WO2021109133A1 - 二次电池及含有它的装置 - Google Patents

二次电池及含有它的装置 Download PDF

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WO2021109133A1
WO2021109133A1 PCT/CN2019/123729 CN2019123729W WO2021109133A1 WO 2021109133 A1 WO2021109133 A1 WO 2021109133A1 CN 2019123729 W CN2019123729 W CN 2019123729W WO 2021109133 A1 WO2021109133 A1 WO 2021109133A1
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Prior art keywords
negative electrode
active material
electrode active
film layer
coi
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PCT/CN2019/123729
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English (en)
French (fr)
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康蒙
董晓斌
王家政
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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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/CN2019/123729 priority Critical patent/WO2021109133A1/zh
Priority to CN201980071539.7A priority patent/CN113228341B/zh
Priority to JP2022520068A priority patent/JP7222147B2/ja
Priority to ES19929189T priority patent/ES2926653T3/es
Priority to KR1020227012041A priority patent/KR102529777B1/ko
Priority to US17/056,958 priority patent/US11961993B2/en
Priority to EP19929189.9A priority patent/EP3859827B1/en
Publication of WO2021109133A1 publication Critical patent/WO2021109133A1/zh

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    • H—ELECTRICITY
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    • 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
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    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
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    • 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
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
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    • H01M4/36—Selection of substances as active materials, active masses, active liquids
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    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
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    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H01M4/386—Silicon or alloys based on silicon
    • H—ELECTRICITY
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    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H01M4/387—Tin or alloys based on tin
    • H—ELECTRICITY
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    • 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
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    • 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
    • C—CHEMISTRY; METALLURGY
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    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/70—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data
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    • C01P2004/61—Micrometer sized, i.e. from 1-100 micrometer
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    • C01P2006/11—Powder tap density
    • C—CHEMISTRY; METALLURGY
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    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/12—Surface area
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    • 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. More specifically, this application relates to a secondary battery and a device containing it.
  • New energy vehicles represent the development direction of the world's automobile industry.
  • lithium-ion 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 new energy vehicles.
  • An object of the present application is to provide a secondary battery that has both good fast charging performance and cycle performance under the premise of higher energy density.
  • the first aspect of the present application provides a secondary battery.
  • the secondary battery includes a negative pole piece, and the negative pole piece includes a negative electrode current collector and a negative electrode film layer, and the negative electrode film layer includes A first negative electrode film layer and a 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 On and including the second negative electrode active material;
  • the first negative electrode active material includes natural graphite, and the second negative electrode active material includes artificial graphite;
  • the first negative electrode active material satisfies: 4.0 ⁇ COI 1 ⁇ 7.0, preferably 4.3 ⁇ COI 1 ⁇ 5.5;
  • the second negative electrode active material satisfies: 2.2 ⁇ COI 2 ⁇ 4.2, preferably 2.5 ⁇ COI 2 ⁇ 3.6;
  • COI 1 is the ratio of the peak area of the 004 characteristic diffraction peak to the peak area of the 110 characteristic diffraction peak in the X-ray diffraction pattern of the first negative electrode active material;
  • COI 2 is the ratio of the peak area of the 004 characteristic diffraction peak to the peak area of the 110 characteristic diffraction peak in the X-ray diffraction pattern of the second negative electrode active material.
  • a device which includes the secondary battery according to the first aspect of the present application.
  • the negative pole piece of the secondary battery of the present application includes a multilayer structure, and each layer contains a specific negative electrode active material and a specific COI range. Under the combined effect, the battery can have both high energy density and high energy density. Better fast charging performance and cycle 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 a battery module.
  • Fig. 3 is a schematic diagram of an embodiment of a battery pack.
  • Fig. 4 is an exploded view of Fig. 3.
  • FIG. 5 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 thickness of the film layer but the increase of the thickness will cause the cycle performance and fast charging performance of the battery to be affected. This is due to the expansion of the negative active material during the cycle, resulting in a decrease in the binding force between the active material and the substrate, and even film release. When the thickness increases, this phenomenon becomes more serious; at the same time, the thickness increases The diffusion path of active ions is increased, so that the fast charging performance of the battery will also be affected. Therefore, how to make the battery have better cycle performance and fast charging performance under the premise of higher energy density is a huge technical challenge.
  • the negative electrode sheet of the present application includes a negative electrode current collector and a negative electrode film layer.
  • the negative electrode film layer includes a first negative electrode film layer and a second negative electrode film layer.
  • the second negative electrode film layer is 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 second negative electrode active material
  • the material includes artificial graphite; the powder OI value COI 1 of the first negative electrode active material satisfies: 4.0 ⁇ COI 1 ⁇ 7.0, and the powder OI value COI 2 of the second negative electrode active material satisfies: 2.2 ⁇ COI 2 ⁇ 4.2 ,
  • COI 1 is the ratio of the peak area of the 004 characteristic diffraction peak in the X-ray diffraction pattern of the first negative electrode active material to the peak area of the 110 characteristic diffraction peak;
  • COI 2 is the 004 in the X-ray diffraction pattern of the second negative electrode active material The ratio of the peak area of the characteristic diffraction peak to the peak area of the 110 characteristic diffraction peak.
  • the battery can have both good cycle performance
  • the negative active material in the second negative film layer can provide more lithium intercalation inlets to ensure that the active ions can be quickly inserted into the negative active material.
  • the negative electrode active material in the first negative electrode film layer can provide more lithium insertion positions to ensure that more active ions can be accepted and inserted, and the lithium insertion entrance and lithium insertion positions of the upper and lower layers are more reasonable, ensuring a high energy density design At the same time, it takes into account the charge exchange resistance of active ions and the solid phase diffusion rate, which effectively improves the fast charging performance of the battery.
  • the first negative electrode active material satisfies: 4.3 ⁇ COI 1 ⁇ 5.5.
  • the second negative electrode active material satisfies: 2.5 ⁇ COI 2 ⁇ 3.6.
  • the powder OI value of the negative electrode active material is used to indicate the orientation index of the active material, that is, the degree of anisotropy of the crystal grain arrangement in the negative electrode film layer.
  • COI 1 is the ratio of the peak area of the 004 characteristic diffraction peak to the peak area of the 110 characteristic diffraction peak in the X-ray diffraction pattern of the first negative electrode active material
  • COI 2 is the ratio of the peak area of the second negative electrode active material in the X-ray diffraction pattern The ratio of the peak area of the 004 characteristic diffraction peak to the peak area of the 110 characteristic diffraction peak.
