A porous graphite negative electrode material and its preparation method and application

Abstract

The present invention provides a porous graphite negative electrode material and its preparation method and application, relating to the technical field of battery negative electrode materials. The preparation method provided by the present invention comprises: adding coke aggregate and metal salt to an asphalt solution, stirring and mixing, evaporating and grinding to obtain a precursor; pre-carbonizing the precursor at 600°C-800°C, and then forming pores in an active gas to obtain porous soft carbon; graphitizing the porous soft carbon at 2000°C-2600°C to obtain porous graphite; mixing the porous graphite with a phosphorus source, ball milling the mixture, and then heat-treating the mixture at 800°C-1200°C in a nitrogen-containing atmosphere for 1 hour to 4 hours, and then cooling the mixture to obtain a porous graphite negative electrode material.

Description

Technical Field

[0001] The present invention relates to the technical field of battery negative electrode materials, and in particular to a porous graphite negative electrode material and a preparation method and application thereof. Background Art

[0002] With the increasing depletion of traditional fossil energy and the rapid rise of new energy vehicles, people's demand for lithium-ion batteries continues to increase, and at the same time, there are higher requirements for their energy density. Graphite materials have become an important negative electrode material for lithium-ion batteries due to their excellent conductivity and cycle stability. However, their low theoretical specific capacity makes it difficult to meet the higher energy density requirements. Silicon materials have attracted widespread attention due to their high theoretical specific capacity, but their large volume expansion makes them difficult to use alone. Therefore, silicon materials are usually mixed with other materials. Among them, the well-developed microporous structure on the surface of porous carbon materials makes them ideal composite sites for silicon materials, which can effectively alleviate the volume expansion problem of silicon materials.

[0003] Currently, the commonly used porous carbon materials are mainly hard carbon materials, but their first coulombic efficiency and capacity retention are low. The electrochemical performance of the composite of hard carbon materials and silicon materials is not sufficient to meet current needs. Compared with hard carbon materials, graphite has higher first coulombic efficiency and capacity retention, which is conducive to improving the electrochemical performance of the composite material. However, the stable lattice structure of graphite materials has high chemical stability, making it difficult to produce a developed pore structure on its surface through physical / chemical activation. In addition, the rate performance of graphite materials themselves is poor and cannot meet the current demand for high-rate fast charging. Therefore, there is an urgent need to provide a solution to improve the above problems. Summary of the Invention

[0004] The purpose of the present invention is to provide a porous graphite negative electrode material and a preparation method and application thereof.

[0005] In the first aspect, the present invention provides a method for preparing a porous graphite negative electrode material, comprising: adding coke aggregate and metal salt into an asphalt solution, stirring and mixing, and then evaporating and grinding to obtain a precursor; pre-carbonizing the precursor at 600°C-800°C and then forming pores in an active gas to obtain porous soft carbon; graphitizing the porous soft carbon at 2000°C-2600°C to obtain porous graphite; mixing the porous graphite with a phosphorus source and ball milling the mixture, and then heat treating the mixture at 800°C-1200°C in a nitrogen-containing atmosphere for 1h-4h and then cooling the mixture to obtain a porous graphite negative electrode material.

[0006] Optionally, the coke aggregate includes one of petroleum coke, needle coke, and isothermal coke.

[0007] Optionally, the metal salt includes one of aluminum salt, copper salt and lead salt.

[0008] Optionally, the mass ratio of the coke aggregate to the metal elements in the metal salt is 1:(0.02-0.1).

[0009] Optionally, the asphalt concentration in the asphalt solution is 3%-10%.

[0010] Optionally, the solvent of the asphalt solution includes one of petroleum ether, tetrahydrofuran, acetone, ethanol, and dichloromethane.

[0011] Optionally, after the metal salt is added to the asphalt solution, the concentration of the metal salt is 5%-10%.

[0012] Optionally, the D50 of the precursor is 7 μm-10 μm.

[0013] Optionally, the coke skeleton, metal salt and activator are added to the asphalt solution and stirred and mixed.

