Novel silicon carbon material as well as preparation process and application thereof

Abstract

The invention relates to a novel silicon-carbon material and a preparation method and application thereof, the silicon-carbon material comprises a graphite substrate, a silicon layer coating the outer surface of the graphite substrate and a silicon carbide layer coating the outer surface of the silicon layer, and a graphite-silicon-silicon carbide three-layer composite structure is formed; wherein the silicon layer and the silicon carbide layer are formed by one-time continuous deposition through a chemical vapor deposition process; the silicon carbon material is applied to a negative electrode material of a lithium ion battery. According to the novel silicon-carbon material as well as the preparation method and the application thereof, a single chemical vapor deposition process is adopted, and selective deposition of a silicon material and a silicon carbide material is realized by accurately regulating and controlling the hydrogen content in a deposition atmosphere on the premise of not changing equipment and raw materials; according to the method, the novel silicon carbon material with the SiC coated silicon structure (SiC coated Si / G) is successfully prepared.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of silicon-carbon materials, and particularly relates to a novel silicon-carbon material, a preparation process thereof and application of the silicon-carbon material in lithium ion batteries. BACKGROUND

[0002] Surface coating treatment of silicon material is a widely recognized key process strategy that can significantly improve the comprehensive performance of the silicon material. The core advantage of this technology is that, by constructing a uniform coating layer, the repeated volume expansion effect of silicon during lithium ion intercalation and deintercalation can be effectively alleviated. This expansion is the main reason for stress accumulation in the interior of silicon particles, which eventually leads to material structure pulverization failure. The existence of the coating structure is like a flexible constraint framework, which significantly improves the structural integrity of the silicon material during the cycle process, thereby greatly enhancing the overall stability of the electrode. Moreover, the coating layer also plays a crucial role as an isolation barrier. It physically separates the silicon active material from the electrolyte, minimizing direct contact between the two. This isolation has a dual positive effect: on the one hand, it helps to induce the formation of a more uniform and structurally dense solid electrolyte interface film (SEI film) on the surface of the silicon-carbon composite material during its participation in electrochemical reactions, and this stable SEI film is crucial for maintaining long-term cycle performance; on the other hand, the coating treatment can effectively reduce the overall specific surface area of the composite material.

[0003] In particular, a smaller specific surface area is directly related to a reduction in the total amount of SEI film formation, which in turn significantly reduces the amount of active lithium ions continuously consumed due to the formation of irreversible SEI film, which is extremely beneficial for improving the initial efficiency and long-term capacity retention rate of the battery.

[0004] In terms of specific preparation process, chemical vapor deposition (CVD) is a common technical means for constructing such silicon-carbon composite materials with a coating structure. However, the traditional CVD process has obvious complexity problems. In order to realize the sequential construction of silicon deposition and subsequent carbon coating layer, multiple independent chemical vapor deposition processes are often carried out in steps. In this process, different reaction precursors (i.e. silicon source and carbon source) must be frequently replaced, which not only increases the number of steps and prolongs the time of the entire preparation process, but also increases the process difficulty and complexity of accurately controlling the thickness, uniformity and final composite structure of the coating layer.

[0005] Therefore, without changing the equipment and raw materials, the present application realizes the selective deposition of silicon material and silicon carbide material by precisely controlling the hydrogen content in the deposition atmosphere, and prepares a novel silicon-carbon material with a SiC-coated silicon (SiC@Si / G) double-layer structure, thereby improving the overall electrochemical stability of the composite material. SUMMARY

[0006] The application aims to provide a novel silicon-carbon material, a preparation process and application thereof, and aims to solve the defects of silicon materials in the prior art and the deficiencies of traditional coating processes.

[0007] The application aims to provide a novel silicon-carbon material, a preparation process and application thereof, and aims to solve the defects of silicon materials in the prior art and the deficiencies of traditional coating processes. The application aims to provide a novel silicon-carbon material, a preparation process and application thereof, and aims to solve the defects of silicon materials in the prior art and the deficiencies of traditional coating processes.

[0008] The application further relates to a preparation process of the novel silicon-carbon material, and the preparation process comprises the following steps. S1, raw material pretreatment: silicon powder and graphite are added into a solvent, and mechanical stirring is combined with ultrasonic treatment to realize uniform dispersion, thereby obtaining a mixture; the mixture is subjected to suction filtration and drying, thereby obtaining a silicon-doped graphite sample; S2, chemical vapor deposition: the silicon-doped graphite sample obtained in S1 is placed in a tube furnace, and is heated to 800-1000 DEG C at an argon atmosphere and a heating rate of 5-15 DEG C / min; then, the sample is kept at the temperature for 5-20 min; during the process, the argon flow rate of a main gas path is set to 0.5-1.0 L / min, the hydrogen flow rate of a branch gas path is set to 0.1-0.5 L / min, and the nitrogen flow rate of a current-carrying gas path is set to 0.05-0.2 L / min; in the first stage, dichlorodimethylsilane which is liquid at room temperature is used as a silicon source, the temperature of a water bath is maintained at 40-60 DEG C to ensure stable vaporization of the silicon source and delivery of the silicon source into the tube furnace, and the silicon-doped graphite sample is subjected to a silicon layer deposition reaction for 30-60 min; in the second stage, the hydrogen of the branch gas path is closed, and other conditions are maintained, and the silicon-doped graphite sample is subjected to a silicon carbide layer deposition reaction for 10-30 min; S3, cooling: after the chemical vapor deposition is completed, heating is stopped, and the sample is naturally cooled to room temperature under the argon atmosphere, thereby obtaining a silicon-carbon material.

[0009] Further, in the above preparation process of the novel silicon-carbon material, the particle size of the silicon powder is 20-60 nm, the graphite is spherical graphite and the particle size is 12-20 um, and the mass ratio of the silicon powder to the graphite is 1:150-250; the solvent is a mixed solution of methanol and ethanol, and the volume ratio of methanol to ethanol is 1:1; and the mechanical stirring is combined with ultrasonic treatment for 20-60 min.

