Preparation method and application of liquid-phase-coated surface-passivated silicon-carbon negative electrode material based on fluidized bed product

Abstract

The invention discloses a preparation method and application of a liquid-phase-coated surface-passivated silicon-carbon negative electrode material based on a fluidized bed product, and belongs to the field of battery negative electrode materials.The preparation method of a silicon-carbon negative electrode comprises the steps that a, the silicon-carbon negative electrode material prepared through a fluidized bed is placed in a fluidized bed reactor; fluidizing gas is introduced, so that the silicon-carbon negative electrode material is in a fluidized state; b) atomizing a coating agent solution containing a carbon precursor and a solvent, and spraying the atomized coating agent solution into the fluidized bed reactor to uniformly coat the surface of the silicon-carbon negative electrode material with the coating agent solution; and c) carrying out heat treatment on the coated silicon-carbon negative electrode material, and converting the carbon precursor into a carbonaceous passivation layer. The method has the advantages of low cost, high efficiency and high quality.

Description

Technical Field

[0001] This invention relates to the field of battery anode materials, and in particular to a method for preparing and applying a liquid-phase coated surface passivated silicon-carbon anode material based on fluidized bed products. Background Technology

[0002] With the rapid development of electric vehicles, portable electronic devices, and large-scale energy storage systems, the market is placing increasingly higher demands on the energy density, cycle life, and safety performance of lithium-ion batteries. The theoretical specific capacity of traditional graphite anodes is relatively low (~372.0 mAh / g), which has become a major limiting factor for improving battery energy density. Silicon (Si), due to its extremely high theoretical specific capacity (~4200.0 mAh / g, approximately 10 times that of graphite), suitable operating potential, abundant reserves, and environmental friendliness, is considered the most promising anode material for next-generation high-energy-density lithium-ion batteries. To overcome the problems of pure silicon anodes, such as huge volume expansion (>300%), severe structural pulverization, and poor cycle life caused by unstable solid electrolyte interphase (SEI) films, the deposition of silanes within porous carbon followed by a small amount of carbon coating to form silicon-carbon (Si / C) anode materials has become the mainstream technical route for current research and industrialization.

[0003] Fluidized bed reactors, due to their excellent heat and mass transfer efficiency, vigorous and uniform particle movement, ability to achieve continuous / large-scale production, and ease of coating and surface modification, have shown great application potential in the preparation of silicon-carbon composite materials (especially for dispersing and loading silicon nanoparticles onto carbon supports or achieving carbon coating), and are widely used to prepare porous silicon-carbon composite particles (Si / C-FB). However, fluidized bed products have two major bottlenecks: 1. Highly active surface defects: newly formed silicon particles exposed in pores and on the surface are prone to reacting with air / electrolyte to form an unstable oxide layer; 2. Volume expansion effect: the silicon phase expands dramatically (>300%) during charge and discharge, leading to particle pulverization, continuous rupture and regeneration of the solid electrolyte interphase (SEI) film, and accelerated capacity decay. Current surface passivation technologies have significant limitations: 1. Dry coating (such as CVD): uniform coating but requires a high-temperature vacuum environment, high energy consumption, complex equipment, and is difficult to adapt to fluidized bed production lines. 2. Traditional liquid phase method: Impregnation or stirring coating is prone to uneven solvent wetting, resulting in local coating that is too thick or missing. Furthermore, subsequent drying can easily cause particle agglomeration and cracking of the coating layer, and it cannot effectively cover the internal pores. Summary of the Invention

[0004] One of the objectives of this invention is to provide a method for preparing liquid-phase coated surface passivated silicon-carbon anode materials based on fluidized bed products, in order to solve the problems of uneven coating, particle agglomeration, and coating layer cracking that are easily caused by traditional liquid-phase methods for processing fluidized bed silicon-carbon materials in the prior art.

