CN114477162A - Preparation method of graphite negative electrode material, product and application thereof - Google Patents
Preparation method of graphite negative electrode material, product and application thereof Download PDFInfo
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- CN114477162A CN114477162A CN202111674379.0A CN202111674379A CN114477162A CN 114477162 A CN114477162 A CN 114477162A CN 202111674379 A CN202111674379 A CN 202111674379A CN 114477162 A CN114477162 A CN 114477162A
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- C01B32/00—Carbon; Compounds thereof
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- H—ELECTRICITY
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- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
- H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
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- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
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- H01M4/00—Electrodes
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- H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
- H01M2004/027—Negative electrodes
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Abstract
The invention provides a preparation method of a graphite cathode material, a product and application thereof, wherein the preparation method comprises the steps of coating, graphitizing and granulating and carbonizing is adopted, the graphite raw material is coated in the preparation early stage, coating modification is carried out under specific conditions, oil organic matters can be filled in the convex-concave corner defects on the surface of the graphite raw material after coating, and then graphitization is carried out to convert the graphite organic matters into a graphite-like crystal structure, so that the purpose of greatly reducing or eliminating the defects is achieved, and the subsequent high-temperature cycle performance is ensured; and then, the graphitized product with less defects and asphalt are granulated, the asphalt can be used as less binder to ensure the granulation strength, and a secondary coating layer is formed on the surface of the graphitized product, so that the OI value of the material is reduced, and the graphite cathode material with good charging performance and long cycle life can be obtained after carbonization, thereby solving the problem of edge and corner defects of the conventional graphite material.
Description
Technical Field
The invention relates to the field of secondary batteries, in particular to a preparation method of a graphite negative electrode material, and a product and application thereof.
Background
Since the commercialization of lithium ion batteries, lithium ion batteries have been widely used due to their high energy density, long cycle life, no memory effect, and the like. Graphite has a low lithium intercalation potential and a stable layered structure, and is the most widely applied negative electrode material of lithium ion batteries. With the increasing demand of consumers for lithium ion batteries with high specific capacity and long cycle life, the graphite negative electrode must meet the requirements of long cycle life and high capacity.
Generally, needle-shaped calcined coke is used as a raw material for a high-capacity graphite material, the dynamic performance of the calcined coke is limited, and in order to improve good dynamics, the particle size of aggregate is usually reduced to make up for the loss of dynamics. However, as the coke after forging is hard, a large amount of corner defects are generated during grinding treatment, and particularly, the defects are generated by small-particle-size design. The existence of the defects can cause the aggravation of side reactions of graphite in the later period of the battery core circulation, particularly high-temperature circulation, so that the polarization of a negative electrode is serious, and the capacity is quickly attenuated. In view of the above, it is necessary to provide a technical solution to the above problems.
Disclosure of Invention
One of the objects of the present invention is: aiming at the defects of the prior art, the preparation method of the graphite cathode material is provided to solve the problem of edge defects of the existing graphite material, so that the high-temperature cycle performance of the graphite cathode material is improved, and the capacity of the graphite cathode material is ensured.
In order to achieve the purpose, the invention adopts the following technical scheme:
a preparation method of a graphite negative electrode material comprises the following steps:
s1, selecting a graphite raw material with the D50 of 5-9 microns, mixing the graphite raw material with an oil organic matter, heating to 300-400 ℃ at the speed of 2-4 ℃/min, preserving heat for 70-100 min, heating to 620-650 ℃ at the speed of 2-4 ℃/min, preserving heat for 60-90 min, and obtaining a coated graphitized precursor;
s2, graphitizing the graphitized precursor obtained in the step S1 in an inert atmosphere at 2800-3000 ℃ for 40-55 h to obtain a graphitized product;
s3, mixing and granulating the graphitized product obtained in the step S2 and asphalt to obtain secondary particles;
and S4, carbonizing the secondary particles obtained in the step S3 at 1050-1150 ℃, and screening to obtain the graphite negative electrode material.
