CN107785560B - A kind of high-performance silicon carbon anode material and preparation method thereof - Google Patents

Abstract

A high-performance silicon-carbon negative electrode material and a preparation method thereof are disclosed, wherein the preparation method comprises the following steps: (1) dispersing silicon in a solvent, performing liquid phase ball milling to obtain a nano silicon dispersion liquid, adding graphite, and performing liquid phase ball milling to realize uniform mixing of nano silicon and graphite; (2) granulating the slurry obtained by mixing in the step (1) to realize graphite/nano silicon composite granulation; (3) performing composite granulation on the product obtained in the step (2) and asphalt by adopting a kneading-pressing-crushing method, and performing mechanical fusion treatment to realize sphericization and uniform coating of the graphite/nano silicon/asphalt composite particles in one step; (4) and carbonizing, scattering and screening to obtain the high-performance silicon-carbon composite negative electrode material. The preparation method is simple, low in cost and easy for large-scale production of the high-performance silicon-carbon anode material.

Description

A kind of high-performance silicon carbon anode material and preparation method thereof

technical field

The invention belongs to the technical field of battery negative electrode materials, and particularly relates to a high-performance silicon carbon negative electrode material and a preparation method thereof.

Background technique

Lithium-ion batteries have been widely used in portable electronic devices, large-scale energy storage power stations and electric vehicles due to their high operating voltage, long cycle life, no memory effect, small self-discharge effect, and environmental friendliness. At present, the commercial lithium-ion battery anode materials mainly use graphite-type anode materials, but the theoretical specific capacity is only 372mAh/g, which cannot meet the requirements for the development of higher specific energy and high power density lithium-ion batteries in the future. Therefore, finding high specific capacity anode materials to replace carbon has become an important development direction.

Due to its highest lithium storage capacity (theoretical specific capacity of 4200mAh/g) and abundant resources, silicon material is considered to have the most potential to become the anode material for next-generation lithium-ion batteries. However, due to the large volume change during the intercalation/delithiation process, the structure damage of the silicon material and the pulverization of the material will lead to the damage of the electrode structure, resulting in the loss of electrical contact of the silicon active components. In addition, the pulverization of the material and the huge volume change will cause the continuous formation of the SEI film, which will lead to the poor electrochemical cycle stability of the battery, and hinder the large-scale application of silicon materials as anode materials for lithium-ion batteries.

In order to solve the problems existing in the application of silicon anode materials, at present, researchers mainly reduce the absolute volume expansion of silicon by means of nanometerization of silicon, and avoid material pulverization. However, pure nano-ization cannot solve the problem of continuous formation of SEI film caused by "electrochemical sintering" of nano-silicon during cycling and aggravated side reactions. Therefore, it is necessary to adopt the means of combining nanometerization and compounding, and solve various problems existing in the practical application of silicon by constructing multi-layered composite materials. Most of the silicon-carbon anode materials reported so far are mostly surface-coated core-shell structures, and the inner core is a loose and porous structure. The porous structure maintains the morphology of the inner core by providing the space required for silicon expansion. However, the internal porosity of this structure is too large, although it is beneficial to improve the cycle stability of the material, but the material is not pressure-resistant, the strength of the coating layer is low, and the tap density of the material is low, thereby reducing the volume density of the battery, while the same areal density Under certain conditions, the thickness of the pole piece will cause the deterioration of the battery performance.

Therefore, in order to meet the needs of the development of a new generation of high specific energy lithium-ion batteries, it is necessary to simultaneously improve the capacity, tap density and areal density of the pole piece of the silicon carbon anode material.

For example, CN103682287A discloses a silicon-based composite negative electrode material for lithium ion batteries with a high compaction density embedded in a composite core-shell structure. The invention realizes the preparation of the silicon-carbon composite material by the combination of mechanical grinding, mechanical fusion, isotropic pressure treatment and carbon coating technology. However, it is mentioned in this method that the process of preparing hollow graphite by mechanical grinding is too ideal, and the actual process is likely to cause graphite fragmentation instead of hollowing; the mechanical fusion process is also mainly to realize the dispersion of nano-silicon on the surface of graphite, and carbon coating is required in the later stage. In addition, the crushing treatment after homogenous pressurization and high-temperature carbonization can easily cause damage to the surface coating layer, and the ideal core-shell structure cannot be achieved. _CN103647056A discloses a SiOx-based composite negative electrode material and a preparation method thereof. In the invention, the method of mechanical fusion is used to realize the dispersion of nano-carbon materials on the surface of particle _SiOx , and further carbon coating treatment is also required in the later stage.

