CN114400327A - A kind of preparation method of nanometer silicon carbon anode material - Google Patents

Abstract

The invention relates to a preparation method of a nano silicon-carbon cathode material, which is used for preparing nano SiO from tetraethoxysilane₂Microspheres, nano SiO₂Uniformly coating a polymer or organic matter layer on the surface of the microsphere to form a nano silicon-carbon precursor; under the protection of argon, the nano silicon-carbon precursor and magnesium powder are pyrolyzed, and the polymer on the surface of the nano silicon-carbon precursor is carbonized to form a coating on SiO₂The carbon shell on the surface, the magnesium powder volatilizes into magnesium vapor, and the magnesium vapor permeates the carbon shell to enter the interior and the nanometerSiO₂And reacting to obtain the nano silicon-carbon cathode material. Compared with the prior art, the nano silicon-carbon cathode material prepared by the invention is of a core-shell structure, silicon in the nano silicon-carbon cathode material is a core, the particle size of the silicon is all in a nano level, and the silicon is uniform in size and accounts for 5-60 wt%; the carbon layer is wrapped on the surface of the nano Si, and the carbon layer is used for protecting the nano Si, so that the capacity of the lithium ion battery is improved, and the cycle life of the lithium ion battery is prolonged.

Description

A kind of preparation method of nanometer silicon carbon anode material

technical field

The invention relates to a material and a preparation method in the technical field of lithium batteries, in particular to a preparation method of a nano _- silicon-carbon negative electrode material with uniform particle size. The specific preparation process of carbon anode material.

Background technique

As an energy storage basis, lithium-ion batteries have many advantages, such as stable voltage, high energy density, long cycle life, etc., so they are widely used in phones, speakers, portable medical equipment, electric motorcycles, and electric vehicles. "Made in China 2025" clarifies the development plan of power lithium batteries: in 2020, the battery energy density will reach 300Wh/kg; in 2025, the battery energy density will reach 400Wh/kg; so there is an urgent need to develop new anode materials. This puts forward higher requirements on the negative electrode material of lithium battery. At present, the negative electrode material of lithium-ion battery is mainly carbon, and the theoretical specific capacity is 372mAh/g. Currently, the capacity of lithium-ion battery on the market has reached more than 300mAh/g, which is close to the theoretical upper limit of battery capacity of carbon negative electrode material, which limits the lithium-ion battery capacity. The future development prospects of batteries. In addition, since the lithium storage site of carbon is close to the precipitation potential of lithium, there is a risk of explosion during fast charging and fast discharging of lithium-ion batteries. Silicon (Si), the theoretical capacity of silicon anode material is as high as 4200mAh/g, which is widely distributed in nature and has appropriate lithium intercalation potential. If silicon anode material is used, the capacity of lithium battery can be greatly improved. However, silicon has a large volume expansion coefficient, which can expand up to 300% of the original volume. After expansion, silicon will break through the SEI film and be lost from the current collector, which greatly reduces the life of lithium-ion batteries. Moreover, silicon has poor conductivity, which makes the rate of silicon negative electrode Performance is not high.

Chinese invention patent CN 106374088 discloses a method for preparing silicon-carbon composite material by using magnesium thermal reduction method for lithium ion battery A. The silicon dioxide is mixed with an organic carbon source, and the reduction and high-temperature carbonization of silicon dioxide are completed in one step, and the cost is low. , which can be mass-produced and effectively preserve the morphology of porous silicon. However, this patent uses diatomite, mesoporous silica or quartzite, and the particle size of silica is large and cannot reach the nanometer level. In the preparation process, the silicon generated by the reduction of large particles of SiO ₂ is prone to agglomeration. These agglomerated silicon cannot avoid the pulverization caused by the volume expansion of silicon, which affects the performance of the silicon carbon anode material.

Chinese invention patent CN110350168 A discloses a method for in-situ preparation of porous silicon-carbon composite materials. The point 1 is to mix the positively charged polymer and the solvent into a mixed solution; the point 2 is to mix the silicon source with the mixed solution in point 1 to obtain the silicon carbon precursor; the point 3 is to mix the silicon carbon precursor magnesium powder to obtain the crude product , and then pickled to obtain a silicon-carbon composite material. During the implementation of the invention, the magnesium powder and the silicon-carbon precursor are directly mixed, and the magnesium powder cannot be fully contacted with SiO ₂ in the process, so that part of the silicon-carbon precursor cannot be completely reduced with magnesium to form a silicon-carbon composite material.

