Preparation method of high-magnification gas-phase silicon-carbon negative electrode material

Abstract

The application discloses a preparation method of high-multiplying gas-phase silicon-carbon negative electrode material and belongs to the technical field of lithium ion batteries. The method comprises the following steps: uniformly dispersing porous carbon fine powder, a binder, a conductive agent and a dispersing agent in deionized water to obtain a porous carbon mixed slurry, performing spray drying on the porous carbon mixed slurry, and then performing drying and high-temperature carbonization. The secondary particles after carbonization are crushed and classified, the classified particles are deposited with silicon and carbon in a fluidized bed, and finally, the particles are deposited with carbon again in a rotary furnace to obtain the gas-phase silicon-carbon negative electrode material. The application performs formula process optimization, adopts spray drying, high-temperature carbonization, crushing and classification, gas-phase deposition and gas-phase coating, reduces the particle size of primary particles, shortens the lithium ion migration path, improves the silicon-carbon surface conductivity, and meanwhile, the small-particle-size primary particles are beneficial to inhibiting the influence caused by silicon expansion. Meanwhile, the secondary particles reduce the specific surface area of silicon-carbon, reduce the particle surface defects and reduce the side reaction between the electrolyte and the silicon-carbon particle surface.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery technology, specifically relating to a method for preparing a high-rate vapor-phase silicon-carbon anode material. Background Technology

[0002] Lithium-ion batteries have advantages such as high energy density, long lifespan, and no memory effect, and are widely used in electronic products, electric vehicles, and energy storage. Graphite, as the most widely commercialized anode material, has already reached a capacity close to the theoretical capacity of 372 mAh / g, leaving limited room for improvement. Graphite also has limitations in areas such as safety and fast charging.

[0003] Compared to graphite, silicon has a high theoretical specific energy of 4200 mAh / g and a low lithium intercalation chemical potential, making it widely recognized in the industry as a key material for the next generation of lithium battery anodes.

[0004] However, silicon has several problems: pure silicon is a semiconductor with poor conductivity; after lithium intercalation, silicon exhibits a large volume effect (300%), leading to continuous breakage, pulverization, and detachment during charging and discharging, resulting in the failure of the battery's negative electrode; and the SEI film continuously grows during battery cycling, consuming active lithium ions, causing rapid capacity decay and poor cycle life. These issues have limited the widespread application of silicon as a negative electrode in lithium-ion batteries.

[0005] The latest generation of fumed silicon-carbon materials uses porous carbon as a framework. Silicon is deposited into the nanoscale pores of the porous carbon via fluidized bed vapor deposition, followed by carbon coating via vapor deposition. The nanoscale silicon deposited within the pores effectively reduces breakage and pulverization caused by expansion. The coated carbon layer increases conductivity while reducing specific surface area, minimizing side reactions. However, fumed silicon-carbon materials suffer from high cost, poor rate performance, and require further expansion reduction. The majority of the cost of fumed silicon-carbon materials lies in the porous carbon. Fluidized bed processes, to ensure the fluidization of the porous carbon, require a narrow particle size distribution. Both coarse and fine particles must be removed in stages; coarse particles can be further pulverized, while fine particles must be discarded, resulting in a yield of only about 70%, further increasing costs. Summary of the Invention

[0006] The purpose of this invention is to reduce the cost of existing fumed silicon-carbon materials and further improve rate performance while reducing expansion. This invention uses fine powder discarded after porous carbon classification as raw material, thus reducing costs; it utilizes spray drying to prepare porous carbon secondary particles as a framework for vapor-phase deposition, thereby improving the rate performance of the fumed silicon-carbon anode material and reducing expansion.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] 1. A method for preparing high-rate fumed silicon-carbon anode material, characterized by comprising the following steps:

[0009] (1) Disperse porous carbon fine powder, binder, conductive agent and dispersant evenly in deionized water to obtain porous carbon mixed slurry;

[0010] (2) The porous carbon mixture slurry is spray-dried to obtain porous carbon secondary particles;

[0011] (3) Dry and carbonize the porous carbon secondary particles at high temperature;

[0012] (4) The carbonized porous carbon secondary particles are crushed and classified;

[0013] (5) The porous carbon secondary particles after classification are deposited with silicon and carbon in a fluidized bed to obtain gaseous silicon-carbon;

[0014] (6) Vaporized silicon carbide is coated with carbon a second time in a rotary kiln to obtain silicon carbide particles;

[0015] (7) The silicon carbon particles are crushed and sieved to obtain the finished gas phase silicon carbon material.

