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

Abstract

The invention belongs to the technical field of lithium batteries, and relates to a preparation method and application of a carbon-coated silicon nanowire negative electrode material. The preparation method comprises the following steps: adding micron-sized silicon powder, an iridium source and a solvent into a container, uniformly dispersing, heating in an oil bath, stirring to remove the solvent, and further drying; the obtained mixture is subjected to ball milling, and the mixture is sieved with a 100-300-mesh sieve after ball milling; and carrying out CVD coating on the powder obtained by sieving, introducing a gaseous carbon source, coating at 850-1050 DEG C for 1-3 hours, and sieving with a 200-450-mesh screen after coating to obtain the carbon-coated silicon nanowire negative electrode material. The low-cost raw materials such as an iridium source and micron-sized silicon are efficiently converted into the silicon nanowire composite negative electrode material, the cost is reduced, the process is simplified, and the battery performance can be effectively improved when the silicon nanowire composite negative electrode material is applied to a battery.

Description

TECHNICAL FIELD

[0001] 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 electrode material. BACKGROUND

[0002] As the current mainstream energy storage technology, the performance improvement of lithium ion batteries highly depends on the innovation of electrode materials. In the field of negative electrodes, the traditional graphite material has been difficult to meet the growing demand for high energy density (such as electric vehicles and portable electronic devices). Silicon (Si) is considered as one of the most potential next-generation negative electrode materials due to its extremely high theoretical specific capacity, abundant reserves and moderate lithium intercalation potential.

[0003] However, silicon materials face severe challenges during the charging and discharging process: accompanied by huge volume expansion / contraction (more than 300%) when lithium ions are intercalated / deintercalated. This dramatic volume effect easily leads to the pulverization of electrode materials, the peeling of active materials from the current collector or conductive network, and the continuous destruction and reconstruction of the solid electrolyte interface (SEI) film. As a result, the capacity of the battery rapidly decays, the cycle life is dramatically shortened, and the coulombic efficiency is low, which seriously hinders the commercial application of silicon-based negative electrodes.

[0004] To overcome the volume effect of silicon materials, a large number of researches have been carried out in the industry, and various nanostructure regulation strategies including nanoparticles, nanotubes, nanosheets, nanowires, etc. have been developed. Among them, silicon nanowires (SiNWs) exhibit significant advantages: 1. Excellent mechanical properties: one-dimensional nanowires have good mechanical flexibility in the axial direction, which can effectively buffer the stress caused by volume change and inhibit pulverization; 2. Efficient ion / electron transport: nanowires are directly grown or in close contact with the current collector, providing a continuous electron conduction path; their radial size is small, which shortens the lithium ion diffusion distance; 3. Structural stability: the voids between nanowires provide accommodation space for volume expansion, which helps to maintain the integrity of the electrode structure.

[0005] Therefore, it is of great significance to construct a silicon-carbon composite negative electrode material containing silicon nanowires. SUMMARY

[0006] The purpose of the present application is to provide a preparation method and application of a carbon-coated silicon nanowire negative electrode material, which adopts the following technical solutions to achieve the purpose of the application: One aspect of the present application provides a preparation method of a carbon-coated silicon nanowire negative electrode material, comprising the following steps: (1) adding micron-sized silicon powder, iridium source and solvent into a container, uniformly dispersing, then oil-bath heating and stirring to remove the solvent, and further drying; (2) ball-milling the mixture obtained in (1) at a rotation speed of 300-500 rpm for 50-100 min, and then sieving the mixture through a 100-300 mesh screen; (3) coating the powder obtained in (2) by chemical vapor deposition (CVD) by introducing a gaseous carbon source and coating at 850-1050 °C for 1-3 h, and then sieving the coated powder through a 200-450 mesh screen to obtain the carbon-coated silicon nanowire negative electrode material.

[0007] Preferably, the particle size of the micron-sized silicon powder is 2-50 μm. Further preferably, the particle size is 3-20 μm.

[0008] Preferably, the iridium source is one or more of iridium nitrate, iridium chloride, and iridium acetate. Further preferably, the iridium source is iridium acetate.

