CN110474034B - Nitrogen-doped porous nanosheet silicon-carbon composite material and preparation method and application thereof - Google Patents

Nitrogen-doped porous nanosheet silicon-carbon composite material and preparation method and application thereof Download PDF

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CN110474034B
CN110474034B CN201910779995.9A CN201910779995A CN110474034B CN 110474034 B CN110474034 B CN 110474034B CN 201910779995 A CN201910779995 A CN 201910779995A CN 110474034 B CN110474034 B CN 110474034B
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silicon
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carbon composite
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CN110474034A (en
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郭守武
宋佳佳
郑鹏
刘毅
张利锋
原晓艳
霍京浩
寇领江
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Shaanxi University of Science and Technology
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    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00Secondary cells; Manufacture thereof
    • H01M10/05Accumulators with non-aqueous electrolyte
    • H01M10/052Li-accumulators
    • H01M10/0525Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00Electrodes
    • H01M4/02Electrodes composed of, or comprising, active material
    • H01M4/36Selection of substances as active materials, active masses, active liquids
    • H01M4/362Composites
    • H01M4/364Composites as mixtures
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00Electrodes
    • H01M4/02Electrodes composed of, or comprising, active material
    • H01M4/36Selection of substances as active materials, active masses, active liquids
    • H01M4/38Selection of substances as active materials, active masses, active liquids of elements or alloys
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00Electrodes
    • H01M4/02Electrodes composed of, or comprising, active material
    • H01M4/36Selection of substances as active materials, active masses, active liquids
    • H01M4/38Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H01M4/386Silicon or alloys based on silicon
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00Electrodes
    • H01M4/02Electrodes composed of, or comprising, active material
    • H01M4/62Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624Electric conductive fillers
    • H01M4/625Carbon or graphite
    • YGENERAL 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
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02EREDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10Energy storage using batteries

Abstract

The invention provides a nitrogen-doped porous nanosheet silicon-carbon composite material and a preparation method and application thereof, and the preparation method comprises the following steps: adding a soluble organic substance into a closed container as a carbon source, then adding ammonium chloride, finally adding silicon dioxide, stirring and dispersing, carrying out hydrothermal reaction at the temperature of 100-250 ℃ for 2-24h, drying to obtain a precursor, adding a proper amount of magnesium powder at the temperature of 650-750 ℃ into the precursor, calcining and reducing, and finally washing and etching with hydrofluoric acid to obtain the nitrogen-doped porous nanosheet silicon-carbon composite material. As a battery negative electrode material; the method has the advantages of simple process and low energy consumption in the preparation process, and the nitrogen-doped porous nanosheet silicon-carbon composite material prepared by the method has the characteristics of distinct structural characteristics, porous nanosheet shape, large specific surface area, distinct structural characteristics and excellent electrochemical performance.

Description

Nitrogen-doped porous nanosheet silicon-carbon composite material and preparation method and application thereof
Technical Field
The invention relates to the technical field of silicon-carbon composite materials, in particular to a nitrogen-doped porous nanosheet silicon-carbon composite material and a preparation method and application thereof.
Background
Energy is the basis on which humans live and develop, traditional energy sources, such as: coal, petroleum, natural gas and the like face the problems of reduced reserves, environmental pollution and the like, and can not meet the future social demands. Lithium ion batteries have the characteristics of high working voltage, high energy density, long cycle life, low self-discharge rate, no pollution and the like, and are considered as ideal energy storage and conversion tools. At present, the electric tool is widely applied to various portable electric tools and digital electronic products. With the continuous pursuit of the functions of electronic products, further improvement of the energy density of the lithium ion battery becomes a research hotspot.
Although silicon has a high theoretical specific capacity (4200mAh g)-1) Lower potential for deintercalating lithium: (<0.5V), abundant reserves, environmental friendliness and the like, but the silicon material generates huge volume expansion and shrinkage in the lithium extraction process, so that the structure of the electrode material collapses, and the specific capacity, stability and coulombic efficiency of the electrode material are affected.
