WO2024040605A1 - 一种硅碳复合材料及其制备方法、二次电池和用电装置 - Google Patents

一种硅碳复合材料及其制备方法、二次电池和用电装置 Download PDF

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WO2024040605A1
WO2024040605A1 PCT/CN2022/115268 CN2022115268W WO2024040605A1 WO 2024040605 A1 WO2024040605 A1 WO 2024040605A1 CN 2022115268 W CN2022115268 W CN 2022115268W WO 2024040605 A1 WO2024040605 A1 WO 2024040605A1
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silicon
carbon
carbon composite
composite material
optionally
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PCT/CN2022/115268
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English (en)
French (fr)
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刘良彬
李圆
王家政
吕子建
董晓斌
熊冬根
邓静娴
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宁德时代新能源科技股份有限公司
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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
    • 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
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • 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

  • This application belongs to the technical field of secondary batteries, and specifically relates to a silicon-carbon composite material and its preparation method, secondary batteries and electrical devices.
  • Silicon-based negative electrode materials have attracted widespread attention due to their high capacity. However, silicon-based materials have serious volume effects and will produce huge volume expansion during charging. However, existing silicon-based anode materials have poor pressure resistance and conductivity and cannot meet the electrochemical performance requirements of batteries.
  • this application provides a silicon-carbon composite material, which can make the battery have better cycle performance, pole plate cyclic expansion performance and rate performance.
  • the silicon-carbon composite material provided in the first aspect of this application includes a carbon nanotube/porous carbon composite matrix and a silicon-based material.
  • the porous carbon and carbon nanotubes in the carbon nanotube/porous carbon composite matrix are connected to each other through connecting units.
  • carbon nanotubes and porous carbon are connected to each other through connecting units and stably combined into one body.
  • the high conductivity of carbon nanotubes can be used to improve the problem of poor conductivity of porous carbon and reduce the cost of silicon-carbon composite materials.
  • the resistivity of the silicon-carbon composite material is improved, and the overall conductivity of the silicon-carbon composite material is improved; the strong mechanical properties of the carbon nanotubes can be used to achieve composite reinforcement, so that the silicon-carbon composite material has better pressure resistance and expansion resistance, thereby improving the silicon-carbon composite material.
  • the structural stability prevents the deterioration of cycle performance caused by particle rupture caused by expansion and contraction during cold pressing of pole pieces and charging and discharging of silicon-carbon composite materials. This application can effectively improve the cycle performance, pole piece cycle expansion performance and rate performance of secondary batteries containing the silicon-carbon composite material.
  • the connecting unit includes at least one of a carbon-carbon bond, a benzene ring, an ester group, and a carbonyl group.
  • a second example of the first aspect is provided, at least a part of the silicon-based material is distributed in the pores of the carbon nanotube/porous carbon composite matrix.
  • At least part of the silicon-based material is distributed in the pores of the carbon nanotube/porous carbon composite matrix.
  • a certain expansion space is reserved in the pores of the carbon nanotube/porous carbon composite matrix, which can effectively alleviate the expansion of the silicon-based material.
  • the silicon-based material can be restricted to a smaller particle size (average particle size ⁇ 50 nm).
  • the porous carbon composite matrix isolates the contact between the silicon-based material and the electrolyte, which can effectively improve the silicon-based material. Cycling performance of materials.
  • a third example of the first aspect is provided, one end of at least a part of the carbon nanotubes protrudes from the surface of the silicon-carbon composite material.
  • One end of at least a part of the carbon nanotubes protrudes from the surface of the silicon-carbon composite material, which is conducive to giving full play to the high conductivity of the carbon nanotubes, thereby improving the conductivity of the silicon-carbon composite material.
  • a fourth example of the first aspect is provided, and the diameter of the carbon nanotubes is 0.5-20 nm.
  • the diameter of the carbon nanotubes is 0.7-10 nm.
  • a fifth example of the first aspect is proposed.
  • the length of the carbon nanotube is denoted as L
  • the volume distribution particle diameter Dv50 of the silicon-carbon composite material is denoted as D0.
  • the silicon-carbon composite material satisfies :L ⁇ 3D0.
  • the silicon carbon composite material satisfies: 3D0 ⁇ L ⁇ 7D0.
  • the aspect ratio of the carbon nanotubes is greater than or equal to 900, and optionally 2500-25000.
  • the content of carbon nanotubes in the silicon-carbon composite material is ⁇ 8%; optionally, 0.2%-5.0%.
  • the content of carbon nanotubes is too low, it will not be able to effectively improve the conductivity of silicon-carbon composite materials. If the content is too high, the cost will be too high and the dispersion and processing effects will be affected.
  • the carbon nanotube/porous carbon composite matrix meets at least one of the following conditions (1)-(4):
  • the interior of the carbon nanotube/porous carbon composite matrix includes mesopores.
  • the pore volume of the mesopores is ⁇ 0.1cm 3 /g, preferably 0.2-2.5cm 3 /g;
  • the interior of the carbon nanotube/porous carbon composite matrix includes micropores.
  • the pore volume of the micropores is ⁇ 0.3cm 3 /g, preferably 0.05-0.2cm 3 /g;
  • the interior of the carbon nanotube/porous carbon composite matrix includes macropores.
  • the pore volume of the macropores is ⁇ 0.5cm 3 /g, preferably 0.05-0.4cm 3 /g;
  • the interior of the carbon nanotube/porous carbon composite matrix includes mesopores and micropores.
  • the ratio of the pore volume of mesopores to the pore volume of micropores is ⁇ 2, preferably 3-15.
  • the pores inside the carbon nanotube/porous carbon composite matrix it is helpful to limit the silicon-based material to a smaller particle size (average particle size ⁇ 50nm), and to isolate the contact between the composite material and the electrolyte.
  • the micropore/ Mesopores/macropores are limited to a certain range, which is conducive to reserving a certain expansion space.
  • the silicon-based material is nano silicon-based particles.
  • the average particle size of the nano silicon-based particles is ⁇ 50 nm, more preferably 3-20 nm.
  • the silicon-based material includes elemental silicon, silicon oxide (such as silicon oxide), silicon carbon composite, silicon nitrogen composite, silicon alloy and at least one of prelithiated silicon oxide compounds.
  • the silicon-based material includes amorphous silicon.
  • the silicon-based material includes a mixture of amorphous silicon and crystalline silicon.
  • the carbon nanotube/porous carbon composite matrix is carbonized from a resin precursor and carbon nanotubes grafted with functional groups and/or polymers. form.
  • Functional groups and/or polymers can react chemically with the resin precursor to connect the carbon nanotubes to the resin precursor and form connecting units after carbonization.
  • Functional groups and/or polymers can react chemically with the resin precursor to chemically connect the carbon nanotubes to the resin precursor, and form connecting units after carbonization to enhance the interfacial bonding between the carbon nanotubes and the resin, thus improving the silicon-carbon Compression resistance of composite materials.
  • a thirteenth example of the first aspect is proposed, infrared spectrum testing of silicon-carbon composite material or carbon nanotube/porous carbon composite matrix, silicon-carbon composite material or carbon nanotube/porous carbon
  • the composite matrix contains at least one of the following connecting units: ester carbonyl group, with an absorption peak of 1750-1735 cm -1 ; ketone carbonyl group, with an absorption peak of 1725-1705 cm -1 ; benzene ring group, with an absorption peak of 1620-1450 cm - 1 ; and carbon-carbon bond, whose absorption peak is 2400 ⁇ 1950cm -1 ; and/or,
  • the pressing conditions are to hold the pressure for 30 seconds under a pressure of 300 MPa and to press it repeatedly 50 times.
  • the compression index P ⁇ 3 indicates that the silicon-carbon composite material has good compression resistance and can better improve the expansion problem of silicon-based materials, so that the silicon-carbon composite material has excellent cycle performance.
  • the resistivity of the silicon-carbon composite material under a pressure of 4MPa is ⁇ 0.4 ⁇ cm, optionally, 0.05 ⁇ cm ⁇ ⁇ 0.3 ⁇ cm.
  • the silicon-carbon composite material satisfies at least one of the following conditions (I)-(V):
  • the volume distribution particle size of the silicon-carbon composite material is Dv50 ⁇ 8 ⁇ m, optionally 3-7 ⁇ m;
  • the porosity of silicon-carbon composite materials is ⁇ 20%, optionally 5%-15%;
  • the specific surface area SSA of the silicon-carbon composite material is ⁇ 5.0m 2 /g, optionally 0.8-4.0m 2 /g;
  • the silicon-carbon composite material includes mesopores inside, optionally, the pore volume of the mesopores is ⁇ 0.3cm 3 /g, preferably 0.05-0.1cm 3 /g;
  • silicon-carbon composite materials By optimizing the particle size of silicon-carbon composite materials, it is possible to avoid deterioration in cycle performance due to too small particle sizes and deterioration in conductivity due to excessive particle sizes.
  • space for expansion of the silicon-based material can be reserved when charging, buffering expansion and improving the cycle performance of the material. If the specific surface area of silicon-carbon composite materials is too high, it will affect the material performance, and if it is too low, it will be difficult to achieve in porous carbon materials. If the pore volume of the mesopores of the silicon-carbon composite material is too low, the reserved expansion space of the silicon-based material will be insufficient, which will affect the cycle performance of the silicon-carbon composite material.
  • the silicon-carbon The volumetric energy density of the composite material is too low, which reduces the practicality, and the pore volume of the mesopores of the silicon-carbon composite material is too high, which will affect the pressure resistance of the silicon-carbon composite material, resulting in the material not being able to withstand pressure.
  • Optimizing the silicon content can ensure the capacity requirements for silicon-carbon composites.
  • Optimizing the carbon content can ensure the effective formation of porous carbon and effectively isolate subsequent deposited silicon-based materials.
  • Optimizing the oxygen content can ensure the flexibility and porousness of porous carbon. Stability of carbon attachment to silicon-based materials and carbon nanotubes.
  • the surface of the silicon-carbon composite material is further provided with a coating layer.
  • the coating layer includes at least one of a carbon coating layer, a polymer coating layer, an inorganic salt coating layer, and a metal oxide coating layer.
  • the coating layer By forming a coating layer on the surface of the silicon-carbon composite material, it is conducive to further isolating the direct contact between the electrolyte and the silicon-carbon composite material, improving the cycle performance, and the coating layer has a certain buffering effect, further buffering expansion and reducing the impact of expansion.
  • the influence of pole pieces, in particular, the use of carbon coatings can further improve the conductivity of silicon-carbon materials.
  • the second aspect of this application provides a method for preparing silicon-carbon composite materials, including the following steps:
  • the mixed solution is solidified to obtain a composite matrix precursor
  • Silicon-based materials are deposited on the porous carbon/carbon nanotube composite matrix to obtain silicon-carbon composite materials.
  • silicon-carbon composite materials with good pressure resistance and electrical conductivity can be obtained through this method.
  • This method is simple to operate, highly reproducible, and is conducive to large-scale industrial production.
  • the mixed solution further includes 0.5% to 30% of catalyst by mass percentage.
  • the catalyst includes one or more of hexamethylenetetramine, ammonium bicarbonate, ammonium carbonate, ammonia, zinc salt, copper salt and chromium salt.
  • a second example of the second aspect is provided, and mixing includes: stirring at 20 to 60°C for 1 to 10 hours.
  • the modified carbon nanotubes and the resin precursor undergo one or more of esterification reaction, addition reaction, addition polymerization reaction, and polycondensation reaction.
  • the functional group includes one or more of carboxyl, hydroxyl, amino, phenyl, and carbonyl; and/or the polymer includes polyamide , one or more of polymethyl methacrylate and polyhydroxyethyl methacrylate.
  • a fourth example of the second aspect is provided, and the curing process includes: pre-curing and full curing.
  • the curing process includes: pre-curing, crushing, and full curing.
  • the pre-curing temperature is 70-140°C, optionally 80-130°C; and/or the pre-curing time is 3- 12h, optional 5-10h.
  • the full curing temperature is 150-220°C, optionally 160-200; and/or the full curing time is 8-20 hours , optional 10-15h.
  • the temperature of the carbonization treatment is 900-3000°C, optionally 1000-2000°C; and/or the time of the carbonization treatment is 2- 6h, optional 3-5h.
  • an eighth example of the second aspect is provided, and the deposition is performed by a chemical vapor deposition method.
  • the deposition gas includes a mixed gas of at least one or more of H 2 , N 2 and Ar and silane gas.
  • Silicon deposition through chemical vapor deposition is conducive to the uniform deposition of silicon-based materials in the porous carbon/carbon nanotube composite matrix, and the growth of silicon particles is limited by the pore size of the porous carbon, which can limit the silicon particles to smaller particles. diameter range, such as the average particle diameter ⁇ 50nm.
  • the porous carbon can be closely combined with the deposited silicon-based material, which can better limit the expansion of the silicon material to a certain extent.
  • a third aspect of the present application provides a secondary battery, including a negative electrode sheet.
  • the negative electrode sheet includes the silicon-carbon composite material of the first aspect of the present application or the silicon-carbon composite material obtained according to the preparation method of the second aspect of the present application.
  • the secondary battery of the present application has improved cycle life. performance.
  • a fourth aspect of the present application provides an electrical device, including the secondary battery of the third aspect of the present application.
  • the electrical device of the present application since the silicon-carbon composite material of the first aspect of the present application or the silicon-carbon composite material obtained according to the preparation method of the second aspect of the present application is used, the electrical device of the present application has improved cycle time. performance.
  • Figure 1 is a schematic structural diagram of the silicon carbon composite material of the present application.
  • Figure 2 is a scanning electron microscope (SEM) picture of the silicon-carbon composite material of the present application.
  • FIG. 3 is a schematic diagram of an embodiment of a secondary battery.
  • FIG. 4 is an exploded view of FIG. 3 .
  • Figure 5 is a schematic diagram of an embodiment of a battery module.
  • Figure 6 is a schematic diagram of an embodiment of a battery pack.
  • FIG. 7 is an exploded view of FIG. 6 .
  • FIG. 8 is a schematic diagram of an embodiment of a device in which a secondary battery is used as a power source.
  • any lower limit can be combined with any upper limit to form an unexpressed range; and any lower limit can be combined with other lower limits to form an unexpressed range, and likewise any upper limit can be combined with any other upper limit to form an unexpressed range.
  • every point or individual value between the endpoints of a range is included in the range.
  • each point or single value may serve as a lower or upper limit on its own in combination with any other point or single value or with other lower or upper limits to form a range not expressly recited.
  • connection refers to the combination of two chemical substances using a connecting unit as a medium.
  • Silicon-based negative electrode materials have attracted widespread attention due to their high capacity. However, silicon-based materials have serious volume effects and will produce huge volume expansion during charging. To this end, researchers have developed silicon-carbon anode materials. However, the existing silicon-carbon anode material has poor pressure resistance, and the material structure is easily damaged during the actual cold pressing process of the electrode piece, thereby affecting the electrochemical performance of the material. In addition, its resistivity is large and its conductivity is poor, which cannot meet the requirements for the electrochemical properties of the material. Therefore, there is an urgent need to develop a silicon-based negative electrode material that can make the battery have better cycle performance, pole piece cyclic expansion performance and rate performance.
  • FIG. 1 includes a carbon nanotube/porous carbon composite matrix and a silicon-based material.
  • the porous carbon and carbon nanotubes in the carbon nanotube/porous carbon composite matrix are connected to each other through connecting units.
  • carbon nanotubes and porous carbon are connected to each other through connecting units and stably combined into one body.
  • the high conductivity of carbon nanotubes can be used to improve the problem of poor conductivity of porous carbon and reduce the cost of silicon-carbon composite materials.
  • the resistivity of the silicon-carbon composite material improves the overall conductivity of the silicon-carbon composite material; the strong mechanical properties of the carbon nanotubes can be used to achieve composite reinforcement, so that the silicon-carbon composite material has better pressure resistance and thus better expansion resistance.
  • the connecting unit includes at least one of a carbon-carbon bond, a benzene ring, an ester group, and a carbonyl group.
  • connecting units are not limited to the above. Any connecting units that can chemically connect carbon nanotubes and porous carbon are included in the scope of this application, and will not be listed one by one here.
  • At least a portion of the silicon-based material is distributed in the pores of the carbon nanotube/porous carbon composite matrix.
  • At least part of the silicon-based material is distributed in the pores of the carbon nanotube/porous carbon composite matrix.
  • a certain expansion space is reserved in the pores of the carbon nanotube/porous carbon composite matrix, which can effectively alleviate the expansion of the silicon-based material.
  • the silicon-based material can be restricted to a smaller particle size (for example, average particle size ⁇ 50 nm).
  • the porous carbon composite matrix isolates the contact between the silicon-based material and the electrolyte, which can effectively improve Cycling performance of silicon-based materials.
  • one end of at least a portion of the carbon nanotubes protrudes from the surface of the silicon-carbon composite material.
