CN109473664B - Preparation method of silicon-carbon composite material - Google Patents
Preparation method of silicon-carbon composite material Download PDFInfo
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- CN109473664B CN109473664B CN201811402842.4A CN201811402842A CN109473664B CN 109473664 B CN109473664 B CN 109473664B CN 201811402842 A CN201811402842 A CN 201811402842A CN 109473664 B CN109473664 B CN 109473664B
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- 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
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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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- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Abstract
The invention provides a preparation method of a silicon-carbon composite material, which relates to the field of new energy batteries and comprises the following steps: s1) adding a silane coupling agent into the nano-silicon dispersion liquid for reaction, then adding graphene oxide for reaction, finally adding a dispersing agent, and uniformly mixing to obtain a dispersion liquid of graphene oxide coated nano-silicon; s2) spraying the dispersion liquid of the graphene oxide coated nano silicon obtained in the step S1) into mixed powder of graphite and asphalt I for shearing granulation under the shearing and stirring state to obtain precursor particles; wherein the mass ratio of the graphite to the asphalt I to the nano silicon is 1 (0.03-0.1) to 0.05-0.2; s3) drying the precursor particles obtained in the step S2), and then sintering to reduce the graphene oxide in the precursor particles into graphene, so as to obtain the silicon-carbon composite material.
Description
Technical Field
The invention relates to the field of new energy batteries, in particular to a preparation method of a silicon-carbon composite material.
Background
Lithium ion batteries have been widely used in the fields of portable consumer electronics, electric tools, medical electronics, and the like because of their advantages of high energy density, long cycle life, no memory effect, low self-discharge efficiency, wide working temperature range, and the like, and have also shown good application prospects in the fields of pure electric vehicles, hybrid electric vehicles, and energy storage.
However, in recent years, the demand for energy density of batteries has rapidly increased in various fields, and lithium ion batteries having higher energy density are urgently required to be developed. Silicon is of interest because it can form a binary alloy with lithium and has a theoretical capacity of approximately 4200 mAh/g. In addition, silicon also has a low lithium-releasing and-inserting voltage platform, low reaction activity with electrolyte and abundant reserves in the earth crust, and is a lithium battery cathode material with great prospect. However, silicon has fatal defects as a lithium battery cathode material, and the expansion caused by lithium ions inserted into crystal lattices in the silicon crystal during charging can reach 300%, so that the SEI film is easily repeatedly damaged and reconstructed due to the huge volume effect, the consumption of the lithium ions is increased, the capacity of the battery is rapidly attenuated, and the service life of the battery is influenced. In order to improve the defect and improve the stability of the silicon negative electrode in the circulating process, carbon coating the silicon material is a common method for improving the expansion of the silicon material.
The graphene serving as a novel material has excellent mechanical property and electrical property, and the graphene is used for coating the nano silicon, so that the expansion of the nano silicon can be inhibited, and the conductivity of the nano silicon can be increased. Patent CN103050666B discloses a preparation method of a graphene-coated silicon-carbon composite negative electrode material, which comprises the steps of adding nano-silicon and graphite micropowder into graphene oxide dispersion to prepare a suspension, then carrying out spray drying and pelletizing on the suspension to obtain a spherical precursor, and finally carrying out heat treatment on the precursor under a protective atmosphere to obtain the silicon-carbon composite negative electrode material. Only simple physical mixing and spray drying granulation are carried out on nano silicon, graphite and graphene oxide in the patent, the binding force between graphite and graphene-coated nano silicon powder particles and between graphene and nano silicon powder in the obtained silicon-carbon composite negative electrode material is poor, and cracking easily occurs in the use process, so that the cycle life of the battery is influenced.
Disclosure of Invention
The invention aims to provide a preparation method of a silicon-carbon composite material, which is used for relieving the technical problems that the bonding force between graphite and graphene-coated nano silicon particles and between graphene and nano silicon in the silicon-carbon composite material obtained by the existing preparation method is poor, and cracking is easy to occur in the using process.
In order to achieve the above purpose of the present invention, the following technical solutions are adopted:
a preparation method of a silicon-carbon composite material comprises the following steps:
s1) adding a silane coupling agent into the nano-silicon dispersion liquid for reaction, adding graphene oxide for reaction, adding a dispersing agent, and uniformly mixing to obtain a dispersion liquid of graphene oxide coated nano-silicon;
s2) spraying the dispersion liquid of the graphene oxide coated nano silicon obtained in the step S1) into mixed powder of graphite and asphalt I for shearing granulation under the shearing and stirring state to obtain precursor particles;
wherein the mass ratio of the graphite to the asphalt I to the nano silicon is 1 (0.03-0.1) to 0.05-0.2;
s3) drying the precursor particles obtained in the step S2), and then sintering to reduce the graphene oxide in the precursor particles into graphene, so as to obtain the silicon-carbon composite material.