In order to alleviate the volume effect of the silicon material in the charging and discharging processes, the conventional method is used for preparing the nano material, so that the specific surface area of the material is increased, such as zero-dimensional nano particles, one-dimensional nanowires, nanotubes and nano rods, two-dimensional nanobelts, nano sheets and three-dimensional porous nano materials. And the nano-spherical silicon dioxide is used as a silicon source, and the nano-material obtained by magnesium thermal reduction is generally in a nano-particle shape, for example, Chinese patent CN106816590A discloses a preparation method of a high-capacity lithium ion battery composite negative electrode material. Although the method relieves the capacity attenuation of the material to a certain extent, the nanoparticles are easy to agglomerate, so that the volume effect in the charge and discharge process cannot be fundamentally inhibited, and the capacity still can be rapidly attenuated along with the increase of the cycle number.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides a nitrogen-doped porous nano-sheet silicon-carbon composite material and a preparation method and application thereof.
The invention is realized by the following technical scheme:
a preparation method of a nitrogen-doped porous nanosheet silicon-carbon composite material comprises the following steps:
step 1, dissolving a carbon source and ammonium chloride in water, adding silicon dioxide, and uniformly stirring and dispersing to obtain a precursor solution;
step 2, carrying out hydrothermal reaction on the precursor liquid at the temperature of 100-250 ℃ for 2-24h, and drying the product to obtain a precursor;
and 3, mixing the precursor with magnesium powder, then calcining and reducing, and finally washing and etching with hydrofluoric acid to obtain the nitrogen-doped porous nano-sheet silicon-carbon composite material.
Preferably, in step 1, the preparation method of the silica comprises: mixing absolute ethyl alcohol, water and ammonia water, stirring uniformly, adding tetraethoxysilane, continuously stirring, centrifuging, washing and drying to obtain the silicon dioxide nano-particles.
Preferably, in step 1, the carbon source is any one of glucose, sucrose, maltose, fructose, lactose, citric acid, dopamine, tannic acid and sodium acetate.
Preferably, in step 1, the mass ratio of the carbon source to the ammonium chloride is: 1, the mass ratio of the silicon dioxide to the carbon source is as follows: (0.01-0.3):1.
Preferably, in step 3, the mass ratio of the magnesium powder to the precursor is as follows: (0.1-2):1.
Preferably, in step 3, the mass concentration of the hydrofluoric acid is: 0.5% -10%, the etching time is as follows: 0.5-10 h.
Preferably, in the step 3, the calcining temperature is 650-750 ℃ and the time is 2-10 h.
The nitrogen-doped porous nanosheet silicon-carbon composite material prepared by the preparation method.
The nitrogen-doped porous nanosheet silicon-carbon composite material is applied to a lithium ion battery as a negative electrode material.
Compared with the prior art, the invention has the following beneficial technical effects:
the invention obtains silicon dioxide and nitrogen-doped carbon composite material by adding carbon source and ammonium chloride in the hydrothermal process, then adding magnesium powder, reducing the silicon dioxide into silicon by magnesiothermic reduction, and generating magnesium oxide by magnesium, wherein the process comprises the following steps: SiO 22And the +2Mg is 2MgO + Si, the magnesium oxide is removed by hydrochloric acid, and the silicon dioxide which is not reduced is etched by hydrofluoric acid to form a porous structure. First, ammonium chloride is used as a nitrogen source, and introduction of nitrogen into the material can improve the conductivity of the material. Secondly, the ammonium chloride can absorb the heat released by the magnesiothermic reaction during the magnesiothermic reduction process. The magnesiothermic reduction process can make the silicon dioxide spheres become nano silicon particles with smaller size, and the nano silicon particles are self-assembled into the composite material of the nitrogen-doped porous silicon carbon nano sheet under the combined action of ammonium chloride and glucose. The nitrogen-doped porous silicon carbon nanosheets are not easy to agglomerate and have good stability, and gaps among the nanosheets can relieve volume expansion and contraction in the process of lithium intercalation and deintercalation, so that the battery has high specific capacity and good cycling stability. In addition, the addition of carbon can enhance the toughness of the material and relieve the structural collapse caused by the volume effect in the process of lithium extraction; and the porous structure can accommodate volume expansion during lithium intercalation, thereby suppressing the volume effect. In addition, the nitrogen doping can shorten the lithium ion diffusion path, effectively improve the conductivity of the material and improve the characteristic of poor conductivity of the silicon material. The method has the characteristics of easily obtained raw materials, low cost, low energy consumption and simple preparation process, and the prepared silicon-carbon composite material is a nano-scale material and is controllable, so that the use performance of the material can be improved, and the method is favorable for industrial production.
