Silicon-carbon negative electrode material, preparation method thereof and secondary battery

Abstract

The application belongs to the technical field of battery manufacturing, and particularly relates to a silicon-carbon negative electrode material, a preparation method thereof and a secondary battery. The preparation method comprises the step of growing a silicon-carbon thin film on the surface of a copper foil by using a cold plasma chemical vapor deposition method, and the deposition source gas is a carbon-containing organosilicon compound or a mixture thereof. The method has a short preparation process, high safety of raw materials, can effectively improve the deposition efficiency, inhibit the crystallization and agglomeration of silicon, improve the carbon coating effect, and enhance the bonding force between the silicon-carbon composite material and the copper foil, so as to improve the overall conductivity, improve the cycle performance and the battery capacity.

Description

Technical Field

[0001] This invention belongs to the field of battery manufacturing technology, specifically relating to a silicon-carbon anode material, its preparation method, and a secondary battery. Background Technology

[0002] Silicon-carbon anodes exhibit good stability, small volume change, and excellent conductivity, and their industrialization has progressed particularly rapidly in recent years.

[0003] In the existing technology, the preparation of silicon-carbon anodes generally involves first preparing silicon-carbon composite materials, then mixing the silicon-carbon composite material powder with graphite powder, conductive agent and binder, and then coating it onto the surface of the current collector to prepare the electrode sheet. The overall preparation process of the anode is relatively long.

[0004] In existing technologies, the mainstream method for preparing silicon-carbon composite materials involves depositing silicon in a porous carbon substrate using a silicon source gas followed by carbon coating. However, in this process, silicon is prone to crystallization, forming crystalline silicon. During repeated lithium insertion and extraction during charge and discharge cycles, the crystalline silicon reverts to an amorphous state. This process is accompanied by the expansion and fracture of the silicon material, leading to performance failure, which manifests macroscopically as poor cycle performance. Furthermore, when some silicon in the negative electrode crystallizes, more conductive binders and other additives need to be added to buffer the effects of volume expansion and fracture. This means a lower proportion of active material in the negative electrode, indirectly hindering capacity improvement. Moreover, this method requires the use of the hazardous gas silane, with extremely stringent safety and control requirements, including production line construction approvals. Silane is also expensive, increasing the production cost of the negative electrode and hindering continuous production and programmed process control. Summary of the Invention

[0005] Therefore, the technical problem to be solved by the present invention is to overcome the defects of silicon-carbon anode preparation methods in the prior art, such as easy crystallization of silicon, long process route, high risk and high cost, so as to provide a silicon-carbon anode material, its preparation method and secondary battery.

[0006] To this end, the present invention provides the following technical solution.

[0007] The method for preparing silicon-carbon anode material provided by the present invention includes the following steps: growing a silicon-carbon thin film on the surface of a copper foil using a cold plasma chemical vapor deposition method; the deposition source gas is a carbon-containing organosilicon compound or a mixture thereof.

[0008] The method for preparing silicon-carbon anode materials of the present invention uses copper foil as the current collector, which can catalyze the growth of graphene microwalls. Specifically, cold plasma chemical vapor deposition is used, which enables the efficient pyrolysis of carbon-containing organosilicon compounds without the formation of silicon carbide. The plasma bombardment energy simultaneously breaks Si-C and CH bonds, thus exciting the deposition source gas to pyrolyze and form carbon-containing and silicon-containing free radical active particles without producing gases such as methane. The active particles are accelerated towards the copper foil under the influence of an electric field, improving deposition efficiency. After the carbon-containing free radicals diffuse to the surface of the copper foil, they grow into nanoscale graphene microwall structures under the catalysis of copper. The nano-silicon formed by the decomposition of silicon-containing free radicals is embedded in the gaps between the graphene microwalls and strictly confined by them, thereby inhibiting crystallization and agglomeration. Moreover, using carbon-containing organosilicon compounds or mixtures thereof as the deposition source gas allows for strict control of the silicon-to-carbon ratio and eliminates the need for highly flammable and explosive silanes and alkynes, improving the safety of the entire process.

