CN105826527B - A kind of porous silicon-carbon composite and its preparation method and application - Google Patents

Abstract

The invention discloses a kind of preparation method of porous Si-C composite material, specially：Silication magnesium dust is placed in CO₂It under/Ar mixed atmospheres, is heat-treated at 700~900 DEG C, then the porous silicon carbon/carbon-copper composite material is obtained through pickling and post processing；The CO₂In/Ar mixed atmospheres, CO₂Volume fraction be 10~90%.The present invention's is simple for process, is easy to repeat, it can be achieved that large-scale industrial production.The porous Si-C composite material being prepared is applied to as negative material in lithium ion battery, will significantly improve the cyclical stability of lithium ion battery.

Description

A kind of porous silicon-carbon composite material and its preparation method and application

technical field

The invention belongs to the field of preparation of composite materials, and in particular relates to a porous silicon-carbon composite material and its preparation method and application.

Background technique

Lithium-ion battery is a rechargeable battery widely used in modern society. Since lithium has an extremely low specific gravity among all metals and has the most negative electrode potential, when lithium is used as a battery material, it will have significant advantages such as high energy density and high charging voltage. However, when lithium is used as a battery negative electrode material, it will produce dendrite segregation during the process of lithium precipitation, forming dendritic lithium dendrites, which will gradually grow to pierce the separator and connect the positive and negative electrodes. Make the battery short circuit, dangerous. Therefore, today's industrialized lithium battery anode material is not metallic lithium, but a layered material. Lithium ions can be continuously intercalated and extracted between them to realize charging and discharging. Therefore, lithium batteries are called lithium ion batteries in full. Or a rocking chair battery.

So far, the anode materials of lithium ion batteries that can realize industrial application are mainly carbon materials represented by graphite. Graphite is a layered material with good conductivity and can intercalate lithium ions very well without volume change. Therefore, graphite has excellent stability during charge-discharge cycles. However, the space between graphite layers that can accommodate lithium ions is limited, so there is only the highest theoretical specific capacity of 372mAh/g, which makes it increasingly difficult for carbon materials represented by graphite to meet the requirements of modern society, especially electronic products and electric vehicles. Demand for high specific capacity batteries in the automotive industry.

Silicon is a semiconductor material with an indirect band gap. It can form various types of alloys with lithium. When used as a negative electrode material for lithium-ion batteries, it has the highest theoretical specific capacity (4200mAh/g) and lower electrode Potential, which makes silicon a popular candidate material for lithium battery anodes with high specific capacity and high charging voltage. However, during the process of intercalation and extraction of lithium ions, silicon will undergo volume expansion and contraction of up to 300%. Under such continuous drastic volume changes, silicon will gradually break or even shatter, until it is completely separated from the electrode and loses electrical activity. . In addition, silicon is not very conductive, and it does not transport charge efficiently, which will reduce the electrical transport efficiency of the entire battery.

In order to solve these problems of using silicon as the anode material of lithium-ion batteries, researchers at home and abroad have proposed many schemes. Among them, the way of silicon-carbon composite has received the most attention. This is because: First, the conductivity of carbon is very good. After silicon and carbon are composited, the conductivity of this system will be greatly improved. Then, the mechanical ductility of carbon is very good, which can effectively alleviate the volume expansion of silicon and improve the cycle stability of the system.

Shilong Jing et al. (Shilong Jin, Hao Jiang, Yanjie Hu, Jianhua Shen, and Chunzhong Li. Face-to-Face Contact and Open-Void Coin Involved SiC Nanohybrids Lithium-Ion Battery Anodes with Extremely Long CycleLife. Adv. Funct. Mater. 2015, 25 , 5395-5401.) designed a graphene/carbon nanotube three-dimensional airgel composite as a carrier, and then loaded nano silicon particles in the middle of the airgel network. In this way, the three-dimensional carbon material network will maintain excellent electrical contact with the silicon particles, making the electrical conductivity of this system significantly improved. In addition, the silicon particles still maintain electrical contact with the three-dimensional carbon material network after swelling, maintaining the activity of silicon. However, graphene and carbon nanotubes and nano-silicon particles are expensive and difficult to mass-produce, so the design of this material is difficult to industrialize.

Qinbai Yun et al. (Qinbai Yun, Xianying Qin, Wei Lv, Yan-Bing He, Baohua Li, Feiyu Kang, Quan-Hong Yang.'Concrete'inspired construction of a silicon carbon hybrid electrode for high performance lithium ion battery. CARBON 93(2015) 59-67.) designed an electrode with a structure similar to cement, that is, graphene, nano-silicon particles, and PAN were first made into slurry and coated on the current collector, and then PAN was cracked into carbon at high temperature, and the obtained negative electrode structure was : Silicon nanoparticles are dispersed in the three-dimensional network composed of graphene and cracked carbon, which improves the conductivity of the system and effectively alleviates the volume expansion of silicon. However, similar to the problem of the above solution, graphene and nano-silicon particles are expensive and difficult to mass-produce. Therefore, it is difficult to achieve industrialization of this material system.

