CN107317012B - High-performance Si/C composite material for negative electrode material of lithium ion secondary battery and preparation method thereof - Google Patents

High-performance Si/C composite material for negative electrode material of lithium ion secondary battery and preparation method thereof Download PDF

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CN107317012B
CN107317012B CN201710508925.0A CN201710508925A CN107317012B CN 107317012 B CN107317012 B CN 107317012B CN 201710508925 A CN201710508925 A CN 201710508925A CN 107317012 B CN107317012 B CN 107317012B
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CN107317012A (en
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徐立强
侯璇
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Shenzhen Research Institute Of Shandong 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
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—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
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    • 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
    • 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
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • 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
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes
    • 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
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    • 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

The invention provides a high-performance Si/C composite material for a negative electrode material of a lithium ion secondary battery and a preparation method thereof, wherein the preparation method comprises the following steps: soaking bagasse in acid solution, washing, drying, and calcining in air to obtain SiO2Powder; grinding and uniformly mixing SiO2 powder and magnesium powder, calcining in the atmosphere of reducing protective gas, soaking in acid solution and hydrofluoric acid aqueous solution, and then washing and drying to obtain Si nano particles; adding the obtained Si nano-particles into an ascorbic acid aqueous solution, stirring at room temperature, and then stirring at 80-100 ℃ for 0.5-1 h; calcining the mixture in a protective gas atmosphere to obtain the Si/C composite material. The raw materials used in the invention are simple and easily available, green and environment-friendly, have low price and can be produced in large batch; the experimental method is simple and easy to operate, and has low requirements on equipment; the prepared material has uniform pore size distribution and excellent electrochemical performance.

Description

High-performance Si/C composite material for negative electrode material of lithium ion secondary battery and preparation method thereof
Technical Field
The invention relates to a high-performance Si/C composite material for a negative electrode material of a lithium ion secondary battery and a preparation method thereof, belonging to the technical field of lithium ion batteries.
Background
Silicon is considered one of the most promising anode materials because its theoretical specific capacity (4200mA h/g) is tens of times higher than that of commercial graphite anodes (370mA h/g). However, silicon negative electrode materials suffer from a serious problem in that the silicon electrode undergoes considerable volume expansion during charge and discharge cycles (up to 300% during electrochemical lithiation), resulting in cracking and pulverization of silicon, ultimately resulting in a rapid and severe loss of capacity of the negative electrode material within a few cycles of charge and discharge cycles.
Researchers have sought to find that the use of nanostructured silicon can effectively solve the above problems because the nano-silicon has a separation distance between them that can act as a structural buffer space to accommodate the volume expansion of silicon. Experimental results have also demonstrated that nano-silicon does have superior electrochemical performance, however, the long cycle performance of silicon is still unsatisfactory. Therefore, researchers are also exploring to design and synthesize a suitable structure so that the silicon material has high specific capacity, good rate and long cycle performance, and the commercialization process of silicon as a potential lithium ion battery negative electrode material is continuously promoted.
Researches on coating carbon and related materials thereof or metal materials on a silicon material have also been carried out, and by using the amorphous carbon and the metal coating as a buffer material of silicon, the mechanical stress caused by huge volume change of silicon in an electrochemical process can be effectively relieved, and meanwhile, the amorphous carbon and the metal coating can also serve as an electronic conductor, so that the conductivity of the material is effectively improved. For example, chinese patent document CN104752691A discloses a silicon/carbon composite negative electrode material for lithium ion batteries and a preparation method thereof. The material consists of a graphite framework material, an intermediate buffer layer SiOC material, carbon fiber and a silicon-containing material coated with carbon on the surface, wherein the silicon-containing material coated with carbon on the surface is combined with the graphite framework material through the buffer layer SiOC and the carbon fiber; in the composite material, the silicon material coated with the amorphous carbon is effectively contacted with graphite under the action of SiOC and carbon fiber, so that the aggregation of the silicon material and the stripping of the silicon material from the graphite are avoided; the composite material has novel structural design but complicated preparation steps, high cost and general electrochemical performance, and long cycle performance needs to be further developed; for another example, chinese patent document CN104466185A discloses a silicon/carbon composite negative electrode material, a preparation method thereof, a lithium ion battery negative electrode, and a lithium ion battery. The silicon/carbon composite negative electrode material is a core-shell coating structure which takes nano silicon particles as a core and takes in-situ carbon as a shell, and a gap is formed between the nano silicon particles and the in-situ carbon shell; the preparation method of the anode material comprises the following steps: coating SiO2 composite material with organic carbon source, carrying out preoxidation treatment on the SiO2 composite material coated with the organic carbon source, and coating SiO2 with the organic carbon source after preoxidation treatment2In-situ carbonization and SiO of composite material2And carrying out a magnesiothermic reduction reaction and the like. The silicon/carbon composite negative electrode material has excellent conductivity and structural stability, and the preparation method is safe and environment-friendly and is suitable for industrial production. However, the preparation steps are troublesome and high in cost, the raw material is the nano silicon dioxide which is purchased, further treatment is needed, and the electrochemical performance needs to be improved.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a high-performance Si/C composite material for a negative electrode material of a lithium ion secondary battery, and the composite material has uniform pore size distribution and excellent electrochemical performance.
