CN110571420B - Method for synthesizing silicon/graphite/amorphous carbon/conductive carbon black quaternary composite material by using industrial metallurgical silicon - Google Patents
Method for synthesizing silicon/graphite/amorphous carbon/conductive carbon black quaternary composite material by using industrial metallurgical silicon Download PDFInfo
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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
- 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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- 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
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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
- H01M4/38—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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- 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
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/624—Electric conductive fillers
- H01M4/625—Carbon or graphite
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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
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/628—Inhibitors, e.g. gassing inhibitors, corrosion inhibitors
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- 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
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Abstract
The invention discloses a method for synthesizing a silicon/graphite/amorphous carbon/conductive carbon black quaternary composite material by using industrial metallurgical silicon, belonging to the technical field of lithium ion battery materials. The silicon/graphite/amorphous carbon/conductive carbon black quaternary composite material prepared by the invention realizes that silicon particles are uniformly dispersed in a carbon matrix, improves the conductivity of the silicon particles, enhances the binding force between silicon-carbon layers and between carbon-carbon layers by secondary high-energy ball milling, obviously improves the stability of a silicon-carbon composite structure, effectively inhibits the volume expansion effect of silicon, and prolongs the charge-discharge cycle life of the silicon-carbon composite material.
Description
Technical Field
The invention belongs to the technical field of lithium ion battery materials, and particularly relates to a method for synthesizing a silicon/graphite/amorphous carbon/conductive carbon black quaternary composite material by using industrial metallurgical silicon.
Background
The specific energy of the next generation lithium ion power battery monomer is developed to be more than 300 watt-hour/kilogram, the realization cannot be realized by adopting the traditional graphite cathode, the silicon-carbon composite cathode material is a necessary way, and the silicon-carbon composite material is a key material of the next generation lithium ion power battery. Compared with graphite materials, the theoretical mass specific capacity of silicon is up to 4200mAh/g, and the volume specific capacity is 7200mAh/cm3Is more than 10 times of graphite (the theoretical specific capacity of the graphite is 372mAh/g), and has rich silicon material, low cost and environmental protection. However, there are three key problems to be solved in practical application of silicon materials: (1) in the charging (lithium embedding) process, because of the severe volume expansion (up to 300%) of the silicon material, the expansion force caused by the volume expansion causes the collision extrusion among the silicon particles and leads to the breakage of the silicon material, and in the discharging process, the mutual contact between the silicon particles is influenced by the volume contraction, and the repeated expansion and contraction causes the pulverization and the shedding of the negative electrode material, the electric contact is lost and the failure of the battery is finally caused; (2) during charging, a Solid Electrolyte Interface (SEI) film is formed on the surface of the negative electrode, and the SEI film can prevent solvent molecules of the Electrolyte from passing through and only allow lithium ions to pass through, so as to protect the negative electrode from contact reaction with the solvent molecules. The volume of the silicon particles expands in the charging process, the SEI film is damaged, the silicon particles are exposed in the electrolyte again, a new SEI film is formed on the surface of the silicon particles in the next charging process, the SEI film is broken and grows again and again, the limited electrolyte and lithium ions are continuously consumed, and the SEI film is thickIt is continuously increased, resulting in an increase in internal impedance. One of the current techniques is to nanosize silicon and coat its surface with a carbon material to form a composite material. The increased surface area to volume ratio of the nano-silicon particles helps to better withstand the stress of volume expansion and greatly limits the extent of cracking. (3) The commercial nano-scale silicon powder is expensive and has a serious agglomeration phenomenon, so that the cost of the electrode is very high if the nano-scale silicon powder is directly adopted, and the cycle life is not ideal due to the easy agglomeration and poor dispersibility of the nano-scale silicon powder. Therefore, the three problems limit that the nano silicon is not suitable to be directly used as a negative electrode material of a lithium ion battery.
Chinese patent CN201310425217.2 discloses a method for preparing a silicon/graphite/carbon composite material for a lithium ion battery, which is technically characterized in that a nano silicon material is dispersed in a liquid medium by adopting an ultra-fine grinding technology to form slurry of the nano silicon material, then a carbon negative electrode material and an organic carbon source are added into the uniformly dispersed slurry of the nano silicon material for compounding, spray drying and heat treatment are carried out to obtain silicon-carbon composite powder, and the bonding strength between silicon and carbon is improved by secondary ultra-fine grinding to achieve good silicon-carbon stable structure and cycle life. However, the invention directly uses the commercial nano silicon powder with high price, has high cost for manufacturing the silicon-carbon composite material and is not beneficial to industrialized production.
Chinese invention patent CN201610050565.X discloses a preparation method of a silicon/graphite/carbon composite anode material of a lithium ion battery, which comprises the following steps: dissolving an amorphous carbon source and a dispersing agent in a solvent, uniformly dispersing, adding nano silicon and graphite, and continuously uniformly dispersing to obtain a mixture; mechanically curing or spray drying the mixture to obtain a precursor of the negative electrode material; and calcining the precursor in an inert atmosphere to obtain the silicon/graphite/carbon composite anode material. The cathode material obtained by the method can improve the dispersion uniformity of nano silicon and relieve the volume expansion effect of silicon, but the bonding force between silicon and carbon and the bonding force between carbon and carbon are not strong, so that the silicon and the carbon are easily separated in the charge-discharge cycle process, and the cycle life is influenced.
