WO2021254142A1 - 二次锂电池用硅碳复合材料及其制备方法 - Google Patents

二次锂电池用硅碳复合材料及其制备方法 Download PDF

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WO2021254142A1
WO2021254142A1 PCT/CN2021/097741 CN2021097741W WO2021254142A1 WO 2021254142 A1 WO2021254142 A1 WO 2021254142A1 CN 2021097741 W CN2021097741 W CN 2021097741W WO 2021254142 A1 WO2021254142 A1 WO 2021254142A1
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coating layer
ion
composite material
carbon
silicon
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PCT/CN2021/097741
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French (fr)
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陈青华
胡盼
姚林林
房冰
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兰溪致德新能源材料有限公司
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Priority to JP2022578878A priority Critical patent/JP2023530031A/ja
Priority to KR1020237002333A priority patent/KR20230028449A/ko
Priority to US18/011,200 priority patent/US20230275215A1/en
Priority to EP21826191.5A priority patent/EP4156331A1/en
Publication of WO2021254142A1 publication Critical patent/WO2021254142A1/zh

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    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
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Definitions

  • the invention relates to the field of lithium ion battery materials, in particular to a silicon carbon negative electrode material for secondary lithium batteries and a preparation method thereof.
  • volume expansion can be solved by controlling the content of silicon in carbon materials and reducing the volume of silicon to nanoscale; or changing the texture and shape of graphite to achieve the best match between carbon and silicon; or using other substances to coat silicon to promote Recovery after expansion; it is also possible to use a composite of silicon and metal or non-metal to form a composite material to better release the stress generated by the volume change and provide space for volume expansion.
  • the present invention provides a silicon-carbon composite material with high strength, high rate and long cycle for secondary lithium batteries and a preparation method of the material.
  • the present application provides a silicon-carbon composite material, comprising a core containing a silicon-based material and a first coating layer and a second coating layer on the surface of the core, the first coating layer is a conductive layer, and the first coating layer is a conductive layer.
  • the second coating layer is an ion-conducting layer, and the order of the first coating layer and the second coating layer is not limited.
  • the present application provides a method for preparing the above-mentioned silicon-carbon composite material.
  • the method includes: a precursor step, a first coating layer coating step, a prelithiation step, and a second coating layer. Covering process.
  • the silicon-carbon negative electrode material for secondary lithium batteries and the preparation method thereof provided by the present invention have the following beneficial effects:
  • the coating layer is a composite material, it combines the conductive (or ion-conducting) ability of the matrix material, and the enhancement and toughness properties of the reinforcing phase, so that the coating layer is not easy to crack after the silicon-based core expands.
  • the coating layer that is not easy to break means less new surface, which reduces the consumption of electrolyte and improves the cycle performance of the battery.
  • the carbon composite material coating layer can effectively buffer the volume expansion of the core and improve the electronic conductivity; while the ion conductor composite material coating layer can provide ion conductive channels, enhance the ion conductive ability of the material, and make the negative electrode material can be prepared for a long life. , High-rate lithium-ion battery.
  • Fig. 3 XRD pattern of the silicon-carbon composite material prepared in Example 11 of the present invention.
  • D50 is the particle size corresponding to when the cumulative volume percentage of the material reaches 50%, and the unit is ⁇ m.
  • a list of items connected by the terms “one or more combinations of”, “at least one of” or other similar terms can mean any combination of the listed items. For example, if items A and B are listed, then the phrase “one or more of A and B" means only A; only B; or A and B; if items A and B are listed, then the phrase “A "At least one of and B” means only A; only B; or A and B. Item A may include a single element or multiple elements, and item B may include a single element or multiple elements.
  • the embodiment of the present application provides a silicon-carbon composite material for a secondary lithium battery, comprising a core containing a silicon-based material and a first coating layer and a second coating layer on the surface of the core, the first coating layer is a conductive layer, The second coating layer is an ion-conducting layer, and the order of the first coating layer and the second coating layer is not limited.
  • the first coating layer covers the surface of the inner core, and the second coating layer covers the surface of the inner core.
  • the surface of the first coating layer; or, the second coating layer is coated on the surface of the core, and the first coating layer is coated on the surface of the second coating layer.
  • the first coating layer includes a carbon composite material, or a combination of a carbon composite material and an ion conductor composite material; based on the total mass of the first coating layer as 100%, the mass percentage of the carbon composite material is 90%. ⁇ 100%, preferably 97-100%, to ensure the conductivity and anti-expansion ability of the first coating layer.
  • the second coating layer includes an ion conductor composite material, or a combination of an ion conductor composite material and a carbon composite material; based on the total mass of the second coating layer as 100%, the mass percentage of the ion conductor composite material It is 90-100%, preferably 97-100%, to ensure the ion conductivity of the second coating layer and the ability to stabilize the SEI film.
  • the total mass of the silicon-carbon composite material is calculated as 100%, and the mass percentage of the core of the silicon-based material is 80-99%, preferably 92-96%. Within this range, the negative electrode material exhibits high The specific capacity and excellent cycle performance.
  • the carbon composite material includes a carbon-reinforced phase and a carbon matrix.
  • the carbon-reinforced phase is compounded with the carbon matrix to form a reinforced concrete structure.
  • the carbon-reinforced phase, the carbon-reinforced phase prevents the material particles from cracking by absorbing or halving the stress; in some embodiments, the mass ratio of the carbon-reinforced phase to the carbon matrix is 0.1-1:1, preferably 0.15-0.5:1, If the mass ratio is less than 0.1:1, the carbon reinforcement phase is too small, the carbon composite material has poor reinforcement effect, and the material structure is easy to collapse; if the mass ratio is greater than 1:1, the carbon matrix is too small, the material conductivity is poor, and the carbon matrix cannot be fixed and Adhesion enhancing phase.
  • the carbon reinforcement phase includes one or more combinations of carbon nanotubes, carbon black, carbon fibers, graphene, and porous carbon; the carbon matrix includes one or more of pitch carbon, resin carbon, and vapor phase pyrolysis carbon. Multiple combinations.
  • the ion conductor composite material includes an ion-enhancing phase and an ion matrix, the ion-enhancing phase and the ion matrix are organically combined to form a reinforced concrete-like structure, and the ion-conductor composite material combines the high strength of the ion matrix and the high toughness of the ion-enhanced phase
  • effective prevention of stress diffusion, better buffer volume expansion, enhanced structural strength, high-strength ion matrix maintains the basic structure of the coating layer, and provides the main ion conduction channel; in some embodiments, the ion-enhancing phase and ion
  • the mass ratio of the matrix is 0.1-1:1, preferably 0.15-0.5:1.
  • the mass ratio is less than 0.1:1, the ion enhancement phase is too small, the ion composite material has a poor enhancement effect, and the ion conductor composite material layer is too strong. It is brittle and easy to break; if the mass ratio is greater than 1:1, the ion conductor matrix is too small, and the ion conductive channel provided is reduced, resulting in an insignificant improvement in the rate performance of the material.
