A densified natural graphite, its preparation method and application

Abstract

The present invention relates to the technical field of modified graphite, and discloses a preparation method of densified natural graphite, comprising the following steps: (1) mixing natural graphite with a conductive polymer solution, adding the mixture into an extruder after mixing evenly for vacuum pumping and extrusion, and then obtaining an intermediate product after heating and drying and cooling; (2) mixing the intermediate product with pitch evenly, and then performing carbonization and pulverization to obtain densified natural graphite. The present invention uses a conductive polymer to fill the pores of natural graphite, and uses an extrusion device for mechanical extrusion to densify the interior of the material, and then obtains a densified natural graphite material through carbonization coating, pulverization and classification. The method is simple, the conditions are mild and controllable, and the modified natural graphite obtained can endow the battery with excellent cycle performance and rate performance when used as a negative electrode material.

Description

Technical Field

[0001] The present invention relates to the technical field of modified graphite, and particularly to a densified natural graphite, a preparation method thereof, and an application thereof. Background Art

[0002] Currently, the commercially available anode materials are mainly artificial graphite anode materials. The key process of artificial graphite, graphitization, consumes a large amount of electricity. It takes about 10,000 kWh of electricity to process each ton of graphite. About 40% of the national graphitization production capacity is concentrated in Inner Mongolia. However, due to power restrictions, the graphitization production capacity in some areas is greatly restricted, resulting in a tight supply of artificial graphite, a significant increase in price, and an increase in cost pressure. Natural graphite has attracted wide attention due to its rich resources, no need for graphitization, and low cost. However, the interlayer spacing of natural graphite is smaller than that of artificial graphite. During the charge-discharge cycle process, the co-insertion of solvents and the lattice expansion during the lithium intercalation and deintercalation processes are prone to cause the exfoliation and shedding of graphite sheets, the destruction of the graphite structure, resulting in capacity attenuation during the cycle process, and the cycle performance and rate performance are worse than those of artificial graphite.

[0003] Currently, the modification technologies for natural graphite anodes mainly include methods such as surface coating, surface oxidation, and doping. These mainly modify the structure and morphology of the surface of graphite particles, but there is no change in the internal pore structure of the particles, and the cycle performance and rate performance of natural graphite have not been fundamentally improved.

[0004] Therefore, how to provide a natural graphite with excellent cycle performance and rate performance is an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0005] In view of this, the present invention provides a preparation method for densified natural graphite to solve the problem that the existing natural graphite modification technologies cannot fundamentally improve the cycle performance and rate performance of natural graphite.

[0006] To solve the above technical problems, the present invention adopts the following technical solutions:

[0007] A preparation method for densified natural graphite includes the following steps:

[0008] (1) Mix natural graphite with a conductive polymer solution, uniformly mix and then add it to an extruder for vacuuming and extrusion, and then obtain an intermediate product after heating and drying and cooling;

[0009] (2) Uniformly mix the intermediate product with pitch, and then obtain densified natural graphite after carbonization and pulverization.

[0010] Preferably, in the above preparation method for densified natural graphite, the mass ratio of the natural graphite to the conductive polymer in step (1) is 1:(0.05 - 0.3).

[0011] Preferably, in the above method for preparing densified natural graphite, the conductive polymer solution in step (1) is obtained by dissolving a conductive polymer in a solvent;

[0012] The conductive polymer includes at least one of polyaniline, polypyrrole, polymethyl methacrylate, polythiophene, and polyphenylacetylene;

[0013] The solvent includes water and organic solvents; further preferably, the organic solvents include, but are not limited to, ethanol, acetic acid, and N-methylpyrrolidone.

[0014] Preferably, in the above method for preparing densified natural graphite, the vacuum pumping time in step (1) is 3 - 8 h, and the pressure is 10 - 100 Pa;

[0015] Further preferably, the vacuum pumping time is 4 - 6 h.

