WO2023050836A1 - 正极极片、二次电池、电池模组、电池包及用电装置 - Google Patents

正极极片、二次电池、电池模组、电池包及用电装置 Download PDF

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WO2023050836A1
WO2023050836A1 PCT/CN2022/094695 CN2022094695W WO2023050836A1 WO 2023050836 A1 WO2023050836 A1 WO 2023050836A1 CN 2022094695 W CN2022094695 W CN 2022094695W WO 2023050836 A1 WO2023050836 A1 WO 2023050836A1
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active material
layer
size distribution
positive electrode
optionally
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PCT/CN2022/094695
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English (en)
French (fr)
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许宝云
欧阳少聪
付成华
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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 EP22874234.2A priority Critical patent/EP4235864A1/en
Priority to KR1020237017282A priority patent/KR102633456B1/ko
Priority to JP2023531055A priority patent/JP7519543B2/ja
Publication of WO2023050836A1 publication Critical patent/WO2023050836A1/zh
Priority to US18/331,696 priority patent/US11811057B2/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • 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
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/134—Electrodes based on metals, Si or alloys
    • 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
    • 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
    • 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
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H01M4/386—Silicon or alloys based on silicon
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/10—Primary casings; Jackets or wrappings
    • H01M50/102—Primary casings; Jackets or wrappings characterised by their shape or physical structure
    • H01M50/103—Primary casings; Jackets or wrappings characterised by their shape or physical structure prismatic or rectangular
    • 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
    • H01M2004/028—Positive electrodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2220/00—Batteries for particular applications
    • H01M2220/20—Batteries in motive systems, e.g. vehicle, ship, plane
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present application relates to the field of batteries, in particular, to a positive pole piece, a secondary battery, a battery module, a battery pack and an electrical device.
  • the secondary battery is mainly composed of a positive pole piece, a negative pole piece, a separator, and an electrolyte.
  • Secondary batteries in a low-temperature environment have the characteristics of a drop in discharge voltage plateau, low discharge capacity, large capacity fading, and poor rate performance. Low temperature performance limits the application of secondary batteries in the fields of electric vehicles, military industry and extreme environments. Therefore, the development of secondary batteries with excellent low-temperature performance is an urgent demand in the market.
  • the present application provides a positive pole piece, a secondary battery, a battery module, a battery pack, and an electrical device.
  • the present application provides a positive electrode sheet, including a positive electrode current collector and a positive electrode active material layer coated on at least one surface of the positive electrode current collector.
  • the positive electrode active material layer sequentially includes an inner active material layer stacked on the surface of the positive electrode current collector and an outer active material layer stacked on the surface of the inner active material layer.
  • the active material layer in the inner layer has a three-level pore size distribution: the first level pore size distribution of the inner layer is 3nm to 10nm, optionally 6nm to 10nm; the second level pore size distribution of the inner layer is 10nm to 100nm, optionally 10nm to 84nm ; The tertiary pore size distribution of the inner layer is 0.1 ⁇ m to 2 ⁇ m, optionally 0.1 ⁇ m to 1.26 ⁇ m.
  • the outer active material layer has a three-level pore size distribution: the first level pore size distribution of the outer layer is 0.5 nm to 3 nm, optionally 1 nm to 3 nm; the second level pore size distribution of the outer layer is 10 nm to 100 nm, optionally 60 nm to 100nm; the tertiary pore size distribution of the outer layer is 0.1 ⁇ m to 2 ⁇ m, optionally 0.45 ⁇ m to 2 ⁇ m.
  • the active material layer of the positive electrode sheet has the characteristics of double-layer and three-level pore size distribution.
  • such a double-layer tertiary pore size distribution not only ensures the ability of the micropores in the active material layer to transport lithium ions, but also makes the inner active material layer and the outer layer active.
  • the lithium ion transport capacity of the material layer is consistent; at the same time, the pore size distribution of the inner active material layer and the outer active material layer is reasonable, which avoids the occupying effect and filling effect, thereby further avoiding or reducing the secondary battery in a low temperature environment.
  • the low-temperature charge-discharge performance of the secondary battery is significantly improved due to the sharp decline in the internal lithium ion transport capacity.