  • the C 003 /C 110 of the natural graphite of the present application needs to satisfy 4.0 ⁇ C 003 /C 110 ⁇ 7.0.
  • the powder OI value of the negative electrode active material can be measured by a method known in the art, for example, by the method described in the Examples section herein.
  • the ratio of the powder OI value COI 1 of the active material in the first negative electrode film layer to the powder OI value COI 2 of the active material in the second negative electrode film layer satisfies: 1.1 ⁇ COI 1 / When COI 2 ⁇ 2.5, preferably 1.3 ⁇ COI 1 /COI 2 ⁇ 1.6, its fast charging performance and capacity can be further improved. This is because when the powder OI value of the active material in the first negative electrode film layer and the powder OI value of the active material in the second negative electrode film layer are within the given range, the pore distribution of the upper and lower film layers is consistent with When charging, the distribution of active ions is more matched, which is more conducive to the high capacity and fast charging design of the battery.
  • the negative pole piece described in the present application includes a current collector and two or more film layers arranged on at least one surface of the current collector.
  • the negative pole piece can be coated on both sides (that is, the film layer is provided on both surfaces of the current collector), or it can be coated only on one side (that is, the film layer is only provided on one surface of the current collector).
  • the negative pole piece of the present application can be prepared by various methods commonly used in the art. Generally, the negative electrode current collector can be prepared first, and then the negative electrode active material slurry is prepared, and the negative electrode active material slurry is coated on one or both surfaces of the negative electrode current collector, and finally dried, welded conductive members (tabs), and cut Wait for post-processing steps to obtain the required negative pole piece.
  • the negative electrode film layer described in this application can be coated on the negative electrode current collector with the first active material slurry and the second active material slurry at the same time, or can be divided into two coatings; preferably, the first active material slurry can be applied at the same time. And the second active material slurry is coated on the negative electrode current collector.
  • the negative electrode film layer usually includes a negative electrode active material, an optional binder, an optional conductive agent, and other optional auxiliary agents.
  • the film slurry coating is usually formed by dispersing the negative electrode active material, the optional conductive agent and the binder, etc. in a solvent and stirring them uniformly.
  • the solvent may be N-methylpyrrolidone (NMP) or deionized water, for example.
  • NMP N-methylpyrrolidone
  • Other optional auxiliary agents can be, for example, thickening and dispersing agents (such as carboxymethyl cellulose CMC), PTC thermistor materials, and the like.
  • the conductive agent may be one or more of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
  • the binder may be 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 negative electrode active material may also include one or more of soft carbon, hard carbon, silicon-based materials, and tin-based materials.
  • the first negative electrode active material may further include one or more of artificial graphite, soft carbon, hard carbon, silicon-based material, and tin-based material.
  • the second negative electrode active material may further include one or more of natural graphite, soft carbon, hard carbon, silicon-based materials, and tin-based materials.
  • the graphitization degree and material particle size of the first negative electrode active material and the second negative electrode active material can be controlled within a certain range, and/or the pole piece CW, PD, pole piece thickness and active specific surface area can be controlled within a certain range In order to further optimize the cell energy density, low temperature power and fast charging performance.
  • the morphology of the natural graphite in the first negative electrode active material is spherical or quasi-spherical.
  • the morphology of the artificial graphite in the second negative electrode active material is flake or block.
  • the average particle diameter Dv50 of the first active material is 9 ⁇ m to 16 ⁇ m, more preferably 11 ⁇ m to 14 ⁇ m.
  • the average particle size Dv50 of the second active material is 11 ⁇ m to 19 ⁇ m, more preferably 13 ⁇ m to 17 ⁇ m.
  • the particle size distribution of the first active material is 0.8 ⁇ (D v 90-D v 10)/D v 50 ⁇ 1.5, more preferably 0.9 ⁇ (D v 90-D v 10)/D v 50 ⁇ 1.3.
  • the particle size distribution of the second active material is 0.9 ⁇ (D v 90-D v 10)/D v 50 ⁇ 2, more preferably 1.1 ⁇ (D v 90-D v 10)/D v 50 ⁇ 1.6.
  • D v 10 refers to the particle size corresponding to when the cumulative volume percentage of material particles or powder reaches 10%
  • D v 90 refers to the particle size corresponding to when the cumulative volume percentage of material particles or powder reaches 90%
  • D v 50 refers to the particle size when the cumulative volume percentage of material particles or powder reaches 50%, that is, the median size of the volume distribution.
  • the units of D v 10, D v 90, and D v 50 are all ⁇ m.
  • the graphitization degree of the first active material is 95% to 99%, more preferably 96% to 98%.
  • the graphitization degree of the second active material is 90%-95%, more preferably 92%-95%.
  • the specific surface area of the first active material of 1.6m 2 /g ⁇ 4.0m 2 / g, preferably 2.1m 2 /g ⁇ 2.7m 2 / g.
  • the specific surface area of the second active material of 0.6m 2 /g ⁇ 2.2m 2 / g, preferably 0.7m 2 /g ⁇ 1.3m 2 / g.
  • the tap density of the first active material is 0.8 g/cm 3 to 1.3 g/cm 3 , more preferably 0.9 g/cm 3 to 1.2 g/cm 3 .
  • the tap density of the second active material is 0.7 g/cm 3 to 1.4 g/cm 3 , more preferably 0.8 g/cm 3 to 1.2 g/cm 3 .
  • the powder compaction density of the first active material under a force of 30,000 N is 1.7 g/cm 3 to 2.0 g/cm 3 , more preferably 1.8 g/cm 3 to 1.9 g/cm 3 .
  • the powder compaction density of the second active material under a force of 30,000 N is 1.65 g/cm 3 to 1.85 g/cm 3 , more preferably 1.71 g/cm 3 to 1.80 g/cm 3 .
  • the surface of the first active material and/or the second negative electrode active material has a coating layer. More preferably, the surfaces of the first anode active material and the second anode active material each have a coating layer.
  • the adhesive force between the negative electrode film layer and the current collector satisfies: 6N/m ⁇ F ⁇ 30N/m, more preferably 10N/m ⁇ F ⁇ 20N/m.
  • the mass ratio of the natural graphite in the first negative electrode active material is ⁇ 60%, more preferably ⁇ 80%.
  • the mass ratio of the artificial graphite in the second negative electrode active material is ⁇ 70%, more preferably ⁇ 90%.
