Preparation and application of silicon-carbon nano composite material with hollow porous yolk shell structure

Abstract

The invention relates to the technical field of nano-particle preparation, and discloses preparation and application of a hollow porous yolk shell structure silicon-carbon nano-composite material. According to the hollow porous yolk shell structure silicon-carbon nano-particle provided by the invention, a silicon nano-sphere is used as a core, and a hollow layer between a carbon shell layer and the core is based on a carbon-coated porous channel; the volume change of the silicon nanoparticles in the charging and discharging process is fully released, and the mechanism stability of the electrode material is kept; meanwhile, the hollow structure and the porous structure are beneficial to de-intercalation migration of lithium ions in the silicon nanoparticles, and the rate capability is increased; in addition, the carbon coating layer can avoid direct contact between the silicon nanoparticles and an electrolyte, so that the electronic and ionic conductivity of the material is ensured, and the first coulombic efficiency is improved. When the carbon-silicon composite material prepared by the method is used as a negative electrode, the battery capacity is relatively high, and the rate capability is relatively long.

Description

Technical Field

[0001] The present invention relates to the technical field of nanoparticle preparation, and more particularly to the preparation and application of a hollow porous yolk-shell structured silicon-carbon nanocomposite material. Background Art

[0002] The energy crisis is one of the most important issues facing human society today, and the collection, storage, and transportation of new clean energy sources have attracted widespread attention. As an important medium for electrical energy conversion and storage, lithium-ion batteries offer advantages such as high energy density, good cycle stability, a wide operating potential window, high safety, and environmental friendliness. They are widely used in portable electronics, large-scale energy storage, and electric vehicles. With the rapid development of new energy vehicles, the increase in driving range has placed higher demands on battery energy density. The energy density of power lithium-ion batteries is expected to reach 300W·h / kg by 2024, and the use of high-capacity silicon-based anode materials instead of traditional graphite materials is one of the key technologies to achieve this goal.

[0003] Silicon has the advantages of high specific capacity, low delithiation potential and abundant resources, and therefore has attracted widespread attention. However, there is a large volume change during the de- / intercalation process of silicon, which can easily lead to particle pulverization and then fall off the current collector. At the same time, the SEI film on the surface of the silicon negative electrode is constantly broken and generated during the charge and discharge process, which continuously consumes active lithium ions, resulting in a decrease in Coulomb efficiency and battery cycle life. Composite silicon with graphite, amorphous carbon or other carbonaceous materials is an effective method to improve the electrochemical performance of silicon negative electrodes. During long cycles, the traditional carbon coating is not sufficient to adapt to its volume change, causing the coating to rupture and lose its function. At present, the methods for preparing porous core-shell structured silicon-carbon nanoparticles mainly include: sol-gel method, chemical vapor deposition method, etc. Although there are many methods, the production process of these technologies is cumbersome, the cost is high, and it is difficult to achieve large-scale production. Summary of the Invention

[0004] Based on traditional carbon coating, the present invention develops a simple, efficient and environmentally friendly preparation method to achieve the controllable preparation of hollow porous yolk-shell structured silicon-carbon nanoparticles, and introduces a carbon coating layer with a hollow mesoporous structure with certain structural strength to improve the stability of silicon-based negative electrode materials during high rate and long cycle processes.

[0005] The present invention proposes a method for preparing hollow porous yolk-shell structured silicon-carbon nanoparticles, which can obtain lithium-ion battery negative electrode materials with high battery capacity, long cycle life and good rate performance. At the same time, the molding process is simple, the processing cost is low, and it is suitable for industrial production.

[0006] The present invention provides a method for preparing a core-shell structured silicon-carbon negative electrode material, comprising the following steps:

[0007] Step 1: Nano-silicon powder, tetrapropoxysilane (TPOS), ethanol, deionized water, 25 wt% ammonia, resorcinol, and 37 wt% formaldehyde were mixed and stirred for 24 hours. The mixture was centrifuged, washed with water and ethanol, and then dried at 70°C overnight to obtain a tetrapropoxysilane / resorcinol formaldehyde resin (TPOS / RF)-coated Si nanoparticle material (Si@TPOS / RF).

[0008] Step 2: The TPOS / RF-coated Si nanoparticle product is subjected to high-temperature carbonization heat treatment to obtain a three-layer core-shell structure product (Si@SiO2@SiO2 / C) with Si as the core, SiO2 as the middle layer, and SiO2 / C composite as the outer layer;

[0009] Step 3: Place the three-layer core-shell structure product (Si@SiO2@SiO2 / C) in an acid solution to react and remove SiO2 to obtain a carbon-coated hollow porous yolk-shell structured silicon nanomaterial (Si@void@C).

[0010] Preferably, in step 1, the particle size of the nano silicon powder is 100-600 nm, preferably 100-200 nm, and the mass of the weighed silicon powder is 0.1-0.3 g.

