WO2013067956A1 - 一种纳米硅碳复合材料及其制备方法 - Google Patents

一种纳米硅碳复合材料及其制备方法 Download PDF

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WO2013067956A1
WO2013067956A1 PCT/CN2012/084351 CN2012084351W WO2013067956A1 WO 2013067956 A1 WO2013067956 A1 WO 2013067956A1 CN 2012084351 W CN2012084351 W CN 2012084351W WO 2013067956 A1 WO2013067956 A1 WO 2013067956A1
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silicon
nano
carbon
composite material
carbon composite
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PCT/CN2012/084351
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French (fr)
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卢世刚
杨娟玉
王星明
丁海洋
高哲峰
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北京有色金属研究总院
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Priority to KR1020147015769A priority Critical patent/KR101685776B1/ko
Priority to EP12848316.1A priority patent/EP2778130B1/en
Priority to JP2014540308A priority patent/JP5826405B2/ja
Priority to US14/357,244 priority patent/US9666863B2/en
Publication of WO2013067956A1 publication Critical patent/WO2013067956A1/zh

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    • H—ELECTRICITY
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    • H01M4/364—Composites as mixtures
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    • C01B32/963—Preparation from compounds containing silicon
    • C01B32/984—Preparation from elemental silicon
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    • C01B33/113—Silicon oxides; Hydrates thereof
    • C01B33/12—Silica; Hydrates thereof, e.g. lepidoic silicic acid
    • C01B33/14—Colloidal silica, e.g. dispersions, gels, sols
    • C01B33/157—After-treatment of gels
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
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    • 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
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    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/483—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides for non-aqueous cells
    • H—ELECTRICITY
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    • 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
    • H—ELECTRICITY
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    • 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
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    • 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
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    • 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
    • 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
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    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H01M4/1393—Processes of manufacture of electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
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    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H01M4/1395—Processes of manufacture of electrodes based on metals, Si or alloys
    • 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

Definitions

  • Nano silicon carbon composite material and preparation method thereof are nano silicon carbon composite material and preparation method thereof.
  • the invention relates to a nano silicon carbon composite material for a lithium ion battery and a preparation method thereof.
  • Lithium-ion batteries have large specific energy, high operating voltage and low self-discharge rate.
  • Other advantages are widely used in the field of mobile electronic terminal equipment, and with the increasing demand for high specific energy sources, lithium ion batteries are moving toward higher energy density.
  • commercial lithium-ion batteries generally use graphite-based carbon materials as anode materials. Due to the lower theoretical electrochemical capacity (theoretical capacity of 372 mAh/g) of the electrode itself, it is difficult to improve battery performance by improving the battery preparation process. Breakthrough progress, the development of new high specific capacity lithium ion battery electrode materials is extremely urgent.
  • Metals such as Si, Sn and Sb are relatively high-capacity anode materials, among which silicon has a theoretical electrochemical capacity (theoretical capacity of 4200 mAh/g) which is 10 times higher than the currently widely used carbon materials, and a low lithium-incorporating voltage. (less than 0.5 V), there is no co-embedding of solvent molecules in the embedding process, and it is rich in the earth's crust, which is one of the preferred negative electrodes for the next generation of high specific energy batteries.
  • nano-silicon Because as the particle size decreases, the volume change of silicon can be reduced to some extent, and the internal stress of the electrode is reduced. However, nanomaterials tend to agglomerate during the cycle, which is not enough to improve the performance of the battery to practical use.
  • the nano-silicon carbon composite material is used to embed or load the electrochemically active nano-silicon or silicon alloy material into the carbon material.
  • the carbon material can improve the conductivity of the active silicon material, and on the other hand, the carbon material can be used as The "buffer skeleton" is used to disperse and buffer the internal stress of the electrode caused by the volume change of the silicon material during charge and discharge, so that the nano-silicon carbon composite material has good cycle stability.
  • the "buffer skeleton" is used to disperse and buffer the internal stress of the electrode caused by the volume change of the silicon material during charge and discharge, so that the nano-silicon carbon composite material has good cycle stability.
  • the silicon nanowire of the shell structure is used for the anode material of the lithium ion battery, wherein the crystalline silicon core in the core-shell structure silicon material serves as a skeleton and an electric conductor in the process of charging and discharging, and the outer layer of the amorphous silicon acts as an active material for intercalating and deintercalating lithium.
  • the silicon nanowires with this structural feature can ensure the structural stability during the charging and discharging process, and the conductivity of the crystalline silicon core is not destroyed.
  • the cyclic stability of the core-shell structural material is compared with that of crystalline silicon nano-crystals.
  • the line has been further improved. Yushin G et al. used the same method to prepare three-dimensional porous carbon-loaded nano-silicon particles.
  • iNature Materials when the composite structure silicon material is used as a negative electrode material for lithium-ion batteries, three-dimensional porous carbon is used as a framework material, which can provide effective nano-silicon particles on the one hand.
  • the conductive network on the other hand, the flexibility of the porous carbon can also buffer the volume expansion of the nano-silicon particles, which can inhibit the volume effect of the silicon material during charging and discharging to a certain extent, and improve the conductivity of the silicon material, thereby improving the conductivity.
  • the nano-silicon material In the process of charging and discharging the nano-silicon carbon composite material, the nano-silicon material must be effectively combined with the carbon material. In order to exert the electrochemical capacity of the silicon material, if the nano-silicon material is detached from the carbon material due to multiple expansion and contraction during repeated charge and discharge, the silicon material loses electrical contact with the material and cannot exert electrochemical capacity. Studies have shown that these nano-silicon-carbon composite materials are mainly deposited on the carbon substrate or coated with carbon on the nano-silicon substrate. Due to the limited ductility of the flexible carbon material, the silicon material cannot be effectively suppressed in the long-term circulation process.
  • the microstructure of nano-silicon materials and their effective combination with carbon materials are the key factors affecting the performance of silicon-carbon composites.
  • the current methods for preparing these nano-silicon carbon composite materials mainly include chemical vapor deposition, thermal vapor deposition, high temperature cracking, high energy ball milling and the like. These preparation methods involve complex processes (such as templating), or processes are difficult to control, and the equipment required is expensive (such as chemical vapor deposition), making it difficult to achieve mass production.
  • the object of the present invention is to overcome the problem that the separation stability of such materials is deteriorated due to the separation of silicon and carbon materials due to the large volume effect of the silicon material during the process of inserting and removing lithium in the lithium-ion battery composite material.
  • the defect provides a nano-silicon carbon composite material with good cycle stability.
  • the invention also provides a preparation method of the nano silicon carbon composite material, which has the advantages of short production process, no pollution, simple operation, easy availability of raw materials, low equipment, and easy continuous production.
  • the invention provides a nano silicon carbon composite material for a lithium ion battery, which is characterized in that: the material comprises a carbon matrix, nano silicon dispersed on the carbon substrate, nano silicon carbide SiC dispersed at the carbon matrix and the nano silicon interface,
  • the mass percentage of each component of the silicon oxide SiO x , 0 ⁇ x ⁇ 2 o coated on the surface of the nano-silicon except the interface connected with the carbon matrix is as follows: 2-40% of nano-silicon, 55-90% Carbon, 0.1 to 3% of nano SiC, 1 to 5% of silicon oxide SiO x .
  • the mass percentage of the nano silicon is further preferably 5 to 35%.
  • the mass percentage of carbon is further preferably 60 to 85%.
  • the carbon matrix in the nano-silicon carbon composite material for a lithium ion battery provided by the present invention has at least one of a spherical shape, a spheroidal shape, a sheet shape, a linear shape, and a tubular shape.
  • the size of the carbon matrix is 0.01-50 ⁇ ⁇ .
  • the nano-silicon is at least one of a spherical particle shape, a linear shape, a tubular shape, and a sheet shape.
  • the nano-silicon is at least one of a nano silicon wire, a nano silicon spherical particle, a nano silicon tube, and a nano silicon wafer.
  • the particle size of the nano silicon spherical particles is less than 100 nm, the diameter of the nano silicon wire is less than 100 nm, the diameter of the nano silicon tube is less than 100 nm, and the thickness of the nano silicon wafer is less than 100 nm.
  • the nano-silicon carbide SiC is at least one of a granular shape, a linear shape, and a sheet shape.
  • the particle size of the nano-SiC is less than 100 nm, the diameter of the linear SiC is less than 100 nm, and the thickness of the sheet-like SiC is less than 100 nm.
  • the silicon oxide SiO x , 0 ⁇ x ⁇ 2, coated on the surface of the nano silicon except the interface between the nano silicon and the carbon, and the thickness of the cladding layer is 1-5 nm.
  • the invention provides a preparation method of a nano silicon carbon composite material, wherein the specific steps are: firstly preparing a silica powder into a silica colloid, and then adding the carbon particle material to a silica colloid, wherein the silicon dioxide powder
  • the mass percentage is: 10 to 90% by weight; the mass percentage of the carbon particulate material is: 90 to 10 wt%, the total mass of the silica powder and the carbon particulate material is 100 wt%; the mixture is uniformly mixed, dried, and broken into dioxide
  • a silicon/carbon mixture which is hot pressed into a porous block, or molded into a porous block after molding or molding. Control the porosity, density, and electrical resistivity of the porous block.
  • a porous block composed of carbon and silica powder combined with a conductive cathode current collector as a cathode, graphite or an inert anode as an anode, and placed in a CaCl 2 electrolyte or a mixed salt melt electrolyte containing CaCl 2 to constitute an electrolysis a tank, applying an electrolytic DC voltage between the cathode and the anode, controlling the electrolysis voltage, the electrolysis current density, and the electrolysis amount, so that the silica in the porous block is electrolytically reduced to nano-silicon, and the nano-carbon silicon for lithium ion battery is obtained at the cathode.
  • Composite material
  • the silica powder has a particle diameter of 10 nm to 1 ⁇ m.
  • the carbon particulate material is selected from at least one of natural graphite, artificial graphite, amorphous carbon, and carbon nanotubes.
  • the carbon particle material has a particle diameter of 10 nm to 50 ⁇ m.
  • the hot pressing temperature is 900 to 1400 ° C, the hot pressing pressure is 8 to 40 MPa, and the holding time is 1 to 5 h; the sintering temperature is 800 to 1500 ° C, and the sintering time is 1 to 8 hours.
  • the porous block has a porosity of 5 to 65 % by volume.
  • the porous block has a density of 0.80 to 2.10 g/cm 3 .
  • the porous block has a specific resistance of 0.001 100 ⁇ .
  • the mixed salt melt containing CaCl 2 electrolyte is CaC + MY 1, wherein the mixed salt melt containing electrolyte CaCl 2, CaCl 2 mole percent of 40 to 95%, the balance being MY 1, M is Ba, Li, Al, Cs, Na, K, Mg, Rb, Be or Sr, Y 1 is CI or F.
  • the electrolyte contains calcium oxide CaO, and the content of calcium oxide is 0.001 to 20% by mole based on the total amount of the electrolyte.
  • Electrolysis is carried out at a temperature of 500 to 1000 °C.
  • the electrolysis voltage is lower than the theoretical decomposition voltage of the electrolyte, and the electrolysis current density is greater than the background current density of the electrolysis cell, and the electrolysis time is the time required for the electrolysis amount to reach the theoretically required amount of electricity and above.
  • the present invention provides a lithium ion battery comprising a positive electrode, a negative electrode and a nonaqueous electrolyte, the negative electrode comprising the nano silicon carbon composite material of the present invention.
  • the ratio of silicon to carbon in the nano-silicon carbon composite material can be adjusted by adjusting the ratio of the raw material silicon dioxide and carbon, and the lithium intercalation capacity of the nano-silicon carbon composite material can be adjusted;
  • 1 is a scanning electron microscope (SEM) image of the carbon fiber-loaded nano-silicon particle composite prepared by the present invention at 900 ° C using a mixture of carbon fiber and silica as a raw material.
  • 2 is a scanning electron microscope (SEM) image of a silicon nanowire composite grown on a graphite sheet prepared by using the graphite sheet and the silica mixture as a raw material at 950 ° C, wherein 1 is a carbon matrix; It is a nano silicon wire.