[0009] Preferably, the solvent is one or more of an alcohol solvent and acetone. Further preferably, the alcohol solvent is ethanol.

[0010] Preferably, the mass ratio of the micron-sized silicon powder to the iridium source is 0.8-1.2:1.

[0011] Preferably, the volume ratio of the total mass of the micron-sized silicon powder and the iridium source to the solvent is 1 g:5-15 ml.

[0012] Preferably, the micron-sized silicon powder, the iridium source, and the solvent are uniformly dispersed by an ultrasonic and / or shearing step.

[0013] Further preferably, the ultrasonic frequency is 20-50 kHz, the ultrasonic power density is 0.5-2 W / cm 2 , and the ultrasonic time is 30-60 min.

[0014] Further preferably, the shearing step comprises the following parameters: a shearing rate of 3000-10000 rpm and a shearing time of 30-60 min.

[0015] Preferably, the oil bath heating temperature is 70-90 °C, and the stirring speed is 200-800 rpm.

[0016] Preferably, the drying in step (1) is vacuum drying or hot air drying, the drying temperature is 70-90 °C, and the drying time is 4-10 h.

[0017] The mixture obtained in (1) is placed in a ball mill tank, ball milling beads are added, the ball mill tank is evacuated and then filled with an inert gas, and then the ball mill tank is placed in a ball mill for ball milling. Preferably, the ball milling beads are one or more of zirconia beads, alumina beads, and steel beads, and the diameter of the ball milling beads is 0.2-50 mm. Preferably, the inert gas is argon or nitrogen. Preferably, the mass ratio of the mixture to the ball milling beads is 1:7-15.

[0018] Preferably, the ball milling is followed by sieving through a 150-250 mesh screen for 20-30 minutes.

[0019] Preferably, the gaseous carbon source is methane and / or acetylene. The flow rate of methane or acetylene is 20-100 sccm.

[0020] Preferably, during the CVD coating process, a carrier gas is also introduced, which is nitrogen or argon, and the volume ratio of the carrier gas to the gaseous carbon source is 10-20:1.

[0021] After coating, the product is sieved through a 300-400 mesh screen for 20-30 minutes.

[0022] The silicon nanowires are prepared based on the following principles: 1) the iridium source is decomposed under heat in an inert atmosphere, and the generated iridium particles are uniformly dispersed on the surface of the micron-sized silicon powder, the iridium particles contact the surface of the micron-sized silicon, and local Ir-Si eutectic alloy droplets are formed; 2) the solid silicon continuously dissolves into the droplets from the droplet / silicon contact interface, the silicon atoms diffuse from the high-temperature side (the contact interface) to the low-temperature side (the top of the droplet) in the droplet, and the silicon precipitates at the interface between the droplet and the gas phase, pushing the droplet to move upwards, thereby forming silicon nanowires.

[0023] In another aspect, the application provides a carbon-coated silicon nanowire negative electrode material prepared by the above method.

[0024] In a third aspect, the application provides a battery comprising the carbon-coated silicon nanowire negative electrode material.

[0025] Preferably, the battery is a lithium ion battery or a sodium ion battery, etc.

[0026] Preferably, the negative electrode sheet of the battery comprises the carbon-coated silicon nanowire negative electrode material.

[0027] Preferably, the negative electrode sheet of the battery is prepared by the following method: The carbon-coated silicon nanowire negative electrode material, a conductive agent, a binder, and a solvent are mixed to obtain a slurry, and the slurry is coated on a current collector to obtain a negative electrode sheet.

[0028] The conductive agent component is not particularly limited, and any commonly used conductive agent component in the art can be used, which can be one or more of conductive carbon black, carbon nanotubes, carbon fibers, and graphene. The binder component is not particularly limited, and any commonly used binder component in the art can be used, which can be one or more of PVDF, polytetrafluoroethylene, sodium carboxymethyl cellulose, and styrene butadiene rubber.

