Method for preparing silicon-carbon nano material by treating silicon sludge through plasma thermal spraying

Abstract

The invention relates to the technical field of solid waste recycling and nano material preparation, in particular to a method for preparing a silicon-carbon nano material by treating silicon sludge through plasma thermal spraying, which comprises the following steps: S1, mechanically mixing silicon sludge waste, a liquid carbon precursor and graphene oxide according to a mass ratio of 1: (0.001-1): (0.001-1); s2, carrying out spray drying on the mixed material at the temperature of below 180 DEG C to obtain spherical precursor powder with the particle size of 5-50 microns; s3, Ar / H2 mixed gas is used as carrier gas, the volume ratio of H2 is 5-20%, and a microwave plasma torch is adopted to heat the precursor powder to 1500-2000 DEG C within 10 seconds; s4, calcining at 600-800 DEG C for 3-10 hours in an Ar / H2 protective atmosphere, so that the carbon precursor is cracked to form a continuous coating layer; according to the preparation method, limitation of a traditional step-by-step process is broken through, cooperative regulation and control of unbalanced etching of the silicon-oxygen layer, gradient growth of the carbon layer and self-assembly of the conductive network are achieved, the obtained material has high specific capacity (larger than 2200 mAh / g) and excellent cycle stability, and an efficient and green solution is provided for resource utilization of photovoltaic silicon sludge.

Description

Technical Field

[0001] The present invention relates to the technical field of solid waste resource utilization and nano material preparation, and in particular to a method for preparing silicon-carbon nano materials by treating silicon mud with plasma thermal spraying. Background Art

[0002] During the crystalline silicon slicing process, the mechanical and thermal composite effects of diamond wire cutting generate a large amount of nano-silicon sludge waste. Although this type of nano-silicon has an extremely high theoretical specific capacity, it faces the problem of triple interfaces. The dense surface oxide layer hinders the diffusion of lithium ions, resulting in low initial coulombic efficiency. Metal impurities trigger catalytic decomposition reactions during the charge and discharge process, accelerating electrolyte consumption. Silicon particles undergo a dramatic volume expansion during the lithiation and delithiation stages, resulting in pulverization of the electrode structure. Current industrial treatment methods have obvious technical shortcomings. Although the acid pickling method can remove some metal impurities, it produces highly polluted fluorine-containing wastewater and forms secondary solid waste. The high surface energy of nano-silicon in the carbon coating process leads to uneven carbon layer coverage, and high-temperature treatment can also cause silicon particles to coarsen. Although the physical vapor deposition method can achieve uniform carbon layer coating, it requires expensive equipment and cannot simultaneously remove the chemical bonds of the silicon-oxygen layer, resulting in a significant increase in interfacial impedance.

[0003] The existing technology system has failed to break through the synergistic effect of three key processes. The non-equilibrium exfoliation of the silicon oxide layer and the deep removal of metal impurities require different reaction conditions. The in-situ graphitization growth of the carbon source depends on a specific temperature field distribution. The traditional step-by-step treatment process produces a mass transfer barrier, resulting in high energy consumption and unstable product performance.

[0004] In response to the above-mentioned defects, the present invention proposes a plasma spraying-carbon source cracking coupling process to solve the technical difficulties of simultaneous purification, nano-sizing and uniform carbon layer coating of silicon mud, and realize the efficient and green preparation of silicon-carbon nanomaterials. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for preparing silicon-carbon nanomaterials by plasma thermal spraying silicon mud, and the oxide layer stripping, deep removal of metal impurities and in-situ cracking and coating of carbon sources of silicon mud waste are achieved by microwave plasma spraying of Ar / H2 mixed gas. A gradient temperature field control strategy is adopted to simultaneously complete the nano-sizing of silicon particles, the construction of a three-dimensional graphene oxide network and the directional deposition of a liquid carbon precursor in a 1500-2000°C plasma field to form a silicon-carbon composite negative electrode material with a core-shell structure. The present invention breaks through the limitations of traditional step-by-step processes and realizes the coordinated control of non-equilibrium etching of the silicon oxide layer, gradient growth of the carbon layer and self-assembly of the conductive network. The obtained material has both high specific capacity (>2200mAh / g) and excellent cycle stability, providing an efficient and green solution for the resource utilization of photovoltaic silicon mud.