[0016] As a preferred technical solution, in step (1), the solid weight percentage of each component in the porous carbon mixed slurry is: 80%~98.48% porous carbon fine powder, 1~10% binder, 0.02%~5% conductive agent, and 0.5%~5% dispersant, with the sum of each component being 100%.

[0017] As a preferred technical solution, in step (1), the porous carbon fine powder has a particle size of ≤2μm, a specific surface area of ​​1600-2400m2 / g, a microporosity of ≥80%, and a pore volume of ≥0.7cm3 / g.

[0018] As a preferred technical solution, in step (1), the adhesive is at least one of waterborne epoxy resin, waterborne acrylic resin, waterborne phenolic resin, polyvinylpyrrolidone or styrene-butadiene latex.

[0019] The conductive agent is at least one of conductive carbon black, multi-walled carbon nanotubes, single-walled carbon nanotubes, graphene, or vapor-grown carbon fibers.

[0020] The dispersant is sodium carboxymethyl cellulose;

[0021] The solid content of the porous carbon mixed slurry is 20%~50%.

[0022] As a preferred technical solution, in step (2), the particle size D50 of the porous carbon secondary particles is 8~12μm.

[0023] As a preferred technical solution, in step (3), the drying temperature is 100-200℃; the carbonization temperature is 600-900℃.

[0024] As a preferred technical solution, in step (4), the particle size D50 of the porous carbon secondary particles is 8~12μm;

[0025] As a preferred technical solution, in step (5), the temperature of silicon deposition is 450~600℃, and the weight of the deposited silicon accounts for 45-55% of the total weight of silicon-carbon after deposition; the temperature of the carbon coating material is 500-650℃, and the weight of the carbon coating accounts for 0.5-5% of the total weight of silicon-carbon after coating.

[0026] As a preferred technical solution, in step (6), after the secondary carbon coating, the total weight of the coated carbon accounts for 1-8% of the total weight of silicon-carbon.

[0027] As a preferred technical solution, in step (7), the particle size D50 of the silicon-carbon anode material is 8~12μm.

[0028] The beneficial effects that may arise from the method for preparing a high-rate vapor-phase silicon-carbon anode material disclosed in this application include, but are not limited to:

[0029] 1. Significantly reduce raw material costs

[0030] Existing fumed silicon carbide materials require precise classification of porous carbon before fluidized bed processing. Powders with excessively fine particle sizes (≤2μm) are discarded because they cannot be stably fluidized in a fluidized bed, resulting in a yield of only about 70%. This application directly utilizes this waste fine powder as raw material, recombining it into fluidizable secondary particles through spray drying, thus realizing the resource utilization of waste and reducing raw material costs by about 30%.

[0031] 2. Improved scaling performance

[0032] By reducing the primary particle size and introducing a conductive agent within the secondary particles, this application significantly improves the lithium-ion diffusion rate and electronic conductivity. Example data demonstrates that:

[0033] The 3C discharge capacity retention rate can reach 95.4% (Example 2), which is better than the comparative example's 92.3%;

[0034] The constant current ratio for 1C charging can reach 87.8% (Example 2), which is better than the 81.2% of the comparative example.

[0035] 3. Extend cycle life

[0036] The secondary particle structure reduces the specific surface area of ​​the material, minimizing side reactions between the electrolyte and the silicon-carbon particle surface. Simultaneously, the introduction of a conductive agent prevents capacity decay due to poor contact during repeated particle expansion and contraction. Example data shows:

[0037] The full battery can retain 80% of its capacity for up to 1,845 cycles (Example 2), which is about 24% higher than the 1,487 cycles of the comparative example.

