WO2022077371A1 - 二次电池、其制备方法、及其相关的电池模块、电池包和装置 - Google Patents

二次电池、其制备方法、及其相关的电池模块、电池包和装置 Download PDF

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WO2022077371A1
WO2022077371A1 PCT/CN2020/121264 CN2020121264W WO2022077371A1 WO 2022077371 A1 WO2022077371 A1 WO 2022077371A1 CN 2020121264 W CN2020121264 W CN 2020121264W WO 2022077371 A1 WO2022077371 A1 WO 2022077371A1
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Prior art keywords
negative electrode
active material
film layer
electrode active
electrode film
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PCT/CN2020/121264
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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 PCT/CN2020/121264 priority Critical patent/WO2022077371A1/zh
Priority to EP20957150.4A priority patent/EP4064385A4/en
Priority to JP2022543793A priority patent/JP7412574B2/ja
Priority to KR1020227024936A priority patent/KR102622786B1/ko
Priority to CN202080084914.4A priority patent/CN114788044A/zh
Publication of WO2022077371A1 publication Critical patent/WO2022077371A1/zh
Priority to US17/853,229 priority patent/US11631852B2/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
    • H01M4/36—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
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • 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
    • H01M4/362—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
    • H01M4/58—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
    • H01M4/621—Binders
    • H01M4/622—Binders being polymers
    • H01M4/623—Binders being polymers fluorinated polymers
    • 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
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/20—Mountings; Secondary casings or frames; Racks, modules or packs; Suspension devices; Shock absorbers; Transport or carrying devices; Holders
    • H01M50/204—Racks, modules or packs for multiple batteries or multiple cells
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/20—Mountings; Secondary casings or frames; Racks, modules or packs; Suspension devices; Shock absorbers; Transport or carrying devices; Holders
    • H01M50/204—Racks, modules or packs for multiple batteries or multiple cells
    • H01M50/207—Racks, modules or packs for multiple batteries or multiple cells characterised by their shape
    • H01M50/209—Racks, modules or packs for multiple batteries or multiple cells characterised by their shape adapted for prismatic or rectangular cells
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2220/00—Batteries for particular applications
    • H01M2220/20—Batteries in motive systems, e.g. vehicle, ship, plane
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present application belongs to the technical field of electrochemistry, and more particularly, relates to a secondary battery, its preparation method, and related battery modules, battery packs and devices.
  • the secondary battery As a new type of high-voltage, high-energy-density rechargeable battery, the secondary battery has outstanding features such as light weight, high energy density, no pollution, no memory effect, and long service life, so it is widely used in the new energy industry.
  • the purpose of the present application is to provide a secondary battery and its preparation method, and its related battery modules, battery packs and devices, aiming to make the battery in a high energy density On the premise, it has good fast charging performance and cycle performance at the same time.
  • a first aspect of the present application provides a secondary battery, comprising a negative electrode pole piece, the negative electrode pole piece is a multi-layer structure, and the multi-layer structure sequentially includes: a negative electrode current collector, an undercoat layer 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, and the first negative electrode film layer is located between the primer layer and the second negative electrode film layer; the The first negative electrode film layer includes a first negative electrode active material, the first negative electrode active material includes a first artificial graphite, at least a part of the particles in the first artificial graphite are secondary particles, and the secondary particles are in the The number ratio A in the total number of particles of the first negative electrode active material satisfies: A ⁇ 50%.
  • the film layer of the negative electrode plate of the secondary battery of the present application includes at least two layers.
  • the first negative electrode active material includes the first artificial graphite with a specific content and shape, and the current collector is simultaneously provided with a primer layer
  • the secondary battery can be made to take into account better fast charging performance and longer cycle life under the premise of higher energy density.
  • the battery module, battery pack and device of the present application all include the secondary battery provided by the present application, and thus have at least the same advantages as the secondary battery.
  • a ⁇ 60%; optionally, 70% ⁇ A ⁇ 100% When A is within the given range, the fast charging performance of the battery can be further improved.
  • the primer layer includes a binder and a conductive agent.
  • the mass proportion of the binder in the primer layer is ⁇ 50%, and may be optionally 30% to 45%.
  • the cycle performance of the battery can be further improved.
  • the mass proportion of the conductive agent in the undercoat layer is ⁇ 50%, and may be optionally 55% to 70%.
  • the content of the conductive agent is within the given range, the fast charging performance of the battery can be further improved.
  • the thickness of the undercoat layer is greater than or equal to 1 ⁇ m; optionally, the thickness of the undercoat layer is 1.5 ⁇ m ⁇ 5 ⁇ m.
  • the primer layer thickness in this range contributes to the balance between the fast charging performance and cycling performance of the battery.
  • the binder in the primer layer may include styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), polyvinylidene fluoride copolymer (eg, polyvinylidene fluoride-hexafluoropropylene) , polystyrene, polyacrylic acid, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyurethane, polyvinyl alcohol, polyvinyl butyral (PVB), polyacrylate, acrylic-acrylonitrile copolymer, ethylene -One or more of vinyl acetate copolymer (EVA), acrylate-acrylonitrile copolymer, and modified compounds of the above materials.
  • SBR styrene-butadiene rubber
  • PVDF polyvinylidene fluoride
  • PVDF polyvinylidene fluoride copolymer
  • EVA vinyl acetate copolymer
  • the conductive agent may include a conductive carbon material; for example, the conductive agent may include one of acetylene black, conductive carbon black, Ketjen black, carbon nanotubes, carbon fibers, graphene, or several.
  • the first negative electrode active material may further include natural graphite; optionally, the mass ratio of the natural graphite in the first negative electrode active material is ⁇ 50%. This helps to improve the power performance of the battery and the fast charging performance of the battery, and helps to flexibly adjust various performances of the battery to meet the usage requirements of different occasions.
  • the volume distribution average particle size D V 50 of the first negative electrode active material satisfies: D V 50 ⁇ 15 ⁇ m, optionally, 17 ⁇ m ⁇ DV 50 ⁇ 23 ⁇ m. This helps to further improve the energy density and cycle performance of the battery.
  • the particle size uniformity (Uniformity) of the first negative electrode active material is greater than or equal to 0.20, optionally 0.20-0.60, or 0.25-0.45. This helps to further improve the fast charging performance and cycling performance of the battery.
  • the specific surface area SSA of the first negative electrode active material satisfies: SSA ⁇ 1.6m 2 /g, optionally, 0.4m 2 /g ⁇ SSA ⁇ 1.5m 2 /g. This helps to further improve the fast charging performance and cycling performance of the battery.
  • the particle size distribution of the first negative electrode active material is 0.6 ⁇ (DV 90-DV 10)/DV 50 ⁇ 3.5 , optionally, 0.7 ⁇ ( DV 90- DV 10 )/D V 50 ⁇ 2.8. This helps to further improve the fast charging performance of the battery.
  • the powder OI of the first negative electrode active material is less than or equal to 8.5, and can be optionally 1.8 to 7.5. This helps to further improve the fast charging performance of the battery and reduce the swelling of the battery.
  • the gram capacity of the first negative electrode active material is greater than or equal to 352 mAh/g, and can be optionally 353 mAh/g to 370 mAh/g. This helps to further increase the energy density of the battery.
  • the second negative electrode active material includes second artificial graphite; optionally, the mass ratio of the second artificial graphite in the second negative electrode active material is ⁇ 80%, for example, ⁇ 90%. This helps to improve the fast charging performance and cycle performance of the battery, and helps to flexibly adjust the performance of the battery to suit the usage requirements of different occasions.
  • At least a part of the particles in the second artificial graphite are secondary particles.
  • the number proportion B of the secondary particles in the total number of particles of the second negative electrode active material satisfies: B ⁇ 60%; optionally, 80% ⁇ B ⁇ 100%. This further improves the fast charging performance of the battery.
  • the volume distribution average particle size D V 50 of the second negative electrode active material satisfies: 7 ⁇ m ⁇ DV50 ⁇ 15 ⁇ m, optionally, 9 ⁇ m ⁇ DV 50 ⁇ 13.5 ⁇ m. This helps to further improve the fast charging and cycling performance of the battery.
  • the particle size uniformity (Uniformity) of the second negative electrode active material is 0.20-0.50, optionally 0.25-0.4. This helps to further improve the fast charging and cycling performance of the battery.
  • the specific surface area SSA of the second negative electrode active material satisfies: SSA ⁇ 1.6m 2 /g, optionally, 0.4m 2 /g ⁇ SSA ⁇ 1.55m 2 /g. This helps to further improve the fast charging and cycling performance of the battery.
  • the particle size distribution of the second negative electrode active material is 0.5 ⁇ (DV 90-DV 10)/DV 50 ⁇ 3.0 , optionally, 0.8 ⁇ ( DV 90- DV 10 )/D V 50 ⁇ 2.8. This helps to further improve the fast charging and cycling performance of the battery.
  • the powder OI of the second negative electrode active material is less than or equal to 6, and can be selected to be 1.5 to 5.5. This helps to further improve the swelling, fast charging and cycling performance of the battery.
  • the gram capacity of the second negative electrode active material is greater than or equal to 345 mAh/g, and can be optionally 348 mAh/g to 360 mAh/g. This helps to further improve the electrical performance of the battery.
  • the ratio of the particle size uniformity (Uniformity) of the second negative electrode active material to the particle size uniformity (Uniformity) of the first negative electrode active material is 0.6-2, optionally 0.8-1.25 . This helps to further improve the fast charging and cycling performance of the battery.
  • the areal density of the negative electrode film layer is ⁇ 0.117 mg/mm 2 , and can be optionally 0.119-0.130 mg/mm 2 . This helps to further improve the energy density of the battery.
  • the compaction density of the negative electrode film layer is 1.4 g/cm 3 to 1.75 g/cm 3 , optionally 1.65 to 1.75 g/cm 3 . This helps to further improve the fast charging performance and energy density of the battery.
  • the thickness ratio of the second negative electrode film layer to the first negative electrode film layer is 1:1 to 3:2. This helps to further improve the fast charging performance of the battery.
  • the ratio of the OI value of the second negative electrode active material to the first negative electrode active material is ⁇ 1.2. This helps to further improve the swelling, fast charging and cycling performance of the battery.
  • a second aspect of the present application provides a method for preparing a secondary battery, comprising at least the following steps:
  • a primer coating is provided on at least one side of the negative electrode current collector
  • the secondary battery includes a negative pole piece, the negative pole piece is a multi-layer structure, and the multi-layer structure sequentially includes: a negative electrode current collector, an undercoat layer and a negative electrode film layer; the negative electrode film layer includes a third a negative electrode film layer and a second negative electrode film layer, and the first negative electrode film layer is located between the primer layer and the second negative electrode film layer; the first negative electrode film layer includes a first negative electrode active material,
  • the first negative active material includes a first artificial graphite, at least a part of the particles in the first artificial graphite are secondary particles, and the number of the secondary particles in the total number of particles of the first negative active material accounts for Ratio A satisfies: A ⁇ 50%.
