Silicon-based graphene as well as preparation method therefor and use thereof

Abstract

A silicon-based graphene as well as a preparation method therefor and the use thereof. The preparation method for the silicon-based graphene comprises the following steps: (1) mixing graphite, silicon powder and silicon dioxide to obtain a first mixture; (2) carrying out intercalation and exfoliation on the graphite in the first mixture by means of using fluid shearing assisted supercritical carbon dioxide technology, so as to exfoliate the graphite in the first mixture into graphene, thus forming a second mixture of graphene, silicon powder and silicon dioxide; and (3) carrying out high-temperature sintering on the second mixture to obtain the silicon-based graphene in which silicon monoxide is covered with spherical graphene.

Description

Silicon-based graphene and its preparation method and application

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This disclosure is based on and claims the priority of Chinese patent application with application number 202410179649.8 and application date on February 18, 2024. The entire content of this Chinese patent application is hereby incorporated into this disclosure by reference. Technical Field

[0003] The present disclosure belongs to the technical field of lithium-ion battery negative electrode materials. Specifically, the present disclosure relates to silicon-based graphene and a preparation method and application thereof. Background Art

[0004] With the widespread application of lithium-ion batteries in electronic products and new energy electric vehicles, the demand for lithium-ion batteries with high energy density is increasing. Traditional graphite negative electrode materials (372mAh / g) can no longer meet the needs. Therefore, there is an urgent need to explore new high-performance and high-capacity negative electrode materials.

[0005] Compared with traditional graphite anode materials, silicon-based materials have extremely high theoretical specific capacity (elemental silicon can reach 3580mAh / g) and their delithiation potential is suitable (0.3-0.4V), making them extremely promising anode materials. Common silicon anode materials include nanosilicon (Si), silicon oxide (SiO), amorphous silicon alloys, etc. Compared with two-dimensional graphite materials that can only provide intercalation / deintercalation paths in the cross-sectional direction, silicon can provide intercalation / deintercalation paths in all directions, and has excellent fast charging performance. However, although silicon has excellent energy density performance, when used as anode, when lithium is intercalated into silicon to form an alloy, the volume change can exceed 300%. Repeated intercalation / deintercalation processes will cause the electrode material to shatter, eventually losing effective electrical contact and causing electrode failure. In addition, the conductivity of silicon-based materials is generally low, and the diffusion rate of lithium ions in silicon is also relatively low, which is not conducive to the transmission of electrons and lithium ions. Therefore, there is an urgent need to develop a lithium-ion battery anode material with excellent comprehensive performance. Summary of the Invention

[0006] The present disclosure aims to solve at least one of the technical problems in the related art to a certain extent. To this end, the present disclosure provides a silicon-based graphene and a preparation method and application thereof.

[0007] In a first aspect, the present disclosure provides a method for preparing silicon-based graphene, comprising the following steps:

[0008] (1) mixing graphite, silicon powder, and silicon dioxide to obtain a first mixed material;

[0009] (2) intercalating and exfoliating the graphite in the first mixture using fluid shear-assisted supercritical carbon dioxide technology, so that the graphite in the first mixture is exfoliated into graphene, thereby forming a second mixture of graphene, silicon powder and silicon dioxide;

[0010] (3) Sintering the second mixture at a high temperature to obtain silicon-based graphene with spherical graphene wrapped in silicon oxide.

[0011] The disclosed embodiment uses graphite, silicon powder and silicon dioxide as reaction raw materials, utilizes fluid shear-assisted supercritical carbon dioxide technology, and physically constructs a structure of spherical graphene wrapped in silicon powder and silicon dioxide, and obtains silicon-based graphene wrapped in spherical graphene through further high-temperature sintering. This physical construction method does not require the use of other chemical reagents, is low-consumption and environmentally friendly, and will not cause graphene defects and affect conductivity; the obtained silicon-based graphene has high conductivity and is conducive to fast charging.

