CN112670466A - Composite graphite negative electrode material, preparation method thereof and lithium ion battery - Google Patents
Composite graphite negative electrode material, preparation method thereof and lithium ion battery Download PDFInfo
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Abstract
The invention discloses a composite graphite negative electrode material, a preparation method thereof and a lithium ion battery. The preparation method comprises the following steps: s1, preparing single particles, which comprises the following steps: sequentially carrying out wet granulation and carbonization treatment on the graphite particles; s2, preparing secondary particles, which comprises the following steps: sequentially carrying out secondary granulation, graphitization treatment, wet granulation and carbonization treatment on the mixture of the substance A and the asphalt; in S2, the substance A is petroleum coke or coal needle coke; in S1 or S2, the coating agent used in the wet granulation is "coal tar or petroleum tar"; and S3, mixing the single particles and the secondary particles to obtain the composite material. The composite graphite cathode material disclosed by the invention is high in discharge capacity, high in first-time efficiency, high in high-rate discharge retention rate, excellent in cycle performance and excellent in comprehensive performance, and the product is easy to produce in mass and can be applied to power lithium batteries of passenger vehicles.
Description
Technical Field
The invention belongs to the field of preparation of negative electrode materials of power lithium batteries of passenger vehicles, and particularly relates to a composite graphite negative electrode material, a preparation method of the composite graphite negative electrode material and a lithium ion battery.
Background
Lithium ion batteries have many advantages of high energy density, long cycle life, small self-discharge, no memory effect, environmental friendliness, etc., and have been widely used in the consumer electronics field. Meanwhile, the electric automobile is gradually popularized in the fields of pure electric, hybrid electric and range-extended electric passenger automobiles, and the market share growth trend is the largest. Meanwhile, the continuous development of the field of electric automobiles puts higher requirements on endurance mileage, multiplying power charge-discharge capacity, service life and the like.
The lithium ion battery mainly comprises a positive electrode, a negative electrode, electrolyte, a diaphragm and the like. In order to obtain better electrochemical performance, the application process of the cathode material is often regulated and optimized by the modes of reducing particle size, carbon coating, blending, special shape design, doping and the like. The blending modification is an effective way for improving the electrochemical comprehensive performance, reducing the cost and improving the safety performance of the material. In order to realize industrialization of the cathode material with excellent comprehensive performance, the research of enhancing physical property matching of the blending material, selecting a charge-discharge mechanism and blending process is urgently needed.
Chinese patent application CN201910941195.2 discloses a method for manufacturing a negative electrode material of a lithium ion battery, which comprises the following steps: crushing and grinding twice to reduce the particle size, mixing and granulating twice, mixing a graphite precursor and a binder, coating, granulating, graphitizing and demagnetizing to obtain the carbon negative electrode material with the surface coated with the artificial graphite layer. The prepared graphite particles are single particles, have large cyclic expansion, and can influence the service life of the battery in the service process of the conventional power lithium battery.
Chinese patent application CN201710159144.5 discloses a preparation method of a high-cycle high-capacity graphite cathode material, which comprises the steps of mixing natural crystalline flake graphite and artificial graphite according to a ratio, crushing by a crusher, finely crushing by an airflow crusher, grading, coating by asphalt and carbonizing; purifying, drying, mixing, shaping, crushing and removing iron; drying and separating the fine powder to obtain the finished product of the lithium battery cathode material. The product uses natural crystalline flake graphite as a main material and artificial graphite as an auxiliary material, and is mixed according to a certain proportion, the mixed material is used as a raw material to be finely crushed and graded, then the asphalt surface is coated, the carbonization treatment is carried out at 1200 ℃, and the mixture is forced to be mixed and sieved. The material obtained by the method is a secondary particle carbonized product, has low tap density and cannot meet the requirement of high rate performance.
Chinese patent application CN201610851983.9 discloses a preparation method of graphite cathode material secondary particles of a lithium ion battery, and the cathode material particles prepared by the method are large, low in transmission efficiency, low in tap density and poor in multiplying power performance.
Disclosure of Invention
The invention aims to solve the technical problem that high discharge capacity and high rate discharge performance in the conventional graphite cathode material are difficult to combine, and provides a composite graphite cathode material, a preparation method thereof and a lithium ion battery. The composite graphite cathode material disclosed by the invention is high in discharge capacity, high in first-time efficiency, high in high-rate discharge retention rate, excellent in cycle performance and excellent in comprehensive performance, and the product is easy to produce in mass and can be applied to power lithium batteries of passenger vehicles.