The invention finally generates the silicon-carbon composite material with a three-dimensional porous structure consisting of nanosheets containing pores.
Drawings
Fig. 1 is a powder diffraction pattern of the nitrogen-doped porous nanosheet silicon-carbon composite prepared in example 1.
Fig. 2 is a scanning electron microscope image and a transmission electron microscope image of the nitrogen-doped porous nanosheet silicon-carbon composite material prepared in example 1 of the present invention.
Fig. 3 is a constant current charging and discharging curve diagram of the nitrogen-doped porous nanosheet silicon-carbon composite material prepared in example 1 of the present invention.
Fig. 4 is a scanning electron microscope image obtained by assembling a sample into a battery, performing a constant current charge and discharge test 250 times, and disassembling the battery.
Fig. 5 is a scanning electron microscope image of the nitrogen-doped porous nanosheet silicon-carbon composite material prepared in example 1 of the present invention.
Detailed Description
The present invention will now be described in further detail with reference to specific examples, which are intended to be illustrative, but not limiting, of the invention.
A preparation method of a nitrogen-doped porous nanosheet silicon-carbon composite material comprises the following steps: adding a soluble organic substance into a closed container as a carbon source, then adding ammonium chloride, finally adding silicon dioxide, stirring and dispersing, carrying out hydrothermal reaction at the temperature of 100-250 ℃ for 2-24h, drying to obtain a precursor, adding a proper amount of magnesium powder at the temperature of 650-750 ℃ into the precursor, calcining and reducing, and finally washing and etching with hydrofluoric acid to obtain the nitrogen-doped porous nanosheet silicon-carbon composite material.
The preparation method of the silicon dioxide comprises the following steps:
mixing absolute ethyl alcohol, water and ammonia water, stirring for 30min at 25 ℃, rapidly adding tetraethoxysilane, continuously stirring, centrifuging, washing with water, washing with alcohol, and drying to obtain the silica nanosphere with the particle size of 200-300 nm.
The preferable temperature of the hydrothermal reaction is 120-200 ℃; the hydrothermal time is preferably 6-20 h; the drying process adopts freeze drying, vacuum drying and supercritical drying, preferably freeze drying or supercritical drying; the calcination time is 2-10h, and the graphitization degree of the carbon is favorably improved in the calcination process.
The carbon source is selected from any one of glucose, sucrose, maltose, fructose, lactose, citric acid, dopamine, tannic acid and sodium acetate.
The mass ratio of the carbon source to the ammonium chloride is as follows: (0.1-10):1.
The mass ratio of the silicon dioxide to the carbon source is as follows: (0.01-0.3) 1, preferably: (0.05-0.2):1.
The mass ratio of the magnesium powder to the precursor is as follows: (0.1-2) 1, preferably: (0.3-1):1.
The mass concentration of the hydrofluoric acid is as follows: 0.5% to 10%, preferably: 1 to 5 percent.
The hydrofluoric acid etching time is as follows: 0.5-10h, preferably: 2-5 h.
In the following examples, the preparation of silica is as follows:
75mL of absolute ethyl alcohol, 10mL of water and 3.15mL of ammonia water are stirred for 30min at 25 ℃, 6mL of ethyl orthosilicate is rapidly added, stirring is continued for 1h, and the silicon dioxide nano-particles with the particle size of 200-300nm are obtained after centrifugation, water washing, alcohol washing and drying.
