Preparation method of carbon microsphere-silicon negative electrode material

Abstract

The invention discloses a carbon microsphere-silicon negative electrode material and a preparation method thereof, mesocarbon microbeads are prepared by adding a nano template agent, porous mesocarbon microbead green pellets are obtained through acid etching, and nano-silicon-loaded mesocarbon microbeads are obtained through hydrothermal reaction reduction deposition of organic silicon in pore channels generated through etching, so that the carbon microsphere-silicon negative electrode material is obtained. And coating the outermost layer with a layer of amorphous carbon, and carbonizing to obtain the carbon microsphere-silicon negative electrode material. The mesocarbon microbeads prepared by taking the nano template agent as an additive have the advantages that the particle size distribution is concentrated, the particle size is moderate, a large amount of nano template agent exists inside and on the surface, and rich nano-scale pore channels are obtained after acid etching; in the hydrothermal process, organic silicon is deposited in situ on the outer surfaces of the mesocarbon microbeads and in pore channels to form uniform coating layers, the organic silicon and the mesocarbon microbeads are combined more tightly, the nanometer silicon loaded mesocarbon microbeads are obtained through magnesiothermic reduction, and the advantages of good conductivity, good rate capability and stable cycle performance are achieved.

Description

Technical Field

[0001] The present invention belongs to the field of lithium-ion battery electrode materials, and relates to a carbon microsphere-silicon anode material and a preparation method thereof. Background Art

[0002] Lithium-ion batteries have the advantages of high capacity, high voltage, high cycle stability, high energy density, etc., and are environmentally friendly, so they are very popular under the current environmental protection situation. In recent years, with the development of electric vehicles, the development scale of the lithium-ion battery industry has gradually expanded. However, the power batteries of current new energy electric vehicles have disadvantages such as low energy density, and there are still major deficiencies in meeting people's growing travel needs. As a lithium-ion battery anode material, Si has become the preferred material for the next generation of lithium-ion battery anodes due to its very high theoretical lithium storage capacity (4200 mAh / g), low lithium insertion potential, high natural abundance, etc. However, Si has a large volume effect (>300%) during charge and discharge, causing active silicon particles to fall off from the electrode sheet and leading to repeated regeneration of the solid electrolyte interface (SEI) film, resulting in poor cycle performance of the battery. Currently, the research focus mainly concerns the structure of silicon particles, such as hollow microspheres, three-dimensional pores, core-shell structures, etc., and the role played by carbon components in the silicon-carbon composite system is also very important.

[0003] Mesocarbon microbeads (MCMB) have a unique lamellar structure and good physical and chemical properties, making them a precursor for the preparation of various carbon materials. As a type of graphite material, combining MCMB with Si can not only improve the cycling stability and conductivity of silicon but also enhance the overall specific capacity of the material. CN115458725A discloses a method of obtaining a "carbon - void - silicon - carbon" four - level structure "yolk - shell" type silicon - carbon composite anode material for lithium - ion batteries by using mesocarbon microbeads and oxygen - containing organosilicon compounds through inorganic acid activation, hydrothermal reaction, magnesiothermic reduction, high - temperature carbonization, and hydrochloric acid etching. CN118790979B provides mesocarbon microbead - based porous carbon materials. Asphalt powder and nano - ceramic fibers are added to silicone oil for emulsification polymerization, pre - oxidation, and carbonization treatment to obtain mesocarbon microbeads with uniformly distributed nano - ceramic fibers inside. Finally, uniformly distributed pore structures with relatively regular pore structures are prepared through pickling and high - temperature carbonization to obtain spherical porous carbon materials. CN113353915B discloses obtaining mesocarbon microbeads using oxidized petroleum coke as a nucleating agent and ethylene tar as a viscosity regulator, and forming a pore structure with a multi - level pore size distribution through alkali etching to obtain high - performance porous spherical carbon materials. CN102225755B discloses using coal liquefaction residue as a raw material, adding chemical additives and nucleation promoters during heat treatment to improve the yield and narrow the particle size distribution of mesocarbon microbeads. The nucleation promoters include one or more of graphite powder, fine mica powder, carbon black particles, alumina particles, kaolin, nano - sized coke powder, nano - sized silica, nano - zirconia, and nano - calcium carbonate. However, the addition of active silicon particles requires the matching graphite material to have certain characteristics, especially its impact on the microstructure. Therefore, by specifically modifying the microstructure of MCMB and constructing abundant nano - scale pores inside it, providing space for the existence of active silicon particles will be a potential way to optimize the electrochemical performance of active silicon. Summary of the Invention

