WO2023093893A1 - 纳米硅氧碳结构复合材料、其制备方法、负极和电化学装置 - Google Patents

纳米硅氧碳结构复合材料、其制备方法、负极和电化学装置 Download PDF

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WO2023093893A1
WO2023093893A1 PCT/CN2022/134811 CN2022134811W WO2023093893A1 WO 2023093893 A1 WO2023093893 A1 WO 2023093893A1 CN 2022134811 W CN2022134811 W CN 2022134811W WO 2023093893 A1 WO2023093893 A1 WO 2023093893A1
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silicon
composite material
oxygen
carbon
nano
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PCT/CN2022/134811
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French (fr)
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陈青华
刘江平
刘瑞芳
房冰
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兰溪致德新能源材料有限公司
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Priority claimed from CN202111438788.0A external-priority patent/CN116190581A/zh
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Priority to EP22897974.6A priority Critical patent/EP4343889A1/en
Publication of WO2023093893A1 publication Critical patent/WO2023093893A1/zh

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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
    • 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
    • H01M4/362—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
    • 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
    • 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
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • 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
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • 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

  • the invention relates to the technical field of battery materials, in particular to a nano-silicon carbon structure composite material, a preparation method thereof, a negative electrode and an electrochemical device.
  • Lithium-ion batteries are playing an increasingly important role in today's human production and life.
  • the performance of its negative electrode materials such as capacity, first storage efficiency, cycle performance, etc., greatly affect the capacity, energy density and service life of the battery. .
  • silicon-based materials have a delithiation potential close to that of lithium metal ( ⁇ 0.5V vs Li/Li + ), are environmentally friendly, and have abundant reserves, so they have become potential anode materials for a new generation of high-energy-density lithium-ion batteries.
  • silicon-based negative electrode materials that is, large volume expansion and contraction occur in the process of lithium intercalation and delithiation (full intercalation of lithium state, volume expansion reaches 300%), which will lead to battery capacity decay and electrode degradation. Pulverization fails. Due to the poor cycle stability of silicon materials, its practical application faces a large technical bottleneck.
  • the root cause of the cycle capacity fading of lithium-ion batteries is the formation of the SEI film.
  • the electrolyte in the electrolyte will react with lithium ions from the positive electrode at the surface active material of the negative electrode to form a solid electrolyte interface (SEI) film until it completely covers the contact surface between the electrode and the electrolyte.
  • SEI solid electrolyte interface
  • the formation of the SEI film is irreversible, and its consumption of lithium competes with the reversible lithium formation on the electrode, which is manifested in the first lithium intercalation-delithiation cycle, because the delithiation capacity is lower than the lithium intercalation capacity, that is, the first Coulombic efficiency ( First effect) is less than 100%.
  • the large volume effect of silicon-based negative electrode materials in the process of intercalating and removing lithium causes the SEI film on the electrode surface to be continuously damaged and regenerated during the cycle charge-discharge process, resulting in corrosion of the active silicon material and continuous decline in electrode capacity.
  • this volume effect also tends to gradually pulverize the negative electrode active material and collapse its structure, which eventually leads to the detachment of the electrode active material from the current collector and the loss of electrical contact, greatly reducing the battery cycle performance. Therefore, suppressing the excessive volume effect of silicon particles during charge and discharge is always a problem that cannot be ignored in the research and development of silicon-based anode materials.
  • Lithium intercalation of silicon particles to irreversible rupture to destroy the SEI film and/or self-crushing is essentially a process of uneven expansion accumulation.
  • a large amount of lithium is first accumulated at the silicon atoms on the surface of silicon particles, and then lithium ions migrate to the inside of the particles at a slow rate, that is, there is a lithium gradient from the inside to the outside of the silicon particles, resulting in uneven expansion, which will lead to silicon particle breakage.
  • the conductivity of silicon itself is low, and it is usually compounded with carbon materials with good conductivity to obtain composite electrode materials with good conductivity. It is one of the common methods to disperse silicon nanoparticles on porous carbon supports, and the pore structure of carbon supports is also It can play a role in alleviating the expansion, but on the other hand, the porous carrier causes the specific surface area of the composite material to increase, which in turn leads to an increase in electrode side reactions and a decrease in the first Coulombic efficiency. Therefore, how to achieve effective deposition and uniformity of silicon nanoparticles on the porous carrier Dispersion, while reducing the specific surface area of the composite material, is the difficulty in the preparation of silicon-carbon composite materials.
  • the Chinese patent application with the application publication number CN110112377A discloses a method for preparing a nano-silicon-carbon composite material by depositing silicon on porous carbon.
  • the Si content of the composite material reaches 90%, the lithium intercalation capacity for the first time can reach 2414mAh/g.
  • the first effect is 82%, but the cycle performance is poor, and the fifth cycle capacity retention rate is only 48%.
  • the Chinese patent application with the application publication number CN110582823A discloses a method for depositing silicon and hydrocarbon carbon successively or simultaneously on porous carbon. Under the condition of controlling the Si content in the composite material to be about 50%, the obtained nano-silicon-carbon structure composite The material capacity reaches 2082mAh/g, the first effect is 82%, and the average Coulombic efficiency of the 7th-10th cycle is 98%.
  • the first effect and cycle efficiency of silicon-carbon composite materials in the prior art are relatively low. There are two reasons. On the one hand, silane gas is deposited directly on the carbon material. Due to the lack of bonding between C and Si, the porous carbon substrate is located in the pores. It is difficult to achieve effective silicon deposition on the surface of the material, the specific surface area of the material is large, there are many side reactions on the electrode surface, and the first efficiency of the battery is low; on the other hand, and more importantly, the decomposition of SiH 4 is a chain reaction process of thermal polymerization. The easy-to-contact surface on the particle nucleates, and then it is very easy to grow rapidly on the formed silicon nucleus.
  • the main purpose of the present invention is to provide a nano-silicon carbon structure composite material, its preparation method, negative electrode and electrochemical device, to solve the problem of poor battery cycle performance caused by the volume expansion of silicon-carbon composite electrodes in the prior art, From the point of view of materials, it is to solve the problem that the structure and preparation method of silicon-carbon composite materials in the prior art are not easy to obtain uniformly dispersed silicon nanoparticles.
  • a nano silicon oxygen carbon structure composite material includes (C x1 -O y1 )-( Siz -O y2 -C x2 ), wherein, C x1 -O y1 is the porous carbon substrate containing the surface oxide layer, including the porous carbon substrate and its surface oxide layer, x1 is the stoichiometric number of carbon, y1 is the stoichiometric number of oxygen in the surface oxide layer, 0.001 ⁇ y1/x1 ⁇ 0.05 ; Si z -O y2 -C x2 includes silicon nanoparticles, oxygen-containing species and optional carbon, and the silicon nanoparticles, oxygen-containing species and optional carbon are dispersed and distributed on the surface of a porous carbon substrate with a surface oxide layer and/or Or in the channel, oxygen-containing substances exist in the form of SiO ⁇ , 0 ⁇ 2, 0.1 ⁇ z/x1 ⁇ 2, 0.
  • a method for preparing a nano-silica carbon structure composite material includes: step S1, providing a porous carbon substrate containing a surface oxide layer, and oxygen in the porous carbon substrate containing a surface oxide layer The molar ratio to carbon is 0.001-0.05; step S2, the silicon-containing precursor and the oxygen-containing precursor are passed into a reaction furnace with a porous carbon substrate containing a surface oxide layer, and are mixed with a surface containing The porous carbon substrate of the oxidized layer is contacted and heat-treated for 5-100 hours, so that silicon, oxygen-containing substances and optional carbon are dispersed and deposited on the surface and/or pores of the porous carbon substrate, and a nano-silicon-carbon-carbon composite material is obtained.
  • a negative electrode including a negative electrode material
  • the negative electrode material is any one of the above-mentioned nano-silica carbon structure composite material or a nano-silica carbon structure composite material obtained by any one of the above-mentioned preparation methods Material.
  • an electrochemical device comprising a negative electrode, the negative electrode being any one of the above-mentioned negative electrodes, preferably the electrochemical device is a lithium ion secondary battery.
  • the silicon nano-particles in the nano-silicon carbon structure composite material of the present application are uniformly dispersed and separated and bound by oxygen-containing substances and optional carbon, thus effectively inhibiting the agglomeration of silicon particles during the deposition process
  • Li-ion secondary batteries comprising anodes prepared from the resulting composites exhibit high gram capacity, high first-time Coulombic efficiency, and good cycle performance.
  • the above preparation method uses the porous carbon substrate containing the surface oxide layer as a carrier and/or support, and deposits silicon nanoparticles, oxygen-containing substances and optional carbon on its surface and pore structure, wherein the oxygen-containing substances and optional
  • the carbon plays the role of separating and binding the silicon nanoparticle deposition layer, and the deposition may end up with a small amount of closed pores in the pores of the porous carbon substrate. Therefore, the volume effect of the uniformly dispersed and bound silicon nanoparticles in the obtained nano-silicon carbon structure composites can be effectively buffered during the process of lithium intercalation and delithiation, and the fusion of silicon nanoparticles during charge and discharge can be effectively buffered. The phenomenon is suppressed, the strength of the material is improved, and the electrochemical performance of an electrochemical device including the silicon-oxygen-carbon composite negative electrode material is improved.
  • Another object of the present invention is to provide a nano-silicon-carbon composite material, its preparation method, negative electrode and electrochemical device, so as to solve the problem of poor battery cycle performance caused by the volume expansion of the silicon-carbon composite material electrode in the prior art .
  • a nano-silicon-carbon composite material in a typical embodiment of the present invention, includes a porous carbon skeleton (equivalent to the aforementioned porous carbon substrate), silicon nanoparticles and SiO ⁇ (0 ⁇ 2), the content of silicon element in the nano silicon oxygen carbon composite material is 25 ⁇ 75wt%, the content of oxygen element is 0.5 ⁇ 10wt%; the N of the nano silicon oxygen carbon composite material Adsorption BET The specific surface area is 0.01-10m 2 /g, and the total pore volume is 0.001-0.05cm 3 /g measured according to the adsorption amount at the point where the N 2 partial pressure is greater than 0.999; the silicon nanoparticles are separated by the SiO ⁇ network and/or wrapped, the silicon nanoparticles and the SiO ⁇ are distributed on the surface and/or in the pores of the porous carbon skeleton, and the porous carbon skeleton and the silicon nanoparticles are connected by CO-Si bonds.
  • the content of silicon element in the nano silicon oxygen carbon composite material is controlled to be 30-65wt%, the content of carbon element is 30-65wt%, the content of oxygen element is 0.5-5wt%, and the content of other elements is 0 ⁇ 5wt%.
  • the XPS test is carried out on the nano-silicon-oxygen-carbon composite material, with Al K ⁇ as the radioactive source, and the amorphous C-C peak binding energy in the C 1s spectrum is located at 284.7eV as the peak position calibration, due to the high-resolution C 1s spectrum Including the C-C peak that exists in the test system, there is a large error in the analysis of its C-Si, so only its high-resolution Si 2p spectrum is analyzed.
  • the XPS test high-resolution Si 2p spectrum of the nano-silicon-carbon composite material is deconvoluted and integrated peak analysis results include that the peak area of Si-O with a binding energy peak at 103 ⁇ 0.5 eV and the peak area of Si-O with a binding energy peak at 99 ⁇ 0.5 eV
  • the ratio of the peak area of Si-Si at eV is 0.5-2, preferably 0.8-1.5;
  • the ratio of the peak areas is 0.01 to 1, preferably 0.01 to 0.5. According to the calculation of the corresponding peak area, the proportion of each bonding form can be obtained.
  • the pore volume of 2-10 nm in the porous carbon skeleton pore structure in the nano-silicon-carbon composite material accounts for more than 50% of the total pore volume.
  • the porous carbon in the nano-silicon-carbon composite material In the skeleton pore structure the proportion of 2-10nm pore volume to the total pore volume is greater than 80%.
  • the pore structure of the porous carbon skeleton in the nano-silicon-carbon composite material can be obtained by testing after obtaining the porous carbon skeleton in the early stage of the preparation process, and the Si in the nano-silicon-carbon composite material can also be mixed with HF and high-concentration NaOH solution.
  • the remaining porous carbon skeleton was obtained by testing the remaining porous carbon skeleton after SiO ⁇ and SiO ⁇ etching. Due to the degree of etching and the possibility of new pores, the understanding of the pore structure of the porous carbon skeleton in nano-silicon carbon composites has a certain deviation, but it is also It can reflect its nature within a certain range.
  • the diffraction peaks overlap, so there is no obvious Si crystallization peak in the XRD diffraction results.
  • the morphology of silicon nanoparticles can also be observed by high-resolution TEM, and the size of a single silicon nanoparticle can be judged by the number of lattice fringes in a group of lattice fringes that match Si crystals.
  • the silicon oxygen carbon material presents as amorphous silicon or silicon grains with a size smaller than 2nm
  • the silicon grains may be recombined to fuse and form larger particles, affecting The cycle performance of the electrode
  • the present invention provides a kind of accelerated aging to analyze the method for the aggregation situation of silicon nano-particles, namely by nano-silicon-carbon carbon structure composite material under N Atmosphere raising temperature processing, and carry out XRD test , to analyze the growth of silicon grains. After testing, the composite material was further processed at 700°C, 800°C, and 900°C.
  • oxygen-containing substances are introduced to disperse silicon nanoparticles and prevent further aggregation and growth, and the pore structure of the porous carbon skeleton finally constrains the size of silicon nanoparticles.
  • the present invention estimates the limit size of the silicon nanoparticles in the nano-silicon carbon structure composite material that increases during the electrochemical process through the XRD results of the composite material under N2 atmosphere and 800 ° C treatment, preferably controlling the silicon
  • the limiting size of nanoparticle growth in electrochemical process is less than 10nm.
  • Completely dense materials have a limited effect on suppressing the volume effect of lithium-silicon alloys.
  • a proper amount of closed cells in the composite material is conducive to alleviating the volume effect of silicon.
  • the pores that are in contact with the surface of the material, the surface is the surface that N2 molecules can touch, that is, the closed pores are the pores that N2 molecules cannot enter or the pores that are basically inaccessible, and these pores closed inside the composite material can be Provide a buffer space for the volume expansion of silicon intercalated lithium.
  • too many closed cells will lead to an increase in the volume of the material, thereby reducing the volume specific capacity. More importantly, too many closed cells will lead to a decrease in the structural strength of the composite material, which may cause the structure to collapse during the subsequent tableting process.
  • closed cells cannot be obtained by conventional physical adsorption methods, because they belong to the area that adsorbed molecules cannot or basically cannot directly reach.
  • N2 adsorption can only detect open pores and their surface area, and this part of the pores and surface will be in contact with the electrolyte. , which is not conducive to the electrode performance of the material.
  • the detection of closed cells is reversed by measuring the true density of the composite material.
  • the true density of the material is less than the true density of a completely dense material with the same elemental composition, it means that there are closed cells, and the closed cell volume is the reciprocal of the true density of the composite material (closed cells + the volume of the skeleton) minus the reciprocal of the true density (skeleton volume) of a fully dense material of the same elemental composition.
  • the densities of pure graphite and silicon are both greater than 2.2 g/cm 3 .
  • the true density of the composite material can be obtained by helium displacement method and/or pycnometer method (acetone immersion method) test. This application adopts the pycnometer method to measure the true density of the composite material.
  • the true density of the nano-silicon carbon composite material is 1.8-2.1 g/cm 3 , indicating that it has a certain amount of closed cells.
  • the nano silicon-oxygen-carbon composite material further includes a cladding layer, and the cladding layer includes a solid electrolyte and/or a conductive polymer.
  • the cladding layer includes a solid electrolyte and/or a conductive polymer.
  • the median particle size D 50 of the composite material can be controlled by means of crushing or the like. In some embodiments, the median particle size D 50 of the composite material is between 2 ⁇ m and 12 ⁇ m.
  • a method for preparing the nano-silicon-oxygen-carbon composite material which is characterized in that the preparation method includes: step S1, mixing carbon precursors and pore-forming agents to form porous carbon skeleton material, and crush and oxidize it to obtain a porous carbon skeleton containing a surface oxide layer with a suitable specific surface and pore structure; step S2, vacuumize the porous carbon skeleton containing a surface oxide layer obtained in step S1, Pass the silicon-containing precursor and the oxygen-containing precursor into the reaction furnace where the porous carbon skeleton containing the surface oxide layer is placed, and contact the porous carbon skeleton containing the surface oxide layer to disperse silicon and oxygen-containing substances Depositing on the surface and/or pores of the porous carbon skeleton; and crushing and shaping the obtained material to obtain a nano-silicon-carbon composite material 1; step S3, performing a deep oxidation treatment on the nano-silicon-carbon composite material 1 obtained in step S2, A nano-silicon-oxygen
  • the above-mentioned reaction furnace is a combination of any one or more of rotary furnace, ladle furnace, liner furnace, roller kiln, pusher kiln, atmosphere box furnace or tube furnace; wherein in steps S2 and S3, solid gas
  • the two-phase contact method is any one or a combination of various methods such as fixed bed, moving bed, fluidized bed, and ebullating bed.
  • the particle size of the porous carbon skeleton containing the surface oxide layer in the step S1 is 5-50 ⁇ m, and the specific surface area of the porous carbon skeleton containing the surface oxide layer is 50-2000 m 2 /g,
  • the pore volume is 0.1-3.0 cm 3 /g, and the pore volume of 2-10 nm in the pore structure of the porous carbon skeleton containing the surface oxide layer accounts for more than 50% of the total pore volume; and/or the step S2 specifically includes
  • the porous carbon skeleton containing the surface oxide layer is evacuated until the vacuum degree is lower than 10 -2 Pa, preferably lower than 10 -6 Pa, and the silicon-containing precursor and the oxygen-containing precursor are passed into the surface containing In the reaction furnace of the porous carbon skeleton of the oxide layer, and contact with the porous carbon skeleton containing the surface oxide layer at 150-700°C for 5-100h, so that silicon and oxygen-containing substances are dispersed and deposited on the surface of the por
  • porous carbon framework affects the size of silicon nanoparticles to a great extent.
  • a suitable porous carbon framework should contain more mesopores (pore diameter 2-50nm) and a small amount of micropores (pore diameter less than 2nm) and macropores. (pore diameter greater than 50nm), mesopores and macropores should be the main areas of silicon deposition, but too many large pores can easily cause silicon nanoparticles to aggregate and grow.
  • the specific surface area of the porous carbon skeleton containing the surface oxide layer in the present invention is 50-2000 m 2 /g, the pore volume is 0.1-3.0 cm 3 /g, and the porous carbon skeleton of the surface oxide layer
  • the particle diameter is 5 ⁇ 50 ⁇ m;
  • the ratio of the micropore volume in the total pore volume in the pore structure of the porous carbon skeleton containing the surface oxide layer is 1 ⁇ 20%, and the ratio of the mesopore volume in the total pore volume is 40 ⁇ 90%, the ratio of the macropore volume in the total pore volume is 0-10%; in the pore structure of the porous carbon skeleton containing the surface oxide layer, the ratio of the 2-10nm pore volume to the total pore volume is greater than 50%, preferably, The proportion of the 2-10nm pore volume to the total pore volume is greater than 80%.
  • the preparation method of the above-mentioned porous carbon skeleton containing a surface oxide layer of the present invention can select a corresponding implementation mode according to different carbon precursors and/or porous carbon skeletons.
  • the porous carbon framework material in the step S1 is formed by carbonization of a homogeneous mixture of a carbon precursor and a pore-forming agent;
  • the carbon precursor is selected from the group consisting of glucose, fructose, sucrose, maltose, lactose, cyclic Dextrin, starch, glycogen, cellulose, hemicellulose, lignin, unsaturated polyester resin, epoxy resin, thermoplastic phenolic resin, thermosetting phenolic resin, polyoxymethylene resin, urea-formaldehyde resin, furfural resin, furfurone resin, One or more of acrylic resin, polyamide, polyimide, asphalt;
  • the pore-forming agent is selected from sodium dodecylbenzenesulfonate, cetyltrimethylammonium bromide, polyethylene glycol Alcohol, polyvinyl alcohol, polyvinylpyrrolidone, oleic acid, oleylamine, polyethylene oxide-polypropylene oxide-polyethylene oxide triblock
  • the oxyethane triblock copolymer is selected from P123, F127 and/or F108.
  • the carbon precursor and the pore-forming agent can be mixed in a manner known to those skilled in the art. In some embodiments, the carbon precursor and the pore-forming agent are mixed by wet ball milling and/or dry ball milling. In some embodiments, The carbon precursor and the pore-forming agent are dissolved in water and/or ethanol, thoroughly mixed by means of ultrasound and/or stirring, and then dried.
  • the carbon precursor After the carbon precursor is mixed with the pore-forming agent, it is pre-stabilized first, and then carbonized. Both prestabilization and carbonization are routine steps in the preparation of carbon materials. Pre-stabilization is carried out in an oxidative atmosphere at a temperature of 100-300°C for 0.1-48 hours; carbonization is carried out in an inert gas at a temperature of 600-1800°C for 0.5-10 hours, and the temperature of carbonization is preferably 800 ⁇ 1500°C, the time is 2 ⁇ 5h.
  • Oxidation treatment of the porous carbon framework material to produce a surface oxide layer to promote efficient deposition of silicon-containing precursors said oxidation treatment includes liquid phase oxidation and/or gas phase oxidation.
  • the oxidation treatment method for the porous carbon framework material in the step S1 includes liquid phase oxidation and/or gas phase oxidation; preferably, the step of the liquid phase oxidation is to place the porous carbon framework material in an oxygen-containing compound and /or in water and/or ethanol solutions of oxygenated compounds, after ultrasonic dispersion for 0.5-2 hours, stir at 0-50°C for 0.5-12 hours, filter and/or centrifuge to separate solid and liquid, use deionized water and/or ethanol washing the solid once, and vacuum-drying and roasting the obtained solid, the oxygen-containing compound is selected from HNO 3 , H 2 SO 4 , acetic acid, propionic acid, butanol, butyric acid, succinic acid, malic acid, citric acid any one or more of them
  • the silicon-containing precursor and the oxygen-containing precursor are combined in any volume ratio; preferably, the silicon-containing precursor is selected from monosilane, disilane , trisilane, halosilane, polysilane, polymethylsilane, silole and its derivatives, silfluorene and its derivatives; preferably, the oxygen-containing precursor is oxygen, carbon dioxide , water vapor, methanol, ethanol, n-propanol, isopropanol, butanol, acetone, butanone or one or more; preferably, the volume ratio of the silicon-containing precursor and the oxygen-containing precursor and the gas phase
  • the deposition temperature varies intermittently and/or periodically with the prolongation of the feeding time; preferably, before changing the gas composition, vacuum treatment is carried out until the vacuum degree is lower than 10 -2 Pa.
  • an inert gas is introduced at the same time as the silicon-containing precursor and the oxygen-containing precursor, so as to adjust the concentration of the silicon-containing precursor and the oxygen-containing precursor, and provide a suitable pressure
  • the inert gas is nitrogen , argon, helium in one or more.
  • the oxygen-containing precursor is methanol, ethanol, n-propanol, One or more of isopropanol, butanol, acetone, butanone.
  • the volume content of the silicon-containing precursor in the first mixed gas is 1-50%, and the volume content of the oxygen-containing precursor is 0.5-10%; preferably, the temperature of the heat treatment when the first mixed gas is fed is 400-700°C, Further preferably, the heat treatment time is 5-50 hours when the first mixed gas is fed.
  • an inert gas is injected before, after, at the same time, or during intervals of introducing the silicon-containing precursor and the oxygen-containing precursor, and the inert gas is one or more of nitrogen, argon, and helium.
  • the silicon-containing precursor and the inert gas are introduced at the same time, the two can be introduced in a mixed manner or separately to form a mixed gas in the reaction furnace.
  • the silicon-containing precursor and the inert gas are simultaneously When passing through, it is referred to as passing through the second mixed gas containing the silicon precursor and the inert gas, and the volume content of the silicon precursor in the second mixed gas is 1-50%.
  • the oxygen-containing precursor and the inert gas are introduced at the same time, the two can be introduced in a mixed manner or separately to form a mixed gas in the reaction furnace.
  • the oxygen-containing precursor and the inert gas are simultaneously When passing through, it is referred to as passing through the third mixed gas of the oxygen-containing precursor and the inert gas, and the volume content of the oxygen-containing precursor in the third mixed gas is 1-50%.
  • the above step S2 includes: step S2-1, passing an inert gas into a reaction furnace with a porous carbon skeleton containing a surface oxide layer, and raising the temperature of the reaction furnace to 400-700°C; step S2-2, feed the second mixed gas of silicon-containing precursor and inert gas, the volume concentration of silicon-containing precursor in the second mixed gas is 1%-50%, and keep the reaction furnace at 400-700°C for 0.5- 15h; step S2-3, stop feeding the silicon-containing precursor, and adjust the temperature of the reaction furnace to 150-600°C; step S2-4, feed the third mixed gas of the oxygen-containing precursor and the inert gas, and the third mixed gas
  • the volume concentration of the oxygen-containing precursor in the gas is 1% to 50%, and the reaction furnace is kept at 150 to 600°C for 0.1 to 5 hours; step S2-5, repeating steps S2-1 to S2-4 for 2 to 50 times; Step S2-6, crushing and shaping the obtained material to obtain a nano-silicon carbon composite material 1 with a median particle size of
  • the deep oxidation treatment in step S3 includes liquid-phase oxidation and/or gas-phase oxidation; preferably, the step of liquid-phase oxidation is that the nano-silica carbon composite material 1 is placed in an oxidizing substance and/or Or in the water and/or ethanol solution of oxidizing substances, after ultrasonic dispersion for 0.5 ⁇ 2h, stir at 0 ⁇ 50°C for 0.5 ⁇ 12h, filter and/or centrifuge to separate the solid and liquid, and use deionized water and/or ethanol several times Wash the solid, and air-dry the obtained solid at 40-200°C for 0.5-24h, then treat it in an inert atmosphere at 200-400°C for 0.5-5h, and the oxygen-containing compound is selected from KMnO 4 , H 2 O 2 , HNO 3 , H 2 SO 4 , acetic acid, propionic acid, butyric acid, succinic acid, malic acid, citric acid, any one or more, the liquid phase oxidation
  • an acid treatment and/or alkali treatment process is added to the nano-silica carbon composite material 1 obtained by crushing step S2; preferably, the acid treatment method is,
  • the nano-silica carbon composite material 1 is dispersed into an acid-containing water/ethanol solution, stirred at 0-50°C for 0.5-12 hours, filtered and/or centrifuged to separate solid and liquid, and washed with deionized water and/or ethanol several times The pH of the solid to the filtrate and/or supernatant is neutral, and the resulting solid is vacuum-dried;
  • the alkali treatment method is to disperse the nano-silica carbon composite material 1 into an alkali-containing water/ethanol solution, Stir at 0-50°C for 0.5-12 hours, filter and/or centrifuge to separate the solid from the liquid, wash the solid with deionized water and/or ethanol several times until the pH of the filtrate and/or supernatant is neutral, and vacuum the resulting solid dry;
  • the acid is one or more of
  • step S3 vacuum treatment and carbon coating are performed on the obtained nano-silicon carbon composite material.
  • the carbon coating method is to use methane, ethane, propane, butane, ethylene, propylene, One or more of butene, acetylene, propyne, methanol, ethanol, n-propanol, isopropanol, butanol, acetone, butanone, and the obtained nano-silica carbon composite material is vapor-phase deposited, or liquid
  • the carbon precursor is coated with liquid carbon.
  • the liquid carbon precursor is selected from resin, pitch and the like.
  • the preparation method further includes the step of wrapping a solid electrolyte and/or a conductive polymer on the nano silicon-oxygen-carbon composite material.
  • the application of nano-silicon-carbon composite materials in the preparation of negative electrode materials is provided, and the nano-silicon-carbon composite materials are the above-mentioned nano-silicon-carbon composite materials or any of the above-mentioned A nano silicon-oxygen-carbon composite material obtained by one of the preparation methods.
  • a negative electrode including a negative electrode material, the negative electrode material is the above-mentioned nano-silica carbon composite material or the nano-silica obtained by any of the above-mentioned preparation methods. Silicon Oxygen Carbon Composite.
  • the present invention provides an electrochemical device, which includes a negative electrode, and the negative electrode is the above-mentioned negative electrode; preferably, the electrochemical device is a lithium-ion secondary battery.
  • the porous carbon carrier and the silicon particles in the nano-silicon carbon composite material of the present application form a stable bond through C-O-Si, and the silicon nanoparticles are uniformly dispersed in the pores and surfaces of the carbon carrier, and by Oxygen-containing species are separated and bound, thus effectively inhibiting the agglomeration of silicon particles during deposition and their volume change and possible fusion during charge-discharge cycles, Li-ion secondary batteries containing negative electrodes prepared from the resulting composites simultaneously It has excellent characteristics such as high gram capacity, high first Coulombic efficiency and good cycle performance.
  • Fig. 1 shows the structural representation of the nano-silicon carbon structure composite material obtained according to Example 1 of the present invention
  • Fig. 2 shows the XRD diffractogram of the nano-silicon carbon structure composite material obtained according to Example 1 of the present invention
  • Fig. 3 shows the HRTEM figure of the nano-silicon carbon structure composite material obtained according to Example 1 of the present invention
  • Fig. 4 shows the galvanostatic charge-discharge curves of the electrode comprising the nano-silicon carbon structure composite material obtained in Example 1 of the present invention, the electrode comprising the composite material of Example 23, and the electrode comprising the composite material of Comparative Example 2;
  • Fig. 5 shows the XRD spectrograms of the nano-silicon carbon structure composite material obtained in Example 1 and Example 23 of the present invention and the composite material of Comparative Example 2 after being treated at 800° C. in an N atmosphere;
  • Figure 6 shows the half-cell cycle performance test results of the electrode comprising the nano-silicon carbon structure composite material of Example 1 and the composite material electrode comprising Comparative Example 2;
  • Figure 7 shows a schematic structural view of the nano-silicon carbon structure composite material obtained according to Example 26 of the present invention.
  • Fig. 8 shows the XPS test high-resolution Si 2p spectrum and its deconvoluted integral peak analysis results figure of the obtained nano-silicon carbon structure composite material according to embodiment 26 of the present invention
  • Fig. 9 is a schematic structural view of the nano silicon-oxygen-carbon composite material of the present invention.
  • Fig. 10 is the XPS test high-resolution Si 2p spectrum of embodiment 1 gained nano silicon oxygen carbon composite material and deconvoluted integrated peak analysis result thereof;
  • Figure 11 is the XRD spectrum of the nano-silicon carbon composite material obtained in Example 1 and the material obtained after treatment at 800 ° C in N atmosphere;
  • Fig. 12 is the high-resolution TEM image of nano silicon oxygen carbon composite material obtained in embodiment 1;
  • Figure 13 is the first constant current charge and discharge curve of the half-cell test results of the electrode comprising the nano-silicon carbon composite material obtained in Example 1;
  • Fig. 14 is the half-cell cycle performance test results of the electrodes comprising the nano-silicon-carbon composite material obtained in Example 1 and the electrode comprising the silicon-oxygen-carbon composite material obtained in Comparative Example 2.
  • the present application provides a nano-silicon carbon structure composite material, its preparation method, negative electrode and electrochemical device.
  • a nano-silicon carbon composite material includes (C x1 -O y1 )-( Siz -O y2 -C x2 ), wherein, C x1 -O y1 is the porous carbon substrate containing the surface oxide layer, including the porous carbon substrate and its surface oxide layer, x1 is the stoichiometric number of carbon, y1 is the stoichiometric number of oxygen in the surface oxide layer, 0.001 ⁇ y1/x1 ⁇ 0.05 ; Si z -O y2 -C x2 includes silicon nanoparticles, oxygen-containing species and optional carbon, and its silicon nanoparticles, oxygen-containing species and optional carbon are dispersed on the surface of the porous carbon substrate containing the surface oxide layer and /or in the pores, oxygen-containing substances exist in the form of SiO ⁇ , 0 ⁇ 2, 0.1 ⁇ z/x1 ⁇ 2, 0.01 ⁇ y2/z ⁇ 0.15, 0
  • silicon nanoparticles are uniformly dispersed, and separated and bound by oxygen-containing substances and optional carbon, thus effectively inhibiting the agglomeration of silicon nanoparticles during the deposition process and their charging and discharging cycles.
  • the volume change and possible fusion in the lithium-ion secondary battery containing the anode prepared from the obtained composite material has a high gram capacity, a high first-time Coulombic efficiency, and good cycle performance.
  • the above C x1 -O y1 is a porous carbon substrate containing a surface oxide layer, including the porous carbon substrate and its surface oxide layer, mainly carbon substance C, and the surface oxide layer can pass through the porous carbon substrate after incomplete carbonization.
  • the formation of oxygen-containing functional groups and/or after oxidative treatment of the porous carbon substrate acts to provide better silicon deposition sites through the formation of CO-Si chemistry.
  • x1 is the stoichiometric number of carbon in it, which is just an algebra in the molecular formula, and the purpose is to better express the content of related substances.
  • the content of the surface oxide layer in the porous carbon substrate is defined and expressed by the molar ratio y1/x1 of the oxygen element to the carbon element in the porous carbon substrate, 0.001 ⁇ y1/x1 ⁇ 0.05. If y1/x1 is too large, the excess oxygen will irreversibly react with lithium during the lithium intercalation process, resulting in the loss of reversible lithium capacity, lower battery first efficiency and cycle efficiency; if it is too small, effective CO-Si chemical contact and/or Bonding, the subsequent silicon deposition process tends to form larger silicon particle aggregates.
