CN116417602A - Silicon-carbon composite material based on three-dimensional network carbon-silicon structure and preparation method and application thereof - Google Patents
Silicon-carbon composite material based on three-dimensional network carbon-silicon structure and preparation method and application thereof Download PDFInfo
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- 238000002360 preparation method Methods 0.000 title claims abstract description 35
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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
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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
- 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
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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
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/624—Electric conductive fillers
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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
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/628—Inhibitors, e.g. gassing inhibitors, corrosion inhibitors
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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
- H01M2004/021—Physical characteristics, e.g. porosity, surface area
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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
- H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
- H01M2004/027—Negative electrodes
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- 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 discloses a silicon-carbon composite material based on a three-dimensional network carbon-silicon structure, a preparation method and application thereof.
Description
Technical Field
The invention belongs to the technical field of silicon-based anode materials of lithium ion batteries, and particularly relates to a silicon-carbon composite material based on a three-dimensional network carbon-silicon structure, and a preparation method and application thereof.
Background
Over the last decade of development of lithium ion batteries, the bottleneck of energy density improvement has occurred so far, and the main problem is that the lithium storage capacity of the commercialized anode and cathode materials basically reaches the theoretical limit. The capacity of the graphite carbon anode material reaches 360mAh/g, which is close to a theoretical value of 372mAh/g, and the rising space is very small. Silicon-based materials with theoretical gram capacities up to 4200mAh/g are of great interest for achieving higher energy densities. Compared with graphite materials, the theoretical energy density of the silicon-based materials exceeds 10 times of that of the graphite materials, and the silicon-based materials are considered to be one of the most potential materials in the lithium ion battery high specific capacity anode materials.
The main problem of the application of the silicon anode material is that the expansion is large, the expansion rate can reach 300 percent, and the large expansion rate finally leads to the pulverization of active substances and the damage of SEI films on the surfaces of electrodes in the application process, so that the cycle performance is deteriorated; meanwhile, due to the semiconductor property of silicon, the conductivity of silicon is poor, and the silicon has poor rate capability. Therefore, silicon anode materials also face significant challenges for lithium ion battery applications.
Disclosure of Invention
The invention provides a silicon-carbon composite material based on a three-dimensional network carbon-silicon structure and a preparation method thereof, and aims to solve the technical problems of large volume change of a silicon-based anode material, particle pulverization of the silicon material and repeated growth of a surface SEI film in the prior art.
In order to solve the technical problems, the technical scheme provided by the invention is as follows:
the invention provides a silicon-carbon composite material based on a three-dimensional network carbon-silicon structure, which consists of a three-dimensional network structure formed by nano silicon and carbon and a coated carbon layer arranged outside the three-dimensional network structure, wherein the three-dimensional network structure takes the carbon structure as a framework, and the nano silicon is uniformly embedded on the carbon framework.
The specific surface area of the three-dimensional network structure is 9-12 m 2 Per gram, the specific surface area of the silicon-carbon composite material is less than 5m 2 /g。
The silicon-carbon composite material is of a three-dimensional network carbon structure, has good electronic conductivity characteristics, and silicon particles are uniformly embedded on the surface of a carbon skeleton or completely embedded in the carbon skeleton, so that electron migration and mutual conduction intercommunication in any direction of a three-dimensional space can be formed for the silicon particles, and furthermore, the three-dimensional network carbon structure can provide an elastic carrier for silicon embedded on the carbon skeleton, so that huge volume expansion of the silicon in the charging and discharging processes is inhibited, the breakage of the silicon particles is prevented, and meanwhile, the expansion and contraction effects of the silicon-carbon composite material in the whole three-dimensional space are reduced. Finally, the silicon-carbon composite material based on the network structure has better performance. Simultaneously, the carbon layer is coated outside the three-dimensional structure, so that after the periphery of the silicon is coated by the carbon, the specific surface area of the material is further reduced from about 10m before coating 2 The/g drops to 5m 2 And the ratio of the material to the catalyst is lower than/g, so that the material is more compact, the conductivity is improved, and the side reaction can be reduced.
