A method for preparing porous graphite powder materials by screw extrusion and its application

Abstract

This invention discloses a method for preparing porous graphite powder materials using screw extrusion, comprising the following steps: preparing graphite powder and coating material at a weight ratio of 5-30:1, feeding them into a screw extruder, then injecting supercritical carbon dioxide foaming agent into the extruder barrel at a rate of 0.8-1.8 kg / h, maintaining a screw temperature of 150-280°C and a die temperature of 150-200°C, and uniformly mixing the mixture under these temperature and pressure conditions; continuously extruding the resulting mixture from the die, with pressure drop inducing bubble nucleation and growth to obtain a graphite / foamed coating material mixture; carbonizing the mixture obtained in the previous step at 750-1200°C to obtain a graphite / porous carbon composite material; and ball milling the obtained graphite / porous carbon composite material to obtain a porous graphite powder material; wherein the carbon layer surface of the graphite powder material has uniformly distributed craters. This method is easy to mass-produce, simple to operate, and allows for continuous preparation of graphite powder materials with controllable pore size.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion batteries, and more specifically to a method for preparing graphite powder materials with a porous surface structure. Background Technology

[0002] Lithium-ion batteries have become the mainstream development direction for rechargeable batteries due to their superior performance. Currently, most lithium batteries use graphite as the anode material, which has advantages such as abundant resources, stable electrochemical performance, high tap density, and low irreversible capacity. However, the market's demand for the energy density of power lithium batteries is increasing year by year, and the theoretical specific capacity limit of graphite materials (372 mAh / g) can no longer meet the growing needs of users. Developing anode material systems with higher specific capacity to further improve the energy density of lithium-ion batteries is the future development direction.

[0003] Silicon can alloy with lithium at room temperature and has a theoretical discharge capacity 10 times that of graphite, effectively increasing the amount of electricity stored per unit volume in lithium batteries. Simultaneously, silicon-based materials possess advantages such as abundant reserves, low cost, and environmental friendliness, making them the preferred choice for next-generation anode materials. However, silicon-based anode materials have low electronic conductivity, and the 100-400% volume expansion and contraction during charging and discharging makes the electrode material extremely prone to pulverization, detaching from the current collector and electrode conductive network. The resulting new surface requires the formation of a new solid electrolyte interface (SEI), leading to significant electrolyte consumption and severely impacting the material's cycle stability. This is the reason why silicon-based anode materials have not yet achieved large-scale commercial application.

[0004] To address this issue, the industry has attempted to combine nanotechnology, inert buffering, and surface coating techniques using physical or chemical methods. This involves combining nano-silicon materials with carbon-based materials through surface coating and loading, leveraging the advantages of multiple materials while mitigating their respective disadvantages. This approach improves the conductivity of silicon-based materials, mitigates breakage during charge-discharge processes, and avoids direct contact between the electrolyte and silicon, thereby reducing side reactions and improving cycle stability. The result is a silicon-carbon composite anode material with high capacity and long cycle life. Therefore, developing a method for preparing a graphite matrix with a controllable porous structure that is continuously produced, environmentally friendly, and simple to operate, for embedding silicon-based materials to prepare high-performance silicon-carbon composite anode materials, is of great significance. Summary of the Invention

[0005] Therefore, the technical problem to be solved by the present invention is to provide a method for preparing graphite powder materials with a porous structure of controllable pore size that is environmentally friendly, simple to operate, and can be continuously prepared, for use in preparing carbon material matrix for silicon-carbon composite anode materials.

[0006] The technical solution of the present invention is a method for preparing porous graphite powder material by screw extrusion, comprising the following steps:

[0007] (1) Prepare graphite powder and coating material at a weight ratio of 5-30:1, feed them into a screw extruder, and then inject supercritical carbon dioxide foaming agent into the extruder barrel at a rate of 0.8-1.8 kg / h. The screw temperature is 150-280℃ and the die temperature is 150-200℃. Mix them uniformly at this temperature. The coating material is one of low-temperature asphalt, phenolic resin, and epoxy resin.

