Preparation method and application of carbon-coated silicon nanowire negative electrode material

Abstract

The application belongs to the technical field of lithium batteries, and relates to a preparation method and application of a carbon-coated silicon nanowire negative material. The preparation method comprises the following steps: adding micro-sized silicon powder, an iridium source and a solvent into a container, uniformly dispersing, then removing the solvent through oil bath heating and stirring, and further drying; ball milling the obtained mixture, and passing the ball-milled mixture through a 100-300 mesh screen; performing CVD coating on the screened powder, introducing a gaseous carbon source, coating for 1-3 hours at 850-1050 DEG C, passing the coated powder through a 200-450 mesh screen, and obtaining the carbon-coated silicon nanowire negative material. The low-cost raw materials such as the iridium source and the micro-sized silicon are efficiently converted into the silicon nanowire composite negative material, the cost is reduced and the process is simplified, and the silicon nanowire composite negative material is applied to a battery, so that the battery performance can be effectively improved.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery technology and relates to a method for preparing carbon-coated silicon nanowire anode materials and their applications. Background Technology

[0002] As the mainstream energy storage technology, the performance improvement of lithium-ion batteries highly depends on the innovation of electrode materials. In the field of anodes, traditional graphite materials are no longer sufficient to meet the ever-increasing demand for high energy density (such as in electric vehicles and portable electronic devices). Silicon (Si), due to its extremely high theoretical specific capacity, abundant reserves, and moderate lithium intercalation potential, is considered one of the most promising next-generation anode materials.

[0003] However, silicon materials face severe challenges during charge and discharge: lithium-ion insertion / extraction is accompanied by enormous volume expansion / contraction (up to 300% or more). This drastic volume effect easily leads to the pulverization of electrode materials, the stripping of active materials from current collectors or conductive networks, and continuous damage and reconstruction of the solid electrolyte interphase (SEI) film. The result is rapid capacity decay, drastically shortened cycle life, and low coulombic efficiency, severely hindering the commercial application of silicon-based anodes.

[0004] To overcome the volume effect of silicon materials, extensive research has been conducted, developing various strategies for controlling nanostructures, including nanoparticles, nanotubes, nanosheets, and nanowires. Among these, silicon nanowires (SiNWs) structures have shown significant advantages:

[0005] 1. Excellent mechanical properties: One-dimensional nanowires have good mechanical flexibility in the axial direction, which can effectively buffer the stress caused by volume changes and inhibit pulverization;

[0006] 2. Highly efficient ion / electron transport: The nanowires are grown directly or in close contact with the current collector, providing a continuous electron conduction path; their small radial size shortens the lithium-ion diffusion distance.

[0007] 3. Structural stability: The gaps between nanowires provide space for volume expansion, which helps maintain the integrity of the electrode structure.

[0008] Therefore, constructing a silicon-carbon composite anode material containing silicon nanowires is of great significance. Summary of the Invention

[0009] The purpose of this invention is to provide a method for preparing carbon-coated silicon nanowire anode materials and their applications. The following technical solutions are used to achieve this purpose:

[0010] One aspect of the present invention provides a method for preparing a carbon-coated silicon nanowire anode material, comprising the following steps:

[0011] (1) Add micron-sized silicon powder, iridium source and solvent to the container, disperse evenly, then heat and stir in an oil bath to remove the solvent, and then dry further;

[0012] (2) The mixture obtained in (1) is ball-milled at a speed of 300-500 rpm for 50-100 min. After ball milling, it is passed through a 100-300 mesh sieve.

[0013] (3) The powder obtained by sieving is coated by chemical vapor deposition (CVD), gaseous carbon source is introduced, and the coating is carried out at 850~1050℃ for 1~3 h. After coating, it is passed through a 200~450 mesh sieve to obtain carbon-coated silicon nanowire anode material.

[0014] Preferably, the particle size of the micron-sized silicon powder is 2~50 μm. More preferably, it is 3~20 μm.

[0015] Preferably, the iridium source is one or more of iridium nitrate, iridium chloride, and iridium acetate. More preferably, it is iridium acetate.

[0016] Preferably, the solvent is one or more selected from alcohol solvents and acetone. More preferably, the alcohol solvent is ethanol.