Example 1
5g of glucose and 5g of ammonium chloride were dissolved in 70ml of water, 1g of silica was sufficiently stirred, and the mixture was transferred to a closed reaction vessel and reacted at 220 ℃ for 3.5 hours. And drying after the reaction is finished to obtain a precursor. Adding magnesium powder with the mass being 1 time of that of the precursor, uniformly grinding, calcining at 650 ℃ for 10h in an argon atmosphere, stirring in 1M HCl for 2h, removing impurities, washing, filtering, drying, etching for 6h by using HF with the mass fraction being 2%, washing and drying to obtain the silicon-carbon composite material, wherein the powder diffraction pattern of the silicon-carbon composite material is shown in figure 1, and three peaks at 28.6, 47.4 and 56.3 degrees correspond to (111), (200) and (311) crystal faces of cubic phase Si (JCPDS 27-1402). Peaks at 35.6, 60.0, 71.8 correspond to SiC peaks, and peaks at 18.0, 26.9, 42.8, 62.1 degrees correspond to C peaks. Fig. 2 a, b and 5 are scanning electron micrographs of the prepared material, which show that the prepared material is a nano-sheet structure self-assembled by nano-particles, and the nano-sheets have small holes and gaps between the sheets. In FIG. 2, c, d and e are transmission electron micrographs of the sample, and it can be seen from the c picture that the prepared sample is sheet-shaped, which is consistent with the scanning result; from the high resolution of the samples in graphs d and e, it is possible to see the lattice fringes, measured with a interplanar spacing of 0.31nm, corresponding to the (111) plane of silicon. The transmission electron microscope energy spectrum of f, g, h, i, j and k shows that the elements Si, C, O and N are uniformly distributed in the sample. Fig. 3 is a constant current charge and discharge curve. Fig. 4 is a scanning electron microscope image of a sample taken after the sample is assembled into a battery and the battery is disassembled after 250 times of constant current charging and discharging tests, and the sample still has a sheet structure, which shows that the sheet has good structural stability.
And uniformly mixing the obtained silicon-carbon composite material with acetylene black and polyvinylidene fluoride according to the mass ratio of 8:1:1, smearing on copper foil, and assembling the button cell as a lithium ion battery negative electrode material. The electrolyte is LiPF6(1mol/L) EC: DMC 1:1:1 (volume ratio). The counter electrode is a lithium plate.
The battery is cycled for 10 times under the voltage interval of 0.01-3V and the current density of 100mA/g, and then the discharge specific capacity of the battery is 830mAh/g after the battery is cycled for 240 times under the current density of 200 mA/g.
Example 2
5.5g of sucrose and 4.5g of ammonium chloride were dissolved in 70ml of water, 1.2g of silica was sufficiently stirred, and the mixture was transferred to a closed reaction vessel and reacted at 200 ℃ for 4 hours. And drying after the reaction is finished to obtain a precursor. Adding magnesium powder with the mass 1.5 times of that of the precursor, uniformly grinding, calcining for 6h at 690 ℃ under the atmosphere of argon, stirring for 2h in 1M HCl, removing impurities, washing, filtering, drying, etching for 10h by using HF with the mass fraction of 0.5%, and washing and drying to obtain the silicon-carbon composite material.
And uniformly mixing the obtained silicon-carbon composite material with acetylene black and polyvinylidene fluoride according to the mass ratio of 8:1:1, smearing on copper foil, and assembling the button cell as a lithium ion battery negative electrode material. The electrolyte is LiPF6(1mol/L) EC: DMC 1:1:1 (volume ratio). The counter electrode is a lithium plate.
The battery is cycled for 10 times under the conditions that the voltage interval is 0.01-3V and the current density is 100mA/g, and then the discharge specific capacity is 840mAh/g after the battery is cycled for 240 times under the current density of 200 mA/g.
Example 3
10g of maltose and 6g of ammonium chloride were dissolved in 120ml of water, then 0.1g of silica was sufficiently stirred, and the mixture was transferred to a closed reaction vessel and reacted at 180 ℃ for 5 hours. And drying after the reaction is finished to obtain a precursor. Adding magnesium powder with the mass being 0.1 time of that of the precursor, uniformly grinding, calcining for 3h at 740 ℃ under the atmosphere of argon, stirring for 2h in 1M HCl, removing impurities, washing, filtering, drying, etching for 0.5h by using HF with the mass fraction of 10%, and washing and drying to obtain the silicon-carbon composite material.