[0008] (2) The mixture obtained in step (1) is continuously extruded from the die head, and the pressure drop induces bubble nucleation and growth to obtain a mixture of graphite / foamed coating material;

[0009] (3) The mixture obtained in step (2) is carbonized at 750-1200℃ to obtain a graphite / porous carbon composite material;

[0010] (4) The graphite / porous carbon composite material obtained in step (3) is ground and pulverized to obtain a graphite powder material with a porous surface; the carbon layer of the graphite powder material has craters evenly distributed on its surface.

[0011] Supercritical carbon dioxide refers to carbon dioxide whose properties change when the temperature is 31.26℃ higher than the critical temperature and the pressure is 72.9 atm higher than the critical pressure. Its density is close to that of a liquid and its viscosity is close to that of a gas. Its characteristic is that it has the best permeability, miscibility and blending properties with other substances.

[0012] The foaming principle of this invention is as follows: After supercritical carbon dioxide and carbon source material are fully and uniformly mixed / diffused, a single-phase mixed sol is formed. Then, the sol is extruded through a die, causing a large pressure drop in the sol, which causes gas to be released and form a large number of bubble nuclei. During the subsequent cooling and molding process, the bubble nuclei inside the sol continue to grow and form, and finally a microporous foamed composite material is obtained.

[0013] According to a method for preparing porous graphite powder material by screw extrusion according to the present invention, preferably, the screw extruder in step (1) is a single screw extruder, a twin screw extruder, or a twin screw tandem single screw extruder.

[0014] According to a method for preparing porous graphite powder material by screw extrusion according to the present invention, preferably, the screw speed of the screw extruder is 10-50 rpm.

[0015] According to a method for preparing porous graphite powder material by screw extrusion according to the present invention, preferably, the graphite powder is one or more of natural graphite, artificial graphite, and mesophase carbon microspheres.

[0016] According to a method for preparing porous graphite powder material by screw extrusion according to the present invention, preferably, the low-temperature asphalt is selected from petroleum asphalt, secondary coal tar pitch, and coal tar pitch; the phenolic resin is selected from water-soluble phenolic resin, alcohol-soluble phenolic resin, and modified phenolic resin; and the epoxy resin is selected from bisphenol A type epoxy resin, bisphenol F type epoxy resin, and phenol-aryl alkyl type epoxy resin.

[0017] According to a method for preparing porous graphite powder material by screw extrusion according to the present invention, preferably, the carbon dioxide injection rate in step (1) is 1-1.5 kg / h; the screw temperature is 150-250℃ and the die temperature is 150-180℃.

[0018] Preferably, the carbonization temperature in step (3) is 800-1100℃.

[0019] According to a method for preparing porous graphite powder material by screw extrusion according to the present invention, preferably, the carbonization treatment time in step (3) is 0.5-5 hours.

[0020] The graphite core of the porous graphite powder material is not affected by foaming, and the coating material has a porous structure after foaming and carbonization. The carbon layer surface of the graphite powder material after grinding and pulverizing has uniformly distributed craters of a certain size.

[0021] Preferably, the grinding and pulverizing in step (4) is ball milling.

[0022] According to a method for preparing porous graphite powder material by screw extrusion according to the present invention, preferably, the crater size on the carbon layer surface of the graphite powder material in step (4) is in the range of 1 nm to 30 μm.

[0023] Furthermore, the size of the crater ranges from 0.2 μm to 5 μm.

[0024] This invention also provides the application of a high-performance silicon-carbon composite anode material with a porous surface graphite powder material prepared by the above preparation method.

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] (1) The material mixing and foaming process is completed continuously by a screw extruder, and graphite powder material is continuously prepared, which is easy to produce on a large scale.

[0027] (2) The present invention uses supercritical carbon dioxide as a foaming agent, which has the advantages of being environmentally friendly and non-toxic, non-flammable, low cost, and able to reach the supercritical state at a lower temperature and pressure.

[0028] (2) A crater structure is created on the carbon layer on the surface of graphite particles by foaming, which has a small average pore size, controllable pore size, narrow pore size distribution and high pore density. Attached Figure Description

[0029] Figure 1 This is a flowchart of the preparation process of the present invention. Detailed Implementation

[0030] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0031] Example 1:

[0032] A method for preparing porous graphite powder materials by screw extrusion comprises the following steps:

[0033] (1) Natural graphite and coal tar pitch are fed into a twin-screw extruder at a weight ratio of 10:1, and supercritical carbon dioxide of 1.5 kg / h is injected at the same time. After being fully mixed by the extruder, the mixture is extruded from the die to form a foamed material, in which the screw temperature is 200℃, the die temperature is 160℃, and the screw speed is 10 rpm.