[0017] Preferably, the mass ratio of micron-sized silicon powder to iridium source is 0.8~1.2:1.

[0018] Preferably, the total mass ratio of micron-sized silicon powder and iridium source to the volume ratio of solvent is 1g:5~15ml.

[0019] Preferably, the micron-sized silicon powder, iridium source, and solvent are dispersed uniformly using ultrasonic and / or shearing steps.

[0020] Further preferred, the ultrasonic frequency is 20~50 kHz, and the ultrasonic power density is 0.5~2 W / cm². 2 The ultrasound time is 30-60 minutes.

[0021] Further preferred, the shearing step includes the following parameters: shearing rate 3000~10000 rpm, shearing time 30~60 min.

[0022] Preferably, the oil bath heating temperature is 70~90 ℃ and the stirring speed is 200~800 rpm.

[0023] Preferably, the drying in step (1) is vacuum drying or hot air drying, with a drying temperature of 70~90 ℃ and a drying time of 4~10 h.

[0024] The mixture obtained in (1) is placed in a ball mill jar, grinding beads are added, the ball mill jar is evacuated and inert gas is introduced, and then it is placed in a ball mill for ball milling. Preferably, the grinding beads are one or more of zirconium oxide beads, alumina beads, steel beads, etc., and the diameter of the grinding beads is 0.2~50 mm. Preferably, the inert gas is argon or nitrogen. Preferably, the mass ratio of the mixture to the grinding beads is 1:7~15.

[0025] Preferably, after ball milling, the material is passed through a 150-250 mesh sieve for 20-30 minutes.

[0026] Preferably, the gaseous carbon source is methane and / or acetylene. The flow rate of methane or acetylene is 20~100 sccm.

[0027] Preferably, during the CVD coating process, a carrier gas, which is nitrogen or argon, is also introduced, and the volume ratio of the carrier gas to the gaseous carbon source is 10~20:1.

[0028] After coating, pass through a 300-400 mesh sieve for 20-30 minutes.

[0029] The present invention is mainly based on the following principles to prepare silicon nanowires: 1) Iridium source is decomposed by heat in an inert atmosphere, and the iridium particles produced by the decomposition are uniformly dispersed on the surface of micron-sized silicon powder. The iridium particles contact the micron-sized silicon surface and form Ir-Si eutectic alloy droplets locally; 2) Solid silicon continuously dissolves from the droplet / silicon contact interface into the droplet. Silicon atoms diffuse from the high-temperature side (contact interface) to the low-temperature side (top of the droplet) in the droplet. Silicon precipitates at the interface between the droplet and the gas phase, pushing the droplet upward, thereby forming silicon nanowires.

[0030] Another aspect of the present invention provides a carbon-coated silicon nanowire anode material, which is prepared by the above-described preparation method.

[0031] A third aspect of the invention provides a battery comprising the aforementioned carbon-coated silicon nanowire anode material.

[0032] Preferably, the battery is a lithium-ion battery or a sodium-ion battery, etc.

[0033] Preferably, the negative electrode of the battery comprises the carbon-coated silicon nanowire negative electrode material.

[0034] Preferably, the negative electrode of the battery is prepared by the following method:

[0035] A slurry is prepared by mixing carbon-coated silicon nanowire anode material, conductive agent, binder and solvent, and then coating the slurry onto a current collector to obtain an anode sheet.

[0036] The conductive agent composition is not particularly limited; any commonly used conductive agent composition in the art is acceptable, such as one or more of conductive carbon black, carbon nanotubes, carbon fibers, and graphene. The binder composition is not particularly limited; any commonly used binder composition in the art is acceptable, such as one or more of PVDF, polytetrafluoroethylene, sodium carboxymethyl cellulose, and styrene-butadiene rubber.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] 1. This invention uses micron-sized silicon powder as the starting material, which is much cheaper than the nano-silicon powder that traditional silicon-based anodes rely on. It also selects low-cost iridium sources such as iridium nitrate, iridium chloride, and iridium acetate as catalysts to efficiently convert iridium sources and low-cost raw materials such as micron-sized silicon into silicon nanowire composite anode materials. This solves the problem of complex and high-cost preparation processes for silicon-carbon anode materials, and removes one of the main obstacles to their large-scale commercial application.

