WO2025218409A1 - 电化学装置和电子装置 - Google Patents

电化学装置和电子装置

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Publication number
WO2025218409A1
WO2025218409A1 PCT/CN2025/082711 CN2025082711W WO2025218409A1 WO 2025218409 A1 WO2025218409 A1 WO 2025218409A1 CN 2025082711 W CN2025082711 W CN 2025082711W WO 2025218409 A1 WO2025218409 A1 WO 2025218409A1
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Prior art keywords
negative electrode
material layer
silicon
electrochemical device
electrode material
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PCT/CN2025/082711
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English (en)
French (fr)
Inventor
刘松松
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Ningde Amperex Technology Ltd
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Ningde Amperex Technology Ltd
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Publication of WO2025218409A1 publication Critical patent/WO2025218409A1/zh
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/364—Composites as mixtures
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—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
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • 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 an electrochemical device and an electronic device.
  • silicon-based materials have extremely high theoretical specific capacity
  • silicon-based materials are mixed with graphite as negative electrode active materials to significantly improve the energy density of lithium-ion batteries.
  • silicon-based materials into graphite will deteriorate the kinetic ability of the negative electrode plate, and lithium will easily be deposited on the surface of the negative electrode plate, affecting the cycle performance of the lithium-ion battery and posing a safety hazard.
  • the purpose of the present application is to provide an electrochemical device and an electronic device to alleviate the problem of lithium deposition on the surface of the negative electrode in the electrochemical device.
  • lithium-ion batteries are used as an example of electrochemical devices to explain this application, but the electrochemical devices of this application are not limited to lithium-ion batteries.
  • the specific technical solutions are as follows:
  • the first aspect of the present application provides an electrochemical device, the electrochemical device comprising a negative electrode sheet, a positive electrode sheet, and a separator disposed between the negative electrode sheet and the positive electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a first negative electrode material layer and a second negative electrode material layer disposed on at least one surface of the negative electrode current collector, the first negative electrode material layer being disposed between the negative electrode current collector and the second negative electrode material layer; when the electrochemical device is charged at a constant current at a maximum non-lithium precipitation rate to an upper limit cut-off voltage, in the X-ray diffraction patterns of the first negative electrode material layer and the second negative electrode material layer, the characteristic peak of LiC 12 satisfies at least one of the following characteristics (1) or (2): (1) in the X-ray diffraction pattern of the second negative electrode material layer, the characteristic peak of LiC 6 does not appear, and the 2 ⁇ at the maximum intensity of the characteristic peak of LiC 12 is A 2 °, 25.15 ⁇ A 2
  • the lithium insertion degree of the surface layer of the negative electrode plate is low, and/or the lithium insertion uniformity of the negative electrode plate is good, and there is no localized increase in lithium insertion on the surface of the negative electrode plate, thereby alleviating the problem of lithium deposition on the surface of the negative electrode plate in the electrochemical device.
  • the first negative electrode material layer includes a first negative electrode active material, which includes a first graphite;
  • the second negative electrode material layer includes a second negative electrode active material, which includes a silicon-carbon material and a second graphite;
  • the weight percentage of the silicon-carbon material in the second negative electrode active material is 15% to 50%, and the weight percentage of the silicon element in the silicon-carbon material is 30% to 60%.
  • the first negative electrode material layer at the bottom of the negative electrode plate includes the first graphite, and the second negative electrode material layer at the surface includes the second graphite and the silicon-carbon material. The weight percentage of the silicon-carbon material and the weight percentage of the silicon element in the silicon-carbon material are controlled within the above ranges.
  • the negative electrode plate to provide sufficient active material and also helps to increase the number of lithium-inserting sites on the surface of the negative electrode plate while reducing the probability of volume expansion of the negative electrode plate caused by the silicon element. This can alleviate the problem of lithium deposition on the surface of the negative electrode plate in the electrochemical device, and also enable the electrochemical device to have a higher energy density and a smaller volume expansion rate.
  • the mass percentage of silicon-carbon material in the second negative electrode active material is 30% to 50%, and the mass percentage of silicon element in the silicon-carbon material is 50% to 60%, which can further improve the problem of lithium deposition on the surface of the negative electrode.
  • the particle size Dv50-1 of the first graphite is 11.0 ⁇ m to 13.5 ⁇ m.
  • the electrochemical device has a higher capacity retention rate based on a lower probability of lithium deposition on the surface of the negative electrode.
  • the particle size Dv50-2 of the second graphite and the particle size Dv50-1 of the first graphite satisfy the following relationship: 1 ⁇ m ⁇ Dv50-1 - Dv50-2 ⁇ 5 ⁇ m .
  • the particle sizes Dv10, Dv50-3 , and Dv90 of the silicon-carbon material satisfy the following conditions: 5 ⁇ m ⁇ Dv10 ⁇ 6 ⁇ m, 8 ⁇ m ⁇ Dv50-3 ⁇ 10.5 ⁇ m, and 13 ⁇ m ⁇ Dv90 ⁇ 17 ⁇ m.
  • the particle sizes Dv10 and Dv90 of the silicon-carbon material satisfy the following relationship: 8 ⁇ m ⁇ Dv90-Dv10 ⁇ 10.5 ⁇ m. Controlling the Dv90-Dv10 value within this range improves the kinetics of the electrochemical device while maintaining a higher energy density.
  • the specific surface area of the silicon-carbon material is 0.5 m 2 /g to 3.5 m 2 /g.
  • the specific surface area of the silicon-carbon material is 1.0 m 2 /g to 2.0 m 2 /g, which is beneficial for further alleviating the problem of lithium deposition on the surface of the negative electrode while maintaining a high capacity retention rate of the electrochemical device.
  • the compacted density C1 of the first negative electrode material layer and the compacted density C2 of the second negative electrode material layer satisfy the following conditions: 1.5 g/cm3 ⁇ C1 ⁇ 1.65 g / cm3 , 1.35 g/ cm3 ⁇ C2 ⁇ 1.5 g / cm3 , and 0.05 g / cm3 ⁇ C1 -C2 ⁇ 0.3 g / cm3 .
  • the electrochemical device has a higher energy density while alleviating the problem of lithium plating on the surface of the negative electrode sheet.
  • a second aspect of the present application provides an electronic device, which includes the electrochemical device described in any one of the aforementioned embodiments. Therefore, the electronic device has good performance.
  • the present application provides an electrochemical device and an electronic device, wherein the electrochemical device comprises a negative electrode sheet, a positive electrode sheet, and a separator disposed between the negative electrode sheet and the positive electrode sheet, the negative electrode sheet comprises a negative electrode current collector, and a first negative electrode material layer and a second negative electrode material layer disposed on at least one surface of the negative electrode current collector, wherein the first negative electrode material layer is disposed between the negative electrode current collector and the second negative electrode material layer; when the electrochemical device is charged at a constant current at a maximum non-lithium precipitation rate to an upper limit cut-off voltage, in the X-ray diffraction patterns of the first negative electrode material layer and the second negative electrode material layer, the characteristic peak of LiC 12 satisfies at least one of the following characteristics (1) or (2): (1) in the X-ray diffraction pattern of the second negative electrode material layer, the characteristic peak of LiC 6 does not appear, and the 2 ⁇ at the maximum intensity of the characteristic peak of LiC 12 is A 2 °, 25.15
  • the lithium insertion degree of the surface layer of the negative electrode plate is low, and/or the lithium insertion uniformity of the negative electrode plate is good, and there is no local increase in lithium insertion on the surface of the negative electrode plate.
  • the problem of lithium deposition on the surface of the negative electrode plate in the electrochemical device can be alleviated, and the cycle performance of the electrochemical device can be improved.
  • FIG1 is a schematic diagram of the cross-sectional structure of a negative electrode sheet along its length and thickness directions according to some embodiments of the present application;
  • FIG2 is an X-ray diffraction pattern of the negative electrode sheet of Example 1-1 of the present application.
  • FIG3 is an X-ray diffraction pattern of the negative electrode sheet of Comparative Example 1 of the present application.
  • Reference numerals 10 - negative electrode plate; 11 - first negative electrode material layer; 12 - second negative electrode material layer; 13 - negative electrode current collector; 131 - first surface; 132 - second surface.
  • a lithium-ion battery is used as an example of an electrochemical device to explain the present application, but the electrochemical device of the present application is not limited to a lithium-ion battery.
  • the first aspect of the present application provides an electrochemical device, which includes a negative electrode sheet, a positive electrode sheet, and a separator arranged between the negative electrode sheet and the positive electrode sheet.
  • the negative electrode sheet includes a negative electrode collector and a first negative electrode material layer and a second negative electrode material layer arranged on at least one surface of the negative electrode collector, and the first negative electrode material layer is arranged between the negative electrode collector and the second negative electrode material layer.
  • the characteristic peak of LiC12 in the X-ray diffraction patterns of the first negative electrode material layer and the second negative electrode material layer satisfies at least one of the following characteristics (1) or (2): (1) the characteristic peak of LiC6 does not appear in the X-ray diffraction pattern of the second negative electrode material layer, and the 2 ⁇ at the maximum intensity of the characteristic peak of LiC12 is A2 °, and 25.15 ⁇ A2 ⁇ 25.30 ; (2) the 2 ⁇ at the maximum intensity of the characteristic peak of LiC12 in the X-ray diffraction pattern of the first negative electrode material layer is A1 °, and the 2 ⁇ at the maximum intensity of the characteristic peak of LiC12 in the X-ray diffraction pattern of the second negative electrode material layer is A2 °, and 0 ⁇ A1 - A2 ⁇ 0.15 .
  • the characteristic peak of LiC 6 does not appear in the X-ray diffraction pattern of the second negative electrode material layer, and the 2 ⁇ at the maximum intensity of the characteristic peak of LiC 12 is A 2 °, and 25.15 ⁇ A 2 ⁇ 25.30.
  • the 2 ⁇ at the maximum intensity of the characteristic peak of LiC 12 in the X-ray diffraction pattern of the first negative electrode material layer is A 1 °
  • the 2 ⁇ at the maximum intensity of the characteristic peak of LiC 12 in the X-ray diffraction pattern of the second negative electrode material layer is A 2 °
  • the 2 ⁇ at the maximum intensity of the characteristic peak of LiC 12 is A 1 °
  • the 2 ⁇ at the maximum intensity of the characteristic peak of LiC 12 is A 2 °, 0 ⁇ A 1 -A 2 ⁇ 0.15, 25.15 ⁇ A 2 ⁇ 25.30.
  • the length direction of the negative electrode sheet itself is defined as X
  • the thickness direction of the negative electrode sheet itself is defined as Z.
  • Figure 1 shows a schematic cross-sectional structure of the negative electrode sheet along its own length direction X and thickness direction Z in some embodiments of the present application.
  • the negative electrode sheet 10 includes a negative electrode collector 13, a first negative electrode material layer 11 and a second negative electrode material layer 12.
  • the negative electrode collector 13 includes a first surface 131 and a second surface 132 arranged along its own thickness direction Z.
  • the first negative electrode material layer 11 and the second negative electrode material layer 12 are arranged on two surfaces of the negative electrode collector 13, namely the first surface 131 and the second surface 132.
  • the first negative electrode material layer 11 and the second negative electrode material layer 12 are arranged on the two surfaces of the negative electrode collector 13, namely the first surface 131 and the second surface 132.
  • the first negative electrode material layer 11 is arranged between the negative electrode collector 13 and the second negative electrode material layer 12. It is understood that, in some other embodiments of the present application, the first negative electrode material layer 11 and the second negative electrode material layer 12 may be disposed on one surface of the negative electrode current collector 13 , namely, the first surface 131 or the second surface 132 .
  • the maximum non-lithium deposition rate refers to the maximum charging rate when the negative electrode of the electrochemical device does not deposit lithium, specifically the maximum non-lithium deposition rate measured according to the test method in the "test of the maximum non-lithium deposition charging rate".
  • the upper limit cutoff voltage of the electrochemical device is 4.5V to 4.55V.
  • the characteristic peak of LiC 6 does not appear in the X-ray diffraction pattern of the second negative electrode material layer, indicating that the lithium insertion degree in the second negative electrode material layer is low, and the lithium insertion degree of the surface first negative electrode material layer and the bottom second negative electrode material layer is relatively uniform; the maximum intensity 2 ⁇ of the characteristic peak of LiC 12 is A 2 °, 25.15 ⁇ A 2 ⁇ 25.30.