[0034] (2) The mixture of graphite / foamed coating material obtained in step (1) is placed in a rotary tube furnace, nitrogen is introduced at high temperature, and carbonization is carried out at 800°C for 2 hours. After the reaction is completed, the temperature is lowered to room temperature to obtain graphite / porous carbon composite material.

[0035] (3) The graphite / porous carbon composite material obtained in step (2) is subjected to ball milling to obtain graphite powder material with a crater structure with a pore size of about 1 μm that is uniformly distributed on the surface.

[0036] Example 2:

[0037] A method for preparing porous graphite powder materials by screw extrusion comprises the following steps:

[0038] (1) Artificial graphite and coal tar pitch are fed into a single screw extruder at a weight ratio of 8:1, and supercritical carbon dioxide of 1.2 kg / h is injected at the same time. After being fully mixed by the extruder, the mixture is extruded from the die to form a foamed material, in which the screw temperature is 210℃, the die temperature is 170℃, and the screw speed is 15 rpm.

[0039] (2) The mixture of graphite / foamed coating material obtained in step (1) is placed in a rotary tube furnace, nitrogen is introduced at high temperature, and carbonization is carried out at 900°C for 3 hours. After the reaction is completed, the temperature is lowered to room temperature to obtain graphite / porous carbon composite material.

[0040] (3) The graphite / porous carbon composite material obtained in step (2) is subjected to ball milling to obtain graphite powder material with a crater structure with a pore size of about 0.8 μm that is uniformly distributed on the surface.

[0041] Example 3:

[0042] A method for preparing porous graphite powder materials by screw extrusion comprises the following steps:

[0043] (1) Natural graphite and petroleum asphalt are fed into a twin-screw extruder at a weight ratio of 8:1, and supercritical carbon dioxide of 1.15 kg / h is injected at the same time. After being fully mixed by the extruder, the mixture is extruded from the die to form a foamed material, in which the screw temperature is 180°C, the die temperature is 150°C, and the screw speed is 20 rpm.

[0044] (2) The mixture of graphite / foamed coating material obtained in step (1) is placed in a rotary tube furnace, nitrogen is introduced at high temperature, and carbonization is carried out at 850°C for 2 hours. After the reaction is completed, the temperature is lowered to room temperature to obtain graphite / porous carbon composite material.

[0045] (3) The graphite / porous carbon composite material obtained in step (2) is subjected to ball milling to obtain graphite powder material with a crater structure with a pore size of about 1.5 μm that is uniformly distributed on the surface.

[0046] Example 4:

[0047] A method for preparing porous graphite powder materials by screw extrusion comprises the following steps:

[0048] (1) Artificial graphite and modified phenolic resin are fed into a twin-screw tandem single-screw extruder at a weight ratio of 10:1, and supercritical carbon dioxide is injected at 1.3 kg / h. After being fully mixed by the extruder, the mixture is extruded from the die and foamed to obtain a mixture of graphite / foamed coating material. The twin-screw temperature is 200℃, the single-screw temperature is 190℃, the die temperature is 170℃, the twin-screw speed is 20 rpm, and the single-screw speed is 10 rpm.

[0049] (2) The mixture of graphite / foamed coating material obtained in step (1) is placed in a rotary tube furnace, nitrogen is introduced at high temperature, and carbonization is carried out at 900°C for 1 hour. After the reaction is completed, the temperature is lowered to room temperature to obtain graphite / porous carbon composite material.

[0050] (3) The graphite / porous carbon composite material obtained in step (2) is subjected to ball milling to obtain graphite powder material with a crater structure with a pore size of about 2 μm that is uniformly distributed on the surface.

[0051] Example 5:

[0052] A method for preparing porous graphite powder materials by screw extrusion comprises the following steps:

[0053] (1) Natural graphite and bisphenol A type epoxy resin are fed into a twin-screw extruder at a weight ratio of 20:1, and supercritical carbon dioxide of 1.0 kg / h is injected at the same time. After being fully mixed by the extruder, the mixture is extruded from the die to form a foamed material, in which the screw temperature is 200℃, the die temperature is 170℃, and the screw speed is 40 rpm.

