CN117682515A - Preparation method of secondary granulated natural graphite, product and application thereof - Google Patents
Preparation method of secondary granulated natural graphite, product and application thereof Download PDFInfo
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- 238000002360 preparation method Methods 0.000 title claims abstract description 33
- 239000007770 graphite material Substances 0.000 claims abstract description 62
- 238000009818 secondary granulation Methods 0.000 claims abstract description 33
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- KXGFMDJXCMQABM-UHFFFAOYSA-N 2-methoxy-6-methylphenol Chemical compound [CH]OC1=CC=CC([CH])=C1O KXGFMDJXCMQABM-UHFFFAOYSA-N 0.000 claims description 2
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Abstract
The invention discloses a preparation method of a secondary granulation natural graphite material, which comprises the following steps: (1) Uniformly mixing natural graphite micropowder tailing with a binder to obtain a mixture; (2) Adding the mixture into a continuous coating granulator for secondary granulation; (3) scattering and grading the product after the secondary granulation; (4) And (3) graphitizing the graded product at high temperature, and finally scattering, screening and demagnetizing to obtain the secondary granulated natural graphite material. According to the preparation method disclosed by the invention, natural graphite micropowder tailing is used as a raw material, and the appearance performance and electrochemical performance of the prepared secondary granulated natural graphite material are equivalent to or even better than those of spherical graphite produced by natural graphite through accurate regulation and control of secondary granulation, scattering and grading processes; in addition, the yield of the secondary granulated natural graphite material obtained by the preparation method is up to more than 98%, and the recycling utilization of natural graphite micropowder tailings with full and high added value can be realized.
Description
Technical Field
The invention relates to the technical field of graphite materials, in particular to a preparation method of secondary granulated natural graphite, a product and application thereof.
Background
Lithium ion batteries have become an important energy storage solution and an indispensable tool in modern society; with thirty years of market development, lithium ion battery technology has achieved significant commercial success. Compared with other types of rechargeable system batteries such as lead-acid batteries, nickel-hydrogen batteries and the like, the lithium ion battery has the advantages of high working voltage, high energy density, long cycle life, small self discharge, no memory effect and the like, and the popularization of consumer portable electronic products is dominant in the energy storage market at present. More importantly, the market for electric vehicles is increasing, and the demand for lithium ion batteries is expected to further increase commercialization of electric vehicles in the next few years.
Currently, the negative electrode material of the commercial lithium ion battery is still a dominant graphite material; natural graphite is widely applied to lithium ion batteries because of the advantages of high charge and discharge capacity, good charge and discharge platform, abundant resources, low cost and the like; spherical graphite with d50=10 to 25 μm is widely used in the market at present, with d50=15 to 20 μm being the most used. In the process of producing the spherical graphite with d50=10-25 μm, the natural graphite needs to undergo the procedures of crushing, sphericizing, classifying and screening for many times, the yield of the product is about 40-50%, and the rest 50-60% of tailings can not be used for lithium ion anode materials due to small granularity, low tap density and large specific surface area, and can only be used as a cheap metallurgical carburant or refractory material, so that the resource waste is caused, and the cost pressure of enterprises is increased.
Many solutions to the above problems have been proposed by researchers. Among them, the recombination with carbon is one of the most important solutions. This is because carbon has high electron conductivity, and recombination with carbon can increase the particle size and conductivity of the system as a whole. Such as:
juan Carlos Abrego-Martinez et al (Abrego-Martinez J C, wang Y, vanpeene V, et al from waste graphite fines to revalorized anode material for Li-ion batteries [ J ]. Carbon,2023, 209:118004.) propose re-agglomeration of graphite micropowder tails from spheroidization of natural graphite by spray-drying granulation to obtain spherical graphite particles of a size comparable to the commercial graphite standard (16-17 μm) as a strategy for waste recovery and possible re-integration into a battery grade graphite production chain. However, the specific surface area of the obtained graphite agglomerate is large, the mechanical strength of the product is insufficient, and the situation can lead to a larger solid electrolyte interface and a higher irreversible capacity of the lithium ion battery, so that the reconstituted graphite agglomerate still cannot meet the market demand.