[0005] This invention is achieved through the following technical solution: a method for preparing a liquid-phase coated surface passivated silicon-carbon anode material based on fluidized bed products, comprising: a) placing the silicon-carbon anode material prepared by fluidized bed in a fluidized bed reactor and introducing fluidizing gas to make the silicon-carbon anode material in a fluidized state; b) atomizing a coating agent solution containing a carbon precursor and a solvent and spraying it into the fluidized bed reactor to make the coating agent solution uniformly coat the surface of the silicon-carbon anode material; c) heat-treating the coated silicon-carbon anode material to convert the carbon precursor into a carbon passivation layer.

[0006] Furthermore, the silicon-carbon anode material is prepared using porous carbon as a matrix. The porous carbon is one of biomass-based porous carbon, resin-based porous carbon, petroleum coke-based porous carbon, and pitch-based porous carbon.

[0007] Further, the carbon precursor is one of asphalt and phenolic resin, or a mixture of two in a certain proportion, with a mass fraction of 1.0~30.0 wt%; the solvent is one of DBE, tetrahydronaphthalene, D-limonene, wash oil, xylene or an alcohol solvent.

[0008] Furthermore, the coating agent solution is heated to 120.0°C before being sprayed; the droplet size formed by atomization is 15.0~20.0 μm; and the gas velocity of the fluidizing gas is controlled at 0.9 m / s.

[0009] Furthermore, the preparation method also includes: after step b) and before step c), in the fluidized bed reactor, the coated silicon-carbon anode material is heat-cured at 250.0°C for 1.0 h.

[0010] Furthermore, the heat treatment described in step c) is performed using a microwave heat treatment apparatus and under an inert atmosphere.

[0011] Furthermore, the heat treatment steps specifically include: first stage pretreatment: heating to 180°C at a heating rate of 10.0°C / min and holding at that temperature for 0.5h; second stage carbonization stabilization: continuing to heat to 480°C at a heating rate of 10.0°C / min and holding at that temperature for 0.5h.

[0012] Furthermore, step c) also includes a post-processing step of sieving and / or removing magnetic impurities from the product.

[0013] Another aspect of the present invention provides a liquid-phase coated surface passivated silicon-carbon anode material based on fluidized bed products, which is prepared according to the preparation method described above.

[0014] Another aspect of the present invention provides an application of liquid-phase coated surface passivated silicon-carbon anode material based on fluidized bed products. The silicon-carbon anode material prepared according to the above preparation method has the following applications: (1) application in the preparation of high energy density lithium batteries; (2) application in the preparation of fast-charging lithium batteries; (3) application in the preparation of long cycle life lithium batteries.

[0015] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0016] 1. This invention fully fluidizes the particles in a fluidized bed and uses atomized spraying to ensure that the coating agent droplets can uniformly and instantaneously contact the surface of each independently moving particle, achieving in-situ and uniform liquid phase coating. This fundamentally solves the problem of poor coating quality caused by uneven wetting in traditional impregnation methods.

[0017] 2. Throughout the entire coating and in-situ curing process, the particles are always separated and supported by the fluidizing gas, avoiding hard agglomeration between particles caused by capillary forces generated by solvent evaporation. This effectively prevents particle agglomeration, ensures good product dispersibility, and the prepared silicon-carbon anode material has a complete and dense carbon passivation layer on its surface, which effectively suppresses side reactions with the electrolyte and buffers the volume expansion of silicon, thereby significantly improving the material's initial coulombic efficiency, cycle stability, and rate performance.

[0018] 3. Compared with the high-temperature CVD process, the coating and curing temperatures of the present invention are both lower, which significantly reduces energy consumption. At the same time, the entire core process can be completed in a fluidized bed reactor, which is easy to connect with the preceding fluidized bed preparation process to form a continuous production line, greatly improving production efficiency. The overall process conditions are mild, energy consumption is low, and it is easy to integrate. Attached Figure Description

[0019] The accompanying drawings, which are included to provide a further understanding of embodiments of the invention and form part of this application, do not constitute a limitation thereof. In the drawings:

[0020] Figure 1 This is a scanning electron microscope image of the silicon-carbon anode material prepared in Example 1 of the present invention.

[0021] Figure 2 This is a comparison chart of the charge-discharge curves of silicon-carbon materials in Example 1 and Comparative Example 1 of the present invention.