SUMMARY OF THE INVENTION

Therefore, one of the purposes of the present invention is to provide a method for preparing a high-performance silicon carbon negative electrode material. The negative electrode material obtained by the preparation method has a high tap density, which solves the problem that the silicon carbon negative electrode material has a high areal density. Under the conditions, the pole piece is thicker and the electrochemical performance is poor. Moreover, the preparation method of the present invention is simple, low-cost, and easy to produce high-performance silicon carbon negative electrode materials on a large scale.

To achieve the above object, the present invention adopts the following technical solutions:

A preparation method of a high-performance silicon carbon anode material, comprising the following steps:

(1) Disperse silicon in a solvent to obtain nano-silicon dispersion liquid by liquid-phase ball milling, and then add graphite to realize uniform mixing of nano-silicon and graphite by liquid-phase ball milling;

(2) granulating the slurry obtained by mixing step (1) to realize graphite/nano-silicon composite granulation, while ensuring the uniform dispersion of nano-silicon on the graphite surface;

(3) the product obtained in step (2) and the asphalt are kneaded-pressed-crushed to realize composite granulation of graphite/nano-silicon/pitch, and then after mechanical fusion treatment, one-step realization of graphite/nano-silicon/pitch composite particles spheroidization and uniform coating;

(4) After carbonization, breaking up and sieving, the high-performance silicon-carbon composite negative electrode material is obtained.

Compared with the prior art, the present invention utilizes the shaping effect of the graphite/nano-silicon/pitch plastic composite particles in the process of mechanical fusion under high rotational speed to improve the sphericity and tap density of the material, wherein the pitch is formed after melt kneading-pressing. continuous phase rather than granular. In this process, the dense, uniform and complete coating of the pitch is achieved, reducing the specific surface area of the material, and successfully preparing an ideal core-shell structure silicon carbon composite anode material. At the same time, through the mechanical fusion process, a carbon coating layer is realized. The tight bonding with the graphite/nano-silicon core increases the bonding strength and provides a stable and effective transport channel for electron and lithium ion transport.

Preferably, the silicon content of the raw material silicon used in step (1) is not less than 99%.

Preferably, the raw silicon used is micron silicon powder, preferably silicon powder with a median particle size of 1-5 μm, more preferably silicon powder with a median particle size of 3 μm.

Preferably, the solvent is one or a combination of two or more of ethanol, methanol, isopropanol, n-butanol, acetone, and toluene.

Preferably, the mass ratio of the used raw material silicon to the solvent is 1:5-15, preferably 1:9.

Preferably, the ball-milling medium is zirconia balls, preferably zirconia balls with a diameter of 0.1-0.5 mm, more preferably zirconia balls with a diameter of 0.3 mm.

Preferably, the mass ratio of balls to material in the ball milling is 5-15:1, preferably 10:1, when preparing the nano-silicon dispersion.

Preferably, the rotation speed of the ball milling is 1500-2000 rpm, preferably 1800 rpm, and the time of the ball milling is more than 5 hours, preferably 10 hours when preparing the nano-silicon dispersion.

Preferably, the mass ratio of graphite to the used raw material silicon is 1-3:1, preferably 1.7:1.

Preferably, the rotation speed of the ball milling after adding graphite is 500-1500 rpm, preferably 1000 rpm, and the time of the ball milling is more than 0.5 hour, preferably 1 hour. The rotation speed of the ball mill after adding the graphite is preferably lower than the rotation speed of the ball mill when the nano-silicon dispersion liquid is prepared.

Preferably, it is advisable to control the ball-to-material ratio of the ball milling to 3:1-15:1 after adding graphite.

Ball milling can be performed using an ultrafine ball mill.

Preferably, the granulation in step (2) adopts the method of spray drying.

Preferably, the composite granulation process of graphite/nano-silicon/asphalt in step (3) is as follows: the product obtained in step (2) is hot-kneaded with asphalt, hot-rolled, and crushed into powder material after cooling; Isostatic pressing to obtain graphite/nano-silicon/asphalt bulk green body; then the green body is crushed and sieved.