Chinese patent 201610003146.0 discloses a method for preparing a silicon/artificial graphite composite material by high-energy ball milling, which is technically characterized by comprising the following steps: adding a solvent into micron silicon powder and an organic carbon source, ball-milling, spray-drying screened slurry and pyrolyzing at high temperature to obtain a silicon/carbon compound; and adding the silicon/carbon composite, the organic carbon source and graphite into the solvent, stirring and mixing, and then carrying out spray drying and high-temperature pyrolysis to obtain the silicon/carbon/graphite composite material. The method has simple process and is easy for industrial production. However, the composite material obtained by the method has unsatisfactory long-term circulation stability and insufficient bonding force between silicon and carbon, and in addition, the agglomeration of silicon particles is difficult to avoid in the drying and compounding process.
The Chinese patent 201410482654.2 discloses a graphite silicon-based composite negative electrode material and a preparation method thereof, and the technical key points are that nano-silicon is obtained by mechanical ball milling with a high-energy wet method, then the nano-silicon is compounded with a polymer with high carbon residue through dispersion polymerization to form a polymer/nano-silicon composite microsphere with nano-silicon embedded in the polymer microsphere, then the microsphere is compounded with graphite, finally the polymer/nano-silicon composite microsphere is coated with an organic carbon source in a solid phase manner, and a final product is obtained through heat treatment. The composite material synthesized by the method has uniform silicon-carbon distribution and good binding force. However, this method uses an organic solvent such as acrylonitrile or azobisisobutyronitrile. Acrylonitrile is inflammable, is easy to cause combustion when meeting open fire and high heat and emits toxic gas, and the acrylonitrile is listed in a 2B class carcinogen list by WHO; the azodiisobutyronitrile organic solvent is also toxic, and the released organic cyanide has great harm to human bodies. Therefore, the method is not environment-friendly and is not beneficial to human health in industrial production.
Therefore, the research on the silicon/graphite/amorphous carbon/conductive carbon black quaternary composite material is very important.
Disclosure of Invention
The invention aims to solve the defects of the prior art and provide a method for synthesizing a silicon/graphite/amorphous carbon/conductive carbon black quaternary composite material by using industrial metallurgical silicon.
The invention adopts the following technical scheme:
the invention provides a method for synthesizing a silicon/graphite/amorphous carbon/conductive carbon black quaternary composite material by using industrial metallurgical silicon, which comprises the following steps:
the method comprises the following steps: weighing an industrial metallurgical grade silicon material, selecting a solid steel ball, filling the industrial metallurgical grade silicon material and the solid steel ball into a ball milling tank, adding grinding fluid, protecting with argon, sealing the ball milling tank, and performing ball milling to obtain silicon powder slurry I;
dispersing silicon particles with a mixture of graphite and conductive carbon black:
weighing graphite powder and conductive carbon black according to a certain weight ratio, adding the graphite powder and the conductive carbon black into the same solvent, and mixing and dispersing to form mixed slurry II;
b: mixing and dispersing the silicon powder slurry I and the mixed slurry II to obtain a mixed material III;
c: under the protection of argon, transferring the mixture III into a ball milling tank, adding steel balls, sealing the ball milling tank, and carrying out ball milling to obtain a silicon/graphite precursor compound;
step three, synthesizing a silicon/graphite/amorphous carbon/conductive carbon black quaternary composite material:
a: weighing a certain weight of amorphous carbon or graphite powder or a mixture of the amorphous carbon or graphite powder and the conductive carbon black, adding the amorphous carbon or graphite powder or the mixture of the amorphous carbon or graphite powder and the conductive carbon black into the same solvent, and mixing and dispersing to obtain mixed slurry IV for later use;
b: mixing and dispersing the silicon/graphite precursor compound obtained in the step two and the mixed slurry IV obtained in the step three to obtain a mixed material V;
c: and (3) under the argon protective atmosphere, transferring the mixture V into a ball milling tank, adding steel balls, sealing the ball milling tank, carrying out ball milling, discharging, carrying out spray drying on the materials, and grinding and sieving to obtain the silicon/graphite/amorphous carbon/carbon black quaternary composite material.
In some embodiments, the weight ratio of the solid steel balls added into the ball milling tank in the step one to the metallurgical grade silicon material is 20-30: 1; in the first step, the grinding fluid is one of absolute ethyl alcohol, ethylene glycol or propanol, and the dosage of the grinding fluid is 1-5 ml/g of raw material to be ground; the weight ratio of the steel balls to the solid phase raw materials added in the step two c is 30-40: 1; the weight ratio of the steel balls to the solid phase raw materials in the third step is 30-40: 1.
In some embodiments, the ball milling in the step one is specifically performed by: the ball milling tank is arranged on an 800D type ball mill to perform ball milling for 10-30 minutes at the clockwise rotation speed of 300-400RPM, the ball milling is suspended for 5-10 minutes, then the ball milling is performed for 10-30 minutes at the same rotation speed in a counter-clockwise mode, and the ball milling is automatically and repeatedly performed for 5-80 hours in an intermittent mode; the specific operation of ball milling in the step two c is as follows: installing the ball milling tank on an 800D type ball mill, designing a ball milling program to perform ball milling for 20 minutes at 200-300RPM (revolution per minute) and pausing for 5 minutes; then performing ball milling for 20 minutes in a counter-clockwise way at the same rotating speed, and performing intermittent automatic alternate repeated ball milling for 5 to 40 hours; the ball milling in the third step is specifically performed by: installing the ball milling tank on an 800D type ball mill, designing a ball milling program to perform ball milling for 20 minutes at 200-300RPM (revolution per minute) and pausing for 5 minutes; then ball milling is carried out for 20 minutes in a counter-clockwise way at the same rotating speed, and the intermittent automatic alternate repeated ball milling time is 5 to 60 hours.
