CN114824238B - Preparation method and application of high specific capacity silicon-carbon anode material functionalized based on polyethyleneimine and polydopamine copolymer - Google Patents
Preparation method and application of high specific capacity silicon-carbon anode material functionalized based on polyethyleneimine and polydopamine copolymer Download PDFInfo
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- 229920002873 Polyethylenimine Polymers 0.000 title claims abstract description 113
- 229920001690 polydopamine Polymers 0.000 title claims abstract description 94
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- 238000002360 preparation method Methods 0.000 title claims abstract description 24
- 239000010405 anode material Substances 0.000 title description 14
- 239000005543 nano-size silicon particle Substances 0.000 claims abstract description 94
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- 230000008569 process Effects 0.000 claims abstract description 12
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- 239000002243 precursor Substances 0.000 claims description 18
- 238000004108 freeze drying Methods 0.000 claims description 13
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- 238000001816 cooling Methods 0.000 claims description 10
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- 229910052786 argon Inorganic materials 0.000 claims description 8
- 238000009210 therapy by ultrasound Methods 0.000 claims description 8
- CTENFNNZBMHDDG-UHFFFAOYSA-N Dopamine hydrochloride Chemical compound Cl.NCCC1=CC=C(O)C(O)=C1 CTENFNNZBMHDDG-UHFFFAOYSA-N 0.000 claims description 7
- 229960001149 dopamine hydrochloride Drugs 0.000 claims description 7
- 238000001132 ultrasonic dispersion Methods 0.000 claims description 7
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- 238000007254 oxidation reaction Methods 0.000 claims description 2
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- 238000002156 mixing Methods 0.000 abstract description 3
- 239000010406 cathode material Substances 0.000 abstract description 2
- 238000012360 testing method Methods 0.000 description 24
- VYFYYTLLBUKUHU-UHFFFAOYSA-N dopamine Chemical compound NCCC1=CC=C(O)C(O)=C1 VYFYYTLLBUKUHU-UHFFFAOYSA-N 0.000 description 14
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 13
- 239000010703 silicon Substances 0.000 description 13
- 229910052710 silicon Inorganic materials 0.000 description 13
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 10
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- OIFBSDVPJOWBCH-UHFFFAOYSA-N Diethyl carbonate Chemical compound CCOC(=O)OCC OIFBSDVPJOWBCH-UHFFFAOYSA-N 0.000 description 4
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- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 4
- 239000004698 Polyethylene Substances 0.000 description 4
- DPXJVFZANSGRMM-UHFFFAOYSA-N acetic acid;2,3,4,5,6-pentahydroxyhexanal;sodium Chemical compound [Na].CC(O)=O.OCC(O)C(O)C(O)C(O)C=O DPXJVFZANSGRMM-UHFFFAOYSA-N 0.000 description 4
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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
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/60—Selection of substances as active materials, active masses, active liquids of organic compounds
- H01M4/602—Polymers
-
- 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
Abstract
A preparation method and application of a high specific capacity silicon-carbon negative electrode material based on polyethyleneimine and polydopamine copolymer functionalization relate to a preparation method and application of a silicon-carbon negative electrode material. The invention aims to solve the problems that the silicon nano particles are easy to agglomerate and easy to fall off carbon frameworks in the preparation process by compounding the silicon nano particles and the carbon materials through a simple physical mixing method in the prior art, thereby influencing the cycling stability of the electrode. The method comprises the following steps: 1. preparing a primary functionalized silicon nanoparticle dispersion; 2. preparing a polyethyleneimine polydopamine copolymer functionalized silicon nanoparticle dispersion liquid; 3. cleaning; 4. preparing graphene oxide dispersion liquid; 5. compounding; 6. and (5) heat treatment. The high specific capacity silicon-carbon negative electrode material based on polyethyleneimine and polydopamine copolymer functionalization has the advantages of good rate capability and stability, simple process and industrialization prospect. The invention can obtain the lithium ion battery cathode material.
Description
Technical Field
The invention relates to a preparation method and application of a silicon-carbon anode material.
Background
With the rise of new energy hot flashes in recent years, the traditional commercial graphite anode materials are more and more difficult to meet the requirement of high energy density of lithium ion batteries, so that development of new generation anode materials with high energy density is urgently needed. Silicon can provide ultra-high energy density as a negative electrode active material, but serious volume change during charge and discharge restricts the application thereof.
The problem of how to limit the volume expansion of silicon is the key of the study of silicon-based materials, and nanocrystallization and silicon-carbon recombination are the most common modification methods in numerous scientific researches: reducing the dimensions of one or more dimensions of the silicon-based material below a critical value (150 nm) that does not fracture, such as silicon nanoparticles, silicon nanowires, and silicon nanoplatelets, however these methods increase the cycling stability of the silicon-based material, but reduce the coulombic efficiency and are costly; the silicon nano particles and the carbon material are compounded, so that various structures can be constructed to provide space for expansion of silicon, but because the silicon and the carbon material have no bonding effect, simple physical mixing can lead to easy agglomeration of the silicon nano particles and easy shedding of a carbon skeleton in the preparation process, thereby influencing the cycling stability of the electrode.
Therefore, if the silicon nano particles and the carbon material can be fixed by adopting a certain bonding effect, the silicon-carbon composite material with stable structure is prepared, the defects of agglomeration of the silicon nano particles and lower coulomb efficiency can be effectively avoided, the advantages of the carbon material can be fully exerted, the overall tap density of the material is improved, and the cost is reduced.