The invention also provides a preparation method of the Si/C composite material for the cathode material of the high-performance lithium ion secondary battery, which is simple and easy to operate, has low requirement on equipment, uses simple and easily-obtained raw materials, is green and environment-friendly, has low price and can be produced in large batch.
The technical scheme of the invention is as follows:
a high-performance lithium ion secondary battery cathode material Si/C composite material comprises a carbon and silicon composite, wherein the mass content of carbon in the composite is 10-35%, and the mass content of silicon in the composite is 65-90%; the micro-morphology of the composite material is as follows: the surface of the Si nano particle is coated with a carbon layer to form a carbon-silicon nano composite ball, and the carbon-silicon nano composite ball is loaded on the surface of the lamellar carbon.
Preferably, according to the present invention, the Si nanoparticles have a size of 15 to 25nm, the carbon layer has a thickness of 3 to 7nm, and the spheres have a diameter of 18 to 32 nm.
According to the invention, the Si/C composite material is preferably prepared by taking bagasse and ascorbic acid as raw materials; firstly, bagasse is taken as raw material to prepare SiO2Reducing to prepare Si nano particles; then the carbon source is ascorbic acid.
Preferably, the mass ratio of the Si nanoparticles to the ascorbic acid is 1: 0.6-5.
A preparation method of a high-performance Si/C composite material of a lithium ion secondary battery cathode material comprises the following steps:
(1) soaking bagasse in 0.5-2mol/L acid solution for 1-12h, washing, drying, and calcining in air atmosphere to obtain SiO2Powder;
(2) grinding and uniformly mixing the SiO2 powder prepared in the step (1) and magnesium powder, and calcining in a reducing protective gas atmosphere to obtain a mixture; soaking the mixture in 0.5-2mol/L acid solution for 5-10h, then soaking in 2-8% hydrofluoric acid water solution for 1-10min, washing, and drying to obtain Si nanoparticles;
(3) adding the Si nano-particles prepared in the step (2) into an ascorbic acid aqueous solution, and stirring at room temperature for 6-10 h; then stirring for 0.5-1h at 80-100 ℃ to obtain sol; and calcining the obtained sol in a protective gas atmosphere to obtain the Si/C composite material.
Preferably according to the invention, the ratio of the mass of the sugar cane to the volume of the acid solution in step (1) is: 0.1-1 g/mL.
Preferably according to the invention, the acid in step (1) is one of hydrochloric acid, sulfuric acid or nitric acid; the acid solution is an aqueous acid solution or a mixed solution of an acid and water and an alcohol.
Further preferably, the alcohol is absolute ethyl alcohol; in the mixed solution of the acid, the water and the alcohol, the volume ratio of the water to the alcohol is 0.1-0.5: 1.
According to the invention, the washing mode in the step (1) is that deionized water and absolute ethyl alcohol are respectively washed alternately.
According to the invention, the drying mode in the step (1) is preferably drying for 2-12h at 80-120 ℃.
According to the invention, the calcination temperature in the step (1) is 500-800 ℃, the calcination time is 2-5h, and the temperature rise rate is 1-5 ℃/min.
According to a preferred embodiment of the present invention, the SiO in step (2)2The mass ratio of the powder to the magnesium powder is 0.5-1: 1.
Preferably, according to the present invention, the reducing protective gas in step (2) is a reducing protective gas having a volume ratio of 95:5, and the volume ratio of Ar/H2 mixed gas is 95:5 Ar/CO mixed gas.
