WO2022077370A1 - 二次电池、其制备方法及含有该二次电池的电池模块、电池包和装置 - Google Patents

二次电池、其制备方法及含有该二次电池的电池模块、电池包和装置 Download PDF

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WO2022077370A1
WO2022077370A1 PCT/CN2020/121255 CN2020121255W WO2022077370A1 WO 2022077370 A1 WO2022077370 A1 WO 2022077370A1 CN 2020121255 W CN2020121255 W CN 2020121255W WO 2022077370 A1 WO2022077370 A1 WO 2022077370A1
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negative electrode
active material
electrode active
film layer
optionally
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PCT/CN2020/121255
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English (en)
French (fr)
Inventor
李二岭
康蒙
邓柏炟
何立兵
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Contemporary Amperex Technology Co Ltd
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Contemporary Amperex Technology Co Ltd
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Priority to KR1020227027436A priority Critical patent/KR102746263B1/ko
Priority to EP20957149.6A priority patent/EP4138154A4/en
Priority to JP2022549890A priority patent/JP7523559B2/ja
Priority to CN202080083164.9A priority patent/CN114747042A/zh
Priority to PCT/CN2020/121255 priority patent/WO2022077370A1/zh
Publication of WO2022077370A1 publication Critical patent/WO2022077370A1/zh
Priority to US18/059,953 priority patent/US12431496B2/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
    • 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
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H01M4/386—Silicon or alloys based on silicon
    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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    • 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
    • H01M4/387—Tin or alloys based on tin
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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    • 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
    • H01M4/485—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of mixed oxides or hydroxides for inserting or intercalating light metals, e.g. LiTi2O4 or LiTi2OxFy
    • 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
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • 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
    • 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
    • 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
    • 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
    • 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
    • H01M4/1393—Processes of manufacture of 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
    • H01M4/36—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
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • 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 in particular relates to a secondary battery, a preparation method thereof, and a battery module, battery pack and device containing the secondary battery.
  • Secondary batteries rely on the reciprocating de-intercalation of active ions between the positive and negative electrodes for charging and discharging. They have outstanding features such as high energy density, long cycle life, no pollution, and no memory effect. Therefore, as a clean energy, secondary batteries have been gradually popularized from electronic products to large-scale devices such as electric vehicles to adapt to the sustainable development strategy of the environment and energy.
  • the purpose of the present application is to provide a secondary battery, a method for preparing the same, and a battery module, battery pack and device containing the secondary battery, so that the battery has a higher energy density and a higher energy density at the same time. Good fast charging performance and cycling performance.
  • a first aspect of the present application provides a secondary battery, which includes a negative electrode piece, the negative electrode piece includes a negative electrode current collector and a negative electrode film layer, and the negative electrode film layer includes a first negative electrode film layer and a negative electrode film layer.
  • a second negative electrode film layer, the second negative electrode film layer is located between the negative electrode current collector and the first negative electrode film layer; the first negative electrode film layer includes a first negative electrode active material; the first negative electrode active material
  • the material includes first graphite, the first graphite is artificial graphite, and the volume particle size distribution D v 99 ⁇ 23 ⁇ m of the first negative electrode active material.
  • the secondary battery of the present application adopts the negative electrode sheet of the multi-film layer structure, and the first negative electrode film layer located on the upper layer contains the first negative electrode active material, and the first negative electrode active material comprises the first graphite, and the first negative electrode active material is satisfied.
  • the graphite is artificial graphite, and the D v 99 of the first negative electrode active material is less than or equal to 23 ⁇ m. Therefore, in the high SOC (State of Charge) state of the battery, the negative electrode plate can also have a good electrochemical reaction interface and relatively high efficiency.
  • the high solid-phase diffusion rate of active ions enables the battery to be charged at a high rate in a high SOC state, thereby significantly improving the fast charging capability.
  • the first negative electrode active material satisfies 17 ⁇ m ⁇ D v 99 ⁇ 23 ⁇ m; optionally, 18 ⁇ m ⁇ D v 99 ⁇ 21 ⁇ m.
  • the Dv 99 of the first negative electrode active material is in an appropriate range, which enables the secondary battery to have a higher energy density and at the same time improve the fast charging capability and cycle performance due to the reduction of the solid-phase conduction impedance.
  • the first negative active material satisfies 8 ⁇ m ⁇ D v 50 ⁇ 13 ⁇ m; optionally, 9 ⁇ m ⁇ D v 50 ⁇ 12 ⁇ m.
  • the Dv 50 of the first negative electrode active material is in an appropriate range, which shortens the migration and diffusion paths of active ions, and can further improve the fast charging capability and cycle performance of the battery.
  • the uniformity of particle size of the first negative electrode active material is 0.28-0.4, optionally 0.30-0.36.
  • the uniformity of the particle size of the first negative electrode active material is within the above range, the active particles can be reasonably matched, the processing performance can be improved, the fast charging ability and cycle performance of the battery can be further improved, and the energy density of the battery can be improved.
  • secondary particles are included in the first graphite.
  • the number of secondary particles in the first graphite accounts for ⁇ 50%.
  • the amount of the secondary particles in the first graphite is 80% to 100%.
  • the particle size specific surface area of the first negative electrode active material is 0.45m 2 /g ⁇ 0.65m 2 /g, optionally 0.5m 2 /g ⁇ 0.63m 2 /g.
  • the particle size specific surface area of the first negative electrode active material is in an appropriate range, which can further improve the fast charging performance, cycle performance and storage performance of the battery.
  • the first negative electrode active material satisfies: 0.6 ⁇ (D v 90-D v 10)/D v 50 ⁇ 1.8; optionally, 0.8 ⁇ (D v 90-D v 10)/D v50 ⁇ 1.4 .
  • the (D v 90-D v 10)/D v 50 of the first negative active material is appropriate, which facilitates the formation of a smooth pore structure distribution in the film layer, which is conducive to the rapid transmission of active ions and reduces the liquid phase conduction impedance, so it can be Further improve the fast charging capability and cycle performance of the battery.
  • the volume particle size distribution D v 10 of the first negative electrode active material is 5 ⁇ m ⁇ 9 ⁇ m, optionally 6 ⁇ m ⁇ 8 ⁇ m.
  • the Dv 10 of the first negative electrode active material is in an appropriate range, which can reduce the irreversible consumption of active ions and improve the quality of the active material per unit volume, which is beneficial to improve the energy density, cycle performance and high temperature storage performance of the battery.
  • the volume particle size distribution D v 90 of the first negative electrode active material is 14 ⁇ m ⁇ 21 ⁇ m, optionally 16 ⁇ m ⁇ 18 ⁇ m.
  • the Dv 90 of the first negative electrode active material is in an appropriate range, which can further improve the fast charging capability and cycle performance of the battery.
  • the powder OI value of the first negative electrode active material is 2.0-4.0, optionally 2.3-3.6.
  • the powder OI value of the first negative electrode active material is in an appropriate range, so that it has more active ion fast insertion channels, thereby further improving the fast charging capability of the battery.
  • the powder OI value of the negative electrode active material is in an appropriate range, which can also reduce the expansion effect of the negative electrode pole piece during the charging process, and can further improve the cycle performance of the battery.
  • the tap density of the first negative electrode active material is 0.85 g/cm 3 to 1.4 g/cm 3 , optionally 0.9 g/cm 3 to 1.2 g/cm 3 .
  • the tap density of the first negative electrode active material is within the given range, which is conducive to maintaining good contact between particles, and obtains a better inter-particle void structure, ensuring a smooth active ion transmission channel, and enabling the battery to obtain better performance. High fast charging capability and energy density.
  • the powder compaction density of the first negative electrode active material under a pressure of 2 kN is 1.55g/cm 3 -1.70g/cm 3 , optionally 1.58g/cm 3 -1.68g/cm 3 .
  • the powder compaction density under the pressure of 2kN of the first negative electrode active material is within the given range, which enables the negative electrode film layer to have a higher compaction density, thereby improving the energy density of the battery.
  • the specific surface area (SSA) of the first negative electrode active material is 0.8 m 2 /g ⁇ 1.3 m 2 /g, optionally 0.9 m 2 /g ⁇ 1.2 m 2 /g.
  • the specific surface area (SSA) of the first negative electrode active material is in an appropriate range, which improves the infiltration of the electrolyte and the liquid phase transport of active ions, which is beneficial to the battery to obtain higher fast charging capability and cycle performance.
  • the gram capacity of the first negative electrode active material is 345mAh/g ⁇ 360mAh/g, and optionally 350mAh/g ⁇ 358mAh/g.
  • the energy density and fast charging capability of the battery can be improved.
  • At least a part of the surface of the first graphite has an amorphous carbon coating layer.
  • a carbon layer that can enrich active ions is formed on the surface of the first graphite, which reduces the charge transfer resistance.
  • Using the first graphite can further improve the cycle performance and fast charging capability of the battery.
  • the mass ratio of the first graphite in the first negative electrode active material is ⁇ 80%.
  • the mass ratio of the first graphite in the first negative electrode active material is 90% to 100%.
  • the first negative electrode film layer contains more first graphite, which can more effectively improve the fast charging capability of the battery.
  • the second negative electrode film layer includes a second negative electrode active material
  • the second negative electrode active material includes a second graphite
  • the second graphite includes one or more of artificial graphite and natural graphite.
  • the mass proportion of artificial graphite in the second graphite is ⁇ 50%.
  • the mass proportion of artificial graphite in the second graphite is 60% to 100%.
  • the second negative electrode active material contains more artificial graphite, which can increase the energy density of the battery, and can improve the cycle performance and high temperature storage performance of the battery.
  • the volume particle size distribution D v 99 of the second negative electrode active material is greater than the volume particle size distribution D v 99 of the first negative electrode active material.
  • the ratio of the volume particle size distribution D v 99 of the second negative electrode active material to the volume particle size distribution D v 99 of the first negative electrode active material is 2.0-2.6, and further optionally 2.1-2.4.
  • the second negative electrode active material and the first negative electrode active material satisfy the above-mentioned conditions, which can improve the energy density, cycle performance and storage performance of the battery, and also enable the battery to have high fast charging capability.
  • the volume average particle size D v 50 of the second negative electrode active material is 15 ⁇ m ⁇ 21 ⁇ m, optionally 16.5 ⁇ m ⁇ 20 ⁇ m.
  • the Dv 50 of the second negative electrode active material is within the above range, which shortens the diffusion path of active ions, and at the same time enables the second negative electrode active material to have a higher gram capacity, enabling the battery to have higher fast charging capability, energy density and cycle performance.
  • primary particles are included in the second graphite.
  • the amount of primary particles in the second graphite is greater than or equal to 50%; optionally, the amount of primary particles in the second graphite is 60% to 100%.
  • the second graphite satisfies the above conditions, so that the material has high anisotropy, ensures the structural stability of the graphite and improves the compaction density of the negative electrode film layer, thereby improving the energy density, high temperature storage performance and cycle performance of the battery.
  • the uniformity of particle size of the second negative electrode active material is 0.3-0.55, optionally 0.4-0.5.
  • the uniformity of particle size of the second negative electrode active material is within the above range, which can further improve the cycle performance and energy density of the battery.
  • the particle size specific surface area of the second negative electrode active material is 0.35 m 2 /g ⁇ 0.55 m 2 /g, optionally 0.38 m 2 /g ⁇ 0.50 m 2 /g.
  • the particle size specific surface area of the second negative electrode active material is within an appropriate range, the irreversible consumption of active ions is reduced, and the cycle performance and storage performance of the battery can be further improved.
  • the second negative electrode active material satisfies: 0.9 ⁇ (D v 90-D v 10)/D v 50 ⁇ 1.6; optionally, 1.0 ⁇ (D v 90-D v 10)/D v50 ⁇ 1.4 .
  • the (D v 90-D v 10)/D v 50 of the second negative electrode active material is within the above range, so that a reasonable pore structure is maintained between particles, which can improve the fast charging performance and volumetric energy density of the battery.
  • the volume particle size distribution D v 10 of the second negative electrode active material is 5 ⁇ m ⁇ 14 ⁇ m, optionally 7 ⁇ m ⁇ 12 ⁇ m.
  • the D v 10 of the second negative electrode active material is in the above range, which can improve the cycle performance and storage performance of the battery.
  • the volume particle size distribution D v 90 of the second negative electrode active material is 24 ⁇ m ⁇ 38 ⁇ m, optionally 26 ⁇ m ⁇ 33 ⁇ m.
  • the Dv 90 of the second negative electrode active material is within the above-mentioned range, which can improve the cycle performance and fast charging capability of the battery, and can further improve the energy density of the battery.
  • the powder OI value of the second negative electrode active material is less than or equal to 14, and is optionally 6 to 11.
  • the OI value of the second negative electrode active material is within the above range, which helps to shorten the insertion path of active ions, reduces the expansion of the battery during charging, and enables the battery to have higher rapid charging capability, cycle performance and energy density.
  • the tap density of the second negative active material is 0.8 g/cm 3 to 1.2 g/cm 3 , optionally 0.9 g/cm 3 to 1.1 g/cm 3 .
  • the tap density of the second negative electrode active material is within the given range, so that an excellent pore structure is maintained between the active particles, which can improve the fast charging capability and the energy density of the battery.
  • the powder compaction density of the second negative electrode active material under a pressure of 2 kN is 1.70 g/cm 3 -1.85 g/cm 3 , optionally 1.75 g/cm 3 -1.82 g/cm 3 .
  • the powder compaction density of the second negative electrode active material under the pressure of 2kN is within an appropriate range, which improves the compaction density of the negative electrode film layer and can improve the energy density of the battery.
  • the specific surface area (SSA) of the second negative electrode active material is 1.0 m 2 /g ⁇ 2.0 m 2 /g, optionally 1.3 m 2 /g ⁇ 1.8 m 2 /g.
  • the specific surface area (SSA) of the second negative electrode active material is in an appropriate range, which is beneficial for the battery to obtain higher storage performance and cycle performance.
  • the gram capacity of the second negative electrode active material is 353mAh/g ⁇ 370mAh/g, and optionally 359mAh/g ⁇ 367mAh/g.
  • the energy density of the battery can be improved, and the cycle performance of the battery can also be improved.
  • the areal density of the negative electrode film layer is 0.117 mg/mm 2 to 0.130 mg/mm 2 , optionally 0.120 mg/mm 2 to 0.127 mg/mm 2 .
  • the areal density of the negative electrode film layer is within the above range, which can further improve the energy density and fast charging capability of the battery.
  • the compaction density of the negative electrode film layer is 1.65 g/cm 3 to 1.75 g/cm 3 , optionally 1.66 g/cm 3 to 1.70 g/cm 3 .
  • the compaction density of the negative film layer is within the given range, which can further improve the energy density, fast charging capability and cycle performance of the battery.
  • the thickness ratio of the second negative electrode film layer to the first negative electrode film layer is 0.7:1 to 2.3:1, optionally 0.7:1 to 1.0:1, and optionally 1.1:1 1 to 2.3:1. Setting the thickness ratio of the second negative electrode film layer to the first negative electrode film layer within an appropriate range can further improve the fast charging capability or energy density of the battery.
  • the first negative electrode active material or the second negative electrode active material further includes one or more of silicon-based materials, tin-based materials, soft carbon, hard carbon, and lithium titanate.
  • the secondary battery includes a positive electrode plate, the positive electrode plate 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, and the positive electrode active material includes a lithium transition metal One or more of oxides, olivine-structured lithium-containing phosphates and their respective modified compounds.
  • the positive electrode active material includes one or more of the lithium transition metal oxide shown in Formula 1 and its modified compound,
  • M is selected from Mn, Al, Zr, Zn , one or more of Cu, Cr, Mg, Fe, V, Ti and B, and A is selected from one or more of N, F, S and Cl.
  • a second aspect of the present application provides a method for preparing a secondary battery, which at least includes the following steps: forming a second negative electrode film layer on at least one side of the negative electrode current collector, the second negative electrode film layer comprising a second negative electrode active material; A first negative electrode film layer is formed on the surface of the second negative electrode film layer, the first negative electrode film layer includes a first negative electrode active material; wherein the first negative electrode active material includes a first graphite, the first negative electrode active material The graphite is artificial graphite, and the volume particle size distribution D v 99 of the first negative electrode active material is ⁇ 23 ⁇ m.
  • a third aspect of the present application provides a battery module including the secondary battery of the present application.
  • a fourth aspect of the present application provides a battery pack including the secondary battery or battery module of the present application.
  • a fifth aspect of the present application provides a device comprising at least one of the secondary battery, battery module, or battery pack of the present application.
  • the battery module, battery pack and device of the present application include the secondary battery provided by the present application, and thus have at least the same advantages as the secondary battery.
  • FIG. 1 is a schematic diagram of an embodiment of the secondary battery of the present application.
  • FIG. 2 is an exploded schematic view of an embodiment of the secondary battery of the present application.
  • FIG. 3 is a schematic diagram of an embodiment of a negative electrode tab in the secondary battery of the present application.
  • FIG. 4 is a schematic diagram of another embodiment of the negative electrode sheet in the secondary battery of the present application.
  • FIG. 5 is a scanning electron microscope (SEM) image of an embodiment of the first negative electrode active material of the present application.
  • FIG. 6 is a SEM image of an embodiment of the second negative electrode active material of the present application.
  • FIG. 7 is a schematic diagram of an embodiment of the battery module of the present application.
  • FIG. 8 is a schematic diagram of an embodiment of the battery pack of the present application.
  • FIG. 9 is an exploded view of FIG. 8 .
  • FIG. 10 is a schematic diagram of an embodiment of a device in which the secondary battery of the present application is used as a power source.
  • any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with any other lower limit to form an unspecified range, and likewise any upper limit can be combined with any other upper limit to form an unspecified range.
  • every point or single value between the endpoints of a range is included within the range, even if not expressly recited.
  • each point or single value may serve as its own lower or upper limit in combination with any other point or single value or with other lower or upper limits to form a range not expressly recited.
  • the term "or” is inclusive.
  • the phrase “A or B” means “A, B, or both A and B.” More specifically, the condition “A or B” is satisfied by either of the following: A is true (or present) and B is false (or absent); A is false (or absent) and B is true (or present) ; or both A and B are true (or present).
  • a secondary battery also known as a rechargeable battery or a secondary battery, refers to a battery that can activate active materials by charging and continue to use after the battery is discharged.
  • a secondary battery typically includes a positive electrode, a negative electrode, a separator, and an electrolyte.
  • active ions such as lithium ions
  • the separator is arranged between the positive pole piece and the negative pole piece, and mainly plays the role of preventing the short circuit of the positive and negative poles, and at the same time, it can allow ions to pass through.
  • the electrolyte is between the positive electrode and the negative electrode, and mainly plays the role of conducting ions.
  • the secondary battery includes a negative electrode piece, which generally includes a negative electrode current collector and a negative electrode film layer disposed on at least one side of the negative electrode current collector.
  • the key to improving the fast charging capability of the secondary battery is to improve the kinetic performance of the negative electrode.
  • the kinetic performance of the negative electrode is mostly improved by thinning the negative electrode film layer or reducing the compaction density of the negative electrode film layer.
  • the above methods for improving the kinetics of the anode only improve the kinetics of the battery in the low SOC state (ie, the initial stage of charging) to a certain extent, and have no obvious effect on the improvement of the kinetic performance of the battery in the high SOC state (ie, the final stage of charging).
  • the rapid charging capability of the secondary battery cannot be effectively improved, and even the secondary battery cannot be actually charged at a high rate.
  • the energy density of the battery will also be significantly reduced.
  • the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer
  • the negative electrode film layer includes a first negative electrode film layer and a second negative electrode film layer
  • the second negative electrode film layer is located in the negative electrode current collector.
  • the first negative electrode film layer includes the first negative electrode active material,
  • the first negative electrode active material includes the first graphite, the first graphite is artificial graphite, and the volume particle size distribution of the first negative electrode active material D v 99 ⁇ 23 ⁇ m.
  • the secondary battery of the present application adopts the negative electrode sheet of the multi-film layer structure, and the first negative electrode film layer located on the upper layer contains the first negative electrode active material, and the first negative electrode active material comprises the first graphite, and the first negative electrode active material is satisfied.
  • Graphite is artificial graphite, and the D v 99 of the first negative electrode active material is ⁇ 23 ⁇ m. Therefore, in the high SOC state of the battery, the negative electrode plate can also have a higher active ion diffusion rate, thereby effectively improving the fast charging capability.
  • the Dv 99 of the anode active material has been ignored by the industry as an insignificant and less controllable parameter.