Compared with the prior art, the invention has the following beneficial effects:
according to the preparation method of the silicon-carbon composite material, firstly, graphene oxide and nano-silicon are connected through a silane coupling agent, then, nano-silicon coated by the graphene oxide is uniformly dispersed into graphite through shearing granulation to prepare precursor particles, and then, the graphene oxide is reduced into graphene through a sintering process, so that the silicon-carbon composite material is obtained. Firstly, bonding nano silicon and graphene oxide together by using a silane coupling agent so as to enable the graphene oxide to be tightly coated on the surface of the nano silicon; and then directly spraying the prepared graphene oxide coated nano-silicon dispersion liquid into graphite powder through shearing granulation, achieving the purposes of uniform dispersion and kneading through shearing and stirring, and preparing precursor particles with required particle size through the cutting action of a shearing knife. In the dispersion liquid, as the silane coupling agent is used, the silane coupling agent can improve the binding force between the graphene oxide and the nano silicon and can effectively inhibit the separation of the graphene oxide and the nano silicon; in the shearing granulation, asphalt is added into graphite powder as a binder, the asphalt has good bonding effect and good compatibility with graphite, and in the granulation process, a proper amount of asphalt is added into the graphite powder to increase the bonding strength between graphite particles in precursor particles and graphene oxide coated nano silicon particles. Therefore, the raw materials and the process are organically combined, so that the prepared silicon-carbon composite material has high binding force between the graphite and the graphene-coated nano silicon particles and between the graphene and the nano silicon, and cracking between the graphite and the graphene-coated nano silicon particles and between the graphene and the nano silicon is effectively prevented.
The silicon-carbon composite material prepared by the preparation method provided by the invention has higher binding force between graphite in particles and graphene-coated nano silicon particles, and is not easy to crack and damage in use. The verification proves that the silicon-carbon composite material prepared by the preparation method provided by the invention has higher primary efficiency and better cycle stability, and the primary efficiency can be improved by more than 5%.
Detailed Description
Embodiments of the present invention will be described in detail below with reference to examples, but it will be understood by those skilled in the art that the following examples are only illustrative of the present invention and should not be construed as limiting the scope of the present invention. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.
In one aspect, the invention provides a preparation method of a silicon-carbon composite material, which comprises the following steps:
s1) adding a silane coupling agent into the nano-silicon dispersion liquid for reaction, adding graphene oxide for reaction, adding a dispersing agent, and uniformly mixing to obtain a dispersion liquid of graphene oxide coated nano-silicon;
s2) spraying the dispersion liquid of the graphene oxide coated nano silicon obtained in the step S1) into mixed powder of graphite and asphalt I for shearing granulation under the shearing and stirring state to obtain precursor particles;
wherein the mass ratio of the graphite to the asphalt I to the nano silicon is 1 (0.03-0.1) to 0.05-0.2;
s3) drying the precursor particles obtained in the step S2), and then sintering to reduce the graphene oxide in the precursor particles into graphene, so as to obtain the silicon-carbon composite material.
According to the preparation method of the silicon-carbon composite material, firstly, graphene oxide and nano-silicon are connected through a silane coupling agent, then, nano-silicon coated by the graphene oxide is uniformly dispersed into graphite through shearing granulation to prepare precursor particles, and then, the graphene oxide is reduced into graphene through a sintering process, so that the silicon-carbon composite material is obtained. Firstly, bonding nano silicon and graphene oxide together by using a silane coupling agent so as to enable the graphene oxide to be tightly coated on the surface of the nano silicon; and then directly spraying the prepared graphene oxide coated nano-silicon dispersion liquid into graphite powder through shearing granulation, achieving the purposes of uniform dispersion and kneading through shearing and stirring, and preparing precursor particles with required particle size through the cutting action of a shearing knife. In the dispersion liquid, as the silane coupling agent is used, the silane coupling agent can improve the binding force between the graphene oxide and the nano silicon and can effectively inhibit the separation of the graphene oxide and the nano silicon; in the shearing granulation, asphalt is added into graphite powder as a binder, the asphalt has good bonding effect and good compatibility with graphite, and in the granulation process, a proper amount of asphalt is added into the graphite powder to increase the bonding strength between graphite particles in precursor particles and graphene oxide coated nano silicon particles. Therefore, the raw materials and the process are organically combined, so that the prepared silicon-carbon composite material has high binding force between the graphite and the graphene-coated nano silicon particles and between the graphene and the nano silicon, and cracking between the graphite and the graphene-coated nano silicon particles and between the graphene and the nano silicon is effectively prevented.
The pitch I can form a carbon material after sintering, and is used for bonding graphite and graphene-coated nano silicon particles and improving the bonding force of the graphite and the graphene.
The silicon-carbon composite material prepared by the preparation method provided by the invention has higher binding force between graphite in particles and graphene-coated nano silicon particles, and is not easy to crack and damage in use. The verification proves that the silicon-carbon composite material prepared by the preparation method provided by the invention has higher primary efficiency and better cycle stability, and the primary efficiency can be improved by more than 5%.
