CN114105145A

CN114105145A - Carbon-coated three-dimensional porous silicon negative electrode material and preparation method and application thereof

Info

Publication number: CN114105145A
Application number: CN202111412011.7A
Authority: CN
Inventors: 霍开富; 项奔; 高标; 付继江; 佘永年
Original assignee: Wuhan University of Science and Engineering WUSE
Current assignee: Wuhan University of Science and Engineering WUSE
Priority date: 2021-11-25
Filing date: 2021-11-25
Publication date: 2022-03-01
Anticipated expiration: 2041-11-25
Also published as: CN114105145B

Abstract

A carbon-coated three-dimensional porous silicon negative electrode material and a preparation method and application thereof are disclosed, wherein metallurgical silicon powder and industrial magnesium powder in a certain mass ratio are placed in a mixer to be mixed, so that the silicon powder and the magnesium powder are uniformly mixed, and then are subjected to thermal reaction in an inert atmosphere; crushing and sanding the crude product containing the magnesium silicide obtained by the reaction to 1-5 mu m; and carrying out nitridation reaction on the fine powder obtained by classification in a nitrogen-containing atmosphere rotary kiln. And when the nitridation reaction is finished, converting the nitrogen-containing atmosphere into a carbon-containing atmosphere, and carrying out a Chemical Vapor Deposition (CVD) reaction. And (3) pickling the product obtained in the step (a) with hydrochloric acid, removing a by-product magnesium nitride, centrifuging, and drying to obtain the core-shell carbon-coated porous silicon negative electrode material. The carbon-coated three-dimensional porous silicon cathode material prepared by the method has the advantages of wide raw material source, simple, continuous and efficient preparation process, large-scale production, excellent cycle performance of the cathode material for the lithium ion battery, low swelling of an electrode film of the battery and good commercial application prospect.

Description

Carbon-coated three-dimensional porous silicon negative electrode material and preparation method and application thereof

Technical Field

The invention relates to carbon-coated three-dimensional porous silicon and application thereof, in particular to a large-scale controllable preparation core-shell carbon-coated porous silicon negative electrode material and a preparation method and application thereof.

Background

As a green energy storage device, the lithium ion battery is widely applied to the fields of various portable electronic devices, electric vehicles, storage of renewable energy sources, distributed mobile power sources, smart power grids and the like, the application proportion of new energy vehicles and new energy sources needs to be greatly improved, and green low-carbon industries such as new energy vehicles, new energy sources, energy conservation and environmental protection are promoted to become a pillar industry. The lithium ion power battery is the core and the engine of the new energy automobile industry and is a bottleneck technical problem restricting the development of the new energy automobile industry. At present, graphite is used as a negative electrode material of the lithium ion battery, the theoretical specific capacity of the lithium ion battery is 372mAh/g, and the specific capacity of a commercialized high-end graphite product is close to the theoretical value. In 2020, the specific energy of the power battery monomer of the new energy automobile reaches 300Wh/Kg, and the aim is to achieve 350 Wh/Kg. However, the energy density of the lithium ion power battery is generally lower than 200 Wh/Kg at present due to the low specific capacity of the graphite cathode, and the requirement of the long-endurance electric vehicle is difficult to meet. Obviously, the development of new electrode materials with high capacity is the core and key to break through the technology of high energy density (300Wh/Kg) lithium ion power batteries.