Preferably, in step S1, the initial material of the graphite raw material is needle-shaped calcined coke, and the needle-shaped calcined coke is ground to obtain a graphite raw material with a D50 of 5-9 μm; wherein the true density of the needle-shaped forged coke is 2.08-2.14 g/cm3The volatile component is 0.5-5%, and the sulfur content is less than 0.5%.
Preferably, the oil organic matter is at least one of coal tar, castor oil and anthracene oil, and the coking value is 15-65%.
Preferably, the weight of the oil organic matter is 5-20% of the weight of the graphite raw material.
Preferably, in step S2, the graphitization product has a graphitization degree of not less than 93%.
Preferably, in step S3, the softening point of the asphalt is 60-75 ℃, and the coking value is less than or equal to 40%.
Preferably, the weight of the asphalt is 10-20% of the weight of the graphitized product.
Preferably, in step S3, the granulation conditions are: under an inert atmosphere, heating to 350-400 ℃ at a stirring speed of 15-30 Hz at a speed of 2-5 ℃/min, preserving heat for 70-100 min, then heating to 520-580 ℃ at a speed of 2-5 ℃/min, and preserving heat for 60-100 min.
Another object of the present invention is to provide a graphite negative electrode material produced by the method for producing a graphite negative electrode material described in any of the above.
Another object of the present invention is to provide a negative electrode sheet comprising the graphite negative electrode material.
The fourth object of the present invention is to provide a secondary battery comprising a positive electrode sheet, a negative electrode sheet and a separator interposed between the positive electrode sheet and the negative electrode sheet, wherein the negative electrode sheet is the negative electrode sheet.
Compared with the prior art, the invention has the beneficial effects that: according to the preparation method provided by the invention, the preparation method of coating, graphitizing and granulating and carbonizing is adopted, the graphite raw material is coated in the preparation early stage, coating modification is carried out under specific conditions, the coated oil organic matter can be filled in the convex-concave corner defects on the surface of the graphite raw material, and then graphitization is carried out to convert the coated oil organic matter into a graphite-like crystal structure, so that the purpose of greatly reducing or eliminating the defects is achieved, and the subsequent high-temperature cycle performance is ensured; and then, the graphitized product with less defects and asphalt are granulated, the asphalt can be used as less binder to ensure the granulation strength, and a secondary coating layer is formed on the surface of the graphitized product, so that the OI value of the material is reduced, and the graphite cathode material with good charging performance and long cycle life can be obtained after carbonization, so that the problem of corner defects of the conventional graphite material is solved.
Drawings
Fig. 1 is an SEM image of a graphite negative electrode material according to example 1 of the present invention.
Fig. 2 is an SEM image of the graphite anode material of example 2 of the present invention.
Detailed Description
1. Graphite negative electrode material
The first aspect of the invention aims to provide a preparation method of a graphite anode material, which comprises the following steps:
s1, selecting a graphite raw material with the D50 of 5-9 microns, mixing the graphite raw material with an oil organic matter, heating to 300-400 ℃ at the speed of 2-4 ℃/min, preserving heat for 70-100 min, heating to 620-650 ℃ at the speed of 2-4 ℃/min, preserving heat for 60-90 min, and obtaining a coated graphitized precursor;
s2, graphitizing the graphitized precursor obtained in the step S1 in an inert atmosphere at 2800-3000 ℃ for 40-55 h to obtain a graphitized product;
s3, mixing and granulating the graphitized product obtained in the step S2 and asphalt to obtain secondary particles;
and S4, carbonizing the secondary particles obtained in the step S3 at 1050-1150 ℃, and screening to obtain the graphite negative electrode material.