  • the mass ratio of the first negative electrode film layer to the second negative electrode film layer is 1:3-9:5, more preferably 1:2-3:2.
  • 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.
  • the parameters of each negative electrode film layer 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, compaction density, areal density and the like mentioned in this application all refer to the pole piece/film parameters after cold compaction and compaction for assembling the battery.
  • the negative electrode current collector can be a conventional metal foil sheet or a composite current collector.
  • the material of the metal foil can be one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy.
  • a copper foil having a thickness of 5 to 30 ⁇ m can be used.
  • the composite current collector is usually formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate.
  • the negative pole piece described in this application does not exclude additional functional layers other than the film layer.
  • the negative pole piece described in this application further includes a conductive primer layer sandwiched between the current collector and the first film layer and arranged on the surface of the current collector (for example, made of a conductive agent and a bonding agent). Agent composition).
  • the negative pole piece described in the present application further includes a protective covering layer covering the surface of the second film layer.
  • a secondary battery usually consists of a negative pole piece (ie, the negative pole piece of the present application), a positive pole piece, a separator, and an electrolyte.
  • the active ions move between the positive and negative electrodes using the electrolyte as a medium to realize battery charging. Discharge.
  • a separator is required to separate the positive and negative electrodes.
  • the positive pole piece includes a positive current collector and a positive active material layer provided on the surface of the positive current collector and including a positive active material.
  • the positive electrode active material may be a transition metal composite oxide, including lithium iron phosphide, lithium iron manganese phosphide, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide , Lithium nickel cobalt aluminum oxide, these lithium transition metal oxides added other transition metals or non-transition metal compounds, or a mixture of two or more of the above substances; but this application is not limited to these materials, can also Other conventionally known materials that can be used as the positive electrode active material of the secondary battery are used. These positive electrode active materials may be used alone or in combination of two or more kinds.
  • the specific types and composition of the separator and the electrolyte are not subject to specific restrictions, and can be selected according to actual needs.
  • the isolation film may be selected from, for example, polyethylene film, polypropylene film, polyvinylidene fluoride film, non-woven fabric and their multilayer composite film.
  • the electrolyte usually includes an organic solvent and an electrolyte salt.
  • Organic solvents can be selected from chain carbonates (such as dimethyl carbonate DMC, diethyl carbonate DEC, ethyl methyl carbonate EMC, methyl propyl carbonate MPC, dipropyl carbonate DPC, etc.), cyclic carbonates (such as carbonic acid Vinyl ester EC, propylene carbonate PC, vinylene carbonate VC, etc.), other chain carboxylic acids (such as methyl propionate, etc.), other cyclic esters (such as ⁇ -butyrolactone, etc.), chain ethers (such as Dimethoxyethane, diethyl ether, diglyme, triglyme, etc.), cyclic ethers (such as tetrahydrofuran, 2-methyltetrahydrofuran, etc.), nitriles (acetonitrile, propionitrile, etc.) Or mixed solvents composed of them.
  • the electrolyte salt is, for example, inorganic lithium salts such as LiClO 4 , LiPF 6 , LiBF 4 , LiAsF 6 , LiSbF 6 , or LiCF 3 SO 3 , LiCF 3 CO 2 , Li 2 C 2 F 4 (SO 3 ) 2 , LiN(CF 3 SO 2 ) 2 , LiC(CF 3 SO 2 ) 3 , LiC n F 2n + 1 SO 3 (n ⁇ 2) and other organic lithium salts.
  • inorganic lithium salts such as LiClO 4 , LiPF 6 , LiBF 4 , LiAsF 6 , LiSbF 6 , or LiCF 3 SO 3 , LiCF 3 CO 2 , Li 2 C 2 F 4 (SO 3 ) 2 , LiN(CF 3 SO 2 ) 2 , LiC(CF 3 SO 2 ) 3 , LiC n F 2n + 1 SO 3 (n ⁇ 2) and other organic lithium salts.
  • 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, and dried to obtain a positive electrode piece.
  • a solvent such as NMP
  • Materials such as metal foil such as aluminum foil or porous metal plate can be used as the positive electrode current collector. Commonly used is aluminum foil with a thickness of 8-30 ⁇ m.
  • a positive electrode coating is not formed on a part of the current collector, and a part of the current collector is left as the positive lead part. Of course, the lead part can also be added later.
  • the secondary battery may include an outer package and a battery cell and electrolyte packaged in the outer package.
  • the number of battery cells in the secondary battery can be one or several, which can be adjusted according to requirements.
  • the outer packaging of the secondary battery may be a soft bag (for example, a bag type, and the material may be plastic, such as polypropylene PP, polybutylene terephthalate PBT, polybutylene succinate). One or more of glycol ester PBS, etc.), or hard shell (for example, aluminum shell, etc.).
  • FIG. 1 shows a secondary battery 5 of a square structure as an example.
  • 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. 2 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.
  • Figures 3 and 4 show the battery pack 1 as an example. 3 and 4, 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.
  • the second aspect of the application provides a device.
  • the device includes the secondary battery of the first aspect of the present application, and the secondary battery provides power to the device.
  • 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.
  • the device can select a secondary battery, a battery module, or a battery pack according to its usage requirements.
  • Figure 5 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.
  • NCM523 lithium nickel cobalt manganese ternary active material LiNi 0.5 Co 0.2 Mn 0.3 O 2
  • PVDF binder polyvinylidene fluoride
  • the first step is to prepare negative electrode slurry 1: the first negative electrode active material natural graphite, binder SBR, thickener CMC and conductive carbon black are weighed to a weight ratio of 96.2:1.8:1.2:0.8 and deionized Water is added to the mixing tank in a certain order and mixed to prepare the first negative electrode slurry; wherein the natural graphite powder has an OI value of COI 1 of 4.5, D v 50 of 12.5, and a degree of graphitization of 96.5%, (D v 90-D v 10)/D v 50 is 0.95.
  • the second step is to prepare negative electrode slurry 2:
  • the second negative electrode active material artificial graphite, binder SBR, thickener CMC-Na and conductive carbon black are weighed to a weight ratio of 96.2:1.8:1.2:0.8 and Deionized water is added to a stirring tank in a certain order and mixed to prepare a second negative electrode slurry; wherein the artificial graphite powder has an OI value COI 2 of 2.9, a D v 50 of 15.0, and a graphitization degree of 91.8%. (D v 90-D v 10)/D v 50 is 1.22.
