CN111477849B - Preparation method of porous Si/SiC/C material and negative electrode material - Google Patents

Preparation method of porous Si/SiC/C material and negative electrode material Download PDF

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CN111477849B
CN111477849B CN202010289292.0A CN202010289292A CN111477849B CN 111477849 B CN111477849 B CN 111477849B CN 202010289292 A CN202010289292 A CN 202010289292A CN 111477849 B CN111477849 B CN 111477849B
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silicon
porous
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magnesium
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CN111477849A (en
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姜春海
周文扬
邹智敏
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Xiamen University of Technology
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H01M4/386—Silicon or alloys based on silicon
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/364—Composites as mixtures
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Abstract

The invention relates to a preparation method of a porous Si/SiC/C material and a negative electrode material, wherein the preparation method comprises the following steps: s1, grinding and mixing the waste silicon powder and the magnesium powder according to the mass ratio, placing the mixture and absolute ethyl alcohol into a planetary ball mill for physical ball milling, and drying to obtain silicon-magnesium alloy powder; s2, under the protection of inert gas, heating the silicon-magnesium alloy powder for reaction, cooling along with a furnace, and grinding to obtain the magnesium silicide powder; s3, in CO2Heating the magnesium silicide powder to react in the atmosphere, cooling along with the furnace, grinding and acid washing to obtain the magnesium silicide powder. The porous Si/SiC/C material is used as the lithium ion battery cathode material, the volume expansion effect of the silicon wrapped inside is relieved by utilizing the porous structure on the SiC/C protective layer, and meanwhile, the SiC/C layer can wrap the silicon more completely, so that the rate capability and the cycle performance of the silicon-carbon cathode material are effectively improved.

Description

Preparation method of porous Si/SiC/C material and negative electrode material
Technical Field
The invention relates to the technical field of lithium batteries, in particular to a preparation method of a porous Si/SiC/C material and a negative electrode material.
Background
Lithium ion batteries are the main choice for power sources of current portable electronic devices (such as mobile phones, digital cameras and portable notebooks), and are also increasingly widely applied to electric vehicles, hybrid electric vehicles, large-scale energy storage, space technology, national defense industry and other fields. With the rapid rise of new energy automobiles in recent years, the energy density and the power performance of the original lithium ion battery can not meet the requirements, the development of novel battery materials and the optimization of battery manufacturing technology are performed, and the improvement of the cruising ability and the power characteristic of the lithium ion battery is the key for promoting the high-level development of the electric automobile industry. It is generally believed that the key to determining the energy density of a lithium ion battery is its electrode material, particularly the positive electrode material. Therefore, the academic world and the industrial world have focused on developing novel cathode materials, such as nickel-cobalt-manganese ternary materials, nickel-cobalt-aluminum ternary materials, lithium-rich manganese-based ternary materials, and the like. However, the attention to the anode material is significantly weaker.
At present, the negative electrode material of the lithium ion battery mainly comprises modified natural graphite and artificial graphite. Although the theoretical specific capacity (372mAh/g) of the graphite material is higher than that of all the existing anode materials, the lithium dendrite deposition caused by the lower lithium intercalation potential of the graphite material causes the hidden trouble of short circuit and the poor rate capability of the graphite material, so that the graphite material is not suitable for being used as a power battery anode material. Therefore, in recent years, the search for new negative electrode materials with high specific capacity and high rate performance has attracted extensive attention in the lithium ion battery industry.
The theoretical specific capacity of the silicon-based negative electrode material is up to 4200mAh/g, and the silicon-based negative electrode material has a lower discharge platform, so that the silicon-based negative electrode material is widely concerned by people. However, the semiconducting properties of silicon and its large volume expansion after lithium insertion make its cycling stability very poor. At present, the main strategies for solving the problem of the cycling stability of the silicon-based negative electrode material comprise silicon nanocrystallization, carbon coating, ceramic layer coating, binder improvement, electrolyte additive research and development and the like. Among them, the carbon coating strategy is most widely applied, but the silicon is subjected to nanocrystallization or porosification, the diffusion distance of lithium ions is shortened, and the volume expansion is relieved, which is the premise for realizing the high performance of the silicon-carbon negative electrode material.
