Silicon-carbon composite negative electrode material and preparation method and application thereof

Abstract

The embodiment of the invention relates to a silicon-carbon composite negative electrode material as well as a preparation method and application thereof. The silicon-carbon composite negative electrode material comprises porous carbon and doping elements, wherein the silicon-carbon composite negative electrode material is prepared by using a chemical vapor deposition method through temperature control of a deposition rate, porous carbon is used as a framework, and doping elements are distributed in pore channels of the porous carbon in a nano-scale manner; the doping elements comprise C, N, Si and F. The silicon-carbon composite negative electrode material has uniformly distributed C-N bonds, so that nitrogen doping of porous carbon is facilitated, the conductivity of the porous carbon material is improved, uniform deposition of nano silicon can be induced due to the existence of the C-N bonds, Li F can be formed by doping fluorine and lithium, the Li F is an important component of a stable SE I film, continuous generation of the SE I film in the circulation process can be reduced, and the service life of the lithium ion battery is prolonged. And the cycle performance of the lithium ion battery is improved.

Description

Technical Field

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

[0002] Currently, the most widely used commercial lithium-ion batteries use graphite materials (including artificial graphite, natural graphite, and mesophase microspheres) as the negative electrode material. However, the development of lithium-ion batteries is limited by low theoretical specific capacity (372 mAh / g) and safety issues, making it difficult to meet the current needs of consumer electronics and power batteries.

[0003] Silicon has attracted widespread attention due to its ultra-high theoretical specific capacity (4200 mAh / g) and abundant reserves, and it has the potential to become the next generation of high-performance lithium-ion battery anode materials. However, silicon-based anodes undergo significant volume changes during battery cycling, which can lead to problems such as dynamic reconstruction of the solid-electrolyte membrane and pulverization of active material particles, directly resulting in loss of electrical contact and rapid capacity and cycle life degradation. Currently, methods to mitigate the volume expansion of silicon-based anodes mainly include: silicon nanostructuring, silicon-carbon composites, and structural design (porous, hollow, core-shell, etc.).

[0004] Examples include patents CN117996038A, CN112331819A, CN114975922A, and CN109659551A. These methods primarily involve simple coating / composite processes of nano-silicon and carbon materials (including porous carbon, hard carbon, soft carbon, and graphite). This structure lacks a buffer space to accommodate the volume expansion of silicon, making it difficult to maintain structural integrity during cycling. Therefore, it cannot fundamentally suppress the negative effects of volumetric effects, and the battery capacity rapidly decreases with increasing cycle count.

[0005] Patent CN114122352A proposes a method of preparing porous carbon by liquid-phase mixing of binder, conductive carbon black, and carbon nanotubes, followed by spray drying. Then, catalyst doping modification is applied to the surface, and finally, silicon deposition and carbon precipitation are performed to obtain a porous carbon doped-induced silicon-carbon anode material. While this method can yield porous carbon materials with conductive networks, it suffers from problems such as high catalyst cost and low doping levels.

[0006] Patent CN115101741A describes coating a silicon-based substrate with nitrogen-doped amorphous carbon and graphene. While this method is less expensive, it has some drawbacks. For example, nitrogen doping is achieved through electrochemical polymerization, which makes industrialization difficult. Furthermore, using a silicon-based substrate as the core results in a large particle size that makes volume expansion a persistent problem. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of existing technologies by providing a silicon-carbon composite anode material, its preparation method, and its application. This silicon-carbon composite anode material incorporates nitrogen doping of porous carbon, increasing the conductivity of the porous carbon material. Furthermore, the presence of CN bonds can induce uniform deposition of nano-silicon. Fluorine doping can interact with lithium LiF, which is an important component of a stable SEI film. This can reduce the continuous formation of the SEI film during cycling and improve the cycle performance of lithium-ion batteries.

[0008] To achieve the above objectives, in a first aspect, the present invention provides a silicon-carbon composite anode material, the silicon-carbon composite anode material comprising: porous carbon and doping elements;

[0009] The silicon-carbon composite anode material is prepared by chemical vapor deposition with temperature-controlled deposition rate, using porous carbon as a framework, and the doping elements are distributed in the pores of the porous carbon at the nanoscale.

[0010] The doping elements include C, N, Si, and F.

