Method for preparing silicon-carbon negative electrode and regulating and controlling floating silicon on line

Abstract

The invention belongs to the technical field of material preparation, and particularly relates to a silicon-carbon negative electrode preparation and online floating silicon regulation and control method, which comprises the following steps: S1, preparing a silicon-carbon material by using a fluidized bed reactor; s2, online floating silicon regulation and control: S21, monitoring the concentration of a silicon element in tail gas discharged by the fluidized bed reactor in real time; s22, comparing the concentration value of the silicon element monitored in real time with a preset concentration threshold value; s23, adjusting process parameters of the fluidized bed reactor in real time according to a comparison result; and floating silicon on the surface of the porous carbon is prevented. According to the method disclosed by the invention, automatic early warning and prompting can be carried out before critical floating silicon of porous carbon, and a silicon deposition process is adjusted and optimized according to a real-time detection result of tail gas components (such as the content of a silicon element), so that floating silicon of a silicon-carbon material is improved, the product quality and the yield are improved, and the production cost is reduced.

Description

Technical Field

[0001] This invention relates to the field of materials preparation technology, specifically to a method for preparing silicon-carbon anodes and controlling online silicon floating. Background Technology

[0002] Silicon-carbon anode materials, due to their significantly higher theoretical specific capacity than traditional graphite, have become one of the key manufacturing materials for next-generation high-energy-density lithium-ion batteries. Among the various material production processes, chemical vapor deposition based on fluidized bed reactors is widely used to prepare silicon-carbon composite materials because it can achieve uniform heating and coating of particles. The standard process is as follows: a porous carbon support (such as biomass-based or resin-based carbon materials) is placed in a fluidized bed reactor, heated under an inert atmosphere, and silane gas (such as SiH4) is introduced to thermally decompose the silane. The resulting nano-silicon, under ideal conditions, will preferentially embed into the micropores / mesopores of the porous carbon support. This can effectively buffer the huge volume expansion of silicon during charge and discharge, thereby improving the cycle stability of the material. Finally, carbon source gases such as acetylene and ethylene are introduced to coat the surface with carbon, thereby enhancing conductivity and stabilizing the interface.

[0003] However, existing fluidized bed CVD technology also has significant drawbacks in practical applications, namely, the difficulty in real-time monitoring and effective control of the "floating silicon" phenomenon on the surface of porous carbon supports. "Floating silicon" refers to the failure of nano-silicon to effectively embed within the pores of the support, instead depositing directly on the outer surface of the carbon support particles. The presence of floating silicon leads to a series of adverse consequences, resulting in deterioration of material performance. For example, direct contact between surface floating silicon and the electrolyte can easily cause side reactions, leading to a decrease in initial coulombic efficiency. Simultaneously, the unconstrained volume expansion of floating silicon during cycling can damage the electrode structure, drastically shortening battery life. Furthermore, the specific situation of floating silicon can usually only be confirmed after batch production, through time-consuming and lagging characterization methods such as offline sample extraction and scanning electron microscopy. During production, operators often rely on experience, roughly and indirectly judging whether silane is excessive by observing phenomena such as "white smoke" or "sparks" in the exhaust gas, lacking precise quantitative indicators. This method of judgment, which relies on human experience and is subject to lag, is prone to reducing the utilization rate of silicon source gas (some silanes are discharged without participating in the deposition) and cannot avoid product defects caused by floating silicon, resulting in a low final product qualification rate and high production costs.

[0004] While some existing technologies exist for optimizing online monitoring of CVD processes, such as CN103710684A which discloses an integrated online monitoring system for chemical vapor deposition reactions, this system integrates mass spectrometers, chromatographs, and other equipment to monitor parameters such as temperature, pressure, and gas concentration within the reactor in real time and achieves PID-based feedback control. However, such systems primarily focus on macroscopic monitoring and stabilization of the basic physical and chemical parameters of the reaction environment, and their functions are general-purpose. They do not address the core issue of predicting and controlling "floating silicon," a unique characteristic of silicon-carbon anode material preparation. Specifically, this system does not establish a correlation model between the exhaust gas composition and the internal deposition state of the porous carbon support, thus failing to provide early warning of critical floating silicon states and unable to accurately and automatically intervene in the silicon deposition process.

