WO2022247613A1 - 一种负极材料及其制备方法与用途 - Google Patents

一种负极材料及其制备方法与用途 Download PDF

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WO2022247613A1
WO2022247613A1 PCT/CN2022/091424 CN2022091424W WO2022247613A1 WO 2022247613 A1 WO2022247613 A1 WO 2022247613A1 CN 2022091424 W CN2022091424 W CN 2022091424W WO 2022247613 A1 WO2022247613 A1 WO 2022247613A1
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negative electrode
electrode material
lithium
preparation
carbon coating
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PCT/CN2022/091424
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French (fr)
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彭友山
胡涛
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蜂巢能源科技股份有限公司
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Publication of WO2022247613A1 publication Critical patent/WO2022247613A1/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
    • H01M4/362—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
    • 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
    • H01M4/04—Processes of manufacture in general
    • H01M4/0402—Methods of deposition of the material
    • H01M4/0421—Methods of deposition of the material involving vapour deposition
    • H01M4/0428—Chemical vapour deposition
    • 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
    • H01M4/04—Processes of manufacture in general
    • H01M4/0471—Processes of manufacture in general involving thermal treatment, e.g. firing, sintering, backing particulate active material, thermal decomposition, pyrolysis
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H01M4/386—Silicon or alloys based on silicon
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—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
    • H01M4/40—Alloys based on alkali metals
    • H01M4/405—Alloys based on lithium
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/628—Inhibitors, e.g. gassing inhibitors, corrosion inhibitors
    • 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
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • 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 disclosure relates to the technical field of lithium ion batteries, for example, to negative electrode materials and their preparation methods and applications.
  • the theoretical capacity of natural graphite and artificial graphite anode materials is 372mAh/g, and it can reach 360mAh/g at present, and it is difficult to increase the capacity of the anode.
  • Graphite anode materials have been difficult to meet the requirements of high energy density batteries.
  • nano-silicon and silicon oxide also have a high specific capacity, the theoretical specific capacity of the nano-silicon negative electrode material is as high as 4200mAh/g (Li 4.4 Si), but the volume expansion is as high as 300% during the lithium intercalation process.
  • the present disclosure provides a method for preparing an anode material, the preparation method comprising the following steps:
  • the molar ratio of lithium in the lithium source in step (2) to silicon in the first matrix is 1 to 4.4 and does not include 1, such as 1, 1.5, 2, 2.5, 3, 3.5, 4 or 4.4.
  • the first substrate provided by the present disclosure is specifically that the surface of nano-silicon is coated with the first carbon coating layer, and the second substrate is specifically that the surface of the amorphous lithium-silicon alloy is coated with the first carbon coating layer.
  • the first carbon coating layer is formed on the surface of nano-silicon, and then the pre-lithiation operation is performed.
  • the lithium source is decomposed in a vacuum sintering environment Lithium metal is obtained, and lithium metal enters through the gap of the first carbon coating layer to react with nano-silicon to obtain a lithium-silicon alloy, which is conducive to forming a protective layer on the surface of the lithium-silicon alloy to be generated, and the obtained lithium-silicon alloy negative electrode
  • the core of the material has both high reversible specific capacity and high first Coulombic efficiency.
  • the outermost layer is coated with carbon to form a dense passivation layer, so that the performance of the inner core will hardly attenuate in dry air, so the final negative electrode material has good environmental stability and high capacity. efficiency and lower expansion.
  • the preparation method provided by the present disclosure has less stringent requirements on the environment than that of the glove box preparation environment, and the synthesis reaction speed is fast, and the purity of the finally obtained material is relatively high.
  • the reason for not using the lithium source to directly react with nano-silicon, and then performing multi-layer carbon coating is to form a carbon protective layer on the silicon surface in advance to passivate the surface of the lithium-silicon alloy to be generated Protect.
  • the carbon source used in the chemical vapor deposition in step (1) includes any one or a combination of at least two of methane, ethylene, acetylene or toluene.
  • the chemical vapor deposition temperature in step (1) is 800-1100°C, such as 800°C, 900°C, 1000°C or 1100°C.
  • the chemical vapor deposition time in step (1) is 1-4 hours, such as 1 hour, 2 hours, 3 hours or 4 hours.
  • the particle size of the nano-silicon in step (1) is ⁇ 100nm, such as 100nm, 90nm, 80nm, 70nm, 60nm or 50nm.
  • the molar ratio of the lithium in the lithium source in step (2) to the silicon in the first matrix is 1.71-3.75, such as 1.71, 3.25 or 3.75.
  • the lithium source in step (2) includes LiH.
  • LiH is used as a lithium source, and the dehydrogenation reaction of LiH and silicon in a vacuum environment is more conducive to the rapid progress of the reaction and lowers the reaction temperature.
  • the mixing method in step (2) is ball milling.
  • the rotational speed of the ball mill is 200-400 rpm, such as 200 rpm, 250 rpm, 300 rpm, 350 rpm or 400 rpm.
  • the ball milling time is 2-5 hours, such as 2 hours, 3 hours, 4 hours or 5 hours.
  • the vacuum sintering temperature in step (2) is 500-700°C, such as 500°C, 550°C, 600°C, 650°C or 700°C.
  • the present disclosure can be sintered at a lower temperature. If the temperature of vacuum sintering is too low, the reaction cannot be carried out or only a part of the reaction will occur. If the sintering temperature is too high, energy will be wasted, because in a certain temperature range The internal reaction can already be completed without excessive temperature.
  • the vacuum sintering time in step (2) is 2-6 hours, such as 2 hours, 3 hours, 4 hours, 5 hours or 6 hours.
  • the drying environment in step (3) is: the dew point temperature is -30°C to -45°C, such as -30°C, -35°C, -40°C or -45°C.
  • the product after vacuum sintering in step (2) is subjected to secondary ball milling.
  • secondary ball milling-high-energy ball milling is performed.
  • High-energy ball milling is beneficial to transform the lithium-silicon alloy material from a crystalline state to an amorphous state, increase the specific capacity of the material, and reduce its expansion.
  • the rotational speed of the secondary ball mill is 400-700 rpm, such as 400 rpm, 500 rpm, 600 rpm, or 700 rpm.
  • the ball-to-material ratio of the secondary ball milling is (30-60):1, such as 30:1, 40:1, 50:1 or 60:1.
  • the method for secondary carbon coating in step (3) includes:
  • the second matrix, the secondary carbon-coated coating agent and the solvent are mixed to obtain a mixture, which is filtered and vacuum-dried, and then carbonized under a protective atmosphere.
  • the method of mixing during the secondary carbon coating in step (2) includes stirring.
  • the stirring speed is 300-600rmp, such as 300rmp, 400rmp, 500rmp or 600rmp.
  • the stirring time is 2-6 hours, such as 2 hours, 3 hours, 4 hours, 5 hours or 6 hours.
