WO2025001491A1 - 硅碳负极材料及其制备方法和应用 - Google Patents

硅碳负极材料及其制备方法和应用 Download PDF

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WO2025001491A1
WO2025001491A1 PCT/CN2024/090910 CN2024090910W WO2025001491A1 WO 2025001491 A1 WO2025001491 A1 WO 2025001491A1 CN 2024090910 W CN2024090910 W CN 2024090910W WO 2025001491 A1 WO2025001491 A1 WO 2025001491A1
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negative electrode
silicon
carbon
electrode material
carbon negative
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French (fr)
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WO2025001491A9 (zh
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易政
邵文龙
苏义松
谢远森
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Ningde Amperex Technology Ltd
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Ningde Amperex Technology Ltd
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Priority to KR1020257043646A priority Critical patent/KR20260008199A/ko
Priority to EP24830139.2A priority patent/EP4738466A1/en
Publication of WO2025001491A1 publication Critical patent/WO2025001491A1/zh
Publication of WO2025001491A9 publication Critical patent/WO2025001491A9/zh
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H01M4/386—Silicon or alloys based on silicon
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/05—Preparation or purification of carbon not covered by groups C01B32/15, C01B32/20, C01B32/25, C01B32/30
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B33/00—Silicon; Compounds thereof
    • C01B33/02—Silicon
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/364—Composites as mixtures
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present application relates to the field of electrochemical energy storage, and in particular to a silicon-carbon negative electrode material and a preparation method thereof, a negative electrode sheet using the silicon-carbon negative electrode material, and an electrochemical device using the negative electrode sheet.
  • Lithium-ion batteries have the advantages of high volume and mass energy density, environmental friendliness, high operating voltage, small size, light weight, and long cycle life, and are widely used in the field of portable consumer electronics.
  • people With the rapid development of electric vehicles and mobile electronic devices in recent years, people have higher and higher demands on battery energy density, safety, cycle performance, etc., and look forward to the emergence of new lithium-ion batteries with comprehensive performance improvements; among them, energy density and cycle performance have become key technical issues that need to be solved urgently, and improving the active materials in the electrode is one of the research directions to solve the above problems.
  • graphite is the most widely used negative electrode material, which has the advantages of high efficiency and stable charge and discharge platform.
  • the performance of commercial graphite has been almost developed to the extreme, and its low capacity and safety hazards of lithium dendrites hinder its further application.
  • elemental silicon is considered to be the most promising lithium battery negative electrode material that can replace graphite due to its ultra-high theoretical specific capacity and suitable operating voltage.
  • low conductivity and huge volume expansion during alloying/de-alloying process seriously restrict the large-scale application of elemental silicon in lithium-ion batteries.
  • the present application provides a silicon-carbon negative electrode material capable of improving conductivity and reducing expansion.
  • the present application also provides a negative electrode sheet using the silicon-carbon negative electrode material and an electrochemical device using the negative electrode sheet.
  • the present application also provides a method for preparing the above-mentioned silicon-carbon negative electrode material.
  • the first aspect of the present application provides a silicon-carbon negative electrode material, comprising a core and a shell, wherein the core comprises a porous carbon skeleton and silicon dispersed in the pores of the porous carbon skeleton. Carbon nanotubes are wrapped and dispersed in the porous carbon skeleton, the silicon-carbon negative electrode material has a silicon content of 25wt% to 55wt%, and the shell comprises a carbon material.
  • the standard deviation of the silicon content variation along the direction from the center to the edge of the cross section does not exceed 200.
  • the silicon-carbon negative electrode material of the present application has good electrical conductivity and mechanical properties because of the carbon nanotubes therein. Therefore, the specific content of carbon nanotubes dispersed in the porous carbon skeleton can improve the electrical conductivity of the silicon-carbon negative electrode material on the one hand, and improve the mechanical properties of the silicon-carbon negative electrode material on the other hand, and restrain the expansion of the silicon-carbon negative electrode material, which is beneficial to improving the stability of the structure. According to the linear scanning electron microscope energy spectrum of the cross section of the carbon-silicon negative electrode material, the carbon nanotubes in the silicon-carbon negative electrode material have good electrical conductivity and mechanical properties. The silicon element is evenly distributed in the carbon negative electrode material, which is conducive to further improving the conductivity and mechanical properties of the silicon-carbon negative electrode material.
  • the improvement of the conductivity of the above silicon-carbon negative electrode material can improve the probability of lithium being captured inside the silicon-carbon negative electrode material, thereby improving the lithium removal capacity of the electrochemical device and improving the initial charge and discharge performance.
  • carbon nanotubes can also alleviate the volume expansion of silicon-carbon during the lithium insertion process, improve the expansion pulverization and structural stability of silicon-carbon during charging and discharging, thereby improving its cycle performance.
  • the electrical conductivity of the silicon-carbon negative electrode material is 9S/cm to 30S/cm.
  • the electrical conductivity within a specific range is conducive to ensuring the electrical conductivity of the silicon-carbon negative electrode material and further improving the cycle performance of the electrochemical device using the silicon-carbon negative electrode material.
  • the particle elastic modulus of the silicon-carbon negative electrode material is 4 GPa to 10 GPa.
  • the particle elastic modulus within a specific range is beneficial to improving the stability of the silicon-carbon negative electrode material structure, and is beneficial to further improving the expansion and cycle performance of the electrochemical device using the silicon-carbon negative electrode material.
  • the content of the carbon nanotubes is 0.2wt% to 7.0wt%.
  • the content of the carbon nanotubes within this range can further alleviate the volume expansion of silicon-carbon during the lithium insertion process, and can control the formation of pores formed when preparing the porous carbon skeleton, reduce the proportion of macropores, improve the deposition uniformity of silicon, further improve the cycle performance of the electrochemical device and reduce the cycle expansion rate of the electrochemical device.
  • the silicon-carbon negative electrode material satisfies at least one of the following conditions: (1) the X-ray diffraction spectrum of the silicon-carbon negative electrode material has a characteristic peak in the range of 20° to 30°, and the half-peak width of the characteristic peak is greater than 2°; (2) the Raman spectrum of the silicon-carbon negative electrode material has a characteristic peak in the range of 450cm -1 to 500cm -1 ; (3) the particle size Dv50 of the silicon-carbon negative electrode material is 3 ⁇ m to 20 ⁇ m, and the particle size Dv99 of the silicon-carbon negative electrode material is 3 ⁇ m to 20 ⁇ m.
  • the pores in the porous carbon skeleton are micropores, that is, 90% of the pores in the porous carbon skeleton have a pore size less than 2 nanometers, that is, it is conducive to making the size of the silicon embedded in the porous carbon skeleton in the silicon-carbon negative electrode material mostly less than 2 nanometers, which is conducive to further reducing the expansion of the silicon-carbon negative electrode material.
  • the size of the silicon in the silicon-carbon negative electrode material is small and amorphous, which is conducive to further reducing the expansion of the silicon-carbon negative electrode material.
  • the silicon-carbon negative electrode material in a specific particle size range is smoother in the subsequent stirring and coating process for preparing the negative electrode sheet, and is easy to match with graphite.
  • the pore volume of the pores with a pore size exceeding 2nm in the silicon-carbon negative electrode material is greater than the pore volume of the pores with a pore size not exceeding 2nm.
  • the pore volume of the pores with a pore size exceeding 2nm ranges from 0.04 to 0.20.
  • silicon is preferentially adsorbed and deposited in micropores.
  • the size of silicon in the silicon-carbon negative electrode material is mostly less than 2 nanometers, which is beneficial to further reduce the expansion of the silicon-carbon negative electrode material.
  • the second aspect of the present application provides a negative electrode sheet, comprising a current collector and a negative electrode active layer.
  • the negative electrode active layer comprises a negative electrode active material, and the negative electrode active material comprises the silicon-carbon negative electrode material as described above.
  • the negative electrode plate of the present application improves the conductivity of the silicon-carbon negative electrode material through the uniform distribution of carbon nanotubes and silicon elements, which can improve the probability of lithium being captured inside the silicon-carbon negative electrode material, thereby improving the lithium removal capacity of the electrochemical device and improving the initial charge and discharge performance.
  • the carbon nanotubes can also alleviate the volume expansion of silicon-carbon during the lithium insertion process, combined with the uniform distribution of silicon elements to improve the expansion and pulverization of silicon-carbon and the structural stability during charging and discharging, thereby improving its cycle performance.
  • the negative electrode active material further includes graphite, and in the negative electrode active material, the content of the silicon-carbon negative electrode material is 5wt% to 40wt%, and the content of the graphite is 95wt% to 60wt%.
  • the silicon-carbon negative electrode material with the above specific content can effectively reduce the effect of silicon expansion on the negative electrode plate while making full use of the characteristics of silicon such as ultra-high theoretical specific capacity and suitable operating voltage, which is beneficial to improving the first coulombic efficiency, energy density and cycle performance of the negative electrode plate.
  • the silicon-carbon negative electrode material is too high, the volume expansion of the negative electrode active layer will be obvious, and the cycle performance will deteriorate; if the silicon-carbon negative electrode material is too low, it will not be conducive to improving the first coulombic efficiency.
  • graphite has a certain degree of flexibility, its combination with the silicon-carbon negative electrode material can alleviate the volume expansion of the negative electrode active layer.
  • the negative electrode plate can also make full use of the advantages of both silicon-carbon negative electrode materials and graphite to achieve better electrochemical performance.
  • a third aspect of the present application provides an electrochemical device, comprising the negative electrode sheet as described above.