[0006] In order to achieve the above technical objectives and the above technical effects, the present invention is implemented through the following technical solutions:

[0007] A method for preparing silicon-carbon nanomaterials by continuously treating silicon sludge waste by plasma thermal spraying comprises the following steps:

[0008] S1: Raw material pretreatment: mechanically mixing silicon mud waste, liquid carbon precursor and graphene oxide in a mass ratio of 1:(0.001-1):(0.001-1), wherein the silicon mud waste contains silicon particles with a particle size of 10-20000 nm and an oxide layer on the surface;

[0009] S2: Granulation: The mixed material is spray-dried at a temperature below 180°C to obtain spherical precursor powder with a particle size of 5-50 μm;

[0010] S3: Plasma treatment: Ar / H2 mixed gas is used as carrier gas, in which H2 accounts for 5-20% by volume, and a microwave plasma spray gun is used at a power density of 10-100kW / cm 3 Under the following conditions, the precursor powder is heated to 1500-2000°C within 10 seconds;

[0011] S4: Powder solidification: Calcinate at 600-800°C for 3-10 hours in an Ar / H2 protective atmosphere to crack the carbon precursor and form a continuous coating layer.

[0012] Furthermore, the processing requirements of step S2 include: the peeling rate of the oxide layer on the surface of the silicon particles is greater than 99%; the graphene oxide instantly expands to form a three-dimensional conductive network; the metal impurities are gasified and removed, and the Fe residual amount is less than 0.01wt%.

[0013] Furthermore, the liquid carbon precursor is selected from at least one of sucrose, phenolic resin, and asphalt.

[0014] Furthermore, during the plasma treatment in step S3, the residence time of the material in the plasma flame is controlled to be 0.1-10 seconds, and the carrier gas flow rate is 5-20 m / s.

[0015] Furthermore, the final product is a core-shell structured silicon-carbon composite, with a silicon particle size of 10-100 nm and a carbon layer thickness of 2-8 nm.

[0016] Beneficial effects of the present invention:

[0017] The present invention uses microwave-excited high-density plasma to construct a unique electron-gas temperature gradient field, forming a highly active hydrogen atom diffusion layer in a hydrogen-argon mixed atmosphere, breaking through traditional thermodynamic limitations to achieve atomic-level etching and removal of the silicon oxide layer. The reduction-gasification synergistic removal of metal impurities is simultaneously completed, and the transient high-temperature characteristics of the plasma are used to induce selective phase changes of impurity elements, combined with carrier gas convection to achieve efficient gas-solid separation. Graphene oxide undergoes interlayer structural reorganization under the thermal shock of the plasma. Through the directional removal of oxygen-containing functional groups and the reconstruction of the carbon skeleton topology, a three-dimensional interconnected conductive network structure is formed, effectively improving the overall conductivity and structural stability of the material.

[0018] The present invention adopts a staged cracking strategy of a liquid carbon precursor in a plasma flame, achieving gradient growth of the carbon layer through temperature-time coordinated regulation. An amorphous carbon buffer layer is preferentially formed on the surface of the silicon substrate. The outer layer completes the orientation arrangement of the graphene sheets through the surface migration of carbon atoms, forming a reinforced interface with dual effects of chemical bonding and physical anchoring. This effectively alleviates the volume expansion stress of the lithiation process while optimizing the carrier transport path. The thermal history of the material in the high-temperature zone is precisely controlled by matching the fluid dynamics parameters, suppressing the melting and agglomeration of silicon particles.