At present, high-quality nano silicon is mostly prepared by adopting a vapor deposition method, so that the cost is high, and the commercial application of the nano silicon is limited. The other method for preparing the nano silicon is ball milling or sand milling, but on one hand, the discharging fineness of the ball milling or sand milling is difficult to achieve a proper nano size, and on the other hand, the high energy generated in the grinding process can induce the growth of an inactive silicon carbide layer, and generally the method is considered to have negative effects on the lithium storage performance of the silicon negative electrode material. However, in recent years, research on a related research group (Nano lett.2019,19,8, 5124-containing 5132) that a thin complete Silicon Carbide (SiC) Layer is introduced to the surface of Silicon particles to form a Si/SiC/C structure, so that the stability of an SEI Layer on the surface of a negative electrode is improved, and thus the cycle stability is improved. However, the introduction method of the SiC layer generally requires a layer of acetylene black to be pre-deposited, and then a high-temperature reaction is performed, so that not only is the process complicated, but also the thickness and uniformity of the silicon carbide layer are difficult to ensure. Therefore, there is still an urgent need to develop a low-cost preparation process of a high-performance Si/SiC/C negative electrode material with controllable SiC coating thickness.
Disclosure of Invention
The invention aims to overcome the defects of the performance of the traditional silicon-based negative electrode material of a lithium battery, and provides a preparation method of a porous Si/SiC/C material.
The specific scheme is as follows:
a preparation method of a porous Si/SiC/C material comprises the following steps:
s1, grinding and mixing the waste silicon powder and the magnesium powder, adding a solvent into the obtained mixture, carrying out physical ball milling, and then drying to obtain silicon-magnesium alloy powder;
s2, under the protection of inert gas, heating the silicon-magnesium alloy powder obtained in the step S1 for reaction, cooling along with a furnace, and grinding to obtain magnesium silicide powder;
s3, in CO2And (4) heating the magnesium silicide powder obtained in the step S2 in an atmosphere, cooling along with a furnace, grinding and acid washing to obtain the porous Si/SiC/C material.
Further, in step S1, the waste silicon powder is high-purity silicon powder produced by cutting silicon ingots in the photovoltaic industry, and the silicon content is greater than or equal to 99.9%;
optionally, in step S1, the waste silicon powder and the magnesium powder are ground and mixed according to the mass ratio of 1: 1.8-1: 2.2;
optionally, in step S1, the solvent is absolute ethyl alcohol, and the physical ball milling is performed by using a planetary ball mill for 15 minutes to 24 hours;
optionally, in step S1, the drying temperature is 40 to 60 ℃.
Further, in step S2, the heating reaction conditions include a temperature of 500 to 550 ℃ and a time of 1 to 6 hours;
optionally, in step S2, the heating reaction is specifically performed by: under the protection of inert gas, the temperature is converted to 500-550 ℃ at the rising/lowering rate of 1-5 ℃/min, and the temperature is kept for 1-6 hours.
Further, in step S3, the heating conditions include a temperature of 600 to 650 ℃ and a time of 30 minutes to 2 hours;
optionally, in step S3, the specific process of the heating treatment is: in CO2In the atmosphere, converting the temperature to 600-650 ℃ at a temperature rising/reducing rate of 5-15 ℃/min, and preserving the temperature for 30 minutes-2 hours;
optionally, in step S3, the acid-washing solution is one or two of a hydrochloric acid aqueous solution and a hydrofluoric acid aqueous solution.
The porous Si/SiC/C material is prepared by the preparation method of the porous Si/SiC/C material, and is nano-scale particles with the size of 100-300 nm.
Further, the porous Si/SiC/C material has the structure that: the silicon particles are arranged inside, the silicon particles are wrapped outside by the carbon-doped silicon carbide layer to form a SiC/C shell layer, and the SiC/C shell layer is provided with a plurality of pores.
Further, the thickness of the SiC/C shell layer is 50-250 nm.
The negative electrode material comprises an active material, a conductive agent and a binder, wherein the active material is the porous Si/SiC/C material.
An anode comprising a current collector, the surface of which is covered with a coating formed of the anode material.
