CN112349890A - Graphene @ yolk-eggshell silicon-carbon composite material and preparation and application thereof - Google Patents

Graphene @ yolk-eggshell silicon-carbon composite material and preparation and application thereof Download PDF

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CN112349890A
CN112349890A CN201910736316.XA CN201910736316A CN112349890A CN 112349890 A CN112349890 A CN 112349890A CN 201910736316 A CN201910736316 A CN 201910736316A CN 112349890 A CN112349890 A CN 112349890A
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silicon
graphene
composite material
eggshell
yolk
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田忠良
赖延清
李松贤
罗飞林
李劼
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Central South University
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
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    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
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Abstract

The invention belongs to the technical field of materials, and particularly relates to a graphene @ yolk-eggshell silicon carbon composite material which comprises graphene and a yolk-eggshell silicon carbon material loaded on the surface of the graphene; the yolk-eggshell silicon carbon material is a composite material taking amorphous carbon as a shell and a silicon-based material as a core, and a gap is formed between the shell and the core. The invention also provides a preparation method of the composite material and application of the composite material in a lithium battery. The invention provides a brand-new composite material, and researches show that the composite material has excellent electrical properties in a lithium ion battery, such as high first-turn coulombic efficiency and long cycle capacity retention rate.

Description

Graphene @ yolk-eggshell silicon-carbon composite material and preparation and application thereof
Technical Field
The invention belongs to the technical field of materials, and particularly relates to a preparation method of a brand-new graphene @ yolk-eggshell silicon-carbon composite material.
Background
Lithium Ion Batteries (LIBs) have been widely used in the fields of 3C digital products and new energy vehicles due to their advantages of high specific energy, wide operating temperature range, no memory effect, etc., and the capacity and energy density of the batteries also need to be improved. The theoretical specific capacity of the graphite cathode of the traditional lithium ion battery is only 372mAh/g, and the market demand cannot be met. Recently, silicon-based (theoretical specific capacity 4200mAh/g) and tin-based (theoretical specific capacity 990mAh/g) materials have been the focus of research due to their higher specific capacities, especially silicon-based materials. However, the silicon negative electrode is easy to cause pulverization and shedding of the active material of the pole piece due to huge volume expansion and shrinkage in the charging and discharging processes, and the cycle performance of the battery is reduced. Therefore, how to reduce the volume expansion effect of the silicon-based material has important significance on the application of the silicon material in the negative electrode of the lithium ion battery.
In the prior art, patent CN201210294469.1 discloses a method for preparing a silicon-carbon composite material, which comprises forming a silicon dioxide layer on the surface of elemental silicon powder by using the oxidation effect of oxygen, then performing amorphous carbon coating, and corroding the silicon dioxide with excessive hydrofluoric acid to obtain the silicon-carbon composite material with a certain gap between a carbon layer and a silicon core, wherein the silicon-carbon composite material has good cycle performance when applied to a lithium ion battery cathode. The method uses excessive hydrofluoric acid, so that simple substance silicon particles in the material are easy to corrode, the appearance of a target product is influenced, and simultaneously the generated SiF4Gas and HF acid wastewater cause serious pollution to the atmosphere, water and soil. Accordingly, there is a need in the art for improvements.
Disclosure of Invention
In order to solve the problems in the prior art, the invention aims to provide a graphene @ yolk-eggshell silicon carbon composite material, and aims to provide a brand new anode material with the advantages of high coulomb efficiency in the first circle, low expansion, long cycle and the like.
The second purpose of the invention is to provide a preparation method of the graphene @ yolk-eggshell silicon carbon composite material, aiming at avoiding the problem thatProduction of SiF during material preparation4The gas and HF acid wastewater pollute the environment, and simultaneously, the graphene @ yolk-eggshell silicon-carbon composite material with a certain gap between the carbon layer and the silicon core can be obtained.
A graphene @ yolk-eggshell silicon carbon composite material comprises graphene and a yolk-eggshell silicon carbon material loaded on the surface of the graphene;
the yolk-eggshell silicon carbon material is a composite material taking amorphous carbon as a shell and a silicon-based material as a core, and a gap is formed between the shell and the core.