Preferably, the pitch is coal pitch or petroleum pitch with a softening temperature above 60°C.

Preferably, the mass ratio of the product obtained in step (2) to asphalt is 1-4:1, preferably 2:1.

Preferably, the temperature of hot kneading is 100-300°C, preferably 120-250°C, and the time is more than 1 h, preferably 2 h.

Preferably, the temperature of the hot rolling is 100-300°C, preferably 120-250°C. The temperature of hot rolling and the temperature of hot kneading may be the same or different, and are preferably the same. It can be hot rolled into a rubber pack with a thickness of about 2mm.

Isostatic pressing can be carried out on an isostatic pressing machine by placing the material in a rubber jacket.

Preferably, the pressure during isostatic pressing is 150-300 MPa, preferably 200 MPa, and the isostatic pressing time is more than 5 minutes, preferably 10 minutes.

The material porosity is controllable through the control of kneading and pressing process parameters.

Preferably, the linear speed during mechanical fusion is 10-50 m/s, and the time for mechanical fusion is 3-60 min, preferably 15-30 min. Mechanofusion can be performed in a mechanofusion machine.

The sphericity and tap density of the material increase with the increase of the mechanical fusion line speed and the fusion time. The linear speed of mechanical fusion is 10-50m/s, and the time of mechanical fusion is 3-60min, which can optimize the sphericity and tap density of the material.

The carbon coating layer of the graphite/nano silicon/pitch composite particles obtained by the above process of the present invention is dense, high in strength and good in uniformity. The thickness of the carbon coating layer is controlled at 0.05-2 μm. Layer thickness is controllable.

In a preferred embodiment, the process of step (3) is as follows: take 2kg of the above-mentioned spray-dried powdery intermediate product and 1kg of modified asphalt, heat and knead for 2 hours at a temperature of 160-180 °C; Under hot rolling treatment, it is made into a rubber pack with a thickness of about 2mm, and then crushed into powder materials after cooling; then the powder materials are put into a rubber casing, and isostatically pressed in an isostatic press for 10 minutes under a pressure of 200MPa. Graphite/nano-silicon/pitch green compacts are obtained; then the graphite/nano-silicon/pitch green compacts are crushed and sieved, and then put into a mechanical fusion machine for mechanical fusion at a linear speed of 45 m/s for 20 minutes to obtain graphite/nano-silicon / Asphalt composite particles.

Preferably, the carbonization in step (4) is carried out under the protection of an inert atmosphere, the carbonization temperature is 800-1000°C, preferably 900°C, and the carbonization time is more than 2h, preferably 4h.

The silicon content in the silicon-carbon composite negative electrode material is 20-40%.

Another object of the present invention is to provide a high-performance silicon carbon negative electrode material prepared by the method of the present invention.

The preparation method of the present invention adopts a mechanical fusion process, utilizes the characteristic of graphite/nano silicon/asphalt composite precursor particles having a certain plasticity, and realizes the synthesis of graphite/nano silicon/asphalt composite precursor particles in one step through the action of shear force and extrusion force. Spheroidization and complete coating of asphalt; greatly improve the tap density of the material, and form a dense and uniform coating layer on the surface.

Through the mechanofusion process, the carbon coating layer and the graphite/nano-silicon core are tightly combined, which increases the bonding strength and provides a stable and effective transport channel for electron and lithium ion transport. The asphalt inside the particles is cracked to form a three-dimensional network conductive structure with good strength, which improves the internal conductivity of the material and the structural stability of the particles.

The nano-silicon is uniformly dispersed on the graphite surface or in the pores of the graphite sheet, and the stability of the core structure and the conductive network is maintained by the three-dimensional pitch cracked carbon with a certain strength, so as to achieve good cycle stability and rate performance.

The silicon-carbon composite material prepared by the preparation method of the present invention has high capacity and good cycle stability; the material has high tap density and excellent processing performance; forms a dense carbon coating layer, reduces the specific surface area of the material, and is beneficial to inhibit the electrolyte solution The side reaction of degradation occurs, which improves the coulombic efficiency of the silicon-carbon composite material; compared with the traditional process, the method of the present invention has a higher material yield, which can reach more than 95%.