  • At least one end of a portion of the carbon nanotubes protrudes from the surface of the silicon-carbon composite material.
  • This design facilitates contact between the carbon nanotubes and the electrolyte, giving full play to the high conductivity of the carbon nanotubes, thereby improving the conductivity of the silicon-carbon composite material. If the carbon nanotubes are completely wrapped inside the porous carbon, the carbon nanotubes cannot be in good contact with the electrolyte, and the conductivity of the carbon nanotubes cannot be fully exerted, which is not conducive to improving the conductivity of the silicon-carbon composite material.
  • the diameter of the carbon nanotubes may be 0.5-20 nm.
  • the diameter of the carbon nanotubes may be 0.7-10 nm.
  • the diameter of the carbon nanotubes can be 0.5nm, 0.7nm, 1nm, 2nm, 3nm, 4nm, 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, 11nm, 12nm, 13nm, 14nm, 15nm , 16nm, 17nm, 18nm, 19nm or 20nm.
  • the diameter of the carbon nanotubes can be 0.7-6nm.
  • the diameter of the carbon nanotube can be within the range of any two of the above-listed values as end values.
  • the length of the carbon nanotube is recorded as L
  • the volume distribution particle size Dv50 of the silicon-carbon composite material is recorded as D0
  • the silicon-carbon composite material satisfies: L ⁇ 3D0.
  • the silicon carbon composite material satisfies: 3D0 ⁇ L ⁇ 7D0.
  • L may be 3D0, 3.5D0, 4D0, 4.5D0, 5D0, 5.5D0, 6D0, 6.5D0, or 7D0.
  • the aspect ratio of the carbon nanotubes is greater than or equal to 900, and can optionally be 2500-25000.
  • the aspect ratio of the carbon nanotubes can be 900, 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, 10000, 11000, 12000, 13000, 14000, 15000, 16000, 17000, 18000, 19000, 20000, 21000, 22000, 23000, 24000 or 25000.
  • the aspect ratio of the carbon nanotube can be within a numerical range formed by any two of the above-listed numerical values as end values.
  • the content of carbon nanotubes in the silicon-carbon composite material is ⁇ 8%; optionally, it is 0.2%-5.0%.
  • the content of carbon nanotubes is too low, it will not be able to effectively improve the conductivity of silicon-carbon composite materials. If the content is too high, the cost will be too high and the dispersion and processing effects will be affected.
  • the content of carbon nanotubes in the silicon-carbon composite material can be 0.2%, 0.3%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5 %, 5.0%, 5.5%, 6.0%, 6.5%, 7.0%, 7.5% or 8.0%.
  • the content of carbon nanotubes in the silicon-carbon composite material can be within a numerical range formed by any two of the above-listed values as end values.
  • the carbon nanotube/porous carbon composite matrix includes mesopores inside; optionally, the pore volume of the mesopores is ⁇ 0.1cm 3 /g, for example, it can be 0.2-2.5cm 3 /g.
  • the pore volume of the mesopores may be 0.1cm 3 /g, 0.2cm 3 /g, 0.5cm 3 /g, 1.0cm 3 /g, 1.5cm 3 /g, 2.0cm 3 / g or 2.5cm 3 /g.
  • the pore volume of the mesopores may be within a numerical range formed by any two of the above-listed numerical values as end values.
  • the carbon nanotube/porous carbon composite matrix includes micropores inside; optionally, the pore volume of the micropores is ⁇ 0.3cm 3 /g, for example, it can be 0.05-0.2cm 3 /g.
  • the pore volume of the micropores may be 0.05cm 3 /g, 0.1cm 3 /g, 0.15cm 3 /g, 0.2cm 3 /g, 0.25cm 3 /g or 0.3cm 3 /g.
  • the pore volume of the micropores may be within a numerical range formed by any two of the above-listed numerical values as end values.
  • the carbon nanotube/porous carbon composite matrix includes macropores inside; optionally, the pore volume of the macropores is ⁇ 0.5cm 3 /g, for example, it can be 0.05-0.4cm 3 /g.
  • the pore volume of the macropores can be 0.05cm 3 /g, 0.1cm 3 /g, 0.15cm 3 /g, 0.2cm 3 /g, 0.25cm 3 /g, 0.3cm 3 /g, 0.35cm 3 /g, 0.4cm 3 /g, 0.45cm 3 /g or 0.5cm 3 /g.
  • the pore volume of the macropores may be within a numerical range formed by any two of the above-listed numerical values as end values.
  • the interior of the carbon nanotube/porous carbon composite matrix includes mesopores and micropores; optionally, the ratio of the pore volume of the mesopores to the pore volume of the micropores is ⁇ 2, for example, it can be 3-15.
  • the ratio of the pore volume of mesopores to the pore volume of micropores may be 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15.
  • the ratio of the pore volume of the mesopores to the pore volume of the micropores may be within a numerical range formed by any two of the above-listed values as end values.
  • the porosity of the porous carbon/carbon nanotube composite matrix is ⁇ 20%, optionally between 20% and 60%.
  • the average pore diameter of the porous carbon/carbon nanotube composite matrix is 1-100 nm, optionally 5-50 nm.
  • the pores inside the carbon nanotube/porous carbon composite matrix it is helpful to limit the silicon-based material to a smaller particle size (for example, average particle size ⁇ 50 nm), and to isolate the contact between the composite material and the electrolyte, while minimizing the The pores/mesopores/macropores are limited to a certain range, which is conducive to reserving a certain expansion space.
  • the expansion and cycle performance of silicon-carbon composite materials are improved.
  • the mass proportion of carbon nanotubes in the carbon nanotube/porous carbon composite matrix can be 0.05%-16%, optionally 0.1%-10%, for example, it can be 0.05%, 0.1%, 0.2 %, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14% or 15%.
  • the mass proportion of carbon nanotubes in the carbon nanotube/porous carbon composite matrix can be within the range of any two of the above-listed values as end values.
  • the silicon-based material is nano silicon-based particles.
  • the average particle size of the nano silicon-based particles is ⁇ 50 nm, more preferably 3-20 nm.
  • the average particle size of the nanosilica-based particles can be 3nm, 4nm, 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, 11nm, 12nm, 13nm, 14nm, 15nm, 16nm, 17nm, 18nm, 19nm , 20nm, 25nm, 30nm, 35nm, 40nm, 45nm or 50nm.
  • the average particle size of the nanosilica-based particles may be within a numerical range formed by any two of the above-listed values as end values.
  • the silicon-based material includes at least one of elemental silicon, silicon oxide (such as silicon oxide), silicon carbon composite, silicon nitrogen composite, silicon alloy, and prelithiated silicon oxygen compound.
  • the silicon-based material includes amorphous silicon.
  • the silicon-based material includes a mixture of amorphous silicon and crystalline silicon.
  • the carbon nanotube/porous carbon composite matrix is formed by carbonization of a resin precursor and carbon nanotubes grafted with functional groups and/or polymers.
  • Functional groups and/or polymers can react chemically with the resin precursor to connect the carbon nanotubes to the resin precursor and form connecting units after carbonization.
  • Functional groups and/or polymers can react chemically with the resin precursor to chemically connect the carbon nanotubes to the resin precursor, and form connecting units after carbonization to enhance the interfacial bonding between the carbon nanotubes and the resin, thus improving the silicon-carbon Compression resistance of composite materials.
  • the functional group may be one or more of carboxyl, hydroxyl, amino, phenyl, and carbonyl.
  • the polymer may be one or more of polyamide, polymethyl methacrylate, and polyhydroxyethyl methacrylate.
  • the infrared spectrum tests the silicon-carbon composite material or the carbon nanotube/porous carbon composite matrix
  • the silicon-carbon composite material or the carbon nanotube/porous carbon composite matrix contains at least one of the following connecting units: ester carbonyl group, which The absorption peak is 1750 ⁇ 1735cm -1 ; ketone carbonyl group, its absorption peak is 1725 ⁇ 1705cm -1 ; benzene ring group, its absorption peak is 1620 ⁇ 1450cm -1 ; and carbon-carbon bond, its absorption peak is 2400 ⁇ 1950cm -1 .
  • transmission electron microscopy is used to test the silicon-carbon composite or the carbon nanotube/porous carbon composite matrix.
  • the carbon atoms around the carbon nanotubes in the silicon-carbon composite or the carbon nanotube/porous carbon composite matrix are different from the outermost carbon nanotubes.
  • the area where the distance between carbon atoms in the layer is ⁇ 0.35nm accounts for ⁇ 50%. This indicates that the porous carbon and the carbon nanotubes are connected together.
  • the "area ratio” here refers to the ratio of the length of the carbon nanotube to the actual length of the carbon nanotube that meets the distance between the carbon atoms around the carbon nanotube and the carbon atoms in the outermost layer of the carbon nanotube ⁇ 0.35nm.
  • the area ratio It means the proportion of the connection area between carbon nanotubes and porous carbon in the overall length of carbon nanotubes. The larger the value, the closer the connection between carbon nanotubes and porous carbon. If the area ratio is >50%, it is considered that carbon Nanotubes and porous carbon are connected together by effective connecting units.
  • the silicon-carbon composite material or the carbon nanotube/porous carbon composite matrix contains connecting units.
  • Transmission electron microscopy tests show that the porous carbon and carbon nanotubes are connected together. These characterization results show that porous carbon and carbon nanotubes are connected as a whole through connecting units, and the interface bonding is enhanced, which can effectively improve the overall compression resistance of silicon-carbon composite materials.
  • the measured volume distribution particle size Dv50 of the material after being pressed is maintained under a pressure of 300MPa for 30 seconds and repeated 50 times.
  • the compression index P ⁇ 3 indicates that the silicon-carbon composite material has good compression resistance and can better improve the expansion problem of silicon-based materials, so that the silicon-carbon composite material has excellent cycle performance.
  • P can be 3, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or 100.
  • the P value can be within a range of values formed by any two of the values listed above as end values.
  • the resistivity of the silicon-carbon composite material under a pressure of 4 MPa is ⁇ 0.4 ⁇ cm, optionally, 0.05 ⁇ cm ⁇ 0.3 ⁇ cm.
  • p may be 0.05 ⁇ cm, 0.1 ⁇ cm, 0.15 ⁇ cm, 0.2 ⁇ cm, 0.25 ⁇ cm, 0.3 ⁇ cm, 0.35 ⁇ cm, or 0.4 ⁇ cm.
  • the resistivity ⁇ can be within a numerical range formed by any two of the above listed values as end values.
  • the volume distribution particle size Dv50 of the silicon-carbon composite material is ⁇ 8 ⁇ m, optionally 3-7 ⁇ m. In some specific embodiments, the volume distribution particle size Dv50 of the silicon-carbon composite material may be 3 ⁇ m, 3.5 ⁇ m, 4 ⁇ m, 4.5 ⁇ m, 5 ⁇ m, 5.5 ⁇ m, 6 ⁇ m, 6.5 ⁇ m, 7 ⁇ m, 7.5 ⁇ m or 8 ⁇ m.
  • the volume distribution particle size Dv50 of the silicon-carbon composite material can be within the range of any two of the above-listed values as end values.
  • the porosity of the silicon-carbon composite material is ⁇ 20%, optionally 5%-15%. In some specific embodiments, the porosity of the silicon-carbon composite material may be 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16% %, 17%, 18%, 19% or 20%.
  • the porosity of the silicon-carbon composite material can be within a numerical range formed by any two of the above-listed values as end values. By reserving a certain porosity inside the silicon-carbon composite material, space for expansion of the silicon-based material can be reserved when charging, buffering expansion and improving the cycle performance of the material.
  • the specific surface area SSA of the silicon-carbon composite material is ⁇ 5.0 m 2 /g, optionally 0.8-4.0 m 2 /g. In some specific embodiments, the specific surface area SSA of the silicon-carbon composite material may be 0.8m 2 /g, 1.0m 2 /g, 1.5m 2 /g, 2m 2 /g, 2.5m 2 /g, 3m 2 /g , 3.5m 2 /g, 4m 2 /g, 4.5m 2 /g or 5m 2 /g.
  • the specific surface area SSA of the silicon-carbon composite material can be within a numerical range formed by any two of the above-listed values as end values. If the specific surface area of silicon-carbon composite materials is too high, it will affect the material performance, and if it is too low, it will be difficult to achieve in silicon-carbon composite materials.
  • the silicon-carbon composite material includes mesopores inside; optionally, the pore volume of the mesopores is ⁇ 0.3cm 3 /g, for example, it can be 0.05-0.1cm 3 /g.
  • the pore volume of the mesopores can be 0.05cm 3 /g, 0.06cm 3 /g, 0.07cm 3 /g, 0.08cm 3 /g, 0.09cm 3 /g, 0.1cm 3 /g, 0.15cm 3 /g, 0.2cm 3 /g, 0.25cm 3 /g or 0.3cm 3 /g.
  • the pore volume of the mesopores may be within a numerical range formed by any two of the above-listed numerical values as end values. If the pore volume of the mesopores of the silicon-carbon composite material is too low, the reserved expansion space of the silicon-based material will be insufficient, which will affect the cycle performance of the silicon-carbon composite material. If the pore volume of the mesopores of the silicon-carbon composite material is too high, the silicon-carbon The volumetric energy density of the composite material is too low, which reduces the practicality, and the pore volume of the mesopores of the silicon-carbon composite material is too high, which will affect the pressure resistance of the silicon-carbon composite material, resulting in the material not being able to withstand pressure.
  • the element mass ratio Si:C:O in the silicon-carbon composite material can be 20:70:10, 30:65:5, 40:55:5, 55:42:3, 55:40: 5.
  • the element mass ratio Si:C:O in the silicon-carbon composite material can be within the numerical range formed by any two of the above-listed values as end values.
  • Optimizing the silicon content can ensure the capacity requirements for silicon-carbon composites.
  • Optimizing the carbon element content ensures the effective formation of porous carbon and effectively isolates subsequently deposited silicon-based materials.
  • Optimizing the oxygen content can ensure the flexibility of porous carbon and the stability of the connection between porous carbon and silicon-based materials and carbon nanotubes.
  • the surface of the silicon-carbon composite material is also provided with a coating layer.
  • the coating layer includes at least one of a carbon coating layer, a polymer coating layer, an inorganic salt coating layer, and a metal oxide coating layer.
  • the coating layer By forming a coating layer on the surface of the silicon-carbon composite material, it is conducive to further isolating the direct contact between the electrolyte and the silicon-carbon composite material, improving the cycle performance, and the coating layer has a certain buffering effect, further buffering expansion and reducing the impact of expansion.
  • the influence of pole pieces, in particular, the use of carbon coatings can further improve the conductivity of silicon-carbon materials.
  • the second aspect of this application provides a method for preparing silicon-carbon composite materials, including the following steps:
  • the mixed solution is solidified to obtain a composite matrix precursor
  • Silicon-based materials are deposited on the porous carbon/carbon nanotube composite matrix to obtain silicon-carbon composite materials.
  • the mixed solution further includes 0.5% to 30% catalyst by mass percentage.
  • the catalyst includes one or more of hexamethylenetetramine, ammonium bicarbonate, ammonium carbonate, ammonia water, zinc salt, copper salt and chromium salt.
  • the mass ratio of the modified carbon nanotubes, catalyst and phenolic resin precursor solution may be (0.05-8): (3-7): (83-96.95).
  • mixing includes: stirring at 20-60°C for 1-10 hours.
  • the modified carbon nanotubes and the resin precursor undergo one or more of esterification reaction, addition reaction, addition polymerization reaction, and polycondensation reaction.
  • the functional group includes one or more of carboxyl, hydroxyl, amino, phenyl, and carbonyl.
  • the polymer includes one or more of polyamide, polymethyl methacrylate, and polyhydroxyethyl methacrylate.
  • the functional groups grafted on carbon nanotubes can be used as curing agents for resin precursors.
  • the functional groups may be acidic or basic functional groups.
  • the curing process includes: pre-curing and full curing.
  • the curing process includes: pre-curing, crushing, and full curing.
  • the volume distribution particle size Dv50 of the powder obtained after crushing can be 3 to 15 ⁇ m, optionally 5 to 10 ⁇ m.
  • the pre-curing temperature is 70-140°C, optionally 80-130°C; and/or the pre-curing time is 3-12 hours, optionally 5-10 hours.
  • the full curing temperature is 150-220°C, optionally 160-200°C; and/or the full curing time is 8-20h, optionally 10-15h.
  • full cure is performed under an inert atmosphere.
  • the inert atmosphere can be nitrogen, argon, etc.
  • the temperature of the carbonization treatment is 900-3000°C, optionally 1000-2000°C; and/or the time of the carbonization treatment is 2-6 hours, optionally 3-5 hours.
  • the carbonization process is performed under an inert atmosphere.
  • the inert atmosphere can be nitrogen, argon, etc.
  • deposition is by chemical vapor deposition.