  • the ionic reinforcing phase includes at least one of fibers, whiskers, and particles, preferably aramid fibers, polyethylene fibers, nylon fibers, glass fibers, Al 2 O 3 fibers, SiC fibers, and BN fibers , Si 3 N 4 fiber, TiC fiber, TiN fiber, B 4 C fiber, ceramic fiber, one or more of the group consisting of;
  • the whiskers are selected from SiC whiskers, K 2 TiO 3 whiskers, aluminum borate One or more of the group consisting of whiskers, CaSO 4 whiskers, CaCO 3 whiskers, Al 2 O 3 whiskers, ZnO whiskers and MgO whiskers;
  • the particles are selected from SiC particles, Al 2 O 3 One or more of the group consisting of particles, BN particles, Si 3 N 4 particles, TiC particles, and B 4 C particles.
  • the ion matrix includes fast ion conductor materials, including but not limited to LISICON solid electrolyte, NASICION solid electrolyte, perovskite solid electrolyte, garnet solid electrolyte, sulfide solid electrolyte, PEO-based polymer
  • the inner core also contains a lithium compound.
  • the purpose of doping with the lithium compound is to Improve the first coulombic efficiency, mainly in the form of lithium silicate salt in silicon-based materials, with the increase of Li doping, the lithium silicate changes to Li 2 Si 2 O 5 , Li 2 SiO 3 , Li 4 SiO in turn 4. Excessive Li doping will cause the slurry to be unstable.
  • the inventors unexpectedly discovered that when the content of Li 2 SiO 3 is the highest, the first coulombic efficiency of the material is the highest and the processability of the material is the best.
  • the thickness of the first coating layer is 2 to 1000 nm, preferably 5 to 200 nm; the thickness of the second coating layer is 1 to 100 nm, preferably 2 to 20 nm.
  • the thickness of the coating layer is within a certain range, The high capacity and high rate performance of silicon-carbon composite materials have been further improved.
  • the preparation method provided by the present invention includes the following steps: a precursor step, a first coating layer coating step, a prelithiation step, and a second coating layer coating step;
  • the precursor process refers to chemical vapor deposition or high-temperature vacuum deposition of silicon raw materials to obtain SiOx (0 ⁇ x ⁇ 2) precursors;
  • the first coating layer coating step refers to coating the SiOx precursor or lithium-doped active particles with a conductive layer by a chemical vapor deposition method
  • the pre-lithiation step refers to the formation of lithium silicate inside the silicon-oxygen compound by inserting lithium into the aforementioned coated material to obtain lithium-doped active particles;
  • the second coating layer coating process refers to mixing the SiOx precursor or lithium-doped active particles with the ion-enhancing phase and the ion matrix, uniformly dispersing them in pure water, and then filtering and drying the mixed solution to conduct the ion-conducting layer ⁇ cladding;
  • the sequence of the first coating layer coating step and the second coating layer coating step can be changed.
  • the sequence of the preparation method is the precursor step, the first coating layer coating step, the prelithiation step, and the second coating step.
  • the precursor process refers to placing the silicon raw material in a chemical vapor deposition (CVD) furnace or a vacuum furnace, and heating 2-28 (such as 2-8 Hours) hours to generate SiO gas, and then cool the SiO gas at a certain temperature into agglomerates, crush and sieving to obtain a SiOx (0 ⁇ x ⁇ 2) precursor with a particle size D50 of 1-10um; among them, the silicon raw material is preferably Use a mixture of silica powder and elemental silicon powder; the physical properties of the silicon raw material are not limited.
  • the first coating layer coating step refers to dissolving the carbon reinforcement in a solvent, and loading the carbon reinforcement on the surface of the SiOx precursor or lithium-doped active particles by filtering and drying. Then the carbon matrix is coated by vapor deposition; wherein the vapor deposition temperature is 500-1000° C., and the solvent includes pure water, ethanol, toluene, xylene or a combination thereof.
  • the pre-lithiation process refers to one or more of the gas phase CVD method, thermal doping method, redox method, or electrochemical method to achieve the purpose of doping lithium silicate.
  • the secondary coating process refers to dispersing the SiOx precursor or lithium-doped active particles in a solvent, adding a certain amount of ion enhancer and ion matrix, and stirring it uniformly before filtering and drying; wherein,
  • the solvent includes pure water, ethanol, toluene, xylene, or a combination thereof.
  • Si powder and SiO 2 powder uniformly, add them to a vacuum furnace for heat treatment, and heat to 1200°C under a vacuum of 500 Pa.
  • the heat treatment time is 1 h.
  • the above powders are sublimated, steam condensed, and heated under high temperature and vacuum conditions. Crushing and sieving to obtain silicon oxide precursor particles with a particle size of 1-10 ⁇ m.
  • CNT carbon nanotubes
  • the particles are loaded into a CVD furnace, heated to 950°C, and fed with acetylene with a flow rate of 9L/min, hydrogen gas with a flow rate of 9L/min and argon gas with a flow rate of 18L/min, and the deposition time is 1h.
  • Acetylene is decomposed at high temperature to form pyrolytic carbon to coat the surface of CNT and particles to obtain a first coating layer.
  • the first coating layer is a carbon composite material, wherein CNT is a reinforcing phase, pyrolysis carbon is a matrix, and the mass ratio of CNT to pyrolysis carbon is 0.3:1, and the thickness of the first coating layer is 60 nm.
  • the composite powder obtained above and a certain amount of Li 3 N powder are mixed uniformly, and at the same time, they are added to a high-temperature furnace for heat treatment.
  • Li 3 N is pyrolyzed at a high temperature of 700 to 900 °C for 1 to 3 hours, and the active lithium is inserted into the silicon oxide
  • the internal pre-lithiation is completed to obtain lithium-doped negative electrode active material particles.
  • the negative electrode active material particles were analyzed with an X-ray diffraction analyzer (D8ADVANCE type).
  • Figure 1 is the XRD diffraction pattern prepared in Example 1. It can be seen that among the diffraction peaks obtained by X-ray diffraction, the diffraction angle 2 ⁇ The diffraction peak of Li 2 SiO 3 near 26.9° shows the greatest intensity.
  • the second coating layer is an ion composite material, in which the whiskers are the reinforcing phase, the lithium phosphate (fast ion conductor material) is the matrix, and the thickness of the second coating layer is 6 nm.
  • the mass ratio of the silicon-based material core measured by an inductively coupled plasma spectrometer (ICP, Optima 2100DV) is 95%.
  • Si powder and SiO 2 powder uniformly, add them to a vacuum furnace for heat treatment, and heat to 1200°C under a vacuum of 500 Pa.
  • the heat treatment time is 1 h.
  • the above powders are sublimated, steam condensed, and heated under high temperature and vacuum conditions. Crushing and sieving to obtain silicon oxide precursor particles with a particle size of 1-10 ⁇ m.
