CN111244414A - A kind of method for preparing silicon carbon anode material by magnesium thermal reduction - Google Patents

Abstract

The invention discloses a method for preparing a silicon carbon negative electrode material by magnesium thermal reduction. The method comprises the following steps: roasting microsilicon powder, then dispersing it in an acid etching solution, heating in a water bath, suction filtration, washing and drying to obtain a pretreated sample; The pretreated sample and magnesium powder are mixed by ball milling, placed in a sealed graphite crucible after natural drying, and transferred to a tube furnace with inert gas for magnesium thermal reaction. The obtained product is acid washed, vacuum filtered, washed with water and dried. Then the porous crystalline silicon is obtained; the obtained porous crystalline silicon and the organic precursor are mixed uniformly, then dried, and then placed in a protective gas for curing to obtain a silicon-based composite material. The invention obtains porous crystalline silicon through acid etching pretreatment and magnesium thermal reduction treatment of micro silicon powder; the silicon material not only has high specific capacity, but also the formed porous structure plays the role of buffering its own volume expansion on the one hand On the other hand, it also shortens the depth and diffusion distance of lithium ion deintercalation, which makes it show excellent electrochemical performance.

Description

A kind of method for preparing silicon carbon anode material by magnesium thermal reduction

technical field

The invention relates to a method for preparing a silicon carbon negative electrode material by magnesium thermal reduction, and belongs to the technical field of silicon materials.

Background technique

Lithium-ion batteries have the advantages of high operating voltage, high specific energy, long cycle life, light weight, and low self-discharge. They are widely used in various portable electronic devices, electric vehicles, etc. As the main lithium storage host of lithium-ion batteries, the anode material has always been dominated by carbon materials. Carbon anodes have disadvantages such as low specific capacity and low initial charge-discharge efficiency. Therefore, the search for a lithium-ion battery anode material with high specific capacity, low price and abundant materials has become the focus of attention. With its theoretical capacity as high as 4200mAh/g and abundant materials, silicon material has become the most promising anode material for next-generation lithium-ion batteries. However, the silicon negative electrode will experience severe volume expansion (300%) in the fully intercalated state of lithium, which causes the pulverization and shedding of material particles, and also leads to the repeated growth of the surface SEI film, which consumes electrolyte and lithium source. affect its electrochemical performance.

In order to solve this problem, many methods have been proposed, such as preparing multiphase composite materials, such as silicon nanoparticles, silicon nanowires, nanotubes, hollow spheres, etc. to alleviate its volume effect, and at the same time improve the silicon anode through carbon coating treatment. The electrical conductivity of the material; although the lithium-ion battery anode materials prepared by these methods show good performance, the preparation cost is high and the preparation process is complicated.

SUMMARY OF THE INVENTION

In order to solve the above technical problems, the purpose of the present invention is to provide a method for preparing silicon-carbon negative electrode material by magnesia thermal reduction. The carbon-coated surface modification treatment makes it show excellent electrochemical performance; this process is not only low in preparation cost, but also simple and easy to implement, and the purpose of the invention is achieved through the following technical solutions:

A method for preparing silicon carbon negative electrode material by magnesium thermal reduction, specifically comprising the following steps:

(1) Pretreatment of micro-silica fume: calcining micro-silica powder, then dispersing in acid etching solution, heating to 60-90°C in a water bath, stirring with power for 1-6 hours, suction filtration, washing and drying to obtain pretreated samples .

(2) Ball milling mixture and magnesium thermal reduction acid etching: Mix the pretreated microsilica powder and magnesium powder by ball milling, place them in a sealed graphite crucible after natural drying, and transfer them to an inert gas tube furnace for magnesium thermal reaction. , the obtained product is subjected to acid washing, vacuum filtration, water washing and drying to obtain porous crystalline silicon.

(3) Coating of the surface carbon layer: the obtained porous crystalline silicon and the organic precursor are mixed uniformly, then dried, then placed in an inert gas, and cured at 800-1100 ° C to obtain a silicon-based composite Material.

Preferably, in step (1) of the present invention, the etching solution is a mixture of one or more of hydrochloric acid, sulfuric acid, nitric acid, oxalic acid, and acetic acid, and the concentration of the etching solution is 3.26 mol/L.

Preferably, the calcination condition in step (1) of the present invention is calcination at 500-1100° C. for 4-10 hours.

Preferably, the mass ratio of the pretreated microsilica powder and the magnesium powder in the present invention is 1:(0.8-1.2).

Preferably, the ball milling parameters described in the step (2) of the present invention are: the rotational speed is 100-300 rpm, the mass ratio of the ball to the material is 1:(1-10), and the ball milling time is 4-12 hours.