[0011] Preferably, in step 1, the volumes of tetrapropoxysilane (TPOS), ethanol, deionized water, 25 wt% ammonia water, and 37 wt% formaldehyde are 0.5-1.5 ml, 70 ml, 10 ml, 3 ml, and 210 μl, respectively, and the mass of resorcinol is 0.15 g.

[0012] Preferably, in step 2, the atmosphere of the carbonization heat treatment is N2 atmosphere, the calcination temperature is 800°C, the heating rate is 2°C / min, and the holding time is 4h.

[0013] Preferably, in step 3, the acid solution comprises one or any combination of hydrochloric acid, sulfuric acid, hydrofluoric acid, nitric acid, perchloric acid, and acetic acid, and the concentration of the acid solution is 5% wt-15% wt.

[0014] Preferably, the diameter of the hollow porous yolk-shell structured silicon-carbon nanoparticles is 200-300 nm, the thickness of the coating carbon layer is 20-30 nm, and the diameter of the hollow layer is 30-50 nm.

[0015] A hollow porous egg-yolk-shell structured silicon-carbon nanomaterial comprises a core composed of silicon nanoparticles and a porous carbon shell layer covering the core, wherein a hollow structure is formed between the outer side of the core and the inner side of the carbon shell layer.

[0016] The application further provides an application of the preparation method of the core-shell structure silicon-carbon negative electrode material.

[0017] The application has the following beneficial effects:

[0018] The hollow porous yolk-shell structure silicon-carbon nanoparticles provided by the application take silicon nanospheres as the core, and the hollow layer between the carbon-coated porous channels and the carbon shell layer and the core fully releases the volume change of the silicon nanoparticles in the charge and discharge process, maintains the structural stability of the electrode material; meanwhile, the hollow structure and the porous structure are beneficial to the deintercalation and migration of lithium ions in the silicon nanoparticles, and improve the rate performance; in addition, the carbon-coated layer can avoid the direct contact of the silicon nanoparticles and the electrolyte, guarantees the electronic and ionic conductivity of the material, and is beneficial to improving the first coulomb efficiency. The carbon-silicon composite material prepared by the application has high battery capacity and long rate performance as the negative electrode. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 is the SEM image of the silicon nanoparticles used in the application;

[0020] Figure 2 is the particle size distribution graph of the silicon nanoparticles used in the application;

[0021] Figure 3 is the Si@TPOS / RF material prepared in example 1;

[0022] Figure 4 is the Si@SiO2@SiO2 / C composite material prepared in example 1;

[0023] Figure 5 is the infrared spectrum of the Si@TPOS / RF material prepared in example 1;

[0024] Figure 6 is the SEM image of the Si@TPOS / RF material prepared in example 1;

[0025] Figure 7 is the particle size distribution graph of the Si@TPOS / RF material prepared in example 1;

[0026] Figure 8 is the SEM and EDS image of Si@SiO2@SiO2 / C prepared in example 1;

[0027] Figure 9 is the SEM image of Si@void@C prepared in example 1;

[0028] Figure 10 is the TEM image of Si@void@C prepared in example 1;

[0029] Figure 11 is the adsorption and desorption curve and pore size distribution curve of Si@void@C prepared in Example 1.

[0030] Figure 12 is the long cycle test graph of the samples of Examples 1-3 in the present application. DETAILED DESCRIPTION

[0031] The subject matter described herein will now be discussed with reference to example implementations. It should be understood that discussions of these implementations are merely provided to enable those skilled in the art to better understand so as to be able to implement the subject matter described herein, and variations of elements discussed can be made by one skilled in the art within the scope of the present specification. Various examples can omit, substitute, or add various procedures or components as appropriate, and the embodiments described should not be taken as limiting. Further, it should be understood that elements described in association with certain examples can be incorporated into or used with other examples.

[0032] Example 1

[0033] In this embodiment, a preparation method of a core-shell structure silicon-carbon negative electrode material is proposed, comprising the following steps:

[0034] Step 1: 0.1 g of nano-silicon powder with a particle size of 100-200 nm, 0.5 ml of tetrapropoxysilane (TPOS), 70 ml of ethanol, 10 ml of deionized water, 3 ml of 25 wt% ammonia water, 210 μl of 37 wt% formaldehyde, and 0.15 g of resorcinol are mixed and reacted, and stirring is maintained for 24 h. After centrifugation, water washing, and ethanol washing, 70°C overnight drying is performed to obtain a tetrapropoxysilane / resorcinol formaldehyde resin (TPOS / RF) coated Si nanoparticle material (Si@TPOS / RF) as shown in Figure 3

[0035] Step 2: The TPOS / RF coated Si nanoparticle product is subjected to high-temperature carbonization heat treatment, and the carbonization heat treatment atmosphere is N2 atmosphere, the calcination temperature is 800°C, the heating rate is 2°C / min, and the holding time is 4 h. A three-layer core-shell structure product (Si@SiO2@SiO2 / C) with Si as the core, SiO2 as the intermediate layer, and SiO2 / C composite as the outer shell layer is obtained; the actual product is as shown in Figure 4

[0036] Step 3: The three-layer core-shell structure product (Si@SiO2@SiO2 / C) is placed in a 5% wt concentration hydrochloric acid solution to remove SiO2, and a carbon-coated hollow porous egg yolk shell structure silicon nano material (Si@void@C) is obtained.