Therefore, the problem of how to fully utilize the graphite micropowder tailings for producing lithium ion battery negative electrode materials has not been really solved; how to efficiently utilize the graphite micropowder tailings to prepare large-particle graphite particles so that the large-particle graphite particles have excellent electrochemical performance characteristics of low specific surface area, high rate performance and long cycle performance is still the key point of current research.
Disclosure of Invention
Aiming at the problems in the prior art, the invention discloses a preparation method of a secondary granulated natural graphite material, which takes natural graphite micropowder tailings as raw materials, and the appearance performance and the electrochemical performance of the prepared secondary granulated natural graphite material are equivalent to and even better than those of spherical graphite produced by natural graphite through the accurate regulation and control of secondary granulation, scattering and grading processes; in addition, the yield of the secondary granulated natural graphite material obtained by the preparation method is up to more than 98%, and the recycling utilization of natural graphite micropowder tailings with full and high added value can be realized.
The specific technical scheme is as follows:
a preparation method of a secondary granulated natural graphite material comprises the following steps:
(1) Uniformly mixing natural graphite micropowder tailing with a binder to obtain a mixture;
(2) Adding the mixture into a continuous coating granulator for secondary granulation;
the secondary granulation is carried out, the granulation temperature is higher than the softening point of the binder, and the temperature difference DeltaT is more than or equal to 200 ℃; the rotation speed is 12+/-3 Hz;
(3) Scattering and grading the product obtained after the secondary granulation in the step (2);
the frequency of the host machine is 30-40 Hz;
the frequency of the grading 1 is 10+/-5 Hz, and the frequency of the grading 2 is 20+/-10 Hz;
when the main machine frequency is 30-35 Hz, the grading 1 frequency is 10-15 Hz, and the grading 2 frequency is 20-30 Hz;
when the main machine frequency is 35-40 Hz, the grading 1 frequency is 5-10 Hz, and the grading 2 frequency is 10-20 Hz;
(4) And (3) graphitizing the graded product in the step (3) at high temperature, and finally scattering, screening and demagnetizing to obtain the secondary granulating natural graphite material.
The natural graphite micropowder tailing is derived from waste materials in the process of producing spherical graphite from natural graphite, and can not be directly used as a negative electrode material for preparing a lithium ion battery due to small granularity, low tap density and large specific surface area; the preparation method disclosed by the invention takes the natural graphite material as a raw material, fully mixes the natural graphite material with a binder, and sequentially carries out secondary granulation, scattering and grading treatment and high-temperature graphitization treatment to obtain the secondary granulated natural graphite material, wherein the apparent performance and electrochemical performance of the secondary granulated natural graphite material are equivalent to those of spherical graphite produced by natural graphite, and even better; in addition, the yield of the secondary granulated natural graphite material obtained by the preparation method is up to more than 98%, and the recycling utilization of natural graphite micropowder tailings with full and high added value can be realized.
The preparation method adopts the original production line for producing the spherical graphite by using the natural graphite, does not need to increase production equipment, only needs to accurately regulate and control a plurality of parameters in secondary granulation, scattering and grading treatment, and can realize the aim by utilizing the cooperation among the parameters.
In the secondary granulation process, the granulation temperature needs to be accurately regulated and controlled, and the granulation temperature needs to be increased to be higher than the softening point temperature of the binder in order to realize the binding effect of the binder on the raw materials, but experiments prove that if the granulation temperature is only increased to be higher than the softening point temperature but the temperature difference DeltaT is not lower than 200 ℃, the apparent performance and the yield of the prepared secondary granulation natural graphite material are not influenced, but the initial efficiency and the cycle stability of a finally assembled battery are obviously reduced.