In some embodiments, the intermittent automatic alternate and repeat ball milling time in the ball milling in the second step is 10 to 30 hours, and the intermittent automatic alternate and repeat ball milling time in the ball milling in the third step is 20 to 50 hours.
In some embodiments, the weight ratio of the graphite powder to the conductive carbon black in the step two a is 100-0:0-100, the solvent is one of absolute ethyl alcohol, ethylene glycol or propanol, the dispersion method comprises mechanical stirring and ultrasonic treatment, and the total time of the dispersion treatment is 0.5-20 hours; the solid phase weight ratio of the silicon powder slurry I to the mixed slurry II in the step two b is 90-40:10-60, the mixing and dispersing treatment in the step two b is mechanical stirring and ultrasonic treatment, and the total dispersing treatment time is 0.5-24 hours; the weight ratio of the amorphous carbon or graphite powder or the mixture of the amorphous carbon and the graphite powder to the conductive carbon black in the step III a is 40-90:60-10, the solvent in the step III a is one of absolute ethyl alcohol, ethylene glycol or propanol, the mixing and dispersing treatment is mechanical stirring for 0.5-18 hours, and the ultrasonic dispersing treatment time is 0.5-2 hours; in the third step, the solid-phase weight ratio of the silicon/graphite precursor compound to the mixed slurry IV is 70-20: 30-80; the mixing and dispersing treatment in the third step is as follows: firstly mechanically stirring and mixing, then ultrasonically dispersing and uniformly mixing, wherein the dispersion treatment time is 0.5-24 hours.
In some embodiments, the weight ratio of the graphite powder to the conductive carbon black in the second step a is 95-70: 5-30; in the second step, the solid phase weight ratio of the silicon powder slurry I to the mixed slurry II is 80-50: 20-50; and in the third step b, the solid-phase weight ratio of the silicon/graphite precursor compound to the mixed slurry IV is 60-30: 40-70.
In some embodiments, the weight ratio of the graphite powder to the conductive carbon black in the second step is 90-80: 10-20; in the second step, the solid phase weight ratio of the silicon powder slurry I to the mixed slurry II is 65-55: 35-45; and in the third step b, the solid-phase weight ratio of the silicon/graphite precursor compound to the mixed slurry IV is 50-40: 50-60.
In some embodiments, the graphite in the second step a is one or more of spherical graphite, flake graphite and artificial graphite, and the conductive carbon black is Super PTMOne of conductive carbon black 350G, Ketjen black ECP, ECP-600JD or EC-300J or carbon nanotube; in the third step a, the graphite is one or more of spherical graphite, flake graphite and artificial graphite, and the conductive carbon black is one of KS6L, KS6/15 or SFG 6/15.
Compared with the prior art, the invention has the beneficial effects that:
the silicon/graphite/amorphous carbon/conductive carbon black quaternary composite material prepared by the invention realizes that silicon particles are uniformly dispersed in a carbon matrix, improves the conductivity of the silicon particles, enhances the binding force between silicon-carbon layers and between carbon-carbon layers by secondary high-energy ball milling, obviously improves the stability of a silicon-carbon composite structure, effectively inhibits the volume expansion effect of silicon, and prolongs the charge-discharge cycle life of the silicon-carbon composite material.
Drawings
FIG. 1 is a scanning electron microscope image of a silicon/graphite/amorphous carbon/conductive carbon black composite synthesized in example 1 of the present invention;
FIG. 2 is a graph of elemental silicon distribution from EDS spectroscopy of the silicon carbon composite of FIG. 1 showing that the silicon component is uniformly dispersed in the carbon matrix;
FIG. 3 is a graph of the distribution of carbon elements from EDS spectroscopy of the silicon carbon composite of FIG. 1, illustrating the uniform distribution of carbon components around the silicon particles;
fig. 4 is a graph showing the electrochemical charge-discharge cycle stability of a negative electrode made of the silicon/graphite/amorphous carbon/conductive carbon black composite material synthesized in example 1 of the present invention as an active material, and it can be seen that the negative electrode has very good electrochemical cycle stability, the discharge capacity is about 602 ma per gram after 200 cycles, and the capacity is maintained at about 500 ma per gram after 700 cycles;
fig. 5 is a stable graph of electrochemical charge-discharge cycle of a negative electrode made of the silicon/graphite/amorphous carbon/conductive carbon black composite material synthesized in example 2 of the present invention as an active material, wherein the maximum electrochemical discharge capacity is 1338 ma per gram, and the discharge capacity is maintained at about 673 ma per gram after 200 cycles;
fig. 6 is a stable graph of electrochemical charge-discharge cycle of negative electrode made of the composite material of silicon/graphite/amorphous carbon/conductive carbon black synthesized in example 3 of the present invention as active material, wherein the maximum electrochemical discharge capacity is 1706 ma per gram, and the discharge capacity after 200 cycles is maintained at 798 ma per gram.
