Silicon-carbon negative electrode composite preparation process for in-situ growth of nano silicon particles

Abstract

The invention relates to the technical field of silicon-carbon negative electrode composite preparation scheme design, in particular to a silicon-carbon negative electrode composite preparation process for in-situ growth of nano silicon particles. The process comprises the following steps: pre-treating a carbon matrix to improve the surface activity; dipping the carbon matrix in a precursor solution containing a silicon source, a reducing agent and a solvent, and reacting under the conditions of 60-200 DEG C and 0.1-3 MPa, so that the silicon source is subjected to in-situ reduction to generate nano silicon particles; the particle size and morphology of the nano silicon are controlled by regulating and controlling the stirring speed, the temperature gradient and the solvent evaporation rate, and a pore forming agent is introduced to form a porous structure; a conductive auxiliary agent is added, and a conductive network is constructed through mechanical stirring and ultrasonic dispersion; heat treatment enhances interface bonding. The first coulombic efficiency of the silicon-carbon negative electrode composite material prepared by the method is greater than or equal to 88%, the cycle performance is stable, and the silicon-carbon negative electrode composite material is suitable for high-energy-density lithium ion batteries. The method is simple in process, low in cost and suitable for large-scale industrial production.

Description

Technical Field

[0001] The present invention relates to the technical field of silicon-carbon negative electrode composite preparation scheme design, and in particular to a silicon-carbon negative electrode composite preparation process for in-situ growth of nano-silicon particles. Background Art

[0002] Improving the energy density of lithium-ion batteries is crucial to the development of new energy vehicles and portable electronic devices. The theoretical specific capacity of commercially available graphite anodes (372 mAh / g) is nearing its upper limit, while silicon-based anodes (theoretical specific capacity of approximately 4200 mAh / g) have become a research hotspot for next-generation electrode materials due to their high lithium storage capacity. However, silicon anodes face three core challenges in practical application:

[0003] (1) During the charge-discharge cycle, the volume of silicon particles expands by more than 300%, resulting in the pulverization and failure of the electrode structure;

[0004] (2) Silicon reacts with liquid electrolyte to form an unstable solid electrolyte interface (SEI) film, resulting in the first irreversible capacity loss and cycle performance degradation;

[0005] (3) Particles are prone to agglomeration, resulting in low electron / ion transmission efficiency.

[0006] Existing technologies primarily improve performance through nano-silicon, carbon composite materials, and coating techniques. For example, while carbon-coated nano-silicon produced by chemical vapor deposition significantly improves cycle life, it is expensive. Silicon-carbon composites produced by mechanical ball milling suffer from uneven particle size distribution (CV value >20%) and weak interfacial bonding (initial efficiency approximately 80%). Furthermore, existing technologies propose high-temperature sintering of silicon particles and a carbon matrix, but this process is complex and energy-intensive.

[0007] Therefore, the existing technology needs to be further developed. Summary of the Invention

[0008] The purpose of the present invention is to overcome the above technical deficiencies and provide a process for preparing a silicon-carbon negative electrode composite by in-situ growing nano-silicon particles, so as to solve the problems existing in the prior art.

[0009] To achieve the above technical objectives, according to a first aspect of the present invention, the present invention provides a process for preparing a silicon-carbon negative electrode composite by in-situ growth of nano-silicon particles, the process comprising:

[0010] S100, pre-treating the carbon matrix material according to a preset method to remove surface impurities and increase surface active sites; preparing a precursor solution containing a silicon source, a reducing agent, and a solvent, wherein the silicon source is at least one of a silicate and an organosilicon compound, the reducing agent is at least one of sodium borohydride and lithium aluminum hydride, and the solvent is at least one of ethanol, isopropanol, and deionized water;

[0011] S200, immersing the pretreated carbon matrix material in a precursor solution, reacting under preset temperature and preset pressure conditions, so that the silicon source is reduced and grown in situ on the surface of the carbon matrix to form nano-silicon particles; after the reaction is completed, washing and drying the product to remove unreacted impurities; and heat-treating the dried product to enhance the interface bonding between the nano-silicon particles and the carbon matrix;

[0012] S300. The size of nano-silicon particles is uniformly controlled by regulating the stirring speed and temperature gradient of the reaction system; the morphology of nano-silicon particles is controlled by using the template method and the surfactant-assisted method; a pore-forming agent is introduced into the reaction system, and the pore-forming agent decomposes to form a porous structure during the heat treatment process, thereby optimizing the pore structure of the composite material; a conductive additive is added to the composite material, and a conductive network is constructed by mechanical stirring and ultrasonic dispersion methods, and finally a silicon-carbon negative electrode composite material with in-situ grown nano-silicon particles is obtained.