In an alternative embodiment, in the silicon-carbon composite material provided by the invention, the thickness of the carbon coating layer is 1-10 nm, and the particle size of the silicon-carbon composite material is 5-20 μm.
The invention provides a preparation method of a silicon-carbon composite material based on a three-dimensional network carbon-silicon structure, which comprises the following steps:
s1, uniformly mixing nano silicon and a high-volatile organic carbon source, and performing isostatic pressing treatment to obtain an isostatic block, wherein the pressure of the isostatic pressing treatment is 50-300 MPa, and the treatment time is 60-90 min.
S2, crushing the isostatic pressing block obtained in the step S1.
S3, performing primary sintering treatment on the crushed particles obtained in the step S2 under the protection of inert gas to obtain original particles with a three-dimensional network structure; the first sintering process comprises three heating stages, wherein the first heating stage is 100-300 ℃; the second heating stage is 600-800 ℃; the third temperature rising stage is 1000-1200 ℃.
S4, crushing the original particles obtained in the step S3, and sieving to obtain original powder.
And S5, uniformly mixing the original powder obtained in the step S4 with a carbon coating agent, performing secondary sintering under the protection of inert gas, crushing the secondary sintering material, and sieving to obtain the silicon-carbon composite material based on the three-dimensional network carbon-silicon structure.
According to the invention, silicon and carbon are tightly combined through isostatic pressing treatment, and are tightly connected before sintering, so that the sintering process is ensured not to be loose, volatile matters in a high-volatile organic carbon source volatilize in the sintering process, a silicon-carbon three-dimensional network structure embedded with silicon is formed after sintering, and then carbon is coated outside the three-dimensional network structure, so that the specific surface area of the material is further reduced, and the conductivity is improved.
In the primary sintering process, the first rapid temperature rise is to accelerate the volatilization of low-boiling-point volatile matters (water vapor, short-chain hydrocarbon and other organic gases), and the design temperature is kept at a temperature which enables the volatilization reaction to be sufficient; the second rapid heating is to accelerate the volatilization of the middle and high boiling point volatile matters (organic gases such as middle and long chain hydrocarbon, benzene ring and the like), and the design and the heat preservation are also to make the volatilization reaction at the temperature sufficient; the two rapid heating is a carbon network structure formed in the process of volatilizing all volatile matters; the third time of slow temperature rise is high temperature carbonization, the volatilization of the organic volatile is completed, and only a small amount of CO is volatilized 2 The gas is slowly heated to stabilize the formed carbon network structure.
In an alternative embodiment, in the preparation method provided by the invention, the high-volatile organic carbon source is selected from one or more of low-temperature softening point asphalt, thermoplastic resin and tar.
In the invention, warm softening point asphalt, thermoplastic resin and tar are selected as high volatile organic carbon sources, a large amount of gas escapes in the carbonization process to form a large amount of internal pores, and the internal pores can be opened due to the large amount of gas, so that the three-dimensional network structure is formed.
As an alternative embodiment, in the preparation method provided by the invention, the particle size D50 of the high-volatile organic carbon source is 2-10 μm.
The particle size D50 of the organic carbon source is 2-10 mu m, in principle, the smaller the particle size is, the more favorable for the dispersion of silicon, but the smaller the particle size is, the more difficult the processing, so that the particle size is limited within 10 mu m, and the dispersion is favorable and the processing is convenient.
In an optional embodiment, in the preparation method provided by the invention, the nano silicon comprises one or more of metal silicon, solar polysilicon, chemical vapor deposition silicon and physical vapor deposition silicon, and the particle size D50 of the nano silicon is 20-100 nm.
The functions in the application can be realized by limiting the particle size of the nano silicon to 20-100 nm, namely the nano silicon prepared by grinding and the nano silicon deposited by vapor phase.
