CN109817957B - Preparation method of asphalt-coated silicon-doped natural crystalline flake graphite negative electrode material - Google Patents
Preparation method of asphalt-coated silicon-doped natural crystalline flake graphite negative electrode material Download PDFInfo
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Abstract
The invention provides a preparation method of an asphalt-coated silicon-doped natural crystalline flake graphite cathode material, belonging to the technical field of cathode material preparation and comprising the following steps of: mixing a nitric acid solution with natural crystalline flake graphite, magnetically stirring for reaction, filtering, washing and drying; weighing nanometer silicon powder, adding the nanometer silicon powder into absolute ethyl alcohol for dissolving, then adding sodium hexametaphosphate, stirring uniformly, carrying out ultrasonic oscillation, adjusting the pH value, adding a silane coupling agent, carrying out magnetic stirring, heating and refluxing, carrying out full reaction, then centrifuging, drying and grinding; mixing the treated natural crystalline flake graphite with the treated nano silicon powder, grinding, adding toluene under the protection of nitrogen, stirring for reaction, filtering, washing and drying; and (3) uniformly mixing the NG/Si composite material with the asphalt toluene solution, taking the material, drying in the shade, drying at constant temperature, grinding and pyrolyzing to obtain the product. The method improves the electrochemical cycle performance and the specific discharge capacity of the natural crystalline flake graphite.
Description
Technical Field
The invention belongs to the technical field of graphite modification, and particularly relates to a preparation method of an asphalt-coated silicon-doped natural crystalline flake graphite negative electrode material.
Background
The lithium ion battery is a representative of the modern high-performance battery, is a green new energy product, and is widely applied to information, telecommunication and power industries. At present, commercial lithium ion batteries widely adopt carbon cathode materials. Among them, graphite-based negative electrode materials are the main type of carbon negative electrode materials due to the advantages of wide sources, stable performance, energy saving, environmental protection, and the like.
The graphite material mainly comprises three types of natural graphite, artificial graphite and various graphitized carbons (such as graphitized coke, graphitized carbon fiber and graphitized mesocarbon microbeads). The natural graphite refers to a natural graphite material obtained by mining, flotation, screening and purifying natural graphite ores. The natural graphite in China is mainly divided into amorphous graphite (microcrystalline graphite) and crystalline flake graphite, and microcrystalline graphite particles are poor in mechanical property and easy to break, so that shaping and spheroidizing are difficult to perform, and the currently practical natural graphite is mainly crystalline flake graphite. The problems of the flake graphite as the negative electrode material of the lithium ion battery mainly exist as follows: the compatibility of natural graphite and electrolyte is poor, in the first charging and discharging process, an organic solvent and lithium ions are jointly inserted into a graphite sheet layer to be reduced to generate gas, and a part of lithium is consumed, so that the first efficiency is low; the graphite spacing is smaller than the crystal face interlayer spacing of a lithium interlayer compound Li-GIC, so that graphite particles repeatedly expand and contract in the charging and discharging processes, graphite layers are peeled off and pulverized, and the cycling stability of the battery is influenced. Modification treatment is generally required to be carried out on the flake graphite, and specific methods comprise shaping classification, surface oxidation, coating, doping and the like.
Patent document CN103972508A provides an inorganic doped/coated modified natural graphite, a preparation method and application thereof. The preparation method comprises the following steps: carrying out hydrothermal reaction on natural graphite, oxidizing acid and inorganic doping raw materials in a reaction kettle at the temperature of 90-180 ℃ for 0.5-12 hours to obtain expanded graphite A; drying the expanded graphite A in an oven to obtain dried expanded graphite B; and (2) carrying out high-temperature treatment on the expanded graphite B at 600-1600 ℃ in a protective atmosphere, and introducing a nitrogen-containing organic matter to form a nitrogen coating layer on the surface of the expanded graphite B, thereby finally obtaining the modified natural graphite. The preparation method has the advantages of simple process, easy control, wide and cheap raw material sources, good material repeatability and consideration of the advantages of doping and coating modification, but the specific capacity of the obtained modified natural graphite is lower.