In the preparation method, the silane coupling agent is added into the graphene oxide and the silicon powder because molecules of the silane coupling agent contain two different reactive groups, and then the dispersing agent is added to form a connecting structure of inorganic phase-silane coupling agent-organic phase. The chemical structure of the silane coupling agent can be Y-R-SiX3And (4) showing. In the formula XDifferent from Y in reaction characteristics, X is a group which can be hydrolyzed to generate silicon hydroxyl (Si-OH), such as alkoxy, acetoxyl, halogen and the like, and X has the capacity of bonding with glass, silicon dioxide, pottery clay and some metals such as aluminum, iron and the like; y is an organic group that can react with the polymer to increase the reactivity and compatibility of the silane with the polymer, such as vinyl, amino, epoxy, and the like; r is a carbon chain with a saturated bond or an unsaturated bond, so that the epoxy resin can be used as a molecular bridge for connecting an inorganic material and an organic material, and the two materials with different properties are connected to form an inorganic phase-silane coupling agent-organic phase combined layer.
In the present invention, the solvent in the nano-silicon dispersion may be, for example, water and ethanol. The silane coupling agent may be, for example, an aminosilane coupling agent or an epoxysilane coupling agent, and further, may be, for example, γ -aminopropyltriethoxysilane, γ -aminopropyltrimethoxysilane, γ -aminopropylmethyldiethoxysilane, γ -glycidoxypropyltrimethoxysilane, γ -glycidoxypropyltriethoxysilane, or γ -glycidoxypropylmethyldiethoxysilane.
And (3) shearing and granulating, wherein the preparation process comprises the steps of spraying a binder into dry powder, uniformly mixing the binder and the dry powder into a cluster by continuously stirring, and crushing into small particles by a shearing knife. Compared with spray drying granulation, the shearing granulation has the advantages of short time, high efficiency, higher compactness of the prepared granules and higher binding force among different materials due to the use of the binder.
In addition, the dispersing agent is used, so that the nano silicon can be dispersed more uniformly, the dispersing agent also plays a role of a binder, graphite particles and the nano silicon coated with graphene are bonded together to form a composite material in subsequent shearing granulation, the binding force between the carbon material and the nano silicon is increased, the dispersing agent is changed into hard carbon after high-temperature carbonization, and the dispersing agent also plays a role in buffering the expansion of silicon.
The dispersant may be, for example, polyvinyl alcohol, polyvinyl pyrrolidone, carboxymethyl cellulose, or the like.
In some embodiments of the invention, in step S1), adding the nano-silicon into the piranha washing solution, reacting at room temperature for 2-24 h, and performing pretreatment to make the surface of the nano-silicon particles have hydroxyl functional groups, and then preparing a nano-silicon dispersion solution; wherein the mass ratio of the nano silicon to the piranha washing liquid is 1 (1-20).
The piranha washing liquid is piranha solution, also called piranha etching liquid, and is a mixture of concentrated sulfuric acid and hydrogen peroxide solution, the volume ratio is 7: 3-3: 1, the mass concentration of the concentrated sulfuric acid is 95-98%, and the mass concentration of the hydrogen peroxide solution is 25-35%. The room temperature may be, for example, 10 to 35 ℃.
After the nano silicon is pretreated by the piranha washing liquid, the surface of the nano silicon is provided with a large number of hydroxyl functional groups, and the graphene oxide sheet layer also contains a plurality of groups with chemical reaction activity, such as carboxyl, epoxy or hydroxyl, so that after the nano silicon is pretreated, the nano silicon is easily combined with the graphene oxide, and the binding force between the nano silicon and the graphene oxide is improved. Wherein, the mass ratio of the nano silicon to the piranha washing liquid can be 1:1, 1:2, 1:4, 1:6, 1:8, 1:10, 1:12, 1:14, 1:16, 1:18 or 1: 20.
In some embodiments of the present invention, in step S1), the mass fraction of the nano silicon in the nano silicon dispersion is 10% to 50%. By optimizing the mass fraction of the nano-silicon dispersion liquid, the stably dispersed graphene oxide coated nano-silicon dispersion liquid can be obtained after the silane coupling agent, the graphene oxide and the dispersing agent are added, and the particles are prevented from being agglomerated and settled. The mass fraction of the nano-silicon dispersion may be, for example, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or 50%.
In some embodiments of the invention, in the step S1), the mass ratio of the nano-silicon, the silane coupling agent, the graphene oxide and the dispersing agent is 1 (0.01-0.05): (0.003-0.05): 0.1-1). By optimizing the mass ratio of the nano-silicon to the silane coupling agent to the graphene oxide to the dispersing agent, the uniformity of the coating of the graphene oxide on the nano-silicon can be further improved.
In some embodiments of the present invention, in step S1), the reaction conditions for adding the silane coupling agent to perform the reaction are as follows: the reaction temperature is 20-60 ℃, and the reaction time is 2-24 h; further, the reaction conditions for adding the graphene oxide to carry out the reaction are as follows: the reaction temperature is 20-60 ℃, and the reaction time is 2-24 h. By controlling the reaction temperature and the reaction time, the silane coupling agent can be fully reacted with the nano silicon and the graphene oxide respectively to generate bonding.