  • a third aspect of the present application provides a battery module comprising the secondary battery described in the first aspect of the present application or the secondary battery manufactured according to the method described in the second aspect of the present application.
  • a fourth aspect of the present application provides a battery pack including the battery module described in the third aspect of the present application.
  • a fifth aspect of the present application provides a device comprising the secondary battery described in the first aspect of the present application, the secondary battery manufactured according to the method described in the second aspect of the present application, and the battery module described in the third aspect of the present application , or at least one of the battery packs described in the fourth aspect of the present application.
  • FIG. 1 is a schematic diagram of an embodiment of a negative electrode sheet in a secondary battery of the present application.
  • FIG. 2 is a schematic diagram of another embodiment of the negative electrode tab in the secondary battery of the present application.
  • FIG. 3 is a SEM image of an embodiment of the first negative electrode active material.
  • FIG. 4 is a SEM image of an embodiment of the second negative electrode active material.
  • FIG. 5 is a schematic diagram of an embodiment of the secondary battery of the present application.
  • FIG. 6 is an exploded schematic view of the secondary battery shown in FIG. 5 .
  • FIG. 7 is a schematic diagram of one embodiment of a battery module.
  • FIG. 8 is a schematic diagram of an embodiment of a battery pack.
  • 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).
  • Secondary battery also known as rechargeable battery or accumulator, refers to a battery that can be used by activating the active material by charging 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 plate, which usually includes a negative electrode current collector and a negative electrode film layer.
  • the thickness of the negative electrode film layer is often increased, but the increase in the thickness will affect both the fast charging performance and the cycle performance of the battery. Therefore, how to make the battery have both good fast charging performance and cycle performance under the premise of high energy density is still a huge technical challenge.
  • the negative pole piece in the secondary battery of the present application has a multi-layer structure, and the multi-layer structure sequentially includes: a negative electrode current collector, an undercoat layer and a negative electrode film layer; the negative electrode film layer includes a first negative electrode film layer and the second negative electrode film layer, and the first negative electrode film layer is located between the primer layer and the second negative electrode film layer; the first negative electrode film layer includes a first negative electrode active material, the first negative electrode film layer A negative electrode active material includes a first artificial graphite, at least a part of the particles in the first artificial graphite are secondary particles, and the number ratio A of the secondary particles in the total number of particles of the first negative electrode active material satisfies : A ⁇ 50%.
  • the secondary battery can have both good fast charging performance and cycle performance under the premise of high energy density.
  • the inventors have found through research that when the negative electrode pole piece includes at least two film layers, and the first negative electrode film layer includes artificial graphite with secondary particle morphology, the energy density and fast charging performance of the battery can be significantly improved; At the same time, the inventor found that when the proportion of secondary particles in the first negative electrode active material is within the range specified in this application, although the fast charging performance of the battery can be effectively improved, the cycle performance will be affected to a certain extent. .
  • the inventor surprisingly found that when the negative pole piece includes at least two film layers, and the proportion of the first artificial graphite with the secondary particle morphology in the first negative film layer is specified in this application within the range of , if a primer layer is also provided between the current collector and the first negative electrode film layer, the cycle performance of the battery can be greatly improved.
  • the inventors found that when a primer layer is provided on the surface of the current collector, the primer layer can bridge the current collector and the angular structure of artificial graphite with secondary particle morphology in the first negative electrode film layer, which significantly improves the The charge transfer ability between the first negative electrode active material and the negative electrode current collector is improved, thereby effectively improving the cycle performance of the battery.
  • the primer 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 film layer can also be arranged on one side or both sides of the negative electrode current collector.
  • the undercoat layer includes a conductive agent and a binder.
  • FIG. 1 shows a schematic diagram of an embodiment of the negative pole piece 10 of the present application.
  • the negative electrode sheet 10 includes a negative electrode current collector 101 , a primer layer 102 respectively disposed on both sides of the negative electrode current collector, a first negative electrode film layer 103 and a second negative electrode film layer 104 .
  • FIG. 2 shows a schematic diagram of another embodiment of the negative pole piece 10 of the present application.
  • the negative electrode sheet 10 includes a negative electrode current collector 101 , a primer layer 102 disposed on one side of the negative electrode current collector, a first negative electrode film layer 103 and a second negative electrode film layer 104 .
  • the negative pole piece of the present application can further improve the performance of the secondary battery if it also optionally satisfies one or more of the following parameters.
  • the mass ratio of the conductive agent in the primer layer is ⁇ 50%, for example, it may be 50%-75%, 55%-70%, 60%-70%, 58%-68%, 65% to 72%.
  • the conductive agent is within the given range, the fast charging performance and cycle performance of the battery can be further improved.
  • the mass proportion of the binder in the primer layer is ⁇ 50%, for example, it can be 25%-50%, 30%-45%, 30%-40%, 32%-42% , 28% to 35%.
  • the conductive agent may include a conductive carbon material; for example, the conductive agent may include one or more of acetylene black, conductive carbon black, Ketjen black, carbon nanotubes, carbon fibers, and graphene .
  • the binder may include styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), copolymers of vinylidene fluoride (eg, vinylidene fluoride-hexafluoropropylene copolymer), polystyrene , polyacrylic acid, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyurethane, polyvinyl alcohol, polyvinyl butyral (PVB), polyacrylate, acrylic-acrylonitrile copolymer, ethylene-vinyl acetate One or more of copolymers (EVA), acrylate-acrylonitrile copolymers, and modified compounds of the above materials.
  • SBR styrene-butadiene rubber
  • PVDF polyvinylidene fluoride
  • VDF polyvinylidene fluoride
  • VDF polyvinylidene fluoride
  • VDF polyvinylidene fluoride
  • the primer layer may also include other conventional adjuvants or additives such as thickeners.
  • the thickener may be sodium carboxymethyl cellulose (CMC-Na).
  • the thickness H of the primer layer (single-side coating) satisfies: H ⁇ 1 ⁇ m; for example, 1.5 ⁇ m ⁇ H ⁇ 5 ⁇ m, 1.5 ⁇ m ⁇ H ⁇ 4 ⁇ m, 2.5 ⁇ H ⁇ 4.5.
  • the number ratio A of the secondary particles in the first negative electrode active material satisfies: A ⁇ 60%, for example, 60% ⁇ A ⁇ 100%, 70% ⁇ A ⁇ 98%, 75% ⁇ A ⁇ 96%, 80% ⁇ A ⁇ 95% or 85% ⁇ A ⁇ 100%.
  • A is within the given range, the fast charging performance of the battery can be further improved.
  • the volume distribution average particle size D V 50 of the first negative electrode active material satisfies: D V 50 ⁇ 14 ⁇ m; for example, the range of D V 50 may be: 15 ⁇ m ⁇ D V 50 ⁇ 25 ⁇ m, 16 ⁇ m ⁇ D V 50 ⁇ 25 ⁇ m, 17 ⁇ m ⁇ DV 50 ⁇ 25 ⁇ m , 17 ⁇ m ⁇ DV 50 ⁇ 24 ⁇ m , 17 ⁇ m ⁇ DV 50 ⁇ 23 ⁇ m, 18.3 ⁇ m ⁇ DV 50 ⁇ 23 ⁇ m.
  • the first negative electrode active material contains the first artificial graphite with a specific content and morphology, and its D V 50 is controlled within a given range, the lithium intercalation capacity and compaction density of the first negative electrode film layer can be kept relatively high.
  • the first negative electrode film layer can effectively share the pressure of the second negative electrode film layer, so that the second negative electrode film layer maintains a better pore structure and reduces the resistance of active ion transfer. , to further improve the fast charging performance of the battery.
  • the uniformity of particle size of the first negative electrode active material satisfies (abbreviated as U): 0.20 ⁇ U ⁇ 0.60; for example, the range of U may be: 0.25 ⁇ U ⁇ 0.60, 0.25 ⁇ U ⁇ 0.55, 0.25 ⁇ U ⁇ 0.45, 0.25 ⁇ U ⁇ 0.50, 0.30 ⁇ U ⁇ 0.50, 0.30 ⁇ U ⁇ 0.40, 0.28 ⁇ U ⁇ 0.35.
  • the active ion transmission paths in the first negative electrode film layer are optimally matched, effectively reducing the The impedance of the active ions in the liquid phase conduction is determined, and the active ions in each region can quickly complete the liquid phase conduction and be embedded in the negative electrode active material, further improving the fast charging performance of the battery.
  • the particle size distribution of the first negative active material (DV 90-DV 10)/DV 50 satisfies 0.6 ⁇ ( DV 90- DV 10)/ DV 50 ⁇ 3.5 ; for example, 1.0 ⁇ (D V 90-D V 10)/D V 50 ⁇ 3.0, 0.8 ⁇ (D V 90-D V 10)/D V 50 ⁇ 2.5, 1.0 ⁇ (D V 90-D V 10)/D V 50 ⁇ 2.3, 1.1 ⁇ (DV 90-DV 10)/DV 50 ⁇ 2.3 , 1.1 ⁇ (DV 90-DV 10)/ DV 50 ⁇ 1.9 , 0.7 ⁇ ( DV 90- DV 10)/ D V 50 ⁇ 1.6, 0.9 ⁇ (D V 90-D V 10)/D V 50 ⁇ 2.0.
  • the first negative electrode active material contains the first artificial graphite with a specific content and morphology, and the particle size distribution is controlled within a given range, during the battery preparation process, it is beneficial to uniformly disperse the active material in the slurry, and can It can effectively prevent the leakage and uneven coating of the negative film layer during the coating process, which can make the negative pole piece have high ion and electron transport performance, and the polarization of the battery can be alleviated, thereby further improving the rapidity of the battery. Charge performance and cycle performance.
  • the specific surface area SSA of the first negative active material satisfies: SSA ⁇ 1.6m 2 /g; for example, the range of SSA may be: 0.4m 2 /g ⁇ SSA ⁇ 1.6m 2 /g, 0.5m 2 /g ⁇ SSA ⁇ 1.5m 2 /g, 0.6m 2 /g ⁇ SSA ⁇ 1.5m 2 /g, 0.7m 2 /g ⁇ SSA ⁇ 1.3m 2 / g.
  • the first negative electrode active material contains the first artificial graphite with a specific content and morphology, and its SSA is controlled within a given range, the charge exchange resistance can be reduced, and the negative electrode film layer can obtain more developed pores, reducing the The liquid-phase conduction impedance of active ions and the consumption of the electrolyte further improve the cycle performance of the battery.
  • the gram capacity C of the first negative active material satisfies: C ⁇ 352mAh/g; for example, the range of C may be: 353mAh/g ⁇ C ⁇ 370mAh/g, 354mAh/g ⁇ C ⁇ 370mAh/g , 355mAh/g ⁇ C ⁇ 365mAh/g, 355mAh/g ⁇ C ⁇ 364mAh/g, etc.
  • the first negative electrode active material contains the first artificial graphite with a specific content and morphology, and its gram capacity C is controlled within a given range, the negative electrode active material can have higher lithium intercalation capacity and higher lithium intercalation capacity. Good structural stability, which can further improve the energy density and cycle performance of the battery.