According to the invention, the calcination temperature in the step (2) is 600-700 ℃, the calcination time is 6-8h, and the temperature rise rate is 2-5 ℃/min.
Preferably according to the invention, the ratio of the mass of the mixture to the volume of the acid solution in step (2) is between 0.02 and 0.15 g/mL; the ratio of the mass of the mixture to the volume of the hydrofluoric acid aqueous solution is 0.05-0.375 g/mL.
Preferably, the acid solution in the step (2) is a mixed solution of hydrochloric acid and water and alcohol, and the volume ratio of water to alcohol in the mixed solution is 0.1-0.5: 1; preferably, the alcohol is absolute ethanol.
According to the invention, the washing mode in the step (2) is that deionized water and absolute ethyl alcohol are respectively washed alternately.
According to the invention, the drying mode in the step (2) is preferably drying at 60-100 ℃ for 2-12 h.
According to the present invention, the mass ratio of the Si nanoparticles to the ascorbic acid in the step (3) is preferably 1:0.6 to 5.
According to the invention, the molar concentration of the ascorbic acid aqueous solution in the step (3) is preferably 0.01-0.15 mol/L.
According to the invention, the protective gas in the step (3) is one of argon, nitrogen, a mixed gas of argon and hydrogen or a mixed gas of nitrogen and hydrogen; the volume ratio of argon to hydrogen in the mixed gas of argon and hydrogen is 95:5, and the volume ratio of nitrogen to hydrogen in the mixed gas of nitrogen and hydrogen is 95: 5.
According to the invention, the calcination temperature in the step (3) is 500-.
The invention has the following technical characteristics and beneficial effects:
the invention prepares silicon dioxide by taking bagasse, a natural resource, as a raw material, reduces the obtained silicon dioxide into silicon by a magnesiothermic reduction method, and removes MgO and Mg in the product2Si and unreduced SiO2Obtaining porous nano Si particles with the size of about 20nm, wherein the prepared nano Si particles have quite excellent specific discharge capacity, but the long cycle performance is still to be improved; therefore, ascorbic acid is selected as a carbon source, and a sol-gel method and a subsequent calcination method are adopted to prepare the porous Si/C composite material. The composite material effectively relieves the huge volume expansion of silicon in the electrochemical process due to the unique micro-morphology, and simultaneously effectively improves the conductivity of the material, so the composite material has very excellent electrochemical performance.
The invention has the following beneficial effects:
(a) the raw materials used in the invention are simple and easily available, green and environment-friendly, and have low price and low cost; meanwhile, the preparation method is simple and easy to operate, has low requirement on equipment, does not generate any toxic and harmful substances in the preparation process, can be produced in large scale, and is suitable for industrial application.
(b) The method for preparing the silicon dioxide by using the bagasse as the raw material is simple, low in cost and easy to industrialize, and can change the bagasse into valuables and realize effective utilization of waste; and it is from natural resources, green and pollution-free and renewable. The silica extracted from bagasse is of nanometer grade and has high purity.
(c) The method adopts the ascorbic acid as the carbon source, is green and environment-friendly, can uniformly coat the surface of the silicon, and ensures that the formed material has uniform size.
(d) The Si/C composite material prepared by the method is uniform in appearance and porous, has excellent electrochemical performance, the first-turn specific discharge capacity and the first-turn specific charge capacity can reach 4109 and 2738mA h/g, and the first-turn coulombic efficiency can reach 66.6%; the discharge specific capacity of the materials at the 1 st circle, the 2 nd circle and the 70 th circle can reach 4109, 2730 and 2125mA h/g, and the excellent electrochemical performance of the materials is shown; meanwhile, the prepared composite material has good reversibility, rate capability and long cycle performance.
Drawings
FIG. 1 is an XRD diffraction pattern of Si nanoparticles and Si/C composite material prepared in example 1 of the present invention;
fig. 2 is an SEM picture of Si nanoparticles prepared in example 1 of the present invention;
FIG. 3 is an SEM picture of a Si/C composite material prepared in example 1 of the present invention;
FIG. 4 is a charge-discharge curve diagram of the Si/C composite material prepared in example 1 of the present invention;
FIG. 5 is a graph of rate capability of a Si/C composite prepared in example 1 of the present invention;
FIG. 6 is a graph comparing cycle performance of Si nanoparticles prepared in example 1 of the present invention, a Si/C composite material, and a carbon material prepared in comparative example 1.