  • the carbonization temperature is 650-900°C, such as 650°C, 700°C, 750°C, 800°C, 850°C or 900°C.
  • the carbonization time is 2-4 hours, such as 2 hours, 3 hours or 4 hours.
  • the protective atmosphere includes any one or a combination of at least two of nitrogen atmosphere, argon atmosphere or helium atmosphere.
  • the coating raw material for the secondary carbon coating in step (3) is polyvinylidene fluoride and/or polytetrafluoroethylene.
  • polyvinylidene fluoride and/or polytetrafluoroethylene are selected as raw materials for secondary carbon coating, and these two coating agents have stable performance and do not react with lithium-silicon alloys.
  • the coating amount of the secondary carbon-coated raw material in step (3) is 5-35%, such as 5%, 10%, 15%, 20%, 25%, 30% or 35%, etc.
  • the mixture before the carbonization, is sequentially filtered and vacuum-dried.
  • the preparation method of the negative electrode material comprises the following steps:
  • the second substrate, the secondary carbon-coated raw material with a coating amount of 5 to 35%, and the solvent are stirred at 300 to 600rmp for 2 to 6 hours, and then sequentially Filtration and vacuum drying, and finally carbonization at 650-900°C for 2-4 hours under a protective atmosphere to obtain the negative electrode material;
  • the molar ratio of the lithium in the lithium source in the step (2) to the silicon in the first matrix is 1.71-3.75, and the lithium source in the step (2) includes LiH.
  • the present disclosure provides a negative electrode material in an embodiment, the negative electrode material is obtained by the preparation method of the negative electrode material provided in an embodiment of the present disclosure, the negative electrode material includes an inner core, the first carbon coated on the surface of the inner core a cladding layer and a second outermost carbon cladding layer;
  • the inner core is an amorphous lithium-silicon alloy
  • the chemical formula of the amorphous lithium-silicon alloy is Li x Si, 1 ⁇ x ⁇ 4.4, such as 1.71, 3.25, 3.75, or 4.4.
  • the lithium-silicon alloy is in an amorphous state, and has higher capacity and less expansion.
  • the second carbon coating layer on the outermost layer forms a dense passivation layer, which improves the stability of the lithium-silicon alloy in the inner core, so that its performance hardly attenuates in dry air , and the lithium-silicon alloy as the core has both high reversible specific capacity and high initial Coulombic efficiency, which makes the final negative electrode material have low expansion and stable environment, which improves the capacity and first effect of the battery.
  • the lithium-silicon alloy is coated with double layers of carbon, and the two-layer carbon coating cooperates with the inner core, which is more conducive to the passivation and protection of the surface of the lithium-silicon alloy, so that it is more stable in the air.
  • the amorphous lithium-silicon alloy matrix includes Li 12 Si 7 , Li 13 Si 4 , Li 15 Si 4 and Li 22 One or more of Si 5 .
  • the particle size of the amorphous lithium-silicon alloy is 100nm-1 ⁇ m, such as 100nm, 200nm, 300nm, 400nm, 500nm, 600nm, 700nm, 800nm, 900nm or 1 ⁇ m.
  • the thickness of the first carbon coating layer is 20-50 nm, such as 20 nm, 30 nm, 40 nm or 50 nm.
  • the thickness of the second carbon coating layer is 30-80 nm, such as 30 nm, 50 nm, 60 nm, 70 nm or 800 nm.
  • the present disclosure provides a lithium-ion battery in an embodiment, and the lithium-ion battery includes the negative electrode material provided in an embodiment of the present disclosure.
  • FIG. 1 is a graph showing the cycle performance of the battery provided in Example 1 at 0.1C.
  • the present disclosure provides a method for preparing an anode material, the preparation method comprising the following steps:
  • the molar ratio of the lithium in the lithium source in step (2) to the silicon in the first matrix is 1-4.4 and 1 is not included.
  • the first substrate provided by the present disclosure is specifically that the surface of nano-silicon is coated with the first carbon coating layer, and the second substrate is specifically that the surface of the amorphous lithium-silicon alloy is coated with the first carbon coating layer.
  • the first carbon coating layer is formed on the surface of nano-silicon, and then the pre-lithiation operation is performed, and the lithium source is mixed with the lithium source in a vacuum sintering environment.
  • the lithium metal which enters through the gap of the first carbon coating layer and reacts with nano-silicon to obtain a lithium-silicon alloy, which is conducive to the formation of a protective layer on the surface of the lithium-silicon alloy to be generated, and the obtained lithium-silicon alloy
  • the core of the anode material has both high reversible specific capacity and high first Coulombic efficiency.
  • the outermost layer is coated with carbon to form a dense passivation layer, so that the performance of the inner core will hardly attenuate in dry air, so the final negative electrode material has good environmental stability and high capacity. efficiency and lower expansion.
  • the preparation method provided by the present disclosure has less stringent requirements on the environment than that of the glove box preparation environment, and the synthesis reaction speed is fast, and the purity of the finally obtained material is relatively high.
  • the reason for not using the lithium source to directly react with nano-silicon, and then performing multi-layer carbon coating is to form a carbon protective layer on the silicon surface in advance to passivate the surface of the lithium-silicon alloy to be generated Protect.
  • the carbon source used in the chemical vapor deposition in step (1) includes any one or a combination of at least two of methane, ethylene, acetylene or toluene.
  • the chemical vapor deposition temperature in step (1) is 800-1100°C, such as 800°C, 900°C, 1000°C or 1100°C.
  • the chemical vapor deposition time in step (1) is 1-4 hours, such as 1 hour, 2 hours, 3 hours or 4 hours.
  • the particle size of the nano-silicon in step (1) is ⁇ 100nm, such as 100nm, 90nm, 80nm, 70nm, 60nm or 50nm.
  • the molar ratio of the lithium in the lithium source in step (2) to the silicon in the first matrix is 1.71-3.75, such as 1.71, 3.25 or 3.75.
  • the lithium source in step (2) includes LiH.
  • LiH is used as a lithium source, and the dehydrogenation reaction of LiH and silicon in a vacuum environment is more conducive to the rapid progress of the reaction and lowers the reaction temperature.
  • the mixing method in step (2) is ball milling.
  • the rotational speed of the ball mill is 200-400 rpm, such as 200 rpm, 250 rpm, 300 rpm, 350 rpm or 400 rpm.
  • the ball milling time is 2-5 hours, such as 2 hours, 3 hours, 4 hours or 5 hours.
  • the vacuum sintering temperature in step (2) is 500-700°C, such as 500°C, 550°C, 600°C, 650°C or 700°C.
  • the present disclosure can be sintered at a lower temperature. If the temperature of vacuum sintering is too low, the reaction cannot be carried out or only a part of the reaction will occur. If the sintering temperature is too high, energy will be wasted, because in a certain temperature range The internal reaction can already be completed without excessive temperature.