Wan-Jing Yu et al. (Wan-Jing Yu, Chang Liu, Peng-Xiang Hou, Lili Zhang, Xu-YiShan, Feng Li and Hui-Ming Cheng. Lithiation of Silicon Nanoparticles Confinedin Carbon Nanotubes. ACS NANO 2015, 5063-5071. ) Deposit silicon particles inside the carbon nanotubes by CVD, so that the silicon can be confined inside the carbon tubes. In this way, when the volume of the silicon particles expands, the carbon nanotubes will also expand, but they will not break, which can effectively relieve the volume of silicon. Expansion effect, so it has high cycle stability. However, the method of CVD to deposit silicon particles in carbon nanotubes has very high requirements on equipment, it is difficult to mass produce, the cost is high, and it is difficult to embark on the road of industrialization.

Contents of the invention

The invention provides a method for preparing a porous silicon-carbon composite material, the process is simple and easy to repeat, and large-scale industrial production can be realized. The prepared porous silicon-carbon composite material is used as an anode material in a lithium-ion battery, which will significantly improve the cycle stability of the lithium-ion battery.

A method for preparing a porous silicon-carbon composite material, specifically comprising the following steps:

The magnesium silicide powder is placed in a CO ₂ /Ar mixed atmosphere, heat-treated at 700-900° C., and then pickled and post-treated to obtain the porous silicon-copper composite material;

In the CO ₂ /Ar mixed atmosphere, the volume fraction of CO ₂ is 10-90%.

In the present invention, using magnesium silicide as raw material and CO ₂ /Ar mixed gas as reaction gas, the porous silicon-carbon composite material is successfully synthesized. This invention utilizes the chemical reaction principle that magnesium silicide is thermally decomposed into silicon and magnesium, and magnesium can reduce carbon in carbon dioxide. The porous silicon-carbon obtained by pickling afterwards has a high specific capacity when used as a lithium ion negative electrode material and excellent cycle stability. The method is very simple, the operation process is simple and convenient, the instruments and equipment used are common and readily available, the raw materials used are all industrial products, and large-scale industrial production can be easily realized.

In the present invention, a very simple process is used to obtain porous silicon. When porous silicon is used as a lithium-ion battery negative electrode material, its surface area is large, the active area is large, the transmission distance of lithium ions and electrons is short, and the charging and discharging efficiency will be greatly improved. improve. Moreover, the porous structure effectively provides space for silicon to expand inwardly, which can well alleviate the dramatic outward volume expansion effect of silicon during lithium intercalation, and achieve high cycle stability and safety. While preparing porous silicon, the invention successfully composites carbon and porous silicon to obtain a porous silicon-carbon composite material. In this composite material, carbon covers the surface of silicon, which greatly improves the conductivity of the system on the one hand, and effectively alleviates the outward volume expansion of silicon on the other hand.

Preferably, in the CO ₂ /Ar mixed atmosphere, the volume fraction of CO ₂ is 20-80%. More preferably, the volume fraction of CO ₂ is 40-60%. It is found through experiments that at this time, the carbon content in the product is the highest. This may be because CO ₂ is a relatively weak oxidizing gas, and its redox reaction with magnesium can only occur in a concentrated CO ₂ or even pure CO ₂ atmosphere. However, since the C produced by the reaction is also reducible, although its reducibility is not as strong as that of metal magnesium, it is still possible to react with concentrated CO ₂ to reduce the carbon content in the product. When the carbon content in the product is higher, the buffering effect of carbon on the volume change of silicon when deintercalating lithium ions is more obvious, and the conductivity of the entire system is also improved. Therefore, when it is used as a negative electrode material for lithium-ion batteries, Its cycle performance is also more stable.

Preferably, the heat treatment time is 10-20 hours.

Preferably, the pickling uses hydrochloric acid with a concentration of 0.5-5 mol/L, and the treatment time is 2-10 hours.

Preferably, the post-treatment includes water washing, product centrifugation and vacuum drying.

The invention also discloses the porous silicon-carbon composite material prepared according to the above method, and its application in lithium ion batteries. It can be known from experiments that using the porous silicon-carbon composite material prepared by the present invention as a negative electrode material for assembling a lithium ion battery can significantly improve the cycle stability of the lithium ion battery.