[0039] 2. The preparation process of this invention includes three core steps: "dispersion drying - ball milling and sieving - CV coating". It does not require complex equipment or multiple purification steps. The process is simple, efficient and low-cost, and there is no generation or discharge of waste throughout the process, avoiding the environmental pollution risks of conventional preparation technologies. This process combines the advantages of low raw material cost, simple process and nanostructure performance, showing great industrialization potential.

[0040] 3. The silicon nanowire structure formed by in-situ growth in this invention has one-dimensional characteristics and internal voids: the nanowires mainly expand and contract along the axial direction during charging and discharging, with low radial stress, reducing the overall damage to the electrode structure; the voids between nanowires and between nanowires and micron-sized silicon particles provide valuable buffer space for the volume expansion of silicon during lithium intercalation, effectively suppressing electrode pulverization; the more stable structure reduces repeated contact between the active material and the electrolyte, reduces the continuous growth and rupture of the SEI film, and improves coulombic efficiency and cycle life.

[0041] 4. In the reaction, the iridium source not only acts as a catalyst to promote the growth of silicon nanowires, but its decomposition products (metallic Ir or iridium silicides such as IrSi) are also embedded or attached in situ to the surface / substrate of silicon nanowires. These highly conductive iridium / iridium silicide particles build efficient electron transport channels between silicon nanowires and between silicon nanowires and current collectors. Faster electron conduction is beneficial to improving the battery's fast charging and discharging capabilities (rate performance).

[0042] 5. This invention directly integrates the silicon nanowire growth process and carbon coating process into a silicon-carbon anode growth process in one step, which greatly reduces the difficulty of the synthesis process. Attached Figure Description

[0043] Figure 1This is a SEM image of the carbon-coated silicon nanowire anode material prepared in Example 1;

[0044] Figure 2 This is a scanning electron microscope (SEM) image of the carbon-coated silicon nanowire anode material prepared in Comparative Example 1.

[0045] Figure 3 SEM image of the carbon-coated silicon nanowire anode material prepared in Comparative Example 2;

[0046] Figure 4 This is the EDAX mapping spectrum of the carbon-coated silicon nanowire anode material prepared in Example 1;

[0047] Figure 5 This is the EDAX mapping spectrum of the carbon-coated silicon nanowire anode material prepared in Comparative Example 3. Detailed Implementation

[0048] In the description of this invention, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, and includes both a and b. "Multiple" includes two, three, four, five, or more.

[0049] The technical solution of the present invention will be further described and illustrated below with reference to specific embodiments and accompanying drawings. It should be understood that the specific embodiments described herein are only for the purpose of helping to understand the present invention and are not intended to limit the specific scope of the present invention. Furthermore, the accompanying drawings used herein are merely for better illustrating the content disclosed in the present invention and do not limit the scope of protection. Unless otherwise specified, the raw materials used in the embodiments of the present invention are all commonly used in the art, and the methods used in the embodiments are all conventional methods in the art.

[0050] Sources of raw materials in the examples and comparative examples:

[0051] Micron-sized silicon powder: Xinnai Metal Materials' 5-micron-sized silicon powder;

[0052] Nanoscale silicon powder: Xinnai Metal Materials 50 nanometer silicon powder.

[0053] Example 1

[0054] The carbon-coated silicon nanowire anode material in this embodiment is prepared by the following steps:

[0055] (1) Add 2000ml of ethanol to a stainless steel bucket, then add 100g of micron-sized silicon raw material and 100g of iridium acetate (Wuhan Lanabai Pharmaceutical Chemical Co., Ltd. 52705-52-9). Sonicate the slurry in the bucket at a frequency of 30 kHz and a power density of 1 W / cm³. 2The ultrasonic treatment lasted for 40 minutes, followed by shear emulsification at a shear rate of 8000 rpm for 40 minutes. The stainless steel container was placed on an oil bath at 80 ℃ and stirred thoroughly at 350 rpm. The mixture was heated and stirred in the oil bath until the solvent evaporated and the solute became solid. The mixture was then placed in a vacuum drying oven and dried at 80 ℃ for 6 hours.

