Silicon-carbon composite material, method for preparing the same, and use thereof

Abstract

The application discloses a silicon-carbon composite material and a preparation method and application thereof, and belongs to the technical field of lithium ion batteries. The silicon-carbon composite material is composed of the following components: graphite or graphite-like carbon framework, silicon particles dispersed in the carbon framework, and an outermost carbon coating layer; the carbon coating layer encapsulates the silicon particles in the interior. The carbon framework is formed by high-temperature transient sintering of elemental carbon material, the silicon particles are formed by melting and spreading of silicon powder, and the carbon coating layer is formed by transient cracking of carbon hydrates; the high-temperature transient sintering, melting and spreading and transient cracking are completed in one step in the same device. The application has the advantages of simple production process, easy operation of equipment, one-step completion of silicon refining and carbon coating, continuous process, low cost of required raw materials, and easy popularization. Two different carbon sources play the roles of framework and bonding and coating, so that the silicon is stably encapsulated in the carbon material, the destruction of the electrode structure caused by the volume expansion of the silicon is effectively relieved, and good cycle performance is exhibited.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion batteries and relates to a silicon-carbon composite material and a preparation method and use thereof. BACKGROUND

[0002] Lithium ion batteries are one of the most successful commercial battery systems at present, which are widely used in various portable consumer electronic products and electric vehicles, and the market demand is very strong. However, the current low capacity and poor fast-charging performance make the experience of electronic products in continuous use poor, especially the limitation of the driving range of electric vehicles affects the further development of new energy vehicles. Therefore, it is necessary to develop lithium ion batteries with higher energy density. The positive and negative electrode materials are the key components that determine the energy of the battery, and the theoretical specific capacity of the current commercial graphite used for the negative electrode is 372 mAh / g, which is difficult to meet the development needs of future high-capacity batteries.

[0003] Silicon has the advantages of high capacity (4200 mAh / g), suitable electrochemical potential (~0.4 V vs Li / Li + ) and natural abundance, and is considered to be a strong contender for the next generation of lithium battery negative materials. However, the severe volume expansion and poor conductivity of silicon during lithiation / delithiation make it have many challenges in the application of lithium ion battery negative electrodes, such as electrode structure damage, material pulverization, and contact failure with the current collector, which further causes rapid capacity decay, repeated growth of SEI film and other problems. The use of flexible, lightweight, highly conductive and thermally stable carbon materials to coat silicon is considered to be the best composite material for improving the performance of silicon. On the one hand, carbon materials can inhibit the volume expansion of silicon; on the other hand, silicon-carbon composites effectively enhance the conductivity of silicon. A method for preparing yolk-shell structure silicon-carbon composites by a sacrificial template method is reported in Nano Letters, 2012, Vol. 12, 3315-3321. A method for preparing high-silicon-content silicon-carbon composites by pyrolysis using polyvinylidene fluoride as a carbon source is reported in Energy Storage Materials, 2016, Vol. 3, 45-54. A method for preparing shell-core structure silicon-carbon composites with a graphite carbon shell on the outside and silicon particles on the inside by an improved CVD method using acetylene as a carbon source is reported in Nano Letters, 2019, Vol. 19, 7236-7245.

[0004] Patent CN116741969A discloses a method for preparing silicon-carbon composites by a sacrificial template method, in which silicon particles, an adhesive, a water-soluble inorganic salt and a conductive carbon material are mixed in a solvent, a curing agent is added after sufficient mixing for curing, and then an organic carbon source is mixed after crushing, and the mixture is subjected to a temperature rising and holding process at different temperatures in multiple stages, to finally obtain a silicon-carbon composite material with a loose and porous intermediate composite layer.

[0005] Patent CN116799169A discloses a method for preparing silicon-carbon composite material by combining electrostatic spinning, heat treatment and magnetron sputtering. First, carbon fibers with porous structure are obtained by electrostatic spinning and heat treatment. Then, a layer of silicon is deposited on the surface of the fibers by magnetron sputtering. Finally, a layer of graphene is coated on the outer layer by chemical vapor deposition to obtain silicon-carbon composite material.

