WO2020088232A1 - 一种负极极片、二次电池、电池模块、电池包及装置 - Google Patents

一种负极极片、二次电池、电池模块、电池包及装置 Download PDF

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WO2020088232A1
WO2020088232A1 PCT/CN2019/111050 CN2019111050W WO2020088232A1 WO 2020088232 A1 WO2020088232 A1 WO 2020088232A1 CN 2019111050 W CN2019111050 W CN 2019111050W WO 2020088232 A1 WO2020088232 A1 WO 2020088232A1
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active material
pole piece
negative electrode
battery
negative pole
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PCT/CN2019/111050
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English (en)
French (fr)
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马建军
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 EP19877955.5A priority Critical patent/EP3796427A4/en
Publication of WO2020088232A1 publication Critical patent/WO2020088232A1/zh
Priority to US17/130,787 priority patent/US11258060B2/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
    • H01M4/64—Carriers or collectors
    • H01M4/66—Selection of materials
    • H01M4/665—Composites
    • H01M4/667—Composites in the form of layers, e.g. coatings
    • 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
    • H01M4/362—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
    • H01M4/485—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of mixed oxides or hydroxides for inserting or intercalating light metals, e.g. LiTi2O4 or LiTi2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—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
    • H01M4/36—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
    • 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
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present application relates to the technical field of secondary batteries, in particular to a negative pole piece, a secondary battery using the negative pole piece, a battery module, a battery pack, and a device.
  • Rechargeable batteries have been widely used in recent years due to their advantages of high energy density, high operating voltage, long service life, and low self-discharge.
  • higher requirements are placed on the energy density and fast charging performance of rechargeable batteries.
  • the present application provides a negative pole piece, a secondary battery, a battery module, a battery pack, and a device.
  • the secondary battery has high energy density, long cycle life and fast charging performance at the same time.
  • the first aspect of the present application provides a negative electrode tab including a negative electrode current collector, a first active material layer provided on at least one surface of the negative electrode current collector, and a A second active material layer on the first active material layer;
  • the first active material layer contains a first negative electrode active material
  • the second active material layer contains a second negative electrode active material
  • A is the average particle size of the first negative electrode active material
  • C is the average particle size of the second negative electrode active material
  • D is the thickness of the second active material layer.
  • the second aspect of the present application provides a secondary battery including the negative electrode tab of the first aspect of the present application.
  • a third aspect of the present application provides a battery module including the secondary battery described in the second aspect of the present application.
  • a fourth aspect of the present application provides a battery pack including the battery module described in the third aspect of the present application.
  • a fifth aspect of the present application provides a device including the secondary battery described in the second aspect of the present application, the secondary battery being used as a power source for the device.
  • the device includes mobile equipment, electric vehicles, electric trains, satellites, ships and energy storage systems.
  • the present application includes at least the following beneficial effects:
  • the negative pole piece of the present application includes a double active material layer structure, and the thickness of each active material layer and the particle size of the active material in the active material layer are adjusted during design, resulting in a balance between high energy density, long cycle life and fast charging performance Secondary battery.
  • the battery module, battery pack, and device of the present application include the secondary battery described above, and thus have at least the same advantages as the secondary battery.
  • FIG. 1 is a schematic diagram of an embodiment of a secondary battery.
  • 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 a secondary battery is used as a power source.
  • the negative electrode tab includes a negative electrode current collector, a first active material layer provided on at least one surface of the negative electrode current collector, and a first active material layer provided on the first active material layer. Two active substance layers;
  • the first active material layer contains a first negative electrode active material
  • the second active material layer contains a second negative electrode active material
  • A is the average particle size of the first negative electrode active material
  • C is the average particle size of the second negative electrode active material
  • D is the thickness of the second active material layer.
  • the inventors of the present application found that under the same raw materials and the same process, the larger the particle size of the negative electrode active material, the higher the gram capacity, the less negative electrode active material is required when the battery reaches the expected capacity, and the higher the energy density of the battery.
  • the particle size of the negative electrode active material is too large, the longer the solid phase diffusion path of the active ions, the greater the resistance, which will affect the rapid charging performance of the battery.
  • the particle size of the negative electrode active material is smaller, the solid phase diffusion path of the active ions is shorter, and the resistance is smaller, which is beneficial to improve the rapid charging performance of the battery.
  • the particle size is too small, the gram capacity is not only low, but the energy density of the cell is affected to a certain extent.
  • the negative electrode slurry is difficult to disperse and stir.
  • the adhesive force between the active material particles of the negative electrode sheet and the current collector and the negative electrode active material particles are poor, which will affect the energy density of the battery. And cycle life.
  • the inventors of the present application also found that the smaller the thickness of the negative electrode active material layer, the more favorable is the infiltration of the negative electrolyte, and the faster the liquid phase conduction speed of the active ions in the pole piece is.
  • the polarization of the battery is not significantly increased, and the side reactions are few, thereby avoiding the safety problems caused by the formation of lithium dendrites on the surface of the negative electrode.
  • the thickness of the diaphragm is too small, the energy density of the battery is greatly affected.
  • the thickness of the negative electrode active material layer is larger, the same negative electrode active material is used, and the energy density of the battery is higher.