[0004] The object of the present invention is to overcome the deficiencies in the prior art and provide a carbon microbead - silicon anode material and its preparation method. First, a nano - template agent is introduced during the preparation process of mesocarbon microbeads to create pores in the mesocarbon microspheres. Then, through hydrothermal reaction and magnesiothermic reduction with organosilicon, the deposition of silicon in the pores of the mesocarbon microspheres is realized. Finally, overall outer coating is carried out using asphalt, and after high - temperature carbonization, a silicon - carbon composite material is prepared as the core, and a "carbon - silicon / void - carbon" three - level silicon - carbon composite structure material with an outer amorphous carbon layer is obtained.

[0005] To achieve the above object, the present invention provides a preparation method for a mesocarbon microbead - silicon electrode material, including the following specific steps:

[0006] Step 1: Using the aromatic-rich heavy oil added with a nano-template agent as the raw material, through liquid-phase carbonization at 380°C - 450°C for 4 h, solvent extraction, washing, filtration, and drying, obtain the green balls of mesophase carbon microspheres embedded with the nano-template agent; the aromatic-rich heavy oil is selected from catalytic cracking slurry or medium-temperature coal tar pitch; the nano-template agent is selected from one of alkali metal carbonates, alkaline earth metal carbonates, alkaline earth metal oxides, oxides or carbonates of transition metals, and alumina, aluminosilicates, with a particle size of 10 nm - 200 nm; the addition amount of the nano-template agent is 0.1 - 20 wt% of the mass of the aromatic-rich heavy oil; the solvent for solvent extraction is toluene, and after filtration, the precipitate is washed with ethanol three times and dried in an oven at 120°C for 8 h;

[0007] Step 2: Immerse the green balls of mesophase carbon microspheres embedded with the nano-template agent in a 1 - 5 mol / L inorganic strong acid solution, stir and etch to obtain the etched green balls of mesophase carbon microspheres; the inorganic strong acid refers to one of hydrochloric acid, sulfuric acid, and nitric acid, with a concentration of 1 - 5 mol / L, and the liquid-solid ratio of it to the green balls of mesophase carbon microspheres embedded with the nano-template agent is 50 - 200 ml:1 g, and the etching condition is to etch for 2 h under stirring at room temperature and 500 r / min;

[0008] Step 3: Ultrasonically disperse the etched green balls of mesophase carbon microspheres in a certain amount of deionized water, and dropwise add a certain amount of organosilicon compound, and continue ultrasonic treatment until completely dispersed to obtain a suspension; the organosilicon compound is selected from one of tetramethoxysilane, (1,1-dimethylethyl)dimethylsilyl ester, 3-tert-butyldimethylsilyl-2-propyn-1-ol, and triisopropylsilyl ester, and the mass ratio of it to the etched green balls of mesophase carbon microspheres is 1:0.5 - 2;

[0009] Step 4: Transfer the suspension to a hydrothermal reaction kettle, react at 300 - 400°C for 4 - 12 h, preferably 8 h, filter the reaction product, wash the precipitate with ethanol and deionized water three times respectively, and place it in an oven at 120°C for 8 h to obtain the hydrothermal reaction product;

[0010] Step 5: Mix the hydrothermal reaction product with Mg powder according to a mass ratio of 10:1, and carry out a magnesiothermic reaction at 600°C for 5 h in an argon / hydrogen mixed gas (hydrogen volume fraction is 5% - 20%) atmosphere to obtain the magnesiothermic reaction product;