  • the inner active material layer includes an inner conductive agent and an inner active material
  • the outer active material layer includes an outer conductive agent and an outer active material
  • the formation of the first-order pore size distribution in the inner active material layer and the outer active material layer can be realized by selecting conductive agent particles with an appropriate specific surface area.
  • the specific surface area of the inner conductive agent is 300m 2 /g ⁇ 1000m 2 /g, optionally, the specific surface area of the inner conductive agent is 800m 2 /g ⁇ 1000m 2 /g.
  • the specific surface area of the outer conductive agent is 1000m 2 /g-2500m 2 /g, optionally, the specific surface area of the outer conductive agent is 2000m 2 /g-2500m 2 /g.
  • the formation of the second and third pore size distributions in the inner active material layer and the outer active material layer can be achieved by selecting a mixture of active material particles with bimodal particle sizes.
  • the particle size distribution of the first active material in the inner layer is 24 nm to 600 nm.
  • the particle size distribution of the first active material in the inner layer is 24 nm to 200 nm; the inner layer
  • the particle size distribution of the second active material is 0.25 ⁇ m ⁇ 13 ⁇ m.
  • the particle size distribution of the second active material in the inner layer is 0.5 ⁇ m ⁇ 3 ⁇ m.
  • the particle size distribution of the first active material in the outer layer is 24 nm to 600 nm.
  • the particle size distribution of the first active material in the outer layer is 200 nm to 400 nm;
  • the particle size distribution of the second active material in the outer layer is is 0.25 ⁇ m to 13 ⁇ m, and optionally, the particle size distribution of the second active material in the outer layer is 3 ⁇ m to 8 ⁇ m.
  • the particle size of the first active material in the inner layer does not coincide with the tertiary pore size of the inner layer; and/or the particle size of the first active material in the outer layer does not overlap with the pore size of the outer layer Layer tertiary aperture coincides. That is, the particle size of the active material forming the second-level pore size in the inner and outer layers is not equal to the third-level pore size, thereby avoiding the occupying effect of the first active material particle.
  • the mass ratio of the first active material in the inner layer to the second active material in the inner layer is (0.3-3):1.
  • the mass ratio of the first active material in the inner layer to the second active material in the inner layer is (1-3):1.
  • the mass ratio of the first active material in the outer layer to the second active material in the outer layer is (0.3-3):1.
  • the mass ratio of the first active material in the outer layer to the second active material in the outer layer is (0.3 ⁇ 1):1.
  • the lamination density of the active material layer and the internal transmission path of lithium ions in the active material are all at a relatively high level. Excellent level, to ensure the energy density and dynamic performance of the secondary battery in the low temperature environment.
  • the mass ratio of the conductive agent in the inner layer to the active material in the inner layer is (0.3 ⁇ 2):100.
  • the mass ratio of the conductive agent in the inner layer to the active material in the inner layer is (1.5-2):100.
  • the mass ratio of the outer conductive agent to the outer active material is (0.3-3):100.
  • the mass ratio of the outer conductive agent to the outer active material is (2.5-3):100.
  • the electrical conductivity and kinetic performance of the pole piece and the energy density of the secondary battery can be optimized. within range.
  • the conductive agent in the inner layer and the conductive agent in the outer layer are each independently selected from activated carbon or carbon nanotubes.
  • Activated carbon or carbon nanotubes have both good electrical conductivity and large specific surface area, and can better form the first-order pore size distribution in the inner active material layer and the outer active material layer.
  • the present application provides a secondary battery, which includes a positive pole piece, a negative pole piece, a separator spaced between the positive pole piece and the negative pole piece, and an electrolyte, wherein the positive pole piece is based on The positive electrode sheet of the first aspect of the present application.
  • the present application provides a battery module, which includes the secondary battery in the second aspect of the present application.
  • the present application provides a battery pack, which includes the secondary battery of the second aspect of the present application or the battery module of the third aspect of the present application.
  • the present application provides an electrical device, which includes the secondary battery of the second aspect of the present application or the battery module of the third aspect of the present application or the battery pack of the fourth aspect of the present application; wherein, the secondary battery or A battery module or battery pack is used as a power source or an energy storage unit for an electrical device.
  • the secondary battery, battery module, battery pack, and electrical device provided by the present application include the positive electrode sheet described in the first aspect of the application, and thus have at least the same or similar technical effects as the above-mentioned positive electrode sheet.
