CN111384384A - Preparation method of silicon-carbon composite material, silicon-carbon negative electrode material and preparation method of silicon-carbon negative electrode material - Google Patents
Preparation method of silicon-carbon composite material, silicon-carbon negative electrode material and preparation method of silicon-carbon negative electrode material Download PDFInfo
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Abstract
The invention discloses a preparation method of a silicon-carbon composite material, a silicon-carbon negative electrode material and a preparation method thereof, wherein a mode of carrying out sanding treatment on micron silicon materials and simultaneously realizing uniform loading of a catalyst on the surfaces of silicon particles obtained by sanding is adopted, so that the metal catalyst can be uniformly loaded on the surfaces of the silicon particles; the prepared silicon-carbon composite material has the characteristics of high reversible specific capacity and excellent cycle performance under the condition of high-rate charge and discharge, and the preparation process is simple, low in cost and capable of being widely applied to industrial production of silicon-carbon cathode materials.
Description
Technical Field
The invention relates to the field of lithium ion batteries, in particular to a preparation method of a silicon-carbon composite material for a lithium ion battery, a silicon-carbon negative electrode material and a preparation method of the silicon-carbon negative electrode material.
Background
The silicon material has high theoretical capacity (4200mAh/g), moderate lithium insertion/removal potential (lower than 0.5V), abundant reserve in the earth crust and low price, and is a new generation of lithium ion battery cathode material following graphite. However, the silicon material has poor conductivity, and has serious volume change (200-400%) in the process of electrochemical lithium extraction, and the generated internal stress easily causes cracking, pulverization and peeling of the negative electrode, so that the battery loses conductive contact and loses efficacy, and the cycle performance of the battery is seriously influenced.
At present, the volume strain of a silicon material is relieved and the conductivity is improved mainly by changing the form (such as nanocrystallization and mesoporous structure) of the silicon material and compounding the silicon material with a carbon material. The carbon material coated on the surface of the material by adopting the method of compounding the carbon material can inhibit the side reaction of the silicon material and the electrolyte, and simultaneously the rate capability and the cycle performance of the material can be improved to a certain extent. At present, the main methods for preparing the silicon-carbon composite material comprise a chemical vapor deposition method, a mechanical ball milling method, a sol-gel method and a high-temperature pyrolysis method, but the methods face two key problems in the preparation of the silicon-carbon composite material: 1) the agglomeration of silicon materials, the size of the silicon particles which are commonly used at present is 5 nm-5 mu m, and the smaller the size of the silicon particles is, the more serious the agglomeration phenomenon of the silicon particles is, thereby influencing the full mixing between the silicon and the carbon materials; 2) the high-conductivity carbon material is difficult to be completely and firmly attached to the silicon surface, so that the specific capacity of the silicon-carbon composite material is low under the condition of high-rate charge and discharge, and the carbon material and the silicon material are easily desorbed due to rapid volume change.
In order to solve the problem of agglomeration, patent documents such as CN102702796A and CN105118996A disclose that a ball milling or ultrasonic method is adopted to fully mix nano-silicon and an anionic dispersant to obtain a pre-dispersion liquid with good dispersion; however, the pre-dispersion liquid has poor storage stability, the problem of silicon agglomeration is still difficult to avoid in the subsequent treatment process of compounding with carbon, the performance of the silicon-carbon composite material is difficult to ensure, and the preparation cost is increased.
In order to solve the problem that a highly conductive carbon material is difficult to be firmly attached to a silicon surface, documents such as chengyuan et al (china science B edition: chemistry, 2009, 39(12), 1593-1597), CN109244432A, CN110034282A and the like propose that carbon nanotubes are grown in situ on the surface of a silicon material, so that the carbon nanotubes are pinned on the surface of silicon particles. Compared with the porous carbon coating layer, the carbon nano tube has good flexibility and excellent conductivity, not only buffers the volume change of silicon in the charging and discharging process, but also improves the electron conduction among silicon particles, and realizes higher reversible capacity of the silicon-carbon cathode under the condition of high multiplying power. However, in the above methods, the silicon particles with the required size are prepared, and then the metal catalyst is loaded on the surface of the silicon nanoparticles by a gas phase, liquid phase or solid phase method to grow the carbon nanotubes in situ, the process is not only complex, but also difficult to avoid the problem of nano-silicon agglomeration, and the carbon nanotubes are lost in part of the surface area of the prepared silicon material, so that the silicon-carbon composite material has insufficient conductive path, and the material has low high-rate specific capacity and poor cycle performance.
