Silicon-carbon composite negative electrode and preparation method thereof

Abstract

The invention discloses a silicon-carbon composite negative electrode and a preparation method thereof, and the method comprises the following steps: S1, preparing micron-sized graphite particles and SiH4 gas, and preparing silicon-carbon particles by adopting a CVD (Chemical Vapor Deposition) process; s2, an injection molding process is adopted, paraffin is used for wrapping the silicon carbon particles, a wax layer is formed on the periphery of the silicon carbon particles, and meanwhile a plurality of wax branches are formed on the periphery of the wax layer; s3, preparing a PP roll film containing the silicon-carbon particles on a biaxial stretching line by using the paraffin-coated silicon-carbon particles and PP particles; s4, paraffin on the PP roll film is removed through an extraction technology, an expansion space for expansion is formed in the periphery of the silicon carbon particles, and meanwhile a plurality of extension channels are formed in the periphery of the expansion space; s5, a protective film is arranged on the single face of the PP roll film with the paraffin removed; s6, copper plating is conducted on the PP roll film with the single face coated with the protective film; and S7, tearing off the protective film to obtain the silicon-carbon composite negative electrode material. According to the silicon-carbon composite negative electrode and the preparation method thereof provided by the invention, the expansion problem and the conductivity problem of lithium intercalation in silicon can be solved.

Description

Technical Field

[0001] The present invention relates to the technical field of negative electrode materials, and in particular to a silicon-carbon composite negative electrode and a preparation method thereof. Background Art

[0002] The negative electrode active material of conventional lithium batteries is carbon material, such as natural graphite and artificial graphite, and the negative electrode current collector is made of pure copper foil or composite copper foil. Graphite materials have low prices, relatively high lithium storage capacity of 372mah / g, extremely high initial efficiency, stable chemical properties, corrosion resistance, conductivity, good layered structure, small volume change before and after lithium insertion, relatively high lithium insertion capacity, and low lithium insertion potential during the reaction. It has become the first choice for negative electrode materials for lithium-ion batteries, but graphite negative electrodes have also encountered bottlenecks. Their deintercalation ability and efficiency restrict the battery capacity and charging performance.

[0003] The emergence of silicon-based negative electrodes can break through this bottleneck. Silicon accepts lithium ions by utilizing the three-dimensional bulk structure of silicon crystals to form a silicon-lithium alloy. The energy density of crystalline silicon is 4200mah / g, which is about 10 times that of graphite. However, its biggest problem is that the volume changes greatly during the lithium insertion process. If pure crystalline silicon is used as the negative electrode, the volume change can reach 300%, and it is not easy to restore after expansion, which will cause the negative electrode material to pulverize over time. Summary of the invention

[0004] The purpose of the present invention is to provide a silicon-carbon composite negative electrode and a preparation method thereof, which can solve the expansion problem and conductivity problem of silicon embedded with lithium.

[0005] Based on the above problems, the technical solution provided by the present invention is:

[0006] A method for preparing a silicon-carbon composite negative electrode comprises the following steps:

[0007] S1. Preparation of micron-sized graphite particles and SiH 4 Gas, using CVD process to prepare silicon carbon particles;

[0008] S2, using an injection molding process to wrap the silicon-carbon particles with paraffin wax, forming a wax layer on the periphery of the silicon-carbon particles, and forming a plurality of wax branches on the periphery of the wax layer;

[0009] S3, preparing a PP roll film containing silicon-carbon particles by placing the silicon-carbon particles and PP particles wrapped in paraffin on a biaxial stretching line;

[0010] S4. The paraffin wax on the PP film roll is removed by an extraction process, and an expansion space for expansion is formed on the periphery of the silicon-carbon particles, and a plurality of extension channels are formed on the periphery of the expansion space;

[0011] S5. Setting a protective film on one side of the PP film roll from which the paraffin is removed;

[0012] S6. Copper plating the PP roll film with a single-sided protective film;

[0013] S7. Remove the protective film to obtain a silicon-carbon composite negative electrode material.

[0014] In some embodiments, in step S1, porous micron-sized graphite particles are placed in a fluidized deposition furnace to form a fluidized state, and the fluidized deposition furnace is heated to generate H 2 Gas and SiH 4 Gas is introduced into the furnace to make SiH 4 The gas and micron-sized graphite are subjected to CVD fluidized deposition in a fluidized deposition furnace to obtain silicon-carbon particles.