Preferably, Δt=250 to 650 ℃.
The rotation speed of the granulator is required to be accurately regulated and controlled in the secondary granulation process, and experiments show that the parameter can influence the particle size distribution of the product after secondary granulation and the stability of the product, and the yield, apparent performance and electrochemical performance of the final product can be influenced by the fact that the parameter is required to be accurately controlled and is too high or too low.
The scattering and grading treatment is very common step in the preparation process of the graphite cathode, but the invention controls the frequency of a host machine in the scattering treatment by carrying out cooperative regulation and control on parameters in the two steps, and simultaneously ensures that the final prepared product has high yield, excellent apparent performance and electrochemical performance by matching with the accurate control of the frequency of the grading 1 and the grading 2 in the grading treatment.
It has been found through experimentation that when the host frequency in the break-up process is too high or too low, or the host frequency in the break-up process does not match the frequencies of stage 1 and stage 2 in the classification process, the yield of the prepared secondary granulated natural graphite material is significantly reduced and the apparent properties of the product, including D50, particularly the specific surface area are significantly changed, resulting in deterioration of the electrochemical properties of the final assembled battery. In step (1):
the D50 of the natural graphite micropowder tailing is selected from 5-10 mu m; the particle size range covers substantially all of the tailings produced during the production of spherical graphite from natural graphite.
The binder is one or more selected from asphalt, phenolic resin, coal tar, polyester resin and epoxy resin;
the mass ratio of the natural graphite micropowder tailing to the binder is 1: (0.05-0.40).
Preferably:
the D50 of the natural graphite micro powder tailing is selected from 5.0-7.5 mu m, and the mass ratio of the natural graphite micro powder tailing to the binder is 1: (0.30 to 0.40);
the D50 of the natural graphite micro powder tailing is 7.5-10.0 mu m, and the mass ratio of the natural graphite micro powder tailing to the binder is 1: (0.25-0.30).
The mass ratio of the more proper binder is matched according to the D50 of different natural graphite micropowder tails, so that the higher yield of the final product and the more excellent apparent performance and electrochemical performance can be ensured.
Further preferred is:
the D50 of the natural graphite micro powder tailing is selected from 5.0-7.5 mu m, and the mass ratio of the natural graphite micro powder tailing to the binder is 1:0.38;
the D50 of the natural graphite micro powder tailing is 7.5-10.0 mu m, and the mass ratio of the natural graphite micro powder tailing to the binder is 1:0.28.
in the step (2):
the secondary granulation is carried out, and the nitrogen flow is 250+/-50 Nm 3 And/h, the feeding frequency is 25+/-5 Hz.
In the step (3):
the feeding frequency is 10+/-2 Hz, and the fan frequency is 40+/-5 Hz.
In the step (4):
in the graphitization process, placing the graded product into a graphitization crucible, loading the graphitization crucible into a graphitization furnace, graphitizing according to an ultrahigh temperature graphitization curve reaching the highest temperature for 55 hours, naturally cooling after heat preservation, and discharging the product after cooling to below 300 ℃. Preferably, the graphitization temperature is 2200-3000 ℃, and the temperature is kept for 4-15 hours at the highest temperature.
Based on the above preferred process parameters, it is further preferred that:
the D50 of the natural graphite micropowder tailing is selected from 5.0-7.5 mu m, and the rotation speed of secondary granulation is 14Hz;
the frequency of the host machine is 31Hz;
the frequency of the grading is 15Hz, and the frequency of the grading is 28Hz.
The D50 of the natural graphite micropowder tailing is 7.5-10.0 mu m, and the rotation speed of secondary granulation is 12Hz;
the frequency of the host machine is 35Hz;
the frequency of the grading is 10Hz, and the frequency of the grading is 20Hz.
The more preferable production process parameters are matched according to the D50 of different natural graphite micropowder tails, so that the higher yield of the final product and the more excellent apparent performance and electrochemical performance can be ensured.
