CN114105145B - Carbon-coated three-dimensional porous silicon anode material and preparation method and application thereof - Google Patents
Carbon-coated three-dimensional porous silicon anode material and preparation method and application thereof Download PDFInfo
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Abstract
The carbon-coated three-dimensional porous silicon anode material and the preparation method and the application thereof are that metallurgical silicon powder and industrial magnesium powder with certain mass ratio are put into a mixer to be mixed, so that the silicon powder and the magnesium powder are uniformly mixed, and then the silicon powder and the magnesium powder are subjected to thermal reaction in inert atmosphere; crushing and sanding the crude product containing magnesium silicide obtained by the reaction to 1-5 mu m; and (3) carrying out nitridation reaction on the fine powder obtained by grading in a nitrogen-containing atmosphere rotary kiln. When the nitriding reaction is completed, converting the atmosphere containing nitrogen into the atmosphere containing carbon, and performing Chemical Vapor Deposition (CVD) reaction. And (3) pickling the product obtained by the method by using hydrochloric acid, removing a byproduct magnesium nitride, and then centrifuging and drying to obtain the core-shell carbon-coated porous silicon anode material. The carbon-coated three-dimensional porous silicon anode material prepared by the method has the advantages of wide raw material sources, simple, continuous and efficient preparation process, large-scale production, excellent cycle performance of the anode material for the lithium ion battery, low swelling of an electrode film of the battery and good commercial application prospect.
Description
Technical Field
The invention relates to carbon-coated three-dimensional porous silicon and application thereof, in particular to a large-scale controllable preparation method of a core-shell carbon-coated porous silicon anode material, and a preparation method and application thereof.
Background
The lithium ion battery is used as a green energy storage device, is widely applied to the fields of various portable electronic equipment, electric automobiles, renewable energy storage, distributed mobile power sources, intelligent power grids and the like, needs to greatly improve the application proportion of new energy automobiles and new energy sources, and promotes green low-carbon industries such as the new energy automobiles, new energy sources, energy conservation, environmental protection and the like to become post industries. The lithium ion power battery is a core and an engine of the new energy automobile industry and is a bottleneck technical problem for 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 commercial 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 new energy automobile strives to achieve 350Wh/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. Clearly, the development of new electrode materials with high capacity is the core and key to break through the high energy density (300 Wh/Kg) lithium ion power battery technology.
The current commercial anode material is mainly made of graphite carbon materials, but the theoretical specific capacity of the traditional graphite materials is only 372mAh/g, and a lithium intercalation potential platform is close to metal lithium, so that the phenomenon of 'lithium precipitation' easily occurs during quick charge or low-temperature charge, and potential safety hazards exist. In addition, graphite has poor solvent compatibility, and is likely to peel off in low-temperature electrolytes such as propylene carbonate, and the like, resulting in capacity fade. The theoretical capacity of the silicon (Si) -based anode material is 4200 mAh/g, which is more than 10 times that of the traditional graphite material. In addition, the silicon-based material has the advantages of abundant reserves, environmental friendliness and the like, and is the first choice of the anode material of the next generation of lithium ion batteries accepted in the industry. In recent years, the development of silicon-based anode materials has been greatly advanced, however, the application of the silicon-based anode materials in lithium ion batteries still has several key bottleneck problems (1) the silicon materials have large volume change in the lithium intercalation process, so that the electrode active materials are pulverized, fall off, the electrode films are greatly swelled and even the structure is damaged, and electrochemical failure is caused; (2) silicon is a semiconductor, and has poor conductivity; (3) The silicon negative electrode electrochemical interface has poor stability, and during cycling, as silicon expands and contracts, a solid electrolyte layer (SEI) continues to grow, resulting in rapid decay of electrode capacity. The current common solutions are: 1. nanocrystallization of silicon; 2. nano-silicon is composited with other materials such as conductive carbon materials or polymers, metals or oxides. While reducing the size of silicon to the nanoscale reduces the absolute volume expansion of silicon, reduces structural damage caused by stresses during lithium intercalation and deintercalation,the cycle performance is improved, the lithium ion deintercalation depth and the diffusion