In an alternative embodiment, in the preparation method provided by the invention, the mass ratio of nano silicon to the high-volatile organic carbon source in the step S1 is (0.7-1): (1.5-3.0).
In the invention, when the mass ratio of the nano silicon to the high-volatile organic carbon source exceeds the above range, the gram specific capacity of the material is influenced, the silicon proportion is increased, and the gram specific capacity of the material is increased.
As an alternative embodiment, in the preparation method provided by the invention, the size of the broken particles in the step S1 is 3-10 mm.
In the preparation method provided by the invention, in the step S3, the temperature rising rate in the first temperature rising stage is 3-7 ℃/min, and the temperature is kept for 60-120 min; the temperature rising rate in the second temperature rising stage is 8-12 ℃/min, and the temperature is kept for 60-120 min; the temperature rising rate in the third temperature rising stage is 0.5-1.5 ℃/min, and the temperature is kept for 60-120 min.
In the preparation method provided by the invention, nitrogen or inert gas is firstly introduced before heating in the step S3, and then the mixture is naturally cooled to room temperature after three times of heating, and nitrogen is introduced for protection in the whole process.
In an alternative embodiment, in the preparation method provided by the invention, the carbon coating agent in the step S5 is added in an amount of 1-10% of the original powder mass. So that the thickness of the carbon coating layer is controlled between 1 and 10 nm.
In an alternative embodiment, in the preparation method provided by the present invention, the carbon coating agent in step S5 is pitch.
In an alternative embodiment, in the preparation method provided by the invention, the carbon coating agent is selected from one of high-temperature softening point asphalt, medium-temperature softening point asphalt and low-temperature softening point asphalt.
In an alternative embodiment, the preparation method provided by the invention, the carbon coating agent is selected from high-temperature softening point asphalt, the ring-and-ball softening point of the asphalt is 200-300 ℃, and the particle size D50 is 2-10 mu m.
In the invention, the carbon coating agent is added to sinter with the original powder, and the effect is to fill and coat the surface of the original powder, so that the specific surface area of the material is reduced.
In an alternative embodiment, in the preparation method provided by the invention, the second sintering in the step S5 includes two heating stages, wherein the first heating stage is 200-400 ℃, and the second heating stage is 800-1000 ℃.
In the invention, in the second sintering process, the first heating and heat preservation are to carry out hot melting on the coating agent to form fluid coating on the carbon-silicon structure; the second heating and heat preservation is to coke and carbonize the coating agent to form a coke structure.
As an optional implementation manner, in the preparation method provided by the invention, nitrogen or inert gas is firstly introduced before heating in the step S5, the heating rate in the first stage is 3-7 ℃/min, and the temperature is kept for 30-120 min; the temperature rising rate in the second stage is 3-7 ℃/min, and the temperature is kept for 60-120 min; and naturally cooling to room temperature, and introducing nitrogen for protection in the whole process.
In the preparation method provided by the invention, as an alternative embodiment, nano silicon and a high-volatile organic carbon source are uniformly mixed in the step S1 by adopting high-speed dispersing equipment under the conditions of inert protective gas and constant temperature.
The third aspect of the invention provides an application of the silicon-carbon composite material based on the three-dimensional network carbon-silicon structure or the silicon-carbon composite material prepared by the preparation method of the silicon-carbon composite material based on the three-dimensional network carbon-silicon structure in a lithium ion battery.
Compared with the prior art, the invention has the beneficial effects that:
(1) The three-dimensional network carbon structure has good electronic conductivity characteristics, and is favorable for forming electromigration and mutual conduction intercommunication in any direction of a three-dimensional space for silicon particles embedded on a carbon skeleton. Meanwhile, the three-dimensional network carbon structure can provide an elastic carrier for silicon embedded on the carbon skeleton, so that huge volume expansion of the silicon in the charge and discharge process is restrained, and the expansion and contraction effect of the silicon-carbon composite material on the whole three-dimensional space is reduced. Finally, the silicon-carbon composite material based on the network structure has better performance, and after the carbon layer is coated outside the three-dimensional structure, the specific surface area of the material is further reduced, the conductivity is improved, and meanwhile, the side reaction can be reduced.
