CN117038946A - Silicon-carbon negative electrode material, preparation method thereof and lithium ion battery - Google Patents
Silicon-carbon negative electrode material, preparation method thereof and lithium ion battery Download PDFInfo
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- CN117038946A CN117038946A CN202311167855.9A CN202311167855A CN117038946A CN 117038946 A CN117038946 A CN 117038946A CN 202311167855 A CN202311167855 A CN 202311167855A CN 117038946 A CN117038946 A CN 117038946A
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Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
- H01M4/386—Silicon or alloys based on silicon
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/04—Processes of manufacture in general
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/362—Composites
- H01M4/366—Composites as layered products
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
- H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
- H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/624—Electric conductive fillers
- H01M4/625—Carbon or graphite
-
- 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
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- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Manufacturing & Machinery (AREA)
- Composite Materials (AREA)
- Inorganic Chemistry (AREA)
- Materials Engineering (AREA)
- Battery Electrode And Active Subsutance (AREA)
Abstract
The invention belongs to the technical field of lithium ion batteries, relates to a lithium ion battery negative electrode material, and in particular relates to a silicon-carbon negative electrode material, a preparation method thereof and a lithium ion battery. Forming aerogel by graphene and porous carbon, wherein an amorphous carbon layer is coated on the surface of the aerogel; in the aerogel, the porous carbon is dispersed among graphene sheets to form a framework, and silicon grains are distributed in the pores of the aerogel; wherein the mass ratio of the graphene to the porous carbon is 1:0.6-1.0. According to the silicon-carbon anode material, the graphene aerogel matrix supported by porous carbon is loaded with silicon, so that the silicon-carbon anode material has more abundant silicon deposition sites, a graphene aerogel rich conductive network is generated, and meanwhile, the porous carbon skeleton is used for supporting the shrinkage and expansion of silicon grains, so that the circulation and multiplying power performance of the material are ensured.
Description
Technical Field
The invention belongs to the technical field of lithium ion batteries, relates to a lithium ion battery negative electrode material, and in particular relates to a silicon-carbon negative electrode material, a preparation method thereof and a lithium ion battery.
Background
The disclosure of this background section is only intended to increase the understanding of the general background of the invention and is not necessarily to be construed as an admission or any form of suggestion that this information forms the prior art already known to those of ordinary skill in the art.
In the negative electrode material of the lithium ion battery, silicon is superior to other materials (such as modified natural graphite or artificial graphite) in theoretical capacity (3579 mAh/g) and initial potential (0.4V), so that the silicon can be used as a high-capacity substitute. However, silicon undergoes a significant volume change (280%) during lithiation and delithiation, wherein pull-ring stresses are generated at the surface of the particles during the first lithiation of the silicon particles and each delithiation of the amorphous particles. It can lead to cracking, shattering, loss of electrical contact, and excessive growth of electronically insulating Solid Electrolyte Interfaces (SEI) of the silicon particles. These effects deteriorate the cycle performance and prevent the use of silicon.
The porous carbon material structure can be used as a silicon load matrix to effectively relieve stress, so that the structural stability of silicon is enhanced. However, the inventors have found that non-uniform deposition results in a large surface area of the porous structure forming more SEI film and irreversible lithium consumption, while porous carbon is rich in sp 3 The structure also causes poor electron conductivity, and thus, the porous carbon material may reduce the energy density of the battery.
The spongy aerogel is used as a silicon load matrix, so that the volume expansion stress can be inhibited, the chemical reaction between silicon and electrolyte can be inhibited, and the electronic conductivity of the material can be improved. At present, aerogel can be prepared by chitin or graphene, and then the silicon-loaded aerogel composite material is obtained by performing magnesian reduction. However, the inventor researches and discovers that the aerogel structure lacks framework support, the volume expansion of the silicon oxide is too large in the circulation process, and the matrix is difficult to support, so that the structural stability is poor, and the circulation and rate performance are reduced.
Disclosure of Invention
In order to solve the defects of the prior art, the invention aims to provide the silicon-carbon negative electrode material, the preparation method thereof and the lithium ion battery, and the silicon-carbon negative electrode material provided by the invention has the advantages that the graphene aerogel matrix supported by porous carbon is loaded with silicon, so that the silicon deposition sites are richer, the graphene aerogel is generated to enrich a conductive network, and meanwhile, the porous carbon skeleton is used for supporting the contraction and expansion of silicon grains, so that the circulation and the multiplying power performance of the material are ensured.
In order to achieve the above purpose, the technical scheme of the invention is as follows:
on one hand, the silicon-carbon negative electrode material is formed by graphene and porous carbon, and an amorphous carbon layer is coated on the surface of the aerogel; in the aerogel, the porous carbon is dispersed among graphene sheets to form a framework, and silicon grains are distributed in the pores of the aerogel; wherein the mass ratio of the graphene to the porous carbon is 1:0.6-1.0.