[0011] Step 6: Wash the product of the magnesiothermic reaction successively with dilute hydrochloric acid, deionized water and ethanol until neutral and then dry it to obtain the silicon-carbon material precursor; the washing conditions of the dilute hydrochloric acid are 2 h at room temperature and the stirring speed is 500 r / min; completely dissolve a certain amount of coal tar pitch or petroleum pitch in a solvent and filter out the insoluble substances, the mass ratio of the coal tar pitch or petroleum pitch to the silicon-carbon material precursor is 1:2 - 5, the solvent is selected from one or several of n-heptane, petroleum ether, toluene, tetrahydrofuran, N-methylpyrrolidone, pyridine in any proportion, and its mass ratio to the silicon-carbon material precursor is 1:0.01, add the silicon-carbon material precursor, stir for 24 h, filter the precipitate and wash it with deionized water;

[0012] Step 7: Place the precipitate obtained in Step 6 in a tube furnace and carbonize it at 800 °C for 2 h under an argon atmosphere to obtain the carbon microsphere-silicon anode material, which has a three-level composite structure of "carbon-silicon / vacancy-carbon".

[0013] The present invention also provides a carbon microsphere-silicon anode material prepared by the above method, which has a three-level composite structure of "carbon-silicon / vacancy-carbon". Most of the silicon exists in the internal pores of the mesophase carbon microspheres in the form of particles, and only a small amount of silicon particles adhere to the outer surface of the mesophase carbon microspheres. The outermost layer is coated with an amorphous carbon layer; the mass content of silicon in the carbon microsphere-silicon anode material is 5 - 20%, preferably 12%. The internal pores of the mesophase carbon microspheres are evenly distributed, and most of them exist in the form of cavities with a diameter of 10 - 200 nm. The cavities are connected by pores or fissures and communicate with the outside world. The inner diameter scale is 5 - 100 nm, and the inner diameter refers to the inner diameter of the pores and the scale of the fissures connecting the cavities.

[0014] The present invention also provides the application of the above carbon microsphere-silicon anode material in a lithium-ion battery. The initial Coulombic efficiency is above 70%, the reversible specific capacity reaches above 870 mAh / g at a current density of 0.1C, and the specific capacity reaches above 620 mAh / g at a large current density of 10C.

[0015] The present invention uses porous mesophase carbon microspheres as a carbon source, and uses a templating agent to etch and create pores inside the mesophase carbon microspheres while retaining the integrity of the surface, so as to reduce the formation of the SEI film. At the same time, the internal pores obtained after etching can be used as the subsequent storage space for silicon. By adjusting the silicon loading amount, the ratio of the internal voids to silicon can be adjusted to achieve different lithium storage effects. Thus, a three-level structure of "carbon-silicon / vacancy-carbon" is constructed, and a silicon-carbon composite electrode material with good performance is prepared.

[0016] Among them, the mesophase carbon microspheres, as the carbon substrate, have a relatively disordered carbon layer arrangement, which is beneficial to the transfer of lithium ions during rapid charge and discharge. The voids created by the template agent can further shorten the lithium ion transmission path and at the same time provide space for the deposition of silicon inside rather than on the surface of the carbon microspheres. The hydrothermal reaction process of organosilicon enables silicon to be uniformly deposited inside the voids of the carbon microspheres, promoting their close combination. The remaining space in the pores of the mesophase carbon microspheres reserves sufficient space for the volume expansion of silicon inside the voids; the outermost carbon coating layer can greatly improve the Coulomb efficiency of the composite material as a whole and restrain the expansion of silicon to a certain extent, finally preparing an electrode material with a high reversible cycle specific capacity and a high Coulomb efficiency.

[0017] Compared with the prior art, the present invention has the following advantages:

[0018] 1. The carbon matrix in the composite material is the mesophase carbon microspheres prepared from heavy oil and a template agent, and then porous mesophase carbon microspheres are obtained through etching to create pores. It has the advantages of simple production process, wide raw material sources, and low cost.

[0019] 2. Utilize the abundant pores inside the porous mesophase carbon microspheres to reserve sufficient space for the attachment and volume expansion of the inner layer of silicon; and the outermost carbon coating layer further restrains the expansion of the material.