The invention provides a brand-new composite material, and researches show that the composite material has excellent electrical properties in a lithium ion battery, such as high first-turn coulombic efficiency and long cycle capacity retention rate.
Preferably, the content of the graphene is 5-15%; the mass content of the silicon-based material is 70-90%.
Preferably, in the yolk-eggshell silicon carbon material, the diameter of the silicon-based material is 10-1000 nm, and preferably 200-400 nm.
Preferably, the thickness of the shell is 5-20 nm; more preferably 5 to 10 nm.
Preferably, the gap distance between the shell and the core is 3-30 nm.
The invention also provides a preparation method of the graphene @ egg yolk-egg shell silicon-carbon composite material, which comprises the following steps:
step (1): dispersing a silicon-based material, graphite oxide and acid to obtain a mixed colloidal solution;
step (2): adding water-soluble salt of transition metal into the mixed colloidal solution, adding alkali, carrying out coprecipitation reaction, and then carrying out solid-liquid separation to obtain a solid A;
and (3): dispersing the solid A and an amorphous carbon source into a solvent, carrying out a solvothermal reaction, and carrying out solid-liquid separation after the reaction is finished to obtain a solid B;
and (4): treating the solid B with acid liquor, and washing with water to be neutral to obtain a precursor;
and (5): and carbonizing the precursor to obtain the graphene @ yolk-eggshell silicon-carbon composite material.
By the method, the silicon-carbon composite material with the yolk-eggshell structure loaded on graphene can be successfully prepared in one step by the action of the graphite oxide and the cooperation of the transition metal coprecipitation, hydrothermal carbonization and acid treatment, and the material with the brand new structure prepared by the preparation method has high first-turn coulombic efficiency and long circulation capacity retention rate.
According to the preparation method, under the action of the graphite oxide, the transition metal can be coprecipitated on the surface of the silicon-based material, so that the agglomeration of coprecipitated particles is avoided, and the MOH @ Si @ Go material (solid A) can be prepared; and then, by matching with the in-situ carbon-coating-acid treatment-carbonization process, the silicon-carbon composite material with a yolk-eggshell structure can be formed on the graphene in situ.
In the present invention, a silicon-based material, graphite oxide, and an acid are dispersed in a solvent (for example, water) in advance to obtain an acidic mixed colloidal solution.
Preferably, the silicon-based material is at least one of amorphous nano-silicon and amorphous silicon oxide SiOx; and x is 0.8-1.5.
Researches find that the particle size of the silicon-based material has certain influence on the subsequently prepared composite material.
Preferably, the particle diameter D50 of the amorphous nano silicon particles is 10-400 nm, preferably 200-400 nm; the grain diameter D50 of the amorphous silicon oxide SiOx is 100 nm-1 um; more preferably 200 to 400 nm.
The quality of the graphite oxide and the silicon-based material also has certain influence on the subsequently prepared composite material.
Preferably, the mass ratio of the silicon-based material to the graphite oxide is 5-10: 1. It was found that, without control in this preferred range, the preparation of the in situ compounded egg yolk-shell material is not facilitated and the electrical properties of the material are greatly affected.
Preferably, the pH of the mixed colloidal solution is 1 to 2. The acid may be a conventional acidic compound.
In the step (1), the mixed colloidal solution is obtained through ultrasonic treatment; the liquid-solid ratio (mL/g) in the mixed colloidal solution is 200-700: 1. The ultrasonic power is 100-400W, the frequency is 10-100 kHz, and the ultrasonic time is 0.5-1.5 h.
The invention creatively carries out coprecipitation on the transition metal source in the mixed colloidal solution, and is beneficial to forming a transition metal hydroxide coating layer on the surface of the silicon-based material by controlling the type of the transition metal source and the proportion of the transition metal source to the silicon-based material and the graphite oxide.
Preferably, the transition metal is at least one of nickel, cobalt, manganese and iron.
Preferably, the water-soluble salt of the transition metal is at least one of a chloride, sulfate and nitrate of the transition metal.
