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WO2021217587A1 - 二次电池、其制备方法及含有该二次电池的装置 - Google Patents

二次电池、其制备方法及含有该二次电池的装置 Download PDF

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Publication number
WO2021217587A1
WO2021217587A1 PCT/CN2020/088301 CN2020088301W WO2021217587A1 WO 2021217587 A1 WO2021217587 A1 WO 2021217587A1 CN 2020088301 W CN2020088301 W CN 2020088301W WO 2021217587 A1 WO2021217587 A1 WO 2021217587A1
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Prior art keywords
negative electrode
active material
electrode active
film layer
secondary battery
Prior art date
Application number
PCT/CN2020/088301
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English (en)
French (fr)
Inventor
王家政
康蒙
董晓斌
申玉良
何立兵
Original Assignee
宁德时代新能源科技股份有限公司
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Priority to KR1020247016253A priority Critical patent/KR20240093683A/ko
Priority to CN202080006126.3A priority patent/CN113875051B/zh
Priority to PL20933502.5T priority patent/PL3961769T3/pl
Priority to EP20933502.5A priority patent/EP3961769B1/en
Priority to HUE20933502A priority patent/HUE061901T2/hu
Priority to KR1020227018612A priority patent/KR20220095221A/ko
Application filed by 宁德时代新能源科技股份有限公司 filed Critical 宁德时代新能源科技股份有限公司
Priority to PCT/CN2020/088301 priority patent/WO2021217587A1/zh
Priority to JP2022532654A priority patent/JP2023503699A/ja
Priority to ES20933502T priority patent/ES2945476T3/es
Publication of WO2021217587A1 publication Critical patent/WO2021217587A1/zh
Priority to US17/566,713 priority patent/US12027695B2/en
Priority to US18/669,551 priority patent/US20240313202A1/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
    • H01M4/36—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
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/20—Graphite
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—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
    • H01M4/364—Composites as mixtures
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/51—Particles with a specific particle size distribution
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/60—Particles characterised by their size
    • 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

  • This application belongs to the field of electrochemical technology, and more specifically, relates to a secondary battery, a preparation method thereof, and a device containing the secondary battery.
  • secondary batteries As a new type of high-voltage, high-energy-density rechargeable battery, secondary batteries have outstanding characteristics such as light weight, high energy density, no pollution, no memory effect, and long service life, so they are widely used in the new energy industry.
  • this application provides a secondary battery and a device containing it, aiming to enable the secondary battery to have a higher energy density while taking into account better dynamic performance (fast Charging performance) and longer cycle life.
  • a first aspect of the present application provides a secondary battery, which includes a negative pole piece, the negative pole piece includes a negative current collector and a negative film layer, the negative film layer includes a first The negative electrode film layer and the second negative electrode film layer; the first negative electrode film layer is disposed on at least one surface of the negative electrode current collector and includes a first negative electrode active material, the first negative electrode active material includes natural graphite; the second negative electrode The film layer is disposed on the first negative electrode film layer and includes a second negative electrode active material.
  • the second negative electrode active material includes artificial graphite.
  • the second negative electrode active material includes secondary particles. The quantity in the second negative electrode active material accounts for S2 ⁇ 20%.
  • a second aspect of the present application provides a method for manufacturing a secondary battery, which includes preparing the negative pole piece of the secondary battery through the following steps:
  • first negative electrode film layer including a first negative electrode active material on at least one surface of a negative electrode current collector, the first negative electrode active material including natural graphite;
  • the second negative electrode active material includes artificial graphite
  • the second negative electrode active material includes secondary particles
  • a third aspect of the present application provides a device including the secondary battery described in the first aspect of the present application or a secondary battery manufactured according to the method described in the second aspect of the present application.
  • the negative electrode sheet includes a double-coated structure, and the first negative electrode film layer and the second negative electrode film layer contain specific negative electrode active materials, so that the battery can have a higher energy density, At the same time, it takes into account fast charging performance and cycle performance. Preferably, the battery can also have better high-temperature storage performance.
  • the device of the present application includes the secondary battery, and thus has at least the same advantages as the secondary battery.
  • FIG. 1 is a schematic diagram of an embodiment of the secondary battery of the present application.
  • FIG. 2 is a schematic diagram of an embodiment of the negative pole piece in the secondary battery of the present application.
  • FIG. 3 is a schematic diagram of another embodiment of the negative pole piece in the secondary battery of the present application.
  • Fig. 4 is an exploded schematic view of an embodiment of the secondary battery of the present application.
  • Fig. 5 is a schematic diagram of an embodiment of a battery module.
  • Fig. 6 is a schematic diagram of an embodiment of a battery pack.
  • Fig. 7 is an exploded view of Fig. 6.
  • FIG. 8 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.
  • FIG. 9 is an SEM image of primary particles in an embodiment of the first negative electrode active material of the present application.
  • FIG. 10 is an SEM image of secondary particles in an embodiment of the second negative electrode active material of the present application.
  • any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, and any upper limit can be combined with any other upper limit to form an unspecified range.
  • each individually disclosed point or single value can be used as a lower limit or upper limit in combination with any other point or single value or with other lower or upper limits to form an unspecified range.
  • the first aspect of the application provides a secondary battery.
  • the secondary battery includes a positive pole piece, a negative pole piece, and an electrolyte.
  • active ions are inserted and extracted back and forth between the positive pole piece and the negative pole piece.
  • the electrolyte conducts ions between the positive pole piece and the negative pole piece.
  • the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer.
  • the negative electrode film layer includes a first negative electrode film layer and a second negative electrode film layer;
  • the negative electrode current collector is on at least one surface and includes a first negative electrode active material, the first negative electrode active material includes natural graphite;
  • the second negative electrode film layer is disposed on the first negative electrode film layer and includes a second negative electrode active material, so
  • the second negative electrode active material includes artificial graphite, and the second negative electrode active material includes secondary particles, and the number of the secondary particles in the second negative electrode active material accounts for S2 ⁇ 20%.
  • the inventor has discovered through research that when the negative electrode of the secondary battery includes a double-film structure, and the upper and lower film layers include a negative active material of a specific composition, the battery can take into account both fast charging performance and cycle performance.
  • the battery When the battery is charging, along the thickness direction of the negative pole piece, the closer to the separator side, the higher the active ion concentration, and the closer to the current collector side, the lower the active ion concentration.
  • the second negative electrode film layer is closer to the side of the diaphragm, and the active ion concentration in the area where it is located is higher. If the active material in the second negative electrode film layer contains a certain content of secondary particles, it can provide more deintercalation active ion channels. It just matches the actual distribution of active ions in this area, which can ensure that the battery has excellent fast charging performance and cycle performance.
  • the range of S2 can be: 30% ⁇ B ⁇ 100%, 40% ⁇ B ⁇ 85%, 45% ⁇ B ⁇ 98%, 50% ⁇ B ⁇ 100%, 55% ⁇ B ⁇ 95% , 60% ⁇ B ⁇ 95%, 80% ⁇ B ⁇ 100%, 90% ⁇ B ⁇ 100%, etc.
  • the quantity of the secondary particles in the second negative electrode active material accounts for S2 ⁇ 50%.
  • the inventor further researched and found that as the content of secondary particles increases, the negative electrode active material will increase a large number of new interfaces during the cold pressing of the pole piece, thereby increasing the side reaction between the negative electrode active material and the electrolyte. It affects the high temperature storage performance of the battery. Therefore, in order to further balance the fast charging performance, cycle performance, and high temperature storage performance, in some embodiments, 50% ⁇ S2 ⁇ 85%.
  • the inventors have found through in-depth research that when the negative pole piece of the secondary battery of the present application satisfies the above design conditions, if one or more of the following designs are optionally satisfied, the secondary battery can be further improved.
  • the performance of the battery if one or more of the following designs are optionally satisfied, the secondary battery can be further improved.