[0016] Preferably, in the above method for preparing densified natural graphite, the extrusion time in step (1) is 2 - 6 h, and the pressure is 0.2 - 0.8 MPa;

[0017] Further preferably, the extrusion time is 3 - 5 h;

[0018] Even more preferably, the extrusion is a 360° mechanical extrusion of natural graphite using an isostatic pressing device.

[0019] Preferably, in the above method for preparing densified natural graphite, the heating and drying temperature in step (1) is 60 - 120 °C, and the time is 10 - 30 min.

[0020] Preferably, in the above method for preparing densified natural graphite, the amount of asphalt added in step (2) is 8 - 25% of the mass of the natural graphite.

[0021] Preferably, in the above method for preparing densified natural graphite, the asphalt includes at least one of coal tar pitch, mesophase pitch, and petroleum pitch;

[0022] Further preferably, the coal tar pitch includes at least one of medium-temperature coal tar pitch, low-temperature coal tar pitch, and high-temperature coal tar pitch.

[0023] Preferably, in the above method for preparing densified natural graphite, the carbonization in step (2) is coating carbonization; and the carbonization is carried out in a protective atmosphere, the carbonization temperature is 1100 - 1500 °C, and the carbonization time is 3 - 8 h;

[0024] Further preferably, the coating carbonization method uses any one of a box furnace, a roller hearth kiln, a pusher kiln, and a tunnel kiln;

[0025] Further preferably, the protective atmosphere is any one or a combination of several of nitrogen, helium, neon, and argon.

[0026] Preferably, in the above method for preparing densified natural graphite, after the crushing in step (2), classification is further included, and the classification is to pass the crushed natural graphite through a 100-mesh sieve.

[0027] The present invention also provides a densified natural graphite prepared by the above method, and the D50 of the natural graphite is 7 - 17 μm.

[0028] The present invention also provides a battery negative electrode, including the densified natural graphite prepared by the above method.

[0029] And the present invention also provides a lithium-ion battery, including the battery negative electrode as described above.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] The present invention uses a conductive polymer to fill the pores of natural graphite, and uses an extrusion device for mechanical extrusion to densify the interior of the material, and then obtains a densified natural graphite material through carbonization coating, crushing, and classification. The method is simple, the conditions are mild and controllable, and the modified natural graphite obtained as a negative electrode material can endow the battery with excellent cycle performance and rate performance. Description of the Drawings

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained according to the provided drawings without creative efforts.

[0033] Figure 1 It is the SEM cross-sectional view of the densified natural graphite material in the embodiment of the present invention;

[0034] Figure 2 It is the SEM cross-sectional view of the conventional natural graphite material in Comparative Example 1 of the present invention. Detailed Embodiments

[0035] The following will clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0036] Example 1

[0037] A method for preparing densified natural graphite, comprising the following steps:

[0038] (1) Dissolve 100 g of polypyrrole conductive polymer in 1000 mL of water, stir for 3 h until the polypyrrole is completely dissolved, to obtain a polypyrrole conductive polymer solution;

[0039] (2) Mix 2000 g of spherical natural graphite with the polypyrrole conductive polymer solution evenly, then add them into an extrusion sleeve extruder. First, use a vacuum pump to evacuate for 3 h, and the evacuation pressure is 50 Pa, so that the conductive polymer solution flows and fills into the internal pores of the natural spherical graphite under the drive of the pressure difference. Then, use the extrusion sleeve extruder to mechanically extrude for 3 h at a pressure of 0.5 Mpa to densify the inside of the graphite particles. Then, heat at 60 °C for 3 h to dry the solvent, and obtain an intermediate product after cooling;

[0040] (3) Mix the intermediate product and 160 g of medium-temperature coal tar pitch evenly, put them into a box furnace for carbonization. Under an argon atmosphere, heat from room temperature to 1200 °C at a heating rate of 5 °C per 5 min, and hold for 3 h at 1200 °C and then take out;

[0041] (4) The carbonized material is pulverized in a disintegrator at 300 r per 5 min for 2 h, and then passed through a 100-mesh vibrating screen to obtain a densified natural graphite material.