[0010] Preferably, the mass ratio of the silicon powder to the graphite is 1:200.

[0011] Further, in the preparation method of the novel silicon-carbon material, the silicon-doped graphite sample obtained in S1 is uniformly spread on carbon paper and placed in a tube furnace, and then heated to 900℃ at a heating rate of 10℃ / min under an argon atmosphere, and kept at 900℃ for 10 minutes, during which the argon flow rate of the main gas path is set to 0.8 L / min, the hydrogen flow rate of the branch gas path is set to 0.2 L / min, and the nitrogen flow rate of the current-carrying gas path is set to 0.1 L / min; in the first stage, the silicon source is ensured to be stably vaporized and transported into the tube furnace by maintaining the temperature of the water bath at 50℃, and the silicon layer deposition reaction time is 50 minutes; and in the second stage, the silicon carbide layer deposition reaction time is 20 minutes.

[0012] The application also relates to a lithium ion battery containing the above-mentioned silicon-carbon material or the silicon-carbon material prepared by the above-mentioned preparation method, and the silicon-carbon material is used in a negative electrode sheet of the lithium ion battery.

[0013] Further, in the lithium ion battery, the negative electrode sheet comprises the following components in parts by weight: 6-9 parts of the silicon-carbon material, 2-0.5 parts of polyvinylidene fluoride, and 2-0.5 parts of carbon black; and the preparation of the negative electrode sheet comprises the following steps: S1 negative electrode slurry preparation: the silicon-carbon material, the polyvinylidene fluoride and the carbon black are added into a solvent, and then mechanically stirred for 6-18 hours to form a uniform negative electrode slurry; S2 coating: the negative electrode slurry obtained in S1 is uniformly coated on a copper foil by using a coating machine; S3 post-treatment and punching and weighing: the copper foil coated with the negative electrode slurry is subjected to vacuum drying and rolling operations, and then punched into negative electrode sheets and accurately weighed, so that the active material load of each negative electrode sheet is controlled to be in the range of 0.90 to 1.05 mg, and the surface density is 62.1 to 70.2 mg / cm2.

[0014] Preferably, the negative electrode sheet comprises the following components in parts by weight: 7 parts of the silicon-carbon material, 2 parts of the polyvinylidene fluoride, and 1 part of the carbon black.

[0015] Preferably, the solvent is N-methyl-2-pyrrolidone (NMP).

[0016] Preferably, the diameter of the negative electrode sheet is 12 mm.

[0017] Further, the lithium ion battery as described above, the lithium ion battery includes a button half battery, a button full battery; when the lithium ion battery is a button half battery, the negative electrode sheet is used as the working electrode, the lithium sheet is used as the counter electrode and the reference electrode; when the lithium ion battery is a button full battery, the negative electrode sheet is used in combination with the positive electrode sheet.

[0018] Preferably, the assembly process of the lithium ion battery (such as a button half battery or a button full battery) is completed in a glove box with a high-purity argon atmosphere, so as to isolate the moisture and oxygen in the environment.

[0019] Further, the lithium ion battery as described above, the electrolyte system used by the lithium ion battery includes: lithium hexafluorophosphate, ethylene carbonate, dimethyl carbonate and fluoroethylene carbonate; the separator used by the lithium ion battery is a polypropylene porous membrane; after the lithium ion battery is assembled, a sealing machine is used for sealing, and then it is placed in an oxygen-free environment for standing, so as to ensure that the electrolyte fully penetrates the electrode material.

[0020] Preferably, the electrolyte system used by the lithium ion battery (such as a button half battery or a button full battery) is 1 mol / L lithium hexafluorophosphate dissolved in a mixed solvent with a volume ratio of ethylene carbonate to dimethyl carbonate being 1:1, and 10% fluoroethylene carbonate by volume fraction is added.

[0021] Preferably, the separator used by the lithium ion battery (such as a button half battery or a button full battery) is a Celgard2400 polypropylene porous membrane; after the lithium ion battery (such as a button half battery or a button full battery) is assembled, a sealing machine is used for sealing, the pressure of the sealing machine is set to 5Mpa, and then it is placed in an oxygen-free environment for standing for 24h, so as to ensure that the electrolyte fully penetrates the electrode material.

[0022] Further, the lithium ion battery as described above, the positive electrode sheet includes the following components in weight fraction: 80-100 parts of ternary positive electrode material, 1-10 parts of polyvinylidene fluoride, and 1-10 parts of carbon black; the preparation of the positive electrode sheet includes the following steps: S1 positive electrode slurry preparation: dry grinding and pre-mixing ternary positive electrode material, polyvinylidene fluoride and carbon black, then mixing and dispersing in a solvent to obtain a positive electrode slurry; S2 coating: using a coating machine to uniformly coat the positive electrode slurry obtained in S1 on an aluminum foil; S3 post-treatment and punching and weighing: vacuum drying and rolling operation are performed on the aluminum foil coated with the positive electrode slurry, and then punching and weighing are performed to control the active material load of each positive electrode sheet to be in the range of 3.24 to 3.78mg.

[0023] Preferably, the ternary positive electrode material is NCM811.

[0024] Preferably, the positive electrode sheet comprises the following components in parts by weight: NCM811 90 parts, polyvinylidene fluoride 5 parts, carbon black 5 parts.

[0025] Preferably, the solvent is N-methyl-2-pyrrolidone (NMP).

[0026] Preferably, the diameter of the positive electrode sheet is 12 millimeters.

