WO2021217576A1 - 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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WO2021217576A1
WO2021217576A1 PCT/CN2020/088255 CN2020088255W WO2021217576A1 WO 2021217576 A1 WO2021217576 A1 WO 2021217576A1 CN 2020088255 W CN2020088255 W CN 2020088255W WO 2021217576 A1 WO2021217576 A1 WO 2021217576A1
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negative electrode
active material
electrode active
secondary battery
film layer
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PCT/CN2020/088255
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English (en)
French (fr)
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马建军
沈睿
何立兵
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宁德时代新能源科技股份有限公司
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Priority to PCT/CN2020/088255 priority Critical patent/WO2021217576A1/zh
Priority to KR1020217034241A priority patent/KR102539346B1/ko
Priority to CN202080005908.5A priority patent/CN113875046B/zh
Priority to CN202310776332.8A priority patent/CN116741938A/zh
Priority to EP20918126.2A priority patent/EP3926713B1/en
Priority to JP2021558703A priority patent/JP7295265B2/ja
Priority to HUE20918126A priority patent/HUE061914T2/hu
Publication of WO2021217576A1 publication Critical patent/WO2021217576A1/zh
Priority to US17/541,297 priority patent/US11450842B2/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
    • 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
    • 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
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/058—Construction or manufacture
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/058—Construction or manufacture
    • H01M10/0585—Construction or manufacture of accumulators having only flat construction elements, i.e. flat positive electrodes, flat negative electrodes and flat separators
    • 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
    • H01M4/139—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
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—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
    • 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
    • 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
    • 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
    • H01M2004/028—Positive electrodes
    • 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 and a device containing the secondary battery.
  • Secondary batteries are widely used in various consumer electronic products and electric vehicles because of their outstanding characteristics such as light weight, no pollution, and no memory effect.
  • the present application provides a secondary battery and a device containing it, which aims to enable the secondary battery to have a higher energy density while taking into account better dynamic performance and longer length. 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 A negative electrode film layer and a 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, and the second negative electrode film layer is disposed on the first negative electrode film layer and Comprising a second negative electrode active material; the first negative electrode active material comprises natural graphite, and the first negative electrode active material satisfies: 6m ⁇ cm ⁇ A ⁇ 12m ⁇ cm; the second negative electrode active material comprises artificial graphite, and The second negative electrode active material satisfies: 13m ⁇ cm ⁇ B ⁇ 20m ⁇ cm; where A is the powder resistivity of the first negative electrode active material tested under a pressure of 8Mpa, and B is the second negative electrode active material tested under a pressure of 8
  • 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:
  • a first negative electrode film layer including a first negative electrode active material is formed on at least one surface of a negative electrode current collector, the first negative electrode active material includes natural graphite, and the first negative electrode active material satisfies: 6m ⁇ cm ⁇ A ⁇ 12m ⁇ cm;
  • a second negative electrode film layer including a second negative electrode active material is formed on the first negative electrode film layer, the second negative electrode active material includes artificial graphite, and the second negative electrode active material satisfies: 13m ⁇ cm ⁇ B ⁇ 20m ⁇ cm;
  • A is the powder resistivity of the first negative electrode active material tested at a pressure of 8Mpa
  • B is the powder resistivity of the second negative active material tested under a pressure of 8Mpa.
  • 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 first negative electrode film layer and a second negative electrode film layer, and a specific negative electrode active material is selected in each negative electrode film layer.
  • the battery has a higher energy density, it also takes into account good dynamic performance and a long cycle life.
  • 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.
  • 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 second negative electrode film layer is disposed on the first negative electrode film layer and includes a second negative electrode active material;
  • the first negative electrode active material includes natural graphite, and
  • the first negative electrode active material satisfies: 6m ⁇ cm ⁇ A ⁇ 12m ⁇ cm;
  • the second negative electrode active material includes artificial graphite, and the second negative electrode active material satisfies: 13m ⁇ cm ⁇ B ⁇ 20m ⁇ cm;
  • A is the powder resistivity of the first negative electrode active material tested under a pressure of 8Mpa
  • B is the powder resistivity of the second negative electrode active material tested under a pressure of 8Mpa.
  • the active sites of the upper and lower membrane layers are reasonably matched, which is conducive to improving the dynamic performance of the battery; at the same time, the specific design of the upper and lower materials can also form a gradient pore distribution, which can effectively improve the infiltration performance of the electrolyte and enhance the liquidity of active ions. Phase conduction, thereby improving the cycle life of the battery.
  • the first negative electrode active material satisfies: 8m ⁇ cm ⁇ A ⁇ 11m ⁇ cm.
  • the second negative electrode active material satisfies: 14m ⁇ cm ⁇ B ⁇ 18m ⁇ cm.
  • the inventors have found through in-depth research that when the anode film of the present application satisfies the above-mentioned design and optionally satisfies one or more of the following parameters, the performance of the battery can be further improved.
  • the gradient resistance of the negative active material of the upper and lower layers can be better matched.
  • the active ions extracted from the positive electrode diffuse to the bottom of the negative electrode active material particles more quickly and orderly, reduce the risk of lithium evolution during the battery cycle, reduce polarization, and further improve the cycle performance and safety performance of the battery.
  • the particle size distribution (Dv90-Dv10)/Dv50 of the first negative electrode active material is smaller than the particle size distribution (Dv90-Dv10)/Dv50 of the second negative electrode active material.
