CN115000368B - Preparation method of high-tap-density silicon-carbon composite material, silicon-carbon composite material and application - Google Patents
Preparation method of high-tap-density silicon-carbon composite material, silicon-carbon composite material and application Download PDFInfo
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- 238000002360 preparation method Methods 0.000 title claims abstract description 21
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- 229910002804 graphite Inorganic materials 0.000 claims abstract description 23
- 239000010439 graphite Substances 0.000 claims abstract description 23
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 claims abstract description 21
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- 238000005096 rolling process Methods 0.000 claims abstract description 21
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- 239000011261 inert gas Substances 0.000 claims abstract description 7
- 239000000203 mixture Substances 0.000 claims abstract description 5
- 238000010000 carbonizing Methods 0.000 claims abstract description 3
- 239000004594 Masterbatch (MB) Substances 0.000 claims description 27
- 239000002194 amorphous carbon material Substances 0.000 claims description 26
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- 239000000463 material Substances 0.000 claims description 14
- 239000005543 nano-size silicon particle Substances 0.000 claims description 13
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- 230000000704 physical effect Effects 0.000 description 5
- 229910052710 silicon Inorganic materials 0.000 description 5
- 239000010703 silicon Substances 0.000 description 5
- 238000003756 stirring Methods 0.000 description 5
- 229910003481 amorphous carbon Inorganic materials 0.000 description 4
- 239000011247 coating layer Substances 0.000 description 4
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- DPXJVFZANSGRMM-UHFFFAOYSA-N acetic acid;2,3,4,5,6-pentahydroxyhexanal;sodium Chemical compound [Na].CC(O)=O.OCC(O)C(O)C(O)C(O)C=O DPXJVFZANSGRMM-UHFFFAOYSA-N 0.000 description 3
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- 239000010405 anode material Substances 0.000 description 2
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- 101150016402 fsn-1 gene Proteins 0.000 description 2
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- 239000007787 solid Substances 0.000 description 2
- 238000012360 testing method Methods 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 2
- 238000004438 BET method Methods 0.000 description 1
- 229920002160 Celluloid Polymers 0.000 description 1
- 241000931913 Cephalotaxus fortunei Species 0.000 description 1
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- 229910052786 argon Inorganic materials 0.000 description 1
- 239000011889 copper foil Substances 0.000 description 1
- 238000005520 cutting process Methods 0.000 description 1
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- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical group C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 1
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Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- 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
- H01M4/362—Composites
- H01M4/364—Composites as mixtures
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- 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
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- 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
- H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
- H01M4/386—Silicon or alloys based on silicon
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- 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
- H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
- H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- 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
- H01M2004/021—Physical characteristics, e.g. porosity, surface area
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- 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
- H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
- H01M2004/027—Negative electrodes
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Abstract
The application relates to the technical field of lithium ion batteries, and particularly discloses a preparation method of a high tap density silicon-carbon composite material, a silicon-carbon composite material and application, wherein the preparation method comprises the following steps: s1, preparing premix; s2, pretreatment: under the protection of inert gas, carrying out hot rolling treatment on the premix at the temperature of 120-240 ℃ and the rolling pressure of 2-10T, then cooling the premix to 30-55 ℃, and carrying out repeated treatment of heating, hot rolling and cooling again for at least 1 time to obtain a pretreated mixture; s3, carbonizing; s4, mixing: and uniformly mixing the carbon-coated silicon material and graphite to obtain the silicon-carbon composite material. The silicon-carbon composite material has the advantages of low granularity, high tap density, high first-time charging specific capacity and high first-time charging efficiency, shows excellent comprehensive performance, enhances the use effect of the silicon-carbon composite material in lithium ion batteries, and meets market demands.
Description
Technical Field
The application relates to the technical field of lithium ion batteries, in particular to a preparation method of a high tap density silicon-carbon composite material, a silicon-carbon composite material and application.
Background
With the development of society, the lithium ion battery industry is also rapidly advancing. The lithium ion battery mainly comprises a negative electrode plate, a positive electrode plate, a porous diaphragm arranged between the positive electrode plate and the negative electrode plate and electrolyte, wherein the negative electrode plate is one of important raw materials of the lithium ion battery. The raw materials of the negative electrode plate are usually graphite negative electrode materials, the theoretical capacity limit value of the graphite negative electrode materials is 372mAh/g, and the development requirement of continuous improvement of the energy density of the lithium ion battery cannot be met.