Detailed Description
The present invention will be further described with reference to the following examples, but is not limited thereto.
Meanwhile, the experimental methods described in the following examples are all conventional methods unless otherwise specified; the reagents and materials are commercially available, unless otherwise specified.
In the examples, bagasse is from the south of China, where bagasse is sourced from the south of China; ascorbic acid is a commercially available product and is available from chemical reagents of the national drug group.
Example 1
A high-performance lithium ion secondary battery cathode material Si/C composite material comprises a carbon and silicon composite, wherein the mass content of carbon in the composite is 30%, and the mass content of silicon in the composite is 70%; the micro-morphology of the composite material is as follows: the surface of the Si nano particle is coated with a carbon layer to form a carbon-silicon nano composite small ball which is loaded on the surface of the lamellar carbon; the size of the Si nano-particles is 20nm, the thickness of the carbon layer is 5nm, and the diameter of the small ball is about 25 nm.
The preparation method of the Si/C composite material of the high-performance lithium ion secondary battery negative electrode material comprises the following steps:
(1) soaking collected 5g bagasse in 50mL of 1mol/L HCl aqueous solution at room temperature for 2 hours to remove inorganic salt impurities, washing with water and absolute ethyl alcohol alternately for three times respectively, and drying in an oven at 80 ℃ for 12 hours; then calcining the mixture for 5 hours at the temperature of 600 ℃ in the air, and setting the heating rate to be 1 ℃/min to obtain white fluffy SiO2Powder;
(2) 0.5g of SiO prepared in step (1)2And 0.5g of magnesium powder are ground and mixed uniformly in a mortar, then the mixture is transferred into a porcelain boat and then is rapidly transferred to Ar/H2Calcining at 650 ℃ for 6h in a tubular furnace with an atmosphere (volume ratio of 95: 5) at a heating rate of 5 ℃/min to obtain a mixture; the mixture was placed in 50mL of 1mol/L HCl solution (HCl: H)2Soaking in absolute ethyl alcohol at a molar ratio of 0.66:4.72:8.88) at room temperature for 6 hours, drying at 60 ℃ for 3 hours, and then soaking in 20mL of HF aqueous solution (with the mass concentration of 5%) at room temperature for 3 minutes; washing with deionized water and anhydrous alcohol alternately for three times respectivelyDrying in an oven at 60 ℃ for 4h to obtain Si nanoparticles;
(3) adding 0.05g of the Si nanoparticles prepared in the step (2) into 10mL of 0.07mol/L ascorbic acid aqueous solution, and stirring at room temperature for 6 hours; then stirring for 30 minutes in a water bath at 90 ℃ to obtain sol; and placing the obtained sol in a tube furnace, calcining for 2h at 600 ℃ under the protective atmosphere of argon, and setting the heating rate to be 1 ℃/min to obtain the black Si/C composite material.
The XRD spectrum of the Si nanoparticle and the Si/C composite material prepared in this example is shown in fig. 1, and it can be seen from fig. 1 that the product prepared in step (2) of the present invention is Si, and the final product prepared in the present invention is a Si/C composite material.
SEM pictures of the Si nanoparticles and the Si/C composite material prepared in this example are shown in fig. 2 and 3, and it can be seen from fig. 2 and 3 that the average size of the Si nanoparticles is about 20nm, the diameter of the carbon-silicon nanocomposite globules is about 25nm, and the globules are supported on the surface of the lamellar carbon.