According to the invention, the porous carbon is dispersed among graphene sheets to form the aerogel formed by the framework, so that not only can rich silicon deposition sites be provided, but also the internal through hole structure of the aerogel promotes the circulation of silane and methane gas in the interior, the uniformity of the deposition process is ensured, and cracks or crushing caused by local volume expansion in the circulation process are avoided; the porous carbon skeleton dispersed between graphene sheets not only provides silane deposition sites, but also serves as a graphene aerogel skeleton to provide structural support, so that the collapse of the whole system in the expansion process is avoided. The final amorphous carbon layer coating can effectively repair surface defects and residual pores of the deposited material, and reduces SEI film formation in the circulation process.
In the preparation process of the silicon-carbon anode material, aerogel can be prepared firstly, then silicon grains are distributed in pores of the aerogel, and finally an amorphous carbon layer is coated; or preparing a compound of silicon dioxide and aerogel, reducing the silicon dioxide through a reduction reaction, and finally coating an amorphous carbon layer.
On the other hand, the preparation method of the silicon-carbon negative electrode material comprises the steps of uniformly dispersing porous carbon and graphene oxide in water and/or a polar solvent to obtain a dispersion liquid, preparing composite gel by treating the dispersion liquid by a hydrothermal method or a solvothermal method, and freeze-drying the composite gel to obtain an aerogel precursor; pyrolyzing the aerogel precursor under the condition of inert atmosphere to pyrolyze graphene oxide in the aerogel precursor into graphene, so as to obtain aerogel; depositing a silicon simple substance into pores of the aerogel by adopting a chemical vapor deposition method, and then coating carbon on the aerogel deposited with the silicon simple substance to coat an amorphous carbon layer on the surface of the aerogel; wherein the temperature of the hydrothermal method or solvothermal method treatment is 150-200 ℃, and the pyrolysis temperature is 700-900 ℃.
According to the invention, porous carbon and graphene oxide are dispersed in water or a polar solvent, wherein the graphene oxide has more oxygen-containing functional groups and higher hydrophilicity, so that the graphene oxide is uniformly dispersed in water and/or the polar solvent, and the porous carbon and the graphene oxide are self-assembled by a hydrothermal method or a solvothermal method at 150-200 ℃ to enable the porous carbon to be dispersed into graphene oxide sheets to form a framework, so that the aerogel precursor containing the graphene oxide is formed. The graphene oxide is favorable for forming an aerogel precursor formed by dispersing porous carbon between graphene sheets to form a framework, but the graphene oxide has poor conductive performance and is unfavorable for improving the electrochemical performance of the graphene oxide as an electrode material, so that the graphene oxide precursor is pyrolyzed at the temperature of 700-900 ℃ to convert the graphene oxide into graphene, and the aerogel formed by dispersing porous carbon between graphene sheets to form the framework can be obtained. When silicon grains are distributed in the pores of the aerogel, the chemical vapor deposition method is selected, so that the distribution of the silicon grains in the pores of the aerogel is facilitated, and the capacity of the silicon grains serving as a negative electrode material of a lithium ion battery is improved. Finally, carbon coating is carried out to coat an amorphous carbon layer on the surface of the material, so that the surface defect and residual pores of the deposited material can be repaired, the SEI film formation in the circulation process is reduced, and the circulation stability and the multiplying power performance are improved.
In a third aspect, a lithium ion battery anode includes an active material, a binder, a conductive agent, and a current collector, where the active material, the binder, and the conductive agent form a composite layer, the composite layer is disposed on the surface of the current collector, and the active material is the silicon-carbon anode material.
In a fourth aspect, a lithium ion battery includes a positive electrode, a negative electrode, an electrolyte, and a separator, where the negative electrode is the negative electrode of the lithium ion battery.
The beneficial effects of the invention are as follows:
1. according to the invention, the porous carbon is dispersed to the aerogel formed between the graphene sheets, and the porous carbon is used as the support of the graphene sheets, and meanwhile, the porous carbon contains pores, so that the strain acting force of the full electricity of silicon can be relieved, the aerogel structure is prevented from being damaged, and the capacity of the battery in the circulation process is ensured.
2. The porous carbon-rich pore structure of the silicon-carbon anode material provided by the invention is favorable for stable combination of silicon and carbon, and can avoid removal of subsequent treatment, thereby improving initial efficiency and capacity.