[0011] Preferably, the porous carbon includes one or more of resin-based porous carbon, biomass-based porous carbon, and metal-organic framework-derived porous carbon; the pore size of the porous carbon is 0.2 nm-100 nm; and the particle size of the silicon-carbon composite anode material is 5 μm-10 μm.

[0012] Preferably, in the silicon-carbon composite anode material, the mass percentage of nitrogen is 5%-10%, the mass percentage of fluorine is 1%-5%, the mass percentage of silicon is 40%-45%, and the mass percentage of carbon is 45%-50%.

[0013] In a second aspect, the present invention provides a method for preparing the silicon-carbon composite anode material according to any one of the first aspects, the method comprising:

[0014] Under an inert atmosphere, carbon source gas and nitrogen source gas are introduced into a reactor containing porous carbon for a first heat treatment, so that the nitrogen source gas and carbon source gas decompose and form CN covalent bonds, which are deposited in the pores of the porous carbon to obtain nitrogen-doped porous carbon.

[0015] Under an inert atmosphere, silicon source gas and fluorine source gas are introduced into the reactor for a second heat treatment, so that the silicon source gas and fluorine source gas decompose and deposit in the pores of nitrogen-doped porous carbon to obtain a silicon-carbon composite anode material, wherein the silicon-carbon composite anode material includes nitrogen and fluorine elements.

[0016] Preferably, the flow rate ratio of the inert atmosphere, carbon source gas, and nitrogen source gas is [30-40]:[5-10]:[5-10]; the specific conditions for the first heat treatment are: temperature 500℃-800℃, time 2 hours-5 hours.

[0017] Preferably, the flow rate ratio of the inert atmosphere, silicon source gas, and fluorine source gas is 20:[20-25]:[5-10]; the specific conditions for the second heat treatment are: temperature 700℃-1000℃, time 4 hours-10 hours.

[0018] Preferably, the carbon source gas includes one or more of methane, acetylene, and ethylene; the nitrogen source gas includes one or more of ammonia, nitric oxide, and nitrogen dioxide.

[0019] Preferably, the silicon source gas includes one or more of silane, silane, and chlorosilane; the fluorine source gas includes one or more of nitrogen trifluoride, carbon tetrafluoride, and fluorinated acetylene.

[0020] Thirdly, the present invention provides a negative electrode sheet, the negative electrode sheet comprising the silicon-carbon composite negative electrode material described in any of the first aspects.

[0021] Fourthly, the present invention provides a lithium-ion battery, the lithium-ion battery comprising the negative electrode sheet described in the third aspect.

[0022] In the silicon-carbon composite anode material provided in this invention, carbon-nitrogen co-doping forms CN bonds, modifying the porous carbon, improving the material's conductivity, and inducing uniform silicon deposition within the porous carbon channels, thus reducing the material's expansion rate. Fluorine atoms can react with lithium in the positive electrode and the electrolyte of the lithium-ion battery to form LiF. LiF is an important component of a stable SEI film, which can reduce the continuous formation of the SEI film during cycling and improve the cycle performance of the lithium-ion battery. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the structure of the silicon-carbon composite anode material provided in an embodiment of the present invention;

[0024] Figure 2 This is a flowchart illustrating the preparation method of the silicon-carbon composite anode material provided in an embodiment of the present invention.

[0025] Figure 3 This is a SEM image of the silicon-carbon composite anode material prepared in Example 1 of the present invention;

[0026] Figure 4 The first charge-discharge curves of the silicon-carbon composite anode materials prepared in Example 1 and Comparative Example 1 of this invention are shown. Detailed Implementation

[0027] 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.

[0028] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0029] This invention provides a silicon-carbon composite anode material, such as... Figure 1 As shown, the silicon-carbon composite anode material specifically includes porous carbon and doping elements.

[0030] Specifically, the porous carbon can include one or more of resin-based porous carbon, biomass-based porous carbon, and metal-organic framework-derived porous carbon. The pore size of the porous carbon can range from 0.2 nm to 100 nm. The porous carbon mainly serves as the framework of this silicon-carbon composite anode material.

[0031] The doping elements include C, N, Si, and F. These doping elements are distributed at the nanoscale within the pores of the porous carbon.