  • the particle size distribution of the first negative electrode active material may be 1.0 ⁇ (Dv90-Dv10)/Dv50 ⁇ 1.5, more preferably 1.0 ⁇ (Dv90-Dv10)/Dv50 ⁇ 1.3.
  • the particle size distribution of the second negative electrode active material may be 1.0 ⁇ (Dv90-Dv10)/Dv50 ⁇ 2, more preferably 1.2 ⁇ (Dv90-Dv10)/Dv50 ⁇ 1.7.
  • the fine powder content in the upper and lower negative electrode active materials is better matched.
  • the diffusion rate of the deintercalation ions makes the stress of the deintercalation ions equivalent, reduces the expansion of the pole pieces during the battery cycle, thereby further improving the cycle performance of the battery; on the other hand, it effectively adjusts the diffusion path of the active ions, which is beneficial to the active ions.
  • the rapid diffusion in the pole piece further improves the dynamic performance of the battery; in addition, the particle size distribution of the upper and lower anode active materials within the given range is also beneficial to increase the compaction density of the anode film layer, thereby further increasing the energy of the battery density.
  • the volume average particle diameter D V 50 of the first negative electrode active material may be 15 ⁇ m to 19 ⁇ m, more preferably 16 ⁇ m to 18 ⁇ m.
  • the volume average particle diameter D V 50 of the second negative electrode active material may be 14 ⁇ m to 18 ⁇ m, more preferably 15 ⁇ m to 17 ⁇ m.
  • volume average particle size D V 50 of the first negative electrode active material and/or the second negative electrode active material is within the given range, it is helpful to control the powder resistivity of the upper and lower negative electrode active materials to the value given in this application. Within the range, thereby further improving the dynamic performance of the battery.
  • the first negative electrode active material volume average particle diameter D V 50 is greater than the second negative electrode active material volume average particle diameter D V 50.
  • the volume of the first negative electrode active material average particle diameter D V 50 is greater than the second volume of the negative electrode active material, the average particle diameter D V 50, the capacity can be reduced differences in the underlying active materials, decrease in the cell cycle of Analyze the risk of lithium, thereby further improving the cycle performance of the battery.
  • the powder compaction density of the first negative electrode active material under a force of 50,000 N may be 1.85 g/cm 3 to 2.1 g/cm 3 ; more preferably 1.9 g/cm 3 to 2.0 g /cm 3 .
  • the powder compaction density of the second negative electrode active material under a force of 50,000 N may be 1.7 g/cm 3 to 1.9 g/cm 3 , more preferably 1.8 g/cm 3 to 1.9 g /cm 3 .
  • the inventor’s research found that when the upper and lower anode active materials still meet the powder compaction density within the given range under a force of 50,000 N, it is helpful to control the powder resistivity of the upper and lower anode active materials in this application. At the same time, the powder compaction of the upper and lower graphite materials is reasonably matched, which is conducive to the formation of gradient pores in the pole pieces, making the active ion liquid phase conduction resistance smaller, and further improving the dynamic performance of the battery.
  • the graphitization degree of the first negative electrode active material may be 95% to 98%; more preferably, 96% to 97%.
  • the graphitization degree of the second negative electrode active material may be 90%-95%, and more preferably 91%-93%.
  • the inventor’s research found that when the upper and lower anode active materials still satisfy the graphitization degree within the given range, it is helpful to control the powder resistivity of the upper and lower anode active materials within the range given in this application; at the same time; , The crystal structure of the upper and lower graphite materials are reasonably matched, which effectively improves the solid-phase diffusion rate of active ions during the charge and discharge cycle, and reduces the side reactions of the battery during the charge and discharge cycle, thereby further improving the battery’s performance Kinetic performance and cycle performance.
  • the morphology of the first negative electrode active material may be one or more of spherical and quasi-spherical. At this time, the anisotropy of the first negative electrode active material can be effectively improved, thereby further improving the electrochemical expansion and electrode processing performance of the battery.
  • the morphology of the second negative electrode active material is one or more of a block shape and a sheet shape.
  • the pores between the particles of the second negative electrode active material can be effectively improved.
  • the block and sheet structures easily cause the "bridging" effect between the particles, which is beneficial to the transmission of lithium ions in the electrolyte, thereby further improving the dynamics of the battery performance.
  • At least a part of the surface of the first negative electrode active material has an amorphous carbon coating layer.
  • the surface of the second negative electrode active material does not have an amorphous carbon coating layer.
  • the mass ratio of the natural graphite in the first negative electrode active material is ⁇ 50%, more preferably 80%-100%.
  • the mass ratio of the artificial graphite in the second negative electrode active material is ⁇ 80%, more preferably 90%-100%.
  • the powder resistivity of the negative electrode active material has the meaning known in the art, and can be tested by methods known in the art.
  • the four-probe method refer to GB/T 30835-2014 for details, use ST2722-SZ powder resistance tester: Weigh a certain amount of powder to be tested and place it in a special mold, set the test pressure to obtain different pressures The powder resistivity.
  • the test pressure can be set to 8Mpa.
  • the D V 10, D V 50, and Dv 90 of the 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 Mastersizer 3000
  • the particle size distribution laser diffraction method for details, please refer to GB/T19077-2016
  • Dv10 refers to the particle size when the cumulative volume percentage of the material reaches 10%
  • Dv50 refers to the particle size when the cumulative volume percentage of the material reaches 50%, that is, the median particle size of the volume distribution
  • Dv90 refers to the cumulative volume percentage of the material The particle size corresponding to 90%.
  • the powder compaction density of the material has a well-known meaning and can be tested by methods known in the art.