The current commercial negative electrode material is mainly made of graphite carbon materials, but the theoretical specific capacity of the traditional graphite material is only 372mAh/g, a lithium-embedded potential platform is close to metal lithium, the phenomenon of lithium precipitation is easy to occur in quick charging or low-temperature charging, and potential safety hazards exist. In addition, the graphite has poor solvent compatibility, and is easy to strip in low-temperature electrolyte containing propylene carbonate and the like, so that capacity attenuation is caused. The theoretical capacity of the silicon (Si) based negative electrode material is 4200 mAh/g, which is more than 10 times of that of the traditional graphite material. In addition, the silicon-based material also has the advantages of abundant reserves, environmental friendliness and the like, and is recognized in the industryThe first choice of the next generation lithium ion battery cathode material. In recent years, the research and development of silicon-based negative electrode materials have made great progress, however, the application of the silicon-based negative electrode materials in lithium ion batteries still has several key bottleneck problems that (1) the volume change of the silicon materials is large in the process of lithium release and insertion, which causes electrode active materials to be pulverized, fall off, large swelling of electrode films and even damage of the structure, and leads to electrochemical failure; (2) silicon is a semiconductor and has poor conductivity; (3) the electrochemical interface stability of the silicon negative electrode is poor, and a solid electrolyte layer (SEI) continuously grows along with the expansion and contraction of silicon in the circulation process, so that the capacity of the electrode is rapidly reduced. The current common solutions are: 1. carrying out silicon nanocrystallization; 2. the nano silicon is compounded with other materials, such as conductive carbon materials or polymers, metals or oxides. Although reducing the size of silicon to nanoscale can reduce the absolute volume expansion of silicon, reduce the structural damage caused by stress in the lithium intercalation and deintercalation process, improve the cycle performance, and simultaneously can shorten the deintercalation depth and diffusion path of lithium ions, thereby bringing about the advantage of dynamics, considering the industrial application of silicon, the synthesis and preparation of nano materials are complex, the cost is relatively expensive, and the large-scale production is difficult; secondly, the specific surface area of the nano-silicon is large, and the tap density is low (0.2 g/cm)³) Resulting in low first coulombic efficiency, unstable Solid Electrolyte Interface (SEI), and low volumetric energy density, limiting its practical applications. The silicon cathode material with micron scale has high tap density and low specific surface area, and the micron silicon has lower synthesis cost and wide source, and can not change the existing industrial preparation system, thereby meeting the commercial application requirement and the urgent need of the high specific energy lithium ion battery at present. However, micron silicon particles face more severe dusting and safety problems during intercalation and cycling than nanoparticles. At present, two main problems are solved, one is to adopt structural design and construct a porous structure in the micron silicon, for example, the document "Ag-mediated charge transport metal-assisted chemical etching of silicon nanowires" proposes a method for producing the micron porous silicon by using a metal-assisted chemical etching process, and the silicon is immersed in HF-AgNO₃-H₂O₂In the mixed solutionIn the meantime, Ag ions on the silicon surface are reduced to silver nanoparticles (AgNPs), and then a Si sample deposited with Ag is immersed by HF and H₂O₂In the etchant, since Ag has electronegativity greater than Si, it is reduced continuously with the formation of SiO on the surface layer₂The pore is formed by etching with HF, the size of the synthesized porous silicon can be easily controlled by controlling the concentration of the etching solution and the etching time, but the method needs to use HF with strong corrosivity and a noble metal salt reagent, has high preparation cost and environmental protection problem, and is not beneficial to industrial application. For example, in the document "a flexible micro/nanostructured Si microsphere cross-linked by high-purity-electron carbon nanotubes heated enhanced depletion layer on battery anodes", silicon-aluminum alloy microspheres are used as raw materials, aluminum components are etched in a high-temperature sulfuric acid aqueous solution, and then nickel acetate is used as a catalyst precursor, so that CNTs grow in through pores in a CVD carbon coating process to improve the conductivity of the whole electrode material and improve the stability of the material. However, the method needs to use strong corrosive high-temperature concentrated sulfuric acid and harmful nickel acetate, is not beneficial to large-scale preparation, and has poor controllability of a cavity structure. For another example, in "a method for preparing formicary porous silicon for lithium ion battery" (CN201710322917.7), a crude product of silicon and magnesium nitride is prepared by ammonification of magnesium silicide, and formicary porous silicon is obtained after washing away magnesium nitride with hydrochloric acid; the second is to adopt a carbon coating strategy to improve the conductivity and the structural stability. For example, the patent "a carbon-coated silicon micron, its preparation method and application" (CN201810135903.9) is prepared by adding magnesium silicide to a solution containing CO₂With CO in the atmosphere₂The redox reaction occurs, carbon is generated on the framework of silicon, and a porous structure is left at the same time, so that the design of the porous structure and in-situ carbon coating are realized at the same time, and although the stability can be improved to a certain extent by the carbon coating, in the practical application of the electrode material, the required expansion of the thickness of the electrode is lower than 20%, but the swelling requirement of a commercial electrode film is difficult to meet by a simple porous structure, a carbon coating strategy or internally coating the porous structure with carbon. Therefore, the development of a high-energy density silicon-based negative electrode material with lower electrode film swelling is currently promoted for lithium ion batteryThe key points of energy density and safety are also one of the problems which need to be solved urgently in commercialization of the silicon-based negative electrode material. For example, in the document "Nonfilling Carbon Coating of Porous Silicon micro meter-Sized Particles for High-Performance Lithium batteries", m-diphenol-formaldehyde resin is coated on the surface of micron SiO, and then SiO is subjected to disproportionation reaction at High temperature to obtain Si and SiO₂In-situ carbonizing the coated organic precursor into a carbon shell, and etching SiO with HF₂After that, porous silicon is formed inside the carbon shell. The proposed strategy of carbon as "armor" to penetrate the porous silicon skeleton to achieve carbon encapsulation can solve the swelling problem of the electrode film well (<10%), but the process still uses corrosive HF, which is not conducive to scale-up. Also, for example, the document "thermal Carbon Shell compounding Microcale Silicon Skeleton as High-Performance alloys for Lithium-Ion Batteries" thermally prepares Mg from glass magnesium silica₂Si/MgO, followed by nitrogen nitridation to obtain Si/Mg₃N₂MgO, obtaining porous silicon after acid cleaning, then internally coating carbon on the porous silicon by CVD, and then secondarily coating carbon on a silicon carbon material by utilizing the characteristic that asphalt is liquid at high temperature to obtain the graded carbon coating of an asphalt carbon shell and skeleton carbon. Also as in the literature "1000 Wh L^-1lithium-ion batteries enabled by cross silicon-coated silicon nanoparticles "are coated with dense graphene on the outside of micron silicon, and then etched with NaOH, leaving some space inside. The volume expansion of micron silicon can be well relieved by the externally coated graphene, so that the stability is certain, but the volume effect is overlarge due to the use of the bulk micron silicon, so that the expansion of an electrode film is large (about 56%), the graphene is required to be used, and the preparation cost is relatively large.