[0038] 4. Maintain high capacity and high first-efficiency

[0039] While improving rate capability and cycling performance, this application still maintains high specific capacity and initial coulombic efficiency:

[0040] The initial discharge specific capacity is ≥1778 mAh / g, and the initial coulombic efficiency is ≥92.5%, which is comparable to existing fumed silicon-carbon materials, without sacrificing energy density due to process adjustments.

[0041] 5. Strong process adaptability

[0042] This application utilizes mature industrial equipment such as spray drying, fluidized bed, and rotary kiln, eliminating the need for additional special equipment and facilitating large-scale production. Furthermore, the particle size (D50 8~12μm) of the secondary particles matches that of existing graphite anode materials, allowing for direct compounding with graphite without requiring adjustments to existing cell manufacturing processes.

[0043] In summary, this invention utilizes fine powder discarded after porous carbon classification as raw material, reducing costs. Spray drying is used to prepare porous carbon secondary particles as a framework for vapor deposition, which reduces the primary particle size and shortens the lithium-ion migration path. Simultaneously, the smaller primary particle size helps suppress the effects of silicon expansion. The secondary particles reduce the specific surface area of ​​silicon-carbon, minimizing surface defects and reducing side reactions between the electrolyte and the silicon-carbon particle surface. Furthermore, a conductive agent is added during the secondary granulation process, ensuring good contact between particles and between particles and the current collector during charge and discharge, regardless of expansion and contraction. These measures reduce the adverse effects of expansion, enhance ionic and electronic conductivity, and improve the material's rate performance and cycle life. Detailed Implementation

[0044] The various exemplary embodiments, features, and aspects of this application will be described in detail below.

[0045] Example 1

[0046] (1) Fine powder with a particle size ≤2μm (specific surface area 1700m²) discarded after porous carbon classification 2 The porous carbon mixed slurry is prepared by uniformly dispersing the following components in deionized water: porous carbon fine powder (89.5%), binder waterborne phenolic resin, conductive agent conductive carbon black Super-P, and dispersant CMC (sodium carboxymethyl cellulose). The weight percentages of each component in the porous carbon mixed slurry are as follows: porous carbon fine powder 89.5%, binder 3.5%, conductive agent 5%, dispersant 2%, and the slurry solids content 35%.

[0047] (2) The porous carbon mixture slurry is spray-dried to obtain porous carbon secondary particles;

[0048] (3) Dry the porous carbon secondary particles at 200°C for 1 hour, and then carbonize them at 600°C under nitrogen protection for 2 hours.

[0049] (4) The carbonized secondary porous carbon particles are crushed and classified. After classification, D50 is 9μm, Dmin is 2μm and Dmax is 22μm.

[0050] (5) The graded secondary porous carbon particles are introduced into a fluidized bed with a mixture of silane and nitrogen, and silicon is deposited in the vapor phase at 500°C. The amount of silicon deposited accounts for 53% of the total weight of silicon-carbon after deposition. After nitrogen replacement in the fluidized bed, a mixture of acetylene and nitrogen is introduced into the fluidized bed, and coated carbon is deposited at 560°C. The amount of carbon coating is 2% of the total weight of silicon-carbon after deposition.

[0051] (6) A mixture of acetylene and nitrogen gas is introduced into the gaseous silicon-carbon in a rotary kiln, and carbon is coated twice at 560°C to obtain silicon-carbon particles. The carbon coating amount is 5% of the total weight of silicon-carbon after deposition.

[0052] (7) The silicon carbon particles are crushed and sieved to obtain the finished gas phase silicon carbon material with a D50 of 9 μm.

[0053] Example 2

[0054] (1) Fine powder with a particle size ≤2μm (specific surface area 1700m²) discarded after porous carbon classification 2 A porous carbon mixed slurry is prepared by uniformly dispersing the following components in deionized water: porous carbon fine powder (94.45%), binder (3.5%), conductive agent (0.05%) (solid), and dispersant (CMC). The solid content of the slurry is 35%.

