Silicon-based negative electrode material with artificial SEI (solid electrolyte interface) film as well as preparation method and application of silicon-based negative electrode material

Abstract

The invention provides a silicon-based negative electrode material with an artificial SEI film and a preparation method and application thereof, the silicon-based negative electrode material comprises a silicon-based material, a carbon layer and a conductive artificial SEI composite layer, the carbon layer and the conductive artificial SEI composite layer are arranged on the silicon-based material, and the carbon layer is located between the silicon-based material and the conductive artificial SEI composite layer; the conductive artificial SEI composite layer is obtained by reacting a reactive precursor with a reactive conductive material. Through the design of a three-layer structure and interaction among layers, uniform, tight and stable coating of the nano conductive material is realized, the utilization rate of the conductive material is improved, the silicon-based negative electrode material has low expansion, high capacity and excellent conductivity and cycling stability, and the cycling performance of the lithium ion battery containing the silicon-based negative electrode material is improved. The silicon-based negative electrode material is used for manufacturing a negative electrode plate and a battery, a nano conductive material does not need to be added, the battery manufacturing process is simplified, and the use cost of the silicon-based negative electrode material is greatly reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of secondary batteries, and particularly relates to a silicon-based anode material, a preparation method and an application thereof, and more particularly to a silicon-based anode material with an artificial SEI film, a preparation method and an application thereof. Background Art

[0002] Lithium-ion batteries have advantages such as high energy density, long cycle life, and low self-discharge rate, and are widely used in multiple fields such as energy storage power systems, mobile electronic products, electric vehicles, electric bicycles, aerospace, etc. A lithium-ion battery is assembled from a positive electrode, a negative electrode, a separator, and an electrolyte. The selection of the positive and negative electrode active materials has a very important impact on the performance of the lithium-ion battery. Currently, the commercially available battery negative electrode material is mainly graphite. However, the theoretical specific capacity of graphite is relatively low (about 372 mAh / g), and it is extremely difficult to further improve, which limits the development of lithium-ion batteries towards high energy density. Therefore, developing a high-capacity negative electrode material is the key to achieving performance breakthroughs in lithium-ion batteries.

[0003] Silicon-based materials are considered to be the most promising next-generation negative electrode materials for lithium-ion batteries. Their advantages mainly include: extremely high theoretical lithium intercalation capacity, appropriate working voltage, and abundant reserves of silicon in the earth's crust. However, currently, silicon-based materials still face many challenges in the application of negative electrodes. Due to the volume change of up to 300% during the lithium intercalation and deintercalation processes of silicon-based materials, the cycle performance of silicon-based negative electrodes is significantly weaker than that of graphite negative electrodes; moreover, the excessive volume expansion will also have an adverse impact on other electrochemical properties of the battery. Currently, pure silicon materials are difficult to directly be used as the negative electrode of lithium-ion batteries. Researchers usually prepare silicon materials into silicon monoxide (SiO x , x < 2) or silicon-carbon composite materials (SiC), and use such materials mixed with graphite as the negative electrode of lithium-ion batteries.

[0004] Compared with pure silicon anodes, the expansion of silicon monoxide and silicon-carbon materials has been inhibited. However, their volume expansion during lithium intercalation still exceeds 100%, and their cycling performance is inferior to that of traditional graphite anodes. To improve the performance of silicon monoxide / silicon-carbon materials, carbon nanotubes are often added as conductive agents during the preparation of the anode slurry. For example, CN116137327A discloses a silicon-containing anode slurry, which includes 10-25% of conductive slurry, 40-55% of silicon-carbon composite material, and 1-5% of an aqueous binder solution with a mass concentration of 30-50%. The conductive slurry includes 0.2-10% of conductive agent, 0.1-3% of dispersant, and 87-99.7% of water, where the conductive agent is single- and double-walled carbon nanotubes, or a mixture of single- and double-walled carbon nanotubes and other carbon-based conductive agents. Carbon nanotubes have a fibrous structure and certain flexibility. As a conductive agent, they can achieve electrical contact between silicon materials and carbon materials (such as graphite) during cycling, reducing the cycling capacity decay of silicon materials. However, the dosage of carbon nanotubes as a conductive agent is relatively high, and it is difficult to disperse them. Their high price significantly increases the process cost of using silicon-based anodes.

[0005] Another method to suppress the expansion of silicon-based anodes and improve the cycling performance is to prepare silicon-carbon nanotube composites. For example, CN113422015A discloses a silicon-graphite-carbon nanotube anode composite material, and the preparation method includes: weighing silicon-graphite materials, dissolving and dispersing them in a first solvent to obtain a pre-dispersed solution of silicon-graphite; diluting the pre-dispersed solution of silicon-graphite with a second solvent, and then mixing it with a single-walled carbon nanotube dispersion to obtain a silicon-graphite / single-walled carbon nanotube composite slurry; subjecting the silicon-graphite / single-walled carbon nanotube composite slurry to spray drying and removing the solvent to obtain a spherical silicon-graphite-carbon nanotube anode composite material, which has good capacity and Coulomb efficiency; however, in this composite material, carbon nanotubes are more likely to adhere to the surface of graphite and a small amount adheres to the surface of silicon, which affects the performance of carbon nanotubes. Moreover, the binding force between carbon nanotubes and silicon is insufficient, and it is easy to fall off during use, unable to effectively suppress the volume expansion of silicon, resulting in poor cycling performance of the battery. CN111146433A discloses a silicon-based particle for an anode, which includes a silicon-containing matrix and a polymer layer, and the polymer layer contains a polymer and carbon nanotubes, wherein the polymer includes carboxymethyl cellulose, polyacrylic acid, polyvinylpyrrolidone, polyaniline, polyimide, etc., and the weight ratio of the polymer to carbon nanotubes in the polymer layer is 0.5:1 - 10:1; the preparation method of the silicon-based particle includes: adding carbon nanotubes to a solution containing a polymer to obtain a slurry; adding the silicon-containing matrix to the above slurry and dispersing to obtain a mixed slurry; removing the solvent in the mixed slurry, crushing and screening to obtain the silicon-based particle. The polymer layer in the silicon-based particle is prone to fall off during the preparation of the anode slurry and the working process of the battery, so that carbon nanotubes cannot be stably distributed on the surface of the silicon-containing matrix, affecting the coating effect, and thus cannot fundamentally solve the expansion problem of silicon-based materials and the cycling problem of the battery.

[0006] CN116093273A discloses a silicon-based material for an anode, which includes a silicon-containing matrix and a polymer layer, and the polymer layer contains a polymer and hydroxylated carbon nanotubes, and the polymer includes acrylate, acrylonitrile, acrylic polyether polyol, etc. The coating of hydroxylated carbon nanotubes and the polymer can improve the cycling performance of silicon materials and suppress expansion. However, this method has high requirements for silicon substrates. The surface of the silicon substrate must contain hydroxyl functional groups to undergo an esterification reaction with the polymer, and the polymer-carbon nanotubes on the surface are bonded to the silicon substrate through ester bonds to ensure the stability of the coating layer. But for silicon materials without hydroxyl groups on the surface after carbon coating, this method is not applicable. In addition, although this method can improve the cycling life of silicon anodes, it cannot replace the additionally added carbon nanotubes, increasing the production cost.

[0007] CN111769266A discloses a silicon-based anode material, which comprises a silicon-based material; a carbon layer coated on the surface of the silicon-based material; a polymer layer coated on the surface of the carbon layer; and carbon nanotubes connected to the surface of the polymer layer through hydrogen bonds and / or covalent bonds. Although this silicon-based anode material can buffer the drastic volume expansion of the silicon anode material to a certain extent during charge and discharge processes, due to the insufficient binding force between the carbon nanotubes and the polymer layer as well as the overall anode material, it is prone to detachment during slurry preparation, electrode sheet processing, and battery cycling, unable to fully play its role, with low utilization rate of carbon nanotubes and unable to replace the additional carbon nanotubes added during the pulping process.

[0008] Therefore, developing a silicon-containing anode material with low volume expansion, good cycling performance, excellent capacity and conductivity, and low usage cost is an urgent problem to be solved in this field. Summary of the Invention

[0009] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a silicon-based anode material with an artificial SEI film, its preparation method and application. Through the design and mutual compounding of the silicon-based material and the carbon layer and conductive artificial SEI composite layer coated thereon, uniform and tight coating of the nano-conductive material is achieved, enabling the silicon-based anode material to have a significantly reduced volume expansion rate, excellent stability and cycling performance, while also having high capacity and excellent conductivity, high utilization rate of the nano-conductive material, good performance exertion, and greatly reducing the usage cost of the silicon-based anode material.

[0010] To achieve the purpose of this invention, the following technical solutions are adopted:

[0011] In the first aspect, the present invention provides a silicon-based anode material with an artificial SEI film, and the silicon-based anode material includes a silicon-based material and a carbon layer and a conductive artificial SEI composite layer provided on the silicon-based material, and the carbon layer is located between the silicon-based material and the conductive artificial SEI composite layer; the conductive artificial SEI composite layer is obtained by reacting a reactive precursor with a reactive conductive material.

[0012] The silicon-based anode material provided by the present invention has a three-layer structure, where the inner layer is a silicon-based material, the middle layer is a carbon layer, and the outer layer is a conductive artificial SEI composite layer; the silicon-based material in the inner layer plays a role in lithium storage and has an obvious high-capacity advantage; the carbon layer in the middle layer can enhance the overall conductivity of the silicon-based anode material and reduce the reaction between the electrolyte and the silicon-based material; the outer conductive artificial SEI composite layer is obtained by reacting a reactive precursor with a reactive conductive material, which includes two components, namely a polymer and a nano-conductive material, and the nano-conductive material and the polymer are combined in a chemical bond form, thereby effectively inhibiting the volume expansion of the silicon material and ensuring the electrical contact of the silicon-based material during the volume expansion and contraction process, significantly improving the cycling performance of the silicon-based anode material.

[0013] For the silicon-based anode material provided by the present invention, at least a part of the conductive material in the conductive artificial SEI composite layer is covered by the product after the reaction of the reactive precursor, that is, in the conductive artificial SEI composite layer, at least a part of the conductive material is covered by the polymer. Through the dual composite of physical form and chemical reaction between the polymer and the conductive material, a strong bond is formed between the conductive material and the polymer, and it is in-situ coated on the surface of the carbon layer, so that a strong and tight bond relationship is also formed between the conductive material and the carbon layer.

[0014] For the silicon-based anode material provided by the present invention, the conductive material in the conductive artificial SEI composite layer is closely attached to the surface of the carbon layer. The conductive material includes dot-shaped nano-conductive material, fibrous nano-conductive material or sheet-shaped nano-conductive material, and the dot-shaped nano-conductive material, fibrous nano-conductive material or sheet-shaped nano-conductive material is closely attached to the surface of the carbon layer. The "close attachment" means that the conductive material is in direct contact with the carbon layer, rather than in a free state without contact with the carbon layer, so as to maximize the effective coating of the conductive material and significantly reduce the volume expansion rate of the silicon-based material.