Description of drawings

Fig. 1 is the process flow diagram of the preparation method of the present invention;

2 is an SEM image of the silicon-carbon composite material prepared in Example 1;

3 is a cross-sectional SEM image of the silicon-carbon composite material prepared in Example 1;

Fig. 4 is the particle size distribution curve of the silicon-carbon composite material prepared in Example 1;

5 is the galvanostatic charge-discharge curve of the silicon-carbon composite material prepared in Example 1;

Fig. 6 is the cycle stability curve of the silicon-carbon composite material prepared in Example 1;

FIG. 7 is the SEM image of the G/Si@C silicon-carbon composite material without mechanical fusion treatment in Comparative Example 1. FIG.

Detailed ways

In order to facilitate the understanding of the present invention, examples of the present invention are as follows. It should be understood by those skilled in the art that the embodiments are only used to help the understanding of the present invention, and should not be regarded as a specific limitation of the present invention.

Fig. 1 is the process flow diagram of the preparation method of the present invention.

Example 1:

Take 2 kg of micron silicon powder with a median particle size of 3 μm and a silicon content of more than 99%, add it to 18 kg of ethanol solvent, and after ultrasonic dispersion for 30 min, pour it into the cavity of an ultrafine ball mill. A zirconia ball with a diameter of 0.3 mm was used as the ball milling medium, the ball-to-material ratio (mass ratio) was 10:1, and the ball was milled at a rotational speed of 1800 rpm for 10 hours to obtain a nano-silicon dispersion. 3.4 kg of flake graphite was added to the nano-silicon dispersion, and a uniform mixed slurry was obtained after ball milling and dispersing at 1000 rpm for 1 hour. The mixed slurry is spray-dried to obtain a granular composite powder.

Take 2kg of the powdered intermediate product obtained by spray drying and 1kg of modified asphalt, and knead it hot at 160-180°C for 2 hours; the kneaded product is hot-rolled at 160-180°C to form a rubber pack with a thickness of about 2mm, and cooled. After crushing into powder materials; then put the powder materials into the rubber casing, and isostatically press for 10 minutes under the pressure of 200MPa in an isostatic press to obtain graphite/nano-silicon/asphalt bulk green bodies; then graphite /Nano-silicon/asphalt green body was crushed and sieved, then put into a mechanical fusion machine for 20 minutes at a linear speed of 45m/s to obtain graphite/nano-silicon/asphalt composite particles; calcined at 900°C for 4 hours under the protection of an inert atmosphere ; After being scattered and sieved, a silicon-carbon composite negative electrode material with a silicon content of 33% was obtained.

FIG. 2 is a SEM (scanning electron microscope) image of the silicon-carbon composite negative electrode material prepared in this example, and it can be seen that the silicon-carbon composite material has good sphericity and a smooth surface. Fig. 3 is a SEM image of the cross-section of the silicon-carbon composite negative electrode material prepared in this example. It can be seen that nano-silicon is uniformly dispersed on the surface of graphite, and there are pores between the graphite sheets, which reserves space for the volume expansion of silicon, and the surface of the material is covered with Coated with a dense layer of amorphous carbon with a thickness of several hundred nanometers. Figure 4 shows the particle size distribution of the silicon-carbon composite material, and the median particle size of the material is about 13 μm.

Table 1 shows the performance test results of the materials prepared in this example. It can be seen from Table 1 that the material has a relatively small specific surface area, reaching 2.4 m ² /g, and the material exhibits a relatively high tap density, reaching 0.96 g/cm ³ . Figure 5 and Figure 6 are the first cycle charge-discharge curve and cycle stability curve of the silicon-carbon composite negative electrode material, respectively. It can be seen that the reversible capacity of the silicon carbon composite is 857mAh/g in the first week, the Coulombic efficiency in the first week is 83.7%, and the 50-cycle capacity retention rate is 75.9%.

Figure 7 is the SEM image of the silicon-carbon composite material prepared by the mechanical fusion process in Comparative Example 1. It can be seen that the sphericity of the material is poor, it is irregular granular, and the surface coating layer is incomplete. It can be seen from Table 1 that the tap density of the material is only 0.63 g/cm ³ , the specific surface area is 6.7 m ² /g, the tap density is low, and the specific surface area is large.

