WO2024145757A1 - 负极极片以及包含其的电极组件、电池单体、电池和用电装置 - Google Patents

负极极片以及包含其的电极组件、电池单体、电池和用电装置 Download PDF

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WO2024145757A1
WO2024145757A1 PCT/CN2023/070150 CN2023070150W WO2024145757A1 WO 2024145757 A1 WO2024145757 A1 WO 2024145757A1 CN 2023070150 W CN2023070150 W CN 2023070150W WO 2024145757 A1 WO2024145757 A1 WO 2024145757A1
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Prior art keywords
negative electrode
film layer
active material
silicon
electrode film
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English (en)
French (fr)
Inventor
游兴艳
王育文
白文龙
郑蔚
武宝珍
吴凯
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Contemporary Amperex Technology Co Ltd
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Contemporary Amperex Technology Co Ltd
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Priority to EP23913919.9A priority Critical patent/EP4611056A4/en
Priority to CN202380009791.1A priority patent/CN116888751B/zh
Priority to PCT/CN2023/070150 priority patent/WO2024145757A1/zh
Publication of WO2024145757A1 publication Critical patent/WO2024145757A1/zh
Priority to US19/034,792 priority patent/US12438149B2/en
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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
    • H01M10/058—Construction or manufacture
    • H01M10/0587—Construction or manufacture of accumulators having only wound construction elements, i.e. wound positive electrodes, wound negative electrodes and wound separators
    • 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
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • 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
    • 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
    • H01M4/134—Electrodes based on metals, Si or alloys
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H01M4/1395—Processes of manufacture of electrodes based on metals, Si or alloys
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/364—Composites as mixtures
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—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
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • 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
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/10—Primary casings; Jackets or wrappings
    • H01M50/102—Primary casings; Jackets or wrappings characterised by their shape or physical structure
    • H01M50/103—Primary casings; Jackets or wrappings characterised by their shape or physical structure prismatic or rectangular
    • 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
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2220/00—Batteries for particular applications
    • H01M2220/20—Batteries in motive systems, e.g. vehicle, ship, plane
    • 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
    • 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
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

  • the present application belongs to the technical field of secondary batteries, and specifically relates to a negative electrode plate and an electrode assembly, a battery cell, a battery and an electrical device containing the same.
  • the purpose of the present application is to provide a negative electrode plate and an electrode assembly, a battery cell, a battery and an electrical device containing the negative electrode plate, so as to enable the secondary battery to have high energy density, high safety performance and good long-term cycle performance.
  • the first aspect of the present application provides a negative electrode sheet, including: a negative electrode current collector having a first surface and a second surface opposite to each other in the thickness direction thereof; a first negative electrode film layer, located on the first surface side, the first negative electrode film layer comprising first silicon-based negative electrode active material particles, the particle size d1 of the crystal grains contained in the first silicon-based negative electrode active material particles and the volume average particle size Dv150 of the first silicon-based negative electrode active material particles satisfy: 0.0003 ⁇ d1 / Dv150 ⁇ 0.004 ; and a second negative electrode film layer, located on the second surface side, the second negative electrode film layer comprising second silicon-based negative electrode active material particles, the particle size d2 of the crystal grains contained in the second silicon-based negative electrode active material particles and the volume average particle size Dv250 of the second silicon-based negative electrode active material particles satisfy: 0.0002 ⁇ d2 / Dv250 ⁇ 0.002 ; wherein the unit area capacity C1 of the first negative
  • the energy density, safety performance and long-term cycle performance of the secondary battery can be significantly improved; when the negative electrode sheet of the present application is applied to an electrode assembly with a stacked structure, the energy density and long-term cycle performance of the secondary battery can be significantly improved.
  • the first negative electrode film layer is located on the outer surface of the negative electrode sheet, and the second negative electrode film layer is located on the inner surface of the negative electrode sheet. Since the first film layer has a larger unit area capacity, after winding, it can still have a high unit area capacity. As a result, the negative electrode film layer located on the outer surface of the negative electrode sheet can accommodate more active lithium ions, thereby reducing the risk of lithium deposition on the surface of the negative electrode sheet.
  • the first silicon-based negative electrode active material particles in the first negative electrode film layer can have a higher capacity.
  • the second silicon-based negative electrode active material particles in the second negative electrode film layer can have a low volume expansion rate. As a result, it is helpful to reduce the risk of pulverization and deactivation of the silicon-based negative electrode active material particles, thereby enabling the secondary battery to have good long-term cycle performance.
  • the first silicon-based negative electrode active material can have a high capacity, which is beneficial to improving the energy density of the secondary battery; the second silicon-based negative electrode active material particles have a low volume expansion rate, which is beneficial to reducing the average volume expansion rate of the silicon-based negative electrode active material particles.
  • the energy density and long-term cycle performance of the secondary battery can be significantly improved.
  • Dv 1 50 is 6 ⁇ m to 10 ⁇ m, and can be optionally 6.5 ⁇ m to 9 ⁇ m.
  • the negative electrode plate of the present application is applied to an electrode assembly of a wound structure, and the first negative electrode film layer is located on the outer surface of the negative electrode plate, and the second negative electrode film layer is located on the inner surface of the negative electrode plate, and Dv 1 50 is within the above-mentioned appropriate range, on the one hand, it is beneficial to reduce the active lithium ions consumed in forming the SEI film; on the other hand, it is beneficial to improve the capacity of the first silicon-based negative electrode active material. As a result, it is not only beneficial to reduce the risk of lithium plating on the outer surface of the negative electrode plate, thereby improving the safety performance of the secondary battery, but also beneficial to improve the first coulomb efficiency and long-term cycle performance of the secondary battery.
  • any embodiment of the present application 5nm ⁇ d 1 ⁇ 12nm, optionally, 7nm ⁇ d 1 ⁇ 12nm.
  • the grain size of the first silicon-based negative electrode active material particles is within a suitable range, the risk of oxidation of the first silicon-based negative electrode active material particles can be reduced, thereby improving the capacity of the first silicon-based negative electrode active material particles, providing more lithium insertion sites for lithium ions, thereby reducing the generation of lithium dendrites, and improving the safety performance of the secondary battery.
  • Dv 2 50 is 2.5 ⁇ m to 5.5 ⁇ m, and can be optionally 3 ⁇ m to 5 ⁇ m.
  • the negative electrode sheet of the present application is applied to an electrode assembly of a winding structure, and the first negative electrode film layer is located on the outer surface of the negative electrode sheet, and the second negative electrode film layer is located on the inner surface of the negative electrode sheet, and Dv 2 50 is within the above-mentioned appropriate range, it is beneficial to shorten the lithium ion transmission path of the negative electrode film layer located on the inner surface of the negative electrode sheet, and further reduce the volume expansion of the second silicon-based negative electrode active material particles, thereby further reducing the electrochemical polarization and improving the cycle stability of the secondary battery.
  • the grain size of the second silicon-based negative electrode active material particles is within a suitable range, during the cycle of the secondary battery, when the second silicon-based negative electrode active material particles expand in volume, the squeezing of the second silicon-based negative electrode active material particles by the internal grains is reduced, which can alleviate the damage rate of the second silicon-based negative electrode active material particles, thereby extending the cycle life of the battery.
  • the secondary battery can have both high energy density and good long-term cycle performance.
  • the negative electrode sheet of the present application is applied to an electrode assembly of a winding structure, and the first negative electrode film layer is located on the outer surface of the negative electrode sheet, and the second negative electrode film layer is located on the inner surface of the negative electrode sheet, the risk of lithium deposition on the surface of the negative electrode sheet can also be reduced, thereby making the secondary battery further have high safety performance.
  • the secondary battery can have both high energy density and high safety performance.
  • the first silicon-based negative electrode active material particles and the second silicon-based negative electrode active material particles are selected from the same type of silicon-based negative electrode active material particles, and the gram capacity of the first silicon-based negative electrode active material is greater than the gram capacity of the second silicon-based negative electrode active material.
  • the gram capacity of the first silicon-based negative electrode active material particles is greater than the gram capacity of the second silicon-based negative electrode active material particles, on the one hand, it is easier to adjust the ratio of the unit area capacity of the first negative electrode film layer to the second negative electrode film layer within the range specified in the present application; on the other hand, it helps to control the ratio of the volume expansion rate of the first silicon-based negative electrode active material particles to the second silicon-based negative electrode active material particles within a suitable range. Thereby, it helps to improve the long-term cycle performance of the secondary battery, and improve the safety performance of the secondary battery using the wound structure electrode assembly.
  • the first negative electrode film layer further comprises a third negative electrode active material, and the third negative electrode active material is selected from artificial graphite, natural graphite, hard carbon, soft carbon or a combination thereof.
  • the second negative electrode film layer further comprises a fourth negative electrode active material, and the fourth negative electrode active material is selected from artificial graphite, natural graphite, hard carbon, soft carbon or a combination thereof.
  • the negative electrode film layer includes other negative electrode active materials in addition to silicon-based negative electrode active material particles, it is not only convenient to adjust the unit area capacity of the negative electrode film layer so that the negative electrode film layer meets the limitations of this application, but also beneficial to flexibly adjust the compaction density, porosity and other parameters of the negative electrode film layer through the combination of silicon-based negative electrode active material particles and other negative electrode active materials, thereby improving the safety performance and electrochemical performance of the secondary battery.
  • the mass percentage of the first silicon-based negative electrode active material particles is 10% to 30%, and can be optionally 12% to 25%.
  • the mass percentage of the first silicon-based negative electrode active material particles in the negative electrode active material in the first negative electrode film layer is within the above-mentioned appropriate range, the first negative electrode film layer can have a higher energy density and reduce the volume expansion of the first negative electrode film layer during the charge and discharge cycle of the secondary battery. As a result, the secondary battery can have high energy density, high safety performance and good long-term cycle performance.
  • the mass percentage of the second silicon-based negative electrode active material particles is 10% to 30%, and can be optionally 12% to 25%.
  • the second negative electrode film layer can have a higher energy density and reduce the volume expansion of the second negative electrode film layer during the charge and discharge cycle of the secondary battery.
  • the secondary battery can have high energy density, high safety performance and good long-term cycle performance.
  • the second aspect of the present application provides an electrode assembly, including the negative electrode plate of the first aspect of the present application.
  • the electrode assembly of the present application includes the negative electrode plate of the first aspect of the present application, which is applied to a secondary battery and can at least enable the secondary battery to have a high energy density and good long-term cycle performance.
  • the positive electrode plate of the electrode assembly includes: a positive electrode current collector, and a first positive electrode film layer and a second positive electrode film layer respectively located on both sides of the positive electrode current collector.
  • the negative electrode sheet is wound with the positive electrode sheet via a separator along a winding direction to form a winding structure.
  • the first positive electrode film layer is arranged opposite to the first negative electrode film layer via the separator.
  • the second positive electrode film layer is arranged opposite to the second negative electrode film layer via the separator.
  • the negative electrode sheet in the electrode assembly of the present application has a first film layer with a larger capacity per unit area, and after winding, it can still have a high capacity per unit area.
  • the negative electrode film layer located on the outer surface of the negative electrode sheet can accommodate more active lithium ions, thereby reducing the risk of lithium precipitation on the surface of the negative electrode sheet.
  • the silicon-based negative electrode material particles contained in the first negative electrode film layer have a larger volume average particle size, so that they can have a higher capacity.
  • the silicon-based negative electrode active material particles contained in the second negative electrode film layer have a smaller volume average particle size, so that they can have a low volume expansion rate and a shorter lithium ion transmission path.
  • the electrode assembly of the present application is applied to a secondary battery, which can significantly improve the energy density, safety performance and long-term cycle performance of the secondary battery.
  • the winding structure includes a bending area and a straight area connected to the bending area.
  • the negative electrode plate includes a plurality of bent portions located in the bent area and a plurality of straight portions located in the straight area, and two ends of the straight portions are respectively connected to the bent portions.
  • At least one bent portion in the negative electrode sheet is a first bent portion
  • at least one straight portion in the negative electrode sheet is a first straight portion connected to the first bent portion
  • the first bent portion and the first straight portion satisfy: C 3 >C 4 , wherein C 3 represents the active material capacity per unit area of the first negative electrode film layer in the first bent portion; C 4 represents the active material capacity per unit area of the first negative electrode film layer in the first straight portion.
  • the capacity of the positive electrode film layer directly facing the bent portion of the negative electrode sheet through the separator is higher than the capacity of the positive electrode film layer directly facing the straight portion of the negative electrode sheet through the separator, which can make the capacity of the negative electrode film layer in the bent portion greater than that of the straight portion, thereby reducing the risk of lithium deposition in the bent portion.
  • the electrode assembly satisfies: CB 1 >CB 2 >1, wherein CB 1 represents the ratio of the capacity of the first negative electrode film layer to the capacity of the first positive electrode film layer; CB 2 represents the ratio of the active material capacity of the second negative electrode film layer to the capacity of the second positive electrode film layer.
  • CB 1 and CB 2 meet the above conditions, it helps to alleviate the lithium insertion pressure of the first negative electrode film layer and reduce the risk of lithium plating, thereby helping to improve the safety performance of the secondary battery.
  • CB 2 and CB 1 satisfy the above relationship, it helps to reduce the risk of lithium deposition on the surface of the first negative electrode film layer and the second negative electrode film layer, thereby improving the safety performance of the secondary battery.
  • a third aspect of the present application provides a battery cell, comprising a housing and the electrode assembly of the second aspect of the present application, wherein the electrode assembly is accommodated in the housing.
  • the battery cell of the present application includes the electrode assembly of the second aspect of the present application, and can at least have high energy density and good long-term cycle performance.
  • a fourth aspect of the present application provides a battery comprising a plurality of battery cells according to the third aspect of the present application.
