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

Abstract

This invention relates to a silicon-carbon composite anode material, its preparation method, and its application. The silicon-carbon composite anode material comprises a core and a shell. The core is at least one spherical silicon-carbon primary particle. The particle size Dv50d1 of the spherical silicon-carbon primary particle is 6 μm-10 μm, and the sphericity Ψ1 ≥ 0.9. The shell covers the outer surface of the core and is a carbon coating layer. The particle size Dv50d2 of the silicon-carbon composite anode material is 10 μm-50 μm, d2 / d1 is 1.5-5, the sphericity is 0.6 ≤ Ψ2 ≤ 0.95, and Ψ1 / Ψ2 is 1-1.5. The silicon-carbon composite anode material provided by this invention has a spherical core, ensuring low expansion rate and stress dispersion capability. The irregular morphology of the shell improves stable contact with the electrolyte and conductive agent, resulting in good cycle performance.

Description

Technical Field

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

[0002] With the widespread application of lithium-ion batteries in electric vehicles, portable electronic devices, and energy storage systems, the requirements for their energy density, cycle life, and safety performance are increasing. Silicon-based anode materials, due to their theoretical specific capacity of approximately 4200 mAh / g, have become a popular research direction for replacing traditional graphite anode materials. However, silicon materials undergo drastic volume changes (exceeding 300%) during lithiation / delithiation, which easily leads to electrode pulverization, conductive network damage, and repeated rupture of the solid electrolyte interphase (SEI) film, severely affecting the cycle life and stability of the battery.

[0003] To address the volume expansion issue of silicon materials during charge and discharge, researchers have widely employed strategies such as carbon coating, nanostructure control, and alloying. Among these, spherical silicon-carbon composites exhibit excellent early-stage electrochemical performance in practical applications due to their dense structure, uniform particle size, good fluidization, and ease of large-scale processing. The spherical structure facilitates uniform current distribution and improved electrode density, while also providing a certain stress buffering capacity, thereby effectively reducing structural damage caused by volume expansion and improving initial cycle stability.

[0004] However, the smooth surface of spherical silicon-carbon materials also presents new challenges. During long-term charge-discharge cycles, spherical particles are prone to slippage or detachment at the electrolyte interface, leading to increased contact resistance and consequently accelerated capacity decay and decreased cycle performance in the later stages of battery life. This problem is particularly pronounced when there is a lack of sufficient mechanical interlocking and surface roughness between the spherical particles. Therefore, overcoming the contact failure problem caused by the smooth surface of spherical silicon-carbon anode materials while maintaining their low expansion rate and excellent cycle performance as in the initial stage has become one of the key challenges that urgently need to be addressed in current technology. Summary of the Invention

[0005] 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 applications.

[0006] To achieve the above objectives, in a first aspect, the present invention provides a silicon-carbon composite anode material, the structure of which includes a core and a shell;

[0007] The core is at least one spherical silicon-carbon primary particle; the particle size Dv50d1 of the spherical silicon-carbon primary particle is 6μm-10μm, and the sphericity Ψ1≥0.9;

[0008] The outer shell covers the outer surface of the core, and the outer shell is a carbon coating layer;

[0009] The silicon-carbon composite anode material has a particle size Dv50d2 of 10μm-50μm, a d2 / d1 ratio of 1.5-5, a sphericity of 0.6≤Ψ2≤0.95, and a Ψ1 / Ψ2 ratio of 1-1.5.

[0010] Preferably, the spherical silicon-carbon primary particles include spherical porous carbon, nano-silicon particles, and carbon layers;

[0011] The nano-silicon particles are deposited in the pores of the spherical porous carbon.

[0012] The carbon layer is located on the outer surface of the spherical porous carbon.

[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] Spherical porous carbon is placed in a vapor deposition furnace, and silicon is deposited by introducing a first protective gas and a silicon source gas to obtain a spherical silicon-carbon precursor.

[0015] The spherical silicon-carbon precursor is placed in the vapor deposition furnace, and a second protective gas and a carbon source gas are introduced to perform carbon layer deposition to obtain spherical silicon-carbon primary particles.

[0016] The carbon source is dissolved in a solvent to obtain a carbon source solution;

[0017] The spherical silicon-carbon primary particles are added to the carbon source solution for hydrothermal treatment, causing the carbon source to undergo a cross-linking reaction to obtain a mixed solution, which is then coated with carbon to obtain the silicon-carbon composite anode material.