  • FIG. 3 is a structural and composition analysis image of a single silicon nanowire grown on a graphite sheet prepared by the present invention at 950 ° C using a graphite sheet and a silica mixture as a raw material, a) TEM image; (b) HRTEM Figure; (c) STEM diagram; (d) EDS line scan.
  • FIG. 4 is a structural analysis image of a silicon nanowire composite material grown on a graphite sheet prepared by the present invention at 950 ° C using a graphite sheet and a silica mixture as a raw material, a. a transmission electron microscope (TEM) image; b. Electron diffraction pattern (SEAD); C. High resolution transmission electron microscope (HRTEM).
  • TEM transmission electron microscope
  • SEAD Electron diffraction pattern
  • HRTEM High resolution transmission electron microscope
  • Figure 5 is an X-ray diffraction pattern of the nano-silicon carbon composite prepared by the present invention at 950 °C. detailed description
  • the invention provides a nano silicon carbon composite material for a lithium ion battery, which comprises a carbon matrix, nano silicon dispersed on a carbon substrate, nano silicon carbide SiC dispersed at a carbon matrix and a nano silicon interface, and coated Silicon oxide SiO x , 0 ⁇ x ⁇ 2 o on the surface of the nano-silicon other than the interface between the nano-silicon and the carbon matrix
  • the composite material firstly forms a silica powder into a silica colloid, and then adds the carbon particle material to the silica colloid, wherein the mass percentage of the silica powder is: 10 to 90% by weight; the mass percentage of the carbon particle material It is: 90 ⁇ 10 wt%, the total mass of the silica powder and the carbon particle material is 100 wt%; the mechanical kneading is uniformly mixed, and after drying, crushing and molding steps, a porous block of carbon and silica is formed.
  • the porosity, density and electrical resistivity of the porous block composed of silicon dioxide and carbon By controlling the porosity, density and electrical resistivity of the porous block composed of silicon dioxide and carbon, the structure and uniformity of the material during the electrochemical reduction of the silicon dioxide into nano-silicon in situ to form the nano-silicon carbon composite material are effectively controlled; At the same time, by controlling the electrolysis voltage, electrolysis current density and electrolysis power, the characteristics of the electrochemical reaction of silica can be utilized, that is, only through silicon dioxide (silicon source phase) / silicon or carbon (conductive phase) / electrolyte (ion-conducting phase) The characteristics of three-phase interface electrolytic reduction control the reduction rate of silica electrolytic reduction to control the dispersion uniformity of the nano-silicon material on the surface of the carbon substrate, the degree of bonding with the carbon interface, and the thickness of the silicon oxide coating layer.
  • the degree of bonding between nano-silicon and carbon materials is mainly determined by the distribution and content of silicon carbide at the carbon-silicon interface.
  • the interface between the nano-silicon and the carbon can form a small amount of rigid silicon carbide with high hardness, which is a metallurgical grade combination, which greatly enhances the bonding force between the nano-silicon and the carbon material; and a small amount of rigid silicon carbide and flexible carbon material.
  • the silicon and carbon in the nano-silicon carbon composite material are not separated from each other due to the increase of the number of cycles, thereby improving the nano-silicon carbon composite. Material circulation Ring stability.
  • the nano-silicon in the material is obtained by electrochemically melting the silica in the raw material of the salt, and the carbon matrix is derived from the carbon material in the raw material. It is therefore possible to adjust the ratio of nano-silicon and carbon matrix in the nano-silicon carbon composite by adjusting the ratio of the raw material silica to carbon. Because the carbon matrix in the silicon-carbon composite mainly plays a role in the volumetric benefit of the conductive and buffered silicon materials, the electrochemical specific capacity is mainly provided by the nano-silicon, so the composite can be adjusted by controlling the ratio of the nano-silicon and the carbon matrix in the nano-silicon-carbon composite. The lithium insertion capacity of the material. The ratio of silicon to carbon is too low (Si% ⁇ 2wt%).
  • the theoretical specific capacity of nano-silicon carbon composite is only 430mAh/g, which is close to the theoretical specific capacity of 372mAh/g of graphite anode. It can not meet the high specific energy of the battery.
  • the proportion of silicon to carbon is too high, and the specific capacity of the nano-silicon carbon composite is higher under the same conditions. However, this will bring about two problems.
  • the content of nano-silicon in the nano-silicon-carbon composite increases, the overall volume effect of the nano-silicon will also increase, affecting the cycle performance of the composite; on the other hand, compound If the content of nano-silicon in the material is too high, some of the nano-silicon can not be combined with the carbon matrix. The conductivity of the silicon material in this part will be poor.
  • the nano-silicon can not be combined with the metallurgical grade of carbon to make the silicon deintercalated. The resulting volume change is also more severe, resulting in poor cycle performance of the battery using the nano-silicon carbon composite.
  • Silicon carbide in the nano-silicon carbon composite is formed during the molten salt electrolysis process.
  • the reaction of bulk carbon and bulk silicon to form silicon carbide is a thermodynamic spontaneous reaction at normal temperature, the kinetic reaction of bulk silicon and bulk carbon materials generally requires temperatures above 1400 °C to occur.
  • nano-silicon is generated in situ by electrochemical reaction and has relatively high reactivity, the carbon material in the nano-silicon and the raw material can be slowly formed into a small amount of nano-silicon carbide by chemical reaction after being immersed in the molten salt for a long time. .
  • silicon carbide can only be produced where nano-silicon and carbon materials are present at the same time.
  • the resulting silicon carbide can limit the volume change of the silicon material in the nano-silicon-carbon composite material due to the high hardness and high strength, so that the silicon and carbon in the nano-silicon carbon composite material are not increased due to the number of cycles. Separation from each other greatly improves the degree of bonding between elemental silicon and elemental carbon, thereby improving the cycle stability of the nano-silicon carbon composite.
  • silicon carbide is not electrochemically active, too high a silicon carbide content will lower the specific capacity of the nano-silicon carbon composite. Therefore, the low silicon carbide content in the nano-silicon carbon composite should be controlled as much as possible.
  • the electrolysis voltage, the electrolysis current density, the electrolysis amount and the electrolysis temperature controls the electrolysis reduction rate of the silica, which can be adjusted.
  • the content of silicon carbide in the nano-silicon carbon composite material of the electrolysis product thereby controlling the degree of metallurgical bonding between silicon and carbon, and improving the electrochemical cycle stability of the nano-silicon carbon composite material under the premise of ensuring the specific capacity of the nano-silicon carbon composite material.
  • the carbon matrix in the nano-silicon carbon composite material is derived from the carbon material in the raw material, and can be commonly used in the field of lithium ion batteries.
  • Graphite-based anode materials such as natural graphite, artificial graphite, mesocarbon microspheres, etc.; can also be conductive carbon materials for lithium-ion batteries, such as black, carbon black, carbon fiber or carbon tube.
  • the carbon material may be one or more of a graphite-based negative electrode and a conductive carbon. Since the carbon matrix in the nano-silicon carbon composite material is the remaining carbon material after the raw material carbon particles react with the nano-silicon in the molten salt to form silicon carbide, the chemical composition, morphology, size, structure and the raw material carbon particles are inherited. Basically the same as the raw material carbon particles.
  • the silicon oxide SiO x cladding layer on the surface of the nano silicon in the nano silicon carbon composite material is derived from the incompletely reduced silicon dioxide in the raw material or the nano silicon generated by the reduction in the nano silicon carbon composite material of the electrolysis product in the post-treatment process. It is oxidized again, so the silicon oxide is coated on the surface of the nano-silicon.
  • the content of silicon oxide in the nano-silicon carbon composite material of the electrolysis product can be adjusted by controlling the electrolysis amount, that is, the electrolysis time.
  • control electrolysis time is sufficient to completely electrolyze the raw material silica, but since the molten salt electrolysis temperature is generally performed at 500 ° C or higher, the nano silicon generated by the reduction is highly active, and the electrolysis product is raised from the electrolytic cell and then washed.
  • the surface of the nano-silicon is partially oxidized, so silicon oxide is always present on the surface of the nano-silicon material, but the thickness of the silicon oxide coating is generally only 1-5 nm.
  • the silicon oxide in the nano-silicon carbon composite material can embed lithium, and the lithium silicate coated on the surface of the nano-silicon formed by lithium intercalation not only has good conductivity, but also can effectively limit the volume change in the process of lithium intercalation and deintercalation.
  • the silicon oxide in the nano-silicon carbon composite material is beneficial to improve the cycle stability of the silicon-carbon composite material, but the lithium silicate formed by the lithium oxide after lithium intercalation cannot completely remove lithium, thereby making the nano-silicon carbon composite material The first time Coulomb was inefficient.
  • the mass percentage of each component in the nano-silicon carbon composite material is as follows: The mass percentage of each component is as follows: 2-40% of nano silicon, 55-90% of carbon, 0.1 to 3% of nano SiC, 1 ⁇ 5% silicon oxide SiO x .
  • the mass percentage of the nano silicon is further preferably 5 to 35%.
  • the mass percentage of carbon is further preferably 60 to 85%.
  • the nano-silicon carbon composite material of the present invention has the following structural features: the carbon matrix has at least one of a spherical shape, a spheroidal shape, a sheet shape, a linear shape, and a tubular shape.
  • the size of the carbon matrix is from 0.01 to 50 m.
  • the nano-silicon is at least one of a granular shape, a linear shape, a tubular shape, and a sheet shape.
  • the nano-silicon is at least one of a nano silicon wire, a nano silicon particle, a nano silicon tube, and a nano silicon wafer.
  • the diameter of the nano silicon particles is less than 100 nm, the diameter of the nano silicon wires is less than 100 nm, the diameter of the nano silicon tubes is less than 100 nm, and the thickness of the nano silicon wafers is less than 100 nm.
  • the nano-silicon carbide SiC is at least one of a granular shape, a linear shape, and a sheet shape.
  • the particle size of the granular nano SiC is less than 100 nm, the diameter of the linear SiC is less than 100 nm, and the thickness of the flaky SiC is less than 100 nm.
  • the silicon oxide SiO x , 0 ⁇ x ⁇ 2, coated on the surface of the nano silicon except the interface between the nano silicon and the carbon, and the thickness of the cladding layer is 1-5 nm.
  • the composition and structure of the nano-silicon carbon composite material are closely related to the electrochemical performance of the material.
  • the nano-silicon carbon composite material is prepared by electrolytic reduction of porous blocks composed of silicon dioxide and carbon materials, and the electrochemical reduction of silicon dioxide into nano-silicon exists only through silicon dioxide (silicon source phase) / silicon or carbon ( Conductive phase) / electrolyte (guide Ionic phase) characteristics of three-phase interface electrolytic reduction.
  • compositions, structure and electrochemical properties of nano-silicon, carbon, silicon carbide and silicon oxide in nano-silicon-carbon composites are as follows: 1) Composition and structure of porous blocks composed of carbon and silicon dioxide And physical properties (such as porosity, pore size, density and electrical resistivity); 2) electrolytic process conditions of molten salt electrolysis (such as electrolysis voltage, electrolysis power, electrolysis current density, electrolysis temperature, electrolyte composition, etc.).
  • the silica powder is made into a silica colloid, and the carbon particle material is added to the silica colloid, uniformly mixed, dried, broken into a silica/carbon mixture, and the mixture is hot pressed into a porous block, or After molding or molding, it is sintered into a porous block.
  • the temperature and pressure of the molding process during the preparation process of the porous block have a decisive influence on the porosity of the porous electrode.
  • the hot pressing pressure is 20 Mpa and the dampening time is It is lh
  • the porosity of the porous block is 63% by volume and 20% by volume, respectively, when the molding temperatures are 900 ° C and 1400 ° C, respectively.
  • the silica in the porous block with a molding temperature of 900 ° and a porosity of 63 vol% still maintains a single particle morphology. Therefore, there are many pores in the silica particles; and the molding temperature is 1400 ° C.
  • silica is sintered into a silica block due to high temperature, and few pores exist in the silica.
  • the difference in morphology and pore structure of the silica directly affects the composition, morphology and structure of the nano-silicon carbon composite of the electrolysis product.
  • the nano-silicon composites obtained by electrolytic reduction of porous blocks with a molding temperature of 900 ° C and a porosity of 63% by volume are mainly composed of spherical nanoparticles, and few silicon nanowires.