Silicon can have a theoretical capacity as high as 4200mAh/g, which is more than 10 times that of graphite material, and is considered to be the most promising alternative to graphite material as the next-generation ideal negative electrode material. However, in the practical use process, silicon has the problems of huge volume change and low conductivity in the lithium intercalation/deintercalation process. The silicon is subjected to nanocrystallization, and then the nano silicon is compounded with graphite to form the silicon-carbon composite material, so that the method is an effective solution.
However, the inventors believe that the silicon has a very high surface energy after nanocrystallization, which renders the material fluffy. After the silicon-carbon composite material is mixed with graphite, the obtained silicon-carbon composite material has larger specific surface area and low tap density, and is difficult to be made into a compact negative electrode plate. When the specific surface area of the silicon-carbon composite material is too high, a large amount of SEI films are formed by lithium ions in the first discharging process of the negative electrode plate and are consumed excessively, the utilization rate of lithium elements is low, and the subsequent first charging efficiency is reduced; when the compaction density of the silicon-carbon composite material is too low, the occupation ratio of the high polymer binder can be improved, the solid content in the electrode slurry can be reduced, the electrical performance of the electrode slurry can be hindered, and the performance and the use effect of the battery performance of the electrode slurry can be influenced.
Disclosure of Invention
In order to increase the tap density of the silicon-carbon composite material, the application provides a preparation method of the silicon-carbon composite material with high tap density, the silicon-carbon composite material and application.
In a first aspect, the application provides a preparation method of a high tap density silicon-carbon composite material, which adopts the following technical scheme: a preparation method of a high tap density silicon-carbon composite material comprises the following steps:
s1, preparing premix: the premix is mainly formed by mixing a silicon-carbon composite master batch and an amorphous carbon material, wherein the addition amount of the amorphous carbon material is 1-20% of the weight of the premix, and the addition amount of the silicon-carbon composite master batch is 80-99% of the weight of the premix;
s2, pretreatment: under the protection of inert gas, carrying out hot rolling treatment on the premix at the temperature of 120-240 ℃ and the rolling pressure of 2-10T, then cooling the premix to 30-55 ℃, and carrying out repeated treatment of heating, hot rolling and cooling again for at least 1 time to obtain a pretreated mixture;
s3, carbonizing: roasting the pretreated mixed material under inert gas, and cooling to obtain a carbon-coated silicon material;
s4, mixing: uniformly mixing a carbon-coated silicon material and graphite to obtain a silicon-carbon composite material;
the addition amount of the carbon-coated silicon material is 5-20% of the weight of the silicon-carbon composite material, and the addition amount of the graphite is 80-95% of the weight of the silicon-carbon composite material.
By adopting the technical scheme, the silicon-carbon composite material is ensured by utilizing the synergistic effect among the stepsMaintaining proper specific surface area of 1.5m 2 Specific surface area of/g < 3.0m 2 Per gram, and also increases the tap density thereof, the tap density is more than 0.7g/cm 3 Exhibiting good physical properties. Meanwhile, the electric performance of the battery is enhanced, the first-time charging specific capacity is more than 510mAh/g, and the first-time charging efficiency is more than 88%. Therefore, the silicon-carbon composite material has good comprehensive performance, enhances the use effect of the silicon-carbon composite material in lithium ion batteries, and meets the market demand.