  • the inventors discovered for the first time in the research process that when the first negative electrode active material in the first negative electrode film layer includes first graphite, the first graphite is artificial graphite, and the first negative electrode active material satisfies D v 99 ⁇ 23 ⁇ m
  • the negative electrode sheet can maintain a good electrochemical reaction interface even at the end of charging (with a high active ion intercalation amount, such as lithium intercalation amount), and the first negative electrode active material particles can have good active ion diffusion performance inside
  • the active ions can be quickly embedded in the bulk phase of the first negative electrode active material and migrate rapidly, which improves the diffusion rate of the active ions in the first negative electrode film layer at this stage, and the active ions can also quickly migrate to the interior through the first negative electrode film layer.
  • the charging speed and charging depth of the entire negative electrode piece at this stage are greatly increased, so that the battery can be charged at a high rate in a high SOC state, and the fast charging capability is significantly improved.
  • the low SOC state generally refers to below 30% SOC
  • the high SOC state generally refers to above 60% SOC.
  • the first negative electrode active material includes a first graphite, the first graphite is artificial graphite, and the first negative electrode active material satisfies D v 99 ⁇ 23 ⁇ m, and can also reduce the ohmic and concentration polarization when the battery is charged in a high SOC state , which is also beneficial to improve the cycle performance of the battery.
  • the first negative active material may satisfy D v 99 ⁇ 23 ⁇ m, ⁇ 22.5 ⁇ m, ⁇ 22 ⁇ m, ⁇ 21.5 ⁇ m, or ⁇ 21 ⁇ m.
  • the Dv 99 of the first negative electrode active material is within the above-mentioned range, which can further improve the lithium intercalation speed of the battery in a high SOC state and reduce polarization, thereby further improving the fast charging capability and cycle performance of the battery.
  • the D v 99 of the first negative active material is > 15 ⁇ m, > 16 ⁇ m, > 17 ⁇ m, > 18 ⁇ m, > 19 ⁇ m, or > 19.5 ⁇ m.
  • the Dv 99 of the first negative electrode active material is within the above-mentioned range, so that the first negative electrode active material can have a higher gram capacity, thereby improving the energy density of the battery.
  • the Dv 99 of the first negative electrode active material is within the above-mentioned range, which is helpful to reduce the smaller particles therein, more active ions can be embedded in the particles, and at the same time, it is helpful to form a smooth pore structure in the negative electrode film layer, Shortening the liquid phase conduction path is also beneficial to improve the fast charging capability and cycle performance of the battery.
  • the reduction of the content of small particles is also conducive to reducing the side reaction of the electrolyte at the negative electrode, so it can also improve the high-temperature storage performance of the battery.
  • the first negative active material satisfies: 17 ⁇ m ⁇ D v 99 ⁇ 23 ⁇ m.
  • the first negative active material may satisfy 17.5 ⁇ m ⁇ D v 99 ⁇ 20.5 ⁇ m, 18 ⁇ m ⁇ D v 99 ⁇ 21 ⁇ m, 18 ⁇ m ⁇ D v 99 ⁇ 19 ⁇ m, 19 ⁇ m ⁇ D v 99 ⁇ 20.5 ⁇ m, 19.5 ⁇ m ⁇ D v 99 ⁇ 21 ⁇ m, or 20 ⁇ m ⁇ D v 99 ⁇ 22 ⁇ m, etc.
  • D v 99 can be 22.9 ⁇ m, 22.6 ⁇ m, 21.7 ⁇ m, 21.1 ⁇ m, 20.4 ⁇ m, 19.9 ⁇ m, 19.2 ⁇ m, 18.1 ⁇ m, or 17.6 ⁇ m.
  • the secondary battery can have high fast charging capability, cycle performance, high temperature storage performance and energy density at the same time.
  • the secondary battery of the present application can further improve the performance of the battery if it optionally satisfies one or more of the following parameters.
  • the first anode active material satisfies 8 ⁇ m ⁇ D v 50 ⁇ 13 ⁇ m.
  • D v 50 of the first negative active material is ⁇ 13 ⁇ m, ⁇ 12.5 ⁇ m, or ⁇ 12 ⁇ m.
  • the D v 50 of the first negative active material is ⁇ 8 ⁇ m, ⁇ 9 ⁇ m, ⁇ 10 ⁇ m, or ⁇ 11 ⁇ m.
  • the first negative active material may satisfy 8.5 ⁇ m ⁇ D v 50 ⁇ 10 ⁇ m, 9 ⁇ m ⁇ D v 50 ⁇ 12 ⁇ m, 9.5 ⁇ m ⁇ D v 50 ⁇ 11.5 ⁇ m, 10 ⁇ m ⁇ D v 50 ⁇ 12 ⁇ m, 11 ⁇ m ⁇ D v 50 ⁇ 12 ⁇ m, 11 ⁇ m ⁇ D v 50 ⁇ 12.5 ⁇ m, or 11.5 ⁇ m ⁇ D v 50 ⁇ 12.8 ⁇ m.
  • Dv50 can be 8.6 ⁇ m, 9.8 ⁇ m, 10.3 ⁇ m, 11.2 ⁇ m, 11.3 ⁇ m, 11.4 ⁇ m, 11.5 ⁇ m, 11.7 ⁇ m, 11.8 ⁇ m, 12.4 ⁇ m, 12.8 ⁇ m, or 14.5 ⁇ m.
  • the Dv 50 of the first negative electrode active material is in an appropriate range, which can shorten the migration path of active ions in the first negative electrode active material particles, and is conducive to the formation of a smooth pore structure in the first negative electrode film layer, thereby making the negative electrode electrode.
  • the sheet has good liquid-phase transport properties and good solid-phase diffusion rate of active ions, thereby further improving the fast charging capability and cycle performance of the battery.
  • the Dv 50 of the first negative electrode active material is in an appropriate range, which can also reduce the side reaction of the electrolyte on the particle surface, and improve the cycle performance and high-temperature storage performance of the battery.
  • the uniformity of particle size of the first negative active material is 0.28-0.4, for example, may be 0.28-0.38, 0.29-0.34, 0.30-0.36, or 0.31-0.35.
  • the uniformity of the particle size of the first negative electrode active material is within the above range, and a short liquid phase transmission path is easily formed in the first negative electrode film layer, and at the same time, the particles can have a larger contact area between the particles, which is beneficial to the negative electrode pole piece.
  • the electron conduction and active ion transport in the battery can improve the fast charging ability and cycling performance of the battery.
  • close contact can be achieved between the particles of the first negative electrode film layer, thereby enabling the negative electrode pole piece to obtain a higher compaction density, thereby improving the energy density of the battery.
  • the uniformity of particle size of the negative electrode active material can characterize the degree of dispersion of the particle diameters of all particles in the negative electrode active material from the volume average particle diameter D v 50 of the negative electrode active material, which can reflect the particle size distribution of the negative electrode active material. uniformity.
  • the first negative active material satisfies: 0.6 ⁇ (D v 90 ⁇ D v 10)/D v 50 ⁇ 1.8.
  • (D v 90-D v 10)/D v 50 of the first negative active material may be 0.8 ⁇ 1.4, 0.9 ⁇ 1.5, 1.0 ⁇ 1.3.
  • the (D v 90-D v 10)/D v 50 of the negative active material reflects the degree to which the particle diameter of the larger particles and the particle diameter of the smaller particles deviate from the volume average particle diameter D v 50 in the negative active material.
  • the (D v 90-D v 10)/D v 50 of the first negative electrode active material is appropriate, which is beneficial to improve the processing performance of the first negative electrode film layer, so that the first negative electrode film layer has a high particle distribution consistency and smoothness as a whole.
  • the pore structure is favorable for the high active ion transport performance in different regions of the negative film layer, which further improves the fast charging ability and cycle performance of the battery.
  • the volume particle size distribution D v 90 of the first negative electrode active material is 14 ⁇ m ⁇ 21 ⁇ m. For example, it may be 16 ⁇ m to 18 ⁇ m, 17 ⁇ m to 19 ⁇ m, or 18 ⁇ m to 20 ⁇ m.
  • the Dv 90 of the first negative electrode active material is in an appropriate range, which can further improve the solid-phase diffusion rate of active ions in the negative electrode film layer, thereby further improving the fast charging capability and cycle performance of the battery.
  • the negative electrode active material can also have a high gram capacity, which helps to improve the energy density of the battery.
  • the volume particle size distribution D v 10 of the first negative electrode active material is 5 ⁇ m ⁇ 9 ⁇ m, for example, may be 6 ⁇ m ⁇ 8 ⁇ m.
  • the content of small particles in the first negative electrode active material is less, which can reduce side reactions between the electrolyte and the material, reduce the irreversible consumption of active ions, and improve cycle performance and high-temperature storage performance.
  • the D v 10 of the first negative electrode active material is in an appropriate range, the proportion of active material per unit volume can be increased, thereby increasing the energy density of the battery.
  • the particle size specific surface area of the first negative electrode active material is 0.45m 2 /g ⁇ 0.65m 2 /g, for example, may be 0.5m 2 /g ⁇ 0.63m 2 /g, 0.48m 2 /g ⁇ 0.55 m 2 /g, or 0.52m 2 /g to 0.6m 2 /g.
  • the "particle size specific surface area” of the negative electrode active material of the present application is not the same as the “specific surface area” of a general negative electrode active material.
  • the specific surface area (SSA) of the negative electrode active material in the industry is mostly obtained by the gas adsorption BET method, which is only used to characterize the physical adsorption specific surface area of the negative electrode active material.
  • the "particle size specific surface area” of the negative electrode active material of the present application is obtained by laser diffraction particle size analysis, which can be used to characterize the degree to which the morphology of the negative electrode active material deviates from sphericity.
  • the above-mentioned particle size specific surface area of the first negative electrode active material also improves the film-forming efficiency of the SEI (solid electrolyte interphase, solid electrolyte interface) film, and can reduce the consumption of electrolyte, and further improve the cycle performance of the battery.
  • the first negative electrode active material has an appropriate particle size specific surface area, and can also enable the particles of the first negative electrode film layer to be closely packed, thereby helping to improve the energy density of the battery.
  • secondary particles may be included in the first negative active material.
  • the number of secondary particles in the first negative electrode active material accounts for ⁇ 50%.
  • the proportion of secondary particles in the first negative electrode active material may be 55%-95%, 60%-100%, 65%-85%, 70%-100%, 75%-90%, 75% ⁇ 85%, 80% ⁇ 100%, 80% ⁇ 90%, 85% ⁇ 95%, or 90% ⁇ 100%.
  • the de-intercalation active ion channels in the first negative electrode film layer are increased, and the active ion intercalation path is shortened, so that the fast charging capability of the battery can be further improved, and the reduction can be reduced.
  • Polarization reduces the side reaction of the electrolyte at the negative electrode, thereby further enabling the battery to have better cycle performance and storage performance.
  • the specific surface area (SSA) of the first negative active material is 0.8m 2 /g ⁇ 1.3m 2 /g, for example, may be 0.85m 2 /g ⁇ 1.15m 2 /g, 0.9m 2 /g ⁇ 1.2m 2 /g, or 0.95 ⁇ 1.25m 2 /g.
  • the specific surface area (SSA) of the first negative electrode active material is in an appropriate range, which can improve the wettability of the electrolyte in the film layer, improve the liquid phase transport of active ions, and the surface of the material can have high electrochemical reactivity.
  • the active ions can be transported in the solid phase in time, and at the same time, it also ensures that there are fewer side reactions between the material and the electrolyte, which is beneficial to the battery to obtain high fast charging capacity and cycle performance.
  • the powder OI value of the first negative electrode active material is 2.0-4.0, for example, may be 2.2-3.2, 2.3-3.6, 2.5-3.4, or 2.8-3.8.
  • the powder OI value of the first negative electrode active material is small, and the particles have active ion insertion ports in all directions, so that active ions from the positive electrode can be quickly received, thereby further improving the fast charging capability.
  • the isotropic particle structure is beneficial to disperse the expansion rate when the active ions are inserted, and reduces the cycle expansion force, thereby further improving the cycle performance.
  • the tap density of the first negative active material is 0.85g/cm 3 -1.4g/cm 3 , for example, it may be 0.9g/cm 3 -1.2g/cm 3 , 0.95g/cm 3 -1.15 g/cm 3 , 1.0 g/cm 3 to 1.25 g/cm 3 , or 1.05 g/cm 3 to 1.35 g/cm 3 .
  • the tap density of the first negative electrode active material is within the given range, so that good contact can be formed between the particles in the first negative electrode film layer, and a better inter-particle void structure can be obtained, ensuring a smooth active ion transmission channel , which can improve the fast charging capability of the battery. At the same time, the dense packing between particles can also improve the energy density of the battery.
  • the powder compaction density of the first negative electrode active material under the pressure of 2kN is 1.55g/cm 3 ⁇ 1.70g/cm 3 , for example, it may be 1.55g/cm 3 ⁇ 1.63g/cm 3 , 1.58 g/cm 3 to 1.68 g/cm 3 , or 1.60 g/cm 3 to 1.68 g/cm 3 .
  • the powder compaction density under the pressure of 2kN of the first negative electrode active material is within the given range, so that the particles in the first negative electrode film layer can be closely contacted, and the content of the active material per unit volume can be increased, thereby improving the The energy density of the battery.
  • the gram capacity of the first negative active material is 345mAh/g ⁇ 360mAh/g, for example, it can be 350mAh/g ⁇ 358mAh/g, 351mAh/g ⁇ 356mAh/g, or 352mAh/g ⁇ 355mAh/g .
  • the gram capacity of the first negative electrode active material is high, which can improve the energy density of the battery.
  • the fact that the gram capacity of the first negative electrode active material is within the above range also means that the active ion migration path of the material is short, so that the fast charging capability of the battery can be improved.
  • At least a portion of the surface of the first negative active material has an amorphous carbon coating layer.
  • more than 80% of the surface of the first negative electrode active material is covered with an amorphous carbon coating layer.
  • 90% to 100% of the surface of the first negative electrode active material is covered with an amorphous carbon coating layer.
  • the amorphous carbon coating can be formed by carbonizing an organic carbon source.
  • the organic carbon source can be selected from high molecular polymers, such as coal pitch, petroleum pitch, phenolic resin, coconut shell and other high molecular materials.
  • the amorphous carbon coating layer can protect the first negative electrode active material by isolating the electrolyte, improve the structural stability, and at the same time increase the active ion diffusion rate of the particles, thereby further improving the cycle performance and fast charging capability of the battery.
  • the mass ratio of the first graphite in the first negative electrode active material is ⁇ 80%.
  • the mass proportion of the first graphite in the first negative electrode active material may be 85%-100%, 90%-100%, or 95%-100%.
  • the first negative electrode film layer contains more first graphite, which can fully exert the effect of the first negative electrode active material to improve the active ion diffusion performance of the negative electrode pole piece when the amount of active ion intercalation is high, so that the negative electrode pole piece as a whole is at this stage. It has high charging speed and charging depth, which can effectively improve the fast charging capacity of the battery.
  • the first negative electrode active material in the negative electrode plate may optionally include a certain amount of other common negative electrode active materials, such as natural graphite, silicon-based material, One or more of tin-based materials, soft carbon, hard carbon, and lithium titanate.
  • other common negative electrode active materials such as natural graphite, silicon-based material, One or more of tin-based materials, soft carbon, hard carbon, and lithium titanate.
  • the first negative active material further includes a silicon-based material.
  • the silicon-based material may include one or more of elemental silicon, silicon oxide (SiO x , 0 ⁇ x ⁇ 2), silicon-carbon composite, silicon-nitrogen composite, and silicon alloy materials.
  • the silicon-based material can improve the pore structure in the first negative electrode film layer, facilitate the infiltration and liquid retention of the electrolyte, and at the same time increase the capacity of the pole piece, thereby further improving the fast charging capability and energy density of the battery.
  • the mass proportion of the silicon-based material in the first negative electrode active material is ⁇ 10%.
  • the mass proportion of the silicon-based material in the first negative electrode active material may be 1%-8%, 2%-6%, or 3%-7%.
  • Including an appropriate amount of silicon-based material in the first negative electrode active material can improve the fast charging capability and energy density of the battery, and at the same time enable the battery to further take into account higher cycle performance and high temperature storage performance.
  • the second negative electrode film layer includes a second negative electrode active material.
  • a second graphite is included in the second negative electrode active material.
  • the material types of the second graphite and the first graphite may be the same or different.
  • the second graphite can be selected from one or more of artificial graphite and natural graphite.
  • the second negative electrode active material can have higher cycle stability and higher gram capacity, thereby enabling the battery to have higher cycle performance and energy density.
  • the second graphite includes artificial graphite.
  • the mass proportion of artificial graphite in the second graphite is ⁇ 50%.
  • the mass proportion of artificial graphite in the second graphite may be 60%-100%, 70%-100%, 80%-100%, or 90%-100%.
  • Artificial graphite has better structural stability.
  • the second negative electrode active material contains more artificial graphite, which is beneficial to maintain a good pore structure in the inner layer of the negative electrode film layer (the second negative electrode film layer), so that the inner layer of the negative electrode film layer also has high electrolyte wettability and liquid retention. Therefore, the overall ion transfer rate of the negative pole piece can be further improved, and the fast charging capability of the battery can be improved.
  • the second negative electrode active material contains more artificial graphite, which can also improve its electrolyte compatibility and improve the cycle performance and high temperature storage performance of the battery.
  • the second graphite may include both artificial graphite and natural graphite.
  • the mass ratio of natural graphite in the second negative electrode active material is ⁇ 40%, for example, 5%-40%, 10%-30%, or 10% to 20%. Including a certain amount of natural graphite in the second negative electrode active material can further improve the dynamic performance of the negative electrode pole piece, so that the battery can obtain higher fast charging capability. By making the ratio of artificial graphite and natural graphite in the second negative electrode active material appropriate, the fast charging ability and cycle performance and high temperature storage performance of the battery can be balanced.
  • the volume particle size distribution D v 99 of the second anode active material is greater than the volume particle size distribution D v 99 of the first anode active material.
  • the Dv 99 of the second negative active material is larger, which is beneficial to increase the capacity of the negative electrode, and can also reduce the side reaction between the electrolyte and the negative active material, thereby improving the energy density, cycle performance and high temperature storage performance of the battery.
  • the D v 99 of the second negative active material may be 28 ⁇ m ⁇ 55 ⁇ m, 30 ⁇ m ⁇ 50 ⁇ m, 40 ⁇ m ⁇ 55 ⁇ m, 40 ⁇ m ⁇ 50 ⁇ m, or 45 ⁇ m ⁇ 50 ⁇ m.
  • the D v 99 of the second negative active material may be 41.6 ⁇ m, 44.5 ⁇ m, 45.2 ⁇ m, 48.7 ⁇ m, 50.1 ⁇ m, 52.3 ⁇ m, or 54.8 ⁇ m.
  • the ratio of D v 99 of the second negative active material to D v 99 of the first negative active material is 2.0-2.6, for example, may be 2.1-2.45, 2.1-2.4, 2.2-2.6, or 2.2-2. 2.5.
  • the ratio of D v 99 of the second negative electrode active material to D v 99 of the first negative electrode active material is within the above range, which can improve the energy density, cycle performance and high temperature storage performance of the battery, and also ensure that the negative electrode has a higher
  • the active ion and electron transport capabilities further enable the battery to further combine high fast charging capabilities.
  • the volume average particle diameter D v 50 of the second negative electrode active material is 15 ⁇ m ⁇ 21 ⁇ m.
  • it may be 15 ⁇ m to 18 ⁇ m, 16 ⁇ m to 19 ⁇ m, 16 ⁇ m to 18 ⁇ m, 16 ⁇ m to 17 ⁇ m, 16.5 ⁇ m to 20 ⁇ m, 17 ⁇ m to 20 ⁇ m, or 17 ⁇ m to 21 ⁇ m.
  • Dv50 can be 15.9 ⁇ m, 16.1 ⁇ m, 16.5 ⁇ m, 16.6 ⁇ m, 16.8 ⁇ m, 16.9 ⁇ m, 17.5 ⁇ m.
  • the Dv 50 of the second negative electrode active material is within the above range, which can not only enable the second negative electrode film layer to have a higher active ion diffusion capacity, but also reduce the side reaction of the electrolyte in the negative electrode, so that the battery has a high rapidity chargeability and cycle performance.
  • the second negative electrode active material can also have a higher gram capacity, which can enable the battery to obtain a higher energy density.
  • the second negative active material satisfies: 0.9 ⁇ (D v 90 ⁇ D v 10)/D v 50 ⁇ 1.6.
  • (D v 90-D v 10)/D v 50 of the second negative active material may be 1.0 ⁇ 1.4, 1.05 ⁇ 1.35, or 1.1 ⁇ 1.25.
  • the (D v 90-D v 10)/D v 50 of the second negative electrode active material is within the above-mentioned range, which can improve the particle stacking performance and increase the proportion of active materials, thereby increasing the volumetric energy density of the battery.