[0013] Specifically, the preset method is at least one of acid washing, alkaline washing, and plasma treatment.

[0014] Specifically, the preset temperature is 60° C.-200° C., and the preset pressure is 0.1 MPa-3 MPa.

[0015] Specifically, the pH value and temperature of the reaction system are monitored in real time during the reaction process to maintain the stability of the reaction system.

[0016] Specifically, the template used in the template method is at least one of a silica template and a polystyrene template, and the surfactant is at least one of sodium dodecylbenzenesulfonate and polyethylene glycol.

[0017] Specifically, the pore-forming agent is at least one of ammonium bicarbonate and ammonium carbonate, and the decomposition temperature of the pore-forming agent during the heat treatment process is lower than the highest temperature of the heat treatment.

[0018] Specifically, the conductive additive is at least one of carbon black, carbon nanotubes, and graphene.

[0019] Specifically, the speed of the mechanical stirring is 200-1000 r / min, the stirring time is 1-5 hours, the power of the ultrasonic dispersion is 100-500 W, and the ultrasonic time is 0.5-2 hours.

[0020] Specifically, the temperature of the heat treatment of the dried product is 400° C.-800° C., and the heat treatment time is 1-5 hours.

[0021] Specifically, the heat treatment is performed under the protection of an inert gas, and the inert gas is at least one of nitrogen and argon.

[0022] Beneficial effects:

[0023] 1. In-situ growth of uniform nano-silicon: By regulating temperature, pressure and chemical reaction parameters, the silicon particles are uniform in size (50±5nm) and tightly integrated with the carbon matrix, with a capacity retention rate of ≥90% after 500 cycles.

[0024] 2. Strong interface bonding improves stability: In-situ polymerization interface modification technology enhances the stability of the SEI film, with the first coulombic efficiency ≥88% and significantly reduced side reactions.

[0025] 3. Porous structure optimizes ion transport: The introduction of pore-forming agents forms a hierarchical porous structure, which greatly shortens the electrode ion diffusion path.

[0026] 4. The process is simple, economical and efficient: no complicated equipment is required, and the one-step reduction method combined with heat treatment is adopted. The production cost is reduced by more than 50% compared with the chemical vapor deposition method.

[0027] 5. Environmentally friendly green production: The process does not emit toxic by-products, the solvent can be recycled, and it meets the green manufacturing requirements of new energy materials.

[0028] In summary, this process has broken through the technical bottleneck of traditional silicon-carbon negative electrodes, achieved a synergistic improvement in high specific capacity and long cycle life, and is expected to promote the industrial application of high-energy-density lithium-ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic flow chart of a process for preparing a silicon-carbon negative electrode composite by in-situ growth of nano-silicon particles provided in a specific embodiment of the present invention. DETAILED DESCRIPTION

[0030] In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention is clearly and completely described below in conjunction with the drawings of the present invention. Based on the embodiments in this application, other similar embodiments obtained by ordinary technicians in this field without making creative work should fall within the scope of protection of this application. In addition, the directional words mentioned in the following embodiments, such as "up", "down", "left" and "right", are only reference to the directions of the drawings. Therefore, the directional words used are used to illustrate rather than limit the invention.

[0031] The present invention will be further described below with reference to the accompanying drawings and preferred embodiments.

[0032] See also Figure 1 The present invention provides a process for preparing a silicon-carbon negative electrode composite by in-situ growing nano-silicon particles, comprising:

[0033] S100. Pre-treating the carbon matrix material according to a preset method to remove surface impurities and increase surface active sites; preparing a precursor solution containing a silicon source, a reducing agent and a solvent, wherein the silicon source is at least one of a silicate and an organosilicon compound, the reducing agent is at least one of sodium borohydride and lithium aluminum hydride, and the solvent is at least one of ethanol, isopropanol and deionized water.