  • the deposition gas includes a mixed gas of at least one or more of H 2 , N 2 and Ar and silane gas.
  • Silicon deposition through chemical vapor deposition is conducive to the uniform deposition of silicon-based materials in the porous carbon/carbon nanotube composite matrix, and the growth of silicon particles is limited by the pore size of the porous carbon, which can limit the silicon particles to smaller particles. diameter range, such as ⁇ 50nm.
  • the porous carbon can be closely combined with the deposited silicon-based material, which can better limit the expansion of the silicon material to a certain extent.
  • the silane gas includes at least one of monosilane, disilane, trisilane, monochlorosilane, dichlorosilane, and trichlorosilane.
  • the volume proportion of silane gas in the mixed gas can be 5%-80%, for example, it can be 5%, 15%, 25%, 35%, 45%, 55%, 65% or 80%. %.
  • the volume proportion of silane gas can be within the range of any two of the above-listed values as end values.
  • the flow rate of the mixed gas can be 100-400mL/min, for example, it can be 100mL/min, 150mL/min, 200mL/min, 250mL/min, 300mL/min, 350mL/min or 400mL/min. min.
  • the flow rate of the mixed gas can be within a numerical range formed by any two of the above-listed values as end values.
  • the deposition temperature may be 400-1000°C, for example, it may be 400°C, 450°C, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, 900°C °C, 950°C or 1000°C.
  • the deposition temperature may be within a range of values formed by any two of the values listed above as end values.
  • the deposition time can be 2-10h, for example, it can be 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h or 10h.
  • the deposition time may be within a range of values formed by any two of the values listed above as end values.
  • the resin precursor may be a furan resin precursor, a urea-formaldehyde resin precursor, a pyrimidine resin precursor, a phenolic resin precursor, an epoxy resin precursor, a polyoxymethylene methyl acrylate resin precursor, or polyacrylonitrile. Any of the resin precursors.
  • the dosage of carbon nanotubes and resin precursor can be adjusted according to material design requirements.
  • the grafting method includes: using one or more of nitric acid, sulfuric acid, acetic acid, ammonia, oxalic acid, etc. to perform acid washing or alkali washing. It is preferred to use organic acids for pickling. Carboxyl groups and the like can be grafted onto carbon nanotubes by acid washing. For example, ammonia water can be used for alkali washing to graft hydroxyl groups. Of course, other known methods can also be used to graft functional groups and/or polymers onto carbon nanotubes, such as grafting polymethylmethacrylate.
  • the preparation method further includes forming a coating layer on the obtained silicon-carbon composite material.
  • the carbon coating layer may be formed by chemical vapor deposition.
  • the deposition gas of chemical vapor deposition can be a mixed gas of C 2 H 2 and N 2 .
  • the volume proportion of C 2 H 2 can be 2%-40%.
  • the flow rate of mixed gas can be 100-300mL/min.
  • the deposition temperature can be 800-1000°C, and the deposition time can be 0.5-2h.
  • Secondary batteries refer to batteries that can be recharged to activate active materials and continue to be used after the battery is discharged.
  • a secondary battery typically includes a positive electrode plate, a negative electrode plate, a separator and an electrolyte.
  • active ions are inserted and detached back and forth between the positive and negative electrodes.
  • the isolation film is arranged between the positive electrode piece and the negative electrode piece to play the role of isolation.
  • the electrolyte plays a role in conducting ions between the positive and negative electrodes.
  • the negative electrode sheet usually includes a negative electrode current collector and a negative electrode film layer disposed on the negative electrode current collector.
  • the negative electrode film layer includes the silicon-carbon composite material provided above in this application.
  • the negative electrode current collector can be a conventional metal foil or a composite current collector (for example, a metal material can be placed on a polymer substrate to form a composite current collector).
  • the negative electrode current collector may be copper foil.
  • the negative electrode film layer also optionally includes binders, conductive agents and other optional auxiliaries.
  • the conductive agent may be one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.
  • the binder can be styrene-butadiene rubber (SBR), water-based acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer One or more of (EVA), polyvinyl alcohol (PVA) and polyvinyl butyral (PVB).
  • SBR styrene-butadiene rubber
  • PVDF polyvinylidene fluoride
  • PTFE polytetrafluoroethylene
  • EVA ethylene-vinyl acetate copolymer
  • EVA polyvinyl alcohol
  • PVB polyvinyl butyral
  • additives may be thickening and dispersing agents (such as carboxymethyl cellulose sodium CMC-Na), PTC thermistor materials, etc.
  • the positive electrode sheet usually includes a positive electrode current collector and a positive electrode film layer disposed on the positive electrode current collector.
  • the positive electrode film layer includes a positive electrode active material.
  • the positive electrode current collector can be a conventional metal foil or a composite current collector (metal materials can be placed on a polymer substrate to form a composite current collector).
  • the positive electrode current collector may be aluminum foil.
  • the specific type of the positive active material is not limited. Active materials known in the art that can be used for the positive electrode of secondary batteries can be used, and those skilled in the art can select according to actual needs.
  • the cathode active material may include, but is not limited to, one or more of lithium transition metal oxides, lithium-containing phosphates with an olivine structure, and their respective modified compounds.
  • lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide One or more of lithium nickel cobalt aluminum oxide and its modified compounds.
  • lithium-containing phosphates with an olivine structure may include, but are not limited to, lithium iron phosphate, composites of lithium iron phosphate and carbon, lithium manganese phosphate, composites of lithium manganese phosphate and carbon, lithium iron manganese phosphate, lithium iron manganese phosphate One or more of the composite materials with carbon and its modified compounds. These materials are commercially available.
  • the modified compounds of each of the above materials may be doping modifications and/or surface coating modifications of the materials.
  • the positive electrode film layer also optionally includes binders, conductive agents and other optional auxiliaries.
  • the conductive agent may be one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, SuperP(SP), graphene and carbon nanofibers.
  • the binder can be styrene-butadiene rubber (SBR), water-based acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer One or more of (EVA), polyacrylic acid (PAA), carboxymethylcellulose (CMC), polyvinyl alcohol (PVA) and polyvinyl butyral (PVB).
  • SBR styrene-butadiene rubber
  • PVDF polyvinylidene fluoride
  • PTFE polytetrafluoroethylene
  • EVA ethylene-vinyl acetate copolymer
  • PAA polyacrylic acid
  • CMC carboxymethylcellulose
  • PVA polyvinyl alcohol
  • PVB polyvinyl butyral
  • the secondary battery further includes a separator film.
  • This application has no special restrictions on the type of isolation membrane, and any well-known porous structure isolation membrane with good chemical stability and mechanical stability can be selected.
  • the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.
  • the isolation film can be a single-layer film or a multi-layer composite film, with no special restrictions. When the isolation film is a multi-layer composite film, the materials of each layer can be the same or different, and there is no particular limitation.
  • the secondary battery may include an electrolyte that serves to conduct ions between a positive electrode and a negative electrode.
  • the electrolyte solution may include electrolyte salts and solvents.
  • the electrolyte salt may be selected from the group consisting of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bisfluorosulfonimide (LiFSI), Lithium trifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluoromethanesulfonylborate (LiDFOB), lithium difluoromethanesulfonylborate (LiBOB), lithium difluorophosphate (LiPO2F2), difluorodifluoride One or more of lithium oxalate phosphate (LiDFOP) and lithium tetrafluorooxalate phosphate (LiTFOP).
  • LiPF6 lithium hexafluor
  • the solvent may be selected from ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), carbonic acid Dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), One or more of ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS) and diethyl sulf
  • additives are also included in the electrolyte.
  • additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain properties of the battery, such as additives that improve the overcharge performance of the battery, additives that improve the high-temperature performance of the battery, and additives that improve the low-temperature performance of the battery. Additives etc.
  • the secondary battery of the present application is a lithium-ion secondary battery.
  • the secondary battery can be prepared according to conventional methods in the art, for example, the positive electrode sheet, the separator film, and the negative electrode sheet are wound (or stacked) in order, so that the separator film is between the positive electrode sheet and the negative electrode sheet for isolation. function to obtain the battery core, place the battery core in the outer package, inject the electrolyte and seal it to obtain a secondary battery.
  • FIG. 3 shows an example of a square-structured secondary battery 5 .
  • the secondary battery may include an outer packaging.
  • the outer packaging is used to encapsulate the positive electrode piece, the negative electrode piece and the electrolyte.
  • the outer package may include a housing 51 and a cover 53 .
  • the housing 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose a receiving cavity.
  • the housing 51 has an opening communicating with the accommodation cavity, and the cover plate 53 can cover the opening to close the accommodation cavity.
  • the positive electrode piece, the negative electrode piece and the isolation film can be formed into the electrode assembly 52 through a winding process or a lamination process.
  • the electrode assembly 52 is packaged in the containing cavity.
  • the electrolyte soaks into the electrode assembly 52 .
  • the number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and can be adjusted according to needs.
  • the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc.
  • the outer packaging of the secondary battery may also be a soft bag, such as a bag-type soft bag.
  • the soft bag may be made of plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), and the like.
  • secondary batteries can be assembled into battery modules, and the number of secondary batteries contained in the battery module can be multiple. The specific number can be adjusted according to the application and capacity of the battery module.
  • FIG. 5 is a battery module 4 as an example.
  • a plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4 .
  • the plurality of secondary batteries 5 can be fixed by fasteners.
  • the battery module 4 may further include a housing having a receiving space in which a plurality of secondary batteries 5 are received.
  • the above-mentioned battery modules can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.
  • the battery pack 1 may include a battery box and a plurality of battery modules 4 arranged in the battery box.
  • the battery box includes an upper box 2 and a lower box 3 .
  • the upper box 2 can be covered with the lower box 3 and form a closed space for accommodating the battery module 4 .
  • Multiple battery modules 4 can be arranged in the battery box in any manner.
  • the present application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack.
  • the secondary battery, battery module or battery pack may be used as a power source for the device or as an energy storage unit for the device.
  • the device may be, but is not limited to, a mobile device (such as a mobile phone, a laptop, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, or an electric golf ball). vehicles, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.
  • the device can select secondary batteries, battery modules or battery packs according to its usage requirements.
  • Figure 8 is an example device.
  • the device is a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, etc.
  • battery packs or battery modules can be used.
  • the device may be a mobile phone, a tablet, a laptop, etc.
  • the device is usually required to be thin and light, and a secondary battery can be used as a power source.
  • the pre-cured material is crushed to obtain powder B.
  • the crushing intensity airflow mill: airflow velocity 1m 3 /min, classification wheel frequency 45HZ, induced draft fan frequency 40HZ,
  • the crushing air pressure is 0.8MPa
  • the feeding speed is 1kg/h
  • the volume distribution particle size Dv50 of powder B is controlled to be 7 ⁇ m;
  • Powder C is placed in a high-temperature furnace, protected by nitrogen gas, and carbonized at 1100°C for 4 hours to form powder D, which is a carbon nanotube/porous carbon composite matrix.
  • Powder D is deposited on silicon by chemical vapor deposition.
  • the deposition gas is a mixed gas of monosilane and H2 , where the volume ratio of monosilane is 20%, the flow rate of the mixed gas is 400mL/min, and the deposition temperature is 500°C. , the deposition time is 10h.
  • the volume distribution particle size Dv50 of the deposited nano silicon-based particles is 10 nm.
  • the carbon coating layer is formed on the silicon-carbon composite material by chemical vapor deposition.
  • the deposition gas of chemical vapor deposition is a mixed gas of C 2 H 2 and N 2 , in which the volume ratio of C 2 H 2 is 20%.
  • the gas flow rate is 300mL/min
  • the deposition temperature is 800°C
  • the deposition time is 0.5h.
  • Examples 2-18 were carried out according to the method described in Example 1, except that the parameters listed in Table 1 below are different from those in Example 1.
  • Comparative Example 1 is basically the same as the scheme described in Example 1, except that no carbon nanotubes are added during the carbon matrix synthesis process, and the phenolic resin precursor is directly used for reaction, pre-curing, crushing, full curing, carbonization, and nano-silicon deposition.
  • the silicon-carbon composite material of Comparative Example 1 was obtained from the base particles.
  • Nano-silica powder (volume distribution particle size Dv50 is 50 nm) and modified carbon nanotubes are added to the phenolic resin precursor to perform a polymerization reaction, and then pre-cured, broken, fully cured, and carbonized to obtain the silicon-carbon composite of Comparative Example 2
  • the materials and related process conditions are the same as those in Example 1, except that nano-silica powder is used instead of depositing nano-silica-based particles.
  • Example 3 The silicon-carbon composite material obtained in Example 1, carbon nanotubes (tube diameter is 2 nm, length is 25 ⁇ m), and a small amount of phenolic resin precursor solution are mixed at a ratio of 92.05%:1.95%:6%, pre-cured, broken, and completely
  • the curing and carbonization processes are the same as those in Example 1, and a CNT-coated silicon-carbon composite material on the surface, that is, the silicon-carbon composite material of Comparative Example 3, can be obtained.
  • Comparative Example 3 is based on Comparative Example 1 and then coated with modified carbon nanotubes to obtain a silicon-carbon composite material.
  • a secondary battery was prepared according to the general preparation method below.
  • the silicon-carbon composite materials, artificial graphite, binder styrene-butadiene rubber (SBR), binder polyacrylic acid (PAA), dispersant (CMC-Na) and conductive carbon black (Super -P, SP) and carbon nanotubes (CNT) are fully stirred and mixed in an appropriate amount of deionized water at a weight ratio of 10%: 85%: 2%: 1%: 1%: 0.7%: 0.3% to prepare a negative electrode slurry Material; the negative electrode slurry is coated on the current collector copper foil through coating equipment, and then dried, cold pressed, and cut to obtain negative electrode pieces.
  • Preparation of the positive electrode sheet Dissolve the positive active material LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811), the binder polyvinylidene fluoride (PVDF), and the conductive agent acetylene black in a mass ratio of 97%:1.5%:1.5%. In the solvent N-methylpyrrolidone (NMP), stir thoroughly and mix evenly to prepare a positive electrode slurry; the positive electrode slurry is evenly coated on the positive electrode current collector aluminum foil, and then dried, cold pressed, and cut to obtain the positive electrode. Extreme piece.
  • NMP N-methylpyrrolidone
  • Electrolyte preparation Mix ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 1:1:1, and then uniformly dissolve LiPF 6 in the above solution to obtain Electrolyte.
  • the concentration of LiPF 6 is 1 mol/L.
  • Preparation of secondary batteries stack and wind the above-mentioned positive electrode sheets, separators, and negative electrode sheets in order to obtain an electrode assembly; put the electrode assembly into the outer packaging, add the electrolyte prepared above, package and let it stand , formation, aging and other processes, a secondary battery is obtained.
  • the pore volume evaluation method can refer to GB/T 19587-2017 and GB/T 21650.2-2008. It is tested using the TriStar II 3020 pore size distribution meter. At a constant temperature, the adsorbed gas is adsorbed on the material to be tested under a series of gradually increasing pressures. Above, the pore size and pore volume distribution of the porous carbon/carbon nanotube composite matrix material can be characterized through the curves of the volumes of pore sizes at each level and the corresponding partial pressures; further calculations can obtain the average pore size. The test results are shown in Table 2 below.
  • the content of carbon nanotubes in the carbon nanotube/porous carbon composite matrix can be determined as follows: Place the carbon nanotube/porous carbon composite matrix powder in an ion polisher (such as IB-19500CP type), and ionize under vacuum conditions. The source ionizes argon gas to produce argon ions. After acceleration and focusing, the high-speed argon ions impact atoms or molecules on the sample surface to achieve ion polishing, so that cross-section detection can be achieved. The obtained cross-section is then tested in a scanning electron microscope (such as ZEISS Sigma 300). 30 carbon nanotube/porous carbon composite matrix particles are selected to compare the area of the carbon nanotubes in the particles (excluding the cross-sectional hole area) of the carbon material.
  • an ion polisher such as IB-19500CP type
  • the mass proportion of carbon nanotubes in the composite matrix can be evaluated according to the area proportion. Taking the average value can be equivalent to carbon nanotubes/ Content of carbon nanotubes in porous carbon composite matrix.
  • Dv50 can be obtained by using a laser particle size analyzer (such as Malvern Master Size 3000), where Dv50 is physically defined as the particle size corresponding to when the cumulative volume distribution percentage of the material reaches 50%.
  • a laser particle size analyzer such as Malvern Master Size 3000
  • the length L of the carbon nanotube can be tested by cross-sectional SEM.
  • the following operation can be performed: Place the silicon-carbon composite powder in an ion polisher (such as IB-19500CP type), and under vacuum conditions, the ion source will argon gas Ionization generates argon ions. After acceleration and focusing, the high-speed argon ions impact atoms or molecules on the sample surface to achieve ion polishing, so that cross-section detection can be achieved.