[0005] Therefore, there is an urgent need in this field for a method that can monitor and provide early warning of the floating silicon state during the preparation of silicon-carbon materials in real time and online, so as to achieve precise closed-loop control of the silicon deposition process and fundamentally improve product quality and production efficiency. Summary of the Invention

[0006] The purpose of this invention is to overcome the above-mentioned shortcomings of the prior art and provide a method for preparing silicon-carbon anodes and controlling online silicon floating, which can automatically provide early warning and prompts before the critical silicon floating of porous carbon, and adjust and optimize the silicon-carbon anode preparation process based on the real-time detection results of exhaust gas composition.

[0007] The technical solution adopted in this invention is: a method for preparing silicon-carbon anodes and controlling online silicon floating, comprising the following steps: S1. Preparation of silicon-carbon materials using a fluidized bed reactor; S2, Online Control: S21. Real-time monitoring of silicon concentration in the exhaust gas emitted from the fluidized bed reactor; S22. Compare the real-time monitored silicon concentration value with the preset concentration threshold; S23. Adjust the process parameters of the fluidized bed reactor in real time based on the comparison results to prevent the formation of floating silicon.

[0008] Furthermore, in step S22, the preset concentration threshold includes a first threshold and a second threshold, wherein the second threshold is greater than the first threshold. The preset concentration threshold is set according to the specific process production conditions.

[0009] Furthermore, step S23 specifically includes: if the silicon element concentration is lower than the first threshold, then maintaining the current process parameters to continue deposition; if the silicon element concentration is not lower than the first threshold but does not exceed the second threshold, then issuing a warning signal; if the silicon element concentration exceeds the second threshold, then cutting off the introduction of silane gas or significantly reducing its flow rate.

[0010] Furthermore, in step S21, the change in hydrogen concentration in the exhaust gas is also monitored, and the hydrogen concentration can reflect the sufficiency of silane decomposition.

[0011] Furthermore, in step S2, an online high-precision exhaust gas composition analyzer is used to sample, detect, and analyze the components in the exhaust gas discharge pipe of the fluidized bed reactor online. Preferably, the online high-precision exhaust gas composition analyzer detects components in the exhaust gas including silicon element concentration (content), hydrogen concentration, etc., and feeds the data back to the automatic control system of the entire fluidized bed process in real time. All data are recorded in real time, and the recorded data are compared with the floating silicon situation in material characterization to record the corresponding relationship.

[0012] Furthermore, three points were selected as sampling points on the exhaust gas duct: near the dilute phase section, in the middle section, and near the exhaust port. The exhaust gas was collected at these sampling points using a pump-suction method, and the silicon concentration was analyzed. The silicon concentration value Y was taken as the average of the three sampling points. The silicon concentration was calculated for all undecomposed SiH4 and insufficiently decomposed SiH4 (SiH3+, SiH2). 2+ SiH 3+ The silicon element is found in nano-silicon (n-Si) and silicon oxide. Preferably, the online high-precision exhaust gas composition analyzer can also monitor changes in hydrogen concentration, which can reflect the sufficiency of silane decomposition.

[0013] Furthermore, before executing step S1, step S0 is performed first: establishing a mathematical model between the silane gas flow rate and the silicon concentration in the tail gas. Preferably, the mathematical model is a linear model Y = aX + b, where Y is the predicted silicon concentration in the tail gas, X is the silane gas flow rate, and a and b are model parameters obtained by fitting historical process data. That is, a large number of process test experiments are conducted in advance to collect relevant parameters such as nitrogen flow rate, silane flow rate, hydrogen concentration in the tail gas, and silicon concentration in the tail gas, to find the correspondence between the composition data in the tail gas and the floating silicon state of the silicon-carbon material. The experimental conditions are set to specific silane decomposition temperature and total fluidizing gas volume, and the corresponding test data are linearly fitted to obtain the linear equation Y = aX + b.

