A nitrogen-sulfur co-doped high-magnification silicon-carbon negative electrode material, a preparation method and application thereof

Abstract

The application relates to a nitrogen-sulfur co-doped high-rate silicon-carbon negative electrode material and a preparation method and application thereof. The high-rate silicon-carbon negative electrode material comprises silicon-carbon composite particles and a carbon coating layer coated on the outer surface of the silicon-carbon particles. The silicon-carbon composite particles comprise a porous carbon matrix, nitrogen and sulfur doped in the porous carbon matrix, and nano-silicon particles uniformly deposited in the pores of the porous carbon matrix. The sulfur and the carbon of the porous carbon matrix form one or more chemical bonds of C-S-C bonds, C=S bonds and C-SO x -C bonds; the nitrogen and the carbon of the porous carbon matrix react to generate one or more compounds of pyrrolic nitrogen, pyridine nitrogen and graphite nitrogen; the high-rate silicon-carbon negative electrode material is used in a lithium ion battery, and in a cycle process, the C-S-C bonds, C=S bonds or C-SO x -C bonds form a transmission channel of lithium ions, and the pyrrolic nitrogen, pyridine nitrogen and graphite nitrogen improve the conductivity of the battery, thereby improving the rate performance of the battery.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, and in particular to a nitrogen-sulfur co-doped high-rate silicon-carbon anode material, its preparation method, and its application. Background Technology

[0002] Currently, when preparing silicon-carbon anode materials, chemical vapor deposition is often used to directly deposit silicon on a porous carbon matrix, resulting in poor overall conductivity and poor rate performance of the material.

[0003] In existing technologies, nitrogen and sulfur elements are doped onto porous carbon matrices to improve the overall conductivity of materials. Nitrogen and sulfur elements are mostly doped using hydrothermal or in-situ methods. In-situ doping involves selecting materials rich in nitrogen and sulfur heteroatoms as carbon precursors, and retaining nitrogen and sulfur heteroatoms through carbonization to achieve the doping purpose. However, hydrothermal methods are inefficient and costly, and it is difficult to precisely control the quality, distribution position, and uniformity of the doped elements using hydrothermal and in-situ doping methods, thus limiting the improvement in the conductivity and rate performance of the material.

[0004] For example, Chinese invention patent CN112670479A (published on April 16, 2021) discloses a sulfur and nitrogen co-doped coaxial core-shell silicon-carbon anode material, its preparation method, and a lithium-ion battery. The method involves mixing silicon oxide-coated carbon nanotubes with a reducing agent and calcining them in an inert atmosphere to remove impurities, thereby obtaining a precursor. Subsequently, the precursor is dissolved in a solvent with thiourea and subjected to a hydrothermal reaction to obtain the sulfur and nitrogen co-doped coaxial core-shell silicon-carbon material. This invention patent uses a hydrothermal method to dope nitrogen and sulfur elements, which is inefficient and not conducive to industrial application. The structural uniformity of the material cannot be guaranteed.

[0005] Chinese invention patent CN116885144A (published on October 13, 2023) discloses a silicon-carbon composite material for lithium-ion battery anode materials and its preparation method. The method involves fixing sulfonated polyaniline onto the surface of hollow silicon spheres to form polyaniline-coated hollow silicon spheres. Potassium hydroxide is used as a pore-forming agent, and the mixture is ground and mixed with the polyaniline-coated hollow silicon spheres. Then, high-temperature carbonization is performed to carbonize the polyaniline into amorphous porous carbon with a porous structure. During carbonization, sulfur from the sulfonic acid groups and nitrogen from the polyaniline structure are incorporated into the porous carbon, resulting in a core-shell type silicon-carbon composite material with amorphous nitrogen and sulfur co-doped porous carbon coating silicon. Although this invention patent achieves in-situ doping of nitrogen and sulfur, the distribution of the doped nitrogen and sulfur in the material is scattered, failing to guarantee point-to-point contact with silicon, thus limiting the improvement in silicon lithium insertion / extraction efficiency. Summary of the Invention

[0006] The purpose of this invention is to address the problems existing in the prior art by providing a nitrogen-sulfur co-doped high-rate silicon-carbon anode material, its preparation method, and its application.

[0007] This invention achieves regulation of the dopant content by adjusting the mass ratio of the dopant element to the porous carbon matrix; the dopant element is adsorbed by the porous structure of the porous carbon matrix, thereby making the dopant element more uniformly distributed inside and on the surface of the matrix pore structure; and the decomposition and deposition of the dopant element can be promoted by appropriately extending the reaction temperature and reaction time, while promoting the uniform distribution and stabilization of the dopant element.

[0008] To achieve the above objectives, in a first aspect, embodiments of the present invention provide a nitrogen-sulfur co-doped high-rate silicon-carbon anode material, the high-rate silicon-carbon anode material comprising: silicon-carbon composite particles, and a carbon coating layer covering the outer surface of the silicon-carbon particles;

[0009] The silicon-carbon composite particles include: a porous carbon matrix, nitrogen and sulfur doped in the porous carbon matrix, and nano-silicon particles uniformly deposited in the pores of the porous carbon matrix.

[0010] The sulfur forms CSC bonds, C=S bonds, and C-SO bonds with the carbon in the porous carbon matrix. x One or more of the -C bonds, where 0 < x ≤ 2;

[0011] The nitrogen reacts with the carbon in the porous carbon matrix to generate one or more compounds selected from pyrrole nitrogen, pyridine nitrogen, and graphitic nitrogen.

[0012] The high-rate silicon-carbon anode material is used in lithium-ion batteries. During the cycling process of the lithium-ion battery, the CSC bond, C=S bond, or C-SO bond... x -C bonds form the transport channels for lithium ions.

[0013] Preferably, the sulfur reacts with carbon in the porous carbon matrix to generate thiophene and its derivatives;

[0014] The mass percentage of sulfur in the total mass of the high-rate silicon-carbon anode material is 2% to 3%.

[0015] The mass percentage of nitrogen in the total mass of the high-rate silicon-carbon anode material is 3% to 5%.