  • the vacuum sintering time in step (2) is 2-6 hours, such as 2 hours, 3 hours, 4 hours, 5 hours or 6 hours.
  • the drying environment in step (3) is: the dew point temperature is -30°C to -45°C, such as -30°C, -35°C, -40°C or -45°C.
  • the product after vacuum sintering in step (2) is subjected to secondary ball milling.
  • secondary ball milling-high-energy ball milling is performed.
  • High-energy ball milling is beneficial to transform the lithium-silicon alloy material from a crystalline state to an amorphous state, increase the specific capacity of the material, and reduce its expansion.
  • the rotational speed of the secondary ball mill is 400-700 rpm, such as 400 rpm, 500 rpm, 600 rpm, or 700 rpm.
  • the ball-to-material ratio of the secondary ball milling is (30-60):1, such as 30:1, 40:1, 50:1 or 60:1.
  • the method for secondary carbon coating in step (3) includes:
  • the second matrix, the secondary carbon-coated coating agent and the solvent are mixed to obtain a mixture, which is filtered and vacuum-dried, and then carbonized under a protective atmosphere.
  • the method of mixing during the secondary carbon coating in step (2) includes stirring.
  • the stirring speed is 300-600rmp, such as 300rmp, 400rmp, 500rmp or 600rmp.
  • the stirring time is 2-6 hours, such as 2 hours, 3 hours, 4 hours, 5 hours or 6 hours.
  • the carbonization temperature is 650-900°C, such as 650°C, 700°C, 750°C, 800°C, 850°C or 900°C.
  • the carbonization time is 2-4 hours, such as 2 hours, 3 hours or 4 hours.
  • the protective atmosphere includes any one or a combination of at least two of nitrogen atmosphere, argon atmosphere or helium atmosphere.
  • the coating raw material for the secondary carbon coating in step (3) is polyvinylidene fluoride and/or polytetrafluoroethylene.
  • polyvinylidene fluoride and/or polytetrafluoroethylene are selected as raw materials for secondary carbon coating, and these two coating agents have stable performance and do not react with lithium-silicon alloys.
  • the coating amount of the secondary carbon-coated raw material in step (3) is 5-35%, such as 5%, 10%, 15%, 20%, 25%, 30% or 35%, etc.
  • the mixture before the carbonization, is sequentially filtered and vacuum-dried.
  • the preparation method of the negative electrode material comprises the following steps:
  • the second substrate, the secondary carbon-coated raw material with a coating amount of 5 to 35%, and the solvent are stirred at 300 to 600rmp for 2 to 6 hours, and then sequentially Filtration and vacuum drying, and finally carbonization at 650-900°C for 2-4 hours under a protective atmosphere to obtain the negative electrode material;
  • the molar ratio of the lithium in the lithium source in the step (2) to the silicon in the first matrix is 1.71-3.75, and the lithium source in the step (2) includes LiH.
  • the present disclosure provides an anode material in an embodiment, the anode material is obtained by the preparation method of the anode material provided in an embodiment, the anode material includes an inner core, a first carbon coating layer coated on the surface of the inner core, and a second carbon coating located on the outermost layer;
  • the inner core is an amorphous lithium-silicon alloy
  • the chemical formula of the amorphous lithium-silicon alloy is Li x Si, 1 ⁇ x ⁇ 4.4, such as 1.71, 3.25, 3.75, or 4.4.
  • the lithium-silicon alloy is in an amorphous state, and has higher capacity and less expansion.
  • the second carbon coating layer on the outermost layer forms a dense passivation layer, which improves the stability of the lithium-silicon alloy in the inner core, so that its performance hardly attenuates in dry air , and the lithium-silicon alloy as the core has both high reversible specific capacity and high initial Coulombic efficiency, which makes the final negative electrode material have low expansion and stable environment, which improves the capacity and first effect of the battery.
  • the lithium-silicon alloy is coated with double-layer carbon, and the two-layer carbon coating cooperates with the inner core, which is more conducive to the surface passivation and protection of the lithium-silicon alloy, so that it is more stable in the air.
  • the amorphous lithium-silicon alloy matrix includes Li 12 Si 7 , Li 13 Si 4 , Li 15 Si 4 and Li 22 One or more of Si 5 .
  • the particle size of the amorphous lithium-silicon alloy is 100nm-1 ⁇ m, such as 100nm, 200nm, 300nm, 400nm, 500nm, 600nm, 700nm, 800nm, 900nm or 1 ⁇ m.
  • the thickness of the first carbon coating layer is 20-50 nm, such as 20 nm, 30 nm, 40 nm or 50 nm.
  • the thickness of the second carbon coating layer is 30-80 nm, such as 30 nm, 50 nm, 60 nm, 70 nm or 800 nm.
  • the present disclosure provides a lithium-ion battery in an embodiment, and the lithium-ion battery includes the negative electrode material provided in an embodiment of the present disclosure.
  • This embodiment provides a negative electrode material, the negative electrode material includes the negative electrode material includes an inner core, a first carbon coating layer coated on the surface of the inner core, and a second carbon coating layer located on the outermost layer;
  • the inner core is an amorphous lithium-silicon alloy with a particle size of 100 nm
  • the chemical formula of the amorphous lithium-silicon alloy is Li 12 Si 7
  • the thickness of the first carbon coating layer is 20 nm
  • the second The thickness of the two-carbon coating layer is 50 nm.
  • the preparation method of the negative electrode material is as follows:
  • the double-layer carbon-coated lithium-silicon alloy anode material has excellent cycle stability, and the capacity retention rate is greater than 90% after 50 weeks of charging and discharging at 0.1C.
  • This embodiment provides a negative electrode material, the negative electrode material includes the negative electrode material includes an inner core, a first carbon coating layer coated on the surface of the inner core, and a second carbon coating layer located on the outermost layer;
  • the inner core is an amorphous lithium-silicon alloy with a grain size of 120nm
  • the chemical formula of the amorphous lithium-silicon alloy is Li 3.25 Si
  • the thickness of the first carbon coating layer is 40nm
  • the second The thickness of the carbon coating layer was 60 nm.
  • the preparation method of the negative electrode material is as follows:
  • This embodiment provides a negative electrode material, the negative electrode material includes the negative electrode material includes an inner core, a first carbon coating layer coated on the surface of the inner core, and a second carbon coating layer located on the outermost layer;
  • the inner core is a lithium-silicon alloy with a particle size of 100 nm
  • the chemical formula of the lithium-silicon alloy is Li 3.75 Si
  • the thickness of the first carbon coating layer is 30 nm
  • the thickness of the second carbon coating layer is 80nm.
  • the preparation method of the negative electrode material is as follows:
  • the thickness of the first carbon coating layer in this embodiment is 60 nm.