[0020] 3. Use organosilicon as the silicon source, adsorb the silicon-containing component onto the carbon substrate through electrostatic action, and then reduce it through a one-step magnesiothermic reaction. Compared with mechanical mixing, the combination of silicon and carbon is closer, and at the same time, silicon is confined in the pores of the mesophase carbon microspheres, avoiding its detachment during charge and discharge. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic structural diagram of the "carbon-silicon / void-carbon" three-level core-shell carbon microsphere-silicon negative electrode material prepared by the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0022] To make the modified preparation method of the carbon microsphere-silicon negative electrode material described in the present invention more understandable, the following is elaborated with examples.

[0023] Example 1: A carbon microsphere-silicon negative electrode material and its preparation method

[0024] (1) Add 10 g of nano-calcium carbonate with a particle size of 100 nm to 200 g of catalytic cracking slurry as the raw material. The addition amount of the nano-calcium carbonate is 5% of the mass of the catalytic cracking slurry. After the raw material is carbonized at 450 °C in liquid phase for 4 h, it is extracted, washed, filtered and dried with toluene to obtain the green balls of mesophase carbon microspheres embedded with nano-calcium carbonate;

[0025] (2) Immerse the green pellets of mesophase carbon microspheres embedded with nano-calcium carbonate into 1 mol / L hydrochloric acid solution, stir and etch to obtain the etched green pellets of mesophase carbon microspheres;

[0026] (3) Ultrasonically disperse 2 g of the etched green pellets of mesophase carbon microspheres in a certain amount of deionized water, and dropwise add 1 mL of triisopropyl silicate, continue ultrasonic treatment until completely dispersed to obtain a suspension;

[0027] (4) Transfer the suspension to a hydrothermal reaction kettle, react at 300 °C for 8 h, filter the reactants, wash the precipitate three times with ethanol and deionized water respectively, and place it in an oven to dry to obtain the hydrothermal reaction product;

[0028] (5) Mix 2 g of the hydrothermal reaction product with 0.2 g of Mg powder, carry out a magnesiothermic reaction at 600 °C for 5 h in an argon / hydrogen mixed gas atmosphere to obtain a magnesiothermic reaction product;

[0029] (6) Wash the magnesiothermic reaction product with dilute hydrochloric acid, ethanol, and deionized water until neutral and dry to obtain a precursor of the silicon-carbon material; completely dissolve 3 g of petroleum pitch in 100 ml of solvent toluene, add 1 g of the silicon-carbon material precursor, stir for 24 h, filter the precipitate and wash it with deionized water;

[0030] (7) Place the precipitate obtained in step 6 in a tubular furnace, carbonize at 800 °C for 2 h under an argon atmosphere to obtain a carbon microsphere-silicon negative electrode material with a three-level composite structure of "carbon-silicon / vacancy-carbon".

[0031] Example 2:

[0032] (1) Add 20 g of nano-magnesium oxide with a particle size of 100 nm to 200 g of catalytic cracking slurry as a raw material. The addition amount of the nano-calcium carbonate is 10% of the mass of the catalytic cracking slurry. After the raw material is subjected to liquid-phase carbonization at 450 °C for 4 h, it is extracted, washed, filtered, and dried with toluene to obtain green pellets of mesophase carbon microspheres embedded with nano-calcium carbonate; (2) Immerse the green pellets of mesophase carbon microspheres embedded with nano-magnesium oxide into 1 mol / L hydrochloric acid solution, stir and etch to obtain the etched green pellets of mesophase carbon microspheres;

[0033] (3) Ultrasonically disperse 2 g of the etched green pellets of mesophase carbon microspheres in a certain amount of deionized water, and dropwise add 1 mL of triisopropyl silicate, continue ultrasonic treatment until completely dispersed to obtain a suspension; (4) Transfer the suspension to a hydrothermal reaction kettle, react at 300 °C for 8 h, filter the reactants, wash the precipitate three times with ethanol and deionized water respectively, and place it in an oven to dry to obtain the hydrothermal reaction product;

