A method for in-situ synthesis of silicon-carbon nanocomposite material for lithium ion battery negative electrode material by inductive thermal plasma

Abstract

The application discloses an in-situ synthesis method of a silicon-carbon nanocomposite material for a lithium ion battery negative electrode material, and belongs to the field of lithium ion batteries. A segmented feeding mode is adopted, and the temperature zone of a silicon nanowire forming process and a carbon-silicon composite process is controlled, so that the carbon-silicon reaction speed is inhibited, and the formation of silicon carbide is effectively avoided. First, a silicon source precursor is axially delivered into an inductive thermal plasma high-temperature zone, silicon vapor is obtained under the action of high temperature, and the silicon vapor is cooled during leaving the high-temperature zone, so that silicon nanowires are obtained through nucleation and growth. In the tail of the inductive thermal plasma arc, acetylene, methane and other gas carbon sources are added, and carbon formed through pyrolysis is nucleated on the silicon surface in a heterogeneous phase, so that a silicon-carbon composite material is obtained. The problems of uneven carbon layer coating and easy oxidation of nanomaterials are solved.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion batteries and relates to an in-situ synthesis method of silicon-carbon nanocomposite materials for lithium-ion battery anode materials using induced thermal plasma. Background Technology

[0002] The rapid development of electronic devices, automobiles, and large-scale energy storage devices has placed higher demands on the energy density and cycle life of lithium-ion batteries. Silicon, with its high theoretical specific capacity (4200 mAh / g), low cost, and abundant reserves, is the most promising anode material for next-generation lithium-ion batteries. However, silicon anodes are prone to severe volume expansion during lithium-ion battery cycling, leading to electrolyte loss and capacity decay. Furthermore, silicon's conductivity as a semiconductor is far lower than that of graphite, severely affecting lithium-ion transport within the silicon anode and significantly limiting its effective performance.

[0003] To improve the structural stability and conductivity of silicon materials, the most common methods include nanostructuring and material compositing. Studies have found that nanowires can efficiently release stress through axial expansion and contraction, inhibiting crack growth and propagation, thus enabling them to withstand greater volume changes and reducing damage to the electrode structure. Furthermore, nanowires can provide rapid electron and ion transport pathways along the axial direction, improving electrochemical reaction rates. Further compositing silicon with carbon materials, utilizing carbon's excellent conductivity to promote charge transfer and transport, can effectively improve the rate performance of batteries. Carbon can also act as a buffer, better maintaining the structural stability of silicon anode materials.

[0004] Due to the relatively stable chemical properties of silicon, nanowires are difficult to synthesize through mild physical or chemical processes. Existing synthesis techniques, including vapor deposition, template methods, and electrochemical etching, are complex and difficult to scale up for mass production. Furthermore, current methods for preparing silicon-carbon composites, such as ball milling, high-temperature pyrolysis, and vapor deposition, mostly employ a two-step process: first preparing silicon nanomaterials, then performing carbon composite formation. This method not only increases the preparation process but also makes it difficult to achieve uniform composite with carbon materials due to the tendency of nanomaterials to agglomerate. Moreover, the composite process is highly susceptible to oxidation, limiting the improvement in electrochemical performance.

[0005] Plasma possesses significant advantages in the preparation of nanoparticles and microparticles due to its high temperature, highly reactive atmosphere, fast reaction speed, and absence of electrode contamination. For example, Seo et al. used a mixture of nickel and magnesium oxide as raw materials, utilizing high-temperature plasma vaporization followed by cooling. The different condensation and precipitation sequences caused by the differences in the melting and boiling points of the materials resulted in magnesium oxide nanorods with nickel particles loaded on their surfaces (Surface and Coatings Technology, 2013, 228, S91-S96). Li et al. employed a similar principle, adding a mixture of raw materials to the high-temperature region of hydrogen plasma, chemically reducing them to generate gaseous tungsten and copper elements, and then synthesizing core-shell structured tungsten-copper nanoparticles through heterogeneous nucleation based on their melting and boiling point differences (Journal of Alloy and Compounds, 2021, 853, 156958). However, carbon and silicon exhibit a strong reaction tendency under high-temperature conditions, leading to the formation of silicon carbide. Therefore, a composite structure of elemental silicon and carbon cannot be obtained using similar methods. Summary of the Invention

[0006] The primary objective of this invention is to provide an in-situ synthesis method of silicon-carbon nanocomposite materials for lithium-ion battery anode materials using induction thermal plasma. This method effectively suppresses the formation of silicon carbide and solves problems such as complex process flow, uneven carbon layer coating, and easy oxidation of nanomaterials in existing technologies.