[0009] Optionally, in the carbon-containing organosilicon compound, each silicon atom is attached to at least two carbon atoms. For example, each Si atom may exist in a group structure such as -SiR1R2, where R1 and R2 are alkyl groups and may be the same.

[0010] Optionally, in the carbon-containing organosilicon compound, each silicon atom is connected to at least two carbon atoms, forming a structure in which the silicon atom is surrounded by surrounding carbon atoms. This is beneficial for better isolating and encapsulating the silicon atom by carbon atoms during the deposition and growth of silicon-carbon thin films.

[0011] Optionally, the carbon-to-silicon atom ratio in the carbon-containing organosilicon compound is ≥2:1. This allows for better encapsulation of silicon atoms by carbon atoms during silicon-carbon film growth.

[0012] Preferably, the carbon:silicon atom ratio in the carbon-containing organosilicon compound is 2:1 to 4:1; specific examples include, but are not limited to, the point values ​​in the embodiments and the following point values: 2.5:1, 3.5:1, 4:1; while ensuring that silicon atoms are better coated by carbon atoms during silicon-carbon film growth, the proportion of silicon in the material is also ensured, so that the resulting material has better electrical properties.

[0013] Optionally, the deposition source gas includes, but is not limited to, at least one of trimethylchlorosilane, trimethylsilane, tetramethylsilane, tetramethyldisiloxane, dimethyldichlorosilane, dimethylsilane, and decamethylcyclopentasiloxane.

[0014] Optionally, the temperature of cold plasma chemical vapor deposition is 0–500°C; preferably, the temperature of cold plasma chemical vapor deposition is 0–200°C; specific examples include, but are not limited to, the point values ​​in the embodiments and the following point values: 20°C, 40°C, 60°C, 80°C, 100°C, 120°C, 140°C, 160°C, 180°C; or any range of two values, for example, 30–50°C, 70–90°C, 110–130°C, 150–170°C; this ensures that silicon exists in a completely amorphous state to obtain optimal electrical performance.

[0015] Preferably, the cold plasma used is dielectric barrier discharge plasma.

[0016] Preferably, the atmosphere for cold plasma chemical vapor deposition is an inert gas, and specific examples include, but are not limited to, the atmosphere used in the embodiments and the following atmospheres: helium, neon, krypton, and xenon.

[0017] Preferably, the volume ratio of the deposition source gas to the inert gas is 5:1 to 1:5; specific examples include, but are not limited to, the point values ​​in the embodiments and the following point values: 5:1, 4:1, 2:1, 1:1, 1:2, 1:3, 1:4, 1:5; or any range of two values, for example, 4:1 to 3:1, 1:1 to 1:2, 1:4 to 1:5.

[0018] Preferably, in cold plasma chemical vapor deposition, the gas flow rate of the mixture of deposition source gas and inert gas is 0.1–50 L / min; specific examples include, but are not limited to, the point values ​​in the embodiments and the following point values: 5 L / min, 10 L / min, 16 L / min, 20 L / min, 25 L / min, 30 L / min, 35 L / min, 40 L / min, 45 L / min, 50 L / min; or any range of two values, for example, 0.1–0.8 L / min, 2–3 L / min, 7–9 L / min, 14–17 L / min, 21–23 L / min, 28–29 L / min, 34–36 L / min, 44–46 L / min.

[0019] Preferably, the copper foil is moved using a roll-to-roll transport method.

[0020] In the method for preparing silicon-carbon anode material provided by this invention, the length and width of the discharge area of ​​the reaction device for generating cold plasma can be selected according to the size of the copper foil and other requirements. Optionally, the discharge area width is 0.1–1 m, and the discharge area length is 0.2–2 m. In practical applications, the discharge power of the cold plasma treatment can be selected within a conventional range without particular limitations; optionally, the discharge power of the cold plasma treatment is 1–50 kW. There are no particular limitations on the residence time of the copper foil; optionally, the residence time is 4–400 min. When the discharge power of the cold plasma treatment is relatively low, a longer residence time within this range can be selected.