[0015] In some embodiments, the particle size of the micron-sized graphite particles in step S1 is 7 to 9 μm, the heating temperature is 950 to 1050° C., and H 2 Gas and SiH 4 The volume ratio of gas is 3-5:1-2.

[0016] In some embodiments, in step S2, silicon-carbon particles are placed in a metal mold, paraffin oil is heated to a liquid state and then injected into the metal mold, and the particles are taken out after cooling to obtain silicon-carbon particles wrapped in paraffin.

[0017] In some embodiments, the wax layer in step S2 has a thickness of 2 to 4 μm, and the wax branches have a length of 3 to 5 μm, a width of 2 to 4 μm, and a thickness of 3 to 5 μm.

[0018] In some of the embodiments, in step S3, PP particles are passed through an extruder to obtain a high-temperature melt, which is then mixed with silicon-carbon particles wrapped in paraffin wax, extruded through a twin-screw extruder to form an oil film, and the oil film is cooled and longitudinally stretched on a stretching roller, and then transversely stretched in a stretching oven to obtain a PP roll film of silicon-carbon particles wrapped in paraffin wax.

[0019] In some embodiments, in step S3, the PP particles are melted at a high temperature of 200 to 300°C, the ratio of PP particles to silicon-carbon particles is 4:6 to 6:4, the oil film is cooled to 10 to 100°C, longitudinally stretched on a stretching roller at 90 to 130°C with a total stretching ratio of 2 to 10 times, and transversely stretched in a stretching oven at 100 to 140°C with a total stretching ratio of 2 to 10 times, to obtain a PP roll film with a thickness of 49.5 to 50.5 μm.

[0020] In some embodiments, in step S4, the paraffin oil in the PP film roll is extracted with dichloromethane, and then the residual dichloromethane is removed by drying, and finally a second horizontal stretching is performed, and the film roll is cooled and shaped to obtain a PP film roll mixed with silicon-carbon particles.

[0021] In some embodiments, in step S4, the extraction temperature is 28-60°C, the drying temperature is 90-110°C, and the cooling and setting temperature is 15-50°C.

[0022] Based on the above problems, the present invention also provides another technical solution:

[0023] A silicon-carbon composite negative electrode is prepared according to the above-mentioned method for preparing the silicon-carbon composite negative electrode.

[0024] In some embodiments, the method comprises a substrate layer and a first copper layer arranged on one side of the substrate layer in the thickness direction, wherein a plurality of silicon-carbon particles are wrapped in the substrate layer, an expansion space is formed at the periphery of each silicon-carbon particle, a plurality of extension channels are formed at the periphery of the expansion space, and the expansion spaces of adjacent silicon-carbon particles are connected via the extension channels, and a second copper layer is provided on the side walls of the expansion space and the extension channels, and the second copper layer is connected to the first copper layer.

[0025] Compared with the prior art, the advantages of the present invention are:

[0026] Silicon-carbon particles are wrapped with paraffin to make a PP roll film, and then the paraffin is extracted and removed. This can form a space for expansion around the silicon-carbon particles, solving the expansion problem of silicon-embedded lithium. During copper plating, a copper layer can be formed in the space left by the extracted paraffin, thereby improving the conductivity. The silicon-carbon composite negative electrode also improves the energy density of the lithium battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. The accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0028] Figures 1 to 6 A schematic diagram of a process for preparing a silicon-carbon composite negative electrode according to the present invention;

[0029] Figure 7 A schematic structural diagram of a silicon-carbon composite negative electrode embodiment of the present invention;

[0030] in:

[0031] 1. Silicon carbon particles;

[0032] 2. Wax layer; 2-1. Expansion space;

[0033] 3. Wax branch; 3-1. Extension channel;

[0034] 4. Base material layer;

[0035] 5. Protective film;

[0036] 6. The first copper layer;

[0037] 7. The second copper layer. DETAILED DESCRIPTION

[0038] The above scheme is further described below in conjunction with specific examples. It should be understood that these examples are used to illustrate the present invention and are not limited to the scope of the present invention. The implementation conditions adopted in the examples can be further adjusted according to the conditions of the specific manufacturer, and the unspecified implementation conditions are usually the conditions in conventional experiments.