[0014] Optionally, the active agent includes one of polyethylene glycol, sodium dodecylbenzenesulfonate, polyvinyl pyrrolidone, and cetyltrimethylammonium bromide.

[0015] Optionally, the mass ratio of the metal salt to the active agent is 7:(4-6).

[0016] Optionally, the mass ratio of the coke skeleton to the activator is 1:(0.01-0.08).

[0017] Optionally, the precursor is pre-carbonized at 600° C.-800° C. in an inert atmosphere.

[0018] Optionally, the pre-carbonization treatment is performed for 1 hour to 3 hours.

[0019] Optionally, the temperature is raised to 600° C.-800° C. at a rate of 1° C. / min-10° C. / min for pre-carbonization.

[0020] Optionally, the active gas includes one of carbon dioxide and water vapor.

[0021] Optionally, the pore-forming treatment is carried out in an active gas for 1 hour to 4 hours.

[0022] Optionally, the total pore volume of the porous carbon is 0.8 cm 3 / g-1.0cm 3 / g.

[0023] Optionally, the average pore size of the porous soft carbon is 2 nm-2.8 nm.

[0024] Optionally, the pores are formed in an active gas with a flow rate of 5 L / min-20 L / min.

[0025] Optionally, graphitization is performed at 2000° C.-2600° C. in an inert gas.

[0026] Optionally, the porous soft carbon is graphitized for 1 h to 4 h.

[0027] Optionally, the phosphorus source includes one of phosphoric acid, triphenylphosphine, sodium hypophosphite, and hexachlorotriphosphazene.

[0028] Optionally, the mass ratio of the porous graphite to the phosphorus source is 1:(0.1-0.3).

[0029] Alternatively, the porous graphite is mixed with a phosphorus source and ball milled in an inert gas.

[0030] Optionally, the heat treatment is performed in a nitrogen-containing atmosphere of -1 kPa to 1 kPa.

[0031] Optionally, the nitrogen-containing atmosphere includes ammonia.

[0032] Optionally, the flow rate of the nitrogen-containing atmosphere is 80 mL / min-120 mL / min.

[0033] In a second aspect, the present invention further provides a porous graphite negative electrode material prepared by any of the above optional preparation methods.

[0034] Optionally, D50 is 7 μm-10 μm.

[0035] Optionally, the specific surface area is 500m 2 / g-1000m 2 / g.

[0036] Optionally, the micropore ratio is 85%-95%.

[0037] In a third aspect, the present invention further provides the use of the porous graphite negative electrode material prepared by any of the above optional preparation methods in lithium-ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 A flowchart of a method for preparing a porous graphite negative electrode material provided by the present invention;

[0039] Figure 2 This is a scanning electron microscope characterization image of the porous graphite negative electrode material prepared in Example 1 of the present invention;

[0040] Figure 3 This is a nitrogen adsorption-desorption curve of the porous graphite negative electrode material prepared in Example 1 of the present invention;

[0041] Figure 4 This is a pore size-pore volume distribution diagram of the porous graphite negative electrode material prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. Unless otherwise defined, the technical terms or scientific terms used herein should be the common meanings understood by people with ordinary skills in the field to which the present invention belongs.

[0043] See also Figure 1 The present invention provides a method for preparing a porous graphite negative electrode material, comprising:

[0044] S1. Adding coke aggregate and metal salt into the asphalt solution, stirring and mixing, and then evaporating and grinding to obtain a precursor;

[0045] S2, pre-carbonizing the precursor at 600°C-800°C and then forming pores in an active gas to produce porous soft carbon;

[0046] S3, graphitizing the porous soft carbon at 2000° C. to 2600° C. to obtain porous graphite;

[0047] S4. After ball-milling the porous graphite and the phosphorus source, heat-treating them at 800° C.-1200° C. in a nitrogen atmosphere for 1 h-4 h, and then cooling them to obtain a porous graphite negative electrode material.