Disclosure of Invention

In order to solve the defects in the prior art, the invention adopts micron Mg₂Nitridation of Si to form Si/Mg₃N₂Followed directly by CVD carbon coating, followed by Mg washing₃N₂The carbon-coated three-dimensional porous silicon is obtained, and the method can realize green batch continuous preparation.

The obtained silicon-carbon material has stable electrochemical performance, the expansion of a battery electrode film is less than 10%, and the silicon-carbon material is beneficial to commercial application, and the technical scheme is as follows:

a preparation method of a carbon-coated three-dimensional porous silicon cathode material, in particular to a preparation method of a large-scale controllable core-shell carbon-coated porous silicon cathode material, which is characterized by comprising the following steps: the method comprises the following steps:

step 1: placing metallurgical silicon powder and industrial magnesium powder in a mixer according to a certain mass ratio, and mixing the silicon powder and the magnesium powder uniformly; preferably: the metallurgical silicon powder and the industrial magnesium powder are mixed according to the mass ratio of 1: 1.8 placing the mixture in a mixer to mix for 1 hour;

step 2: putting the uniformly mixed powder in the step 1 into a crucible, then placing a dry pot into an argon atmosphere box-type furnace, heating to 500-600 ℃ at a heating rate of 1-10 ℃/min, preserving heat for 3-6h, and taking out along with furnace cooling after the heat preservation is finished; the heating rate of a conventional experimental furnace is generally within 20 ℃/min, so that the default general heating rate in the general industry is controlled within 10 ℃/min, the resistance wire of the furnace can be damaged by the excessively fast heating rate, and the more the heating rate is fast, the more the accurate degree of temperature control is poor. The initial alloying temperature of the silicon powder and the magnesium powder is 500 ℃, Mg2Si cannot be formed when the temperature is lower than 500 ℃, and magnesium is easier to evaporate when the temperature is higher than 600 ℃, so that excessive loss of magnesium is easy to cause, and silicon does not participate in the alloying reaction. The lowest time for finishing the reaction is the standard when the time is selected, and the time is related to the amount of the reaction materials, so that the less the materials are, the shorter the alloying time is;

and step 3: performing jet milling and screening on the product obtained in the step 2 to obtain alloy powder with certain micron-level particle size distribution; preferably: the alloy powder with the particle size distribution of 1-5 um has small particle size, can influence tap density, and can influence performance and dealloying reaction kinetics;