[0006] Patent CN109546108A discloses a method for preparing low-expansion silicon-based composite material. Carbon microporous tubes with attached silicon particles are used as the core, and a carbon coating layer is used as the shell to form a core-shell structure. This structure effectively reduces the volume expansion of the material during charging and discharging, improves the electrical conductivity and structural stability of the material, and is beneficial to the formation of a stable SEI film, reducing the exposure and fragmentation of silicon particles during charging and discharging.

[0007] Patent CN112382740A discloses a method for preparing silicon / carbon / graphene composite material. Nanosilicon solution, phenolic resin solution, graphene slurry and graphite are mixed and dried to obtain composite material powder. The composite material powder, carbon source and foaming agent are mixed uniformly and then heat treated to obtain silicon / carbon / graphene composite material.

[0008] Patent CN111106338A discloses a method for preparing silicon / amorphous carbon / graphene lithium ion battery negative electrode material. First, nanosilica particles are obtained by hydrolysis of tetraethyl orthosilicate. Then, nanosilicon particles are obtained by magnesium thermal reduction. Subsequently, carbon-coated nanosilicon particles are prepared using nanosilicon and glucose as raw materials. Finally, the carbon-coated nanosilicon particles and graphene oxide are mixed, freeze-dried and heat-treated to obtain the silicon / amorphous carbon / graphene lithium ion battery negative electrode material.

[0009] Patent CN117276510A discloses a method for preparing silicon-carbon composite material. Porous carbon and organic silicon resin are mixed in a vacuum and dried to obtain a precursor. Then, the precursor is mixed with silane gas and nitrogen gas, and decomposed at high temperature to obtain the silicon-carbon composite material.

[0010] It can be seen that silicon-carbon composite material has attracted widespread attention from researchers, and a large amount of research has been conducted on preparation methods, selection of precursor carbon source and special structure construction. However, there are still some problems, such as the use of general carbon sources at low temperature for a long time, which results in poor carbon skeleton strength and easy particle fragmentation during the actual battery manufacturing process, causing silicon to be exposed to the electrolyte again. In addition, long-time carbonization at high temperature can easily produce a large amount of silicon carbide. Furthermore, the deposition of carbon using silane and silicon tetrachloride as gas-phase silicon source not only has high raw material cost and long deposition process time, but also has low initial efficiency of the obtained silicon-carbon composite material. In summary, the existing methods for preparing silicon-carbon composite material have the disadvantages of complex process and high raw material cost, which limits the large-scale industrial application of silicon-carbon composite material. Therefore, it is still a great challenge to obtain high-performance silicon-carbon composite material using inexpensive materials through a simple method.

[0011] In view of this, the present application is proposed. SUMMARY

[0012] The purpose of the present application is to provide a silicon-carbon composite material and its preparation method and use, taking graphite / graphite-like carbon as the basic carbon skeleton, cracking the carbohydrate to form a carbon coating layer, and encapsulating the fine melted silicon particles in the carbon material. The composite material has the advantages of two different carbon source carbon materials: graphite / graphite-like carbon provides a stable skeleton for the attachment of fine silicon, forming a silicon-carbon material with ultra-fine silicon and carbon skeleton closely combined, strengthening the electronic transmission capability of the silicon material, improving the electrical conductivity of the silicon-carbon material, and maintaining the stability of the electrode structure; the carbohydrate is cracked to form a carbon coating layer on the above-mentioned silicon-carbon material, forming a silicon-carbon composite material, which can alleviate or inhibit the decline of electrode performance caused by volume expansion of silicon during the cycle process. The purpose of the present application is achieved by the following technical solutions.

[0013] The primary aspect of the present application is to provide a silicon-carbon composite material, which is composed of the following components: graphite or graphite-like carbon skeleton, silicon particles dispersed in the carbon skeleton, and an outermost carbon coating layer; the carbon coating layer encapsulates the silicon particles inside.

[0014] Further, the carbon skeleton is formed by transient high-temperature sintering of elemental carbon material, the silicon particles are formed by melting and spreading of silicon powder, and the carbon coating layer is formed by transient cracking of carbohydrate, and the transient high-temperature sintering, melting and spreading, and transient cracking are completed in one step in the same device.

[0015] Further, the silicon content in the silicon-carbon composite material is 10-50wt%, the particle size of the silicon particles is below 150nm, and the particle size of the silicon-carbon composite material is between 5-25μm.