[0034] (5) Mix 2 g of the hydrothermal reaction product with 0.2 g of Mg powder, and carry out a magnesiothermic reaction at 600 °C for 5 h in an argon / hydrogen mixed gas atmosphere to obtain a magnesiothermic reaction product;

[0035] (6) Wash the magnesiothermic reaction product with dilute hydrochloric acid, ethanol, and deionized water until neutral and dry to obtain a silicon-carbon material precursor; completely dissolve 3 g of petroleum pitch in 100 ml of solvent toluene, add 1 g of the silicon-carbon material precursor, stir for 24 h, filter the precipitate and wash it with deionized water;

[0036] (7) Place the precipitate obtained in step (6) in a tubular furnace and carbonize it at 800 °C for 2 h in an argon atmosphere to obtain a carbon microsphere-silicon negative electrode material with a three-level composite structure of "carbon-silicon / vacancy-carbon".

[0037] Example 3:

[0038] (1) Add 20 g of nano-calcium carbonate with a particle size of 100 nm to 200 g of catalytic cracking slurry as a raw material. The addition amount of the nano-calcium carbonate is 10% of the mass of the catalytic cracking slurry. After the raw material is carbonized by liquid phase at 450 °C for 4 h, it is extracted, washed, filtered, and dried with toluene to obtain green balls of mesophase carbon microspheres embedded with nano-calcium carbonate;

[0039] (2) Immerse the green balls of mesophase carbon microspheres embedded with nano-calcium carbonate in a 1 mol / L hydrochloric acid solution and stir for etching to obtain etched green balls of mesophase carbon microspheres;

[0040] (3) Ultrasonically disperse 2 g of the etched green balls of mesophase carbon microspheres in a certain amount of deionized water, and dropwise add 1 mL of 3-tert-butyldimethylsilyl-2-propyn-1-ol, and continue ultrasonic treatment until completely dispersed to obtain a suspension;

[0041] (4) Transfer the suspension to a hydrothermal reaction kettle, react at 300 °C for 8 h, filter the reactants, wash the precipitate three times with ethanol and deionized water respectively, and dry it in an oven to obtain a hydrothermal reaction product;

[0042] (5) Mix 2 g of the hydrothermal reaction product with 0.2 g of Mg powder, and carry out a magnesiothermic reaction at 600 °C for 5 h in an argon / hydrogen mixed gas atmosphere to obtain a magnesiothermic reaction product;

[0043] (6) Wash the magnesiothermic reaction product with dilute hydrochloric acid, ethanol, and deionized water until neutral and dry to obtain a silicon-carbon material precursor; completely dissolve 3 g of petroleum pitch in 100 ml of solvent toluene, add 1 g of the silicon-carbon material precursor, stir for 24 h, filter the precipitate and wash it with deionized water;

[0044] (7) Place the precipitate obtained in step 6 in a tubular furnace and carbonize it at 800 °C for 2 h under an argon atmosphere to obtain a carbon microsphere-silicon anode material with a three-level composite structure of "carbon-silicon / vacancy-carbon".

[0045] Example 4:

[0046] (1) Add 20 g of nano-calcium carbonate with a particle size of 100 nm to 200 g of medium-temperature coal tar pitch as raw materials. The addition amount of nano-calcium carbonate is 10% of the mass of medium-temperature coal tar pitch. After liquid-phase carbonization at 420 °C for 4 h, extract with toluene, wash, filter and dry to obtain green balls of mesophase carbon microspheres embedded with nano-calcium carbonate; (2) Immerse the green balls of mesophase carbon microspheres embedded with nano-calcium carbonate in a 1 mol / L hydrochloric acid solution, stir and etch to obtain the etched green balls of mesophase carbon microspheres;

[0047] (3) Ultrasonically disperse 2 g of the etched green balls of mesophase carbon microspheres in a certain amount of deionized water, and dropwise add 1 mL of 3-tert-butyldimethylsilyl-2-propyn-1-ol, and continue ultrasonic treatment until completely dispersed to obtain a suspension;