[0016] The mass of the nano-silicon particles accounts for 48% to 52% of the total mass of the high-rate silicon-carbon anode material.

[0017] Preferably, the average particle size D of the porous carbon matrix is... 50 Between 10μm and 12μm;

[0018] The specific surface area of ​​the porous carbon matrix is ​​1800 m². 2 / g~2000m 2 / g;

[0019] The average pore size of the porous carbon matrix is ​​between 2.0 nm and 2.8 nm.

[0020] The porous carbon matrix has a pore volume of 0.8 cm³. 3 / g~1.0cm 3 / g;

[0021] The porous carbon matrix contains 65% to 75% micropores.

[0022] Preferably, the average particle size D of the high-rate silicon-carbon anode material is... 50 Between 10μm and 12μm;

[0023] The specific surface area of ​​the high-rate silicon-carbon anode material is 1.0 m². 2 / g~3.0m 2 Between / g.

[0024] In a second aspect, embodiments of the present invention provide a method for preparing the high-rate silicon-carbon anode material described in the first aspect above, the method comprising:

[0025] Step S1: After uniformly mixing porous carbon, nitrogen source, and sulfur source in a certain proportion, the mixture is placed in a coating furnace and subjected to high-temperature heat treatment under a protective atmosphere. After cooling to room temperature, the material is discharged to obtain nitrogen-sulfur co-doped porous carbon material. The sulfur source, during the high-temperature heat treatment, forms a solution that wets the porous carbon matrix or diffuses as vapor into the surface and pores of the porous carbon matrix, causing the sulfur in the sulfur source to form CSC bonds, C=S bonds, and C-SO bonds with the carbon. x One or more of the -C bonds; the nitrogen-containing gas obtained from the decomposition of the nitrogen source is adsorbed by the pores of the porous carbon matrix, causing the nitrogen from the nitrogen source to react with the carbon of the porous carbon matrix to generate one or more compounds of pyrrole nitrogen, pyridine nitrogen, and graphitic nitrogen;

[0026] Step S2: The nitrogen-sulfur co-doped porous carbon material is placed in a vapor deposition furnace. Under a protective atmosphere, the vapor deposition furnace is heated to 450°C to 600°C. A mixture of carrier gas and silicon source gas is introduced and kept at this temperature for 2 to 5 hours. This allows the silicon element decomposed from the silicon source gas to be deposited in the pores of the nitrogen-sulfur co-doped porous carbon material and grow into nano-silicon particles. Then, only the carrier gas is introduced and the temperature is maintained for another 0.5 to 1 hour. After cooling, the precursor material is obtained.

[0027] Step S3: Carbon coating treatment is performed on the precursor material to form a carbon coating layer on the outer surface of the precursor material, thereby obtaining a high-rate silicon-carbon anode material.

[0028] Preferably, in step S1, the nitrogen source includes one or more of urea, ammonium nitrate, or ammonium sulfate;

[0029] The sulfur source includes one or more of elemental sulfur, thiourea, or ammonium sulfate.

[0030] The average particle size D of the porous carbon matrix 50 The porous carbon matrix has a surface area between 10 μm and 12 μm and a specific surface area of ​​1800 m². 2 / g~2000m 2 / g; the average pore size of the porous carbon matrix is ​​between 2.0 nm and 2.8 nm, and the pore volume is 0.8 cm³. 3 / g~1.0cm 3 / g;

[0031] The porous carbon matrix contains 65% to 75% micropores.

[0032] The mass ratio of the porous carbon, nitrogen, and sulfur sources is 75–85:8–12:3–8;

[0033] The protective atmosphere includes: nitrogen atmosphere and / or argon atmosphere;

[0034] The high-temperature heat treatment involves heating to 300℃ to 600℃ at a heating rate of 1℃ / min to 5℃ / min, and holding at that temperature for 2 to 5 hours.

[0035] The rotation speed of the coating furnace is 0.25 revolutions / min to 1 revolution / min;

[0036] The nitrogen-containing gas includes one or more of NH3, NO, NO2, and N2O.

[0037] Preferably, in step S2, the protective atmosphere includes: a nitrogen atmosphere and / or an argon atmosphere;

[0038] The carrier gas includes: nitrogen and / or argon;

[0039] The silicon source gas includes one or more of the following: silane, disilane, and dichlorosilane;

[0040] The volumetric flow rate ratio of the carrier gas to the silicon source gas in the mixed gas is 3:1 to 1:1;

[0041] The flow rate of the mixed gas is 20 L / min to 30 L / min.

[0042] Preferably, the carbon coating process in step S3 is a gas phase coating, specifically including: heating the gas phase deposition furnace to 500℃~600℃, introducing a mixture of carrier gas and carbon source gas, holding it at that temperature for 2 hours~6 hours, so that a carbon coating layer is formed on the outer surface of the precursor material, cooling it to room temperature, and obtaining a high-ratio silicon-carbon anode material after breaking it down, sieving and demagnetizing it.

[0043] The carrier gas includes nitrogen and / or argon.

[0044] The carbon source gas includes one or more of methane, acetylene, ethylene, and propylene.

[0045] The volumetric flow rate ratio of the carrier gas to the carbon source gas in the mixture is 3:1 to 4:1;

[0046] The flow rate of the mixed gas is 40 L / min to 50 L / min.

[0047] Thirdly, embodiments of the present invention provide a negative electrode sheet, the negative electrode sheet comprising the high-rate silicon-carbon negative electrode material described in the first aspect above.

[0048] Fourthly, embodiments of the present invention provide a lithium-ion battery, the lithium-ion battery comprising the negative electrode sheet described in the third aspect above.