[0015] In the present invention, the conductive artificial SEI composite layer is obtained by the reaction of a reactive precursor and a reactive conductive material, and the conductive material is uniformly distributed on the surface of the silicon-based material (the silicon-based material provided with a carbon layer) without agglomeration. On the one hand, the conductive artificial SEI composite layer grows in-situ on the surface of the silicon material (including the surface carbon layer) in a network form, so that the nano-conductive material is tightly combined with the silicon-based material (and the carbon layer on its surface). On the other hand, the conductive artificial SEI composite layer has extremely strong adhesion to the intermediate carbon layer. During the production process of the negative electrode plate and the battery and during the operation of the battery, the conductive artificial SEI composite layer will not fall off and can be stably combined on the surface of the silicon-based anode material for a long time, thus playing the following advantages: (1) The surface-modified conductive material and polymer play a binding role on the silicon-based material, reducing the volume expansion of the negative electrode; (2) The introduction of some filamentous conductive materials ensures the electrical contact between the silicon-based anode material and other active materials (such as graphite materials) and the current collector, significantly improving the cycle performance of the silicon-based anode material; (3) The conductive artificial SEI composite layer can ensure the electrical contact during the expansion and contraction process of the silicon-based material, and good performance can be achieved without adding additional nano-conductive materials during the production process of the negative electrode plate and the battery, greatly reducing the use cost of the silicon-based anode material and at the same time improving the cycle performance of the battery.

[0016] Through the design of the three-layer structure of the silicon-based material, the carbon layer, and the conductive artificial SEI composite layer and the interaction between the layers, the uniform, tight, and stable coating of the nano-conductive material and the polymer is achieved, and the coating layer will not fall off, so that the silicon-based anode material has a significantly reduced volume expansion rate and significantly improved cycle performance. The silicon-based anode material provided by the present invention improves the cycle performance of the lithium-ion battery containing the same, reduces the manufacturing cost, and has broad application prospects.

[0017] The following are the preferred technical solutions of the present invention, but do not limit the technical solutions provided by the present invention. Through the following preferred technical solutions, the objectives and beneficial effects of the present invention can be better achieved.

[0018] Preferably, the D 50 particle size of the silicon-based anode material is 0.2 - 20.0 μm; for example, it can be 0.2 μm, 0.5 μm, 1.0 μm, 2.0 μm, 5.0 μm, 8.0 μm, 10.0 μm, 12.0 μm, 15.0 μm, or 18.0 μm, as well as the specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the above range.

[0019] Preferably, the specific surface area of the silicon-based anode material is 0.1 - 20.0 m 2 / g, for example, it can be 0.2 m 2 / g, 0.5 m 2 / g, 0.8 m 2 / g, 1.0 m 2 / g, 2.0 m 2 / g, 3.0 m 2 / g, 4.0 m 2 / g, 5.0 m 2 / g, 6.0 m 2 / g, 8.0 m 2 / g, 10.0 m 2 / g, 12.0 m 2 / g, 15.0 m 2 / g, or 18.0 m 2 / g, as well as the specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the above range.

[0020] Preferably, the powder resistivity of the silicon-based anode material is 0.5-15.0 Ω·cm, and can be, for example, 0.8 Ω·cm, 0.9 Ω·cm, 1.0 Ω·cm, 2.0 Ω·cm, 3.0 Ω·cm, 4.0 Ω·cm, 5.0 Ω·cm, 6.0 Ω·cm, 7.0 Ω·cm, 8.0 Ω·cm, 9.0 Ω·cm, 10.0 Ω·cm, 11.0 Ω·cm, 12.0 Ω·cm, 13.0 Ω·cm, 14.0 Ω·cm or 15.0 Ω·cm, as well as the specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the range.

[0021] Preferably, the silicon-based material includes any one or a combination of at least two of silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy.

[0022] Among them, the silicon oxide includes SiO x , where x < 2, and x can be, for example, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6 or 1.8, as well as the specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the range; preferably, the SiO x is silicon monoxide.

[0023] Preferably, the D 50 particle size of the silicon-based material is 0.2-20.0 μm, and can be, for example, 0.2 μm, 0.5 μm, 1.0 μm, 2.0 μm, 5.0 μm, 8.0 μm, 10.0 μm, 12.0 μm, 15.0 μm or 18.0 μm, as well as the specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the range.

[0024] Preferably, the specific surface area of the silicon-based material is 0.1-20.0 m 2 / g, and can be, for example, 0.2 m 2 / g, 0.5 m 2 / g, 0.8 m 2 / g, 1.0 m 2 / g, 2.0 m 2 / g, 3.0 m 2 / g, 4.0 m 2 / g, 5.0 m 2 / g, 6.0 m 2 / g, 8.0 m 2 / g, 10.0 m 2 / g, 12.0 m 2 / g, 15.0 m2 / g or 18.0 m 2 / g, and specific point values between the above point values. Due to space limitations and for the sake of brevity, the present invention does not exhaustively list the specific point values included in the said range.

[0025] Preferably, the thickness of the carbon layer is 1.0 - 30.0 nm, for example, it can be 2.0 nm, 3.0 nm, 4.0 nm, 5.0 nm, 6.0 nm, 8.0 nm, 10.0 nm, 12.0 nm, 15.0 nm, 18.0 nm, 20.0 nm, 22.0 nm, 25.0 nm or 28.0 nm, and specific point values between the above point values. Due to space limitations and for the sake of brevity, the present invention does not exhaustively list the specific point values included in the said range.

[0026] As a preferred technical solution of the present invention, the thickness of the carbon layer is 1 - 30 nm, which is located between the silicon-based material and the conductive artificial SEI composite layer, can improve the conductivity, and act together with the conductive artificial SEI composite layer to synergistically inhibit the volume expansion of the silicon-based material and improve its cycling performance. If the thickness of the carbon layer is too low, it is not conducive to the improvement of conductivity; if the thickness of the carbon layer is too large, the proportion of carbon material in the silicon-based anode material increases, thus losing the high-capacity advantage of the silicon-based material.

[0027] Preferably, based on the mass of the silicon-based material being 100%, the mass of the carbon layer is 0.01% - 10.00%, for example, it can be 0.02%, 0.05%, 0.08%, 0.10%, 0.20%, 0.50%, 0.80%, 1.00%, 2.00%, 3.00%, 4.00%, 5.00%, 6.00%, 7.00%, 8.00% or 9.00%, and specific point values between the above point values. Due to space limitations and for the sake of brevity, the present invention does not exhaustively list the specific point values included in the said range.

[0028] Preferably, based on the total mass of the silicon-based material and the carbon layer being 100%, the mass of the conductive artificial SEI composite layer is 0.01% - 15.00%, for example, it can be 0.02%, 0.10%, 0.80%, 1.50%, 2.00%, 2.50%, 3.00%, 4.00%, 5.00%, 6.00%, 7.00%, 8.00%, 9.00%, 10.00%, 12.00% or 14.00%, and specific point values between the above point values. Due to space limitations and for the sake of brevity, the present invention does not exhaustively list the specific point values included in the said range. Further preferably, the mass of the conductive artificial SEI composite layer is 0.01% - 5.00%, and within this range, a silicon anode material with more excellent comprehensive performance can be obtained.

[0029] Preferably, based on the total mass of the silicon-based material and the carbon layer being 100%, the mass of the precursor is 0.01% - 10.00%, for example, it can be 0.02%, 0.10%, 0.80%, 1.50%, 2.00%, 2.50%, 3.00%, 4.00%, 5.00%, 6.00%, 7.00%, 8.00% or 9.00%, as well as the specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the range. Further preferably, the mass of the precursor is 0.01% - 5.00%. Within this range, a silicon negative electrode material with more excellent comprehensive performance can be obtained, and the negative impact brought by the introduction of the polymer can be reduced.

[0030] As a preferred technical solution of the present invention, based on the total mass of the silicon-based material and the carbon layer being 100%, the mass of the conductive artificial SEI composite layer is 0.01% - 15%. It is obtained by the reaction of a reactive precursor and a reactive conductive material, including two components: a polymer and a nano conductive material. And the mass of the precursor is 0.01% - 10%. The formed polymer and nano conductive material are combined in a chemical bond form to form a stable polymer - nano conductive material composite layer, so that the nano conductive material uniformly and tightly wraps on the surface of the silicon-based material (and the carbon layer on its surface). If the mass of the precursor (polymer) is too low, it will affect the coating stability of the nano conductive material, resulting in its inability to continuously and stably play the role of inhibiting silicon expansion and conducting electrical contact, and affecting the cycle stability of the silicon-based negative electrode material; if the mass of the precursor (polymer) is too high, it will not only affect ion transport, but also relatively reduce the proportion of the silicon-based material in the silicon-based negative electrode material, resulting in capacity loss.

[0031] Preferably, the reactive precursor includes a double bond-containing monomer. Further preferably, it is any one or at least two combinations of a double bond-containing cyano monomer, a double bond-containing acidic monomer, a double bond-containing carboxylic acid ester monomer, a double bond-containing amide monomer, a double bond-containing hydroxyl monomer, an aromatic vinyl monomer, an aliphatic conjugated diene monomer, a fluorinated olefin monomer, and a vinyl azacyclic monomer.

[0032] Preferably, the double bond-containing cyano monomer is an α,β-unsaturated nitrile monomer, specifically, it can be selected from one or two combinations of acrylonitrile and methacrylonitrile.

[0033] Preferably, the mass percentage content of the double bond-containing cyano monomer in the double bond-containing monomer is ≤70%, preferably 0 - 40%, for example: 0, 1%, 2%, 5%, 8%, 10%, 15%, 20%, 25%, 30% or 35%, as well as the specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the range.

[0034] Preferably, the acidic monomer containing a double bond is selected from any one or a combination of at least two of carboxylic acid monomers containing a double bond, sulfonic acid monomers containing a double bond, and phosphoric acid monomers containing a double bond.

[0035] Preferably, the carboxylic acid monomer containing a double bond includes monocarboxylic acid, dicarboxylic acid, and their derivatives, etc., and specifically can be selected from any one or a combination of at least two of acrylic acid, methacrylic acid, crotonic acid, 2-ethylacrylic acid, isocrotonic acid, maleic acid, fumaric acid, itaconic acid, methylmaleic acid.

[0036] The sulfonic acid monomer containing a double bond is not particularly limited, and specifically can be selected from any one or a combination of at least two of vinylsulfonic acid, methylvinylsulfonic acid, (meth)allylsulfonic acid, styrenesulfonic acid, 2-sulfonic acid ethyl (meth)acrylate, 2-acrylamido-2-methylpropane sulfonic acid, 3-allyloxy-2-hydroxypropane sulfonic acid, 2-(N-acryloyl)amino-2-methyl-1,3-propane disulfonic acid.

[0037] The phosphoric acid monomer containing a double bond refers to a monomer having a -PO 3 H 2 group and a phosphoric acid group such as -PO(OH)(OR) group (R represents a hydrocarbon group), and specifically can be selected from any one or a combination of at least two of 2-(meth)acryloyloxyethyl phosphate, methyl-2-(meth)acryloyloxyethyl phosphate, ethyl-(meth)acryloyloxyethyl phosphate.

[0038] In addition, salts of the above various monomers can also be used as acidic group-containing monomers. Moreover, among the above acidic group-containing monomers, carboxylic acid group-containing monomers are preferably used, and further preferably the above monocarboxylic acid, and particularly preferably methacrylic acid or / and acrylic acid.

[0039] Preferably, the mass percentage content of the acidic monomer containing a double bond in the double bond-containing monomer ≤ 80%, preferably 0 - 70%, for example: 0, 1%, 5%, 10%, 20%, 30%, 40%, 45%, 60%, 65%, 70%, and specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the range.

[0040] The carboxylic acid ester monomer containing a double bond is preferably an alkyl acrylate or an alkyl methacrylate, and specifically may be selected from any one or a combination of at least two of methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate (butyl acrylate), isobutyl acrylate, tert-butyl acrylate, n-pentyl acrylate, isopentyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, 2-methoxyethyl acrylate, 2-ethoxyethyl acrylate, hexyl acrylate, nonyl acrylate, lauryl acrylate, stearyl acrylate, benzyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, n-pentyl methacrylate, isopentyl methacrylate, n-hexyl methacrylate, 2-ethylhexyl methacrylate, octyl methacrylate, isodecyl methacrylate, lauryl methacrylate, tridecyl methacrylate, stearyl methacrylate, benzyl methacrylate.