Chinese invention patent CN103427073 A discloses a preparation method of mesoporous Si/C composite microspheres as negative electrodes of lithium batteries. The main point is to mix and react ethyl orthosilicate, resorcinol and formaldehyde together, and after drying, carbonize at 750-1000 ℃ under the protection to obtain SiO ₂ /C composite microspheres. Then, the SiO ₂ /C composite microspheres were mixed with magnesium powder and reduced under the protection of argon to obtain mesoporous Si/C composite microspheres. This reaction requires a two-step method to obtain Si/C material, the process is more complicated, and the magnesium added in the formula is too much. According to the patent requirements, the reaction ratio of _SiO2 and magnesium is 1:2.5, and it is difficult for magnesium powder to be uniform with _SiO2 . Reaction occurs, and a large amount of magnesium will react with Si to form magnesium silicide, which affects the performance of the final product.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a method for preparing a nano-silicon carbon negative electrode material in order to overcome the defects existing in the above-mentioned prior art, adopt a one-step method to prepare a silicon carbon negative electrode material, introduce carbon with better conductivity to coat the outside of the silicon, and the carbon shell can Limit the expansion of silicon and protect silicon from loss.

The object of the present invention can be achieved by the following technical solutions: a method for preparing nano-silicon carbon negative electrode material, characterized in that, nano-SiO ₂ microspheres are prepared from ethyl orthosilicate, and the surface of the nano-SiO ₂ microspheres is uniformly coated with polymer Or organic layer to form nano-silicon-carbon precursor; under the protection of argon, nano-silicon-carbon precursor and magnesium powder are pyrolyzed, and the polymer on the surface of nano-silicon-carbon precursor is carbonized to form a carbon shell covering the surface of SiO ₂ At the same time, the magnesium powder is volatilized into magnesium vapor, and the magnesium vapor penetrates the carbon shell and enters the interior to react with nano-SiO ₂ to obtain nano-silicon carbon anode material.

Further, the diameter of the nano-SiO ₂ microspheres ranges from 80nm to 800nm.

Further, the nano-SiO ₂ microspheres are prepared by the following method: prepared by reacting ethyl orthosilicate with ammonia water, sodium hydroxide, potassium hydroxide, oxalic acid, dilute hydrochloric acid or citric acid.

Further, the nano-silicon carbon precursor is obtained by the following method:

Disperse the nano-SiO ₂ microspheres in the solution, add polymer monomers and initiators, and under stirring at 40-90 °C, make the organic matter evenly coat the surface of the nano-SiO ₂ micro-spheres to form a polymer containing nano-SiO ₂ The microsphere solution is dried to obtain the nano-silicon carbon precursor. The dosage ratio of the nano-SiO ₂ microspheres to the polymer monomer and the initiator is 9:0.9:0.1-6:2.5:0.5.

Further, the polymer monomer is one or more of styrene, acrylonitrile, methacrylic acid, methyl methacrylate, aromatic carbonate, diamine, dibasic acid, phenol or formaldehyde ;

Further, described initiator is one or more in potassium persulfate, benzoyl peroxide, dodecanoyl peroxide, azobisisobutyronitrile or azobisisoheptane;

Further, the solvent is benzene, toluene, dimethylformamide or water.

Further, the nano-silicon carbon precursor is obtained by the following method:

Dissolve the polymer or organic matter in the solvent, add nano-SiO ₂ microspheres to the solution, and then uniformly disperse the nano-SiO ₂ microspheres in the solution by stirring or ultrasonic vibration to prepare a polymer microsphere solution, dry That is, the nano-silicon carbon precursor is obtained. The dosage ratio of the nano-SiO ₂ microspheres to the polymer or organic matter is 9:0.9:0.1-6:2.5:0.5.

Further, the polymer or organic matter is polystyrene, polyacrylonitrile, polymethacrylic acid, polymethyl methacrylate, polypyrrole, polyamide, polyimide, polyvinyl alcohol, polyvinyl acetate , one or more of polycarbonate, phenolic resin, epoxy resin, glucose, sucrose, chitin, starch and lignin;

Further, the solvent is benzene, toluene, dimethylformamide or water.

Further, in the drying, the polymer microsphere solution is dried and then crushed by ball milling, or freeze-dried, or spray-dried to obtain particles, which are passed through a 400-mesh sieve to form a nano-silicon carbon precursor.

