CN108736006B

CN108736006B - A kind of method for preparing silicon-carbon composite material

Info

Publication number: CN108736006B
Application number: CN201810830729.XA
Authority: CN
Inventors: 洪若瑜; 高茂川; 王芳芳; 王为旺
Original assignee: Fuzhou University
Current assignee: Fuzhou University
Priority date: 2018-07-26
Filing date: 2018-07-26
Publication date: 2021-06-22
Anticipated expiration: 2038-07-26
Also published as: CN108736006A

Abstract

The invention discloses a method for preparing a silicon-carbon composite material. After mechanically crushing bulk polycrystalline silicon raw materials, dry grinding and ultra-fine grinding techniques are used to grind them to powder, and with the aid of a water-soluble surfactant, multi-stage grinding is carried out. A nano-silicon slurry is prepared; an appropriate proportion of graphene and nano-silicon are mixed uniformly by vacuum homogenization technology, and then a silicon-carbon composite material is obtained through processes such as spray drying, granulation and sieving. In the process of preparing nano-silicon, the method does not need to use toxic reagents, and does not need complex processes such as acid dissolution, etching and washing, is clean and environmentally friendly, has high product purity, and is the most efficient and most economical method; Slurry, spray drying, granulation, sieving, etc. are all industrially mature operations, that is, this method can realize large-scale industrial production of silicon-carbon composite materials, and prepare silicon-carbon materials with different properties by designing process parameters.

Description

Method for preparing silicon-carbon composite material

Technical Field

The invention relates to the technical field of preparation of lithium battery cathode materials, in particular to a method for preparing a silicon-carbon composite material.

Background

With the economic globalization and the large use of fossil fuels, the problems of environmental pollution and energy shortage are becoming prominent. The search for new replaceable, renewable and sustainable new energy is an important development direction, and the lithium ion battery is taken as an important representative in the field of new energy and has been widely applied to multiple fields of life, production, military, scientific research and the like. The specific capacity of the lithium ion battery is improved, the cycle performance of the lithium ion battery is improved, the service life of the lithium ion battery is prolonged, the future development of the lithium ion battery is emphasized, and the electrochemical performance of the negative electrode material plays a significant role in the industrialization and development prospects of the lithium ion battery.

The negative electrode material is one of the key materials of the lithium ion battery, and from the development history of the lithium ion battery, the development of the negative electrode material promotes the lithium ion battery to enter into commercial application. In the first lithium ion battery, metallic lithium was used as a negative electrode material, but metallic lithium is likely to cause lithium dendrite during charging, which leads to safety problems such as ignition and explosion. Lithium alloy materials have been developed later, and it is expected to solve the above-mentioned safety problem, but the alloy materials are liable to undergo volume expansion upon lithium intercalation and deintercalation, resulting in a decrease in cycle performance. Through further research and comparison, graphitized carbon is finally selected as a commercial negative electrode material of a lithium ion battery. The carbonaceous material has mainly the following advantages: the specific capacity is higher, the electrode potential is low, the cycle efficiency is high, and the cycle life is long, but with the continuous improvement of the requirement of the new energy automobile on the endurance mileage in the practical application, the related materials of the power battery are developed towards the direction of higher energy density. The graphite cathode of the traditional lithium ion battery can not meet the existing requirements, and the cathode material with high energy density becomes a new hot spot pursued by enterprises.

Graphene has excellent thermal, electrical and mechanical properties, and has important application prospects in the aspects of materials science, micro-nano processing, energy, biomedicine and the like, and since physicists Andeli Gammaste university in England and Constantine NorW Shoulov in 2004, after graphene is obtained from graphite for the first time by a micro-mechanical stripping method, research on graphene is vigorously carried out in all countries. In recent years, researches show that graphene has excellent electronic conduction performance and can form a three-dimensional electronic and ion transmission network structure among electrode material particles. The charging and discharging speed of the lithium ion battery is determined by the transmission and de-intercalation speed of lithium ions in an electrode, namely, the graphene material is applied to the lithium ion battery, so that the charging and discharging speed of the lithium ion battery can be greatly improved, the great breakthrough of the battery technology is realized, and the leap-in development of the new energy industry is promoted.