  • the obtained cross section is then tested in a scanning electron microscope (such as ZEISS Sigma 300), 30 carbon nanotubes are selected for length measurement, and the average value is calculated as the length L of the carbon nanotube.
  • Table 3 The test results are shown in Table 3 below.
  • the content of carbon nanotubes in silicon-carbon composite materials can be determined as follows: Place the silicon-carbon composite material powder in an ion polisher (such as IB-19500CP model). Under vacuum conditions, the ion source ionizes argon gas to generate argon ions. , after acceleration and focusing, high-speed argon ions impact atoms or molecules on the sample surface to achieve ion polishing, so that cross-section detection can be achieved. The obtained cross-section is then tested in a scanning electron microscope (such as ZEISS Sigma 300), and 30 silicon-carbon composite particles are selected to measure the area ratio of the carbon nanotubes in the particles.
  • an ion polisher such as IB-19500CP model
  • the ion source ionizes argon gas to generate argon ions.
  • high-speed argon ions impact atoms or molecules on the sample surface to achieve ion polishing, so that cross-section detection can be achieved.
  • the obtained cross-section is then tested in a scanning electron
  • the area ratio of carbon nanotubes in the silicon-carbon composite particles can be approximated as the content of carbon nanotubes in the silicon-carbon composite material, and the average value is calculated as the content of carbon nanotubes in the silicon-carbon composite material.
  • the oxygen content in silicon-carbon composite materials is based on "Quantitative Analysis by Microbeam Analysis Energy Spectrometry" in GB/T 17359-2012, and is evaluated using cross-sectional EDS energy spectrum.
  • the specific operation is: place the powder to be measured in an ion polisher (such as In the IB-19500CP type), under vacuum conditions, the ion source ionizes argon gas to produce argon ions. After acceleration and focusing, the high-speed argon ions impact atoms or molecules on the sample surface to achieve ion polishing, thereby enabling cross-section detection. .
  • the oxygen content of the material can be obtained by averaging 10 points.
  • the silicon content in silicon-carbon composite materials is evaluated using an inductively coupled plasma emission spectrometer (ICP) in accordance with the U.S. Environmental Protection Agency standard EPA6010D-2018.
  • ICP inductively coupled plasma emission spectrometer
  • the specific operation is: place the powder to be measured in a microwave digestion instrument (such as CEM-Mars6 type ), the digested solution is passed into an ICP tester (such as ICAP7400), and the silicon content in the material is calculated by comparing the silicon concentration in the standard solution.
  • the carbon content in silicon-carbon composite materials is tested using a carbon and sulfur analyzer (such as Dekai HCS-140 infrared carbon and sulfur analyzer) with reference to GB/T 20123-2006/ISO 15350:200.
  • a carbon and sulfur analyzer such as Dekai HCS-140 infrared carbon and sulfur analyzer
  • the principle is: the sample is tested under oxygen-rich conditions. It is heated and burned by a high-frequency furnace at high temperature to oxidize carbon into carbon dioxide. The gas enters the absorption pool and absorbs the corresponding infrared radiation. It is then converted into a corresponding signal by the detector, and the carbon content in the material is calculated.
  • the test results are shown in Table 3 below.
  • the true density of the material is obtained by testing with a true density meter (such as AccuPycII1340).
  • the specific operation is to weigh a sample of a certain mass, place it in a true density tester, seal the test system, and pass in helium gas according to the procedure.
  • the specific surface area SSA of silicon-carbon composite materials refers to GB/T 19587-2017 “Testing the specific surface area of solid materials by gas adsorption BET method", using a specific surface area tester (such as TriStarII3020 type) to test, at constant temperature and low temperature, measuring the specific surface area at different relative pressures After measuring the amount of gas adsorbed on the solid surface, based on the Brownauer-Etter-Taylor (BET) multilayer adsorption theory, the monolayer adsorption amount of the sample is calculated, thereby calculating the specific surface area of the solid.
  • BET Brownauer-Etter-Taylor
  • the average particle size of nano-silicon-based particles in silicon-carbon composite materials can be measured by a transmission electron microscope (such as Thermo Fisher F200i S/TEM) (TEM test).
  • the average particle size can be obtained by averaging the measurements. .
  • the particle size is based on the particle size at the largest particle size. The test results are shown in Table 3 below.
  • a resistivity tester such as Suzhou Lattice Electronics ST2722
  • Table 3 The test results are shown in Table 3 below.
  • Capacity retention rate CR45°C (%) of the secondary battery after 300 cycles at 45°C discharge capacity of the 300th cycle/discharge capacity of the first cycle ⁇ 100%.
  • the test results are shown in Table 4 below.
  • the thickness of the negative electrode plate of the secondary battery when the cold pressing process is completed is recorded as h0.
  • the secondary battery is cycled for 300cls and charged at a constant current rate of 1C to The voltage is 4.25V, and then charged at a constant voltage of 4.25V until the current is less than or equal to 0.05mA, and then left to stand for 5 minutes.
  • Dismantle the cycled battery core in a drying room record the thickness of the negative electrode piece after 300cls cycle as h300, and the 300cls cycle expansion rate of the secondary battery electrode piece at 45°C as ⁇ h300.
  • the test results are shown in Table 4 below.
  • the capacity retention rate of the silicon carbon composite materials of Examples 1 to 18 after 300 cycles at 45°C is 93.4% to 97.3%
  • the cyclic expansion rate ⁇ h300 is 33.8% to 37.7%
  • the rate performance The DR is 80.2% to 84.7%.
  • the secondary battery has good cycle stability, small cycle expansion, and good kinetic properties.
  • the silicon-carbon composite material of Comparative Example 1 does not contain CNTs. After 300 cycles at 45°C, the capacity retention rate is 88.3%, the cyclic expansion rate ⁇ h300 is 42.7%, and the rate performance DR is 75.8%.
  • the silicon-carbon composite material of Comparative Example 2 uses 50nm nano-silica powder, which is the current advanced level of nano-silica powder and non-deposited nano-silica-based particles. After 300 cycles at 45°C, the capacity retention rate is 82.5%, and the cyclic expansion rate ⁇ h300 is 47.2%, and the rate performance DR is 77.4%.
  • the silicon-carbon composite material of Comparative Example 3 is coated with CNT on the silicon-carbon material substrate of Comparative Example 1. After 300 cycles at 45°C, the capacity retention rate is 89.5%, the cyclic expansion rate ⁇ h300 is 40.5%, and the rate performance DR is 78.1%. .