The invention also discloses a secondary granulated natural graphite material prepared by the method, the yield of the method is up to more than 98wt%, and the recycling utilization of natural graphite micropowder tailings with full and high added value is realized. The D50 of the prepared secondary granulated natural graphite material is controlled to be 10-25 mu m, and the secondary granulated natural graphite material has low specific surface area, high tap density and excellent apparent performance.
The secondary battery adopts the secondary granulated natural graphite material as the negative electrode, the electrochemical performance of the secondary granulated natural graphite material can reach the level equivalent to that of spherical graphite prepared from natural graphite, and even better, the secondary battery can be directly used as the negative electrode material instead of the secondary granulated natural graphite material.
Compared with the prior art, the invention has the following advantages:
according to the preparation method disclosed by the invention, the waste material-natural graphite micropowder tailing in the process of producing the spherical graphite from the natural graphite is taken as a raw material, on the premise that the original production line for producing the spherical graphite from the natural graphite is used, production process parameters, especially a plurality of parameters in secondary granulation, scattering and grading treatment, are precisely regulated and controlled on the premise that production equipment is not required to be increased, and the apparent performance and electrochemical performance of the spherical graphite produced from the natural graphite are equivalent to those of even better secondary granulated natural graphite materials can be prepared by utilizing the cooperation among the parameters; in addition, the yield of the secondary granulated natural graphite material obtained by the preparation method is up to more than 98wt%, and the recycling utilization of natural graphite micropowder tailings with full and high added value can be realized.
Drawings
FIG. 1 is an SEM photograph of natural graphite micropowder tailings;
fig. 2 is an SEM photograph of the secondary particulate natural graphite material prepared in example 1.
Detailed Description
The following examples are provided to further illustrate the present invention and should not be construed as limiting the scope of the invention.
Example 1
(1) Mixing natural graphite micropowder tailings (D50=8-9 μm) with coal tar according to a ratio of 78:22, and uniformly mixing the materials to obtain a mixture;
(2) Adding the mixture into a continuous coating granulator for secondary granulation; the nitrogen flow was 250Nm 3 The feeding frequency is 25Hz, the rotating speed is 12Hz, and the temperature is 600 ℃;
(3) Scattering the product obtained after the secondary granulation in the step (2), wherein the host frequency of a scattering machine is 35Hz; then classifying, wherein the feeding frequency of a classifier is 10Hz, the frequency of classification 1 is 10Hz, the frequency of classification 2 is 20Hz, and the frequency of a fan is 40Hz;
(4) Carrying out high-temperature graphitization on the product classified in the step (3), wherein the graphitization temperature is 3000 ℃, preserving heat for 4 hours, naturally cooling after the heat preservation is finished, and discharging after cooling to below 300 ℃;
(5) And (3) scattering and screening the product subjected to the high-temperature graphitization treatment in the step (4), collecting the product with the D50 of 10-25 mu m, and finally carrying out demagnetization to obtain a secondary granulation natural graphite material finished product.
The particle diameter D50, specific surface area and tap density of the secondary particulate natural graphite material prepared in this example are shown in table 1 below, and the yield of the secondary particulate natural graphite material prepared in this example is also shown in table 1 below.
Fig. 1 is an SEM photograph of a natural graphite fine powder tailing material used as a raw material in this example, and fig. 2 is an SEM photograph of a secondary particle natural graphite material prepared in this example, and it can be found that spherical graphite fine powder clusters together after a series of preparation processes, graphite fine powder is closely connected with each other by a binder, and secondary granulation natural graphite surface coating is uniform, complete and firm.
Example 2
The preparation process is basically the same as in example 1, except that the mass ratio of the natural graphite micropowder tailing to the coal tar in step (1) is replaced by 75:25.
the particle diameter D50, specific surface area, tap density and product yield of the secondary particle natural graphite material prepared in this example are listed in table 1 below.