  • the electrochemical device of the present application improves the conductivity of the silicon-carbon negative electrode material by uniformly distributing carbon nanotubes and silicon elements in the negative electrode plate, which can improve the probability of lithium being captured inside the silicon-carbon negative electrode material, thereby improving the lithium removal capacity of the electrochemical device and enhancing the initial charge and discharge performance.
  • the carbon nanotubes can also alleviate the volume expansion of silicon-carbon during the lithium insertion process, and combined with the uniform distribution of silicon elements, improve the expansion pulverization and structural stability of silicon-carbon during charging and discharging, thereby improving its cycle performance.
  • the fifth aspect of the present application provides a method for preparing the silicon-carbon negative electrode material as described above, comprising: mixing a resin and carbon nanotubes to form a mixture and curing the mixture; carbonizing the cured mixture and activating it to obtain a porous carbon skeleton; and depositing silane on the porous carbon skeleton to form a core and then forming a shell through alkanes.
  • the preparation method of the above-mentioned silicon-carbon negative electrode material of the present application first mixes the resin and the carbon nanotubes to form a mixture, solidifies it, and then carbonizes it to form a porous skeleton, which is convenient for the dispersion of the carbon nanotubes in the porous skeleton, thereby facilitating the carbon nanotubes to bind the prepared silicon-carbon negative electrode material, thereby alleviating the volume expansion of the silicon-carbon negative electrode material to improve the expansion pulverization and structural stability of silicon-carbon during charging and discharging, and improving its cycle performance; at the same time, it is also beneficial to improve the overall conductivity of the silicon-carbon negative electrode material, thereby improving the probability of lithium being captured inside the silicon-carbon negative electrode material to improve the lithium removal capacity of the electrochemical device and Improve the initial charge and discharge performance.
  • the carbonization conditions are to raise the temperature to 700°C to 1100°C and keep it warm for 1 to 5 hours, and the activation is specifically to activate by carbon dioxide, water vapor, sodium hydroxide, potassium hydroxide or phosphoric acid after the carbonization temperature is lowered.
  • the step of "depositing silane on the porous carbon skeleton to form a core and then forming a shell through alkanes" is specifically as follows: slowly heating the porous carbon skeleton to 400°C to 600°C under an inert atmosphere and then keeping it warm, and then switching the atmosphere to a silane mixture for deposition for 1 to 20 hours, wherein the silane mixture contains 2% to 20% silane by mass and 80% to 98% inert gas by mass; at a temperature of 500°C to 1000°C, switching the atmosphere to an alkane mixture for 10 hours to form a shell, then switching the atmosphere to an inert atmosphere and cooling to room temperature, wherein the alkane mixture contains 5% to 100% alkanes by mass and 95% to 0% inert gas by mass.
  • the phrase "at least one of A and B" means only A; only B; or A and B.
  • the phrase "at least one of A, B and C” means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B and C.
  • the parameter values being greater than, less than, or not equal to the designed relationship need to exclude the reasonable errors of the measuring equipment.
  • An embodiment of the present application provides an electrochemical device, wherein the electrochemical device comprises a positive electrode sheet, a negative electrode sheet and an insulator.
  • the separator is disposed between the positive electrode sheet and the negative electrode sheet.
  • the positive electrode sheet, the separator and the negative electrode sheet can be alternately stacked in sequence to form a laminated electrode assembly, or the positive electrode sheet, the separator and the negative electrode sheet can be stacked in sequence and then wound to form a wound electrode assembly.
  • the electrochemical device further comprises a housing and an electrolyte, wherein the positive electrode sheet, the negative electrode sheet, the separator and the electrolyte are contained in the housing.
  • the housing may be a packaging bag obtained by packaging with a packaging film such as, but not limited to, an aluminum-plastic film, that is, the electrochemical device may be a soft-pack battery.
  • the housing may also be, but not limited to, a housing disclosed in the prior art such as a steel shell battery and an aluminum shell battery.
  • the positive electrode plate includes a positive current collector and a positive active layer disposed on the positive current collector.
  • the positive current collector may be aluminum foil or nickel foil, or may be any composite current collector disclosed in the prior art, such as but not limited to a current collector formed by combining the aforementioned conductive foil and a polymer substrate.
  • the positive active layer contains a positive active material, and the positive active material includes a compound that reversibly intercalates and deintercalates lithium ions (i.e., a lithiated intercalation compound).
  • the positive active material may include a lithium transition metal composite oxide.
  • the lithium transition metal composite oxide contains lithium and at least one element selected from cobalt, manganese and nickel.
  • the positive active material may include but is not limited to at least one of lithium cobalt oxide (LiCoO 2 ), lithium nickel manganese cobalt ternary material (NCM), lithium manganese oxide (LiMn 2 O 4 ), lithium nickel manganese oxide (LiNi 0.5 Mn 1.5 O 4 ) or lithium iron phosphate (LiFePO 4 ).
  • LiCoO 2 lithium cobalt oxide
  • NCM lithium nickel manganese cobalt ternary material
  • LiMn 2 O 4 lithium manganese oxide
  • LiNi 0.5 Mn 1.5 O 4 lithium iron phosphate
  • LiFePO 4 lithium iron phosphate
  • the positive electrode active layer further comprises a binder for bonding the positive electrode active material particles so as to form a film layer and also to improve the binding force between the positive electrode active layer and the positive electrode current collector.
  • the binder may include but is not limited to at least one of polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin or nylon.
  • the positive electrode active layer may also include a conductive material, including but not limited to a carbon-based material, a metal-based material, a conductive polymer, or any combination thereof.
  • the carbon-based material may include but is not limited to natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof.
  • the metal-based material may include but is not limited to metal powder or metal fiber, such as copper, nickel, aluminum, or silver.
  • the conductive polymer may be a polyphenylene derivative.
  • the negative electrode plate includes a negative electrode current collector and a negative electrode active layer disposed on the negative electrode current collector.
  • the negative electrode current collector may be at least one of copper foil, nickel foil, stainless steel foil, titanium foil or carbon-based current collector, or may be any composite current collector disclosed in the prior art, such as but not limited to a current collector formed by combining the aforementioned conductive foil and a polymer substrate.
  • the negative electrode active layer includes a negative electrode active material, and the negative electrode active material includes a silicon-carbon negative electrode material.
  • the silicon-carbon negative electrode material comprises a core body and a shell, wherein the core body comprises a porous carbon skeleton and a porous carbon skeleton dispersed in the porous carbon skeleton. Silicon in the pores of the skeleton. Carbon nanotubes are wrapped and dispersed in the porous carbon skeleton.
  • the content of silicon in the silicon-carbon negative electrode material is 25wt% to 55wt%
  • the shell includes carbon material.
  • the standard deviation of the content change of the silicon element along the direction from the center to the edge of the cross section does not exceed 200.
  • the cross section of the silicon-carbon negative electrode material particles is cut out by ion polishing as a test surface.
  • the cut silicon-carbon negative electrode material is transferred to a field emission scanning electron microscope and the test surface is scanned from the center to the outside to record the content distribution of each element. For example, 100 data points are taken at equal distances from the silicon element content data obtained by line scanning, and mathematical statistics standard deviation analysis is performed on the 100 data points taken to obtain the standard deviation of the silicon element content change.
  • the above-mentioned silicon-carbon negative electrode material has good electrical conductivity and mechanical properties because the carbon nanotubes therein have good electrical conductivity and mechanical properties. Therefore, the specific content of carbon nanotubes dispersed in the porous carbon skeleton can improve the electrical conductivity of the silicon-carbon negative electrode material on the one hand, and can also improve the mechanical properties of the silicon-carbon negative electrode material on the other hand, and restrain the expansion of the silicon-carbon negative electrode material, which is beneficial to improving the stability of the structure. According to the linear scanning electron microscope energy spectrum of the cross-section of the carbon-silicon negative electrode material, it can be seen that the silicon element is uniformly distributed in the silicon-carbon negative electrode material.
  • the dispersion of carbon nanotubes and the uniform distribution of silicon elements can improve the conductivity and strength of the silicon-carbon negative electrode material, reduce the capture of lithium in the silicon-carbon negative electrode material, alleviate the expansion of the silicon-carbon negative electrode material, and improve the first coulomb efficiency of the electrochemical device using the negative electrode plate, thereby improving the energy density and cycle performance of the electrochemical device.
  • the silicon content is 20% to 45%, which can further reduce the expansion of the silicon-carbon negative electrode material and improve the cycle performance of the electrochemical device.
  • the electrical conductivity of the silicon-carbon negative electrode material is 9S/cm to 30S/cm. In some embodiments, the electrical conductivity of the silicon-carbon negative electrode material is 11S/cm to 25S/cm. In some embodiments, the electrical conductivity of the silicon-carbon negative electrode material is 9S/cm, 11S/cm, 14S/cm, 20S/cm, 25S/cm, 30S/cm, or a value within the range formed by any two of the above values. When the electrical conductivity of the silicon-carbon negative electrode material is within the above range, the electrical conductivity of the silicon-carbon negative electrode material can be guaranteed, and the cycle performance of the electrochemical device can be further improved.
  • the particle elastic modulus of the silicon-carbon negative electrode material is 4 GPa to 10 GPa, which is beneficial to ensure the mechanical strength of the silicon-carbon negative electrode material to relieve internal stress, further reduce the expansion of the silicon-carbon negative electrode material and improve the cycle performance of the electrochemical device.