  • the first negative electrode active material includes primary particles, and the number of the primary particles in the first negative electrode active material accounts for S1 ⁇ 80%; more preferably, 90% ⁇ S1 ⁇ 100% .
  • the first negative electrode film layer is closer to the negative electrode current collector side, and the active ion concentration in the area where it is located is lower. Therefore, the first negative electrode active material is preferably mainly composed of primary particles, and the battery capacity is higher; at the same time, the proportion of primary particles The increase can enhance the adhesion between the first negative electrode film layer and the current collector, thereby further improving the cycle performance of the battery.
  • the first volume of the negative electrode active material particle size distribution D V 50 is greater than the volume of the second negative electrode active material particle size distribution D V 50.
  • the inventors have found that, when the volume of the first negative electrode active material particle size distribution of 50 D V 50 is greater than the volume of the second negative electrode active material particle size distribution D V, it is conducive in particular to adjust the pore structure of the porous electrode of the second active layer optimization , which helps to further improve the fast charging performance of the battery. At the same time, the optimization of the pore structure helps to reduce the local polarization of the electrode, thereby further improving the cycle performance of the battery.
  • the volume distribution particle diameter D V 50 of the first negative electrode active material may be 11 ⁇ m-20 ⁇ m, more preferably 13 ⁇ m-20 ⁇ m.
  • the volume distribution particle diameter D V 50 of the second negative electrode active material may be 11 ⁇ m to 18 ⁇ m, more preferably 12 ⁇ m to 16 ⁇ m.
  • the ratio of the compacted density of the first negative active material under a pressure of 20000N to the compacted density of the second negative active material under a pressure of 20000N is ⁇ 0.78, preferably 0.84-0.98.
  • the compacted density of the first negative electrode active material under a pressure of 20000N is 1.6 g/cm 3 ⁇ 1.88 g/cm 3 , more preferably 1.70 g/cm 3 ⁇ 1.85 g/cm 3 .
  • the compacted density of the second negative electrode active material under a pressure of 20000 N is 1.58 g/cm 3 ⁇ 1.82 g/cm 3 , more preferably 1.64 g/cm 3 ⁇ 1.74 g/cm 3 .
  • the volume distribution particle diameter D V 10 of the first negative electrode active material is 6 ⁇ m to 11 ⁇ m, more preferably 7 ⁇ m to 8 ⁇ m.
  • the volume distribution particle diameter D V 99 of the first negative electrode active material is 24 ⁇ m to 38 ⁇ m, more preferably 30 ⁇ m to 38 ⁇ m.
  • the particle size distribution (D V 90-D V 10)/D V 50 of the first negative electrode active material is 0.7 to 1.5, more preferably 0.9 to 1.3.
  • the graphitization degree of the first negative electrode active material is ⁇ 95.5%, more preferably 96.5%-98.5%.
  • the volume distribution particle diameter D V 10 of the second negative electrode active material is 6.2 ⁇ m to 9.2 ⁇ m, more preferably 6.6 ⁇ m to 8.8 ⁇ m.
  • the volume distribution particle diameter D V 99 of the second negative electrode active material is 29 ⁇ m to 43 ⁇ m, more preferably 37 ⁇ m to 41 ⁇ m.
  • the particle size distribution (D V 90-D V 10)/D V 50 of the second negative electrode active material is 0.9-1.6, more preferably 1.1-1.4.
  • the graphitization degree of the second negative electrode active material is 92.5%-96.5%, more preferably 93.1%-95.1%.
  • the mass proportion of the natural graphite in the first negative electrode active material is ⁇ 60%, more preferably, the mass proportion of the natural graphite in the first negative electrode active material is 80% to 100%.
  • the mass proportion of the artificial graphite in the second negative electrode active material is ⁇ 90%; more preferably, the mass proportion of the artificial graphite in the second negative electrode active material is 95% ⁇ 100%.
  • the thickness of the negative electrode film layer is greater than or equal to 60 ⁇ m, more preferably 65 ⁇ m to 80 ⁇ m. It should be noted that the thickness of the negative electrode film layer refers to the total thickness of the negative electrode film layer (that is, the sum of the thicknesses of the first negative electrode film layer and the second negative electrode film layer).
  • the areal density of the negative electrode film layer is 9 mg/cm 2 -14 mg/cm 2 , more preferably 11 mg/cm 2 -13 mg/cm 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 (that is, the sum of the areal densities of the first negative electrode film layer and the second negative electrode film layer).
  • the thickness ratio of the second negative electrode film layer to the first negative electrode film layer is 0.7 to 1.2, more preferably 0.75 to 1.15.
  • Accumulation on the surface layer causes the probability of lithium evolution problems, and the uniform diffusion of active ions in the membrane layer is beneficial to reduce polarization and further improve the dynamic performance and cycle performance of the battery.
  • the primary particles and the secondary particles have the meanings known in the art.
  • Primary particles refer to particles that have not formed an agglomerated state.
  • the 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 a SEM image using a scanning electron microscope. For example, FIG. 9 shows an SEM image of primary particles in a typical first negative electrode active material, and FIG. 10 shows an SEM image of secondary particles in a typical second negative electrode active material.
  • the proportion of the primary particles or the secondary particles in the negative electrode active material can be measured with an instrument and method known in the art, for example, can be measured with a scanning electron microscope.
  • the test can refer to JY/T010-1996.
  • the percentage of the total number of particles is the percentage of the number of secondary particles in the area
  • the average of the test results of multiple test areas is taken as the percentage of the number of secondary particles in the negative electrode active material.
  • the test of the proportion of the primary particles in the negative electrode active material can also be performed.
  • the D V 10, D V 50, Dv 90, and Dv 99 of the negative electrode active material all have the meanings known in the art, and can be tested by methods known in the art.
  • a laser diffraction particle size distribution measuring instrument such as the Malvern Mastersizer 3000 laser particle size analyzer.
  • Dv10 refers to the particle size when the cumulative volume percentage of the negative active material reaches 10%
  • Dv50 refers to the particle size when the cumulative volume percentage of the negative active material reaches 50%
  • Dv90 refers to the cumulative volume percentage of the negative active material reaches 90 %
  • Dv99 refers to the particle size when the cumulative volume percentage of the negative electrode active material reaches 99%.
  • the tap density of the negative electrode active material has a well-known meaning in the art, and can be tested by a method known in the art.
  • the graphitization degree of the negative electrode active material has a well-known meaning in the art, and can be tested by a method known in the art.
  • use an X-ray diffractometer such as Bruker D8 Discover
  • CuK ⁇ rays are used as the radiation source, and the wavelength of the rays is The scanning 2 ⁇ angle range is 20° ⁇ 80°, and the scanning rate can be 4°/min.
  • the powder compaction density of the material has the meaning known in the art, and can be tested by methods known in the art.
  • an electronic pressure testing machine such as UTM7305
  • the pressure is set to 20000N.
  • the thickness of the negative electrode film layer can be measured by a micrometer, for example, it can be measured by a micrometer with a model of Mitutoyo293-100 and an accuracy of 0.1 ⁇ m.
  • each of the first negative electrode film layer and the second negative electrode film layer can be tested by using a scanning electron microscope (such as ZEISS Sigma300).
  • the sample preparation is as follows: firstly, the negative pole piece is cut into a sample to be tested of a certain size (for example, 2cm ⁇ 2cm), and the negative pole piece is fixed on the sample table by paraffin wax.
  • sample stage into the sample rack, lock and fix it, turn on the power of the argon ion cross-section polisher (such as IB-19500CP) and vacuum (such as 10 -4 Pa), set the argon flow (such as 0.15 MPa) and voltage (such as 8KV) and polishing time (for example, 2 hours), adjust the sample stage to swing mode to start polishing.