  • 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 both surfaces of the current collector to form a first negative electrode film layer
  • the negative electrode slurry 2 is coated on the first negative electrode film layer to form a second negative electrode film layer.
  • the mass ratio of the first negative electrode film layer to the second negative electrode film layer is 1:1.
  • 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 slitting and cutting.
  • EC ethylene carbonate
  • EMC ethyl methyl carbonate
  • DEC diethyl carbonate
  • Example 2 to 18 and Comparative Examples 1 to 4 are similar to those of Example 1, but the composition and product parameters of the negative pole piece are adjusted.
  • the different product parameters are shown in Table 1 to Table 3 in detail.
  • the powder OI value of the negative electrode active material can be obtained by using an X-ray powder diffractometer (X'pert PRO), according to the general rules of X-ray diffraction analysis and the determination method of graphite lattice parameters JIS K 0131-1996, JB/T4220-2011 ,
  • the method for testing the powder OI value of the negative electrode active material is: placing a certain quality of the negative electrode active material powder in an X-ray powder diffractometer, and obtaining the peak area of the 004 crystal plane diffraction peak and the 110 crystal surface by X-ray diffraction analysis. The peak area of the surface diffraction peak, and then the COI value of the negative electrode active material.
  • the particle size Dv50 of the negative electrode active material can be measured using the laser diffraction particle size distribution measuring instrument (Mastersizer 3000), according to the particle size distribution laser diffraction method (refer to GB/T19077-2016), and the median value Dv50 of the volume distribution is used. Represents the average particle size.
  • the areal density of the negative electrode film layer m/s, m represents the weight of the film layer, s represents the area of the film layer, and m can be obtained by weighing with an electronic balance with an accuracy of 0.01g or more.
  • the compaction density of the negative electrode film layer m/V
  • m represents the weight of the film layer
  • V represents the volume of the film layer
  • m can be obtained by weighing with an electronic balance with an accuracy of 0.01g or more
  • the product is the volume V of the film, where the thickness of the film can be measured using a spiral micrometer with an accuracy of 0.5 ⁇ m.
  • the produced lithium-ion battery (including three electrodes) is charged and discharged for the first time with a current of 1C (that is, the current value of completely discharging the theoretical capacity within 1h).
  • the charging is constant current and constant voltage charging, and the termination voltage is 4.2 V, the cut-off current is 0.05C, the discharge end voltage is 2.8V, and its theoretical capacity is recorded as C0; then the battery is constant at 0.5C0, 1C0, 1.5C0, 2C0, 2.5C0, 3C0, 3.5C0, 4C0, 4.5C0 Charge to 4.2V full power cut-off voltage or 0V negative cut-off potential.
  • the charging window is respectively denoted as C 10% SOC , C 20% SOC , C 30% SOC , C 40% SOC , C 50% SOC , C 60% SOC , C 70% SOC , C 80% SOC , according to the formula (60 /C 20%SOC +60/C 30%SOC +60/C 40%SOC +60/C 50%SOC +60/C 60%SOC +60/C 70%SOC +60/C 80%SOC )*10 %
  • the charging time T of the battery from 10% to 80% SOC is calculated. The shorter the time, the better the fast charging performance of the battery.
  • the produced lithium-ion battery cell is charged and discharged for the first time with a current of 1C (that is, the current value of completely discharging the theoretical capacity within 1h).
  • the charging is constant current and constant voltage charging, and the termination voltage is 4.2V.
  • the current is 0.05C
  • the end-of-discharge voltage is 2.8V
  • the discharge capacity Cb at the first cycle of the cell is recorded.
  • carry out cycle life test The test condition is 1C/1C cycle under normal temperature conditions, and the discharge capacity Ce of the cell is recorded at any time.
  • the ratio of Ce to Cb is the cycle over capacity retention rate. When the capacity retention rate is lower than or equal to 80 Stop the test at% and record the number of cycles.
  • test sample Take the coated and cold-pressed negative pole piece, and cut a test sample with a length of 100 mm and a width of 10 mm. Take a stainless steel plate with a width of 25mm, paste the double-sided tape (width 11mm), paste the test sample on the double-sided tape on the stainless steel plate, and roll it back and forth three times (300mm/min) with a 2000g pressure roller on its surface. Bend the test sample 180 degrees, manually peel off the negative film and current collector of the test sample by 25mm, and fix the test sample on the testing machine so that the peeling surface is consistent with the force line of the testing machine. The testing machine is continuous at 300mm/min.
  • Example 13 From the comparison between Example 13 and Example 3, as well as the comparison between Example 2 and Example 14, it can be seen that within a certain range, the larger the COI 1 /COI 2 value, the better the fast charging and cycle performance. However, combining the various examples and comparative examples shows that the overall performance is better when the COI 1 /COI 2 value is in the range of 1.1 to 2.5, especially when 1.3 ⁇ COI 1 /COI 2 ⁇ 1.6.

