WO2025185441A1 - 一种二次电池及其制备方法和电子装置 - Google Patents

一种二次电池及其制备方法和电子装置

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Publication number
WO2025185441A1
WO2025185441A1 PCT/CN2025/077863 CN2025077863W WO2025185441A1 WO 2025185441 A1 WO2025185441 A1 WO 2025185441A1 CN 2025077863 W CN2025077863 W CN 2025077863W WO 2025185441 A1 WO2025185441 A1 WO 2025185441A1
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silicon
particle
carbon composite
composite particles
negative electrode
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French (fr)
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WO2025185441A8 (zh
Inventor
黄国梁
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Ningde Amperex Technology Ltd
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Ningde Amperex Technology Ltd
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Publication of WO2025185441A1 publication Critical patent/WO2025185441A1/zh
Publication of WO2025185441A8 publication Critical patent/WO2025185441A8/zh
Pending legal-status Critical Current
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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
    • 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
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/058—Construction or manufacture
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • 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
    • H01M4/58—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
    • 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 application relates to the field of electrochemical technology, and in particular to a secondary battery, a preparation method thereof, and an electronic device.
  • lithium-ion batteries have attracted widespread attention due to the widespread application of portable electronic devices, electric vehicles, and energy storage components.
  • the development of lithium-ion batteries with higher energy density is of great significance.
  • silicon-based anode active materials have become an excellent choice due to their abundant reserves and high theoretical specific capacity (4200 mAh/g).
  • the huge volume expansion (over 300%) of silicon-based anode active materials during lithiation and delithiation causes rapid fragmentation of silicon particles and even delamination from the anode current collector, which affects the cycling performance of lithium-ion batteries.
  • the volume effect of silicon triggers many side reactions, such as the repeated fragmentation and formation of solid electrolyte interface (SEI) films.
  • SEI solid electrolyte interface
  • silicon nano-sizing and porous silicon can alleviate the volume expansion of elemental silicon to a certain extent, the high specific surface area and low compaction density limit their large-scale application.
  • the new silicon-carbon composite material uses chemical vapor deposition (CVD) to unsaturatedly deposit silicon in the pores of the carbon skeleton, reserving space for silicon expansion, and successfully realizing the first commercial application of the new silicon-carbon composite material.
  • CVD chemical vapor deposition
  • most of the new silicon-carbon composite materials on the market still have the problems of high stress in the negative electrode sheet and easy peeling of the negative electrode material layer from the negative electrode current collector, which affects the cycle performance of lithium-ion batteries.
  • the purpose of this application is to provide a secondary battery and its preparation method and electronic device to improve the cycle performance of the secondary battery.
  • the specific technical solution is as follows:
  • a first aspect of the present application provides a secondary battery, comprising a negative electrode plate, the negative electrode plate comprising a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector, the negative electrode material layer comprising a negative electrode active material, the negative electrode active material comprising silicon-carbon composite particles, a first counting region with a cross-sectional area of 1000 ⁇ m2 in a cross-section along the thickness direction of the negative electrode plate, wherein within the first counting region, the mass percentage of silicon element based on the mass of a single silicon-carbon composite particle is the particle silicon content, the ratio of the sum of the cross-sectional areas of silicon-carbon composite particles having the same particle silicon content to the sum of the cross-sectional areas of all silicon-carbon composite particles within the first counting region is the particle area ratio, and a particle silicon content area distribution diagram is obtained with the particle silicon content as the horizontal axis and the particle area ratio as the vertical axis; the particle silicon content is arranged in ascending order, and the particle area ratios
  • a particle silicon content corresponding to a cumulative particle area ratio of 50% is DA50
  • a particle silicon content corresponding to a cumulative particle area ratio of 90% is DA50
  • the particle silicon content corresponding to a cumulative particle area ratio of 99% is DA99
  • the present application can reduce the volume expansion differences between different silicon-carbon composite particles and different regions of the same negative electrode plate, reduce the internal stress generated by the repeated expansion and contraction of the negative electrode plate, reduce the risk of the negative electrode material layer being peeled off from the negative electrode current collector, and reduce the capacity decay of the secondary battery, thereby improving the cycle performance of the secondary battery.
  • the cumulative particle area corresponding to a granular silicon content of 5% is DB5 , and 0.93% ⁇ DB5 ⁇ 7.26 %.
  • the silicon-carbon composite particles with a granular silicon content of 5% have a smaller cumulative particle area and are fewer in number, while the silicon-carbon composite particles with a granular silicon content greater than 5% have a larger cumulative particle area and are more in number, which can improve the energy density of the secondary battery and also make the distribution of the granular silicon content narrower.
  • the volume expansion difference between different silicon-carbon composite particles and different regions of the same negative electrode plate is reduced, the internal stress generated by the repeated expansion and contraction of the negative electrode plate is reduced, the risk of the negative electrode material layer being peeled off from the negative electrode current collector is reduced, and the capacity decay of the secondary battery is reduced, thereby facilitating the improvement of the cycle performance of the secondary battery.
  • the cross-sectional area of a single silicon-carbon composite particle is the particle area
  • the ratio of the number of silicon-carbon composite particles having the same particle area to the total number of all silicon-carbon composite particles in the first counting region is the particle number percentage
  • a particle area number distribution graph is obtained with the particle area as the horizontal axis and the particle number percentage as the vertical axis; the particle areas are arranged in order from small to large, and the sum of the particle number percentages corresponding to the particle areas is the cumulative particle number percentage.
  • the particle area corresponding to a cumulative particle number percentage of 50% is DS 50 ⁇ m 2
  • the particle area corresponding to a cumulative particle number percentage of 90% is DS 90 ⁇ m 2
  • the particle area corresponding to a cumulative particle number percentage of 99% is DS 99 ⁇ m 2
  • the specific surface area of the silicon-carbon composite particles is 4.5 m 2 /g to 8.9 m 2 /g.
  • the silicon-carbon composite particles meet at least one of the following characteristics: (a) the mass percentage of silicon in the silicon-carbon composite particles is 35% to 55%; (b) the mass percentage of oxygen in the silicon-carbon composite particles is 1% to 4%; (c) a second counting area with an area of 4 cm2 is included on the surface of the negative electrode plate, and the total area of the silicon-carbon composite particles in the second counting area is A1 cm2 , 0.05 ⁇ A1 / 4 ⁇ 0.95; (d) the total area of the silicon-carbon composite particles in the first counting area is A2 ⁇ m2 , 0.05 ⁇ A2 / 1000 ⁇ 0.95; (e) the negative electrode active material further includes at least one of graphite or hard carbon; (f) the mass percentage of the silicon-carbon composite particles based on the mass of the negative electrode material layer is 5% to 95%. Silicon-carbon composite particles that meet the above characteristics are conducive to further improving the cycle performance of secondary batteries.
  • the silicon-carbon composite particles include a carbon skeleton containing silicon.
  • the use of silicon-carbon composite particles with the above structure is conducive to reducing the volume expansion of the silicon-carbon composite particles, thereby facilitating improved cycle performance of the secondary battery.
  • the silicon-carbon composite particles include a protective layer located on at least a portion of the surface of the carbon skeleton.
  • the protective layer includes at least one of amorphous carbon, a metal oxide, or a non-metallic oxide.
  • the metal oxide includes at least one of aluminum oxide, copper oxide, or titanium oxide.
  • the non-metallic oxide includes at least one of silicon dioxide or silicon monoxide. Silicon-carbon composite particles having the above structure have a high structural strength. This not only reduces the volume expansion of the silicon-carbon composite particles, but also reduces electrolyte erosion of the silicon-carbon composite particles, thereby improving the cycle performance of the secondary battery.
  • the second aspect of the present application provides a method for preparing the secondary battery of the first aspect of the present application, wherein the method for preparing the silicon-carbon composite particles comprises the following steps:
  • S1 providing a carbon skeleton material, crushing and classifying the carbon skeleton material, and then performing a first heat treatment on the carbon skeleton material, wherein the temperature of the first heat treatment is 700° C. to 900° C., and the time of the first heat treatment is 4 hours to 6 hours;
  • the carbon skeleton material by depositing the carbon skeleton material once and regulating the pressure of the first deposition to be negative, a small amount of silicon can be deposited in advance inside the pores of the carbon skeleton material, thereby providing active induction sites for the secondary deposition of silicon inside the pores of the carbon skeleton material, improving the uniformity of silane deposition, and reducing the deposition of silane outside the pores of the carbon skeleton material, thereby facilitating the preparation of silicon-carbon composite particles with high silicon deposition uniformity.
  • the silicon-carbon composite particles obtained by the above preparation method have small differences in silicon content between the silicon-carbon composite particles.
  • the method for preparing silicon-carbon composite particles meets at least one of the following characteristics: (1) the carbon skeleton material includes at least one of artificial graphite, natural graphite, mesophase carbon microbeads, soft carbon, or hard carbon; (2) the first mixed gas and the second mixed gas each independently further include at least one of nitrogen, hydrogen, or argon; (3) the source material of the protective layer includes a first source material for preparing amorphous carbon, a second source material for preparing metal oxides, and a third source material for preparing non-metallic oxides, the first source material including at least one of acetylene, methane, propylene, ethylene, or propane, the second source material including at least one of titanium isopropoxide, trimethylaluminum, or copper acetate, and the third source material including at least one of ethyl orthosilicate, triethoxysilane, or monosilane.
  • the method for preparing silicon-carbon composite particles meeting the above characteristics is conducive to obtaining silicon-carbon composite particles with high silicon deposition uniformity and narrow particle silicon content distribution, and the difference in particle silicon content between the silicon-carbon composite particles is small, thereby facilitating improved cycle performance of secondary batteries.
  • the third aspect of the present application provides an electronic device comprising the secondary battery provided in the first aspect of the present application or a secondary battery prepared according to the preparation method provided in the second aspect of the present application.
  • the secondary battery provided in the present application has good cycle performance, thereby providing the electronic device provided in the present application with a long service life and good performance.
  • the present application provides a secondary battery, a preparation method thereof, and an electronic device.
  • the secondary battery includes a negative electrode plate, the negative electrode plate including a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector, the negative electrode material layer including a negative electrode active material, the negative electrode active material including silicon-carbon composite particles, and satisfying 0.23 ⁇ DA99 / DA50 - DA90 / DA50 ⁇ 0.57 .
  • the present application can reduce the volume expansion difference between different silicon-carbon composite particles and different regions of the same negative electrode plate, reduce the internal stress generated by repeated expansion and contraction of the negative electrode plate, reduce the risk of separation of the negative electrode material layer from the negative electrode current collector, reduce the capacity decay of the secondary battery, and thus improve the cycle performance of the secondary battery.
  • FIG1 is a scanning electron microscope (SEM) image of Example 1-1 of the present application.
  • FIG2 is an area distribution diagram of the granular silicon content and an area cumulative distribution diagram of the granular silicon content of Example 1-1 of the present application;
  • FIG3 is a particle area quantity distribution diagram and a cumulative quantity distribution diagram of Example 1-1 and Example 2-7 of the present application.
  • lithium-ion batteries are used as an example of secondary batteries to explain the present application, but the secondary batteries of the present application are not limited to lithium-ion batteries.
  • the first aspect of the present application provides a secondary battery, which includes a negative electrode plate, the negative electrode plate includes a negative electrode current collector and a negative electrode material layer arranged on at least one surface of the negative electrode current collector, the negative electrode material layer includes a negative electrode active material, and the negative electrode active material includes silicon-carbon composite particles.
  • the cross-section of the negative electrode sheet along the thickness direction includes a first counting region with a cross-sectional area of 1000 ⁇ m 2.
  • the mass percentage of silicon element is the granular silicon content
  • the ratio of the sum of the cross-sectional areas of silicon-carbon composite particles having the same granular silicon content to the sum of the cross-sectional areas of all silicon-carbon composite particles in the first counting region is the particle area ratio.
  • a granular silicon content area distribution diagram is obtained with the granular silicon content as the horizontal axis and the particle area ratio as the vertical axis. The granular silicon content is arranged in order from small to large, and the sum of the particle area ratios corresponding to the granular silicon contents is the cumulative particle area ratio.
  • the granular silicon content corresponding to a cumulative particle area ratio of 50% is DA50
  • the granular silicon content corresponding to a cumulative particle area ratio of 90% is DA90
  • the granular silicon content corresponding to a cumulative particle area ratio of 99 % is DA99
  • the value of DA99 / DA50 - DA90 / DA50 can be 0.23, 0.25, 0.30, 0.33, 0.36, 0.40, 0.44, 0.47, 0.50, 0.55, 0.57, or a range consisting of any two of the above values.
  • the value of DA99 / DA50 - DA90 / DA50 can reflect the difference in silicon content between silicon-carbon composite particles and represent the distribution trend of silicon among the silicon-carbon composite particles.
  • the present application reduces the difference in silicon content between silicon-carbon composite particles.
  • the volume expansion differences between different silicon-carbon composite particles and different regions of the same negative electrode plate can be reduced, reducing the internal stress generated by the repeated expansion and contraction of the negative electrode plate, reducing the risk of the negative electrode material layer peeling from the negative electrode current collector, and reducing the capacity decay of the secondary battery, thereby improving the cycle performance of the secondary battery.
  • DA99 / DA50 - DA90 / DA50 When the value of DA99 / DA50 - DA90 / DA50 is too large, for example, greater than 0.57, it indicates that the granular silicon content of some silicon-carbon composite particles is much greater than the average.
  • the volume expansion of these silicon-carbon composite particles during cycling is much greater than that of other silicon-carbon composite particles, resulting in increased internal stress caused by repeated expansion and contraction of the negative electrode pole piece, easy separation of the negative electrode material layer from the negative electrode current collector, and severe capacity decay of the secondary battery, which is not conducive to improving the cycle performance of the secondary battery.
  • the negative electrode active material includes silicon-carbon composite particles, and DA 99/ DA 50- DA 90/ DA 50 is adjusted to satisfy the above relationship, which can improve the cycle performance of the secondary battery.
  • the negative electrode active material includes silicon-carbon composite particles and graphite particles.
  • the area distribution diagram of the particle silicon content can be obtained by: ion polishing the negative electrode sheet along the thickness direction using a cross-sectional ion polishing instrument, the ion polishing voltage is 7.5kV, and the time is 1.5h to obtain a cross section of the negative electrode sheet in the thickness direction.
  • the cross section of the negative electrode sheet is subjected to a scanning electron microscope (SEM) test using a backscattered mode, a test voltage of 5kV to 10kV, a magnification of 1000 ⁇ to 5000 ⁇ , and a working distance of 9.8mm to 10.2mm.
  • SEM scanning electron microscope
  • the contrast is adjusted so that the average grayscale value of the graphite particles is between 60 and 70, the average grayscale value of the negative current collector is between 250 and 255, and the average grayscale value of the silicon-carbon composite particles is between 70 and 250.
  • the contrast is adjusted so that the graphite particles 10 are dark black with a grayscale value ⁇ 70, while the silicon-carbon composite particles 20 are off-white with a grayscale value >90.
  • the grayscale difference creates a clear boundary between the two types of particles.
  • EDS analysis is performed on all silicon-carbon composite particles within a first counting area with a cross-sectional area of 1000 ⁇ m2 along the thickness of the negative electrode sheet. The particle silicon content of each silicon-carbon composite particle is determined and the resulting image is saved. EDS analysis is then performed on randomly selected first counting areas with different cross-sectional areas of 1000 ⁇ m2 within the cross-section of the negative electrode sheet, and 5 to 10 backscatter images are saved. In this mode, the grayscale value of all graphite particles is ⁇ 70, while the grayscale value of silicon-carbon composite particles is >90. This grayscale value is positively correlated with the particle silicon content of the silicon-carbon composite particles.
  • Use image processing software e.g., HALCON machine vision software
  • Pixel size is calibrated using the scale of the backscattered photographs. Since the grayscale value of graphite particles is ⁇ 70 and the grayscale value of silicon-carbon composite particles is >90, edge detection is used to analyze and segment the silicon-carbon composite particles and graphite particles in the backscattered photographs.
  • the images of the silicon-carbon composite particles are retained, and grayscale distribution data and a grayscale distribution histogram are output.
  • the total number of pixels in the selected area multiplied by the calibrated single-pixel area is the total area A of all selected silicon-carbon composite particles.
  • the particle silicon content area distribution diagram can be obtained.
  • the particle silicon content area cumulative distribution diagram can be obtained.
  • the negative electrode active material includes silicon-carbon composite particles and hard carbon.
  • the method for obtaining an area distribution map of particulate silicon content is similar to that described above for the negative electrode active material including silicon-carbon composite particles and graphite particles.
  • the method can be as follows: ion polish the negative electrode electrode sheet along the thickness direction to obtain a cross-section of the negative electrode electrode sheet along the thickness direction.
  • a cross-sectional image of the negative electrode electrode sheet along the thickness direction is analyzed using a scanning electron microscope (SEM) in backscattered mode.
  • SEM scanning electron microscope
  • a first counting area with a cross-sectional area of 1000 ⁇ m2 is selected, and the contrast is adjusted to achieve different grayscale values for different negative electrode active materials and negative electrode current collectors.
  • An image of the silicon-carbon composite particles within the selected first counting area is obtained.
  • the negative electrode active material also includes hard carbon
  • the average grayscale value of the hard carbon is adjusted to between 60 and 70
  • the average grayscale value of the negative electrode current collector is adjusted to between 250 and 255
  • the average grayscale value of the silicon-carbon composite particles is adjusted to between 70 and 250.
  • EDS analysis is performed on the silicon-carbon composite particles within the selected first counting area to obtain the particulate silicon content of each silicon-carbon composite particle within the selected first counting area.
  • Image processing software can be used to determine the area of each silicon-carbon composite particle within the selected first counting area and calculate the particle area percentage.
  • a particle silicon content area distribution graph is plotted with particle silicon content on the horizontal axis and particle area percentage on the vertical axis.
  • a cumulative particle silicon content area distribution graph is plotted with particle silicon content on the horizontal axis and cumulative particle area percentage on the vertical axis.
  • the value of DA 50 can be 30%, 32%, 34%, 36%, 38%, 40%, 43%, 45%, or a range consisting of any two of the above values.
  • the value of DA 90 can be 42%, 45%, 48%, 50%, 54%, 57%, 60%, 63%, 65%, or a range consisting of any two of the above values.
  • the value of DA 99 can be 55%, 58%, 61%, 64%, 67%, 70%, 73%, 75%, or a range consisting of any two of the above values.
  • the distribution of the granular silicon content can be made narrower, and the difference in granular silicon content between the silicon-carbon composite particles can be smaller.
  • the difference in volume expansion of different silicon-carbon composite particles and different regions of the same negative electrode plate can be reduced, the internal stress generated by repeated expansion and contraction of the negative electrode plate can be reduced, the risk of separation of the negative electrode material layer from the negative electrode current collector can be reduced, and the capacity decay of the secondary battery can be reduced, thereby helping to improve the cycle performance of the secondary battery.
