Silicon-carbon composite negative electrode material and preparation method thereof
By designing a core-shell structure and composite coating, the structural stability and conductivity issues of silicon-carbon composite anode materials during lithiation were solved, achieving high specific capacity, long cycle life, and efficient charge-discharge, making it suitable for high-energy-density lithium-ion batteries.
Patent Information
- Application Number
- CN202511750962.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-26
- Publication Date
- 2026-02-17
AI Technical Summary
Traditional silicon-carbon composite anode materials suffer from cracking of the carbon skeleton due to the expansion stress of silicon particles during lithiation, resulting in discontinuous conductive networks and poor bonding of conductive dielectrics, which affects specific capacity, cycle stability and charge/discharge efficiency.
Hollow carbon spheres loaded with boron-doped silicon quantum dots of a core-shell structure are combined with nitrogen-doped carbon nanofibers to construct a conductive network. A stable interface is formed by a fluorophosphate-alumina composite coating layer and lithium titanate-modified montmorillonite, which inhibits material agglomeration and optimizes material performance.
It significantly improves the specific capacity, cycle stability and first charge-discharge efficiency of the material, meeting the needs of high energy density lithium-ion batteries, and the preparation process is controllable, facilitating large-scale production.
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Abstract
Description
Technical Field
[0001] This invention relates to the field of composite anode materials technology, specifically to a silicon-carbon composite anode material and its preparation method. Background Technology
[0002] Silicon-carbon composite anode materials are the core active materials for lithium-ion batteries. They are composite materials with high-specific-capacity silicon-based materials as the core lithium storage unit, combined with carbon-based materials with excellent conductivity, and their performance is optimized through modification methods such as coating and doping.
[0003] Traditional silicon-carbon composite anode materials mostly employ a simple mixing or mechanical coating of silicon particles with a carbon matrix, lacking an independent and suitable expansion buffer space. Silicon undergoes a volume expansion rate of 300%-400% during lithiation. In simple mixing systems, the expansion stress of silicon particles is directly transferred to the carbon matrix, leading to cracking of the carbon framework and material structure collapse. Furthermore, the conductive network of traditional silicon-carbon composite anodes often relies on amorphous carbon, graphite powder, or a small amount of carbon nanotubes. These conductive media have significant drawbacks: amorphous carbon has limited conductivity, graphite powder is prone to agglomeration leading to interrupted conduction pathways, and while carbon nanotubes exhibit excellent conductivity, they have few surface active sites and poor interfacial bonding with silicon particles, making it difficult to form a continuous and efficient three-dimensional conductive network. Summary of the Invention
[0004] The purpose of this invention is to provide a silicon-carbon composite anode material and its preparation method. The synergistic advantages of the core-shell structure buffering silicon expansion, nitrogen-doped carbon fiber constructing a highly efficient conductive network, composite coating layer stabilizing the interface, and inorganic dispersed phase inhibiting agglomeration can significantly improve the specific capacity, cycle stability, and first charge-discharge efficiency of lithium-ion batteries, thus solving the problems in the prior art.
[0005] To achieve the above objectives, the present invention provides the following technical solution: A silicon-carbon composite anode material includes a core-shell active unit, a conductive network layer, and a composite coating layer. The core-shell active unit is a structure formed by boron-doped silicon quantum dots loaded inside hollow carbon spheres. The components, by mass percentage, include: 11-18 wt% boron-doped silicon quantum dots, 24-36 wt% hollow carbon spheres, 31-42 wt% polyimide-derived nitrogen-doped carbon nanofibers, 3-8 wt% fluorophosphate-alumina composite coating layer, and 2-5 wt% lithium titanate-modified montmorillonite.
[0006] Preferably, the mass ratio of fluorophosphate to alumina in the fluorophosphate-alumina composite coating layer is 3:1.
[0007] It is worth noting that by fixing the mass ratio to 3:1, the optimal component ratio of the composite coating layer was determined. Under this ratio, the ability of fluorophosphate to form a stable LiF-based SEI film and the advantage of alumina in improving mechanical strength can work synergistically, avoiding performance imbalance caused by excessive amounts of a single component. At the same time, it provides a precise quantitative basis for material preparation, ensuring the consistency of performance of different batches of products and reducing the risk of production fluctuations. However, it is necessary to verify the universality of this mass ratio through a large number of experiments to avoid the ratio becoming invalid due to differences in the purity and particle size of fluorophosphate or alumina raw materials.