Further, in the pyrolysis, the nano-silicon carbon precursor and the magnesium powder are placed in a crucible, placed separately, placed in an electric furnace, and heated to 650-1000 ° C under the protection of argon or a mixed atmosphere of argon and hydrogen. , heat preservation for 2-6h, and then cooled to obtain nano-silicon carbon material containing impurities. The dosage ratio of the nano-silicon carbon precursor and the magnesium powder is 9:1-7:3.

The impurity-containing nano-silicon-carbon material is washed with deionized water, pickled, and filtered to obtain the nano-silicon-carbon material.

Compared with the prior art, the present invention has the following beneficial effects:

1) In the present invention, a one-step method is used to generate the nano-silicon carbon negative electrode material, the process is simple, and the cost is low.

2) The particle size of silicon in the nano-silicon carbon negative electrode material prepared by the present invention is all nano-scale, because nano-silicon has a special size effect, which can reduce the pulverization phenomenon caused by volume expansion when silicon is used as the negative electrode of lithium ion battery, Reduce battery capacity decay.

3) The size of silicon in the nano-silicon carbon negative electrode material prepared by the present invention is uniform, and the size of silicon is 30-500nm,

4) The silicon content in the nano-silicon carbon negative electrode material prepared by the present invention can be adjusted, and the silicon content can be from 5wt% to 50wt%.

5) The nano-silicon-carbon negative electrode material of the present invention is a carbon layer outside the nano-silicon to avoid agglomeration between the nano-silicons.

6) The carbon layer of the nano-silicon-carbon negative electrode material of the present invention limits the expansion of nano-silicon, which can reduce the capacity attenuation of the lithium-ion battery caused by the loss of powder during the charging and discharging process of the lithium battery.

Description of drawings

Fig. 1 is the scanning electron microscope photograph of the nano-silicon carbon negative electrode of embodiment 1 gained;

Fig. 2 is the charge-discharge curve of the nano-silicon carbon negative electrode obtained in Example 1;

Fig. 3 is the rate performance of the nano-silicon carbon negative electrode obtained in Example 1;

Fig. 4 is the charge-discharge curve of the nano-silicon carbon negative electrode obtained in Example 2;

5 is the rate performance of the nano-silicon carbon negative electrode obtained in Example 2.

Detailed ways

The present invention will be described in detail below with reference to specific embodiments. The following examples will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that, for those skilled in the art, several modifications and improvements can be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

The present invention can be realized by the following technical solutions, including the steps as follows:

(1) Preparation of organic-coated nano-SiO ₂ particles with uniform particle size;

(1-1) Mix ethyl orthosilicate and ammonia water in a mass ratio of 8:2 to 1:9, stir and react at a constant temperature at 28°C to obtain nano-SiO ₂ with uniform particle size, and wash with ethanol and deionized water for several times;

(1-2) Disperse the above-mentioned nano-SiO ₂ in the solution, because it is dispersed in the solvent, with ultrasonic vibration, the nano-SiO ₂ can be fully dispersed without agglomeration, adding polymer monomers, initiators, etc., by Solution or emulsion polymerization, under a certain temperature and stirring speed, the organic matter is uniformly coated on the surface of nano-SiO ₂ particles to form a polymer microsphere solution containing nano-SiO ₂ . It is also possible to dissolve the polymer or organic matter in a certain solvent and add nano-SiO ₂ to the solution. Then, the nano-SiO ₂ is uniformly dispersed in the solution by stirring or ultrasonic vibration, and then the polymer microsphere solution is prepared.

(2) Preparation of nano-silicon carbon anode material;

(2-1) Prepare the nano-silicon-carbon precursor by spray-drying the organic-coated nano-SiO prepared in ( ₁ ) above, or by drying at a certain temperature and then processing by ball milling or powder crusher, or freeze-drying, and then mixing with Magnesium powder is placed in a crucible according to a certain proportion, and argon gas or argon/hydrogen gas is introduced into the muffle furnace. After heating up, the crucible is fully heated, the polymer on the surface of the nano-silicon-carbon precursor is carbonized to form a carbon shell, and the magnesium powder volatilizes to form magnesium vapor. When the magnesium vapor permeates the nano-silicon-carbon precursor, it penetrates into the carbon layer and the inner SiO ₂ react, generate nano-silicon, and cool to obtain a mixture containing nano-silicon and carbon;

(2-2) Wash the above nano-silicon-carbon mixture with deionized water, dilute hydrochloric acid or sulfuric acid, and hydrofluoric acid, respectively, to remove impurities to obtain nano-silicon-carbon particles.