  • the thickness of the second carbon coating layer in this embodiment is 90 nm.
  • the difference between this embodiment and Embodiment 1 is that the vacuum sintering temperature in step (2) of this embodiment is 750°C.
  • This comparative example provides a negative electrode material, the negative electrode material includes the negative electrode material includes an inner core and a first carbon coating layer coated on the surface of the inner core;
  • the inner core is an amorphous lithium-silicon alloy with a grain size of 100 nm
  • the chemical formula of the amorphous lithium-silicon alloy is Li 12 Si 7
  • the thickness of the first carbon coating layer is 20 nm.
  • step (3) is not performed, that is, there is no secondary carbon coating process.
  • This comparative example provides a commercially available silicon oxide negative electrode material with a particle size of 5 ⁇ m. All the other preparation methods and parameters are consistent with Example 1.
  • the negative electrode material provided by the present disclosure not only has good environmental stability, but also has high capacity and first effect, so that the battery provided by the present disclosure has a reversible charge-discharge capacity Above 1680mAh/g, the first coulombic efficiency can reach above 122%, and the capacity retention rate after 50 cycles is above 90%.
  • the thickness of the first carbon coating layer and the second carbon coating layer are within a certain range, the battery The charge-discharge reversible capacity is above 2124mAh/g, the first Coulombic efficiency can reach above 135.3%, and the capacity retention rate after 50 cycles is above 92%.
  • Example 1 From the data results of Example 1, Example 4 and Example 5, it can be seen that no matter whether the thickness of the first carbon coating layer or the second carbon coating layer becomes thicker, the first effect of the negative electrode material increases with the increase of the coating thickness. The decline is obvious, but the passivation effect on the surface becomes better, and the cycle performance of the material will be improved.
  • Example 1 From the data results of Example 1 and Example 6, it can be seen that when the vacuum heat treatment temperature rises to 750°C, the obtained lithium-silicon alloy material capacity, first effect and cycle performance have little change, indicating that when the pre-lithium reaction temperature is reached, Increasing the reaction temperature has little effect on the performance of the material, but only increases energy consumption.
  • Example 1 From the data results of Example 1 and Comparative Example 1, it can be seen that after the lithium-silicon alloy core is prepared, without secondary carbon coating, the passivation protection effect of the material surface is obviously not as good as that of Example 1, resulting in a significant decline in the cycle performance of the material.
  • the second carbon coating layer on the outermost layer forms a dense passivation layer, which improves the stability of the amorphous lithium-silicon alloy in the inner core, making it stable in dry air. There is almost no attenuation in the medium performance.
