co-carbonized coating agent is as follows: the recycled PET bottle is crushed to Dv50 of 30-40 μm, swelled in 1 wt.% ethanol-water solution at 80 °C for 30 min; and the softening point of the coal tar is 95±3 °C, which is added into a 150 °C kneader at a weight ratio of 2:8 to shear for 20 min to obtain a slurry; the slurry is spray dried at 180 °C (nitrogen protection), and instantaneously solidified into spherical precursors with Dv50 of 10-15 μm; the spherical precursors are oxidized (heated at 250 °C for 1 h in air atmosphere); and then carbonized at 1000 °C for 4 h at a rate of 3 °C / min in nitrogen atmosphere; and sieved with a 325 mesh screen while the Dv50 is 5-10 μm.

[0146] The preparation method of the graphite composite negative electrode material of the present comparative example comprises the following steps.

[0147] S1, in a double-shaft mortar mixer, the petroleum coke tailings, needle coke, natural flake graphite, hard carbon, and conductive carbon black are dry mixed at a rotation speed of 100 rpm for 10 min, distilled water is slowly added (total amount is 10% of the weight of the previous powder), and stirring is continued for 30 min until a viscous and uniform slurry is formed, which is a mixed prebody.

[0148] S2, the mixed prebody is sent into a Φ300 mm drum granulator (rotation speed of 20 r / min), and spheroidized for 30 min, then sieved through two-stage vibration screens of 40 μm and 10 μm, and the spherical granules with Dv50 of 10-20 μm are retained. The Dv50 of the spherical granules is 12 μm, the span is about 1.2, and the tap density test shows that the tap density is 0.85 g / cm 3 .

[0149] S3, the spherical granules were placed in a tube furnace, high-purity nitrogen was introduced (flow rate was 200 mL / min), and the temperature was raised to 550℃ at a rate of 10℃ / min and maintained for 1.5 h, and then reduced to room temperature at a rate of 5℃ / min, to obtain carbonized particles. TEM (JEOL JEM-2100) was used to measure that the formed carbon connecting layer was about 60 nm, and the BET specific surface area was 5.2 m 2 / g.

[0150] S4, the carbonized particles were loaded into a graphitization resistance furnace, and the temperature was raised to 2800℃ at a rate of 8℃ / min under a high-purity argon atmosphere and maintained for 6 h, and then reduced to room temperature at a rate of 3℃ / min, to obtain graphitized particles. XRD (CuKα, Bruker D8 Advance) was used to test the (002) peak position of the graphitized particles 2θ≈26.60°, and the calculation d-spacing≈0.3359 nm (d=λ / 2sinθ), the crystallinity >96%, and the Raman spectrum (Renishaw inVia) ID / IG≈0.12.

[0151] S5, the graphitized particles and co-carbonization coating agent were mixed and transferred into a tube furnace (nitrogen atmosphere, flow rate was 150 mL / min), and the temperature was raised to 900℃ at a rate of 5℃ / min and maintained for 1 h, and then treated at 700℃ under a nitrogen atmosphere for 0.5 h, and then cooled to room temperature, and then sieved.

[0152] The graphite composite negative electrode materials in Examples 1 to 4 and Comparative Examples 2 to 5 and the natural flake graphite in Comparative Example 1 were subjected to physical property tests, and the results are shown in Table 1.

[0153] The test conditions were as follows: (1) Particle size test was performed using a Malvern laser particle size analyzer MS3000.

[0154] (2) Specific surface area was measured using a Micromeritics specific surface area analyzer Tristar 3020.

[0155] (3) Tap density was tested using a Dandong Bettersize BT-302 tap density instrument.

[0156] (4) Pore volume and pore size distribution curves were obtained by nitrogen isothermal adsorption-desorption curves Table 1 Physical property test results of graphite materials in Examples 1 to 4 and Comparative Examples 1 to 5

[0157] The graphite composite negative electrode materials in Examples 1 to 4 and Comparative Examples 2 to 5 and the natural flake graphite in Comparative Example 1 were subjected to electrochemical performance tests, and the test conditions were as follows, and the test results are shown in Table 2.