[0056] (2) Place the mixture obtained in step (1) into a clean vacuum ball mill jar, and put the prepared zirconium beads into the ball mill jar together. The ball mill beads are 1000g of 20mm zirconium beads, 600g of 2mm zirconium beads, and 400g of 1mm zirconium beads. Vacuum the ball mill jar and introduce argon gas. Then place it in a ball mill for ball milling. The ball mill speed is 420rpm and the ball milling time is 60min. After ball milling, pass the powder through a 200-mesh sieve for 30 minutes to obtain a total of 175g of sieved powder.

[0057] (3) The powder passed through 200 mesh in step (2) is subjected to CVD coating. Nitrogen is introduced as the carrier gas. The gaseous carbon sources are methane and acetylene. The nitrogen flow rate is 800 sccm, the methane flow rate is 30 sccm, and the acetylene flow rate is 20 sccm. The coating temperature is 950 ℃ and the coating time is 2 h. The coated powder is passed through a 325 mesh sieve for 30 minutes. The carbon-coated silicon nanowire anode material is obtained after passing through a 325 mesh sieve.

[0058] Example 2

[0059] The difference between the carbon-coated silicon nanowire anode material in this embodiment and that in embodiment 1 is that iridium chloride is used instead of iridium acetate in embodiment 1 in embodiment 2, while the rest is the same as in embodiment 1, and the carbon-coated silicon nanowire anode material is obtained.

[0060] Comparative Example 1

[0061] The difference between Comparative Example 1 and Example 1 is that Comparative Example 1 uses 100g of nano-sized silicon material instead of 100g of micron-sized silicon material in Example 1, while the rest is the same as Comparative Example 1.

[0062] Figure 1 , Figure 2 The images are SEM images of the carbon-coated silicon nanowire anode materials prepared in Example 1 and Comparative Example 1, respectively. It can be seen that both micron-sized and nano-sized silicon powder can grow a large number of silicon nanowires under the induction of iridium acetate.

[0063] Comparative Example 2

[0064] The difference between Comparative Example 2 and Example 1 is that graphite was added instead of iridium acetate in Comparative Example 2, while the rest is the same as in Example 1.

[0065] like Figure 3As shown in the SEM image of the product prepared in Comparative Example 2, only silicon nanowires are sparsely distributed.

[0066] Comparative Example 3

[0067] The negative electrode material of Comparative Example 3 was prepared by the following steps:

[0068] (1) Place 100g of micron-sized silicon raw material and 100g of iridium acetate in a clean vacuum ball mill jar. Add the prepared zirconium beads to the ball mill jar. The ball mill beads are 1000g of 20mm zirconium beads, 600g of 2mm zirconium beads, and 400g of 1mm zirconium beads. Evacuate the ball mill jar and introduce argon gas. Then place it in a ball mill for ball milling. The ball mill speed is 420rpm and the ball milling time is 60min. After ball milling, pass the powder through a 200-mesh sieve for 30 minutes. A total of 175g of powder is obtained through the sieve.

[0069] (2) The powder that has passed through 200 mesh in step (1) is coated by CVD. Nitrogen is introduced as the carrier gas. The gaseous carbon sources are methane and acetylene. The nitrogen flow rate is 800 sccm, the methane flow rate is 30 sccm, and the acetylene flow rate is 20 sccm. The coating temperature is 950 ℃ and the coating time is 2 h. The coated powder is passed through a 325 mesh sieve for 30 minutes. The negative electrode material is obtained after passing through a 325 mesh sieve.

[0070] Figure 4 , Figure 5 These are mapping images of the carbon-coated silicon nanowire anode materials prepared in Example 1 and Comparative Example 3, respectively. In Comparative Example 3, the micron-sized silicon raw material and iridium acetate were not uniformly dispersed before coating, resulting in a very uneven silicon distribution.