[0027] Compared with the prior art, the application has the following beneficial effects: The novel silicon-carbon material, the preparation method and application thereof disclosed by the application, by using a single chemical vapor deposition process, without changing the equipment and raw materials, by precisely controlling the hydrogen content in the deposition atmosphere, the selective deposition of silicon material and silicon carbide material is realized; by the preparation method, a novel silicon-carbon material with a silicon carbide-coated silicon (SiC@Si / G) structure is successfully prepared, wherein the silicon carbide layer is coated on the outer surface of the silicon layer, which effectively isolates the direct contact between silicon and electrolyte, thereby significantly improving the overall electrochemical stability of the negative electrode material; the preparation method selects dichlorodimethylsilane as a silicon source, in the same deposition period, by controlling the atmosphere condition: in the hydrogen-rich atmosphere, the existence of hydrogen inhibits the generation of SiC, and silicon nanofibers are preferentially deposited on the surface of the spherical graphite substrate; then, switching to a non-hydrogen atmosphere, a silicon carbide layer is deposited on the surface of the silicon layer; this selective deposition strategy based on atmosphere control not only simplifies the preparation process, improves the efficiency and product quality, but also can obtain pure silicon and SiC two deposition products under different atmosphere conditions; finally, the SiC@Si / G composite material is successfully prepared by taking spherical graphite as the substrate, which has important application value and market prospect in the field of lithium ion batteries. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 EDX surface element distribution maps of the graphite of the comparative example 3 ((a), (b), (c)), the silicon-carbon material of the comparative example 2 ((d), (e), (f)), and the silicon-carbon material of the example 1 ((g), (h), (i)); Figure 2 Electrochemical impedance spectrograms of the graphite of the comparative example 3, the silicon-carbon material (Si / G) of the comparative example 2, the carbon-silicon material (Si@G) of the comparative example 1, and the silicon-carbon material (SiC@Si / G) of the example 1; Figure 3 Cycle performance graphs of button cells using the graphite of the comparative example 3, the silicon-carbon material (Si / G) of the comparative example 2, the carbon-silicon material (Si@G) of the comparative example 1, and the silicon-carbon material (SiC@Si / G) of the example 1 as negative electrodes; Figure 4Scanning electron microscope images of the changes before and after 100 cycles of the graphite of Comparative Example 3 of the present application, the silicon-carbon material (SiC@Si / G) of Example 1 as an anode. DETAILED DESCRIPTION

[0029] The following describes the technical solutions in the examples of the present application in combination with the accompanying drawings of Example 1, Comparative Examples 1-3, Figure 1 2 , 3, 4, and specific experimental data. Obviously, the described examples are only some of the examples of the present application, but not all. Based on the examples in the present application, all other examples obtained by those skilled in the art without creative labor are within the protection scope of the present application.

[0030] In the following examples of the present application, the graphite is selected from EP5-H of Shanghai Sun Sun Technology Co., Ltd., the silicon powder is selected from S130843 of Aladdin, the polyvinylidene fluoride is selected from 5130 of Solvay, the conductive agent carbon black is selected from SP of Yireisi, and the ternary positive electrode material (NCM811) is selected from nickel-cobalt-manganese 811 positive electrode of Kouroude.

[0031] Unless otherwise specified, the materials, methods and devices used in the examples of the present application are conventional materials, methods and devices in the technical field.

[0032] The following Example 1, Comparative Examples 1-3 provide a silicon-carbon material, a preparation method thereof and an application thereof in a lithium ion battery.

[0033] Example 1 The silicon-carbon material of Example 1 is prepared including the following contents: S1 raw material pretreatment: 100 mg of silicon powder (particle size of 20-60 nm) and 20 g of graphite (particle size of ) are added into 200 ml of solvent (the solvent is mixed and configured according to a volume ratio of 1:1 of methanol and ethanol), and mechanical stirring combined with ultrasonic treatment is performed for 30 min to achieve uniform dispersion, to obtain a mixture. The mixture is suction filtered and dried to obtain a silicon-doped graphite sample; ​S2 Chemical vapor deposition: The silicon-doped graphite sample obtained in S1 was evenly spread on carbon paper and placed in a tube furnace. The temperature was raised to 900°C at a rate of 10°C / min under an argon atmosphere. After the temperature reached 900°C, it was held for 10 minutes. During this period, the argon flow rate of the main gas path was set to 0.8 L / min, the hydrogen flow rate of the branch gas path was set to 0.2 L / min, and the nitrogen flow rate of the carrier gas path was set to 0.1 L / min. Under these conditions, in the first stage, dichlorodimethylsilane, which is liquid at room temperature, was used as the silicon source. The temperature of the water bath was maintained at 50°C to ensure stable vaporization of the silicon source and its delivery to the reaction zone in the tube furnace. The silicon-doped graphite sample underwent silicon layer deposition reaction for 50 minutes. In the second stage, the other conditions remained unchanged, and only the hydrogen in the branch gas path was turned off. At this time, the silicon-doped graphite sample underwent silicon carbide layer deposition reaction for 20 minutes. S3 Cooling: After the completion of chemical vapor deposition, the heating was stopped, and the sample was naturally cooled to room temperature under an argon atmosphere. A silicon-carbon material with a graphite-silicon-silicon carbide three-layer structure (SiC@Si / G) was obtained.

[0034] The negative electrode sheet of Example 1 was prepared, including the following contents: S1 Negative electrode slurry preparation: The silicon-carbon material of Example 1, polyvinylidene fluoride, and carbon black were added to N-methyl-2-pyrrolidone (NMP) in a mass ratio of 7:2:1. After mechanical stirring for 12 hours, a uniform negative electrode slurry was formed. S2 Coating: The negative electrode slurry obtained in S1 was evenly coated on a copper foil using a coating machine. S3 Post-treatment and punching and weighing: The copper foil coated with the negative electrode slurry was subjected to vacuum drying and rolling operations, then punched into negative electrode sheets with a diameter of 12 mm and accurately weighed. The active material load of each negative electrode sheet was controlled to be in the range of 0.90 to 1.05 mg, corresponding to a surface density of 62.1 to 70.2 mg / cm2.

