CN108767220B - Silicon-carbon composite material, preparation method thereof, battery cathode material and battery - Google Patents

Silicon-carbon composite material, preparation method thereof, battery cathode material and battery Download PDF

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CN108767220B
CN108767220B CN201810510703.7A CN201810510703A CN108767220B CN 108767220 B CN108767220 B CN 108767220B CN 201810510703 A CN201810510703 A CN 201810510703A CN 108767220 B CN108767220 B CN 108767220B
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silicon
composite material
sio
carbon composite
battery
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CN108767220A (en
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池子翔
苗力孝
朱坤磊
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Soundon New Energy Technology Co Ltd
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Sander New Energy Technology Development Co ltd
Soundon New Energy Technology Co Ltd
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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
    • 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
    • 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
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Abstract

The invention provides a silicon-carbon composite material, a preparation method thereof, a battery cathode material and a battery, and relates to the technical field of batteries, wherein the silicon-carbon composite material is in a hollow microsphere structure and comprises a shell and a cavity, the shell covers the cavity, the shell is mainly formed by compounding silicon and carbon, the outer diameter of the shell is 1-10 mu m, the inner diameter of the shell is 0.1-5 mu m, and the wall thickness of the shell is 0.1-3 mu m, so that the technical problems of poor conductivity of simple substance silicon and poor cycle performance caused by large volume change in the charging and discharging process are solved. The silicon-carbon composite material provided by the invention can provide space for the volume change of silicon in the charging and discharging processes through the cavity, so that the problems of volume expansion and structure collapse of silicon in the charging and discharging processes are effectively relieved, and the cycle stability and the battery capacity of a battery are improved; but also can improve the conductivity of the composite material through the synergistic effect of silicon and carbon.

Description

Silicon-carbon composite material, preparation method thereof, battery cathode material and battery
Technical Field
The invention relates to the technical field of batteries, in particular to a silicon-carbon composite material, a preparation method of the silicon-carbon composite material, a battery cathode material and a battery.
Background
At present, the lithium ion battery cathode material in practical application is mainly made of the traditional graphite material, the actual specific capacity of the lithium ion battery cathode material is close to the theoretical value of 372mAh/g, and the capacity is difficult to further improve.
In order to further improve the energy density of the lithium ion battery and meet the increasing requirements of the power battery, a new cathode material system is imperatively developed. Elemental silicon has a very high specific capacity (4200mAh/g) and a moderate voltage plateau (0.4Vvs Li/Li)+) The specific capacity of the graphite is almost more than ten times of the theoretical specific capacity of the natural graphite, and the graphite is a negative electrode material with good application prospect and becomes a hotspot of current research.
However, elemental silicon has poor conductivity and large volume change in the charging and discharging processes, so that the material is easy to collapse and pulverize in structure and further fall off from a current collector, and the specific capacity in the charging and discharging cycle process is rapidly attenuated.
In view of the above, the present invention is particularly proposed.
Disclosure of Invention
One of the objectives of the present invention is to provide a silicon-carbon composite material to alleviate the technical problems of poor conductivity of elemental silicon and large volume change during charging and discharging, which leads to easy structural collapse and pulverization of the material and further falling off from a current collector, and rapid attenuation of specific capacity during charging and discharging cycles.
The silicon-carbon composite material provided by the invention is of a hollow microsphere structure, the hollow microsphere comprises a shell and a cavity, the shell coats the cavity, and the shell comprises silicon and carbon.
Further, the outer diameter of the shell is 1-10 μm, the inner diameter of the shell is 0.1-5 μm, and the wall thickness of the shell is 0.1-3 μm.
Further, the silicon content in the shell is 30-90 wt%.
The invention also aims to provide a preparation method of the silicon-carbon composite material, which comprises the following steps:
(a) providing SiO2Sol and monomer solution containing C element, and forming SiO2And solid microspheres of a polymer;
(b) sintering the solid microspheres to obtain SiO with a cavity2C, microspheres;
(c) mixing SiO2the/C microspheres are reduced into the silicon-carbon composite material with a hollow microsphere structure, wherein the hollow microspheres comprise shells and cavities, the shells cover the cavities, and the shells comprise silicon and carbon.