  • A2 is 25.15, 25.18, 25.20, 25.22, 25.24, 25.25, 25.27, 25.28, 25.29, 25.30, or any value between any two of the above numerical ranges.
  • A2 being within the above range indicates that when the electrochemical device is constantly charged at the highest non-lithium deposition rate to the upper limit cutoff voltage, the lithium insertion degree in the second negative electrode material layer on the surface of the negative electrode sheet is low, and lithium deposition on the surface of the negative electrode sheet is small.
  • the electrochemical device is constantly charged at the highest non-lithium deposition rate to the upper limit cutoff voltage.
  • the 2 ⁇ at the maximum intensity in the characteristic peak of LiC12 is A1 °
  • the 2 ⁇ at the maximum intensity in the characteristic peak of LiC12 is A2 °
  • 0 ⁇ A1 - A2 ⁇ 0.15 is 0.00, 0.01, 0.02, 0.03, 0.04, 0.07, 0.09, 0.10, 0.12, 0.15 or any value between any two of the above numerical ranges.
  • a 1 -A 2 is within the above range, indicating that when the electrochemical device is charged at the highest non-lithium deposition rate, the electrochemical device is in an undercharged state, and the lithium insertion degrees of the first negative electrode material layer and the second negative electrode material layer in the negative electrode plate are relatively consistent, indicating that the lithium insertion uniformity in the negative electrode plate is good, and there is no local increase in lithium insertion, thereby reducing the probability of lithium deposition on the surface of the negative electrode plate.
  • the lithium insertion degree of the surface layer of the negative electrode plate is low, and/or the lithium insertion uniformity of the negative electrode plate is good, and there is no local increase in lithium insertion on the surface of the negative electrode plate, and the problem of lithium deposition on the surface of the negative electrode plate in the electrochemical device is alleviated.
  • the present application has no particular limitation on the range A 1 ° of 2 ⁇ at the maximum intensity of the characteristic peak of LiC 12 in the X-ray diffraction pattern of the first negative electrode material layer, as long as the purpose of the present application can be achieved. For example, 25.27° ⁇ A 1 ⁇ 25.5°.
  • the present application has no particular limitation on the method for controlling the 2 ⁇ range A 1 ° at the maximum intensity of the characteristic peak of LiC 12 in the X-ray diffraction pattern of the first negative electrode material layer, as long as the purpose of the present application can be achieved. For example, this can be achieved by controlling the thickness of the negative electrode sheet.
  • the present application does not particularly limit the method for regulating the 2 ⁇ range A 2 ° at the maximum intensity of the characteristic peak of LiC 12 in the X-ray diffraction pattern of the second negative electrode material layer, as long as the objectives of the present application can be achieved.
  • this can be achieved by regulating at least one of the mass percentage of the silicon-carbon material in the second negative electrode active material or the mass percentage of the silicon element in the silicon-carbon material.
  • the first negative electrode material layer includes a first negative electrode active material, which includes a first graphite;
  • the second negative electrode material layer includes a second negative electrode active material, which includes a silicon-carbon material and a second graphite;
  • the mass percentage of the silicon-carbon material in the second negative electrode active material is 15% to 50%, and the mass percentage of silicon in the silicon-carbon material is 30% to 60%.
  • the mass percentage of the silicon-carbon material in the second negative electrode active material is 15%, 20%, 26%, 32%, 40%, 46%, 50%, or any value between any two of the above numerical ranges.
  • the mass percentage of silicon in the silicon-carbon material is 30%, 34%, 39%, 42%, 50%, 53%, 60%, or any value between any two of the above numerical ranges.
  • Adding silicon-carbon material to the second negative electrode material layer provided on the surface of the negative electrode plate can increase the gram capacity of the surface of the negative electrode plate, increase the number of lithium insertion sites, and thus reduce the degree of lithium insertion in the second negative electrode material layer, which is beneficial to alleviating the problem of lithium deposition on the surface of the negative electrode plate in the electrochemical device.
  • the first negative electrode material layer at the bottom of the negative electrode plate includes a first graphite
  • the second negative electrode material layer on the surface includes a second graphite and a silicon-carbon material.
  • the mass percentage of the silicon-carbon material and the mass percentage of the silicon element in the silicon-carbon material are controlled within the above range.
  • the negative electrode plate can provide sufficient active material, and is also beneficial to the silicon element in the surface of the negative electrode plate.
  • the probability of volume expansion of the negative electrode plate caused by the silicon element is reduced.
  • the problem of lithium deposition on the surface of the negative electrode plate in the electrochemical device is alleviated, and the electrochemical device has a higher energy density and a smaller volume expansion rate.
  • the present application does not impose any particular restrictions on the method for regulating the mass percentage of silicon in the silicon-carbon material, as long as the purpose of the present application can be achieved.
  • the mass percentage of silicon in the silicon-carbon material can be changed by regulating the deposition content of silicon during the preparation process. It is also possible to directly purchase silicon-carbon materials with different silicon content, and in combination with the "Test of the Mass Percentage of Silicon in Silicon-carbon Materials" provided in this application, select the silicon-carbon material with the required silicon content.
  • the mass percentage of the second graphite in the second negative electrode active material is 50% to 85%.
  • the first graphite and the second graphite are each independently selected from natural graphite or artificial graphite.
  • the particle size Dv50-1 of the first graphite is 11.0 ⁇ m to 13.5 ⁇ m.
  • the particle size Dv50-1 of the first graphite is 11.0 ⁇ m, 11.3 ⁇ m, 11.7 ⁇ m, 12.0 ⁇ m, 12.8 ⁇ m, 13.0 ⁇ m, 13.5 ⁇ m or any value between any two of the above numerical ranges.
  • the first graphite is less likely to agglomerate, the first graphite can be evenly distributed in the first negative electrode material layer, and the surface area of the first graphite can enable it to be in sufficient contact with the electrolyte, so that the first graphite can fully exert its activity and the first negative electrode material layer has a higher capacity.
  • the electrochemical device has a higher energy density on the basis of having a lower probability of lithium plating on the surface of the negative electrode plate. It also enables the electrochemical device to have a higher capacity retention rate.
  • the particle size Dv50-2 of the second graphite and the particle size Dv50-1 of the first graphite satisfy: 1 ⁇ m ⁇ Dv50-1 - Dv50-2 ⁇ 5 ⁇ m .
  • the value of Dv50-1- Dv50-2 is 1 ⁇ m, 2 ⁇ m, 3 ⁇ m, 4 ⁇ m, 5 ⁇ m or any value between any two of the above numerical ranges.
  • the difference Dv50-1 - Dv50-2 between the particle size Dv50-2 of the second graphite and the particle size Dv50-1 of the first graphite is regulated within the above range.
  • the first graphite and the second graphite have a suitable kinetic ability difference, which matches the difference in lithium insertion rate required by the first negative electrode material layer and the second negative electrode material layer, which is beneficial for the electrochemical device to have a high energy density while further reducing the probability of surface decomposition of the negative electrode sheet, and also making the electrochemical device have a higher capacity retention rate.
  • the present application has no particular limitation on the particle size Dv50-2 of the second graphite, as long as the purpose of the present application can be achieved.
  • the particle size Dv50-2 of the second graphite is 8.5 ⁇ m to 13.5 ⁇ m.
  • the particle sizes Dv10, Dv50-3 , and Dv90 of the silicon-carbon material satisfy the following conditions: 5 ⁇ m ⁇ Dv10 ⁇ 6 ⁇ m, 8 ⁇ m ⁇ Dv50-3 ⁇ 10.5 ⁇ m, and 13 ⁇ m ⁇ Dv90 ⁇ 17 ⁇ m.
  • the particle size Dv10 of the silicon-carbon material is 5 ⁇ m, 5.2 ⁇ m, 5.4 ⁇ m, 5.7 ⁇ m, 5.8 ⁇ m, 6 ⁇ m, or any value between any two of the above numerical ranges.
  • the particle size Dv50-3 of the silicon-carbon material is 8 ⁇ m, 8.2 ⁇ m, 8.7 ⁇ m, 9.1 ⁇ m, 9.8 ⁇ m, 10.0 ⁇ m, 10.5 ⁇ m, or any value between any two of the above numerical ranges.
  • the particle size Dv90 of the silicon-carbon material is 13 ⁇ m, 13.6 ⁇ m, 14.4 ⁇ m, 14.7 ⁇ m, 15.3 ⁇ m, 16 ⁇ m, 16.5 ⁇ m, 17 ⁇ m, or any value between any two of the above numerical ranges.
  • the silicon-carbon material has a particle size of suitable size and small size differences between each particle.
  • the probability of agglomeration is low, which is conducive to uniform distribution in the second negative electrode material layer, thereby facilitating the improvement of the electrolyte's wettability to the negative electrode sheet and improving the electrolyte's ability to wet and retain the negative electrode sheet.
  • the utilization rate of the silicon-carbon material is improved, the problem of lithium deposition on the surface of the negative electrode sheet in the electrochemical device is alleviated, its energy density is improved, and it also has a high capacity retention rate.
  • the particle sizes Dv10 and Dv90 of the silicon-carbon material satisfy the following conditions: 8 ⁇ m ⁇ Dv90-Dv10 ⁇ 10.5 ⁇ m.
  • the value of Dv90-Dv10 is 8.0 ⁇ m, 9.7 ⁇ m, 10.2 ⁇ m, 10.5 ⁇ m, or any value between any two of the above numerical ranges.
  • silicon-carbon materials of different particle sizes are distributed in a suitable gradient, which is conducive to the close and uniform distribution of the silicon-carbon material in the second negative electrode material layer, and enhances the rapid lithium insertion ability of the silicon-carbon material, so that the electrochemical device has improved its kinetics on the basis of having a higher energy density, and has a higher minimum charge rate and capacity retention rate.
  • Dv10 refers to the particle size at which the volume-based particle size distribution reaches 10% of the cumulative volume from the smallest particle size
  • Dv50 refers to the particle size at which the volume-based particle size distribution reaches 50% of the cumulative volume from the smallest particle size
  • Dv90 refers to the particle size at which the volume-based particle size distribution reaches 90% of the cumulative volume from the smallest particle size.
  • the aforementioned “particles” may be a silicon-carbon material, a first graphite, or a second graphite.
  • the present application does not particularly limit the method for regulating the particle size of the silicon-carbon material, the first graphite, and the second graphite, as long as the purpose of the present application can be achieved.
  • it can be achieved by crushing or screening.
  • the particle size Dv50-1 of the first graphite, the particle size Dv50-2 of the second graphite, and the particle sizes Dv10, Dv50-3 , and Dv90 of the silicon-carbon material can be determined by purchasing commercially available silicon-carbon materials, the first graphite, and the second graphite, in combination with the test method of "Particle Size Test" in this application, and the desired materials can be selected.
  • the specific surface area of the silicon-carbon material is 0.5m 2 /g to 3.5m 2 /g.
  • the specific surface area of the silicon-carbon material is 0.5m 2 /g, 0.7m 2 /g, 1.0m 2 /g, 1.5m 2 /g, 2.0m 2 /g, 2.5m 2 /g, 3.0m 2 / g , 3.5m 2 / g or any value between any two of the above numerical ranges.
  • the surface of the silicon-carbon material can have more lithium insertion sites, which is beneficial to reducing the probability of lithium plating on the negative electrode sheet, and the surface of the silicon-carbon material can be in full contact with the electrolyte, so that the silicon-carbon material can exert its high capacity characteristics, and the negative electrode sheet has a higher capacity.
  • the electrochemical device has a higher energy density and capacity retention rate on the basis of alleviating the problem of lithium plating on the negative electrode surface.
  • the specific surface area of the silicon-carbon material is 1.0 m 2 /g to 2.0 m 2 /g.
  • the specific surface area of the silicon-carbon material is 1.0 m 2 /g, 1.2 m 2 /g, 1.3 m 2 /g, 1.5 m 2 /g, 1.7 m 2 /g, 2.0 m 2 /g, or any value between any two of the above ranges. Regulating the specific surface area of the silicon-carbon material within the above range is beneficial for achieving a higher energy density and capacity retention rate for the electrochemical device while further alleviating the problem of lithium plating on the surface of the negative electrode.
  • the present application does not particularly limit the method for regulating the specific surface area of the silicon-carbon material, as long as the purpose of the present application can be achieved.
  • it can be achieved by regulating the particle size of the silicon-carbon material or regulating the pore size distribution of porous carbon when preparing the silicon-carbon material by a deposition method, or it can be achieved by directly purchasing a silicon-carbon material with a specific surface area within the scope of the present application, and combining it with the test method of "Testing the specific surface area of silicon-carbon material" in the present application to determine the specific surface area of the silicon-carbon material, and selecting a silicon-carbon material with the required specific surface area.