  • a fifth aspect of the present application provides an electrical device, which includes the battery cell of the third aspect of the present application, and the battery cell is used to provide electrical energy.
  • the battery and the electric device of the present application include the battery cell provided by the present application, and thus have at least the same advantages as the battery cell.
  • FIG. 1 is a schematic diagram of an electrode assembly according to an embodiment of the present application.
  • FIG. 2 is a schematic diagram of another embodiment of an electrode assembly of the present application.
  • FIG. 5 is a schematic diagram of an embodiment of a battery module of the present application.
  • FIG. 7 is an exploded view of the battery pack of the present application shown in FIG. 6 .
  • any lower limit can be combined with any upper limit to form an unambiguous range; and any lower limit can be combined with other lower limits to form an unambiguous range, and any upper limit can be combined with any other upper limit to form an unambiguous range.
  • each point or single value between the range endpoints is included in the range.
  • each point or single value can be combined as its own lower limit or upper limit with any other point or single value or with other lower limits or upper limits to form an unambiguous range.
  • the term "or” is inclusive.
  • the phrase “A or B” means “A, B, or both A and B”. More specifically, any of the following conditions satisfies the condition "A or B”: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).
  • Lithium plating not only reduces the performance of secondary batteries, such as a significant shortening of the cycle life, but also, after the lithium plating phenomenon continues to occur, the lithium metal will grow into a tree-like structure, namely lithium dendrites.
  • the growth of lithium dendrites will destroy the solid electrolyte interface (SEI) film on the surface of the negative electrode active material, causing irreversible consumption of active ions; the growth of lithium dendrites will also pierce the isolation membrane to cause an internal short circuit, which may cause safety risks such as combustion and explosion.
  • SEI solid electrolyte interface
  • the silicon-based negative electrode active material particles are usually coated to inhibit the volume expansion of the silicon-based materials through the coating layer.
  • coating the silicon-based materials is not only complicated, but also has an unsatisfactory effect on inhibiting the volume expansion of the silicon-based materials.
  • the inventors after in-depth research and extensive experiments, provide a negative electrode plate and an electrode assembly, a battery cell, a battery and an electrical device containing the same.
  • the first silicon-based negative electrode active material particles and the second silicon-based active material particles may be the same type of silicon-based negative electrode active material, or may be different types of silicon-based negative electrode active materials.
  • the present application does not limit the type of silicon-based negative electrode active material, which may include silicon-based negative electrode active materials known in the art.
  • the first silicon-based silicon-based negative electrode active material particles and the second silicon-based negative electrode active material particles may each be independently selected from one or more of pre-lithiated or non-pre-lithiated silicon particles, pre-lithiated or non-pre-lithiated silicon oxygen composite particles, pre-lithiated or non-pre-lithiated silicon carbon composite particles, or pre-lithiated or non-pre-lithiated silicon alloy particles.
  • first negative electrode film layer and the second negative electrode film layer also contain other negative electrode active materials
  • the other negative electrode active materials may include negative electrode active materials known in the art and applicable to secondary batteries, for example, may include but are not limited to carbon-based negative electrode materials and tin-based negative electrode materials.
  • the above C1 and C2 can be achieved by adjusting the thickness of the first negative electrode film layer and the second negative electrode film layer, the content of the negative electrode active material in the film layer, the composition of the negative electrode active material, etc., and are not limited here.
  • the thickness of the first negative electrode film layer can be adjusted to be greater than the thickness of the second negative electrode film layer, so that C 2 ⁇ C 1 ; in some embodiments, when the thickness of the first negative electrode film layer and the second negative electrode film layer, the composition of negative electrode active materials and the like are the same, the mass percentage of negative electrode active materials in the first negative electrode film layer can be adjusted to be greater than the content of negative electrode active materials in the second negative electrode film layer, so that C 2 ⁇ C 1 ; in some embodiments, when the thickness of the first negative electrode film layer and the second negative electrode film layer, the mass percentage of negative electrode active materials in the film layers and the like are the same, the composition of negative electrode active materials in the first negative electrode film layer and the second negative electrode film layer can be adjusted, for example, by adding other negative electrode active materials of different types, so that C 2 ⁇ C 1 .
  • the inventor unexpectedly discovered that when the negative electrode plate of the present application is applied to an electrode assembly with a wound structure, and the first negative electrode film layer is located on the outer surface of the negative electrode plate, and the second negative electrode film layer is on the inner surface of the negative electrode plate, the energy density, safety performance and long-term cycle performance of the secondary battery can be significantly improved; when the negative electrode plate of the present application is applied to an electrode assembly with a stacked structure, the energy density and long-term cycle performance of the secondary battery can be significantly improved.
  • the electrode film layer located on the outer surface especially the electrode film layer located on the outer surface of the bending portion of the electrode assembly, is stretched during the winding process, resulting in a capacity per unit area that is smaller than the capacity per unit area before winding; accordingly, the electrode film layer located at the corner of the inner surface, especially the electrode film layer located on the inner surface of the bending portion of the electrode assembly, is squeezed during the winding process, resulting in a capacity per unit area that is larger than the capacity per unit area before winding.
  • the grain size of the first silicon-based negative electrode active material particles is within the above range, the risk of oxidation of the first silicon-based negative electrode active material particles can be reduced, thereby improving the capacity of the first silicon-based negative electrode active material particles, providing more lithium insertion sites for lithium ions, thereby reducing the generation of lithium dendrites and improving the safety performance of the secondary battery.
  • the negative electrode plate of the present application when the negative electrode plate of the present application is applied to an electrode assembly of a wound structure, and the first negative electrode film layer is located on the outer surface of the negative electrode plate, and the second negative electrode film layer is located on the inner surface of the negative electrode plate, and Dv 2 50 is within the above-mentioned appropriate range, it is beneficial to shorten the lithium ion transmission path of the negative electrode film layer located on the inner surface of the negative electrode plate, and further reduce the volume expansion of the second silicon-based negative electrode active material particles, thereby helping to further reduce electrochemical polarization and improve the cycle stability of the secondary battery.
  • the grain size d2 of the second silicon-based negative electrode active material particles may satisfy: 3nm ⁇ d2 ⁇ 5nm , for example, d2 may be 3nm, 3.5nm, 4nm, 4.5nm, 5nm, or within the range of any of the above values.
  • d2 may be 3nm, 3.5nm, 4nm, 4.5nm, 5nm, or within the range of any of the above values.
  • 3.5nm ⁇ d2 ⁇ 5nm for example, d2 may be 3.5nm, 3.8nm, 4nm, 4.2nm, 4.5nm, 4.8nm, 5nm, or within the range of any of the above values.
  • the grain size of the second silicon-based negative electrode active material particles is within the above range, during the cycle of the secondary battery, when the second silicon-based negative electrode active material particles expand in volume, the squeezing of the second silicon-based negative electrode active material particles by the internal grains is reduced, which can alleviate the breakage rate of the second silicon-based negative electrode active material particles, thereby extending the cycle life of the battery.
  • the volume average particle size Dv 1 50 of the first silicon-based negative electrode active material particles and the volume average particle size Dv 2 50 of the second silicon-based negative electrode active material particles may satisfy: 0.2 ⁇ Dv 2 50/Dv 1 50 ⁇ 0.9, for example, Dv 2 50/Dv 1 50 may be 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, or in the range of any of the above values.
  • 0.3 ⁇ Dv 2 50/Dv 1 50 ⁇ 0.8 for example, Dv 2 50/Dv 1 50 may be 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, or in the range of any of the above values.
  • the negative electrode sheet of the present application when the negative electrode sheet of the present application is applied to an electrode assembly of a winding structure, and the first negative electrode film layer is located on the outer surface of the negative electrode sheet, and the second negative electrode film layer is located on the inner surface of the negative electrode sheet, the risk of lithium deposition on the surface of the negative electrode sheet can also be reduced, so that the secondary battery further has high safety performance.
  • the ratio of C1 to C2 is within the above-mentioned appropriate range, which can make the negative electrode film layer located on the inner surface of the negative electrode plate have an appropriate capacity per unit area, thereby reducing the risk of lithium deposition on the inner surface of the negative electrode plate due to the low capacity per unit area of the negative electrode film layer on the inner surface, thereby improving the safety performance of the secondary battery;
  • the ratio of C1 to C2 is within the above-mentioned appropriate range, which can make the negative electrode film layer located on the outer side of the negative electrode plate have an appropriate capacity per unit area, thereby reducing the waste of negative electrode capacity due to the high capacity per unit area of the negative electrode film layer on the outer surface, thereby improving the energy density of the secondary battery.
  • the gram capacity of the first silicon-based negative electrode active material particles is greater than the gram capacity of the second silicon-based negative electrode active material particles, on the one hand, it is easier to adjust the ratio of the unit area capacity of the first negative electrode film layer to the second negative electrode film layer within the range specified in this application; on the other hand, it helps to control the ratio of the volume expansion rate of the first silicon-based negative electrode active material particles to the second silicon-based negative electrode active material particles within a suitable range. Thus, it helps to improve the long-term cycle performance of the secondary battery and improve the safety performance of the secondary battery using the wound structure electrode assembly.
  • the negative electrode sheet of the present application can be prepared without adjusting the preparation parameters such as the thickness and compaction density of the negative electrode film layer, thereby simplifying the processing technology of the negative electrode sheet of the present application, thereby improving the production capacity of the negative electrode sheet of the present application.
  • the first negative electrode film layer may further include a third negative electrode active material, and the third negative electrode active material may be selected from artificial graphite, natural graphite, hard carbon, soft carbon or a combination thereof.
  • the second negative electrode film layer may further include a fourth negative electrode active material, and the fourth negative electrode active material may be selected from artificial graphite, natural graphite, hard carbon, soft carbon or a combination thereof.
  • the negative electrode film layer includes other negative electrode active materials in addition to silicon-based negative electrode active material particles, it is not only convenient to adjust the unit area capacity of the negative electrode film layer so that the negative electrode film layer meets the limitations of this application, but also beneficial to flexibly adjust the compaction density, porosity and other parameters of the negative electrode film layer through the combination of silicon-based negative electrode active material particles and other negative electrode active materials, thereby improving the safety performance and electrochemical performance of the secondary battery.
  • the mass percentage of the first silicon-based negative electrode active material particles may be 10% to 30%, for example, 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, or within the range of any of the above values.
  • the mass percentage of the second silicon-based negative electrode active material particles may be 10% to 30%, for example, 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, or within the range of any of the above values.
  • the mass percentage of the second silicon-based negative electrode active material particles may be 12% to 25%, for example, it may be 12%, 14%, 16%, 18%, 20%, 22%, 24%, 25%, or within the range of any of the above values.
  • the composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).
  • a metal material copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.
  • a polymer material substrate such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.
  • the first negative electrode layer and the second negative electrode layer may further optionally include a binder.
  • the binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).
  • SBR styrene-butadiene rubber
  • PAA polyacrylic acid
  • PAAS sodium polyacrylate
  • PAM polyacrylamide
  • PVA polyvinyl alcohol
  • SA sodium alginate
  • PMAA polymethacrylic acid
  • CMCS carboxymethyl chitosan
  • the negative electrode plate does not exclude other additional functional layers in addition to the negative electrode film layer.
  • the negative electrode plate described in the present application may also include a conductive primer layer (e.g., composed of a conductive agent and a binder) disposed between the negative electrode current collector and the negative electrode film layer.
  • the negative electrode plate described in the present application also includes a protective layer covering the surface of the negative electrode film layer.
  • the first silicon-based negative electrode active material particles and the second silicon-based negative electrode active material particles can be obtained in a variety of ways, which are not limited here.
  • the first silicon-based negative electrode active material particles and the second silicon-based negative electrode active material particles that meet the conditions of the present application can be selected by performing XRD testing and volume average particle size testing on the silicon-based negative electrode active material.
  • the first silicon-based negative electrode active material particles and the second silicon-based negative electrode active material particles that meet the conditions of the present application can be prepared based on the preparation method of silicon-based negative electrode active material particles known in the art by controlling the particle size, preparation temperature, etc. of the silicon-based negative electrode active material particles.
  • the unit area capacity of the first negative electrode film layer and the unit area capacity of the second negative electrode film layer have the meanings known in the art and can be measured by methods and instruments known in the art.
  • the volume average particle size D V 50 has a well-known meaning in the art, which indicates that in the particle size distribution of the silicon-based negative electrode active material particles on a volume basis, 50% of the particle sizes are smaller than this value.
  • Dv 1 50 and Dv 2 50 can be measured by methods known in the art. For example, it can be measured by a laser particle size analyzer (e.g., Mastersizer 2000E, Malvern, UK) with reference to the particle size distribution laser diffraction method of GB/T 19077-2016, or by scanning the silicon-based negative electrode active material particles with a scanning electron microscope (SEM) to measure the volume average particle size of the silicon-based negative electrode active material particles.
  • a laser particle size analyzer e.g., Mastersizer 2000E, Malvern, UK
  • SEM scanning electron microscope
  • the gram capacity play has a well-known meaning in the art, which can represent the ratio of the capacitance that can be actually released by the material to be tested to its mass.
  • step (2) The negative electrode sheet dried in step (1) is baked at a certain temperature and time (e.g., 400° C., 2 hours), and a region of the baked negative electrode sheet is selected to sample the negative electrode active material (sampling can be performed by scraping powder with a blade).
  • a certain temperature and time e.g. 400° C., 2 hours
  • step (3) The negative electrode active material collected in step (2) is sieved (for example, sieved with a 200-mesh sieve) to finally obtain a sample that can be used to test the parameters of the negative electrode active material mentioned above in the present application.
  • a second aspect of the present application provides an electrode assembly, which includes the negative electrode plate of the first aspect of the present application.