[0048] (4) Transfer the suspension to a hydrothermal reaction kettle, react at 300 °C for 8 h, filter the reactants, wash the precipitate three times with ethanol and deionized water respectively, and dry it in an oven to obtain a hydrothermal reaction product;

[0049] (5) Mix 2 g of the hydrothermal reaction product with 0.2 g of Mg powder, and carry out a magnesiothermic reaction at 600 °C for 5 h under an argon / hydrogen mixed gas atmosphere to obtain a magnesiothermic reaction product;

[0050] (6) Wash the magnesiothermic reaction product with dilute hydrochloric acid, ethanol and deionized water until neutral and dry it to obtain a silicon-carbon material precursor; Completely dissolve 3 g of petroleum pitch in 100 ml of solvent toluene, add 1 g of the silicon-carbon material precursor, stir for 24 h, filter the precipitate and wash it with deionized water;

[0051] (7) Place the precipitate obtained in step 6 in a tubular furnace and carbonize it at 800 °C for 2 h under an argon atmosphere to obtain a carbon microsphere-silicon anode material with a three-level composite structure of "carbon-silicon / vacancy-carbon".

[0052] Example 5:

[0053] (1) Using 200 g of catalytic cracking slurry as raw materials, after liquid-phase carbonization at 450 °C for 4 h, extract with toluene, wash, filter and dry to obtain green balls of mesophase carbon microspheres;

[0054] (2) Ultrasonically disperse 2 g of the green balls of mesophase carbon microspheres in a certain amount of deionized water, and dropwise add 1 mL of 3-tert-butyldimethylsilyl-2-propyn-1-ol, and continue ultrasonic treatment until completely dispersed to obtain a suspension;

[0055] (3) Transfer the suspension to a hydrothermal reactor, react at 300 °C for 8 h, filter the reactants, wash the precipitate three times with ethanol and deionized water respectively, and dry it in an oven to obtain the hydrothermal reaction product;

[0056] (4) Mix 2 g of the hydrothermal reaction product with 0.2 g of Mg powder, and carry out a magnesiothermal reaction at 600 °C for 5 h in an argon / hydrogen mixed gas atmosphere to obtain the magnesiothermal reaction product;

[0057] (5) Wash the magnesiothermal reaction product with dilute hydrochloric acid, ethanol, and deionized water until neutral and dry it to obtain the precursor of the silicon-carbon material; completely dissolve 3 g of petroleum pitch in 100 ml of the solvent toluene, add 1 g of the silicon-carbon material precursor, stir for 24 h, filter the precipitate and wash it with deionized water;

[0058] (6) Place the precipitate obtained in step 5 in a tube furnace, carbonize it at 800 °C for 2 h under an argon atmosphere to obtain the carbon microsphere-silicon negative electrode material, which has a three-level composite structure of "carbon-silicon-carbon".

[0059] Example 6:

[0060] (1) Add 20 g of nano-calcium carbonate with a particle size of 100 nm to 200 g of medium-temperature coal tar pitch as raw materials. The addition amount of nano-calcium carbonate is 10% of the mass of medium-temperature coal tar pitch. After the raw materials are carbonized by liquid phase at 420 °C for 4 h, extract, wash, filter and dry with toluene to obtain the green balls of mesophase carbon microspheres embedded with nano-calcium carbonate;

[0061] (2) Immerse the green balls of mesophase carbon microspheres embedded with nano-calcium carbonate in a 1 mol / L hydrochloric acid solution, stir and etch to obtain the etched green balls of mesophase carbon microspheres;

[0062] (3) Completely dissolve 3 g of petroleum pitch in 100 ml of the solvent toluene, add 1 g of the etched green balls of mesophase carbon microspheres, stir for 24 h, filter the precipitate and wash it with deionized water;

[0063] (4) Place the precipitate obtained in step 3 in a tube furnace, carbonize it at 800 °C for 2 h under an argon atmosphere to obtain the mesophase carbon microsphere-based electrode material, which has a three-level composite structure of "carbon-void-carbon".