Example 2:

Take 2 kg of micron silicon powder with a median particle size of 3 μm and a silicon content of more than 99%, add it to 18 kg of ethanol solvent, and after ultrasonic dispersion for 30 min, pour it into the cavity of an ultrafine ball mill. A zirconia ball with a diameter of 0.3 mm was used as the ball milling medium, the ball-to-material ratio (mass ratio) was 10:1, and the ball was milled at a rotational speed of 1800 rpm for 10 hours to obtain a nano-silicon dispersion. 3.4 kg of flake graphite was added to the nano-silicon dispersion, and a uniform mixed slurry was obtained after ball milling and dispersing at 1000 rpm for 1 hour. The mixed slurry is spray-dried to obtain a granular composite powder.

Take 2kg of the powdered intermediate product obtained by spray drying and 1kg of modified coal tar pitch, and knead it hot at 120-140℃ for 2 hours; the kneaded product is hot-rolled at 120-140℃ to form a rubber pack with a thickness of about 2mm. After cooling, it is crushed into powder materials; the powder materials are then put into a rubber jacket, and isostatically pressed in an isostatic press for 10 minutes under a pressure of 200 MPa to obtain graphite/nano-silicon/asphalt bulk green bodies; After the graphite/nano-silicon/asphalt green body was crushed and sieved, it was put into a mechanical fusion machine for mechanical fusion at a linear speed of 40 m/s for 30 minutes to obtain graphite/nano-silicon/asphalt composite particles; calcined at 900 °C under the protection of an inert atmosphere for 4 hour; the silicon-carbon composite negative electrode material with a silicon content of 33% was obtained after being dispersed and sieved.

Example 3:

Take 2 kg of micron silicon powder with a median particle size of 3 μm and a silicon content of more than 99%, add it to 18 kg of ethanol solvent, and after ultrasonic dispersion for 30 min, pour it into the cavity of an ultrafine ball mill. A zirconia ball with a diameter of 0.3 mm was used as the ball milling medium, the ball-to-material ratio (mass ratio) was 10:1, and the ball was milled at a rotational speed of 1800 rpm for 10 hours to obtain a nano-silicon dispersion. 3.4 kg of flake graphite was added to the nano-silicon dispersion, and a uniform mixed slurry was obtained after ball milling and dispersing at 1000 rpm for 1 hour. The mixed slurry is spray-dried to obtain a granular composite powder.

Take 2kg of the powdered intermediate product obtained by spray drying and 1kg of modified coal tar pitch, and knead it hot at 120-140℃ for 2 hours; the kneaded product is hot-rolled at 120-140℃ to form a rubber pack with a thickness of about 2mm. After cooling, it is crushed into powder materials; the powder materials are then put into a rubber jacket, and isostatically pressed in an isostatic press for 10 minutes under a pressure of 200 MPa to obtain graphite/nano-silicon/asphalt bulk green bodies; After the graphite/nano-silicon/asphalt green body was crushed and sieved, it was put into a mechanical fusion machine and mechanically fused at a linear speed of 35 m/s for 30 minutes to obtain graphite/nano-silicon/asphalt composite particles; calcined at 900 °C under the protection of an inert atmosphere for 4 hour; the silicon-carbon composite negative electrode material with a silicon content of 33% was obtained after being dispersed and sieved.

Example 4:

Take 2 kg of micron silicon powder with a median particle size of 3 μm and a silicon content of more than 99%, add it to 18 kg of ethanol solvent, and after ultrasonic dispersion for 30 min, pour it into the cavity of an ultrafine ball mill. A zirconia ball with a diameter of 0.3 mm was used as the ball milling medium, the ball-to-material ratio (mass ratio) was 10:1, and the ball was milled at a rotational speed of 1800 rpm for 10 hours to obtain a nano-silicon dispersion. 3.4 kg of flake graphite was added to the nano-silicon dispersion, and a uniform mixed slurry was obtained after ball milling and dispersing at 1000 rpm for 1 hour. The mixed slurry is spray-dried to obtain a granular composite powder.

Take 2kg of the powder intermediate product obtained by spray drying and 1kg of medium-temperature coal tar pitch, and knead it hot at 120-140°C for 2 hours; heat the kneaded product at 120-140°C by hot rolling to form a rubber pack with a thickness of about 2mm, and cool it. After crushing into powder materials; then put the powder materials into the rubber casing, and isostatically press for 10 minutes under the pressure of 200MPa in an isostatic press to obtain graphite/nano-silicon/asphalt bulk green bodies; then graphite /Nano-silicon/asphalt green body was crushed and sieved, then put into a mechanical fusion machine for 30 minutes at a linear speed of 45m/s to obtain graphite/nano-silicon/asphalt composite particles; calcined at 900 °C for 4 hours under the protection of an inert atmosphere ; After being scattered and sieved, a silicon-carbon composite negative electrode material with a silicon content of 33% was obtained.