  • the second coating layer is an ion composite material, in which the whiskers are the reinforcing phase, the lithium phosphate is the matrix, and the thickness of the second coating layer is 6 nm.
  • Li 3 N is pyrolyzed at high temperature to activate lithium Insert into the silicon oxide to complete the prelithiation, and obtain lithium-doped negative electrode active material particles.
  • the negative electrode active material particles were analyzed with an X-ray diffraction analyzer (D8ADVANCE type).
  • Figure 2 is the XRD diffraction pattern prepared in Example 2. It can be seen that among the diffraction peaks obtained by X-ray diffraction, the diffraction angle 2 ⁇ The diffraction peak of Li 2 SiO 3 near 26.9° shows the greatest intensity.
  • the particles obtained in the step are put into a CVD furnace, heated to 950°C, and fed with acetylene with a flow rate of 9L/min, hydrogen gas with a flow rate of 9L/min and argon gas with a flow rate of 18L/min, and the deposition time is 1h.
  • Acetylene is decomposed at high temperature to form pyrolytic carbon to coat the surface of CNT and particles to obtain a first coating layer.
  • the first coating layer is a carbon composite material, wherein CNT is a reinforcing phase, pyrolysis carbon is a matrix, and the mass ratio of CNT to pyrolysis carbon is 0.3:1, and the thickness of the first coating layer is 60 nm.
  • the first coating layer also contains an ion-conducting composite material composed of lithium phosphate whiskers and lithium phosphate particles.
  • the second coating layer also contains a conductive composite material composed of CNT and pyrolytic carbon.
  • the difference is that the first coating layer also contains the ion conductive composite material composed of lithium phosphate whiskers and lithium phosphate particles in a mass ratio of 0.2:1, and the second coating layer also contains Contains a conductive composite material composed of CNT and pyrolytic carbon in a mass ratio of 0.3:1.
  • the above powders are sublimated, steam condensed, and heated under high temperature and vacuum conditions. Crushing and sieving to obtain silicon oxide precursor particles with a particle size of 1-10um.
  • the precursor particles are heated to 950°C in a CVD furnace, the vacuum degree in the furnace is controlled at 300Pa, and acetylene with a flow rate of 9L/min and argon with a flow rate of 18L/min are introduced, and the deposition time is 1h to obtain a carbon-coated Silicon particles, and the thickness of the carbon coating layer is 60 nm.
  • the carbon-coated silicon particles are uniformly mixed with a certain amount of Li 3 N powder, and at the same time they are added to a high-temperature furnace for heat treatment.
  • Li 3 N is pyrolyzed at a high temperature, and active lithium is inserted into the silicon oxide to complete the prelithiation.
  • Lithium-doped negative electrode active particles Mix lithium-doped negative electrode active particles with 1.5wt% LiPO 3 , add pure water, stir evenly, filter and dry to obtain the required SiO/C/LiPO 3 composite powder, in which the thickness of the LiPO 3 coating layer is 6nm .
  • Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that the coating layers of Comparative Example 1 are all continuous phases.
  • Example 11 The other steps and process parameters are the same as in Example 1, except that the weight ratio of lithium nitride to carbon-coated silicon particles is changed, thereby changing the degree of Li doping.
  • the negative electrode active material particles of Example 11 were analyzed with an X-ray diffraction analyzer (D8ADVANCE type).
  • Figure 3 is the XRD diffraction pattern prepared in Example 11. It can be seen that among the diffraction peaks obtained by X-ray diffraction, The diffraction peak of Li 2 Si 2 O 5 having a diffraction angle 2 ⁇ near 24.5° exhibits the greatest intensity.
  • the first Coulomb efficiency test Mix the prepared anode material powder: SP (carbon black): CNT (carbon nanotube): PAA (polyacrylic acid) at a mass ratio of 80:9:1:10, add an appropriate amount of deionized water as a solvent, and use a magnetic stirrer to continue Stir for 8h to paste.
  • the stirred slurry was poured on a copper foil with a thickness of 9 ⁇ m, coated with an experimental coater, and dried at 85° C. under vacuum (-0.1 MPa) for 6 hours to obtain a negative electrode sheet.
  • the prepared button battery was allowed to stand at room temperature for 12 hours, and then in the LAND battery test system constant current charge and discharge test, charge and discharge at a current of 0.1C, the cut-off voltage of lithium removal was 1.5V, and the first negative electrode material was obtained. efficient.
  • the CR2032 button battery was prepared by the above method, and the battery was charged and discharged with the LAND battery test system. After standing for 6 hours, the battery was discharged at 0.05C to 0.005V, and then at 0.01C to 0.005V; After 5min, charge at 0.05C constant current to 1.5V; after standing for 5min, repeat the above steps twice; then discharge at 0.25C to 0.005V; after standing for 5min, charge at 0.25C constant current to 1.5V, after 20 cycles , Disassemble the button in the glove box, and then measure the thickness of the pole piece.
  • the calculation method of expansion ratio is: (thickness of pole piece after circulation-thickness of fresh pole piece)/thickness of fresh pole piece ⁇ 100%.
  • the resistance is determined by measuring the voltage at both ends of the resistance to be measured and the current flowing through it, and the conductivity is calculated by combining the height and bottom area of the resistance to be measured. Take a certain amount of powder and add it to the test mold, shake it gently, then place the gasket on the mold on the sample; after the sample is loaded, place the mold on the worktable of the electronic pressure testing machine at a rate of 5mm/min Raise to 500kg (159Mpa), constant pressure for 60s, and then relieve the pressure to 0; when the sample constant pressure reaches 5000 ⁇ 2kg (about 15-25s after the pressure is increased to 1 to 5000kg), record the sample pressure and read the deformation height of the sample, Record the displayed value of the resistance tester at this time, and then use the formula (I) to calculate the electronic conductivity.
  • Lithium ion conductivity test use the above method to prepare CR2032 button battery, use the LAND battery test system to charge and discharge the battery, after standing for 6 hours, discharge at 0.05C to 0.005V, and then at 0.01 C discharge to 0.005V; after standing for 5 minutes, 0.05C constant current charge to 1.5V; after standing for 5 minutes, repeat the above steps twice, and then use electrochemical workstation to conduct electrochemical impedance spectroscopy test on the button.
  • the frequency range is 0.01 ⁇ 105Hz
  • the voltage amplitude is 0.005V
  • the last 5 data points are selected from the data points obtained by the test
  • the linear slope of Z'vs. rotation speed w ⁇ -0.5 at low frequency is obtained.
  • the slope value is the warburg parameter, in the same test Under the conditions, the smaller the warburg parameter, the higher the lithium ion conductivity.
  • Capacity retention rate test Mix the prepared anode material powder with graphite anode (mass ratio 20:80) to obtain mixed anode powder, and then mix the anode powder, SP, CNT, CMC (carboxymethyl Base cellulose sodium) and SBR (styrene butadiene rubber) are mixed, and continuously stirred with a magnetic stirrer for 8 hours to a paste.