[0064] Test Example: Battery Performance Test

[0065] 1. Electrode preparation: Mix the mesophase carbon microsphere-based electrode materials prepared in Examples 1-6 with acetylene black and PVDF in a mass ratio of 8:1:1, use NMP (N-methylpyrrolidone) as a solvent, grind to form a uniform slurry and coat it on a copper foil, and dry it in vacuum at 90 °C for 24 h, then roll press to obtain electrode sheets 1-6 respectively.

[0066] 2. Battery performance test: The electrode sheets 1-6 were respectively cut into electrode sheets with a diameter of 12 mm for battery assembly. The assembly process was carried out in a glove box filled with Ar gas, and the water and oxygen content was less than 0.01 ppm. The battery used a CR2032 type button battery, with a lithium metal sheet as the counter electrode, a polypropylene film as the separator, and 1 M lithium hexafluorophosphate (its solvent was a mixed solution of ethylene carbonate and dimethyl carbonate with a volume ratio of 1:1, adding 5% fluoroethylene carbonate) as the electrolyte. The assembled button battery was subjected to a 0.1C charge-discharge cycle performance test and a 10C high-current discharge performance test at 25°C within a voltage range of 0.05V - 2.2V. The measured initial specific capacity (mAh / g), first charge-discharge efficiency (%), and reversible cycle specific capacity (mAh / g, 500 cycles) of the battery were recorded, and the silicon content in each electrode material was also given. The results are shown in Table 1.

[0067] Table 1 Battery performance data of electrode sheets

[0068]

[0069] It can be seen from the data in Table 1 that compared with the existing graphite anode (reversible cycle specific capacity of 360 mAh / g), the mesophase carbon microsphere-based electrode materials prepared by the method are used as electrode sheets, and all have a higher reversible specific capacity (in Examples 1-4, all above 630 mAh / g). By comparing the silicon content in each example, it can be found that as the silicon content in the mesophase carbon microsphere-based electrode material increases, the specific capacity of the electrode sheet shows a trend of first increasing and then decreasing. This is because too high a silicon content will cause a large volume expansion in the electrode material, and too much silicon will cause a part of it to be unable to enter the pore capacity and decay rapidly. According to the experimental test results, the optimal silicon mass content in the mesophase carbon microsphere-based electrode material is 12%. Compared with Examples 1-4, the reversible cycle capacity of Example 5 is further reduced, which can prove that the amorphous carbon layer coated on the outermost layer of the mesophase carbon microsphere-based electrode material has a certain role in protecting the silicon particles from excessive capacity decay during charge and discharge. By comparing Example 6 with Examples 1-4, it can be seen that the overall capacity improvement of the carbon microsphere-silicon anode material is provided by the silicon particles inside the MCMB pores.

[0070] In addition, it should be noted that all the test results of this patent are not listed in the implementation cases, and only a few typical cases are used to help understand the present invention. In actual operation, the relevant parameters of the preparation process can be appropriately adjusted as needed. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A preparation method of a carbon microsphere-silicon anode material, characterized in that, It includes the following steps: Step 1: Using the heavy aromatic hydrocarbon oil added with a nano-template agent as a raw material, through liquid-phase carbonization at 380°C - 450°C for 4 h, solvent extraction and drying, green balls of mesophase carbon microspheres embedded with the nano-template agent are obtained; Step 2: Immersing the green balls of mesophase carbon microspheres embedded with the nano-template agent into an inorganic strong acid solution, stirring and etching to obtain the etched green balls of mesophase carbon microspheres; Step 3: Ultrasonically dispersing the etched green balls of mesophase carbon microspheres in a certain amount of deionized water, and dropwise adding an organosilicon compound, continuing ultrasonic treatment until completely dispersed to obtain a suspension; Step 4: Transferring the suspension to a hydrothermal reaction kettle, reacting at 300 - 400°C for 4 - 12 h, filtering the reaction product, washing the precipitate three times with ethanol and deionized water respectively, and drying it in an oven to obtain a hydrothermal reaction product; Step 5: Mixing the hydrothermal reaction product with Mg powder according to a mass ratio of 10:1, carrying out a magnesiothermal reaction at 600°C for 5 h in an argon / hydrogen mixed gas atmosphere to obtain a magnesiothermal reaction product; Step 6: Washing the magnesiothermal reaction product with dilute hydrochloric acid, deionized water and ethanol in sequence until neutral and drying to obtain a silicon-carbon material precursor; completely dissolving a certain amount of coal tar pitch or petroleum pitch in a solvent, adding the silicon-carbon material precursor, stirring for 24 h, filtering the precipitate and washing it with deionized water; Step 7: Placing the precipitate obtained in Step 6 in a tubular furnace, carbonizing at 800 - 1000°C for 2 h under an argon atmosphere to obtain a carbon microsphere-silicon anode material.