[0042] Example 2

[0043] A method for preparing densified natural graphite, comprising the following steps:

[0044] (1) Dissolve 150 g of polypyrrole conductive polymer in 1000 mL of water, stir for 3 h until the polypyrrole is completely dissolved, to obtain a polypyrrole conductive polymer solution;

[0045] (2) Mix 2000 g of spherical natural graphite with the polypyrrole conductive polymer solution evenly, then add them into an extrusion sleeve extruder. First, use a vacuum pump to evacuate for 5 h, and the evacuation pressure is 60 Pa, so that the conductive polymer solution flows and fills into the internal pores of the natural spherical graphite under the drive of the pressure difference. Then, use the extrusion sleeve extruder to mechanically extrude for 2 h at a pressure of 0.8 Mpa to densify the inside of the graphite particles. Then, heat at 80 °C for 3 h to dry the solvent, and obtain an intermediate product after cooling;

[0046] (3) Mix the intermediate product and 240 g of petroleum pitch evenly, put them into a box furnace for carbonization. Under an argon atmosphere, heat from room temperature to 1300 °C at a heating rate of 5 °C per 5 min, and hold for 3 h at 1300 °C and then take out;

[0047] (4) The carbonized material is pulverized in a disintegrator at 300 r / min for 2 h, and then passed through a 100-mesh vibrating screen to obtain the densified natural graphite material.

[0048] Example 3

[0049] A preparation method of densified natural graphite includes the following steps:

[0050] (1) Dissolve 200 g of polypyrrole conductive polymer in 1000 mL of water, and stir for 3 h until the polypyrrole is completely dissolved to obtain a polypyrrole conductive polymer solution;

[0051] (2) Mix 2000 g of spherical natural graphite with the polypyrrole conductive polymer solution evenly, then add them into an extrusion sleeve extruder. First, use a vacuum pump to evacuate for 4 h, and the evacuation pressure is 30 Pa, so that the conductive polymer solution flows and fills the internal pores of the natural spherical graphite under the drive of the pressure difference. Then, use the extrusion sleeve extruder to mechanically extrude at a pressure of 0.5 Mpa for 3 h to densify the inside of the graphite particles. Then, heat at 120 °C for 3 h to dry the solvent, and obtain an intermediate product after cooling;

[0052] (3) Mix the intermediate product and 500 g of mesophase pitch evenly, put them into a box furnace for carbonization. Under an argon atmosphere, heat from room temperature to 1500 °C at a heating rate of 5 °C / min, and hold at 1500 °C for 3 h, then take it out;

[0053] (4) The carbonized material is pulverized in a disintegrator at 300 r / min for 2 h, and then passed through a 100-mesh vibrating screen to obtain the densified natural graphite material.

[0054] Example 4

[0055] A preparation method of densified natural graphite includes the following steps:

[0056] (1) Dissolve 600 g of polypyrrole conductive polymer in 2500 mL of water, and stir for 3 h until the polypyrrole is completely dissolved to obtain a polypyrrole conductive polymer solution;

[0057] (2) Mix 2000 g of spherical natural graphite with the polypyrrole conductive polymer solution evenly, then add them into an extrusion sleeve extruder. First, use a vacuum pump to evacuate for 6 h, and the evacuation pressure is 20 Pa, so that the conductive polymer solution flows and fills the internal pores of the natural spherical graphite under the drive of the pressure difference. Then, use the extrusion sleeve extruder to mechanically extrude at a pressure of 0.2 Mpa for 6 h to densify the inside of the graphite particles. Then, heat at 100 °C for 3 h to dry the solvent, and obtain an intermediate product after cooling;

[0058] (3) Mix the intermediate product and 400 g of medium-temperature coal tar pitch evenly and put them into a box furnace for carbonization. Under an argon atmosphere, heat from room temperature to 1100 °C at a heating rate of 5 °C per 5 min, and keep it at 1100 °C for 8 h before taking it out;

[0059] (4) The carbonized material is pulverized in a disintegrator at 300 r per 5 min for 2 h, and then passed through a 100-mesh vibrating screen to obtain a densified natural graphite material.