  • Comparative Examples 1-3 are not as good as those of Examples 1-18. It can be seen that nano-silicon is deposited in the carbon nanotube/porous carbon composite matrix by connecting porous carbon and carbon nanotubes to each other through connecting units. Based on materials, its secondary batteries can have both good cycle performance and low cycle expansion, and have advantages in rate performance.

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Abstract

本申请涉及一种硅碳复合材料，包括碳纳米管/多孔碳复合基体和硅基材料，碳纳米管/多孔碳复合基体中的多孔碳与碳纳米管通过连接单元相互连接。利用碳纳米管的高导电性和强机械性能，能够提高硅碳复合材料整体导电性、抗压性及抗膨胀性，从而改善二次电池的循环性能、极片循环膨胀性能及倍率性能。

Description

一种硅碳复合材料及其制备方法、二次电池和用电装置 技术领域
本申请属于二次电池技术领域，具体涉及一种硅碳复合材料及其制备方法、二次电池和用电装置。
背景技术
二次电池现已被广泛用于纯电动汽车、混合电动汽车、智能电网等领域。随着新能源行业的不断发展，客户对二次电池提出了更高的使用需求。
硅基负极材料因具有较高的容量被广泛关注，但是硅基材料存在严重的体积效应，充电过程中会产生巨大的体积膨胀。然而，现有的硅基负极材料的抗压性和导电性差，无法满足电池的电化学性能要求。
因此，需要开发一种硅基负极材料，可以使电池具有较好的循环性能、极片循环膨胀性能及倍率性能。
发明内容
鉴于背景技术中存在的问题，本申请提供一种硅碳复合材料，可以使电池具有较好的循环性能、极片循环膨胀性能及倍率性能。
本申请第一方面提供的硅碳复合材料包括碳纳米管/多孔碳复合基体和硅基材料。碳纳米管/多孔碳复合基体中的多孔碳与碳纳米 管通过连接单元相互连接。
本申请实施例的技术方案中，碳纳米管与多孔碳通过连接单元相互连接，稳定地结合为一体，利用碳纳米管的高导电性，能够改善多孔碳导电性差的问题，降低硅碳复合材料的电阻率，提高硅碳复合材料整体导电性；利用碳纳米管的强机械性能，能够实现复合增强，使硅碳复合材料具有较好的抗压性及抗膨胀性，进而改善硅碳复合材料的结构稳定性，避免极片冷压加工时及硅碳复合材料充放电时因膨胀收缩导致的颗粒破裂而引起循环性能恶化。本申请可有效改善含有该硅碳复合材料的二次电池的循环性能、极片循环膨胀性能及倍率性能。
在一些实施例中，根据第一方面，提出第一方面的第一种示例，连接单元包括碳碳键、苯环、酯基、羰基中的至少一种。
通过优化连接单元的种类，有利于加强碳纳米管与多孔碳的结合，从而提高硅碳复合材料的抗压性。
在一些实施例中，根据第一方面，提出第一方面的第二种示例，硅基材料中至少一部分分布在碳纳米管/多孔碳复合基体的孔中。
硅基材料中至少一部分分布在碳纳米管/多孔碳复合基体的孔中，碳纳米管/多孔碳复合基体的孔中预留了一定的膨胀空间，可有效缓解硅基材料的膨胀。同时通过限定多孔碳复合基体的孔径，可以限制硅基材料在较小的粒径(平均粒径≤50nm)，同时多孔碳复合基体隔绝了硅基材料与电解液的接触，可以有效改善硅基材料的循环性能。
在一些实施例中，根据第一方面，提出第一方面的第三种示例，碳纳米管中至少一部分的一端伸出硅碳复合材料表面。
碳纳米管中至少一部分的一端伸出硅碳复合材料表面，有利于充分发挥碳纳米管的高导电性，从而提高硅碳复合材料的导电性。
在一些实施例中，根据第一方面，提出第一方面的第四种示例，碳纳米管的管径为0.5-20nm。可选地，碳纳米管的管径为0.7-10nm。
碳纳米管的管径越小其导电性能及其机械性能越好，但太小将导致难以合成且成本高。
在一些实施例中，根据第一方面，提出第一方面的第五种示例，碳纳米管的长度记为L，硅碳复合材料的体积分布粒径Dv50记为D0，则硅碳复合材料满足：L≥3D0。可选地，硅碳复合材料满足：3D0≤L≤7D0。
保证碳纳米管长度满足以上公式，可以确保硅碳复合材料的整个颗粒上分布有碳纳米管，充分发挥碳纳米管的导电性能及机械性能，从而提高硅碳复合材料整体的导电性和抗压性。
在一些实施例中，根据第一方面，提出第一方面的第六种示例，碳纳米管的长径比大于等于900，可选为2500-25000。
在一些实施例中，根据第一方面，提出第一方面的第七种示例，硅碳复合材料中碳纳米管的含量≤8％；可选为0.2％-5.0％。
碳纳米管含量太低则无法有效改善硅碳复合材料的导电性，含量太高则成本过高，且影响分散及加工效果。
在一些实施例中，根据第一方面，提出第一方面的第八种示例， 碳纳米管/多孔碳复合基体符合下述(1)-(4)中的至少一个条件：
(1)碳纳米管/多孔碳复合基体内部包括介孔，可选地，介孔的孔体积≥0.1cm 3/g，优选为0.2-2.5cm 3/g；
(2)碳纳米管/多孔碳复合基体内部包括微孔，可选地，微孔的孔体积≤0.3cm 3/g，优选为0.05-0.2cm 3/g；
(3)碳纳米管/多孔碳复合基体内部包括大孔，可选地，大孔的孔体积≤0.5cm 3/g，优选为0.05-0.4cm 3/g；
(4)碳纳米管/多孔碳复合基体内部包括介孔和微孔，可选地，介孔的孔体积与微孔的孔体积之比≥2，优选为3-15。
通过优化碳纳米管/多孔碳复合基体内部的孔隙，有利于限制硅基材料在较小的粒径(平均粒径≤50nm)，同时有利于隔绝复合材料与电解液的接触，同时微孔/介孔/大孔限定在一定范围，有利于预留一定的膨胀空间，通过以上有益效果，改善硅碳复合材料的膨胀及循环性能。
在一些实施例中，根据第一方面，提出第一方面的第九种示例，硅基材料为纳米硅基颗粒。可选地，纳米硅基颗粒的平均粒径≤50nm，更可选为3-20nm。
纳米硅基颗粒的粒径过大将导致局部充电膨胀过大，影响硅碳复合材料的结构稳定性，进而影响硅碳复合材料的循环性能。
在一些实施例中，根据第一方面，提出第一方面的第十种示例，硅基材料包括单质硅、硅氧化物(如氧化亚硅)、硅碳复合物、硅氮复合物、硅合金和预锂化硅氧化合物中的至少一种。
通过进一步优化硅基材料的种类，有利于进一步提高硅碳复合材料的容量，从而提高电池的能量密度。
在一些实施例中，根据第一方面，提出第一方面的第十一种示例，硅基材料包括非晶态硅。可选地，硅基材料包括非晶态硅与晶态硅的混合物。
通过优化硅基材料的种类，有利于提高硅碳复合材料的容量，从而提高电池的能量密度。
在一些实施例中，根据第一方面，提出第一方面的第十二种示例，碳纳米管/多孔碳复合基体由树脂前驱体和接枝有官能团和/或聚合物的碳纳米管经炭化形成。官能团和/或聚合物均能够与树脂前驱体发生化学反应，使碳纳米管与树脂前驱体连接，并在炭化后形成连接单元。
官能团和/或聚合物均能够与树脂前驱体发生化学反应，使碳纳米管与树脂前驱体发生化学连接，并在炭化后形成连接单元，增强碳纳米管与树脂的界面结合，从而提高硅碳复合材料的抗压性。
在一些实施例中，根据第一方面，提出第一方面的第十三种示例，红外光谱测试硅碳复合材料或碳纳米管/多孔碳复合基体，硅碳复合材料或碳纳米管/多孔碳复合基体含有以下连接单元中的至少一种：酯羰基，其吸收峰为1750～1735cm -1；酮羰基，其吸收峰为1725～1705cm -1；苯环基，其吸收峰为1620～1450cm -1；以及碳碳键，其吸收峰为2400～1950cm -1；和/或，
透射电镜测试硅碳复合材料或碳纳米管/多孔碳复合基体，硅碳 复合材料或碳纳米管/多孔碳复合基体中碳纳米管周边的碳原子与碳纳米管最外层碳原子间距≤0.35nm的区域占比≥50％。
通过红外光谱测试，表征出硅碳复合材料或碳纳米管/多孔碳复合基体中含有连接单元，通过透射电镜测试表明多孔碳和碳纳米管连接在一起。这些表征结果表明多孔碳和碳纳米管通过连接单元连接为一个整体，界面结合增强。
在一些实施例中，根据第一方面，提出第一方面的第十四种示例，定义硅碳复合材料的抗压指数P＝D0/(D0-D1)，则P≥3，其中，D0为硅碳复合材料的体积分布粒径Dv50，D1为硅碳复合材料被压制后测试的体积分布粒径Dv50，压制的条件为在300MPa压力下保压30s并反复压制50次。
抗压指数P≥3表明硅碳复合材料具有较好的抗压性，可较好地改善硅基材料的膨胀问题，从而使硅碳复合材料具有极佳的循环性能。
在一些实施例中，根据第一方面，提出第一方面的第十五种示例，硅碳复合材料在4MPa压力下的电阻率ρ≤0.4Ω·cm，可选地，0.05Ω·cm≤ρ≤0.3Ω·cm。
硅碳复合材料在4MPa压力下的电阻率越小，则其导电性越好。通过优化硅碳复合材料的电阻率，有利于提高导电性。
在一些实施例中，根据第一方面，提出第一方面的第十六种示例，硅碳复合材料满足下述(Ⅰ)-(Ⅴ)中至少一个条件：
(Ⅰ)硅碳复合材料的体积分布粒径Dv50≤8μm，可选为3-7μm；
(Ⅱ)硅碳复合材料的孔隙率≤20％，可选为5％-15％；
(Ⅲ)硅碳复合材料的比表面积SSA≤5.0m 2/g，可选为0.8-4.0m 2/g；
(Ⅳ)硅碳复合材料内部包括介孔，可选地，介孔的孔体积≤0.3cm 3/g，优选为0.05-0.1cm 3/g；
(Ⅴ)硅碳复合材料中元素质量比为Si:C:O＝(20-55):(40-70):(3-10)。
通过优化硅碳复合材料的粒径，可避免因粒径过小导致循环性能变差，避免因粒径过大导致导电性变差。通过在硅碳复合材料内部预留一定的孔隙率，可预留硅基材料充电时的膨胀空间，缓冲膨胀，改善材料的循环性能。硅碳复合材料的比表面积太高会影响材料性能，太低则在多孔碳材料中难以实现。如果硅碳复合材料中介孔的孔体积过低，则预留的硅基材料膨胀空间不足，将影响硅碳复合材料的循环性能，如果硅碳复合材料中介孔的孔体积过高，则硅碳复合材料的体积能量密度过低，实用性降低，且硅碳复合材料中介孔的孔体积过高会影响硅碳复合材料的抗压性，导致材料不耐压。。优化硅元素含量可以确保对硅碳复合材料的容量需求，优化碳元素含量可确保多孔碳的有效形成，并有效隔离后续沉积的硅基材料，优化氧元素含量可保证多孔碳的柔韧性以及多孔碳与硅基材料和碳纳米管的连接稳定性。
在一些实施例中，根据第一方面，提出第一方面的第十七种示例，硅碳复合材料的表面还设有包覆层。可选地，包覆层包括碳包 覆层、聚合物包覆层、无机盐包覆层、金属氧化物包覆层中的至少一种。
通过在硅碳复合材料的表面形成包覆层，有利于进一步隔绝电解液与硅碳复合材料的直接接触，改善循环性性能，且包覆层具有一定缓冲作用，进一步缓冲膨胀，减小膨胀对极片的影响，特别地，利用碳包覆层可进一步改善硅碳材料的导电性。
本申请的第二方面提供一种硅碳复合材料的制备方法，包括以下步骤：
在碳纳米管上接枝官能团和/或聚合物，得到改性碳纳米管；
将改性碳纳米管与树脂前驱体溶液混合，得到混合溶液，其中，改性碳纳米管上的官能团和聚合物均能够与树脂前驱体发生化学反应，使改性碳纳米管与树脂前驱体连接；
对混合溶液进行固化处理，得到复合基体前驱体；
对复合基体前驱体进行炭化处理，得到多孔碳/碳纳米管复合基体；以及
在多孔碳/碳纳米管复合基体上沉积硅基材料，得到硅碳复合材料。
本申请实施例的技术方案中，通过该方法能够获得具有较好的抗压性和导电性的硅碳复合材料。该方法操作简单、可重复性强，有利于大规模工业化生产。
在一些实施例中，根据第二方面，提出第二方面的第一种示例，按质量百分比计，混合溶液还包括0.5％～30％的催化剂。可选地，催 化剂包括六次甲基四胺、碳酸氢铵、碳酸铵、氨水、锌盐、铜盐和铬盐中一种或多种。
通过优化反应条件，有利于缩短改性碳纳米管与树脂前驱体的反应时间，提高反应转化率。
在一些实施例中，根据第二方面，提出第二方面的第二种示例，混合包括：在20～60℃下，搅拌1～10h。改性碳纳米管与树脂前驱体发生酯化反应、加成反应、加聚反应、缩聚反应中的一种或多种。
在一些实施例中，根据第二方面，提出第二方面的第三种示例，官能团包括羧基、羟基、氨基、苯基、羰基中的一种或多种；和/或，聚合物包括聚酰胺、聚甲基丙烯酸甲酯、聚甲基丙烯酸羟乙酯中的一种或多种。
通过优化接枝在碳纳米管上的官能团和/或聚合物的种类，有利于在碳纳米管与多孔碳之间形成更加稳定的连接单元，实现界面结合增强，以提高硅碳复合材料的抗压性。
在一些实施例中，根据第二方面，提出第二方面的第四种示例，固化处理包括：预固化、全固化。可选地，固化处理包括：预固化、粉碎、全固化。
通过优化固化处理过程，有利于提高固化效果，并且有利于提高硅碳复合材料内部均匀性。
在一些实施例中，根据第二方面，提出第二方面的第五种示例，预固化的温度为70-140℃，可选为80-130℃；和/或，预固化的时间为3-12h，可选为5-10h。
通过优化预固化的温度和时间，有利于提高硅碳复合材料内部均匀性，提高孔隙分布及大小均匀性。
在一些实施例中，根据第二方面，提出第二方面的第六种示例，全固化的温度为150-220℃，可选为160-200；和/或，全固化的时间为8-20h，可选为10-15h。
通过优化全固化的温度和时间，有利于提高固化效果，提高硅碳复合材料内部均匀性。
在一些实施例中，根据第二方面，提出第二方面的第七种示例，炭化处理的温度为900-3000℃，可选为1000-2000℃；和/或，炭化处理的时间为2-6h，可选为3-5h。
通过优化炭化处理的温度和时间，有利于在碳纳米管与多孔碳之间形成更加稳定的连接单元，实现界面结合增强，以提高硅碳复合材料的抗压性。
在一些实施例中，根据第二方面，提出第二方面的第八种示例，沉积通过化学气相沉积法进行。可选地，沉积气体包括H 2、N 2和Ar中的至少一种或多种与硅烷气体的混合气体。
通过化学气相沉积法进行硅沉积，有利于实现在多孔碳/碳纳米管复合基体中均匀沉积硅基材料，且硅颗粒长大受多孔碳的孔径限制，可将硅颗粒限制在较小的粒径范围，如平均粒径≤50nm，另一方面，可实现多孔碳与沉积硅基材料的紧密结合，一定程度上更好限制硅材料的膨胀。
本申请的第三方面提供一种二次电池，包括负极极片，负极极 片包括本申请第一方面的硅碳复合材料或根据本申请第二方面的制备方法获得的硅碳复合材料。
本申请实施例的技术方案中，由于采用了本申请第一方面的硅碳复合材料或根据本申请第二方面的制备方法获得的硅碳复合材料，因此本申请的二次电池具有提高的循环性能。
本申请的第四方面提供一种用电装置，包括本申请第三方面的二次电池。
本申请实施例的技术方案中，由于采用了本申请第一方面的硅碳复合材料或根据本申请第二方面的制备方法获得的硅碳复合材料，因此本申请的用电装置具有提高的循环性能。
上述说明仅是本申请技术方案的概述，为了能够更清楚了解本申请的技术手段，可依照说明书的内容予以实施，并且为了让本申请的上述和其它目的、特征和优点能够更明显易懂，以下特举本申请的具体实施方式。
附图说明
通过阅读下文优选实施方式的详细描述，各种其他的优点和益处对于本领域普通技术人员将变得清楚明了。附图仅用于示出优选实施方式的目的，而并不认为是对本发明的限制。而且在整个附图中，用相同的参考符号表示相同的部件。在附图中：
图1为本申请的硅碳复合材料的结构示意图。
图2为本申请的硅碳复合材料的扫描电子显微镜(SEM)图片。
图3是二次电池的一实施方式的示意图。
图4是图3的分解图。
图5是电池模块的一实施方式的示意图。
图6是电池包的一实施方式的示意图。
图7是图6的分解图。
图8是二次电池用作电源的装置的一实施方式的示意图。
附图标记说明：
1、电池包；2、上箱体；3、下箱体；4、电池模块；5、二次电池；51、壳体；52、电极组件；53、盖板。
具体实施方式
下面将参照附图更详细地描述本公开的示例性实施方式。虽然附图中显示了本公开的示例性实施方式，然而应当理解，可以以各种形式实现本公开而不应被这里阐述的实施方式所限制。相反，提供这些实施方式是为了能够更透彻地理解本公开，并且能够将本公开的范围完整的传达给本领域的技术人员。
除非另有定义，本文所使用的所有的技术和科学术语与属于本申请的技术领域的技术人员通常理解的含义相同；本文中所使用的术语只是为了描述具体的实施例的目的，不是旨在于限制本申请。本申请的说明书和权利要求书及上述附图说明中的术语“包括”和“具有”以及它们的任何变形，意图在于覆盖不排他的包含。
为了简便，本文仅明确地公开了一些数值范围。然而，任意下 限可以与任何上限组合形成未明确记载的范围；以及任意下限可以与其它下限组合形成未明确记载的范围，同样任意上限可以与任意其它上限组合形成未明确记载的范围。此外，尽管未明确记载，但是范围端点间的每个点或单个数值都包含在该范围内。因而，每个点或单个数值可以作为自身的下限或上限与任意其它点或单个数值组合或与其它下限或上限组合形成未明确记载的范围。
在本文的描述中，需要说明的是，除非另有说明，“以上”、“以下”为包含本数，“一种或多种”中“多种”的含义是两种以上(包括两种)。
在本申请实施例的描述中，除非另有明确的规定和限定，技术术语“连接”是指两种化学物质以连接单元为媒介进行的结合。对于本领域的普通技术人员而言，可以根据具体情况理解上述术语在本申请实施例中的具体含义。
本申请的上述发明内容并不意欲描述本申请中的每个公开的实施方式或每种实现方式。如下描述更具体地举例说明示例性实施方式。在整篇申请中的多处，通过一系列实施例提供了指导，这些实施例可以以各种组合形式使用。在各个实例中，列举仅作为代表性组，不应解释为穷举。