[0055] (2) The porous carbon mixture slurry is spray-dried to obtain porous carbon secondary particles;

[0056] (3) Dry the porous carbon secondary particles at 200°C for 1 hour, and then carbonize them at 600°C under nitrogen protection for 2 hours.

[0057] (4) The carbonized secondary porous carbon particles are crushed and classified. After classification, D50 is 9μm, Dmin is 2μm and Dmax is 22μm.

[0058] (5) The graded secondary porous carbon particles are introduced into a fluidized bed with a mixture of silane and nitrogen, and silicon is deposited in the vapor phase at 500°C. The amount of silicon deposited accounts for 54% of the total weight of silicon-carbon after deposition. After nitrogen replacement in the fluidized bed, a mixture of acetylene and nitrogen is introduced into the fluidized bed, and coated carbon is deposited at 560°C. The amount of carbon coating is 2% of the total weight of silicon-carbon after deposition.

[0059] (6) Gas-phase silicon carbon is introduced into a rotary kiln with a mixture of acetylene and nitrogen, and carbon is coated twice at 560°C to obtain silicon carbon particles;

[0060] (7) The silicon carbon particles are crushed and sieved to obtain the finished gas phase silicon carbon material with a D50 of 9 μm.

[0061] Comparative Example

[0062] (1) The porous carbon (specific surface area 1700m2 / g) was crushed and classified. After classification, the D50 was 9μm, the Dmin was 2μm, and the Dmax was 22μm.

[0063] (2) The graded secondary porous carbon particles were introduced into a fluidized bed with a mixture of silane and nitrogen, and silicon was deposited in the vapor phase at 500°C. The amount of silicon deposited accounted for 55% of the total weight of silicon and carbon after deposition. After nitrogen replacement in the fluidized bed, a mixture of acetylene and nitrogen was introduced into the fluidized bed, and coated carbon was deposited at 560°C. The amount of carbon coated was 2% of the total weight of silicon and carbon after deposition.

[0064] (3) A mixture of acetylene and nitrogen gas is introduced into the gaseous silicon-carbon in a rotary kiln, and carbon is coated twice at 560°C to obtain silicon-carbon particles. The carbon coating amount is 5% of the total weight of silicon-carbon after deposition.

[0065] (4) The silicon carbon particles are crushed and sieved to obtain the finished gas phase silicon carbon material with a D50 of 9 μm.

[0066] The silicon-carbon materials used in Examples 1, 2, and the comparative example were used to assemble coin cells, and their capacity and initial efficiency were tested. The coin cells were assembled as follows: silicon-carbon material, conductive agent (super-P), CMC, and SBR were mixed in a mass ratio of 94:2:1:3 to form a slurry. Deionized water was used as the solvent, and the slurry had a solid content of 48%. This slurry was coated onto copper foil, vacuum dried, and then assembled into a half-cell with a lithium foil as the counter electrode and a separator between the positive and negative electrodes. Electrolyte was then injected, and 2032 coin cells were assembled for testing. The initial charge-discharge capacity and initial coulombic efficiency were tested. The charge-discharge current was 0.1C, and the voltage range was 0.005V-1.5V.

[0067] The rate capability and cycle performance of silicon-carbon materials were tested by assembling 21700 full cells. The 21700 full cells were assembled as follows: silicon-carbon material was mixed with commercial graphite anode material to a concentration of 600 mAh / g. Silicon-carbon material, conductive carbon black (super-P), single-walled carbon nanotubes, CMC, SBR, and PAA were mixed at a mass ratio of 94.95:1:0.05:1:1.5:1.5 to form a slurry, using deionized water as the solvent. The slurry had a solid content of 48% and was coated onto copper foil as the anode. Commercial LiNi alloy was used. 0.8 Co 0.1 Mn 0.1 O2 (NCM811) was used as the positive electrode material. NCM811, conductive agent (super-P), and PVDF were mixed in a 96:2:2 ratio to form a slurry. N-methylpyrrolidone was used as the solvent, with a solid content of 69%. This slurry was coated onto aluminum foil to form the positive electrode. The positive electrode, negative electrode, separator, and electrolyte were used to assemble the battery cell. After formation and capacity testing, the cell was charged at a constant current of 0.5C, then charged at a constant voltage to a cutoff current of 0.05C, followed by discharge at currents of 0.2C, 0.5C, 3C, and 5C. The rate discharge performance was tested using the 0.2C discharge capacity as a baseline (100%). The rate charging performance was tested by charging at 0.5C and 1C constant current, then charging at a constant voltage to a cutoff current of 0.05C, followed by discharge at 0.5C (calculating the percentage of constant current charging capacity to total charging capacity). Finally, the number of cycles with 80% capacity retention was tested using a 1C charge-discharge cycle within a voltage range of 4.2V-2.5V.