[0041] Preferably, the mass percentage content of the carboxylic acid ester monomer containing a double bond in the monomer containing a double bond is ≤ 50%, preferably 0 - 30%, such as: 0, 1%, 5%, 10%, 15%, 20%, 25%, 30%, and the specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the range.

[0042] The amide monomer containing a double bond is preferably an acrylamide monomer, and specifically may be selected from any one or a combination of at least two of acrylamide, methacrylamide, N-methoxymethyl methacrylamide, and N-methoxymethyl acrylamide. Among them, acrylamide and methacrylamide are preferred.

[0043] Preferably, the mass percentage content of the amide monomer containing a double bond in the monomer containing a double bond is ≤ 50%, preferably 0 - 30%, such as: 0, 1%, 5%, 10%, 15%, 20%, 25%, 30%, and the specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the range.

[0044] The hydroxyl monomer containing double bonds is preferably a hydroxyalkyl acrylate and an N-hydroxyacrylamide monomer, and specifically may be selected from any one or a combination of at least two of methyl hydroxyacrylate, methyl methacrylate hydroxyester, β-hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate, hydroxybutyl methacrylate, N-hydroxymethyl acrylamide, N-hydroxymethyl methyl acrylamide, N-hydroxyethyl acrylamide, and N-hydroxyethyl methyl acrylamide. Further preferably, it is hydroxyethyl methacrylate, β-hydroxyethyl acrylate, N-hydroxymethyl acrylamide, and N-hydroxyethyl acrylamide.

[0045] Preferably, the mass percentage content of the hydroxyl monomer containing double bonds in the double bond-containing monomer is ≤50%, preferably 0-30%. For example: 0, 1%, 5%, 10%, 15%, 20%, 25%, 30%, and specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the range.

[0046] The aromatic vinyl monomer is not particularly limited, and specifically may be selected from any one or a combination of at least two of styrene, α-methylstyrene, vinyltoluene, and divinylbenzene.

[0047] Preferably, the mass percentage content of the aromatic vinyl monomer in the double bond-containing monomer is ≤80%, and further preferably 0-60%. For example: 0, 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, and specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the range.

[0048] The aliphatic conjugated diene monomer is not particularly limited, including but not limited to 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, etc. These can be used alone or in combination of two or more in any ratio.

[0049] Preferably, the mass percentage content of the aliphatic conjugated diene monomer in the double bond-containing monomer is ≤80%, and further preferably 0-20%. For example: 0, 1%, 5%, 10%, 15%, 20%, and specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the range.

[0050] The fluorinated olefin monomer is not particularly limited, and specifically may be selected from vinylidene fluoride, tetrafluoroethylene, hexafluoropropylene, chlorotrifluoroethylene, fluoroethylene, perfluoroalkyl vinyl ether, etc. These can be used alone or in combination of two or more in any ratio.

[0051] Preferably, the mass percentage content of the fluorinated monomer in the double-bond-containing monomer is ≤80%, and more preferably 0-20%. For example: 0, 1%, 5%, 10%, 15%, 20%, and the specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the above range.

[0052] The vinyl heterocyclic monomer is preferably N-vinylpyrrolidone or vinylpyrrolidone.

[0053] Preferably, the mass percentage content of the vinyl heterocyclic monomer in the double-bond-containing monomer is ≤80%, and more preferably 0-20%. For example: 0, 1%, 5%, 10%, 15%, 20%, and the specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the above range.

[0054] The polymer in the conductive artificial SEI composite layer is copolymerized from the above-mentioned various double-bond-containing monomers.

[0055] As some technical solutions of the present invention, the double-bond-containing monomer includes any one or a combination of at least two of a double-bond-containing cyano monomer, a double-bond-containing carboxylic acid monomer, a double-bond-containing sulfonic acid monomer, a double-bond-containing carboxylic acid ester monomer, a double-bond-containing amide monomer, and a double-bond-containing hydroxyl monomer.

[0056] As some technical solutions of the present invention, the double-bond-containing monomer includes any one or a combination of at least two of a double-bond-containing carboxylic acid monomer, a double-bond-containing carboxylic acid ester monomer, a double-bond-containing amide monomer, a double-bond-containing hydroxyl monomer, and an aromatic vinyl monomer.

[0057] As some technical solutions of the present invention, the double-bond-containing monomer includes any one or a combination of at least two of an aromatic vinyl monomer, an aliphatic conjugated diene monomer, a fluorinated olefin monomer, a double-bond-containing acidic monomer, and an N-vinylpyrrolidone monomer.

[0058] As a preferred technical solution of the present invention, the double-bond-containing monomer includes a combination of an aromatic vinyl monomer and a second monomer; the second monomer includes any one or a combination of at least two of a double-bond-containing cyano monomer, a double-bond-containing amide monomer, a double-bond-containing carboxylic acid ester monomer, a double-bond-containing carboxylic acid monomer, and an N-vinylpyrrolidone monomer.

[0059] As a preferred technical solution of the present invention, the double-bond-containing monomer includes aromatic vinyl monomers, especially styrene monomers, so that the formed polymer contains styrene-based structural units. The benzene ring structure in the polymer side chain can undergo π-π interaction with the carbon layer on the silicon material surface, having a very strong adhesion ability to the surface carbon layer, further ensuring the coating stability and the cycling performance of the silicon-based anode material.

[0060] Preferably, the mass percentage content of styrene monomers in the double-bond-containing monomer ≤ 80%, for example, it can be 1%, 5%, 10%, 15%, 20%, 25%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70% or 75%, as well as specific point values between the above point values. Due to space limitations and for the sake of brevity, the present invention does not exhaustively list the specific point values included in the range. Further preferably, it is 1% - 60%, for example, 5% - 60%, 10% - 60%, 15% - 60%, 20% - 60%, 30% - 60%, 1% - 50%, 3% - 50%, 5% - 50%, 10% - 50%, etc.

[0061] Preferably, the double-bond-containing cyano monomer includes acrylonitrile and / or methacrylonitrile.

[0062] Preferably, the double-bond-containing amide monomer includes acrylamide and / or methacrylamide.

[0063] Preferably, the double-bond-containing carboxylic acid ester monomer includes acrylic acid alkyl esters and / or methacrylic acid alkyl esters, exemplarily including but not limited to: any one or a combination of at least two of methyl acrylate, methyl methacrylate, ethyl acrylate, 2-hydroxyethyl acrylate, ethyl methacrylate, 2-hydroxyethyl methacrylate, propyl acrylate, propyl methacrylate, butyl acrylate, and butyl methacrylate.

[0064] Preferably, the double-bond-containing carboxylic acid monomer includes acrylic acid and / or methacrylic acid.

[0065] Preferably, the mass percentage content of the second monomer in the double-bond-containing monomer ≤ 70%, for example, it can be 0.5%, 1%, 2%, 3%, 4%, 5%, 8%, 10%, 15%, 20%, 25%, 35%, 40%, 45%, 50%, 55%, 60%, 62%, 65% or 68%, as well as specific point values between the above point values. Due to space limitations and for the sake of brevity, the present invention does not exhaustively list the specific point values included in the range. Further preferably, it is 1% - 65%.

[0066] It should be noted that in addition to the monomers specifically listed in the present invention, other monomers commonly used in the art can also be used in the present invention. The present invention only lists one of the preferred solutions and should not be construed as a limitation on the double-bond-containing monomers of the present invention.

[0067] Preferably, based on the total mass of the silicon-based material and the carbon layer being 100%, the mass of the reactive conductive material is 0.01% - 10.00%. For example, it can be 0.02%, 0.05%, 0.08%, 0.10%, 0.50%, 0.80%, 1.00%, 2.00%, 3.00%, 4.00%, 5.00%, 6.00%, 7.00%, 8.00% or 9.00%, as well as the specific point values between the above point values. Due to space limitations and for the sake of brevity, the present invention does not exhaustively list the specific point values included in the above range.

[0068] Preferably, the reactive conductive material is a nano-conductive material with its surface modified by reactive functional groups.

[0069] Preferably, the reactive functional groups in the reactive conductive material are functional groups containing unsaturated double bonds.

[0070] Preferably, the reactive conductive material includes any one or a combination of at least two of the following conductive materials modified by reactive functional groups: conductive graphite, carbon black, Ketjen black, conductive carbon black Super P, nano-carbon fiber, single-walled carbon nanotube, multi-walled carbon nanotube, few-walled carbon nanotube, graphene.

[0071] Preferably, the particle sizes of the conductive graphite, carbon black, Ketjen black, and conductive carbon black Super P are each independently 10.0 - 1000.0 nm. For example, it can be 20.0 nm, 50.0 nm, 80.0 nm, 100.0 nm, 200.0 nm, 300.0 nm, 400.0 nm, 500.0 nm, 600.0 nm, 700.0 nm, 800.0 nm or 900.0 nm, as well as the specific point values between the above point values. Due to space limitations and for the sake of brevity, the present invention does not exhaustively list the specific point values included in the above range.

[0072] Preferably, the diameters of the nano-carbon fiber, single-walled carbon nanotube, multi-walled carbon nanotube, and few-walled carbon nanotube are each independently 1.0 - 60.0 nm. For example, it can be 2.0 nm, 5.0 nm, 8.0 nm, 10.0 nm, 15.0 nm, 20.0 nm, 25.0 nm, 30.0 nm, 35.0 nm, 40.0 nm, 45.0 nm, 50.0 nm or 55.0 nm, as well as the specific point values between the above point values. Due to space limitations and for the sake of brevity, the present invention does not exhaustively list the specific point values included in the above range.

[0073] Preferably, the lengths of the nano-carbon fibers, single-walled carbon nanotubes, multi-walled carbon nanotubes, and few-walled carbon nanotubes are each independently 0.1 - 80.0 μm. For example, they can be 0.5 μm, 1.0 μm, 2.0 μm, 5.0 μm, 8.0 μm, 10.0 μm, 20.0 μm, 30.0 μm, 40.0 μm, 50.0 μm, 60.0 μm, or 70.0 μm, as well as the specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the range.

[0074] Preferably, the specific surface area of the conductive material is 50 - 2000 m 2 / g. For example, it can be 80 m 2 / g, 100 m 2 / g, 200 m 2 / g, 400 m 2 / g, 500 m 2 / g, 600 m 2 / g, 800 m 2 / g, 1000 m 2 / g, 1200 m 2 / g, 1500 m 2 / g, or 1800 m 2 / g, as well as the specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the range.

[0075] As a preferred technical solution of the present invention, the conductive material includes carbon nanotubes. Thus, a silicon-based anode material is obtained. In the conductive artificial SEI composite layer, at least part of the carbon nanotubes are covered by the polymer. The polymer and the carbon nanotubes are combined through a double composite of physical form and chemical reaction, so that a strong bond is formed between the carbon nanotubes and the polymer, and it is in-situ coated on the surface of the carbon layer, so that a strong and tight bond relationship is also formed between the carbon nanotubes and the carbon layer. The carbon nanotubes are distributed in a filamentous form and are tightly attached to the surface of the carbon-coated silicon-based material, effectively restricting the expansion of the silicon-based material.