[0029] Compared with the prior art, the application has the following beneficial effects: 1. The application uses micron-sized silicon powder as a starting material, which is much cheaper than the traditional silicon-based negative electrode dependent on nano-silicon powder, and selects low-cost iridium sources such as iridium nitrate, iridium chloride and iridium acetate as catalysts, which efficiently convert the low-cost raw materials such as iridium sources and micron-sized silicon into silicon nanowire composite negative electrode materials, solving the problems of complex preparation process and high cost of current silicon-carbon negative electrode materials, and removing one of the main obstacles for large-scale commercial application.

[0030] 2. The preparation process of the application includes three core steps of "dispersion drying-ball milling-screening-CV coating", which does not need complex equipment and multi-step purification, and has the advantages of simple process, high efficiency and low cost, and no three wastes are generated and discharged in the whole process, avoiding environmental pollution hidden dangers in conventional preparation techniques; the process combines low raw material cost, simple process and nanometer structure performance advantages, and has great industrialization potential.

[0031] 3. The silicon nanowire structure formed in situ has one-dimensional characteristics and internal voids: the nanowires mainly expand and contract along the axial direction during charging and discharging, the radial stress is small, and the overall destruction of the electrode structure is reduced; the voids between the nanowires and the voids between the nanowires and the micron-sized silicon particles provide valuable buffer space for the volume expansion of silicon during lithium intercalation, effectively inhibiting the electrode pulverization; the more stable structure reduces the repeated contact of active materials and electrolyte, reduces the continuous growth and rupture of the SEI film, improves the coulombic efficiency and cycle life.

[0032] 4. The iridium source not only acts as a catalyst to promote the growth of silicon nanowires in the reaction, but also decomposes products (metal Ir or iridium silicide such as IrSi) which are in-situ embedded or attached to the surface / matrix of the silicon nanowires; these high-conductivity iridium / iridium silicide particles construct an efficient electron transport channel between the silicon nanowires and between the silicon nanowires and the current collector, and faster electron conduction is beneficial to improve the fast charging and discharging capacity (rate performance) of the battery.

[0033] 5. The application integrates the silicon nanowire growth process and the carbon coating process into a one-step silicon-carbon negative electrode growth process, greatly reducing the process difficulty of synthesis. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 is the SEM scanning electron microscope image of the carbon-coated silicon nanowire negative electrode material prepared in Example 1; Figure 2 is the SEM scanning electron microscope image of the carbon-coated silicon nanowire negative electrode material prepared in Comparative Example 1; Figure 3 is the SEM scanning electron microscope image of the carbon-coated silicon nanowire negative electrode material prepared in Comparative Example 2; Figure 4 is the EDAX Mapping spectrum of the carbon-coated silicon nanowire negative electrode material prepared in Example 1; Figure 5 EDAX Mapping pattern of carbon-coated silicon nanowire negative electrode material prepared in Comparative Example 3. DETAILED DESCRIPTION

[0035] In the description of the present application, unless otherwise specified, the numerical range "a~b" represents a shorthand notation for any real combination between a and b, and includes a and b. Various numbers include two, three, four, five, and more than five.

[0036] The technical solutions of the present application are further described and explained below through specific examples and drawings. It should be understood that the specific examples described herein are only used to help understand the present application, and are not used to specifically limit the present application. The drawings used herein are only used to better illustrate the disclosed content of the present application, and do not limit the scope of protection. If not otherwise specified, the raw materials used in the examples of the present application are all commonly used raw materials in the art, and the methods used in the examples are all conventional methods in the art.

[0037] Raw material sources in examples and comparative examples: Micron-sized silicon powder: Xini metal material 5 micron-sized silicon powder; Nanosized silicon powder: Xini metal material 50 nanosized silicon powder.