[0068] Table 1 Battery performance of silicon-carbon materials in Examples 1-2 and comparative examples

[0069] First discharge specific capacity of half-cell (mAh / g) 1778 1804 1837 First charge capacity of half-cell battery (mAh / g) 1645 1676 1712 Half-cell first charge-discharge coulombic efficiency (%) 92.5 92.9 93.2 0.5C discharge capacity retention rate (%) 97.8 98.2 97.1 3C discharge capacity retention rate (%) 94.5 95.4 92.3 5C discharge capacity retention rate (%) 92.9 93.7 90.4 0.5C charging constant current ratio (%) 90.2 91.9 86.0 1C charging constant current ratio (%) 86.3 87.8 81.2 Full battery cycle life (80% capacity retention) 1679 1845 1487

[0070] The core principle of the high-rate vapor phase silicon-carbon anode material preparation method described in this application lies in the synergistic optimization of lithium-ion transport paths, silicon expansion stress release mechanisms, and electrode interface stability through secondary particle structure design and multi-scale conductive network construction.

[0071] 1. Optimization of Lithium-ion Transport by Secondary Particle Structure

[0072] This application employs spray drying technology to granulate porous carbon fine powder (≤2μm) with binders, conductive agents, and dispersants, forming secondary particles with a particle size D50 of 8~12μm. This structure exhibits the following mechanism of action:

[0073] Shortening the lithium-ion diffusion path: The primary particle size is ≤2μm, which is much smaller than the porous carbon particles used in traditional vapor-phase silicon-carbon materials (usually 5~10μm), significantly shortening the diffusion distance of lithium ions in the solid phase.

[0074] Preservation of nanopores: The microporous structure of the original porous carbon is preserved inside the secondary particles (microporosity ≥80%, pore volume ≥0.7cm³ / g), which provides a confined space for silicon vapor deposition, allowing silicon to be deposited at the nanoscale inside the pores, effectively suppressing the volume expansion (approximately 300%) during silicon lithium intercalation.

[0075] 2. Bridging effect of conductive agents

[0076] The mechanism of action of introducing conductive agents (such as conductive carbon black, carbon nanotubes, graphene, etc.) during the secondary granulation process is as follows:

[0077] A three-dimensional conductive network is constructed inside the secondary particles. Even if silicon expands and contracts in volume during charging and discharging, the conductive agent can still maintain the electrical contact between the primary particles and between the secondary particles and the current collector.

[0078] Especially for one-dimensional / two-dimensional conductive agents such as carbon nanotubes and graphene, a "point-line-surface" composite conductive structure can be formed inside the particles, reducing contact resistance and improving electronic conductivity.

[0079] 3. Improved Interface Stability through Multi-Level Encapsulation Strategy

[0080] This application employs a two-step coating process of "fluidized bed primary carbon deposition + rotary kiln secondary carbon coating," the mechanism of which is as follows:

[0081] Primary carbon deposition: In a fluidized bed, carbon source gas (such as acetylene) is deposited in situ after silicon deposition to form a uniform and dense thin carbon shell that covers the silicon surface and reduces direct contact between silicon and electrolyte.

[0082] Secondary carbon coating: Secondary coating is carried out in a rotary kiln to further repair surface defects, reduce the specific surface area of ​​silicon-carbon materials, reduce the excessive growth of SEI film, and thus reduce the irreversible consumption of active lithium.