and 4, step 4: placing the powder sieved in the step 3 in a rotary kiln, and introducing nitrogen for Mg₂Nitriding reaction of Si; preferably: the rotating speed in the rotary kiln is 5-30rpm (the rotating speed of the rotary kiln is selected according to the added materials, so that the materials are fully turned over in the kiln body and react with the reaction atmosphereTo the optimum effect), a nitrogen-containing atmosphere (N) is introduced₂、 NH₃Or N₂/NH₃Mixed gas) for Mg₂Nitriding reaction of Si at the gas flow rate of 0.5L/min, keeping the temperature at 800 ℃ of 700-;

and 5: after the heat preservation in the step 4 is finished, keeping introducing nitrogen, heating to a certain temperature, and then introducing acetylene gas to perform a CVD carbon coating reaction for a certain time;

step 6: after the step 5 is finished, transferring the reacted materials to an oxygen-free transition chamber for cooling by lifting the furnace chamber at the air inlet end, reducing the furnace chamber to be horizontal after the materials are taken out, then adding the next batch of magnesium silicide into the furnace for reaction, and the temperature of the furnace chamber does not need to be reduced to the room temperature in the whole process, so that batch continuous preparation can be realized;

and 7: and (4) taking out the material cooled to room temperature in the transition cabin in the step 6, then pickling with hydrochloric acid, centrifuging to be neutral after the pickling time is up, and then drying in vacuum.

The invention also discloses a preparation method of the large-scale controllable preparation core-shell type carbon-coated porous silicon cathode material and the prepared carbon-coated porous silicon cathode material.

The invention also discloses application of the carbon-coated porous silicon negative electrode material to a lithium ion battery negative electrode.

Has the advantages that:

1. nitriding of magnesium silicide and carbon coating are combined by utilizing an industrial rotary kiln;

2. can continuously prepare the core-shell type carbon-coated porous silicon in large scale

3. The prepared cathode material has good cycle performance when used in a lithium ion battery, has low swelling behavior in the charge and discharge processes of an electrode film, and has good commercial application prospect.

Drawings

FIG. 1: the equipment used for batch continuous nitridation of magnesium silicide and CVD carbon coating in example 1 is schematically illustrated.

FIG. 2: in example 1, the raman spectra of the phase (a) during the reaction and the prepared carbon-coated porous silicon in fig. 2(b) and 2(c) are the laser particle size diagrams of the carbon-coated porous silicon, and fig. 2(d) is the TG-DSC curve of the carbon-coated porous silicon in the air atmosphere. .

FIG. 3: scanning electron micrographs (a-c) and transmission electron micrographs (d) of carbon-coated porous silicon prepared in example 1.

FIG. 4: example 1a cycle performance graph (a) of carbon-coated porous silicon and graphs (b-c) of electrode film thickness change before and after 50 cycles of cycle were prepared.

FIG. 5: phase (a) before and after acid washing and thermogravimetric analysis (b) of the final product of the product prepared in example 2.

FIG. 6: phase a before and after acid washing for the product prepared in example 3; obtaining a BET diagram b of the final product carbon-coated porous silicon; and the first specific capacity-voltage curve c of the packaged half-point cell.

Detailed Description

A large-scale controllable preparation method of a core-shell carbon-coated three-dimensional porous silicon negative electrode material is characterized by comprising the following steps: the method comprises the following steps:

step 1: placing metallurgical silicon powder and industrial magnesium powder in a certain mass ratio (1: 1.8) into a mixer to be mixed, and uniformly mixing the silicon powder and the magnesium powder;

step 2: the method comprises the following steps: 1, placing the uniformly mixed powder in a crucible, then placing a dry pot in an argon atmosphere box-type furnace, heating to 500-600 ℃ at a heating rate of 1-10 ℃/min, preserving heat for 3-6h, and taking out along with furnace cooling after the heat preservation is finished; the alloying starting temperature of the silicon powder and the magnesium powder is 500 ℃, Mg2Si cannot be formed when the alloying starting temperature is lower than 500 ℃, and magnesium is easier to evaporate when the alloying starting temperature is higher than 600 ℃, so that excessive loss of magnesium is easy to cause, and partial silicon does not participate in the alloying reaction. The lowest time for finishing the reaction is the standard when the time is selected, and the time is related to the amount of the reaction materials, so that the less the materials are, the shorter the alloying time is;