  • an electronic pressure testing machine such as UTM7305
  • the pressure is set to 50000N.
  • the degree of graphitization of the material has a well-known meaning in the art, and can be tested using methods known in the art.
  • the degree of graphitization can be tested with an X-ray diffractometer (such as Bruker D8 Discover).
  • the morphology of the material has a well-known meaning in the art, and can be tested using methods known in the art. For example, stick the material on the conductive adhesive and use a scanning electron microscope (such as ZEISS Sigma300) to test the morphology of the particles. The test can refer to JY/T010-1996.
  • 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 thickness of the negative electrode film layer is greater than or equal to 50 ⁇ m, preferably 60 ⁇ m to 75 ⁇ 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 to 14 mg/cm 2 , more preferably 11 mg/cm 2 to 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 first negative electrode film layer to the second negative electrode film layer is 1:1.01 to 1:1.1, more preferably 1:1.02 to 1:1.06.
  • the thickness of the upper and lower layers is in 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 from the positive electrode on the surface of the negative electrode film layer is reduced, and the accumulation of ions on the surface layer will not cause the problem of lithium evolution.
  • 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.
  • any two circular regions with the same area are taken on the negative pole piece, which are respectively marked as the first region and the second region, and the center of the first region and the second region
  • the distance between the pole piece resistance R11 of the first region and the pole piece resistance R12 of the second region satisfies: ⁇ R11-R12 ⁇ 3m ⁇ cm; more preferably, ⁇ R11-R12 ⁇ 1m ⁇ ⁇ Cm.
  • the resistance difference between any two circular areas with the same area and a center distance of 20cm on the negative pole piece is small, indicating that the resistance of the negative pole piece is less fluctuating, that is, the uniformity of the dispersion of the first material and the second material in the negative electrode film layer better.
  • the compaction density, cycle stability and electrolyte distribution uniformity at each position in the negative pole piece can be improved, so that the active ion transport performance and electronic conduction performance at different positions in the negative pole piece are basically at the same level , So that the capacity of each position of the negative pole piece, cycle and storage life and dynamic performance are improved.
  • the overall consistency of the negative pole piece is good, which can further improve the energy density, high temperature performance and low temperature power performance of the secondary battery.
  • the pole piece resistance of the negative pole piece has a well-known meaning in the art, and can be tested by a method known in the art. For example, use the BER1300 multi-function pole piece resistance tester for testing. First, cut the negative pole piece into a sample to be tested of a certain size (a small disc with a diameter of 40mm); place the sample to be tested between the two probes, and record the test result. In order to ensure the accuracy of the test result, multiple groups (for example, 5 groups) of samples to be tested can be taken at the same time, and the average value of the multiple groups of samples to be tested can be calculated as the test result.
  • a certain size a small disc with a diameter of 40mm
  • multiple groups for example, 5 groups
  • the thickness of the negative electrode film layer can be measured by a ten-meter ruler, for example, it can be measured by a ten-meter ruler with a model of Mitutoyo293-100 and an accuracy of 0.1 as t.
  • 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 a sigma300 type).
  • 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.
  • the first negative electrode film layer and/or the second negative electrode film layer generally include a negative electrode active material, an optional binder, an optional conductive agent, and other optional auxiliary agents.
  • 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
  • additives may include thickening and dispersing agents (such as sodium carboxymethyl cellulose CMC-Na), PTC thermistor materials, and the like.
  • the first negative electrode active material and/or the second negative electrode active material may optionally add a certain amount of other commonly used negative electrode active materials in addition to the graphite material specified above in this application, for example, One or more of soft carbon, hard carbon, silicon-based materials, tin-based materials, 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. These materials can be obtained commercially. Those skilled in the art can make an appropriate choice according to the actual use environment.
  • 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).
  • 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 negative electrode current collector has two opposite surfaces in its thickness direction, and the negative electrode film layer can be disposed on either or both of the two opposite surfaces of the negative electrode current collector.
  • FIG. 2 shows a schematic diagram of an embodiment of the negative pole piece 10 of the present application.
  • the negative electrode piece 10 is composed of a negative electrode current collector 101, a 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 of 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 (such as film thickness, areal density, etc.) given in this application all refer to the parameter range of a single-sided film.
  • the film layer parameters on any one of the surfaces meet the requirements of this application, that is, it is considered to fall within the protection scope of this 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 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 conventional 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 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 One or more of the compounds, lithium nickel cobalt aluminum oxide and its modified compounds.
  • 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/or 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.
  • the isolation film is arranged between the positive pole piece and the negative pole piece to play a role of isolation.
  • 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 accommodating cavity, and a cover plate 53 can 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 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 can be covered on the lower box body 3 and forms 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.
  • a method for preparing a secondary battery which includes preparing the negative pole piece of the secondary battery through the following steps:
  • a first negative electrode film layer including a first negative electrode active material is formed on at least one surface of the negative electrode current collector, the first negative electrode active material includes natural graphite and satisfies 6m ⁇ cm ⁇ A ⁇ 12m ⁇ cm, where A is the first A powder resistivity of the negative electrode active material tested under a pressure of 8Mpa;
  • a second negative electrode film layer including a second negative electrode active material is formed on the first negative electrode film layer, the second negative electrode active material includes artificial graphite and satisfies 13m ⁇ cm ⁇ B ⁇ 20m ⁇ cm, where B is the first The powder resistivity of the second negative electrode active material tested under a pressure of 8Mpa.