[0018] Preferably, the first protective gas is nitrogen and / or argon; the flow rate of the first protective gas is 20 L / min to 100 L / min.

[0019] Preferably, the flow ratio of the first protective gas to the silicon source gas is 1:1 to 20:1; the silicon source gas includes one or more of silane, disilane, and trichlorosilane; the silicon deposition temperature is 400℃ to 600℃, and the time is 8 hours to 24 hours.

[0020] Preferably, the heating rate of the carbon layer deposition is 5℃ / min-10℃ / min, the temperature is 500℃-700℃, and the time is 1 hour-10 hours; the carbon source gas includes one or more of methane, acetylene, ethylene, and propylene.

[0021] Preferably, the carbon coating treatment specifically includes:

[0022] The mixed solution is dried at room temperature or spray-dried to obtain a silicon-carbon composite anode material precursor.

[0023] The silicon-carbon composite anode material precursor is subjected to heat treatment; the heat treatment temperature is 400℃-600℃ and the time is 1 hour-3 hours.

[0024] Preferably, the carbon source includes one or more of polyacrylonitrile, polyvinyl alcohol, asphalt, cellulose, resin, sugar, and tar; the solvent includes one or more of deionized water, ethanol, and glycerol; and the hydrothermal treatment is performed at a temperature of 80℃-100℃ for 2-10 hours.

[0025] 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 above, or the silicon-carbon composite negative electrode material prepared by any of the preparation methods described in any of the second aspects above.

[0026] Fourthly, the present invention provides a lithium-ion battery, the lithium-ion battery comprising the negative electrode sheet described in the third aspect above.

[0027] This invention provides a silicon-carbon composite anode material. The spherical porous carbon possesses excellent fluidization and stacking characteristics, enabling the formation of a compact electrode structure with uniform porosity. This facilitates uniform current distribution, reduces local overcurrent reactions, and slows down structural degradation. Silicon deposition within the spherical porous carbon ensures uniform dispersion of silicon expansion stress, preventing localized stress concentration and delaying the breakage of the core spherical particles. The irregular shell structure formed by the carbon coating further restricts silicon expansion. Simultaneously, carbon's flexibility allows it to absorb some expansion energy and maintain the continuity of the conductive network. It also increases contact points with the electrolyte, improving stable contact with both the electrolyte and the conductive agent, thus enhancing battery cycle stability and overcoming the drawback of poor later-stage cycle performance due to loss of electrical contact. Attached Figure Description

[0028] 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;

[0029] Figure 2 A scanning electron microscope (SEM) image of a spherical silicon-carbon precursor provided in an embodiment of the present invention;

[0030] Figure 3 This is a schematic diagram of the synthesis process of the silicon-carbon composite anode material provided in an embodiment of the present invention;

[0031] Figure 4 A flowchart illustrating the preparation method of the silicon-carbon composite anode material provided in this embodiment of the invention. Detailed Implementation

[0032] 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 merely some embodiments of this invention, and not all embodiments. 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.

[0033] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0034] The present invention provides a silicon-carbon composite anode material with the following structure: Figure 1 As shown, it includes the kernel and the shell.

[0035] The core consists of at least one spherical silicon-carbon primary particle. The particle size Dv50d1 of the spherical silicon-carbon primary particle is 6μm-10μm, and the sphericity Ψ1 ≥ 0.9.

[0036] Wherein, particle size Dv50 refers to the median particle size of the material, which is the median value sorted by volume. In the various embodiments of the present invention, the median particle size sorted by volume is specifically used, representing the particle size in the 50% of spherical silicon-carbon primary particles according to volume distribution. Particle size Dv50 is a well-known meaning in the art. The particle size Dv50 of the material provided in the embodiments of the present invention can be determined by instruments and conventional methods known in the art. Specifically, in the various embodiments of the present invention, the particle size Dv50 is determined using a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0037] Sphericity is calculated using the formula defined by Waudelaire for sphericity, as follows:

[0038]

[0039] Where ψ is the Waddle sphericity. dsphere_ is the diameter of a sphere of equal volume (i.e., if the particle is nearly spherical, it is assumed to be spherical, then the diameter of the particle is the diameter of a sphere with the same volume), calculated based on the particle's volume V, i.e., dsphere = (6V / π). 1 / 3 dequiv_ is the equivalent diameter of the particle (i.e., if the particle is close to spherical, it is assumed to be spherical, and the equivalent diameter of the particle is the diameter of a sphere with the same surface area), calculated based on the particle's surface area A, i.e., dequiv = (6A / π). 1 / 2 .