[0076] As a preferred technical solution of the present invention, the silicon-based anode material includes a silicon-based material, a carbon layer disposed on the silicon-based material, and a conductive artificial SEI composite layer. The carbon layer is located between the silicon-based material and the conductive artificial SEI composite layer; the conductive artificial SEI composite layer is a polymer-carbon nanotube composite layer, which is obtained by reacting a reactive precursor (preferably a double-bond-containing monomer) with a reactive conductive material (double-bond-modified carbon nanotubes).

[0077] Second aspect, the present invention provides a preparation method of the silicon-based anode material as described in the first aspect, and the preparation method includes:

[0078] (1) A carbon layer is provided on the silicon-based material to obtain a carbon-coated silicon-based material;

[0079] (2) The carbon-coated silicon-based material reacts with a reactive precursor and a reactive conductive material to obtain the silicon-based anode material.

[0080] In the preparation method of the silicon-based anode material provided by the present invention, the reactive precursor and the reactive conductive material are in-situ polymerized on the carbon-coated silicon-based material to form a polymer-nano conductive material composite layer, and the silicon-based anode material with a three-layer structure is obtained. The present invention combines the reactive conductive material with the in-situ reaction coating technology, so that the nano conductive material and the polymer network are bonded in a covalent bond manner, and at least part of the nano conductive material is covered by the polymer, and the formed conductive artificial SEI network tightly coats the surface of the silicon anode.

[0081] Since it is difficult for the nano conductive material itself to be dispersed in the solution, as a preferred technical solution of the present invention, the present invention provides an atomic layer deposition (ALD)-like technology, so that the nano conductive material and the polymer can be uniformly and tightly coated on the surface of the carbon-coated silicon-based material, the coating layer is stable, and the binding force is strong, and it will not fall off during the process of making the battery, so that the nano conductive material can continuously and stably play the role of inhibiting silicon expansion and ensuring electrical contact between the silicon-based anode material and other active materials (such as graphite material) and the current collector, and improving the cycle performance of the silicon-based anode material and the battery.

[0082] Preferably, the method for providing the carbon layer includes chemical vapor deposition (CVD, Chemical Vapor Deposition).

[0083] Preferably, the carbon source used in the chemical vapor deposition includes any one or a combination of at least two of acetylene, ethylene, methane, and ethane.

[0084] Preferably, the pressure of the chemical vapor deposition is 1-10 MPa, for example, it can be 1.5 MPa, 2 MPa, 2.5 MPa, 3 MPa, 3.5 MPa, 4 MPa, 4.5 MPa, 5 MPa, 5.5 MPa, 6 MPa, 6.5 MPa, 7 MPa, 7.5 MPa, 8 MPa, 8.5 MPa, 9 MPa or 9.5 MPa, as well as the specific point values between the above point values. Due to space limitations and for the sake of brevity, the present invention does not exhaustively list the specific point values included in the above range.

[0085] Preferably, the temperature of the chemical vapor deposition is 400 - 1000 °C, for example, it can be 420 °C, 450 °C, 480 °C, 500 °C, 520 °C, 550 °C, 580 °C, 600 °C, 620 °C, 650 °C, 680 °C, 700 °C, 750 °C, 800 °C, 850 °C, 900 °C, 950 °C or 980 °C, as well as the specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the range.

[0086] Preferably, the time of the chemical vapor deposition is 0.5 - 8 h, for example, it can be 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, 5 h, 5.5 h, 6 h, 6.5 h, 7 h or 7.5 h, as well as the specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the range.

[0087] In the present invention, the preparation method of the reactive conductive material can be carried out by any method known in the art. To better understand the present invention, the following preparation method is provided.

[0088] Preferably, the preparation method of the reactive conductive material includes: activating the conductive material in an acidic activation solution to obtain an activated conductive material; and subjecting the activated conductive material to condensation modification to obtain the reactive conductive material.

[0089] As a preferred technical solution of the present invention, first, the conductive material (nano - conductive material) is activated in an acidic activation solution to introduce hydroxyl groups at the defect sites on the surface of the nano - conductive material to obtain an activated conductive material; the activated conductive material undergoes a condensation reaction with an unsaturated amine compound under catalytic conditions to obtain the reactive conductive material, the surface functional groups (unsaturated bonds) of which can chemically react with the precursor to form chemical bonds, and at least part of the nano - conductive material is covered by the polymer, and the formed polymer - conductive material network tightly coats the surface of the silicon negative electrode. Since the nano - conductive material and the polymer network are bonded by covalent bonds, the nano - conductive material can be stably coated on the surface of the silicon negative electrode without falling off.

[0090] Preferably, the acidic activation solution includes an aqueous solution of an acidic substance, which contains a large amount of hydroxyl groups.

[0091] Preferably, the acidic substance includes any one or a combination of at least two of nitric acid, hydrochloric acid, and sulfuric acid, and further preferably nitric acid and / or hydrochloric acid.

[0092] Preferably, the concentration of the acidic substance in the acidic activation solution is ≥ 30%, for example, it can be 32%, 35%, 38%, 40%, 42%, 45%, 48%, 50%, 52%, 55%, 58%, 60%, 62%, 65%, 68% or 70%, as well as the specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the range. Further preferably, it is ≥ 40%.

[0093] Preferably, the activation treatment is carried out under the conditions of ultrasonic oscillation and / or stirring (such as mechanical stirring).

[0094] Preferably, the temperature of the activation treatment is 40 - 80 °C, for example, it can be 42 °C, 45 °C, 48 °C, 50 °C, 52 °C, 55 °C, 58 °C, 60 °C, 62 °C, 65 °C, 68 °C, 70 °C, 72 °C, 75 °C or 78 °C, as well as the specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the range.

[0095] Preferably, the time of the activation treatment is 1 - 8 h, for example, it can be 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, 5 h, 5.5 h, 6 h, 6.5 h, 7 h or 7.5 h, as well as the specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the range.

[0096] Preferably, the unsaturated amine compound is not particularly limited. For example, it can be CH 2 =CH-(CH 2 )n-CH 2 -NH 2 (n ≥ 1, for example, it can be 2, 3, 4, 5, 6, etc.). As a specific example, 3 - butene - 1 - amine can be cited.

[0097] Preferably, the mass ratio of the activated conductive material to the unsaturated amine compound is (1 - 50):1. For example, it can be 2:1, 5:1, 10:1, 12:1, 15:1, 18:1, 20:1, 22:1, 25:1, 28:1, 30:1, 32:1, 35:1, 38:1, 40:1 or 45:1, etc. Further preferably, it is (10 - 40):1.

[0098] Preferably, the condensation modification is carried out in the presence of a catalyst. The catalyst includes any one or at least two combinations of 1 - ethyl - (3 - dimethylaminopropyl) carbodiimide hydrochloride / 1 - hydroxybenzotriazole, dicyclohexylcarbodiimide, 4 - dimethylaminopyridine, 4 - (4,6 - dimethoxytriazin - 2 - yl) - 4 - methylmorpholine hydrochloride.

[0099] Preferably, based on the mass of the unsaturated amine compound being 100%, the mass of the catalyst is 0-10%, for example, it can be 0.1%, 0.5%, 0.8%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8% or 9%, etc.

[0100] Preferably, after the activation treatment, it includes the steps of solid-liquid separation, collecting the solid phase, washing and drying to obtain the activated conductive material.

[0101] Preferably, the reaction (condensation reaction) of the activated conductive material and the unsaturated amine compound is carried out in the presence of a solvent.

[0102] Preferably, the solvent includes any one or a combination of at least two of water, aromatic hydrocarbon solvents, ether solvents, sulfone solvents, and halogenated alkane solvents.

[0103] Preferably, the solvent includes any one or a combination of at least two of water, toluene, tetrahydrofuran, and dimethyl sulfoxide. The solvent is preferably water.

[0104] Preferably, the reaction (condensation reaction) of the activated conductive material and the unsaturated amine compound is carried out under the conditions of ultrasonic oscillation and / or stirring (such as mechanical stirring).

[0105] Preferably, the temperature of the reaction (condensation reaction) of the activated conductive material and the unsaturated amine compound is 10-45°C. For example, it can be 12°C, 15°C, 18°C, 20°C, 22°C, 25°C, 28°C, 30°C, 32°C, 35°C, 38°C, 40°C, 42°C or 44°C, as well as the specific point values between the above point values. Due to space limitations and for the sake of brevity, the present invention does not exhaustively list the specific point values included in the above range.

[0106] Preferably, the reaction time of the activated conductive material and the unsaturated amine compound (condensation reaction) is 1-8 h. For example, it can be 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, 5 h, 5.5 h, 6 h, 6.5 h, 7 h or 7.5 h, as well as the specific point values between the above point values. Due to space limitations and for the sake of brevity, the present invention does not exhaustively list the specific point values included in the above range.

[0107] Preferably, in step (2), based on the mass of the carbon-coated silicon-based material being 100%, the mass of the reactive precursor is 0.01%-5%. For example, it can be 0.02%, 0.05%, 0.08%, 0.1%, 0.2%, 0.5%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4% or 4.5%, as well as the specific point values between the above point values. Due to space limitations and for the sake of brevity, the present invention does not exhaustively list the specific point values included in the above range.

[0108] Preferably, in step (2), based on the mass of the carbon-coated silicon-based material being 100%, the mass of the reactive conductive material is 0.01% - 2%. For example, it can be 0.02%, 0.05%, 0.08%, 0.1%, 0.2%, 0.5%, 0.8%, 1%, 1.2%, 1.5% or 1.8%, as well as the specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the range.

[0109] Preferably, the reaction in step (2) can be carried out under thermally initiated conditions.

[0110] Preferably, the reaction is carried out in the presence of an initiator, and the initiator is a free radical initiator. Further preferably, it is any one or a combination of at least two of persulfates, azo initiators, peroxides, and redox initiators.

[0111] Preferably, the persulfates include any one or a combination of at least two of ammonium persulfate, sodium persulfate, and potassium persulfate.

[0112] Preferably, the azo initiators include any one or a combination of at least two of azodiisobutyronitrile, azodiisobutyronitrile, and azodiamidinium dihydrochloride.

[0113] Preferably, the peroxides include any one or a combination of at least two of benzoyl peroxide, lauroyl peroxide, and tert-butyl hydroperoxide.

[0114] Preferably, the redox initiators include any one or a combination of at least two of tert-butyl hydroperoxide - sodium metabisulfite, hydrogen peroxide - ferrous chloride, and cumene hydroperoxide - tetraethylenimine.

[0115] Preferably, based on the mass of the reactive precursor being 100%, the mass of the initiator used in the reaction ≤ 2%. For example, it can be 0, 0.1%, 0.2%, 0.5%, 0.8%, 1%, 1.2%, 1.5% or 1.8%, as well as the specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the range.

[0116] Preferably, the reaction in step (2) is carried out in the presence of a solvent.

[0117] Preferably, the solvent includes water and / or organic solvents, and further preferably water.

[0118] Preferably, the reaction in step (2) can be carried out in an atmosphere of air, nitrogen, or argon, and further preferably nitrogen.

[0119] Preferably, the temperature of the reaction in step (2) is 50-200 °C, for example, it can be 52 °C, 55 °C, 58 °C, 60 °C, 62 °C, 65 °C, 68 °C, 70 °C, 72 °C, 75 °C, 78 °C, 80 °C, 90 °C, 100 °C, 110 °C, 120 °C, 130 °C, 140 °C, 150 °C, 160 °C, 180 °C or 190 °C, as well as the specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the said range.

[0120] Preferably, the time of the reaction in step (2) is 0.5-24 h, for example, it can be 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 8 h, 10 h, 12 h, 14 h, 16 h, 18 h, 20 h, 22 h or 24 h, as well as the specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the said range.