And uniformly mixing the obtained silicon-carbon composite material with acetylene black and polyvinylidene fluoride according to the mass ratio of 8:1:1, smearing on copper foil, and assembling the button cell as a lithium ion battery negative electrode material. The electrolyte is LiPF6(1mol/L) EC: DMC 1:1:1 (volume ratio). The counter electrode is a lithium plate.
The battery is cycled for 10 times under the conditions that the voltage interval is 0.01-3V and the current density is 100mA/g, and then the battery is cycled for 240 times under the current density of 200mA/g, and the discharge specific capacity is 400 mAh/g.
Example 4
5g of dopamine and 0.5g of ammonium chloride are dissolved in 50ml of water, then 1.5g of silicon dioxide is fully stirred, and the mixed solution is transferred to a closed reaction kettle and reacts for 6 hours at 160 ℃. And drying after the reaction is finished to obtain a precursor. Adding magnesium powder with the mass 2 times of that of the precursor, uniformly grinding, calcining for 7h at 680 ℃ under the argon atmosphere, stirring for 2h in 1M HCl, removing impurities, washing, filtering, drying, etching for 2h by using HF with the mass fraction of 6%, and washing and drying to obtain the silicon-carbon composite material.
And uniformly mixing the obtained silicon-carbon composite material with acetylene black and polyvinylidene fluoride according to the mass ratio of 8:1:1, smearing on copper foil, and assembling the button cell as a lithium ion battery negative electrode material. The electrolyte is LiPF6(1mol/L) EC: DMC 1:1:1 (volume ratio). The counter electrode is a lithium plate.
The battery is cycled for 10 times under the conditions that the voltage interval is 0.01-3V and the current density is 100mA/g, and then the discharge specific capacity is 820mAh/g after the battery is cycled for 240 times under the current density of 200 mA/g.
Example 5
7g of dopamine and 1g of ammonium chloride are dissolved in 60ml of water, then 1g of silicon dioxide is fully stirred, and the mixed solution is transferred to a closed reaction kettle and reacts for 10 hours at the temperature of 140 ℃. And drying after the reaction is finished to obtain a precursor. Adding magnesium powder with the mass 1.2 times of that of the precursor, uniformly grinding, calcining for 9h at 660 ℃ under the atmosphere of argon, stirring for 2h in 1M HCl, removing impurities, washing, filtering, drying, etching for 1.5h by using HF with the mass fraction of 7%, and washing and drying to obtain the silicon-carbon composite material.
And uniformly mixing the obtained silicon-carbon composite material with acetylene black and polyvinylidene fluoride according to the mass ratio of 8:1:1, smearing on copper foil, and assembling the button cell as a lithium ion battery negative electrode material. The electrolyte is LiPF6(1mol/L) EC: DMC 1:1:1 (volume ratio). The counter electrode is a lithium plate.
The battery is cycled for 10 times under the conditions that the voltage interval is 0.01-3V and the current density is 100mA/g, and then the discharge specific capacity is 780mAh/g after the battery is cycled for 240 times under the current density of 200 mA/g.
Example 6
7.5g of dopamine and 5g of ammonium chloride are dissolved in 80ml of water, then 0.8g of silicon dioxide is fully stirred, and the mixed solution is transferred to a closed reaction kettle and reacts for 2 hours at 250 ℃. And drying after the reaction is finished to obtain a precursor. Adding magnesium powder with the mass being 0.25 times of that of the precursor, uniformly grinding, calcining for 5 hours at 700 ℃ under the atmosphere of argon, stirring for 2 hours in 1M HCl, removing impurities, washing, filtering, drying, etching for 5 hours by using HF with the mass fraction being 3%, and washing and drying to obtain the silicon-carbon composite material.