Example 3
The preparation process is basically the same as that in example 1, except that the mass ratio of the natural graphite micro powder tailing to the coal tar in the step (1) is replaced by 95:5.
the particle diameter D50, specific surface area, tap density and product yield of the secondary particle natural graphite material prepared in this example are listed in table 1 below.
Comparative example 1
The preparation process is basically the same as that in example 1, except that the mass ratio of the natural graphite micro powder tailing to the coal tar in the step (1) is replaced by 99:1.
the particle diameter D50, specific surface area, tap density and product yield of the secondary particle natural graphite material prepared in this comparative example are listed in table 1 below.
Example 4
The preparation process was essentially the same as in example 1, except that the rotational speed in step (2) was replaced with 15Hz.
The particle diameter D50, specific surface area, tap density and product yield of the secondary particle natural graphite material prepared in this example are listed in table 1 below.
Example 5
The preparation process was essentially the same as in example 1, except that the rotational speed in step (2) was replaced with 9Hz.
The particle diameter D50, specific surface area, tap density and product yield of the secondary particle natural graphite material prepared in this example are listed in table 1 below.
Comparative example 2
The preparation process was essentially the same as in example 1, except that the rotational speed in step (2) was replaced with 20Hz.
The particle diameter D50, specific surface area, tap density and product yield of the secondary particle natural graphite material prepared in this comparative example are listed in table 1 below.
Comparative example 3
The preparation process was essentially the same as in example 1, except that the rotational speed in step (2) was replaced with 5Hz.
The particle diameter D50, specific surface area, tap density and product yield of the secondary particle natural graphite material prepared in this comparative example are listed in table 1 below.
Comparative example 4
The preparation process was essentially the same as in example 1, except that the temperature of the secondary granulation in step (2) was replaced by 300 ℃.
The particle diameter D50, specific surface area, tap density and product yield of the secondary particle natural graphite material prepared in this comparative example are listed in table 1 below.
Example 6
The preparation process was essentially the same as in example 1, except that the host frequency in step (3) was replaced by 40Hz.
The particle diameter D50, specific surface area, tap density and product yield of the secondary particle natural graphite material prepared in this example are listed in table 1 below.
Example 7
The preparation process was essentially the same as in example 1, except that the host frequency in step (3) was replaced by 30Hz.
The particle diameter D50, specific surface area, tap density and product yield of the secondary particle natural graphite material prepared in this example are listed in table 1 below.
Comparative example 5
The preparation process was essentially the same as in example 1, except that the host frequency in step (3) was replaced with 50Hz.
The particle diameter D50, specific surface area, tap density and product yield of the secondary particle natural graphite material prepared in this comparative example are listed in table 1 below.
Comparative example 6
The preparation process was essentially the same as in example 1, except that the host frequency in step (3) was replaced with 20Hz.
The particle diameter D50, specific surface area, tap density and product yield of the secondary particle natural graphite material prepared in this comparative example are listed in table 1 below.
Comparative example 7
The preparation process was essentially the same as in example 1, except that in step (3):
the host frequency was replaced with 40Hz, the grade 1 frequency with 15Hz, and the grade 2 frequency with 30Hz.
The particle diameter D50, specific surface area, tap density and product yield of the secondary particle natural graphite material prepared in this comparative example are listed in table 1 below.
Comparative example 8
The preparation process was essentially the same as in example 1, except that in step (3):
the host frequency was replaced with 30Hz, the step 1 frequency was replaced with 5Hz, and the step 2 frequency was replaced with 10Hz.
The particle diameter D50, specific surface area, tap density and product yield of the secondary particle natural graphite material prepared in this comparative example are listed in table 1 below.