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Abstract

一种二次电池（5）及含有它的装置，二次电池（5）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的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，所述第二负极活性材料包括人造石墨；所述第一负极活性材料满足：4.0≤COI 1≤7.0；所述第二负极活性材料满足：2.2≤COI 2≤4.2。该二次电池（5）在具有较高能量密度的前提下，同时兼具较好的快速充电性能和循环性能。

Description

二次电池及含有它的装置 技术领域
本申请属于电化学技术领域，更具体地说，本申请涉及一种二次电池及含有它的装置。
背景技术
新能源汽车代表了世界汽车产业发展的方向。锂离子二次电池作为新型高电压、高能量密度动力电池，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汽车。
随着动力电池市场的需求逐渐扩大，对动力电池的能量密度的需求也越来越高。但是，现有技术中采用的改善电池能量密度的技术手段往往会导致电池其他方面性能的劣化。因此，急需一种能够改善电池的能量密度同时又不会降低或甚至改善电池的其他电性能的新技术。
发明内容
本申请的一个目的在于提供一种二次电池，所述电池在具有较高能量密度的前提下，同时兼具较好的快速充电性能和循环性能。
为实现上述发明目的，本申请的第一方面提供了一种二次电池，所述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，所述第二负极活性材料包括人造石墨；
所述第一负极活性材料满足：4.0≤COI 1≤7.0，优选为4.3≤COI 1≤5.5；
所述第二负极活性材料满足：2.2≤COI 2≤4.2，优选为2.5≤COI 2≤3.6；
其中，
COI 1为第一负极活性材料在X射线衍射图谱中004特征衍射峰的峰面积与110特征衍射峰的峰面积的比值；
COI 2为第二负极活性材料在X射线衍射图谱中004特征衍射峰的峰面积与110特征衍射峰的峰面积的比值。
在本申请的第二方面，提供一种装置，其包括本申请第一方面所述的二次电池。
本申请至少包括下述有益效果：
本申请二次电池的负极极片包括多层结构，且各层包含特定的负极活性材料及特定的COI范围，在其共同作用下，电池在具有较高能量密度的前提下，可以同时兼具较好的快速充电性能和循环性能。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是电池模块的一实施方式的示意图。
图3是电池包的一实施方式的示意图。
图4是图3的分解图。
图5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
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)。
二次电池中，为了增加电池的能量密度，往往会增加极片
膜层的厚度，但厚度增加会导致电池的循环性能和快速充电性能均受到影响。这是由于负极活性材料在循环过程中会存在膨胀，导致活性物质与基材之间的粘结力下降，甚至会发生脱膜，当厚度增加时，这种现象更为严重；同时，厚度增加使活性离子的扩散路径增长，从而电池的快速充电性能也会受到影响。因此，如何使电池在具有较高能量密度的前提下，兼具较好的循环性能和快速充电性能，在技术方面是一个巨大的挑战。
发明人通过大量实验发现，可以通过调整负极极片的组成和结构来实现本申请的技术目标。具体地，本申请的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，所述第二负极活性材料包括人造石墨；所述第一负极活性材料的粉体OI值COI 1满足：4.0≤COI 1≤7.0，所述第二负极活性材料的粉体OI值COI 2满足：2.2≤COI 2≤4.2，其中，COI 1为第一负极活性材料在X射线衍射图谱中004特征衍射峰的峰面积与110特征衍射峰的峰面积的比值；COI 2为第二负极活性材料在X射线衍射图谱中004特征衍射峰的峰面积与110特征衍射峰的峰面积的比值。电池在具有较高能量密度的前提下，可以同时兼具较好的循环性能和快速充电性能。
发明人研究发现，当负极极片满足上述设计要求(4.0≤COI 1≤7.0，且2.2≤COI 2≤4.2)时，一方面，有效提高了负极膜层和集流体之间的粘结力，改善了极片的脱膜现象，从而改善电池的循环性能；另一方面，将上下膜层中活性 材料的OI值控制在所给范围内，第二负极膜层的负极活性材料在辊压时可以保持丰富的孔道结构，保证活性离子可以快速迁移至负极膜层中；第一负极膜层在辊压时有利于压力由第二负极膜层传导到第一负极膜层，保证第一负极膜层具备较高的填充密度，上下层的孔道结构分配更加合理，有效提高了电池的动力学性能，即使在涂布厚度增加的情况下，也能确保活性离子的液相扩散速率，有效改善了电池的快速充电性能。发明人发现，上下层的活性材料的粉体OI值在所给范围内时，第二负极膜层中的负极活性材料可提供较多的嵌锂入口，保证活性离子可快速嵌入负极活性物质内部，而第一负极膜层中的负极活性材料可提供较多的嵌锂位置，保证可接纳嵌入更多的活性离子，上下层的嵌锂入口和嵌锂位置分配更加合理，确保高能量密度设计的同时，兼顾了活性离子的电荷交换阻抗和固相扩散速率，有效改善了电池的快速充电性能。在一些优选实施方式中，所述第一负极活性材料满足：4.3≤COI 1≤5.5。在一些优选实施方式中，所述第二负极活性材料满足：2.5≤COI 2≤3.6。
本领域技术人员理解：负极活性材料的粉体OI值用于表示活性材料的取向指数，即负极膜层中晶粒排列的各向异性程度。
在本申请中，COI被定义为材料在X射线衍射谱图中(004)特征衍射峰和(110)特征衍射峰的面积比。即，COI＝C 004/C 110，其中，C 004为004特征衍射峰的峰面积，C 110为110特征衍射峰的峰面积。更具体地，COI 1为第一负极活性材料在X射线衍射图谱中004特征衍射峰的峰面积与110特征衍射峰的峰面积的比值；COI 2为第二负极活性材料在X射线衍射图谱中004特征衍射峰的峰面积与110特征衍射峰的峰面积的比值。
天然石墨的粉体OI值也可以用其在X射线衍射谱图中(003)特征衍射峰的峰面积和(110)特征衍射峰的峰面积比来表征。即，天然石墨的粉体OI值＝C 003/C 110，其中，C 003为003特征衍射峰的峰面积，C 110为110特征衍射峰的峰面积。此时，本申请的天然石墨的C 003/C 110需满足4.0≤C 003/C 110≤7.0。
负极活性材料的粉体OI值可以用本领域公知的方法进行测定，例如用本文实施例部分所述方法进行测定。
在一些实施例中，所述第一负极膜层中活性材料的粉体OI值COI 1与所述第二负极膜层中活性材料的粉体OI值COI 2的比值满足：1.1≤COI 1/COI 2≤2.5，优选为1.3≤COI 1/COI 2≤1.6时，其快速充电性能和容量可进一步提升。这是因为，当第一负极膜层中活性材料的粉体OI值与所述第二负极膜层中活性材料的 粉体OI值在所给范围内时，上、下膜层的孔道分布与充电时活性离子分布更加匹配，越有利于电芯高容量和快速充电设计。