Detailed Description
The invention is described in detail below with reference to specific embodiments so that the advantages and features of the invention may be more readily understood by those skilled in the art, and thus the scope of the invention may be more clearly and clearly defined.
The invention provides a method for synthesizing a silicon/graphite/amorphous carbon/conductive carbon black quaternary composite material by using industrial metallurgical silicon, which comprises the following steps:
the method comprises the following steps: weighing an industrial metallurgical grade silicon material, selecting a solid steel ball, filling the industrial metallurgical grade silicon material and the solid steel ball into a ball milling tank, adding grinding fluid, protecting with argon, sealing the ball milling tank, and performing ball milling to obtain silicon powder slurry I;
dispersing silicon particles with a mixture of graphite and conductive carbon black:
weighing graphite powder and conductive carbon black according to a certain weight ratio, adding the graphite powder and the conductive carbon black into the same solvent, and mixing and dispersing to form mixed slurry II;
b: mixing and dispersing the silicon powder slurry I and the mixed slurry II to obtain a mixed material III;
c: under the protection of argon, transferring the mixture III into a ball milling tank, adding steel balls, sealing the ball milling tank, and carrying out ball milling to obtain a silicon/graphite precursor compound;
step three, synthesizing a silicon/graphite/amorphous carbon/conductive carbon black quaternary composite material:
a: weighing a certain weight of amorphous carbon or graphite powder or a mixture of the amorphous carbon or graphite powder and the conductive carbon black, adding the amorphous carbon or graphite powder or the mixture of the amorphous carbon or graphite powder and the conductive carbon black into the same solvent, and mixing and dispersing to obtain mixed slurry IV for later use;
b: mixing and dispersing the silicon/graphite precursor compound obtained in the step two and the mixed slurry IV obtained in the step three to obtain a mixed material V;
c: and (3) under the argon protective atmosphere, transferring the mixture V into a ball milling tank, adding steel balls, sealing the ball milling tank, carrying out ball milling, discharging, carrying out spray drying on the materials, and grinding and sieving to obtain the silicon/graphite/amorphous carbon/carbon black quaternary composite material.
In one embodiment, the weight ratio of the solid steel balls added into the ball milling tank in the step one to the metallurgical grade silicon material is 20-30: 1; in the first step, the grinding fluid is one of absolute ethyl alcohol, ethylene glycol or propanol, and the dosage of the grinding fluid is 1-5 ml/g of raw material to be ground; the weight ratio of the steel balls to the solid phase raw materials added in the step two c is 30-40: 1; the weight ratio of the steel balls to the solid phase raw materials in the third step is 30-40: 1.
In one embodiment, the ball milling in the step one is specifically performed by: the ball milling tank is arranged on an 800D type ball mill to perform ball milling for 10-30 minutes at the clockwise rotation speed of 300-400RPM, the ball milling is suspended for 5-10 minutes, then the ball milling is performed for 10-30 minutes at the same rotation speed in a counter-clockwise mode, and the ball milling is automatically and repeatedly performed for 5-80 hours in an intermittent mode; the specific operation of ball milling in the step two c is as follows: installing the ball milling tank on an 800D type ball mill, designing a ball milling program to perform ball milling for 20 minutes at 200-300RPM (revolution per minute) and pausing for 5 minutes; then performing ball milling for 20 minutes in a counter-clockwise way at the same rotating speed, and performing intermittent automatic alternate repeated ball milling for 5 to 40 hours; the ball milling in the third step is specifically performed by: installing the ball milling tank on an 800D type ball mill, designing a ball milling program to perform ball milling for 20 minutes at 200-300RPM (revolution per minute) and pausing for 5 minutes; then ball milling is carried out for 20 minutes in a counter-clockwise way at the same rotating speed, and the intermittent automatic alternate repeated ball milling time is 5 to 60 hours.
In one embodiment, the intermittent automatic alternate and repeat ball milling time is 10 to 30 hours when the ball milling is performed in the second step, and the intermittent automatic alternate and repeat ball milling time is 20 to 50 hours when the ball milling is performed in the third step.
In one embodiment, the weight ratio of the graphite powder to the conductive carbon black in the step two a is 100-0:0-100, the solvent is one of absolute ethyl alcohol, ethylene glycol or propanol, the dispersion method comprises the steps of firstly mechanically stirring and then ultrasonically processing, and the total time of the dispersion processing is 0.5-20 hours; the solid phase weight ratio of the silicon powder slurry I to the mixed slurry II in the step two b is 90-40:10-60, the mixing and dispersing treatment in the step two b is mechanical stirring and ultrasonic treatment, and the total dispersing treatment time is 0.5-24 hours; the weight ratio of the amorphous carbon or graphite powder or the mixture of the amorphous carbon and the graphite powder to the conductive carbon black in the step III a is 40-90:60-10, the solvent in the step III a is one of absolute ethyl alcohol, ethylene glycol or propanol, the mixing and dispersing treatment is mechanical stirring for 0.5-18 hours, and the ultrasonic dispersing treatment time is 0.5-2 hours; in the third step, the solid-phase weight ratio of the silicon/graphite precursor compound to the mixed slurry IV is 70-20: 30-80; the mixing and dispersing treatment in the third step is as follows: firstly mechanically stirring and mixing, then ultrasonically dispersing and uniformly mixing, wherein the dispersion treatment time is 0.5-24 hours.