  • the electrode assembly of the present application includes the negative electrode plate of the first aspect of the present application, and is applied to a secondary battery, which can at least enable the secondary battery to have a high energy density and good long-term cycle performance.
  • the present application does not limit the type of the electrode assembly, and the electrode assembly may have a structure known in the art.
  • the electrode assembly may include a negative electrode plate and a positive electrode plate.
  • the electrode assembly may further include a separator.
  • the separator is disposed between the positive electrode plate and the negative electrode plate to serve as an isolation.
  • the present application has no particular restrictions on the type of separator, and any known porous structure separator with good chemical stability and mechanical stability may be selected.
  • the material of the separator may be selected from one or more of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.
  • the separator may be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer may be the same or different.
  • the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector and including a positive electrode active material.
  • the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.
  • the positive electrode film layer generally comprises a positive electrode active material and an optional binder and an optional conductive agent, and is generally formed by coating a positive electrode slurry, drying, and cold pressing.
  • the positive electrode slurry is generally formed by dispersing the positive electrode active material and the optional conductive agent and binder in a solvent and stirring them uniformly.
  • the solvent may be N-methylpyrrolidone (NMP).
  • the binder for the positive electrode film layer may include one or more of polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE).
  • PVDF polyvinylidene fluoride
  • PTFE polytetrafluoroethylene
  • the conductive agent used for the positive electrode film layer may include one or more of superconducting carbon, carbon black (eg, acetylene black, Ketjen black), carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
  • carbon black eg, acetylene black, Ketjen black
  • carbon dots carbon nanotubes, graphene, and carbon nanofibers.
  • the positive electrode current collector may be a metal foil or a composite current collector (a metal material may be disposed on a polymer substrate to form a composite current collector).
  • the positive electrode current collector may be an aluminum foil.
  • the positive electrode sheet, the separator, and the negative electrode sheet may be formed into an electrode assembly of a laminated structure through a lamination process.
  • FIG1 is a schematic diagram of an embodiment of an electrode assembly of the present application.
  • the exemplary electrode assembly includes a negative electrode sheet 10, a separator 20, and a positive electrode sheet 30, and the negative electrode sheet 10 and the positive electrode sheet 30 are arranged in sequence.
  • the negative electrode sheet 10 includes a first surface 10a and a second surface 10b along its thickness direction, wherein the first surface 10a is the surface of the negative electrode sheet 10 facing the outside of the electrode assembly, and the second surface 10b is the surface of the negative electrode sheet 10 facing away from the outside of the electrode assembly.
  • a negative electrode film layer (not shown in the figure) is provided on the first surface 10a of the negative electrode sheet 10, and such a negative electrode film layer is an embodiment of the first negative electrode film layer according to the embodiment of the present application;
  • a negative electrode film layer (not shown in the figure) is also provided on the second surface 10b of the negative electrode sheet 10, and such a negative electrode film layer is an embodiment of the second negative electrode film layer according to the embodiment of the present application.
  • a negative electrode film layer (not shown in the figure) is provided on the first surface 10a of the negative electrode plate 10, and such a negative electrode film layer is an embodiment of the second negative electrode film layer according to the embodiment of the present application; a negative electrode film layer (not shown in the figure) is also provided on the second surface 10b of the negative electrode plate 10, and such a negative electrode film layer is an embodiment of the first negative electrode film layer according to the embodiment of the present application.
  • the negative electrode sheet is wound with the positive electrode sheet via the separator in a winding direction to form a winding structure.
  • the first positive electrode film layer is arranged opposite to the first negative electrode film layer via the separator, and the second positive electrode film layer is arranged opposite to the second negative electrode film layer via the separator.
  • the first positive electrode film layer is located on the outside of the first negative electrode film layer, and the second positive electrode film layer is located on the inside of the second negative electrode film layer.
  • FIG2 is a schematic diagram of an embodiment of an electrode assembly of the present application.
  • the exemplary electrode assembly includes a negative electrode sheet 10, a separator 20, and a positive electrode sheet 30, wherein the negative electrode sheet 10 is wound with the positive electrode sheet 30 through the separator 20 in a winding direction to form a winding structure.
  • the negative electrode sheet includes an outer surface 10c and an inner surface 10d.
  • a negative electrode film layer (not shown in the figure) is provided on the outer surface 10c of the negative electrode sheet 10, and such a negative electrode film layer is an embodiment of the first negative electrode film layer according to the embodiment of the present application.
  • a negative electrode film layer (not shown in the figure) is also provided on the inner surface 10d of the negative electrode sheet 10, and such a negative electrode film layer is an embodiment of the second negative electrode film layer according to the embodiment of the present application.
  • the positive electrode sheet 30 includes an inner surface 30a disposed opposite to the outer surface 10c of the negative electrode sheet, and an outer surface 30b of the positive electrode sheet disposed opposite to the inner surface 10d of the negative electrode sheet 10.