[0034] Specifically, the preset method is at least one of acid washing, alkaline washing, and plasma treatment.

[0035] It is understood that the pretreatment method can select at least one of acid washing, alkaline washing or plasma treatment to pretreat the carbon matrix material according to actual conditions. In a preferred embodiment of the present invention, when acid washing is selected, the carbon matrix material can be immersed in a nitric acid solution of a certain concentration, the concentration of the nitric acid solution is 1-5 mol / L, and the immersion time is 1-3 hours to remove metal impurities on the surface; if plasma treatment is used, the plasma treatment equipment can be set with appropriate power (including 300-800 W in the preferred embodiment of the present invention) and treatment time (including 10-30 minutes in the preferred embodiment of the present invention) to increase the surface active sites of the carbon matrix material.

[0036] It should be further explained that, regarding the pretreatment of the carbon-based material, in a preferred embodiment of the present invention, the following steps are included:

[0037] Equipment selection:

[0038] Pickling equipment: corrosion-resistant plastic reactor (50L capacity, polypropylene) with magnetic stirrer (speed adjustable from 0-1000 rpm);

[0039] Ion equipment: radio frequency ion cleaning machine (power 0-1000W adjustable, vacuum degree 1-100Pa adjustable).

[0040] Specific parameters:

[0041] Nitric acid solution concentration: 1.5 mol / L (error ± 0.1 mol / L);

[0042] Soaking time: 2 hours ± 5 minutes;

[0043] Plasma treatment parameters: power 600 W, oxygen flow rate 20 L / min, treatment time 25 minutes;

[0044] Water washing standard: conductivity <5μS / cm (tested after three times of pure water washing).

[0045] Quality Control:

[0046] The surface roughness was observed by SEM (Ra value should reach 50-100 nm), and the surface functional groups were analyzed by XPS (hydroxyl / carboxyl content>3 atomic %).

[0047] It is understood that when preparing the precursor solution, the silicon source is selected from at least one of a silicate (including sodium silicate in a preferred embodiment of the present invention) and an organosilicon compound (including tetraethyl orthosilicate in a preferred embodiment of the present invention); the reducing agent is selected from at least one of sodium borohydride and lithium aluminum hydride; and the solvent is selected from at least one of ethanol, isopropanol, and deionized water. In preferred embodiments of the present invention, the ratio of the silicon source, reducing agent, and solvent can be adjusted according to actual needs when preparing the precursor solution.

[0048] Specifically, in a preferred embodiment of the present invention, the raw material selection scheme for preparing the precursor solution includes:

[0049] The raw material specifications in the preferred embodiment of the present invention include those shown in Table 1:

[0050] Table 1 Raw material specifications

[0051] raw material Purity requirements Treatment Tetraethyl orthosilicate (TEOS) 99.9％ Vacuum distillation purification Sodium borohydride AR-class Pretreatment deoxidation treatment Anhydrous ethanol Chromatographically pure Molecular sieve water removal

[0052] Preparation process:

[0053] Primary solution: TEOS and anhydrous ethanol were mixed in a volume ratio of 1:3 and magnetically stirred for 1 h (300 rpm);

[0054] Reducing agent solution: sodium borohydride prepared into a 5 wt% ethanol solution (prepare immediately for use and store in the dark);

[0055] Final mixing: the primary solution and the reducing agent solution were mixed in a volume ratio of 5:1 and stirred continuously for 45 minutes;

[0056] Additives: 0.1 wt% sodium dodecylbenzenesulfonate was added as a dispersant.

[0057] Stability Control:

[0058] Temperature control: The whole preparation process is carried out at 15±2℃;

[0059] Vacuum degassing: Use a rotary vane vacuum pump (ultimate vacuum degree 5 Pa) to degas for 20 minutes.

[0060] S200, immersing the pretreated carbon matrix material in a precursor solution, reacting under preset temperature and preset pressure conditions, so that the silicon source is reduced in situ on the surface of the carbon matrix to grow nano-silicon particles; after the reaction is completed, washing and drying the product to remove unreacted impurities; and heat-treating the dried product to enhance the interface bonding between the nano-silicon particles and the carbon matrix.