Disclosure of Invention
The invention aims to solve the problem that the silicon nano particles are easy to agglomerate and easy to fall off a carbon skeleton in the preparation process by compounding the silicon nano particles and a carbon material through a simple physical mixing method in the prior art, thereby influencing the cycling stability of an electrode, and provides a preparation method and application of a high specific capacity silicon-carbon negative electrode material based on polyethyleneimine and polydopamine copolymer functionalization.
The invention provides a preparation method of a silicon-carbon negative electrode material based on a liquid phase self-assembly and self-polymerization principle, which has the characteristics of simplicity, rapidness and easiness in industrialization, and the self-assembly and self-polymerization principle is utilized to carry out functional modification on the surfaces of silicon nano particles by adopting polyethyleneimine and dopamine, so that polyethyleneimine-polydopamine copolymer is generated on the surfaces of the particles, and meanwhile, the surfaces are positively charged; then, a large amount of amino groups on the surfaces of the functionalized silicon particles are utilized to generate hydrogen bonds with oxygen-containing functional groups on the surfaces of the graphene oxide, so that the nano silicon particles can be firmly anchored on the sheet layers to obtain an intermediate; finally, carrying out heat treatment on the intermediate to carbonize the polymer and reduce the graphene, and finally obtaining the carbon-coated silicon particle embedded graphene layer material with a stable structure; according to the invention, the nano silicon is firmly fixed on the surface of the graphene sheet layer through the bonding effect brought by functionalization, the carbon coating layer after the carbonization of the copolymer further ensures the interface bonding degree of the silicon and the graphene, so that the nano silicon is not easy to fall off in circulation, and the stability of the material is ensured; the silicon-carbon anode material prepared by the preparation method has the advantages of good rate capability and stability, simple process and industrialization prospect;
the invention discloses a preparation method of a high specific capacity silicon-carbon negative electrode material based on polyethyleneimine and polydopamine copolymer functionalization, which comprises the following steps:
1. preparing a primary functionalized silicon nanoparticle dispersion liquid:
adding ethanol dispersion liquid of the silicon nano particles into deionized water, continuously performing ultrasonic dispersion and continuously stirring, finally adding a polyethyleneimine solution, and stirring to obtain primary functionalized silicon nano particle dispersion liquid;
2. preparing a polyethyleneimine polydopamine copolymer functionalized silicon nanoparticle dispersion liquid:
adding dopamine hydrochloride into the primary functionalized silicon nanoparticle dispersion liquid, continuously stirring and intermittently performing ultrasonic treatment to obtain a polyethyleneimine polydopamine copolymer functionalized silicon nanoparticle dispersion liquid;
3. cleaning:
centrifuging and washing the polyethyleneimine polydopamine copolymer functionalized silicon nanoparticle dispersion liquid for a plurality of times, removing redundant polyethyleneimine polydopamine copolymer, and finally dispersing the polyethyleneimine polydopamine copolymer into deionized water to obtain washed copolymer functionalized silicon nanoparticle dispersion liquid;
4. ultrasonically dispersing graphene oxide in deionized water to obtain graphene oxide dispersion liquid;
5. compounding:
dropwise adding the washed copolymer functionalized silicon nanoparticle dispersion liquid into graphene oxide dispersion liquid, continuously stirring, and then centrifugally collecting precipitate, and performing freeze drying treatment to obtain a nano silicon/polyethyleneimine polydopamine/graphene oxide precursor;
6. and (3) heat treatment:
and carrying out heat treatment on the nano silicon/polyethyleneimine polydopamine/graphene oxide precursor to obtain the polyethyleneimine and polydopamine copolymer functionalized high specific capacity silicon-carbon negative electrode material.
The invention has the beneficial effects that:
1. according to the invention, the silicon nano particles are subjected to secondary functionalization treatment in a unique manner of initiating dopamine polymerization by polyethyleneimine, self-assembly is realized by virtue of electrostatic attraction and hydrogen bond acting force under a liquid phase condition with graphene oxide containing carboxyl on the surface, the two are tightly combined to enable the silicon particles to be anchored on the surface of a graphene oxide sheet, then the graphene oxide is reduced by high-temperature heat treatment, and the polyethyleneimine polydopamine copolymer on the surface of the silicon particles is carbonized into an amorphous carbon coating; a loose porous structure is formed inside the sintering process, so that lithium ions can be diffused; the graphene is used as a carbon matrix to construct a conductive network, and the excellent flexibility and mechanical strength of the graphene can relieve the stress of silicon volume expansion; the carbon coating layer can ensure the stable formation of the surface SEI film, strengthen the binding force of silicon and graphene interface, and ensure that nano silicon is not easy to separate from a conductive network in circulation; compared with a silicon-carbon negative electrode material obtained by primary functionalization treatment only with polyethyleneimine, the silicon-carbon negative electrode material prepared by secondary treatment with dopamine has higher specific capacity and stability;
2. the high specific capacity silicon-carbon negative electrode material based on polyethyleneimine and polydopamine copolymer functionalization has the advantages of good rate capability and stability, simple process and industrialization prospect.
The invention can obtain the lithium ion battery cathode material.