[0021] The method for preparing silicon-carbon anode material provided by this invention may specifically include: using a roll-to-roll device equipped with a dielectric barrier discharge plasma (DBD plasma) reaction device, wherein the DBD plasma reaction device has a discharge width of 0.1–1 m, a length of 0.2–2 m, and a discharge power of 1–50 kW; fixing copper foil onto the roll-to-roll device, setting the travel speed to 0.01–0.5 m / min, and slowly and continuously passing the copper foil roll through the DBD plasma reaction chamber by a drive shaft, under normal pressure or slightly negative pressure conditions (absolute pressure 0.05–0.1 MPa), and a temperature of 0–500 °C, introducing a deposition source gas and an inert gas with a volume ratio of 5:1–1:5 into the reaction device at a rate of 0.1–50 L / min to obtain a rolled copper foil loaded with a silicon-carbon thin film, which can be directly used for the next step of coating conductive paste.

[0022] The present invention provides an apparatus for preparing silicon-carbon anodes, including a cold plasma reaction device and a conveying device disposed therein; the conveying device is used to lay copper foil thereon and convey the copper foil.

[0023] Optionally, the cold plasma reaction device is a dielectric barrier discharge plasma reaction device.

[0024] Optionally, the dielectric barrier discharge plasma reaction device includes a reaction chamber, and a first electrode, a second electrode, and a dielectric barrier layer disposed inside the reaction chamber.

[0025] Optionally, the first electrode and the second electrode are arranged opposite to each other, and the material passes between the first electrode and the second electrode through the reaction chamber.

[0026] Optionally, the dielectric barrier layer is disposed on the side of the first electrode near the second electrode.

[0027] Optionally, the dielectric barrier discharge plasma reaction device includes an air inlet and an exhaust outlet disposed on the reaction chamber.

[0028] Optionally, the conveying device includes a drive reel and a power unit.

[0029] The method for preparing silicon-carbon anode material provided by the present invention, using the above-mentioned preparation apparatus, includes the following steps: growing a silicon-carbon thin film on the surface of a copper foil using a cold plasma chemical vapor deposition method in a cold plasma reactor, wherein the deposition source gas is a carbon-containing organosilicon compound or a mixture thereof, and the copper foil is moved with a conveying device.

[0030] Optionally, the copper foil can be fixed to a drive reel and moved using a roll-to-roll transport method.

[0031] The present invention provides a silicon-carbon anode material prepared by the above-described preparation method or the above-described preparation apparatus.

[0032] Optionally, the silicon-carbon anode material includes graphene microwalls grown on copper foil and nano-silicon embedded between the graphene microwalls.

[0033] Optionally, the nano-silicon is amorphous nano-silicon.

[0034] Optionally, the silicon content in the silicon-carbon anode material is 20%-50%.

[0035] This invention provides a method for preparing a negative electrode sheet, using the aforementioned silicon-carbon negative electrode material, and coating the surface of the silicon-carbon negative electrode material with a conductive paste. When coating the surface of the silicon-carbon negative electrode material with the conductive paste, there is no particular limitation on the conductive paste used; it can be a conventional mixed paste formed from conductive additives, binders, and solvents. Specifically, the conductive additive includes at least one of carbon black, carbon fiber, and graphene, preferably carbon black; the binder includes at least one of sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and polyacrylic acid (PAA), preferably sodium carboxymethyl cellulose and styrene-butadiene rubber; the solvent can be deionized water. Preferably, the conductive paste is coated in a conventional ratio; specifically, the mass ratio of conductive additive to binder can be 1:2, and the coating thickness (the thickness of the electrode sheet excluding the copper foil, the same below) is 100–300 μm.