[0040] The particle volume was determined using a Topsizer laser particle size analyzer from Zhuhai Omec Instruments Co., Ltd., and the particle volume was further calculated. The particle surface area was determined using a JW-BK122F specific surface area and pore size analyzer from Beijing Jingwei Gaobo Science and Technology Co., Ltd., based on the principle of gas (nitrogen, argon, etc.) adsorption and desorption.

[0041] The spherical silicon-carbon primary particles can specifically include spherical porous carbon, nano-silicon particles, and a carbon layer. Nano-silicon particles are deposited within the pores of the spherical porous carbon. The carbon layer is located on the outer surface of the spherical porous carbon.

[0042] The outer shell is a carbon coating layer, specifically covering the outer surface of the core.

[0043] The particle size Dv50d2 of the silicon-carbon composite anode material is 10μm-50μm, d2 / d1 is 1.5-5, sphericity is 0.6≤Ψ2≤0.95, and Ψ1 / Ψ2 is 1-1.5.

[0044] This invention provides a silicon-carbon composite anode material. The spherical porous carbon possesses excellent fluidization and stacking characteristics, enabling the formation of a compact electrode structure with uniform porosity. This facilitates uniform current distribution, reduces local overcurrent reactions, and slows down structural degradation. Silicon deposition within the spherical porous carbon ensures uniform dispersion of silicon expansion stress, preventing localized stress concentration and delaying the breakage of the core spherical particles. The irregular shell structure formed by the carbon coating further restricts silicon expansion. Simultaneously, carbon's flexibility allows it to absorb some expansion energy and maintain the continuity of the conductive network. It also increases contact points with the electrolyte, improving stable contact with both the electrolyte and the conductive agent, thus enhancing battery cycle stability and overcoming the drawback of poor later-stage cycle performance due to loss of electrical contact.

[0045] The aforementioned silicon-carbon composite anode material can be prepared by the following method, the process of which is as follows: Figure 4 As shown, it includes the following steps:

[0046] Step 110: Place the spherical porous carbon in a vapor deposition furnace, introduce the first protective gas and silicon source gas to perform silicon deposition, and obtain a spherical silicon-carbon precursor.

[0047] Specifically, the first protective gas can be nitrogen and / or argon. The silicon source gas can include one or more of silane, disilane, and trichlorosilane, preferably silane. The flow rate of the first protective gas is 20 L / min to 100 L / min. The flow ratio of the first protective gas to the silicon source gas can be 1:1 to 20:1. The silicon deposition temperature can be 400℃ to 600℃, preferably 520℃, and the time is 8 hours to 24 hours, preferably 10 hours.

[0048] Silicon deposition can improve the energy density of silicon-carbon anode composite materials.

[0049] SEM image of spherical silicon-carbon precursor as shown Figure 2 As shown in the image.

[0050] Step 120: Place the spherical silicon-carbon precursor in a vapor deposition furnace, introduce a second protective gas and a carbon source gas to deposit a carbon layer, and obtain spherical silicon-carbon primary particles.

[0051] The second protective gas can be nitrogen and / or argon. The carbon source gas can be one or more of methane, acetylene, ethylene, and propylene, preferably acetylene. The heating rate for carbon layer deposition can be 5°C / min-10°C / min, the temperature can be 500°C-700°C, preferably 580°C-600°C, and the time can be 1 hour-10 hours, preferably 6 hours.

[0052] Combination Figure 1 and Figure 3 As shown, the shape of the spherical silicon-carbon primary particles remains unchanged; only a carbon layer forms on the surface of the spherical silicon-carbon precursor. This carbon layer reduces the specific surface area of ​​the spherical silicon-carbon precursor, avoiding the risk of spontaneous combustion caused by direct contact between the silicon particles and air.

[0053] Step 130: Dissolve the carbon source in a solvent to obtain a carbon source solution;

[0054] Specifically, the carbon source may include one or more of polyacrylonitrile, polyvinyl alcohol, asphalt, cellulose, resin, sugars, and tar, with sugars being preferred. Sugars may specifically include one or more of glucose, fructose, sucrose, maltose, starch, lactose, and furfural. The solvent may include one or more of deionized water, ethanol, and glycerol, with deionized water being preferred.

