Porous silicon-carbon composite negative electrode material and preparation method and application thereof

Abstract

The invention particularly relates to a preparation method of a porous silicon-carbon composite negative electrode material, and the preparation method comprises the following steps: depositing nano silicon on the surface of a carbon nanotube through CVD (Chemical Vapor Deposition) to obtain a Si / CNT compound; adding the Si / CNT compound and a surfactant into water, uniformly mixing, adding a mixed solution containing a resin material and ethanol, uniformly stirring, and drying to obtain a Si / CNT / C precursor material; sintering the precursor material under the protection of inert gas to obtain a Si / CNT / C material; and mixing the Si / CNT / C material with a biomass material, and sintering under the protection of inert gas to obtain the porous silicon-carbon composite negative electrode material. According to the preparation method disclosed by the invention, by controlling the size of silicon particles and a carbon coating structure, the problem of volume expansion of silicon in charging and discharging processes is effectively relieved, and the electrochemical performance and the cycling stability of the negative electrode material are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of preparation of electrode materials, and particularly relates to a porous silicon-carbon composite anode material, a preparation method thereof, and an application thereof. Background Art

[0002] As a material with a high theoretical specific capacity (about 4200 mAh / g), silicon can form a stable Li-Si alloy when reacting with lithium, thereby providing a higher lithium storage capacity. Therefore, silicon is considered to be one of the ideal choices for the anode materials of next-generation lithium-ion batteries. However, in practical applications, silicon-based anode materials face some challenges. Mainly because silicon will undergo huge volume expansion and contraction during the lithiation and delithiation processes, this volume change will lead to the pulverization of silicon particles and the destruction of the electrode structure, thereby accelerating the attenuation of battery performance. In addition, the side reaction between silicon and the electrolyte will also cause the instability of the solid electrolyte interface, further affecting the cycle life and safety of the battery.

[0003] To solve these problems, researchers have tried various methods, including nanostructuring, compositing, and surface coating, etc., to improve the cycle stability and electrochemical performance of silicon-based anode materials. Among them, silicon-carbon composite materials are considered to be an effective solution due to their excellent electrical conductivity, chemical stability, and good mechanical properties. By combining silicon nanoparticles with carbon materials, silicon-carbon composite materials can not only buffer the volume change of silicon during charge and discharge, but also improve the electrical conductivity and structural stability of the electrode. Although significant progress has been made in silicon-carbon composite materials in the laboratory, there are still some challenges in large-scale preparation, such as cost control, production efficiency, and material consistency. In addition, there are various preparation methods for silicon-carbon composite materials, including sol-gel method, chemical vapor deposition, mechanical ball milling, etc., and each method has its specific advantages and limitations.

[0004] Chinese Patent CN117996047A discloses a preparation method of a biomass hard carbon composite silicon-carbon anode material, specifically as follows: Step 1, pre-carbonize, pulverize, and calcine the biomass raw material to obtain a biomass carbon material; Step 2, prepare a nano-silicon slurry; Step 3, put the biomass carbon material, nano-silicon slurry, and asphalt into a dispersion tank in a certain proportion respectively, use ethanol as a solvent, stir, and then perform spray granulation to obtain Reaction Product III; Step 4, add asphalt to Reaction Product III for solid-phase mixing and primary granulation to obtain Reaction Product V; Step 5, add asphalt to Reaction Product V for solid-phase mixing and secondary granulation to obtain Reaction Product VII, and then screen Reaction Product VII to obtain the final product. However, the silicon particles used in this patent are relatively large in size (D50 = 100 - 120 nm), and are prone to breakage during the charge and discharge process of the battery. Moreover, due to the poor conductivity of silicon, the lithium-ion mobility is low. Especially at high rates, it is difficult for lithium ions to penetrate deep into the silicon particles, affecting the performance of the battery. Summary of the Invention

[0005] In view of the technical problems existing in the prior art, the present invention provides a porous silicon-carbon composite anode material, its preparation method and application. The preparation method promotes the penetration of the electrolyte and alleviates the volume expansion problem of silicon during the charge and discharge process by controlling the silicon particle size and carbon coating structure, which is beneficial to improving the stability and rate performance of the material. The prepared porous silicon-carbon composite anode material has a high initial discharge specific capacity, charge and discharge efficiency, capacity retention rate, and a low electrode expansion rate, showing good electrochemical performance and cycle stability.

