A method for preparing silicon-carbon composite material

Abstract

The present application provides a method for preparing a silicon-carbon composite material, the preparation method comprising: allowing a first airflow containing porous silicon and a second airflow containing carbon material to intersect and collide in a chamber. By subjecting the carbon material and the porous silicon material to airflow pulverization to form a fresh contact surface, and in the preparation process, using differential convection impact, the porous silicon material can be better embedded into the graphite structure, the graphite and the porous silicon can be better combined, and the resulting silicon-carbon material has extremely strong bonding force, and the prepared silicon-carbon composite material has less oxidation, high material utilization rate, and high electrochemical performance. Compared with the prior art, the present application can solve the problem of silicon itself expanding by more than 300% in the charge and discharge cycle process, and the prepared silicon-carbon composite material has better cycle stability, improves the first-cycle coulomb efficiency of the material, and effectively improves the electrochemical performance of the material.

Description

Technical Field

[0001] This article relates to but is not limited to inorganic composite materials, relates to but is not limited to a method for preparing silicon-carbon composite materials, and in particular relates to but is not limited to a simple method for synthesizing silicon-carbon composite materials based on porous silicon airflow counteraction. Background Art

[0002] As society's expectations for the energy density of lithium-ion batteries continue to rise, the development of high-energy-density cathode and anode materials is urgently needed. Compared to graphite, which has a theoretical capacity of only 372 mAh / g, silicon, with its theoretical capacity of 4200 mAh / g, has become a hot topic in both research and industry. However, silicon's volume expansion of over 300% during charge-discharge cycles, the repeated formation and dissolution of a solid electrolyte interface (SEI) on its surface, and its extremely poor electrical conductivity have limited its further application. Therefore, various highly conductive carbon materials are often used to form composite materials to improve their performance. Common carbon materials include amorphous carbon, carbon nanotubes, graphene, and graphite. The resulting composite structures include core-shell, hollow, sandwich, and three-dimensional structures. The methods used are mainly divided into vapor deposition, liquid coating, and sand milling. Vapor deposition often uses explosive silane to deposit on a carbon substrate, resulting in low loading capacity, poor safety, and low production efficiency. The resulting nano-silicon materials easily agglomerate and lack a strong bond with the carbon matrix. Liquid-phase coating methods often use phenolic resins to coat silicon in liquid phase, and then pyrolyze it at high temperature. However, the carbon layer formed is uneven and brittle, and has a poor inhibitory effect on silicon. The commonly used industrial method is the sand grinding method, which often mixes silicon sources and carbon and sand grinds them in an organic solution system. However, graphite has self-lubricating properties, making it difficult to form an effective carbon-coated silicon structure. Even if a carbon-coated silicon structure is formed by sand grinding, the sand grinding method is prone to poor connectivity between silicon and carbon, severe oxidation, poor performance, and low production efficiency. In addition, the sand grinding method uses a large amount of organic solvents, which is dangerous and has serious environmental problems, resulting in slow production and application of silicon-carbon composite materials. Summary of the Invention

[0003] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

[0004] The present application provides a method for preparing a silicon-carbon composite material, the preparation method comprising:

[0005] The first gas flow containing porous silicon and the second gas flow containing carbon material are intersected and collided in the chamber.

[0006] In one embodiment provided in the present application, the carbon material is selected from any one or more of artificial graphite, natural graphite, graphite nanosheets, hard carbon and soft carbon.

[0007] In one embodiment provided in the present application, the carbon material is battery-grade artificial graphite. The artificial graphite selected has a low degree of graphitization and is soft. Graphite flakes with fresh graphite surfaces are formed during airflow milling. The electrochemical stability of this material is higher than that of other carbon materials.

[0008] In one embodiment provided in the present application, the particle size D50 of the carbon material is 20 μm to 40 μm.

[0009] In one embodiment provided in the present application, the carbon material is any one or more of artificial graphite, natural graphite and graphite nanosheets, and the degree of graphitization of the carbon material is 88% to 92%.

[0010] In one embodiment provided in the present application, the particle size D50 of the porous silicon is 5 μm to 12 μm.

[0011] In one embodiment provided in the present application, the bulk density of the porous silicon is 0.15 g / cm 3 to 0.8g / cm 3 .

[0012] In one embodiment provided in the present application, the porous silicon is selected from any one or more of pure elemental silicon, porous silicon with a surface coated with a carbon layer, and porous silicon with a surface pre-oxidation modification.

[0013] In one embodiment provided in the present application, the thickness of the carbon layer of the porous silicon with the surface-coated carbon layer is 5 nm to 20 nm.