Patent document No. CN105977489A discloses a preparation method of modified microcrystalline graphite negative electrode material for lithium ion battery, which comprises the following steps: 1) shaping and crushing: adding natural microcrystalline graphite into a stirring ball mill for ball milling for 1-4 h, and then filtering and drying to obtain ball-milled graphite powder; 2) coating: mixing the graphite powder obtained in the step 1) with a catalyst and asphalt, vacuumizing, and heating and stirring for 0.5-1 h at 150-200 ℃; the vacuum degree is 500-2000 Pa, and the stirring speed is 2500-3000 rpm; 3) graphitization: and (3) carrying out graphitization treatment on the coated graphite powder for 10-48 h at the carbonization temperature of 2800-3200 ℃, thus obtaining the modified microcrystalline graphite cathode material. The method uses graphitization to purify the natural microcrystalline graphite, does not relate to toxic and harmful reagents in a chemical purification method, and is environment-friendly and green; the catalyst is added in the coating process of the method, so that the graphitization degree can be improved, the capacity of the catalyst is greatly improved, the surface can be effectively coated by coating under vacuum, the tap density is improved, the specific surface area is reduced, and the cycle performance is greatly improved. But the specific capacity of the negative electrode material obtained by the method is lower.
Disclosure of Invention
The invention aims to solve the technical problem of providing a preparation method of an asphalt-coated silicon-doped natural crystalline flake graphite negative electrode material aiming at the defects of the prior art so as to improve the specific capacity and the cycle performance of the natural crystalline flake graphite.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows:
a preparation method of an asphalt-coated silicon-doped natural crystalline flake graphite negative electrode material comprises the following steps:
s1: mixing a nitric acid solution with natural crystalline flake graphite, reacting for 2-4 hours under magnetic stirring, filtering to obtain a first precipitate, washing the first precipitate, and drying to obtain treated natural crystalline flake graphite;
s2: weighing nanometer silicon powder, adding the nanometer silicon powder into absolute ethyl alcohol for dissolving, adding sodium hexametaphosphate, stirring uniformly, carrying out ultrasonic oscillation, adjusting the pH value with glacial acetic acid, adding a silane coupling agent, carrying out magnetic stirring, heating for refluxing, carrying out full reaction, then carrying out centrifugal ethanol removal, drying, and grinding to obtain treated nanometer silicon powder;
s3: mixing the treated natural crystalline flake graphite with the treated nano silicon powder, grinding, adding toluene into the obtained mixture, stirring and reacting for 5-6 hours at 70-75 ℃ under the protection of nitrogen, filtering to obtain a second precipitate, washing the second precipitate, and drying to obtain the NG/Si composite material;
s4: adding the NG/Si composite material into a powder mixer, pouring an asphalt toluene solution into a top spraying device, starting the top spraying device, stirring to uniformly mix the NG/Si composite material and the asphalt toluene solution, taking materials, drying in the shade, drying at a constant temperature, grinding, and pyrolyzing to obtain a product.
Preferably, the concentration of the nitric acid solution is 0.1-0.25mol/l, and the ratio of the mass of the natural crystalline flake graphite to the volume of the nitric acid solution is 1: (40-50) g/ml.
Preferably, the natural crystalline flake graphite has a particle size D90Is 5-15 microns.
Preferably, the temperature of the magnetic stirring in the step S1 is 23-28 ℃, and the temperature of the drying is 80-85 ℃.
Preferably, the pH is 6.2-6.5.
Preferably, the mass ratio of the nano silicon powder, the sodium hexametaphosphate and the silane coupling agent is 100: (2-5): (9-12).
Preferably, the ratio of the mass of asphalt to the volume of toluene in the asphalt toluene solution is 0.08-0.12 g/ml.
Preferably, the mass ratio of the asphalt to the natural crystalline flake graphite is (7-12): 100.
preferably, the constant temperature drying temperature in the step S4 is 60-65 ℃.
Preferably, the pyrolysis process conditions are: in N2Under protection, the temperature is raised to 400-.
Compared with the prior art, the invention has the following beneficial effects:
aiming at the defects of the prior art, the invention provides a preparation method of an asphalt-coated silicon-doped natural crystalline flake graphite cathode material, so that the electrochemical cycle performance and the specific discharge capacity of the natural crystalline flake graphite are improved, and the natural crystalline flake graphite has higher compatibility with a solvent.