[0006] The technical solutions adopted by the present invention to solve the above problems are as follows:

[0007] A preparation method of a porous silicon-carbon composite anode material, comprising the following steps:

[0008] S1. Deposit nano-silicon on the surface of carbon nanotubes by chemical vapor deposition to obtain a Si / CNT composite;

[0009] S2. Add the Si / CNT composite and a surfactant to water and mix evenly, then add a mixed solution containing a resin material and ethanol, stir evenly, and then dry to obtain a Si / CNT / C precursor material;

[0010] S3. Sinter the Si / CNT / C precursor material under the protection of an inert gas to obtain a Si / CNT / C material;

[0011] S4. Add the Si / CNT / C material and the biomass material to an organic solvent, stir evenly, evaporate to remove the solvent, and sinter the obtained solid particles under the protection of an inert gas to obtain a porous silicon-carbon composite anode material.

[0012] Preferably, the deposition temperature of the chemical vapor deposition is 400 - 600 °C.

[0013] Preferably, the carbon nanotubes are at least one of single-walled carbon nanotubes, few-walled carbon nanotubes, and multi-walled carbon nanotubes.

[0014] More preferably, the carbon nanotubes are single-walled carbon nanotubes.

[0015] Preferably, the carbon nanotubes have a diameter of 1 - 10 nm and a length of 10 - 60 μm.

[0016] Preferably, in the Si / CNT composite, the D50 particle size of the nano-silicon is 7 - 20 nm, and the mass ratio of the Si to the CNT is (4 - 10):1.

[0017] Preferably, the mass ratio of the Si / CNT composite, the surfactant, and the resin material is (1 - 2):(0.5 - 3):(1 - 3).

[0018] Preferably, the surfactant is a cationic surfactant.

[0019] More preferably, the surfactant is at least one of alkyl quaternary ammonium salts, alkyl pyridinium chlorides, amine salts, alkyl imidazolines, amino amides, and quaternized polysaccharides.

[0020] Preferably, the resin material is a polymer monomer or its reactant.

[0021] More preferably, the resin material is at least one of phenolic resins, epoxy resins, polyfurfuryl alcohol, formaldehyde, phenol, resorcinol, phloroglucinol, and ammonia.

[0022] Preferably, in step S2, the stirring is ultrasonic stirring or water bath stirring. In the above technical solution, water bath stirring can create a reaction environment for the polymerization reaction of the polymer monomer, and its purpose is to carry out a polymerization reaction on the surface of the Si / CNT composite.

[0023] Preferably, the inert gas is argon.

[0024] Preferably, the pressure during sintering is 0.1 - 1 atmosphere. The size of the nano-silicon is controlled by the deposition temperature and the pressure.

[0025] Preferably, the sintering temperature is 600 - 900 °C.

[0026] Preferably, the sintering time is 2 - 3 h.

[0027] Preferably, the biomass material is at least one of rice straw, corn straw, wheat straw, corn, soybean, sugarcane, coconut shell, litchi shell, shrimp shell, crab shell, fish oil, and lignin.

[0028] Preferably, after the biomass material is cleaned, it is ground into powder for use.

[0029] Preferably, the organic solvent is at least one of ethanol, methanol, isopropanol, acetic acid, acetone, DMSO, and NMP.

[0030] In the above technical solution, the organic solvent for dissolving the biomass material is determined by the type of the specifically selected biomass material. Exemplarily, DMSO can be used for the rice straw, coconut shell, and litchi shell; acetic acid, acetone, or DMSO can be used for the straw and lignin; and alcohol solvents can be used for the shrimp shell, crab shell, and fish oil.

[0031] Preferably, the method for preparing the porous silicon-carbon composite negative electrode material further includes the following steps: after sintering in the step S4, the obtained porous silicon-carbon composite negative electrode material is pulverized by a jet mill to obtain a porous silicon-carbon composite negative electrode material with a D50 particle size of 7-11 μm.

[0032] The present invention provides a porous silicon-carbon composite negative electrode material prepared by the above-described preparation method.

[0033] The present invention provides an application of the above-described porous silicon-carbon composite negative electrode material in a lithium-ion battery.

[0034] Preferably, the application is used as a negative electrode active material of a lithium-ion battery.

[0035] The present invention also provides a lithium-ion battery including the above-described porous silicon-carbon composite negative electrode material.