Preferably, the mass ratio of the silicon-based material to the water-soluble salt of the transition metal is 10-1: 1. It has been found that the absence of control within this preferred range can affect the electrical properties of the resulting material to some extent.
Preferably, the alkali is at least one of alkali metal hydroxide and ammonia water.
Preferably, the pH value in the coprecipitation process is maintained between 6 and 10.
According to the invention, the solid A is subjected to solvothermal reaction, and carbon is further coated on the solid A to prepare the amorphous carbon @ MOH @ Si @ Go material (solid B).
Preferably, the amorphous carbon source is at least one of ferrocene, nickelocene, cobaltocene, manganocene, glucose, sucrose, citric acid, carboxymethyl cellulose and phenolic resin; more preferably at least one of ferrocene, nickelocene, cobaltocene and manganocene. It has been found that the preferred amorphous carbon source unexpectedly further enhances the electrical properties of the resulting composite.
In the step (3), the dispersion process is ultrasonic dispersion, the ultrasonic power is 400-800W, the frequency is 20-300 kHz, and the ultrasonic time is 1-4 h.
Preferably, the mass ratio of the solid A to the amorphous carbon source is 1: 1-4. It is found that, by controlling the preferred ratio, the shell and core-shell gap can be controlled to a suitable degree, so that the shell and core-shell gap have better electrical properties. It has been found that the absence of such a preferred ratio, which is not conducive to the in situ composite construction of the yolk-shell material, may affect the electrical properties of the material to some extent.
Preferably, the solvent of the starting solution of the solvothermal reaction is at least one of water, acetone, diethyl ether, ethylene glycol, glycerol, N-Dimethylacetamide (DMA), N-Dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and Tetrahydrofuran (THF).
Preferably, the liquid-solid ratio of the initial solution of the solvothermal reaction is 10-20: 1 (mL/g).
The solvothermal operation is carried out in a closed vessel.
Preferably, the temperature of the solvothermal is 150 to 300 ℃. The research finds that under the preferable conditions, the material is beneficial to the modification of functional groups and the in-situ composite construction of the yolk-eggshell material, and the material with excellent electrical properties can be obtained.
Preferably, the solvothermal reaction time is 12-48 h.
The invention innovatively carries out acid liquor treatment on the solid B, and then washes the solid B with water until the solid B is neutral, so that the precursor is finally obtained.
Preferably, the acid solution is HCl or H2SO4、HNO3、H3PO4、HPO3、HClO3、HClO、 H2FeO4HCOOH and CH3An aqueous solution of at least one of COOH.
Preferably, the concentration of the acid solution is 3-10 mol/L.
The carbonization process is carried out under a protective atmosphere. The protective gas is at least one of nitrogen and argon, and the gas flow is 30-100 mL/min.
The temperature in the carbonization process is 600-1000 ℃; preferably 800 to 1000 ℃.
The carbonization time is 3-7 h.
The carbonization heating rate is 1-10 ℃/min;
a preferred method for preparing a silicon carbon composite material comprises the following steps:
(a) weighing silica-based core and FeCl3·6H2O、NiCl2·6H2O、CoCl2·6H2O、MnCl2·4H2Placing at least one solid in the O into the graphite oxide colloid solution, wherein the mass ratio of the two solids is 10-1: 1, and the liquid-solid ratio is 700:1, carrying out ultrasonic treatment at 0-50 ℃. Dropwise adding ammonia water with the concentration of 25-28% while mechanically stirring until the pH value is 6-10, washing precipitates obtained by centrifugation with deionized water until the pH value of an eluate is 7, and drying to obtain a solid A.
(b) Mixing solid A and ferrocene (C)10H10Fe), nickelocene (C)10H10Ni), cobaltocene (C)10H10Co), manganese bis (cyclopentadienyl) (C)10H10Mn), glucose (C)6H12O6) Sucrose (C)12H22O11) Citric acid (C)6H8O7) At least one solid of carboxymethyl cellulose (CMC) and phenolic resin is placed in a solvent, the mass ratio of the two solids is 1: 1-4, the liquid-solid ratio (mL/g) is 10-20: 1, ultrasonic treatment is carried out at 0-50 ℃, the ultrasonic power is 400-800W, the frequency is 20-300 kHz, and the ultrasonic time is 1-4 h. A mixed solution was obtained. The solvent is at least one of water, acetone, diethyl ether, ethylene glycol, glycerol, N-Dimethylacetamide (DMA), N-Dimethylformamide (DMF), dimethyl sulfoxide (DMSO) and Tetrahydrofuran (THF).