  • the above Si z -O y2 -C x2 is silicon nanoparticles and oxygen-containing substances and optional carbon, silicon nanoparticles and oxygen-containing substances uniformly dispersed in the pores and surfaces of the above-mentioned porous carbon substrate C x1 -O y1 and optional Carbon is evenly interlaced, oxygen-containing substances exist in the form of SiO ⁇ (0 ⁇ 2), and the Si z -O y2 -C x2 structural component can be regarded as a Si-OC (Si-SiO ⁇ -C) structural unit
  • the repetition of can be written as (S z1 -O y -C x ) n , n ⁇ 1, as shown in the schematic diagram in Figure 1.
  • silane decomposition is a chain reaction process of thermal polymerization, the uncontrolled result is that silane aggregates and grows up rapidly.
  • oxygen-containing substances and optional carbon between Si nanoparticles that is, a small amount of oxygen-containing substances and available
  • the selected carbon disperses and binds silicon nanoparticles, avoids their uncontrolled aggregation and growth during deposition, and effectively controls the volume expansion and contraction of silicon and the fusion between silicon particles during charge and discharge.
  • the loading of silicon needs to be within an appropriate range to obtain higher gram capacity and higher first effect of the composite material.
  • the present invention controls 0.1 ⁇ z/x1 ⁇ 2, preferably 0.2 ⁇ z/x1 ⁇ 1, and more It is preferably 0.3 ⁇ z/x1 ⁇ 0.6.
  • Oxygen-containing substances and optional carbon in Si z -O y2 -C x2 are used to disperse silicon particles, realize nanonization of silicon particles, and also play a role in binding silicon nanoparticles.
  • Oxygen-containing substances exist in the form of SiO ⁇ in nano-silicon carbon structure composites, which can restrain the volume expansion and contraction of silicon nanoparticles during charge and discharge, and prevent silicon nanoparticles from melting and forming large particles during charge and discharge, Cause electrode cycle performance to deteriorate.
  • the amount of oxygen-containing substances and optional carbon should not be too much, too much will lead to a decrease in the overall Si content, and the gram capacity and first effect of the composite electrode will be reduced; too little will not be able to effectively disperse and bind, so control 0.01 ⁇ y2/z ⁇ 0.15, 0 ⁇ x2/z ⁇ 0.15.
  • the present invention provides a nano-silicon carbon structure composite material, including a porous carbon substrate C x1 -O y1 containing a surface oxide layer, and two structures of Si z -O y2 -C x2 uniformly dispersed inside and outside the pores Components whose surface oxide layer on the porous carbon substrate facilitates the formation of CO-Si for more stable Si loading; in Si z -O y2 -C x2 , Si nanoparticles with oxygen-containing species and optional carbon Uniform dispersion, oxygen-containing substances and optional carbon separate silicon substances to form a repeating structure similar to ( Siz1 -O y -C x ) n (n ⁇ 1), realizing effective nanonization and uniform dispersion of silicon particles, while The oxygen-containing species and optionally carbon also serve to bind the silicon particles.
  • the total oxygen content of the composite material is between 0.5wt% and 5wt%.
  • the results of deconvoluted and integrated peak analysis of the XPS test high-resolution Si 2p spectrum of the nano-silicon carbon structure composite material include the peak area and the binding energy of Si-O whose binding energy peak is located at 103 ⁇ 0.5eV
  • the peak area ratio of Si-Si with a peak at 99 ⁇ 0.5eV is 0.5-2, preferably 0.8-1.5; the peak area of Si-C with a binding energy peak at 100.5 ⁇ 0.5eV is at 99 ⁇ 0.5eV
  • the peak area ratio of Si—Si is 0.01 to 1, preferably 0.01 to 0.5. According to the calculation of the corresponding peak area, the proportion of each bonding form can be obtained.
  • the diffraction peaks overlap, so there is no obvious Si crystallization peak in the XRD diffraction results.
  • the nano-silicon carbon structure composite material is mainly amorphous structure, there are a few extremely small silicon grains, and its lattice fringe spacing is about 0.314nm, which is close to the crystal plane spacing of Si(111). There are only 4-5 ordered lattice fringes, and the corresponding silicon grain size is less than 2nm.
  • the present invention provides a method for indirect analysis of the aggregation state of the silicon particles.
  • the results can be effectively correlated with the electrochemical performance of the composite material, that is, the nano-silicon carbon structure composite material is treated under N 2 atmosphere at 800 ° C, and XRD test is performed to analyze the growth of silicon grains.
  • the composite material was further processed at 700°C, 800°C, and 900°C.
  • the silicon crystallization peak in the XRD curve was basically stable and no longer changed due to temperature rise.
  • the silicon particles in the nano-silicon carbon structure composite undergo amorphous to crystal transformation under high temperature conditions, and further grain growth occurs, while the porous carbon substrate in the composite material does not undergo obvious crystallization under this treatment condition.
  • the grain size after high temperature treatment can be calculated from the half peak width of the silicon crystallization peak, and the number of grains involved in crystallization can be inferred from the relative intensity of the silicon crystallization peak and the amorphous carbon peak. , which indirectly reflects the aggregation state of silicon particles in the nano-silicon carbon structure composite.
  • the XRD test results after high temperature treatment are shown in Figure 5. It can be seen that the higher the oxygen content, the smaller the silicon grain size and the lower the crystallization degree after high temperature treatment, reflecting the smaller size of silicon nanoparticles in the composite material.
  • the charge-discharge curve in Fig. 4 shows a delithiation curve with a larger slope.
  • the silicon nanoparticles are dispersed and prevented from further agglomeration and growth; in addition, the pore structure of the porous carbon substrate also finally constrains the size of the silicon nanoparticles.
  • the size of silicon particles is difficult to directly detect and determine.
  • the present invention estimates the size of silicon nanoparticles in the nano-silicon carbon structure composite material through the XRD results after the composite material is treated at 800°C under N2 atmosphere.
  • the size of the silicon nanoparticles is controlled to be less than 20 nm, more preferably, the size of the silicon nanoparticles is less than 10 nm.
  • the composite material has a specific surface area (N 2 adsorption, multi-point BET) of 0.1-15 m 2 /g, and a total pore volume (N 2 adsorption, measured by p/p0>0.999) of 0.001-0.05 cm 3 /g.
  • the specific surface area of the composite material is 0.1-10 m 2 /g, and the total pore volume is 0.001-0.035 cm 3 /g. The lower specific surface area and total pore volume effectively suppressed the occurrence of interfacial side reactions in the composite electrode.
  • Completely dense materials have a limited effect on suppressing the volume effect of lithium-silicon alloys.
  • a moderate amount of closed cells in the composite material is beneficial to alleviate the volume effect of silicon, but too much closed cells will lead to an increase in the volume of the material, thereby reducing the volume specific capacity and making it more complex.
  • the important thing is that too many closed cells will lead to a decrease in the structural strength of the composite material, which may cause the structure to collapse during the subsequent tableting process, so the amount of closed cells should not be too much.
  • Closed pores cannot be obtained by conventional physical adsorption methods, because they belong to the area that adsorbed molecules cannot directly reach. For example, N2 adsorption can only detect open pores and their surface area.
  • the detection of closed cells is reversed by measuring the true density of the composite material.
  • the true density of the material is less than the true density of a completely dense material with the same elemental composition, it means that there are closed cells, and the closed cell volume is the reciprocal of the true density of the composite material (closed cells + the volume of the skeleton) minus the reciprocal of the true density (skeleton volume) of a fully dense material of the same elemental composition.
  • the densities of pure graphite and silicon are both greater than 2.2 g/cm 3 .
  • the true density of the composite material can be obtained by helium displacement method and/or pycnometer method (acetone immersion method) test.
  • the present application adopts the pycnometer method to measure the true density of the composite material.
  • the true density of the nano-silicon carbon structure composite material is 1.8-2.1 g/cm 3 , indicating that it has a certain amount of closed cells.
  • the composite material further includes a cladding layer comprising a solid electrolyte and/or a conductive polymer. to further improve its electrical performance.
  • a cladding layer comprising a solid electrolyte and/or a conductive polymer.
  • the median particle size D 50 of the composite material can be controlled by means of crushing or the like. In some embodiments, the median particle size D 50 of the composite material is between 4 ⁇ m and 12 ⁇ m.
  • a method for preparing a nano-silicon carbon structure composite material comprising: Step S1, providing a porous carbon substrate containing a surface oxide layer, containing a surface oxide layer The molar ratio of oxygen to carbon in the porous carbon substrate is 0.001 to 0.05; step S2, the silicon-containing precursor and the oxygen-containing precursor are passed into a reaction furnace with a porous carbon substrate containing a surface oxide layer, and the temperature is 150 to 700 Contact with the porous carbon substrate containing the surface oxide layer at °C for 5-100 hours, so that silicon, oxygen-containing substances and optional carbon are dispersed and deposited on the surface and/or pores of the porous carbon substrate to obtain a nano-silicon carbon structure composite material.
  • Carbonization of carbon precursors and silane vapor deposition are technical means known to those skilled in the art, but it is difficult to obtain uniformly dispersed silicon nanoparticles deposition in actual operation, which is related to many reasons, such as carbon precursor structure, treatment method, carbonization Conditions, surface properties after carbonization, silicon deposition methods and conditions, etc.
  • the decomposition of silane is a chain reaction of thermal polymerization. It is difficult to react at low temperature, and the utilization rate of silane is low. However, the decomposition rate is very fast at high temperature, and the silicon particles inevitably grow rapidly.
  • the preparation method of the present application first provides a small amount of oxygen-containing functional groups on the surface of the porous carbon substrate, that is, the porous carbon substrate of the present application containing a surface oxide layer, which can promote the adsorption and reaction of silane molecules; In the process, an oxygen-containing precursor is introduced to form an oxidized separation layer for silicon nanoparticles to achieve uniform dispersion of silicon nanoparticles.
  • the above-mentioned preparation method uses the porous carbon substrate containing the surface oxide layer as the carrier and/or support (equivalent to the porous carbon skeleton containing the surface oxide layer in the priority document (CN application number is 202210114895.6), in its surface and pore structure Deposition of silicon nanoparticles and oxygen-containing species and optional carbon, wherein the oxygen-containing species and optional carbon act to separate and confine the deposited layer of silicon nanoparticles, which may eventually remain in the pores of the porous carbon substrate There are a few closed pores.
  • the volume effect of the uniformly dispersed and bound silicon nanoparticles in the obtained nano-silicon carbon structure composites can be effectively buffered during the process of lithium intercalation and delithiation, and the fusion of silicon nanoparticles during charge and discharge can be effectively buffered.
  • the phenomenon is suppressed, the strength of the material is improved, and the electrochemical performance of an electrochemical device including the silicon-oxygen-carbon composite negative electrode material is improved.
  • the porous carbon substrate containing the surface oxide layer can be vacuumed or not vacuumed. Vacuum processing can speed up the rate at which silicon-containing precursors are initially deposited.
  • the structure, composition and physical properties of the composite material obtained by the above preparation method can refer to the aforementioned structure, composition and physical properties of the composite material, and will not be repeated here.
  • the above-mentioned reaction furnace is any one or more combinations of rotary furnace, ladle furnace, liner furnace, roller kiln, pusher kiln, atmosphere box furnace or tube furnace; wherein in step S2, solid-gas two-phase
  • the contact mode is any one or a combination of multiple modes such as fixed bed, moving bed, fluidized bed, and ebullating bed.
  • the preparation method of the above-mentioned porous carbon substrate containing a surface oxide layer of the present application can be implemented according to different carbon precursors and/or porous carbon substrates.
  • the above step S1 includes: pre-stabilizing the carbon precursor to obtain a pre-stabilized precursor, the carbon precursor is selected from monosaccharides, disaccharides, polysaccharides, unsaturated polyester resins, epoxy resins , phenolic resin, polyoxymethylene resin, urea-formaldehyde resin, furfural resin, furfurone resin, acrylic resin, polyamide, polyimide, polyvinyl alcohol and asphalt, pre-stabilized in the first oxidation
  • the first oxidizing gas is oxygen and/or ozone
  • the inert gas is one or more of nitrogen, argon, helium
  • the pre-stabilization temperature is 100 ⁇ 300°C
  • the time is 0.1-48h, preferably the pre-stabilization temperature is 170-220°C, the time is 1-48h
  • the temperature of carbonization is 600-1800°C, and the time is 0.5-10h. More preferably, the temperature of carbonization is 800-1500°C, and the time is 2-5h.
  • some oxygen-containing functional groups can be retained as the oxide layer by adjusting the carbonization conditions.
  • the porous carbon substrate is oxidized to obtain a porous carbon substrate containing an oxidized surface layer.
  • pre-stabilization and carbonization are routine steps in the preparation of carbon materials, and the pre-stabilization and carbonization in the priority document (CN application number is 202210114895.6) are similar to the above pre-stabilization and carbonization.
  • the preparation method of the porous carbon substrate containing the surface oxide layer in the above step S1 is to mix the carbon precursor and the pore-forming agent to form a carbonized material, and then crush the carbonized material and oxidation treatment.
  • the above step S1 includes: pre-stabilizing the homogeneous mixture of the carbon precursor and the pore-forming agent to obtain a pre-stabilized material; then carbonizing the pre-stabilized material to obtain a porous carbon substrate; The substrate is crushed and oxidized to obtain a porous carbon substrate with a surface oxide layer.
  • the carbon precursor is selected from glucose, fructose, sucrose, maltose, lactose, cyclodextrin, starch, glycogen, cellulose, hemicellulose, lignin, unsaturated polyester resin, epoxy resin, thermoplastic phenolic resin, One or more of thermosetting phenolic resins, polyoxymethylene resins, urea-formaldehyde resins, furfural resins, furfurone resins, acrylic resins, polyamides, polyimides, and asphalt; the pore-forming agent is selected from dodecylbenzenesulfonic acid Sodium, cetyltrimethylammonium bromide, polyethylene glycol, polyvinyl alcohol, polyvinylpyrrolidone, oleic acid, oleylamine, polyethylene oxide-polypropylene oxide-polyethylene oxide triembede One or more of block copolymer, citric acid, malic acid, succinic acid, NH 4 HCO 3 , (NH 4 )
  • the carbon precursor and the pore-forming agent can be mixed in a manner known to those skilled in the art.
  • the carbon precursor and the pore-forming agent are mixed by wet ball milling and/or dry ball milling.
  • the carbon precursor and the pore-forming agent are dissolved in water and/or ethanol, thoroughly mixed by means of ultrasound and/or stirring, and then dried. Both prestabilization and carbonization are routine steps in the preparation of carbon materials.
  • Pre-stabilization is carried out in an oxidative atmosphere at a temperature of 100-300°C for 0.1-48 hours; carbonization is carried out in an inert gas at a temperature of 600-1800°C for 0.5-10 hours, and the temperature of carbonization is preferably 800 ⁇ 1500°C, the time is 2 ⁇ 5h.
  • the above-mentioned oxidation is carried out in a fifth mixed gas comprising a second oxidizing gas and an inert gas
  • the second oxidizing gas is selected from any one or more of oxygen, carbon dioxide, and water vapor
  • the inert gas One or more of nitrogen, argon, and helium; preferably, the oxidation temperature is 300-1600°C, and the time is 0.1-5h, more preferably, the oxidation temperature is 600-900°C, and the time is 2-4h .
  • the above step S1 also includes: directly oxidizing the porous carbon substrate to obtain a porous carbon substrate containing an oxide layer on the surface, the porous carbon substrate is selected from soft carbon, hard carbon, carbon black, graphite, graphene, One or more of carbon nanotubes, carbon fibers, mesocarbon microspheres, preferably, the oxidation is carried out in a fifth mixed gas comprising a second oxidizing gas and an inert gas, and the second oxidizing gas is selected from oxygen, carbon dioxide , any one or more of water vapor, and the inert gas is one or more of nitrogen, argon, and helium; preferably, the oxidation temperature is 300-1600°C, and the time is 0.1-5h, more preferably The oxidation temperature is 600-900° C. and the time is 2-4 hours. That is, the porous carbon substrate containing the surface oxide layer of the present application can also be obtained by performing the above oxidation on the porous carbon material in the prior art as the substrate.
  • the above-mentioned second oxidizing gas can also be selected from any one or more of methanol, ethanol, acetic acid, propanol, butanol, and acetone; before the porous carbon substrate is oxidized, the porous carbon can be The substrate is vacuumed or not vacuumed, and the surface of the porous carbon substrate can be cleaned by vacuuming, which is more conducive to oxidation.
  • the ratio of the second oxidizing gas and the inert gas can be referred to in the prior art, but usually the inert gas accounts for the main part to avoid burning of the porous carbon material, such as the first active oxygen gas Mixing with the inert gas at a volume ratio of 1:99-20:80; preferably, the second oxidizing gas accounts for 0.5-20% of the fifth mixed gas.
  • the above-mentioned oxidation is carried out in water and/or ethanol solutions comprising oxygenates and/or oxygenates selected from the group consisting of HNO 3 , H 2 SO 4 , acetic acid, propionic acid, butanol , butyric acid, succinic acid, malic acid, citric acid in any one or more;
  • the oxidation step is, the porous carbon substrate is placed in the oxygen-containing compound and/or the water and/or ethanol of the oxygen-containing compound In the solution, after ultrasonic dispersion for 0.5-2 hours, stir at 0-50°C for 0.5-12 hours, filter and/or centrifuge to separate the solid from the liquid, wash the solid with deionized water and/or ethanol several times, and vacuum-dry the obtained solid and roasting.
  • the nano-silicon carbon structure composite material is based on porous carbon, which has a large specific surface area and rich pore structure, providing a region for the deposition of silicon nanoparticles.
  • the specific surface area and pore distribution of the porous carbon substrate directly affect the silicon deposition effect and the specific surface area of the composite. While achieving sufficient loading of silicon nanoparticles, it is also necessary to avoid the problem of excessive side reactions caused by excessive specific surface area.
  • a suitable porous carbon substrate should contain more mesopores (pore diameter 2-50nm), and contain a small amount of micropores (pore diameter less than 2nm) and macropores (pore diameter greater than 50nm), mesopores and macropores should be the main areas of silicon deposition, However, on the one hand, too many macropores will easily lead to the aggregation of silicon particles in the pores; on the other hand, when the silicon particles cannot fill the macropores, some pore structures will remain in the final composite material, resulting in too large a specific surface area to meet the requirements. Requirements: An appropriate amount of micropores may cause silicon to deposit at the pores to form closed cells.
  • the specific surface area of the porous carbon substrate containing the surface oxide layer is 50-2000m 2 /g
  • the pore volume is 0.1-3.0cm 3 /g, including micropores, mesopores and macropores; preferably, wherein The proportion of the micropore volume in the total pore volume is 1-40%, the proportion of the mesopore volume in the total pore volume is 30-80%, and the proportion of the macropore volume in the total pore volume is 1-40%.
  • the specific surface area of the porous carbon substrate containing the surface oxide layer is 100-1000 m 2 /g, and the pore volume is 0.3-1.5 cm 3 /g.
  • the ratio of the micropore pore volume to the total pore volume is 1 ⁇ 20%, the proportion of mesopore volume in the total pore volume is 60 ⁇ 80%, and the proportion of macropore volume in the total pore volume is 1 ⁇ 20%.
  • the obtained composite material has suitable silicon content and specific surface area.
  • the silicon-containing precursor and the oxygen-containing precursor are combined in any volume ratio, preferably, the silicon-containing precursor is selected from monosilane , disilane, trisilane, halosilane, polysilane, silole and its derivatives, silfluorene and its derivatives, etc., preferably, the oxygen-containing precursor is oxygen, carbon dioxide, water vapor , methanol, ethanol, n-propanol, isopropanol, butanol, acetone, butanone or one or more.
  • the silicon-containing precursor is selected from monosilane , disilane, trisilane, halosilane, polysilane, silole and its derivatives, silfluorene and its derivatives, etc.
  • the oxygen-containing precursor is oxygen, carbon dioxide, water vapor , methanol, ethanol, n-propanol, isopropanol, butanol, acetone, butanone or one or more.
  • an inert gas is introduced at the same time as the silicon-containing precursor and the oxygen-containing precursor, so as to adjust the concentration of the silicon-containing precursor and the oxygen-containing precursor, and provide a suitable pressure
  • the inert gas is nitrogen , argon, helium in one or more.
  • the oxygen-containing precursor is methanol, ethanol, n-propanol, One or more of isopropanol, butanol, acetone, butanone, the volume content of the silicon-containing precursor in the first mixed gas is 1-50%, and the volume content of the oxygen-containing precursor is 0.5-10%;
  • the heat treatment temperature is 400-700° C. when the first mixed gas is fed, and more preferably, the heat treatment time is 5-50 hours when the first mixed gas is fed.
  • an inert gas is introduced before, after, simultaneously or in between the introduction of the silicon-containing precursor and the oxygen-containing precursor, and the inert gas is one or more of nitrogen, argon, and helium.
  • the silicon-containing precursor and the inert gas are introduced at the same time, the two can be introduced in a mixed manner or separately to form a mixed gas in the reaction furnace. In any case, as long as the silicon-containing precursor and the inert gas are simultaneously When passing through, it is referred to as passing through the second mixed gas containing the silicon precursor and the inert gas, and the volume content of the silicon precursor in the second mixed gas is 1-50%.
  • the two can be introduced in a mixed manner or separately to form a mixed gas in the reaction furnace.
  • the oxygen-containing precursor and the inert gas are simultaneously When passing through, it is referred to as passing through the third mixed gas of the oxygen-containing precursor and the inert gas, and the volume content of the oxygen-containing precursor in the third mixed gas is 1-50%.
  • the temperature in step S2 varies with the concentration of the silicon-containing precursor and the oxygen-containing precursor.
  • the heat treatment temperature is 400-700° C. when the silicon-containing precursor is passed in, and the heat treatment temperature is 150-600° C. when the oxygen-containing precursor is passed.
  • the above step S2 includes: step S2-1, passing an inert gas into a reaction furnace with a porous carbon substrate containing a surface oxide layer, and raising the temperature of the reaction furnace to 400-700 °C; step S2-2, feed the second mixed gas of silicon-containing precursor and inert gas, the volume concentration of silicon-containing precursor in the second mixed gas is 1%-50%, and keep the reaction furnace at 400-700°C for 0.5- 15h; step S2-3, stop feeding the silicon-containing precursor, and adjust the temperature of the reaction furnace to 150-600°C; step S2-4, feed the third mixed gas of the oxygen-containing precursor and the inert gas, and the third mixed gas The volume concentration of the oxygen-containing precursor in the gas is 1%-50%, and the reaction furnace is kept at 150-600°C for 0.1-5h; step S2-5, repeating steps S2-1 to S2-4 for 2-50 times.
  • the above preparation method further includes step S3, crushing and classifying the nano-silicon carbon structure composite material in step S2 to obtain classified particles of the nano-silicon carbon structure composite material with a median particle size of 4-12 ⁇ m, preferably
  • the crushing and grading method is any one or more of manual grinding, mechanical milling, ball milling, and jet milling. To adjust the compacted density of the composite material.
  • the above crushing and grading is equivalent to the crushing and shaping in step S2 in the priority document (CN application number is 202210114895.6).
  • the above-mentioned preparation method further includes: step S4, performing deep oxidation treatment on the graded particles of the nano-silica carbon structure composite material in step S3, preferably the deep oxidation treatment includes combining the graded particles of the nano-silica carbon structure composite material with the The solution and/or gas of the oxidizing substance is contacted at 0-400°C for 0.5-12 hours.
  • the solid-gas two-phase contact mode is any one or a combination of multiple modes such as fixed bed, moving bed, fluidized bed, and ebullating bed.
  • the deep oxidation treatment includes liquid-phase oxidation and/or gas-phase oxidation; preferably, the step of liquid-phase oxidation is to place the classified particles of the nano-silica carbon structure composite material in an oxidizing substance and /or in water and/or ethanol solutions of oxidizing substances, after ultrasonic dispersion for 0.5-2 hours, stir at 0-50°C for 0.5-12 hours, filter and/or centrifuge to separate solid and liquid, use deionized water and/or ethanol The solid is washed once, and the obtained solid is air-dried at 40-200°C for 0.5-24h, and then treated in an inert atmosphere at 200-400°C for 0.5-5h.
  • the oxygen-containing compound is selected from KMnO 4 , H 2 O 2 , HNO 3 , Any one or more of H 2 SO 4 , acetic acid, propionic acid, butyric acid, succinic acid, malic acid, and citric acid, and the liquid phase oxidation is carried out under the action of ultraviolet light and/or microwave radiation; preferably,
  • the gas-phase oxidation step is to evacuate the graded particles of the nano-silica structure composite material to a vacuum degree lower than 10 -2 Pa, and then pass in a mixed gas containing an oxidizing gas and an inert gas, and control the heating rate to 1-10°C /min, rise from room temperature to 200-400°C, and treat at 200-400°C for 0.1-5h
  • the oxidizing gas is selected from any one or more of oxygen, ozone, carbon dioxide, and water vapor
  • the inert gas is nitrogen , argon, and helium
  • the proportion of oxidizing gas in the mixed gas is 0.5-20%.
  • the acid treatment and/or alkali treatment process of the classified particles of the nano-silicon carbon structure composite material is added; preferably, the method of acid treatment is, the nano-silicon carbon structure composite
  • the graded particles are dispersed into the acid-containing water/ethanol solution, stirred at 0-50°C for 0.5-12 hours, filtered and/or centrifuged to separate the solid and liquid, and the solid is washed with deionized water and/or ethanol several times until the filtrate and/or The pH of the supernatant is neutral, and the resulting solid is vacuum-dried;
  • the method of alkali treatment is to disperse the graded particles of the nano-silica carbon structure composite material into the water/ethanol solution containing alkali, and stir at 0-50°C for 0.5- 12h, filter and/or centrifuge to separate the solid from the liquid, wash the solid with deionized water and/or ethanol several times until the pH of the filtrate and/or supernatant is neutral,
  • the above preparation method further includes: step S5, wrapping a solid electrolyte and/or a conductive polymer on the nano-silicon carbon composite material.
  • the nano-silicon carbon structure composite material referred to in step S5 has a relatively broad meaning, including: the nano-silicon carbon structure composite material referred to in S2, the nano-silicon carbon structure composite material in step S3
  • the graded particles of the nano-silicon carbon structure composite material obtained by the further classification treatment of the material the oxidized nano-silicon carbon structure composite material obtained by the further deep oxidation treatment of the graded particles of the nano-silicon carbon structure composite material in step S4
  • the above preparation method further includes: step S6, vacuum treatment and carbon coating on the nano-silicon carbon structure composite material, the way of carbon coating is to use methane, ethane, propane, butane, ethylene, One or more of propylene, butene, acetylene, propyne, methanol, ethanol, n-propanol, isopropanol, butanol, acetone, butanone, for vapor deposition of composite materials, or using liquid carbon precursors
  • the liquid carbon precursor is selected from resin and pitch.
  • the nano-silicon-carbon-carbon composite material referred to in step S6 has a relatively broad meaning, including: the nano-silicon-carbon-carbon structure obtained by further classifying the nano-silicon-carbon composite material in step S3 Composite material graded particles, oxidized nano-silica carbon structure composite material obtained by further deep oxidation treatment of nano-silicon carbon structure composite material graded particles in step S4, nano-silicon carbon structure composite material graded particles before step S4
  • a negative electrode including a negative electrode material
  • the negative electrode material is any one of the above-mentioned nano-silicon carbon structure composite materials or any one of the above-mentioned preparation methods to obtain nano-silicon oxide Carbon structural composites.
  • an electrochemical device comprising a negative electrode, the negative electrode being the above-mentioned negative electrode, preferably the electrochemical device is a lithium ion secondary battery.
  • silicon nanoparticles are uniformly dispersed, and are separated and bound by oxygen-containing species and optional carbon, thus effectively inhibiting the agglomeration of silicon particles during the deposition process and their performance during charge-discharge cycles.
  • the volume change and possible fusion, the lithium-ion secondary battery containing the negative electrode prepared from the obtained composite material has a high gram capacity, a high first Coulombic efficiency and good cycle performance.
  • Step S1 preparation of porous carbon substrate with surface oxide layer: using starch as carbon precursor, raising from room temperature to 220°C in air atmosphere, and keeping at this temperature for 48h for pre-stabilization; then changing to N 2 , Raise the temperature to 1500°C at 2°C/min, and keep at this temperature for 2h to complete the carbonization; then cool down to 600°C in N 2 atmosphere, switch to 2% O 2 -N 2 mixed gas, and oxidize at 600°C for 2h, A porous carbon substrate with a surface oxide layer is obtained.
  • the molar ratio of oxygen to carbon in the obtained porous carbon substrate is 0.031
  • the specific surface area of the porous carbon substrate is 380m 2 /g
  • the pore volume is 0.74cm 3 /g
  • the proportions of micropores, mesopores and macropores are respectively 9%. , 70% and 21%.
  • Step S2 silicon deposition and oxygen-containing treatment: the porous carbon substrate was heated from room temperature to 600°C at 2°C/min in N 2 atmosphere, then changed to 20% SiH 4 -N 2 mixed gas; in 20% SiH 4 - In N 2 mixed gas atmosphere, keep at 600°C for 2h to deposit silicon; then change to N 2 , after cooling down to 200°C, change to 1%O 2 -N 2 mixed gas; in 1%O 2 -N 2 In a mixed gas atmosphere, keep at 200°C for 12 minutes for oxygen-containing treatment; then change to N 2 and raise the temperature to 600°C, so that the silicon deposition-oxygen treatment cycle is performed on the porous carbon substrate for 15 times, under the protection of N 2 The temperature is naturally lowered to obtain a nano-silicon carbon structure composite material.
  • Step S3 crushing: crushing and classifying the nano-silica structure composite material obtained in step S2 by using a jet mill to obtain classified particles of the nano-silica structure composite material with a median particle size of 6 ⁇ m.
  • Electrode, half-cell preparation and electrochemical performance test method (applicable to this application enumerating all embodiments and comparative examples):
  • EC ethyl carbonate
  • DEC diethyl carbonate
  • the CR2032 type buckle After the CR2032 type buckle was left standing for 6 hours, it was discharged to 0.005V at 0.05C, and then discharged to 0.005V at 0.01C; after standing for 5 minutes, it was charged to 1.5V at a constant current of 0.05C; the first delithiation capacity and the first lithium intercalation The ratio of capacity is the first Coulombic efficiency of the battery.
  • the following method is used to test the expansion rate of the pole piece: after the CR2032 type buckle is left standing for 6 hours, it is discharged to 0.005V at 0.05C, and then discharged to 0.005V at 0.01C; then the buckle is disassembled in the glove box and cleaned with DEC Pole piece and measure the thickness of the pole piece.
  • the calculation method of the expansion rate is: (thickness of the pole piece in the first fully charged state-thickness of the fresh pole piece)/thickness of the fresh pole piece ⁇ 100%.
  • FIG. 1 shows a schematic structural view of the graded particles of the nano-silicon carbon structure composite material obtained in Example 1.
  • the core composition (C x1 -O y1 )-(S z -O y2 -C x2 ) of the nano-silicon carbon composite material graded particles includes the porous carbon substrate C x1 - O y1 and Siz -O y2 -C x2 supported on the surface and pores of the porous carbon substrate are two main parts, the latter includes uniformly dispersed silicon nanoparticles and a small amount of oxygen-containing species and optional carbon, which can also be written as ( Si z1 -O y -C x ) n , n ⁇ 1.
  • the composite material has a multi-level structure, with the porous carbon substrate containing the surface oxide layer as the carrier and/or scaffold, silicon nanoparticles (ie Si in Figure 1) and oxygen-containing species and optional
  • the deposition of carbon i.e., SiO ⁇ +C in Fig. 1), where the oxygen-containing species and optionally carbon act to separate and bind the silicon nanoparticles, may leave a small amount of closed pores in the pores of the porous carbon substrate at the end of the deposition. hole.
  • the specific surface area of the obtained nano-silicon carbon structure composite classified particles was 4.7m 2 /g
  • the pore volume was 0.024cm 3 /g
  • the true density was 1.97g/cm 3 .
  • the mass contents of silicon, oxygen and carbon in the nano-silicon carbon structure composite material obtained in Example 1 were 50.2%, 1.9% and 47.9%, respectively.
  • the galvanostatic charge-discharge curve of the electrode comprising the nano-silicon carbon structure composite material obtained in Example 1 is shown in Figure 4, its gram capacity is 2029mAh/g, the first Coulombic efficiency at 1.5V is 92.6%, and the pole piece expansion rate is 124%. , the gram capacity retention rate after 50 cycles of charging and discharging is 95.6%.
  • Table 1 shows the porous carbon substrates containing surface oxide layers used in Examples 1 to 25 and Comparative Examples 1 and 2 and their preparation conditions.
  • Table 2 shows the oxygen content, specific surface area and pore properties of the porous carbon substrates containing the surface oxide layer.
  • the porous carbon substrate is mainly composed of mesopores, and contains some micropores and macropores.
  • Table 3 shows the preparation conditions of Examples 1 to 25 and Comparative Examples 1 and 2 of the graded particles of nano-silicon carbon composite material.
  • concentration of silicon-containing precursors and/or oxygen-containing precursors and their corresponding processing temperatures in the examples listed in this specification are pulsed periodic or non-periodic changes. For the convenience of expression, they are placed in the same table, using "deposition Cycle” to describe this difference, and the cycle number is 1 when there is no periodic change.
  • silicon-containing precursors and oxygen-containing precursors are introduced separately, they are represented in Table 3 as “deposition mixed gas 1" and “deposition mixed gas 2", and correspondingly, the respective contact temperatures and residence times They are “deposition temperature 1” and “deposition time 1", “deposition temperature 2” and “deposition time 2", respectively.
  • the nano-silicon-carbon-carbon composite material required by the present invention can also be realized by adopting different precursor concentrations and treatment temperature and time between periods without excluding.
  • Table 4 shows the basic physical properties and electrochemical properties of Examples 1 to 36 and Comparative Examples 1 and 2 of the graded particles of the nano-silicon carbon composite material.
  • the content of each substance can be regulated by the pore structure of the porous carbon carrier, the concentration of the deposition mixed gas, the deposition temperature and time, etc. The optimum temperature required for different precursors is different. Inside, when the deposition temperature is higher, the deposition amount of the corresponding substance will increase.