Firstly, the natural crystalline flake graphite is subjected to oxidation modification by using concentrated nitric acid, and through surface oxidation treatment, not only can nano-scale micropores be added on the surface of the graphite, but also more space is provided for lithium ion intercalation, and the reversible capacity of the graphite material is improved; the position with higher activity on the graphite surface can be eliminated, so that the graphite surface has more uniform reactivity, charge aggregation caused by nonuniform activity, larger surface curvature, tip effect and the like is prevented, and the generated SEI film is different in thickness due to more severe reaction between the position with higher reactivity and the electrolyte; uneven SEI films are more prone to damage in the charging and discharging processes, and influence is caused on the electrochemical performance of active materials. Furthermore, control of the degree of oxidation has a critical effect on surface oxidation. Proper oxidation is beneficial to improving the charge-discharge performance of the material; however, the graphite surface is oxidized too violently, a large number of oxygen-containing groups appear, and surface irregularity is greatly improved, so that irreversible lithium ion loss in the first charge-discharge process is increased, the properties of a formed SEI film are deteriorated, and solvated lithium ions enter the graphite interlayer, and the electrochemical performance of the graphite is reduced. According to the invention, through intensive research and combination of integral performance, concentrated nitric acid is used as an oxidant to uniformly oxidize the graphite surface, and when the concentration of a nitric acid solution is 0.1-0.25mol/l, the ratio of the mass of natural crystalline flake graphite to the volume of the nitric acid solution is 1: (40-50) g/ml, the oxide material exhibits more excellent charge-discharge capacity and cycle performance.
Secondly, the invention takes silicon element as doping element, firstly adopts sodium hexametaphosphate to improve the dispersibility of the nano-silicon in ethanol solution, then adjusts to proper pH value, and utilizes silane coupling agent, for example: KH550, KH560 carry out surface modification to nano-silicon, improve its and organic environment's compatibility through carrying out the organic cladding of surface to nano-silicon, can also effectively prevent the particle reunion, improve its dispersibility to improve the compound efficiency of nano-silicon particle and natural crystalline flake graphite, the experiment shows, doping silicon element can effectively improve the electrochemical property of graphite, and silicon belongs to and stores up lithium active material moreover, can form compound active material with graphite, exert the two synergistic effect, make the circulation performance improve.
Thirdly, the graphite surface is coated with the asphalt, and a layer of amorphous carbon with smaller specific surface area is formed on the graphite surface after high-temperature carbonization, so that on one hand, the direct contact between a solvent and the graphite is avoided, the falling-off phenomenon of a graphite sheet layer caused by the insertion of solvent molecules is inhibited, the selection range of the electrolyte is expanded, on the other hand, the existence of a large number of disordered structures in the amorphous carbon layer reduces the diffusion directionality and the blocking effect among particles, and the performance of the graphite electrode is greatly improved
According to the invention, the surface oxidation, silicon element doping and asphalt coating treatment are carried out on the natural crystalline flake graphite, so that the first discharge capacity of the natural crystalline flake graphite cathode material is improved by more than 30%; the capacity retention rate after 50 times of circulation is about 76%; the material treated by the method shows good electrochemical performance.
Detailed Description
In order to better understand the present invention, the following examples are further provided to clearly illustrate the contents of the present invention, but the contents of the present invention are not limited to the following examples. In the following description, numerous specific details are set forth in order to provide a more thorough understanding of the present invention. It will be apparent, however, to one skilled in the art, that the present invention may be practiced without one or more of these specific details. In other instances, well-known features have not been described in order to avoid obscuring the invention.
Example 1
A preparation method of an asphalt-coated silicon-doped natural crystalline flake graphite negative electrode material comprises the following steps:
s1: mixing a nitric acid solution with natural crystalline flake graphite, reacting for 2 hours under magnetic stirring, filtering to obtain a first precipitate, washing the first precipitate, and drying to obtain treated natural crystalline flake graphite;
s2: weighing nanometer silicon powder, adding the nanometer silicon powder into absolute ethyl alcohol for dissolving, adding sodium hexametaphosphate, stirring uniformly, carrying out ultrasonic oscillation, adjusting the pH value with glacial acetic acid, adding a silane coupling agent, carrying out magnetic stirring, heating for refluxing, carrying out full reaction, then carrying out centrifugal ethanol removal, drying, and grinding to obtain treated nanometer silicon powder;
s3: mixing the treated natural crystalline flake graphite with the treated nano silicon powder, grinding, adding toluene into the obtained mixture, stirring and reacting for 6 hours at 70 ℃ under the protection of nitrogen, filtering to obtain a second precipitate, washing the second precipitate, and drying to obtain the NG/Si composite material;
s4: adding the NG/Si composite material into a powder mixer, pouring the asphalt toluene solution into a top spraying device, starting the top spraying device, stirring to uniformly mix the NG/Si composite material and the asphalt toluene solution, taking materials, drying in the shade, drying at constant temperature, grinding, and pyrolyzing to obtain a product.