[0049] The present invention provides a nitrogen-sulfur co-doped high-rate silicon-carbon anode material, its preparation method, and its application, which have the following beneficial effects:

[0050] (1) The present invention provides a method for preparing a nitrogen-sulfur co-doped high-rate silicon-carbon anode material. First, a nitrogen source, a sulfur source, and a porous carbon matrix are mixed uniformly in a specific ratio. Under high-temperature heat treatment, the sulfur source is dissolved or vaporized and diffused into the porous carbon matrix, allowing the nitrogen source to decompose and diffuse into nitrogen-containing small molecules into the pores of the porous carbon matrix. Then, silicon is deposited to grow nano-silicon particles, followed by vapor-phase carbon coating treatment, ultimately yielding a nitrogen-sulfur co-doped high-rate silicon-carbon anode material. The preparation method provided by the present invention achieves co-doping of nitrogen and sulfur elements in a porous carbon matrix in a one-step process. Under high-temperature heat treatment, the nitrogen and sulfur sources achieve better contact within the porous carbon matrix, which is beneficial for controlling the doping ratio and uniformity, reducing industrial production costs. Furthermore, the entire process is carried out under a protective atmosphere, effectively avoiding interference from other heteroatoms and ensuring the purity of the obtained material.

[0051] (2) The nitrogen-sulfur co-doped high-rate silicon-carbon anode material obtained by the above preparation method in this embodiment of the invention simultaneously dops nitrogen and sulfur elements on a porous carbon matrix. Nitrogen doping can improve the quality and efficiency of silicon deposition obtained from silane decomposition, and at the same time, it can give the final material good charge transfer ability and good wettability, thereby achieving better charge adsorption capacity. Sulfur doping can modify the surface of porous carbon and promote charge transfer. Under the synergistic effect of nitrogen and sulfur doping, the electronic structure and surface chemical properties of porous carbon are changed, thereby enhancing the adsorption capacity of porous carbon substrate for silane molecules and improving the reactivity of silane decomposition. In addition, the presence of nitrogen and sulfur elements can reduce the activation energy required for silane thermal decomposition, promote more efficient silicon grain deposition, and improve the uniformity and density of deposited silicon. The presence of dopants can also improve the thermal stability of porous carbon matrix, providing a guarantee for long-term silicon deposition process.

[0052] (3) The nitrogen-sulfur co-doped high-rate silicon-carbon anode material provided in the embodiments of the present invention is used to prepare a negative electrode sheet and applied to a lithium-ion battery. The nitrogen and sulfur elements doped in the material can form negatively charged groups to provide additional conductive channels, thereby improving the electronic conductivity of the material. The presence of nitrogen and sulfur can also improve the interfacial compatibility between the electrode material and the electrolyte, reduce charge transfer impedance, and improve the electrochemical activity and reaction rate of the material in the reaction. The doping of nitrogen and sulfur can reduce the electrochemical performance decay of the material due to phase change or mechanism change during cycling. The chemical bond formed by sulfur and carbon can provide additional channels for lithium-ion transport. The doping of nitrogen and sulfur enables the material to maintain excellent high-rate performance and structural stability, thereby improving the rate performance and cycle stability of the lithium-ion battery. For example, the rate performance test of the coin cell prepared in the embodiments of the present invention shows that the first charge specific capacity is greater than 1800 mAh / g, the first coulombic efficiency is greater than 93%, the cycle capacity retention rate at 2C is greater than 40%, and the cycle capacity retention rate at 0.1C is greater than 90%. Attached Figure Description

[0053] Figure 1 The flowchart illustrates the preparation method of nitrogen-sulfur co-doped high-rate silicon-carbon anode material provided in this embodiment of the invention.

[0054] Figure 2 The graphs show the rate performance test curves of the button half-cell assembled in Embodiment 1 of the present invention and the button half-cells assembled in Comparative Examples 1-3. Detailed Implementation

[0055] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0056] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0057] This invention provides a nitrogen-sulfur co-doped high-rate silicon-carbon anode material, comprising: silicon-carbon composite particles and a carbon coating layer covering the outer surface of the silicon-carbon particles. The silicon-carbon composite particles comprise: a porous carbon matrix, nitrogen and sulfur doped into the porous carbon matrix, and nano-silicon particles uniformly deposited in the pores of the porous carbon matrix. The average particle size D of the high-rate silicon-carbon anode material is... 50 Between 10μm and 12μm, the specific surface area is 1.0m². 2 / g~3.0m 2 Between / g.

[0058] Among them, the average particle size D of the porous carbon matrix 50 Between 10μm and 12μm, the specific surface area is 1800m². 2 / g~2000m 2 / g; the average pore size of the porous carbon matrix is ​​between 2.0 nm and 2.8 nm, and the pore volume is 0.8 cm³. 3 / g~1.0cm 3 / g; the proportion of micropores in the porous carbon matrix is ​​65% to 75%.

[0059] Sulfur forms CSC bonds, C=S bonds, and C-SO bonds with carbon in a porous carbon matrix. x One or more of the -C bonds, where 0 < x ≤ 2; preferably, sulfur reacts with carbon in the porous carbon matrix to generate thiophene and its derivatives. The mass percentage of sulfur in the total mass of the high-rate silicon-carbon anode material is 2% to 3%.

[0060] Nitrogen reacts with carbon in the porous carbon matrix to form one or more compounds among pyrrole nitrogen, pyridine nitrogen, and graphitic nitrogen; the mass of nitrogen accounts for 3% to 5% of the total mass of the high-rate silicon-carbon anode material.

[0061] The mass percentage of nano-silicon particles in the total mass of high-rate silicon-carbon anode materials is 48%–52%. High-rate silicon-carbon anode materials are used in lithium-ion batteries. During lithium-ion battery cycling, CSC bonds, C=S bonds, or C-SO bonds are formed. x -C bonds form the transport channels for lithium ions.

[0062] CSC bond, C=S bond and C-SO x -C bonds enhance the overall performance of materials by providing different insertion sites, strengthening electronic and ion interactions, and improving conductivity, thus promoting efficient lithium-ion transport. Specifically, the CSC-type structure provides lithium-ion insertion sites; when lithium ions approach these sites, the interaction forces increase, promoting faster lithium-ion transfer. The C=S bond makes nearby C atoms better electron donors, improving conductivity. The polarity of the sulfur atoms in the C=S bond enhances the stability of lithium ions in the material, making them easier to insert or de-intercalate. C-SO... x The oxygen atom in the -C structure can coordinate with lithium ions, providing more lithium ion insertion sites and further promoting lithium ion capture and transport.