[0014] In one embodiment provided in the present application, the thickness of the oxide layer of the surface pre-oxidation-modified porous silicon is 0.1 nm to 5 nm.

[0015] In one embodiment provided herein, the porous silicon is easily pulverized by airflow, creating sharp edges that easily embed into the graphite structure. This results in a stronger bond between the silicon and carbon materials, enabling efficient composite bonding and high composite stability. The porous nature of the porous silicon also helps eliminate volume expansion during circulation.

[0016] In one embodiment provided in the present application, the first gas flow and the second gas flow are each independently selected from any one or more of nitrogen, carbon dioxide, helium, neon and argon.

[0017] In one embodiment provided in the present application, the porous silicon is crushed in a first crusher until the particle size D50 of the porous silicon is less than 2 μm, and then output to the chamber through a first nozzle together with the first air flow;

[0018] The graphite is pulverized in a second pulverizer until the particle size D50 of the graphite is less than 10 μm, and then output to the chamber through a second nozzle together with the second air flow.

[0019] In one embodiment provided in the present application, the chamber is a third pulverizer, the first nozzle is connected to the third pulverizer, the second nozzle is connected to the third pulverizer, the first nozzle and the second nozzle are configured to be placed opposite each other so that the airflows intersect, and the angle between the first nozzle and the second nozzle is 150° to 180°.

[0020] In one embodiment provided in the present application, the ratio of the pressure of the gas ejected from the first nozzle to the pressure of the gas ejected from the second nozzle is (0.5 to 0.875):0.8.

[0021] In one embodiment provided in the present application, the first pulverizer, the second pulverizer and the third pulverizer are each independently selected from a jet mill.

[0022] In one embodiment provided in the present application, the air flow mill is any one or more of a horizontal disc air flow mill, a fluidized bed jet air flow mill, a circulating tube air flow mill, a jet air flow mill and a target air flow mill.

[0023] The jet mill compresses air through a pipe and sends it to the nozzle of the jet mill. After passing through the nozzle (pressure changes to speed), a supersonic airflow is generated, which is many times the speed of sound. The supersonic airflow carries the material and continuously increases its speed (accelerating motion, with several nozzles blowing several streams of material simultaneously). Then, at the midpoint (the intersection point), the airflow collides with each other, generating intense collision, friction, and shearing, achieving ultra-fine grinding of the particles.

[0024] In another aspect, the present application provides a silicon-carbon composite material prepared by the above-described preparation method, wherein the porous silicon in the composite material accounts for 4 wt.% to 30 wt.% of the silicon-carbon composite material. Excessive or insufficient proportions of porous silicon and graphite can affect the bonding strength of the composite material to some extent, preventing optimal results.

[0025] In one embodiment provided in the present application, the particle size D50 of the silicon-carbon composite material is 6 μm to 12 μm.

[0026] On the other hand, the present application provides an electrochemical cell, which comprises the above-mentioned silicon-carbon composite material.

[0027] In one embodiment provided herein, the electrochemical cell is a lithium-ion battery.

[0028] On the other hand, the present application provides a device, which includes a device housing, and a motor and / or circuit board located inside the device housing. The device housing also includes a battery, which is electrically connected to the motor and / or circuit board for powering the motor and / or circuit board. The battery includes the above-mentioned electrochemical cell.

[0029] The beneficial effects of the technical solution of this application include:

[0030] By subjecting the carbon material and the porous silicon material to air flow crushing to form a fresh contact surface, and using differential convection impact during the preparation process, the porous silicon material can be better embedded into the graphite structure, and the graphite and porous silicon can be better combined. The resulting silicon-carbon material has extremely strong bonding force, and the obtained silicon-carbon composite material has less oxidation, high material utilization rate, and high electrochemical performance.

[0031] Compared with the existing technology, this application can solve the problem of silicon itself expanding by more than 300% in the charge and discharge cycle. The prepared silicon-carbon composite material has better cycle stability, improves the first-cycle coulombic efficiency of the material, and effectively improves the electrochemical performance of the material.

[0032] The method provided in the present application is simple and easy to implement, and its production efficiency is much higher than that of the sand milling method. It does not use any organic solvents, and the closed-circulation protective gas system does not cause safety and environmental problems.

[0033] The method provided in this application is highly applicable. It can not only process porous silicon after coating and modification, but also serve as an intermediate material to obtain a stable silicon-carbon negative electrode for further modification. It has great market application prospects.