[0048] The preparation method provided by the present invention uses coke aggregate as a carbon-based skeleton to provide a carbon source and provide macroscopic structural support for the loading of metal salts and asphalt. The metal salt loaded on the surface of the coke skeleton can not only serve as a pore-forming template, but also form a metal composite skeleton with the carbon skeleton, thereby effectively improving the structural stability. At the same time, the asphalt can be wrapped on the surface of the coke aggregate and form a carbon skeleton during the pre-carbonization process, and can form a multi-level pore structure (micropores, mesopores, and macropores) during the pore-forming process.

[0049] In addition, the porous soft carbon is graphitized to form a highly ordered microcrystalline structure, which can effectively improve the electronic conductivity and structural stability of the negative electrode material. After ball milling with a phosphorus source and heat treatment in a nitrogen-containing atmosphere, phosphorus and nitrogen elements can be doped into the negative electrode material, forming a synergistic effect in the negative electrode material, effectively improving the first effect and cycle life of the negative electrode material.

[0050] In some embodiments, the coke aggregate used in step S1 includes one of petroleum coke, needle coke, and isotropic coke. In practice, before adding the coke aggregate to the asphalt solution, the coke aggregate may be pre-treated with a treatment such as pickling to reduce impurities in the coke aggregate, thereby effectively improving the structural properties of the resulting negative electrode material. Specifically, the coke aggregate used may be recycled from byproducts of the petroleum industry.

[0051] In some embodiments, the metal salt used in step S1 includes one of an aluminum salt, a copper salt, and a lead salt. Specifically, the metal salt used can be one of aluminum chloride, aluminum sulfate, copper sulfate, and lead acetate. In some further embodiments, the metal salt can be pre-formed into a metal salt solution, which is then blended with the coke aggregate and the asphalt solution.

[0052] In some embodiments, the asphalt solution used in step S1 has an asphalt concentration of 3%-10%, and the solvent of the asphalt solution includes one of petroleum ether, tetrahydrofuran, acetone, ethanol, and dichloromethane. In practice, preparing the asphalt as a solution facilitates the coating of the asphalt on the surface of the coke aggregate and the uniform dispersion of the metal salt within the asphalt solution, thereby improving the uniformity of the dispersion of the metal salt within the coke aggregate and the asphalt, and facilitating the formation of a uniform pore structure during the pore-forming process.

[0053] In some embodiments, in step S1, the coke skeleton, metal salt, and activator are added to the asphalt solution and stirred. In practice, the addition of the activator can effectively increase the surface activity of the coke skeleton, preventing agglomeration and sedimentation of the coke aggregate in the asphalt solution. This can further improve the uniformity of the metal salt doping on the coke aggregate surface and facilitate asphalt coating of the coke aggregate during solvent evaporation.

[0054] Specifically, the active agent used includes one of polyethylene glycol, sodium dodecylbenzenesulfonate, polyvinylpyrrolidone, and cetyltrimethylammonium bromide. Furthermore, the mass ratio of the metal salt to the active agent can be 7:(4-6), and the mass ratio of the coke skeleton to the active agent is 1:0.01-0.08. In practice, the active agent can be pre-mixed with the asphalt before adding the solvent to form a mixed solvent. Alternatively, a portion of the active agent can be pre-mixed with the asphalt, and the remaining amount can be added to the coke aggregate at the same time.

[0055] In some embodiments, the mass ratio of coke aggregate added in step S1 to the metal element in the metal salt is 1:0.02-0.1. In practice, after the metal salt is added to the asphalt solution and stirred, the concentration of the metal salt solution in the mixed solution is 5%-10%. By adjusting the amounts of asphalt, metal salt, and coke aggregate in the asphalt solution, the pore structure formed in the negative electrode material can be effectively adjusted.