The present invention solves the above-described problems by the following technical means.
The invention provides a preparation method of a composite graphite cathode material, which comprises the following steps:
s1, preparing single particles, which comprises the following steps: sequentially carrying out wet granulation and carbonization treatment on the graphite particles;
in S1, the median diameter D50 of the single particles is 6.0-9.0 μm;
s2, preparing secondary particles, which comprises the following steps: sequentially carrying out secondary granulation, graphitization treatment, wet granulation and carbonization treatment on the mixture of the substance A and the asphalt;
in S2, the substance A is petroleum coke or coal needle coke;
in S2, the softening point of the asphalt is 110-130 ℃;
in S2, the median diameter D50 of the secondary particles is 12.0-15.0 μm;
in S1 or S2, the coating agent used in the wet granulation is "coal tar or petroleum tar";
s3, mixing the single particles and the secondary particles to obtain the composite material; wherein the mass ratio of the single particles to the secondary particles is 1 (0.11-9).
In S1, the graphite particles may be graphite particles as conventionally described in the art. As a preferred scheme, the graphite particles are prepared by sequentially carrying out heat treatment and graphitization treatment on petroleum coke or shaping materials of coal needle coke.
Wherein the petroleum coke may be conventional in the art. The coal needle coke may be conventional in the art. Preferably, the S content in the petroleum coke or the coal needle coke is less than or equal to 0.45 percent, and the ash content is less than or equal to 0.2 percent.
The median particle diameter D50 of the shaping material is preferably 5.5-8.4 μm, more preferably 6.5-8.0 μm, for example 6.8 μm.
The shaping material can be prepared by a conventional method in the field, and is generally obtained by sequentially crushing, shaping and removing fine powder from the petroleum coke or the coal needle coke. The manner of comminution may be conventional in the art, such as roll milling. The median particle diameter D50 of the pulverized material is preferably 5.0 to 8.0 μm, for example 6.5 μm.
The operation and conditions of the heat treatment can be conventional in the art, and are generally carried out in a horizontal reaction kettle under the protection of inert gas.
Wherein, the inert gas is preferably nitrogen and/or argon.
Wherein the temperature of the heat treatment is preferably 550 to 850 ℃, for example 700 ℃.
The time of the heat treatment is preferably 6 to 20 hours, for example 8 hours.
The operation and conditions of the graphitization treatment may be conventional in the art, among others.
The graphitization treatment temperature is preferably 2800-3200 ℃, for example 3000 ℃.
The graphitization treatment time is preferably 20-60 h, for example 30 h.
The operation and conditions of the wet granulation in S1 or S2 may be conventional in the art, and the treatment is capable of rounding the particle structure.
In S1 or S2, the coal tar may be conventional in the art. The petroleum tar may be conventional in the art. Preferably, the coking value of the coal tar or the petroleum tar is 20-30%. When the coating agent used in wet granulation is asphalt powder, the uniformity of the coating effect is poor, and the structural stability and the cycle performance of the obtained composite graphite cathode material are affected.
Preferably, the wet granulated coating agents in S1 and S2 are the same.
In S1 or S2, the wet granulation is generally carried out in a fusion machine apparatus. In the wet granulation process, the rotation speed is preferably 250 to 1400r/min, for example 280r/min or 300 r/min.
In S1, the time for wet granulation is preferably 8 to 70min, for example, 20 min.
In the wet granulation in S1, the mass ratio of the graphite particles to the coating agent used in the wet granulation in S1 is preferably 100 (2 to 6), for example, 100: 4.
Wherein, preferably, no solvent is involved in the wet granulation process.
In S1 or S2, the carbonization treatment may be carried out under conventional conditions in the art, and is generally carried out under an inert gas atmosphere.
Wherein the temperature of the carbonization treatment is preferably 1000 to 1350 ℃, more preferably 1100 to 1250 ℃, for example 1250 ℃.
Wherein, the inert gas is preferably nitrogen or argon.
The carbonization time is preferably 0.5 to 24 hours, for example, 12 hours.
In S1, the median diameter D50 of the single particles is 6.0-9.0 μm; when the particle diameter of the single particle is greater than 9.0 μm, the high rate performance of the resulting composite graphite anode material may be degraded. The median particle diameter D50 of the individual particles is preferably 7.5 μm.