(c) And transferring the mixed solution into a high-pressure reaction kettle, wherein the volume of the solution accounts for 40-70% of the volume of the inner container of the reaction kettle, the reaction temperature is 150-300 ℃, the reaction time is 12-48 h, and after the reaction is finished, filtering and drying are carried out to obtain a solid B.
(d) And (3) placing the solid B in acid liquor, stirring for 6-12 h at 30-60 ℃, washing filter residues obtained by filtering with deionized water until the pH of an eluate is 7, and drying to obtain a precursor. The stirring manner is at least one selected from mechanical stirring, gas flow stirring and jet flow stirring.
(e) Placing the precursor in an inert atmosphere for high-temperature carbonization to obtain a silicon-carbon composite material; the high-temperature carbonization conditions are as follows: the heating rate is 1-10 ℃/min, the carbonization temperature is 600-1000 ℃, the carbonization time is 3-7 h, and the inert gas is nitrogen or argon.
The invention also provides an application of the graphene @ egg yolk-eggshell silicon-carbon composite material, and the graphene @ egg yolk-eggshell silicon-carbon composite material is used as a lithium ion battery negative electrode material.
Compared with the prior art, the invention has the following beneficial effects:
(1) according to research, the brand new composite material disclosed by the invention has excellent electrical properties in a lithium ion battery, such as high first-turn coulombic efficiency and long cycle capacity retention rate.
(2) According to the preparation method, under the action of the graphite oxide, the transition metal can be coprecipitated on the surface of the silicon-based material, so that the agglomeration of coprecipitated particles is avoided, and the MOH @ Si @ Go material (solid A) can be prepared; and then, by matching with the in-situ carbon-coating-acid treatment-carbonization process, the silicon-carbon composite material with a yolk-eggshell structure can be formed on the graphene in situ.
However, in the prior art for preparing silicon-carbon composite material, hydrofluoric acid is required to corrode the silicon substrate in order to obtain the silicon-carbon composite material with a certain gap between the carbon layer and the silicon core, and SiF is easily generated in the process4Gas and gas containing F-Waste water poses serious threat to environment. The invention uses hydrochloric acid or sulfuric acid or nitric acid as the substitute acid, and can also obtain the silicon-carbon composite material with a certain gap between the carbon layer and the silicon core, thereby reducing the fluorine pollution in the prior art.
(3) According to the scheme provided by the invention, the silicon-based core with the surface covered with the transition metal hydroxide is dispersed on the graphite oxide with larger specific surface area by an alkaline coprecipitation method, so that the silicon-based material is prevented from re-agglomerating in the subsequent preparation process. Then, an amorphous carbon source is used for coating to form a precursor, a metal oxide and amorphous carbon double-layer coated silicon-based core-shell structure is obtained through high-temperature carbonization, and the metal oxide is removed through acid liquor to obtain the core-shell structure with a certain gap between the silicon-based core and outer-layer carbon. The method can realize the isolation of the silicon-based material and avoid the re-agglomeration of the silicon-based material; the 'gap' can effectively relieve the volume expansion of the silicon-based material during charging and discharging, inhibit the pulverization of the material and improve the cycle performance during charging and discharging; the graphite oxide added in the preparation process can be converted into a graphene (RGO) material with better performance after a series of ultrasonic and high-temperature treatment, so that the conductivity of the silicon-based material is improved, and the rate capability is improved.
(4) The inventor of the invention discovers unexpectedly through research that the novel in-situ composite material can be successfully constructed, the form and modification mode of the material can be reasonably controlled, and the initial capacity and the cycle performance of the material can be obviously improved by synergistically controlling the particle size of a silicon-based material, the use of graphite oxide, the proportion of silicon to graphite oxide, the use and proportion of transition metal, and the selection and use amount of an amorphous carbon source.