  • the active sites in the negative electrode film can be maintained within a suitable range, it is helpful to improve the dynamic performance of the battery; at the same time, the specific design of the upper and lower materials can also form a gradient pore distribution, which can effectively improve the infiltration performance of the electrolyte, and enhance the liquid phase conduction of active ions, thereby enhancing the battery Cycle life.
  • 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 structure and manufacturing method of the secondary battery of the present application may be as follows:
  • the battery positive pole piece is prepared according to the conventional method in the field.
  • This application does not limit the positive active material used in the positive pole piece.
  • a conductive agent for example, carbon material such as carbon black
  • a binder for example, PVDF
  • other additives such as PTC thermistor materials can also be added.
  • these materials are mixed together and dispersed in a solvent (such as NMP), stirred evenly, and evenly coated on the positive electrode current collector. After drying, the positive electrode is obtained by cold pressing and other processes.
  • 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 film layer is not formed on a part of the current collector, and a part of the current collector is left as the positive electrode lead part. Of course, the lead part can also be added later.
  • the negative pole piece of the present application (as a negative pole piece) is prepared as described above.
  • the positive pole piece, the separator film, and the negative pole piece can be stacked in sequence, so that the separator film is located between the positive and negative pole pieces for isolation, and then wind (or laminate) to obtain the electrode assembly;
  • the components are placed in the outer packaging, the electrolyte is injected after drying, and the secondary battery is obtained through the processes of vacuum packaging, standing, forming, and shaping.
  • 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 according to 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 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 and mixed to prepare negative electrode slurry 1.
  • the powder resistivity of natural graphite tested under a pressure of 8Mpa is 6.1m ⁇ cm.
  • 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 powder resistivity of artificial graphite tested under a pressure of 8Mpa is 16.1m ⁇ cm.
  • 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 negative electrode 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 mass ratio is 1:1; the areal density of the negative electrode film layer is 11.5 mg/cm 2 ; the compacted density of the negative electrode film layer is 1.65 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 secondary batteries of Examples 2-22 and 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 shown in Table 1 to Table 2. .
  • the parameters of the negative electrode active material and the test methods of the parameters of the battery structure are described in the preamble of the specification of this application.
  • the performance test method of the secondary battery is as follows.
  • the batteries of the examples and comparative examples were subjected to charge and discharge tests, and a discharge current of 1.0C (that is, the current value at which the theoretical capacity was completely discharged within 1h) was subjected to constant current discharge until the discharge cut-off voltage was 2.8 V. Then charge with a constant current of 1.0C until the charge cut-off voltage is 4.2V, and continue constant voltage charging until the current is 0.05C. At this time, the battery is in a fully charged state. After the fully charged battery is allowed to stand for 5 minutes, discharge at a constant current of 1.0C to the discharge cut-off voltage. The discharge capacity at this time is the actual capacity of the battery at 1.0C, denoted as C0.
  • 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 particle size distribution (Dv90-Dv10)/Dv50 of the negative electrode active material also has a greater impact on battery performance.
  • the particle size distribution (Dv90-Dv10)/Dv50 of the first negative electrode active material is preferably smaller than that of the second negative electrode active material Distribution (Dv90-Dv10)/Dv50, otherwise the cycle performance and dynamic performance are relatively poor (Examples 20, 21).
  • the particle size distribution of the first negative electrode active material is 1.0 ⁇ (Dv90-Dv10)/Dv50 ⁇ 1.5, preferably 1.0 ⁇ (Dv90-Dv10)/Dv50 ⁇ 1.3; and/or, the second negative electrode
  • the particle size distribution of the active material is 1.0 ⁇ (Dv90-Dv10)/Dv50 ⁇ 2, preferably 1.2 ⁇ (Dv90-Dv10)/Dv50 ⁇ 1.7, the overall performance of the battery is better.
  • the secondary battery in order to maintain the secondary battery with a higher energy density, while taking into account good dynamic performance and long cycle life, the secondary battery should meet 6m ⁇ cm ⁇ A ⁇ 12m ⁇ cm and 13m ⁇ cm ⁇ B ⁇ 20m ⁇ cm.