[0063] This invention provides a method for preparing the above-mentioned high-rate silicon-carbon anode material, such as... Figure 1 As shown, the specific steps include:

[0064] Step S1: After the porous carbon, nitrogen source and sulfur source are mixed evenly in proportion, they are placed in a coating furnace and subjected to high-temperature heat treatment under a protective atmosphere. After being discharged at room temperature, nitrogen and sulfur co-doped porous carbon material is obtained.

[0065] The nitrogen source includes one or more of urea, ammonium nitrate, or ammonium sulfate.

[0066] Sulfur sources include one or more of elemental sulfur, thiourea, or ammonium sulfate;

[0067] Average particle size D of porous carbon matrix 50 The surface area is between 10 μm and 12 μm; the specific surface area of ​​the porous carbon matrix is ​​1800 m². 2 / g~2000m 2 / g; the average pore size of the porous carbon matrix is ​​between 2.0 nm and 2.8 nm, and the pore volume is 0.8 cm³. 3 / g~1.0cm 3 / g;

[0068] The proportion of micropores in the pores of porous carbon matrix is ​​65% to 75%;

[0069] The mass ratio of porous carbon, nitrogen source and sulfur source is 75-85:8-12:3-8, preferably 80-85:8-10:3-5;

[0070] The protective atmosphere includes: nitrogen atmosphere and / or argon atmosphere;

[0071] High-temperature heat treatment involves heating to 300℃ to 600℃ at a heating rate of 1℃ / min to 5℃ / min, and holding at that temperature for 2 to 5 hours; the preferred temperature range for high-temperature heat treatment is 400℃ to 500℃.

[0072] The rotation speed of the coating furnace is 0.25 revolutions / min to 1 revolution / min;

[0073] In this step, the sulfur source is either solution-wetted or vaporized under high-temperature heat treatment and diffuses into the surface and pores of the porous carbon matrix, causing the sulfur in the sulfur source to form CSC bonds, C=S bonds, and C-SO bonds with the carbon. x One or more of the -C bonds, where 0 < x ≤ 2; nitrogen-containing gases obtained from the decomposition of the nitrogen source, such as one or more of NH3, NO, NO2, and N2O, are adsorbed by the pores of the porous carbon matrix, causing the nitrogen from the nitrogen source to react with the carbon in the porous carbon matrix to generate one or more compounds of pyrrole nitrogen, pyridine nitrogen, and graphitic nitrogen.

[0074] Step S2: Place the nitrogen-sulfur co-doped porous carbon material in a vapor deposition furnace. Under a protective atmosphere, heat the vapor deposition furnace to 450℃~600℃, introduce a mixture of carrier gas and silicon source gas, and hold for 2 hours to 5 hours. This allows the silicon element decomposed from the silicon source gas to be deposited in the pores of the nitrogen-sulfur co-doped porous carbon material and grow into nano-silicon particles. Then, only the carrier gas is introduced and the temperature is maintained for another 0.5 hours to 1 hour. After cooling, the precursor material is obtained.

[0075] The protective atmosphere includes: nitrogen atmosphere and / or argon atmosphere;

[0076] Carrier gases include: nitrogen and / or argon;

[0077] The silicon source gas includes one or more of the following: silane, disilane, and dichlorosilane;

[0078] The volumetric flow rate ratio of the carrier gas to the silicon source gas in the mixed gas is 3:1 to 1:1; the flow rate of the mixed gas is 20 L / min to 30 L / min.

[0079] In this step, the temperature of the vapor deposition furnace is preferably raised to 460℃~540℃ under a protective atmosphere. It can be any temperature within this range, such as 460℃, 470℃, 480℃, 490℃, 500℃, 510℃, 520℃, 530℃, 540℃, etc., but is not limited to the listed temperatures; other unlisted temperatures within this range are also applicable. The preferred temperature range for vapor deposition of silicon in this invention provides good deposition rate, deposition quality, structural uniformity, and relatively low defect density for silicon chemical vapor deposition. Furthermore, the preferred temperature range ensures the doping effect, keeps the substrate relatively stable, and avoids affecting the dopant elements.

[0080] Step S3: Carbon coating treatment is performed on the precursor material to form a carbon coating layer on the outer surface of the precursor material, thereby obtaining a high-rate silicon-carbon anode material.

[0081] The carbon coating process is a gas phase coating, specifically including: heating the vapor phase deposition furnace to 500℃~600℃, preferably 550℃~600℃, introducing a mixture of carrier gas and carbon source gas, holding it at this temperature for 2 hours~6 hours, preferably 3 hours~5 hours, so that a carbon coating layer is formed on the outer surface of the precursor material, cooling it to room temperature, and obtaining a high-ratio silicon-carbon anode material after dispersing, sieving and demagnetizing.

[0082] The carrier gas includes nitrogen and / or argon.

[0083] The carbon source gas includes one or more of methane, acetylene, ethylene, and propylene; preferably acetylene and / or propylene.

[0084] The volumetric flow rate ratio of the carrier gas to the carbon source gas in the mixture is 3:1 to 4:1; the flow rate of the mixture is 40 L / min to 50 L / min.

[0085] In this invention, the nitrogen source readily decomposes after heat treatment, yielding a large amount of small molecules such as NH3, NO, NO2, and N2O. These nitrogen-containing small molecules diffuse into the pores of the porous carbon matrix and adsorb onto the pore surface. Upon reaction with carbon at high temperatures, they generate pyrrole nitrogen, pyridine nitrogen, graphitic nitrogen, etc., successfully achieving nitrogen doping. Nitrogen-doped porous carbon can endow the material with excellent charge transfer and wettability, thereby enabling better charge adsorption.