[0036] The present invention has the following beneficial effects:

[0037] In the present invention, nano-silicon is deposited on the surface of carbon nanotubes (CNT) by chemical vapor deposition to form a Si / CNT composite with a one-dimensional structure. The formed Si / CNT composite not only has high conductivity, and the carbon nanotubes can also provide a fast transmission channel for lithium ions, which is particularly suitable for high-rate charge and discharge scenarios; the nano-silicon has a small size and can effectively relieve the volume expansion caused by lithium insertion, and is also beneficial for lithium to be more easily and uniformly inserted into silicon to form a lithium-silicon alloy.

[0038] Furthermore, the present invention prepares a Si / CNT / C precursor material by mixing a Si / CNT composite with a surfactant and a resin material, followed by ultrasonic treatment and drying. The precursor material is sintered under an inert gas protection, which not only enhances the overall structural stability of the material but also forms a double-layer carbon coating structure. Among them, the inner layer of carbon is used to isolate the contact between the electrolyte and silicon, and the outer layer of carbon is made of a biomass material. Due to the porous characteristics of the biomass material, there is no need to add a pore-forming agent. The porous structure of the biomass material is conducive to promoting the penetration of the electrolyte, increasing the contact area between the electrolyte and silicon-carbon, and also helping to alleviate the expansion of silicon.

[0039] The preparation method of the present invention promotes the penetration of the electrolyte and alleviates the volume expansion problem of silicon during charge and discharge by controlling the silicon particle size and the carbon coating structure, which is beneficial to improving the stability and rate performance of the material. The prepared porous silicon-carbon composite anode material has a high initial discharge specific capacity, charge-discharge efficiency, capacity retention rate, and a low electrode expansion rate, showing good electrochemical performance and cycle stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 Scanning electron micrograph of the Si / CNT composite prepared in Example 1;

[0041] Figure 2 Scanning electron micrograph of the porous silicon-carbon composite anode material prepared in Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0042] To make the technical problems, technical solutions, and technical advantages to be solved by the present invention clearer, the following will be described in detail with specific examples. However, the protection scope of the present invention is not limited to the following specific examples. The described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments, and even less a limitation to the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

[0043] Unless otherwise defined, all professional terms used hereinafter have the same meaning as commonly understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the protection scope of the present invention.

[0044] Unless otherwise specifically stated, various raw materials, reagents, instruments, and equipment used in the present invention can be obtained through the market or can be prepared by existing methods.

[0045] A preparation method of a porous silicon-carbon composite anode material includes the following steps:

[0046] S1. Deposit nanosilicon on the surface of carbon nanotubes by chemical vapor deposition to obtain a Si / CNT composite;

[0047] S2. Add the Si / CNT composite and a surfactant to water and mix evenly, then add a mixed solution containing a resin material and ethanol, stir evenly, and then dry to obtain a Si / CNT / C precursor material;

[0048] S3. Sinter the Si / CNT / C precursor material under inert gas protection to obtain a Si / CNT / C material;

[0049] S4. Add the Si / CNT / C material and a biomass material to an organic solvent, stir evenly, evaporate to remove the solvent, and sinter the obtained solid particles under inert gas protection to obtain a porous silicon-carbon composite anode material.

[0050] In some preferred embodiments, the deposition temperature of the chemical vapor deposition is 400 - 600 °C.

[0051] In some preferred embodiments, the carbon nanotubes are at least one of single-walled carbon nanotubes, few-walled carbon nanotubes, and multi-walled carbon nanotubes.

[0052] In some more preferred embodiments, the carbon nanotubes are single-walled carbon nanotubes.

[0053] In some preferred embodiments, the carbon nanotubes have a diameter of 1 - 10 nm and a length of 10 - 60 μm.

[0054] In some preferred embodiments, in the Si / CNT composite, the particle size D50 of the nanosilicon is 7 - 20 nm; the mass ratio of Si to CNT is (4 - 10):1.

[0055] In some preferred embodiments, the mass ratio of the Si / CNT composite, the surfactant, and the resin material is (1 - 2):(0.5 - 3):(1 - 3). For the finally prepared silicon-carbon composite anode material, the mass ratio of silicon to carbon (amorphous carbon and CNT) is 1 - 1.5:2. The present invention realizes the uniform distribution of silicon particles by controlling the dispersion of CNT in the resin. After the resin is carbonized, amorphous carbon cross-linked with carbon nanotubes can be formed, which can evenly coat the surface of Si / CNT, facilitating the improvement of the structural stability and conductivity of the material.