  • the inventor of the present application has conducted extensive research to design the negative electrode sheet into a double-layer structure, and by adjusting the ratio of the thickness of the active material layer to the particle diameter of the negative electrode active material, the negative electrode sheet simultaneously satisfies the following relationship: 2.0 ⁇ B / A ⁇ 4.0, and 2.2 ⁇ D / C ⁇ 5.0, can make the battery have the characteristics of long cycle life, high energy density and fast charging.
  • the first negative electrode active material in the first active material layer has a larger particle size, and at the same thickness, on the one hand, it can provide a higher capacity, which increases the capacity per unit area .
  • the larger the particle size of the negative electrode active material the smaller the number of active material accumulation layers in the active material layer when the thickness is the same, less side reactions when charge exchange occurs on the surface of the active material, and SEI formed on the surface
  • the layer is more stable and dense, which is beneficial to improve the cycle performance of the battery.
  • B / A is less than 2.0, it means that the average particle size of the first active material is too large, the thickness of the active material layer is too small, that is, the number of active material accumulation layers is too small, and the solid phase diffusion path of active ions inside the negative electrode active material Longer, the internal resistance increases, affecting the battery's rapid charging ability. In addition, the thickness of the active material layer is too small, and the pole pieces are prone to particle scratches, resulting in poor appearance. If B / A is greater than 4.0, it means that the average particle diameter of the first active material is too small, and the thickness of the active material layer is too large, that is, the number of active material accumulation layers is too large, making the active ion liquid phase transmission path too long, affecting the battery Fast charging capability.
  • the second negative electrode active material in the second active material layer has a smaller particle size, and in the case of the same thickness, there are more small particle size active materials.
  • increasing the porosity of the surface pole piece is conducive to electrolyte infiltration and liquid phase transmission of active ions.
  • the diffusion path of the active ions within the small particle size active material particles is shortened, thereby reducing the solid phase diffusion resistance of the active ions, which is beneficial to the rapid insertion and extraction of active ions, and thus can improve the rapid charging performance of the battery.
  • D / C is less than 2.2, it means that the average particle size of the second active material is too large, the thickness of the active material layer is too small, the material particles may be larger than the thickness of the active material layer, and large particles and wire drawing are likely to exist in the processing of pole pieces The problem.
  • D / C is greater than 5.0, it indicates that the thickness of the second active material layer is large, and the particle size of the second active material is too small. Too small particle size leads to certain difficulties in slurry mixing, which affects the appearance and adhesion of the pole piece, thereby affecting the cycle performance of the battery core.
  • the larger thickness of the second active material layer will cause the transmission path of the active ions to be too long, which affects the rapid charging ability of the battery.
  • the lower limit of B / A may be 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7; the upper limit of B / A may be 2.8, 2.9, 3.0, 3.1 , 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0.
  • the lower limit of D / C may be 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0; the upper limit of D / C may be 3.2, 3.4, 3.6 , 3.8, 4.0, 4.2, 4.4, 4.6, 4.8, 5.0.
  • the average particle diameter A of the first negative electrode active material is greater than or equal to the average particle diameter C of the second negative electrode active material; more preferably, in the negative electrode sheet, 0.4 ⁇ C / A ⁇ 1.0.
  • the second negative electrode active material has a smaller particle size than the first negative electrode active material, it is beneficial to the rapid insertion and extraction of active ions, thereby improving the rapid charging performance of the battery; at the same time, the first active material has a larger particle size, It can make the battery have a thinner thickness of the active material layer under the premise of reaching the same energy density, which is more conducive to the diffusion of active ions, avoids the generation of polarization and lithium precipitation, and thus reduces the occurrence of side reactions, thereby further improving The cycle life of the battery.
  • the thickness B of the first active material layer is greater than or equal to the thickness D of the second active material layer; more preferably, in the negative electrode sheet, 0.2 ⁇ D / B ⁇ 1.0.
  • the active ions can be inserted into the first active material layer through the second active material layer in a shorter time, avoiding the active ions on the surface of the pole piece Lithium deposition occurs due to accumulation, which can further improve the fast charging performance of the battery.
  • the negative pole piece of the present application D / C ⁇ B / A.
  • the second active material layer has a larger number of active ion accumulation layers than the first active material layer, and there are more active ion accumulation layers.
  • the electrochemical reaction activity is enhanced, and the liquid phase and solid phase impedance of the active ion are reduced, so that the active ion After the positive electrode is released, it can quickly pass through the second active material layer to reach the first active material layer, thereby avoiding the accumulation of active ions on the surface of the pole piece, forming dendrites, which leads to safety problems.
  • the average particle size A of the first negative electrode active material satisfies the following relationship: 12 ⁇ m ⁇ A ⁇ 25 ⁇ m, more preferably 15 ⁇ m ⁇ A ⁇ 19 ⁇ m.
  • the thickness B of the first active material layer satisfies the following relationship: 35 ⁇ m ⁇ B ⁇ 105 ⁇ m, more preferably 40 ⁇ m ⁇ B ⁇ 60 ⁇ m.
  • the average particle diameter C of the second negative electrode active material satisfies the following relationship: 4 ⁇ m ⁇ C ⁇ 18 ⁇ m, more preferably 7 ⁇ m ⁇ C ⁇ 15 ⁇ m.