  • the deposition method of the oxygen-containing species and the relative time of deposition with silicon largely determine the degree of dispersion of the oxygen-containing layer on the silicon nanoparticles, which in turn affects the electrochemical properties of the composite material such as the expansion rate of the pole piece and the cycle time. performance etc.
  • Embodiments of the present application mainly revolve around these factors.
  • the present invention prepares a relatively dense silicon-oxygen-carbon composite material, so the pore volume of the carbon substrate determines the maximum loading of silicon precursors and oxygen-containing precursors.
  • the concentration of silicon precursor and oxygen-containing precursor, deposition temperature and relative time, and the pore volume of the carbon substrate jointly determine the silicon content, oxygen content, and correspondingly, the carbon content of the nano-silicon carbon structure composite.
  • the flow rate of the deposition gas is related to the volume of the reaction furnace, the amount of the carbon substrate, the concentration of the silicon precursor and the oxygen-containing precursor in the deposition mixture gas, and can be adjusted accordingly according to the situation, and will not be described in detail in this specification.
  • the total silicon deposition time is controlled to be consistent so as to meet the amount that can be accommodated by the pore volume of the carbon substrate used.
  • Examples 1 to 20, 23, 24 and 25 all adopt the alternate deposition mode of silicon precursor and oxygen-containing precursor to carry out the loading of silicon and oxygen-containing species, and the deposition conditions used in each deposition cycle include The gas concentration, deposition temperature, and time are consistent (but the rights claimed by the present invention are not limited to the complete repetition of the deposition cycle, and the deposition conditions in each cycle can also be changed according to the situation).
  • the oxygen-containing precursor used in step S2 in Examples 1-12 is a mixed gas of O 2 and N 2 .
  • the deposition mixed gas 1 and the deposition mixed gas 2 both use 20% SiH 4 -N 2 and 1% O 2 -N 2 respectively;
  • Example 10 uses increased concentrations of silicon-containing precursors and oxygen-containing precursors
  • the mixed gas used in Examples 11 and 12 was deposited using other silicon-containing precursors, such as Si 2 H 6 and Si 3 H 8 .
  • Example 2 The difference between Example 2 and Example 1 is that the treatment time of the oxygen-containing precursor is relatively long, which will lead to an increase in the oxygen content and a decrease in the first effect of the electrode.
  • Embodiment 3-6 changed the time of silicon deposition in a single deposition cycle, and correspondingly changed the time of oxygen-containing substance treatment and the number of deposition cycles. It can be seen that when the time of silicon deposition in a single deposition cycle is longer, as in Example 5 And Example 6, 10h and 15h respectively, the separation effect of oxygen-containing substances on silicon nanoparticles is reduced, the pole piece expansion rate of the obtained nano-silicon carbon structure composite material is increased, and the capacity retention rate is reduced after multiple cycles.
  • the porous carbon substrate used in Example 7 has a smaller pore volume of 0.33 cm 3 /g, so the amount of silicon loaded is significantly lower than that of Example 1, resulting in a significantly lower gram capacity for the first cycle than that of Example 1, which is only 1639 mAh/g. g.
  • the 9# porous carbon substrate with a specific surface area of 581m 2 /g and a pore volume of 1.1cm 3 /g was used to deposit silicon, and the silicon content of the obtained nano-silicon carbon structure composite material was as high as 68.7%.
  • the gram capacity of the electrode reaches more than 2500mAh/g, and the first effect reaches 92.8%, but the expansion rate of the pole piece is relatively large, and the capacity retention rate after 50 cycles is only 90.4%.
  • Example 9 Compared with Example 1, the difference between Example 9 and Example 1 is that the number of silicon deposition-oxygen treatment cycles in step S2 is reduced to 10 times, the silicon content is relatively low (35.4%), and the electrode capacity of the composite material is less than 1500mAh/g, but relatively low.
  • the low silicon content also makes the electrode expansion rate of the composite material low; in addition, because the silicon and oxygen-containing substances cannot completely fill the pore volume of the carbon substrate, the specific surface area and pore volume of the material increase significantly, which are 41.8m 2 /g and 0.217cm 3 /g, the larger pore volume further alleviates the expansion of silicon, so the first full-charge lithium intercalation electrode expansion rate of the electrode containing the composite material is significantly reduced, only 31%, but the larger specific surface area leads to side reactions increase, the first effect of the electrode decreases, and the first effect is only 84.6% under the voltage of 1.5V.
  • the mixed gas of silicon precursor and oxygen-containing precursor that embodiment 10 increases concentration, the content of silicon and oxygen in the composite material and the relative concentration and a
  • the relative deposition time of the two in the cycle is related.
  • Examples 11 and 12 were deposited using other silicon-containing precursors, such as Si 2 H 6 and Si 3 H 8 .
  • these two examples use a porous carbon substrate with a relatively low pore volume as the carbon carrier for silicon deposition.
  • the pore volume of the carbon substrate determines that the silicon content in the two examples is limited, so the electrode capacity of the composite material is low.
  • Examples 13-17 are examples in which CO is used as an oxygen-containing precursor in step S2.
  • the deposition temperature used is low, the silicon content in the obtained silicon-oxygen-carbon composite material decreases, and the gram capacity of the electrode decreases. Other factors such as deposition time, The relative time etc. are similar to those disclosed in Examples 1-10.
  • Examples 18-21 are examples in which acetone is used as an oxygen-containing precursor in step S2.
  • Examples 18-20 are the silicon-containing precursor and acetone respectively passed into the reaction furnace containing a porous carbon substrate.
  • Example 21 is a silicon-containing The precursor and acetone are passed into the reaction furnace containing the porous carbon substrate at the same time.
  • the silicon-containing precursor and methanol are simultaneously passed into the reaction furnace containing the porous carbon substrate.
  • deposition temperature and oxygen-containing precursor concentration leads to the difference in silicon and oxygen content in the composite material.
  • High temperature and high concentration of acetone lead to higher oxygen content in the composite material, and then the first effect of the electrode containing the composite material is reduced.
  • Example 23 a higher concentration of oxygen-containing precursors, a higher temperature and a longer deposition time were used in the oxygen-containing treatment process, and the total oxygen content of the composite material was higher, exceeding 5wt%, which played a good role in separating silicon particles
  • the degree of crystallization of the comparative sample treated at 800°C is still low, so the expansion rate of the electrode piece containing this material is low, only 72%.
  • too high oxygen content leads to more SiO ⁇ substances in the composite material, more side reactions in the electrode reaction, the capacity and the first effect are greatly reduced, and the capacity is only 1219mAh/g.
  • Example 1 The difference from Example 1 is that the deep oxidation treatment step is increased:
  • Step S4 deep oxidation treatment: place the graded particles of the nano-silica carbon structure composite material obtained in step S3 in a tube furnace, evacuate to a vacuum degree of 10 ⁇ 3 Pa, and then inject 1% O 2 —Ar mixed gas, Control the temperature rise rate at 1°C/min, rise from room temperature to 200°C, and treat at 200°C for 2 hours, then cool down to obtain an oxidized nano-silicon carbon structure composite material.
  • the structure diagram of the oxidized nano-silicon carbon structure composite material See Figure 7.
  • the nano silicon oxygen carbon composite material obtained in Example 26 was tested by XPS, and the amorphous C-C peak binding energy in the C 1s spectrum was calibrated at 284.7eV as the peak position. Since the high-resolution C 1s spectrum contains the C-C peak in the test system, There is a large error in the analysis of its C-Si, so only its high-resolution Si 2p spectrum is analyzed ( Figure 8).
  • the nano silicon oxygen carbon composite material XPS test high-resolution Si 2p spectrum of embodiment 26 obtained and its deconvoluted integral peak analysis result show that, Si-C binding energy peak area is obviously smaller than Si-O and Si-Si, calculate according to corresponding peak area The proportion of each bonding form can be obtained.
  • the ratio of Si-O to Si-Si in the Si 2p spectrum is 0.96, and the ratio of Si-C to Si-Si is 0.40. It can be seen that the nano-silicon carbon obtained in Example 1
  • the porous carbon skeleton and silicon nanoparticles in the composite are mainly connected by C-O-Si, and the proportion of C-Si is small.
  • Example 1 The difference from Example 1 is that the deep oxidation treatment step is increased:
  • Step S4 deep oxidation treatment: place the graded particles of the nano-silicon carbon structure composite material obtained in step S3 in a tube furnace, evacuate, and then pass in 1% O 2 -Ar mixed gas, and control the heating rate to 1°C/min , from room temperature to 300°C, and treated at 300°C for 2h, then lowered the temperature to obtain an oxidized nano-silicon carbon structure composite material.
  • Example 1 The difference from Example 1 is that the deep oxidation treatment step is increased:
  • Step S4 deep oxidation treatment: place the graded particles of the nano-silicon carbon structure composite material obtained in step S3 in a tube furnace, evacuate, and then pass in 1% O 2 -Ar mixed gas, and control the heating rate to 1°C/min , raised from room temperature to 350°C, and treated at 350°C for 2h, then lowered the temperature to obtain an oxidized nano-silicon carbon structure composite material.
  • Example 1 The difference from Example 1 is that the deep oxidation treatment step is increased:
  • Step S4 deep oxidation treatment: place the graded particles of the nano-silicon carbon structure composite material obtained in step S3 in a tube furnace, vacuumize, and then pass in 5% O 2 -Ar mixed gas, and control the heating rate to 1°C/min , from room temperature to 200°C, and treated at 200°C for 2h, then lowered the temperature to obtain an oxidized nano-silicon carbon structure composite material.
  • Example 1 The difference from Example 1 is that the deep oxidation treatment step is increased:
  • Step S4 deep oxidation treatment: put the graded particles of the nano-silicon carbon structure composite material obtained in step S3 in a tube furnace, vacuumize, and then pass in 20% O 2 -Ar mixed gas, and control the heating rate to 1°C/min , from room temperature to 200°C, and treated at 200°C for 2h, then lowered the temperature to obtain an oxidized nano-silicon carbon structure composite material.
  • Example 1 The difference from Example 1 is that the deep oxidation treatment and pretreatment steps thereof are increased:
  • Step S3+ performing acid treatment on the graded particles of the nano-silica carbon structure composite material obtained in step S3: dispersing the graded particles of the nano-silica carbon structure composite material in a 1M HNO 3 water/ethanol (50/50) solution, ultrasonically dispersing for 2 hours, Stir at 60°C for 8h, filter, wash the solid with deionized water several times, and air-dry the obtained solid at 120°C for 24h, then raise the temperature to 400°C at 2°C/min in N2 atmosphere, and at this temperature Keep it under the temperature for 2h, lower the temperature, and obtain the acid-treated composite material.
  • a 1M HNO 3 water/ethanol (50/50) solution ultrasonically dispersing for 2 hours, Stir at 60°C for 8h, filter, wash the solid with deionized water several times, and air-dry the obtained solid at 120°C for 24h, then raise the temperature to 400°C at 2°C/min in N2 atmosphere, and at this temperature Keep it under the temperature for 2h,
  • Step S4 deep oxidation treatment: put the acid-treated composite material obtained in step S3+ into a tube furnace, vacuumize, and then inject 1% O 2 -Ar mixed gas, control the heating rate to 1°C/min, from room temperature to to 200°C, and treated at 200°C for 2 hours, then cooled to obtain an oxidized nano-silicon carbon structure composite material.
  • Example 31 The difference from Example 31 is that the pretreatment steps of the deep oxidation treatment are different:
  • Step S3+ performing acid treatment on the graded particles of the nano-silica carbon structure composite material obtained in step S3: dispersing the graded particles of the nano-silica carbon structure composite material in a 1M NaOH water/ethanol (50/50) solution, ultrasonically dispersing for 2 hours, and then Stir at 60°C for 8h, filter, wash the solid with deionized water several times, and air-dry the obtained solid at 120°C for 24h, then raise the temperature to 400°C at 2°C/min in N2 atmosphere, and at this temperature Keep it for 2 hours, lower the temperature, and obtain the acid-treated composite material, and finally obtain the oxidized nano-silicon carbon structure composite material.
  • a 1M NaOH water/ethanol (50/50) solution ultrasonically dispersing for 2 hours, and then Stir at 60°C for 8h, filter, wash the solid with deionized water several times, and air-dry the obtained solid at 120°C for 24h, then raise the temperature to 400°C at 2°C/min in N2
  • Example 1 The difference from Example 1 is that the deep oxidation treatment step is increased:
  • Step S4 deep oxidation treatment: disperse the graded particles of the nano-silica carbon structure composite material obtained in step S3 in a 0.5M KMnO 4 water/ethanol (50/50) solution, ultrasonically disperse for 2 hours, stir at 50° C. for 2 hours, filter, and use Wash the solid several times with deionized water, and air-dry the obtained solid at 60°C for 24 hours, then raise the temperature to 400°C at 2°C/min in N2 atmosphere, and keep it at this temperature for 2 hours, cool down, and finally get the oxidized Nano-Silicon Carbon Structured Composite Materials.
  • a 0.5M KMnO 4 water/ethanol (50/50) solution ultrasonically disperse for 2 hours, stir at 50° C. for 2 hours, filter, and use Wash the solid several times with deionized water, and air-dry the obtained solid at 60°C for 24 hours, then raise the temperature to 400°C at 2°C/min in N2 atmosphere, and keep it at this temperature for 2 hours
  • Example 1 The difference from Example 1 is to increase the outer coating step:
  • Step S5 outer layer cladding: place the oxidized nano-silica carbon structure composite material obtained in step S4 in a tube furnace, vacuumize, then pass in N 2 , raise the temperature to 700°C at 2°C/min, switch to C 2 H 2 gas was kept at 700° C. for 2 hours, and the temperature was lowered to obtain a carbon-coated nano-silicon-carbon composite material.
  • Example 26 The difference from Example 26 is that the outer coating step is added, that is, the difference from Example 1 is that the steps of deep oxidation treatment and outer coating are added:
  • Example 26 The difference from Example 26 is that the outer coating step is added, that is, the difference from Example 1 is that the steps of deep oxidation treatment and outer coating are added:
  • Step S6 outer layer coating-II: heat up to 700°C at 2°C/min, switch to C 2 H 2 gas, keep at 700°C for 2 hours, and lower the temperature to obtain carbon-coated and Al 2 O 3 -coated Nano-Silicon Carbon Structured Composite Materials.
  • Silicon deposition was performed directly on porous carbon substrates without a surface oxide layer without a silicon deposition-oxygen treatment cycle.
  • Porous carbon substrate Commercial porous carbon was used as the porous carbon substrate, and the C content in the test was 99.99%.
  • the silicon-carbon composite material prepared by this method has a structure of C-Si.
  • the Si particles are seriously agglomerated, and the silicon-carbon is separated during the crushing process, which cannot form an effective silicon-carbon composite material. chemical test.
  • Silicon deposition on porous carbon substrates with a surface oxide layer without oxygen-containing treatment Silicon deposition on porous carbon substrates with a surface oxide layer without oxygen-containing treatment.
  • the carbonized porous carbon substrate is subjected to surface oxidation treatment to obtain a porous carbon substrate containing a surface oxide layer, and then silicon is deposited.
  • the prepared silicon-oxygen-carbon composite material has a structure of C-O-Si. Compared with Comparative Example 1, This material can obtain the Si of effective load, and Si particle and porous carbon substrate are combined firmly, and silicon-carbon separation can not occur in crushing process, and electrochemical test result shows that 1.5V first effect can reach 91.2%, but because silicon particle is bigger (800 After the treatment at °C, the silicon grain size is greater than 20nm (accompanying drawing 5), and the expansion rate of the pole piece is relatively high, reaching 157%, which will affect its cycle performance (accompanying drawing 6).
  • Table 4 The physical properties and electrochemical properties of the examples and comparative examples of nano-silicon carbon structure composites
  • Fig. 4 shows the constant current charge and discharge curves of the first cycle of the half-cell (the counter electrode is a lithium metal electrode) of the electrodes of Example 1, Example 23 and Comparative Example 2.
  • Example 1 Since the composite material has uniformly dispersed silicon nanoparticles, the electrode containing it exhibits a higher gram capacity (2029mAh/g) and first effect (92.6%, 1.5V), and the delithiation curve shows a slope type.
  • Example 23 adopts a higher oxygen content, and the electrode shows greater polarization.
  • the gram capacity and the first effect are lower, respectively 1219mAh/g and 84.3%, and the slope of the slope-type delithiation curve is compared with the implementation Case 1 is significantly larger.
  • Comparative Example 2 oxygen-containing treatment was not performed in the silicon deposition step, so the silicon nanoparticles in the composite material were large and without separation, the gram capacity and first effect were correspondingly reduced, and the voltage plateau was reached rapidly during the charging process.
  • Fig. 5 shows the XRD patterns of the nano-silicon carbon structure composite materials Example 1, Example 23 and Comparative Example 2 after being treated in N 2 atmosphere at 800°C.
  • the XRD spectrum of Example 1 before heat treatment is also shown, and the XRD spectrum of Example 23 and Comparative Example 2 before heat treatment is close to that of Example 1, and also shows a broadened peak package, which is not shown here. It reflects that silicon is in/or close to amorphous state in the three composite materials. It can be seen that the silicon particles in the composite material after treatment at 800°C have obvious crystallization, but the crystallization degree and grain size are related to the degree of oxygen-containing treatment.
  • Comparative Example 2 did not undergo oxygen-containing treatment, and its crystallization degree was very high after high-temperature treatment , grain size greater than 20nm, embodiment 1 also shows a certain degree of crystallization, its grain size is 7.7nm, embodiment 23 adopts higher oxygen-containing treatment temperature and longer oxygen-containing treatment time than embodiment 1, The oxygen content in the composite is relatively high, and it is still close to amorphous after heat treatment.
  • the crystallization degree and grain size of the composite material after treatment at 800 °C and the results in the electrode constant current charge and discharge curve in Figure 4. It shows that adopting the technical solution of the present invention can effectively control the agglomeration of silicon nanoparticles during the silicon deposition process, obtain well-dispersed and smaller-sized silicon nanoparticles, and then regulate the electrochemical performance of the composite electrode.
  • FIG. 6 shows the cycle performance of the half-cell (the counter electrode is a lithium metal electrode) containing the electrodes of the nano-silicon carbon structure composite material Example 1 and Comparative Example 2.
  • Example 1 has evenly dispersed silicon nanoparticles, and the electrode containing it has a capacity retention rate of 95.6% after 50 cycles.
  • Comparative example 2 is not treated with oxygen, the silicon nanoparticles are not separated, and the gram capacity and first effect are low.
  • the expansion rate of the pole piece is high, and the capacity retention rate after 50 cycles is only 86.5%.
  • Example 24 uses a porous carbon substrate with a macropore volume greater than 50% for silicon deposition. Due to the large number of macropores in the porous carbon substrate, it is difficult for silicon particles to completely fill the macropores. Part of the macropores become mesopores after being loaded with silicon, and the specific surface area of the composite material is large, resulting in more side reactions in the electrode process. lower.
  • Example 25 uses a porous carbon substrate with a micropore volume greater than 50% for silicon deposition. Due to the large number of micropores in the porous carbon substrate, the pores may be blocked during the silicon deposition process, and then the silicon particles gather outside the pores. After the composite material is broken, some closed pores become open pores, the specific surface area increases, and there are more closed pores. As a result, the true density of the composite material is low, and structural collapse may occur during the tableting process, resulting in relatively low gram capacity and first effect of the composite material.
  • Example 1 Compared with Example 1, the crushing and classification of materials and the subsequent deep oxidation treatment in Examples 26 to 33 further ensure that the silicon nanoparticles in the finished nano-silicon carbon structure composite material are all wrapped by an extremely low-expansion oxide layer. Therefore, the volume effect of the uniformly dispersed and bound silicon nanoparticles in the obtained nano-silicon carbon structure composite material can be effectively buffered and suppressed in the process of lithium intercalation and delithiation, so that the expansion rate of the pole piece is significantly reduced, and the The capacity retention rate is significantly improved.
  • the specific surface area of the composite material is reduced by the outer coating, so the first effect of the battery is significantly improved, and it has a high cycle capacity retention rate, but due to the decrease in the silicon content, the battery capacity is slightly reduced .
  • the porous carbon substrate containing the surface oxide layer is selected as the carrier for silicon deposition, and the effective deposition of silicon substances in the pores and surface of the porous carbon substrate is realized through the CO-Si chemical interaction between the surface oxide layer of the carbon substrate and the silicon-containing precursor; Then, by controlling the deposition conditions of silicon-containing precursors and oxygen-containing precursors in the preparation process, the uniformly dispersed deposition of silicon nanoparticles with oxygen-containing species and optional carbon is achieved, forming similar ( Siz1 - Oy - Cx ) n (n ⁇ 1) repeating structure. Oxygen-containing substances and optional carbon in the composite material disperse silicon substances to realize effective nano-silicon particles.
  • the volume effect of the silicon nanoparticles in the lithium intercalation and delithiation process can be effectively buffered, and the material strength is improved, which is conducive to the improvement of the electrochemical performance of the silicon-oxygen-carbon composite negative electrode material and the electrochemical device containing it.
  • the size of silicon nano-particles in the nano-silicon carbon structure composite material is small, and the combination with the porous carbon substrate is stable, and it is uniformly dispersed in the pores and on the surface of the porous carbon substrate.
  • the appropriate content of oxygen-containing substances and optional carbon contributes to the Silicon nanoparticles are well dispersed, and at the same time can restrain the expansion of silicon in the lithium intercalation process, the material strength is high, the expansion rate of the electrode sheet is low, and the battery cycle performance is good.
  • the nano-silicon carbon structure composite material has a small specific surface area and pore volume, which can effectively reduce the side reaction on the electrode surface, help to improve the Coulombic efficiency of the material, and obtain a super-high first-efficiency silicon-oxygen-carbon composite negative electrode material.
  • the nano-silicon carbon structure composite material contains closed pores, which can buffer the volume expansion of silicon during the lithium intercalation process to a certain extent.
  • the electrode sheet containing the composite material has a low expansion rate, thereby further improving the
  • the present invention crushes and classifies the obtained material, on the one hand, it releases the stress caused by different phases in the material, and on the other hand, it can obtain uniform, suitable size and shape.
  • Composite particles for homogenization and subsequent electrode preparation After crushing and grading, the surface of fresh silicon particles is exposed, and slowly oxidizes in the air to form an oxide layer, which can also play a role in relieving and restraining expansion.
  • a stable oxide layer is controllably generated on the surface of the exposed silicon nanoparticle, and the oxide layer exists in the form of SiO ⁇ (0 ⁇ 2).
  • the uniform and structure-controllable oxide layer on the surface of silicon nanoparticles can further alleviate and restrain the expansion of silicon intercalated lithium.
  • the composite material is crushed and classified to release the possible stress between different phases, and the material has a suitable size and shape distribution required for homogenization; finally, the crushed and classified composite material is subjected to deep oxidation treatment, and the silicon nano A stable oxide layer is formed on the particle surface.
  • the crushing and shaping and the subsequent oxidation treatment further ensure that the silicon nanoparticles in the finished nano-silicon carbon structure composite are wrapped by an extremely low-expansion oxide layer. Therefore, the volume effect of the uniformly dispersed and bound silicon nanoparticles in the obtained nano-silicon carbon structure composite material can be effectively buffered and suppressed in the process of lithium intercalation and delithiation, and the strength of the material is improved, which helps to improve the volume effect of the contained silicon nanoparticles. Electrochemical performance of electrochemical devices based on nanostructured silicon-oxygen-carbon composites.
  • the nano silicon oxygen carbon structure composite material provided by the present invention includes porous carbon skeleton and silicon nanoparticles uniformly distributed in its pores and on the surface, the stable compounding of carbon and silicon, the nanometerization and uniform dispersion of silicon particles are composed of three Hierarchical oxygen protection: (1) through the formation of CO-Si bonds between the oxygen-containing groups on the surface of the porous carbon substrate and the silicon nanoparticles, to ensure a stable bond between the silicon nanoparticles and the porous carbon substrate; (2) in the porous carbon substrate In the pores of the carbon substrate, silicon nanoparticles are separated by oxygen-containing substances to avoid uncontrolled aggregation and growth during the deposition process, thereby controlling the size of silicon nanoparticles and realizing the separation and separation of silicon nanoparticles by oxygen-containing substances.
  • the silicon nanoparticles in the obtained nano-silicon carbon structure composite are completely separated and/or wrapped by the network of SiO ⁇ (0 ⁇ 2), and the silicon nanoparticles and SiO ⁇ are evenly distributed on the surface and surface of the porous carbon substrate. / or in the tunnel.
  • the separation and/or wrapping of silicon nanoparticles by SiO ⁇ can effectively control the volume expansion and contraction of silicon and the fusion between silicon particles in the composite material during charge and discharge.
  • the appropriate range of silicon, oxygen, carbon element content and composite specific surface area can make nano-silicon carbon structure composites exhibit optimal gram capacity, first Coulombic efficiency, extremely low expansion rate and excellent cycle performance.
  • the gram capacity of the lithium-ion secondary battery is greater than or equal to 1500mAh/g
  • the first coulombic efficiency of 1.5V is greater than or equal to 85%
  • the pole piece expansion rate is lower than 120%
  • the gram capacity retention rate after 50 cycles of charging and discharging Greater than or equal to 95%.
  • the gram capacity of the lithium-ion secondary battery is greater than or equal to 2000mAh/g
  • the first coulombic efficiency of 1.5V is greater than or equal to 90%
  • the pole piece expansion rate is lower than 150%
  • the gram capacity retention rate after 50 cycles of charging and discharging Greater than or equal to 95%.
  • the present invention provides nano-silicon-carbon composite material, its preparation method, negative electrode and electrochemical device.
  • the porous carbon skeleton and the silicon nanoparticle are connected by a CO-Si bond, the combination between the silicon nanoparticle and the porous carbon skeleton is stable, and the silicon nanoparticle is separated by a network of SiO ⁇ and / or wrapped, and uniformly dispersed in the pores and surfaces of the porous carbon skeleton, thus effectively inhibiting the agglomeration of silicon nanoparticles during the deposition process and their volume change and possible fusion during the charge-discharge cycle, including the obtained composite
  • the negative electrode lithium ion secondary battery prepared by the material has higher gram capacity, higher first Coulombic efficiency and good cycle performance.
  • Fig. 9 is a schematic diagram of the structure of the nanocomposite material of the present invention.
  • silicon and carbon have different lithium intercalation capabilities in negative electrode materials, although the oxygen-containing species in the form of SiO ⁇ can relieve and bind the expansion, it also causes irreversible lithium intercalation and reduces the first effect of the negative electrode.
  • the content of , oxygen, and carbon has a great influence on the capacity, first effect, and expansion rate of the electrode sheet of the composite material, and it needs to be reasonably controlled during the preparation process.
  • silicon and oxygen-containing substances are mainly deposited inside the pores of the porous carbon skeleton, and a little is deposited on the surface outside the pores of the carbon skeleton.
  • the present invention prepares a relatively dense nano-silicon-carbon composite material, so the pore volume of the porous carbon framework determines the maximum loading of silicon precursors and oxygen-containing precursors.
  • the concentration of silicon precursor and oxygen-containing precursor, deposition temperature and relative time, and the pore volume of the porous carbon framework jointly determine the silicon content, oxygen content, and correspondingly, the carbon content of the nano-silicon carbon composite.
  • the flow rate of the deposition gas is related to the volume of the reaction furnace, the amount of the porous carbon skeleton, the concentration of the silicon precursor and the oxygen-containing precursor in the deposition mixture gas, and can be adjusted accordingly according to the situation, and will not be described in detail in this specification.
  • Step S1 preparation of porous carbon skeleton with surface oxide layer: starch is used as carbon precursor, triblock copolymer P123 is used as pore-forming agent, starch is added to the water/ethanol solution of P123, and stirred at 50°C until the solvent evaporates completely , the obtained solid was raised from room temperature to 220°C in an air atmosphere, and kept at this temperature for 48h for pre-stabilization; then changed to N 2 , heated at 2°C/min to 800°C, and kept at this temperature for 2h , to complete carbonization; change the gas to 5% CO 2 -N 2 , (with N 2 as the balance gas, which contains 5% CO 2 ) heat up to 900 ° C, and in a 10% CO 2 -N 2 atmosphere, 900 ° C, Keep it for 2 hours; then lower the temperature to a specific temperature in N2 atmosphere for use, and obtain a porous carbon skeleton with a surface oxide layer; and use a jet mill to crush it to particles with a median particle size of about 10
  • the specific surface area of the obtained porous carbon skeleton particles is 809m 2 /g, the pore volume is 0.68cm 3 /g, and the proportions of micropores, mesopores and macropores are 16%, 75% and 9% respectively, of which, 2-10nm
  • the ratio of the pore volume to the total pore volume was 68%.
  • Step S2 silicon deposition and oxygen-containing treatment: place the porous carbon skeleton particles with a surface oxide layer with a median particle size of about 10-20 ⁇ m in step S1 in a tube furnace, and evacuate to a vacuum degree of 10 -3 Pa , in the N 2 atmosphere, the temperature was raised to 600°C at 2°C/min, and changed to 20% SiH 4 -N 2 mixed gas; in the 20% SiH 4 -N 2 mixed gas atmosphere, kept at 600°C for 2h, silicon Then change to N 2 , after cooling down to 200 ° C, change to 1% O 2 -N 2 mixed gas; in the 1% O 2 -N 2 mixed gas atmosphere, keep at 200 ° C for 12 minutes for oxygen treatment ; Then change to N 2 and raise the temperature to 600°C, carry out silicon deposition-oxygen treatment cycles on the porous carbon skeleton for 15 times, and naturally cool down under the protection of N 2 ; and use wet ball milling to crush and reshape the obtained material to obtain A nano-sili
  • Step S3 deep oxidation treatment: place the nano silicon oxygen carbon composite material 1 obtained in step S2 in a tube furnace, evacuate to a vacuum degree of 10 -3 Pa, and then inject 1% O 2 -Ar mixed gas to control the temperature rise The rate is 1°C/min, from room temperature to 200°C, and treated at 200°C for 2 hours, and the temperature is lowered to obtain a nano-silicon-carbon composite material.
  • Electrode, half-cell preparation and electrochemical performance test method (applicable to this application enumerating all embodiments and comparative examples):
  • EC ethyl carbonate
  • DEC diethyl carbonate
  • the CR2032 type buckle After the CR2032 type buckle was left standing for 6 hours, it was discharged at 0.05C to 0.005V, and then at 0.01C to 0.005V; after standing for 5 minutes, it was charged to 1.5V at a constant current of 0.05C; the first delithiation gram capacity was the electrode
  • the gram capacity (or mass specific capacity) of the material, the ratio of the first delithiation capacity to the first lithium intercalation capacity is the first coulombic efficiency of the battery.
  • the following method is used to test the expansion rate of the pole piece: after the CR2032 type buckle is left standing for 6 hours, it is discharged to 0.005V at 0.05C, and then discharged to 0.005V at 0.01C; then the buckle is disassembled in the glove box and cleaned with DEC Pole piece and measure the thickness of the pole piece.
  • the calculation method of the expansion rate is: (thickness of the pole piece in the first fully charged state-thickness of the fresh pole piece)/thickness of the fresh pole piece ⁇ 100%.
  • the ratio of Si-O and Si-Si in the Si 2p spectrum is 0.95, and the ratio of Si-C and Si-Si is 0.41, as can be seen, the nano silicon oxygen carbon obtained in embodiment 1
  • the porous carbon skeleton and silicon nanoparticles in the composite are mainly connected by C-O-Si, and the proportion of C-Si is small.
  • the XRD test results of the nano-silicon-carbon composite material obtained in Example 1 after being treated at 800°C are shown in FIG. 11 , and the limit size of the grain size increase is 7nm.
  • the specific surface area of the obtained nano silicon oxygen carbon composite material is 4.1m2/g
  • the pore volume is 0.021cm3/g
  • the true density is 2.00g/cm3.
  • the mass contents of silicon, oxygen and carbon in the nano-silicon-oxygen-carbon composite material obtained in Example 1 were 52.6%, 2.1% and 45.3%, respectively.
  • the galvanostatic charge-discharge curve of the electrode comprising the nano-silicon-oxygen-carbon composite material obtained in Example 1 is shown in Figure 13, its gram capacity is 2011mAh/g, the first coulombic efficiency at 1.5V is 92.8%, and the pole piece expansion rate is 75%.
  • the gram capacity retention rate after 50 cycles of charging and discharging is 97.1%, and the change trend of the gram capacity with the increase of the number of cycles is shown in Figure 14.
  • Step S1 preparation of porous carbon skeleton: use starch as carbon precursor, raise from room temperature to 220°C in air atmosphere, and keep at this temperature for 48h for pre-stabilization; then change to N 2 at 2°C/min Raise the temperature to 800°C and keep it at this temperature for 2 hours to complete carbonization, then cool down in N2 atmosphere to obtain a porous carbon skeleton, and use a jet mill to crush it to particles with a median particle size of about 10-20 ⁇ m for use.
  • the specific surface area of the obtained porous carbon skeleton particles is 331m 2 /g, the pore volume is 0.35cm 3 /g, and the proportions of micropores, mesopores and macropores are 21%, 63% and 16% respectively.
  • Step S2 silicon deposition: After the porous carbon skeleton is raised from room temperature to 600°C at 2°C/min in N 2 atmosphere, it is changed to 20% SiH 4 -N 2 mixed gas; in 20% SiH 4 -N 2 mixed gas In the atmosphere, keep at 600°C for 30 hours to deposit silicon; naturally cool down under the protection of N 2 , and use wet grinding for crushing and shaping to obtain nano-silicon-carbon composites with a median particle size of 6 ⁇ m.
  • Step S1 same as embodiment 1.
  • Step S2 Same as Comparative Example 1.