  • the tap density of the silicon-carbon material is 0.8 g/cm 3 to 1.05 g/cm 3.
  • the tap density of the silicon-carbon material is 0.8 g/cm 3 , 0.85 g/cm 3 , 0.87 g/cm 3 , 0.91 g/cm 3 , 0.96 g/cm 3 , 1.00 g/cm 3 , 1.05 g/cm 3 , or any value between any two of the above numerical ranges.
  • Regulating the tap density of the silicon-carbon material within the above range facilitates the close packing of the silicon-carbon material in the second negative electrode material layer and having an appropriate porosity, thereby enabling the electrochemical device to have a low volume expansion rate while having a high energy density.
  • the compacted density C1 of the first negative electrode material layer and the compacted density C2 of the second negative electrode material layer satisfy the following conditions: 1.5 g/cm3 ⁇ C1 ⁇ 1.65 g / cm3 , 1.35 g/ cm3 ⁇ C2 ⁇ 1.5 g / cm3 , and 0.05 g/ cm3 ⁇ C1 - C2 ⁇ 0.3 g / cm3 .
  • the compacted density C1 of the first negative electrode material layer is 1.5 g/ cm3 , 1.52 g/ cm3 , 1.55 g/ cm3 , 1.57 g/ cm3 , 1.60 g/ cm3 , 1.62 g/ cm3 , 1.65 g/ cm3, or any value between any two of the above numerical ranges.
  • the compacted density C2 of the second negative electrode material layer is 1.35 g/ cm3 , 1.37 g/ cm3 , 1.40 g/ cm3 , 1.43 g/ cm3 , 1.47 g/ cm3 , 1.5 g/ cm3 , or any value between any two of the foregoing numerical ranges.
  • the value of C1 - C2 is 0.05 g/ cm3 , 0.1 g/ cm3 , 0.15 g/ cm3 , 0.2 g/ cm3 , 0.25 g/ cm3 , 0.3 g/ cm3 , or any value between any two of the foregoing numerical ranges.
  • the compaction density C1 of the first negative electrode material layer, the compaction density C2 of the second negative electrode material layer, and the value of C1 - C2 are regulated within the scope of this application.
  • the gaps between the particles in the first negative electrode material layer and the second negative electrode material layer can enable the electrolyte to have a shorter transmission path and a larger number of transmission channels in the first negative electrode material layer and the second negative electrode material layer.
  • the electrolyte can be evenly distributed in the first negative electrode material layer and the second negative electrode material layer, the transmission rate of lithium ions and electrons is improved, the probability of lithium plating on the surface of the negative electrode plate is reduced, and the negative electrode plate also has a higher capacity.
  • the electrochemical device has a higher energy density while the problem of lithium plating on the surface of the negative electrode plate is alleviated.
  • 0.1 g/cm 3 ⁇ C 1 - C 2 ⁇ 0.2 g/cm 3 the value of C 1 - C 2 is 0.1 g/cm 3 , 0.12 g/cm 3 , 0.14 g/cm 3 , 0.17 g/cm 3 , 0.2 g/cm 3 , or any value between any two of the above ranges. Adjusting the difference C 1 - C 2 between the compacted density C 1 of the first negative electrode material layer and the compacted density C 2 of the second negative electrode material layer within the range of the present application can accelerate the rapid transport of the electrolyte within the pores of the negative electrode sheet, thereby further improving the rate performance of the electrochemical device.
  • the present application does not particularly limit the method for regulating the compaction density of the first negative electrode material layer, as long as the purpose of the present application can be achieved. For example, it can be achieved by regulating the particle size of the first negative electrode active material in the first negative electrode material layer, or it can be achieved by regulating the pressure during the cold pressing of the negative electrode pole piece.
  • the present application does not particularly limit the method for regulating the compaction density of the second negative electrode material layer, as long as the purpose of the present application can be achieved. For example, it can be achieved by regulating the particle size of the second negative electrode active material in the second negative electrode material layer, or it can be achieved by regulating the pressure during the cold pressing of the negative electrode pole piece.
  • the mass percentage of the first negative electrode active material is 90% to 98.5%.
  • the first negative electrode material layer further includes a conductive agent, a thickener, and a binder.
  • the present application has no particular restrictions on the mass percentages of the conductive agent, thickener, and binder in the first negative electrode material layer, as long as the purpose of the present application can be achieved.
  • the mass percentage of the conductive agent is 0% to 0.5%
  • the mass percentage of the thickener is 0.05% to 0.5%
  • the mass percentage of the binder is 1% to 5%.
  • the mass percentage of the second negative electrode active material is 89.8% to 98.5%.
  • the second negative electrode material layer further includes a conductive agent, a thickener, and a binder.
  • the present application has no particular restrictions on the mass percentages of the conductive agent, thickener, and binder in the second negative electrode material layer, as long as the purpose of the present application can be achieved.
  • the mass percentage of the conductive agent is 0.1% to 2%
  • the mass percentage of the thickener is 0.05% to 0.5%
  • the mass percentage of the binder is 1% to 10%.
  • the present application has no particular limitation on the types of conductive agents, thickeners, and binders. Conductive agents, thickeners, and binders known in the art may be selected as long as the purpose of the present application can be achieved.
  • the present application has no particular restrictions on the negative electrode current collector, as long as the purpose of the present application can be achieved.
  • the negative electrode current collector includes but is not limited to copper foil, copper alloy foil, nickel foil, titanium foil, nickel foam or copper foam, etc.
  • the thickness of the negative electrode current collector is 4 ⁇ m to 20 ⁇ m.
  • the present application has no particular restrictions on the thickness of the first negative electrode material layer and the second negative electrode material layer, as long as the purpose of the present application can be achieved.
  • the thickness of the first negative electrode material layer is 20 ⁇ m to 50 ⁇ m
  • the thickness of the second negative electrode material layer is 20 ⁇ m to 50 ⁇ m.
  • the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer.
  • the positive electrode active material layer is disposed on one or both surfaces of the positive electrode current collector.
  • the "surface” mentioned above can be a portion of the surface of the positive electrode current collector or the entire surface of the positive electrode current collector.
  • the positive electrode current collector can include aluminum foil or aluminum alloy foil.
  • the positive electrode active material layer of this application includes a positive electrode active material. This application does not specifically limit the type of positive electrode active material, as long as it can achieve the objectives of this application.
  • the positive electrode active material can include at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide, lithium manganese oxide, lithium iron manganese phosphate, or lithium titanate.
  • the positive electrode active material may also include non-metallic elements.
  • the non-metallic elements may include at least one of fluorine, phosphorus, boron, chlorine, silicon, or sulfur. These elements can further improve the stability of the positive electrode active material.
  • the thickness of the positive electrode current collector is 5 ⁇ m to 20 ⁇ m.
  • the thickness of the single-layer positive electrode active material layer is 30 ⁇ m to 120 ⁇ m.
  • the positive electrode active material layer may also include at least one of a conductive agent or a binder.
  • the present application does not particularly limit the types of conductive agents and binders in the positive electrode active material layer, as long as the purpose of the present application can be achieved.
  • the present application does not particularly limit the mass ratio of the positive electrode active material, conductive agent, and binder in the positive electrode active material layer. Those skilled in the art can choose according to actual needs, as long as the purpose of the present application can be achieved.
  • the material of the diaphragm may include, but is not limited to, at least one of polyethylene (PE), polypropylene (PP)-based polyolefins (PO), polyesters (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid.
  • the type of diaphragm may include at least one of a woven membrane, a non-woven membrane, a microporous membrane, a composite membrane, a rolled membrane, or a spun membrane.
  • the present application has no particular restrictions on the thickness of the diaphragm, as long as the purpose of the present application can be achieved.
  • the electrochemical device of the present application also includes an electrolyte.
  • the present application does not particularly limit the electrolyte, as long as the purpose of the present application can be achieved.
  • the electrolyte includes a lithium salt and a non-aqueous solvent.
  • the lithium salt may include at least one of LiPF6 , LiNO3 , LiBF4 , LiClO4 , LiB( C6H5 ) 4 , LiCH3SO3 , LiCF3SO3, LiN ( SO2CF3 ) 2 , LiC( SO2CF3 ) 3 , Li2SiF6 , lithium bis(oxalatoborate) (LiBOB), lithium bis ( trifluoromethanesulfonyl imide) (LiTFSI), or lithium difluoroborate.
  • LiPF6 LiNO3 , LiBF4 , LiClO4 , LiB( C6H5 ) 4
  • LiCH3SO3 , LiCF3SO3, LiN ( SO2CF3 ) 2 , LiC( SO2CF3 ) 3 , Li2SiF6 lithium bis(oxalatoborate) (LiBOB), lithium bis ( trifluoromethanesulfonyl imide) (LiTFSI
  • the non-aqueous solvent may include, but is not limited to, at least one of a carbonate compound, a carboxylate compound, an ether compound, or other organic solvents.
  • the carbonate compound may include but is not limited to at least one of a linear carbonate compound, a cyclic carbonate compound or a fluorocarbonate compound.
  • the linear carbonate compound may include but is not limited to at least one of dimethyl carbonate (DMC), diethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate or methylethyl carbonate.
  • DMC dimethyl carbonate
  • the cyclic carbonate may include but is not limited to at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate or vinyl ethylene carbonate.
  • the fluorocarbonate compound may include but is not limited to at least one of fluoroethylene carbonate, 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 at least one of trifluoromethylethylene carbonate.
  • the 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, valerolactone or caprolactone.
  • the ether compound may include but is not limited to at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran or tetrahydrofuran.
  • the other organic solvents may include but are 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 electrochemical device of the present application also includes a housing, which is used to accommodate the positive electrode sheet, the negative electrode sheet, the separator, and the electrolyte, as well as other components of electrochemical devices known in the art. This application does not limit these other components. This application does not specifically limit the housing, and can be any housing known in the art, as long as it can achieve the purpose of this application.
  • the present application does not particularly limit the type of electrochemical device, which may include any device that undergoes an electrochemical reaction.
  • the electrochemical device may include, but is not limited to, a lithium-ion secondary battery (lithium-ion battery), a lithium polymer secondary battery, or a lithium-ion polymer secondary battery.
  • the preparation method of the negative electrode sheet includes but is not limited to the following steps: (1) after uniformly mixing a first negative electrode active material, a conductive agent, a thickener, and a binder, a solvent is added, and the mixture is stirred to obtain a first negative electrode slurry; (2) after uniformly mixing a second negative electrode active material, a conductive agent, a thickener, and a binder, a solvent is added, and the mixture is stirred to obtain a second negative electrode slurry; (3) the first negative electrode slurry is applied to both surfaces of the negative electrode current collector, and after drying, a first negative electrode material layer is formed; then, the second negative electrode slurry is applied to the surfaces of the two first negative electrode material layers away from the negative electrode current collector, and after drying, a second negative electrode material layer is formed; and after cold pressing and slitting, a negative electrode
  • the preparation method of the negative electrode sheet includes but is not limited to the following steps: (1) after uniformly mixing the first negative electrode active material, the conductive agent, the thickener, and the binder, a solvent is added, and the mixture is stirred to obtain a first negative electrode slurry; (2) after uniformly mixing the second negative electrode active material, the conductive agent, the thickener, and the binder, a solvent is added, and the mixture is stirred to obtain a second negative electrode slurry; (3) the first negative electrode slurry is applied on one surface of the negative electrode current collector, and after drying, a first negative electrode material layer is formed on the surface of the negative electrode current collector, and the second negative electrode slurry is applied on the surface of the first negative electrode material layer away from the negative electrode current collector, and after drying, the second negative electrode slurry is cold pressed and cut to obtain a negative electrode sheet with a first negative electrode material layer and a second negative electrode material layer on one side.
  • This application does not particularly limit the type of solvent in the above steps (1) and (2), as long as the purpose of this application can be achieved.
  • This application does not particularly limit the solid content of the above-mentioned first negative electrode slurry and the second negative electrode slurry, as long as the purpose of this application can be achieved.
  • the present application does not particularly limit the temperature and time of drying in the above step (3), and those skilled in the art can select according to actual conditions as long as the purpose of the present application can be achieved.
  • the preparation process of the electrochemical device of the present application is well known to those skilled in the art and is not particularly limited in the present application.