  • the OI of the first negative active material satisfies: OI ⁇ 8.5; for example, the range of OI may be: 1.8 ⁇ OI ⁇ 7.5, 1.9 ⁇ OI ⁇ 6.5, 2.0 ⁇ OI ⁇ 5.5, 2.2 ⁇ OI ⁇ 3.8 Wait.
  • the active material has better isotropy, which is conducive to the rapid insertion and extraction of active ions, and further Improve the fast charging performance of the battery; and the higher isotropy can disperse the Z-axis expansion when the active particles are embedded, thereby further improving the cycling performance of the battery.
  • the second negative active material includes a second artificial graphite.
  • the mass ratio of the second artificial graphite in the second negative electrode active material is ⁇ 80%; for example, it may be 80%-100%, 90%-100%, 95%-100% .
  • the second negative active material includes a second artificial graphite in a secondary particle morphology.
  • the number ratio B of the second artificial graphite with the secondary particle morphology in the second negative electrode active material satisfies: B ⁇ 60%; for example, B may be 60% ⁇ B ⁇ 100%, 65% ⁇ B ⁇ 98%, 70% ⁇ B ⁇ 100%, 70% ⁇ B ⁇ 95%, 75% ⁇ B ⁇ 95%, 80% ⁇ B ⁇ 100%, or 85% ⁇ B ⁇ 95%.
  • the secondary particle ratio B of the second negative electrode active material is controlled within the given range, the expansion of the active material during cycling can be significantly reduced, thereby further improving the cycle performance of the battery;
  • the artificial graphite with a specific content of secondary particles is used, the accumulation and connection between the upper and lower active material particles are more closely, and at the same time, the contact area of the active material particles at the interface of the first negative electrode film layer and the second negative electrode film layer can be increased.
  • a three-dimensional, ordered and high-speed active ion entry and exit channel is formed, which improves the electronic conductance and shortens the migration path of the active ion, thereby further improving the fast charging performance of the battery.
  • the volume distribution average particle size D V 50 of the second negative electrode active material satisfies: D V 50 ⁇ 18 ⁇ m; for example, the range of D V 50 may be: 7 ⁇ m ⁇ DV 50 ⁇ 18 ⁇ m, 7 ⁇ m ⁇ DV 50 ⁇ 15 ⁇ m, 8 ⁇ m ⁇ D V 50 ⁇ 17 ⁇ m, 9 ⁇ m ⁇ D V 50 ⁇ 17 ⁇ m, 10 ⁇ m ⁇ D V 50 ⁇ 15 ⁇ m, 9 ⁇ m ⁇ D V 50 ⁇ 13.5 ⁇ m, 10.5 ⁇ m ⁇ D V 50 ⁇ 14 ⁇ m, 11.5 ⁇ m ⁇ D V 50 ⁇ 13.5 ⁇ m.
  • the pore structures in the first negative electrode film layer and the second negative electrode film layer are optimally maintained, and the active ion transmission paths are optimally matched, effectively reducing the The liquid-phase conduction impedance of active ions is improved, and the fast charging performance of the battery is further improved.
  • other negative active materials may also be included in the first negative active material or the second negative active material.
  • Other negative active materials may include one or more of natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and titanium-based materials.
  • the silicon-based material may be selected from one or more of elemental silicon, silicon-oxygen compound, silicon-carbon composite, and silicon alloy.
  • the tin-based material can be selected from one or more of elemental tin, tin oxide compounds, and tin alloys. Methods for the preparation of these materials are well known and commercially available. Those skilled in the art can make appropriate choices according to the actual use environment.
  • the first negative active material may further include natural graphite.
  • the mass ratio of the natural graphite in the first negative electrode active material is ⁇ 40%; 30%, or 10% to 20%.
  • the second negative active material may further include a silicon-based material.
  • the mass ratio of the silicon-based material in the second negative electrode active material is ⁇ 10%; for example, it may be 2% to 6%.
  • the negative electrode current collector can be a conventional 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 first artificial graphite and the second artificial graphite may be different in at least one of parameters such as degree of graphitization, particle size distribution, particle shape, tap density and the like.
  • the first negative active material and the second negative active material described in the present application may be different in material composition or material kind.
  • the first negative electrode film layer or the second negative electrode film layer generally optionally includes a binder, a conductive agent and other auxiliary agents.
  • the negative electrode film layer slurry coating is usually formed by dispersing the negative electrode active material and optional binders, conductive agents and other auxiliary agents in a solvent and stirring it evenly.
  • the solvent can be N-methylpyrrolidone (NMP) or deionized water.
  • NMP N-methylpyrrolidone
  • Other optional adjuvants can be, for example, thickening and dispersing agents (eg, sodium carboxymethyl cellulose CMC-Na), PTC thermistor materials, and the like.
  • the conductive agent in the first negative electrode film layer or the second negative electrode film layer may include one or more of superconducting carbon, acetylene black, conductive carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon fibers. several.
  • the mass proportion of the conductive agent in the first negative electrode film layer or the second negative electrode film layer is ⁇ 5%.
  • the binder in the first negative electrode film layer or the second negative electrode film layer may include styrene butadiene rubber (SBR), polyvinylidene fluoride (PVDF), polyvinylidene fluoride copolymer (eg, polyvinylidene fluoride-hexafluoroethylene) Fluoropropylene), polystyrene, polyacrylic acid, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyurethane, polyvinyl alcohol, polyvinyl butyral (PVB), polyacrylate, acrylic-acrylonitrile copolymer One or more of ethylene-vinyl acetate copolymer (EVA) and acrylate-acrylonitrile copolymer.
  • EVA ethylene-vinyl acetate copolymer
  • the mass ratio of the binder in the first negative electrode film layer or the second negative electrode film layer is ⁇ 5%.
  • the thickness of the negative electrode film layer is greater than or equal to 60 ⁇ m; for example, it may be 65 ⁇ m ⁇ 80 ⁇ m. It should be noted that the thickness of the negative electrode film layer refers to the total thickness of the first negative electrode film layer and the second negative electrode film layer coated on one side of the negative electrode current collector.
  • the thickness ratio of the second negative electrode film layer to the first negative electrode film layer is 1:1 ⁇ 3:2.
  • the thickness ratio of the first and second negative electrode film layers is within the given range, it is beneficial to form a gradient pore distribution in the upper and lower layers, so that the liquid phase conduction resistance of the active ions extracted from the positive electrode on the surface of the negative electrode film layer is reduced, and it will not cause ions in the surface layer.
  • the accumulation causes the problem of lithium deposition, and the uniform diffusion of active ions in the membrane layer is beneficial to reduce polarization, which can further improve the fast charging performance and cycle performance of the battery.
  • the areal density of the negative electrode film layer is ⁇ 0.117 mg/mm 2 ; for example, it may be 0.117 mg/mm 2 to 0.13 mg/mm 2 , or 0.119 mg/mm 2 to 0.13 mg/mm 2 . It should be noted that 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 compaction density of the negative electrode film layer is 1.4g/cm 3 -1.75g/cm 3 ; for example, it may be 1.65-1.75g/cm 3 or 1.55g/cm 3 -1.7g/cm 3 .
  • the compaction density of the negative electrode film layer refers to the compaction density of the entire negative electrode film layer coated on one side of the negative electrode current collector, that is, including the first negative electrode film layer and the second 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.
  • primary particles and secondary particles have the 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. For example, FIG. 3 shows an SEM image of an embodiment of a first negative active material, and FIG. 4 shows an SEM image of an embodiment of a second negative active material.
  • the quantity ratio of the primary particles or the secondary particles in the negative electrode active material can be tested by methods known in the art, for example, it can be determined by scanning electron microscopy.
  • the test can refer to JY/T010-1996.
  • test results randomly select multiple (for example, 5) different areas in the sample to be tested for scanning test, and at a certain magnification (for example, 500 times or 1000 times), calculate the two in each test area.
  • the percentage of the number of secondary particles to the total number of particles is the proportion of the number of secondary particles in this area, and the average of the calculation results of multiple test areas is taken as the proportion of the number of secondary particles in the negative electrode active material.
  • 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.
  • the test of the quantity proportion of the primary particles in the negative electrode active material can also be carried out.
  • Dv10, Dv50, and Dv90 of the negative electrode active material all have meanings known in the art, and can be tested by methods known in the art.
  • Dv10, Dv50, and Dv90 are as follows:
  • Dv10 the particle size corresponding to the cumulative volume distribution percentage of the negative active material reaching 10%
  • Dv50 The particle size corresponding to the cumulative volume distribution percentage of the negative active material reaching 50%
  • Dv90 the particle size corresponding to the cumulative volume distribution percentage of the negative active material reaching 90%.
  • the uniformity of particle size of the negative electrode active material has a meaning well known in the art. Specifically, the uniformity of particle size of the negative electrode active material can indicate that the particle size of all particles in the negative electrode active material deviates from the volume average particle size of the negative electrode active material.
  • the uniformity of particle size of the negative active material can be tested by methods known in the art. For example, you can refer to the standard GB/T 19077.1-2016, and use a laser particle size analyzer (such as Malvern Master Size 3000) to test.
  • a laser particle size analyzer such as Malvern Master Size 3000
  • 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 specific surface area (SSA) of the negative electrode active material has the meaning known in the art, and can be tested by methods known in the art.
  • the nitrogen adsorption specific surface area analysis test method can be used to test, and the BET (Brunauer Emmett Teller) method can be used to calculate it.
  • the nitrogen adsorption specific surface area analysis test can pass the Tri-Star 3020 type of Micromeritics Company in the United States.
  • the specific surface area pore size analysis tester was used for testing.
  • the thickness of the negative electrode film layer can be measured with a micrometer, for example, a micrometer with a model of Mitutoyo293-100 and an accuracy of 0.1 ⁇ m can be used.
  • the respective thicknesses of the primer layer, the first negative electrode film layer and the second negative electrode film layer can be tested by using a scanning electron microscope (eg, ZEISS Sigma300).
  • the test method can be as follows: first, cut the negative pole piece into a sample to be tested of a certain size (for example, 2cm ⁇ 2cm), and fix the negative pole piece on the sample stage by paraffin.
  • Sample test can refer to JY/T010-1996. In order to ensure the accuracy of the test results, you can randomly select multiple (for example, 10) different areas in the sample to be tested for scanning test, and read the primer layer in the scale test area under a certain magnification (for example, 500 times). , the respective thicknesses of the first negative electrode film layer and the second negative electrode film layer, and the average value of the test results of multiple test areas is taken as the thickness of the primer layer, the first negative electrode film layer and the second negative electrode film layer.
  • the areal density of the negative electrode film layer has a meaning known in the art, and can be tested by a method known in the art.
  • 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 (2) Bake the dried negative pole piece in step (1) at a certain temperature and time (for example, 400° C., 2 h), select a region in the baked negative pole piece, and first activate the second negative pole 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 first negative electrode active material in the same way.
  • a certain temperature and time for example, 400° C., 2 h
  • the mutual fusion layer can be scraped off first, and then the first 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.