(2) The preparation method of the silicon-carbon composite material mainly comprises an isostatic pressing process, a first sintering process and a second sintering process, wherein the isostatic pressing process enables silicon and carbon to be tightly connected, the sintering process is guaranteed not to be loose, a carbon three-dimensional network structure with silicon embedded in a carbon skeleton is formed after the first sintering, at the moment, defects exist on the surface of the formed carbon three-dimensional network structure, the specific surface area of the material is overlarge, and therefore the surface of the material is filled and wrapped through the second sintering, so that the specific surface area of the material is reduced. The invention has simple process and high equipment maturity, and is suitable for large-scale production.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
Fig. 1 is a schematic structural diagram of a three-dimensional network carbon-silicon structure in the invention, wherein fig. a is a schematic structural diagram of a prepared original material, and fig. B is a schematic structural diagram of a carbon-silicon structure coated with a carbon layer;
FIG. 2 is an electron microscope image of the three-dimensional network carbon silicon structure prepared in example 1;
FIG. 3 is an enlarged view of FIG. 2;
fig. 4 is an electron microscope image of a silicon-carbon composite material of a three-dimensional network carbon-silicon structure prepared in example 1.
Detailed Description
The present invention will be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments are shown, for the purpose of illustrating the invention, but the scope of the invention is not limited to the specific embodiments shown.
Unless defined otherwise, all technical and scientific terms used hereinafter have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the scope of the present invention.
Unless otherwise specifically indicated, the various raw materials, reagents, instruments, equipment and the like used in the present invention are commercially available or may be prepared by existing methods.
1. Preparation of silicon-carbon composite material based on three-dimensional network carbon-silicon structure
Example 1
A preparation method of a silicon-carbon composite material based on a three-dimensional network carbon-silicon structure comprises the following steps:
(1) Mixing the raw materials: taking a certain amount of chemical vapor deposition nano silicon powder (D50 approximately 80 nm) and asphalt powder (asphalt PE150, about 45% of coking value, D50 approximately 5 μm) for physical mixing; the mass ratio of the nano silicon powder to the asphalt powder is 1:2; adopting high-speed dispersing equipment (model VCH-5L), and firstly mixing for 20min at a dispersing speed of 500rpm under the protection of nitrogen; the dispersion rate is 1000rpm and is mixed for 30min; meanwhile, circulating cooling water is started in the whole process; and (5) sealing and storing the raw materials by adopting a PE bag after the mixing of the raw materials is finished.
(2) Isostatic pressing: filling the powder in the step (1) into a silica gel soft mold, vacuum sealing by using a PE bag, and placing the sealed charging mold into an isostatic pressing cavity (model 600MPa-5L of ultrahigh pressure equipment), wherein the isostatic pressing parameters require 200MPa of pressure and the dwell time is 60min; and tearing off the PE bag after the end to take out the block in the mould, thus obtaining the isostatic block.
(3) Crushing: crushing the isostatic pressing lump material in the step (2), and adopting a jaw small crusher (model PE100 x 125), wherein the crushing can be performed for a plurality of times until the granularity is controlled below 10mm.
(4) Sintering: sintering the crushed material in the step (3) at a high temperature, wherein the temperature of the tube furnace is controlled according to the following requirements, nitrogen or other inert gases are introduced for 30min, and the ventilation amount is 1.5L/min; then the temperature is raised to 150 ℃ from room temperature, the heating rate is 5 ℃/min, and the temperature is kept for 120min; then heating to 700 ℃, wherein the heating rate is 10 ℃/min, and preserving heat for 120min; then heating to 1100 ℃, wherein the heating rate is 1 ℃/min, and preserving heat for 120min; and naturally cooling to room temperature, and introducing nitrogen as protective gas in the whole process, wherein the ventilation rate is 1.0L/min. The original material with the three-dimensional network carbon-silicon structure is obtained, and the original material is shown in fig. 2 and 3.