  • the nano-silicon-carbon composite has a first lithium-incorporating capacity of 1108 mAh/g, a first coulombic efficiency of 73%, a cycle 100-minute capacity retention rate of 90%, and a 1400°C porosity of 20% of the porous block obtained by electrolytic reduction. It is a nano-silicon carbon composite material mainly composed of silicon nanowires. Its first lithium insertion capacity is 1132 mAh/g, the first coulombic efficiency is 86%, and the cycle 100-minute capacity retention rate is 93%.
  • the porosity of the porous block composed of carbon and silica is large, for example, when the porosity of the porous block is more than 65 vol%, the silicon generated by the electrolytic reduction of silica during the electrolysis process is reduced in volume by 50% due to oxygen evolution. %, the porosity of the porous block composed of carbon and silicon after reduction is increased, so that the porous block is insufficient in strength and cannot be completely removed from the molten salt.
  • the porosity of the porous block composed of carbon and silica is relatively small, for example, when the porosity of the porous block is less than 5% by volume, the pores in the porous block through which the molten electrolyte calcium chloride can pass are less, and the rate of electrolytic reduction reaction Lowering, the electrolysis time is too long, resulting in too much silicon carbide in the product.
  • the properties of the nano-silicon-carbon composite obtained by the molten salt electrolysis process conditions are different. Electrolysis was carried out with a porous block composed of 40 wt% Si0 2 and 60 wt% carbon and having a porosity of 23%. The electrolysis temperature was 850 ° C, the electrolysis voltage was 2.7 V, and the electrolysis power was controlled to be 1.2 times and 1.5 times the theoretical amount, respectively. Carbon composite. 1.2 times the amount of nano-silicon carbon composite material for the first time in lithium The capacity is 1112mAh/g, the first coulon efficiency is 86%, and the cycle 100-year capacity retention rate is 91%. The theoretical lithium-carbon composite material has a lithium-incorporated capacity of 1148mAh/g for the first time, and the first coulombic efficiency is 87%. The cycle retention rate of 100 cycles was 90%.
  • the preparation method of the nano silicon carbon composite material provided by the invention comprises the following steps:
  • the present invention provides a method for preparing a nano-silicon carbon composite material, the specific steps of which are: combining a porous block composed of carbon and silica powder with a conductive cathode current collector as a cathode, using graphite or an inert anode as a cathode
  • the anode is placed in a CaCl 2 electrolyte or a mixed salt melt electrolyte containing CaCl 2 to form an electrolytic cell, and an electrolytic DC voltage is applied between the cathode and the anode to control the electrolysis voltage, the electrolysis current density, and the electrolysis amount, so that the porous block is
  • the silicon dioxide is electrolytically reduced to nano silicon, and a nano silicon carbon composite material for a lithium ion battery is obtained at the cathode.
  • the preparation process of the porous block composed of the carbon and silica powder firstly adding lOnm to ⁇ silica powder to distilled water, absolute ethanol, ethylene glycol having a mass percentage of 60% to 400% Or one or two of propanol, wherein one or both of distilled water, absolute ethanol, ethylene glycol, propanol, etc., having a mass percentage of 60% to 400%, is relative to dioxide 100% by mass of the silicon powder; a colloid in a planetary stirred tank, the stirring time is l ⁇ 12h; and then the carbon particle material having a particle diameter of lOnm to 50 ⁇ is added to the silica colloid, wherein
  • the mass percentage of the silica powder is: 10 to 90% by weight; the mass percentage of the carbon particulate material is: 90 to 10 wt%, and the total mass of the silica powder and the carbon particulate material is 100 wt%; using a kneading machine or kneading The machine is evenly
  • the dried material is mechanically crushed and then hot pressed into a porous block; the hot pressing temperature is 900 to 1400 ° C, and the hot pressing pressure is 8 to 40 MPa. , the holding time is l ⁇ 5h; Alternatively, the wet-mixed slurry may be directly molded or molded, and then sintered in an inert protective atmosphere at a temperature of 800 to 1500 ° C for a period of 1 to 8 hours to obtain a porous block.
  • the carbon particulate material is selected from at least one of natural graphite, artificial graphite, amorphous carbon, and carbon nanotubes.
  • the porous block has a porosity of 5 to 65 vol%.
  • the porous block has a density of 0.80 to 2.10 g/cm 3 .
  • the porous block has a specific resistance of 0.001 to 100 ⁇ ' cm .
  • the mixture containing CaCl 2 electrolyte salt melt is CaC + MY 1, wherein the mixed electrolyte comprising a salt melt of CaCl 2, CaCl 2 mass percentage of 40 to 95wt%, the balance being MY 1 , M is Ba,
  • Li, Al, Cs, Na, K, Mg, Rb, Be or Sr, Y 1 is CI or F.
  • the electrolyte contains calcium oxide CaO, and the content of calcium oxide accounts for the mole percent of the total electrolyte. It is 0.001 ⁇ 20%.
  • Electrolysis is carried out at a temperature of 500-1000 °C.
  • the electrolysis voltage is lower than the theoretical decomposition voltage of the electrolyte, and the electrolysis current density is greater than the background current density of the electrolysis cell, and the electrolysis time is the time required for the electrolysis amount to reach the theoretically required amount of electricity and above.
  • the product can be taken out from the molten salt with the working electrode, and if necessary, a porous block electrode composed of carbon and silicon dioxide can be placed to start a new round. Electrolysis, thereby achieving continuous production of nano-silicon carbon composites.
  • the electrolytic product is taken out, it is cooled to room temperature under an inert atmosphere, and then sufficiently washed in a dilute mineral acid, water and an organic solvent to remove the molten salt electrolyte contained in the product.
  • the dilute mineral acid may be from 1% to 3% by volume of hydrochloric acid.
  • the washed electrolysis product is dried in a vacuum for 12 hours or more.
  • the dried electrolysis product is ground and crushed, and sieved to obtain a nano-silicon carbon composite material.
  • nano-SiO 2 powder in the raw materials described in the examples refers to a powder having a particle diameter of 100 nm or less.
  • the dried material was incubated under mechanical pressure at 20 MPa and 1300 ° C for 2 h under argon atmosphere, and pressed into a porous disc having a diameter of about 80 mm and a thickness of 10 mm, a porosity of 21% by volume, a density of 1.70 g/cm 3 , and electrical resistance.
  • the rate is 0.08 ⁇ ⁇ cm .
  • the wafer is combined with a conductive cathode current collector as a cathode, a graphite rod is used as an anode, CaCl 2 is used as an electrolyte, and in an argon atmosphere, the temperature is 950 ° C, and a voltage is controlled by a voltage regulator for constant voltage electrolysis.
  • the voltage is 2.5V.
  • the electrolyzed product was sequentially washed with 1% by volume of dilute hydrochloric acid, water and absolute ethanol, vacuum dried, and sieved to obtain a product nano-silica composite material.
  • the mass percentage of carbon in the nano-silicon carbon composite material was 67%, the mass percentage of nano-silicon is 29%, the mass percentage of silicon carbide is 1%, the content of silicon oxide SiO 2 is 3%, and the scanning electron microscope SEM image of 67C29SilSiC3Si0 from the material As shown in Fig. 2, it can be seen that a linear nano-silicon material is grown on the graphite sheet.
  • a nano silicon wire 2 is grown on the carbon substrate 1; a TEM image of a single silicon nanowire 2 in the black coil of FIG. 2 (FIG. 3a) shows that the silicon nanowire is a core-shell structure, in the middle The part is about 80 nm and the outer layer is 5 nm thick.
  • Fig. 3b is an HRTEM image of a silicon nanowire. It can be seen from the figure that in the core-shell structure of the silicon nanowire, the internal regular lattice fringe indicates that the core is a single crystal structure, and the outer shell layer is an amorphous structure.
  • the internal single crystal plane spacing is 0.31 nm, which corresponds to the ⁇ 111 ⁇ interplanar spacing of the cubic diamond structure.
  • Figure 3d is an energy dispersive X-ray spectroscopy (EDS) line scan analysis of the individual silicon nanowires of Figure 3c. It can be seen from the figure that the radial distribution of Si and 0 along the silicon nanowires shows different laws. The middle part of the silicon nanowire is mainly silicon, and the beginning and end of the on-line scanning of the oxygen element is significantly higher than the middle part.
  • the experimental results directly reflect that the silicon nanowires are composed of single crystal silicon core, and the surface is coated with a core-shell structure of amorphous silica.
  • the obtained composite material was prepared by the following method: The obtained electrolytic product nano-silicon carbon composite material was used as an active material, Super-P carbon black was used as a conductive agent, and PVDF was a binder, and the mass ratio was 7 : 2 : 1 After mixing uniformly, the slurry was prepared by using N-methylpyrrolidone as a solvent, and the slurry was coated on a copper foil of 8 ⁇ thick to make a pole piece of 1.0 cm ⁇ 1.5 cm, dried at 70 ° C, and rolled to a pole piece. The required thickness was dried under vacuum at 120 °C for 12 h.
  • the charge and discharge performance of the test battery was tested with a blue battery test system CT2001A tester.
  • the charge and discharge voltage range is 0.005 ⁇ 2.0V
  • the charge and discharge current density is 80mA/g
  • the capacity retention rate of the test battery cycle for 100 weeks is doo/C ⁇
  • the small wafer is combined with a conductive cathode current collector as a cathode, a graphite rod is used as an anode, CaCl 2 is used as an electrolyte, and in an argon atmosphere, the temperature is 850 ° C, and a constant voltage voltage is controlled by a voltage regulator. Solution, the tank voltage is 2.9V.
  • the electrolysis product was sequentially washed with a volume percentage of 1% dilute hydrochloric acid, water, absolute ethanol, vacuum dried, and sieved to obtain a carbon fiber-loaded nano-silicon particle composite material 56C40SilSiC3SiO.
  • the composite material was tested in the same manner as in Example 1. Methods Material composition and structural analysis were performed.
  • the obtained composite material was prepared in the same manner as in Example 1 to carry out an electrochemical performance test.
  • the nano-SiO 2 powder with a purity of 99.95% was added to the ethylene glycol mass percentage of 100% ethylene glycol, and the gel was prepared in a planetary stirred tank for a stirring time of lh; then 35wt % (100% by weight of Si0 2 powder and carbon fiber), commercially available in diameter from 20 to 150 nm, length 2 to ⁇ carbon fiber, added to silica colloid, mixed with dough mixer, mixed slurry air After drying for 6 hours in the atmosphere, the dried material was mechanically crushed and then hot pressed into a porous block at 1000 °C.
  • the porous block had a porosity of 22%, a density of 1.70 g/cm 3 and a specific resistance of 0.5 ⁇ ⁇ cm.
  • the porous block is machined into a rectangular block having a length of 50 mm, a width of 30 mm and a height of 10 mm, and the rectangular block is combined with a conductive cathode current collector as a cathode, a graphite rod is used as an anode, CaCl 2 is used as an electrolyte, and argon is used.
  • a gas atmosphere the temperature is 900 ° C, and the voltage is controlled by a voltage regulator for constant voltage electrolysis.
  • the cell voltage is 2.8V.
  • the electrolyzed product was sequentially washed with a volume percentage of 1% dilute hydrochloric acid, water, absolute ethanol, vacuum dried, and sieved to obtain a product such as the carbon fiber-loaded nano-silicon particle composite material shown in Fig. 1, nano-silicon carbide.
  • the flakes are intermittently dispersed on the nano-silicon.
  • the prepared carbon fiber-loaded nano-silicon particle composite material 57C38Si2SiC3Si0 was subjected to the same test method as in Example 1 for material composition and structural analysis.
  • the obtained composite material was prepared in the same manner as in Example 1 to carry out an electrochemical performance test.
  • the rectangular block after demolding is sintered in a 1400 ° argon atmosphere for 2 h to form a porous cuboid. .
  • the porous block had a porosity of 32% by volume, a density of 1.50 g/cm 3 and a specific resistance of 0.18 Q * cm .
  • the rectangular block is combined with a conductive cathode current collector as a cathode, a graphite rod is used as an anode, CaCl 2 is used as an electrolyte, and in an argon atmosphere, the temperature is 800 ° C, and a constant voltage electrolysis is performed by a voltage regulator control voltage.