[0038] Example 1

[0039] The carbon-coated silicon nanowire negative electrode material of the present example is prepared by the following steps: (1) Add 2000 ml of ethanol into a stainless steel barrel, then add 100 g of micron-sized silicon raw material and 100 g of iridium acetate (52705-52-9, Wuhan Lanna Bai Medicine Chemical Co., Ltd.), and perform ultrasonic treatment on the slurry in the barrel, with an ultrasonic frequency of 30 kHz and an ultrasonic power density of 1 W / cm 2 ; then perform shear emulsification, with a shear rate of 8000 rpm and a shear time of 40 min; place the stainless steel barrel in an oil bath set at 80 ℃, and use a stirrer to fully stir at a rotation speed of 350 rpm, and continue to heat and stir in the oil bath until the solvent evaporates and the solute becomes solid, then place the mixture in a vacuum drying oven and dry at a temperature of 80 ℃ for 6 h.

[0040] (2) Put the mixture obtained in step (1) into a clean vacuum ball mill tank, and put the zirconium beads of the prepared quality into the ball mill tank together, 1000 g of 20 mm zirconium beads, 600 g of 2 mm zirconium beads, and 400 g of 1 mm zirconium beads, vacuumize the ball mill tank and introduce argon, and then put it into the ball mill for ball milling, the rotation speed of the ball mill is 420 rpm, and the ball milling time is 60 min; the milled powder is sieved through a 200 mesh sieve, and the sieving time is 30 minutes, and a total of 175 g of undersize powder is obtained.

[0041] (3) The 200 mesh sieved powder in step (2) is coated by CVD, and the carrier gas nitrogen is introduced, and the gaseous carbon source is methane and acetylene gas, the nitrogen flow is 800 sccm, the methane flow is 30 sccm, the acetylene flow is 20 sccm, the coating temperature is 950 ℃, and the coating time is 2 h; the coated powder is sieved through a 325 mesh sieve, and the sieving time is 30 minutes, and the 325 mesh sieved powder is obtained as the carbon-coated silicon nanowire negative electrode material.

[0042] Example 2

[0043] The carbon-coated silicon nanowire negative electrode material of the present embodiment is different from that of Example 1 in that iridium chloride is used instead of iridium acetate in Example 1, and the rest is the same as Example 1, and the carbon-coated silicon nanowire negative electrode material is prepared.

[0044] Comparative Example 1 Comparative Example 1 is different from Example 1 in that 100 g of nanoscale silicon raw material is used instead of 100 g of micrometer-scale silicon raw material in Example 1, and the rest is the same as Comparative Example 1.

[0045] Figure 1 、 Figure 2 The SEM scanning electron microscope images of the carbon-coated silicon nanowire negative electrode materials prepared in Example 1 and Comparative Example 1, respectively, can be seen that both micrometer-scale silicon powder and nanoscale silicon powder can grow more silicon nanowires under the induction of iridium acetate.

[0046] Comparative Example 2 Comparative Example 2 is different from Example 1 in that graphite is used instead of iridium acetate, and the rest is the same as Example 1.

[0047] As shown in Figure 3 , the SEM image of the product prepared in Comparative Example 2 shows only sporadic distribution of silicon nanowires.

[0048] Comparative Example 3 The negative electrode material of Comparative Example 3 is prepared by the following steps: (1) Put 100 g of micron-sized silicon raw material and 100 g of iridium acetate into a clean vacuum ball mill jar, and put the zirconium beads of the prepared quality together into the ball mill jar. The ball milling beads are 1000 g of 20 mm zirconium beads, 600 g of 2 mm zirconium beads, and 400 g of 1 mm zirconium beads. The ball mill jar is vacuumed and argon is introduced, and then it is placed in a ball mill. The rotation speed of the ball mill is 420 rpm, and the ball milling time is 60 min. The milled powder is sieved through a 200 mesh sieve for 30 min, and 175 g of undersize powder is obtained.

[0049] (2) The powder sieved through a 200 mesh sieve in step (1) is coated by CVD. Nitrogen gas is introduced as the carrier gas, and gaseous carbon sources are methane and acetylene gas. 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°C, and the coating time is 2 h. The coated powder is sieved through a 325 mesh sieve for 30 min, and the powder sieved through a 325 mesh sieve is obtained as the negative electrode material.