A lithium ion battery comprises a negative electrode, a positive electrode and an electrolyte, wherein the negative electrode is prepared by the method.
Has the advantages that:
according to the preparation method of the porous Si/SiC/C material, the recycled waste silicon and magnesium powder are reacted to generate magnesium silicide, and the magnesium silicide is oxidized and reduced to generate the porous Si/SiC/C material, so that the use of high-price raw materials such as acetylene black and graphene is avoided, the problem of garbage treatment in the photovoltaic industry is effectively solved, a rich and low-cost silicon source is provided for the application of lithium ion batteries, and great environmental benefits and economic benefits are generated.
The negative electrode material made of the porous Si/SiC/C material is applied to lithium ion batteries, and shows better rate performance and cycle performance, and the possible reasons are as follows: in the porous Si/SiC/C material, the volume expansion effect of silicon wrapped inside is relieved by the porous structure on the SiC/C protective layer, meanwhile, the SiC/C layer can wrap the silicon more completely, the silicon exposed outside is reduced, and the side reaction caused by the direct contact of the silicon and electrolyte is avoided.
Drawings
In order to illustrate the technical solution of the present invention more clearly, the drawings will be briefly described below, and it is apparent that the drawings in the following description relate only to some embodiments of the present invention and are not intended to limit the present invention.
FIG. 1 is a flow chart of a manufacturing process provided in one embodiment 1 of the present invention;
FIG. 2 is a Scanning Electron Microscope (SEM) photograph of a material provided in accordance with one embodiment of the present invention 1;
FIG. 3 is a Transmission Electron Microscope (TEM) photograph of a material provided in one embodiment 1 of the present invention;
FIG. 4 is an X-ray diffraction (XRD) spectrum of a material provided in accordance with one embodiment of the present invention 1;
FIG. 5 is a graph showing the charge and discharge curves of a battery according to an embodiment 3 of the present invention at a current density of 400 mA/g;
FIG. 6 is a graph of battery rate performance provided by one embodiment 3 of the present invention;
fig. 7 is a graph showing charge and discharge curves of a battery according to a comparative example 3 of the present invention.
Detailed Description
The definitions of some of the terms used in the present invention are given below, and other non-mentioned terms have definitions and meanings known in the art:
waste silicon powder: the waste silicon powder is silicon simple substance waste generated in the production process, has the purity of more than or equal to 99 percent and the granularity of 1-1000 microns, and is preferably high-purity silicon powder generated by cutting silicon ingots in the photovoltaic industry.
Magnesium powder: the size of the powdery magnesium is 1-1000 microns, preferably 10-500 microns, and more preferably 100-300 microns.
In the present invention, in step S1, the waste silicon powder and the magnesium powder are preferably mixed in a mass ratio of 1:1.8 to 1:2.2, and more preferably 1:2.
In the present invention, the physical ball milling is preferably performed by a planetary ball mill, and then drying is performed at 40-60 ℃ to volatilize the solvent, preferably 50 ℃.
In the present invention, the inert gas protection is to protect the silicon-magnesium alloy powder from reacting to generate magnesium silicide, and the inert gas may be at least one of nitrogen and a gas of a group zero element in the periodic table of elements, which is known to those skilled in the art and will not be described herein again.
In the present invention, the heating reaction temperature in step S2 is 500-550 ℃, the time is 1-6 hours, preferably 510-540 ℃, such as 520 ℃, 530 ℃, 525 ℃.
In the present invention, the heating treatment temperature in step S3 is 600-650 deg.C, the time is 30 minutes-2 hours, preferably 610-640 deg.C, such as 620 deg.C, 625 deg.C, 630 deg.C.
In the invention, step S2 is mainly to react the waste silicon powder with the magnesium simple substance to generate magnesium silicide; subsequently, in step S3, the magnesium silicide is decomposed into porous silicon and elemental magnesium by heating, the elemental magnesium and carbon dioxide react to generate magnesium oxide and amorphous carbon in the carbon dioxide atmosphere, and the amorphous carbon reacts with the porous silicon to generate a silicon carbide layer.