And uniformly mixing the obtained silicon-carbon composite material with acetylene black and polyvinylidene fluoride according to the mass ratio of 8:1:1, smearing on copper foil, and assembling the button cell as a lithium ion battery negative electrode material. The electrolyte is LiPF6(1mol/L) EC: DMC 1:1:1 (volume ratio). The counter electrode is a lithium plate.
The battery is cycled for 10 times under the voltage interval of 0.01-3V and the current density of 100mA/g, and then the discharge specific capacity of the battery is 755mAh/g after the battery is cycled for 240 times under the current density of 200 mA/g.
Example 7
5g of tannic acid and 6g of ammonium chloride were dissolved in 75ml of water, then 0.25g of silica was sufficiently stirred, and the mixture was transferred to a closed reaction vessel and reacted at 100 ℃ for 24 hours. And drying after the reaction is finished to obtain a precursor. Adding magnesium powder with the mass being 0.15 times of that of the precursor, uniformly grinding, calcining for 3h at 740 ℃ under the atmosphere of argon, stirring for 2h in 1M HCl, removing impurities, washing, filtering, drying, etching for 3h by using HF with the mass fraction of 5%, and washing and drying to obtain the silicon-carbon composite material.
And uniformly mixing the obtained silicon-carbon composite material with acetylene black and polyvinylidene fluoride according to the mass ratio of 8:1:1, smearing on copper foil, and assembling the button cell as a lithium ion battery negative electrode material. The electrolyte is LiPF6(1mol/L) EC: DMC 1:1:1 (volume ratio). The counter electrode is a lithium plate.
The battery is cycled for 10 times under the conditions that the voltage interval is 0.01-3V and the current density is 100mA/g, and then the battery is cycled for 240 times under the current density of 200mA/g, and the discharge specific capacity is 550 mAh/g.
Example 8
4.5g of tannic acid and 7g of ammonium chloride were dissolved in 75ml of water, 1g of silica was sufficiently stirred, and the mixture was transferred to a closed reaction vessel and reacted at 140 ℃ for 14 hours. And drying after the reaction is finished to obtain a precursor. Adding magnesium powder with the mass 1 time of that of the precursor, uniformly grinding, calcining for 2h at 750 ℃ in argon atmosphere, stirring for 2h in 1M HCl, removing impurities, washing, filtering, drying, etching for 4h by using HF with the mass fraction of 4%, and washing and drying to obtain the silicon-carbon composite material.
And uniformly mixing the obtained silicon-carbon composite material with acetylene black and polyvinylidene fluoride according to the mass ratio of 8:1:1, smearing on copper foil, and assembling the button cell as a lithium ion battery negative electrode material. The electrolyte is LiPF6(1mol/L) EC: DMC 1:1:1 (volume ratio). The counter electrode is a lithium plate.
The battery is cycled for 10 times under the conditions that the voltage interval is 0.01-3V and the current density is 100mA/g, and then the battery is cycled for 240 times under the current density of 200mA/g, and the discharge specific capacity is 795 mAh/g.
Example 9
4g of citric acid and 7.5g of ammonium chloride were dissolved in 70ml of water, 1.2g of silica was sufficiently stirred, and the mixture was transferred to a closed reaction vessel and reacted at 120 ℃ for 16 hours. And drying after the reaction is finished to obtain a precursor. Adding magnesium powder with the mass 1.2 times of that of the precursor, uniformly grinding, calcining for 3.5h at 730 ℃ under the argon atmosphere, stirring for 2h in 1M HCl, removing impurities, washing, filtering, drying, etching for 9h by using HF with the mass fraction of 0.8%, and washing and drying to obtain the silicon-carbon composite material.
And uniformly mixing the obtained silicon-carbon composite material with acetylene black and polyvinylidene fluoride according to the mass ratio of 8:1:1, smearing on copper foil, and assembling the button cell as a lithium ion battery negative electrode material. The electrolyte is LiPF6(1mol/L) EC: DMC 1:1:1 (volume ratio). The counter electrode is a lithium plate.
The battery is cycled for 10 times under the conditions that the voltage interval is 0.01-3V and the current density is 100mA/g, and then the discharge specific capacity is 770mAh/g after the battery is cycled for 240 times under the current density of 200 mA/g.