In this example, the mass of the natural flake graphite was 10g, and the same was applied to the following examples.
The concentration of the nitric acid solution is 0.25mol/l, and the ratio of the mass of the natural crystalline flake graphite to the volume of the nitric acid solution is 1: 40 g/ml.
Particle size D of natural crystalline flake graphite90Is 5-8 microns.
The temperature of the magnetic stirring in step S1 was 25 ℃ and the temperature of the drying was 80 ℃.
The ultrasonic oscillation frequency in step S2 was 20kHz, the power was 300W, and the treatment time was 25 to 30 minutes, as in the following examples.
In step S2, the mass of the nano silicon powder is 0.5g, and the pH value is 6.2. The mass ratio of the nano silicon powder, the sodium hexametaphosphate and the silane coupling agent is 100: 2: 9. the heating reflux temperature is controlled at 120 + -5 deg.C, and the time is controlled at 4.5-5 hr. The silane coupling agent is KH 550.
The drying temperature in step S3 was 85 ℃.
In the step S4, the amount of asphalt is 0.7g, and the ratio of the asphalt mass to the toluene volume in the asphalt toluene solution is 0.08 g/ml.
The temperature of the constant temperature drying in step S4 is 60 ℃. Drying in the shade is carried out at room temperature in a non-light and well ventilated environment.
The powder mixer adopts MX series rotary mixer, is suitable for solid-solid mixing, and is suitable for coating the NG/Si composite material by using the asphalt toluene solution.
The pyrolysis process conditions are as follows: in N2Under protection, the temperature is raised to 400 ℃ at the speed of 12 ℃/min, the temperature is kept for 5h, then the temperature is raised to 850 ℃ at the speed of 8 ℃/min, the temperature is kept for 1h, and the temperature is naturally cooled to the room temperature. In the present invention, room temperature means 23. + -. 2 ℃.
Example 2
A preparation method of an asphalt-coated silicon-doped natural crystalline flake graphite negative electrode material comprises the following steps:
s1: mixing a nitric acid solution with natural crystalline flake graphite, reacting for 3 hours under magnetic stirring, filtering to obtain a first precipitate, washing the first precipitate, and drying to obtain treated natural crystalline flake graphite;
s2: weighing nanometer silicon powder, adding the nanometer silicon powder into absolute ethyl alcohol for dissolving, adding sodium hexametaphosphate, stirring uniformly, carrying out ultrasonic oscillation, adjusting the pH value with glacial acetic acid, adding a silane coupling agent, carrying out magnetic stirring, heating for refluxing, carrying out full reaction, then carrying out centrifugal ethanol removal, drying, and grinding to obtain treated nanometer silicon powder;
s3: mixing the treated natural crystalline flake graphite with the treated nano silicon powder, grinding, adding toluene into the obtained mixture, stirring and reacting for 5.5 hours at 72 ℃ under the protection of nitrogen, filtering to obtain a second precipitate, washing the second precipitate, and drying to obtain the NG/Si composite material;
s4: adding the NG/Si composite material into a powder mixer, pouring the asphalt toluene solution into a top spraying device, starting the top spraying device, stirring to uniformly mix the NG/Si composite material and the asphalt toluene solution, taking materials, drying in the shade, drying at constant temperature, grinding, and pyrolyzing to obtain a product.
The concentration of the nitric acid solution is 0.2mol/l, and the ratio of the mass of the natural crystalline flake graphite to the volume of the nitric acid solution is 1: 42 g/ml.
Particle size D of natural crystalline flake graphite90Is 8-10 microns.