Drawings
FIG. 1 is a graph showing the color of a solution over time during the synthesis of a polydopamine polyethyleneimine copolymer;
FIG. 2 is an SEM image of a polydopamine polyethyleneimine copolymer;
FIG. 3 is a scanning electron microscope image of the high specific capacity silicon carbon negative electrode material functionalized based on the copolymer of polyethylene imine and polydopamine prepared in example 1 at different magnifications;
FIG. 4 is a transmission electron microscope image of the high specific capacity silicon carbon negative electrode material functionalized based on the copolymer of polyethyleneimine and polydopamine prepared in example 1 at a scale of 50nm;
FIG. 5 is a transmission electron microscope image of the high specific capacity silicon carbon negative electrode material functionalized based on the copolymer of polyethylenimine and polydopamine prepared in example 1 at a scale of 10 nm;
FIG. 6 is a graph showing the rate performance of the high specific capacity silicon carbon negative electrode material functionalized based on a copolymer of polyethyleneimine and polydopamine prepared in example 1 under constant current full electrical test at different current densities;
FIG. 7 shows that the high specific capacity silicon carbon negative electrode material functionalized based on the copolymer of polyethyleneimine and polydopamine prepared in example 1 is 0.3 A.g -1 A cycle performance curve graph of constant current charge and discharge test is carried out under the current density;
FIG. 8 is a graph showing the rate performance of the silicon carbon negative electrode material prepared in example 2 under constant current full electrical test at different current densities;
FIG. 9 shows that the SiCzochralski negative electrode material prepared in example 2 was prepared at 0.3A.g -1 A cycle performance curve graph of constant current charge and discharge test is carried out under the current density;
FIG. 10 is a graph showing the rate performance of the high specific capacity silicon carbon negative electrode material functionalized based on a copolymer of polyethyleneimine and polydopamine prepared in example 3 under constant current full electrical test at different current densities;
FIG. 11 is a schematic illustration of the preparation of example 3 based on polyethyleneimine and polydopamineThe high specific capacity silicon-carbon negative electrode material functionalized by the copolymer is 0.3A.g -1 A cycle performance curve graph of constant current charge and discharge test is carried out under the current density;
FIG. 12 is a graph showing the rate performance of the high specific capacity SiC anode material functionalized based on a copolymer of polyethyleneimine and polydopamine prepared in example 4 under constant current full electrical test at different current densities;
FIG. 13 shows that the high specific capacity silicon-carbon negative electrode material functionalized based on the copolymer of polyethyleneimine and polydopamine prepared in example 4 is 0.3 A.g -1 And (3) carrying out a cycle performance curve graph of constant current charge and discharge test under the current density.
Detailed Description
The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention, and the described embodiments are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without any inventive effort, are intended to be within the scope of the invention.
The first embodiment is as follows: the preparation method of the high specific capacity silicon-carbon negative electrode material based on polyethyleneimine and polydopamine copolymer functionalization in the embodiment is prepared according to the following steps:
1. preparing a primary functionalized silicon nanoparticle dispersion liquid:
adding ethanol dispersion liquid of the silicon nano particles into deionized water, continuously performing ultrasonic dispersion and continuously stirring, finally adding a polyethyleneimine solution, and stirring to obtain primary functionalized silicon nano particle dispersion liquid;
2. preparing a polyethyleneimine polydopamine copolymer functionalized silicon nanoparticle dispersion liquid:
adding dopamine hydrochloride into the primary functionalized silicon nanoparticle dispersion liquid, continuously stirring and intermittently performing ultrasonic treatment to obtain a polyethyleneimine polydopamine copolymer functionalized silicon nanoparticle dispersion liquid;
3. cleaning:
centrifuging and washing the polyethyleneimine polydopamine copolymer functionalized silicon nanoparticle dispersion liquid for a plurality of times, removing redundant polyethyleneimine polydopamine copolymer, and finally dispersing the polyethyleneimine polydopamine copolymer into deionized water to obtain washed copolymer functionalized silicon nanoparticle dispersion liquid;
4. ultrasonically dispersing graphene oxide in deionized water to obtain graphene oxide dispersion liquid;
5. compounding:
dropwise adding the washed copolymer functionalized silicon nanoparticle dispersion liquid into graphene oxide dispersion liquid, continuously stirring, and then centrifugally collecting precipitate, and performing freeze drying treatment to obtain a nano silicon/polyethyleneimine polydopamine/graphene oxide precursor;
6. and (3) heat treatment:
and carrying out heat treatment on the nano silicon/polyethyleneimine polydopamine/graphene oxide precursor to obtain the polyethyleneimine and polydopamine copolymer functionalized high specific capacity silicon-carbon negative electrode material.
The second embodiment is as follows: the present embodiment differs from the specific embodiment in that: the mass fraction of the ethanol dispersion liquid of the silicon nano particles in the first step is 10.89-15.77%; the median diameter of the silicon nano particles is 20-50 nm. The other steps are the same as in the first embodiment.
And a third specific embodiment: this embodiment differs from the first or second embodiment in that: the concentration of the polyethyleneimine solution in the step one is 0.005 g.multidot.mL -1 ～0.02g·mL -1 The molecular weight of the polyethyleneimine was 70000. The other steps are the same as those of the first or second embodiment.
The specific embodiment IV is as follows: one difference between this embodiment and the first to third embodiments is that: the volume ratio of the polyethyleneimine solution to the deionized water in the first step is 5mL to 30mL; the volume ratio of the ethanol dispersion liquid of the silicon nano particles to the deionized water in the first step is 1.27g:30mL; the time of continuous ultrasonic dispersion and continuous stirring in the first step is 20 min-30 min; the stirring time is 10 min-20 min. The other steps are the same as those of the first to third embodiments.