Description of the drawings:
FIG. 1 is a cycle chart of the material prepared in example 1.
Detailed Description
The invention will be further illustrated with reference to the following specific examples. It should be noted that these examples are only for illustrating the present invention and are not intended to limit the scope of the present invention. In practice, the technical personnel according to the invention make improvements and modifications, which still belong to the protection scope of the invention.
Example 1
(1) Ultrasonically dispersing graphite oxide in a dilute hydrochloric acid solution with the pH value of 1, wherein the liquid-solid ratio is 700:1, adding a silicon-based material (D50-400 nm amorphous nano silicon) according to the mass ratio of silicon-based cores to the graphite oxide of 10:1, and then carrying out ultrasonic treatment at 50 ℃, wherein the ultrasonic power is 400W, the ultrasonic frequency is 100kHz, and the ultrasonic time is 1.5h, so as to obtain the mixed colloidal solution. Addition of FeCl3·6H2O (amorphous nano-silicon and FeCl)3·6H2The proportion of O is 10:1), uniformly mixing, adding ammonia water with the concentration of 25-28% dropwise while mechanically stirring until the pH value is 10, washing precipitates obtained by centrifugation with deionized water until the pH value of an eluate is 7, and drying to obtain a solid A.
(2) Placing two solids, namely solid A and ferrocene, in acetone, wherein the mass ratio of the two solids is 1:1, the liquid-solid ratio is 20:1, carrying out ultrasonic treatment at 50 ℃, wherein the ultrasonic power is 800W, the ultrasonic frequency is 300kHz, and the ultrasonic time is 4h, thus obtaining a mixed solution.
(3) And transferring the mixed solution into a high-pressure reaction kettle, wherein the volume of the solution accounts for 70% of the volume of the inner container of the reaction kettle, the reaction temperature is 300 ℃, the reaction time is 48 hours, and after the reaction is finished, filtering and drying are carried out to obtain a solid B.
(4) And (3) placing the solid B into an HCl aqueous solution, mechanically stirring for 12h at the temperature of 60 ℃ when the acid concentration is 10mol/L, washing filter residues obtained by filtering with deionized water until the pH value of an eluate is 7, and drying to obtain a precursor.
(5) And (3) putting the precursor in a nitrogen atmosphere for high-temperature carbonization, wherein the gas flow is 100mL/min, the heating rate is 10 ℃/min, and keeping the temperature at 1000 ℃ for 7h to obtain the silicon-carbon composite material.
The silicon-carbon composite material prepared in the embodiment has the structural characteristics of graphene @ yolk-eggshell, the gap between the silicon-based core (yolk) and the amorphous carbon (eggshell) is 3nm, and the coating thickness of the amorphous carbon is 5 nm.
Example 2
(1) Ultrasonically dispersing graphite oxide in a dilute hydrochloric acid solution with the pH value of 1, wherein the liquid-solid ratio is 500:1, adding a silicon-based material (amorphous nano silicon with the diameter of 200nm D50) according to the mass ratio of silicon-based cores to the graphite oxide of 8:1, and then carrying out ultrasonic treatment at the temperature of 25 ℃, wherein the ultrasonic power is 200W, the ultrasonic frequency is 50kHz, and the ultrasonic time is 1.0h, so as to obtain the mixed colloidal solution. Adding NiSO4·6H2O (amorphous nano-silicon and NiCl)2·6H2The ratio of O was 5:1), after mixing, 0.05mol/L NaOH solution was added dropwise with mechanical stirring to pH 8, the precipitate obtained by centrifugation was washed with deionized water until the pH of the eluate was 7, and after drying, solid a was obtained.
(2) Putting the solid A and the nickelocene into glycerol, wherein the mass ratio of the two solids is 1:2, the liquid-solid ratio is 15:1, carrying out ultrasonic treatment at 25 ℃, wherein the ultrasonic power is 600W, the ultrasonic frequency is 100kHz, and the ultrasonic time is 2h to obtain a mixed solution.