[0086] Under heat treatment conditions, the sulfur source forms a molten liquid or vapor that comes into full contact with the porous carbon matrix and diffuses into the surface and pore structure of the porous carbon matrix, forming CSC bonds, C=S bonds, and C-SO bonds with the carbon atoms of the porous carbon matrix. x -C bonds ultimately lead to sulfur doping, primarily in the form of thiophene and its derivatives. Sulfur doping can modify the surface of porous carbon, promoting charge transfer.

[0087] This invention can detect CSC bonds, C=S bonds, and C-SO bonds in materials using Fourier transform infrared spectroscopy (FTIR). x The presence of a specific chemical bond (-C bond); as indicated by nuclear magnetic resonance (NMR). 15 N NMR identifies and quantifies different types of pyrrole nitrogen, pyridine nitrogen, and graphitic nitrogen; X-ray photoelectron spectroscopy (XPS) is used to analyze the valence states of sulfur and nitrogen, as well as their binding with carbon.

[0088] In this invention, nitrogen and sulfur doping alters the electronic structure and surface chemistry of porous carbon, thereby enhancing the adsorption capacity of the porous carbon substrate for silane molecules and increasing the reactivity of silane decomposition. Furthermore, the presence of nitrogen and sulfur reduces the activation energy required for silane thermal decomposition, promoting more efficient silicon grain deposition and improving the uniformity and density of the deposited silicon. The presence of doping elements also enhances the thermal stability of the porous carbon matrix, ensuring a smooth silicon deposition process over extended periods.

[0089] The high-rate silicon-carbon anode material provided in this invention can be used together with conductive agents, binders, and additives to prepare anode sheets. The anode sheets containing the high-rate silicon-carbon anode material can be used in lithium-ion batteries to improve the rate performance and cycle performance of lithium-ion batteries.

[0090] This is because, in the high-rate silicon-carbon anode material provided in this invention, the nitrogen and sulfur doping elements can form negatively charged groups to provide additional conductive channels, thereby improving the electronic conductivity of the material. The presence of nitrogen and sulfur also improves the interfacial compatibility between the electrode material and the electrolyte, reduces charge transfer impedance, and improves the electrochemical activity and reaction rate of the material during reactions. Nitrogen and sulfur doping can reduce the electrochemical performance degradation caused by phase transitions or mechanistic changes during cycling, allowing the material to maintain excellent high-rate performance and structural stability, thus improving the rate performance and cycle stability of lithium-ion batteries.

[0091] To better understand the technical solution provided by this invention, the following examples illustrate the preparation process and characteristics of the high-rate silicon-carbon anode material of this invention.

[0092] Example 1

[0093] This embodiment provides a process for preparing a high-rate silicon-carbon anode material co-doped with nitrogen and sulfur, as detailed below.

[0094] (1) Weigh 1 kg of porous carbon, urea and elemental sulfur in a mass ratio of 82:10:8, mix them evenly and place them in a coating furnace. Heat the furnace to 500°C at 5°C / min under an argon atmosphere. The furnace tube rotation speed is 1 revolution / min. Keep the temperature for 3 hours and then discharge the material at room temperature to obtain nitrogen-sulfur co-doped porous carbon material.

[0095] In this process, elemental sulfur, under high-temperature heat treatment, forms vapor that diffuses into the surface and pores of the porous carbon matrix, causing the sulfur source to form CSC bonds, C=S bonds, and C-SO bonds with carbon. x -C bond; the nitrogen-containing gas obtained from the decomposition of urea is adsorbed by the pores of the porous carbon matrix, causing the nitrogen from the nitrogen source to react with the carbon in the porous carbon matrix to generate pyrrole nitrogen, pyridine nitrogen, and graphitic nitrogen.

[0096] (2) The nitrogen-sulfur co-doped porous carbon material was placed in a vapor deposition furnace. The vapor deposition furnace was heated to 480°C under an argon atmosphere. A mixed gas consisting of argon and silane with a volume flow rate of 25 L / min was introduced and kept at this temperature for 3 hours. The silicon element decomposed from the silicon source gas was deposited in the pores of the nitrogen-sulfur co-doped porous carbon material and grew into nano-silicon particles. Then, only the carrier gas argon with a flow rate of 15 L / min was introduced and kept at this temperature for another 0.5 hours. The surface of the material was purged and cooled to obtain the precursor material.

[0097] (3) The precursor material is vapor-coated, specifically: the vapor deposition furnace is heated to 550°C, a mixed gas of argon and acetylene with a volume flow ratio of 4:1 and a flow rate of 40 L / min is introduced, and the temperature is maintained for 3 hours to form a carbon coating layer on the outer surface of the precursor material. After cooling to room temperature, the nitrogen-sulfur co-doped high-rate silicon-carbon anode material is obtained after dispersing, sieving and demagnetizing.

[0098] In this embodiment, the silicon content in high-rate silicon-carbon anode materials was measured by the burning method. See Table 1 for test results.

[0099] The nitrogen content in the high-rate silicon-carbon anode material prepared in this embodiment was determined to be 3.97% using a nitrogen, oxygen, and hydrogen analyzer.

[0100] The sulfur content in the high-rate silicon-carbon anode material prepared in this embodiment was determined to be 2.82% using gas chromatography.

[0101] The high-rate silicon-carbon anode material prepared in this embodiment was used to prepare anode sheets and assembled into coin cells for testing. The specific process is as follows.

[0102] Preparation of the negative electrode sheet: High-ratio silicon-carbon negative electrode material, Super P conductive agent, sodium carboxymethyl cellulose, and styrene-butadiene rubber (2g total) were mixed in a mass ratio of 16:2:1:1 to prepare an aqueous negative electrode slurry. The solid content of the slurry was controlled at approximately 45wt%. The slurry was homogenized using a homogenizer. The slurry was coated onto copper foil to a thickness of 100 micrometers. After drying at 80℃, rolling, cutting, and vacuum drying at 110℃ for 24 hours, the negative electrode sheet was obtained. The loading of high-ratio silicon-carbon negative electrode material on a single electrode sheet was approximately 5mg.