  • sieving treatment for example, sieving with a 200-mesh sieve
  • Parameters such as material morphology, particle size, specific surface area, etc.
  • 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 parameters of the primer layer and the negative electrode film layer given in this application such as the thickness of the primer layer, the thickness of the negative electrode film layer, the layer density of the negative electrode film layer, the compaction density of the negative electrode film layer, etc., all refer to the single film layer.
  • the parameter range of the layer When both surfaces of the negative electrode current collector are provided with a primer layer or a negative electrode film layer, the parameters of the primer layer or negative electrode film layer on any one of the surfaces satisfy the present application, that is, it is considered to fall within the protection scope of the present application .
  • the ranges of the thickness of the negative electrode film layer and the areal density described in this application all refer to the film layer parameters after cold pressing and compaction and used for assembling the battery.
  • 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 opposite surfaces in the thickness direction of the positive electrode current collector, and the positive electrode film layer may be laminated on either or both of the two opposite surfaces of the positive electrode current collector.
  • the positive electrode current collector can be a conventional metal foil 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 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 modified compounds 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 , one or more of Zn, 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 and/or surface coating modification of the material.
  • the positive electrode film layer may optionally include a binder and a conductive agent.
  • 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, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
  • the electrolyte plays the role of conducting ions between the positive electrode and the negative electrode.
  • the type of electrolyte in this application 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 (difluorosulfonic acid) 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).
  • LiPF 6 lithium hexafluorophosphate
  • LiBF 4 lithium
  • 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.
  • Secondary batteries using electrolyte solutions also include separators.
  • the separator is arranged between the positive pole piece and the negative pole piece, and plays the role of isolation.
  • There is no particular limitation on 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 can be 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.
  • the shape of the secondary battery is not particularly limited in the present application, and it may be cylindrical, square or any other shape.
  • FIG. 5 shows 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.
  • a second aspect of the present application provides a method for preparing a secondary battery, comprising at least preparing a negative pole piece of the secondary battery through the following steps:
  • a primer coating is provided on at least one side of the negative electrode current collector
  • the secondary battery includes a negative pole piece, the negative pole piece is a multi-layer structure, and the multi-layer structure sequentially includes: a negative electrode current collector, an undercoat layer and a negative electrode film layer; the negative electrode film layer includes a third a negative electrode film layer and a second negative electrode film layer, and the first negative electrode film layer is located between the primer layer and the second negative electrode film layer; the first negative electrode film layer includes a first negative electrode active material,
  • the first negative active material includes a first artificial graphite, at least a part of the particles in the first artificial graphite are secondary particles, and the number of the secondary particles in the total number of particles of the first negative active material accounts for Ratio A satisfies: A ⁇ 50%.
  • the first negative electrode film layer and the second negative electrode film layer may be coated simultaneously, or may be coated twice.
  • the adhesion between the upper and lower negative electrode film layers can be better, which is helpful to further improve the cycle performance of the battery.
  • the positive electrode sheet of the present application can be prepared as follows: the positive electrode active material, optional conductive agent (such as carbon black and other carbon materials), binder (such as PVDF), etc. are mixed and dispersed in a solvent (such as NMP) , after stirring evenly, coating on the positive electrode current collector, and drying to obtain a positive electrode piece.
  • a solvent such as NMP
  • the positive electrode current collector a metal foil such as aluminum foil or a material such as a porous metal plate can be used.
  • the positive electrode tab can be obtained by punching or laser die-cutting in the uncoated area of the positive electrode current collector.
  • the secondary batteries can optionally 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 body 2 and a lower box body 3.
  • the upper box body 2 is used to cover the lower box body 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.
  • a third aspect of the present application provides an apparatus.
  • the device includes at least one of the secondary batteries, battery modules, or battery packs described in 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.
  • 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
  • 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.
  • the positive active material LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811), conductive carbon black Super-P, and binder polyvinylidene fluoride (PVDF) in a weight ratio of 96.8:1:2.2 in N-methylpyrrolidone solvent
  • NCM811 conductive carbon black Super-P
  • PVDF binder polyvinylidene fluoride
  • the primer slurry is uniformly coated on both surfaces of the current collector, and the primer layer is dried.
  • the thickness of the undercoat layer was 3 ⁇ m.
  • the second step is to prepare the negative electrode slurry 1: the first negative electrode active material, binder (SBR), thickener (CMC-Na) and conductive carbon black (Super-P) are mixed in a ratio of 96.2:1.8:1.2:0.8 The weight ratio is fully stirred and mixed in an appropriate amount of deionized water to prepare negative electrode slurry 1.
  • the proportion A of the number of secondary particles in the first negative electrode active material is 50%.
  • the third step, preparation of negative electrode slurry 2 the second negative electrode active material, binder SBR, thickener (CMC-Na) and conductive carbon black (Super-P) in a weight ratio of 96.2:1.8:1.2:0.8
  • a suitable amount of deionized water was fully stirred and mixed to prepare negative electrode slurry 2 .
  • the proportion B of the number of secondary particles in the second negative electrode active material is 90%.
  • the negative electrode slurry 1 and the negative electrode slurry 2 are extruded simultaneously through the double-chamber coating equipment.
  • the negative electrode slurry 1 is coated on the current collector to form a first negative electrode film layer
  • the negative electrode slurry 2 is coated on the first negative electrode film layer to form a second negative electrode film layer.
  • the areal density of the negative electrode film layer was 0.123 mg/mm 2
  • the compaction density was 1.65 g/cm 3 .
  • the negative pole piece prepared in the fourth step is subjected to processes such as drying, cold pressing, slitting and cutting to obtain the negative pole piece.
  • Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1, and then the fully dried lithium salt LiPF 6 was dissolved in a ratio of 1 mol/L In a mixed organic solvent, the electrolyte is prepared.
  • the above-mentioned positive pole piece, separator, and negative pole piece are stacked in order, and the electrode assembly is obtained after winding, and the electrode assembly is put into the outer package, and the above-mentioned electrolyte is injected. Then, a secondary battery was obtained.
  • the secondary batteries of Examples 2 to 44 and Comparative Examples 1 to 6 were prepared in a similar manner to the secondary battery of Example 1, but the composition and product parameters of the negative electrode plates were adjusted. See Table 2 for different product parameters.
  • the batteries of each embodiment and comparative example 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).
  • the charging was constant current and constant voltage charging, and the termination voltage was 4.25 V, the cut-off current is 0.05C, the end-of-discharge voltage is 2.8V, and the theoretical capacity is recorded as C0; then the battery is charged with constant current of 0.5C0, 1C0, 1.5C0, 2C0, 2.5C0, 3C0, 3.5C0, 4C0 to 4.25V full power cut-off voltage or 0V negative cut-off potential, after each charge, it needs to be discharged to 2.8V at 1C0, and record the corresponding charge when charging to 10%, 20%, 30%...80% SOC state at different charging rates Anode potential, draw the rate-anode potential curve under different SOC states, and obtain the corresponding charging rate when the anode potential is 0V under different SOC states after linear fitting, and the charging rate
  • 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 discharge cut-off voltage of 2.8V record its initial capacity as C0.
  • charge according to the strategy described in Table 1 discharge at 0.33C, record the discharge capacity Cn of each cycle, until the cycle capacity retention rate (Cn/C0 ⁇ 100%) is 80%, and record the number of cycles. The more cycles, the higher the cycle life of the battery.
  • test data of Examples 7 to 13 show that when the volume distribution average particle size D V 50 of the first negative electrode active material satisfies D V 50 ⁇ 15 ⁇ m, especially 17 ⁇ m ⁇ D V 50 ⁇ 23 ⁇ m, the battery performance is better.
  • the test data of Examples 14 to 19 show that when the particle size uniformity (Uniformity) of the first negative electrode active material is in the range of 0.25 to 0.45, the battery performance is all excellent.
  • test data of Examples 20 to 23 show that when the mass proportion of the conductive agent in the undercoat layer is ⁇ 50%, especially in the range of 55% to 70%, the battery performance is excellent.
  • the second negative electrode active material preferably also contains artificial graphite in the form of secondary particles, and the secondary particles are in the total number of particles of the second negative electrode active material.
  • the number ratio B preferably satisfies B ⁇ 50%, preferably B ⁇ 60%, more preferably 80% ⁇ B ⁇ 100%;
  • the volume distribution average particle size D V50 of the second negative electrode active material preferably satisfies 7 ⁇ m ⁇ D V 50 ⁇ 15 ⁇ m;
  • the particle size uniformity (Uniformity) of the second negative electrode active material is preferably in the range of 0.20 to 0.50, most preferably in the range of 0.25 to 0.4.
  • test data of Examples 42 to 44 show that in the secondary battery of the present application, both the first negative electrode active material and/or the second negative electrode active material may include optional other negative electrode active materials.