  • the overall particle distribution consistency of the negative film layer is good, and a reasonable pore structure is formed between the particles, which can improve the fast charging capability of the battery.
  • the volume particle size distribution D v 10 of the second negative active material is 5 ⁇ m ⁇ 14 ⁇ m, for example, may be 6 ⁇ m ⁇ 10 ⁇ m, 7 ⁇ m ⁇ 12 ⁇ m, or 7 ⁇ m ⁇ 9 ⁇ m.
  • There are fewer small particles in the second negative electrode active material which can reduce the side reaction of the electrolyte in the negative electrode and the irreversible consumption of active ions, thereby improving the cycle performance and storage performance of the battery.
  • the volume particle size distribution D v 90 of the second negative electrode active material is 24 ⁇ m ⁇ 38 ⁇ m, for example, may be 26 ⁇ m ⁇ 33 ⁇ m.
  • the second negative electrode active material can also have a higher gram capacity, which can further improve the energy density of the battery.
  • the second graphite includes primary particles, and the number of primary particles in the second graphite accounts for ⁇ 50%.
  • the proportion of primary particles in the second graphite may be 55%-95%, 60%-100%, 65%-90%, 65%-80%, 70%-100%, 75%-90% , 80% to 100%, 90% to 100%, or 95% to 100%.
  • the second negative electrode active material contains an appropriate proportion of primary particles, which can achieve higher structural stability and reduce side reactions of the electrolyte at the negative electrode, thereby improving the high-temperature storage performance and cycle performance of the battery.
  • the use of the second negative electrode active material can also improve the compaction density of the negative electrode film layer, thereby improving the energy density of the battery.
  • the uniformity of particle size of the second negative electrode active material is 0.3-0.55.
  • the uniformity of particle size of the second negative electrode active material is 0.39-0.49, 0.4-0.5, 0.42-0.48, or 0.43-0.46.
  • the uniformity of particle size of the second negative electrode active material is within the above range, which can further improve the compaction density of the negative electrode film layer, thereby improving the energy density of the battery; at the same time, the second negative electrode film layer can have good electrolytic infiltration pores, As a result, the battery can have higher cycle performance.
  • the particle size specific surface area of the second negative active material is 0.35m 2 /g ⁇ 0.55m 2 /g, for example, it may be 0.36m 2 /g ⁇ 0.48m 2 /g, 0.38m 2 /g ⁇ 0.50 m 2 /g, or 0.42m 2 /g to 0.53m 2 / g.
  • the particle size specific surface area of the second negative electrode active material is within an appropriate range, so that the second negative electrode film layer has more de-intercalating ion channels and a suitable pore structure, ensuring that the negative electrode has a low impedance, and at the same time, it further reduces the impact on electrolysis.
  • the consumption of liquid and active ions can further improve the cycle performance and storage performance of the battery.
  • the second negative electrode active material has an appropriate particle size specific surface area, and can also enable the particles of the second negative electrode film layer to be closely packed, thereby improving the energy density of the battery.
  • the specific surface area (SSA) of the second negative active material is 1.0 m 2 /g ⁇ 2.0 m 2 /g, for example, may be 1.3 m 2 /g ⁇ 1.8 m 2 /g.
  • the specific surface area (SSA) of the second negative electrode active material is in an appropriate range, so that the second negative electrode film layer has higher active ion solid-phase diffusion performance, and at the same time, it also ensures less side reactions between the material and the electrolyte, so that It is beneficial for the battery to obtain higher fast charging capacity, cycle performance and storage performance.
  • the powder OI value of the second negative electrode active material is ⁇ 14, optionally 5-14, 6-11, 7-10.
  • the second negative electrode active material not only has good active ion intercalation performance, but also enables the negative electrode film layer to have lower cycle expansion, thereby enabling the battery to have higher fast charging capability, cycle performance and energy density.
  • the gram capacity of the second negative active material is 353 mAh/g to 370 mAh/g, for example, it may be 359 mAh/g to 367 mAh/g, or 360 mAh/g to 365 mAh/g.
  • the gram capacity of the second negative electrode active material is higher, which can further improve the energy density of the battery.
  • the gram capacity of the second negative electrode active material is within the above range, which also means that the material has better cycle stability, thereby improving the cycle performance of the battery.
  • the tap density of the second negative active material is 0.8 g/cm 3 to 1.2 g/cm 3 , for example, 0.9 g/cm 3 to 1.1 g/cm 3 , or 0.95 g/cm 3 to 0.95 g/cm 3 . 1.08 g/cm 3 .
  • the tap density of the second negative electrode active material is within the given range, so that the particles in the second negative electrode film layer can form close contact, and at the same time keep the excellent pore structure between the active particles, thereby improving the fast charging capability of the battery and energy density.
  • the powder compaction density of the second negative electrode active material under a pressure of 2 kN is 1.70 g/cm 3 to 1.85 g/cm 3 , for example, it may be 1.75 g/cm 3 to 1.82 g/cm 3 .
  • the powder compaction density of the second negative electrode active material under the pressure of 2kN is within an appropriate range, which can improve the compaction density of the negative electrode film layer, thereby improving the energy density of the battery.
  • the second negative electrode active material may optionally include a certain amount of other common negative electrode active materials, for example, silicon-based materials, tin-based materials, One or more of soft carbon, hard carbon and lithium titanate.
  • the negative electrode film layer of the present application is usually formed by coating and drying the negative electrode slurry.
  • the negative electrode slurry coating is usually formed by dispersing the negative electrode active material and optional conductive agent and binder in a solvent and stirring uniformly.
  • the solvent can be N-methylpyrrolidone (NMP) or deionized water.
  • the first negative electrode film layer or the second negative electrode film layer usually contains a negative electrode active material and an optional binder, an optional conductive agent and other optional auxiliary agents.
  • the conductive agent may include one or more of superconducting carbon, carbon black (eg, acetylene black, ketjen black, etc.), carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
  • the binder can include styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin, polyvinyl alcohol (PVA), sodium alginate (SA) and carboxymethyl chitosan (CMCS). one or more.
  • Other optional auxiliary agents are, for example, thickeners (such as sodium carboxymethyl cellulose CMC-Na), PTC thermistor materials, and the like.
  • the areal density of the negative electrode film layer is 0.117mg/mm 2 -0.130mg/mm 2 , for example, 0.117mg/mm 2 -0.125mg/mm 2 , 0.118mg/mm 2 -0.122mg /mm 2 , 0.120 mg/mm 2 to 0.127 mg/mm 2 , or 0.121 mg/mm 2 to 0.125 mg/mm 2 .
  • the areal density of the negative electrode film layer refers to the areal density of the entire negative electrode film layer (ie, the sum of the areal densities of the first negative electrode film layer and the second negative electrode film layer).
  • the areal density of the negative electrode film layer is within the above range, which can make the negative electrode pole piece have higher capacity, and reduce the migration distance and impedance of active ions and electrons in the film layer, thereby further improving the energy density and fast charging capability of the battery .
  • the compaction density of the negative electrode film layer is 1.65g/cm 3 -1.75g/cm 3 , for example, it may be 1.65g/cm 3 -1.68g/cm 3 , 1.66g/cm 3 -1.70g/ cm 3 , or 1.68 g/cm 3 to 1.72 g/cm 3 .
  • the compaction density of the negative electrode film layer refers to the compaction density of the negative electrode film layer as a whole (ie, the ratio of the area density to the thickness of the negative electrode film layer).
  • the compaction density of the negative film layer is within the given range, so that the negative pole piece has a high reversible capacity, and also has a good low cycle expansion performance and dynamic performance, thereby further improving the energy density of the battery, fast speed chargeability and cycle performance.
  • the thickness ratio of the second negative electrode film layer to the first negative electrode film layer is 0.7:1 to 2.3:1.
  • the fast charging capability or energy density of the battery can be further improved.
  • the thickness ratio of the second negative electrode film layer to the first negative electrode film layer may be 0.7:1-1.0:1, 0.75:1-0.9:1, or 0.8:1- 1.0:1.
  • the thickness ratio of the second negative electrode film layer to the first negative electrode film layer may be 1.1:1-2.3:1, 1.3-2.1:1, or 1.5-2:1.
  • the total thickness of the negative electrode film layer may be 60 ⁇ m ⁇ 90 ⁇ m, for example, 65 ⁇ m ⁇ 80 ⁇ m.
  • the total thickness of the negative electrode film layer is the sum of the thicknesses of the first negative electrode film layer and the second negative electrode film layer.
  • the negative electrode current collector can be a metal foil or a composite current collector (a metal material can be arranged on a polymer substrate to form a composite current collector).
  • the negative electrode current collector may use copper foil.
  • the negative electrode film layer may be provided on one side of the negative electrode current collector, or may be provided on both sides of the negative electrode current collector at the same time.
  • the negative electrode current collector has opposite sides in its own thickness direction, and the negative electrode film layer is provided on any one or both sides of the opposite sides of the negative electrode current collector.
  • FIG. 3 shows a schematic diagram of an embodiment of the negative pole piece 10 of the present application.
  • the negative electrode piece 10 is composed of a negative electrode current collector 101, a second negative electrode film layer 103 disposed on both sides of the negative electrode current collector 101, and a first negative electrode film layer 102 disposed on the second negative electrode film layer 103.
  • FIG. 4 shows a schematic diagram of another embodiment of the negative pole piece 10 of the present application.
  • the negative electrode sheet 10 is composed of a negative electrode current collector 101 , a second negative electrode film layer 103 provided on one side of the negative electrode current collector, and a first negative electrode film layer 102 provided on the second negative electrode film layer 103 .
  • each negative electrode film layer (such as film layer thickness, compaction density, areal density, etc.) given in this application all refer to the parameter range of the single-sided film layer.
  • the film layer parameters of any one side satisfy the present application, that is, it is considered to fall within the protection scope of the present application.
  • the ranges of film thickness, compaction density, areal density, etc. mentioned in this application all refer to the parameters of the film layer after being compacted by cold pressing and used for assembling the battery.
  • the negative electrode sheet does not exclude other additional functional layers other than the negative electrode film layer.
  • the negative electrode sheet described in the present application may further include a conductive primer layer (eg, composed of a conductive agent and a binder) disposed between the negative electrode current collector and the second negative electrode film layer.
  • the negative electrode plate described in the present application further includes a cover protective layer covering the surface of the first negative electrode film layer.
  • D v 99, D v 90, D v 50, D v 10 particle size uniformity, and particle size specific surface area of the negative electrode active material can be determined by laser diffraction particle size analysis.
  • a laser particle size analyzer eg Malvern Master Size 3000
  • primary particles and secondary particles have meanings known in the art.
  • Primary particles refer to particles that do not form an agglomerated state.
  • Secondary particles refer to the agglomerated particles formed by the aggregation of two or more primary particles.
  • Primary particles and secondary particles can be easily distinguished by taking SEM images using a scanning electron microscope.
  • the quantitative proportion of the primary particles or the secondary particles in the negative electrode active material can be determined by instruments and methods known in the art, for example, by scanning electron microscopy.
  • An exemplary test method for the proportion of secondary particles by number includes: laying and sticking the negative electrode active material on the conductive adhesive to make a test sample with a length of 6cm ⁇ width of 1.1cm; using a scanning electron microscope (such as ZEISS Sigma 300) The shape is tested. The test can refer to JY/T010-1996. In order to ensure the accuracy of the test results, randomly select multiple (for example, 5) different areas in the sample to be tested for scanning test, and under a certain magnification (for example, 1000 times), calculate the proportion of secondary particles in each area.
  • the percentage of the total number of particles is the proportion of the number of secondary particles in this area. Take the average of the test results of multiple test areas as the test result. In order to ensure the accuracy of the test results, multiple test samples (for example, 10) can be taken to repeat the above test, and the average value of each test sample is taken as the final test result. Similarly, the proportion of the primary particles in the second negative electrode active material can also be tested.
  • the powder OI value of the negative electrode active material has the meaning known in the art, and can be tested by methods known in the art.
  • the powder OI value of the negative electrode active material was obtained.
  • C 004 is the peak area of the characteristic diffraction peak of the 004 crystal plane of graphite
  • C 110 is the peak area of the characteristic diffraction peak of the 110 crystal plane of the graphite.
  • a copper target can be used as the anode target
  • CuK ⁇ rays are used as the radiation source
  • the ray wavelength The scanning 2 ⁇ angle range is 20° ⁇ 80°, and the scanning rate can be 4°/min.
  • the tap density of the negative electrode active material is the meaning known in the art, and can be tested by methods known in the art.
  • the test parameters are as follows: vibration frequency: 250 ⁇ 15 times/min, amplitude: 3 ⁇ 0.2mm, vibration frequency: 5000 times, measuring cylinder: 25mL.
  • the powder compaction density of the negative electrode active material under a pressure of 2 kN is a meaning known in the art, and can be determined by a method known in the art. For example, referring to the standard GB/T24533-2009, it is determined by an electronic pressure testing machine (such as UTM7305).
  • An exemplary test method is as follows: weigh 1 g of negative active material, add it into a mold with a bottom area of 1.327 cm 2 , pressurize to 200 kg (equivalent to 2 kN), hold the pressure for 30 s, then release the pressure for 10 s, then record and calculate Powder compaction density of negative active material under 2kN pressure.
  • the specific surface area (SSA) of the negative electrode active material is a meaning known in the art, and can be determined by a method known in the art.
  • the nitrogen adsorption specific surface area analysis test method is used to test, and the BET (Brunauer Emmett Teller) method is used to calculate it.
  • the nitrogen adsorption specific surface area analysis test can pass the Tri-Star 3020 type ratio of the Micromeritics company in the United States. Surface area pore size analysis tester.
  • the gram capacity of the negative electrode active material is the meaning known in the art, and can be tested by methods known in the art.
  • An exemplary test method is as follows: the prepared negative active material, conductive agent carbon black (Super P), binder polyvinylidene fluoride (PVDF) in a mass ratio of 91.6:1.8:6.6 and solvent N-methylpyrrolidone (NMP) Mix evenly in the medium to prepare slurry; apply the prepared slurry on the copper foil current collector, and dry it in an oven for later use.
  • the metal lithium sheet is used as the counter electrode, and the polyethylene (PE) film is used as the separator.
  • the CR2430 type coin cell was assembled in an argon gas-protected glove box. After standing the obtained button battery for 12 hours, at 25°C, it was discharged to 0.005V with a constant current of 0.05C, left for 10 minutes, and then discharged to 0.005V with a current of 50 ⁇ A at a constant current, and left for 10 minutes, and the battery was discharged with a constant current of 10 ⁇ A. Then discharge at constant current to 0.005V; then charge at 0.1C constant current to 2V, and record the charging capacity.
  • the ratio of the charging capacity to the mass of the negative active material is the gram capacity of the prepared negative active material.
  • the thickness of the negative electrode film layer has a meaning known in the art, and can be measured by a method known in the art, such as a micrometer (eg Mitutoyo 293-100, with an accuracy of 0.1 ⁇ m).
  • a micrometer eg Mitutoyo 293-100, with an accuracy of 0.1 ⁇ m.
  • the respective thicknesses of the first negative electrode film layer and the second negative electrode film layer may be tested by using a scanning electron microscope (eg, ZEISS Sigma 300).
  • the sample preparation is as follows: first, the negative pole piece is cut into a sample to be tested of a certain size (for example, 2cm ⁇ 2cm), and the negative pole piece is fixed on the sample stage by paraffin.
  • sample stage into the sample holder and lock it firmly, turn on the power of the argon ion cross section polisher (such as IB-19500CP) and evacuate (such as 10 -4 Pa), set the argon flow (such as 0.15MPa) and voltage (such as 8KV) and polishing time (for example, 2 hours), adjust the sample stage to rocking mode to start polishing.
  • Sample test can refer to JY/T010-1996.
  • the compaction density of the negative electrode film layer is the meaning known in the art, and can be tested by methods known in the art.
  • the compaction density of the negative electrode film layer area density of the negative electrode film layer/thickness of the negative electrode film layer.
  • test sample When the above-mentioned test sample is sampled from the prepared secondary battery, as an example, the sample can be sampled as follows:
  • step (1) Bake the dried negative electrode piece in step (1) at a certain temperature and time (for example, 400° C., 2 h), select a region in the baked negative electrode piece, and activate the first negative electrode first.
  • Material sampling blade scraping powder sampling can be used, the scraping powder depth does not exceed the boundary area between the first negative electrode film layer and the second negative electrode film layer; then sample the second negative electrode active material in the same way.
  • the mutual fusion layer in the boundary area between the first negative electrode film layer and the second negative electrode film layer (that is, the first negative electrode active material and the second negative electrode active material exist in the mutual fusion layer at the same time) , for the accuracy of the test, when sampling the second negative electrode active material, the mutual fusion layer can be scraped off first, and then the second negative electrode active material scraping powder can be sampled.
  • step (3) The first negative electrode active material and the second negative electrode active material collected in step (2) are subjected to sieving treatment (for example, sieving with a 200-mesh sieve), and finally each material that can be used to test the above-mentioned application is obtained. Parameters of the first negative active material and the second negative active material samples.
  • an optical microscope or a scanning electron microscope can be used to assist in determining the position of the boundary region between the first negative electrode film layer and the second negative electrode film layer.
  • 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 in its thickness direction, and the positive electrode film layer is provided on either or both of the two opposite surfaces of the positive electrode current collector.
  • the positive electrode active material may be a known positive electrode active material for secondary batteries in the art.
  • the positive electrode active material may include one or more of lithium transition metal oxides, olivine-structured lithium-containing phosphates, and their respective modified compounds.
  • lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide One or more of lithium nickel cobalt aluminum oxide and its modified compounds.
  • olivine-structured lithium-containing phosphates may include, but are not limited to, lithium iron phosphate, composites of lithium iron phosphate and carbon, lithium manganese phosphate, composites of lithium manganese phosphate and carbon, lithium iron manganese phosphate, lithium iron manganese phosphate
  • One or more of the composite materials with carbon and their respective modified compounds may be used. The present application is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials for secondary batteries can also be used.
  • the positive electrode active material may include one or more of the lithium transition metal oxides shown in formula 1 and modified compounds thereof,
  • M is selected from Mn, Al, Zr, Zn , one or more of Cu, Cr, Mg, Fe, V, Ti and B, and A is selected from one or more of N, F, S and Cl.
  • the modification compound of each of the above materials may be doping modification or surface coating modification of the positive electrode active material.
  • the positive electrode film layer usually contains a positive electrode active material, an optional binder and an optional conductive agent, and is usually coated with a positive electrode slurry, dried and cold-pressed.
  • the positive electrode slurry is usually formed by dispersing the positive electrode active material and optional conductive agent and binder in a solvent and stirring 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 can be a metal foil sheet or a composite current collector (a metal material can be arranged on a polymer substrate to form a composite current collector).
  • the positive electrode current collector may use aluminum foil.
  • the secondary battery of the present application has no specific restrictions on the type of electrolyte, which can be selected according to requirements.
  • the electrolyte may be selected from at least one of solid electrolytes and liquid electrolytes (ie, electrolytes).
  • the electrolyte is an electrolyte.
  • the electrolytic solution includes an electrolyte salt and a solvent.
  • the electrolyte salt may be selected from LiPF 6 (lithium hexafluorophosphate), LiBF 4 (lithium tetrafluoroborate), LiClO 4 (lithium perchlorate), LiAsF 6 (lithium hexafluoroarsenate), LiFSI (lithium hexafluoroarsenate), LiFSI (lithium tetrafluoroborate) Lithium Imide), LiTFSI (Lithium Bistrifluoromethanesulfonimide), LiTFS (Lithium Trifluoromethanesulfonate), LiDFOB (Lithium Difluorooxalate Borate), LiBOB (Lithium Dioxalate Borate), LiPO 2 F 2 (Lithium difluorophosphate), one or more of LiDFOP (lithium difluorodioxalate phosphate) and LiTFOP (lithium tetrafluorooxalate phosphate
  • the solvent may be selected from ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), Dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate ester (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB) , one or more of ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS) and diethyl s
  • EC
  • additives are also optionally included in the electrolyte.
  • the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain performance of the battery, such as additives to improve battery overcharge performance, additives to improve battery high temperature performance, and additives to improve battery low temperature performance. additives, etc.
  • a separator is also included in secondary batteries using an electrolytic solution, and some secondary batteries using a solid electrolyte.
  • the separator is arranged between the positive pole piece and the negative pole piece, and plays the role of isolation.
  • the type of separator in the present application, and any well-known porous-structure separator with good chemical stability and mechanical stability can be selected.
  • the material of the separator can be selected from one or more of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.
  • the separator can 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 are the same or different.