Example 8
(1) Mixing natural graphite micropowder tailings (D50=5-6 μm) with asphalt according to a ratio of 72:28, uniformly mixing to obtain a mixture;
(2) Adding the mixture into a continuous coating granulator for secondary granulation; the nitrogen flow was 250Nm 3 The feeding frequency is 25Hz, the rotating speed is 14Hz, and the temperature is 500 ℃;
(3) Scattering the product after secondary granulation, wherein the host frequency of a scattering machine is 31Hz; then classifying, wherein the feeding frequency of a classifier is 10Hz, the frequency of classification 1 is 15Hz, the frequency of classification 2 is 28Hz, and the frequency of a fan is 40Hz;
(4) Carrying out high-temperature graphitization on the product classified in the step (3), wherein the graphitization temperature is 3000 ℃, preserving heat for 4 hours, naturally cooling after the heat preservation is finished, and discharging after cooling to below 300 ℃;
(5) Scattering and screening the product subjected to the high-temperature graphitization treatment in the step (4), collecting the product with the D50 of 10-25 mu m, and finally carrying out demagnetization to obtain a secondary granulation natural graphite material finished product.
The particle diameter D50, specific surface area, tap density and product yield of the secondary particle natural graphite material prepared in this example are listed in table 1 below.
TABLE 1
a. The standard is spherical graphite prepared from natural graphite, and the same explanation as the standard in table 2 is made.
Application example
1. The secondary granulated natural graphite materials prepared in each example and each comparative example are used as negative electrode materials to prepare the button cell with the molding number 2032 respectively, and the specific steps are as follows:
mixing a secondary granulated natural graphite material, a conductive agent SP, a dispersing agent CMC and a binder AONE according to the mass ratio of 96:1:0.5:2.5, and preparing negative electrode slurry with the solid content of 45.30wt% by taking water as a solvent; and coating the cathode slurry on a copper foil, and preparing the button cell by taking a lithium sheet as a counter electrode and taking a Celgard 2400 microporous polypropylene film as a diaphragm.
And (3) carrying out charge and discharge circulation on the prepared button battery, wherein the charge and discharge conditions are as follows:
the charge/discharge cutoff voltage was 0.01 to 1.5V, the discharge rate was set to 0.005V at 0.1C and then to 0.005V at 0.2C, the discharge was completed, the charge rate was set to 0.5C and charged to 1.5V, and the reversible capacity and the first discharge efficiency of the coin cell were measured, and the results are shown in table 2 below.
2. The secondary granulated natural graphite materials prepared in each example and each comparative example are respectively prepared into small soft-package batteries as cathode materials, and the specific steps are as follows:
mixing the secondary granulated natural graphite material with commercial artificial graphite according to the weight ratio of 8.1:91.9 mass ratio is mixed into active material with 390mAh/g capacity, the active material, binder lithium polyacrylate and conductive agent Super P are dispersed and pulped according to the mass ratio of 95.5:4:0.5, and the battery core preparation procedures of coating, rolling, cutting and the like are carried out, and the battery core preparation procedures are matched with NCM811 positive electrode to prepare a small soft package battery.
And (3) testing the cycle performance: at 25 ℃, the battery subjected to chemical composition is charged to 4.2V at constant current and constant voltage of 0.5C, the cut-off current is 0.02C, the battery is placed for 5min, then the battery is discharged to 2.5V at constant current of 1C, and the battery is placed for 5min. According to the cycle, the 100 th cycle capacity retention rate (500 weeks test and 100 weeks test) is calculated after 100 charge/discharge cycles, and the calculation formula is as follows:
the 100 th cycle capacity retention (%) = (100 th cycle reversible capacity/1 st cycle reversible capacity) ×100%.
The 500 th cycle capacity retention data of the small pouch battery assembled with each comparative example at normal temperature are shown in table 2 below.
TABLE 2
The foregoing is merely a specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and the present invention is described by using the specific examples, which are only for aiding in understanding the present invention, and are not limited thereto. Several simple deductions, variations, substitutions or combinations may also be made by those skilled in the art to which the invention pertains based on the inventive concept. Such deductions, modifications, substitutions or combinations are also within the scope of the claims of the present invention.