[0019] The core-shell-network composite structure constructed by the present invention achieves size control and spatial confinement of nano-silicon grains. Through the carbon layer slip mechanism and the stress dispersion effect of the three-dimensional conductive network, the volume expansion effect is limited to the structural tolerance. The special configuration of the gradient carbon layer forms a rapid lithium ion transmission channel, and the precise regulation of its interlayer spacing balances electronic conductivity and ion diffusion dynamics. The silicon surface crystal plane reconstruction induced by plasma treatment enhances the structural stability of the material. Combined with the carbon layer defect engineering, the interfacial charge distribution state is optimized, ultimately achieving a synergistic improvement in high specific capacity and long cycle life.

[0020] Of course, any product implementing the present invention does not necessarily need to achieve all of the advantages described above at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0022] Figure 1 This is a scanning electron microscope image of the silicon-carbon nanomaterial prepared in Example 1. DETAILED DESCRIPTION

[0023] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0024] Example 1

[0025] The method for preparing silicon-carbon nanomaterials by continuously treating silicon sludge waste with plasma thermal spraying described in this embodiment includes the following steps:

[0026] S1: Raw material pretreatment: mechanically mixing silicon mud waste, liquid carbon precursor and graphene oxide in a mass ratio of 1:(0.001-1):(0.001-1), wherein the silicon mud waste contains silicon particles with a particle size of 10-20000 nm and an oxide layer on the surface;

[0027] S2: Granulation: The mixed material is spray-dried at a temperature below 180°C to obtain spherical precursor powder with a particle size of 5-50 μm;

[0028] S3: Plasma treatment: Ar / H2 mixed gas is used as carrier gas, in which H2 accounts for 5-20% by volume, and a microwave plasma spray gun is used at a power density of 10-100kW / cm 3 Under the following conditions, the precursor powder is heated to 1500-2000°C within 10 seconds;

[0029] S4: Powder solidification: Calcinate at 600-800°C for 3-10 hours in an Ar / H2 protective atmosphere to crack the carbon precursor and form a continuous coating layer.

[0030] In this embodiment, the processing requirements of step S2 include: the peeling rate of the oxide layer on the surface of the silicon particles is greater than 99%; the graphene oxide instantly expands to form a three-dimensional conductive network; the metal impurities are gasified and removed, and the Fe residual amount is less than 0.01wt%.

[0031] In this embodiment, the liquid carbon precursor is selected from at least one of sucrose, phenolic resin, and asphalt.

[0032] In this embodiment, during the plasma treatment in step S3, the residence time of the material in the plasma flame is controlled to be 0.1-10 seconds, and the carrier gas flow rate is 5-20 m / s.

[0033] In this embodiment, the final product is a core-shell structured silicon-carbon composite, with a silicon particle size of 10-100 nm and a carbon layer thickness of 2-8 nm.

[0034] Example 2

[0035] 1 kg of photovoltaic silicon mud waste (Si content 92 wt%, Fe content 0.8 wt%, surface oxide layer thickness 2-5 nm as determined by ICP-OES) was placed in a planetary ball mill and processed according to the following process:

[0036] 1. Raw material pretreatment:

[0037] The liquid carbon precursor was analytically pure sucrose (C 12 H 22 O 11 , purity ≥99.5%) 0.3kg;

[0038] 0.05 kg of graphene oxide (sheet diameter 5-20 μm, number of layers 3-5, oxygen content 28 wt%);

[0039] Ball milling parameters: stainless steel tank (argon protection), zirconia grinding balls (three-grade ratio of Φ3 / Φ5 / Φ10mm), ball-to-material ratio of 10:1;

[0040] Mixing process: planetary ball milling at 400 rpm for 2 h, switching the rotation direction every 30 min;

[0041] 2. Granulation treatment:

[0042] Use centrifugal spray drying tower;

[0043] Process parameters: inlet air temperature 175±3℃, outlet air temperature 85±2℃, atomizing disk speed 18000rpm;