  • the power of the argon ion cross-section polisher such as IB-19500CP
  • vacuum such as 10 -4 Pa
  • argon flow such as 0.15 MPa
  • voltage such as 8KV
  • polishing time for example, 2 hours
  • the average value of the test results of a plurality of test areas is taken as the average value of the thickness of the first negative electrode film layer and the second negative electrode film layer.
  • the areal density of the negative electrode film layer has a well-known meaning in the art, and can be tested by a method known in the art. For example, take a single-sided coated and cold-pressed negative electrode piece (if it is a double-sided coated negative electrode piece, wipe off the negative electrode film on one side first), die cut into a small wafer with an area of S1, and weigh Its weight is recorded as M1. Then wipe off the negative electrode film of the above-mentioned weighed negative electrode sheet, weigh the weight of the negative electrode current collector, and record it as M0.
  • the area density of the negative electrode film layer (weight of the negative electrode sheet M1-weight of the negative electrode current collector M0 )/S1.
  • multiple groups for example, 10 groups) of samples to be tested can be tested, and the average value can be calculated as the test result.
  • test sample is taken from the negative electrode film after cold pressing, as an example, the sample can be taken as follows:
  • an optical microscope or a scanning electron microscope can be used to assist in determining the position of the boundary between the first negative electrode film layer and the second negative electrode film layer.
  • the negative electrode film layer can be provided on one surface of the negative electrode current collector, or can be provided on both surfaces of the negative electrode current collector at the same time.
  • FIG. 2 shows a schematic diagram of an embodiment of the negative pole piece 10 according to the present application.
  • the negative electrode piece 10 is composed of a negative electrode current collector 101, a first negative electrode film layer 103 respectively disposed on both surfaces of the negative electrode current collector, and a second negative electrode film layer 102 disposed on the first negative electrode film layer 103.
  • FIG. 3 shows a schematic diagram of another embodiment of the negative pole piece 10 according to the present application.
  • the negative electrode piece 10 is composed of a negative electrode current collector 101, a first negative electrode film layer 103 disposed on one surface of the negative electrode current collector, and a second negative electrode film layer 102 disposed on the first negative electrode film layer 103.
  • each negative electrode film layer (such as film thickness, areal density, compaction density, etc.) given in this application all refer to the parameter range of a single-sided film layer.
  • the film layer parameters on any one of the surfaces meet the requirements of the present application, which is considered to fall within the protection scope of the present application.
  • the ranges of film thickness, areal density and the like mentioned in this application all refer to the film parameters after being compacted by cold pressing and used for assembling the battery.
  • the negative electrode current collector can be a metal foil or a composite current collector (a metal material can be arranged on a polymer substrate to form a composite current collector).
  • a metal material can be arranged on a polymer substrate to form a composite current collector.
  • copper foil may be used as the negative electrode current collector.
  • the first negative electrode film layer and/or the second negative electrode film layer usually include a negative electrode active material, an optional binder, an optional conductive agent, and other optional auxiliary agents, It is usually formed by coating and drying the negative electrode film slurry.
  • the negative electrode film slurry coating is usually formed by dispersing the negative electrode active material and optional conductive agent and binder in a solvent and stirring uniformly.
  • the solvent can be N-methylpyrrolidone (NMP) or deionized water, for example.
  • Other optional additives can be, for example, thickening and dispersing agents (such as sodium carboxymethyl cellulose CMC-Na), PTC thermistor materials, and the like.
  • the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
  • the binder may include styrene-butadiene rubber (SBR), water-based acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer One or more of (EVA), polyvinyl alcohol (PVA) and polyvinyl butyral (PVB).
  • SBR styrene-butadiene rubber
  • PVDF polyvinylidene fluoride
  • PTFE polytetrafluoroethylene
  • EVA ethylene-vinyl acetate copolymer
  • EVA polyvinyl alcohol
  • PVB polyvinyl butyral
  • the first negative electrode active material and/or the second negative electrode active material may optionally include a certain amount of other commonly used negative electrode active materials in addition to the aforementioned negative electrode active material of the present application, For example, one or more of soft carbon, hard carbon, silicon-based material, tin-based material, and lithium titanate.
  • the silicon-based material can be selected from one or more of elemental silicon, silicon-oxygen compounds, silicon-carbon composites, and silicon alloys.
  • the tin-based material can be selected from one or more of elemental tin, tin oxide compounds, and tin alloys. The preparation methods of these materials are well known and can be obtained commercially. Those skilled in the art can make an appropriate choice according to the actual use environment.
  • the negative electrode sheet does not exclude other additional functional layers besides the above-mentioned negative electrode film layer.
  • the negative pole piece of the present application may further include a conductive coating (for example, composed of a conductive agent and a binder) disposed between the negative current collector and the first film layer.
  • the negative pole piece of the present application may further include a protective layer provided on the surface of the second film layer.
  • the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer provided 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 its thickness direction, 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 metal foil or a composite current collector (a metal material can be arranged on a polymer substrate to form a composite current collector).
  • a metal material can be arranged on a polymer substrate to form a composite current collector.
  • aluminum foil may be used as the positive electrode current collector.
  • the positive active material may be a positive active material for secondary batteries that is well known in the art.
  • the positive electrode active material may include one or more of lithium transition metal oxides, lithium-containing phosphates with an olivine structure, 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
  • lithium-containing phosphates with an olivine structure may include, but are not limited to, lithium iron phosphate, lithium iron phosphate and carbon composite material, lithium manganese phosphate, lithium manganese phosphate and carbon composite material, lithium iron manganese phosphate, lithium iron manganese phosphate
  • One or more of the composite materials with carbon and its modified compounds may be used. The present application is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials for secondary batteries can also be used.
  • the positive electrode active material may include one or more of the lithium transition metal oxide and its modified compounds shown in Formula 1.
  • M is selected from Mn, Al, Zr
  • Zn is selected from Mn, Al, Zr
  • Zn is selected from Mn, Al, Zr
  • Zn is selected from Mn, Al, Zr
  • Zn is selected from Mn, Al, Zr
  • Zn is selected from Mn, Al, Zr
  • Zn is selected from Mn, Al, Zr
  • Zn is selected from Mn, Al, Zr
  • Zn 0.5 ⁇ b ⁇ 1, 0 ⁇ c ⁇ 1, 0 ⁇ d ⁇ 1, 1 ⁇ e ⁇ 2, 0 ⁇ f ⁇ 1, M is selected from Mn, Al, Zr
  • Zn is selected from Mn, Al, Zr
  • Zn is selected from Cu, Cr, Mg, Fe, V, Ti and B
  • A is selected from one or more of N, F, S and Cl.
  • the modification compound of each of the above-mentioned 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 used 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 conducts ions between the positive pole piece and the negative pole piece.
  • the type of electrolyte in this application can be selected according to requirements.
  • the electrolyte may be selected from at least one of solid electrolytes and liquid electrolytes (ie, electrolytes).
  • an electrolyte is used as the electrolyte.
  • the electrolyte includes electrolyte salt and solvent.
  • the electrolyte salt can be selected from LiPF 6 (lithium hexafluorophosphate), LiBF 4 (lithium tetrafluoroborate), LiClO 4 (lithium perchlorate), LiAsF 6 (lithium hexafluoroarsenate), LiFSI (bisfluorosulfonate) Lithium imide), LiTFSI (lithium bistrifluoromethanesulfonimide), LiTFS (lithium trifluoromethanesulfonate), LiDFOB (lithium difluorooxalate), LiBOB (lithium bisoxalate), LiPO 2 F 2 (Lithium difluorophosphate), LiDFOP (lithium difluorodioxalate phosphate) and LiTFOP (lithium tetrafluorooxalate phosphate) one or more.
  • LiPF 6 lithium hexafluorophosphate
  • LiBF 4 lithium tetrafluoroborate
  • 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), ethylene 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) , Ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS) and diethyl sulfone (ESE) one
  • the electrolyte may also optionally include additives.
  • the additives can include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and battery low-temperature performance. Additives, etc.