  • the content of the carbon nanotubes is 0.2wt% to 7.0wt%. In some embodiments, the content of the carbon nanotubes is 1.0wt% to 6.0wt%. In some embodiments, the content of the carbon nanotubes is 0.2wt%, 1.0wt%, 1.5wt%, 2.5wt%, 4.5wt%, 6.0wt%, 6.5wt%, 7.0wt% or a value within the range formed by any two of the above values.
  • the content of carbon nanotubes within the above range helps to further alleviate the volume expansion of silicon carbon during lithium insertion, and can control the formation of pores formed during the preparation of the porous carbon skeleton, reduce the proportion of macropores, improve the deposition uniformity of silicon, ensure the first efficiency of the electrochemical device (i.e., the first coulombic efficiency), and further Improve the cycle performance of electrochemical devices and reduce the cycle expansion rate of electrochemical devices.
  • the X-ray diffraction spectrum of the silicon-carbon negative electrode material has a characteristic peak in the range of 20° to 30°, and the half-peak width of the characteristic peak is greater than 2°, that is, the pores in the porous carbon skeleton are micropores, and the pore diameter of 90% of the pores in the porous carbon skeleton is less than 2 nanometers.
  • the pore volume of the pores with a pore size exceeding 2 nm in the silicon-carbon negative electrode material is greater than the pore volume of the pores with a pore size not exceeding 2 nm. Since the adsorption effect of micropores is better, silicon is preferentially adsorbed and deposited in micropores. Therefore, the size of silicon in the silicon-carbon negative electrode material is mostly less than 2 nanometers, which is conducive to further reducing the expansion of the silicon-carbon negative electrode material. In some embodiments, the pore volume of pores with a pore size exceeding 2 nm ranges from 0.04 to 0.20.
  • the Raman spectrum of the silicon-carbon negative electrode material has a characteristic peak in the range of 450 cm -1 to 500 cm -1 , that is, the silicon in the silicon-carbon negative electrode material is small in size and amorphous, which is beneficial to further reduce the expansion of the silicon-carbon negative electrode material.
  • the particle size Dv50 of the silicon-carbon negative electrode material can be 3 ⁇ m to 20 ⁇ m, and the particle size Dv99 of the silicon-carbon negative electrode material can be 3 ⁇ m to 20 ⁇ m, so that it can be smoother when mixed, stirred and coated with other materials (such as binders) to form a negative electrode active layer, and it is easy to mix and match other materials.
  • the negative electrode active material may further include graphite. Since graphite has a certain degree of flexibility, it can alleviate the volume expansion of the negative electrode active layer when combined with the silicon-carbon negative electrode material. At the same time, the graphite and the silicon-carbon negative electrode material are simultaneously used as active materials to reduce the overall expansion of the negative electrode active layer, and can also fully utilize the advantages of both the silicon-carbon negative electrode material and graphite to achieve better electrochemical performance.
  • the content of the silicon-carbon negative electrode material may be 5wt% to 40wt%. Further, the content of the graphite may be 95wt% to 60wt%.
  • the negative electrode active layer also contains a binder for binding the positive electrode active material particles to form a film layer and also to improve the binding force between the negative electrode active layer and the negative electrode current collector.
  • the binder may include but is not limited to polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylic (ester) styrene-butadiene rubber, epoxy resin or nylon, etc.
  • the negative electrode active layer may further include a conductive material, including but not limited to a carbon-based material, a metal-based material, a conductive polymer, or any combination thereof.
  • the carbon-based material may include but is not limited to natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof.
  • the metal-based material may include but is not limited to metal powder or metal fiber, such as copper, nickel, aluminum or silver.
  • the conductive polymer may be a polyphenylene derivative.
  • the isolation membrane includes a membrane layer with a porous structure, and its material includes but is not limited to at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide or aramid.
  • the isolation membrane can be a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene non-woven fabric, a polyethylene non-woven fabric or a polypropylene-polyethylene-polypropylene porous composite membrane.
  • the electrolyte may be in one or more of a gel state, a solid state, and a liquid state.
  • the liquid electrolyte includes a lithium salt and an organic solvent.
  • the lithium salt may be selected from, but is not limited to, one or more of lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium hexafluoroarsenate (LiAsF 6 ), lithium perchlorate (LiClO 4 ), lithium tetraphenylborate (LiB(C 6 H 5 ) 4 ), lithium methanesulfonate (LiCH 3 SO 3 ), lithium bisfluorosulfonyl imide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiCF 3 SO 3 ), lithium bis(trifluoromethylsulfonyl)imide
  • the lithium salt may be selected from LiPF 6
  • the organic solvent may be a carbonate compound, a carboxylate compound, an ether compound, a nitrile compound, other organic solvents or a combination thereof.
  • carbonate compounds include but are not limited to diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), ethyl methyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), Butylene carbonate (BC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbon
  • the electrochemical device is applied to an electronic device to power other electronic components in the electronic device. Since the silicon-carbon negative electrode material in the electrochemical device is conducive to improving the cycle performance and energy density, it is conducive to improving the service life of the electronic device.
  • the electronic device may include but is not limited to a laptop computer, a pen-input computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, an electric tool, a flashlight, a camera, a large household battery
  • the present application also provides a method for preparing a silicon-carbon negative electrode material, which comprises the following steps:
  • Step S1 mixing resin and carbon nanotubes to form a mixture and curing the mixture.
  • the method of forming the mixture includes but is not limited to ball milling.
  • An organic solvent may also be added during the mixing to facilitate The carbon nanotubes are dispersed.
  • the above-mentioned curing is to dry and shape the mixture, and the curing conditions commonly used in the prior art can be applied, which will not be described in detail here.
  • Step S2 carbonizing and activating the solidified mixture to obtain a porous carbon skeleton.
  • the solidified mixture is heated to 700° C. to 1100° C. in an inert atmosphere (for example, but not limited to a nitrogen atmosphere) for carbonization for 1 to 5 hours, and then activated to form a porous carbon skeleton after cooling to room temperature.
  • the activation can be performed by carbonizing the structure with carbon dioxide or water vapor, or by alkali etching or acid etching.
  • the alkali etching can usually be performed with sodium hydroxide or potassium hydroxide
  • the acid etching can usually be performed with phosphoric acid.
  • Step S3 performing silane deposition on the porous carbon skeleton to form a core body and then coating the core body with a shell formed by an alkane-based carbon coating layer.
  • the porous carbon skeleton is slowly heated to 400°C to 600°C in an inert atmosphere (such as but not limited to argon atmosphere), and then the atmosphere is switched to a silane mixed gas for deposition for 1 hour to 20 hours to form a nucleus.
  • the heating rate of the slow heating may be but not limited to 0.5°C/min to 5°C/min, and the silane mixed gas contains 2% to 20% by mass of silane and 80% to 98% of an inert gas (such as but not limited to argon).
  • the atmosphere is switched to an alkane mixture at a temperature of 500° C. to 1000° C. and maintained for 2 to 20 hours to form a shell of the carbon coating layer covering the core body, and then the atmosphere is switched to an inert atmosphere (such as but not limited to a nitrogen atmosphere) and cooled to room temperature to finally obtain the silicon-carbon negative electrode material.
  • the alkane mixture contains 5% to 100% by mass of an alkane (such as but not limited to acetylene) and 0% to 95% of an inert gas (such as but not limited to argon).
  • the cured mixture is transferred to a box furnace, and the temperature is raised to 900°C for carbonization for 2h in a nitrogen atmosphere, and then after cooling, it is transferred to a rotary kiln and activated in a carbon dioxide atmosphere for 9h to obtain a porous carbon skeleton.
  • the porous carbon skeleton continues to be heated to 500°C at a rate of 2°C/min in an argon atmosphere, the atmosphere is switched to a silane mixture (20% silane and 80% argon by mass), and deposited at 500°C for 10 hours to form a nucleus.
  • the atmosphere is then switched to an acetylene mixture (20% acetylene and 80% argon by mass) and continues to be deposited at 500°C for 10 hours, then switched to nitrogen, and then cooled to room temperature 25°C to obtain a silicon-carbon negative electrode material.
  • Preparation of positive electrode sheet The positive electrode active material lithium cobalt oxide (LiCoO 2 ), conductive carbon black Super P and polyvinylidene fluoride (PVDF) were fully stirred and mixed in a proper amount of N-methylpyrrolidone (NMP) solvent at a weight ratio of 97:1.4:1.6 to form a uniform positive electrode slurry, wherein the solid content of the positive electrode slurry was 72wt%.
  • NMP N-methylpyrrolidone
  • the slurry was coated on the positive electrode current collector aluminum foil, dried at 85°C, and then cold pressed, cut and slit, and dried under vacuum conditions at 85°C for 4 hours to obtain a positive electrode sheet.
  • isolation membrane A 7 ⁇ m thick polyethylene (PE) porous polymer film was used as the isolation membrane.
  • Preparation of lithium-ion battery The positive electrode sheet, the separator, and the negative electrode sheet are stacked and wound in sequence, and the tabs are welded and placed in an aluminum-plastic film packaging bag. Then, the electrolyte is injected, and the soft-pack lithium-ion battery is obtained after vacuum packaging, static, formation, shaping, capacity testing and other processes.
  • the button cells formed by the negative electrode sheets of the above-mentioned embodiments and comparative examples are tested for the initial efficiency of lithium-ion batteries.
