Preparation method of high-safety silicon-carbon negative electrode

Abstract

The invention provides a preparation method of a high-safety silicon-carbon negative electrode, and relates to the technical field of lithium ion battery silicon-carbon negative electrode materials. The method comprises the following steps: adding porous carbon into a fluidized bed reactor through a feeding device, heating the reactor to a required temperature, and introducing fluidizing gas and silicon source gas to carry out deposition reaction; after the deposition reaction of the nano silicon is completed, stopping the silicon source gas, and switching to the protective gas to purge the pipeline and the reactor; raising the temperature to the temperature required by the reaction of the carbon source gas, keeping the temperature, and reducing the flow of the fluidizing gas; introducing a carbon source gas into the reactor at a relatively low flow rate; and increasing the flow of carbon source gas and fluidizing gas. According to the invention, the problem of poor safety in the CVD silicon-carbon negative electrode synthesis process is radically analyzed, and the method is provided from the aspect of process synthesis, so that the occurrence of a large number of side reactions in the material synthesis process is avoided, and various properties of the silicon-carbon negative electrode material are slightly improved while the safety in the production process is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of silicon-carbon negative electrode materials for lithium-ion batteries, and in particular to a method for preparing a highly safe silicon-carbon negative electrode. Background Art

[0002] With the trend towards increasingly high energy density in lithium-ion batteries, traditional graphite anodes are gradually unable to meet the performance requirements of future batteries. In recent years, silicon has been a research hotspot for anode materials and has attracted much attention due to its excellent lithium storage capacity. Silicon materials have an extremely high theoretical specific capacity (4200mAh / g) during the charging process, far exceeding the 372mAh / g of graphite. However, silicon undergoes a volume expansion of up to 300% during the lithium insertion process, resulting in structural fractures and a sharp decline in capacity, which limits the practical application of silicon-based materials in batteries. How to effectively control the volume effect of silicon and improve cycle stability has become the key to the research and development of high-performance silicon-based anode materials.

[0003] Against this backdrop, researchers are continuously developing novel silicon-carbon anodes to address this challenge. After several generations of evolution, the third generation of silicon-based anode materials is currently the dominant type. The primary method involves chemical vapor deposition (CVD) of organic gases containing silicon atoms into the pores of a porous carbon matrix that meets the requirements. These gases are then in situ cracked at high temperatures to form amorphous silicon nanoparticles. This technique offers the advantage of maximizing control over the size of the silicon nanoparticles through pre-designed pores, allowing for precise control of the microstructure of the silicon-carbon composite. Compared to traditional silicon-carbon materials, silicon-carbon composites prepared by chemical vapor deposition effectively reduce the structural damage of silicon during cycling, while also improving electrical conductivity and interfacial stability. In summary, CVD-prepared silicon-carbon composites, thanks to their innovative and controllable structural design, demonstrate unique advantages in improving the specific capacity and cycle life of lithium batteries. This innovative research not only meets the demands of today's high-performance lithium batteries but also paves the way for the development of intelligent energy storage technologies.

[0004] Since a large amount of organic gas is used in the preparation process of CVD silicon-carbon negative electrode, there are great safety hazards in the production process. The main reason is that the exothermic reaction occurs at high temperature during the switching process between silicon-containing organic gas and carbon-containing organic gas, causing the internal pressure of the reactor to rise rapidly, thereby bringing production risk problems such as explosion.

[0005] The Chinese patent with publication number CN118621304A discloses a method for preparing silicon-carbon negative electrodes by heat-extraction chemical vapor deposition. The method mainly adds a heat-extraction component around the reactor, uses a temperature measuring element to detect the temperature change in the reactor, and when a sudden increase in the temperature in the reactor is detected, increases the working flow of the heat-extraction component to ensure that the reactor temperature is in a constant temperature state. This method controls the temperature of the reaction that has already occurred from the perspective of the equipment, but does not prevent the occurrence of violent reactions from the root. Therefore, how to effectively avoid the sudden occurrence of high temperature and high pressure in the reactor from a process perspective, while also ensuring the stability of the performance of the silicon-carbon negative electrode material, is a technical problem that urgently needs to be solved. Summary of the Invention

[0006] In response to the above problems, the present invention provides a highly safe method for preparing a silicon-carbon negative electrode. The flow rate of the silicon source gas and the carbon source gas in the conversion stage is reduced through a segmented process, and a protective gas is introduced before the conversion gas to purge the pipeline and reactor, thereby significantly improving the safety of the silicon-carbon negative electrode preparation process. At the same time, the obtained silicon-carbon negative electrode has good performance.