  • FIG. 1 is a perspective view of a secondary battery according to a specific embodiment of the present application.
  • Fig. 2 is an exploded view of the secondary battery shown in Fig. 1;
  • FIG. 3 is a perspective view of a battery module according to a specific embodiment of the present application.
  • Fig. 4 is a perspective view of a battery pack according to a specific embodiment of the present application.
  • Fig. 5 is an exploded view of the battery pack shown in Fig. 4;
  • Fig. 6 is a schematic diagram of an electrical device according to a specific embodiment of the present application.
  • an embodiment means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the present application.
  • the occurrences of this phrase in various places in the specification are not necessarily all referring to the same embodiment, nor are independent or alternative embodiments mutually exclusive of other embodiments. It is understood explicitly and implicitly by those skilled in the art that the embodiments described herein can be combined with other embodiments.
  • the first aspect of the present application provides a positive electrode sheet, including a positive electrode current collector and a positive electrode active material layer coated on at least one surface of the positive electrode current collector.
  • the positive electrode active material layer sequentially includes an inner active material layer stacked on the surface of the positive electrode current collector and an outer active material layer stacked on the surface of the inner active material layer.
  • the active material layer in the inner layer has a three-level pore size distribution: the first level pore size distribution of the inner layer is 3nm to 10nm, optionally 6nm to 10nm; the second level pore size distribution of the inner layer is 10nm to 100nm, optionally 10nm to 84nm ; The tertiary pore size distribution of the inner layer is 0.1 ⁇ m to 2 ⁇ m, optionally 0.1 ⁇ m to 1.26 ⁇ m.
  • the outer active material layer has a three-level pore size distribution: the first level pore size distribution of the outer layer is 0.5 nm to 3 nm, optionally 1 nm to 3 nm; the second level pore size distribution of the outer layer is 10 nm to 100 nm, optionally 60 nm to 100nm; the tertiary pore size distribution of the outer layer is 0.1 ⁇ m to 2 ⁇ m, optionally 0.45 ⁇ m to 2 ⁇ m.
  • the pore size distribution described in this application refers to the equivalent diameter distribution of pores in porous solids, which can be determined by gas adsorption and/or mercury porosimetry, for example, referring to GB T 21650.1-2008 "Measurement of solids by mercury porosimetry and gas adsorption" Material pore size distribution and porosity" were tested.
  • the inventor believes that the rapid increase in viscosity of the secondary battery at low temperature and the sharp decline in the ability to transport lithium ions inside the secondary battery are an important reason for its poor charge and discharge performance in a low temperature environment.
  • the inventors further propose that: on the one hand, when there are micropores with smaller pore diameters in the positive electrode active material layer, the micropores become the main factor affecting the transport capacity of lithium ions.
  • the micropore diameter is less than the size of a solvated lithium ion (the diameter of the solvated lithium ion is about 1nm), the solvated lithium ion cannot pass through the micropore, and the lithium ion transport capacity is extremely low; when the micropore diameter is 1 to 3 When the size of the solvated lithium ions is 1, the lithium ion transport capacity is medium; when the micropore diameter is 4 to 10 solvated lithium ions, the lithium ion transport capacity reaches the best.
  • the particle size distribution of the active material on the surface of the positive electrode sheet is wide, which means that the particle size of the active material is different and the degree of irregularity is high.
  • the large particles occupy a larger position, thereby reducing the pores formed by particle accumulation and forming Occupancy effect; while small particles will fill in the pores where other particles accumulate to form a filling effect. Both the occupation effect and the filling effect are not conducive to the transportation of lithium ions.
  • the technical solution provided by this application is: form a double-coated active material layer on the surface of the positive electrode collector, and form an inner layer of 3nm to 10nm (optionally 6nm to 10nm), 10nm to 100nm (optional) 10nm ⁇ 84nm), 0.1 ⁇ m-2 ⁇ m (optionally 0.1 ⁇ m ⁇ 1.26 ⁇ m) tertiary pore size distribution; the outer layer forms 0.5nm ⁇ 3nm (optionally 1nm ⁇ 3nm), 10nm-100nm (optionally 60nm ⁇ 100nm), 0.1 ⁇ m ⁇ 2 ⁇ m (optionally 0.45 ⁇ m ⁇ 2 ⁇ m) tertiary pore size distribution.
