Indium-doped high-rate silicon-carbon composite negative electrode material and preparation method thereof

Abstract

The invention discloses an indium-doped high-rate silicon-carbon composite negative electrode material and a preparation method thereof. The method comprises the following steps: S1, mixing a low-molecular-weight phenolic resin-ethanol solution, polyethylene glycol and nano ZnCl2 to obtain uniform and stable precursor slurry; s2, performing spray drying on the precursor slurry to form primary particles; s3, the primary particles and indium oxide are heated in inert gas, then the temperature is increased to 850-1150 DEG C, heat preservation is conducted for 2-4 h, and a carbonized material is obtained; s4, heating the carbonized material to 800-1000 DEG C in the presence of inert gas, introducing CO2, and reacting for 18-22 hours to obtain secondary particles; s5, crushing the secondary particles, and uniformly mixing the crushed secondary particles with irregular porous carbon to obtain a composite carbon matrix; and S6, placing the composite carbon substrate in a reactor, introducing silane gas under inert gas, heating to 450-550 DEG C, depositing nanoscale amorphous silicon, then switching to introduce carbon source gas to form a carbon coating layer, and cooling to obtain the silicon-carbon composite negative electrode material.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and more specifically, to an indium-doped high-rate silicon-carbon composite anode material and its preparation method. Background Technology

[0002] The pursuit of high energy density in next-generation lithium-ion batteries has driven the shift towards silicon-based anode materials. Silicon-based anodes have a theoretical specific capacity of 4200 mAh / g, far exceeding the 372 mAh / g of traditional graphite, and the raw materials are abundant. However, their large-scale application faces two major obstacles: ① Dramatic volume expansion (300%-400%) leads to particle pulverization and SEI film damage, causing rapid capacity decay; ② Low electronic conductivity and lithium-ion diffusion coefficient result in poor rate performance, failing to meet fast charging requirements.

[0003] Constructing silicon-carbon composite materials, combining the structural buffering properties of the carbon matrix with the high capacity characteristics of silicon, has become an effective strategy for mitigating volume changes and improving electrochemical performance. Therefore, developing novel silicon-carbon composite anodes with high capacity, low volume expansion, high rate performance, and long cycle life is not only crucial for improving the energy density of lithium-ion batteries, but also of significant research value for promoting the practical application of energy storage technologies. Summary of the Invention

[0004] The technical problem to be solved by the present invention is that existing silicon-carbon anode materials have large volume expansion, poor cycle stability, and insufficient rate performance. In order to overcome the above defects of the prior art, the present invention provides an indium-doped high-rate silicon-carbon composite anode material and its preparation method.

[0005] The technical solution of this invention is: a method for preparing an indium-doped high-rate silicon-carbon composite anode material, comprising the following steps: S1. A uniform and stable precursor slurry is obtained by ultrasonically dispersing a mixture of low molecular weight phenolic resin-ethanol solution, polyethylene glycol and nano ZnCl2. S2. Spray dry the precursor slurry to form submicron-sized precursor microspheres, which are primary particles. S3. The primary particles and indium oxide are heated and pre-oxidized and cross-linked under an inert atmosphere, and then heated to 850~1150℃ and held for 2~4 hours to obtain carbonized material. S4. The carbonized material is heated to 800~1000℃ under an inert atmosphere, CO2 is introduced, and the reaction is carried out for 18~22h to activate and create pores, thereby obtaining secondary particles. S5. After the secondary particles are crushed, they are uniformly mixed with irregular porous carbon to obtain a composite carbon matrix. S6. Place the composite carbon matrix in a reactor, introduce silane gas under inert gas protection, heat to 450-550℃, deposit nanoscale amorphous silicon, then switch to carbon source gas to form a carbon coating layer at the same temperature, and then cool to obtain indium-doped high-rate silicon-carbon composite anode material.

[0006] In the above scheme, a dual-phase synergistic porous carbon matrix of "secondary particles-irregular porous carbon" is constructed, combined with in-situ generation of nano-silicon via low-temperature chemical vapor deposition (CVD), and supplemented with a surface carbon coating protective layer. The resulting silicon-carbon composite anode material has high capacity and small volume expansion. In addition, indium doping forms a small number of defects in the silicon-carbon lattice, which serve as shortcuts for lithium-ion transport, reducing the lithium-ion diffusion barrier, accelerating the migration speed of lithium ions within the material, and improving the battery's charge-discharge efficiency and rate performance. At the same time, indium doping can refine the silicon-carbon grains, and the flexibility of indium can buffer the stress generated by volume changes, inhibit crack formation, and improve the material's cycle stability.