[0039] A method for preparing a silicon-carbon composite negative electrode comprises the following steps:

[0040] S1. Preparation of micron-sized graphite particles and SiH 4 Gas, using CVD process to prepare silicon carbon particles 1, such as Figure 1 As shown;

[0041] S2, using an injection molding process, wrapping the silicon-carbon particles 1 with paraffin wax, forming a wax layer 2 on the periphery of the silicon-carbon particles 1, and forming a plurality of wax branches 3 on the periphery of the wax layer 2, such as Figure 2 As shown;

[0042] S3, the silicon-carbon particles 1 and PP particles wrapped in paraffin are stretched on a biaxial stretching line to prepare a PP roll film containing silicon-carbon particles, such as Figure 3 As shown;

[0043] S4, removing the paraffin wax on the PP film roll by an extraction process, forming an expansion space 2-1 for expansion on the periphery of the silicon-carbon particles 1, and forming a plurality of extension channels 3-1 on the periphery of the expansion space 2-1;

[0044] S5, a protective film 5 is provided on one side of the PP film roll from which the paraffin is removed, such as Figure 4 As shown;

[0045] S6, copper plating is performed on the PP film roll with the protective film 5 on one side, such as Figure 5 As shown;

[0046] S7, remove the protective film to obtain a silicon-carbon composite negative electrode material, such as Figure 6 shown.

[0047] In step S1, purchased micron-sized graphite particles of 8±1 μm are placed in the feed port of the fluidized bed deposition device, and then nitrogen is introduced for gas replacement, with a gas flow rate of 3 Nm 3 / h, so that the pressure in the fluidized deposition furnace reaches 1.2bar, and the micron-sized graphite particles are fed into the fluidized deposition furnace through the feeder, and the guide plate is adjusted to fluidize the micron-sized graphite particles. The heating device is turned on to heat the fluidized deposition furnace to raise the temperature in the fluidized deposition furnace to 1000±50℃, and the H2O2 in a ratio of 3~5:1~2 is added through the air supply mechanism. 2 With SiH 4 Enter the furnace to make SiH 4 The CVD fluidized deposition is carried out with micron-sized graphite particles in a fluidized deposition furnace to form a fluidized deposition material. After 4 hours, the input of SiH 4 , open the recovery component to extract and collect the unreacted micron-sized graphite particles, and continuously input N 2 The gas cools the fluidized deposition furnace, and after the temperature drops to room temperature, 8±1 μm silicon-carbon negative electrode material particles can be obtained in the collection hopper. The fluidized deposition device is a commonly used device in the prior art, and will not be described in detail unless otherwise disclosed.

[0048] In step S2, silicon-carbon particles are placed in a metal mold, paraffin oil is heated to a liquid state and then injected into the metal mold, and the particles are taken out after cooling. At this time, the surface of the silicon-carbon particles is coated with paraffin oil, the thickness of the wax layer is 2 to 4 μm, and the length of the wax branches is 3 to 5 μm, the width is 2 to 4 μm, and the thickness is 3 to 5 μm.

[0049] In step S3, PP particles are passed through an extruder at 200-300°C to obtain a high-temperature melt, and then silicon-carbon particles wrapped in paraffin are added and mixed at a mixing ratio of 4:6-6:4. The mixture is extruded through a twin-screw extruder to form an oil film, which is rapidly cooled to 10-100°C and longitudinally stretched on a stretching roller at 90-130°C with a total stretching ratio of 2-10 times. The film is then transversely stretched in a stretching oven at 100-140°C with a stretching ratio of 2-10 times. At this time, a roll of PP film containing a certain proportion of silicon-carbon particles wrapped in paraffin is obtained, and the thickness of the film is 50±0.5μm.

[0050] In step S4, the paraffin oil in the PP film roll is extracted with dichloromethane at 28-60°C, and the residual dichloromethane is removed by drying at 90-110°C. Finally, a second horizontal stretching is performed and the film is cooled and shaped at 15-50°C to obtain a roll of PP film mixed with silicon-carbon particles. The space left by the paraffin is removed for expansion when silicon is embedded with lithium.