[0036] Further preferred embodiments include adding other active ingredients, such as graphite, to the conductive paste; the amount of graphite added can be selected according to the actual electrode design and is not particularly limited. The graphite, conductive additive, and binder can be mixed in a conventional ratio. Specifically, for example, the mass ratio of graphite, conductive additive, and binder can be 94:2:4, and the coating thickness is 100–300 μm.

[0037] In the method for preparing silicon-carbon anode material provided by the present invention, if the size of the anode obtained does not meet the requirements for use, the required size can be obtained by cutting.

[0038] The present invention provides a negative electrode sheet prepared by the above preparation method.

[0039] The present invention also provides a secondary battery comprising the aforementioned silicon-carbon anode material or the aforementioned anode sheet. Specifically, the secondary battery is a lithium-ion battery, and the other components and preparation methods of the lithium-ion battery are conventional choices in the art.

[0040] The beneficial effects of this invention are:

[0041] The present invention provides a method for preparing silicon-carbon anode materials, comprising the following steps: growing a silicon-carbon thin film on a copper foil surface using cold plasma chemical vapor deposition; the deposition source gas is a carbon-containing organosilicon compound or a mixture thereof. This method has a simple preparation process, uses highly safe raw materials, effectively improves deposition efficiency, inhibits silicon crystallization and agglomeration, improves carbon coating, and enhances the bonding force between the silicon-carbon composite material and the copper foil, thereby improving overall conductivity, cycle performance, and battery capacity.

[0042] The method for preparing silicon-carbon anode materials provided by this invention allows the copper foil to be moved using a roll-to-roll transport method. Because this invention uses a co-precipitation method to grow silicon-carbon thin films, and the selected deposition source gas is an organosilicon compound or a mixture thereof, it offers high safety and allows for continuous roll-to-roll production, facilitating large-scale production. Attached Figure Description

[0043] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0044] Figure 1 This is a front view of the apparatus for preparing silicon-carbon anode material in this invention;

[0045] Figure 2 This is a left view of the apparatus for preparing silicon-carbon anode material in this invention.

[0046] Explanation of reference numerals in the attached figures:

[0047] 1-Reaction chamber; 21-First electrode; 22-Second electrode; 3-Dielectric barrier layer; 4-Drive reel; 5-Air inlet; 6-Air outlet; 7-Copper foil roll. Detailed Implementation

[0048] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0049] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0050] Example 1

[0051] This embodiment provides a method for preparing silicon-carbon anode materials, using methods such as... Figure 1 and Figure 2 The apparatus shown includes a cold plasma reactor and a conveying device disposed within it. The cold plasma reactor is a dielectric barrier discharge plasma reactor, which includes a reaction chamber 1, and a first electrode 21, a second electrode 22, and a dielectric barrier layer 3 disposed within the reaction chamber 1. The first electrode 21 and the second electrode 22 are arranged opposite to each other, and a copper foil passes between the first electrode 21 and the second electrode 22 through the reaction chamber 1. The dielectric barrier layer 3 is disposed on the side of the first electrode 21 closest to the second electrode 22.

[0052] The conveying device includes a drive shaft 4 and a power unit. The copper foil roll 7 is fixed on the drive shaft 4. The power unit drives the drive shaft 4 to move, and the drive shaft 4 then drives the copper foil roll 7 to move to realize roll-to-roll transportation, which can realize large-scale production.

[0053] The reaction chamber 1 is equipped with an air inlet 5 and an exhaust outlet 6.

[0054] In this embodiment, the discharge area of ​​the first electrode 21 and the second electrode 22 is 0.4m wide and 2m long. The specific preparation steps are as follows:

[0055] The copper foil roll 7 is fixed on the drive shaft 4. The discharge power of the first electrode 21 and the second electrode 22 is set to 20kW. A mixture of argon and trimethylsilane with a volume ratio of 1:1 is introduced into the reaction chamber 1 at a speed of 2L / min through the inlet 5 at room temperature and pressure. The exhaust gas is discharged from the exhaust port 6. The discharge forms plasma and a reaction occurs. The copper foil roll 7 is pulled by the drive shaft 4 and slowly passes through the reaction chamber 1 continuously at a speed of 0.01m / min. A vapor deposition reaction occurs on the surface of the copper foil to obtain a copper foil loaded with a silicon carbon film, which is then re-rolled up. The reaction is stopped after 30 hours.

