Porous graphite negative electrode material and preparation method and application thereof

Abstract

The invention provides a porous graphite negative electrode material as well as a preparation method and application thereof, and relates to the technical field of battery negative electrode materials. The preparation method provided by the invention comprises the following steps: adding coke aggregate and metal salt into an asphalt solution, stirring and mixing, evaporating to dryness, and grinding to obtain a precursor; pre-carbonizing the precursor at the temperature of 600-800 DEG C, and then forming pores in active gas to obtain porous soft carbon; graphitizing the porous soft carbon at the temperature of 2000-2600 DEG C to obtain porous graphite; mixing and ball-milling the porous graphite and a phosphorus source, performing heat treatment at 800-1200 DEG C in a nitrogen-containing atmosphere for 1-4 hours, and cooling to obtain the 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 important negative electrode materials for lithium-ion batteries due to their excellent conductivity and cycle stability, but 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 unable to be used alone. Therefore, silicon materials are usually mixed with other materials. Among them, the porous carbon material has a developed microporous structure on the surface, which becomes an ideal composite site for silicon materials, which can effectively alleviate the volume expansion problem of silicon materials.

[0003] At present, the commonly used porous carbon materials are mainly hard carbon materials, but their first coulombic efficiency and capacity retention rate are low. The electrochemical performance of the composite of hard carbon materials and silicon materials is not enough to meet the current needs. Compared with hard carbon materials, graphite has higher first coulombic efficiency and capacity retention rate, which is beneficial to improve the electrochemical performance of composite materials. However, the stable lattice structure of graphite materials has high chemical stability, and it is 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, it is urgent 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, 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 it, and then heat treating it at 800°C-1200°C in a nitrogen-containing atmosphere for 1h-4h and then cooling it to obtain a porous graphite negative electrode material.

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

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

[0008] Optionally, the mass ratio of coke aggregate to 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 adding the metal salt 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 into the asphalt solution and stirred and mixed.

[0014] Optionally, the active agent includes one of polyethylene glycol, sodium dodecylbenzene sulfonate, polyvinyl pyrrolidone, and hexadecyltrimethylammonium 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 h to 3 h.

[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 h to 4 h.

[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 at 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 porous graphite to 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 also 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 also provides the use of the porous graphite negative electrode material prepared by any of the above optional preparation methods in a lithium ion battery. 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; 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; Figure 3 This is a nitrogen adsorption-desorption curve diagram of the porous graphite negative electrode material prepared in Example 1 of the present invention; 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

[0039] 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 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 general skills in the field to which the present invention belongs.

[0040] See also Figure 1 The present invention provides a method for preparing a porous graphite negative electrode material, comprising: S1, adding coke aggregate and metal salt into the asphalt solution, stirring and mixing, evaporating and grinding to obtain a precursor; S2, pre-carbonizing the precursor at 600°C-800°C and then forming pores in an active gas to obtain porous soft carbon; S3, graphitizing the porous soft carbon at 2000° C.-2600° C. to obtain porous graphite; S4. After the porous graphite and the phosphorus source are mixed and ball-milled, the mixture is heat-treated at 800° C.-1200° C. in a nitrogen atmosphere for 1 h-4 h and then cooled to obtain a porous graphite negative electrode material.

[0041] 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, and 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, macropores) during the pore-forming process.

[0042] 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 impurities can be doped into the negative electrode material, and a synergistic effect can be formed in the negative electrode material, effectively improving the first effect and cycle life of the negative electrode material.

[0043] In some embodiments, the coke aggregate used in step S1 includes one of petroleum coke, needle coke, and isotropic coke. In fact, when the coke aggregate is added to the asphalt solution, the coke aggregate can be pre-treated by pickling or the like to reduce the impurity components in the coke aggregate, thereby effectively improving the structural properties of the obtained negative electrode material. Specifically, the coke aggregate used can be recovered from by-products in the petroleum industry.

[0044] In some embodiments, the metal salt used in step S1 includes one of aluminum salt, copper salt, and 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 prepared into a metal salt solution in advance, and then the metal salt solution is blended with the coke aggregate and the asphalt solution.