  • the cumulative granular area corresponding to a granular silicon content of 5% is DB 5, and 0.93% ⁇ DB 5 ⁇ 7.26%.
  • the value of DB 5 can be 0.93%, 1.6%, 2%, 2.8%, 3%, 3.4%, 4%, 4.5%, 5%, 5.6%, 6%, 6.4%, 7.0%, 7.26%, or a range consisting of any two of the above values.
  • the silicon-carbon composite particles with a granular silicon content of 5% have a small cumulative particle area ratio and a small number, while the silicon-carbon composite particles with a granular silicon content greater than 5% have a large cumulative particle area ratio and a large number, which can improve the energy density of the secondary battery and simultaneously make the distribution of the granular silicon content narrower.
  • the volume expansion difference between different silicon-carbon composite particles and different regions of the same negative electrode plate is reduced, the internal stress generated by the repeated expansion and contraction of the negative electrode plate is reduced, the risk of the negative electrode material layer being peeled off from the negative electrode current collector is reduced, and the capacity decay of the secondary battery is reduced, thereby facilitating the improvement of the cycle performance of the secondary battery.
  • the cross-sectional area of a single silicon-carbon composite particle is the particle area
  • the ratio of the number of silicon-carbon composite particles having the same particle area to the total number of all silicon-carbon composite particles in the first counting region is the particle number percentage
  • a particle area number distribution graph is obtained with the particle area as the horizontal axis and the particle number percentage as the vertical axis; the particle areas are arranged in order from small to large, and the sum of the particle number percentages corresponding to the particle areas is the cumulative particle number percentage.
  • the particle area corresponding to a cumulative particle number percentage of 50% is DS 50 ⁇ m 2
  • the particle area corresponding to a cumulative particle number percentage of 90% is DS 90 ⁇ m 2
  • the particle area corresponding to a cumulative particle number percentage of 99% is DS 99 ⁇ m 2
  • 1.66 ⁇ DS 99/ DS 50- DS 90 / DS 50 ⁇ 4.7 the value of DS99 / DS50 - DS90 / DS50 can be 1.66, 2.0, 2.5, 3.0, 3.6, 4.0, 4.4, 4.7, or a range consisting of any two of the above values.
  • the value of DS99 / DS50 - DS90 / DS50 can reflect the size difference between the silicon-carbon composite particles.
  • the value of DS99 / DS50 - DS90 / DS50 can reflect the size difference between the silicon-carbon composite particles.
  • the size difference between the silicon-carbon composite particles is small, and during the charge and discharge cycle of the secondary battery, the absolute value of the volume expansion of the silicon-carbon composite particles is small, and the difference in the volume expansion rate is also small.
  • the same method as the particle silicon content area distribution diagram described above can be used to determine the particle area and particle number percentage of the silicon-carbon composite particles within a first counting region with a cross-sectional area of 1000 ⁇ m2 in the cross-section of the negative electrode sheet along the thickness direction.
  • a particle area distribution diagram is obtained with particle area as the horizontal axis and particle number percentage as the vertical axis.
  • a particle area cumulative distribution diagram is obtained with particle area as the horizontal axis and cumulative particle number percentage as the vertical axis.
  • the value of DS50 can be 25, 30, 36, 40, 44, 50, 55, 60, or a range consisting of any two of the above values.
  • the value of DS90 can be 98, 105, 110, 114, 120, 126, 130, 135, 140, 144, 150, or a range consisting of any two of the above values.
  • the value of DS99 can be 181, 195, 200, 206, 210, 215, 220, 224, 230, 235, 240, 246, 250, 255, or a range consisting of any two of the above values.
  • the particle area distribution of the silicon-carbon composite particles can be narrowed, the size difference between the silicon-carbon composite particles can be small, the absolute value difference and the volume expansion rate difference of the silicon-carbon composite particles during the charge and discharge cycle of the secondary battery can be reduced, and the volume expansion difference between different silicon-carbon composite particles and different regions of the same negative electrode plate can be further reduced.
  • the internal stress generated by the repeated expansion and contraction of the negative electrode plate is reduced, the risk of the negative electrode material layer being peeled off from the negative electrode current collector is reduced, and the capacity decay of the secondary battery is reduced, which is conducive to further improving the cycle performance of the secondary battery.
  • the specific surface area of the silicon-carbon composite particles is 4.5 m 2 /g to 8.9 m 2 /g.
  • the specific surface area of the silicon-carbon composite particles can be 4.5 m 2 /g, 5.0 m 2 /g, 6.4 m 2 /g, 7.0 m 2 /g, 7.6 m 2 / g, 8.0 m 2 /g, 8.9 m 2 /g, or a range consisting of any two of the above values.
  • the erosion of the silicon inside the silicon-carbon composite particles by the solvent (e.g., aqueous solvent) in the negative electrode slurry can be reduced, thereby reducing the risk of gas production during the stirring process of the negative electrode slurry, and reducing the risk of problems such as pinholes and exposure of the negative electrode current collector during the coating process of the negative electrode slurry.
  • the distribution of the negative electrode material layer on the negative electrode current collector is more uniform, and the difference in silicon content between the silicon-carbon composite particles is small.
  • the difference in volume expansion of different silicon-carbon composite particles and different regions of the same negative electrode plate can be reduced, the internal stress generated by the repeated expansion and contraction of the negative electrode plate is reduced, and the risk of the negative electrode material layer being peeled off from the negative electrode current collector is reduced, which is beneficial to improving the cycle performance of the secondary battery.
  • the mass percentage of silicon in the silicon-carbon composite particles is 35% to 55%.
  • the mass percentage of silicon in the silicon-carbon composite particles can be 35%, 40%, 42%, 45%, 48%, 50%, 52%, 55%, or a range consisting of any two of the above values.
  • the volume expansion rate of the silicon-carbon composite particles and the difference in volume expansion rate between the silicon-carbon composite particles can be reduced, and the volume expansion difference between different silicon-carbon composite particles and different regions of the same negative electrode plate can be further reduced, the internal stress generated by repeated expansion and contraction of the negative electrode plate is reduced, the risk of the negative electrode material layer being peeled off from the negative electrode current collector is reduced, and the capacity decay of the secondary battery is reduced, thereby facilitating further improving the cycle performance of the secondary battery.
  • the weight percentage of oxygen in the silicon-carbon composite particles is 1% to 4%.
  • the weight percentage of oxygen in the silicon-carbon composite particles can be 1%, 1.5%, 2%, 2.4%, 3%, 3.6%, 4%, or a range consisting of any two of the foregoing values.
  • the oxygen in the silicon-carbon composite particles is derived from oxidation of the carbon skeleton material and during the preparation of the silicon-carbon composite particles.
  • the irreversible reaction of silicon to form lithium silicate salt can be reduced, and the consumption of electrolyte and lithium ions by side reactions during the first cycle can be reduced, which is beneficial to improving the first cycle efficiency and capacity of the secondary battery.
  • the difference in silicon content between the silicon-carbon composite particles is small.
  • the difference in volume expansion of different silicon-carbon composite particles and different regions of the same negative electrode plate can be reduced, the internal stress generated by repeated expansion and contraction of the negative electrode plate is reduced, the risk of separation of the negative electrode material layer from the negative electrode current collector is reduced, and the capacity decay of the secondary battery is reduced, which is beneficial to improving the cycle performance of the secondary battery.
  • a second counting region with an area of 4 cm 2 is included on the surface of the negative electrode sheet.
  • the total area of the silicon-carbon composite particles is A 1 cm 2 , with 0.05 ⁇ A 1 /4 ⁇ 0.95.
  • the remaining area of the second counting region comprises the remaining components of the negative electrode material layer, including but not limited to the negative electrode active material (e.g., graphite), negative electrode binder, and negative electrode conductive agent other than the silicon-carbon composite particles.
  • the value of A 1 /4 can be 0.05, 0.12, 0.20, 0.33, 0.40, 0.50, 0.60, 0.74, 0.80, 0.95, or a range consisting of any two of the foregoing values.
  • the silicon-carbon composite particles are more uniformly distributed on the surface of the negative electrode sheet. This can reduce the volume expansion differences between different regions of the same negative electrode sheet, reduce the internal stress generated by repeated expansion and contraction of the negative electrode sheet, reduce the risk of the negative electrode material layer peeling from the negative electrode current collector, and reduce the capacity decay of the secondary battery, thereby further improving the cycle performance of the secondary battery.
  • the difference between A1 within different 4 cm2 second counting areas on the surface of the negative electrode sheet is 0.01 to 0.1.
  • the total area of the silicon-carbon composite particles is A 2 ⁇ m 2 , 0.05 ⁇ A 2 /1000 ⁇ 0.95
  • the remaining area of the first counting region is the remaining components in the negative electrode material layer, including but not limited to negative electrode active materials (such as graphite), negative electrode binders, negative electrode conductive agents, etc.
  • the value of A 2 /1000 can be 0.05, 0.14, 0.20, 0.35, 0.40, 0.52, 0.60, 0.76, 0.80, 0.95, or a range consisting of any two of the above values.
  • the silicon-carbon composite particles are more abundant and more evenly distributed throughout the thickness of the negative electrode sheet. This can reduce the volume expansion differences between different regions of the same negative electrode sheet, reduce the internal stress generated by repeated expansion and contraction of the negative electrode sheet, lower the risk of separation of the negative electrode material layer from the negative electrode current collector, and reduce the capacity decay of the secondary battery, thereby further improving the cycle performance of the secondary battery.
  • the difference between A2 within different 1000 ⁇ m2 first counting areas in a cross-section of the negative electrode sheet along the thickness direction is 0.01 to 0.1.
  • the surface of the negative electrode sheet includes a second counting area with an area of 4 cm2 .
  • the total area of the silicon-carbon composite particles is A1 cm2 , with 0.05 ⁇ A1 / 4 ⁇ 0.95.
  • the total area of the silicon-carbon composite particles is A2 ⁇ m2 , with 0.05 ⁇ A2 / 1000 ⁇ 0.95.
  • the negative electrode active material further comprises at least one of graphite or hard carbon.
  • the mass percentage of the aforementioned substances can range from 0.5% to 93.5% based on the mass of the negative electrode material layer.
  • the inclusion of the aforementioned substances in the negative electrode active material can reduce the mass percentage of silicon-carbon composite particles in the negative electrode active material, reducing the volume expansion of the negative electrode active material, thereby improving the cycle performance of the secondary battery.
  • the mass percentage of the silicon-carbon composite particles is 5% to 95% based on the mass of the negative electrode material layer.
  • the mass percentage of the silicon-carbon composite particles can be 5%, 12%, 20%, 34%, 40%, 50%, 60%, 75%, 80%, 95% or a range consisting of any two of the above values.
  • the negative electrode material layer in the present application may also include a negative electrode binder and a negative electrode conductor. Based on the mass of the negative electrode material layer, the mass percentage of the negative electrode binder may be 1% to 30%, and the mass percentage of the negative electrode conductor may be 0.5% to 30%.
  • the present application has no particular restrictions on the types of negative electrode binders and negative electrode conductors, as long as the purpose of the present application can be achieved.
  • the negative electrode binder may include but is not limited to polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylic (ester) styrene-butadiene rubber, epoxy resin or nylon;
  • the negative electrode conductor may include but is not limited to at least one of carbon-based materials, metal-based materials or conductive polymers;
  • the carbon-based material may include at least one of natural graphite, artificial graphite, conductive carbon black (Super P) or carbon fiber
  • the metal-based material may include but is not limited to at least one of metal powder, metal fiber, copper, nickel, aluminum or silver
  • the conductive polymer may include
  • silicon-carbon composite particles include a carbon skeleton containing silicon. Using silicon-carbon composite particles with such a structure can increase the energy density of a secondary battery and also help reduce volume expansion of the silicon-carbon composite particles, thereby improving the cycling performance of the secondary battery.
  • the silicon can be in the form of amorphous silicon.
  • the silicon-carbon composite particles include a protective layer located on at least a portion of the surface of the carbon skeleton, the protective layer including at least one of amorphous carbon, metal oxide or non-metal oxide, the metal oxide including at least one of aluminum oxide, copper oxide or titanium oxide, and the non-metal oxide including at least one of silicon dioxide or silicon monoxide.
  • the protective layer located on at least a portion of the surface of the carbon skeleton in the silicon-carbon composite particles has a high structural strength, which can not only reduce the volume expansion of the silicon-carbon composite particles, but also reduce the erosion of the electrolyte on the silicon-carbon composite particles, thereby helping to improve the cycle performance of the secondary battery.
  • the second aspect of the present application provides a method for preparing the secondary battery of the first aspect of the present application, wherein the method for preparing the silicon-carbon composite particles comprises the following steps:
  • the negative pressure of the first deposition can be -60kPa, -65kPa, -70kPa, -76kPa, -80kPa, -84kPa, -90kPa, -93kPa, -97kPa, -101kPa, or a range consisting of any two of the above values.
  • the volume fraction of silane in the first mixed gas can be 5%, 10%, 16%, 20%, 25%, 30%, 34%, 40%, 45%, 50%, or a range consisting of any two of the above values.
  • the reaction time of the secondary deposition can be 1h, 1.6h, 2h, 2.4h, 3h, 3.5h, 4h, 4.6h, 5h, 5.3h, 6h or a range consisting of any two of the above values.
  • the present application has no particular limitation on the pressure of the secondary deposition, as long as the purpose of the present application can be achieved.
  • the pressure of the secondary deposition can be negative pressure or positive pressure.
  • the pressure of the secondary deposition can be -60kPa to 120kPa.
  • a carbon skeleton material including silicon in the pores of the carbon skeleton material can be obtained.
  • silicon can be dehydrogenated, thereby reducing the generation of SiC during the preparation of the protective layer.
  • the protective layer has a high structural strength and can be applied to secondary batteries to reduce the volume expansion of silicon-carbon composite particles and reduce the erosion of the electrolyte on the silicon-carbon composite particles, thereby improving the cycle performance of the secondary battery.
  • the silicon-carbon composite particles obtained by the above preparation method have high silicon deposition uniformity and a narrow distribution of particle silicon content.
  • the difference in particle silicon content between the silicon-carbon composite particles is small. When applied to secondary batteries, it can reduce the volume expansion difference between different silicon-carbon composite particles and different regions of the same negative electrode plate, reduce the internal stress generated by repeated expansion and contraction of the negative electrode plate, reduce the risk of the negative electrode material layer being peeled off from the negative electrode current collector, reduce the capacity decay of the secondary battery, and thus improve the cycle performance of the secondary battery.
  • the silane may include but is not limited to at least one of monosilane, disilane or triethoxysilane.
  • the carbon skeleton material includes at least one of artificial graphite, natural graphite, mesophase carbon microbeads, soft carbon or hard carbon.
  • the present application has no particular restrictions on the pore structure of the carbon skeleton material, as long as the purpose of the present application can be achieved.
  • the pore volume of the carbon skeleton material is 0.5 cm 3 /g to 1.5 cm 3 /g, and the average pore size is 2.5nm to 4nm.
  • the above-mentioned carbon skeleton material is selected to achieve a better fluidized state in the fluidized bed, so that the solid-gas contact is more uniform, which is conducive to the preparation of silicon-carbon composite particles with high silicon deposition uniformity and narrow particle silicon content distribution.
  • the difference in particle silicon content between the silicon-carbon composite particles is small. When applied to secondary batteries, it can reduce the volume expansion difference between different silicon-carbon composite particles and different regions of the same negative electrode, reduce the internal stress generated by repeated expansion and contraction of the negative electrode, reduce the risk of the negative electrode material layer being peeled off from the negative electrode current collector, reduce the capacity decay of the secondary battery, and thus help improve the cycle performance of the secondary battery.
  • the first mixed gas and the second mixed gas also include the above-mentioned gas, which can dilute the silane concentration, regulate the adsorption rate and cracking deposition rate of silane, and ensure that the gas flow in the fluidized bed meets the requirements of the carbon skeleton material or the carbon skeleton material deposited once to reach a fluidized state, which is conducive to the preparation of silicon-carbon composite particles with high silicon deposition uniformity and narrow particle silicon content distribution.
  • the difference in particle silicon content between silicon-carbon composite particles is small.
  • the source material of the protective layer includes a first source material for preparing amorphous carbon
  • the first source material includes at least one of acetylene, methane, propylene, ethylene or propane.
  • the deposition temperature for preparing the amorphous carbon protective layer is 550°C to 850°C.
  • the source material of the protective layer includes a second source material for preparing a metal oxide, and the second source material includes at least one of titanium isopropoxide, trimethylaluminum or copper acetate.
  • the second source material is used to prepare a metal oxide protective layer by CVD method combined with high-temperature oxidation, and the temperature of high-temperature oxidation is 150°C to 250°C, and the time is 2h to 6h.
  • the above-mentioned type of second source material is selected to form a metal oxide protective layer on at least a portion of the surface of the carbon skeleton material including silicon.
  • the protective layer has a high structural strength and can be applied to secondary batteries to reduce the volume expansion of silicon-carbon composite particles. At the same time, it can also reduce the erosion of the silicon-carbon composite particles by the electrolyte, thereby helping to improve the cycle performance of the secondary battery.
  • the source material of the protective layer includes a third source material for preparing a non-metallic oxide
  • the third source material includes at least one of ethyl orthosilicate, triethoxysilane or monosilane.
  • the non-metallic oxide protective layer is prepared by a CVD method combined with high-temperature oxidation using a third source material, and the temperature of the high-temperature oxidation is 150°C to 250°C, and the time is 2h to 6h.
  • the silicon dioxide protective layer can be formed by depositing silane on the surface of a carbon skeleton material including silicon to form a silicon element, and then oxidizing it at room temperature to form silicon dioxide.
  • the above-mentioned type of third source material is selected to form a non-metallic oxide protective layer on at least a portion of the surface of the carbon skeleton material including silicon.
  • the protective layer has a high structural strength and can be applied to secondary batteries to reduce the volume expansion of silicon-carbon composite particles. At the same time, it can also reduce the erosion of the electrolyte on the silicon-carbon composite particles, thereby helping to improve the cycle performance of the secondary battery.
  • the carbon skeleton material after crushing and classification, has a D V 10 of 1 ⁇ m to 5.9 ⁇ m, a D V 50 of 5.65 ⁇ m to 8.7 ⁇ m, and a D V 99 of 15.2 ⁇ m to 78.3 ⁇ m.
  • the present application does not particularly limit the method of crushing and classifying, as long as the purpose of the present application can be achieved.
  • the carbon skeleton material can be crushed by ball milling, and the crushed carbon skeleton material can be classified by a jet classifier or a cyclone classifier.
  • the present application does not particularly limit the process parameters of crushing and classifying, and those skilled in the art can select according to actual needs, as long as the purpose of the present application can be achieved.
  • the present application does not particularly limit the heating rates of the first heat treatment, the first deposition, the second deposition, and the second heat treatment in the process of preparing silicon-carbon composite particles, as long as the purpose of the present application can be achieved.