[0016] Another aspect of the present application is to provide a preparation method of the above-mentioned silicon-carbon composite material, characterized in that it comprises the following steps:

[0017] S1 preparing a carbon / silicon / carbohydrate mixed precursor powder, specifically comprising:

[0018] S1-1 ball milling the coarse silicon powder in a protective atmosphere with an organic solvent as the dispersion medium to obtain ball-milled silicon powder;

[0019] S1-2 separately weighing the elemental carbon material, the ball-milled silicon powder obtained in step S1, and the carbohydrate, adding an organic solvent, and fully stirring to mix the three materials uniformly to obtain a mixed slurry;

[0020] S1-3 granulating the mixed slurry obtained in step S1-2, drying, and obtaining a carbon / silicon / carbohydrate mixed precursor powder;

[0021] S2 preparing silicon-carbon composite material by using high-frequency thermal plasma device, specifically comprising:

[0022] S2-1 after the high-frequency thermal plasma device generates stable thermal plasma arc, the above-mentioned precursor powder is transported into the plasma arc through a feeder;

[0023] S2-2 in the plasma arc and the reactor, the elemental carbon material is sintered at a high temperature to form a graphite or graphite-like carbon skeleton; the silicon powder is melted and spread, further refined to form ultra-fine silicon particles, which are dispersed and filled in the surface and gaps of the carbon skeleton; the carbon hydrate is instantaneously cracked to form a carbon coating layer, which completely encapsulates the silicon particles to form a silicon-carbon composite material;

[0024] S2-3 the carrier gas transports the silicon-carbon composite material to a product collection system to collect the silicon-carbon composite material product.

[0025] Further, the ball milling method in step S1-1 includes planetary milling or sand milling, and the particle size of the silicon powder is below 200 nm after ball milling.

[0026] Further, the coarse silicon powder in step S1-1 is metallurgical silicon or polycrystalline silicon powder; the elemental carbon material in step S1-2 is one or more of artificial graphite, natural flake graphite and porous carbon, and the particle size is between 1 and 10 μm; the carbon hydrate in step S1-2 is one or more of glucose, sucrose and starch; and the organic solvent in steps S1-1 and S1-2 is one or more of ethanol, methanol and acetone.

[0027] Further, the granulation method in step S1-3 is spray granulation or dry crushing granulation.

[0028] Further, the mass ratio of silicon element and carbon element in the precursor powder obtained in step S1-3 is (1-4) : (6-9), and the mass ratio of carbon element contained in the carbon hydrate and carbon element contained in the elemental carbon material is 1 : (1-3). The silicon element in the precursor powder is referred to as silicon source, the carbon element in the precursor powder is referred to as carbon source, and the mass ratio of carbon element contained in the carbon hydrate and carbon element contained in the elemental carbon material is referred to as the mass ratio of coating carbon and skeleton carbon.

[0029] Further, the power of the plasma device in step S2-1 is 10-200 kW, and the feeding rate of the feeder is 1-8 g / min per 10 kW of power.

[0030] Another aspect of the present application is to provide the use of the above-mentioned silicon-carbon composite material as a negative electrode material of a lithium ion battery.

[0031] Compared with the prior art, the present application has the following beneficial technical effects:

[0032] 1. The raw materials required for the carbon skeleton are commercially available artificial graphite, natural flake graphite, or porous carbon; the silicon particle raw material is metallurgical silicon or polycrystalline silicon; and the carbon coating layer raw material is carbohydrates such as glucose, sucrose, or starch. All raw materials are inexpensive and readily available. The mixed precursor powder is obtained through a simple ball milling and granulation process, which is simple and easy to scale up industrially.

[0033] 2. In a high-frequency thermal plasma arc and reactor, the mixed precursor powders utilize the transient high temperature characteristics of high-frequency thermal plasma to complete the transient high-temperature sintering of elemental carbon materials, the melting and spreading of silicon powder, and the transient pyrolysis of carbohydrates in one step. This can further improve the graphitization of carbon materials and refine silicon powder through high-temperature transient melting and spreading, while avoiding the formation of excessive silicon carbide. The high-frequency thermal plasma preparation method is simple, low-cost, and can be used for large-scale continuous production.