[0007] The object of the present invention is to provide a method for preparing a highly safe silicon-carbon negative electrode.

[0008] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are adopted:

[0009] The present invention provides a method for preparing a highly safe silicon-carbon negative electrode, comprising the following steps:

[0010] S1. Add porous carbon into a fluidized bed reactor through a feeding device, heat the reactor to a desired temperature, and introduce fluidizing gas and silicon source gas to carry out a deposition reaction;

[0011] S2. After the nano-silicon deposition reaction is completed, the silicon source gas is stopped and switched to the protective gas to purge the pipeline and reactor;

[0012] S3, raising the temperature to the temperature required for the carbon source gas reaction, maintaining the temperature, and reducing the fluidizing gas flow rate;

[0013] S4, introducing the carbon source gas into the reactor at a relatively low flow rate;

[0014] S5. Increase the flow rates of the carbon source gas and the fluidizing gas to obtain a silicon-carbon negative electrode material.

[0015] The inventors have analyzed and found that during the production and preparation of CVD silicon-carbon anodes, the reasons for the major safety risks in the reactor are:

[0016] During the switching process, residual gases may remain in the pipelines or reactors. If silane and acetylene are not completely purged during the switching process, they can react dangerously at high concentrations, resulting in high temperatures or explosions. Both silane and acetylene decompose and release significant heat, further exacerbating the severity of the reaction.

[0017] Fluidized bed reactors typically contain high-surface-area carbon particles, which readily adsorb gases. The silicon layer or byproducts formed by silane decomposition on the surface can react with acetylene during the switch to acetylene, leading to uncontrolled chemical reactions. Furthermore, unreacted silicide or silicon source gas may remain on the surface of the carbon particles, triggering side reactions when switching to acetylene.

[0018] Since the size of the nano-silicon deposited in the pores of porous carbon is very small (<10nm), the proportion of surface atoms is high, the uncoordinated atoms are more active and chemically more reactive, and it is easier to react chemically with acetylene than micron silicon, releasing a large amount of heat and causing the temperature and pressure inside the reactor to rise.

[0019] The present invention adopts corresponding process methods to address the safety issues of fluidized bed process:

[0020] For the residual silicon source gas in the pipeline and reactor, switch to high-purity inert protective gas for thorough purging to ensure that the residual silicon source gas is completely removed.

[0021] The silicon source gas adsorbed by the carbon base material and the unreacted silicide are kept warm under the condition of higher carbon source gas temperature requirement to ensure their full reaction, and the fluidizing gas flow rate is reduced to control the fluidization velocity of the particles and the accumulation of static electricity.

[0022] First, a low-flow carbon source gas is introduced to form a stable coating layer, and then the carbon source gas flow rate is increased to improve the coating efficiency.

[0023] In some embodiments, the specific surface area of ​​the porous carbon in step S1 is 1400-2000 m 2 / g, pore volume of 0.5-2.2cm 3 / g, pore size is 1-10nm, and particle size D50 is 5-9μm.

[0024] In some embodiments, the fluidizing gas in step S1 is liquid nitrogen.

[0025] In some embodiments, the silicon source gas in step S1 is one or more of silane, disilane, trisilane, tetrasilane, dichlorosilane, trichlorosilane, and tetrachlorosilane.

[0026] In some embodiments, in step S1, the reactor temperature is 400-800° C., the fluidizing gas flow rate is 10-20 L / min, the silicon source gas flow rate is 2-5 L / min, and the introduction time is 200-500 min.

[0027] In some embodiments, the protective gas in step S2 is one or more of nitrogen, argon, helium, neon, and krypton.

[0028] In some embodiments, the protective gas flow rate in step S2 is 2-5 L / min, and the introduction time is 20-60 min.

[0029] In some embodiments, the carbon source gas in step S3 is one or more of methane, propane, acetylene, and cyclohexane.

[0030] In some embodiments, in step S3, the temperature is raised to 500-900° C., the holding time is 20-60 min, and the fluidizing gas flow rate is reduced to 5-10 L / min.

[0031] In some embodiments, the carbon source gas flow rate in step S4 is 0.5-1.5 L / min, and the introduction time is 20-60 min.