3. The invention has more abundant silicon deposition sites and conductive networks, and the porous carbon skeleton supports the contraction and expansion of silicon grains, and simultaneously, the surface defects and residual pores of the deposited material can be effectively repaired by coating the amorphous carbon layer, and the SEI film formation in the circulation process is reduced, so that the circulation and multiplying power performance of the silicon-carbon anode material are ensured.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the invention.
FIG. 1 is a schematic illustration of the process of preparing graphene aerogel according to example 1 of the present invention;
FIG. 2 is a schematic illustration of the process of preparing graphene/porous carbon aerogel according to example 3 of the present invention;
fig. 3 is a transmission electron microscope image of the silicon-carbon negative electrode material prepared in example 3 of the present invention.
Detailed Description
It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the invention. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the present invention. As used herein, the singular is also intended to include the plural unless the context clearly indicates otherwise, and furthermore, it is to be understood that the terms "comprises" and/or "comprising" when used in this specification are taken to specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof.
In view of the problems of circulation, rate performance reduction and the like of the existing silicon-loaded aerogel, the invention provides a silicon-carbon anode material, a preparation method thereof and a lithium ion battery.
According to an exemplary embodiment of the invention, a silicon-carbon anode material is provided, graphene and porous carbon form aerogel, and an amorphous carbon layer is coated on the surface of the aerogel; in the aerogel, the porous carbon is dispersed among graphene sheets to form a framework, and silicon grains are distributed in the pores of the aerogel; wherein the mass ratio of the graphene to the porous carbon is 1:0.6-1.0.
The voids of the aerogel according to the present invention refer not only to the voids that form the structure of the aerogel, but also to the voids of the porous carbon itself.
In some embodiments, the amorphous carbon layer has a thickness of 200-300 nm. The condition is more favorable for reducing the formation of SEI films, and simultaneously ensures the electrochemical performance of the silicon-carbon anode material.
In some embodiments, the silicon grains are 2-3 nm in size.
In some embodiments, the silicon carbon anode material has a particle size of 0.8 to 48 μm.
In some embodiments, the silicon grains are 35-55% of the aerogel mass.
In another embodiment of the present invention, a preparation method of the silicon-carbon negative electrode material is provided, wherein porous carbon and graphene oxide are uniformly dispersed in water and/or a polar solvent to obtain a dispersion liquid, the dispersion liquid is processed by a hydrothermal method or a solvothermal method to prepare a composite gel, and the composite gel is freeze-dried to obtain an aerogel precursor; pyrolyzing the aerogel precursor under the condition of inert atmosphere to pyrolyze graphene oxide in the aerogel precursor into graphene, so as to obtain aerogel; depositing a silicon simple substance into pores of the aerogel by adopting a chemical vapor deposition method, and then coating carbon on the aerogel deposited with the silicon simple substance to coat an amorphous carbon layer on the surface of the aerogel; wherein the temperature of the hydrothermal method or solvothermal method treatment is 150-200 ℃, and the pyrolysis temperature is 700-900 ℃.
Compared with graphene, graphene oxide has more polar functional groups, and can form uniform dispersion liquid in polar solvents such as water or ethanol so as to facilitate the subsequent formation of composite gel or aerogel.
In some embodiments, the porous carbon is obtained by carbonization and activation of a resin. The resin can be one or more of melamine resin, phenolic resin or urea resin. Melamine resins are preferred. The porous carbon prepared by taking melamine resin as a precursor has rich gaps, stable structure and pore size suitable for silicon grain embedding. The specific preparation process of the resin comprises the following steps: melamine, phenolic monomer or urea and water are mixed (the mass ratio of the precursor is 10-15%), and the precursor is generally stirred and heated. By NaCO 3 The pH of the mixture was adjusted to be slightly alkaline (ph=9 to 10). Then formaldehyde is dripped to carry out aldol condensation reaction (the volume ratio of the reaction solution to the formaldehyde solution is 1:1-1.5). After the reaction was completed, the solution was allowed to stand to obtain a precipitate (time: 18 to 24 hours). The reaction conditions are different, the molecular weight of the product is different, the product can be from water-soluble to water-insoluble or even insoluble solid, and the pH value has a great influence on the reaction rate. The silicon-carbon negative electrode material prepared from the porous carbon obtained by the resin prepared by the conditions has better effect.
In one or more embodiments, the carbonization temperature is 600 to 1000 ℃ for 2 to 4 hours.
The activating agent used for activation is potassium hydroxide, magnesium oxide, etc. In one or more embodiments, the activator used for activation is potassium hydroxide and the activation temperature is 600 to 1000 ℃. The activation effect of potassium hydroxide is better.