[0034] 3. Two different types of carbon sources were employed. Framework carbon maintained structural stability, while carbohydrates acted as a binder during granulation, bonding silicon and framework carbon together. Furthermore, during plasma high-temperature transient sintering, carbohydrates served as a filler and surface coating agent, filling and encapsulating silicon particles and further carbonizing to improve the material's conductivity. The synergistic effect of these two different carbon sources maintained the stability of the electrode structure, effectively mitigating silicon volume expansion and exhibiting superior electrochemical performance. Attached Figure Description

[0035] Figure 1 This is a scanning electron microscope (SEM) image of the silicon-carbon composite material obtained in Example 1.

[0036] Figure 2 The image shows the X-ray diffraction (XRD) pattern of the silicon-carbon composite material obtained in Example 1.

[0037] Figure 3 The constant current charge-discharge curve of the silicon-carbon composite material obtained in Example 2 is shown.

[0038] Figure 4 The image shows the cycling performance curve of the silicon-carbon composite material obtained in Example 3. Detailed Implementation

[0039] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention. Unless otherwise specified, the experimental methods described in the following embodiments are conventional methods; the reagents and materials, unless otherwise specified, are commercially available. Example 1

[0040] Step 1) Preparation of precursor powder: Metallurgical silicon powder was ball-milled using a planetary ball mill to obtain nano-silicon powder. Artificial graphite, nano-silicon powder, and glucose were dispersed in ethanol to form a slurry, which was then spray-granulated to obtain the precursor powder. The mass ratio of silicon source to carbon source in the precursor powder was 4:6, and the mass ratio of coated carbon to framework carbon in the carbon source was 1:2.

[0041] Step 2) Preparation of silicon-carbon composite material: A 36 kW high-frequency thermal plasma device was used, mainly comprising a gas control system, a thermal plasma generation system, a feeding system, a product collection system, and a tail gas emission system. First, argon gas was introduced into the plasma, and an electric spark generator was used to ignite the argon gas to form a plasma arc. After stable operation for 5 minutes, precursor powder was added to the plasma system through a feeder at a feeding rate of 3.8 g / min. After feeding was stopped, the arc was extinguished, and the silicon-carbon composite material was collected.

[0042] Characterization of silicon-carbon composite materials:

[0043] The morphology of the silicon-carbon composite material obtained under the above conditions was observed using a Japanese scanning electron microscope (JSM-7001F), as follows: Figure 1 As shown, the carbon coating formed by glucose pyrolysis encapsulates silicon particles within the carbon material, making the exposed silicon particles almost invisible. This structure promises to improve the conductivity of the material while mitigating silicon volume expansion.

[0044] The phase composition of the silicon-carbon composite material prepared under the above conditions was analyzed using X-ray powder diffraction (X'Pert PRO MPD). For example... Figure 2 As shown: the main phases are graphite and silicon, with a small amount of silicon carbide.

[0045] Electrochemical performance characterization of silicon-carbon composite materials:

[0046] The prepared silicon-carbon composite material, Super P (conductive agent), and sodium carboxymethyl cellulose (binder) were mixed in a mass ratio of 8:1:1 with deionized water as solvent to form a slurry, which was then uniformly coated onto a copper foil current collector to obtain an electrode sheet. Using lithium metal as the counter electrode, a polypropylene microporous membrane as the separator, and 1 mol / L LiPF6 (a 1:1 volume mixture of ethylene carbonate and dimethyl carbonate containing 10% fluoroethyl carbonate) as the electrolyte, a button cell was assembled in an argon-protected glove box. Charge-discharge tests were conducted at a current density of 50 mA / g and a charge-discharge voltage range of 0.01–3.0 V. The battery test results are listed in Table 1. Example 2

[0047] Step 1) Preparation of precursor powder: metallurgical silicon powder was ball-milled by a planetary ball mill to obtain nanosilicon powder. Natural flake graphite, nanosilicon powder and glucose were dispersed in methanol to form a slurry, and a precursor powder was obtained by spray granulation. The mass ratio of silicon source to carbon source in the precursor powder was 3:7, and the mass ratio of coated carbon to skeleton carbon in the carbon source was 1:2.