[0121] Preferably, the reaction method in step (2) includes uniform coating by pseudo atomic layer deposition (ALD). The method of uniform coating by pseudo atomic layer deposition includes: reacting a carbon-coated silicon-based material, a reactive precursor, and a reactive conductive material in the presence of a solvent to obtain a dispersion; drying the dispersion to obtain the silicon-based anode material.

[0122] More preferably, the method of uniform coating by pseudo atomic layer deposition includes: placing a carbon-coated silicon-based material, a reactive precursor, a reactive conductive material, and a solvent in a reaction device for reaction, and obtaining a dispersion under high shear force conditions; the dispersion is dried by a drying device. During the drying process, the dispersion is dispersed into micro-droplets by high-speed rotary shearing or high-speed air flow impact, and dried under heat flow conditions to obtain the silicon-based anode material.

[0123] Preferably, the reaction device includes a shear dispersion device capable of obtaining a dispersion under high shear force conditions; the shear dispersion device is more preferably any one or a combination of at least two of a sand mill, a ball mill, a high-speed disperser, a double planetary mixer, and a homogenizer.

[0124] Preferably, the solvent includes water and / or an organic solvent.

[0125] Preferably, the reaction is carried out in the presence of a surfactant.

[0126] Preferably, the surfactant includes any one or a combination of at least two of sodium dodecylbenzenesulfonate, stearic acid, oleic acid, lauric acid, polyethylene glycol, polyvinyl alcohol, 15-crown-5, 18-crown-6, and tetrabutylammonium bromide, and more preferably sodium dodecylbenzenesulfonate.

[0127] Preferably, based on the mass of the carbon-coated silicon-based material being 100%, the mass of the surfactant is 0.01% - 5.00%. For example, it can be 0.05%, 0.10%, 0.20%, 0.30%, 0.40%, 0.50%, 0.60%, 0.80%, 1.00%, 1.50%, 2.00%, 2.50%, 3.00%, 3.50%, 4.00% or 4.50%, as well as the specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the scope.

[0128] As a preferred technical solution of the present invention, the characteristics of the atomic layer deposition (ALD) uniform coating technology are as follows: Active substances such as carbon-coated silicon-based materials, reactive precursors, and reactive conductive materials, water, and / or organic solvents are added to a strong shear force dispersion device and uniformly dispersed with the assistance of a surfactant. After the dispersion is completed or the chemical reaction is completed, the dispersion is instantaneously dried through a drying device. During the drying process, the dispersion is dispersed into micro-droplets by high-speed rotary shearing or high-speed air flow impact. Under the action of heat flow, the micro-droplets are dried in a short time to obtain the silicon-based anode material uniformly coated with a conductive artificial SEI composite layer.

[0129] Preferably, the shear dispersion device uses a high-speed disperser with a rotation speed of 400 - 4000 rpm (revolutions per minute). For example, it can be 500 rpm, 600 rpm, 800 rpm, 1000 rpm, 1200 rpm, 1500 rpm, 1600 rpm, 1800 rpm, 2000 rpm, 2200 rpm, 2500 rpm, 2800 rpm, 3000 rpm, 3200 rpm, 3500 rpm or 3800 rpm, as well as the specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the scope.

[0130] Preferably, the dispersion time of the high-speed disperser is 1 - 6 h. For example, it can be 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, 5 h or 5.5 h, as well as the specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the scope.

[0131] Preferably, the drying device includes any one or a combination of at least two of a spray drying device, a fluidized bed, a flash air dryer, a rotary evaporation flash dryer, and a rotary kiln. Further preferably, it is a spray drying device.

[0132] Preferably, the drying method includes: The dispersion is dispersed into micro-droplets by high-speed rotary shearing or high-speed air flow impact and dried under heat flow conditions to obtain the silicon-based anode material.

[0133] Preferably, the drying temperature is 50 - 400°C, for example, it can be 80°C, 100°C, 120°C, 150°C, 180°C, 200°C, 220°C, 250°C, 280°C, 300°C, 320°C, 350°C or 380°C, as well as the specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the above range.

[0134] In a third aspect, the present invention provides a preparation device for a silicon-based anode material. The preparation device includes a first reaction device, a second reaction device, and a drying device connected in sequence; the silicon-based anode material as described in the first aspect is prepared by the preparation device.

[0135] Preferably, the first reaction device includes a chemical vapor deposition device; carbon coating is achieved on the silicon-based material in the chemical vapor deposition device to obtain a carbon-coated silicon-based material.

[0136] Preferably, the second reaction device includes a shearing and dispersing device, and more preferably any one or a combination of at least two of a sand mill, a ball mill, a high-speed disperser, a double planetary mixer, and a homogenizer.

[0137] Preferably, the drying device includes any one or a combination of at least two of a spray drying device, a fluidized bed, a flash dryer, a rotary evaporation flash dryer, and a rotary kiln.

[0138] In a fourth aspect, the present invention provides a negative electrode material composition. The negative electrode material composition includes a combination of an active material, a binder, and a conductive material, and the active material includes the silicon-based anode material as described in the first aspect.

[0139] In order to ensure the performance of silicon materials, during the production process of existing silicon-containing negative electrode sheets (negative electrode material compositions, negative electrode slurries), a certain amount of nano-conductive materials (such as carbon nanotubes) are added to ensure the electrical contact between silicon, graphite, and the current collector; if carbon nanotubes are not introduced, the cycling performance of silicon materials will seriously decline, but the introduction of carbon nanotubes increases the preparation difficulty of negative electrode slurries on the one hand and also raises the production cost of batteries on the other hand. The silicon-based anode material provided by the present invention can be used for the preparation of negative electrode material compositions, negative electrode slurries, and negative electrode sheets, and other carbon nanotubes do not need to be added, enabling the silicon-based material to achieve better performance.

[0140] Preferably, the active material includes the silicon-based anode material and optionally a carbon material, and more preferably a combination of the silicon-based anode material and a carbon material.

[0141] Preferably, the carbon material includes any one or a combination of at least two of graphite, carbon black, carbon fiber, mesophase carbon microspheres, and petroleum coke, and further preferably graphite.

[0142] Preferably, the graphite is natural graphite and / or artificial graphite.

[0143] Preferably, the mass percentage content of the silicon-based anode material in the active material is 1-80%, for example, it can be 5%, 10%, 20%, 30%, 40%, 50%, 60% or 70%, as well as specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the above range.

[0144] Preferably, the mass percentage content of the active material in the anode material composition is 80-98%, for example, it can be 82%, 85%, 88%, 90%, 92%, 95% or 97%, as well as specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the above range.

[0145] Preferably, the binder includes any one or a combination of at least two of acrylic polymers, polyacrylonitrile, and styrene-based copolymers.

[0146] Preferably, the styrene-based copolymer includes styrene-butadiene rubber (SBR).

[0147] Preferably, the mass percentage content of the binder in the anode material composition is 0.1-12%, for example, it can be 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or 11%, as well as specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the above range.

[0148] Preferably, the conductive agent includes any one or a combination of at least two of carbon black, graphite, and carbon fiber.

[0149] Preferably, the mass percentage content of the conductive agent in the anode material composition is 0.1-10%, for example, it can be 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8% or 9%, as well as specific point values between the above point values. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the above range.

[0150] Preferably, the anode material composition further includes a thickening agent.

[0151] Preferably, the thickening agent includes sodium carboxymethyl cellulose (CMC).

[0152] Preferably, the mass percentage content of the thickener in the negative electrode material composition is ≤5%, and can be, for example, 0, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4% or 4.5%, as well as specific point values between the above point values. Due to space limitations and for the sake of simplicity, the specific point values included in the scope of the present invention are not exhaustively listed herein.

[0153] In a fifth aspect, the present invention provides a negative electrode plate, which includes a current collector and a coating disposed on the current collector, and the material of the coating includes the negative electrode material composition as described in the fourth aspect.

[0154] Preferably, the method for preparing the negative electrode plate includes: uniformly mixing the negative electrode material composition with a solvent to obtain a negative electrode slurry; coating the negative electrode slurry on the current collector and drying to obtain the negative electrode plate.

[0155] Preferably, a rolling step is further included after drying.

[0156] In a sixth aspect, the present invention provides an electrochemical energy storage device, which includes at least one of the silicon-based negative electrode material as described in the first aspect, the negative electrode material composition as described in the fourth aspect, and the negative electrode plate as described in the fifth aspect.

[0157] Preferably, the electrochemical energy storage device includes any one of a lithium-ion battery, a sodium-ion battery, a supercapacitor, and a solid-state battery, and a lithium-ion battery is further preferred.

[0158] Compared with the prior art, the present invention has the following beneficial effects:

[0159] (1) In the silicon-based negative electrode material provided by the present invention, through the design of the three-layer structure of the silicon-based material, the carbon layer, and the conductive artificial SEI composite layer and the interaction between the layers, the uniform, tight, and stable coating of the nano-conductive material is achieved, and the coating layer will not fall off, so that the silicon-based negative electrode material has a significantly reduced volume expansion rate, and at the same time has high capacity and excellent electrical conductivity, improving the cycle performance of the lithium-ion battery containing it. The silicon-based negative electrode material is used for the production of negative electrode plates and batteries, and there is no need to add carbon nanotubes, greatly reducing the use cost of the silicon-based negative electrode material.

[0160] (2) In the preparation method of the silicon-based anode material provided by the present invention, the reactive precursor and the reactive conductive material undergo an in-situ reaction on the silicon-based material coated with a carbon layer to obtain a silicon-based anode material with a three-layer structure. The present invention combines the reactive conductive material with the in-situ reaction coating technology, enabling the nano-conductive material and the polymer network to be bonded in a covalent bond manner, and at least part of the nano-conductive material is covered by the polymer, so that the nano-conductive material can be tightly coated on the surface of the silicon-based anode material. The coating layer is stable and has a strong binding force, and will not fall off during the battery manufacturing process, so that the nano-conductive material can continuously and stably play the role of suppressing silicon expansion and ensuring electrical contact between the silicon-based anode material and other active materials (such as graphite materials) and the current collector, improving the cycle performance of the silicon-based anode material and the battery.

[0161] (3) By optimizing the precursor and the polymer in the present invention, the polymer contains a planar benzene ring structure. The benzene ring structure of the polymer side chain can have a π-π interaction with the carbon layer on the surface of the silicon material, and has a very strong adhesion ability to the surface carbon layer, further improving the coating stability and the cycle performance of the silicon-based anode material.

[0162] (4) The present invention preferably adopts a pseudo atomic layer deposition (ALD) uniform coating technology. By dispersing the reactive precursor, the reactive conductive material and the carbon-coated silicon-based material uniformly in the solvent under the assistance of a surfactant and the action of strong shear force, the problem of difficult dispersion of the nano-conductive material and the silicon-based material is solved; after instant drying, the conductive artificial SEI composite layer containing the polymer and the nano-conductive material can uniformly wrap on the surface of the silicon-based material. The pseudo-ALD technology significantly improves the uniformity and integrity of the coating on the surface of the silicon-based material, and improves the performance of the silicon material. Description of the Drawings

[0163] Figure 1 Scanning electron microscope image of the silicon-based anode material provided in Example 1;

[0164] Figure 2 Scanning electron microscope image of the negative electrode sheet made of the silicon-based anode material provided in Example 1;

[0165] Figure 3 Scanning electron microscope image of the negative electrode sheet made of the silicon-based anode material provided in Comparative Example 1. Detailed Embodiments

[0166] The technical solutions of the present invention will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations to the present invention.