The temperature of the magnetic stirring in step S1 was 23 ℃ and the temperature of the drying was 82 ℃.
In step S2, the mass of the nano silicon powder is 0.6g, and the pH value is 6.5.
The mass ratio of the nano silicon powder, the sodium hexametaphosphate and the silane coupling agent is 100: 3: 10. the silane coupling agent is KH 550.
In the step S4, the amount of asphalt is 0.8g, and the ratio of the mass of asphalt in the asphalt toluene solution to the volume of toluene is 0.09 g/ml.
The temperature of the constant temperature drying in the draining step S4 is 62 ℃.
The pyrolysis process conditions are as follows: in N2Under protection, the temperature is started to be 13 DEG CHeating to 420 ℃ at a speed of/min, preserving heat for 4h, heating to 830 ℃ at a speed of 7 ℃/min, preserving heat for 2h, and naturally cooling to room temperature.
Example 3
A preparation method of an asphalt-coated silicon-doped natural crystalline flake graphite negative electrode material comprises the following steps:
s1: mixing a nitric acid solution with natural crystalline flake graphite, reacting for 4 hours under magnetic stirring, filtering to obtain a first precipitate, washing the first precipitate, and drying to obtain treated natural crystalline flake graphite;
s2: weighing nanometer silicon powder, adding the nanometer silicon powder into absolute ethyl alcohol for dissolving, adding sodium hexametaphosphate, stirring uniformly, carrying out ultrasonic oscillation, adjusting the pH value with glacial acetic acid, adding a silane coupling agent, carrying out magnetic stirring, heating for refluxing, carrying out full reaction, then carrying out centrifugal ethanol removal, drying, and grinding to obtain treated nanometer silicon powder;
s3: mixing the treated natural crystalline flake graphite with the treated nano silicon powder, grinding, adding toluene into the obtained mixture, stirring and reacting for 5 hours at 75 ℃ under the protection of nitrogen, filtering to obtain a second precipitate, washing the second precipitate, and drying to obtain the NG/Si composite material;
s4: adding the NG/Si composite material into a powder mixer, pouring the asphalt toluene solution into a top spraying device, starting the top spraying device, stirring to uniformly mix the NG/Si composite material and the asphalt toluene solution, taking materials, drying in the shade, drying at constant temperature, grinding, and pyrolyzing to obtain a product.
The concentration of the nitric acid solution is 0.15mol/l, and the ratio of the mass of the natural crystalline flake graphite to the volume of the nitric acid solution is 1: 45 g/ml.
Particle size D of natural crystalline flake graphite90Is 10-12 microns.
The temperature of the magnetic stirring in step S1 was 28 ℃ and the temperature of the drying was 85 ℃.
In step S2, the mass of the nano silicon powder is 0.8g, and the pH value is 6.3.
The mass ratio of the nano silicon powder, the sodium hexametaphosphate and the silane coupling agent is 100: 4: 11. the silane coupling agent is KH 550.
In the step S4, the amount of asphalt is 0.9g, and the ratio of the mass of asphalt in the asphalt toluene solution to the volume of toluene is 0.1 g/ml.
The temperature of the constant temperature drying in step S4 was 65 ℃.
The pyrolysis process conditions are as follows: in N2Under protection, the temperature is raised to 450 ℃ at the speed of 15 ℃/min, the temperature is kept for 3h, then the temperature is raised to 800 ℃ at the speed of 6 ℃/min, the temperature is kept for 3h, and the temperature is naturally cooled to the room temperature.
Example 4
The preparation method of the asphalt-coated silicon-doped natural crystalline flake graphite negative electrode material of the embodiment is basically the same as the embodiment 1 in specific steps, except that:
the concentration of the nitric acid solution is 0.12mol/l, and the ratio of the mass of the natural crystalline flake graphite to the volume of the nitric acid solution is 1: 46 g/ml.
Particle size D of natural crystalline flake graphite90Is 12-15 microns.
The temperature of the magnetic stirring in step S1 was 23 ℃ and the temperature of the drying was 82 ℃.
In step S2, the mass of the nano silicon powder is 0.9g, and the pH value is 6.2.
The mass ratio of the nano silicon powder, the sodium hexametaphosphate and the silane coupling agent is 100: 5: 12. the silane coupling agent is KH 560.