In S2, the petroleum coke or the coal needle coke may be conventional in the art, and the substance a is preferably petroleum coke or pulverized coal needle coke.
Wherein, the crushed material is obtained by crushing the petroleum coke and/or the coal needle coke. The manner of comminution may be conventional in the art, such as roll milling.
The median particle diameter D50 of the substance A is preferably 8.0-10.0 μm, more preferably 9.0-9.5 μm, for example 9.2 μm.
In S2, the mass ratio of the substance A to the asphalt is preferably 100 (3.5-10.5), for example 100: 6.
the operation and parameters of mixing of said substance a with said bitumen in S2 may be conventional in the art, for example in a CDLW-8000 ribbon mixer.
The time for mixing the substance A and the asphalt is preferably 30-80 min, for example 50 min.
In S2, the operation and conditions of the secondary granulation may be conventional in the art, and are generally carried out in a horizontal reaction vessel.
In S2, the asphalt can be asphalt with a softening point of 110-130 ℃ which is conventional in the art. When the raw material adopted by the secondary granulation is not asphalt or the softening point of the asphalt is not 110-130 ℃, such as petroleum coke, the discharge capacity and high rate performance of the obtained composite graphite negative electrode material are reduced.
Wherein, the temperature of the secondary granulation is preferably 600 to 700 ℃, more preferably 630 to 670 ℃; for example 670 deg.c.
The time for the secondary granulation is preferably 6 to 20 hours, for example, 10 hours.
In S2, the operation and conditions of the graphitization treatment may be conventional in the art.
The graphitization treatment temperature is preferably 2800-3200 ℃, for example 3050 ℃.
The graphitization treatment time is preferably 20-60 h, for example 30 h.
In S2, the time for wet granulation is preferably 5 to 60min, for example, 6 min.
In the wet granulation in S2, the mass ratio of the particles obtained by graphitization treatment to the coating agent used in the wet granulation in S2 is preferably 100 (5 to 10), for example, 100: 7.
Wherein, preferably, no solvent is involved in the wet granulation process.
In S2, the median diameter D50 of the secondary particles is 12.0-15.0 μm; when the particle size of the secondary particles is less than 12.0 μm, even if the secondary particles are mixed with the single particles in the S1, the obtained composite graphite anode material is influenced in the aspects of high rate performance, discharge capacity, compaction density and cycle performance; when the particle size of the secondary particles is larger than 15.0 μm, the difficulty of the granulation process is increased, and advantages are difficult to bring to the electrochemical performance of the obtained composite graphite anode material. The median particle diameter D50 of the secondary particles is preferably 14.7 μm.
In S3, the mixing operations and conditions may be conventional in the art, for example in a CDLW-6000 ribbon blender.
Wherein the mixing time is preferably 40-60 min, more preferably 50-55 min.
In S3, the mass ratio of the single particles to the secondary particles is preferably 1 (0.2 to 4), for example, 20:80, 30:70, 40:60, 50:50, 60:40, 70:30, 80: 20.
The invention also provides the composite graphite cathode material prepared by the preparation method of the composite graphite cathode material.
Preferably, the median particle diameter D50 of the composite graphite negative electrode material is 10.1-12.1 μm; the particle size distribution of the particles of the composite graphite negative electrode materialThe range is 0.4-38.5 μm; the tap density of the composite graphite cathode material is more than or equal to 1.1g/cm3The specific surface area is more than or equal to 1.65m2G, the compacted density is more than or equal to 1.61g/cm3The discharge capacity is more than or equal to 353.8mAh/g, and the first efficiency is more than or equal to 92.9 percent.
The invention also provides a lithium ion battery which contains the composite graphite negative electrode material.
On the basis of the common knowledge in the field, the above preferred conditions can be combined randomly to obtain the preferred embodiments of the invention.
The reagents and starting materials used in the present invention are commercially available.
The positive progress effects of the invention are as follows:
according to the preparation method, the particle sizes of the single-particle structure and the secondary-particle structure are accurately regulated and controlled, the preparation procedures (including selection of a coating agent for wet granulation, binder asphalt in the secondary granulation process and the like) are accurately regulated and controlled, and the single-particle structure and the secondary-particle structure are mixed according to a specific proportion, so that the prepared composite graphite negative electrode material has excellent performance in the aspects of indexes such as discharge capacity, primary efficiency, high-rate discharge and circulation.