[0032] In silicon-carbon composite anode materials, the mass percentage of nitrogen is 5%-10%, the mass percentage of fluorine is 1%-5%, the mass percentage of silicon is 40%-45%, and the mass percentage of carbon is 45%-50%.

[0033] The particle size of silicon-carbon composite anode material is 5μm-10μm.

[0034] Carbon doping facilitates the formation of CN bonds, which in turn helps to dope porous carbon with nitrogen.

[0035] Nitrogen doping offers several advantages: First, nitrogen atoms can act as electron donors or acceptors, altering the electron density on the carbon surface and thus enhancing the catalytic activity of porous carbon. This can increase the specific capacitance and energy density of porous carbon. Second, nitrogen doping induces structural changes in porous carbon, introducing defects that improve its lithium storage capacity. Third, nitrogen doping increases the conductivity of porous carbon materials because nitrogen atoms alter the electronic structure, thereby increasing the electron transport rate and effectively promoting charge transfer. Fourth, CN bonds provide surface active sites conducive to silicon atom adsorption and nucleation, modifying porous carbon and allowing silicon to be uniformly deposited within the pores, reducing the material's expansion rate.

[0036] The advantages of silicon doping are: it increases the specific capacity of porous carbon. When this silicon-carbon composite anode material is used in lithium-ion batteries, it can improve the energy density and cycle stability of lithium-ion batteries.

[0037] The advantages of fluorine doping include: improved lithium storage mechanism in silicon-carbon composite anode materials, effectively increasing the specific capacity and energy density of lithium-ion batteries when applied in them. For example... Figure 1 As shown, fluorine atoms can react with lithium in the cathode and electrolyte of a lithium-ion battery to form LiF. LiF is an important component of a stable SEI film, which can reduce the continuous formation of SEI film during cycling and improve the cycle performance of lithium-ion batteries.

[0038] This invention also provides a method for preparing the above-mentioned silicon-carbon composite anode material, the process of which is as follows: Figure 2 As shown, it includes the following steps:

[0039] Step 110: Under an inert atmosphere, carbon source gas and nitrogen source gas are introduced into a reactor containing porous carbon for the first heat treatment, so that the nitrogen source gas and carbon source gas decompose and form CN covalent bonds, which are deposited in the pores of the porous carbon to obtain nitrogen-doped porous carbon.

[0040] Specifically, the inert atmosphere may include one or both of nitrogen and argon. Nitrogen is preferred. The porous carbon may include one or more of resin-based porous carbon, biomass-based porous carbon, and metal-organic framework-derived porous carbon. Biomass-based porous carbon is preferred. The pore size of the porous carbon may be 0.2 nm to 100 nm. The carbon source gas may include one or more of methane, acetylene, and ethylene. Acetylene is preferred. The nitrogen source gas may include one or more of ammonia, nitric oxide, and nitrogen dioxide. Ammonia is preferred. The flow rate ratio of the inert atmosphere, carbon source gas, and nitrogen source gas may be [30-40]:[5-10]:[5-10], preferably 30:10:10.

[0041] The specific conditions for the first heat treatment are as follows: the temperature adjustment rate of the reactor is 5℃ / min-10℃ / min, preferably 5℃ / min; the temperature is 500℃-800℃, and the time is 2-5 hours, preferably 600℃, and the time is 4 hours. The nitrogen source gas decomposes upon heating, releasing nitrogen atoms, and the carbon source gas decomposes upon heating, releasing carbon atoms. The nitrogen and carbon atoms react to form CN covalent bonds, which are then deposited in the pores of the porous carbon. The CN covalent bonds play the following role in subsequent silicon deposition:

[0042] First, as a catalyst or catalyst support, it promotes the decomposition of silicon source gas, thereby inducing silicon deposition. Nitrogen doping can alter the electronic properties of carbon materials, enhancing their catalytic activity.

[0043] Second, at high temperatures, the surface of porous carbon materials containing CN bonds reacts with silicon source gas, causing silicon atoms to deposit near the CN bonds and form nano-silicon structures. This is because the CN bonds provide surface active sites conducive to silicon atom adsorption and nucleation, improving the uniform distribution of nano-silicon within the porous carbon's pore structure.

[0044] Third, the introduction of nitrogen atoms can change the electron density on the surface of porous carbon materials, affecting the adsorption and dissociation process of silicon source gas molecules, thereby promoting the deposition of silicon atoms.