path can be shortened, and the dynamic advantage is brought, but the synthesis and preparation of the nano material are complex in consideration of the industrialized application of silicon, the cost is relatively high, and the large-scale production is difficult; secondly, the specific surface area of the nano silicon is large, and the tap density is low (about 0.2 g/cm) 3 ) Resulting in low first coulombic efficiency, unstable Solid Electrolyte Interface (SEI), and low volumetric energy density, limiting its practical application. The micron-scale silicon anode material has high tap density and low specific surface area, and the synthesis cost of micron silicon is lower, the source is wide, and the existing industrial preparation system is not changed, so that the commercial application requirements and the urgent requirements of the current high-specific-energy lithium ion battery are met. However, micron silicon particles face more serious pulverization and safety problems than nanoparticles during lithium intercalation and cycling. At present, two main problems of micron silicon are solved, one is to construct a porous structure in micron silicon by adopting structural design, for example, the document "Ag-mediated charge transport during metal-assisted chemical etching of silicon nanowires" proposes a method for producing micron porous silicon by using a metal-assisted chemical etching process, and the silicon is immersed into HF-AgNO 3 -H 2 O 2 When mixed with the solution, ag ions on the silicon surface are reduced to silver nano-particles (AgNPs), and then the Si sample deposited with Ag is immersed in a solution composed of HF and H 2 O 2 In the etchant, since Ag has electronegativity larger than Si, siO is formed by continuous reduction of Ag and formation of surface layer 2 The method is etched by HF to form pores, the size of the synthesized porous silicon can be controlled easily by controlling the concentration of etching solution and etching time, but the method needs to use HF and noble metal salt reagent with strong corrosiveness, has high preparation cost, has environmental protection problem and is not beneficial to industrialized application. For example, the literature A flexible micro/nanostructured Si microsphere cross-linked by high-elastic carbon nanotubes toward enhanced lithium ion battery anodes takes silicon-aluminum alloy microspheres as raw materials, and aluminum components are etched in high-temperature sulfuric acid aqueous solution, then nickel acetate is used as a catalyst precursor, and CNTs are grown in through pore channels in the process of CVD carbon coating to improve the overall electricityThe conductivity of the electrode material improves the stability of the material. However, the method needs to use high-temperature concentrated sulfuric acid with strong corrosiveness and harmful nickel acetate, is unfavorable for large-scale preparation, and has poor controllability of a cavity structure. In another example, patent "a preparation method of formic nest-shaped porous silicon for lithium ion battery" (CN 201710322917.7) adopts ammoniation reaction of magnesium silicide to prepare coarse products of silicon and magnesium nitride, and hydrochloric acid washing to remove magnesium nitride to obtain formic nest-shaped porous silicon; the second is to adopt a carbon coating strategy to improve conductivity and structural stability. For example, patent "a carbon-coated micron silicon, its preparation method and application" (CN 201810135903.9) discloses the use of magnesium silicide in the presence of CO 2 CO in the atmosphere of (2) 2 The oxidation-reduction reaction occurs, carbon is generated on the framework of silicon while a porous structure is left, so that the design of the porous structure and in-situ carbon coating are realized at the same time, although the carbon coating can bring stability improvement to a certain extent, in the practical application of the electrode material, the required electrode thickness expansion is lower than 20%, however, the swelling requirement of a commercial electrode film is difficult to be met by a simple porous structure, a carbon coating strategy or the internal carbon coating of the porous structure. Therefore, developing a high-energy density silicon-based anode material with lower electrode film swelling is a key for improving the volume energy density and the safety of a lithium ion battery at present, and is one of the problems to be solved in commercialization of the silicon-based anode material. As in the document "Nonfilling Carbon Coating of Porous Silicon Micrometer-Sized Particles for High-Performance Lithium BatteryAnodes", the surface of micron SiO is coated with meta-diphenol-formaldehyde resin, and then the SiO is disproportionated at high temperature to obtain Si and SiO 2 Carbonizing the coated organic precursor in situ to form a carbon shell, and etching SiO by HF 2 Thereafter, porous silicon is formed inside the carbon shell. The proposed method uses carbon as 'armor' to penetrate out of the porous silicon framework, and realizes the carbon coating strategy to well solve the swelling problem of the electrode film<10%) but the process still uses corrosive HF, which is not conducive to large scale production. As another example, the document "Hierarchical Carbon Shell Compositing Microscale Silicon Skeleton as