Example 5:

Take 2 kg of micron silicon powder with a median particle size of 3 μm and a silicon content of more than 99%, add it to 18 kg of ethanol solvent, and after ultrasonic dispersion for 30 min, pour it into the cavity of an ultrafine ball mill. A zirconia ball with a diameter of 0.3 mm was used as the ball milling medium, the ball-to-material ratio (mass ratio) was 10:1, and the ball was milled at a rotational speed of 1800 rpm for 10 hours to obtain a nano-silicon dispersion. 3.4 kg of flake graphite was added to the nano-silicon dispersion, and a uniform mixed slurry was obtained after ball milling and dispersing at 1000 rpm for 1 hour. The mixed slurry is spray-dried to obtain a granular composite powder.

Take 2kg of the above-mentioned spray-dried powdery intermediate product and 0.88kg of high-temperature coal tar pitch, and heat-knead at 220-250°C for 2 hours; the kneaded product is hot-rolled at 220-250°C to form a rubber pack with a thickness of about 2mm. After cooling, it is crushed into powder materials; the powder materials are then put into a rubber jacket, and isostatically pressed in an isostatic press for 10 minutes under a pressure of 200 MPa to obtain graphite/nano-silicon/asphalt bulk green bodies; After the graphite/nano-silicon/asphalt green body was crushed and sieved, it was put into a mechanical fusion machine for mechanical fusion at a linear speed of 45 m/s for 20 minutes to obtain graphite/nano-silicon/asphalt composite particles; calcined at 900 °C under the protection of an inert atmosphere for 4 hour; the silicon-carbon composite negative electrode material with a silicon content of 33% was obtained after being dispersed and sieved.

Example 6:

Take 2 kg of micron silicon powder with a median particle size of 3 μm and a silicon content of more than 99%, add it to 18 kg of ethanol solvent, and after ultrasonic dispersion for 30 min, pour it into the cavity of an ultrafine ball mill. A zirconia ball with a diameter of 0.3 mm was used as the ball milling medium, the ball-to-material ratio (mass ratio) was 10:1, and the ball was milled at a rotational speed of 1800 rpm for 10 hours to obtain a nano-silicon dispersion. 5.5 kg of flake graphite was added to the nano-silicon dispersion liquid, and a uniform mixed slurry was obtained after ball milling and dispersing at 1000 rpm for 1 hour. The mixed slurry is spray-dried to obtain a granular composite powder.

Take 2kg of the powdered intermediate product obtained by spray drying and 1kg of modified coal tar pitch, and knead it for 2 hours at a temperature of 160-180°C. After cooling, it is crushed into powder materials; the powder materials are then put into a rubber jacket, and isostatically pressed in an isostatic press for 10 minutes under a pressure of 200 MPa to obtain graphite/nano-silicon/asphalt bulk green bodies; After the graphite/nano-silicon/asphalt green body was crushed and sieved, it was put into a mechanical fusion machine for mechanical fusion at a linear speed of 45 m/s for 20 minutes to obtain graphite/nano-silicon/asphalt composite particles; calcined at 900 °C under the protection of an inert atmosphere for 4 hour; the silicon-carbon composite negative electrode material with silicon content of 22% is obtained after being scattered and sieved.

Comparative Example 1:

Take 2 kg of micron silicon powder with a median particle size of 3 μm and a silicon content of more than 99%, add it to 18 kg of ethanol solvent, and after ultrasonic dispersion for 30 min, pour it into the cavity of an ultrafine ball mill. A zirconia ball with a diameter of 0.3 mm was used as the ball milling medium, the ball-to-material ratio (mass ratio) was 10:1, and the ball was milled at a rotational speed of 1800 rpm for 10 hours to obtain a nano-silicon dispersion. 3.4 kg of flake graphite was added to the nano-silicon dispersion, and a uniform mixed slurry was obtained after ball milling and dispersing at 1000 rpm for 1 hour. The mixed slurry is spray-dried to obtain a granular composite powder.