[0008] Preferably, the boron-doped silicon quantum dots have a particle size of 2-5 nm, a boron doping amount of 1-3 at%, and a purity of not less than 99.95%; the hollow carbon spheres have an inner diameter of 100-200 nm, a wall thickness of 10-20 nm, and a specific surface area of 300-500 m². 2 / g.
[0009] It is worth noting that: silicon quantum dot particle size of 2-5nm can exert quantum size effect, improve specific capacity and lithium diffusion rate, and boron doping of 1-3at% can accurately reduce the lithiation barrier and avoid the decrease in conductivity caused by insufficient or excessive doping; however, it is necessary to pay attention to the wall thickness of hollow carbon spheres, which must match the expansion rate of silicon quantum dots to prevent the carbon spheres from breaking due to excessively thin walls or reducing the specific capacity of the material due to excessively thick walls.
[0010] Preferably, the polyimide-derived nitrogen-doped carbon nanofibers have a diameter of 50-100 nm, a length of 5-15 μm, and a nitrogen content of 8-15 wt%, wherein the content of pyridine nitrogen and pyrrole nitrogen accounts for more than 60% of the total nitrogen content.
[0011] It is worth noting that a diameter of 50-100nm and a length of 5-15μm ensure that the fibers can interweave to form a continuous three-dimensional network, while avoiding agglomeration problems caused by excessive length and fineness; however, it is necessary to ensure that the nitrogen content and morphology are accurately characterized by X-ray photoelectron spectroscopy and other methods to avoid ambiguity in the description.
[0012] Preferably, the thickness of the fluorophosphate-alumina composite coating layer is 20-60 nm, wherein the fluorophosphate is trifluoroethyl phosphate, and the alumina has an amorphous structure with a particle size of 5-10 nm.
[0013] It is worth noting that a coating thickness of 20-60nm ensures that the material surface is completely covered to block the electrolyte, while avoiding an increase in lithium-ion conduction resistance due to excessive thickness. However, it is important to ensure that the coating thickness is uniform to avoid localized thinness that could lead to SEI film failure or excessive thickness that could affect rate performance.
[0014] Preferably, the lithium titanate loading in the lithium titanate modified montmorillonite is 15-25% of the montmorillonite mass, the lithium titanate particle size is 5-10 nm, and the montmorillonite sheet thickness is 1-5 nm.
[0015] It is worth noting that a lithium titanate loading of 15-25% can provide additional lithium storage sites while playing a dispersing role, avoiding insufficient dispersion due to too low a loading or affecting the overall conductivity of the material due to too high a loading; however, it should be noted that the lithium titanate loading needs to be accurately determined by methods such as thermogravimetric analysis.
[0016] Preferably, the material has an initial charge-discharge efficiency of not less than 85%, a capacity retention rate of not less than 80% after 100 cycles, and a specific capacity of not less than 1500 mAh / g.
[0017] It is worth noting that the indicators of first charge-discharge efficiency ≥85%, capacity retention rate ≥80% after 100 cycles, and specific capacity ≥1500mAh / g clearly demonstrate the practical value of the material and directly address the shortcomings of traditional materials. However, it is important to note that the performance indicators must be measured under standard test conditions to avoid data differences due to different test conditions.
[0018] A method for preparing a silicon-carbon composite anode material as described above, characterized by comprising the following steps: S1: Preparation of core-shell active units Boron-doped silicon quantum dot dispersion was mixed with hollow carbon spheres, dispersed under ultrasonic power of 250-350W for 40-80 min, and then vacuum dried at 80-100℃ for 6-8 h to obtain core-shell active units. S2: Constructing a conductive network The core-shell active unit is mixed with a polyimide solution and stirred evenly. The composite fiber is then obtained by electrospinning. The composite fiber is carbonized at 900-1100℃ for 3-5 hours under inert gas protection at a heating rate of 3-5℃ / min to obtain an intermediate containing a conductive network. S3: Preparation of composite coating layer An intermediate containing a conductive network is immersed in a mixture of trifluoroethyl phosphate and alumina sol, ultrasonically impregnated for 20-40 minutes, and then heat-treated at 150-200℃ for 2-3 hours to obtain a silicon-carbon composite anode material.
[0019] Preferably, the concentration of the boron-doped silicon quantum dot dispersion in S1 is 5-10 mg / mL, and the dispersion medium is N-methylpyrrolidone; the concentration of the polyimide solution in S2 is 15-25 wt%, the solvent is dimethylacetamide, the electrospinning voltage is 15-25 kV, and the receiving distance is 15-20 cm.