  • the carbonized porous carbon skeleton contains a surface oxide layer, and then silicon is deposited (oxygen-free treatment), and the prepared silicon-oxygen-carbon composite material has a structure of C-O-Si.
  • the material can be obtained Effectively loaded Si, Si particles are firmly combined with the porous carbon skeleton, and silicon-carbon separation will not occur during the crushing process.
  • the electrochemical test results show that the first effect of 1.5V can reach 91.8%, but because there is almost no oxide layer separation between silicon particles and Confinement, the expansion rate of the pole piece is high, reaching 163%, which will affect its cycle performance, and the capacity retention rate after 50 cycles is only 86.2%.
  • Step S1 same as embodiment 1.
  • Step S2 Same as Comparative Example 1.
  • Step S3 same as embodiment 1.
  • Steps S1-S2 Same as Embodiment 1.
  • Comparative Example 3 and Comparative Example 4 use the same porous carbon skeleton as in Example 1 as the silicon deposition carrier, so when silicon is deposited, it will form a CO-Si chemical bond with the oxygen-containing layer on the surface of the porous carbon skeleton to obtain a stable silicon-oxygen-carbon composite.
  • Material. Comparative Example 3 is the silicon-oxygen-carbon composite material obtained after the subsequent deep oxidation treatment compared with Comparative Example 2. Although there is a late deep oxidation treatment, since the silane deposition process is not supplemented with oxygen-containing substances, the aggregation and growth of silicon particles is only Limited by the pore structure of the porous carbon skeleton, an effective SiO ⁇ network cannot be formed, so the cycle performance is worse than that of Example 1.
  • Comparative Example 4 does not carry out deep oxidation treatment after crushing and shaping, but after crushing, a large number of fresh silicon nanoparticles are exposed on the surface, and the thin oxide layer formed by natural oxidation is not enough to bind silicon in the process of electrode use. Lithium intercalation expands, so the expansion rate of the pole piece is still high, reaching 125%, and the capacity retention rate after 50 cycles is 89.5%.
  • Step S1 preparation of porous carbon skeleton with surface oxide layer: S1-1, starch is used as carbon precursor, triblock copolymer F127 is used as pore-forming agent, starch is added to the water/ethanol solution of F127, and stirred at 50°C After the solvent is completely evaporated, the obtained solid is raised from room temperature to 220°C in an air atmosphere, and kept at this temperature for 48 hours for pre-stabilization; then changed to N 2 , heated to 800°C at 2°C/min, and Keep at the temperature for 2 hours to complete carbonization, then lower the temperature in N2 atmosphere to obtain a porous carbon skeleton with a surface oxide layer, and use a jet mill to crush it to particles with a median particle size of about 10-20 ⁇ m for further processing.
  • the specific surface area of the obtained porous carbon skeleton particles containing the surface oxide layer is 705m 2 /g, the pore volume is 0.65cm 3 /g, and the proportions of micropores, mesopores and macropores are 12%, 83% and 5% respectively, Among them, the proportion of 2-10nm pore volume to the total pore volume is 72%.
  • Step S1 preparation of porous carbon skeleton containing surface oxide layer: S1-1, mixing thermoplastic phenolic resin and thermosetting phenolic resin at a ratio of 1:50 as a carbon precursor, and ball milling with triblock copolymer F127 as a pore-forming agent, The obtained solid was raised from room temperature to 180°C in an air atmosphere, and kept at this temperature for 4 hours for pre-stabilization; then changed to N 2 , heated at 2°C/min to 900°C, and kept at this temperature for 2 hours, After carbonization is completed, the temperature is lowered in N2 atmosphere to obtain a porous carbon skeleton containing an oxide layer on the surface.
  • the specific surface area of the obtained porous carbon skeleton particles containing the surface oxide layer is 837m2 /g, the pore volume is 0.74cm3/g, and the proportions of micropores, mesopores and macropores are 13%, 81% and 6% respectively, wherein , 2-10nm pore volume accounted for 69% of the total pore volume.
  • Step S1 preparation of porous carbon skeleton containing surface oxide layer: mixing thermoplastic phenolic resin and thermosetting phenolic resin at a ratio of 1:50 as a carbon precursor, and ball milling with cetyltrimethylammonium bromide, and the resulting mixture was air-
  • the atmosphere was raised from room temperature to 180°C, and kept at this temperature for 4 hours for pre-stabilization; then changed to N 2 , raised to 900°C at 2°C/min, and kept at this temperature for 2 hours to complete carbonization; then In the N 2 atmosphere, the temperature was raised to 1200°C at 2°C/min, switched to 5% CO 2 -Ar, and kept at 1200°C for 2h, and the temperature was lowered in the N 2 atmosphere to obtain a porous carbon skeleton with a surface oxide layer.
  • the specific surface area of the obtained porous carbon skeleton particles is 922m 2 /g, the pore volume is 0.78cm 3 /g, and the proportions of micropores, mesopores and macropores are 15%, 8% and 0% respectively, among which, 2-10nm
  • the ratio of the pore volume to the total pore volume was 63%.
  • Step S1 Same as Embodiment 2.
  • Step S2 silicon deposition and oxygen-containing treatment: place the porous carbon skeleton particles with a surface oxide layer with a median particle size of about 10-20 ⁇ m in step S1 in a tube furnace, and evacuate to a vacuum degree of 10 -3 Pa , in the N 2 atmosphere, the temperature was raised to 600°C at 2°C/min, and changed to 20% SiH 4 -N 2 mixed gas; in the 20% SiH 4 -N 2 mixed gas atmosphere, kept at 600°C for 5h, silicon Then change to N 2 , after cooling down to 200°C, change to 1% O 2 -N 2 mixed gas; in 1% O 2 -N 2 mixed gas atmosphere, keep at 200°C for 30min for oxygen treatment ; Then change to N 2 and raise the temperature to 600°C, carry out silicon deposition-oxygen treatment cycles on the porous carbon skeleton for 6 times, and naturally cool down under the protection of N 2 ; and use wet ball milling to crush and reshape the obtained material to obtain A nano-silicon-carbon
  • Step S3 same as embodiment 1.
  • Embodiment 6 is a diagrammatic representation of Embodiment 6
  • Step S1 Same as Embodiment 2.
  • Step S2 silicon deposition and oxygen-containing treatment: place the porous carbon skeleton particles with a surface oxide layer with a median particle size of about 10-20 ⁇ m in step S1 in a tube furnace, and evacuate to a vacuum degree of 10 -3 Pa , after rising from room temperature to 600°C at 2°C/min in N 2 atmosphere, change to 20% SiH 4 -N 2 mixed gas; in 20% SiH 4 -N 2 mixed gas atmosphere, keep at 600°C 2h, carry out silicon deposition; then change to N 2 , after cooling down to 200°C, change to 1%O 2 -N 2 mixed gas; in 1%O 2 -N 2 mixed gas atmosphere, keep at 200°C for 12min Carry out oxygen-containing treatment; then change to N2 and raise the temperature to 600 ° C, so that the silicon deposition-oxygen treatment cycle is carried out on the porous carbon skeleton for 10 times, and the temperature is naturally lowered under the protection of N2 ; and the obtained material is processed by wet ball milling Crushed and re
  • Step S3 same as embodiment 1.
  • Embodiment 7 is a diagrammatic representation of Embodiment 7:
  • Step S1 Same as Embodiment 2.
  • Step S2 silicon deposition and oxygen-containing treatment: place the porous carbon skeleton particles with a surface oxide layer with a median particle size of about 10-20 ⁇ m in step S1 in a tube furnace, and evacuate to a vacuum degree of 10 -3 Pa , after rising from room temperature to 450°C at 2°C/min in N 2 atmosphere, change to 20% SiH 4 -N 2 mixed gas; in 20% SiH 4 -N 2 mixed gas atmosphere, keep at 450°C 2h, carry out silicon deposition; then change to N 2 , after cooling down to 200°C, change to 0.5% O 2 -N 2 mixed gas; in 1% O 2 -N 2 mixed gas atmosphere, keep at 200°C for 12min Carry out oxygen-containing treatment; then change to N2 and raise the temperature to 600 ° C, so that the silicon deposition-oxygen treatment cycle is carried out on the porous carbon framework for 15 times, and the temperature is naturally lowered under the protection of N2 ; and the obtained material is processed by wet ball milling Crushed and re
  • Step S3 same as embodiment 1.
  • Embodiment 8 is a diagrammatic representation of Embodiment 8
  • Step S1 Same as Embodiment 2.
  • Step S2 silicon deposition and oxygen-containing treatment: place the porous carbon skeleton particles with a surface oxide layer with a median particle size of about 10-20 ⁇ m in step S1 in a tube furnace, and evacuate to a vacuum degree of 10 -3 Pa , after rising from room temperature to 700°C at 2°C/min in N 2 atmosphere, change to 20% SiH 4 -N 2 mixed gas; in 20% SiH 4 -N 2 mixed gas atmosphere, keep at 700°C 2h, carry out silicon deposition; then change to N 2 , after cooling down to 350°C, change to 1%O 2 -N 2 mixed gas; in 1%O 2 -N 2 mixed gas atmosphere, keep at 350°C for 12min Carry out oxygen-containing treatment; then change to N2 and raise the temperature to 700 °C, so that the silicon deposition-oxygen treatment cycle is carried out on the porous carbon framework for 15 times, and the temperature is naturally lowered under the protection of N2 ; and the obtained material is processed by wet ball milling Crushed and reshaped to
  • Step S3 same as embodiment 1.
  • Embodiment 9 is a diagrammatic representation of Embodiment 9:
  • Step S1 Same as Embodiment 2.
  • Step S2 silicon deposition and oxygen-containing treatment: place the porous carbon skeleton particles with a surface oxide layer with a median particle size of about 10-20 ⁇ m in step S1 in a tube furnace, and evacuate to a vacuum degree of 10 -3 Pa , after rising from room temperature to 600°C at 2°C/min in N 2 atmosphere, change to 20% SiH 4 -N 2 mixed gas; in 20% SiH 4 -N 2 mixed gas atmosphere, keep at 600°C 2h, carry out silicon deposition; then change to N 2 , purging 2h, change to 5% CO 2 -N 2 mixed gas; in 5% CO 2 -N 2 mixed gas atmosphere, keep at 600°C for 12min to carry out Oxygen treatment; then change to N2 and raise the temperature to 600 ° C, so that the silicon deposition-oxygen treatment cycle is carried out on the porous carbon framework for 15 times, and the temperature is naturally lowered under the protection of N2 ; and the obtained material is crushed and shaped by wet ball milling , to obtain a nano
  • Step S3 same as embodiment 1.
  • Step S1 Same as Embodiment 2.
  • Step S2 silicon deposition and oxygen-containing treatment: place the porous carbon skeleton particles with a surface oxide layer with a median particle size of about 10-20 ⁇ m in step S1 in a tube furnace, and evacuate to a vacuum degree of 10 -3 Pa , after rising from room temperature to 600°C at 2°C/min in N 2 atmosphere, change to 10% Si 2 H 6 -N 2 mixed gas; in 10% Si 2 H 6 -N 2 mixed gas atmosphere, at Keep at 600°C for 2 hours to deposit silicon; then change to N 2 , after cooling down to 200°C, change to 1% O 2 -N 2 mixed gas; in 1% O 2 -N 2 mixed gas atmosphere, at 200 Keep at °C for 12min for oxygen treatment; then change to N 2 and raise the temperature to 600 °C, so that the silicon deposition-oxygen treatment cycle is carried out on the porous carbon framework for 15 times, and the temperature is naturally lowered under the protection of N 2 ; and wet ball milling The obtained material was crushed and shaped to obtain a nano-
  • Step S3 same as embodiment 1.
  • Step S1 Same as Embodiment 2.
  • Step S2 silicon deposition and oxygen-containing treatment: place the porous carbon skeleton particles with a surface oxide layer with a median particle size of about 10-20 ⁇ m in step S1 in a tube furnace, and evacuate to a vacuum degree of 10 -3 Pa , after rising from room temperature to 600°C at 2°C/min in N 2 atmosphere, change to 20% SiH 4 -0.5% acetone-N 2 mixed gas; in 20% SiH 4 -0.5% acetone-N 2 mixed gas In the atmosphere, keep at 600°C for 30h, carry out silicon deposition and oxygen-containing treatment simultaneously, and naturally cool down under the protection of N2 ; and use wet ball milling to crush and shape the obtained material to obtain nano-silica with a median particle size of 6 ⁇ m carbon composite material to obtain nano silicon oxygen carbon composite material 1.
  • Step S3 same as embodiment 1.
  • Steps S1-S2 Same as Embodiment 1.
  • Step S3 deep oxidation treatment: place the nano silicon oxygen carbon composite material 1 obtained in step S2 in a tube furnace, evacuate, and then inject 1% O 2 -Ar mixed gas, control the heating rate to 1°C/min, from The room temperature was raised to 300°C, and treated at 300°C for 2 hours, and the temperature was lowered to obtain a nano-silicon-carbon composite material.
  • Steps S1-S2 Same as Embodiment 1.
  • Step S3 deep oxidation treatment: place the nano silicon oxygen carbon composite material 1 obtained in step S2 in a tube furnace, evacuate, and then inject 1% O 2 -Ar mixed gas, control the heating rate to 1°C/min, from The room temperature was raised to 350°C, and treated at 350°C for 2 hours, and the temperature was lowered to obtain a nano-silicon-carbon composite material.
  • Steps S1-S2 Same as Embodiment 1.
  • Step S3 deep oxidation treatment: place the nano silicon oxygen carbon composite material 1 obtained in step S2 in a tube furnace, evacuate, and then pass in 5% O 2 -Ar mixed gas, control the heating rate to 1°C/min, from The room temperature was raised to 200°C, and treated at 200°C for 2 hours, and the temperature was lowered to obtain a nano-silicon-carbon composite material.
  • Steps S1-S2 Same as Embodiment 1.
  • Step S3 deep oxidation treatment: place the nano silicon oxygen carbon composite material 1 obtained in step S2 in a tube furnace, evacuate, and then pass in 20% O 2 -Ar mixed gas, control the heating rate to 1°C/min, from The room temperature was raised to 200°C, and treated at 200°C for 2 hours, and the temperature was lowered to obtain a nano-silicon-carbon composite material.
  • Steps S1-S2 Same as Embodiment 1.
  • Step S2+ performing acid treatment on the crushed and shaped nano-silicon carbon composite material 1 obtained in step S2: dispersing the nano-silicon carbon composite material 1 in a 1M HNO 3 water/ethanol (50/50) solution, ultrasonically dispersing for 2 hours, Stir at 60°C for 8h, filter, wash the solid with deionized water several times, and air-dry the obtained solid at 120°C for 24h, then raise the temperature to 400°C at 2°C/min in N2 atmosphere, and at this temperature The temperature was kept at low temperature for 2 hours, and the temperature was lowered to obtain the nano-silicon-carbon composite material 2.
  • a 1M HNO 3 water/ethanol (50/50) solution ultrasonically dispersing for 2 hours, Stir at 60°C for 8h, filter, wash the solid with deionized water several times, and air-dry the obtained solid at 120°C for 24h, then raise the temperature to 400°C at 2°C/min in N2 atmosphere, and at this temperature The temperature was kept at low temperature for
  • Step S3 deep oxidation treatment: place the nano silicon oxygen carbon composite material 2 obtained in step S2+ in a tube furnace, vacuumize, and then inject 1% O 2 -Ar mixed gas, control the heating rate to 1°C/min, from The room temperature was raised to 200°C, and treated at 200°C for 2 hours, and the temperature was lowered to obtain a nano-silicon-carbon composite material.
  • Steps S1-S2 Same as Embodiment 1.
  • Step S2+ performing acid treatment on the crushed and shaped nano-silicon carbon composite material 1 obtained in step S2: dispersing the nano-silicon carbon composite material 1 in a 1M NaOH water/ethanol (50/50) solution, ultrasonically dispersing for 2 hours, and then Stir at 60°C for 8h, filter, wash the solid with deionized water several times, and air-dry the obtained solid at 120°C for 24h, then raise the temperature to 400°C at 2°C/min in N2 atmosphere, and at this temperature Keep it for 2 hours, lower the temperature, and obtain the nano-silicon-carbon composite material 2.
  • a 1M NaOH water/ethanol (50/50) solution ultrasonically dispersing for 2 hours, and then Stir at 60°C for 8h, filter, wash the solid with deionized water several times, and air-dry the obtained solid at 120°C for 24h, then raise the temperature to 400°C at 2°C/min in N2 atmosphere, and at this temperature Keep it for 2 hours, lower the temperature, and obtain the
  • Step S3 Same as Embodiment 16.
  • Steps S1-S2 Same as Embodiment 1.
  • Step S3 deep oxidation treatment: disperse the nano silicon oxygen carbon composite material 1 obtained in step S2 in 0.5M KMnO 4 water/ethanol (50/50) solution, ultrasonically disperse for 2 hours, stir at 50°C for 2 hours, filter, and use deionized The solid was washed with water several times, and the obtained solid was air-dried at 60°C for 24 hours, and then heated to 400°C at 2°C/min in an N2 atmosphere, and kept at this temperature for 2 hours, and then cooled to obtain nano-silicon carbon composite material.
  • 0.5M KMnO 4 water/ethanol (50/50) solution ultrasonically disperse for 2 hours, stir at 50°C for 2 hours, filter, and use deionized
  • the solid was washed with water several times, and the obtained solid was air-dried at 60°C for 24 hours, and then heated to 400°C at 2°C/min in an N2 atmosphere, and kept at this temperature for 2 hours, and then cooled to obtain nano-sili
  • Steps S1-S3 Same as Embodiment 1.
  • Step S4 outer layer coating: place the nano silicon oxygen carbon composite material obtained in step S3 in a tube furnace, vacuumize, then pass in N 2 , raise the temperature to 700°C at 2°C/min, and switch to C 2 H 2 gas, keep at 700°C for 2h, then cool down to obtain a carbon-coated nano-silicon-oxygen-carbon composite material.
  • Steps S1-S3 Same as Embodiment 1.
  • Steps S1-S3 Same as Embodiment 1.
  • the main categories and investigation factors of the preparation conditions are: Examples 1-4 modulate the porous carbon skeleton and its surface treatment method, Examples 5-11 adjust Various factors in the process of variable silicon deposition plus oxygen-containing treatment, examples 12-18 investigate the deep oxidation mode, and examples 19-21 give examples for the outer coating of composite materials.
  • Comparative examples 1 to 4 are set for the three levels of oxygen in the nano-material silicon-oxygen-carbon composite material of the present invention.
  • the surface of the porous carbon skeleton has almost no surface oxygen-containing groups.
  • the oxygen-containing treatment produces separation of the oxygen-containing layer, and the deposited composite material is not subjected to deep oxidation treatment.
  • Comparative example 3 adopts silicon deposition plus oxygen-containing treatment, but no further oxidation treatment is carried out after crushing and shaping. Oxygen treatment was not carried out during deposition but deep oxidation treatment was carried out after crushing and shaping.
  • Table 1 shows the basic physical properties and electrochemical properties of Examples 1-21 and Comparative Examples 1-4 of the nano-silicon-carbon composite material.
  • Table 1 The basic physical properties and electrochemical properties of the examples and comparative examples of nano-silicon carbon composites
  • the porous carbon skeleton in the composite material is connected with the silicon nanoparticle through the CO-Si bond, so that a stable and uniform nano silicon-oxygen-carbon composite material can be obtained.
  • This connection mode can be reflected by the XPS test results, as shown in Figure 10, the Si 2p fine spectrum of the nano-silicon-oxygen-carbon composite material obtained in Example 1 shows that the bonding of Si is mainly in the form of Si-Si and Si-O.
  • the binding energy peaks are located at 99 ⁇ 0.5eV and 103 ⁇ 0.5eV respectively, and the peak area of C-Si with the binding energy peak at 100.5 ⁇ 0.5eV is small, and Si-Si exists in silicon nanoparticles , Si-O is due to the presence of CO-Si and SiO ⁇ in the composite.
  • the pore structure is the main place to accommodate silicon nanoparticles.
  • the pore size distribution of porous carbon is usually wide, from micropores ⁇ 2nm to macropores >50nm, and some porous carbons may have ⁇ m-scale macropores.
  • the decomposition of silane is a chain reaction of thermal polymerization. It is difficult to react at low temperature, and the utilization rate of silane is low. However, the decomposition rate is very fast at high temperature, and the silicon particles inevitably grow rapidly.
  • the silicon-containing precursors are usually first decomposed on the surface of the pores of porous carbon and deposited as small particles, and then fill the interior of the pores with time.
  • the present invention controls the pore structure of the porous carbon skeleton, especially increases the proportion of pores with a pore size of 2 to 10 nm in the total pore volume; on the other hand, by controlling the deposition process of silicon-containing precursors and introducing the deposition and growth of oxygen-containing substances, Realize the effective separation of silicon nanoparticles by oxygen-containing substances, and finally realize the size control and uniform dispersion of silicon nanoparticles in the composite material.
  • Si particles are easily oxidized, oxygen-containing substances will oxidize the Si nanoparticles at the interface between Si and oxygen-containing substances, thereby forming an oxide layer with a concentration gradient of Si, SiO and SiO 2 , which can be written as SiO ⁇ (0 ⁇ 2).
  • the present invention crushes and shapes the obtained material, on the one hand, releases the stress caused by different phases in the material, and on the other hand, obtains a material with uniform and suitable size and shape.
  • Composite material particles to facilitate homogenization and subsequent electrode preparation After plastic surgery, the surface of fresh silicon particles is exposed and slowly oxidized in the air to form an oxide layer, which can also play a role in relieving and restraining expansion.
  • a stable oxide layer is controllably generated on the surface of the exposed silicon nanoparticle, and the oxide layer exists in the form of SiO ⁇ (0 ⁇ 2).
  • the uniform and structure-controllable oxide layer on the surface of silicon nanoparticles can further alleviate and restrain the expansion of silicon intercalated lithium.
  • the present invention first regulates the surface structure and pore structure of the porous carbon skeleton, and then introduces an oxygen-containing precursor during the silane decomposition and deposition process to form an oxidized separation layer for silicon nanoparticles to achieve uniform dispersion of silicon nanoparticles; on this basis , to crush and shape the composite material, release the possible stress between different phases, and make the material have the appropriate size and shape distribution required for homogenization; finally, carry out deep oxidation treatment on the composite material after crushing and shaping, in silicon A stable oxide layer is formed on the surface of the nanoparticles. The crushing and shaping and subsequent oxidation treatment further ensure that the silicon nanoparticles in the finished nano-silicon-carbon composite material are all wrapped by an extremely low-expansion oxide layer.
  • the volume effect of the uniformly dispersed and bound silicon nanoparticles in the obtained nano-silicon carbon composite material can be effectively buffered and suppressed in the process of lithium intercalation and delithiation, and the strength of the material is improved, which helps to improve the volume effect of the silicon nanoparticles containing the silicon.
  • Electrochemical properties of oxygen-carbon composite anode materials for electrochemical devices are described.
  • the silicon nanoparticles are amorphous and/or crystal grains less than 2nm, the silicon nanoparticles are separated and/or wrapped by the network of SiO ⁇ , and are combined with the porous carbon skeleton through CO-Si to be stable
  • the composite material, and the silicon nanoparticles and SiO ⁇ are uniformly dispersed in the pores of the porous carbon framework and on the surface.
  • the appropriate content of SiO ⁇ helps the silicon nanoparticles to disperse well, and at the same time can restrain the expansion of silicon during the lithium intercalation process, making
  • the limit aggregation size of silicon nanoparticles is less than 10nm, the expansion rate of the electrode sheet is low, the material strength is high, and the battery cycle performance is good.
  • the nano-silicon-carbon composite material has a small specific surface area and pore volume, which can effectively reduce the side reaction on the electrode surface, help to improve the Coulombic efficiency of the material, and obtain a super-high first-efficiency silicon-oxygen-carbon composite negative electrode material.
  • the nano silicon oxygen carbon composite material contains closed pores, which can buffer the volume expansion of silicon during the lithium intercalation process to a certain extent, and the expansion rate of the electrode sheet containing the composite material is low, thereby further improving the battery cycle performance.
  • the nano-silicon-oxygen-carbon composite material provided by the present invention includes a porous carbon skeleton and silicon nanoparticles uniformly distributed in its pores and on the surface, and the stable compounding of carbon and silicon, and the nanometerization and uniform dispersion of silicon particles are composed of three levels.
  • the silicon nanoparticles in the obtained nano-silicon carbon composite material are completely separated and/or wrapped by the network of SiO ⁇ (0 ⁇ 2), and the silicon nanoparticles and SiO ⁇ are evenly distributed on the surface of the porous carbon skeleton and/or or in the tunnel.
  • the separation and/or wrapping of silicon nanoparticles by SiO ⁇ can effectively control the volume expansion and contraction of silicon and the fusion between silicon particles in the composite material during charge and discharge.
  • the appropriate range of silicon, oxygen, carbon element content and composite specific surface area can make nano silicon oxygen carbon composites exhibit optimal gram capacity, first Coulombic efficiency, extremely low expansion rate and excellent cycle performance.
  • the gram capacity of the lithium-ion secondary battery is greater than or equal to 1500mAh/g
  • the first coulombic efficiency of 1.5V is greater than or equal to 90%
  • the expansion rate of the pole piece is lower than 100%.
  • the gram capacity retention rate is greater than or equal to 97%.