[0034] While the method provided herein produces a silicon-carbon composite material, the remaining free graphite and porous silicon in the material make up a relatively small proportion of the total material. Due to its light weight, the remaining porous silicon is difficult to remove from the crusher. Even if a small amount of free material is combined with the silicon-carbon composite material to form the negative electrode, it does not affect the overall performance. Furthermore, the remaining graphite has no impact on performance.

[0035] Other features and advantages of the present application will be described in the following description, and in part will become apparent from the description, or will be understood by practicing the present application. Other advantages of the present application can be invented and obtained through the solutions described in the description. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The accompanying drawings are used to provide an understanding of the technical solution of the present application and constitute a part of the specification. Together with the embodiments of the present application, they are used to explain the technical solution of the present application and do not constitute a limitation on the technical solution of the present application.

[0037] Figure 1This is the SEM image of the silicon-carbon composite material in Example 1 of this application.

[0038] Figure 2 This is the first cycle charge and discharge curve of the battery made based on the silicon-carbon composite material of Example 1 of the present application.

[0039] Figure 3 This is a cyclic charge and discharge curve of a battery made based on the silicon-carbon composite material of Example 1 of the present application.

[0040] Figure 4 This is a cyclic charge and discharge curve of a battery made based on the silicon-carbon composite material of Example 2 of the present application.

[0041] Figure 5 This is the first cycle charge and discharge curve of the battery made based on the silicon-carbon composite material of Example 3 of the present application.

[0042] Figure 6 The charge-discharge curve is a cyclic charge-discharge curve of a battery made from the silicon-carbon composite material according to Comparative Example 1 of the present application.

[0043] Figure 7 The charge-discharge curve of the battery prepared based on the silicon-carbon composite material of Comparative Example 2 of the present application is shown in FIG.

[0044] Figure 8 It is a schematic diagram of the working principle and structure of the horizontal disc (flat) air flow mill.

[0045] Reference numerals: 1. Venturi nozzle; 2. Nozzle; 3. Crushing chamber; 4. Outer shell; 5. Liner. DETAILED DESCRIPTION

[0046] To make the purpose, technical solutions and advantages of this application more clear, the embodiments of this application are described in detail below. It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of this application can be combined with each other in any way.

[0047] Example 1 Preparation of porous silicon-based silicon-carbon composite material

[0048] 80 parts of battery-grade artificial graphite with a graphitization degree of 92% and a D50 of 20 μm were added to the first pulverizer and pulverized by air flow until the D50 was less than 10 μm. The first air flow in the first pulverizer was nitrogen. 20 parts of D50 of 6 μm with a bulk density of 0.58 g / cm were added to the second pulverizer. 3 The porous silicon is subjected to air flow grinding to a D50 of less than 1 μm. The second air flow in the second grinder is nitrogen. The first grinder air flow and the second grinder air flow are introduced into the third grinder respectively. The third grinder is provided with two counter-jet nozzles (for example, the first nozzle and the second nozzle are placed at an angle of 180° to each other so that the air flows can intersect) Figure 8 As shown, Figure 8 The venturi nozzle 1 in the nozzle ejects porous silicon and graphite, and the nozzle 2 is a gas nozzle that assists the counter-punching of porous silicon and graphite. The inlet pressure of the first airflow containing graphite is adjusted to 0.6 MPa, and the inlet pressure of the second airflow containing porous silicon is adjusted to 0.8 MPa. The counter-punching composite molding of porous silicon and graphite is performed. The material D50 obtained by cyclone separation is 8.4 μm, which is a porous silicon-based silicon-carbon composite material. The porous silicon in the product accounts for 19.2%. The micromorphology is shown in FIG. Figure 1 shown.

[0049] The prepared silicon-carbon composite material was assembled into a button-type lithium-ion half-cell test, such as Figure 2 As shown in the figure, at a current density of 100mA / g, its discharge capacity is 975.8mAh / g, its charge capacity is 849.5mAh / g, and its first cycle coulombic efficiency is 87.05%. The electrochemical performance is excellent, showing the high specific capacity characteristics of porous silicon materials. It is cycled 100 times at a current density of 100mA / g. Figure 3 As shown in the figure, it can be seen that its capacity retention rate is 102.48%, and the cycle performance is good. It also reduces the volume expansion of the battery during the charge and discharge cycle to a certain extent.