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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，本申请的二次电池中，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；所述第一负极活性材料包括天然石墨，且所述第一负极活性材料满足：6mΩ·cm≤A≤12mΩ·cm；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满足：13mΩ·cm≤B≤20mΩ·cm；其中，A为第一负极活性材料在8Mpa压强下测试的粉末电阻率，B为第二负极活性材料在8Mpa压强下测试的粉末电阻率。该二次电池可以在较高能量密度的前提下，兼顾较好的动力学性能和较长的循环寿命。

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，涉及一种二次电池及含有该二次电池的装置。
背景技术
二次电池因具有重量轻、无污染、无记忆效应等突出特点，被广泛应用于各类消费类电子产品和电动车辆中。
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。如何使二次电池在具有更高能量密度的前提下，同时兼顾其它电化学性能，仍然是二次电池领域的关键挑战所在。
有鉴于此，确有必要提供一种可兼顾多种性能的二次电池，从而满足客户的使用需求。
发明内容
鉴于背景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；所述第一负极活性材料包括天然石墨，且所述第一负极活性材料满足：6mΩ·cm≤A≤12mΩ·cm；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满足：13mΩ·cm≤B≤20mΩ·cm；其中，A为第一负极活性材料在8Mpa压强下测试的粉末电阻率，B为第二负极活性材料在8Mpa压强下 测试的粉末电阻率。
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，且所述第一负极活性材料满足：6mΩ·cm≤A≤12mΩ·cm；
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满足：13mΩ·cm≤B≤20mΩ·cm；
其中，
A为第一负极活性材料在8Mpa压强下测试的粉末电阻率，
B为第二负极活性材料在8Mpa压强下测试的粉末电阻率。
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，负极极片包括第一负极膜层和第二负极膜层，且各负极膜层中选择特定的负极活性材料，通过上下层的合理设计，使得本申请的二次电池在具有较高能量密度的前提下，同时兼顾良好的动力学性能和较长的循环寿命。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。
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；所述第一负极活性材料包括天然石墨，且所述第一负极活性材料满足：6mΩ·cm≤A≤12mΩ·cm；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满足：13mΩ·cm≤B≤20mΩ·cm；其中，A为第一负极活性材料在8Mpa压强下测试的粉末电阻率，B为第二负极活性材料在8Mpa压强下测试的粉末电阻率。
发明人发现，当第一负极活性材料包括天然石墨，第二负极活性材料包括人造石墨，且第一负极活性材料和第二负极活性材料具有特定范围的粉末电阻率时，可以使负极膜层中上下膜层的活性位点得到合理匹配，从而有利于改善电池的动力学性能；同时，上下层材料的特定设计，还可以形成梯度孔隙分布，有效改善电解液的浸润性能，提升活性离子的液相传导，从而提升电池的循环寿命。
在一些优选的实施方式中，所述第一负极活性材料满足：8mΩ·cm≤A≤11mΩ·cm。
在一些优选的实施方式中，所述第二负极活性材料满足：14mΩ·cm≤B≤18mΩ·cm。
本发明人经深入研究发现，当本申请的负极膜层在满足上述设计的基础上，如果还可选地满足下述参数中的一个或几个时，可以进一步改善电池的性能。
在一些优选的实施方式中，1.4≤B/A≤3；更优选地，1.5≤B/A≤2.0。当B/A控制在所给范围内时，上下层的负极活性材料的梯度电阻可以更好的匹配。从而使正极中脱出的活性离子更快速有序扩散到底部负极活性材料颗粒内部，减少电池在循环过程中的析锂风险，降低极化，进一步改善电池的循环性能和安全性能。
在一些优选的实施方式中，所述第一负极活性材料的粒径分布(Dv90-Dv10)/Dv50小于所述第二负极活性材料的粒径分布(Dv90-Dv10)/Dv50。
在一些优选的实施方式中，所述第一负极活性材料的粒径分布可以为1.0≤(Dv90-Dv10)/Dv50≤1.5，更优选为1.0≤(Dv90-Dv10)/Dv50≤1.3。
在一些优选的实施方式中，所述第二负极活性材料的粒径分布可以为1.0 ≤(Dv90-Dv10)/Dv50≤2，更优选为1.2≤(Dv90-Dv10)/Dv50≤1.7。
当第一负极活性材料的粒径分布小于第二负极活性材料的粒径分布时，上下层的负极活性材料中细粉含量得到较好的匹配，一方面，有效调节了活性离子在不同颗粒内部的扩散速率，使脱嵌离子应力相当，降低极片在电池在循环过程中的膨胀，从而进一步改善了电池的循环性能；另一方面，有效调节了活性离子的扩散路径，有利于活性离子在极片中的快速扩散，从而进一步改善电池的动力学性能；此外，上下层负极活性材料的粒径分布在所给范围内还有利于提升负极膜层的压实密度，从而进一步提升电池的能量密度。
在一些优选的实施方式中，所述第一负极活性材料的体积平均粒径D V50可以为15μm～19μm，更优选为16μm～18μm。
在一些优选的实施方式中，所述第二负极活性材料的体积平均粒径D V50可以为14μm～18μm，更优选为15μm～17μm。
当第一负极活性材料和/或第二负极活性材料的体积平均粒径D V50在所给范围内时，有助于将上、下层负极活性材料的粉末电阻率控制在本申请所给的范围内，从而进一步提高电池的动力学性能。
在一些优选的实施方式中，所述第一负极活性材料的体积平均粒径D V50大于所述第二负极活性材料的体积平均粒径D V50。
当第一负极活性材料的体积平均粒径D V50大于所述第二负极活性材料的体积平均粒径D V50时，可以减小上下层活性材料的容量差异，降低电池在循环过程中的析锂风险，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在50000N作用力下粉体压实密度可以为1.85g/cm 3～2.1g/cm 3；更优选为1.9g/cm 3～2.0g/cm 3。
在一些优选的实施方式中，所述第二负极活性材料在50000N作用力下粉体压实密度可以为1.7g/cm 3～1.9g/cm 3，更优选为1.8g/cm 3～1.9g/cm 3。
发明人研究发现，当上、下层的负极活性材料还满足在50000N作用力下粉体压实密度在所给范围内时，有助于将上、下层负极活性材料的粉末电阻率控制在本申请所给的范围内；同时，上、下层石墨材料的粉体压实得到合理匹配，有利于极片形成梯度孔隙，使得活性离子液相传导阻力较小，进一步提升电池的动力学性能。