[0103] Assembly of coin cells: Using lithium metal sheets as counter and reference electrodes, along with a CR2032 battery case, a Cel gard2500 separator, and a 1 mol / L LiPF6 electrolyte (the solvents being ethylene carbonate and dimethyl carbonate in a 1:1 volume ratio, with the addition of 5.0 vol 1% ethylene fluorocarbonate and 1.0 vol 1% ethylene carbonate), the coin cells were assembled in a glove box, resulting in the assembly of 6 coin cells.

[0104] Test Procedure: The six assembled button cells were simultaneously subjected to constant current cyclic charge-discharge tests at different current densities on the LAND Blue Electric series battery testing system. The test voltage range was 0.005V to 2V, and the test was conducted at 25℃. First, the cells were discharged to 0.005V at 0.1C (1C = 2000mAh / g) and allowed to stand for 2 minutes. Then, they were charged to 2V at 0.1C and allowed to stand for 2 minutes. The cells were then cycled 5 times at 0.1C, 5 times at 0.5C, 5 times at 1C, 5 times at 2C, and finally 5 times at 0.1C. The charge and discharge specific capacities after each cycle were recorded, and the coulombic efficiency corresponding to each cycle was calculated. Each battery underwent the same testing procedure: 0.1C for cycles 1-5, 0.5C for cycles 6-10, 1C for cycles 11-15, 2C for cycles 16-20, and 0.1C for cycles 21-25, for a total of 25 charge-discharge cycles. The capacity retention rate of each battery sample at cycles 10 (0.5C), 15 (1C), 20 (2C), and 25 (0.1C) was calculated. This was achieved by comparing the specific charge capacity at cycles 10 (0.5C), 15 (1C), 20 (2C), and 25 (0.1C) with the specific charge capacity at cycle 5. The comparison reflects the capacity retention of the material at higher current densities compared to lower current densities. The test results are shown in Table 1. The rate performance curves of the coin cells are also shown in Table 1. Figure 2 As shown.

[0105] Example 2

[0106] This embodiment provides a process for preparing a high-rate silicon-carbon anode material co-doped with nitrogen and sulfur. The difference from Embodiment 1 is that the sulfur source used in step (1) is thiourea, while the other preparation processes are the same as in Embodiment 1.

[0107] In this embodiment, the silicon content in high-rate silicon-carbon anode materials was measured by the burning method. See Table 1 for test results.

[0108] The nitrogen content in the high-rate silicon-carbon anode material prepared in this embodiment was determined to be 4.48% using a nitrogen, oxygen, and hydrogen analyzer.

[0109] The sulfur content in the high-rate silicon-carbon anode material prepared in this embodiment was determined to be 2.8% using gas chromatography.

[0110] The high-rate silicon-carbon anode material prepared in this embodiment was used to prepare a negative electrode sheet and assembled into a coin cell for testing. The preparation method of the negative electrode sheet, the battery assembly and testing process were the same as in Example 1. The test results are detailed in Table 1.

[0111] Example 3

[0112] This embodiment provides a preparation process for a high-rate silicon-carbon anode material co-doped with nitrogen and sulfur. The difference from Embodiment 1 is that the mass ratio of porous carbon, urea and elemental sulfur in step (1) is 85:10:5, while the other preparation processes are the same as in Embodiment 1.

[0113] In this embodiment, the silicon content in high-rate silicon-carbon anode materials was measured by the burning method. See Table 1 for test results.

[0114] The nitrogen content in the high-rate silicon-carbon anode material prepared in this embodiment was determined to be 3.58% using a nitrogen, oxygen, and hydrogen analyzer.

[0115] The sulfur content in the high-rate silicon-carbon anode material prepared in this embodiment was determined to be 1.97% using gas chromatography.

[0116] The high-rate silicon-carbon anode material prepared in this embodiment was used to prepare a negative electrode sheet and assembled into a coin cell for testing. The preparation method of the negative electrode sheet, the battery assembly and testing process were the same as in Example 1. The test results are detailed in Table 1.

[0117] Example 4

[0118] This embodiment provides a preparation process for a high-rate silicon-carbon anode material co-doped with nitrogen and sulfur. The difference from Embodiment 1 is that the high-temperature heat treatment temperature in step (1) is 450°C, while the other preparation processes are the same as in Embodiment 1.

[0119] In this embodiment, the silicon content in high-rate silicon-carbon anode materials was measured by the burning method. See Table 1 for test results.

[0120] The nitrogen content in the high-rate silicon-carbon anode material prepared in this embodiment was determined to be 3.82% using a nitrogen, oxygen, and hydrogen analyzer.

[0121] The sulfur content in the high-rate silicon-carbon anode material prepared in this embodiment was determined to be 2.78% using gas chromatography.

[0122] The high-rate silicon-carbon anode material prepared in this embodiment was used to prepare a negative electrode sheet and assembled into a coin cell for testing. The preparation method of the negative electrode sheet, the battery assembly and testing process were the same as in Example 1. The test results are detailed in Table 1.

[0123] To better illustrate the effects of the embodiments of the present invention, a comparative example is provided to be made with the embodiments described above.

[0124] Comparative Example 1

[0125] The sulfur-doped silicon-carbon composite material provided in this comparative example differs from that in Example 1 in that urea is not used in step (1), that is, 1 kg of porous carbon and elemental sulfur are weighed in a mass ratio of 82:18, and the other preparation process is the same as in Example 1.

[0126] In this comparative example, the silicon content in sulfur-doped silicon-carbon composite material was measured by the ignition method. The test results are detailed in Table 1.

[0127] The sulfur content in the sulfur-doped silicon-carbon composite material prepared in this comparative example was determined to be 3.11% using gas chromatography.

[0128] The sulfur-doped silicon-carbon composite material prepared in this comparative example was used to fabricate a negative electrode sheet and assemble it into a coin cell for testing. The fabrication method of the negative electrode sheet, the battery assembly, and the testing process were all the same as in Example 1. The test results are detailed in Table 1. The rate performance curves of the coin cell assembled in this comparative example are shown in the figure. Figure 2 As shown.