In one embodiment, the weight ratio of the graphite powder to the conductive carbon black in the second step a is 95-70: 5-30; in the second step, the solid phase weight ratio of the silicon powder slurry I to the mixed slurry II is 80-50: 20-50; and in the third step b, the solid-phase weight ratio of the silicon/graphite precursor compound to the mixed slurry IV is 60-30: 40-70.
In one embodiment, the weight ratio of the graphite powder to the conductive carbon black in the second step is 90-80: 10-20; in the second step, the solid phase weight ratio of the silicon powder slurry I to the mixed slurry II is 65-55: 35-45; and in the third step b, the solid-phase weight ratio of the silicon/graphite precursor compound to the mixed slurry IV is 50-40: 50-60.
In an embodiment, the graphite in the second step a is one or more of spherical graphite, flake graphite and artificial graphite, and the conductive carbon black is Super PTMOne of conductive carbon black 350G, Ketjen black ECP, ECP-600JD or EC-300J or carbon nanotube; in the third step a, the graphite is one or more of spherical graphite, flake graphite and artificial graphite, and the conductive carbon black is one of KS6L, KS6/15 or SFG 6/15.
The invention is further illustrated below with reference to several examples.
Example 1
1) Weighing 4.2 g of industrial silicon material with metallurgical grade purity of 99.8% after powder breaking, wherein the particle size of the industrial silicon material is in the range of 0.08-0.1 mm, putting 8 mm solid steel balls into a ball milling tank together, wherein the weight ratio of the steel balls to the silicon material is 30:1, adding 12.6 ml of absolute ethyl alcohol, the protective atmosphere is argon, the ball milling tank is arranged on an 800D type ball mill, performing ball milling at 400RPM (revolution speed) for 20 minutes clockwise, pausing for 8 minutes, performing ball milling at the same revolution speed for 20 minutes anticlockwise, pausing for 8 minutes, intermittently and automatically and repeatedly performing ball milling for 40 hours to obtain silicon powder slurry I, and analyzing the silicon powder particles to be mainly distributed between 80-150 nanometers by a laser diffraction particle size distribution tester (S3500-Mictrroc).
2) 2.24 g of spherical graphite powder and conductive carbon black (Super P) are weighedTM)0.56 g of the mixture is sequentially added into 14 ml of absolute ethyl alcohol solvent, firstly magnetic stirring, dispersion and mixing are carried out for 16 hours, and then ultrasonic oscillation, dispersion and mixing are carried out for 1 hour, so as to form mixed slurry II. Adding the mixed slurry II into the silicon powder slurry I, flushing the residual slurry II with a small amount of absolute ethyl alcohol solvent, magnetically stirring, dispersing and mixing for 18 hours, and ultrasonically oscillating and uniformly dispersingAnd mixing for 2 hours to obtain mixed slurry III. Adding steel balls, wherein the weight ratio of the steel balls to the solid phase raw materials is 40:1, the protective atmosphere is argon, mounting a ball milling tank on a 800D type ball mill, performing ball milling at 300RPM (revolution per minute) for 20 minutes in a clockwise manner, and pausing for 5 minutes; then ball milling is carried out for 20 minutes in a counter-clockwise way at the same rotating speed, and the intermittent automatic alternate repeated ball milling time is 20 hours, thus forming the silicon/graphite precursor compound.
3) Amorphous carbon 4.9 g and conductive carbon black (KS6L) (2.1 g) were weighed, sequentially added to 35 ml of an anhydrous ethanol solvent, and first subjected to magnetic stirring dispersion and mixing for 16 hours, and then subjected to ultrasonic oscillation dispersion and mixing for 1 hour to form a mixed slurry IV. And (3) adding the mixed slurry IV into the silicon/graphite precursor obtained in the step two, washing the residual slurry IV by a small amount of absolute ethyl alcohol solvent, performing magnetic stirring, dispersing and mixing for 18 hours, performing ultrasonic oscillation, dispersing and mixing for 2 hours, and performing mixing and dispersing treatment to obtain mixed slurry V. The weight ratio of the added steel balls to the solid phase of the raw material is 40:1, the protective atmosphere is argon, the ball milling tank is arranged on an 800D type ball mill, the ball milling is carried out for 20 minutes at the clockwise rotating speed of 200RPM, and the ball milling is suspended for 5 minutes; and then performing ball milling on the mixture for 20 minutes in a counter-clockwise way at the same rotating speed, performing intermittent automatic alternate repeated ball milling for 50 hours, and performing spray drying, grinding and sieving on the slurry to obtain the silicon/graphite/amorphous carbon/conductive carbon black quaternary composite material.
The results of the observation of the sample by a scanning electron microscope and the analysis of element distribution are respectively shown in fig. 1, fig. 2 and fig. 3, wherein fig. 1 shows that the particle size of the silicon-carbon composite material particles is mainly between 0.5 and 5.0 microns; FIG. 2 is a distribution diagram of the elemental silicon of the composite material showing the silicon component uniformly dispersed in the carbon matrix; fig. 3 is a distribution diagram of the carbon element of the composite material, illustrating that the carbon component is uniformly distributed around the silicon particles.