  • the cell voltage is 2.8V for 4 hours and then converted to constant current density electrolysis.
  • the electrolyzed product was sequentially washed with a volume percentage of 1% dilute hydrochloric acid, water, and absolute ethanol, vacuum dried, and sieved to obtain a spherical graphite-supported silicon nanowire composite material 75C21Si0.5SiC3.5SiO 2 .
  • the composite material was subjected to material composition and structural analysis in accordance with the same test method as in Example 1.
  • the obtained composite material was prepared in the same manner as in Example 1 to carry out an electrochemical performance test.
  • 20% of the 0.2 mSiO 2 powder with a purity of 99.9% was added to the ethylene glycol content of 70% by mass of ethylene glycol, and the gel was prepared in a planetary stirred tank for 2 hours; then 50 ⁇ % of the particle size of 3 to 6 ⁇ flake graphite and 30wt% of the diameter of 20 ⁇ 200nm, the length of 5 ⁇ 10 ⁇ carbon fiber is sequentially added to the silica colloid, in the mixture (with SiO 2 powder, flake graphite and carbon fiber The total weight is 100%), 90% of the distilled water with the weight of the above solid powder is added, mechanically vigorously stirred by a planetary ball mill for 4 hours, and the uniformly stirred slurry is molded by molding to form a length of 50 mm, a width of 30 mm, and a height of 10 mm.
  • Rectangular block It was sintered at 1200 ° C for 3 hours to form a porous rectangular parallelepiped having a porosity of 40% by volume, a density of 1.32 g/cm 3 and a specific resistance of 0.3 ⁇ * cm .
  • the rectangular block and the conductive cathode current collector are combined as a cathode, the graphite rod is used as an anode, CaCl 2 is used as an electrolyte, and the temperature is 800 ° C in an argon atmosphere, and the current density is controlled by a voltage regulator for constant current electrolysis.
  • the current density is 3000 A/cm 2 .
  • the electrolysis product was sequentially washed with a volume percentage of 1% dilute hydrochloric acid, water, absolute ethanol, vacuum dried, and sieved to obtain a product nano-silicon carbon composite material 85C9Si3SiC3Si0 2 o.
  • the composite material was the same as in Example 1. The test method was carried out for material composition and structural analysis.
  • the obtained composite material was prepared in the same manner as in Example 1 to carry out an electrochemical performance test.
  • the uniformly stirred slurry was dried by microwave drying, and the dried material was molded by mechanical pressure to form a rectangular block having a length of 50 mm, a width of 30 mm, and a height of 10 mm.
  • the temperature is raised to 1300 ° C for 3 hours, and the sintered carbon fiber and the SiO 2 and the phenolic resin pyrolytic carbon mixture are porous rectangular blocks, and the porosity of the porous block is 32.
  • the volume %, the density is 1.50 g/cm 3 , and the specific resistance is 0.45 ⁇ ⁇ cm .
  • the rectangular block is combined with a conductive cathode current collector as a cathode, a graphite rod is used as an anode, CaCl 2 is used as an electrolyte, and in an argon atmosphere, the temperature is 850 ° C, and a constant voltage electrolysis is performed by a voltage regulator control voltage.
  • the cell voltage is 2.9V.
  • the electrolyzed product was sequentially washed with 1% by volume of dilute hydrochloric acid, water and absolute ethanol, vacuum dried, and sieved to obtain a nano-silicon carbon composite material 57C39SilSiC3Si0 2 .
  • the composite material was subjected to material composition and structural analysis in accordance with the same test method as in Example 1.
  • the obtained composite material was prepared in the same manner as in Example 1 to carry out an electrochemical performance test.
  • the volume % has a density of 1.40 g/cm 3 and a specific resistance of 0.60 ⁇ ⁇ cm .
  • the rectangular block is combined with a conductive cathode current collector as a cathode, a graphite rod is used as an anode, CaCl 2 is used as an electrolyte, and in an argon atmosphere, the temperature is 950 ° C, and a constant voltage electrolysis is performed by a voltage regulator control voltage.
  • the cell voltage is 2.6V.
  • the electrolyzed product was sequentially washed with 1% by volume of dilute hydrochloric acid, water and absolute ethanol, vacuum dried, and sieved to obtain a nano-silicon carbon composite material 72C24SilSiC3Si0 2 .
  • the composite material was subjected to material composition and structural analysis in accordance with the same test method as in Example 1.
  • the temperature was raised to 1100 ° C for 3 hours, and the sintered graphite sheet and the SiO 2 and the pitch pyrolytic carbon mixture porous rectangular block having a porosity of 36 were obtained.
  • the volume % has a density of 1.40 g/cm 3 and a specific resistance of 0.60 ⁇ ⁇ cm .
  • the rectangular block is combined with a conductive cathode current collector as a cathode, a graphite rod is used as an anode, and a CaCl 2 -NaCl (80:20 mol%) mixed salt is used as an electrolyte.
  • the temperature is 750 ° C.
  • Example 9 The voltage was controlled by a voltage regulator for constant voltage electrolysis, and the cell voltage was 2.8V. After 12 hours of electrolysis, the electrolysis product was sequentially washed with a volume percentage of 1% dilute hydrochloric acid, water, absolute ethanol, vacuum dried, and sieved to obtain a nano-silicon carbon composite material 72C24SilSiC3Si0 2 . The composite material was subjected to material composition and structural analysis in accordance with the same test method as in Example 1. Example 9