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Abstract

一种二次电池（5）、其制备方法、以及含有该二次电池（5）的装置。所述二次电池（5）包括负极极片（10），所述负极极片（10）为多层结构，且所述多层结构依次包括：负极集流体（101）、底涂层（102）及负极膜层；其中，所述负极膜层包括第一负极膜层（103）和第二负极膜层（104），且所述第一负极膜层（103）位于所述底涂层（102）和所述第二负极膜层（104）之间；所述第一负极膜层（103）包括第一负极活性材料，所述第一负极活性材料包括第一人造石墨，所述第一人造石墨中的至少一部分颗粒为二次颗粒，且所述二次颗粒在所述第一负极活性材料的颗粒总数中的数量占比A满足：A≥50％。该二次电池（5）兼具良好的快速充电性能和长循环寿命等特点。

Description

二次电池、其制备方法、及其相关的电池模块、电池包和装置 技术领域
本申请属于电化学技术领域，更具体地说，涉及一种二次电池、其制备方法、及其相关的电池模块、电池包和装置。
背景技术
二次电池作为新型高电压、高能量密度的可充电电池，具有重量轻、能量密度高、无污染、无记忆效应、使用寿命长等突出特点，从而被广泛应用于新能源行业。
随着新能源行业的发展，人们对二次电池提出了更高的使用要求。然而，二次电池的能量密度提升，往往对于电池的动力学性能和使用寿命有不利影响。因此，如何在高能量密度的前提下，还可以同时兼顾其它电化学性能是电池设计领域的关键挑战所在。
有鉴于此，确有必要提供一种能够解决上述问题的二次电池。
发明内容
鉴于背景技术中存在的技术问题，本申请的目的在于提供一种二次电池及其制备方法、及其相关的电池模块、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。
为实现上述发明目的，本申请的第一方面提供一种二次电池，包括负极极片，所述负极极片为多层结构，且所述多层结构依次包括：负极集流体、底涂层及负极膜层；所述负极膜层包括第一负极膜层和第二负极膜层，且所述第一负极膜层位于所述底涂层和所述第二负极膜层之间；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人造石墨，所述第一人造石墨中的至少一部分颗粒为二次颗粒，且所述二次颗粒在所述第一负极活性材料的颗粒总数中的数量占比A满足：A≥50％。
本申请的二次电池的负极极片的膜层包括至少两层结构，当第一负极活性材料中包括特定含量及形貌的第一人造石墨，且集流体上同时设置有底涂层时，可以使二次电池在较高能量密度的前提下，同时兼顾较好的快速充电性能和较长的循环寿命。本申请的电池模块、电池包及装置均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。
在本申请任意实施方式中，A≥60％；可选地，70％≤A≤100％。当A在所给范围内时，可以进一步改善电池的快速充电性能。
在本申请任意实施方式中，所述底涂层包括粘结剂和导电剂。
在本申请任意实施方式中，所述粘结剂在所述底涂层中的质量占比≤50％，可选为30％～45％。粘结剂的含量在所给范围内，可以进一步改善电池的循环性能。
在本申请任意实施方式中，所述导电剂在所述底涂层中的质量占比≥50％，可选为55％～70％。导电剂的含量在所给范围内，可以进一步改善电池的快速充电性能。
在本申请任意实施方式中，所述底涂层的厚度≥1μm；可选地，所述底涂层的厚度为1.5μm～5μm。这个范围的底涂层厚度有助于电池的快速充电性能和循环性能之间的平衡。
在本申请任意实施方式中，底涂层中的粘结剂可以包括丁苯橡胶(SBR)、聚偏氟乙烯(PVDF)、聚偏氟乙烯共聚物(如聚偏氟乙烯-六氟丙烯)、聚苯乙烯、聚丙烯酸、聚四氟乙烯、聚丙烯腈、聚酰亚胺、聚氨酯、聚乙烯醇、聚乙烯醇缩丁醛(PVB)、聚丙烯酸酯、丙烯酸-丙烯腈共聚物、乙烯-醋酸乙烯酯共聚物(EVA)、丙烯酸酯-丙烯腈共聚物、及上述各材料的改性化合物中的一种或几种。
在本申请任意实施方式中，所述导电剂可以包括导电碳材料；例如，所述导电剂可以包括乙炔黑、导电炭黑、科琴黑、碳纳米管、碳纤维、石墨烯中的一种或几种。
在本申请任意实施方式中，所述第一负极活性材料还可以包括天然石墨；可选地，所述天然石墨在所述第一负极活性材料中的质量占比≤50％。这有助于提高电池的功率性能及提高电池的快速充电性能，且有助于灵活调整电池的各项性能以便适应不同场合的使用要求。
在本申请任意实施方式中，所述第一负极活性材料的体积分布平均粒径D V50满足：D V50≥15μm，可选地，17μm≤D V50≤23μm。这有助于进一步提升电池的能量密度及循环性能。
在本申请任意实施方式中，所述第一负极活性材料的粒度一致性(Uniformity)≥0.20，可选为0.20～0.60，或0.25～0.45。这有助于进一步改善电池的快速充电性能及循环性能。
在本申请任意实施方式中，所述第一负极活性材料的比表面积SSA满足：SSA≤1.6m 2/g，可选地，0.4m 2/g≤SSA≤1.5m 2/g。这有助于进一步改善电池的快速充电性能及循环性能。
在本申请任意实施方式中，所述第一负极活性材料的粒度分布0.6≤(D V90-D V10)/D V50≤3.5，可选地，0.7≤(D V90-D V10)/D V50≤2.8。这有助于进一步改善电池的快速充电性能。
在本申请任意实施方式中，所述第一负极活性材料的粉体OI≤8.5，可选为1.8～7.5。这有助于进一步改善电池的快速充电性能及降低电池的膨胀。
在本申请任意实施方式中，所述第一负极活性材料的克容量≥352mAh/g，可选为353mAh/g～370mAh/g。这有助于进一步提高电池的能量密度。
在本申请任意实施方式中，所述第二负极活性材料包括第二人造石墨；可选地，所述第二人造石墨在所述第二负极活性材料中的质量占比≥80％，例如≥90％。这有助于提高电池的快速充电性能和循环性能，且有助于灵活调整电池的各项性能以便适应 不同场合的使用要求。
在本申请任意实施方式中，第二人造石墨中的至少一部分颗粒为二次颗粒。可选地，二次颗粒在所述第二负极活性材料的颗粒总数中的数量占比B满足：B≥60％；可选地，80％≤B≤100％。这样可以进一步改善电池的快速充电性能。
在本申请任意实施方式中，所述第二负极活性材料的体积分布平均粒径D V50满足：7μm≤DV50≤15μm，可选地，9μm≤D V50≤13.5μm。这有助于进一步改善电池的快速充电及循环性能。
在本申请任意实施方式中，所述第二负极活性材料的粒度一致性(Uniformity)为0.20～0.50，可选为0.25～0.4。这有助于进一步改善电池的快速充电及循环性能。
在本申请任意实施方式中，所述第二负极活性材料的比表面积SSA满足：SSA≤1.6m 2/g，可选地，0.4m 2/g≤SSA≤1.55m 2/g。这有助于进一步改善电池的快速充电及循环性能。
在本申请任意实施方式中，所述第二负极活性材料的粒度分布0.5≤(D V90-D V10)/D V50≤3.0，可选地，0.8≤(D V90-D V10)/D V50≤2.8。这有助于进一步改善电池的快速充电及循环性能。
在本申请任意实施方式中，所述第二负极活性材料的粉体OI≤6，可选为1.5～5.5。这有助于进一步改善电池的膨胀、快速充电及循环性能。
在本申请任意实施方式中，所述第二负极活性材料的克容量≥345mAh/g，可选为348mAh/g～360mAh/g。这有助于进一步改善电池的电性能。
在本申请任意实施方式中，所述第二负极活性材料的粒度一致性(Uniformity)与所述第一负极活性材料的粒度一致性(Uniformity)的比值为0.6～2，可选为0.8～1.25。这有助于进一步改善电池的快速充电及循环性能。
在本申请任意实施方式中，所述负极膜层的面密度为≥0.117mg/mm 2，可选为0.119～0.130mg/mm 2。这有助于进一步改善电池的能量密度。
在本申请任意实施方式中，所述负极膜层的压实密度为1.4g/cm 3～1.75g/cm 3，可选为1.65～1.75g/cm 3。这有助于进一步改善电池的快速充电性能及能量密度。
在本申请任意实施方式中，所述第二负极膜层与所述第一负极膜层的厚度比为1∶1～3∶2。这有助于进一步改善电池的快速充电性能。
在本申请任意实施方式中，所述第二负极活性材料与第一负极活性材料的OI值的比值≤1.2。这有助于进一步改善电池的膨胀、快速充电及循环性能。
本申请的第二方面提供一种二次电池的制备方法，至少包括如下步骤：
1)在负极集流体至少一侧设置底涂层；
2)在所述底涂层上设置第一负极膜层；
3)在所述第一负极膜层上设置第二负极膜层；
其中，所述二次电池包括负极极片，所述负极极片为多层结构，且所述多层结构依次包括：负极集流体、底涂层及负极膜层；所述负极膜层包括第一负极膜层和第二负极膜层，且所述第一负极膜层位于所述底涂层和所述第二负极膜层之间；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人造石墨，所述 第一人造石墨中的至少一部分颗粒为二次颗粒，且所述二次颗粒在所述第一负极活性材料的颗粒总数中的数量占比A满足：A≥50％。
本申请的第三方面提供一种电池模块，其包括本申请第一方面所述的二次电池或按照本申请第二方面所述方法制造的二次电池。
本申请的第四方面提供一种电池包，其包括本申请第三方面所述的电池模块。
本申请的第五方面提供一种装置，其包括本申请第一方面所述的二次电池、按照本申请第二方面所述方法制造的二次电池、本申请第三方面所述的电池模块，或本申请第四方面所述的电池包中的至少一种。
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例，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中负极极片的一实施方式的示意图。
图2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3是第一负极活性材料的一实施方式的SEM图。
图4是第二负极活性材料的一实施方式的SEM图。
图5是本申请的二次电池的一实施方式的示意图。
图6是图5所示二次电池的分解示意图。
图7是电池模块的一实施方式的示意图。
图8是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。
在附图中，各部件并未按照实际的比例绘制。其中，附图标记说明如下：1-电池包；2-上箱体；3-下箱体；4-电池模块；5-二次电池；51-壳体；52-电极组件；53-盖板；10-负极极片；101-负极集流体；102-底涂层；103-第一负极膜层；104-第二负极膜 层。
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，以下结合具体实施例对本申请进行详细说明。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”的含义是两种及两种以上。
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)。
除非另有说明，本申请中使用的术语具有本领域技术人员通常所理解的公知含义。除非另有说明，本申请中提到的各参数的数值可以用本领域常用的各种测量方法进行测量(例如，可以按照在本申请的实施例中给出的方法进行测试)。
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负极膜层。
一般情况下，为了增加电池的能量密度，往往会增加负极膜层的厚度，但厚度增加会导致电池的快速充电性能和循环性能均受到影响。因此，如何使电池在具有较高能量密度的前提下，兼具较好的快速充电性能和循环性能，在技术方面仍是一个巨大的挑战。
发明人通过大量实验发现，可以通过调整负极极片的结构来实现本申请的技术目标。具体地，本申请的二次电池中的负极极片为多层结构，且所述多层结构依次包括：负极集流体、底涂层及负极膜层；所述负极膜层包括第一负极膜层和第二负极膜层，且所述第一负极膜层位于所述底涂层和所述第二负极膜层之间；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人造石墨，所述第一人造石墨中的至少一部分颗粒为二次颗粒，且所述二次颗粒在所述第一负极活性材料的颗粒总数中的数量占比A满足：A≥50％。当负极极片满足上述设计条件时，能使得二次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。
发明人经研究发现，当负极极片中包括至少两层膜层，且第一负极膜层中包括二次颗粒形貌的人造石墨时，可以显著提高电池的能量密度和快速充电性能；但与此同时，发明人发现，当二次颗粒在第一负极活性材料中的数量占比在本申请规定的范围内时，虽然电池的快速充电性能可以得到有效改善，但循环性能会受到一定的影响。