  • it may include but is not limited to the following steps: stacking the diaphragm, positive electrode sheet, diaphragm and negative electrode sheet in sequence, 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 the electrolyte into the packaging bag and sealing it, and obtaining the electrochemical device through process flows such as formation, degassing and shaping; or stacking the diaphragm, positive electrode sheet, diaphragm and negative electrode sheet in sequence, 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 the electrolyte into the packaging bag and sealing it, and obtaining the electrochemical device through process flows such as formation, degassing and shaping.
  • a second aspect of the present application provides an electronic device, which includes the electrochemical device described in any one of the aforementioned embodiments. Therefore, the electronic device has 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 particle size distribution was tested using a laser particle size analyzer MasterSizer 2000, and the particle sizes of the silicon-carbon material were Dv10, Dv50 ⁇ 3 , and Dv90, the particle size of the first graphite was Dv50 ⁇ 1 , and the particle size of the second graphite was Dv50 ⁇ 2 .
  • the silicon content of silicon-carbon materials was measured using an inductively coupled plasma (ICP) spectrometer.
  • ICP inductively coupled plasma
  • a sample of silicon-carbon material (0.05-0.2 g) was placed in a nickel crucible, and 1.5 g of potassium hydroxide (KOH) was added. The mixture was then heated at 400°C for 45 minutes. The mixture was then leached in 50 ml of boiling water for 60 minutes. The mixture was then brought to volume in a 100 ml volumetric flask. A portion of the diluted solution was removed for ICP analysis.
  • KOH potassium hydroxide
  • the specific surface area of the silicon-carbon materials of each embodiment and comparative example was measured by nitrogen adsorption using a surface area analyzer (Tristar II 3020M, Micromeritics Instruments, USA). The specific test was conducted in accordance with the national standard GB/T19587-2017 "Determination of the Specific Surface Area of Solids by Gas Adsorption BET Method".
  • the lithium-ion batteries of each embodiment and comparative example were charged and discharged at 25°C according to the following steps: standing for 30 minutes, discharging at a constant current of 0.2C to 3.0V; standing for 30 minutes; charging at a constant current of 0.5C to 4.5V, and then charging at a constant voltage of 4.5V to 0.05C, stopping charging (this is a full charge); this constitutes one charge and discharge process. After 50 cycles of this charge and discharge process, the fully charged lithium-ion battery was disassembled and the negative electrode plate was observed for lithium deposition. If white or gray lithium appeared on the surface of the negative electrode plate, lithium deposition was determined; otherwise, lithium deposition was determined to be absent.
  • the lithium-ion battery prepared in the same embodiment or comparative example is taken and the charging rate is gradually increased by 0.1C while other charge and discharge parameters remain unchanged, and the above steps are repeated until lithium deposition occurs on the negative electrode.
  • the charge rate at which the negative electrode last exhibited no lithium deposition is defined as the maximum charge rate without lithium deposition for the lithium-ion battery.
  • a higher maximum charge rate without lithium deposition indicates a less proneness to lithium deposition. This means the more effectively lithium deposition on the negative electrode surface is mitigated, the better the battery's cycling performance.
  • the lithium-ion battery was placed in an environment of 25 ⁇ 3°C for 30 minutes, discharged to 3.0V at a current of 0.2C, and then charged to 4.5V at a constant current at the highest non-lithium precipitation rate.
  • the lithium-ion battery was disassembled to obtain the negative electrode plate, and the second negative electrode material layer on the surface was adhered with tape for the second graphite lithium insertion degree test of the second negative electrode material layer.
  • the negative electrode plate after removing the second negative electrode material layer was used for the first graphite lithium insertion degree test of the first negative electrode material layer, and the graphite of the second negative electrode material layer and the first negative electrode material layer were characterized by XRD.
  • the distinction between the second negative electrode material layer and the first negative electrode material layer is as follows: take a cross section of the electrode sheet for SEM/EDS characterization. In the EDS image, the color of the Si element area is different from the color of the area without Si element, and there is a clear boundary between the two areas. Draw a straight line here to obtain the boundary line between the first negative electrode material layer and the second negative electrode material layer. For each embodiment and comparative example 2, first use tape to tear off the surface layer of the negative electrode sheet for the second graphite lithium insertion degree test of the second negative electrode material layer.
  • the maximum non-lithium deposition rate is obtained according to the test method in the "Test of the maximum non-lithium deposition charging rate", and the maximum charging rate without lithium deposition on the negative electrode is defined as the maximum non-lithium deposition rate of the lithium-ion battery.
  • Discharge Discharge to 3.0V at a constant current of 0.2C, and obtain the discharge energy E 1 ;
  • the first negative electrode active material, first graphite (artificial graphite, 95% graphitization), a binder, polyacrylic acid (weight-average molecular weight Mw 3500), and a conductive agent, single-walled carbon nanotubes, were mixed in a mass ratio of 97:2.8:0.2, deionized water was added as a solvent, and the mixture was stirred to form a first negative electrode slurry with a solid content of 42 wt%.
  • the first negative electrode slurry was applied to both surfaces of a 6 ⁇ m thick negative electrode current collector copper foil and dried at 100°C to form a first negative electrode material layer.
  • the mixture was applied to the surfaces of the two first negative electrode material layers away from the copper foil and dried at 100°C to form a second negative electrode material layer.
  • the negative electrode nickel tabs are cold pressed, cut and welded to obtain negative electrode sheets with a specification of 1000 mm ⁇ 80 mm.
  • the mass percentage W1 of the silicon-carbon material in the second negative electrode active material is 40%, and the mass percentage W2 of the silicon element in the silicon-carbon material is 50%.
  • the specific surface area of the silicon-carbon material is 1.4 m2 /g.
  • the ratio P of the coating weight per unit area of the second negative electrode material layer to the coating weight per unit area of the negative electrode sheet is 1/4.
  • the positive electrode active material, lithium cobalt oxide, the conductive agent, conductive carbon black (Super P), and the binder, polyvinylidene fluoride (PVDF, Mw 600,000), were mixed in a mass ratio of 97.8:1.4:0.8.
  • N-methylpyrrolidone (NMP) was added as a solvent and stirred in a vacuum mixer until a solid content of 72 wt% and a uniform system was obtained.
  • 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 with a single-sided positive electrode active material layer (90 ⁇ m thick).
  • a polyethylene (PE) porous film with a thickness of 8 ⁇ m was used as the separator.
  • ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed uniformly at a mass ratio of 1:1, and lithium hexafluorophosphate (LIPF) was added and stirred to prepare an electrolyte.
  • the concentration of the lithium salt was 1 mol/L.
  • the separator, positive electrode sheet, separator, and negative electrode sheet are stacked in sequence and wound to form an electrode assembly.
  • the electrode assembly is placed in an aluminum-plastic film packaging bag, dehydrated at 80°C, injected with electrolyte, and packaged. After the formation, degassing, and shaping processes, a lithium-ion battery is obtained.
  • Example 1-1 Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-1.
  • Example 1-3 Except for adjusting the relevant preparation parameters according to Table 2, the rest is the same as Example 1-3.
  • Example 2-2 Except for adjusting the relevant preparation parameters according to Table 3, the rest is the same as Example 2-2.
  • Example 3-1 Except for adjusting the relevant preparation parameters according to Table 4, the rest is the same as Example 3-1.
  • ⁇ Preparation of positive electrode sheet>, ⁇ Preparation of separator>, ⁇ Preparation of electrolyte>, and ⁇ Preparation of lithium-ion battery> are the same as those in Example 1-1.
  • Table 1 Note: “P” in Table 1 represents the ratio of the coating weight per unit area of the second negative electrode material layer to the coating weight per unit area of the negative electrode sheet; “ ⁇ ” indicates that there is no relevant parameter.
  • Figure 2 shows the X-ray diffraction pattern of the negative electrode sheet of Example 1-1
  • Figure 3 shows the X-ray diffraction pattern of the negative electrode sheet of Comparative Example 1.
  • the X-ray diffraction pattern of the second negative electrode material layer does not show the characteristic peak of LiC 6
  • the 2 ⁇ at the maximum intensity of the characteristic peak of LiC 12 is 25.24°.
  • the 2 ⁇ at the maximum intensity of the characteristic peak of LiC 12 is 25.26°.
  • the 2 ⁇ at the maximum intensity of the characteristic peak of LiC 12 is relatively close, indicating that the negative electrode sheet has good lithium insertion uniformity.
  • the X-ray diffraction pattern of the surface layer shows the characteristic peak of LiC 6 , and the 2 ⁇ at the maximum intensity of the characteristic peak of LiC 12 is 25.12°.
  • the 2 ⁇ at the maximum intensity of the characteristic peak of LiC 12 is 25.35°.
  • the mass percentage of the silicon-carbon material in the second negative electrode active material and the mass percentage of the silicon element in the silicon-carbon material generally also affect the lithium deposition on the surface of the negative electrode plate in the electrochemical device.
  • electrochemical devices using the mass percentage of the silicon-carbon material in the second negative electrode active material and the mass percentage of the silicon element in the silicon-carbon material within the range of this application have a large maximum lithium deposition-free rate, indicating that the problem of lithium deposition on the surface of the negative electrode plate in the electrochemical device is alleviated and the electrochemical device has good cycling performance.
  • the particle size Dv50-1 of the first graphite and the difference Dv50-2 between the particle size Dv50-1 and the particle size Dv50-2 of the second graphite also generally affect the lithium deposition on the surface of the negative electrode sheet and the capacity retention rate in the electrochemical device.
  • the electrochemical device in which the particle size Dv50-1 of the first graphite and the difference Dv50-2 between the particle size Dv50-1 and the particle size Dv50-2 of the second graphite are within the scope of the present application has a larger maximum non-lithium deposition rate on the basis of a higher capacity retention rate, indicating that the electrochemical device has alleviated the problem of lithium deposition on the surface of the negative electrode sheet on the basis of a longer cycle life.
  • the particle sizes Dv10, Dv50-3 , Dv90, and Dv90-Dv10 of the silicon-carbon material generally affect the lithium deposition on the surface of the negative electrode and the capacity retention rate in an electrochemical device.
  • electrochemical devices using silicon-carbon material with particle sizes Dv10, Dv50-3 , Dv90, and Dv90-Dv10 within the ranges of this application exhibit a higher maximum non-lithium deposition rate while maintaining a higher capacity retention rate. This indicates that the electrochemical device alleviates the problem of lithium deposition on the surface of the negative electrode while maintaining a longer cycle life.
  • the specific surface area of silicon-carbon materials typically affects lithium deposition on the surface of the negative electrode sheet and capacity retention in electrochemical devices.
  • electrochemical devices using silicon-carbon materials with specific surface areas within the range of this application exhibit a high maximum non-lithium deposition rate, while maintaining a high capacity retention rate. This indicates that the problem of lithium deposition on the surface of the negative electrode sheet is alleviated while maintaining a long cycle life.
  • the compacted density C1 of the first negative electrode material layer, the compacted density C2 of the second negative electrode material layer, and the difference C1 - C2 between the two generally affect the lithium deposition on the surface of the negative electrode plate in the electrochemical device and the energy density of the electrochemical device.
  • the electrochemical device with the compacted density C1 of the first negative electrode material layer, the compacted density C2 of the second negative electrode material layer, and the difference C1 - C2 between the two within the scope of the present application has little change in energy density and has a large maximum non-lithium deposition rate, indicating that the problem of lithium deposition on the surface of the negative electrode plate in the electrochemical device is alleviated, and the electrochemical device has a higher energy density.