[0056] In some preferred embodiments, the surfactant is a cationic surfactant.

[0057] In some more preferred embodiments, the surfactant is at least one of alkyl quaternary ammonium salts, alkyl pyridine chlorides, amine salts, alkyl imidazolines, amino amides, and quaternized polysaccharides.

[0058] In some preferred embodiments, the resin material is a polymer monomer or its reaction product.

[0059] More preferably, the resin material is at least one of phenolic resin, epoxy resin, polyfurfuryl alcohol, formaldehyde, phenol, resorcinol, phloroglucinol, ammonia.

[0060] Preferably, in step S2, the stirring is ultrasonic stirring or water bath stirring. In the above technical solution, water bath stirring can create a reaction environment for the polymerization reaction of polymer monomers, and its purpose is to carry out a polymerization reaction on the surface of the Si / CNT composite.

[0061] Specifically, the ultrasonic power during ultrasonic stirring includes but is not limited to 30W, 40W, 50W, 60W, 70W, 80W, 90W, 100W; the stirring speed includes but is not limited to 300rpm, 400rpm, 500rpm, 600rpm, 800rpm, 1000rpm, 1500rpm, 2000rpm, 3000rpm.

[0062] Specifically, the temperature of the water bath stirring is 60°C and the time is 6h.

[0063] In some preferred embodiments, the inert gas is argon.

[0064] In some preferred embodiments, the pressure during sintering is 0.1 to 1 atmosphere. The size of nano-silicon is controlled by the deposition temperature and pressure.

[0065] In some preferred embodiments, the sintering temperature is 600 to 900°C.

[0066] In some preferred embodiments, the sintering time is 2 to 3h.

[0067] In some preferred embodiments, the biomass material is at least one of rice straw, corn straw, wheat straw, corn, soybean, sugarcane, coconut shell, litchi shell, shrimp shell, crab shell, fish oil.

[0068] Preferably, the biomass material is ground into powder for use after being cleaned.

[0069] In some preferred embodiments, the organic solvent is at least one of ethanol, methanol, isopropanol, acetic acid, acetone, DMSO, NMP.

[0070] In the above technical solution, the organic solvent for dissolving the biomass material is determined by the specific type of biomass material selected. Exemplarily, DMSO can be used for rice straw, coconut shell, litchi shell; acetic acid, acetone or DMSO can be used for straw, lignin; alcohol solvents can be used for shrimp shell, crab shell, fish oil.

[0071] In some preferred embodiments, the method for preparing the porous silicon-carbon composite negative electrode material further comprises the following steps: after sintering in the step S4, the obtained porous silicon-carbon composite negative electrode material is pulverized by a jet mill to obtain a porous silicon-carbon composite negative electrode material with a D50 particle size of 7-11 μm.

[0072] The present invention provides a porous silicon-carbon composite negative electrode material prepared by the preparation method as described above.

[0073] The present invention provides an application of the porous silicon-carbon composite negative electrode material as described above in a lithium-ion battery.

[0074] In some preferred embodiments, the application is used as the negative electrode active material of a lithium-ion battery.

[0075] The present invention further provides a lithium-ion battery comprising the porous silicon-carbon composite negative electrode material.

[0076] The following is the specific embodiment part.

[0077] Example 1

[0078] Prepare a porous silicon-carbon composite negative electrode material, including the following steps:

[0079] S1. Place 0.3 g of single-walled carbon nanotubes in a fluidized bed, heat to 500 °C at a rate of 5 °C / min, and introduce a gas mixture of 95% Ar and 5% SiH4 at a rate of 200 ml / min. After 120 min, change to Ar and cool to room temperature to obtain 1.5 g of Si / CNT composite ( Figure 1 );

[0080] S2. Add 1.5 g of Si / CNT composite and 0.2 g of cetyltrimethylammonium bromide (CTAB) to 50 ml of deionized water and stir evenly. Then add a mixed solution containing 0.5 g of resorcinol, 0.8 g of paraformaldehyde, 0.6 g of phenolic resin, and 25 ml of ethanol. After ultrasonic stirring evenly, place the mixed solution at 80 °C for drying and curing to obtain a Si / CNT / C precursor;