The preparation method adopts the oil organic matter and other hard carbon-like materials to carry out low-temperature heat treatment coating on the graphite raw material, compared with the conventional hard carbon or soft carbon treatment coating, the coating modification of the invention is more uniform, the modification effect is better, the oil organic matter can be ensured to be better filled in the convex-concave corner defect on the surface of the graphite raw material through the temperature-rising curve treatment, and the coating structure can be converted into a graphite-like crystal through the graphitization treatment, so that the purpose of greatly reducing or eliminating the defect is achieved, the problem of aggravation of the side reaction of the graphite in the later cycle period of the battery cell is effectively avoided, and the cycle performance, especially the high-temperature cycle performance, of the battery is ensured. The preparation method effectively solves the defect problem of the graphite material, and the graphite material with the small particle size of 5-9 microns is adopted for preparation in the early period, so that the defect cannot be aggravated due to the small particle size design, and the rate performance of the battery is ensured. In addition, after the coating and graphitization treatment, the method is also beneficial to improving the subsequent granulation structural strength, and further improves the cycle performance of the battery.
Preferably, the conditions for the mixed coating treatment of the graphite raw material and the oil organic matter are as follows: under the stirring speed of 5-30 Hz, firstly heating to 350 ℃ at the speed of 2-4 ℃/min, preserving heat for 70-100 min, then heating to 640 ℃ at the speed of 2-4 ℃/min, and preserving heat for 60-90 min.
In some embodiments, in step S1, the initial material of the graphite raw material is needle-shaped calcined coke, and the needle-shaped calcined coke is ground to obtain a graphite raw material with a D50 of 5 to 9 μm; wherein the true density of the needle-shaped forged coke is 2.08-2.14 g/cm3The volatile content is 0.5-5%, and the sulfur content is less than 0.5%. The needle-shaped coke after forging with the parameters is used as an initial material of the graphite raw material, so that the capacity, the compaction density and the energy density of a subsequent graphite cathode material can be better ensured; and the needle-shaped forged coke raw material is easy to obtain, and the material cost is low. Preferably, the graphite raw material has a D50 of 6 to 8 μm.
In some embodiments, the oil organic matter is at least one of coal tar, castor oil and anthracene oil, and the coking value is 15-65%. Through a plurality of experiments and researches of the inventor, the oil organic matter with 15-65% coking value is adopted, the coating modification effect on the graphite raw material is better, the compaction density and the capacity of the graphite negative electrode material can be reduced when the coking value is too large, and the modification on the defect position of the graphite raw material is not facilitated when the coking value is too small.
In some embodiments, the weight of the oily organic matter is 5 to 20% of the weight of the graphite raw material. Specifically, the weight of the oil organic matter can be 5-7%, 7-10%, 10-13%, 13-15%, 15-18% or 18-20% of the weight of the graphite raw material. Preferably, the weight of the oil organic matter is 8-15% of the weight of the graphite raw material. By uniformly mixing and coating the oil organic matters and the graphite raw material according to the proportion, the content of the oil organic matters can better coat and fill the edge defects on the surface of the graphite raw material, so that the defects of graphite can be eliminated as soon as possible, and the subsequent cycle performance of the battery can be ensured.
In some embodiments, in step S2, the graphitized article has a graphitization degree of 93% or more. Specifically, the degree of graphitization of the graphitized article may be 93%, 94%, 95%, 96%, 97%, 98%, or 99%.
In some embodiments, in step S3, the asphalt has a softening point of 60-75 ℃ and a coking value of less than or equal to 40%. The asphalt adopted by the invention is low-temperature asphalt which can be used as a binder to ensure the granulation strength on one hand, and the granulation strength can be ensured by adding a small amount of asphalt binder after graphitization because the graphite raw material is coated and modified in the prior period; on the other hand, the graphite anode material can be used as a secondary coating layer, so that the charging performance of the graphite anode material can be further improved, the graphite anode material is more suitable for the quick charging condition, and the application range is wider.