Disclosure of Invention
The invention aims to solve the problems of low high-rate specific capacity and poor cycle performance of the prepared silicon-carbon negative electrode material due to the complex preparation process and easy agglomeration of the silicon material of the existing silicon-carbon composite material, and provides a preparation method of the silicon-carbon composite material, the silicon-carbon negative electrode material and a preparation method thereof, so as to effectively solve the problem of agglomeration of the silicon material in the preparation process, and the prepared silicon-carbon composite material has the characteristics of high reversible specific capacity and excellent cycle performance under the condition of high-rate charge and discharge.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows:
a silicon-carbon composite material preparation method, regard nanometer or sub-micron silicon powder particle as the substrate, adhere the metal catalyst on the surface of silicon particle evenly, utilize the catalytic activity of the metal catalyst, grow the carbon nanotube on the surface of silicon particle in situ;
the step of uniformly attaching the metal catalyst to the surface of the silicon particles comprises:
1) dissolving a metal catalyst and an organic matter containing a plurality of carboxyl groups in an alcohol solvent, uniformly stirring at 40-60 ℃, adding silicon powder with the particle size of 5-100 microns, and stirring and wetting to form a pre-dispersion liquid;
2) and adding the pre-dispersion liquid into a sand mill, sanding for 4-100 h, and grinding the silicon powder in the pre-dispersion liquid to the required particle size.
In the above technical solution, the organic substance containing a plurality of carboxyl groups is a polycarboxylic acid branched polymer.
In the technical scheme, the molar ratio of the carboxyl functional group to the metal element in the pre-dispersion liquid is 1: 1-3: 1.
In the above technical scheme, further, the solid content of the pre-dispersion liquid is 1% -30%.
In the technical scheme, the mass ratio of the metal elements to the silicon particles in the pre-dispersion liquid is 0.5: 100-10: 100.
In the above technical scheme, further, the silicon powder is silicon oxide or elemental silicon, the size of the silicon oxide obtained after sanding treatment is 0.5 μm to 1 μm, and the size of the elemental silicon is 5nm to 200 nm.
In the above technical solution, further, the step of growing the carbon nanotube in situ on the surface of the silicon particle includes:
1) performing spray drying on the pre-dispersion liquid after sanding to obtain powder A;
2) calcining the powder A in an inert gas atmosphere at the temperature of 300-600 ℃ to enable metal elements to form an alloy on the surface layer of the silicon particles to obtain powder B;
3) catalyzing the carbon source gas to crack by using the powder B as a catalyst, and growing carbon nanotubes on the surfaces of the silicon particles to obtain a silicon-carbon composite material; preferably, the cracking temperature is 600-1100 ℃, and the cracking time is 5-60 min.
At present, in a process method for growing a carbon nano tube on the surface of a silicon particle in situ, how to overcome the influence caused by the agglomeration of the silicon particle is a key link for influencing the final quality of a product by uniformly adhering a catalyst on the surface of the silicon particle. In the prior art, nano silicon particles are usually subjected to dispersion treatment and then mixed with a metal catalyst for loading, due to the agglomeration phenomenon of the nano silicon particles, complete dispersion of the nano silicon particles is difficult to realize, and when the nano silicon particles are mixed with the catalyst after dispersion, part of the surfaces of the silicon particles are not loaded by the catalyst due to the agglomeration problem, and carbon nanotubes cannot be formed on the surfaces of the silicon particles which are not loaded by the catalyst, so that the conductive path of the material is insufficient, the rate performance of the material is influenced, the utilization rate of the silicon material is influenced, and the performance of the material cannot be fully exerted.