  • a positive electrode film layer (not shown in the figure) is provided on the inner surface 30a of the positive electrode plate 30, and such a positive electrode film layer is an example of a first positive electrode film layer according to an embodiment of the present application.
  • a positive electrode film layer (not shown in the figure) is also provided on the outer surface 30b of the positive electrode plate 30, and such a positive electrode film layer is an example of a second positive electrode film layer according to an embodiment of the present application.
  • the negative electrode sheet in the electrode assembly of the present application has a first film layer with a larger capacity per unit area, and after winding, it can still have a high capacity per unit area.
  • the negative electrode film layer located on the outer surface of the negative electrode sheet can accommodate more active lithium ions, thereby reducing the risk of lithium precipitation on the surface of the negative electrode sheet.
  • the silicon-based negative electrode material particles contained in the first negative electrode film layer have a larger volume average particle size, so that they can have a higher capacity.
  • the silicon-based negative electrode active material particles contained in the second negative electrode film layer have a smaller volume average particle size, so that they can have a low volume expansion rate and a shorter lithium ion transmission path.
  • the electrode assembly of the present application is applied to a secondary battery, which can significantly improve the energy density, safety performance and long-term cycle performance of the secondary battery.
  • the winding structure includes a bending zone and a straight zone connected to the bending zone;
  • the negative electrode plate includes a plurality of bending portions located in the bending zone and a plurality of straight portions located in the straight zone, and both ends of the straight portions are respectively connected to the bending portions.
  • At least one bent portion in the negative electrode sheet is a first bent portion, and at least one straight portion in the negative electrode sheet is a first straight portion connected to the first bent portion, and the first bent portion and the first straight portion satisfy: C 3 >C 4 , wherein C 3 represents the active material capacity per unit area of the first negative electrode film layer in the first bent portion; C 4 represents the active material capacity per unit area of the first negative electrode film layer in the first straight portion.
  • the capacity of the positive electrode film layer facing the bent portion of the negative electrode plate through the isolation membrane is higher than the capacity of the positive electrode film layer facing the straight portion of the negative electrode plate through the isolation membrane.
  • the capacity of the negative electrode film layer at the bent portion can be greater than that of the straight portion, thereby reducing the risk of lithium plating at the bent portion.
  • the electrode assembly may satisfy: CB 1 >CB 2 >1, wherein CB 1 represents the ratio of the capacity of the first negative electrode film layer to the capacity of the first positive electrode film layer; CB 2 represents the ratio of the active material capacity of the second negative electrode film layer to the capacity of the second positive electrode film layer.
  • CB 1 and CB 2 meet the above conditions, it helps to relieve the lithium insertion pressure of the first negative electrode film layer and reduce the risk of lithium plating, thereby facilitating improving the safety performance of the secondary battery.
  • the electrolyte may also optionally include additives.
  • the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high temperature performance, and additives that improve battery low temperature power performance.
  • a fourth aspect of the present application provides a battery, which includes the battery cell of the third aspect of the present application.
  • the battery mentioned in this application refers to a single physical module that includes one or more battery cells to provide higher voltage and capacity.
  • the battery mentioned in this application can be a battery module or a battery pack.
  • the battery generally includes a box for encapsulating one or more battery cells. The box can prevent liquid or other foreign matter from affecting the charging or discharging of the battery cells.
  • the multiple battery cells may be connected in series, in parallel, or in a hybrid connection.
  • a hybrid connection means that the multiple battery cells are both connected in series and in parallel.
  • the multiple battery cells may be directly connected in series, in parallel, or in a hybrid connection, and then the whole formed by the multiple battery cells is accommodated in the box; of course, multiple battery cells may be first connected in series, in parallel, or in a hybrid connection to form a battery module, and then the multiple battery modules are connected in series, in parallel, or in a hybrid connection to form a whole, and then accommodated in the box.
  • the second negative electrode active material (second silicon oxide particles and graphite are mixed in a mass ratio of 15:85), conductive carbon black, thickener sodium carboxymethyl cellulose (CMC-Na), and binder styrene-butadiene rubber latex (SBR) are fully stirred and mixed in a proper amount of deionized water in a weight ratio of 96:0.8:1.2:2 to form a uniform second negative electrode slurry; the second negative electrode slurry is coated on the other surface of the copper foil with a coating weight of 0.13g/ 1540.25mm2 ; after drying and other processes, a second negative electrode film layer is formed on the surface of the copper foil; and then cold pressing is performed to obtain a negative electrode sheet with a compaction density of the negative electrode film layer of 1.6g/ cm3 .

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Abstract

一种负极极片以及包含其的电极组件、电池单体、电池和用电装置。负极极片（10）包括：负极集流体，具有在其厚度方向相对的第一表面（10a）和第二表面（10b）；第一负极膜层，位于第一表面侧，第一负极膜层包含第一硅基负极活性材料颗粒；以及第二负极膜层，位于第二表面侧，第二负极膜层包含第二硅基负极活性材料颗粒；其中，第一负极膜层的单位面积容量C 1与第二负极膜层的单位面积容量C 2满足：0.005 mAh/mm 2≤C 2＜C 1≤0.2 mAh/mm 2。

Description

负极极片以及包含其的电极组件、电池单体、电池和用电装置 技术领域
本申请属于二次电池技术领域，具体涉及一种负极极片以及包含其的电极组件、电池单体、电池和用电装置。
背景技术
二次电池依靠活性离子在正极和负极之间往复脱嵌来进行充电和放电，其具有能量密度高、循环寿命长，以及无污染、无记忆效应等突出特点。因此，二次电池作为清洁能源，已由电子产品逐渐普及到电动汽车等大型装置领域，以适应环境和能源的可持续发展战略。
随着二次电池市场地位的提升，人们不仅期望二次电池具有更高的能量密度，还期望二次电池具有良好的安全性能和长期循环性能。
发明内容
本申请的目的在于提供一种负极极片以及包含其的电极组件、电池单体、电池和用电装置，旨在使二次电池兼具高能量密度、高安全性能以及良好的长期循环性能。
为了实现上述发明目的，本申请第一方面提供一种负极极片，包括：负极集流体，具有在其厚度方向相对的第一表面和第二表面；第一负极膜层，位于所述第一表面侧，所述第一负极膜层包含第一硅基负极活性材料颗粒，所述第一硅基负极活性材料颗粒所包含晶粒的粒径d 1与所述第一硅基负极活性材料颗粒的体积平均粒径Dv 150满足：0.0003≤d 1/Dv 150≤0.004；以及第二负极膜层，位于所述第二表面侧，所述第二负极膜层包含第二硅基负极活性材料颗粒，所述第二硅基负极活性材料颗粒所包含晶粒的粒径d 2与所述第二硅基负极活性材料颗粒的体积平均粒径Dv 250满足：0.0002≤d 2/Dv 250≤0.002；其中，所述第一负极膜层的单位面积容量C 1与所述第二负极膜层的单位面积容量C 2满足：mAh/(g·mm 2)≤C 2＜C 1≤0.2mAh/(g·mm 2)。