[0035] The positive electrode sheet of Example 1 was prepared, including the following contents: S1 Positive electrode slurry preparation: The ternary positive electrode material NCM811 was selected as the active material. NCM811, polyvinylidene fluoride, and carbon black were dry-mixed and pre-mixed in a mass ratio of 95:5:5, then mixed and dispersed in N-methyl-2-pyrrolidone (NMP) by mechanical stirring for 12 hours to obtain a positive electrode slurry. S2 Coating: The positive electrode slurry obtained in S1 was evenly coated on an aluminum foil using a coating machine. S3 Post-treatment and punching and weighing: The aluminum foil coated with the positive electrode slurry was subjected to vacuum drying and rolling operations, then punched into positive electrode sheets with a diameter of 12 mm and accurately weighed. In order to ensure that the negative electrode capacity is about 120% of the positive electrode capacity, the NCM811 active material load of each positive electrode sheet was controlled to be in the range of about 3.24 to 3.78 mg.

[0036] The coin-type half cell of Example 1 was assembled including the following: The assembly process was completed in an argon glovebox to isolate the moisture and oxygen in the environment. The CR2032 type battery shell was used, the negative electrode sheet of Example 1 was used as the working electrode, and the lithium metal sheet was used as the counter electrode and reference electrode. The electrolyte system was 1 mol / L lithium hexafluorophosphate (LiPF6) dissolved in ethylene carbonate (EC) and dimethyl carbonate (DMC) mixed solvents with a volume ratio of 1:1, and 10% volume fraction of fluoroethylene carbonate (FEC) was added, and the Celgard 2400 polypropylene porous membrane was selected as the separator. The assembly sequence was as follows: placing the positive electrode shell, placing the working electrode (negative electrode sheet of Example 1), adding electrolyte, laying the separator, adding electrolyte again, placing the lithium metal sheet, adding the gasket, placing the spring sheet, and covering the negative electrode shell. The assembled coin-type half cell was sealed using an automatic sealing machine, and the pressure of the automatic sealing machine was set to 5 MPa. The sealed coin-type half cell was placed in an oxygen-free environment for 24 hours to ensure that the electrolyte was fully infiltrated into the electrode material, and then the electrochemical performance was characterized.

[0037] The coin-type full cell of Example 1 was assembled including the following: The assembly environment was the same as the coin-type half cell described above (argon glovebox). The negative electrode sheet of Example 1 was used as the negative electrode, and the positive electrode sheet of Example 1 was used as the positive electrode. The electrolyte (1M LiPF6 in EC / DMC (1:1 v / v) + 10% FEC) and the separator (Celgard 2400) remained unchanged. The assembly sequence was as follows: placing the positive electrode shell, placing the positive electrode sheet, adding electrolyte, laying the separator, adding electrolyte again, placing the negative electrode sheet, adding the gasket, placing the spring sheet, and covering the negative electrode shell. The subsequent packaging and standing steps were consistent with the coin-type half cell assembly.

[0038] Comparative Example 1 The silicon-carbon material of Comparative Example 1 was prepared including the following: Preparation of S1: 100 mg of silicon powder (particle size of 20-60 nm) and 20 g of graphite (particle size of ) were added to 200 ml of solvent (a mixture of methanol and ethanol with a volume ratio of 1:1), and mechanical stirring combined with ultrasonic treatment for 30 min was used to achieve uniform dispersion. The mixture was filtered and dried to obtain a silicon-doped graphite sample. S2 Chemical vapor deposition: The silicon-doped graphite sample obtained in S1 was evenly spread on carbon paper and placed in a tube furnace. The temperature was raised to 900°C at a rate of 10°C / min under an argon atmosphere. After the temperature reached 900°C, the sample was kept at this temperature for 10 minutes. During this time, the argon flow rate of the main gas path was set to 0.8 L / min, the hydrogen flow of the branch gas path was closed, and the nitrogen flow rate of the carrier gas path was 0.1 L / min. Under these conditions, dichlorodimethylsilane, which was liquid at room temperature, was used as the silicon source. The temperature of the water bath was maintained at 50°C to ensure stable vaporization of the silicon source and its delivery to the reaction zone in the tube furnace. The silicon-doped graphite sample underwent silicon carbide deposition for 20 minutes. S3 Cooling: After the completion of chemical vapor deposition, the heating was stopped, and the sample was naturally cooled to room temperature under an argon atmosphere. A silicon-carbon material with a graphite-silicon carbide bilayer structure (SiC@G) was obtained.

[0039] The negative electrode sheet of Comparative Example 1 was prepared as follows: S1 Preparation of negative electrode slurry: The silicon-carbon material of Comparative Example 1, polyvinylidene fluoride, and carbon black were added to N-methyl-2-pyrrolidone (NMP) at a mass ratio of 7:2:1. Mechanical stirring was performed for 12 hours to form a uniform negative electrode slurry. S2 Coating: The negative electrode slurry obtained in S1 was uniformly coated on a copper foil using a coating machine. S3 Post-processing and punching and weighing: The copper foil coated with the negative electrode slurry was subjected to vacuum drying and rolling operations, then punched into negative electrode sheets with a diameter of 12 mm and accurately weighed. The active material loading of each negative electrode sheet was controlled to be within the range of 0.90 to 1.05 mg, corresponding to a surface density of 62.1 to 70.2 mg / cm2.

[0040] The positive electrode sheet of Comparative Example 1 was prepared as follows: S1 Preparation of positive electrode slurry: The ternary positive electrode material NCM811 was selected as the active material. NCM811, polyvinylidene fluoride, and carbon black were dry-mixed and pre-mixed at a mass ratio of 95:5:5, then mixed and dispersed in N-methyl-2-pyrrolidone (NMP) by mechanical stirring for 12 hours to obtain a positive electrode slurry. S2 Coating: The positive electrode slurry obtained in S1 was uniformly coated on an aluminum foil using a coating machine. S3 Post-processing and punching and weighing: The aluminum foil coated with the positive electrode slurry was subjected to vacuum drying and rolling operations, then punched into positive electrode sheets with a diameter of 12 mm and accurately weighed. In order to ensure that the negative electrode capacity is about 120% of the positive electrode capacity, the NCM811 active material loading of each positive electrode sheet was controlled to be within the range of about 3.24 to 3.78 mg.