The invention adopts a mode of carrying out sanding treatment on the micron silicon material and simultaneously realizing uniform loading of the catalyst on the surface of the silicon particles obtained by sanding, and has the advantages that: when the micron silicon material is sanded, the catalyst can be uniformly loaded on the original surface of the silicon material or a new surface generated by sanding; in the preparation process of the pre-dispersion liquid, a complex solution obtained by mixing a metal catalyst, a polycarboxylic acid branched polymer and an alcohol solvent is wetted to load the catalyst on the original surface of the silicon material, the newly generated surface of the silicon material is infiltrated by the complex solution containing the metal catalyst due to thermodynamic driving in the sanding process, and the metal catalyst in the complex solution is attached to the newly generated surface, so that the metal catalyst can be uniformly loaded on the surface of the silicon particle.
After the catalyst is uniformly loaded on the surfaces of the silicon particles by adopting the process, the powder A is obtained by spray drying, and the problem of agglomeration among the silicon particles in the powder is not needed to be considered. Even though agglomeration occurs among the silicon particles, the agglomerated silicon particles are pushed open by the carbon nanotubes along with the growth of the carbon nanotubes in the process of in-situ growth of the carbon nanotubes because the agglomerated parts of the silicon particles also load the metal catalyst, and a silicon-carbon composite material with good dispersion and high conductivity carbon nanotube network can be formed; compared with the existing silicon dispersion liquid, the powder A prepared by the invention has better storage stability and is beneficial to the industrial production of the silicon-carbon composite material.
The polycarboxylic acid branched polymer is added into the pre-dispersion liquid, carboxyl in the polymer can form a complex with metal ions in the pre-dispersion liquid and can also form hydrogen bonds with hydroxyl on the surface of silicon particles, the coupling effect can promote the metal catalyst to be uniformly attached to the surface of the silicon, metal elements can be favorably alloyed with atoms on the surface of the silicon particles, and the alloy formed on the surface of the silicon particles can help the growth of carbon nanotubes on the surface of the silicon particles and ensure that the carbon nanotubes can be firmly attached to the surface of the silicon particles.
The polycarboxylic acid branched polymer may be prepared from polycarboxylic acid molecules (functionality f)COOHNot less than 3) and polyol (functionality f)OHNot less than 2), for example, dissolving citric acid and ethylene glycol in water according to a certain proportion, and stirring at 100-140 ℃ for 2-4 h to obtain the required polycarboxylic acid branched polymer; or the above-mentioned polycarboxylic acid-branched polymer can be obtained by a polymerization method such as radical polymerization. In the pre-dispersion liquid, in the process of forming a complex solution by a metal catalyst, metal ions enter cavities in the branched polymer molecules and cooperate with carboxyl in the cavities in the molecules to form a metal organic complex; silicon powder is added into the pre-dispersion liquid, carboxyl on the surface of the metal organic complex and hydroxyl on the surface of the silicon (the original surface and the newly formed surface) form hydrogen bonds in the sanding process, and the metal catalyst can be more uniformly and stably attached to the surface of the silicon in the process of forming the hydrogen bonds between the metal complex and the surface of the silicon.
The molar ratio of carboxyl to metal elements in the pre-dispersion liquid needs to be controlled within a proper range, and when the molar ratio is too low, the proportion of hydrogen bonds formed with the silicon surface is reduced, so that the metal catalyst is difficult to be ensured to be uniformly and firmly attached to the surface of silicon particles; when the molar ratio is too high, excessive carbides are formed on the surface of the powder A to wrap the metal catalyst on the surface of the silicon particles when the formed powder A is calcined, so that the contact of the metal catalyst and a carbon source gas is hindered in the process of in-situ growth of the carbon nanotubes, and the carbon nanotubes cannot grow on the surface of the silicon particles.
The preparation method of the invention not only solves the problem of silicon agglomeration, but also realizes the uniform and firm adhesion of the carbon nano tube on the surface of the silicon particle, and effectively improves the rate capability of the silicon-carbon composite material; simple process, high production efficiency and contribution to industrial large-scale production.
The invention also relates to a silicon-carbon negative electrode material and a preparation method thereof, and the preparation method specifically comprises the following steps:
a silicon-carbon negative electrode material comprises silicon-carbon nanotube particles formed by silicon particles and carbon nanotubes pinned on the surfaces of the silicon particles and a hollow carbon film for coating the silicon-carbon nanotube particles, wherein a plurality of silicon-carbon nanotube particles are coated in the carbon film, and the other ends of the carbon nanotubes pinned on the surfaces of the silicon particles in the carbon film can extend out of the carbon film through the carbon film.