Compared with the prior art, the present invention has the following beneficial technical effects:

1) In the field of preparation of anode materials for lithium batteries, it was proposed for the first time to use carbon dioxide as a carbon source to prepare silicon-carbon composite materials. In comparison, industrially coated carbon is often obtained by high-temperature cracking of organic matter such as pitch in an inert atmosphere. During the cracking process of these carbon sources, a large amount of toxic and harmful gases will be released, and carbon dioxide as a carbon source is not only a source Abundant, cheap, without any environmental pollution, and consumes a large amount of gas that causes the greenhouse effect-carbon dioxide, it is an environmentally friendly carbon source.

2) While preparing porous silicon, the reaction of magnesium and carbon dioxide is cleverly used, so that the process steps of carbon coating are incorporated into the preparation process of porous silicon, and the porous silicon-carbon composite material is prepared in one step. The carbon encapsulation process in the prior art needs to be ball-milled and mixed with liquid or solid organic matter carbon sources first, then dried, and then subjected to high-temperature heat treatment. Uniformity makes it difficult for the carbon on the bag to be even, and even many places cannot be covered. In contrast, carbon dioxide as a gaseous carbon source can fully contact with silicon, and the generated carbon can also be more uniformly coated on the surface of silicon, forming a more uniform and denser carbon film. Applying it as a cathode material in a lithium-ion battery will improve the cycle stability of the battery.

3) The process is simple and easy to repeat, and the source of raw materials is abundant and cheap, and large-scale industrial production can be realized.

Description of drawings

Fig. 1 is the test result of the porous silicon-carbon composite material that embodiment 1 prepares; Fig. 1 a and Fig. 1 b are its scanning electron micrograph (SEM), Fig. 1 c is its transmission electron micrograph (TEM), Fig. 1 d is its x-ray probe Needle Energy Spectroscopy (EDS).

Fig. 2 is a comparison chart of the cycle specific capacity curve and Coulombic efficiency of the lithium-ion battery assembled with the porous silicon-carbon composite material prepared in Example 1 and Comparative Example respectively as the negative electrode material. Wherein, the solid ones are the data points of the product of this embodiment, and the hollow ones are the data points of the product of Comparative Example 1.

Fig. 3 is a comparison chart of cycle specific capacity curves and coulombic efficiency of lithium-ion batteries assembled with porous silicon-carbon composite materials prepared in Example 3 and Comparative Example respectively as negative electrode materials. Wherein, the solid ones are the data points of the product of this embodiment, and the hollow ones are the data points of the product of Comparative Example 1.

Fig. 4 is a comparison chart of cycle specific capacity curves and coulombic efficiency of lithium-ion batteries assembled with porous silicon-carbon composite materials prepared in Example 5 and Comparative Example respectively as negative electrode materials. Wherein, the solid ones are the data points of the product of this embodiment, and the hollow ones are the data points of the product of Comparative Example 1.

Detailed ways

The present invention will be further described below through specific examples, but the protection scope of the present invention is not limited to the following examples.

Example 1

1) Magnesium silicide is heat-treated at 700° C. for 20 hours, and an excess CO ₂ /Ar mixed gas with a volume fraction of 80% of CO ₂ is used as a reaction gas during the heat treatment.

2) The product obtained in step 1) was treated for 10 hours in a certain concentration of hydrochloric acid solution, wherein the concentration of hydrochloric acid was 0.5 mol/liter, after the acid treatment, it was washed 5 times with deionized water, then centrifuged, and finally vacuum-dried.

The relevant characterization results of the porous silicon-carbon composite material prepared in this example are shown in FIG. 1 . It can be seen from the figure that the product of this example is a porous structure with a large number of uniformly distributed nanoscale pores, the mass fraction of carbon is about 40%, and it is uniformly coated on the surface of silicon in the form of an amorphous carbon film, forming a porous structure with a core. -Silicon-carbon composite material with shell structure characteristics.

The porous silicon-carbon composite material prepared in this example was made into a button battery for performance testing, and its cycle capacity curve and Coulombic efficiency of each cycle were obtained.

The cycle specific capacity and coulombic efficiency were compared with the porous silicon-carbon composite material prepared in the comparative example, and the results are shown in Figure 2. It can be seen from the figure that after 50 cycles, the capacity of the porous silicon-carbon prepared by this process is much higher than that of the comparison material, the cycle stability is more excellent, and the superiority of its performance is very obvious.

Example 2

The preparation process is exactly the same as that of Example 1, except that in the CO ₂ /Ar gas mixture, the volume fraction of CO ₂ is 60%. The morphology of the prepared porous silicon-carbon composite material is similar to that of Example 1, but the mass fraction of carbon is about 45%.