[0041] The button-type half-cell of Comparative Example 1 was assembled as follows: The assembly process was completed in a glove box with high-purity argon atmosphere to isolate moisture and oxygen in the environment. Using a CR2032 battery shell, the negative electrode sheet of Comparative Example 1 was used as the working electrode, and a lithium metal sheet was used as the counter electrode and reference electrode. The electrolyte system was 1 mole / liter concentration of lithium hexafluorophosphate (LiPF6) dissolved in ethylene carbonate (EC) and dimethyl carbonate (DMC) mixed solvent with a volume ratio of 1:1, and 10% by volume of fluoroethylene carbonate (FEC) was added, and the separator was Celgard 2400 polypropylene porous membrane. The assembly sequence was as follows: place the positive electrode shell, insert the working electrode (negative electrode sheet of Comparative Example 1), drop the electrolyte, lay the separator, drop the electrolyte again, place the lithium metal sheet, add the gasket, place the spring sheet, and cover the negative electrode shell. The assembled button half-cell was sealed using an automatic sealing machine, and the pressure of the automatic sealing machine was set to 5Mpa. The sealed button half-cell was left to stand in an oxygen-free environment for 24 hours to ensure that the electrolyte was fully penetrated into the electrode material, and then the electrochemical performance was characterized.

[0042] The assembly of the button full cell of Comparative Example 1 included the following: The assembly environment was the same as the button half-cell described above (argon glove box). The negative electrode sheet of Comparative Example 1 was used as the negative electrode, and the positive electrode sheet of Comparative Example 1 was used as the positive electrode. The electrolyte (1M LiPF6 in EC / DMC (1:1 v / v) + 10% FEC) and the separator (Celgard 2400) remained unchanged. The assembly sequence was as follows: place the positive electrode shell, insert the positive electrode sheet, drop the electrolyte, lay the separator, drop the electrolyte again, insert the negative electrode sheet, add the gasket, place the spring sheet, and cover the negative electrode shell. The subsequent packaging and standing steps were consistent with the button half-cell assembly.

[0043] Comparative Example 2 The preparation of the silicon-carbon material of Comparative Example 2 included the following: S1 raw material pretreatment: 100 milligrams of silicon powder (particle size 20-60 nm) and 20 grams of graphite (particle size ) were added to 200 milliliters of solvent (a mixture of methanol and ethanol with a volume ratio of 1:1), and mechanical stirring combined with ultrasonic treatment for 30 min to achieve uniform dispersion, to obtain a mixture. The mixture was suction filtered and dried to obtain a silicon-doped graphite sample; S2 Chemical vapor deposition: The silicon-doped graphite sample obtained in S1 was evenly spread on carbon paper and placed in a tube furnace. The temperature was raised to 900°C at a rate of 10°C / min under an argon atmosphere. After the temperature reached 900°C, the sample was kept at this temperature for 10 minutes. During this time, the argon flow rate of the main gas path was set to 0.8 L / min, the hydrogen flow rate of the branch gas path was set to 0.2 L / min, and the nitrogen flow rate of the carrier gas path was set to 0.1 L / min. Under these conditions, dichlorodimethylsilane, which was liquid at room temperature, was used as the silicon source. The temperature of the water bath was maintained at 50°C to ensure stable vaporization of the silicon source and its delivery to the reaction zone in the tube furnace. The silicon-doped graphite sample underwent a silicon layer deposition reaction for 30 minutes. S3 Cooling: After the completion of the chemical vapor deposition, the heating was stopped, and the sample was naturally cooled to room temperature under an argon atmosphere. A silicon-carbon material with a silicon layer-coated graphite structure (Si / G) was obtained.

[0044] The negative electrode sheet of Comparative Example 2 was prepared as follows: S1 Preparation of negative electrode slurry: The silicon-carbon material, polyvinylidene fluoride, and carbon black of Comparative Example 2 were added to N-methyl-2-pyrrolidone (NMP) at a mass ratio of 7:2:1. Mechanical stirring was performed for 12 hours to form a uniform negative electrode slurry. S2 Coating: The negative electrode slurry obtained in S1 was uniformly coated on a copper foil using a coating machine. S3 Post-treatment and punching and weighing: The copper foil coated with the negative electrode slurry was subjected to vacuum drying and rolling operations, and then punched into negative electrode sheets with a diameter of 12 mm and accurately weighed. The active material load of each negative electrode sheet was controlled to be within the range of 0.90 to 1.05 mg, corresponding to a surface density of 62.1 to 70.2 mg / cm2.

[0045] The positive electrode sheet of Comparative Example 2 was prepared as follows: S1 Preparation of positive electrode slurry: The ternary positive electrode material NCM811 was selected as the active material. NCM811, polyvinylidene fluoride, and carbon black were dry-mixed and pre-mixed at a mass ratio of 95:5:5, and then mixed and dispersed in N-methyl-2-pyrrolidone (NMP) by mechanical stirring for 12 hours to obtain a positive electrode slurry. S2 Coating: The positive electrode slurry obtained in S1 was uniformly coated on an aluminum foil using a coating machine. S3 Post-treatment and punching and weighing: The aluminum foil coated with the positive electrode slurry was subjected to vacuum drying and rolling operations, and then punched into positive electrode sheets with a diameter of 12 mm and accurately weighed. In order to ensure that the negative electrode capacity is about 120% of the positive electrode capacity, the NCM811 active material load of each positive electrode sheet was controlled to be within the range of about 3.24 to 3.78 mg.