Example 2
A preparation method of a high-performance Si/C composite material of a lithium ion secondary battery cathode material comprises the following steps:
(1) soaking collected 10g bagasse in 50mL of 1mol/L HCl aqueous solution at room temperature for 4 hours to remove inorganic salt impurities, washing with water and absolute ethyl alcohol alternately for three times respectively, and drying in an oven at 90 ℃ for 10 hours; then calcining the mixture for 4 hours at the temperature of 650 ℃ in the air, and setting the heating rate to be 2 ℃/min to obtain white fluffy SiO2Powder;
(2) 1g of SiO prepared in step (1)2And 1.5g of magnesium powder are ground and mixed uniformly in a mortar, then transferred into a porcelain boat and then rapidly transferred to Ar/H2Calcining at 600 deg.C for 7h in a tubular furnace with 95:5 (volume ratio) atmosphere at a heating rate of 2 deg.C/min to obtain a mixture; the mixture was placed in 50mL of 1mol/L HCl solution (HCl: H)2O, absolute ethyl alcohol with the molar ratio of 0.66:4.72:8.88) for 8 hours at room temperature, drying at 80 ℃ for 2 hours, and then soaking in 20mL of HF aqueous solution (with the mass concentration of 3%) for 5 minutes at room temperature; alternately washing with deionized water and anhydrous ethanol for three times, respectively, and oven drying at 80 deg.CDrying for 2h to obtain Si nanoparticles;
(3) adding 0.05g of the Si nanoparticles prepared in the step (2) into 10mL of 0.1mol/L ascorbic acid aqueous solution, and stirring at room temperature for 8 hours; then stirring for 40 minutes in a water bath at the temperature of 95 ℃ to obtain sol; and placing the obtained sol in a tube furnace, calcining for 3h at 700 ℃ under the protective atmosphere of argon, and setting the heating rate to be 2 ℃/min to obtain the black Si/C composite material.
Example 3
A preparation method of a high-performance Si/C composite material of a lithium ion secondary battery cathode material comprises the following steps:
(1) soaking collected 15g bagasse in 50mL of 1mol/L HCl aqueous solution at room temperature for 6 hours to remove inorganic salt impurities, washing with water and absolute ethyl alcohol alternately for three times respectively, and drying in an oven at 100 ℃ for 8 hours; then calcining the mixture for 3 hours at 700 ℃ in the air, and setting the heating rate to be 5 ℃/min to obtain white fluffy SiO2Powder;
(2) 1g of SiO prepared in step (1)2Grinding and mixing 2g of magnesium powder in a mortar, transferring the mixture into a porcelain boat, and then quickly transferring the mixture into Ar/H2Calcining at 700 deg.C for 6.5h in a tubular furnace with 95:5 (volume ratio) atmosphere at a temperature rise rate of 5 deg.C/min to obtain a mixture; the mixture was placed in 50mL of 1mol/L HCl solution (HCl: H)2O, absolute ethyl alcohol with the molar ratio of 0.66:4.72:8.88) for 8 hours at room temperature, drying at 90 ℃ for 2 hours, and then soaking in 20mL of HF aqueous solution (with the mass concentration of 4%) for 6 minutes at room temperature; washing with deionized water and absolute ethyl alcohol alternately for three times respectively, and drying in a drying oven at 100 ℃ for 2h to obtain Si nanoparticles;
(3) adding 0.05g of the Si nano-particles prepared in the step (2) into 10mL of 0.035mol/L ascorbic acid aqueous solution, and stirring at room temperature for 6 hours; then stirring for 30 minutes in a water bath at 100 ℃ to obtain sol; and placing the obtained sol in a tube furnace, calcining for 2h at 750 ℃ under the protective atmosphere of argon, and setting the heating rate to be 2 ℃/min to obtain the black Si/C composite material.
Example 4
A preparation method of a high-performance Si/C composite material of a lithium ion secondary battery cathode material comprises the following steps:
(1) soaking collected 25g bagasse in 50mL of 1mol/L HCl aqueous solution at room temperature for 8 hours to remove inorganic salt impurities, washing with water and absolute ethyl alcohol alternately for three times respectively, and drying in an oven at 110 ℃ for 6 hours; then calcining the mixture for 2 hours at 800 ℃ in the air, and setting the heating rate to be 5 ℃/min to obtain white fluffy SiO2Powder;
(2) 2g of SiO prepared in step (1)2Grinding and mixing 3g of magnesium powder in a mortar, transferring the mixture into a porcelain boat, and then quickly transferring the mixture into Ar/H2Calcining at 650 ℃ for 6h in a tubular furnace with an atmosphere (volume ratio of 95: 5) at a heating rate of 5 ℃/min to obtain a mixture; the mixture was placed in 50mL of 1mol/L HCl solution (HCl: H)2Soaking in absolute ethyl alcohol at a molar ratio of 0.66:4.72:8.88) at room temperature for 10 hours, drying at 100 ℃ for 2 hours, and then soaking in 20mL of HF aqueous solution (with the mass concentration of 2%) at room temperature for 8 minutes; washing with deionized water and absolute ethyl alcohol alternately for three times respectively, and drying in an oven at 80 ℃ for 2h to obtain Si nanoparticles;
(3) adding 0.05g of the Si nanoparticles prepared in the step (2) into 10mL of 0.14mol/L ascorbic acid aqueous solution, and stirring at room temperature for 10 hours; then stirring for 40 minutes in a water bath at the temperature of 95 ℃ to obtain sol; and placing the obtained sol in a tube furnace, calcining for 2h at 800 ℃ under the protective atmosphere of argon, and setting the heating rate to be 5 ℃/min to obtain the black Si/C composite material.