[0061] It should be noted that, regarding the in-situ growth of nano-silicon particles, the design scheme of the present invention includes the following in a preferred embodiment of the present invention:

[0062] Control of impregnation and reaction conditions: The pretreated carbon matrix material is immersed in the precursor solution, and then reacted at 60°C-200°C and normal pressure-5MPa.

[0063] Uniform size control of nano-silicon particles: Uniform size control of nano-silicon particles is achieved by regulating the stirring speed and temperature gradient of the reaction system. Specifically, the stirring speed can be controlled within a range of 200-1000 r / min by installing an agitator and setting an appropriate speed. The temperature gradient can be controlled by installing zoned heating or cooling devices in the reaction vessel to create a certain temperature difference at different locations in the reaction system. In a preferred embodiment of the present invention, the temperature difference is controlled within a range of 5-20°C.

[0064] Real-time monitoring and stability maintenance: During the reaction process, the pH and temperature of the reaction system are monitored in real time to maintain the stability of the reaction system. A pH meter and temperature sensor can be installed. When the pH value deviates from the set range (3-7 in the preferred embodiment of this invention), it is adjusted by adding an appropriate amount of acid or base. When the temperature fluctuates by more than ±5°C, the heating or cooling system is adjusted to ensure uniform size of the nano-silicon particles.

[0065] It should be noted here that, with respect to product processing, the design scheme of the present invention includes the following in a preferred embodiment of the present invention:

[0066] Washing and drying: After the reaction is completed, the product is washed with deionized water for multiple times to remove unreacted impurities, and then dried. The drying temperature can be set at 60-100°C and the drying time is 6-12 hours.

[0067] Specifically, the preset temperature is 60° C.-200° C., and the preset pressure is 0.1 MPa-3 MPa.

[0068] Specifically, the pH value and temperature of the reaction system are monitored in real time during the reaction process to maintain the stability of the reaction system.

[0069] Specifically, the temperature of the heat treatment of the dried product is 400° C.-800° C., and the heat treatment time is 1-5 hours.

[0070] Specifically, the heat treatment is performed under the protection of an inert gas, and the inert gas is at least one of nitrogen and argon.

[0071] It should be noted that, regarding heat treatment to enhance interface bonding, the design scheme of the present invention includes the following in a preferred embodiment of the present invention:

[0072] Heat treatment conditions: The dried product is heat treated at a temperature of 400°C to 800°C for 1 to 5 hours. The heat treatment is carried out under the protection of an inert gas (including at least one of nitrogen and argon in a preferred embodiment of the present invention). The flow rate of the inert gas can be controlled at 10 to 50 ml / min.

[0073] Morphology control by template method and surfactant-assisted method: The morphology of nano-silicon particles can be precisely controlled by using template method and surfactant-assisted method. In the template method, the template used can be at least one of a silica template and a polystyrene template. In a preferred embodiment of the present invention, when a silica template is used, the template can be first immersed in a precursor solution containing a silicon source and a reducing agent, and then the above-mentioned reaction and heat treatment steps are carried out, and finally the template is removed by a chemical etching method to obtain nano-silicon particles with a specific morphology. The surfactant can be at least one of sodium dodecylbenzenesulfonate and polyethylene glycol, and an appropriate amount of surfactant is added to the reaction system to adjust the growth environment of the nano-silicon particles and achieve precise control of the morphology.

[0074] It should be further explained that, with respect to the in-situ growth reaction system, the design scheme of the present invention includes the following in a preferred embodiment of the present invention:

[0075] The reaction device is designed as a multi-layer reactor structure:

[0076] Inner layer: corrosion-resistant Hastelloy alloy reactor (volume 2L);

[0077] Middle layer: oil bath heating layer (temperature control accuracy ±0.5℃);

[0078] Outer layer: inert gas protective layer (nitrogen flow rate 0-50ml / min adjustable);

[0079] Stirring system: anchor type stirring paddle + ultrasonic disperser (dual-mode drive).