众所周知，本领域已知影响电池循环性能的因素非常多，例如，极片结构的设计、活性材料的选择、活性材料层中不同组分之间的配比、电 解液的选择及隔离膜的选择等，而每一项参数的调整都可能会同时影响电池的循环性能和其他性能，如快速充电性能、能量密度等。
在上述众多的影响因素中，发明人惊奇的发现，当负极极片包括至少两层膜层，且第一负极膜层中二次颗粒形貌的第一人造石墨的数量占比在本申请规定的范围内时，如果在集流体和第一负极膜层中间还同时设置有底涂层，可以大幅改善电池的循环性能。不希望限于任何理论，发明人发现，当在集流体表面设置底涂层时，底涂层可以桥联集流体与第一负极膜层中二次颗粒形貌的人造石墨的棱角结构，显著提升了第一负极活性材料与负极集流体之间的电荷转移能力，从而有效改善了电池的循环性能。
本申请的二次电池中，所述底涂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。相应地，所述负极膜层也可以设置在负极集流体的一侧或两侧。
本申请的二次电池中，所述底涂层包括导电剂和粘结剂。
图1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包括负极集流体101、分别设置在负极集流体两侧的底涂层102、第一负极膜层103和第二负极膜层104。
图2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包括负极集流体101、设置在负极集流体一侧的底涂层102、第一负极膜层103和第二负极膜层104。
本发明人经深入研究发现，当本申请的负极极片在满足上述设计条件的基础上，若还可选地满足下述参数中的一个或几个时，可以进一步改善二次电池的性能。
在一些实施方式中，所述导电剂在底涂层中的质量占比≥50％，例如可以为50％～75％，55％～70％，60％～70％，58％～68％，65％～72％。当导电剂在所给范围内时，可以进一步改善电池的快速充电性能和循环性能。
在一些实施方式中，所述粘结剂在底涂层中的质量占比≤50％，例如可以为25％～50％，30％～45％，30％～40％，32％～42％，28％～35％。
在一些实施方式中，所述导电剂可以包括导电碳材料；例如，所述导电剂可以包括乙炔黑、导电炭黑、科琴黑、碳纳米管、碳纤维、石墨烯 中的一种或几种。
在一些实施方式中，所述粘结剂可以包括丁苯橡胶(SBR)、聚偏氟乙烯(PVDF)、偏氟乙烯的共聚物(如偏氟乙烯-六氟丙烯共聚物)、聚苯乙烯、聚丙烯酸、聚四氟乙烯、聚丙烯腈、聚酰亚胺、聚氨酯、聚乙烯醇、聚乙烯醇缩丁醛(PVB)、聚丙烯酸酯、丙烯酸-丙烯腈共聚物、乙烯-醋酸乙烯酯共聚物(EVA)、丙烯酸酯-丙烯腈共聚物、及上述各材料的改性化合物中的一种或几种。
在一些实施方式中，所述底涂层还可以包括增稠剂等其他常规助剂或添加剂。可选地，增稠剂可以为羧甲基纤维素钠(CMC-Na)。
在一些实施方式中，底涂层的厚度H(单面涂层)满足：H≥1μm；例如，1.5μm≤H≤5μm，1.5μm≤H≤4μm，2.5≤H≤4.5。
在一些实施方式中，所述二次颗粒在所述第一负极活性材料中的数量占比A满足：A≥60％，例如，60％≤A≤100％，70％≤A≤98％，75％≤A≤96％，80％≤A≤95％或85％≤A≤100％。当A在所给范围内时，可以进一步改善电池的快速充电性能。
在一些实施方式中，第一负极活性材料的体积分布平均粒径D V50满足：D V50≥14μm；例如，D V50的范围可以为：15μm≤D V50≤25μm，16μm≤D V50≤25μm，17μm≤D V50≤25μm，17μm≤D V50≤24μm，17μm≤D V50≤23μm，18.3μm≤D V50≤23μm。当第一负极活性材料包含特定含量及形貌的第一人造石墨，且将其D V50控制在所给范围内时，可使第一负极膜层的嵌锂容量和压实密度均保持较高的水平，进一步提高电池的能量密度；同时，第一负极膜层可以有效分担第二负极膜层的压力，使得第二负极膜层保持更好的孔隙结构，减小了活性离子转移的阻力，进一步改善电池的快速充电性能。
在一些实施方式中，第一负极活性材料的粒度一致性Uniformity满足(简写为U)：0.20≤U≤0.60；例如，U的范围可以为：0.25≤U≤0.60，0.25≤U≤0.55，0.25≤U≤0.45，0.25≤U≤0.50，0.30≤U≤0.50，0.30≤U≤0.40，0.28≤U≤0.35。当第一负极活性材料包含特定含量及形貌的第一人造石墨，且将粒度一致性Uniformity控制在所给范围内时，第一负 极膜层中的活性离子传输路径得到最优匹配，有效降低了活性离子在液相传导中的阻抗，各区域中的活性离子可快速完成液相传导并嵌入负极活性材料中，进一步改善电池的快速充电性能。
在一些实施方式中，第一负极活性材料的粒度分布(D V90-D V10)/D V50满足0.6≤(D V90-D V10)/D V50≤3.5；例如，1.0≤(D V90-D V10)/D V50≤3.0，0.8≤(D V90-D V10)/D V50≤2.5，1.0≤(D V90-D V10)/D V50≤2.3，1.1≤(D V90-D V10)/D V50≤2.3，1.1≤(D V90-D V10)/D V50≤1.9，0.7≤(D V90-D V10)/D V50≤1.6，0.9≤(D V90-D V10)/D V50≤2.0。当第一负极活性材料包含特定含量及形貌的第一人造石墨，且将粒度分布控制在所给范围内时，在电池制备过程中，有利于使活性材料在浆料中均匀分散，并且能有效预防负极膜层在涂布过程中出现漏涂、涂布不均等问题，可以使负极极片具有较高的离子和电子传输性能，且电池的极化现象得到缓解，从而进一步改善电池的快速充电性能和循环性能。
在一些实施方式中，第一负极活性材料的比表面积SSA满足：SSA≤1.6m 2/g；例如，SSA的范围可以为：0.4m 2/g≤SSA≤1.6m 2/g，0.5m 2/g≤SSA≤1.5m 2/g，0.6m 2/g≤SSA≤1.5m 2/g，0.7m 2/g≤SSA≤1.3m 2/g。当第一负极活性材料包含特定含量及形貌的第一人造石墨，且将其SSA控制在所给范围内时，可以减小电荷交换阻抗，并且使负极膜层获得更为发达的孔隙，降低活性离子的液相传导阻抗及对电解液的消耗，从而进一步改善电池的循环性能。
在一些实施方式中，第一负极活性材料的克容量C满足：C≥352mAh/g；例如，C的范围可以为：353mAh/g≤C≤370mAh/g，354mAh/g≤C≤370mAh/g，355mAh/g≤C≤365mAh/g，355mAh/g≤C≤364mAh/g等。当第一负极活性材料包含特定含量及形貌的第一人造石墨，且将其克容量C控制在所给范围内时，可以使负极活性材料在具有较高嵌锂容量的同时，还具有较好的结构稳定性，从而可以进一步改善电池的能量密度和循环性能。
在一些实施方式中，第一负极活性材料的OI满足：OI≤8.5；例如，OI的范围可以为：1.8≤OI≤7.5，1.9≤OI≤6.5，2.0≤OI≤5.5，2.2≤ OI≤3.8等。当第一负极活性材料包含特定含量及形貌的第一人造石墨，且将其OI控制在所给范围内时，活性材料具有更好的各向同性，有利于活性离子的快速嵌入脱出，进一步改善电池的快速充电性能；且较高的各向同性可分散活性粒子嵌入时的Z轴膨胀，从而进一步改善电池的循环性能。
在一些实施方式中，所述第二负极活性材料包括第二人造石墨。
在一些实施方式中，所述第二人造石墨在所述第二负极活性材料中的质量占比≥80％；例如，可以为80％～100％，90％～100％，95％～100％。
在一些实施方式中，所述第二负极活性材料包括二次颗粒形貌的第二人造石墨。
在一些实施方式中，所述二次颗粒形貌的第二人造石墨在第二负极活性材料中的数量占比B满足：B≥60％；例如，B可以为60％≤B≤100％，65％≤B≤98％，70％≤B≤100％，70％≤B≤95％，75％≤B≤95％，80％≤B≤100％，或85％≤B≤95％。当第二负极活性材料的二次颗粒比例B控制在所给范围内时，可显著降低活性材料在循环过程中的膨胀，从而进一步改善电池的循环性能；尤其是，上下层的负极活性材料同时具有特定含量的二次颗粒的人造石墨时，上下层活性材料颗粒之间堆积衔接更为紧密，同时还可以增大第一负极膜层和第二负极膜层界面处活性材料颗粒的接触面积，形成立体、有序且高速的活性离子进出通道，提高了电子电导且缩短了活性离子的迁移路径，从而进一步改善电池的快速充电性能。
在一些实施方式中，第二负极活性材料的体积分布平均粒径D V50满足：D V50≤18μm；例如，D V50的范围可以为：7μm≤D V50≤18μm，7μm≤D V50≤15μm，8μm≤D V50≤17μm，9μm≤D V50≤17μm，10μm≤D V50≤15μm，9μm≤D V50≤13.5μm，10.5μm≤D V50≤14μm，11.5μm≤D V50≤13.5μm。当第二负极活性材料的D V50控制在所给范围内时，第一负极膜层和第二负极膜层中的孔道结构得到最优的保持，活性离子传输路径得到最优匹配，有效降低了活性离子的液相传导阻抗，进一步改善电池的快速充电性能；同时，上下层活性粒子之间互相滑移桥联，显著提高极片压实密度，从而进一步改善电池的能量密度。
在一些实施方式中，第一负极活性材料或第二负极活性材料中还可 以包括其它负极活性材料。其它负极活性材料可以包括天然石墨、软碳、硬碳、硅基材料、锡基、钛基材料中的一种或几种。所述硅基材料可选自单质硅、硅氧化合物、硅碳复合物、硅合金中的一种或几种。所述锡基材料可选自单质锡、锡氧化合物、锡合金中的一种或几种。这些材料的制备方法是公知的，且可以通过商业途径获得。本领域技术人员可以根据实际使用环境做出恰当选择。
在一些实施方式中，所述第一负极活性材料还可以包括天然石墨。
在一些实施方式中，当第一负极活性材料中还包括天然石墨时，所述天然石墨在第一负极活性材料中的质量占比≤40％；例如可以为10％～40％，10％～30％，或10％～20％。
在一些实施方式中，所述第二负极活性材料还可以包括硅基材料。
在一些实施方式中，当第二负极活性材料中还包括硅基材料时，所述硅基材料在第二负极活性材料中的质量占比≤10％；例如可以为2％～6％。
本申请的二次电池中，所述负极集流体可以采用常规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，负极集流体可以采用铜箔。
本申请的二次电池中，所述第一人造石墨和所述第二人造石墨可以在石墨化度、粒径分布、颗粒形态、振实密度等参数中至少有一个是不同的。本申请所述第一负极活性材料和第二负极活性材料在材料组成或材料种类方面可以是不同的。
本申请的二次电池中，所述第一负极膜层或所述第二负极膜层通常还可选地包括粘结剂、导电剂和其他助剂。负极膜层浆料涂通常是将负极活性材料以及可选的粘结剂、导电剂和其他助剂等分散于溶剂中并搅拌均匀而形成的，溶剂例如可以是N-甲基吡咯烷酮(NMP)或去离子水。其他可选助剂例如可以是增稠及分散剂(例如羧甲基纤维素钠CMC-Na)、PTC热敏电阻材料等。
作为示例，第一负极膜层或第二负极膜层中的导电剂可以包括超导碳、乙炔黑、导电炭黑、科琴黑、碳点、碳纳米管、石墨烯及碳纤维中一种或几种。可选地，所述导电剂在第一负极膜层或第二负极膜层中的质 量占比≤5％。
作为示例，第一负极膜层或第二负极膜层中的粘结剂可以包括丁苯橡胶(SBR)、聚偏氟乙烯(PVDF)、聚偏氟乙烯共聚物(如聚偏氟乙烯-六氟丙烯)、聚苯乙烯、聚丙烯酸、聚四氟乙烯、聚丙烯腈、聚酰亚胺、聚氨酯、聚乙烯醇、聚乙烯醇缩丁醛(PVB)、聚丙烯酸酯、丙烯酸-丙烯腈共聚物、乙烯-醋酸乙烯酯共聚物(EVA)、丙烯酸酯-丙烯腈共聚物中的一种或几种。可选地，所述粘结剂在第一负极膜层或第二负极膜层中的质量占比≤5％。
在一些实施方式中，所述负极膜层的厚度≥60μm；例如可以为65μm～80μm。需要说明的是，所述负极膜层的厚度是指负极集流体单面涂覆的第一负极膜层和第二负极膜层的厚度总和。
在一些实施方式中，所述第二负极膜层与所述第一负极膜层的厚度比为1∶1～3∶2。第一、第二负极膜层的厚度比在所给范围时，有利于上下层形成梯度孔隙分布，使得正极脱出活性离子在负极膜层表面的液相传导阻力减小，不会导致离子在表层堆积引起析锂问题，同时活性离子在膜层中的均匀扩散有利于减小极化，可以进一步提升电池的快速充电性能和循环性能。
在一些实施方式中，所述负极膜层的面密度为≥0.117mg/mm 2；例如可以为0.117mg/mm 2～0.13mg/mm 2，或0.119mg/mm 2～0.13mg/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)。