[0055] Step 140: Add spherical silicon-carbon primary particles to a carbon source solution for hydrothermal treatment to allow the carbon source to undergo a cross-linking reaction, resulting in a mixed solution. Then, after carbon coating treatment, silicon-carbon composite anode material is obtained.

[0056] Specifically, the hydrothermal treatment temperature is 80℃-100℃, preferably 100℃, and the time is 2 hours-10 hours, preferably 2 hours. During the hydrothermal treatment, the carbon source undergoes a cross-linking reaction after heating, thereby uniformly coating the spherical silicon-carbon primary particles to form spherical silicon-carbon hydrothermal material, such as... Figure 3 As shown in the image.

[0057] The carbon coating process is as follows:

[0058] First, the mixed solution is dried at room temperature or spray-dried to obtain the silicon-carbon composite anode material precursor.

[0059] The room temperature drying can be carried out in an oven under a nitrogen and / or argon atmosphere. The spray drying process can be carried out in a spray drying device, which can be a centrifugal spray dryer, an airflow spray dryer, or a pressure spray dryer. Specific conditions are: inlet air temperature 150℃-170℃, preferably 165℃; outlet air temperature 80℃-90℃, preferably 85℃; and atomizer frequency 210Hz-230Hz, preferably 220Hz.

[0060] Then, the silicon-carbon composite anode material precursor is subjected to heat treatment.

[0061] The heat treatment can be carried out in a tube furnace, with a nitrogen and / or argon atmosphere, a temperature of 400℃-600℃, preferably 600℃, and a time of 1 hour-3 hours, preferably 2 hours.

[0062] After carbon coating treatment, a carbon coating layer is formed on the surface of the spherical silicon-carbon primary particles, making the surface of the particles no longer a smooth sphere, but an irregular shape, such as... Figure 2 As shown in the image.

[0063] The method for preparing silicon-carbon composite anode material provided in this invention involves depositing silicon in spherical porous carbon, which uniformly disperses the stress caused by silicon expansion, avoids local stress concentration, and slows down the fracture rate of the spherical core particles. The shell structure formed by the carbon coating layer further restricts the expansion of silicon. Simultaneously, carbon's flexibility allows it to absorb some of the expansion energy and maintain the continuity of the conductive network, contributing to improved cycle stability. Furthermore, coating the spherical core with carbon to create an irregular morphology maintains the advantages of low expansion rate and good pressure resistance of spherical particles while overcoming the disadvantage of loss of electrical contact with the electrolyte due to a smooth surface, thereby enhancing the electrochemical performance of the silicon-carbon composite anode material.

[0064] The silicon-carbon composite anode material provided by this invention can be used as an electrode material in energy storage devices such as supercapacitors, lithium-ion batteries, sodium-ion batteries, and dye-sensitized batteries.

[0065] 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.

[0066] Example 1

[0067] The first step involves placing spherical porous carbon in a vapor deposition furnace, introducing nitrogen gas at a rate of 20 L / min, heating the furnace to 520 °C at a rate of 5 °C / min, then introducing silane at a rate of 20 L / min for silicon deposition for 10 hours, and finally cooling the furnace to room temperature by introducing nitrogen gas at a rate of 20 L / min to obtain a spherical silicon-carbon precursor.

[0068] The second step involves placing the spherical silicon-carbon precursor in a vapor deposition furnace, introducing nitrogen gas at a rate of 10 L / min, heating it to 600 °C at a rate of 5 °C / min, and then introducing acetylene at a rate of 10 L / min to deposit a carbon layer for 6 hours, thereby obtaining spherical silicon-carbon primary particles.

[0069] The third step is to dissolve 10g of glucose in 200mL of deionized water to obtain a glucose solution.

[0070] Fourth step: Take 100g of spherical silicon carbide primary particles and add them to the glucose solution, then transfer them to a hydrothermal reactor. Place the hydrothermal reactor in an oven at 100℃ and carry out the hydrothermal reaction for 2 hours to obtain a mixed solution. The stirring speed of the hydrothermal reactor is 300rpm.

[0071] The fifth step involves placing the mixed solution in a tube furnace, introducing nitrogen gas at a rate of 1 L / min, heating it to 600°C at a rate of 3°C / min, holding it at that temperature for 2 hours to perform carbon coating treatment, and then cooling it to obtain the silicon-carbon composite anode material.