Fifth embodiment: one to four differences between the present embodiment and the specific embodiment are: the mass ratio of the dopamine hydrochloride to the silicon nano particles in the primary functionalized silicon nano particle dispersion liquid is (0.5-1) 1; the stirring time in the second step is 18-24 h, ultrasonic treatment is carried out for 30min every 6-8 h, and the ultrasonic temperature cannot exceed 40 ℃. Other steps are the same as those of the first to fourth embodiments.
Specific embodiment six: the present embodiment differs from the first to fifth embodiments in that: the rotational speed of the centrifugation in the third step is 8000-10000 rpm, the time of each centrifugation is 30min, and the repetition times of centrifugation and water washing are not less than 4 times. Other steps are the same as those of the first to fifth embodiments.
Seventh embodiment: one difference between the present embodiment and the first to sixth embodiments is that: the concentration of the graphene oxide dispersion liquid in the step four is 5 mg.mL -1 The graphene oxide is prepared by a modified Hummers method, the oxidation degree is 40%, and the number of graphene layers is not more than 10. Other steps are the same as those of embodiments one to six.
Eighth embodiment: one difference between the present embodiment and the first to seventh embodiments is that: the continuous stirring time in the fifth step is 20-24 h, the centrifugation speed is 6000-10000 rpm, and the centrifugation time is not less than 15min; the freeze drying time is not less than 12 hours, and the freeze drying temperature is-50 ℃ to-40 ℃; and step five, the mass ratio of the silicon nano particles to the graphene oxide in the nano silicon/polyethyleneimine polydopamine/graphene oxide precursor is (0.5-3) 1. The other steps are the same as those of embodiments one to seven.
Detailed description nine: one of the differences between this embodiment and the first to eighth embodiments is: the heat treatment process in the step six is as follows: heating the nano silicon/polyethylene imine polydopamine/graphene oxide precursor from room temperature to 800-1000 ℃ at a heating rate of 2-5 ℃/min, then preserving heat for 1-2 h, cooling to 150 ℃ at a cooling rate of 2-5 ℃/min, and finally naturally cooling to room temperature, wherein the whole heat treatment process is carried out in argon or hydrogen-argon mixed gas; the volume fraction of hydrogen in the hydrogen-argon mixed gas is 5% or 10%. Other steps are the same as those of embodiments one to eight.
Detailed description ten: the embodiment is that the high specific capacity silicon carbon negative electrode material functionalized based on the polyethyleneimine and polydopamine copolymer is used as a negative electrode material of a lithium ion battery.
The present invention will be described in detail with reference to examples.
Example 1: the preparation method of the high specific capacity silicon-carbon negative electrode material based on polyethyleneimine and polydopamine copolymer functionalization comprises the following steps:
1. preparing a primary functionalized silicon nanoparticle dispersion liquid:
1.27g of ethanol dispersion of silicon nano particles with mass fraction of 15.77% is added into 30mL of deionized water, ultrasonic dispersion is continued and stirring is continued for 20min, and then 5mL of ethanol dispersion with concentration of 0.02 g.mL is added -1 Stirring for 10min to obtain a primary functionalized silicon nanoparticle dispersion;
in the first step, the median diameter of the silicon nano particles is 20-50 nm;
the molecular weight of the polyethyleneimine in the first step is 70000;
2. preparing a polyethyleneimine polydopamine copolymer functionalized silicon nanoparticle dispersion liquid:
adding 0.2g of dopamine hydrochloride into the primary functionalized silicon nanoparticle dispersion liquid, continuously stirring and intermittently performing ultrasonic treatment to obtain a polyethyleneimine polydopamine copolymer functionalized silicon nanoparticle dispersion liquid;
the stirring time in the second step is 24 hours, ultrasonic treatment is carried out for 30 minutes every 8 hours, and the ultrasonic temperature cannot exceed 40 ℃;
3. cleaning:
centrifuging and washing the polyethyleneimine polydopamine copolymer functionalized silicon nanoparticle dispersion liquid for a plurality of times, removing redundant polyethyleneimine polydopamine copolymer, and finally dispersing the polyethyleneimine polydopamine copolymer into 50mL of deionized water to obtain 50mL of washed copolymer functionalized silicon nanoparticle dispersion liquid;
the rotational speed of the centrifugation in the third step is 8000rpm, the time of each centrifugation is 30min, and the times of centrifugation and water washing are both 4 times;
4. ultrasonically dispersing 0.5g of graphene oxide in 100mL of deionized water to obtain graphene oxide dispersion liquid;
5. compounding:
taking 13.34mL of graphene oxide dispersion liquid, and diluting the graphene oxide dispersion liquid to 50mL by using deionized water to obtain diluted graphene oxide dispersion liquid; dropwise adding 50mL of the washed copolymer functionalized silicon nanoparticle dispersion liquid into the diluted graphene oxide dispersion liquid, continuously stirring for 24 hours, and then centrifugally collecting sediment, and performing freeze-drying treatment to obtain a nano silicon/polyethyleneimine polydopamine/graphene oxide precursor;
in the fifth step, the centrifugation speed is 9000rpm, and the centrifugation time is 30min; the freeze drying time is 12 hours;
6. and (3) heat treatment:
carrying out heat treatment on the nano silicon/polyethyleneimine polydopamine/graphene oxide precursor to obtain a high specific capacity silicon-carbon negative electrode material functionalized based on polyethyleneimine and polydopamine copolymer;
the heat treatment process in the step six is as follows: the method comprises the steps of heating a nano silicon/polyethylene imine polydopamine/graphene oxide precursor from room temperature to 900 ℃ at a heating rate of 5 ℃/min, preserving heat for 1.5 hours, cooling to 150 ℃ at a cooling rate of 5 ℃/min, and naturally cooling to room temperature, wherein the whole heat treatment process is carried out in argon.