[0007] To achieve the aforementioned objectives, this invention employs a segmented feeding method. By controlling the temperature range of the silicon nanowire formation and silicon-carbon composite processes, the silicon-carbon reaction rate is suppressed, effectively preventing the formation of silicon carbide. First, the silicon source precursor is axially fed into the high-temperature region of the induction thermal plasma. Silicon vapor is obtained under high temperature and cooled as it leaves the high-temperature region, resulting in silicon nanowires through nucleation growth. Then, gaseous carbon sources such as acetylene and methane are added to the arc tail of the induction thermal plasma. The carbon formed by pyrolysis undergoes heterogeneous nucleation on the silicon surface, yielding a silicon-carbon composite material. Because the silicon-carbon reaction rate is significantly suppressed at low temperatures, the formation of silicon carbide is avoided, and the composite process does not affect the formation of silicon nanowires.

[0008] Another objective of this invention is to provide the application of the aforementioned silicon-carbon nanocomposite material as a negative electrode in lithium-ion batteries. The silicon-carbon composite material obtained by this method, as a negative electrode material, can effectively improve the cycle stability of lithium-ion batteries and has promising application prospects.

[0009] The present invention discloses an in-situ synthesis method of silicon-carbon nanocomposite material for lithium-ion battery anodes using induced thermal plasma, comprising the following steps:

[0010] (1) A medium gas and a side gas are introduced into the induction thermal plasma device, and a negative pressure device is turned on to form a stable induction thermal plasma; the power of the induction thermal plasma device is 10-100KW, the medium gas is argon, and the flow rate of the medium gas is 0.1-10m³. 3 / h, preferably 0.2-5m 3 / h; the edge gas is one or more inert gases such as argon and nitrogen, and the edge gas flow rate is 0.1-10m³ / h. 3 / h, preferably 0.2-8m 3 / h. The negative pressure range of the negative pressure device is 10-500 mm water column, preferably 20-200 mm water column;

[0011] (2) Micron-sized silicon powder or silicon-containing gas is used as a precursor; the particle size of the micron-sized silicon powder is 1-200μm, preferably 20-100μm; the silicon-containing gas includes gases such as silane;

[0012] (3) The carrier gas axially carries the silicon precursor into the induction thermal plasma of step (1) for reaction. The carrier gas is one or more of gases such as argon and hydrogen, and the carrier gas flow rate is 0.05-5m³. 3 / h, preferably 0.1-2m 3 / h. If the precursor is silicon powder, the feed rate is 1-100 g / min, preferably 5-50 g / min; if the precursor is silicon-containing gas, the flow rate is 0.1-2 m³ / min. 3 / h, preferably 0.5-1m 3 / h.

[0013] (4) After delivering the silicon precursor for 2 seconds, a carbon source is simultaneously delivered to the tail flame region of the induction thermal plasma described in step (1). The carbon source is a carbon-containing gas such as methane or acetylene, and the carbon source flow rate is 0.01-2 m³ / s. 3 / h, preferably 0.05-1m 3 / h;

[0014] (5) After the reaction is complete, stop the delivery of silicon precursor first, and then stop the delivery of carbon source 2 seconds later. The product enters the collector for collection.

[0015] Because the entire synthesis process takes place in a continuously moving airflow, the particles are well dispersed, effectively preventing silicon agglomeration. This results in uniform carbon coating on the silicon nanowires (the center of the nanowires is mainly composed of silicon nanoparticles, while the outer layer is mainly a carbon layer formed by carbon nanoparticles). The nanowire diameter can range from 10 to 50 nm. This in-situ coating method also effectively avoids the oxidation of the silicon nanoparticles and is relatively easy to implement in continuous production. Furthermore, the method described in this invention has advantages such as simple process, wide selection of raw materials, and being green, environmentally friendly, and pollution-free. Attached Figure Description

[0016] Figure 1 The X-ray diffraction pattern of the silicon-carbon nanocomposite material prepared in Example 1 of this invention;

[0017] Figure 2 A scanning electron microscope image of the silicon-carbon nanocomposite material prepared in Example 1 of this invention;

[0018] Figure 3 Transmission electron microscopy image of the silicon-carbon nanocomposite material prepared in Example 1 of the present invention;

[0019] Figure 4 The image shows the elemental distribution of the silicon-carbon nanocomposite material prepared in Example 1 of this invention.

[0020] Figure 5 Battery cycle data of the silicon-carbon nanocomposite material prepared in Example 1 of this invention, tested at a current density of 0.1C. Detailed Implementation

[0021] To better illustrate the content of this invention, the following examples will be used to further explain the invention, but the invention is not limited to the following embodiments.

[0022] Example 1

[0023] The induction thermal plasma reactor is 10 kW. First, silicon powder with a particle size of 50 μm is placed in the feeder of the induction thermal plasma reactor. A central gas (argon) and a side gas are introduced at a flow rate of 0.2 m / s². 3 / h, the side gas is argon, and the flow rate is 1m. 3 / h. Open the negative pressure device to evacuate air to 20mm water column. Simultaneously, introduce carrier gas and open the feeder to add argon gas at a flow rate of 0.2m. 3 The feed rate is 5 g / min. After 2 seconds of reaction, a carbon source, acetylene gas, is introduced into the tail flame of the induced thermal plasma at a flow rate of 0.3 m / s. 3 / h. After the reaction is complete, stop feeding the silicon precursor first, and then stop feeding the carbon source 2 seconds later. The product is then collected in a collector.