在一些实施方式中，所述负极膜层的压实密度为1.4g/cm 3～1.75g/cm 3；例如可以为1.65～1.75g/cm 3或1.55g/cm 3～1.7g/cm 3。需要说明的是，所述负极膜层的压实密度是指负极集流体单面涂覆的负极膜层整体，即包括第一负极膜层和第二负极膜层，的压实密度。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。
在本申请中，上述负极活性材料均可以通过商业途径获得。
在本申请中，一次颗粒及二次颗粒具有本领域公知的含义。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。例如，图3示出了第一负极活性材料的一种实施方式的SEM图像，图4示出了第二负极活性材料的一种实施方式的SEM图像。
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方法进行测试，例如可以采用扫描电子显微镜测定。作为示例，二次颗粒的数量占比的测试方法可以为：将负极活性材料铺设并粘于导电胶上，制成长×宽＝6cm×1.1cm的待测样品；使用扫描电子显微镜(如ZEISS Sigma300)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500倍或1000倍)下，计算各测试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，取多个测试区域的计算结果的平均值作为负极活性材料中二次颗粒的数量占比。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。同理也可以进行所述一次颗粒在负极活性材料中的数量占比的测试。
在本申请中，负极活性材料的Dv10、Dv50、Dv90均具有本领域公知的含义，可以采用本领域已知的方法进行测试。例如可以参照标准GB/T 19077.1-2016，使用激光粒度分析仪(如Malvern Master Size 3000)进行测试。
其中，Dv10、Dv50、Dv90的物理定义如下：
Dv10：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；
Dv50：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；
Dv90：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。
在本申请中，负极活性材料的粒度一致性Uniformity具有本领域公知的含义，具体地，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(Dv50) 的离散程度，其反映了负极活性材料的粒径分布均匀性。
负极活性材料的粒度一致性Uniformity可以采用本领域已知的方法进行测试。例如可以参照标准GB/T 19077.1-2016，使用激光粒度分析仪(如Malvern Master Size 3000)进行测试。
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 PCTCN2020121264-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，负极活性材料的比表面积(Specific surface area，SSA)具有本领域公知的含义，可以采用本领域已知的方法进行测试。例如可以参照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测试。
在本申请中，负极膜层的厚度可采用万分尺测量得到，例如可使用型号为Mitutoyo293-100、精度为0.1μm的万分尺测量得到。
在本申请中，底涂层、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(如ZEISS Sigma300)进行测试。作为示例，测试方法可以为：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10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底涂层、第一负极膜层和第二负极膜层各自的厚度，取多个测试区域的测试结果的平均值作为底涂层、第一负极膜层和第二负极膜层的厚度。
在本申请中，负极膜层的面密度具有本领域公知的含义，可采用本领域已知的方法进行测试。作为示例，测试方法可以为：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，则：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。为了确保测试结果的准确性，可以测试多组(例如10组)待测样品，并计算其平均值作为测试结果。
在本申请中，负极膜层的压实密度具有本领域公知的含义，可采用本领域已知的方法测试。例如先按照上述的测试方法得出负极膜层的面密度和厚度，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片相关的各参数。(例如负极膜片的面密度、压实密度、厚度等)。
(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，先对第二负极活性材料取样(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一负极活性材料取样。 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，在对第一负极活性材料取样时，可以先将互融层刮掉，然后再对第一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(例如材料形貌、粒径、比表面积等)的第一负极活性材料样品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。
另外需要说明的是，本申请所给的底涂层及负极膜层的各参数，例如底涂层厚度、负极膜层厚度、负极膜层面密度、负极膜层压实密度等，均指单面膜层的参数范围。当负极集流体的两个表面上均设置有底涂层或负极膜层时，其中任意一个表面上的底涂层或负极膜层的参数满足本申请，即认为落入本申请的保护范围内。且本申请所述的负极膜层厚度、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。
[正极极片]
本申请的二次电池中，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。
可以理解的是，正极集流体具有在自身厚度方向相对的两个表面，正极膜层可以是层合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，所述正极集流体可以采用常规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，正极集流体可以采用铝箔。
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，正极活性材料可以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，
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。
在本申请中，上述各材料的改性化合物可以是对材料进行掺杂改性和/或表面包覆改性。
本申请的二次电池中，所述正极膜层中还可选的包括粘结剂和导电剂。
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、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯及碳纳米纤维中的一种或几种。
[电解质]
电解质在正极极片和负极极片之间起到传导离子的作用。本申请对电解质的种类没有具体的限制，可根据需求进行选择。例如，电解质可以选自固态电解质及液态电解质(即电解液)中的至少一种。
在一些实施方式中，电解质采用电解液。电解液包括电解质盐和溶剂。
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，各层的材料可以相同或不同。
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。
本申请对所述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5示出了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6，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。
二次电池的制备方法
本申请的第二方面提供一种二次电池的制备方法，至少包括通过如下步骤制备所述二次电池的负极极片：
1)在负极集流体至少一侧设置底涂层；
2)在所述底涂层上设置第一负极膜层；
3)在所述第一负极膜层上设置第二负极膜层；
其中，所述二次电池包括负极极片，所述负极极片为多层结构，且所述多层结构依次包括：负极集流体、底涂层及负极膜层；所述负极膜层包括第一负极膜层和第二负极膜层，且所述第一负极膜层位于所述底涂层和所述第二负极膜层之间；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人造石墨，所述第一人造石墨中的至少一部分颗粒为二次颗粒，且所述二次颗粒在所述第一负极活性材料的颗粒总数中的数量占比A满足：A≥50％。
在上述制备步骤中，所述第一负极膜层和第二负极膜层可以同时涂布，也可以分两次进行涂布。当第一负极膜层和第二负极膜层同时涂布 时，可以使上下负极膜层之间的粘结性更好，有助于进一步改善电池的循环性能。
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本身是公知的。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(例如碳黑等碳素材料)、粘结剂(例如PVDF)等混合后分散于溶剂(例如NMP)中，搅拌均匀后涂覆在正极集流体上，烘干后即得到正极极片。可以使用铝箔等金属箔或多孔金属板等材料作为正极集流体。在制作正极极片时，可以在正极集流体的未涂覆区域，通过冲切或激光模切等方式得到正极极耳。
最后，将正极极片、隔离膜、负极极片按顺序叠好，使隔离膜处于正、负极极片之间起到隔离的作用，然后采用卷绕(或叠片)工艺形成电极组件；将电极组件置于外包装中，干燥后注入电解液，经过真空封装、静置、化成、整形等工序，获得二次电池。
电池模块
在一些实施方式中，可选地，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。
电池包
在一些实施方式中，可选地，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。
装置
本申请的第三方面提供一种装置。所述装置包括本申请所述的二次电池、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作为所述装置的电源，也可以作为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。为了满足该装置对二次电池的高倍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。
以下结合实施例进一步说明本申请的有益效果。
实施例
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，以下结合实施例进一步详细描述本申请。但是，应当理解的是，本申请的实施例仅仅是为了解释本申请，并非为了限制本申请，且本申请的实施例并不局限于说明书中给出的实施例。实施例中未注明具体实验条件或操作条件的按常规条件制作，或按材料供应商推荐的条件制作。
一、用于测试的电池的制备
实施例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)与导电炭黑Super-P、 粘结剂聚偏二氟乙烯(PVDF)按重量比96.8∶1∶2.2在N-甲基吡咯烷酮溶剂中充分搅拌混合均匀后，将浆料涂覆于铝箔基材上，通过烘干、冷压、分条、裁切，得到正极极片。其中，正极膜层的面密度为0.196mg/mm 2，压实密度为3.5g/cm 3。
(2)负极极片的制备
第一步，底涂层：将导电炭黑(Super-P)、粘结剂(SBR)和增稠剂(CMC-Na)62.5∶33.8∶3.7溶于去离子水中充分搅拌混合，配成底涂浆料。将底涂浆料均匀涂覆于集流体的两个表面上，并对底涂层进行干燥。所述底涂层的厚度为3μm。