  • the thickness D of the second active material layer satisfies the following relationship: 10 ⁇ m ⁇ D ⁇ 45 ⁇ m, more preferably 20 ⁇ m ⁇ D ⁇ 40 ⁇ m.
  • the first negative electrode active material and the second negative electrode active material are respectively selected from one of artificial graphite, natural graphite, mesophase carbon microspheres, soft carbon, and hard carbon Kind or several.
  • the degree of graphitization of the first negative electrode active material is greater than the degree of graphitization of the second negative electrode active material.
  • the higher the degree of graphitization of the first active material the higher the degree of ordering of the active material, fewer defects such as stacking faults and dislocations in the crystal, and low surface activity. It is easy to form a stable and dense SEI film during the cycle, which is beneficial to the cycle Performance improvement.
  • the lower the degree of graphitization of the second active material the greater the spacing between the crystal planes of the material, which facilitates the entry and exit of active ions in the active material, reduces resistance, avoids the accumulation of active ions on the surface of the pole piece, and affects the rapid charging ability of the battery. Therefore, it is ensured that the graphitization degree of the first negative electrode active material is greater than that of the second negative electrode active material, which can not only satisfy the energy density requirement of the battery cell but also ensure the rapid charging capability of the battery cell.
  • a second aspect of the present application provides a secondary battery including a positive pole piece, a negative pole piece, a separator and an electrolyte, wherein the negative pole piece is the negative pole piece provided in one aspect of the present application.
  • the positive electrode tab includes a positive electrode current collector and a positive electrode membrane provided on at least one surface of the positive electrode current collector and including a positive electrode active material.
  • the type of positive electrode active material is not specifically limited, and may be a conventionally known material that can be used as a positive electrode active material of a secondary battery in existing batteries, for example, it may be selected from lithium cobalt Oxides, lithium nickel oxides, lithium manganese oxides, lithium nickel manganese oxides, lithium nickel cobalt manganese oxides, lithium nickel cobalt aluminum oxides, lithium-containing phosphates of olivine structure, etc. Only one type of these positive electrode active materials may be used alone, or two or more types may be used in combination.
  • the positive electrode active material is selected from LiCoO 2 , LiNiO 2 , LiMnO 2 , LiMn 2 O 4 , LiNi 1/3 Co 1/3 Mn 1/3 O 2 (NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O 2 ( NCM 523 ), LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM 811 ), LiNi 0.85 Co 0.15 Al 0.05 O 2 , LiFePO4 (LFP), LiMnPO 4 Or several.
  • the type of the separator is not specifically limited, and may be any separator material used in existing batteries, such as polyethylene, polypropylene, polyvinylidene fluoride, and Their multilayer composite films, but not limited to these.
  • the electrolyte includes an electrolyte salt and an organic solvent, and the specific types and compositions of the electrolyte salt and the organic solvent are not subject to specific restrictions, and can be selected according to actual needs.
  • the electrolyte may also include additives, and the type of additives is not particularly limited. It may be a negative electrode film-forming additive, a positive electrode film-forming additive, or an additive that can improve certain performance of the battery, such as improving the battery's overcharge performance. Additives, additives to improve the high temperature performance of batteries, additives to improve the low temperature performance of batteries, etc.
  • a third aspect of the present application provides a battery module, which includes any one or more of the secondary batteries described in the second aspect of the present application.
  • the number of secondary batteries included in the battery module can be adjusted according to the application and capacity of the battery module.
  • a plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4.
  • the plurality of secondary batteries 5 can be fixed by fasteners.
  • the battery module 4 may further include a case having an accommodation space, and the plurality of secondary batteries 5 are accommodated in the accommodation space.
  • a fourth aspect of the present application provides a battery pack, which includes any one or more of the battery modules described in the third aspect of the present application. That is, the battery pack includes any one or more of the secondary batteries described in the first aspect of the present application.
  • the number of battery modules 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 disposed 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 an enclosed space for accommodating the battery module 4.
  • the plurality of battery modules 4 can be arranged in the battery box in any manner.
  • a fifth aspect of the present application provides an apparatus including any one or more of the secondary batteries described in the first aspect of the present application.
  • the secondary battery can be used as a power source for the device.
  • the device may be, but not limited to, a mobile device (such as a mobile phone, a laptop, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, Electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.
  • a mobile device such as a mobile phone, a laptop, etc.
  • an electric vehicle such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, Electric golf carts, electric trucks, etc.
  • electric trains ships and satellites, energy storage systems, etc.
  • FIG. 5 shows a device including the secondary battery of the present application, which is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc.
  • the secondary battery of the present application is the device powered by.
  • the above battery module, battery pack and device include the secondary battery provided by the present application, and therefore have at least the same advantages as the secondary battery, which will not be described in detail here.
  • Positive pole piece the active material LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NCM 811 ), the conductive agent acetylene black, the binder polyvinylidene fluoride (PVDF) in a weight ratio of 96.8: 2.2: 1 in N-methylpyrrolidone solvent After the system is fully stirred and mixed, it is coated on aluminum foil, dried, and cold pressed to obtain a positive pole piece.