[0012] In some embodiments, in step (1), the mass content of the graphite accounts for 10 to 70% of the first mixture, and can be optionally 10 to 50%;

[0013] And / or, the mass ratio of the silicon powder to the silicon dioxide is 1:(0.1-1), and can be optionally 1:1.

[0014] In some embodiments, in step (2), the fluid shearing temperature is 40-65° C., the shearing pressure is 8-11.5 MPa, the shearing speed is 1500-2500 r / min, and the shearing time is 10-60 min.

[0015] In some embodiments, in step (3), the high-temperature sintering temperature is 1000-2000° C., optionally 1000-1200° C.; the sintering time is 0.5-3 h, optionally 1-2 h;

[0016] Furthermore, the high-temperature sintering is carried out under an inert gas protective atmosphere, and the inert gas includes at least one of nitrogen, argon, and helium.

[0017] In a second aspect, an embodiment of the present disclosure further proposes a silicon-based graphene, which is prepared by the preparation method described in the first aspect.

[0018] In some embodiments, the silicon-based graphene includes graphene and silicon monoxide; wherein the graphene has a three-dimensional spherical structure, and the graphene wraps the silicon monoxide.

[0019] In the silicon-based graphene in the embodiment of the present disclosure, the three-dimensional spherical graphene structure wraps silicon oxide, providing a buffer space for the volume expansion of silicon oxide, and at the same time providing a three-dimensional conductive network to prevent structural rupture and contact failure, thereby losing electrical contact and causing failure of the electrode active material; silicon oxide is isotropic and easy to charge quickly, and combined with the spherical graphene conductive network architecture, its fast charging performance can be further improved.

[0020] In a third aspect, the embodiments of the present disclosure further propose an application of the silicon-based graphene as described in the second aspect in a lithium-ion battery, wherein the silicon-based graphene is used as a negative electrode material of the lithium-ion battery.

[0021] A lithium-ion battery is prepared using the silicon-based graphene of the embodiment of the present disclosure as the negative electrode material, and the resulting lithium-ion battery has excellent stability and fast charging performance.

[0022] The advantages and beneficial effects of the embodiments of the present disclosure are as follows:

[0023] (1) In the preparation process of the silicon-based graphene in the embodiment of the present disclosure, no liquid solvents or other chemical reagents are required, which is low-consumption, environmentally friendly, and easy to promote. In addition, graphite is physically stripped into graphene based on supercritical fluid, and the graphene has fewer defects and high conductivity, which is conducive to fast charging.

[0024] (2) The disclosed embodiment constructs a special structure of three-dimensional spherical graphene wrapped in silicon oxide. The three-dimensional spherical structure can provide a buffer space for the volume expansion of silicon oxide, and also provides a three-dimensional conductive network to prevent structural rupture and contact failure, thereby preventing the loss of electrical contact and causing failure of the electrode active material.

[0025] (3) In the silicon-based graphene of the disclosed embodiment, silicon oxide has isotropy, which is beneficial to improving the fast charging performance of the material, and combined with the spherical graphene conductive network architecture, the fast charging performance is further improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] FIG1 is a schematic diagram of a process for obtaining graphene by exfoliating graphite using fluid shear-assisted supercritical carbon dioxide technology in a preparation method according to an embodiment of the present disclosure.

[0027] FIG2 is a schematic diagram of the structure of silicon-based graphene according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0028] To make the purpose, technical solutions, and advantages of the embodiments of the present disclosure more clear, the technical solutions of the embodiments of the present disclosure are clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present disclosure, not all of them. Based on the described embodiments of the present disclosure, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present disclosure.

[0029] Unless otherwise defined, technical or scientific terms used in the present disclosure should have the same meaning as commonly understood by persons having ordinary skills in the field to which the present disclosure belongs.

[0030] Where values ​​are described herein as ranges, it should be understood that such disclosure includes disclosure of all possible sub-ranges within that range, as well as specific values ​​falling within that range, regardless of whether a specific value or sub-range is explicitly stated.

[0031] As used herein, the words "comprise," "include," and "includes" and variations thereof mean that additional elements or integers may be included although permitted but not specifically described.