  • such a double-layer tertiary pore size distribution not only ensures the ability of the micropores in the active material layer to transport lithium ions, but also makes the inner active material layer and the outer layer active.
  • the lithium ion transport capacity of the material layer is consistent; at the same time, the pore size distribution of the inner active material layer and the outer active material layer is reasonable, which avoids the occupying effect and filling effect.
  • the conductivity of the pole piece is improved, which can avoid Or reduce the sharp decline in the ability of the secondary battery to transport lithium ions inside at low temperatures, so that the low-temperature charge and discharge performance of the secondary battery is significantly improved.
  • the inner active material layer may include an inner conductive agent and an inner active material
  • the outer active material layer may include an outer conductive agent and an outer active material
  • the formation of the first-order pore size distribution in the inner and outer layers can be achieved by selecting conductive agent particles within a specific specific surface area range.
  • the specific surface area of the inner conductive agent may be 300m 2 /g-1000m 2 /g (optionally 800m 2 /g-1000m 2 /g).
  • the specific surface area of the outer conductive agent may be 1000m 2 /g-2500m 2 /g (optionally 2000m 2 /g-2500m 2 /g).
  • the specific surface area of the active material particles described in the present application can be measured by using a gas adsorption method (BET) or a mercury intrusion method.
  • BET gas adsorption method
  • the specific surface area is a meaning known in the art, and can be measured with instruments and methods known in the art.
  • it can refer to GB/T 19587-2017, use the nitrogen adsorption specific surface area analysis test method, and use the BET (Brunauer Emmett Teller) method to calculate.
  • the nitrogen adsorption specific surface area analysis test can be obtained through the Tri-Star 3020 type of Micromeritics in the United States Specific surface area pore size analysis tester.
  • the formation of the second and third pore diameters in the inner and outer layers can be achieved by selecting active material particles with bimodal particle diameters.
  • the particle size distribution of the first active material in the inner layer may be 24 nm to 600 nm.
  • the particle size distribution of the first active material in the inner layer may be 24 nm to 200 nm.
  • the particle size distribution of the second active material in the inner layer may be 0.25 ⁇ m to 13 ⁇ m.
  • the particle size distribution of the second active material in the inner layer may be 0.5 ⁇ m to 3 ⁇ m.
  • the particle size distribution of the first active material in the outer layer may be 24 nm to 600 nm.
  • the particle size distribution of the first active material in the outer layer may be 200 nm to 400 nm.
  • the particle size distribution of the second active material in the outer layer may be 0.25 ⁇ m to 13 ⁇ m.
  • the particle size distribution of the second active material in the outer layer may be 3 ⁇ m to 8 ⁇ m.
  • the particle size of the first active material in the inner layer may not coincide with the third-level pore size of the inner layer; the particle size of the first active material in the outer layer may not coincide with the third-level pore size of the outer layer. coincide. That is, the particle size of the active material forming the second-level pore size in the inner and outer layers is not equal to the third-level pore size, thereby avoiding the occupying effect of the first active material particle.
  • the particle size described in this application refers to the equivalent diameter of the active substance particles, and when the measured active substance particles are closest to a homogeneous sphere (or combination of spheres) of a certain diameter, the diameter of the sphere ( Or sphere combination) as the particle size distribution (or particle size distribution) of the measured particles.
  • a laser particle size analyzer can be used to detect the particle size distribution of the active material particles.
  • the mass ratio of the first active material in the inner layer to the second active material in the inner layer may be (0.3-3):1.
  • the mass ratio of the first active material in the inner layer to the second active material in the inner layer may be (1-3):1.
  • the mass ratio of the first active material in the outer layer to the second active material in the outer layer may be (0.3-3):1.
  • the mass ratio of the first active material in the outer layer to the second active material in the outer layer may be (0.3 ⁇ 1):1.
  • the mass ratio of the active material forming the second pore diameter (i.e. the first active material) to the active material forming the third pore diameter (i.e. the second active material) is too large , leading to a smaller compaction of the active material layer, resulting in a reduction in the energy density of the secondary battery.