  • the heating rate of the first heat treatment can be 5°C/min to 10°C/min
  • the heating rate of the first deposition can be 5°C/min to 10°C/min
  • the heating rate of the second deposition can be 5°C/min to 10°C/min
  • the heating rate of the second heat treatment can be 5°C/min to 10°C/min.
  • DA 50, DA 90, DA 99, DA 99/DA 50- DA 90/ DA 50 , and DB 5 can be controlled by regulating the pressure of the primary deposition process and the temperature of the secondary deposition process during the preparation of silicon -carbon composite particles.
  • DS50 , DS90 , and DS99 can be controlled by regulating the crushing time during the silicon-carbon composite particle preparation process. For example, when other conditions remain unchanged, a longer crushing time decreases DS50 , while a shorter crushing time increases DS50 . When other conditions remain unchanged, a longer crushing time decreases DS90 , while a shorter crushing time increases DS90 . When other conditions remain unchanged, a longer crushing time decreases DS99 , while a shorter crushing time increases DS99 . By regulating DS50 , DS90 , and DS99 , the value of DS99 / DS50 - DS90 / DS50 can be adjusted.
  • silicon-carbon composite particles with different specific surface areas can be obtained by regulating the temperature of the secondary deposition process and the reaction time for preparing the protective layer. For example, when other conditions remain unchanged, the temperature of the secondary deposition process increases, and the specific surface area of the silicon-carbon composite particles decreases; the temperature of the secondary deposition process decreases, and the specific surface area of the silicon-carbon composite particles increases. When other conditions remain unchanged, the reaction time for preparing the protective layer increases, and the specific surface area of the silicon-carbon composite particles decreases; the reaction time for preparing the protective layer decreases, and the specific surface area of the silicon-carbon composite particles increases.
  • a negative electrode sheet includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector. It should be noted that the "surface” here can refer to the entire area of the negative electrode current collector or a portion of the negative electrode current collector. This application is not particularly limited, as long as the purpose of this application can be achieved.
  • the present application has no special restrictions on the negative electrode current collector, as long as the purpose of the present application can be achieved.
  • it may include but is not limited to copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam or composite current collector (such as carbon copper composite current collector, nickel copper composite current collector, titanium copper composite current collector, etc.).
  • the present application has no special restrictions on the thickness of the negative electrode current collector and the negative electrode material layer, as long as the purpose of the present application can be achieved.
  • the thickness of the negative electrode current collector is 6 ⁇ m to 12 ⁇ m, and the thickness of the negative electrode material layer is 30 ⁇ m to 150 ⁇ m.
  • the present application has no special restrictions on the thickness of the negative electrode sheet, as long as the purpose of the present application can be achieved.
  • the thickness of the negative electrode sheet is 50 ⁇ m to 350 ⁇ m.
  • a positive electrode sheet includes a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector. It should be noted that the "surface” here can refer to the entire area of the positive electrode current collector or a portion of the positive electrode current collector. This application does not specifically limit this, as long as the purpose of this application can be achieved.
  • This application has no special restrictions on the positive electrode current collector, as long as the purpose of this application can be achieved.
  • it may include but is not limited to aluminum foil, aluminum alloy foil or a composite current collector (such as an aluminum-carbon composite current collector).
  • This application has no special restrictions on the thickness of the positive electrode current collector and the positive electrode material layer, as long as the purpose of this application can be achieved.
  • the thickness of the positive electrode current collector is 6 ⁇ m to 12 ⁇ m, and the thickness of the positive electrode material layer is 30 ⁇ m to 120 ⁇ m.
  • This application has no special restrictions on the thickness of the positive electrode sheet, as long as the purpose of this application can be achieved, for example, the thickness of the positive electrode sheet is 50 ⁇ m to 250 ⁇ m.
  • the positive electrode material layer of the present application includes a positive electrode active material, which includes a substance that can reversibly insert and extract active ions such as lithium ions.
  • the positive electrode material layer can be one or more layers, and each layer of the multi-layer positive electrode material layer can contain the same or different positive electrode active materials.
  • the present application has no particular restrictions on the positive electrode active material, as long as it can achieve the purpose of the present application.
  • the positive electrode active material can include but is not limited to lithium nickel cobalt manganese oxide (such as NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide ( LiCoO2 ), lithium manganese oxide, lithium iron manganese phosphate, lithium titanate, lithium vanadium phosphate, lithium cobalt phosphate, lithium manganese phosphate, lithium iron silicate, lithium vanadium silicate, lithium cobalt silicate or lithium manganese silicate.
  • lithium nickel cobalt manganese oxide such as NCM811, NCM622, NCM523, NCM111
  • lithium nickel cobalt aluminum oxide lithium iron phosphate
  • Li-rich manganese-based materials lithium cobalt oxide ( LiCoO2 )
  • lithium manganese oxide lithium iron manganese phosphate
  • LiCoO2 lithium manganese oxide
  • lithium iron manganese phosphate lithium titanate
  • the chemical formula of the above - mentioned lithium-rich manganese-based material is ⁇ Li2MnO3 ⁇ (1- ⁇ ) LiGO2 , 0 ⁇ 1, G is a transition metal such as nickel, cobalt or iron.
  • G is a transition metal such as nickel, cobalt or iron.
  • a substance having a different composition than that of the positive electrode active material may be attached to the surface of the positive electrode active material.
  • the surface-attached substance may include, but is not limited to, at least one of aluminum oxide, silicon dioxide, titanium dioxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, bismuth oxide, lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate, aluminum sulfate, lithium carbonate, calcium carbonate, magnesium carbonate, or carbon.
  • the positive electrode material layer may also include a positive electrode conductive agent and a positive electrode binder.
  • This application does not specifically limit the types of the positive electrode conductive agent and the positive electrode binder, as long as they can achieve the objectives of this application.
  • the positive electrode binder may include, but is not limited to, at least one of the aforementioned negative electrode binders;
  • the positive electrode conductive agent may include, but is not limited to, at least one of the aforementioned negative electrode conductive agents.
  • This application does not specifically limit the mass ratio of the positive electrode active material, positive electrode conductive agent, and positive electrode binder in the positive electrode material layer, and can be selected based on actual needs, as long as the objectives of this application can be achieved.
  • the secondary battery of the present application also includes an electrolyte.
  • the electrolyte includes a lithium salt and a non-aqueous solvent.
  • the lithium salt may include various lithium salts commonly used in the art, such as lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium difluorophosphate (LiPO 2 F 2 ), lithium bis(trifluoromethanesulfonyl)imide (LiN(CF 3 SO 2 ) 2 ), lithium bis(fluorosulfonyl)imide (Li(N(SO 2 F) 2 )), lithium bis(oxalatoborate) (LiB(C 2 O 4 ) 2 ) or lithium difluorooxalatoborate (LiBF 2 (C 2 O 4 )).
  • the present application does not particularly limit the concentration of the lithium salt in the electrolyte, as long as the purpose of the present application can be achieved.
  • the present application does not particularly limit the non-aqueous solvent, as long as the purpose of the present application can be achieved, for example, it may include but is not limited to at least one of a carbonate compound, a carboxylate compound, an ether compound or other organic solvent.
  • Above-mentioned carbonate compound can include but not limited to at least one in linear carbonate compound, cyclic carbonate compound or fluorinated carbonate compound.
  • Above-mentioned linear carbonate compound can include but not limited to at least one in dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC) or methyl ethyl carbonate (MEC).
  • Above-mentioned cyclic carbonate compound can include but not limited to at least one in ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC) or vinyl ethylene carbonate (VEC).
  • the fluorinated carbonate compound may include, but is not limited to, at least one of 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 carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethylethylene carbonate.
  • FEC fluoroethylene carbonate
  • the above-mentioned carboxylate compound may include, but is not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, ⁇ -butyrolactone, decanoic acid lactone, valerolactone, or caprolactone.
  • the ether compound may include, but is not limited to, at least one of dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran.
  • the other organic solvent may include, but is not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate.
  • the secondary battery of the present application also includes a separator to separate the positive and negative electrode plates, prevent internal short circuits in the secondary battery, allow electrolyte ions to pass freely, and not affect the electrochemical charge and discharge process.
  • the present application does not particularly limit the separator, as long as it can achieve the purpose of the present application.
  • the material of the separator can include, but is not limited to, at least one of polyethylene (PE), polypropylene (PP)-based polyolefins (PO), polyesters (such as polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid;
  • the type of separator can include at least one of woven membranes, non-woven membranes, microporous membranes, composite membranes, rolled membranes, or spun membranes.
  • the separator can include a substrate layer and a surface treatment layer.
  • the substrate layer can be a non-woven fabric, membrane, or composite membrane with a porous structure, and the material of the substrate layer can include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide.
  • 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 can be used.
  • a surface treatment layer is provided on at least one surface of the substrate layer.
  • the surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by a mixed polymer and an inorganic material.
  • the inorganic layer includes inorganic particles and a binder.
  • This application does not particularly limit the inorganic particles.
  • it may include at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate.
  • This application does not particularly limit the binder.
  • it may be at least one of the above-mentioned negative electrode binders.
  • the polymer layer includes a polymer. This application does not particularly limit the polymer.
  • the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinyl pyrrolidone, polyvinyl ether, polyvinylidene fluoride, or poly(vinylidene fluoride-hexafluoropropylene).
  • the thickness of the separator is not particularly limited, as long as it can achieve the purpose of this application.
  • the thickness of the separator can be 5 ⁇ m to 500 ⁇ m.
  • the secondary battery of this application also includes a packaging bag for containing the positive electrode sheet, separator, negative electrode sheet, and electrolyte, as well as other components of secondary batteries known in the art.
  • a packaging bag for containing the positive electrode sheet, separator, negative electrode sheet, and electrolyte, as well as other components of secondary batteries known in the art.
  • This application does not particularly limit these other components.
  • This application does not particularly limit the packaging bag and can be any packaging bag known in the art, as long as it can achieve the purpose of this application. For example, an aluminum-plastic film packaging bag can be used.
  • secondary batteries may include, but are not limited to: lithium metal secondary batteries, lithium ion secondary batteries (lithium ion batteries), sodium ion secondary batteries (sodium ion batteries), lithium polymer secondary batteries, and lithium ion polymer secondary batteries.
  • the preparation process of a secondary battery is well known to those skilled in the art and is not particularly limited in this application.
  • it may include but is not limited to the following steps: stacking the positive electrode sheet, the separator, and the negative electrode sheet in order, and winding, folding, and other operations as needed to obtain an electrode assembly with a wound structure, placing the electrode assembly in a packaging bag, injecting an electrolyte into the packaging bag and sealing it to obtain a secondary battery; or stacking the positive electrode sheet, the separator, and the negative electrode sheet in order, and then fixing the four corners of the entire stacked structure with tape to obtain an electrode assembly with a stacked structure, placing the electrode assembly in a packaging bag, injecting an electrolyte into the packaging bag and sealing it to obtain a secondary battery.
  • overcurrent protection elements, guide plates, etc. may be placed in the packaging bag to prevent pressure rise and overcharging and discharging inside the secondary battery.
  • the third aspect of the present application provides an electronic device comprising the secondary battery provided in the first aspect of the present application or a secondary battery prepared according to the preparation method provided in the second aspect of the present application.
  • the secondary battery provided in the present application has good cycle performance, thereby providing the electronic device provided in the present application with a long service life and good performance.
  • the electronic device of the present application is not particularly limited and can be any electronic device known in the art.
  • the electronic device can include, but is not limited to, a laptop computer, a pen-type computer, a mobile computer, an electronic book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a headset, a video recorder, an LCD 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, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor.
  • the negative electrode sheet to be tested was ion polished along the thickness direction using a cross-sectional ion polisher (IB-19520CCP, provided by JEOL Ltd. (JEOL)) at a voltage of 7.5 kV for 1.5 h to obtain a cross-section of the negative electrode sheet in the thickness direction.
  • a scanning electron microscope (Sigma-02-33, provided by ZEISS, Germany) was used to examine the cross-section of the negative electrode sheet using backscatter mode, a test voltage of 10 kV, a magnification of 1000 ⁇ , and a working distance of 9.9 mm.
  • the contrast was adjusted so that the graphite particles were dark black with a grayscale value of ⁇ 70, and the silicon-carbon composite particles were off-white with a grayscale value of >90. A clear boundary was established between the two particles due to the grayscale difference.
  • a first counting area with a cross-sectional area of 1000 ⁇ m2 was selected from the cross-section of the negative electrode sheet along the thickness direction. All silicon-carbon composite particles within this first counting area were analyzed by energy dispersive spectroscopy (EDS) to determine the silicon content of the different silicon-carbon composite particles, and a photograph was saved. EDS analysis was performed by randomly switching between different first counting areas of 1000 ⁇ m2 within the cross-section of the negative electrode sheet, and 10 backscattered images were saved.
  • EDS energy dispersive spectroscopy
  • grayscale value of graphite particles is ⁇ 70 and the grayscale value of silicon-carbon composite particles is >90
  • edge detection was used to analyze and segment the silicon-carbon composite particles and graphite particles in the backscattered image.
  • the image of the silicon-carbon composite particles was retained, and grayscale distribution data and a grayscale distribution histogram were output.
  • the total number of pixels in the selected area multiplied by the calibrated single pixel area was the total area A of all selected silicon-carbon composite particles.
  • the grayscale distribution histogram was converted into a particle silicon content area distribution map.
  • the particle silicon content area distribution map was obtained with the particle silicon content as the horizontal axis and the particle area percentage as the vertical axis.
  • the area distribution diagram of granular silicon content the granular silicon content corresponding to the cumulative particle area proportion of 50% is DA 50, the granular silicon content corresponding to the cumulative particle area proportion of 90% is DA 90, the granular silicon content corresponding to the cumulative particle area proportion of 99% is DA 99, and the cumulative particle area proportion of 5% is DB 5.
  • the particle area and particle count of the silicon-carbon composite particles within the first counting region with a cross-sectional area of 1000 ⁇ m2 along the thickness direction of the negative electrode sheet were obtained.
  • a particle area distribution graph was generated, with particle area as the horizontal axis and particle count percentage as the vertical axis.
  • the particle area corresponding to a cumulative particle count percentage of 50% is DS 50 ⁇ m2
  • the particle area corresponding to a cumulative particle count percentage of 90% is DS 90 ⁇ m2
  • the particle area corresponding to a cumulative particle count percentage of 99% is DS 99 ⁇ m2 .
  • the specific surface area of the silicon-carbon composite particles in each example and comparative example was measured by nitrogen adsorption using a TriStar II 3020M surface area analyzer (supplied by Micromeritics, USA). The specific testing was conducted in accordance with the national standard GB/T 19587-2017, "Determination of the Specific Surface Area of Solids by the BET Method for Gas Adsorption.”
  • the negative electrode sheet to be tested was ion polished in the thickness direction using a cross-section ion polisher (IB-19520CCP, provided by JEOL Ltd. (JEOL)).
  • the ion polishing voltage was 7.5 kV and the time was 1.5 h to obtain the cross section of the negative electrode sheet in the thickness direction.
  • the mass percentage of silicon in the silicon-carbon composite particles was tested by EDS point scanning. Silicon-carbon composite particles were selected from the cross section of the negative electrode sheet in the thickness direction, and 5 points were randomly selected from the center of a single silicon-carbon composite particle for EDS point scanning to obtain the mass percentage of silicon.
  • the arithmetic mean of the mass percentage of silicon at the above 5 points was calculated to obtain the mass percentage X of silicon in a single silicon-carbon composite particle.
  • 20 silicon-carbon composite particles were randomly selected from the cross section of the negative electrode sheet in the thickness direction, and the X of the 20 silicon-carbon composite particles was obtained by testing.
  • the arithmetic mean of X of the above 20 silicon-carbon composite particles was calculated to obtain the mass percentage of silicon in the silicon-carbon composite particles.
  • the center of a single silicon-carbon composite particle refers to a region greater than 0.5 ⁇ m away from the edge of the silicon-carbon composite particle.
  • the negative electrode sheet to be tested was ion polished along the thickness direction using a cross-section ion polisher (IB-19520CCP, provided by JEOL Ltd. (JEOL)).
  • the ion polishing voltage was 7.5 kV and the time was 1.5 h to obtain the cross section of the negative electrode sheet in the thickness direction.
  • the mass percentage of the oxygen element in the silicon-carbon composite particles was tested by EDS point scanning. Silicon-carbon composite particles were selected from the cross section of the negative electrode sheet in the thickness direction, and 5 points were randomly selected from the center of a single silicon-carbon composite particle for EDS point scanning to obtain the mass percentage of the oxygen element.
  • the arithmetic mean of the mass percentage of the oxygen element at the above 5 points was calculated to obtain the mass percentage Y of the oxygen element in a single silicon-carbon composite particle.
  • 20 silicon-carbon composite particles in the cross section of the negative electrode sheet in the thickness direction were randomly selected and tested to obtain the Y of the 20 silicon-carbon composite particles.
  • the arithmetic mean of the Y of the above 20 silicon-carbon composite particles was calculated to obtain the mass percentage of the oxygen element in the silicon-carbon composite particles.
  • the center of a single silicon-carbon composite particle refers to a region greater than 0.5 ⁇ m away from the edge of the silicon-carbon composite particle.
  • the nitrogen flow rate was adjusted to 1 L/min, and the temperature was heated to 800 ° C at a heating rate of 5 ° C/min. It was kept at 800 ° C for 6 h, and then the heating was turned off and purged with nitrogen at 5 L/min to cool to room temperature.
  • the graphite crucible was taken out at room temperature to collect the porous carbon powder.
  • S2 Deposit the carbon skeleton material once.
  • the deposition process is as follows: take 1kg of porous carbon after heat treatment, put it into the CVD furnace, evacuate to a negative pressure of -101kPa, then stop evacuating, pass nitrogen to a pressure of 2kPa and then turn off the nitrogen, repeat evacuating and passing nitrogen, and detect the oxygen content inside the cavity until the oxygen content drops below 10ppm, then stop the above evacuating and passing nitrogen. Then open the tail gas valve, turn the cavity to rotate 1 turn/min, pass nitrogen at a rate of 2L/min, heat at a heating rate of 5°C/min, heat to 460°C, and keep warm for 1h.
  • the temperature is raised to 500 ° C at a heating rate of 5 ° C/min and kept warm for 1 hour.
  • the valve of the fluidized bed air inlet pipeline was switched to introduce a second monosilane/nitrogen mixture into the fluidized bed.
  • the volume fraction of monosilane was 10%, the gas flow rate was 20 L/min, the stirring paddle speed was adjusted to 120 rpm, and the reaction time was 60 min; then the volume fraction of monosilane was adjusted to 20%, the gas flow rate was 25 L/min, the stirring paddle speed was 150 rpm, and the reaction time was 120 min; finally, the volume fraction of monosilane was adjusted to 5%, the gas flow rate was 30 L/min, the stirring paddle speed was 200 rpm, and the reaction time was 60 min to obtain a carbon skeleton material including silicon.
  • S4 The carbon skeleton material including silicon is subjected to a second heat treatment.