[0037] Figure 5 ​​is the infrared spectrum of Si@TPOS / RF material prepared in Example 1; from the figure, the wide absorption peak at 3390.47 cm -1 is -OH, the absorption peak at 2812.79 cm -1 is -CH2-, the absorption peak at 1350.93 cm -1 is the C-O stretching absorption peak of aldehyde.

[0038] Figure 6 and Figure 7 is the SEM image and particle size distribution of Si@TPOS / RF material prepared in Example 1; from the figure, the sample surface is relatively rough, and the particle size is about 200 nm, indicating that the TPOS / RF material is successfully coated.

[0039] Figure 8 is the SEM image and EDS image of Si@SiO2@SiO2 / C prepared in Example 1; it can be analyzed that the carbon element is the main element in the sample element, and also contains a lot of silicon and oxygen elements.

[0040] Figure 9 is the SEM and EDS images of Si@void@C prepared in Example 1; the results show that there is basically no oxygen element, only surface carbon element and core silicon element. It is proved that acid washing can remove a large amount of SiO2.

[0041] Figure 10 is the TEM image of Si@void@C prepared in Example 1; the sample after removing SiO2 by acid washing is hollow, which shows that the middle layer of the carbonized sample is SiO2, proving the hollow structure of Si@C, and the diameter of the hollow layer is about 36.562 nm.

[0042] Figure 11 is the adsorption and desorption curve and pore size distribution curve of Si@void@C prepared in Example 1. The sample after acid washing has larger mesopores, most of which are distributed at about 33.7 nm, which is basically consistent with the hollow layer diameter of 36.562 nm of the sample Si@C tested by transmission electron microscope. Not only does it show the increase of mesopores on the surface of the carbon layer after acid washing, but also further verifies the hollow structure.

[0043] Example 2

[0044] In this embodiment, a hollow porous egg yolk shell structure silicon-carbon nanomaterial is provided, which comprises a core composed of silicon nanoparticles and a porous carbon shell layer covering the core, and a hollow structure between the outside of the core and the inside of the carbon shell layer.

[0045] Step 1: 0.2 g of nano-silicon powder with a particle size of 100-200 nm, 1 ml of tetrapropoxysilane (TPOS), 70 ml of ethanol, 10 ml of deionized water, 3 ml of 25 wt% ammonia water, 210 μl of 37 wt% formaldehyde and 0.15 g of resorcinol were mixed and reacted, and stirring was maintained for 24 h. After centrifugation, water washing and ethanol washing, drying was performed at 70°C overnight to obtain a tetrapropoxysilane / resorcinol / formaldehyde resin (TPOS / RF) coated Si nanoparticle material (Si@TPOS / RF);

[0046] Step 2: The TPOS / RF coated Si nanoparticle product was subjected to high-temperature carbonization heat treatment, the carbonization heat treatment atmosphere was N2 atmosphere, the calcination temperature was 800°C, the heating rate was 2°C / min, and the holding time was 4 h. A three-layer core-shell structure product (Si@SiO2@SiO2 / C) was obtained, with Si as the core, SiO2 as the intermediate layer, and SiO2 / C composite as the outer shell layer;

[0047] Step 3: The three-layer core-shell structure product (Si@SiO2@SiO2 / C) was placed in a 10% wt hydrochloric acid solution to remove SiO2, obtaining a carbon-coated hollow porous yolk-shell structure silicon nanomaterial (Si@void@C).

[0048] Example 3

[0049] In this example, the application of a preparation method of a core-shell structure silicon-carbon negative electrode material is proposed, and the silicon-carbon negative electrode material obtained by the preparation method in Example 1 is made.