  • NCM 811 the active material LiNi 0.8 Mn 0.1 Co 0.1 O 2
  • PVDF binder polyvinylidene fluoride
  • Negative pole piece the first negative active material (see Table 1 for details), Super P, sodium carboxymethyl cellulose, and styrene-butadiene rubber (SBR) emulsion are mixed according to the weight ratio of 96.2: 0.8: 1.2: 1.8 to prepare the first A negative electrode active material slurry, coated on both surfaces of the current collector (copper foil) to obtain the first active material layer; the second negative electrode active material (see Table 1 for details), Super P, sodium carboxymethyl cellulose 3.
  • SBR styrene-butadiene rubber
  • a styrene-butadiene rubber (SBR) emulsion is mixed in a weight ratio of 96.2: 0.8: 1.2: 1.8 to prepare a second negative electrode active material slurry, which is coated on the first active material layer to obtain a second active material layer. Then cold press and cut to make negative pole piece.
  • SBR styrene-butadiene rubber
  • Electrolyte Mix ethylene carbonate (EC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC) in a volume ratio of 3: 6: 1, and then fully dry the lithium salt LiPF 6 at 1 mol / L The ratio is dissolved in a mixed organic solvent and formulated into an electrolyte.
  • EC ethylene carbonate
  • EMC ethyl methyl carbonate
  • DEC diethyl carbonate
  • Full battery preparation stack the above positive pole piece, separator and negative pole piece in order, so that the separator is in the middle of the positive and negative poles to play the role of isolation, and wound to obtain a bare cell. Place the bare cell in the outer packaging case, inject the prepared electrolyte into the dried bare cell, and go through the steps of vacuum packaging, standing, forming, and shaping to obtain a lithium ion secondary battery.
  • Example 2 to 13 and Comparative Examples 1 to 6 were all prepared in a similar manner to Example 1, and the specific differences are shown in Table 1.
  • Table 1 shows the parameters of Examples 1 to 13 and Comparative Examples 1 to 6.
  • Cycle capacity retention rate (discharge capacity at the nth cycle / discharge capacity at the first cycle) ⁇ 100
  • 2C rate capacity retention rate (2C discharge capacity / 1C discharge capacity) x 100%.
  • the negative electrode sheet simultaneously satisfies the following relations 2.0 ⁇ B / A ⁇ 4.0 and 2.2 ⁇ D / C ⁇ 5.0 can make the battery have the characteristics of long cycle life, high energy density and large rate charging.
  • the particle size of the second negative electrode active material in Comparative Example 1 is not in the range of 4 m to 18 m. On the one hand, if the particle size is too small, the slurry dispersion is difficult. On the other hand, high surface activity causes side reactions to occur, thereby deteriorating the cycle performance of the battery.