[0020] It is worth noting that a silicon quantum dot dispersion concentration of 5-10 mg / mL and a polyimide solution concentration of 15-25 wt% are necessary to ensure uniform dispersion and spinning feasibility, avoiding agglomeration due to excessively high concentrations or affecting spinning quality due to excessively low concentrations. However, it is important to note that the solution concentration needs to be finely adjusted according to the particle size and purity of the raw materials to avoid a one-size-fits-all approach.
[0021] Preferably, the inert gas in S2 is a mixture of nitrogen and hydrogen in a volume ratio of 9:1, and the gas flow rate is 80-120 mL / min; the solid content of the alumina sol in S3 is 5-10 wt%, and the pH value is 3-5.
[0022] It is worth noting that the 9:1 ratio of nitrogen to hydrogen in the mixed gas ensures an inert atmosphere during the carbonization process to prevent oxidation, while also achieving a slight reduction of the carbon material through a small amount of hydrogen, thus improving conductivity. However, it is important to note that the ratio of the mixed gas must be strictly controlled. Too high a hydrogen content poses a safety risk, while too low a content will prevent the reduction process from taking effect.
[0023] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention significantly improves the specific capacity, cycle stability, and first charge / discharge efficiency of the material by using a core-shell structure to buffer silicon expansion, nitrogen-doped carbon nanofibers to construct a highly efficient conductive network, a composite coating layer to stabilize the interface, and an inorganic dispersed phase to suppress agglomeration. This solves the defects of traditional materials, and the preparation process is controllable, which is convenient for large-scale production and meets the needs of high-energy-density lithium-ion batteries. Detailed Implementation
[0024] Example 1 The following are the application scenarios for silicon-carbon composite anode materials used in power batteries for new energy vehicles: High specific capacity, long cycle life, vibration resistance, and adaptable to operating temperatures from -20℃ to 60℃, meeting the needs of fast charging and long battery life.
[0025] A silicon-carbon composite anode material with a total mass of 100g includes 15g (15wt%) of boron-doped silicon quantum dots with a particle size of 3-4nm, a boron doping amount of 2at%, and a purity of 99.96%. Hollow carbon spheres: 30g (30wt%), inner diameter 150-180nm, wall thickness 15-18nm, specific surface area 420m² 2 / g; Polyimide-derived nitrogen-doped carbon nanofibers: 38g (38wt%), diameter 70-90nm, length 8-12μm, nitrogen content 12wt%; Fluorophosphate-alumina coating: 5g (5wt%), trifluoroethyl phosphate 3.75g, amorphous alumina 1.25g, thickness 40-50nm; Lithium titanate modified montmorillonite: 12g (12wt%), lithium titanate loading 20%, particle size 6-8nm.
[0026] A method for preparing a silicon-carbon composite anode material as described above includes the following steps: S1: 1875 mL of 8 mg / mL silicon quantum dot N-methylpyrrolidone dispersion was mixed with hollow carbon spheres, sonicated at 300 W for 60 min, and vacuum dried at 90 °C for 7 h. S2: Mix with 190g of 20wt% polyimide dimethylacetamide solution, electrospin at 20kV (receiving distance 18cm), and carbonize at 1000℃ for 4h under the protection of 9:1 nitrogen-hydrogen mixed gas (100mL / min) at 4℃ / min. S3: Immerse in a mixture of 8wt% alumina sol (pH=4) and trifluoroethyl phosphate, ultrasonically impregnate for 30 min, and heat-treat at 180℃ for 2.5 h.
[0027] Example 2 The following are the application requirements for silicon-carbon composite anode materials for portable electronic devices: High volumetric capacity, small size adaptability, low cost, suitable for normal temperature environment, and cycle life ≥500 times.
[0028] A silicon-carbon composite anode material, with a total mass of 100g, includes 12g (12wt%) of boron-doped silicon quantum dots with a particle size of 2-3nm, a boron doping amount of 1.5at%, and a purity of 99.95%. Hollow carbon spheres: 35g (35wt%), inner diameter 120-150nm, wall thickness 12-15nm, specific surface area 380m² 2 / g; Polyimide-derived nitrogen-doped carbon nanofibers: 39g (39wt%), diameter 50-70nm, length 5-8μm, nitrogen content 10wt%; Fluorophosphate-alumina coating: 6g (6wt%), trifluoroethyl phosphate 4.5g, amorphous alumina 1.5g, thickness 30-40nm; Lithium titanate modified montmorillonite: 8g (8wt%), lithium titanate loading 18%, particle size 5-6nm.