Claims (10)
1. The preparation method of the secondary granulated natural graphite material is characterized by comprising the following steps of:
(1) Uniformly mixing natural graphite micropowder tailing with a binder to obtain a mixture;
(2) Adding the mixture into a continuous coating granulator for secondary granulation;
the secondary granulation is carried out, the granulation temperature is higher than the softening point of the binder, and the temperature difference DeltaT is more than or equal to 200 ℃; the rotation speed is 12+/-3 Hz;
(3) Scattering and grading the product obtained after the secondary granulation in the step (2);
the frequency of the host machine is 30-40 Hz;
the frequency of the grading 1 is 10+/-5 Hz, and the frequency of the grading 2 is 20+/-10 Hz;
when the main machine frequency is 30-35 Hz, the grading 1 frequency is 10-15 Hz, and the grading 2 frequency is 20-30 Hz;
when the main machine frequency is 35-40 Hz, the grading 1 frequency is 5-10 Hz, and the grading 2 frequency is 10-20 Hz;
(4) And (3) graphitizing the graded product in the step (3) at high temperature, and finally scattering, screening and demagnetizing to obtain the secondary granulating natural graphite material.
2. The method of producing a secondary granulated natural graphite material as claimed in claim 1, wherein in the step (1):
the D50 of the natural graphite micropowder tailing is selected from 5-10 mu m;
the binder is one or more selected from asphalt, phenolic resin, coal tar, polyester resin and epoxy resin;
the mass ratio of the natural graphite micropowder tailing to the binder is 1: (0.05-0.40).
3. The method of producing a secondary granulated natural graphite material as claimed in claim 1, wherein in the step (2):
the secondary granulation is carried out, and the nitrogen flow is 250+/-50 Nm 3 And/h, the feeding frequency is 25+/-5 Hz.
4. The method of producing a secondary granulated natural graphite material as claimed in claim 1, wherein in the step (3):
the feeding frequency is 10+/-2 Hz, and the fan frequency is 40+/-5 Hz.
5. The method of producing a secondary granulated natural graphite material as claimed in claim 1, wherein in the step (4):
the high-temperature graphitization is carried out at 2200-3000 ℃ for 4-15 h.
6. The method for producing a secondary granulated natural graphite material as claimed in any one of claims 1 to 5, wherein in step (1):
the D50 of the natural graphite micro powder tailing is selected from 5.0-7.5 mu m, and the mass ratio of the natural graphite micro powder tailing to the binder is 1: (0.30 to 0.40);
the D50 of the natural graphite micro powder tailing is 7.5-10.0 mu m, and the mass ratio of the natural graphite micro powder tailing to the binder is 1: (0.25-0.30).
7. The method of producing a secondary granulated natural graphite material as claimed in claim 6, wherein in the step (2):
the D50 of the natural graphite micropowder tailing is selected from 5.0-7.5 mu m, and the rotation speed of secondary granulation is 14Hz;
the D50 of the natural graphite micropowder tailing is 7.5-10.0 mu m, and the rotation speed of secondary granulation is 12Hz.
8. The method of producing a secondary granulated natural graphite material as claimed in claim 7, wherein in the step (3):
the D50 of the natural graphite micropowder tailing is selected from 5.0-7.5 mu m, the scattering is carried out, and the host frequency is 31Hz; the frequency of the grading 1 is 15Hz, and the frequency of the grading 2 is 28Hz;
the D50 of the natural graphite micropowder tailing is 7.5-10.0 mu m, the scattering is carried out, and the host frequency is 35Hz; the frequency of the grading is 10Hz, and the frequency of the grading is 20Hz.
9. A secondary granulated natural graphite material produced according to the method of any of claims 1 to 8.
10. A secondary battery characterized by using the secondary granulated natural graphite material comprising the secondary granulation according to claim 9 as a negative electrode.
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