In the step S4, the amount of asphalt is 1.0g, and the ratio of the asphalt mass to the toluene volume in the asphalt toluene solution is 0.11 g/ml.
The temperature of the constant temperature drying in step S4 was 65 ℃.
The pyrolysis process conditions are as follows: in N2Under protection, the temperature is raised to 430 ℃ at the speed of 14 ℃/min, the temperature is kept for 3.5h, then the temperature is raised to 820 ℃ at the speed of 7.5 ℃/min, the temperature is kept for 2.5h, and the temperature is naturally cooled to the room temperature.
Example 5
The preparation method of the asphalt-coated silicon-doped natural crystalline flake graphite negative electrode material of the embodiment is basically the same as the embodiment 2 in specific steps, except that:
the concentration of the nitric acid solution is 0.1mol/l, and the ratio of the mass of the natural crystalline flake graphite to the volume of the nitric acid solution is 1: 50 g/ml.
Particle size D of natural crystalline flake graphite90Is 8-10 microns.
The temperature of the magnetic stirring in step S1 was 25 ℃ and the temperature of the drying was 85 ℃.
In step S2, the mass of the nano silicon powder is 0.7g, and the pH value is 6.3.
The mass ratio of the nano silicon powder, the sodium hexametaphosphate and the silane coupling agent is 100: 2.5: 10. the silane coupling agent is KH 560.
In the step S4, the amount of asphalt is 1.1g, and the ratio of the asphalt mass to the toluene volume in the asphalt toluene solution is 0.12 g/ml.
The temperature of the constant temperature drying in step S4 was 63 ℃.
The pyrolysis process conditions are as follows: in N2Under protection, the temperature is raised to 425 ℃ at the speed of 15 ℃/min, the temperature is kept for 4h, then the temperature is raised to 845 ℃ at the speed of 6.5 ℃/min, the temperature is kept for 1.5h, and the temperature is naturally cooled to the room temperature.
Example 6
The preparation method of the asphalt-coated silicon-doped natural crystalline flake graphite negative electrode material of the embodiment is basically the same as the embodiment 1 in specific steps, except that:
the concentration of the nitric acid solution is 0.18mol/l, and the ratio of the mass of the natural crystalline flake graphite to the volume of the nitric acid solution is 1: 44 g/ml.
In the step S2, the mass of the nano silicon powder is 0.5g, and the mass ratio of the nano silicon powder, the sodium hexametaphosphate and the silane coupling agent is 100: 3.5: 10.5.
in the step S4, the amount of asphalt is 1.2g, and the ratio of the asphalt mass to the toluene volume in the asphalt toluene solution is 0.1 g/ml.
Example 7
The preparation method of the asphalt-coated silicon-doped natural crystalline flake graphite negative electrode material of the embodiment is basically the same as the embodiment 3 in specific steps, except that:
the concentration of the nitric acid solution is 0.23mol/l, and the ratio of the mass of the natural crystalline flake graphite to the volume of the nitric acid solution is 1: 48 g/ml.
In the step S2, the mass of the nano silicon powder is 0.6g, and the mass ratio of the nano silicon powder, the sodium hexametaphosphate and the silane coupling agent is 100: 4.5: 12.
in the step S4, the amount of asphalt is 1.0g, and the ratio of the asphalt mass to the toluene volume in the asphalt toluene solution is 0.12 g/ml.
The mass ratio of the asphalt to the natural crystalline flake graphite is 8: 100.
comparative example 1
The preparation method of the coated modified silicon-doped natural crystalline flake graphite negative electrode material in the comparative example is basically the same as that in example 1, except that:
s4: adding the NG/Si composite material into a powder mixer, pouring an ethanol solution of phenolic resin into a top spraying device, starting the top spraying device, stirring to uniformly mix the NG/Si composite material and the ethanol solution of the phenolic resin, stirring for 6 hours at 25 ℃, heating to 70 ℃, evaporating the ethanol solution, and drying to obtain a product; under the protection of nitrogen, curing the product at 100 ℃ for 1 hour, then heating to 900 ℃ at the heating rate of 2 ℃/min for carbonization for 3 hours, and sieving the product after carbonization to obtain the phenolic resin coated silicon-doped natural crystalline flake graphite;
wherein the mass ratio of the phenolic resin to the natural crystalline flake graphite is 9: 100.
comparative example 2
The preparation method of the asphalt-coated silicon-doped natural crystalline flake graphite negative electrode material in the comparative example is basically the same as that in example 2, except that:
in step S1, the concentration of the nitric acid solution is 0.3mol/l, and the ratio of the mass of the natural crystalline flake graphite to the volume of the nitric acid solution is 1: 55 g/ml.