Further, the polymer is a copolymer, the monomers include a first monomer and a second monomer, wherein,
in step (a), SiO is first introduced2Dispersing the sol in a first monomer solution, and then adding a second monomer for copolymerization to obtain a solution containing SiO2And solid microspheres of a polymer, wherein the first monomer and/or the second monomer contains a C element;
preferably, the first monomer is selected from at least one of urea, melamine, phenol, resorcinol, and 3-aminophenol; and/or
Preferably, the second monomer is selected from at least one of C1-C6 low carbon aldehyde;
further, in the step (b), during sintering, the temperature is first raised from room temperature to 220 ℃ at a heating rate of 2-5 ℃/min, then raised to 380 ℃ at a heating rate of 0.5-1 ℃/min, and then raised to 800 ℃ at a heating rate of 2-5 ℃/min, and the temperature is maintained for 6-10 hours.
Further, in the step (c), SiO is reduced by using a reducing agent2C, microspheres;
preferably, the reducing agent is magnesium, iron, copper or manganese.
The invention also aims to provide a battery negative electrode material which comprises the silicon-carbon composite material.
The fourth purpose of the invention is to provide a battery, which comprises the silicon-carbon composite material or the battery negative electrode material provided by the invention.
According to the silicon-carbon composite material provided by the invention, the cavity is arranged in the silicon-carbon composite material, and the hollow microsphere structure of the shell comprising silicon and carbon is coated outside the cavity, so that a space can be provided for the volume change of silicon in the charging and discharging processes through the cavity, the problems of volume expansion and structure collapse of silicon in the charging and discharging processes are effectively relieved, and the cycle stability and the battery capacity of a battery are improved; but also can improve the conductivity of the composite material through the synergistic effect of silicon and carbon.
The preparation method of the silicon-carbon composite material provided by the invention combines a polymerization induction colloid aggregation and a sintering system to prepare the silicon-carbon composite material with the hollow microsphere structure, has simple process and convenient operation, can be suitable for industrial mass production, and improves the production efficiency.
The battery cathode material provided by the invention adopts the silicon-carbon composite material provided by the invention as a cathode active material, so that the cycling stability and the battery capacity of the battery are effectively improved.
According to the battery provided by the invention, the silicon-carbon composite material provided by the invention is used as a negative active material or the battery negative material provided by the invention is used as a negative material, so that the cycling stability and the battery capacity of the battery are effectively improved.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts.
FIG. 1 is an SEM image of a silicon carbon composite material provided in example 3 of the present invention;
FIG. 2 is an SEM image of the silicon-carbon composite material of FIG. 1 after being cut by a Focused Ion Beam (FIB);
fig. 3 is a first charge-discharge curve at 0.1C for the battery provided in example 19;
fig. 4 is a graph showing the results of 300-cycle tests at 0.1C for the batteries provided in example 19 and comparative example 5, respectively.
Detailed Description
The technical solutions of the present invention will be described clearly and completely with reference to the accompanying drawings, and it should be understood that the described embodiments are some, but not all embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
According to a first aspect of the present invention, the present invention provides a silicon-carbon composite material, wherein the silicon-carbon composite material is a hollow microsphere structure, the hollow microsphere comprises a shell and a cavity, the shell covers the cavity, and the shell comprises silicon and carbon.
According to the silicon-carbon composite material, the hollow microsphere structure of the shell is arranged, the cavity is formed inside the silicon-carbon composite material, and the shell of silicon and carbon is coated outside the cavity, so that space can be provided for volume change of silicon in the charging and discharging processes through the cavity, the problems of volume expansion and structure collapse of silicon in the charging and discharging processes are effectively solved, and the cycling stability and the battery capacity of a battery are improved; but also can improve the conductivity through the synergistic action of silicon and carbon.
In a preferred embodiment of the invention, the outer diameter of the housing is 1-10 μm, the inner diameter of the housing is 0.1-5 μm, and the wall thickness of the housing is 0.1-3 μm.
In the present invention, typical but non-limiting outer diameters of the housing are, for example, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5 or 10 μm.
Typical but non-limiting internal diameters of the housing are 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.2, 1.5, 1.8, 2, 2.5, 3, 3.5, 4, 4.5 or 5 μm.