High-Performance Anodes for Lithium-Ion Batteries" is used for heating glass silica magnesiumPreparing Mg to obtain 2 Si/MgO, followed by nitrogen nitridation to give Si/Mg 3 N 2 MgO, acid washing to obtain porous silicon, then carrying out carbon inclusion on the porous silicon by CVD, and carrying out secondary carbon inclusion on a silicon carbon material of the porous silicon by utilizing the characteristic that asphalt is liquid at high temperature to obtain the graded carbon inclusion of an asphalt carbon shell and skeleton carbon. As another example, document "1000Wh L -1 The lithium-ion batteries enabled by crosslink-shrunk tough carbon encapsulated silicon microparticle anodes "coats dense graphene outside of the micron silicon, and then is etched with NaOH leaving some space inside. The externally coated graphene can well relieve the volume expansion of the micron silicon, so that the stability is certain, but the volume effect is overlarge because the micron silicon of a block is used, so that the expansion of an electrode film is larger (about 56%), the graphene is needed, and the preparation cost is relatively higher.
Disclosure of Invention
In order to solve the defects in the prior art, the invention uses micron Mg 2 Nitriding Si to form Si/Mg 3 N 2 Directly carrying out CVD carbon coating and then washing out Mg 3 N 2 The method can realize green batch continuous preparation.
The obtained silicon-carbon material has stable electrochemical performance, and the expansion of the battery electrode film is less than 10%, which is beneficial to commercial application, and the technical scheme is as follows:
the preparation method of the carbon-coated three-dimensional porous silicon anode material, in particular to a preparation method for large-scale controllable preparation of a core-shell carbon-coated porous silicon anode 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 for mixing according to a certain mass ratio, so that the silicon powder and the magnesium powder are uniformly mixed; preferably, it is: the metallurgical silicon powder and the industrial magnesium powder are prepared from the following components in percentage by mass: 1.8, placing the mixture in a mixer for mixing for 1h;
step 2: placing the powder uniformly mixed in the step 1 into a crucible, then placing the dry pot into an argon atmosphere box-type furnace, heating to 500-600 ℃ at a heating rate of 1-10 ℃/min, preserving heat for 3-6 hours, and cooling along with the furnace after the heat preservation is finished and taking out; the heating rate of the conventional experimental furnace is generally within 20 ℃/min, so 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 accuracy of temperature control is poorer as the heating rate is higher. The initial alloying temperature of the silicon powder and the magnesium powder is 500 ℃, mg2Si can not be formed below 500 ℃, and when the temperature is higher than 600 ℃, magnesium is easier to evaporate, excessive loss of magnesium is easy to cause, and silicon does not participate in the alloying reaction. The lowest time of the reaction is the standard when the time is selected, the time is related to more reaction materials, the less the materials are, and the shorter the alloying time is;
step 3: carrying out jet milling and screening on the product obtained in the step 2 to obtain alloy powder with certain micron-sized particle size distribution; preferably, it is: alloy powder with the granularity distribution of 1-5 um has small granularity which can affect tap density and large reaction dynamics which can affect performance and dealloying;
step 4: placing the powder sieved in the step 3 into a rotary kiln, and introducing nitrogen to perform Mg 2 Nitriding Si; preferably, it is: the rotating speed in the rotary kiln is 5-30rpm (the rotating speed of the converter is selected according to the added materials, the materials are guaranteed to be fully overturned in the kiln body and react with the reaction atmosphere to achieve the optimal effect), and the nitrogen-containing atmosphere (N) 2 、 NH 3 Or N 2 /NH 3 Mixture gas) Mg 2 The nitriding reaction of Si, the gas flow rate is 0.5L/min, the temperature is kept for 3-6h at 700-800 ℃, the lowest nitriding temperature is 700 ℃, the temperature in a furnace body cannot exceed 900 ℃, otherwise, the byproduct MgSiN2 is generated, and the heating rate is 5-10 ℃/min;
step 5: after the heat preservation in the step 4 is finished, nitrogen is kept to be introduced, the temperature is raised to a certain temperature, and then acetylene gas is introduced to carry out CVD carbon-coated reaction for a certain time;
step 6: transferring the reacted materials to an anaerobic transition cabin for cooling by lifting a furnace chamber at the air inlet end after the step 5 is finished, reducing the furnace chamber to a level after the materials are taken out, adding the next batch of magnesium silicide for furnace feeding reaction, and cooling the furnace chamber to room temperature in the whole process without reducing the temperature of the furnace chamber, so that batch continuous preparation can be realized;
step 7: and (3) taking out the material cooled to room temperature in the transition cabin in the step (6), then washing with hydrochloric acid, centrifuging to be neutral after the washing time is up, and then drying in vacuum.