  • the process of the second heat treatment is as follows: after turning off the monosilane, nitrogen is passed at a flow rate of 10 L/min, the stirring blade speed is adjusted to 100 rpm, the temperature is increased to 650°C at a rate of 5°C/min, and then kept warm for 30 minutes.
  • P conductive carbon black
  • PAA polyacrylic acid
  • the above steps were repeated on the other surface of the copper foil to produce a negative electrode sheet coated on both sides with a negative electrode material layer.
  • the sheet was then cold-pressed (at a pressure of 10 tons), cut, and welded to nickel tabs to produce a 76mm ⁇ 867mm negative electrode sheet ready for use.
  • the compacted density of the negative electrode material layer was 1.72 g/ cm3 .
  • N-methylpyrrolidone (NMP) was added as a solvent and stirred uniformly in a vacuum mixer to obtain a positive electrode slurry with a solid content of 75 wt%.
  • the positive electrode slurry was evenly coated on one surface of a 10 ⁇ m thick positive electrode current collector aluminum foil and dried at 85°C to obtain a positive electrode sheet coated on one side with a 50 ⁇ m thick positive electrode material layer.
  • the above steps were then repeated on the other side of the aluminum foil to obtain a positive electrode sheet coated on both sides with a positive electrode material layer.
  • the sheet was then cold pressed (cold pressed at a pressure of 15 tons), cut into pieces, and welded to the positive electrode tabs to obtain a 74 mm ⁇ 851 mm positive electrode sheet for future use.
  • the compacted density of the positive electrode material layer was 4.15 g/ cm ⁇ .
  • PC propylene carbonate
  • EC ethylene carbonate
  • DEC diethyl carbonate
  • LiPF6 lithium hexafluorophosphate
  • FEC fluoroethylene carbonate
  • PE polyethylene
  • the negative electrode sheet, separator, and positive electrode sheet prepared above are stacked and wound in sequence to form a wound electrode assembly.
  • the electrode assembly is placed in an aluminum-plastic film packaging bag, dried, and then injected with electrolyte.
  • the lithium-ion battery is produced through vacuum packaging, static standing, formation (charging at a constant current of 0.2C for 120 seconds, then at a constant current of 1C for 180 seconds, and finally at a constant current of 1.5C to 4.78V), capacity evaluation, degassing, and trimming.
  • the preparation process was the same as that of Example 1-1, except that in step S1 of ⁇ Preparation of Silicon-Carbon Composite Particles>, the parameters of ball milling and classification were adjusted so that DA99 / DA50 - DA90 / DA50 , DA50 , DA90, DA99 , DS99 / DS50 - DS90 / DS50 , DS50 , DS90, and DS99 of the silicon-carbon composite particles were as shown in Table 2.
  • step S5 of ⁇ Preparation of Silicon-Carbon Composite Particles> adopts the following steps, the rest is the same as Example 1-1.
  • step S5 of ⁇ Preparation of Silicon-Carbon Composite Particles> adopts the following steps, the rest is the same as Example 1-1.
  • the negative electrode active material graphite the negative electrode active material silicon-carbon composite particles
  • the negative electrode conductive agent conductive carbon black Super P
  • PAA negative electrode binder polyacrylic acid
  • the negative electrode active material graphite the negative electrode active material silicon-carbon composite particles
  • the negative electrode conductive agent conductive carbon black Super P
  • PAA negative electrode binder polyacrylic acid
  • step S2 is not included and the porous carbon obtained in step S1 is directly used as the raw material for step S3.
  • step S2 of ⁇ Preparation of Silicon-Carbon Composite Particles> adopts the following preparation method, the rest is the same as Example 1-1.
  • S2 Deposit the carbon skeleton material once.
  • the deposition process is as follows: take 1kg of heat-treated porous carbon, put it into the CVD furnace, evacuate to a negative pressure of -101kPa, stop evacuating, pass nitrogen to a pressure of 2kPa, then turn off the nitrogen, repeat evacuating and passing nitrogen, and detect the oxygen content inside the cavity until the oxygen content drops below 10ppm, then stop the above evacuating and passing nitrogen. Then open the tail gas valve, open the cavity and rotate 1 revolution/min, pass nitrogen at a rate of 2L/min, heat at a heating rate of 5°C/min, heat to 460°C, and keep warm for 1h.
  • the ventilation time is 120min. Close the first mixed gas intake, keep warm for 30min, and purge with nitrogen at a rate of 2L/min for 30min; repeat the above first mixed gas and nitrogen purge, and repeat the above deposition process twice.
  • Table 1 Note: “ ⁇ ” in Table 1 indicates no corresponding parameter.
  • the negative electrode active materials of the secondary batteries in the examples of the present application include silicon-carbon composite particles and satisfy the relationship: 0.23 ⁇ DA 99/ DA 50 - DA 90/ DA 50 ⁇ 0.57. This allows the secondary batteries to have a higher number of cycles at 25°C and 45°C, indicating that the secondary batteries have good cycling performance.
  • the secondary batteries in Comparative Examples 1-1 to 1-4 do not satisfy the above relationship: DA 99/ DA 50 - DA 90/ DA 50. Consequently, the secondary batteries have lower numbers of cycles at 25°C and 45°C, indicating that the cycling performance of the secondary batteries is poorer.
  • the values of DA50 , DA90 , and DA99 generally affect the cycling performance of a secondary battery. As can be seen from Examples 1-1 to 1-10, when the values of DA50 , DA90 , and DA99 are within the ranges of this application, the secondary battery has a relatively high number of cycles at 25°C and 45°C, indicating that the secondary battery has good cycling performance.
  • the value of DB5 usually affects the cycle performance of the secondary battery. From Examples 1-1 to 1-10, it can be seen that when the value of DB5 is within the range of this application, the secondary battery has a large number of cycles at 25°C and 45°C, indicating that the secondary battery has good cycle performance.
  • the specific surface area of silicon-carbon composite particles generally affects the cycling performance of secondary batteries. As can be seen from Examples 1-1 to 1-10, when the specific surface area of the silicon-carbon composite particles is within the range of this application, the secondary batteries have a high number of cycles at 25°C and 45°C, indicating good cycling performance.
  • the mass percentage of silicon in the silicon-carbon composite particles generally affects the cycling performance of secondary batteries. As can be seen from Examples 1-1 to 1-10, when the mass percentage of silicon in the silicon-carbon composite particles is within the range of this application, the secondary batteries have a high number of cycles at 25°C and 45°C, indicating good cycling performance.
  • the mass percentage of oxygen in the silicon-carbon composite particles generally affects the cycling performance of secondary batteries. As can be seen from Examples 1-1 to 1-10, when the mass percentage of oxygen in the silicon-carbon composite particles is within the range of this application, the secondary batteries have a high number of cycles at 25°C and 45°C, indicating good cycling performance.
  • the distribution of the granular silicon content of the silicon-carbon composite particles of Example 1-1 is relatively narrow, and the granular silicon content is mainly distributed between 18% and 45%.
  • the difference in granular silicon content between the silicon-carbon composite particles is relatively small.
  • the value of DS99 / DS50 - DS90 / DS50 generally affects the cycling performance of a secondary battery. As can be seen from Examples 1-1 and 2-1 to 2-9, when the value of DS99 / DS50 - DS90 / DS50 is within the range of this application, the secondary battery has more cycles at 25°C and 45°C, indicating that the secondary battery has good cycling performance.
  • the values of DS50 , DS90 , and DS99 generally affect the cycling performance of secondary batteries. As can be seen from Examples 1-1 and 2-1 to 2-9, when the values of DS50 , DS90 , and DS99 are within the ranges of this application, the secondary batteries have a high number of cycles at 25°C and 45°C, indicating good cycling performance.