  • the specific test method is as follows: take the single-sided coated negative electrode sheet obtained in the corresponding embodiment or comparative example, cut it into an area of 1.54 cm2 and use it as a working electrode, then use a lithium sheet as a counter electrode, use a porous polyethylene film as a separator, inject electrolyte and assemble to obtain a button cell; first discharge the button cell to 0V with a three-stage small current of 0.05C/50 ⁇ A/20 ⁇ A, and record the initial discharge capacity of the button cell; then charge it to 2.0V with a constant current of 0.1C, and record the initial charging capacity of the button cell.
  • the electrolyte contains 12.5% by weight of lithium salt LiPF 6 , and the solvent is obtained by mixing ethylene carbonate (EC) and diethyl carbonate (DEC) in a mass ratio of 1:1.
  • EC ethylene carbonate
  • DEC diethyl carbonate
  • the silicon-carbon negative electrode materials of the above-mentioned embodiments and comparative examples were subjected to scanning electron microscope line scanning element analysis.
  • the specific method is as follows: the negative electrode sheet prepared in the corresponding embodiment or comparative example was cut into a cross section by an ion polishing method, and then the cross section of the cut carbon-silicon negative electrode material was used as the test surface of the sample to be tested, and then transferred into a field emission scanning electron microscope and tested after focusing.
  • a line scan was performed from the center of the particle to the outside to test the silicon element in the carbon-silicon negative electrode material, and the content distribution of the silicon element was recorded, and then the scanned value was subjected to variance analysis to obtain the standard deviation, which was recorded in Table 2.
  • the silicon-carbon negative electrode materials of the above-mentioned embodiments and comparative examples were tested for the content of silicon element and the content of carbon nanotubes.
  • ICP inductively coupled plasma spectrometer
  • the conductivity test of the silicon-carbon negative electrode material of each embodiment and comparative example is carried out, and the specific test method is as follows: a powder conductivity meter (model FT-8100) is used to test the conductivity of the silicon-carbon negative electrode material powder, based on the four-probe test principle, and referring to the standard GB/T1552-1995. A known amount of silicon-carbon negative electrode material powder is used, and the volume is compressed to a set pressure value or pressure under hydraulic power, and the conductivity of the silicon-carbon negative electrode material powder is measured online, and the data is recorded in Table 2.
  • a powder conductivity meter model FT-8100
  • the particle strength test of the silicon-carbon negative electrode material of each embodiment and comparative example is carried out, and the specific test method is as follows: a nanoindenter (model: Hysitron TI 950) is used to test the hardness and elastic modulus of a single particle of the silicon-carbon negative electrode material, and the test standard is JB/T 12721-2016. Before the test, the silicon-carbon negative electrode material powder is dispersed in epoxy resin for curing, and the cured resin is cut by ion polishing. A nanoprobe is used to apply pressure to a single particle, and the indentation depth on the particle surface is monitored to convert the elastic modulus of the particle. The elastic modulus of five particles of the same sample is tested in parallel and the average value is taken to obtain the particle elastic modulus of the silicon-carbon negative electrode material, which is recorded in Table 2.
  • the soft-pack lithium-ion batteries of the embodiments and comparative examples were subjected to cycle performance tests and battery full charge expansion rate tests.
  • the specific method of the cycle performance test is as follows: charge to 4.4V at a constant current of 0.7C, charge to 0.025C at a constant voltage, and discharge to 3.0V at 0.5C after standing for 5 minutes.
  • the capacity obtained in this step is taken as the initial capacity, and a cycle test is performed with 0.7C charging/0.5C discharging.
  • the capacity of each step is compared with the initial capacity to obtain a capacity decay curve.
  • the number of cycles at 25°C until the capacity retention rate is 90% (recorded in Table 2) is recorded as the room temperature cycle performance of the battery, and the number of cycles at 45°C until the capacity retention rate is 80% (recorded in Table 2) is recorded as the high temperature cycle performance of the battery.
  • the cycle performance of the material is compared by comparing the number of cycles in the above two cases.
  • the specific method for testing the battery full charge expansion rate is as follows: Use a spiral micrometer to test the thickness of a fresh soft-pack lithium-ion battery at half charge (50% state of charge (SOC)). When the battery is fully charged (100% SOC) after 400 cycles, use a spiral micrometer to test the thickness of the battery at this time. Compare it with the thickness of the fresh battery at the initial half charge (50% SOC), and the expansion rate of the fully charged (100% SOC) battery at this time can be obtained and recorded in Table 2.
  • SOC state of charge
  • the silicon-carbon negative electrode material was loaded on a flat glass slide for Raman testing in the range of 100 cm -1 to 1200 cm -1 ; after the test, the characteristic peaks in the range of 450 cm -1 to 550 cm -1 were focused on, the maximum point of the peak was taken as the peak position, and 1/2 of the difference of the horizontal coordinates at half the peak was taken as the half-peak width of the peak.
  • the silicon-carbon negative electrode material was loaded onto a sample carrier for powder XRD testing in a test range of 10° to 90° and a scanning speed of 5°/min. After the test was completed, attention was paid to the characteristic peaks in the range of 15° to 35°, the maximum point of the peak was taken as the peak position, and 1/2 of the difference in the horizontal coordinates at half the peak was taken as the half-peak width of the peak.
  • the pore volume of the silicon-carbon negative electrode material was measured by N2 gas adsorption method. After obtaining the adsorption/desorption data, the pore structure was fitted using the NRDFT model to obtain pore volume data of ⁇ 2nm and >2nm, respectively.
  • the strength of the silicon-carbon negative electrode material is improved after the addition of carbon nanotubes, so the ability to buffer the volume expansion of the battery is improved, which is beneficial to improve the cycle performance of the battery.
  • the conductivity of the silicon-carbon negative electrode material is also improved after the addition of carbon nanotubes, so that the electron diffusion capacity of the silicon-carbon negative electrode material is improved, and the probability of lithium ions being trapped (trapping) inside the silicon-carbon is reduced, so that its first efficiency is improved and the energy density is improved.
  • the carbon nanotube content is too high, it is easy to affect the first charge efficiency.
  • the formation of pores when forming a porous carbon skeleton is easy to make the proportion of macropores too high, making it difficult for subsequent silicon to deposit, resulting in an increase in the specific surface area of the final product, thereby increasing the SEI film formation in the electrochemical device, thereby affecting the first charge efficiency.
  • the silicon content in Comparative Example 2 is too low, so that the pores in the porous carbon skeleton are not filled enough, resulting in an increase in the specific surface area of the final product, thereby increasing the SEI film formation in the electrochemical device, thereby affecting the first charge efficiency.
  • Comparative Example 3 it can be seen that the silicon content in the silicon-carbon negative electrode material is too high, the binding capacity of the carbon nanotubes is limited, the battery expands severely, resulting in poor cycle performance.