[0032] In this article, the term "and / or" is merely a description of the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone.

[0033] In a first aspect, the present disclosure provides a method for preparing silicon-based graphene, comprising the following steps:

[0034] (1) mixing graphite, silicon powder, and silicon dioxide to obtain a first mixed material;

[0035] (2) intercalating and exfoliating the graphite in the first mixture using fluid shear-assisted supercritical carbon dioxide technology, so that the graphite in the first mixture is exfoliated into graphene, thereby forming a second mixture of graphene, silicon powder and silicon dioxide;

[0036] (3) Sintering the second mixture at a high temperature to obtain silicon-based graphene with spherical graphene wrapped in silicon oxide.

[0037] In some embodiments, in step (1), the mass content of the graphite accounts for 10-70% (non-limiting examples: 10%, 20%, 30%, 45%, 50%, 60%, 70%, etc.) of the first mixture, and can be optionally 10-50% (non-limiting examples: 10%, 20%, 35%, 40%, 50%, etc.); the inventors have found through research that if the graphite content is too high, it will lead to insufficient shearing; but if the graphite content is too low, it will cause insufficient content of the conductive agent in the final reactant, thereby affecting the conductive performance. Therefore, the embodiment of the present disclosure controls the mass content of graphite within the range of 10-70%, and can be optionally 10-50%; in addition, it should be noted that the number of graphite layers is not particularly limited, and those skilled in the art can choose according to actual needs;

[0038] And / or, the mass ratio of the silicon powder to the silicon dioxide is 1:(0.1~1), non-limiting examples include: 1:0.1, 1:0.5, 1:0.8, 1:1, etc.), which can be selected as 1:1; the inventors have found through research that if the mass ratio of silicon dioxide is too high, the valence of silicon will be too high and the product will be unstable; but if the mass ratio of silicon dioxide is too low, silicon will not be able to react fully, and it will be difficult to obtain a sufficient amount of silicon iodide. Therefore, the embodiment of the present disclosure controls the mass ratio of silicon powder to silicon dioxide within the range of 1:(0.1~1), which can be selected as 1:1; in addition, it should be noted that the sizes of silicon powder and silicon dioxide are not subject to special restrictions, and those skilled in the art can make choices according to actual needs.

[0039] In some embodiments, in step (2), the fluid shear temperature is 40-65°C (non-limiting examples include 40°C, 45°C, 50°C, 58°C, 60°C, 65°C, etc.), the shear pressure is 8-11.5 MPa (non-limiting examples include 8 MPa, 8.5 MPa, 9 MPa, 9.2 MPa, 10 MPa, 10.5 MPa, 11 MPa, 11.5 MPa, etc.), the shear speed is 1500-2500 r / min (non-limiting examples include 1500 r / min, 1800 r / min, 2000 r / min, 2200 r / min, 2500 r / min, etc.), and the shear time is 10-60 min (non-limiting examples include 10 min, 20 min, 35 min, 40 min, 45 min, 50 min, 60 min, etc.).

[0040] As shown in Figure 1, in step (2) of the method for preparing silicon-based graphene in the disclosed embodiment, by means of the power of shearing of supercritical carbon dioxide fluid, during the process of efficient exfoliation of graphite into graphene, silicon powder and silicon dioxide can be mixed evenly and simultaneously fully inserted into the graphite interlayer, fully contacting the graphene surface, and based on the high specific surface area and surface tension of graphene, a spherical structure of graphene-wrapped silicon powder and silicon dioxide is formed. Among them, the process of exfoliating graphite into graphene and constructing three-dimensional spherical graphene is a physical process, without the need for other chemical reagents, green and pollution-free, and with low energy consumption, and at the same time will not cause graphene defects and affect conductivity.