[0046] The button-type half-cell of Comparative Example 2 was assembled as follows: The assembly process was completed in a glove box with high-purity argon atmosphere to isolate moisture and oxygen in the environment. The negative electrode sheet of Comparative Example 2 was used as the working electrode, and a lithium metal sheet was used as the counter electrode and reference electrode using a CR2032 battery shell. The electrolyte system was 1 mol / L lithium hexafluorophosphate (LiPF6) dissolved in a mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) with a volume ratio of 1:1, and 10% by volume of fluoroethylene carbonate (FEC) was added. The separator was a Celgard 2400 polypropylene porous membrane. The assembly sequence was as follows: place the positive electrode shell, insert the working electrode (negative electrode sheet of Comparative Example 2), drop the electrolyte, lay the separator, drop the electrolyte again, place the lithium metal sheet, add the gasket, place the spring sheet, and cover the negative electrode shell. The assembled button half-cell was sealed using an automatic sealing machine, and the pressure of the automatic sealing machine was set to 5 MPa. The sealed button half-cell was left to stand for 24 hours in an oxygen-free environment to ensure that the electrolyte fully penetrated the electrode material, and then the electrochemical performance was characterized.

[0047] The assembly of the button full cell of Comparative Example 2 included the following: The assembly environment was the same as the button half-cell described above (argon glove box). The negative electrode sheet of Comparative Example 2 was used as the negative electrode, and the positive electrode sheet of Comparative Example 2 was used as the positive electrode. The electrolyte (1M LiPF6 in EC / DMC (1:1 v / v) + 10% FEC) and the separator (Celgard 2400) remained unchanged. The assembly sequence was as follows: place the positive electrode shell, insert the positive electrode sheet, drop the electrolyte, lay the separator, drop the electrolyte again, insert the negative electrode sheet, add the gasket, place the spring sheet, and cover the negative electrode shell. The subsequent packaging and standing steps were consistent with the button half-cell assembly.

[0048] Comparative Example 3 The negative electrode sheet of Comparative Example 3 was prepared as follows: S1 negative electrode slurry preparation: graphite, polyvinylidene fluoride, and carbon black were added to N-methyl-2-pyrrolidone (NMP) in a mass ratio of 7:2:1, and mechanical stirring was performed for 12 hours to form a uniform negative electrode slurry; S2 coating: the negative electrode slurry obtained in S1 was uniformly coated on a copper foil using a coating machine; S3 post-treatment and punching and weighing: the copper foil coated with the negative electrode slurry was vacuum dried and rolled, then punched into a negative electrode sheet with a diameter of 12 mm and accurately weighed, with the active material loading of each negative electrode sheet controlled within the range of 0.90 to 1.05 mg, corresponding to a surface density of 62.1 to 70.2 mg / cm2.

[0049] The positive electrode sheet of Comparative Example 3 was prepared as follows: S1 positive electrode slurry preparation: Select ternary positive electrode material NCM811 as active material, dry grinding pre-mixing NCM811, polyvinylidene fluoride, carbon black according to the mass ratio of 95:5:5, then mixing and dispersing in N-methyl-2-pyrrolidone (NMP) for 12 hours by mechanical stirring, to obtain positive electrode slurry; S2 coating: using coating machine to uniformly coat the positive electrode slurry obtained in S1 on the aluminum foil; S3 post-processing and punching and weighing: vacuum drying and rolling operation on the aluminum foil coated with positive electrode slurry, then punching into positive electrode sheet with a diameter of 12 millimeters and accurately weighing, in order to ensure that the negative electrode capacity is about 120% of the positive electrode capacity, control the NCM811 active material loading of each positive electrode sheet in the range of about 3.24 to 3.78 milligrams.

[0050] The assembly of the coin-type half battery of Comparative Example 3 includes the following contents: The assembly process is completed in a glove box with high-purity argon atmosphere to isolate moisture and oxygen in the environment. Using CR2032 type battery shell, the negative electrode sheet of Comparative Example 3 is used as the working electrode, and the lithium sheet simultaneously serves as the counter electrode and reference electrode. The electrolyte system is 1 mol / L lithium hexafluorophosphate (LiPF6) dissolved in a mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) with a volume ratio of 1:1, and 10% volume fraction of fluoroethylene carbonate (FEC) is added, and the separator is selected as Celgard 2400 polypropylene porous membrane. The assembly sequence is as follows: placing the positive electrode shell, putting in the working electrode (the negative electrode sheet of Comparative Example 3), dropping the electrolyte, laying the separator, dropping the electrolyte again, placing the lithium sheet, adding the gasket, placing the spring sheet, and covering the negative electrode shell. The assembled coin-type half battery is sealed using an automatic sealing machine, and the pressure of the automatic sealing machine is set to 5Mpa. The sealed coin-type half battery is placed in an oxygen-free environment for 24 hours to ensure that the electrolyte fully penetrates the electrode material, and then the electrochemical performance is characterized.

[0051] The assembly of the coin-type full battery of Comparative Example 3 includes the following contents: The assembly environment is the same as the coin-type half battery described above (argon glove box). The negative electrode sheet of Comparative Example 3 is used as the negative electrode, and the positive electrode sheet of Comparative Example 3 is used as the positive electrode. The electrolyte (1M LiPF6 in EC / DMC (1:1 v / v) + 10% FEC) and the separator (Celgard 2400) remain unchanged. The assembly sequence is as follows: placing the positive electrode shell, putting in the positive electrode sheet, dropping the electrolyte, laying the separator, dropping the electrolyte again, putting in the negative electrode sheet, adding the gasket, placing the spring sheet, and covering the negative electrode shell. The subsequent packaging and standing steps are consistent with the coin-type half battery assembly.