[0045] As a preferred embodiment, prior to step 110, this application further includes:

[0046] Porous carbon is placed in a reactor for a third heat treatment under an inert atmosphere. The inert atmosphere may specifically include one or both of nitrogen and argon, with nitrogen being preferred. The flow rate of the inert atmosphere is 20 L / min-40 L / min, preferably 30 L / min. The specific conditions for the third heat treatment are: a reactor temperature adjustment rate of 3℃ / min-10℃ / min, preferably 5℃ / min; a temperature of 700℃-1000℃; and a time of 20 min-60 min, preferably 800℃ for 30 min. The purpose of the third heat treatment is to remove moisture and air from the pores of the porous carbon, ensuring its structural stability.

[0047] Step 120: Under an inert atmosphere, silicon source gas and fluorine source gas are introduced into the reactor for a second heat treatment, so that the silicon source gas and fluorine source gas decompose and deposit in the pores of nitrogen-doped porous carbon to obtain silicon-carbon composite anode material.

[0048] Specifically, the inert atmosphere may include one or both of nitrogen and argon. Nitrogen is preferred. The silicon source gas may include one or more of silane, silane, and chlorosilane. The fluorine source gas may include one or more of nitrogen trifluoride, carbon tetrafluoride, and fluorinated acetylene. The flow rate ratio of the inert atmosphere, silicon source gas, and fluorine source gas is 20:[20-25]:[5-10], preferably 20:25:5.

[0049] The specific conditions for the second heat treatment are as follows: Reactor temperature control rate: heating at 2℃ / min-8℃ / min, cooling at 3℃ / min-6℃ / min. Temperature 700℃-1000℃, time 4-10 hours. Preferably, the temperature is 800℃, time 6 hours. In the silicon-carbon composite anode material, the mass percentage of nitrogen is 5%-10%, the mass percentage of fluorine is 5%-10%, the mass percentage of silicon is 40%-45%, and the mass percentage of carbon is 50%-55%.

[0050] The particle size of silicon-carbon composite anode materials is 5μm-10μm. These materials contain both nitrogen and fluorine elements.

[0051] Silicon deposition improves the specific capacity of this silicon-carbon composite anode material. When this silicon-carbon composite anode material is used in lithium-ion batteries, fluorine atoms can also form lithium fluoride with lithium, which is beneficial for the formation of a stable SE I film, thereby improving the cycle stability of the lithium-ion battery.

[0052] This invention provides a method for preparing a silicon-carbon composite anode material. First, carbon / nitrogen co-deposition forms porous carbon with CN bonds, which is beneficial for nitrogen doping. The porous carbon is then modified to provide surface active sites for silicon atom adsorption and nucleation, improving the uniformity of silicon deposition. Next, silicon / fluorine co-deposition is performed. Silicon can increase the specific capacity of the silicon-carbon composite anode material, while fluorine can form lithium fluoride, which is beneficial for the formation of an SE I film, thereby improving the cycle stability of the lithium-ion battery.

[0053] The silicon-carbon composite anode material provided in this invention can be used as an electrode material in energy storage devices such as supercapacitors, lithium-ion batteries, and dye-sensitized batteries.

[0054] To better understand the technical solution provided by the present invention, the following uses several specific examples to illustrate the specific process of preparing silicon-carbon composite anode materials using the method provided in the above embodiments of the present invention, as well as the electrochemical characteristics of the prepared silicon-carbon composite anode materials.

[0055] Example 1

[0056] The first step is to introduce nitrogen gas into the reactor at a flow rate of 30 L / min to form a protective atmosphere. Then, 10 kg of biomass-based porous carbon material is placed in the reactor, and the reactor is heated to 800°C at a heating rate of 5°C / min and held at that temperature for 30 min.

[0057] The second step involves cooling the reactor to 600°C under a nitrogen atmosphere at a cooling rate of 5°C / min. Then, nitrogen, acetylene, and ammonia are introduced into the reactor at a gas flow rate ratio of 30:10:10, and the reactor is kept at 600°C for 4 hours to obtain nitrogen-doped porous carbon.