  • the gram capacity of the lithium-ion secondary battery is greater than or equal to 2000mAh/g
  • the first coulombic efficiency of 1.5V is greater than or equal to 90%
  • the pole piece expansion rate is lower than 120%

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Abstract

本发明提供了一种纳米硅氧碳结构复合材料、其制备方法、负极和电化学装置。复合材料包括(C x1-O y1)-(Si z-O y2-C x2)，C x1-O y1为含表面氧化层的多孔炭基底，0.001≤y1/x1≤0.05；Si z-O y2-C x2包括硅纳米颗粒、含氧物质和可选的碳，硅纳米颗粒、含氧物质和可选的碳分散分布在含表面氧化层的多孔炭基底的表面和/或孔道内，含氧物质以SiO δ形式存在，0＜δ≤2，0.1≤z/x1≤2，0.01≤y2/z≤0.15，0≤x2/z≤0.15。复合材料中硅纳米颗粒均匀分散，由含氧物质和可选的碳分隔和束缚，控制了其在充放电循环中的体积变化和可能的融并，改善了锂电池的循环性能。

Description

纳米硅氧碳结构复合材料、其制备方法、负极和电化学装置
本申请是以CN申请号为202111438788.0，申请日为2021年11月27日的中国申请为基础，并主张其优先权，该CN申请的公开内容再次作为整体引入本申请中。
本申请是以CN申请号为202210114895.6，申请日为2022年01月31日的中国申请为基础，并主张其优先权，该CN申请的公开内容可以部分引入本申请中。
技术领域
本发明涉及电池材料技术领域，具体而言，涉及一种纳米硅氧碳结构复合材料、其制备方法、负极和电化学装置。
背景技术
锂离子电池在当今人类的生产生活中发挥着越来越重要的作用，其负极材料的性能如容量、首次库效率、循环性能等在很大程度上影响着电池的容量、能量密度和使用寿命。
传统的锂离子电池负极通常以碳材料作为活性成分，尤以石墨为典型，基于石墨的层间嵌锂机理，其理论克容量仅为372mAh/g，目前石墨负极的克容量已接近理论容量，这使得电池整体能量密度的提高受到较大的局限。因此有必要开发多种嵌锂机理的负极材料。其中，合金化嵌锂机理通常可以实现较大的嵌锂容量，如硅材料，其在嵌锂过程中形成锂硅合金Li xSi，x最高可达4.4，对应的硅负极理论容量达到4200mAh/g。此外，硅基材料具有接近锂金属的脱锂电位(＜0.5V v.s Li/Li +)，且环境友好，储量丰富，因而成为极具潜力的新一代高能量密度锂离子电池负极材料。但硅基负极材料存在一个严重的问题，即其在嵌锂和脱锂过程中发生较大的体积膨胀和收缩(满嵌锂状态，体积膨胀达300％)，这将导致电池容量衰减及电极粉化失效。由于硅材料较差的循环稳定性，其实际应用面临较大的技术瓶颈。
锂离子电池循环容量衰减的根本原因在于SEI膜的形成。锂离子电池在充电过程中，电解液中的电解质会与来自正极的锂离子在负极表面活性物质处发生反应，形成固体电解质界面(SEI)膜，直至完全覆盖电极与电解液接触面。SEI膜的形成是不可逆的，其对锂的消耗与电极上可逆的锂形成竞争，表现在第一次嵌锂-脱锂循环中，为脱锂容量低于嵌锂容量，即首次库仑效率(首效)低于100％。在首次充放电完成后，若能形成稳定的SEI膜，则后续容量不再明显衰减，电池循环性能较好。反之，若SEI膜受到破坏，则在暴露出的新鲜活性物质处会生成新的SEI膜，由是，正极可逆锂离子持续消耗，电池容量不断衰减。故化学和机械稳定的SEI膜对于锂离子电池保持较高的容量、能量密度和循环性能非常重要。
硅基负极材料在嵌脱锂过程中较大的体积效应，使得电极表面的SEI膜在循环充放电过程中持续受到破坏和再生，造成活性硅材料的腐蚀和电极容量持续衰减。另外，这种体积效应也易使负极活性材料逐渐粉化、结构坍塌，最终导致电极活性物质与集流体脱离而丧失电 接触，电池循环性能大大降低。因此，抑制硅颗粒在充放电过程中过大的体积效应始终是硅基负极材料研发中一个不可忽视的问题。
硅颗粒嵌锂至发生不可逆的破裂从而破坏SEI膜和/或自身粉碎，实质是一个不均匀膨胀累积的过程。锂嵌入期间，首先在硅颗粒表面硅原子处累积大量的锂，锂离子进而以缓慢的速率向颗粒内部迁移，即硅颗粒由内向外存在锂的梯度，产生不均匀的膨胀，这将导致硅颗粒的破裂。研究表明，纳米化的硅颗粒由于尺寸较小，可以弱化颗粒内锂离子梯度，且颗粒之间的间隙也有助于缓冲膨胀-收缩带来的体积效应，是降低负极极片膨胀、保持良好的电极性能的有效方法。
硅自身的电导率较低，通常与导电性好的碳材料复合以获得导电良好的复合电极材料，将硅纳米颗粒分散在多孔炭载体上，是常用的做法之一，炭载体的孔结构也可以起到缓解膨胀的作用，但多孔载体另一方面又造成复合材料比表面积增大，进而导致电极副反应增多，首次库仑效率降低，因此，如何实现多孔载体上硅纳米粒子的有效沉积和均匀分散，同时降低复合材料的比表面积，是硅碳复合材料制备的难点所在。
现有技术中，有研究者将硅烷气体通过气相沉积的方式沉积到多孔炭载体上，可以大批量制备纳米硅氧碳结构复合材料，并抑制硅粒子在充放电过程中过大的体积效应。如申请公布号为CN110112377A的中国专利申请公开了一种在多孔炭上沉积硅制备纳米硅碳结构复合材料的方法，当复合材料Si含量达到90％时，首次嵌锂容量可达到2414mAh/g，首效为82％，但循环性能较差，第五循环容量保持率仅为48％。申请公布号为CN110582823A的中国专利申请公开了一种在多孔炭上先后或同时沉积硅和烃类炭的方法，在控制复合材料中Si含量约为50％的条件下，所得纳米硅碳结构复合材料容量达到2082mAh/g，首效82％，第7-10次循环的平均库仑效率为98％。
现有技术中硅碳复合材料首效和循环效率相对较低，有两方面的原因，一方面直接在碳材料上沉积硅烷气体，由于C和Si之间缺乏键联，多孔炭基底位于孔内的表面难以实现有效硅沉积，材料比表面积较大，电极表面副反应多，电池首效较低；另一方面，也是更重要的，SiH 4分解是一个热聚合的链反应过程，首先在碳颗粒上易于接触的表面成核，然后极易在已形成的硅核上快速长大，硅烷沉积过程中硅纳米颗粒生长不易控制，尺寸较大，这导致复合材料电极在充放电过程中由于锂硅合金化反应而发生显著的体积膨胀，进而导致循环过程中SEI膜反复破坏和再生，消耗正极的可逆锂，电池循环性能变差。此外，硅碳复合材料在充放电过程中，随着锂硅合金化正逆反应的进行，相邻的硅颗粒之间会发生融并，导致复合材料中硅颗粒进一步长大，电极循环性能恶化。如何成功制备小尺寸硅纳米颗粒均匀分散的硅碳复合材料，并防止硅纳米颗粒在电极反应过程中融并成为大颗粒，目前尚未有研究报道和相关专利公开。
发明内容
本发明的主要目的在于提供一种纳米硅氧碳结构复合材料、其制备方法、负极和电化学装置，以解决现有技术中的硅碳复合材料电极体积膨胀导致电池循环性能变差的问题，从材 料的角度来讲是要解决现有技术中硅碳复合材料结构和制备方法不易获得均匀分散硅纳米颗粒的问题。
为了实现上述目的，根据本发明的一个方面，提供了一种纳米硅氧碳结构复合材料，复合材料包括(C x1-O y1)-(Si z-O y2-C x2)，其中，C x1-O y1为含表面氧化层的多孔炭基底，包括多孔炭基底及其表面氧化层，x1为碳的化学计量数，y1为表面氧化层中氧的化学计量数，0.001≤y1/x1≤0.05；Si z-O y2-C x2包括硅纳米颗粒、含氧物质和可选的碳，硅纳米颗粒、含氧物质和可选的碳分散分布在含表面氧化层的多孔炭基底的表面和/或孔道内，含氧物质以SiO δ形式存在，0＜δ≤2，0.1≤z/x1≤2，0.01≤y2/z≤0.15，0≤x2/z≤0.15；Si z-O y2-C x2可视为Si-O-C(Si-SiO δ-C)结构单元的重复，可写作(Si z1-O y-C x) n，n≥1。
根据本发明的另一方面，提供了一种纳米硅氧碳结构复合材料的制备方法，制备方法包括：步骤S1，提供含表面氧化层的多孔炭基底，含表面氧化层的多孔炭基底中氧与碳的摩尔比为0.001～0.05；步骤S2，将含硅前体和含氧前体通入放置有含表面氧化层的多孔炭基底的反应炉中，并在150～700℃下与含表面氧化层的多孔炭基底接触进行热处理5～100h，使硅与含氧物质和可选的碳分散沉积到多孔炭基底的表面和/或孔道内，得到纳米硅氧碳结构复合材料。
根据本发明的另一方面，提供了一种负极，包括负极材料，该负极材料为上述任一种的纳米硅氧碳结构复合材料或者上述任一种的制备方法得到的纳米硅氧碳结构复合材料。
根据本发明的另一方面，提供了一种电化学装置，包含负极，该负极为上述任一种负极，优选电化学装置为锂离子二次电池。
应用本发明的技术方案，本申请的纳米硅氧碳结构复合材料中硅纳米颗粒均匀分散，且由含氧物质和可选的碳分隔和束缚，因此有效抑制了硅粒子在沉积过程中的团聚及其在充放电循环中的体积变化和可能的融并，包含由所得复合材料制备的负极的锂离子二次电池具有较高的克容量、较高的首次库仑效率和良好的循环性能。
上述制备方法以含表面氧化层的多孔炭基底为载体和/或支架，在其表面和孔结构中进行硅纳米颗粒和含氧物质和可选的碳的沉积，其中含氧物质和可选的碳起到分隔和束缚硅纳米颗粒沉积层的作用，沉积最后可能会在多孔炭基底的孔道内留有少量闭孔。因而所得到的纳米硅氧碳结构复合材料中均匀分散的、被束缚的硅纳米颗粒在嵌锂和脱锂过程中的体积效应可以得到有效缓冲，且硅纳米颗粒在充放电过程中的融并现象得到抑制，材料强度提高，有助于提升包含该硅氧碳复合负极材料的电化学装置的电化学性能。
根据本发明的另一目的在于提供一种纳米硅氧碳复合材料、其制备方法、负极和电化学装置，以解决现有技术中的硅碳复合材料电极体积膨胀导致电池循环性能变差的问题。
(一)技术方案
为实现以上目的，本发明通过以下技术方案予以实现：
在本发明一种典型的实施方式中，提供了一种纳米硅氧碳复合材料，所述纳米硅氧碳复合材料包括多孔炭骨架(相当于前述的多孔炭基底)、硅纳米粒子和SiO δ(0＜δ≤2)，所述纳米硅氧碳复合材料中硅元素的含量为25～75wt％，氧元素的含量为0.5～10wt％；所述纳米硅氧碳复合材料的N 2吸附BET比表面积为0.01～10m 2/g，按照N 2分压大于0.999处点的吸附量测得的总孔容为0.001～0.05cm 3/g；所述硅纳米粒子由所述SiO δ的网络分隔和/或包裹，所述硅纳米粒子和所述SiO δ分布在所述多孔炭骨架的表面和/或孔道内，所述多孔炭骨架与硅纳米粒子之间通过C-O-Si键相连接。
在一些实施例中，控制纳米硅氧碳复合材料中硅元素的含量为30～65wt％，碳元素的含量为30～65wt％，氧元素的含量为0.5～5wt％，其它元素的含量为0～5wt％。
在一些实施例中，对纳米硅氧碳复合材料进行XPS测试，以Al Kα作为放射源，以C 1s谱中无定形C-C峰结合能位于284.7eV为峰位校准，由于高分辨C 1s谱中包含测试系统中存在的C-C峰，其C-Si的分析存在较大误差，因此仅分析其高分辨Si 2p谱。对所述纳米硅氧碳复合材料的XPS测试高分辨Si 2p谱进行去卷积分峰分析的结果包括，结合能峰值位于103±0.5eV的Si-O的峰面积与结合能峰值位于99±0.5eV的Si-Si的峰面积之比为0.5～2，优选为0.8～1.5；结合能峰值位于100.5±0.5eV的Si-C的峰面积与结合能峰值位于99±0.5eV的Si-Si的峰面积之比为0.01～1，优选为0.01～0.5。根据相应的峰面积计算可得各键合形式所占比例。
在一些实施例中，所述纳米硅氧碳复合材料中多孔炭骨架孔结构中2～10nm孔体积占总孔体积的比例大于50％，优选地，所述纳米硅氧碳复合材料中多孔炭骨架孔结构中2～10nm孔体积占总孔体积的比例大于80％。所述纳米硅氧碳复合材料中多孔炭骨架的孔结构可以是在制备过程前期获得多孔炭骨架后测试获得也可以采用HF和高浓度NaOH溶液等将所述纳米硅氧碳复合材料中的Si和SiO δ刻蚀后对剩余多孔炭骨架进行测试获得，后者由于刻蚀程度以及可能产生新孔而导致对纳米硅氧碳复合材料中多孔炭骨架的孔结构的了解产生一定偏差，但也可以在一定范围内反映其性质。
在一些实施例中，所述硅纳米粒子包括硅晶粒和/或非晶硅，优选硅晶粒尺寸小于5nm，进一步优选硅晶粒的尺寸小于2nm。通过XRD衍射结果中位于2θ＝28.4°的Si晶特征峰的半峰宽来计算，所用公式为谢乐公式。由于炭材料在2θ＝26.6°附近存在衍射，无定形炭通常表现为一个峰包，对晶粒尺寸小于2nm或接近非晶的硅纳米粒子，其2θ＝28.4°处的Si晶特征峰与炭衍射峰相重叠，故XRD衍射结果中无明显的Si结晶峰。也可通过高分辨TEM来观察硅纳米粒子的形貌，通过其与Si晶体相符合的一组晶格条纹中晶格条纹的数目来判断单个硅纳米粒子的大小。Si晶体中最强衍射峰2θ＝28.4°对应Si(111)的晶面间距为0.312nm，当有序的晶格条纹小于6条时，相应硅晶粒尺寸小于2nm。
另一方面，虽然所述硅氧碳材料表现为非晶硅或尺寸小于2nm的硅晶粒，但在电极电化学过程中，硅晶粒可能会发生重组从而融并形成较大的颗粒，影响电极的循环性能，鉴于此，本发明提供了一种加速老化以分析硅纳米粒子聚集情况的方法，即通过将纳米硅氧碳结构复合材料在N 2气氛下升高温度处理，并进行XRD测试，分析其硅晶粒长大情况。经测 试，复合材料在700℃、800℃、900℃进行进一步处理，700℃处理后在2θ＝28.4°处表现出一定的结晶峰，说明Si晶开始形成，800℃处理后XRD曲线中硅结晶峰强度增加，900℃处理的复合材料样品中Si结晶峰与800℃处理后的结果基本相同，说明Si晶粒的长大达到极限。根据硅结晶峰的半峰宽可以计算高温处理后的晶粒尺寸，从而间接反映Si晶粒在电化学过程中融并聚集所能达到的程度。本发明中通过引入含氧物质分散硅纳米粒子并阻止其进一步聚集长大，多孔炭骨架的孔道结构也最终束缚着硅纳米粒子的尺寸。如上所述，本发明通过对复合材料进行N 2气氛下、800℃处理后的XRD结果来估算纳米硅氧碳结构复合材料中硅纳米粒子在电化学过程中增大的极限尺寸，优选控制硅纳米粒子在电化学过程中增大的极限尺寸小于10nm。
完全密实的材料对于抑制锂硅合金体积效应的作用是有限的，复合材料中适量闭孔有利于缓解硅的体积效应，所述闭孔为封闭在复合材料表面内部、孔的任何一点均不与材料表面相接触的孔，所述表面为N 2分子可以接触到的表面，即所述闭孔为N 2分子无法进入的孔或者是基本无法进入的孔，这些封闭在复合材料内部的孔可以为硅嵌锂的体积膨胀提供缓冲空间。但过多闭孔则导致材料体积增大，从而体积比容量降低，更重要的是，过多闭孔导致复合材料结构强度降低，在后续压片过程中可能导致结构坍塌，因此闭孔量不宜太多。闭孔不能由常规的物理吸附方法获得，因为其属于吸附分子无法或基本无法直接到达的区域，如N 2吸附能够只能检测到开孔及其表面积，这一部分孔及表面会与电解液接触，不利于材料的电极性能。闭孔的检测通过复合材料真密度的测量来反推，当材料真密度小于元素组成相同的完全密实材料的真密度时，说明存在闭孔，闭孔容积为复合材料真密度的倒数(闭孔+骨架的体积)减去元素组成相同的完全密实材料的真密度的倒数(骨架体积)。纯石墨和硅的密度均大于2.2g/cm 3。复合材料的真密度可通过氦气置换法和/或比重瓶法(丙酮浸液法)测试获得。本申请采用比重瓶法测量复合材料的真密度，在一些实施例中，纳米硅氧碳复合材料的真密度为1.8～2.1g/cm 3，说明具有一定量的闭孔。
在一些实施例中，所述纳米硅氧碳复合材料还包括包覆层，所述包覆层包括固体电解质和/或导电聚合物。具体的固体电解质和导电聚合物可以参考现有技术，本申请不再赘述。
为了提高复合材料的压实密度，可以通过破碎等方式控制复合材料的中位粒径D 50，在一些实施例中，复合材料的中位粒径D 50在2～12μm之间。
在本发明另一种典型的实施方式中，提供所述纳米硅氧碳复合材料的制备方法，其特征在于，所述制备方法包括：步骤S1，将碳前驱体和造孔剂混合炭化后形成多孔炭骨架材料，并对其进行破碎和氧化处理，得到具有合适比表面和孔结构的含表面氧化层的多孔炭骨架；步骤S2，将步骤S1所得含表面氧化层的多孔炭骨架抽真空，将含硅前体和含氧前体通入放置有所述含表面氧化层的多孔炭骨架的反应炉中，并与所述含表面氧化层的多孔炭骨架接触，使硅与含氧物质分散沉积到多孔炭骨架的表面和/或孔道内；并对所得材料进行破碎整形，得到纳米硅氧碳复合材料1；步骤S3，对步骤S2所得纳米硅氧碳复合材料1然后进行深度氧化处理，得到纳米硅氧碳复合材料。
上述反应炉为回转炉、钢包炉、内胆炉、辊道窑、推板窑、气氛箱式炉或管式炉中的任 意一种或多种的组合；其中步骤S2和S3中，固气两相接触方式为固定床、移动床、流化床、沸腾床等多种方式中的任意一种或多种的组合。
在一些实施例中，所述步骤S1中所述含表面氧化层的多孔炭骨架的粒径为5～50μm，所述含表面氧化层的多孔炭骨架的比表面积为50～2000m 2/g、孔容为0.1～3.0cm 3/g，所述含表面氧化层的多孔炭骨架的孔结构中2～10nm孔体积占总孔体积的比例大于50％；和/或所述步骤S2具体包括将步骤S1所述含表面氧化层的多孔炭骨架抽真空至真空度低于10 -2Pa，优选低于10 -6Pa，将含硅前体和含氧前体通入放置有所述含表面氧化层的多孔炭骨架的反应炉中，并在150～700℃下与所述含表面氧化层的多孔炭骨架接触5～100h，使硅与含氧物质分散沉积到多孔炭骨架的表面和/或孔道内；并对所得材料进行破碎整形，得到中位粒径为2～12μm的纳米硅氧碳复合材料1；和/或所述步骤S3中所述深度氧化处理包括将纳米硅氧碳复合材料1与包含氧化性物质的溶液和/或气体于0～400℃接触0.5～12h。
多孔炭骨架的孔尺寸分布在很大程度上影响硅纳米粒子的尺寸，合适的多孔炭骨架应含有较多介孔(孔径2～50nm)，并含有少量微孔(孔径小于2nm)和大孔(孔径大于50nm)，介孔和大孔应是硅沉积的主要区域，但过多的大孔易造成硅纳米粒子聚集长大。在一些实施例中，本发明中所述含表面氧化层的多孔炭骨架的比表面积为50～2000m 2/g、孔容为0.1～3.0cm 3/g，所述表面氧化层的多孔炭骨架的粒径为5～50μm；所述含表面氧化层的多孔多孔炭骨架的孔结构中微孔孔容在总孔容中的比例为1～20％，介孔孔容在总孔容中的比例为40～90％，大孔孔容在总孔容中的比例为0～10％；所述含表面氧化层的多孔炭骨架的孔结构中2～10nm孔体积占总孔体积的比例大于50％，优选地，2～10nm孔体积占总孔体积的比例大于80％。
本发明的上述含表面氧化层的多孔炭骨架的制备方法可以根据不同的碳前驱体和/或多孔炭骨架来选择相应的实现方式。
在一些实施例中，所述步骤S1中多孔炭骨架材料由碳前驱体与造孔剂的均匀混合物共同炭化形成；所述碳前驱体选自葡萄糖、果糖、蔗糖、麦牙糖、乳糖、环糊精、淀粉、糖原、纤维素、半纤维素、木质素、不饱和聚酯树脂、环氧树脂、热塑性酚醛树脂、热固性酚醛树脂、聚甲醛树脂、脲醛树脂、糠醛树脂、糠酮树脂、丙烯酸树脂、聚酰胺、聚酰亚胺、沥青中的一种或多种；所述造孔剂选自十二烷基苯磺酸钠、十六烷基三甲基溴化铵、聚乙二醇、聚乙烯醇、聚乙烯吡咯烷酮、油酸、油胺、聚环氧乙烷-聚环氧丙烷-聚环氧乙烷三嵌段共聚物、柠檬酸、苹果酸、琥珀酸、NH 4HCO 3、(NH 4) 2CO 3、HNO 3、H 2SO 4、LiOH、NaOH、KOH等中的一种或多种，优选地，所述聚环氧乙烷-聚环氧丙烷-聚环氧乙烷三嵌段共聚物选自P123、F127和/或F108。碳前驱体与造孔剂的混合可以采用本领域技术人员熟知的方式，在一些实施例中，碳前驱体与造孔剂采用湿法球磨和/或干法球磨混合，在一些实施例中，碳前驱体与造孔剂共同溶解于水和/或乙醇中，通过超声和/或搅拌等方式充分混合后干燥。碳前驱体与造孔剂混合后先进行预稳定化，再进行炭化。预稳定化和炭化均为炭材料制备过程中的常规步骤。预稳定化在氧化性气氛中进行，温度为100～300℃，时间为0.1～48h；炭化在惰性气体中进行，温度为600～1800℃、时间为0.5～10h，进一步优选炭化的温度为800～1500℃、时间为2～5h。
对多孔炭骨架材料进行氧化处理以产生表面氧化层从而促进含硅前体的有效沉积，所述 氧化处理包括液相氧化和/或气相氧化。优选地，所述步骤S1中对多孔炭骨架材料的氧化处理方法包括液相氧化和/或气相氧化；优选地，所述液相氧化的步骤为，将多孔炭骨架材料置于含氧化合物和/或含氧化合物的水和/或乙醇溶液中，超声分散0.5～2h后，于0～50℃搅拌0.5～12h，过滤和/或离心使固液分离，用去离子水和/或乙醇多次洗涤固体，并将所得固体进行真空干燥和焙烧，所述含氧化合物选自HNO 3、H 2SO 4、乙酸、丙酸、丁醇、丁酸、丁二酸、苹果酸、柠檬酸中的任意一种或多种；优选地，所述气相氧化的步骤为，将多孔炭骨架材料抽真空至真空度低于10 -2Pa，然后通入包含氧化性气体和惰性气体的混合气，于300～1600℃接触0.1～5h，优选地，于600～900℃接触2～4h；所述氧化性气体选自二氧化碳、水蒸气、甲醇、乙醇、乙酸、丙醇、丁醇、丙酮中的任意一种或多种，惰性气体为氮气、氩气、氦气中的一种或多种，所述氧化性气体占所述混合气的比例为0.5～20％。
在一些实施例中，所述步骤S2的实施过程中，所述含硅前体和所述含氧前体以任意体积比组合；优选地，所述含硅前体选自甲硅烷、乙硅烷、丙硅烷、卤代硅烷、聚硅烷、聚甲基硅烷、噻咯及其衍生物、硅芴及其衍生物中的一种或多种；优选地，所述含氧前体为氧气、二氧化碳、水蒸气、甲醇、乙醇、正丙醇、异丙醇、丁醇、丙酮、丁酮中的一种或多种；优选地，所述含硅前体和含氧前体的体积比和气相沉积温度均随着通入时间的延长存在间歇和/或周期性变化；优选地，改变气体组分前均进行抽真空处理，至真空度低于10 -2Pa。
在一些实施例中，步骤S2在通入含硅前体和含氧前体同时通入惰性气体，以调节含硅前体和含氧前体的浓度，并提供合适的压力，惰性气体为氮气、氩气、氦气中的一种或多种。当含硅前体和含氧前体与惰性气体同时通入时，三者可以混合的方式通入或者分别通入后在反应炉中形成混合气，无论是何种情况，只要含硅前体和含氧前体与惰性气体同时通入时，都称为通入含硅前体和含氧前体与惰性气体的第一混合气时，含氧前体为甲醇、乙醇、正丙醇、异丙醇、丁醇、丙酮、丁酮中的一种或多种。第一混合气中含硅前体的体积含量为1～50％，含氧前体的体积含量为0.5～10％；优选地，第一混合气通入时热处理的温度为400～700℃，进一步优选地，第一混合气通入时热处理的时间为5～50h。
在一些实施例中，步骤S2在通入含硅前体和含氧前体之前、之后、同时或间隙通入惰性气体，惰性气体为氮气、氩气、氦气中的一种或多种。以调节含硅前体和含氧前体的浓度，并提供合适的压力。当含硅前体和惰性气体同时通入时，二者可以以混合的方式通入或者分别通入后在反应炉中形成混合气，无论是何种情况，只要含硅前体和惰性气体同时通入时，都称为通入含硅前体与惰性气体的第二混合气时，第二混合气中所述硅前体的体积含量为1～50％。当含氧前体和惰性气体同时通入时，二者可以以混合的方式通入或者分别通入后在反应炉中形成混合气，无论是何种情况，只要含氧前体和惰性气体同时通入时，都称为通入含氧前体与惰性气体的第三混合气时，第三混合气中含氧前体的体积含量为1～50％。
在一些实施例中，上述步骤S2包括：步骤S2-1，将惰性气体通入放置有含表面氧化层的多孔炭骨架的反应炉中，并将反应炉的温度升至400～700℃；步骤S2-2，通入含硅前体与惰性气体的第二混合气，第二混合气中含硅前体的体积浓度为1％～50％，并将反应炉在400～700℃保持0.5～15h；步骤S2-3，停止通入含硅前体，将反应炉的温度调节至 150～600℃；步骤S2-4，通入含氧前体与惰性气体的第三混合气，第三混合气中含氧前体的体积浓度为1％～50％，并将反应炉在150～600℃保持0.1～5h；步骤S2-5，重复2～50次步骤S2-1至步骤S2-4；步骤S2-6，对所得材料进行破碎整形，得到中位粒径为2～12μm的纳米硅氧碳复合材料1，所述破碎整形通过气流磨、干法球磨、湿法球磨等方式中的一种或多种进行。
在一些实施例中，步骤S3所述深度氧化处理包括液相氧化和/或气相氧化；优选地，所述液相氧化的步骤为，将纳米硅氧碳复合材料1置于氧化性物质和/或氧化性物质的水和/或乙醇溶液中，超声分散0.5～2h后，于0～50℃搅拌0.5～12h，过滤和/或离心使固液分离，用去离子水和/或乙醇多次洗涤固体，并将所得固体于40～200℃鼓风干燥0.5～24h后，于惰性气氛中200～400℃处理0.5～5h，所述含氧化合物选自KMnO 4、H 2O 2、HNO 3、H 2SO 4、乙酸、丙酸、丁酸、丁二酸、苹果酸、柠檬酸中的任意一种或多种，所述液相氧化在紫外光和/或微波辐射的作用下进行；优选地，所述气相氧化的步骤为，将纳米硅氧碳复合材料1抽真空至真空度低于10 -2Pa，然后通入包含氧化性气体和惰性气体的混合气，控制升温速率为1～10℃/min，从室温升至200～400℃，并于200～400℃处理0.1～5h，所述氧化性气体选自氧气、臭氧、二氧化碳、水蒸气中的任意一种或多种，所述惰性气体为氮气、氩气、氦气中的一种或多种，所述氧化性气体占所述混合气的比例为0.5～20％。
在一些实施例中，在步骤S3之前，增加对步骤S2破碎得到的所述纳米硅氧碳复合材料1的酸处理和/或碱处理过程；优选地，所述酸处理的方法为，将所述纳米硅氧碳复合材料1分散至含酸的水/乙醇溶液中，于0～50℃搅拌0.5～12h，过滤和/或离心使固液分离，用去离子水和/或乙醇多次洗涤固体至滤液和/或上清液pH为中性，对所得固体进行真空干燥；所述碱处理的方法为，将所述纳米硅氧碳复合材料1分散至含碱的水/乙醇溶液中，于0～50℃搅拌0.5～12h，过滤和/或离心使固液分离，用去离子水和/或乙醇多次洗涤固体至滤液和/或上清液pH为中性，对所得固体进行真空干燥；所述酸为HCl、H 2SO 4、HNO 3、H 3PO 4中的一种或多种，所述碱为NaOH、KOH、Na 2CO 3、K 2CO 3、NH 3H 2O、NH 4HCO 3、(NH 4) 2CO 3、尿素等中的一种或多种。
在一些实施例中，在步骤S3之后，对所得纳米硅氧碳复合材料进行真空处理及碳包覆，所述碳包覆的方式为采用甲烷、乙烷、丙烷、丁烷、乙烯、丙烯、丁烯、乙炔、丙炔、甲醇、乙醇、正丙醇、异丙醇、丁醇、丙酮、丁酮中的一种或多种，对所得纳米硅氧碳复合材料进行气相沉积，或采用液体碳前驱体进行液相碳包覆，优选地，所述液体碳前驱体选自树脂、沥青等。
在一些实施例中，所述制备方法还包括在所述纳米硅氧碳复合材料上包裹固体电解质和/或导电聚合物的步骤。
在本发明另一种典型的实施方式中，提供了纳米硅氧碳复合材料在制备负极材料方面的应用，所述纳米硅氧碳复合材料为上述所述的纳米硅氧碳复合材料或者上述任一项所述的制备方法得到的纳米硅氧碳复合材料。
在本发明另一种典型的实施方式中，提供了一种负极，包括负极材料，所述负极材料为上述所述的纳米硅氧碳复合材料或者上述任一项所述的制备方法得到的纳米硅氧碳复合材料。
在本发明另一种典型的实施方式中，本发明提供了一种电化学装置，其包含负极，所述负极为上述的负极；优选地，所述电化学装置为锂离子二次电池。
(二)有益效果
与现有技术相比，具备以下有益效果：
应用本发明的技术方案，本申请的纳米硅氧碳复合材料中多孔炭载体和硅粒子之间通过C-O-Si形成稳定的结合，硅纳米粒子均匀分散于炭载体的孔道内和表面，且由含氧物质分隔和束缚，因此有效抑制了硅粒子在沉积过程中的团聚及其在充放电循环中的体积变化和可能的融并，包含由所得复合材料制备的负极的锂离子二次电池同时具有较高的克容量、较高的首次库仑效率和良好的循环性能等优良特性。
附图说明
构成本申请的一部分的说明书附图用来提供对本发明的进一步理解，本发明的示意性实施例及其说明用于解释本发明，并不构成对本发明的不当限定。在附图中：
图1示出了根据本发明的实施例1所得纳米硅氧碳结构复合材料的结构示意图；
图2示出了根据本发明的实施例1所得纳米硅氧碳结构复合材料的XRD衍射图；
图3示出了根据本发明的实施例1所得纳米硅氧碳结构复合材料的HRTEM图；
图4示出了包含本发明的实施例1所得纳米硅氧碳结构复合材料的电极、包含实施例23复合材料的电极和包含对比例2复合材料的电极的恒流充放电曲线；
图5示出了根据本发明的实施例1、实施例23所得纳米硅氧碳结构复合材料以及对比例2复合材料经800℃、N 2气氛中处理后的XRD谱图；
图6示出了包含实施例1的纳米硅氧碳结构复合材料的电极和包含对比例2的复合材料电极的半电池循环性能测试结果；
图7示出了根据本发明的实施例26所得纳米硅氧碳结构复合材料的结构示意图；以及
图8示出了根据本发明的实施例26所得纳米硅氧碳结构复合材料的XPS测试高分辨Si 2p谱及其去卷积分峰分析结果图；
图9为本发明纳米硅氧碳复合材料的结构示意图；
图10为实施例1所得纳米硅氧碳复合材料的XPS测试高分辨Si 2p谱及其去卷积分峰分析结果；
图11为实施例1所得纳米硅氧碳复合材料及其在N 2气氛中、800℃处理后所得材料的XRD图谱；
图12为实施例1所得纳米硅氧碳复合材料的高分辨TEM图像；
图13为包含实施例1所得纳米硅氧碳复合材料的电极的半电池测试结果之首次恒流充放电曲线；
图14为包含实施例1所得纳米硅氧碳复合材料的电极和包含对比例2所得硅氧碳复合材料的电极的半电池循环性能测试结果。
具体实施方式
需要说明的是，在不冲突的情况下，本申请中的实施例及实施例中的特征可以相互组合。下面将参考附图并结合实施例来详细说明本发明。
如本申请背景所分析的，现有技术中硅碳复合材料在制备过程中难以实现多孔载体上硅纳米颗粒的有效沉积和均匀分散，因而难以抑制电极在充放电过程中发生显著的体积膨胀与收缩，最终导致电极循环性能恶化。此外在电池充放电过程中，相邻的硅颗粒之间可能发生融并，导致电极循环性能进一步变差。为了控制硅碳复合材料在制备过程中硅纳米粒子的快速长大和团聚，从而获得含均匀分散硅纳米颗粒的复合材料，并控制电极充放电过程中的体积效应及相邻硅纳米颗粒的融并，本申请提供了一种纳米硅氧碳结构复合材料、其制备方法、负极和电化学装置。
在本申请一种典型的实施方式中，提供了一种纳米硅氧碳结构复合材料，该复合材料包括(C x1-O y1)-(Si z-O y2-C x2)，其中，C x1-O y1为含表面氧化层的多孔炭基底，包括多孔炭基底及其表面氧化层，x1为碳的化学计量数，y1为表面氧化层中氧的化学计量数，0.001≤y1/x1≤0.05；Si z-O y2-C x2包括硅纳米颗粒、含氧物质和可选的碳，其硅纳米颗粒、含氧物质和可选的碳分散分布在含表面氧化层的多孔炭基底的表面和/或孔道内，含氧物质以SiO δ形式存在，0＜δ≤2，0.1≤z/x1≤2，0.01≤y2/z≤0.15，0≤x2/z≤0.15。
本申请的纳米硅氧碳结构复合材料中硅纳米颗粒均匀分散，且由含氧物质和可选的碳分隔和束缚，因此有效抑制了硅纳米粒子在沉积过程中的团聚及其在充放电循环中的体积变化和可能的融并，包含由所得复合材料制备的负极的锂离子二次电池具有较高的克容量、较高的首次库仑效率和良好的循环性能。