[0052] Effect verification AsFigure 1 As shown, by EDS elemental distribution analysis on the surface of three different samples (graphite of Comparative Example 3, Si / C material (Si / G) of Comparative Example 2, Si / C material (Si@G) of Comparative Example 1, Si / C material (SiC@Si / G) of Example 1), it is shown that: the original graphite substrate only contains carbon element, and no silicon element is detected. In the Si / C material of Si / G, the silicon layer is successfully and uniformly deposited on the surface of the graphite substrate, and the coverage leads to the difficulty in detecting the carbon signal in the graphite substrate. Further energy spectrum analysis on the Si / C material of SiC@Si / G after chemical vapor deposition shows that the silicon atoms and carbon atoms are uniformly distributed on the surface of the material, and the atomic ratio is close to 1:1, which confirms the formation of uniform SiC coating layer. The SiC coating layer has a certain thickness, which can completely cover the underlying silicon film. In combination with the above results, the Si / C material of SiC@Si / G with uniform element distribution and coating layer thickness is successfully prepared by chemical vapor deposition technology.

[0053] Figure 2 Electrochemical impedance spectroscopy (EIS) of four samples of graphite, SiC@G, Si / G and SiC@Si / G is shown. As shown in the figure, the equivalent circuit in the figure includes electrode ohmic impedance (Rs), charge transfer resistance (Rct), constant phase element (CPE) and Warburg impedance (W). Figure 2 As shown, the equivalent circuit in the figure includes electrode ohmic impedance (Rs), charge transfer resistance (Rct), constant phase element (CPE) and Warburg impedance (W). As the substrate, graphite shows the highest conductivity, with the lowest Rct of 13.4 Ω. After silicon deposition (Si / G) and silicon carbide deposition (SiC@G), the conductivity of the material decreases significantly, and the Rct value increases to 90.17 Ω and 40.29 Ω, respectively. This is due to the fact that the conductivity of silicon and silicon carbide is much lower than that of graphite, and when they are directly deposited on the surface of graphite to form a composite material, the overall conductivity is lower than the original substrate. In contrast, the Rct of the SiC@Si / G sample (57.06 Ω) is lower than that of the pure Si / G composite material, indicating that the deposition of the SiC coating layer on the surface of Si / G can improve the overall conductivity of the sample to a certain extent, which is more beneficial to battery application.

[0054] Figure 3 Graphite (G), Si / C material (Si / G), Si / C material (SiC@G) and Si / C material (SiC@Si / G) are shown. Figure 3Four samples, labeled Graphite, SiC@G, Si / G, and SiC@Si / G, were used as anodes to evaluate the cycling performance of coin cells at a current density of 0.1C. As a control, graphite was used as the anode, resulting in coin cells with initial charge-discharge capacities of 355.0 mAh g⁻¹ and 397.2 mAh g⁻¹, respectively, and an initial coulombic efficiency (CE) of 79.13%. The capacity of the coin cells using SiC@G as the anode (357.2 mAh g⁻¹ / 339.3 mAh g⁻¹) did not show a significant decrease compared to those using graphite. This is because SiC itself has a capacity of 309.0 mAh g⁻¹, and the coating structure helps reduce the specific surface area, slightly improving the initial coulombic efficiency. After silicon deposition, the first-cycle reversible capacities of coin cells using Si / G and SiC@Si / G as anodes were 743.9 mAh g⁻¹ and 702.1 mAh g⁻¹, respectively, with initial coulombic efficiencies of 81.46% and 82.25%, respectively, showing similar efficiencies. However, the specific capacity of SiC@Si / G was lower than that of Si / G because the SiC coating reduced the proportion of silicon material in the overall composite material. After 100 cycles, the capacities of coin cells using graphite, SiC@G, Si / G, and SiC@Si / G as anodes were 347.2 mAh g⁻¹, 332.7 mAh g⁻¹, 489.2 mAh g⁻¹, and 547.1 mAh g⁻¹, respectively. The coin cells using Si / G and SiC@Si / G as anodes exhibited higher capacities compared to those using graphite as anodes, mainly due to the contribution of silicon material. However, the coin cell using Si / G as the negative electrode retained only 65.84% of its capacity after 100 cycles (decreasing to 489.2 mAh g⁻¹), while the coin cell using SiC@Si / G as the negative electrode exhibited superior cycle stability, with a capacity retention of 77.9% (547.1 mAh g⁻¹). This improvement is attributed to the dense SiC coating layer, which effectively suppresses the volume expansion and pulverization of silicon during charge and discharge, thereby delaying material failure and better preserving capacity.

[0055] Figure 4 SEM images of graphite anodes and SiC@Si / G anodes after 100 cycles are shown. Figure 4 As shown, compared to the graphite anode, the SiC@Si / G anode maintains a complete surface without cracks, and the active material particles on its surface are clearly visible. Before cycling, the coating thickness of the graphite anode was approximately 7.28 μm, increasing to 7.44 μm after 100 cycles, with an expansion rate of 3.19%. In contrast, the SiC@Si / G anode had a thickness of 4.39 μm before cycling, increasing to 4.86 μm after cycling, with an expansion rate of 10.7%.

[0056] To sum up, the present application realizes the selective deposition of silicon material and silicon carbide material by precisely controlling the hydrogen content in the deposition atmosphere in a single chemical vapor deposition process without changing the equipment and raw materials. The silicon-carbon composite material with SiC-coated silicon (SiC@Si / G) structure is successfully prepared by using the technical solution of the present application. The SiC layer covers the outside of the silicon material, effectively isolating the direct contact between silicon and electrolyte, thereby significantly improving the overall electrochemical stability of the composite material. This selective deposition strategy based on atmosphere control not only simplifies the preparation process, improves efficiency and product quality, but also can obtain pure silicon and SiC deposition products under different atmosphere conditions.

[0057] The present application has many specific application approaches, and the above description is only the preferred embodiment of the present application. It should be noted that the above examples are only used to illustrate the present application and are not used to limit the protection scope of the present application. For ordinary skilled persons in the art, several improvements can be made without departing from the principles of the present application, and these improvements should be considered as the protection scope of the present application.