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可以为95％ ～98％；更优选为96％～97％。
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可以为90％～95％，更优选为91％～93％。
发明人研究发现，当上、下层的负极活性材料还满足石墨化度在所给范围内时，有助于将上、下层负极活性材料的粉末电阻率控制在本申请所给的范围内；同时，上、下层石墨材料的晶型结构得到合理匹配，有效提高了活性离子在充放电循环过程中的固相扩散速率，且降低了电池在充放电循环过程中的副反应，从而进一步改善电池的动力学性能和循环性能。
在一些优选的实施方式中，所述第一负极活性材料的形貌可以为球形及类球形中的一种或几种。此时，可有效改善第一负极活性材料的各向异性，从而进一步改善电池的电化学膨胀和极片加工性能。
在一些优选的实施方式中，所述第二负极活性材料的形貌为块状及片状中的一种或几种。此时，可有效改善第二负极活性材料颗粒间的孔隙，块状和片状结构容易使颗粒间造成“架桥”效应，有利于电解液浸润锂离子的传输，从而进一步改善电池的动力学性能。
在一些优选的实施方式中，所述第一负极活性材料的表面至少一部分具有无定形碳包覆层。
在一些优选的实施方式中，所述第二负极活性材料的表面不具有无定形碳包覆层。
在一些优选的实施方式中，所述天然石墨在所述第一负极活性材料中的质量占比≥50％，更优选为80％～100％。
在一些优选的实施方式中，所述人造石墨在所述第二负极活性材料中的质量占比≥80％，更优选为90％～100％。
在本申请中，负极活性材料的粉末电阻率具有本领域公知的含义，可以采用本领域已知的方法测试。例如四探针法，具体可参照GB/T 30835-2014，使用ST2722-SZ粉末电阻仪测试：称取一定量的待测样品粉末置于专用模具中，设置测试压强，即可得到不同压强下的粉末电阻率。本申请中，测试压强可以设置为8Mpa。
在本申请中，材料的D V10、D V50、Dv90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。例如使用激光衍射粒度分布测量仪(如Mastersizer  3000)，依据粒度分布激光衍射法(具体可参照GB/T19077-2016)测量得到。其中，Dv10是指材料累计体积百分数达到10％时所对应的粒径；Dv50指材料累计体积百分数达到50％时所对应的粒径，即体积分布中位粒径；Dv90是指材料累计体积百分数达到90％时所对应的粒径。
在本申请中，材料的粉体压实密度具有公知的含义，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50000N。
在本申请中，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。例如石墨化度可以使用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d 002的大小，然后根据公式G＝(0.344-d 002)/(0.344-0.3354)×100％计算得出石墨化度，其中d 002是以纳米(nm)表示的材料晶体结构中的层间距。
在本申请中，材料的形貌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，将材料粘于导电胶上，使用扫描电子显微镜(如ZEISS Sigma300)，对颗粒的形貌进行测试。测试可参考JY/T010-1996。
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。
本申请所使用的天然石墨和人造石墨均可以通过商业途径获得。
在本申请优选的实施方式中，所述负极膜层的厚度≥50μm，优选为60μm～75μm。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)。
在本申请优选的实施方式中，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)。
在本申请优选的实施方式中，所述第一负极膜层与所述第二负极膜层的厚度比为1:1.01～1:1.1，更优选为1:1.02～1:1.06。
上、下层的厚度在所给范围时，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，进一步提升电池的动力学性能和循环性能。
在本申请优选的实施方式中，在所述负极极片上任取两个面积相同的圆形区域，分别记为第一区域和第二区域，所述第一区域与所述第二区域的中心距为20cm，所述第一区域的极片电阻R11与所述第二区域的极片电阻R12之间满足：∣R11-R12∣≤3mΩ·cm；更优选地，∣R11-R12∣≤1mΩ·cm。
负极极片上任意两个面积相同且中心距为20cm的圆形区域之间电阻差较小，表明负极极片的电阻波动较小，即负极膜层中第一材料和第二材料的分散均匀性较好。负极极片中各位置处的压实密度、循环稳定性以及电解液分布均匀性均能得到提高，由此使负极极片中不同位置处的活性离子传输性能和电子传导性能基本上处于同一水平，从而使负极极片各位置处的容量发挥、循环和存储寿命及动力学性能均得到提高。负极极片的整体一致性好，能进一步提高二次电池的能量密度、高温性能及低温功率性能。
负极极片的极片电阻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，采用BER1300多功能极片电阻仪进行测试。首先将负极极片裁成一 定尺寸(直径为40mm的小圆片)的待测样品；将待测样品放置于两个探针之间，记录测试结果。为了确保测试结果的准确性，可以同时取多组(例如5组)待测样品，并计算多组待测样品的平均值作为测试结果。
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0.1为t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sigma300型)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。
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。
在本申请中，所述第一负极膜层和/或所述第二负极膜层通常包括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。
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)中的一种或几种。
作为示例，其他可选助剂可以包括增稠及分散剂(例如羧甲基纤维素钠CMC-Na)、PTC热敏电阻材料等。
在本申请中，所述第一负极活性材料和/或所述第二负极活性材料除了使用本申请上述规定的石墨材料外，还可以可选地添加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。
可以理解的是，负极集流体具有在自身厚度方向相对的两个表面，负极膜层可以设置于负极集流体的两个相对表面中的任意一者或两者上。