  • the first carbon coating layer on the surface of the core is first coated on the nano-silicon surface, and then lithium metal enters through the gaps in the carbon coating layer to form an amorphous lithium-silicon alloy, and the lithium-silicon alloy acts as
  • the core has both high reversible specific capacity and high initial Coulombic efficiency, which makes the final negative electrode material have a low expansion coefficient and a stable environment, which improves the capacity and first effect of the battery.

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Abstract

本公开提供一种负极材料及其制备方法与用途。所述负极材料包括内核、包覆于内核表面的第一碳包覆层和位于最外层的第二碳包覆层；其中，所述内核为非晶态锂硅合金。本公开通过在锂硅合金表面进行双层碳包覆，使得锂硅合金内核在干燥空气中性能几乎不发生衰减，可以使负极材料具有较好的环境稳定性以及循环稳定性。

Description

一种负极材料及其制备方法与用途 技术领域
本公开涉及锂离子电池技术领域，例如涉及负极材料及其制备方法与用途。
背景技术
现随着动力电池能量密度以及其他综合性能要求不断提高，天然石墨和人造石墨负极材料理论容量为372mAh/g,目前已经能做到360mAh/g，再提高负极容量已经比较困难，天然石墨和人造石墨负极材料已经很难满足高能量密度电池的要求。而纳米硅，氧化亚硅虽也具有较高的比容量，纳米硅负极材料理论比容量高达4200mAh/g(Li 4.4Si)，但是在嵌锂过程中体积膨胀高达300％以上，这不仅仅会破坏电极的结构，造成掉料等问题，还会导致Si颗粒表面形成的SEI膜出现裂纹，导致电解液持续的分解。氧化亚硅负极材料膨胀相对硅负极较小，但其首次库伦效率较低，只有75％左右。
因此如何得到一种具有高容量、高首效和低膨胀系数等综合性能较优的负极材料，是目前亟待解决的技术问题。
发明内容
本公开在一实施例中提供一种负极材料的制备方法，所述制备方法包括以下步骤：
(1)通过化学气相沉积法在纳米硅表面沉积第一碳包覆层，得到第一基体；
(2)将第一基体和锂源混合，真空烧结，得到第二基体；
(3)对第二基体在干燥环境下进行二次碳包覆，得到所述负极材料；
其中，步骤(2)所述锂源中的锂与第一基体中的硅的摩尔比为1～4.4且不包括1，例如1、1.5、2、2.5、3、3.5、4或4.4等。
本公开所提供的第一基体具体为纳米硅表面包覆有第一碳包覆层，第二基体具体为非晶态锂硅合金表面包覆有第一碳包覆层。
本公开一实施例所提供的制备方法，通过先于纳米硅表面形成第一碳包覆层，然后再进行预锂化的操作，通过与锂源混合，在真空烧结的环境下使得锂源分解得到锂金属，锂金属通过第一碳包覆层的空隙处进入与纳米硅发生反应，得到锂硅合金，这样有利于在即将生成的锂硅合金表面形成保护层，且得到的锂硅合金负极材料内核既有较高的可逆比容量，又有很高的首次库伦效率。最 外层再进行碳包覆，可以形成一层致密的钝化层，使得内核在干燥空气中性能几乎不发生衰减，因此最终得到的负极材料环境稳定性好，且具有较高的容量，首效以及较低的膨胀。同时本公开所提供的制备方法对环境要求比在手套箱制备环境要求不那么苛刻，且合成反应速度快，最终得到的材料纯度较高。
在本公开提供的一实施例中，不采用锂源直接与纳米硅反应，再进行多层碳包覆的原因为预先在硅表面形成碳保护层，对将要生成的锂硅合金表面进行钝化保护。
在一实施例中，步骤(1)所述化学气相沉积中采用的碳源包括甲烷、乙烯、乙炔或甲苯中的任意一种或至少两种的组合。
在一实施例中，步骤(1)所述化学气相沉积的温度为800～1100℃，例如800℃、900℃、1000℃或1100℃等。
在一实施例中，步骤(1)所述化学气相沉积的时间为1～4h，例如1h、2h、3h或4h等。
在一实施例中，步骤(1)所述纳米硅的粒径≤100nm，例如100nm、90nm、80nm、70nm、60nm或50nm等。
在一实施例中，步骤(2)所述锂源中的锂与第一基体中的硅的摩尔比为1.71～3.75，例如1.71、3.25或3.75等。
在一实施例中，步骤(2)中所述锂源包括LiH。
本公开的一实施例中，以LiH作为锂源，LiH与硅在真空环境下脱氢反应更有利于反应的快速进行，并且降低反应的温度。
在一实施例中，步骤(2)所述混合的方法为球磨。
在一实施例中，所述球磨的转速为200～400rmp，例如200rmp、250rmp、300rmp、350rmp或400rmp等。
在一实施例中，所述球磨的时间为2～5h，例如2h、3h、4h或5h等。
在一实施例中，步骤(2)所述真空烧结的温度为500～700℃，例如500℃、550℃、600℃、650℃或700℃等。
本公开可以在较低的温度下进行烧结，如果真空烧结的温度过低，会导致反应不能进行或只发生部分反应，而烧结温度过高，会形成对能源的浪费，因为在一定的温度范围内反应已经可以完成，不需要过高的温度。
在一实施例中，步骤(2)所述真空烧结的时间为2～6h，例如2h、3h、4h、5h或6h等。
在一实施例中，步骤(3)所述干燥环境为：露点温度为-30～-45℃，例如-30℃、-35℃、-40℃或-45℃等。
在一实施例中，步骤(2)所述真空烧结后，对真空烧结后的产物进行二次球磨。
本公开的一实施例中，在真空烧结后，进行二次球磨-高能球磨，高能球磨有利于使锂硅合金材料由晶态转变成非晶态，提升材料的比容量，并降低其膨胀。
在一实施例中，所述二次球磨的转速为400～700rmp，例如400rmp、500rmp、600rmp或700rmp等。
在一实施例中，所述二次球磨的球料比为(30～60):1，例如30:1、40:1、50:1或60:1等。
在一实施例中，步骤(3)所述二次碳包覆的方法包括：
将第二基体、二次碳包覆的包覆剂和溶剂混合，得到混合物，过滤和真空干燥，然后在保护性气氛下炭化。
在一实施例中，步骤(2)所述二次碳包覆过程中混合的方法包括搅拌。
在一实施例中，所述搅拌的转速为300～600rmp，例如300rmp、400rmp、500rmp或600rmp等。
在一实施例中，所述搅拌的时间为2～6h，例如2h、3h、4h、5h或6h等。
在一实施例中，所述炭化的温度为650～900℃，例如650℃、700℃、750℃、800℃、850℃或900℃等。
在一实施例中，所述炭化的时间为2～4h，例如2h、3h或4h等。
在一实施例中，所述保护性气氛包括氮气气氛、氩气气氛或氦气气氛中的任意一种或至少两种的组合。
在一实施例中，步骤(3)所述二次碳包覆的包覆原料为聚偏氟乙烯和/或聚四氟乙烯。