In some embodiments, the weight of the pitch is 10 to 20% of the weight of the graphitized article. Specifically, the weight of the asphalt can be 10-12%, 12-15%, 15-18% or 18-20% of the weight of the graphitized product. Preferably, the weight of the asphalt is 12-16% of the weight of the graphitized product.
In some embodiments, in step S3, the process conditions for granulation are: under an inert atmosphere, heating to 350-400 ℃ at a stirring speed of 15-30 Hz at a speed of 2-5 ℃/min, preserving heat for 70-100 min, then heating to 520-580 ℃ at a speed of 2-5 ℃/min, and preserving heat for 60-100 min. Preferably, the granulation conditions are: under inert atmosphere, heating to 370 ℃ at a stirring speed of 15-30 Hz at a speed of 2-5 ℃/min, preserving heat for 70-100 min, then heating to 550 ℃ at a speed of 2-5 ℃/min, and preserving heat for 60-100 min.
In some embodiments, in step S4, the highest temperature of the carbonization treatment is 1150 ℃, and the carbonization time is 5-10 h.
The second aspect of the present invention is directed to a graphite negative electrode material prepared by the above-mentioned method for preparing a graphite negative electrode material.
2. Negative plate
The third aspect of the invention aims to provide a negative electrode sheet comprising the graphite negative electrode material.
The negative plate comprises a negative current collector and a negative active material layer coated on at least one surface of the negative current collector, wherein the active material of the negative active material layer is the graphite negative material prepared by the invention, the negative active material layer also comprises a conductive agent and a thickening agent, the conductive agent and the thickening agent are uniformly mixed with a solvent to prepare negative slurry, the negative slurry is coated on the negative current collector, and the negative active material layer can be obtained by drying.
3. Secondary battery
The fourth aspect of the present invention is directed to a secondary battery, which includes a positive plate, a negative plate and a diaphragm spaced between the positive plate and the negative plate, wherein the negative plate is the negative plate.
Wherein, the active material layer coated on the positive plate, and the positive active material can be of chemical formula including but not limited to LiaNixCoyMzO2-bNb(wherein a is more than or equal to 0.95 and less than or equal to 1.2, x>0, y is more than or equal to 0, z is more than or equal to 0, and x + y + z is 1,0 is more than or equal to b and less than or equal to 1, M is selected from one or more of Mn and Al, N is selected from one or more of F, P and S), and the positive electrode active material can also be selected from one or more of LiCoO (lithium LiCoO), but not limited to2、LiNiO2、LiVO2、LiCrO2、LiMn2O4、LiCoMnO4、Li2NiMn3O8、LiNi0.5Mn1.5O4、LiCoPO4、LiMnPO4、LiFePO4、LiNiPO4、LiCoFSO4、CuS2、FeS2、MoS2、NiS、TiS2And the like. The positive electrode active material may be further modified, and the method of modifying the positive electrode active material is known to those skilled in the art, for example, the positive electrode active material may be modified by coating, doping, and the like, and the material used in the modification may be one or a combination of more of Al, B, P, Zr, Si, Ti, Ge, Sn, Mg, Ce, W, and the like. The positive electrode current collector adopted by the positive electrode plate is generally a structure or a part for collecting current, and the positive electrode current collector can be various materials suitable for serving as a positive electrode current collector of a lithium ion battery in the field, for example, the positive electrode current collector can include but is not limited to metal foil and the like, and more specifically, can include but is not limited to aluminum foil and the like.
And the separator may be various materials suitable for a lithium ion battery separator in the art, for example, may be one or a combination of more of polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester, natural fiber, and the like, which include but are not limited thereto.
In order to make the technical solutions and advantages of the present invention clearer, the present invention and its advantages will be described in further detail below with reference to the following detailed description and the accompanying drawings, but the embodiments of the present invention are not limited thereto.