[0056] Example 2

[0057] This embodiment provides a method for preparing silicon-carbon anode material, using the same preparation apparatus as in Example 1. The specific steps are as follows:

[0058] The copper foil roll 7 is fixed on the drive shaft 4. The discharge power of the first electrode 21 and the second electrode 22 is set to 20kW. A mixture of argon and trimethylchlorosilane with a volume ratio of 1:1 is introduced into the reaction chamber 1 at a speed of 3L / min through the inlet 5 at atmospheric pressure and 200℃. The exhaust gas is discharged from the exhaust port 6. The discharge forms plasma and a reaction occurs. The copper foil roll 7 is pulled by the drive shaft 4 and slowly passes through the reaction chamber 1 continuously at a speed of 0.01m / min. A vapor deposition reaction occurs on the surface of the copper foil to obtain a copper foil loaded with a silicon carbon film, which is then re-rolled up. The reaction is stopped after 30 hours.

[0059] Example 3

[0060] This embodiment provides a method for preparing silicon-carbon anode material, using the same preparation apparatus as in Example 1. The specific steps are as follows:

[0061] The copper foil roll 7 is fixed on the drive shaft 4. The discharge power of the first electrode 21 and the second electrode 22 is set to 20kW. A mixture of argon and tetramethyldisiloxane with a volume ratio of 1:1 is introduced into the reaction chamber 1 at an absolute pressure of 0.8MPa and a temperature of 250℃ through the inlet 5 at a speed of 4L / min. The exhaust gas is discharged from the outlet 6. The discharge forms plasma and a reaction occurs. The copper foil roll 7 is pulled by the drive shaft 4 and slowly passes through the reaction chamber 1 continuously at a speed of 0.01m / min. A vapor deposition reaction occurs on the surface of the copper foil to obtain a copper foil loaded with a silicon carbon film, which is then re-rolled up. The reaction is stopped after 30 hours.

[0062] Example 4

[0063] This embodiment provides a method for preparing silicon-carbon anode material, using the same preparation apparatus as in Example 1. The specific steps are as follows:

[0064] The copper foil roll 7 is fixed on the drive shaft 4. The discharge power of the first electrode 21 and the second electrode 22 is set to 20kW. A mixture of argon and decamethylcyclopentasiloxane with a volume ratio of 3:1 is introduced into the reaction chamber 1 at an absolute pressure of 0.5MPa and a temperature of 350℃ through the inlet 5 at a speed of 15L / min. The exhaust gas is discharged from the outlet 6. The discharge forms plasma and a reaction occurs. The copper foil roll 7 is pulled by the drive shaft 4 and slowly and continuously passes through the reaction chamber 1 at a speed of 0.03m / min. A vapor deposition reaction occurs on the surface of the copper foil to obtain a copper foil loaded with a silicon carbon film, which is then re-rolled up. The reaction is stopped after 10 hours.

[0065] Examples 5-8

[0066] This embodiment provides a method for preparing a negative electrode sheet, specifically as follows:

[0067] Conductive paste was coated onto the surface of the silicon-carbon anode materials prepared in Examples 1-4, respectively. The conductive paste contained conductive additive carbon black and binder (sodium carboxymethyl cellulose and styrene-butadiene rubber in a 1:1 mass ratio, the same below) in a 1:2 mass ratio, with a coating thickness of 250 μm. After drying and cutting, integrated silicon-carbon anode sheets were obtained. The silicon-carbon anode materials used in Examples 5-8 corresponded to those in Examples 1-4, respectively.