[0071] The composite materials prepared in Examples 1-2 and Comparative Examples 1-3, single-walled carbon nanotubes (SWCNTs), polyacrylic acid (PAA), and SBR were added to deionized water in a ratio of 94.55:1:0.15:1.3:3, respectively. The mixture was stirred to form a uniform slurry, coated onto copper foil, and dried in a vacuum drying oven at 110°C for 12 hours before being cut into negative electrode sheets with a diameter of 14 mm. Using lithium metal sheets as the counter electrode, PE as the diaphragm, and a 1M LiPF6 solution (1:1:1 volume ratio of ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC)) as the electrolyte, coin cells were assembled. Conventional electrochemical performance tests and four-probe powder resistance tests were performed. The results are shown in Table 1.

[0072] Table 1. Test results of Examples 1-2 and Comparative Examples 1-3

[0073]

[0074] Comparing Examples 1 and 2, it is evident that silicon nanowires induced by iridium acetate exhibit better performance than those induced by iridium chloride. Comparing Example 1 and Comparative Example 1, while Comparative Example 1 also induced a large number of silicon nanowires using nano-silicon powder, the resulting powder exhibited severe agglomeration, leading to weaker battery performance compared to Example 1. Comparative Example 2, using graphite to induce silicon nanowires, only induced a very small amount of silicon nanowires, resulting in high powder resistivity and poor battery performance, especially cycle performance. Comparative Example 3, lacking pre-uniform dispersion of micron-sized silicon raw materials and iridium acetate, resulted in highly uneven silicon distribution and poor battery performance.

[0075] In the preparation method of this invention, the order of the steps is not limited to the listed order. For those skilled in the art, variations in the order of the steps without creative effort are also within the scope of protection of this invention. Furthermore, two or more steps or actions can be performed simultaneously.

[0076] Finally, it should be noted that the specific embodiments described herein are merely illustrative examples of the invention and are not intended to limit the implementation of the invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to replace them; it is neither necessary nor possible to exemplify all embodiments here. However, these obvious variations or modifications derived from the essential spirit of the invention still fall within the scope of protection of the invention, and interpreting them as any additional limitation would contradict the spirit of the invention.

Claims

1. A method for preparing a carbon-coated silicon nanowire anode material, characterized in that, Includes the following steps: (1) Add micron-sized silicon powder, iridium source and solvent to the container, disperse evenly, then heat and stir in an oil bath to remove the solvent, and then dry further; (2) The mixture obtained in (1) is ball-milled at a speed of 300-500 rpm for 50-100 min. After ball milling, it is passed through a 100-300 mesh sieve. (3) The powder obtained by sieving is coated by chemical vapor deposition, gaseous carbon source is introduced, and the coating is carried out at 850~1050 ℃ for 1~3 h. After coating, it is passed through a 200~450 mesh sieve to obtain carbon-coated silicon nanowire anode material.

2. The preparation method according to claim 1, characterized in that, The particle size of micron-sized silicon powder is 2~50 μm.

3. The preparation method according to claim 1, characterized in that, The iridium source is one or more of iridium nitrate, iridium chloride, and iridium acetate; The solvent is one or more of alcohols and acetone.

4. The preparation method according to claim 1, characterized in that, The mass ratio of micron-sized silicon powder to iridium source is 0.8~1.2:

1.

5. The preparation method according to claim 1, characterized in that, The total mass ratio of micron-sized silicon powder and iridium source to solvent volume is 1g:5~15ml.

6. The preparation method according to claim 1, characterized in that, Micron-sized silicon powder, iridium source, and solvent are uniformly dispersed using ultrasonic and / or shearing steps; The ultrasonic frequency is 20~50 kHz, and the ultrasonic power density is 0.5~2 W / cm². 2 The ultrasound time is 30-60 minutes; The shearing process includes the following parameters: shearing rate 3000~10000 rpm, shearing time 30~60 min.

7. The preparation method according to claim 1, characterized in that, The oil bath heating temperature is 70~90 ℃, and the stirring speed is 200~800 rpm.

8. The preparation method according to claim 1, characterized in that, The gaseous carbon source is methane and / or acetylene; The flow rate of methane or acetylene is 20~100 sccm.

9. A carbon-coated silicon nanowire anode material, characterized in that, It is prepared by the preparation method as described in any one of claims 1 to 8.

10. A battery, characterized in that, The battery includes the carbon-coated silicon nanowire anode material as described in claim 9.

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