本公开的一实施例中，二次碳包覆的原料选用聚偏氟乙烯和/或聚四氟乙烯， 这两种包覆剂性能稳定，不与锂硅合金发生反应。
在一实施例中，以所述负极材料的质量为100％计，步骤(3)所述二次碳包覆原料的包覆量为5～35％，例如5％、10％、15％、20％、25％、30％或35％等。
在一实施例中，所述炭化前，对所述混合物依次进行过滤和真空干燥。
在一实施例中，所述负极材料的制备方法包括以下步骤：
(1)通过化学气相沉积法在粒径≤100nm的纳米硅表面沉积第一碳包覆层，化学气相沉积过程中，温度为800～1100℃，时间为1～4h，得到第一基体；
(2)将第一基体和锂源以200～400rmp球磨2～5h，在500～700℃下真空烧结2～6h，对真空烧结后的产物以400～700rmp的转速进行二次球磨，球料比为(30～60):1，得到第二基体；
(3)在露点温度为-30～-45℃下，将第二基体、包覆量为5～35％的二次碳包覆的原料和溶剂以300～600rmp搅拌2～6h，然后依次进行过滤和真空干燥，最后在保护性气氛下以650～900℃炭化2～4h，得到所述负极材料；
其中，步骤(2)所述锂源中的锂与第一基体中的硅的摩尔比为1.71～3.75，步骤(2)中所述锂源包括LiH。
本公开在一实施例中提供一种负极材料，所述负极材料通过本公开提供的一实施例提供的负极材料的制备方法得到，所述负极材料包括内核、包覆于内核表面的第一碳包覆层和位于最外层的第二碳包覆层；
其中，所述内核为非晶态锂硅合金，所述非晶态锂硅合金的化学式为Li xSi，1＜x≤4.4，例如1.71、3.25、3.75、或4.4等。
本公开的一实施例中，锂硅合金为非晶态，非具有较高的容量以及较小的膨胀。
本公开所提供的负极材料，最外层的第二碳包覆层形成了一层致密的钝化层，提高了内核中锂硅合金的稳定性，使其在干燥空气中性能几乎不发生衰减，且锂硅合金作为内核，既有较高的可逆比容量，又有很高的首次库伦效率，使得最终得到的负极材料膨胀低，环境稳定好，提升了电池的容量和首效。且本公开中锂硅合金外进行了双层碳包覆，两层碳包覆与内核相互配合，更有利于锂硅合金的表面钝化及保护，从而在空气中更稳定。
在一实施例中，所述Li xSi中，1.71≤x≤3.75，从组成上，所述非晶态锂硅合金基体包括Li 12Si 7、Li 13Si 4、Li 15Si 4和Li 22Si 5中的一种或多种。
在一实施例中，所述非晶态锂硅合金的粒径为100nm～1μm，例如100nm、200nm、300nm、400nm、500nm、600nm、700nm、800nm、900nm或1μm等。
在一实施例中，所述第一碳包覆层的厚度为20～50nm，例如20nm、30nm、40nm或50nm等。
在一实施例中，所述第二碳包覆层的厚度为30～80nm，例如30nm、50nm、60nm、70nm或800nm等。
本公开在一实施例中提供一种锂离子电池，所述锂离子电池包括本公开一实施例中提供的负极材料。
附图说明
附图用来提供对本文技术方案的进一步理解，并且构成说明书的一部分，与本申请的实施例一起用于解释本文的技术方案，并不构成对本文技术方案的限制。
图1为实施例1所提供的电池在0.1C的循环性能曲线图。
具体实施方式
本公开在一实施例中提供一种负极材料的制备方法，所述制备方法包括以下步骤：
(1)通过化学气相沉积法在纳米硅表面沉积第一碳包覆层，得到第一基体；
(2)将第一基体和锂源混合，真空烧结，得到第二基体；
(3)对第二基体在干燥环境下进行二次碳包覆，得到所述负极材料；
其中，步骤(2)所述锂源中的锂与第一基体中的硅的摩尔比为1～4.4且不包括1。
本公开所提供的第一基体具体为纳米硅表面包覆有第一碳包覆层，第二基体具体为非晶态锂硅合金表面包覆有第一碳包覆层。
本公开一实施例中所提供的制备方法，通过先于纳米硅表面形成第一碳包覆层，然后再进行预锂化的操作，通过与锂源混合，在真空烧结的环境下使得锂源分解得到锂金属，锂金属通过第一碳包覆层的空隙处进入与纳米硅发生反应，得到锂硅合金，这样有利于在即将生成的锂硅合金表面形成保护层，且得 到的锂硅合金负极材料内核既有较高的可逆比容量，又有很高的首次库伦效率。最外层再进行碳包覆，可以形成一层致密的钝化层，使得内核在干燥空气中性能几乎不发生衰减，因此最终得到的负极材料环境稳定性好，且具有较高的容量，首效以及较低的膨胀。同时本公开所提供的制备方法对环境要求比在手套箱制备环境要求不那么苛刻，且合成反应速度快，最终得到的材料纯度较高。
在本公开提供的一实施例中，不采用锂源直接与纳米硅反应，再进行多层碳包覆的原因为预先在硅表面形成碳保护层，对将要生成的锂硅合金表面进行钝化保护。
在一实施例中，步骤(1)所述化学气相沉积中采用的碳源包括甲烷、乙烯、乙炔或甲苯中的任意一种或至少两种的组合。
在一实施例中，步骤(1)所述化学气相沉积的温度为800～1100℃，例如800℃、900℃、1000℃或1100℃等。
在一实施例中，步骤(1)所述化学气相沉积的时间为1～4h，例如1h、2h、3h或4h等。
在一实施例中，步骤(1)所述纳米硅的粒径≤100nm，例如100nm、90nm、80nm、70nm、60nm或50nm等。
在一实施例中，步骤(2)所述锂源中的锂与第一基体中的硅的摩尔比为1.71～3.75，例如1.71、3.25或3.75等。
在一实施例中，步骤(2)中所述锂源包括LiH。
本公开的一实施例中，以LiH作为锂源，LiH与硅在真空环境下脱氢反应更有利于反应的快速进行，并且降低反应的温度。
在一实施例中，步骤(2)所述混合的方法为球磨。
在一实施例中，所述球磨的转速为200～400rmp，例如200rmp、250rmp、300rmp、350rmp或400rmp等。
在一实施例中，所述球磨的时间为2～5h，例如2h、3h、4h或5h等。
在一实施例中，步骤(2)所述真空烧结的温度为500～700℃，例如500℃、550℃、600℃、650℃或700℃等。
本公开可以在较低的温度下进行烧结，如果真空烧结的温度过低，会导致反应不能进行或只发生部分反应，而烧结温度过高，会形成对能源的浪费，因 为在一定的温度范围内反应已经可以完成，不需要过高的温度。
在一实施例中，步骤(2)所述真空烧结的时间为2～6h，例如2h、3h、4h、5h或6h等。
在一实施例中，步骤(3)所述干燥环境为：露点温度为-30～-45℃，例如-30℃、-35℃、-40℃或-45℃等。
在一实施例中，步骤(2)所述真空烧结后，对真空烧结后的产物进行二次球磨。
本公开的一实施例中，在真空烧结后，进行二次球磨-高能球磨，高能球磨有利于使锂硅合金材料由晶态转变成非晶态，提升材料的比容量，并降低其膨胀。
在一实施例中，所述二次球磨的转速为400～700rmp，例如400rmp、500rmp、600rmp或700rmp等。
在一实施例中，所述二次球磨的球料比为(30～60):1，例如30:1、40:1、50:1或60:1等。
在一实施例中，步骤(3)所述二次碳包覆的方法包括：
将第二基体、二次碳包覆的包覆剂和溶剂混合，得到混合物，过滤和真空干燥，然后在保护性气氛下炭化。
在一实施例中，步骤(2)所述二次碳包覆过程中混合的方法包括搅拌。
在一实施例中，所述搅拌的转速为300～600rmp，例如300rmp、400rmp、500rmp或600rmp等。
在一实施例中，所述搅拌的时间为2～6h，例如2h、3h、4h、5h或6h等。