[0068] Comparative Example 1

[0069] This comparative example provides a method for preparing a negative electrode sheet, the specific steps of which are as follows:

[0070] (1) Mix 20g of polyethylene glycol 10000, 1kg of amorphous nano-silicon particles (D50=60nm) and 4kg of anhydrous ethanol evenly and then add them to a horizontal sand mill and sand mill for 1h to obtain a dispersion; mix the dispersion with 500g of phenolic resin 2123 and stir until the phenolic resin is completely dissolved, then spray dry; under nitrogen atmosphere, the precursor is obtained.

[0071] (2) The precursor and asphalt with a softening point of 200℃ are mixed at a mass ratio of 92:8, heated to 800℃ at 3℃ / min, and kept at the temperature for 2h for heat treatment; then graded and demagnetized to obtain silicon-carbon anode material.

[0072] (3) Mix the silicon-carbon anode material with the conductive slurry evenly (so that the mass ratio of silicon-carbon anode material to conductive additive carbon black and binder is 94:2:4) to obtain a mixed slurry. Coat the mixed slurry onto copper foil with a coating thickness of 250μm and dry it to obtain the anode sheet.

[0073] Comparative Example 2

[0074] This comparative example provides a method for preparing a negative electrode sheet, the specific steps of which are as follows:

[0075] (1) Take 1.5 kg of porous carbon (D50 = 10 μm, specific surface area approximately 1900 m²). 2 Using a silicon-carbon anode material with a pore size distribution of 2–10 nm as a carrier, methylsilane as the silicon source, a flow rate of 6 L / min, and deposition at atmospheric pressure and 590 °C for 5 h, and then using butadiene as the carbon source, a flow rate of 1 L / min, and carbon coating at atmospheric pressure and 650 °C for 0.5 h, the silicon-carbon anode material was obtained.

[0076] (2) Mix the silicon-carbon anode material with the conductive slurry evenly (so that the mass ratio of silicon-carbon anode material to conductive additive carbon black and binder is 94:2:4) to obtain a mixed slurry. Coat the mixed slurry onto copper foil with a coating thickness of 250μm and dry it to obtain the anode sheet.

[0077] Test Example 1

[0078] The negative electrode sheets obtained in Examples 5-8 and Comparative Examples 1 and 2 were used to prepare CR2032 coin cells. The specific steps are as follows:

[0079] Using the negative electrode sheets prepared in Examples 5-8 and Comparative Examples 1 and 2 as negative electrodes, respectively, a Celgard 2400 polypropylene separator was used, a lithium metal sheet was selected as the positive electrode, and a LiPF6 system electrolyte [a 1 mol / L LiPF6 solution with an EC / DC 1:1 (volume ratio) mixture as the solvent] was used to assemble CR2032 coin cells in a glove box.

[0080] The prepared CR2032 coin cells were subjected to constant current charge-discharge tests using a charge-discharge apparatus. The discharge cutoff voltage was 0.005V, and the charging cutoff voltage was 2V. The first week of charge-discharge testing was conducted at a current density of 0.1C. The charge-discharge capacity and initial coulombic efficiency of the material were thus obtained. The test results are shown in Table 1.

[0081] Table 1

[0082] Example 5 2720 2576 94.7 Example 6 2680 2543 94.9 Example 7 2370 2207 93.1 Example 8 2490 2303 92.5 Comparative Example 1 1440 1276 88.6 Comparative Example 2 2130 1955 91.8

[0083] As can be seen from the test data of the examples and comparative examples, the silicon-carbon anode material prepared by the method provided in this invention significantly improves the charge-discharge specific capacity and first-time efficiency of the battery.