  • the particle size of the second negative electrode active material in Comparative Example 2 is not in the range of 4 ⁇ m to 18 ⁇ m. If the particle size is too large, the solid phase diffusion resistance of the active ions increases and the polarization increases, which affects the battery rate and lithium deposition performance.
  • the thickness of the first negative electrode active material layer is not in the range of 35 ⁇ m to 105 ⁇ m.
  • the thickness of the first active material layer is too small, on the one hand, it is easy to cause processing abnormalities and affect battery performance, on the other hand, the number of active material accumulation layers is too Less, the contact area between the active material and the electrolyte is insufficient, which is not conducive to the liquid phase transmission of the active material, resulting in deterioration of the battery cycle and lithium deposition performance.

Abstract

一种负极极片、二次电池、电池模块、电池包及装置，该负极极片包括负极集流体和形成于负极集流体上的多层活性物质层；所述多层活性物质层至少包括第一活性物质层和第二活性物质层；第一活性物质层包含第一负极活性物质，第二活性物质层包含第二负极活性物质；第一活性物质层的厚度与第一负极活性物质的平均粒径的比值为2.0-4.0。第二活性物质层的厚度与第二负极活性物质的平均粒径的比值为2.2-5.0。使用该负极极片的电池可以同时具有良好的循环寿命和快速充电性能。

Description

一种负极极片、二次电池、电池模块、电池包及装置
本申请要求于2018年10月31日提交中国专利局、申请号为201811284002.2、发明名称为“一种负极极片以及二次电池”的中国专利申请的优先权，其全部内容通过引用结合在本申请中。
技术领域
本申请涉及二次电池技术领域，具体地涉及一种负极极片、使用该负极极片的二次电池、电池模块、电池包及装置。
背景技术
可充电电池由于具有能量密度高、工作电压高和使用寿命长以及低自放电的优点，近年来已经得到广泛的应用。但随着电动汽车的日益普及，对于可充电电池的能量密度及快速充电性能提出了更高要求。
如何让电池兼顾高能量密度及快速充电的能力，仍是行业内面临的重要问题之一。因此，需要不断付出努力来解决这一问题。
申请内容
鉴于背景技术中存在的问题，本申请提供了一种负极极片、二次电池、电池模块、电池包及装置。所述二次电池同时具有高能量密度、长循环寿命和快速充电性能。
为了实现本申请的目的，本申请的第一方面提供了一种负极极片，所述负极极片包括负极集流体、设置在负极集流体的至少一个表面上的第一活性物质层以及设置在第一活性物质层上的第二活性物质层；
其中第一活性物质层包含第一负极活性物质，第二活性物质层包含第二负极活性物质；
在所述负极极片中，满足以下关系：2.0≤B/A≤4.0，且2.2≤D/C≤5.0，其中，
A为第一负极活性物质的平均粒径，
B为第一活性物质层的厚度，
C为第二负极活性物质的平均粒径，
D为第二活性物质层的厚度。
本申请的第二方面提供了一种二次电池，包括本申请第一方面的负极极片。
本申请的第三方面提供了一种电池模块，其包括本申请的第二方面所述的二次电池。
本申请的第四方面提供了一种电池包，其包括本申请的第三方面所述的电池模块。
本申请的第五方面提供了一种装置，其包括本申请的第二方面所述的二次电池，所述二次电池用作所述装置的电源。
优选地，所述装置包括移动设备、电动车辆、电气列车、卫星、船舶及储能系统。
相对于现有技术，本申请至少包括如下所述的有益效果：
本申请的负极极片包括双活性物质层结构，且在设计时调节各活性物质层的厚度与活性物质层中活性物质的粒径，得到了兼顾高能量密度、长循环寿命和快速充电性能的二次电池。
本申请的电池模块、电池包和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
下面详细说明根据本申请的负极极片、二次电池、电池模块、电池包及装置。
首先说明本申请第一方面提供的负极极片，所述负极极片包括负极集流体、设置在负极集流体的至少一个表面上的第一活性物质层以及设置在第一活性物质层上的第二活性物质层；
其中第一活性物质层包含第一负极活性物质，第二活性物质层包含第二负极活性物质；
在所述负极极片中，满足以下关系：2.0≤B/A≤4.0，且2.2≤D/C≤5.0，其中，
A为第一负极活性物质的平均粒径，
B为第一活性物质层的厚度，
C为第二负极活性物质的平均粒径，
D为第二活性物质层的厚度。
优选地，在本申请的负极极片中，2.5≤B/A≤3.5。
优选地，在本申请的负极极片中，2.8≤D/C≤4.5。