In some embodiments of the present invention, in step S2), graphite having a particle size of 0.5 to 5 μm and asphalt i having a particle size of 0.5 to 3 μm are mixed to obtain a mixed powder of graphite and asphalt. By limiting the particle sizes of the graphite and the asphalt, the shearing granulation uniformity can be improved, the subsequent secondary granulation operation is facilitated, and the granulation cost is reduced.
In some embodiments of the present invention, in step S2), the softening point of asphalt I is 150-260 ℃. The asphalt with the softening point has relatively small molecular weight and better wettability with graphite, is easier to adhere with graphite and graphene oxide, and granules formed after shearing granulation are not easy to damage, and have smaller specific surface area and better binding power after carbonization. The softening point of the pitch used in the process may be, for example, 150 ℃, 170 ℃, 200 ℃, 220 ℃, 240 ℃ or 260 ℃.
In some embodiments of the invention, in the step S2), the shearing speed during the shearing granulation is 2000 to 3000r/min, and the stirring speed is 150 to 950 r/min. Furthermore, the particle size of the precursor particles obtained in the shearing granulation is 50-500 μm.
In the granulation process, the stirring function is to uniformly mix the powder and the sprayed dispersion liquid and knead the mixture into a mass, and the shearing function is to cut the large mass into small particles. Too fast stirring speed can cause the powder to gather on the equipment inner wall, and too slow stirring can make the intensity of kneading not enough, causes the later stage secondary particle adhesive strength not enough. The rotating speed of the shearing has an important influence on the size of the finally obtained particles, the particles obtained at high rotating speed are smaller, and the particles obtained at low rotating speed are larger. Therefore, the stirring speed and the shearing speed are strictly controlled, so that precursor particles with high strength and small size can be obtained.
In some embodiments of the invention, in the step S3), the drying is vacuum freeze-drying, and further, the drying temperature of the vacuum freeze-drying is-30 to 0 ℃.
And (3) the precursor particles obtained after shearing and granulation are wet particles, and the wet particles are subjected to vacuum freeze drying, wherein the freeze drying belongs to low-temperature drying, the temperature is below 0 ℃, and compared with spray drying at a high temperature of more than 200 ℃, the nano silicon can be effectively prevented from being oxidized in a high-temperature environment, so that the specific capacity of the silicon-carbon composite material is improved.
In some embodiments of the invention, in the step S3), the temperature during the sintering process is 800 to 1300 ℃ for 1 to 4 hours. By optimizing the sintering temperature, the graphene oxide can be fully reduced into graphene, so that the expansion of nano silicon is effectively inhibited, and the conductivity of the silicon-carbon composite material is improved.
In some embodiments of the invention, in the step S3), the graphene-coated nano-silicon-carbon composite material with a particle size of 8 to 25 μm is obtained by crushing after sintering. By optimizing the particle size of the silicon-carbon composite material with the nano-silicon coated by the graphene, the specific surface area of the material can be increased, and the subsequent processing and use are facilitated.
In some embodiments of the invention, the silicon-carbon composite material obtained in step S3) is coated with pitch ii, and then calcined at 900-1200 ℃ for 1-6 hours, so as to complete surface repair of the silicon-carbon composite material; further, the softening point of the asphalt II is 260-320 ℃.
Coating the silicon-carbon composite material obtained in the step S3) with asphalt II and calcining, wherein a carbon coating layer can be formed on the surface of graphene by selecting asphalt with a softening point of 260-320 ℃ to reduce surface defects formed in the previous step; meanwhile, the coating layer obtained by coating and calcining the asphalt is soft carbon, has better affinity to electrolyte and can improve the first efficiency of the battery.
In some embodiments of the invention, the mass ratio of the silicon-carbon composite material to the asphalt II is 1 (0.03-0.15). By optimizing the mass ratio between the silicon-carbon composite material and the electrolyte, the uniformity of asphalt coating can be improved, the thickness of the coating layer can be effectively controlled, and the affinity between the silicon-carbon composite material and the electrolyte can be effectively improved while the surface defect of the graphene coating layer is repaired.
In some embodiments of the present invention, a method of preparing a silicon carbon composite material comprises the steps of:
s1) adding nano silicon into the piranha washing liquid to react for 2-24 h for pretreatment, wherein the mass ratio of the nano silicon to the piranha washing liquid is 1 (1-20); preparing the pretreated nano silicon into a dispersion liquid with the solid content of 10-50%, adding a silane coupling agent, and stirring and reacting for 2-24 hours at the temperature of 20-60 ℃; after the reaction is finished, adding graphene oxide, and continuously stirring and reacting for 2-24 hours at the temperature of 20-60 ℃; after the reaction is finished, adding a dispersing agent, and uniformly stirring to prepare a dispersion liquid of graphene oxide coated nano silicon;
s2) uniformly mixing graphite with the particle size of 0.5-5 microns and asphalt I with the particle size of 0.5-3 microns according to the mass ratio of 1 (0.03-0.1), and adding into a high-shear granulator; meanwhile, spraying the dispersion liquid of the graphene oxide coated nano silicon obtained in the step S1) into a high-shear granulator for shearing granulation to obtain precursor particles;
wherein the mass ratio of the graphite to the nano silicon is 1 (0.05-0.2); the shearing speed is 2000-3000 r/min, and the stirring speed is 150-950 r/min; the softening point of the asphalt I is 150-260 ℃;
s3), carrying out vacuum freeze drying treatment on the precursor particles obtained in the step B) at-30-0 ℃, sintering for 1-4 h at 800-1300 ℃ after completely drying, and crushing to obtain a silicon-carbon composite material with the particle size of 8-25 mu m;
s4) coating the silicon-carbon composite material obtained in the step S3) with asphalt II with the softening point of 260-320 ℃, and then calcining for 1-6 hours at 900-1200 ℃ in a protective atmosphere to complete surface repair of the silicon-carbon composite material;
wherein the mass ratio of the silicon-carbon composite material to the asphalt II is 1 (0.03-0.15).