In some embodiments, the graphene oxide is synthesized using a modified Hummers method. Specifically, graphite is mixed with a strong acid (1 g of graphite powder is dissolved in 50-80 mL of the strong acid, preferably 1g of graphite powder is dissolved in 60mL of the strong acid), and the strong acid is one or two of concentrated sulfuric acid and concentrated nitric acid and NaNO 3 Preferably concentrated sulfuric acid and NaNO 3 The concentrated sulfuric acid can effectively remove impurity components and bound water in the graphite powder, and the nitrate radical is matched with the mixture to efficiently oxidize the surface of the graphite at the same time, so that oxygen-containing functional groups are formed. Then stirring in ice bath (ice bath time is 30-90 min). And (2) adding a strong oxidant, and stirring (the mass ratio of the graphite powder to the strong oxidant is 1:2-4), wherein the strong oxidant is generally one or two of potassium dichromate and potassium permanganate, and preferably, the potassium permanganate is generally selected, so that the potassium dichromate can generate heavy metal pollution, and the subsequent cleaning of the potassium permanganate is more convenient. Deionized water and hydrogen peroxide (the volume ratio of the strong acid to the mixed solution is 1:1.5-2) with the volume ratio of 1:2 are added dropwise. And then repeatedly washing with deionized water and hydrochloric acid to obtain a final solution (the pH value after washing is 5.5-6.5).
In some embodiments, the porous carbon is added into ethanol, dispersed uniformly, then added with the aqueous solution of graphene oxide, dispersed uniformly, then added into a high-pressure reactor, sealed and heated to 150-200 ℃ for reaction. The graphene oxide and the porous carbon are self-assembled and arranged in the hydrothermal reaction to form a composite material taking the graphene oxide as a substrate and the porous carbon as a framework, and the graphene oxide is changed into graphene through pyrolysis. Compared with the traditional graphene aerogel structure, the structure has the advantages that a porous carbon skeleton is used as a support, the structure is not easy to collapse in the cyclic charge and discharge process, and the cyclic stability of the anode material is improved; meanwhile, compared with the porous carbon aerogel without graphene, the porous carbon aerogel has the advantages that the deposition sites of silane are increased, and meanwhile, the matrix of the graphene aerogel provides rich conductive network structures and ion channels. The ionic conductivity and the electronic conductivity of the cathode are enhanced, and the dynamic performance of the material is enhanced.
In some embodiments, the hydrothermal or solvothermal treatment time is 15 to 20 hours.
In some embodiments, the pyrolysis time is 2 to 4 hours.
In some embodiments, metal Organic Chemical Vapor Deposition (MOCVD) is used to deposit elemental silicon into the pores of the aerogel. Specifically, the silane gas is heated to 450-550 ℃ to carry out cracking reaction, and silicon grains generated by cracking are distributed in the pores of the aerogel. The time of the cracking reaction is 1-3 h. The silane is ensured to be fully deposited in the inner pores of the graphene/porous carbon composite aerogel after being cracked.
In some embodiments, the carbon coating is performed by chemical vapor deposition. Specifically, the carbon source gas is heated to 550-650 ℃ to carry out decomposition reaction, and amorphous carbon generated by decomposition coats the aerogel deposited with the silicon simple substance. The carbon source gas is a carbon-containing gas such as methane, ethylene, ethane, propane, acetylene gas (purity 99.99%), or the like. Preferably, the carbon source gas with high carbon-hydrogen ratio, such as methane, ethane and the like, can generate carbon structures with more plane morphology, the plane structures have better electronic conductive property, and the SP of carbon in the formed conductive network 2 The structure is more, and the conjugated pi bond structure is more stable; and carbon source gases with low carbon to hydrogen ratio, such as acetylene, etc., can generate irregular carbon structures.
In some embodiments, the carbon coating is followed by sieving. The large-particle products can be removed by sieving, and the crushing effect can be achieved.
The invention provides a lithium ion battery anode, which comprises an active material, a binder, a conductive agent and a current collector, wherein the active material, the binder and the conductive agent form a composite layer, the composite layer is arranged on the surface of the current collector, and the active material is the silicon-carbon anode material. Such as polyvinyl alcohol (PVA), polytetrafluoroethylene (PTFE). Such as carbon black, conductive graphite, and the like. Such as copper foil, aluminum foil, copper mesh, and the like.
In a fourth embodiment of the present invention, a lithium ion battery is providedThe battery comprises a positive electrode, a negative electrode, electrolyte and a diaphragm, wherein the negative electrode is the negative electrode of the lithium ion battery. The positive electrode may be a lithium sheet. The solute in the electrolyte is lithium salt (such as LiPF 6 ) The solvent is one or more of Ethylene Carbonate (EC), dimethyl carbonate (DMC) and methyl ethyl carbonate.