[0048] Step 2) Preparation of silicon-carbon composite material: a 36 kW high-frequency thermal plasma device was used, which mainly includes a gas control system, a thermal plasma generation system, a feeding system, a product collection system and a tail gas discharge system, etc. First, argon gas was introduced into the plasma, and an electric spark generator was used to ignite the argon gas to form a plasma arc. After stable operation for 5 minutes, the precursor powder was added into the plasma system through the feeder at a feeding rate of 4.0 g / min. After stopping feeding, the arc was extinguished, and the silicon-carbon composite material was collected.

[0049] The physical characterization of the silicon-carbon composite material was the same as that of Example 1.

[0050] The battery performance characterization of the silicon-carbon composite material was the same as that of Example 1. The battery test results are listed in Table 1.

[0051] Figure 3 The first constant current charge-discharge curve of the silicon-carbon composite material was shown, which showed typical silicon and carbon charge-discharge platforms. Example 3

[0052] Step 1) Preparation of precursor powder: metallurgical silicon powder was ball-milled by a planetary ball mill to obtain nanosilicon powder. Natural flake graphite, nanosilicon powder and glucose were dispersed in methanol to form a slurry, and a precursor powder was obtained by spray granulation. The mass ratio of silicon source to carbon source in the precursor powder was 3:7, and the mass ratio of coated carbon to skeleton carbon in the carbon source was 1:2.

[0053] Step 2) Preparation of silicon-carbon composite material: a 36 kW high-frequency thermal plasma device was used, which mainly includes a gas control system, a thermal plasma generation system, a feeding system, a product collection system and a tail gas discharge system, etc. First, argon gas was introduced into the plasma, and an electric spark generator was used to ignite the argon gas to form a plasma arc. After stable operation for 5 minutes, the precursor powder was added into the plasma system through the feeder at a feeding rate of 4.0 g / min. After stopping feeding, the arc was extinguished, and the silicon-carbon composite material was collected.

[0054] The physical characterization of the silicon-carbon composite material was the same as that of Example 1.

[0055] The battery performance characterization of the silicon-carbon composite material was the same as that of Example 1. The battery test results are listed in Table 1.

[0056] Figure 4 The cycle performance curve of the prepared silicon-carbon composite material. Example 4

[0057] Step 1) Preparation of precursor powder: metallurgical silicon powder was ball-milled by a planetary ball mill to obtain nanosilicon powder. Artificial graphite, nanosilicon powder and glucose were dispersed in ethanol to form a slurry, and the precursor powder was obtained by spray granulation. The mass ratio of silicon source to carbon source in the precursor powder was 3:7, and the mass ratio of coating carbon to skeleton carbon in the carbon source was 1:1.

[0058] Step 2) Preparation of silicon-carbon composite material: a 100 kW high-frequency thermal plasma device was used, which mainly included a gas control system, a thermal plasma generation system, a feeding system, a product collection system and a tail gas discharge system, etc. First, argon gas was introduced into the plasma, and an electric spark generator was used to ignite the argon gas to form a plasma arc. After stable operation for 5 minutes, the precursor powder was added into the plasma system through the feeder at a feeding rate of 12.3 g / min. After stopping feeding, the arc was extinguished, and the silicon-carbon composite material was collected.

[0059] The physical characterization of the silicon-carbon composite material was the same as that of Example 1.

[0060] The battery performance characterization of the silicon-carbon composite material was the same as that of Example 1. The battery test results are listed in Table 1. Example 5

[0061] Step 1) Preparation of precursor powder: metallurgical silicon powder was ball-milled by a planetary ball mill to obtain nanosilicon powder. Artificial graphite, nanosilicon powder and glucose were dispersed in ethanol to form a slurry, and the precursor powder was obtained by spray granulation. The mass ratio of silicon source to carbon source in the precursor powder was 3:7, and the mass ratio of coating carbon to skeleton carbon in the carbon source was 1:3.

[0062] Step 2) Preparation of silicon-carbon composite material: a 100 kW high-frequency thermal plasma device was used, which mainly included a gas control system, a thermal plasma generation system, a feeding system, a product collection system and a tail gas discharge system, etc. First, argon gas was introduced into the plasma, and an electric spark generator was used to ignite the argon gas to form a plasma arc. After stable operation for 5 minutes, the precursor powder was added into the plasma system through the feeder at a feeding rate of 11.7 g / min. After stopping feeding, the arc was extinguished, and the silicon-carbon composite material was collected.

[0063] The physical characterization of the silicon-carbon composite material was the same as that of Example 1.