[0167] In this application, "conductive material" and "nano-conductive material" have the same meaning and refer to the same thing.

[0168] As used herein, the terms "comprising", "including", "having", "containing" or any other variation thereof are intended to cover a non-exclusive inclusion. For example, a composition, step, method, article or apparatus containing the listed elements is not necessarily limited to those elements, but may also include other elements not expressly listed or elements inherent to such composition, step, method, article or apparatus.

[0169] "Optionally", "alternatively", "any one" means that the matter or event described thereafter may or may not occur, and the description includes the case where the event occurs and the case where the event does not occur.

[0170] The indefinite articles "a" and "an" before the elements or components of the present invention do not limit the quantity requirements (i.e., the number of occurrences) of the elements or components. Therefore, "a" or "an" should be interpreted as including one or at least one, and the singular form of the element or component also includes the plural form, unless the quantity clearly refers only to the singular form.

[0171] The descriptions of the terms "one embodiment", "some embodiments", "exemplarily", "specific examples" or "some examples" etc. described in the present invention mean that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this document, the schematic representations of the above terms are not necessarily directed to the same embodiment or example.

[0172] Moreover, the technical features involved in the various embodiments of the present invention can be combined with each other as long as they do not conflict with each other.

[0173] In the following specific embodiments of the present invention, the silicon-based materials, nano-conductive materials, monomers, initiators, solvents, etc. used are all commercially available products. Specifically, the nano-conductive material is a single-walled carbon nanotube with a tube diameter of 1-3 nm and a length of 3-30 μm; the silicon-carbon composite is SiC with a median particle size of 7-12 μm, purchased from Zhejiang Carbon One New Energy.

[0174] Example 1

[0175] Silicon-based anode material and its preparation:

[0176] A silicon-based anode material, which comprises a silicon-carbon composite, and a carbon layer and a conductive artificial SEI composite layer sequentially disposed on the silicon-carbon composite, and the conductive artificial SEI composite layer is obtained by the reaction of styrene, acrylic acid and double-bond modified carbon nanotubes. The preparation method of the silicon-based anode material is as follows:

[0177] (1) Preparation of double-bond modified carbon nanotubes: Add 30 g of single-walled carbon nanotubes into 200 mL of nitric acid solution with a concentration of 40%, ultrasonically vibrate at 45 °C for 2 h, filter, collect the powder, wash it with water until the filtrate is neutral, and dry it at 100 °C for 3 h to obtain acidified carbon nanotubes; Add the acidified carbon nanotubes into 200 mL of water, ultrasonically vibrate for 0.5 h to form a dispersion, stir at 25 °C and slowly add 1 g of 3-butene-1-amine dropwise to the dispersion, add 0.08 g of 4-(4,6-dimethoxytriazin-2-yl)-4-methylmorpholine hydrochloride, and continue stirring and reacting for 4 h; Filter, collect the powder, wash the powder with 100 mL of water, and then dry it at 60 °C for 3 h to obtain double-bond modified carbon nanotubes.

[0178] (2) Coating carbon layer by CVD method: Place 200 g of silicon-carbon composite in a deposition furnace at 500 °C, under argon protection, introduce acetylene gas at 500 °C with a flow rate of 10 L / min and a furnace pressure of 6 MPa. After continuously introducing gas for 4 h, cool to room temperature to form a carbon layer on the silicon-carbon composite and obtain an intermediate.

[0179] (3) Preparation of silicon-based anode material: Take 0.6 g of the double-bond modified carbon nanotubes obtained in step (1), 100 g of the intermediate obtained in step (2), 0.8 g of styrene, 1.2 g of acrylic acid, and 0.5 g of sodium dodecylbenzenesulfonate, and place them in 400 mL of deionized water. Disperse with a high-speed disperser at 3000 revolutions per minute for 3 hours. Reduce the rotation speed to 500 revolutions per minute, introduce nitrogen gas, heat to 70 °C, and continue stirring for 0.5 h. Add 0.02 g of ammonium persulfate to the system and continue stirring and reacting at 70 °C for 6 h. After cooling to room temperature, atomize the dispersion into micro-droplets by a high-speed centrifugal atomizer at 12000 revolutions per minute, and instantaneously dry with hot air at 200 °C. Collect the powder, screen it, and demagnetize it to obtain the silicon-based anode material.

[0180] Anode electrode and its preparation:

[0181] Mix the silicon-based anode material provided in this example and artificial graphite in a mass ratio of 1:1 to obtain the active material; Mix the active material, thickener sodium carboxymethyl cellulose (CMC), conductive agent Super P, and binder styrene-butadiene rubber (SBR) in a mass ratio of 88:2:3:7, add the solvent deionized water, and stir in a vacuum mixer until the system is homogeneous to obtain the anode slurry; Uniformly coat the anode slurry on the anode current collector copper foil, transfer it to a vacuum drying oven for drying, and then roll and punch to obtain small round pieces, which are the anode electrodes.

[0182] Preparation of battery:

[0183] Using a lithium metal sheet as the counter electrode, Celgard 2400 as the separator, and injecting the electrolyte, a button cell was assembled.

[0184] Example 2

[0185] A silicon-based anode material includes a silicon-carbon composite, and a carbon layer and a conductive artificial SEI composite layer sequentially disposed on the silicon-carbon composite. The conductive artificial SEI composite layer is obtained by reacting styrene, acrylic acid, and double-bond modified carbon nanotubes. The difference between the preparation method of the silicon-based anode material of this example and that of Example 1 is only that the amount of double-bond modified carbon nanotubes in step (3) is 0.2 g, and the types, amounts, preparation steps, and process parameters of other materials are the same as those in Example 1, obtaining the silicon-based anode material.

[0186] The silicon-based anode material provided in this example was mixed with artificial graphite at a mass ratio of 1:1 to obtain the active material, and the negative electrode sheet was prepared and the button cell was assembled in the same manner as in Example 1.

[0187] Example 3

[0188] A silicon-based anode material includes a silicon-carbon composite, and a carbon layer and a conductive artificial SEI composite layer sequentially disposed on the silicon-carbon composite. The conductive artificial SEI composite layer is obtained by reacting styrene, acrylic acid, and double-bond modified carbon nanotubes. The difference between the preparation method of the silicon-based anode material of this example and that of Example 1 is only that the amount of double-bond modified carbon nanotubes in step (3) is 1.0 g, and the types, amounts, preparation steps, and process parameters of other materials are the same as those in Example 1, obtaining the silicon-based anode material.

[0189] The silicon-based anode material provided in this example was mixed with artificial graphite at a mass ratio of 1:1 to obtain the active material, and the negative electrode sheet was prepared and the button cell was assembled in the same manner as in Example 1.

[0190] Example 4

[0191] A silicon-based anode material includes a silicon-carbon composite, and a carbon layer and a conductive artificial SEI composite layer sequentially disposed on the silicon-carbon composite. The conductive artificial SEI composite layer is obtained by reacting styrene, acrylic acid, and double-bond modified carbon nanotubes. The difference between the preparation method of the silicon-based anode material of this example and that of Example 1 is only that in step (3), 0.4 g of styrene and 0.6 g of acrylic acid are used, and the types, amounts, preparation steps, and process parameters of other materials are the same as those in Example 1, obtaining the silicon-based anode material.

[0192] The silicon-based anode material provided in this example was mixed with artificial graphite at a mass ratio of 1:1 to obtain the active material, and the negative electrode sheet was prepared and the button cell was assembled in the same manner as in Example 1.

[0193] Example 5

[0194] A silicon-based anode material, which comprises a silicon-carbon composite, and a carbon layer and a conductive artificial SEI composite layer sequentially arranged on the silicon-carbon composite. The conductive artificial SEI composite layer is obtained by the reaction of styrene, acrylic acid and double-bond modified carbon nanotubes. The preparation method of the silicon-based anode material is only different from that of Example 1 in that in step (3), 1.6 g of styrene and 2.4 g of acrylic acid are used, and the types, amounts, preparation steps and process parameters of other materials are the same as those in Example 1, and the silicon-based anode material is obtained.

[0195] Mix the silicon-based anode material provided in this example with artificial graphite in a mass ratio of 1:1 to obtain the active material, and prepare the negative electrode sheet and assemble the button battery in the same manner as in Example 1.

[0196] Example 6

[0197] A silicon-based anode material, which comprises a silicon-carbon composite, and a carbon layer and a conductive artificial SEI composite layer sequentially arranged on the silicon-carbon composite. The conductive artificial SEI composite layer is obtained by the reaction of styrene, acrylic acid and double-bond modified carbon nanotubes. The preparation method of the silicon-based anode material is only different from that of Example 1 in that in step (3), 0.2 g of styrene and 1.8 g of acrylic acid are used, and the types, amounts, preparation steps and process parameters of other materials are the same as those in Example 1, and the silicon-based anode material is obtained.

[0198] Mix the silicon-based anode material provided in this example with artificial graphite in a mass ratio of 1:1 to obtain the active material, and prepare the negative electrode sheet and assemble the button battery in the same manner as in Example 1.

[0199] Example 7

[0200] A silicon-based anode material, which is different from that of Example 1 in that the ALD-like coating technology is not used. The preparation method includes: obtaining double-bond modified carbon nanotubes and an intermediate (i.e., a silicon-carbon composite coated with a surface carbon layer) in the same manner as in Example 1; putting 0.6 g of double-bond modified carbon nanotubes, 0.8 g of styrene, 1.2 g of acrylic acid, 0.5 g of sodium dodecylbenzenesulfonate and 100 g of the intermediate into 400 mL of deionized water. Stir at 500 revolutions per minute, introduce nitrogen, heat to 70 °C, and continue to stir for 0.5 h. Add 0.02 g of ammonium persulfate to the system, and continue to stir and react at 70 °C for 6 h. Cool down to room temperature, dry in a blast drying oven at 120 °C for 24 hours to remove the residual moisture, crush, screen and demagnetize to obtain the silicon-based anode material.

[0201] Mix the silicon-based anode material provided in this example with artificial graphite in a mass ratio of 1:1 to obtain the active material, and prepare the negative electrode sheet and assemble the button battery in the same manner as in Example 1.

[0202] Comparative Example 1

[0203] Silicon-based anode material and its preparation:

[0204] A silicon-based anode material includes a silicon-carbon composite and a carbon layer disposed on the silicon-carbon composite. Its preparation method includes: placing 200 g of the silicon-carbon composite in a deposition furnace at 500 °C, and forming a carbon layer on the silicon-carbon composite by the same method as in step (2) of Example 1 to obtain the silicon-based anode material.

[0205] Negative electrode sheet and its preparation:

[0206] Mix the silicon-based anode material provided in this comparative example with artificial graphite in a mass ratio of 1:1 to obtain the active material; mix the active material, single-walled carbon nanotubes, thickening agent CMC, conductive agent Super P, and binder SBR in a mass ratio of 87:1:2:3:7, add the solvent deionized water, and stir in a vacuum mixer until the system is homogeneous to obtain the negative electrode slurry; uniformly coat the negative electrode slurry on the negative electrode current collector copper foil, transfer it to a vacuum drying oven for drying, and then roll and punch to obtain small round pieces, which are the negative electrode sheets.

[0207] Preparation of battery:

[0208] Using a lithium metal sheet as the counter electrode, assemble a button battery by the same method as in Example 1.

[0209] Comparative Example 2

[0210] A silicon-based anode material includes a silicon-carbon composite and a carbon layer disposed on the silicon-carbon composite. Its preparation method includes: placing 200 g of the silicon-carbon composite in a deposition furnace at 500 °C, and forming a carbon layer on the silicon-carbon composite by the same method as in step (2) of Example 1 to obtain the silicon-based anode material.