Silicon particles in the silicon-carbon negative electrode material are silicon monoxide or nano simple substance silicon, the size of the silicon monoxide is 0.5-1 mu m, and the size of the nano simple substance silicon is 5-200 nm; the content of the carbon nano tube and the carbon film in the silicon-carbon negative electrode material is 5 to 90 weight percent, wherein the content of the carbon nano tube is 1 to 25 weight percent, and preferably 5 to 15 weight percent.
Adding the prepared silicon-carbon composite material into a carbon source precursor solution, uniformly mixing, spray-drying, and carbonizing at 900-1200 ℃ to obtain a silicon-carbon negative electrode material;
the mixing operation process of the silicon-carbon composite material and the carbon source precursor solution comprises the following steps: controlling the temperature of the carbon source precursor solution at 20-40 ℃, gradually and uniformly adding the silicon-carbon composite material into the carbon source precursor solution which is continuously stirred, and continuously stirring for 1-4 hours after the addition is finished; preferably, the stirring speed is 30 to 90 revolutions/min.
In the silicon-carbon composite material prepared by the invention, because a large number of gaps exist among carbon nanotube networks on the surface of silicon particles, electrolyte is easy to permeate the surface of the silicon particles to generate side reaction with silicon, so that the consumption of lithium ions is caused, and the rapid attenuation of battery capacity is easily caused, therefore, the silicon-carbon composite material needs to be subjected to carbon coating treatment to obtain the silicon-carbon cathode material for the lithium ion battery. In the silicon-carbon negative electrode material, a plurality of silicon particles and silicon-carbon nanotube particles formed by carbon nanotubes pinned on the surfaces of the silicon particles are coated in a carbon film, and the silicon-carbon nanotube particles are tangled by the carbon nanotubes to form a secondary aggregate and then coated by the carbon film. The silicon-carbon negative electrode material can prevent silicon particles from contacting with electrolyte through the carbon film, and simultaneously, the rapid volume strain generated in the high-rate charge-discharge process is absorbed by the carbon nano tube elastic conductive network filled among the silicon particles, so that the volume strain generated by the silicon-carbon nano tube particles can be inhibited from being transmitted to the carbon film, the influence on the carbon film under the high-rate charge-discharge condition is reduced, the integrity of the carbon film is ensured, the silicon and the electrolyte can be better prevented, and the silicon-carbon negative electrode material has good high-rate cycle performance.
In the preparation method of the silicon-carbon cathode material, the silicon-carbon composite material and the carbon source precursor solution are mixed by adopting a low-shearing-force mixing operation mode, and compared with the traditional high-shearing-force mixing mode such as ultrasonic, ball milling and grinding, the acting force of the silicon-carbon nanotube composite material on the silicon-carbon nanotube particles and the aggregate formed by the silicon-carbon nanotube particles is small, so that a structure that a carbon film coats a plurality of silicon-carbon nanotube particles is favorably formed. Meanwhile, the carbon nanotubes are easily sheared or separated from the surface of the silicon particles by adopting a mixing mode of high shearing force such as ultrasound, ball milling, grinding and the like, so that the conductivity of the silicon-carbon composite material is influenced, the problems can be effectively avoided by adopting a low-speed stirring mixing mode, and the rate capability of the silicon-carbon cathode material is further improved. Moreover, the low-speed stirring and mixing mode can greatly reduce the energy consumption of equipment, simplify the preparation process and reduce the production cost.