[0064] The battery performance characterization of the silicon-carbon composite material was the same as that of Example 1. The battery test results are listed in Table 1. Example 6

[0065] Step 1) Preparation of precursor powder: Polycrystalline silicon powder was ball-milled by a sand mill to obtain nanosilicon powder. Natural flake graphite, nanosilicon powder and glucose were dispersed in ethanol to form a slurry, and the precursor powder was obtained by dry crushing and granulation. The mass ratio of silicon source to carbon source in the precursor powder was 2:8, and the mass ratio of coating carbon to skeleton carbon in the carbon source was 1:1.

[0066] Step 2) Preparation of silicon-carbon composite material: A 10 kW high-frequency thermal plasma device was used, which mainly includes a gas control system, a thermal plasma generation system, a feeding system, a product collection system and a tail gas discharge system, etc. First, argon gas was introduced into the plasma, and an electric spark generator was used to ignite the argon gas to form a plasma arc. After stable operation for 5 minutes, the precursor powder was added into the plasma system through the feeder at a feeding rate of 1.9 g / min. After stopping feeding, the arc was extinguished, and the silicon-carbon composite material was collected.

[0067] The physical characterization of the silicon-carbon composite material was the same as that of Example 1.

[0068] The battery performance characterization of the silicon-carbon composite material was the same as that of Example 1. The battery test results are listed in Table 1. Example 7

[0069] Step 1) Preparation of precursor powder: Polycrystalline silicon powder was ball-milled by a sand mill to obtain nanosilicon powder. Natural flake graphite, nanosilicon powder and sucrose were dispersed in ethanol to form a slurry, and the precursor powder was obtained by dry crushing and granulation. The mass ratio of silicon source to carbon source in the precursor powder was 2:8, and the mass ratio of coating carbon to skeleton carbon in the carbon source was 2:1.

[0070] Step 2) Preparation of silicon-carbon composite material: A 10 kW high-frequency thermal plasma device was used, which mainly includes a gas control system, a thermal plasma generation system, a feeding system, a product collection system and a tail gas discharge system, etc. First, argon gas was introduced into the plasma, and an electric spark generator was used to ignite the argon gas to form a plasma arc. After stable operation for 5 minutes, the precursor powder was added into the plasma system through the feeder at a feeding rate of 2.1 g / min. After stopping feeding, the arc was extinguished, and the silicon-carbon composite material was collected.

[0071] The physical characterization of the silicon-carbon composite material was the same as that of Example 1.

[0072] The battery performance characterization of the silicon-carbon composite material was the same as that of Example 1. The battery test results are listed in Table 1. Example 8

[0073] Step 1) Preparation of precursor powder: The polysilicon powder was ball-milled by a sand mill to obtain nanosilicon powder. The porous carbon, nanosilicon powder and starch were dispersed in ethanol to form a slurry, and the precursor powder was obtained by dry crushing and granulation. The mass ratio of silicon source to carbon source in the mixed powder was 1:9, and the mass ratio of coated carbon to skeleton carbon in the carbon source was 1:1.

[0074] Step 2) Preparation of silicon-carbon composite material: A 10 kW high-frequency thermal plasma device was used, which mainly included a gas control system, a thermal plasma generation system, a feeding system, a product collection system and a tail gas discharge system, etc. First, argon gas was introduced into the plasma, and an electric spark generator was used to ignite the argon gas to form a plasma arc. After stable operation for 5 minutes, the precursor powder was added into the plasma system through the feeder at a feeding rate of 1.7 g / min. After stopping feeding, the arc was extinguished, and the silicon-carbon composite material was collected.

[0075] The physical characterization of the silicon-carbon composite material was the same as that of Example 1.

[0076] The battery performance characterization of the silicon-carbon composite material was the same as that of Example 1. The battery test results are listed in Table 1. Comparative Example 1

[0077] Step 1) Preparation of precursor powder: The metallurgical silicon powder was ball-milled by a planetary ball mill to obtain nanosilicon powder. The artificial graphite, nanosilicon powder and glucose were dispersed in ethanol to form a slurry, and the precursor powder was obtained by spray granulation. The mass ratio of silicon source to carbon source in the precursor powder was 4:6, and the mass ratio of coated carbon to skeleton carbon in the carbon source was 1:2.