[0211] Mix the silicon-based anode material provided in this comparative example with artificial graphite in a mass ratio of 1:1 to obtain the active material, and prepare the negative electrode sheet and assemble the button battery by the same method as in Example 1.

[0212] Comparative Example 3

[0213] A silicon-based anode material includes a silicon-carbon composite and a carbon layer and a conductive artificial SEI composite layer sequentially disposed on the silicon-carbon composite. The conductive artificial SEI composite layer is prepared from styrene, acrylic acid, and carbon nanotubes. The preparation method of the silicon-based anode material is as follows:

[0214] (1) Coating the carbon layer by CVD method: Place 200 g of silicon-carbon composite in a deposition furnace at 500 °C, under argon protection. Pass acetylene gas at 500 °C, with a flow rate of 10 L / min, the pressure in the furnace is 6 MPa. After continuous gas injection for 4 h, cool to room temperature, thereby forming a carbon layer on the silicon-carbon composite to obtain an intermediate;

[0215] (2) Preparation of silicon-based anode material: Take 0.6 g of carbon nanotubes, 100 g of the intermediate obtained in step (1), 0.8 g of styrene, 1.2 g of acrylic acid, and 0.5 g of sodium dodecylbenzenesulfonate, and place them in 400 mL of deionized water. Disperse with a high-speed disperser, disperse for 3 h at 3000 revolutions per minute. Reduce the rotation speed to 500 revolutions per minute, pass nitrogen gas, heat to 70 °C, and continue stirring for 0.5 h. Add 0.02 g of ammonium persulfate to the system, and continue stirring and reacting at 70 °C for 6 h. After cooling to room temperature, atomize the dispersion into micro-droplets by a high-speed centrifugal atomizer at 12000 revolutions per minute, and instantaneously dry with hot air at 200 °C, collect the powder, sieve, and demagnetize to obtain the silicon-based anode material.

[0216] Mix the silicon-based anode material provided in this comparative example with artificial graphite at a mass ratio of 1:1 to obtain the active material, and prepare the anode electrode sheet and assemble the button cell by the same method as in Example 1.

[0217] Comparative Example 4

[0218] A silicon-based anode material, which includes a silicon-carbon composite and a carbon layer and a conductive artificial SEI composite layer sequentially arranged on the silicon-carbon composite. The conductive artificial SEI composite layer is prepared from a styrene-acrylic acid copolymer and double-bond modified carbon nanotubes. The preparation method of the silicon-based anode material is as follows:

[0219] (1) Preparation of styrene-acrylic acid copolymer:

[0220] Place 4 g of styrene and 6 g of acrylic acid in 1500 mL of deionized water, pass nitrogen gas, stir at room temperature for 0.5 h, heat to 70 °C, and continue stirring for 0.5 h. Add 0.1 g of ammonium persulfate to the system, and continue stirring and reacting at 70 °C for 6 h. Evacuate for 0.5 h, restore to normal pressure, cool to room temperature, to obtain an aqueous solution of styrene-acrylic acid copolymer, and test the solid content to be 7.5%.

[0221] (2) Preparation of silicon-based anode material:

[0222] The double-bond modified carbon nanotubes and the intermediate were obtained by the same method as in Example 1. 0.6 g of the double-bond modified carbon nanotubes, 100 g of the intermediate, 0.5 g of sodium dodecylbenzenesulfonate, and 26.7 g of the prepared styrene-acrylic copolymer aqueous solution (containing 2 g of the polymer) were placed in 400 mL of deionized water, dispersed with a high-speed disperser, dispersed for 3 hours at 3000 revolutions per minute, the rotation speed was reduced to 500 revolutions per minute, and stirred at 70 °C for 6 h. After cooling to room temperature, the dispersion was atomized into micro-droplets by a high-speed centrifugal atomizer at 12000 revolutions per minute, instantaneously dried by hot air at 200 °C, and the powder was collected, sieved, and demagnetized to obtain the silicon-based anode material.

[0223] The silicon-based anode material provided in this comparative example was mixed with artificial graphite at a mass ratio of 1:1 to obtain the active material, and the negative electrode sheet was prepared and the button cell was assembled by the same method as in Example 1.

[0224] Comparative Example 5

[0225] A silicon-based anode material, which includes a silicon-carbon composite, a carbon layer and a conductive artificial SEI composite layer sequentially arranged on the silicon-carbon composite, and the conductive artificial SEI composite layer is prepared from styrene, acrylic acid and double-bond modified carbon nanotubes. The preparation method of the silicon-based anode material is as follows:

[0226] The double-bond modified carbon nanotubes and the intermediate (i.e., the silicon-carbon composite coated with a surface carbon layer) were obtained by the same method as in Example 1; then 0.6 g of the double-bond modified carbon nanotubes, 0.8 g of styrene, 1.2 g of acrylic acid, and 0.5 g of sodium dodecylbenzenesulfonate were placed in 400 mL of deionized water. Dispersed with a high-speed disperser, dispersed for 3 hours at 3000 revolutions per minute. The rotation speed was decreased to 500 revolutions per minute, nitrogen was introduced, heated to 70 °C, and continued to stir for 0.5 h. 0.02 g of ammonium persulfate was added to the system, and the reaction was continued to stir at 70 °C for 6 h. Then 100 g of the intermediate was added to the system, stirred for 1 h, cooled to room temperature, the dispersion was atomized into micro-droplets by a high-speed centrifugal atomizer at 12000 revolutions per minute, instantaneously dried by hot air at 200 °C, and the powder was collected, sieved, and demagnetized to obtain the silicon-based anode material.

[0227] The silicon-based anode material provided in this comparative example was mixed with artificial graphite at a mass ratio of 1:1 to obtain the active material, and the negative electrode sheet was prepared and the button cell was assembled by the same method as in Example 1.

[0228] Comparative Example 6

[0229] A silicon-based anode material, which is different from that in Example 1 in that no carbon layer is provided, that is, the silicon-based anode material includes a silicon-carbon composite and a conductive artificial SEI composite layer disposed thereon, and the conductive artificial SEI composite layer is prepared from styrene, acrylic acid, and double-bond modified carbon nanotubes. The preparation method of the silicon-based anode material is different from that in Example 1 only in that step (2) is not carried out, and the intermediate used in step (3) is replaced with an equal mass of silicon-carbon composite, and the types, dosages, preparation steps, and process parameters of other materials are the same as those in Example 1, to obtain the silicon-based anode material.

[0230] Mix the silicon-based anode material provided in this comparative example with artificial graphite at a mass ratio of 1:1 to obtain the active material, and prepare the negative electrode sheet and assemble the button cell by the same method as in Example 1.

[0231] Performance test:

[0232] (1) Basic performance test of the silicon-based anode material

[0233] Use a scanning tunneling electron microscope to test the surface morphology of the silicon-based anode material. The morphology of the silicon-based anode material provided in Example 1 is as Figure 1 shown. The filamentous carbon nanotubes are completely integrated on the silicon surface, and the carbon nanotubes are tightly attached to the surface of the carbon-coated silicon-based anode material in a network form.

[0234] Use a Malvern laser particle size analyzer to test the median particle size (D 50 particle size) of the silicon-based anode material. The test results are shown in Table 1 in detail.

[0235] Use a powder resistance tester to test the powder resistance of the silicon-based anode material. The test results are shown in Table 1 in detail.

[0236] (2) Morphology test of the negative electrode sheet

[0237] Use a scanning tunneling electron microscope to test the surface morphology of the negative electrode sheet. Among them, the scanning electron microscope image of the negative electrode sheet made of the silicon-based anode material provided in Example 1 is as Figure 2 shown. The filamentous carbon nanotubes are completely integrated on the silicon surface, and the carbon nanotubes are tightly and stably coated on the surface of the silicon-based anode material in a network form. There is no carbon nanotube distribution on the graphite surface, so that the carbon nanotubes can effectively play the role of suppressing the volume expansion of silicon and ensure the electrical contact of the silicon-based material during the volume expansion and contraction process.

[0238] The scanning electron microscope image of the negative electrode sheet made of the silicon-based anode material provided in Comparative Example 1 is as Figure 3 shown. The filamentous carbon nanotubes are evenly distributed on the surfaces of graphite and silicon, which not only affects the performance of the carbon nanotubes, but also requires more carbon nanotubes, resulting in waste and increased costs.

[0239] (2) Performance Test of the Battery

[0240] Initial charge-discharge regime: 0.1C - 0.02C / 0.1C, voltage range 0.005V - 1.5V, to obtain the initial lithium extraction capacity of the battery. Charge-discharge regime for 2 - 30 weeks of cycling: 0.2C - 0.02C / 0.2C, voltage range 0.005V - 1.5V, and the battery was cycled for 30 weeks. After the cycling test, the capacity retention rate was calculated; the button cell was disassembled, the thickness of the negative electrode sheet under full charge was measured, and the negative electrode full charge swelling rate was calculated;

[0241] Capacity retention rate after 30 weeks of cycling = lithium extraction capacity in the 30th week of cycling / lithium extraction capacity in the 1st week × 100%, swelling of the electrode sheet after 10 weeks = (thickness of the electrode sheet after 10 weeks of cycling - initial thickness of the electrode sheet) / initial thickness of the electrode sheet × 100%;

[0242] The test results are shown in Table 1:

[0243] Table 1

[0244]

[0245]

[0246] According to the test results in Table 1, the silicon-based anode material provided by the present invention includes a three-layer structure of a silicon-based material, a carbon layer, and a conductive artificial SEI composite layer. By combining a reactive conductive material (reaction functional group modified carbon nanotubes) with an in-situ polymerization coating technique, the carbon nanotubes can be uniformly and tightly coated on the surface of the silicon anode, without falling off during the production of the negative electrode sheet and the battery, and can effectively inhibit the volume expansion of the silicon-based material, improving the cycling performance of the battery. At the same time, the introduction of the polymer and nano-conductive material composite layer does not significantly increase the powder resistivity of the silicon anode material, causing adverse effects on the material.

[0247] As can be seen from Comparative Example 1, based on the surface carbon-coated silicon-carbon material, under the condition of adding 1% carbon nanotubes to the anode material composition, the capacity retention rate of the battery after 30 weeks of cycling is 91.1%. As can be seen from Examples 1-6, when the silicon-based anode material is used to prepare the anode electrode sheet, without adding any additional carbon nanotubes, the capacity retention rate of the battery still reaches 91.2%-94.5% after 30 weeks of cycling, indicating that the introduction of the conductive artificial SEI composite layer in the present invention achieves an effect superior to that of adding carbon nanotubes, can more effectively inhibit volume expansion, and makes the cycling performance of the battery better. The mechanism is that in the solution of Comparative Example 1 using additional carbon nanotubes, most of the carbon nanotubes are distributed on the surface of graphite, and only a small part of the carbon nanotubes adhere to the silicon surface; because carbon nanotubes can only play a role on the silicon surface, the distribution mode of carbon nanotubes in Comparative Example 1 causes a large amount of waste. In the silicon-based anode materials of Examples 1-6 of the present invention, the carbon nanotubes are all concentrated on the surface of the silicon-based material, maximizing the role of the carbon nanotubes. Compared with Comparative Example 1, the total amount of carbon nanotubes in Examples 1-5 is reduced by more than 50%, greatly reducing the battery manufacturing cost, and achieving a more significant effect of suppressing expansion and improving cycling performance.