[0032] In some embodiments, in step S5, the flow rate of the fluidizing gas is increased to 10-20 L / min, the flow rate of the carbon source gas is increased to 2-5 L / min, and the introduction time is 50-150 min.

[0033] Beneficial effects:

[0034] The present invention conducts a root cause analysis of the poor safety problem in the CVD silicon-carbon negative electrode synthesis process, proposes a method from the perspective of process synthesis, avoids the occurrence of a large number of side reactions during the material synthesis process, and slightly improves the various performances of the silicon-carbon negative electrode material while improving the safety of the production process.

[0035] The present invention has been described in detail above, but the above embodiments are merely illustrative in nature and are not intended to limit the present invention. In addition, the present invention is not limited by any theory described in the above prior art or invention summary or the following examples. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is the XRD pattern of the silicon-carbon negative electrode prepared in Example 1;

[0037] Figure 2 This is the XRD pattern of the silicon-carbon negative electrode prepared in Example 2;

[0038] Figure 3 This is the XRD pattern of the silicon-carbon negative electrode prepared in Example 3;

[0039] Figure 4 This is the XRD pattern of the silicon-carbon negative electrode prepared in Comparative Example 1;

[0040] Figure 5 This is the XRD pattern of the silicon-carbon negative electrode prepared in Comparative Example 2;

[0041] Figure 6 This is the XRD pattern of the silicon-carbon negative electrode prepared in Comparative Example 3. DETAILED DESCRIPTION

[0042] The present invention will be further described below with reference to the examples. It should be noted that the following examples are provided for illustrative purposes only and do not constitute a limitation on the scope of protection claimed in the present invention.

[0043] Unless otherwise specified, the raw materials, reagents, methods, etc. used in the examples are conventional raw materials, reagents, and methods in the art.

[0044] The specific surface area of ​​the porous carbon in the embodiment of the present invention is analyzed by BET, and the pore volume and pore diameter are analyzed by DFT.

[0045] The gram capacity and first coulombic efficiency of the obtained silicon-carbon negative electrode were analyzed using a button cell 2032, in which the counter electrode was a lithium metal sheet and the current collector was a copper foil.

[0046] Battery slurry ratio:

[0047] Silicon carbon:Super P:CMC:SBR=8:1:0.5:0.5;

[0048] Button Cell Battery Testing Procedure:

[0049] After standing for 10 hours, discharge at 0.05C to 0.005V;

[0050] Let it stand for 10 minutes, then discharge at 0.01C to 0.005V;

[0051] Let it stand for 10 minutes, then charge at 0.05C to 1.5V;

[0052] Let it stand for 10 minutes, jump to step 2, and repeat for 5 weeks.

[0053] The electrolyte formula is:

[0054] EC:EMC:DMC=1:1:1, LiPF6=1mol / L, 5%FEC.

[0055] Example 1

[0056] The preparation method of the silicon-carbon negative electrode comprises the following steps:

[0057] Step 1: Set the specific surface area to 1900m2 / g, pore volume 0.8cm 3 / g, an average pore size of 1.8nm, and 500g of commercial porous carbon with D50=6.8μm were put into the feeding device of a fluidized bed reactor (model: FBCVD100). The reactor was heated to 480℃ at 5℃ / min, and liquid nitrogen was introduced from the bottom of the equipment at a flow rate of 15L / min. After heating to 480℃, silane gas was introduced at a flow rate of 3L / min for 200min.

[0058] Step 2: After the reaction time is over, stop the silane gas and introduce high-purity nitrogen at a flow rate of 3 L / min for 45 minutes.

[0059] Step 3: Stop the high-purity nitrogen, raise the temperature to 680°C and keep it for 45 minutes, and adjust the liquid nitrogen flow rate to 10L / min.

[0060] Step 4: A mixture of acetylene and methane in a ratio of 3:1 was introduced into the reactor at a flow rate of 0.5 L / min for 45 min.

[0061] Step 5: Restore the liquid nitrogen flow rate to 15 L / min, increase the flow rate of the acetylene and methane mixture to 2 L / min, and pass it for 80 minutes.

[0062] Example 2

[0063] Step 1: Same as Example 1.

[0064] Step 2: After the reaction time is over, stop the silane gas and introduce high-purity nitrogen at a flow rate of 2 L / min for 30 minutes.

[0065] Step 3: Stop the high-purity nitrogen, raise the temperature to 680°C and keep it for 30 minutes, and adjust the liquid nitrogen flow rate to 10L / min.