The wall thickness of the housing is for example 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8 or 3 μm.
In a preferred embodiment of the invention, the silicon content in the outer shell is 30-90 wt%.
In typical, but non-limiting embodiments of the invention, the silicon content in the housing is, for example, 30 wt%, 32 wt%, 35 wt%, 38 wt%, 40 wt%, 42 wt%, 45 wt%, 48 wt%, 50 wt%, 52 wt%, 55 wt%, 58 wt%, 60 wt%, 62 wt%, 65 wt%, 68 wt%, 70 wt%, 72 wt%, 75 wt%, 78 wt%, 80 wt%, 82 wt%, 85 wt%, 88 wt%, or 90 wt%.
Experiments have shown that when the silicon content in the outer shell is less than 30 wt%, the energy density of the battery is too low, and when the silicon content in the outer shell is greater than 90%, it is difficult to form good hollow microspheres.
According to a second aspect of the present invention, there is provided a method for preparing a silicon-carbon composite material, comprising the steps of:
(a) providing SiO2Sol and monomer solution containing C element, andwhich forms a film containing SiO2And solid microspheres of a polymer;
(b) sintering the solid microspheres to obtain SiO with a cavity2C, microspheres;
(c) mixing SiO2the/C microsphere is reduced into a silicon-carbon composite material with a cavity, wherein the hollow microsphere comprises a shell and the cavity, the shell coats the cavity, and the shell comprises silicon and carbon.
The preparation method of the silicon-carbon composite material provided by the invention combines a polymerization induction colloid aggregation and a sintering system to prepare the silicon-carbon composite material with the hollow microsphere structure, has simple process and convenient operation, can be suitable for industrial mass production, and improves the production efficiency.
The silicon-carbon composite material prepared by the preparation method of the silicon-carbon composite material provided by the invention not only can provide space for the volume change of silicon in the charging and discharging process through the cavity, but also can improve the conductivity through the silicon-carbon synergistic effect, thereby effectively relieving the problems of volume expansion and structure collapse of silicon in the charging and discharging process, and improving the cycle stability and the battery capacity of a battery.
In a preferred embodiment of the invention, the polymer is a copolymer, the monomers comprising a single monomer and a second monomer, wherein,
in step (a), SiO is first introduced2Dispersing the sol in a first monomer solution, and then adding a second monomer for copolymerization to obtain the SiO-containing material2And solid microspheres of a polymer, wherein the first monomer and/or the second monomer contains a C element.
By first SiO2Dispersing the sol in the first monomer solution, and adding a second monomer for copolymerization to obtain SiO2The sol is uniformly distributed in the polymer microspheres generated by the polymerization of the first monomer and the second monomer.
In a preferred embodiment of the present invention, the first monomer is selected from at least one of urea, melamine, phenol, resorcinol, and 3-aminophenol.
In a preferred embodiment of the present invention, the second monomer is at least one selected from the group consisting of C1-C6 lower aldehydes.
In a typical but non-limiting embodiment of the invention, a first monomer and a second monomer are copolymerized to form a three-dimensional network polymer, resulting in a polymer containing SiO2And solid microspheres of polymer, which are convenient for subsequent sintering to form SiO2C microspheres.
In a preferred embodiment of the present invention, the molar ratio of the first monomer to the second monomer is 1: 1-2.
In typical, but non-limiting embodiments of the invention, the molar ratio of the first monomer to the second monomer is, for example, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, or 1:2.
By limiting the mass of the first monomer and the second monomer to 1 (1-2) so that the first monomer and the second monomer react completely, the resulting polymer is capable of SiO2The sol is completely coated.
In a typical but non-limiting embodiment of the invention, in step (b), solid microspheres comprising SiO2 and a polymer are sintered in an inert or reducing atmosphere to carbonize the polymer, and the SiO2Sol shrinkage to obtain SiO with cavity2C microspheres.
When the solid microspheres containing SiO2 and polymer are sintered in inert or reducing atmosphere, the solid microspheres are coated on SiO2The polymerization outside the sol is carbonized at high temperature to leave C element and SiO inside the polymer microsphere2The solvent in the sol evaporates, so that SiO2The sol shrinks to obtain SiO with a cavity2C microspheres.