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Abstract

一种电化学装置和电子装置，电化学装置包括负极极片(10)，负极极片(10)包括负极集流体(13)、第一负极材料层(11)和第二负极材料层(12)，第一负极材料层(11)设置于负极集流体(13)和第二负极材料层(12)之间；电化学装置以最高不析锂倍率恒流充电至上限截止电压时，第一负极材料层(11)与第二负极材料层(12)的X射线衍射图谱中，LiC 12的特征峰满足以下特征(1)或(2)中的至少一者：(1)第二负极材料层(12)的X射线衍射图谱中，未出现LiC 6的特征峰，LiC 12的特征峰中最大强度处的2θ为A 2°，25.15≤A 2°≤25.30；(2)第一负极材料层(11)X射线衍射图谱中，LiC 12的特征峰中最大强度处的2θ为A 1°，第二负极材料层(12)的X射线衍射图谱中，LiC 12的特征峰中最大强度处的2θ为A 2°，0≤A 1°-A 2°≤0.15。

Description

电化学装置和电子装置
本申请要求于2024年4月19日提交中国国家知识产权局专利局、申请号为202410479582.X、发明名称为“电化学装置和电子装置”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，特别是涉及一种电化学装置和电子装置。
背景技术
伴随着社会的快速发展，对电化学装置(如锂离子电池)的能量密度提出了更高的要求。由于硅基材料具有极高的理论比容量，将硅基材料与石墨混合作为负极活性材料，以显著提升锂离子电池的能量密度。但是，在石墨中混入硅基材料，将恶化负极极片的动力学能力，负极极片表面容易析锂，影响锂离子电池的循环性能，并带来安全隐患。其他设计相同时，硅基材料占比越高，动力学恶化越严重，相同充电制度下负极极片表面析锂越多。因此，如何缓解电化学装置中负极极片表面的析锂现象成为本领域技术人员亟待解决的技术问题。
发明内容
本申请的目的在于提供一种电化学装置和电子装置，以缓解电化学装置中负极极片表面析锂的问题。
需要说明的是，本申请的发明内容中，以锂离子电池作为电化学装置的例子来解释本申请，但是本申请的电化学装置并不仅限于锂离子电池。具体技术方案如下：
本申请的第一方面提供了一种电化学装置，电化学装置包括负极极片、正极极片以及设置于负极极片和正极极片之间的隔膜，负极极片包括负极集流体以及设置于负极集流体至少一个表面上的第一负极材料层和第二负极材料层，第一负极材料层设置于负极集流体和第二负极材料层之间；电化学装置以最高不析锂倍率恒流充电至上限截止电压时，第一负极材料层与第二负极材料层的X射线衍射图谱中，LiC12的特征峰满足以下特征(1)或(2)中的至少一者：(1)第二负极材料层的X射线衍射图谱中，未出现LiC6的特征峰，LiC12的特征峰中最大强度处的2θ为A2°，25.15≤A2≤25.30；(2)第一负极材料层X射线衍射图谱中，LiC12的特征峰中最大强度处的2θ为A1°，第二负极材料层的X射线衍射图谱中，LiC12的特征峰中最大强度处的2θ为A2°，0≤A1-A2≤0.15。通过上述设置，负极极片表层的嵌锂度低，和/或负极极片嵌锂均匀性好，负极极片表面未出现局部嵌锂增多的现象，电化学装置中负极极片表面析锂的问题得到缓解。
在本申请的一些实施方案中，第一负极材料层包括第一负极活性材料，第一负极活性材料包括第一石墨；第二负极材料层包括第二负极活性材料，第二负极活性材料包括硅碳材料和第二石墨；第二负极活性材料中硅碳材料的质量百分含量为15％至50％，硅碳材料中硅元素的质量百分含量为30％至60％。负极极片底层第一负极材料层包括第一石墨，表层第二负极材料层包括第二石墨和硅碳材料，且将硅碳材料的质量百分含量以及硅碳材料中硅元素的质量百分含量调控在上述范围内，负极极片能够提供足够的活性材料，也有利于使负极极片表层中的硅元素，在提高负极极片表层可嵌锂点位的基础上，降低硅元素带来的负极极片体积膨胀的概率。由此，能够使电化学装置中负极极片表面析锂的问题得到缓解，也使电化学装置具有较高的能量密度和较小的体积膨胀率。
在本申请的一些实施方案中，第二负极活性材料中硅碳材料的质量百分含量为30％至50％，硅碳材料中硅元素的质量百分含量为50％至60％，能进一步改善负极极片表面析锂的问题。
在本申请的一些实施方案中，第一石墨的粒径Dv50-1为11.0μm至13.5μm。将第一石墨的粒径Dv50-1调控在上述范围内，电化学装置在负极极片表面具有较少析锂概率的基础上，具有较高的容量保持率。
在本申请的一些实施方案中，第二石墨的粒径Dv50-2与第一石墨的粒径Dv50-1满足：1μm≤Dv50-1-Dv50-2≤5μm。将第二石墨的粒径Dv50-2与第一石墨的粒径Dv50-1的差值Dv50-1-Dv50-2的值调控在上述范围内，能够使电化学装置在具有高容量保持率的同时，进一步降低负极极片表面析理的概率。
在本申请的一些实施方案中，硅碳材料的粒径Dv10、Dv50-3和Dv90满足：5μm≤Dv10≤6μm、8μm≤Dv50-3≤10.5μm、13μm≤Dv90≤17μm。将硅碳材料的粒径Dv10、Dv50-4和Dv90调控在上述范围内，电化学装置中负极极片表面析锂的问题得到缓解的基础上，具有较高的容量保持率。
在本申请的一些实施方案中，硅碳材料的粒径Dv10和Dv90满足：8μm≤Dv90-Dv10≤10.5μm。将Dv90-Dv10的值调控在上述范围内，使电化学装置在具有较高的能量密度的基础上，改善其动力学能力。
在本申请的一些实施方案中，硅碳材料的比表面积为0.5m2/g至3.5m2/g。将硅碳材料的比表面积调控在上述范围内，电化学装置在缓解负极极表面析锂问题的基础上，具有较高的容量保持率。
在本申请的一些实施方案中，硅碳材料的比表面积为1.0m2/g至2.0m2/g。有利于使电化学装置在具有较高的容量保持率的情况下，进一步缓解负极极片表面析锂的问题。
在本申请的一些实施方案中，第一负极材料层的压实密度C1和第二负极材料层的压实密度C2满足：1.5g/cm3≤C1≤1.65g/cm3，1.35g/cm3≤C2≤1.5g/cm3，0.05g/cm3≤C1-C2≤0.3g/cm3。将第一负极材料层的压实密度C1、第二负极材料层的压实密度C2以及C1-C2的值调控在本申请范围内，电化学装置在负极极片表面的析锂问题得到缓解的情况下，具有较高的能量密度。
在本申请的一些实施方案中，0.1g/cm3≤C1-C2≤0.2g/cm3。
本申请的第二方面提供了一种电子装置，该电子装置包括前述任一实施方案所述的电化学装置。因此，电子装置具有良好的使用性能。
本申请的有益效果：
本申请提供了一种电化学装置和电子装置，电化学装置包括负极极片、正极极片以及设置于负极极片和正极极片之间的隔膜，负极极片包括负极集流体以及设置于负极集流体至少一个表面上的第一负极材料层和第二负极材料层，第一负极材料层设置于负极集流体和第二负极材料层之间；电化学装置以最高不析锂倍率恒流充电至上限截止电压时，第一负极材料层与第二负极材料层的X射线衍射图谱中，LiC12的特征峰满足以下特征(1)或(2)中的至少一者：(1)第二负极材料层的X射线衍射图谱中，未出现LiC6的特征峰，LiC12的特征峰中最大强度处的2θ为A2°，25.15≤A2≤25.30；(2)第一负极材料层X射线衍射图谱中，LiC12的特征峰中最大强度处的2θ为A1°，第二负极材料层的X射线衍射图谱中，LiC12的特征峰中最大强度处的2θ为A2°，0≤A1-A2≤0.15。通过上述设置，负极极片表层的嵌锂度低，和/或负极极片嵌锂均匀性好，负极极片表面未出现局部嵌锂增多的现象。由此，能够缓解电化学装置中负极极片表面析锂的问题，提高电化学装置的循环性能。
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为本申请一些实施方案的负极极片沿自身长度方向和厚度方向的剖面结构示意图；
图2为本申请实施例1-1的负极极片的X射线衍射图谱；
图3为本申请对比例1的负极极片的X射线衍射图谱。
附图标记：
10-负极极片；11-第一负极材料层；12-第二负极材料层；13-负极集流体；131-第一表
面；132-第二表面。
具体实施方式
为使本申请的目的、技术方案、及优点更加清楚明白，以下参照附图并举实施例，对本申请进一步详细说明。显然，所描述的实施例仅仅是本申请一部分实施例，而不是全部的实施例。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，以锂离子电池作为电化学装置的例子来解释本申请，但是本申请的电化学装置并不仅限于锂离子电池。
本申请的第一方面提供了一种电化学装置，电化学装置包括负极极片、正极极片以及设置于负极极片和正极极片之间的隔膜，负极极片包括负极集流体以及设置于负极集流体至少一个表面上的第一负极材料层和第二负极材料层，第一负极材料层设置于负极集流体和第二负极材料层之间。电化学装置以最高不析锂倍率恒流充电至上限截止电压时，第一负极材料层与第二负极材料层的X射线衍射图谱中，LiC12的特征峰满足以下特征(1)或(2)中的至少一者：(1)第二负极材料层的X射线衍射图谱中，未出现LiC6的特征峰，LiC12的特征峰中最大强度处的2θ为A2°，25.15≤A2≤25.30；(2)第一负极材料层X射线衍射图谱中，LiC12的特征峰中最大强度处的2θ为A1°，第二负极材料层的X射线衍射图谱中，LiC12的特征峰中最大强度处的2θ为A2°，0≤A1-A2≤0.15。在一些实施方案中，电化学装置以最高不析锂倍率恒流充电至上限截止电压时，第二负极材料层的X射线衍射图谱中，未出现LiC6的特征峰，LiC12的特征峰中最大强度处的2θ为A2°，25.15≤A2≤25.30。在另一些实施方案中，电化学装置以最高不析锂倍率恒流充电至上限截止电压时，第一负极材料层X射线衍射图谱中，LiC12的特征峰中最大强度处的2θ为A1°，第二负极材料层的X射线衍射图谱中，LiC12的特征峰中最大强度处的2θ为A2°，0≤A1-A2≤0.15。在再一些实施方案中，电化学装置以最高不析锂倍率恒流充电至上限截止电压时，第一负极材料层X射线衍射图谱中，LiC12的特征峰中最大强度处的2θ为A1°，第二负极材料层的X射线衍射图谱中，LiC12的特征峰中最大强度处的2θ为A2°，0≤A1-A2≤0.15，25.15≤A2≤25.30。
为方便理解，在本申请中，定义负极极片的自身长度方向为X，自身厚度方向为Z。应理解，以上对于方向的定义是为了方便描述本申请的目的，可以根据附图与实际产品元素的相对位置来理解本申请定义的方向。可以理解的是，负极集流体、第一负极材料层、第二负极材料层自身的长度方向和厚度方向与负极极片相同。图1示出了本申请一些实施方案中的负极极片沿自身长度方向X和厚度方向Z的剖面结构示意图，如图1所示，负极极片10包括负极集流体13、第一负极材料层11和第二负极材料层12，负极集流体13包括沿自身厚度方向Z设置的第一表面131和第二表面132，第一负极材料层11和第二负极材料层12设置于负极集流体13的两个表面，即第一表面131和第二表面132上，第一负极材料层11设置于负极集流体13和第二负极材料层12之间。可以理解的是，在本申请的另一些实施方案中，第一负极材料层11和第二负极材料层12可以设置于负极集流体13的一个表面上，即第一表面131或第二表面132上。