In the method, the silicon-carbon composite material and the carbon source precursor solution are mixed by adopting a low-speed stirring mixing mode with low shearing force, so that the integrity of a carbon nano tube network in the silicon-carbon composite material is ensured, the carbon nano tube can keep a better original growth form in a mixing system, the carbon source precursor solution is diffused into the gaps of the carbon nano tube network in the stirring process, and the carbon nano tube can still be better exposed on the surface of a silicon particle after spray drying; in the silicon-carbon cathode material obtained after carbonization treatment, the other ends of the carbon nanotubes partially pinned on the surface of the silicon particles in the carbon film can be promoted to penetrate through the carbon film and extend out of the carbon film. The carbon nano tube penetrating through the carbon film enables good contact between the carbon film and the silicon-carbon nano tube particle-coated carbon film structure formed by the carbon film and the silicon-carbon nano tube particles coated in the carbon film and between the carbon film-coated silicon-carbon particles and the current collector, further inhibits pulverization of the silicon-carbon negative electrode material under the condition of high-rate charge and discharge, and enables the silicon-carbon negative electrode material to have good cycle performance and high cycle specific capacity.
Drawings
FIG. 1 is a schematic diagram of a process for preparing a silicon-carbon anode material of the present invention.
Fig. 2 is a scanning electron microscope image of the silicon-carbon composite material prepared in example 1 of the present invention.
Fig. 3 is a scanning electron microscope image of the silicon-carbon negative electrode material prepared in example 1 of the present invention.
In the figure: 1. micron silicon particles, 2, nanometer silicon or submicron particles, 3, a metal catalyst, 4, carbon nanotubes, 5 and a carbon film.
Detailed Description
The preparation process of the silicon-carbon composite material and the silicon-carbon cathode material can be carried out according to the following steps:
step 1: dissolving a metal catalyst (one or more of iron salt, cobalt salt or nickel salt) and a polycarboxylic acid branched polymer in an alcohol solvent, stirring at 40-60 ℃ for 10-40 min, uniformly stirring to form a metal complex solution, adding silicon powder (simple substance silicon or silicon monoxide) with the particle size of 5-100 microns, and stirring and wetting to form a pre-dispersion liquid;
step 2: adding the pre-dispersion liquid into a sand mill, sanding for 4-100 h, and grinding silicon powder in the pre-dispersion liquid to the required particle size (the size of the silicon monoxide is 0.5-1 mu m, and the size of the simple substance silicon is 5-200 nm); performing spray drying on the pre-dispersion liquid after sanding to obtain powder A;
and step 3: calcining the powder A in an inert gas (one or more of nitrogen, helium, argon and the like) atmosphere at the temperature of 300-600 ℃ to form an alloy of metal elements on the surface layer of the silicon particles to obtain powder B;
and 4, step 4: using the powder B as a catalyst to catalyze the cracking of carbon source gases such as alkane, alkene or alkyne (the cracking temperature is 600-1100 ℃, and the cracking time is 5-60 min), and growing carbon nanotubes on the surfaces of silicon particles to obtain the silicon-carbon composite material;
and 5: and C, adding the silicon-carbon composite material obtained in the fourth step into a carbon source precursor solution of pitch, natural polymer and artificially synthesized polymer materials, uniformly mixing, spray-drying, and carbonizing at 900-1200 ℃ to obtain the silicon-carbon cathode material.
The process of the present invention is further illustrated with reference to specific examples.
Example 1
Step 1: dissolving polycarboxylic acid branched polymer and cobalt nitrate in ethanol, stirring at 50 deg.C for 20min, and adding silica (D50 about 50 μm) for pre-dispersion for 60min to obtain pre-dispersion solution; wherein the molar ratio of the carboxyl to the cobalt element is 1.2:1, the mass ratio of the cobalt element to the silicon monoxide is 5:100, and the solid content in the pre-dispersion liquid is 27%;
step 2: adding the pre-dispersion liquid into a sand mill, sanding for 6 hours until the content of the silicon monoxide D50 reaches 1 mu m, and spray-drying the obtained dispersion liquid to obtain powder A;
and step 3: calcining the powder A in nitrogen at 450 ℃ for 30min to obtain powder B;
and 4, step 4: catalyzing propylene to crack by using the powder B as a catalyst to grow a carbon nano tube, wherein the cracking temperature is 690 ℃, and the cracking time is 10min, so as to obtain a silicon-carbon composite material;
and 5: and stirring and mixing the obtained silicon-carbon composite material with a sucrose aqueous solution, spray drying, and carbonizing at 900 ℃ to obtain the silicon-carbon negative electrode material.