Example 1
A preparation method of a graphite negative electrode material comprises the following steps:
s1, crushing, grinding and grading needle-shaped forged coke to obtain a graphite raw material with D50 of 6-8 mu m, stirring and mixing the graphite raw material and coal tar in a horizontal reaction kettle, wherein the weight of the coal tar is 8% of the weight of the graphite raw material, heating to 350 ℃ at the speed of 2-4 ℃/min at the stirring speed of 15Hz, preserving heat for 70-100 min, heating to 640 ℃ at the speed of 2-4 ℃/min, and preserving heat for 60-90 min to obtain a coated graphitized precursor;
s2, screening the graphitized precursor, then loading the graphitized precursor into a graphite crucible for graphitization treatment, and treating for 48h at 3000 ℃ in an inert atmosphere to obtain a graphitized product;
s3, mixing and granulating the obtained graphitized product and low-temperature asphalt, wherein the weight of the asphalt is 15% of that of the graphitized product, and the granulation treatment conditions are as follows: under an inert atmosphere, heating to 370 ℃ at a stirring speed of 15-30 Hz at a speed of 2-5 ℃/min, preserving heat for 70-100 min, then heating to 550 ℃ at a speed of 2-5 ℃/min, and preserving heat for 60-100 min; obtaining secondary particles;
and S4, putting the obtained secondary particles into a graphite crucible, sending the graphite crucible into a roller kiln for carbonization at the highest carbonization temperature of 1150 ℃ for 7h, and screening and demagnetizing after carbonization to obtain the graphite cathode material.
Example 2
Unlike example 1, in step S1, the weight of coal tar added in this example was 15% of the weight of the graphite raw material.
The rest is the same as embodiment 1, and the description is omitted here.
Example 3
The difference from example 1 is that in step S1, the weight of coal tar added in this example is 25% of the weight of the graphite raw material.
The rest is the same as embodiment 1, and the description is omitted here.
Example 4
Unlike example 1, in step S1, the weight of coal tar added in this example was 2% of the weight of the graphite raw material.
The rest is the same as embodiment 1, and the description is omitted here.
Example 5
Unlike example 1, in step S1, the weight of coal tar added in this example was 5% of the weight of the graphite raw material.
The rest is the same as embodiment 1, and the description is omitted here.
Example 6
The difference from example 1 is in step S1, and the conditions of the coating modification treatment in this example are: heating to 200 ℃ at a speed of 2-4 ℃/min under a stirring speed of 15Hz, preserving heat for 70-100 min, then heating to 640 ℃ at a speed of 2-4 ℃/min, preserving heat for 60-90 min, and obtaining the coated graphitized precursor.
The rest is the same as embodiment 1, and the description is omitted here.
Example 7
The difference from example 1 is in step S1, and the conditions of the coating modification treatment in this example are: heating to 350 ℃ at a speed of 2-4 ℃/min under a stirring speed of 15Hz, preserving heat for 70-100 min, then heating to 800 ℃ at a speed of 2-4 ℃/min, preserving heat for 60-90 min, and obtaining the coated graphitized precursor.
The rest is the same as embodiment 1, and the description is omitted here.
Example 8
The difference from example 1 is in step S1, and the conditions of the coating modification treatment in this example are: heating to 600 ℃ at a speed of 2-4 ℃/min under a stirring speed of 15Hz, preserving heat for 70-100 min, then heating to 800 ℃ at a speed of 2-4 ℃/min, preserving heat for 60-90 min, and obtaining the coated graphitized precursor.
The rest is the same as embodiment 1, and the description is omitted here.
Example 9
The difference from the embodiment 2 is the step S1, and the coating modification conditions of the embodiment are: heating to 200 ℃ at a speed of 2-4 ℃/min under a stirring speed of 15Hz, preserving heat for 70-100 min, then heating to 640 ℃ at a speed of 2-4 ℃/min, preserving heat for 60-90 min, and obtaining the coated graphitized precursor.
The rest is the same as embodiment 2, and the description is omitted here.