[0056] In some embodiments, in step S1, after the coke skeleton and metal salt are added to the asphalt solution and stirred, the solution is heated to evaporate the solvent, thereby obtaining a solid. In practice, the stirring and mixing process includes high-temperature stirring, solvent evaporation, and drying. The high-temperature stirring process promotes uniform coating of the asphalt on the surface of the coke skeleton. Simultaneously, the solvent evaporation and drying processes form a composite coating material, and the precursor having a D50 of 7 μm-10 μm is obtained through grinding.

[0057] In some embodiments, during step S2, the precursor is pre-carbonized at 600°C-800°C under an inert atmosphere for 1-3 hours. This facilitates the pyrolysis of the pitch coated on the surface of the coke skeleton to form a carbon skeleton, and further allows the metal salt to be sintered within the carbon skeleton formed by the coke skeleton and pitch. This not only improves the structural stability of the negative electrode material but also facilitates the formation of a microporous structure during the subsequent pore formation process. Specifically, the inert atmosphere used includes helium or argon.

[0058] In some embodiments, during step S2, the precursor may be placed in a tube furnace, and the temperature of the tube furnace may be raised to 600°C-800°C at a rate of 1°C / min-10°C / min to pre-carbonize the precursor. Controlling the heating rate of the precursor can improve temperature uniformity between the inside and outside of the precursor, thereby preventing variations in the degree of carbonization between the inside and outside of the precursor.

[0059] In some embodiments, the active gas used in step S2 includes one of carbon dioxide and water vapor. In fact, the precursor can be pre-carbonized in an inert atmosphere at 600°C-800°C, and then the gas atmosphere can be replaced with an active gas, so that activation and pore formation can be performed immediately after the pre-carbonization treatment, thereby forming a porous soft carbon material with a porous structure. Specifically, the total pore volume of the porous soft carbon is 0.8 cm 3 / g-1.0cm 3 / g, and an average pore size of 2nm-2.8nm. In practice, the precursor after pre-carbonization treatment can be subjected to pore formation in an active gas at a flow rate of 5L / min-20L / min.

[0060] In some embodiments, when executing step S3, graphitization treatment is performed at 2000°C-2600°C in an inert gas atmosphere for 1h-4h. In fact, through graphitization treatment, the disordered structure in the porous soft carbon can be transformed into a highly ordered graphite-like microcrystalline structure by utilizing high-temperature thermal rearrangement, thereby effectively improving the electronic conductivity and the structural stability of the negative electrode material. At the same time, by pre-porous treatment and then graphitization, a graphite material with a porous structure can be formed, which can not only improve the efficiency and capacity retention rate of the negative electrode material, but also improve the rate performance of the negative electrode material.

[0061] In some embodiments, the phosphorus source used in step S4 includes one of phosphoric acid, triphenylphosphine, sodium hypophosphite, and hexachlorotriphosphazene. In practice, mechanical ball milling is advantageous in causing the phosphorus source to enter the pores of the porous graphite and adhere to the surface, thereby introducing phosphorus into the porous graphite. Specifically, the porous graphite and the phosphorus source can be mixed and placed in a ball milling jar, using zirconium oxide as the milling balls, and ball milling mixing is performed at a rotation speed of 200 rpm to 500 rpm for 1 hour to 10 hours.

[0062] In some embodiments, when executing step S4, the mass ratio of porous graphite to phosphorus source is 1:(0.1-0.3). In fact, by adjusting the mass ratio of porous graphite to phosphorus source, the doping ratio of phosphorus in the negative electrode material can be adjusted to avoid the introduction of excessive phosphorus leading to lattice stress accumulation and thus structural differentiation, and at the same time, the rate performance and capacity of the negative electrode material can be comprehensively optimized.

[0063] In some embodiments, during step S4, the porous graphite and a phosphorus source may be mixed and ball-milled in an inert gas atmosphere to facilitate phosphorus doping. Specifically, nitrogen doping is performed after heat treatment in a nitrogen-containing atmosphere. In practice, the nitrogen-containing atmosphere includes ammonia. Furthermore, the heat treatment may be performed in a nitrogen-containing atmosphere at a pressure of -1 kPa to 1 kPa and a flow rate of 80 mL / min to 120 mL / min.