[0081] S3. Put the Si / CNT / C precursor material into a tubular furnace, place it under argon protection, heat to 800 °C at a rate of 5 °C / min, and keep the temperature for 2 h to obtain a Si / CNT / C material;

[0082] S4. Add 2 g of Si / CNT / C material to 20 ml of a DMSO solution containing 2 g of coconut shell, stir evenly, evaporate to remove the solvent, transfer the obtained solid particles to a tube furnace, place it under argon protection, heat it to 800 °C at a rate of 5 °C / min, hold for 2 h to obtain the negative electrode silicon-carbon material, and crush the obtained negative electrode silicon-carbon material by a jet mill to obtain a porous silicon-carbon composite negative electrode material with a particle size D50 of 7 - 11 μm( Figure 2 ).

[0083] Example 2

[0084] Prepare a porous silicon-carbon composite negative electrode material, which includes the following steps:

[0085] S1. Place 0.3 g of single-walled carbon nanotubes in a fluidized bed, heat it to 450 °C at a rate of 5 °C / min, and introduce 95% Ar and 5% SiH4 gas at a rate of 200 ml / min. After 120 min, change to Ar and cool to room temperature to obtain 1.5 g of Si / CNT composite;

[0086] S2. Add 1.5 g of Si / CNT composite and 0.2 g of cetyltrimethylammonium bromide (CTAB) to 50 ml of deionized water, stir evenly, then add a mixture containing 2 g of epoxy resin and 25 ml of ethanol, stir evenly by ultrasonic, and place the mixture at 80 °C for drying and curing to obtain a Si / CNT / C precursor;

[0087] S3. Place the Si / CNT / C precursor material in a tube furnace, place it under argon protection, heat it to 800 °C at a rate of 5 °C / min, hold for 2 h to obtain the Si / CNT / C material;

[0088] S4. Add 2 g of Si / CNT / C material to 20 ml of an acetone solution containing 2 g of lignin, stir evenly, evaporate to remove the solvent, transfer the obtained solid particles to a tube furnace, place it under argon protection, heat it to 800 °C at a rate of 5 °C / min, hold for 2 h to obtain the negative electrode silicon-carbon material, and crush the obtained negative electrode silicon-carbon material by a jet mill to obtain a porous silicon-carbon composite negative electrode material with a particle size D50 of 7 - 11 μm.

[0089] Example 3

[0090] Prepare a porous silicon-carbon composite negative electrode material, which includes the following steps:

[0091] S1. Place 0.3 g of few - walled carbon nanotubes in a fluidized bed, heat it to 500 °C at a rate of 5 °C / min, use a vacuum pump to keep the internal pressure of the tube at 100 - 200 MPa, introduce 95% Ar and 5% SiH4 gas at a rate of 250 ml / min, after 150 min, change to Ar and cool it to room temperature to obtain 1.5 g of Si / CNT composite;

[0092] S2. Add 1.5 g of Si / CNT composite and 0.15 g of PVP to 50 ml of deionized water and stir evenly, then add a mixed solution containing 0.5 g of resorcinol, 0.8 g of formaldehyde, 0.45 ml of ammonia and 25 ml of ethanol, stir in a water bath at 60 °C for 6 h, wash the obtained product with pure water multiple times to obtain a Si / CNT / C precursor;

[0093] S3. Put the Si / CNT / C precursor material into a tube furnace, place it under argon protection, heat it to 800 °C at a rate of 5 °C / min, and keep it warm for 2 h to obtain Si / CNT / C material;

[0094] S4. Add 2 g of Si / CNT / C material to 20 ml of a DMSO solution containing 2 g of corn straw and stir evenly, evaporate to remove the solvent, transfer the obtained solid particles to a tube furnace, place it under argon protection, heat it to 800 °C at a rate of 5 °C / min, and keep it warm for 2 h to obtain a negative electrode silicon - carbon material, and pulverize the obtained negative electrode silicon - carbon material by a jet mill to obtain a porous silicon - carbon composite negative electrode material with a D50 particle size of 7 - 11 μm.