[0050] Example 2 Preparation of Carbon-coated Porous Silicon-based Silicon-carbon Composite Material

[0051] 95 parts of battery-grade artificial graphite with a graphitization degree of 88% and a D50 of 30 μm were added to the first pulverizer and pulverized to a D50 of less than 10 μm. The airflow in the first pulverizer was nitrogen. 5 parts of D50 of 8 μm and a bulk density of 0.45 g / cm were added to the second pulverizer. 3 The vapor-deposited carbon-coated porous silicon (the thickness of the carbon layer on the surface of the vapor-deposited carbon-coated porous silicon is 10 nm) is pulverized by air flow to D50 = 1 μm or less, and the air flow in the second pulverizer is nitrogen. The first and second pulverizer air flows are respectively introduced into the third pulverizer, and two counter-nozzles are set in the third pulverizer, which are capable of making the air flows intersect, and the first nozzle and the second nozzle are placed opposite to each other at an angle of 180°. The air inlet pressure of the first air flow containing graphite is adjusted to 0.5 MPa, and the air inlet pressure of the second air flow containing porous silicon is adjusted to 0.8 MPa. The porous silicon and graphite are subjected to counter-composite molding. The material D50 obtained by cyclone separation is 9.5 μm, which is a carbon-coated porous silicon-based silicon-carbon composite material. The porous silicon in the product accounts for 4.85%.

[0052] The prepared silicon-carbon composite material was assembled into a button-type lithium-ion half-cell test, such as Figure 4As shown in the figure, after 100 cycles of charge and discharge at a current density of 100 mA / g, its capacity retention rate is 98.29%. Due to the protection of the dual-level carbon layer on the porous silicon surface, its cycling stability is enhanced. It also reduces the volume expansion of the battery during the charge and discharge cycle to a certain extent.

[0053] Example 3 Preparation of Surface Pre-Oxidation Modified Porous Silicon-Based Silicon-Carbon Composite Material

[0054] 90 parts of battery-grade natural graphite with a graphitization degree of 91% and a D50 of 32 μm were added to the first pulverizer and pulverized to a D50 of less than 12 μm. The airflow in the first pulverizer was argon. 10 parts of D50 of 10 μm and a bulk density of 0.72 g / cm were added to the second pulverizer. 3 The pre-oxidized porous silicon is pulverized by air flow to below D50=2μm. The air flow in the second pulverizer is argon, and the pre-oxidation thickness is 3nm. The first and second pulverizer air flows are respectively introduced into the third pulverizer. Two counter-nozzles are set in the third pulverizer, which can make the first nozzle and the second nozzle intersect and are placed opposite to each other at an angle of 180°. The air inlet pressure of the first air flow containing graphite is adjusted to 0.7Mpa, and the air inlet pressure of the second air flow containing pre-oxidized porous silicon is adjusted to 0.8MPa. The pre-oxidized porous silicon and graphite are subjected to counter-composite composite molding. The material D50 obtained by cyclone separation is 10.5μm, which is a pre-oxidized porous silicon-based silicon-carbon composite material. The porous silicon in the product accounts for 9.56%.

[0055] The prepared silicon-carbon composite material was assembled into a button-type lithium-ion half-cell test, such as Figure 5 As shown, at a current density of 100mA / g, its discharge specific capacity is 637.6mAh / g, its charge specific capacity is 568.5mAh / g, and its first cycle coulombic efficiency is 89.16%, with excellent electrochemical performance. Example 3 uses pre-oxidized porous silicon with a suitable dense oxide layer to prevent further oxidation and deep oxidation. Although some performance will be lost, higher cycle performance can be achieved. It also reduces the volume expansion of the battery during the charge and discharge cycle to a certain extent.

[0056] Comparative Example 1

[0057] 80 parts of battery-grade artificial graphite with a graphitization degree of 92% and D50 = 20 μm and 20 parts of D50 = 6 μm and a bulk density of 0.58 g / cm 3 The porous silicon was placed in a horizontal ball mill and ball milled at full speed for 2 hours with a ball-to-material mass ratio of 10:1. Nitrogen protection was introduced throughout the process to obtain a silicon-carbon composite material with D50 = 21.4 μm.

[0058] The prepared silicon-carbon composite material was assembled into a button-type lithium-ion half-cell test, such as Figure 6As shown, after 100 cycles at a current density of 100 mA / g, it can be seen that its capacity retention rate is 74.02%, indicating poor cycle performance. When the batteries of Example 1 and Comparative Example 1 were disassembled after 100 cycles, it was found that the thickness of the battery electrode of Comparative Example 1 was 1.3 times that of Example 1, indicating that the operation of Example 1 can suppress the expansion of the silicon-carbon negative electrode. This is due to the difference in specific gravity and particle size between the two materials. Ball milling cannot effectively combine the two materials, and an effective carbon-coated silicon structure cannot be formed. Local overheating also causes uneven oxidation of silicon, resulting in reduced cycle performance.