[0041] In some embodiments, in step (3), the high-temperature sintering temperature is 1000-2000°C (non-limiting examples include: 1000°C, 1200°C, 1500°C, 1800°C, 2000°C, etc.), and can be optionally 1000-1200°C (non-limiting examples include: 1000°C, 1050°C, 1100°C, 1200°C, etc.); the sintering time is 0.5-3h (non-limiting examples include: 0.5h, 0.8h, 1h, 1.5h, 2h, 2.4h, 2.8h, 3h, etc.), and can be optionally 1-2h (non-limiting examples include: 1h, 1.5h, 1.8h, 2h, etc.).

[0042] Furthermore, the high-temperature sintering is carried out under an inert gas protective atmosphere, and the inert gas includes at least one of nitrogen, argon, and helium.

[0043] By sintering a mixture of spherical graphene-coated silicon powder and silicon dioxide at high temperature under an inert gas atmosphere, the silicon powder and silicon dioxide react at high temperature to form silicon oxide, thereby obtaining a composite material of spherical graphene-coated silicon oxide. In this composite material, silicon oxide provides high energy density and fast charging performance, while graphene provides a three-dimensional skeleton that can buffer the volume expansion and collapse of silicon oxide. The three-dimensional skeleton maintains sufficient electrical contact, which helps to fully realize the fast charging performance.

[0044] In the second aspect, as shown in FIG2 , an embodiment of the present disclosure further proposes a silicon-based graphene, which is prepared by the preparation method described in the first aspect.

[0045] In some embodiments, the silicon-based graphene includes graphene and silicon monoxide; wherein the graphene has a three-dimensional spherical structure, and the graphene wraps the silicon monoxide.

[0046] In the silicon-based graphene of the disclosed embodiment, silicon iodide provides high energy density and excellent fast-charging performance. Graphene provides expansion buffer space and a conductive network to maintain electrical contact with the electrode active materials and ensure continuous electrical connection after the material structure is broken. It has good stability and a long service life, as well as excellent fast-charging performance.

[0047] In a third aspect, the embodiments of the present disclosure further propose an application of the silicon-based graphene as described in the second aspect in a lithium-ion battery, wherein the silicon-based graphene is used as a negative electrode material of the lithium-ion battery.

[0048] The following are non-limiting examples and comparative examples of the present disclosure. It should be noted that the comparative examples are not related art and are provided solely for comparison with the examples and are not intended to limit the present disclosure. Unless otherwise noted, the various raw materials used in the examples and comparative examples are conventional commercially available products or can be prepared by known methods.

[0049] Example 1

[0050] A method for preparing silicon-based graphene comprises the following steps:

[0051] (1) 0.5 g of graphite, 1 g of silicon powder, and 1 g of silicon dioxide were mixed to obtain a first mixture;

[0052] (2) adding the first mixture into an autoclave, introducing carbon dioxide fluid, and subjecting the graphite in the first mixture to fluid shearing in a supercritical carbon dioxide system, controlling the fluid shearing temperature to 40° C., the shearing pressure to 9 MPa, the shearing rate to 1500 r / min, and the shearing time to 20 min. After the shearing is completed, the pressure is quickly released and the carbon dioxide is discharged, thereby exfoliating the graphite in the first mixture into graphene, and obtaining a second mixture of graphene, silicon powder, and silicon dioxide;

[0053] (3) Under the protection of argon atmosphere, the second mixture is sintered at a high temperature of 1000° C. and kept at this temperature for 1 hour to obtain spherical graphene-wrapped silicon-based graphene containing silicon oxide.

[0054] Example 2

[0055] A method for preparing silicon-based graphene comprises the following steps:

[0056] (1) 1 g of graphite, 1 g of silicon powder, and 1 g of silicon dioxide were mixed to obtain a first mixture;

[0057] (2) adding the first mixture into an autoclave, introducing carbon dioxide fluid, and subjecting the graphite in the first mixture to fluid shearing in a supercritical carbon dioxide system, controlling the fluid shearing temperature to 45° C., the shearing pressure to 8 MPa, the shearing rate to 1800 r / min, and the shearing time to 15 min. After the shearing is completed, the pressure is quickly released and the carbon dioxide is discharged, thereby exfoliating the graphite in the first mixture into graphene, and obtaining a second mixture of graphene, silicon powder, and silicon dioxide;

[0058] (3) Under the protection of argon atmosphere, the second mixture is sintered at a high temperature of 1050° C. and kept at this temperature for 1 hour to obtain spherical graphene-wrapped silicon-based graphene containing silicon oxide.