当本申请的负极极片应用于卷绕结构的电极组件，并使得第一负极膜层位于负极极片的外侧表面，且第二负极膜层负极极片的内侧表面时，能够显著提升二次电池的能量密度、安全性能和长期循环性能；当本申请的负极极片应用于叠片式结构的电极组件时，能够显著提升二次电池的能量密度和长期循环性能。
并非意在受限于任何理论或解释，当硅基负极活性材料所包含的晶粒的粒径，与硅基负极活性材料颗粒的体积平均粒径之比在0.0003至0.004时，在充放电循环过程中，能够减少硅基负极活性材料的氧化反应，从而使得硅基负极活性材料颗粒具备高容量发挥，由此能够提升二次电池的能量密度；当硅基负极活性材料所包含的晶粒的粒径，与硅基负极活性材料颗粒的体积平均粒径之比在0.0002至0.002时，在充活性锂离子嵌入硅 基负极活性材料颗粒的过程中，硅基负极活性材料颗粒内部能够产生较小的应力，从而能够降低硅基负极活性材料颗粒内部产生裂纹的风险，从而能够降低第二硅基负极活性材料颗粒破裂，继而与电解液发生副反应的可能性，进而提升二次电池的循环性能。
当本申请的负极极片应用于具有卷绕结构的电极组件时，使第一负极膜层位于负极极片的外侧表面，且第二负极膜层负极极片的内侧表面，由于第一膜层具有更大的单位面积容量，经卷绕后，仍能够具有高单位面积容量。由此，位于负极极片外侧表面的负极膜层能够容纳更多的活性锂离子，从而能够降低负极极片表面发生析锂现象的风险。
进一步地，d 1/Dv 150在上述合适的范围内，能够使得第一负极膜层中的第一硅基负极活性材料颗粒具有更高的容量发挥。由此，不仅有助于提升位于负极极片外侧表面的负极膜层的单位面积容量，从而进一步提升二次电池的安全性能，而且有助于提升二次电池的首次库伦效率。相应地，d 2/Dv 250在上述合适的范围内，能够使得第二负极膜层中的第二硅基负极活性材料颗粒具有低体积膨胀率。由此，有利于降低硅基负极活性材料颗粒粉化失活的风险，从而使得二次电池具备良好的长期循环性能。
因此，当本申请的负极极片应用于卷绕结构的电极组件，并使得第一负极膜层位于负极极片的外侧表面，且第二负极膜层负极极片的内侧表面时，硅基负极活性材料能够具有高容量发挥、较小的平均体积膨胀率，且位于负极极片外侧表面的负极膜层具有高单位面积容量。由此，能够显著提升二次电池的能量密度、安全性能和长期循环性能。
同样地，当本申请的负极极片应用于叠片式结构的电极组件时，第一硅基负极活性材料能够具有高容量发挥，从而有利于提升二次电池的能量密度；第二硅基负极活性材料颗粒具有低体积膨胀率，从而有利于降低硅基负极活性材料颗粒的平均体积膨胀率。由此，能够显著提升二次电池的能量密度和长期循环性能。
在本申请任意实施方式中，Dv 150为6μm～10μm，可选为6.5μm～9μm。当本申请的负极极片应用于卷绕结构的电极组件，并使得第一负极膜层位于负极极片的外侧表面，第二负极膜层负极极片的内侧表面，且Dv 150在上述合适的范围内时，一方面有利于减少形成SEI膜所消耗的活性锂离子；另一方面有利于提升第一硅基负极活性材料的容量发挥。由此，不仅有利于降低负极极片外侧表面发生析锂现象的风险，从而提升二次电池的安全性能，而且有利于提升二次电池的首次库伦效率和长期循环性能
在本申请任意实施方式中，5nm≤d 1≤12nm，可选地，7nm≤d 1≤12nm。当第一硅基负极活性材料颗粒所包含的晶粒粒径在合适的范围时，能够降低第一硅基负极活性材料颗粒发生氧化的风险，从而提升第一硅基负极活性材料颗粒的容量发挥，为锂离子提供更多的嵌锂位点，进而减少锂枝晶的产生，提升二次电池的安全性能。
在本申请任意实施方式中，Dv 250为2.5μm～5.5μm，可选为3μm～5μm。当本申请的负极极片应用于卷绕结构的电极组件，并使得第一负极膜层位于负极极片的外侧表面，第二负极膜层负极极片的内侧表面，且Dv 250在上述合适的范围内时，有利于缩短位于负极极片内侧表面的负极膜层的锂离子传输路径，以及进一步降低第二硅基负极活性材料颗粒的体积膨胀，从而有利于进一步降低电化学极化、提升二次电池的循环稳定性。
在本申请任意实施方式中，3nm≤d 2≤5nm，可选地，3.5nm≤d 2≤5nm。当第二硅基负极活性材料颗粒所包含的晶粒粒径在合适的范围时，在二次电池循环过程中，第二硅基负极活性材料颗粒发生体积膨胀时，内部晶粒对第二硅基负极活性材料颗粒的挤压减 少，可缓解第二硅基负极活性材料颗粒的破损速度，从而延长电池的循环寿命。
在本申请任意实施方式中，0.2≤Dv 250/Dv 150≤0.9，可选地，0.3≤Dv 250/Dv 150≤0.8。当Dv 250/Dv 150的值在上述合适的范围内时，能够使得二次电池兼具高能量密度和良好的长期循环性能。特别地，当本申请的负极极片应用于卷绕结构的电极组件，并使得第一负极膜层位于负极极片的外侧表面，且第二负极膜层负极极片的内侧表面时，还能够降低负极极片表面发生析锂的风险，从而使得二次电池进一步具备高安全性能。
在本申请任意实施方式中，0.7≤C 2/C 1≤0.9，可选地，0.75≤C 2/C 1≤0.85。当本申请的负极极片应用于卷绕结构的电极组件，并使得第一负极膜层位于负极极片的外侧表面，第二负极膜层负极极片的内侧表面，且C 1和C 2的比值在上述合适的范围内时，能够允许二次电池兼具高能量密度和高安全性能。
在本申请任意实施方式中，所述第一硅基负极活性材料颗粒和所述第二硅基负极活性材料颗粒选自相同种类的硅基负极活性材料颗粒，所述第一硅基负极活性材料的克容量发挥大于所述第二硅基负极活性材料的克容量发挥。当第一硅基负极活性材料颗粒的克容量发挥大于第二硅基负极活性材料颗粒的克容量发挥时，一方面，更便于调整第一负极膜层与第二负极膜层的单位面积容量之比在本申请限定的范围内；另一方面，有助于将第一硅基负极活性材料颗粒和第二硅基负极活性材料颗粒的体积膨胀率之比控制在合适的范围内。由此，有助于提升二次电池的长期循环性能，以及提升应用卷绕结构电极组件的二次电池的安全性能。
在本申请任意实施方式中，所述第一负极膜层还包含第三负极活性材料，所述第三负极活性材料选自人造石墨、天然石墨、硬碳、软碳或其组合。
在本申请任意实施方式中，所述第二负极膜层还包含第四负极活性材料，所述第四负极活性材料选自人造石墨、天然石墨、硬碳、软碳或其组合。
当负极膜层中除硅基负极活性材料颗粒外，还包括其他负极活性材料时，不仅能够便于调整负极膜层的单位面积容量，以使得负极膜层满足本申请的限定，而且有利于通过硅基负极活性材料颗粒与其他负极活性材料的搭配，灵活地调整负极膜层的压实密度、孔隙率等参数，从而提升二次电池的安全性能和电化学性能。
在本申请任意实施方式中，基于所述第一硅基负极活性材料颗粒与所述第三负极活性材料的总质量，所述第一硅基负极活性材料颗粒的质量百分含量为10％～30％，可选为12％～25％。当第一负极膜层中，第一硅基负极活性材料颗粒在负极活性材料中的质量百分含量在上述合适的范围内时，既能够使得第一负极膜层具备较高的能量密度，又能够降低第一负极膜层在二次电池的充放电循环过程中产生的体积膨胀。由此，二次电池能够兼具高能量密度、高安全性能和良好的长期循环性能。
在本申请任意实施方式中，基于所述第二硅基负极活性材料颗粒与所述第四负极活性材料的总质量，所述第二硅基负极活性材料颗粒的质量百分含量为10％～30％，可选为12％～25％。当第二负极膜层中，第二硅基负极活性材料颗粒在负极活性材料中的质量百分含量在上述合适的范围内时，既能够使得第二负极膜层具备较高的能量密度，又能够降低第二负极膜层在二次电池的充放电循环过程中产生的体积膨胀。由此，二次电池能够兼具高能量密度、高安全性能和良好的长期循环性能。
本申请第二方面提供电极组件，包括本申请第一方面的负极极片。
本申请的电极组件包括本申请第一方面的负极极片，应用于二次电池，能够至少 使得二次电池具备高能量密度和良好的长期循环性能。
在本申请任意实施方式中，所述电极组件的正极极片包括：正极集流体，以及分别位于所述正极集流体两侧的第一正极膜层与第二正极膜层。
所述负极极片隔着隔离膜与所述正极极片沿卷绕方向卷绕以形成卷绕结构，所述第一正极膜层隔着所述隔离膜与所述第一负极膜层相对设置，所述第二正极膜层隔着所述隔离膜与所述第二负极膜层相对设置。
其中，所述第一正极膜层位于所述第一负极膜层的外侧，所述第二正极膜层位于所述第二负极膜层的内侧。
本申请的电极组件中的负极极片，其第一膜层具有更大的单位面积容量，经卷绕后，仍能够具有高单位面积容量。由此，位于负极极片外侧表面的负极膜层能够容纳更多的活性锂离子，从而能够降低负极极片表面发生析锂现象的风险。进一步地，相较于第二负极膜层，第一负极膜层包含的硅基负极材料颗粒具有更大的体积平均粒径，从而能够具有更高的容量发挥。由此，不仅有助于提升位于负极极片外侧表面的负极膜层的单位面积容量，从而进一步提升二次电池的安全性能，而且有助于提升二次电池的首次库伦效率。相应地，第二负极膜层包含的硅基负极活性材料颗粒具有更小的体积平均粒径，从而能够具有低体积膨胀率和较短的锂离子传输路径。由此，有利于降低硅基负极活性材料颗粒粉化失活的风险和电化学极化，从而使得二次电池具备良好的长期循环性能。因此，本申请的电极组件应用于二次电池，能够显著提升二次电池的能量密度、安全性能和长期循环性能。
在本申请任意实施方式中，所述卷绕结构包括弯折区和连接于所述弯折区的平直区。
所述负极极片包括位于所述弯折区的多个弯折部和位于所述平直区的多个平直部，所述平直部的两端分别与所述弯折部连接。
其中，所述负极极片中的至少一个弯折部为第一弯折部，所述负极极片中的至少一个平直部为连接于所述第一弯折部的第一平直部，所述第一弯折部和所述第一平直部满足：C 3＞C 4，其中，C 3表示所述第一弯折部中，第一负极膜层的单位面积活性物质容量；C 4表示所述第一平直部中，第一负极膜层的单位面积活性物质容量。负极极片的弯折部隔着隔离膜所正对的正极膜层容量高于负极极片的平直部隔着隔离膜所正对的正极膜层容量，能够使得弯折部负极膜层容量大于平直部，从而降低弯折部析锂风险。
在本申请任意实施方式中，电极组件满足：CB 1＞CB 2＞1，其中，CB 1表示所述第一负极膜层的容量与所述第一正极膜层的容量之比；CB 2表示所述第二负极膜层的活性物质容量与所述第二正极膜层的容量之比。当CB 1、CB 2满足上述条件时，有助于减缓第一负极膜层的嵌锂压力，降低析锂风险，从而有利于提升二次电池的安全性能。
在本申请任意实施方式中，0.7≤CB 2/CB 1≤0.99，可选地，0.75≤CB 2/CB 1≤0.98。当CB 2与CB 1满足上述关系时，有助于降低第一负极膜层以及第二负极膜层表面析锂的风险，从而有利于提升二次电池的安全性能。
本申请第三方面提供一种电池单体，包括外壳和本申请第二方面的电极组件，所述电极组件容纳于所述外壳内。
本申请的电池单体包括本申请第二方面的电极组件，能够至少具备高能量密度和 良好的长期循环性能。
本申请第四方面提供一种电池，包括多个本申请第三方面的电池单体。
本申请第五方面提供一种用电装置，其包括本申请第三方面的电池单体，所述电池单体用于提供电能。
本申请的电池和用电装置包括本申请提供的电池单体，因而至少具有与所述电池单体相同的优势。
附图说明
为了更清楚地说明本申请实施例的技术方案，下面将对本申请实施例中所需要使用的附图作简单地介绍，显而易见地，下面所描述的附图仅仅是本申请的一些实施方式，对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据附图获得其他的附图。
图1是本申请的电极组件的一实施方式的示意图。
图2是本申请的电极组件的另一实施方式的示意图。
图3是本申请的电池单体的一实施方式的示意图。
图4是图3所示的电池单体的实施方式的分解示意图。
图5是本申请的电池模块的一实施方式的示意图。
图6是本申请的电池包的一实施方式的示意图。
图7是图6所示的本申请的电池包的实施方式分解图。
图8是本申请的二次电池的实施例用作电源的用电装置的示意图。
附图标记说明：
10负极极片；10a第一表面；10b第二表面；10c负极极片的外侧表面；10d负极极片的内侧表面；20隔离膜；30正极极片；30a正极极片的内侧表面；30b正极极片的外侧表面；1电池包；2上箱体；3下箱体；4电池模块；5电池单体；51壳体；52电极组件；53盖板。
具体实施方式
为了使本申请的发明目的、技术方案和有益技术效果更加清晰，以下结合实施例对本申请进行进一步详细说明。应当理解的是，本说明书中描述的实施例仅仅是为了解释本申请，并非为了限定本申请。
为了简便，本文仅明确地公开了一些数值范围。然而，任意下限可以与任何上限组合形成未明确记载的范围；以及任意下限可以与其它下限组合形成未明确记载的范围，同样任意上限可以与任意其它上限组合形成未明确记载的范围。此外，尽管未明确记载，但是范围端点间的每个点或单个数值都包含在该范围内。因而，每个点或单个数值可以作为自身的下限或上限与任意其它点或单个数值组合或与其它下限或上限组合形成未明确记载的范围。
在本文的描述中，需要说明的是，除非另有说明，“以上”、“以下”为包含本数，“一种或几种”中“几种”的含义是两种或两种以上。
在本文的描述中，除非另有说明，术语“或”是包括性的。举例来说，短语“A或B”表示“A，B，或A和B两者”。更具体地，以下任一条件均满足条件“A或B”：A为真(或存在)并且B为假(或不存在)；A为假(或不存在)而B为真(或存在)；或A和B都为真(或存在)。
应理解，术语“第一”、“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，而不一定要求或暗示这些实体或操作之间存在任何实际的关系或顺序。
本申请的上述发明内容并不意欲描述本申请中的每个公开的实施方式或每种实现方式。如下描述更具体地举例说明示例性实施方式。在整篇申请中的多处，通过一系列实施例提供了指导，这些实施例可以以各种组合形式使用。在各个实例中，列举仅作为代表性组，不应解释为穷举。
如背景技术所述，提升二次电池的能量密度、安全性能和长期循环性能，是二次电池发展的重要方向。
硅基材料的克容量远高于碳材料，是极具发展潜力的负极活性材料，但是，硅基材料在充电过程中产生的体积膨胀会对其本身的容量发挥、二次电池的循环性能以及安全性能产生负面影响。
此外，析锂现象也是二次电池领域亟待解决的安全问题之一。在充电过程中，锂离子从正极脱出，嵌入负极。当正极脱出锂离子的速率大于负极嵌入锂离子的速率，或者正极脱出的锂离子总量大于负极所能容纳的锂离子总量时，无法及时嵌入负极的锂离子只能在负极极片表面得到电子并还原形成锂金属，这就是析锂现象。析锂不仅使二次电池性能下降，例如循环寿命大幅缩短，并且析锂现象持续发生后，锂金属会生长成像树枝一样的结构，即锂枝晶。锂枝晶的生长会破坏负极活性材料表面的固体电解质界面(solid electrolyte interface，SEI)膜，造成活性离子的不可逆消耗；锂枝晶的生长还会刺穿隔离膜造成内短路，有可能引起燃烧、爆炸等安全风险。
特别地，对于以硅基材料为负极活性材料的二次电池来说，在充放电过程中，硅基材料的体积膨胀收缩会使得部分硅基材料粉化失活。由此，随着充放电循环的进行，负极容量衰减，从而加剧了负极产生析锂现象的风险。
因此，抑制硅基材料的体积膨胀，以及减少以硅基材料为负极活性材料的二次电池的析锂现象，对提升二次电池的能量密度、循环性能及安全性能来说，是极具潜力的研究方向之一。
相关技术中，为了降低硅基材料的体积膨胀，多是对硅基负极活性材料颗粒进行包覆，通过包覆层抑制硅基材料的体积膨胀。然而，对硅基材料进行包覆不仅工艺复杂，而且对于硅基材料体积膨胀的抑制效果并不理想。