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Abstract

一种硅碳负极材料，包括核体和壳体，所述核体包括多孔碳骨架以及分散于所述多孔碳骨架的孔洞内的硅。所述多孔碳骨架内包裹并分散有碳纳米管，在所述碳硅负极材料中，所述硅碳负极材料中硅元素的含量为25wt％至55wt％，所述壳体包括碳材料。在所述碳硅负极材料的截面的线性扫描电镜能谱中，沿所述截面的中心至边缘的方向，所述硅元素的含量变化标准差不超过200。提供一种电化学装置以及一种硅碳负极材料的制备方法。

Description

硅碳负极材料及其制备方法和应用
本申请要求于2023年6月29日提交中国专利局、申请号为202310786717.2、发明名称为“硅碳负极材料及其制备方法和应用”的中国专利申请的优先权，其全部内容通过引用结合在本申请中。
技术领域
本申请涉及电化学储能领域，尤其是涉及一种硅碳负极材料及其制备方法、一种应用所述硅碳负极材料的负极极片、一种应用所述负极极片的电化学装置。
背景技术
锂离子电池具有体积和质量能量密度大、环境友好、工作电压高、体积小、重量轻、循环寿命长等优点，在便携式消费电子领域具有广泛的应用。随着近年来电动汽车和可移动电子设备的高速发展，人们对电池的能量密度、安全性、循环性能等相关需求越来越高，期待着综合性能全面提升的新型锂离子电池的出现；其中，能量密度、循环性能已成为亟待解决的关键技术问题，改进电极中的活性材料是解决上述问题的研究方向之一。
目前，石墨是应用最广泛的负极材料，它具有效率高，充放电平台稳定等优势。然而，目前的商业石墨的性能几乎开发到了极致，较低的容量以及锂枝晶安全隐患阻碍了其进一步应用。而和石墨作为负极材料相比，单质硅由于超高的理论比容量和合适的工作电压等特点，被认为是可以替代石墨的最有前途的锂电负极材料。然而，低导电性以及在合金化/去合金化过程中巨大的体积膨胀，严重制约了单质硅在锂离子电池中的大规模应用。
发明内容
本申请提供一种能够提升导电性和降低膨胀的硅碳负极材料。
另，本申请还提供一种应用所述硅碳负极材料的负极极片以及一种应用所述负极极片的电化学装置，本申请还提供一种上述硅碳负极材料的制备方法。
本申请第一方面提供一种硅碳负极材料，包括核体和壳体，所述核体包括多孔碳骨架以及分散于所述多孔碳骨架的孔洞内的硅。所述多孔碳骨架内包裹并分散有碳纳米管，所述硅碳负极材料中硅元素的含量为25wt％至55wt％，所述壳体包括碳材料。在所述碳硅负极材料的截面的线性扫描电镜能谱中，沿所述截面的中心至边缘的方向，所述硅元素的含量变化标准差不超过200。
本申请的硅碳负极材料，由于其内的碳纳米管具有良好的导电性和力学性能，因此分散于所述多孔碳骨架中的特定含量的碳纳米管一方面能够提升所述硅碳负极材料的导电性，另一方面还能够改善所述硅碳负极材料的力学性能，并束缚所述硅碳负极材料的膨胀，有利于提升结构的稳定性。而根据碳硅负极材料的截面的线性扫描电镜能谱可知在所述硅 碳负极材料中硅元素均匀分布，从而有利于进一步地提升所述硅碳负极材料的导电性和力学性能。在上述硅碳负极材料应用于电化学装置中的负极极片中时，上述硅碳负极材料导电性的提升能够改善锂在硅碳负极材料内部被捕获的概率，从而改善电化学装置的脱锂容量并提升首次充放电性能，同时碳纳米管还能够在嵌锂过程中缓解硅碳的体积膨胀，改善硅碳在充放电中的膨胀粉化和结构稳定性，从而提升其循环性能。
基于第一方面，在一些可能的实施方式中，所述硅碳负极材料的电导率为9S/cm至30S/cm。在上述可能的实施方式中，特定范围内的电导率有利于保障硅碳负极材料的导电性，进一步改善应用所述硅碳负极材料的电化学装置的循环性能。
基于第一方面，在一些可能的实施方式中，所述硅碳负极材料的颗粒弹性模量为4GPa至10GPa，特定范围内的颗粒弹性模量则有利于提升硅碳负极材料结构的稳定性，有利于进一步改善应用所述硅碳负极材料的电化学装置的膨胀和循环性能。
基于第一方面，在所述碳硅负极材料中，所述碳纳米管的含量为0.2wt％至7.0wt％，在该范围内的碳纳米管含量，能够进一步缓解嵌锂过程中硅碳的体积膨胀，且可以控制多孔碳骨架制备时形成孔的形成，降低大孔的比例，改善硅的沉积均匀性，进一步改善电化学装置的循环性能和降低电化学装置的循环膨胀率。
基于第一方面，在一些可能的实施方式中，所述硅碳负极材料满足以下条件中的至少一者：(1)所述硅碳负极材料的X射线衍射图谱在20°至30°的范围内具有一个特征峰，且所述特征峰的半峰宽大于2°；(2)所述硅碳负极材料的拉曼光谱中在450cm-1至500cm-1的范围内具有一个特征峰；(3)所述硅碳负极材料的粒径Dv50为3μm至20μm，且所述硅碳负极材料的粒径Dv99为3μm至20μm。
在上述可能的实施方式中，通过硅碳负极材料的X射线衍射图谱的特征可知所述多孔碳骨架中的孔为微孔，即所述多孔碳骨架中90％的孔的孔径小于2纳米，也就是说，有利于使得在所述硅碳负极材料中嵌入所述多孔碳骨架的硅的尺寸大部分小于2纳米，从而有利于进一步降低所述硅碳负极材料的膨胀。通过所述硅碳负极材料的拉曼光谱的特征可知所述硅碳负极材料中硅的尺寸小且为非晶态，有利于进一步降低所述硅碳负极材料的膨胀。而特定粒径范围的所述硅碳负极材料在后续搅拌涂布等制备负极极片的加工过程更加顺畅，且便于与石墨进行搭配。
基于第一方面，在一些可能的实施方式中，所述硅碳负极材料中孔径超过2nm的孔的孔容大于孔径不超过2nm的孔的孔容。在一些可能的实施方式中，孔径超过2nm的孔的孔容范围为0.04至0.20。在上述可能的实施方式中，由于微孔的吸附效果更好，所以硅优先在微孔中吸附并沉积，结合所述多孔碳骨架中90％的孔的孔径小于2纳米的前提可知， 所述硅碳负极材料中的硅的尺寸大部分小于2纳米，从而有利于进一步降低所述硅碳负极材料的膨胀。
本申请的第二方面提供一种负极极片，包括集流体以及负极活性层。所述负极活性层包括负极活性材料，所述负极活性材料包括如上所述的硅碳负极材料。
本申请的负极极片，通过碳纳米管以及硅元素的均匀分布提高所述硅碳负极材料的导电性，能够改善锂在硅碳负极材料内部被捕获的概率，从而改善电化学装置的脱锂容量并提升首次充放电性能，同时碳纳米管还能够在嵌锂过程中缓解硅碳的体积膨胀，结合硅元素的均匀分布以改善硅碳在充放电中的膨胀粉化和结构稳定性，从而提升其循环性能。
基于第二方面，在一些可能的实施方式中，所述负极活性材料还包括石墨，在所述负极活性材料中，所述硅碳负极材料的含量为5wt％至40wt％，所述石墨的含量为95wt％至60wt％。
在上述可能的实施方式中，上述特定含量的所述硅碳负极材料能够在充分利用硅超高的理论比容量和合适的工作电压等特点的同时有效地降低硅膨胀对负极极片的影响，有利于提升负极极片的首次库伦效率、能量密度和循环性能。具体的，硅碳负极材料过高负极活性层体积膨胀明显，循环性能变差；硅碳负极材料过低则不利于提升首次库伦效率。由于石墨具有一定的柔韧性，其与硅碳负极材料配合能够缓解负极活性层体积膨胀的情况。另外，负极极片还能够充分利用硅碳负极材料和石墨两者的优势以达到较好的电化学性能。
本申请的第三方面提供一种电化学装置，包括如上所述的负极极片。
本申请的电化学装置，其负极极片中通过碳纳米管以及硅元素的均匀分布提高所述硅碳负极材料的导电性，能够改善锂在硅碳负极材料内部被捕获的概率，从而改善电化学装置的脱锂容量并提升首次充放电性能，同时碳纳米管还能够在嵌锂过程中缓解硅碳的体积膨胀，结合硅元素的均匀分布以改善硅碳在充放电中的膨胀粉化和结构稳定性，从而提升其循环性能。
本申请的第五方面提供一种如上所述的硅碳负极材料的制备方法，包括：将树脂和碳纳米管混合形成混合物并固化；将上述固化后的所述混合物碳化后并活化获得多孔碳骨架；以及对所述多孔碳骨架进行硅烷沉积形成核体后再通过烷烃形成壳体。
本申请的上述硅碳负极材料的制备方法，先将树脂和碳纳米管混合形成混合物固化后再碳化形成多孔骨架，便于所述碳纳米管在所述多孔骨架中的分散，从而有利于提升碳纳米管对制得的硅碳负极材料的束缚，进而缓解硅碳负极材料的体积膨胀以改善硅碳在充放电中的膨胀粉化和结构稳定性，提升其循环性能；同时，还有利于提升硅碳负极材料整体的导电性，进而改善锂在硅碳负极材料内部被捕获的概率以改善电化学装置的脱锂容量并 提升首次充放电性能。
基于第二方面，在一些可能的实施方式中，所述碳化的条件为升温至700℃至1100℃并保温1小时至5小时，所述活化具体为在碳化降温后通过二氧化碳、水蒸气、氢氧化钠、氢氧化钾或者磷酸进行活化。