Example 2
1) Silicon powder slurry i was obtained in the same manner as in the first step of example 1.
2) Weighing a graphite powder mixture (spherical graphite and flake graphite in a weight ratio of 60: 40 mix) 2.38 grams and conductive carbon black (Super P)TM)0.42 g of the mixture is sequentially added into 14 ml of absolute ethyl alcohol solvent, magnetic stirring, dispersion and mixing are carried out for 15 hours, and ultrasonic oscillation, dispersion and mixing are carried out for 1 hour to form mixed slurry II. Adding the mixed slurry II into the silicon powder slurryAnd (3) washing residual slurry II in the material I by using a small amount of absolute ethyl alcohol solvent, then carrying out magnetic stirring, dispersing and mixing for 18 hours, and then carrying out ultrasonic oscillation, dispersing and uniformly mixing for 2 hours to obtain mixed slurry III. Adding steel balls, wherein the weight ratio of the steel balls to the solid phase raw materials is 40:1, the protective atmosphere is argon, installing a ball milling tank on a 800D type ball mill, performing ball milling for 20 minutes at 200RPM (revolution per minute) in a clockwise mode, and pausing for 5 minutes; then ball milling is carried out for 20 minutes in a counter-clockwise way at the same rotating speed, and the intermittent automatic alternate repeated ball milling time is 30 hours, thus forming the silicon/graphite precursor compound.
3) 3.6 g of amorphous carbon, 2.4 g of flake graphite powder and 2.56 g of conductive carbon black (KS6/15) are weighed and sequentially added into 35 ml of absolute ethyl alcohol solvent, firstly, magnetic stirring, dispersion and mixing are carried out for 16 hours, and then, ultrasonic oscillation, dispersion and mixing are carried out for 1 hour, so as to form mixed slurry IV. And (3) adding the mixed slurry IV into the silicon/graphite precursor obtained in the step two, washing the residual slurry IV by a small amount of absolute ethyl alcohol solvent, magnetically stirring, dispersing and mixing for 18 hours, then ultrasonically oscillating, dispersing and mixing for 2 hours, and mixing and dispersing to obtain a mixed slurry V. The weight ratio of the added steel balls to the solid phase of the raw material is 40:1, the protective atmosphere is argon, the ball milling tank is arranged on an 800D type ball mill, the ball milling is carried out for 20 minutes at the clockwise rotating speed of 200RPM, and the ball milling is suspended for 5 minutes; and then performing ball milling on the mixture for 20 minutes in a counter-clockwise way at the same rotating speed, performing intermittent automatic alternate repeated ball milling for 40 hours, and performing spray drying, grinding and sieving on the slurry to obtain the silicon/graphite/amorphous carbon/conductive carbon black quaternary composite material.
Example 3
1) Silicon powder slurry i was obtained in the same manner as in the first step of example 1.
2) Weighing 1.65G of spherical graphite powder, 1.11G of flake graphite powder and 0.68G of conductive carbon black (350G), sequentially adding the spherical graphite powder, the flake graphite powder and the conductive carbon black into 17 ml of absolute ethyl alcohol solvent, carrying out magnetic stirring, dispersing and mixing for 15 hours, and then carrying out ultrasonic oscillation, dispersing and mixing for 1 hour to form mixed slurry II. And adding the mixed slurry II into the silicon powder slurry I, flushing the residual slurry II with a small amount of absolute ethyl alcohol solvent, performing magnetic stirring, dispersing and mixing for 18 hours, and performing ultrasonic oscillation, dispersing and uniformly mixing for 2 hours to obtain mixed slurry III. Adding steel balls, wherein the weight ratio of the steel balls to the solid phase raw materials is 40:1, the protective atmosphere is argon, mounting a ball milling tank on a 800D type ball mill, performing ball milling at 300RPM (revolution per minute) for 20 minutes in a clockwise manner, and pausing for 5 minutes; then ball milling is carried out for 20 minutes in a counter-clockwise way at the same rotating speed, and the intermittent automatic alternate repeated ball milling time is 30 hours, thus forming the silicon/graphite precursor compound.
3) Weighing 4.67 g of amorphous carbon, 2.8 g of flake graphite powder and 1.86 g of conductive carbon black (KS6/15), sequentially adding into 47 ml of absolute ethyl alcohol solvent, firstly carrying out magnetic stirring, dispersing and mixing for 15 hours, and then carrying out ultrasonic oscillation, dispersing and mixing for 1 hour to form mixed slurry IV. And (3) adding the mixed slurry IV into the silicon/graphite precursor obtained in the step two, washing the residual slurry IV by a small amount of absolute ethyl alcohol solvent, performing magnetic stirring, dispersing and mixing for 18 hours, performing ultrasonic oscillation, dispersing and mixing for 2 hours, and performing mixing and dispersing treatment to obtain mixed slurry V. The weight ratio of the added steel balls to the solid phase of the raw material is 40:1, the protective atmosphere is argon, the ball milling tank is arranged on an 800D type ball mill, the ball milling is carried out for 20 minutes at the clockwise rotating speed of 300RPM, and the ball milling is suspended for 5 minutes; and then performing ball milling on the mixture for 20 minutes in a counter-clockwise way at the same rotating speed, performing intermittent automatic alternate repeated ball milling for 30 hours, and performing spray drying, grinding and sieving on the slurry to obtain the silicon/graphite/amorphous carbon/conductive carbon black quaternary composite material.