  • the stirred negative electrode slurry was poured on a copper foil with a thickness of 9 ⁇ m, coated with an experimental coater, and dried under vacuum (-0.1 MPa) conditions at 85° C. for 6 hours to obtain a negative electrode sheet.
  • the positive and negative electrode sheets were rolled to 100 ⁇ m in sequence on a manual counter-roller, and then a sheet with a diameter of 12mm was obtained by a punching mechanism, dried at 85°C under vacuum (-0.1MPa) for 8h, weighed and calculated the weight of the active material.
  • the prepared button cell battery was allowed to stand at room temperature for 12 hours, and then subjected to a constant current charge-discharge test on a blue power test system. Charge and discharge with a current of 0.25C, the charge-discharge cut-off voltage was 3.0-4.25V. Calculate the capacity retention rate by calculating the discharge capacity of the 100th circle/the discharge capacity of the first circle ⁇ 100%.
  • Rate performance test The prepared button-type battery was allowed to stand at room temperature for 12 hours, and then subjected to a constant current charge and discharge test on a blue power test system, with a charge-discharge cut-off voltage of 3.0-4.25V, and first charge and discharge with a current of 0.25C, and cycle 3 times. Then charge and discharge with 0.5C current for 3 cycles. Finally, charge and discharge with 1C current for 3 cycles.
  • the discharge capacity of the 9th circle/the discharge capacity of the first circle ⁇ 100% is calculated to obtain the capacity retention rate. The higher the value, the better the rate performance.
  • test results of each embodiment and comparative example are shown in Table 1 and Table 2.
  • the diameter of the carbon fiber in Table 1 is 0.1 to 1 ⁇ m, and the length is 1 to 5 ⁇ m;
  • the resin carbon is phenolic resin carbon or epoxy resin carbon, and there is no significant difference in the results when the two are applied to the corresponding embodiments;
  • the porous carbon is activated carbon.
  • the cladding layer is a composite material with a structure similar to reinforced concrete, the material exhibits a lower expansion rate and excellent electrochemical performance, and by controlling the mass ratio of the reinforcing phase and the matrix, the material can be maximized. Good overall performance. From Example 11 and Example 1, it can be seen that a suitable Li doping amount can obtain a better first-time coulombic efficiency.
  • the coating layer has both conductive composite material and ion conductive composite material, the material exhibits higher electronic conductivity, ionic conductivity and better rate performance, and the conductive composite material in the coating layer is adjusted
  • the mass ratio of the material and the ion-conducting composite material can obtain a negative electrode material with better performance.

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Abstract