  • isolation film is arranged between the positive pole piece and the negative pole piece to play a role of isolation.
  • isolation membrane there is no particular limitation on the type of isolation membrane in this application, and any well-known porous structure isolation membrane with good chemical stability and mechanical stability can be selected.
  • the material of the isolation membrane can be selected from one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride.
  • the isolation film can be a single-layer film or a multilayer composite film. When the isolation film is a multilayer composite film, the materials of each layer can be the same or different.
  • the positive pole piece, the negative pole piece, and the separator can be made into an electrode assembly through a winding process or a lamination process.
  • the secondary battery may include an outer package.
  • the outer packaging 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, aluminum case, steel case, or the like.
  • the outer packaging of the secondary battery may also be a soft bag, such as a pouch type soft bag.
  • the material of the soft bag can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), and the like.
  • FIG. 1 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 enclose a receiving cavity.
  • the housing 51 has an opening communicating with the containing cavity, and the cover plate 53 is used to cover the opening to close the containing 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 is infiltrated in the electrode assembly 52.
  • the number of electrode assemblies 52 included in the secondary battery 5 can be one or several, which can be adjusted according to requirements.
  • the secondary battery can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.
  • Fig. 5 is a battery module 4 as an example.
  • a plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4. Of course, it can also be arranged in any other manner. Furthermore, the plurality of secondary batteries 5 can be fixed by fasteners.
  • the battery module 4 may further include a housing having an accommodating space, and a plurality of secondary batteries 5 are accommodated in the accommodating space.
  • the above-mentioned battery modules can also be assembled into a battery pack, and the number of battery modules contained 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 box and a plurality of battery modules 4 provided in the battery box.
  • 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 module 4.
  • a plurality of battery modules 4 can be arranged in the battery box in any manner.
  • the second aspect of the present application provides a method for preparing a secondary battery, which includes preparing the negative pole piece of the secondary battery through the following steps:
  • first negative electrode film layer including a first negative electrode active material on at least one surface of a negative electrode current collector, the first negative electrode active material including natural graphite;
  • the second negative electrode active material includes artificial graphite
  • the second negative electrode active material includes secondary particles
  • the first negative electrode active material slurry and the second negative electrode active material slurry may be applied at the same time at one time, or may be applied in two separate steps.
  • the first negative active material slurry and the second negative active material slurry are simultaneously coated at one time. Coating at the same time can make the adhesion between the upper and lower negative film layers better, which helps to further improve the cycle performance of the battery.
  • the positive pole piece 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) In the process, after stirring, it is coated on the positive electrode current collector, and the positive electrode piece is obtained after drying. Materials such as metal foil such as aluminum foil or porous metal plate can be used as the positive electrode current collector.
  • the positive electrode tab can be obtained by punching or laser die cutting in the uncoated area of the positive electrode current collector.
  • the third aspect of the present application provides a device.
  • the device includes the secondary battery of the first aspect of the present application or the secondary battery prepared by the method of the second aspect of the present application.
  • the secondary battery 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 of the present application uses the secondary battery provided by the present application, and therefore has at least the same advantages as the secondary battery.
  • the device can be, but is not limited to, mobile devices (such as mobile phones, laptop computers, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf Vehicles, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.
  • mobile devices such as mobile phones, laptop computers, etc.
  • electric vehicles such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf Vehicles, electric trucks, etc.
  • electric trains ships and satellites, energy storage systems, etc.
  • the device can select a secondary battery, a battery module, or a battery pack according to its usage requirements.
  • Fig. 8 is a device as an example.
  • the device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc.
  • a battery pack or a battery module can be used.
  • the device may be a mobile phone, a tablet computer, a notebook 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 areal density of the positive electrode film layer is 19.0 mg/cm 2 ; the compacted density of the positive electrode film layer is 3.4 g/cm 3 .
  • the first step is to prepare negative electrode slurry 1: the first negative electrode active material natural graphite, binder SBR, thickener sodium carboxymethyl cellulose (CMC-Na) and conductive carbon black (Super P) are weighed to The weight ratio of 96.2:1.8:1.2:0.8 and deionized water are added to the stirring tank in a certain order for mixing to prepare negative electrode slurry 1.
  • the first negative electrode active material natural graphite, binder SBR, thickener sodium carboxymethyl cellulose (CMC-Na) and conductive carbon black (Super P) are weighed to The weight ratio of 96.2:1.8:1.2:0.8 and deionized water are added to the stirring tank in a certain order for mixing to prepare negative electrode slurry 1.
  • the second step is to prepare negative electrode slurry 2: the second negative electrode active material artificial graphite, binder SBR, thickener sodium carboxymethyl cellulose (CMC-Na) and conductive carbon black (Super P) are weighed to The weight ratio of 96.2:1.8:1.2:0.8 and deionized water are added to the stirring tank in a certain order and mixed to prepare negative electrode slurry 2.
  • the second negative electrode active material artificial graphite, binder SBR, thickener sodium carboxymethyl cellulose (CMC-Na) and conductive carbon black (Super P) are weighed to The weight ratio of 96.2:1.8:1.2:0.8 and deionized water are added to the stirring tank in a certain order and mixed to prepare negative electrode slurry 2.
  • the negative electrode slurry 1 and the negative electrode slurry 2 are simultaneously extruded through a dual-cavity coating device.
  • the negative electrode slurry 1 is coated on the current collector to form the first negative electrode film layer
  • the negative electrode slurry 2 is coated on the first negative electrode film layer to form the second negative electrode film layer; the quality of the first negative electrode film layer and the second negative electrode film layer
  • the ratio is 1:1; the areal density of the negative electrode film layer is 12 mg/cm 2 ; the compaction density of the negative electrode film layer is 1.67 g/cm 3 .
  • the coated wet film is baked in an oven through different temperature zones to obtain dry pole pieces, and then cold-pressed to obtain the required negative electrode film layer, and then to obtain negative pole pieces through processes such as slitting and cutting.
  • EC ethylene carbonate
  • EMC ethyl methyl carbonate
  • DEC diethyl carbonate
  • the reference electrode is used for the subsequent performance testing of battery samples, you can choose lithium, lithium Metal wire, etc., and the reference electrode should be separated by a separator to prevent contact with either side of the positive and negative electrodes).
  • the electrode assembly is obtained.
  • a secondary battery is obtained.
  • the secondary batteries of Examples 2-21 and the secondary batteries of Comparative Examples 1-4 are similar to the preparation method of the secondary battery of Example 1, but the composition and product parameters of the battery pole pieces are adjusted. The different product parameters are detailed in the table 1 and Table 2.
  • the secondary batteries prepared in the above examples and comparative examples were charged and discharged for the first time with a current of 1C (that is, the current value at which the theoretical capacity was completely discharged within 1h), which specifically includes: Charge at a constant current rate to the charge cut-off voltage V1, then charge at a constant voltage to a current ⁇ 0.05C, stand for 5 minutes, and discharge at a constant current rate of 0.33C to the discharge cut-off voltage V2, and record its actual capacity as C0.
  • a current of 1C that is, the current value at which the theoretical capacity was completely discharged within 1h
  • the secondary batteries prepared in each of the above examples and comparative examples were charged according to the charging strategy corresponding to the maximum charging time T, discharged at a rate of 1C, and subjected to a full charge and discharge cycle test until the capacity of the battery decays to the initial 80% of the capacity, record the number of cycles.
  • the secondary batteries prepared in the above examples and comparative examples were charged to the charge cut-off voltage V1 at a rate of 1C, then charged at a constant voltage to a current of 0.05C, allowed to stand for 5 minutes, and then discharged at a rate of 0.33C at a constant current Until the discharge cut-off voltage V2, the initial capacity of the battery is obtained. Then charge the battery to the charge cut-off voltage V1 at a rate of 1C at 25°C, and then charge it to a current of 0.05C at a constant voltage. At this time, the battery is fully charged, and the fully charged battery is stored in a thermostat at 60°C. .