The silicon-carbon quaternary composite materials prepared in the embodiments 1-3 of the invention are respectively prepared into the negative electrodes of the lithium ion batteries. The preparation process comprises the following steps of adding 5% of PVDF adhesive by weight into the prepared nano silicon-carbon composite material, using N-methyl pyrrolidone (NMP) as a solvent for size mixing, uniformly mixing, coating the slurry on circular foam copper with the diameter of 1.0 cm to prepare a pole piece, then drying for 1h under vacuum at 80 ℃, then drying for 1h under vacuum at 200 ℃ to remove the NMP solvent, tabletting at room temperature, weighing to obtain an active material loaded on the pole piece, transferring a negative electrode into an argon protective atmosphere glove box for later use, preparing a circular metal lithium piece with the diameter of 1.2 cm in the glove box as a counter electrode, using a polymer film with the thickness of 25 micrometers of Celgard 2500 as a diaphragm, and using 1.0mol/L LiPF6/EC + DMC (volume ratio of 1: 1) of Aldrich as an electrolyte to assemble a test battery. The batteries were tested for constant current charge and discharge performance at room temperature by an Arbin electrochemical cell test workstation.
Fig. 4 is a graph showing the electrochemical charge-discharge cycle stability of a negative electrode made of the silicon/graphite/amorphous carbon/conductive carbon black quaternary composite material synthesized in example 1 of the present invention as an active material, and it can be seen that the negative electrode made of the silicon-carbon composite material synthesized in example 1 of the present invention has very good electrochemical cycle stability, the discharge capacity after 200 cycles is about 602 ma per gram, and the capacity after 700 cycles of charge and discharge is maintained at about 500 ma per gram. The secondary high-energy ball milling can obviously enhance the adhesive force and the mechanical property of the carbon layer and improve the capability of the carbon layer for resisting the volume expansion stress of the silicon particles; the stability of the silicon-carbon composite structure is obviously improved, the volume expansion effect of silicon is effectively inhibited, and the charge-discharge cycle life of the silicon-carbon composite structure is prolonged.
Fig. 5 is a stable graph of electrochemical charge-discharge cycle of a negative electrode made of the silicon/graphite/amorphous carbon/conductive carbon black composite material synthesized in example 2 of the present invention as an active material, and it is found that the first charge capacity is 1340 ma per gram, the first discharge capacity is 1100 ma per gram, the first charge efficiency is 82%, the maximum electrochemical discharge capacity is 1338 ma per gram, and the discharge capacity after 200 cycles is maintained at about 673 ma per gram. Example 2 of the present invention again demonstrates that the secondary high energy ball milling enhances the binding force between silicon-carbon layers and between carbon-carbon layers, and maintains the silicon-carbon integral composite structure during repeated charging and discharging processes, resulting in improved electrode stability.
Fig. 6 is a stable graph of electrochemical charge-discharge cycles of a negative electrode made of the silicon/graphite/amorphous carbon/conductive carbon black quaternary composite material synthesized in example 3 of the present invention as an active material, and it is found that the first charge capacity is 1881 ma per gram, the first discharge capacity is 1568 ma per gram, the first charge efficiency is 83.3%, the cycle efficiency of charge in week 2 is 90.3%, and then slowly increases, the cycle efficiency of charge in week 5 is 96.1%, the cycle efficiency of charge in week 10 is 97.3%, and the cycle efficiency of charge in week 20 is 98.8%, therefore, the silicon/graphite/amorphous carbon/conductive carbon black quaternary composite material synthesized by the present invention has good compatibility with organic solvents, and the reversible specific capacity of the silicon carbon composite material is high.
The invention adopts the secondary high-energy ball milling to enhance the binding force between silicon-carbon layers and between carbon-carbon layers, improve the stability of the silicon-carbon composite structure and inhibit the volume expansion effect of silicon, and the electrolyte adopts the common traditional electrolyte, and the components of the electrolyte do not contain fluorine and other expensive film-forming agent additives (such as fluorine-containing solvents such as FEC and the like) of the new generation.
In conclusion, the silicon/graphite/amorphous carbon/conductive carbon black quaternary composite material synthesized by using the metallurgical silicon has the advantages of low material cost, simple synthesis method and environmental friendliness, and the composite material has good charge and discharge capacity, charge and discharge efficiency and excellent cycle performance, can meet the requirement of the next generation of lithium ion power battery monomer with the specific energy of 300-350 watt-hour/kg, and has wide market prospect.
The embodiments of the present invention have been described in detail with reference to the above examples, but the present invention is not limited to the above embodiments, and various changes can be made without departing from the spirit of the present invention within the knowledge of those skilled in the art.