[0050] Figure 4 、 Figure 5 The Mapping images of the carbon-coated silicon nanowire negative electrode materials prepared in Example 1 and Comparative Example 3 are shown in FIG. 1. In Comparative Example 3, the micron-sized silicon raw material and iridium acetate were not uniformly dispersed in advance before coating, and the silicon distribution was very uneven.

[0051] The composite materials, single-walled carbon nanotubes (SWCNTs), polyacrylic acid (PAA), and SBR prepared in Examples 1-2 and Comparative Examples 1-3 are added to deionized water in a ratio of 94.55:1:0.15:1.3:3, stirred and mixed to form a uniform slurry, coated on a copper foil, and dried in a vacuum drying oven at 110°C for 12 h. The slurry is cut into negative electrode sheets with a diameter of 14 mm. A metal lithium sheet is used as the counter electrode, PE is used as the diaphragm, and a 1M LiPF6 solution dissolved in a volume ratio of 1:1:1 of ethylene carbonate (EC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC) is used as the electrolyte. After assembling the coin cell, the conventional electrochemical performance test and four-probe powder resistance test are performed, and the results are shown in Table 1.

[0052] Table 1 Test results of Examples 1-2 and Comparative Examples 1-3

[0053] It can be seen from Comparative Example 1 and Example 2 that the use of iridium acetate to induce silicon nanowires exhibits better performance than the use of iridium chloride. It can be seen from Comparative Example 1 and Comparative Example 1 that although the use of nanosilicon powder in Comparative Example 1 can induce the generation of a large amount of silicon nanowires, the powder prepared in Comparative Example 1 has a serious powder agglomeration phenomenon and the battery performance is weaker than that of Example 1. The use of graphite to induce silicon nanowires in Comparative Example 2 can only induce the generation of a small amount of silicon nanowires, the powder has a high resistivity, and the battery performance, especially the cycle performance, is poor. In Comparative Example 3, the micron-sized silicon raw material and iridium acetate are not uniformly dispersed in advance before coating, the silicon distribution is very uneven, and the battery prepared has very poor performance.

[0054] In the preparation method of the present application, the order of the steps is not limited to the order listed, and for those skilled in the art, changes in the order of the steps without creative labor are also within the protection scope of the present application. In addition, two or more steps or actions can be performed simultaneously.

[0055] Finally, it should be noted that the specific examples described herein are merely illustrative of the present application and are not intended to limit the embodiments of the present application. Those skilled in the art can make various modifications or supplements to the described specific examples or use similar ways to replace them, and it is not necessary or possible to fully describe all embodiments. Any obvious changes or variations derived from the essential spirit of the present application still fall within the protection scope of the present application, and any additional limitation is contrary to the spirit of the present application.

Claims

1. A method for preparing a carbon-coated silicon nanowire negative electrode material, characterized in that: The following steps are involved: (1) Add micron-sized silicon powder, iridium source and solvent into a container, disperse them evenly, then heat and stir in an oil bath to remove the solvent, and then further dry; (2) ball mill the mixture obtained in (1) at a speed of 300-500 rpm for 50-100 min, and then pass through a 100-300 mesh sieve. (3) The powder obtained by sieving is coated by chemical vapor deposition, a gaseous carbon source is introduced, and the coating is carried out at 850-1050 °C for 1-3 h. After coating, the powder is passed through a 200-450 mesh sieve to obtain a carbon-coated silicon nanowire negative electrode 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 alcohol solvents 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 volume ratio of the total mass of micron-sized silicon powder and iridium source to the solvent 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 by ultrasonic and / or shearing steps; The ultrasonic frequency is 20~50 kHz and the ultrasonic power density is 0.5~2 W / cm 2 , ultrasound time is 30~60 min; The shearing step includes the following parameters: shear rate 3000~10000 rpm, shear 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 20~100sccm.

9. A carbon-coated silicon nanowire negative electrode material, characterized in that: It is prepared by the preparation method according to any one of claims 1 to 8.

10. A battery, characterized in that: The battery comprises the carbon-coated silicon nanowire negative electrode material according to claim 9.

Images