(3) And transferring the mixed solution into a high-pressure reaction kettle, wherein the volume of the solution accounts for 60% of the volume of the inner container of the reaction kettle, the reaction temperature is 200 ℃, the reaction time is 36 hours, and after the reaction is finished, filtering and drying are carried out to obtain a solid B.
(4) Placing solid B in H2SO4The acid concentration of the aqueous solution of (1) is 6mol/L, the mechanical stirring is carried out for 8h at the temperature of 40 ℃, filter residue obtained by filtering is washed by deionized water until the pH value of an eluate is 7, and a precursor is obtained after drying.
(5) And (3) putting the precursor in a nitrogen atmosphere for high-temperature carbonization, wherein the gas flow is 70mL/min, the heating rate is 5 ℃/min, and keeping the temperature at 800 ℃ for 5h to obtain the silicon-carbon composite material.
The silicon-carbon composite material prepared in the embodiment has the structural characteristics of graphene @ yolk-eggshell, the gap between the silicon-based core (yolk) and the amorphous carbon (eggshell) is 10nm, and the coating thickness of the amorphous carbon is 10 nm.
Example 3
(1) Ultrasonically dispersing graphite oxide in a dilute hydrochloric acid solution with the pH value of 1, wherein the liquid-solid ratio is 200:1, and adding a silicon-based material (D50-400 nm SiO) according to the mass ratio of the silicon-based core to the graphite oxide of 5:11.5) And then carrying out ultrasonic treatment at 0 ℃, wherein the ultrasonic power is 100W, the ultrasonic frequency is 10kHz, and the ultrasonic time is 0.5h, so as to obtain the mixed colloidal solution. Addition of MnCl2·4H2O(SiO1.5And MnCl2·4H2The ratio of O is 1:1), uniformly mixing, dropwise adding 25-28% ammonia water while mechanically stirring until the pH value is 6, washing precipitates obtained by centrifugation with deionized water until the pH value of an eluate is 7, and drying to obtain a solid A.
(2) Putting the solid A and the glucose into DMF at a mass ratio of 1:4 and a liquid-solid ratio of 10:1, carrying out ultrasonic treatment at 0 ℃ with ultrasonic power of 400W, ultrasonic frequency of 20kHz and ultrasonic time of 1h to obtain a mixed solution.
(3) And transferring the mixed solution into a high-pressure reaction kettle, wherein the volume of the solution accounts for 40% of the volume of the inner container of the reaction kettle, the reaction temperature is 150 ℃, the reaction time is 12 hours, and after the reaction is finished, filtering and drying to obtain a solid B.
(4) Placing the solid B inIn HNO3The acid concentration of the aqueous solution of (1) is 3mol/L, the mechanical stirring is carried out for 6h at 40 ℃, filter residue obtained by filtering is washed by deionized water until the pH value of an eluate is 7, and a precursor is obtained after drying.
(5) And (3) putting the precursor in a nitrogen atmosphere for high-temperature carbonization, wherein the gas flow is 30mL/min, the heating rate is 1 ℃/min, and the heat is preserved for 3h at 600 ℃ to obtain the silicon-carbon composite material.
The silicon-carbon composite material prepared in this example has a graphene @ yolk-eggshell structure, a gap between a silicon-based core (yolk) and amorphous carbon (eggshell) is 30nm, and a coating thickness of the amorphous carbon is 20 nm.
Comparative example 1
The difference from example 1 is that graphite oxide is not added in step (1), a large amount of agglomerates, Fe (OH), exist in the coprecipitation process3Not well deposited on the silicon surface. Through subsequent preparation, only the silicon-based core @ amorphous carbon material is obtained, the shell and the core have no gap basically, and the silicon-carbon composite material is not a silicon-carbon composite material with a graphene @ yolk-eggshell structure.
Comparative example 2
The difference from example 1 is that in step (1), the mass ratio of the silicon-based core to the graphite oxide is 20:1, a large number of agglomerates, Fe (OH), exist in the coprecipitation process3Not well deposited on the silicon surface. Through subsequent preparation, only the silicon-based core @ amorphous carbon material is obtained, and the shell and the core basically have no gap and are not a silicon-carbon composite material with a graphene @ yolk-eggshell structure.