  • the battery needs to be charged to the charge cut-off voltage V1 at a rate of 1C, and then charged to a current of 0.05C at a constant voltage to keep the battery in a fully charged state, and then placed Store in a 60°C incubator.
  • the batteries of each embodiment and comparative example were prepared according to the above methods, and various performance parameters were measured. The results are shown in Table 1 and Table 2 below.
  • the negative electrode film layer includes a double coating structure
  • the negative electrode active material of the lower layer includes natural graphite
  • the negative electrode active material of the upper layer includes artificial graphite, only when the second negative electrode
  • the battery can have better fast charging performance and longer cycle life at the same time.
  • S2 ⁇ 50% Preferably, S2 ⁇ 50%.
  • the negative electrode active material of the lower layer includes natural graphite
  • the negative electrode active material of the upper layer includes artificial graphite
  • S2 is the preferred value
  • the negative electrode active material of each layer a volume distribution of particle diameter D V of the relation between the battery 50 has a greater impact on performance; when the first volume of the negative electrode active material particle size distribution D V 50 is greater than the volume of the second negative electrode active material 50 of the particle size distribution D V, The fast charge performance and cycle performance of the battery are better.

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Abstract

本申请涉及一种二次电池、其制备方法及含有该二次电池的装置。具体地，本申请的二次电池包括负极极片，所述负极极片包括负极集流体及负极膜层，所述负极膜层包括第一负极膜层和第二负极膜层；所述第一负极膜层设置在负极集流体至少一个表面上且包括第一负极活性材料，所述第一负极活性材料包括天然石墨；所述第二负极膜层设置在第一负极膜层上且包括第二负极活性材料，所述第二负极活性材料包括人造石墨，且所述第二负极活性材料中包括二次颗粒，所述二次颗粒在所述第二负极活性材料中的数量占比S2≥20％。本申请的二次电池在具有较高能量密度的前提下，兼顾较好的快速充电性能、循环性能及高温存储性能。

Description

二次电池、其制备方法及含有该二次电池的装置 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、其制备方法及含有该二次电池的装置。
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。
随着新能源行业的不断发展，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性能和使用寿命有不利影响。如何使二次电池在具有较高能量密度的前提下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，有必要提供一种能够解决上述问题的二次电池。
发明内容
鉴于现有技术中存在的技术问题，本申请提供一种二次电池及含有它的装置，旨在使二次电池在具有较高能量密度的前提下，同时兼顾较好的动力学性能(快速充电性能)和较长的循环寿命。
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，该二次电池包括负极极片，所述负极极片包括负极集流体及负极膜层，所述负极膜层包括第一负极膜层和第二负极膜层；所述第一负极膜层设置在负极集流体至少一个表面上且包括第一负极活性材料，所述第一负极活性材料包括天然石墨；所述第二负极膜层设置在第一负极膜层上且包括第二负极活性材料，所述第二负极活性材料包括人造石墨，且所述第二负极活性材料中包括二次颗粒，所述二次颗粒在所述第二负极活性材料中的数量占比S2≥20％。
本申请的第二方面提供一种二次电池的制造方法，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个表面上形成包括第一负极活性材料的第一负极膜层，所述第一负极活性材料包括天然石墨；
2)在所述第一负极膜层上形成包括第二负极活性材料的第二负极膜层，所述第二负极活性材料包括人造石墨，且所述第二负极活性材料中包括二次颗粒，所述二次颗粒在所述第二负极活性材料中的数量占比S2≥20％。
本申请的第三方面提供一种装置，其包括本申请第一方面所述的二次电池或按照本申请第二方面所述方法制造的二次电池。
相对于现有技术，本申请至少包括如下所述的有益效果：
本申请的二次电池中，负极极片包括双涂层结构，且第一负极膜层和第二负极膜层包含特定的负极活性材料，从而使电池可在具有较高能量密度的前提下，同时兼顾快速充电性能及循环性能。优选地，电池还能具有较好的高温存储性能。本申请的装置包括所述的二次电池，因而至少具有与所述二次电池相同的优势。
附图说明
图1是本申请的二次电池的一实施方式的示意图。
图2是本申请的二次电池中负极极片的一实施方式的示意图。
图3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4是本申请的二次电池的一实施方式的分解示意图。
图5是电池模块的一实施方式的示意图。
图6是电池包的一实施方式的示意图。
图7是图6的分解图。
图8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。
图9是本申请第一负极活性材料的一实施方式中一次颗粒的SEM图像。
图10是本申请第二负极活性材料的一实施方式中二次颗粒的SEM图像。
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第二负极膜层
103第一负极膜层
具体实施方式
下面结合具体实施方式，进一步阐述本申请。应理解，这些具体实施方式仅用于说明本申请而不用于限制本申请的范围。
为了简明，本文仅具体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，每个单独公开的点或单个数值自身可以作为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。
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)。
二次电池
本申请的第一方面提供一种二次电池。该二次电池包括正极极片、负极极片、及电解质。在电池充放电过程中，活性离子在正极极片和负极极片之间往返嵌入和脱出。电解质在正极极片和负极极片之间起到传导离子的作用。
[负极极片]
在本申请的二次电池中，所述负极极片包括负极集流体及负极膜层，所述负极膜层包括第一负极膜层和第二负极膜层；所述第一负极膜层设置在负极集流 体至少一个表面上且包括第一负极活性材料，所述第一负极活性材料包括天然石墨；所述第二负极膜层设置在第一负极膜层上且包括第二负极活性材料，所述第二负极活性材料包括人造石墨，且所述第二负极活性材料中包括二次颗粒，所述二次颗粒在所述第二负极活性材料中的数量占比S2≥20％。
发明人经研究发现，当二次电池的负极极片包括双膜层结构，且上、下膜层包括特定组成的负极活性材料时，电池可同时兼顾快速充电性能和循环性能。当电池在充电过程中时，沿负极极片厚度方向，越靠近隔离膜侧，活性离子浓度越高，越靠近集流体侧，活性离子浓度越小。第二负极膜层更加靠近隔膜侧，其所在区域的活性离子浓度较高，若第二负极膜层中活性材料包含一定含量的二次颗粒时，其可提供的脱嵌活性离子通道增多，其正好与该区域的活性离子实际分布匹配，可保证电池兼具优异的快速充电性能和循环性能。