[0095] Comparative Example 1

[0096] S1. Add 20 g of micron - sized silicon (D50 is 5 μm), 5 g of carbon nanotubes, and 3.3 g of CTAB to 171.7 g of ethanol, take it out after sanding at a rate of 2000 rpm for 2 h to obtain a Si / CNT slurry with a D50 of 100 - 120 nm;

[0097] S2. Add 12 g of Si / CNT slurry to a mixed solution containing 0.5 g of resorcinol, 0.8 g of paraformaldehyde, 0.6 g of phenolic resin and 25 ml of ethanol, stir evenly by ultrasonic wave, and then dry and cure the mixed solution at 80 °C to obtain a Si / CNT / C precursor;

[0098] S3. Put the Si / CNT / C precursor material into a tube furnace, place it under argon protection, heat it to 800 °C at a rate of 5 °C / min, and keep it warm for 2 h to obtain Si / CNT / C material;

[0099] S4. Add 2 g of Si / CNT / C material to 20 ml of a DMSO solution containing 2 g of coconut shell and stir evenly. Evaporate to remove the solvent. Transfer the obtained solid particles to a tube furnace, place it under argon protection, heat it to 800 °C at a rate of 5 °C / min, hold for 2 h to obtain the negative electrode silicon-carbon material. Crush the obtained negative electrode silicon-carbon material with a jet mill to obtain a silicon-carbon composite negative electrode material with a particle size D50 of 7 - 11 μm.

[0100] Comparative Example 2

[0101] The difference between this Comparative Example 2 and Example 1 is that step S4 is not adopted, and the product obtained in step S3 is directly used as the negative electrode material, and the remaining steps are the same.

[0102] Comparative Example 3

[0103] The difference between this Comparative Example 3 and Example 1 is that Comparative Example 3 does not adopt steps S2 and S3. Instead, the product obtained in step S1 is added to 20 ml of a DMSO solution containing 2 g of coconut shell and stirred evenly. Evaporate to remove the solvent. Transfer the obtained solid particles to a tube furnace, place it under argon protection, heat it to 800 °C at a rate of 5 °C / min, hold for 2 h to obtain the negative electrode silicon-carbon material. Crush the obtained negative electrode silicon-carbon material with a jet mill to obtain a silicon-carbon composite negative electrode material with a particle size D50 of 7 - 11 μm, and the remaining steps are the same.

[0104] Comparative Example 4

[0105] The difference between this Comparative Example 4 and Example 1 is that in step S4, the coconut shell is changed to an equal amount of asphalt, and the remaining steps are the same.

[0106] Comparative Example 5

[0107] S1. Add 1.5 g of nano-Si (particle size D50 = 10 - 15 nm) and 0.2 g of cetyltrimethylammonium bromide (CTAB) to 50 ml of deionized water and stir evenly. Then add a mixed solution containing 0.5 g of resorcinol, 0.8 g of paraformaldehyde, 0.6 g of phenolic resin and 25 ml of ethanol. After ultrasonic stirring evenly, place the mixed solution at 80 °C for drying and curing to obtain a Si / C precursor;

[0108] S2. Put the Si / C precursor material into a tube furnace, place it under argon protection, heat it to 800 °C at a rate of 5 °C / min, hold for 2 h to obtain a Si / C material;

[0109] S3. Add 2 g of Si / C material to 20 ml of a DMSO solution containing 2 g of coconut shell, stir evenly, evaporate to remove the solvent, transfer the obtained solid particles to a tubular furnace, place them under argon protection, heat up to 800 °C at a rate of 5 °C / min, hold for 2 h to obtain the negative electrode silicon-carbon material, and pulverize the obtained negative electrode silicon-carbon material by a jet mill to obtain a silicon-carbon composite negative electrode material with a D50 particle size of 7 - 11 μm.

[0110] Performance test:

[0111] Fabricate coin cells with the silicon-carbon composite negative electrode materials provided in the above examples and comparative examples, and conduct electrochemical performance tests.

[0112] The preparation steps of the coin cell include: stirring and mixing the negative electrode silicon-carbon material, binder LA133, conductive carbon black, and deionized water to obtain a negative electrode slurry; wherein, the mass-volume ratio of the silicon-carbon composite negative electrode material, conductive carbon black, binder LA132, SBR, and deionized water is 3 g: 0.03148 g: 0.04722 g: 0.21 g: 5.5 g; coat the negative electrode slurry on a copper foil, dry and roll it to prepare a negative electrode sheet; the electrolyte is a solution with LiPF6 and 10% FEC as electrolytes, with a concentration of 1 mol / L, wherein the solvent uses a mixed solution of ethylene carbonate and diethyl carbonate with a volume ratio of 1:1; a lithium metal sheet is used as the counter electrode, and a polypropylene membrane is used as the separator.