硅基负极材料因具有较高的容量被广泛关注，但是硅基材料存在严重的体积效应，充电过程中会产生巨大的体积膨胀。为此，研究人员开发了硅碳负极材料。然而，现有的硅碳负极材料的抗压性差，在实际极片冷压加工时材料结构易被破坏，进而影响材料的电 化学性能。另外，其电阻率大，导电性差，无法满足对材料电化学性能的要求。因此，亟需开发一种硅基负极材料，可以使电池具有较好的循环性能、极片循环膨胀性能及倍率性能。
发明人经过深入研究，设计了一种硅碳复合材料，参考图1，其包括碳纳米管/多孔碳复合基体和硅基材料。碳纳米管/多孔碳复合基体中的多孔碳与碳纳米管通过连接单元相互连接。
本申请实施例的技术方案中，碳纳米管与多孔碳通过连接单元相互连接，稳定地结合为一体，利用碳纳米管的高导电性，能够改善多孔碳导电性差的问题，降低硅碳复合材料的电阻率，提高硅碳复合材料整体导电性；利用碳纳米管的强机械性能，能够实现复合增强，使硅碳复合材料具有较好的抗压性，从而具有较好的抗膨胀性，进而改善硅碳复合材料的结构稳定性，避免极片冷压加工时颗粒破裂而导致循环性能恶化。本申请可有效改善含有该硅碳复合材料的二次电池的循环性能、极片循环膨胀性能及倍率性能。
在一些实施例中，连接单元包括碳碳键、苯环、酯基、羰基中的至少一种。
通过优化连接单元的种类，有利于加强碳纳米管与多孔碳的结合，从而提高硅碳复合材料的抗压性。
当然，连接单元的种类并不局限于上述几种，凡是能够将碳纳米管与多孔碳化学连接的连接单元，均包含在本申请范围内，在此不再一一列举。
在一些实施例中，硅基材料中至少一部分分布在碳纳米管/多孔 碳复合基体的孔中。
硅基材料中至少一部分分布在碳纳米管/多孔碳复合基体的孔中，碳纳米管/多孔碳复合基体的孔中预留了一定的膨胀空间，可有效缓解硅基材料的膨胀。同时通过限定多孔碳复合基体的孔径，可以限制硅基材料在较小的粒径(例如，平均粒径≤50nm)，同时多孔碳复合基体隔绝了硅基材料与电解液的接触，可以有效改善硅基材料的循环性能。
在一些实施例中，参考图2，碳纳米管中至少一部分的一端伸出硅碳复合材料表面。
至少一部分碳纳米管的一端伸出硅碳复合材料表面，这样设计有利于碳纳米管与电解液接触，充分发挥碳纳米管的高导电性，从而提高硅碳复合材料的导电性。若碳纳米管完全包裹在多孔碳内部，碳纳米管不能很好地与电解液接触，则碳纳米管的导电性无法充分发挥，因此不利于硅碳复合材料导电性的提高。
在一些实施例中，碳纳米管的管径可为0.5-20nm。可选地，碳纳米管的管径可为0.7-10nm。
碳纳米管的管径越小其导电性能及其机械性能越好，但太小将导致难以合成且成本高。
在一些具体实施例中，碳纳米管的管径可为0.5nm、0.7nm、1nm、2nm、3nm、4nm、5nm、6nm、7nm、8nm、9nm、10nm、11nm、12nm、13nm、14nm、15nm、16nm、17nm、18nm、19nm或20nm。可选地，碳纳米管的管径可为0.7-6nm。碳纳米管的管径可以在上述所列数值 中任意两个作为端值而构成的数值范围之内。
在一些实施例中，碳纳米管的长度记为L，硅碳复合材料的体积分布粒径Dv50记为D0，则硅碳复合材料满足：L≥3D0。可选地，硅碳复合材料满足：3D0≤L≤7D0。
保证碳纳米管长度满足以上公式，可以确保硅碳复合材料的整个颗粒上分布有碳纳米管，充分发挥碳纳米管的导电性能及机械性能，从而提高硅碳复合材料整体的导电性和抗压性。此外，保证碳纳米管长度大于硅碳复合材料的体积分布粒径，还有利于使至少一部分碳纳米管的一端伸出硅碳复合材料表面。碳纳米管过短，易被包裹在多孔碳内部，使之难以与电解液接触，不利于其导电性的发挥。
在一些具体实施例中，L可为3D0、3.5D0、4D0、4.5D0、5D0、5.5D0、6D0、6.5D0或7D0。
在一些实施例中，碳纳米管的长径比大于等于900，可选为2500-25000。
在一些具体实施例中，碳纳米管的长径比可为900、1000、2000、3000、4000、5000、6000、7000、8000、9000、10000、11000、12000、13000、14000、15000、16000、17000、18000、19000、20000、21000、22000、23000、24000或25000。碳纳米管的长径比可以在上述所列数值中任意两个作为端值而构成的数值范围之内。
在一些实施例中，硅碳复合材料中碳纳米管的含量≤8％；可选为0.2％-5.0％。
碳纳米管含量太低则无法有效改善硅碳复合材料的导电性，含量太高则成本过高，且影响分散及加工效果。
在一些具体实施例中，硅碳复合材料中碳纳米管的含量可为0.2％、0.3％、0.5％、1.0％、1.5％、2.0％、2.5％、3.0％、3.5％、4.0％、4.5％、5.0％、5.5％、6.0％、6.5％、7.0％、7.5％或8.0％。硅碳复合材料中碳纳米管的含量可以在上述所列数值中任意两个作为端值而构成的数值范围之内。
在一些实施例中，碳纳米管/多孔碳复合基体内部包括介孔；可选地，介孔的孔体积≥0.1cm 3/g，例如可以为0.2-2.5cm 3/g。
在一些具体实施例中，介孔的孔体积可为0.1cm 3/g、0.2cm 3/g、0.5cm 3/g、1.0cm 3/g、1.5cm 3/g、2.0cm 3/g或2.5cm 3/g。介孔的孔体积可以在上述所列数值中任意两个作为端值而构成的数值范围之内。
在一些实施例中，碳纳米管/多孔碳复合基体内部包括微孔；可选地，微孔的孔体积≤0.3cm 3/g，例如可以为0.05-0.2cm 3/g。
在一些具体实施例中，微孔的孔体积可为0.05cm 3/g、0.1cm 3/g、0.15cm 3/g、0.2cm 3/g、0.25cm 3/g或0.3cm 3/g。微孔的孔体积可以在上述所列数值中任意两个作为端值而构成的数值范围之内。
在一些实施例中，碳纳米管/多孔碳复合基体内部包括大孔；可选地，大孔的孔体积≤0.5cm 3/g，例如可以为0.05-0.4cm 3/g。
在一些具体实施例中，大孔的孔体积可为0.05cm 3/g、0.1cm 3/g、0.15cm 3/g、0.2cm 3/g、0.25cm 3/g、0.3cm 3/g、0.35cm 3/g、0.4cm 3/g、0.45cm 3/g或0.5cm 3/g。大孔的孔体积可以在上述所列数值中任意两 个作为端值而构成的数值范围之内。
在一些实施例中，碳纳米管/多孔碳复合基体内部包括介孔和微孔；可选地，介孔的孔体积与微孔的孔体积之比≥2，例如可以为3-15。
在一些具体实施例中，介孔的孔体积与微孔的孔体积之比可为2、3、4、5、6、7、8、9、10、11、12、13、14或15。介孔的孔体积与微孔的孔体积之比可以在上述所列数值中任意两个作为端值而构成的数值范围之内。
在一些实施例中，多孔碳/碳纳米管复合基体的孔隙率≥20％，可选为20％～60％。
在一些实施例中，多孔碳/碳纳米管复合基体的平均孔径为1～100nm，可选为5～50nm。
通过优化碳纳米管/多孔碳复合基体内部的孔隙，有利于限制硅基材料在较小的粒径(例如，平均粒径≤50nm)，同时有利于隔绝复合材料与电解液的接触，同时微孔/介孔/大孔限定在一定范围，有利于预留一定的膨胀空间，通过以上有益效果，改善硅碳复合材料的膨胀及循环性能。
在一些实施例中，碳纳米管在碳纳米管/多孔碳复合基体中的质量占比可为0.05％-16％，可选为0.1％-10％，例如可为0.05％、0.1％、0.2％、0.5％、1％、2％、3％、4％、5％、6％、7％、8％、9％、10％、11％、12％、13％、14％或15％。碳纳米管在碳纳米管/多孔碳复合基体中的质量占比可以在上述所列数值中任意两个作为端值而构成的数值范围之内。
在一些实施例中，硅基材料为纳米硅基颗粒。可选地，纳米硅基颗粒的平均粒径≤50nm，更可选为3-20nm。
发明人发现，纳米硅基颗粒的粒径过大将导致局部充电膨胀过大，影响硅碳复合材料的结构稳定性，进而影响硅碳复合材料的循环性能。
在一些具体实施例中，纳米硅基颗粒的平均粒径可为3nm、4nm、5nm、6nm、7nm、8nm、9nm、10nm、11nm、12nm、13nm、14nm、15nm、16nm、17nm、18nm、19nm、20nm、25nm、30nm、35nm、40nm、45nm或50nm。纳米硅基颗粒的平均粒径可以在上述所列数值中任意两个作为端值而构成的数值范围之内。
在一些实施例中，硅基材料包括单质硅、硅氧化物(如氧化亚硅)、硅碳复合物、硅氮复合物、硅合金和预锂化硅氧化合物中的至少一种。
在一些实施例中，硅基材料包括非晶态硅。可选地，硅基材料包括非晶态硅与晶态硅的混合物。
通过进一步优化硅基材料的种类，有利于进一步提高硅碳复合材料的容量，从而提高电池的能量密度。
在一些实施例中，碳纳米管/多孔碳复合基体由树脂前驱体和接枝有官能团和/或聚合物的碳纳米管经炭化形成。官能团和/或聚合物均能够与树脂前驱体发生化学反应，使碳纳米管与树脂前驱体连接，并在炭化后形成连接单元。
官能团和/或聚合物均能够与树脂前驱体发生化学反应，使碳纳 米管与树脂前驱体发生化学连接，并在炭化后形成连接单元，增强碳纳米管与树脂的界面结合，从而提高硅碳复合材料的抗压性。
在一些具体实施例中，官能团可为羧基、羟基、氨基、苯基、羰基中的一种或多种。聚合物可为聚酰胺、聚甲基丙烯酸甲酯、聚甲基丙烯酸羟乙酯中的一种或多种。
在一些实施例中，红外光谱测试硅碳复合材料或碳纳米管/多孔碳复合基体，硅碳复合材料或碳纳米管/多孔碳复合基体含有以下连接单元中的至少一种：酯羰基，其吸收峰为1750～1735cm -1；酮羰基，其吸收峰为1725～1705cm -1；苯环基，其吸收峰为1620～1450cm -1；以及碳碳键，其吸收峰为2400～1950cm -1。
在一些实施例中，透射电镜测试硅碳复合材料或碳纳米管/多孔碳复合基体，硅碳复合材料或碳纳米管/多孔碳复合基体中碳纳米管周边的碳原子与碳纳米管最外层碳原子间距≤0.35nm的区域占比≥50％。这表明所述多孔碳和所述碳纳米管连接在一起。这里的“区域占比”是指符合碳纳米管周边的碳原子与所述碳纳米管最外层碳原子间距≤0.35nm的碳纳米管长度与碳纳米管实际长度之比，区域占比的含义为碳纳米管与多孔碳有连接单元的连接区域在碳纳米管整体长度中的占比，其值越大，碳纳米管与多孔碳连接越紧密，区域占比＞50％，则认为碳纳米管与多孔碳有有效连接单元连接在一起。
通过红外光谱测试，表征出硅碳复合材料或碳纳米管/多孔碳复合基体中含有连接单元。通过透射电镜测试表明多孔碳和碳纳米管 连接在一起。这些表征结果表明多孔碳和碳纳米管通过连接单元连接为一个整体，界面结合增强，能够有效提高硅碳复合材料整体的抗压性能。
在一些实施例中，定义硅碳复合材料的抗压指数P＝D0/(D0-D1)，则P≥3，其中，D0为硅碳复合材料的体积分布粒径Dv50，D1为硅碳复合材料被压制后测试的体积分布粒径Dv50，压制的条件为在300MPa压力下保压30s并反复压制50次。
抗压指数P≥3表明硅碳复合材料具有较好的抗压性，可较好地改善硅基材料的膨胀问题，从而使硅碳复合材料具有极佳的循环性能。
可选地，5≤P≤100，P值越大，说明压制对材料粒径影响越小，硅碳复合材料越抗压。
在一些具体实施例中，P可为3、5、10、15、20、25、30、35、40、45、50、55、60、65、70、75、80、85、90、95或100。P值可以在上述所列数值中任意两个作为端值而构成的数值范围之内。
在一些实施例中，硅碳复合材料在4MPa压力下的电阻率ρ≤0.4Ω·cm，可选地，0.05Ω·cm≤ρ≤0.3Ω·cm。
硅碳复合材料在4MPa压力下的电阻率越小，则其导电性越好。通过优化硅碳复合材料的电阻率，有利于提高导电性。
在一些具体实施例中，ρ可为0.05Ω·cm、0.1Ω·cm、0.15Ω·cm、0.2Ω·cm、0.25Ω·cm、0.3Ω·cm、0.35Ω·cm或0.4Ω·cm。电阻率ρ可以在上述所列数值中任意两个作为端值而构成的数值范围之内。
在一些实施例中，硅碳复合材料的体积分布粒径Dv50≤8μm，可选为3-7μm。在一些具体实施例中，硅碳复合材料的体积分布粒径Dv50可为3μm、3.5μm、4μm、4.5μm、5μm、5.5μm、6μm、6.5μm、7μm、7.5μm或8μm。硅碳复合材料的体积分布粒径Dv50可以在上述所列数值中任意两个作为端值而构成的数值范围之内。通过优化硅碳复合材料的粒径，可避免因粒径过小导致循环性能变差，避免因粒径过大导致导电性变差。
在一些实施例中，硅碳复合材料的孔隙率≤20％，可选为5％-15％。在一些具体实施例中，硅碳复合材料的孔隙率可为5％、6％、7％、8％、9％、10％、11％、12％、13％、14％、15％、16％、17％、18％、19％或20％。硅碳复合材料的孔隙率可以在上述所列数值中任意两个作为端值而构成的数值范围之内。通过在硅碳复合材料内部预留一定的孔隙率，可预留硅基材料充电时的膨胀空间，缓冲膨胀，改善材料的循环性能。
在一些实施例中，硅碳复合材料的比表面积SSA≤5.0m 2/g，可选为0.8-4.0m 2/g。在一些具体实施例中，硅碳复合材料的比表面积SSA可为0.8m 2/g、1.0m 2/g、1.5m 2/g、2m 2/g、2.5m 2/g、3m 2/g、3.5m 2/g、4m 2/g、4.5m 2/g或5m 2/g。硅碳复合材料的比表面积SSA可以在上述所列数值中任意两个作为端值而构成的数值范围之内。硅碳复合材料的比表面积太高会影响材料性能，太低则在硅碳复合材料中难以实现。
在一些实施例中，硅碳复合材料内部包括介孔；可选地，介孔 的孔体积≤0.3cm 3/g，例如可以为0.05-0.1cm 3/g。在一些具体实施例中，介孔的孔体积可为0.05cm 3/g、0.06cm 3/g、0.07cm 3/g、0.08cm 3/g、0.09cm 3/g、0.1cm 3/g、0.15cm 3/g、0.2cm 3/g、0.25cm 3/g或0.3cm 3/g。介孔的孔体积可以在上述所列数值中任意两个作为端值而构成的数值范围之内。如果硅碳复合材料中介孔的孔体积过低，则预留的硅基材料膨胀空间不足，将影响硅碳复合材料的循环性能，如果硅碳复合材料中介孔的孔体积过高，则硅碳复合材料的体积能量密度过低，实用性降低，且硅碳复合材料中介孔的孔体积过高会影响硅碳复合材料的抗压性，导致材料不耐压。
在一些实施例中，硅碳复合材料中元素质量比为Si:C:O＝(20-55):(40-70):(3-10)。
在一些具体实施例中，硅碳复合材料中元素质量比Si:C:O可为20:70:10，30:65:5，40:55:5，55:42:3，55:40:5。硅碳复合材料中元素质量比Si:C:O可以在上述所列数值中任意两个作为端值而构成的数值范围之内。优化硅元素含量可以确保对硅碳复合材料的容量需求。优化碳元素含量可确保多孔碳的有效形成，并有效隔离后续沉积的硅基材料。优化氧元素含量可保证多孔碳的柔韧性以及多孔碳与硅基材料和碳纳米管的连接稳定性。
在一些实施例中，硅碳复合材料的表面还设有包覆层。可选地，包覆层包括碳包覆层、聚合物包覆层、无机盐包覆层、金属氧化物包覆层中的至少一种。
通过在硅碳复合材料的表面形成包覆层，有利于进一步隔绝电 解液与硅碳复合材料的直接接触，改善循环性性能，且包覆层具有一定缓冲作用，进一步缓冲膨胀，减小膨胀对极片的影响，特别地，利用碳包覆层可进一步改善硅碳材料的导电性。
本申请的第二方面提供一种硅碳复合材料的制备方法，包括以下步骤：
在碳纳米管上接枝官能团和/或聚合物，得到改性碳纳米管；
将改性碳纳米管与树脂前驱体溶液混合，得到混合溶液，其中，改性碳纳米管上的官能团和聚合物均能够与树脂前驱体发生化学反应，使改性碳纳米管与树脂前驱体连接；
对混合溶液进行固化处理，得到复合基体前驱体；
对复合基体前驱体进行炭化处理，得到多孔碳/碳纳米管复合基体；以及
在多孔碳/碳纳米管复合基体上沉积硅基材料，得到硅碳复合材料。
通过该方法能够获得具有较好的抗压性和导电性的硅碳复合材料。该方法操作简单、可重复性强，有利于大规模工业化生产。
在一些实施例中，按质量百分比计，混合溶液还包括0.5％～30％的催化剂。可选地，催化剂包括六次甲基四胺、碳酸氢铵、碳酸铵、氨水、锌盐、铜盐和铬盐中一种或多种。在一些具体实施例中，改性碳纳米管、催化剂和酚醛树脂前驱体溶液的质量比可为(0.05-8)：(3-7):(83-96.95)。
通过优化反应条件，有利于缩短改性碳纳米管与树脂前驱体的 反应时间，提高反应转化率。
在一些实施例中，混合包括：在20～60℃下，搅拌1～10h。改性碳纳米管与树脂前驱体发生酯化反应、加成反应、加聚反应、缩聚反应中的一种或多种。
在一些实施例中，官能团包括羧基、羟基、氨基、苯基、羰基中的一种或多种。聚合物包括聚酰胺、聚甲基丙烯酸甲酯、聚甲基丙烯酸羟乙酯中的一种或多种。
通过优化接枝在碳纳米管上的官能团和/或聚合物的种类，有利于在碳纳米管与多孔碳之间形成更加稳定的连接单元，实现界面结合增强，以提高硅碳复合材料的抗压性。
碳纳米管上接枝的官能团可以作为树脂前驱体的固化剂。可选地，官能团可为酸性或碱性官能团。
在一些实施例中，固化处理包括：预固化、全固化。可选地，固化处理包括：预固化、粉碎、全固化。
通过优化固化处理过程，有利于提高固化效果，并且有利于提高硅碳复合材料内部均匀性。
在一些具体实施中，粉碎后所得粉体的体积分布粒径Dv50可为3～15μm，可选为5～10μm。
在一些实施例中，预固化的温度为70-140℃，可选为80-130℃；和/或，预固化的时间为3-12h，可选为5-10h。