上述C x1-O y1为含表面氧化层的多孔炭基底，包括多孔炭基底及其表面氧化层，以碳物质C为主，表面氧化层可以通过多孔炭基底在不完全炭化后表面残留的少量含氧官能团形成和/或对多孔炭基底进行氧化处理后形成，其作用在于通过形成C-O-Si化学作用提供更好的硅沉积位点。x1为其中碳的化学计量数，在分子式中只是一个代数，目的是为了更好地表达相关物质含量。多孔炭基底中表面氧化层的含量用其中氧元素与多孔炭基底中碳元素的摩尔比值y1/x1来定义和表达，0.001≤y1/x1≤0.05。y1/x1过大则多余的氧在嵌锂过程中与锂发生不可逆 反应，造成可逆锂容量的损失，电池首效和循环效率降低；过小则无法形成有效的C-O-Si化学接触和/或键合，后续硅沉积过程易形成较大的硅颗粒聚集。
上述Si z-O y2-C x2为上述多孔炭基底C x1-O y1孔道内和表面均匀分散的硅纳米颗粒及含氧物质和可选的碳，硅纳米颗粒与含氧物质和可选的碳均匀地交错存在，含氧物质以SiO δ(0＜δ≤2)形式存在，该Si z-O y2-C x2结构组分可视为Si-O-C(Si-SiO δ-C)结构单元的重复，可写作(Si z1-O y-C x) n，n≥1，如附图1中示意图所示。由于硅烷分解是一个热聚合的链反应过程，不加控制的结果是硅烷迅速聚集长大，本发明中Si纳米颗粒之间存在含氧物质和可选的碳，即用少量含氧物质和可选的碳分散、束缚硅纳米颗粒，避免其在沉积过程中不受控制的聚集长大，并有效控制其在充放电过程中硅的体积膨胀和收缩以及硅颗粒之间的融并。硅的负载量需在一个合适的范围内方能获得较高的复合材料克容量和较高的首效，本发明控制0.1≤z/x1≤2，优选为0.2≤z/x1≤1，更优选为0.3≤z/x1≤0.6。利用上述z/x1的值控制复合材料的理化性质，避免以下：硅负载量过低则不足以获得较高的复合材料克容量，且多孔炭基底尚有较多孔结构保留，最终产品比表面积增大，电池首效降低，同时也会导致材料强度降低，在压片和电极反应过程中容易发生结构坍塌；硅负载量过高则容易导致硅颗粒在多孔炭基底外表面聚集长大，较大的硅颗粒无法有效控制复合材料电极在充放电过程中的体积效应，电池循环性能下降。
Si z-O y2-C x2中含氧物质和可选的碳用于分散硅颗粒，实现硅颗粒的纳米化，同时也起到束缚硅纳米颗粒的作用。含氧物质以SiO δ形式存在于纳米硅氧碳结构复合材料中，可以束缚硅纳米颗粒在充放电过程中的体积膨胀和收缩，并防止硅纳米颗粒在充放电过程中融并形成大颗粒，造成电极循环性能恶化。含氧物质和可选的碳的量不宜过多，过多会导致整体Si含量下降，复合材料电极克容量和首效均降低；过少则无法起到有效的分散和束缚作用，因此控制0.01≤y2/z≤0.15，0≤x2/z≤0.15。
综合以上，本发明提供纳米硅氧碳结构复合材料，包括含表面氧化层的多孔炭基底C x1-O y1、及其孔道内部和外表面均匀分散的Si z-O y2-C x2两个结构组成部分，其多孔炭基底的表面氧化层有助于C-O-Si的形成，从而实现更稳定的硅负载；Si z-O y2-C x2中，硅纳米颗粒与含氧物质和可选的碳均匀分散，含氧物质和可选的碳对硅物质进行分隔，形成类似(Si z1-O y-C x) n(n≥1)的重复结构，实现硅颗粒有效纳米化和均匀分散，同时含氧物质和可选的碳也起到对硅颗粒的束缚作用。
如上，当复合材料中氧材料的含量控制在更合适的范围时，可避免氧含量过高导致整体Si含量下降、电极克容量和首效降低，以及过低时无法起到有效的分散和束缚硅颗粒的作用的问题。在一些实施例中，复合材料的总氧含量在0.5wt％～5wt％。
在一些实施例中，对纳米硅氧碳结构复合材料的XPS测试高分辨Si 2p谱进行去卷积分峰分析的结果包括，结合能峰值位于103±0.5eV的Si-O的峰面积与结合能峰值位于99±0.5eV的Si-Si的峰面积之比为0.5～2，优选为0.8～1.5；结合能峰值位于100.5±0.5eV的Si-C的峰面积与结合能峰值位于99±0.5eV的Si-Si的峰面积之比为0.01～1，优选为0.01～0.5。根据相应的峰面积计算可得各键合形式所占比例。
在一些实施例中，纳米硅氧碳结构复合材料中硅纳米颗粒包括硅晶粒和/或非晶硅，优选硅晶粒尺寸小于5nm，进一步优选硅晶粒的尺寸小于2nm。通过XRD衍射结果中位于2θ＝28.4°的Si晶特征峰的半峰宽来计算，所用公式为谢乐公式。由于炭材料在2θ＝26.6°附近存在衍射，无定形炭通常表现为一个峰包，对晶粒尺寸小于2nm或接近非晶的硅纳米粒子，其2θ＝28.4°处的Si晶特征峰与炭衍射峰相重叠，故XRD衍射结果中无明显的Si结晶峰。事实上，本发明中通过硅烷气相沉积获得的硅氧碳材料的XRD衍射结果中均无明显的Si结晶峰，即通常为非晶硅(如附图2)，TEM(附图3)也显示，纳米硅氧碳结构复合材料主要呈无定形结构，存在少数极小的硅晶粒，其晶格条纹间距约为0.314nm，接近Si(111)的晶面间距。有序的晶格条纹仅为4-5个，相应硅晶粒尺寸小于2nm。
但另一方面，虽硅氧碳材料均表现为非晶硅，仍会因氧含量的不同而表现出截然不同的电化学性质(附图4)，不仅体现在上述氧含量可能导致容量和首效的不同上，更为显著的是氧含量高的复合材料表现出明显的斜坡型脱锂曲线，推测与不同复合材料中硅粒子的聚集状态(硅纳米颗粒的尺寸)有关。由于纳米硅氧碳结构复合材料为致密材料，硅氧碳均匀分布，无法通过SEM和TEM观察准确获得硅粒子聚集状态，鉴于此，本发明提供了一种间接分析硅粒子聚集状态的方法，其结果可与复合材料电化学性能有效关联，即通过将纳米硅氧碳结构复合材料在N 2气氛下、800℃处理，并进行XRD测试，分析其硅晶粒长大情况。经测试，复合材料在700℃、800℃、900℃进行进一步处理，800℃处理后XRD曲线中硅结晶峰基本稳定，不再因温度升高而改变。纳米硅氧碳结构复合材料中硅颗粒在高温条件下发生非晶向晶体的转变，并进一步发生晶粒长大，而复合材料中的多孔炭基底在这一处理条件下尚不至于发生明显的变化，仍为无定形碳材料，此时，从硅结晶峰的半峰宽可以计算高温处理后的晶粒尺寸，从硅结晶峰与无定形碳峰的相对强度可以推测参与结晶的晶粒多少，由此间接反映纳米硅氧碳结构复合材料中硅粒子的聚集状态。高温处理后XRD测试结果显示在附图5中，可以看出，氧含量越高，高温处理后硅晶粒尺寸越小，结晶程度也越低，反映了复合材料中硅纳米颗粒尺寸越小，相应地，附图4充放电曲线中表现为斜率越大的脱锂曲线。
硅纳米颗粒越小防止颗粒内部不均匀形变梯度产生不可逆的破坏的效果越好，且当其均匀分散于多孔炭载体中时，炭载体中的类石墨结构和其孔结构可为硅嵌锂时的体积膨胀提供一定的缓冲。但是，难以避免地，复合材料制备过程中硅晶粒会存在一定程度的聚集而形成较大的硅纳米颗粒。本发明中，主要通过引入含氧物质和可选的碳，分散硅纳米颗粒并阻止其进一步聚集长大；此外，多孔炭基底的孔道结构也最终束缚着硅纳粒度颗粒的尺寸。如上，硅颗粒的大小难于直接检测确定，本发明通过对复合材料进行N 2气氛下、800℃处理后的XRD结果来估算纳米硅氧碳结构复合材料中硅纳米颗粒的尺寸。优选控制硅纳米颗粒尺寸小于20nm，进一步优选硅纳米颗粒尺寸小于10nm。
过大的比表面积将导致复合材料电极与电解液接触面积增大，增加界面副反应，SEI膜的形成也消耗更多可逆锂，从而导致电池首次库仑效率和循环性能降低。在一些实施例中，复合材料的比表面积(N 2吸附，多点BET)为0.1～15m 2/g，总孔容(N 2吸附，p/p0＞0.999测得)为0.001～0.05cm 3/g。优选地，复合材料的比表面积为0.1～10m 2/g，总孔容为0.001～0.035cm 3/g。较低的比表面积和总孔容有效抑制了复合材料电极中界面副反应的发生。
完全密实的材料对于抑制锂硅合金体积效应的作用是有限的，复合材料中适量闭孔有利于缓解硅的体积效应，但过多闭孔则导致材料体积增大，从而体积比容量降低，更重要的是，过多闭孔导致复合材料结构强度降低，在后续压片过程中可能导致结构坍塌，因此闭孔量不宜太多。闭孔不能由常规的物理吸附方法获得，因为其属于吸附分子无法直接到达的区域，如N 2吸附能够只能检测到开孔及其表面积，这一部分孔及表面会与电解液接触，不利于材料的电极性能。闭孔的检测通过复合材料真密度的测量来反推，当材料真密度小于元素组成相同的完全密实材料的真密度时，说明存在闭孔，闭孔容积为复合材料真密度的倒数(闭孔+骨架的体积)减去元素组成相同的完全密实材料的真密度的倒数(骨架体积)。纯石墨和硅的密度均大于2.2g/cm 3。复合材料的真密度可通过氦气置换法和/或比重瓶法(丙酮浸液法)测试获得。本申请采用比重瓶法测量复合材料的真密度，在一些实施例中，纳米硅氧碳结构复合材料的真密度为1.8～2.1g/cm 3，说明具有一定量的闭孔。
在一些实施例中，复合材料还包括包覆层，包覆层包括固体电解质和/或导电聚合物。以进一步提高其电性能。具体的固体电解质和导电聚合物可以参考现有技术，本申请不再赘述。
为了提高复合材料的压实密度，可以通过破碎等方式控制复合材料的中位粒径D 50，在一些实施例中，复合材料的中位粒径D 50在4～12μm之间。
在本申请另一种典型的实施方式中，提供了一种纳米硅氧碳结构复合材料的制备方法，该制备方法包括：步骤S1，提供含表面氧化层的多孔炭基底，含表面氧化层的多孔炭基底中氧与碳的摩尔比为0.001～0.05；步骤S2，将含硅前体和含氧前体通入放置有含表面氧化层的多孔炭基底的反应炉中，并在150～700℃下与含表面氧化层的多孔炭基底接触5～100h，使硅与含氧物质和可选的碳分散沉积到多孔炭基底的表面和/或孔道内，得到纳米硅氧碳结构复合材料。
碳前驱体炭化和硅烷气相沉积是本领域技术人员知悉的技术手段，但是在实际操作中很难获得均匀分散的硅纳米颗粒沉积，这与很多原因有关，如碳前驱体结构、处理方式、炭化条件、炭化后表面性能、硅沉积方式和条件等。硅烷分解是一个热聚合的链式反应，低温较难发生反应，硅烷利用率低，而在高温下分解速率很快，硅颗粒不可避免快速长大。本申请的制备方法，首先提供保留少量含氧官能团在多孔炭基底表面，即本申请的含表面氧化层的多孔炭基底，该表面氧化层可以促进硅烷分子的吸附和反应；在硅烷分解沉积过程中，引入含氧前体，形成对硅纳米颗粒的氧化分隔层，实现硅纳米颗粒的均匀分散。
上述制备方法以含表面氧化层的多孔炭基底为载体和/或支架(相当于优先权文件(CN申请号为202210114895.6)中的含表面氧化层的多孔炭骨架)，在其表面和孔结构中进行硅纳米粒子和含氧物质和可选的碳的沉积，其中含氧物质和可选的碳起到分隔和束缚硅纳米粒子沉积层的作用，沉积最后可能会在多孔炭基底的孔道内留有少量闭孔。因而所得到的纳米硅氧碳结构复合材料中均匀分散的、被束缚的硅纳米颗粒在嵌锂和脱锂过程中的体积效应可以得到有效缓冲，且硅纳米颗粒在充放电过程中的融并现象得到抑制，材料强度提高，有助于提升包含该硅氧碳复合负极材料的电化学装置的电化学性能。
上述步骤S2中将含硅前体和含氧前体通入放置有含表面氧化层的多孔炭基底之前可对含表面氧化层的多孔炭基底进行抽真空或不抽真空处理，其中，进行抽真空处理可以加速初期沉积含硅前体时的速率。
上述制备方法所得到的复合材料的结构、组成和物理性能可以参考前述的复合材料的结构、组成和物理性能，在此不再赘述。
上述反应炉为回转炉、钢包炉、内胆炉、辊道窑、推板窑、气氛箱式炉或管式炉中的任意一种或多种的组合；其中步骤S2中，固气两相接触方式为固定床、移动床、流化床、沸腾床等多种方式中的任意一种或多种的组合。
本申请的上述含表面氧化层的多孔炭基底的制备方法可以根据不同的碳前驱体和/或多孔炭基底来选择相应的实现方式。
在一些实施例中，上述步骤S1包括：对碳前驱体进行预稳定化，得到预稳定化的前驱体，碳前驱体选自单糖、二糖、多糖、不饱和聚酯树脂、环氧树脂、酚醛树脂、聚甲醛树脂、脲醛树脂、糠醛树脂、糠酮树脂、丙烯酸树脂、聚酰胺、聚酰亚胺、聚乙烯醇和沥青中的一种或多种，预稳定化在包括第一氧化性气体和惰性气体的第四混合气中进行，第一氧化性气体为氧气和/或臭氧，惰性气体为氮气、氩气、氦气中的一种或多种，预稳定化的温度为100～300℃，时间为0.1～48h，优选预稳定化的温度为170～220℃，时间为1～48h；对预稳定化前驱体进行炭化，得到多孔炭基底，炭化在惰性气体中进行，惰性气体为氮气、氩气、氦气中的一种或多种，优选炭化的温度为600～1800℃、时间为0.5～10h，进一步优选炭化的温度为800～1500℃、时间为2～5h。在炭化过程中，对炭化条件进行调节，可以保留部分含氧官能团作为氧化层。或者对多孔炭基底进行氧化，得到含表面氧化层的多孔炭基底。
以上预稳定化和炭化均为炭材料制备过程中的常规步骤，优先权文件(CN申请号为202210114895.6)中的预稳定化和炭化与以上预稳定化和炭化类似。
在本申请的一种实施例中，上述步骤S1中含表面氧化层的多孔炭基底的制备方法为，将碳前驱体和造孔剂混合炭化后形成炭化后材料，并对炭化后材料进行破碎和氧化处理。
具体地，优选上述步骤S1包括：对碳前驱体和造孔剂的均匀混合物进行预稳定化，得到预稳定化的材料；再对预稳定化的材料进行炭化，得到多孔炭基底；对多孔炭基底进行破碎和氧化，得到含表面氧化层的多孔炭基底。碳前驱体选自葡萄糖、果糖、蔗糖、麦牙糖、乳糖、环糊精、淀粉、糖原、纤维素、半纤维素、木质素、不饱和聚酯树脂、环氧树脂、热塑性酚醛树脂、热固性酚醛树脂、聚甲醛树脂、脲醛树脂、糠醛树脂、糠酮树脂、丙烯酸树脂、聚酰胺、聚酰亚胺、沥青中的一种或多种；造孔剂选自十二烷基苯磺酸钠、十六烷基三甲基溴化铵、聚乙二醇、聚乙烯醇、聚乙烯吡咯烷酮、油酸、油胺、聚环氧乙烷-聚环氧丙烷-聚环氧乙烷三嵌段共聚物、柠檬酸、苹果酸、琥珀酸、NH 4HCO 3、(NH 4) 2CO 3、HNO 3、H 2SO 4、LiOH、NaOH、KOH等中的一种或多种，优选地，聚环氧乙烷-聚环氧丙烷-聚环氧乙烷三嵌段共聚物选自P123、F127和/或F108。碳前驱体与造孔剂的混合可以采用本领域技术人员熟知的方式，在一些实施例中，碳前驱体与造孔剂采用湿法球磨和/或干法球磨混合，在一些实施例中，碳 前驱体与造孔剂共同溶解于水和/或乙醇中，通过超声和/或搅拌等方式充分混合后干燥。预稳定化和炭化均为炭材料制备过程中的常规步骤。预稳定化在氧化性气氛中进行，温度为100～300℃，时间为0.1～48h；炭化在惰性气体中进行，温度为600～1800℃、时间为0.5～10h，进一步优选炭化的温度为800～1500℃、时间为2～5h。
在一些实施例中，上述氧化在包括第二氧化性气体和惰性气体的第五混合气中进行，第二氧化性气体选自氧气、二氧化碳、水蒸气中的任意一种或多种，惰性气体为氮气、氩气、氦气中的一种或多种；优选地，氧化的温度为300～1600℃、时间为0.1～5h，进一步优选氧化的温度为600～900℃、时间为2～4h。以在尽可能保留多孔结构的基础上，形成稳定的氧化层。
在另一些实施例中，上述步骤S1还包括：对多孔炭基底直接进行氧化，得到含表面氧化层的多孔炭基底，多孔炭基底选自软碳、硬碳、炭黑、石墨、石墨烯、碳纳米管、碳纤维、中间相碳微球中的一种或多种，优选地，氧化在包括第二氧化气体和惰性气体的第五混合气中进行，第二氧化性气体选自氧气、二氧化碳、水蒸气中的任意一种或多种，惰性气体为氮气、氩气、氦气中的一种或多种；优选地，氧化的温度为300～1600℃、时间为0.1～5h，进一步优选氧化的温度为600～900℃、时间为2～4h。即以现有技术中的多孔碳材料为基底进行上述氧化也可以得到本申请的含表面氧化层的多孔炭基底。
在一些实施例中，上述第二氧化性气体还可以选自甲醇、乙醇、乙酸、丙醇、丁醇、丙酮中的任意一种或多种；对多孔炭基底进行氧化之前，可以对多孔炭基底进行抽真空或不抽真空处理，对多孔炭基底进行抽真空可以洁净其表面，更有利于氧化的进行。
上述氧化中，第二氧化性气体和惰性气体的比例可以以现有技术为参考，但是通常是以惰性气体占主要部分为主，以避免对多孔碳材料的烧损，比如第一活性氧气体和惰性气体以1∶99～20∶80的体积比进行混合；优选地，第二氧化性气体占第五混合气的比例为0.5～20％。
在又一些实施例中，上述氧化在包括含氧化合物和/或含氧化合物的水和/或乙醇溶液中进行，含氧化合物选自HNO 3、H 2SO 4、乙酸、丙酸、丁醇、丁酸、丁二酸、苹果酸、柠檬酸中的任意一种或多种；优选地，氧化步骤为，将多孔炭基底置于含氧化合物和/或含氧化合物的水和/或乙醇溶液中，超声分散0.5～2h后，于0～50℃搅拌0.5～12h，过滤和/或离心使固液分离，用去离子水和/或乙醇多次洗涤固体，并将所得固体进行真空干燥和焙烧。
纳米硅氧碳结构复合材料以多孔炭为基底，具有较大的比表面积和丰富的孔结构，提供硅纳米粒子沉积的区域。多孔炭基底的比表面积和孔分布直接影响硅沉积效果和复合材料的比表面积。在实现对硅纳米粒子充分负载的同时，还需避免比表面积过大导致副反应过多的问题。合适的多孔炭基底应含有较多介孔(孔径2～50nm)，并含有少量微孔(孔径小于2nm)和大孔(孔径大于50nm)，介孔和大孔应是硅沉积的主要区域，但过多的大孔一方面易导致硅颗粒在孔内聚集，另一方面当硅颗粒无法填满大孔时则会在最终的复合材料中留有部分孔隙结构，导致比表面积过大无法满足需求；适量的微孔可能导致硅在孔口沉积而形成闭孔，适量闭孔有利于缓解硅在嵌锂过程中的体积膨胀，但过多闭孔则导致材料结构强度降低。在一些实施例中，含表面氧化层的多孔炭基底的比表面积为50～2000m 2/g、孔容为0.1～3.0cm 3/g， 包含微孔、介孔和大孔；优选地，其中微孔孔容在总孔容中的比例为1～40％，介孔孔容在总孔容中的比例为30～80％，大孔孔容在总孔容中的比例为1～40％。在一些实施例中，含表面氧化层的多孔炭基底的比表面积为100～1000m 2/g、孔容为0.3～1.5cm 3/g，优选地，微孔孔容在总孔容中的比例为1～20％，介孔孔容在总孔容中的比例为60～80％，大孔孔容在总孔容中的比例为1～20％。以实现硅纳米粒子与含氧物质和可选的碳在多孔炭基底上的充分负载，使得所得复合材料具有合适的硅含量和比表面积。
为了实现对硅纳米颗粒的充分阻隔，在一些实施例中，上述步骤S2的实施过程中，含硅前体和含氧前体以任意体积比组合，优选地，含硅前体选自甲硅烷、乙硅烷、丙硅烷、卤代硅烷、聚硅烷、噻咯及其衍生物、硅芴及其衍生物等中的一种或多种，优选地，含氧前体为氧气、二氧化碳、水蒸气、甲醇、乙醇、正丙醇、异丙醇、丁醇、丙酮、丁酮中的一种或多种。
在一些实施例中，步骤S2在通入含硅前体和含氧前体同时通入惰性气体，以调节含硅前体和含氧前体的浓度，并提供合适的压力，惰性气体为氮气、氩气、氦气中的一种或多种。当含硅前体和含氧前体与惰性气体同时通入时，三者可以混合的方式通入或者分别通入后在反应炉中形成混合气，无论是何种情况，只要含硅前体和含氧前体与惰性气体同时通入时，都称为通入含硅前体和含氧前体与惰性气体的第一混合气时，含氧前体为甲醇、乙醇、正丙醇、异丙醇、丁醇、丙酮、丁酮中的一种或多种，第一混合气中含硅前体的体积含量为1～50％，含氧前体的体积含量为0.5～10％；优选地，第一混合气通入时热处理的温度为400～700℃，进一步优选地，第一混合气通入时热处理的时间为5～50h。
优选地，步骤S2在通入含硅前体和含氧前体之前、之后、同时或间隙通入惰性气体，惰性气体为氮气、氩气、氦气中的一种或多种。以调节含硅前体和含氧前体的浓度，并提供合适的压力。当含硅前体和惰性气体同时通入时，二者可以以混合的方式通入或者分别通入后在反应炉中形成混合气，无论是何种情况，只要含硅前体和惰性气体同时通入时，都称为通入含硅前体与惰性气体的第二混合气时，第二混合气中硅前体的体积含量为1～50％。当含氧前体和惰性气体同时通入时，二者可以以混合的方式通入或者分别通入后在反应炉中形成混合气，无论是何种情况，只要含氧前体和惰性气体同时通入时，都称为通入含氧前体与惰性气体的第三混合气时，第三混合气中含氧前体的体积含量为1～50％。
在一些实施例中，步骤S2中的温度随含硅前体和含氧前体的浓度变化。为了实现硅和氧的高效沉积，进一步优选地，含硅前体通入时热处理的温度为400～700℃，含氧前体通入时热处理的温度为150～600℃。
在一些实施例中，上述步骤S2包括：步骤S2-1，将惰性气体通入放置有含表面氧化层的多孔炭基底的反应炉中，并将反应炉的温度升至400～700℃；步骤S2-2，通入含硅前体与惰性气体的第二混合气，第二混合气中含硅前体的体积浓度为1％～50％，并将反应炉在400～700℃保持0.5～15h；步骤S2-3，停止通入含硅前体，将反应炉的温度调节至150～600℃；步骤S2-4，通入含氧前体与惰性气体的第三混合气，第三混合气中含氧前体的体积浓度为 1％～50％，并将反应炉在150～600℃保持0.1～5h；步骤S2-5，重复2～50次步骤S2-1至步骤S2-4。
在一些实施例中，上述制备方法还包括步骤S3，对步骤S2的纳米硅氧碳结构复合材料进行破碎分级，得到中位粒径为4～12μm的纳米硅氧碳结构复合材料分级颗粒，优选破碎分级的方式为人工研磨、机械磨、球磨、气流磨中的任意一种或多种。以对复合材料的压实密度进行调整。
上述破碎分级相当于优先权文件(CN申请号为202210114895.6)中步骤S2的破碎整形。
在一些实施例中，上述制备方法还包括：步骤S4，对步骤S3的纳米硅氧碳结构复合材料分级颗粒进行深度氧化处理，优选深度氧化处理包括将纳米硅氧碳结构复合材料分级颗粒与包含氧化性物质的溶液和/或气体于0～400℃接触0.5～12h。
优选上述步骤S4中，固气两相接触方式为固定床、移动床、流化床、沸腾床等多种方式中的任意一种或多种的组合。
在一些实施例中，上述步骤S4中，深度氧化处理包括液相氧化和/或气相氧化；优选地，液相氧化的步骤为，将纳米硅氧碳结构复合材料分级颗粒置于氧化性物质和/或氧化性物质的水和/或乙醇溶液中，超声分散0.5～2h后，于0～50℃搅拌0.5～12h，过滤和/或离心使固液分离，用去离子水和/或乙醇多次洗涤固体，并将所得固体于40～200℃鼓风干燥0.5～24h后，于惰性气氛中200～400℃处理0.5～5h，含氧化合物选自KMnO 4、H 2O 2、HNO 3、H 2SO 4、乙酸、丙酸、丁酸、丁二酸、苹果酸、柠檬酸中的任意一种或多种，液相氧化在紫外光和/或微波辐射的作用下进行；优选地，气相氧化的步骤为，将纳米硅氧碳结构复合材料分级颗粒抽真空至真空度低于10 -2Pa，然后通入包含氧化性气体和惰性气体的混合气，控制升温速率为1～10℃/min，从室温升至200～400℃，并于200～400℃处理0.1～5h，氧化性气体选自氧气、臭氧、二氧化碳、水蒸气中的任意一种或多种，惰性气体为氮气、氩气、氦气中的一种或多种，氧化性气体占混合气的比例为0.5～20％。
在一些实施例中，在上述步骤S4之前，增加对纳米硅氧碳结构复合材料分级颗粒的酸处理和/或碱处理过程；优选地，酸处理的方法为，将纳米硅氧碳结构复合材料分级颗粒分散至含酸的水/乙醇溶液中，于0～50℃搅拌0.5～12h，过滤和/或离心使固液分离，用去离子水和/或乙醇多次洗涤固体至滤液和/或上清液pH为中性，对所得固体进行真空干燥；碱处理的方法为，将纳米硅氧碳结构复合材料分级颗粒分散至含碱的水/乙醇溶液中，于0～50℃搅拌0.5～12h，过滤和/或离心使固液分离，用去离子水和/或乙醇多次洗涤固体至滤液和/或上清液pH为中性，对所得固体进行真空干燥；酸为HCl、H 2SO 4、HNO 3、H 3PO 4中的一种或多种，碱为NaOH、KOH、Na 2CO 3、K 2CO 3、NH 3H 2O、NH 4HCO 3、(NH 4) 2CO 3、尿素中的一种或多种。
为了进一步提高所制备的复合材料的电化学性能，在一些实施例中，优选上述制备方法还包括：步骤S5，在纳米硅氧碳结构复合材料上包裹固体电解质和/或导电聚合物。
上述固体电解质和导电聚合物均采用现有常规的对应物质即可，在此不再赘述。
需要说明的是，步骤S5中所称的纳米硅氧碳结构复合材料具有相对广泛的含义，即包括：S2中所称的纳米硅氧碳结构复合材料、步骤S3中对纳米硅氧碳结构复合材料进一步地的分级处理得到的纳米硅氧碳结构复合材料分级颗粒、步骤S4中对纳米硅氧碳结构复合材料分级颗粒进一步地的深度氧化处理得到的氧化的纳米硅氧碳结构复合材料、步骤S4之前对纳米硅氧碳结构复合材料分级颗粒的酸处理和/或碱处理过程得到的酸和/或碱处理后深度氧化的纳米硅氧碳结构复合材料中的任意一种。
在一些实施例中，上述制备方法还包括：步骤S6，对纳米硅氧碳结构复合材料进行真空处理及碳包覆，碳包覆的方式为采用甲烷、乙烷、丙烷、丁烷、乙烯、丙烯、丁烯、乙炔、丙炔、甲醇、乙醇、正丙醇、异丙醇、丁醇、丙酮、丁酮中的一种或多种，对复合材料进行气相沉积，或采用液体碳前驱体进行液相碳包覆，优选地，液体碳前驱体选自树脂、沥青。
需要说明的是，步骤S6中所称的纳米硅氧碳结构复合材料具有相对广泛的含义，即包括：步骤S3中对纳米硅氧碳结构复合材料进一步地的分级处理得到的纳米硅氧碳结构复合材料分级颗粒、步骤S4中对纳米硅氧碳结构复合材料分级颗粒进一步地的深度氧化处理得到的氧化的纳米硅氧碳结构复合材料、步骤S4之前对纳米硅氧碳结构复合材料分级颗粒的酸处理和/或碱处理过程得到的酸和/或碱处理后深度氧化的纳米硅氧碳结构复合材料、步骤S5中得到的包裹固体电解质和/或导电聚合物的纳米硅氧碳结构复合材料中的任意一种。
在本申请另一种典型的实施方式中，提供了一种负极，包括负极材料，该负极材料为上述任一种的纳米硅氧碳结构复合材料或者上述任一种的制备方法得到纳米硅氧碳结构复合材料。
在本申请又一种典型的实施方式中，提供了一种电化学装置，包含负极，负极为上述的负极，优选电化学装置为锂离子二次电池。
本申请的纳米硅氧碳结构复合材料中硅纳米颗粒均匀分散，且由含氧物质和可选的碳分隔和束缚，因此有效抑制了硅粒子在沉积过程中的团聚及其在充放电循环中的体积变化和可能的融并，包含由所得复合材料制备的负极的锂离子二次电池具有较高的克容量、较高的首次库仑效率和良好的循环性能。
以下结合实施例和对比例，进一步说明本申请的有益效果。本申请的实施例不应该被解释为对本申请的限制。
实施例1：
纳米硅氧碳结构复合材料的制备：
步骤S1，含表面氧化层的多孔炭基底制备：以淀粉为碳前驱体，在空气气氛中由室温升至220℃，并在该温度下保持48h进行预稳定化；然后改变为N 2，以2℃/min升温至1500℃，并在该温度下保持2h，完成炭化；然后于N 2气氛中降温至600℃，切换为2％O 2-N 2混合气， 于600℃氧化2h，获得含表面氧化层的多孔炭基底。所得多孔炭基底中氧与碳的摩尔比为0.031，多孔炭基底的比表面积为380m 2/g，孔容为0.74cm 3/g，微孔、介孔和大孔所占比例分别为9％、70％和21％。
步骤S2，硅沉积和含氧处理：多孔炭基底在N 2气氛中以2℃/min由室温升至600℃后，改变为20％SiH 4-N 2混合气；在20％SiH 4-N 2混合气气氛中，于600℃下保持2h，进行硅的沉积；然后改变为N 2，降温至200℃后，改变为1％O 2-N 2混合气；在1％O 2-N 2混合气气氛中，于200℃下保持12min进行含氧处理；然后改变为N 2并升温至600℃，如此在多孔炭基底上进行硅沉积-含氧处理循环15次，在N 2保护下自然降温，得到纳米硅氧碳结构复合材料。
步骤S3，破碎：将步骤S2所得纳米硅氧碳结构复合材料采用气流磨进行破碎分级，得到中位粒径为6μm的纳米硅氧碳结构复合材料分级颗粒。
对所得中位粒径为6μm的纳米硅氧碳结构复合材料分级颗粒进行XRD、N 2吸附测试和TEM检测，制作电极并进行电化测试。
电极、半电池制备及电化学性能测试方法(适用于本申请列举所有实施例和对比例)：
将包含各实施例及对比例复合材料的极片采用常规方法制备CR2032型扣式电池并进行电学性能测试。在手套箱中组装CR2032型扣式电池，以金属锂片为对电极，聚丙烯微孔膜为隔膜，电解液为LiPF 6溶解于碳酸乙酯(EC)和碳酸二乙酯(DEC)混合液(体积比EC∶DEC＝1∶1)中，其中LiPF 6浓度为1mol/L。
用蓝电(LAND)电池测试系统对电池进行充放电测试。
所述CR2032型扣电静置6h后，以0.05C放电至0.005V，再以0.01C放电至0.005V；静置5min后，0.05C恒流充电至1.5V；首次脱锂容量与首次嵌锂容量的比值即为电池的首次库仑效率。
静置5min后，重复两次上述充放电步骤；
然后采用0.25C放电至0.005V；静置5min后，0.25C恒流充电至1.5V，循环50次。第50圈的充电比容量/第1圈的充电容量×100％，计算得到容量保持率。
采用以下方法测试极片膨胀率：所述CR2032型扣电静置6h后，以0.05C放电至0.005V，再以0.01C放电至0.005V；然后在手套箱中拆解扣电，用DEC清洗极片并测量极片的厚度。膨胀率计算方式为：(首次满电态极片厚度-新鲜极片厚度)/新鲜极片厚度×100％。
图1示出了实施例1所得纳米硅氧碳结构复合材料分级颗粒的结构示意图。根据上述过程，可以推测纳米硅氧碳结构复合材料分级颗粒中，其核心组成(C x1-O y1)-(Si z-O y2-C x2)包括含表面氧化层的多孔炭基底C x1-O y1和负载于多孔炭基底表面和孔隙中的Si z-O y2-C x2两个主要部分，后者包括均匀分散的硅纳米颗粒及少量含氧物质和可选的碳，亦可写作(Si z1-O y-C x) n，n≥1。复合材料呈多级结构，以含表面氧化层的多孔炭基底为载体和/或支架，在其表面和孔结构中进行硅纳米粒子(即图1中的Si)和含氧物质和可选的碳(即图1中的SiO δ+C)的沉积，其中 含氧物质和可选的碳起到分隔和束缚硅纳米颗粒的作用，沉积最后可能会在多孔炭基底的孔道内留有少量闭孔。
另外，如图2所示，由实施例1所得纳米硅氧碳结构复合材料分级颗粒的XRD图谱中无明显结晶峰，反映了其中硅粒子为非晶，炭亦为无定形，相应地在图3的HRTEM图中可以看出，复合材料主要呈无定形，无明显的长程有序结构，与XRD图谱相吻合。图3中白圈内晶格条纹间距约为0.314nm，对应Si晶粒中(111)晶面间距，从有序的晶格条纹的数量可以看出，Si晶粒尺寸均小于2nm。N 2吸附和丙酮浸液法测得，所得纳米硅氧碳结构复合材料分级颗粒的比表面积为4.7m 2/g，孔容为0.024cm 3/g，真密度为1.97g/cm 3。实施例1所得纳米硅氧碳结构复合材料中硅、氧、碳质量含量分别为50.2％、1.9％和47.9％。
对实施例1所得纳米硅氧碳结构复合材料分级颗粒进行800℃、N 2气氛中处理后，然后进行XRD测试，结果见图5，通过对2θ＝28.4°处的峰半峰宽测量并通过谢乐公式计算晶粒尺寸，结果显示800℃处理后材料中硅晶粒尺寸为7.7nm，表明材料中合适的氧含量对硅纳米颗粒起到了很好的分隔作用，限制了硅晶粒和/或非晶硅间的团聚。包含实施例1所得纳米硅氧碳结构复合材料的电极的恒流充放电曲线显示在图4中，其克容量为2029mAh/g，1.5V首次库仑效率为92.6％，极片膨胀率为124％，循环充放电50次后的克容量保持率为95.6％。
表1为实施例1至25与对比例1和2所采用的含表面氧化层的多孔炭基底及其制备条件。
表2为含表面氧化层的多孔炭基底的氧含量、比表面积和孔性质。多孔炭基底以介孔为主，并含部分微孔和大孔。
表3为纳米硅氧碳结构复合材料分级颗粒的实施例1至25与对比例1和2的制备条件。本说明书所列举实施例中含硅前体和/或含氧前体的浓度及其相应处理温度为脉冲式周期性或非周期性变化，为了方便表达，放在同一个表格中，采用“沉积周期”来描述这种不同，非周期性变化时周期数为1。由于存在含硅前体和含氧前体分别引入的实施例，故在表3中分别以“沉积混合气1”和“沉积混合气2”来表示，相应地，各自的接触温度和停留时间分别为“沉积温度1”和“沉积时间1”、“沉积温度2”和“沉积时间2”。不排除周期之间采用不同的前体浓度和处理温度时间等的方式也可以实现本发明所要求的纳米硅氧碳结构复合材料。