In order to enable those skilled in the art to more clearly understand the technical scheme of the present invention, the technical scheme of the present invention will be described in detail with reference to specific embodiments.
Example 1
The preparation method of the graphene aerogel silicon carbon anode material comprises the following specific steps:
1. improved Hummers method for preparing Graphene Oxide (GO): taking 2g of graphite powder and NaNO 3 1g，H 2 SO 4 (98%) 120mL, and mixed with an ice bath for 1h. Adding KMnO 4 After 6g, stirring for 2 hours and preserving at 30 ℃ for 0.5 hours. 150mL of deionized water and H were added dropwise 2 O 2 (5%) 50mL. And repeatedly washing with deionized water and hydrochloric acid (5%) to obtain a final solution, namely graphene oxide dispersion liquid. And adding strong acid/strong oxidant to fully oxidize the graphite sheet layers to enable the surface of the graphite to generate oxygen-containing defects, so that the spacing between the graphite layers is gradually increased until the graphite sheets are completely peeled off, and graphene oxide is generated. Compared with graphene, graphene oxide has more polar functional groups, and can form uniform dispersion liquid in polar solvents such as water or ethanol so as to facilitate the subsequent formation of hydrogel and aerogel.
2. Preparing graphene aerogel: and (3) carrying out ultrasonic treatment on the graphene oxide dispersion liquid for 1h, transferring the graphene oxide dispersion liquid into a 25mL high-pressure hydrothermal reaction kettle, and preserving the graphene oxide dispersion liquid at 180 ℃ for 16h to obtain the graphene hydrogel. The hydrogel was freeze-dried at-60 ℃ for 24 hours to obtain an aerogel. The preparation process is shown in figure 1. Through high-pressure hydrothermal reaction, graphene sheets are connected with each other to form a 3D interconnection framework of aerogel, and a good pore foundation is provided for subsequent silane deposition. Meanwhile, the spongy 3D structure also comprises a large number of through holes, so that silane gas can circulate inside the graphene aerogel conveniently, the utilization rate of internal pores is guaranteed, dead lithium sites which are difficult to release after lithium intercalation are reduced, and the first charge and discharge efficiency and the cycle performance of the anode material are improved.
3. Preparing a silicon-carbon anode material: and (3) placing the blocky graphene aerogel in the obtained reaction kettle into a carbonization furnace, heating for 3 hours at 800 ℃ in a nitrogen atmosphere, cooling, and transferring into the MOCVD furnace. Argon is firstly introduced into the furnace to purify the cavity, silane gas is introduced after 5min, the temperature is 500 ℃, and the reaction time is 2h. The silane is ensured to be fully deposited in the internal pores of the graphene aerogel after being cracked, and the deposited silicon grains are 45% of the mass of the graphene aerogel. The obtained material is crushed, and then crushed products with the particle size of 5-12 mu m are obtained by classification. And then placing the product into a CVD rotary furnace, firstly introducing argon to purify the cavity, and then introducing methane gas after 5min, wherein the temperature is 600 ℃, and the reaction time is 2h, so that the surface defects and the internal uncovered pores of the graphene aerogel are ensured to be repaired or coated by an amorphous carbon layer, the embedded silicon crystal grains are not directly contacted with electrolyte in the charging and discharging process, the generation of an SEI film is reduced, and the consumption of irreversible lithium is also reduced. And (3) sieving the pyrolyzed product with a 2-channel 300-mesh sieve to obtain the product.
Example 2
The preparation method of the porous carbon aerogel silicon-carbon anode material comprises the following specific steps:
1. melamine preparation melamine resin (melamine formaldehyde resin) preparation: melamine (4.67 g,2,4, 6-triamino-1, 3, 5-triazine) was mixed with water (30 mL) and heated to 80℃with stirring. With Na 2 CO 3 The pH of the mixture was adjusted to 9. Then 36% formaldehyde CH is added dropwise 2 O aqueous solution 40mL, after 30min of reaction, the solution was allowed to stand for 24 hours to obtain a precipitate, namely melamine resin. Wherein the molar ratio of formaldehyde to melamine is 2.5.
2. Preparing porous carbon: carbonizing melamine resin at 800 ℃ for 1h, and activating with potassium hydroxide at 800 ℃ for 1h in nitrogen atmosphere, wherein the mass ratio of the melamine resin to the potassium hydroxide is 4:1, so as to obtain the porous carbon.
3. Preparing porous carbon aerogel: porous carbon (14 mg) and ethanol (8 mL) were sonicated for 0.5h, then transferred to a 25mL autoclave and stored at 180℃for 16h to give a porous carbon hydrogel. The hydrogel was freeze-dried at-60 ℃ for 24 hours to obtain an aerogel. Through hydrothermal reaction, the porous carbon is interlinked to form a honeycomb network structure, so that silicon crystal grains are deposited conveniently.