Take 2kg of the powdered intermediate product obtained by spray drying and 1kg of modified coal tar pitch, and knead it for 2 hours at a temperature of 160-180°C. After cooling, it is crushed into powder materials; the powder materials are then put into a rubber jacket, and isostatically pressed in an isostatic press for 10 minutes under a pressure of 200 MPa to obtain graphite/nano-silicon/asphalt bulk green bodies; After the graphite/nano-silicon/asphalt green body was crushed and sieved, it was calcined at 900° C. for 4 hours under the protection of an inert atmosphere; after being dispersed and sieved, a silicon-carbon composite negative electrode material with a silicon content of 33% was obtained.

Comparative Example 2:

Take 2 kg of micron silicon powder with a median particle size of 3 μm and a silicon content of more than 99%, add it to 18 kg of ethanol solvent, and after ultrasonic dispersion for 30 min, pour it into the cavity of an ultrafine ball mill. A zirconia ball with a diameter of 0.3 mm was used as the ball milling medium, the ball-to-material ratio (mass ratio) was 10:1, and the ball was milled at a rotational speed of 1800 rpm for 10 hours to obtain a nano-silicon dispersion. 3.4 kg of flake graphite was added to the nano-silicon dispersion, and a uniform mixed slurry was obtained after ball milling and dispersing at 1000 rpm for 1 hour. The mixed slurry is spray-dried to obtain a granular composite powder.

Take 2kg of the above-mentioned spray-dried powder intermediate product and 780g of PVP binder and an appropriate amount of water solvent, knead at room temperature for 2h; after drying and crushing the kneaded product; then isostatically press the powder material under 200MPa pressure for 10 minutes. , to obtain a massive green body; then the green body is crushed and sieved, and then placed in a mechanical fusion machine for mechanical fusion at a linear speed of 45 m/s for 20 minutes to obtain composite particles; calcined at 900 ° C for 4 hours under the protection of an inert atmosphere; The silicon-carbon composite negative electrode material with a silicon content of 33% was obtained after being scattered and sieved.

Comparative Example 3:

Take 2 kg of micron silicon powder with a median particle size of 3 μm and a silicon content of more than 99%, add it to 18 kg of ethanol solvent, and after ultrasonic dispersion for 30 min, pour it into the cavity of an ultrafine ball mill. A zirconia ball with a diameter of 0.3 mm was used as the ball milling medium, the ball-to-material ratio (mass ratio) was 10:1, and the ball was milled at a rotational speed of 1800 rpm for 10 hours to obtain a nano-silicon dispersion. 3.4 kg of flake graphite was added to the nano-silicon dispersion, and a uniform mixed slurry was obtained after ball milling and dispersing at 1000 rpm for 1 hour. The mixed slurry is spray-dried to obtain a granular composite powder.

Take 2kg of the above-mentioned spray-dried powdery intermediate product and 1kg of phenolic resin and an appropriate amount of ethanol solvent, knead at room temperature for 2h; after drying and crushing the kneaded product; then isostatically press the powder material under 200MPa pressure for 10 minutes, Graphite/nano-silicon/phenolic resin bulk green body is obtained; then the graphite/pitch/phenolic resin green body is crushed and sieved, and then placed in a mechanical fusion machine for mechanical fusion at a line speed of 45 m/s for 20 minutes to obtain composite particles ; calcined at 900° C. for 4 hours under the protection of an inert atmosphere; after being dispersed and sieved, a silicon-carbon composite negative electrode material with a silicon content of 33% was obtained.

Examples 1-6 and Comparative Examples 1-3 all adopt the following methods to prepare electrodes and test the electrochemical properties of the materials. The test results are shown in Table 1.

The silicon-carbon composite negative electrode material, the conductive agent and the binder are dissolved in a solvent in a ratio of 86:6:8 by mass percentage, and the solid content is 30%. The binder is a 1:1 sodium carboxymethyl cellulose (CMC, 2wt% CMC aqueous solution) styrene-butadiene rubber (SBR, 50wt% SBR aqueous solution) composite water-based binder. 0.8 wt % of oxalic acid was added as an acid substance for etching copper foil, and a uniform slurry was obtained after thorough stirring. Coated on 10 μm copper foil, dried at room temperature for 4 hours, punched into pole pieces with a 14 mm diameter punch, pressed at a pressure of 100 kg/cm ^-2 , and dried in a 120°C vacuum oven for 8 hours.