[0024] The silicon-carbon nanocomposite material, carbon black, and sodium carboxymethyl cellulose obtained by the above method were thoroughly mixed at a mass ratio of 8:1:1, and the negative electrode slurry was obtained by adjusting the deionized water ratio. The slurry was uniformly coated onto copper foil using a 100 μm doctor blade and dried under vacuum at 80 °C for 10 h to obtain the negative electrode sheet. Finally, lithium metal was used as the counter electrode, a polypropylene membrane as the separator, and LiPF6 (LX-025) with a molar concentration of 1 mol / L was used as the electrolyte. A button cell was assembled in an argon glove box, and its electrochemical performance was tested. The charge / discharge voltage range was 0.01 V–3.0 V, and the current density was 0.1 C. Figure 5The graph shows the cycling performance of the silicon-carbon nanocomposite material obtained in Example 1. The initial discharge specific capacity of the silicon-carbon nanocomposite material is 2626.74 mAh / g, the charge specific capacity is 2128.81 mAh / g, and the coulombic efficiency of the first cycle is 81.04%. After 100 cycles, the capacity remains at 1127.81 mAh / g, with a single-cycle coulombic efficiency as high as 98%.

[0025] Example 2

[0026] The induction thermal plasma reactor is 10 kW. First, silicon powder with a particle size of 40 μm is placed in the feeder of the induction thermal plasma reactor. A central gas (argon) and a side gas are introduced at a flow rate of 0.5 m / s². 3 / h, the side gas is argon, and the flow rate is 1.5m. 3 / h. Open the negative pressure device to evacuate air to 30mm water column. Simultaneously, introduce carrier gas and open the feeder to add argon gas at a flow rate of 0.8m. 3 The feed rate is 10 g / min. After 2 seconds of reaction, a carbon source, acetylene gas, is introduced into the tail flame of the induction thermal plasma at a flow rate of 0.2 m / s. 3 / h. After the reaction is complete, stop feeding the silicon precursor first, and then stop feeding the carbon source 2 seconds later. The product is then collected in a collector.

[0027] Example 3

[0028] The induction thermal plasma reactor is 10 kW. First, silicon powder with a particle size of 30 μm is placed in the feeder of the induction thermal plasma reactor. A central gas (argon) and a secondary gas (argon gas) are introduced at a flow rate of 1 m / s². 3 / h, the side gas is argon, and the flow rate is 2m. 3 / h. Open the negative pressure device to evacuate air to 40mm water column. Simultaneously, introduce carrier gas and open the feeder to add argon gas at a flow rate of 1m. 3 The feed rate is 15 g / min. After 2 seconds of reaction, a carbon source, acetylene gas, is introduced into the tail flame of the induction thermal plasma at a flow rate of 0.1 m / s. 3 / h. After the reaction is complete, stop feeding the silicon precursor first, and then stop feeding the carbon source 2 seconds later. The product is then collected in a collector.

Claims

1. A method for preparing a lithium-ion battery negative electrode slurry, characterized in that: First, carbon-silicon nanocomposites are synthesized in situ using induced thermal plasma, specifically including the following steps: (1) A medium gas and a side gas are introduced into the induction thermal plasma device, and a negative pressure device is turned on to form a stable induction thermal plasma; the power of the induction thermal plasma device is 10-100 KW, the medium gas is argon, and the flow rate of the medium gas is 0.2-5 m³ / h. 3 / h; the edge gas is argon, and the edge gas flow rate is 0.2-8 m³ / h. 3 / h; the negative pressure range of the negative pressure device is 20-200 mm water column; (2) Micron-sized silicon powder is used as a precursor; the particle size of the micron-sized silicon powder is 20-100 μm; (3) The carrier gas axially carries the silicon precursor into the induction thermal plasma device described in step (1) for reaction. The carrier gas is argon, and the carrier gas flow rate is 0.1-2 m³ / h. 3 / h, feeding rate is 5-50 g / min; (4) After delivering the silicon precursor for 2 seconds, a carbon source, which is methane or acetylene, is simultaneously delivered to the tail flame region of the induction thermal plasma described in step (1), with a carbon source flow rate of 0.05-1 m³ / s. 3 / h; (5) After the reaction is complete, stop the delivery of silicon precursor first, and then stop the delivery of carbon source after 2 s. The product enters the collector for collection to obtain carbon silicon nanocomposite material. The obtained carbon-silicon nanocomposite material has a nanowire structure, with carbon uniformly coated on the silicon nanowires, and the nanowire diameter is 10-50 nm. Then, the obtained carbon-silicon nanocomposite material, carbon black, and sodium carboxymethyl cellulose are thoroughly mixed at a mass ratio of 8:1:1, and the negative electrode slurry is obtained by adjusting the proportion of deionized water.

2. The lithium-ion battery negative electrode slurry prepared according to the method of claim 1.

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