Comparative example 3
The preparation method of the asphalt-coated silicon-doped natural crystalline flake graphite negative electrode material in the comparative example is basically the same as that in example 3, except that:
steps S2-S4 are replaced by the following steps S2 '-S4':
step S2': weighing nano silicon powder, adding the nano silicon powder into a toluene solution, adding a silane coupling agent, and carrying out ultrasonic treatment for 20min to form a uniform suspension;
step S3': then preparing an asphalt toluene solution, mixing the obtained suspension with the asphalt toluene solution, and performing ultrasonic treatment for 50min to obtain a mixed solution;
step S4': and (4) weighing the natural crystalline flake graphite treated in the step S1, adding the natural crystalline flake graphite into a powder mixer, filling the mixed solution into a top spraying device, starting the top spraying device, stirring and uniformly mixing, taking materials, drying in the shade, drying at constant temperature, grinding, and pyrolyzing to obtain a product.
The amounts of the nano silicon powder, the silane coupling agent, the pitch toluene solution and the natural crystalline flake graphite in the comparative example were the same as those in example 3, and the mass-to-volume ratio of the nano silicon powder to the toluene solution in step S2' was 0.8 g: 12 ml.
Evaluation of Effect
The natural crystalline flake graphite, the negative electrode materials prepared in examples 1 to 3 and comparative examples 1 to 3, a binder polyvinylidene fluoride (PVDF), and conductive carbon black were mixed in a mass ratio of 85: 10: 5, adding N-methyl pyrrolidone (NMP), grinding for more than 30min to uniformly mix the mixture, then uniformly coating the mixture on a copper foil by using a scraper, setting the thickness of the scraper to be 0.2mm, then putting the coated copper foil into an oven, drying for more than 4h at 80 ℃, taking out, then pressing the membrane to 200 mu m thickness by using a roller press, then punching the membrane into a circular sheet with the diameter of 10mm by using a punch, and then drying for 12h at 120 ℃ under the vacuum condition, and accurately weighing the mass of the circular sheet. The cell assembly was completed in an argon-filled glove box, with a metallic lithium sheet as the counter electrode, Ethylene Carbonate (EC): dimethyl carbonate (DMC): ethyl Methyl Carbonate (EMC) = 1: 1: 1 (volume ratio), 1mol/L LiPF6+The solution is electrolyte, and the porous polypropylene diaphragm is a diaphragm, so that the button cell is prepared. And standing for 24 hours after the battery is assembled to enable the electrolyte to completely infiltrate the diaphragm and the electrode diaphragm, and then performing battery test.
The battery capacity cycle performance test method comprises the following steps: and connecting the assembled button cell to a formulated channel of a LandCT2001A battery tester, and controlling constant current to charge and discharge the battery by adopting a computer. The cut-off potential of charge and discharge is 0.001-2.0V, and the mixture is kept still for 10s between charge and discharge program switches, and the cycle number is 50. The capacity, efficiency and cycle performance information of the tested sample can be directly obtained through battery testing software, and the test results are shown in tables 1-1, tables 1-2 and tables 1-3.
TABLE 1-1 Battery Performance test results (1)
As can be seen from table 1-1, the natural crystalline flake graphite in example 1 and comparative example 1, which is modified by different methods, shows more excellent charge-discharge specific capacity and cycle performance than the natural crystalline flake graphite, wherein the effect of example 1 is more significant, which indicates that the asphalt coating modification effect is better for the present invention.
TABLE 1-2 Battery Performance test results (2)
As can be seen from tables 1-2, the natural flake graphite was modified by the oxidation treatment methods in example 2 and comparative example 2, and the test results show that the first discharge specific capacity values are greatly different from each other, and the oxidation treatment conditions in example 2 are obviously more suitable.