[0058] The third step involves raising the temperature of the reactor to 800°C under a nitrogen atmosphere at a heating rate of 5°C / min. Then, nitrogen, silane, and nitrogen trifluoride are introduced into the reactor at a gas flow rate ratio of 20:25:5, and the reactor is held at 800°C for 6 hours to obtain the silicon-carbon composite anode material.

[0059] Subsequently, the prepared silicon-carbon composite anode material was used to fabricate a lithium-ion battery electrode, and this electrode was used to assemble a coin cell for testing, as detailed below:

[0060] First, silicon-carbon composite anode material, acetylene black, and sodium carboxymethyl cellulose are added to deionized water in a mass ratio of 90:5:5 and mixed evenly. The mixture is then prepared into a slurry using a pulping machine, coated onto a copper foil current collector, and dried at 80°C for 10 hours to obtain the electrode sheet.

[0061] Secondly, the dried electrode sheets are cut into 14mm round pieces to serve as electrodes for lithium-ion batteries.

[0062] Then, the above-mentioned electrodes were assembled into a CR2032 coin cell in an argon-filled glove box. The electrolyte of the CR2032 coin cell was 1 mol / L lithium hexafluorophosphate (LiPF6), and the solvents were ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC), with a volume ratio of EC, DMC, and DEC of 1:1:1. The counter electrode was a lithium sheet. The separator was a polyethylene membrane.

[0063] Finally, the CR2032 button cell was left to stand for 8 hours at room temperature, and then charge and discharge tests were conducted on the Blue Battery Testing System (CT2001A), as follows:

[0064] 1. Testing the initial expansion rate of the electrode: At room temperature, the prepared electrode is cut by ion beam, and the cross-section is photographed using a scanning electron microscope. The measured electrode thickness is recorded as D1, and the thickness of the copper foil current collector substrate is also measured and recorded as D2. Under a current density of 0.1C and a charging cutoff voltage of 2V, the coin cell is fully charged. Then, the battery is disassembled in a glove box, the electrode is removed, and after ion beam cutting, the cross-section is photographed again, and the electrode thickness at this point is measured and recorded as D3. The initial expansion rate is then calculated using the following formula:

[0065] First-cycle expansion rate = (D3-D1) / (D1-D2)×100%.

[0066] 2. Test the first-cycle coulombic efficiency and cycle capacity retention: The voltage window is 0.005V-2V, the discharge rate is 0.1C, and the discharge cutoff voltage is 0.005V. Test the first-cycle coulombic efficiency, and then cycle 200 times to test the cycle capacity retention.

[0067] Example 2

[0068] The first step is the same as in Example 1.

[0069] The second step involves cooling the reactor to 600°C at a rate of 5°C / min under a nitrogen atmosphere. Then, nitrogen, acetylene, and ammonia are introduced into the reactor at a gas flow rate ratio of 40:5:5, and the reactor is kept at 600°C for 4 hours to obtain nitrogen-doped porous carbon.

[0070] The third step and testing process are the same as in Example 1.

[0071] Example 3

[0072] The first step is the same as in Example 1.

[0073] The second step involves cooling the reactor to 600°C at a rate of 5°C / min under a nitrogen atmosphere. Then, nitrogen, acetylene, and ammonia are introduced into the reactor at a gas flow rate ratio of 38:6:6, and the reactor is kept at 600°C for 4 hours to obtain nitrogen-doped porous carbon.

[0074] The third step and testing process are the same as in Example 1.

[0075] Example 4

[0076] The first step is the same as in Example 1.

[0077] The second step involves cooling the reactor to 600°C at a rate of 5°C / min under a nitrogen atmosphere. Then, nitrogen, acetylene, and ammonia are introduced into the reactor at a gas flow rate ratio of 30:10:10, and the reactor is kept at 600°C for 5 hours to obtain nitrogen-doped porous carbon.

[0078] The third step and testing process are the same as in Example 1.

[0079] Example 5

[0080] The first and second steps, as well as the testing process, are the same as in Example 1.

[0081] The third step involves raising the temperature of the reactor to 800°C under a nitrogen atmosphere at a heating rate of 5°C / min. Then, nitrogen, silane, and nitrogen trifluoride are introduced into the reactor at a gas flow rate ratio of 20:22:8, and the reactor is kept at 800°C for 6 hours to obtain the silicon-carbon composite anode material.