[0050] Step 1: 0.3 g of nano-silicon powder with a particle size of 100-200 nm, 1.5 ml of tetrapropoxysilane (TPOS), 70 ml of ethanol, 10 ml of deionized water, 3 ml of 25 wt% ammonia water, 210 μl of 37 wt% formaldehyde and 0.15 g of resorcinol were mixed and reacted, and stirring was maintained for 24 h. After centrifugation, water washing and ethanol washing, drying was performed at 70°C overnight to obtain a tetrapropoxysilane / resorcinol / formaldehyde resin (TPOS / RF) coated Si nanoparticle material (Si@TPOS / RF);

[0051] Step 2: The TPOS / RF coated Si nanoparticle product was subjected to high-temperature carbonization heat treatment, the carbonization heat treatment atmosphere was N2 atmosphere, the calcination temperature was 800°C, the heating rate was 2°C / min, and the holding time was 4 h. A three-layer core-shell structure product (Si@SiO2@SiO2 / C) was obtained, with Si as the core, SiO2 as the intermediate layer, and SiO2 / C composite as the outer shell layer;

[0052] Step 3: Place the three-layer core-shell structure product (Si@SiO2@SiO2 / C) in a hydrofluoric acid solution with a concentration of 15% wt to react and remove SiO2 to obtain a carbon-coated hollow porous yolk-shell structured silicon nanomaterial (Si@void@C).

[0053] Figure 12 The long-cycle test graphs for samples from Examples 1-3 of the present invention show that the long-cycle performance of the carbon-coated hollow porous yolk-shell silicon nanomaterial (Si@void@C) is significantly improved with increasing Si nanoparticle content and pickling concentration.

[0054] The above describes an embodiment of the present invention, but this embodiment is not limited to the above-mentioned specific implementation methods. The above-mentioned specific implementation methods are merely illustrative and not restrictive. Ordinary technicians in this field can also make more forms of equivalent embodiments based on the inspiration of this embodiment, all of which are protected by this embodiment.

Claims

1. A method for preparing hollow porous yolk-shell structured silicon-carbon nanoparticles, characterized in that: The following steps are involved: Step 1: Nano-silicon powder, tetrapropoxysilane, ethanol, deionized water, 25 wt% ammonia water, resorcinol and 37 wt% formaldehyde were mixed and stirred for 24 hours; centrifuged, washed with water and ethanol, and then dried at 70°C overnight to obtain a tetrapropoxysilane / resorcinol formaldehyde resin-coated Si nanoparticle material; Step 2: subjecting the tetrapropoxysilane / resorcinol formaldehyde resin-coated Si nanoparticle product to a high-temperature carbonization heat treatment to obtain a three-layer core-shell structure product with Si as the core, SiO2 as the middle layer, and SiO2 / C composite as the outer shell layer; Step 3: Place the three-layer core-shell structure product in an acid solution to react and remove SiO2, thereby obtaining a carbon-coated hollow porous yolk-shell structured silicon nanomaterial.

2. The method for preparing hollow porous yolk-shell structured silicon-carbon nanoparticles according to claim 1, characterized in that: In the step 1, the particle size of the nano silicon powder is 100-600 nm.

3. The method for preparing hollow porous yolk-shell structured silicon-carbon nanoparticles according to claim 1, characterized in that: In step 1, the volumes of tetrapropoxysilane (TPOS), ethanol, deionized water, 25 wt% ammonia water, and 37 wt% formaldehyde are 0.5 ml, 70 ml, 10 ml, 3 ml, and 210 μl, respectively, and the mass of resorcinol is 0.15 g.

4. The method for preparing hollow porous yolk-shell structured silicon-carbon nanoparticles according to claim 1, characterized in that: In the step 2, the atmosphere of the carbonization heat treatment is N2 atmosphere, the calcination temperature is 800°C, the heating rate is 2°C / min, and the holding time is 4h.

5. The method for preparing hollow porous yolk-shell structured silicon-carbon nanoparticles according to claim 1, characterized in that: In step 3, the acid solution includes one or any combination of hydrochloric acid, sulfuric acid, hydrofluoric acid, nitric acid, perchloric acid, and acetic acid, and the concentration of the acid solution is 5% wt-15% wt.

6. The method for preparing hollow porous yolk-shell structured silicon-carbon nanoparticles according to claim 1, characterized in that: The diameter of the hollow porous yolk-shell structured silicon-carbon nanoparticles is 200-300 nm, the thickness of the coating carbon layer is 20-30 nm, and the diameter of the hollow layer is 30-50 nm.

7. A hollow porous yolk-shell structured silicon-carbon nanomaterial, characterized in that: The hollow porous yolk-shell structured silicon-carbon nanoparticles are prepared by the preparation method of any one of claims 1-6, comprising a core composed of silicon nanoparticles and a porous carbon shell layer covering the core, and a hollow structure is formed between the outer side of the core and the inner side of the carbon shell layer.

8. The hollow porous yolk-shell structured silicon-carbon nanomaterial according to claim 1, characterized in that: The mass fraction of the carbon is 10%-60%, and the optimal value is 16.8%.

9. Application of a method for preparing hollow porous yolk-shell structured silicon-carbon nanoparticles, characterized in that: Used in the preparation of silicon-carbon negative electrode materials.

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