[0080] The reaction parameters in the preferred embodiment of the present invention include those shown in Table 2:

[0081] Table 2 Reaction parameters

[0082] parameter scope Control accuracy temperature 80-180℃ ±0.5℃ pressure 0.1-3MPa ±0.05MPa stirring speed 300-800rpm ±10rpm Mixing time 4-8 hours ±1 minute

[0083] Online monitoring system;

[0084] pH online monitoring: glass electrode sensor (accuracy ±0.02pH);

[0085] Viscosity monitoring: digital viscometer (range 0.1-1000mPa·s);

[0086] Pressure monitoring: Piezoresistive sensor (accuracy ±0.1% FS).

[0087] It should be further explained that, regarding the interface strengthening heat treatment, the heat treatment process designed by the present invention includes the following in a preferred embodiment of the present invention:

[0088] Heat treatment process:

[0089] Heating program:

[0090] Heat up to 200°C at 10°C / min (keep warm for 30 minutes);

[0091] Heat up to 400°C at 5°C / min (keep for 60 min);

[0092] Raise the temperature at 2°C / min to the final temperature (600-800°C).

[0093] Keep warm time: 2-4 hours;

[0094] Cooling method: Inert gas protection cooling with furnace (≤50℃ / min);

[0095] Equipment requirements:

[0096] Tube furnace: Maximum operating temperature 1200℃, furnace size Φ60×200mm;

[0097] Temperature control: PID four-channel temperature controller (temperature control accuracy ±2°C);

[0098] Atmosphere system: Nitrogen purity ≥99.999%, flow rate 0-500ml / min adjustable.

[0099] S300. The size of nano-silicon particles is uniformly controlled by regulating the stirring speed, temperature gradient and solvent volatilization rate of the reaction system; the morphology of nano-silicon particles is controlled by using the template method and the surfactant-assisted method; a pore-forming agent is introduced into the reaction system, and the pore-forming agent decomposes to form a porous structure during the heat treatment process, thereby optimizing the pore structure of the composite material; a conductive additive is added to the composite material, and a conductive network is constructed by mechanical stirring and ultrasonic dispersion methods, and finally a silicon-carbon negative electrode composite material with in-situ grown nano-silicon particles is obtained.

[0100] It should be noted that regarding the hole formation and conductive network construction, the design scheme of the present invention includes:

[0101] Introduction of a pore-forming agent and optimization of the pore structure: A pore-forming agent is introduced into the reaction system. The pore-forming agent can be selected from at least one of ammonium bicarbonate and ammonium carbonate. During the heat treatment process, the pore-forming agent decomposes to form a porous structure. In a preferred embodiment of the present invention, a certain amount (5-20 wt % in the preferred embodiment of the present invention) of ammonium bicarbonate is added to the reaction system. During the heat treatment, the ammonium bicarbonate decomposes to produce carbon dioxide gas, thereby forming a porous structure in the composite material. By controlling the amount of pore-forming agent and the heat treatment conditions, the pore structure of the composite material can be optimized, with the porosity controlled within 10-30% and the pore size distribution within the range of 10-100 nm.

[0102] Adding a conductive agent and constructing a conductive network: A conductive agent is added to the composite material. The conductive agent is at least one of carbon black, carbon nanotubes, and graphene. In a preferred embodiment of the present invention, carbon black is selected as the conductive agent, and the added amount is 1-5% of the total mass of the composite material. A complete conductive network is then constructed through mechanical stirring and ultrasonic dispersion. The mechanical stirring speed is 200-1000 r / min, the stirring time is 1-5 hours, and the ultrasonic dispersion power is 100-500 W, and the ultrasonic dispersion time is 0.5-2 hours. The conductive agent is evenly dispersed in the composite material, thereby enhancing its conductivity.

[0103] Specifically, the speed of the mechanical stirring is 200-1000 r / min, the stirring time is 1-5 hours, the power of the ultrasonic dispersion is 100-500 W, and the ultrasonic time is 0.5-2 hours.

[0104] Specifically, the template used in the template method is at least one of a silica template and a polystyrene template, and the surfactant is at least one of sodium dodecylbenzenesulfonate and polyethylene glycol.

[0105] Specifically, the pore-forming agent is at least one of ammonium bicarbonate and ammonium carbonate, and the decomposition temperature of the pore-forming agent during the heat treatment process is lower than the highest temperature of the heat treatment.