基于第二方面，在一些可能的实施方式中，步骤“对所述多孔碳骨架进行硅烷沉积形成核体后再通过烷烃形成壳体”具体为：将所述多孔碳骨架在惰性气氛下缓慢升温至400℃至600℃后保温，而后将气氛切换为硅烷混合气沉积1小时至20小时，所述硅烷混合气包含质量百分含量为2％至20％的硅烷和80％至98％的惰性气体；在500℃至1000℃的温度下再将气氛切换为烷烃混合气保持10小时以形成壳体后将气氛切换为惰性气氛并降温至室温，所述烷烃混合气包含质量百分含量为5％至100％的烷烃和95％至0％的惰性气体。
具体实施方式
下面对本申请实施例中的技术方案进行清楚、详细地描述，显然，所描述的实施例是本申请一部分实施例，而不是全部的实施例。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。在本申请的说明书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。
下文，将详细地描述本申请的实施方式。但是，本申请可体现为许多不同的形式，并且不应解释为限于本文阐释的示例性实施方式。而是，提供这些示例性实施方式，从而使本申请透彻的和详细的向本领域技术人员传达。
进一步，当描述本申请的实施方式时使用“可”指“本申请的一个或多个实施方式”。
本文使用的专业术语是为了描述具体实施方式的目的并且不旨在限制本申请。如本文所使用，单数形式旨在也包括复数形式，除非上下文另外明确指出。应进一步理解，术语“包括”，当在本说明书中使用时，指存在叙述的特征、数值、步骤、操作、要素和/或组分，但是不排除存在或增加一个或多个其他特征、数值、步骤、操作、要素、组分和/或其组合。术语“中的至少一者”、“中的至少一个”、“中的至少一种”或其他相似术语所连接的项目的列表可意味着所列项目的任何组合。例如，如果列出项目A及B，那么短语“A及B中的至少一者”意味着仅A；仅B；或A及B。在另一实例中，如果列出项目A、B及C，那么短语“A、B及C中的至少一者”意味着仅A；或仅B；仅C；A及B(排除C)；A及C(排除B)；B及C(排除A)；或A、B及C的全部。
在本申请中，参数数值之间的大于、小于或不等于设计关系，需要排除测量设备的合理误差。
本申请一实施方式提供一电化学装置，所述电化学装置包括正极极片、负极极片和隔 离膜。所述隔离膜设于所述正极极片和所述负极极片之间。所述正极极片、所述隔离膜和所述负极极片可依次交替层叠形成叠片式电极组件，或者所述正极极片、所述隔离膜和所述负极极片依次层叠后卷绕以形成卷绕式电极组件。
所述电化学装置还包括壳体和电解液，所述正极极片、所述负极极片、所述隔离膜和所述电解液收容于所述壳体内。所述壳体可为采用封装膜例如但不仅限于铝塑膜封装得到的包装袋，即所述电化学装置可为软包电池。所述壳体也可为但不仅限于钢壳电池、铝壳电池等现有技术中公开的壳体。
所述正极极片包括正极集流体和设于所述正极集流体上的正极活性层。所述正极集流体可以使用铝箔或镍箔等，也可为任何现有技术中公开的复合集流体，例如但不仅限于前述导电箔和聚合物基底结合形成的集流体。所述正极活性层包含正极活性材料，所述正极活性材料包括可逆地嵌入和脱嵌锂离子的化合物(即，锂化插层化合物)。在一些实施例中，正极活性材料可以包括锂过渡金属复合氧化物。该锂过渡金属复合氧化物含有锂以及从钴、锰和镍中选择的至少一种元素。在一些实施例中，正极活性材料可包括但不仅限于钴酸锂(LiCoO2)、锂镍锰钴三元材料(NCM)、锰酸锂(LiMn2O4)、镍锰酸锂(LiNi0.5Mn1.5O4)或磷酸铁锂(LiFePO4)中的至少一种。
所述正极活性层还包含粘合剂，用以粘结正极活性材料颗粒从而便于形成膜层，同时还能够提高正极活性层与正极集流体之间的结合力。
在一些实施例中，所述粘合剂可包括但不仅限于聚乙烯醇、羟丙基纤维素、二乙酰基纤维素、聚氯乙烯、羧化的聚氯乙烯、聚氟乙烯、含亚乙基氧的聚合物、聚乙烯吡咯烷酮、聚氨酯、聚四氟乙烯、聚偏1,1-二氟乙烯、聚乙烯、聚丙烯、丁苯橡胶、丙烯酸(酯)化的丁苯橡胶、环氧树脂或尼龙等中的至少一种。
所述正极活性层还可包含导电材料，所述导电材料包括但不限于基于碳的材料、基于金属的材料、导电聚合物或其任意组合。在一些实施例中，所述基于碳的材料可包括但不仅限于自天然石墨、人造石墨、碳黑、乙炔黑、科琴黑、碳纤维或其任意组合。在一些实施例中，所述基于金属的材料可包括但不仅限于金属粉或金属纤维，例如铜、镍、铝或银。在一些实施例中，所述导电聚合物可为聚亚苯基衍生物。
所述负极极片包括负极集流体和设于所述负极集流体上的负极活性层。所述负极集流体可以使用铜箔、镍箔、不锈钢箔、钛箔或碳基集流体等中的至少一种，也可为任何现有技术中公开的复合集流体，例如但不仅限于前述导电箔和聚合物基底结合形成的集流体。所述负极活性层包含负极活性材料，所述负极活性材料包括硅碳负极材料。
所述硅碳负极材料包括核体和壳体，所述核体包括多孔碳骨架以及分散于所述多孔碳 骨架的孔洞内的硅。所述多孔碳骨架内包裹并分散有碳纳米管，在所述碳硅负极材料中，所述硅碳负极材料中硅元素的含量为25wt％至55wt％，所述壳体包括碳材料。在所述碳硅负极材料的截面的线性扫描电镜能谱中，沿所述截面的中心至边缘的方向，所述硅元素的含量变化标准差不超过200。具体的，将硅碳负极材料颗粒用离子抛光的方法切出截面作为测试面。将切割后的硅碳负极材料转入场发射扫描电镜中并对测试面从中心向外进行线扫，记录各元素的含量分布。例如，将线扫获得的硅元素的含量数据等距离地取100个数据点，并对所取的100个数据点进行数理统计标准差分析，获得硅元素的含量变化标准差。
上述硅碳负极材料，由于其内的碳纳米管具有良好的导电性和力学性能，因此分散于所述多孔碳骨架中的特定含量的碳纳米管一方面能够提升所述硅碳负极材料的导电性，另一方面还能够改善所述硅碳负极材料的力学性能，并束缚所述硅碳负极材料的膨胀，有利于提升结构的稳定性。而根据碳硅负极材料的截面的线性扫描电镜能谱可知在所述硅碳负极材料中硅元素均匀分布。通过碳纳米管的分散以及硅元素的均匀分布能够提升所述硅碳负极材料的导电性和强度，减少锂在硅碳负极材料中的捕获，缓解硅碳负极材料的膨胀并提高应用所述负极极片的电化学装置的首次库伦效率，进而提升所述电化学装置的能量密度和循环性能。
在一些实施例中，所述硅元素的含量为20％至45％，可进一步降低硅碳负极材料的膨胀和改善电化学装置的循环性能。
在一些实施例中，所述硅碳负极材料的电导率为9S/cm至30S/cm。在一些实施例中，所述硅碳负极材料的电导率为11S/cm至25S/cm。在一些实施例中，所述硅碳负极材料的电导率为9S/cm、11S/cm、14S/cm、20S/cm、25S/cm、30S/cm或在上述任意两个数值所组成的范围内的值。当硅碳负极材料的电导率在上述范围内时，可保障硅碳负极材料的导电性，进一步改善电化学装置的循环性能。
在一些实施例中，所述硅碳负极材料的颗粒弹性模量为4GPa至10Gpa，有利于保障硅碳负极材料的机械强度以缓解内部应力，进一步降低硅碳负极材料的膨胀和改善电化学装置的循环性能。
在一些实施例中，在所述碳硅负极材料中，所述碳纳米管的含量为0.2wt％至7.0wt％。在一些实施例中，所述碳纳米管的含量为1.0wt％至6.0wt％。在一些实施例中，所述碳纳米管的含量为0.2wt％、1.0wt％、1.5wt％、2.5wt％、4.5wt％、6.0wt％、6.5wt％、7.0wt％或在上述任意两个数值所组成的范围内的值。在上述范围内的碳纳米管含量，有助于进一步缓解嵌锂过程中硅碳的体积膨胀，且可以控制多孔碳骨架制备时形成孔的形成，降低大孔的比例，改善硅的沉积均匀性，保证电化学装置的首次效率(即首次库伦效率)，进一步 改善电化学装置的循环性能和降低电化学装置的循环膨胀率。
在一些实施例中，所述硅碳负极材料的X射线衍射图谱在20°至30°的范围内具有一个特征峰，且所述特征峰的半峰宽大于2°，即所述多孔碳骨架中的孔为微孔，所述多孔碳骨架中90％的孔的孔径小于2纳米。也就是说，有利于使得在所述硅碳负极材料中嵌入所述多孔碳骨架的硅的尺寸大部分小于2纳米，从而有利于进一步地降低所述硅碳负极材料的膨胀。
进一步地，所述硅碳负极材料中孔径超过2nm的孔的孔容大于孔径不超过2nm的孔的孔容。由于微孔的吸附效果更好，所以硅优先在微孔中吸附并沉积。因此，所述硅碳负极材料中的硅的尺寸大部分小于2纳米，从而有利于进一步地降低所述硅碳负极材料的膨胀。在一些实施例中，孔径超过2nm的孔的孔容范围为0.04至0.20。
在一些实施例中，所述硅碳负极材料的拉曼光谱在450cm-1至500cm-1的范围内具有一个特征峰，即所述硅碳负极材料中硅的尺寸小且为非晶态，从而有利于进一步地降低所述硅碳负极材料的膨胀。
所述硅碳负极材料的粒径Dv50可为3μm至20μm，且所述硅碳负极材料的粒径Dv99可为3μm至20μm，以便于在后续与其他材料(例如粘结剂)混合搅拌涂布形成负极活性层时更加的顺畅，且易于其他材料进行混合搭配。