[0248] As can be seen from Example 1 and Examples 2 and 3, as the carbon nanotube content of the conductive artificial SEI composite layer increases, the capacity retention rate of the battery after 30 weeks of cycling increases accordingly. After reaching a certain level, continuing to increase the carbon nanotube content, the performance does not change significantly.

[0249] As can be seen from Example 1 and Examples 4 and 5, too much or too little of the polymer part of the conductive artificial SEI composite layer will affect the performance of the material. Too little polymer is not conducive to the stability of the coating layer, while too much coating will hinder ion transport and affect the capacity of the silicon material.

[0250] As can be seen from Example 1 and Example 6, the structural unit based on styrene in the polymer plays a key role. Reducing the proportion of styrene will affect the stability of the coating layer, the cycling performance and volume expansion of the silicon material. The mechanism is that the interaction between the benzene ring of the polymer side chain and the carbon layer increases the binding force between the coating layer and the intermediate carbon layer.

[0251] As can be seen from Example 1 and Example 7, the ALD-like uniform coating technology of the present invention is a more preferred solution. The products prepared without using this technology have relatively large expansion and a decrease in cycling performance. This is due to the decrease in the uniformity of the surface conductive artificial SEI composite layer coating of the products prepared without using this technology.

[0252] From the comparison of Example 1, Comparative Example 1 and Comparative Example 2, it can be seen that carbon nanotubes are crucial for the performance of silicon-based anode materials. Whether adding carbon nanotubes externally during battery fabrication or integrating carbon nanotubes on the surface of silicon materials in the form of a conductive artificial SEI composite layer coating, the cycling performance of the silicon-carbon anode can be significantly improved. Compared with the solution of adding carbon nanotubes externally in Comparative Example 1, the silicon-based anode material designed in the present invention containing a conductive artificial SEI composite layer can achieve more excellent effects of suppressing expansion and improving cycling performance while reducing the amount of carbon nanotubes used and saving costs.

[0253] From the comparison of Example 1, Comparative Example 3, Comparative Example 4 and Comparative Example 5, it can be seen that both the modification of double bond functional groups on the surface of carbon nanotubes and in-situ polymerization are essential. The double bonds introduced by the surface modification of carbon nanotubes endow it with reactivity, enabling it to combine with the polymer in the form of chemical bonds. If the carbon nanotubes are not modified with functional groups, their stability on the surface of the silicon anode is poor and they are prone to falling off, and the improvement of the cycling performance of the silicon material fails to reach the expected effect. If the in-situ polymerization method is not adopted and the carbon nanotubes and the polymer are directly mixed and then coated on the surface of the silicon-based material, the stability of the coating layer is also poor and the cycling performance of the silicon-based anode material is not good. If the polymer grows on the surface of the carbon nanotubes and no chemical bond is formed between the polymer and the carbon nanotubes, or the in-situ polymerization is not adopted but it is directly wrapped on the surface of the silicon carbon, the stability of the coating layer is poor and it is prone to falling off, and the expected effect cannot be achieved.

[0254] From Example 1 and Comparative Example 6, it can be seen that the presence of the intermediate carbon layer plays a crucial role in the silicon-based anode material provided by the present invention; if the carbon layer is not provided, the cycling performance of the silicon anode decreases significantly and the swelling of the electrode sheet increases.

[0255] The above results show that the silicon-based anode material designed in the present invention with a surface-modified conductive artificial SEI composite layer can inhibit the full-charge swelling of the silicon material, weaken the pulverization of the negative electrode sheet after multiple cycles, and the cycling performance of the battery using the said silicon-based anode material will be greatly improved. Compared with ordinary anode materials, the silicon-based anode material containing a conductive artificial SEI composite layer provided by the present invention has lower volume expansion and higher cycling capacity retention rate; at the same time, it can integrate carbon nanotubes on the surface of the silicon anode without adding carbon nanotubes externally, greatly reducing the amount of carbon nanotubes used; the preparation method is simple, with less energy consumption, low cost, no environmental protection pressure, and is convenient for large-scale production.

[0256] The applicant declares that the present invention illustrates the silicon-based anode material and its preparation method and application through the above-mentioned embodiments, but the present invention is not limited to the above process steps, that is, it does not mean that the present invention must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvement to the present invention, the equivalent substitution of the raw materials selected for the present invention, the addition of auxiliary components, the selection of specific methods, etc., all fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A silicon-based negative electrode material, characterized in that: The silicon-based negative electrode material includes a silicon-based material and a carbon layer and a conductive artificial SEI composite layer arranged on the silicon-based material, wherein the carbon layer is located between the silicon-based material and the conductive artificial SEI composite layer; the conductive artificial SEI composite layer is obtained by reacting a reactive precursor with a reactive conductive material.

2. The silicon-based negative electrode material according to claim 1, characterized in that: The silicon-based negative electrode material meets at least one of the following conditions: (1) The conductive material in the conductive artificial SEI composite layer is at least partially covered by the product of the reaction of the reactive precursor; (2) The conductive material in the conductive artificial SEI composite layer is tightly attached to the surface of the carbon layer.

3. The silicon-based negative electrode material according to claim 1 or 2, characterized in that: The silicon-based negative electrode material meets at least one of the following conditions: (1) D of the silicon-based negative electrode material 50 Particle size: 0.2-20.0μm; (2) The specific surface area of ​​the silicon-based negative electrode material is 0.1-20.0 m 2 / g; (3) The powder resistivity of the silicon-based negative electrode material is 0.5-15.0 Ω·cm.

4. The silicon-based negative electrode material according to any one of claims 1 to 3, characterized in that: The silicon-based material includes any one of silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy, or a combination of at least two thereof; Preferably, D of the silicon-based material 50 Particle size: 0.2-20.0μm; Preferably, the specific surface area of ​​the silicon-based material is 0.1-20.0 m 2 / g.

5. The silicon-based negative electrode material according to any one of claims 1 to 4, characterized in that: The thickness of the carbon layer is 1.0-30.0 nm; Preferably, based on the mass of the silicon-based material being 100%, the mass of the carbon layer is 0.01%-10.00%; Preferably, based on the total mass of the silicon-based material and the carbon layer being 100%, the mass of the conductive artificial SEI composite layer is 0.01%-15.00%; Preferably, based on the total mass of the silicon-based material and the carbon layer being 100%, the mass of the reactive precursor is 0.01%-10.00%; Preferably, the reactive precursor comprises a double bond-containing monomer, and the double bond-containing monomer is further preferably any one or a combination of at least two of a double bond-containing cyano monomer, a double bond-containing acidic monomer, a double bond-containing carboxylate monomer, a double bond-containing amide monomer, a double bond-containing hydroxyl monomer, an aromatic vinyl monomer, an aliphatic conjugated diene monomer, a fluorine-containing olefin monomer, and a vinyl nitrogen heterocyclic monomer; Preferably, the mass percentage of the aromatic vinyl monomer in the double bond-containing monomer is ≤80%, more preferably 30%-60%; Preferably, based on the total mass of the silicon-based material and the carbon layer being 100%, the mass of the reactive conductive material is 0.01%-10.00%; Preferably, the reactive conductive material comprises any one or a combination of at least two of the following conductive materials modified with reactive functional groups: conductive graphite, carbon black, Ketjen black, conductive carbon black Super P, nanocarbon fiber, single-walled carbon nanotube, multi-walled carbon nanotube, oligo-walled carbon nanotube, graphene; Preferably, the particle sizes of the conductive graphite, carbon black, Ketjen black, and conductive carbon black Super P are independently 10.0-1000.0 nm; Preferably, the diameters of the nano-carbon fibers, single-walled carbon nanotubes, multi-walled carbon nanotubes, and oligo-walled carbon nanotubes are each independently 1.0-60.0 nm; Preferably, the lengths of the nano-carbon fibers, single-walled carbon nanotubes, multi-walled carbon nanotubes, and oligo-walled carbon nanotubes are each independently 0.1-80.0 μm; Preferably, the specific surface area of ​​the conductive material is 50-2000m 2 / g.

6. A method for preparing a silicon-based negative electrode material according to any one of claims 1 to 5, characterized in that: The preparation method comprises: (1) providing a carbon layer on a silicon-based material to obtain a carbon-coated silicon-based material; (2) The carbon-coated silicon-based material reacts with a reactive precursor and a reactive conductive material to obtain the silicon-based negative electrode material.

7. The preparation method according to claim 6, characterized in that: The method of providing the carbon layer includes chemical vapor deposition; Preferably, the method for preparing the reactive conductive material comprises: subjecting the conductive material to an activation treatment in an acidic activation solution to obtain an activated conductive material; and subjecting the activated conductive material to condensation modification to obtain a reactive conductive material.

8. The preparation method according to claim 6 or 7, characterized in that: The reaction in step (2) is carried out under thermal initiation conditions; Preferably, based on the mass of the reactive precursor being 100%, the mass of the reaction initiator is ≤ 2%; Preferably, the initiator is a free radical initiator, and more preferably any one or a combination of at least two of persulfate, azo initiator, peroxide, and redox initiator; Preferably, the reaction temperature in step (2) is 50-200°C. Preferably, the reaction time in step (2) is 0.5-24h; Preferably, the reaction method in step (2) includes uniform coating by atomic layer deposition, and the uniform coating by atomic layer deposition includes: reacting a carbon-coated silicon-based material, a reactive precursor, and a reactive conductive material in the presence of a solvent to obtain a dispersion; drying the dispersion to obtain the silicon-based negative electrode material; Preferably, the solvent comprises water and / or an organic solvent; Preferably, the reaction is carried out in the presence of a surfactant; Preferably, the surfactant includes any one or a combination of at least two of sodium dodecylbenzene sulfonate, stearic acid, oleic acid, lauric acid, polyethylene glycol, polyvinyl alcohol, 15-crown-5, 18-crown-6, and tetrabutylammonium bromide; Preferably, based on the mass of the carbon-coated silicon-based material being 100%, the mass of the surfactant is 0.01%-5.00%; Preferably, the drying method comprises: the dispersion liquid is dispersed into micro droplets by high-speed rotary shearing or high-speed airflow impact, and dried under heat flow conditions to obtain the silicon-based negative electrode material; Preferably, the drying temperature is 50-400°C.

9. A device for preparing a silicon-based negative electrode material, characterized in that: The preparation device comprises a first reaction device, a second reaction device and a drying device connected in sequence; the silicon-based negative electrode material according to any one of claims 1 to 5 is prepared by the preparation device; Preferably, the first reaction device comprises a chemical vapor deposition device; Preferably, the second reaction device comprises a shearing and dispersing device, and more preferably any one of a sand mill, a ball mill, a high-speed disperser, a double planetary mixer, and a homogenizer, or a combination of at least two thereof; Preferably, the drying device comprises any one of a spray drying device, a fluidized bed, an airflow flash dryer, a rotary flash dryer, and a rotary kiln, or a combination of at least two of them.

10. A negative electrode material composition, characterized in that: The negative electrode material composition comprises a combination of an active material, a binder and a conductive material, and the active material comprises the silicon-based negative electrode material according to any one of claims 1 to 5.

11. A negative electrode plate, characterized in that: The negative electrode plate comprises a current collector and a coating disposed on the current collector, and the material of the coating comprises the negative electrode material composition as claimed in claim 10.

12. An electrochemical energy storage device, characterized in that: The electrochemical energy storage device comprises at least one of the silicon-based negative electrode material according to any one of claims 1 to 5, the negative electrode material composition according to claim 10, and the negative electrode plate according to claim 11; Preferably, the electrochemical energy storage device includes any one of a lithium-ion battery, a sodium-ion battery, a supercapacitor, and a solid-state battery.

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