In the preparation method provided by the embodiment, the graphene oxide is tightly coated on the surface of the nano silicon by using the silane coupling agent, so that the connection and dispersion effects of the nano silicon and the graphene oxide are enhanced; then, uniformly dispersing the graphene oxide coated nano silicon into graphite through high-shear granulation to prepare precursor particles compounded by the graphene oxide coated nano silicon and the graphite; and then the carbon/graphene-coated nano-silicon-carbon composite material is prepared through the steps of vacuum freeze drying, heat treatment, crushing, coating and the like. In the silicon-carbon composite material, the bonding force among substances is stronger, so that the structural stability of the material is stronger in the use process, and the acting force generated by the volume expansion of silicon can be resisted. Meanwhile, the volume expansion of silicon is greatly inhibited due to the coating of the graphene, the stability of the silicon is enhanced, and meanwhile, the conductivity of the silicon is greatly improved, so that the material has higher capacity and good cycle stability.
Example 1
The embodiment is a preparation method of a silicon-carbon composite material, which comprises the following steps:
s1) adding a silane coupling agent into the nano-silicon dispersion liquid with the solid content of 30%, and stirring and reacting for 10h at the temperature of 50 ℃; after the reaction is finished, adding graphene oxide, and continuously stirring and reacting for 14 hours at the temperature of 50 ℃; after the reaction is finished, adding a dispersing agent, and uniformly stirring to prepare a dispersion liquid of graphene oxide coated nano silicon;
s2) uniformly mixing graphite with the particle size of 0.5-5 microns and asphalt I with the particle size of 0.5-3 microns according to the mass ratio of 1:0.08, and adding into a high-shear granulator; meanwhile, spraying the dispersion liquid of the graphene oxide coated nano silicon obtained in the step S1) into a high-shear granulator for shearing granulation to obtain precursor particles;
wherein the mass ratio of the graphite to the nano silicon is 1: 0.1; the shearing speed is 2500r/min, and the stirring speed is 700 r/min; the softening point of the asphalt I is 220 ℃;
s3), carrying out vacuum freeze drying treatment on the precursor particles obtained in the step B) at-5 ℃, sintering for 2h at 1100 ℃ after complete drying, and crushing to obtain a silicon-carbon composite material with the particle size of 8-25 mu m;
s4) coating the silicon-carbon composite material obtained in the step S3) with asphalt II with the softening point of 300 ℃, and then calcining for 3 hours at 1100 ℃ in a protective atmosphere to finish surface repair of the silicon-carbon composite material;
wherein the mass ratio of the silicon-carbon composite material to the asphalt II is 1: 0.1.
Example 2
The embodiment is a preparation method of a silicon-carbon composite material, which comprises the following steps:
s1) adding nano silicon into the piranha washing liquid to react for 10h for pretreatment, wherein the mass ratio of the nano silicon to the piranha washing liquid is 1: 10; preparing the pretreated nano silicon into a dispersion liquid with the solid content of 30%, adding a silane coupling agent, and stirring and reacting for 10 hours at the temperature of 50 ℃; after the reaction is finished, adding graphene oxide, and continuously stirring and reacting for 14 hours at the temperature of 50 ℃; after the reaction is finished, adding a dispersing agent, and uniformly stirring to prepare a dispersion liquid of graphene oxide coated nano silicon;
s2) uniformly mixing graphite with the particle size of 0.5-5 microns and asphalt I with the particle size of 0.5-3 microns according to the mass ratio of 1:0.08, and adding into a high-shear granulator; meanwhile, spraying the dispersion liquid of the graphene oxide coated nano silicon obtained in the step S1) into a high-shear granulator for shearing granulation to obtain precursor particles;
wherein the mass ratio of the graphite to the nano silicon is 1: 0.1; the shearing speed is 2500r/min, and the stirring speed is 700 r/min; the softening point of the asphalt I is 220 ℃;
s3), carrying out vacuum freeze drying treatment on the precursor particles obtained in the step B) at-30-0 ℃, sintering for 2h at 1100 ℃ after complete drying, and crushing to obtain the silicon-carbon composite material with the particle size of 8-25 mu m.