本申请所述的负极极片包括集流体和设置于所述集流体至少一个表面上的两层或多层膜层。负极极片既可以双面涂布(即膜层设置于集流体的两个表面)，也可以仅单面涂布(即膜层仅设置于集流体的一个表面上)。本申请的负极极片可以采用本领域常用的各种方法进行制备。通常，可以先准备负极集流体，再制备负极活性材料浆料，将负极活性材料浆料涂覆到负极集流体的一个或两个表面，最后经干燥、焊接导电构件(极耳)、裁切等后处理步骤得到所需负极极片。
本申请所述的负极膜层可以将第一活性材料浆料和第二活性材料浆料一次同时涂在负极集流体上，也可以分两次涂布；优选为一次同时将第一活性材料浆料和第二活性材料浆料涂在负极集流体上。
所述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。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CMC)、PTC热敏电阻材料等。
作为示例，导电剂可以为石墨、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多种。
作为示例，粘结剂可以为丁苯橡胶(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。
在本申请所述的负极极片中，负极活性材料还可以包括软碳、硬碳、硅基材料、锡基材料中的一种或几种。在某些实施方式中，所述第一负极活性材料还可以包括人造石墨、软碳、硬碳、硅基材料、锡基材料中的一种或几种。在某些实施方式中，所述第二负极活性材料还可以包括天然石墨、软碳、硬碳、硅基材料、锡基材料中的一种或几种。
为了进一步优化电池性能，还可以控制调整负极活性材料和极片的其他参数。例如，可以将第一负极活性材料和第二负极活性材料的石墨化度和材料粒 径控制在一定范围内，和/或将极片CW、PD、极片厚度和活性比表面积控制在一定范围内，以便进一步优化电芯能量密度、低温功率和快速充电性能。
优选地，所述第一负极活性材料中的天然石墨的形貌为球形或类球形。
优选地，所述第二负极活性材料中的人造石墨的形貌为片状或块状。
优选地，所述第一活性材料的平均粒径Dv50为9μm～16μm，更优选为11μm～14μm。
优选地，所述第二活性材料的平均粒径Dv50为11μm～19μm，更优选为13μm～17μm。
优选地，所述第一活性材料的粒径分布为0.8≤(D v90-D v10)/D v50≤1.5，更优选为0.9＜(D v90-D v10)/D v50≤1.3。
优选地，所述第二活性材料的粒径分布为0.9≤(D v90-D v10)/D v50≤2，更优选为1.1≤(D v90-D v10)/D v50≤1.6。
本申请中，D v10是指材料颗粒或粉末累计体积百分数达到10％时所对应的粒径，D v90是指材料颗粒或粉末累计体积百分数达到90％时所对应的粒径，D v50指材料颗粒或粉末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，D v10、D v90、D v50单位均为μm。
优选地，所述第一活性材料的石墨化度为95％～99％，更优选为96％～98％。
优选地，所述第二活性材料的石墨化度为90％～95％，更优选为92％～94％。
优选地，所述第一活性材料的比表面积(BET)为1.6m 2/g～4.0m 2/g，优选为2.1m 2/g～2.7m 2/g。
优选地，所述第二活性材料的比表面积(BET)为0.6m 2/g～2.2m 2/g，优选为0.7m 2/g～1.3m 2/g。
优选地，所述第一活性材料的振实密度为0.8g/cm 3～1.3g/cm 3，更优选为0.9g/cm 3～1.2g/cm 3。
优选地，所述第二活性材料的振实密度为0.7g/cm 3～1.4g/cm 3，更优选为0.8g/cm 3～1.2g/cm 3。
优选地，所述第一活性材料在30000N作用力下粉体压实密度为1.7g/cm 3～2.0g/cm 3，更优选为1.8g/cm 3～1.9g/cm 3。
优选地，所述第二活性材料在30000N作用力下粉体压实密度为1.65g/cm 3～1.85g/cm 3，更优选为1.71g/cm 3～1.80g/cm 3。
优选地，所述第一活性材料和/或第二负极活性材料的表面具有包覆层。更优选地，所述第一负极活性材料和所述第二负极活性材料的表面均具有包覆层。
进一步地，所述负极膜层与集流体间的粘接力满足：6N/m≤F≤30N/m，更优选为10N/m≤F≤20N/m。
在一些优选实施方式中，所述天然石墨在第一负极活性材料中的质量占比≥60％，更优选为≥80％。
在一些优选实施方式中，所述人造石墨在第二负极活性材料中的质量占比≥70％，更优选为≥90％。
在一些优选实施方式中，所述第一负极膜层与所述第二负极膜层的质量比为1∶3～9∶5，更优选为1∶2～3∶2。
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。需要说明的是，本申请所给的各负极膜层参数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、压实密度、面密度等范围均是指经冷压压实后并用于组装电池的极片/膜层参数。
对于本申请所述的负极极片，负极集流体可以采用常规金属箔片或复合集流体。金属箔片的材料可为铜、铜合金、镍、镍合金、钛、钛合金、银及银合金中的一种或多种。例如，可以使用厚度为5至30μm的铜箔。复合集流体通常通过将金属材料(铜、铜合金、镍、镍合金、钛、钛合金、银及银合金等)形成在高分子基材上而形成。
另外，本申请所述的负极极片并不排除除了膜层之外的其他附加功能层。例如在某些优选的实施方式中，本申请所述的负极极片还包括夹在集流体和第一膜层之间、设置于集流体表面的导电底涂层(例如由导电剂和粘结剂组成)。在另外一些实施方式中，本申请所述的负极极片还包括覆盖在第二膜层表面的覆盖保护层。
除了使用了本申请的负极极片外，本申请的二次电池的构造和制备方法本身是公知的。例如二次电池通常主要由负极极片(即本申请的负极极片)、正 极极片、隔离膜和电解液组成，活性离子以电解液为介质在正负极之间运动，实现电池的充放电。为避免正负极通过电解液发生短路，需要用隔离膜将正负极分隔。
本申请的二次电池中，正极极片包括正极集流体以及设置在正极集流体表面且包括正极活性材料的正极活性材料层。正极活性材料可以是过渡金属复合氧化物，包含锂铁磷化物、锂铁锰磷化物、锂钴氧化物、锂镍氧化物、锂锰氧化物、锂镍锰氧化物、锂镍钴锰氧化物、锂镍钴铝氧化物、这些锂过渡金属氧化物添加其他过渡金属或非过渡金属得到的化合物、或上述物质的两种种或多种的混合物；但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。这些正极活性材料可以仅单独使用一种，也可以将两种以上组合使用。
在本申请的二次电池中，隔离膜以及电解液的具体种类及组成均不受到具体的限制，可根据实际需求进行选择。
具体地，所述隔离膜例如可选自聚乙烯膜、聚丙烯膜、聚偏氟乙烯膜、无纺布以及它们的多层复合膜。
具体地，电解液通常包括有机溶剂和电解质盐。有机溶剂可以选自链状碳酸酯(例如碳酸二甲酯DMC、碳酸二乙酯DEC、碳酸甲乙酯EMC、碳酸甲丙酯MPC、碳酸二丙酯DPC等)、环状碳酸酯(如碳酸乙烯酯EC、碳酸丙烯酯PC、碳酸亚乙烯酯VC等)、其它链状羧酸(如丙酸甲酯等)，其它环状酯(如γ-丁内酯等)、链状醚(如二甲氧基乙烷、二乙醚、二甘醇二甲醚、三甘醇二甲醚等)、环状醚(如四氢呋喃、2-甲基四氢呋喃等)、腈类(乙腈、丙腈等)或它们组成的混合溶剂。电解质盐例如是LiClO 4、LiPF 6、LiBF 4、LiAsF 6、LiSbF 6等无机锂盐、或者LiCF 3SO 3、LiCF 3CO 2、Li 2C 2F 4(SO 3) 2、LiN(CF 3SO 2) 2、LiC(CF 3SO 2) 3、LiC nF 2n+ 1SO 3(n≥2)等有机锂盐。