(5) Crushing: taking out the sintered material after high-temperature carbonization, grinding and crushing, and passing the crushed material through a 325-target standard sieve, wherein the granularity D50 is controlled to be 5-20 mu m, so as to obtain the original powder.
(6) Secondary carbon mixing coating agent: physically mixing the original powder in the step (5) with carbon cladding powder (high temperature asphalt MQ280, ring and ball softening point 280 ℃); the addition amount of the carbon coating agent is 5% of the mass of the original powder; adopting high-speed dispersing equipment (model VCH-5L), and firstly mixing for 20min at a dispersing speed of 500rpm under the protection of nitrogen; the dispersion rate is 1000rpm and is mixed for 30min; meanwhile, circulating cooling water is started in the whole process; and (5) sealing and storing the mixture by adopting a PE bag after the end of mixing the materials.
(7) Secondary sintering: carrying out secondary sintering treatment on the mixed powder in the step (6), wherein the temperature control of the tube furnace is carried out according to the following requirements: firstly, introducing nitrogen or other inert gases for 30min, wherein the ventilation amount is 1.0L/min; then the temperature is raised to 300 ℃ from room temperature, the heating rate is 5 ℃/min, and the temperature is kept for 120min; then heating to 1000 ℃, wherein the heating rate is 5 ℃/min, and preserving heat for 120min; naturally cooling to room temperature, and introducing nitrogen as a protective gas in the whole process; the ventilation was 0.5L/min.
(8) Crushing: crushing the secondary sintering material obtained in the step (7) and sieving the crushed secondary sintering material with a 325-mesh sieve, wherein the granularity D50 is controlled to be 15.0+/-5.0 mu m, and thus the silicon-carbon composite material based on the three-dimensional network carbon-silicon structure is obtained, and is shown in figure 4.
The obtained silicon carbon composite material was designated as A1.
Example 2
The preparation method of the silicon-carbon composite material based on the three-dimensional network carbon-silicon structure is different from the embodiment 1 in that:
the asphalt PE150 powder in the step (1) is changed into asphalt PE100 powder (asphalt PE100, coking value 42%, D50≡5 μm); the isostatic pressing treatment pressure in the step (2) is 100MPa, and the dwell time is 80min; other steps were consistent with example 1. The obtained silicon-carbon composite material based on the three-dimensional network carbon-silicon structure is named as A2.
Example 3
The preparation method of the silicon-carbon composite material based on the three-dimensional network carbon-silicon structure is different from the embodiment 1 in that:
the pitch PE150 powder in step (1) was changed to phenolic resin powder (phenolic resin 2123, coking value 38%, D50≡8 μm), the carbon-coated agent was added in an amount of 2% of the original powder mass in step (6), and the other steps were the same as in example 1. The obtained silicon-carbon composite material based on the three-dimensional network carbon-silicon structure is named as A3.
Example 4
The preparation method of the silicon-carbon composite material based on the three-dimensional network carbon-silicon structure is different from the embodiment 1 in that:
in the step (1), the pitch PE150 powder is changed into Polyacrylonitrile (PAN) powder (PAN powder, coking value is 44%, D50 is about 10 μm), the addition amount of the carbon coating agent in the step (6) is 10% of the mass of the original powder, and other steps are the same as those in the example 1. The obtained silicon-carbon composite material based on the three-dimensional network carbon-silicon structure is named as A4.