[0078] Step 2) Preparation of silicon-carbon composite material: The precursor powder was heat treated by a tube furnace. The precursor powder was loaded into a magnetic boat and sent into the tube furnace, argon gas was introduced to replace the internal gas, and the temperature was raised to 800℃ under argon protection and kept for 2h. After natural cooling to room temperature, it was taken out to obtain the silicon-carbon composite material.

[0079] The physical characterization of the silicon-carbon composite material was the same as that of Example 1.

[0080] The battery performance characterization of the silicon-carbon composite material was the same as that of Example 1. The battery test results are listed in Table 1. Comparative Example 2

[0081] Step 1) Preparation of mixed precursor powder: The metallurgical silicon powder was ball-milled by a planetary ball mill to obtain nanosilicon powder. The artificial graphite, nanosilicon powder and glucose were dispersed in acetone to form a slurry, and the precursor powder was obtained by spray granulation. The mass ratio of silicon source to carbon source in the precursor powder was 2:8, and the mass ratio of coated carbon to skeleton carbon in the carbon source was 1:2.

[0082] Step 2) Preparation of silicon-carbon composite material: The precursor powder was heat treated in a tube furnace. The precursor powder was loaded into a magnetic boat and sent into the tube furnace. Argon was introduced to replace the internal gas. The temperature was raised to 800℃ and kept for 2h under argon protection. After natural cooling to room temperature, the silicon-carbon composite material was obtained.

[0083] The physical characterization of the silicon-carbon composite material was the same as that of Example 1.

[0084] The battery performance characterization of the silicon-carbon composite material was the same as that of Example 1. The battery test results are shown in Table 1.

[0085] Table 1 Battery performance test results

[0086]

[0087] As can be seen from the data in Table 1, as the silicon content increases, the capacity that can be released by the composite material is also higher. Under the same ratio of coated carbon to skeletal carbon, the first coulombic efficiency gradually increases, but when the silicon content is higher than 40%, it decreases, which may be due to the fact that part of the silicon is not completely coated. When the silicon-carbon ratio is constant, as the skeletal carbon content in the carbon source increases, the first discharge capacity and the first coulombic efficiency of the composite material also increase, which is because the skeletal carbon has a higher graphitization degree and stronger reversible lithium storage capacity, and at the same time, it gives the composite material higher electrical conductivity. When the coated carbon content increases, the capacity changes little, but the first coulombic efficiency decreases significantly, which is because when the carbon hydrates are cracked, the cracking products escape in the form of small gas molecules, resulting in a large surface area of carbon, which irreversibly consumes more lithium ions to form a solid electrolyte membrane. Compared with the tube furnace carbonization method, the first coulombic efficiency of the composite material obtained by the plasma carbonization method is higher, which may be due to the fact that at very high temperatures, the nanometer pores produced by the cracking of carbon hydrates can easily collapse, thereby reducing the irreversible lithium loss caused by the excessive surface area of the composite material.

[0088] Although the embodiments of the present application have been shown and described above, it should be understood that the above embodiments are exemplary and should not be construed as limiting the present application, and those of ordinary skill in the art can make changes, modifications, replacements and variations to the above embodiments without departing from the principles and spirit of the present application within the scope of the present application. The scope of protection of the present application is defined by the claims and their equivalent technical solutions.

Claims

1. A silicon-carbon composite material, characterized by, The silicon-carbon composite material is composed of a graphite or graphite-like carbon framework, silicon particles dispersed in the carbon framework, and an outermost carbon coating layer; the carbon coating layer encapsulates the silicon particles inside; and the preparation method of the silicon-carbon composite material comprises the following steps: S1, preparing a carbon / silicon / carbohydrate mixed precursor powder, specifically comprising: S1-1, ball-milling a coarse silicon powder in a protective atmosphere with an organic solvent as a dispersion medium to obtain a ball-milled silicon powder; S1-2, respectively weighing an elemental carbon material, the ball-milled silicon powder obtained in step S1, and a carbohydrate, adding an organic solvent, and fully stirring to mix the three materials uniformly to obtain a mixed slurry; S1-3, granulating and drying the mixed slurry obtained in step S1-2 to obtain a carbon / silicon / carbohydrate mixed precursor powder; S2, preparing a silicon-carbon composite material by using a high-frequency thermal plasma device, specifically comprising: S2-1, after the high-frequency thermal plasma device generates a stable thermal plasma arc, feeding the above mixed precursor powder into the plasma arc through a feeder; S2-2, in the plasma arc and the reactor, the elemental carbon material is instantaneously high-temperature sintered to form a graphite or graphite-like carbon framework; the silicon powder is melted, spread, further refined, and formed into ultra-fine silicon particles, which are dispersed and filled in the surface and gaps of the carbon framework; the carbohydrate is instantaneously cracked to form a carbon coating layer, which completely encapsulates the silicon particles to form a silicon-carbon composite material; S2-3, a carrier gas is used to transport the silicon-carbon composite material to a product collection system to collect the silicon-carbon composite material product.