[0029] A method for preparing a silicon-carbon composite anode material as described above includes the following steps: S1: 2000 mL of 6 mg / mL silicon quantum dot dispersion was mixed with hollow carbon spheres, sonicated at 280 W for 70 min, and vacuum dried at 85 °C for 8 h; S2: Mix with 216.7g of 18wt% polyimide solution, electrospin at 18kV (receiving distance 16cm), and carbonize at 950℃ for 5h under the protection of 9:1 nitrogen-hydrogen mixed gas (90mL / min) at 3.5℃ / min. S3: Immerse in a mixture of 6wt% alumina sol (pH=3.5), ultrasonically impregnate for 35 min, and heat-treat at 160℃ for 3 h.
[0030] Example 3 For silicon-carbon composite anode materials used in cryogenic energy storage devices, the following application scenarios are required: Capacity retention rate ≥60% at -40℃, high safety, and adaptable to long-term static and intermittent charging and discharging conditions of energy storage power stations.
[0031] A silicon-carbon composite anode material with a total mass of 100g includes 18g (18wt%) of boron-doped silicon quantum dots with a particle size of 4-5nm, a boron doping amount of 3at%, and a purity of 99.97%. Hollow carbon spheres: 26g (26wt%), inner diameter 180-200nm, wall thickness 18-20nm, specific surface area 480m² 2 / g; Polyimide-derived nitrogen-doped carbon nanofibers: 39g (39wt%), diameter 90-100nm, length 12-15μm, nitrogen content 15wt%; Fluorophosphate-alumina coating: 7g (7wt%), trifluoroethyl phosphate 5.25g, amorphous alumina 1.75g, thickness 50-60nm; Lithium titanate modified montmorillonite: 10g (10wt%), lithium titanate loading 25%, particle size 8-10nm.
[0032] A method for preparing a silicon-carbon composite anode material as described above includes the following steps: S1: 1800 mL of 10 mg / mL silicon quantum dot dispersion was mixed with hollow carbon spheres, sonicated at 350 W for 40 min, and vacuum dried at 100 °C for 6 h; S2: Mix with 156g of 25wt% polyimide solution, electrospin at 25kV (receiving distance 20cm), and carbonize at 1100℃ for 3h under the protection of 9:1 nitrogen-hydrogen mixed gas (120mL / min) at 5℃ / min. S3: Immerse in a 10wt% alumina sol (pH=5) mixture, ultrasonically impregnate for 20 min, and heat-treat at 200℃ for 2 h.
[0033] Experimental Example A conventional silicon-carbon material containing 15wt% silicon particles, 50wt% graphite powder, 30wt% amorphous carbon, and 5wt% PVP dispersant was placed as a control group. Then, the materials from Examples 1-3 and the control group were used to make Φ14mm electrode sheets, wherein the active material accounted for 90wt%, the binder for 5wt%, and the conductive agent for 5wt%. CR2032 coin cells were assembled with lithium sheets as counter electrodes and 1mol / L LiPF6 electrolyte. Test items: initial charge / discharge efficiency (0.1C), specific capacity (0.2C), capacity retention rate after 100 / 500 cycles (0.5C), capacity retention rate at room temperature (-40℃ / -20℃) (0.2C), internal resistance (AC impedance method); Experimental environment: ambient temperature group 25℃±2℃, low temperature group -20℃ / -40℃ constant temperature chamber, humidity 45%±5%.
[0034] The experimental results are shown in Table 1 below:
[0035] Table 1 The materials in Examples 1-3 are significantly superior to traditional silicon-carbon materials in all performance indicators: specific capacity is increased by 54%-74%, first charge-discharge efficiency is increased by 14%-19 percentage points, cycle stability is increased by 1.4-2 times, low-temperature performance is increased by 2-3 times, and internal resistance is reduced by 67%-69%. Among them, Example 1 is adapted to the high cycle and rate requirements of new energy vehicles, Example 2 balances the capacity and cost of portable devices, and Example 3 highlights the low-temperature resistance of cryogenic energy storage, demonstrating the precision of the composition adjustment in adapting to the scenario.