Example 10
The difference from example 2 is in step S1, and the conditions of the coating modification treatment in this example are: heating to 350 ℃ at a speed of 2-4 ℃/min under a stirring speed of 15Hz, preserving heat for 70-100 min, then heating to 800 ℃ at a speed of 2-4 ℃/min, preserving heat for 60-90 min, and obtaining the coated graphitized precursor.
The rest is the same as embodiment 2, and the description is omitted here.
Example 11
The difference from example 2 is in step S1, and the conditions of the coating modification treatment in this example are: heating to 600 ℃ at a speed of 2-4 ℃/min under a stirring speed of 15Hz, preserving heat for 70-100 min, then heating to 800 ℃ at a speed of 2-4 ℃/min, preserving heat for 60-90 min, and obtaining the coated graphitized precursor.
The rest is the same as embodiment 2, and the description is omitted here.
Example 12
Unlike example 1, in step S1, castor oil is used as the oily organic substance in this example.
The rest is the same as embodiment 1, and the description is omitted here.
Example 13
Unlike example 2, in step S1, castor oil is used as the oil-based organic material in this example.
The rest is the same as embodiment 2, and the description is omitted here.
Example 14
The difference from example 1 is in step S3, and the processing conditions for granulation in this example are: under an inert atmosphere, heating to 480 ℃ at a stirring speed of 15-30 Hz at a speed of 2-5 ℃/min, preserving heat for 70-100 min, then heating to 650 ℃ at a speed of 2-5 ℃/min, and preserving heat for 60-100 min; secondary particles were obtained.
The rest is the same as embodiment 1, and the description is omitted here.
Example 15
The difference from example 1 is in step S3, and the processing conditions for granulation in this example are: under an inert atmosphere, heating to 250 ℃ at a stirring speed of 15-30 Hz at a speed of 2-5 ℃/min, preserving heat for 70-100 min, then heating to 550 ℃ at a speed of 2-5 ℃/min, and preserving heat for 60-100 min; secondary particles were obtained.
The rest is the same as embodiment 1, and the description is omitted here.
Comparative example 1
A preparation method of a graphite negative electrode material comprises the following steps:
s1, crushing, grinding and grading the needle-shaped forged coke to obtain a graphite raw material with D50 of 6-8 mu m,
s2, screening the graphite raw material, then loading the raw material into a graphite crucible for graphitization treatment, and treating for 48h at 3000 ℃ in an inert atmosphere to obtain a graphitized product;
s3, mixing and granulating the obtained graphitized product and low-temperature asphalt, wherein the weight of the asphalt is 15% of that of the graphitized product, and the granulation treatment conditions are as follows: under an inert atmosphere, heating to 370 ℃ at a stirring speed of 15-30 Hz at a speed of 2-5 ℃/min, preserving heat for 70-100 min, then heating to 550 ℃ at a speed of 2-5 ℃/min, and preserving heat for 60-100 min; obtaining secondary particles;
and S4, putting the obtained secondary particles into a graphite crucible, sending the graphite crucible into a roller kiln for carbonization at the highest carbonization temperature of 1150 ℃ for 7h, and screening and demagnetizing after carbonization to obtain the graphite cathode material.
The graphite negative electrode materials obtained in the above examples 1 to 15 and comparative example 1 are applied to the manufacture of a lithium ion half cell, wherein a lithium sheet is a counter electrode, and the lithium sheet, a diaphragm and an electrolyte are assembled into a button lithium ion half cell in a glove box filled with argon.
The specific surface area, the gram capacity and the high-temperature cycle performance at 45 ℃ of the graphite are tested, and the test method comprises the following steps:
1) and (3) gram capacity test: and (3) standing the button half cell to be tested in an environment of 25 +/-3 ℃ for 30 minutes, carrying out constant current charging at a rate of 0.05 ℃ until the voltage is 4.48V, then carrying out constant voltage charging until the current is 0.005C, and recording gram capacity.