在本申请中，S2的范围可以为：30％≤B≤100％，40％≤B≤85％，45％≤B≤98％，50％≤B≤100％，55％≤B≤95％，60％≤B≤95％，80％≤B≤100％，90％≤B≤100％等。
在一些优选的实施方式中，所述二次颗粒在第二负极活性材料中的数量占比S2≥50％。
发明人进一步研究发现，随着二次颗粒的含量增加，负极活性材料在极片冷压过程中会增加大量的新界面，从而增加了负极活性材料与电解液之间的副反应，在一定程度上影响电池的高温存储性能。所以，为了进一步平衡快速充电性能、循环性能及高温存储性能，在一些实施方式中，50％≤S2≤85％。
本发明人经深入研究发现，当本申请的二次电池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设计中的一个或几个时，可以进一步改善二次电池的性能。
在一些优选的实施方式中，所述第一负极活性材料包括一次颗粒，所述一次颗粒在第一负极活性材料中的数量占比S1≥80％；更优选地，90％≤S1≤100％。第一负极膜层更加靠近负极集流体侧，其所在区域的活性离子浓度较低，因此第一负极活性材料中优选以一次颗粒居多，此时电池的容量较高；同时，一次颗粒的占比增大可以使第一负极膜层与集流体之间的粘接性增强，从而进一步改善电池的循环性能。
在一些优选的实施方式中，所述第一负极活性材料的体积分布粒径D V50大 于所述第二负极活性材料的体积分布粒径D V50。发明人研究发现，当第一负极活性材料的体积分布粒径D V50大于第二负极活性材料的体积分布粒径D V50时，有利于调整多孔电极特别是第二活性层的孔道结构优化，有助于进一步改善电池的快速充电性能，同时，孔道结构的优化有助于减少电极的局部极化，从而进一步提升电池的循环性能。
在一些优选的实施方式中，所述第一负极活性材料的体积分布粒径D V50可以为11μm～20μm，更优选为13μm～20μm。
在一些优选的实施方式中，所述第二负极活性材料的体积分布粒径D V50可以为11μm～18μm，更优选为12μm～16μm。
在一些优选的实施方式中，所述第一负极活性材料在20000N压力下的压实密度与所述第二负极活性材料在20000N压力下的压实密度的比值≥0.78，优选为0.84～0.98。
在一些优选的实施方式中，所述第一负极活性材料在20000N压力下的压实密度为1.6g/cm 3～1.88g/cm 3，更优选为1.70g/cm 3～1.85g/cm 3。
在一些优选的实施方式中，所述第二负极活性材料在20000N压力下的压实密度为1.58g/cm 3～1.82g/cm 3，更优选为1.64g/cm 3～1.74g/cm 3。
在一些优选的实施方式中，所述第一负极活性材料的体积分布粒径D V10为6μm～11μm，更优选为7μm～8μm。
在一些优选的实施方式中，所述第一负极活性材料的体积分布粒径D V99为24μm～38μm，更优选为30μm～38μm。
在一些优选的实施方式中，所述第一负极活性材料的粒度分布(D V90-D V10)/D V50为0.7～1.5，更优选为0.9～1.3。
在一些优选的实施方式中，所述第一负极活性材料的石墨化度为≥95.5％，更优选为96.5％～98.5％。
在一些优选的实施方式中，所述第二负极活性材料的体积分布粒径D V10为6.2μm～9.2μm，更优选为6.6μm～8.8μm。
在一些优选的实施方式中，所述第二负极活性材料的体积分布粒径D V99为29μm～43μm，更优选为37μm～41μm。
在一些优选的实施方式中，所述第二负极活性材料的粒度分布(D V90-D V10)/D V50为0.9～1.6，更优选为1.1～1.4。
在一些优选的实施方式中，所述第二负极活性材料的石墨化度为92.5％～96.5％，更优选为93.1％～95.1％。
在一些优选实施方式中，所述天然石墨在所述第一负极活性材料中的质量占比≥60％，更优选地，所述天然石墨在所述第一负极活性材料中的质量占比为80％～100％。
在一些优选实施方式中，所述人造石墨在所述第二负极活性材料中的质量占比≥90％；更优选地，所述人造石墨在所述第二负极活性材料中的质量占比为95％～100％。
在一些优选的实施方式中，所述负极膜层的厚度≥60μm，更优选为65μm～80μm。需要说明的是，所述负极膜层的厚度是指负极膜层的总厚度(即第一负极膜层和第二负极膜层的厚度总和)。
在一些优选的实施方式中，所述负极膜层的面密度为9mg/cm 2～14mg/cm 2，更优选为11mg/cm 2～13mg/cm 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)。
在一些优选的实施方式中，所述第二负极膜层与所述第一负极膜层的厚度比值为0.7～1.2，更优选为0.75～1.15。第一、第二负极膜层的厚度比值在所给范围内时，有利于上下层形成合适的梯度孔隙分布，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，有效降低离子在表层堆积引起析锂问题的概率，同时活性离子在膜层中的均匀扩散有利于减小极化，进一步提升电池的动力学性能和循环性能。
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9示出了典型的第一负极活性材料中一次颗粒的SEM图像，图10示出了典型的第二负极活性材料中二次颗粒的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仪器及方法进行测定，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20个)不同区域进行扫描测试，并在一定放大倍率(例如1000倍)下，计算各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，取多个测试区域的测试结果的平均值作为负极活性材料中二次颗粒的数量占比。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D V10、D V50、Dv90、Dv99均具有本领域公知的含义，可以采用本领域已知的方法测试。例如参照标准GB/T 19077.1-2016，用激光衍射粒度分布测量仪(如Malvern Mastersizer 3000激光粒度仪)直接测试得到。其中，Dv10是指负极活性材料累计体积百分数达到10％时所对应的粒径；Dv50指负极活性材料累计体积百分数达到50％时所对应的粒径；Dv90是指负极活性材料累计体积百分数达到90％时所对应的粒径；Dv99是指负极活性材料累计体积百分数达到99％时所对应的粒径。
在本申请中，负极活性材料的振实密度具有本领域公知的含义，可以采用本领域已知的方法测试。例如可参照标准GB/T 5162-2006，使用粉体振实密度测试仪(如丹东百特BT-301)测试。
在本申请中，负极活性材料的石墨化度具有本领域公知的含义，可以采用本领域已知的方法测试。例如使用X射线衍射仪(如Bruker D8 Discover)测试。测试可参考JIS K 0131-1996、JB/T 4220-2011，测出d002的大小，然后根据公式G＝(0.344-d002)/(0.344-0.3354)×100％计算得出石墨化度，其中d002是以nm计的石墨晶体结构中的层间距。在X射线衍射分析测试中以CuKα射线为辐射源，射线波长
Figure PCTCN2020088301-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，材料的粉体压实密度具有本领域公知的含义，可以采用本领域已知的方法测试。例如可参照GB/T 24533-2009，使用电子压力试验机(如UTM7305)测试：将一定量的粉末放于压实专用模具上，设置不同压力，在设备上可以读出不同压力下粉末的厚度，计算可得不同压力下的压实密度。在本申请中，将压力设置为20000N。
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，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。样品制备如下：首先将负极极片 裁成一定尺寸的待测样品(例如2cm×2cm)，通过石蜡将负极极片固定在样品台上。然后将样品台装进样品架上锁好固定，打开氩离子截面抛光仪(例如IB-19500CP)电源和抽真空(例如10 -4Pa)，设置氩气流量(例如0.15MPa)和电压(例如8KV)以及抛光时间(例如2小时)，调整样品台为摇摆模式开始抛光。样品测试可参考JY/T010-1996。为了确保测试结果的准确性，可以在待测样品中随机选取多个(例如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第一负极膜层和第二负极膜层的厚度均值。
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测试。例如取单面涂布且经冷压后的负极极片(若是双面涂布的负极极片，可先擦拭掉其中一面的负极膜层)，冲切成面积为S1的小圆片，称其重量，记录为M1。然后将上述称重后的负极极片的负极膜层擦拭掉，称量负极集流体的重量，记录为M0，负极膜层的面密度＝(负极极片的重量M1-负极集流体的重量M0)/S1。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，并计算平均值作为测试结果。