Claims
1. A silicon-carbon composite negative electrode material, characterized by, The material comprises a core-shell active unit, a conductive network layer and a composite coating layer, the core-shell active unit is a structure formed by loading boron-doped silicon quantum dots inside hollow carbon spheres; wherein, The components comprise, by mass percentage: boron-doped silicon quantum dots 11-18wt%, hollow carbon spheres 24-36wt%, polyimide-derived nitrogen-doped carbon nanofibers 31-42wt%, a fluorophosphate-alumina composite coating layer 3-8wt% and lithium titanate modified montmorillonite 2-5wt%. 2.The silicon-carbon composite negative electrode material of claim 1, characterized in that, The mass ratio of fluorophosphate to alumina in the fluorophosphate-alumina composite coating layer is 3:
1. 3.The silicon-carbon composite negative electrode material of claim 2, characterized in that, The boron-doped silicon quantum dots have a particle size of 2-5 nm, a boron element doping amount of 1-3 at%, and a purity of not less than 99.95%; the hollow carbon spheres have an inner diameter of 100-200 nm, a wall thickness of 10-20 nm, and a specific surface area of 300-500 m 2 / g.
4. The silicon-carbon composite negative electrode material of claim 3, wherein the carbon material is a carbon material having a graphitic structure. The polyimide-derived nitrogen-doped carbon nanofibers have a diameter of 50-100nm, a length of 5-15μm and a nitrogen content of 8-15wt%, wherein the content of pyridine nitrogen and pyrrole nitrogen accounts for more than 60% of the total nitrogen content.
5. The silicon-carbon composite anode material according to claim 4, characterized in that, The fluorophosphate-alumina composite coating layer has a thickness of 20-60nm, wherein the fluorophosphate is trifluoroethyl phosphate and the alumina is amorphous with a particle size of 5-10nm.
6. The silicon-carbon composite negative electrode material of claim 5, wherein the carbon material is a carbon material having a graphitic structure. The loading amount of lithium titanate in the lithium titanate modified montmorillonite is 15-25% of the mass of the montmorillonite, the particle size of the lithium titanate is 5-10nm and the sheet thickness of the montmorillonite is 1-5nm.
7. The silicon-carbon composite anode material according to claim 6, characterized in that, The first charge-discharge efficiency of the material is not less than 85%, the capacity retention rate after 100 cycles is not less than 80% and the specific capacity is not less than 1500mAh / g.
8. The method of claim 7, wherein the silicon-carbon composite negative electrode material is prepared by the steps of: mixing a silicon powder and a carbon powder; and sintering the mixture at a temperature of 1,000°C to 1,500°C in a non-oxidizing atmosphere. The method comprises the following steps: S1: preparing a core-shell active unit Mixing a boron-doped silicon quantum dot dispersion liquid with hollow carbon spheres, dispersing for 40-80min under an ultrasonic power of 250-350W and then vacuum drying at 80-100℃ for 6-8h to obtain a core-shell active unit; S2: constructing a conductive network Mixing the core-shell active unit with a polyimide solution, stirring uniformly and then preparing a composite fiber by electrospinning, carbonizing the composite fiber under inert gas protection at a temperature rising rate of 3-5℃ / min to 900-1100℃ for 3-5h to obtain an intermediate containing a conductive network; S3: preparing a composite coating layer Immersion of the intermediate containing the conductive network in a mixed liquid of trifluoroethyl phosphate and alumina sol, ultrasonic immersion for 20-40min, taking out and then heat treatment at 150-200℃ for 2-3h to obtain a silicon-carbon composite negative electrode material.
9. The method of claim 8, wherein the silicon-carbon composite negative electrode material is prepared by the steps of: mixing a silicon source and a carbon source to form a mixture; and heating the mixture at a temperature of 800-1,200°C for 1-10 hours in an inert atmosphere. The concentration of the boron-doped silicon quantum dot dispersion liquid in S1 is 5-10mg / mL and the dispersion medium is N-methylpyrrolidone; the concentration of the polyimide solution in S2 is 15-25wt% and the solvent is dimethylacetamide; the voltage of electrospinning is 15-25kV and the receiving distance is 15-20cm.
10. The method of claim 9, wherein the silicon-carbon composite negative electrode material is prepared by the steps of: mixing a silicon source and a carbon source to form a mixture; and heating the mixture at a temperature of 800-1,200°C for 1-10 hours in an inert atmosphere. The inert gas in S2 is a mixed gas of nitrogen and hydrogen with a volume ratio of 9:1 and a gas flow rate of 80-120mL / min; the solid content of the alumina sol in S3 is 5-10wt% and the pH value is 3-5.