Example 3
The embodiment is a preparation method of a silicon-carbon composite material, which comprises the following steps:
s1) adding nano silicon into the piranha washing liquid to react for 10h for pretreatment, wherein the mass ratio of the nano silicon to the piranha washing liquid is 1: 10; preparing the pretreated nano silicon into a dispersion liquid with the solid content of 30%, adding a silane coupling agent, and stirring and reacting for 10 hours at the temperature of 50 ℃; after the reaction is finished, adding graphene oxide, and continuously stirring and reacting for 14 hours at the temperature of 50 ℃; after the reaction is finished, adding a dispersing agent, and uniformly stirring to prepare a dispersion liquid of graphene oxide coated nano silicon;
s2) uniformly mixing graphite with the particle size of 0.5-5 microns and asphalt I with the particle size of 0.5-3 microns according to the mass ratio of 1:0.08, and adding into a high-shear granulator; meanwhile, spraying the dispersion liquid of the graphene oxide coated nano silicon obtained in the step S1) into a high-shear granulator for shearing granulation to obtain precursor particles;
wherein the mass ratio of the graphite to the nano silicon is 1: 0.1; the shearing speed is 2500r/min, and the stirring speed is 700 r/min; the softening point of the asphalt I is 220 ℃;
s3), carrying out vacuum freeze drying treatment on the precursor particles obtained in the step B) at-30-0 ℃, sintering for 2h at 1100 ℃ after complete drying, and crushing to obtain a silicon-carbon composite material with the particle size of 8-25 mu m;
s4) coating the silicon-carbon composite material obtained in the step S3) with asphalt II with the softening point of 300 ℃, and then calcining for 3 hours at 1100 ℃ in a protective atmosphere to finish surface repair of the silicon-carbon composite material;
wherein the mass ratio of the silicon-carbon composite material to the asphalt II is 1: 0.1.
Example 4
The embodiment is a preparation method of a silicon-carbon composite material, which comprises the following steps:
s1) adding nano silicon into the piranha washing liquid to react for 5h for pretreatment, wherein the mass ratio of the nano silicon to the piranha washing liquid is 1: 3; preparing the pretreated nano silicon into a dispersion liquid with the solid content of 20%, adding a silane coupling agent, and stirring and reacting for 20 hours at the temperature of 20 ℃; after the reaction is finished, adding graphene oxide, and continuously stirring and reacting for 24 hours at the temperature of 20 ℃; after the reaction is finished, adding a dispersing agent, and uniformly stirring to prepare a dispersion liquid of graphene oxide coated nano silicon;
s2) uniformly mixing graphite with the particle size of 0.5-5 microns and asphalt I with the particle size of 0.5-3 microns according to the mass ratio of 1:0.03, and adding into a high-shear granulator; meanwhile, spraying the dispersion liquid of the graphene oxide coated nano silicon obtained in the step S1) into a high-shear granulator for shearing granulation to obtain precursor particles;
wherein the mass ratio of the graphite to the nano silicon is 1: 0.05; the shearing speed is 2000r/min, and the stirring speed is 300 r/min; the softening point of the asphalt I is 180 ℃;
s3), carrying out vacuum freeze drying treatment on the precursor particles obtained in the step B) at-20 ℃, sintering for 3h at 1000 ℃ after complete drying, and crushing to obtain a silicon-carbon composite material with the particle size of 8-25 mu m;
s4) coating the silicon-carbon composite material obtained in the step S3) with asphalt II with the softening point of 280 ℃, and then calcining for 6 hours at 900 ℃ under the protective atmosphere to finish surface repair of the silicon-carbon composite material;
wherein the mass ratio of the silicon-carbon composite material to the asphalt II is 1: 0.03.
Example 5
The embodiment is a preparation method of a silicon-carbon composite material, which comprises the following steps:
s1) adding nano silicon into the piranha washing liquid to react for 20h for pretreatment, wherein the mass ratio of the nano silicon to the piranha washing liquid is 1: 20; preparing the pretreated nano silicon into dispersion liquid with the solid content of 10%, adding a silane coupling agent, and stirring and reacting for 5 hours at the temperature of 60 ℃; after the reaction is finished, adding graphene oxide, and continuously stirring and reacting for 4 hours at the temperature of 60 ℃; after the reaction is finished, adding a dispersing agent, and uniformly stirring to prepare a dispersion liquid of graphene oxide coated nano silicon;
s2) uniformly mixing graphite with the particle size of 0.5-5 microns and asphalt I with the particle size of 0.5-3 microns according to the mass ratio of 1:0.1, and adding into a high-shear granulator; meanwhile, spraying the dispersion liquid of the graphene oxide coated nano silicon obtained in the step S1) into a high-shear granulator for shearing granulation to obtain precursor particles;
wherein the mass ratio of the graphite to the nano silicon is 1: 0.2; the shearing speed is 3000r/min, and the stirring speed is 950 r/min; the softening point of the asphalt I is 250 ℃;
s3), carrying out vacuum freeze drying treatment on the precursor particles obtained in the step B) at-5 ℃, sintering for 1h at 1300 ℃ after complete drying, and crushing to obtain a silicon-carbon composite material with the particle size of 8-25 mu m;
s4) coating the silicon-carbon composite material obtained in the step S3) with asphalt II with the softening point of 320 ℃, and then calcining for 2 hours at 1200 ℃ in a protective atmosphere to finish surface repair of the silicon-carbon composite material;
wherein the mass ratio of the silicon-carbon composite material to the asphalt II is 1: 0.15.