2. The preparation method of the carbon microsphere-silicon negative electrode material according to claim 1, characterized in that, The heavy aromatic hydrocarbon oil is selected from catalytic cracking slurry or medium-temperature coal tar pitch; the nano-template agent is selected from one of transition metal oxides or carbonates, alkali metal carbonates, alkaline earth metal carbonates, alkaline earth metal oxides, and alumina, aluminosilicates, with a particle size of 10 nm - 200 nm; the addition amount of the nano-template agent is 0.1 - 20 wt% of the mass of the heavy aromatic hydrocarbon oil; the solvent for solvent extraction in Step 1 is toluene, and after filtration, the precipitate is washed with ethanol 3 times and dried in an oven at 120°C for 8 h.

3. The preparation method of the carbon microsphere-silicon negative electrode material according to claim 1, characterized in that, The inorganic strong acid is one of hydrochloric acid, sulfuric acid, and nitric acid, with a concentration of 1 - 5 mol / L, and the liquid-solid ratio of it to the green balls of mesophase carbon microspheres embedded with the nano-template agent is 50 - 200 ml:1 g, and the etching condition is etching at room temperature under stirring at 500 r / min for 2 h.

4. The preparation method of the carbon microsphere-silicon negative electrode material according to claim 1, characterized in that, The organosilicon compound is selected from one of tetramethoxysilane, (1,1-dimethylethyl)dimethylsilyl ester, 3-tert-butyldimethylsilyl-2-propyn-1-ol or triisopropylsilyl ester, and the mass ratio of it to the etched green balls of mesophase carbon microspheres is 1:0.5 - 2.

5. The preparation method of the carbon microsphere-silicon negative electrode material according to claim 1, characterized in that, In Step 6, the mass ratio of the amount of coal tar pitch or petroleum pitch to the silicon-carbon material precursor is 1:2 - 5, the solvent is selected from one or several of n-heptane, petroleum ether, toluene, tetrahydrofuran, N-methylpyrrolidone, pyridine in any proportion, and the mass ratio of it to the silicon-carbon material precursor is 1:0.

01.

6. The carbon microsphere-silicon anode material prepared by the method according to any one of claims 1-5, characterized in that, It has a three-level composite structure of "carbon-silicon / vacancy-carbon". Most of the silicon exists in the form of particles in the internal pores of the mesophase carbon microspheres, and only a small amount of silicon particles adhere to the outer surface of the mesophase carbon microspheres. The outermost layer is coated with an amorphous carbon layer.

7. The carbon microsphere-silicon negative electrode material according to claim 6, characterized in that, In the carbon microsphere-silicon anode material, the silicon mass content is 5-20%. The internal pores of the mesophase carbon microspheres are evenly distributed, and most of them exist in the form of cavities with a diameter of 10-200 nm. The cavities are connected by pores or fissures and communicate with the outside world. The inner diameter of the pores or fissures is 5-100 nm.

8. The carbon microsphere-silicon negative electrode material according to claim 7, characterized in that, The silicon mass content in the carbon microsphere-silicon anode material is 12%.

9. Use of the carbon microsphere-silicon negative electrode material according to any one of claims 6-8 in a lithium-ion battery, characterized in that, The first-cycle Coulombic efficiency is above 70%. The reversible specific capacity reaches above 870 mAh / g at a current density of 0.1C, and the specific capacity reaches above 620 mAh / g at a large current density of 10C.

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