[0059] Example 3

[0060] A method for preparing silicon-based graphene comprises the following steps:

[0061] (1) 1.5 g of graphite, 1 g of silicon powder, and 1 g of silicon dioxide were mixed to obtain a first mixture;

[0062] (2) adding the first mixture into an autoclave, introducing carbon dioxide fluid, and subjecting the graphite in the first mixture to fluid shearing in a supercritical carbon dioxide system, controlling the fluid shearing temperature to 50° C., the shearing pressure to 10 MPa, the shearing rate to 1500 r / min, and the shearing time to 20 min. After the shearing is completed, the pressure is quickly released and the carbon dioxide is discharged, thereby exfoliating the graphite in the first mixture into graphene, and obtaining a second mixture of graphene, silicon powder, and silicon dioxide;

[0063] (3) Under the protection of argon atmosphere, the second mixture is sintered at a high temperature of 1100° C. and kept at this temperature for 1.5 hours to obtain spherical graphene-wrapped silicon-based graphene containing silicon oxide.

[0064] Example 4

[0065] A method for preparing silicon-based graphene comprises the following steps:

[0066] (1) 1.8 g of graphite, 1 g of silicon powder, and 1 g of silicon dioxide were mixed to obtain a first mixture;

[0067] (2) adding the first mixture into an autoclave, introducing carbon dioxide fluid, and subjecting the graphite in the first mixture to fluid shearing in a supercritical carbon dioxide system, controlling the fluid shearing temperature to 60° C., the shearing pressure to 10 MPa, the shearing rate to 2000 r / min, and the shearing time to 60 min. After the shearing is completed, the pressure is quickly released and the carbon dioxide is discharged, thereby exfoliating the graphite in the first mixture into graphene, and obtaining a second mixture of graphene, silicon powder, and silicon dioxide;

[0068] (3) Under the protection of argon atmosphere, the second mixture is sintered at a high temperature of 1200° C. and kept at this temperature for 2 hours to obtain spherical graphene-wrapped silicon-based graphene containing silicon oxide.

[0069] Example 5

[0070] A method for preparing silicon-based graphene comprises the following steps:

[0071] (1) 2 g of graphite, 1 g of silicon powder, and 1 g of silicon dioxide were mixed to obtain a first mixture;

[0072] (2) adding the first mixture into an autoclave, introducing carbon dioxide fluid, and subjecting the graphite in the first mixture to fluid shearing in a supercritical carbon dioxide system, controlling the fluid shearing temperature to 65° C., the shearing pressure to 11 MPa, the shearing rate to 2500 r / min, and the shearing time to 50 min. After the shearing is completed, the pressure is quickly released and the carbon dioxide is discharged, thereby exfoliating the graphite in the first mixture into graphene, and obtaining a second mixture of graphene, silicon powder, and silicon dioxide;

[0073] (3) Under the protection of argon atmosphere, the second mixture is sintered at a high temperature of 1500° C. and kept at this temperature for 3 hours to obtain spherical graphene-wrapped silicon-based graphene containing silicon oxide.

[0074] Comparative Example 1

[0075] A method for preparing a graphite-silicon dioxide composite material comprises the following steps:

[0076] (1) 0.5 g of graphite, 1 g of silicon powder, and 1 g of silicon dioxide were mixed uniformly to obtain a mixture;

[0077] (2) Under the protection of argon atmosphere, the mixture is sintered at a high temperature of 1000°C and kept at this temperature for 1 hour to obtain a graphite-silicon oxide composite material.