In order to intuitively express the rapid polymerization process of dopamine under the initiation of polyethyleneimine, 5 mg.mL of the preparation method is additionally prepared -1 0.2g of dopamine hydrochloride is added into 40mL of polyethyleneimine solution, and stirring is continued, wherein the phenomenon is shown in figure 1;
FIG. 1 is a graph showing the color of a solution over time during the synthesis of a polydopamine polyethyleneimine copolymer;
from fig. 1 it can be observed that the solution rapidly changes from colorless to rose gold, after which the color gradually deepens with time, completely changing to dark brown after 24 hours, masking the rotor in the beaker; this phenomenon proves that the cross-linking polymerization reaction of dopamine is very rapid in the presence of polyethyleneimine, and copolymers are rapidly generated by means of self-polymerization of dopamine and cross-linking polymerization with polyethyleneimine, and the concentration and the polymerization degree of the copolymers are gradually increased along with the time; fig. 2 is an SEM image of the resulting polyethyleneimine polydopamine copolymer, and from fig. 2 it can be observed that the copolymer surface is very smooth, and has a large volume, indicating deep polymerization.
A trace of high specific capacity silicon-carbon negative electrode material based on polyethyleneimine and polydopamine copolymer functionalization prepared in the example 1 is smeared on the surface of conductive adhesive, and is placed on a metal copper sample carrying table, and morphology observation is carried out through a field emission scanning electron microscope, and the result is shown in figure 3;
FIG. 3 is a scanning electron microscope image of the high specific capacity silicon carbon negative electrode material functionalized based on the copolymer of polyethylene imine and polydopamine prepared in example 1 at different magnifications;
as can be seen from fig. 3, the whole material is micron-sized irregular secondary particles, and a large number of particles are distributed on the surface; from the figure, the reduced graphene oxide sheets with wrinkling features and silicon nanoparticles distributed over the surface thereof can be clearly distinguished, demonstrating the successful construction of a sandwich structure in which carbon-coated silicon particles are anchored to the graphene surface. The silicon particles are fixed on the surface of graphene oxide under the action of static electricity and hydrogen bonds of the polyethylene imine polydopamine copolymer and the polar groups of the graphene oxide, and after heat treatment, the silicon particles are converted into amorphous carbon by the polyethylene imine polydopamine copolymer, so that the combination of silicon and the reduced graphene oxide is firmer; in addition, the silicon carbon particles on the surface of the reduced graphene oxide are uniformly distributed, agglomeration is not obvious, the overall size is below 200nm, but the state of the surface amorphous carbon coating layer cannot be observed in an SEM (scanning electron microscope).
In order to observe the distribution condition of silicon nano particles in graphene and the state of a silicon surface amorphous carbon layer, a trace amount of high specific capacity silicon carbon anode material functionalized based on a polyethyleneimine and polydopamine copolymer prepared in example 1 is taken to be dispersed in ethanol, ultrasonic treatment is carried out for 40min, the dispersed liquid is dropped on a copper mesh sample carrying table, and observation is carried out through a transmission electron microscope, wherein the results are shown in fig. 4 and 5;
FIG. 4 is a transmission electron microscope image of the high specific capacity silicon carbon negative electrode material functionalized based on the copolymer of polyethyleneimine and polydopamine prepared in example 1 at a scale of 50nm;
FIG. 5 is a transmission electron microscope image of the high specific capacity silicon carbon negative electrode material functionalized based on the copolymer of polyethylenimine and polydopamine prepared in example 1 at a scale of 10 nm;
as can be seen from fig. 4 and 5, the silicon particles are encapsulated by graphene, and an amorphous carbon layer having a thickness of about 10nm exists on the surface, which reduces the possibility that silicon is separated from a conductive network due to volume expansion during charge and discharge, and stabilizes the formation of an SEI film.
The high specific capacity silicon-carbon negative electrode material based on polyethyleneimine and polydopamine copolymer functionalization prepared in the example 1 is prepared into an electrode, and is assembled into a lithium ion half-cell for constant current charge and discharge test, and the electrode is specifically assembled according to the following method:
preparing slurry from the high specific capacity silicon-carbon negative electrode material functionalized based on the polyethyleneimine and polydopamine copolymer prepared in the embodiment 1, a conductive agent acetylene black and a binder according to a mass ratio of 8:1:1, uniformly coating the slurry on a copper foil, and drying the copper foil to prepare an electrode, wherein the binder is prepared from battery-grade sodium carboxymethyl cellulose and styrene-butadiene rubber according to a mass ratio of 1:1; the electrolyte is 1.0mol.L -1 The mixed organic solution of lithium hexafluorophosphate is prepared from ethylene carbonate, diethyl carbonate and 5% fluoroethylene carbonate serving as additives in a mass ratio of 1:1. The diaphragm is a microporous polyethylene diaphragm, the anode is a lithium sheet, and the CR2025 button cell is assembled; the charge-discharge voltage range is 0.01-1.5V, and the test is carried out under the constant temperature condition of 25 ℃ and is shown in figures 6-7; .