The following are more detailed implementation cases, which further illustrate the technical solutions of the present invention and the technical effects that can be obtained.

Example 1

Ethyl orthosilicate and ammonia water were mixed in a mass ratio of 8:2, and reacted at a constant temperature of 28 °C to obtain nano-SiO ₂ , and a solution containing nano-SiO ₂ microspheres was prepared. After washing, take a solution containing 1 g of nano-SiO ₂ The solution was dispersed into 170ml of deionized water, ultrasonically dispersed for 10min, added 10.5mg of styrene monomer and 0.35mg of methacrylic acid, fully mixed with electromagnetic stirring, heated in a water bath at 80°C, and kept at a constant temperature for 30min, then added 0.037mg of potassium persulfate, Under the protection of nitrogen, the mixture was stirred at a constant speed, reacted at a constant temperature of 80 °C for 10 h, and then cooled to room temperature to obtain polymer microspheres with nano-Si as the core. After washing with deionized water, vacuum filtration, and drying in an oven at 50 °C for 12 h. After grinding, pass through a 400-mesh sieve to obtain coated nano _- SiO particles, and obtain nano-silicon-carbon precursor. The above-mentioned nano-silicon-carbon precursor and 0.8g of magnesium powder are respectively put into a crucible, and then placed in an electric furnace, argon gas protection, heated to 700°C at a heating rate of 5°C/min, kept at a constant temperature for 4 hours, and took out after cooling. Wash once with 100ml of deionized water, then wash with 100ml of 5% HCl and 1% HF, and dry to obtain a nano-silicon carbon anode material, as shown in Figure 1, which is the scanning electron microscope photo of the nano-silicon carbon anode material. It can be seen that, The nano-silicon carbon negative electrode material obtained by the method of the invention has a uniform size.

FIG. 2 is the charge-discharge curve of the nano-silicon carbon negative electrode obtained in Example 1. It can be seen that the nano-silicon carbon negative electrode has a discharge specific capacity as high as 2450mAh/g.

Figure 3 shows the rate performance of the nano-silicon carbon anode obtained in Example 1. It can be seen that the nano-silicon carbon anode has excellent rate performance, and the discharge specific capacities at 2C and 5C discharge current are 1320mAh/g and 940mAh/g respectively. .

Example 2

Ethyl orthosilicate and ammonia water were mixed in a ratio of 7:3, and reacted at a constant temperature of 28 °C to obtain nano-SiO ₂ , and a solution containing nano-SiO ₂ microspheres was prepared. After washing, take a solution containing 2 g of nano-SiO ₂ . The solution, ultrasonically dispersed for 10min, added 10.5mg of styrene monomer, and 0.35mg of methacrylic acid, fully mixed with electromagnetic stirring, heated in a water bath at 80 °C, after constant temperature for 30min, added 0.040 mg of potassium persulfate, stirred at a constant speed under nitrogen protection, 80 °C The reaction was performed at a constant temperature for 10 h, cooled to room temperature, and freeze-dried to obtain coated nano-SiO ₂ microspheres. The above-mentioned microspheres were passed through a 400-mesh sieve to obtain nano-silicon-carbon precursors. The above-mentioned nano-silicon carbon precursor and 1.6 g of magnesium powder were put into crucibles respectively, then placed in an electric furnace, protected by argon gas, heated to 800 °C at a heating rate of 10 °C/min, kept at a constant temperature for 3 hours, and taken out after cooling. Wash with 100 ml of deionized water once, then with 100 ml of 5% HCl and 1% HF, and dry to obtain nano-silicon carbon anode material. FIG. 4 is the charge-discharge curve of the nano-silicon carbon negative electrode obtained in Example 2. It can be seen that the nano-silicon carbon negative electrode has a discharge specific capacity as high as 2300mAh/g.

Figure 5 shows the rate performance of the nano-silicon carbon anode obtained in Example 2. It can be seen that the nano-silicon carbon anode has excellent rate performance, and the discharge specific capacities at 2C and 5C discharge current are 1410mAh/g and 1020mAh/g respectively. .