[0014] Furthermore, step S1 specifically includes the following operations: S11. The porous carbon carrier is transported to the material storage tank under negative pressure, and the oxygen content is replaced by an inert atmosphere to be less than 100 ppm. S12. The porous carbon support is transported into the fluidized bed reactor furnace under positive nitrogen pressure. After the oxygen content is replaced by nitrogen and the oxygen content is lowered to below 30 ppm, the temperature is increased according to the set program. Nitrogen and silane are introduced at 400-500℃, so that the silane decomposes and embeds nano-silicon inside the porous carbon support. The temperature of 400-500℃ can ensure the decomposition efficiency of silane. The deposited nano-silicon has an amorphous structure. In this temperature range, the nanoparticles formed by the decomposition of silane are smaller and easier to embed inside the porous carbon, which improves the expansion characteristics of the material during the electrochemical cycle.

[0015] S13. Continue heating to 500-600℃, introduce nitrogen gas, and coat the nano-carbon layer on the surface of nano-silicon with acetylene / ethylene. The temperature is selected at 500-600℃. If the carbon coating temperature is too high, it will cause silicon to crystallize. Acetylene / ethylene has a high decomposition efficiency in this temperature range, which can effectively achieve carbon coating on the surface of nano-silicon, improve the conductivity of the material, and achieve isolation from air to ensure the stability of the material in an air atmosphere.

[0016] Furthermore, in step S1, the silane flow rate ranges from 0.5 to 80 L / min, the acetylene flow rate ranges from 1.0 to 60 L / min, and the nitrogen flow rate ranges from 5.0 L / min to 300 L / min, matching the fluidized bed capacity of 3.0 to 100 kg / furnace. Specifically, to ensure uniform fluidization of materials within the reactor and safe operation of the equipment, the concentration ranges for silane, acetylene, and ethylene are selected as 5.0% to 60.0%, and the fluidizing gas flow rate ranges from 15 L / min to 300 L / min.

[0017] The advantages of this invention compared to the prior art are as follows: 1. The method in this invention can automatically provide early warning and prompts before the critical floating of porous carbon silicon, and adjust and optimize the silicon deposition process based on the real-time detection results of the tail gas composition (hydrogen concentration, silicon content). The adjustable process includes silane flow rate, fluidizing gas flow rate, deposition temperature, etc. 2. This invention can improve the floating silicon situation of silicon-carbon materials, improve product quality and yield, and reduce production costs; it can significantly reduce the amount of floating silicon in silicon-carbon material particles, and the carrier can be selected as biomass / resin-based, with a designed silicon content of 45-48%, an initial capacity of 1850-1950mAh / g, reduced full electrode sheet expansion in the first cycle (<70%), and significantly improved cycle performance. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the process in an embodiment of the present invention, in which silicon element concentration is selected as the change quantity to feedback the state of floating silicon. Figure 2 This is a schematic diagram of linear fitting using corresponding test data under certain experimental conditions in an embodiment of the present invention; Figure 3 This is a schematic diagram of the silicon-carbon anode preparation and online silicon floating control system used in the embodiments of the present invention; Figure 4 This is an electron microscope image of a porous carbon surface with a large amount of floating silicon in an embodiment of the present invention; Figure 5 This is a schematic diagram of the specific capacity of silicon-carbon materials in different floating silicon states in embodiments of the present invention; Figure 6 This is a schematic diagram of the differential capacitance curves of silicon-carbon anodes in different floating silicon states in embodiments of the present invention. Detailed Implementation

[0019] To make the objectives, technical solutions and advantages of the present invention clearer, descriptions of well-known structures and technologies are omitted in the following description in order to avoid unnecessarily obscuring the concepts in the present invention. Example