FIG. 6 is a graph showing the rate performance of the high specific capacity silicon carbon negative electrode material functionalized based on a copolymer of polyethyleneimine and polydopamine prepared in example 1 under constant current full electrical test at different current densities;
FIG. 7 is a schematic illustration of a copolymer based on polyethyleneimine and polydopamine prepared in example 1The material of the functionalized high specific capacity silicon-carbon anode material is 0.3A.g -1 A cycle performance curve graph of constant current charge and discharge test is carried out under the current density;
as can be seen from FIGS. 6 to 7, the ratio of the total weight of the catalyst to the total weight of the catalyst is 0.1 A.g -1 The reversible capacity at current density is 1486mA.h.g -1 ，1A·g -1 The reversible capacity still has 1037mA.h.g -1 The high-magnification performance is shown; and has excellent restorability: when the current density is 10 A.g -1 Returning to 0.1 A.g -1 After that, the performance can also be restored to the original level; and at 0.3 A.g -1 The capacity retention rate of 83.3% after 100 times of circulation under the current density is achieved, and the circulation stability is excellent.
Example 2: the preparation method of the silicon-carbon anode material comprises the following steps:
1. preparing a primary functionalized silicon nanoparticle dispersion liquid:
1.27g of ethanol dispersion of silicon nano particles with mass fraction of 15.77% is added into 30mL of deionized water, ultrasonic dispersion is continued and stirring is continued for 20min, and then 5mL of ethanol dispersion with concentration of 0.02 g.mL is added -1 Stirring for 10min to obtain a primary functionalized silicon nanoparticle dispersion;
in the first step, the median diameter of the silicon nano particles is 20-50 nm;
the molecular weight of the polyethyleneimine in the first step is 70000;
2. cleaning:
centrifuging and washing the primary functionalized silicon nanoparticle dispersion liquid for multiple times, and finally dispersing the primary functionalized silicon nanoparticle dispersion liquid into 50mL of deionized water to obtain 50mL of washed primary functionalized silicon nanoparticle dispersion liquid;
the rotational speed of the centrifugation in the second step is 8000rpm, the time of each centrifugation is 30min, and the times of centrifugation and water washing are both 4 times;
3. ultrasonically dispersing 0.5g of graphene oxide in 100mL of deionized water to obtain graphene oxide dispersion liquid;
4. compounding:
taking 13.34mL of graphene oxide dispersion liquid, and diluting the graphene oxide dispersion liquid to 50mL by using deionized water to obtain diluted graphene oxide dispersion liquid; dropwise adding 50mL of the washed primary functionalized silicon nanoparticle dispersion liquid into the diluted graphene oxide dispersion liquid, continuously stirring for 24 hours, and then centrifugally collecting sediment, and performing freeze-drying treatment to obtain a precursor;
in the fourth step, the centrifugation speed is 9000rpm, and the centrifugation time is 30min; the freeze drying time is 12 hours;
5. and (3) heat treatment:
carrying out heat treatment on the precursor to obtain a silicon-carbon anode material;
the heat treatment process in the fifth step is as follows: the precursor is heated from room temperature to 900 ℃ at a heating rate of 5 ℃/min, then is insulated for 1.5h, is cooled to 150 ℃ at a cooling rate of 5 ℃/min, and finally is naturally cooled to room temperature, and the whole heat treatment process is carried out in argon.
The silicon-carbon negative electrode material obtained in the example 2 is prepared into an electrode and assembled into a lithium ion half battery for constant current charge and discharge test, and the electrode is specifically assembled according to the following method:
preparing a slurry from the silicon-carbon anode material obtained in the embodiment 2, acetylene black serving as a conductive agent and a binder according to a mass ratio of 8:1:1, uniformly coating the slurry on a copper foil, and drying the copper foil to obtain an electrode, wherein the binder is prepared from battery-grade sodium carboxymethyl cellulose and styrene-butadiene rubber according to a mass ratio of 1:1; the electrolyte is 1.0mol.L -1 The mixed organic solution of lithium hexafluorophosphate is prepared from ethylene carbonate, diethyl carbonate and 5% fluoroethylene carbonate serving as additives in a mass ratio of 1:1. The diaphragm is a microporous polyethylene diaphragm, the anode is a lithium sheet, and the CR2025 button cell is assembled; the charge-discharge voltage range is 0.01-1.5V, and the test is carried out under the constant temperature condition of 25 ℃ and is shown in figures 8-9; .
FIG. 8 is a graph showing the rate performance of the silicon carbon negative electrode material prepared in example 2 under constant current full electrical test at different current densities;
FIG. 9 shows that the SiCzochralski negative electrode material prepared in example 2 was prepared at 0.3A.g -1 A cycle performance curve graph of constant current charge and discharge test is carried out under the current density;
from FIG. 8 to FIG. 89, at 0.1 A.g -1 The reversible capacity at current density is only 457mA.h.g -1 The initial coulombic effect was only 33.7%, although at 0.3 A.g -1 After the current density circulates for 100 times, the capacity is improved, but still the reasonable silicon-carbon negative electrode material level is not achieved; the silicon-carbon composite material prepared by only treating the polyethyleneimine is unreliable, and the direct combination of the silicon nano particles and the graphene is not firm, so that a large amount of active silicon falls off during the first discharge, and therefore, the specific capacity and the first effect of the material are low. This also demonstrates the important role of dopamine addition in material preparation.
Example 3: the difference between this embodiment and embodiment 1 is that: in the fifth step, 13.34mL of graphene oxide dispersion liquid is taken, and diluted to 50mL by deionized water, so as to obtain diluted graphene oxide dispersion liquid; and dropwise adding 20mL of the washed copolymer functionalized silicon nanoparticle dispersion liquid into the diluted graphene oxide dispersion liquid, continuously stirring for 24 hours, and then centrifugally collecting sediment, and performing freeze-drying treatment to obtain the nano silicon/polyethyleneimine polydopamine/graphene oxide precursor. Other steps and parameters were the same as in example 1.