[0054] (2) The mixture of graphite / foamed coating material obtained in step (1) is placed in a rotary tube furnace, nitrogen is introduced at high temperature, and carbonization is carried out at 950°C for 1.5 hours. After the reaction is completed, the temperature is lowered to room temperature to obtain graphite / porous carbon composite material.

[0055] (3) The graphite / porous carbon composite material obtained in step (2) is subjected to ball milling to obtain graphite powder material with a crater structure with a pore size of about 0.5 μm that is uniformly distributed on the surface.

[0056] Example 6:

[0057] A method for preparing porous graphite powder materials by screw extrusion comprises the following steps:

[0058] (1) Artificial graphite and petroleum asphalt are fed into a twin-screw extruder at a weight ratio of 15:1, and supercritical carbon dioxide of 1.5 kg / h is injected at the same time. After being fully mixed by the extruder, the mixture is extruded from the die to form a foamed material, and a mixture of graphite / foamed coating material is obtained. The screw temperature is 185°C, the die temperature is 165°C, and the screw speed is 30 rpm.

[0059] (2) The mixture of graphite / foamed coating material obtained in step (1) is placed in a rotary tube furnace, nitrogen is introduced at high temperature, and carbonization is carried out at 1000℃ for 2 hours. After the reaction is completed, the temperature is lowered to room temperature to obtain graphite / porous carbon composite material.

[0060] (3) The graphite / porous carbon composite material obtained in step (2) is subjected to ball milling to obtain graphite powder material with a crater structure with a pore size of about 1.2 μm that is uniformly distributed on the surface.

[0061] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A method for preparing porous graphite powder material by screw extrusion, characterized in that: Includes the following steps: (1) Prepare graphite powder and coating material at a weight ratio of 5-30:1, feed them into a screw extruder, and then inject supercritical carbon dioxide foaming agent into the extruder barrel at a rate of 0.8-1.8 kg / h. The screw temperature is 150-280℃ and the die temperature is 150-200℃. Mix them uniformly at this temperature. The screw speed of the screw extruder is 10-50 rpm. The coating material is low-temperature asphalt. (2) The mixture obtained in step (1) is continuously extruded from the die head, and the pressure drop induces bubble nucleation and growth to obtain a mixture of graphite / foamed coating material; (3) The mixture obtained in step (2) is carbonized at 750-1200℃ to obtain a graphite / porous carbon composite material; (4) The graphite / porous carbon composite material obtained in step (3) is ground and pulverized to obtain a graphite powder material with a porous surface; the carbon layer surface of the graphite powder material has craters uniformly distributed; the size range of the craters on the carbon layer surface of the graphite powder material is 1nm-30μm.

2. The method for preparing porous graphite powder material by screw extrusion according to claim 1, characterized in that: The screw extruder mentioned in step (1) is one of a single screw extruder, a twin screw extruder, or a twin screw tandem single screw extruder.

3. The method for preparing porous graphite powder material by screw extrusion according to claim 1, characterized in that: The graphite powder is one or more of natural graphite, artificial graphite, and mesophase carbon microspheres.

4. The method for preparing porous graphite powder material by screw extrusion according to claim 1, characterized in that: The low-temperature asphalt is selected from one of petroleum asphalt, secondary coal tar pitch, and coal tar pitch.

5. The method for preparing porous graphite powder material by screw extrusion according to claim 1, characterized in that: In step (1), the carbon dioxide injection rate is 1-1.5 kg / h; the screw temperature is 150-250℃, and the die head temperature is 150-180℃.

6. The method for preparing porous graphite powder material by screw extrusion according to claim 1, characterized in that: The carbonization temperature in step (3) is 800-1100℃; the carbonization time in step (3) is 0.5-5 hours.

7. The method for preparing porous graphite powder material by screw extrusion according to claim 1, characterized in that: The size of the crater ranges from 0.2 μm to 5 μm.

8. The application of a graphite powder material with a porous surface structure prepared by the preparation method of claim 1 in high-performance silicon-carbon composite anode materials.

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