Comparative example 1
The comparative example is a preparation method of a silicon-carbon composite material, and comprises the following steps:
preparing a graphene oxide dispersion liquid with a certain concentration by adopting a Hummer method, adjusting the concentration of the graphene oxide dispersion liquid to be 1mg/ml, simultaneously adding graphite micro powder (D50: 0.5 mu m) and nano silicon (D50: 50nm) into the dispersion liquid, wherein the mass ratio of the graphite micro powder to the nano silicon is 9: 1, simultaneously adding a dispersant polyethylene glycol 200 (the addition amount is 1 wt% of the total mass of the nano silicon/graphite micropowder), and controlling the mass ratio of graphene oxide to the nano silicon to the graphite micropowder to be 1:20, dispersing for 1 hour by ultrasonic and mechanical stirring to obtain uniformly dispersed suspension, and spray drying the suspension at 170-200 ℃ to obtain a composite material precursor; and transferring the obtained powder into an argon atmosphere, carrying out constant temperature treatment at 500 ℃ for 2h, and cooling along with the furnace to obtain the silicon-carbon composite negative electrode material.
Comparative example 2
The comparative example is a preparation method of a silicon-carbon composite material, and comprises the following steps:
s1) adding nano silicon into the piranha washing liquid to react for 10h for pretreatment, wherein the mass ratio of the nano silicon to the piranha washing liquid is 1: 10; preparing the pretreated nano silicon into a dispersion liquid with the solid content of 30%, adding a silane coupling agent, and stirring and reacting for 10 hours at the temperature of 50 ℃; after the reaction is finished, adding graphene oxide, and continuously stirring and reacting for 14 hours at the temperature of 50 ℃; after the reaction is finished, adding a dispersing agent, and uniformly stirring to prepare a dispersion liquid of graphene oxide coated nano silicon;
s2) uniformly mixing graphite with the particle size of 0.5-5 microns and asphalt with the particle size of 0.5-3 microns according to the mass ratio of 1:0.08, then uniformly mixing the graphite with the dispersion liquid of the graphene oxide coated nano silicon obtained in the step S1) to obtain a suspension, and performing spray drying on the suspension at 170-200 ℃ to obtain a composite material precursor;
wherein the mass ratio of the graphite to the nano silicon is 1: 0.1; the stirring speed is 700 r/min; the softening point of the asphalt is 220 ℃;
s3) sintering at 1100 ℃ for 2h to obtain the silicon-carbon composite material.
Button cells were prepared using the silicon-carbon composites obtained in examples 1-4 and comparative examples 1-2, respectively, and then the first efficiency, the first charge specific capacity, and the charge-discharge cycle stability of each group of cells were tested, and the test results are listed in table 1. The button cell prepared is the same as the button cell except that the silicon-carbon composite material is different, wherein the counter electrode is lithium. Wherein, the charging and discharging current used in the charging and discharging cycle stability test process is 0.1C.
TABLE 1 test results
As can be seen from the data in table 1, when the silicon-carbon negative electrode material provided by the invention is used as an electrode active material, the prepared button cell has high first efficiency and specific capacity and good cycling stability, and particularly, under 0.1C, after 120 charging and discharging cycles, the button cell can still maintain a high capacity retention rate.
As can be seen from a comparison of example 2 and comparative example 2, the capacity retention rate of the battery can be significantly improved also when the mixing manner is shear mixing. It is shown that the mixing mode of the materials also has an important influence on the cycle performance of the silicon-carbon negative electrode material.
While particular embodiments of the present invention have been illustrated and described, it would be obvious that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.
Claims (19)
1. The preparation method of the silicon-carbon composite material is characterized by comprising the following steps:
s1) adding a silane coupling agent into the nano-silicon dispersion liquid for reaction, adding graphene oxide for reaction, adding a dispersing agent, and uniformly mixing to obtain a dispersion liquid of graphene oxide coated nano-silicon;
s2) spraying the dispersion liquid of the graphene oxide coated nano silicon obtained in the step S1) into mixed powder of graphite and asphalt I for shearing granulation under the shearing and stirring state to obtain precursor particles;
wherein the mass ratio of the graphite to the asphalt I to the nano silicon is 1 (0.03-0.1) to 0.05-0.2;
s3) drying the precursor particles obtained in the step S2), and then sintering to reduce the graphene oxide in the precursor particles into graphene, so as to obtain the silicon-carbon composite material.