Drawings
Fig. 1 is a Scanning Electron Microscope (SEM) image of a composite graphite anode material prepared according to example 1 of the present invention.
Detailed Description
The invention is further illustrated by the following examples, which are not intended to limit the scope of the invention. The experimental methods without specifying specific conditions in the following examples were selected according to the conventional methods and conditions, or according to the commercial instructions.
The term "single particles" as used herein refers to particles that are agglomerated without binding.
The median particle diameter D50 and the particle size distribution are measured by a laser particle size distribution instrument MS 3000.
In the examples and comparative examples of the present invention:
the petroleum coke is commercially available, and mainly comprises carbon atoms and hydrogen atoms, water content is 0.65%, ash content is 0.2%, volatile matter is 7.1%, and S content is less than or equal to 0.45%.
The asphalt is commercially available and has a softening point of 110-130 ℃.
The coal tar is commercially available, and the coking value of the coal tar is 20-30%.
Example 1
The preparation method of the composite graphite negative electrode material of the embodiment specifically comprises the following steps:
preparation of mono-and single-particles
(1) Grinding and crushing petroleum coke raw materials by a roller, wherein the median particle size D50 of the crushed materials is 6.5 mu m, and shaping and removing fine powder to obtain a shaped material, wherein the median particle size D50 of the shaped material is 6.8 mu m;
(2) carrying out heat treatment on the shaping material in a horizontal reaction kettle under the protection of inert gas, wherein the temperature is 700 ℃, and the time is 8 hours;
(3) graphitizing at 3000 deg.C for 30h to obtain graphite particles;
(4) carrying out wet granulation in a fusion machine device, rounding the granules, wherein the rotating speed of the fusion machine is 280r/min, the time is 20min, the coating agent is coal tar, and no solvent is involved in the wet granulation process; the mass ratio of the graphite particles to the coal tar is 100: 4;
(5) under the protection of inert gas, heating in a calcining device for carbonization treatment, keeping the temperature at 1250 ℃ for 12 hours to obtain a single-particle structure with a surface carbon coating, wherein the median particle diameter D50 is 7.5 mu m;
preparation of secondary particles
(6) Grinding and crushing petroleum coke raw materials by a roller, wherein the median particle size D50 of the crushed materials is 9.2 mu m;
(7) mixing the crushed materials with asphalt according to a mass ratio of 100: 6.0 fully mixing in a CDLW-8000 ribbon mixer for 50 minutes;
(8) under the protection of inert gas, carrying out secondary granulation in a horizontal reaction kettle, wherein the temperature of the secondary granulation is 670 ℃ and the time is 10 hours;
(9) graphitizing at 3050 ℃ for 30 h;
(10) performing wet granulation in a fusion machine device, rounding the granules, wherein the rotating speed of the fusion machine is 300r/min, the time is 6min, and the coating agent is the coal tar used in the step (4); no solvent is involved in the wet granulation process; the mass ratio of the particles obtained by graphitization treatment in the step (9) to the coating agent is 100: 7;
(11) under the protection of inert gas, heating in a calcining device for carbonization treatment, keeping the temperature at 1250 ℃ for 12 hours to obtain a secondary particle structure with a surface carbon coating, wherein the median particle diameter D50 is 14.7 mu m;
thirdly, mixing the single particles and the secondary particles
(12) And (3) mixing the surface carbon-coated single particles obtained in the step (5) and the surface carbon-coated secondary particles obtained in the step (11) in a CDLW-6000 mixed material, wherein the feeding proportion is 40: and 60, mixing for 50 minutes. The obtained composite graphite cathode material has a median particle diameter D50 of 12.1 μm, a particle diameter distribution range of 0.8-38.5 μm, and a tap density of 1.18g/cm3Specific surface area of 1.67m2The specific weight percentage is as follows,/g, the discharge capacity is 354.5mAh/g, and the first efficiency is 93.8%.
Example 2:
the present embodiment is different from embodiment 1 in that: and (3) mixing the surface carbon-coated single particles obtained in the step (5) and the surface carbon-coated secondary particles obtained in the step (11) according to the weight ratio of 50: 50. The median particle diameter D50 of the obtained composite graphite is 11.1 μm, the particle diameter distribution range of the particles is 0.6-35.8 μm, and the tap density is 1.15g/cm3Specific surface area of 1.72m2The specific weight percentage is as follows,/g, the discharge capacity is 354.2mAh/g, and the first efficiency is 93.3%.