  • the silicon-carbon composite particles of Example 1-1 have a narrow particle area distribution, with the particle area mainly distributed between 10 ⁇ m2 and 250 ⁇ m2 , and the size difference between the silicon-carbon composite particles is small.
  • the silicon-carbon composite particles of Examples 2-7 have a wider particle area distribution, with the particle area mainly distributed between 8 ⁇ m2 and 5000 ⁇ m2 , and the size difference between the silicon-carbon composite particles is large.
  • the material of the silicon-carbon composite particle protective layer usually affects the cycle performance of the secondary battery. It can be seen from Example 1-1, Example 3-1 to Example 3-2 that when the material of the silicon-carbon composite particle protective layer is within the scope of this application, the secondary battery has more 25°C cycle circles and 45°C cycle circles, indicating that the secondary battery has good cycle performance.
  • the mass percentage of silicon-carbon composite particles and the values of A 1 /4 and A 2 /1000 usually affect the cycle performance of secondary batteries. It can be seen from Examples 1-1, 4-1 and 4-3 that when the mass percentage of silicon-carbon composite particles and the values of A 1 /4 and A 2 /1000 are adjusted within the range of this application, the secondary battery has a large number of cycles at 25°C and 45°C, indicating that the secondary battery has good cycle performance.

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Abstract

提供了一种二次电池及其制备方法和电子装置。该二次电池的负极活性材料包括硅碳复合颗粒，并且满足：0.23≤D A99/D A50-D A90/D A50≤0.57。通过选用具有上述特征的硅碳复合颗粒作为负极活性材料，能够提高二次电池的循环性能。

Description

一种二次电池及其制备方法和电子装置
本申请要求于2024年3月5日提交中国专利局、申请号为202410250975.3、发明名称为“一种二次电池及其制备方法和电子装置”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
本申请涉及电化学技术领域，特别是涉及一种二次电池及其制备方法和电子装置。
背景技术
近年来，由于便携式电子设备、电动汽车和储能元件的广泛应用，二次电池，例如锂离子电池，受到了广泛关注。开发更高能量密度的锂离子电池具有重要意义。在已报道的负极活性材料中，硅基负极活性材料由于其丰富的储量和高的理论比容量(4200mAh/g)而成为一种极好的选择。然而，硅基负极活性材料在锂化以及脱锂过程中巨大的体积膨胀(超过300％)，导致硅颗粒快速破碎，甚至从负极集流体上剥离而影响锂离子电池的循环性能。此外，硅的体积效应会引发许多副反应，如固体电解质界面(SEI)膜的反复碎裂和形成。上述缺陷会引起负极极片的容量迅速下降、电接触不良、倍率性能差、循环稳定性低等问题，导致采用硅基负极活性材料的锂离子电池的循环性能相较于采用石墨负极活性材料的锂离子电池有较大差距，严重制约了硅基负极活性材料在锂离子电池中的大规模应用。
为了解决以上问题，现有技术多采用硅纳米化、多孔硅、硅碳复合以及引入过渡金属氧化物等方法。硅纳米化和多孔硅虽然在一定程度上可以缓解单质硅的体积膨胀，但是高的比表面积、低的压实密度限制了它们的大规模应用。新型硅碳复合材料，通过化学气相沉积法(CVD)在碳骨架的孔隙中不饱和沉积硅，预留了硅的膨胀空间，成功实现了新型硅碳复合材料的首次商业化应用。但是目前市场上的大部分新型硅碳复合材料，仍存在负极极片内应力大、负极材料层易从负极集流体剥离的问题，从而影响锂离子电池的循环性能。
发明内容
本申请的目的在于提供一种二次电池及其制备方法和电子装置，以提高二次电池的循环性能。具体技术方案如下：
本申请的第一方面提供了一种二次电池，其包括负极极片，负极极片包括负极集流体和设置于负极集流体至少一个表面的负极材料层，负极材料层包括负极活性材料，负极活性材料包括硅碳复合颗粒，在负极极片沿厚度方向的截面中包括截面积为1000μm2的第一计数区域，在第一计数区域内，基于单个硅碳复合颗粒的质量，硅元素的质量百分含量为颗粒硅含量，具有相同颗粒硅含量的硅碳复合颗粒的截面积之和与第一计数区域内所有硅碳复合颗粒的截面积之和的比值为颗粒面积占比，以颗粒硅含量为横轴，颗粒面积占比为纵轴，得到颗粒硅含量面积分布图；颗粒硅含量按从小到大的顺序排列，颗粒硅含量所对应的颗粒面积占比依次相加得到的颗粒面积占比之和为累计颗粒面积占比，在颗粒硅含量面积分布图中，累计颗粒面积占比为50％所对应的颗粒硅含量为DA50，累计颗粒面积占比为90％所对应的颗粒硅含量为DA90，累计颗粒面积占比为99％所对应的颗粒硅含量为DA99，0.23≤DA99/DA50-DA90/DA50≤0.57。本申请通过选用包括上述硅碳复合颗粒的负极活性材料，并且调控DA99/DA50-DA90/DA50满足上述关系，能够缩小不同硅碳复合颗粒以及同一负极极片不同区域的体积膨胀差异，减小负极极片反复膨胀收缩所产生的内应力，降低负极材料层从负极集流体剥离的风险，减少二次电池的容量衰减，从而提高二次电池的循环性能。
在本申请的一些实施方案中，30％≤DA50≤45％，42％≤DA90≤65％，55％≤DA99≤75％。通过调控DA50、DA90、DA99的值在上述范围内，能够使得颗粒硅含量的分布较窄，硅碳复合颗粒之间颗粒硅含量的差异较小，从而有利于提高二次电池的循环性能。
在本申请的一些实施方案中，在颗粒硅含量面积分布图中，颗粒硅含量为5％所对应的累计颗粒面积占比为DB5，0.93％≤DB5≤7.26％。在满足0.23≤DA99/DA50-DA90/DA50≤0.57的基础上，通过调控DB5的值在上述范围内，颗粒硅含量为5％的硅碳复合颗粒累计颗粒面积占比较小，数量较少，而颗粒硅含量大于5％的硅碳复合颗粒累计颗粒面积占比较大，数量较多，能够提高二次电池的能量密度，同时还能够使得颗粒硅含量的分布较窄，在二次电池的充放电过程中，缩小不同硅碳复合颗粒以及同一负极极片不同区域的体积膨胀差异，减小负极极片反复膨胀收缩所产生的内应力，降低负极材料层从负极集流体剥离的风险，减少二次电池的容量衰减，从而有利于提高二次电池的循环性能。
在本申请的一些实施方案中，在第一计数区域内，单个硅碳复合颗粒的截面积为颗粒面积，具有相同颗粒面积的硅碳复合颗粒的颗粒数量与第一计数区域内所有硅碳复合颗粒的颗粒总数量的比值为颗粒数量占比，以颗粒面积为横轴，颗粒数量占比为纵轴，得到颗粒面积数量分布图；颗粒面积按从小到大的顺序排列，颗粒面积所对应的颗粒数量占比依次相加得到的颗粒数量占比之和为累计颗粒数量占比，在颗粒面积数量分布图中，累计颗粒数量占比为50％所对应的颗粒面积为DS50μm2，累计颗粒数量占比为90％所对应的颗粒面积为DS90μm2，累计颗粒数量占比为99％所对应的颗粒面积为DS99μm2，1.66≤DS99/DS50-DS90/DS50≤4.7。在满足0.23≤DA99/DA50-DA90/DA50≤0.57的基础上，通过调控DS99/DS50-DS90/DS50的值在上述范围内，硅碳复合颗粒之间的尺寸差异较小，在二次电池的充放电循环过程中，硅碳复合颗粒的体积膨胀的绝对值差异较小，体积膨胀率的差异也较小，能够进一步缩小不同硅碳复合颗粒以及同一负极极片不同区域的体积膨胀差异，减小负极极片反复膨胀收缩所产生的内应力，降低负极材料层从负极集流体剥离的风险，减少二次电池的容量衰减，从而有利于进一步提高二次电池的循环性能。
在本申请的一些实施方案中，25≤DS50≤60，98≤DS90≤150，181≤DS99≤255。通过调控DS50、DS90、DS99的值在上述范围内，能够使得硅碳复合颗粒的颗粒面积分布较窄，硅碳复合颗粒之间的尺寸差异较小，从而有利于进一步提高二次电池的循环性能。
在本申请的一些实施方案中，硅碳复合颗粒的比表面积为4.5m2/g至8.9m2/g。通过调控硅碳复合颗粒的比表面积在上述范围内，有利于提高二次电池的循环性能。
在本申请的一些实施方案中，硅碳复合颗粒满足以下特征中的至少一者：(a)硅碳复合颗粒中的硅元素的质量百分含量为35％至55％；(b)硅碳复合颗粒中的氧元素的质量百分含量为1％至4％；(c)在负极极片的表面上包括面积为4cm2的第二计数区域，在第二计数区域内，硅碳复合颗粒的面积总和为A1 cm2，0.05≤A1/4≤0.95；(d)在第一计数区域内，硅碳复合颗粒的面积总和为A2μm2，0.05≤A2/1000≤0.95；(e)负极活性材料还包括石墨或硬碳中的至少一种；(f)基于负极材料层的质量，硅碳复合颗粒的质量百分含量为5％至95％。硅碳复合颗粒满足以上特征，有利于进一步提高二次电池的循环性能。
在本申请的一些实施方案中，硅碳复合颗粒包括碳骨架，碳骨架中含有硅元素。选用上述结构的硅碳复合颗粒，有利于减少硅碳复合颗粒的体积膨胀，从而有利于提高二次电池的循环性能。
在本申请的一些实施方案中，硅碳复合颗粒包括位于碳骨架至少部分表面的保护层，保护层包括无定形碳、金属氧化物或非金属氧化物中的至少一种，金属氧化物包括氧化铝、氧化铜或氧化钛中的至少一种，非金属氧化物包括二氧化硅或氧化亚硅中的至少一种。选用上述结构的硅碳复合颗粒，位于碳骨架至少部分表面的保护层具有较高的结构强度，不仅能够减小硅碳复合颗粒的体积膨胀，同时还可以减小电解液对硅碳复合颗粒的侵蚀，从而有利于提高二次电池的循环性能。
本申请的第二方面提供了本申请第一方面的二次电池的制备方法，其中，硅碳复合颗粒的制备方法包括以下步骤：
S1：提供碳骨架材料，对碳骨架材料进行破碎分级，然后对碳骨架材料进行第一次热处理，第一次热处理的温度为700℃至900℃，第一次热处理的时间为4h至6h；
S2：对碳骨架材料进行一次沉积，升温至430℃至550℃后，在-60kPa至-101kPa的负压环境下，通入含有体积分数为5％至50％的硅烷的第一混合气，反应2h至6h，一次沉积重复进行2至5次；
S3：将经一次沉积的碳骨架材料转移到流化床中进行加热，通入含有体积分数为5％至50％的硅烷的第二混合气，进行二次沉积得到包括硅的碳骨架材料；二次沉积的温度为430℃至550℃，二次沉积的反应时间为1h至6h；
S4：将包括硅的碳骨架材料在620℃至700℃温度下进行第二次热处理，第二次热处理时长为0.5h至1h；
S5：然后在包括硅的碳骨架材料的表面制备保护层，得到硅碳复合颗粒。
上述制备方法中，通过对碳骨架材料进行一次沉积，调控一次沉积的压力为负压，能够预先在碳骨架材料的孔隙内部沉积少量硅，从而在碳骨架材料的孔隙内部为硅的二次沉积提供活性诱导点位，提高硅烷沉积的均匀性，同时减小硅烷在碳骨架材料孔隙外的沉积，从而有利于制得硅沉积均匀性较高的硅碳复合颗粒。采用以上制备方法得到的硅碳复合颗粒，硅碳复合颗粒之间颗粒硅含量的差异较小，应用于二次电池能够缩小不同硅碳复合颗粒以及同一负极极片不同区域的体积膨胀差异，减小负极极片反复膨胀收缩所产生的内应力，降低负极材料层从负极集流体剥离的风险，减少二次电池的容量衰减，从而提高二次电池的循环性能。
在本申请的一些实施方案中，硅碳复合颗粒的制备方法满足以下特征中的至少一者：(1)碳骨架材料包括人造石墨、天然石墨、中间相碳微球、软碳或硬碳中的至少一种；(2)第一混合气和第二混合气各自独立地还包括氮气、氢气或氩气中的至少一种；(3)保护层的源材料包括用于制备无定形碳的第一源材料、用于制备金属氧化物的第二源材料、用于制备非金属氧化物的第三源材料，第一源材料包括乙炔、甲烷、丙烯、乙烯或丙烷中的至少一种，第二源材料包括异丙醇钛、三甲基铝或乙酸铜中的至少一种，第三源材料包括正硅酸乙酯、三乙氧基硅烷或甲硅烷中的至少一种。硅碳复合颗粒的制备方法满足以上特征，有利于获得高的硅沉积均匀性以及窄的颗粒硅含量分布的硅碳复合颗粒，硅碳复合颗粒之间颗粒硅含量的差异较小，从而有利于提高二次电池的循环性能。
本申请的第三方面提供了一种电子装置，其包括本申请第一方面提供的二次电池或根据本申请第二方面提供的制备方法制得的二次电池。本申请提供的二次电池具有良好的循环性能，从而本申请提供的电子装置具有较长的使用寿命和良好的性能。
本申请的有益效果：
本申请提供了一种二次电池及其制备方法和电子装置。该二次电池包括负极极片，负极极片包括负极集流体和设置于负极集流体至少一个表面的负极材料层，负极材料层包括负极活性材料，负极活性材料包括硅碳复合颗粒，并且满足0.23≤DA99/DA50-DA90/DA50≤0.57。本申请通过选用包括上述硅碳复合颗粒的负极活性材料，并且调控DA99/DA50-DA90/DA50满足上述关系，能够缩小不同硅碳复合颗粒以及同一负极极片不同区域的体积膨胀差异，减小负极极片反复膨胀收缩所产生的内应力，降低负极材料层从负极集流体剥离的风险，减少二次电池的容量衰减，从而提高二次电池的循环性能。
当然，实施本申请的任一产品或方法并不一定需要同时达到以上所述的所有优点。
附图说明
为了更清楚地说明本申请实施例或现有技术中的技术方案，下面将对实施例或现有技术描述中所需要使用的附图作简单地介绍，显而易见地，下面描述中的附图仅仅是本申请的一些实施例，对于本领域普通技术人员来讲，还可以根据这些附图获得其他的实施例。
图1为本申请实施例1-1的扫描电子显微镜(SEM)图；
图2为本申请实施例1-1的颗粒硅含量面积分布图以及颗粒硅含量面积累计分布图；
图3为本申请实施例1-1、实施例2-7的颗粒面积数量分布图及数量累计分布图。
具体实施方式
下面将结合本申请实施例中的附图，对本申请实施例中的技术方案进行清楚、完整地描述，显然，所描述的实施例仅仅是本申请一部分实施例，而不是全部的实施例。本领域技术人员基于本申请所获得的所有其他实施例，都属于本申请保护的范围。
需要说明的是，本申请的具体实施方式中，以锂离子电池作为二次电池的例子来解释本申请，但是本申请的二次电池并不仅限于锂离子电池。
本申请的第一方面提供了一种二次电池，其包括负极极片，负极极片包括负极集流体和设置于负极集流体至少一个表面的负极材料层，负极材料层包括负极活性材料，负极活性材料包括硅碳复合颗粒。在负极极片沿厚度方向的截面中包括截面积为1000μm2的第一计数区域，在第一计数区域内，基于单个硅碳复合颗粒的质量，硅元素的质量百分含量为颗粒硅含量，具有相同颗粒硅含量的硅碳复合颗粒的截面积之和与第一计数区域内所有硅碳复合颗粒的截面积之和的比值为颗粒面积占比，以颗粒硅含量为横轴，颗粒面积占比为纵轴，得到颗粒硅含量面积分布图；颗粒硅含量按从小到大的顺序排列，颗粒硅含量所对应的颗粒面积占比依次相加得到的颗粒面积占比之和为累计颗粒面积占比，在颗粒硅含量面积分布图中，累计颗粒面积占比为50％所对应的颗粒硅含量为DA50，累计颗粒面积占比为90％所对应的颗粒硅含量为DA90，累计颗粒面积占比为99％所对应的颗粒硅含量为DA99，0.23≤DA99/DA50-DA90/DA50≤0.57。例如，DA99/DA50-DA90/DA50的值可以为0.23、0.25、0.30、0.33、0.36、0.40、0.44、0.47、0.50、0.55、0.57或上述任意两个数值组成的范围。
DA99/DA50-DA90/DA50的值可以反映硅碳复合颗粒之间的颗粒硅含量差异，代表硅元素在硅碳复合颗粒之间分配的趋势。本申请通过调控DA99/DA50-DA90/DA50满足上述关系，硅碳复合颗粒之间颗粒硅含量的差异较小，在二次电池的充放电循环过程中，能够缩小不同硅碳复合颗粒以及同一负极极片不同区域的体积膨胀差异，减小负极极片反复膨胀收缩所产生的内应力，降低负极材料层从负极集流体剥离的风险，减少二次电池的容量衰减，从而提高二次电池的循环性能。当DA99/DA50-DA90/DA50的值过大时，例如大于0.57，说明部分硅碳复合颗粒的颗粒硅含量远大于平均值，这部分硅碳复合颗粒在循环过程中的体积膨胀远超其它硅碳复合颗粒，导致负极极片反复膨胀收缩所产生的内应力增大，负极材料层易从负极集流体剥离，二次电池的容量衰减严重，从而不利于提高二次电池的循环性能。当DA99/DA50-DA90/DA50的值过小时，例如小于0.23，说明硅碳复合颗粒的平均颗粒硅含量过大，硅碳复合颗粒的体积膨胀严重，导致负极极片反复膨胀收缩所产生的内应力增大，负极材料层易从负极集流体剥离，二次电池的容量衰减严重，从而不利于提高二次电池的循环性能。从而，负极活性材料包括硅碳复合颗粒，并且调控DA99/DA50-DA90/DA50满足上述关系，可以提高二次电池的循环性能。
在本申请的一些实施方案中，负极活性材料包括硅碳复合颗粒和石墨颗粒。颗粒硅含量面积分布图可以通过以下方式得到：将负极极片使用截面离子抛光仪器沿厚度方向进行离子抛光，离子抛光电压为7.5kV，时间为1.5h，得到厚度方向的负极极片截面。对负极极片截面进行扫描电子显微镜(SEM)测试，使用背散模式，测试电压为5kV至10kV，放大倍数为1000×至5000×，工作距离9.8mm至10.2mm。在背散模式下调整对比度使石墨颗粒的平均灰度值在60至70之间，负极集流体的平均灰度值在250至255之间，硅碳复合颗粒的平均灰度值在70至250之间。具体地，如图1所示，在背散模式下调整对比度，使得石墨颗粒10为深黑色，其灰度值<70，硅碳复合颗粒20为灰白色，其灰度值>90，两种颗粒间因为灰度差异而具有明显分界线。对负极极片沿厚度方向截面中截面积为1000μm2的第一计数区域内所有的硅碳复合颗粒进行能谱仪(EDS)分析，得到不同硅碳复合颗粒的颗粒硅含量，并保存该张照片。在负极极片截面内随机切换不同截面积为1000μm2的第一计数区域进行EDS分析，保存5张至10张背散照片。在该模式下，所有的石墨颗粒灰度值<70，硅碳复合颗粒的灰度值>90且灰度值与硅碳复合颗粒的颗粒硅含量呈现正相关，颗粒硅含量越大，硅碳复合颗粒亮度越高灰度值越大，因而可以得到硅碳复合颗粒灰度值与颗粒硅含量的线性关系式。利用图像处理软件(例如HALCON机器视觉软件)对保存的背散照片进行处理。利用背散照片的比例尺对像素尺寸进行标定，由于石墨颗粒灰度值<70，硅碳复合颗粒的灰度值>90，通过边缘检测功能对背散照片中的硅碳复合颗粒及石墨颗粒进行边缘分析与图像分割，保留硅碳复合颗粒的图像，并输出灰度分布数据及灰度分布直方图，选定区域所包含的总像素数量乘以标定的单像素面积即为所有被选定的硅碳复合颗粒的总面积A，单个硅碳复合颗粒的面积也可得到，记为S1、S2、S3、……、Sn，则A＝S1+S2+S3……+Sn。由于EDS分析时已得到硅碳复合颗粒灰度值与颗粒硅含量的线性关系式，灰度值与硅碳复合颗粒的颗粒硅含量线性相关，即可将灰度分布直方图转化为颗粒硅含量面积分布图以及颗粒硅含量面积累计分布图。以颗粒硅含量为横轴，颗粒面积占比为纵轴，即可得到颗粒硅含量面积分布图。以颗粒硅含量为横轴，累计颗粒面积占比为纵轴，则得到颗粒硅含量面积累计分布图。