In the preparation method, the premix is pretreated, and inert gas is adopted for protection in pretreatment to prevent the material from being oxidized. And the rolling treatment is carried out under the rolling pressure of 2-10T, so that the gaps of the premix can be effectively reduced, the specific surface area is reduced, and the tap density is improved. And (3) rolling at 120-240 ℃, wherein the temperature range is higher than the softening temperature of the amorphous carbon, so that the amorphous carbon material can be fully softened, the silicon-carbon composite master batch can be better coated, and the combination of the rolling treatment and the combination of the amorphous carbon material and the silicon-carbon composite master batch can enhance the combination of the amorphous carbon material and the silicon-carbon composite master batch. And then cooling to 30-35 ℃, adopting a rapid cooling mode, and enabling the rapidly softened amorphous carbon and the silicon-carbon composite master batch coated in the amorphous carbon to be shaped together to further form a more compact and thinner carbon coating layer, so that lithium ions in the electrolyte can smoothly enter and reach the surface of the silicon-carbon composite master batch, and the carbon coating layer can completely wrap the silicon-carbon composite master batch without dew point, thereby enhancing the electrical property of the silicon-carbon composite material. The synergy between the hot rolling treatment and the cooling treatment is combined, so that the tap density of the silicon-carbon composite material can be effectively increased, and the electrical property of the silicon-carbon composite material is improved.
Further, in step S2, the rolling temperature is 160-200 ℃, preferably 180 ℃; the rolling pressure is 4-6T, preferably 5T. The conditions in the pretreatment of the step S2 are optimized, the specific surface area of the silicon-carbon composite material is proper, the first-time charging specific capacity and the first-time charging efficiency of the silicon-carbon composite material are enhanced, and the electrical performance of the silicon-carbon composite material is improved.
Further, the amorphous carbon material is added in an amount of 5 to 10% by weight, preferably 7% by weight, of the premix; the addition amount of the silicon-carbon composite master batch is 90-95% of the weight of the premix, preferably 93%; the addition amount of the carbon-coated silicon material is 10-15% of the weight of the silicon-carbon composite material, preferably 12%; the addition amount of graphite is 85-90%, preferably 88% of the weight of the silicon-carbon composite material.
Optionally, in the step S2, the rotating speed of the roller is 5-15r/min and the diameter of the roller is 200-400mm in the hot rolling treatment.
Optionally, in step S2, the cooling rate is 1-10 ℃/min in the cooling treatment.
By adopting the technical scheme, the roller rotating speed, the roller diameter and the cooling rate are optimized, the hot rolling treatment time and the cooling time are convenient to control, and the physical property and the electrical property of the silicon-carbon composite material are improved.
Optionally, in step S3, the roasting temperature is 800-1200 ℃ and the roasting time is 8-12h.
By adopting the technical scheme, the roasting temperature and the roasting time are optimized, the carbonization of amorphous carbon is facilitated, a dense carbon coating layer is formed, and the electrical property of the silicon-carbon composite material is enhanced.
Further, the temperature rising rate of the roasting temperature is 1-10 ℃/min.
Optionally, in step S3, crushing after cooling, and then sieving with a 100-300 mesh sieve to obtain the carbon-coated silicon material.
By adopting the technical scheme, the granularity uniformity of the silicon-carbon composite material is enhanced.
Further, the crushing equipment adopted in the crushing mode is one or more of a jaw crusher, a counterattack crusher, a cone crusher and an impact crusher. Jaw crushers are preferred.
In step S2 and step S3, the inert gas is one or more of nitrogen and argon. Preferably nitrogen, the raw materials of the nitrogen are easy to obtain, and the cost is reduced.
Optionally, the silicon-carbon composite master batch is mainly prepared by mixing nano silicon and carbon materials, and the weight ratio of the nano silicon to the carbon materials is (0.1-0.6): 1.
By adopting the technical scheme, the proportion of the nano silicon and carbon materials is optimized, so that the silicon-carbon composite master batch has higher gram capacity, and the electrical property of the silicon-carbon composite material is improved.
Further, the silicon-carbon composite master batch is prepared by the following method: the nano silicon and carbon materials are uniformly mixed to obtain the silicon-carbon composite master batch, so that the preparation and control of the silicon-carbon composite master batch are facilitated.
The premix is prepared by the following steps: and uniformly mixing the silicon-carbon composite master batch and the amorphous carbon material to obtain a premix, so that the preparation and control of the premix are facilitated.
Optionally, the carbon material is one or more of graphene, activated carbon, artificial graphite and natural graphite; the amorphous carbon material is one or more of polyvinylpyrrolidone, carboxymethyl cellulose, lauric acid, starch, asphalt, polyvinylidene fluoride and glucose.