Example 3:
the present embodiment is different from embodiment 1 in that: and (3) mixing the surface carbon-coated single particles obtained in the step (5) with the surface carbon-coated secondary particles obtained in the step (11) according to the weight ratio of 70: 30. The median particle diameter D50 of the obtained composite graphite is 10.7 μm, the particle diameter distribution range of the particles is 0.6-29.4 μm, and the tap density is 1.14g/cm3Specific surface area of 1.76m2The specific weight percentage is as follows,/g, the discharge capacity is 354.3mAh/g, and the first efficiency is 93.1%.
Example 4:
this example is different from example 1The method is characterized in that: and (3) mixing the surface carbon-coated single particles obtained in the step (5) with the surface carbon-coated secondary particles obtained in the step (11) according to a weight ratio of 90: 10. The median particle diameter D50 of the obtained composite graphite is 10.1 μm, the particle diameter distribution range of the particles is 0.4-27.9 μm, and the tap density is 1.12g/cm3Specific surface area of 2.02m2The discharge capacity is 353.8mAh/g, and the first efficiency is 92.9%.
Example 5:
the present embodiment is different from embodiment 1 in that: and (3) mixing the surface carbon-coated single particles obtained in the step (5) with the surface carbon-coated secondary particles obtained in the step (11) according to the weight ratio of 30: 70. The median particle diameter D50 of the obtained composite graphite is 11.9 μm, the particle diameter distribution range of the particles is 0.6-36.2 μm, and the tap density is 1.18g/cm3Specific surface area of 1.68m2The specific weight percentage is as follows,/g, the discharge capacity is 354.6mAh/g, and the first efficiency is 93.5%.
Example 6:
the present embodiment is different from embodiment 1 in that: and (3) mixing the surface carbon-coated single particles obtained in the step (5) with the surface carbon-coated secondary particles obtained in the step (11) according to the weight ratio of 10: 90. The median particle diameter D50 of the obtained composite graphite is 12.7 mu m, the particle diameter distribution range of the particles is 0.5-36.5 mu m, and the tap density is 1.17g/cm3Specific surface area of 1.67m2The specific weight percentage is as follows,/g, the discharge capacity is 354.5mAh/g, and the first efficiency is 93.6%.
Comparative example 1:
comparative example 1 differs from example 1 in that: comparative example 1 only a single particle of example 1 was prepared. Median particle diameter D50 of 7.5 μm, particle diameter distribution range of 0.7-28.5 μm, and tap density of 1.13g/cm3Specific surface area of 2.17m2The discharge capacity is 352.9mAh/g, and the first efficiency is 92.2 percent.
Comparative example 2:
comparative example 2 differs from example 1 in that: comparative example 2 only the secondary particles of example 1 were prepared. The median diameter D50 is 14.7 μm, the particle diameter distribution range is 0.8-39.0 μm, and the tap density is 1.03g/cm3Specific surface area of 1.39m2The discharge capacity is 355.8mAh/g, and the first efficiency is 92.9 percent.
Comparative example 3:
comparative example 3 differs from example 1 in that: comparative example 3 only the steps (1) to (3) of example 1 were carried out, and a single granule was obtained (i.e., wet granulation and carbonization treatment were not carried out). The median diameter D50 is 5.9 μm, the particle diameter distribution range is 0.4-19.8 μm, and the tap density is 0.69g/cm3Specific surface area of 3.9m2The discharge capacity is 337.3mAh/g, and the first efficiency is 92.0 percent.
Comparative example 4:
comparative example 4 differs from example 1 in that: the process for preparing the single particle structure of comparative example 4 was conducted only with steps (1) to (3) of example 1; the procedure for preparing the secondary particle structure of comparative example 4 was conducted only with step (6) to step (9) of example 1; the single particles and the secondary particles of comparative example 4 were mixed in a weight ratio of 40: 60. The median particle diameter D50 of the obtained composite graphite is 11.8 μm, the particle diameter distribution range of the particles is 0.5-34.5 μm, and the tap density is 1.07g/cm3Specific surface area of 1.57m2The discharge capacity is 354.8mAh/g, and the first efficiency is 92.2 percent.
The graphite negative electrode materials prepared in the examples and the comparative examples were respectively tested for particle size, tap density, specific surface area, etc., and the results are shown in table 1. The name and model of the instrument used for the test are as follows: particle size, laser particle size distribution instrument MS 3000; tap density, vibrometer TF-100B; specific surface area, specific surface area determinator NOVATouch 2000; compacted Density, FT-100F powder Autodensitometer compacted.