[0072] Subsequently, the prepared silicon-carbon anode material was used to fabricate electrodes for lithium-ion batteries, and these electrodes were then used to assemble coin-type half-cells for testing, as detailed below:

[0073] First, silicon-carbon composite anode material, conductive agent acetylene black, and binder are added to deionized water in a mass ratio of 8:1:1 and mixed evenly. The binder is sodium carboxymethyl cellulose and styrene-butadiene rubber in a mass ratio of 1:1. The mixture is prepared into a slurry using a pulping machine, coated onto a copper foil current collector, and dried at 80°C for 12 hours to obtain the electrode sheet.

[0074] Next, cut the dried electrode into 12mm round pieces.

[0075] 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) and dimethyl carbonate (DMC), with a volume ratio of EC to DMC of 1:1. The counter electrode was a lithium sheet.

[0076] 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). The test conditions were as follows: the initial coulombic efficiency was tested at a rate of 0.1C, the charging cutoff voltage was 3V, the discharging cutoff voltage was 0V, and then charge and discharge cycle tests were conducted at a rate of 0.2C.

[0077] Example 2

[0078] The first step involves placing spherical porous carbon in a vapor deposition furnace, introducing nitrogen gas at a rate of 20 L / min, heating the furnace to 520 °C at a rate of 5 °C / min, then introducing silane at a rate of 20 L / min for silicon deposition for 10 hours, and finally cooling the furnace to room temperature by introducing nitrogen gas at a rate of 20 L / min to obtain a spherical silicon-carbon precursor.

[0079] The second step involves placing the spherical silicon-carbon precursor in a vapor deposition furnace, introducing nitrogen gas at a rate of 10 L / min, heating it to 600 °C at a rate of 5 °C / min, and then introducing acetylene at a rate of 10 L / min to deposit a carbon layer for 6 hours, thereby obtaining spherical silicon-carbon primary particles.

[0080] The third step is to dissolve 20g of glucose in 200mL of deionized water to obtain a glucose solution.

[0081] Fourth step: Take 100g of spherical silicon carbide primary particles and add them to the glucose solution, then transfer them to a hydrothermal reactor. Place the hydrothermal reactor in an oven at 100℃ and carry out the hydrothermal reaction for 2 hours to obtain a mixed solution. The stirring speed of the hydrothermal reactor is 300rpm.

[0082] The fifth step involves placing the mixed solution in a tube furnace, introducing nitrogen gas at a rate of 1 L / min, heating it to 600°C at a rate of 3°C / min, holding it at that temperature for 2 hours to perform carbon coating treatment, and then cooling it to obtain the silicon-carbon composite anode material.

[0083] The testing process is the same as in Example 1.

[0084] Example 3

[0085] The first step involves placing spherical porous carbon in a vapor deposition furnace, introducing nitrogen gas at a rate of 20 L / min, heating the furnace to 520 °C at a rate of 5 °C / min, then introducing silane at a rate of 20 L / min for silicon deposition for 10 hours, and finally cooling the furnace to room temperature by introducing nitrogen gas at a rate of 20 L / min to obtain a spherical silicon-carbon precursor.

[0086] The second step involves placing the spherical silicon-carbon precursor in a vapor deposition furnace, introducing nitrogen gas at a rate of 10 L / min, heating it to 600 °C at a rate of 5 °C / min, and then introducing acetylene at a rate of 10 L / min to deposit a carbon layer for 6 hours, thereby obtaining spherical silicon-carbon primary particles.

[0087] The third step is to dissolve 30g of glucose in 200mL of deionized water to obtain a glucose solution.

[0088] Fourth step: Take 100g of spherical silicon carbide primary particles and add them to the glucose solution, then transfer them to a hydrothermal reactor. Place the hydrothermal reactor in an oven at 100℃ and carry out the hydrothermal reaction for 2 hours to obtain a mixed solution. The stirring speed of the hydrothermal reactor is 300rpm.

[0089] The fifth step involves placing the mixed solution in a tube furnace, introducing nitrogen gas at a rate of 1 L / min, heating it to 600°C at a rate of 3°C / min, holding it at that temperature for 2 hours to perform carbon coating treatment, and then cooling it to obtain the silicon-carbon composite anode material.

[0090] The testing process is the same as in Example 1.

[0091] Example 4

[0092] The first step involves placing spherical porous carbon in a vapor deposition furnace, introducing nitrogen gas at a rate of 20 L / min, heating the furnace to 520 °C at a rate of 5 °C / min, then introducing silane at a rate of 20 L / min for silicon deposition for 10 hours, and finally cooling the furnace to room temperature by introducing nitrogen gas at a rate of 20 L / min to obtain a spherical silicon-carbon precursor.