  • the volume % has a density of 1.40 g/cm 3 and a specific resistance of 0.60 ⁇ ⁇ cm .
  • the rectangular block is combined with a conductive cathode current collector as a cathode, a graphite rod is used as an anode, and a mixed salt of CaCl 2 -LiCl-KCl (36.1:52.3: 11.6 mol%) is used as an electrolyte.
  • the temperature is At 600 ° C
  • the voltage is controlled by a voltage regulator for constant voltage electrolysis, and the cell voltage is 2.9V.
  • the electrolysis product was sequentially washed with a volume percentage of 1% dilute hydrochloric acid, water, absolute ethanol, vacuum dried, and sieved to obtain a nano-silicon carbon composite material 72C24SilSiC3Si0 2 o.
  • the composite material was tested in the same manner as in Example 1. Methods Material composition and structural analysis were performed.
  • the obtained composite material was prepared in the same manner as in Example 1 to carry out an electrochemical performance test.
  • Nano-silicon carbon composite material composed of silicon nanowires grown on graphite sheets prepared by chemical vapor deposition

Abstract

一种锂离子电池用纳米硅碳复合负极材料及其制备方法，其以二氧化硅和碳组成的多孔电极为原料，通过熔盐电解方法二氧化硅原位电化学还原形成碳载纳米硅的纳米硅碳复合材料。该材料硅和碳之间通过纳米碳化硅连接，是一种冶金级的结合，提高了纳米硅和碳复合材料的电化学循环稳定性。本发明提供的纳米硅碳复合材料的制备方法是将碳和二氧化硅粉末组成的多孔块体，与导电的阴极集流体复合作为阴极，以石墨或惰性阳极作为阳极，置于以 CaCl2电解质或含有 CaCl2的混盐熔体电解质中构成电解槽，在阴极和阳极之间施加电解直流电压，控制电解电压、电解电流密度和电解电量，使得多孔块体中的二氧化硅电解还原成纳米硅，在阴极制得锂离子电池用纳米硅碳复合材料。

Description

一种纳米硅碳复合材料及其制备方法 技术领域
本发明涉及一种锂离子电池用纳米硅碳复合材料及其制备方法。
背景技术
随着各种便携式电子设备的广泛应用和电动汽车的快速发展，对其动力***——化 学电源的需求和性能要求急剧增长， 锂离子电池以其比能量大、 工作电压高、 自放电率 小等优势广泛应用于移动电子终端设备领域， 并且随着对高比能电源需求的增长， 使得 锂离子电池向着更高能量密度的方向发展。 当前， 商业化的锂离子电池普遍采用石墨类 碳材料作为阳极材料， 由于该电极本身较低的理论电化学容量（理论容量 372mAh/g )限 制， 通过改进电池制备工艺来提高电池性能已难以取得突破性进展， 新型高比容量的锂 离子电池电极材料的开发极具迫切性。 Si、 Sn和 Sb等金属是人们研究比较多的高容量 阳极材料， 其中硅具有比目前广泛使用的碳材料高 10倍多的理论电化学容量（理论容量 4200mAh/g ) ， 低的嵌锂电压 （低于 0. 5 V), 嵌入过程中不存在溶剂分子的共嵌入， 在 地壳中含量丰富等优点而成为下一代高比能动力电池优选负极之一。但由于硅材料本身 导电性能差， 加之在电化学嵌脱锂时产生的严重体积效应 (体积变化率： 280%〜310%)， 造成材料结构的破坏和机械粉化， 导致电极材料间及电极材料与集流体的分离， 进而失 去电接触， 致使电极的循环性能急剧下降。
目前人们提出解决这一问题的办法主要有两种： 方法之一就是将硅纳米化。 因为随 着颗粒的减小， 在一定程度上能够降低硅的体积变化， 减小电极内部应力。 但纳米材料 在循环过程中易团聚， 不足以使电池的性能改善到实用化。 第二， 采用纳米硅碳复合材 料， 即将具有电化学活性的纳米硅或硅合金材料嵌入或负载到碳材料中， 碳材料一方面 可以改善活性硅材料的导电性， 另一方面碳材料可以作为"缓冲骨架"来分散和缓冲硅材 料在充放电过程中由于体积变化所造成的电极内部应力，使纳米硅碳复合材料具有好的 循环稳定性。 最近有学者报道 （A¾fMre, 2008, 3: 31-35 )， 当硅纳米线用作锂离子电池负极 材料时， 它不仅具有接近理论值的电化学容量和较好的大电流充放电性能， 也具有极其 稳定的循环性， 分析认为， 由于电子在硅纳米线中沿径向一维传导， 在充放电过程中晶 体硅转变为非晶硅引起了纳米线相组成和结构发生变化， 但其一维的结构特征保持不 变， 维持了电极良好的导电性和结构的稳定性。 常温下锂离子的嵌入破坏纳米硅的晶体 结构， 生成亚稳态的锂和硅的化合物， 脱锂后晶体硅转变为非晶硅， 使其体积变化， 导 致电池循环性能下降。 有研究结果表明非晶硅材料具有更好的容量保持能力和循环性 能。 在此基础上， Cui Y等 (Nano Lett., 2009,9:3370-3374, WO2010/138617 ) 提出采用 化学气相沉积法在不锈钢基体上制备内核为晶体硅、 外层为非晶硅的核-壳结构的硅纳 米线用于锂离子电池负极材料， 该核-壳结构硅材料中晶体硅内核充当充放电过程中的 骨架和导电体， 非晶硅外层作为嵌脱锂的活性物质， 具有这一结构特征的硅纳米线在充 放电过程中由于非晶硅能保证结构稳定性， 晶体硅内核的导电性也不会被破坏， 因此该 核壳结构材料的循环稳定性相比晶体硅纳米线得到了进一步提高。 Yushin G等采用同样 的方法制备了三维多孔碳载纳米硅颗粒 iNature Materials, ) 复合结构 硅材料用作锂离子电池负极材料时， 三维多孔碳作为骨架材料， 一方面可以为纳米硅颗 粒提供有效的导电网络， 另一方面多孔碳的柔韧性也可以缓冲纳米硅颗粒的体积膨胀， 在一定程度上能抑制硅材料在充放电过程中的体积效应， 同时改善了硅材料的导电性 能， 从而提高了该类材料的循环稳定性。 Esmanski A等采用模板法制备三维多孔碳包覆 硅复合结构硅材料（ Adv. Funct. Mater. , 2009, ^: 1999-2010)用作锂离子电池负极材料 时， 碳包覆能提供导电网络和缓冲硅的体积效应， 同时三维多孔结构也能容纳硅材料在 充放电循环过程中的体积效应， 具有好的循环稳定性。 由此我们可以知道， 在纳米硅碳 复合材料中， 碳材料主要起到导电和缓冲硅材料的体积膨胀的作用， 在纳米硅碳复合材 料充放电过程中， 纳米硅材料必须跟碳材料有效结合才能发挥硅材料的电化学容量， 如 果在反复充放电过程中纳米硅材料由于多次膨胀和收縮从碳材料上脱落，那么硅材料与 材料失去电接触而不能发挥电化学容量。有研究表明， 这些纳米硅碳复合材料由于都是 在碳基体上沉积纳米硅或在纳米硅基体上包覆碳， 由于柔性碳材料的延展性有限， 在长 期循环过程中不能有效抑制硅材料巨大的体积效应， 随着循环的进行， 硅和碳之间的物 理结合会变得越来越差， 最终导致硅和碳材料的分离失去电接触， 使得材料的循环稳定 性变差， 无法满足锂离子电池用负极材料循环稳定性的要求。 综上所述， 纳米硅材料的 微观结构及与碳材料的有效结合是影响硅碳复合材料性能的关键因素。 另外， 目前制备 这些纳米硅碳复合材料方法主要包括化学气相沉积法、 热气相沉积法、 高温裂解、 高能 球磨等方法。 这些制备方法或涉及工艺过程复杂 （如模板法）， 或过程难以控制、 所需 设备昂贵 （如化学气相沉积法）， 很难实现批量生产。
发明内容
本发明的目的在于克服现有硅碳复合材料用作锂离子电池负极材料时嵌脱锂过程 中由于硅材料的巨大体积效应导致硅和碳材料的分离使得此类材料的循环稳定性变差 的缺陷， 提供一种循环稳定性好的纳米硅碳复合材料。 本发明同时还提供一种纳米硅碳 复合材料的制备方法， 该方法生产流程短、 无污染、 操作简单、 原料易得、 设备便宜， 易于连续生产。
本发明采用以下技术方案：
本发明提供一种锂离子电池用纳米硅碳复合材料， 其特征在于： 该材料中含有碳基 体、 分散在碳基体上的纳米硅、 分散在碳基体和纳米硅界面处的纳米碳化硅 SiC、 包覆 在纳米硅除与碳基体相连的界面以外的表面的硅氧化物 SiOx， 0<x^2 o各组分的质量百 分比例为： 2-40%的纳米硅， 55-90%的碳， 0.1〜3%的纳米 SiC， 1〜5%的硅氧化物 SiOx。 纳米硅的质量百分比例进一步优选为 5〜35%。碳的质量百分比例进一步优选为 60〜85%。
本发明提供的锂离子电池用纳米硅碳复合材料中的碳基体呈球形状、类球形状、 片 状、 线状、 管状中的至少一种。 碳基体的尺寸为 0.01-50 μ ηι。 纳米硅呈球形颗粒状、 线 状、 管状、 片状中的至少一种。 纳米硅为纳米硅线、 纳米硅球形颗粒、 纳米硅管、 纳米 硅片中的至少一种。 纳米硅球形颗粒的粒径小于 lOOnm, 纳米硅线的直径小于 lOOnm, 纳米硅管的直径小于 lOOnm, 纳米硅片的厚度小于 100nm。 纳米碳化硅 SiC呈颗粒状、 线状、 片状中的至少一种。 颗粒状纳米 SiC 的粒径小于 lOOnm, 线状 SiC 的直径小于 lOOnm, 片状 SiC的厚度小于 100nm。 包覆在除纳米硅与碳相连的界面以外的纳米硅表 面上的硅氧化物 SiOx， 0<x^2, 包覆层的厚度为 l-5nm。
本发明提供一种纳米硅碳复合材料的制备方法， 其具体步骤是： 先将二氧化硅粉末 制成二氧化硅胶体， 再将碳颗粒材料加入二氧化硅胶体中， 其中， 二氧化硅粉末的质量 百分比为： 10〜90wt%; 碳颗粒材料的质量百分比为： 90〜10 wt%， 二氧化硅粉末和碳 颗粒材料的总质量为 100 wt %； 混合均匀， 经干燥、 破碎成二氧化硅 /碳混合物， 该混 合物热压成多孔块体， 或模压或模灌成型后烧结成多孔块体。 控制多孔块体孔隙率、 密 度、电阻率。将碳和二氧化硅粉末组成的多孔块体，与导电的阴极集流体复合作为阴极， 以石墨或惰性阳极作为阳极， 置于以 CaCl2电解质或含有 CaCl2的混盐熔体电解质中构 成电解槽， 在阴极和阳极之间施加电解直流电压， 控制电解电压、 电解电流密度和电解 电量， 使得多孔块体中的二氧化硅电解还原成纳米硅， 在阴极制得锂离子电池用纳米碳 硅复合材料。
所述二氧化硅粉末粒径为 10nm至 1μηι。
所述碳颗粒材料选自天然石墨、 人造石墨、 无定形碳、 碳纳米管中的至少一种。 所述碳颗粒材料粒径为 10nm至 50μηι。 所述热压温度为 900〜1400°C， 热压压力为 8〜40Mpa， 保温时间为 l〜5h; 所述烧结 温度为 800-1500 °C , 烧结的时间为 1〜8小时。
所述多孔块体的孔隙率为 5〜65体积％。
所述多孔块体的密度为 0.80〜2.10 g/cm3。
所述多孔块体的电阻率为 0.001 100 Ω·αη。
所述含有 CaCl2的混盐熔体电解质为 CaC + MY1 , 其中， 在含有 CaCl2的混盐熔体 电解质中， CaCl2的摩尔百分比为 40至 95%， 余量为 MY1, M为 Ba、 Li、 Al、 Cs 、 Na、 K、 Mg、 Rb、 Be或 Sr， Y1为 CI或 F。