Preparing the prepared silicon-carbon negative electrode material, carbon black and sodium methyl cellulose into slurry according to the mass ratio of 8:1:1, coating the slurry on a copper foil, punching the slurry into a wafer with the diameter of 12mm, drying the wafer in a vacuum drying oven at the temperature of 105 ℃ for 12 hours, assembling a lithium wafer into a half battery, performing constant current charge-discharge cycle according to the first two weeks at 0.05A/g, and performing cycle performance evaluation according to the current density of 1.0A/g, 2.0A/g or 3.0A/g.
The corresponding performance data in this example are shown in table 1.
Example 2
Step 1: dissolving a polycarboxylic acid branched polymer and nickel nitrate in ethanol, stirring for 20min at 50 ℃, and then adding simple substance silicon (D50 is about 40 mu m) for pre-dispersion for 60min to obtain a pre-dispersion liquid; wherein the molar ratio of carboxyl to nickel element is 1.5:1, the mass ratio of nickel element to simple substance silicon is 2:100, and the solid content in the pre-dispersion liquid is 20%;
step 2: adding the pre-dispersion liquid into a sand mill, sanding for 40h until the simple substance silicon D50 reaches 50nm, and spray-drying the obtained dispersion liquid to obtain powder A;
and step 3: calcining the powder A in nitrogen at 400 ℃ for 20min to obtain powder B;
and 4, step 4: catalyzing ethylene to crack by using the powder B as a catalyst, and growing a carbon nano tube, wherein the cracking temperature is 650 ℃, and the cracking time is 20min, so as to obtain a silicon-carbon composite material;
and 5: and stirring and mixing the obtained silicon-carbon composite material with a sucrose aqueous solution, spray drying, and carbonizing at 900 ℃ to obtain the silicon-carbon negative electrode material.
A half cell was assembled in accordance with the method of example 1, and the constant current charge-discharge cycle was evaluated for cycle performance at a current density of 0.05A/g for the first two weeks, and then at a current density of 1.5A/g, 3.0A/g, or 4.5A/g.
The corresponding performance data in this example are shown in table 1.
Comparative example
The difference between the comparative example and the examples 1 and 2 is that the existing conventional operation process is adopted in the step of mixing the silicon material and the catalyst and the step of mixing the silicon-carbon composite material and the carbon source precursor in the preparation method, and the specific steps are as follows:
step 1: mixing silicon core (SiO, D50 about 1 micron) and cobalt nitrate water solution by ultrasonic method for 60min, and spray drying to obtain powder C;
step 2: calcining the powder C in nitrogen atmosphere at 450 ℃ for 30min to obtain powder D;
and step 3: catalyzing propylene to crack by using the powder D as a catalyst, wherein the cracking temperature is 690 ℃, and the cracking time is 10min, so as to obtain a silicon-carbon composite material;
and 4, step 4: and uniformly mixing the silicon-carbon composite material with a sucrose aqueous solution in an ultrasonic mode, carrying out spray drying, and carbonizing at 900 ℃ to obtain the silicon-carbon negative electrode material.
The electrochemical performance of the silicon-carbon negative electrode material was evaluated by the method of example 1, wherein the first two weeks were 0.05A/g, and the subsequent cycle performance evaluation was performed at a current density of 1.0A/g.
The corresponding performance data in this comparative example are shown in table 1.
The electrochemical performance comparison results of the silicon-carbon negative electrode materials prepared in the example 1 and the example 2 and the comparative example are shown in the table 1:
TABLE 1 comparison of Performance data for inventive and comparative examples
As can be seen by comparing the performance data, the reversible capacity of the material in the comparative example 1 in the first week is basically the same as that of the material in the example 1, but under the current density of 1.0A/g, the specific capacity retention rate after 200 weeks is only 46.3%, which indicates that the large-rate cycle performance is poor. The specific capacity retention rate of the silicon-carbon negative electrode material obtained by the preparation method provided by the invention is not lower than 85% and is far higher than the performance index in the comparative example after the silicon-carbon negative electrode material is charged and discharged for 200 weeks under the condition of high current density, so that the silicon-carbon negative electrode material has the advantages of high cyclic specific capacity, excellent high-rate cycle performance, simple preparation process and low cost, and can be widely applied to industrial production of the silicon-carbon negative electrode material.