[0093] The second step involves placing the spherical silicon-carbon precursor in a vapor deposition furnace, introducing nitrogen gas at a rate of 10 L / min, heating it to 600 °C at a rate of 5 °C / min, and then introducing acetylene at a rate of 10 L / min to deposit a carbon layer for 6 hours, thereby obtaining spherical silicon-carbon primary particles.

[0094] The third step is to dissolve 40g of glucose in 200mL of deionized water to obtain a glucose solution.

[0095] Fourth step: Take 100g of spherical silicon carbide primary particles and add them to the glucose solution, then transfer them to a hydrothermal reactor. Place the hydrothermal reactor in an oven at 100℃ and carry out the hydrothermal reaction for 2 hours to obtain a mixed solution. The stirring speed of the hydrothermal reactor is 300rpm.

[0096] The fifth step involves placing the mixed solution in a tube furnace, introducing nitrogen gas at a rate of 1 L / min, heating it to 600°C at a rate of 3°C / min, holding it at that temperature for 2 hours to perform carbon coating treatment, and then cooling it to obtain the silicon-carbon composite anode material.

[0097] The testing process is the same as in Example 1.

[0098] Example 5

[0099] The first step involves placing spherical porous carbon in a vapor deposition furnace, introducing nitrogen gas at a rate of 20 L / min, heating the furnace to 520 °C at a rate of 5 °C / min, then introducing silane at a rate of 20 L / min for silicon deposition for 10 hours, and finally cooling the furnace to room temperature by introducing nitrogen gas at a rate of 20 L / min to obtain a spherical silicon-carbon precursor.

[0100] The second step involves placing the spherical silicon-carbon precursor in a vapor deposition furnace, introducing nitrogen gas at a rate of 10 L / min, heating it to 600 °C at a rate of 5 °C / min, and then introducing acetylene at a rate of 10 L / min to deposit a carbon layer for 6 hours, thereby obtaining spherical silicon-carbon primary particles.

[0101] The third step is to dissolve 10g of glucose in 200mL of deionized water to obtain a glucose solution.

[0102] Fourth step: Take 100g of spherical silicon carbide primary particles and add them to the glucose solution. After stirring evenly, perform spray drying treatment. The inlet temperature is 165℃, the outlet temperature is 85℃, and the atomizer frequency is 220Hz.

[0103] The fifth step involves placing the mixed solution in a tube furnace, introducing nitrogen gas at a rate of 1 L / min, heating it to 600°C at a rate of 3°C / min, holding it at that temperature for 2 hours to perform carbon coating treatment, and then cooling it to obtain the silicon-carbon composite anode material.

[0104] The testing process is the same as in Example 1.

[0105] Example 6

[0106] The first step involves placing spherical porous carbon in a vapor deposition furnace, introducing argon gas at a rate of 100 L / min, heating the furnace to 400 °C at a rate of 5 °C / min, then introducing disilane at a rate of 50 L / min for silicon deposition for 24 hours, and finally introducing argon gas at a rate of 20 L / min to cool the furnace to room temperature, thus obtaining a spherical silicon-carbon precursor.

[0107] The second step involves placing the spherical silicon-carbon precursor in a vapor deposition furnace, introducing argon gas at a rate of 10 L / min, heating it to 500 °C at a rate of 10 °C / min, and then introducing ethylene at a rate of 10 L / min to deposit a carbon layer for 10 hours, thereby obtaining spherical silicon-carbon primary particles.

[0108] The third step is to dissolve 10g of fructose in 200mL of deionized water to obtain a fructose solution.

[0109] Fourth step: Take 100g of spherical silicon carbide primary particles and add them to the fructose solution, then transfer them to a hydrothermal reactor. Place the hydrothermal reactor in an oven at 80℃ and carry out the hydrothermal reaction for 10 hours to obtain a mixed solution. The stirring speed of the hydrothermal reactor is 300rpm.

[0110] The fifth step involves placing the mixed solution in a tube furnace, introducing argon gas at a rate of 1 L / min, heating it to 400°C at a rate of 3°C / min, holding it at that temperature for 3 hours to perform carbon coating treatment, and then cooling it to obtain the silicon-carbon composite anode material.

[0111] The testing process is the same as in Example 1.