The high specific capacity silicon-carbon negative electrode material based on polyethyleneimine and polydopamine copolymer functionalization obtained in the example 3 is prepared into an electrode, and is assembled into a lithium ion half battery for constant current charge and discharge test, and the electrode is specifically assembled according to the following method:
preparing slurry from the high specific capacity silicon-carbon negative electrode material functionalized based on the polyethyleneimine and polydopamine copolymer obtained in the embodiment 3, a conductive agent acetylene black and a binder according to a mass ratio of 8:1:1, uniformly coating the slurry on a copper foil, and drying the copper foil to obtain an electrode, wherein the binder is prepared from battery-grade sodium carboxymethyl cellulose and styrene-butadiene rubber according to a mass ratio of 1:1; the electrolyte is 1.0mol.L -1 The mixed organic solution of lithium hexafluorophosphate is prepared from ethylene carbonate, diethyl carbonate and 5% fluoroethylene carbonate serving as additives in a mass ratio of 1:1. The diaphragm is a microporous polyethylene diaphragm, the anode is a lithium sheet, and the CR2025 button cell is assembled; the charge-discharge voltage ranges from 0.01V to 1.5V, and the test is carried out under the constant temperature condition of 25 ℃ as shown in figure 10 to 11.
FIG. 10 is a graph showing the rate performance of the high specific capacity silicon carbon negative electrode material functionalized based on a copolymer of polyethyleneimine and polydopamine prepared in example 3 under constant current full electrical test at different current densities;
FIG. 11 shows that the high specific capacity silicon carbon negative electrode material functionalized based on the copolymer of polyethyleneimine and polydopamine prepared in example 3 is 0.3 A.g -1 A cycle performance curve graph of constant current charge and discharge test is carried out under the current density;
as can be seen from fig. 10 and 11: at 0.1 A.g -1 The reversible capacity at current density is 1154mA.h.g -1 But 1 A.g -1 The reversible capacity is only 586 mA.h.g -1 At 0.3 A.g -1 Has reversible specific capacity of 583mA.h.g after 100 times of circulation under current density -1 The capacity retention was 71.0%. The multiplying power performance and the cycling stability of the material are different from those of the silicon-carbon anode material prepared in the embodiment 1 to a certain extent.
Example 4: the difference between this embodiment and embodiment 1 is that: in the fifth step, 13.34mL of graphene oxide dispersion liquid is taken, and diluted to 50mL by deionized water, so as to obtain diluted graphene oxide dispersion liquid; and (3) dropwise adding 40mL of the washed copolymer functionalized silicon nanoparticle dispersion liquid into the diluted graphene oxide dispersion liquid, continuously stirring for 24 hours, and then centrifugally collecting sediment, and performing freeze-drying treatment to obtain the nano silicon/polyethyleneimine polydopamine/graphene oxide precursor. Other steps and parameters were the same as in example 1.
The high specific capacity silicon-carbon negative electrode material based on polyethyleneimine and polydopamine copolymer functionalization obtained in the example 4 is prepared into an electrode, and is assembled into a lithium ion half battery for constant current charge and discharge test, and the electrode is specifically assembled according to the following method:
preparing slurry from the high specific capacity silicon-carbon negative electrode material functionalized based on the polyethyleneimine and polydopamine copolymer obtained in the example 4, a conductive agent acetylene black and a binder according to a mass ratio of 8:1:1, uniformly coating the slurry on a copper foil, and drying the copper foil to obtain an electrode, wherein the binder is battery-grade sodium carboxymethyl cellulose and styrene-butadiene rubber according to mass ratioThe weight ratio is 1:1; the electrolyte is 1.0mol.L -1 The mixed organic solution of lithium hexafluorophosphate is prepared from ethylene carbonate, diethyl carbonate and 5% fluoroethylene carbonate serving as additives in a mass ratio of 1:1. The diaphragm is a microporous polyethylene diaphragm, the anode is a lithium sheet, and the CR2025 button cell is assembled; the charge-discharge voltage range is 0.01-1.5V, and the test is carried out under the constant temperature condition of 25 ℃ and is shown in figures 12-13; .
FIG. 12 is a graph showing the rate performance of the high specific capacity SiC anode material functionalized based on a copolymer of polyethyleneimine and polydopamine prepared in example 4 under constant current full electrical test at different current densities;
FIG. 13 shows that the high specific capacity silicon-carbon negative electrode material functionalized based on the copolymer of polyethyleneimine and polydopamine prepared in example 4 is 0.3 A.g -1 A cycle performance curve graph of constant current charge and discharge test is carried out under the current density;
as can be seen from FIGS. 12 and 13, the ratio of the total weight of the catalyst to the total weight of the catalyst is 0.1 A.g -1 The reversible capacity at current density is 700 mA.h.g -1 At 0.3 A.g -1 Has reversible specific capacity 675mA h g after 100 times of circulation under current density -1 The capacity retention was 98.0%; the reversible specific capacity of the material was not as good as that of example 1, but gradually activated to the highest capacity after 40 cycles, and the overall capacity retention was excellent.