  • the positive electrode sheet, the negative electrode sheet and the separator may be fabricated into an electrode assembly through a winding process or a lamination process.
  • the secondary battery may include an outer package.
  • the outer package can be used to encapsulate the above-mentioned electrode assembly and electrolyte.
  • the outer packaging of the secondary battery may be a hard case, such as a hard plastic case, an aluminum case, a steel case, and the like.
  • the outer package of the secondary battery may also be a soft package, such as a pouch-type soft package.
  • the material of the soft bag may be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), and the like.
  • FIG. 1 is a secondary battery 5 of a square structure as an example.
  • the outer package may include a housing 51 and a cover 53 .
  • the housing 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate are enclosed to form a accommodating cavity.
  • the housing 51 has an opening communicating with the accommodating cavity, and the cover plate 53 is used to cover the opening to close the accommodating cavity.
  • the positive pole piece, the negative pole piece and the separator may be formed into the electrode assembly 52 through a winding process or a lamination process.
  • the electrode assembly 52 is packaged in the receiving cavity.
  • the electrolyte solution is infiltrated in the electrode assembly 52 .
  • the number of electrode assemblies 52 contained in the secondary battery 5 may be one or several, and may be adjusted according to requirements.
  • the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.
  • FIG. 7 shows the battery module 4 as an example.
  • the plurality of secondary batteries 5 may be arranged in sequence along the longitudinal direction of the battery module 4 .
  • the plurality of secondary batteries 5 can be fixed with fasteners.
  • the battery module 4 may further include a housing having an accommodating space in which the plurality of secondary batteries 5 are accommodated.
  • the above-mentioned battery modules can also be assembled into a battery pack, and the number of battery modules included in the battery pack can be adjusted according to the application and capacity of the battery pack.
  • the battery pack 1 may include a battery case and a plurality of battery modules 4 disposed in the battery case.
  • the battery box includes an upper box 2 and a lower box 3 .
  • the upper box 2 is used to cover the lower box 3 and form a closed space for accommodating the battery modules 4 .
  • the plurality of battery modules 4 may be arranged in the battery case in any manner.
  • An embodiment of the second aspect of the present application provides a method for preparing a secondary battery, including preparing a negative electrode plate of the secondary battery through the following steps: forming a second negative electrode film layer on at least one side of a negative electrode current collector, the The second negative electrode film layer includes a second negative electrode active material; a first negative electrode film layer is formed on the surface of the second negative electrode film layer, and the first negative electrode film layer includes a first negative electrode active material; wherein the first negative electrode film layer is The negative electrode active material includes first graphite, the first graphite is artificial graphite, and the volume particle size distribution D v 99 ⁇ 23 ⁇ m of the first negative electrode active material.
  • the first negative electrode active material and optional conductive agent, optional binder and other optional auxiliary agents can be dispersed in a solvent (eg deionized water) to form the first negative electrode active material.
  • a solvent eg deionized water
  • the second negative active material may be dispersed in a solvent (eg, deionized water), along with optional conductive agents, optional binders, and other optional auxiliary agents, to form the second negative active material slurry.
  • the first negative electrode active material slurry and the second negative electrode active material slurry may be applied simultaneously at one time, or may be applied twice.
  • the first anode active material slurry and the second anode active material slurry are applied simultaneously at one time. Coating at the same time can make the adhesion between the first negative electrode film layer and the second negative electrode film layer better, help to reduce the interfacial resistance of the film layer, and further improve the fast charging ability and cycle performance of the battery.
  • the second negative electrode active material used in the present application can be obtained through commercial channels or prepared by methods known in the art. Those skilled in the art can make appropriate choices according to the actual use environment.
  • the first graphite can be prepared by a method developed by the inventors themselves. Specifically, the preparation method of the first graphite includes the following steps a) to e).
  • the D v 99 of the petroleum coke raw material is 15 ⁇ m ⁇ 21 ⁇ m.
  • the D v 99 of the petroleum coke raw material is 16 ⁇ m ⁇ 21 ⁇ m, 17 ⁇ m ⁇ 21 ⁇ m, 17 ⁇ m ⁇ 20 ⁇ m, or 17 ⁇ m ⁇ 19 ⁇ m.
  • the D v 99 of the precursor is 16 ⁇ m ⁇ 22 ⁇ m.
  • the D v 99 of the precursor is 17 ⁇ m ⁇ 22 ⁇ m, 17.5 ⁇ m ⁇ 20 ⁇ m, 18 ⁇ m ⁇ 21 ⁇ m, or 18 ⁇ m ⁇ 20 ⁇ m.
  • the D v 99 of the granulated product is 17 ⁇ m ⁇ 24 ⁇ m.
  • the granulated product D v 99 is 18 ⁇ m ⁇ 24 ⁇ m, 19 ⁇ m ⁇ 22 ⁇ m, or 19 ⁇ m ⁇ 21 ⁇ m.
  • the D v 99 of the artificial graphite being 17 ⁇ m ⁇ 26 ⁇ m.
  • the D v 99 of the artificial graphite is 18 ⁇ m ⁇ 24 ⁇ m, 19 ⁇ m ⁇ 26 ⁇ m, 21 ⁇ m ⁇ 26 ⁇ m, 20 ⁇ m ⁇ 25 ⁇ m, 20 ⁇ m ⁇ 23 ⁇ m, or 19.5 ⁇ m ⁇ 22 ⁇ m.
  • the petroleum coke raw material in step a) may include one or more of petroleum-based non-needle coke and petroleum-based needle coke.
  • the petroleum coke raw material is selected from one or more of petroleum calcined coke, needle petroleum green coke and non-needle petroleum green coke.
  • the petroleum coke feedstock includes non-needle petroleum green coke.
  • the D v 50 of the petroleum coke raw material in step a) is 5.5 ⁇ m to 11 ⁇ m;
  • the D v 50 of the petroleum coke raw material is within an appropriate range, so that the D v 50 of the first graphite can be adjusted within a desired range.
  • the volatile content C 1 of the petroleum coke raw material in step a) may be 1%-12%; for example, 3%-10%, 5%-9%, 6%-8%, 7%-8.5% %, or 7.5% to 8.5%, etc. This can improve the particle size distribution of the first graphite.
  • the volatile content of the petroleum coke feedstock can be tested using methods known in the art. For example, the determination is carried out with reference to SH/T 0026-1990.
  • the D v 50 of the precursor in step b) is 7 ⁇ m to 12 ⁇ m; for example, 7.5 ⁇ m to 11 ⁇ m, or 8 ⁇ m to 10 ⁇ m.
  • the particle size uniformity U 1 of the precursor in step b) satisfies 0.2 ⁇ U 1 ⁇ 0.55; for example, 0.2 ⁇ U 1 ⁇ 0.5, 0.25 ⁇ U 1 ⁇ 0.45, 0.3 ⁇ U 1 ⁇ 0.45, 0.3 ⁇ U1 ⁇ 0.4 , 0.35 ⁇ U1 ⁇ 0.55 , or 0.35 ⁇ U1 ⁇ 0.45 . This can improve the particle size consistency of the first graphite.
  • the D v 50 of the granulated product in step c) is between 8 ⁇ m and 14 ⁇ m; for example, between 10 ⁇ m and 14 ⁇ m, or between 11 ⁇ m and 13 ⁇ m.
  • the precursor and the binder in step c), can be mixed; followed by high temperature granulation.
  • the binder can be bitumen.
  • Granulation in step c) can be carried out using equipment known in the art, such as a granulator.
  • the mixing temperature can be controlled to be 20°C to 40°C, the mixing frequency to be 35Hz to 38Hz, and the mixing time to be 50min to 65min; then the temperature is raised to 300°C to 400°C at 6 to 10°C/min, and the temperature is kept for 1h to 2h; Then the temperature is raised to 500°C to 600°C at 6 ⁇ 10°C/min, and kept for 1h ⁇ 2h; then the temperature is raised to 700°C ⁇ 800°C at 6 ⁇ 10°C/min, and the temperature is kept for 1h ⁇ 2h; then the temperature is naturally cooled to obtain a granulated product .
  • step c) the amount of binder C 2 added in the granulation process and the volatile content C 1 of the petroleum coke raw material satisfy 8% ⁇ C1 + C2 ⁇ 17%.
  • the degree of granulation can be improved, so that the proportion of the secondary particles of the first graphite can meet the demand.
  • the amount of binder C2 added in the granulation process is the percentage of the weight of the binder added in the granulation process to the total weight of the precursor.
  • step c) the amount of binder C 2 added in the granulation process, the volatile content C 1 of the petroleum coke raw material and the particle size consistency U 1 of the precursor satisfies 21% ⁇ (C 1 +C 2 )/U 1 ⁇ 100% ⁇ 50%. This can further improve the degree of granulation.
  • 0% ⁇ C2 ⁇ 16% eg, 1 % ⁇ C2 ⁇ 12%, 2 % ⁇ C2 ⁇ 10%, 4 % ⁇ C2 ⁇ 7 %, or 5% ⁇ C2 ⁇ 9%.
  • the uniformity of particle size U 2 of the artificial graphite obtained in step d) may satisfy 0.22 ⁇ U 2 ⁇ 0.48.
  • the organic carbon source in step e), can be selected from one or more of pitches (eg, coal pitch, petroleum pitch), phenolic resins, coconut shells, and the like.
  • pitches eg, coal pitch, petroleum pitch
  • phenolic resins e.g., phenolic resins, coconut shells, and the like.
  • the temperature of the heat treatment may be 700°C to 1800°C, eg, 1000°C to 1300°C.
  • step e) the amount C of the organic carbon source added in the coating process, the volatile content C1 of the petroleum coke raw material and the amount of binder C2 added in the granulation process satisfy 10 % ⁇ C1 +C2 + C3 ⁇ 25 %; eg, 11% ⁇ C1 +C2 + C3 ⁇ 20 %, 12% ⁇ C1 +C2 + C3 ⁇ 18 %, or 13% ⁇ C1 +C 2 +C 3 ⁇ 16%.
  • the above relationship is satisfied between the amount of organic carbon source added in the coating process C3 and the volatile content of the petroleum coke raw material C1 and the amount of binder added in the granulation process C2 satisfies the above relationship, which can improve the secondary The proportion of the number of particles.
  • the amount of organic carbon source C3 added in the coating process is the percentage of the weight of the organic carbon source added in the coating process to the total weight of the artificial graphite. In some embodiments, 2% ⁇ C3 ⁇ 8%, 2 % ⁇ C3 ⁇ 5%, 3 % ⁇ C3 ⁇ 5%, or 2 % ⁇ C3 ⁇ 3 %.
  • step e) the amount of organic carbon source C3 added in the coating process and the volatile content C1 of the coke raw material, the amount of binder C2 added in the granulation process, and the particle size consistency of the artificial graphite U 2 satisfies 20% ⁇ (C 1 +C 2 +C 3 )/U 2 ⁇ 100% ⁇ 56%; for example, 30% ⁇ (C 1 +C 2 +C 3 )/U 2 ⁇ 100% ⁇ 48%, 40% ⁇ (C 1 +C 2 +C 3 )/U 2 ⁇ 100% ⁇ 48%.
  • the organic carbon source satisfies 1.2% ⁇ C 3 ⁇ residual carbon rate ⁇ 2.5%; for example, 1.5% ⁇ C 3 ⁇ residual carbon rate ⁇ 2.4%, 1.8% ⁇ C 3 ⁇ residual rate Carbon rate ⁇ 2.3%, or 2% ⁇ C 3 ⁇ residual carbon rate ⁇ 2.2%.
  • step e) also satisfies the above process conditions, the particle size consistency of the negative electrode active material, as well as the particle size specific surface area and the proportion of the number of secondary particles can be further optimized, thereby further improving the performance of the battery.
  • the residual carbon rate is the residual carbon rate of the organic carbon source, which can be measured by the LP-5731 Coal Pitch Coking Value Tester.
  • the test can refer to GB/T268 "Determination of Carbon Residues in Petroleum Products" and GB/T8727-2008 “Determination of Coking Value of Coal Pitch Products”.
  • negative active materials in the first negative active material can be obtained commercially or prepared by methods known in the art.
  • the positive electrode sheet of the present application can be prepared as follows: the positive electrode active material and optional conductive agent and binder are mixed and dispersed in a solvent (such as NMP), and then coated on the positive electrode current collector after stirring evenly, After drying and cold pressing, the positive pole piece is obtained.
  • a solvent such as NMP
  • the negative electrode sheet, the positive electrode sheet, the separator, and the electrolyte may be assembled to form a secondary battery.
  • the positive pole piece, separator film, and negative pole piece can be formed into an electrode assembly through a winding process or a lamination process; the electrode assembly is placed in an outer package, injected with an electrolyte, and then vacuum-sealed, left to stand, formed, and shaped. and other steps to obtain a secondary battery.
  • Embodiments of the third aspect of the present application provide an apparatus including at least one of a secondary battery, a battery module, or a battery pack of the present application.
  • the secondary battery, battery module, or battery pack can be used as a power source of the device, and can also be used as an energy storage unit of the device.
  • the device may be, but is not limited to, mobile devices (eg, cell phones, laptops, etc.), electric vehicles (eg, pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf balls) vehicles, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.
  • the device may select a secondary battery, a battery module or a battery pack according to its usage requirements.
  • Figure 10 is an apparatus as an example.
  • the device is a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, or the like.
  • battery packs or battery modules can be employed.
  • the device may be a mobile phone, a tablet computer, a laptop computer, and the like.
  • the device is generally required to be thin and light, and a secondary battery can be used as a power source.
  • artificial graphite A and natural graphite used in the second negative electrode active material, artificial graphite C and silicon oxide SiO used in the first negative electrode active material can be obtained commercially, or can be It is prepared by the following method.
  • the artificial graphite B (ie, the first graphite) used in the first negative electrode active material can be prepared by the method described herein.
  • non-needle petroleum green coke pulverizing to obtain petroleum coke raw material; shaping and classifying the petroleum coke raw material to obtain a precursor;
  • binder pitch can be used to granulate the precursor, so as to adjust the particle morphology of artificial graphite A (for example, the proportion of primary particles in artificial graphite A can be adjusted) .
  • the artificial graphite A satisfies: 15 ⁇ m ⁇ D v 50 ⁇ 17.5 ⁇ m, 40 ⁇ m ⁇ D v 99 ⁇ 55 ⁇ m, and the gram capacity is 353mAh/g ⁇ 370mAh/g.
  • the artificial graphite B satisfies: 8 ⁇ m ⁇ D v 50 ⁇ 13 ⁇ m, D v 99 ⁇ 23 ⁇ m, and the gram capacity is 348mAh/g ⁇ 360mAh/g.
  • the raw materials are pulverized, shaped and classified to obtain precursors.
  • the precursors are granulated with binder pitch, and then the granulated products are granulated at 2800°C ⁇ 3200°C.
  • Graphitization treatment is carried out at high temperature, and artificial graphite C is obtained after carbonization treatment and screening after coating artificial graphite with pitch.
  • the artificial graphite C satisfies: 12 ⁇ m ⁇ D v 50 ⁇ 17 ⁇ m, 25 ⁇ m ⁇ D v 99 ⁇ 45 ⁇ m, and the gram capacity is 350mAh/g ⁇ 360mAh/g.
  • Natural graphite can be purchased from Shenzhen Betterray New Energy Technology Co., Ltd.
  • the natural graphite meets: 12 ⁇ m ⁇ D v 50 ⁇ 19 ⁇ m, 24 ⁇ m ⁇ D v 99 ⁇ 37 ⁇ m, and the gram capacity is 360mAh/g ⁇ 370mAh/g .
  • Silica SiO can be purchased from Shin-Etsu Chemical Industry Co., Ltd.
  • the second negative electrode active material artificial graphite A, conductive agent carbon black (Super P), binder styrene-butadiene rubber (SBR) and thickener sodium carboxymethyl cellulose (CMC-Na) are 96:1.5:1.5: The mass ratio of 1 is fully stirred and mixed in an appropriate amount of solvent deionized water to form a uniform second negative electrode slurry; wherein, the D v 99 1 of the second negative electrode active material is 45.2 ⁇ m.
  • the first negative electrode active material artificial graphite B, conductive agent carbon black (Super P), binder styrene-butadiene rubber (SBR) and thickener sodium carboxymethyl cellulose (CMC-Na) are 96:1.5:1.5: The mass ratio of 1 is fully stirred and mixed in an appropriate amount of solvent deionized water to form a uniform first negative electrode slurry; wherein, the D v 99 2 of the first negative electrode active material is 22.9 ⁇ m.
  • the second negative electrode slurry and the first negative electrode slurry are simultaneously extruded through a dual-chamber coating device.
  • the second negative electrode slurry is coated on the copper foil of the negative current collector to form the second negative electrode film layer
  • the first negative electrode slurry is coated on the second negative electrode film layer to form the first negative electrode film layer; after drying and cold pressing, the obtained Negative pole piece.
  • the areal density of the negative electrode film layer is 0.123 mg/cm 2
  • the compaction density is 1.7 g/cm 3
  • the thickness ratio of the second negative electrode film layer to the first negative electrode film layer is 1:1.
  • the positive active material LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811), the conductive agent Super P, and the binder polyvinylidene fluoride (PVDF) were mixed in an appropriate amount of solvent N-methylpyrrolidone (NMP) in a mass ratio of 97:1.5:1.5. ) to fully stir and mix to form a uniform positive electrode slurry; the positive electrode slurry is coated on the surface of the positive electrode current collector aluminum foil, and after drying and cold pressing, a positive electrode pole piece is obtained.
  • the areal density of the positive electrode film layer was 0.188 mg/cm 2 , and the compaction density was 3.5 g/cm 3 .
  • EC ethylene carbonate
  • EMC ethyl methyl carbonate
  • DEC diethyl carbonate
  • the positive pole piece, the separator, and the negative pole piece are stacked and wound in order to obtain an electrode assembly; the electrode assembly is added to the outer package, the above-mentioned electrolyte is added, and the secondary battery is obtained after the processes of packaging, standing, forming, and aging. .
  • the preparation method is similar to that of Example 1, except that the relevant parameters in the preparation step of the negative electrode pole piece are adjusted and controlled to obtain the corresponding secondary battery, as shown in Table 2 and Table 3 for details.
  • the batteries of the above examples and comparative examples were charged and discharged for the first time with a current of 1C (that is, the current value that completely discharges the theoretical capacity within 1h), specifically including: charging the batteries with a constant current at a rate of 1C. To the voltage of 4.25V, then constant voltage charge to the current ⁇ 0.05C, stand for 5 minutes, and then discharge to the voltage of 2.8V at a rate of 0.33C constant current, record its actual capacity as C0.
  • a current of 1C that is, the current value that completely discharges the theoretical capacity within 1h
  • the charge rate is The charging window in this SOC state is recorded as C10% SOC, C20% SOC, C30% SOC, C40% SOC, C50% SOC, C60% SOC, C70% SOC, C80% SOC, according to the formula (60/C20% SOC SOC+60/C30%SOC+60/C40%SOC+60/C50%SOC+60/C60%SOC+60/C70%SOC+60/C80%SOC) ⁇ 10% Calculated to get the battery charged from 10%SOC
  • the charging time T to 80% SOC (on the premise that the battery does not precipitate lithium), the unit is min. The shorter the time, the better the fast charging capability of the battery.
  • the secondary batteries prepared in the examples and comparative examples were discharged to 2.8V at a constant current of 1.0C; then charged to 4.25V at a constant current of 1.0C, and continued to be charged at a constant voltage until the current ⁇ 0.05C.
  • the battery is fully charged, i.e. 100% SOC.
  • the discharge capacity at this time is the actual capacity of the battery at 1C/1C, and is recorded as C 0 .
  • the discharge capacity at this time is the reversible capacity after one storage cycle, denoted as C n ; the capacity retention rate of this storage cycle is C n /C 0 ⁇ 100% .
  • the capacity retention rate is 80%, stop the test, and record the storage time (days) at this time.
  • the battery needs to be charged to 4.25V at 1C 0 , and then charged with constant voltage until the current is less than or equal to 0.05C, so that the battery is fully charged, and then placed at 60°C storage.
  • the secondary batteries prepared in the examples and comparative examples were charged at a constant current of 0.33C to a charge cut-off voltage of 4.25V, and then charged at a constant voltage to a current of 0.05C, left standing for 5 minutes, and then discharged at a constant current of 0.33C.
  • the initial capacity was recorded as C 0 .
  • charge according to the strategy described in Table 1 discharge at 0.33C, record the discharge capacity C n for each cycle, until the cycle capacity retention rate (C n /C 0 ⁇ 100%) is 80%, and record the number of cycles. The more cycles, the higher the cycle life of the battery.