[0112] Example 7

[0113] The first step involves placing spherical porous carbon in a vapor deposition furnace, introducing argon gas at a rate of 50 L / min, heating to 600 °C at a rate of 5 °C / min, then introducing trichlorosilane at a rate of 25 L / min for silicon deposition for 11 hours, and finally cooling to room temperature by introducing argon gas at a rate of 10 L / min to obtain a spherical silicon-carbon precursor.

[0114] The second step involves placing the spherical silicon-carbon precursor in a vapor deposition furnace, introducing argon gas at a rate of 10 L / min, heating it to 700 °C at a rate of 8 °C / min, and then introducing propylene at a rate of 10 L / min to deposit a carbon layer for 1 hour, thereby obtaining spherical silicon-carbon primary particles.

[0115] The third step is to dissolve 10g of furfural in 200mL of deionized water to obtain a furfural solution.

[0116] Fourth step: Take 100g of spherical silicon carbon primary particles and add them to furfural solution. After stirring evenly, perform spray drying treatment. The inlet temperature is 150℃, the outlet temperature is 90℃, and the atomizer frequency is 210Hz.

[0117] The fifth step involves placing the mixed solution in a tube furnace, introducing nitrogen gas at a rate of 1 L / min, heating it to 500°C at a rate of 3°C / min, holding it at that temperature for 1 hour to perform carbon coating treatment, and then cooling it to obtain the silicon-carbon composite anode material.

[0118] The testing process is the same as in Example 1.

[0119] Comparative Example 1

[0120] The first step involves placing spherical porous carbon in a vapor deposition furnace, introducing nitrogen gas at a rate of 20 L / min, heating the furnace to 520 °C at a rate of 5 °C / min, then introducing silane at a rate of 20 L / min for silicon deposition for 10 hours, and finally cooling the furnace to room temperature by introducing nitrogen gas at a rate of 20 L / min to obtain a spherical silicon-carbon precursor.

[0121] The second step involves placing the spherical silicon-carbon precursor in a vapor deposition furnace, introducing nitrogen gas at a rate of 10 L / min, heating it to 600 °C at a rate of 5 °C / min, and then introducing acetylene at a rate of 10 L / min to deposit a carbon layer for 6 hours, thereby obtaining spherical silicon-carbon primary particles.

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

[0123] Comparative Example 2

[0124] The first step involves placing irregular porous carbon in a vapor deposition furnace, introducing nitrogen gas at a rate of 20 L / min, heating the furnace to 520 °C at a rate of 5 °C / min, then introducing silane at a rate of 20 L / min for silicon deposition for 10 hours, and finally introducing nitrogen gas at a rate of 20 L / min to cool the furnace to room temperature, thus obtaining a spherical silicon-carbon precursor.

[0125] The second step involves placing the spherical silicon-carbon precursor in a vapor deposition furnace, introducing nitrogen gas at a rate of 10 L / min, heating it to 600 °C at a rate of 5 °C / min, and then introducing acetylene at a rate of 10 L / min to deposit a carbon layer for 6 hours, thereby obtaining spherical silicon-carbon primary particles.

[0126] The third step is to dissolve 10g of glucose in 200mL of deionized water to obtain a glucose solution.

[0127] Fourth step: Take 100g of spherical silicon carbide primary particles and add them to the glucose solution, then transfer them to a hydrothermal reactor. Place the hydrothermal reactor in an oven at 100℃ and carry out the hydrothermal reaction for 2 hours to obtain a mixed solution. The stirring speed of the hydrothermal reactor is 300rpm.

[0128] The fifth step involves placing the mixed solution in a tube furnace, introducing nitrogen gas at a rate of 1 L / min, heating it to 600°C at a rate of 3°C / min, holding it at that temperature for 2 hours to perform carbon coating treatment, and then cooling it to obtain the silicon-carbon composite anode material.

[0129] The testing process is the same as in Example 1.

[0130] The test results for each parameter are recorded in Table 1 below.