[0083] 4. Buffering of expansion stress by small-diameter primary particles

[0084] The primary particles have a diameter of ≤2μm. Compared with larger particles, they have less internal silicon deposition and more uniform distribution. The expansion stress generated during lithium intercalation is smaller, and the stress can be released in the porous structure inside the secondary particles, avoiding the overall breakage of the particles.

[0085] The above embodiments illustrate in detail the specific implementation of the technical solution of the present invention, the logical and connection relationships of each component, and the complete working process. Those skilled in the art will understand that various changes and modifications can be made to the above embodiments without departing from the principles and spirit of the present invention, and all such changes and modifications should fall within the protection scope of the appended claims.

Claims

1. A method for preparing high-rate fumed silicon-carbon anode material, characterized in that... Includes the following steps: (1) Disperse porous carbon fine powder, binder, conductive agent and dispersant evenly in deionized water to obtain porous carbon mixed slurry; (2) The porous carbon mixture slurry is spray-dried to obtain porous carbon secondary particles; (3) Dry and carbonize the porous carbon secondary particles at high temperature; (4) The carbonized porous carbon secondary particles are crushed and classified; (5) The porous carbon secondary particles after classification are deposited with silicon and carbon in a fluidized bed to obtain gaseous silicon-carbon; (6) Vaporized silicon carbide is coated with carbon a second time in a rotary kiln to obtain silicon carbide particles; (7) The silicon carbon particles are crushed and sieved to obtain the finished gas phase silicon carbon material.

2. The method for preparing the silicon-carbon anode material for lithium-ion batteries according to claim 1, characterized in that: In step (1), The porous carbon mixed slurry contains the following solid weight percentages: porous carbon fine powder 80%~98.48%, binder 1~10%, conductive agent 0.02%~5%, dispersant 0.5%~5%, and the sum of all components is 100%.

3. The method for preparing the silicon-carbon anode material for lithium-ion batteries according to claim 1, characterized in that: In step (1), the porous carbon fine powder has a particle size of ≤2μm, a specific surface area of ​​1600-2400m2 / g, a microporosity of ≥80%, and a pore volume of ≥0.7cm3 / g.

4. The method for preparing the silicon-carbon anode material for lithium-ion batteries according to claim 1, characterized in that: In step (1), the adhesive is at least one of waterborne epoxy resin, waterborne acrylic resin, waterborne phenolic resin, polyvinylpyrrolidone, or styrene-butadiene latex. The conductive agent is at least one of conductive carbon black, multi-walled carbon nanotubes, single-walled carbon nanotubes, graphene, or vapor-grown carbon fibers. The dispersant is sodium carboxymethyl cellulose; The solid content of the porous carbon mixed slurry is 20%~50%.

5. The method for preparing the silicon-carbon anode material for lithium-ion batteries according to claim 1, characterized in that: In step (2), the particle size D50 of the porous carbon secondary particles is 8~12μm.

6. The method for preparing the silicon-carbon anode material for lithium-ion batteries according to claim 1, characterized in that: In step (3), the drying temperature is 100-200℃; the carbonization temperature is 600-900℃.

7. The method for preparing the silicon-carbon anode material for lithium-ion batteries according to claim 1, characterized in that: In step (4), the particle size D50 of the porous carbon secondary particles is 8~12μm.

8. The method for preparing the silicon-carbon anode material for lithium-ion batteries according to claim 1, characterized in that: In step (5), the temperature for depositing silicon is 450-600℃, and the weight of the deposited silicon accounts for 45-55% of the total weight of the silicon-carbon after deposition; the temperature for coating carbon material is 500-650℃, and the weight of the coating carbon accounts for 0.5-5% of the total weight of the silicon-carbon after coating.

9. The method for preparing the silicon-carbon anode material for lithium-ion batteries according to claim 1, characterized in that: In step (6), after the secondary carbon coating, the total weight of the coated carbon accounts for 1-8% of the total weight of silicon-carbon.

10. The method for preparing the silicon-carbon anode material for lithium-ion batteries according to claim 1, characterized in that: In step (7), the particle size D50 of the silicon-carbon anode material is 8~12μm.