[0051] In step S5, on a roll-to-roll rewinder, one side of the silicon-carbon PP roll film is covered with a CPP protective film (i.e., a cast polypropylene protective film), the thickness of the CPP protective film is 50±20 μm, the winding speed is 100±50 m / min, the unwinding tension is 200±100 N, and the winding tension is 150±80 N.

[0052] In step S6, the silicon-carbon PP roll film with a single-sided CPP protective film is plated with copper by an integrated electroplating and water electroplating line, with a total running speed of 14±4m / min. The film material is first degreased with a degreaser at a temperature of 50±20°C, followed by a triple water wash; then pre-soaked in hydrochloric acid at room temperature of 200-250ml / L; then target activation is performed, and the activation conditions are: hydrochloric acid: 250-300ml / L, metal target: 2-5PPM / L, divalent tin: 2.8g / L, temperature: 30-35°C; after the quadruple water wash is cleaned, chemical copper deposition is performed, and the copper deposition conditions are: Cu 2+ : 1.8N2.2g / L, HCHO: 3.0N4.5g / L, NaOH: 9.5~11.5g / L, EDTA: 24~40g / L, temperature: 30~35℃; after chemical plating, four water washes are carried out to clean the chemical agents. At this time, the thickness of the copper layer is 100±30nm; followed by water electroplating to quickly thicken the copper layer to 1000nm. The water plating parameters are single-sided total current: 12000±2000A, sulfuric acid: 120~150g / L, five-water copper sulfate: 120-150g / L, chloride ion: 30~80ppm, temperature: 24~28℃; four water washes are carried out to clean the chemical agents; temperature: drying and rolling at 80~140℃; at this time, the copper layer square resistance is 14~20mΩ / □.

[0053] In step S7, the protective film is torn off when the chemical plating and water electroplating integrated line is wound up, and the total thickness of the obtained silicon-carbon composite electrode is 51±0.5 μm.

[0054] like Figure 7 As shown, it is a schematic diagram of the structure of a silicon-carbon composite negative electrode obtained by the preparation method of the above-mentioned silicon-carbon composite negative electrode, which includes a substrate layer 3 and a first copper layer 6 arranged on one side of the substrate layer 3 in the thickness direction, the substrate layer 3 is wrapped with a plurality of silicon-carbon particles 1, an expansion space 2-1 is formed on the periphery of the silicon-carbon particles 1, and a plurality of extension channels 3-1 are formed on the periphery of the expansion space 2-1, and the expansion spaces 2-1 of adjacent silicon-carbon particles 1 are connected through the extension channels 3-1, and the side walls of the expansion space 2-1 and the extension channels 3-1 form a second copper layer 7, wherein the extension channel 3-1 close to the first copper layer 6 extends to the surface of the substrate layer 3, so that the second copper layer 7 is connected to the first copper layer 6.

[0055] The following are specific embodiments

[0056] Example 1

[0057] In step S1, purchased 8 μm micron-sized graphite particles are placed in the feed port of the fluidized bed deposition device, and then nitrogen is introduced for gas replacement, with a gas flow rate of 3 Nm 3 / h, so that the pressure in the fluidized deposition furnace reaches 1.2bar, and the micron-sized graphite particles are fed into the fluidized deposition furnace through the feeder, and the guide plate is adjusted to fluidize the micron-sized graphite particles. The heating device is turned on to heat the fluidized deposition furnace, and the temperature in the fluidized deposition furnace is raised to 1000℃. The 4:1.5 H 2 With SiH 4 Enter the furnace to make SiH 4 The CVD fluidized deposition is carried out with micron-sized graphite particles in a fluidized deposition furnace to form a fluidized deposition material. After 4 hours, the input of SiH 4 , open the recovery component to extract and collect the unreacted micron-sized graphite particles, and continuously input N 2 The gas cools the fluidized deposition furnace, and after the temperature drops to room temperature, 8μm silicon-carbon negative electrode material particles can be obtained in the collecting hopper.

[0058] In step S2, silicon-carbon particles are placed in a metal mold, paraffin oil is heated to a liquid state and then injected into the metal mold, and the particles are taken out after cooling. At this time, the surface of the silicon-carbon particles is covered with paraffin oil, the thickness of the wax layer is 3 μm, and the length, width and thickness of the wax branches are 4 μm, 3 μm and 4 μm respectively.