本发明公开了一种二次锂电池用硅碳复合材料及其制备方法，所述二次锂电池用硅碳复合材料包括含硅基材料的内核以及第一包覆层和第二包覆层，所述第一包覆层为导电层，所述第二包覆层为导离子层，所述第一包覆层和所述第二包覆层没有顺序限定。本发明提供的硅碳复合材料，包覆层为复合材料，结合了基体材料的导电(或导离子)能力，以及增强相的增强、增韧性能，使得材料具有很强的抗膨胀能力。在二次电池中，不易破裂的包覆层意味着更少的新生表面，降低了电解液消耗，提高了电池循环性能。此外，本发明制备方法简单易实施，适合大规模产业化生产。

Description

二次锂电池用硅碳复合材料及其制备方法 技术领域
本发明涉及锂离子电池材料领域，具体涉及一种二次锂电池用硅碳负极材料及其制备方法。
背景技术
近年来，硅基材料取代碳素材料作为锂离子电池负极材料成为学术界和产业界的研究热点，但硅在锂合金化过程中的体积膨胀效应尤为严重，这将导致电极材料严重粉化，电极结构的坍塌以及活性材料与集流体失去电接触，从而使得电池循环性能差。解决体积膨胀的问题可以通过控制碳材料中硅的含量、减小硅体积到纳米级；或改变石墨质地、形态，实现碳和硅的最佳匹配；或者采用其他物质对硅进行包覆，促进膨胀后的复原；还可以采用硅和金属或非金属复合构成复合材料，以更好释放体积变化产生的应力，提供体积膨胀的空间。
实践证实，要想取得比较理想的电化学性能，复合材料中的硅颗粒粒径不能超过200-300nm，但是在比表面、粒径分布、杂质以及表面钝化层厚度等关键指标技术壁垒都很高，目前还都未实现。
发明内容
为克服现有技术存在强度低、倍率低、循环差的缺陷，本发明提供了一种二次锂电池用具有高强度、高倍率、长循环的硅碳复合材料以及该材料的制备方法。
在一个实施例中，本申请提供了一种硅碳复合材料，包括含硅基材料的内核以及内核表面的第一包覆层和第二包覆层，第一包覆层为导电层，第二包覆层为导离子层，第一包覆层和第二包覆层没有顺序限定。
在另一个实施例中，本申请提供了一种制备上述硅碳复合材料的方法，所述方法包括：前驱体工序、第一包覆层包覆工序、预锂化工序、第二包覆层包覆工序。
与现有技术相比，本发明提供的二次锂电池用硅碳负极材料及其制备方法具有以下有益效果：
(1)材料结构方面，由于包覆层为复合材料，结合了基体材料的导电(或导离子)能力，以及增强相的增强、增韧性能，使得包覆层在硅基内核膨胀后不易破裂，在二次电池中，不易破裂的包覆层意味着更少的新生表面，降低了电解液消耗，提高了电池循环性能。
(2)碳复合材料包覆层可以有效缓冲内核体积膨胀并提高电子导电性；而离子导体复合材料包覆层则可提供导离子通道，增强材料的导离子能力，使得负极材料可以制备长寿命、高倍率的锂离子电池。
(3)制备工艺方面，只包覆导电层，材料加工性能差，浆料不稳定，但首效效果好；只包覆导离子层，则不能缓冲硅基内核的体积膨胀，循环稳定性太差，但材料加工性能好，浆料最稳定。进行双层包覆，可结合两者优点，提高材料性能。
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本发明实施例1所制得的硅碳复合材料的XRD图谱；
图2本发明实施例2所制得的硅碳复合材料的XRD图谱；
图3本发明实施例11所制得的硅碳复合材料的XRD图谱。
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。本申请的实施例将会被详细的描述在下文中。本申请的实施例不应该被解释为对被申请的限制。
在本申请中，以范围格式呈现量、比率和其他数值，应理解，此类范围格式是用于便利及简洁起见，且应灵活地理解，不仅包含明确地指定为范围限制的数值，而且包含涵盖于所述范围内的所有个别数值或子范围，如同明确地指定每一数值及子范围一般。
在本申请中，D50为材料累计体积百分数达到50％时所对应的粒径，单位为μm。
在权利要求书及具体实施方式中，由术语“中的一种或多种组合”、“中的至少一种”或其他相似术语所连接的项目的列表可意味着所列项目的任何组合。例如，如果列出项目A及B，那么短语“A及B中的一种或多种组合”意味着仅A；仅B；或A及B；如果列出项目A及B，那么短语“A及B中的至少一种”意味着仅A；仅B；或A及B。项目A可包含单个元件或多个元件，项目B可包含单个元件或多个元件。
一、硅碳复合材料
本申请实施例提供了一种二次锂电池用硅碳复合材料，包括含硅基材料的内核以及内核表面的第一包覆层和第二包覆层，第一包覆层为导电层，第二包覆层为导离子层，第一包覆层和第二包覆层没有顺序限定，具体地可以是，述第一包覆层包覆在内核表面，第二包覆层包覆在第一包覆层表面；或者是，第二包覆层包覆在内核表面，第一包覆层包覆在第二包覆层表面。
在一些实施例中，第一包覆层包括碳复合材料、或者碳复合材料和离子导体复合材料的组合；以第一包覆层的总质量为100％计，碳复合材料的质量百分比为90～100％，优选地为97～100％，以保证第一包覆层的导电及抗膨胀能力。
在一些实施例中，第二包覆层包括离子导体复合材料、或者离子导体复合材料和碳复合材料的组合；以第二包覆层的总质量为100％计，离子导体复合材料的质量百分比为90～100％，优选地为97～100％，以保证第二包覆层的导离子及稳定SEI膜的能力。
在一些实施例中，以硅碳复合材料的总质量为100％计算，硅基材料内核的质量百分比为80～99％，优选地为92～96％，在此范围内，负极材料表现出高的比容量以及优异的循环性能。
在一些实施例中，碳复合材料包括碳增强相和炭基体，碳增强相与炭基体复合形成类钢筋混凝土结构，硅基材料内核膨胀应力传递至碳复合材料时，通过连续相炭基体传送至碳增强相，碳增强相通过吸收或平分应力而使材料颗粒不破裂；在一些实施例中，碳增强相和炭基体的质量比为0.1～1：1，优选地为0.15～0.5：1，若质量比小于0.1:1，碳增强相过少，碳复合材料增强效果差，材料结构易坍塌；若质量比大于1:1，炭基体过少，材料导电性能差，且炭基体无法固定和粘附增强相。
在一些实施例中，碳增强相包括碳纳米管、炭黑、碳纤维、石墨烯、多孔炭中的一种或多种组合；炭基体包括沥青炭、树脂炭、气相裂解炭中的一种或多种组合。
在一些实施例中，离子导体复合材料包括离子增强相和离子基体，离子增强相和离子基体有机复合形成类钢筋混凝土结构，离子导体复合材料结合了离子基体的高强度和离子增强相的高韧性优点，有效阻止应力扩散，更好的缓冲体积膨胀，加强结构强度，高强度的离子基体维持包覆层的基本结构，并提供主要的导离子通道；在一些实施例中，离子增强相和离子基体的质量比为0.1～1：1，优选的为0.15～0.5：1，若质量比小于0.1:1，离子增强相过少，离子复合材料增强效果差，离子导体复合材料层强度过高，脆性大、易破裂；若质量比大于1:1，离子导体基体过少，所提供的导离子通道减少，导致材料倍率性能提升不明显。
在一些实施例中，离子增强相包括纤维、晶须、颗粒中的至少一种，优选地是芳纶纤维、聚乙烯纤维、尼龙纤维、玻璃纤维、Al 2O 3纤维、SiC纤维、BN纤维、Si 3N 4纤维、TiC纤维、TiN纤维、B 4C纤维、陶瓷纤维组成的组中的一种或多种；所述晶须选自SiC晶须、K 2TiO 3晶须、硼酸铝晶须、CaSO 4晶须、CaCO 3晶须、Al 2O 3晶须、ZnO晶须、MgO晶须组成的组中的一种或多种；所述颗粒选自SiC颗粒、Al 2O 3颗粒、BN颗粒、Si 3N 4颗粒、TiC颗粒、B 4C颗粒组成的组中的一种或多种。