[0022] Figure 3 This is a comparison chart of the silicon-carbon materials of Example 1 and Comparative Example 1 after 100 cycles at a 0.1C rate. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.

[0024] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated herein by reference to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail. The terms “comprising,” “including,” “having,” “containing,” etc., as used herein are open-ended terms, meaning that they include but are not limited to. Unless the context clearly indicates otherwise, the expressions “a” and “an” as used herein include plural references. It should be noted that “first,” “second,” etc., are used merely for convenience of description and distinction and should not be construed as indicating or implying relative importance. The term “about” as used herein indicates a range of ±20% of the following numerical value. In some embodiments, the term “about” indicates a range of ±10% of the following numerical value. In some embodiments, the term “about” indicates a range of ±5% of the following numerical value.

[0025] Existing technologies have significant shortcomings in the efficient, uniform, and mild surface passivation treatment of silicon-carbon anode materials (Si / C-FB) prepared by fluidized bed processes, lacking a passivation method that can be efficiently integrated with fluidized bed processes. Traditional liquid-phase processing (Si / C-FB) easily leads to uneven coating, particle agglomeration, solvent residue, and structural damage. Existing methods (especially CVD) are costly, energy-intensive, and complex, hindering large-scale production. It is difficult to achieve comprehensive and uniform passivation of Si / C-FB particles (especially internal pores and surfaces) under mild conditions.

[0026] Therefore, there is an urgent need to develop a passivation method suitable for the characteristics of fluidized bed silicon-carbon anode materials (Si / C-FB) that can effectively overcome their surface defects. This invention proposes an innovative liquid-phase coating surface passivation method that combines liquid-phase coating technology with fluidized bed technology to achieve in-situ particle treatment directly within a fluidized bed reactor. This method utilizes the vigorous movement of particles and the excellent gas-liquid contact characteristics under fluidized conditions to ensure that the coating precursor solution is uniformly dispersed and precisely atomized or coated onto the surface of each particle and the pore inlet, effectively preventing agglomeration. This process can be carried out under mild temperature and pressure conditions, which helps reduce energy consumption and production costs. It is also easily integrated with fluidized bed preparation processes to form in-situ or near-line processing units, thereby significantly simplifying the process, improving production efficiency, and possessing good potential for large-scale application.

[0027] Building upon this foundation, the present invention further introduces a microwave heat treatment process to promote the carbonization and stabilization of the coating layer. Microwave sintering offers advantages such as bulk heating, rapid temperature rise, and high energy utilization, enabling efficient densification of the coating layer under low-temperature, short-time conditions, forming a uniform and firmly bonded amorphous carbon passivation layer. This composite process ultimately constructs a complete, dense, and uniform protective layer on and near the surface of Si / C-FB particles, significantly improving its initial coulombic efficiency, cycle stability, and rate performance as a lithium-ion battery anode material.

[0028] Example 1

[0029] Step 1: Precursor preparation.

[0030] Fluidized bed silicon-carbon composite material based on biomass-derived porous carbon was selected as the precursor. Its key physical properties are as follows: particle size distribution: Dv10 = 1.79 μm, Dv50 = 7.61 μm, Dv100 = 23.52 μm; tap density: 0.87 g / cm³; specific surface area: 19.87 m² / g. This material is designated as sample A.

[0031] Step 2: Preparation of coating agent.

[0032] Using medium-temperature asphalt as the carbon precursor and wash oil as the solvent, a homogeneous coating agent solution with a solid content of 8.0 wt% was prepared by continuous mechanical stirring at a constant temperature of 85.0°C until the asphalt was completely dissolved. Based on the asphalt carbon residue rate (approximately 60%), the theoretical carbon residue value of this coating agent is approximately 4.8%. The prepared solution is designated as Sample B.

[0033] Step 3: Fluidized bed liquid phase coating.