4. Preparing a silicon-carbon anode material: and (3) placing the blocky porous carbon aerogel in the obtained reaction kettle into a carbonization furnace, heating for 3 hours at 800 ℃ in a nitrogen atmosphere, cooling, and transferring into the MOCVD furnace. Argon is firstly introduced into the furnace to purify the cavity, silane gas is introduced after 5min, the temperature is 500 ℃, and the reaction time is 2h. Ensures that silane is fully deposited in the pores inside the porous carbon aerogel after being cracked, and the deposited silicon grains are 45% of the mass of the porous carbon aerogel. The obtained material is crushed, and then crushed products with the particle size of 5-12 mu m are obtained by classification. And then placing the product into a CVD rotary furnace, firstly introducing argon to purify the cavity, and then introducing methane gas after 5min at 600 ℃ for 2h.
Compared with example 1, the aerogel constituent material of this example was replaced with porous carbon by graphene oxide. Structurally, graphene aerogel has a denser structure and a richer conductive network, but graphene has soft texture and poor structural stability compared with a porous carbon base. For silicon deposition sites, the graphene deposition sites are mostly on the inner surface of the aerogel honeycomb shape, and the deposition structure is not firm; the porous carbon-based deposition sites are mostly in the pores inside the porous carbon, and the deposition structure is stable.
Example 3
1. Preparation of raw materials: including the preparation of graphene oxide and the preparation of porous carbon. Wherein the preparation of graphene oxide is the same as in example 1, and the preparation of porous carbon is the same as in example 2.
2. Preparing graphene/porous carbon composite aerogel: porous carbon (14 mg) and ethanol (8 mL) were sonicated for 0.5h. 8mL of graphene oxide solution (2 mg/mL) was added. And (3) after ultrasonic treatment is carried out for 1h again, transferring the obtained graphene oxide solution with uniformly dispersed porous carbon into a 25mL high-pressure hydrothermal reaction kettle, and preserving at 180 ℃ for 16h to obtain the graphene/porous carbon composite hydrogel. And freeze-drying the graphene/porous carbon composite hydrogel for 24 hours at the temperature of minus 60 ℃ to obtain the graphene/porous carbon composite aerogel. The preparation process is shown in figure 2.
3. Preparing a silicon-carbon anode material: and (3) placing the graphene/porous carbon composite aerogel glue into a carbonization furnace, heating for 3 hours at 800 ℃ in a nitrogen atmosphere, cooling, and transferring into the MOCVD furnace. Argon is firstly introduced into the furnace to purify the cavity, silane gas is introduced after 5min, the temperature is 500 ℃, and the reaction time is 2h. The silane is ensured to be fully deposited in the inner pores of the graphene/porous carbon composite aerogel after being cracked, and the deposited silicon grains are 45% of the mass of the graphene/porous carbon composite aerogel. The obtained material is crushed, and then crushed products with the particle size of 5-12 mu m are obtained by classification. And then placing the product into a CVD rotary furnace, introducing argon to purify the cavity, introducing methane gas after 5min, and reacting for 2h at 600 ℃ to obtain the silicon-carbon anode material, as shown in figure 3.
Compared with the embodiment 1 and the embodiment 2, the self-assembled arrangement of the graphene sheets and the porous carbon in the hydrothermal reaction forms the composite material taking the graphene as the substrate porous carbon as the framework, and compared with the traditional graphene aerogel structure, the structure has the advantages that the porous carbon framework is more than the traditional graphene aerogel structure as the support, the structure is not easy to collapse in the cyclic charge and discharge process, and the cyclic stability of the anode material is improved; meanwhile, compared with the porous carbon aerogel without graphene, the porous carbon aerogel has the advantages that the deposition sites of silane are increased, and meanwhile, the matrix of the graphene aerogel provides rich conductive network structures and ion channels. The ionic conductivity and the electronic conductivity of the cathode are enhanced, and the dynamic performance of the material is enhanced.
Example 4
The preparation method of the silicon-carbon composite anode material comprises the following specific steps:
1. preparation of porous carbon (melamine formaldehyde resin): the same as in example 2.
2. Preparing a silicon-carbon anode material: and (3) placing the porous carbon into a carbonization furnace, heating at 800 ℃ for 3 hours under a nitrogen atmosphere, cooling, and transferring into the MOCVD furnace. Argon is firstly introduced into the furnace to purify the cavity, silane gas is introduced after 5min, the temperature is 500 ℃, and the reaction time is 2h. Ensures that the silane is fully deposited in the pores inside the porous carbon after being cracked, and the deposited silicon grains are 45 percent of the mass of the porous carbon. The obtained material is crushed, and then crushed products with the particle size of 5-12 mu m are obtained by classification. And then placing the product into a CVD rotary furnace, firstly introducing argon to purify the cavity, and then introducing methane gas after 5min at 600 ℃ for 2h.