Example 5
A preparation method of a high-performance Si/C composite material of a lithium ion secondary battery cathode material comprises the following steps:
(1) soaking collected 35g bagasse in 50mL of 1mol/L HCl aqueous solution at room temperature for 10 hours to remove inorganic salt impurities, washing with water and absolute ethyl alcohol alternately for three times respectively, and drying in an oven at 120 ℃ for 4 hours; then calcining the mixture for 2 hours at 800 ℃ in the air, and setting the heating rate to be 2 ℃/min to obtain white fluffy SiO2Powder;
(2) 2.5g of SiO prepared in step (1)2And 5g of magnesium powder are ground and mixed uniformly in a mortar and then transferred toIn a porcelain boat, then quickly transferred to Ar/H2Calcining at 650 ℃ for 8h in a tubular furnace with an atmosphere (volume ratio of 95: 5) at a heating rate of 5 ℃/min to obtain a mixture; the mixture was placed in 50mL of 1mol/L HCl solution (HCl: H)2Soaking in absolute ethyl alcohol at a molar ratio of 0.66:4.72:8.88) at room temperature for 10 hours, drying at 100 ℃ for 2 hours, and then soaking in 20mL of HF aqueous solution (with the mass concentration of 5%) at room temperature for 10 minutes; washing with deionized water and absolute ethyl alcohol alternately for three times respectively, and drying in a drying oven at 60 ℃ for 4h to obtain Si nanoparticles;
(3) adding 0.05g of the Si nanoparticles prepared in the step (2) into 10mL of 0.0175mol/L ascorbic acid aqueous solution, and stirring at room temperature for 6 hours; then stirring for 40 minutes in a water bath at the temperature of 95 ℃ to obtain sol; and placing the obtained sol in a tube furnace, calcining for 2h at 600 ℃ under the protective atmosphere of argon, and setting the heating rate to be 1 ℃/min to obtain the black Si/C composite material.
Comparative example 1
A method for preparing a carbon material, comprising the steps of:
0.12g of ascorbic acid is placed in a tube furnace and calcined for 2h at 600 ℃ under the protective atmosphere of argon, and the heating rate is set to be 1 ℃/min, so that the carbon material is obtained.
Test example 1
Product performance testing
The Si nanoparticles and Si/C composite material prepared in example 1 and the carbon material prepared in comparative example 1 were used as negative electrode materials for lithium ion secondary batteries, and electrodes were prepared by a coating method.
Mixing and dispersing an active substance, Super P (conductive carbon black) and sodium alginate (binder) in deionized water according to a mass ratio of 60:30:10, grinding the mixture uniformly in a mortar to prepare slurry, coating the slurry on a copper foil, drying the copper foil in a vacuum oven at 60 ℃ for 3 hours, and cutting the copper foil into circular pole pieces with the diameter of 12 mm. Metal lithium is adopted as a counter electrode, a Celgard2300 polymer film is used as a diaphragm, and LiPF is used as electrolyte6Dissolving in a mixed solution of diethyl carbonate (DEC)/dimethyl carbonate (DMC)/Ethylene Carbonate (EC) (volume ratio of 1: 1: 1), and adding LiPF in the mixed solution6The concentration of (2) is 1 mol/L. Charge/discharge curves andthe cycling test was performed on a Land-CT2001A battery test system at 25 ℃ with a voltage setting of between 0.01 and 2.0V.
FIG. 4 is a charge-discharge curve diagram of the Si/C composite material prepared in example 1, and FIG. 4 shows that the charge-discharge curves of the material under the voltage range of 0.01-2V and the current density of 0.1A/g at the 1 st cycle, the 2 nd cycle and the 70 th cycle have first-cycle discharge and charge specific capacities of 4109 and 2738mA h/g respectively, and the first-cycle coulombic efficiency can reach 66.6%; the specific discharge capacity of the material at the first circle, the 2 nd circle and the 70 th circle is 4109, 2730 and 2125mA h/g respectively, and the excellent electrochemical performance of the material is shown.