By adopting the technical scheme, the selection and control of the carbon material are facilitated, and the electrical property of the silicon-carbon composite material is improved. The amorphous carbon material is also convenient to select, so that the amorphous carbon material forms a compact carbon coating layer on the surface of the silicon-carbon composite master batch, and the electrical property of the silicon-carbon composite material is improved.
Further, the graphite is one or more of EA-1, G9 and FSN-1. EA-1 is selected from inner Mongolia Cheng Danmo; g9 is selected from Jiangxi purple; FSN-1 is selected from Cephalotaxus fortunei.
By adopting the technical scheme, the selection and control of graphite are facilitated, and the electrical property of the silicon-carbon composite material is improved. EA-1 from inner Mongolia da Cheng graphite is preferred.
Further, the average particle size of the nano-silicon is 80-120nm, preferably 100nm; the average particle size of the carbon material is 1 to 25. Mu.m, preferably 10. Mu.m; the amorphous carbon material has an average particle size of 1-10 μm; preferably 3 μm; the average particle size of the graphite is 10 to 20. Mu.m, preferably 16. Mu.m.
In a second aspect, the application provides a silicon-carbon composite material, which adopts the following technical scheme:
a silicon-carbon composite material prepared by the method.
In a third aspect, the application provides a lithium ion battery anode material, which adopts the following technical scheme:
the raw materials of the lithium ion battery anode material comprise the silicon-carbon composite material.
In a fourth aspect, the present application provides a lithium ion battery, which adopts the following technical scheme:
a lithium ion battery comprises the negative electrode plate prepared from the negative electrode material of the lithium ion battery.
In summary, the application has at least the following advantages:
the preparation method of the high tap density silicon-carbon composite material comprises the steps of pre-treating a premix, carrying out hot rolling treatment on the premix at the temperature of 120-240 ℃ and rolling pressure of 2-10T, cooling the premix to 30-55 ℃ and ensuring that the specific surface area of the silicon-carbon composite material is 1.98-2.75m 2 And/g, maintaining proper specific surface area, effectively reducing granularity, increasing tap density, showing good physical properties, simultaneously increasing first-time charging specific capacity and first-time charging efficiency, showing good electrical properties, enhancing the use effect of the lithium ion battery and meeting market demands.
Drawings
Fig. 1 is an electron micrograph of the silicon carbon composite of example 1.
Fig. 2 is a first discharge charge profile of the silicon carbon composite of example 1.
Fig. 3 is a first discharge charge change curve of the silicon carbon composite of comparative example 1.
Detailed Description
The present application will be described in further detail with reference to examples.
Examples
Example 1
A preparation method of a high tap density silicon-carbon composite material comprises the following steps:
s1, preparing premix
930g of silicon-carbon composite master batch and 70g of amorphous carbon material are added into a planetary mixer, and then stirred for 1.5 hours under the conditions of revolution of 25r/min and autorotation of 1000r/min, so as to obtain a premix.
At this time, the addition amount of the amorphous carbon material was 7% by weight of the premix and the addition amount of the silicon carbon composite master batch was 93% by weight of the premix.
The silicon-carbon composite master batch is a mixture of nano silicon and carbon materials, and the weight ratio of the nano silicon to the carbon materials is 0.4:1. Wherein the average granularity of the nano silicon is 100nm, the silicon purity is 99.9%, the carbon material is graphene, and the average granularity is 10 mu m; the amorphous carbon material is asphalt, and the average particle size of the amorphous carbon material is 3 mu m, the melting temperature is 250 ℃, and the ash content is less than or equal to 0.1.
S2, preprocessing, namely introducing nitrogen into a roller seal box of the roller machine, and keeping the pressure of the roller seal box at 200Pa to form nitrogen protection. Adding premix into a roller machine, carrying out hot rolling treatment on the premix at 180 ℃ and rolling pressure of 5T, wherein the roller rotating speed is 10r/min, and the diameter of the roller is 200mm. The rolled material enters a cooling collecting barrel through a conveying pipe, and the material is cooled to 45 ℃ at a cooling rate of 3 ℃/min. And adding the cooled material into a roller machine again for heating, rolling and cooling, and repeating the treatment for 5 times to obtain the pretreated mixed material.