The invention also discloses a preparation method for preparing the core-shell carbon-coated porous silicon anode material in a large-scale controllable manner and the prepared carbon-coated porous silicon anode material.
The invention also discloses application of the carbon-coated porous silicon anode material to the anode of the lithium ion battery.
The beneficial effects are that:
1. nitriding magnesium silicide and carbon coating are combined by using an industrial rotary kiln;
2. can continuously prepare core-shell type carbon coated porous silicon in large scale
3. The prepared negative electrode material has good cycle performance when used in a lithium ion battery, has low swelling behavior in the process of charging and discharging an electrode film, and has good commercial application prospect.
Drawings
Fig. 1: schematic of the equipment used for batch continuous magnesium silicide nitride and CVD carbon coating in example 1.
Fig. 2: the raman spectra of phase (a) during the reaction and the prepared carbon-coated porous silicon in example 1 are shown in fig. 2 (b) and 2 (c) as laser particle size diagrams of the carbon-coated porous silicon, and fig. 2 (d) as TG-DSC curves of the carbon-coated porous silicon in an air atmosphere. .
Fig. 3: example 1 scanning electron microscopy images (a-c) and transmission electron microscopy images (d) of carbon-coated porous silicon were prepared.
Fig. 4: example 1a graph (a) of the cycling performance of carbon-coated porous silicon and a graph (b-c) of the electrode film thickness variation before and after 50 cycles were prepared.
Fig. 5: thermogravimetric analysis of the product prepared in example 2, phase (a) before and after pickling and of the final product (b).
Fig. 6: phase a before and after pickling of the product prepared in example 3; obtaining BET diagram b of the final product carbon-coated porous silicon; and the first specific capacity-voltage curve c of the packaged half-pel cell.
Detailed Description
A preparation method for large-scale controllable preparation of a core-shell type carbon-coated three-dimensional porous silicon anode 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 for mixing, so that the silicon powder and the magnesium powder are uniformly mixed;
step 2: the method comprises the following steps: 1, placing the uniformly mixed powder into a crucible, then placing the dry pot into an argon atmosphere box-type furnace, heating to 500-600 ℃ at a heating rate of 1-10 ℃/min, preserving heat for 3-6 hours, and cooling along with the furnace after the heat preservation is finished and taking out; the alloying starting temperature of the silicon powder and the magnesium powder is 500 ℃, mg2Si is not formed below 500 ℃, and when the temperature is higher than 600 ℃, magnesium is easier to evaporate, so that excessive loss of magnesium is easy to cause, and part of silicon does not participate in the alloying reaction. The lowest time of the reaction is the standard when the time is selected, the time is related to more reaction materials, the less the materials are, and the shorter the alloying time is;
step 3: carrying out 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 granularity is small, so that the tap density can be influenced, and the reaction dynamics of performance and dealloying can be greatly influenced;
step 4: placing the powder sieved in the step 3 into a rotary kiln, and introducing N 2 By Mg 2 Nitriding Si;
step 5: in the steps of: 4 after the heat preservation is finished, keeping N 2 Then introducing acetylene gas for CVD carbon coating duration;
step 6: transferring the reacted materials to an anaerobic transition cabin for cooling by lifting a furnace chamber at the air inlet end after the step 5 is finished, reducing the furnace chamber to a level after the materials are taken out, adding the next batch of magnesium silicide for furnace feeding reaction, and cooling the furnace chamber to room temperature in the whole process without reducing the temperature of the furnace chamber, so that batch continuous preparation can be realized;