[0106] Specifically, the conductive additive is at least one of carbon black, carbon nanotubes, and graphene.

[0107] It should be further explained that, regarding the control of the composite structure, the design scheme of the present invention includes the following in the preferred embodiment of the present invention:

[0108] Shape control technology:

[0109] Template method:

[0110] Template selection: mesoporous silica (pore size 20-50 nm);

[0111] Loading amount: 20-30 wt% (relative to carbon matrix);

[0112] Etching process: immersion in 1M NaOH solution at 60°C for 4 hours.

[0113] The surfactant compounding scheme in the preferred embodiment of the present invention includes the following as shown in Table 3:

[0114] Table 3 Surfactant compounding scheme

[0115] surfactants Addition amount Mechanism of action F127 0.5wt% Parental regulation of growth DDBAC 0.1wt% Anti-agglomeration effect

[0116] Pore ​​structure optimization:

[0117] Pore ​​forming agent selection: ammonium bicarbonate (particle size 2-5 μm);

[0118] Addition amount gradient experiment: 5-15wt% (optimized at intervals of 1wt%);

[0119] Decomposition control: CO2 evolution rate 1.5 ml / (g·min) (determined by TGA).

[0120] It should be further explained that, regarding the construction of the conductive network, the design scheme of the present invention includes the following in the preferred embodiment of the present invention:

[0121] The auxiliary agent compounding scheme in the preferred embodiment of the present invention includes the following as shown in Table 4:

[0122] Table 4 Additive compounding scheme

[0123] additives Addition amount Distributed carbon nanotubes 1-3wt% Wet ball milling (800 rpm × 1h) graphene 0.5-2wt% Ultrasonic assisted dispersion (40kHz×30min)

[0124] Dispersion equipment parameters:

[0125] Ball mill: 316L stainless steel tank, medium is zirconia balls (Φ1-3mm);

[0126] Ultrasonic equipment: power 300W, operating frequency 40kHz, pulse mode operation (on 5s, off 2s).

[0127] It should be further explained that, regarding the process amplification technology, the design scheme of the present invention includes the following in the preferred embodiment of the present invention:

[0128] Pilot equipment parameters:

[0129] Equipment scale: 50L reactor (400mm diameter × 800mm height);

[0130] Mass transfer system: double-layer mechanical stirring (main stirring 500rpm + auxiliary stirring 200rpm);

[0131] Heating system: Jacketed oil bath (temperature control accuracy ±1°C);

[0132] Product collection: continuous centrifugation + three-stage washing.

[0133] Process monitoring:

[0134] Online viscometer: Brookfield RVDV-I I+Pro (measuring range 0.1-10 5 cP);

[0135] Particle size analyzer: Malvern Nano-ZS (dynamic light scattering, particle size range 1-1000 nm);

[0136] Online XRD: Bruker D8 Advance (real-time monitoring of crystal growth).

[0137] Below, the process of preparing silicon-carbon anode (laboratory level) is explained through a specific case:

[0138] Material ratio:

[0139] Nano-silicon content: 8wt% (relative to the composite material);

[0140] Carbon matrix: graphite (gram capacity ≥ 350mAh / g);

[0141] Interface modifier: PVDF content 3wt%.

[0142] The performance test results are shown in Table 5:

[0143] Table 5 Performance test results

[0144] Test items Standard method Test results First coulombic efficiency GB / T 36276-2018 ≥88％ Cycle life IEC 62620:2010 1C / 1C cycle 500 weeks capacity retention rate ≥90% Rate performance GB / T 31486-2015 5C discharge capacity / 1C discharge capacity ≥80%

[0145] Below, the process of process scale-up (pilot line) is explained through a specific case:

[0146] Equipment parameters:

[0147] Reactor volume: 30L;

[0148] Production efficiency: 2kg / batch;

[0149] Product consistency: standard deviation <5% (based on d50 particle size).