S3, carbonization
And (3) introducing nitrogen into the carbonization furnace, and keeping the pressure in the carbonization furnace at 200Pa to form nitrogen protection. Adding the pretreatment mixed material into a carbonization furnace, heating to 1150 ℃ at a heating rate of 8 ℃/min, and roasting for 12 hours. Then cooling to 45 ℃, crushing, and sieving with a 200-mesh sieve to obtain the carbon-coated silicon material.
S4, mixing materials
Adding a carbon-coated silicon material and graphite into a planetary mixer, and stirring for 2 hours under the conditions that revolution is 25r/min and rotation is 800r/min to obtain the silicon-carbon composite material.
The addition amount of the carbon-coated silicon material is 12% of the weight of the silicon-carbon composite material, and the addition amount of the graphite is 88% of the weight of the silicon-carbon composite material; the graphite is selected from EA-1 of inner Mongolia da Cheng graphite.
Performance of EA-1 of inner mongolia da Cheng graphite: specific surface area of 2.14m 2 Per gram, tap density of 0.99g/cm 3 The specific capacity for the first charge is 347.7mAh +.g, the first charge efficiency is 92.8%.
Example 2
The preparation method of the high tap density silicon-carbon composite material is different from that of the embodiment 1 in that in the step S2, the pressure of the hot rolling treatment is different, and the rolling pressure is 2T.
Example 3
The preparation method of the high tap density silicon-carbon composite material is different from that of the embodiment 1 in that in the step S2, the pressure of the hot rolling treatment is different, and the rolling pressure is 10T.
Example 4
A preparation method of a high tap density silicon-carbon composite material is different from that of the embodiment 1 in that in the step S2, the temperature of hot rolling treatment is different, and the rolling temperature is 120 ℃.
Example 5
A preparation method of a high tap density silicon-carbon composite material is different from that of the embodiment 1 in that in the step S2, the temperature of hot rolling treatment is different, and the rolling temperature is 240 ℃.
Example 6
A preparation method of a high tap density silicon-carbon composite material is different from that of the embodiment 1 in that in the step S2, the cooling rate is different, and the cooling rate is 1 ℃/min.
Example 7
A preparation method of a high tap density silicon-carbon composite material is different from that of the embodiment 1 in that in the step S2, the cooling rate is different, and the cooling rate is 10 ℃/min.
Comparative example
Comparative example 1
A preparation method of a high tap density silicon-carbon composite material comprises the following steps:
s1, preparing premix
930g of silicon-carbon composite master batch and 70g of amorphous carbon material are added into a planetary mixer, and then stirred for 1.5 hours under the conditions of revolution of 25r/min and autorotation of 1000r/min, so as to obtain a premix.
At this time, the addition amount of the amorphous carbon material was 7% by weight of the premix and the addition amount of the silicon carbon composite master batch was 93% by weight of the premix.
The silicon-carbon composite master batch is a mixture of nano silicon and carbon materials, the average granularity of the nano silicon is 100nm, the carbon material is graphene, and the average granularity of the carbon material is 10 mu m; the amorphous carbon material is pitch and the average particle size of the amorphous carbon material is 3 μm.
S2, carbonization
And (3) introducing nitrogen into the carbonization furnace, and keeping the pressure in the carbonization furnace at 100Pa to form nitrogen protection. Adding premix into the carbonization furnace, heating to 1150 ℃ at a heating rate of 8 ℃/min, and roasting for 12 hours. Then cooling to 45 ℃, crushing, and sieving with a 200-mesh sieve to obtain the carbon-coated silicon material.
S3, mixing materials
Adding a carbon-coated silicon material and graphite into a planetary mixer, and stirring for 2 hours under the conditions that revolution is 25r/min and rotation is 800r/min to obtain the silicon-carbon composite material.
The addition amount of the carbon-coated silicon material is 12% of the weight of the silicon-carbon composite material, and the addition amount of the graphite is 88% of the weight of the silicon-carbon composite material; the graphite is selected from EA-1 of inner Mongolia da Cheng graphite.