  • the secondary batteries of the embodiments of the present application adopt the negative pole piece of the multi-film layer structure, and the first negative electrode film layer located in the upper layer contains the first negative electrode active material, and satisfies the first negative electrode active material.
  • the first graphite is included, and the D v 99 of the first negative electrode active material is less than or equal to 23 ⁇ m, so that the battery can be charged at a high rate in a high SOC state, thereby significantly improving the fast charging capability.
  • the battery can also take into account higher cycle performance and higher storage performance.
  • the batteries of Comparative Examples 1 to 6 do not meet the above conditions, their fast charging ability is poor, and the cycle life is short, which is not conducive to the improvement of storage performance.

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Abstract

一种二次电池（5）及其制备方法与含有该二次电池（5）的电池模块（4）、电池包（1）和装置。二次电池（5）包括负极极片（10），所述负极极片（10）包括负极集流体（101）及负极膜层，所述负极膜层包括第一负极膜层（102）和第二负极膜层（103），所述第二负极膜层（103）位于所述负极集流体（101）和所述第一负极膜层（102）之间；所述第一负极膜层（102）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，所述第一石墨为人造石墨，且所述第一负极活性材料的体积粒径分布Dv99≤23μm。

Description

二次电池、其制备方法及含有该二次电池的电池模块、电池包和装置 技术领域
本申请属于二次电池技术领域，具体涉及一种二次电池及其制备方法与含有该二次电池的电池模块、电池包和装置。
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。
然而，与传统的燃油车能快速及时的加油相比，电动汽车一般是以较小的倍率充电，这常常需要较长的充电时间，因此给消费者造成了续航里程的焦虑，限制了电动汽车的快速普及。因此，为了提高电动汽车的市场竞争力，有必要提供一种能具有良好的快速充电性能二次电池。
发明内容
本申请的目的在于提供一种二次电池、其制备方法及含有该二次电池的电池模块、电池包和装置，旨在使所述电池在具有较高能量密度的前提下，同时兼具较好的快速充电性能和循环性能。
为了实现上述发明目的，本申请第一方面提供一种二次电池，其包括负极极片，所述负极极片包括负极集流体及负极膜层，所述负极膜层包括第一负极膜层和第二负极膜层，所述第二负极膜层位于所述负极集流体和所述第一负极膜层之间；所述第一负极膜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，所述第一石墨为人造石墨，且所述第一负极活性材料的体积粒径分布D v99≤23μm。
本申请的二次电池通过采用多膜层结构的负极极片，并且使位于上层的第一负极膜层包含第一负极活性材料，且满足第一负极活性材料包括第一石墨，所述第一石墨为人造石墨，且第一负极活性材料的D v99≤23μm，由此在电池的高SOC(State of Charge，荷电状态)态，负极极片也能具有良好的电化学反应界面和较高的活性离子固相扩散速度，实现电池在高SOC态进行大倍率充电，从而显著提升快速充电能力。
在本申请任意实施方式中，第一负极活性材料满足17μm≤D v99≤23μm；可选的，18μm≤D v99≤21μm。第一负极活性材料的D v99在适当范围内，能使二次电池在具有较高能量密度的同时，还兼顾由于固相传导阻抗降低带来的快速充电能力及循环性 能改善。
在本申请任意实施方式中，第一负极活性材料满足8μm≤D v50≤13μm；可选的，9μm≤D v50≤12μm。第一负极活性材料的D v50在适当范围内，缩短了活性离子的迁移扩散路径，能进一步提升电池的快速充电能力及循环性能。
在本申请任意实施方式中，第一负极活性材料的粒度一致性Uniformity为0.28～0.4，可选的为0.30～0.36。第一负极活性材料的粒度一致性Uniformity在上述范围内，活性粒子得以合理搭配，改善加工性能，能进一步提高电池的快速充电能力和循环性能，还能提升电池的能量密度。
在本申请任意实施方式中，第一石墨中包括二次颗粒。可选的，二次颗粒在第一石墨中的数量占比≥50％。可选的，二次颗粒在第一石墨中的数量占比为80％～100％。第一负极活性材料中包含较多的二次颗粒时，活性粒子各向同性提高，缩短了活性离子嵌入的路径，能进一步提高电池的快速充电能力，兼顾提升循环性能。
在本申请任意实施方式中，第一负极活性材料的粒度比表面积为0.45m 2/g～0.65m 2/g，可选的为0.5m 2/g～0.63m 2/g。第一负极活性材料的粒度比表面积在适当范围内，能进一步提升电池的快速充电性能、循环性能及存储性能。
在本申请任意实施方式中，第一负极活性材料满足：0.6≤(D v90-D v10)/D v50≤1.8；可选的，0.8≤(D v90-D v10)/D v50≤1.4。第一负极活性材料的(D v90-D v10)/D v50适当，便于在膜层中形成通畅的孔道结构分布，有利于活性离子的快速传输，降低了液相传导阻抗，因此可进一步改善电池的快速充电能力和循环性能。
在本申请任意实施方式中，第一负极活性材料的体积粒径分布D v10为5μm～9μm，可选的为6μm～8μm。第一负极活性材料的D v10在适当范围内，能减少对活性离子的不可逆消耗，并且提高单位体积内活性物质的质量，有利于提高电池的能量密度、循环性能和高温存储性能。
在本申请任意实施方式中，第一负极活性材料的体积粒径分布D v90为14μm～21μm，可选的为16μm～18μm。第一负极活性材料的D v90在适当范围内，能进一步提高电池的快速充电能力和循环性能。
在本申请任意实施方式中，第一负极活性材料的粉体OI值为2.0～4.0，可选的为2.3～3.6。第一负极活性材料的粉体OI值在适当范围内，能使其具有较多的活性离子快速嵌入通道，从而进一步提升电池的快速充电能力。并且，负极活性材料的粉体OI值在适当范围内，还能减小负极极片在充电过程中的膨胀效应，能进一步提升电池的循环性能。
在本申请任意实施方式中，第一负极活性材料的振实密度为0.85g/cm 3～1.4g/cm 3，可选地为0.9g/cm 3～1.2g/cm 3。第一负极活性材料的振实密度在所给范围内，有利于颗粒间保持较好的接触，且可获得更好的粒子间空隙结构，保证了通畅的活性离子传输通道，能使电池获得较高的快速充电能力和能量密度。
在本申请任意实施方式中，第一负极活性材料在2kN压力下的粉体压实密度为1.55g/cm 3～1.70g/cm 3，可选地为1.58g/cm 3～1.68g/cm 3。第一负极活性材料的在2kN压力下的粉体压实密度在所给范围内，能使负极膜层具有较高的压实密度，从而可提升电池的能量密度。
在本申请任意实施方式中，第一负极活性材料的比表面积(SSA)为0.8m 2/g～1.3m 2/g，可选的为0.9m 2/g～1.2m 2/g。第一负极活性材料的比表面积(SSA)在适当范围内，提高了电解液的浸润及活性离子的液相传输，有利于电池获得较高的快速充电能力和循环性能。
在本申请任意实施方式中，第一负极活性材料的克容量为345mAh/g～360mAh/g，可选的为350mAh/g～358mAh/g。第一负极活性材料的克容量在上述范围内，能提高电池的能量密度及快速充电能力。
在本申请任意实施方式中，第一石墨的至少一部分表面具有无定形碳包覆层。第一石墨表面形成可富集活性离子的碳层，降低了电荷转移阻抗。采用该第一石墨能进一步提升电池的循环性能和快速充电能力。
在本申请任意实施方式中，第一石墨在第一负极活性材料中的质量占比≥80％。可选的，第一石墨在第一负极活性材料中的质量占比为90％～100％。第一负极膜层中包含较多的第一石墨，能更有效地提升电池的快速充电能力。
在本申请任意实施方式中，第二负极膜层包括第二负极活性材料，第二负极活性材料包括第二石墨，第二石墨包括人造石墨、天然石墨中的一种或几种。
在本申请任意实施方式中，第二石墨中人造石墨的质量占比≥50％。可选的，第二石墨中人造石墨的质量占比为60％～100％。第二负极活性材料包含较多的人造石墨，能提升电池的能量密度，且可改善电池的循环性能和高温存储性能。
在本申请任意实施方式中，第二负极活性材料的体积粒径分布D v99大于第一负极活性材料的体积粒径分布D v99。可选的，第二负极活性材料的体积粒径分布D v99与第一负极活性材料的体积粒径分布D v99之比为2.0～2.6，进一步可选的为2.1～2.4。第二负极活性材料与第一负极活性材料满足上述条件，能在改善电池的能量密度、循环性能和存储性能的同时，还使电池兼具较高的快速充电能力。
在本申请任意实施方式中，第二负极活性材料的体积平均粒径D v50为15μm～21μm，可选的为16.5μm～20μm。第二负极活性材料的D v50在上述范围内，缩短了活性离子的扩散路径，同时使第二负极活性材料具有较高的克容量，能使电池具有较高的快速充电能力、能量密度和循环性能。
在本申请任意实施方式中，第二石墨中包括一次颗粒。可选的，一次颗粒在第二石墨中的数量占比≥50％；可选的，一次颗粒在第二石墨中的数量占比为60％～100％。第二石墨满足上述条件，使得材料具有较高的各向异性，保证石墨的结构稳定性及提高负极膜层的压实密度，从而能提升电池的能量密度、高温存储性能和循环性能。
在本申请任意实施方式中，第二负极活性材料的粒度一致性Uniformity为0.3～0.55，可选的为0.4～0.5。第二负极活性材料的粒度一致性Uniformity在上述范围内，能进一步提高电池的循环性能和能量密度。
在本申请任意实施方式中，第二负极活性材料的粒度比表面积为0.35m 2/g～0.55m 2/g，可选的为0.38m 2/g～0.50m 2/g。第二负极活性材料的粒度比表面积在适当范围内时，减少了对活性离子的不可逆消耗，能进一步提升电池的循环性能和存储性能。
在本申请任意实施方式中，第二负极活性材料满足：0.9≤(D v90-D v10)/D v50≤1.6；可选的，1.0≤(D v90-D v10)/D v50≤1.4。第二负极活性材料的(D v90-D v10)/D v50在上 述范围内，使得粒子间保持合理的孔道结构，能提升电池的快速充电性能及体积能量密度。
在本申请任意实施方式中，第二负极活性材料的体积粒径分布D v10为5μm～14μm，可选的为7μm～12μm。第二负极活性材料的D v10在上述范围内，能提升电池的循环性能和存储性能。
在本申请任意实施方式中，第二负极活性材料的体积粒径分布D v90为24μm～38μm，可选的为26μm～33μm。第二负极活性材料的D v90在上述范围内，能提高电池的循环性能和快速充电能力，还可进一步提升电池的能量密度。
在本申请任意实施方式中，第二负极活性材料的粉体OI值≤14，可选的为6～11。第二负极活性材料的OI值在上述范围内，有助于缩短活性离子的嵌入路径，减小电池在充电过程中的膨胀，使电池具有较高的快速充电能力、循环性能和能量密度。
在本申请任意实施方式中，第二负极活性材料的振实密度为0.8g/cm 3～1.2g/cm 3，可选地为0.9g/cm 3～1.1g/cm 3。第二负极活性材料的振实密度在所给范围内，使得活性粒子间保持优异的孔隙结构，能提高电池的快速充电能力和能量密度。
在本申请任意实施方式中，第二负极活性材料在2kN压力下的粉体压实密度为1.70g/cm 3～1.85g/cm 3，可选地为1.75g/cm 3～1.82g/cm 3。第二负极活性材料在2kN压力下的粉体压实密度在适当范围内，提高了负极膜层的压实密度，能提升电池的能量密度。
在本申请任意实施方式中，第二负极活性材料的比表面积(SSA)为1.0m 2/g～2.0m 2/g，可选的为1.3m 2/g～1.8m 2/g。第二负极活性材料的比表面积(SSA)在适当范围内，有利于电池获得较高的存储性能和循环性能。
在本申请任意实施方式中，第二负极活性材料的克容量为353mAh/g～370mAh/g，可选的为359mAh/g～367mAh/g。第二负极活性材料的克容量在上述范围内，能提高电池的能量密度，还能提高电池的循环性能。
在本申请任意实施方式中，负极膜层的面密度为0.117mg/mm 2～0.130mg/mm 2，可选的为0.120mg/mm 2～0.127mg/mm 2。负极膜层的面密度在上述范围内，可以进一步改善电池的能量密度和快速充电能力。
在本申请任意实施方式中，负极膜层的压实密度为1.65g/cm 3～1.75g/cm 3，可选的为1.66g/cm 3～1.70g/cm 3。负极膜层的压实密度在所给范围内，能进一步改善电池的能量密度、快速充电能力和循环性能。
在本申请任意实施方式中，第二负极膜层与第一负极膜层的厚度比为0.7∶1～2.3∶1，可选的为0.7∶1～1.0∶1，再可选的为1.1∶1～2.3∶1。使第二负极膜层和第一负极膜层的厚度比在适当范围内，能进一步改善电池的快速充电能力或能量密度。
在本申请任意实施方式中，第一负极活性材料或第二负极活性材料中还包括硅基材料、锡基材料、软碳、硬碳、钛酸锂中的一种或几种。
在本申请任意实施方式中，二次电池包括正极极片，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上且包括正极活性材料的正极膜层，正极活性材料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改性化合物中的一种或几种。可选的，正极活性材料包括式1所示的锂过渡金属氧化物及其改性化合物中的一种或几 种，
Li aNi bCo cM dO eA f  式1，
式1中，0.8≤a≤1.2，0.5≤b＜1，0＜c＜1，0＜d＜1，1≤e≤2，0≤f≤1，M选自Mn、Al、Zr、Zn、Cu、Cr、Mg、Fe、V、Ti及B中的一种或几种，A选自N、F、S及Cl中的一种或几种。
本申请第二方面提供一种二次电池的制备方法，其至少包括如下步骤：在负极集流体的至少一侧形成第二负极膜层，所述第二负极膜层包括第二负极活性材料；在所述第二负极膜层的表面上形成第一负极膜层，所述第一负极膜层包括第一负极活性材料；其中，所述第一负极活性材料包括第一石墨，所述第一石墨为人造石墨，且所述第一负极活性材料的体积粒径分布D v99≤23μm。
本申请第三方面提供一种电池模块，其包括本申请的二次电池。
本申请第四方面提供一种电池包，其包括本申请的二次电池或电池模块。
本申请第五方面提供一种装置，其包括本申请的二次电池、电池模块、或电池包中的至少一种。
本申请的电池模块、电池包和装置包括本申请提供的二次电池，因而至少具有与所述二次电池相同的优势。
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是本申请的二次电池的一实施方式的示意图。
图2是本申请的二次电池的一实施方式的分解示意图。
图3是本申请的二次电池中负极极片的一实施方式的示意图。
图4是本申请的二次电池中负极极片的另一实施方式的示意图。
图5是本申请第一负极活性材料的一实施方式的扫描电子显微镜(SEM)图。
图6是本申请第二负极活性材料的一实施方式的SEM图。
图7是本申请的电池模块的一实施方式的示意图。
图8是本申请的电池包的一实施方式的示意图。
图9是图8的分解图。
图10是本申请的二次电池用作电源的装置的一实施方式的示意图。
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。
[二次电池]
二次电池又称为充电电池或蓄电池，是指在电池放电后可通过充电的方式使活性物质激活而继续使用的电池。
通常情况下，二次电池包括正极极片、负极极片、隔离膜及电解质。在电池充放电过程中，活性离子(例如锂离子)在正极极片和负极极片之间往返嵌入和脱出。隔离膜设置在正极极片和负极极片之间，主要起到防止正负极短路的作用，同时可以使离子通过。电解质在正极极片和负极极片之间，主要起到传导离子的作用。
[负极极片]
二次电池包括负极极片，负极极片通常包括负极集流体和设置在负极集流体至少一侧的负极膜层。
发明人发现，提升二次电池的快速充电能力的关键在于提升负极的动力学性能。目前，大多通过减薄负极膜层或降低负极膜层的压实密度的方式来提升负极的动力学性能。但是大量研究证明，以上提升负极动力学的方法仅一定程度上提升了电池低SOC态(即充电初期)的动力学，对电池高SOC态(即充电末期)的动力学性能的改善无明显作用，造成二次电池的快速充电能力未能得到有效提升，甚至导致无法实际上对二次电池进行大倍率充电。另外，电池的能量密度也会明显降低。
发明人进一步进行了大量研究，巧妙地改进了负极膜层的构成，打破了上述瓶颈。具体地，本申请的二次电池中，负极极片包括负极集流体及负极膜层，所述负极膜层包括第一负极膜层和第二负极膜层，第二负极膜层位于负极集流体和第一负极膜层之间；第一负极膜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，第一石墨为人造石墨，且第一负极活性材料的体积粒径分布D v99≤23μm。
本申请的二次电池通过采用多膜层结构的负极极片，并且使位于上层的第一负极膜层包含第一负极活性材料，且满足第一负极活性材料包括第一石墨，所述第一石墨为人造石墨，且第一负极活性材料的D v99≤23μm，由此在电池的高SOC态，负极极片也能具有较高的活性离子扩散速度，从而有效提升快速充电能力。
不期望受任何理论限制，负极活性材料的D v99一直被业界认为是无关紧要且较难控制的参数，从而被忽视。而本发明人在研究过程中首次发现，当第一负极膜层中的第一负极活性材料包括第一石墨，所述第一石墨为人造石墨，且第一负极活性材料满足D v99≤23μm时，负极极片即使在充电末期(具有较高的活性离子嵌入量，例如嵌锂量)仍能保持良好的电化学反应界面，且第一负极活性材料颗粒内部能具有良好的活性离子扩散性能，活性离子能快速嵌入第一负极活性材料的体相并进行快速迁移，提升此阶段中活性离子在第一负极膜层的扩散速度，并且活性离子还能经第一负极膜层快速迁移至内部的第二负极膜层，因此使得负极极片整体在此阶段的充电速度和充电深度大大增加，从而实现电池在高SOC态进行大倍率充电，显著提升快速充电能力。通常情况下，低SOC态一般指30％SOC以下，高SOC态一般指60％SOC以上。
第一负极活性材料包括第一石墨，所述第一石墨为人造石墨，且第一负极活性材料满足D v99≤23μm，还能减小电池在高SOC态下充电的欧姆和浓差极化，从而还有利于提高电池的循环性能。
在一些实施方式中，第一负极活性材料可满足D v99≤23μm，≤22.5μm，≤22μm，≤21.5μm，或≤21μm。第一负极活性材料的D v99在上述范围内，能进一步提高电池高SOC态时的嵌锂速度，减小极化，从而进一步提高电池的快速充电能力和循环性能。
在一些实施方式中，所述第一负极活性材料的D v99≥15μm，≥16μm，≥17μm，≥18μm，≥19μm，或≥19.5μm。第一负极活性材料的D v99在上述范围内，能使第一负极活性材料具有较高的克容量，从而能提升电池的能量密度。另外，第一负极活性材料的D v99在上述范围内，有助于减少其中的较小颗粒，颗粒内可嵌入较多的活性离子，同时有利于使负极膜层中形成通畅的孔道结构，缩短液相传导路径，从而还有利于提升电池的快速充电能力和循环性能。小颗粒的含量减少，还有利于减少电解液在负极的副反应，因此还能提升电池的高温存储性能。
在一些可选的实施例中，第一负极活性材料满足：17μm≤D v99≤23μm。例如，第一负极活性材料可以满足17.5μm≤D v99≤20.5μm，18μm≤D v99≤21μm，18μm≤D v99≤19μm，19μm≤D v99≤20.5μm，19.5μm≤D v99≤21μm，或20μm≤D v99≤22μm等。例如，D v99可以为22.9μm，22.6μm，21.7μm，21.1μm，20.4μm，19.9μm，19.2μm，18.1μm，或17.6μm。采用该第一负极活性材料，能使二次电池同时兼顾较高的快速充电能力、循环性能、高温存储性能和能量密度。