[0082] Example 6

[0083] The first and second steps, as well as the testing process, are the same as in Example 1.

[0084] The third step involves raising the temperature of the reactor to 800°C under a nitrogen atmosphere at a heating rate of 5°C / min. Then, nitrogen, silane, and nitrogen trifluoride are introduced into the reactor at a gas flow rate ratio of 20:20:10, and the reactor is kept at 800°C for 4 hours to obtain the silicon-carbon composite anode material.

[0085] Example 7

[0086] The first step is the same as in Example 1.

[0087] The second step involves cooling the reactor to 600°C under a nitrogen atmosphere at a cooling rate of 5°C / min. Then, argon, methane, and ammonia are introduced into the reactor at a gas flow rate ratio of 40:10:10, and the reactor is held at 600°C for 4 hours to obtain nitrogen-doped porous carbon.

[0088] The third step and testing process are the same as in Example 1.

[0089] Example 8

[0090] The first step is the same as in Example 1.

[0091] The second step involves cooling the reactor to 600°C at a rate of 5°C / min under a nitrogen atmosphere. Then, nitrogen, ethylene, and ammonia are introduced into the reactor at a gas flow rate ratio of 30:10:10, and the reactor is kept at 600°C for 2 hours to obtain nitrogen-doped porous carbon.

[0092] The third step and testing process are the same as in Example 1.

[0093] Example 9

[0094] The first and second steps, as well as the testing process, are the same as in Example 1.

[0095] The third step involves raising the temperature of the reactor to 800°C under a nitrogen atmosphere at a heating rate of 5°C / min. Then, nitrogen, silane, and nitrogen trifluoride are introduced into the reactor at a gas flow rate ratio of 20:25:10, and the reactor is kept at 800°C for 4 hours to obtain the silicon-carbon composite anode material.

[0096] Example 10

[0097] The first and second steps, as well as the testing process, are the same as in Example 1.

[0098] The third step involves raising the temperature of the reactor to 800°C under a nitrogen atmosphere at a heating rate of 5°C / min. Then, argon, silane, and nitrogen trifluoride are introduced into the reactor at a gas flow rate ratio of 20:20:5, and the reactor is kept at 800°C for 10 hours to obtain the silicon-carbon composite anode material.

[0099] Example 11

[0100] The first step is to introduce nitrogen gas into the reactor at a flow rate of 40 L / min to form a protective atmosphere. Then, 10 kg of resin-based porous carbon material is placed in the reactor, and the reactor is heated to 1000 °C at a heating rate of 3 °C / min and held at that temperature for 20 min.

[0101] The second step involves cooling the reactor to 500°C at a rate of 8°C / min under an argon atmosphere. Then, argon, propylene, and nitric oxide are introduced into the reactor at a gas flow rate ratio of 35:8:6, and the reactor is held at 500°C for 5 hours to obtain nitrogen-doped porous carbon.

[0102] The third step involves raising the temperature of the reactor to 1000°C at a heating rate of 8°C / min under an argon atmosphere. Then, argon, chlorosilane, and carbon tetrafluoride are introduced into the reactor at a gas flow rate ratio of 20:23:9, and the reactor is kept at 1000°C for 5 hours to obtain the silicon-carbon composite anode material.

[0103] The testing process is the same as in Example 1.

[0104] Example 12

[0105] The first step involves introducing nitrogen gas into the reactor at a flow rate of 20 L / min to create a protective atmosphere. Then, 10 kg of metal-organic framework-derived porous carbon is placed in the reactor, and the reactor is heated to 700 °C at a heating rate of 10 °C / min and held at that temperature for 60 min.

[0106] The second step involves raising the temperature of the reactor to 800°C at a heating rate of 6°C / min under an argon atmosphere. Then, argon, propylene, and nitrogen dioxide are introduced into the reactor at a gas flow rate ratio of 38:10:5, and the reactor is held at 800°C for 2 hours to obtain nitrogen-doped porous carbon.

[0107] The third step involves lowering the temperature of the reactor to 700°C at a rate of 6°C / min under an argon atmosphere. Then, argon, chlorosilane, and fluorinated acetylene are introduced into the reactor at a gas flow rate ratio of 20:25:8, and the reactor is kept at 700°C for 8 hours to obtain the silicon-carbon composite anode material.