需要说明的是，上述针对负极活性材料的各种参数测试，可以在涂布前取样测试，也可以从冷压后的负极膜层中取样测试。
当上述测试样品是从经冷压后的负极膜层中取样时，作为示例，可以按如下步骤进行取样：
(1)首先，任意选取一冷压后的负极膜层，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；
(2)其次，对第一负极活性材料取样，因在负极膜层冷压过程中，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活性材料和第二活性材料)，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)将上述收集到的第一负极活性材料和第二负极活性材料分别置于去离子水中，并将第一负极活性材料和第二负极活性材料进行抽滤，烘干，再将烘干后的各负极活性材料在一定温度及时间下烧结(例如400℃，2h)，去除粘结剂和导电碳，即得到第一负极活性材料和第二负极活性材料的测试样品。
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。
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。
本申请作为负极活性材料使用的天然石墨和人造石墨均可以通过商业途径获得。
本申请的二次电池中，所述负极膜层可以设置在负极集流体的一个表面上，也可以同时设置在负极集流体的两个表面上。
图2示出了根据本申请的负极极片10的一种实施方式的示意图。负极极片10由负极集流体101、分别设置在负极集流体两个表面上的第一负极膜层103和设置在第一负极膜层103上的第二负极膜层102构成。
图3示出了根据本申请的负极极片10的另一种实施方式的示意图。负极极片10由负极集流体101、设置在负极集流体一个表面上的第一负极膜层103和设置在第一负极膜层103上的第二负极膜层102构成。
需要说明的是，本申请所给的各负极膜层参数(例如膜层厚度、面密度、压实密度等)均指单面膜层的参数范围。当负极膜层设置在负极集流体的两个表面上时，其中任意一个表面上的膜层参数满足本申请，即认为落入本申请的保护范围内。且本申请所述的膜层厚度、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。
本申请的二次电池中，所述负极集流体可以采用金属箔片或复合集流体(可以将金属材料设置在高分子基材上形成复合集流体)。作为示例，负极集流体可以采用铜箔。
本申请的二次电池中，所述第一负极膜层和/或所述第二负极膜层通常包含负极活性材料以及可选的粘结剂、可选的导电剂和其他可选助剂，通常是由负极膜层浆料涂布干燥而成的。负极膜层浆料涂通常是将负极活性材料以及可选的导电剂和粘结剂等分散于溶剂中并搅拌均匀而形成的，溶剂例如可以是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，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一种或几种。
作为示例，粘结剂可以包括丁苯橡胶(SBR)、水性丙烯酸树脂(water-based acrylic resin)、聚偏二氟乙烯(PVDF)、聚四氟乙烯(PTFE)、乙烯-醋酸乙烯酯共聚物(EVA)、聚乙烯醇(PVA)及聚乙烯醇缩丁醛(PVB)中的一种或多种。
本申请的二次电池中，所述第一负极活性材料和/或所述第二负极活性材料除了包括本申请上述的负极活性材料外，还可选地包括一定量的其他常用负极活性材料，例如，软炭、硬炭、硅基材料、锡基材料、钛酸锂中的一种或几种。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。
本申请的二次电池中，所述负极极片并不排除除了上述负极膜层之外的其他附加功能层。例如在一些实施方式中，本申请的负极极片还可以包括设置在负极集流体和第一膜层之间的导电涂层(例如由导电剂和粘结剂组成)。在另外一些实施方式中，本申请的负极极片还可以包括设置在第二膜层表面上的保护层。
[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。
在一些优选的实施方式中，为了进一步提高电池的能量密度，正极活性材料可以包括式1所示的锂过渡金属氧化物及其改性化合物中的一种或几种，
Li aNi bCo cM dO eA f     式1，
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1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4，外包装可包括壳体51和盖板53。其中，壳体51可包括底板和连接于底板上的侧板，底板和侧板围合形成容纳腔。壳体51具有与容纳腔连通的开口，盖板53用于盖设所述开口，以封闭所述容纳腔。正极极片、负极极片和隔离膜可经卷绕工艺或叠片工艺形成电极组件52。电极组件52封装于所述容纳腔。电解液浸润于电极组件52中。二次电池5所含电极组件52的数量可以为一个或几个，可根据需求来调节。
在一些实施方式中，二次电池可以组装成电池模块，电池模块所含二次电池的数量可以为多个，具体数量可根据电池模块的应用和容量来调节。
图5是作为一个示例的电池模块4。参照图5，在电池模块4中，多个二次电池5可以是沿电池模块4的长度方向依次排列设置。当然，也可以按照其他任意的方式进行排布。进一步可以通过紧固件将该多个二次电池5进行固定。
可选地，电池模块4还可以包括具有容纳空间的外壳，多个二次电池5容纳于该容纳空间。
在一些实施方式中，上述电池模块还可以组装成电池包，电池包所含电池模块的数量可以根据电池包的应用和容量进行调节。
图6和图7是作为一个示例的电池包1。参照图6和图7，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。
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，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个表面上形成包括第一负极活性材料的第一负极膜层，所述第一负极活性材料包括天然石墨；
2)在所述第一负极膜层上形成包括第二负极活性材料的第二负极膜层，所述第二负极活性材料包括人造石墨，且所述第二负极活性材料中包括二次颗粒，所述二次颗粒在所述第二负极活性材料中的数量占比S2≥20％。
本申请二次电池的制备方法中，第一负极活性材料浆料和第二负极活性材料浆料可以一次同时涂布，也可以分两次涂布。
在一些优选的实施方式中，第一负极活性材料浆料和第二负极活性材料浆料一次同时涂布。一次同时涂布可以使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，然后通过卷绕(或叠片)工艺得到电极组件；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。
装置
本申请的第三方面提供一种装置。该装置包括本申请第一方面的二次电池或包括通过本申请第二方面的方法制备得到的二次电池。所述二次电池可以用作所述装置的电源，也可以用作所述装置的能量存储单元。本申请的装置采用了本申请所提供的二次电池，因此至少具有与所述二次电池相同的优势。
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8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、二次电池的制备
实施例1
1)正极极片的制备
将锂镍钴锰三元活性物质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94：3：3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、裁切等工序得到正极极片。正极膜层的面密度为19.0mg/cm 2；正极膜层的压实密度为3.4g/cm 3。
2)负极极片的制备
第一步，制备负极浆料1：将第一负极活性材料天然石墨、粘结剂SBR、增稠剂羧甲基纤维素钠(CMC-Na)以及导电炭黑(Super P)进行称重以96.2：1.8：1.2：0.8的重量比和去离子水，按一定顺序加入搅拌罐中进行混合，制备负极浆料1。
第二步，制备负极浆料2：将第二负极活性材料人造石墨、粘结剂SBR、增稠剂羧甲基纤维素钠(CMC-Na)以及导电炭黑(Super P)进行称重以96.2：1.8：1.2：0.8的重量比和去离子水，按一定顺序加入搅拌罐中进行混合，制备负极浆料2。
第三步，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；第一负极膜层与第二负极膜层的质量比为1:1；负极膜层的面密度为12mg/cm 2；负极膜层的压实密度为1.67g/cm 3。
第四步，涂覆出的湿膜经过烘箱通过不同温区进行烘烤得到干燥极片，再经过冷压得到需要的负极膜层，再经分条、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，并在隔离膜和负极极片之间增加参比电极(参比电极用于电池样品后续的性能检测，可选择锂片、锂金属丝等，且参比电极应通过隔离膜隔开，防止和正负极任意一侧接触)，经卷绕后得到电极组件，将电极组件装入外包装中，加入上述电解液，经封装、静置、化成、老化等工序后，得到二次电池。