图2示出了本申请的负极极片10的一种实施方式的示意图。负极极片10由负极集流体101、分别设置在负极集流体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、面密度等)均指单面膜层的参数范围。当负极膜层同时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。
[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/或导电剂。
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能够盖设于所述开口，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能够盖设于下箱体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
在本申请的第二方面，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且满足6mΩ·cm≤A≤12mΩ·cm，其中 A为第一负极活性材料在8Mpa压强下测试的粉末电阻率；
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，第二负极活性材料包括人造石墨且满足13mΩ·cm≤B≤20mΩ·cm，其中，B为第二负极活性材料在8Mpa压强下测试的粉末电阻率。
在二次电池的制备的过程中，通过控制和调整负极极片的第一负极活性材料组成、第二负极活性材料组成及其各自的粉末电阻率，可以使负极膜层中的活性位点保持在合适范围内，从而有利于改善电池的动力学性能；同时，上下层材料的特定设计，还可以形成梯度孔隙分布，有效改善电解液的浸润性能，提升活性离子的液相传导，从而提升电池的循环寿命。
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。
除了负极极片的制备方法外，本申请的二次电池的构造和制备方法本身是公知的。
作为示例，本申请的二次电池的构造和制备方法可以如下：
首先，按照本领域常规方法制备电池正极极片。本申请对于正极极片所使用的正极活性材料不进行限定。通常，在上述正极活性材料中，需要添加导电剂(例如碳黑等碳素材料)、粘结剂(例如PVDF)等。视需要，也可以添加其他添加剂，例如PTC热敏电阻材料等。通常将这些材料混合在一起分散于溶剂(例如NMP)中，搅拌均匀后均匀涂覆在正极集流体上，烘干后经冷压等工序即得到正极极片。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。通常在制作正极极片时，在集流体的一部分上不形成正极膜层，留下集流体的一部分作为正极引线部。当然，引线部也可以是后加的。
然后，按照上文所述准备本申请的负极极片(作为负极极片)。
最后，可以将正极极片、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，然后卷绕(或叠片)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根据本申请第二方面的方法制备所得的二次电池。所述二次电池可以用作装置的电源，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。其中，正极膜层的面密度为17.5mg/cm 2，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，制备成负极浆料1。其中，天然石墨在8Mpa压强下测试的粉末电阻率为6.1mΩ·cm。
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，制备成负极浆料2。其中，人造石墨在8Mpa压强下测试的粉末电阻率为16.1mΩ·cm。
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涂覆在负极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11.5mg/cm 2；负极膜层的压实密度为1.65g/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，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2～22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至表2。
二、性能参数测试方法
负极活性材料的各参数以及电池结构的各参数的测试方法见本申请说明书前文所述。二次电池的性能测试方法如下。
1)电池的动力学性能测试(室温析锂性能)
在25℃的环境中，将各实施例和对比例的电池进行充放电测试，以1.0C(即1h内完全放掉理论容量的电流值)的放电电流进行恒流放电至放电截止电压为2.8V。然后以1.0C的充电电流恒流充电至充电截止电压为4.2V，继续恒压充电至电流为0.05C，此时电池为满充状态。将满充的电池静置5min后，以1.0C的放电电流恒流放电至放电截止电压，此时的放电容量为电池的1.0C下的实际容量，记为C0。而后在将电池在x C0恒流充电直到截止电压上限，再恒压充电至电流为0.05C0，静置5min，拆解电池观察界面析锂情况。如果负极表面未析锂，则增大充电倍率再次进行测试，直至负极表面析锂。记录负极表面未析锂的最大充电倍率，用以表征电池的动力学性能。
2)电池的高温循环性能测试
在60℃的环境中，进行第一次充电和放电，在1.0C(即1h内完全放掉理论容量的电流值)的充电电流下进行恒流和恒压充电，直到充电截止电压为4.2V，然后在1.0C的放电电流下进行恒流放电，直到放电截止电压为2.8V。此为一个充放电循环，此次的放电容量即为第1次循环的放电容量。随后，进行不断的充电和放电循环，记录每次循环的放电容量值，并根据第N次循环的容量保持率＝(第N次循环的放电容量/第1次循环的放电容量)×100％，计算每次循环的容量保持率。当循环容量保持率下降到80％时，记录电池的循环次数。
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，结果见下面表1和表2。
首先，从表1中实施例1～10和对比例1～4的数据可知：只有第一负极活性材料中的天然石墨满足6mΩ·cm≤A≤12mΩ·cm且同时第二负极活性材料中的人造石墨满足13mΩ·cm≤B≤20mΩ·cm时，二次电池才能同时具有高循环性能和优异的快充性能(动力学性能)。在8mΩ·cm≤A≤11mΩ·cm和14mΩ·cm≤B≤18mΩ·cm时，二次电池的综合性能最优。尤其是1.5≤B/A≤2.0，二次电池表现更佳。
另外，从表2中实施例11～18和实施例19～22的对比可以看出，负极活性 材料的粒径分布(Dv90-Dv10)/Dv50对电池性能影响也较大。在6mΩ·cm≤A≤12mΩ·cm且13mΩ·cm≤B≤20mΩ·cm的前提下，第一负极活性材料的粒径分布(Dv90-Dv10)/Dv50优选小于第二负极活性材料的粒径分布(Dv90-Dv10)/Dv50，否则循环性能和动力学性能相对较差(实施例20、21)。由表2数据可知，当第一负极活性材料的粒径分布为1.0≤(Dv90-Dv10)/Dv50≤1.5，优选为1.0≤(Dv90-Dv10)/Dv50≤1.3；和/或，第二负极活性材料的粒径分布为1.0≤(Dv90-Dv10)/Dv50≤2，优选为1.2＜(Dv90-Dv10)/Dv50≤1.7时，电池的综合性能较好。