在本申请中，“最高不析锂倍率”是指电化学装置的负极极片不析锂情况下的最大充电倍率，具体为根据“最高不析锂充电倍率的测试”中的测试方法测得的最高不析锂倍率。在本申请中，电化学装置的上限截止电压为4.5V至4.55V。电化学装置以最高不析锂倍率恒流充电至上限截止电压时，第二负极材料层的X射线衍射图谱中，未出现LiC6的特征峰，表明第二负极材料层中的嵌锂度低，表层第一负极材料层和底层第二负极材料层的嵌锂度比较均匀；LiC12的特征峰中最大强度的2θ为A2°，25.15≤A2≤25.30。例如，A2为25.15、25.18、25.20、25.22、25.24、25.25、25.27、25.28、25.29、25.30或上述任两个数值范围间的任一数值。A2处于上述范围内，表明以最高不析锂倍率对电化学装置恒流充电至上限截止电压时，负极极片中处于表层的第二负极材料层中的嵌锂度低，负极极片表面的析锂较少。电化学装置以最高不析锂倍率恒流充电至上限截止电压，第一负极材料层X射线衍射图谱中，LiC12的特征峰中最大强度处的2θ为A1°，第二负极材料层的X射线衍射图谱中，LiC12的特征峰中最大强度处的2θ为A2°，0≤A1-A2≤0.15。例如，A1-A2为0.00、0.01、0.02、0.03、0.04、0.07、0.09、0.10、0.12、0.15或上述任两个数值范围间的任一数值。A1-A2的值处于上述范围内，表明以最高不析锂倍率对电化学装置进行充电时，电化学装置在未满充状态下，负极极片中第一负极材料层和第二负极材料层的嵌锂度较一致，说明负极极片中嵌锂均匀性较好，并未出现局部嵌锂增多的现象，从而降低负极极片表面发生析锂的概率。通过上述设置，负极极片表层的嵌锂度低，和/或负极极片嵌锂均匀性好，负极极片表面未出现局部嵌锂增多的现象，电化学装置中负极极片表面析锂的问题得到缓解。
本申请对第一负极材料层X射线衍射图谱中，LiC12的特征峰中最大强度处2θ的范围A1°没有特别限制，只要能够实现本申请目的即可。例如，25.27°≤A1≤25.5°。
本申请对第一负极材料层X射线衍射图谱中LiC12的特征峰中最大强度处2θ的范围A1°的调控方式没有特别限制，只要能够实现本申请目的即可。例如，可以通过调控负极极片的厚度来实现。
本申请对第二负极材料层X射线衍射图谱中LiC12的特征峰中最大强度处2θ的范围A2°的调控方式没有特别限制，只要能够实现本申请目的即可。例如，可以通过调控第二负极活性材料中硅碳材料的质量百分含量或硅碳材料中硅元素的质量百分含量中的至少一者来实现。
在本申请的一些实施方案中，第一负极材料层包括第一负极活性材料，第一负极活性材料包括第一石墨；第二负极材料层包括第二负极活性材料，第二负极活性材料包括硅碳材料和第二石墨；第二负极活性材料中硅碳材料的质量百分含量为15％至50％，硅碳材料中硅元素的质量百分含量为30％至60％。例如，第二负极活性材料中硅碳材料的质量百分含量为15％、20％、26％、32％、40％、46％、50％或上述任两个数值范围间的任一数值。例如，硅碳材料中硅元素的质量百分含量为30％、34％、39％、42％、50％、53％、60％或上述任两个数值范围间的任一数值。将设置于负极极片表层的第二负极材料层中加入硅碳材料，能够使负极极片表层的克容量得到提高，可嵌锂点位增多，从而能够使第二负极材料层中的嵌锂度降低，有利于缓解电化学装置中负极极片表面析锂的问题。负极极片底层第一负极材料层包括第一石墨，表层第二负极材料层包括第二石墨和硅碳材料，且将硅碳材料的质量百分含量以及硅碳材料中硅元素的质量百分含量调控在上述范围内，负极极片能够提供足够的活性材料，也有利于使负极极片表层中的硅元素，在提高负极极片表层可嵌锂点位的基础上，降低硅元素带来的负极极片体积膨胀的概率。由此，有利于使电化学装置中负极极片表面析锂的问题得到缓解，也使电化学装置具有较高的能量密度和较小的体积膨胀率。
本申请对硅碳材料中硅元素的质量百分含量的调控方式没有特别限制，只要能够实现本申请目的即可。例如，通过在多孔碳中沉积硅的方法制备硅碳材料时，在制备过程中，可以通过调控硅的沉积含量来使硅碳材料中硅元素的质量百分含量发生变化。也可以直接购买硅元素含量不同的硅碳材料，并结合本申请提供的“硅碳材料中硅元素的质量百分含量的测试”，选择所需硅元素含量的硅碳材料即可。
在本申请的一些实施方案中，第二负极活性材料中第二石墨的质量百分含量为50％至85％。
在本申请中，第一石墨和第二石墨各自独立地选自天然石墨或人造石墨。
在本申请的一些实施方案中，第一石墨的粒径Dv50-1为11.0μm至13.5μm。例如，第一石墨的粒径Dv50-1为11.0μm、11.3μm、11.7μm、12.0μm、12.8μm、13.0μm、13.5μm或上述任两个数值范围间的任一数值。将第一石墨的粒径Dv50-1调控在上述范围内，第一石墨发生团聚的可能性较小，第一石墨能够均匀分布于第一负极材料层中，且第一石墨的表面积能够使其与电解液发生充分的接触，从而使第一石墨充分发挥其活性，使第一负极材料层具有较高的容量。由此，电化学装置在负极极片表面具有较少析锂概率的基础上，具有较高的能量密度。也使得电化学装置具有较高的容量保持率。
在本申请的一些实施方案中，第二石墨的粒径Dv50-2与第一石墨的粒径Dv50-1满足：1μm≤Dv50-1-Dv50-2≤5μm。例如，Dv50-1-Dv50-2的值为1μm、2μm、3μm、4μm、5μm或上述任两个数值范围间的任一数值。将第二石墨的粒径Dv50-2与第一石墨的粒径Dv50-1的差值Dv50-1-Dv50-2的值调控在上述范围内，第一石墨与第二石墨具有合适的动力学能力差异，与第一负极材料层和第二负极材料层所需求的嵌锂速率差异匹配，有利于使电化学装置在具有高能量密度的同时，进一步降低负极极片表面析理的概率，也使电化学装置具有较高的容量保持率。
本申请对第二石墨的粒径Dv50-2没有特别限制，只要能够实现本申请目的即可。例如，第二石墨的粒径Dv50-2为8.5μm至13.5μm。
在本申请的一些实施方案中，硅碳材料的粒径Dv10、Dv50-3和Dv90满足：5μm≤Dv10≤6μm、8μm≤Dv50-3≤10.5μm、13μm≤Dv90≤17μm。例如，硅碳材料的粒径Dv10为5μm、5.2μm、5.4μm、5.7μm、5.8μm、6μm或上述任两个数值范围间的任一数值。例如，硅碳材料的粒径Dv50-3为8μm、8.2μm、8.7μm、9.1μm、9.8μm、10.0μm、10.5μm或上述任两个数值范围间的任一数值。例如，硅碳材料的粒径Dv90为13μm、13.6μm、14.4μm、14.7μm、15.3μm、16μm、16.5μm、17μm或上述任两个数值范围间的任一数值。将硅碳材料的粒径Dv10、Dv50-4和Dv90调控在上述范围内，硅碳材料具有合适大小且各颗粒间尺寸差别较小的粒径，分布于第二负极材料层时，发生团聚的概率较小，有利于在第二负极材料层中均匀分布，从而有利于提升电解液对负极极片的浸润性，提高电解液对负极极片的浸润和保液能力。这样，硅碳材料的利用率得到提高，电化学装置中负极极片表面析锂的问题得到缓解，其能量密度得到提高，也具有较高的容量保持率。
在本申请的一些实施方案中，硅碳材料的粒径Dv10和Dv90满足：8μm≤Dv90-Dv10≤10.5μm。例如，Dv90-Dv10的值为8.0μm、9.7μm、10.2μm、10.5μm或上述任两个数值范围间的任一数值。将Dv90-Dv10的值调控在上述范围内，硅碳材料中的大颗粒和小颗粒之间尺寸差别较小，硅碳材料分布于第二负极材料层时，不同粒径的硅碳材料以合适的梯度分级分布，有利于硅碳材料在第二负极材料层中紧密均匀地分布，并提升硅碳材料的快速嵌锂能力，使电化学装置在具有较高的能量密度的基础上，改善其动力学能力，具有较高的最低充电倍率和容量保持率。
在本申请中，Dv10是指表示颗粒在体积基准的粒度分布中，从小粒径侧起，达到体积累积10％的粒径；Dv50表示颗粒在体积基准的粒度分布中，从小粒径侧起，达到体积累积50％的粒径；Dv90表示颗粒在体积基准的粒度分布中，从小粒径侧起，达到体积累积90％的粒径。上述的“颗粒”可以为硅碳材料、第一石墨、第二石墨。
本申请对硅碳材料、第一石墨和第二石墨的粒径的调控方式没有特别限制，只要能够实现本申请目的即可。例如，可以通过破碎、筛分的方式实现。或者，可以通过购买市售的硅碳材料、第一石墨和第二石墨，并结合本申请中“粒径的测试”的测试方法来确定第一石墨的粒径Dv50-1、第二石墨的粒径Dv50-2、硅碳材料的粒径Dv10、Dv50-3和Dv90，并选择所需材料即可。
在本申请的一些实施方案中，硅碳材料的比表面积为0.5m2/g至3.5m2/g。例如，硅碳材料的比表面积为0.5m2/g、0.7m2/g、1.0m2/g、1.5m2/g、2.0m2/g、2.5m2/g、3.0m2/g、3.5m2/g或上述任两个数值范围间的任一数值。将硅碳材料的比表面积调控在上述范围内，硅碳材料表面能够具有较多的嵌锂点位，有利于降低负极极片发生析锂的概率，且硅碳材料表面与电解液能够充分接触，使得硅碳材料能够发挥其高容量特性，负极极片具有较高的容量。由此，电化学装置在缓解负极极表面析锂问题的基础上，具有较高的能量密度和容量保持率。
在本申请的一些实施方案中，硅碳材料的比表面积为1.0m2/g至2.0m2/g。例如，硅碳材料的比表面积为1.0m2/g、1.2m2/g、1.3m2/g、1.5m2/g、1.7m2/g、2.0m2/g或上述任两个数值范围间的任一数值。将硅碳材料的比表面积调控在上述范围内，有利于使电化学装置在具有较高的能量密度和容量保持率的情况下，进一步缓解负极极片表面析锂的问题。
本申请对硅碳材料的比表面积的调控方式没有特别限制，只要能够实现本申请目的即可。例如，可以通过调控硅碳材料的粒径或者采用沉积法制备硅碳材料时调控多孔碳的孔径分布等来实现，或者，也可以通过直接购买比表面积处于本申请范围内的硅碳材料，并结合本申请中“硅碳材料的比表面积的测试”的测试方法来确定硅碳材料的比表面积，选择所需比表面积的硅碳材料。
在本申请的一些实施方案中，硅碳材料的振实密度为0.8g/cm3至1.05g/cm3。例如，硅碳材料的振实密度为0.8g/cm3、0.85g/cm3、0.87g/cm3、0.91g/cm3、0.96g/cm3、1.00g/cm3、1.05g/cm3或上述任两个数值范围间的任一数值。将硅碳材料的振实密度调控在上述范围内，有利于硅碳材料在第二负极材料层中紧密堆积并具有合适的孔隙率，使得电化学装置在具有较高能量密度的基础上，具有较低的体积膨胀率。
在本申请的一些实施方案中，第一负极材料层的压实密度C1和第二负极材料层的压实密度C2满足：1.5g/cm3≤C1≤1.65g/cm3，1.35g/cm3≤C2≤1.5g/cm3，0.05g/cm3≤C1-C2≤0.3g/cm3。例如，第一负极材料层的压实密度C1为1.5g/cm3、1.52g/cm3、1.55g/cm3、1.57g/cm3、1.60g/cm3、1.62g/cm3、1.65g/cm3或上述任两个数值范围间的任一数值。例如，第二负极材料层的压实密度C2为1.35g/cm3、1.37g/cm3、1.40g/cm3、1.43g/cm3、1.47g/cm3、1.5g/cm3或上述任两个数值范围间的任一数值。例如，C1-C2的值为0.05g/cm3、0.1g/cm3、0.15g/cm3、0.2g/cm3、0.25g/cm3、0.3g/cm3或上述任两个数值范围间的任一数值。将第一负极材料层的压实密度C1、第二负极材料层的压实密度C2以及C1-C2的值调控在本申请范围内，第一负极材料层和第二负极材料层具有较高容量的情况下，第一负极材料层和第二负极材料层中各颗粒之间的间隙，能够使电解液在第一负极材料层和第二负极材料层中具有较短的传输路径以及较多数量的传输通道。这样，电解液能够均匀分布于第一负极材料层和第二负极材料层中，锂离子、电子的传输速率得到提升，负极极片表面发生析锂的概率得到降低，负极极片还具有较高的容量。由此，电化学装置在负极极片表面的析锂问题得到缓解的情况下，具有较高的能量密度。
在本申请的一些实施方案中，0.1g/cm3≤C1-C2≤0.2g/cm3。例如，C1-C2的值为0.1g/cm3、0.12g/cm3、0.14g/cm3、0.17g/cm3、0.2g/cm3或上述任两个数值范围间的任一数值。将第一负极材料层的压实密度C1和第二负极材料层的压实密度C2的差值C1-C2调控在本申请范围内，能够加速电解液在负极极片孔隙内的快速传输，因此，能够进一步提高电化学装置的倍率性能。
本申请对第一负极材料层的压实密度的调控方式没有特别限定，只要能够实现本申请目的即可。例如，可以通过调控第一负极材料层中第一负极活性材料的粒径来实现，或者，可以通过调控负极极片冷压过程中的压力来实现。本申请对第二负极材料层的压实密度的调控方式没有特别限定，只要能够实现本申请目的即可。例如，可以通过调控第二负极材料层中第二负极活性材料的粒径来实现，或者，可以通过调控负极极片冷压过程中的压力来实现。