[0108] The testing process is the same as in Example 1.

[0109] Comparative Example 1

[0110] The first step is to introduce nitrogen gas into the reactor at a flow rate of 30 L / min to form a protective atmosphere. Then, 10 kg of biomass-based porous carbon material is placed in the reactor, and the reactor is heated to 800°C at a heating rate of 5°C / min and held at that temperature for 30 min.

[0111] The second step involves introducing nitrogen, silane, and nitrogen trifluoride into a reactor at a gas flow rate ratio of 20:25:5 under a nitrogen atmosphere, and holding the reactor at 800°C for 6 hours to obtain a fluorine-doped silicon-carbon composite anode material.

[0112] The testing process is the same as in Example 1.

[0113] Comparative Example 2

[0114] The first step is to introduce nitrogen gas into the reactor at a flow rate of 30 L / min to form a protective atmosphere. Then, 10 kg of biomass-based porous carbon material is placed in the reactor, and the reactor is heated to 800°C at a heating rate of 5°C / min and held at that temperature for 30 min.

[0115] The second step involves cooling the reactor to 600°C at a rate of 5°C / min under a nitrogen atmosphere. Then, nitrogen and acetylene are introduced into the reactor at a gas flow rate ratio of 30:20, and the reactor is kept at 600°C for 4 hours to obtain a porous carbon matrix.

[0116] The third step involves raising the temperature of the reactor to 800°C under a nitrogen atmosphere at a heating rate of 5°C / min. Then, nitrogen, silane, and nitrogen trifluoride are introduced into the reactor at a gas flow rate ratio of 20:25:5, and the reactor is held at 800°C for 6 hours to obtain a fluorine-doped silicon-carbon composite anode material.

[0117] The testing process is the same as in Example 1.

[0118] Comparative Example 3

[0119] The first step is to introduce nitrogen gas into the reactor at a flow rate of 30 L / min to form a protective atmosphere. Then, 10 kg of biomass-based porous carbon material is placed in the reactor, and the reactor is heated to 800°C at a heating rate of 5°C / min and held at that temperature for 30 min.

[0120] The second step involves cooling the reactor to 600°C at a rate of 5°C / min under a nitrogen atmosphere. Then, nitrogen and ammonia are introduced into the reactor at a gas flow rate ratio of 30:20, and the reactor is kept at 600°C for 4 hours to obtain nitrogen-doped porous carbon.

[0121] The third step involves raising the temperature of the reactor to 800°C under a nitrogen atmosphere at a heating rate of 5°C / min. Then, nitrogen, silane, and nitrogen trifluoride are introduced into the reactor at a gas flow rate ratio of 20:25:5, and the reactor is held at 800°C for 6 hours to obtain the silicon-carbon composite anode material.

[0122] The testing process is the same as in Example 1.

[0123] Comparative Example 4

[0124] The first step is to introduce nitrogen gas into the reactor at a flow rate of 30 L / min to form a protective atmosphere. Then, 10 kg of biomass-based porous carbon material is placed in the reactor, and the reactor is heated to 800°C at a heating rate of 5°C / min and held at that temperature for 30 min.

[0125] The second step involves cooling the reactor to 600°C under a nitrogen atmosphere at a cooling rate of 5°C / min. Then, nitrogen, acetylene, and ammonia are introduced into the reactor at a gas flow rate ratio of 30:10:10, and the reactor is kept at 600°C for 4 hours to obtain nitrogen-doped porous carbon.

[0126] The third step involves raising the temperature of the reactor to 800°C under a nitrogen atmosphere at a heating rate of 5°C / min. Then, nitrogen and silane are introduced into the reactor at a gas flow rate ratio of 20:25, and the reactor is kept at 800°C for 6 hours to obtain nitrogen-doped silicon-carbon composite anode material.

[0127] The testing process is the same as in Example 1.

[0128] Table 1 summarizes the test results of Examples 1-12 and Comparative Examples 1-4 of the present invention.

[0129]

[0130] Table 1

[0131] As can be seen from the data in Table 1, the 1.5V lithium intercalation capacity and first-cycle coulombic efficiency of Examples 1-12 of the present invention are higher than those of Comparative Examples 1-4. This is because silicon doping can improve the specific capacity of porous carbon. Nitrogen doping induces uniform silicon deposition, reduces irreversible lithium consumption during battery cycling, and improves the first-cycle coulombic efficiency.