[0034] Sample A was loaded into a fluidized bed reactor, and high-purity nitrogen (N2, purity ≥ 99.99%) was introduced as the fluidizing gas. The gas flow rate was adjusted by real-time monitoring of the bed pressure drop, controlling the gas velocity to 0.9 m / s (corresponding to a nitrogen volumetric flow rate of approximately 12.5 L / min), ensuring the bed was in a turbulent fluidized state and that the particles were fully fluidized. After fluidization and temperature stabilization, Sample B was transferred to a constant-temperature jacketed storage tank, maintained at 120.0°C to prevent asphalt precipitation and maintain suitable viscosity. A dual-fluid atomizing nozzle was used to atomize the coating agent into droplets with a particle size of 15.0–20.0 μm, spraying them into the fluidized bed at a coating agent to silicon-carbon mass ratio of 1:8 (mL / g), continuously coating for 90.0 min. After coating, the mixture was kept at 250.0°C for 1.0 h for curing, achieving initial cross-linking of the coating layer. The sample obtained at this stage is designated as Sample C.

[0035] Step 4: Microwave sintering heat treatment.

[0036] Sample C was transferred to a microwave heat treatment apparatus and subjected to the following temperature program under a high-purity nitrogen atmosphere (purity ≥ 99.99%):

[0037] First stage pretreatment: Heat to 180°C at 10.0°C / min and hold at that temperature for 0.5 h to completely remove residual solvent and achieve pre-curing of the coating layer;

[0038] The second stage of carbonization and stabilization involved further heating to 480°C at a rate of 10.0°C / min, followed by a hold at that temperature for 0.5 h. Temperature fluctuations were strictly controlled to be ≤±2°C, ensuring thorough carbonization and structural stabilization of the coating layer through selective microwave heating. This resulted in a continuous, dense, and uniform amorphous carbon passivation layer forming on the surface of the silicon-carbon particles. After heat treatment, the sample was cooled to 25.0°C in the furnace and then removed; this sample was designated as sample D.

[0039] Step 5: Post-processing.

[0040] Sample D was subjected to a vibratory sieve (325 mesh) and electromagnetic iron removal treatment in sequence to remove trace agglomerates and magnetic foreign matter that may be generated during sintering, and the final product, a biomass-based silicon-carbon anode material with a uniform surface passivation layer, was obtained.

[0041] Example 2

[0042] In this embodiment, a silicon-carbon composite material is prepared using resin-based porous carbon as a precursor via a fluidized bed process. Its key physicochemical parameters are as follows: particle size distribution D... V10 D V50 D V100 The micrometers are 1.51 μm, 7.03 μm, and 21.55 μm, respectively, with a tap density of 0.94 g / cm³ and a specific surface area of ​​32.11 m² / g.

[0043] Subsequent experiments were conducted strictly following the steps described in Example 1. A resin-based silicon-carbon anode material with a surface passivation layer was successfully prepared using fluidized bed vapor deposition and liquid-phase coating processes. The physicochemical properties of the material were characterized according to the standard methods described in Comparative Example 1.

[0044] Example 3

[0045] In this embodiment, petroleum coke-based porous carbon is used as a precursor to prepare silicon-carbon composite material via a fluidized bed process. Its core physicochemical parameters are as follows: particle size distribution D V10 D V50 D v100 The micrometers are 1.63 μm, 8.25 μm, and 23.26 μm, respectively, the tap density is 0.89 g / cm³, and the specific surface area is 29.87 m² / g.

[0046] Subsequent material synthesis strictly followed the process described in Example 1. Petroleum coke-based silicon-carbon anode material with a surface passivation layer was successfully prepared using fluidized bed vapor deposition and liquid-phase coating techniques. All physicochemical properties of the obtained material were systematically characterized according to the method described in Comparative Example 1.

[0047] Example 4

[0048] In this embodiment, asphalt-based porous carbon is used as a precursor to prepare silicon-carbon composite material via a fluidized bed process. Its core physical parameters are as follows: particle size distribution D V10 D V50 D v100 The micrometers are 1.65 μm, 8.59 μm, and 24.08 μm, respectively, the tap density is 0.90 g / cm³, and the specific surface area is 23.39 m² / g.