[0129] Comparative Example 2

[0130] The nitrogen-doped silicon-carbon composite material provided in this comparative example differs from that in Example 1 in that elemental sulfur is not used in step (1), that is, porous carbon and urea are weighed in a mass ratio of 82:18, totaling 1 kg. The other preparation process is the same as in Example 1.

[0131] In this comparative example, the silicon content in nitrogen-doped silicon-carbon composite material was measured by the ignition method. The test results are detailed in Table 1.

[0132] The nitrogen content in the nitrogen-doped silicon-carbon composite material prepared in this comparative example was determined to be 5.40% using a nitrogen, oxygen, and hydrogen analyzer.

[0133] The nitrogen-doped silicon-carbon composite material prepared in this comparative example was used to fabricate a negative electrode sheet and assemble it into a coin cell for testing. The fabrication method of the negative electrode sheet, the cell assembly, and the testing process were all the same as in Example 1. The test results are detailed in Table 1. The rate performance curves of the coin cell assembled in this comparative example are shown in the figure. Figure 2 As shown.

[0134] Comparative Example 3

[0135] The silicon-carbon composite material provided in this comparative example differs from that in Example 1 in that urea and elemental sulfur are not used in step (1), i.e. no doping is performed, while the other preparation processes are the same as in Example 1.

[0136] The silicon content in the silicon-carbon composite material was measured by the ignition method in this comparative example. The test results are detailed in Table 1.

[0137] The silicon-carbon composite material prepared in this comparative example was used to prepare a negative electrode sheet and assembled into a coin cell for testing. The preparation method of the negative electrode sheet, the battery assembly and testing process were the same as in Example 1. The test results are detailed in Table 1.

[0138] The rate performance curve of the coin cell assembled in this comparative example is shown in the figure. Figure 2 As shown, the coin cell assembled in Example 1 exhibits the best rate performance.

[0139] Comparative Example 4

[0140] The preparation process of the nitrogen- and sulfur co-doped silicon-carbon composite material provided in this comparative example differs from that in Example 1 in that step (1) uses a hydrothermal method for doping. The specific steps are as follows: 1 kg of porous carbon matrix, urea, and elemental sulfur are weighed in a mass ratio of 82:10:8 and uniformly dispersed in deionized water. The mixture is soaked for 5 hours to ensure that the urea and elemental sulfur fully penetrate into the carbon matrix structure. The solution is then transferred to a hydrothermal reactor and reacted at 200°C for 6 hours. After cooling, the mixture is washed three times with deionized water to remove unreacted precursors and byproducts. After vacuum drying at 80°C for 12 hours, a nitrogen- and sulfur co-doped porous carbon matrix is ​​obtained. Other preparation processes are the same as in Example 1.

[0141] The silicon content in the silicon-carbon composite material was measured by the ignition method in this comparative example. The test results are detailed in Table 1.

[0142] The nitrogen content in the nitrogen- and sulfur-doped silicon-carbon composite material prepared in this comparative example was determined to be 2.93% using a nitrogen, oxygen, and hydrogen analyzer.

[0143] The sulfur content in the nitrogen- and sulfur-co-doped silicon-carbon composite material prepared in this comparative example was determined to be 2.47% using gas chromatography.

[0144] Table 1 summarizes the test data for Examples 1-4 and Comparative Examples 1-4:

[0145]

[0146]

[0147] Table 1

[0148] The test data comparison in Table 1 shows that the batteries assembled in Examples 1-4 have better first-cycle coulombic efficiency, charge specific capacity, and cycle capacity retention than the batteries assembled in Comparative Examples 1-4. The reason why the batteries assembled in Examples 1-4 have higher first-cycle coulombic efficiency and exhibit better rate performance is that they use the nitrogen-sulfur co-doped high-rate silicon-carbon anode material of this invention. The co-doping of nitrogen and sulfur produces a synergistic effect, resulting in a faster electron / ion transfer rate and more abundant electrochemical active centers, effectively improving the material's conductivity. Simultaneously, it improves interfacial compatibility between materials, reduces charge transfer impedance, and imparts higher lithium insertion / extraction efficiency. Furthermore, the co-doping of nitrogen and sulfur also reduces the electrochemical performance degradation during cycling, maintaining good rate performance and a stable structure.

[0149] As shown in Comparative Example 1, sulfur doping of porous carbon matrix can improve the deposition of silane molecules, and at the same time slightly improve the specific capacity, coulombic efficiency and capacity retention at different rates of the composite material.

[0150] As shown in Comparative Example 2, nitrogen doping of porous carbon matrix can also improve the deposition of silane molecules. The negatively charged groups formed by nitrogen doping can improve the conductivity of the material and reduce the electrochemical performance decay during cycling. Nitrogen doping can improve the specific capacity, coulombic efficiency and capacity retention at different rates of the composite material to a certain extent.

[0151] The sulfur, nitrogen, and silicon contents of the nitrogen-sulfur co-doped high-rate silicon-carbon anode material prepared in Example 1 were all higher than those in the material of Comparative Example 4. This is because the uniformity of sulfur and nitrogen doping in the nitrogen-sulfur co-doped silicon-carbon composite material prepared by the hydrothermal method in Comparative Example 4 could not be guaranteed. Furthermore, the relatively low nitrogen content also affected the silicon content during silicon deposition.

[0152] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A nitrogen-sulfur co-doped high-rate silicon-carbon anode material, characterized in that, The high-rate silicon-carbon anode material includes: silicon-carbon composite particles, and a carbon coating layer covering the outer surface of the silicon-carbon particles; The silicon-carbon composite particles include: a porous carbon matrix, nitrogen and sulfur doped in the porous carbon matrix, and nano-silicon particles uniformly deposited in the pores of the porous carbon matrix. The sulfur forms CSC bonds, C=S bonds, and C-SO bonds with the carbon in the porous carbon matrix. x One or more of the -C bonds, where 0 < x ≤ 2; The nitrogen reacts with the carbon in the porous carbon matrix to generate one or more compounds selected from pyrrole nitrogen, pyridine nitrogen, and graphitic nitrogen. The high-rate silicon-carbon anode material is used in lithium-ion batteries. During the cycling process of the lithium-ion battery, the CSC bond, C=S bond, or C-SO bond... x -C bonds form the transport channels for lithium ions.