[0132] The first-cycle expansion rate of the electrodes in Examples 1-12 is significantly lower than that in Comparative Examples 1-4. This is because the material in this application has undergone carbon / nitrogen co-deposition, forming CN bonds, which on the one hand helps nitrogen doping, and on the other hand ensures the uniformity of silicon deposition.

[0133] Examples 1-12 showed significantly better capacity retention after 200 cycles compared to Comparative Examples 1-4. This is because fluorine doping facilitates the formation of a stable SE I film during cycling, thereby improving cycle stability.

[0134] Figure 3 The image shows the SEM image of the silicon-carbon composite anode material prepared in Example 1 of this invention. It can be seen that the size of the silicon-carbon composite anode material is about 6 μm, which is a spherical structure.

[0135] Figure 4 The figures show the first-cycle charge-discharge curves of the silicon-carbon composite anode materials prepared in Example 1 and Comparative Example 1 of this invention. It can be seen from the figures that the first-cycle coulombic efficiency of the coin cell in Example 1 is significantly better than that in Comparative Example 1. This is because nitrogen doping induces uniform silicon deposition, reducing irreversible lithium consumption during cycling and thus improving the first-cycle coulombic efficiency.

[0136] 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 silicon-carbon composite anode material, characterized in that, The silicon-carbon composite anode material comprises porous carbon and doping elements; The silicon-carbon composite anode material is prepared by chemical vapor deposition with temperature-controlled deposition rate, using porous carbon as a framework, and the doping elements are distributed in the pores of the porous carbon at the nanoscale. The doping elements include C, N, Si, and F.

2. The silicon-carbon composite anode material according to claim 1, characterized in that, The porous carbon includes one or more of resin-based porous carbon, biomass-based porous carbon, and metal-organic framework-derived porous carbon; the pore size of the porous carbon is 0.2 nm-100 nm; the particle size of the silicon-carbon composite anode material is 5 μm-10 μm.

3. The silicon-carbon composite anode material according to claim 1, characterized in that, In the silicon-carbon composite anode material, the mass percentage of nitrogen is 5%-10%, the mass percentage of fluorine is 1%-5%, the mass percentage of silicon is 40%-45%, and the mass percentage of carbon is 45%-50%.

4. A method for preparing the silicon-carbon composite anode material according to any one of claims 1-3, characterized in that, The preparation method includes: Under an inert atmosphere, carbon source gas and nitrogen source gas are introduced into a reactor containing porous carbon for a first heat treatment, so that the nitrogen source gas and carbon source gas decompose and form CN covalent bonds, which are deposited in the pores of the porous carbon to obtain nitrogen-doped porous carbon. Under an inert atmosphere, silicon source gas and fluorine source gas are introduced into the reactor for a second heat treatment, so that the silicon source gas and fluorine source gas decompose and deposit in the pores of nitrogen-doped porous carbon to obtain a silicon-carbon composite anode material, wherein the silicon-carbon composite anode material includes nitrogen and fluorine elements.

5. The preparation method according to claim 4, characterized in that, The flow rate ratio of the inert atmosphere, carbon source gas, and nitrogen source gas is [30-40]:[5-10]:[5-10]; the specific conditions for the first heat treatment are: temperature 500℃-800℃, time 2 hours-5 hours.

6. The preparation method according to claim 4, characterized in that, The flow rate ratio of the inert atmosphere, silicon source gas, and fluorine source gas is 20:[20-25]:[5-10]; the specific conditions for the second heat treatment are: temperature 700℃-1000℃, time 4 hours-10 hours.

7. The preparation method according to claim 4, characterized in that, The carbon source gas includes one or more of methane, acetylene, and ethylene; the nitrogen source gas includes one or more of ammonia, nitric oxide, and nitrogen dioxide.

8. The preparation method according to claim 4, characterized in that, The silicon source gas includes one or more of silane, silane, and chlorosilane; the fluorine source gas includes one or more of nitrogen trifluoride, carbon tetrafluoride, and fluorinated acetylene.

9. A negative electrode sheet, characterized in that, The negative electrode sheet comprises the silicon-carbon composite negative electrode material as described in any one of claims 1-3.

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

Images