[0066] Step 4: A mixture of acetylene and methane in a ratio of 3:1 was introduced into the reactor at a flow rate of 1 L / min for 30 min.

[0067] Step 5: Restore the liquid nitrogen flow rate to 15 L / min, increase the flow rate of the acetylene and methane mixture to 2 L / min, and pass it for 80 minutes.

[0068] Example 3

[0069] Step 1: Same as Example 1.

[0070] Step 2: After the reaction time is over, stop the silane gas and introduce high-purity nitrogen at a flow rate of 1 L / min for 15 minutes.

[0071] Step 3: Stop the high-purity nitrogen gas, raise the temperature to 680°C and keep it for 15 minutes, and adjust the liquid nitrogen flow rate to 10L / min.

[0072] Step 4: A mixture of acetylene and methane in a ratio of 3:1 was introduced into the reactor at a flow rate of 1.5 L / min for 15 min.

[0073] Step 5: Restore the liquid nitrogen flow rate to 15 L / min, increase the flow rate of the acetylene and methane mixture to 2 L / min, and pass it for 80 minutes.

[0074] Comparative Example 1

[0075] Compared with Example 1, step 2 is eliminated and the remaining steps are the same, including:

[0076] Step 1: Same as Example 1.

[0077] Step 2: Heat to 680°C and keep warm for 45 minutes. Adjust the liquid nitrogen flow rate to 10 L / min.

[0078] Step 3: A mixture of acetylene and methane in a ratio of 3:1 was introduced into the reactor at a flow rate of 0.5 L / min for 45 min.

[0079] Step 4: Restore the liquid nitrogen flow rate to 15 L / min, increase the flow rate of the acetylene and methane mixture to 2 L / min, and pass it for 80 minutes.

[0080] Comparative Example 2

[0081] Compared with Example 1, step 3 is omitted and heat preservation is not performed. The remaining steps are the same. Specifically, they include:

[0082] Step 1: Same as Example 1.

[0083] Step 2: After the reaction time is over, stop the silane gas and introduce high-purity nitrogen at a flow rate of 3 L / min for 45 minutes.

[0084] Step 3: Raise the temperature to 680°C, introduce liquid nitrogen at a flow rate of 10 L / min, and introduce a mixture of acetylene and methane with a ratio of 3:1 into the reactor at a flow rate of 0.5 L / min for 45 minutes.

[0085] Step 4: Increase the liquid nitrogen flow rate to 15 L / min and the flow rate of the acetylene and methane mixture to 2 L / min and flow for 80 minutes.

[0086] Comparative Example 3

[0087] Compared with Example 1, step 4 is eliminated and the remaining steps are the same, including:

[0088] Step 1: Same as Example 1.

[0089] Step 2: After the reaction time is over, stop the silane gas and introduce high-purity nitrogen at a flow rate of 3 L / min for 45 minutes.

[0090] Step 3: Stop the high-purity nitrogen, raise the temperature to 680°C and keep it for 45 minutes, and adjust the liquid nitrogen flow rate to 10L / min.

[0091] Step 4: Increase the liquid nitrogen flow rate to 15 L / min, and introduce a mixture of acetylene and methane with a ratio of 3:1 into the reactor at a flow rate of 2 L / min for 80 min.

[0092] The pressures at the top, middle, and bottom of the reactor were monitored in real time for Examples 1-3 and Comparative Examples 1-3, respectively, and the highest internal pressure during the entire reaction process was recorded. The specific data are shown in the following table:

[0093] Reactor upper part (kpa) Reactor middle (kpa) Reactor lower part (kpa) Example 1 10 8 9 Example 2 12 11 11 Example 3 13 12 11 Comparative Example 1 19 18 19 Comparative Example 2 15 13 14 Comparative Example 3 13 12 12

[0094] From the above table, it can be seen that Example 1 has the lowest reactor pressure throughout the entire process and the best safety. In Example 2, step 2 reduces the purge flow rate and time of high-purity nitrogen as a protective gas, step 3 reduces the high-temperature holding time, and step 4 increases the acetylene gas flow rate to reduce the introduction time. During this process, the reactor pressure increases, indicating that the method of the present invention has a certain help for the safety of the reactor. Example 3 is further adjusted according to the trend of Example 2, and the change in reactor pressure is not obvious. After step 2 is eliminated in comparative example 1, the reactor pressure rises sharply, indicating that the residual silane gas and acetylene gas in the pipeline will seriously affect the safety of the silicon-carbon negative electrode preparation process. After step 3 is eliminated in comparative example 2, the reactor pressure is also high, indicating that the silane molecules adsorbed on the surface of the material and the incompletely reacted silicides also have a certain impact on safety. In comparative example 3, the small amount of acetylene gas in step 4 is eliminated, and the reactor pressure does not rise significantly, but the amorphous silicon after silane deposition crystallizes, indicating that the large flow of acetylene gas and the highly active nano-silicon react and instantly heat up, resulting in silicon crystallization.