step 7: and (3) taking out the material cooled to room temperature in the transition cabin in the step (6), then washing with hydrochloric acid, centrifuging to the center after the washing 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 1h, so that the silicon powder and the magnesium powder are uniformly mixed;
(2) Placing the powder uniformly mixed in the step (1) into a crucible, then placing the dry pot into an argon atmosphere box-type furnace, keeping the temperature at 550 ℃ for 6 hours at the heating rate of 10 ℃/min, and cooling along with the furnace after the heat preservation is finished and taking out; from the XRD pattern of the alloying in FIG. 2a, it can be seen that the alloy powder prepared is Mg 2 Si, a weak magnesium oxide peak may be an oxidation problem caused by oxygen adsorbed by the magnesium powder itself;
(3) Carrying out jet milling and screening on the product obtained in the step (2) to obtain alloy powder with the granularity distribution of 1-5 mu m;
(4) Placing the powder sieved in the step (3) in a rotary kiln shown in the figure (1), discharging oxygen in a furnace chamber at 10rpm, and introducing N 2 By Mg 2 Nitriding Si at gas flow rate of 0.5L/min and heating rate of 10 deg.C/min, and maintaining at 750 deg.C for 6 hr; from the XRD pattern of nitriding in FIG. 2a, it can be seen that the nitriding sample contains Si and Mg 3 N 2 And MgO;
(5) After the heat preservation in the step (4) is finished, N is maintained 2 Introducing acetylene gas for CVD carbon coating, wherein the duration of CVD is 2h, the flow rate of the acetylene gas is controlled to be 0.3L/min through an electromagnetic valve, and the acetylene gas is turned off after the CVD time is over; from the XRD spectrum of the carbon-coated sample of FIG. 2a and the Raman spectrum of FIG. 2b, it can be seen that carbon was 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 graphitization.
(6) After the step (5) is finished, transferring the reacted materials to an anaerobic transition cabin for cooling by lifting a furnace chamber at an air inlet end, reducing the furnace chamber to a horizontal level after the materials are taken out, adding the next batch of magnesium silicide for furnace feeding reaction, and cooling the furnace chamber to room temperature in the whole process without the need of continuously preparing batches;
(7) And (3) taking out the material cooled to room temperature in the transition cabin in the step (6), then pickling for 2 hours by using hydrochloric acid, centrifuging to the center after pickling time, and then drying in vacuum. As can be seen from the laser particle size diagram of the acid-washed sample in fig. 2c, the particle size d50=2.61 μm of the sample, 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 relieve the volume expansion of silicon and improve the cycle stability of silicon. The scanning electron microscope images of fig. 3a-c and the projection electron microscope image of fig. 3d show that carbon is uniformly wrapped outside the whole porous silicon, so that the carbon is an outer wrapping, and like putting a layer of "armor" on the porous silicon, the structure has the advantages that the porous silicon has a certain self-volume effect, and the outer carbon wrapping further reserves some external expansion spaces to adapt to the outward expansion of the silicon, and meanwhile, the conductivity of the porous silicon can be improved. Fig. 4a shows that the capacity of the carbon-coated porous silicon exceeds 1600mA h/g at a current density of 1A/g after 50 cycles, the initial coulomb efficiency is up to 83.04%, the coulomb efficiency after 15 cycles is up to 99.8%, good cycling stability is shown, fig. 4b and c show that the thickness of the electrode film changes before and after 50 cycles, the electrode film only expands by 7.6% after 50 cycles, and excellent swelling behavior of the electrode film is shown.