2. The silicon-carbon composite material of claim 1, wherein, The carbon framework is formed by instantaneously high-temperature sintering of the elemental carbon material, the silicon particles are formed by melting and spreading of the silicon powder, and the carbon coating layer is formed by instantaneously cracking of the carbohydrate, and the instantaneously high-temperature sintering, melting and spreading, and instantaneously cracking are completed in one step in the same device.

3. The silicon-carbon composite material according to claim 1 or 2, characterized in that, The silicon content in the silicon-carbon composite material is 10-50wt%, the particle size of the silicon particles is below 150nm, and the particle size of the silicon-carbon composite material is between 5-25μm.

4. The method of making a silicon-carbon composite material according to any one of claims 1-3, wherein, comprising the following steps: S1, preparing a carbon / silicon / carbohydrate mixed precursor powder, specifically comprising: S1-1, ball-milling a coarse silicon powder in a protective atmosphere with an organic solvent as a dispersion medium to obtain a ball-milled silicon powder; S1-2, respectively weighing an elemental carbon material, the ball-milled silicon powder obtained in step S1, and a carbohydrate, adding an organic solvent, and fully stirring to mix the three materials uniformly to obtain a mixed slurry; S1-3, granulating and drying the mixed slurry obtained in step S1-2 to obtain a carbon / silicon / carbohydrate mixed precursor powder; S2, preparing a silicon-carbon composite material by using a high-frequency thermal plasma device, specifically comprising: S2-1, after the high-frequency thermal plasma device generates a stable thermal plasma arc, feeding the above mixed precursor powder into the plasma arc through a feeder; S2-2, in the plasma arc and the reactor, the elemental carbon material is instantaneously high-temperature sintered to form a graphite or graphite-like carbon framework; the silicon powder is melted, spread, further refined, and formed into ultra-fine silicon particles, which are dispersed and filled in the surface and gaps of the carbon framework; the carbohydrate is instantaneously cracked to form a carbon coating layer, which completely encapsulates the silicon particles to form a silicon-carbon composite material; S2-3 carrier gas transports the silicon-carbon composite material to a product collection system, and a silicon-carbon composite material product is collected.

5. The production method according to claim 4, characterized by, The ball milling method in step S1-1 includes planetary milling or sand milling, and the particle size of the silicon powder after ball milling is below 200 nm.

6. The production method according to claim 4, characterized by, The coarse silicon powder in step S1-1 is metallurgical silicon or polycrystalline silicon powder; the elemental carbon material in step S1-2 is one or more of artificial graphite, natural flake graphite and porous carbon, and the particle size is between 1 and 10 μm; the carbohydrate in step S1-2 is one or more of glucose, sucrose and starch; and the organic solvent in steps S1-1 and S1-2 is one or more of ethanol, methanol and acetone.

7. The preparation method according to claim 4, characterized in that, The granulation method in step S1-3 is spray granulation or dry crushing granulation.

8. The preparation method according to claim 4, characterized in that, The mass ratio of silicon element to carbon element in the precursor powder obtained in step S1-3 is (1-4) : (6-9), and the mass ratio of the carbon element contained in the carbohydrate to the carbon element contained in the elemental carbon material is 1 : (1-3).

9. The production method according to claim 4, characterized by, The power of the plasma device in step S2-1 is 10-200 kW, and the feeding rate of the feeder is 1-8 g / min per 10 kW of power.

10. Use of the silicon-carbon composite material according to any one of claims 1-3 as a negative electrode material for a lithium ion battery.

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