在一些实施例中，离子基体包括快离子导体材料，包括但不限于LISICON型固体电解质、NASICION型固体电解质、钙钛矿型固体电解质、石榴石型固体电解质、硫化物固态电解质、PEO基聚合物电解质的一种或多种组合，优选地是Al 2O 3、TiO 2、ZrO 2、V 2O 5、ZnO、CoO、P 2O 5、B 2O 3、SiO 2、AlPO 4、Co 3(PO 4) 3、Al(PO 3) 3、LiPO 3、Co(PO 3) 2、LiF、AlF 3、FeF 2、Li 3PO 4、LiM 2(PO 4) 3(M＝Ge、Ti、Zr、Sn)、Li 3xLa 2/3-xTiO 3(x＞0)、Li 5La 3A 2O 12(A＝Nb、Ta、Sb、Bi)、Li 7La 3B 2O 12(B＝Zr、Sn)、Li 2ZnGeS 4、Li 10GeP 2O 12中的一种或多种组合。
在一些实施例中，内核中还包含锂化合物，在Cu-Kα线的X射线衍射中归属于2θ＝26.9±0.2°的Li 2SiO 3的峰强度最强，锂化合物掺杂的目的是为了提高首次库伦效率，主要以硅酸锂盐的形式存在于硅基材料中，随着Li掺杂量的增加，硅酸锂依次变化为Li 2Si 2O 5、Li 2SiO 3、 Li 4SiO 4，过多的Li掺杂会导致浆料不稳定，发明人预料不到的发现，当Li 2SiO 3含量最高时，材料的首次库伦效率最高且材料可加工性能最佳。
在一些实施例中，第一包覆层厚度为2～1000nm，优选为5～200nm；第二包覆层厚度为1～100nm，优选为2～20nm，当包覆层厚度在一定范围时，硅碳复合材料的高容量以及高倍率性能得到进一步改善。
二、制备方法
本发明提供的制备方法包括以下工序：前驱体工序、第一包覆层包覆工序、预锂化工序、第二包覆层包覆工序；
前驱体工序是指将硅原料进行化学气相沉积或高温真空沉积，得到SiOx(0＜x＜2)前驱体；
第一包覆层包覆工序是指通过化学气相沉积法对SiOx前驱体或锂掺杂的活性颗粒进行导电层包覆；
(可选的)预锂化工序是指通过在前述包覆后的材料中插入锂，在硅氧化合物内部生成硅酸锂，得到锂掺杂的活性颗粒；
第二包覆层包覆工序是指将SiOx前驱体或锂掺杂的活性颗粒与离子增强相和离子基体混合，均匀分散到纯水中，然后将混合溶液进行过滤、干燥，进行导离子层的包覆；
第一包覆层包覆工序和第二包覆层包覆工序的顺序可调换，具体的，制备方法工序顺序为前驱体工序、第一包覆层包覆工序、预锂化工序、第二包覆层包覆工序；或是前驱体工序、第二包覆层包覆工序、预锂化工序、第一包覆层包覆工序。
在一些实施例中，前驱体工序是指将硅原料置于化学气相沉积(CVD)炉或真空炉中，在温度900-1300℃、气压0-5000Pa条件下加热2～28(比如2～8小时)小时生成SiO气体，然后将SiO气体在一定温度下冷却成块、破碎、筛分，得到粒径D50为1～10um的SiOx(0＜x＜2)前驱体；其中，硅原料，优选使用二氧化硅粉末与单质硅粉末的混合物；不对硅原料的物性进行限定。
在一些实施例中，第一包覆层包覆工序是指将碳增强体溶于溶剂中，通过过滤、干燥的方式，将碳增强体负载于SiOx前驱体或锂掺杂的活性颗粒表面，然后通过气相沉积包覆炭基体；其中，气相沉积温度为500～1000℃，溶剂包括纯水、乙醇、甲苯、二甲苯或其组合。
在一些实施例中，预锂化工序是指通过气相CVD法、热掺杂法、氧化还原法或电化学法中的一种或多种方法以达到掺杂锂硅酸盐的目的。
在一些实施例中，二次包覆工序是指将SiOx前驱体或锂掺杂的活性颗粒分散在溶剂中，加入一定量的离子增强体和离子基体，搅拌均匀后进行过滤、干燥；其中，溶剂包括纯水、乙醇、甲苯、二甲苯或其组合。
为更好地理解本发明提出的该材料的制备过程及性能特性，下面结合具体的实施例进行说明。下述实施例中实验方法，如无特殊说明，均为常规方法；试剂和材料，如无特殊说明，均可从商业途径获得。
三、实施例
实施例1
将一定量Si粉与SiO 2粉混合均匀，加入到真空炉中进行热处理，在500Pa真空度的条件下加热到1200℃，热处理时间为1h，上述粉末在高温和真空条件下升华、蒸汽冷凝、破碎、筛分，得到粒径1～10μm的氧化亚硅前驱体颗粒。
将以上得到的颗粒均匀分散到纯水中，再加入1％质量分数的CNT(碳纳米管)，继续搅拌均匀后过滤、干燥，得到表面附着CNT的氧化亚硅颗粒，再将上步得到的颗粒装入CVD炉中，加热到950℃，并通入流量为9L/min的乙炔、9L/min的氢气和流量为18L/min的氩气，沉积时间1h。乙炔在高温下裂解形成热解碳包覆在CNT和颗粒表面，得到第一包覆层。该第一包覆层为碳复合材料，其中CNT为增强相，热解碳为基体，且CNT与热解碳的质量比为0.3：1，第一包覆层的厚度为60nm。
将以上得到的复合粉末与一定量的Li 3N粉混合均匀，同时加入到高温炉中进行热处理，Li 3N在700～900℃高温下热解处理1～3h，活性锂插入到氧化亚硅内部完成预锂化，得到锂掺杂的负极活性物质颗粒。用X射线衍射分析仪(D8ADVANCE型)分析该负极活性物质颗粒，图1是实施例1所制得的XRD衍射图谱，可以看出，在由X射线衍射而得到的衍射峰中，衍射角2θ在26.9°附近具有的Li 2SiO 3的衍射峰表现出最大的强度。
将以上得到的Li掺杂颗粒均匀分散到纯水中，再加入3％质量分数的磷酸锂晶须和磷酸锂颗粒(磷酸锂晶须与磷酸锂颗粒的质量比为0.2：1)，继续搅拌均匀后过滤、干燥，磷酸锂晶须和磷酸锂颗粒附着在颗粒表面，得到第二包覆层。该第二包覆层为离子复合材料，其中晶须为增强相，磷酸锂(快离子导体材料)为基体，且第二包覆层的厚度为6nm。采用电感耦合等离子光谱发生仪(ICP，Optima 2100DV)测得硅基材料内核的质量比为95％。
实施例2
按照制备实施例1相同的方法操作，区别在于先包覆导离子层(第二包覆层)、后包覆导电层(第一包覆层)。
具体过程如下：
将一定量Si粉与SiO 2粉混合均匀，加入到真空炉中进行热处理，在500Pa真空度的条件下加热到1200℃，热处理时间为1h，上述粉末在高温和真空条件下升华、蒸汽冷凝、破碎、筛分，得到粒径1～10μm的氧化亚硅前驱体颗粒。
将以上得到的氧化亚硅前驱体颗粒均匀分散到纯水中，再加入3％质量分数的磷酸锂晶须和磷酸锂颗粒(磷酸锂晶须与磷酸锂颗粒的质量比为0.2：1)，继续搅拌均匀后过滤、干燥， 磷酸锂晶须和磷酸锂颗粒附着在颗粒表面，得到第二包覆层。该第二包覆层为离子复合材料，其中晶须为增强相，磷酸锂为基体，且第二包覆层的厚度为6nm。
将以上包覆有第二包覆层的颗粒与一定量的Li 3N粉混合均匀，同时加入到高温炉中700～900℃进行热处理1～3h，Li 3N在高温下热解，活性锂插入到氧化亚硅内部完成预锂化，得到锂掺杂的负极活性物质颗粒。用X射线衍射分析仪(D8ADVANCE型)分析该负极活性物质颗粒，图2是实施例2所制得的XRD衍射图谱，可以看出，在由X射线衍射而得到的衍射峰中，衍射角2θ在26.9°附近具有的Li 2SiO 3的衍射峰表现出最大的强度。