[0064] The present invention also provides a porous graphite negative electrode material prepared by the preparation method of any of the above embodiments, wherein the D50 of the porous graphite negative electrode material is 7 μm-10 μm and the specific surface area is 500 m 2 / g-1000m 2 / g, and the proportion of micropores is 85%-95%.

[0065] In fact, the present invention also provides an application of a porous graphite anode material prepared by the preparation method of any of the above embodiments in a lithium-ion battery. Specifically, the porous graphite anode material can be used as a carbon material to be composited with a silicon material to form a silicon-carbon anode material. Alternatively, the porous graphite anode material can be directly mixed with a binder and a conductive agent to form a negative electrode, which can then be used in a lithium-ion battery.

[0066] Example 1

[0067] This embodiment 1 provides a method for preparing a porous graphite negative electrode material, comprising the following steps:

[0068] S1. Copper sulfate solution and sodium dodecylbenzene sulfonate (the mass ratio of copper sulfate to sodium dodecylbenzene sulfonate is 7:5) are mixed and added into a 5% asphalt solution, and the concentration of copper sulfate in the mixed solution is adjusted to 7%. Coke aggregate (the mass ratio of coke aggregate to copper element is 1:0.03) is added to the mixed solution, and ultrasonically dispersed in an 80°C water bath for 10 minutes. After stirring at 200 rpm and evaporating the solvent, the resulting solid is dried in an 80°C oven and ground to obtain a precursor (D50 is 8 μm).

[0069] S2. The precursor is placed in the furnace of a tube furnace, argon gas is introduced and the argon pressure is adjusted to normal pressure. The tube furnace is heated to 700°C at a rate of 5°C / min and kept at this temperature for 2 hours to perform pre-carbonization. The temperature is maintained and active gas (carbon dioxide and water vapor volume ratio of 1:1) is introduced to replace the gas in the tube furnace. The tube furnace is subjected to a pore forming treatment at a pressure of 1 kPa for 3 hours. The porous soft carbon is obtained after the furnace is cooled to room temperature.

[0070] S3, placing the porous soft carbon in a graphitization furnace, heating it to 2500°C at a rate of 5°C / min in an argon atmosphere, and then keeping it at that temperature for 3 hours to perform graphitization treatment, and then cooling it to room temperature to obtain porous graphite;

[0071] S4. Porous graphite and phosphoric acid are mixed in a mass ratio of 1:0.2 and put into a ball mill jar. 0.5 mm zirconia is used as a ball milling bead. Ball milling treatment is carried out for 2 h in an argon atmosphere with a ball-to-material ratio of 10:1 to obtain a ball-milled mixture. The ball-milled mixture is placed in an atmosphere furnace, ammonia is used as a nitrogen-containing atmosphere, the temperature is raised to 1000°C at a rate of 5°C / min, and heat-treated for 2 h. The mixture is then cooled to room temperature in the furnace to obtain a porous graphite negative electrode material.

[0072] Example 2

[0073] This embodiment 2 provides a method for preparing a porous graphite negative electrode material, which is different from embodiment 1 in that the metal salt used in step S1 is aluminum trichloride, and the mass ratio of coke aggregate to aluminum element is 1:0.06.

[0074] Example 3

[0075] This embodiment 3 provides a method for preparing a porous graphite negative electrode material, which is different from embodiment 1 in that the metal salt used in step S1 is lead acetate, and the mass ratio of coke aggregate to lead element is 1:0.02.

[0076] Example 4

[0077] This embodiment 4 provides a method for preparing a porous graphite negative electrode material, which is different from embodiment 1 in that sodium dodecylbenzenesulfonate is not added in step S1.

[0078] Comparative Example 1

[0079] This comparative example 1 provides a method for preparing a porous graphite negative electrode material, which is different from Example 4 in that no copper sulfate solution is added in step S1, and the mass ratio of coke aggregate to asphalt in the asphalt solution is 1:0.05.