[0044] Feed rate control: peristaltic pump set at 15 mL / min;

[0045] Obtained spherical precursor powder: D50 = 25 μm, tap density 0.85 g / cm 3 ;

[0046] 3. Plasma treatment:

[0047] Equipment configuration: 40kW microwave plasma spraying system;

[0048] Carrier gas composition: Ar + 15 vol% H2;

[0049] Gas dynamics control: total flow rate 18 SLM, nozzle Mach number 1.2, flame length 120 mm;

[0050] Thermodynamic parameters: power density 58kW / cm 3 , powder residence time 2.3s;

[0051] Temperature field monitoring: dual-wavelength infrared thermometer real-time monitoring 1800±50℃;

[0052] 4. Carbon layer curing:

[0053] Using atmosphere tube furnace;

[0054] Heat treatment procedure: heating to 700°C at 5°C / min and holding at this temperature for 5h;

[0055] Cooling method: After the furnace is cooled to 300℃, helium injection cooling is used;

[0056] Product characterization:

[0057] Scanning electron microscopy: shows that silicon particles are uniformly embedded in the three-dimensional graphene network;

[0058] Transmission electron microscopy: carbon coating thickness 5.0±0.2nm;

[0059] Electrochemical performance: The first discharge capacity reaches 2200mAh / g.

[0060] The preferred embodiments of the present invention disclosed above are intended only to help illustrate the present invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the present invention to the specific embodiments described. Obviously, many modifications and variations are possible based on the content of this specification. These embodiments are selected and described in detail in this specification to better explain the principles and practical applications of the present invention, thereby enabling those skilled in the art to better understand and utilize the present invention. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for preparing silicon-carbon nanomaterials by continuously treating silicon mud waste by plasma thermal spraying, characterized in that: The following steps are involved: S1: Mechanically mixing silicon mud waste, liquid carbon precursor and graphene oxide in a mass ratio of 1:(0.001-1):(0.001-1), wherein the silicon mud waste contains silicon particles with a particle size of 10-20000 nm and an oxide layer on the surface; S2: spray drying the mixed material at a temperature below 180°C to obtain a spherical precursor powder with a particle size of 5-50 μm; S3: Ar / H2 mixed gas is used as carrier gas, in which H2 accounts for 5-20% by volume, and a plasma spray gun is used at a power density of 10-100kW / cm 3 Under the following conditions, the precursor powder is heated to 1500-2000°C within 10 seconds; S4: Powder carbonization: Calcinate at 600-800°C for 3-10 hours in an Ar / H2 protective atmosphere to crack the carbon precursor and form a continuous coating layer.

2. The method for preparing silicon-carbon nanomaterials by continuously treating silicon sludge waste by plasma thermal spraying according to claim 1, wherein: The processing requirements of step S2 include: the peeling rate of the oxide layer on the surface of the silicon particles is greater than 99%; the graphene oxide instantly expands to form a three-dimensional conductive network; the metal impurities are gasified and removed, and the Fe residual amount is less than 0.01wt%.

3. The method for preparing silicon-carbon nanomaterials by continuously treating silicon sludge waste by plasma thermal spraying according to claim 1, wherein: The liquid carbon precursor is selected from at least one of sucrose, phenolic resin and asphalt.

4. The method for preparing silicon-carbon nanomaterials by continuously treating silicon sludge waste by plasma thermal spraying according to claim 1, wherein: During the plasma treatment in step S3, the residence time of the material in the plasma flame is controlled to be 0.1-10 seconds, and the carrier gas flow rate is 5-20 m / s.

5. The method for preparing silicon-carbon nanomaterials by continuously treating silicon sludge waste by plasma thermal spraying according to claim 1, characterized in that: The final product is a core-shell structured silicon-carbon composite with a silicon particle size of 10-100 nm and a carbon layer thickness of 2-8 nm.

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