The discharge capacity and the first efficiency of the graphite anode materials in each example and each comparative example were measured by half-cell test method, and the results are shown in table 1.
The half cell test method comprises the following steps: weighing a graphite sample, conductive carbon black SP, CMC and SBR according to a mass ratio of 95:1:2:2, uniformly stirring in water to prepare negative electrode slurry, uniformly coating the negative electrode slurry on copper foil by using a coater, putting the coated electrode piece into a vacuum drying oven at the temperature of 110 ℃ for vacuum drying for 4 hours, and then pressing the electrode piece to prepare the negative electrode. Wherein the compacted density is the surface density/(the thickness of the rolled pole piece-the thickness of the current collector). The CR-2430 button cell was assembled in a German Braun glove box filled with argon, with an electrolyte of 1M LiPF6+ EC: EMC: DMC 1:1 (volume ratio), a metallic lithium plate as counter electrode, and electrochemical performance tests were carried out on an ArbinBT2000 cell tester, USA, with a charge-discharge voltage range of 0.005V to 1.0V and a charge-discharge rate of 0.1C.
The graphite negative electrode materials in the examples and comparative examples were subjected to a rate discharge test using a full cell test method, and the results are shown in table 2.
The full battery test method comprises the following steps: the graphite of the examples and comparative examples of the present invention was used as a negative electrode, and lithium cobaltate: PVDF: adding NMP as solvent, homogenizing, coating on the surface of aluminium foil, baking and tabletting to obtain positive electrode. The polypropylene diaphragm, 1M LiPF6+ EC: DMC: EMC 1:1 (volume ratio) solution as electrolyte to assemble the full cell. Wherein, the capacity retention rate of 500 weeks of charging and discharging at 1C is tested at 24 ℃. When the multiplying power performance is tested, the test flow is as follows: discharging to 5mV with a constant current of 0.6mA in the first period, then discharging at a constant voltage, wherein the cut-off current is 0.06mA, and charging to 2V at a constant current of 0.1C; a constant current of 0.1C was discharged to 5mV (representing a capacity of "0.1C constant") and then discharged at constant voltage (representing a capacity of "0.1C total"), with a cutoff current of 0.06mA, with a 0.2C constant current charge to 2V; then multiplying discharge current is 0.2C, 0.5C, 1C, 2C, 3C; after 3C, returning to 0.2C again, the rate charging current is 0.1C, and the constant current ratio is constant current charging capacity/(constant current charging capacity + constant voltage charging capacity), where the total charging capacity is constant current charging capacity + constant voltage charging capacity. The results are shown in Table 2.
Table 1 materials powders and electrochemical performance test results:
as can be seen from Table 1, the composite graphite material prepared in the embodiment has the characteristics of high capacity, high compaction, excellent processability and good cycle performance, is suitable for a lithium ion secondary battery with high power energy density requirements, and has the first discharge capacity of more than 353.8mAh/g, the first coulombic efficiency of more than 92.9 percent and the capacity retention rate of more than 92.9 percent after 1C/1C cycle for 500 weeks. The pole piece of the coated single-particle artificial graphite in the comparative example 1 has lower secondary compaction and capacity and poorer cycle performance, and the coated secondary particle graphite in the comparative example 2 has higher capacity and compaction but low tap and poorer capacity retention rate.
Table 2 electrochemical rate performance test results of materials:
as can be seen from the results of table 2, the full cells of the examples have significantly better discharge retention than the comparative examples. The secondary particle structure has better isotropy, the pole piece cyclic expansion is small, the multiplying power type small particles are distributed around the secondary particles, large gaps of large particles are filled, carbon modification is carried out on the surfaces of the large particles, and the rapid transfer and transportation of lithium ion conductors can be realized. Therefore, the coated single-particle artificial graphite secondary particle graphite is compounded, so that the high energy density is maintained, the rate capability is improved, and the composite material can be used as a negative electrode material of a power lithium ion secondary battery of a passenger vehicle.
The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments disclosed and described, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and they are included in the scope of the present invention.