and step 3: performing jet milling and screening on the product obtained in the step 2 to obtain alloy powder with the particle size distribution of 1-5 mu m; the small granularity can influence the tap density and the large granularity can influence the performance and the reaction kinetics of dealloying;

and 4, step 4: placing the powder sieved in the step 3 in a rotary kiln, and introducing N₂Carrying out Mg₂Nitriding reaction of Si;

and 5: in the following steps: 4 after the heat preservation is finished, keeping N₂Heating, and then introducing acetylene gas for CVD carbon coating duration;

and 7: and (4) taking out the material cooled to room temperature in the transition cabin in the step 6, then pickling with hydrochloric acid, centrifuging to the center after the pickling time is up, and then drying in vacuum.

Example 1

(1) 1kg of metallurgical silicon powder and 1.8kg of industrial magnesium powder are placed in a mixer to be mixed for 1 hour, so that the silicon powder and the magnesium powder are uniformly mixed;

(2) putting the uniformly mixed powder in the step (1) into a crucible, then placing a dry pot into an argon atmosphere box-type furnace, heating at a rate of 10 ℃/min, preserving heat at 550 ℃ for 6h, and taking out the powder after the heat preservation is finished along with the cooling of the furnace; the XRD pattern of the alloy in FIG. 2a shows that the alloy powder prepared is Mg₂Si, a weak magnesium oxide peak may be an oxidation problem caused by oxygen adsorbed by magnesium powder;

(3) performing jet milling and screening on the product obtained in the step (2) to obtain alloy powder with the particle size distribution of 1-5 microns;

(4) placing the powder sieved in the step (3) in a rotary kiln as shown in a figure (1), discharging oxygen in the kiln chamber at the rotation speed of 10rpm, and introducing N₂Carrying out Mg₂Nitriding reaction of Si, wherein the gas flow rate is 0.5L/min, the heating rate is 10 ℃/min, and the temperature is kept at 750 ℃ for 6 h; from the XRD pattern of nitridation in FIG. 2a, it can be seen that the components of the nitrided sample are Si and Mg₃N₂And MgO;

(5) after the heat preservation in the step (4) is finished, keeping N₂Then introducing acetylene gas for CVD carbon coating, wherein the CVD duration is 2h, the flow rate of the acetylene gas is controlled at 0.3L/min by an electromagnetic valve, and the acetylene gas is turned off after the CVD time is over; from the XRD of the carbon-coated sample in fig. 2a and the raman spectrum in fig. 2b, it can be known that carbon is successfully coated on the sample, and the ratio of the G peak to the D peak in the raman spectrum indicates that carbon has some degree of graphitization.

(6) After the step (5) is finished, transferring the reacted materials to an oxygen-free transition chamber for cooling by lifting the furnace chamber at the air inlet end, cooling the furnace chamber to be horizontal after the materials are taken out, then adding the next batch of magnesium silicide to enter the furnace for reaction, and the temperature of the furnace chamber does not need to be reduced to the room temperature in the whole process, so that batch continuous preparation can be realized;

(7) and (4) taking out the material cooled to room temperature in the transition cabin in the step (6), then washing with hydrochloric acid for 2 hours, centrifuging to the center after the acid washing time is up, and then drying in vacuum. As can be seen from the laser particle size diagram of the sample after acid cleaning in fig. 2c, the particle size D50 of the sample is 2.61 μm, and as can be seen from the thermogravimetric analysis diagram in fig. 2D, the carbon content in the silicon-carbon material is 6.1%, and the appropriate carbon content can alleviate the volume expansion of silicon and improve the cycle stability of silicon. From the scanning electron microscope images of fig. 3a-c and the projection electron microscope image of fig. 3d, it can be seen that carbon is uniformly wrapped outside the porous silicon as an outer wrapping, and like a layer of armor is worn on the porous silicon, the structure has the advantages that the porous silicon has a certain self-volume effect, and the outer carbon wrapping can further reserve some external expansion spaces to adapt to the outward expansion of the silicon, and can also improve the conductivity of the porous silicon. Fig. 4a shows that the capacity of the carbon-coated porous silicon exceeds 1600mA h/g under the current density of 1A/g after 50 cycles, the first coulombic efficiency reaches 83.04%, the coulombic efficiency reaches 99.8% after 15 cycles of cycles, and good cycle stability is shown, fig. 4b and c show the thickness change of the electrode film before and after 50 cycles of cycles, and the electrode film only expands 7.6% after 50 cycles of cycles, so that the excellent swelling behavior of the electrode film is shown.