[0060] Example 5

[0061] A preparation method of densified natural graphite includes the following steps:

[0062] (1) Dissolve 100 g of polyaniline conductive polymer in 1000 mL of N-methylpyrrolidone, stir for 3 h until the polyaniline is completely dissolved to obtain a polyaniline conductive polymer solution;

[0063] (2) Mix 2000 g of spherical natural graphite with the polyaniline conductive polymer solution evenly, then add them into an extrusion sleeve extruder. First, use a vacuum pump to evacuate for 4 h at a vacuum pressure of 100 Pa, so that the conductive polymer solution flows and fills the internal pores of the natural spherical graphite under the drive of the pressure difference. Then, use the extrusion sleeve extruder to mechanically extrude at a pressure of 0.5 Mpa for 6 h to densify the inside of the graphite particles, and then heat at 80 °C for 3 h to dry the solvent. After cooling, an intermediate product is obtained;

[0064] (3) Mix the intermediate product and 300 g of low-temperature coal tar pitch evenly and put them into a box furnace for carbonization. Under an argon atmosphere, heat from room temperature to 1100 °C at a heating rate of 5 °C per 5 min, and keep it at 1100 °C for 5 h before taking it out;

[0065] (4) The carbonized material is pulverized in a disintegrator at 300 r per 5 min for 2 h, and then passed through a 100-mesh vibrating screen to obtain a densified natural graphite material.

[0066] Example 6

[0067] A preparation method of densified natural graphite includes the following steps:

[0068] (1) Dissolve 100 g of polymethyl methacrylate conductive polymer in 1000 mL of acetic acid, stir for 3 h until the polymethyl methacrylate is completely dissolved to obtain a polymethyl methacrylate conductive polymer solution;

[0069] (2) Mix 2000 g of spherical natural graphite with the polymethyl methacrylate conductive polymer solution evenly, then add it into an extrusion sleeve extruder. First, use a vacuum pump to evacuate for 8 h at a vacuum pressure of 80 Pa, so that the conductive polymer solution flows and fills the internal pores of the natural spherical graphite under the drive of the pressure difference. Then, use the extrusion sleeve extruder to mechanically extrude for 4 h at a pressure of 0.5 Mpa to densify the inside of the graphite particles. Then, heat and dry the solvent at 80 °C for 3 h, and obtain an intermediate product after cooling;

[0070] (3) Mix the intermediate product and 200 g of high-temperature coal tar pitch evenly and put them into a box furnace for carbonization. Under an argon atmosphere, heat from room temperature to 1200 °C at a heating rate of 5 °C every 5 min, and hold for 3 h at 1200 °C and then take out;

[0071] (4) The carbonized material is pulverized in a disintegrator at 300 r every 5 min for 2 h, and then passed through a 100-mesh vibrating screen to obtain a densified natural graphite material.

[0072] As Figure 1 shown, it is the SEM sectional view of the natural graphite material prepared in the embodiment of the present invention. The internal pore structure of the particles is dense and the gaps are significantly less, effectively improving the internal structure of natural graphite.

[0073] Comparative Example 1

[0074] Comparative Example 1 provides a preparation method of conventional natural graphite, including the following steps:

[0075] 1) Mix 2000 g of spherical natural graphite and 160 g of medium-temperature coal tar pitch evenly and put them into a box furnace for carbonization. Under an argon atmosphere, at a heating rate of 5 °C every 5 min, hold for 3 h at 1200 °C and then take out;

[0076] 2) The carbonized material is pulverized in a disintegrator at 300 r every 5 min for 2 h, and then passed through a 100-mesh vibrating screen to obtain a conventional natural graphite material.

[0077] As Figure 2 shown, it is the SEM sectional view of the natural graphite material prepared in Comparative Example 1. The internal pores of the particles are large and numerous, and the density is poor, and the internal structure of natural graphite cannot be significantly improved.