Claims (10)
1. The preparation method of the composite graphite negative electrode material is characterized by comprising the following steps of:
s1, preparing single particles, which comprises the following steps: sequentially carrying out wet granulation and carbonization treatment on the graphite particles;
in S1, the median diameter D50 of the single particles is 6.0-9.0 μm;
s2, preparing secondary particles, which comprises the following steps: sequentially carrying out secondary granulation, graphitization treatment, wet granulation and carbonization treatment on the mixture of the substance A and the asphalt;
in S2, the substance A is petroleum coke or coal needle coke;
in S2, the softening point of the asphalt is 110-130 ℃;
in S2, the median diameter D50 of the secondary particles is 12.0-15.0 μm;
in S1 or S2, the coating agent used in the wet granulation is "coal tar or petroleum tar";
s3, mixing the single particles and the secondary particles to obtain the composite material; wherein the mass ratio of the single particles to the secondary particles is 1 (0.11-9).
2. The method for preparing the composite graphite negative electrode material according to claim 1, wherein the graphite particles are prepared by sequentially performing heat treatment and graphitization treatment on petroleum coke or shaping materials of coal needle coke;
wherein the median particle diameter D50 of the shaping material is 5.5-8.4 μm, preferably 6.5-8.0 μm.
3. The preparation method of the composite graphite anode material as claimed in claim 2, wherein the S content in the petroleum coke or the coal needle coke is less than or equal to 0.45% and the ash content is less than or equal to 0.2%;
and/or the temperature of the heat treatment is 550-850 ℃;
and/or the time of the heat treatment is 6-20 h;
and/or the temperature of the graphitization treatment is 2800-3200 ℃;
and/or the graphitization treatment time is 20-60 h;
and/or the shaping material is prepared by sequentially crushing, shaping and removing fine powder from the petroleum coke or the coal needle coke;
wherein the median particle diameter D50 of the crushed material is 5.0-8.0 μm.
4. The method for preparing the composite graphite anode material of claim 1, wherein in S1 or S2, the coking value of the coating agent used in the wet granulation is 20-30%;
and/or in S1 or S2, the rotating speed of the fusion machine is 250-1400 r/min in the wet granulation process;
and/or in S1, the wet granulation time is 8-70 min;
and/or in S1, in the wet granulation, the mass ratio of the graphite particles to the coating agent adopted in the wet granulation in S1 is 100 (2-6);
and/or in S2, the wet granulation time is 5-60 min;
and/or in S2, the mass ratio of the particles obtained by graphitization treatment in the wet granulation to the coating agent adopted in the wet granulation in S2 is (5-10);
and/or in S1 or S2, the temperature of the carbonization treatment is 1000-1350 ℃, preferably 1100-1250 ℃;
and/or in S1 or S2, the carbonization treatment time is 0.5-24 h;
and/or, in S1, the single particles have a median particle diameter D50 of 7.5 μm.
5. The method for preparing the composite graphite anode material of claim 1, wherein the wet granulated coating agents in the S1 and the S2 are the same;
and/or, in S1 or S2, no solvent is involved in the wet granulation process.
6. The method for preparing the composite graphite anode material according to claim 1, wherein in S2, the substance A is petroleum coke or pulverized coal needle coke;
and/or in S2, the median particle diameter D50 of the substance A is 8.0-10.0 μm, preferably 9.0-9.5 μm;
and/or in S2, the mass ratio of the substance A to the asphalt is 100 (3.5-10.5);
and/or in S2, in the preparation process of the mixture, the mixing time of the substance A and the asphalt is 30-80 min;
and/or in S2, the temperature of the secondary granulation is 600-700 ℃, preferably 630-670 ℃;
and/or in S2, the time for secondary granulation is 6-20 h;
and/or in S2, the graphitization treatment temperature is 2800-3200 ℃;
and/or in S2, the graphitization treatment time is 20-60 h;
and/or, in S2, the secondary particles have a median particle diameter D50 of 14.7 μm.
7. The method for preparing the composite graphite anode material of claim 1, wherein in S3, the mixing time is 40-60 min, preferably 50-55 min;
and/or in S3, the mass ratio of the single particles to the secondary particles is 1 (0.2-4).
8. The composite graphite anode material prepared by the preparation method of the composite graphite anode material as claimed in any one of claims 1 to 7.
9. The composite graphite anode material according to claim 8, wherein the composite graphite anode material has a median particle diameter D50 of 10.1 to 12.1 μm;
and/or the particle size distribution range of the particles of the composite graphite negative electrode material is 0.4-38.5 microns.
10. A lithium ion battery comprising the composite graphite negative electrode material according to claim 8 or 9.
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