Claims

1. A novel silicon-carbon material, characterized in that, The silicon-carbon material includes a graphite substrate, a silicon layer covering the outer surface of the graphite substrate, and a silicon carbide layer covering the outer surface of the silicon layer, forming a three-layer composite structure of graphite-silicon-silicon carbide; wherein the silicon layer and the silicon carbide layer are formed by continuous deposition in one step through a chemical vapor deposition process.

2. A method for preparing the novel silicon-carbon material as described in claim 1, characterized in that, Includes the following steps: S1 raw material pretreatment: Silicon powder and graphite are added to a solvent, and uniform dispersion is achieved by mechanical stirring combined with ultrasonic treatment to obtain a mixture. The mixture is then filtered and dried to obtain a silicon-doped graphite sample. S2 Chemical Vapor Deposition: The silicon-doped graphite sample obtained in S1 is placed in a tube furnace and heated to 800-1000℃ at a heating rate of 5-15℃ / min under an argon atmosphere, and then held at that temperature for 5-20min. During this period, the argon flow rate in the main gas path is set to 0.5-1.0 L / min, the hydrogen flow rate in the branch gas path is set to 0.1-0.5 L / min, and the nitrogen flow rate in the carrier gas path is set to 0.05-0.2 L / min. In the first stage, dichlorodimethylsilane, which is liquid at room temperature, is used as the silicon source. The silicon source is stably vaporized and transported to the tube furnace by maintaining the water bath temperature at 40-60℃. The silicon-doped graphite sample undergoes a silicon layer deposition reaction for 30-60 minutes. In the second stage, the hydrogen in the branch gas path is turned off, while other conditions are maintained. The silicon-doped graphite sample undergoes a silicon carbide layer deposition reaction for 10-30 minutes. S3 Cooling: After chemical vapor deposition is completed, heating is stopped, and the material is naturally cooled to room temperature under an argon atmosphere to obtain silicon-carbon material.

3. The method for preparing the novel silicon-carbon material according to claim 2, characterized in that, In step S1, the silicon powder has a particle size of 20-60 nm, the graphite is spherical graphite with a particle size of 12-20 μm, and the mass ratio of silicon powder to graphite is 1:150-200; the solvent is a mixed solution of methanol and ethanol, and the volume ratio of methanol to ethanol is 1:1; mechanical stirring combined with ultrasonic treatment for 20-60 min.

4. The method for preparing the novel silicon-carbon material according to claim 2, characterized in that, In step S2, the silicon-doped graphite sample obtained in step S1 is uniformly spread on carbon paper and placed in a tube furnace. Under an argon atmosphere, the temperature is increased to 900°C at a rate of 10°C / min, and then held at 900°C for 10 minutes. During this period, the argon flow rate of the main gas path is set to 0.8 L / min, the hydrogen flow rate of the branch gas path is set to 0.2 L / min, and the nitrogen flow rate of the carrier gas path is set to 0.1 L / min. In the first stage, the silicon source is stably vaporized and transported to the tube furnace by maintaining the water bath temperature at 50°C. The silicon layer deposition reaction time is 50 minutes. In the second stage, the silicon carbide layer deposition reaction time is 20 minutes.

5. A lithium-ion battery, characterized in that, The material comprises the silicon-carbon material as described in claim 1, or the silicon-carbon material prepared by any one of claims 2-4; the silicon-carbon material is used as the negative electrode of a lithium-ion battery.

6. The lithium-ion battery according to claim 5, characterized in that, The negative electrode sheet comprises the following components in parts by weight: 6-9 parts silicon carbon material, 2-0.5 parts polyvinylidene fluoride, and 2-0.5 parts carbon black; the preparation of the negative electrode sheet includes the following steps: S1 Negative electrode slurry preparation: silicon carbon material, polyvinylidene fluoride, and carbon black are added to a solvent and mechanically stirred for 6-18 hours to form a uniform negative electrode slurry; S2 Coating: The negative electrode slurry obtained in S1 is uniformly coated onto the copper foil using a coating machine; S3 Post-processing and punching / weighing: The copper foil coated with negative electrode slurry is vacuum dried and rolled, then punched into negative electrode sheets and weighed precisely. The active material loading of each negative electrode sheet is controlled within the range of 0.90 to 1.05 mg, corresponding to an areal density of 62.1 to 70.2 mg / cm².

7. The lithium-ion battery according to claim 5, characterized in that, The lithium-ion battery includes coin cell half-cells and coin cell full-cells; when the lithium-ion battery is a coin cell half-cell, the negative electrode is used as the working electrode, and the lithium metal sheet is used as the counter electrode and reference electrode; when the lithium-ion battery is a coin cell full-cell, the negative electrode is used in conjunction with the positive electrode.

8. The lithium-ion battery according to claim 6, characterized in that, The electrolyte system used in the lithium-ion battery includes: lithium hexafluorophosphate, ethylene carbonate, dimethyl carbonate, and fluoroethylene carbonate; the separator used in the lithium-ion battery is a polypropylene porous membrane; after the lithium-ion battery is assembled, it is sealed using a sealing machine and then placed in an oxygen-free environment to ensure that the electrolyte fully penetrates the electrode material.

9. The lithium-ion battery according to claim 7, characterized in that, The positive electrode sheet comprises the following components in parts by weight: 80-100 parts of ternary positive electrode material, 1-10 parts of polyvinylidene fluoride, and 1-10 parts of carbon black; the preparation of the positive electrode sheet includes the following steps: S1 cathode slurry preparation: Ternary cathode material, polyvinylidene fluoride and carbon black are dry-milled and premixed, and then mixed and dispersed in a solvent to obtain cathode slurry; S2 Coating: The positive electrode slurry obtained in S1 is uniformly coated onto aluminum foil using a coating machine; S3 Post-processing and punching / weighing: The aluminum foil coated with positive electrode slurry is vacuum dried and rolled, then punched into positive electrode sheets and weighed precisely, controlling the active material loading of each positive electrode sheet to be within the range of 3.24 to 3.78 mg.

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