Example 10
3.5g of citric acid and 8g of ammonium chloride were dissolved in 70ml of water, then 0.5g of silica was sufficiently stirred, and the mixture was transferred to a closed reaction vessel and reacted at 130 ℃ for 15 hours. And drying after the reaction is finished to obtain a precursor. Adding magnesium powder with the mass being 0.2 times of that of the precursor, uniformly grinding, calcining for 3h at 740 ℃ under the atmosphere of argon, stirring for 2h in 1M HCl, removing impurities, washing, filtering, drying, etching for 8h by using HF with the mass fraction being 1.5%, and washing and drying to obtain the silicon-carbon composite material.
And uniformly mixing the obtained silicon-carbon composite material with acetylene black and polyvinylidene fluoride according to the mass ratio of 8:1:1, smearing on copper foil, and assembling the button cell as a lithium ion battery negative electrode material. The electrolyte is LiPF6(1mol/L) EC: DMC 1:1:1 (volume ratio). The counter electrode is a lithium plate.
The battery is cycled for 10 times under the conditions that the voltage interval is 0.01-3V and the current density is 100mA/g, and then the discharge specific capacity is 610mAh/g after the battery is cycled for 240 times under the current density of 200 mA/g.
Example 11
3g of fructose and 8.5g of ammonium chloride were dissolved in 70ml of water, then 0.8g of silica was sufficiently stirred, and the mixture was transferred to a closed reaction vessel and reacted at 120 ℃ for 16 hours. And drying after the reaction is finished to obtain a precursor. Adding magnesium powder with the mass being 0.3 times of that of the precursor, uniformly grinding, calcining for 4.5h at 710 ℃ under the atmosphere of argon, stirring for 2h in 1M HCl, removing impurities, washing, filtering, drying, etching for 7h by using HF with the mass fraction being 2.5%, and washing and drying to obtain the silicon-carbon composite material.
And uniformly mixing the obtained silicon-carbon composite material with acetylene black and polyvinylidene fluoride according to the mass ratio of 8:1:1, smearing on copper foil, and assembling the button cell as a lithium ion battery negative electrode material. The electrolyte is LiPF6(1mol/L) EC: DMC 1:1:1 (volume ratio). The counter electrode is a lithium plate.
The battery is cycled for 10 times under the conditions that the voltage interval is 0.01-3V and the current density is 100mA/g, and then the discharge specific capacity is 705mAh/g after the battery is cycled for 240 times under the current density of 200 mA/g.
Example 12
1g of fructose and 10g of ammonium chloride were dissolved in 70ml of water, then 0.3g of silica was sufficiently stirred, and the mixture was transferred to a closed reaction vessel and reacted at 110 ℃ for 20 hours. And drying after the reaction is finished to obtain a precursor. Adding magnesium powder with the mass being 0.15 times of that of the precursor, uniformly grinding, calcining for 8h at 670 ℃ under the atmosphere of argon, stirring for 2h in 1M HCl, removing impurities, washing, filtering, drying, etching for 8h by using HF with the mass fraction being 1%, and washing and drying to obtain the silicon-carbon composite material.
And uniformly mixing the obtained silicon-carbon composite material with acetylene black and polyvinylidene fluoride according to the mass ratio of 8:1:1, smearing on copper foil, and assembling the button cell as a lithium ion battery negative electrode material. The electrolyte is LiPF6(1mol/L) EC: DMC 1:1:1 (volume ratio). The counter electrode is a lithium plate.
The battery is cycled for 10 times under the voltage interval of 0.01-3V and the current density of 100mA/g, and then the discharge specific capacity of the battery is 415mAh/g after the battery is cycled for 240 times under the current density of 200 mA/g.