Example 5
The preparation method of the silicon-carbon composite material based on the three-dimensional network carbon-silicon structure is different from the embodiment 1 in that:
in the step (1), chemical vapor deposition nano silicon powder is changed into physical vapor deposition nano silicon powder (D50 approximately 75 nm), and the mass ratio of the nano silicon powder to the asphalt powder is 1:3; the isostatic pressing treatment pressure in the step (2) is 50MPa, and the pressure maintaining time is 90min; other steps were consistent with example 1. The obtained silicon-carbon composite material based on the three-dimensional network carbon-silicon structure is named as A5.
Comparative example 1
The preparation method of the silicon-carbon composite material is different from the embodiment 1 in that:
the isostatic pressing process in step (2) and the crushing process in step (3) are not included, and all other steps are consistent with example 1. The obtained powder material is a primary material with a carbon-silicon structure (without a three-dimensional network carbon-silicon structure) in which silicon and carbon are mutually dispersed, and is named as B1.
Comparative example 2
The preparation method of the silicon-carbon composite material is different from the embodiment 1 in that:
the procedure of step (6), secondary carbon mixing coating agent, step (7), secondary sintering step (8) and pulverization were not included, and the other steps were the same as in example 1. The obtained powder material is a primary material with a carbon-silicon structure of a three-dimensional network structure, and is named as B2.
Comparative example 3
The preparation method of the silicon-carbon composite material is different from the embodiment 1 in that:
the process of isostatic pressing treatment in the step (2) and crushing in the step (3) is not included, the process of secondary carbon mixing coating agent in the step (6) and crushing in the step (7) and secondary sintering in the step (8) are not included, and all other steps are consistent with the embodiment 1. The obtained powder material is a primary material with a carbon-silicon structure (without a three-dimensional network carbon-silicon structure) in which silicon and carbon are mutually dispersed, and is named as B3.
2. Preparation of button electrode
Electrode manufacturing: the negative electrode materials prepared in the above examples 1 to 5 and comparative examples 1 to 3 were respectively prepared into uniform slurries with a conductive agent SP, a binder LA133, and deionized water according to a certain ratio, wherein the silicon carbon negative electrode materials: conductive agent SP: the mass ratio of the binder LA133 is 50:30:20; the homogenizing equipment adopts a vacuum deaeration machine, and the rotating speed is 2000rpm, and the time is 10min.
Uniformly coating the prepared slurry on copper foil, and then placing the copper foil in a 100 ℃ blast drying oven for drying; the baked pole piece is processed into a round electrode with a certain size by cutting and tabletting, accurately weighed (0.0001 g), and then placed into a vacuum drying oven to be baked for 8 hours at 120 ℃ under vacuum condition, thus obtaining the button electrode.
The button cell obtained by corresponding assembly of the A1 material is denoted as an A1 button cell, and the button cells A1, A2, A3, A4, A5, B1, B2 and B3 are obtained by analogy.
3. Performance detection
1. And detecting the performance of the silicon-carbon composite material based on the three-dimensional network carbon-silicon structure.
For the original material of the carbon-silicon structure prepared in the embodiment 1 and the silicon-carbon composite material obtained after carbon coating, the structure schematic diagram is shown in fig. 1, the silicon-carbon composite material is of a three-dimensional network structure composed of nano silicon and carbon, the nano silicon is uniformly embedded on a carbon skeleton, white particles represent silicon and are embedded on the surface of the carbon skeleton or completely embedded in the carbon skeleton, and the carbon layer is coated outside the three-dimensional network structure. Scanning Electron Microscope (SEM) detection is carried out on the material, and the detection result is shown in fig. 2-4, wherein fig. 2 is an original material of a three-dimensional network carbon-silicon structure obtained by primary sintering, fig. 3 is an enlarged view of fig. 2, wherein white small particles are nano-silicon (including arrow pointing in fig. 2 and 3), and gray areas are carbon, so that a three-dimensional network structure with multiple pores is formed. Fig. 4 shows the resulting silicon-carbon composite material, and it can be seen from fig. 4 that the silicon-carbon composite material is coated with a dense carbon layer. The specific surface area of the starting material of the carbon-silicon structure prepared in example 1 was about 10m as measured by electron microscopy 2 Per gram, the specific surface area of the finally obtained composite material is about 5m 2 And/g, the material is more compact.