In comparison with example 2, this example performs a high temperature activation of porous carbon and then a vapor deposition process.
Example 5
The preparation method of the silicon-carbon composite anode material comprises the following specific steps:
1. improved Hummers method for preparing Graphene Oxide (GO): the same as in example 1.
2. Preparing nano silicon dioxide/GO composite aerogel: and mixing the graphene oxide dispersion liquid with nano silicon dioxide (1:1) for ultrasonic treatment for 1h, and then transferring the mixture into a 25mL high-pressure hydrothermal reaction kettle, and preserving heat at 180 ℃ for 16h to obtain the nano silicon dioxide/GO composite hydrogel. And freeze-drying the hydrogel to obtain the aerogel.
3. Preparing a silicon-carbon anode material: the aerogel obtained was carbonized at 800 ℃ for 1h, then activated with 800 ℃ potassium hydroxide for 1h in a nitrogen atmosphere with a mass ratio of 4:1. And then transferred to an MOCVD furnace for magnesian reduction. The adopted magnesium source is magnesium carbonyl, and the deposition temperature is 650 ℃; the content of magnesium obtained by deposition is 40% of the mass of the silica template (calculated according to the feeding amount); calcining the obtained product in argon atmosphere; wherein the calcination temperature is 650 ℃, and the calcination time is 4 hours. Immersing the calcined product in a 2M aqueous sulfuric acid solution, wherein the ratio of the amount of sulfuric acid species in the aqueous sulfuric acid solution to the amount of magnesium species deposited is 2:1; the end point of the acid washing is that the content of magnesium ions in the sulfuric acid aqueous solution is not increased any more. Washing the washed solid product with water until the washing liquid is nearly neutral, and drying. Grinding and crushing the obtained product, and grading to obtain a crushed product with the particle size of 5-12 mu m; mixing the crushed product and medium-temperature asphalt according to a mass ratio of 0.5:10; the temperature of the mixing is higher than the softening point of the medium-temperature asphalt and is about 100 ℃; the mixture was pyrolysed at 600 ℃ for 7h under nitrogen atmosphere, after which it was warmed to 900 ℃ and incubated for 3h. And (3) sieving the pyrolyzed product with a 2-channel 300-mesh sieve to obtain the product.
The silicon anode materials provided in examples 1 to 5 were used to prepare batteries, and the specific steps for preparing batteries were as follows:
mixing and dissolving a silicon negative electrode material, a conductive agent and a binder in a solvent according to a mass ratio of 94:2:4, controlling the solid content to be 50%, coating the mixture on a copper foil current collector, and vacuum drying to prepare a button cell assembled by a negative electrode plate, an electrolyte, an SK diaphragm, a lithium plate and a shell by adopting a conventional production process; wherein, the solvent of the electrolyte is Ethylene Carbonate (EC) and dimethyl carbonate (DMC) and ethylene carbonate (EMC) in the volume ratio of 1:1:1; the solute is LiPF6, and the concentration of the solute is 1mol/L; on the battery test system, the electrical performance of the battery is tested. The test conditions were: at normal temperature, 0.1C constant current charge and discharge, the charge and discharge cut-off voltage is 0.01V-1.5V, and the test results are shown in Table 1.
TABLE 1 Electrical performance test results of batteries prepared using the silicon negative electrode materials prepared in examples 1 to 5
Table 1 shows that:
comparison of examples 1-3 shows that the aerogel form of the silicon carbon negative electrode substrate exhibits higher volume retention and lower volume expansion due to the confinement of the aerogel framework, relieving the strain forces upon full silicon charge. The structure is prevented from being damaged by stress to generate more irregular contact surfaces, higher irreversible lithium consumption is generated, and the battery capacity is reduced.
Comparison of examples 2-4 shows that the silicon-carbon precursor with porous carbon as the substrate shows higher capacity, because the porous carbon-rich pore structure can generate more stable silicon-carbon bonding form, and the graphene planar structure is more, and the bonded silicon-carbon structure is easy to remove in the subsequent treatment process, thus the porous carbon-rich porous silicon-carbon precursor has low initial efficiency and low capacity.
Comparison of example 3 and example 5 shows that silane deposition precursor substrates can improve more capacity performance than directly reducing silicon dioxide in the structure, since the deposited silicon is mostly small particle monocrystalline silicon that can be utilized, while the silicon grains produced by the magnesian reduction process have an oversized grain size or a larger ratio of unreduced silicon.