在一实施例中，所述炭化的温度为650～900℃，例如650℃、700℃、750℃、800℃、850℃或900℃等。
在一实施例中，所述炭化的时间为2～4h，例如2h、3h或4h等。
在一实施例中，所述保护性气氛包括氮气气氛、氩气气氛或氦气气氛中的任意一种或至少两种的组合。
在一实施例中，步骤(3)所述二次碳包覆的包覆原料为聚偏氟乙烯和/或聚四氟乙烯。
本公开的一实施例中，二次碳包覆的原料选用聚偏氟乙烯和/或聚四氟乙烯，这两种包覆剂性能稳定，不与锂硅合金发生反应。
在一实施例中，以所述负极材料的质量为100％计，步骤(3)所述二次碳包覆原料的包覆量为5～35％，例如5％、10％、15％、20％、25％、30％或35％等。
在一实施例中，所述炭化前，对所述混合物依次进行过滤和真空干燥。
在一实施例中，所述负极材料的制备方法包括以下步骤：
(1)通过化学气相沉积法在粒径≤100nm的纳米硅表面沉积第一碳包覆层，化学气相沉积过程中，温度为800～1100℃，时间为1～4h，得到第一基体；
(2)将第一基体和锂源以200～400rmp球磨2～5h，在500～700℃下真空烧结2～6h，对真空烧结后的产物以400～700rmp的转速进行二次球磨，球料比为(30～60):1，得到第二基体；
(3)在露点温度为-30～-45℃下，将第二基体、包覆量为5～35％的二次碳包覆的原料和溶剂以300～600rmp搅拌2～6h，然后依次进行过滤和真空干燥，最后在保护性气氛下以650～900℃炭化2～4h，得到所述负极材料；
其中，步骤(2)所述锂源中的锂与第一基体中的硅的摩尔比为1.71～3.75，步骤(2)中所述锂源包括LiH。
本公开在一实施例中提供一种负极材料，所述负极材料通过一实施例提供的负极材料的制备方法得到，所述负极材料包括内核、包覆于内核表面的第一碳包覆层和位于最外层的第二碳包覆层；
其中，所述内核为非晶态锂硅合金，所述非晶态锂硅合金的化学式为Li xSi，1＜x≤4.4，例如1.71、3.25、3.75、或4.4等。
本公开的一实施例中，锂硅合金为非晶态，非具有较高的容量以及较小的膨胀。
本公开所提供的负极材料，最外层的第二碳包覆层形成了一层致密的钝化层，提高了内核中锂硅合金的稳定性，使其在干燥空气中性能几乎不发生衰减，且锂硅合金作为内核，既有较高的可逆比容量，又有很高的首次库伦效率，使得最终得到的负极材料膨胀低，环境稳定好，提升了电池的容量和首效。且本公开中锂硅合金外进行了双层碳包覆，两层碳包覆与内核相互配合，更有利于 锂硅合金的表面钝化及保护，从而在空气中更稳定。
在一实施例中，所述Li xSi中，1.71≤x≤3.75，从组成上，所述非晶态锂硅合金基体包括Li 12Si 7、Li 13Si 4、Li 15Si 4和Li 22Si 5中的一种或多种。
在一实施例中，所述非晶态锂硅合金的粒径为100nm～1μm，例如100nm、200nm、300nm、400nm、500nm、600nm、700nm、800nm、900nm或1μm等。
在一实施例中，所述第一碳包覆层的厚度为20～50nm，例如20nm、30nm、40nm或50nm等。
在一实施例中，所述第二碳包覆层的厚度为30～80nm，例如30nm、50nm、60nm、70nm或800nm等。
本公开在一实施例中提供一种锂离子电池，所述锂离子电池包括本公开一实施例中提供的负极材料。
实施例1
本实施例提供一种负极材料，所述负极材料包括所述负极材料包括内核、包覆于内核表面的第一碳包覆层和位于最外层的第二碳包覆层；
其中，所述内核为粒径为100nm的非晶态锂硅合金，所述非晶态锂硅合金的化学式为Li 12Si 7，所述第一碳包覆层的厚度为20nm，所述第二碳包覆层的厚度为50nm。
所述负极材料的制备方法如下：
(1)将5g粒径为60nm的纳米硅放入CVD炉中，先通入氩气进行置换，再通入甲烷进行气相沉积，沉积温度为900℃，时间为1h，得到第一基体；
(2)将LiH和第一基体以12:7的摩尔比加入混料机中，球料比为30:1，以300rmp球磨4h，在600℃下真空烧结5h，然后将真空烧结后的产物以600rmp的转速球磨48h，球料比为60:1，得到第二基体；
(3)在露点温度-45℃的环境下，将第二基体、包覆量为10wt％的聚偏氟乙烯和四氢呋喃以400rmp搅拌3h，然后依次进行过滤和真空干燥，最后在氩气气氛下以700℃炭化2h，得到所述负极材料。
从图1可以看出，经过双层碳包覆的锂硅合金负极材料具有优异的循环稳定性，0.1C充放50周后容量保持率大于90％。
实施例2
本实施例提供一种负极材料，所述负极材料包括所述负极材料包括内核、包覆于内核表面的第一碳包覆层和位于最外层的第二碳包覆层；
其中，所述内核为粒径为120nm的非晶态锂硅合金，所述非晶态锂硅合金的化学式为Li 3.25Si，所述第一碳包覆层的厚度为40nm，所述第二碳包覆层的厚度为60nm。
所述负极材料的制备方法如下：
(1)将5g粒径为100nm的纳米硅放入CVD炉中，先通入氩气进行置换，再通入乙炔进行气相沉积，沉积温度为1100℃，时间为4h，得到第一基体；
(2)将LiH和第一基体以3.25:1的摩尔比加入混料机中，球料比为30:1，以400rmp球磨5h，在700℃下真空烧结2h，然后将真空烧结后的产物以500rmp的转速球磨60h，球料比为40:1，得到第二基体；
(3)在露点温度-40℃的环境下，将第二基体、包覆量为15wt％的聚四氟乙烯和四氢呋喃以300rmp搅拌2h，然后依次进行过滤和真空干燥，最后在氩气气氛下以900℃炭化4h，得到所述负极材料。
实施例3
本实施例提供一种负极材料，所述负极材料包括所述负极材料包括内核、包覆于内核表面的第一碳包覆层和位于最外层的第二碳包覆层；
其中，所述内核为粒径为100nm的锂硅合金，所述锂硅合金的化学式为Li 3.75Si，所述第一碳包覆层的厚度为30nm，所述第二碳包覆层的厚度为80nm。
所述负极材料的制备方法如下：
(1)将5g粒径为70nm的纳米硅放入CVD炉中，先通入氩气进行置换，再通入乙烯进行气相沉积，沉积温度为950℃，时间为2h，得到第一基体；
(2)将LiH和第一基体以3.75:1的摩尔比加入混料机中，球料比为30:1，以600rmp球磨5h，在500℃下真空烧结6h，然后将真空烧结后的产物以700rmp的转速球磨48h，球料比为30:1，得到第二基体；
(3)在露点温度-30℃的环境下，将第二基体、包覆量为20wt％的聚四氟乙烯和四氢呋喃以300rmp搅拌2h，然后依次进行过滤和真空干燥，最后在氩气气氛下以800℃炭化3h，得到所述负极材料。
实施例4
本实施例与实施例1的区别为，本实施例中所述第一碳包覆层的厚度为60nm。
其余制备方法与参数与实施例1保持一致。
实施例5
本实施例与实施例1的区别为，本实施例中所述第二碳包覆层的厚度为90nm。
其余制备方法与参数与实施例1保持一致。
实施例6
本实施例与实施例1的区别为，本实施例步骤(2)中的真空烧结温度为750℃。
其余制备方法与参数与实施例1保持一致。
对比例1
本对比例提供一种负极材料，所述负极材料包括所述负极材料包括内核和包覆于内核表面的第一碳包覆层；
其中，所述内核为粒径为100nm的非晶态锂硅合金，所述非晶态锂硅合金的化学式为Li 12Si 7，所述第一碳包覆层的厚度为20nm。
本对比例与实施例1的区别为，不进行步骤(3)，即没有二次碳包覆的过程。
其余制备方法与参数与实施例1保持一致。
对比例2
本对比例提供一种市售的粒径为5μm的氧化亚硅负极材料。其余制备方法与参数与实施例1保持一致。