2. Performance test of button electrode
Carrying out open circuit voltage test on the assembled battery, and selecting the battery with the open circuit voltage of more than 2.0V to carry out 0.1C primary charge-discharge efficiency and reversible capacity test; the electrical performance pairs of several cells are shown in table 1.
Table 1: electrical performance of button cell
The silicon-based negative electrode material has the advantages that in the application of a lithium ion battery, irreversible lithium consumption is increased due to large volume change, particle pulverization of the silicon material and repeated growth of a surface SEI film, and the reversible lithium is relatively reduced; the lithium battery performance is directly reflected by high lithium intercalation capacity, and the capacity of the extracted reversible lithium is relatively low, so that the first charge and discharge efficiency is low; as can be seen from the above table, the three-dimensional network-based carbon-silicon structure constructed by the invention effectively relieves the expansion of the silicon-based anode material in the three-dimensional space volume, the carbon chains inlaid by nano silicon in the network structure can prevent the breakage of silicon particles, and meanwhile, the carbon chains also have the function of increasing the electron conductance between silicon and silicon particles, compared with the silicon-carbon composite material (such as B1 in the table) without forming the three-dimensional network-based carbon-silicon structure, the electrical property of the composite material (such as B2 in the table) is better improved; in addition, by carrying out secondary coating on the original particles with the three-dimensional network carbon-silicon structure, the specific surface area of the material is further reduced, the conductivity is improved, and side reactions can be reduced, for example, the reversible capacity and the first efficiency of A1-A5 are higher than those of B2; in B3, the composite material has no three-dimensional network structure or carbon coating, and the lithium intercalation capacity, reversible capacity and first-effect height ratio A1-A5 are worse. The silicon-carbon composite material based on the three-dimensional network carbon-silicon structure finally prepared by the invention has the electrical performance level of market competitiveness in the application field of lithium ion battery cathodes.
The foregoing is a further detailed description of the invention in connection with the preferred embodiments, and it is not intended that the invention be limited to the specific embodiments described. It will be apparent to those skilled in the art that several simple deductions or substitutions may be made without departing from the spirit of the invention, and these should be considered to be within the scope of the invention.
Claims (14)
1. The silicon-carbon composite material based on the three-dimensional network carbon-silicon structure is characterized by comprising a three-dimensional network structure formed by nano silicon and carbon and a coated carbon layer arranged outside the three-dimensional network structure, wherein the three-dimensional network structure takes carbon as a framework, and the nano silicon is uniformly embedded on the carbon framework;
the specific surface area of the three-dimensional network structure is 9-12 m 2 Per gram, the specific surface area of the silicon-carbon composite material is less than 5m 2 /g。
2. The silicon-carbon composite material based on the three-dimensional network carbon-silicon structure according to claim 1, wherein the thickness of the carbon coating layer is 1-10 nm, and the particle size of the silicon-carbon composite material is 5-20 μm.
3. The preparation method of the silicon-carbon composite material based on the three-dimensional network carbon-silicon structure is characterized by comprising the following steps of:
s1, uniformly mixing nano silicon and a high-volatile organic carbon source, and then carrying out isostatic pressing treatment to obtain an isostatic block, wherein the pressure of the isostatic pressing treatment is 50-300 MPa, and the treatment time is 60-90 min;
s2, crushing the isostatic pressing block obtained in the step S1;
s3, performing primary sintering treatment on the crushed particles obtained in the step S2 under the protection of inert gas to obtain original particles with a three-dimensional network structure; the first sintering process comprises three heating stages, wherein the first heating stage is 100-300 ℃; the second heating stage is 600-800 ℃; the third temperature rising stage is 1000-1200 ℃;
s4, crushing the original particles obtained in the step S3, and sieving to obtain original powder;
and S5, uniformly mixing the original powder obtained in the step S4 with a carbon coating agent, performing secondary sintering under the protection of inert gas, crushing the secondary sintering material, and sieving to obtain the silicon-carbon composite material based on the three-dimensional network carbon-silicon structure.