[0020] The method for preparing silicon-carbon anodes and controlling online silicon floating in this embodiment can be adopted as follows: Figure 3 The carbon anode fabrication system shown uses silicon elemental concentration as a feedback mechanism to assess the state of the porous carbon-supported silicon (the feedback process is as follows). Figure 1 As shown), the specific steps include: S1. Preparation of silicon-carbon materials using a fluidized bed reactor: S11. The porous carbon carrier (biomass-based / resin-based) is transported to the material storage tank under negative pressure and the oxygen content is replaced by an inert atmosphere to be less than 100 ppm. S12. The porous carbon support is transported into the fluidized bed reactor furnace under positive nitrogen pressure. After the oxygen content is replaced by nitrogen and the oxygen content is lower than 30ppm, the temperature is increased according to the set program. Nitrogen and silane are introduced at 400-500℃, so that the silane decomposes and embeds nano-silicon inside the porous carbon support. S13. Continue heating to 500-600℃, and introduce nitrogen gas and acetylene / ethylene to coat the nano-carbon layer on the nano-silicon surface. In the above process: the flow rate of silane is 0.5-80L / min, the flow rate of acetylene is 1.0-60L / min, the flow rate of nitrogen is 5.0L / min-300L / min, and the flow rate matches the fluidized bed capacity of 3.0-100KG / furnace.

[0021] S2, Online Control: S21. Real-time monitoring of silicon concentration in the exhaust gas emitted from the fluidized bed reactor; online high-precision exhaust gas composition analyzer for online sampling, detection, and analysis of components in the exhaust gas pipeline of the fluidized bed reactor. Three points are selected as sampling points on the exhaust gas pipeline, namely near the dilute phase section, the middle section, and near the exhaust port. The exhaust gas is collected by pump suction at the sampling points and the silicon concentration is analyzed. The silicon concentration value Y is the average value of the three sampling points. S22. Compare the real-time monitored silicon concentration value with a preset concentration threshold; the preset concentration threshold includes a first threshold and a second threshold, wherein the second threshold is greater than the first threshold; S23. Adjust the process parameters of the fluidized bed reactor in real time according to the comparison results to prevent the formation of floating silicon; specifically including: if the silicon concentration is lower than the first threshold, maintain the current process parameters and continue deposition; if the silicon concentration reaches or exceeds the first threshold but is lower than the second threshold, issue a warning signal; if the silicon concentration reaches or exceeds the second threshold, cut off the introduction of silane gas or significantly reduce its flow rate, or reduce the temperature of the reaction equipment, etc.

[0022] Before performing step S1, step S0 is also included: establishing a mathematical model between the silane gas flow rate and the silicon concentration in the tail gas. Specifically, this involves conducting numerous process testing experiments beforehand, under specific silane decomposition temperatures and total fluidized gas volumes; collecting data such as nitrogen flow rate, silane flow rate, hydrogen concentration in the tail gas, and silicon concentration in the tail gas; and identifying the correspondence between the tail gas composition data and the floating silicon state of the silicon-carbon material. In this embodiment, the test data for 3-100KG fluidized beds were fitted (e.g., ...). Figure 2 As shown in Table 1), the linear equation obtained is: Y = aX + b; where Y is the silicon concentration in the exhaust gas (ppm) and X is the silane flow rate (L / min); Y = aX + b is the relationship between the silane flow rate and the silicon content in the exhaust gas.

[0023]

[0024] The preset concentration threshold is set according to the specific process production conditions; for example, in this embodiment, the first threshold is set to 10 ppm and the second threshold is set to 50 ppm. Therefore, silicon-carbon material testing is performed under the conditions of Y < 10 ppm, 10 ppm ≤ Y ≤ 50 ppm, and 50 ppm < Y. When Y < 10 ppm, the amount of silicon floating on the porous carbon surface is relatively small. As the Y value increases, the amount of floating silicon increases, especially when 50 ppm < Y, the floating silicon is significant, and a large number of silicon particles (such as...) appear on the porous carbon surface. Figure 4 As shown); electrochemical performance tests showed initial improvements in reversible capacity and efficiency (e.g. Figure 5As shown in Table 2), the sample expands and increases (as shown in Table 2), and the differential capacitance curves of silicon-carbon anodes in different floating silicon states (as shown in Table 2) are also presented. Figure 6 (As shown).