[0059] In step S3, PP particles are passed through an extruder at 250°C to obtain a high-temperature melt, and then silicon-carbon particles wrapped in paraffin are added and mixed. The mass mixing ratio of PP particles and silicon-carbon particles wrapped in paraffin is 4:6. The particles are extruded through a twin-screw extruder to form an oil film, which is rapidly cooled to 80°C and longitudinally stretched on a stretching roller at 110°C with a total stretching ratio of 6 times. Subsequently, the particles are transversely stretched in a stretching oven at 120°C with a stretching ratio of 5 times. At this time, a roll of PP film containing a certain proportion of silicon-carbon particles wrapped in paraffin is obtained, and the thickness of the film is 50 μm.

[0060] In step S4, the paraffin oil in the PP film roll is extracted with dichloromethane at 50°C, and the residual dichloromethane is removed by drying at 100°C. Finally, a second horizontal stretching is performed and the film is cooled and formed at 40°C to obtain a roll of PP film mixed with silicon-carbon particles. The space left by the paraffin is removed to provide space for silicon to expand when lithium is embedded.

[0061] In step S5, on a roll-to-roll rewinder, one side of the silicon-carbon PP roll film is covered with a CPP protective film (i.e., a cast polypropylene protective film), the thickness of the CPP protective film is 50 μm, the winding speed is 100 m / min, the unwinding tension is 200 N, and the winding tension is 150 N.

[0062] In step S6, the silicon-carbon PP roll film with a single-sided CPP protective film is plated with copper by an integrated electroplating and water electroplating line, with a total running speed of 14 m / min. The film material is first degreased with a degreaser at a temperature of 50°C, followed by a triple water wash; then pre-soaked in 230 ml / L hydrochloric acid at room temperature; then target activation is performed, and the activation conditions are: hydrochloric acid: 280 ml / L, metal target: 4 PPM / L, divalent tin: 2.8 g / L, temperature: 33°C; after the quadruple water wash is cleaned, chemical copper deposition is performed, and the copper deposition conditions are: Cu 2+ : 2g / L, HCHO: 3.5g / L, NaOH: 10g / L, EDTA: 30g / L, temperature: 33℃; after chemical plating, four water washes are carried out to clean the chemical agents. At this time, the copper layer thickness is 100nm; followed by water electroplating to quickly thicken the copper layer by 1000nm. The water plating parameters are single-sided total current: 12000A, sulfuric acid: 130g / L, five-hydrate copper sulfate: 140g / L, chloride ion: 60ppm, temperature: 26℃; four water washes are carried out to clean the chemical agents; drying and rolling at 100℃; at this time, the copper layer square resistance is 18~20mΩ / □.

[0063] In step S7, the protective film is torn off when the chemical plating and water electroplating integrated line is wound up, and the total thickness of the obtained silicon-carbon composite electrode is 51 μm.

[0064] Example 2

[0065] In step S1, purchased 8 μm micron-sized graphite particles are placed in the feed port of the fluidized bed deposition device, and then nitrogen is introduced for gas replacement, with a gas flow rate of 3 Nm 3 / h, so that the pressure in the fluidized deposition furnace reaches 1.2bar, and the micron-sized graphite particles are fed into the fluidized deposition furnace through the feeder, and the guide plate is adjusted to fluidize the micron-sized graphite particles. The heating device is turned on to heat the fluidized deposition furnace, and the temperature in the fluidized deposition furnace is raised to 1000℃. The 4:1.5 H 2 With SiH 4 Enter the furnace to make SiH 4 The CVD fluidized deposition is carried out with micron-sized graphite particles in a fluidized deposition furnace to form a fluidized deposition material. After 4 hours, the input of SiH 4 , open the recovery component to extract and collect the unreacted micron-sized graphite particles, and continuously input N 2 The gas cools the fluidized deposition furnace, and after the temperature drops to room temperature, 8μm silicon-carbon negative electrode material particles can be obtained in the collecting hopper.

[0066] In step S2, silicon-carbon particles are placed in a metal mold, paraffin oil is heated to a liquid state and then injected into the metal mold, and the particles are taken out after cooling. At this time, the surface of the silicon-carbon particles is covered with paraffin oil, the thickness of the wax layer is 3 μm, and the length, width and thickness of the wax branches are 4 μm, 3 μm and 4 μm respectively.