[0095]

[0096]

[0097] From the electrical performance results, it can be seen that Example 1 has the highest gram capacity and first coulombic efficiency, followed by Example 2 and Example 3, indicating that the method of the present invention also has a slight advantage in gram capacity and first coulombic efficiency, mainly because the more stable reaction environment has a certain positive effect on the material. The electrical properties of the comparative examples are generally lower than those of the examples, especially the comparative example 1 in which step 2 is eliminated, which has the worst electrical performance, indicating that the protective gas plays a very critical role in the purging of the pipeline.

[0098] As can be seen from the XRD diagram of the accompanying drawings, Examples 1-3 using the method of the present invention do not have obvious silicon crystallization, Comparative Example 1 has obvious crystallization, and Comparative Examples 2 and 3 also have a small amount of crystallization peaks, indicating that the method of the present invention provides relatively stable temperature control during the material synthesis process, and there is no phenomenon of material heating and crystallization due to excessive side reactions.

[0099] The above embodiments are intended only to illustrate the technical solutions of the present invention and are not intended to limit the same. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions described in the above embodiments may be modified, or some or all of the technical features thereof may be replaced with equivalents, without departing from the spirit and substance of the claims of the present invention; and such modifications or replacements remain within the scope of the claims of the present invention.

Claims

1. A method for preparing a highly safe silicon-carbon negative electrode, characterized in that: The following steps are involved: S1. Add porous carbon into a fluidized bed reactor through a feeding device, heat the reactor to a desired temperature, and introduce fluidizing gas and silicon source gas to carry out a deposition reaction; S2. After the nano-silicon deposition reaction is completed, the silicon source gas is stopped and switched to the protective gas to purge the pipeline and reactor; S3, raising the temperature to the temperature required for the carbon source gas reaction, maintaining the temperature, and reducing the fluidizing gas flow rate; S4, introducing the carbon source gas into the reactor at a relatively low flow rate; S5. Increase the flow rates of the carbon source gas and the fluidizing gas to obtain a silicon-carbon negative electrode material.

2. The preparation method according to claim 1, characterized in that The specific surface area of ​​the porous carbon in step S1 is 1400-2000m 2 / g, pore volume of 0.5-2.2cm 3 / g, pore size is 1-10nm, and particle size D50 is 5-9μm.

3. The preparation method according to claim 1, characterized in that In step S1, the fluidizing gas is liquid nitrogen.

4. The preparation method according to claim 1, characterized in that In step S1 , the silicon source gas is one or more of silane, disilane, trisilane, tetrasilane, dichlorosilane, trichlorosilane, and tetrachlorosilane.

5. The preparation method according to claim 1, characterized in that In step S1, the reactor temperature is 400-800° C., the fluidizing gas flow rate is 10-20 L / min, the silicon source gas flow rate is 2-5 L / min, and the introduction time is 200-500 min.

6. The preparation method according to claim 1, characterized in that In step S2, the protective gas is one or more of nitrogen, argon, helium, neon, and krypton.

7. The preparation method according to claim 1, characterized in that In step S2, the protective gas flow rate is 2-5 L / min, and the introduction time is 20-60 min.

8. The preparation method according to claim 1, characterized in that In step S3, the carbon source gas is one or more of methane, propane, acetylene, and cyclohexane; In step S3, the temperature is raised to 500-900° C., the holding time is 20-60 min, and the fluidizing gas flow rate is reduced to 5-10 L / min.

9. The preparation method according to claim 1, characterized in that In step S4, the flow rate of the carbon source gas is 0.5-1.5 L / min, and the introduction time is 20-60 min.

10. The preparation method according to claim 1, characterized in that In step S5, the flow rate of the fluidizing gas is increased to 10-20 L / min, the flow rate of the carbon source gas is increased to 2-5 L / min, and the introduction time is 50-150 min.

Images