[0045] In some embodiments, the asphalt concentration in the asphalt solution used in step S1 is 3%-10%, and the solvent of the asphalt solution includes one of petroleum ether, tetrahydrofuran, acetone, ethanol, and dichloromethane. In fact, by configuring the asphalt into a solution, it is beneficial for the asphalt to be wrapped on the surface of the coke aggregate, and it is also beneficial for the metal salt to be evenly dispersed in the asphalt solution, which is beneficial to improve the uniformity of the dispersion of the metal salt in the coke aggregate and the asphalt, and it is beneficial to form a uniform pore structure during the pore formation process.

[0046] In some embodiments, in step S1, the coke skeleton, metal salt and active agent are added to the asphalt solution and stirred and mixed. In fact, by adding the active agent, the surface activity of the coke skeleton can be effectively improved, and the agglomeration and sedimentation of the coke aggregate in the asphalt solution can be avoided, thereby further improving the doping uniformity of the metal salt on the surface of the coke aggregate, and at the same time, it is beneficial to the coating of the asphalt on the coke aggregate during the process of evaporating the solvent.

[0047] Specifically, the active agent used includes one of polyethylene glycol, sodium dodecylbenzene sulfonate, polyvinyl pyrrolidone, and hexadecyl trimethyl ammonium bromide. In addition, 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 fact, before adding the active agent, the active agent can be mixed with asphalt in advance and then the solvent is added to make a mixed solvent. It is also possible to pre-mix a part of the active agent with the asphalt and then add the remaining amount of the active agent and the coke aggregate in the same batch.

[0048] In some embodiments, the mass ratio of the coke aggregate added in step S1 to the metal element in the metal salt is 1:0.02-0.1. In fact, after the metal salt is added to the asphalt solution and stirred and mixed, the concentration of the metal salt solution in the mixed solution is 5%-10%. In fact, by adjusting the amount of asphalt, metal salt, and coke aggregate in the asphalt solution, the pore structure formed in the negative electrode material can be effectively adjusted.

[0049] In some embodiments, after adding the coke skeleton and the metal salt into the asphalt solution and stirring and mixing in step S1, heating is performed to cause the solvent to evaporate to obtain a solid. In fact, the stirring and mixing process includes high-temperature stirring, solvent evaporation and drying processes. By stirring in a high-temperature environment, the asphalt can be evenly coated on the surface of the coke skeleton. At the same time, a composite coating material can be formed through the solvent evaporation and drying process, and a precursor with a D50 of 7μm-10μm can be obtained through grinding.

[0050] In some embodiments, when performing step S2, the precursor is pre-carbonized at 600°C-800°C in an inert atmosphere for 1h-3h, which is conducive to the pyrolysis of the pitch coated on the surface of the coke skeleton to form a carbon skeleton, and the metal salt can be further sintered in the carbon skeleton formed by the coke skeleton and the pitch, which is not only conducive to improving the structural stability of the negative electrode material, but also conducive to forming a microporous structure in the subsequent pore formation process. Specifically, the inert atmosphere used includes helium and argon.

[0051] In some embodiments, when executing step S2, the precursor may be placed in a furnace of a tube furnace, and the tube furnace may be heated to 600°C-800°C at a rate of 1°C / min-10°C / min to perform a pre-carbonization treatment on the precursor. In fact, controlling the heating rate of the precursor is helpful to improve the temperature uniformity inside and outside the precursor, and avoid differences in the carbonization degree inside and outside the precursor.

[0052] 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 fact, the precursor after pre-carbonization treatment can be pore-formed in an active gas at 5L / min-20L / min.

[0053] In some embodiments, when executing step S3, graphitization treatment is performed at 2000°C-2600°C and in an inert gas 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.

[0054] In some embodiments, the phosphorus source used in step S4 includes one of phosphoric acid, triphenylphosphine, sodium hypophosphite, and hexachlorotriphosphazene. In fact, mechanical ball milling is beneficial to promote the phosphorus source to enter the pores of 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 put into a ball mill, zirconium oxide is used as a ball mill, and ball milling mixing is performed at a rotation speed of 200rpm-500rpm for 1h-10h.

[0055] 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 structural differentiation, while the rate performance and capacity of the negative electrode material can be comprehensively optimized.