鉴于此，发明人经深入研究与大量实验，提供了一种负极极片以及包含其的电极组件、电池单体、电池和用电装置。
负极极片
本申请的第一方面提供一种负极极片，其包括：负极集流体，具有在其厚度方向相对的第一表面和第二表面；第一负极膜层，位于所述第一表面侧，所述第一负极膜层包含第一硅基负极活性材料颗粒，所述第一硅基负极活性材料颗粒所包含晶粒的粒径d 1 与所述第一硅基负极活性材料颗粒的体积平均粒径Dv 150满足：0.0003≤d 1/Dv 150≤0.004；以及第二负极膜层，位于所述第二表面侧，所述第二负极膜层包含第二硅基负极活性颗粒，所述第二硅基负极活性材料颗粒所包含晶粒的粒径d 2与所述第二硅基负极活性材料颗粒的体积平均粒径Dv 250满足：0.0002≤d 2/Dv 250≤0.002。例如，d 1/Dv 150可以为0.0003，0.0005，0.0008，0.001，0.0015，0.002，0.0025，0.003，0.0035，0.004，或处于以上任何数值所组成的范围内；d 2/Dv 250可以为0.0002，0.0005，0.0008，0.001，0.0012，0.0015，0.0018，0.002，或处于以上任何数值所组成的范围内。
其中，所述第一负极膜层的单位面积容量C 1与所述第二负极膜层的单位面积容量C 2满足：0.005mAh/(g·mm 2)≤C 2＜C 1≤0.2mAh/(g·mm 2)。
第一硅基负极活性材料颗粒和第二硅基活性材料颗粒可以为相同种类的硅基负极活性材料，也可以为不同种类的硅基负极活性材料。本申请对硅基负极活性材料的种类不作限制，其可以包括本领域已知的硅基负极活性材料。在一些实施方式中，第一硅基硅基负极活性材料颗粒和第二硅基负极活性材料颗粒可各自独立地选自经预锂化或未经预锂化的硅颗粒、经预锂化或未经预锂化的硅氧复合物颗粒、经预锂化或未经预锂化的硅碳复合物颗粒或经预锂化或未经预锂化的硅合金颗粒中的一种或几种。
本申请并不排除第一负极膜层和第二负极膜层中还包含其他负极活性材料的情况，所述其他负极活性材料可以包括本领域已知的、可用于二次电池的负极活性材料，例如可以包括但不限于碳基负极材料、锡基负极材料。上述C 1、C 2可以通过调整第一负极膜层和第二负极膜层的厚度、膜层中负极活性材料的含量、负极活性材料的组成等实现，在此不作限制。例如，在一些实施例中，在第一负极膜层和第二负极膜层中负极活性材料的质量百分含量、负极活性材料的组成等相同的情况下，可调整第一负极膜层的厚度大于第二负极膜层的厚度，使得C 2＜C 1；在一些实施例中，在第一负极膜层和第二负极膜层的厚度、负极活性材料的组成等相同的情况下，可调整第一负极膜层中负极活性材料的质量百分含量大于第二负极膜层中负极活性材料的含量，使得C 2＜C 1；在一些实施例中，在第一负极膜层和第二负极膜层的厚度、膜层中负极活性材料的质量百分含量等相同的情况下，可调整第一负极膜层和第二负极膜层中负极活性材料的组成，例如，添加不同种类的其他负极活性材料等，使得C 2＜C 1。
本申请的负极极片可应用于卷绕结构的电极组件，并使得第一负极膜层位于负极极片的外侧表面，且第二负极膜层负极极片的内侧表面。本申请的负极极片也可应用于叠片式结构的电极组件，在叠片式结构的电极组件中，第一负极膜层和第二负极膜层的位置不受具体限制。
虽然机理尚不明确，发明人意外地发现，当本申请的负极极片应用于卷绕结构的电极组件，并使得第一负极膜层位于负极极片的外侧表面，且第二负极膜层负极极片的内侧表面时，能够显著提升二次电池的能量密度、安全性能和长期循环性能；当本申请的负极极片应用于叠片式结构的电极组件时，能够显著提升二次电池的能量密度和长期循环性能。
并非意在受限于任何理论或解释，发明人发现，当硅基负极活性材料所包含的晶粒的粒径，与硅基负极活性材料颗粒的体积平均粒径之比在0.0003至0.004时，在充放电循环过程中，能够减少硅基负极活性材料的氧化反应，从而使得硅基负极活性材料颗粒 具备高容量发挥，由此能够提升二次电池的能量密度；当硅基负极活性材料所包含的晶粒的粒径，与硅基负极活性材料颗粒的体积平均粒径之比在0.0002至0.002时，在充活性锂离子嵌入硅基负极活性材料颗粒的过程中，硅基负极活性材料颗粒内部能够产生较小的应力，从而能够降低硅基负极活性材料颗粒内部产生裂纹的风险，从而能够降低第二硅基负极活性材料颗粒破裂，继而与电解液发生副反应的可能性，进而提升二次电池的循环性能。
在具有卷绕结构的电极组件的电极极片中，位于外侧表面的电极膜层，尤其是位于电极组件弯折部外侧表面的电极膜层，在卷绕过程中被拉伸，从而导致单位面积容量小于卷绕前的单位面积容量；相应地，位于内侧表面拐角处的电极膜层，尤其是位于电极组件弯折部内侧表面的电极膜层在卷绕过程中被挤压，从而导致单位面积容量大于卷绕前的单位面积容量。位于负极极片外侧的负极膜层和与其隔着隔离膜正对的正极膜层发生电化学反应，而该正对的正极膜层为位于正极极片内侧的正极膜层，由此，可能会因为负极膜层容量小于正极膜层容量，而在负极极片表面发生析锂。因此，相较于负极极片的内侧表面，负极极片的外侧表面更容易产生析锂现象。当本申请的负极极片应用于具有卷绕结构的电极组件时，使第一负极膜层位于负极极片的外侧表面，且第二负极膜层负极极片的内侧表面，由于第一膜层具有更大的单位面积容量，经卷绕后，仍能够具有高单位面积容量。由此，位于负极极片外侧表面的负极膜层能够容纳更多的活性锂离子，从而能够降低负极极片表面发生析锂现象的风险。
进一步地，d 1/Dv 150在上述合适的范围内，能够使得第一负极膜层中的第一硅基负极活性材料颗粒具有更高的容量发挥。由此，不仅有助于提升位于负极极片外侧表面的负极膜层的单位面积容量，从而进一步提升二次电池的安全性能，而且有助于提升二次电池的首次库伦效率。相应地，d 2/Dv 250在上述合适的范围内，能够使得第二负极膜层中的第二硅基负极活性材料颗粒具有低体积膨胀率。由此，有利于降低硅基负极活性材料颗粒粉化失活的风险，从而使得二次电池具备良好的长期循环性能。
因此，当本申请的负极极片应用于卷绕结构的电极组件，并使得第一负极膜层位于负极极片的外侧表面，且第二负极膜层负极极片的内侧表面时，硅基负极活性材料能够具有高容量发挥、较小的平均体积膨胀率，且位于负极极片外侧表面的负极膜层具有高单位面积容量。由此，能够显著提升二次电池的能量密度、安全性能和长期循环性能。
同样地，当本申请的负极极片应用于叠片式结构的电极组件时，第一硅基负极活性材料能够具有高容量发挥，从而有利于提升二次电池的能量密度；第二硅基负极活性材料颗粒具有低体积膨胀率，从而有利于降低硅基负极活性材料颗粒的平均体积膨胀率。由此，能够显著提升二次电池的能量密度和长期循环性能。
在一些实施方式中，Dv 150可为6μm～10μm，例如，Dv 150可为6μm，7μm，8μm，9μm，10μm，或处于以上任何数值所组成的范围内。可选地，Dv 150可为6.5μm～9μm，例如Dv 150可为6.5μm，7μm，7.5μm，8μm，8.5μm，9μm，或处于以上任何数值所组成的范围内。
并非意在受限于任何理论或解释，当本申请的负极极片应用于卷绕结构的电极组件，并使得第一负极膜层位于负极极片的外侧表面，第二负极膜层负极极片的内侧表面，且Dv 150在上述合适的范围内时，一方面，第一硅基负极活性材料颗粒能够具有合适的比 表面积，从而有利于减少形成SEI膜所消耗的活性锂离子；另一方面，第一硅基负极活性材料颗粒能够具有合适的体积膨胀率，从而不仅不易被氧化，而且能够具有高容量发挥。由此，不仅有利于降低负极极片外侧表面发生析锂现象的风险，从而提升二次电池的安全性能，而且有利于提升二次电池的首次库伦效率和长期循环性能。
在一些实施方式中，第一硅基负极活性材料颗粒所包含的晶粒粒径d 1可满足：5nm≤d 1≤12nm，例如，d 1可以为5nm，6nm，7nm，8nm，9nm，10nm，11nm，12nm，或处于以上任何数值所组成的范围内。可选地，7nm≤d 1≤12nm，例如，d 1可以为7nm，7.5nm，8nm，8.5nm，9nm，9.5nm，10nm，10.5nm，11nm，11.5nm，12nm，或处于以上任何数值所组成的范围内。
当第一硅基负极活性材料颗粒所包含的晶粒粒径在上述范围时，能够降低第一硅基负极活性材料颗粒发生氧化的风险，从而提升第一硅基负极活性材料颗粒的容量发挥，为锂离子提供更多的嵌锂位点，进而减少锂枝晶的产生，提升二次电池的安全性能。
在一些实施方式中，Dv 250可为2.5μm～5.5μm，例如，Dv 250可为2.5μm，3μm，3.5μm，4μm，4.5μm，5μm，5.5μm，或处于以上任何数值所组成的范围内。可选地，Dv 250可为3μm～5μm，例如，Dv 250可为3μm，3.5μm，4μm，4.5μm，5μm，或处于以上任何数值所组成的范围内。
并非意在受限于任何理论或解释，当本申请的负极极片应用于卷绕结构的电极组件，并使得第一负极膜层位于负极极片的外侧表面，第二负极膜层负极极片的内侧表面，且Dv 250在上述合适的范围内时，有利于缩短位于负极极片内侧表面的负极膜层的锂离子传输路径，以及进一步降低第二硅基负极活性材料颗粒的体积膨胀，从而有利于进一步降低电化学极化、提升二次电池的循环稳定性。
在一些实施方式中，第二硅基负极活性材料颗粒所包含的晶粒粒径d 2可满足：3nm≤d 2≤5nm，例如，d 2可以为3nm，3.5nm，4nm，4.5nm，5nm，或处于以上任何数值所组成的范围内。可选地，3.5nm≤d 2≤5nm，例如，d 2可以为3.5nm，3.8nm，4nm，4.2nm，4.5nm，4.8nm，5nm或处于以上任何数值所组成的范围内。
当第二硅基负极活性材料颗粒所包含的晶粒粒径在上述范围时，在二次电池循环过程中，第二硅基负极活性材料颗粒发生体积膨胀时，内部晶粒对第二硅基负极活性材料颗粒的挤压减少，可缓解第二硅基负极活性材料颗粒的破损速度，从而延长电池的循环寿命。
在一些实施方式中，所述第一硅基负极活性材料颗粒的体积平均粒径Dv 150与所述第二硅基负极活性材料颗粒的体积平均粒径Dv 250可满足：0.2≤Dv 250/Dv 150≤0.9，例如，Dv 250/Dv 150可以为0.2，0.3，0.4，0.5，0.6，0.7，0.8，0.9，或处于以上任何数值所组成的范围内。可选地，0.3≤Dv 250/Dv 150≤0.8，例如，Dv 250/Dv 150可以为0.3，0.35，0.4，0.45，0.5，0.55，0.6，0.65，0.7，0.75，0.8，或处于以上任何数值所组成的范围内。
并非意在受限于任何理论或解释，当Dv 250/Dv 150的值在上述合适的范围内时，能够降低第一硅基负极活性材料颗粒的体积平均粒径过大，或者第二硅基负极活性材料颗粒的体积平均粒径过小的风险。因此，能够允许第一硅基负极活性材料颗粒具有高容量发挥，以及允许能够第二硅基负极活性材料颗粒具有低体积膨胀率和较短的锂离子传输路径。由此，本申请的负极极片应用于二次电池，能够使得二次电池兼具高能量密度 和良好的长期循环性能。特别地，当本申请的负极极片应用于卷绕结构的电极组件，并使得第一负极膜层位于负极极片的外侧表面，且第二负极膜层负极极片的内侧表面时，还能够降低负极极片表面发生析锂的风险，从而使得二次电池进一步具备高安全性能。
在一些实施方式中，所述第一负极膜层的单位面积容量C 1与所述第二负极膜层的单位面积容量C 2可满足：0.7≤C 2/C 1≤0.9，例如，C 2/C 1可以为0.7，0.75，0.8，0.85，0.9，或处于以上任何数值所组成的范围内。可选地，0.75≤C 2/C 1≤0.85，例如，C 2/C 1可以为0.75，0.78，0.8，0.82，0.85，或处于以上任何数值所组成的范围内。
并非意在受限于任何理论或解释，当本申请的负极极片应用于卷绕结构的电极组件，并使得第一负极膜层位于负极极片的外侧表面，第二负极膜层负极极片的内侧表面，且C 1和C 2的比值在上述合适的范围内时，能够允许二次电池兼具高能量密度和高安全性能。一方面，当位于负极极片外侧表面的负极膜层的单位面积容量一定时，C 1和C 2的比值在上述合适的范围内，能够使得位于负极极片内侧表面的负极膜层具有合适的单位面积容量，从而降低内侧表面的负极膜层的单位面积容量过低，而导致的负极极片内侧表面发生析锂现象的风险，进而提升二次电池的安全性能；另一方面，当位于负极极片内侧表面的负极膜层的单位面积容量一定时，C 1和C 2的比值在上述合适的范围内，能够使得位于负极极片外侧的负极膜层具有合适的单位面积容量，从而减少由于外侧表面的负极膜层的单位面积容量过高，而导致的负极容量浪费，进而提升二次电池的能量密度。
在一些实施方式中，所述第一硅基负极活性材料颗粒和所述第二硅基负极活性材料颗粒选自相同种类的硅基负极活性材料颗粒。例如，第一硅基负极活性材料颗粒可以为第一硅颗粒，第二负极活性材料颗粒可以为第二硅颗粒。所述第一硅基负极活性材料的克容量发挥可大于所述第二硅基负极活性材料的克容量发挥。
并非意在受限于任何理论或解释，当第一硅基负极活性材料颗粒的克容量发挥大于第二硅基负极活性材料颗粒的克容量发挥时，一方面，更便于调整第一负极膜层与第二负极膜层的单位面积容量之比在本申请限定的范围内；另一方面，有助于将第一硅基负极活性材料颗粒和第二硅基负极活性材料颗粒的体积膨胀率之比控制在合适的范围内。由此，有助于提升二次电池的长期循环性能，以及提升应用卷绕结构电极组件的二次电池的安全性能。在一些实施方式中，当第一硅基负极活性材料颗粒的克容量发挥大于第二硅基负极活性材料颗粒的克容量发挥时，无需调整负极膜层的厚度、压实密度等制备参数，即可制备得到本申请的负极极片，由此能够简化本申请负极极片的加工工艺，从而提升本申请负极极片的产能。
在一些实施方式中，所述第一负极膜层还可包含第三负极活性材料，所述第三负极活性材料可选自人造石墨、天然石墨、硬碳、软碳或其组合。
在一些实施方式中，所述第二负极膜层还可包含第四负极活性材料，所述第四负极活性材料可选自人造石墨、天然石墨、硬碳、软碳或其组合。
并非意在受限于任何理论或解释，当负极膜层中除硅基负极活性材料颗粒外，还包括其他负极活性材料时，不仅能够便于调整负极膜层的单位面积容量，以使得负极膜层满足本申请的限定，而且有利于通过硅基负极活性材料颗粒与其他负极活性材料的搭配，灵活地调整负极膜层的压实密度、孔隙率等参数，从而提升二次电池的安全性能和电化学性能。
在一些实施方式中，基于所述第一硅基负极活性材料颗粒与所述第三负极活性材 料的总质量，所述第一硅基负极活性材料颗粒的质量百分含量可为10％～30％，例如，可以为10％，12％，15％，18％，20％，22％，25％，28％，30％，或处于以上任何数值所组成的范围内。
可选地，基于所述第一硅基负极活性材料颗粒与所述第三负极活性材料的总质量，所述第一硅基负极活性材料颗粒的质量百分含量可为12％～25％，例如，可以为12％，14％，16％，18％，20％，22％，24％，25％，或处于以上任何数值所组成的范围内。
并非意在受限于任何理论或解释，当第一负极膜层中，第一硅基负极活性材料颗粒在负极活性材料中的质量百分含量在上述合适的范围内时，既能够使得第一负极膜层具备较高的能量密度，又能够降低第一负极膜层在二次电池的充放电循环过程中产生的体积膨胀，从而能够降低二次电池整体的体积膨胀。由此，二次电池能够兼具高能量密度、高安全性能和良好的长期循环性能。
在一些实施方式中，基于所述第二硅基负极活性材料颗粒与所述第四负极活性材料的总质量，所述第二硅基负极活性材料颗粒的质量百分含量可为10％～30％，例如，可以为10％，12％，15％，18％，20％，22％，25％，28％，30％，或处于以上任何数值所组成的范围内。
可选地，基于所述第二硅基负极活性材料颗粒与所述第四负极活性材料的总质量，所述第二硅基负极活性材料颗粒的质量百分含量可为12％～25％，例如，可以为12％，14％，16％，18％，20％，22％，24％，25％，或处于以上任何数值所组成的范围内。