所述的电解质中包含氧化钙 CaO， 氧化钙含量占电解质总量的摩尔百分比为 0.001〜20%。
电解在 500-1000°C的温度下进行。
所述电解电压低于电解质的理论分解电压， 电解电流密度为大于电解槽的背景电流 密度， 电解时间为电解电量达到理论所需电量及以上所需要的时间。
本发明提供了一种锂离子电池， 该电池包括正极、 负极及非水电解液， 所述负极包 括本发明中所述纳米硅碳复合材料。
本发明具备如下特点：
( 1 ) 通过调节原料二氧化硅和碳的比例可以调节纳米硅碳复合材料中的硅碳比 例， 纳米硅碳复合材料的嵌锂容量即比容量可以调节；
(2) 通过控制二氧化硅和碳组成的多孔块体的孔隙率、密度和电阻率使得二氧化 硅电化学还原成纳米硅原位形成纳米硅碳复合材料过程中材料的结构和均 匀性得到有效控制；
( 3 ) 通过控制电解电压、电解电流密度和电解电量可以调节电解产物纳米硅碳复 合材料中碳化硅含量，控制硅和碳之间的冶金结合程度，从而提高纳米硅碳 复合材料的电化学循环稳定性；
(4) 所用原料来源丰富， 价格便宜， 原材料及制备过程均对环境无污染；
( 5 ) 工艺过程简单， 操作简便， 设备简易；
( 6) 原料和产物均以固态形式加入或移出， 易于实现连续化生产。
附图说明
附图 1为实施例 3以碳纤维与二氧化硅混合物为原料在 900°C下本发明制备碳纤维 负载纳米硅颗粒复合材料的扫描电子显微镜 （SEM) 图像。 附图 2为实施例 1以石墨片与二氧化硅混合物为原料在 950°C下本发明制备石墨片 上生长硅纳米线复合材料的扫描电子显微镜 （SEM) 图像， 其中， 1 为碳基体； 2为纳 米硅线。
附图 3为实施例 1以石墨片与二氧化硅混合物为原料在 950°C下本发明制备石墨片 上生长的单根硅纳米线的结构和组成分析图像， a) TEM图； （b) HRTEM图； （c) STEM 图； （d) EDS线扫描图。
附图 4为实施例 1以石墨片与二氧化硅混合物为原料在 950°C下本发明制备石墨片 上生长硅纳米线复合材料的结构分析图像， a. 透射电镜 （TEM) 图； b. 选区电子衍射 花样 （SEAD) 图； C. 高分辨透射电镜 （HRTEM) 图。
附图 5 为实施例 1在 950°C下本发明制备的纳米硅碳复合材料的 X射线衍射图谱。 具体实施方式
下面将进一步结合附图和实施例对本发明进行描述。这些描述只是为了进一步对本 发明进行说明， 而不是对本发明进行限制。
本发明提供一种锂离子电池用纳米硅碳复合材料， 该材料中含有碳基体、 分散在碳 基体上的纳米硅、 分散在碳基体和纳米硅界面处的纳米碳化硅 SiC、 包覆在除纳米硅与 碳基体相连的界面以外的纳米硅表面的硅氧化物 SiOx， 0<x^2 o
该复合材料先将二氧化硅粉末制成二氧化硅胶体，再将碳颗粒材料加入二氧化硅胶 体中， 其中， 二氧化硅粉末的质量百分比为： 10〜90wt%； 碳颗粒材料的质量百分比为： 90〜10 wt%， 二氧化硅粉末和碳颗粒材料的总质量为 100 wt %; 机械混捏混合均匀， 经 干燥、 破碎、 成型步骤后制成碳和二氧化硅多孔块体。 通过控制二氧化硅和碳组成的多 孔块体的孔隙率、密度和电阻率使得二氧化硅电化学还原成纳米硅原位形成纳米硅碳复 合材料过程中材料的结构和均匀性得到有效控制； 同时通过控制电解电压、 电解电流密 度和电解电量， 利用二氧化硅电化学反应的特点， 即只能通过二氧化硅（硅源相） /硅或 碳（导电相） /电解质（导离子相）三相界面电解还原的特点， 控制二氧化硅电解还原速 度， 达到控制纳米硅材料在碳基体表面的分散均匀性、 与碳界面结合程度、 及硅氧化物 包覆层厚度。 纳米硅与碳材料的结合程度主要是由碳硅界面处碳化硅的分布与含量决 定。纳米硅与碳连接处界面可以形成少量高硬度的刚性碳化硅，这是一种冶金级的结合， 大大增强了纳米硅和碳材料之间的结合力； 同时少量的刚性碳化硅与柔性碳材料相比可 以大大降低纳米硅碳复合材料在嵌脱锂过程中纳米硅材料体积变化，使得纳米硅碳复合 材料中硅和碳不会因为循环次数的增加而彼此分离，从而提高了纳米硅碳复合材料的循 环稳定性。
该材料中的纳米硅是通过电化学方法熔盐电解原料中的二氧化硅而得到的，而碳基 体来源于原料中的碳材料。因此可以通过调节原料二氧化硅和碳的比例来调节纳米硅碳 复合材料中的纳米硅和碳基体的比例。因为硅碳复合材料中碳基体主要起导电和缓冲硅 材料体积效益的作用， 电化学比容量主要由纳米硅提供， 因此通过控制纳米硅碳复合材 料中纳米硅和碳基体的比例可以调节该复合材料的嵌锂容量。 硅碳比例过低 ( Si%<2wt%), 纳米硅碳复合材料的理论比容量仅为 430mAh/g与单纯石墨负极的理论 比容量 372mAh/g接近， 不能满足电池高比能量的需要。 硅碳比例过高， 在其他条件完 全相同的情况下，该纳米硅碳复合材料的比容量也越高。但由此会带来两个方面的问题， 由于纳米硅碳复合材料中纳米硅的含量增加， 纳米硅所产生的总体的体积效应也会增 强， 影响复合材料的循环性能； 另一方面， 复合材料中纳米硅含量过高， 会导致有部分 纳米硅不能与碳基体结合， 此部分的硅材料导电性能会比较差， 同时该部分纳米硅不能 跟碳形成冶金级有效结合使得硅因嵌脱锂导致的体积变化也越厉害，从而导致使用该纳 米硅碳复合材料的电池的循环性能差。
纳米硅碳复合材料中的碳化硅是熔盐电解过程中形成的。虽然块体碳和块体硅生成 碳化硅的反应在常温下是热力学自发反应，但块体硅和块体碳材料动力学反应发生一般 需要温度在 1400°C以上才能发生。在该申请中由于纳米硅是电化学反应原位生成的，具 有比较高的反应活性， 因此纳米硅和原料中的碳材料在熔融盐中长时间浸泡后通过化学 反应可缓慢生成少量纳米碳化硅。事实上只有在纳米硅和碳材料同时存在的地方才能生 成碳化硅。 生成的碳化硅由于具有高硬度和高的强度， 可以限制纳米硅碳复合材料在嵌 脱锂过程中硅材料的体积变化，使得纳米硅碳复合材料中硅和碳不会因为循环次数的增 加而彼此分离， 大大提高了单质硅和单质碳之间的结合程度， 从而提高了纳米硅碳复合 材料的循环稳定性。但由于碳化硅是没有电化学活性的， 碳化硅含量过高会降低纳米硅 碳复合材料的比容量。 因此， 应尽量控制纳米硅碳复合材料中低的碳化硅含量。 由于碳 化硅动力学反应极难进行， 必须在熔融盐中长时间浸泡后才能缓慢生成， 因此， 通过控 制电解电压、 电解电流密度和电解电量及电解温度来控制二氧化硅电解还原速率， 可以 调节电解产物纳米硅碳复合材料中碳化硅的含量， 从而控制硅和碳之间的冶金结合程 度，在保证纳米硅碳复合材料的比容量的前提下达到提高纳米硅碳复合材料的电化学循 环稳定性的目的。
纳米硅碳复合材料中的碳基体来源于原料中的碳材料，可以为锂离子电池领域常用 的石墨类负极材料， 如天然石墨、 人造石墨、 中间相碳微球等； 也可以是锂离子电池用 的导电类碳材料， 如乙块黑、碳黑、碳纤维或碳管等。此外， 碳材料可以为石墨类负极、 导电类碳中的一种或几种。 由于纳米硅碳复合材料中的碳基体是原料碳颗粒在熔盐中与 纳米硅反应生成碳化硅后的剩余的碳材料， 其化学组成、 形貌、 尺寸、 结构与原料碳颗 粒具有继承性， 基本与原料碳颗粒相同。
纳米硅碳复合材料中的纳米硅表面的硅氧化物 SiOx包覆层来源于原料中未完全还 原的二氧化硅或电解产物纳米硅碳复合材料中的还原生成的纳米硅在后处理过程中被 再次氧化， 因此硅氧化物包覆在纳米硅表面。 通过控制电解电量即电解时间可以调节电 解产物纳米硅碳复合材料中硅氧化物的含量。如控制电解时间足够使得原料二氧化硅彻 底电解，但由于熔盐电解温度一般都在 500°C及以上进行，还原生成的纳米硅活性很高， 在电解产物从电解槽中提出后洗涤过程中纳米硅表面会有部分氧化， 因此硅氧化物在纳 米硅材料表面总是存在的， 但硅氧化物包覆层厚度一般只有 l-5nm。 纳米硅碳复合材料 中硅氧化物由于能嵌锂，嵌锂后形成的包覆在纳米硅表面的硅酸锂不但具有良好的导电 性， 并且能够有效限制硅嵌脱锂过程中的体积变化。 因此， 纳米硅碳复合材料中的硅氧 化物有利于提高硅碳复合材料的循环稳定性，但由于硅氧化合物嵌锂后形成的硅酸锂不 能完全将锂脱出， 因此使得纳米硅碳复合材料的首次库伦效率较低。
因此， 纳米硅碳复合材料中各组分的质量百分比例为： 各组分的质量百分比例为： 2-40%的纳米硅， 55-90%的碳， 0.1〜3%的纳米 SiC， 1〜5%的硅氧化物 SiOx。 纳米硅的质 量百分比例进一步优选为 5〜35%。 碳的质量百分比例进一步优选为 60〜85%。
本发明的纳米硅碳复合材料具有以下结构特征：碳基体呈球形状、类球形状、片状、 线状、管状中的至少一种。碳基体的尺寸为 0.01-50 m。纳米硅呈颗粒状、线状、管状、 片状中的至少一种。 纳米硅为纳米硅线、 纳米硅颗粒、 纳米硅管、 纳米硅片中的至少一 种。 纳米硅颗粒的粒径小于 lOOnm, 纳米硅线的直径小于 lOOnm, 纳米硅管的直径小于 lOOnm, 纳米硅片的厚度小于 100nm。 纳米碳化硅 SiC呈颗粒状、 线状、 片状中的至少 一种。 颗粒状纳米 SiC的粒径小于 lOOnm, 线状 SiC的直径小于 lOOnm, 片状 SiC的厚 度小于 100nm。 包覆在除纳米硅与碳相连的界面以外的纳米硅表面上的硅氧化物 SiOx， 0<x^2, 包覆层的厚度为 l-5nm。
由此可见， 纳米硅碳复合材料的组成、 结构与该材料电化学性能是息息相关。 以二 氧化硅和碳材料组成的多孔块体为原料电解还原制备纳米硅碳复合材料， 由于二氧化硅 电化学还原成纳米硅存在只能通过二氧化硅 （硅源相） /硅或碳 （导电相） /电解质 （导 离子相）三相界面电解还原的特点。 因此， 影响纳米硅碳复合材料中纳米硅、 碳、 碳化 硅及硅氧化物的组成、 结构与电化学性能的关键因素有： 1 ) 以碳和二氧化硅组成的多 孔块体的组成、 结构与物理性能 （如孔隙率、 孔径、 密度和电阻率）； 2)熔盐电解的电 解工艺条件 （如电解电压、 电解电量、 电解电流密度、 电解温度， 电解质组成等）。
以碳和二氧化硅组成的多孔块体的性能对纳米硅碳复合材料有何影响？ 先将二氧 化硅粉末制成二氧化硅胶体，再将碳颗粒材料加入二氧化硅胶体中，混合均匀，经干燥、 破碎成二氧化硅 /碳混合物，该混合物热压成多孔块体，或模压或模灌成型后烧结成多孔 块体。在多孔块体制备工艺过程中成型工艺的温度和压力对多孔电极孔隙率有决定性影 响。 以热压成型为例， 以 40^%的纯度为 99.9%的纳米 Si02粉末与 60^%的粒径为 10 至 21μηι类球形石墨为原料， 当热压压力都是 20Mpa、保压时间都是 lh， 成型温度分别 为 900 °C和 1400 °C时， 多孔块体孔隙率分别为 63体积％和 20体积％。 成型温度为 900 °〇孔隙率为 63 体积％的多孔块体中二氧化硅仍然保持单个颗粒形貌， 因此， 二氧化硅 颗粒中存在较多的孔； 而成型温度为 1400°C孔隙率为 20体积％的多孔块体中二氧化硅 由于高温烧结成二氧化硅块体， 在二氧化硅中很少有孔存在。 这种二氧化硅形貌和孔结 构的差异， 直接影响电解产物纳米硅碳复合材料的组成、 形貌和结构。 在相同的电解工 艺条件下，成型温度为 900°C孔隙率为 63体积％的多孔块体电解还原得到的纳米硅碳复 合材料中纳米硅主要是以球形纳米颗粒存在， 很少有硅纳米线， 纳米硅碳复合材料的首 次嵌锂容量为 1108mAh/g， 首次库伦效率为 73%， 循环 100周容量保持率为 90%; 而 1400°C孔隙率为 20%的多孔块体电解还原得到的是以硅纳米线为主的纳米硅碳复合材 料， 其首次嵌锂容量为 1132mAh/g， 首次库伦效率为 86%， 循环 100周容量保持率为 93%。 碳和二氧化硅组成的多孔块体的孔隙率较大时， 例如多孔块体孔隙率大于 65 体 积％时， 电解过程中由于二氧化硅电解还原生成硅由于氧的脱出会造成体积縮小 50体 积％， 还原后由碳和硅组成的多孔块体孔隙率的增大， 使得多孔块体强度不够而不能完 整的从熔盐中取出。碳和二氧化硅组成的多孔块体的孔隙率较较小时， 例如多孔块体孔 隙率小于 5体积％时， 多孔块体中能供熔融电解质氯化钙通过的孔隙较少， 电解还原反 应速度降低， 电解时间过长， 导致产物中碳化硅含量过多。
即使在多孔块体的组成、 结构与物理性能相同的情况下， 若熔盐电解工艺条件不同 所得到的纳米硅碳复合材料性能也有差异。 以 40wt% Si02与 60wt%碳组成的孔隙率为 23%的多孔块体进行电解， 电解温度 850°C， 电解电压 2.7V， 分别控制电解电量为理论 电量的 1.2倍和 1.5倍制备纳米硅碳复合材料。 1.2倍电量的纳米硅碳复合材料首次嵌锂 容量为 1112mAh/g， 首次库伦效率为 86%， 循环 100周容量保持率为 91%; 而理论电量 1.5倍制备纳米硅碳复合材料首次嵌锂容量为 1148mAh/g， 首次库伦效率为 87%， 循环 100周容量保持率为 90%。