本发明人经深入研究发现，当本申请的二次电池在满足上述设计条件的基础上，若还可选的满足下述参数中的一个或几个时，可以进一步改善电池的性能。
在一些实施方式中，第一负极活性材料满足8μm≤D v50≤13μm。可选的，第一负极活性材料的D v50≤13μm，≤12.5μm，或≤12μm。可选的，第一负极活性材料的D v50≥8μm，≥9μm，≥10μm，或≥11μm。例如，第一负极活性材料可以满足 8.5μm≤D v50≤10μm，9μm≤D v50≤12μm，9.5μm≤D v50≤11.5μm，10μm≤D v50≤12μm，11μm≤D v50≤12μm，11μm≤D v50≤12.5μm，或11.5μm≤D v50≤12.8μm。例如，D v50可以为8.6μm，9.8μm，10.3μm，11.2μm，11.3μm，11.4μm，11.5μm，11.7μm，11.8μm，12.4μm，12.8μm，或14.5μm。
第一负极活性材料的D v50在适当范围内，能缩短活性离子在第一负极活性材料颗粒中的迁移路径，同时有利于使第一负极膜层形成通畅的孔隙结构，由此使负极极片具有良好的液相传输性能以及良好的活性离子固相扩散速度，从而进一步提升电池的快速充电能力和循环性能。另外，第一负极活性材料的D v50在适当范围内，还能减少电解液在颗粒表面的副反应，提高电池的循环性能和高温存储性能。
在一些实施方式中，第一负极活性材料的粒度一致性Uniformity为0.28～0.4，例如可以为0.28～0.38，0.29～0.34，0.30～0.36，或0.31～0.35。第一负极活性材料的粒度一致性Uniformity在上述范围内，第一负极膜层中易于形成较短的液相传输路径，同时颗粒与颗粒之间能具有较大的接触面积，有利于负极极片中的电子传导和活性离子传输，提高电池的快速充电能力和循环性能。此外，第一负极膜层的颗粒之间能实现紧密接触，由此能使负极极片获得较高的压实密度，从而提升电池的能量密度。
需要说明的是，负极活性材料的粒度一致性Uniformity可以表征负极活性材料中所有颗粒的粒径偏离负极活性材料的体积平均粒径D v50的离散程度，其可以反映负极活性材料的粒径分布均匀性。
在一些实施方式中，第一负极活性材料满足：0.6≤(D v90-D v10)/D v50≤1.8。例如，第一负极活性材料的(D v90-D v10)/D v50可以为0.8～1.4，0.9～1.5，1.0～1.3。负极活性材料的(D v90-D v10)/D v50反应了负极活性材料中较大颗粒的粒径和较小颗粒的粒径偏离体积平均粒径D v50的程度。第一负极活性材料的(D v90-D v10)/D v50适当，有利于改善第一负极膜层的加工性能，使第一负极膜层整体具有较高的颗粒分布一致性和通畅的孔道结构，由此有利于负极膜层不同区域处均表现出较高的活性离子传输性能，进一步改善电池的快速充电能力和循环性能。
在一些实施方式中，第一负极活性材料的体积粒径分布D v90为14μm～21μm。例如，可以为16μm～18μm，17μm～19μm，或18μm～20μm。第一负极活性材料的D v90在适当范围内，能进一步提高活性离子在负极膜层中的固相扩散速度，从而进一步提高电池的快速充电能力和循环性能。另外，负极活性材料还能具有较高的克容量，有助于提升电池的能量密度。
在一些实施方式中，第一负极活性材料的体积粒径分布D v10为5μm～9μm，例如可以为6μm～8μm。第一负极活性材料中小颗粒的含量较少，能减少电解液与材料之间副反应，并且减少活性离子的不可逆消耗，提高循环性能和高温存储性能。第一负极活性材料的D v10在适当范围内，还能提高单位体积内的活性材料占比，从而提高电池的能量密度。
在一些实施方式中，第一负极活性材料的粒度比表面积为0.45m 2/g～0.65m 2/g，例如可以为0.5m 2/g～0.63m 2/g，0.48m 2/g～0.55m 2/g，或0.52m 2/g～0.6m 2/g。
需要说明的是，本申请的负极活性材料的“粒度比表面积”与通常的负极活性材料的“比表面积”并不相同。目前业界的负极活性材料的比表面积(SSA)多采用气体吸 附BET法得到，其仅用来表征负极活性材料的物理吸附比表面积。而本申请的负极活性材料的“粒度比表面积”是采用激光衍射粒度分析法得到，其可以用来表征负极活性材料的形貌偏离球形度的程度。
发明人发现，当第一负极活性材料的粒度比表面积在适当范围内时，能进一步改善第一负极膜层内的脱嵌离子通道，减小电荷交换阻抗，并且使第一负极膜层获得更通畅的孔道，提升电解液浸润性，从而进一步提升负极极片中的活性离子固相和液相传输速度，因此进一步提升电池的快速充电性能和循环性能。第一负极活性材料的上述粒度比表面积还提高了SEI(solid electrolyte interphase，固体电解质界面)膜的成膜效率，并且可以减少对电解液的消耗，进一步改善电池的循环性能。另外，第一负极活性材料具有适当的粒度比表面积，还能使第一负极膜层的颗粒之间紧密堆积，有助于提升电池的能量密度。
在一些实施方式中，如图5所示，第一负极活性材料中可以包括二次颗粒。可选的，二次颗粒在第一负极活性材料中的数量占比≥50％。例如，二次颗粒在第一负极活性材料中的数量占比可以为55％～95％，60％～100％，65％～85％，70％～100％，75％～90％，75％～85％，80％～100％，80％～90％，85％～95％，或90％～100％。第一负极活性材料中包含适当比例的二次颗粒时，第一负极膜层中的脱嵌活性离子通道增多，活性离子嵌入路径缩短，从而能进一步提高电池的快速充电能力，并且还能减小极化，降低电解液在负极的副反应，从而进一步使电池兼顾较好的循环性能和存储性能。
在一些实施方式中，第一负极活性材料的比表面积(SSA)为0.8m 2/g～1.3m 2/g，例如可以为0.85m 2/g～1.15m 2/g，0.9m 2/g～1.2m 2/g，或0.95～1.25m 2/g。第一负极活性材料的比表面积(SSA)在适当范围内，能改善电解液在膜层中的浸润性，提高活性离子的液相传输，并且材料表面可具有较高的电化学反应活性，嵌入时活性离子在固相中能及时传输，同时还保证材料与电解液之间的副反应较少，从而有利于电池获得较高的快速充电能力和循环性能。
在一些实施方式中，第一负极活性材料的粉体OI值为2.0～4.0，例如可以为2.2～3.2，2.3～3.6，2.5～3.4，或2.8～3.8。第一负极活性材料的粉体OI值较小，颗粒的各个方向均具有活性离子嵌入口，由此能快速地接收来自正极的活性离子，从而进一步提升快速充电能力。并且，各相同性的颗粒结构有利于分散活性离子嵌入时的膨胀率，降低循环膨胀力，由此能进一步提高循环性能。
在一些实施方式中，第一负极活性材料的振实密度为0.85g/cm 3～1.4g/cm 3，例如可以为0.9g/cm 3～1.2g/cm 3，0.95g/cm 3～1.15g/cm 3，1.0g/cm 3～1.25g/cm 3，或1.05g/cm 3～1.35g/cm 3。第一负极活性材料的振实密度在所给范围内，能使第一负极膜层中的颗粒之间形成良好接触，且可获得更好的粒子间空隙结构，保证了通畅的活性离子传输通道，从而能提高电池的快速充电能力。同时，颗粒之间紧密堆积，还能提高电池的能量密度。
在一些实施方式中，第一负极活性材料在2kN压力下的粉体压实密度为1.55g/cm 3～1.70g/cm 3，例如可以为1.55g/cm 3～1.63g/cm 3，1.58g/cm 3～1.68g/cm 3，或1.60g/cm 3～1.68g/cm 3。第一负极活性材料的在2kN压力下的粉体压实密度在所给范围内，能使第一负极膜层中的颗粒之间紧密接触，提高单位体积内的活性材料含量，由此能提升 电池的能量密度。
在一些实施方式中，第一负极活性材料的克容量为345mAh/g～360mAh/g，例如可以为350mAh/g～358mAh/g，351mAh/g～356mAh/g，或352mAh/g～355mAh/g。第一负极活性材料的克容量较高，能提高电池能量密度。第一负极活性材料的克容量在上述范围内，还意味着材料的活性离子迁移路径较短，从而能提高电池的快速充电能力。
在一些实施方式中，第一负极活性材料的至少一部分表面具有无定形碳包覆层。可选的，第一负极活性材料的80％以上的表面覆盖有无定形碳包覆层。进一步地，第一负极活性材料的90％～100％的表面覆盖有无定形碳包覆层。
无定形碳包覆层可以是有机碳源经炭化形成的。例如，有机碳源可选自高分子聚合物，如煤沥青、石油沥青、酚醛树脂、椰壳等高分子材料。
无定形碳包覆层能对第一负极活性材料起到隔离电解液的保护作用，提高结构稳定性，同时还能提高颗粒的活性离子扩散速率，从而进一步提升电池的循环性能和快速充电能力。
在一些实施方式中，第一石墨在第一负极活性材料中的质量占比≥80％。例如，第一石墨在第一负极活性材料中的质量占比可以为85％～100％，90％～100％，或95％～100％。第一负极膜层中包含较多的第一石墨，能充分地发挥第一负极活性材料改善负极极片在高活性离子嵌入量时的活性离子扩散性能的作用，使得负极极片整体在此阶段具有较高的充电速度和充电深度，达到有效提升电池快速充电能力的效果。
在一些实施方式中，负极极片中的第一负极活性材料除了包括本申请上述的第一石墨外，还可选地包括一定量的其它常用负极活性材料，例如，天然石墨、硅基材料、锡基材料、软炭、硬炭、钛酸锂中的一种或几种。
在一些实施方式中，第一负极活性材料还包括硅基材料。硅基材料可包括单质硅、硅氧化物(SiO x，0＜x＜2)、硅碳复合物、硅氮复合物、硅合金材料中的一种或几种。硅基材料能在第一负极膜层可以起到改善孔隙结构的作用，便于电解液的浸润与保液，同时还能提升极片容量，从而能进一步提高电池的快速充电能力和能量密度。
在一些实施方式中，当第一负极活性材料还包括硅基材料时，硅基材料在第一负极活性材料中的质量占比≤10％。例如，硅基材料在第一负极活性材料中的质量占比可以为1％～8％，2％～6％，或3％～7％。在第一负极活性材料中包含适量的硅基材料，能在提升电池的快速充电能力和能量密度的同时，可以使电池进一步兼顾较高的循环性能和高温存储性能。
本申请的二次电池中，第二负极膜层包括第二负极活性材料。第二负极活性材料中包括第二石墨。第二石墨与第一石墨的材料种类可以相同或不同。
本申请的二次电池中，第二石墨可选自人造石墨、天然石墨中的一种或几种。第二负极活性材料能具有较高的循环稳定性和较高的克容量，从而使电池具有较高的循环性能和能量密度。
在一些实施方式中，第二石墨包括人造石墨。可选的，人造石墨在第二石墨中的质量占比≥50％。例如，人造石墨在第二石墨中的质量占比可以为60％～100％，70％～100％，80％～100％，或90％～100％。人造石墨的结构稳定性较好。第二负极活性材料包含较多的人造石墨，有利于保持负极膜层内层(第二负极膜层)良好的孔道结构，使 负极膜层内层也具有较高的电解液浸润性和保液率，由此能进一步提升负极极片整体的离子传输速率，提高电池的快速充电能力。另外，第二负极活性材料中包含较多的人造石墨，还能提高其电解液相容性，改善电池的循环性能和高温存储性能。
在一些实施方式中，第二石墨可以同时包括人造石墨和天然石墨。
在一些实施方式中，当第二石墨同时包括人造石墨和天然石墨时，天然石墨在第二负极活性材料中的质量占比≤40％，例如为5％～40％，10％～30％，或10％～20％。在第二负极活性材料中包含一定量的天然石墨，能进一步提高负极极片的动力学性能，使电池获得较高的快速充电能力。通过使第二负极活性材料中人造石墨和天然石墨的比例适当，能平衡电池的快速充电能力与循环性能和高温存储性能。
在一些实施方式中，第二负极活性材料的体积粒径分布D v99大于第一负极活性材料的体积粒径分布D v99。第二负极活性材料的D v99较大，有利于提升负极的容量，还能减少电解液与负极活性材料之间的副反应，从而改善电池的能量密度、循环性能和高温存储性能。
在一些实施方式中，第二负极活性材料的D v99可以为28μm～55μm，30μm～50μm，40μm～55μm，40μm～50μm，或45μm～50μm。例如，第二负极活性材料的D v99可以为41.6μm，44.5μm，45.2μm，48.7μm，50.1μm，52.3μm，或54.8μm。
在一些实施方式中，第二负极活性材料的D v99与第一负极活性材料的D v99之比为2.0～2.6，例如可以为2.1～2.45，2.1～2.4，2.2～2.6，或2.2～2.5。第二负极活性材料的D v99与第一负极活性材料的D v99之比在上述范围内，能在改善电池的能量密度、循环性能和高温存储性能的同时，还确保负极具有较高的活性离子和电子传输能力，使电池进一步兼具较高的快速充电能力。
在一些实施方式中，第二负极活性材料的体积平均粒径D v50为15μm～21μm。例如可以为15μm～18μm，16μm～19μm，16μm～18μm，16μm～17μm，16.5μm～20μm，17μm～20μm或17μm～21μm。例如，D v50可以为15.9μm，16.1μm，16.5μm，16.6μm，16.8μm，16.9μm，17.5μm。第二负极活性材料的D v50在上述范围内，既能使第二负极膜层具有较高的活性离子扩散能力，又能减少电解液在负极的副反应，从而使电池具有较高的快速充电能力和循环性能。另外，该第二负极活性材料还能具有较高的克容量，可以使电池获得较高的能量密度。
在一些实施方式中，第二负极活性材料满足：0.9≤(D v90-D v10)/D v50≤1.6。例如，第二负极活性材料的(D v90-D v10)/D v50可以为1.0～1.4，1.05～1.35，或1.1～1.25。第二负极活性材料的(D v90-D v10)/D v50在上述范围内，能改善颗粒的堆积性能，提高活性材料占比，从而提升电池的体积能量密度。特别地，负极膜层整体的颗粒分布一致性较好，且颗粒间形成合理的孔道结构，能提升电池的快速充电能力。
在一些实施方式中，第二负极活性材料的体积粒径分布D v10为5μm～14μm，例如可以为6μm～10μm，7μm～12μm，或7μm～9μm。第二负极活性材料中的小颗粒较少，能减少电解液在负极的副反应和对活性离子的不可逆消耗，从而提升电池的循环性能和存储性能。
在一些实施方式中，第二负极活性材料的体积粒径分布D v90为24μm～38μm，例如可以为26μm～33μm。第二负极活性材料中的大颗粒较少，能提升负极膜层的活性离子 和电子传输性能，减少极化，提高电池的循环性能和快速充电能力。另外，第二负极活性材料还能具有较高的克容量，可进一步提升电池的能量密度。
在一些实施方式中，可选的，如图6所示，第二石墨中包括一次颗粒，且一次颗粒在第二石墨中的数量占比≥50％。例如，一次颗粒在第二石墨中的数量占比可以为55％～95％，60％～100％，65％～90％，65％～80％，70％～100％，75％～90％，80％～100％，90％～100％，或95％～100％。第二负极活性材料包含适当比例的一次颗粒，能获得较高的结构稳定性，还能减少电解液在负极的副反应，从而提升电池的高温存储性能和循环性能。另外，采用该第二负极活性材料还能提高负极膜层的压实密度，从而提高电池的能量密度。
在一些实施方式中，第二负极活性材料的粒度一致性Uniformity为0.3～0.55。例如，第二负极活性材料的粒度一致性Uniformity为0.39～0.49，0.4～0.5，0.42～0.48，或0.43～0.46。第二负极活性材料的粒度一致性Uniformity在上述范围内，能进一步提高负极膜层的压实密度，从而能提升电池的能量密度；同时，第二负极膜层内可以具有良好的电解浸润孔道，由此可使电池具有较高的循环性能。
在一些实施方式中，第二负极活性材料的粒度比表面积为0.35m 2/g～0.55m 2/g，例如可以为0.36m 2/g～0.48m 2/g，0.38m 2/g～0.50m 2/g，或0.42m 2/g～0.53m 2/g。第二负极活性材料的粒度比表面积在适当范围内，能使第二负极膜层内具有较多的脱嵌离子通道和适宜的孔隙结构，保证负极具有较低的阻抗，同时还进一步减少对电解液和活性离子的消耗，从而进一步提升电池的循环性能和存储性能。另外，第二负极活性材料具有适当的粒度比表面积，还能使第二负极膜层的颗粒之间紧密堆积，提升电池能量密度。
在一些实施方式中，第二负极活性材料的比表面积(SSA)为1.0m 2/g～2.0m 2/g，例如可以为1.3m 2/g～1.8m 2/g。第二负极活性材料的比表面积(SSA)在适当范围内，能使第二负极膜层具有较高的活性离子固相扩散性能，同时还保证材料与电解液之间的副反应较少，从而有利于电池获得较高的快速充电能力、循环性能和存储性能。
在一些实施方式中，第二负极活性材料的粉体OI值≤14，可选的为5～14，6～11，7～10。第二负极活性材料不仅具有较好的活性离子嵌入性能，还能使负极膜层具有较低的循环膨胀，从而使电池具有较高的快速充电能力、循环性能和能量密度。
在一些实施方式中，第二负极活性材料的克容量为353mAh/g～370mAh/g，例如可以为359mAh/g～367mAh/g，或360mAh/g～365mAh/g。第二负极活性材料的克容量较高，能进一步提升电池的能量密度。第二负极活性材料的克容量在上述范围内，还意味着材料的循环稳定性较好，从而能提高电池的循环性能。
在一些实施方式中，第二负极活性材料的振实密度为0.8g/cm 3～1.2g/cm 3，例如可以为0.9g/cm 3～1.1g/cm 3，或0.95g/cm 3～1.08g/cm 3。第二负极活性材料的振实密度在所给范围内，能使第二负极膜层中的颗粒之间形成紧密接触，同时使得活性粒子间保持优异的孔隙结构，从而能提高电池的快速充电能力和能量密度。
在一些实施方式中，第二负极活性材料在2kN压力下的粉体压实密度为1.70g/cm 3～1.85g/cm 3，例如可以为1.75g/cm 3～1.82g/cm 3。第二负极活性材料在2kN压力下的粉体压实密度在适当范围内，能提高负极膜层的压实密度，从而提升电池能量密度。
本申请的二次电池中，所述第二负极活性材料除了包括本申请上述的第二石墨 外，还可选地包括一定量的其它常用负极活性材料，例如，硅基材料、锡基材料、软炭、硬炭、钛酸锂中的一种或几种。
本申请的负极膜层通常是由负极浆料涂布干燥而成的。负极浆料涂通常是将负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)或去离子水。
本申请的二次电池中，所述第一负极膜层或第二负极膜层通常包含负极活性材料以及可选的粘结剂、可选的导电剂和其他可选助剂。本领域技术人员可以根据实际需求做出选择。作为示例，导电剂可包括超导碳、炭黑(例如乙炔黑、科琴黑等)、碳点、碳纳米管、石墨烯及碳纳米纤维中一种或几种。粘结剂可包括丁苯橡胶(SBR)、水溶性不饱和树脂SR-1B、水性丙烯酸树脂、聚乙烯醇(PVA)、海藻酸钠(SA)及羧甲基壳聚糖(CMCS)中的一种或几种。其他可选助剂例如是增稠剂(如羧甲基纤维素钠CMC-Na)、PTC热敏电阻材料等。
在一些实施方式中，所述负极膜层的面密度为0.117mg/mm 2～0.130mg/mm 2，例如可以为0.117mg/mm 2～0.125mg/mm 2，0.118mg/mm 2～0.122mg/mm 2，0.120mg/mm 2～0.127mg/mm 2，或0.121mg/mm 2～0.125mg/mm 2。需要说明的是，所述负极膜层的面密度是指负极膜层整体的面密度(即第一负极膜层和第二负极膜层的面密度总和)。负极膜层的面密度在上述范围内，可以使负极极片具有较高的容量，并减小活性离子和电子在膜层中的迁移距离和阻抗，从而进一步改善电池的能量密度和快速充电能力。
在一些实施方式中，负极膜层的压实密度为1.65g/cm 3～1.75g/cm 3，例如可以为1.65g/cm 3～1.68g/cm 3，1.66g/cm 3～1.70g/cm 3，或1.68g/cm 3～1.72g/cm 3。需要说明的是，所述负极膜层的压实密度是指负极膜层整体的压实密度(即负极膜层的面密度与厚度之比)。负极膜层的压实密度在所给范围内，能使负极极片在具有较高的可逆容量的同时，还具有良好的低循环膨胀性能和动力学性能，从而进一步改善电池的能量密度、快速充电能力和循环性能。
在一些实施方式中，第二负极膜层与第一负极膜层的厚度比为0.7∶1～2.3∶1。通过使第二负极膜层和第一负极膜层的厚度比在适当范围内，能进一步改善电池的快速充电能力或能量密度。为了获得更高的快速充电能力，可选的，第二负极膜层与第一负极膜层的厚度比可以为0.7∶1～1.0∶1，0.75∶1～0.9∶1，或0.8∶1～1.0∶1。为了获得更高的能量密度，可选的，第二负极膜层与第一负极膜层的厚度比可以为1.1∶1～2.3∶1，1.3～2.1∶1，或1.5～2∶1。
在一些实施方式中，负极膜层的总厚度可选为60μm～90μm，例如可以为65μm～80μm。所述负极膜层的总厚度是第一负极膜层和第二负极膜层的厚度总和。
本申请的二次电池中，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)。作为示例，负极集流体可采用铜箔。
本申请的二次电池中，负极膜层可以设置在负极集流体的一侧，也可以同时设置在负极集流体的两侧。例如，负极集流体具有在其自身厚度方向相对的两侧，负极膜层设置在负极集流体相对的两侧中的任意一侧或两侧上。