Performance test
(1) Microscopic observation
The silicon-carbon composite material obtained in example 1 was taken as a sample, and the microstructure of the sample was observed by using a scanning electron microscope ZEISS SUPRA 55.
As shown in FIG. 1, the silicon-carbon composite material of the application has smooth surface and uniform distribution.
(2) Physical Properties
The negative electrode materials obtained in examples 1 to 7 and comparative example 1 were each taken as a sample, and the following performance test was performed on the samples, and the test results are shown in table 1.
The specific surface area and average particle size of the sample were measured by the BET method.
(3) Electrochemical Properties
The negative electrode materials obtained in examples 1 to 7 and comparative example 1 were respectively taken as samples, and were respectively processed into negative electrode tabs, and the negative electrode tabs were assembled into button half-cells CR2032, and the following performance tests were performed, the test results of which are shown in fig. 2, 3, and table 1.
The negative electrode plate is prepared by the following steps:
SA, adding water and sodium carboxymethyl cellulose thickener into a planetary mixer, and stirring for 0.5h under the conditions that revolution is 25r/min and rotation is 1500 r/min. Then adding the silicon-carbon composite material and the conductive agent, and continuing stirring for 2 hours. Adding styrene-butadiene rubber binder, stirring for 0.5h, and removing bubbles in vacuum to obtain the cathode slurry.
The cathode slurry takes water as a dispersing solvent, the solid content of the cathode slurry is 48%, and the weight ratio of the silicon-carbon composite material, the conductive agent, the sodium carboxymethyl cellulose thickener and the styrene-butadiene rubber binder is 90:5:2.5:2.5 based on dry materials, wherein the conductive agent is conductive carbon black and is selected from Super P Li with Super density; the sodium carboxymethyl cellulose thickener is selected from the group consisting of large celluloid CMC2200; the styrene-butadiene rubber binder is selected from the group consisting of Rayleigh BM-430B.
SB, coating the negative electrode slurry on the surface of a copper foil, drying, tabletting, forming a negative electrode coating by the negative electrode slurry, cutting into pieces, and welding lugs to obtain a negative electrode plate, wherein the thickness of the negative electrode coating is 4 mu m.
TABLE 1 detection results
As can be seen from Table 1, the silicon-carbon composite material of the present application has a good specific surface area of 1.98-2.75m 2 /g, i.e. 1.5m 2 Specific surface area of/g < 3.0m 2 /g; and it also has higher tap density of 0.79-0.98g/cm 3 I.e. tap density > 0.7g/cm 3 At the same time, it has lower granularity, average granularity of 14.22-18.10 mu m, and shows good physical property. More importantly, the battery also has higher specific charge and discharge capacity and first charge efficiency, the first charge specific capacity is 511.8-547.8mAh/g, and the first charge efficiency is 86.5591.26 percent, namely the first-time charging specific capacity is more than 510mAh/g, the first-time charging efficiency is more than 88 percent, the high-performance lithium ion battery has good electrical performance, the comprehensive performance of the silicon-carbon composite material is enhanced, the use effect of the silicon-carbon composite material in the lithium ion battery is improved, and the market demand is met.
Comparing example 1 with comparative example, and combining fig. 2 and 3, it can be seen that the particle size of the silicon-carbon composite material can be effectively reduced, the tap density of the silicon-carbon composite material can be effectively increased, the specific charge-discharge capacity and the first charge efficiency of the silicon-carbon composite material can be increased, and excellent comprehensive performance can be shown.
Comparing example 1 with examples 2-3, it can be seen that as the crushing pressure increases, the first charge efficiency tends to increase and then decrease. This is mainly because the compaction pressure is too small, and compaction effect weakens, and the compaction pressure is too big, has destroyed original structure to influence first charging efficiency. And shows that the silicon-carbon composite material shows better performance at the rolling pressure of 5T.
Comparing example 1 with examples 4-5, it can be seen that as the rolling temperature increases, the first charge efficiency also tends to increase and then decrease. This is mainly because the rolling temperature is too low to fully soften the amorphous carbon material, resulting in uneven encapsulation of the amorphous carbon material in the silicon-carbon composite masterbatch, while too high rolling temperature may cause partial carbonization of the amorphous carbon material, and also result in incomplete encapsulation of the amorphous carbon material in the silicon-carbon composite masterbatch, thereby affecting the primary charging efficiency. It also shows that the silicon carbon composite material shows better performance at the rolling temperature of 180 ℃.