[0084] Examples 9-12

[0085] This embodiment provides a method for preparing a negative electrode sheet, specifically as follows:

[0086] Graphite (specific capacity 360 mAh / g) was added to a conductive slurry and mixed evenly to obtain a conductive slurry with added graphite. The mass ratio of graphite, conductive additive carbon black, and binder in the conductive slurry with added graphite was 94:2:4. The conductive slurry with added graphite was then coated onto the surface of the silicon-carbon anode materials prepared in Examples 1-4, with a coating thickness of 250 μm. After drying and cutting, integrated silicon-carbon anode sheets were obtained. The silicon-carbon anode materials used in Examples 9-12 correspond to those in Examples 1-4, respectively.

[0087] Comparative Examples 3 and 4

[0088] This comparative example provides a method for preparing a negative electrode sheet, specifically as follows:

[0089] Graphite was added to the conductive slurry and mixed evenly to obtain a conductive slurry with added graphite. The silicon-carbon anode material obtained in step (2) of Comparative Example 1 and step (1) of Comparative Example 2 was mixed evenly with the conductive slurry with added graphite (so that the mass ratio of graphite to silicon-carbon anode material was 93:7, and the mass ratio of the total mass of graphite and silicon-carbon anode material to the conductive additive carbon black and binder was 94:2:4) to obtain a mixed slurry. The mixed slurry was coated on copper foil with a coating thickness of 250 μm and dried to obtain the anode. The silicon-carbon anode materials used in Comparative Examples 3 and 4 correspond to those in Comparative Examples 1 and 2, respectively.

[0090] Test Example 2

[0091] The negative electrode sheets obtained in Examples 9-12 and Comparative Examples 3-4 were used to prepare a complete battery cell. The specific steps are as follows:

[0092] Using the negative electrode sheets prepared in Examples 9-12 and Comparative Examples 3-4 as negative electrode sheets, the active material LiCoO2, conductive carbon black, and binder polyvinylidene fluoride (PVDF) were thoroughly mixed in an N-methylpyrrolidone solvent system at a weight ratio of 96.7:1.7:1.6. The mixture was then coated onto Al foil, dried, and cold-pressed to obtain the positive electrode sheet for later use. Using a porous PE polymer film as a separator, the above-mentioned positive electrode sheet, separator, and negative electrode sheet were stacked in sequence, with the separator acting as a separator between the positive and negative electrode sheets, and then wound to obtain a bare battery cell. The bare battery cell was placed in an outer packaging, and electrolyte was injected to prepare a 404865 model battery cell (positive electrode areal density 17.9 g / cm³). 2 The negative electrode surface density is 7.0 g / cm³. 2 The electrolyte used is Xinzhoubang LBC421B10 and encapsulated. After formation, degassing, and edge trimming processes, a complete cell is obtained. The length, width and thickness of the obtained cell are 64.5mm, 48mm and 4.1mm respectively, and the platform voltage is 3.6V.

[0093] The fabricated battery cells were subjected to constant current charge-discharge tests using a charge-discharge apparatus. The discharge cutoff voltage was 2.75V, and the charging cutoff voltage was 4.2V. Both charge-discharge tests were conducted at a current density of 1C. The cell capacity and capacity retention after 100 and 300 cycles were tested. The test results are shown in Table 2.

[0094] Table 2

[0095]

[0096] As can be seen from the test data of the examples and comparative examples, compared with the prior art, the full battery prepared by the negative electrode obtained by the present invention significantly improves the volumetric energy density and gravimetric energy density while ensuring a significant improvement in the capacity retention rate after 300 full-cycle charging. At the same time, the preparation method of the present invention significantly shortens the entire process from negative electrode material to cell production, simplifies lithium battery technology and related equipment, and does not involve hazardous chemicals such as silane and acetylene.

[0097] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a silicon-carbon anode material, characterized in that, Includes the following steps: Silicon-carbon thin films were grown on the surface of copper foil using cold plasma chemical vapor deposition. The source gas for deposition is a carbon-containing organosilicon compound or a mixture thereof; The temperature range for cold plasma chemical vapor deposition is 0~500℃; The silicon-carbon anode material includes graphene microwalls grown on copper foil and nano-silicon embedded between the graphene microwalls.