本发明提供的纳米硅碳复合材料的制备方法包括以下步骤：
1. 本发明提供一种纳米硅碳复合材料的制备方法，其具体步骤是：将碳和二氧 化硅粉末组成的多孔块体， 与导电的阴极集流体复合作为阴极， 以石墨或惰性阳极 作为阳极， 置于以 CaCl2电解质或含有 CaCl2的混盐熔体电解质中构成电解槽， 在 阴极和阳极之间施加电解直流电压， 控制电解电压、 电解电流密度和电解电量， 使 得多孔块体中的二氧化硅电解还原成纳米硅，在阴极制得锂离子电池用纳米硅碳复 合材料。
2. 所述碳和二氧化硅粉末组成的多孔块体的制作过程： 先将为 lOnm至 Ιμηι 二氧化硅粉末加入到质量百分含量 60%〜400%的蒸馏水、 无水乙醇、 乙二醇、 丙 醇等中的一种或两种， 其中， 质量百分含量 60%〜400%的蒸馏水、 无水乙醇、 乙 二醇、丙醇等中的一种或两种， 是相对于二氧化硅粉末的 100%质量百分含量来说； 在行星式搅拌罐中制成胶体， 搅拌时间为 l〜12h; 然后再将粒径为 lOnm至 50μιη 碳颗粒材料加入二氧化硅胶体中， 其中， 二氧化硅粉末的质量百分比为： 10〜 90wt%; 碳颗粒材料的质量百分比为： 90〜10 wt%， 二氧化硅粉末和碳颗粒材料的 总质量为 100 wt %； 采用揉面机或混捏机等混合均匀， 混合后的浆料空气气氛下干 燥 6〜24h， 干燥后的物料经机械破碎后热压成多孔块体； 热压温度为 900〜1400°C， 热压压力为 8〜40Mpa， 保温时间为 l〜5h; 或直接将湿混后的浆料模压或模灌成型， 然后在惰性保护气氛中烧结温度为 800〜1500°C， 烧结的时间为 1〜8小时， 得到多 孔块体。
3. 所述碳颗粒材料选自天然石墨、人造石墨、无定形碳、碳纳米管中的至少一 种。
4. 所述多孔块体的孔隙率为 5〜65 体积％。 所述多孔块体的密度为 0.80〜2.10 g/cm3。 所述多孔块体的电阻率为 0.001〜 100 Ω ' cm。
5. 所述含有 CaCl2的混盐熔体电解质为 CaC + MY1,其中，在含有 CaCl2的混 盐熔体电解质中， CaCl2的质量百分含量为 40至 95wt%， 余量为 MY1 , M为 Ba、
Li、 Al、 Cs 、 Na、 K、 Mg、 Rb、 Be或 Sr， Y1为 CI或 F。
6. 所述的电解质中包含氧化钙 CaO， 氧化钙含量占电解质总量的摩尔百分比 为 0.001〜20%。
7. 电解在 500-1000°C的温度下进行。
8. 所述电解电压低于电解质的理论分解电压，电解电流密度为大于电解槽的背 景电流密度， 电解时间为电解电量达到理论所需电量及以上所需要的时间。
9. 根据步骤 1所述的制备方法， 电解过程完成后，产物即可随工作电极从熔盐 中取出， 如有必要可放入以碳和二氧化硅组成的多孔块体电极开始新一轮电解， 从 而实现纳米硅碳复合材料的连续生产。
10. 根据步骤 1所述的制备方法， 电解产物取出后， 在惰性气氛下冷却至室 温，然后在稀的无机酸、水和有机溶剂中充分洗涤， 出去产物中夹杂的熔盐电解质。 所述的稀的无机酸可以是 1 %〜3 %体积百分比的盐酸。
11. 根据步骤 1所述的制备方法，洗净后的电解产物在真空中干燥 12h以上。
12. 根据步骤 1所述的制备方法， 干燥后的电解产物研磨破碎， 过筛后得到 纳米硅碳复合材料。
下面的实施例用以说明本发明， 实施例所述的原料中的 "纳米 Si02粉末"是指粒 径在 lOOnm以下的粉末。
实施例 1
将 50^%的纯度为 99.95%的纳米 Si02粉末加入到二氧化硅质量百分含量 300%的 去离子水中， 在行星式搅拌罐中制成胶体， 搅拌时间为 10h; 然后再将 50wt% (以 Si02 粉末和石墨片的总重量为 100%) 的粒径为 3至 6μηι石墨片加入二氧化硅胶体中， 采用 混捏机混合均匀， 将搅拌均匀的浆料采用鼓风干燥方式进行干燥， 干燥后的物料通过机 械压力在 20MPa、 1300°C氩气气氛下保温 2h， 压制为直径大约 80mm， 厚度 10mm的多 孔圆片， 孔隙率为 21体积％， 密度为 1.70 g/cm3， 电阻率为 0.08 Ω · cm。 将圆片与导电 的阴极集流体复合作为阴极， 以石墨棒作为阳极， 以 CaCl2为电解质， 在氩气的环境中， 温度为 950°C， 用稳压器控制电压进行恒电压电解， 槽电压为 2.5V。 经过 12小时电解 后将电解产物依次用体积百分比 1%稀盐酸、 水、 无水乙醇冲洗， 真空干燥， 过筛后得 到产物纳米硅线复合材料， 纳米硅碳复合材料中碳的质量百分含量为 67%， 纳米硅的质 量百分含量为 29%， 碳化硅的质量百分含量为 1%， 硅氧化物 Si02的含量为 3%， 67C29SilSiC3Si0 从该材料的扫描电子显微镜 SEM图 （如附图 2所示） 可以看出， 石墨片上生长有线状纳米硅材料。 在图 2中， 碳基体 1上生长有纳米硅线 2; 附图 2黑 色线圈内的单根硅纳米线 2的 TEM图 （附图 3a) 表明硅纳米线为一种核壳结构， 中间 部分为 80nm左右， 外层厚度为 5nm。 附图 3b为硅纳米线的 HRTEM图像， 从图中可以 看出， 硅纳米线的核壳结构中， 内部规整的晶格条纹， 表明核为单晶结构， 外部壳层为 无定形结构。根据 HRTEM测试所提供的 Digital Micrograph软件计算， 内部单晶晶面间 距为 0.31nm， 对应于立方金刚石结构的 {111 }晶面间距。 附图 3d是对附图 3c中单根硅 纳米线的能量色散 X射线光谱 （EDS ) 线扫描分析结果。 由图可以看出， Si和 0沿硅 纳米线径向分布表现出不同的规律。在硅纳米线的中间部分主要为硅元素， 氧元素在线 扫描的开始和结束部分明显高于中间部分。这一实验结果直接反映了硅纳米线由单晶硅 组成内核， 表面包覆非晶二氧化硅的核壳结构。 从纳米硅碳复合材料的 TEM照片 （附 图 4a)可以清楚地观察到线状纳米硅直接长在石墨片上， 纳米硅线与石墨片的界面（附 图 4a中黑色圆圈中） 的选区电子衍射 SEAD花样 （附图 4b) 表明该界面为晶体 SiC衍 射花样； 附图 4c为该界面的 HETRM图， 高分辨二维图像显示该界面的晶面间距 d值 为 0.263nm， 正好是 β-SiC ( 111 ) 晶面间距， 这与 XRD (图 5 ) 测试结果相符合。 说明 纳米碳化硅存在于纳米硅线和石墨片基体的界面处。
所得复合材料按下述方法制备锂离子电池电极： 以制得的电解产物纳米硅碳复合材 料为活性物质， Super-P炭黑为导电剂， PVDF为粘结剂，按质量比 7 : 2 : 1混合均匀后， 用 N-甲基吡咯烷酮为溶剂调浆，将浆料涂覆在 8 μ ηι厚的铜箔上制成 1.0 cmX 1.5 cm的 极片， 在 70°C干燥后辊压至极片所需厚度， 在 120 °C真空下干燥 12h， 备用。 以金属锂 片为对电极， Celgard 2300膜为隔膜， 1 mol/L LiPF6/EC+DEC+DMC (体积比 1 : 1 : 1 ) 为电解液组装实验电池 （自行设计、 直径 D=30mm， 长 L=100mm)。 用蓝电电池测试系 统 CT2001A测试仪测试实验电池的充放电性能。 充放电电压范围为 0.005〜2.0V， 充放 电电流密度 80mA/g， 测试电池循环 100周的容量保持率 doo/C^
实施例 2
将 65^%的纯度为 99.95%的纳米 Si02粉末加入到二氧化硅质量百分含量 100%的 乙二醇中， 在行星式搅拌罐中制成胶体， 搅拌时间为 lh; 然后再将 35wt% (以 Si02粉 末和碳纤维的总重量为 100%) 的市售直径为 20至 150nm， 长度为 2至 ΙΟμηι碳纤维加 入二氧化硅胶体中， 采用揉面机混合均匀， 通过机械压力在 15MPa压制为直径大约 10mm, 厚度 1.5mm， 在 150°C氩气中加热约 1.5小时后升温至 1100°C保温 3小时， 将 烧结成型的碳纤维和 Si02混合物多孔小圆片， 孔隙率为 55体积％， 密度为 l .OO g/cm3, 电阻率为 98 Ω * cm。 将小圆片与导电的阴极集流体复合作为阴极， 以石墨棒作为阳极， 以 CaCl2为电解质， 在氩气的环境中， 温度为 850°C， 用稳压器控制电压进行恒电压电 解， 槽电压为 2.9V。 经过 6小时电解后将电解产物依次用体积百分比 1%稀盐酸、 水、 无水乙醇冲洗， 真空干燥， 过筛后得到碳纤维负载纳米硅颗粒复合材料 56C40SilSiC3SiO 所述复合材料按照实施例 1相同的测试方法进行材料组成与结构分 析。
所得复合材料按照与实施例 1相同的方法制备电极， 进行电化学性能测试。
实施例 3
将 65^%的纯度为 99.95%的纳米 Si02粉末加入到二氧化硅质量百分含量 100%的 乙二醇中， 在行星式搅拌罐中制成胶体， 搅拌时间为 lh; 然后再将 35wt% (以 Si02粉 末和碳纤维的总重量为 100%) 的市售直径为 20至 150nm， 长度为 2至 ΙΟμηι碳纤维加 入二氧化硅胶体中， 采用揉面机混合均匀， 混合后的浆料空气气氛下干燥 6h， 干燥后的 物料经机械破碎后 1000°C热压成多孔块体。 该多孔块体的孔隙率为 22%， 密度为 1.70 g/cm3,电阻率为 0.5 Ω · cm。将该多孔块体机加工成长度 50mm，宽度 30mm，高度 10mm 长方形块体，再将该长方形块体与导电的阴极集流体复合作为阴极，以石墨棒作为阳极， 以 CaCl2为电解质， 在氩气的环境中， 温度为 900°C， 用稳压器控制电压进行恒电压电 解， 槽电压为 2.8V。 经过 5小时电解后将电解产物依次用体积百分比 1%稀盐酸、 水、 无水乙醇冲洗， 真空干燥， 过筛后得到产物如附图 1所示的碳纤维负载纳米硅颗粒复合 材料， 纳米碳化硅薄片间断分散在纳米硅上。 所制备的碳纤维负载纳米硅颗粒复合材料 57C38Si2SiC3Si0 所述复合材料按照实施例 1相同的测试方法进行材料组成与结构分 析。
所得复合材料按照与实施例 1相同的方法制备电极， 进行电化学性能测试。
实施例 4
将 40^%的纯度为 99.95%的纳米 Si02粉末加入到二氧化硅质量百分含量 80%的乙 二醇中， 在行星式搅拌罐中制成胶体， 搅拌时间为 2h; 然后再将 60wt% (以 Si02粉末 和类球形石墨的总重量为 100%)的粒径为 10至 21μηι类球形石墨加入二氧化硅胶体中， 采用连续混捏机混炼 5h， 将混炼均匀的浆料放入长度 50mm， 宽度 30mm， 高度 10mm 的长方体模具中成型， 在 120°C下进行干燥， 干燥后脱模， 脱模后的长方形块体在 1400 °〇氩气气氛下烧结 2h，制成多孔长方体。该多孔块体的孔隙率为 32体积％，密度为 1.50 g/cm3, 电阻率为 0.18 Q * cm。 将该长方形块体与导电的阴极集流体复合作为阴极， 以 石墨棒作为阳极， 以 CaCl2为电解质， 在氩气的环境中， 温度为 800°C， 用稳压器控制 电压进行恒电压电解， 槽电压为 2.8V电解 4小时后再转恒电流密度电解。 经过 20小时 电解后将电解产物依次用体积百分比 1%稀盐酸、 水、 无水乙醇冲洗， 真空干燥， 过筛 后得到类球形石墨负载硅纳米线复合材料 75C21Si0.5SiC3.5SiO2。 所述复合材料按照实 施例 1相同的测试方法进行材料组成与结构分析。
所得复合材料按照与实施例 1相同的方法制备电极， 进行电化学性能测试。
实施例 5
将 20^%的纯度为 99.9%的 0.2 mSiO2粉末加入到二氧化硅质量百分含量 70%的乙 二醇中，在行星式搅拌罐中制成胶体，搅拌时间为 2h;然后再将 50^%的粒径为 3至 6μηι 片状石墨和 30wt%直径为 20〜200nm， 长度为 5〜10μηι的碳纤维依次加入二氧化硅胶体 中， 在混合物 （以 Si02粉末、 片状石墨和碳纤维的总重量为 100%) 中加入重量为上述 固体粉末的 90%的蒸馏水， 采用行星式球磨机进行机械强力搅拌 4h， 将搅拌均匀的浆 料采用模灌成型， 制成长度 50mm， 宽度 30mm， 高度 10mm长方形块体。 在 1200°C氩 气气氛下烧结 3h，制成多孔长方体，该多孔块体的孔隙率为 40体积％，密度为 1.32 g/cm3, 电阻率为 0.3 Ω * cm。 将长方形块体与导电的阴极集流体复合作为阴极， 以石墨棒作为 阳极， 以 CaCl2为电解质， 在氩气的环境中， 温度为 800°C， 用稳压器控制电流密度进 行恒流电解， 电流密度为 3000A/cm2。 经过 20小时电解后将电解产物依次用体积百分 比 1%稀盐酸、 水、 无水乙醇冲洗， 真空干燥， 过筛后得到产物纳米硅碳复合材料 85C9Si3SiC3Si02 o 所述复合材料按照实施例 1 相同的测试方法进行材料组成与结构分 析。