Example 3

Ethyl orthosilicate and ammonia water were mixed at a ratio of 6:4, and reacted at a constant temperature of 28 °C to obtain nano-SiO ₂ , and a solution containing nano-SiO ₂ microspheres was prepared. After washing, a solution containing 4g of nano-SiO 2 was taken. , and 0.4 g of glucose was added to obtain a uniformly dispersed mixed solution; the mixed solution was dried at 105° C. for 24 h to remove moisture to obtain dry nano-SiO ₂ particles coated with glucose. After crushing with a ball mill, pass through a 400-mesh sieve to obtain nano-SiO ₂ microspheres coated with glucose, and obtain nano-silicon carbon precursor. The SiO2 and 3.2g magnesium powder in the above particles were put into crucibles respectively, then placed in an electric furnace, protected by argon gas, heated to 850°C at a heating rate of 15°C/min, kept at a constant temperature for 2 hours, and taken out after cooling. That is, the nano-silicon carbon negative electrode material is obtained.

Example 4

Ethyl orthosilicate and ammonia water were mixed in a ratio of 5:5, reacted at a constant temperature of 28 °C to obtain self-assembled nano-SiO ₂ , and a solution containing nano-SiO ₂ microspheres was prepared. After washing, take a solution containing 4 g of nano-SiO ₂ solution, 0.2 g of glucose was added to obtain a uniformly dispersed mixed solution; the mixed solution was dried at 105° C. for 24 h to remove moisture to obtain dry nano-SiO ₂ particles coated with glucose. Glucose-coated nano-silicon-carbon precursor is obtained by spray drying. The above nano-silicon carbon precursor and 3.2 g of magnesium powder were placed in a crucible respectively, placed in an electric furnace, protected by argon gas, heated to 900 °C at a heating rate of 15 °C/min, kept at a constant temperature for 2 hours, and taken out after cooling. That is, the nano-silicon carbon negative electrode material is obtained.

The nano-silicon carbon negative electrode material obtained in the above-mentioned Examples 1-4 is used as the negative electrode of the lithium-sulfur battery, and the electrode active material, the conductive agent and the binder are mixed and ground in the proportions of 80%, 10% and 10% by mass, respectively, An appropriate amount of nitrogen methyl pyrrolidone solution is added, and ultrasonically stirred to form a slurry, which is then coated on copper foil to obtain a lithium selenium battery positive electrode sheet, and the lithium sheet is used as a counter electrode to assemble a battery.

The lithium battery assembled by the above method is tested for performance, and the detection method is as follows:

Specific capacity: place the assembled battery on the battery tester, set the charge and discharge voltage interval and constant current parameters, test the battery capacity by constant current charge and discharge, and then calculate the specific capacity of the battery according to the quality of the electrode active material.

Energy density: place the assembled battery on the battery tester, set the charge and discharge voltage range and constant current parameters, test the battery energy by constant current charge and discharge, and then calculate the energy density according to the quality of the battery.

Electronic conductivity: place the assembled battery on the electrochemical workstation, set the frequency, and test the electrochemical impedance of the battery. Equivalent circuit fitting is performed on the impedance to obtain the resistance of each part, thereby judging the electronic conductivity.

Ion transmission rate: Place the assembled battery on the electrochemical workstation, set the voltage interval and voltage sweep speed, and test the cyclic voltammetry curve of the battery under different sweep speeds. The ion transport rate of the battery was calculated from the cyclic voltammetry results.

Rate performance: Place the assembled battery on the battery tester, set the charge-discharge voltage range, and set the current parameters that gradually increase, and obtain the battery rate performance according to the charge-discharge capacity and the quality of the electrode active material under different charge-discharge currents. .

The comparative example adopts the silica-derived diatomite with coarse particles (that is, commercially available diatomite, with a general particle size of 10-100 microns) and an organic source (styrene monomer) mixed and obtained by the same method as in Example 1. The carbon-silicon composite material was used to make the lithium battery described in the comparative example. The test results are shown in the following table:

As can be seen from the above table, the use of the silica-derived diatomite with coarse particles in the comparative example cannot produce nano-effect, and the battery performance is far inferior to the present invention.