4. The method for preparing the silicon-carbon composite material based on the three-dimensional network carbon-silicon structure according to claim 2, wherein the high-volatile organic carbon source is selected from one or more of low-temperature softening point asphalt, thermoplastic resin and tar, and the particle size D50 of the high-volatile organic carbon source is 2-10 μm.
5. The method for preparing the silicon-carbon composite material based on the three-dimensional network carbon-silicon structure according to claim 2, wherein in the step S1, the mass ratio of nano silicon to high-volatile organic carbon source is (0.7-1): (1.5-3.0).
6. The method for preparing the silicon-carbon composite material based on the three-dimensional network carbon-silicon structure according to claim 2, wherein in the step S3, the temperature rising rate in the first temperature rising stage is 3-7 ℃/min, and the temperature is kept for 60-120 min; the temperature rising rate in the second temperature rising stage is 8-12 ℃/min, and the temperature is kept for 60-120 min; the temperature rising rate in the third temperature rising stage is 0.5-1.5 ℃/min, and the temperature is kept for 60-120 min.
7. The method for preparing the silicon-carbon composite material based on the three-dimensional network carbon-silicon structure according to any one of claims 2 to 6, wherein nitrogen or inert gas is firstly introduced before heating in the step S3, and the three-time heating is followed by natural cooling to room temperature, and nitrogen is introduced for protection in the whole process.
8. The method for preparing a silicon-carbon composite material based on a three-dimensional network carbon-silicon structure according to claim 2, wherein the addition amount of the carbon coating agent in the step S5 is 1-10% of the mass of the original powder.
9. The method for preparing a silicon-carbon composite material based on a three-dimensional network carbon-silicon structure according to claim 2, wherein the carbon coating agent is one selected from high-temperature softening point asphalt, medium-temperature softening point asphalt and low-temperature softening point asphalt.
10. The method for preparing a silicon-carbon composite material based on a three-dimensional network carbon-silicon structure according to claim 2, wherein the carbon coating agent is selected from high-temperature softening point asphalt, the ring-ball softening point of which is 200-300 ℃, and the particle size D50 of which is 2-10 μm.
11. The method for preparing a silicon-carbon composite material based on a three-dimensional network carbon-silicon structure according to claim 2, wherein the second sintering in the step S5 comprises two heating stages, wherein the first heating stage is 200-400 ℃ and the second heating stage is 800-1000 ℃.
12. The preparation method of the silicon-carbon composite material based on the three-dimensional network carbon-silicon structure, which is characterized in that nitrogen or inert gas is firstly introduced before heating in the step S5, the heating rate in the first heating stage is 3-7 ℃/min, and the temperature is kept for 30-120 min; the temperature rising rate in the second temperature rising stage is 3-7 ℃/min, and the temperature is kept for 60-120 min; and naturally cooling to room temperature, and introducing nitrogen for protection in the whole process.
13. The method for preparing the silicon-carbon composite material based on the three-dimensional network carbon-silicon structure according to claim 2, wherein in the step S1, nano silicon and a high-volatile organic carbon source are uniformly mixed under the conditions of inert protective gas and constant temperature by adopting high-speed dispersing equipment.
14. Use of the silicon-carbon composite material based on a three-dimensional network carbon-silicon structure according to claim 1 or 2 or the silicon-carbon composite material prepared by the preparation method of the silicon-carbon composite material based on the three-dimensional network carbon-silicon structure according to any one of claims 3 to 13 in lithium ion batteries.
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| CN116885158B (en) * | 2023-09-08 | 2023-12-01 | 琥崧智能装备(太仓)有限公司 | Carbon-silicon composite anode active material and preparation method and application thereof |
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