2. The preparation method according to claim 1, wherein in step S1), the nano-silicon is added into the piranha washing solution to react for 2-24 hours at room temperature, and then the nano-silicon dispersion liquid is prepared after the nano-silicon particles have hydroxyl functional groups on the surfaces; wherein the mass ratio of the nano silicon to the piranha washing liquid is 1 (1-20).
3. The method according to claim 1, wherein in step S1), the nano-silicon dispersion liquid contains 10 to 50% by mass of nano-silicon.
4. The preparation method according to claim 3, wherein in the step S1), the mass ratio of the nano-silicon to the silane coupling agent to the graphene oxide to the dispersing agent is 1 (0.01-0.05) to (0.003-0.05) to (0.1-1).
5. The method according to claim 3, wherein in step S1), the reaction conditions for adding the silane coupling agent are as follows: the reaction temperature is 20-60 ℃, and the reaction time is 2-24 h.
6. The preparation method according to claim 3, wherein in the step S1), the reaction conditions for adding the graphene oxide to perform the reaction are as follows: the reaction temperature is 20-60 ℃, and the reaction time is 2-24 h.
7. The method as claimed in claim 1, wherein in step S2), graphite particles having a particle size of 0.5 to 5 μm and pitch i particles having a particle size of 0.5 to 3 μm are mixed to obtain a mixed powder of graphite particles and pitch i particles.
8. The method according to claim 7, wherein in step S2), the asphalt I has a softening point of 150-260 ℃.
9. The preparation method according to claim 7, wherein in the step S2), the shearing speed in the shearing and granulating process is 2000-3000 r/min, and the stirring speed is 150-950 r/min.
10. The method according to claim 7, wherein in step S2), the precursor particles have a particle size of 50 to 500 μm.
11. The method according to claim 1, wherein the drying in step S3) is vacuum freeze-drying at a temperature of-30 to 0 ℃.
12. The preparation method according to claim 11, wherein in the step S3), the temperature during the sintering process is 800-1300 ℃ and the time is 1-4 h.
13. The preparation method according to claim 11, wherein in the step S3), the graphene-coated nano-silicon-carbon composite material with the particle size of 8-25 μm is obtained by crushing after sintering.
14. The production method according to any one of claims 1 to 10, wherein the silane coupling agent is an aminosilane coupling agent or an epoxysilane coupling agent.
15. The method according to claim 14, wherein the silane coupling agent is γ -aminopropyltriethoxysilane, γ -aminopropyltrimethoxysilane, γ -aminopropylmethyldiethoxysilane, γ -glycidoxypropyltrimethoxysilane, γ -glycidoxypropyltriethoxysilane, or γ -glycidoxypropylmethyldiethoxysilane.
16. The preparation method of any one of claims 1 to 10, wherein the silicon-carbon composite material obtained in step S3) is coated with pitch ii, and then calcined at 900 to 1200 ℃ for 1 to 6 hours to complete surface repair of the silicon-carbon composite material.
17. The preparation method of the silicon-carbon composite material as claimed in claim 16, wherein the mass ratio of the silicon-carbon composite material to the asphalt II is 1 (0.03-0.15).
18. The process according to claim 17, wherein the asphalt II has a softening point of 260 to 320 ℃.
19. The method for preparing a silicon-carbon composite material according to claim 1, comprising the steps of:
s1) adding nano silicon into the piranha washing liquid to react for 2-24 h for pretreatment, wherein the mass ratio of the nano silicon to the piranha washing liquid is 1 (1-20); preparing the pretreated nano silicon into a dispersion liquid with the solid content of 10-50%, adding a silane coupling agent, and stirring and reacting for 2-24 hours at the temperature of 20-60 ℃; after the reaction is finished, adding graphene oxide, and continuously stirring and reacting for 2-24 hours at the temperature of 20-60 ℃; after the reaction is finished, adding a dispersing agent, and uniformly stirring to prepare a dispersion liquid of graphene oxide coated nano silicon;
s2) uniformly mixing graphite with the particle size of 0.5-5 microns and asphalt I with the particle size of 0.5-3 microns according to the mass ratio of 1 (0.03-0.1), and adding into a high-shear granulator; meanwhile, spraying the dispersion liquid of the graphene oxide coated nano silicon obtained in the step S1) into a high-shear granulator for shearing granulation to obtain precursor particles;
wherein the mass ratio of the graphite to the nano silicon is 1 (0.05-0.2); the shearing speed is 2000-3000 r/min, and the stirring speed is 150-950 r/min; the softening point of the asphalt I is 150-260 ℃;
s3), carrying out vacuum freeze drying treatment on the precursor particles obtained in the step B) at-30-0 ℃, sintering for 1-4 h at 800-1300 ℃ after completely drying, and crushing to obtain a silicon-carbon composite material with the particle size of 8-25 mu m;
s4) coating the graphene-coated silicon-carbon composite material obtained in the step S3) with asphalt II with the softening point of 260-320 ℃, and then calcining for 1-6 h at 900-1200 ℃ in a protective atmosphere to complete surface repair of the silicon-carbon composite material;
wherein the mass ratio of the silicon-carbon composite material to the asphalt II is 1 (0.03-0.15).
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