表4为纳米硅氧碳结构复合材料分级颗粒的实施例1至36与对比例1和2的基本物理性质和电化学性能。
由于硅和碳在负极材料中嵌锂能力不同，以SiO δ形式存在的氧会导致不可逆嵌锂，降低负极首效，因此纳米硅氧碳结构复合材料中硅、氧、碳的含量对复合材料首效有很大影响，各物质含量可通过多孔炭载体的孔结构、沉积混合气的浓度、沉积温度和时间等来调控，不同前体物所需的最适温度有所不同，在一定范围内，沉积温度较高时相应物质沉积量会提高。另一方面，含氧物质的沉积方式及与硅沉积的相对时间在很大程度上决定了含氧层对硅纳米颗粒的分散程度，进而影响复合材料的电化学性能如极片膨胀率和循环性能等。本申请的实施例主要围绕这些因素展开。
纳米硅氧碳结构复合材料中，硅和含氧物质主要沉积在多孔炭基底的孔道内部，少许在炭骨架孔道外的表面上进行沉积，另一方面，本发明制备较为致密的硅氧碳复合材料，因此炭基底的孔容决定了硅前体和含氧前体的最大负载量。硅前体和含氧前体的浓度、沉积温度和相对时间，以及炭基底的孔容，共同决定了纳米硅氧碳结构复合材料的硅含量、氧含量，相应地也决定了碳含量。沉积气体的流量与反应炉容积、炭基底用量、硅前体和含氧前体在沉积混合气中的浓度有关，可根据情况相应调节，本说明书中不作详述。多数实施例通过控制总的硅沉积时间一致从而满足所用炭基底孔容能够容纳的量。
如表3所列，实施例1至20、23、24和25均采用硅前体和含氧前体交替沉积的方式来进行硅和含氧物质的负载，每个沉积周期中所用沉积条件包括气体浓度和沉积温度、时间是一致的(但本发明主张的权利不限于沉积周期完全重复，也可以根据情况对各个周期中的沉积条件进行改变)。实施例1-12中步骤S2所用含氧前体均为O 2与N 2的混合气。实施例1-9中沉积混合气1和沉积混合气2均分别采用20％SiH 4-N 2和1％O 2-N 2；实施例10采用提高浓度的含硅前体和含氧前体的混合气，实施例11和12采用其它含硅前体进行沉积，如Si 2H 6和Si 3H 8。
实施例2相比实施例1，其区别在于含氧前体处理的时间相对较长，这将导致其氧含量增高，电极首效降低。实施例3-6改变了单个沉积周期中硅沉积的时间，相应地改变含氧物质处理的时间和沉积周期数，可以看出，单个沉积周期中硅沉积的时间较长时，如实施例5和实施例6，分别为10h和15h，含氧物质对硅纳米颗粒的分隔作用降低，所得纳米硅氧碳结构复合材料的极片膨胀率增大，多次循环后容量保持率降低。
实施例7所用多孔炭基底的孔容较小，为0.33cm 3/g，因而负载硅的量相比实施例1显著降低，导致其首次循环克容量明显低于实施例1，仅为1639mAh/g。实施例8则采用比表面积为581m 2/g、孔容为1.1cm 3/g的9#多孔炭基底进行硅的沉积，所得纳米硅氧碳结构复合材料的硅含量高达68.7％，包含其的电极克容量达到2500mAh/g以上，首效达到92.8％，但极片膨胀率较大，50圈后容量保持率仅为90.4％。
实施例9与实施例1相比，区别在于步骤S2中硅沉积-含氧处理循环周期数减少为10次，硅含量相对较低(35.4％)，复合材料电极容量不足1500mAh/g，但较低的硅含量也使得复合材料电极膨胀率较低；另外由于硅和含氧物质未能完全填充炭基底孔容，材料比表面积和孔容显著增大，分别为41.8m 2/g和0.217cm 3/g，较大的孔容进一步缓解了硅的膨胀，因此包含该复合材料的电极首次满电嵌锂的极片膨胀率显著降低，仅为31％，但较大的比表面积导致副反应增多，电极首效降低，1.5V电压下首效仅为84.6％。
实施例10所用提高浓度的硅前体和含氧前体的混合气，复合材料中硅和氧的含量以及由此导致的电化学性能与含硅前体和含氧前体的相对浓度和一个周期内二者相对沉积时间有关。
实施例11和12采用其它含硅前体进行沉积，如Si 2H 6和Si 3H 8。此外，这两个实施例采用具有相对较低孔容的多孔炭基底作为炭载体进行硅的沉积，炭基底的孔容决定了两个实施例中硅含量有限，因而复合材料电极容量较低。
实施例13-17为步骤S2中以CO 2为含氧前体的实施例，所用沉积温度较低时，所得硅氧碳复合材料中硅含量降低，电极克容量降低，其它因素如沉积时间、相对时间等与实施例1-10揭示的相近。实施例18-21为步骤S2中以丙酮为含氧前体的实施例，实施例18-20为含硅前体和丙酮分别通入含多孔炭基底的反应炉中，实施例21为含硅前体和丙酮同时通入含多孔炭基底的反应炉中，实施例22为含硅前体和甲醇同时通入含多孔炭基底的反应炉中。沉积方式、沉积温度和含氧前体浓度的不同导致复合材料中硅和氧含量的不同，高温、高浓度丙酮导致复合材料中较高的氧含量，进而包含该复合材料的电极首效降低。
实施例23在含氧处理过程中采用较高浓度的含氧前体、较高的温度和较长的沉积时间，复合材料总氧含量较高，超过5wt％，起到了很好的分隔硅颗粒的作用，从附图5中可以看出，800℃处理后的该对比例样品结晶程度仍较低，因而包含该材料的电极极片膨胀率较低，仅为72％。但另一方面，过高的氧含量导致复合材料中较多SiO δ物质，电极反应中副反应较多，容量和首效均大大降低，容量仅为1219mAh/g。
实施例26
与实施例1的不同在于，增加深度氧化处理步骤：
步骤S4，深度氧化处理：将步骤S3所得纳米硅氧碳结构复合材料分级颗粒置于管式炉中，抽真空至真空度为10 -3Pa，然后通入1％O 2-Ar混合气，控制升温速率为1℃/min，从室温升至200℃，并于200℃处理2h，降温，得到氧化的纳米硅氧碳结构复合材料，该氧化的纳米硅氧碳结构复合材料的结构示意图见图7。
对实施例26所得纳米硅氧碳复合材料进行了XPS测试，以C 1s谱中无定形C-C峰结合能位于284.7eV为峰位校准，由于高分辨C 1s谱中包含测试系统中存在C-C峰，其C-Si的分析存在较大误差，因此仅分析其高分辨Si 2p谱(图8)。实施例26所得纳米硅氧碳复合材料XPS测试高分辨Si 2p谱及其去卷积分峰分析结果显示，Si-C结合能峰面积明显小于Si-O和Si-Si，根据相应的峰面积计算可得各键合形式所占比例。实施例26所得纳米硅氧碳复合材料中，Si 2p谱中Si-O与Si-Si的比例为0.96，Si-C与Si-Si的比例为0.40，可知，实施例1所得纳米硅氧碳复合材料中多孔炭骨架与硅纳米粒子之间主要通过C-O-Si相连接，C-Si所占比例较小。
实施例27
与实施例1的不同在于，增加深度氧化处理步骤：
步骤S4，深度氧化处理：将步骤S3所得纳米硅氧碳结构复合材料分级颗粒置于管式炉中，抽真空，然后通入1％O 2-Ar混合气，控制升温速率为1℃/min，从室温升至300℃，并于300℃处理2h，降温，得到氧化的纳米硅氧碳结构复合材料。
实施例28
与实施例1的不同在于，增加深度氧化处理步骤：
步骤S4，深度氧化处理：将步骤S3所得纳米硅氧碳结构复合材料分级颗粒置于管式炉中，抽真空，然后通入1％O 2-Ar混合气，控制升温速率为1℃/min，从室温升至350℃，并于350℃处理2h，降温，得到氧化的纳米硅氧碳结构复合材料。
实施例29
与实施例1的不同在于，增加深度氧化处理步骤：
步骤S4，深度氧化处理：将步骤S3所得纳米硅氧碳结构复合材料分级颗粒置于管式炉中，抽真空，然后通入5％O 2-Ar混合气，控制升温速率为1℃/min，从室温升至200℃，并于200℃处理2h，降温，得到氧化的纳米硅氧碳结构复合材料。
实施例30
与实施例1的不同在于，增加深度氧化处理步骤：
步骤S4，深度氧化处理：将步骤S3所得纳米硅氧碳结构复合材料分级颗粒置于管式炉中，抽真空，然后通入20％O 2-Ar混合气，控制升温速率为1℃/min，从室温升至200℃，并于200℃处理2h，降温，得到氧化的纳米硅氧碳结构复合材料。
实施例31
与实施例1的不同在于，增加深度氧化处理及其前处理步骤：
步骤S3+，对步骤S3所得纳米硅氧碳结构复合材料分级颗粒进行酸处理：将纳米硅氧碳结构复合材料分级颗粒分散于1M HNO 3水/乙醇(50/50)溶液中，超声分散2h，于60℃搅拌8h，过滤，用去离子水多次洗涤固体，并将所得固体于120℃鼓风干燥24h，再于N 2气氛中，以2℃/min升温至400℃，并在该温度下保持2h，降温，得到酸处理复合材料。
步骤S4，深度氧化处理：将步骤S3+所得酸处理复合材料置于管式炉中，抽真空，然后通入1％O 2-Ar混合气，控制升温速率为1℃/min，从室温升至200℃，并于200℃处理2h，降温，得到氧化的纳米硅氧碳结构复合材料。
实施例32
与实施例31的不同在于，深度氧化处理的前处理步骤不同：
步骤S3+，对步骤S3所得纳米硅氧碳结构复合材料分级颗粒进行酸处理：将纳米硅氧碳结构复合材料分级颗粒分散于1M NaOH水/乙醇(50/50)溶液中，超声分散2h，于60℃搅拌8h，过滤，用去离子水多次洗涤固体，并将所得固体于120℃鼓风干燥24h，再于N 2气氛中，以2℃/min升温至400℃，并在该温度下保持2h，降温，得到酸处理复合材料，最终得到氧化的纳米硅氧碳结构复合材料。
实施例33
与实施例1的不同在于，增加深度氧化处理步骤：
步骤S4，深度氧化处理：将步骤S3所得纳米硅氧碳结构复合材料分级颗粒分散于0.5M KMnO 4水/乙醇(50/50)溶液中，超声分散2h，于50℃搅拌2h，过滤，用去离子水多次洗涤固体，并将所得固体于60℃鼓风干燥24h，再于N 2气氛中，以2℃/min升温至400℃，并在该温度下保持2h，降温，最终得到氧化的纳米硅氧碳结构复合材料。
实施例34
与实施例1的不同在于，增加外层包覆步骤：
步骤S5，外层包覆：将步骤S4所得氧化的纳米硅氧碳结构复合材料置于管式炉中，抽真空处理，然后通入N 2，以2℃/min升温至700℃，切换为C 2H 2气体，在700℃保持2h，降温，得到碳包覆的纳米硅氧碳结构复合材料。
实施例35
与实施例26的不同在于，增加外层包覆步骤，即与实施例1的不同在于增加深度氧化处理和外层包覆步骤：
步骤S6，外层包覆：将步骤S4所得氧化的纳米硅氧碳结构复合材料分散于0.1MAl(NO 3) 3水/乙醇(50/50)溶液中，超声分散2h，加入适量Na 2CO 3水溶液(n(Na 2CO 3)＝1.8n(Al))，于80℃搅拌3h，过滤，用去离子水多次洗涤固体，并将所得固体于60℃鼓风干燥24h，再于N 2气氛中，以2℃/min升温至400℃，并在该温度下保持2h，降温，得到Al 2O 3包覆的纳米硅氧碳结构复合材料。
实施例36
与实施例26的不同在于，增加外层包覆步骤，即与实施例1的不同在于增加深度氧化处理和外层包覆步骤：
步骤S5，外层包覆-I：将步骤S4所得氧化的纳米硅氧碳结构复合材料分散于0.1M Al(NO 3) 3水/乙醇(50/50)溶液中，超声分散2h，加入适量Na 2CO 3水溶液(n(Na 2CO 3)＝1.8n(Al))，于80℃搅拌3h，过滤，用去离子水多次洗涤固体，并将所得固体于60℃鼓风干燥24h，再于N 2气氛中，以2℃/min升温至400℃，并在该温度下保持2h；
步骤S6，外层包覆-II：再以2℃/min升温至700℃，切换为C 2H 2气体，在700℃保持2h，降温，得到碳包覆的、Al 2O 3包覆的纳米硅氧碳结构复合材料。
对比例1：
在无表面氧化层的多孔炭基底上直接进行硅沉积，而不进行硅沉积-含氧处理循环。
(1)多孔炭基底：以商业多孔炭作为多孔炭基底，测试C含量为99.99％。
(2)硅沉积：多孔炭基底在N 2气氛中以2℃/min由室温升至600℃后，改变为20％SiH 4-N 2混合气；在20％SiH 4-N 2混合气气氛中，于600℃下保持30h，进行硅的沉积；然后改变为N 2；自然降温，得到硅碳复合材料。
(3)破碎：将(2)所得硅碳复合材料采用气流磨进行破碎分级，得到中位粒径为6μm的硅碳复合材料。
该方法制备的硅碳复合材料，其结构为C-Si，该材料中，Si颗粒结块严重，在破碎过程中硅碳分离，无法形成有效的硅碳复合材料，不再进行后续表征和电化学测试。
对比例2：
在有表面氧化层的多孔炭基底上进行硅沉积，无含氧处理。
(1)含表面氧化层的多孔炭基底制备：以淀粉为碳前驱体，在空气气氛中由室温升至220℃，并在该温度下保持48h进行预稳定化；然后改变为N 2，以2℃/min升温至1500℃，并在该温度下保持2h，完成炭化；然后于N 2气氛中降温至600℃，切换为2％O 2-N 2混合气，于600℃氧化2h，获得含表面氧化层的多孔炭基底。
(2)硅沉积：多孔炭基底在N 2气氛中以2℃/min由室温升至600℃后，改变为20％SiH 4-N 2混合气；在20％SiH 4-N 2混合气气氛中，于600℃下保持30h，进行硅的沉积；然后改变为N 2，自然降温，得到硅氧碳复合材料。
(3)破碎：将(2)所得纳米硅氧碳结构复合材料采用气流磨进行破碎分级，得到中位粒径为6μm的硅氧碳复合材料。
该方法对炭化后的多孔炭基底进行表面氧化处理，得到含表面氧化层的多孔炭基底，进而进行硅的沉积，所制备的硅氧碳复合材料结构为C-O-Si，相比对比例1，该材料可以得到有效负载的Si，Si颗粒与多孔炭基底结合牢固，破碎过程中不会发生硅碳分离，电化学测试结果显示1.5V首效可达到91.2％，但由于硅颗粒较大(800℃处理后硅晶粒尺寸大于20nm，附图5)，极片膨胀率较高，达到157％，这将影响其循环性能(附图6)。
表1 多孔炭基底及其制备条件
Figure PCTCN2022134811-appb-000001
Figure PCTCN2022134811-appb-000002
表2 多孔炭基底比表面及孔性质
Figure PCTCN2022134811-appb-000003
表3 纳米硅氧碳结构复合材料的实施例及对比例的步骤S1和步骤S2的制备条件
Figure PCTCN2022134811-appb-000004
Figure PCTCN2022134811-appb-000005
表4 纳米硅氧碳结构复合材料的实施例及对比例的物理性质和电化学性能
Figure PCTCN2022134811-appb-000006
Figure PCTCN2022134811-appb-000007
图4示出了实施例1、实施例23和对比例2的电极的半电池(对电极为锂金属电极)首圈循环的恒流充放电曲线。实施例1由于复合材料具有均匀分散的硅纳米颗粒，因而包含其的电极表现出较高的克容量(2029mAh/g)和首效(92.6％，1.5V)，脱锂曲线表现为斜坡型。实施例23采用较高氧含量较高，电极表现出较大的极化，同时克容量和首效均较低，分别为1219mAh/g和84.3％，其斜坡型脱锂曲线的斜率相比实施例1明显增大。对比例2在硅沉积步骤中未进行含氧处理，因而复合材料中硅纳米颗粒较大且无分隔，克容量和首效相应降低，且在充电过程中迅速达到电压平台。
图5示出了纳米硅氧碳结构复合材料实施例1、实施例23和对比例2在N 2气氛中、800℃处理后的XRD图谱。作为对比，也展示了实施例1在热处理前的XRD图谱，实施例23和对比例2在热处理前的XRD图谱与实施例1接近，也表现为宽化的峰包，在此不做展示，反映了硅在3个复合材料中均为/或接近非晶状态。可以看出，800℃处理后复合材料中硅粒子出现明显的结晶，但结晶程度及晶粒大小与含氧处理的程度有关，对比例2未进行含氧处理，其高温处理后结晶程度很高，晶粒尺寸大于20nm，实施例1也表现出一定的结晶程度，其晶粒尺寸为7.7nm，实施例23采用比实施例1更高的含氧处理温度和更长的含氧处理时间，复合材料中氧含量较高，热处理后仍接近无定形。800℃处理后复合材料的结晶程度和晶粒尺寸大小与图4中电极恒流充放电曲线中结果存在对应关系。说明采用本发明的技术方案，可以有效控制硅沉积过程中硅纳米粒子的团聚，获得分散良好且具有较小尺寸的硅纳米颗粒，进而调控复合材料电极的电化学性能。
图6示出了包含纳米硅氧碳结构复合材料实施例1和对比例2的电极的半电池(对电极为锂金属电极)循环性能。实施例1具有均匀分散的硅纳米颗粒，包含其的电极在50圈循环后容量保持率为95.6％，对比例2未进行含氧处理，硅纳米颗粒无分隔，克容量和首效较低，极片膨胀率高，50圈循环后容量保持率仅为86.5％。
实施例24采用大孔体积大于50％的多孔炭基底进行硅沉积。由于多孔炭基底大孔较多，硅颗粒较难完全填充大孔，部分大孔经硅负载后变为介孔，复合材料的比表面积较大，因而造成电极过程中副反应较多，首效较低。
实施例25采用微孔体积大于50％的多孔炭基底进行硅沉积。由于多孔炭基底微孔较多，在硅沉积过程中可能发生堵孔，然后硅粒子在孔外聚集，复合材料经破碎后部分闭孔变为开 孔，比表面积增大，且较多闭孔导致复合材料真密度较低，在压片过程中可能发生结构坍塌，最终导致复合材料克容量和首效均相对较低。
与实施例1相比，实施例26至33对材料的破碎分级和后续深度氧化处理进一步确保成品纳米硅氧碳结构复合材料中硅纳米粒子均被极低膨胀的氧化层包裹。因而所得到的纳米硅氧碳结构复合材料中均匀分散的、被束缚的硅纳米粒子在嵌锂和脱锂过程中的体积效应可以得到有效缓冲和抑制，从而使得极片膨胀率明显降低，克容量保持率明显提高。
实施例34至36中，通过外层包覆使得复合材料的比表面积下降，因而电池的首效明显提高，且具有较高的循环容量保持率，但由于硅含量下降，电池容量稍微有所降低。
从以上的描述中，可以看出，本发明上述的实施例实现了如下技术效果：
首先选择含表面氧化层的多孔炭基底作为硅沉积的载体，通过炭基底表面氧化层与含硅前体间C-O-Si化学作用，实现硅物质在多孔炭基底的孔道内和表面的有效沉积；然后，通过在制备方法中控制含硅前体和含氧前体的沉积条件，实现硅纳米粒子与含氧物质和可选的碳的均匀分散沉积，形成类似(Si z1-O y-C x) n(n≥1)的重复结构。复合材料中含氧物质和可选的碳对硅物质进行分散，实现硅颗粒有效纳米化，同时含氧物质和可选的碳也起到对硅颗粒的束缚作用，从而均匀分散的、被束缚的硅纳米颗粒在嵌锂和脱锂过程中的体积效应可以得到有效缓冲，且材料强度提高，有助于所述硅氧碳复合负极材料和包含其的电化学装置电化学性能的提升。
纳米硅氧碳结构复合材料中硅纳米颗粒尺寸较小，与多孔炭基底结合稳定，且在多孔炭基底孔道内和表面上均匀分散，其合适含量的含氧物质和可选的碳有助于硅纳米颗粒良好分散，同时可以束缚硅在嵌锂过程中的膨胀，材料强度高，电极极片膨胀率低，电池循环性能好。纳米硅氧碳结构复合材料具有较小的比表面积和孔容，有效减少电极表面的副反应，有利于提高材料的库仑效率，获得超高首效的硅氧碳复合负极材料。纳米硅氧碳结构复合材料中含有闭孔，可以在一定程度上缓冲硅在嵌锂过程中的体积膨胀，包含该复合材料的电极极片膨胀率较低，从而进一步提高电池循环性能。
在多孔炭基底上沉积硅纳米粒子后，本发明通过对所得材料进行破碎分级，一方面释放了材料中由于不同物相造成的应力，另一方面可获得具有均匀的、合适的尺寸和形状的复合材料颗粒，以利于进行匀浆和后续电极制备。破碎分级后新鲜的硅粒子表面暴露出来，在空气中缓慢氧化形成氧化层，该氧化层也能起到一定的缓解和束缚膨胀的作用。另外，本发明通过一定步骤，在裸露的硅纳米粒子表面可控地产生稳定的氧化层，该氧化层以SiO δ(0＜δ≤2)形式存在。硅纳米粒子表面均匀的、结构可控的氧化层可以进一步缓解和束缚硅嵌锂膨胀。
对复合材料进行破碎分级，释放不同物相之间的可能应力，并使材料具有匀浆所需的合适的尺寸和形状分布；最后，对破碎分级后的复合材料进行深度氧化处理，在硅纳米粒子表面形成稳定的氧化层。破碎整形和后续氧化处理进一步确保成品纳米硅氧碳结构复合材料中硅纳米粒子均被极低膨胀的氧化层包裹。因而所得到的纳米硅氧碳结构复合材料中均匀分散 的、被束缚的硅纳米粒子在嵌锂和脱锂过程中的体积效应可以得到有效缓冲和抑制，材料强度提高，有助于提升包含该纳米硅氧碳结构复合材料的电化学装置的电化学性能。
综合以上，本发明提供的纳米硅氧碳结构复合材料，包括多孔炭骨架及均匀分布于其孔道内和表面上的硅纳米粒子，碳硅稳定复合、硅粒子的纳米化和均匀分散由三个层次的氧保障：(1)通过多孔炭基底表面的含氧基团与硅纳米粒子间形成C-O-Si键，保证硅纳米粒子与多孔炭基底之间有稳定的键联；(2)在多孔炭基底的孔道内，通过含氧物质对硅纳米粒子进行分隔，避免其在沉积过程中不受控制的聚集长大，从而控制硅纳米粒子尺寸，并实现含氧物质对硅纳米粒子的分隔和/或包裹；(3)在破碎分级后裸露出来的新鲜硅粒子表面，均匀生长氧化层，进一步实现含氧物质对硅纳米粒子的包裹。由此，所得纳米硅氧碳结构复合材料中硅纳米粒子完全由SiO δ(0＜δ≤2)的网络分隔和/或包裹，且硅纳米粒子和SiO δ均匀分布于多孔炭基底的表面和/或孔道内。SiO δ对硅纳米粒子的分隔和/或包裹可以有效控制复合材料在充放电过程中硅的体积膨胀和收缩以及硅粒子之间的融并。此外，合适范围的硅、氧、碳元素含量和复合材料比表面积可以使纳米硅氧碳结构复合材料表现出最优的克容量、首次库仑效率、极低的膨胀率和优异的循环性能。
在一些实施例中，锂离子二次电池的克容量大于等于1500mAh/g，1.5V首次库仑效率大于等于85％，极片膨胀率低于120％，循环充放电50次后的克容量保持率大于等于95％。
在一些实施例中，锂离子二次电池的克容量大于等于2000mAh/g，1.5V首次库仑效率大于等于90％，极片膨胀率低于150％，循环充放电50次后的克容量保持率大于等于95％。
如本发明背景所分析的，现有技术中硅碳复合材料在制备过程中难以实现多孔载体上硅纳米粒子的有效沉积和均匀分散，因而难以抑制电极在充放电过程中发生显著的体积膨胀与收缩，最终导致电极循环性能恶化。此外在电池充放电过程中，相邻的硅粒子之间可能发生融并，导致电极循环性能进一步变差。为了解决上述技术问题，本发明提供纳米硅氧碳复合材料、其制备方法、负极和电化学装置。
本发明的纳米硅氧碳复合材料中多孔炭骨架与硅纳米粒子之间通过C-O-Si键相连接，硅纳米粒子与多孔炭骨架之间结合稳定，硅纳米粒子均由SiO δ的网络分隔和/或包裹，并均匀分散在多孔炭骨架的孔道内和表面，因此有效抑制了硅纳米粒子在沉积过程中的团聚及其在充放电循环中的体积变化和可能的融并，包含由所得复合材料制备的负极的锂离子二次电池具有较高的克容量、较高的首次库仑效率和良好的循环性能。图9为本发明纳米复合材料的结构示意图。
由于硅和碳在负极材料中嵌锂能力不同，以SiO δ形式存在的含氧物质虽然可以缓解和束缚膨胀，但同时导致不可逆嵌锂，降低负极首效，因此纳米硅氧碳复合材料中硅、氧、碳的含量对复合材料的容量、首效和极片膨胀率等有很大影响，需要在制备过程中进行合理控制。纳米硅氧碳复合材料中，硅和含氧物质主要沉积在多孔炭骨架的孔道内部，少许在炭骨架孔道外的表面上进行沉积，另一方面，本发明制备较为致密的纳米硅氧碳复合材料，因此多孔炭骨架的孔容决定了硅前体和含氧前体的最大负载量。硅前体和含氧前体的浓度、沉积 温度和相对时间，以及多孔炭骨架的孔容，共同决定了纳米硅氧碳复合材料的硅含量、氧含量，相应地也决定了碳含量。沉积气体的流量与反应炉容积、多孔炭骨架用量、硅前体和含氧前体在沉积混合气中的浓度有关，可根据情况相应调节，本说明书中不作详述。
实施例1：
纳米硅氧碳复合材料的制备：
步骤S1，含表面氧化层的多孔炭骨架制备：以淀粉为碳前驱体，三嵌段共聚物P123为造孔剂，将淀粉加入P123的水/乙醇溶液中，于50℃搅拌至溶剂挥发完全，所得固体在空气气氛中由室温升至220℃，并在该温度下保持48h进行预稳定化；然后改变为N 2，以2℃/min升温至800℃，并在该温度下保持2h，完成炭化；改变气体为5％CO 2-N 2，(以N 2为平衡气，其中含5％CO 2)升温至900℃，并于10％CO 2-N 2气氛中、900℃，保持2h；然后于N 2气氛中降温至特定温度待用，获得含表面氧化层的多孔炭骨架；并采用气流磨将其破碎至中位粒径约10～20μm的颗粒待用。所得多孔炭骨架颗粒的比表面积为809m 2/g，孔容为0.68cm 3/g，微孔、介孔和大孔所占比例分别为16％、75％和9％，其中，2～10nm孔体积占总孔体积的比例为68％。
步骤S2，硅沉积和含氧处理：将步骤S1所述中位粒径约10～20μm的含表面氧化层的多孔炭骨架颗粒置于管式炉中，抽真空至真空度为10 -3Pa，在N 2气氛中以2℃/min升温至600℃，改变为20％SiH 4-N 2混合气；在20％SiH 4-N 2混合气气氛中，于600℃下保持2h，进行硅的沉积；然后改变为N 2，降温至200℃后，改变为1％O 2-N 2混合气；在1％O 2-N 2混合气气氛中，于200℃下保持12min进行含氧处理；然后改变为N 2并升温至600℃，如此在多孔炭骨架上进行硅沉积-含氧处理循环15次，在N 2保护下自然降温；并采用湿法球磨对所得材料进行破碎整形，得到中位粒径为6μm的纳米硅氧碳复合材料，得到纳米硅氧碳复合材料1。
步骤S3，深度氧化处理：将步骤S2所得纳米硅氧碳复合材料1置于管式炉中，抽真空至真空度为10 -3Pa，然后通入1％O 2-Ar混合气，控制升温速率为1℃/min，从室温升至200℃，并于200℃处理2h，降温，得到纳米硅氧碳复合材料。
对所得纳米硅氧碳复合材料进行XRD、N 2吸附测试、XPS测试和TEM检测，制作电极并进行电化学测试。
电极、半电池制备及电化学性能测试方法(适用于本申请列举所有实施例和对比例)：
将包含各实施例及对比例复合材料的极片采用常规方法制备CR2032型扣式电池并进行电学性能测试。在手套箱中组装CR2032型扣式电池，以金属锂片为对电极，聚丙烯微孔膜为隔膜，电解液为LiPF 6溶解于碳酸乙酯(EC)和碳酸二乙酯(DEC)混合液(体积比EC∶DEC＝1∶1)中，其中LiPF 6浓度为1mol/L。
用蓝电(LAND)电池测试系统对电池进行充放电测试。
所述CR2032型扣电静置6h后，以0.05C放电至0.005V，再以0.01C放电至0.005V；静置5min后，0.05C恒流充电至1.5V；首次脱锂克容量即为电极材料的克容量(或称质量比容量)，首次脱锂容量与首次嵌锂容量的比值为电池的首次库仑效率。
静置5min后，重复两次上述充放电步骤；
然后采用0.25C放电至0.005V；静置5min后，0.25C恒流充电至1.5V，循环50次。第50圈的充电比容量/第1圈的充电容量×100％，计算得到容量保持率。
采用以下方法测试极片膨胀率：所述CR2032型扣电静置6h后，以0.05C放电至0.005V，再以0.01C放电至0.005V；然后在手套箱中拆解扣电，用DEC清洗极片并测量极片的厚度。膨胀率计算方式为：(首次满电态极片厚度-新鲜极片厚度)/新鲜极片厚度×100％。
对实施例1所得纳米硅氧碳复合材料进行了XPS测试，以C 1s谱中无定形C-C峰结合能位于284.7eV为峰位校准，由于高分辨C 1s谱中包含测试系统中存在C-C峰，其C-Si的分析存在较大误差，因此仅分析其高分辨Si 2p谱(图10)。实施例1所得纳米硅氧碳复合材料XPS测试高分辨Si 2p谱及其去卷积分峰分析结果显示，Si-C结合能峰面积明显小于Si-O和Si-Si，根据相应的峰面积计算可得各键合形式所占比例。实施例1所得纳米硅氧碳复合材料中，Si 2p谱中Si-O与Si-Si的比例为0.95，Si-C与Si-Si的比例为0.41，可知，实施例1所得纳米硅氧碳复合材料中多孔炭骨架与硅纳米粒子之间主要通过C-O-Si相连接，C-Si所占比例较小。
如图11所示，由实施例1所得纳米硅氧碳复合材料的XRD图谱中无明显结晶峰，反映了其中硅粒子为非晶，炭亦为无定形，相应地在图12的HRTEM图中可以看出，复合材料主要呈无定形，无明显的长程有序结构，与XRD图谱相吻合。图12中白圈内晶格条纹间距约为0.314nm，对应Si晶粒中(111)晶面间距，可以看出，有序的晶格条纹的数均小于5，故Si晶粒尺寸均小于2nm。实施例1所得纳米硅氧碳复合材料经800℃处理后XRD测试结果显示在图11中，其晶粒尺寸增大的极限尺寸为7nm。由于N2吸附和丙酮浸液法测得，所得纳米硅氧碳复合材料的比表面积为4.1m2/g，孔容为0.021cm3/g，真密度为2.00g/cm3。实施例1所得纳米硅氧碳复合材料中硅、氧、碳质量含量分别为52.6％、2.1％和45.3％。包含实施例1所得纳米硅氧碳复合材料的电极的恒流充放电曲线显示在图13中，其克容量为2011mAh/g，1.5V首次库仑效率为92.8％，极片膨胀率为75％，循环充放电50次后的克容量保持率为97.1％，其克容量随循环次数的增加的变化趋势见图14。
对比例1：
纳米硅氧碳复合材料的制备：
步骤S1，多孔炭骨架制备：以淀粉为碳前驱体，在空气气氛中由室温升至220℃，并在该温度下保持48h进行预稳定化；然后改变为N 2，以2℃/min升温至800℃，并在该温度下保持2h，完成炭化，然后于N 2气氛中降温，获得多孔炭骨架，并采用气流磨将其破碎至中位粒径约10～20μm的颗粒待用。所得多孔炭骨架颗粒的比表面积为331m 2/g，孔容为 0.35cm 3/g，微孔、介孔和大孔所占比例分别为21％、63％和16％。
步骤S2，硅沉积：多孔炭骨架在N 2气氛中以2℃/min由室温升至600℃后，改变为20％SiH 4-N 2混合气；在20％SiH 4-N 2混合气气氛中，于600℃下保持30h，进行硅的沉积；在N 2保护下自然降温，采用湿法研磨进行破碎整形，得到中位粒径为6μm的纳米硅氧碳复合材料。
无步骤S3之深度氧化处理。
该方法制备的硅碳复合材料，多孔炭骨架在制备过程中未引入造孔剂，炭化后也未进行氧化处理，其结构为C-Si，该材料中，Si颗粒结块严重，在破碎过程中硅碳分离，无法形成有效的硅碳复合材料，不再进行后续表征和电化学测试。
对比例2：
纳米硅氧碳复合材料的制备：
步骤S1：同实施例1。
步骤S2：同对比例1。
无步骤S3之深度氧化处理。
该方法对炭化后的多孔炭骨架含表面氧化层，进而进行硅的沉积(无含氧处理)，所制备的硅氧碳复合材料结构为C-O-Si，相比对比例1，该材料可以得到有效负载的Si，Si颗粒与多孔炭骨架结合牢固，破碎过程中不会发生硅碳分离，电化学测试结果显示1.5V首效可达到91.8％，但由于硅粒子之间几乎无氧化层分隔和束缚，极片膨胀率较高，达到163％，这将影响其循环性能，50圈循环后容量保持率仅为86.2％。
对比例3：
纳米硅氧碳复合材料的制备：
步骤S1：同实施例1。
步骤S2：同对比例1。
步骤S3：同实施例1。
对比例4：
纳米硅氧碳复合材料的制备：
步骤S1～S2：同实施例1。
无步骤S3之深度氧化处理。
对比例3和对比例4采用与实施例1相同的多孔炭骨架作为硅沉积载体，故硅沉积时会 与多孔炭骨架表面的含氧层形成C-O-Si化学键联，获得稳定的硅氧碳复合材料。对比例3为对对比例2进行后续深度氧化处理后得到的硅氧碳复合材料，虽有后期深度氧化处理，但由于硅烷沉积过程中未辅以含氧物质处理，硅粒子的聚集长大仅受多孔炭骨架孔结构的限制，未能形成有效的SiO δ网络，故循环性能较实施例1较差，50圈循环后容量保持率仅为86.9％，满嵌锂极片膨胀率高达147％。对比例4相比实施例1，未进行破碎整形后的深度氧化处理，而破碎后大量新鲜的硅纳米粒子表面暴露出来，其自然氧化形成的薄层氧化层在电极使用过程中不足以束缚硅嵌锂膨胀，故其极片膨胀率仍较高，达到125％，50圈循环后容量保持率为89.5％。
实施例2：
纳米硅氧碳复合材料的制备：