[0113] In an argon glove box, assemble the coin cell on a Neware CT-4008Tn type battery tester to conduct an electrochemical cycling performance test, with a charge-discharge voltage range of 0.01 V to 2.0 V and a charge-discharge rate of 1 C.

[0114] Conduct an expansion test on the negative electrode sheet of the above coin cell. The specific test process is as follows: measure the thickness D1 of the negative electrode sheet of the coin cell after rolling, then fully charge the coin cell, and then disassemble the coin cell to measure the thickness D2 of the negative electrode sheet under full charge, and then calculate the electrode sheet expansion rate (electrode sheet expansion rate = (D2 - D1) / D1 * 100%).

[0115] In addition, conduct a rate discharge retention test on the above coin cell. The specific test process is as follows: after formation, cycle 3 times at 0.1 C (record the average specific capacity Q1), 0.3 C, 0.5 C, 1 C, 2 C, and 3 C respectively, and then cycle 3 times at a rate of 0.1 C (record the average specific capacity Q2), and the rate discharge retention = Q2 / Q1 × 100%.

[0116] The test results of the examples and comparative examples are shown in Table 1.

[0117] Table 1:

[0118]

[0119]

[0120] As can be seen from the above table, the preparation method of the present invention not only effectively reduces the irreversible capacity of the silicon-carbon composite anode material, but also improves the first efficiency and cycle stability of the silicon-carbon composite anode material; and improves the rate performance of the material.

[0121] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0122] In addition, it should be noted that, in the case of no contradiction, the various specific technical features described in the above specific embodiments can be combined in any appropriate manner. To avoid unnecessary repetition, the present invention will not separately describe various possible combination manners.

[0123] In addition, any combination can be made between various different embodiments of the present invention, as long as it does not violate the idea of the present invention, it should also be regarded as the content disclosed by the present invention.

Claims

1. A preparation method of a porous silicon-carbon composite anode material, characterized in that, It includes the following steps: S1. Deposit nano-silicon on the surface of carbon nanotubes by chemical vapor deposition to obtain a Si / CNT composite; S2. Add the Si / CNT composite and a surfactant into water and mix evenly, then add a mixed solution containing a resin material and ethanol, stir evenly, and then dry to obtain a Si / CNT / C precursor material; S3. Sinter the Si / CNT / C precursor material under the protection of an inert gas to obtain a Si / CNT / C material; S4. Add the Si / CNT / C material and a biomass material into an organic solvent and stir evenly, evaporate to remove the solvent, and sinter the obtained solid particles under the protection of an inert gas to obtain a porous silicon-carbon composite anode material.

2. The preparation method of the porous silicon-carbon composite negative electrode material according to claim 1, wherein In the Si / CNT composite, the particle size D50 of the nano-silicon is 7-20 nm; the mass ratio of Si to CNT is (4-10):

1.

3. The preparation method of the porous silicon-carbon composite negative electrode material according to claim 1, characterized in that, The mass ratio of the Si / CNT composite, the surfactant, and the resin material is (1-2):(0.5-3):(1-3).

4. The preparation method of the porous silicon-carbon composite negative electrode material according to claim 1, characterized in that The surfactant is a cationic surfactant.

5. The preparation method of the porous silicon-carbon composite negative electrode material according to claim 1, wherein, The resin material is a polymer monomer or its reactant.

6. The preparation method of the porous silicon-carbon composite negative electrode material according to claim 1, characterized in that, The biomass material is at least one of rice straw, corn straw, wheat straw, corn, soybean, sugarcane, coconut shell, litchi shell, shrimp shell, crab shell, fish oil, lignin; the organic solvent is at least one of ethanol, methanol, isopropanol, acetic acid, acetone, DMSO, NMP.

7. The preparation method of the porous silicon-carbon composite negative electrode material according to claim 1, characterized in that It further includes the following step: after sintering in the step S4, crush the obtained porous silicon-carbon composite anode material by a jet mill to obtain a porous silicon-carbon composite anode material with a particle size D50 of 7-11 μm.

8. A porous silicon-carbon composite anode material prepared by the preparation method according to any one of claims 1 to 7.

9. An application of the porous silicon-carbon composite anode material according to claim 8 in a lithium-ion battery.

10. A lithium-ion battery, characterized in that, It contains the porous silicon-carbon composite anode material according to claim 11.

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