[0078] Comparative Example 2

[0079] A method for preparing a graphene-silicon dioxide composite material comprises the following steps:

[0080] (1) 0.5 g of graphene, 1 g of silicon powder, and 1 g of silicon dioxide were mixed to obtain a mixture;

[0081] (2) Under the protection of argon atmosphere, the mixture is sintered at 1000°C and kept warm for 1 hour to obtain a graphene-silicon oxide composite material.

[0082] Comparative Example 3

[0083] A method for preparing a graphene oxide-silicon dioxide composite material comprises the following steps:

[0084] (1) 0.5 g of graphene oxide, 1 g of silicon powder, and 1 g of silicon dioxide were mixed to obtain a mixture;

[0085] (2) Under the protection of argon atmosphere, the mixture is sintered at a high temperature of 1000°C and kept warm for 1 hour to obtain a graphene oxide-silicon dioxide composite material.

[0086] The conductivity of the products prepared in the above examples and comparative examples was tested, and lithium-ion batteries were prepared using the products prepared in the above examples and comparative examples as negative electrode materials, and the electrochemical properties of the lithium-ion batteries were tested. The results are shown in Table 1.

[0087] Table 1

[0088] As can be seen from Table 1, compared with Comparative Examples 1-3, the silicon-based graphene prepared in Examples 1-5 has higher conductivity. The excellent conductivity can accelerate the transmission of electrons, realize the rapid transmission of lithium ions, and has excellent fast charging performance and rate performance. It shows a higher specific capacity at a 3C rate.

[0089] In the present disclosure, the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present disclosure. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0090] Although the embodiments of the present disclosure have been shown and described above, it is understood that the above embodiments are illustrative and are not to be construed as limitations on the present disclosure. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present disclosure.

Claims

1. A method for preparing silicon-based graphene, comprising the following steps: (1) mixing graphite, silicon powder, and silicon dioxide to obtain a first mixed material; (2) intercalating and exfoliating the graphite in the first mixture using fluid shear-assisted supercritical carbon dioxide technology, so that the graphite in the first mixture is exfoliated into graphene, thereby forming a second mixture of graphene, silicon powder and silicon dioxide; (3) Sintering the second mixture at a high temperature to obtain silicon-based graphene with spherical graphene wrapped in silicon oxide.

2. The method for preparing silicon-based graphene according to claim 1, wherein In the step (1), the mass content of the graphite accounts for 10 to 70% of the first mixture; And / or, the mass ratio of the silicon powder to the silicon dioxide is 1:(0.1-1).

3. The method for preparing silicon-based graphene according to claim 2, wherein: The mass content of the graphite accounts for 10 to 50% of the first mixed material; And / or, the mass ratio of the silicon to the silicon dioxide is 1:

1.

4. The method for preparing silicon-based graphene according to any one of claims 1 to 3, wherein In the step (2), the fluid shearing temperature is 40-65° C., the shearing pressure is 8-11.5 MPa, the shearing speed is 1500-2500 r / min, and the shearing time is 10-60 min.

5. The method for preparing silicon-based graphene according to any one of claims 1 to 4, wherein: In the step (3), the high-temperature sintering temperature is 1000-2000° C., and the sintering time is 0.5-3 hours.

6. The method for preparing silicon-based graphene according to claim 5, wherein: The high-temperature sintering temperature is 1000-1200° C., and the sintering time is 1-2 hours.

7. The method for preparing silicon-based graphene according to claim 5 or 6, wherein: The high-temperature sintering is performed under an inert gas protective atmosphere, and the inert gas includes at least one of nitrogen, argon, and helium.

8. A silicon-based graphene, wherein the silicon-based graphene is prepared by the preparation method according to any one of claims 1 to 7.

9. The silicon-based graphene according to claim 8, wherein The silicon-based graphene includes graphene and silicon oxide; wherein the graphene is in a three-dimensional spherical structure, and the graphene wraps the silicon oxide.

10. Use of the silicon-based graphene according to claim 8 or 9 in a lithium-ion battery, wherein the silicon-based graphene is used as a negative electrode material of the lithium-ion battery.

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