在本申请的一些实施方案中，负极活性材料包括硅碳复合颗粒，还包括硬碳。颗粒硅含量面积分布图的获取方式与上述负极活性材料包括硅碳复合颗粒和石墨颗粒相似，可以通过以下方式得到：对负极极片沿厚度方向进行离子抛光，得到厚度方向的负极极片截面。利用扫描电子显微镜(SEM)在背散模式下对负极极片沿厚度方向的截面图像进行分析。选取截面积为1000μm2的第一计数区域，调整对比度使不同负极活性材料、负极集流体的灰度值不同，得到选定第一计数区域内硅碳复合颗粒的图像。例如，当负极活性材料还包括硬碳时，调整硬碳的平均灰度值在60至70之间，负极集流体的平均灰度值在250至255之间，硅碳复合颗粒的平均灰度值在70至250之间。对选定第一计数区域内的硅碳复合颗粒进行EDS分析，得到选定第一计数区域内各个硅碳复合颗粒的颗粒硅含量。利用图像处理软件可以得到选定第一计数区域内各个硅碳复合颗粒的面积，计算得到颗粒面积占比。以颗粒硅含量为横轴，颗粒面积占比为纵轴，得到颗粒硅含量面积分布图。以颗粒硅含量为横轴，累计颗粒面积占比为纵轴，得到颗粒硅含量面积累计分布图。
在本申请的一些实施方案中，30％≤DA50≤45％，42％≤DA90≤65％，55％≤DA99≤75％。例如，DA50的值可以为30％、32％、34％、36％、38％、40％、43％、45％或上述任意两个数值组成的范围。DA90的值可以为42％、45％、48％、50％、54％、57％、60％、63％、65％或上述任意两个数值组成的范围。DA99的值可以为55％、58％、61％、64％、67％、70％、73％、75％或上述任意两个数值组成的范围。通过调控DA50、DA90、DA99的值在上述范围内，能够使得颗粒硅含量的分布较窄，硅碳复合颗粒之间颗粒硅含量的差异较小，在二次电池的充放电过程中，能够缩小不同硅碳复合颗粒以及同一负极极片不同区域的体积膨胀差异，减小负极极片反复膨胀收缩所产生的内应力，降低负极材料层从负极集流体剥离的风险，减少二次电池的容量衰减，从而有利于提高二次电池的循环性能。
在本申请的一些实施方案中，在颗粒硅含量面积分布图中，颗粒硅含量为5％所对应的累计颗粒面积占比为DB5，0.93％≤DB5≤7.26％。例如，DB5的值可以为0.93％、1.6％、2％、2.8％、3％、3.4％、4％、4.5％、5％、5.6％、6％、6.4％、7.0％、7.26％或上述任意两个数值组成的范围。在满足0.23≤DA99/DA50-DA90/DA50≤0.57的基础上，通过调控DB5的值在上述范围内，颗粒硅含量为5％的硅碳复合颗粒累计颗粒面积占比较小，数量较少，而颗粒硅含量大于5％的硅碳复合颗粒累计颗粒面积占比较大，数量较多，能够提高二次电池的能量密度，同时还能够使得颗粒硅含量的分布较窄，在二次电池的充放电过程中，缩小不同硅碳复合颗粒以及同一负极极片不同区域的体积膨胀差异，减小负极极片反复膨胀收缩所产生的内应力，降低负极材料层从负极集流体剥离的风险，减少二次电池的容量衰减，从而有利于提高二次电池的循环性能。
在本申请的一些实施方案中，在第一计数区域内，单个硅碳复合颗粒的截面积为颗粒面积，具有相同颗粒面积的硅碳复合颗粒的颗粒数量与第一计数区域内所有硅碳复合颗粒的颗粒总数量的比值为颗粒数量占比，以颗粒面积为横轴，颗粒数量占比为纵轴，得到颗粒面积数量分布图；颗粒面积按从小到大的顺序排列，颗粒面积所对应的颗粒数量占比依次相加得到的颗粒数量占比之和为累计颗粒数量占比，在颗粒面积数量分布图中，累计颗粒数量占比为50％所对应的颗粒面积为DS50μm2，累计颗粒数量占比为90％所对应的颗粒面积为DS90μm2，累计颗粒数量占比为99％所对应的颗粒面积为DS99μm2，1.66≤DS99/DS50-DS90/DS50≤4.7。例如，DS99/DS50-DS90/DS50的值可以为1.66、2.0、2.5、3.0、3.6、4.0、4.4、4.7或上述任意两个数值组成的范围。DS99/DS50-DS90/DS50的值可以反映硅碳复合颗粒之间的尺寸差异。在满足0.23≤DA99/DA50-DA90/DA50≤0.57的基础上，通过调控DS99/DS50-DS90/DS50的值在上述范围内，硅碳复合颗粒之间的尺寸差异较小，在二次电池的充放电循环过程中，硅碳复合颗粒的体积膨胀的绝对值差异较小，体积膨胀率的差异也较小，能够进一步缩小不同硅碳复合颗粒以及同一负极极片不同区域的体积膨胀差异，减小负极极片反复膨胀收缩所产生的内应力，降低负极材料层从负极集流体剥离的风险，减少二次电池的容量衰减，从而有利于进一步提高二次电池的循环性能。
在本申请中，可以采用与上述颗粒硅含量面积分布图相同的方法得到负极极片沿厚度方向的截面中截面积为1000μm2的第一计数区域内硅碳复合颗粒的颗粒面积以及颗粒数量占比。以颗粒面积为横轴，颗粒数量占比为纵轴，得到颗粒面积数量分布图。以颗粒面积为横轴，累计颗粒数量占比为纵轴，得到颗粒面积数量累计分布图。
在本申请的一些实施方案中，25≤DS50≤60，98≤DS90≤150，181≤DS99≤255。例如，DS50的值可以为25、30、36、40、44、50、55、60或上述任意两个数值组成的范围。DS90的值可以为98、105、110、114、120、126、130、135、140、144、150或上述任意两个数值组成的范围。DS99的值可以为181、195、200、206、210、215、220、224、230、235、240、246、250、255或上述任意两个数值组成的范围。通过调控DS50、DS90、DS99的值在上述范围内，能够使得硅碳复合颗粒的颗粒面积分布较窄，硅碳复合颗粒之间的尺寸差异较小，减小在二次电池的充放电循环过程中硅碳复合颗粒的体积膨胀的绝对值差异和体积膨胀率差异，进一步缩小不同硅碳复合颗粒以及同一负极极片不同区域的体积膨胀差异，减小负极极片反复膨胀收缩所产生的内应力，降低负极材料层从负极集流体剥离的风险，减少二次电池的容量衰减，从而有利于进一步提高二次电池的循环性能。
在本申请的一些实施方案中，硅碳复合颗粒的比表面积为4.5m2/g至8.9m2/g。例如，硅碳复合颗粒的比表面积可以为4.5m2/g、5.0m2/g、6.4m2/g、7.0m2/g、7.6m2/g、8.0m2/g、8.9m2/g或上述任意两个数值组成的范围。在满足0.23≤DA99/DA50-DA90/DA50≤0.57的基础上，通过调控硅碳复合颗粒的比表面积在上述范围内，能够减小负极浆料中的溶剂(例如水溶剂)对硅碳复合颗粒内部硅的侵蚀，从而降低负极浆料搅拌过程中的产气风险，降低负极浆料涂布过程中出现针孔、负极集流体露出等问题的风险，从而使负极材料层在负极集流体上的分布更均匀，并且硅碳复合颗粒之间颗粒硅含量的差异较小，在二次电池的充放电循环过程中，能够缩小不同硅碳复合颗粒以及同一负极极片不同区域的体积膨胀差异，减小负极极片反复膨胀收缩所产生的内应力，降低负极材料层从负极集流体剥离的风险，从而有利于提高二次电池的循环性能。
在本申请的一些实施方案中，硅碳复合颗粒中的硅元素的质量百分含量为35％至55％。例如，硅碳复合颗粒中的硅元素的质量百分含量可以为35％、40％、42％、45％、48％、50％、52％、55％或上述任意两个数值组成的范围。在满足0.23≤DA99/DA50-DA90/DA50≤0.57的基础上，通过调控硅碳复合颗粒中硅元素的质量百分含量在上述范围内，能够减小硅碳复合颗粒的体积膨胀率以及硅碳复合颗粒之间体积膨胀率的差异，进一步缩小不同硅碳复合颗粒以及同一负极极片不同区域的体积膨胀差异，减小负极极片反复膨胀收缩所产生的内应力，降低负极材料层从负极集流体剥离的风险，减少二次电池的容量衰减，从而有利于进一步提高二次电池的循环性能。
在本申请的一些实施方案中，硅碳复合颗粒中的氧元素的质量百分含量为1％至4％。例如，硅碳复合颗粒中的氧元素的质量百分含量可以为1％、1.5％、2％、2.4％、3％、3.6％、4％或上述任意两个数值组成的范围。硅碳复合颗粒中的氧元素来源于碳骨架材料以及制备硅碳复合颗粒过程中的氧化。在满足0.23≤DA99/DA50-DA90/DA50≤0.57的基础上，通过调控硅碳复合颗粒中氧元素的质量百分含量在上述范围内，能够减少硅生成硅酸锂盐的不可逆反应，降低首次循环过程中的副反应对电解液和锂离子的消耗，有利于提高二次电池的首次循环效率和容量，同时硅碳复合颗粒之间颗粒硅含量的差异较小，在二次电池的充放电循环过程中，能够缩小不同硅碳复合颗粒以及同一负极极片不同区域的体积膨胀差异，减小负极极片反复膨胀收缩所产生的内应力，降低负极材料层从负极集流体剥离的风险，减少二次电池的容量衰减，从而有利于提高二次电池的循环性能。
在本申请的一些实施方案中，在负极极片的表面上包括面积为4cm2的第二计数区域，在第二计数区域内，硅碳复合颗粒的面积总和为A1 cm2，0.05≤A1/4≤0.95，上述第二计数区域其余部分面积为负极材料层中的其余组分，包括但不限于除硅碳复合颗粒外的负极活性材料(例如石墨)、负极粘结剂、负极导电剂等。例如，A1/4的值可以为0.05、0.12、0.20、0.33、0.40、0.50、0.60、0.74、0.80、0.95或上述任意两个数值组成的范围。在满足0.23≤DA99/DA50-DA90/DA50≤0.57的基础上，通过调控A1/4的值在上述范围内，硅碳复合颗粒在负极极片的表面分布较多且较为均匀，能够缩小同一负极极片不同区域的体积膨胀差异，减小负极极片反复膨胀收缩所产生的内应力，降低负极材料层从负极集流体剥离的风险，减少二次电池的容量衰减，从而有利于进一步提高二次电池的循环性能。在一些实施方案中，在负极极片的表面上不同的4cm2的第二计数区域内，A1之间的差值为0.01至0.1。
在本申请的一些实施方案中，在第一计数区域内，硅碳复合颗粒的面积总和为A2μm2，0.05≤A2/1000≤0.95，上述第一计数区域其余部分面积为负极材料层中的其余组分，包括但不限于除硅碳复合颗粒外的负极活性材料(例如石墨)、负极粘结剂、负极导电剂等。例如，A2/1000的值可以为0.05、0.14、0.20、0.35、0.40、0.52、0.60、0.76、0.80、0.95或上述任意两个数值组成的范围。在满足0.23≤DA99/DA50-DA90/DA50≤0.57的基础上，通过调控A2/1000的值在上述范围内，硅碳复合颗粒在负极极片的厚度方向上分布较多且较为均匀，能够缩小同一负极极片不同区域的体积膨胀差异，减小负极极片反复膨胀收缩所产生的内应力，降低负极材料层从负极集流体剥离的风险，减少二次电池的容量衰减，从而有利于进一步提高二次电池的循环性能。在一些实施方案中，在负极极片沿厚度方向的截面中不同的1000μm2的第一计数区域内，A2之间的差值为0.01至0.1。
在本申请的一些实施方案中，在负极极片的表面上包括面积为4cm2的第二计数区域，在第二计数区域内，硅碳复合颗粒的面积总和为A1 cm2，0.05≤A1/4≤0.95。在第一计数区域内，硅碳复合颗粒的面积总和为A2μm2，0.05≤A2/1000≤0.95。通过调控A1/4和A2/1000的值同时在上述范围内，硅碳复合颗粒在负极极片的表面和厚度方向分布相似，硅碳复合颗粒在负极极片的表面和厚度方向分布较多且较为均匀，能够进一步缩小同一负极极片不同区域的体积膨胀差异，减小负极极片反复膨胀收缩所产生的内应力，降低负极材料层从负极集流体剥离的风险，减少二次电池的容量衰减，从而有利于更进一步提高二次电池的循环性能。
在本申请的一些实施方案中，负极活性材料还包括石墨或硬碳中的至少一种。基于负极材料层的质量，上述物质的质量百分含量可以为0.5％至93.5％。负极活性材料还包括上述物质，能够减小负极活性材料中硅碳复合颗粒的质量百分含量，减小负极活性材料的体积膨胀，从而有利于提高二次电池的循环性能。
在本申请的一些实施方案中，基于负极材料层的质量，硅碳复合颗粒的质量百分含量为5％至95％。例如，硅碳复合颗粒的质量百分含量可以为5％、12％、20％、34％、40％、50％、60％、75％、80％、95％或上述任意两个数值组成的范围。通过调控硅碳复合颗粒的质量百分含量在上述范围内，有利于减小负极活性材料的体积膨胀，降低负极材料层从负极集流体剥离的风险，减少二次电池的容量衰减，从而有利于提高二次电池的循环性能。同时，还可以提高二次电池的能量密度。
本申请中的负极材料层还可以包括负极粘结剂和负极导电剂。基于负极材料层的质量，负极粘结剂的质量百分含量可以为1％至30％，负极导电剂的质量百分含量可以为0.5％至30％。本申请对负极粘结剂和负极导电剂的种类没有特别限制，只要能够实现本申请目的即可，例如，负极粘结剂可以包括但不限于聚乙烯醇、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、环氧树脂或尼龙中的至少一种；负极导电剂可以包括但不限于基于碳的材料、基于金属的材料或导电聚合物中的至少一种。示例性地，基于碳的材料可以包括天然石墨、人造石墨、导电炭黑(Super P)或碳纤维中的至少一种，基于金属的材料可以包括但不限于金属粉、金属纤维、铜、镍、铝或银中的至少一种；导电聚合物可以包括但不限于聚亚苯基衍生物。
在本申请的一些实施方案中，硅碳复合颗粒包括碳骨架，碳骨架中含有硅元素。选用上述结构的硅碳复合颗粒，能够提高二次电池的能量密度，还有利于减少硅碳复合颗粒的体积膨胀，从而提高二次电池的循环性能。在本申请中，上述硅元素可以以无定形硅的形式存在。
在本申请的一些实施方案中，硅碳复合颗粒包括位于碳骨架至少部分表面的保护层，保护层包括无定形碳、金属氧化物或非金属氧化物中的至少一种，金属氧化物包括氧化铝、氧化铜或氧化钛中的至少一种，非金属氧化物包括二氧化硅或氧化亚硅中的至少一种。硅碳复合颗粒中位于碳骨架至少部分表面的保护层具有较高的结构强度，不仅能够减小硅碳复合颗粒的体积膨胀，同时还可以减小电解液对硅碳复合颗粒的侵蚀，从而有利于提高二次电池的循环性能。在本申请中，硅碳复合颗粒的保护层可以位于碳骨架的全部表面，也可以位于碳骨架的部分表面。由于硅碳复合颗粒中保护层仅几纳米级别，保护层的材料种类不会影响硅碳复合颗粒的平均灰度值。
本申请的第二方面提供了本申请第一方面的二次电池的制备方法，其中，硅碳复合颗粒的制备方法包括以下步骤：
S1：提供碳骨架材料，对碳骨架材料进行破碎分级，然后对碳骨架材料进行第一次热处理，第一次热处理的温度为700℃至900℃，第一次热处理的时间为4h至6h；
S2：对碳骨架材料进行一次沉积，升温至430℃至550℃后，在-60kPa至-101kPa的负压环境下，通入含有体积分数为5％至50％的硅烷的第一混合气，反应2h至6h，一次沉积重复进行2至5次；
S3：将经一次沉积的碳骨架材料转移到流化床中进行加热，通入含有体积分数为5％至50％的硅烷的第二混合气，进行二次沉积得到包括硅的碳骨架材料；二次沉积的温度为430℃至550℃，二次沉积的反应时间为1h至6h；
S4：将包括硅的碳骨架材料在620℃至700℃温度下进行第二次热处理，第二次热处理时长为0.5h至1h；
S5：然后在包括硅的碳骨架材料的表面制备保护层，得到硅碳复合颗粒。
例如，第一次热处理的温度可以为700℃、730℃、760℃、800℃、840℃、880℃、900℃或上述任意两个数值组成的范围。第一次热处理的时间可以为4h、4.5h、5h、5.3h、5.7h、6h或上述任意两个数值组成的范围。一次沉积的温度可以为430℃、450℃、480℃、510℃、530℃、550℃或上述任意两个数值组成的范围。一次沉积的负压压力可以为-60kPa、-65kPa、-70kPa、-76kPa、-80kPa、-84kPa、-90kPa、-93kPa、-97kPa、-101kPa或上述任意两个数值组成的范围。第一混合气硅烷的体积分数可以为5％、10％、16％、20％、25％、30％、34％、40％、45％、50％或上述任意两个数值组成的范围。一次沉积的反应时间可以为2h、2.5h、3h、3.5h、4h、4.5h、5h、5.5h、6h或上述任意两个数值组成的范围。一次沉积的次数可以为2次、3次、4次或5次。第二混合气硅烷的体积分数可以为5％、10％、16％、20％、25％、30％、34％、40％、45％、50％或上述任意两个数值组成的范围。二次沉积的温度可以为430℃、460℃、490℃、520℃、550℃或上述任意两个数值组成的范围。二次沉积的反应时间可以为1h、1.6h、2h、2.4h、3h、3.5h、4h、4.6h、5h、5.3h、6h或上述任意两个数值组成的范围。本申请对二次沉积的压力没有特别限制，只要能够实现本申请目的即可。二次沉积的压力可以为负压，也可以为正压。二次沉积的压力可以为-60kPa至120kPa。例如，二次沉积的压力可以为-60kPa、-40kPa、-20kPa、0kPa、20kPa、40kPa、60kPa、80kPa、100kPa或120kPa或上述任意两个数值组成的范围。第二次热处理的温度可以为620℃、640℃、660℃、680℃、700℃或上述任意两个数值组成的范围。第二次热处理的时间可以为0.5h、0.6h、0.7h、0.8h、0.9h、1h或上述任意两个数值组成的范围。
本申请通过对碳骨架材料进行破碎分级能够调控碳骨架材料的粒径大小以及粒径分布。通过对碳骨架材料进行第一次热处理，能够减少碳骨架材料表面的官能团及缺陷，减少后续一次沉积和二次沉积过程中SiC的生成。通过对碳骨架材料进行一次沉积，调控一次沉积的压力为负压，能够预先在碳骨架材料的孔隙内部沉积少量硅，从而在碳骨架材料的孔隙内部为硅的二次沉积提供活性诱导点位，提高硅烷沉积的均匀性，同时减小硅烷在碳骨架材料孔隙外的沉积。通过对碳骨架材料进行二次沉积，能够得到碳骨架材料孔隙中包括硅的碳骨架材料。通过对包括硅的碳骨架材料进行第二次热处理，能够使硅脱氢，从而减小保护层的制备过程中SiC的生成。通过在包括硅的碳骨架材料的表面制备保护层，保护层具有较高的结构强度，应用于二次电池能够减小硅碳复合颗粒的体积膨胀，同时还能够减小电解液对硅碳复合颗粒的侵蚀，从而提高二次电池的循环性能。采用以上制备方法得到的硅碳复合颗粒具有高的硅沉积均匀性以及窄的颗粒硅含量分布，硅碳复合颗粒之间颗粒硅含量的差异较小，应用于二次电池能够缩小不同硅碳复合颗粒以及同一负极极片不同区域的体积膨胀差异，减小负极极片反复膨胀收缩所产生的内应力，降低负极材料层从负极集流体剥离的风险，减少二次电池的容量衰减，从而提高二次电池的循环性能。在本申请中，硅烷可以包括但不限于甲硅烷、乙硅烷或三乙氧基硅烷中的至少一种。
在本申请的一些实施方案中，碳骨架材料包括人造石墨、天然石墨、中间相碳微球、软碳或硬碳中的至少一种。本申请对碳骨架材料的孔结构没有特别限制，只要能实现本申请的目的即可，例如，碳骨架材料的孔容为0.5cm3/g至1.5cm3/g，平均孔径为2.5nm至4nm。选用上述碳骨架材料，能够在流化床中达到更好的流化状态，使固气接触更均匀，有利于制备得到具有高硅沉积均匀性以及窄颗粒硅含量分布的硅碳复合颗粒，硅碳复合颗粒之间颗粒硅含量的差异较小，应用于二次电池能够缩小不同硅碳复合颗粒以及同一负极极片不同区域的体积膨胀差异，减小负极极片反复膨胀收缩所产生的内应力，降低负极材料层从负极集流体剥离的风险，减少二次电池的容量衰减，从而有利于提高二次电池的循环性能。