[0080] Comparative Example 2

[0081] This comparative example 2 provides a method for preparing a porous graphite negative electrode material, which is different from Example 4 in that no active gas pore-forming treatment is performed in step S2, and step S3 is directly performed after the soft carbon material is obtained.

[0082] Performance testing

[0083] The porous graphite negative electrode material prepared in Example 1 was characterized by scanning electron microscopy. Figure 2 As shown, from Figure 2 It can be seen from the figure that the negative electrode material has a layered structure of graphite, and after nitrogen adsorption and desorption characterization, Figure 3 and Figure 4 As shown in Figure 2, this indicates that the prepared porous graphite negative electrode material has a type I adsorption isotherm, and the pore structure is mainly micropores. Figure 4 It can be seen from the pore size-pore volume distribution diagram in that the pore volume mainly comes from pores below 2.5 nm.

[0084] The specific surface area, micro volume, micropore ratio and average particle size of the porous graphite negative electrode materials in Examples 1 to 4 and Comparative Examples 1 to 2 were tested, as shown in Table 1 below.

[0085] Table 1 Structural parameters of porous graphite anode materials

[0086] <![CDATA[Specific surface area (m 2 / g)]]> <![CDATA[Micro volume (cm 3 / g)]]> Micropore ratio / % Average particle size (D50) Example 1 866.69 0.45 81 7.96 Example 2 919.48 0.46 85 8.03 Example 3 972.68 0.49 87 7.52 Example 4 573.99 0.28 72 8.21 Comparative Example 1 215.26 0.11 82 7.85 Comparative Example 2 0.2124 0.000907 99 7.92

[0087] The porous graphite from Examples 1 to 4 and Comparative Examples 1 and 2 was mixed with PCSC-1800 silicon-based material in a mass ratio of 9:1 to prepare a silicon-carbon material. An active slurry was prepared by mixing the silicon-carbon material, conductive carbon black, and a binder (carboxymethyl cellulose) in a mass ratio of 8:1:1. The active slurry was coated and cured onto a copper current collector to produce the negative electrode. Lithium-ion batteries were assembled in a glove box using sodium hexafluorophosphate as the electrolyte, a lithium sheet as the counter electrode, and Celgard 250 as the separator. Electrochemical testing was conducted under the Newway test environment to examine initial efficiency, capacity, and cycle performance, as shown in Table 2 below.

[0088] Table 2 Electrochemical properties of silicon-carbon materials in the examples

[0089] Sample name First coulombic efficiency% First reversible capacity mAh / g Capacity retention rate% (100 cycles) Example 1 - Silicon Carbon Material 92% 903 91% Example 2 - Silicon Carbon Material 88% 872 85% Example 3 - Silicon Carbon Material 86% 886 80% Example 4 - Silicon Carbon Material 79% 865 58% Comparative Example 1-Silicon Carbon Material 73% 868 42% Comparative Example 2-Silicon Carbon Material 70% 841 35%

[0090] While the embodiments of the present invention have been described in detail above, it will be apparent to those skilled in the art that various modifications and variations of these embodiments are possible. However, it should be understood that such modifications and variations are within the scope and spirit of the present invention as set forth in the claims. Furthermore, the invention described herein is susceptible to other embodiments and may be practiced or implemented in a variety of ways.

Claims

1. A method for preparing a porous graphite negative electrode material, characterized in that: include: Coke aggregate, metal salt and active agent are added to asphalt solution, stirred and mixed, evaporated and ground to obtain a precursor; the precursor is pre-carbonized at 600℃-800℃ and then pores are formed in active gas to obtain porous soft carbon; the porous soft carbon is graphitized at 2000℃-2600℃ to obtain porous graphite; the porous graphite is mixed with a phosphorus source and ball-milled, and then heat-treated at 800℃-1200℃ in a nitrogen atmosphere for 1h-4h and then cooled to obtain a porous graphite negative electrode material.

2. The preparation method according to claim 1, characterized in that Coke aggregate includes one of petroleum coke, needle coke and isotropic coke.