Example 2

(2) putting the uniformly mixed powder in the step (1) into a crucible, then placing a dry pot into an argon atmosphere box-type furnace, preserving heat for 6 hours at 550 ℃, keeping the temperature at the rate of 5 ℃/min, and taking out the powder after the heat preservation is finished along with the cooling of the furnace;

(3) performing jet milling and screening on the product obtained in the step (2) to obtain alloy powder with the particle size distribution of 1-5 um;

(4) placing the powder sieved in the step (3) in a rotary kiln as shown in a figure (1), discharging oxygen in the kiln chamber at the rotating speed of 20rpm, and introducing NH₃Carrying out Mg₂Nitriding Si at the gas flow rate of 0.5L/min, keeping the temperature at 750 ℃ for 6h, and heating at the rate of 5 ℃/min;

(5) after the heat preservation in the step (4) is finished, the NH is turned off₃Then introducing N₂After the residual ammonia gas is exhausted, raising the temperature to 800 ℃, then introducing acetylene gas to carry out CVD carbon coating, wherein the CVD duration is 2 hours, the flow rate of the acetylene gas is controlled at 0.5L/min through an electromagnetic valve, and the acetylene gas is turned off after the CVD time is over;

(6) after the step (5) is finished, transferring the reacted materials to an oxygen-free transition cabin for cooling by raising the furnace chamber at the air inlet end, reducing the furnace chamber to the level after the materials are taken out, and simultaneously setting the temperature back to Mg₂The nitriding temperature of Si is 750 ℃, then the next batch of magnesium silicide is added into the furnace for reaction, and the temperature of the furnace chamber does not need to be reduced to room temperature in the whole process, so that the batch continuous preparation can be realized;

(7) and (4) taking out the material cooled to room temperature in the transition cabin in the step (6), then washing with hydrochloric acid for 2 hours, centrifuging to the center after the acid washing time is up, and then drying in vacuum. As can be seen from XRD before and after acid washing of the reaction product in FIG. 5a, when the temperature of CVD deposited carbon is too high (not less than 800 ℃), Mg is present in the reducing atmosphere₃N₂Reduced and then carries out alloying reaction with silicon again to obtain Mg₂Si and Mg2Si are easy to react with acid to generate silane, so that the danger is high, and impurities which are difficult to remove are generated by a certain corrosion effect on the stainless steel lining. From the thermogravimetric analysis of fig. 5b, the deposited carbon content was 8.8% under this condition.

Example 3

(2) putting the uniformly mixed powder in the step (1) into a crucible, then placing a dry pot into an argon atmosphere box-type furnace, preserving heat for 6 hours at 550 ℃, wherein the heating rate is 1 ℃/min, and taking out the powder after the heat preservation along with the furnace cooling;

(4) placing the powder sieved in the step (3) in a rotary kiln as shown in the figure (1), discharging oxygen in the kiln chamber at the rotating speed of 15rpm, and introducing N₂/NH₃Carrying out Mg on the mixed gas₂Nitriding Si at the gas flow rate of 0.5L/min, keeping the temperature at 700 ℃ for 6h, and heating at the temperature rise rate of 8 ℃/min;

(5) after the heat preservation in the step (4) is finished, the NH is turned off₃Of (2) maintaining N₂To remove residual NH₃After the discharge, introducing acetylene gas for CVD carbon coating, wherein the CVD duration is 2h, the flow rate of the acetylene gas is controlled at 0.3L/min through an electromagnetic valve, and the acetylene gas is turned off after the CVD time is over;