在本申请的一些实施方案中，第一混合气和第二混合气各自独立地还包括氮气、氢气或氩气中的至少一种。在本申请的一些实施方案中，第一混合气的气体流量为0.1L/min至0.5L/min，第二混合气的气体流量为10L/min至50L/min。第一混合气和第二混合气还包括上述气体，能够稀释硅烷浓度，调控硅烷的吸附速率与裂解沉积速率，并保证流化床中的气体流量满足碳骨架材料或经一次沉积的碳骨架材料达到流化状态的需求，有利于制备得到具有高硅沉积均匀性以及窄颗粒硅含量分布的硅碳复合颗粒，硅碳复合颗粒之间颗粒硅含量的差异较小，应用于二次电池能够缩小不同硅碳复合颗粒以及同一负极极片不同区域的体积膨胀差异，减小负极极片反复膨胀收缩所产生的内应力，降低负极材料层从负极集流体剥离的风险，减少二次电池的容量衰减，从而有利于提高二次电池的循环性能。
在本申请的一些实施方案中，保护层的源材料包括用于制备无定形碳的第一源材料，第一源材料包括乙炔、甲烷、丙烯、乙烯或丙烷中的至少一种。在本申请的一些实施方案中，制备无定形碳保护层的沉积温度为550℃至850℃。选用上述种类的第一源材料，能够在包括硅的碳骨架材料的至少部分表面形成无定形碳保护层，保护层具有较高的结构强度，应用于二次电池能够减小硅碳复合颗粒的体积膨胀，同时还能够减小电解液对硅碳复合颗粒的侵蚀，从而有利于提高二次电池的循环性能。
在本申请的一些实施方案中，保护层的源材料包括用于制备金属氧化物的第二源材料，第二源材料包括异丙醇钛、三甲基铝或乙酸铜中的至少一种。在本申请的一些实施方案中，采用第二源材料通过CVD法结合高温氧化制备金属氧化物保护层，高温氧化的温度为150℃至250℃，时间为2h至6h。选用上述种类的第二源材料，能够在包括硅的碳骨架材料的至少部分表面形成金属氧化物保护层，保护层具有较高的结构强度，应用于二次电池能够减小硅碳复合颗粒的体积膨胀，同时还能够减小电解液对硅碳复合颗粒的侵蚀，从而有利于提高二次电池的循环性能。
在本申请的一些实施方案中，保护层的源材料包括用于制备非金属氧化物的第三源材料，第三源材料包括正硅酸乙酯、三乙氧基硅烷或甲硅烷中的至少一种。在本申请的一些实施方案中，采用第三源材料通过CVD法结合高温氧化制备非金属氧化物保护层，高温氧化的温度为150℃至250℃，时间为2h至6h。在本申请的另一些实施方案中，二氧化硅保护层可以通过沉积硅烷在包括硅的碳骨架材料表面形成硅单质，然后在室温下氧化形成二氧化硅。选用上述种类的第三源材料，能够在包括硅的碳骨架材料的至少部分表面形成非金属氧化物保护层，保护层具有较高的结构强度，应用于二次电池能够减小硅碳复合颗粒的体积膨胀，同时还能够减小电解液对硅碳复合颗粒的侵蚀，从而有利于提高二次电池的循环性能。
在本申请的一些实施方案中，破碎分级后碳骨架材料的DV10为1μm至5.9μm，DV50为5.65μm至8.7μm，DV99为15.2μm至78.3μm。
本申请对破碎分级的方式没有特别限制，只要能够实现本申请目的即可。例如，可以通过球磨对碳骨架材料进行破碎，可以通过射流分级机或旋风分级器对破碎后的碳骨架材料进行分级。本申请对破碎分级的工艺参数没有特别限制，本领域技术人员可以根据实际需要选择，只要能够实现本申请目的即可。
本申请对制备硅碳复合颗粒过程中第一次热处理、一次沉积、二次沉积、第二次热处理的升温速率没有特别限制，只要能够实现本申请目的即可。例如，第一次热处理的升温速率可以为5℃/min至10℃/min，一次沉积的升温速率可以为5℃/min至10℃/min，二次沉积的升温速率可以为5℃/min至10℃/min，第二次热处理的升温速率可以为5℃/min至10℃/min。
通常情况下，可以通过调控硅碳复合颗粒制备过程中一次沉积过程的压力、二次沉积过程的温度调控DA50、DA90、DA99、DA99/DA50-DA90/DA50、DB5。
通常情况下，可以通过调控硅碳复合颗粒制备过程中的破碎处理的时间调控DS50、DS90、DS99。例如，当其它条件不变时，破碎时间延长，DS50减小；破碎时间缩短，DS50增大。当其它条件不变时，破碎时间延长，DS90减小；破碎时间缩短，DS90增大。当其它条件不变时，破碎时间延长，DS99减小；破碎时间缩短，DS99增大。通过调控DS50、DS90、DS99的值可以调控DS99/DS50-DS90/DS50的值。
本申请对调控硅碳复合颗粒比表面积的方法没有特别限制，只要能够实现本申请目的即可。例如，不同比表面积的硅碳复合颗粒可以通过调控二次沉积过程的温度及制备保护层的反应时间得到。示例性地，当其它条件不变时，二次沉积过程的温度增大，硅碳复合颗粒比表面积减小；二次沉积过程的温度减小，硅碳复合颗粒比表面积增大。当其它条件不变时，制备保护层的反应时间增大，硅碳复合颗粒比表面积减小；制备保护层的反应时间减小，硅碳复合颗粒比表面积增大。
在本申请中，负极极片包括负极集流体和设置于负极集流体至少一个表面的负极材料层。需要说明，这里的“表面”可以是负极集流体的全部区域，也可以是负极集流体的部分区域，本申请没有特别限制，只要能实现本申请目的即可。
本申请对负极集流体没有特别限制，只要能够实现本申请目的即可。例如，可以包括但不限于铜箔、铜合金箔、镍箔、不锈钢箔、钛箔、泡沫镍、泡沫铜或复合集流体(例如碳铜复合集流体、镍铜复合集流体、钛铜复合集流体等)等。本申请对负极集流体和负极材料层的厚度没有特别限制，只要能够实现本申请目的即可，例如，负极集流体的厚度为6μm至12μm，负极材料层的厚度为30μm至150μm。本申请对负极极片的厚度没有特别限制，只要能够实现本申请目的即可，例如，负极极片的厚度为50μm至350μm。
在本申请中，正极极片包括正极集流体和设置于正极集流体至少一个表面的正极材料层。需要说明，这里的“表面”可以是正极集流体的全部区域，也可以是正极集流体的部分区域，本申请没有特别限制，只要能实现本申请目的即可。
本申请对正极集流体没有特别限制，只要能够实现本申请目的即可。例如，可以包括但不限于铝箔、铝合金箔或复合集流体(例如铝碳复合集流体)。本申请对正极集流体和正极材料层的厚度没有特别限制，只要能够实现本申请目的即可。例如，正极集流体的厚度为6μm至12μm，正极材料层的厚度为30μm至120μm。本申请对正极极片的厚度没有特别限制，只要能够实现本申请目的即可，例如，正极极片的厚度为50μm至250μm。
本申请的正极材料层包括正极活性材料，正极活性材料包括能够可逆地嵌入和脱出活性离子如锂离子的物质。正极材料层可以是一层或多层，多层正极材料层中的每层可以包含相同或不同的正极活性材料。本申请对正极活性材料没有特别限制，只要能够实现本申请目的即可，例如，正极活性材料可以包括但不限于镍钴锰酸锂(例如NCM811、NCM622、NCM523、NCM111)、镍钴铝酸锂、磷酸铁锂、富锂锰基材料、钴酸锂(LiCoO2)、锰酸锂、磷酸锰铁锂、钛酸锂、磷酸钒锂、磷酸钴锂、磷酸锰锂、硅酸铁锂、硅酸钒锂、硅酸钴锂或硅酸锰锂中的至少一种。上述富锂锰基材料的化学式为γLi2MnO3·(1-γ)LiGO2，0<γ<1，G为过渡金属镍、钴或铁等。本申请中，正极活性材料表面可以附着有与其组成不同的物质，示例性地，表面附着的物质可以包括但不限于氧化铝、二氧化硅、二氧化钛、氧化锆、氧化镁、氧化钙、氧化硼、氧化锑、氧化铋、硫酸锂、硫酸钠、硫酸钾、硫酸镁、硫酸钙、硫酸铝、碳酸锂、碳酸钙、碳酸镁或碳中的至少一种。通过在正极活性材料表面附着上述物质，可以抑制正极活性材料表面的电解液的氧化反应，从而提高二次电池的使用寿命。
正极材料层还可以包括正极导电剂和正极粘结剂，本申请对正极导电剂和正极粘结剂的种类没有特别限制，只要能够实现本申请目的即可，例如，正极粘结剂可以包括但不限于上述负极粘结剂中的至少一种；正极导电剂可以包括但不限于上述负极导电剂中的至少一种。本申请对正极材料层中正极活性材料、正极导电剂、正极粘结剂的质量比没有特别限制，可以根据实际需要选择，只要能够实现本申请目的即可。
本申请的二次电池还包括电解液。在本申请的一些实施方案中，电解液包括锂盐和非水溶剂。锂盐可以包括本领域常用的各种锂盐，例如六氟磷酸锂(LiPF6)、四氟硼酸锂(LiBF4)、二氟磷酸锂(LiPO2F2)、双三氟甲烷磺酰亚胺锂(LiN(CF3SO2)2)、双(氟磺酰)亚胺锂(Li(N(SO2F)2))、双草酸硼酸锂(LiB(C2O4)2)或二氟草酸硼酸锂(LiBF2(C2O4))中的至少一种。本申请对锂盐在电解液中的浓度没有特别限制，只要能实现本申请的目的即可。本申请对非水溶剂没有特别限制，只要能实现本申请的目的即可，例如可以包括但不限于碳酸酯化合物、羧酸酯化合物、醚化合物或其它有机溶剂中的至少一种。上述碳酸酯化合物可以包括但不限于链状碳酸酯化合物、环状碳酸酯化合物或氟代碳酸酯化合物中的至少一种。上述链状碳酸酯化合物可以包括但不限于碳酸二甲酯(DMC)、碳酸二乙酯(DEC)、碳酸二丙酯(DPC)、碳酸甲丙酯(MPC)、碳酸乙丙酯(EPC)或碳酸甲乙酯(MEC)中的至少一种。上述环状碳酸酯化合物可以包括但不限于碳酸乙烯酯(EC)、碳酸丙烯酯(PC)、碳酸亚丁酯(BC)或碳酸乙烯基亚乙酯(VEC)中的至少一种。氟代碳酸酯化合物可以包括但不限于氟代碳酸乙烯酯(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-甲基亚乙酯或碳酸三氟甲基亚乙酯中的至少一种。上述羧酸酯化合物可以包括但不限于甲酸甲酯、乙酸甲酯、乙酸乙酯、乙酸正丙酯、乙酸叔丁酯、丙酸甲酯、丙酸乙酯、丙酸丙酯、γ-丁内酯、癸内酯、戊内酯或己内酯中的至少一种。上述醚化合物可以包括但不限于二丁醚、四甘醇二甲醚、二甘醇二甲醚、1,2-二甲氧基乙烷、1,2-二乙氧基乙烷、1-乙氧基-1-甲氧基乙烷、2-甲基四氢呋喃或四氢呋喃中的至少一种。上述其它有机溶剂可以包括但不限于二甲亚砜、1,2-二氧戊环、环丁砜、甲基环丁砜、1,3-二甲基-2-咪唑烷酮、N-甲基-2-吡咯烷酮、二甲基甲酰胺、乙腈、磷酸三甲酯、磷酸三乙酯或磷酸三辛酯中的至少一种。
本申请的二次电池还包括隔离膜，用以分隔正极极片和负极极片，防止二次电池内部短路，允许电解质离子自由通过，且不影响电化学充放电过程的进行。本申请对隔离膜没有特别限制，只要能够实现本申请目的即可。例如，隔离膜的材料可以包括但不限于聚乙烯(PE)、聚丙烯(PP)为主的聚烯烃(PO)类、聚酯(例如聚对苯二甲酸二乙酯(PET)膜)、纤维素、聚酰亚胺(PI)、聚酰胺(PA)、氨纶或芳纶中的至少一种；隔离膜的类型可以包括织造膜、非织造膜、微孔膜、复合膜、碾压膜或纺丝膜中的至少一种。例如，隔离膜可以包括基材层和表面处理层。基材层可以为具有多孔结构的无纺布、膜或复合膜，基材层的材料可以包括聚乙烯、聚丙烯、聚对苯二甲酸乙二醇酯或聚酰亚胺中的至少一种。任选地，可以使用聚丙烯多孔膜、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。任选地，基材层的至少一个表面上设置有表面处理层，表面处理层可以是聚合物层或无机物层，也可以是混合聚合物与无机物所形成的层。例如，无机物层包括无机颗粒和粘结剂，本申请对无机颗粒没有特别限制，例如可以包括氧化铝、氧化硅、氧化镁、氧化钛、二氧化铪、氧化锡、二氧化铈、氧化镍、氧化锌、氧化钙、氧化锆、氧化钇、碳化硅、勃姆石、氢氧化铝、氢氧化镁、氢氧化钙或硫酸钡中的至少一种。本申请对粘结剂没有特别限制，例如可以是上述负极粘结剂中的至少一种。聚合物层中包含聚合物，本申请对聚合物没有特别限制，例如聚合物包括聚酰胺、聚丙烯腈、丙烯酸酯聚合物、聚丙烯酸、聚丙烯酸盐、聚乙烯吡咯烷酮、聚乙烯醚或聚偏氟乙烯或聚(偏氟乙烯-六氟丙烯)中的至少一种。在本申请中，隔离膜的厚度没有特别限制，只要能实现本申请的目的即可，例如隔离膜的厚度可以为5μm至500μm。
本申请的二次电池还包括包装袋，用于容纳正极极片、隔离膜、负极极片和电解液，以及二次电池中本领域已知的其它部件，本申请对上述其它部件没有特别限制。本申请对包装袋没有特别限制，可以为本领域公知的包装袋，只要能够实现本申请目的即可。例如，可采用铝塑膜包装袋。
本申请对二次电池的种类没有特别限制，其可以包括发生电化学反应的任何装置。例如，二次电池可以包括但不限于：锂金属二次电池、锂离子二次电池(锂离子电池)、钠离子二次电池(钠离子电池)、锂聚合物二次电池、锂离子聚合物二次电池。
二次电池的制备过程为本领域技术人员所熟知的，本申请没有特别的限制，例如，可以包括但不限于以下步骤：将正极极片、隔离膜和负极极片按顺序堆叠，并根据需要将其卷绕、折叠等操作得到卷绕结构的电极组件，将电极组件放入包装袋内，将电解液注入包装袋并封口，得到二次电池；或者，将正极极片、隔离膜和负极极片按顺序堆叠，然后用胶带将整个叠片结构的四个角固定好得到叠片结构的电极组件，将电极组件置入包装袋内，将电解液注入包装袋并封口，得到二次电池。此外，也可以根据需要将防过电流元件、导板等置于包装袋中，从而防止二次电池内部的压力上升、过充放电。
本申请的第三方面提供了一种电子装置，其包括本申请第一方面提供的二次电池或根据本申请第二方面提供的制备方法制得的二次电池。本申请提供的二次电池具有良好的循环性能，从而本申请提供的电子装置具有较长的使用寿命和良好的性能。
本申请的电子装置没有特别限定，其可以是用于现有技术中已知的任何电子装置。例如，电子装置可以包括但不限于笔记本电脑、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。
实施例
以下，举出实施例及对比例来对本申请的实施方式进行更具体地说明。各种的试验及评价按照下述的方法进行。另外，只要无特别说明，“份”、“％”为质量基准。
测试方法和设备：
DA99、DA50、DA90、DB5的测试
使用截面离子抛光仪(IB-19520CCP，日本电子株式会社(JEOL)提供)对待测负极极片沿厚度方向进行离子抛光，离子抛光电压为7.5kV，时间为1.5h，得到厚度方向的负极极片截面。使用扫描电子显微镜(Sigma-02-33，德国蔡司(ZEISS)提供)对负极极片截面进行测试，使用背散模式，测试电压为10kV，放大倍数为1000×，工作距离9.9mm。在背散模式下调整对比度，使得石墨颗粒为深黑色，其灰度值<70，硅碳复合颗粒为灰白色，其灰度值>90，两种颗粒间因为灰度差异而具有明显分界线。在负极极片沿厚度方向截面中选取截面积为1000μm2的第一计数区域，对该第一计数区域内所有的硅碳复合颗粒进行能谱仪(EDS)分析，得到不同硅碳复合颗粒的颗粒硅含量，并保存该张照片。在负极极片截面内随机切换不同截面积为1000μm2的第一计数区域进行EDS分析，保存10张背散照片。在该模式下，所有的石墨颗粒灰度值<70，硅碳复合颗粒的灰度值>90且灰度值与硅碳复合颗粒的颗粒硅含量呈现正相关，颗粒硅含量越大，硅碳复合颗粒亮度越高灰度值越大，因而可以得到硅碳复合颗粒灰度值与颗粒硅含量的线性关系式。利用HALCON图像处理软件，对保存的10张背散照片进行处理。利用背散照片的比例尺对像素尺寸进行标定，由于石墨颗粒灰度值<70，硅碳复合颗粒的灰度值>90，通过边缘检测功能对背散照片中的硅碳复合颗粒及石墨颗粒进行边缘分析与图像分割，保留硅碳复合颗粒的图像，并输出灰度分布数据及灰度分布直方图，选定区域所包含的总像素数量乘以标定的单像素面积即为所有被选定的硅碳复合颗粒的总面积A，单个硅碳复合颗粒的面积也可得到，记为S1、S2、S3、……、Sn，则A＝S1+S2+S3……+Sn。由于EDS分析时已得到硅碳复合颗粒灰度值与颗粒硅含量的线性关系式，灰度值与硅碳复合颗粒的颗粒硅含量线性相关，即可将灰度分布直方图转化为颗粒硅含量面积分布图。以颗粒硅含量为横轴，颗粒面积占比为纵轴，得到颗粒硅含量面积分布图。在颗粒硅含量面积分布图中，累计颗粒面积占比为50％所对应的颗粒硅含量为DA50，累计颗粒面积占比为90％所对应的颗粒硅含量为DA90，累计颗粒面积占比为99％所对应的颗粒硅含量为DA99，颗粒硅含量为5％所对应的累计颗粒面积占比为DB5。
DS99、DS90、DS50的测试
采用与上述DA99、DA50、DA90、DB5相同的测试方法，得到负极极片沿厚度方向的截面中截面积为1000μm2的第一计数区域内，硅碳复合颗粒的颗粒面积和颗粒数量，以颗粒面积为横轴，颗粒数量占比为纵轴，得到颗粒面积数量分布图。在颗粒面积数量分布图中，累计颗粒数量占比为50％所对应的颗粒面积为DS50μm2，累计颗粒数量占比为90％所对应的颗粒面积为DS90μm2，累计颗粒数量占比为99％所对应的颗粒面积为DS99μm2。
比表面积的测试
使用比表面积分析仪(TriStar II 3020M，美国麦克提供)，通过氮吸附法对各实施例和对比例的硅碳复合颗粒进行比表面积测试。其中，具体的测试依据国家标准GB/T 19587-2017《气体吸附BET法测定固态物质比表面积》进行。
硅碳复合颗粒中硅元素的质量百分含量的测试
使用截面离子抛光仪(IB-19520CCP，日本电子株式会社(JEOL)提供)对待测负极极片沿厚度方向进行离子抛光，离子抛光电压为7.5kV，时间为1.5h，得到厚度方向的负极极片截面。通过EDS点扫描测试硅碳复合颗粒中硅元素的质量百分含量。在上述厚度方向的负极极片截面中选取硅碳复合颗粒，在单个硅碳复合颗粒的中心部随机选取5个点进行EDS点扫描，得到硅元素的质量百分含量。计算上述5个点的硅元素的质量百分含量的算数平均值得到单个硅碳复合颗粒中硅元素的质量百分含量X。随机选取上述厚度方向的负极极片截面中的20个硅碳复合颗粒，测试得到20个硅碳复合颗粒的X。计算上述20个硅碳复合颗粒的X的算数平均值得到硅碳复合颗粒中硅元素的质量百分含量。其中，单个硅碳复合颗粒的中心部是指距离硅碳复合颗粒边缘大于0.5μm的区域。
硅碳复合颗粒中的氧元素的质量百分含量的测试
使用截面离子抛光仪(IB-19520CCP，日本电子株式会社(JEOL)提供)对待测负极极片沿厚度方向进行离子抛光，离子抛光电压为7.5kV，时间为1.5h，得到厚度方向的负极极片截面。通过EDS点扫描测试硅碳复合颗粒中氧元素的质量百分含量。在上述厚度方向的负极极片截面中选取硅碳复合颗粒，在单个硅碳复合颗粒的中心部随机选取5个点进行EDS点扫描，得到氧元素的质量百分含量。计算上述5个点的氧元素的质量百分含量的算数平均值得到单个硅碳复合颗粒中氧元素的质量百分含量Y。随机选取上述厚度方向的负极极片截面中的20个硅碳复合颗粒，测试得到20个硅碳复合颗粒的Y。计算上述20个硅碳复合颗粒的Y的算数平均值得到硅碳复合颗粒中氧元素的质量百分含量。其中，单个硅碳复合颗粒的中心部是指距离硅碳复合颗粒边缘大于0.5μm的区域。
循环性能的测试
(1)25℃循环圈数的测试
将锂离子电池置于25℃环境中，以3.4C恒流充电至4.4V，然后以4.4V恒压充电至0.025C，静置5分钟后以0.5C恒流放电至3.0V，此为一个充放电循环，此时为首次循环，首次循环的放电容量记为初始放电容量。将锂离子电池按照上述方法进行充放电循环，记录每一次循环的放电容量，以每一次循环的放电容量与初始放电容量做比值，得到25℃循环容量衰减曲线。在25℃循环容量衰减曲线中，锂离子电池的放电容量与初始放电容量的比值为90％时，记录此时充放电循环的圈数，记为25℃循环圈数。
(2)45℃循环圈数的测试
将锂离子电池置于45℃环境中，以3.4C恒流充电至4.4V，然后以4.4V恒压充电至0.025C，静置5分钟后以0.5C恒流放电至3.0V，此为一个充放电循环，此时为首次循环，首次循环的放电容量记为初始放电容量。将锂离子电池按照上述方法进行充放电循环，记录每一次循环的放电容量，以每一次循环的放电容量与初始放电容量做比值，得到45℃循环容量衰减曲线。在45℃循环容量衰减曲线中，锂离子电池的放电容量与初始放电容量的比值为90％时，记录此时充放电循环的圈数，记为45℃循环圈数。
实施例1-1
<硅碳复合颗粒的制备>