Example 3

1) Magnesium silicide is heat-treated at 800° C. for 15 hours, and an excess CO ₂ /Ar mixed gas with a volume fraction of 50% of CO ₂ is used as a reaction gas during the heat treatment.

2) The product obtained in step 1) was treated for 5 hours in a certain concentration of hydrochloric acid solution, wherein the concentration of hydrochloric acid was 2.0 mol/liter, after the acid treatment, it was washed 7 times with deionized water, then centrifuged, and finally vacuum-dried.

The morphology of the porous silicon-carbon composite material prepared in this example is similar to that of Example 1, but the mass fraction of carbon is about 46%.

The porous silicon-carbon composite material prepared in this example was made into a button battery for performance testing, and the cycle specific capacity and coulombic efficiency were compared with the porous silicon-carbon composite material prepared in the comparative example, as shown in FIG. 3 . It can be seen from the figure that after 50 cycles, the capacity of the porous silicon-carbon prepared by this process is much higher than that of the comparison material, the cycle stability is more excellent, and the superiority of its performance is very obvious.

Example 4

The preparation process is exactly the same as that of Example 1, except that in the CO ₂ /Ar gas mixture, the volume fraction of CO ₂ is 40%. The morphology of the prepared porous silicon-carbon composite material is similar to that of Example 1, but the mass fraction of carbon is about 46%.

Example 5

1) Magnesium silicide is heat-treated at 900° C. for 10 h, and an excess CO ₂ /Ar mixed gas with a volume fraction of 20% of CO ₂ is used as a reaction gas during the heat treatment.

2) The product obtained in step 1) was treated for 2 hours in a certain concentration of hydrochloric acid solution, wherein the concentration of hydrochloric acid was 5 mol/liter, after the acid treatment, it was washed 8 times with deionized water, then centrifuged, and finally vacuum-dried. The relevant test results of the obtained porous silicon are shown in FIG. 1 .

The morphology of the porous silicon-carbon composite material prepared in this example is similar to that of Example 1, but the mass fraction of carbon is about 41%.

The porous silicon-carbon composite material prepared in this example was made into a button battery for performance testing, and the cycle specific capacity and coulombic efficiency were compared with the porous silicon-carbon composite material prepared in the comparative example, as shown in FIG. 4 . It can be seen from the figure that after 50 cycles, the capacity of the porous silicon-carbon prepared by this process is much higher than that of the comparison material, the cycle stability is more excellent, and the superiority of its performance is very obvious.

comparative example

Adopting the preparation method in the patent document whose publication number is CN103779544A, specifically:

First, ball mill and mix magnesium silicide and polyvinyl alcohol with a mass ratio of 1:2. Then, heat treatment at 350° C. for 5 hours, and then heat treatment at 700° C. for 15 hours. The heat treatment atmosphere is a mixture of argon and air, and the fraction of argon gas is 90%. Finally, the heat-treated product was treated in a mixed acid solution of hydrochloric acid and hydrofluoric acid for 5 hours, then centrifuged, and dried to obtain porous silicon-carbon particles with organic matter as the carbon source (here, polyvinyl alcohol).

Claims (8)

1. A method for preparing porous silicon-carbon composite material, characterized in that, the steps are as follows: The magnesium silicide powder is placed in a CO ₂ /Ar mixed atmosphere, heat-treated at 700-900° C., and then pickled and post-treated to obtain the porous silicon-carbon composite material; In the CO ₂ /Ar mixed atmosphere, the volume fraction of CO ₂ is 10-90%. 2. The method for preparing porous silicon-carbon composite material according to claim 1, characterized in that, in the CO ₂ /Ar mixed atmosphere, the volume fraction of CO ₂ is 20-80%. 3. The method for preparing porous silicon-carbon composite material according to claim 1, characterized in that, in the CO ₂ /Ar mixed atmosphere, the volume fraction of CO ₂ is 40-60%. 4. The method for preparing porous silicon-carbon composite material according to claim 1, characterized in that, the heat treatment time is 10-20 hours. 5 . The method for preparing porous silicon-carbon composite material according to claim 1 , characterized in that, the pickling uses hydrochloric acid with a concentration of 0.5-5 mol/L, and the treatment time is 2-10 hours. 6. The method for preparing porous silicon-carbon composite material according to claim 1, characterized in that, the post-treatment includes water washing, product centrifugation and vacuum drying. 7. A porous silicon-carbon composite material prepared by the method according to any one of claims 1-6. 8. An application of the porous silicon-carbon composite material according to claim 7 in lithium ion batteries.