Preferably, the temperature of the magnesium thermal reaction in step (2) of the present invention is 600-800° C., and the time is 1-10 hours.

Preferably, the inert gas described in step (2) of the present invention is a mixture of one or more of air, argon, and nitrogen.

Preferably, the acid used for pickling in step (2) of the present invention is hydrochloric acid, and the concentration of hydrochloric acid is 0.5-5 mol/L.

Preferably, the organic matter described in the step (3) of the present invention is one or more of sucrose, asphalt, polyaniline, phenolic resin, PVDF; the mass ratio of porous crystalline silicon to the organic matter precursor of the organic matter is 1:( 0.1-1).

The beneficial effects of the present invention are:

(1) In the present invention, nano-porous crystalline silicon is prepared by performing magnesium thermal reduction acid etching on micro-silicon, which is a waste product of silicon metallurgy industry; the pore structure not only buffers its own volume expansion, but also shortens the depth and diffusion of lithium ion deintercalation. distance, and the preparation cost is low, and the method is simple and easy to implement.

(2) A silicon/carbon composite structure is formed by coating a carbon layer on the surface of the silicon material by using the method of high temperature pyrolysis of organic matter, and the composite structure greatly improves the electrical conductivity and cycle stability of the silicon negative electrode material.

Description of drawings

FIG. 1 is the nitrogen adsorption-desorption diagram of the porous silicon prepared in Example 1. FIG.

FIG. 2 is a scanning electron microscope image of the porous silicon-based composite material prepared in Example 2. FIG.

FIG. 3 is a transmission electron microscope image of the porous silicon-based composite material prepared in Example 2. FIG.

FIG. 4 is a graph showing the electrochemical cycle of the silicon-based composite material at a current density of 0.5 A/g in Example 2. FIG.

Detailed ways

The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited to the content.

Example 1

A method for preparing silicon carbon negative electrode material by magnesium thermal reduction, specifically comprising the following steps:

(1) Pretreatment of micro-silica fume: calcining micro-silica powder at 500°C for 10 hours, then dispersing in a sulfuric acid solution with a concentration of 3.26 mol/L, heating to 60°C in a water bath, and stirring with suction for 6 hours, suction filtration, Washed and dried to obtain pretreated samples.

(2) The pretreated sample and the magnesium powder are mixed in a mass ratio of 1:0.8, using a planetary ball mill, the mass ratio of the ball to the material is 1:2, and the rotational speed is 150 rpm. The reaction mass was dried.

(3) the reaction mass was placed in a sealed graphite crucible, transferred to a tube furnace under an argon atmosphere, and kept at 600°C for 10 hours; the resulting product was acid-etched with 0.5mol/L hydrochloric acid for 12 hours to remove magnesium oxide and The by-product of magnesium silicide is filtered and dried to obtain porous crystalline silicon.

(4) The dried porous crystalline silicon and the phenolic resin are mixed in a mass ratio of 1:0.1 and then dried, and then the dried product is placed in an argon gas temperature environment of 800° C. for curing treatment to obtain a porous crystalline silicon composite material.

(5) The porous silicon-based composite material obtained above is used as a silicon negative electrode material for a lithium ion battery, and electrochemical performance tests are carried out. The ratio of the pole piece is: porous silicon composite material: acetylene black: PVDF = 7:2:2, and the lithium plate is used as the reference electrode to prepare a CR2025 button battery; at a current density of 0.5A/g, the first discharge ratio The capacity is 2766mAh/g. Compared with the commercial silicon composite negative electrode, the silicon negative electrode composite material prepared by the present invention has higher capacity (see attached table 1).

Fig. 1 is a nitrogen adsorption-desorption curve diagram of crystalline silicon obtained by magnesium thermal reduction and acid etching in this example. It can be seen from the figure that crystalline silicon has a rich mesoporous structure and a large specific surface area (127.0 m ² /g), indicating that porous crystalline silicon was obtained after magnesium thermal reduction acid etching.

Example 2

A method for preparing silicon carbon negative electrode material by magnesium thermal reduction, specifically comprising the following steps:

(1) Pretreatment of microsilica fume: The microsilica powder was roasted at 800°C for 6 hours, then dispersed in a hydrochloric acid solution with a concentration of 3.26 mol/L, heated to 80°C in a water bath, and kept for 3 hours to obtain a pretreated sample.