[0007] In one possible implementation, in step S1, the molecular weight of the low molecular weight phenolic resin is 800-1000, the mass fraction of the low molecular weight phenolic resin in the solution is 30-50 wt%, the amount of polyethylene glycol added is 0.5-3 wt% of the total raw materials, and the amount of nano ZnCl2 added is 6-10 wt% of the total raw materials.

[0008] In one possible implementation, the precursor slurry in step S1 has a solid content of 12-15% and a viscosity of 15-20 mPa·s.

[0009] In one possible implementation, the particle size of the primary particles obtained by spray drying in step S2 is 0.6-0.9 μm.

[0010] In one possible implementation, the heating temperature for pre-oxidative crosslinking in step S3 is 200-300°C, and the heating time is 2-4 hours.

[0011] In one possible implementation, the secondary particle pulverization in step S5 controls the particle size to be 10-30 μm, with a micropore ratio ≥85%, a pore size <1.85 nm, and a specific surface area ≥1950 m². 2 / g.

[0012] In one possible implementation, the silicon content of the deposited nanoscale amorphous silicon in step S6 is controlled to be 45%-55% of the total mass of the final product.

[0013] In one possible implementation, the carbon source gas in step S6 is acetylene or methane.

[0014] In one possible implementation, the thickness of the carbon coating layer in step S6 is 5-15 nm.

[0015] Another aspect of the present invention is to provide an indium-doped high-rate silicon-carbon composite anode material, which is prepared by the preparation method described above.

[0016] The beneficial effects of this invention are as follows: 1. A synergistic construction of a biphase porous carbon matrix resolves the capacity-rate performance contradiction. Indium-doped secondary particles significantly reduce lithium-ion mass transfer resistance, ensuring high-rate performance. Simultaneously, the introduction of irregular porous carbon constructs a three-dimensional interwoven conductive network, greatly enhancing electronic conductivity. The synergistic effect of these two components enables the maintenance of good electrochemical kinetic performance even with a silicon content as high as 45%–55%.

[0017] 2. Due to the construction of a composite porous carbon matrix, the reversible specific capacity of the obtained silicon-carbon composite anode material can reach 1900-2000 mAh / g at a current density of 0.1C, and the capacity can still be maintained above 500 mAh / g at a high rate of 4C, thus combining the advantages of high energy density and high power density.

[0018] 3. The process is highly controllable and easy to scale up. Both spray drying and CVD are mature industrial technologies with adjustable parameters and good repeatability, making them suitable for continuous production and possessing good industrialization prospects. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the secondary particles formed in the preparation method of the indium-doped high-rate silicon-carbon composite anode material of the present invention. Figure 2 The image shows the SEM image and corresponding mapping results of the indium-doped high-rate silicon-carbon composite anode material obtained in Example 1. Detailed Implementation

[0020] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described in detail below. It should be noted that the following embodiments are only used to illustrate the implementation methods and typical parameters of the present invention, and are not intended to limit the parameter range described in the present invention. Reasonable variations derived therefrom are still within the protection scope of the claims of the present invention.

[0021] It should be noted that the endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0022] Unless otherwise defined, all terms, symbols, and other scientific terms used herein are intended to have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. In some instances, terms having a conventional meaning are defined herein for clarification or ease of reference, and such definitions should not be construed as indicating a significant difference from conventional understanding in the art. The technical methods described or referenced herein are generally well understood by those skilled in the art and employed by conventional methods. Unless otherwise stated, the use of commercially available kits, reagents, and instruments shall be performed according to the manufacturer's instructions and parameters.

[0023] This invention proposes an innovative structural design and stepwise controllable preparation process for silicon-carbon composite anode materials. The core of this invention is to construct a dual-phase synergistic porous carbon matrix of "secondary particles-irregular porous carbon" and combine it with in-situ generation of nano-silicon by low-temperature chemical vapor deposition (CVD), supplemented by a surface carbon coating protective layer.