图3示出了本申请的负极极片10的一种实施方式的示意图。负极极片10由负极集流体101、分别设置在负极集流体101两侧的第二负极膜层103和设置在第二负极膜层 103上的第一负极膜层102构成。
图4示出了本申请的负极极片10的另一种实施方式的示意图。负极极片10由负极集流体101、设置在负极集流体一侧的第二负极膜层103和设置在第二负极膜层103上的第一负极膜层102构成。
需要说明的是，本申请所给的各负极膜层参数(例如膜层厚度、压实密度、面密度等)均指单侧膜层的参数范围。当负极膜层设置在负极集流体的两侧时，其中任意一侧的膜层参数满足本申请，即认为落入本申请的保护范围内。且本申请所述的膜层厚度、压实密度、面密度等范围均是指经冷压压实后并用于组装电池的膜层参数。
另外，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第二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第一负极膜层表面的覆盖保护层。
在本申请中，负极活性材料的D v99、D v90、D v50、D v10、粒度一致性(Uniformity)、粒度比表面积均可采用激光衍射粒度分析法测定。例如参照标准GB/T 19077.1-2016，使用激光粒度分析仪(例如Malvern Master Size 3000)测定。
其中，D v99为所述负极活性材料累计体积分布百分数达到99％时所对应的粒径；D v90为所述负极活性材料累计体积分布百分数达到90％时所对应的粒径；D v50为所述负极活性材料累计体积分布百分数达到50％时所对应的粒径；D v10为所述负极活性材料累计体积分布百分数达到10％时所对应的粒径。
在本申请中，一次颗粒及二次颗粒为本领域公知的含义。一次颗粒是指没有形成团聚状态的颗粒。二次颗粒是指由两个或两个以上一次颗粒聚集而成的团聚态的颗粒。一次颗粒和二次颗粒可以通过使用扫描电子显微镜拍摄SEM图像容易地区分。
一次颗粒或二次颗粒在负极活性材料中的数量占比可以用本领域已知的仪器及方法进行测定，例如采用扫描电子显微镜测定。二次颗粒的数量占比的示例性测试方法包括：将负极活性材料铺设并粘于导电胶上，制成长6cm×宽1.1cm的待测样品；使用扫描电子显微镜(例如ZEISS Sigma 300)对颗粒形貌进行测试。测试可参考JY/T010-1996。为了确保测试结果的准确性，可在待测样品中随机选取多个(例如5个)不同区域进行扫描测试，并在一定放大倍率(例如1000倍)下，计算各区域中二次颗粒数量占总颗粒数量的百分比，即为该区域中二次颗粒的数量占比。取多个测试区域的测试结果的平均值作为测试结果。为了确保测试结果的准确性，可以取多个测试样品(例如10个)重复进行上述测试，取各个测试样品的平均值作为最终的测试结果。同理也可以测试所述一次颗粒在第二负极活性材料中的数量占比。
在本申请中，负极活性材料的粉体OI值为本领域公知的含义，可以采用本领域已知的方法测试。例如可使用X射线粉末衍射仪(例如Bruker D8 Discover)，依据JIS K 0131-1996、JB/T4220-2011，得到负极活性材料的X射线衍射谱图；然后根据OI值＝C 004/C 110计算得到负极活性材料的粉体OI值。其中，C 004为石墨004晶面的特征衍射峰的峰面积，C 110为石墨110晶面的特征衍射峰的峰面积。
在本申请的X射线衍射分析测试中，可采用铜靶作为阳极靶，以CuKα射线为辐射源，射线波长
Figure PCTCN2020121255-appb-000001
扫描2θ角范围为20°～80°，扫描速率可以为4°/min。
在本申请中，负极活性材料的振实密度为本领域公知的含义，可以采用本领域已知的方法测试。例如可参照标准GB/T 5162-2006，使用粉体振实密度测试仪进行测定。如采用丹东百特BT-301，测试参数如下：振动频率：250±15次/分钟，振幅：3±0.2mm，振动次数：5000次，量筒：25mL。
在本申请中，负极活性材料在2kN压力下的粉体压实密度为本领域公知的含义，可以用本领域已知的方法测定。例如参照标准GB/T24533-2009，通过电子压力试验机(例如UTM7305型)测定。示例性测试方法如下：称取1g负极活性材料，加入底面积为1.327cm 2的模具中，加压至200kg(相当于2kN)，保压30s，然后卸压，保持10s，然后记录并计算得到负极活性材料在2kN压力下的粉体压实密度。
在本申请中，负极活性材料的比表面积(SSA)为本领域公知的含义，可以用本领域已知的方法测定。例如参照GB/T 19587-2017，采用氮气吸附比表面积分析测试方法测试，并用BET(Brunauer Emmett Teller)法计算得出，其中氮气吸附比表面积分析测试可以通过美国Micromeritics公司的Tri-Star 3020型比表面积孔径分析测试仪进行。
负极活性材料的克容量为本领域公知的含义，可以采用本领域已知的方法测试。示例性测试方法如下：将制备的负极活性材料、导电剂炭黑(Super P)、粘结剂聚偏氟乙烯(PVDF)按质量比91.6∶1.8∶6.6与溶剂N-甲基吡咯烷酮(NMP)中混合均匀，制成浆料；将制备好的浆料涂覆于铜箔集流体上，于烘箱中干燥后备用。以金属锂片为对电极，聚乙烯(PE)薄膜作为隔离膜。将碳酸亚乙酯(EC)、碳酸甲乙酯(EMC)、碳酸二乙酯(DEC)按体积比1∶1∶1混合，然后将LiPF 6均匀溶解在上述溶液中得到电解液，其中LiPF 6的浓度为1mol/L。在氩气保护的手套箱组装成CR2430型扣式电池。将所得扣式电池静置12小时后，在25℃下，以0.05C恒流放电至0.005V，静置10分钟，以50μA的电流再恒流放电至0.005V，静置10分钟，以10μA再恒流放电至0.005V；然后以0.1C恒流充电至2V，记录充电容量。充电容量与负极活性材料质量的比值即为所制备负极活性材料的克容量。
在本申请中，负极膜层的厚度为本领域公知的含义，可采用本领域已知的方法测试，例如万分尺(例如Mitutoyo293-100型，精度为0.1μm)。
在本申请中，第一负极膜层和第二负极膜层各自的厚度可以通过使用扫描电子显微镜(例如ZEISS Sigma 300)进行测试。样品制备如下：首先将负极极片裁成一定尺寸的待测样品(例如2cm×2cm)，通过石蜡将负极极片固定在样品台上。然后将样品台装进样品架上锁好固定，打开氩离子截面抛光仪(例如IB-19500CP)电源和抽真空(例如10 -4Pa)，设置氩气流量(例如0.15MPa)和电压(例如8KV)以及抛光时间(例如2小时)，调整样品台为摇摆模式开始抛光。样品测试可参考JY/T010-1996。为了确保测试结果的准确性，可以在待测样品中随机选取多个(例如5个)不同区域进行扫描测试，并在一定放大倍率(例如500倍)下，读取标尺测试区域中第一负极膜层和第二负极膜层各自的厚度，取多个测试区域的平均值作为测试结果。
在本申请中，负极膜层的面密度为本领域公知的含义，可采用本领域已知的方法测试。例如取单面涂布且经冷压后的负极极片(若是双面涂布的负极极片，可先擦拭掉其中一面的负极膜层)，冲切成面积为S1的小圆片，称其重量，记录为M1。然后将上述称重后的负极极片的负极膜层擦拭掉，称量负极集流体的重量，记录为M0，负极膜层 的面密度＝(负极极片的重量M1-负极集流体的重量M0)/S1。
在本申请中，负极膜层的压实密度为本领域公知的含义，可采用本领域已知的方法测试。负极膜层的压实密度＝负极膜层的面密度/负极膜层的厚度。
需要说明的是，上述针对负极膜层或负极活性材料的各种参数测试，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二次电池中取样时，作为示例，可以按如下步骤进行取样：
(1)将二次电池做放电处理(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2～10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℃，4h)，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℃，2h)，在烘烤后的负极极片中任选一区域，先对第一负极活性材料取样(可以选用刀片刮粉取样)，刮粉深度不超过第一负极膜层与第二负极膜层的分界区；然后用同样的方式对第二负极活性材料取样。
因在负极膜层制备过程中，第一负极膜层和第二负极膜层之间的分界区可能存在互融层(即互融层中同时存在第一负极活性材料和第二负极活性材料)，为了测试的准确性，在对第二负极活性材料取样时，可以先将互融层刮掉，然后再对第二负极活性材料刮粉取样。
(3)将步骤(2)收集到的第一负极活性材料和第二负极活性材料分别做过筛处理(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材料参数的第一负极活性材料和第二负极活性材料样品。
在上述取样过程中，可以用光学显微镜或扫描电子显微镜辅助判断第一负极膜层与第二负极膜层之间的分界区位置。
[正极极片]
本申请的二次电池中，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。
本申请的二次电池中，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。
在一些可选的实施方式中，为了进一步提高电池的能量密度，正极活性材料可以 包括式1所示的锂过渡金属氧化物及其改性化合物中的一种或几种，
Li aNi bCo cM dO eA f  式1，
式1中，0.8≤a≤1.2，0.5≤b＜1，0＜c＜1，0＜d＜1，1≤e≤2，0≤f≤1，M选自Mn、Al、Zr、Zn、Cu、Cr、Mg、Fe、V、Ti及B中的一种或几种，A选自N、F、S及Cl中的一种或几种。
在本申请中，上述各材料的改性化合物可以是对正极活性材料进行掺杂改性或表面包覆改性。
本申请的二次电池中，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。
本申请的二次电池中，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。
[电解质]
本申请的二次电池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。
在一些实施方式中，电解质盐可选自LiPF 6(六氟磷酸锂)、LiBF 4(四氟硼酸锂)、LiClO 4(高氯酸锂)、LiAsF 6(六氟砷酸锂)、LiFSI(双氟磺酰亚胺锂)、LiTFSI(双三氟甲磺酰亚胺锂)、LiTFS(三氟甲磺酸锂)、LiDFOB(二氟草酸硼酸锂)、LiBOB(二草酸硼酸锂)、LiPO 2F 2(二氟磷酸锂)、LiDFOP(二氟二草酸磷酸锂)及LiTFOP(四氟草酸磷酸锂)中的一种或几种。
在一些实施方式中，溶剂可选自碳酸亚乙酯(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)中的一种或几种。
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、改善电池低温性能的添加剂等。
[隔离膜]
采用电解液的二次电池、以及一些采用固态电解质的二次电池中，还包括隔离 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。
在一些实施方式中，正极极片、负极极片和隔离膜可通过卷绕工艺或叠片工艺制成电极组件。
在一些实施方式中，二次电池可包括外包装。该外包装可用于封装上述电极组件及电解质。
在一些实施方式中，二次电池的外包装可以是硬壳，例如硬塑料壳、铝壳、钢壳等。二次电池的外包装也可以是软包，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)等中的一种或几种。
本申请对二次电池的形状没有特别的限制，其可以是圆柱形、方形或其他任意的形状。如图1是作为一个示例的方形结构的二次电池5。
在一些实施方式中，参照图2，外包装可包括壳体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，底板和侧板围合形成容纳腔。壳体51具有与容纳腔连通的开口，盖板53用于盖设所述开口，以封闭所述容纳腔。正极极片、负极极片和隔离膜可经卷绕工艺或叠片工艺形成电极组件52。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。二次电池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。
在一些实施方式中，二次电池可以组装成电池模块，电池模块所含二次电池的数量可以为多个，具体数量可根据电池模块的应用和容量来调节。
图7是作为一个示例的电池模块4。参照图7，在电池模块4中，多个二次电池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二次电池5进行固定。
可选地，电池模块4还可以包括具有容纳空间的外壳，多个二次电池5容纳于该容纳空间。
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8和图9是作为一个示例的电池包1。参照图8和图9，在电池包1中可以包括电池箱和设置于电池箱中的多个电池模块4。电池箱包括上箱体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。
制备方法
本申请第二方面的实施方式提供一种二次电池的制备方法，包括通过如下步骤制备所述二次电池的负极极片：在负极集流体的至少一侧形成第二负极膜层，所述第二负极膜层包括第二负极活性材料；在所述第二负极膜层的表面上形成第一负极膜层，所述第一负极膜层包括第一负极活性材料；其中，所述第一负极活性材料包括第一石墨，所 述第一石墨为人造石墨，且所述第一负极活性材料的体积粒径分布D v99≤23μm。
本申请二次电池的制备方法中，可以将第一负极活性材料以及可选的导电剂、可选的粘结剂和其它可选助剂分散于溶剂(例如去离子水)中，形成第一负极活性材料浆料。可以将第二负极活性材料以及可选的导电剂、可选的粘结剂和其它可选助剂分散于溶剂(例如去离子水)中，形成第二负极活性材料浆料。
本申请二次电池的制备方法中，第一负极活性材料浆料和第二负极活性材料浆料可以一次同时涂布，也可以分两次涂布。
在一些实施方式中，第一负极活性材料浆料和第二负极活性材料浆料一次同时涂布。一次同时涂布可以使第一负极膜层和第二负极膜层之间的粘结性更好，有助于降低膜层界面电阻，进一步改善电池的快速充电能力和循环性能。
本申请所使用的第二负极活性材料以通过商业途径获得或本领域已知的方法制备得到。本领域技术人员可以根据实际使用环境做出恰当选择。
本申请所使用的第一负极活性材料中，第一石墨可采用本发明人自研的方法制备得到。具体的，第一石墨的制备方法包括以下步骤a)～e)。
a)提供石油焦原料，所述石油焦原料的D v99为15μm～21μm。可选的，石油焦原料的D v99为16μm～21μm，17μm～21μm，17μm～20μm，或17μm～19μm。
b)对石油焦原料进行整形、分级处理，得到前驱体，其中前驱体的D v99为16μm～22μm。可选的，前驱体的D v99为17μm～22μm，17.5μm～20μm，18μm～21μm，或18μm～20μm。
c)对所述前驱体进行造粒，得到造粒产物，所述造粒产物的D v99为17μm～24μm。可选的，造粒产物D v99为18μm～24μm，19μm～22μm，或19μm～21μm。
d)对所述造粒产物在2800℃～3200℃的温度下进行石墨化处理，经筛分，得到人造石墨，所述人造石墨的D v99为17μm～26μm。可选的，人造石墨的D v99为18μm～24μm，19μm～26μm，21μm～26μm，20μm～25μm，20μm～23μm，或19.5μm～22μm。
e)采用有机碳源对所述人造石墨进行包覆，经热处理，以在人造石墨的至少一部分表面形成无定形碳包覆层，经筛分，得到第一石墨。所述第一石墨的D v99≤23μm。
在一些实施方式中，步骤a)所述石油焦原料可包括石油系非针状焦、石油系针状焦中的一种或几种。作为示例，石油焦原料选自石油煅后焦、针状石油生焦和非针状石油生焦中的一种或几种。例如，所述石油焦原料包括非针状石油生焦。
在一些实施方式中，步骤a)所述石油焦原料的D v50为5.5μm～11μm；例如为6μm～11μm，7μm～10μm，6.5μm～8μm，7μm～8.5μm，或8μm～11μm。使石油焦原料的D v50在适当范围内，便于调控第一石墨的D v50在所需范围内。
在一些实施方式中，步骤a)中石油焦原料的挥发份含量C 1可以为1％～12％；例如为3％～10％，5％～9％，6％～8％，7％～8.5％，或7.5％～8.5％等。这样可以改善第一石墨的粒度分布。石油焦原料的挥发分含量可以采用本领域已知的方法测试。例如参照SH/T 0026-1990进行测定。
在一些实施方式中，步骤b)中前驱体的D v50为7μm～12μm；例如为7.5μm～11μm，或8μm～10μm。
在一些实施方式中，步骤b)中前驱体的粒度一致性(uniformity)U 1满足0.2≤U 1≤0.55；例如，0.2≤U 1≤0.5，0.25≤U 1≤0.45，0.3≤U 1≤0.45，0.3≤U 1≤0.4，0.35≤U 1≤0.55，或0.35≤U 1≤0.45。这样可以改善第一石墨的粒度一致性。
在一些实施方式中，步骤c)中造粒产物的D v50为8μm～14μm；例如为10μm～14μm，或11μm～13μm。
在一些实施方式中，在步骤c)，可以将前驱体与粘结剂进行混合；之后进行高温造粒。粘结剂可以为沥青。在步骤c)可采用本领域已知的设备进行造粒，例如造粒机。可选的，可以控制混合温度为20℃～40℃，混合频率为35Hz～38Hz，混合时间为50min～65min；然后以6～10℃/min升温至300℃～400℃，保温1h～2h；再以6～10℃/min升温至500℃～600℃，保温1h～2h；再以6～10℃/min升温至700℃～800℃，保温1h～2h；之后自然降温，得到造粒产物。
在一些实施方式中，在步骤c)，造粒过程加入的粘结剂用量C 2与石油焦原料的挥发份含量C 1之间满足8％≤C 1+C 2≤17％。这样可以改善造粒程度，使第一石墨的二次颗粒数量占比满足需求。例如，8％≤C 1+C 2≤15％，9％≤C 1+C 2≤14％，或10％≤C 1+C 2≤13％。造粒过程加入的粘结剂用量C 2是造粒过程加入粘结剂的重量占前驱体总重量的百分比。
在一些实施方式中，在步骤c)，造粒过程加入的粘结剂用量C 2与石油焦原料的挥发份含量C 1和前驱体的粒度一致性U 1之间满足21％≤(C 1+C 2)/U 1×100％≤50％。这样可以进一步改善造粒程度。例如，25％≤(C 1+C 2)/U 1×100％≤45％，25％≤(C 1+C 2)/U 1×100％≤38％，27％≤(C 1+C 2)/U 1×100％≤38％，30％≤(C 1+C 2)/U 1×100％≤40％，或31％≤(C 1+C 2)/U 1×100％≤35％。
在一些实施方式中，0％≤C 2≤16％；例如，1％≤C 2≤12％，2％≤C 2≤10％，4％≤C 2≤7％，或5％≤C 2≤9％。
在一些实施方式中，为了改善第一石墨的粒度一致性uniformity，步骤d)所得人造石墨的粒度一致性U 2可满足0.22≤U 2≤0.48。可选的，0.25≤U 2≤0.45，0.26≤U 2≤0.43，0.3≤U 2≤0.4，或0.33≤U 2≤0.38。
在一些实施方式中，在步骤e)，有机碳源可以选自沥青(例如煤沥青、石油沥青)、酚醛树脂、椰壳等中的一种或几种。
在一些实施方式中，在步骤e)，热处理的温度可以为700℃～1800℃，例如1000℃～1300℃。
在一些实施方式中，在步骤e)，包覆过程加入的有机碳源用量C 3与石油焦原料的挥发份含量C 1和造粒过程加入的粘结剂用量C 2之间满足10％≤C 1+C 2+C 3≤25％；例如，11％≤C 1+C 2+C 3≤20％，12％≤C 1+C 2+C 3≤18％，或13％≤C 1+C 2+C 3≤16％。包覆过程加入的有机碳源用量C 3与石油焦原料的挥发份含量C 1和造粒过程加入的粘结剂用量C 2之间满足之间满足上述关系，可以改善第一石墨中二次颗粒的数量占比。
包覆过程加入的有机碳源用量C 3是包覆过程加入有机碳源的重量占人造石墨总重量的百分比。在一些实施方式中，2％≤C 3≤8％，2％≤C 3≤5％，3％≤C 3≤5％，或2％≤C 3≤3％。
在一些实施方式中，在步骤e)，包覆过程加入的有机碳源用量C 3与焦原料的挥 发份含量C 1、造粒过程加入的粘结剂用量C 2以及人造石墨的粒度一致性U 2之间满足20％≤(C 1+C 2+C 3)/U 2×100％≤56％；例如，30％≤(C 1+C 2+C 3)/U 2×100％≤48％，40％≤(C 1+C 2+C 3)/U 2×100％≤48％。
在一些实施方式中，在步骤e)，有机碳源满足1.2％≤C 3×残炭率≤2.5％；例如，1.5％≤C 3×残炭率≤2.4％，1.8％≤C 3×残炭率≤2.3％，或2％≤C 3×残炭率≤2.2％。
当步骤e)还满足上述工艺条件时，可以进一步优化负极活性材料的粒度一致性，以及粒度比表面积和二次颗粒数量占比，从而进一步改善电池的性能。