第二步，制备负极浆料1：将第一负极活性材料、粘结剂(SBR)、增稠剂(CMC-Na)以及导电炭黑(Super-P)按96.2∶1.8∶1.2∶0.8的重量比在适量的去离子水中充分搅拌混合，制备负极浆料1。其中，第一负极活性材料中二次颗粒的数量占比A为50％。
第三步，制备负极浆料2：将第二负极活性材料、粘结剂SBR、增稠剂(CMC-Na)以及导电炭黑(Super-P)按96.2∶1.8∶1.2∶0.8的重量比在适量的去离子水中充分搅拌混合，制备负极浆料2。其中，第二负极活性材料中二次颗粒的数量占比B为90％。
第四步，通过双腔涂布设备，将负极浆料1和负极浆料2同时挤出。负极浆料1涂覆在集流体上形成第一负极膜层，负极浆料2涂覆在第一负极膜层上形成第二负极膜层。其中，负极膜层的面密度为0.123mg/mm 2，压实密度为1.65g/cm 3。
第五步，将第四步制备的负极极片经过烘干、冷压、分条、裁切等工序得到负极极片。
(3)隔离膜
选用PE薄膜作为隔离膜。
(4)电解液的制备
将碳酸乙烯酯(EC)、碳酸甲乙酯(EMC)、碳酸二乙酯(DEC)按照体积比1∶1∶1进行混合，接着将充分干燥的锂盐LiPF 6按照1mol/L的比例溶解于混合有机溶剂中，配制成电解液。
(5)电池的制备
将上述正极极片、隔离膜、负极极片按顺序叠好，经卷绕后得到电极组件，将电极组件装入外包装中，注入上述电解液，经封装、静置、化成、老化等工序后，得到二次电池。
实施例2～44和对比例1～6的二次电池与实施例1的二次电池制备方法相似，但是调整了负极极片的组成和产品参数，不同的产品参数详见表2。
二、性能参数的测试方法
1、快速充电性能测试
25℃下，将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，充电为恒流恒压充电，终止电压为4.25V，截至电流为0.05C，放电终止电压为2.8V，记录其理论容量为C0；然后电池依此以0.5C0、1C0、1.5C0、2C0、2.5C0、3C0、3.5C0、4C0恒流充电至4.25V全电截止电压或者0V负极截止电位，每次充电完成后需以1C0放电至2.8V，记录不同充电倍率下充电至10％、20％、30％……80％SOC态时所对应的阳极电位，绘制出不同SOC态下的倍率-阳极电位曲线，线性拟合后得出不同SOC态下阳极电位为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C 10％SOC、C 20％SOC、C 30％SOC、C 40％SOC、C 50％SOC、C 60％SOC、C 70％SOC、C 80％SOC，根据公式(60/C 20％SOC+60/C 30％SOC+60/C 40％SOC+60/C 50％SOC+60/C 60％SOC+60/C 70％SOC+60/C 80％SOC)*10％计算得到该电池从10％～80％SOC的充电时间T，该时间越短，则代表电池的快速充电性能越优秀。
2、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C0。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Cn，直至循环容量保持率(Cn/C0×100％)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
Figure PCTCN2020121264-appb-000002
三、各实施例、对比例测试结果
按照上述方法分别制备各实施例和对比例的电池，并测量各项性能参数，结果见下表2。
首先，从实施例1～6和对比例5、6的数据可知：在设置了底涂层的情况下，只有二次颗粒形貌的人造石墨在第一负极活性材料的颗粒总数中的数量占比A≥50％时，才能保证所得二次电池兼具良好的循环性能和快速充电性能。此外，从实施例1～6和对比例3、4的数据可知：在A≥50％而不设置底涂层时，电池的循环性能无法得到保证。而在对比例1、2中，既未设置底涂层也未在第一负极活性材料层中使用高含量的二次颗粒形貌的人造石墨，此时快速充电性能和循环性能都非常差。
实施例7至13的测试数据表明：当第一负极活性材料的体积分布平均粒径D V50满足D V50≥15μm，尤其是17μm≤D V50≤23μm时，电池性能更佳。
实施例14至19的测试数据表明：当第一负极活性材料的粒度一致性(Uniformity)在0.25至0.45范围内时，电池性能均较优异。
实施例20至23的测试数据表明：当所述导电剂在所述底涂层中的 质量占比≥50％，尤其是在55％～70％范围内时，电池性能均较优异。
实施例24至41的测试数据表明：为了进一步改善电池性能，第二负极活性材料优选地也含有二次颗粒形貌的人造石墨，且所述二次颗粒在第二负极活性材料的颗粒总数中的数量占比B优选地满足B≥50％，优选地B≥60％，更优选地80％≤B≤100％；第二负极活性材料的体积分布平均粒径D V50优选地满足7μm≤D V50≤15μm；第二负极活性材料的粒度一致性(Uniformity)优选地在0.20至0.50范围内，最优选地在0.25至0.4的范围内。
实施例42至44的测试数据表明：本申请的二次电池中，第一负极活性材料和/或第二负极活性材料都可以包括可选的其他负极活性材料。
根据上述说明书的揭示和指导，本申请所属领域的技术人员还可以对上述实施方式进行适当的变更和修改。因此，本申请并不局限于上面揭示和描述的具体实方式，对本申请的一些修改和变更也落入本申请的权利要求的保护范围内。尤其是，只要不存在冲突，各个实施例中所提到的各项技术特征均可以任意方式组合起来。
Figure PCTCN2020121264-appb-000003
Figure PCTCN2020121264-appb-000004
Figure PCTCN2020121264-appb-000005
Figure PCTCN2020121264-appb-000006

Claims (17)

  1. 一种二次电池，包括负极极片(10)，所述负极极片(10)为多层结构，且所述多层结构依次包括：负极集流体(101)、底涂层(102)及负极膜层；
    所述负极膜层包括第一负极膜层(103)和第二负极膜层(104)，且所述第一负极膜层(103)位于所述底涂层(102)和所述第二负极膜层(104)之间；
    所述第一负极膜层(103)包括第一负极活性材料，所述第一负极活性材料包括第一人造石墨，所述第一人造石墨中的至少一部分颗粒为二次颗粒，且所述二次颗粒在所述第一负极活性材料的颗粒总数中的数量占比A满足：A≥50％。
  2. 根据权利要求1所述的二次电池，其中，所述底涂层(102)包括导电剂和粘结剂。
  3. 根据权利要求1～2任一项所述的二次电池，其中，A≥60％；可选地，70％≤A≤100％。
  4. 根据权利要求1～3任一项所述的二次电池，其中，所述底涂层(102)的厚度≥1μm；可选地，所述底涂层(102)的厚度为1.5μm～5μm。
  5. 根据权利要求2～4任一项所述的二次电池，其中，所述导电剂在所述底涂层(102)中的质量占比≥50％，可选为55％～70％；或，
    所述粘结剂在所述底涂层(102)中的质量占比≤50％，可选为30％～45％。
  6. 根据权利要求2～5任一项所述的二次电池，其中，所述导电剂包括导电碳材料；可选地，所述导电剂包括乙炔黑、导电炭黑、科琴黑、碳纳米管、碳纤维、石墨烯中的一种或几种。
  7. 根据权利要求2～6任一项所述的二次电池，其中，所述粘结剂包括丁苯橡胶(SBR)、聚偏氟乙烯(PVDF)、偏氟乙烯的共聚物、聚苯乙烯、聚丙烯酸、聚四氟乙烯、聚丙烯腈、聚酰亚胺、聚氨酯、聚乙烯醇、聚乙烯醇缩丁醛(PVB)、聚丙烯酸酯、丙烯酸-丙烯腈共聚物、乙烯-醋酸乙烯酯共聚物(EVA)、丙烯酸酯-丙烯腈共聚物、及上述各材料的改性化合物中的一种或几种。
  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还包括天然石墨；可选地，所述天然石墨在所述第一负极活性材料中的质量占比≤50％。
  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以下(1)～(6)中的一个或几个：
    (1)所述第一负极活性材料的体积分布平均粒径D v50满足：D v50≥15μm，可选地，17μm≤D v50≤23μm；
    (2)所述第一负极活性材料的粒度一致性Uniformity为0.20～0.60，可选 为0.25～0.45；
    (3)所述第一负极活性材料的比表面积SSA满足：SSA≤1.6m 2/g，可选地，0.4m 2/g≤SSA≤1.5m 2/g；
    (4)所述第一负极活性材料的粒度分布0.6≤(D v90-D v10)/D v50≤3.5，可选地，0.7≤(D v90-D v10)/D v50≤2.8；
    (5)所述第一负极活性材料的粉体OI≤8.5，可选为1.8～7.5；
    (6)所述第一负极活性材料的克容量≥352mAh/g，可选为353mAh/g～370mAh/g。
  10. 根据权利要求1～9任一项所述的二次电池，其中，所述第二负极活性材料包括第二人造石墨；可选地，所述第二人造石墨在所述第二负极活性材料中的质量占比≥80％。
  11. 根据权利要求10所述的二次电池，其中，所述第二人造石墨中的至少一部分颗粒为二次颗粒，且所述二次颗粒在所述第二负极活性材料的颗粒总数中的数量占比B满足：B≥60％；可选地，80％≤B≤100％。
  12. 根据权利要求1～11任一项所述的二次电池，其中，所述第二负极活性材料还满足以下(a)～(f)中的一个或几个：
    (a)所述第二负极活性材料的体积分布平均粒径D v50满足：7μm≤D v50≤15μm，可选地，9μm≤D v50≤13.5μm；
    (b)所述第二负极活性材料的粒度一致性Uniformity为0.20～0.50，可选为0.25～0.40；
    (c)所述第二负极活性材料的比表面积SSA满足：SSA≤1.6m 2/g，可选地，0.4m 2/g≤SSA≤1.55m 2/g；
    (d)所述第二负极活性材料的粒度分布0.5≤(D v90-D v10)/D v50≤3.0，可选地，0.8≤(D v90-D v10)/D v50≤2.8；
    (e)所述第二负极活性材料的粉体OI≤6，可选为1.5～5.5；
    (f)所述第二负极活性材料的克容量≥345mAh/g，可选为348mAh/g～360mAh/g。
  13. 根据权利要求1～12任一项所述的二次电池，其中，所述二次电池还满足下述(I)～(VI)中的一个或几个：
    (I)所述第二负极活性材料的粒度一致性Uniformity与所述第一负极活性材料的粒度一致性Uniformity的比值为0.6～2，可选为0.8～1.25；
    (II)所述第二负极活性材料的体积分布平均粒径D v50小于所述第一负极活性材料的体积分布平均粒径D v50；
    (III)所述负极膜层的面密度为≥0.117mg/mm 2，可选为0.119～0.130mg/mm 2；
    (IV)所述负极膜层的压实密度为1.4g/cm 3～1.75g/cm 3，可选为1.65～1.75g/cm 3；
    (V)所述第二负极膜层(104)与所述第一负极膜层(103)的厚度比为1∶1～3∶2；
    (VI)所述第二负极活性材料与第一负极活性材料的OI值比值为≤1.2。
  14. 一种制备权利要求1～13任一项所述的二次电池的方法，至少包括如下步骤：
    1)在负极集流体(101)至少一侧设置底涂层(102)；
    2)在所述底涂层(102)上设置第一负极膜层(103)；
    3)在所述第一负极膜层(103)上设置第二负极膜层(104)；
    其中，所述二次电池包括负极极片(10)，所述负极极片(10)为多层结构，且所述多层结构依次包括：负极集流体(101)、底涂层(102)及负极膜层；所述负极膜层包括第一负极膜层(103)和第二负极膜层(104)，且所述第一负极膜层(103)位于所述底涂层(102)和所述第二负极膜层(104)之间；
    所述第一负极膜层(103)包括第一负极活性材料，所述第一负极活性材料包括第一人造石墨，所述第一人造石墨中的至少一部分颗粒为二次颗粒，且所述二次颗粒在所述第一负极活性材料的颗粒总数中的数量占比A满足：A≥50％。
  15. 一种电池模块，包括根据权利要求1～13任一项所述的二次电池或根据权利要求14所述的方法制备的二次电池。
  16. 一种电池包，包括根据权利要求15所述的电池模块。
  17. 一种装置，包括根据权利要求1～13任一项所述的二次电池，或根据权利要求14所述的方法制备的二次电池，根据权利要求15所述的电池模块，或根据权利要求16所述的电池包中的至少一种。
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