2) High-temperature cycle performance test: charging the lithium ion battery to 4.48V at a constant current of 0.7C at 45 ℃, then charging to a current of 0.05C at a constant voltage of 4.48V, standing for 5min, and then discharging to 3.0V at a constant current of 1C, wherein the process is a charge-discharge cycle process, and the discharge capacity at this time is the discharge capacity of the first cycle. Cyclic charge and discharge tests were performed as described above and the discharge capacity per cycle was recorded.
The test results are shown in table 1 below.
TABLE 1
The test results show that the graphite cathode material prepared by the preparation method of the invention still has more than 80% of cycle capacity after 400 cycles at the high temperature of 45 ℃ and the high voltage of 4.48V. Therefore, the graphite cathode material obtained by the invention greatly relieves or eliminates the defect structure of the graphite cathode material, and greatly relieves the progress of side reaction at high temperature, thereby effectively ensuring the cycle performance of the battery at high temperature.
In addition, as can be seen from the comparison of examples 1 to 5, when the graphite raw material is subjected to coating modification, the content of the added oil organic matter has a great influence on the modification effect of the graphite raw material, as in examples 3 to 4, when the content is too low or too high, the high-temperature cycle performance of the battery cannot be significantly improved, mainly because the defect cannot be effectively modified by the too low content during the coating modification, and the gram capacity is reduced by the too high content, and meanwhile, the excessive filling of the redundant oil organic matter is not beneficial to the subsequent graphitization and transformation into graphite-like crystal crystals, so that the purpose of significantly improving the high-temperature cycle performance of the battery cannot be achieved.
In addition, as can be seen from the comparison between examples 1 and 6 to 8, and between example 2 and 9 to 11, when the conditions of the coating reaction between the graphite raw material and the organic oil are reasonably controlled, the high-temperature cycle performance of the battery can be improved to a greater extent, and particularly, as in the temperature rise curve of example 1, the battery can still maintain the capacity of more than 80% after being cycled for 540 cycles. In addition, the subsequent granulation treatment conditions also have influence on the electrochemical performance of the graphite, and the high-temperature cycle performance of the battery can be improved to a greater extent by keeping the granulation temperature rise curve described in example 1.
In addition, the graphite negative electrode materials obtained in the above examples 1 to 15 and comparative example 1 are applied to a lithium ion full cell to manufacture, and the preparation method comprises the following steps:
1) preparing a positive electrode into a sheet: uniformly mixing lithium cobaltate (the charge cut-off voltage is more than 4.48V), conductive carbon and an adhesive (polyvinylidene fluoride) in an N-methylpyrrolidone solvent according to the mass ratio of 97.6:1.1:1.3 to prepare positive electrode slurry, then coating the positive electrode slurry on an aluminum foil, drying the aluminum foil, and then performing cold pressing and cutting to prepare a positive electrode sheet.
2) And (3) preparing a negative electrode: the graphite negative electrode materials prepared in the examples 1-15 and the comparative example 1, CMC and SBR are mixed according to the mass ratio of 98: and (3) mixing the materials uniformly in deionized water at a ratio of 0.8:1.2 to prepare negative electrode slurry, then coating the negative electrode slurry on a copper foil, drying the copper foil, and then performing cold pressing and cutting to prepare a negative electrode sheet.
3) Manufacturing an electric core: superposing the positive plate, the conventional PE diaphragm and the negative plate to prepare a laminated cell, wherein the positive electrode is led out by spot welding of an aluminum tab, and the negative electrode is led out by spot welding of a nickel tab; then the cell is placed in an aluminum-plastic packaging bag, and is injected with conventional high-voltage electrolyte to be made into a battery through the procedures of packaging, formation and capacity grading.
And testing a lithium precipitation window of the battery at room temperature by charging, wherein the testing method comprises the following steps: discharging to 3V at constant current of 0.7C, standing for 5min, charging to 4.48V at constant current and constant voltage of 2.4C, stopping multiplying power of 0.025C, repeating for 20 times, disassembling, and observing lithium precipitation condition of the negative plate. The test results are given in table 2 below.