残炭率是有机碳源的残炭率，可采用LP-5731煤沥青结焦值测试仪测定。测试可参考GB/T268《石油产品残炭测定法》、GB/T8727-2008《煤沥青类产品结焦值的测定方法》。
第一负极活性材料中的其它负极活性材料可以通过商业途径获得或本领域已知的方法制备得到。
除了本申请负极极片的制备方法外，本申请的二次电池的其它构造和制备方法是公知的。例如本申请的正极极片可以按如下制备方法：将正极活性材料以及可选的导电剂和粘结剂等混合后分散于溶剂(如NMP)中，搅拌均匀后涂覆在正极集流体上，烘干、冷压后，即得到正极极片。
在一些实施方式中，可将负极极片、正极极片、隔离膜和电解液组装形成二次电池。作为示例，可将正极极片、隔离膜、负极极片经卷绕工艺或叠片工艺形成电极组件；将电极组件置于外包装中，注入电解液，经过真空封装、静置、化成、整形等工序，得到二次电池。
本申请的二次电池的可选技术特征也同样适用于本申请的制备方法中。
装置
本申请第三方面的实施方式提供一种装置，所述装置包括本申请的二次电池、电池模块、或电池包中的至少一种。所述二次电池、电池模块或电池包可以用作所述装置的电源，也可以用作所述装置的能量存储单元。所述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。
所述装置可以根据其使用需求来选择二次电池、电池模块或电池包。
图10是作为一个示例的装置。该装置为纯电动车、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，可以采用电池包或电池模块。
作为另一个示例的装置可以是手机、平板电脑、笔记本电脑等。该装置通常要求轻薄化，可以采用二次电池作为电源。
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。
以下各实施例和对比例中，第二负极活性材料所采用的人造石墨A及天然石墨，第一负极活性材料中所采用的人造石墨C以及氧化亚硅SiO均可以通过商购获得，也可以通过如下方法制备获得。第一负极活性材料所采用的人造石墨B(即，第一石墨)可以通过本文所述的方法制备获得。
(一)人造石墨A的制备：
采用非针状石油生焦，粉碎得到石油焦原料；对石油焦原料进行整形、分级处理，得到前驱体；然后对前驱体在2800℃～3200℃下进行石墨化处理，得到人造石墨A。
在上述制备方法中，可选地，还可以采用粘结剂沥青对前驱体进行造粒，从而调整人造石墨A的颗粒形貌(例如，可以调整一次颗粒在人造石墨A中的数量占比)。
在上述过程中，通过调控材料制备工艺，使得人造石墨A满足：15μm≤D v50≤17.5μm，40μm≤D v99≤55μm，克容量为353mAh/g～370mAh/g。
(二)人造石墨B的制备：
采用石油焦，粉碎得到石油焦原料；对石油焦原料进行整形、分级得到前驱体；采用粘结剂沥青对前驱体进行造粒，然后对造粒产物在2800℃～3200℃下进行石墨化处理，得到人造石墨；再用沥青包覆人造石墨后，经炭化处理，筛分，得到人造石墨B。
在上述过程中，可以按照本申请前述所给制备工艺进行调控(详见表2)，使得人造石墨B满足：8μm≤D v50≤13μm，D v99≤23μm，克容量为348mAh/g～360mAh/g。
(三)人造石墨C的制备：
采用非针状石油生焦或石油煅后焦原料，对原料进行粉碎、整形、分级得到前驱体，采用粘结剂沥青对前驱体进行造粒，然后对造粒产物在2800℃～3200℃的温度下进行石墨化处理，再用沥青包覆人造石墨后，经炭化处理，筛分，得到人造石墨C。
在上述过程中，通过调控材料制备工艺，人造石墨C满足：12μm≤D v50≤17μm，25μm≤D v99≤45μm，克容量为350mAh/g～360mAh/g。
(四)天然石墨可购于深圳市贝特瑞新能源科技股份有限公司，天然石墨满足：12μm≤D v50≤19μm，24μm≤D v99≤37μm，克容量为360mAh/g～370mAh/g。
(五)氧化亚硅SiO可购于信越化学工业株式会社。
实施例1
负极极片的制备
将第二负极活性材料人造石墨A、导电剂炭黑(Super P)、粘结剂丁苯橡胶(SBR)和增稠剂羧甲基纤维素钠(CMC-Na)按96∶1.5∶1.5∶1的质量比在适量的溶剂去离子水中充分搅拌混合，使其形成均匀的第二负极浆料；其中，第二负极活性材料的D v99 1为45.2μm。
将第一负极活性材料人造石墨B、导电剂炭黑(Super P)、粘结剂丁苯橡胶(SBR)和增稠剂羧甲基纤维素钠(CMC-Na)按96∶1.5∶1.5∶1的质量比在适量的溶剂去离子水中充分搅拌混合，使其形成均匀的第一负极浆料；其中，第一负极活性材料的D v99 2为22.9μm。
通过双腔涂布设备，将第二负极浆料和第一负极浆料同时挤出。第二负极浆料涂覆在负极集流体铜箔上形成第二负极膜层，第一负极浆料涂覆在第二负极膜层上形成第一负极膜层；经干燥、冷压后，得到负极极片。其中，负极膜层的面密度为0.123mg/cm 2，压实密度为1.7g/cm 3，其中第二负极膜层与第一负极膜层的厚度之比为1∶1。
正极极片的制备
将正极活性材料LiNi 0.8Co 0.1Mn 0.1O 2(NCM811)、导电剂Super P、粘结剂聚偏氟乙烯(PVDF)按质量比97∶1.5∶1.5在适量的溶剂N-甲基吡咯烷酮(NMP)中充分搅拌混合，形成均匀的正极浆料；将正极浆料涂覆于正极集流体铝箔的表面，经干燥、冷压后，得到正极极片。其中，正极膜层的面密度为0.188mg/cm 2，压实密度为3.5g/cm 3。
电解液的制备
将碳酸亚乙酯(EC)、碳酸甲乙酯(EMC)、碳酸二乙酯(DEC)体积比4∶3∶3混合，然后将LiPF 6均匀溶解在上述溶液中得到电解液，其中LiPF 6的浓度为1mol/L。
隔离膜
采用PE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；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2～30及对比例1～6
制备方法与实施例1类似，不同的是：调控负极极片制备步骤中的相关参数，得到相应的二次电池，详见表2和表3。
测试部分
1)电池的快速充电能力测试
25℃下，将上述各实施例和对比例的电池以1C(即1h内完全放掉理论容量的电流值)的电流进行第一次充电和放电，具体包括：将电池以1C倍率恒流充电至电压4.25V，之后恒压充电至电流≤0.05C，静置5min，再以0.33C倍率恒流放电至电压2.8V，记录其实际容量为C0。
然后将电池依次以1.0C0、1.3C0、1.5C0、1.8C0、2.0C0、2.3C0、2.5C0、3.0C0、恒流充电至全电池充电截止电压4.25V或者0V负极截止电位(以先达到者为准)，每次充电完成后需以1C0放电至全电池放电截止电压2.8V，记录不同充电倍率下充电至10％、20％、30％、……、80％SOC(State of Charge，荷电状态)时所对应的负极电位，绘制出不同SOC态下的充电倍率-负极电位曲线，线性拟合后得出不同SOC态下负极电位为0V时所对应的充电倍率，该充电倍率即为该SOC态下的充电窗口，分别记为C10％SOC、C20％SOC、C30％SOC、C40％SOC、C50％SOC、C60％SOC、C70％SOC、C80％SOC，根据公式(60/C20％SOC+60/C30％SOC+60/C40％SOC+60/C50％SOC+60/C60％SOC+60/C70％SOC+60/C80％SOC)×10％计算得到该电池从10％SOC充电至80％SOC的充电时间T(在电池不析锂的前提下)，单位为min。该时间越短，则电池的快速充电能力越优秀。
2)电池存储性能测试
25℃下，将实施例和对比例制备得到的二次电池以1.0C恒流放电至2.8V；然后 以1.0C恒流充电至4.25V，继续恒压充电至电流≤0.05C，此时电池为满充状态，即100％SOC。将满充状态的电池静置5min后，以1.0C恒流放电至2.8V，此时的放电容量为电池1C/1C下的实际容量，记为C 0。
然后在25℃下，将电池以1C 0恒流充电至4.25V，继续恒压充电至电流≤0.05C，此时电池为满充状态。将满充状态的电池置于60℃的环境下存储。按照既定容量测试流程，不定期将电池取出，在25℃先将电池以1C 0恒流放电至2.8V，然后以1C 0恒流充电至4.25V，继续恒压充电至电流≤0.05C，静置5min后，以1.0C恒流放电至2.8V，此时的放电容量即为一个存储周期后的可逆容量，记为C n；此存储周期的容量保持率为C n/C 0×100％。重复存储测试流程，直至容量保持率为80％停止测试，记录此时的存储时间(天)。
需说明的是，每次将电池取出测试完容量后，均需将电池以1C 0充电至4.25V，之后恒压充电至电流≤0.05C，使电池为满充状态，然后置于60℃下存储。
3)电池的循环性能测试
25℃下，将实施例和对比例制备得到的二次电池以0.33C恒流充电至充电截止电压4.25V，之后恒压充电至电流为0.05C，静置5min，再以0.33C恒流放电至放电截止电压2.8V，记录其初始容量为C 0。然后按照表1所述策略进行充电，0.33C放电，记录每次循环的放电容量C n，直至循环容量保持率(C n/C 0×100％)为80％，记录循环圈数。循环圈数越多，则代表电池的循环寿命越高。
表1
电池的荷电状态SOC 充电倍率(C)
0～10％ 0.33
10％～20％ 4
20％～30％ 3
30％～40％ 2.4
40％～50％ 2
50％～60％ 1.6
60％～70％ 1.4
70％～80％ 1
80％～100％ 0.33
实施例1～30及对比例1～6的测试结果详见表3。
Figure PCTCN2020121255-appb-000002
Figure PCTCN2020121255-appb-000003
Figure PCTCN2020121255-appb-000004
由表3的结果可知，本申请实施例的二次电池通过采用多膜层结构的负极极片，并且使位于上层的第一负极膜层包含第一负极活性材料，且满足第一负极活性材料包括第一石墨，且第一负极活性材料的D v99≤23μm，由此使得电池在高SOC态可进行大倍率充电，从而显著提升快速充电能力。另外，电池还能兼顾更高的循环性能和较高的存储性能。
对比例1～6的电池不满足上述条件，其快速充电能力较差，循环寿命较短，还不利于存储性能的提升。
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 (26)

  1. 一种二次电池，包括负极极片(10)，所述负极极片(10)包括负极集流体(101)及负极膜层，所述负极膜层包括第一负极膜层(102)和第二负极膜层(103)，所述第二负极膜层(103)位于所述负极集流体(101)和所述第一负极膜层(102)之间；
    所述第一负极膜层(102)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，所述第一石墨为人造石墨，且所述第一负极活性材料的体积粒径分布D v99≤23μm。
  2. 根据权利要求1所述的二次电池，其中，所述第一负极活性材料满足17μm≤D v99≤23μm；可选的，18μm≤D v99≤21μm。
  3. 根据权利要求1～2任一项所述的二次电池，其中，所述第一负极活性材料满足8μm≤D v50≤13μm；可选的，9μm≤D v50≤12μm。
  4. 根据权利要求1～3任一项所述的二次电池，其中，所述第一负极活性材料的粒度一致性Uniformity为0.28～0.4，可选的为0.30～0.36。
  5. 根据权利要求1～4任一项所述的二次电池，其中，所述第一石墨中包括二次颗粒；可选的，所述二次颗粒在所述第一石墨中的数量占比≥50％；可选的，所述二次颗粒在所述第一石墨中的数量占比为80％～100％。
  6. 根据权利要求1～5任一项所述的二次电池，其中，所述第一负极活性材料的粒度比表面积为0.45m 2/g～0.65m 2/g，可选的为0.5m 2/g～0.63m 2/g。
  7. 根据权利要求1～6任一项所述的二次电池，其中，所述第一负极活性材料满足：0.6≤(D v90-D v10)/D v50≤1.8；可选的，0.8≤(D v90-D v10)/D v50≤1.4。
  8. 根据权利要求1～7任一项所述的二次电池，其中，所述第一负极活性材料的体积粒径分布D v10为5μm～9μm，可选的为6μm～8μm；或，
    所述第一负极活性材料的体积粒径分布D v90为14μm～21μm，可选的为16μm～18μm。
  9. 根据权利要求1～8任一项所述的二次电池，其中，所述第一负极活性材料还满足下述(1)～(5)中的一个或几个：
    (1)所述第一负极活性材料的粉体OI值为2.0～4.0，可选的为2.3～3.6；
    (2)所述第一负极活性材料的振实密度为0.85g/cm 3～1.4g/cm 3，可选地为0.9g/cm 3～1.2g/cm 3；
    (3)所述第一负极活性材料在2kN压力下的粉体压实密度为1.55g/cm 3～1.70g/cm 3，可选地为1.58g/cm 3～1.68g/cm 3
    (4)所述第一负极活性材料的比表面积(SSA)为0.8m 2/g～1.3m 2/g，可选的为0.9m 2/g～1.2m 2/g；
    (5)所述第一负极活性材料的克容量为345mAh/g～360mAh/g，可选的为350mAh/g～358mAh/g。
  10. 根据权利要求1～9任一项所述的二次电池，其中，所述第一石墨的至少一部分表面具有无定形碳包覆层。
  11. 根据权利要求1～10任一项所述的二次电池，其中，所述第一石墨在所述第一负极活性材料中的质量占比≥80％；可选的，所述第一石墨在所述第一负极活性材料中的质量占比为90％～100％。
  12. 根据权利要求1～11任一项所述的二次电池，其中，所述第二负极膜层(103)包括第二负极活性材料，所述第二负极活性材料包括第二石墨，所述第二石墨包括人造石墨、天然石墨中的一种或几种。
  13. 根据权利要求12所述的二次电池，其中，所述第二石墨中人造石墨的质量占比≥50％；可选的，所述第二石墨中人造石墨的质量占比为60％～100％。
  14. 根据权利要求12～13任一项所述的二次电池，其中，所述第二负极活性材料的体积粒径分布D v99大于所述第一负极活性材料的体积粒径分布D v99；
    可选的，所述第二负极活性材料的体积粒径分布D v99与所述第一负极活性材料的体积粒径分布D v99之比为2.0～2.6，可选的为2.1～2.4。
  15. 根据权利要求12～14任一项所述的二次电池，其中，所述第二负极活性材料的体积平均粒径D v50为15μm～21μm，可选的为16.5μm～20μm。
  16. 根据权利要求12～15任一项所述的二次电池，其中，所述第二负极活性材料的粒度一致性Uniformity为0.3～0.55，可选的为0.4～0.5。
  17. 根据权利要求12～16任一项所述的二次电池，其中，所述第二石墨中包括一次颗粒；可选的，所述一次颗粒在所述第二石墨中的数量占比≥50％；可选的，所述一次颗粒在所述第二石墨中的数量占比为60％～100％。
  18. 根据权利要求12～17任一项所述的二次电池，其中，所述第二负极活性材料的粒度比表面积为0.35m 2/g～0.55m 2/g，可选的为0.38m 2/g～0.50m 2/g。
  19. 根据权利要求12～18任一项所述的二次电池，其中，所述第二负极活性材料还满足下述(1)～(8)中的一个或几个：
    (1)所述第二负极活性材料满足：0.9≤(D v90-D v10)/D v50≤1.6；可选的，1.0≤(D v90-D v10)/D v50≤1.4；
    (2)所述第二负极活性材料的体积粒径分布D v10为5μm～14μm，可选的为7μm～12μm；
    (3)所述第二负极活性材料的体积粒径分布D v90为24μm～38μm，可选的为26μm～33μm；
    (4)所述第二负极活性材料的粉体OI值≤14，可选的为6～11；
    (5)所述第二负极活性材料的振实密度为0.8g/cm 3～1.2g/cm 3，可选地为0.9g/cm 3～1.1g/cm 3；
    (6)所述第二负极活性材料在2kN压力下的粉体压实密度为1.70g/cm 3～1.85g/cm 3，可选地为1.75g/cm 3～1.82g/cm 3；
    (7)所述第二负极活性材料的比表面积(SSA)为1.0m 2/g～2.0m 2/g，可选的为1.3m 2/g～1.8m 2/g；
    (8)所述第二负极活性材料的克容量为353mAh/g～370mAh/g，可选的为359mAh/g～367mAh/g。
  20. 根据权利要求1～19任一项所述的二次电池，其中，所述负极膜层还满足下述(1)～ (3)中的一个或几个：
    (1)所述负极膜层的面密度为0.117mg/mm 2～0.130mg/mm 2，可选的为0.120mg/mm 2～0.127mg/mm 2；
    (2)所述负极膜层的压实密度为1.65g/cm 3～1.75g/cm 3，可选的为1.66g/cm 3～1.70g/cm 3；
    (3)所述第二负极膜层(103)与所述第一负极膜层(102)的厚度比为0.7∶1～2.3∶1，可选的为0.7∶1～1.0∶1，再可选的为1.1∶1～2.3∶1。
  21. 根据权利要求12～20任一项所述的二次电池，其中，所述第一负极活性材料或所述第二负极活性材料中还包括硅基材料、锡基材料、软碳、硬碳、钛酸锂中的一种或几种。
  22. 根据权利要求1～21任一项所述的二次电池，其中，所述二次电池包括正极极片，所述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上且包括正极活性材料的正极膜层，所述正极活性材料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改性化合物中的一种或几种；
    可选的，所述正极活性材料包括式1所示的锂过渡金属氧化物及其改性化合物中的一种或几种，
    Li aNi bCo cM dO eA f  式1，
    所述式1中，0.8≤a≤1.2，0.5≤b＜1，0＜c＜1，0＜d＜1，1≤e≤2，0≤f≤1，M选自Mn、Al、Zr、Zn、Cu、Cr、Mg、Fe、V、Ti及B中的一种或几种，A选自N、F、S及Cl中的一种或几种。
  23. 一种二次电池的制备方法，至少包括如下步骤：
    在负极集流体的至少一侧形成第二负极膜层，所述第二负极膜层包括第二负极活性材料；
    在所述第二负极膜层的表面上形成第一负极膜层，所述第一负极膜层包括第一负极活性材料；
    其中，所述第一负极活性材料包括第一石墨，所述第一石墨为人造石墨，且所述第一负极活性材料的体积粒径分布D v99≤23μm。
  24. 一种电池模块，包括根据权利要求1～22任一项所述的二次电池、或根据权利要求23所述的方法制备的二次电池。
  25. 一种电池包，包括根据权利要求1～22任一项所述的二次电池、根据权利要求23所述的方法制备的二次电池、或根据权利要求24所述的电池模块。
  26. 一种装置，包括根据权利要求1～22任一项所述的二次电池、根据权利要求23所述的方法制备的二次电池、根据权利要求24所述的电池模块、或根据权利要求25所述的电池包中的至少一种。
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JP2025524996A (ja) * 2023-02-13 2025-08-01 香港時代新能源科技有限公司 二次電池及び電力消費装置
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WO2026020380A1 (zh) * 2024-07-24 2026-01-29 宁德时代新能源科技股份有限公司 电池单体、电池装置以及用电装置
CN118538913A (zh) * 2024-07-25 2024-08-23 国科炭美新材料(湖州)有限公司 一种硬炭微球负极材料及其制备方法和应用
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CN119852479A (zh) * 2024-09-18 2025-04-18 宁德时代新能源科技股份有限公司 二次电池和用电装置
CN119852479B (zh) * 2024-09-18 2025-10-10 宁德时代新能源科技股份有限公司 二次电池和用电装置
WO2026060957A1 (zh) * 2024-09-18 2026-03-26 宁德时代新能源科技股份有限公司 二次电池和用电装置
CN120127103A (zh) * 2025-02-17 2025-06-10 宁德时代新能源科技股份有限公司 电池单体、电池装置、用电装置

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EP4138154A4 (en) 2024-03-06
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US12431496B2 (en) 2025-09-30
US20230117662A1 (en) 2023-04-20

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