所得复合材料按照与实施例 1相同的方法制备电极， 进行电化学性能测试。
实施例 6
将 65^%的纯度为 99.95%的纳米 Si02粉末加入到二氧化硅质量百分含量 100%的 乙二醇中， 在行星式搅拌罐中制成胶体， 搅拌时间为 lh; 然后再将 25wt%的市售直径 为 20至 150nm， 长度为 2至 ΙΟμηι碳纤维加入二氧化硅胶体中， 加入含含热解碳 10 wt %的酚醛树脂无水乙醇溶液， 采用行星式球磨机进行机械强力搅拌 12h， 将搅拌均匀的 浆料采用微波干燥方式进行干燥， 干燥后的物料通过机械压力成型， 制成长度 50mm， 宽度 30mm， 高度 10mm长方形块体。 在 150°C氩气中加热约 1.5小时后升温至 1300°C 保温 3小时， 将烧结成型的碳纤维和 Si02以及酚醛树脂热解碳混合物多孔长方形块体， 该多孔块体的孔隙率为 32体积％， 密度为 1.50 g/cm3， 电阻率为 0.45 Ω · cm。 将长方形 块体与导电的阴极集流体复合作为阴极， 以石墨棒作为阳极， 以 CaCl2为电解质， 在氩 气的环境中， 温度为 850°C， 用稳压器控制电压进行恒电压电解， 槽电压为 2.9V。 经过 10小时电解后将电解产物依次用体积百分比 1%稀盐酸、水、无水乙醇冲洗， 真空干燥， 过筛后得到纳米硅碳复合材料 57C39SilSiC3Si02。所述复合材料按照实施例 1相同的测 试方法进行材料组成与结构分析。
所得复合材料按照与实施例 1相同的方法制备电极， 进行电化学性能测试。
实施例 7
将 40^%的纯度为 99.95%的纳米 Si02粉末加入到二氧化硅质量百分含量 200%的 去离子水中， 在行星式搅拌罐中制成胶体， 搅拌时间为 4h; 然后将 45wt%的市售 6μηι 石墨片加入到二氧化硅胶体中， 再加入含热解碳 15 wt %沥青， 100°C采用机械强力搅拌 12h, 将搅拌均匀的浆料采用微波干燥方式进行干燥， 干燥后的物料通过机械压力成型， 制成长度 50mm， 宽度 30mm， 高度 10mm长方形块体。在 150°C氩气中加热约 1.5小时 后升温至 1100°C保温 3小时， 将烧结成型的石墨片和 Si02以及沥青热解碳混合物多孔 长方形块体，该多孔块体的孔隙率为 36体积％，密度为 1.40 g/cm3，电阻率为 0.60 Ω · cm。 将长方形块体与导电的阴极集流体复合作为阴极， 以石墨棒作为阳极， 以 CaCl2为电解 质，在氩气的环境中，温度为 950°C，用稳压器控制电压进行恒电压电解，槽电压为 2.6V。 经过 12小时电解后将电解产物依次用体积百分比 1%稀盐酸、 水、 无水乙醇冲洗， 真空 干燥， 过筛后得到纳米硅碳复合材料 72C24SilSiC3Si02。所述复合材料按照实施例 1相 同的测试方法进行材料组成与结构分析。
实施例 8
将 40^%的纯度为 99.95%的纳米 Si02粉末加入到二氧化硅质量百分含量 200%的 去离子水中， 在行星式搅拌罐中制成胶体， 搅拌时间为 4h; 然后将 45wt%的市售 6μηι 石墨片加入到二氧化硅胶体中， 再加入含热解碳 15 wt %沥青， 100°C采用机械强力搅拌 12h, 将搅拌均匀的浆料采用微波干燥方式进行干燥， 干燥后的物料通过机械压力成型， 制成长度 50mm， 宽度 30mm， 高度 10mm长方形块体。在 150°C氩气中加热约 1.5小时 后升温至 1100°C保温 3小时， 将烧结成型的石墨片和 Si02以及沥青热解碳混合物多孔 长方形块体，该多孔块体的孔隙率为 36体积％，密度为 1.40 g/cm3,电阻率为 0.60 Ω · cm。 将长方形块体与导电的阴极集流体复合作为阴极， 以石墨棒作为阳极， 以 CaCl2-NaCl ( 80:20 mol%)混盐为电解质， 在氩气的环境中， 温度为 750°C， 用稳压器控制电压进行 恒电压电解， 槽电压为 2.8V。 经过 12小时电解后将电解产物依次用体积百分比 1%稀 盐酸、水、无水乙醇冲洗，真空干燥，过筛后得到纳米硅碳复合材料 72C24SilSiC3Si02。 所述复合材料按照实施例 1相同的测试方法进行材料组成与结构分析。 实施例 9
将 40^%的纯度为 99.95%的纳米 Si02粉末加入到二氧化硅质量百分含量 200%的 去离子水中， 在行星式搅拌罐中制成胶体， 搅拌时间为 4h; 然后将 45wt%的市售 6μηι 石墨片加入到二氧化硅胶体中， 再加入含热解碳 15 wt %沥青， 100°C采用机械强力搅拌 12h， 将搅拌均匀的浆料采用微波干燥方式进行干燥， 干燥后的物料通过机械压力成型， 制成长度 50mm， 宽度 30mm， 高度 10mm长方形块体。在 150°C氩气中加热约 1.5小时 后升温至 1100°C保温 3小时， 将烧结成型的石墨片和 Si02以及沥青热解碳混合物多孔 长方形块体，该多孔块体的孔隙率为 36体积％，密度为 1.40 g/cm3，电阻率为 0.60 Ω · cm。 将长方形块体与导电的阴极集流体复合作为阴极，以石墨棒作为阳极，以 CaCl2-LiCl-KCl ( 36.1 :52.3: 11.6 mol%)混盐为电解质， 在氩气的环境中， 温度为 600°C， 用稳压器控制 电压进行恒电压电解， 槽电压为 2.9V。 经过 12小时电解后将电解产物依次用体积百分 比 1%稀盐酸、 水、 无水乙醇冲洗， 真空干燥， 过筛后得到纳米硅碳复合材料 72C24SilSiC3Si02 o 所述复合材料按照实施例 1相同的测试方法进行材料组成与结构分 析。
所得复合材料按照与实施例 1相同的方法制备电极， 进行电化学性能测试。
对比例 1
将采用化学气相沉积法制备的石墨片上生长硅纳米线所构成的纳米硅碳复合材料
75C25S1, 采用相同的条件进行电化学性能测试并与实施例的电化学性能测试结果进行 对比。
对比例 2
将 10^%平均粒径 15nm的纳米硅颗粒、含碳量 3^%的蔗糖， 依次加入 1000ml无 水乙醇中， 机械强力分散 4小时。 再加入 87wt%的同实施例 3相同型号的石墨片， 再加 入 250ml无水乙醇， 并用纳米砂磨机将浆料分散 2小时。将上述悬浊液加入喷雾干燥器 中进行喷雾干燥， 得到前躯体。 将上述前躯体装入石墨坩埚， 放入井式电阻炉中， 氩气 保护下热处理。 热解温度为 900°C， 所得样品过 300 目筛后， 得到纳米硅碳复合材料 90C9SilSiC,采用相同的条件进行电化学性能测试并与实施例的电化学性能测试结果进 行对比， 结果如表 1所示。
表 1 纳米硅碳复合材料的电化学性能
实施例编号 首次嵌锂容 首次库伦效率 100周循环后容量保持率 mAh/g % % 实施例 1 1408 81 93 实施例 2 1484 84 81 实施例 3 1105 85 96 实施例 4 856 78 90 实施例 5 624 80 97 实施例 6 1680 72 99 实施例 7 1082 88 98 实施例 8 1124 79 98 实施例 9 1236 78 98 对比例 1 1170 81 67 对比例 2 652 80 85

Claims

权利要求
1. 一种锂离子电池用纳米硅碳复合材料， 其特征在于： 该材料中含有作为基体的 碳、 分散在作为基体的碳上的纳米硅、 分散在作为基体的碳和纳米硅界面处的 纳米碳化硅 SiC、 包覆在除纳米硅与碳相连的界面以外的纳米硅表面上的硅氧 化物 SiOx，
Figure imgf000019_0001
2. 按照权利要求 1所述的锂离子电池用纳米硅碳复合材料， 其特征在于： 各组分 的质量百分比例为： 2-40%的纳米硅， 55-90%的碳， 0.1〜3%的纳米 SiC， 1-5% 的硅氧化物 SiOx。
3. 按照权利要求 1所述的锂离子电池用纳米硅碳复合材料， 其特征在于： 所述纳 米硅的质量百分比例为 5〜35%。
4. 按照权利要求 1所述的锂离子电池用纳米硅碳复合材料， 其特征在于： 所述碳 的质量百分比例为 60〜85%。
5. 按照权利要求 1所述的锂离子电池用纳米硅碳复合材料， 其特征在于： 所述的 碳呈球形状、 类球形状、 片状、 线状、 管状中的至少一种。
6. 按照权利要求 1所述的锂离子电池用纳米硅碳复合材料， 其特征在于： 所述纳 米硅为纳米硅线、 纳米硅球形颗粒、 纳米硅管、 纳米硅片中的至少一种。
7. 按照权利要求 6所述的锂离子电池用纳米硅碳复合材料， 其特征在于： 所述纳 米硅球形颗粒的粒径小于 lOOnm, 纳米硅线的直径小于 lOOnm, 纳米硅管的直 径小于 lOOnm, 纳米硅片的厚度小于 100nm。
8. 按照权利要求 1所述的锂离子电池用纳米硅碳复合材料， 其特征在于： 所述纳 米碳化硅 SiC呈颗粒状、 线状、 片状中的至少一种。
9. 按照权利要求 8所述的锂离子电池用纳米硅碳复合材料， 其特征在于： 所述颗 粒状纳米 SiC的粒径小于 lOOnm, 线状纳米 SiC的直径小于 lOOnm, 片状纳米 SiC的厚度小于 100nm。
10. 一种权利要求 1-9中任一项所述锂离子电池用纳米硅碳复合材料的制备方法， 其特征在于： 先将二氧化硅粉末制成二氧化硅胶体， 再将碳颗粒材料加入二氧 化硅胶体中， 其中， 二氧化硅粉末的质量百分比为： 10〜90wt%； 碳颗粒材料 的质量百分比为： 90〜10 wt%， 二氧化硅粉末和碳颗粒材料的总质量为 100 wt %; 混合均匀， 经干燥、 破碎成碳和二氧化硅混合物， 该混合物热压成多孔块 体， 或模压或模灌成型后烧结成多孔块体； 控制多孔块体孔隙率、 密度、 电阻 率； 将碳和二氧化硅组成的多孔块体， 与导电的阴极集流体复合作为阴极， 以 石墨或惰性阳极作为阳极， 置于以 CaCl2电解质或含有 CaCl2的混盐熔体电解 质中构成电解槽， 在阴极和阳极之间施加电解直流电压， 控制电解电压、 电解 电流密度和电解电量， 使得多孔块体中的二氧化硅电解还原成纳米硅， 在阴极 制得锂离子电池用纳米碳硅复合材料。
11. 按照权利要求 10 所述的制备方法， 其特征在于： 所述二氧化硅粉末的粒径为
10nm至 1μη。
12. 按照权利要求 10所述的制备方法，其特征在于:所述碳颗粒材料选自天然石墨、 人造石墨、 无定形碳、 碳纳米管中的至少一种。
13. 按照权利要求 10所述的制备方法， 其特征在于： 所述碳颗粒材料粒径为 lOnm 至 50μηι。
14. 按照权利要求 10所述的制备方法， 其特征在于： 所述热压温度为 900〜1400°C， 热压压力为 8〜40Mpa， 保温时间为 l〜5h; 所述烧结温度为 800〜1500°C， 烧结 的时间为 1〜8小时。
15. 按照权利要求 10所述的制备方法，其特征在于：所述多孔块体的孔隙率为 5〜65 体积％。
16. 按照权利要求 10 所述的制备方法， 其特征在于： 所述多孔块体的密度为 0.80〜2.10 g/cm3。
17. 按照权利要求 10 所述的制备方法， 其特征在于： 所述多孔块体的电阻率为 0.001〜 100 Ω·αη。
18. 按照权利要求 10所述的制备方法， 其特征在于： 所述含有 CaCl2的混盐熔体电 解质为 CaCl2+ MY1 , 其中， 在含有 CaCl2的混盐熔体电解质中， CaCl2的摩尔 百分比 40至 95%， 余量为 MY1 , M为 Ba、 Li、 Al、 Cs 、 Na、 K、 Mg、 Rb、 Be或 Sr， Y1为〔1或？。
19. 按照权利要求 10 所述的制备方法， 其特征在于： 所述的电解质中包含氧化钙 CaO， 氧化钙含量占电解质总量的摩尔百分比为 0.001〜20%。
20. 按照权利要求 10所述的制备方法， 其特征在于： 电解在 500-1000°C的温度下 进行。
21. 按照权利要求 10所述的制备方法，其特征在于：所述电解电压低于电解质的理 论分解电压， 电解电流密度为大于电解槽的背景电流密度， 电解时间为电解电 量达到理论所需电量及以上所需要的时间。
一种锂离子电池， 该电池包括正极、 负极及非水电解液， 其特征在于： 所述负 极包括权利要求 1-9中任一所述纳米硅碳复合材料。
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