However, such lithium ion batteries suffer from complexity of the graphene preparation process, and are relatively expensive; in addition, although the graphene material has very high electric and thermal conduction rates, when the graphene material is used as a negative electrode material of a lithium battery, the problems of low first-cycle coulomb efficiency, serious charge-discharge curve hysteresis and the like exist, so that the graphene material is difficult to be used as an electrode material independently. Nevertheless, graphene has the advantage of being unique if its unique flexible structure is composited with high capacity metals or other nanoparticles for use as a negative electrode material.

Many studies have been reported on graphene-based composite materials for lithium ion battery negative electrodes, and the graphene-based composite materials are mainly compounded with metals, metal oxides, silicon, or the like. The silicon has the highest energy density in the existing numerous cathode materials, and the addition of the graphene powder can solve the problems of shortened service life and poor cycle stability of the battery caused by severe volume expansion and crushing of the silicon cathode material in the lithium storage and discharge processes of the battery. Meanwhile, the specific capacity of the silicon material can reach 4200 mA.h/g, and the silicon material has rich reserve capacity, low price, greenness and no toxicity; namely, the graphene and the silicon material both have certain advantages of being used as the lithium ion battery cathode, and the combination of the graphene and the silicon material can make up respective defects and give play to respective advantages to prepare the high-performance lithium battery cathode material. The silicon-graphene composite material is certainly applied to the field of power lithium ion batteries with high energy density and high power density requirements, the comprehensive performance of the power batteries is greatly improved, and the development of the fields of electric tools, new energy automobiles, aerospace and the like is promoted.

At present, many researchers have proposed a method for preparing a silicon-graphene composite material, for example, university of electronic technology discloses a graphene-silicon composite material, a preparation method and applications thereof (patent application No. 201611082895.3), in which graphene oxide and nano-silicon are dispersed in water under ultrasonic stirring, silicon and graphene uniformly grow in nickel foam through hydrothermal reaction, and then the silicon and graphene are freeze-dried in vacuum, and the composite material is obtained through high-temperature reduction under a protective atmosphere. On one hand, the preparation method requires harsh operating conditions and environment, and is difficult to apply to industrial production; on the other hand, graphene oxide is selected as a raw material, high-temperature reduction is needed later, and meanwhile, in the existing graphene oxide preparation process, the processes of washing, pickling, ultrasonic treatment, centrifugation, drying and the like are needed, so that waste liquid and waste gas are generated in the production process, and the environment is polluted.

In order to improve the preparation environment and harsh conditions of composite materials, griffith automobile gmbh discloses a silicon-based negative electrode material and a preparation method and application thereof (patent application No. 201410531148.8), the method comprises dispersing nano silicon particles in an ethanol solution of graphene, adding the graphene embedded with nano silicon into a solution containing metal salt after separation and washing, adding hydrofluoric acid with a certain concentration, obtaining the graphene embedded with nano silicon and nano metal by centrifugation, and then calcining to obtain the silicon-based negative electrode material. Although the method overcomes the harsh conditions of the preparation process, the whole preparation process is complex, and the condition of the composite material in each step is difficult to accurately judge, so that the quality of a target product is difficult to ensure; meanwhile, the metal salt solution and hydrofluoric acid are used in the preparation process, and the washing and separating process can cause the problems of consumption of a large amount of water resources and wastewater treatment; and meanwhile, the residual ions can influence the subsequent application of the composite material.

In order to enable the preparation process of the graphene-nano silicon composite material to be simpler, more efficient, cleaner and environmentally friendly, Beijing aerospace university discloses a method for preparing a graphene/nano silicon lithium ion battery cathode material by a liquid phase physical method (patent CN 201510294379), wherein the preparation method comprises the steps of carrying out suction filtration and centrifugation on obtained supernatant liquid through ultrasonic graphite powder and nano silicon powder dispersion liquid, and carrying out calcination treatment to obtain the graphene and nano silicon composite material. Although the method has simple process, because a plurality of nano-silicon are exposed outside, the capacity is low and the cycle is poor.

The method comprises the steps of grinding blocky polycrystalline silicon into nano silicon slurry by utilizing a multistage grinding technology, and adding graphene powder into the nano silicon slurry obtained by grinding according to a proper proportion; and uniformly mixing the graphene and the nano-silicon by a vacuum homogenizer under a certain condition, and then carrying out spray drying, granulation and sieving to obtain the nano-silicon-graphene composite material.