综合表1、表2中数据可知：为了在保持二次电池在具有较高能量密度的前提下，同时兼顾良好的动力学性能和较长的循环寿命，二次电池应满足6mΩ·cm≤A≤12mΩ·cm和13mΩ·cm≤B≤20mΩ·cm。
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 PCTCN2020088255-appb-000001
Figure PCTCN2020088255-appb-000002

Claims (15)

  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；
    所述第一负极活性材料包括天然石墨，且所述第一负极活性材料满足：6mΩ·cm≤A≤12mΩ·cm；
    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满足：13mΩ·cm≤B≤20mΩ·cm；
    其中，
    A为第一负极活性材料在8Mpa压强下测试的粉末电阻率，
    B为第二负极活性材料在8Mpa压强下测试的粉末电阻率。
  2. 根据权利要求1所述的二次电池，其中，8mΩ·cm≤A≤11mΩ·cm；和/或，14mΩ·cm≤B≤18mΩ·cm。
  3. 如权利要求1至2任一项所述的二次电池，其中，1.4≤B/A≤3；优选地，1.5≤B/A≤2.0。
  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≥50％，优选为80％～100％；和/或，
    所述人造石墨在所述第二负极活性材料中的质量占比≥80％，优选为90％～100％。
  5. 如权利要求1至4任一项所述的二次电池，其中，所述第一负极活性材料的粒径分布(Dv90-Dv10)/Dv50小于所述第二负极活性材料的粒径分布(Dv90-Dv10)/Dv50。
  6. 如权利要求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的粒径分布为1.0≤(Dv90-Dv10)/Dv50≤1.5，优选为1.0≤(Dv90-Dv10)/Dv50≤1.3；和/或，
    所述第二负极活性材料的粒径分布为1.0≤(Dv90-Dv10)/Dv50≤2，优选为1.2≤(Dv90-Dv10)/Dv50≤1.7。
  7. 如权利要求1至6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平均粒径D V50大于所述第二负极活性材料的体积平均粒径D V50。
  8. 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平均粒径D V50为15μm～19μm，优选为16μm～18μm；和/或，
    所述第二负极活性材料的体积平均粒径D V50为14μm～18μm，优选为15μm～17μm。
  9. 如权利要求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还满足下述(1)～(4)中的一个或几个：
    (1)所述第一负极活性材料在50000N作用力下粉体压实密度为1.85g/cm 3～2.1g/cm 3，优选为1.9g/cm 3～2.0g/cm 3；
    (2)所述第一负极活性材料的石墨化度为95％～98％，优选为96％～97％；
    (3)所述第一负极活性材料的形貌为球形及类球形中的一种或几种；
    (4)所述第一负极活性材料的表面至少一部分具有无定形碳包覆层。
  10. 根据权利要求1至9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)～(4)中的一个或几个：
    (1)所述第二负极活性材料在50000N作用力下粉体压实密度为1.7g/cm 3～1.9g/cm 3，优选为1.8g/cm 3～1.9g/cm 3；
    (2)所述第二负极活性材料的石墨化度为90％～95％，优选为91％～93％；
    (3)所述第二负极活性材料的形貌为块状及片状中的一种或几种；
    (4)所述第二负极活性材料的表面不具有无定形碳包覆层。
  11. 根据权利要求1至10任一项所述的二次电池，其中，所述二次电池还满足下述(1)～(3)中的一个或几个：
    (1)所述负极膜层的厚度≥50μm，优选为60μm～75μm；
    (2)所述负极膜层的面密度为9mg/cm 2～14mg/cm 2，优选为11mg/cm 2～13mg/cm 2。
    (3)所述第一负极膜层与所述第二负极膜层的厚度比为1:1.01～1:1.1，优选为1:1.02～1:1.06。
  12. 根据权利要求1至11任一项所述的二次电池，其中，当在所述负极膜 层上任取两个面积相同的圆形区域，分别记为第一区域和第二区域，所述第一区域与所述第二区域的中心距为20cm，所述第一区域的极片电阻R11与所述第二区域的极片电阻R12之间满足：∣R11-R12∣≤3mΩ·cm；优选地，∣R11-R12∣≤1mΩ·cm。
  13. 根据权利要求1至12任一项所述的二次电池，其中，所述二次电池包括正极极片，所述正极极片包括正极集流体以及设置在正极集流体至少一个表面上且包括正极活性材料的正极膜层，所述正极活性材料包括锂过渡金属氧化物、橄榄石结构的含锂磷酸盐及其各自改性化合物中的一种或几种；
    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。
  14. 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，且所述第一负极活性材料满足：6mΩ·cm≤A≤12mΩ·cm；
    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满足：13mΩ·cm≤B≤20mΩ·cm；
    其中，
    A为第一负极活性材料在8Mpa压强下测试的粉末电阻率，
    B为第二负极活性材料在8Mpa压强下测试的粉末电阻率。
  15. 一种装置，其特征在于：包括权利要求1至13中任一项所述的二次电池或根据权利要求14所述方法制造的二次电池。
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CN108701816A (zh) * 2016-09-29 2018-10-23 株式会社Lg化学 包括天然石墨和人造石墨的多层负极以及包括该多层负极的锂二次电池
KR20190060719A (ko) * 2017-11-24 2019-06-03 주식회사 엘지화학 이중층 구조의 활물질층을 포함하는 음극, 이의 제조방법 및 이를 포함하는 이차전지

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CN116888798A (zh) * 2022-10-17 2023-10-13 宁德时代新能源科技股份有限公司 二次电池以及包含其的用电装置
WO2024082287A1 (zh) * 2022-10-21 2024-04-25 宁德时代新能源科技股份有限公司 具有改善的电解液粘度和cb值的锂离子电池和用电装置

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