通过优化预固化的温度和时间，有利于提高硅碳复合材料内部均匀性，提高孔隙分布及大小均匀性。
在一些实施例中，全固化的温度为150-220℃，可选为160-200；和/或，全固化的时间为8-20h，可选为10-15h。
通过优化全固化的温度和时间，有利于提高固化效果，提高硅碳复合材料内部均匀性。
在一些具体实施例中，全固化在惰性气氛下进行。惰性气氛可为氮气、氩气等。
在一些实施例中，炭化处理的温度为900-3000℃，可选为1000-2000；和/或，炭化处理的时间为2-6h，可选为3-5h。
通过优化炭化处理的温度和时间，有利于在碳纳米管与多孔碳之间形成更加稳定的连接单元，实现界面结合增强，以提高硅碳复合材料的抗压性。
在一些具体实施例中，炭化处理在惰性气氛下进行。惰性气氛可为氮气、氩气等。
在一些实施例中，沉积通过化学气相沉积法进行。可选地，沉积气体包括H 2、N 2和Ar中的至少一种或多种与硅烷气体的混合气体。
通过化学气相沉积法进行硅沉积，有利于实现在多孔碳/碳纳米管复合基体中均匀沉积硅基材料，且硅颗粒长大受多孔碳的孔径限制，可将硅颗粒限制在较小的粒径范围，如≤50nm，另一方面，可实现多孔碳与沉积硅基材料的紧密结合，一定程度上更好限制硅材料的膨胀。
在一些具体实施例中，硅烷气体包括甲硅烷、乙硅烷、丙硅烷、 一氯硅烷、二氯硅烷及三氯硅烷中的至少一种。
在一些具体实施例中，混合气体中，硅烷气体的体积占比可为5％-80％，例如可为5％、15％、25％、35％，45％，55％，65％或80％。硅烷气体的体积占比可以在上述所列数值中任意两个作为端值而构成的数值范围之内。
在一些具体实施例中，混合气体的通入流量可为100-400mL/min，例如可为100mL/min、150mL/min、200mL/min、250mL/min、300mL/min、350mL/min或400mL/min。混合气体的通入流量可以在上述所列数值中任意两个作为端值而构成的数值范围之内。
在一些具体实施例中，沉积温度可为400-1000℃，例如可为400℃、450℃、500℃、550℃、600℃、650℃、700℃、750℃、800℃、850℃、900℃、950℃或1000℃。沉积温度可以在上述所列数值中任意两个作为端值而构成的数值范围之内。沉积时间可为2-10h，例如可为2h、3h、4h、5h、6h、7h、8h、9h或10h。沉积时间可以在上述所列数值中任意两个作为端值而构成的数值范围之内。
在一些实施例中，树脂前驱体可为呋喃树脂前驱体、脲醛树脂前驱体、嘧胺树脂前驱体、酚醛树脂前驱体、环氧树脂前驱体、聚甲醛丙烯酸甲酯树脂前驱体、聚丙烯腈树脂前驱体中的任一种。
碳纳米管与树脂前驱体的用量可根据材料设计需求调整配比。
在一些实施例中，接枝方法包括：采用硝酸、硫酸、醋酸、氨水和草酸等中的一种或多种进行酸洗或碱洗。优选采用有机酸进行 酸洗。通过酸洗可以在碳纳米管上接枝羧基等。例如，可采用氨水进行碱洗以接枝羟基。当然，也可采用其他已知方法在碳纳米管上接枝官能团和/或聚合物，例如接枝聚甲基丙烯酸甲酯。
在一些实施例中，制备方法还包括在所得硅碳复合材料上形成包覆层。
在一些具体实施例中，可通过化学气相沉积法形成碳包覆层。化学气相沉积的沉积气体可为C 2H 2和N 2的混合气体。混合气体中，C 2H 2的体积占比可为2％-40％。混合气体的通入流量可为100-300mL/min。沉积温度可为800-1000℃，沉积时间可为0.5-2h。
[二次电池]
二次电池，是指在电池放电后可通过充电的方式使活性材料激活而继续使用的电池。
通常情况下，二次电池包括正极极片、负极极片、隔离膜及电解质。在电池充放电过程中，活性离子在正极极片和负极极片之间往返嵌入和脱出。隔离膜设置在正极极片和负极极片之间，起到隔离的作用。电解质在正极极片和负极极片之间起到传导离子的作用。
[负极极片]
在二次电池中，所述负极极片通常包括负极集流体及设置在负极集流体上的负极膜层，所述负极膜层包括本申请上述提供的硅碳复合材料。
所述负极集流体可以采用常规金属箔片或复合集流体(例如可以将金属材料设置在高分子基材上形成复合集流体)。作为示例，负极集流体可以采用铜箔。
所述负极膜层通常还可选地包括粘结剂、导电剂和其他可选助剂。
作为示例，导电剂可以为超导碳、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯及碳纳米纤维中一种或几种。
作为示例，粘结剂可以为丁苯橡胶(SBR)、水性丙烯酸树脂(water-based acrylic resin)、聚偏二氟乙烯(PVDF)、聚四氟乙烯(PTFE)、乙烯-醋酸乙烯酯共聚物(EVA)、聚乙烯醇(PVA)及聚乙烯醇缩丁醛(PVB)中的一种或几种。
作为示例，其他可选助剂可以是增稠及分散剂(例如羧甲基纤维素钠CMC-Na)、PTC热敏电阻材料等。
[正极极片]
在二次电池中，所述正极极片通常包括正极集流体及设置在正极集流体上的正极膜层，所述正极膜层包括正极活性材料。
所述正极集流体可以采用常规金属箔片或复合集流体(可以将金属材料设置在高分子基材上形成复合集流体)。作为示例，正极集流体可以采用铝箔。
所述正极活性材料的具体种类不做限制，可以采用本领域已知的能够用于二次电池正极的活性材料，本领域技术人员可以根据实际需求进行选择。
作为示例，所述正极活性材料可以包括，但不限于，锂过渡金属氧化物，橄榄石结构的含锂磷酸盐及其各自的改性化合物中的一种或几种。锂过渡金属氧化物的示例可包括但不限于锂钴氧化物、锂镍氧化物、锂锰氧化物、锂镍钴氧化物、锂锰钴氧化物、锂镍锰氧化物、锂镍钴锰氧化物、锂镍钴铝氧化物及其改性化合物中的一种或几种。橄榄石结构的含锂磷酸盐的示例可包括但不限于磷酸铁锂、磷酸铁锂与碳的复合材料、磷酸锰锂、磷酸锰锂与碳的复合材料、磷酸锰铁锂、磷酸锰铁锂与碳的复合材料及其改性化合物中的一种或几种。这些材料均可以通过商业途径获得。
在一些实施方式中，上述各材料的改性化合物可以是对材料进行掺杂改性和/或表面包覆改性。
所述正极膜层通常还可选地包括粘结剂、导电剂和其他可选助剂。
作为示例，导电剂可以为超导碳、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、SuperP(SP)、石墨烯及碳纳米纤维中一种或几种。
作为示例，粘结剂可以为丁苯橡胶(SBR)、水性丙烯酸树脂(water-based acrylic resin)、聚偏二氟乙烯(PVDF)、聚四氟乙烯(PTFE)、乙烯-醋酸乙烯酯共聚物(EVA)、聚丙烯酸(PAA)、羧甲基纤维素(CMC)、聚乙烯醇(PVA)及聚乙烯醇缩丁醛(PVB)中的一种或几种。
[隔离膜]
在一些实施方式中，二次电池中还包括隔离膜。本申请对隔离 膜的种类没有特别的限制，可以选用任意公知的具有良好的化学稳定性和机械稳定性的多孔结构隔离膜。
在一些实施方式中，隔离膜的材质可选自玻璃纤维、无纺布、聚乙烯、聚丙烯及聚偏二氟乙烯中的至少一种。隔离膜可以是单层薄膜，也可以是多层复合薄膜，没有特别限制。在隔离膜为多层复合薄膜时，各层的材料可以相同或不同，没有特别限制。
[电解液]
二次电池可以包括电解液，电解液在正极和负极之间起到传导离子的作用。所述电解液可以包括电解质盐和溶剂。
作为示例，电解质盐可选自六氟磷酸锂(LiPF6)、四氟硼酸锂(LiBF4)、高氯酸锂(LiClO4)、六氟砷酸锂(LiAsF6)、双氟磺酰亚胺锂(LiFSI)、双三氟甲磺酰亚胺锂(LiTFSI)、三氟甲磺酸锂(LiTFS)、二氟草酸硼酸锂(LiDFOB)、二草酸硼酸锂(LiBOB)、二氟磷酸锂(LiPO2F2)、二氟二草酸磷酸锂(LiDFOP)及四氟草酸磷酸锂(LiTFOP)中的一种或几种。
作为示例，所述溶剂可选自碳酸亚乙酯(EC)、碳酸亚丙酯(PC)、碳酸甲乙酯(EMC)、碳酸二乙酯(DEC)、碳酸二甲酯(DMC)、碳酸二丙酯(DPC)、碳酸甲丙酯(MPC)、碳酸乙丙酯(EPC)、碳酸亚丁酯(BC)、氟代碳酸亚乙酯(FEC)、甲酸甲酯(MF)、乙酸甲酯(MA)、乙酸乙酯(EA)、乙酸丙酯(PA)、丙酸甲酯(MP)、丙酸乙酯(EP)、丙酸丙酯(PP)、丁酸甲酯(MB)、丁酸乙酯(EB)、1,4-丁内酯(GBL)、环丁砜(SF)、二甲砜(MSM)、 甲乙砜(EMS)及二乙砜(ESE)中的一种或几种。
在一些实施方式中，电解液中还包括添加剂。例如添加剂可以包括负极成膜添加剂，也可以包括正极成膜添加剂，还可以包括能够改善电池某些性能的添加剂，例如改善电池过充性能的添加剂、改善电池高温性能的添加剂、改善电池低温性能的添加剂等。
在一些实施方式中，本申请的二次电池为锂离子二次电池。
可以按照本领域常规方法制备二次电池，例如将正极极片、隔离膜、负极极片按顺序卷绕(或叠片)，使隔离膜处于正极极片与负极极片之间起到隔离的作用，得到电芯，将电芯置于外包装中，注入电解液并封口，得到二次电池。
本申请实施例对二次电池的形状没有特别的限制，其可以是圆柱形、方形或其他任意的形状。如图3是作为一个示例的方形结构的二次电池5。
在一些实施例中，二次电池可包括外包装。该外包装用于封装正极极片、负极极片和电解液。
在一些实施例中，参照图4，外包装可包括壳体51和盖板53。其中，壳体51可包括底板和连接于底板上的侧板，底板和侧板围合形成容纳腔。壳体51具有与容纳腔连通的开口，盖板53能够盖设于所述开口，以封闭所述容纳腔。
正极极片、负极极片和隔离膜可经卷绕工艺或叠片工艺形成电极组件52。电极组件52封装于所述容纳腔。电解液浸润于电极组件52中。二次电池5所含电极组件52的数量可以为一个或多个，可根 据需求来调节。
在一些实施例中，二次电池的外包装可以是硬壳，例如硬塑料壳、铝壳、钢壳等。二次电池的外包装也可以是软包，例如袋式软包。软包的材质可以是塑料，如可包括聚丙烯(PP)、聚对苯二甲酸丁二醇酯(PBT)、聚丁二酸丁二醇酯(PBS)等中的一种或几种。
在一些实施例中，二次电池可以组装成电池模块，电池模块所含二次电池的数量可以为多个，具体数量可根据电池模块的应用和容量来调节。
图5是作为一个示例的电池模块4。在电池模块4中，多个二次电池5可以是沿电池模块4的长度方向依次排列设置。当然，也可以按照其他任意的方式进行排布。进一步可以通过紧固件将该多个二次电池5进行固定。
可选地，电池模块4还可以包括具有容纳空间的外壳，多个二次电池5容纳于该容纳空间。
在一些实施例中，上述电池模块还可以组装成电池包，电池包所含电池模块的数量可以根据电池包的应用和容量进行调节。
图6和图7是作为一个示例的电池包1。在电池包1中可以包括电池箱和设置于电池箱中的多个电池模块4。电池箱包括上箱体2和下箱体3，上箱体2能够盖设于下箱体3，并形成用于容纳电池模块4的封闭空间。多个电池模块4可以按照任意的方式排布于电池箱中。
[用电装置]
本申请还提供一种用电装置，所述用电装置包括所述的二次电池、电池模块、或电池包中的至少一种。所述二次电池、电池模块或电池包可以用作所述装置的电源，也可以作为所述装置的能量存储单元。所述装置可以但不限于是移动设备(例如手机、笔记本电脑等)、电动车辆(例如纯电动车、混合动力电动车、插电式混合动力电动车、电动自行车、电动踏板车、电动高尔夫球车、电动卡车等)、电气列车、船舶及卫星、储能系统等。
所述装置可以根据其使用需求来选择二次电池、电池模块或电池包。
图8是作为一个示例的装置。该装置为纯电动车、混合动力电动车、或插电式混合动力电动车等。为了满足该装置对二次电池的高功率和高能量密度的需求，可以采用电池包或电池模块。
作为另一个示例的装置可以是手机、平板电脑、笔记本电脑等。该装置通常要求轻薄化，可以采用二次电池作为电源。
以下结合实施例进一步说明本申请的有益效果。
实施例
为了使本申请所解决的技术问题、技术方案及有益效果更加清楚，以下将结合实施例和附图进行进一步详细说明。显然，所描述的实施例仅仅是本申请一部分实施例，而不是全部的实施例。以下对至少一个示例性实施例的描述实际上仅仅是说明性的，决不作为 对本申请及其应用的任何限制。基于本申请中的实施例，本领域普通技术人员在没有付出创造性劳动前提下所获得的所有其他实施例都属于本申请保护的范围。
本申请的实施例中所用的材料均可以通过商购获得。
制备硅碳复合材料
实施例1
(1)改性碳纳米管的制备
准备碳纳米管原料，采用单壁碳纳米管，其管径为2nm，长度为35μm；
采用醋酸对碳纳米管进行酸洗，从而在碳纳米管上接枝羧基官能团，得到改性碳纳米管；
(2)碳纳米管/多孔碳复合基体的制备
将所制备的改性碳纳米管、碳酸氢铵催化剂和酚醛树脂前驱体溶液按质量比2％:5％:93％(表1中表示为：原料质量比)混合，在60℃下搅拌1h后，得到混合溶液A，其中，改性碳纳米管上的羧基官能团能够与酚醛树脂前驱体发生化学反应，使改性碳纳米管与酚醛树脂前驱体连接；
将混合溶液A放入80℃烘箱中预固化10h，将预固化后材料破碎得到粉体B，通过控制破碎强度：气流磨：气流流速1m 3/min，分级轮频率45HZ，引风机频率40HZ，粉碎气压力0.8MPa，喂料速度1kg/h，控制粉体B的体积分布粒径Dv50为7μm；
将粉体B置于烘箱中，通氮气保护，在160℃下全固化15h，得 到粉体C；
将粉体C置于高温炉中，通氮气保护，在1100℃下炭化4h，形成粉体D，即碳纳米管/多孔碳复合基体。
(3)沉积纳米硅基颗粒
粉体D通过化学气相沉积法进行硅沉积，沉积气体是甲硅烷和H 2的混合气体，其中甲硅烷的体积比为20％，混合气体的通入流量为400mL/min，沉积温度为500℃，沉积时间为10h。所沉积的纳米硅基颗粒的体积分布粒径Dv50为10nm。该步骤完成后，得到硅碳复合材料。
(4)包覆层的制备
在硅碳复合材料上采用化学气相沉积法形成碳包覆层，其中化学气相沉积的沉积气体是C 2H 2和N 2的混合气体，其中C 2H 2的体积比为20％，通入的气流量为300mL/min，沉积温度为800℃，沉积时间为0.5h。该步骤完成后，得到表面包覆有碳包覆层的硅碳复合材料。
实施例2-18
按照实施例1描述的方法进行实施例2-18，不同之处在于，下表1中所列参数与实施例1不同。
对比例1
对比例1与实施例1描述方案基本相同，不同之处在于在碳基体合成过程中不添加碳纳米管，直接采用酚醛树脂前驱体进行反应，预固化，破碎，全固化，炭化，沉积纳米硅基颗粒得到对比例1的 硅碳复合材料。
对比例2
将纳米硅粉(体积分布粒径Dv50为50nm)和改性碳纳米管加入到酚醛树脂前驱体中，进行聚合反应，然后进预固化，破碎，全固化，炭化得到对比例2的硅碳复合材料，相关过程工艺条件与实施例1相同，不同之处在于采用纳米硅粉，而非沉积纳米硅基颗粒。
对比例3
将对比例1中所得的硅碳复合材料、碳纳米管(管径为2nm，长度为25μm)、少量酚醛树脂前驱体溶液按92.05％:1.95％:6％混合，进行预固化，破碎，全固化，炭化，过程工艺与实施例1相同，即可得到表面含CNT包覆的硅碳复合材料，即对比例3的硅碳复合材料。对比例3是在对比例1基础上，再进行改性碳纳米管包覆，得到硅碳复合材料。
表1
Figure PCTCN2022115268-appb-000001
Figure PCTCN2022115268-appb-000002
利用以上实施例和对比例制备的硅碳复合材料，按照下文通用的制备方法制备二次电池。
制备二次电池
负极极片制备：
将上述各实施例和对比例制备的硅碳复合材料、人造石墨、粘结剂丁苯橡胶(SBR)、粘结剂聚丙烯酸(PAA)、分散剂(CMC-Na)以及导电炭黑(Super-P，SP)、碳纳米管(CNT)按10％：85％：2％：1％：1％：0.7％：0.3％的重量比在适量的去离子水中充分搅拌混合，制备成负极浆料；通过涂布设备，将负极浆料涂敷在集流体铜箔上，之后经过烘干、冷压、分切，得到负极极片。
正极极片的制备：将正极活性材料LiNi 0.8Co 0.1Mn 0.1O 2(NCM811)、粘结剂聚偏氟乙烯(PVDF)、导电剂乙炔黑按照质量比为97％:1.5％:1.5％溶于溶剂N-甲基吡咯烷酮(NMP)中，充分搅拌混合均匀后制备成正极浆料；将正极浆料均匀涂覆在正极集流体铝箔上，之后经过烘干、冷压、分切，得到正极极片。
电解液制备：将碳酸亚乙酯(EC)、碳酸甲乙酯(EMC)、碳酸二乙酯(DEC)按体积比1:1:1混合，然后将LiPF 6均匀溶解在上述溶液中，得到电解液。该电解液中，LiPF 6的浓度为1mol/L。
二次电池的制备：将上述正极极片、隔离膜、负极极片按顺序堆叠并卷绕，得到电极组件；将电极组件放入外包装中，加入上述制备的电解液，经封装、静置、化成、老化等工序后，得到二次电池。
多孔碳/碳纳米管复合基体(即粉体D)表征测试
1.碳纳米管/多孔碳复合基体内部微孔、介孔、大孔的孔体积测试：
孔体积评估方法可参考GB/T 19587-2017和GB/T 21650.2-2008，采用TriStarⅡ3020型孔径分布仪测试，通过在恒定温度下，吸附气在一系列逐步升高的压力下吸附在待测材料上，通过各级孔径的体积与对应的分压下的曲线图，可以表征多孔碳/碳纳米管复合基体材料的孔径及孔体积分布；进一步计算可以得到平均孔径。测试结果如下表2所示。
2.碳纳米管在碳纳米管/多孔碳复合基体中的质量占比测试：