[0067] In step S3, PP particles are passed through an extruder at 250°C to obtain a high-temperature melt, and then silicon-carbon particles wrapped in paraffin are added and mixed. The mass mixing ratio of PP particles and silicon-carbon particles wrapped in paraffin is 6:4. The particles are extruded through a twin-screw extruder to form an oil film, which is rapidly cooled to 90°C and longitudinally stretched on a stretching roller at 130°C with a total stretching ratio of 8 times. Subsequently, the particles are transversely stretched in a stretching oven at 140°C with a stretching ratio of 7 times. At this time, a roll of PP film containing a certain proportion of silicon-carbon particles wrapped in paraffin is obtained, and the thickness of the film is 50 μm.

[0068] In step S4, the paraffin oil in the PP film roll is extracted with dichloromethane at 50°C, and the residual dichloromethane is removed by drying at 100°C. Finally, a second horizontal stretching is performed and the film is cooled and formed at 40°C. At this time, a roll of PP film mixed with silicon-carbon particles is obtained. The space left by removing the paraffin is used for expansion when silicon is embedded with lithium.

[0069] In step S5, on a roll-to-roll rewinder, one side of the silicon-carbon PP roll film is covered with a CPP protective film (i.e., a cast polypropylene protective film), the thickness of the CPP protective film is 50 μm, the winding speed is 90 m / min, the unwinding tension is 180 N, and the winding tension is 140 N.

[0070] In step S6, the silicon-carbon PP roll film with a single-sided CPP protective film is plated with copper by an integrated electroplating and water electroplating line, with a total running speed of 12 m / min. The film material is first degreased with a degreaser at a temperature of 50°C, followed by a triple water wash; then pre-soaked in 230 ml / L hydrochloric acid at room temperature; then target activation is performed, and the activation conditions are: hydrochloric acid: 280 ml / L, metal target: 4 PPM / L, divalent tin: 2.8 g / L, temperature: 33°C; after the quadruple water wash is cleaned, chemical copper deposition is performed, and the copper deposition conditions are: Cu 2+ : 2g / L, HCHO: 3.5g / L, NaOH: 10g / L, EDTA: 30g / L, temperature: 33℃; after chemical plating, four water washes are carried out to clean the chemical agents. At this time, the copper layer thickness is 100nm; followed by water electroplating to quickly thicken the copper layer to 1000nm. The water plating parameters are single-sided total current: 12000A, sulfuric acid: 130g / L, five-hydrated copper sulfate: 140g / L, chloride ion: 60ppm, temperature: 26℃; four water washes are carried out to clean the chemical agents; temperature: drying and rolling at 100℃; at this time, the copper layer square resistance is 18~20mΩ / □.

[0071] In step S7, the protective film is torn off when the chemical plating and water electroplating integrated line is wound up, and the total thickness of the obtained silicon-carbon composite electrode is 51 μm.

[0072] The silicon-carbon composite negative electrode and the commercial graphite negative electrode were made into button batteries, and the constant current charge and discharge test was performed using the LAND CT3002A battery test system. The discharge voltage was 0.005V, the charge voltage was 1.5V, and the charge and discharge test was performed at a current of 0.1C. The test data is shown in Table 1:

[0073] Table 1 Charge and discharge test data

[0074]

[0075] The comparison results show that the charging capacity ratio of the silicon-carbon composite negative electrode is more than three times that of the commercial graphite negative electrode, which improves the battery energy density and basically approaches the first coulomb efficiency. Although the battery thickness growth rate after expansion is greater than that of the commercial graphite negative electrode, it has been greatly reduced compared to the 300% expansion coefficient of single crystal silicon and can be used commercially.

[0076] In summary, the silicon-carbon composite negative electrode can solve the problems of silicon-embedded lithium expansion and conductivity, and improve the energy density of lithium batteries.