[0049] Subsequent material synthesis strictly followed the process parameters and experimental procedures established in Example 1. Through fluidized bed vapor deposition and liquid-phase coating techniques, a pitch-based silicon-carbon anode material with a surface passivation layer was successfully prepared. All physicochemical properties of the obtained material were systematically characterized according to the standard methods in Comparative Example 1.

[0050] Comparative Example 1

[0051] This comparative example is used to illustrate the effect of liquid phase coating on the specific surface area, initial discharge efficiency, and cycle stability of fluidized bed silicon-carbon materials.

[0052] In this comparative example, in order to scientifically evaluate the effect of liquid phase coating on the improvement of electrochemical performance of fluidized bed silicon-carbon anode materials, the comparative experimental group set up in this study is: the same batch of fluidized bed silicon-carbon anode materials without liquid phase coating is used as blank control sample.

[0053] Through systematic electrochemical testing, the improvement in the initial discharge efficiency and cycle stability of silicon-carbon anode materials before and after liquid phase coating was examined and compared.

[0054] To conduct a systematic comparative evaluation, in this comparative example, the biomass fluidized bed derived silicon-carbon composite material prepared by the method in Example 1 was used as a reference. Parallel electrochemical experiments were carried out under completely identical test conditions, and the obtained comprehensive performance data were compared and analyzed.

[0055] In this comparative example, the electrochemical performance of the silicon-carbon composite anode material was evaluated by assembling a CR2032 coin cell and testing it on a Blue Electric testing system. The electrode preparation process was as follows: Active material (silicon-carbon material), conductive agent (SuperP, single-walled carbon nanotubes), and binder (sodium carboxymethyl cellulose and styrene-butadiene latex) were uniformly mixed at a mass ratio of 95.0:1.0:1.0:1.5:1.5 and coated onto a 6.0 μm thick copper foil current collector. The areal density of the electrode was controlled at approximately 1.5 mg / cm². Subsequently, the electrode was heat-treated in a vacuum drying oven at 100.0 °C for 6.0 hours, then rolled to achieve a compaction density of approximately 1.2 g / cm³, and finally punched into circular sheets with a diameter of 14.0 mm.

[0056] The counter electrode is a 14.0 mm diameter lithium metal sheet, the separator is a Celgard 2500 polypropylene membrane, and the electrolyte is 1 M LiPF6 dissolved in EC / DMC (1:1, w / w) solvent with 5.0 wt% FEC added as a film-forming additive. All battery assembly processes were completed in an argon-protected glove box.

[0057] Electrochemical tests were conducted in constant current mode, with the voltage range set from 0.005 to 2.0 V (vs. Li+ / Li). The first cycle was performed at a charge-discharge rate of 0.1C to examine the initial performance, and subsequent cycle tests were also conducted at a rate of 0.1C to evaluate the cycling stability of the material. Figure 2 A comparison graph of charge-discharge curves of this comparative example and Example 1 is shown; Figure 3 The diagram shows a comparison of this comparative example and Example 1 after 100 cycles at a 0.1C magnification.

[0058] Comparative Example 2

[0059] This comparative example uses the resin-based fluidized bed silicon-carbon material described in Example 2 as a control group. Parallel experiments were conducted under the same testing conditions, and a systematic comparison and comprehensive analysis of several key electrochemical performance indicators were performed. In this comparative example, the same batch of fluidized bed silicon-carbon anode material without liquid phase coating was used as a blank control sample.

[0060] Comparative Example 3

[0061] To systematically evaluate the material performance, this comparative example selected the same petroleum coke-based fluidized bed silicon-carbon material as in Example 3 as the control group. Electrochemical performance was characterized under identical testing conditions, and comprehensive data analysis and comparison were performed on key indicators. In this comparative example, the same batch of uncoated fluidized bed silicon-carbon anode material was used as a blank control sample.

[0062] Comparative Example 4

[0063] This comparative example uses the pitch-based fluidized bed silicon-carbon material employed in Example 4 as a control group. The system's electrochemical performance was characterized under identical testing conditions, and comprehensive data comparison and analysis were conducted on multiple key indicators. In this comparative example, the same batch of fluidized bed silicon-carbon anode material without liquid phase coating was used as a blank control sample.