In the present invention, one or both of hydrochloric acid and hydrofluoric acid are used for pickling in step S3, and preferably, hydrochloric acid is used for pickling and then pickling with a hydrofluoric acid solution, hydrochloric acid is used for removing magnesium oxide impurities, and hydrofluoric acid is used for removing an excess silicon oxide layer.
The porous Si/SiC/C material is nano-scale particles, and the size of the porous Si/SiC/C material is 100-300nm, preferably 150-250 nm. The porous Si/SiC/C material has high porosity and specific surfaceThe product reaches 500m2More than g, pore volume up to 0.4cm3More than g, the silicon/carbon composite material can be used for a lithium ion battery cathode, the volume expansion effect of silicon is relieved due to the porous structure of the silicon/carbon composite material, meanwhile, the silicon can be more completely coated by the SiC/C layer, the silicon exposed outside is reduced, and the side reaction caused by the direct contact of the silicon and electrolyte is avoided, so that the rate capability and the cycle performance of the silicon-carbon cathode material are effectively improved.
Preferred embodiments of the present invention will be described in more detail below. While the following describes preferred embodiments of the present invention, it should be understood that the present invention may be embodied in various forms and should not be limited by the embodiments set forth herein. The examples do not specify particular techniques or conditions, and are performed according to the techniques or conditions described in the literature in the art or according to the product specifications. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products commercially available. In the following examples, "%" means weight percent, unless otherwise specified.
The silicon powder adopted in the embodiment is waste high-purity silicon powder produced by cutting silicon ingots in the photovoltaic industry.
Example 1
Referring to the process flow in fig. 1, the porous Si/SiC/C material is prepared as follows:
s1, grinding and mixing 1g of silicon powder and 1.8g of magnesium powder, placing the mixture and 10ml of absolute ethyl alcohol into a planetary ball mill for physical ball milling for 24 hours, and drying to obtain silicon-magnesium alloy powder;
s2, in a nitrogen atmosphere, containing silicon-magnesium alloy powder by a crucible, placing the silicon-magnesium alloy powder in an atmosphere sintering furnace, heating to 550 ℃ at the speed of 3 ℃/min, preserving heat for 5 hours, cooling along with the furnace, and grinding to obtain the magnesium silicide powder;
s3, containing the magnesium silicide powder by a crucible, placing the crucible in an atmosphere sintering furnace, and then adding CO2And then, heating to 650 ℃ at the speed of 10 ℃/min, preserving heat for 1 hour, cooling along with the furnace, grinding, pickling with 1mol/L hydrochloric acid aqueous solution, pickling with 1 wt% hydrofluoric acid aqueous solution, filtering and drying to obtain the porous Si/SiC/C material.
The scanning electron micrograph, the transmission electron micrograph and the X-ray diffraction spectrum of the porous Si/SiC/C material are respectively shown in figure 2, figure 3 and figure 4.
As can be seen from the results in FIG. 2, the surface of the porous Si/SiC/C material is coated with a relatively uniform SiC/C protective layer, and the overall size is 100-300 nm. In combination with the manufacturing process, it is known that silicon particles are formed inside the SiC/C protective layer, in which magnesium silicide is reduced in a carbon dioxide atmosphere.
As can be seen from the results of FIG. 3, the porous Si/SiC/C material has a porous structure, which is mainly produced by etching silicon during the reaction of magnesium with silicon to form magnesium silicide, and the thickness of the SiC/C protective layer is 50-250 nm.
From the results of fig. 4, it can be calculated that the synthesized porous Si/SiC/C material is free of residual impurities in the original waste silicon powder.
Example 2
A lithium ion battery was prepared, and a button type half cell (CR-2025) was prepared using the porous Si/SiC/C material prepared in example 1 as an active material. The method comprises the following steps: mixing 60 wt% of active substance, 20 wt% of Super P and 20 wt% of sodium alginate adhesive to form uniform slurry; the obtained slurry was pasted on a copper foil, vacuum-dried in an oven at 100 ℃ for 12 hours, and then the copper foil was punched into a disc. The half cells were assembled in an argon-filled glove box using pure lithium foil as the counter electrode and a porous membrane (Celgard2400) as the separator, and the electrolyte was purchased from a multi-chemical reagent grid, model LX-025.