FIG. 5 is a graph of rate performance for the Si/C composite made in example 1, showing in FIG. 5 the rate performance of the composite at different current densities of 0.1,0.2,0.5,1,2 and 3A/g, showing reversible specific capacities of 2680,2456,2187,1487 and 1420mA h/g, respectively. In addition, after the high current density is tested and then the low current is recovered to 0.1A/g, the reversible specific capacity can still be recovered to 2200mA h/g, and the specific capacity is not obviously attenuated in 10 cycles under each current density, which shows that the Si/C composite material has excellent reversibility and rate capability.
Fig. 6 is a graph comparing cycle performance of the Si nanoparticles prepared in example 1 of the present invention, the Si/C composite material, and the carbon material prepared in comparative example 1, and fig. 6 shows that the cycle performance of the Si/C composite material, the carbon material, and the Si nanoparticles at 0.5A/g, the Si/C composite material shows the optimal cycle performance, indicating that carbon coating can effectively improve cycle stability of the material and effectively suppress rapid decay of capacity.

Claims (4)

1. The preparation method of the high-performance Si/C composite material for the cathode material of the lithium ion secondary battery is characterized in that the composite material comprises a carbon and silicon composite, wherein the mass content of carbon in the composite is 10-35%, and the mass content of silicon in the composite is 65-90%; the micro-morphology of the composite material is as follows: the surface of the Si nano particle is coated with a carbon layer to form a silicon-carbon nano composite ball, and the silicon-carbon nano composite ball is loaded on the surface of the lamellar carbon; the size of the Si nano-particles is 15-25nm, the thickness of the carbon layer is 3-7nm, and the diameter of the ball is 18-32 nm;
the preparation method comprises the following steps:
(1) soaking bagasse in 0.5-2mol/L acid solution for 1-12h, washing, drying, and calcining in air atmosphere to obtain SiO2Powder; the calcination temperature is 500-800 ℃, the calcination time is 2-5h, and the heating rate is 1-5 ℃/min;
(2) SiO prepared in the step (1)2Grinding and uniformly mixing the powder and magnesium powder, and calcining in a reductive protective gas atmosphere to obtain a mixture; soaking the mixture in 0.5-2mol/L acid solution for 5-10h, then soaking in 2-8% hydrofluoric acid water solution for 1-10min, washing, and drying to obtain Si nanoparticles; the SiO2The mass ratio of the powder to the magnesium powder is 0.5-1: 1; the acid solution is a mixed solution of hydrochloric acid, water and absolute ethyl alcohol, and the volume ratio of the water to the ethyl alcohol in the mixed solution is 0.1-0.5: 1; the calcination temperature is 600-700 ℃, the calcination time is 6-8h, and the heating rate is 2-5 ℃/min;
(3) adding the Si nano-particles prepared in the step (2) into an ascorbic acid aqueous solution, and stirring at room temperature for 6-10 h; then stirring for 0.5-1h at 80-100 ℃ to obtain sol; calcining the obtained sol in a protective gas atmosphere to obtain a Si/C composite material; the mass ratio of the Si nano particles to the ascorbic acid is 1: 0.6-5; the molar concentration of the ascorbic acid aqueous solution is 0.01-0.15 mol/L; the calcination temperature is 500-800 ℃, the calcination time is 2-4h, and the heating rate is 1-5 ℃/min.
2. The preparation method of the Si/C composite material as the negative electrode material of the high-performance lithium ion secondary battery as claimed in claim 1, wherein the mass of the sugarcane and the volume ratio of the acid solution in the step (1) are as follows: 0.1-1 g/mL.
3. The method for preparing the Si/C composite material as the negative electrode material of the high-performance lithium ion secondary battery as claimed in claim 1, wherein the acid in the step (1) is one of hydrochloric acid, sulfuric acid or nitric acid; the acid solution is an aqueous acid solution or a mixed solution of an acid and water and an alcohol.
4. The method for preparing the Si/C composite material for the negative electrode material of the high-performance lithium ion secondary battery according to claim 3, wherein the alcohol is absolute ethyl alcohol; in the mixed solution of the acid, the water and the alcohol, the volume ratio of the water to the alcohol is 0.1-0.5: 1.
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