将以上得到的Li掺杂颗粒均匀分散到纯水中，再加入1％质量分数的CNT(碳纳米管)，继续搅拌均匀后过滤、干燥，得到表面附着CNT的氧化亚硅颗粒，再将上步得到的颗粒装入CVD炉中，加热到950℃，并通入流量为9L/min的乙炔、9L/min的氢气和流量为18L/min的氩气，沉积时间1h。乙炔在高温下裂解形成热解碳包覆在CNT和颗粒表面，得到第一包覆层。该第一包覆层为碳复合材料，其中CNT为增强相，热解碳为基体，且CNT与热解碳的质量比为0.3：1，第一包覆层的厚度为60nm。
实施例3～6
按照制备实施例1相同的方法操作，区别在于包覆层的增强相、基体以及增强相与基体的质量比不同。
实施例7
按照制备实施例1相同的方法操作，区别在于第一包覆层中还含有由磷酸锂晶须和磷酸锂颗粒组成的导离子复合材料。
实施例8
按照制备实施例1相同的方法操作，区别在于第二包覆层中还含有由CNT和热解碳组成的导电复合材料。
实施例9～10
按照制备实施例1相同的方法操作，区别在于第一包覆层中还含有由磷酸锂晶须和磷酸锂颗粒以0.2：1的质量比组成的导离子复合材料、第二包覆层中还含有由CNT和热解碳以0.3：1的质量比组成的导电复合材料。
对比例1
将一定量Si粉与SiO 2粉混合均匀，加入到真空炉中进行热处理，在500Pa真空度的条件下加热到1200℃，热处理时间为1h，上述粉末在高温和真空条件下升华、蒸汽冷凝、破碎、筛分，得到粒径1～10um的氧化亚硅前驱体颗粒。将前驱体颗粒在CVD炉中加热到950℃，炉内真空度控制在300Pa，并通入流量为9L/min的乙炔和流量为18L/min的氩气，沉积时间1h，得到碳包覆的硅颗粒，且碳包覆层厚度为60nm。将碳包覆的硅颗粒与一定量的Li 3N粉混合均匀，同时加入到高温炉中进行热处理，Li 3N在高温下热解，活性锂插入到氧化亚硅内部 完成预锂化，得到锂掺杂的负极活性颗粒。将锂掺杂的负极活性颗粒与1.5wt％的LiPO 3混合，加入纯水，搅拌均匀后过滤、干燥，得到需要的SiO/C/LiPO 3复合粉末，其中LiPO 3包覆层的厚度为6nm。
对比例1与实施例1的区别在于：对比例1的包覆层均为连续相。
实施例11
其他步骤与工艺参数与实施例1相同，区别在于改变氮化锂与碳包覆的硅颗粒的重量比，从而改变Li的掺杂程度。用X射线衍射分析仪(D8ADVANCE型)分析实施例11的负极活性物质颗粒，图3是实施例11所制得的XRD衍射图谱，可以看出，在由X射线衍射而得到的衍射峰中，衍射角2θ在24.5°附近具有的Li 2Si 2O 5的衍射峰表现出最大的强度。
测试方法
1、首次库伦效率测试。按质量比80：9：1：10将制备得到的负极材料粉末：SP(碳黑)：CNT(碳纳米管)：PAA(聚丙烯酸)混合，加入适量去离子水作溶剂，用磁力搅拌机连续搅拌8h至糊状。将搅拌好的浆料倒在厚度9μm的铜箔上，用实验型涂布机涂布后在85℃真空(-0.1MPa)条件下干燥6h，得到负极电极片。在手动对辊机上将电极片轧至100μm，再用冲片机制得直径12mm的圆片，在85℃真空(-0.1MPa)条件下干燥8h，称重并计算活性物质重量。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，1mol/L LiPF 6in EC:DEC＝1:1Vol％with 5.0％FEC为电解液。将制得的扣式电池在室温下静置12h，再在蓝电(LAND)电池测试系统恒流充放电测试，以0.1C电流进行充放电，脱锂截止电压1.5V，得到负极材料的首次效率。
2、膨胀率测试。采用上述方法制备CR2032型扣式电池，用蓝电(LAND)电池测试系统对电池进行充放电测试，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；静置5min后，重复两次上述步骤；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20次之后，在手套箱中拆解扣电，然后测量极片的厚度。膨胀率计算方式为：(循环后极片厚度-新鲜极片厚度)/新鲜极片厚度×100％。
3、电子电导率测试。采用四线两端子法，通过测量待测电阻两端电压和流经电流确定电阻，结合待测电阻的高度和底面积计算电导率。取一定量粉末加入到测试模具中，轻轻震平后，再将模具上的垫片放置在样品上；装样完毕后将模具置于电子压力试验机工作台面上，以5mm/min的速率升至500kg(159Mpa)，恒压60s，再卸压至0；当样品恒压至5000±2kg(升压到1达5000kg后约15～25s)时记录样品压力，并读取样品变形高度，记录此时的电阻测试仪显示数值，即可采用公式(Ⅰ)计算电子电导率。
Figure PCTCN2021097741-appb-000001
4、锂离子电导率测试：采用上述方法制备CR2032型扣式电池，用蓝电(LAND)电池测试系统对电池进行充放电测试，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；静置5min后，重复两次上述步骤，然后采用电化学工作站对扣电进行电化学阻抗谱测试。频率范围为0.01～105Hz，电压振幅为0.005V，测试得到的数据点取最后5个数据点，得到低频下Z’对转速w^-0.5的线性斜率，该斜率值为warburg参数，在同等测试条件下warburg参数越小表明锂离子电导率越高。
5、容量保持率测试。将制备得到的负极材料粉末与石墨负极混合(质量比20：80)，得到混合负极粉末，再按质量比95.2：0.85：0.15：1.2：2.6将混合负极粉末、SP、CNT、CMC(羧甲基纤维素钠)、SBR(丁苯橡胶)混合，用磁力搅拌机连续搅拌8h至糊状。将搅拌好的负极浆料倒在厚度9μm的铜箔上，用实验型涂布机涂布后在85℃真空(-0.1MPa)条件下干燥6h，得到负极电极片。接着按质量比90：2：1：7将811正极材料、SP、CNT、PVDF(聚偏氟乙烯)混合，加入适量NMP(N-甲基吡咯烷酮)作溶剂，用磁力搅拌机连续搅拌8h至糊状。将搅拌好的浆料倒在厚度16μm的铝箔上，用实验型涂布机涂布后在85℃真空(-0.1MPa)条件下干燥6h，得到正极电极片。在手动对辊机上依次将正、负电极片轧至100μm，再用冲片机制得直径12mm的圆片，在85℃真空(-0.1MPa)条件下干燥8h，称重并计算活性物质重量。在手套箱中组装CR2032型扣式全电池，以聚丙烯微孔膜为隔膜，1mol/L LiPF 6in EC:DEC＝1:1Vol％with 5.0％FEC为电解液。将制得的扣式全电池在室温下静置12h，再在蓝电测试系统上恒流充放电测试，以0.25C电流进行充放电，充放电截止电压3.0～4.25V。将第100圈的放电容量/第1圈的放电容量×100％，计算得到容量保持率。
6、倍率性能测试。将制得的扣式全电池在室温下静置12h，再在蓝电测试系统上恒流充放电测试，充放电截止电压3.0～4.25V，先以0.25C电流进行充放电，循环3次。再以0.5C电流进行充放电，循环3次。最后以1C电流进行充放电，循环3次。将第9圈的放电容量/第1圈的放电容量×100％，计算得到容量保持率，数值越高被认为倍率性能越好。
各实施例及对比例的测试结果如表1及表2所示。