In a preferred embodiment of the present invention, in the step (b), during the sintering, the temperature is first raised from room temperature to 220 ℃ at a heating rate of 2-5 ℃/min, then raised to 380 ℃ at a heating rate of 0.5-1 ℃/min, and then raised to 800 ℃ at a heating rate of 2-5 ℃/min and kept for 6-10 hours.
In a typical but non-limiting embodiment of the invention, in step (b), the sintering temperature is brought from room temperature by a single temperature increaseRaising the temperature to 180-2the/C microspheres have defects.
In the present invention, a typical but non-limiting temperature rise rate of the primary temperature rise is, for example, 2, 2.5, 3, 3.5, 4, 4.5 or 5 ℃/min; typical but non-limiting heating rates for the secondary heating are, for example, 0.5, 0.6, 0.7, 0.8, 0.9, 1 deg.C/min; typical but non-limiting ramp rates for the three ramp times are, for example, 2, 2.5, 3, 3.5, 4, 4.5, or 5 deg.C/min.
In the present invention, typical but non-limiting temperatures after one temperature increase are, for example, 180, 185, 190, 195, 200, 205, 210, 215, or 220 ℃; typical but non-limiting temperatures after the second temperature increase are, for example, 330, 335, 340, 345, 350, 355, 360, 365, 370, 375, or 380 ℃; typical but non-limiting temperatures after three temperature increases are 700, 705, 710, 715, 720, 725, 730, 735, 740, 745, 750, 755, 760, 765, 770, 775, 780, 785, 790, 795, or 800 ℃.
Typical but non-limiting incubation times after three temperature increases in the present invention are, for example, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5 or 10 hours.
In a preferred embodiment of the invention, in step (c), SiO is reduced with a reducing agent2C microspheres.
By reducing SiO with a reducing agent2C microspheres of SiO2And reducing to obtain the silicon-carbon composite material with the cavity.
In a preferred embodiment of the present invention, the reducing agent is at least one of magnesium, iron, copper or manganese, and particularly when the reducing agent is magnesium, the reducing effect is more excellent.
In a preferred embodiment of the invention, SiO2The mass ratio of the/C microspheres to the reducing agent is 1 (1-5).
In a typical but non-limiting embodiment of the invention, SiO2The mass ratio of the/C microspheres to the reducing agent is 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5 or 1: 5; especially when SiO2micro/CThe mass ratio of the balls to the reducing agent is 1: (2-3), the reduction effect is more excellent.
In a preferred embodiment of the invention, in step (c), SiO is first introduced2Mixing the/C microspheres with a reducing agent, and then sintering at the temperature of 700-800 ℃ for 6-20 hours to obtain the silicon-carbon composite material with the hollow structure.
In typical, but non-limiting embodiments of the invention, the sintering temperature is, for example, 700, 710, 720, 730, 740, 750, 760, 770, 780, 790 or 800 ℃; the sintering time is, for example, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20 h.
In a preferred embodiment of the invention, SiO2According to the sol
Figure BDA0001672431240000082
The preparation method is adopted.
The stober process is a physicochemical process for the synthesis of monodisperse silicon particles, by Werner
Figure BDA0001672431240000081
Et al first discovered, generally referred to as a method of producing nano-silicon particles by adding TEOS to ethanol and ammonia water.
In a preferred embodiment of the invention, SiO2The sol is prepared according to the following steps: sequentially adding ammonia water and tetraethoxysilane into a solvent, uniformly mixing, stirring, reacting to generate SiO2And (3) sol.
In a preferred embodiment of the invention, the concentration of ethyl orthosilicate is from 0.01 to 0.5mol/L and the concentration of ammonia is from 0.1 to 2 mol/L.
In the present invention, typical but non-limiting concentrations of ethyl orthosilicate are, for example, 0.01, 0.02, 0.03, 0.04, 0.05, 0.08, 0.1, 0.12, 0.15, 0.18, 0.2, 0.22, 0.25, 0.28, 0.3, 0.32, 0.35, 0.38, 0.4, 0.42, 0.45, 0.48 or 0.5 mol/L; typical, but not limiting, concentrations of aqueous ammonia are, for example, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9 or 2 mol/L.