在本申请的一些实施方案中，基于第一负极材料层的质量，第一负极活性材料的质量百分含量为90％至98.5％。任选地，第一负极材料层还包括导电剂、增稠剂和粘结剂。本申请对第一负极材料层中导电剂、增稠剂和粘结剂的质量百分含量没有特别限制，只要能够实现本申请目的即可。例如，基于第一负极材料层的质量，导电剂的质量百分含量为0％至0.5％，增稠剂的质量百分含量为0.05％至0.5％，粘结剂的质量百分含量为1％至5％。
在本申请的一些实施方案中，基于第二负极材料层的质量，第二负极活性材料的质量百分含量为89.8％至98.5％。任选地，第二负极材料层还包括导电剂、增稠剂和粘结剂。本申请对第二负极材料层中导电剂、增稠剂和粘结剂的质量百分含量没有特别限制，只要能够实现本申请目的即可。例如，基于第二负极材料层的质量，导电剂的质量百分含量为0.1％至2％，增稠剂的质量百分含量为0.05％至0.5％，粘结剂的质量百分含量为1％至10％。
本申请对导电剂、增稠剂和粘结剂的种类没有特别限制，可以选用本领域公知的导电剂、增稠剂和粘结剂，只要能够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，负极集流体包括但不限于铜箔、铜合金箔、镍箔、钛箔、泡沫镍或泡沫铜等。在本申请中，对负极集流体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4μm至20μm。本申请对第一负极材料层和第二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，第一负极材料层的厚度为20μm至50μm，第二负极材料层的厚度为20μm至50μm。
本申请对正极极片没有特别限制，只要能够实现本申请目的即可。在一些实施方案中，正极极片包括正极集流体和正极活性材料层，正极活性材料层设置于正极集流体的一个表面或两个表面上，上述“表面”可以是正极集流体的部分表面，也可以是正极集流体的全部表面。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，正极集流体可以包含铝箔或铝合金箔等。本申请的正极活性材料层包含正极活性材料。本申请对正极活性材料的种类没有特别限制，只要能够实现本申请目的即可。例如，正极活性材料可以包含镍钴锰酸锂、镍钴铝酸锂、磷酸铁锂、富锂锰基材料、钴酸锂、锰酸锂、磷酸锰铁锂或钛酸锂等中的至少一种。在本申请中，正极活性材料还可以包含非金属元素，非金属元素可以包括氟、磷、硼、氯、硅或硫中的至少一种，这些元素能进一步提高正极活性材料的稳定性。在本申请中，对正极集流体和正极活性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5μm至20μm。单层正极活性材料层的厚度为30μm至120μm。任选地，正极活性材料层还可以包括导电剂或粘结剂中的至少一种。本申请对正极活性材料层中的导电剂和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。本申请对正极活性材料层中正极活性材料、导电剂、粘结剂的质量比没有特别限制，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。
本申请对隔膜没有特别限制，只要能够实现本申请目的即可。例如，隔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。本申请对隔膜的厚度没有特别限制，只要能够实现本申请的目的即可。
本申请的电化学装置还包括电解液，本申请对电解液没有特别限制，只要能够实现本申请目的即可。例如，在一些实施方案中，电解液包括锂盐和非水溶剂。锂盐可以包括LiPF6、LiNO3、LiBF4、LiClO4、LiB(C6H5)4、LiCH3SO3、LiCF3SO3、LiN(SO2CF3)2、LiC(SO2CF3)3、Li2SiF6、双草酸硼酸锂(LiBOB)、双三氟甲磺酰亚胺锂(LiTFSI)或二氟硼酸锂中的至少一种。本申请对锂盐在电解液中的含量不做限定，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，非水溶剂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、碳酸二丙酯、碳酸甲丙酯、碳酸乙丙酯或碳酸甲乙酯中的至少一种。上述环状碳酸酯可以包括但不限于碳酸乙烯酯(EC)、碳酸丙烯酯(PC)、碳酸亚丁酯或碳酸乙烯基亚乙酯中的至少一种。氟代碳酸酯化合物可以包括但不限于氟代碳酸乙烯酯、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。
本申请的电化学装置还包括壳体，壳体用于容纳正极极片、负极极片、隔膜和电解液，以及本领域已知的电化学装置中的其它部件，本申请对上述其它部件不做限定。本申请对壳体没有特别限制，可以为本领域公知的壳体，只要能够实现本申请目的即可。
本申请对电化学装置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，电化学装置可以包括但不限于：锂离子二次电池(锂离子电池)、锂聚合物二次电池或锂离子聚合物二次电池等。
本申请对负极极片的制备方法没有特别限制，只要能够实现本申请目的即可。例如，在一些实施方案中，负极极片的制备方法包括但不限于以下步骤：(1)将第一负极活性材料、导电剂、增稠剂、粘结剂混合均匀后，加入溶剂，搅拌均匀得到第一负极浆料；(2)将第二负极活性材料、导电剂、增稠剂、粘结剂混合均匀后，加入溶剂，搅拌均匀得到第二负极浆料；(3)在负极集流体的两个表面分别涂布第一负极浆料，烘干后，形成第一负极材料层，然后，分别在两个第一负极材料层远离负极集流体的表面上涂布第二负极浆料，烘干后，形成第二负极材料层，经冷压、分切即得到双面设有第一负极材料层和第二负极材料层的负极极片。在另一些实施方案中，负极极片的制备方法包括但不限于以下步骤(1)将第一负极活性材料、导电剂、增稠剂、粘结剂混合均匀后，加入溶剂，搅拌均匀得到第一负极浆料；(2)将第二负极活性材料、导电剂、增稠剂、粘结剂混合均匀后，加入溶剂，搅拌均匀得到第二负极浆料；(3)在负极集流体的一个表面涂布第一负极浆料，烘干后，在负极集流体的表面形成第一负极材料层，在第一负极材料层远离负极集流体的表面涂布第二负极浆料，烘干后，经冷压、分切即得到单面设有第一负极材料层和第二负极材料层的负极极片。本申请对上述步骤(1)和(2)中溶剂的种类没有特别限制，只要能够实现本申请目的即可。本申请对上述第一负极浆料和第二负极浆料的固含量没有特别限制，只要能够实现本申请目的即可。本申请对上述步骤(3)中烘干的温度和时间没有特别限制，本领域技术人员可以根据实际情况选择，只要能够实现本申请目的即可。
本申请的电化学装置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：将隔膜、正极极片、隔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，经过化成、脱气、整形等工艺流程得到电化学装置；或者，将隔膜、正极极片、隔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，经过化成、脱气、整形等工艺流程得到电化学装置。
本申请的第二方面提供了一种电子装置，该电子装置包括前述任一实施方案所述的电化学装置。因此，电子装置具有良好的使用性能。
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。
测试方法和设备：
粒径的测试：
采用激光粒度仪MasterSizer 2000测试粒度分布，得到硅碳材料的粒径Dv10、Dv50-3、Dv90，第一石墨的粒径Dv50-1，第二石墨的Dv50-2。
硅碳材料中硅元素的质量百分含量的测试：
使用等离子体发射光谱仪(ICP)测量硅碳材料中的硅元素含量。将硅碳材料(0.05～0.2g)置于镍坩埚中，加入1.5g KOH(氢氧化钾)加盖碱融(400℃下加热45min)，然后使用50ml沸水浸取60min，置于100ml容量瓶中定容，取出部分稀释后的溶液进行ICP测试。
硅碳材料的比表面积的测试：
使用比表面积分析仪(美国麦克仪器公司，TristarⅡ3020M)，通过氮吸附法测量对各实施例和对比例的硅碳材料进行比表面积测试。其中，具体的测试依据国家标准GB/T19587-2017《气体吸附BET法测定固态物质比表面积》进行。
压实密度的测试：
将锂离子电池的电压控制在3.95V后(若锂离子电池电压低于3.95V，以0.2C充电至3.95V；若锂离子电池的电压高于3.95V，以0.2C放电至3.95V)，拆解得到负极极片。在负极极片上冲取面积为S的小圆片，得到小圆片的质量和厚度，分别记为m和h；将小圆片上的第二负极材料层通过刻蚀的方式除掉，得到剥离第二负极材料层的小圆片的质量和厚度，分别记为m1和h1，将小圆片上的第一负极材料层通过刻蚀的方式除掉，得到负极集流体的质量和厚度，分别记为m2和h2。
第一负极材料层的压实密度C1＝(m1-m2)/(h1-h2)/S。
第二负极材料层的压实密度C2＝(m-m1)/(h-h1)/S。
最高不析锂充电倍率的测试：
将各实施例和对比例的锂离子电池在25℃下按照下述步骤进行充放电：静置30min，以0.2C电流恒流放电至3.0V；静置30min；以充电倍率0.5C恒流充电至4.5V，之后以4.5V恒压充电至0.05C时停止充电(此时为满充状态)；即为一个充放电流程。对上述充放电流程循环50个周期后，对满充状态的锂离子电池进行拆解，观察负极极片是否析锂：若负极极片表面出现白色或灰色锂，则判定为析锂；反之，则判定为不析锂。
若不析锂，则取同一实施例或对比例制得的锂离子电池，以充电倍率逐次增大0.1C，其余充放电参数不变的情况下，重复上述步骤，直至负极极片出现析锂为止。
负极极片最后一次出现不析锂情况下的充电倍率定义为该锂离子电池析锂的最高不析锂倍率。最高不析锂倍率越大，表示锂离子电池越不容易发生析锂，即锂离子电池中负极极片表面析锂的问题得到越充分的缓解，锂离子电池的循环性能越好。
X射线衍射图谱(XRD)的测试：
将锂离子电池在25±3℃环境中静置30min，以0.2C电流将锂离子电池放电至3.0V，再以最高不析锂倍率恒流充电至4.5V后，将锂离子电池拆解得到负极极片，使用胶带将表层第二负极材料层粘下，用于第二负极材料层的第二石墨嵌锂度测试，将去除第二负极材料层后的负极极片用于第一负极材料层的第一石墨嵌锂度测试，分别对第二负极材料层和第一负极材料层石墨进行XRD表征。
对于第二负极材料层和第一负极材料层的区分，具体如下：取极片截面进行SEM/EDS表征，在EDS图像中Si元素区域的颜色与不含Si元素的区域颜色不同，两个区域之间有明显的分界，在此处作直线即得到第一负极材料层和第二负极材料层的分界线。对于各实施例以及对比例2，首先用胶带撕下负极极片表层，用于第二负极材料层的第二石墨嵌锂度测试。然后重复使用胶带撕掉部分负极极片，直至剩余负极极片厚度首次小于第一负极材料层和负极集流体的厚度之和，用于第一负极材料层的第一石墨嵌锂度测试。对于对比例1，只有第一负极材料层，表层和底层为负极极片厚度方向不同位置的差异，不必须以不同负极极片组成作为区分条件，首先用胶带撕下负极极片表层，用于表层石墨嵌锂度测试，然后重复使用胶带撕掉部分负极极片，直至剩余负极极片厚度首次小于第一负极材料层总厚度的1/2与负极集流体厚度之和，用于底层石墨嵌锂度测试。
其中，最高不析锂倍率根据“最高不析锂充电倍率的测试”中的测试方法得到，以负极极片不析锂情况下的最大充电倍率定义为锂离子电池的最高不析锂倍率。
容量保持率的测试：
将锂离子电池在25±3℃环境中静置30min，以最高不析理倍率恒流充电至4.5V，锂离子电池以4.5V恒压充电至0.05C时停止充电；锂离子电池静置30min；以0.5C电流将锂离子电池放电至3.0V，静置30min；按照同样的充放电流程循环300圈(cls)，记录第300圈的放电容量为C300。以第2圈的放电容量作为100％容量基准值，记录第2圈的放电容量为C2。容量保持率(％)＝C300/C2×100％。
能量密度的测试：
首先对锂离子电池按照下述操作流程充电，再进行放电，得出锂离子电池的放电容量。
充电：以0.2C恒流充电至4.5V，再以4.5V恒压充电至0.05C；