[0078] Comparative Example 2

[0079] Comparative Example 2 provides a preparation method of natural graphite, which is basically the same as that of Example 1, and the difference is only in step (1):

[0080] (1) Dissolve 80 g of polypyrrole conductive polymer in 1000 mL of water, stir for 3 h until the polypyrrole is completely dissolved, and obtain a polypyrrole conductive polymer solution.

[0081] Comparative Example 3

[0082] Comparative Example 3 provides a method for preparing natural graphite, which is basically the same as that of Example 1, except for the difference in step (1):

[0083] (1) Dissolve 60 g of polypyrrole conductive polymer in 1000 mL of water, stir for 3 h until the polypyrrole is completely dissolved, and obtain a polypyrrole conductive polymer solution.

[0084] Comparative Example 4

[0085] Comparative Example 4 provides a method for preparing natural graphite, which is basically the same as that of Example 1, except for the difference in step (1):

[0086] (1) Dissolve 700 g of polypyrrole conductive polymer in 5000 mL of water, stir for 3 h until the polypyrrole is completely dissolved, and obtain a polypyrrole conductive polymer solution.

[0087] Comparative Example 5

[0088] Comparative Example 5 provides a method for preparing natural graphite, which is basically the same as that of Example 1, except for the difference in step (3):

[0089] (3) Mix the intermediate product and 140 g of medium-temperature coal tar pitch evenly, put them into a box furnace for carbonization, heat from room temperature to 1200 °C at a heating rate of 5 °C every 5 min under an argon atmosphere, and keep it at 1200 °C for 3 h and then take it out.

[0090] Comparative Example 6

[0091] Comparative Example 6 provides a method for preparing natural graphite, which is basically the same as that of Example 1, except for the difference in step (3):

[0092] (3) Mix the intermediate product and 100 g of medium-temperature coal tar pitch evenly, put them into a box furnace for carbonization, heat from room temperature to 1200 °C at a heating rate of 5 °C every 5 min under an argon atmosphere, and keep it at 1200 °C for 3 h and then take it out.

[0093] Comparative Example 7

[0094] Comparative Example 7 provides a method for preparing natural graphite, which is basically the same as that of Example 1, except for the difference in step (3):

[0095] (3) Mix the intermediate product and 500 g of medium-temperature coal tar pitch evenly, put them into a box furnace for carbonization, heat from room temperature to 1200 °C at a heating rate of 5 °C every 5 min under an argon atmosphere, and keep it at 1200 °C for 3 h and then take it out.

[0096] Comparative Example 8

[0097] Comparative Example 8 provides a method for preparing natural graphite, which is substantially the same as Example 1, except that step (3) is different:

[0098] (3) The intermediate product and 520 g of medium-temperature coal tar pitch were mixed evenly and placed in a box furnace for carbonization. The temperature was raised from room temperature to 1200 °C at a heating rate of 5 °C 5 min under an argon atmosphere, and kept at 1200 °C for 3 h before being taken out.

[0099] Comparative Example 9

[0100] Comparative Example 9 provides a method for preparing natural graphite, which is substantially the same as Example 1, except that step (2) is different:

[0101] (2) 2000 g of spherical natural graphite and polypyrrole conductive polymer solution were mixed evenly, then heated at 60° C. for 3 h to dry the solvent, and then cooled to obtain an intermediate product.

[0102] Comparative Example 10

[0103] Comparative Example 10 provides a method for preparing natural graphite, which is substantially the same as Example 1, except that step (2) is different:

[0104] (2) 2000 g of spherical natural graphite and polypyrrole conductive polymer solution were mixed evenly and added to an extrusion sleeve extruder. The mixture was first vacuumed for 3 h with a vacuum pump at a pressure of 50 Pa, and then heated at 60 ° C for 3 h to dry the solvent. The intermediate product was obtained after cooling.