(6) after the step (5) is finished, transferring the reacted materials to an oxygen-free transition cabin for cooling by raising the furnace chamber at the air inlet end, reducing the furnace chamber to the level after the materials are taken out, and simultaneously setting the temperature back to Mg₂The nitriding temperature of Si is 700 ℃, then the next batch of magnesium silicide is added to enter the furnace for reaction, and the temperature of the furnace chamber does not need to be reduced to the room temperature in the whole process, so that the batch continuous preparation can be realized;

(7) and (4) taking out the material cooled to room temperature in the transition cabin in the step (6), then washing with hydrochloric acid for 2 hours, centrifuging to the center after the acid washing time is up, and then drying in vacuum. From the XRD of the reaction product in FIG. 6a, it can be seen that when the nitriding temperature is 700 deg.C, the reaction is not sufficient and there is residual Mg due to the large amount of material, low temperature and slow reaction₂Si, and when the temperature of CVD deposited carbon is low (≦ 700 ℃), the crystallinity of carbon is poor, the amorphous carbon content is high, resulting in too large specific surface area of the material (see FIG. 6b), which reduces the first coulombic efficiency of the Si-C material (see FIG. 6c, the first coulombic efficiency is 73.3%)

The foregoing shows and describes the general principles, essential features, and advantages of the invention. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are merely illustrative of the principles of the invention, but that various changes and modifications may be made without departing from the spirit and scope of the invention, which fall within the scope of the invention as claimed. The scope of the invention is defined by the appended claims and equivalents thereof.

Claims

1. The preparation method of the carbon-coated three-dimensional porous silicon cathode material is characterized in that the carbon-coated porous silicon cathode material is a large-scale controllable core-shell carbon-coated porous silicon cathode material which is prepared by the following steps: the preparation method comprises the following steps:

step 1: placing metallurgical silicon powder and industrial magnesium powder in a mixer according to a certain mass ratio, and mixing the silicon powder and the magnesium powder uniformly;

step 2: putting the uniformly mixed powder in the step 1 into a crucible, then putting a dry pot into an argon atmosphere box-type furnace, heating to a certain temperature at a heating rate of 1-10 ℃/min, preserving heat for a certain time, and taking out the powder after the heat preservation along with the cooling of the furnace;

and step 3: performing jet milling and screening on the product obtained in the step 2 to obtain alloy powder with certain particle size distribution;

and 4, step 4: placing the powder sieved in the step 3 in a rotary kiln, discharging oxygen in a furnace chamber of the rotary kiln, and introducing N₂Or mixed gas of NH3, NH3/N2 and NH3/Ar for Mg₂Nitriding reaction of Si;

and 5: after the heat preservation is finished in the step 4, keeping N₂Heating, then introducing acetylene gas to carry out CVD carbon coating, and continuing the process for a period of time;

2. The method for preparing the carbon-coated three-dimensional porous silicon negative electrode material according to claim 1, wherein the method comprises the following steps: the step 1 further comprises the following steps of mixing metallurgical silicon powder and industrial magnesium powder according to the mass ratio of 1: 1.8 placing the mixture in a mixer to mix for 1 hour.

3. The method for preparing the carbon-coated three-dimensional porous silicon negative electrode material according to claim 1, wherein the method comprises the following steps: the step 2 further comprises the step of placing the dry pot in an argon atmosphere box furnace, wherein the heating rate is 1-10 ℃/min to 500-600 ℃, and the temperature is kept for 3-6 h.

4. The method for preparing the carbon-coated three-dimensional porous silicon negative electrode material according to claim 1, wherein the method comprises the following steps: and the step 3 further comprises alloy powder with the particle size distribution of 1-5 um.

5. The method for preparing the carbon-coated three-dimensional porous silicon negative electrode material according to claim 1, wherein the method comprises the following steps: step 4 further comprises the steps of discharging oxygen in the furnace chamber at the rotating speed of 5-30rpm in the rotary kiln, and introducing nitrogen-containing atmosphere (N)₂、NH₃Or N₂/NH₃Mixed gas) for Mg₂Nitriding reaction of Si at gas flow rate of 0.5L/min, maintaining at 800 deg.c of 700-.

6. The carbon-coated porous silicon anode material prepared by the preparation method of the carbon-coated three-dimensional porous silicon anode material according to any one of claims 1 to 5.

7. The carbon-coated porous silicon negative electrode material of claim 6 is applied to a lithium ion battery negative electrode.