(2) The pretreated sample and the magnesium powder are mixed in a mass ratio of 1:0.85, using a planetary ball mill, the mass ratio of the ball to the material is 1:2, and the rotational speed is 150 rpm. The reaction material is obtained by drying;

(3) the reaction mass was placed in a sealed graphite crucible, transferred to a tube furnace under an argon atmosphere, and kept at 700°C for 5 hours; the resulting product was acid-etched with 1 mol/L hydrochloric acid for 12 hours to remove magnesium oxide and silicidation The magnesium by-product is filtered and dried to obtain porous crystalline silicon;

(4) The dried porous crystalline silicon and the phenolic resin are mixed in a mass ratio of 1:0.25 and then dried, and then the dried product is placed in an argon gas temperature environment of 1000° C. for curing treatment to obtain a porous crystalline silicon composite material.

(5) The porous silicon-based composite material obtained above is used as a silicon negative electrode material for a lithium ion battery, and electrochemical performance tests are carried out. The ratio of the pole pieces is: porous silicon composite material: acetylene black: PVDF=7:2:2, and the lithium plate is used as the reference electrode to prepare a CR2025 type button battery. At a current density of 0.5A/g, the first discharge specific capacity is 3078mAh/g. Compared with the commercial silicon composite negative electrode, the silicon negative electrode composite material prepared by the present invention has higher capacity (see attached table 1).

Fig. 2 is a scanning electron microscope image of the porous silicon-based composite material described in this embodiment. It can be seen from the figure that the size of the crystalline silicon remains in the sub-micron level after reduction and acid etching, and it has a spherical or quasi-spherical nanostructure; Some particles were slightly sintered due to high temperature. After being pyrolyzed with organic phenolic resin at high temperature, a carbon layer is formed on its surface, and the carbon layer structure surrounding it can be clearly observed from the figure.

FIG. 3 is a transmission electron microscope image of the porous silicon-based composite material described in this embodiment. It can be seen from the figure that the surface of the crystalline silicon is covered with a layer of carbon layer structure, which further improves the conductivity of the crystalline silicon.

Figure 4 is the electrochemical cycle curve diagram of the porous silicon-based composite material described in this example at a current density of 0.5 A/g. It can be seen from the figure that the porous silicon-based composite material exhibits excellent cycle stability , its first Coulombic efficiency reached 77.6%, and its capacity retention rate was 62.8% after 300 charge-discharge cycles, showing excellent electrochemical performance.

Example 3

A method for preparing silicon carbon negative electrode material by magnesium thermal reduction, comprising the following steps:

(1) Pretreatment of microsilica fume: The microsilica powder was calcined at 900°C for 8 hours, then dispersed in a nitric acid solution with a concentration of 3.26 mol/L, heated to 70°C in a water bath, and kept for 5 hours to obtain a pretreated sample.

(2) The pretreated sample and the magnesium powder are mixed in a mass ratio of 1:0.9, using a planetary ball mill, the mass ratio of the ball to the material is 1:2, the rotational speed is 150 rpm, and after 8 hours of ball milling, the natural The reaction material is obtained by drying;

(3) the reaction mass was placed in a sealed graphite crucible, transferred to a tube furnace under an argon atmosphere, and kept at 700°C for 10 hours; the resulting product was acid-etched with 5mol/L hydrochloric acid for 12 hours to remove magnesium oxide and silicidation The magnesium by-product is filtered and dried to obtain porous crystalline silicon;

(4) The dried porous crystalline silicon and the phenolic resin are mixed in a mass ratio of 1:0.5 and then dried, and then the dried product is placed in an argon gas temperature environment of 1100° C. for curing treatment to obtain a porous crystalline silicon composite material.

(5) The porous silicon-based composite material obtained above is used as a silicon negative electrode material for a lithium ion battery, and electrochemical performance tests are carried out. The ratio of the pole pieces is: porous silicon composite material: acetylene black: PVDF=7:2:2, and the lithium plate is used as the reference electrode to prepare a CR2025 type button battery. At a current density of 0.5A/g, the first discharge specific capacity was 2796mAh/g. Compared with the commercial silicon composite negative electrode, the silicon negative electrode composite material prepared by the present invention has higher capacity (see attached table 1).

Example 4

A method for preparing silicon carbon negative electrode material by magnesium thermal reduction, comprising the following steps:

(1) Pretreatment of micro-silica fume: The micro-silica powder was calcined at 1100°C for 4 hours, then dispersed in an oxalic acid solution with a concentration of 3.26 mol/L, heated to 90°C in a water bath, and kept for 1 hour to obtain a pretreated sample.

(2) The pretreated sample and the magnesium powder are mixed in a mass ratio of 1:1.2, using a planetary ball mill, the mass ratio of the balls is 1:2, and the rotational speed is 150 rpm. The reaction material is obtained by drying;

(3) The reaction mass was placed in a sealed graphite crucible, transferred to a tube furnace under an argon atmosphere, and kept at 800°C for 1 hour; the resulting product was acid-etched with 1 mol/L hydrochloric acid for 12 hours to remove magnesium oxide and silicidation The magnesium by-product is filtered and dried to obtain porous crystalline silicon;

(4) The dried porous crystalline silicon and the phenolic resin are mixed in a mass ratio of 1:1 and then dried, and then the dried product is placed in an argon gas temperature environment of 800° C. for curing treatment to obtain a porous crystalline silicon composite material.