Preparation of nanosilicon, phase, using multistage millingFor the traditional nano silicon preparation technology, the method has the following advantages: firstly, the multistage grinding technology and the industrial use of SiH are used₄、SiCl₄Compared with the safer process for producing the nano silicon by gas cracking, the process can ensure that the preparation process of the nano silicon is safer, does not generate waste gas and is more environment-friendly; the ecological civilized construction connotation advocated by the state at present is met. And secondly, continuous production can be carried out by using a multistage grinding technology, equipment required by the whole production line can be completely obtained in the market, the production process of grinding and preparing the nano silicon is simple, and a complex production process and harsh production conditions are not required, so that the nano silicon grinding technology can be applied to industrial production. Compared with other production processes, the nano silicon prepared by multistage grinding has high purity and few impurities, and the impurities mainly comprise silicon carbide and zirconia, so that the nano silicon has almost no influence on subsequent application in the field of lithium batteries.

According to the invention, graphene is selected as a carbon source of the silicon-carbon composite material, and the high conductivity, the high specific surface area, the high flexibility and the sheet structure of the graphene can well improve the conductivity of the silicon-carbon material and contain the volume change of silicon during charging and discharging. Meanwhile, nano-grade silicon is selected as a silicon material, so that the stress generated by the volume change of the nano-grade silicon during charging and discharging is dispersed, and the nano-grade silicon can be well compounded with graphene to generate a silicon-carbon composite material with a better structure and stable performance. Although the prepared silicon-carbon composite material is likely to have relatively low capacity compared with the silicon-carbon material with ultrahigh performance, the silicon-carbon composite material can be industrially produced in batches, the preparation process is simple and feasible, and the performance of the prepared silicon-carbon composite material is obviously improved in specific capacity and cycle stability compared with that of a commercial graphite cathode material, so that the requirements of a power battery can be met.

Disclosure of Invention

The invention aims to provide a method for preparing a silicon-carbon composite material aiming at the defects of the prior art, the process comprises two parts, namely preparation of nano silicon slurry and preparation of the silicon-carbon composite material, and the specific steps are as follows:

(1) preparing nano silicon slurry: putting the blocky polycrystalline silicon raw material into a full-ceramic machine for mechanical crushing, grinding polycrystalline silicon powder by using a double-roller high-pressure grinding machine in a dry method, then carrying out superfine grinding, and carrying out graded wet grinding by using a horizontal grinding machine and a vertical circulating grinding machine respectively under the assistance of a water-soluble surfactant to obtain nano silicon slurry;

(2) preparation of silicon-carbon composite material: adding graphene powder into the nano silicon slurry obtained by grinding in the step (1) according to a proper proportion, and uniformly mixing graphene and nano silicon by using a vacuum homogenizer to obtain nano silicon-graphene slurry; and then the silicon-carbon composite material is obtained through the processes of spray drying, granulation and sieving.

Putting the blocky polycrystalline silicon raw material into a full ceramic machine for crushing, grinding polycrystalline silicon powder by using a double-roller high-pressure grinding machine in a dry method, and then carrying out superfine grinding; wherein the grain size of the blocky polycrystalline silicon is 30 mm-250 mm, the polycrystalline silicon powder is ground to 1 mm-7 mm by a double-roller high-pressure grinding machine in a dry method, and is superfine ground to the grain size of 10 mu m-80 mu m.

The water-soluble surfactant comprises polyethylene glycol and water-soluble polyaniline.

In the step (1), a horizontal grinding machine and a vertical circulating grinding machine are respectively used for carrying out classification wet grinding; wherein the grinding time by a horizontal grinder is 3-6 hours (preferably 4-5.5 hours), and the particle size is 300-600 nm (preferably 400-500 nm); the grinding time is 6-28 hours (preferably 8-14 hours) by using a vertical grinder, and the particle size is 60 nm-160 nm (preferably 90 nm-140 nm).

In the step (2), the mass ratio of the nano silicon to the graphene is 0.5: 9.5-6.5: 3.5 (preferably 2.5: 7.5-4.5: 5.5).

In the spray drying in the step (2), the temperature of an air inlet is 180-280 ℃ (preferably 200-240 ℃), and the temperature of an outlet is 90-170 ℃ (preferably 110-130 ℃).