实施例2～21的二次电池和对比例1～4的二次电池与实施例1的二次电池制备方法相似，但是调整了电池极片的组成和产品参数，不同的产品参数详见表1和表2。
二、电池性能测试
1、快速充电性能测试
25℃下，将上述各实施例和对比例制备得到的二次电池以1C(即1h内完全放掉理论容量的电流值)的电流进行第一次充电和放电，具体包括：将电池以1C倍率恒流充电至充电截止电压V1，之后恒压充电至电流≤0.05C，静置5min，再以0.33C倍率恒流放电至放电截止电压V2，记录其实际容量为C0。
然后将电池依次以2.8C0、3C0、3.2C0、3.5C0、3.8C0、4.1C0、4.4C0、4.7C0、5C0、5.3C0、5.6C0、5.9C0恒流充电至全电池充电截止电压V1或者0V负极截止电位(以先达到者为准)，每次充电完成后需以1C0放电至全电池放电截止电压V2，记录不同充电倍率下充电至10％、20％、30％、……、80％SOC(State of Charge，荷电状态)时所对应的负极电位，绘制出不同SOC态下的充电倍率-负极电位曲线，线性拟合后得出不同SOC态下负极电位为0V时所对应的充电倍率，该充电倍率即为该SOC态下的充电窗口，分别记为C10％SOC、C20％SOC、C30％SOC、C40％SOC、C50％SOC、C60％SOC、C70％SOC、C80％SOC，根据公式(60/C20％SOC+60/C30％SOC+60/C40％SOC+60/C50％SOC+60/C60％SOC+60/C70％SOC+60/C80％SOC)×10％计算得到该电池从10％SOC充电至80％SOC的充电时间T，单位为min。该时间越短，则电池的快速充电性能越优秀。
2、循环性能测试
在25℃下，将上述各实施例和对比例制备得到的二次电池以上述最大充电时间T对应的充电策略充电、以1C倍率放电，进行满充满放循环测试，直至电池的容量衰减至初始容量的80％，记录循环次数。
3、高温存储性能测试
25℃下，将上述各实施例和对比例制备得到的二次电池，以1C倍率充电至充电截止电压V1，之后恒压充电至电流0.05C，静置5min，再以0.33C倍率恒流放电至放电截止电压V2，获得电池的初始容量。然后在25℃下，将电池以1C倍率充电至充电截止电压V1，之后恒压充电至电流0.05C，此时电池为满充状态，将满充后的电池置于60℃的恒温箱中保存。每隔7天将电池取出一次，并在25℃下以0.33C倍率放电至放电截止电压V2，静置5min，然后以1C充电至充电截止电压V1，之后恒压充电至电流0.05C，静置5min，再以0.33C倍率恒流放电，测试此时电池的容量。直至容量衰减至初始容量的80％时，记录存储的天数。(需说明的是，每次将电池取出测试完容量后，均需将电池以1C倍率充电至充电截止电压V1，之后恒压充电至电流0.05C，使电池保持满充状态，然后再置于60℃恒温箱保存。)
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1和表2。
从实施例1～7和对比例1～4的对比可知：当负极膜层包括双涂层结构，下层的负极活性材料包括天然石墨，上层的负极活性材料包括人造石墨时，只有当第二负极活性材料中包括二次颗粒，且所述二次颗粒在第二负极活性材料中的数量占比S2≥20％时，电池才能同时具有较好的快速充电性能和较长的循环寿命。优选地，S2≥50％。
从实施例8～21的对比可知：当负极膜层包括双涂层结构、下层的负极活性材料包括天然石墨、上层的负极活性材料包括人造石墨且S2均取优选值时，各层负极活性材料的体积分布粒径D V50之间的关系对于电池性能有较大影响；当第一负极活性材料的体积分布粒径D V50大于第二负极活性材料的体积分布粒径D V50时，电池的快充性能和循环性能均较佳。
还需补充说明的是，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。此外，尽管本说明书中使用了一些特定的术语，但这些术语只是为了方便说明，并不对本申请构成任何限制。
Figure PCTCN2020088301-appb-000002
Figure PCTCN2020088301-appb-000003

Claims (13)

  1. 一种二次电池，包括负极极片，所述负极极片包括负极集流体及负极膜层，所述负极膜层包括第一负极膜层和第二负极膜层；
    所述第一负极膜层设置在负极集流体至少一个表面上且包括第一负极活性材料，所述第一负极活性材料包括天然石墨；
    所述第二负极膜层设置在第一负极膜层上且包括第二负极活性材料，所述第二负极活性材料包括人造石墨，且所述第二负极活性材料中包括二次颗粒，所述二次颗粒在所述第二负极活性材料中的数量占比S2≥20％。
  2. 根据权利要求1所述的二次电池，其中，所述二次颗粒在所述第二负极活性材料中的数量占比S2≥50％。
  3. 根据权利要求1或2所述的二次电池，其中，所述第一负极活性材料包括一次颗粒，且所述一次颗粒在第一负极活性材料中的数量占比S1≥80％；优选地，90％≤S1≤100％。
  4. 根据权利要求1至3任一项所述的二次电池，其中，所述天然石墨在所述第一负极活性材料中的质量占比≥60％，优选地，所述天然石墨在所述第一负极活性材料中的质量占比为80％～100％。
  5. 根据权利要求1至4任一项所述的二次电池，其中，所述人造石墨在所述第二负极活性材料中的质量占比≥90％；优选地，所述人造石墨在所述第二负极活性材料中的质量占比为95％～100％。
  6. 根据权利要求1至7任一项所述的二次电池，其中，所述第一负极活性材料的体积分布粒径D V50大于所述第二负极活性材料的体积分布粒径D V50。
  7. 根据权利要求1至8任一项所述的二次电池，其中,所述第一负极活性材料在20000N压力下的压实密度与所述第二负极活性材料在20000N压力下的压实密度的比值≥0.78，优选为0.84～0.98。
  8. 根据权利要求1至5任一项所述的二次电池，其中，所述第一负极活性材料还满足下述(1)～(6)中的一个或几个：
    (1)所述第一负极活性材料的体积分布粒径D V10为6μm～11μm，优选为 7μm～8μm；
    (2)所述第一负极活性材料的体积分布粒径D V50为11μm～20μm，优选为15μm～20μm；
    (3)所述第一负极活性材料的体积分布粒径D V99为24μm～38μm，优选为30μm～38μm；
    (4)所述第一负极活性材料的粒度分布(D V90-D V10)/D V50为0.7～1.5，优选为0.9～1.3；
    (5)所述第一负极活性材料在20000N压力下的压实密度为1.6g/cm 3～1.88g/cm 3，优选为1.70g/cm 3～1.85g/cm 3；
    (6)所述第一负极活性材料的石墨化度≥95.5％，优选为96.5％～98.5％。
  9. 根据权利要求1至6任一项所述的二次电池，其中，所述第二负极活性材料还满足下述(1)～(6)中的一个或几个：
    (1)所述第二负极活性材料的体积分布粒径D V10为6.2μm～9.2μm，优选为6.6μm～8.8μm；
    (2)所述第二负极活性材料的体积分布粒径D V50为11μm～18μm，优选为12μm～16μm；
    (3)所述第二负极活性材料的体积分布粒径D V99为29μm～43μm，优选为37μm～41μm；
    (4)所述第二负极活性材料的粒度分布(D V90-D V10)/D V50为0.9～1.6，优选为1.1～1.4；
    (5)所述第二负极活性材料在20000N压力下的压实密度为1.58g/cm 3～1.82g/cm 3，优选为1.64g/cm 3～1.74g/cm 3；
    (6)所述第二负极活性材料的石墨化度为92.5％～96.5％，更优选为93.1％～95.1％。
  10. 根据权利要求1至9任一项所述的二次电池，其特征在于：所述二次电池包括正极极片，所述正极极片包括正极集流体以及设置在正极集流体至少一个表面上且包括正极活性材料的正极膜层，所述正极活性材料包括锂过渡金属氧化物、橄榄石结构的含锂磷酸盐及其各自改性化合物中的一种或几种；
    优选地，所述正极活性材料包括式1所示的锂过渡金属氧化物及其改性化合物中的一种或几种，
    Li aNi bCo cM dO eA f  式1，
    所述式1中，0.8≤a≤1.2，0.5≤b＜1，0＜c＜1，0＜d＜1，1≤e≤2，0≤f≤1，M选自Mn、Al、Zr、Zn、Cu、Cr、Mg、Fe、V、Ti及B中的一种或几种，A选自N、F、S及Cl中的一种或几种。
  11. 一种二次电池的制造方法，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个表面上形成包括第一负极活性材料的第一负极膜层，所述第一负极活性材料包括天然石墨；
    2)在所述第一负极膜层上形成包括第二负极活性材料的第二负极膜层，所述第二负极活性材料包括人造石墨，且所述第二负极活性材料中包括二次颗粒，所述二次颗粒在所述第二负极活性材料中的数量占比S2≥20％。
  12. 根据权利要求11所述的二次电池的制造方法，其中，所述第一负极膜层和所述第二负极膜层同时涂布。
  13. 一种装置，其特征在于，包括根据权利要求1至10中任一项所述的二次电池或根据权利要求11或12所述方法制造的二次电池。
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