[0025]

[0026] The above are only some embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various combinations and modifications of the aforementioned technical features. Any improvements, modifications, equivalent substitutions, or applications of the structure or method of the present invention to other fields to achieve the same effect without departing from the spirit and scope of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for preparing silicon-carbon anodes and controlling online silicon floating, characterized in that, Includes the following steps: S1. Preparation of silicon-carbon materials using a fluidized bed reactor; S2, Online Floating Silicon Control: S21. Real-time monitoring of silicon concentration in the exhaust gas emitted from the fluidized bed reactor; S22. Compare the real-time monitored silicon concentration value with the preset concentration threshold; S23. Adjust the process parameters of the fluidized bed reactor in real time based on the comparison results; To prevent the formation of floating silicon.

2. The method for preparing silicon-carbon anodes and controlling online silicon floating as described in claim 1, characterized in that: In step S22, the preset concentration threshold includes a first threshold and a second threshold, wherein the second threshold is greater than the first threshold.

3. The method for preparing silicon-carbon anodes and controlling online silicon floating as described in claim 2, characterized in that: Step S23 specifically includes: If the silicon concentration is lower than the first threshold, the current process parameters are maintained and deposition continues. If the silicon concentration is not lower than the first threshold but does not exceed the second threshold, a warning signal is issued; If the silicon concentration exceeds the second threshold, the flow of silane gas is cut off or its flow rate is reduced.

4. The method for preparing a silicon-carbon anode and controlling online silicon floating as described in claim 1, characterized in that: Step S21 also includes a step of monitoring changes in hydrogen concentration in the exhaust gas.

5. The method for preparing a silicon-carbon anode and controlling online silicon floating as described in claim 1, characterized in that: In S2, an online high-precision exhaust gas composition analyzer is used to sample, detect, and analyze the components in the exhaust gas emission pipe of the fluidized bed reactor online.

6. The method for preparing a silicon-carbon anode and controlling online silicon floating as described in claim 5, characterized in that: Three points were selected on the exhaust pipe as sampling points, namely near the dilute phase section, the middle section, and near the exhaust port. The exhaust gas was collected by pumping at the sampling points and the silicon concentration was analyzed. The silicon concentration value was the average value of the three sampling points.

7. The method for preparing a silicon-carbon anode and controlling online silicon floating as described in claim 1, characterized in that: Before performing step S1, step S0 is performed first: establishing a mathematical model between the silane gas flow rate and the silicon concentration in the tail gas.

8. The method for preparing silicon-carbon anodes and controlling online silicon floating as described in claim 7, characterized in that: The mathematical model is a linear model Y = aX + b, where Y is the predicted concentration of silicon in the exhaust gas, X is the silane gas flow rate, and a and b are model parameters obtained by fitting historical process data.

9. The method for preparing a silicon-carbon anode and controlling online silicon floating according to claim 1, characterized in that, Step S1 specifically includes: S11. The porous carbon carrier is transported to the material storage tank under negative pressure, and the oxygen content is replaced by an inert atmosphere to be less than 100 ppm. S12. The porous carbon support is transported into the fluidized bed reactor furnace under positive nitrogen pressure. After the oxygen content is replaced by nitrogen and the oxygen content is lower than 30ppm, the temperature is increased according to the set program. Nitrogen and silane gas are introduced at 400-500℃, so that the silane gas decomposes and embeds nano-silicon inside the porous carbon support. S13. Continue heating to 500-600℃, and introduce nitrogen gas and acetylene / ethylene to coat the nano-carbon layer on the nano-silicon surface.

10. The method for preparing a silicon-carbon anode and controlling online silicon floating according to claim 9, characterized in that, In step S1: the flow rate of silane gas is 0.5-80 L / min, the flow rate of acetylene is 1.0-60 L / min, and the flow rate of nitrogen is 5.0 L / min-300 L / min, matching the fluidized bed capacity of 3.0-100 KG / furnace.

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