以下简要说明本申请的二次电池的构造和制备方法。
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。常用的是厚度为8～30μm的铝箔。通常在制作正极极片时，在集流体的一部分上不形成正极涂层，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，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)得到裸电芯；将裸电芯置于外包装中，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。
作为一个示例，所述二次电池可以包括外包装和封装在外包装内的电芯和电解液。所述二次电池中电芯的数量可以为一个或几个，可以根据需求进行调节。
在一些实施例中，所述二次电池的外包装可以是软包(例如袋式，其材质可以是塑料，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)，也可以是硬壳(例如铝壳等)。
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。
在一些实施例中，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2是作为一个示例的电池模块4。参照图2，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壳体，多个二次电池5容纳于该容纳空间。
在一些实施例中，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3和图4是作为一个示例的电池包1。参照图3和图4，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。
本申请的第二方面提供一种装置。所述装置包括本申请第一方面的二次电池，所述二次电池为所述装置提供电源。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5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功率和高能量密度的需求，可以采用电池包或电池模块。
作为另一个示例的装置可以是手机、平板电脑、笔记本电脑等。该装置通常要求轻薄化，可以采用二次电池作为电源。
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、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 0.5Co 0.2Mn 0.3O 2(NCM523)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，得到正极极片。
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、增稠剂的CMC以及导电炭黑进行称重以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成第一负极浆料；其中，所述天然石墨的粉体OI值COI 1为4.5，D v50为12.5，石墨化度为96.5％，(D v90-D v10)/D v50为0.95。
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、增稠剂的CMC-Na以及导电炭黑进行称重以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成第二负极浆料；其中，所述人造石墨的粉体OI值COI 2为2.9，D v50为15.0，石墨化度为91.8％，(D v90-D v10)/D v50为1.22。
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涂覆在集流体两个表面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。
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，经卷绕后得到电芯，将电芯装入外包装中，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2～18和对比例1～4与实施例1的制备方法相似，但是调整了负极极片的组成和产品参数，不同的产品参数详见表1至表3。
二、性能参数测试方法
1、负极活性材料及负极膜层的各参数测试
(1)OI值测试
负极活性材料的粉体OI值可通过使用X射线粉末衍射仪(X′pert PRO)得到，依据X射线衍射分析法通则以及石墨的点阵参数测定方法JIS K 0131-1996、JB/T4220-2011，得到X射线衍射图谱，COI＝C004/C110，其中，C004为004特征衍射峰的峰面积，C110为110特征衍射峰的峰面积。
具体地，负极活性材料的粉体OI值测试方法为：将一定质量的负极活性材料粉末置于X射线粉末衍射仪中，通过X射线衍射分析法得到004晶面衍射峰的峰面积以及110晶面衍射峰的峰面积，进而得到负极活性材料的COI值。
(2)负极活性材料的粒径
负极活性材料的粒径Dv50可使用激光衍射粒度分布测量仪(Mastersizer 3000)，依据粒度分布激光衍射法(具体参照GB/T19077-2016)，测量出粒径分布，使用体积分布的中位值Dv50表示平均粒径。
(3)负极膜层的面密度
负极膜层的面密度＝m/s，m表示膜层的重量，s表示膜层的面积，m可使用精度为0.01g以上的电子天平称量得到。
(4)负极膜层的压实密度
负极膜层的压实密度＝m/V，m表示膜层的重量，V表示膜层的体积，m可使用精度为0.01g以上的电子天平称量得到，膜层的表面积与膜层厚度的乘积即为膜层的体积V，其中膜层厚度可使用精度为0.5μm的螺旋千分尺测量得到。
2、电池性能测试
(1)快速充电性能测试
常温下，所制作锂离子电池(含三电极)以1C(即1h内完全放掉理论容量的电流值)的电流进行第一次充电和放电，充电为恒流恒压充电，终止电压为4.2V，截至电流为0.05C，放电终止电压为2.8V，记录其理论容量为C0；然后电池依此以0.5C0、1C0、1.5C0、2C0、2.5C0、3C0、3.5C0、4C0、4.5C0恒流充电至4.2V全电截止电压或者0V负极截止电位，每次充电完成后需以1C0放电至2.8V，记录不同充电倍率下充电至10％、20％、30％……80％SOC态时所对应的阳极电位，绘制出不同SOC态下的倍率-阳极电位曲线，线性拟合后得出不同SOC态下阳极电位为0V时所对应的充电倍率，该充电倍率即为该SOC态下的充电窗口，分别记为C 10％SOC、C 20％SOC、C 30％SOC、C 40％SOC、 C 50％SOC、C 60％SOC、C 70％SOC、C 80％SOC，根据公式(60/C 20％SOC+60/C 30％SOC+60/C 40％SOC+60/C 50％SOC+60/C 60％SOC+60/C 70％SOC+60/C 80％SOC)*10％
计算得到该电池从10％～80％SOC的充电时间T，该时间越短，则代表电池的快速充电性能越优秀。