本申请的发明人发现，在相同原料相同工艺下，负极活性物质的粒径越大，克容量越高，电池达到预期容量时所需要的负极活性物质越少，电池的能量密度越高。但是当负极活性物质的粒径过大时，活性离子的固相扩散路径越长，阻力越大，将影响电池快速充电性能。相反，当负极活性物质的粒径越小时，活性离子的固相扩散路径越短，阻力越小，有利于提升电池的快速充电性能。但过小的粒径不仅克容量偏低，电芯能量密度受到一定的影响。同时负极浆料难于分散、搅拌，制成的负极极片活性物质颗粒与集流体之间的粘接力、负极活性物质颗粒与颗粒之间的粘接力均较差，将影响电池的能 量密度和循环寿命。
本申请的发明人还发现，当负极活性物质层的厚度越小时，越有利于负电解液的浸润，活性离子在极片中的液相传导速度越快。电池在长期循环过程中，电池极化增加不明显，副反应少，从而避免锂枝晶在负极表面的形成引起安全问题。但是膜片厚度过小，对电池的能量密度影响较大。相反，当负极活性物质层的厚度越大时，使用相同负极活性物质，电池的能量密度越高。但是在电池循环过程中，过厚的膜片使得电解液浸润困难，导致活性离子传输阻力增加，电池极化增加，导致电池局部电流分布不均，引起析锂，导致电池容量衰减加快，影响电池循环寿命。
如果仅是从负极活性物质的粒径和极片活性物质层的厚度各自优化的角度出发，对实现兼顾高能量密度、长循环寿命和快速充电性能的二次电池存在很大的局限性。
本申请的发明人通过大量研究，将负极极片设计成双层结构，通过调整活性物质层的厚度与负极活性物质的粒径比值，使得负极极片同时满足以下关系：2.0≤B/A≤4.0，且2.2≤D/C≤5.0，可以使电池可兼具长循环寿命、高能量密度以及快速充电的特点。
在本申请设计的负极极片中，第一活性物质层中的第一负极活性物质具有较大的粒径，在相同厚度的情况下，一方面可以提供更高的容量，使得单位面积容量增加。另一方面，负极活性物质的粒径越大，在厚度相同的情况下，活性物质层中活性物质的堆积层数更少，活性物质的表面发生电荷交换时副反应较少，表面形成的SEI层更加稳定致密，有利于提升电池的循环性能。如果B/A小于2.0时，表明第一活性物质的平均粒径太大，活性物质层的厚度太小，即活性物质的堆积层数过少，活性离子在负极活性物质内部的固相扩散路径较长，内阻增加，影响电池的快速充电能力。此外活性物质层的厚度太小，极片容易出现颗粒划痕导致外观不良。如果B/A大于4.0时，表明第一活性物质的平均粒径太小，活性物质层的厚度太大，即活性物质的堆积层数过多，使得活性离子液相传输路径过长，影响电池快速充电能力。
在本申请设计的负极极片中，第二活性物质层中的第二负极活性物质具有较小的粒径，在相同厚度的情况下，小粒径活性物质更多，一方面可以在冷压后快速反弹，增加表层极片的孔隙率，有利于电解液的浸润和活性离子的液相传输。另一方面，活性离子在小粒径活性物质颗粒内部的扩散路径缩 短，从而减小活性离子的固相扩散阻力，有利于活性离子的快速嵌入和脱出，从而可以提升电池的快速充电性能。如果D/C小于2.2时，表明第二活性物质的平均粒径太大，活性物质层的厚度太小，材料颗粒可能大于活性物质层的厚度，容易出现大颗粒及拉丝等极片加工中存在的问题。当D/C大于5.0时，表明第二活性物质层的厚度大，第二活性物质的粒径过小。过小的粒径导致浆料搅拌存在一定的困难，影响极片外观和粘结力，从而影响电芯的循环性能。此外，第二活性物质层的厚度较大，将导致活性离子的传输路径过长，影响电池快速充电能力。
在本申请的一些实施方式中，B/A的下限值可以为2.0、2.1、2.2、2.3、2.4、2.5、2.6、2.7；B/A的上限值可以为2.8、2.9、3.0、3.1、3.2、3.3、3.4、3.5、3.6、3.7、3.8、3.9、4.0。
在本申请的一些实施方式中，D/C的下限值可以为2.2、2.3、2.4、2.5、2.6、2.7、2.8、2.9、3.0；D/C的上限值可以为3.2、3.4、3.6、3.8、4.0、4.2、4.4、4.6、4.8、5.0。
优选地，在本申请的负极极片中，第一负极活性物质的平均粒径A大于或等于第二负极活性物质的平均粒径C；更优选地，在所述负极极片中，0.4≤C/A≤1.0。当第二负极活性物质相对于第一负极活性物质具有更小的粒径时，有利于活性离子的快速嵌入和脱出，从而提升电池的快速充电性能；同时第一活性物质的粒径较大，可以使电池在达到相同能量密度的前提下，具有更薄的活性物质层的厚度，其更有利于活性离子的扩散，避免极化和析锂的产生，进而减少副反应的发生，从而进一步提升电池的循环寿命。
优选地，在本申请的负极极片中，第一活性物质层的厚度B大于或等于第二活性物质层的厚度D；更优选地，在所述负极极片中，0.2≤D/B≤1.0。在电池循环过程中，若第二活性物质层的厚度相对较薄，可以使活性离子能够在较短的时间内通过第二活性物质层嵌入到第一活性物质层，避免活性离子在极片表面堆积而发生析锂，从而可以进一步提升电池的快速充电性能。
优选地，在本申请的负极极片中，D/C≥B/A。第二活性物质层的活性离子的堆积层数大于第一活性物质层，活性离子的堆积层数较多，电化学反应活性增强，活性离子的液相和固相阻抗减小，使得活性离子从正极脱出后能够快速通过第二活性物质层到达第一活性物质层，从而避免活性离子在极片表面的堆积，形成枝晶，导致安全问题。
优选地，在本申请的负极极片中，所述第一负极活性物质的平均粒径A满足以下关系：12μm≤A≤25μm，更优选15μm≤A≤19μm。
优选地，在本申请的负极极片中，所述第一活性物质层的厚度B满足以下关系：35μm≤B≤105μm，更优选40μm≤B≤60μm。
优选地，在本申请的负极极片中，所述第二负极活性物质的平均粒径C满足以下关系：4μm≤C≤18μm，更优选7μm≤C≤15μm。
优选地，在本申请的负极极片中，所述第二活性物质层的厚度D满足以下关系：10μm≤D≤45μm，更优选20μm≤D≤40μm。
优选地，在本申请的负极极片中，所述第一负极活性物质和所述第二负极活性物质分别选自人造石墨、天然石墨、中间相碳微球、软碳、硬碳中的一种或几种。
优选地，在本申请的负极极片中，所述第一负极活性物质的石墨化度大于所述第二负极活性物质的石墨化度。第一活性物质的石墨化度越高，活性物质有序化程度越高，晶体中层错和位错等缺陷较少，表面活性低，在循环过程中容易形成稳定致密的SEI膜，有利于循环性能的提升。第二活性物质石墨化度越低，材料晶面间距越大，有利于活性离子在活性物质内的进出，减小阻力，避免活性离子在极片表面堆积，影响电池快速充电能力。因而保证第一负极活性物质的石墨化度大于第二负极活性物质的石墨化度，可以既满足电芯能量密度需求又能够保证电芯的快速充电能力。