Comparative example 3
The difference from example 1 is that in step (1), D50 of amorphous nano-si is 1 um. The silicon-carbon composite material with the structural characteristics of graphene @ yolk-eggshell is prepared in the comparative example, but no gap is formed between the silicon-based core (yolk) and the amorphous carbon (eggshell), and the coating thickness of the amorphous carbon is 5 nm.
Comparative example 4
The difference from example 1 is that, in step (2), no transition metal water-soluble salt is added, and the silicon-carbon composite material with the structural characteristics of graphene @ yolk-eggshell is prepared in this comparative example, but the gap between the silicon-based core (yolk) and the amorphous carbon (eggshell) is less than 1nm, and the coating thickness of the amorphous carbon is 5 nm.
Comparative example 5
The difference from example 1 is that the mass ratio of the silicon-based material to the transition metal water-soluble salt in step (2) is 20: 1. The silicon-carbon composite material with the structural characteristics of graphene @ yolk-eggshell is prepared in the comparative example, but no gap is formed between the silicon-based core (yolk) and the amorphous carbon (eggshell), and the coating thickness of the amorphous carbon is 5 nm.
Comparative example 6
The difference from example 1 is that, in step (3), the mass ratio of the solid a to the ferrocene is 1:10, the silicon-carbon composite material prepared in this comparative example has the structural characteristics of graphene @ yolk-eggshell, and the gap between the silicon-based core (yolk) and the amorphous carbon (eggshell) is 3nm, but the coating thickness of the amorphous carbon is 50 nm.
Comparative example 7
The same as example 1 except that the reaction temperature in step (3) was 100 ℃. Amorphous carbon does not coat well on silicon-based cores during solvothermal reactions. Through subsequent preparation, only the graphene @ silicon-based core material is obtained, and the silicon-carbon composite material is not a silicon-carbon composite material with a graphene @ yolk-eggshell structure.
And (3) performance testing: the silicon-carbon composite materials obtained in the above examples 1, 2, 3 and comparative examples 1, 2, 3, 4, 5, 6, 7 were mixed according to the following ratio of active material: conductive agent super-p: preparing a negative electrode slurry from the binder PVDF in a ratio of 8:1:1, uniformly mixing with NMP, uniformly coating on a copper foil, drying in vacuum at 80 ℃ for 12h, and slicing to obtain the electrode to be detected. The metal lithium sheet is taken as a counter electrode, and the electrolyte contains 1M LiPF6In a glove box filled with high-purity argon, the membranes were assembled with polypropylene Celgard 2400 to form a CR2025 button cell. And after the assembled battery is kept still for 12 hours, the battery is charged and discharged at a current of 0.2C, and the cut-off voltage is 0.01-3V. The test results are shown in table 1 below. Wherein the first 200 cycles of the charge-discharge cycle of example 1 is shown in figure 1.
TABLE 1
Figure BDA0002162283240000101
Researches show that the composite material required by the invention can effectively improve the coulombic efficiency of the first circle and the capacity retention rate after long circulation.

Claims (10)

1. The graphene @ yolk-eggshell silicon carbon composite material is characterized by comprising graphene and a yolk-eggshell silicon carbon material loaded on the surface of the graphene;
the yolk-eggshell silicon carbon material is a composite material taking amorphous carbon as a shell and a silicon-based material as a core, and a gap is formed between the shell and the core.
2. The graphene @ egg yolk-eggshell silicon carbon composite material as claimed in claim 1, wherein the content of graphene is 5-15%; the mass content of the silicon-based material is 70-90%;
preferably, in the yolk-eggshell silicon carbon material, the diameter of the core is 10 nm-1000 nm, preferably 200-400 nm;
preferably, the thickness of the shell is 5-20 nm;
preferably, the gap distance between the shell and the core is 3-30 nm.