所述负极活性材料还可进一步地包含石墨，由于石墨具有一定的柔韧性，其与硅碳负极材料配合能够缓解负极活性层体积膨胀的情况。同时，所述石墨与所述硅碳负极材料同时作为活性材料有利于降低所述负极活性层整体的膨胀，并且还能够充分利用硅碳负极材料和石墨两者的优势以达到较好的电化学性能。
在所述负极活性材料中，所述硅碳负极材料的含量可为5wt％至40wt％。进一步地，所述石墨的含量可为95wt％至60wt％。
所述负极活性层还包含粘结剂，用以粘结正极活性材料颗粒从而便于形成膜层，同时还能够提高负极活性层与负极集流体之间的结合力。
在一些实施例中，所述粘结剂可包括但不仅限于聚乙烯醇、羟丙基纤维素、二乙酰基纤维素、聚氯乙烯、羧化的聚氯乙烯、聚氟乙烯、含亚乙基氧的聚合物、聚乙烯吡咯烷酮、聚氨酯、聚四氟乙烯、聚偏1,1-二氟乙烯、聚乙烯、聚丙烯、丁苯橡胶、丙烯酸(酯)化的丁苯橡胶、环氧树脂或尼龙等。
所述负极活性层还可包括导电材料，所述导电材料包括但不限于基于碳的材料、基于金属的材料、导电聚合物或其任意组合。在一些实施例中，所述基于碳的材料可包括但不仅限于自天然石墨、人造石墨、碳黑、乙炔黑、科琴黑、碳纤维或其任意组合。在一些实 施例中，所述基于金属的材料可包括但不仅限于金属粉或金属纤维，例如铜、镍、铝或银。在一些实施例中，所述导电聚合物可为聚亚苯基衍生物。
所述隔离膜包括具有多孔结构的膜层，其材质包括但不仅限于聚乙烯、聚丙烯、聚偏氟乙烯、聚对苯二甲酸乙二醇酯、聚酰亚胺或芳纶中的至少一种。例如，所述隔离膜可为聚丙烯多孔膜、聚乙烯多孔膜、聚丙烯无纺布、聚乙烯无纺布或聚丙烯-聚乙烯-聚丙烯多孔复合膜等。
所述电解液的状态可以是凝胶态、固态和液态中的一种或多种。在一些实施例中，所述液态电解液包括锂盐和有机溶剂。锂盐可选自但不仅限于六氟磷酸锂(LiPF6)、四氟硼酸锂(LiBF4)、六氟砷酸锂(LiAsF6)、高氯酸锂(LiClO4)、四苯硼酸锂(LiB(C6H5)4)、甲磺酸锂(LiCH3SO3)、双氟磺酰亚胺锂(LiFSI)、双三氟甲烷磺酰亚胺锂(LiTFSI)、三氟甲磺酸锂(LiCF3SO3)、双(三氟甲基磺酰)亚胺锂(LiN(SO2CF3)2、三(三氟甲基磺酰)甲基锂(LiC(SO2CF3)3)、二草酸硼酸锂(LiBOB)和二氟磷酸锂(LiPO2F2)中的一种或多种。例如，锂盐选用LiPF6，因为它可以给出高的离子导电率并改善循环特性。有机溶剂可为碳酸酯化合物、羧酸酯化合物、醚化合物、腈化合物、其它有机溶剂或它们的组合。碳酸酯化合物的实例包括但不仅限于碳酸二乙酯(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)、碳酸甲乙酯(MEC)、碳酸亚乙酯(EC)、碳酸亚丙酯(PC)、碳酸亚丁酯(BC)、碳酸乙烯基亚乙酯(VEC)、碳酸氟代亚乙酯(FEC)、碳酸1,2-二氟亚乙酯、碳酸1,1-二氟亚乙酯、碳酸1,1,2-三氟亚乙酯、碳酸1,1,2,2-四氟亚乙酯、碳酸1-氟-2-甲基亚乙酯、碳酸1-氟-1-甲基亚乙酯、碳酸1,2-二氟-1-甲基亚乙酯、碳酸1,1,2-三氟-2-甲基亚乙酯、碳酸三氟甲基亚乙酯或其组合。
将上述电化学装置应用于电子装置中，以为所述电子装置中其他电子元件进行供电。由于上述电化学装置中的硅碳负极材料有利于提升循环性能和能量密度，因此有利于所述电子装置提升使用寿命。所述电子装置可包括但不仅限于笔记本电脑、笔输入型计算机、移动电脑、电子书播放器、便携式电话、便携式传真机、便携式复印机、便携式打印机、头戴式立体声耳机、录像机、液晶电视、手提式清洁器、便携CD机、迷你光盘、收发机、电子记事本、计算器、存储卡、便携式录音机、收音机、备用电源、电机、汽车、摩托车、助力自行车、自行车、照明器具、玩具、游戏机、钟表、电动工具、闪光灯、照相机、家庭用大型蓄电池和锂离子电容器等。
本申请还提供一种硅碳负极材料的制备方法，其包括以下步骤：
步骤S1，将树脂和碳纳米管混合形成混合物并固化。
形成混合物的方式包括但不仅限于球磨。混合时还可另外加入有机溶剂，从而便于将 碳纳米管进行分散。上述固化即将混合物干燥定型，应用现有技术中常用的固化条件即可，在此不进行赘述。
步骤S2，将上述固化后的所述混合物碳化后并活化获得多孔碳骨架。
具体的，将固化后的所述混合物在惰性气氛(例如但不仅限于氮气气氛)下升温至700℃至1100℃碳化1小时至5小时，待降温至室温后活化形成多孔碳骨架。所述活化可通过二氧化碳、水蒸气对碳化后的结构进行活化，也可通过碱刻蚀或者酸刻蚀对谈话后的结构进行活化。所述碱刻蚀通常可为利用氢氧化钠或者氢氧化钾进行刻蚀，所述酸刻蚀通常可为利用磷酸进行刻蚀。
步骤S3，对所述多孔碳骨架进行硅烷沉积形成核体后再通过烷烃形成碳包覆层的壳体包覆所述核体。
具体的，将所述多孔碳骨架在惰性气氛(例如但不仅限于氩气气氛)下缓慢升温至400℃至600℃后，将气氛切换为硅烷混合气沉积1小时至20小时形成核体。其中，缓慢升温的升温速率可为但不仅限于0.5℃/min至5℃/min，所述硅烷混合气包含质量百分含量为2％至20％的硅烷和80％至98％的惰性气体(例如但不仅限于氩气)。
而后在500℃至1000℃的温度下再将气氛切换为烷烃混合气保持2小时至20小时以形成包覆所述核体的碳包覆层的壳体后将气氛切换为惰性气氛(例如但不仅限于氮气气氛)并降温至室温，最终获得所述硅碳负极材料。其中，所述烷烃混合气包含质量百分含量为5％至100％的烷烃(例如但不仅限于乙炔)和0％至95％的惰性气体(例如但不仅限于氩气)。
实施例1
负极极片的制备：
1)硅碳负极材料的制备：将线性酚醛树脂(RF)：乌洛托品(HMT)：碳纳米管(CNTs)按重量比例(记载于表1)混合形成混合物，混合方式为球磨，且球磨转速为500r/min，球磨时间为6h。将颜色为暗黑色的球磨后的混合物升温至130℃并保温10h进行固化。将固化后的混合物转移至箱式炉中，并在氮气气氛下升温至900℃碳化2h，而后降温后转入回转炉中在二氧化碳气氛下活化9h获得多孔碳骨架。多孔碳骨架继续在氩气气氛下以2℃/min的速度升温至500℃后，将气氛切换为硅烷混合气(按质量百分含量计，20％的硅烷和80％的氩气)，在500℃条件下沉积10h形成核体，再将气氛切换为乙炔混合气(按质量百分含量计，20％的乙炔和80％的氩气)继续在500℃沉积10h后切换为氮气，而后降温至室温25℃获得硅碳负极材料。
2)以重量比为80:20的石墨和上述硅碳负极材料的混合物作为负极活性材料，将所述 负极活性材料、丁苯橡胶(SBP)和羧甲基纤维素钠(CMC)按重量比97:2:1在适量的去离子水中充分搅拌混合，使其形成均匀的负极浆料，其中负极浆料的固含量为40wt％。将此浆料涂覆于负极集流体铜箔上，在85℃下烘干，然后经过冷压、裁片、分切后，在120℃的真空条件下干燥12小时，得到负极极片。
正极极片的制备：将正极活性材料钴酸锂(LiCoO2)、导电炭黑Super P和聚偏二氟乙烯(PVDF)按重量比97:1.4:1.6在适量的N-甲基吡咯烷酮(NMP)溶剂中充分搅拌混合，使其形成均匀的正极浆料，其中正极浆料的固含量为72wt％。将此浆料涂覆于正极集流体铝箔上，在85℃下烘干，然后经过冷压、裁片、分切后，在85℃的真空条件下干燥4小时，得到正极极片。
电解液的制备：在干燥的氩气气氛手套箱中，将碳酸乙烯酯(EC)、碳酸甲乙酯(EMC)、碳酸二乙酯(DEC)按照质量比为EC:EMC:DEC＝30:50:20混合均匀，然后加入锂盐LiPF6，混合均匀后获得电解液，在所述电解液中，LiPF6的质量百分含量为12.5％。
隔离膜的制备：以7微米厚的聚乙烯(PE)多孔聚合物薄膜作为隔离膜。
锂离子电池的制备：将上述正极极片、上述隔离膜、上述负极极片依次层叠卷绕并焊接极耳后置于铝塑膜包装袋中。而后注入电解液，并经过真空封装、静置、化成、整形、容量测试等工序，获得软包锂离子电池。
实施例2-12以及对比例1-3的锂离子电池的制备具体步骤参照实施例1，不同之处可从表1中获知。
表1

对上述各个实施例和各个对比例的负极极片形成的纽扣电池进行锂离子电池的首次效率测试，具体的测试方法如下：取相应实施例或对比例制得的单面涂覆的负极极片，将其裁切成面积大小为1.54cm2后作为工作电极，之后以锂片作为对电极，以多孔聚乙烯膜作为隔膜，注入电解液后组装得到纽扣电池；将纽扣电池先分别以0.05C/50μA/20μA三阶段小电流放电至0V后，记录纽扣电池的首次放电容量；再以0.1C恒流充电至2.0V，记录纽扣电池的首次充电容量。首次效率＝首次充电容量/首次放电容量×100％；所述负极活性材料在0V至2.0V的首次可逆克容量＝纽扣电池的首次充电容量/负极活性材料的质量。所述电解液包含质量百分含量为12.5％的锂盐LiPF6，溶剂由碳酸乙烯酯(EC)和碳酸二乙酯(DEC)按照质量比1:1混合得到。其中，经测试所得的各实施例和对比例对应的纽扣电池的首次效率记载于表2中。