3. The preparation method according to claim 1, characterized in that The metal salt includes one of aluminum salt, copper salt and lead salt.

4. The preparation method according to claim 1, characterized in that The mass ratio of the coke aggregate to the metal elements in the metal salt is 1:(0.02-0.1).

5. The preparation method according to claim 1, characterized in that The asphalt concentration in the asphalt solution is 3%-10%.

6. The preparation method according to claim 1, characterized in that The solvent of the asphalt solution includes one of petroleum ether, tetrahydrofuran, acetone, ethanol and dichloromethane.

7. The preparation method according to claim 1, characterized in that After the metal salt is added to the asphalt solution, the concentration of the metal salt is 5%-10%.

8. The preparation method according to claim 1, characterized in that The D50 of the precursor is 7 μm-10 μm.

9. The preparation method according to claim 1, characterized in that The active agent includes one of polyethylene glycol, sodium dodecylbenzenesulfonate, polyvinyl pyrrolidone, and cetyltrimethylammonium bromide.

10. The preparation method according to claim 1, characterized in that The mass ratio of the metal salt to the active agent is 7:(4-6).

11. The preparation method according to claim 1, characterized in that The mass ratio of the coke skeleton to the activator is 1:(0.01-0.08).

12. The preparation method according to claim 1, characterized in that The precursor is pre-carbonized at 600°C-800°C in an inert atmosphere.

13. The preparation method according to claim 1, characterized in that Pre-carbonization treatment lasts 1h-3h.

14. The preparation method according to claim 1, characterized in that The temperature is raised to 600°C-800°C at a rate of 1°C / min-10°C / min for pre-carbonization.

15. The preparation method according to claim 1, characterized in that The active gas includes one of carbon dioxide and water vapor.

16. The preparation method according to claim 1, characterized in that The pore-forming treatment is carried out in active gas for 1h-4h.

17. The preparation method according to claim 1, characterized in that The total pore volume of porous soft carbon is 0.8 cm 3 / g-1.0cm 3 / g.

18. The preparation method according to claim 1, characterized in that The average pore size of porous soft carbon is 2nm-2.8nm.

19. The preparation method according to claim 1, characterized in that The pores are formed in an active gas at a flow rate of 5 L / min-20 L / min.

20. The preparation method according to claim 1, characterized in that Graphitization is carried out at 2000℃-2600℃ in an inert gas.

21. The preparation method according to claim 1, characterized in that The porous soft carbon is graphitized for 1 h to 4 h.

22. The preparation method according to claim 1, characterized in that The phosphorus source includes one of phosphoric acid, triphenylphosphine, sodium hypophosphite, and hexachlorotriphosphazene.

23. The preparation method according to claim 1, characterized in that The mass ratio of the porous graphite to the phosphorus source is 1:(0.1-0.3).

24. The preparation method according to claim 1, characterized in that The porous graphite and the phosphorus source are mixed and ball-milled in an inert gas atmosphere.

25. The preparation method according to claim 1, characterized in that The nitrogen-containing atmosphere includes ammonia.

26. The preparation method according to claim 1, characterized in that Heat treatment in a nitrogen atmosphere of -1kPa~1kPa.

27. The preparation method according to claim 1, characterized in that The flow rate of the nitrogen-containing atmosphere is 80 mL / min-120 mL / min.

28. A porous graphite negative electrode material prepared by the preparation method according to any one of claims 1 to 27.

29. The porous graphite negative electrode material according to claim 28, characterized in that D50 is 7μm-10μm.

30. The porous graphite negative electrode material according to claim 28, characterized in that Specific surface area is 500m 2 / g-1000m 2 / g.

31. The porous graphite negative electrode material according to claim 28, characterized in that Micropores account for 85%-95%.

32. Use of the porous graphite negative electrode material prepared by the preparation method according to any one of claims 1 to 27 or the porous graphite negative electrode material according to any one of claims 28 to 31 in a lithium ion battery.

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