步骤S1，含表面氧化层的多孔炭骨架制备：S1-1，以淀粉为碳前驱体，三嵌段共聚物F127为造孔剂，将淀粉加入F127的水/乙醇溶液中，于50℃搅拌至溶剂挥发完全，所得固体在空气气氛中由室温升至220℃，并在该温度下保持48h进行预稳定化；然后改变为N 2，以2℃/min升温至800℃，并在该温度下保持2h，完成炭化，然后于N 2气氛中降温，获得含表面氧化层的多孔炭骨架，采用气流磨将其破碎至中位粒径约10～20μm的颗粒待下一步处理。S1-2，将所得多孔炭骨架颗粒分散于1M HNO 3水/乙醇(50/50)溶液中，超声分散2h，于60℃搅拌8h，过滤，用去离子水多次洗涤固体，并将所得固体进行真空干燥，再于N 2气氛中，以2℃/min升温至400℃，并在该温度下保持2h，得到含表面氧化层的多孔炭骨架颗粒。所得含表面氧化层的多孔炭骨架颗粒的比表面积为705m 2/g，孔容为0.65cm 3/g，微孔、介孔和大孔所占比例分别为12％、83％和5％，其中，2～10nm孔体积占总孔体积的比例为72％。
步骤S2～S3：同实施例1。
实施例3：
纳米硅氧碳复合材料的制备：
步骤S1，含表面氧化层的多孔炭骨架制备：S1-1，将热塑性酚醛树脂与热固性酚醛树脂以1∶50比例混合作为碳前驱体，与三嵌段共聚物F127作为造孔剂球磨混合，所得固体在空气气氛中由室温升至180℃，并在该温度下保持4h进行预稳定化；然后改变为N 2，以2℃/min升温至900℃，并在该温度下保持2h，完成炭化，于N 2气氛中降温，获得含表面氧化层的多孔炭骨架。并采用气流磨将其破碎至中位粒径约10～20μm的颗粒待下一步处理。S1-2，将所得多孔炭骨架颗粒分散于1M HNO 3水/乙醇(50/50)溶液中，超声分散2h，于60℃搅拌8h，过滤，用去离子水多次洗涤固体，并将所得固体进行真空干燥，再于N 2气氛中，以2℃/min升温至400℃，并在该温度下保持2h，得到含表面氧化层的多孔炭骨架颗粒。所得含表面氧化层的多孔炭骨架颗粒的比表面积为837m 2/g，孔容为0.74cm3/g，微孔、介孔和大孔所占比例分别为13％、81％和6％，其中，2～10nm孔体积占总孔体积的比例为69％。
步骤S2～S3：同实施例1。
实施例4：
纳米硅氧碳复合材料的制备：
步骤S1，含表面氧化层的多孔炭骨架制备：将热塑性酚醛树脂与热固性酚醛树脂以1∶50比例混合作为碳前驱体，与十六烷基三甲基溴化铵球磨混合，所得混合物在空气气氛中由室温升至180℃，并在该温度下保持4h进行预稳定化；然后改变为N 2，以2℃/min升温至900℃，并在该温度下保持2h，完成炭化；然后于N 2气氛中以2℃/min升温至1200℃，切换为5％CO 2-Ar，并在1200℃保持2h，于N 2气氛中降温，获得含表面氧化层的多孔炭骨架。并采用气流磨将其破碎至中位粒径约10～20μm的颗粒待用。所得多孔炭骨架颗粒的比表面积为922m 2/g，孔容为0.78cm 3/g，微孔、介孔和大孔所占比例分别为15％、8％和0％，其中，2～10nm孔体积占总孔体积的比例为63％。
步骤S2～S3：同实施例1。
实施例5：
纳米硅氧碳复合材料的制备：
步骤S1：同实施例2。
步骤S2，硅沉积和含氧处理：将步骤S1所述中位粒径约10～20μm的含表面氧化层的多孔炭骨架颗粒置于管式炉中，抽真空至真空度为10 -3Pa，在N 2气氛中以2℃/min升温至600℃，改变为20％SiH 4-N 2混合气；在20％SiH 4-N 2混合气气氛中，于600℃下保持5h，进行硅的沉积；然后改变为N 2，降温至200℃后，改变为1％O 2-N 2混合气；在1％O 2-N 2混合气气氛中，于200℃下保持30min进行含氧处理；然后改变为N 2并升温至600℃，如此在多孔炭骨架上进行硅沉积-含氧处理循环6次，在N 2保护下自然降温；并采用湿法球磨对所得材料进行破碎整形，得到中位粒径为6μm的纳米硅氧碳复合材料，得到纳米硅氧碳复合材料1。
步骤S3：同实施例1。
实施例6：
纳米硅氧碳复合材料的制备：
步骤S1：同实施例2。
步骤S2，硅沉积和含氧处理：将步骤S1所述中位粒径约10～20μm的含表面氧化层的多孔炭骨架颗粒置于管式炉中，抽真空至真空度为10 -3Pa，在N 2气氛中以2℃/min由室温升至600℃后，改变为20％SiH 4-N 2混合气；在20％SiH 4-N 2混合气气氛中，于600℃下保持2h，进行硅的沉积；然后改变为N 2，降温至200℃后，改变为1％O 2-N 2混合气；在1％O 2-N 2混合气气氛中，于200℃下保持12min进行含氧处理；然后改变为N 2并升温至600℃，如此在 多孔炭骨架上进行硅沉积-含氧处理循环10次，在N 2保护下自然降温；并采用湿法球磨对所得材料进行破碎整形，得到中位粒径为6μm的纳米硅氧碳复合材料，得到纳米硅氧碳复合材料1。
步骤S3：同实施例1。
实施例7：
纳米硅氧碳复合材料的制备：
步骤S1：同实施例2。
步骤S2，硅沉积和含氧处理：将步骤S1所述中位粒径约10～20μm的含表面氧化层的多孔炭骨架颗粒置于管式炉中，抽真空至真空度为10 -3Pa，在N 2气氛中以2℃/min由室温升至450℃后，改变为20％SiH 4-N 2混合气；在20％SiH 4-N 2混合气气氛中，于450℃下保持2h，进行硅的沉积；然后改变为N 2，降温至200℃后，改变为0.5％O 2-N 2混合气；在1％O 2-N 2混合气气氛中，于200℃下保持12min进行含氧处理；然后改变为N 2并升温至600℃，如此在多孔炭骨架上进行硅沉积-含氧处理循环15次，在N 2保护下自然降温；并采用湿法球磨对所得材料进行破碎整形，得到中位粒径为6μm的纳米硅氧碳复合材料，得到纳米硅氧碳复合材料1。
步骤S3：同实施例1。
实施例8：
纳米硅氧碳复合材料的制备：
步骤S1：同实施例2。
步骤S2，硅沉积和含氧处理：将步骤S1所述中位粒径约10～20μm的含表面氧化层的多孔炭骨架颗粒置于管式炉中，抽真空至真空度为10 -3Pa，在N 2气氛中以2℃/min由室温升至700℃后，改变为20％SiH 4-N 2混合气；在20％SiH 4-N 2混合气气氛中，于700℃下保持2h，进行硅的沉积；然后改变为N 2，降温至350℃后，改变为1％O 2-N 2混合气；在1％O 2-N 2混合气气氛中，于350℃下保持12min进行含氧处理；然后改变为N 2并升温至700℃，如此在多孔炭骨架上进行硅沉积-含氧处理循环15次，在N 2保护下自然降温；并采用湿法球磨对所得材料进行破碎整形，得到中位粒径为6μm的纳米硅氧碳复合材料，得到纳米硅氧碳复合材料1。
步骤S3：同实施例1。
实施例9：
纳米硅氧碳复合材料的制备：
步骤S1：同实施例2。
步骤S2，硅沉积和含氧处理：将步骤S1所述中位粒径约10～20μm的含表面氧化层的多孔炭骨架颗粒置于管式炉中，抽真空至真空度为10 -3Pa，在N 2气氛中以2℃/min由室温升至600℃后，改变为20％SiH 4-N 2混合气；在20％SiH 4-N 2混合气气氛中，于600℃下保持2h，进行硅的沉积；然后改变为N 2，吹扫2h，改变为5％CO 2-N 2混合气；在5％CO 2-N 2混合气气氛中，于600℃下保持12min进行含氧处理；然后改变为N 2并升温至600℃，如此在多孔炭骨架上进行硅沉积-含氧处理循环15次，在N 2保护下自然降温；并采用湿法球磨对所得材料进行破碎整形，得到中位粒径为6μm的纳米硅氧碳复合材料，得到纳米硅氧碳复合材料1。
步骤S3：同实施例1。
实施例10：
纳米硅氧碳复合材料的制备：
步骤S1：同实施例2。
步骤S2，硅沉积和含氧处理：将步骤S1所述中位粒径约10～20μm的含表面氧化层的多孔炭骨架颗粒置于管式炉中，抽真空至真空度为10 -3Pa，在N 2气氛中以2℃/min由室温升至600℃后，改变为10％Si 2H 6-N 2混合气；在10％Si 2H 6-N 2混合气气氛中，于600℃下保持2h，进行硅的沉积；然后改变为N 2，降温至200℃后，改变为1％O 2-N 2混合气；在1％O 2-N 2混合气气氛中，于200℃下保持12min进行含氧处理；然后改变为N 2并升温至600℃，如此在多孔炭骨架上进行硅沉积-含氧处理循环15次，在N 2保护下自然降温；并采用湿法球磨对所得材料进行破碎整形，得到中位粒径为6μm的纳米硅氧碳复合材料，得到纳米硅氧碳复合材料1。
步骤S3：同实施例1。
实施例11：
纳米硅氧碳复合材料的制备：
步骤S1：同实施例2。
步骤S2，硅沉积和含氧处理：将步骤S1所述中位粒径约10～20μm的含表面氧化层的多孔炭骨架颗粒置于管式炉中，抽真空至真空度为10 -3Pa，在N 2气氛中以2℃/min由室温升至600℃后，改变为20％SiH 4-0.5％丙酮-N 2混合气；在20％SiH 4-0.5％丙酮-N 2混合气气氛中，于600℃下保持30h，同步进行硅沉积和含氧处理，在N 2保护下自然降温；并采用湿法球磨对所得材料进行破碎整形，得到中位粒径为6μm的纳米硅氧碳复合材料，得到纳米硅氧碳复合材料1。
步骤S3：同实施例1。
实施例12：
纳米硅氧碳复合材料的制备：
步骤S1～S2：同实施例1。
步骤S3，深度氧化处理：将步骤S2所得纳米硅氧碳复合材料1置于管式炉中，抽真空，然后通入1％O 2-Ar混合气，控制升温速率为1℃/min，从室温升至300℃，并于300℃处理2h，降温，得到纳米硅氧碳复合材料。
实施例13：
纳米硅氧碳复合材料的制备：
步骤S1～S2：同实施例1。
步骤S3，深度氧化处理：将步骤S2所得纳米硅氧碳复合材料1置于管式炉中，抽真空，然后通入1％O 2-Ar混合气，控制升温速率为1℃/min，从室温升至350℃，并于350℃处理2h，降温，得到纳米硅氧碳复合材料。
实施例14：
纳米硅氧碳复合材料的制备：
步骤S1～S2：同实施例1。
步骤S3，深度氧化处理：将步骤S2所得纳米硅氧碳复合材料1置于管式炉中，抽真空，然后通入5％O 2-Ar混合气，控制升温速率为1℃/min，从室温升至200℃，并于200℃处理2h，降温，得到纳米硅氧碳复合材料。
实施例15：
纳米硅氧碳复合材料的制备：
步骤S1～S2：同实施例1。
步骤S3，深度氧化处理：将步骤S2所得纳米硅氧碳复合材料1置于管式炉中，抽真空，然后通入20％O 2-Ar混合气，控制升温速率为1℃/min，从室温升至200℃，并于200℃处理2h，降温，得到纳米硅氧碳复合材料。
实施例16：
纳米硅氧碳复合材料的制备：
步骤S1～S2：同实施例1。
步骤S2+，对步骤S2所得破碎整形后的纳米硅氧碳复合材料1进行酸处理：将纳米硅氧碳复合材料1分散于1M HNO 3水/乙醇(50/50)溶液中，超声分散2h，于60℃搅拌8h，过滤，用去离子水多次洗涤固体，并将所得固体于120℃鼓风干燥24h，再于N 2气氛中，以2℃/min升温至400℃，并在该温度下保持2h，降温，得到纳米硅氧碳复合材料2。
步骤S3，深度氧化处理：将步骤S2+所得纳米硅氧碳复合材料2置于管式炉中，抽真空，然后通入1％O 2-Ar混合气，控制升温速率为1℃/min，从室温升至200℃，并于200℃处理2h，降温，得到纳米硅氧碳复合材料。
实施例17：
纳米硅氧碳复合材料的制备：
步骤S1～S2：同实施例1。
步骤S2+，对步骤S2所得破碎整形后的纳米硅氧碳复合材料1进行酸处理：将纳米硅氧碳复合材料1分散于1M NaOH水/乙醇(50/50)溶液中，超声分散2h，于60℃搅拌8h，过滤，用去离子水多次洗涤固体，并将所得固体于120℃鼓风干燥24h，再于N 2气氛中，以2℃/min升温至400℃，并在该温度下保持2h，降温，得到纳米硅氧碳复合材料2。
步骤S3：同实施例16。
实施例18：
纳米硅氧碳复合材料的制备：
步骤S1～S2：同实施例1。
步骤S3，深度氧化处理：将步骤S2所得纳米硅氧碳复合材料1分散于0.5M KMnO 4水/乙醇(50/50)溶液中，超声分散2h，于50℃搅拌2h，过滤，用去离子水多次洗涤固体，并将所得固体于60℃鼓风干燥24h，再于N 2气氛中，以2℃/min升温至400℃，并在该温度下保持2h，降温，得到纳米硅氧碳复合材料。
实施例19：
纳米硅氧碳复合材料的制备：
步骤S1～S3：同实施例1。
步骤S4，外层包覆：将步骤S3所得纳米硅氧碳复合材料置于管式炉中，抽真空处理，然后通入N 2，以2℃/min升温至700℃，切换为C 2H 2气体，在700℃保持2h，降温，得到碳包覆的纳米硅氧碳复合材料。
实施例20：
纳米硅氧碳复合材料的制备：
步骤S1～S3：同实施例1。
步骤S4，外层包覆：将步骤S3所得纳米硅氧碳复合材料分散于0.1M Al(NO 3) 3水/乙醇(50/50)溶液中，超声分散2h，加入适量Na 2CO 3水溶液(n(Na 2CO 3)＝1.8n(Al))，于80℃搅拌3h，过滤，用去离子水多次洗涤固体，并将所得固体于60℃鼓风干燥24h，再于N 2气 氛中，以2℃/min升温至400℃，并在该温度下保持2h，降温，得到Al 2O 3包覆的纳米硅氧碳复合材料。
实施例21：
纳米硅氧碳复合材料的制备：
步骤S1～S3：同实施例1。
步骤S4，外层包覆：将步骤S4所得纳米硅氧碳复合材料分散于0.1M Al(NO 3) 3水/乙醇(50/50)溶液中，超声分散2h，加入适量Na 2CO 3水溶液(n(Na 2CO 3)＝1.8n(Al))，于80℃搅拌3h，过滤，用去离子水多次洗涤固体，并将所得固体于60℃鼓风干燥24h，再于N 2气氛中，以2℃/min升温至400℃，并在该温度下保持2h；再以2℃/min升温至700℃，切换为C 2H 2气体，在700℃保持2h，降温，得到碳包覆的、Al 2O 3包覆的纳米硅氧碳复合材料。
如上所述，各实施例中纳米硅氧碳复合材料的制备，其制备条件的主要类别和考察因素为：实施例1～4调变多孔炭骨架及其表面处理方式，实施例5～11调变硅沉积加含氧处理过程中各因素，实施例12～18考察深度氧化方式，实施例19～21对复合材料外层包覆进行举例。针对本发明纳料硅氧碳复合材料中三个层次的氧设置了对比例1～4，对比例1中多孔炭骨架表面几乎无表面含氧基团，对比例2在硅沉积过程中未进行含氧处理产生含氧层的分隔，沉积所得复合材料也未进行深度氧化处理，对比例3采用了硅沉积加含氧处理，但在破碎整形后未进行进一步的氧化处理，对比例4在硅沉积过程中未进行含氧处理但在破碎整形后进行了深度氧化处理。
表1为纳米硅氧碳复合材料的实施例1～21与对比例1～4的基本物理性质和电化学性能。
表1 纳米硅氧碳复合材料的实施例及对比例的基本物理性质和电化学性能
Figure PCTCN2022134811-appb-000008
Figure PCTCN2022134811-appb-000009
从以上的描述中，可以看出，本发明上述的实施例实现了如下技术效果：
本发明通过合适的制备方法，使复合材料中多孔炭骨架与硅纳米粒子之间通过C-O-Si键相连接，可以获得稳定的、均匀的纳米硅氧碳复合材料。这一连接方式可以通过XPS测试结果来反映，如图10所示，实施例1获得的纳米硅氧碳复合材料的Si 2p精细谱显示，Si的键合主要以Si-Si和Si-O两种形式存在，结合能峰分别位于99±0.5eV和103±0.5eV结合能处，结合能峰位于100.5±0.5eV)的C-Si的峰面积较小，Si-Si存在于硅纳米粒子中，Si-O则是由于复合材料中C-O-Si和SiO δ的存在。
多孔炭材料中，其孔结构是容纳硅纳米粒子的主要场所，多孔炭的孔径分布通常较宽，从＜2nm的微孔至＞50nm的大孔，部分多孔炭可能存在μm级大孔。硅烷分解是一个热聚合的链式反应，低温较难发生反应，硅烷利用率低，而在高温下分解速率很快，硅粒子不可避免快速长大。含硅前体的气相沉积工艺中，含硅前体通常首先在多孔炭的孔道表面上分解并沉积为小颗粒，继而随着时间的延长而填充满孔道内部，在此过程中，硅纳米粒子生长的最终束缚为多孔炭骨架的孔道尺寸，因此不可避免会形成尺寸较大的硅粒子，造成硅粒子尺寸、分布不均匀。本发明一方面控制多孔炭骨架的孔结构，尤其是提高孔径尺寸在2～10nm的孔在总孔容中的比例，另一方面通过控制含硅前体沉积过程、引入含氧物质的沉积和生长，实现含氧物质对硅纳米粒子的有效分隔，最终实现复合材料中硅纳米粒子的尺寸控制和均匀分散。由于Si颗粒易被氧化，故含氧物质会氧化Si和含氧物质界面处的Si纳米颗粒，从而形成包含Si、SiO和SiO 2的浓度梯度的氧化层，该氧化层可写作SiO δ(0＜δ≤2)。
在多孔炭骨架上沉积硅纳米粒子后，本发明通过对所得材料进行破碎和整形，一方面释放了材料中由于不同物相造成的应力，另一方面可获得具有均匀的、合适的尺寸和形状的复合材料颗粒，以利于进行匀浆和后续电极制备。整形后新鲜的硅粒子表面暴露出来，在空气中缓慢氧化形成氧化层，该氧化层也能起到一定的缓解和束缚膨胀的作用。另外，本发明通过一定步骤，在裸露的硅纳米粒子表面可控地产生稳定的氧化层，该氧化层以SiO δ(0＜δ≤2)形式存在。硅纳米粒子表面均匀的、结构可控的氧化层可以进一步缓解和束缚硅嵌锂膨胀。
本发明首先调控多孔炭骨架的表面结构和孔结构，然后在硅烷分解沉积过程中，引入含氧前体，形成对硅纳米粒子的氧化分隔层，实现硅纳米粒子的均匀分散；在此基础上，对复 合材料进行破碎整形，释放不同物相之间的可能应力，并使材料具有匀浆所需的合适的尺寸和形状分布；最后，对破碎整形后的复合材料进行深度氧化处理，在硅纳米粒子表面形成稳定的氧化层。破碎整形和后续氧化处理进一步确保成品纳米硅氧碳复合材料中硅纳米粒子均被极低膨胀的氧化层包裹。因而所得到的纳米硅氧碳复合材料中均匀分散的、被束缚的硅纳米粒子在嵌锂和脱锂过程中的体积效应可以得到有效缓冲和抑制，材料强度提高，有助于提升包含该硅氧碳复合负极材料的电化学装置的电化学性能。
本发明的纳米硅氧碳复合材料中硅纳米粒子为非晶和/或小于2nm的晶粒，硅纳米粒子由SiO δ的网络分隔和/或包裹，与多孔炭骨架通过C-O-Si结合为稳定的复合材料，且硅纳米粒子和SiO δ在多孔炭骨架孔道内和表面上均匀分散，合适含量的SiO δ有助于硅纳米粒子良好分散，同时可以束缚硅在嵌锂过程中的膨胀，使得硅纳米粒子的极限聚集尺寸小于10nm，电极极片膨胀率低，材料强度高，电池循环性能好。纳米硅氧碳复合材料具有较小的比表面积和孔容，有效减少电极表面的副反应，有利于提高材料的库仑效率，获得超高首效的硅氧碳复合负极材料。纳米硅氧碳复合材料中含有闭孔，可以在一定程度上缓冲硅在嵌锂过程中的体积膨胀，包含该复合材料的电极极片膨胀率较低，从而进一步提高电池循环性能。
综合以上，本发明提供的纳米硅氧碳复合材料，包括多孔炭骨架及均匀分布于其孔道内和表面上的硅纳米粒子，碳硅稳定复合、硅粒子的纳米化和均匀分散由三个层次的氧保障：(1)通过多孔炭骨架表面的含氧基团与硅纳米粒子间形成C-O-Si键，保证硅纳米粒子与多孔炭骨架之间有稳定的键联；(2)在多孔炭骨架的孔道内，通过含氧物质对硅纳米粒子进行分隔，避免其在沉积过程中不受控制的聚集长大，从而控制硅纳米粒子尺寸，并实现含氧物质对硅纳米粒子的分隔和/或包裹；(3)在整形后裸露出来的新鲜硅粒子表面，均匀生长氧化层，进一步实现含氧物质对硅纳米粒子的包裹。由此，所得纳米硅氧碳复合材料中硅纳米粒子完全由SiO δ(0＜δ≤2)的网络分隔和/或包裹，且硅纳米粒子和SiO δ均匀分布于多孔炭骨架的表面和/或孔道内。SiO δ对硅纳米粒子的分隔和/或包裹可以有效控制复合材料在充放电过程中硅的体积膨胀和收缩以及硅粒子之间的融并。此外，合适范围的硅、氧、碳元素含量和复合材料比表面积可以使纳米硅氧碳复合材料表现出最优的克容量、首次库仑效率、极低的膨胀率和优异的循环性能。
因此，在本发明在一些实施例中，锂离子二次电池的克容量大于等于1500mAh/g，1.5V首次库仑效率大于等于90％，极片膨胀率低于100％，循环充放电50次后的克容量保持率大于等于97％。在一些实施例中，锂离子二次电池的克容量大于等于2000mAh/g，1.5V首次库仑效率大于等于90％，极片膨胀率低于120％，循环充放电50次后的克容量保持率大于等于96％。
需要说明的是，在本文中，诸如第一和第二等之类的关系术语仅仅用来将一个实体或者操作与另一个实体或操作区分开来，而不一定要求或者暗示这些实体或操作之间存在任何这种实际的关系或者顺序。而且，术语“包括”、“包含”或者其任何其他变体意在涵盖非排他性的包含，从而使得包括一系列要素的过程、方法、物品或者设备不仅包括那些要素，而且还包括没有明确列出的其他要素，或者是还包括为这种过程、方法、物品或者设备所固有 的要素。在没有更多限制的情况下，由语句“包括一个……”限定的要素，并不排除在包括所述要素的过程、方法、物品或者设备中还存在另外的相同要素。
以上所述仅为本发明的优选实施例而已，并不用于限制本发明，对于本领域的技术人员来说，本发明可以有各种更改和变化。凡在本发明的精神和原则之内，所作的任何修改、等同替换、改进等，均应包含在本发明的保护范围之内。

Claims (23)

  1. 一种纳米硅氧碳结构复合材料，其特征在于，所述复合材料包括(C x1-O y1)-(Si z-O y2-C x2)，其中，
    C x1-O y1为含表面氧化层的多孔炭基底，包括多孔炭基底及其表面氧化层，x1为碳的化学计量数，y1为表面氧化层中氧的化学计量数，0.001≤y1/x1≤0.05；
    Si z-O y2-C x2包括硅纳米颗粒、含氧物质和可选的碳，所述硅纳米颗粒、含氧物质和可选的碳分散分布在所述含表面氧化层的多孔炭基底的表面和/或孔道内，所述含氧物质以SiO δ形式存在，0＜δ≤2，0.1≤z/x1≤2，0.01≤y2/z≤0.15，0≤x2/z≤0.15。
  2. 根据权利要求1所述的复合材料，其特征在于，所述复合材料中，总氧含量为0.5wt％～5wt％。
  3. 根据权利要求1或2所述的复合材料，其特征在于，对所述纳米硅氧碳结构复合材料的XPS测试高分辨Si 2p谱进行去卷积分峰分析的结果包括，结合能峰值位于103±0.5eV的Si-O的峰面积与结合能峰值位于99±0.5eV的Si-Si的峰面积之比为0.5～2，优选为0.8～1.5；结合能峰值位于100.5±0.5eV的Si-C的峰面积与结合能峰值位于99±0.5eV的Si-Si的峰面积之比为0.01～1，优选为0.01～0.5。
  4. 根据权利要求1至3中任一项所述的复合材料，其特征在于，所述硅纳米颗粒包括硅晶粒和/或非晶硅，所述硅晶粒的尺寸小于5nm，进一步优选所述硅晶粒的尺寸小于2nm。
  5. 根据权利要求1至4中任一项所述的复合材料，其特征在于，所述硅纳米颗粒尺寸小于20nm，优选所述硅纳米颗粒尺寸小于10nm。
  6. 根据权利要求1至5中任一项所述的复合材料，其特征在于，所述复合材料的比表面积为0.1～15m 2/g，总孔容为0.001～0.05cm 3/g，优选所述复合材料的比表面积为0.1～10m 2/g，总孔容为0.001～0.035cm 3/g。
  7. 根据权利要求1至6中任一项所述的复合材料，其特征在于，所述复合材料的真密度为1.8～2.1g/cm 3。
  8. 根据权利要求1至7中任一项所述的复合材料，其特征在于，所述复合材料还包括包覆层，所述包覆层包括固体电解质和/或导电聚合物。
  9. 根据权利要求1至8中任一项所述的复合材料，其特征在于，所述复合材料的中位粒径D 50在4～12μm之间。
  10. 一种纳米硅氧碳结构复合材料的制备方法，其特征在于，所述制备方法包括：
    步骤S1，提供含表面氧化层的多孔炭基底，所述含表面氧化层的多孔炭基底中氧与碳的摩尔比为0.001～0.05；
    步骤S2，将含硅前体和含氧前体通入放置有所述含表面氧化层的多孔炭基底的反应炉中，并在150～700℃下与所述含表面氧化层的多孔炭基底接触，进行热处理5～100 h，使硅与含氧物质和可选的碳分散沉积到多孔炭基底的表面和/或孔道内，得到纳米硅氧碳结构复合材料。
  11. 根据权利要求10所述的制备方法，其特征在于，所述步骤S1中所述含表面氧化层的多孔炭基底的制备方法为，将碳前驱体和造孔剂混合炭化后形成炭化后材料，并对所述炭化后材料进行破碎和氧化处理。
  12. 根据权利要求10或11所述的制备方法，其特征在于，所述含表面氧化层的多孔炭基底的比表面积为50～2000m 2/g、孔容为0.1～3.0cm 3/g，所述含表面氧化层的多孔炭基底的孔结构包含微孔、介孔和大孔；优选地，所述微孔孔容在总孔容中的比例为1～40％，所述介孔孔容在总孔容中的比例为30～80％，所述大孔孔容在总孔容中的比例为1～40％；
    优选地，所述含表面氧化层的多孔炭基底的比表面积为100～1000m 2/g、孔容为0.3～1.5cm 3/g；进一步优选地，所述微孔孔容在总孔容中的比例为1～20％，所述介孔孔容在总孔容中的比例为60～80％，所述大孔孔容在总孔容中的比例为1～20％。
  13. 根据权利要求10至12中任一项所述的制备方法，其特征在于，所述步骤S2的实施过程中，所述含硅前体和所述含氧前体以任意体积比组合，优选地，所述含硅前体选自甲硅烷、乙硅烷、丙硅烷、卤代硅烷、聚硅烷、噻咯及其衍生物、硅芴及其衍生物等中的一种或多种，优选地，所述含氧前体为氧气、二氧化碳、水蒸气、甲醇、乙醇、正丙醇、异丙醇、丁醇、丙酮、丁酮中的一种或多种，
    优选地，所述含硅前体和含氧前体的体积比随着通入时间的延长存在连续变化和/或周期性变化。
  14. 根据权利要求10至13中任一项所述的制备方法，其特征在于，所述步骤S2在通入所述含硅前体和所述含氧前体同时通入惰性气体，所述惰性气体为氮气、氩气、氦气中的一种或多种；优选地，通入所述含硅前体和含氧前体与所述惰性气体的第一混合气时，所述含氧前体为甲醇、乙醇、正丙醇、异丙醇、丁醇、丙酮、丁酮中的一种或多种，所述第一混合气中所述含硅前体的体积含量为1～50％，所述含氧前体的体积含量为0.5～10％；优选地，所述第一混合气通入时所述热处理的温度为400～700℃，进一步优选地，所述第一混合气通入时所述热处理的时间为5-50h。
  15. 根据权利要求10至13中任一项所述的制备方法，其特征在于，所述步骤S2在通入所述含硅前体和所述含氧前体之前、之后、同时或间隙通入惰性气体，所述惰性气体为氮气、氩气、氦气中的一种或多种；优选地，通入所述含硅前体与所述惰性气体的第二混合气时，所述第二混合气中所述硅前体的体积含量为1～50％，通入所述含氧前体与所述惰性气体的第三混合气时，所述第三混合气中所述含氧前体的体积含量为1～50％；进一步优选地，所述含硅前体通入时所述热处理的温度为400～700℃，所述含氧前体通入时所述热处理的温度为150～600℃，优选地，所述步骤S2包括：
    步骤S2-1，将惰性气体通入放置有含表面氧化层的多孔炭基底的反应炉中，并将所 述反应炉的温度升至400～700℃；
    步骤S2-2，通入所述含硅前体与所述惰性气体的第二混合气，所述第二混合气中所述含硅前体的体积浓度为1％～50％，并将所述反应炉在400～700℃保持0.5～15h；
    步骤S2-3，停止通入所述含硅前体，仅通入所述惰性气体，将所述反应炉的温度调节至150～600℃；
    步骤S2-4，通入所述含氧前体与所述惰性气体的第三混合气，所述第三混合气中所述含氧前体的体积浓度为1％～50％，并将所述反应炉在150～600℃保持0.1～5h；
    步骤S2-5，重复2～50次所述步骤S2-1至步骤S2-4。
  16. 根据权利要求10至15中任一项所述的制备方法，其特征在于，所述制备方法还包括：
    步骤S3，对所述步骤S2的所述纳米硅氧碳结构复合材料进行破碎分级，得到中位粒径为4～12μm的纳米硅氧碳结构复合材料分级颗粒，优选所述破碎分级的方式为人工研磨、机械磨、球磨、气流磨中的任意一种或多种。
  17. 根据权利要求16所述的制备方法，其特征在于，所述制备方法还包括：
    步骤S4，对所述步骤S3的所述纳米硅氧碳结构复合材料分级颗粒进行深度氧化处理，优选所述深度氧化处理包括将所述纳米硅氧碳结构复合材料分级颗粒与包含氧化性物质的溶液和/或气体于0～400℃接触0.5～12h。
  18. 根据权利要求17所述的制备方法，其特征在于，所述步骤S4中，所述深度氧化处理包括液相氧化和/或气相氧化；
    优选地，所述液相氧化的步骤为，将所述纳米硅氧碳结构复合材料分级颗粒置于氧化性物质和/或氧化性物质的水和/或乙醇溶液中，超声分散0.5～2h后，于0～50℃搅拌0.5～12h，过滤和/或离心使固液分离，用去离子水和/或乙醇多次洗涤固体，并将所得固体于40～200℃鼓风干燥0.5～24h后，于惰性气氛中200～400℃处理0.5～5h，所述含氧化合物选自KMnO 4、H 2O 2、HNO 3、H 2SO 4、乙酸、丙酸、丁酸、丁二酸、苹果酸、柠檬酸中的任意一种或多种，所述液相氧化在紫外光和/或微波辐射的作用下进行；
    优选地，所述气相氧化的步骤为，将所述纳米硅氧碳结构复合材料分级颗粒抽真空至真空度低于10 -2Pa，然后通入包含氧化性气体和惰性气体的混合气，控制升温速率为1～10℃/min，从室温升至200～400℃，并于200～400℃处理0.1～5h，所述氧化性气体选自氧气、臭氧、二氧化碳、水蒸气中的任意一种或多种，所述惰性气体为氮气、氩气、氦气中的一种或多种，所述氧化性气体占所述混合气的比例为0.5～20％。
  19. 根据权利要求17或18所述的制备方法，其特征在于，在所述步骤S4之前，增加对所述纳米硅氧碳结构复合材料分级颗粒的酸处理和/或碱处理过程；
    优选地，所述酸处理的方法为，将所述纳米硅氧碳结构复合材料分级颗粒分散至含 酸的水/乙醇溶液中，于0～50℃搅拌0.5～12h，过滤和/或离心使固液分离，用去离子水和/或乙醇多次洗涤固体至滤液和/或上清液pH为中性，对所得固体进行真空干燥；
    所述碱处理的方法为，将所述纳米硅氧碳结构复合材料分级颗粒分散至含碱的水/乙醇溶液中，于0～50℃搅拌0.5～12h，过滤和/或离心使固液分离，用去离子水和/或乙醇多次洗涤固体至滤液和/或上清液pH为中性，对所得固体进行真空干燥；所述酸为HCl、H 2SO 4、HNO 3、H 3PO 4中的一种或多种，所述碱为NaOH、KOH、Na 2CO 3、K 2CO 3、NH 3H 2O、NH 4HCO 3、(NH 4) 2CO 3、尿素中的一种或多种。
  20. 根据权利要求10至19中任一项所述的制备方法，其特征在于，所述制备方法还包括：
    步骤S5，在所述纳米硅氧碳结构复合材料上包裹固体电解质和/或导电聚合物。
  21. 根据权利要求10至20中任一项所述的制备方法，其特征在于，所述制备方法还包括：
    步骤S6，对所述纳米硅氧碳结构复合材料进行真空处理及碳包覆，所述碳包覆的方式为采用甲烷、乙烷、丙烷、丁烷、乙烯、丙烯、丁烯、乙炔、丙炔、甲醇、乙醇、正丙醇、异丙醇、丁醇、丙酮、丁酮中的一种或多种，对所述复合材料进行气相沉积，或采用液体碳前驱体进行液相碳包覆，优选地，所述液体碳前驱体选自树脂、沥青。
  22. 一种负极，包括负极材料，其特征在于，所述负极材料为权利要求1至9中任一项所述的纳米硅氧碳结构复合材料或者权利要求10至21中任一项所述制备方法得到的纳米硅氧碳结构复合材料。
  23. 一种电化学装置，包含负极，其特征在于，所述负极为权利要求22所述的负极，优选所述电化学装置为锂离子二次电池。
PCT/CN2022/134811 2021-11-27 2022-11-28 纳米硅氧碳结构复合材料、其制备方法、负极和电化学装置 WO2023093893A1 (zh)

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