Example 13
8g of maltose and 3g of ammonium chloride were dissolved in 70ml of water, then 0.7g of silica was sufficiently stirred, and the mixture was transferred to a closed reaction vessel and reacted at 240 ℃ for 3 hours. And drying after the reaction is finished to obtain a precursor. Adding magnesium powder with the mass being 0.25 times of that of the precursor, uniformly grinding, calcining for 9 hours at 650 ℃ under the atmosphere of argon, stirring for 2 hours in 1M HCl, removing impurities, washing, filtering, drying, etching for 6 hours by using HF with the mass fraction being 2%, and washing and drying to obtain the silicon-carbon composite material.
And uniformly mixing the obtained silicon-carbon composite material with acetylene black and polyvinylidene fluoride according to the mass ratio of 8:1:1, smearing on copper foil, and assembling the button cell as a lithium ion battery negative electrode material. The electrolyte is LiPF6(1mol/L) EC: DMC 1:1:1 (volume ratio). The counter electrode is a lithium plate.
The battery is cycled for 10 times under the conditions that the voltage interval is 0.01-3V and the current density is 100mA/g, and then the discharge specific capacity of the battery is 685mAh/g after the battery is cycled for 240 times under the current density of 200 mA/g.
Example 14
10g of lactose and 1g of ammonium chloride are dissolved in 70ml of water, then 2.5g of silicon dioxide are fully stirred, and the mixture is transferred to a closed reaction kettle and reacted for 4.5h at 190 ℃. And drying after the reaction is finished to obtain a precursor. Adding magnesium powder with the mass 1.8 times of that of the precursor, uniformly grinding, calcining for 2h at 750 ℃ under the atmosphere of argon, stirring for 2h in 1M HCl, removing impurities, washing, filtering, drying, etching for 5h by using HF with the mass fraction of 3%, and washing and drying to obtain the silicon-carbon composite material.
And uniformly mixing the obtained silicon-carbon composite material with acetylene black and polyvinylidene fluoride according to the mass ratio of 8:1:1, smearing on copper foil, and assembling the button cell as a lithium ion battery negative electrode material. The electrolyte is LiPF6(1mol/L) EC: DMC 1:1:1 (volume ratio). The counter electrode is a lithium plate.
The battery is cycled for 10 times under the conditions that the voltage interval is 0.01-3V and the current density is 100mA/g, and then the discharge specific capacity is 820mAh/g after the battery is cycled for 240 times under the current density of 200 mA/g.

Claims (4)

1. A preparation method of a nitrogen-doped porous nanosheet silicon-carbon composite material is characterized by comprising the following steps:
step 1, dissolving a carbon source and ammonium chloride in water, adding silicon dioxide, and uniformly stirring and dispersing to obtain a precursor solution;
step 2, carrying out hydrothermal reaction on the precursor liquid at the temperature of 100-250 ℃ for 2-24h, and drying the product to obtain a precursor;
step 3, mixing the precursor with magnesium powder, then calcining and reducing, and finally washing and etching with hydrofluoric acid to obtain the nitrogen-doped porous nanosheet silicon-carbon composite material;
in the step 1, the carbon source is any one of glucose, sucrose, maltose, fructose, lactose, citric acid, dopamine, tannic acid and sodium acetate;
in the step 1, the mass ratio of the carbon source to the ammonium chloride is as follows: 1, the mass ratio of the silicon dioxide to the carbon source is as follows: (0.01-0.3) 1;
in the step 3, the mass ratio of the magnesium powder to the precursor is as follows: (0.1-2) 1;
in step 3, the mass concentration of the hydrofluoric acid is as follows: 0.5% -10%, the etching time is as follows: 0.5-10 h;
in the step 3, the calcining temperature is 650-750 ℃ and the time is 2-10 h.
2. The method for preparing the nitrogen-doped porous nanosheet silicon-carbon composite material of claim 1, wherein in step 1, the method for preparing the silica is: mixing absolute ethyl alcohol, water and ammonia water, stirring uniformly, adding tetraethoxysilane, continuously stirring, centrifuging, washing and drying to obtain the silicon dioxide nano-particles.
3. The nitrogen-doped porous nanosheet silicon-carbon composite prepared by the preparation method of any one of claims 1-2.
4. The application of the nitrogen-doped porous nanosheet silicon-carbon composite material of claim 3 as a negative electrode material in a lithium ion battery.
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