[0150] The cost analysis results are shown in Table 6:

[0151] Table 6 Cost analysis results

[0152] project Unit cost Compared with before optimization Raw material costs ￥85 / kg 15% decrease Energy costs ￥15 / kWh 20% drop Labor costs ￥5 / kg 30% drop

[0153] The following is a specific example to illustrate the workflow of the present invention:

[0154] Carbon matrix material pretreatment: Graphite was selected as the carbon matrix material and soaked in a 3 mol / L nitric acid solution for 2 hours. It was then rinsed with deionized water until neutral and dried in an oven at 80°C. The dried graphite was then placed in a plasma treatment device with a power setting of 500 W and a treatment time of 20 minutes to obtain the pretreated carbon matrix material.

[0155] Prepare the precursor solution at a mass ratio of 1:1:80: silicon source (tetraethyl orthosilicate): reducing agent (sodium borohydride): solvent (a mixture of ethanol and deionized water, 3:1 by volume). Slowly add the tetraethyl orthosilicate to the mixture of ethanol and deionized water, stirring thoroughly. Then add the sodium borohydride and continue stirring until completely dissolved.

[0156] In situ growth of nano-silicon particles: The pretreated carbon matrix material is immersed in the precursor solution, and the reaction vessel is placed in an oil bath, the temperature is controlled at 120°C, and the pressure is normal pressure. The stirring speed is controlled at 500r / min by a magnetic stirrer, and a zone heating device is set in the reaction vessel to control the temperature gradient at 10°C. The solvent evaporation rate is controlled at 0.5ml / min by adjusting the sealing cover of the reaction vessel. During the reaction process, the pH value of the reaction system is monitored in real time by a pH meter. When the pH value deviates from 5, an appropriate amount of ammonia water or dilute hydrochloric acid is added for adjustment; the temperature is monitored by a temperature sensor. When the temperature fluctuation exceeds ±5°C, the heating power of the oil bath is adjusted. The reaction time is 6 hours.

[0157] Product treatment: After the reaction is complete, the product is filtered and washed with deionized water several times until the pH value of the washing solution is close to neutral. The product is then placed in an oven and dried at 80°C for 10 hours.

[0158] Heat treatment to enhance interfacial bonding: The dried product was placed in a tube furnace and heat treated under nitrogen protection. The nitrogen flow rate was set to 20 ml / min, and the temperature was increased to 600°C at a rate of 5°C / min. The temperature was maintained for 3 hours and then naturally cooled to room temperature.

[0159] Morphology control using template and surfactant-assisted methods: A certain amount of silica template and sodium dodecylbenzenesulfonate as a surfactant were added to the above reaction system. The silica template was pretreated before the reaction to remove surface impurities. The template was added at a mass ratio of 1:5 template: carbon matrix material, and the amount of sodium dodecylbenzenesulfonate added was 1% of the mass of the precursor solution. The above steps for in situ growth of nano-silicon particles were repeated. After heat treatment, the product was immersed in a 5 mol / L sodium hydroxide solution for 12 hours to remove the silica template. The product was then rinsed with deionized water until neutral and dried.

[0160] Pore ​​Formation and Conductive Network Construction: During the in-situ growth of nano-silicon particles, 10 wt% ammonium bicarbonate was added as a pore-forming agent. Carbon black was added as a conductive additive at a mass ratio of 3:100. The composite material and carbon black were mixed and stirred in a blender at 800 rpm for 3 hours. Ultrasonic dispersion was then performed at 300 W for 1 hour to obtain a silicon-carbon anode composite material with in-situ grown nano-silicon particles.

[0161] It is understood that the present invention also has the following technical effects in the preferred embodiments of the present invention:

[0162] 1. By optimizing the reaction conditions and adopting a variety of control methods, the size and morphology of nano-silicon particles can be effectively controlled, and the dispersion uniformity of nano-silicon particles on the carbon matrix surface can be improved, thereby improving the electrochemical performance of silicon-carbon negative electrode composite materials.

[0163] 2. The interfacial bonding between nano-silicon particles and the carbon matrix is ​​enhanced during the heat treatment process, which reduces the occurrence of interfacial side reactions and improves the cycle stability and first coulombic efficiency of the battery.

[0164] 3. The introduction of pore-forming agents and the construction of a conductive network optimize the pore structure and conductivity of the composite material, improve the rate performance of the battery, facilitate process amplification, and reduce production costs.