2. The method for preparing the silicon-carbon anode material according to claim 1, characterized in that, In the carbon-containing organosilicon compound, each silicon atom is bonded to at least two carbon atoms.

3. The method for preparing the silicon-carbon anode material according to claim 2, characterized in that, The carbon-containing organosilicon compound has a structure in which silicon atoms are surrounded by carbon atoms.

4. The method for preparing the silicon-carbon anode material according to claim 2, characterized in that, The carbon-containing organosilicon compound has a carbon:silicon atomic ratio ≥2:

1.

5. The method for preparing the silicon-carbon anode material according to claim 4, characterized in that, The carbon-containing organosilicon compound has a carbon:silicon atomic ratio of 2:1 to 4:

1.

6. The method for preparing the silicon-carbon anode material according to claim 4, characterized in that, The carbon-containing organosilicon compound includes at least one of trimethylchlorosilane, trimethylsilane, tetramethylsilane, tetramethyldisiloxane, dimethyldichlorosilane, dimethylsilane, and decamethylcyclopentasiloxane.

7. The method for preparing the silicon-carbon anode material according to any one of claims 1 to 6, characterized in that, The temperature range for cold plasma chemical vapor deposition is 0~200℃.

8. The method for preparing the silicon-carbon anode material according to any one of claims 1 to 6, characterized in that, The cold plasma used is dielectric barrier discharge plasma; And / or, the atmosphere for cold plasma chemical vapor deposition is an inert gas; And / or, the volume ratio of the deposition source gas to the inert gas is 5:1 to 1:5; And / or, in cold plasma chemical vapor deposition, the gas flow rate of the mixture of deposition source gas and inert gas is 0.1~50 L / min.

9. The method for preparing the silicon-carbon anode material according to any one of claims 1 to 6, characterized in that, The copper foil is moved using a roll-to-roll transport method.

10. A method for preparing a silicon-carbon anode material, characterized in that, The process includes the following steps: growing a silicon-carbon thin film on the surface of a copper foil using cold plasma chemical vapor deposition in a cold plasma reactor, wherein the deposition source gas is a carbon-containing organosilicon compound or a mixture thereof; moving the copper foil with a conveyor; fixing the copper foil on a drive reel and moving it using a roll-to-roll transport method; The following apparatus is used to prepare silicon-carbon anode material, which includes a cold plasma reactor and a conveying device disposed therein; the conveying device is used to lay copper foil on it and convey the copper foil. The cold plasma reaction device is a dielectric barrier discharge plasma reaction device; The dielectric barrier discharge plasma reaction device includes a reaction chamber, and a first electrode, a second electrode, and a dielectric barrier layer disposed inside the reaction chamber. The first electrode and the second electrode are arranged opposite to each other, and the material passes between the first electrode and the second electrode through the reaction chamber; The dielectric barrier layer is disposed on the side of the first electrode near the second electrode; The dielectric barrier discharge plasma reaction device includes an air inlet and an exhaust outlet disposed on the reaction chamber. The conveying device includes a drive reel and a power unit.

11. A silicon-carbon anode material prepared by the preparation method according to any one of claims 1 to 9 or 10.

12. The silicon-carbon anode material according to claim 11, characterized in that, The nano-silicon is amorphous nano-silicon.

13. The silicon-carbon anode material according to claim 11, characterized in that, The silicon content in the silicon-carbon anode material is 20% to 50%.

14. A method for preparing a negative electrode sheet, characterized in that, A conductive paste is coated onto the surface of the silicon-carbon anode material as described in claim 11.

15. The method for preparing the negative electrode sheet according to claim 14, characterized in that, The conductive paste contains graphite.

16. A negative electrode sheet prepared by the preparation method as described in claim 14 or 15.

17. A secondary battery, characterized in that, Includes the silicon-carbon anode material as described in any one of claims 11 to 13 or the anode sheet as described in claim 16.

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