The present specification and figures are to be regarded as illustrative rather than restrictive, and it is intended that all such alterations and modifications that fall within the true spirit and scope of the invention, and that all such modifications and variations are included within the scope of the invention as determined by the appended claims without the use of inventive faculty.
Claims (9)
1. A preparation method of a silicon-carbon composite material is characterized by comprising the following steps: using nano-scale or submicron-scale silicon powder particles as a substrate, uniformly attaching a metal catalyst on the surface of the silicon particles, and growing a carbon nano tube on the surface of the silicon particles in situ by utilizing the catalytic activity of the metal catalyst;
the step of uniformly attaching the metal catalyst to the surface of the silicon particles comprises:
1) dissolving a metal catalyst and an organic matter containing a plurality of carboxyl groups in an alcohol solvent, uniformly stirring at 40-60 ℃, adding silicon powder with the particle size of 5-100 microns, and stirring and wetting to form a pre-dispersion liquid;
2) and adding the pre-dispersion liquid into a sand mill, and sanding for 4-100 hours to enable the silicon powder in the pre-dispersion liquid to reach the required particle size.
2. The method for preparing a silicon-carbon composite material according to claim 1, wherein: the organic matter containing a plurality of carboxyl groups is a polycarboxylic acid branched polymer.
3. The method for producing a silicon-carbon composite material according to claim 1 or 2, characterized in that: the molar ratio of the carboxyl functional group to the metal element in the pre-dispersion liquid is 1: 1-3: 1.
4. The method for preparing a silicon-carbon composite material according to claim 1, wherein: the solid content of the pre-dispersion liquid is 1-30%.
5. The method for preparing a silicon-carbon composite material according to claim 1, wherein: the mass ratio of the metal elements to the silicon particles in the pre-dispersion liquid is 0.5: 100-10: 100.
6. The method for preparing a silicon-carbon composite material according to claim 1, wherein: the silicon powder is silicon oxide or simple substance silicon, the size of the silicon oxide obtained after sanding treatment is 0.5-1 μm, and the size of the simple substance silicon is 5-200 nm.
7. The method for producing a silicon-carbon composite material according to any one of claims 1 to 6, characterized in that: the step of growing the carbon nano tube on the surface of the silicon particle in situ comprises the following steps:
1) performing spray drying on the pre-dispersion liquid after sanding to obtain powder A;
2) calcining the powder A in an inert gas atmosphere at the temperature of 300-600 ℃ to enable metal elements to form an alloy on the surface layer of the silicon particles to obtain powder B;
3) catalyzing the carbon source gas to crack by using the powder B as a catalyst, and growing carbon nanotubes on the surfaces of the silicon particles to obtain a silicon-carbon composite material; preferably, the cracking temperature is 600-1100 ℃, and the cracking time is 5-60 min.
8. A silicon-carbon negative electrode material is characterized in that: the carbon film comprises silicon-carbon nanotube particles formed by silicon particles and carbon nanotubes pinned on the surfaces of the silicon particles and a hollow carbon film coating the silicon-carbon nanotube particles, wherein a plurality of silicon-carbon nanotube particles are coated in the carbon film, and the other ends of the carbon nanotubes pinned on the surfaces of the silicon particles in the carbon film can penetrate through the carbon film and extend out of the carbon film.
9. A preparation method of a silicon-carbon negative electrode material is characterized by comprising the following steps: adding the silicon-carbon composite material obtained by the preparation method of any one of claims 1 to 7 into a carbon source precursor solution, uniformly mixing, spray-drying, and carbonizing at 900-1200 ℃ to obtain a silicon-carbon negative electrode material;
the mixing operation process of the silicon-carbon composite material and the carbon source precursor solution comprises the following steps: controlling the temperature of the carbon source precursor solution at 20-40 ℃, gradually and uniformly adding the silicon-carbon composite material into the carbon source precursor solution which is continuously stirred, and continuously stirring for 1-4 hours after the addition is finished; preferably, the stirring speed is 30 to 90 revolutions/min.
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