并非意在受限于任何理论或解释，当第二负极膜层中，第二硅基负极活性材料颗粒在负极活性材料中的质量百分含量在上述合适的范围内时，既能够使得第二负极膜层具备较高的能量密度，又能够降低第二负极膜层在二次电池的充放电循环过程中产生的体积膨胀，从而能够降低二次电池整体的体积膨胀。由此，二次电池能够兼具高能量密度、高安全性能和良好的长期循环性能。
本申请对负极极片的负极集流体不作限定，所述负极集流体可采用金属箔片或复合集流体(可以将金属材料设置在高分子基材上形成复合集流体)。例如，作为金属箔片，可以采用铜箔。复合集流体可包括高分子材料基层和形成于高分子材料基材至少一个表面上的金属层。复合集流体可通过将金属材料(铜、铜合金、镍、镍合金、钛、钛合金、银及银合金等)形成在高分子材料基材(如聚丙烯(PP)、聚对苯二甲酸乙二醇酯(PET)、聚对苯二甲酸丁二醇酯(PBT)、聚苯乙烯(PS)、聚乙烯(PE)等的基材)上而形成。
在一些实施方式中，第一负极层和第二负极层还可选地包括粘结剂。所述粘结剂可选自丁苯橡胶(SBR)、聚丙烯酸(PAA)、聚丙烯酸钠(PAAS)、聚丙烯酰胺(PAM)、聚乙烯醇(PVA)、海藻酸钠(SA)、聚甲基丙烯酸(PMAA)及羧甲基壳聚糖(CMCS)中的至少一种。
在一些实施方式中，第一负极层和第二负极层还可选地包括导电剂。导电剂可选自超导碳、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯及碳纳米纤维中的至少一种。
在一些实施方式中，第一负极层和第二负极层还可选地包括其他助剂，例如增稠剂(如羧甲基纤维素钠(CMC-Na))等。
在一些实施方式中，可以通过以下方式制备负极极片：将上述用于制备负极极片的组分，例如第一硅基负极活性材料颗粒、可选的石墨、导电剂、粘结剂和任意其他组分分散于溶剂(例如去离子水)中，形成第一负极浆料；第二硅基负极活性材料颗粒、可选的石墨、导电剂、粘结剂和任意其他组分分散于溶剂(例如去离子水)中，形成第二负极浆料；将第一负极浆料涂覆在负极集流体的一个表面，经烘干后在负极集流体的一个表面形成第一负极膜层；然后将第二负极浆料涂敷在负极集流体的另外一个表面，经烘干后形成第二负极膜层；经烘干、冷压等工序后，即可得到本申请的负极极片。
需要说明的是，本申请的二次电池中，负极极片并不排除除了负极膜层之外的其他附加功能层。例如在某些实施方式中，本申请所述的负极极片还可以包括设置在负极集流体和负极膜层之间的导电底涂层(例如由导电剂和粘结剂组成)。在另外一些实施方式中，本申请所述的负极极片还包括覆盖在负极膜层表面的保护层。
本申请中，第一硅基负极活性材料颗粒和第二硅基负极活性材料颗粒可通过多种方式获得，在此不作限定。作为一个示例，可以通过对硅基负极活性材料进行XRD测试以及体积平均粒径测试，以选取满足本申请的条件的第一硅基负极活性材料颗粒和第二硅基负极活性材料颗粒。作为另一个示例，可以基于本领域已知的硅基负极活性材料颗粒的制备方法，通过控制硅基负极活性材料颗粒的粒径、制备温度等，制备得到满足本申请的条件的第一硅基负极活性材料颗粒和第二硅基负极活性材料颗粒。
本申请中，第一负极膜层的单位面积容量和第二负极膜层的单位面积容量具有本领域公知的含义，可以通过本领域已知的方法和仪器测定。例如，第一负极膜层的单位面积容量可通过如下步骤测定：将负极极片冲切为面积为S的小圆片；擦除小圆片上的第二负极膜层；将小圆片与锂片制备得到扣式电池，对扣式电池进行容量测试，得到小圆片的第一负极膜层的容量C 10，则第一负极膜层的单位面积容量C 1＝C 10/S。例如，第二负极膜层的单位面积容量可通过如下步骤测定：将负极极片冲切为面积为S的小圆片；擦除小圆片上的第一负极膜层；将小圆片与锂片制备得到扣式电池，对扣式电池进行容量测试，得到小圆片的第二负极膜层的容量C 20，则第二负极膜层的单位面积容量C 2＝C 20/S。
体积平均粒径D V50具有本领域公知的含义，其表示硅基负极活性材料颗粒在体积基准的粒度分布中，50％的颗粒粒径小于该值，Dv 150、Dv 250可采用本领域已知的方法测定。例如，可以参照GB/T 19077-2016粒度分布激光衍射法，采用激光粒度分析仪(例如英国马尔文Mastersizer 2000E)测定，或者用扫描电子显微镜(SEM)对硅基负极活性材料颗粒进行扫描，以测得硅基负极活性材料颗粒的体积平均粒径。当测试样品是从制备好的锂离子电池中取样时，可以从锂离子电池的负极极片取样，得到负极活性材料后，再经筛分处理得到待测硅基负极活性材料颗粒；或者从负极活性材料的SEM图标记出硅基负极活性材料颗粒，经统计后得到硅基负极活性材料颗粒的体积平均粒径。
本申请中，晶粒的粒径具有本领域公知的含义，可以通过本领域已知的方法测定。例如，可以通过X射线衍射(XRD)分析测定硅基负极活性材料颗粒的XRD图，分析得到硅基负极活性材料颗粒的衍射半峰宽或积分宽度B，再通过谢乐公式D＝Kγ/BCOSθ分析得到，其中，D表示晶粒粒径，K表示谢乐常数，θ为布拉格角，γ为X射线的波长，γ＝1.54056A。当测试样品是从制备好的锂离子电池中取样时，可以从锂离子电池的负极极片取样，得到负极活性材料后，经筛分处理得到待测硅基负极活性材料颗粒，然后， 再测定硅基负极活性材料颗粒的XRD图，以分析测定晶粒的粒径；或者，从负极活性材料的XRD图中确定硅基负极活性材料颗粒的特征峰，对特征峰进行分析，以测定晶粒的粒径。
本申请中，克容量发挥具有本领域公知的含义，其可以表示待测材料实际所能释放出的电容量与其质量之比。作为示例，待测材料的克容量发挥可通过如下步骤测定：称取质量为m的待测材料；用待测材料与可选的导电剂、可选的粘结剂混合制备负极浆料；将负极浆料涂布于铜箔表面，经烘干、冷压，制成负极极片；将负极极片与锂片制备得到扣式电池，以0.1C的倍率充电，并以0.1C的倍率放电，以对扣式电池进行容量测试，得到负极极片的负极膜层容量C 30，则待测材料的克容量发挥＝C 30/m。
需要说明的是，本申请中，针对负极活性材料或负极膜层的各种参数测试，可以在电池制备过程中取样测试，也可以从制备好的二次电池中取样测试。
当上述测试样品是从制备好的锂离子电池中取样时，作为示例，可以按如下步骤(1)至(3)进行取样。
(1)将锂离子电池做放电处理(为了安全起见，一般使电池处于满放状态)；将电池拆卸后取出负极极片，使用碳酸二甲酯(DMC)将负极极片浸泡一定时间(例如2至10小时)；然后将负极极片取出并在一定温度和时间下干燥处理(例如60℃，4小时)，干燥后取出负极极片。此时即可以在干燥后的负极极片中取样测试本申请上述的负极膜层相关的各参数。
(2)将步骤(1)干燥后的负极极片在一定温度及时间下烘烤(例如400℃，2小时)，在烘烤后的负极极片中任选一区域，对负极活性材料取样(可以选用刀片刮粉取样)。
(3)将步骤(2)收集到的负极活性材料做过筛处理(例如用200目的筛网过筛)，最终得到可以用于测试本申请上述的各负极活性材料参数的样品。
电极组件
本申请第二方面提供一种电极组件，其包括本申请第一方面的负极极片。
本申请的电极组件包括本申请第一方面的负极极片，应用于二次电池，能够至少使得二次电池具备高能量密度和良好的长期循环性能。
本申请对电极组件的类型不作限制，其可以具有为本领域已知的结构的电极组件。
电极组件可以包括负极极片以及正极极片。在一些实施方式中，电极组件还可以包括隔离膜。隔离膜设置在正极极片和负极极片之间，起到隔离的作用。本申请对隔离膜的种类没有特别的限制，可以选用任意公知的具有良好的化学稳定性和机械稳定性的多孔结构隔离膜。在一些实施方式中，隔离膜的材质可以选自玻璃纤维、无纺布、聚乙烯、聚丙烯及聚偏二氟乙烯中的一种或几种。隔离膜可以是单层薄膜，也可以是多层复合薄膜。隔离膜为多层复合薄膜时，各层的材料相同或不同。
本申请的电极组件中，正极极片包括正极集流体以及设置在正极集流体至少一个表面且包括正极活性材料的正极膜层。例如，正极集流体具有在自身厚度方向相对的两个表面，正极膜层设置于正极集流体的两个相对表面中的任意一者或两者上。
本申请的电极组件中，所述正极活性材料可采用本领域公知的用于二次电池的正极活性材料。例如，正极活性材料可包括锂过渡金属氧化物、橄榄石结构的含锂磷酸盐 及其各自的改性化合物中的一种或几种。锂过渡金属氧化物的示例可包括但不限于锂钴氧化物、锂镍氧化物、锂锰氧化物、锂镍钴氧化物、锂锰钴氧化物、锂镍锰氧化物、锂镍钴锰氧化物、锂镍钴铝氧化物及其改性化合物中的一种或几种。橄榄石结构的含锂磷酸盐的示例可包括但不限于磷酸铁锂、磷酸铁锂与碳的复合材料、磷酸锰锂、磷酸锰锂与碳的复合材料、磷酸锰铁锂、磷酸锰铁锂与碳的复合材料及其各自的改性化合物中的一种或几种。本申请并不限定于这些材料，还可以使用其他可被用作二次电池正极活性材料的传统公知的材料。
本申请的电极组件中，所述正极膜层通常包含正极活性材料以及可选的粘结剂和可选的导电剂，通常是由正极浆料涂布，并经干燥、冷压而成的。正极浆料通常是将正极活性材料以及可选的导电剂和粘结剂等分散于溶剂中并搅拌均匀而形成的。溶剂可以是N-甲基吡咯烷酮(NMP)。
作为示例，用于正极膜层的粘结剂可以包括聚偏氟乙烯(PVDF)和聚四氟乙烯(PTFE)中的一种或几种。
作为示例，用于正极膜层的导电剂可以包括超导碳、炭黑(例如，乙炔黑、科琴黑)、碳点、碳纳米管、石墨烯及碳纳米纤维中的一种或几种。
本申请的电极组件中，所述正极集流体可采用金属箔片或复合集流体(可以将金属材料设置在高分子基材上形成复合集流体)。作为示例，正极集流体可采用铝箔。
在一些实施方式中，正极极片、隔离膜和负极极片可通过叠片工艺制成叠片式结构的电极组件。
图1是本申请的电极组件的一实施方式的示意图。该示例性的电极组件包括负极极片10，隔离膜20，以及正极极片30，负极极片10与正极极片30依次间隔排列。如图2所示，负极极片10沿自身厚度方向包括第一表面10a，以及第二表面10b，其中，第一表面10a为负极极片10中朝向电极组件外侧的表面，第二表面10b为负极极片10中背向电极组件外侧的表面。在一些实施方式中，在负极极片10的第一表面10a上设置有负极膜层(图中未示出)，这样的负极膜层是根据本申请实施方式的第一负极膜层的实施例；在负极极片10的第二表面10b上也设置有负极膜层(图中未示出)，这样的负极膜层是根据本申请实施方式的第二负极膜层的实施例。在一些实施方式中，在负极极片10的第一表面10a上设置有负极膜层(图中未示出)，这样的负极膜层是根据本申请实施方式的第二负极膜层的实施例；在负极极片10的第二表面10b上也设置有负极膜层(图中未示出)，这样的负极膜层是根据本申请实施方式的第一负极膜层的实施例。
在一些实施方式中，所述负极极片隔着所述隔离膜与所述正极极片沿卷绕方向卷绕以形成卷绕结构。所述第一正极膜层隔着所述隔离膜与所述第一负极膜层相对设置，所述第二正极膜层隔着所述隔离膜与所述第二负极膜层相对设置。其中，所述第一正极膜层位于所述第一负极膜层的外侧，所述第二正极膜层位于所述第二负极膜层的内侧。
图2是本申请的电极组件的一实施方式的示意图。该示例性的电极组件包括负极极片10，隔离膜20，以及正极极片30，负极极片10隔着隔离膜20与正极极片30沿卷绕方向卷绕并形成卷绕结构。如图1所示，负极极片包括外侧表面10c，以及内侧表面10d。在负极极片10的外侧表面10c上设置有负极膜层(图中未示出)，这样的负极膜层是根据本申请实施方式的第一负极膜层的实施例。在负极极片10的内侧表面10d上也设置有 负极膜层(图中未示出)，这样的负极膜层是根据本申请实施方式的第二负极膜层的实施例。相应地，正极极片30包括与负极极片的外侧表面10c相对设置的内侧表面30a，以及与负极极片10的内侧表面10d相对设置的正极极片外侧表面30b。在正极极片30的内侧表面30a上设置有正极膜层(图中未示出)，这样的正极膜层时根据本申请实施方式的第一正极膜层的实施例。在正极极片30的外侧表面30b上也设置有正极膜层(图中未示出)，这样的正极膜层是根据本申请实施方式的第二正极膜层的实施例。
本申请的电极组件中的负极极片，其第一膜层具有更大的单位面积容量，经卷绕后，仍能够具有高单位面积容量。由此，位于负极极片外侧表面的负极膜层能够容纳更多的活性锂离子，从而能够降低负极极片表面发生析锂现象的风险。进一步地，相较于第二负极膜层，第一负极膜层包含的硅基负极材料颗粒具有更大的体积平均粒径，从而能够具有更高的容量发挥。由此，不仅有助于提升位于负极极片外侧表面的负极膜层的单位面积容量，从而进一步提升二次电池的安全性能，而且有助于提升二次电池的首次库伦效率。相应地，第二负极膜层包含的硅基负极活性材料颗粒具有更小的体积平均粒径，从而能够具有低体积膨胀率和较短的锂离子传输路径。由此，有利于降低硅基负极活性材料颗粒粉化失活的风险和电化学极化，从而使得二次电池具备良好的长期循环性能。因此，本申请的电极组件应用于二次电池，能够显著提升二次电池的能量密度、安全性能和长期循环性能。
在一些实施方式中，所述卷绕结构包括弯折区和连接于所述弯折区的平直区；所述负极极片包括位于所述弯折区的多个弯折部和位于所述平直区的多个平直部，所述平直部的两端分别与所述弯折部连接。
所述负极极片中的至少一个弯折部为第一弯折部，所述负极极片中的至少一个平直部为连接于所述第一弯折部的第一平直部，所述第一弯折部和所述第一平直部满足：C 3＞C 4，其中，C 3表示所述第一弯折部中，第一负极膜层的单位面积活性物质容量；C 4表示所述第一平直部中，第一负极膜层的单位面积活性物质容量。
并非意在受限于任何理论或解释，负极极片的弯折部隔着隔离膜所正对的正极膜层容量高于负极极片的平直部隔着隔离膜所正对的正极膜层容量，能够使得弯折部负极膜层容量大于平直部，从而降低弯折部析锂风险。
在一些实施方式中，所述电极组件可满足：CB 1＞CB 2＞1，其中，CB 1表示所述第一负极膜层的容量与所述第一正极膜层的容量之比；CB 2表示所述第二负极膜层的活性物质容量与所述第二正极膜层的容量之比。
并非意在受限于任何理论或解释，当CB 1、CB 2满足上述条件时，有助于减缓第一负极膜层的嵌锂压力，降低析锂风险，从而有利于提升二次电池的安全性能。
在一些实施方式中，所述电极组件可满足：0.7≤CB 2/CB 1≤0.99，可选地，0.75≤CB 2/CB 1≤0.98。
并非意在受限于任何理论或解释，当CB 2与CB 1满足上述关系时，有助于降低第一负极膜层以及第二负极膜层表面析锂的风险，从而有利于提升二次电池的安全性能。
电池单体
本申请第三方面提供一种电池单体，其包括外壳和本申请实施方式第一方面的电极组件。
一般来说，电池单体还包括电解质，电解质在正极极片和负极极片之间起到传导活性离子的作用。本申请对电解质的种类没有具体的限制，可根据需求进行选择。例如，电解质可以选自固态电解质及液态电解质(即电解液)中的至少一种。
在一些实施方式中，电解质采用电解液。电解液包括电解质盐和溶剂。
电解质盐的种类不受具体的限制，可根据实际需求进行选择。例如，电解质盐包括选自用于锂离子电池的锂盐、用于钠离子电池的钠盐中的一种或多种。作为示例，所述锂盐包括选自六氟磷酸锂(LiPF 6)、四氟硼酸锂(LiBF 4)、高氯酸锂(LiClO 4)、六氟砷酸锂(LiAsF 6)、双氟磺酰亚胺锂(LiFSI)、双三氟甲磺酰亚胺锂(LiTFSI)、三氟甲磺酸锂(LiTFS)、二氟草酸硼酸锂(LiDFOB)、二草酸硼酸锂(LiBOB)、二氟磷酸锂(LiPO 2F 2)、二氟二草酸磷酸锂(LiDFOP)、四氟草酸磷酸锂(LiTFOP)中的一种或多种。
溶剂的种类不受具体的限制，可根据实际需求进行选择。在一些实施方式中，作为示例，溶剂可包括选自碳酸乙烯酯(EC)、碳酸亚丙酯(PC)、碳酸甲乙酯(EMC)、碳酸二乙酯(DEC)、碳酸二甲酯(DMC)、碳酸二丙酯(DPC)、碳酸甲丙酯(MPC)、碳酸乙丙酯(EPC)、碳酸亚丁酯(BC)、氟代碳酸亚乙酯(FEC)、甲酸甲酯(MF)、乙酸甲酯(MA)、乙酸乙酯(EA)、乙酸丙酯(PA)、丙酸甲酯(MP)、丙酸乙酯(EP)、丙酸丙酯(PP)、丁酸甲酯(MB)、丁酸乙酯(EB)、1,4-丁内酯(GBL)、环丁砜(SF)、二甲砜(MSM)、甲乙砜(EMS)及二乙砜(ESE)中的一种或多种。