[0024] The silicon-carbon composite anode material comprises the following components: The multi-level porous carbon framework consists of secondary particles and irregular porous carbon; nanoscale amorphous silicon is uniformly dispersed inside the carbon framework; and a uniform carbon layer coats the outer surface of the composite particles.

[0025] The specific preparation method includes the following steps: Step 1: Preparation of Aggregated Submicron Porous Carbon Spheres Raw material slurry preparation: Use low molecular weight phenolic resin (30-50% ethanol solution) with a number average molecular weight of 800-1000 as a carbon source, add 0.5-3 wt% polyethylene glycol (PEG400) as a dispersant, and 6-10 wt% nano ZnCl2 as a pore-forming agent; after mixing, ultrasonically disperse for 60-120 minutes, adjust to a solid content of 12-15% and a viscosity of 15-20 mPa·s to obtain a uniform and stable precursor slurry; Spray drying molding solidifies the above precursor slurry into small spherical particles: A centrifugal spray dryer is used, with the inlet temperature set at 110-120℃, the outlet temperature at 50-55℃, the atomizing disc speed at 35000-40000rpm, the feed rate at 2-3mL / min, and the carrier gas flow rate at 30-35m³ / h. The precursor slurry is atomized and dried to form submicron-sized precursor microspheres, thus obtaining primary particles with a particle size of 0.6-0.9μm. Indium doping and carbonization: Primary particles and indium oxide are placed in an inert gas atmosphere such as nitrogen. The temperature is increased to 200-300℃ at 1℃ / min and held for 2-4 hours for pre-oxidation cross-linking. Then, the temperature is increased to 850-1150℃ at 3℃ / min and held for 2-4 hours to complete the reaction, yielding carbonized material. Indium oxide reacts with carbon at approximately 800-1000℃ to generate metallic indium (liquid, melting point approximately 100℃). Simultaneously, organic matter in the system is carbonized, and ZnCl2 (boiling point 723℃, volatilized directly during high-temperature carbonization) is removed, constructing initial pores. The carbonized carbon particles are then bonded and granulated by indium during the cooling stage. The role of indium doping: 1. Indium doping creates a small number of defects (such as vacancies and interstitial atoms) in the silicon-carbon lattice. These defects can act as "shortcuts" for lithium-ion transport, reducing the lithium-ion diffusion barrier, accelerating the migration speed of lithium ions within the material, and improving battery charge / discharge efficiency and rate performance. 2. Indium has a moderately different atomic radius from silicon. After doping, it can refine silicon-carbon grains. At the same time, the flexibility of indium can buffer the stress generated by volume changes, inhibit crack formation, and improve the cycle stability of the material.

[0026] Activation and pore formation: The carbonized material is transferred to a fluidized bed reactor and heated to 800~1000℃ under inert gas protection. CO2 is introduced and the reaction is carried out for 18~22h to physically activate and form pores, thereby obtaining secondary particles.

[0027] The secondary particles are pulverized and classified (pulverization and classification to obtain the target particle size). The resulting pulverized secondary particles have a size of 10~30μm, a micropore ratio of ≥85% (pore size <1.85nm), and a specific surface area of ​​≥1950m². 2 / g.

[0028] Step 2: Construction of composite porous carbon matrix The secondary particles obtained after pulverization are mixed with irregular porous carbon with an average particle size of 2-30 μm at a mass ratio of 10-30%:1. The mixture is then ball-milled or stirred at high speed to achieve uniform blending, forming a synergistic porous carbon matrix. Pure secondary particles have low capacity; adding irregular porous carbon increases capacity, thus balancing the capacity-ratio relationship.

[0029] Step 3: Low-temperature silane deposition and carbon coating The composite carbon matrix is ​​loaded into a fluidized bed reactor and heated to 450-550℃ under inert gas protection; Nitrogen (N2) and silane (SiH4) gases are introduced, and a thermal decomposition reaction occurs under low-temperature conditions, causing nanoscale amorphous silicon to be deposited in situ on the inner walls and surface of the pores of the carbon matrix, while controlling the silicon content to be 45%-55% of the total mass. After deposition, acetylene (C2H2) or methane (CH4) is switched to be introduced as the carbon source gas, and the coating process is carried out in the same temperature range to form a uniform amorphous carbon coating layer with a thickness of 5-15 nm. The target silicon-carbon composite anode material is obtained by cooling the above-mentioned deposited product.