In a preferred embodiment of the present invention, the solvent is water or a mixed solution of water and ethanol.
In a further preferred embodiment of the present invention, the volume ratio of water to ethanol in the mixed solution of water and ethanol is 1 to 25: 1.
In a typical but non-limiting embodiment of the invention, the solvent is a mixed solution of water and ethanol, and the volume ratio of water to ethanol is 1:1, 2:1, 5:1, 8:1, 10:1, 12:1, 15:1, 18:1, 20:1, 22:1, or 25: 1.
In a preferred embodiment of the invention, SiO is prepared2When the sol is dissolved, the stirring time is 2 to 4 hours, and the stirring temperature is 25 to 90 ℃.
In the preparation of SiO2In the case of sols, stirring is typically, but not limited to, for example, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, 3.8 or 4 hours and at a temperature of, for example, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85 or 90 ℃.
According to a third aspect of the invention, the invention provides a battery negative electrode material, which comprises the silicon-carbon composite material provided by the invention, a conductive agent and a binder.
The battery cathode material provided by the invention adopts the silicon-carbon composite material provided by the invention as a cathode active material, so that the cycling stability and the battery capacity of the battery are effectively improved.
In a preferred embodiment of the present invention, the conductive agent is selected from one or at least two of graphite, carbon black, acetylene black, graphene, carbon fiber, and carbon nanotube.
In a preferred embodiment of the present invention, the binder is selected from one or at least two of polyvinylidene chloride, soluble polytetrafluoroethylene, styrene-butadiene rubber, hydroxypropylmethyl cellulose, methyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, acrylonitrile copolymer, sodium alginate, chitosan, and chitosan derivative.
According to a fourth aspect of the invention, there is provided a battery comprising a silicon carbon composite material as provided by the invention or a battery anode material as provided by the invention.
According to the battery provided by the invention, the silicon-carbon composite material provided by the invention is used as a negative active material or the battery negative material provided by the invention is used as a negative material, so that the cycling stability and the battery capacity of the battery are effectively improved.
The technical solution provided by the present invention is further described below with reference to examples and comparative examples.
Example 1
The embodiment provides a silicon-carbon composite material, which is a hollow microsphere structure, wherein a shell is formed by compounding silicon and carbon, the content of Si accounts for 30 wt%, and the silicon-carbon composite material is prepared by the following method:
(s) preparation of SiO2Sol gel
Adding ammonia water and TEOS into a mixed solution of water and ethanol (the mass ratio of water to ethanol is 1:1) in sequence, wherein the concentration of TEOS is 0.01mol/L, the concentration of ammonia water is 0.1mol/L, stirring and reacting for 48 hours, heating to 90 ℃ until the solution becomes white sol suspension, and obtaining SiO2Sol;
(a) preparation of a catalyst containing SiO2And solid microspheres of a polymer
In SiO2Adding urea and formaldehyde into the sol in sequence, adjusting the pH value of a reaction system to be 0.5, stirring uniformly, reacting, and centrifugally washing to obtain the SiO-containing sol2And solid microspheres of a polymer, wherein the molar ratio of urea to formaldehyde is 1:1, SiO2The volume ratio of the sol to the reaction system is 1: 15;
(b) preparation of SiO2C microspheres
Will contain SiO2Placing the solid microspheres of the polymer and a tube furnace in an inert or reducing atmosphere, heating the temperature from room temperature to 200 ℃ at the heating rate of 2 ℃/min, then heating the temperature to 350 ℃ at the heating rate of 1 ℃/min, then heating the temperature to 750 ℃ at the heating rate of 2 ℃/min, and keeping the temperature for 8 hours to obtain SiO with a cavity structure2C, microspheres;
(c) preparation of Si/C composite
Mixing SiO2The ratio of the/C microspheres to the Mg powder is 1:1, placing the mixture in a tubular furnace in an inert or reducing atmosphere at a temperature of 7Sintering at 50 ℃ for 6 hours, carrying out a magnesiothermic reduction reaction, and then washing with diluted HCl to remove excess Mg powder, thereby obtaining the Si/C composite material.