Example 3
Electrochemical tests were performed at room temperature within a voltage window of 0.01V to 1.5V using the button half cell (CR-2025) prepared in example 2. The test results are shown in fig. 5 and 6.
As can be seen from FIG. 5, the first discharge specific capacity of the battery under the current density of 400mA/g is 903mAh/g, and after the first 20 cycles, the specific capacity retention rate is more than or equal to 90%; after 100 times of circulation, the specific capacity is 594mAh/g, and the good circulation performance is achieved.
As can be seen from fig. 6, the battery exhibited more stable rate performance. The specific discharge capacity is kept at 617mAh/g under the current density of 3A/g.
Example 4
Preparing a porous Si/SiC/C material, which comprises the following steps:
s1, grinding and mixing 1g of silicon powder and 2.0g of magnesium powder, placing the mixture and 10ml of absolute ethyl alcohol into a planetary ball mill for physical ball milling for 6 hours, and drying to obtain silicon-magnesium alloy powder;
s2, in a nitrogen atmosphere, containing silicon-magnesium alloy powder by a crucible, placing the silicon-magnesium alloy powder in an atmosphere sintering furnace, heating to 520 ℃ at the speed of 1 ℃/min, preserving heat for 5 hours, cooling along with the furnace, and grinding to obtain the magnesium silicide powder;
s3, containing the magnesium silicide powder by a crucible, placing the crucible in an atmosphere sintering furnace, and then adding CO2And then, heating to 630 ℃ at the speed of 5 ℃/min, preserving heat for 1 hour, cooling along with the furnace, grinding, pickling with 1mol/L hydrochloric acid aqueous solution, filtering and drying to obtain the porous Si/SiC/C material.
Example 5
Preparing a porous Si/SiC/C material, which comprises the following steps:
s1, grinding and mixing 1g of silicon powder and 2.2g of magnesium powder, placing the mixture and 10ml of absolute ethyl alcohol into a planetary ball mill for physical ball milling for 12 hours, and drying to obtain silicon-magnesium alloy powder;
s2, in a nitrogen atmosphere, containing silicon-magnesium alloy powder by a crucible, placing the silicon-magnesium alloy powder in an atmosphere sintering furnace, heating to 500 ℃ at the speed of 5 ℃/min, preserving heat for 5 hours, cooling along with the furnace, and grinding to obtain the magnesium silicide powder;
s3, containing the magnesium silicide powder by a crucible, placing the crucible in an atmosphere sintering furnace, and then adding CO2And then, heating to 600 ℃ at the speed of 15 ℃/min, preserving heat for 1 hour, cooling along with the furnace, grinding, pickling with 1 wt% hydrofluoric acid aqueous solution, filtering and drying to obtain the porous Si/SiC/C material.
Comparative example 1
The comparative example is the same as example 1, except that in step S3, the magnesium silicide powder and graphene are uniformly mixed and then contained in a crucible, placed in an atmosphere sintering furnace, heated to 650 ℃ at a rate of 10 ℃/min under nitrogen, kept warm for 1 hour, cooled along with the furnace, ground, pickled with 1mol/L hydrochloric acid aqueous solution, pickled with 1 wt% hydrofluoric acid aqueous solution, filtered and dried to obtain a comparative sample.
Analysis shows that no silicon carbide protective layer appears in a comparative sample, and the graphene and the porous silicon are only simply physically mixed, so that the specific capacity of the battery is reduced quickly and the cycle performance is poor in the charging and discharging processes.
Comparative example 2
This comparative example is the same as example 1 except that no acid washing was performed in step S3, and it was found that a large amount of magnesium oxide impurities were present, the specific capacity of the material was drastically reduced, and the cycle stability was deteriorated.
Comparative example 3
The silicon powder used in example 1 was not subjected to the treatments of steps S1, S2 and S3, but was subjected to acid washing with 1mol/L hydrochloric acid aqueous solution, then acid washing with 1 wt% hydrofluoric acid aqueous solution, and then filtered and dried to obtain a comparative sample.
As shown in fig. 7, analysis shows that the waste silicon powder after acid washing has extremely poor cycle performance, and the specific discharge capacity is reduced to below 10mAh/g after less than 20 times of charging and discharging.