[0030] The present invention will be further described in detail below with reference to specific embodiments, but it should not be construed as a limitation of the present invention.

[0031] Example 1 1. Secondary particle preparation: Take 1250g of a 40wt% phenolic resin-ethanol solution (containing 500g of phenolic resin), add 18.75g of PEG400 and 100g of nano-ZnCl2, and ultrasonically disperse for 60min to obtain a precursor slurry. Adjust the solid content to 13.5% and the viscosity to 18mPa·s. Use a centrifugal spray dryer to spray dry the precursor slurry, setting the inlet temperature to 115℃, the outlet temperature to 52℃, the atomizing disc speed to 38000rpm, the feed rate to 150mL / min, and the carrier gas flow rate to 32m³ / h, and collect the primary particles.

[0032] Subsequently, 12.5 g of In₂O₃ was added, and the mixture was pre-crosslinked oxidized in a N₂ atmosphere by heating to 250°C at a rate of 1°C / min and holding for 3 h, followed by carbonization by heating to 1000°C at a rate of 3°C / min and holding for 3 h. The carbonized product was placed in a fluidized bed reactor, purged with N₂, heated to 1000°C, and then CO₂ was introduced at a flow rate of 800 mL / min. The reaction was carried out for 19 h to obtain secondary particles, which were then pulverized and classified. The primary particles had a particle size of approximately 0.75 μm, while the pulverized secondary particles had a particle size of 15-25 μm, a BET specific surface area of ​​2050 m² / g, a micropore ratio of 88%, and an average pore size of 1.6 nm.

[0033] 2. Construction of composite porous carbon matrix: Take 100g of the above-mentioned pulverized secondary particles and 400g of irregular porous carbon with an average particle size of 10μm, and mix them in a V-type mixer for 2h to obtain a uniform spherical-irregular synergistic composite porous carbon matrix.

[0034] 3. Silicon deposition and carbon coating: A composite porous carbon matrix was placed in a fluidized bed reactor, purged with N2, and heated to 500℃. The volume ratio of nitrogen to silane (SiH4) was adjusted to 4:1, and the mixture was introduced into the reactor at a total flow rate of 650 mL / min. The reaction was carried out for 9 hours to achieve nano-silicon deposition, with a measured silicon content of 51 wt%. Subsequently, a mixture of nitrogen and acetylene (C2H2) at a volume ratio of 3:1 was introduced at a total flow rate of 500 mL / min for carbon coating treatment for 6 hours. After natural cooling, the material was removed to obtain the target silicon-carbon composite anode material.

[0035] 4. Electrochemical performance testing: The obtained target silicon-carbon composite anode material was mixed with SuperP, conductive carbon black, and CMC binder in a ratio of 7:0.5:0.5:2 to form a slurry, which was then coated onto copper foil to form a coin cell (Li|Si-C). At 0.1C, the first-cycle discharge specific capacity was 1953 mAh / g, with a coulombic efficiency of 91.5%. At 4C, the capacity reached 523 mAh / g. After five cycles each at different rates (0.2C, 0.5C, 1C, 2C, 3C, and 4C), the efficiency remained at 91.4% even after returning to 0.2C, demonstrating excellent rate performance.

[0036] Example 2 In this embodiment, the mass ratio of secondary particles to random carbon was adjusted to 10%, with other conditions remaining the same as in Example 1. The measured discharge specific capacity of the material in the first cycle was 2036 mAh / g, with a coulombic efficiency of 92.1%; the capacity reached 436 mAh / g at 4C rate. After 5 cycles each at different rates of 0.2C, 0.5C, 1C, 2C, 3C, and 4C, the efficiency remained at 90% when the material returned to 0.2C.

[0037] Example 3 In this embodiment, the mass ratio of secondary particles to irregular porous carbon was adjusted to 30%, with other conditions remaining the same as in Example 1. The measured discharge specific capacity of the material in the first cycle was 1900 mAh / g, with a coulombic efficiency of 90.6%; the capacity reached 552 mAh / g at 4C rate. After 5 cycles each at different rates of 0.2C, 0.5C, 1C, 2C, 3C, and 4C, the efficiency remained at 90% when the material returned to 0.2C.