2. The high-rate silicon-carbon anode material according to claim 1, characterized in that, The sulfur reacts with the carbon in the porous carbon matrix to generate thiophene and its derivatives. The mass percentage of sulfur in the total mass of the high-rate silicon-carbon anode material is 2% to 3%. The mass percentage of nitrogen in the total mass of the high-rate silicon-carbon anode material is 3% to 5%. The mass of the nano-silicon particles accounts for 48% to 52% of the total mass of the high-rate silicon-carbon anode material.

3. The high-rate silicon-carbon anode material according to claim 1, characterized in that, The average particle size D of the porous carbon matrix 50 Between 10μm and 12μm; The specific surface area of ​​the porous carbon matrix is ​​1800 m². 2 / g~2000m 2 / g; The average pore size of the porous carbon matrix is ​​between 2.0 nm and 2.8 nm. The porous carbon matrix has a pore volume of 0.8 cm³. 3 / g~1.0cm 3 / g; The porous carbon matrix contains 65% to 75% micropores.

4. The high-rate silicon-carbon anode material according to claim 1, characterized in that, The average particle size D of the high-rate silicon-carbon anode material 50 Between 10μm and 12μm; The specific surface area of ​​the high-rate silicon-carbon anode material is 1.0 m². 2 / g~3.0m 2 Between / g.

5. A method for preparing the high-rate silicon-carbon anode material according to any one of claims 1-4, characterized in that, The preparation method includes: Step S1: After uniformly mixing porous carbon, nitrogen source, and sulfur source in a certain proportion, the mixture is placed in a coating furnace and subjected to high-temperature heat treatment under a protective atmosphere. After cooling to room temperature, the material is discharged to obtain nitrogen-sulfur co-doped porous carbon material. The sulfur source, during the high-temperature heat treatment, forms a solution that wets the porous carbon matrix or diffuses as vapor into the surface and pores of the porous carbon matrix, causing the sulfur in the sulfur source to form CSC bonds, C=S bonds, and C-SO bonds with the carbon. x One or more of the -C bonds; the nitrogen-containing gas obtained from the decomposition of the nitrogen source is adsorbed by the pores of the porous carbon matrix, causing the nitrogen from the nitrogen source to react with the carbon of the porous carbon matrix to generate one or more compounds of pyrrole nitrogen, pyridine nitrogen, and graphitic nitrogen; Step S2: The nitrogen-sulfur co-doped porous carbon material is placed in a vapor deposition furnace. Under a protective atmosphere, the vapor deposition furnace is heated to 450°C to 600°C. A mixture of carrier gas and silicon source gas is introduced and kept at this temperature for 2 to 5 hours. This allows the silicon element decomposed from the silicon source gas to be deposited in the pores of the nitrogen-sulfur co-doped porous carbon material and grow into nano-silicon particles. Then, only the carrier gas is introduced and the temperature is maintained for another 0.5 to 1 hour. After cooling, the precursor material is obtained. Step S3: Carbon coating treatment is performed on the precursor material to form a carbon coating layer on the outer surface of the precursor material, thereby obtaining a high-rate silicon-carbon anode material.

6. The preparation method according to claim 5, characterized in that, In step S1, the nitrogen source includes one or more of urea, ammonium nitrate, or ammonium sulfate. The sulfur source includes one or more of elemental sulfur, thiourea, or ammonium sulfate. The average particle size D of the porous carbon matrix 50 The porous carbon matrix has a surface area between 10 μm and 12 μm and a specific surface area of ​​1800 m². 2 / g~2000m 2 / g; the average pore size of the porous carbon matrix is ​​between 2.0 nm and 2.8 nm, and the pore volume is 0.8 cm³. 3 / g~1.0cm 3 / g; The porous carbon matrix contains 65% to 75% micropores. The mass ratio of the porous carbon, nitrogen, and sulfur sources is 75–85:8–12:3–8; The protective atmosphere includes: nitrogen atmosphere and / or argon atmosphere; The high-temperature heat treatment involves heating to 300℃ to 600℃ at a heating rate of 1℃ / min to 5℃ / min, and holding at that temperature for 2 to 5 hours. The rotation speed of the coating furnace is 0.25 revolutions / min to 1 revolution / min; The nitrogen-containing gas includes one or more of NH3, NO, NO2, and N2O.

7. The preparation method according to claim 5, characterized in that, In step S2, the protective atmosphere includes: a nitrogen atmosphere and / or an argon atmosphere; The carrier gas includes: nitrogen and / or argon; The silicon source gas includes one or more of the following: silane, disilane, and dichlorosilane; The volumetric flow rate ratio of the carrier gas to the silicon source gas in the mixed gas is 3:1 to 1:1; The flow rate of the mixed gas is 20 L / min to 30 L / min.

8. The preparation method according to claim 5, characterized in that, The carbon coating process in step S3 is a gas phase coating, specifically including: heating the gas phase deposition furnace to 500℃~600℃, introducing a mixture of carrier gas and carbon source gas, holding it at that temperature for 2 hours~6 hours, so that a carbon coating layer is formed on the outer surface of the precursor material, cooling it to room temperature, and obtaining a high-ratio silicon-carbon anode material after breaking it down, sieving it, and demagnetizing it. The carrier gas includes nitrogen and / or argon. The carbon source gas includes one or more of methane, acetylene, ethylene, and propylene. The volumetric flow rate ratio of the carrier gas to the carbon source gas in the mixture is 3:1 to 4:1; The flow rate of the mixed gas is 40 L / min to 50 L / min.

9. A negative electrode sheet, characterized in that, The negative electrode sheet comprises the high-rate silicon-carbon negative electrode material as described in any one of claims 1-4.

10. A lithium-ion battery, characterized in that, The lithium-ion battery includes the negative electrode sheet as described in claim 9.

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