In the description of this specification, description with reference to the terms "one embodiment," "example," "specific example," etc. means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one aspect of the present invention. in one embodiment or example. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

The foregoing description of the embodiments is provided to facilitate understanding and use of the invention by those of ordinary skill in the art. It will be apparent to those skilled in the art that various modifications to these embodiments can be readily made, and the generic principles described herein can be applied to other embodiments without inventive step. Therefore, the present invention is not limited to the above-mentioned embodiments, and improvements and modifications made by those skilled in the art according to the disclosure of the present invention without departing from the scope of the present invention should all fall within the protection scope of the present invention.

Claims (10)

1. The preparation method of the nano silicon-carbon cathode material is characterized in that nano SiO is prepared from tetraethoxysilane₂Microspheres, nano SiO₂Uniformly coating a polymer or organic matter layer on the surface of the microsphere to form a nano silicon-carbon precursor; under the protection of argon, the nano silicon-carbon precursor and magnesium powder are pyrolyzed before nano silicon-carbonThe polymer on the surface of the driver is carbonized to form a coating on SiO₂The carbon shell on the surface, the magnesium powder volatilizes into magnesium vapor, and the magnesium vapor permeates the carbon shell to enter the interior and the nano SiO₂And reacting to obtain the nano silicon-carbon cathode material.

2. The method for preparing nano silicon carbon anode material according to claim 1, wherein the nano SiO is₂The diameter range of the microspheres is 80nm-800 nm.

3. The method for preparing nano silicon carbon anode material according to claim 1 or 2, wherein the nano SiO is₂The microspheres are prepared by the following method: the ethyl orthosilicate is reacted with ammonia water, sodium hydroxide, potassium hydroxide, oxalic acid, dilute hydrochloric acid or citric acid to prepare the catalyst.

4. The method for preparing the nano silicon-carbon anode material according to claim 1, wherein the nano silicon-carbon precursor is prepared by the following steps:

mixing nano SiO₂Dispersing the microspheres in the solution, adding polymer monomer and initiator, stirring at 40-90 deg.C to coat the organic matter on the SiO nanoparticles₂Forming a microsphere surface containing nano SiO₂Drying the polymer microsphere solution to obtain the nano silicon-carbon precursor.

5. The preparation method of the nano silicon-carbon anode material as claimed in claim 4, wherein the polymer monomer is one or more of styrene, acrylonitrile, methacrylic acid, methyl methacrylate, aromatic carbonate, diamine, dibasic acid, phenol or formaldehyde;

the initiator is one or more of potassium persulfate, benzoyl peroxide, lauroyl peroxide, azodiisobutyronitrile or azodiisoheptylene;

the solvent is benzene, toluene, dimethylformamide or water.

6. The method for preparing the nano silicon-carbon anode material according to claim 1, wherein the nano silicon-carbon precursor is prepared by the following steps:

dissolving polymer or organic matter in solvent to obtain nano SiO₂Adding the microspheres into the solution, and stirring or ultrasonically vibrating to obtain nanometer SiO₂The microspheres are uniformly dispersed in the solution to prepare a polymer microsphere solution, and the polymer microsphere solution is dried to obtain the nano silicon-carbon precursor.

7. The method for preparing the nano silicon-carbon negative electrode material according to claim 6, wherein the polymer or organic matter is one or more of polystyrene, polyacrylonitrile, polymethacrylic acid, polymethyl methacrylate, polypyrrole, polyamide, polyimide, polyvinyl alcohol, polyvinyl acetate, polycarbonate, phenolic resin, epoxy resin, glucose, sucrose, chitin, starch and lignin;

the solvent is benzene, toluene, dimethylformamide or water.

8. The preparation method of the nano silicon-carbon anode material according to claim 4 or 6, wherein the drying is to dry the polymer microsphere solution and then ball mill and crush the dried polymer microsphere solution, or freeze-dry the dried polymer microsphere solution or spray-dry the dried polymer microsphere solution to obtain particles, and the particles are screened by a 400-mesh screen to form a nano silicon-carbon precursor.

9. The method for preparing nano silicon-carbon anode material according to claim 1, wherein the pyrolysis is to place the nano silicon-carbon precursor and magnesium powder in a crucible, separately place them, place them in an electric furnace, heat them to 650-1000 ℃ under the protection of argon or the mixed atmosphere of argon and hydrogen, preserve heat for 2-6h, and then cool them to obtain the nano silicon-carbon material containing impurities.

10. The method for preparing nano silicon-carbon anode material according to claim 9, wherein the nano silicon-carbon material containing impurities is washed with deionized water, acid-washed, and filtered to obtain the nano silicon-carbon material.

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