放电：以0.2C恒流放电至3.0V，得出放电能量E1；
锂离子电池充电步骤完成后，用激光测厚仪测试锂离子电池的长L、宽W、高H，得到锂离子电池的体积V＝L×W×H。其体积能量密度(ED)可通过如下公式计算得到：ED(Wh/L)＝E1/V。
实施例1-1
<负极极片的制备>
将第一负极活性材料第一石墨(人造石墨，石墨化度95％)、粘结剂聚丙烯酸(重均分子量Mw＝3500)、导电剂单壁碳纳米管按照质量比97:2.8:0.2进行混合，加入去离子水作为溶剂，搅拌制成固含量为42wt％的第一负极浆料，将第一负极浆料分别涂覆在厚度为6μm的负极集流体铜箔的两个表面，经100℃烘干形成第一负极材料层。将第二负极活性材料第二石墨(人造石墨，石墨化度95％)和硅碳材料、粘结剂聚丙烯酸(Mw＝3500)、导电剂单壁碳纳米管按照质量比58.2:38.8:2.8:0.2的充分混合，加入去离子水搅拌制成固含量为42wt％的第二负极浆料，分别涂覆在两个第一负极材料层远离铜箔的表面上，经100℃烘干后形成第二负极材料层。冷压、分切、焊接负极极耳镍极耳，得到规格为1000mm×80mm的负极极片。
其中，第二负极活性材料中硅碳材料的质量百分含量W1为40％，硅碳材料中硅元素的质量百分含量W2为50％。硅碳材料的粒径Dv10＝5.5μm、Dv50-4＝9.1μm、Dv90＝15μm。硅碳材料的比表面积为1.4m2/g。第一石墨的粒径Dv50-1＝12μm，第二石墨的粒径Dv 50- 2＝10μm。第一负极材料层的单位面积涂布重量CW1＝90mg/1540.25mm2，第二负极材料层的单位面积涂布重量CW2＝30mg/1540.25mm2，负极极片的单位面积涂布重量CW12＝CW1+CW2＝120mg/1540.25mm2，第二负极材料层的单位面积涂布重量占负极极片单位面积涂布重量的比例P＝1/4。第一负极材料层的压实密度C1＝1.6g/cm3，第二负极材料层的压实密度C2＝1.4g/cm3。
<正极极片的制备>
将正极活性材料钴酸锂、导电剂导电炭黑(Super P)、粘结剂聚偏氟乙烯(PVDF，Mw＝600000)按照质量比97.8:1.4:0.8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至固含量为72wt％且体系均匀的正极浆料。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，得到单面涂布正极活性材料层(厚度90μm)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活性材料层的正极极片。再经冷压、裁片、焊接正极极耳铝极耳，得到规格为990mm×76mm正极极片待用。
<隔膜的制备>
以厚度为8μm的聚乙烯(PE)多孔薄膜作为隔膜。
<电解液的制备>
在干燥氩气气氛中，将非水溶剂碳酸乙烯酯(EC)和碳酸二甲酯(DMC)以质量比1:1混合均匀，加入锂盐六氟磷酸锂搅拌均匀制得电解液。锂盐浓度为1mol/L。
<锂离子电池的制备>
将隔膜、正极极片、隔膜、负极极片按顺序依次叠好，并卷绕得到电极组件。将电极组件置于包装袋铝塑膜中，在80℃下脱去水分后，注入电解液并封装，经过化成、脱气、整形等工艺流程得到锂离子电池。
实施例1-2至实施例1-13
除了按照表1调整相关制备参数以外，其余与实施例1-1相同。
实施例2-1至实施例2-6
除了按照表2调整相关制备参数以外，其余与实施例1-3相同。
实施例3-1至实施例3-8
除了按照表3调整相关制备参数以外，其余与实施例2-2相同。
实施例4-1至实施例4-11
除了按照表4调整相关制备参数以外，其余与实施例3-1相同。
对比例1
<负极极片的制备>
将人造石墨(石墨化度95％)、硅碳材料(Dv50＝8.6μm)、粘结剂聚丙烯酸(重均分子量Mw＝3500)、导电剂单壁碳纳米管按照质量比87.3:9.7:2.8:0.2进行混合，加入去离子水作为溶剂，搅拌制成固含量为42wt％的负极浆料，将负极浆料分别涂覆在负极集流体铜箔的两个表面，经100℃烘干形成第一负极材料层。冷压、分切、焊接负极极耳镍极耳，得到规格为1000mm×80mm的负极极片。第一负极材料层的涂布重量为150mg/1540.25mm2。
<正极极片的制备>、<隔膜的制备>、<电解液的制备>、<锂离子电池的制备>与实施例1-1相同。
对比例2
除了将<负极极片的制备>中的第一负极材料层和第二负极材料层调换位置以外，其余与实施例1-1相同。
各实施例和对比例的制备参数和性能数据如表1至表4所示。
表1

注：表1中的“P”表示第二负极材料层的单位面积涂布重量占负极极片单位面积涂布
重量的比例；“\”表示不存在相关的参数。
从实施例1-1至实施例1-11、对比例1和对比例2可以看出，本申请实施例的电化学装置，通过在负极极片中同时设置位于底层的第一负极材料层和位于表层的第二负极材料层，且电化学装置以最高不析锂倍率恒流充电至4.5V时，第二负极材料层的X射线衍射图谱中，未出现LiC6的特征峰，LiC12的特征峰中最大强度处的2θ为A2°，25.15≤A2≤25.30；和/或，第一负极材料层X射线衍射图谱中，LiC12的特征峰中最大强度处的2θ为A1°，第二负极材料层的X射线衍射图谱中，LiC12的特征峰中最大强度处的2θ为A2°，0≤A1-A2≤0.15。使得实施例的电化学装置最高不析锂倍率更大，表明电化学装置中负极极片表面更不易发生析锂，电化学装置中负极极片表面析锂的问题得到了缓解，电化学装置具有更好的循环性能。而对比例的电化学装置最高不析锂倍率更小，表明对比例的电化学装置具有负极极片表面更容易析锂。
图2示出了实施例1-1的负极极片的X射线衍射图谱；图3示出了对比例1的负极极片的X射线衍射图谱。从图2可以看出，实施例1-1的负极极片中，第二负极材料层的X射线衍射图谱中，未出现LiC6的特征峰，LiC12的特征峰中最大强度处的2θ为25.24°，第一负极材料层X射线衍射图谱中，LiC12的特征峰中最大强度处的2θ为25.26°，LiC12的特征峰最大强度处的2θ比较接近，说明负极极片嵌锂均匀性好。从图3中可以看出，对比例1的负极极片中，表层的X射线衍射图谱中，出现了LiC6的特征峰，LiC12的特征峰中最大强度处的2θ为25.12°，底层的X射线衍射图谱中，LiC12的特征峰中最大强度处的2θ为25.35°。
第二负极活性材料中硅碳材料的质量百分含量以及硅碳材料中硅元素的质量百分含量通常也会影响电化学装置中负极极片表面的析锂情况。从实施例1-1至实施例1-13可以看出，选用第二负极活性材料中硅碳材料的质量百分含量以及硅碳材料中硅元素的质量百分含量处于本申请范围内的电化学装置，其具有较大的最高不析锂倍率，表明电化学装置中负极极片表面析锂的问题得到了缓解，电化学装置具有良好的循环性能。
表2
第一石墨的粒径Dv50-1及其与第二石墨的粒径的Dv50-2差值Dv50-1-Dv50-2通常也会影响电化学装置中负极极片表面的析锂情况和容量保持率。从实施例1-3、实施例2-1至实施例2-6可以看出，选用第一石墨的粒径Dv50-1及其与第二石墨的粒径的Dv50-2差值Dv50- 1-Dv50-2处于本申请范围内的电化学装置，其在具有较高容量保持率的基础上，具有较大的最高不析锂倍率，表明电化学装置在具有较长循环寿命的基础上，使负极极片表面析锂的问题得到了缓解。
表3
硅碳材料的粒径Dv10、Dv50-3、Dv90以及Dv90-Dv10的值通常会影响电化学装置中负极极片表面的析锂情况和容量保持率。从实施例2-2、实施例3-1至实施例3-4可以看出，选用硅碳材料的粒径Dv10、Dv50-3、Dv90以及Dv90-Dv10的值处于本申请范围内的电化学装置，其在具有较高容量保持率的基础上，具有较大的最高不析锂倍率，表明电化学装置在具有较长循环寿命的基础上，使负极极片表面析锂的问题得到了缓解。
硅碳材料的比表面积通常会影响电化学装置中负极极片表面的析锂情况和容量保持率。从实施例2-2、实施例3-5至实施例3-8可以看出，选用硅碳材料的比表面积处于本申请范围内的电化学装置，其在具有较高容量保持率的基础上，具有较大的最高不析锂倍率，表明电化学装置在具有较长循环寿命的基础上，使负极极片表面析锂的问题得到了缓解。
表4

第一负极材料层的压实密度C1、第二负极材料层的压实密度C2以及二者的差值C1-C2通常会影响电化学装置中负极极片表面的析锂情况和电化学装置的能量密度。从实施例3-1、实施例4-1至实施例4-11可以看出，选用第一负极材料层的压实密度C1、第二负极材料层的压实密度C2以及二者的差值C1-C2处于本申请范围内的电化学装置，能量密度变化不大，切其具有较大的最高不析锂倍率，表明电化学装置中负极极片表面析锂的问题得到缓解的基础上，电化学装置具有较高的能量密度。
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. 一种电化学装置，包括负极极片、正极极片以及设置于所述负极极片和所述正极极片之间的隔膜，所述负极极片包括负极集流体以及设置于所述负极集流体至少一个表面上的第一负极材料层和第二负极材料层，所述第一负极材料层设置于所述负极集流体和所述第二负极材料层之间；
    所述电化学装置以最高不析锂倍率恒流充电至上限截止电压时，所述第一负极材料层与所述第二负极材料层的X射线衍射图谱中，LiC12的特征峰满足以下特征(1)或(2)中的至少一者：
    (1)所述第二负极材料层的X射线衍射图谱中，未出现LiC6的特征峰，LiC12的特征峰中最大强度处的2θ为A2°，25.15≤A2≤25.30；
    (2)所述第一负极材料层X射线衍射图谱中，LiC12的特征峰中最大强度处的2θ为A1°，所述第二负极材料层的X射线衍射图谱中，LiC12的特征峰中最大强度处的2θ为A2°，0≤A1-A2≤0.15。
  2. 根据权利要求1所述的电化学装置，其中，所述第一负极材料层包括第一负极活性材料，所述第一负极活性材料包括第一石墨；
    所述第二负极材料层包括第二负极活性材料，所述第二负极活性材料包括硅碳材料和第二石墨；
    所述第二负极活性材料中所述硅碳材料的质量百分含量为15％至50％，所述硅碳材料中硅元素的质量百分含量为30％至60％。
  3. 根据权利要求2所述的电化学装置，其中，所述第二负极活性材料中所述硅碳材料的质量百分含量为30％至50％，所述硅碳材料中硅元素的质量百分含量为50％至60％。
  4. 根据权利要求2所述的电化学装置，其中，所述第一石墨的粒径Dv50-1为11.0μm至13.5μm。
  5. 根据权利要求4所述的电化学装置，其中，所述第二石墨的粒径Dv50-2与所述第一石墨的粒径Dv50-1满足：1μm≤Dv50-1-Dv50-2≤5μm。
  6. 根据权利要求2或3所述的电化学装置，其中，所述硅碳材料的粒径Dv10、Dv50-3和Dv90满足：5μm≤Dv10≤6μm、8μm≤Dv50-3≤10.5μm、13μm≤Dv90≤17μm。
  7. 根据权利要求6所述的电化学装置，其中，所述硅碳材料的粒径Dv10和Dv90满足：8μm≤Dv90-Dv10≤10.5μm。
  8. 根据权利要求2或3所述的电化学装置，其中，所述硅碳材料的比表面积为0.5m2/g至3.5m2/g。
  9. 根据权利要求8所述的电化学装置，其中，所述硅碳材料的比表面积为1.0m2/g至2.0m2/g。
  10. 根据权利要求6所述的电化学装置，其中，所述第一负极材料层的压实密度C1和所述第二负极材料层的压实密度C2满足：1.5g/cm3≤C1≤1.65g/cm3，1.35g/cm3≤C2≤1.5g/cm3，0.05g/cm3≤C1-C2≤0.3g/cm3。
  11. 根据权利要求10所述的电化学装置，其中，0.1g/cm3≤C1-C2≤0.2g/cm3。
  12. 一种电子装置，其中，所述电子装置包括权利要求1至11中任一项所述的电化学装置。
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CN118380632A (zh) * 2024-04-19 2024-07-23 宁德新能源科技有限公司 电化学装置和电子装置

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