Comparison of example 2 and example 3 shows that byThe graphene sheet is taken as a substrate, porous carbon is embedded as a silicon-carbon anode material of an aerogel framework, and the graphene sheet has high silicon loading sites (high capacity), and has obvious advantages in full-charge expansion and cyclic capacity retention rate, because the graphene sheet relieves partial volume expansion, meanwhile, aerogel pores between graphene and porous carbon provide more silicon deposition sites, and the sp enrichment of graphene is improved 2 Silicon loading instability caused by planar structures. Meanwhile, the graphene structure layer also builds a rich 3D conductive network, and the rich internal through holes also ensure the stability of silane deposition and the uniformity of the material, thereby indirectly improving the multiplying power and the cycle performance of the material.
The above description is only of the preferred embodiments of the present invention and is not intended to limit the present invention, but various modifications and variations can be made to the present invention by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. The silicon-carbon negative electrode material is characterized in that graphene and porous carbon form aerogel, and an amorphous carbon layer is coated on the surface of the aerogel; in the aerogel, the porous carbon is dispersed among graphene sheets to form a framework, and silicon grains are distributed in the pores of the aerogel; wherein the mass ratio of the graphene to the porous carbon is 1:0.6-1.0.
2. The silicon-carbon negative electrode material according to claim 1, wherein the amorphous carbon layer has a thickness of 200 to 300nm;
or the size of the silicon crystal grain is 2-3 nm;
or the grain diameter of the silicon carbon anode material is 0.8-48 mu m.
3. The silicon-carbon negative electrode material according to claim 1, wherein the silicon crystal grains are 35 to 55% of the mass of the aerogel.
4. A method for preparing a silicon-carbon negative electrode material according to any one of claims 1 to 3, characterized in that porous carbon and graphene oxide are uniformly dispersed in water and/or a polar solvent to obtain a dispersion liquid, the dispersion liquid is treated by a hydrothermal method or a solvothermal method to prepare a composite gel, and the composite gel is subjected to freeze drying to obtain an aerogel precursor; pyrolyzing the aerogel precursor under the condition of inert atmosphere to pyrolyze graphene oxide in the aerogel precursor into graphene, so as to obtain aerogel; depositing a silicon simple substance into pores of the aerogel by adopting a chemical vapor deposition method, and then coating carbon on the aerogel deposited with the silicon simple substance to coat an amorphous carbon layer on the surface of the aerogel; wherein the temperature of the hydrothermal method or solvothermal method treatment is 150-200 ℃, and the pyrolysis temperature is 700-900 ℃.
5. The method for producing a silicon-carbon negative electrode material according to claim 4, wherein the porous carbon is obtained by carbonization and activation of a resin;
preferably, the carbonization temperature is 600-1000 ℃ and the time is 2-4 hours;
preferably, the activating agent used for activation is potassium hydroxide, and the activating temperature is 600-1000 ℃.
6. The method for preparing a silicon-carbon negative electrode material according to claim 4, wherein porous carbon is added into ethanol, uniformly dispersed, added with an aqueous solution of graphene oxide, uniformly dispersed, then added into a high-pressure reactor, sealed, and heated to 150-200 ℃ for reaction;
or the treatment time of the hydrothermal method or the solvothermal method is 15-20 hours;
or pyrolysis time is 2-4 h.
7. The method for preparing a silicon-carbon negative electrode material according to claim 4, wherein the simple substance of silicon is deposited into the pores of the aerogel by adopting metal organic compound chemical vapor deposition; preferably, the silane gas is heated to 450-550 ℃ to carry out cracking reaction, and silicon grains generated by cracking are distributed in the pores of the aerogel; preferably, the time of the cleavage reaction is 1 to 3 hours.
8. The method for preparing a silicon-carbon negative electrode material according to claim 4, wherein the carbon coating is performed by chemical vapor deposition; preferably, the carbon source gas is heated to 550-650 ℃ to carry out decomposition reaction, and amorphous carbon generated by decomposition coats the aerogel deposited with the silicon simple substance; further preferably, the carbon source gas is methane, ethylene, ethane, propane or acetylene; still more preferably, the carbon source gas is methane or ethane;
or, sieving after carbon coating.
9. The negative electrode of the lithium ion battery comprises an active material, a binder, a conductive agent and a current collector, wherein the active material, the binder and the conductive agent form a composite layer, and the composite layer is arranged on the surface of the current collector.
10. A lithium ion battery comprising a positive electrode, a negative electrode, an electrolyte and a separator, wherein the negative electrode is the lithium ion battery negative electrode of claim 9.
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