本申请第二方面提供了一种二次电池，包括正极极片、负极极片、隔离膜和电解液，其中所述负极极片为本申请一方面所提供的负极极片。
在本申请第二方面的二次电池中，正极极片包括正极集流体以及设置在正极集流体至少一个表面上且包括正极活性物质的正极膜片。
在本申请第二方面的二次电池中，正极活性物质的种类不受到具体限制，可以是现有电池中可被用作二次电池正极活性物质的传统公知的材料，例如可选自锂钴氧化物、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、橄榄石结构的含锂磷酸盐等。这些正极活性物质可以仅单独使用一种，也可以将两种以上组合使用。优选地，正极活性物质选自LiCoO 2、LiNiO 2、LiMnO 2、LiMn 2O 4、LiNi 1/3Co 1/3Mn 1/3O 2(NCM 333)、LiNi 0.5Co 0.2Mn 0.3O 2(NCM 523)、LiNi 0.6Co 0.2Mn 0.2O 2(NCM 622)、LiNi 0.8Co 0.1Mn 0.1O 2(NCM 811)、LiNi 0.85Co 0.15Al 0.05O 2、LiFePO4(LFP)、LiMnPO 4中的一种或几种。
在本申请第二方面的二次电池中，所述隔离膜的种类并不受到具体的限制，可以是现有电池中使用的任何隔离膜材料，例如聚乙烯、聚丙烯、聚偏氟乙烯以及它们的多层复合膜，但不仅限于这些。
在本申请第二方面的二次电池中，所述电解液包括电解质盐以及有机溶剂，其中电解质盐和有机溶剂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。所述电解液还可包括添加剂，添加剂种类没有特别的限制，可以为负极成膜添加剂，也可为正极成膜添加剂，也可以为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。
本申请的第三方面提供了一种电池模块，其包括本申请的第二方面所述的任意一种或几种二次电池。
进一步，包括在所述电池模块中的二次电池的数量可以根据电池模块的应用和容量进行调节。
在一些实施例中，参照图1和图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。
本申请第四方面提供了一种电池包，其包括本申请第三方面所述的任意一种或几种电池模块。也就是，该电池包包括本申请第一方面所述的任意一种或几种二次电池。
所述电池包中电池模块的数量可以根据电池包的应用和容量进行调节。
在一些实施例中，请参照图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组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。
本申请第五方面提供一种装置，其包括本申请第一方面所述的任意一种 或几种二次电池。所述二次电池可以用作所述装置的电源。
优选地，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。
例如，图5示出了一种包含本申请的二次电池的装置，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，本申请的二次电池为该装置供电。
上述电池模块、电池包和装置包括本申请提供的二次电池，因而至少具有与所述二次电池相同的优势，在此不再详细描述。
下面以锂离子电池为例，通过具体的实施例和对比例进一步说明本申请，这些实施例只是用于说明本申请，本申请不限于以下实施例。凡是对本申请技术方案进行修改或者等同替换，而不脱离本申请技术方案的范围，均应涵盖在本申请的保护范围中。
实施例1
正极极片：将活性物质LiNi 0.8Mn 0.1Co 0.1O 2(NCM 811)、导电剂乙炔黑、粘结剂聚偏氟乙烯(PVDF)按重量比96.8∶2.2∶1在N-甲基吡咯烷酮溶剂体系中充分搅拌混合均匀后，涂覆于铝箔上烘干、冷压，得到正极极片。
负极极片：将第一负极活性物质(详见表1)、Super P、羧甲基纤维素钠、丁苯橡胶(SBR)乳液按照96.2∶0.8∶1.2∶1.8的重量比例混合，制得第一负极活性物质浆料，涂布于集流体(铜箔)的两个表面上得到第一活性物质层；将第二负极活性物质(详见表1)、Super P、羧甲基纤维素钠、丁苯橡胶(SBR)乳液按照96.2∶0.8∶1.2∶1.8的重量比例混合，制得第二负极活性物质浆料，涂布于第一活性物质层上得到第二活性物质层。然后冷压、裁切制成负极极片。
隔离膜：以PE多孔聚合薄膜作为隔离膜。
电解液：将碳酸乙烯酯(EC)、碳酸甲乙酯(EMC)、碳酸二乙酯(DEC)按照体积比3∶6∶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。
全电池制备：将上述正极极片、隔离膜、负极极片按顺序叠好，使隔离 膜处于正负极中间起到隔离的作用，并卷绕得到裸电池。将裸电池置于外包装壳中，将上述制备好的电解液注入到干燥后的裸电池中，经过真空封装、静置、化成、整形等工序，获得锂离子二次电池。
实施例2～13和对比例1～6的电池均按照与实施例1类似的方法进行制备，具体区别示于表1中。表1示出了实施例1～13以及对比例1～6的参数。
表1
Figure PCTCN2019111050-appb-000001
表中，A－第一负极活性物质的粒径(μm)；B－第一活性物质层的厚度(μm)；C－第二负极活性物质的粒径(μm)；D－第二活性物质层的厚度(μm)。
电池性能测试
(一)循环性能测试：
各实施例和对比例的全电池循环性能测试按照如下方法进行：
在25℃的环境中，进行第一次充电和放电，在1.0C(即1小时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，直到上限电压为4.2V，然后在1.0C的放电电流下进行恒流放电，直到最终电压为2.8V，记录首次循环的放电容量；而后进行持续充放电循环。
循环容量保持率＝(第n次循环的放电容量/首次循环的放电容量)×100
(二)倍率性能测试：