(5) The porous silicon-based composite material obtained above was used as the silicon negative electrode material of lithium ion battery, and the electrochemical performance was tested; The lithium sheet was used as the reference electrode to prepare a CR2025 button battery; at a current density of 0.5A/g, the first discharge specific capacity was 3287mAh/g. Compared with the commercial silicon composite negative electrode, the silicon negative electrode composite material prepared by the present invention has higher capacity (see attached table 1).

Table 1. Charge-discharge performance of silicon anode composites in the examples

To sum up, in the present invention, micro-silicon powder from silicon metallurgy industrial waste is subjected to magnesium thermal reduction and acid etching, and then subjected to surface modification, coated with a conductive carbon layer, and used as an electrode material for lithium ion batteries; the micro-silicon powder is fully utilized. Porous crystalline silicon was prepared based on the structural characteristics of submicron primary particles and the shape retention effect of magnesium thermal reduction. The formation of this silicon body channel not only buffers the volume expansion of the silicon negative electrode during the process of de/lithium intercalation, but also promotes the immersion of the electrolyte, shortening the depth and diffusion distance of lithium ion deintercalation, showing excellent performance. electrochemical performance. It not only provides excellent electrode materials for lithium-ion batteries, but also realizes the high value-added utilization of micro-silicon powder. In addition, the whole preparation process has the advantages of simple and easy technology, low cost and simple equipment.

Claims (9)

1. The method for preparing the silicon-carbon cathode material by magnesiothermic reduction is characterized by comprising the following steps:

(1) pretreating the micro silicon powder: roasting the micro silicon powder, dispersing the micro silicon powder in acid etching liquid, heating the micro silicon powder to 60-90 ℃ in a water bath, performing dynamic stirring for 1-6 hours, performing suction filtration, washing with water, and drying to obtain a pretreated sample;

(2) ball milling, mixing and magnesium thermal reduction acid etching: mixing the pretreated micro silicon powder and magnesium powder by ball milling, placing the mixture in a sealed graphite crucible after natural drying, transferring the mixture to a tubular furnace of inert gas for magnesium thermal reaction, and carrying out acid washing, vacuum filtration, water washing and drying on the obtained product to obtain porous crystalline silicon;

(3) coating of the surface carbon layer: and uniformly mixing the prepared porous crystalline silicon and the organic matter precursor, drying, placing in inert gas, and curing at the temperature of 800-1100 ℃ to obtain the silicon-based composite material.

2. The method for preparing the silicon-carbon anode material by the magnesiothermic reduction according to claim 1, wherein: the acid etching solution in the step (1) is one or a mixture of more of hydrochloric acid, sulfuric acid, nitric acid, oxalic acid and acetic acid, and the concentration of the acid etching solution is 3.26 mol/L.

3. The method for preparing the silicon-carbon anode material by the magnesiothermic reduction according to claim 1, wherein: the roasting condition in the step (1) is that the roasting is carried out for 4 to 10 hours at the temperature of 500 ℃ and 1100 ℃.

4. The method for preparing the silicon-carbon anode material by the magnesiothermic reduction according to claim 1, wherein: the mass ratio of the pretreated micro silicon powder to the magnesium powder is 1 (0.8-1.2).

5. The method for preparing the silicon-carbon anode material by the magnesiothermic reduction according to claim 1, wherein: the ball milling parameters in the step (2) are as follows: the rotating speed is 100-.

6. The method for preparing the silicon-carbon anode material by the magnesiothermic reduction according to claim 1, wherein: the temperature of the magnesium thermal reaction in the step (2) is 600-800 ℃, and the time is 1-10 hours.

7. The method for preparing the silicon-carbon anode material by the magnesiothermic reduction according to claim 1, wherein: the inert gas in the step (2) is one or a mixture of air, argon and nitrogen.

8. The method for preparing the silicon-carbon anode material by the magnesiothermic reduction according to claim 1, wherein: the acid used in the acid washing in the step (2) is hydrochloric acid, and the concentration of the hydrochloric acid is 0.5-5 mol/L.

9. The method for preparing the silicon-carbon anode material by the magnesiothermic reduction according to claim 1, wherein: the organic matter in the step (3) is one or more of sucrose, asphalt, polyaniline, phenolic resin and PVDF; the mass ratio of the porous crystalline silicon to the organic precursor is 1 (0.1-1).

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