在一些实施方式中，电解液中还可选地包括添加剂。例如添加剂可以包括负极成膜添加剂，也可以包括正极成膜添加剂，还可以包括能够改善电池某些性能的添加剂，例如改善电池过充性能的添加剂、改善电池高温性能的添加剂、改善电池低温功率性能的添加剂等。
在一些实施方式中，电池单体的外壳可用于封装上述电极组件及电解质。
在一些实施方式中，电池单体的外壳可以是硬壳，例如硬塑料壳、铝壳、钢壳等。电池单体的外壳也可以是软包，例如袋式软包。软包的材质可以是塑料，如聚丙烯(PP)、聚对苯二甲酸丁二醇酯(PBT)、聚丁二酸丁二醇酯(PBS)等中的一种或多种。
本申请对电池单体的形状没有特别的限制，其可以是扁平体、长方体或其他形状。如图3是作为一个示例的长方体结构的电池单体5。
图4为图3所示的电池单体的分解示意图。在一些实施方式中，如图3所示，外壳可包括壳体51和盖板53。其中，壳体51可包括底板和连接于底板上的侧板，底板和侧板合围形成容纳腔。壳体51具有与所述容纳腔连通的开口，盖板53用于盖设所述开口，以封闭所述容纳腔。本申请实施方式第一方面的电极组件52封装于所述容纳腔。电解液浸润于电极组件52中。电池单体5所含电极组件52的数量可以为一个或几个，可根据需求来调节。
本申请的电池单体的制备方法是公知的。在一些实施方式中，可将电极组件置于外包装中，烘干后注入电解液，经过真空封装、静置、化成、整形等工序，得到电池单体。
电池
本申请第四方面提供一种电池，其包括本申请第三方面的电池单体。
本申请所提到的电池是指包括一个或多个电池单体以提供更高的电压和容量的单一物理模块。例如，本申请中所提到的电池可以是电池模块或电池包等。电池一般包括用于封装一个或多个电池单体的箱体。箱体可以避免液体或其他异物影响电池单体的充电或放电。
在一些实施方式中，电池中的电池单体可以为多个，多个电池单体之间可串联或并联或混联，混联是指多个电池单体中既有串联又有并联。多个电池单体之间可直接串联或并联或混联在一起，再将多个电池单体构成的整体容纳于箱体内；当然，也可以是多个电池单体先串联或并联或混联组成电池模块，多个电池模块再串联或并联或混联形成一个整体，并容纳于箱体内。
图5是作为一个示例的电池模块4的示意图。如图5所示，电池单体5为多个，多个电池单体5先串联或并联或混联组成电池模块4。电池模块4中的多个电池单体5之间可通过汇流部件实现电连接，以实现电池模块4中的多个电池单体5的串联或并联或混联。在电池模块4中，多个电池单体5可以是沿电池模块4的长度方向依次排列设置。当然，也可以按照其他任意的方式进行排布。进一步可以通过紧固件将该多个电池单体5进行固定。
在一些实施方式中，上述电池模块还可以组装成电池包，电池包所含电池模块的数量可以根据电池包的应用和容量进行调节。
图6和图7是作为一个示例的电池包1的示意图。如图6和图7所示，在电池包1中可以包括箱体和设置于箱体中的多个电池模块4。电池包1中的多个电池模块4之间可通过汇流部件实现电连接，以实现电池包1中的多个电池模块4的串联或并联或混联。箱体包括上箱体2和下箱体3，上箱体2用于盖设下箱体3，并形成用于容纳电池模块4的封闭空间。多个电池模块4可以按照任意的方式排布于电池箱中
用电装置
本申请还提供一种用电装置，所述用电装置包括本申请的电池单体。所述电池单体可以用作所述用电装置的电源，也可以用作所述用电装置的能量存储单元。所述用电装置可以但不限于是移动设备(例如手机、笔记本电脑等)、电动车辆(例如纯电动车、混合动力电动车、插电式混合动力电动车、电动自行车、电动踏板车、电动高尔夫球车、电动卡车等)、电气列车、船舶及卫星、储能系统等。
图8是作为一个示例的用电装置。该用电装置为纯电动车、混合动力电动车、或插电式混合动力电动车等。为了满足该装置对高功率和高能量密度的需求，可以采用包括本申请的电池单体的电池包或电池模块。
作为另一个示例的用电装置可以是手机、平板电脑、笔记本电脑等。该用电装置通常要求轻薄化，可以采用电池单体作为电源。
实施例
下述实施例更具体地描述了本申请公开的内容，这些实施例仅仅用于阐述性说明，因为在本申请公开内容的范围内进行各种修改和变化对本领域技术人员来说是明显的。除非另有声明，以下实施例中所报道的所有份、百分比、和比值都是基于重量计， 而且实施例中使用的所有试剂都可商购获得或是按照常规方法进行合成获得，并且可直接使用而无需进一步处理，以及实施例中使用的仪器均可商购获得。
实施例1
正极极片的制备
将正极活性材料LiNi 0.8Co 0.1Mn 0.1O 2、导电炭黑、粘结剂聚偏二氟乙烯(PVDF)按98:1:1的重量比在适量的N-甲基吡咯烷酮(NMP)溶剂中充分搅拌混合，使其形成均匀的正极浆料；将正极浆料涂覆于正极集流体(厚度为13μm的铝箔)的表面上，经烘干、冷压、分切等工序后，得到正极极片。
负极极片的制备
将第一负极活性材料(第一硅氧颗粒和石墨按质量比15:85混合而成)、导电炭黑、增稠剂羧甲基纤维素钠(CMC-Na)、粘结剂丁苯橡胶乳液(SBR)按96:0.8:1.2:2重量比在适量的去离子水中充分搅拌混合，使其形成均匀的第一负极浆料；将第一负极浆料涂覆于铜箔的一个表面上，涂布重量为0.13g/1540.25mm 2；经烘干等工序后，在铜箔表面形成第一负极膜层；
将第二负极活性材料(第二硅氧颗粒和石墨按质量比15:85混合而成)、导电炭黑、增稠剂羧甲基纤维素钠(CMC-Na)、粘结剂丁苯橡胶乳液(SBR)按96:0.8:1.2:2重量比在适量的去离子水中充分搅拌混合，使其形成均匀的第二负极浆料；将第二负极浆料涂覆于铜箔的另一个表面上，涂布重量为0.13g/1540.25mm 2；经烘干等工序后，在铜箔表面形成第二负极膜层；再经冷压，得到负极膜层的压实密度为1.6g/cm 3的负极极片。
电解液的制备
在干燥氩气气氛手套箱中(H 2O<0.1ppm，O 2<0.1ppm)，将有机溶剂碳酸丙烯酯(PC)、碳酸乙烯酯(EC)、碳酸二乙酯(DEC)按照1:1:1的重量比混合均匀，加入充分干燥的锂盐LiPF 6溶解于上述有机溶剂中，充分搅拌混合均匀后，后得到锂盐浓度为1mol/L的电解液。
隔离膜
采用聚乙烯隔离膜。
二次电池的制备
将正极极片、隔离膜、负极极片按顺序堆叠并卷绕，得到电极组件，该电极组件中，第一负极膜层位于负极极片的外侧表面，且第二负极膜层负极极片的内侧表面；将电极组件加入外包装，加入上述电解液，经封装、静置、化成、老化等工序后得到二次电池。
实施例2～27
基于实施例1的制备过程，根据表1中所示调整制备参数，制备实施例2～27的正极极片、负极极片、电解液、隔离膜以及二次电池。
其中，C 2/C 1可以通过调整第一负极膜层和/或第二负极膜层的涂布重量控制。CB 1/CB 2可通过调整C 2/C 1、第一正极膜层容量和第二正极膜层容量控制，第一硅氧颗粒的克容量发挥为1250mAh/g～1300mAh/g，第二硅氧颗粒的克容量发挥为1150mAh/g～1200mAh/g。
对比例1～5
基于实施例1的制备过程，根据表1中所示调整制备参数，制备对比例1～5的正极极片、负极极片、电解液、隔离膜以及二次电池。
其中，C 2/C 1可以通过调整第一负极膜层和/或第二负极膜层的涂布重量控制。CB 1/CB 2可通过调整C 2/C 1、第一正极膜层容量和第二正极膜层容量控制。
上述各实施例及对比例中，不同的第一硅氧颗粒和第二硅氧颗粒可通过对不同温度下制备的不同粒度的硅氧颗粒进行选取得到，具体地，可以对硅氧颗粒进行XRD测试以及体积平均粒径测试，以选取满足d 1/Dv 150在特定范围内的第一硅基负极活性材料颗粒和d 2/Dv 250在特定范围内的第二硅基负极活性材料颗粒。
对实施例1～27及对比例1～5的二次电池如下测试，得到的测试结果如表2中所示。
充电能力测试
在25℃下，将二次电池以nC满充(例如n＝0.1、0.2、0.3、0.4、0.5)，以1C满放，如此循环10圈，再将二次电池以1C满充，然后拆解负极极片观察负极极片表面的析锂情况，若未析锂则以(n+0.1)C满充，再次进行测试，以此递增，直至负极表面析锂为止，以此时的倍率减去0.1C即为二次电池的充电能力。
能量密度测试
在25℃下，将二次电池以0.33C倍率满充、以0.33C倍率满放，循环3圈，取最后一圈放电能量(E)，使用电子天平称重二次电池的质量(m)，W＝E/m，以实施例2的二次电池能量密度100％，确定其他二次电池的能量密度。
存储寿命测试
将二次电池满充至97％荷电状态(97％SOC)，在60℃下存储，容量衰减到80％SOC截止，记录此时的存储时间，作为二次电池的存储寿命。
循环寿命测试
在25℃下，将二次电池以3C倍率充电，以1C倍率放电，进行3％～97％SOC循环测试，直至二次电池的容量小于初始容量的80％，记录循环圈数，作为二次电池的循环寿命。
表1
Figure PCTCN2023070150-appb-000001
表2-1
序号 充电能力 存储寿命/天 循环圈数 能量密度
实施例1 5.60C 400 1700 95％
实施例2 5.58C 390 1680 100％
实施例3 5.55C 385 1650 102％
实施例4 5.50C 380 1600 105％
实施例5 5.46C 360 1500 109％
实施例6 5.43C 350 1450 111％
对比例1 4.90C 340 1200 115％
表2-2
Figure PCTCN2023070150-appb-000002
表2-3
Figure PCTCN2023070150-appb-000003
表2-4
Figure PCTCN2023070150-appb-000004
综合表1、表2-1至2-4的测试结果可知，当电极组件的负极极片中，d 1/Dv 150、d 2/Dv 250、C 1、C 2在本申请的范围内，能够使得二次电池兼具较高的能量密度、良好的长期存储性能和长期循环性能。
而相对于此，对比例1的C 1、C 2不满足C 2＜C 1，其对应的二次电池的充电能力明显低于实施例1至6。对比例2的d 1/Dv 150低于本申请限定的范围，其对应的二次电池的充电能力、长期循环性能和能量密度均不理想。对比例3的d 1/Dv 150高于本申请限定的范围，其对应的二次电池的充电能力、存储寿命和循环寿命均显著降低。对比例4中，第二硅氧颗粒的晶粒粒径较小，这虽然有利于降低第二硅氧颗粒被氧化的风险、提升二次电池的存储性能，但是对比例4的d 2/Dv 250低于本申请限定的范围，导致二次电池的充电能力、长期循环性能和能量密度均有所降低。对比例5的d 2/Dv 250高于本申请限定的范围，其对应的二次电池的充电能力、存储寿命和循环寿命相较于实施例4、15-23均有所降低。以上所述，仅为本申请的具体实施方式，但本申请的保护范围并不局限于此，任何熟悉本技术领域的技术人员在本申请揭露的技术范围内，可轻易想到各种等效的修改或替换，这些修改或替换都应涵盖在本申请的保护范围之内。因此，本申请的保护范围应以权利要求的保护范围为准。

Claims (15)

  1. 一种负极极片，包括：
    负极集流体，具有在其厚度方向相对的第一表面和第二表面；
    第一负极膜层，位于所述第一表面侧，所述第一负极膜层包含第一硅基负极活性材料颗粒，所述第一硅基负极活性材料颗粒所包含晶粒的粒径d 1与所述第一硅基负极活性材料颗粒的体积平均粒径Dv 150满足：0.0003≤d 1/Dv 150≤0.004；以及
    第二负极膜层，位于所述第二表面侧，所述第二负极膜层包含第二硅基负极活性材料颗粒，所述第二硅基负极活性材料颗粒所包含晶粒的粒径d 2与所述第二硅基负极活性材料颗粒的体积平均粒径Dv 250满足：0.0002≤d 2/Dv 250≤0.002；
    其中，
    所述第一负极膜层的单位面积容量C 1与所述第二负极膜层的单位面积容量C 2满足：0.005mAh/(g·mm 2)≤C 2＜C 1≤0.2mAh/(g·mm 2)。
  2. 根据权利要求1所述的负极极片，其中，所述负极极片满足如下至少一者：
    (1)Dv 150为6μm～10μm，可选为6.5μm～9μm；
    (2)5nm≤d 1≤12nm，可选地，7nm≤d 1≤12nm；
    (3)Dv 250为2.5μm～5.5μm，可选为3μm～5μm；
    (4)3nm≤d 2≤5nm，可选地，3.5nm≤d 2≤5nm。
  3. 根据权利要求1或2所述的负极极片，其中，0.2≤Dv 250/Dv 150≤0.9，可选地，0.3≤Dv 250/Dv 150≤0.8。
  4. 根据权利要求1-3中任一项所述的负极极片，其中，0.7≤C 2/C 1≤0.9，可选地，0.75≤C 2/C 1≤0.85。
  5. 根据权利要求1-4中任一项所述的负极极片，其中，所述第一硅基负极活性材料颗粒和所述第二硅基负极活性材料颗粒选自相同种类的硅基负极活性材料颗粒，所述第一硅基负极活性材料的克容量发挥大于所述第二硅基负极活性材料的克容量发挥。
  6. 根据权利要求1-5中任一项所述的负极极片，其中，所述第一负极膜层还包含第三负极活性材料，所述第三负极活性材料选自人造石墨、天然石墨、硬碳、软碳或其组合；和/或
    所述第二负极膜层还包含第四负极活性材料，所述第四负极活性材料选自人造石墨、天然石墨、硬碳、软碳或其组合。
  7. 根据权利要求6所述的负极极片，其中，基于所述第一硅基负极活性材料颗粒与所述第三负极活性材料的总质量，所述第一硅负极活性材料颗粒的质量百分含量为10％～30％，可选为12％～25％；和/或
    基于所述第二硅基负极活性材料颗粒与所述第四负极活性材料的总质量，所述第二硅负极活性材料颗粒的质量百分含量为10％～30％，可选为12％～25％。
  8. 一种电极组件，包括如权利要求1-7中任一项所述的负极极片。
  9. 根据权利要求8所述的电极组件，其中，所述电极组件的正极极片包括：正极集流体，以及分别位于所述正极集流体两侧的第一正极膜层与第二正极膜层，
    所述负极极片隔着隔离膜与所述正极极片沿卷绕方向卷绕以形成卷绕结构，所述第一正极膜层隔着所述隔离膜与所述第一负极膜层相对设置，所述第二正极膜层隔着所述隔离膜与所述第二负极膜层相对设置；
    其中，所述第一正极膜层位于所述第一负极膜层的外侧，所述第二正极膜层位于所述第二负极膜层的内侧。
  10. 根据权利要求9所述的电极组件，所述卷绕结构包括弯折区和连接于所述弯折区的平直区；
    所述负极极片包括位于所述弯折区的多个弯折部和位于所述平直区的多个平直部，所述平直部的两端分别与所述弯折部连接；
    其中，所述负极极片中的至少一个弯折部为第一弯折部，所述负极极片中的至少一个平直部为连接于所述第一弯折部的第一平直部，所述第一弯折部和所述第一平直部满足：C 3＞C 4，其中，C 3表示所述第一弯折部中，第一负极膜层的单位面积活性物质容量；C 4表示所述第一平直部中，第一负极膜层的单位面积活性物质容量。
  11. 根据权利要求9或10所述的电极组件，其满足：CB 1＞CB 2＞1，其中，CB 1表示所述第一负极膜层的容量与所述第一正极膜层的容量之比；CB 2表示所述第二负极膜层的活性物质容量与所述第二正极膜层的容量之比。
  12. 根据权利要求11所述的电极组件，其中，0.7≤CB 2/CB 1≤0.99，可选地，0.75≤CB 2/CB 1≤0.98。
  13. 一种电池单体，包括外壳和电极组件，所述电极组件容纳于所述外壳内，所述电极组件选自根据权利要求8-12中任一项所述的电极组件。
  14. 一种电池，包括多个根据权利要求13所述的电池单体。
  15. 一种用电装置，包括根据权利要求13所述的电池单体，所述电池单体用于提供电能。
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