在25℃的环境中，进行充放电测试，在1.0C(即1小时内完全放掉理论容量的电流值)的放电电流下进行恒流放电，直到电压为2.8V。然后在1.0C的充电电流下恒流充电至电压为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，在1.0C的放电电流下恒流放电至2.8V，此时的放电容量为电池的1.0C下的实际容量，记为C0。然后再将电池在1C恒流充电至4.2V，再恒压充电至电流为0.05C，静置5min，2C恒流放电至2.8V，记录放电容量C1为2C放电容量。
2C倍率容量保持率＝(2C的放电容量/1C的放电容量)×100％。
(三)析锂倍率测试
在25℃的环境中，进行充放电测试，在1.0C(即1小时内完全放掉理论容量的电流值)的放电电流下进行恒流放电，直到电压为2.8V。然后在1.0C的充电电流下恒流充电至电压为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，在1.0C的放电电流下恒流放电至2.8V，此时的放电容量为电池的1.0C下的实际容量，记为C0。然后再将电池在xC0恒流充电至4.2V，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，调整充电倍率，直至出现析锂，确定析锂倍率。
按照上述方法，测量各实施例和对比例电池的循环、倍率及析锂性能。各实施例和对比例的测试结果详见表2。表2示出了实施例1～13以及对比例1～6的性能测试结果。
表2
Figure PCTCN2019111050-appb-000002
Figure PCTCN2019111050-appb-000003
表中，A－第一负极活性物质的粒径(μm)；B－第一活性物质层的厚度(μm)；C－第二负极活性物质的粒径(μm)；D－第二活性物质层的厚度(μm)。
在实施例1～13中，通过合理调节各活性物质层的厚度和各层活性物质的粒径之间比值，使得负极极片同时满足以下关系2.0≤B/A≤4.0，且2.2≤D/C≤5.0，可以使电池可兼具长循环寿命、高能量密度以及大倍率充电的特点。
与实施例1～13相比，在对比例1～6中，电池均未同时处在B/A和D/C所给的范围内，电池无法同时兼具长循环寿命、高能量密度以及大倍率充电的特点。
在对比例1～2中，B/A在所给范围内，D/C不在所给范围内，电池的循环、倍率和析锂性能明显降低。对比例1中第二负极活性物质的粒径不在4μm～18μm的范围内，粒径过小一方面导致浆料分散困难，一方面表面活性高引起副 反应发生，从而恶化电池的循环性能。对比例2中第二负极活性物质的粒径不在4μm～18μm的范围内，粒径过大导致活性离子的固相扩散阻力增加，极化增加，影响电池倍率和析锂性能。
在对比例3～4中，B/A不在所给范围内，D/C在所给范围内，电池的循环、倍率和析锂性能明显降低。对比例3中第一负极活性物质层的厚度不在35μm～105μm的范围内，第一活性物质层的厚度过小，一方面容易导致加工异常从而影响电池性能，另一方面活性物质堆积层数过少，活性物质与电解液接触面积不足，不利于活性物质的液相传输，导致电池循环及析锂性能恶化。
在对比例5～6中，虽然活性物质的粒径及活性物质层的厚度均在所给定的范围内，但B/A和D/C均不在所给范围内，导致电池的循环、倍率和析锂性能恶化明显。
本申请虽然以较佳实施例公开如上，但并不是用来限定权利要求，任何本领域技术人员在不脱离本申请构思的前提下，都可以做出若干可能的变动和修改，因此本申请的保护范围应当以本申请权利要求所界定的范围为准。

Claims (15)

  1. 一种负极极片，其特征在于，所述负极极片包括：
    负极集流体、设置在所述负极集流体的至少一个表面上的第一活性物质层以及设置在第一活性物质层上的第二活性物质层；
    其中所述第一活性物质层包含第一负极活性物质，所述第二活性物质层包含第二负极活性物质；
    在所述负极极片中，满足以下关系：2.0≤B/A≤4.0，且2.2≤D/C≤5.0，其中，
    A为第一负极活性物质的平均粒径，
    B为第一活性物质层的厚度，
    C为第二负极活性物质的平均粒径，
    D为第二活性物质层的厚度。
  2. 根据权利要求1所述的负极极片，其特征在于，在所述负极极片中，2.5≤B/A≤3.5。
  3. 根据权利要求1所述的负极极片，其特征在于，在所述负极极片中，2.8≤D/C≤4.5。
  4. 根据权利要求1所述的负极极片，其特征在于，在所述负极极片中，A≥C。
  5. 根据权利要求4所述的负极极片，其特征在于，在所述负极极片中，0.4≤C/A≤1.0。
  6. 根据权利要求1所述的负极极片，其特征在于，在所述负极极片中，B≥D。
  7. 根据权利要求6所述的负极极片，其特征在于，在所述负极极片中， 0.2≤D/B≤1.0。
  8. 根据权利要求1至7任一项所述的负极极片，其特征在于，在所述负极极片中，D/C≥B/A。
  9. 根据权利要求1所述的负极极片，其特征在于，在所述负极极片中，12μm≤A≤25μm，优选15μm≤A≤19μm；
    和/或，35μm≤B≤105μm，优选40μm≤B≤60μm；
    和/或，4μm≤C≤18μm，优选7μm≤C≤15μm；
    和/或，10μm≤D≤45μm，优选20μm≤D≤40μm。
  10. 根据权利要求1所述的负极极片，其特征在于，所述第一负极活性物质和所述第二负极活性物质分别选自人造石墨、天然石墨、中间相碳微球、软碳、硬碳中的一种或几种。
  11. 根据权利要求10所述的负极极片，其特征在于，所述第一负极活性物质的石墨化度大于第二负极活性物质的石墨化度。
  12. 一种二次电池，包括正极极片、负极极片、隔离膜和电解液，其特征在于，所述负极极片为权利要求1至11任一项所述的负极极片。
  13. 一种电池模块，其特征在于，包括权利要求12所述的二次电池。
  14. 一种电池包，其特征在于，包括权利要求13所述的电池模块。
  15. 一种装置，其特征在于，包括权利要求12所述的二次电池，所述二次电池用作所述装置的电源；
    优选的，所述装置包括移动设备、电动车辆、电气列车、卫星、船舶及储能系统。
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