对上述各个实施例和对比例的硅碳负极材料进行扫描电镜线扫元素分析，具体方法如下：将相应实施例或对比例制得的负极极片用离子抛光的方法切出截面，然后将切出的碳硅负极材料的截面作为待测样品的测试面，转入场发射扫描电镜中并在聚焦后进行测试。测试时从颗粒的中心向外进行线扫，测试碳硅负极材料中的硅元素，并记录硅元素的含量分布，而后将扫描的值进行方差分析，获得标准差，并记载于表2中。
对上述各个实施例和对比例的硅碳负极材料进行硅元素的含量测试和碳纳米管的含量测试。
其中，通过ICP(电感耦合等离子光谱发生仪)表征测试硅碳负极材料中的硅含量。
碳纳米管含量测试的具体方法如下：首先根据对比例1所加入的RF和HMT的总量和得到的多孔碳骨架的重量，计算出RF+HMT在混料/固化/碳化/和活化过程的收率，记为d％；然后记录其他实施例中RF+HMT+CNTs在混料/固化/碳化/和活化过程的收率，记为e％；那么CNTs在实施例多孔碳骨架中的比例为f％＝(e-d)/e×100％，其余多孔碳骨架组分为g％＝1-f％；则在实施例硅碳负极材料中的CNTs含量为h％＝f/(f+g+b)×100％，并记载于表2中，其余多孔碳骨架的组分的含量为i％＝1-h％-b％。
对各实施例和对比例的硅碳负极材料进行电导测试，具体的测试方法如下：采用粉末电导率仪(型号为FT-8100)测试硅碳负极材料粉末的电导率，基于四探针测试原理，参照标准GB/T1552-1995。使用已知量的硅碳负极材料粉体，在液压动力下压缩体积至设定压力值或压强，在线测量硅碳负极材料粉体的电导率，并记录数据于表2中。
对各实施例和对比例的硅碳负极材料进行颗粒强度测试，具体测试方法如下：采用纳米压痕仪(型号为Hysitron TI 950)测试硅碳负极材料单个颗粒的硬度与弹性模量，测试标准为JB/T 12721-2016。在测试前，将硅碳负极材料粉末分散于环氧树脂中固化，通过离子抛光法将固化后的树脂切开，使用纳米探针对单个颗粒施压，监控颗粒表面压痕深度，换算出颗粒的弹性模量。同一个样品平行测试五个颗粒弹性模量后取平均值，从而获得硅碳负极材料的颗粒弹性模量记载于表2中。
对各实施例和对比例的软包锂离子电池进行循环性能测试和电池满充膨胀率测试。
其中，循环性能测试的具体方法如下：以0.7C恒流充电到4.4V，恒压充电到0.025C，静置5分钟后以0.5C放电到3.0V。以此步骤得到的容量为初始容量，进行0.7C充电/0.5C放电进行循环测试，以每一步的容量与初始容量做比值，得到容量衰减曲线。以25℃循环截至到容量保持率为90％的圈数(记载于表2中)记为电池的室温循环性能，以45℃循环截至到容量保持率为80％的圈数(记载于表2中)记为电池的高温循环性能，通过比较上述两种情况下的循环圈数比较材料的循环性能。
电池满充膨胀率测试的具体方法如下：用螺旋千分尺测试半充(50％充电状态(SOC))时新鲜软包锂离子电池的厚度，循环至400圈时，电池处于满充(100％SOC)状态下，再用螺旋千分尺测试此时电池的厚度，与初始半充(50％SOC)时新鲜电池的厚度对比，即可得此时满充(100％SOC)电池膨胀率并记载于表2中。
颗粒尺寸测试：
在50ml洁净烧杯中加入约0.02g硅碳负极材料粉末样品，加入约20ml去离子水，再滴加3滴1％的表面活性剂，使硅碳负极材料粉末完全分散于水中，使用120W超声清洗机中超声5分钟，利用MasterSizer 2000测试其颗粒尺寸。
Raman测试
将硅碳负极材料装载于平整的载玻片上进行Raman测试，测试范围为100cm-1至1200cm-1；测试完成后，关注450cm-1至550cm-1范围内的特征峰，取峰值最大点为该峰的峰位置，取一半峰值处横坐标的差值的1/2为该峰的半峰宽。
XRD测试
将硅碳负极材料装载于载样台上进行粉末XRD测试，测试范围为10°至90°，扫描速度为5°/min；测试完成后，关注15°至35°范围内的特征峰，取峰值最大点为该峰的峰位置，取一半峰值处横坐标的差值的1/2为该峰的半峰宽。
孔容的确定/测试方法
硅碳负极材料的孔容的测试采用N2气体吸附方法测定，获得吸附/脱附数据后用NRDFT模型进行孔结构拟合，分别获得＜2nm和＞2nm的孔容数据。
由表1和表2记载的数据可知，尤其是对比例1和其他实施例对比而言，加入碳纳米管后所述硅碳负极材料的强度得以提升，因此缓冲电池体积膨胀的能力得以提升，进而有利于提升电池的循环性能。此外，加入碳纳米管后所述硅碳负极材料的电导率也得以提升，使得硅碳负极材料的电子扩散能力得以改善，锂离子在硅碳内部被捕获(trapping)的几率得以降低，从而使得其首次效率得以提升，能量密度得以提升。当碳纳米管含量过高容易影响首充效率，具体的，碳纳米管含量过高，在形成多孔碳骨架时形成孔的形成，容易使得大孔的比例过高，使得后续硅不易沉积，导致最终产品的比表面积增加，从而使得电化学装置中SEI成膜增加，进而影响首充效率。同样的，对比例2中硅含量过低，使得多孔碳骨架中的孔的填充不足，导致最终产品的比表面积增加，从而使得电化学装置中SEI成膜增加，进而影响首充效率。而由对比例3和其他实施例对比而言可知，硅碳负极材料中硅含量过高，碳纳米管的束缚能力有限，电池膨胀严重，导致循环性能变差。
以上所揭露的仅为本申请较佳实施方式而已，当然不能以此来限定本申请，因此依本 申请所作的等同变化，仍属本申请所涵盖的范围。

Claims (10)

  1. 一种硅碳负极材料，其中，包括核体和壳体，所述核体包括多孔碳骨架以及分散于所述多孔碳骨架的孔洞内的硅，所述多孔碳骨架内包裹并分散有碳纳米管，在所述碳硅负极材料中，所述硅碳负极材料中硅元素的含量为25wt％至55wt％，所述壳体包括碳材料；
    在所述碳硅负极材料的截面的线性扫描电镜能谱中，沿所述截面的中心至边缘的方向，所述硅元素的含量变化标准差不超过200。
  2. 如权利要求1所述的硅碳负极材料，其中，所述硅碳负极材料的电导率为9S/cm至30S/cm，和/或所述硅碳负极材料的颗粒弹性模量为4GPa至10GPa。
  3. 如权利要求1或2所述的硅碳负极材料，其中，所述碳纳米管的含量为0.2wt％至7wt％。
  4. 如权利要求1至3中任一项所述的硅碳负极材料，其中，所述硅碳负极材料满足以下条件中的至少一者：
    (1)所述硅碳负极材料的X射线衍射图谱在20°至30°的范围内具有一个特征峰，且所述特征峰的半峰宽大于2°；
    (2)所述硅碳负极材料的拉曼光谱中在450cm-1至500cm-1的范围内具有一个特征峰；
    (3)所述硅碳负极材料的粒径Dv50为3μm至20μm，且所述硅碳负极材料的粒径Dv99为3μm至20μm。
  5. 如权利要求1至4中任一项所述的硅碳负极材料，其中，所述硅碳负极材料中孔径超过2nm的孔的孔容大于孔径不超过2nm的孔的孔容。
  6. 一种电化学装置，包括正极极片、负极极片和隔离膜，所述负极极片包括负极集流体和负极活性层，所述负极活性层包括负极活性材料，其中，所述负极活性材料包括如权利要求1至5中任一项所述的硅碳负极材料。
  7. 如权利要求6所述的电化学装置，其中，所述负极活性材料还包括石墨，在所述负极活性材料中，所述硅碳负极材料的含量为5wt％至40wt％，所述石墨的含量为95wt％至60wt％。
  8. 一种制备如权利要求1所述的硅碳负极材料的制备方法，包括：
    将树脂和碳纳米管混合形成混合物并固化；
    将上述固化后的所述混合物碳化后并活化获得多孔碳骨架；以及
    对所述多孔碳骨架进行硅烷沉积形成核体后再通过烷烃形成壳体。
  9. 如权利要求8所述的硅碳负极材料的制备方法，其中，所述碳化的条件为升温至 700℃至1100℃并保温1小时至5小时，所述活化具体为在碳化降温后通过二氧化碳、水蒸气、氢氧化钠、氢氧化钾或者磷酸进行活化。
  10. 如权利要求8或9所述的硅碳负极材料的制备方法，其中，步骤“对所述多孔碳骨架进行硅烷沉积形成核体后再通过烷烃形成壳体”具体为：
    将所述多孔碳骨架在惰性气氛下缓慢升温至400℃至600℃后保温，而后将气氛切换为硅烷混合气沉积1小时至20小时，所述硅烷混合气包含质量百分含量为2％至20％的硅烷和80％至98％的惰性气体；在500℃至1000℃的温度下再将气氛切换为烷烃混合气保持10小时以形成壳体后将气氛切换为惰性气氛并降温至室温，所述烷烃混合气包含质量百分含量为5％至100％的烷烃和0％至95％的惰性气体。
PCT/CN2024/090910 2023-06-29 2024-04-30 硅碳负极材料及其制备方法和应用 Ceased WO2025001491A1 (zh)

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