The preferred embodiments of the present invention have been described in detail, however, the present invention is not limited to the specific details of the above embodiments, and various simple modifications may be made to the technical solution of the present invention within the technical idea of the present invention, and these simple modifications are within the protective scope of the present invention.
It should be noted that the various features described in the above embodiments may be combined in any suitable manner without departing from the scope of the invention. The invention is not described in detail in order to avoid unnecessary repetition.
In addition, any combination of the various embodiments of the present invention is also possible, and the same should be considered as the disclosure of the present invention as long as it does not depart from the spirit of the present invention.

Claims (10)

1. A preparation method of a porous Si/SiC/C material is characterized by comprising the following steps:
s1, grinding and mixing the waste silicon powder and the magnesium powder, adding a solvent into the obtained mixture, carrying out physical ball milling, and then drying to obtain silicon-magnesium alloy powder;
s2, under the protection of inert gas, heating the silicon-magnesium alloy powder obtained in the step S1 for reaction, cooling along with a furnace, and grinding to obtain magnesium silicide powder;
s3, in CO2Heating the magnesium silicide powder obtained in the step S2 in an atmosphere, wherein the temperature of the heating is 600-650 ℃, the time is 30 minutes-2 hours, then cooling along with a furnace, grinding and acid washing are carried out, so as to obtain the porous Si/SiC/C material, and the porous Si/SiC/C material is nano-scale particles with the size of 100-300 nm; the SiC/C protective layer is internally provided with silicon particles generated by reducing magnesium silicide in carbon dioxide atmosphere, and the thickness of the SiC/C protective layer is 50-250 nm.
2. The method for preparing the porous Si/SiC/C material according to claim 1, wherein in step S1, the waste silicon powder is high-purity silicon powder produced by cutting silicon ingots in photovoltaic industry, and the silicon content is greater than or equal to 99.9%;
optionally, in step S1, the waste silicon powder and the magnesium powder are ground and mixed according to the mass ratio of 1: 1.8-1: 2.2;
optionally, in step S1, the solvent is absolute ethyl alcohol, and the physical ball milling is performed by using a planetary ball mill for 15 minutes to 24 hours;
optionally, in step S1, the drying temperature is 40 to 60 ℃.
3. The method for preparing a porous Si/SiC/C material according to claim 1 or 2, wherein in step S2, the heating reaction conditions include a temperature of 500-550 ℃ and a time of 1-6 hours;
optionally, in step S2, the heating reaction is specifically performed by: under the protection of inert gas, the temperature is converted to 500-550 ℃ at the rising/lowering rate of 1-5 ℃/min, and the temperature is kept for 1-6 hours.
4. The method for preparing a porous Si/SiC/C material according to claim 1 or 2, wherein in step S3, the specific process of the heat treatment is as follows: in CO2In the atmosphere, converting the temperature to 600-650 ℃ at a temperature rising/reducing rate of 5-15 ℃/min, and preserving the temperature for 30 minutes-2 hours;
optionally, in step S3, the acid-washing solution is one or two of a hydrochloric acid aqueous solution and a hydrofluoric acid aqueous solution.
5. A porous Si/SiC/C material prepared by the preparation method of the porous Si/SiC/C material according to any one of claims 1 to 4, wherein the porous Si/SiC/C material is nano-scale particles with the size of 100 to 300 nm.
6. The porous Si/SiC/C material of claim 5, wherein the porous Si/SiC/C material has the structure: the silicon particles are arranged inside, the silicon particles are wrapped outside by the carbon-doped silicon carbide layer to form a SiC/C shell layer, and the SiC/C shell layer is provided with a plurality of pores.
7. The porous Si/SiC/C material of claim 6, wherein the thickness of the SiC/C shell layer is 50 to 250 nm.
8. An anode material comprising an active material, a conductive agent and a binder, characterized in that the active material is a porous Si/SiC/C material according to any one of claims 5 to 7.
9. A negative electrode comprising a current collector, wherein the surface of said current collector is covered with a coating formed from the negative electrode material of claim 8.
10. A lithium ion battery comprising a negative electrode, a positive electrode and an electrolyte, wherein the negative electrode is the negative electrode of claim 9.
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