[0059] Comparative Example 2

[0060] The only difference between this comparative example and Example 1 is that nano non-porous silicon is used instead of porous silicon, and other raw materials and preparation methods are the same.

[0061] The prepared silicon-carbon composite material was assembled into a button-type lithium-ion half-cell test, such as Figure 7 As shown in the figure, after 100 cycles at a current density of 100 mA / g, it can be seen that its capacity retention rate is 97.23%, which shows good cycle performance. However, the charge capacity is about 240 mAh / g lower than that in Example 1, indicating a large amount of silicon loss. Because the nano-silicon has too low a deadweight and low kinetic energy, it cannot be effectively embedded in the graphite matrix, but instead disperses in the air flow system and becomes waste. In addition, nanomaterials have a very large specific surface area, and when in contact with the electrolyte, they are prone to irreversible side reactions that consume a large amount of lithium salt to form an SEI film, resulting in reduced efficiency and capacity decay.

Claims

1. A method for preparing a silicon-carbon composite material, characterized in that: The preparation method comprises: The first gas flow containing porous silicon and the second gas flow containing carbon material are intersected and collided in the chamber; The porous silicon is crushed in a second crusher until the particle size D50 of the porous silicon is less than 2 μm, and then output to the chamber through a first nozzle together with the first air flow; The carbon material is crushed in a first crusher until the particle size D50 of the carbon material is less than 10 μm, and then output to the chamber through a second nozzle together with the second air flow; The chamber is a third pulverizer, the first nozzle is in communication with the third pulverizer, the second nozzle is in communication with the third pulverizer, the first nozzle and the second nozzle are arranged to be oppositely positioned so that airflows intersect, and the angle between the first nozzle and the second nozzle is 150° to 180°; The ratio of the pressure of the gas ejected from the first nozzle to the pressure of the gas ejected from the second nozzle is (0.5 to 0.875):0.

8.

2. The preparation method according to claim 1, characterized in that The carbon material is selected from any one or more of artificial graphite, natural graphite, graphite nanosheets, hard carbon and soft carbon.

3. The preparation method according to claim 2, characterized in that The particle size D50 of the carbon material is 20 μm to 40 μm.

4. The preparation method according to claim 3, characterized in that The carbon material is any one or more of artificial graphite, natural graphite and graphite nanosheets, and the graphitization degree of the carbon material is 88% to 92%.

5. The preparation method according to claim 1, characterized in that The particle size D50 of the porous silicon is 5 μm to 12 μm.

6. The preparation method according to claim 5, characterized in that The bulk density of the porous silicon is 0.15 g / cm 3 to 0.8g / cm 3 .

7. The preparation method according to claim 5, characterized in that The porous silicon is selected from any one or more of pure elemental silicon, porous silicon with a carbon layer coated on the surface, and porous silicon with a surface pre-oxidation modification.

8. The preparation method according to claim 7, characterized in that The thickness of the carbon layer of the porous silicon covered with the carbon layer is 5 nm to 20 nm.

9. The preparation method according to claim 7, characterized in that The thickness of the oxide layer of the surface pre-oxidized modified porous silicon is 0.1 nm to 5 nm.

10. The preparation method according to claim 1, characterized in that The first gas flow and the second gas flow are each independently selected from any one or more of nitrogen, helium, neon and argon.

11. The preparation method according to claim 1, characterized in that The first pulverizer, the second pulverizer and the third pulverizer are each independently selected from a jet mill.

12. The preparation method according to claim 11, characterized in that The air flow mill is any one or more of a horizontal disc air flow mill, a fluidized bed opposed-jet air flow mill, a circulating tube air flow mill, an opposed-jet air flow mill and a target air flow mill.

13. The silicon-carbon composite material obtained by the preparation method according to any one of claims 1 to 12, characterized in that: The porous silicon in the composite material accounts for 4 wt.% to 30 wt.% of the silicon-carbon composite material.

14. The silicon-carbon composite material according to claim 13, characterized in that The particle size D50 of the silicon-carbon composite material is 6 μm to 12 μm.

15. An electrochemical cell, characterized in that The electrochemical cell comprises the silicon-carbon composite material according to claim 13 or 14.

16. The electrochemical cell according to claim 15, characterized in that The electrochemical cell is a lithium ion battery.

17. A device, characterized in that The device includes a device housing, and a motor and / or circuit board located inside the device housing. The device housing also includes a battery, which is electrically connected to the motor and / or circuit board for powering the motor and / or circuit board. The battery includes the electrochemical cell described in claim 15 or 16.

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