[0038] Example 4 In this embodiment, the mass of In2O3 was adjusted to 25g, and the other conditions were the same as in Example 1. The measured discharge specific capacity of the material in the first cycle was 1910mAh / g, with a coulombic efficiency of 91.7%; the capacity reached 530mAh / g at 4C rate; after 5 cycles each at different rates of 0.2C, 0.5C, 1C, 2C, 3C, and 4C, the efficiency remained at 91% when returning to 0.2C.

[0039] Example 5 In this embodiment, the mass of In2O3 was adjusted to 5g, and the other conditions were the same as in Example 1. The measured discharge specific capacity of the material in the first cycle was 1982mAh / g, with a coulombic efficiency of 91.2%; the capacity reached 418mAh / g at 4C rate. After 5 cycles each at different rates of 0.2C, 0.5C, 1C, 2C, 3C, and 4C, the efficiency remained at 90.8% when the material returned to 0.2C.

[0040] Comparative Example 1 This comparative example uses only secondary particles as the matrix and does not mix with irregular porous carbon; other conditions are the same as in Example 1. Performance test results show that the material has a high resistivity, but the capacity, first-efficiency, and rate performance are significantly reduced, with a 4C capacity of only 120 mAh / g, verifying the importance of the conductive network.

[0041] Comparative Example 2 In this comparative example, indium was not doped, and other conditions were the same as in Example 1. Performance test results showed a significant decrease in rate performance, with a 4C capacity of 220 mAh / g, verifying the importance of indium doping.

[0042] The test results of each embodiment and comparative example are summarized in Table 1 below.

[0043] Table 1 Performance test results of Examples 1-5 and Comparative Examples 1-2 The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for preparing an indium-doped high-rate silicon-carbon composite anode material, characterized in that, Includes the following steps: S1. A uniform and stable precursor slurry is obtained by ultrasonically dispersing a mixture of low molecular weight phenolic resin-ethanol solution, polyethylene glycol and nano ZnCl2. S2. Spray dry the precursor slurry to form submicron-sized precursor microspheres, which are primary particles. S3. Under an inert atmosphere, the primary particles and indium oxide are heated for pre-oxidation and cross-linking, and then heated to 850~1150℃ and held for 2~4 hours to obtain carbonized material; S4. The carbonized material is heated to 800~1000℃ under an inert atmosphere, CO2 is introduced, and the reaction is carried out for 18~22h to activate and create pores, thereby obtaining secondary particles. S5. After the secondary particles are crushed, they are uniformly mixed with irregular porous carbon to obtain a composite carbon matrix. S6. Place the composite carbon matrix in a reactor, introduce silane gas under inert gas protection, heat to 450-550℃, deposit nanoscale amorphous silicon, then switch to carbon source gas to form a carbon coating layer at the same temperature, and then cool to obtain indium-doped high-rate silicon-carbon composite anode material.

2. The preparation method according to claim 1, characterized in that, In step S1, the molecular weight of the low molecular weight phenolic resin is 800-1000, the mass fraction of the low molecular weight phenolic resin in the phenolic resin-ethanol solution is 30-50 wt%, the amount of polyethylene glycol added is 0.5-3 wt% of the total raw materials, and the amount of nano ZnCl2 added is 6-10 wt% of the total raw materials.

3. The preparation method according to claim 1, characterized in that, In step S1, the precursor slurry has a solid content of 12-15% and a viscosity of 15-20 mPa·s.

4. The preparation method according to claim 1, characterized in that, The particle size of the primary particles in step S2 is 0.6-0.9 μm.

5. The preparation method according to claim 1, characterized in that, The heating temperature for pre-oxidative crosslinking in step S3 is 200-300℃, and the heating time is 2-4h.

6. The preparation method according to claim 1, characterized in that, In step S5, the secondary particle pulverization controls the particle size to be 10-30 μm, with a micropore ratio ≥85%, a pore size <1.85 nm, and a specific surface area ≥1950 m². 2 / g.

7. The preparation method according to claim 1, characterized in that, In step S6, the silicon content of the deposited nanoscale amorphous silicon is controlled to be 45%-55% of the total mass of the final product.

8. The preparation method according to claim 1, characterized in that, In step S6, the carbon source gas is acetylene or methane.

9. The preparation method according to claim 1, characterized in that, The thickness of the carbon coating layer in step S6 is 5-15 nm.

10. An indium-doped high-rate silicon-carbon composite anode material, characterized in that, It is prepared by the preparation method according to any one of claims 1-9.

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