Example 2
The embodiment provides a silicon-carbon composite material, which is a hollow microsphere structure, wherein a shell is formed by compounding silicon and carbon, the content of Si accounts for 90 wt%, and the silicon-carbon composite material is prepared by the following method:
(s) preparation of SiO2Sol gel
Adding ammonia water and TEOS into a mixed solution of water and ethanol (the mass ratio of water to ethanol is 1:1) in sequence, wherein the concentration of TEOS is 0.5mol/L, the concentration of ammonia water is 2mol/L, stirring and reacting for 2 hours, heating to 25 ℃ until the solution becomes white sol suspension, and obtaining SiO2Sol;
(a) preparation of a catalyst containing SiO2And solid microspheres of a polymer
In SiO2Adding urea and formaldehyde into the sol in sequence, adjusting the pH value of a reaction system to be 2, stirring uniformly, reacting, and centrifugally washing to obtain the SiO-containing sol2And solid microspheres of a polymer, wherein the molar ratio of urea to formaldehyde is 1:2, SiO2The volume ratio of the sol to the reaction system is 1: 2;
(b) preparation of SiO2C microspheres
Will contain SiO2Placing the solid microspheres of the polymer and a tube furnace in an inert or reducing atmosphere, heating the temperature from room temperature to 200 ℃ at a heating rate of 5 ℃/min, then heating the temperature to 350 ℃ at a heating rate of 0.5 ℃/min, then heating the temperature to 800 ℃ at a heating rate of 5 ℃/min, and keeping the temperature for 8 hours to obtain SiO with a cavity structure2C, microspheres;
(c) preparation of Si/C composite
Mixing SiO2The ratio of the/C microspheres to the Mg powder is 1:5, placing the mixture in a tubular furnace in an inert or reducing atmosphere, sintering the mixture for 6 hours at the temperature of 750 ℃, carrying out a magnesiothermic reduction reaction, and then washing the mixture by using diluted HCl to remove redundant Mg powder to obtain the Si/C composite material.
Example 3
The embodiment provides a silicon-carbon composite material, which is a hollow microsphere structure, wherein a shell is formed by compounding silicon and carbon, the content of Si accounts for 60 wt%, and the silicon-carbon composite material is prepared by the following method:
(s) preparation of SiO2Sol gel
Adding ammonia water and TEOS into a mixed solution of water and ethanol (the mass ratio of water to ethanol is 1:1) in sequence, wherein the concentration of TEOS is 0.2mol/L, the concentration of ammonia water is 1mol/L, stirring and reacting for 20 hours, heating to 45 ℃ until the solution becomes white sol suspension, and obtaining SiO2Sol;
(a) preparation of a catalyst containing SiO2And solid microspheres of a polymer
In SiO2Adding urea and formaldehyde into the sol in sequence, adjusting the pH value of a reaction system to be 1, stirring uniformly, reacting, and centrifugally washing to obtain the SiO-containing sol2And solid microspheres of a polymer, wherein the molar ratio of urea to formaldehyde is 1:1.8, SiO2The volume ratio of the sol to the reaction system is 1: 5;
(b) preparation of SiO2C microspheres
Will contain SiO2Placing the solid microspheres of the polymer and a tube furnace in an inert or reducing atmosphere, heating the temperature from room temperature to 200 ℃ at a heating rate of 5 ℃/min, then heating the temperature to 350 ℃ at a heating rate of 0.5 ℃/min, then heating the temperature to 800 ℃ at a heating rate of 5 ℃/min, and keeping the temperature for 8 hours to obtain SiO with a cavity structure2C, microspheres;
(c) preparation of Si/C composite
Mixing SiO2The ratio of the/C microspheres to the Mg powder is 1:2, placing the mixture in a tubular furnace in an inert or reducing atmosphere, sintering the mixture for 6 hours at the temperature of 750 ℃, carrying out a magnesiothermic reduction reaction, and then washing the mixture by using diluted HCl to remove redundant Mg powder to obtain the Si/C composite material.
Example 4
This example provides a silicon carbon composite, and differs from example 3 in that the silicon content is 10%.
Example 5
This example provides a silicon carbon composite, and differs from example 3 in that the silicon content is 99%.
Example 6
This example provides a silicon carbon composite, and differs from example 3 in that in step (a), the molar ratio of urea to formaldehyde is 1: 0.5.