Example 2
(1) 1kg of metallurgical silicon powder and 1.8kg of industrial magnesium powder are placed in a mixer to be mixed for 1h, so that the silicon powder and the magnesium powder are uniformly mixed;
(2) Placing the powder uniformly mixed in the step (1) into a crucible, then placing the dry pot into an argon atmosphere box-type furnace, preserving heat for 6 hours at 550 ℃, wherein the temperature rising rate is 5 ℃/min, and cooling and taking out along with the furnace after the heat preservation is finished;
(3) Carrying out jet milling and screening on the product obtained in the step (2) to obtain alloy powder with the granularity distribution of 1-5 um;
(4) Placing the powder sieved in the step (3) into a rotary kiln shown in the figure (1), discharging oxygen in a furnace chamber at 20rpm, and introducing NH 3 By Mg 2 The nitriding reaction of Si, the gas flow rate is 0.5L/min, the temperature is kept for 6 hours at 750 ℃, and the heating rate is 5 ℃/min;
(5) Turning off NH after the heat preservation in the step (4) is finished 3 Is then introduced with N 2 After the residual ammonia gas is exhausted, the temperature is increased to 800 ℃, then acetylene gas is introduced to carry out CVD carbon coating, and the duration of CVD is 2h, controlling the flow rate of acetylene gas at 0.5L/min through an electromagnetic valve, and turning off the acetylene gas after the CVD time is over;
(6) Transferring the reacted material to an anaerobic transition cabin for cooling by lifting a furnace chamber of an air inlet end after the step (5) is finished, reducing the furnace chamber to a horizontal level after the material is taken out, and setting the temperature back to Mg 2 The Si nitriding temperature is 750 ℃, then the next batch of magnesium silicide is added to enter a furnace for reaction, and the furnace chamber is not required to be cooled to the room temperature in the whole process, so that batch continuous preparation is realized;
(7) And (3) taking out the material cooled to room temperature in the transition cabin in the step (6), then pickling for 2 hours by using hydrochloric acid, centrifuging to the center after pickling time, and then drying in vacuum. As can be seen from XRD of the reaction product before and after pickling in FIG. 5a, when the temperature of the CVD-deposited carbon is too high (. Gtoreq.800 ℃), mg is contained in a reducing atmosphere 3 N 2 After being reduced, the alloy is re-alloyed with silicon to obtain Mg 2 Si, while Mg2Si is easy to react with acid to generate silane, has high risk, and generates impurities which are difficult to remove due to certain corrosion on the stainless steel lining. From the thermogravimetric analysis of fig. 5b, the deposited carbon content was 8.8% under this condition.
Example 3
(1) 1kg of metallurgical silicon powder and 1.8kg of industrial magnesium powder are placed in a mixer to be mixed for 1h, so that the silicon powder and the magnesium powder are uniformly mixed;
(2) Placing the powder uniformly mixed in the step (1) into a crucible, then placing the dry pot into an argon atmosphere box-type furnace, preserving heat for 6 hours at 550 ℃, wherein the temperature rising rate is 1 ℃/min, and cooling and taking out along with the furnace after the heat preservation is finished;
(3) Carrying out jet milling and screening on the product obtained in the step (2) to obtain alloy powder with the granularity distribution of 1-5 um;
(4) Placing the powder sieved in the step (3) in a rotary kiln shown in the figure (1), and introducing N after the oxygen in the kiln chamber is exhausted at 15rpm 2 /NH 3 Mg by mixed gas 2 The nitriding reaction of Si, the gas flow rate is 0.5L/min, the temperature is kept at 700 ℃ for 6 hours, and the heating rate is 8 ℃/min;
(5) Turning off NH after the heat preservation in the step (4) is finished 3 Is kept N 2 Is passed in to carry out the reaction of residual NH 3 After the discharge, introducing acetylene gas to carry out CVD carbon coating, wherein the duration of CVD is 2 hours, 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 finished;
(6) Transferring the reacted material to an anaerobic transition cabin for cooling by lifting a furnace chamber of an air inlet end after the step (5) is finished, reducing the furnace chamber to a horizontal level after the material is taken out, and setting the temperature back to Mg 2 The Si nitriding temperature is 700 ℃, then the next batch of magnesium silicide is added to enter a furnace for reaction, and the furnace chamber is not required to be cooled to the room temperature in the whole process, so that batch continuous preparation is realized;
(7) And (3) taking out the material cooled to room temperature in the transition cabin in the step (6), then pickling for 2 hours by using hydrochloric acid, centrifuging to the center after pickling time, and then drying in vacuum. As can be seen from XRD of the reaction product of FIG. 6a, when the nitriding temperature is 700 ℃, the reaction is insufficient due to the large amount of materials, low temperature and slow reaction, and residual Mg is present 2 Si, and when the temperature of CVD deposited carbon is low (+.700℃ C.), the crystallinity of carbon is poor, the amorphous carbon content is high, resulting in an excessively large specific surface area of the material (FIG. 6 b), which reduces the first coulombic efficiency of the silicon-carbon material (FIG. 6c, first coulombic efficiency 73.3%)
The foregoing has shown and described the basic principles, principal 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, and that the above embodiments and descriptions are merely illustrative of the principles of the present invention, and various changes and modifications may be made therein without departing from the spirit and scope of the invention, which is defined by the appended claims. The scope of the invention is defined by the appended claims and equivalents thereof.