3. A preparation method of a graphene @ egg yolk-egg shell silicon-carbon composite material is characterized by comprising the following steps:
step (1): dispersing a silicon-based material, graphite oxide and acid to obtain a mixed colloidal solution;
step (2): adding water-soluble salt of transition metal into the mixed colloidal solution, adding alkali, carrying out coprecipitation reaction, and then carrying out solid-liquid separation to obtain a solid A;
and (3): dispersing the solid A and an amorphous carbon source into a solvent, carrying out a solvothermal reaction, and carrying out solid-liquid separation after the reaction is finished to obtain a solid B;
and (4): treating the solid B with acid liquor, and washing with water to be neutral to obtain a precursor;
and (5): and carbonizing the precursor to obtain the graphene @ yolk-eggshell silicon-carbon composite material.
4. The graphene @ egg yolk-eggshell silicon carbon composite material as claimed in claim 3, wherein the silicon-based material is at least one of amorphous nano-silicon, amorphous silicon oxide SiOx; x is 0.8-1.5;
wherein the particle size D50 of the amorphous nano silicon particles is 10-400 nm; the grain diameter D50 of the amorphous silicon oxide SiOx is 100 nm-1 um.
5. The preparation method of the graphene @ yolk-eggshell silicon-carbon composite material as claimed in claim 3, wherein the mass ratio of the silicon-based material to the graphite oxide is 5-10: 1;
the pH value of the mixed colloidal solution is 1-2;
in the step (1), the mixed colloidal solution is obtained through ultrasonic dispersion treatment; in the mixed colloidal solution, the liquid-solid ratio is 200-700: 1 mL/g; the ultrasonic power is 100-400W, the frequency is 10-100 kHz, and the ultrasonic time is 0.5-1.5 h.
6. The graphene @ egg yolk-eggshell silicon carbon composite material as claimed in claim 3, wherein said transition metal is at least one of nickel, cobalt, manganese, iron;
the water-soluble salt of the transition metal is at least one of chloride, sulfate and nitrate of the transition metal;
the mass ratio of the silicon-based material to the water-soluble salt of the transition metal is 10-1: 1;
the alkali is at least one of alkali metal hydroxide and ammonia water;
and the pH value in the coprecipitation process is maintained at 6-10.
7. The graphene @ egg yolk-eggshell silicon carbon composite material as claimed in claim 3, wherein the amorphous carbon source is at least one of ferrocene, nickelocene, cobaltocene, manganocene, glucose, sucrose, citric acid, carboxymethyl cellulose, phenolic resin;
in the step (3), the dispersion process is ultrasonic dispersion, the ultrasonic power is 400-800W, the frequency is 20-300 kHz, and the ultrasonic time is 1-4 h;
the mass ratio of the solid A to the amorphous carbon source is 1: 1-4;
the solvent of the initial solution of the solvent thermal reaction is at least one of water, acetone, diethyl ether, ethylene glycol, glycerol, N-Dimethylacetamide (DMA), N-Dimethylformamide (DMF), dimethyl sulfoxide (DMSO) and Tetrahydrofuran (THF);
the liquid-solid ratio of the initial solution of the solvothermal reaction is 10-20: 1 (mL/g);
preferably, the temperature of the solvothermal reaction is 150-300 ℃, and the reaction time is 12-48 h.
8. The method of preparing the graphene @ egg yolk-egg shell silicon carbon composite material of claim 3, wherein the acid solution is HCl or H2SO4、HNO3、H3PO4、HPO3、HClO3、HClO、H2FeO4HCOOH and CH3At least one aqueous solution of COOH, wherein the concentration of the acid liquid is 3-10 mol/L.
9. The method of preparing a graphene @ egg yolk-eggshell silicon carbon composite material as claimed in claim 3, wherein the carbonization process is performed under a protective atmosphere;
the temperature in the carbonization process is 600-1000 ℃;
the carbonization heating rate is 1-10 ℃/min;
the carbonization time is 3-7 h.
10. The graphene @ egg yolk-eggshell silicon-carbon composite material as defined in claim 1 or 2 or the graphene @ egg yolk-eggshell silicon-carbon composite material prepared by the preparation method as defined in any one of claims 3 to 9, wherein the graphene @ egg yolk-eggshell silicon-carbon composite material is used as a negative electrode material of a lithium ion battery.
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