Claims (10)
1. The preparation method of the high specific capacity silicon-carbon negative electrode material based on polyethyleneimine and polydopamine copolymer functionalization is characterized by comprising the following steps:
1. preparing a primary functionalized silicon nanoparticle dispersion liquid:
adding ethanol dispersion liquid of the silicon nano particles into deionized water, continuously performing ultrasonic dispersion and continuously stirring, finally adding a polyethyleneimine solution, and stirring to obtain primary functionalized silicon nano particle dispersion liquid;
2. preparing a polyethyleneimine polydopamine copolymer functionalized silicon nanoparticle dispersion liquid:
adding dopamine hydrochloride into the primary functionalized silicon nanoparticle dispersion liquid, continuously stirring and intermittently performing ultrasonic treatment to obtain a polyethyleneimine polydopamine copolymer functionalized silicon nanoparticle dispersion liquid;
3. cleaning:
centrifuging and washing the polyethyleneimine polydopamine copolymer functionalized silicon nanoparticle dispersion liquid for a plurality of times, removing redundant polyethyleneimine polydopamine copolymer, and finally dispersing the polyethyleneimine polydopamine copolymer into deionized water to obtain washed copolymer functionalized silicon nanoparticle dispersion liquid;
4. ultrasonically dispersing graphene oxide in deionized water to obtain graphene oxide dispersion liquid;
5. compounding:
dropwise adding the washed copolymer functionalized silicon nanoparticle dispersion liquid into graphene oxide dispersion liquid, continuously stirring, and then centrifugally collecting precipitate, and performing freeze drying treatment to obtain a nano silicon/polyethyleneimine polydopamine/graphene oxide precursor;
6. and (3) heat treatment:
and carrying out heat treatment on the nano silicon/polyethyleneimine polydopamine/graphene oxide precursor to obtain the polyethyleneimine and polydopamine copolymer functionalized high specific capacity silicon-carbon negative electrode material.
2. The preparation method of the high specific capacity silicon-carbon negative electrode material based on polyethyleneimine and polydopamine copolymer functionalization, which is characterized in that the mass fraction of the ethanol dispersion liquid of the silicon nano particles in the first step is 10.89% -15% by mass; the median diameter of the silicon nano particles is 20-50 nm.
3. The method for preparing a high specific capacity silicon-carbon negative electrode material based on polyethyleneimine and polydopamine copolymer functionalization according to claim 1, wherein the concentration of the polyethyleneimine solution in the step one is 0.005 g.ml -1 ~0.02g·mL -1 The molecular weight of the polyethyleneimine was 70000.
4. The method for preparing the high specific capacity silicon-carbon negative electrode material based on the functionalization of the polyethyleneimine and polydopamine copolymer according to claim 1, wherein the volume ratio of the polyethyleneimine solution to the deionized water in the first step is 5ml to 30ml; the volume ratio of the ethanol dispersion liquid of the silicon nano particles to the deionized water in the first step is 1.27g:30mL; in the first step, the continuous ultrasonic dispersion and continuous stirring are carried out for 20-30 min; stirring time is 10-20 min.
5. The preparation method of the high specific capacity silicon-carbon negative electrode material based on polyethyleneimine and polydopamine copolymer functionalization, which is characterized in that the mass ratio of dopamine hydrochloride to silicon nano particles in the primary functionalized silicon nano particle dispersion liquid in the second step is (0.5-1) 1; and step two, stirring for 18-24 hours, and carrying out ultrasonic treatment for 30 minutes every 6-8 hours, wherein the ultrasonic temperature cannot exceed 40 ℃.
6. The preparation method of the high specific capacity silicon-carbon negative electrode material based on polyethyleneimine and polydopamine copolymer functionalization, which is disclosed in claim 1, is characterized in that the rotational speed of centrifugation in the third step is 8000-10000 rpm, the time of each centrifugation is 30min, and the repetition times of centrifugation and water washing are not less than 4 times.
7. The method for preparing a high specific capacity silicon-carbon negative electrode material based on polyethyleneimine and polydopamine copolymer functionalization according to claim 1, wherein the concentration of the graphene oxide dispersion liquid in the fourth step is 5 mg/mL -1 Graphene oxide was prepared by modified Hummers, with a degree of oxidation of 40%.
8. The preparation method of the high specific capacity silicon-carbon negative electrode material based on polyethyleneimine and polydopamine copolymer functionalization, according to claim 1, is characterized in that the continuous stirring time in the fifth step is 20-24 h, the centrifugation speed is 6000-10000 rpm, and the centrifugation time is not less than 15min; the freeze drying time is not less than 12 hours, and the freeze drying temperature is-50 ℃ to-40 ℃; and step five, the mass ratio of the silicon nano particles to the graphene oxide in the nano silicon/polyethyleneimine polydopamine/graphene oxide precursor is (0.5-3) 1.
9. The method for preparing the high specific capacity silicon-carbon negative electrode material based on polyethyleneimine and polydopamine copolymer functionalization according to claim 1, wherein the heat treatment process in the step six is characterized in that: heating the nano silicon/polyethylene imine polydopamine/graphene oxide precursor from room temperature to 800-1000 ℃ at a heating rate of 2-5 ℃/min, then preserving heat for 1-2 h, cooling to 150 ℃ at a cooling rate of 2-5 ℃/min, and finally naturally cooling to room temperature, wherein the whole heat treatment process is carried out in argon or hydrogen-argon mixed gas; the volume fraction of hydrogen in the hydrogen-argon mixed gas is 5% or 10%.
10. The application of the high specific capacity silicon-carbon negative electrode material based on the functionalization of the polyethyleneimine and polydopamine copolymer prepared by the preparation method of claim 1 is characterized in that the high specific capacity silicon-carbon negative electrode material based on the functionalization of the polyethyleneimine and polydopamine copolymer is used as a negative electrode material of a lithium ion battery.
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