[0056] In some embodiments, porous graphite and a phosphorus source may be mixed and ball-milled in an inert gas during step S4, which is conducive to doping phosphorus. Specifically, nitrogen doping is performed after heat treatment in a nitrogen-containing atmosphere. In fact, the nitrogen-containing atmosphere includes ammonia. In addition, heat treatment may be performed in a nitrogen-containing atmosphere at -1 kPa to 1 kPa and a flow rate of 80 mL / min to 120 mL / min.

[0057] The present invention also provides a porous graphite negative electrode material prepared by the preparation method in any of the above embodiments, and 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 micropores account for 85%-95%.

[0058] In fact, the present invention also provides an application of a porous graphite negative electrode material prepared by the preparation method in any of the above embodiments in a lithium-ion battery. Specifically, the porous graphite negative electrode material can be used as a carbon material and composited with a silicon material to form a silicon-carbon negative electrode material, and the porous graphite negative electrode material can also be directly mixed with a binder and a conductive agent to form a negative electrode, and applied to a lithium-ion battery.

[0059] Example 1

[0060] This embodiment 1 provides a method for preparing a porous graphite negative electrode material, comprising the following steps: S1. Mix copper sulfate solution and sodium dodecylbenzene sulfonate (the mass ratio of copper sulfate to sodium dodecylbenzene sulfonate is 7:5) and add them into 5% asphalt solution, stir and mix to obtain a mixed solution, and adjust the concentration of copper sulfate in the mixed solution to 7%; add coke aggregate (the mass ratio of coke aggregate to copper element is 1:0.03) into the mixed solution, ultrasonically disperse in a water bath environment at 80°C for 10 minutes, stir at a speed of 200 rpm and evaporate the solvent, and then dry the obtained solid in an oven at 80°C and grind to obtain a precursor (D50 is 8 μm); S2. Place the precursor in the furnace of a tube furnace, introduce argon gas and adjust the argon gas pressure to normal pressure. Heat the tube furnace to 700°C at a rate of 5°C / min and keep it warm for 2 hours to perform pre-carbonization. Maintain the temperature and introduce active gas (the volume ratio of carbon dioxide to water vapor is 1:1) to replace the gas in the tube furnace. Perform pore formation treatment at a pressure of 1 kPa for 3 hours, and cool the furnace to room temperature to obtain porous soft carbon. 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 with the furnace to obtain porous graphite; S4. Mix porous graphite and phosphoric acid in a mass ratio of 1:0.2 and put them into a ball mill, use 0.5 mm zirconium oxide as ball milling beads, and ball mill for 2 hours in an argon atmosphere with a ball-to-material ratio of 10:1 to obtain a ball-milled mixture; place the ball-milled mixture in an atmosphere furnace, use ammonia as a nitrogen-containing atmosphere, heat it to 1000°C at a rate of 5°C / min, heat treat it for 2 hours, and then cool it to room temperature to obtain a porous graphite negative electrode material.

[0061] Example 2

[0062] This embodiment 2 provides a method for preparing a porous graphite negative electrode material, which is different from the 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.

[0063] Example 3

[0064] This embodiment 3 provides a method for preparing a porous graphite negative electrode material, which is different from the 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.

[0065] Example 4

[0066] This embodiment 4 provides a method for preparing a porous graphite negative electrode material, which is different from the embodiment 1 in that sodium dodecylbenzene sulfonate is not added in step S1.

[0067] Comparative Example 1

[0068] 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.

[0069] Comparative Example 2

[0070] 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.

[0071] Performance Testing

[0072] 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 graphite layered structure, and after nitrogen adsorption and desorption characterization, Figure 3 and Figure 4 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 that the pore volume mainly comes from pores below 2.5 nm.

[0073] 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.

[0074] Table 1 Structural parameters of porous graphite anode materials

[0075] <![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

[0076] The porous graphite in Examples 1 to 4 and Comparative Examples 1 to 2 was mixed with PCSC-1800 silicon-based material at a mass ratio of 9:1 to prepare silicon-carbon material, and the silicon-carbon material, conductive carbon black, and adhesive (carboxymethyl cellulose) were mixed at a mass ratio of 8:1:1 to prepare active slurry, and the active slurry was coated and cured on a copper current collector to prepare a negative electrode, and sodium hexafluorophosphate was used as an electrolyte, a lithium sheet as a counter electrode, and Celgard250 as a diaphragm, and a lithium-ion battery was assembled in a glove box. Electrochemical tests were carried out under the new test environment to detect the first effect, capacity, and cycle performance, as shown in Table 2 below.