表1实施例1～6、10及对比例1测试结果对比
Figure PCTCN2021097741-appb-000002
Figure PCTCN2021097741-appb-000003
表1中的碳纤维的直径为0.1～1μm，长度为1～5μm；树脂碳为酚醛树脂碳或环氧树脂碳，二者应用至相应实施例中结果没有明显差异；多孔碳为活性炭。
由表1可知，当包覆层为具有类似钢筋混凝土结构的复合材料时，材料表现出较低的膨胀率以及优异的电化学性能，且通过控制增强相及基体质量比，可使材料获得最佳综合性能。而通过实施例11和实施例1可知，合适的Li掺杂量可获得更好的首次库伦效率。
表2实施例1和实施例7～10测试结果对比
Figure PCTCN2021097741-appb-000004
Figure PCTCN2021097741-appb-000005
由表2可知，当包覆层同时具有导电复合材料和导离子复合材料时，材料表现出较高的电子电导率、离子电导率以及较好的倍率性能，且通过调节包覆层中导电复合材料和导离子复合材料的质量比，可获得性能较佳的负极材料。
以上实施例仅用以说明本发明的技术方案，而非对其限制；尽管参照前述实施例对本发明进行了详细的说明，本领域的普通技术人员应当理解：其依然可以对前述各实施例所记载的技术方案进行修改，或者对其中部分技术特征进行等同替换；而这些修改或者替换，并不使相应技术方案的本质脱离本发明各实施例技术方案的精神和范围。

Claims (11)

  1. 一种二次锂电池用硅碳复合材料，包括含硅基材料的内核以及内核表面的第一包覆层和第二包覆层，其特征在于，所述第一包覆层为导电层，所述第二包覆层为导离子层，所述第一包覆层和所述第二包覆层没有顺序限定。
  2. 如权利要求1所述的二次锂电池用硅碳复合材料，其特征在于，所述第一包覆层包括碳复合材料、或者碳复合材料和离子导体复合材料的组合；以所述第一包覆层的总质量为100％计，所述碳复合材料的质量百分比为90～100％。
  3. 如权利要求1所述的二次锂电池用硅碳复合材料，其特征在于，所述第二包覆层包括离子导体复合材料、或者离子导体复合材料和碳复合材料的组合；以所述第二包覆层的总质量为100％计，所述离子导体复合材料的质量百分比为90～100％。
  4. 如权利要求1所述的二次锂电池用硅碳复合材料，其特征在于，以所述硅碳复合材料的总质量为100％计算，所述硅基材料内核的质量百分比为80～99％。
  5. 如权利要求2或3所述的二次锂电池用硅碳复合材料，其特征在于，所述第一包覆层的碳复合材料和所述第二包覆层的碳复合材料各自独立地包括碳增强相和炭基体，所述碳增强相与所述炭基体复合形成类钢筋混凝土结构；优选所述碳增强相和炭基体的质量比为0.1～1：1；优选所述碳增强相包括碳纳米管、炭黑、碳纤维、石墨烯、多孔炭中的一种或多种组合；优选所述炭基体包括沥青炭、树脂炭、气相裂解炭中的一种或多种组合。
  6. 如权利要求2或3所述的二次锂电池用硅碳复合材料，其特征在于，所述第一包覆层的离子导体复合材料和所述第二包覆层的离子导体复合材料各自独立地包括离子增强相和离子基体，所述离子增强相和所述离子基体有机复合形成类钢筋混凝土结构；优选所述离子增强相和所述离子基体的质量比为0.1～1：1；优选所述离子增强相包括纤维、晶须、颗粒中的至少一种；优选所述离子基体包括快离子导体材料，优选所述离子基体选自LISICON型固体电解质、NASICION型固体电解质、钙钛矿型固体电解质、石榴石型固体电解质、硫化物固态电解质、PEO基聚合物电解质组成的组的一种或多种组合。
  7. 如权利要求6所述的二次锂电池用硅碳复合材料，其特征在于，所述纤维包括选自芳纶纤维、聚乙烯纤维、尼龙纤维、玻璃纤维、Al 2O 3纤维、SiC纤维、BN纤维、Si 3N 4纤维、TiC纤维、TiN纤维、B 4C纤维、陶瓷纤维组成的组中的一种或多种；所述晶须选自SiC晶须、K 2TiO 3晶须、硼酸铝晶须、CaSO 4晶须、CaCO 3晶须、Al 2O 3晶须、ZnO晶须、MgO晶须组成的组中的一种或多种；所述颗粒选自SiC颗粒、Al 2O 3颗粒、BN颗粒、Si 3N 4颗粒、TiC颗粒、B 4C颗粒组成的组中的一种或多种。
  8. 如权利要求1或4所述的二次锂电池用硅碳复合材料，其特征在于，所述内核中还包含锂化合物，优选锂化合物包括Li 2Si 2O 5、Li 2SiO 3、Li 4SiO 4中的任意一种或多种，优选在Cu-Kα线的X射线衍射中归属于2θ＝26.9±0.2°的Li 2SiO 3的峰强度最强。
  9. 如权利要求1所述的二次锂电池用硅碳复合材料，其特征在于，所述第一包覆层厚度为2～1000nm，优选为5～200nm；所述第二包覆层厚度为1～100nm，优选为2～20nm。
  10. 一种制备二次锂电池用硅碳复合材料的方法，所述方法包括以下工序：前驱体工序、第一包覆层包覆工序、预锂化工序、第二包覆层包覆工序；
    所述前驱体工序是指将硅原料进行化学气相沉积或高温真空沉积，得到SiO x前驱体，0＜x＜2；
    所述第一包覆层包覆工序是指通过化学气相沉积法对SiO x前驱体进行导电层包覆；
    所述预锂化工序是指通过在前述包覆后的材料中插入锂，在硅氧化合物内部生成硅酸锂，得到锂掺杂的活性颗粒；
    所述第二包覆层包覆工序是指将锂掺杂的活性颗粒与离子增强相和离子基体混合，分散到纯水中得到混合浆液，然后将混合浆液进行过滤、干燥，以进行导离子层的包覆；
    或者，
    所述前驱体工序是指将硅原料进行化学气相沉积或高温真空沉积，得到SiO x前驱体，0＜x＜2；
    所述第一包覆层包覆工序是指将SiO x前驱体与离子增强相和离子基体混合，分散到纯水中形成混合浆液，然后将混合浆液进行过滤、干燥，进行导离子层的包覆；
    所述预锂化工序是指通过在前述包覆后的材料中插入锂，在硅氧化合物内部生成硅酸锂，得到锂掺杂的活性颗粒；
    所述第二包覆层包覆工序是指通过化学气相沉积法对锂掺杂的活性颗粒进行导电层包覆。
  11. 一种制备二次锂电池用硅碳复合材料的方法，所述方法包括以下工序：前驱体工序、第一包覆层包覆工序、第二包覆层包覆工序；
    所述前驱体工序是指将硅原料进行化学气相沉积或高温真空沉积，得到SiO x前驱体，0＜x＜2；
    所述第一包覆层包覆工序是指通过化学气相沉积法对SiO x前驱体进行导电层包覆；
    所述第二包覆层包覆工序是指将导电层包覆的SiO x前驱体与离子增强相和离子基体混合，分散到纯水中得到混合浆液，然后将混合浆液进行过滤、干燥，以进行导离子层的包覆；
    或者，
    所述前驱体工序是指将硅原料进行化学气相沉积或高温真空沉积，得到SiO x前驱体，0＜x＜2；
    所述第一包覆层包覆工序是指将SiO x前驱体与离子增强相和离子基体混合，分散到纯水中形成混合浆液，然后将混合浆液进行过滤、干燥，进行导离子层的包覆；
    所述第二包覆层包覆工序是指通过化学气相沉积法对导离子层的包覆的SiO x前驱体进行导电层包覆。
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