TABLE 2
From the above test results, it can be seen that the graphite negative electrode material obtained by the preparation method of the present invention can still achieve superior effects under the RT 2.4C direct charging, and particularly, the graphite negative electrode materials as in examples 1 and 12 still have superior effects under the RT 2.8C direct charging. The reason is that the graphite cathode material prepared under the condition effectively solves the problem of edge defects, so that lithium ions can be smoothly inserted and inserted even if the high-rate high-voltage charging is carried out, and the safety performance of the battery is ensured.
In conclusion, the graphite cathode material prepared by the preparation method can give consideration to the cycle performance and the capacity of the battery,
Variations and modifications to the above-described embodiments may also occur to those skilled in the art, which fall within the scope of the invention as disclosed and taught herein. Therefore, the present invention is not limited to the above-mentioned embodiments, and any obvious improvement, replacement or modification made by those skilled in the art based on the present invention is within the protection scope of the present invention. Furthermore, although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.
Claims (10)
1. The preparation method of the graphite negative electrode material is characterized by comprising the following steps of:
s1, selecting a graphite raw material with the D50 of 5-9 microns, mixing the graphite raw material with an oil organic matter, heating to 300-400 ℃ at the speed of 2-4 ℃/min, preserving heat for 70-100 min, heating to 620-650 ℃ at the speed of 2-4 ℃/min, preserving heat for 60-90 min, and obtaining a coated graphitized precursor;
s2, graphitizing the graphitized precursor obtained in the step S1 in an inert atmosphere at 2800-3000 ℃ for 40-55 h to obtain a graphitized product;
s3, mixing and granulating the graphitized product obtained in the step S2 and asphalt to obtain secondary particles;
and S4, carbonizing the secondary particles obtained in the step S3 at 1050-1150 ℃, and screening to obtain the graphite negative electrode material.
2. The preparation method of the graphite negative electrode material according to claim 1, wherein in step S1, the initial material of the graphite raw material is needle-shaped calcined coke, and the needle-shaped calcined coke is ground to obtain a graphite raw material with a D50 of 5-9 μm; wherein the true density of the needle-shaped forged coke is 2.08-2.14 g/cm3The volatile content is 0.5-5%, and the sulfur content is less than 0.5%.
3. The preparation method of the graphite negative electrode material of claim 1, wherein the oil organic matter is at least one of coal tar, castor oil and anthracene oil, and the coking value is 15-65%.
4. The method for preparing the graphite negative electrode material according to any one of claims 1 to 3, wherein the weight of the oily organic matter is 5 to 20% of the weight of the graphite raw material.
5. The preparation method of the graphite anode material as claimed in claim 1, wherein in step S3, the softening point of the asphalt is 60-75 ℃, and the coking value is less than or equal to 40%.
6. The method for preparing the graphite negative electrode material according to claim 1, wherein the weight of the pitch is 10 to 20% of the weight of the graphitized article.
7. The method for producing a graphite negative electrode material according to any one of claims 1 and 5 to 6, wherein in step S3, the granulation conditions are as follows: under an inert atmosphere, heating to 350-400 ℃ at a stirring speed of 15-30 Hz at a speed of 2-5 ℃/min, preserving heat for 70-100 min, then heating to 520-580 ℃ at a speed of 2-5 ℃/min, and preserving heat for 60-100 min.
8. A graphite negative electrode material prepared by the preparation method of the graphite negative electrode material as claimed in any one of claims 1 to 7.
9. A negative electrode sheet comprising the graphite negative electrode material according to claim 8.
10. A secondary battery comprising a positive electrode sheet, a negative electrode sheet, and a separator interposed between the positive electrode sheet and the negative electrode sheet, wherein the negative electrode sheet is the negative electrode sheet according to claim 9.
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