S1：取10kg碳骨架材料商用多孔碳(YP-50F，日本可乐丽提供)进行球磨破碎并通过射流分级机对破碎后的碳骨架材料进行分级，所得碳骨架材料的DV10为5.3μm，DV50为8.7μm，DV99为17.7μm。然后对碳骨架材料进行第一次热处理，第一次热处理的过程为：将破碎分级后的多孔碳加入石墨坩埚中，置于箱式炉中，关闭炉门，以5L/min的速率向箱体中通入氮气进行吹扫，吹扫时间为30min，然后将氮气流量调整为1L/min，以5℃/min的升温速率加热至800℃，在800℃条件下保温6h，然后关闭加热以5L/min的氮气进行吹扫降至室温，室温下取出石墨坩埚收集多孔碳粉末。
S2：对碳骨架材料进行一次沉积，一次沉积的过程为：取1kg热处理后的多孔碳，投入CVD炉中，抽真空至负压-101kPa后停止抽真空，通氮气至压力为2kPa即关闭氮气，重复抽真空通氮气，并检测腔体内部氧含量，直至氧含量降至10ppm以下，停止上述抽真空通氮气过程。然后打开尾气阀门，开启腔体转动1转/min，以2L/min的速率通氮气，以5℃/min的升温速率进行升温，升温至460℃后，保温1h。关闭氮气进气，关闭尾气阀门，关闭腔体转动，抽真空至-101kPa后关闭抽真空。开启腔体转动1转/min，以0.5L/min的速率通入甲硅烷体积分数为20％的甲硅烷/氮气的第一混合气至2kPa后，关闭第一混合气进气，保温30min，然后打开尾气阀，以2L/min的速率通氮气进行吹扫30min；重复以上抽真空、通第一混合气、氮气吹扫，上述一次沉积过程重复进行2次。
S3：通过高压传送管路将1kg经一次沉积的多孔碳投料到流化床中，静置约30min后，关闭流化床进气阀门及尾气阀门进行抽真空，腔体压力至-101kPa，然后关闭抽真空并以30L/min的速率通入氮气至2kPa，重复抽真空通氮气，并检测腔体内部氧含量，直至氧含量降至10ppm以下，停止上述抽真空通氮气过程。然后打开尾气阀门，启动流化床搅拌桨，转速为100转/min，以15L/min的速率通入氮气，在5℃/min的升温速率下升温至500℃，保温1h。在500℃条件下，切换流化床进气管路阀门，向流化床中通入甲硅烷/氮气第二混合气，甲硅烷体积分数为10％，气体流速为20L/min，搅拌桨转速调整为120转/min，反应时长为60min；然后调整甲硅烷体积分数为20％，气体流速为25L/min，搅拌桨转速150转/min，反应时长120min；最后调整甲硅烷体积分数为5％，气体流速为30L/min，搅拌桨转速为200转/min，反应时长60min，得到包括硅的碳骨架材料。
S4：对包括硅的碳骨架材料进行第二次热处理，第二次热处理的过程为：关闭甲硅烷后，以10L/min的流量通氮气，搅拌桨转速调整为100转/min，以5℃/min的速率升温至650℃后保温30min。
S5：降温至600℃后，搅拌桨转速调整为200转/min，向流化床中通入乙炔/氮气混合气，乙炔体积分数为50％，混合气流速为20L/min，反应时长为3h。反应结束后以10L/min的流量通氮气，搅拌桨转速调整为100转/min进行降温，降至室温出料，得到保护层的材料为无定形碳的硅碳复合颗粒，无定形碳位于碳骨架材料的至少部分表面。
<负极极片的制备>
将负极活性材料石墨、负极活性材料硅碳复合颗粒、负极导电剂导电炭黑(Super P)、负极粘结剂聚丙烯酸(PAA，重均分子量Mw＝4.5×105)按照质量比70:15:5:10进行混合，然后加入去离子水作为溶剂，在真空搅拌机作用下搅拌均匀，得到固含量为65wt％的负极浆料。将负极浆料均匀涂覆在厚度为8μm的负极集流体铜箔的一个表面上，85℃条件下烘干，得到单面涂布厚度为60μm的负极材料层的负极极片。之后，在该铜箔的另一个表面上重复以上步骤，得到双面涂布负极材料层的负极极片。再经冷压(冷压压力为10吨)、裁片、焊接负极极耳镍极耳，得到规格为76mm×867mm的负极极片待用。负极材料层的压实密度为1.72g/cm3。
<正极极片的制备>
将正极活性材料LiCoO2、正极导电剂导电炭黑(Super P)、正极粘结剂聚偏氟乙烯(PVDF，Mw＝7×106)按照质量比95:2.5:2.5进行混合，加入N-甲基吡咯烷酮(NMP)作为溶剂，在真空搅拌机作用下搅拌均匀，得到固含量为75wt％的正极浆料。将正极浆料均匀涂覆在厚度为10μm的正极集流体铝箔的一个表面上，85℃条件下烘干，得到单面涂布厚度为50μm的正极材料层的正极极片。之后，在该铝箔的另一个表面上重复以上步骤，即得到双面涂布正极材料层的正极极片。再经冷压(冷压压力为15吨)、裁片、焊接正极极耳铝极耳，得到规格为74mm×851mm正极极片待用。正极材料层的压实密度为4.15g/cm3。
<电解液的制备>
在干燥氩气气氛中，首先将非水溶剂碳酸丙烯酯(PC)、碳酸乙烯酯(EC)、碳酸二乙酯(DEC)以质量比PC:EC:DEC＝1:1:1混合均匀得到基础溶剂，然后向基础溶剂中加入锂盐六氟磷酸锂(LiPF6)、氟代碳酸乙烯酯(FEC)，混合均匀后得到电解液。其中，基于电解液的质量，锂盐LiPF6的质量百分含量为12.5％，FEC的质量百分含量为12.5％，其余为基础溶剂。
<隔离膜的制备>
以厚度为8μm的聚乙烯(PE)多孔聚合物薄膜(Celgard公司提供)作为隔离膜。
<锂离子电池的制备>
将上述制备得到的负极极片、隔离膜以及正极极片按顺序堆叠卷绕得到卷绕结构的电极组件。将电极组件置于铝塑膜包装袋中，干燥后注入电解液，经过真空封装、静置、化成(0.2C恒流充电120s，再以1C恒流充电180s，最后再以1.5C恒流充电至4.78V)、容量、脱气、切边等工序得到锂离子电池。
实施例1-2至实施例1-10
除了在<硅碳复合颗粒的制备>按照表1调整硅碳复合颗粒的制备参数外，其余与实施例1-1相同。
实施例2-1至实施例2-9
除了在<硅碳复合颗粒的制备>步骤S1中，通过调控球磨破碎以及分级的参数，使硅碳复合颗粒的DA99/DA50-DA90/DA50、DA50、DA90、DA99、DS99/DS50-DS90/DS50、DS50、DS90、DS99如表2所示以外，其余与实施例1-1相同。
实施例3-1
除了<硅碳复合颗粒的制备>的步骤S5采用以下步骤以外，其余与实施例1-1相同。
<硅碳复合颗粒的制备>
S5：降温至200℃后，搅拌桨转速调整为200转/min，向流化床中通过预热至200℃的二氧化碳/氮气混合气以鼓泡的形式将三甲基铝溶液带入流化床中，二氧化碳体积分数为10％，混合气流速为20L/min，反应时长为3h。反应结束后以10L/min的流量通常温氮气，搅拌桨转速调整为100转/min进行降温，降至室温出料，得到保护层的材料为氧化铝的硅碳复合颗粒，氧化铝位于碳骨架材料的至少部分表面。
实施例3-2
除了<硅碳复合颗粒的制备>的步骤S5采用以下步骤以外，其余与实施例1-1相同。
<硅碳复合颗粒的制备>
S5：降温至600℃后，搅拌桨转速调整为200转/min，向流化床中通入甲硅烷/氮气混合气，甲硅烷体积分数为5％，混合气流速为20L/min，反应时长为1h。反应结束后以10L/min的流量通氮气，搅拌桨转速调整为100转/min进行降温，降至室温出料，所得粉末放置于空气气氛下进行氧化散热，得到保护层的材料为二氧化硅的硅碳复合颗粒，二氧化硅位于碳骨架材料的至少部分表面。
实施例4-1
除了<负极极片的制备>中负极活性材料石墨、负极活性材料硅碳复合颗粒、负极导电剂导电炭黑(Super P)、负极粘结剂聚丙烯酸(PAA，重均分子量Mw＝4.5×105)按照质量比80:5:5:10进行混合以外，其余与实施例1-1相同。
实施例4-2
除了<负极极片的制备>中负极活性材料石墨、负极活性材料硅碳复合颗粒、负极导电剂导电炭黑(Super P)、负极粘结剂聚丙烯酸(PAA，重均分子量Mw＝4.5×105)按照质量比35:50:5:10进行混合以外，其余与实施例1-1相同。
实施例4-3
除了<负极极片的制备>中负极活性材料石墨、负极活性材料硅碳复合颗粒、负极导电剂导电炭黑(Super P)、负极粘结剂聚丙烯酸(PAA，重均分子量Mw＝4.5×105)按照质量比0.5:95:0.5:4进行混合以外，其余与实施例1-1相同。
对比例1-1至对比例1-2
除了在<硅碳复合颗粒的制备>按照表1调整硅碳复合颗粒的制备参数外，其余与实施例1-1相同。
对比例1-3
除了<硅碳复合颗粒的制备>不包括步骤S2，直接将步骤S1得到的多孔碳用作步骤S3的原料以外，其余与实施例1-1相同。
对比例1-4
除了<硅碳复合颗粒的制备>的步骤S2采用以下制备方法以外，其余与实施例1-1相同。
<硅碳复合颗粒的制备>
S2：对碳骨架材料进行一次沉积，一次沉积的过程为：取1kg热处理后的多孔碳，投入CVD炉中，抽真空至负压-101kPa后停止抽真空，通氮气至压力为2kPa即关闭氮气，重复抽真空通氮气，并检测腔体内部氧含量，直至氧含量降至10ppm以下，停止上述抽真空通氮气过程。然后打开尾气阀门，开启腔体转动1转/min，以2L/min的速率通氮气，以5℃/min的升温速率进行升温，升温至460℃后，保温1h。保持尾气阀门开启，控制炉内压力为105kPa，腔体转动1转/min，以0.5L/min的速率通入甲硅烷体积分数为20％的甲硅烷/氮气第一混合气，通气时长为120min，关闭第一混合气进气，保温30min，以2L/min的速率通氮气进行吹扫30min；重复以上通第一混合气、氮气吹扫，上述一次沉积过程重复进行2次。
各实施例和对比例的制备参数和性能参数如表1至表4所示。
表1

注：表1中的“\”表示无对应参数。
从实施例1-1至实施例1-10、对比例1-1至对比例1-4可以看出，本申请实施例中的二次电池的负极活性材料包括硅碳复合颗粒，并且满足：0.23≤DA99/DA50-DA90/DA50≤0.57，可以使得二次电池具有更多的25℃循环圈数和45℃循环圈数，表明二次电池具有良好的循环性能。而对比例1-1至对比例1-4的二次电池，DA99/DA50-DA90/DA50不满足上述关系，二次电池的25℃循环圈数和45℃循环圈数更少，表明二次电池的循环性能更差。
DA50、DA90、DA99的值通常会影响二次电池的循环性能。从实施例1-1至实施例1-10可以看出，当DA50、DA90、DA99的值在本申请范围内时，二次电池具有较多的25℃循环圈数和45℃循环圈数，表明二次电池具有良好的循环性能。
DB5的值通常会影响二次电池的循环性能。从实施例1-1至实施例1-10可以看出，当DB5的值在本申请范围内时，二次电池具有较多的25℃循环圈数和45℃循环圈数，表明二次电池具有良好的循环性能。
硅碳复合颗粒的比表面积通常会影响二次电池的循环性能。从实施例1-1至实施例1-10可以看出，当硅碳复合颗粒的比表面积在本申请范围内时，二次电池具有较多的25℃循环圈数和45℃循环圈数，表明二次电池具有良好的循环性能。
硅碳复合颗粒中的硅元素的质量百分含量通常会影响二次电池的循环性能。从实施例1-1至实施例1-10可以看出，当硅碳复合颗粒中的硅元素的质量百分含量在本申请范围内时，二次电池具有较多的25℃循环圈数和45℃循环圈数，表明二次电池具有良好的循环性能。
硅碳复合颗粒中的氧元素的质量百分含量通常会影响二次电池的循环性能。从实施例1-1至实施例1-10可以看出，当硅碳复合颗粒中的氧元素的质量百分含量在本申请范围内时，二次电池具有较多的25℃循环圈数和45℃循环圈数，表明二次电池具有良好的循环性能。
从图2可以看出，实施例1-1的硅碳复合颗粒的颗粒硅含量分布较窄，颗粒硅含量主要分布在18％至45％之间，硅碳复合颗粒之间颗粒硅含量的差异较小。
表2
DS99/DS50-DS90/DS50的值通常会影响二次电池的循环性能。从实施例1-1、实施例2-1至实施例2-9可以看出，当DS99/DS50-DS90/DS50的值在本申请范围内时，二次电池具有更多的25℃循环圈数和45℃循环圈数，表明二次电池具有良好的循环性能。
DS50、DS90、DS99的值通常会影响二次电池的循环性能。从实施例1-1、实施例2-1至实施例2-9可以看出，当DS50、DS90、DS99的值在本申请范围内时，二次电池具有较多的25℃循环圈数和45℃循环圈数，表明二次电池具有良好的循环性能。
从图3可以看出，实施例1-1的硅碳复合颗粒的颗粒面积分布较窄，颗粒面积主要分布在10μm2至250μm2之间，硅碳复合颗粒之间尺寸差异较小。而实施例2-7的硅碳复合颗粒的颗粒面积分布较宽，颗粒面积主要分布在8μm2至5000μm2之间，硅碳复合颗粒之间尺寸差异较大。
表3
硅碳复合颗粒保护层的材料通常会影响二次电池的循环性能，从实施例1-1、实施例3-1至实施例3-2可以看出，当硅碳复合颗粒保护层的材料在本申请范围内时，二次电池具有较多的25℃循环圈数和45℃循环圈数，表明二次电池具有良好的循环性能。
表4
硅碳复合颗粒的质量百分含量以及A1/4、A2/1000的值通常会影响二次电池的循环性能，从实施例1-1、实施例4-1至实施例4-3可以看出，调整硅碳复合颗粒的质量百分含量以及A1/4、A2/1000的值在本申请范围内时，二次电池具有较多的25℃循环圈数和45℃循环圈数，表明二次电池具有良好的循环性能。
需要说明的是，在本文中，诸如第一和第二等之类的关系术语仅仅用来将一个实体或者操作与另一个实体或操作区分开来，而不一定要求或者暗示这些实体或操作之间存在任何这种实际的关系或者顺序。而且，术语“包括”、“包含”或者其任何其他变体意在涵盖非排他性的包含，从而使得包括一系列要素的过程、方法或者物品不仅包括那些要素，而且还包括没有明确列出的其他要素，或者是还包括为这种过程、方法或者物品所固有的要素。
本说明书中的各个实施例均采用相关的方式描述，各个实施例之间相同相似的部分互相参见即可，每个实施例重点说明的都是与其他实施例的不同之处。
以上所述仅为本申请的较佳实施例，并不用以限制本申请，凡在本申请的精神和原则之内，所做的任何修改、等同替换、改进等，均应包含在本申请保护的范围之内。

Claims (12)

  1. 一种二次电池，其包括负极极片，所述负极极片包括负极集流体和设置于所述负极集流体至少一个表面的负极材料层，所述负极材料层包括负极活性材料，所述负极活性材料包括硅碳复合颗粒，
    在所述负极极片沿厚度方向的截面中包括截面积为1000μm2的第一计数区域，在所述第一计数区域内，基于单个所述硅碳复合颗粒的质量，硅元素的质量百分含量为颗粒硅含量，具有相同所述颗粒硅含量的硅碳复合颗粒的截面积之和与所述第一计数区域内所有硅碳复合颗粒的截面积之和的比值为颗粒面积占比，以所述颗粒硅含量为横轴，所述颗粒面积占比为纵轴，得到颗粒硅含量面积分布图；所述颗粒硅含量按从小到大的顺序排列，所述颗粒硅含量所对应的颗粒面积占比依次相加得到的颗粒面积占比之和为累计颗粒面积占比，在所述颗粒硅含量面积分布图中，所述累计颗粒面积占比为50％所对应的颗粒硅含量为DA50，所述累计颗粒面积占比为90％所对应的颗粒硅含量为DA90，所述累计颗粒面积占比为99％所对应的颗粒硅含量为DA99，0.23≤DA99/DA50-DA90/DA50≤0.57。
  2. 根据权利要求1所述的二次电池，其中，30％≤DA50≤45％，42％≤DA90≤65％，55％≤DA99≤75％。
  3. 根据权利要求1所述的二次电池，其中，在所述颗粒硅含量面积分布图中，所述颗粒硅含量为5％所对应的累计颗粒面积占比为DB5，0.93％≤DB5≤7.26％。
  4. 根据权利要求1至3中任一项所述的二次电池，其中，在所述第一计数区域内，单个所述硅碳复合颗粒的截面积为颗粒面积，具有相同所述颗粒面积的硅碳复合颗粒的颗粒数量与所述第一计数区域内所有硅碳复合颗粒的颗粒总数量的比值为颗粒数量占比，以所述颗粒面积为横轴，所述颗粒数量占比为纵轴，得到颗粒面积数量分布图；所述颗粒面积按从小到大的顺序排列，所述颗粒面积所对应的颗粒数量占比依次相加得到的颗粒数量占比之和为累计颗粒数量占比，在所述颗粒面积数量分布图中，所述累计颗粒数量占比为50％所对应的颗粒面积为DS50μm2，所述累计颗粒数量占比为90％所对应的颗粒面积为DS90μm2，所述累计颗粒数量占比为99％所对应的颗粒面积为DS99μm2，1.66≤DS99/DS50-DS90/DS50≤4.7。
  5. 根据权利要求4所述的二次电池，其中，25≤DS50≤60，98≤DS90≤150，181≤DS99≤255。
  6. 根据权利要求1至3中任一项所述的二次电池，其中，所述硅碳复合颗粒的比表面积为4.5m2/g至8.9m2/g。
  7. 根据权利要求1至3中任一项所述的二次电池，其中，所述硅碳复合颗粒满足以下特征中的至少一者：
    (a)所述硅碳复合颗粒中的硅元素的质量百分含量为35％至55％；
    (b)所述硅碳复合颗粒中的氧元素的质量百分含量为1％至4％；
    (c)在所述负极极片的表面上包括面积为4cm2的第二计数区域，在所述第二计数区域内，所述硅碳复合颗粒的面积总和为A1cm2，0.05≤A1/4≤0.95；
    (d)在所述第一计数区域内，所述硅碳复合颗粒的面积总和为A2μm2，0.05≤A2/1000≤0.95；
    (e)所述负极活性材料还包括石墨或硬碳中的至少一种；
    (f)基于所述负极材料层的质量，所述硅碳复合颗粒的质量百分含量为5％至95％。
  8. 根据权利要求1至3中任一项所述的二次电池，所述硅碳复合颗粒包括碳骨架，所述碳骨架中含有硅元素。
  9. 根据权利要求8所述的二次电池，所述硅碳复合颗粒包括位于所述碳骨架至少部分表面的保护层，所述保护层包括无定形碳、金属氧化物或非金属氧化物中的至少一种，所述金属氧化物包括氧化铝、氧化铜或氧化钛中的至少一种，所述非金属氧化物包括二氧化硅或氧化亚硅中的至少一种。
  10. 一种权利要求1至9中任一项所述的二次电池的制备方法，其中，所述硅碳复合颗粒的制备方法包括以下步骤：
    S1：提供碳骨架材料，对所述碳骨架材料进行破碎分级，然后对所述碳骨架材料进行第一次热处理，所述第一次热处理的温度为700℃至900℃，所述第一次热处理的时间为4h至6h；
    S2：对所述碳骨架材料进行一次沉积，升温至430℃至550℃后，在-60kPa至-101kPa的负压环境下，通入含有体积分数为5％至50％的硅烷的第一混合气，反应2h至6h，所述一次沉积重复进行2至5次；
    S3：将经一次沉积的所述碳骨架材料转移到流化床中进行加热，通入含有体积分数为5％至50％的硅烷的第二混合气，进行二次沉积得到包括硅的碳骨架材料；所述二次沉积的温度为430℃至550℃，所述二次沉积的反应时间为1h至6h；
    S4：将所述包括硅的碳骨架材料在620℃至700℃温度下进行第二次热处理，所述第二次热处理时长为0.5h至1h；
    S5：然后在所述包括硅的碳骨架材料的表面制备保护层，得到所述硅碳复合颗粒。
  11. 根据权利要求10所述的制备方法，其满足以下特征中的至少一者：
    (1)所述碳骨架材料包括人造石墨、天然石墨、中间相碳微球、软碳或硬碳中的至少一种；
    (2)所述第一混合气和所述第二混合气各自独立地还包括氮气、氢气或氩气中的至少一种；
    (3)所述保护层的源材料包括用于制备无定形碳的第一源材料、用于制备金属氧化物的第二源材料、用于制备非金属氧化物的第三源材料，所述第一源材料包括乙炔、甲烷、丙烯、乙烯或丙烷中的至少一种，所述第二源材料包括异丙醇钛、三甲基铝或乙酸铜中的至少一种，所述第三源材料包括正硅酸乙酯、三乙氧基硅烷或甲硅烷中的至少一种。
  12. 一种电子装置，其中，所述电子装置包括权利要求1至9中任一项所述的二次电池或根据权利要求10或11所述的制备方法制得的二次电池。
PCT/CN2025/077863 2024-03-05 2025-02-18 一种二次电池及其制备方法和电子装置 Pending WO2025185441A1 (zh)

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