[0105] Comparative Example 11

[0106] Comparative Example 11 provides a method for preparing natural graphite, which is substantially the same as Example 1, except that step (2) is different:

[0107] (2) 2000 g of spherical natural graphite and polypyrrole conductive polymer solution were mixed evenly, and then mechanically extruded for 3 h at a pressure of 0.5 MPa using an extrusion sleeve extruder to densify the interior of the graphite particles. The solvent was then dried by heating at 60° C. for 3 h, and the intermediate product was obtained after cooling.

[0108] Comparative Example 12

[0109] Comparative Example 12 provides a method for preparing natural graphite, which is substantially the same as Example 1, except that step (2) is different:

[0110] (2) After mixing 2000 g of spherical natural graphite with a polypyrrole conductive polymer solution evenly, add them into an extrusion sleeve extruder. First, use a vacuum pump to evacuate for 2 h at a vacuum pressure of 50 Pa, so that the conductive polymer solution flows and fills into the internal pores of the natural spherical graphite under the drive of the pressure difference. Then, use the extrusion sleeve extruder to mechanically extrude at a pressure of 0.5 Mpa for 3 h to densify the inside of the graphite particles. Then, heat at 60 °C for 3 h to dry the solvent, and obtain an intermediate product after cooling.

[0111] Comparative Example 13

[0112] Comparative Example 13 provides a preparation method of natural graphite, which is basically the same as that of Example 1, and the difference is only in step (2):

[0113] (2) After mixing 2000 g of spherical natural graphite with a polypyrrole conductive polymer solution evenly, add them into an extrusion sleeve extruder. First, use a vacuum pump to evacuate for 3 h at a vacuum pressure of 50 Pa, so that the conductive polymer solution flows and fills into the internal pores of the natural spherical graphite under the drive of the pressure difference. Then, use the extrusion sleeve extruder to mechanically extrude at a pressure of 0.1 Mpa for 7 h to densify the inside of the graphite particles. Then, heat at 60 °C for 3 h to dry the solvent, and obtain an intermediate product after cooling.

[0114] Comparative Example 14

[0115] Comparative Example 14 provides a preparation method of natural graphite, which is basically the same as that of Example 1, and the difference is only in step (2):

[0116] (2) After mixing 2000 g of spherical natural graphite with a polypyrrole conductive polymer solution evenly, add them into an extrusion sleeve extruder. First, use a vacuum pump to evacuate for 3 h at a vacuum pressure of 50 Pa, so that the conductive polymer solution flows and fills into the internal pores of the natural spherical graphite under the drive of the pressure difference. Then, use the extrusion sleeve extruder to mechanically extrude at a pressure of 1 Mpa for 1.5 h to densify the inside of the graphite particles. Then, heat at 60 °C for 3 h to dry the solvent, and obtain an intermediate product after cooling.

[0117] In addition, the present invention measures the electrochemical performance of the material by applying the prepared natural graphite material to the negative electrode of the battery.

[0118] Among them, the preparation method of the battery is as follows:

[0119] (a) Prepare several copper foils with a diameter of 8 mm and a thickness of 6 μm, and ultrasonically clean them in a 1 mol 5 L dilute hydrochloric acid and acetone solution for 3 - 5 min to wash away the surface oxides and oil stains. Then, wash them with deionized water and alcohol 3 - 4 times respectively, and then dry and weigh them;

[0120] (b) Prepare a 100 mg / 5 mL polyvinylidene fluoride solution with N-methylpyrrolidone as the solvent. Mix natural graphite material, carbon black, and polyvinylidene fluoride in a mass ratio of 8:1:1, and grind them to make them evenly mixed to obtain electrode paste;

[0121] (c) Coat the prepared electrode paste evenly on the copper foil treated in step (a), put it into a vacuum drying oven, and vacuum dry it at 70 °C for 24 h to obtain an electrode sheet;

[0122] (d) Wrap the electrode sheet prepared in step (c) with clean copper foil on both the upper and lower sides, place it in a flat, rigid, and clean stainless steel mold, and press it into shape under a pressure of 10 MPa to obtain a sample electrode sheet. Then assemble it into a button-type half-cell in a glove box filled with argon.