[0077] The above examples are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent transformation or modification made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a silicon-carbon composite negative electrode, characterized in that: The following steps are involved: S1, preparing micron-sized graphite particles and SiHH4 gas, and preparing silicon-carbon particles by CVD process; S2, using an injection molding process to wrap the silicon-carbon particles with paraffin wax, forming a wax layer on the periphery of the silicon-carbon particles, and forming a plurality of wax branches on the periphery of the wax layer; S3, preparing a PP roll film containing silicon-carbon particles by placing the silicon-carbon particles and PP particles wrapped in paraffin on a biaxial stretching line; S4. The paraffin wax on the PP film roll is removed by an extraction process, and an expansion space for expansion is formed on the periphery of the silicon-carbon particles, and a plurality of extension channels are formed on the periphery of the expansion space; S5. Setting a protective film on one side of the PP film roll from which the paraffin is removed; S6. Copper plating the PP roll film with a single-sided protective film; S7. Remove the protective film to obtain a silicon-carbon composite negative electrode material.

2. The method for preparing a silicon-carbon composite negative electrode according to claim 1, characterized in that: In step S1, porous micron-sized graphite particles are placed in a fluidized deposition furnace to form fluidization, the fluidized deposition furnace is heated, H2 gas and SiH4 gas are input into the furnace, and SiH4 gas and micron-sized graphite are subjected to CVD fluidized deposition in the fluidized deposition furnace to obtain silicon-carbon particles.

3. The method for preparing a silicon-carbon composite negative electrode according to claim 2, characterized in that: In step S1, the particle size of the micron-sized graphite particles is 7-9 μm, the heating temperature is 950-1050° C., and the volume ratio of H 2 gas to SiHH 4 gas is 3-5:1-2.

4. The method for preparing a silicon-carbon composite negative electrode according to claim 1, characterized in that: In step S2, silicon carbon particles are placed in a metal mold, paraffin oil is heated to a liquid state and then injected into the metal mold, and the particles are taken out after cooling to obtain silicon carbon particles wrapped in paraffin wax; the thickness of the wax layer is 2 to 4 μm, and the length of the wax branches is 3 to 5 μm, the width is 2 to 4 μm, and the thickness is 3 to 5 μm.

5. The method for preparing a silicon-carbon composite negative electrode according to claim 1, characterized in that: In step S3, the PP particles are passed through an extruder to obtain a high-temperature melt, which is then mixed with silicon-carbon particles wrapped in paraffin wax and extruded through a twin-screw extruder to form an oil film. After the oil film is cooled, it is longitudinally stretched on a stretching roller, and then transversely stretched in a stretching oven to obtain a PP roll film of silicon-carbon particles wrapped in paraffin wax.

6. The method for preparing a silicon-carbon composite negative electrode according to claim 5, characterized in that: In step S3, the PP particles are melted at a high temperature of 200 to 300°C, the ratio of PP particles to silicon carbon particles is 4:6 to 6:4, the oil film is cooled to 10 to 100°C, longitudinally stretched on a stretching roller at 90 to 130°C, with a total stretching ratio of 2 to 10 times, and transversely stretched in a stretching oven at 100 to 140°C, with a total stretching ratio of 2 to 10 times, to obtain a PP roll film with a thickness of 49.5 to 50.5 μm.

7. The method for preparing a silicon-carbon composite negative electrode according to claim 1, characterized in that: In step S4, the paraffin oil in the PP film roll is extracted with dichloromethane, and then the residual dichloromethane is removed by drying. Finally, a second horizontal stretching is performed, and the film roll is cooled and shaped to obtain a PP film roll mixed with silicon-carbon particles.

8. The method for preparing a silicon-carbon composite negative electrode according to claim 7, characterized in that: In step S4, the extraction temperature is 28-60°C, the drying temperature is 90-110°C, and the cooling and setting temperature is 15-50°C.

9. A silicon-carbon composite negative electrode, characterized in that: It is prepared according to the method for preparing the silicon-carbon composite negative electrode according to any one of claims 1 to 8.

10. A silicon-carbon composite negative electrode, characterized in that: It includes a substrate layer and a first copper layer arranged on one side of the substrate layer in the thickness direction, wherein a plurality of silicon-carbon particles are wrapped in the substrate layer, an expansion space is formed on the periphery of each silicon-carbon particle, a plurality of extension channels are formed on the periphery of the expansion space, and the expansion spaces of adjacent silicon-carbon particles are connected via the extension channels, and a second copper layer is arranged on the side walls of the expansion space and the extension channels, and the second copper layer is connected to the first copper layer.

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