The invention has the beneficial effects that:

1) the nano silicon is prepared by grinding, toxic reagents are not needed in the preparation process, and complex processes such as acid dissolution, etching, washing and the like are not needed, so that the method is the most efficient and most economic; meanwhile, the nano silicon prepared by grinding has high purity and few impurities which have subsequent influences (a small amount of impurities are mainly silicon carbide and zirconium oxide); vacuum homogenization, spray drying, granulation and sieving are all industrialized mature operations, namely large-scale industrial production of the silicon-carbon composite material can be realized by the method, the production process is more environment-friendly and has less pollution, and simultaneously, the production of nano silicon by multistage grinding can easily realize the annual production of 500 tons (dry powder quality), thereby ensuring the productivity of 1500 tons/year of silicon-carbon composite material;

2) meanwhile, aiming at the process, silicon-carbon composite materials with different performances can be prepared by adjusting process parameters, for medium-high-end lithium battery materials, nano silicon slurry with smaller particle size can be prepared by increasing the multistage grinding time of nano silicon, and meanwhile, high-performance silicon-carbon composite materials can be obtained by using high-quality graphene powder, controlling the proportion of nano silicon and graphene, increasing the vacuum homogenization time and the like; the production process can give consideration to both production cost and product performance, and can design process parameters to produce the performance of the silicon-carbon composite material with different performances according to different requirements.

Drawings

FIG. 1 is a flow chart of the preparation of nano-silicon slurry according to the embodiment of the present invention;

FIG. 2 is a scanning electron micrograph of a silicon-carbon composite;

FIG. 3 is a TEM image, an AFM topography image, and a height information map of a silicon-carbon composite;

FIG. 4 is a test chart of a silicon-carbon composite material as a negative active material for a lithium battery.

Detailed Description

Hereinafter, embodiments of the present invention will be described in detail with reference to examples, and it will be understood by those skilled in the art that the following examples are only preferred examples of the present invention in order to better understand the present invention, and thus should not be construed as limiting the scope of the present invention.

Example 1

Placing a polysilicon raw material with the particle size of about 15cm into a full-ceramic crusher for mechanical crushing, then grinding polysilicon powder to the particle size of about 2 mm by using a double-roller high-pressure grinding machine in a dry method, carrying out superfine grinding to about 500 meshes, and grinding for 4 hours to the particle size of about 500 nm by using a horizontal grinding machine with the assistance of a water-soluble surfactant polyethylene glycol; separating by a tubular centrifuge, returning materials with the particle size of more than 500 nm to mix and grind, grinding the slurry with the particle size of less than 500 nm in a vertical grinder for 8 hours to obtain the nano silicon slurry with the particle size of about 140 nm, and separating to obtain the nano silicon slurry. Adding graphene powder into the nano silicon slurry according to the ratio of 2:8 of nano silicon to graphene, uniformly mixing by using a vacuum homogenizer, and then carrying out spray drying, granulation and sieving under the conditions that the inlet temperature is 260 ℃ and the outlet temperature is 100 ℃ to obtain the silicon-carbon composite material. The scanning electron micrograph of the prepared silicon-carbon composite material is shown in fig. 2.

Example 2

Placing a polycrystalline silicon raw material with the particle size of about 18cm into a full-ceramic crusher for mechanical crushing, then using a double-roller high-pressure grinding machine for dry grinding polycrystalline silicon powder to the particle size of about 2 mm, carrying out superfine grinding to about 500 meshes, and using a horizontal grinding machine for grinding for 6 hours to the particle size of about 350 nm with the aid of surfactant water-soluble polyaniline; separating by a tubular centrifuge, returning materials with the particle size of more than 350 nm to mix and grind, grinding the slurry with the particle size of less than 350 nm in a vertical grinder for 12 hours to obtain the nano silicon slurry with the particle size of about 100 nm, and separating to obtain the nano silicon slurry. Adding graphene powder into nano silicon slurry according to the ratio of nano silicon to graphene of 2.5:7.5, uniformly mixing by using a vacuum homogenizer, and then carrying out spray drying, granulation and sieving under the conditions that the inlet temperature is 280 ℃ and the outlet temperature is 110 ℃ to obtain the silicon-carbon composite material. The TEM layer number image and the AFM topography image of the prepared product are shown in the attached figure 3.