[0064] Table 1 shows a summary table of the physicochemical properties of silicon-carbon anode materials prepared in different embodiments of this application; Table 2 shows a summary table of the charging rate performance data of silicon-carbon anode materials prepared in different embodiments of this application.

[0065] Table 1. Summary of Physicochemical Properties of Silicon-Carbon Anode Materials

[0066]

[0067] Table 2. Summary of Charging Rate Performance Data for Silicon-Carbon Anode Materials

[0068]

[0069] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing liquid-phase coated surface-passivated silicon-carbon anode material based on fluidized bed products, characterized in that, The preparation method includes: a) The silicon-carbon anode material prepared by fluidized bed is placed in a fluidized bed reactor, and fluidizing gas is introduced to make the silicon-carbon anode material fluidized; b) After atomizing the coating agent solution containing carbon precursor and solvent, spray it into the fluidized bed reactor so that the coating agent solution uniformly coats the surface of the silicon-carbon anode material; c) The coated silicon-carbon anode material is heat-treated to convert the carbon precursor into a carbon passivation layer.

2. The method for preparing liquid-phase coated surface-passivated silicon-carbon anode material based on fluidized bed products according to claim 1, characterized in that, The silicon-carbon anode material is prepared using porous carbon as a matrix. The porous carbon is one of biomass-based porous carbon, resin-based porous carbon, petroleum coke-based porous carbon, and pitch-based porous carbon.

3. The method for preparing liquid-phase coated surface-passivated silicon-carbon anode material based on fluidized bed products according to claim 1 or 2, characterized in that, The carbon precursor is one of asphalt or phenolic resin. Or a mixture of two in a certain proportion, with a mass fraction of 1.0~30.0 wt%; The solvent is one of DBE, tetrahydronaphthalene, D-limonene, wash oil, xylene, or an alcohol solvent.

4. The method for preparing liquid-phase coated surface-passivated silicon-carbon anode material based on fluidized bed products according to claim 1, characterized in that, The coating agent solution is heated to 120.0°C before being sprayed; The droplet size formed by atomization is 15.0~20.0 μm; The velocity of the fluidizing gas is controlled at 0.9 m / s.

5. The method for preparing liquid-phase coated surface-passivated silicon-carbon anode material based on fluidized bed products according to claim 1, characterized in that, The preparation method further includes: After step b) and before step c), the coated silicon-carbon anode material is subjected to thermal curing at 250.0°C for 1.0 h in the fluidized bed reactor.

6. The method for preparing liquid-phase coated surface-passivated silicon-carbon anode material based on fluidized bed products according to claim 1, characterized in that, The heat treatment described in step c) is performed using a microwave heat treatment device. And it was carried out under an inert atmosphere.

7. The method for preparing liquid-phase coated surface-passivated silicon-carbon anode material based on fluidized bed products according to claim 6, characterized in that, The heat treatment steps specifically include: First stage pretreatment: Heat to 180°C at a heating rate of 10.0°C / min and hold at that temperature for 0.5h; Second stage of carbonization stabilization: Continue heating at a rate of 10.0°C / min to 480°C and hold at that temperature for 0.5 h.

8. The method for preparing liquid-phase coated surface-passivated silicon-carbon anode material based on fluidized bed products according to claim 1, characterized in that, Step c) further includes a post-processing step of sieving and / or removing magnetic impurities from the product.

9. A liquid-phase coated surface-passivated silicon-carbon anode material based on fluidized bed products, characterized in that, The silicon-carbon anode material is prepared according to the preparation method described in any one of claims 1 to 8.

10. An application of a liquid-phase coated surface-passivated silicon-carbon anode material based on fluidized bed products, characterized in that, The silicon-carbon anode material prepared according to the preparation method described in any one of claims 1 to 8 It includes the following applications: (1) Application in the preparation of high energy density lithium batteries; (2) Application in the preparation of fast-charging lithium batteries; (3) Application in the preparation of long cycle life lithium batteries.

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