将实施例1-6与对比例1-2所提供的负极材料作为负极活性物质，以负极活性物质:SP:PVDF＝70:15:15的质量比，制备得到负极，然后制备得到扣式电池，进行电化学性能测试，0.1C充放电，其结果如表1所示：
表1
  充放电可逆容量 首次库伦效率％ 50周循环容
  mAh/g   量保持率(％)
实施例1 2124 135.3 92
实施例2 2160 138 94
实施例3 2276 141 95
实施例4 1805 122 92
实施例5 1680 147.6 94
实施例6 2130 136.4 90
对比例1 2258 137.5 70
对比例2 1220 86.8 93
从表1中的实施例1-6的数据结果可知，本公开所提供的负极材料，不仅环境稳定性好，且具有较高的容量和首效，使得本公开提供的电池，充放电可逆容量在1680mAh/g以上，首次库伦效率可达122％以上，且循环50周后其容量保持率在90％以上，当第一碳包覆层和第二碳包覆厚度在一定范围内时，电池的充放电可逆容量在2124mAh/g以上，首次库伦效率可达135.3％以上，且循环50周后其容量保持率在92％以上。
从实施例1与实施例4和实施例5的数据结果可知，无论是第一碳包覆层还是第二碳包覆层厚度变厚，负极材料的首效都随着包覆厚度的增加而下降明显，但却对其表面钝化效果变好，从材料的循环性能会有所提升。
从实施例1与实施例6的数据结果可知，当真空热处理温度升到750℃时，得到的锂硅合金材料容量，首效以及循环性能变化都不大，说明当达到预锂反应温度时，再提高反应温度对材料的性能影响不大，徒增加能源的消耗。
从实施例1与对比例1的数据结果可知，制备得到锂硅合金内核后，不进行二次碳包覆，材料表面的钝化保护效果明显不如实施例1，导致材料的循环性能衰退明显。
从实施例1-6与对比例2的数据结果可知，氧化亚硅预锂后的容量与硅预锂的容量和首效下降明显，这是因为氧化亚硅中的氧与锂发生反应生成了硅酸锂， 为非活性物质。但同时由于硅酸锂的存在使得循环性能提升。
综上，本公开所提供的负极材料，最外层的第二碳包覆层形成了一层致密的钝化层，提高了内核中非晶态锂硅合金的稳定性，使其在干燥空气中性能几乎不发生衰减，内核表面的第一碳包覆层先包覆于纳米硅表面，然后锂金属通过碳包覆层的空隙处进入，形成非晶态锂硅合金，且锂硅合金作为内核，既有较高的可逆比容量，又有很高的首次库伦效率，使得最终得到的负极材料膨胀系数低，环境稳定好，提升了电池的容量和首效。

Claims (15)

  1. 一种负极材料的制备方法，所述制备方法包括以下步骤：
    (1)通过化学气相沉积法在纳米硅表面沉积第一碳包覆层，得到第一基体；
    (2)将第一基体和锂源混合，真空烧结，得到第二基体；
    (3)对第二基体在干燥环境下进行二次碳包覆，得到所述负极材料；
    其中，步骤(2)所述锂源中的锂与第一基体中的硅的摩尔比为1～4.4且不包括1。
  2. 如权利要求1所述的负极材料的制备方法，其中，步骤(1)所述化学气相沉积中采用的碳源包括甲烷、乙烯、乙炔或甲苯中的任意一种或至少两种的组合；步骤(1)所述化学气相沉积的温度为800～1100℃；步骤(1)所述化学气相沉积的时间为1～4h；步骤(1)所述纳米硅的粒径≤100nm。
  3. 如权利要求1或2所述的负极材料的制备方法，其中，步骤(2)所述锂源中的锂与第一基体中的硅的摩尔比为1.71～3.75；步骤(2)中所述锂源包括LiH。
  4. 如权利要求1-3任一项所述的负极材料的制备方法，其中，步骤(2)所述混合的方法为球磨；所述球磨的转速为200～400rmp；所述球磨的时间为2～5h。
  5. 如权利要求1-4任一项所述的负极材料的制备方法，其中，步骤(2)所述真空烧结的温度为500～700℃；步骤(2)所述真空烧结的时间为2～6h。
  6. 如权利要求1-5任一项所述的负极材料的制备方法，其中，步骤(2)所述真空烧结后，对真空烧结后的产物进行二次球磨；所述二次球磨的转速为400～700rmp；所述二次球磨的球料比为(30～60):1。
  7. 如权利要求1-6任一项所述的负极材料的制备方法，其中，步骤(3)所述干燥环境下为：露点温度为-30～-45℃。
  8. 如权利要求1-7任一项所述的负极材料的制备方法，其中，步骤(3)所述二次碳包覆的方法包括：
    将第二基体、二次碳包覆的原料和溶剂混合，得到混合物，然后在保护性气氛下炭化；步骤(2)所述二次碳包覆过程中混合的方法包括搅拌；所述搅拌的转速为300～600rmp；所述搅拌的时间为2～6h；所述炭化的温度为650～900℃；所述炭化的时间为2～4h；所述保护性气氛包括氮气气氛、氩气气氛或氦气气氛中的任意一种或至少两种的组合。
  9. 如权利要求8所述的负极材料的制备方法，其中，步骤(3)所述二次碳包覆的包覆原料为聚偏氟乙烯和/或聚四氟乙烯；以所述负极材料的质量为100％计，步骤(3)所述二次碳包覆原料的包覆量为5～35％；所述炭化前，对所述混合物依次进行过滤和真空干燥。
  10. 如权利要求1-9任一项所述的负极材料的制备方法，其中，所述制备方法包括以下步骤：
    (1)通过化学气相沉积法在粒径≤100nm的纳米硅表面沉积第一碳包覆层，化学气相沉积过程中，温度为800～1100℃，时间为1～4h，得到第一基体；
    (2)将第一基体和锂源以200～400rmp球磨2～5h，在500～700℃下真空烧结2～6h，对真空烧结后的产物以400～700rmp的转速进行二次球磨，球料比为(30～60):1，得到第二基体；
    (3)在露点温度为-30～-45℃下，将第二基体、包覆量为5～35％的二次碳包覆的原料和溶剂以300～600rmp搅拌2～6h，然后依次进行过滤和真空干燥，最后在保护性气氛下以650～900℃炭化2～4h，得到所述负极材料；
    其中，步骤(2)所述锂源中的锂与第一基体中的硅的摩尔比为1.71～3.75， 步骤(2)中所述锂源包括LiH。
  11. 一种负极材料，所述负极材料由如权利要求1-10任一项所述的负极材料的制备方法制备得到，所述负极材料包括内核、包覆于内核表面的第一碳包覆层和位于最外层的第二碳包覆层；
    其中，所述内核为非晶态锂硅合金，所述非晶态锂硅合金的化学式为Li xSi，1＜x≤4.4。
  12. 如权利要求11所述的负极材料，其中，所述Li xSi中，1.71≤x≤3.75。
  13. 如权利要求11或12所述的负极材料，其中，所述非晶态锂硅合金的粒径为100nm～1μm。
  14. 如权利要求11-13任一项所述的负极材料，其中，所述第一碳包覆层的厚度为20～50nm；所述第二碳包覆层的厚度为30～80nm。
  15. 一种锂离子电池，所述锂离子电池包括如权利要求11-14任一项所述的负极材料。
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CN112201779A (zh) * 2020-10-14 2021-01-08 江西壹金新能源科技有限公司 一种硅基复合材料浆料的制备方法及其应用
CN113314703A (zh) * 2021-05-28 2021-08-27 蜂巢能源科技有限公司 一种负极材料及其制备方法与用途

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