[0165] The various technical features described above can be combined arbitrarily. Although not all possible combinations of these technical features are described, any combination of these technical features should be considered to be covered by this specification as long as such combination does not conflict.

[0166] The specific embodiments of the present invention described above do not limit the scope of protection of the present invention. Any other corresponding changes and modifications made based on the technical concept of the present invention should be included in the scope of protection of the claims of the present invention.

Claims

1. A process for preparing a silicon-carbon negative electrode composite by in-situ growth of nano-silicon particles, characterized in that: The process comprises: S100, pre-treating the carbon matrix material according to a preset method to remove surface impurities and increase surface active sites; preparing a precursor solution containing a silicon source, a reducing agent, and a solvent, wherein the silicon source is at least one of a silicate and an organosilicon compound, the reducing agent is at least one of sodium borohydride and lithium aluminum hydride, and the solvent is at least one of ethanol, isopropanol, and deionized water; S200, immersing the pretreated carbon matrix material in a precursor solution, reacting under preset temperature and preset pressure conditions, so that the silicon source is reduced and grown in situ on the surface of the carbon matrix to form nano-silicon particles; after the reaction is completed, washing and drying the product to remove unreacted impurities; and heat-treating the dried product to enhance the interface bonding between the nano-silicon particles and the carbon matrix; S300. The size of nano-silicon particles is uniformly controlled by regulating the stirring speed and temperature gradient of the reaction system; the morphology of nano-silicon particles is controlled by using the template method and the surfactant-assisted method; a pore-forming agent is introduced into the reaction system, and the pore-forming agent decomposes to form a porous structure during the heat treatment process, thereby optimizing the pore structure of the composite material; a conductive additive is added to the composite material, and a conductive network is constructed by mechanical stirring and ultrasonic dispersion methods, and finally a silicon-carbon negative electrode composite material with in-situ grown nano-silicon particles is obtained.

2. The process for preparing a silicon-carbon negative electrode composite by in-situ growth of nano-silicon particles according to claim 1, characterized in that: The preset method is at least one of acid cleaning, alkali cleaning, and plasma treatment.

3. The process for preparing a silicon-carbon negative electrode composite by in-situ growth of nano-silicon particles according to claim 2, characterized in that: The preset temperature is 60° C.-200° C., and the preset pressure is 0.1 MPa-3 MPa.

4. The process for preparing a silicon-carbon negative electrode composite by in-situ growth of nano-silicon particles according to claim 3, characterized in that: During the reaction, the pH value and temperature of the reaction system are monitored in real time to maintain the stability of the reaction system.

5. The process for preparing a silicon-carbon negative electrode composite by in-situ growth of nano-silicon particles according to claim 1, characterized in that: The template used in the template method is at least one of a silica template and a polystyrene template, and the surfactant is at least one of sodium dodecylbenzenesulfonate and polyethylene glycol.

6. The process for preparing a silicon-carbon negative electrode composite by in-situ growth of nano-silicon particles according to claim 1, characterized in that: The pore-forming agent is at least one of ammonium bicarbonate and ammonium carbonate, and the decomposition temperature of the pore-forming agent during the heat treatment process is lower than the highest temperature of the heat treatment.

7. The process for preparing a silicon-carbon negative electrode composite by in-situ growth of nano-silicon particles according to claim 1, characterized in that: The conductive additive is at least one of carbon black, carbon nanotubes, and graphene.

8. The process for preparing a silicon-carbon negative electrode composite by in-situ growth of nano-silicon particles according to claim 1, characterized in that: The speed of the mechanical stirring is 200-1000 r / min, the stirring time is 1-5 hours, the power of the ultrasonic dispersion is 100-500 W, and the ultrasonic time is 0.5-2 hours.

9. The process for preparing a silicon-carbon negative electrode composite by in-situ growth of nano-silicon particles according to claim 3, characterized in that: The temperature of the heat treatment of the dried product is 400° C.-800° C., and the heat treatment time is 1-5 hours.

10. The process for preparing a silicon-carbon negative electrode composite by in-situ growth of nano-silicon particles according to claim 1, characterized in that: The heat treatment is performed under the protection of an inert gas, and the inert gas is at least one of nitrogen and argon.

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