Example 7
This example provides a silicon carbon composite material, and differs from the preparation method of the silicon carbon composite material provided in example 3 in that in step (a), the molar ratio of urea to formaldehyde is 1: 5.
Example 8
This example provides a silicon carbon composite material, and differs from the preparation method of the silicon carbon composite material provided in example 3 in that in step (c), SiO is present2The mass ratio of the/C hollow microspheres to the Mg powder is 1: 0.5.
Comparative example 1
The comparative example provides a silicon-carbon composite material, which is microspherical and is formed by compounding silicon and carbon, wherein the silicon is used as a core, the carbon is used as a shell, and the content of Si accounts for 60 wt%.
Comparative example 2
This comparative example provides a tin-carbon composite material having the same structure as the silicon-carbon composite material provided in example 3, except that the outer shell thereof is composed of tin-carbon.
Examples 9 to 16
Examples 10 to 18 each provide a battery negative electrode material, which uses the silicon-carbon composite material provided in examples 1 to 8 as a negative electrode active material, and further includes carbon black and polyvinylidene chloride (PVDF), and the mass ratio of the carbon black to the polyvinylidene chloride is 90% to 5%.
Comparative examples 3 to 4
Comparative examples 3 to 4 respectively provide a battery negative electrode material, which respectively takes the silicon-carbon composite material provided in comparative examples 1 to 2 as a negative electrode active material, and simultaneously comprises carbon black and polyvinylidene chloride (PVDF), and the mass ratio of the carbon black to the polyvinylidene chloride is 90% to 5%.
Examples 17 to 24
Examples 17-24 each provide a battery having a negative electrode prepared by coating the electrode negative electrode materials provided in examples 9-16 on copper foil.
Comparative examples 5 to 6
Comparative examples 5 to 6 each provide a battery in which a negative electrode is prepared by coating the negative electrode material provided in comparative examples 4 to 6 on a copper foil.
Test example 1
Scanning electron microscope testing is performed on the silicon-carbon composite material provided in example 3, and fig. 1 is an SEM image of the silicon-carbon composite material provided in the example of the present invention; fig. 2 is a SEM image result of the silicon-carbon composite material shown in fig. 1 after being cut by a Focused Ion Beam (FIB), as shown in fig. 1 and fig. 2, the silicon-carbon composite material provided in example 3 is a microsphere structure having a cavity inside, and the outer diameter is between 1 μm and 10 μm, which indicates that the silicon-carbon composite material can provide a space for the volume change of silicon during the charging and discharging process through the cavity inside the silicon-carbon composite material, and effectively alleviates the problems of volume expansion and structure collapse of silicon during the charging and discharging process, and meanwhile, as can be seen from the figure, the silicon-carbon composite material has a larger particle size, and can effectively improve the compaction density and the volume energy density, thereby effectively improving the cycle stability and the battery capacity of the battery.
Test example 2
The battery provided in example 19 (using the silicon-carbon composite material provided in example 3 as the negative active material) was subjected to the first charge and discharge test at 0.1C, and the test result is shown in fig. 3, and it can be seen from fig. 3 that the first charge and discharge capacity of the battery provided in example 19 can reach 1200
mAh/g, which indicates that the battery using the silicon carbon composite material provided in example 3 as a negative active material has a high first charge and discharge capacity.
Test example 3
The batteries provided in example 19 and comparative example 5 were respectively subjected to 300 cycle tests at 0.1C, and the test results are shown in fig. 4, and it can be seen from fig. 4 that the cycle performance of the battery provided in example 19 is significantly higher than that of the battery provided in comparative example 5, which indicates that the battery provided in example 19 employs the silicon-carbon composite material provided in example 3 as a negative electrode active material, and since the silicon-carbon composite material has a cavity inside, space is provided for volume change of silicon generated during charge and discharge, the problems of volume expansion and structure collapse of silicon during charge and discharge are effectively alleviated, and the cycle stability and the battery capacity of the battery are improved.
Test example 4
The batteries provided in examples 17 to 24 and comparative examples 5 to 6 were subjected to constant current charge and discharge test at a current density of 0.1C at a test temperature of 25℃, and the test results are shown in table 1.