[0077] Table 2 Electrochemical properties of silicon-carbon materials in the examples

[0078] 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%

[0079] Although the embodiments of the present invention are described in detail above, it is obvious to those skilled in the art that various modifications and variations can be made to these embodiments. However, it should be understood that such modifications and variations are within the scope and spirit of the present invention as described in the claims. Moreover, the present invention described herein may have other embodiments and may be implemented or realized in a variety of ways.

Claims

1. A method for preparing a porous graphite negative electrode material, characterized in that: include: Add coke aggregate and metal salt into asphalt solution, stir and mix, evaporate and grind to obtain a precursor; pre-carbonize the precursor at 600°C-800°C and make pores in active gas to obtain porous soft carbon; graphitize the porous soft carbon at 2000°C-2600°C to obtain porous graphite; mix the porous graphite with a phosphorus source and ball mill, heat treat at 800°C-1200°C in a nitrogen atmosphere for 1h-4h and then cool to obtain a porous graphite negative electrode material.

2. The preparation method according to claim 1, characterized in that: The coke aggregate comprises one of petroleum coke, needle coke, and isotropic coke; and / or the metal salt comprises one of aluminum salt, copper salt, and lead salt; and / or the mass ratio of the coke aggregate to the metal element in the metal salt is 1:(0.02-0.1); and / or the asphalt concentration in the asphalt solution is 3%-10%; and / or the solvent of the asphalt solution comprises one of petroleum ether, tetrahydrofuran, acetone, ethanol, and dichloromethane; and / or the concentration of the metal salt after adding the metal salt to the asphalt solution is 5%-10%; and / or the D50 of the precursor is 7μm-10μm.

3. The preparation method according to claim 1, characterized in that: Add coke skeleton, metal salt and active agent into asphalt solution and stir and mix; wherein: the active agent includes one of polyethylene glycol, sodium dodecylbenzene sulfonate, polyvinyl pyrrolidone and hexadecyltrimethylammonium bromide; and / or, the mass ratio of metal salt to active agent is 7:(4-6); and / or, the mass ratio of coke skeleton to active agent is 1:(0.01-0.08).

4. The preparation method according to claim 1, characterized in that: The precursor is pre-carbonized at 600°C-800°C in an inert atmosphere; and / or, the pre-carbonization treatment is performed for 1h-3h; and / or, the temperature is raised to 600°C-800°C at a rate of 1°C / min-10°C / min for pre-carbonization; and / or, the active gas includes one of carbon dioxide and water vapor; and / or, the pore formation treatment is performed in the active gas for 1h-4h; and / or, the total pore volume of the porous soft carbon is 0.8cm 3 / g-1.0cm 3 / g; and / or, the average pore size of the porous soft carbon is 2nm-2.8nm; and / or, pore formation is carried out in an active gas with a flow rate of 5L / min-20L / min.

5. The preparation method according to claim 1, characterized in that: Graphitization is carried out at 2000°C-2600°C in an inert gas; and / or, the porous soft carbon is graphitized for 1h-4h; and / or, the phosphorus source includes one of phosphoric acid, triphenylphosphine, sodium hypophosphite, and hexachlorotriphosphazene; and / or, the mass ratio of porous graphite to phosphorus source is 1:(0.1-0.3); and / or, the porous graphite and the phosphorus source are mixed and ball-milled in an inert gas.

6. The preparation method according to claim 1, characterized in that: The nitrogen-containing atmosphere includes ammonia; and / or, heat treatment is performed in a nitrogen-containing atmosphere of -1 kPa to 1 kPa; and / or, the flow rate of the nitrogen-containing atmosphere is 80 mL / min to 120 mL / min.

7. A porous graphite negative electrode material prepared by the preparation method according to any one of claims 1 to 6.

8. The porous graphite negative electrode material according to claim 7, characterized in that: D50 is 7 μm-10 μm; and / or, the specific surface area is 500 m 2 / g-1000m 2 / g; and / or, the micropore ratio is 85%-95%.

9. Use of the porous graphite negative electrode material prepared by the preparation method according to any one of claims 1 to 6 or the porous graphite negative electrode material according to any one of claims 7 to 8 in a lithium ion battery.

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