(2)循环性能测试
常温下，所制作锂离子电池电芯以1C(即1h内完全放掉理论容量的电流值)的电流进行第一次充电和放电，充电为恒流恒压充电，终止电压为4.2V，截至电流为0.05C，放电终止电压为2.8V，记录电芯首次循环时放电容量Cb。然后进行循环寿命检测，测试条件为常温条件下，进行1C/1C循环，随时记录电芯时放电容量Ce，Ce与Cb的比值即为循环过容量保持率，在容量保持率低于或等于80％时停止测试，记录循环圈数。
(3)粘结力测试
取涂布、冷压后的负极极片，裁成长100mm、宽10mm的测试样品。取一条宽度25mm的不锈钢板，贴双面胶(宽度11mm)，将测试样品粘帖在不锈钢板上的双面胶上，用2000g压辊在其表面来回滚压三次(300mm/min)。将测试样品180度弯折，手动将测试样品的负极膜片与集流体剥开25mm，将该测试样品固定在试验机上，使剥离面与试验机力线保持一致，试验机以300mm/min连续剥离，得到的剥离力曲线，取平稳断的均值作为剥离力F0，则测试样品中负极膜片与集流体之间的粘结力F＝F0/测试样品的宽度(F的计量单位：N/m)。
四、各实施例、对比例测试结果
按照上述方法分别制备实施例和对比例的电池，并测量各项性能参数，结果见下面的表格。
Figure PCTCN2019123729-appb-000001
Figure PCTCN2019123729-appb-000002
Figure PCTCN2019123729-appb-000003
从实施例1～5和对比例1～2的数据可知：当第一负极膜层使用天然石墨作为第一负极活性材料、第二负极膜层使用人造石墨作为第二负极活性材料时，两种负极活性材料的粉体OI值需同时落在本申请的范围内相互匹配才能兼顾良好的快充性能和循环性能。对比例1中COI 1值过小、对比例2中COI 1值过大，这两种情况下都会导致电池循环性能显著恶化，同时快充性能也相对较差。从各对比例和实施例的膜层粘结力数据可知：COI 1值越大，膜层的粘结力越大。为了确保良好的快充性能和循环性能，COI 1应在4.0至7.0的范围内，最好是在4.3至5.5的范围内。
从实施例6～10和对比例3～4的数据可知：当第一负极膜层使用天然石墨作为第一负极活性材料、第二负极膜层使用人造石墨作为第二负极活性材料时，两种负极活性材料的粉体OI值需同时落在本申请的范围内相互匹配才能兼顾良好的快充性能和循环性能。对比例3中COI 2值过小、对比例2中COI 2值过大，这两种情况下都会导致电池循环性能显著恶化，同时快充性能也相对较差。为了确保良好的快充性能和循环性能，COI 2应在2.2至4.2的范围内，最好是在2.5至3.6的范围内。
从实施例13和实施例3的对比，以及实施例2和实施例14的对比可知：在一定范围内，COI 1/COI 2值越大越有利于快充和循环性能。但是，综合各个实施例和对比例可知，COI 1/COI 2值在1.1至2.5的范围内时综合性能较好，尤其是1.3≤COI 1/COI 2≤1.6时。
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。

Claims (12)

  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，所述第二负极活性材料包括人造石墨；
    所述第一负极活性材料的粉体OI值COI 1满足：4.0≤COI 1≤7.0；
    所述第二负极活性材料的粉体OI值COI 2满足：2.2≤COI 2≤4.2；
    其中，
    COI 1为第一负极活性材料在X射线衍射图谱中004特征衍射峰的峰面积与110特征衍射峰的峰面积的比值；
    COI 2为第二负极活性材料在X射线衍射图谱中004特征衍射峰的峰面积与110特征衍射峰的峰面积的比值。
  2. 根据权利要求1所述的二次电池，其特征在于：所述第一负极活性材料满足：4.3≤COI 1≤5.5。
  3. 根据权利要求1或2所述的二次电池，其特征在于：所述第二负极活性材料满足：2.5≤COI 2≤3.6。
  4. 根据权利要求1至3任一项所述的二次电池，其特征在于：所述第一负极活性材料和第二负极活性材料还满足1.1≤COI 1/COI 2≤2.5，优选为1.3≤COI 1/COI 2≤1.6。
  5. 根据权利要求1至4任一项所述的二次电池，其特征在于：
    所述天然石墨的形貌为球形或类球形；和/或，
    所述人造石墨的形貌为片状或块状。
  6. 根据权利要求1至5任一项所述的二次电池，其特征在于：
    所述天然石墨在第一负极活性材料中的质量占比≥60％，优选为80％～100％；和/或，
    所述人造石墨在第二负极活性材料中的质量占比≥70％，优选为90％～100％。
  7. 根据权利要求1至6任一项所述的二次电池，其特征在于：所述第一负极活性材料满足以下(1)～(6)中的一种或几种：
    (1)平均粒径D V50为9μm～16μm，优选为11μm～14μm；
    (2)粒径分布满足0.8≤(D v90-D v10)/D v50≤1.5，优选满足0.9＜(Dv90-Dv10)/Dv50≤1.3；
    (3)石墨化度为95％～99％，优选为96％～98％；
    (4)比表面积(BET)为1.6m 2/g～4.0m 2/g，优选为2.1m 2/g～2.7m 2/g。
    (5)振实密度为0.8g/cm 3～1.3g/cm 3，优选为0.9g/cm 3～1.2g/cm 3；
    (6)在30000N作用力下粉体压实密度为1.7g/cm 3～2.0g/cm 3，优选为1.8g/cm 3～1.9g/cm 3。
  8. 根据权利要求1至7任一项所述的二次电池，其特征在于：所述第二负极活性材料满足以下(1)～(6)中的一种或几种：
    (1)平均粒径D V50为11μm～19μm，优选为13μm～17μm；
    (2)粒径分布为0.9≤(D v90-D v10)/D v50≤2，优选为1.1≤(D v90-D v10)/D v50≤1.6；
    (3)石墨化度为90％～95％，更优选为92％～94％；
    (4)比表面积(BET)为0.6m 2/g～2.2m 2/g，优选为0.7m 2/g～1.3m 2/g；
    (5)振实密度为0.7g/cm 3～1.4g/cm 3，更优选为0.8g/cm 3～1.2g/cm 3；
    (6)在30000N作用力下粉体压实密度为1.65g/cm 3～1.85g/cm 3，优选为1.71g/cm 3～1.80g/cm 3。
  9. 根据权利要求1至8任一项所述的二次电池，其特征在于：所述第一负极活性材料和/或所述第二负极活性材料的表面具有包覆层；优选地，所述第一负极活性材料和所述第二负极活性材料的表面均具有包覆层。
  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：所述第一负极膜层与所述第二负极膜层的质量比为1∶3～9∶5；优选为1∶2～3∶2。
  11. 根据权利要求1至10任一项所述的二次电池，其特征在于：所述第一负极活性材料还包括人造石墨、软碳、硬碳、硅基材料、锡基材料中的一种或几种；和/或，所述第二负极活性材料还包括天然石墨、软碳、硬碳、硅基材料、锡基材料中的一种或几种。
  12. 一种装置，其特征在于，包括根据权利要求1至11任一项所述的二次电池。
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