[0123] Prepare batteries using the natural graphite materials of Examples 1-6 and Comparative Examples 1-11 as raw materials according to the above method, and test the charge-discharge performance of the batteries. Specifically, use the LAND battery test system to perform charge-discharge performance tests at a rate of 1 C. The results are shown in Table 1:

[0124] Table 1 Charge-discharge performance test results

[0125]

[0126]

[0127] As can be seen from Table 1, after 500 cycles at a rate of 1 C, the capacities of the batteries containing the natural graphite materials of the embodiments of the present invention are all above 330 mAh / g, and the highest capacity is 350.97 mAh / g; -1 and the capacity retention rates are all greater than 92%, and the highest capacity retention rate is 95.92%; while the capacity of the battery containing the natural graphite material of Comparative Example 1 after 500 cycles at a rate of 1 C is 320.94 mAh / g, -1 and the capacity retention rate is 89.10%; -1

[0128] In addition, it can be respectively obtained from Comparative Examples 2-4, Comparative Examples 5-8, and Comparative Examples 9-14 that the changes in the addition amount of conductive polymer, the addition amount of pitch, and conditions such as vacuum pumping and extrusion have extremely important effects on the capacity retention rate, cycle performance, and charging ability of the battery;

[0129] And the 25 °C 50% S2C charging constant current ratio DCR of the batteries containing the natural graphite materials of the embodiments of the present invention is less than 60 mΩ, and the charging ability is better than that of the comparative examples, and there is more excellent rate performance.

[0130] Therefore, the battery containing the natural graphite material prepared by the method of the present invention has better capacity retention performance, Coulomb efficiency and rate performance.

[0131] In this specification, each embodiment is described in a progressive manner. The key point of each embodiment is to illustrate the differences from other embodiments. For the same or similar parts among the embodiments, reference can be made to each other. For the solutions disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the descriptions are relatively simple. For the relevant parts, reference can be made to the description in the method part.

[0132] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but will be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing densified natural graphite, characterized in that, The following steps are involved: (1) mixing natural graphite with a conductive polymer solution, adding the mixed mixture into an extruder for vacuuming and extrusion, and then heating, drying, and cooling to obtain an intermediate product; (2) uniformly mixing the intermediate product with asphalt, carbonizing, and pulverizing to obtain densified natural graphite; The mass ratio of the natural graphite to the conductive polymer in step (1) is 1:(0.05-0.3); The amount of asphalt added in step (2) is 8-25% of the mass of the natural graphite; The asphalt includes at least one of coal asphalt, mesophase asphalt, and petroleum asphalt.

2. The method for preparing densified natural graphite according to claim 1, wherein The conductive polymer in step (1) includes at least one of polyaniline, polypyrrole, polymethyl methacrylate, polythiophene, and polyphenylene vinylene.

3. The method for preparing densified natural graphite according to claim 1, wherein The vacuuming time in step (1) is 3-8 hours and the pressure is 10-100 Pa.

4. The method for preparing densified natural graphite according to claim 1, wherein The extrusion time in step (1) is 2-6 hours and the pressure is 0.2-0.8 MPa.

5. The method for preparing densified natural graphite according to claim 1, wherein The heating and drying temperature in step (1) is 60-120° C., and the time is 10-30 min.

6. The method for preparing densified natural graphite according to claim 1, wherein The carbonization in step (2) is coating carbonization; and the carbonization is carried out under a protective atmosphere, the carbonization temperature is 1100-1500° C., and the carbonization time is 3-8 hours.

7. A densified natural graphite prepared by the method according to any one of claims 1 to 6, characterized in that: The D50 of the natural graphite is 7-17 μm.

8. Use of the densified natural graphite prepared by the method according to any one of claims 1 to 6 in a battery negative electrode.

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