Claims (5)
1. A method for synthesizing silicon/graphite/conductive carbon black/amorphous carbon/KS carbon black composite material by using industrial metallurgical silicon is characterized by comprising the following steps:
the method comprises the following steps: weighing an industrial metallurgical grade silicon material, selecting solid steel balls, filling the industrial metallurgical grade silicon material and the solid steel balls into a ball milling tank, adding grinding fluid, protecting with argon gas, sealing the ball milling tank, and performing high-energy ball milling to obtain silicon powder slurry I, wherein the specific operations during ball milling are as follows: installing the ball milling tank on a ball mill, performing ball milling for 10-20 minutes at the clockwise rotation speed of 300-400RPM, pausing for 8-10 minutes, performing ball milling for 10-20 minutes at the same rotation speed in a counter-clockwise manner, and performing intermittent automatic and repeated ball milling for 40-80 hours;
dispersing silicon particles with a mixture of graphite and conductive carbon black:
weighing graphite and conductive carbon black according to a certain weight ratio, adding the graphite and the conductive carbon black into the same solvent, and performing mechanical stirring and ultrasonic mixing dispersion treatment in advance to form mixed slurry II, wherein the graphite is one or more of spherical graphite, flake graphite and artificial graphite, and the conductive carbon black is Super PTMConductive carbon black 350G, Ketjen black ECP, ECP-600JD or EC-300JSeed growing;
b: mechanically stirring and ultrasonically mixing and dispersing the silicon powder slurry I and the mixed slurry II obtained in the step one to obtain a mixed material III;
c: under the protection of argon, transferring the mixture III into a ball milling tank, adding steel balls, sealing the ball milling tank, and carrying out high-energy ball milling to obtain a silicon/graphite/conductive carbon black precursor compound, wherein the ball milling time is 20-30 hours;
step three, synthesizing a silicon/graphite/conductive carbon black/amorphous carbon/KS carbon black composite material:
a: weighing a certain weight of amorphous carbon or a mixture of the amorphous carbon and the flaky graphite powder and KS carbon black, adding the amorphous carbon or the mixture of the amorphous carbon and the flaky graphite powder and the KS carbon black into the same solvent, and performing mechanical stirring and ultrasonic mixing dispersion treatment in advance to obtain mixed slurry IV for later use, wherein the KS carbon black is KS 6L;
b: mechanically stirring and ultrasonically mixing and dispersing the silicon/graphite/conductive carbon black precursor compound obtained in the step two and the mixed slurry IV obtained in the step three to obtain a mixed material V;
c: and (2) moving the mixture V into a ball milling tank under the argon protective atmosphere, adding steel balls, sealing the ball milling tank, carrying out high-energy ball milling, discharging, carrying out spray drying on the materials, and grinding and sieving to obtain the silicon/graphite/conductive carbon black/amorphous carbon/KS carbon black composite material, wherein the ball milling time is 30-50 hours.
2. The method for synthesizing the silicon/graphite/conductive carbon black/amorphous carbon/KS carbon black composite material by the metallurgical silicon is characterized in that the weight ratio of the solid steel balls added into the ball milling tank and the metallurgical grade silicon material in the step one is 20-30: 1; in the first step, the grinding fluid is one of absolute ethyl alcohol, ethylene glycol or propanol; the weight ratio of the steel balls to the solid phase raw materials added in the step two c is 30-40: 1; the weight ratio of the steel balls to the solid phase raw materials in the third step is 30-40: 1.
3. The method for synthesizing the silicon/graphite/conductive carbon black/amorphous carbon/KS carbon black composite material by using the metallurgical silicon as the claim 1, wherein the solvent in the step two a is one of absolute ethyl alcohol, ethylene glycol or propyl alcohol, and the total time of the mechanical stirring and the ultrasonic dispersion treatment in the step two a is 0.5-20 hours; the solid phase weight ratio of the silicon powder slurry I to the mixed slurry II in the step two b is 90-40:10-60, and the total time of the mechanical stirring and ultrasonic dispersion treatment in the step two b is 0.5-24 hours; in the third step a, the weight ratio of the amorphous carbon or the mixture of the amorphous carbon and the crystalline flake graphite powder to the KS carbon black is 40-90: 60-10; the solvent in the third step a is one of absolute ethyl alcohol, ethylene glycol or propanol, the mechanical stirring time in the third step a is 0.5-18 hours, and the ultrasonic dispersion treatment time is 0.5-2 hours; in the third step, the solid-phase weight ratio of the silicon/graphite/conductive carbon black precursor compound to the mixed slurry IV is 70-20: 30-80; and the mechanical stirring and ultrasonic dispersion treatment time of the step three b is 0.5-24 hours.
4. The method for synthesizing the silicon/graphite/conductive carbon black/amorphous carbon/KS carbon black composite material by using the metallurgical silicon as the claim 3, wherein the weight ratio of the graphite to the conductive carbon black in the step two a is 95-70: 5-30; in the second step, the solid phase weight ratio of the silicon powder slurry I to the mixed slurry II is 80-50: 20-50; and in the third step b, the solid-phase weight ratio of the silicon/graphite/conductive carbon black precursor compound to the mixed slurry IV is 60-30: 40-70.
5. The method for synthesizing the silicon/graphite/conductive carbon black/amorphous carbon/KS carbon black composite material by using the metallurgical silicon as the raw material according to claim 4, wherein the weight ratio of the graphite to the conductive carbon black in the step two a is 90-80: 10-20; in the second step, the solid phase weight ratio of the silicon powder slurry I to the mixed slurry II is 65-55: 35-45; and in the third step b, the solid-phase weight ratio of the silicon/graphite/conductive carbon black precursor compound to the mixed slurry IV is 50-40: 50-60.
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