[0158] (1) Capacity and initial performance test The graphite composite negative electrode materials in Examples 1 to 4 and Comparative Examples 2 to 5 and the natural flake graphite in Comparative Example 1 were respectively mixed with CMC, SBR, conductive carbon black C65 at a mass ratio of 99:1:1:2, and an appropriate amount of N-methyl pyrrolidone was added as a solvent to make a slurry, which was then uniformly coated on a 9 μm copper foil, and vacuum dried at 120°C for 2 h, and rolled to prepare a negative electrode sheet with a loading of 3.0 mg / cm 2 The CR2032 button cell was assembled in an inert gas glove box using a lithium metal sheet as the counter electrode, 1 mol / L LiPF6 as the solute, EC:DMC:EMC = 1:1:1 (v / v) as the solvent, and a polypropylene microporous membrane as the separator. The charge and discharge test of the button cell was performed on a battery test system of Blue Electric Co., Ltd., maintained at a constant temperature of 25±1°C, with a constant current rate of 0.5C and an EIS frequency of 10 5 ~10 -2 Hz (Bio-Logic VMP3), and a CV scan of 0.1 mV / s was performed to obtain the initial discharge capacity and the first coulombic efficiency, and the capacity after 300 cycles was obtained and the capacity retention rate after 300 cycles was calculated. The capacity retention rate at the 300th cycle was the ratio of the capacity at the 300th cycle to the initial discharge capacity.

[0159] Table 2 Electrochemical performance test results of the graphite materials in Examples 1 to 4 and Comparative Examples 1 to 5

[0160] According to the results in Tables 1 and 2, the graphite composite negative electrode materials in Examples 1 to 4 have a large specific surface area, and have nanometer pores with an average pore size of 2-50 nm, nanometer pores with an average pore size of less than 2 nm, and micrometer pores with an average pore size of more than 0.1 μm, and have a hierarchical pore structure, so they exhibit better electrochemical performance in Table 2.

[0161] In addition, after the batteries in Example 1 and Comparative Example 2 were cycled for 300 cycles, the negative electrodes were taken out for SEM analysis, and the results are shown in Figure 3 and Figure 4 As can be seen from the figures, the SEI film in Example 1 is complete and the coating layer is complete, while the coating film in Comparative Example 2 is only partially retained, indicating that the carbide including PET powder and coal tar mixture used as the coating material in Example 1 has a high contact density with the graphitized particles, so it can form a protective film on the surface of the graphitized particles even after long cycling.

[0162] It should be pointed out finally that the above embodiments are only used to illustrate the technical solutions of the present application and not to limit the protection scope of the present application, and although the present application has been described in detail with reference to the preferred embodiments, it is not limited to the listed in the embodiments, and those skilled in the art should understand that the technical solutions of the present application can be modified or replaced equivalently without departing from the essence and scope of the technical solutions of the present application.

Claims

1. A graphite composite negative electrode material, characterized by, The multi-level pore structure includes a first pore structure, a second pore structure and a third pore structure, the first pore structure is nanopore and the average pore size is 2-50 nm, the second pore structure is nanopore and the average pore size is less than 2 nm, and the third pore structure is micropore and the average pore size is greater than 0.1 μm, the carbon coating layer includes a graphitized particle and a carbon coating layer covering the graphitized particle, the preparation raw materials include 70-100 parts of a carbon skeleton material, 7-10 parts of a pitch binder, 2-3 parts of conductive carbon black and 2-5 parts of a co-carbonization coating agent, the carbon skeleton material includes petroleum coke tail powder, needle coke and porous hard carbon, the co-carbonization coating agent includes a carbonized product of a PET powder and a coal tar mixture, and the carbon coating layer is made of the co-carbonization coating agent.

2. The graphite composite negative material according to claim 1, characterized in that, The carbon skeleton material further includes natural flake graphite.

3. The graphite composite negative material according to claim 2, characterized in that, The carbon skeleton material includes petroleum coke tail powder, needle coke, natural flake graphite and porous hard carbon, and the weight ratio of the four is 10-15:45-55:10-15:5-15.

4. The graphite composite negative material of claim 1, wherein, The petroleum coke tail powder is obtained by purifying tail powder of a raw material for producing medium coke.