Example 3

Placing a polycrystalline silicon raw material with the particle size of about 12cm into a full-ceramic crusher for mechanical crushing, then grinding polycrystalline silicon powder to the particle size of about 2 mm by using a double-roller high-pressure grinding machine in a dry method, carrying out superfine grinding to about 500 meshes, and grinding for 6 hours to the particle size of about 350 nm by using a horizontal grinding machine with the assistance of water-soluble polyaniline serving as a surfactant; separating by a tubular centrifuge, returning materials with the particle size of more than 350 nm to mix and grind, grinding the slurry with the particle size of less than 350 nm in a vertical grinder for 18 hours to obtain the nano silicon slurry with the particle size of about 70 nm, and separating to obtain the nano silicon slurry. Adding graphene powder into nano silicon slurry according to the ratio of nano silicon to graphene of 3.5:6.5, uniformly mixing by using a vacuum homogenizer, and then carrying out spray drying, granulation and sieving under the conditions that the inlet temperature is 240 ℃ and the outlet temperature is 120 ℃ to obtain the silicon-carbon composite material. The test chart of the silicon-carbon composite material prepared as the negative active material of the lithium battery is shown in figure 4.

The above description is only a preferred embodiment of the present invention, and all equivalent changes and modifications made in accordance with the claims of the present invention should be covered by the present invention.

Claims

1. a method for preparing silicon-carbon composite material, is characterized in that: process comprises the preparation of nano-silicon slurry and the preparation of silicon-carbon composite material, and concrete steps are as follows:

(1) Preparation of nano-silicon slurry: After the bulk polysilicon raw material is put into all-ceramic mechanical crushing, the polysilicon powder is dry-ground with a double-roll high-pressure grinder, and then ultra-finely pulverized. With the assistance of water-soluble surfactants , respectively use a horizontal grinder and a vertical circulating grinder to perform graded wet grinding to obtain nano-silicon slurry;

(2) Preparation of silicon-carbon composite material: adding graphene powder to the nano-silicon slurry obtained by grinding in step (1), and using a vacuum homogenizer to uniformly mix graphene and nano-silicon to obtain nano-silicon-graphite olefin slurry; and then through the process of spray drying, granulation and sieving, the silicon-carbon composite material is obtained;

After the bulk polysilicon raw material is put into the all-ceramic mechanical crushing, the polysilicon powder is dry ground by a double-roll high-pressure grinder, and then ultra-finely pulverized; the particle size of the bulk polysilicon is 30 mm~250 mm, and the double-roll high-pressure grinder is used. Dry grinding the polysilicon powder to 1 mm~7 mm, and ultrafinely pulverize it to a particle size of 10 μm~80 μm;

In step (1), a horizontal grinder and a vertical circulating grinder are used for classified wet grinding; wherein the horizontal grinder is used for grinding for 3 to 6 hours, and the particle size is 300 nm to 600 nm; The grinding time of the grinding machine is 6-28 hours, and the particle size is 60 nm-160 nm; the mass ratio of the nano-silicon slurry to the graphene powder is 0.5:9.5-6.5:3.5.

2 . The method of claim 1 , wherein the water-soluble surfactant comprises polyethylene glycol and water-soluble polyaniline. 3 .

3. A method for preparing silicon-carbon composite material according to claim 1, characterized in that: in step (1), a horizontal grinding machine and a vertical circulating grinding machine are respectively used for graded wet grinding; wherein using The grinding time of the horizontal mill is 3~6 hours, and the particle size is 300 nm~600 nm; the grinding time of the vertical mill is 6~28 hours, and the particle size is 60 nm~160 nm.

4. The method for preparing a silicon-carbon composite material according to claim 1, wherein the mass ratio of the nano-silicon slurry to the graphene powder is 2.5:7.5~4.5:5.5.

5 . The method for preparing silicon-carbon composite material according to claim 1 , wherein in the spray drying in step (2), the temperature of the air inlet is 180°C to 280°C, and the temperature of the outlet is 90°C. 6 . ~170°C.

6. The method for preparing a silicon-carbon composite material according to claim 5, wherein the air inlet temperature is 200°C to 240°C and the outlet temperature is 110°C to 130°C during spray drying.