Claims (5)
1. The preparation method of the carbon-coated three-dimensional porous silicon anode material is characterized in that the carbon-coated porous silicon anode material is prepared in a large-scale controllable manner by a core-shell type carbon-coated porous silicon anode material, and is characterized in that: the preparation method comprises the following steps:
step 1: placing metallurgical silicon powder and industrial magnesium powder in a mixer for mixing according to a certain mass ratio, so that the silicon powder and the magnesium powder are uniformly mixed;
step 2: placing the powder uniformly mixed in the step 1 into a crucible, then placing the crucible 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 cooling along with the furnace after the heat preservation is finished and taking out;
step 3: carrying out jet milling and screening on the product obtained in the step 2 to obtain alloy powder with certain micron particle size distribution;
step 4: placing the powder sieved in the step 3 into a rotary kiln, discharging oxygen in the furnace chamber of the rotary kiln, and introducing N 2 、NH 3 、NH 3 /N 2 Or NH 3 Ar mixture, mg 2 Nitriding Si;
step 5: after the heat preservation in the step 4 is finished, N is maintained 2 Then introducing acetylene gas to carry out CVD carbon coating, and the process lasts for a period of time;
step 6: transferring the reacted materials to an anaerobic transition cabin for cooling by lifting a furnace chamber at the air inlet end after the step 5 is finished, reducing the furnace chamber to a level after the materials are taken out, adding the next batch of magnesium silicide for furnace feeding reaction, and cooling the furnace chamber to room temperature in the whole process without reducing the temperature of the furnace chamber, so that batch continuous preparation can be realized;
step 7: and (3) taking out the material cooled to room temperature in the transition cabin in the step (6), then washing with hydrochloric acid, centrifuging to be neutral after the washing time is up, and then drying in vacuum.
2. The method for preparing the carbon-coated three-dimensional porous silicon anode material according to claim 1, which is characterized in that: the step 1 further comprises the steps of mixing metallurgical silicon powder and industrial magnesium powder according to a mass ratio of 1:1.8 are placed in a mixer and mixed for 1h.
3. The method for preparing the carbon-coated three-dimensional porous silicon anode material according to claim 1, which is characterized in that: the step 2 further comprises placing the crucible in an argon atmosphere box-type furnace, heating to 500-600 ℃ at a heating rate of 1-10 ℃/min, and preserving heat for 3-6h.
4. The method for preparing the carbon-coated three-dimensional porous silicon anode material according to claim 1, which is characterized in that: the step 3 further comprises alloy powder with the granularity distribution of 1-5 um.
5. The method for preparing the carbon-coated three-dimensional porous silicon anode material according to claim 1, which is characterized in that: step 4 further comprises rotating the kiln at a speed of 5-30rpm, discharging oxygen from the furnace chamber, and introducing N 2 、NH 3 Or N 2 /NH 3 Mg in nitrogen-containing atmosphere of gas mixture 2 The nitriding reaction of Si, the gas flow rate is 0.5L/min, the temperature is kept at 700-800 ℃ for 3-6h, and the heating rate is 5-10 ℃/min.
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