TABLE 1 Battery charging and discharging test data sheet
Figure BDA0001672431240000161
As can be seen from table 1 comparing examples 17 to 19 with comparative example 5, the first cycle specific capacities of the batteries provided in examples 17 to 19 are all higher than 1200mAh/g, and the capacity retention rate after 300 cycles is still higher than 94%, which indicates that when the silicon-carbon composite material having a cavity structure provided in examples 1 to 3 is used as a negative active material, the specific capacity of the battery is significantly improved, and the cycle stability of the battery is significantly improved.
It can be seen from the comparison between examples 17-19 and examples 20-21 that the first cycle specific capacity of the battery provided by example 20 is significantly lower than that of examples 17-19, and the capacity retention rate of the battery provided by example 21 is significantly lower than that of examples 17-19, which indicates that when the silicon carbon composite material used as the negative active material in the battery is too high or too low, the silicon content of the silicon carbon composite material affects the first cycle specific capacity and the capacity retention rate of the battery, i.e. when the silicon carbon composite material contains 30-90 wt% of silicon, the battery has both good first cycle specific capacity and good cycle stability, and the overall performance is better.
It can be seen from comparison between examples 17-19 and examples 22-23 that the first cycle specific capacity and the capacity retention rate of the batteries provided by examples 22-23 are slightly lower than those of examples 17-19, which indicates that when the molar ratio of the first monomer to the second monomer is 1:1-2 during preparation of the silicon-carbon composite material, the prepared silicon-carbon composite material as a negative electrode active material can be used for preparing batteries with more stable cycle performance and better battery capacity retention rate.
As can be seen by comparing examples 17-19 with example 24, example 24 provides batteries having lower initial specific capacity and lower cycling stability than examples 17-19, which indicates that batteries made therefrom have reduced initial specific capacity and lower cycling stability when a portion of the silicon in the silicon carbon composite is present as an oxide and not fully reduced.
As can be seen from comparison of examples 17 to 19 with comparative example 2, examples 17 to 19 provided batteries having higher initial specific capacity and higher cycle stability than comparative example 2, which indicates that batteries using a silicon carbon composite as the negative active material of the batteries had higher initial specific capacity and higher cycle stability than batteries using a tin carbon composite as the negative active material.
Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.

Claims (6)

1. The preparation method of the silicon-carbon composite material is characterized by comprising the following steps:
(a) providing SiO2Sol and monomer solution containing C element, and forming SiO2And solid microspheres of a polymer;
(b) sintering the solid microspheres to obtain the microspheres with cavitiesSiO of (2)2C, microspheres;
(c) subjecting the SiO2the/C microspheres are reduced into the silicon-carbon composite material with a hollow microsphere structure, wherein,
the hollow microsphere comprises a shell and a cavity, the shell covers the cavity, and the shell comprises silicon and carbon;
in the step (b), during sintering, the temperature is first raised from room temperature to 220 ℃ at a heating rate of 2-5 ℃/min, then raised to 380 ℃ at a heating rate of 0.5-1 ℃/min, and then raised to 800 ℃ at a heating rate of 2-5 ℃/min, and the temperature is maintained for 6-10 hours.
2. The production method according to claim 1, wherein the outer diameter of the outer shell is 1 to 10 μm, the inner diameter of the outer shell is 0.1 to 5 μm, and the wall thickness of the outer shell is 0.1 to 3 μm.
3. The method of claim 1, wherein the silicon content in the outer shell is 30 to 90 wt%.
4. The method of claim 1, wherein the polymer is a copolymer and the monomers comprise a first monomer and a second monomer, wherein,
in step (a), SiO is first introduced2Dispersing the sol in the first monomer solution, and then adding the second monomer for copolymerization to obtain the SiO-containing material2And solid microspheres of a polymer; wherein the first monomer and/or the second monomer contain a C element.
5. The method according to claim 4, wherein the first monomer is at least one selected from urea, melamine, phenol, resorcinol, and 3-aminophenol;
and/or the presence of a gas in the gas,
the second monomer is one selected from C1-C6 low carbon aldehyde.
6. According to claim1 the production method according to (c), wherein in the step (c), SiO is reduced with a reducing agent2The reducing agent is magnesium, iron, copper or manganese.
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