碳纳米管/多孔碳复合基体中碳纳米管的含量可以按照如下操作：将碳纳米管/多孔碳复合基体粉体置于离子抛光仪(例如IB-19500CP型)中，在真空条件下，离子源将氩气电离产生氩离子，经过加速、聚焦后，高速氩离子将样品表面的原子或分子撞击出去，实现离子抛光，从而可以实现截面检测。然后将得到的截面置于扫描电子显微镜(例如ZEISS Sigma 300)中测试，选取30颗碳纳米管/多孔碳复合基体颗粒对其中的碳纳米管在颗粒中碳材料(除去截面孔面积)的面积占比进行测量，因碳纳米管真密度与多孔碳材料真密度相当，可以按面积占比评估碳纳米管在复合基体中的质量占比，取其平均值可等效计为碳纳米管/多孔碳复合基体中碳纳米管的含量。
表2
Figure PCTCN2022115268-appb-000003
硅碳复合材料表征测试
1.材料的体积分布粒径Dv50测试
参照标准GB/T 19077.1-2016，使用激光粒度分析仪(例如Malvern Master Size 3000)测定即可得到Dv50，其中Dv50物理定义为材料累计体积分布百分数达到50％时所对应的粒径。
2.材料被压制后体积分布粒径Dv50的测试
在一定压制条件下(例如本申请可以为：在300MPa压力下保压30s并反复压制50次)对材料进行压制后，按照上述方法测试被压制后材料的体积分布粒径Dv50。
3.硅碳复合材料中碳纳米管的长度L测试
碳纳米管的长度L可通过截面SEM测试，例如，可以按照如下操作：将硅碳复合材料粉体置于离子抛光仪(例如IB-19500CP型)中，在真空条件下，离子源将氩气电离产生氩离子，经过加速、聚焦后，高速氩离子将样品表面的原子或分子撞击出去，实现离子抛光，从而可以实现截面检测。然后将得到的截面置于扫描电子显微镜(例如ZEISS Sigma 300)中测试，选取30根碳纳米管进行长度测量，取其平均值计为碳纳米管长度L。测试结果如下表3所示。
4.硅碳复合材料中碳纳米管的含量测试
硅碳复合材料中碳纳米管的含量可以按照如下操作：将硅碳复合材料粉体置于离子抛光仪(例如IB-19500CP型)中，在真空条件下，离子源将氩气电离产生氩离子，经过加速、聚焦后，高速氩离子将样品表面的原子或分子撞击出去，实现离子抛光，从而可以实现截面检测。然后将得到的截面置于扫描电子显微镜(例如ZEISS Sigma 300)中测试，选取30颗硅碳复合材料颗粒对其中的碳纳米 管在颗粒中的面积占比进行测量，因硅与碳的真密度接近，可将碳纳米管在硅碳复合材料颗粒中的面积占比近似为硅碳复合材料中碳纳米管的含量，取其平均值计为硅碳复合材料中碳纳米管的含量。
5.硅碳复合材料中元素质量比Si:C:O的测试
硅碳复合材料中氧含量基于GB/T 17359-2012中“微束分析能谱法定量分析”，采用截面EDS能谱进行评估，具体操作为：将待测粉体置于离子抛光仪(例如IB-19500CP型)中，在真空条件下，离子源将氩气电离产生氩离子，经过加速、聚焦后，高速氩离子将样品表面的原子或分子撞击出去，实现离子抛光，从而可以实现截面检测。将得到的粉体截面置于能谱分析仪(例如OXFORD型)中，测试材料截面各点位氧含量，测试10个点取平均值即可得到材料氧含量。
硅碳复合材料中硅含量参照美国环境保护署标准EPA6010D-2018，采用电感耦合等离子体发射光谱仪(ICP)进行评估，具体操作为：将待测粉体置于微波消解仪(例如CEM-Mars6型)中进行消解，消解后溶液通入ICP测试仪(例如ICAP7400型)中，通过比对标准液中硅浓度，计算得到材料中硅含量。
硅碳复合材料中碳含量采用碳硫分析仪(例如德凯HCS-140红外碳硫分析仪)，参照GB/T 20123-2006/ISO 15350:200进行测试，原理为：样品在富氧条件下由高频炉高温加热燃烧，使碳氧化成二氧化碳，该气体进入吸收池，对相应的红外辐射进行吸收，再由探测器转化为对应的信号，通过计算得到材料中碳含量。测试结果如 下表3所示。
6.材料的孔隙率测试
通过真密度仪(例如AccuPycⅡ1340型)测试得到材料的真密度。具体操作为，称取一定质量的样品，置于真密度测试仪中，密闭测试系统，按程序通入氦气。通过检测样品室和膨胀室中的气体压力，再根据波尔定律(PV＝nRT)可计算真实体积Vr，则真实密度ρr＝m/Vr。材料表观密度可通过将一定质量粉体装入内径为10mm的圆柱模具中，施加200MPa的压力得到对应粉体的表观体积V0，则材料的表观密度为ρ0＝m/V0。
材料孔隙率P＝1-ρ0/ρr×100％。。
测试结果如下表3所示。
7.硅碳复合材料的比表面积SSA测试
硅碳复合材料的比表面积SSA参照GB/T 19587-2017《气体吸附BET法测试固态物质比表面积》，采用比表面积测试仪(例如TriStarⅡ3020型)测试，在恒温低温下，测定不同相对压力时的气体在固体表面的吸附量后，基于布朗诺尔-埃特-泰勒(BET)的多层吸附理论，求得试样单分子层吸附量，从而计算出固体的比表面积。测试结果如下表3所示。
8.硅碳复合材料中纳米硅基颗粒的平均粒径的测试
硅碳复合材料中纳米硅基颗粒的平均粒径可通过透射电镜(例如赛默飞F200i S/TEM)(TEM测试)测试100颗纳米硅基颗粒的粒径，通过测量取均值得到平均粒径。对于不规则形状的颗粒，其 粒径以最大粒径处的粒径为准。测试结果如下表3所示。
9.硅碳复合材料在4MPa压力下的电阻率测试
采用电阻率测试仪(例如苏州晶格电子ST2722)，取1g粉末样品，将样品置于测试仪电极间，用电子压力机恒压至不同压强，维持15-25s，读取样品高度h(cm)，两端电压U，电流I，电阻R(KΩ)，粉压片后的面积S＝1cm 2，根据公式δ＝S*R*1000/h计算得到粉末电阻导率，单位为Ω·cm。测试结果如下表3所示。
表3
Figure PCTCN2022115268-appb-000004
Figure PCTCN2022115268-appb-000005
Figure PCTCN2022115268-appb-000006
Figure PCTCN2022115268-appb-000007
二次电池的电性能表征
45℃循环性能测试：
将制作好的二次电池在45℃的恒温环境下，以1C倍率恒流充电至电压为4.25V，再在4.25V电压下恒压充电至电流小于等于0.05mA，之后静置5min，然后以1C倍率恒流放电至电压为2.5V，静置5min，此为一个循环充放电过程，此次的放电容量记为二次电池第1次循环的放电容量。将二次电池按照上述方法进行300次循环充放电测试，记录第300次循环的放电容量。
二次电池45℃循环300次后的容量保持率CR45℃(％)＝第300次循环的放电容量/第1次循环的放电容量×100％。测试结果如下表4所示。
二次电池在45℃下的极片循环膨胀性能测试：
将二次电池的负极极片完成冷压工序时的极片厚度记为h0，按上述二次电池在45℃下的循环性能测试方法，将二次电池循环300cls，以1C倍率恒流充电至电压为4.25V，再在4.25V电压下恒压充电至电流小于等于0.05mA，之后静置5min。在干燥房中拆解循环后的电芯，将300cls循环后的负极极片厚度记为h300，二次电池在45℃下的极片300cls循环膨胀率Δh300。
Δh300(％)＝(h300-h0)/h0*100％。测试结果如下表4所示。
倍率性能测试方法：
25℃下，将制作好的二次电池以0.33C(即3h内完全放掉理论容量的电流值)恒流充电至充电截止电压4.25V，之后恒压充电至电 流为0.05C，静置5min，再以0.33C恒流放电至放电截止电压2.5V，记录其实际容量为C0。
然后将电池以0.33C恒流充电至充电截止电压4.25V，之后恒压充电至电流为0.05C，静置5min，再以3C恒流放电至放电截止电压2.5V，记录其实际容量为C3。
二次电池的倍率性能可表征为DR＝C3/C0×100％。DR值越高，说明材料的倍率性能越好。测试结果如下表4所示。
测试结果如下表4所示。
表4
Figure PCTCN2022115268-appb-000008
Figure PCTCN2022115268-appb-000009
从表4相关数据可以看出，实施例1～18的硅碳复合材料在45℃循环300圈后的容量保持率为93.4％～97.3％，循环膨胀率Δh300为33.8％～37.7％，倍率性能DR为80.2％～84.7％，二次电池具有较好的循环稳定性及较小的循环膨胀，且动力学性能较好。对比例1的硅碳复合材料中不含有CNT，45℃循环300圈后的容量保持率为88.3％，循环膨胀率Δh300为42.7％，倍率性能DR为75.8％。对比例2的硅碳复合材料中采用50nm纳米硅粉，为当前较优水平纳米硅粉，非沉积纳米硅基颗粒，45℃循环300圈后的容量保持率为82.5％，循环膨胀率Δh300为47.2％，倍率性能DR为77.4％。对比例3的硅碳复合材料在对比例1硅碳材料基材上包覆CNT，45℃循环300圈后的容量保持率为89.5％，循环膨胀率Δh300为40.5％，倍率性能DR为78.1％。对比例1-3的循环性能、循环膨胀及动力学性能均不及实施例1～18，可见通过将多孔碳与碳纳米管通过连接单元相互连接的碳纳米管/多孔碳复合基体中沉积纳米硅基材料，其二次电池能够兼具较好的循环性能及较低的循环膨胀，且倍率性能有优势。
以上所述，仅为本发明较佳的具体实施方式，但本发明的保护 范围并不局限于此，任何熟悉本技术领域的技术人员在本发明揭露的技术范围内，可轻易想到的变化或替换，都应涵盖在本发明的保护范围之内。因此，本发明的保护范围应以所述权利要求的保护范围为准。

Claims (29)

  1. 一种硅碳复合材料，所述硅碳复合材料包括碳纳米管/多孔碳复合基体和硅基材料，所述碳纳米管/多孔碳复合基体中的多孔碳与碳纳米管通过连接单元相互连接。
  2. 根据权利要求1所述的硅碳复合材料，其中，所述连接单元包括碳碳键、苯环、酯基、羰基中的至少一种。
  3. 根据权利要求1或2所述的硅碳复合材料，其中，所述硅基材料中至少一部分分布在所述碳纳米管/多孔碳复合基体的孔中。
  4. 根据权利要求1-3任一项所述的硅碳复合材料，其中，所述碳纳米管中至少一部分的一端伸出所述硅碳复合材料表面。
  5. 根据权利要求1-4任一项所述的硅碳复合材料，其中，所述碳纳米管的管径为0.5-20nm；可选地，所述碳纳米管的管径为0.7-10nm。
  6. 根据权利要求1-5任一项所述的硅碳复合材料，其中，所述碳纳米管的长度记为L，所述硅碳复合材料的体积分布粒径Dv50记为D0，则所述硅碳复合材料满足：L≥3D0；可选地，所述硅碳复合材料满足：3D0≤L≤7D0。
  7. 根据权利要求1-6任一项所述的硅碳复合材料，其中，所述碳纳米管的长径比大于等于900，可选为2500-25000。
  8. 根据权利要求1-7任一项所述的硅碳复合材料，其中，所述硅碳复合材料中所述碳纳米管的含量≤8％；可选为0.2％-5.0％。
  9. 根据权利要求1-8任一项所述的硅碳复合材料，其中，所述碳纳米管/多孔碳复合基体符合下述(1)-(4)中的至少一个条件：
    (1)所述碳纳米管/多孔碳复合基体内部包括介孔，可选地，所述介孔的孔体积≥0.1cm 3/g，优选为0.2-2.5cm 3/g；
    (2)所述碳纳米管/多孔碳复合基体内部包括微孔，可选地，所述微孔的孔体积≤0.3cm 3/g，优选为0.05-0.2cm 3/g；
    (3)所述碳纳米管/多孔碳复合基体内部包括大孔，可选地，所述大孔的孔体积≤0.5cm 3/g，优选为0.05-0.4cm 3/g；
    (4)所述碳纳米管/多孔碳复合基体内部包括介孔和微孔，可选地，所述介孔的孔体积与所述微孔的孔体积之比≥2，优选为3-15。
  10. 根据权利要求1-9任一项所述的硅碳复合材料，其中，所述硅基材料为纳米硅基颗粒；可选地，所述纳米硅基颗粒的平均粒径≤50nm，更可选为3-20nm。
  11. 根据权利要求1-10任一项所述的硅碳复合材料，其中，所述硅基材料包括单质硅、硅氧化物(如氧化亚硅)、硅碳复合物、硅氮复合物、硅合金和预锂化硅氧化合物中的至少一种。
  12. 根据权利要求1-11任一项所述的硅碳复合材料，其中，所述硅基材料包括非晶态硅；可选地，所述硅基材料包括非晶态硅与晶态硅的混合物。
  13. 根据权利要求1-12任一项所述的硅碳复合材料，其中，所述碳纳米管/多孔碳复合基体由树脂前驱体和接枝有官能团和/或聚合物的碳纳米管经炭化形成，所述官能团和/或所述聚合物均能够与所述树脂前驱体发生化学反应，使所述碳纳米管与所述树脂前驱体连接，并在炭化后形成所述连接单元。
  14. 根据权利要求1-13任一项所述的硅碳复合材料，其中，红外光谱测试所述硅碳复合材料或所述碳纳米管/多孔碳复合基体，所述硅碳复合材料或所述碳纳米管/多孔碳复合基体含有以下连接单元中的至少一种：酯羰基，其吸收峰为1750～1735cm -1；酮羰基，其吸收峰为1725～1705cm -1；苯环基，其吸收峰为1620～1450cm -1；以及碳碳键，其吸收峰为2400～1950cm -1；和/或，
    透射电镜测试所述硅碳复合材料或所述碳纳米管/多孔碳复合基体，所述硅碳复合材料或所述碳纳米管/多孔碳复合基体中所述碳纳米管周边的碳原子与所述碳纳米管最外层碳原子间距≤0.35nm的区域占比≥50％。
  15. 根据权利要求1-14任一项所述的硅碳复合材料，其中，定义所述硅碳复合材料的抗压指数P＝D0/(D0-D1)，则P≥3，其中，D0为所述硅碳复合材料的体积分布粒径Dv50，D1为所述硅碳复合材料被压制后测试的体积分布粒径Dv50，所述压制的条件为在300MPa压力下保压30s并反复压制50次。
  16. 根据权利要求1-15任一项所述的硅碳复合材料，其中，所述硅碳复合材料在4MPa压力下的电阻率ρ≤0.4Ω·cm，可选地，0.05Ω·cm≤ρ≤0.3Ω·cm。
  17. 根据权利要求1-16任一项所述的硅碳复合材料，其中，所述硅碳复合材料满足下述(Ⅰ)-(Ⅴ)中至少一个条件：
    (Ⅰ)所述硅碳复合材料的体积分布粒径Dv50≤8μm，可选为3-7μm；
    (Ⅱ)所述硅碳复合材料的孔隙率≤20％，可选为5％-15％；
    (Ⅲ)所述硅碳复合材料的比表面积SSA≤5.0m 2/g，可选为0.8-4.0m 2/g；
    (Ⅳ)所述硅碳复合材料内部包括介孔，可选地，所述介孔的孔体积≤0.3cm 3/g，优选为0.05-0.1cm 3/g；
    (Ⅴ)所述硅碳复合材料中元素质量比为Si:C:O＝(20-55):(40-70):(3-10)。
  18. 根据权利要求1-17任一项所述的硅碳复合材料，其中，所述硅碳复合材料的表面还设有包覆层；可选地，所述包覆层包括碳包覆层、聚合物包覆层、无机盐包覆层、金属氧化物包覆层中的至少一种。
  19. 一种硅碳复合材料的制备方法，其中，包括以下步骤：
    在碳纳米管上接枝官能团和/或聚合物，得到改性碳纳米管；
    将所述改性碳纳米管与树脂前驱体溶液混合，得到混合溶液，其中，所述改性碳纳米管上的所述官能团和所述聚合物均能够与所述树脂前驱体发生化学反应，使所述改性碳纳米管与所述树脂前驱体连接；
    对所述混合溶液进行固化处理，得到复合基体前驱体；
    对所述复合基体前驱体进行炭化处理，得到多孔碳/碳纳米管复合基体；以及
    在所述多孔碳/碳纳米管复合基体上沉积硅基材料，得到硅碳复合材料。
  20. 根据权利要求19所述的制备方法，其中，按质量百分比计，所述混合溶液还包括0.5％～30％的催化剂；可选地，所述催化剂包括六次甲基四胺、碳酸氢铵、碳酸铵、氨水、锌盐、铜盐和铬盐中一种或多种。
  21. 根据权利要求19或20所述的制备方法，其中，所述混合包括：在20～60℃下，搅拌1～10h，所述改性碳纳米管与所述树脂前驱体发生酯化反应、加成反应、加聚反应、缩聚反应中的一种或多种。
  22. 根据权利要求19-21任一项所述的制备方法，其中，所述官能团包括羧基、羟基、氨基、苯基、羰基中的一种或多种；和/或，
    所述聚合物包括聚酰胺、聚甲基丙烯酸甲酯、聚甲基丙烯酸羟乙酯中的一种或多种。
  23. 根据权利要求19-22任一项所述的制备方法，其中，
    所述固化处理包括：预固化、全固化；
    可选地，所述固化处理包括：预固化、粉碎、全固化。
  24. 根据权利要求19-23任一项所述的制备方法，其中，
    所述预固化的温度为70-140℃，可选为80-130℃；和/或，
    所述预固化的时间为3-12h，可选为5-10h。
  25. 根据权利要求19-24任一项所述的制备方法，其中，
    所述全固化的温度为150-220℃，可选为160-200；和/或，
    所述全固化的时间为8-20h，可选为10-15h。
  26. 根据权利要求19-25任一项所述的制备方法，其中，
    所述炭化处理的温度为900-3000℃，可选为1000-2000；和/或，
    所述炭化处理的时间为2-6h，可选为3-5h。
  27. 根据权利要求19-26任一项所述的制备方法，其中，所述沉积通过化学气相沉积法进行；可选地，沉积气体包括H 2、N 2和Ar中的至少一种与硅烷气体的混合气体。
  28. 一种二次电池，包括负极极片，所述负极极片包括权利要求1-18中任一项所述的硅碳复合材料或根据权利要求19-27中任一项所述的制备方法获得的硅碳复合材料。
  29. 一种用电装置，其中，包括权利要求28所述的二次电池。
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