TABLE 1-3 Battery Performance test results (3)
As can be seen from tables 1 to 3, in example 3 and comparative example 3, the natural flake graphite was modified by different doping and coating methods, respectively, and the test results show that: the first discharge specific capacity value of example 3 is obviously higher than that of comparative example 3, and the capacity retention rate of 50 cycles is also higher than that of comparative example 3, which shows that the doping and coating method of the invention has more excellent modification effect on natural crystalline flake graphite.
Finally, the above embodiments are only used for illustrating the technical solutions of the present invention and not for limiting, and other modifications or equivalent substitutions made by the technical solutions of the present invention by those of ordinary skill in the art should be covered within the scope of the claims of the present invention as long as they do not depart from the spirit and scope of the technical solutions of the present invention.
Claims (8)
1. A preparation method of an asphalt-coated silicon-doped natural crystalline flake graphite cathode material is characterized by comprising the following steps of:
s1: mixing a nitric acid solution with natural crystalline flake graphite, reacting for 2-4 hours under magnetic stirring, filtering to obtain a first precipitate, washing the first precipitate, and drying to obtain treated natural crystalline flake graphite;
the concentration of the nitric acid solution is 0.1-0.25mol/l, and the ratio of the mass of the natural crystalline flake graphite to the volume of the nitric acid solution is 1: (40-50) g/ml;
s2: weighing nanometer silicon powder, adding the nanometer silicon powder into absolute ethyl alcohol for dissolving, adding sodium hexametaphosphate, stirring uniformly, carrying out ultrasonic oscillation, adjusting the pH value with glacial acetic acid, adding a silane coupling agent, carrying out magnetic stirring, heating for refluxing, carrying out full reaction, then carrying out centrifugal ethanol removal, drying, and grinding to obtain treated nanometer silicon powder;
s3: mixing the treated natural crystalline flake graphite with the treated nano silicon powder, grinding, adding toluene into the obtained mixture, stirring and reacting for 5-6 hours at 70-75 ℃ under the protection of nitrogen, filtering to obtain a second precipitate, washing the second precipitate, and drying to obtain the NG/Si composite material;
s4: adding the NG/Si composite material into a powder mixer, pouring an asphalt toluene solution into a top spraying device, starting the top spraying device, stirring to uniformly mix the NG/Si composite material and the asphalt toluene solution, taking materials, drying in the shade, drying at constant temperature, grinding, pyrolyzing to obtain a product,
the pyrolysis process conditions are as follows: in N2Under protection, the temperature is raised to 400-.
2. The preparation method of the asphalt-coated silicon-doped natural crystalline flake graphite negative electrode material according to claim 1, characterized by comprising the following steps: the particle diameter D of the natural crystalline flake graphite90Is 5-15 microns.
3. The preparation method of the asphalt-coated silicon-doped natural crystalline flake graphite negative electrode material according to claim 2, characterized by comprising the following steps: in the step S1, the magnetic stirring temperature is 23-28 ℃, and the drying temperature is 80-85 ℃.
4. The preparation method of the asphalt-coated silicon-doped natural crystalline flake graphite negative electrode material according to claim 3, characterized by comprising the following steps: the pH value is 6.2-6.5.
5. The preparation method of the asphalt-coated silicon-doped natural crystalline flake graphite negative electrode material according to claim 4, characterized by comprising the following steps: the mass ratio of the nano silicon powder, the sodium hexametaphosphate and the silane coupling agent is 100: (2-5): (9-12).
6. The preparation method of the asphalt-coated silicon-doped natural crystalline flake graphite negative electrode material according to claim 5, characterized by comprising the following steps: the ratio of the asphalt mass to the toluene volume in the asphalt toluene solution is 0.08-0.12 g/ml.
7. The preparation method of the asphalt-coated silicon-doped natural crystalline flake graphite negative electrode material according to claim 6, characterized by comprising the following steps: the mass ratio of the asphalt to the natural crystalline flake graphite is (7-12): 100.
8. the preparation method of the asphalt-coated silicon-doped natural crystalline flake graphite negative electrode material according to claim 1, characterized by comprising the following steps: the temperature of the constant temperature drying in the step S4 is 60-65 ℃.
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| CN113130876A (en) * | 2021-04-19 | 2021-07-16 | 合肥国轩高科动力能源有限公司 | Preparation method and application of acid-modified spherical natural graphite negative electrode material |
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