5. The graphite composite negative material according to claim 4, characterized in that, The purification includes impurity removal by acid immersion, alkali washing and neutralization and drying in sequence. 6.The graphite composite negative material of claim 2, characterized in that, At least one of the following features (i) to (xv) is included: (i) Dv50 of the graphite composite negative electrode material is 18-30 μm; (ii) the tap density of the graphite composite negative electrode material is 1.00-1.25 g / cm 3 ; (iii) the specific surface area of the graphite composite negative electrode material is 2.1-5.5 m 2 / g; (iv) d002 of the graphite composite negative electrode material is 0.33-0.34 nm; (v) the thickness of the carbon coating layer is 10-20 nm; (vi) Dv50 of the needle coke is 15-35 μm; (vii) Dv50 of the petroleum coke tail powder is 1-10 μm, and the carbon content is >95%; (viii) the viscosity of the pitch binder is 1000-1200 Pa·s, and the softening point is 75-100 ℃; (ix) Dv50 of the natural flake graphite is 10-25 μm, and the carbon content is >99%; (x) the specific surface area of the porous hard carbon is 50 to 150 m 2 / g, the pore diameter is 2 to 10 nm, and the pore volume is 0.20 to 0.45 cm 3 / g, and the porosity is 35 to 55%. (xi) Dv50 of the conductive carbon black is 40-60 nm; (xii) Dv50 of the PET powder is 20-50 μm; (xiii) the softening point of the coal tar is 90-110 ℃; (xiv) the weight ratio of the PET powder to the coal tar is 1-3:7-9; (xv) the volume ratio of the first pore structure, the second pore structure and the third pore structure in the multi-level pore structure is 45-50%, 30-40% and 15-25% respectively.

7. A method for preparing a graphite composite negative electrode material, characterized by, The steps include: S1, adding a pitch binder and conductive carbon black to a carbon skeleton material to stir to obtain a mixed prebody, the carbon skeleton material including petroleum coke tail powder, needle coke and porous hard carbon; S2, wet granulating the mixed prebody to screen to obtain spherical granules; S3, carbonizing the spherical granules in an inert atmosphere to obtain carbonized particles; S4, graphitizing the carbonized particles in an inert atmosphere to obtain graphitized particles; S5, blending the graphitized particles with a co-carbonization coating agent and heat treating in an inert atmosphere to perform carbon coating, the co-carbonization coating agent including a carbonized product of a PET powder and a coal tar mixture.

8. The method of claim 7, wherein the graphite composite negative electrode material is prepared by mixing the graphite powder, the carbon nanotube, and the binder in a weight ratio of 70:20:

10. comprising at least one of features (1) to (9): (1) the Dv50 of the spherical granules is 10-20 μm; (2) the carbonization temperature is 500-600℃, the heating rate is 1-10℃ / min, and the time is 1-2h; (3) the graphitization temperature is 2700-3000℃, the heating rate is 1-10℃ / min, and the time is 5-8h; (4) the heat treatment temperature is 800-1000℃, the heating rate is 1-10℃ / min, and the time is 1-2h; (5) the inert atmosphere in step S3, step S4 and step S5 is independently selected from nitrogen, helium, neon or argon, and the flow rate of the inert atmosphere is 120-220 mL / min; (6) the wet granulation comprises mixing the mixed pre-bodies and water, then adding into a granulator, and then spheroidizing and screening; (7) the carbonization forms a carbon connection layer with a thickness of 50-100 nm by pyrolysis of the pitch binder; (8) the interplanar spacing of the graphitized particles is ≤0.336 nm, and the content of graphite is >95wt.%; (9) after step S5, the process further comprises a post-treatment, and the post-treatment comprises heat treatment at 600-780℃ for 0.5-2.0h, and then screening.

9. The method of claim 7, wherein the graphite composite negative electrode material is prepared by mixing the graphite powder, the carbon nanotube, and the binder in a weight ratio of 70:20:

10. The preparation of the co-carbonized coating agent comprises: swelling the PET micro-powder in an ethanol aqueous solution, adding into the coal tar for kneading to obtain a slurry, spray-drying the slurry to obtain spherical precursors, oxidizing the spherical precursors, and then carbonizing, grinding and screening.

10. Use of the graphite composite negative electrode material according to any one of claims 1 to 6 as a negative electrode active material in a negative electrode.

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