Transfer the pole piece to the glove box, use lithium metal piece as the negative electrode, Celgard2400 separator, 1mol/L LiPF ₆ /EC+DMC+EMC+2%VC (v/v/v=1:1:1) electrolyte , CR2016 battery shell assembly button battery. The constant current charge and discharge test was carried out on the Wuhan Jinnuo LandCT2001A battery test system. The charge and discharge cycle was performed at a rate of 0.2C, and the charge and discharge cut-off voltage was 0.005-2V relative to Li/Li ⁺ .

Table 1 Performance test results of high tap density silicon carbon anode materials.

It can be seen from the table that the tap density of the silicon-carbon composite anode material obtained by the preparation method of the silicon-carbon anode material including the mechanofusion process steps is improved, the specific surface area is reduced, the first-week coulombic efficiency and cycle stability of the material are improved. have been greatly improved.

Obviously, the above-mentioned embodiments are only examples for clear description, and are not intended to limit the implementation manner. For those of ordinary skill in the art, changes or modifications in other different forms can also be made on the basis of the above description. There is no need and cannot be exhaustive of all implementations here. And the obvious changes or changes derived from this are still within the protection scope of the present invention.

Claims (9)

1. a preparation method of high performance silicon carbon anode material, comprising the steps: (1) disperse silicon in a solvent to obtain nano-silicon dispersion liquid by liquid-phase ball milling, then add graphite to realize uniform mixing of nano-silicon and graphite by liquid-phase ball milling; the mass ratio of raw material silicon and solvent used is 1:5-15; In step (1), the mass ratio of graphite and used raw material silicon is 1-3:1; (2) granulating the slurry obtained by mixing step (1) to realize graphite/nano-silicon composite granulation; (3) the product obtained in step (2) and the asphalt are kneaded-pressed-crushed to realize composite granulation of graphite/nano-silicon/pitch, and then after mechanical fusion treatment, one-step realization of graphite/nano-silicon/pitch composite particles The mass ratio of the product obtained in step (2) to asphalt is 1-4:1; the linear velocity during mechanical fusion is 10-50m/s, and the time for mechanical fusion is 3-60min; (4) After carbonization, breaking up and sieving, the high-performance silicon-carbon composite negative electrode material is obtained. 2. preparation method according to claim 1, is characterized in that, silicon content in used raw material silicon in step (1) is not less than 99%; The raw material silicon used is micron silicon powder; The solvent is one or a combination of two or more of ethanol, methanol, isopropanol, n-butanol, acetone, and toluene; The mass ratio of the used raw material silicon to the solvent is 1:9. 3. preparation method according to claim 1 and 2 is characterized in that, in step (1), ball milling medium is zirconia ball; When preparing the nano-silicon dispersion liquid, the mass ratio of balls to material in ball milling is 5-15:1; When preparing the nano-silicon dispersion liquid, the rotating speed of the ball milling is 1500-2000 rpm, and the time of the ball milling is more than 5 hours. 4. preparation method according to claim 1 and 2 is characterized in that, the rotating speed of ball milling after adding graphite is 500-1500rpm, and the time of ball milling is more than 0.5 hour; After adding graphite, the ball-to-material ratio of ball milling is 3-15:1; The granulation in step (2) adopts the method of spray drying. 5. preparation method according to claim 1, is characterized in that, in step (3), the composite granulation process of graphite/nano silicon/pitch is: step (2) obtained product and pitch are hot-kneaded after hot rolling, After cooling, it is crushed into powder materials; the powder materials are then isostatically pressed to obtain graphite/nano silicon/asphalt bulk green bodies; then the green bodies are crushed and sieved. 6. The preparation method according to claim 5, wherein the pitch is coal pitch or petroleum pitch with a softening temperature of more than 60°C; The mass ratio of the product obtained in the step (2) to the asphalt is 2:1. 7. The preparation method according to claim 5, wherein the temperature of hot kneading is 100-300 DEG C, and the time is more than 1h; The temperature of hot rolling is 100-300℃; The pressure of isostatic pressing is 150-300MPa, and the time of isostatic pressing is more than 5min. 8. The preparation method according to any one of claims 5-7, wherein the time for mechanical fusion is 15-30 min. 9 . The preparation method according to claim 1 , wherein the carbonization in step (4) is carried out under the protection of an inert atmosphere, the carbonization temperature is 800-1000° C., and the carbonization time is more than 2h. 10 .

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