[0131]

[0132]

[0133] Table 1

[0134] As shown in Table 1, adding glucose as a carbon source can reduce the sphericity of the silicon-carbon composite anode material, thereby improving the capacity retention rate after 500 cycles. This is because carbon coating overcomes the disadvantage of spherical silicon-carbon materials, which, due to their smooth surface, lose electrical contact with the electrolyte later, resulting in poor cycle performance. Simultaneously, it maintains the stress dispersion effect of the spherical silicon-carbon material itself, leading to better voltage resistance of the silicon-carbon composite anode material. While increasing the amount of glucose reduces sphericity, the cycle retention rate does not improve. This is because larger particle size results in a smaller specific surface area, leading to less contact with the electrolyte and fewer active sites, affecting charge and discharge efficiency. Larger gaps between particles prevent the formation of a tight conductive network, resulting in low current conduction efficiency. Larger particles may also be more prone to cracking or damage during this process because they cannot distribute stress as uniformly as smaller particles, causing structural collapse and breakage of the conductive path in the silicon-carbon composite anode material during cycling, leading to rapid performance degradation. Comparative Example 1, lacking carbon coating, only maintained the spherical shape of the silicon-carbon material. Spherical particles are prone to slippage or detachment at the electrolyte interface, leading to increased contact resistance and accelerated capacity decay in later stages. Therefore, the capacity retention rate after 500 cycles decreased significantly. Comparative Example 2, using non-spherical porous carbon, exhibited poor contact with the electrolyte, resulting in a low cycle capacity retention rate.

[0135] 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 method for preparing a silicon-carbon composite negative electrode material, characterized by, The preparation method includes: Spherical porous carbon is placed in a vapor deposition furnace, and silicon is deposited by introducing a first protective gas and a silicon source gas to obtain a spherical silicon-carbon precursor. The spherical silicon-carbon precursor is placed in the vapor deposition furnace, and a second protective gas and a carbon source gas are introduced to perform carbon layer deposition to obtain spherical silicon-carbon primary particles. The carbon source is dissolved in a solvent to obtain a carbon source solution; The spherical silicon-carbon primary particles are added to the carbon source solution for hydrothermal treatment, which causes the carbon source to undergo a cross-linking reaction to obtain a mixed solution. The solution is then coated with carbon to obtain the silicon-carbon composite anode material. The structure of the silicon-carbon composite anode material includes a core and a shell; The core is at least one spherical silicon-carbon primary particle; the particle size Dv50d1 of the spherical silicon-carbon primary particle is 6μm-10μm, and the sphericity Ψ1≥0.9; The outer shell covers the outer surface of the core, and the outer shell is a carbon coating layer; The silicon-carbon composite anode material has a particle size Dv50d2 of 10μm-50μm, a d2 / d1 ratio of 1.5-5, a sphericity of 0.6≤Ψ2≤0.95, and a Ψ1 / Ψ2 ratio of 1-1.

5.

2. The production method according to claim 1, characterized by, The spherical silicon-carbon primary particles include spherical porous carbon, nano-silicon particles, and carbon layers. The nano-silicon particles are deposited in the pores of the spherical porous carbon. The carbon layer is located on the outer surface of the spherical porous carbon.

3. The preparation method according to claim 1, characterized in that, The first protective gas is nitrogen and / or argon; the flow rate of the first protective gas is 20 L / min to 100 L / min.

4. The preparation method according to claim 1, characterized in that, The flow ratio of the first protective gas to the silicon source gas is 1:1 to 20:1; the silicon source gas includes one or more of silane, disilane, and trichlorosilane; the silicon deposition temperature is 400℃ to 600℃, and the time is 8 hours to 24 hours.

5. The preparation method according to claim 1, characterized in that, The heating rate for carbon layer deposition is 5℃ / min-10℃ / min, the temperature is 500℃-700℃, and the time is 1 hour-10 hours; the carbon source gas includes one or more of methane, acetylene, ethylene, and propylene.

6. The preparation method according to claim 1, characterized in that, The carbon coating treatment specifically includes: The mixed solution is dried at room temperature or spray-dried to obtain a silicon-carbon composite anode material precursor. The silicon-carbon composite anode material precursor is subjected to heat treatment; the heat treatment temperature is 400℃-600℃ and the time is 1 hour-3 hours.

7. The preparation method according to claim 1, characterized in that, The carbon source includes one or more of polyacrylonitrile, polyvinyl alcohol, asphalt, cellulose, resin, sugar, and tar; the solvent includes one or more of deionized water, ethanol, and glycerol; the hydrothermal treatment is performed at a temperature of 80℃-100℃ for 2 hours-10 hours.

8. A negative electrode sheet, characterized in that, The negative electrode sheet comprises a silicon-carbon composite negative electrode material prepared by any one of the preparation methods described in claims 1-7.

9. A lithium-ion battery, characterized in that, The lithium-ion battery includes the negative electrode sheet as described in claim 8.

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