Comparing example 1 with examples 6-7, it can be seen that in the pretreatment of step S2, the first charging efficiency tends to increase and then decrease with increasing cooling rate. This is mainly because the cooling rate is too slow, and the actual heating time of material has the delay, and the cooling rate is too fast, and the material granule solidifies into the bulk fast easily, and the internal area can't be fully utilized to influence first charge efficiency. And shows that the silicon-carbon composite material shows better performance when the cooling rate is 3 ℃/min.
The present embodiment is only for explanation of the present application and is not to be construed as limiting the present application, and modifications to the present embodiment, which may not creatively contribute to the present application as required by those skilled in the art after reading the present specification, are all protected by patent laws within the scope of claims of the present application.
Claims (6)
1. A preparation method of a high tap density silicon-carbon composite material is characterized by comprising the following steps: the method comprises the following steps:
s1, preparing premix: the premix is formed by mixing a silicon-carbon composite master batch and an amorphous carbon material, wherein the addition amount of the amorphous carbon material is 1-20% of the weight of the premix, and the addition amount of the silicon-carbon composite master batch is 80-99% of the weight of the premix;
s2, pretreatment: under the protection of inert gas, carrying out hot rolling treatment on the premix at the temperature of 120-240 ℃ and the rolling pressure of 2-10T, then cooling the premix to 30-55 ℃, and carrying out repeated treatment of heating, hot rolling and cooling again for at least 1 time to obtain a pretreated mixture;
s3, carbonizing: roasting the pretreated mixed material under inert gas, and cooling to obtain a carbon-coated silicon material;
s4, mixing: uniformly mixing a carbon-coated silicon material and graphite to obtain a silicon-carbon composite material;
the addition amount of the carbon-coated silicon material is 5-20% of the weight of the silicon-carbon composite material, and the addition amount of the graphite is 80-95% of the weight of the silicon-carbon composite material;
s2, in the hot rolling treatment, the rotating speed of a roller is 5-15r/min, and the diameter of the roller is 200-400mm; in the cooling treatment, the cooling rate is 1-10 ℃/min; in the step S4, the silicon-carbon composite master batch is formed by mixing nano silicon and carbon materials, and the weight ratio of the nano silicon to the carbon materials is (0.1-0.6): 1;
the carbon material is one or more of graphene, activated carbon, artificial graphite and natural graphite; the amorphous carbon material is one or more of polyvinylpyrrolidone, carboxymethyl cellulose, lauric acid, starch, asphalt, polyvinylidene fluoride and glucose.
2. The method for preparing the high tap density silicon-carbon composite material according to claim 1, which is characterized in that: and step S3, in the roasting treatment, the roasting temperature is 800-1200 ℃ and the roasting time is 8-12h.
3. The method for preparing the high tap density silicon-carbon composite material according to claim 1, which is characterized in that: in the step S3, crushing after cooling, and then sieving with a 100-300 mesh sieve to obtain the carbon-coated silicon material.
4. A silicon carbon composite material characterized by: a silicon carbon composite material prepared by the method of any one of claims 1-3.
5. A lithium ion battery cathode material is characterized in that: the raw material comprises the silicon-carbon composite material as claimed in claim 4.
6. A lithium ion battery, characterized in that: a negative electrode tab comprising the negative electrode material of a lithium ion battery of claim 5.
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| CN112234179A (en) * | 2020-10-26 | 2021-01-15 | 郑州中科新兴产业技术研究院 | Preparation method of high-capacity silicon-based negative electrode material |
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| CN111653745A (en) * | 2020-05-28 | 2020-09-11 | 长沙矿冶研究院有限责任公司 | Silicon-carbon negative electrode precursor material, silicon-carbon negative electrode material and preparation method thereof |
| CN112234179A (en) * | 2020-10-26 | 2021-01-15 | 郑州中科新兴产业技术研究院 | Preparation method of high-capacity silicon-based negative electrode material |
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