  • the mass ratio of the active material forming the second-level pore size (i.e. the first active material) to the active material forming the third-level pore size (i.e. the second active material) is too small, due to the lithium ions in the large particle size active material The internal transport path is too long, which has an adverse effect on the kinetic performance of the secondary battery.
  • the mass ratio of the conductive agent in the inner layer to the active material in the inner layer may be (0.3 ⁇ 2):100.
  • the mass ratio of the conductive agent in the inner layer to the active material in the inner layer may be (1.5 ⁇ 2):100.
  • the mass ratio of the outer conductive agent to the outer active material may be (0.3-3):100; optionally, the mass ratio of the outer conductive agent to the outer active material may be (2.5 ⁇ 3): 100.
  • the mass ratio of the conductive agent to the active material is too small, the electrical conductivity will deteriorate, which is not conducive to the performance of the dynamic performance. Conversely, if the mass ratio of the conductive agent to the active material is too large, although the increase of the conductive agent can increase the conductivity between the active materials, thereby improving the energy retention rate of the secondary battery to a certain extent, it is not conducive to the energy retention of the secondary battery. increase in density.
  • the amount of conductive agent used in each layer is also related to the specific surface area of the active material in the layer and the particle size of the conductive agent.
  • the particle size of the active material in the inner layer may be larger than that in the outer layer. Therefore, the amount of the conductive agent in the inner layer may also be slightly smaller than that in the outer layer.
  • the inner conductive agent and the outer conductive agent can be independently selected from activated carbon or carbon nanotubes.
  • Activated carbon or carbon nanotubes have both good electrical conductivity and large specific surface area, and can better form the first-order pore size distribution in the inner active material layer and the outer active material layer.
  • the specific type of positive electrode active material is not particularly limited, as long as it can meet the requirements of inserting and extracting lithium ions.
  • the positive electrode active material can be either a layered structure material, allowing lithium ions to diffuse in a two-dimensional space, or a spinel structure, allowing lithium ions to diffuse in a three-dimensional space.
  • the positive electrode active material may be selected from one or more of lithium transition metal oxides, compounds obtained by adding other transition metals or non-transition metals or non-metals to lithium transition metal oxides.
  • the positive electrode active material can be selected from lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, olivine structure lithium-containing One or more of the phosphates.
  • the general formula of lithium-containing phosphate with olivine structure can be LiFe 1-xy Mn x M' y PO 4 , 0 ⁇ x ⁇ 1, 0 ⁇ y ⁇ 1, 0 ⁇ x+y ⁇ 1, M' can be One or more selected from other transition metal elements or non-transition metal elements except Fe and Mn, M' can be selected from one or more of Cr, Mg, Ti, Al, Zn, W, Nb, Zr kind. More optionally, the lithium-containing phosphate of olivine structure can be selected from one or more of lithium iron phosphate, lithium manganese phosphate, and lithium manganese iron phosphate.
  • the lithium transition metal oxide may be selected from LiCoO 2 , LiMnO 2 , LiNiO 2 , LiMn 2 O 4 , LiNi x Co y Mn 1-xy O 2 , LiNi x Co y Al 1-xy O 2 , LiNi x Mn 2-x One or more of O 4 , where 0 ⁇ x ⁇ 1, 0 ⁇ y ⁇ 1, 0 ⁇ x+y ⁇ 1.
  • the lithium transition metal oxide may be selected from LiCoO 2 , LiNi 1/3 Co 1/3 Mn 1/3 O 2 , LiNi 0.5 Co 0.2 Mn 0.3 O 2 , LiNi 0.6 Co 0.2 Mn 0.2 O 2 , LiNi 0.8 One or more of Co 0.1 Mn 0.1 O 2 , LiNi 0.8 Co 0.15 Mn 0.05 O 2 , LiNi 0.8 Co 0.15 Al 0.05 O 2 , LiNi 0.5 Mn 1.5 O 4 , LiMn 2 O 4 .
  • the positive electrode active material layer may further include a binder, wherein the type and content of the binder are not specifically limited, and may be selected according to actual needs.
  • the binder may generally include a fluorine-containing polyolefin binder, and water is generally a good solvent relative to the fluorine-containing polyolefin binder, that is, the fluorine-containing polyolefin binder generally It has good solubility in water.
  • the fluorine-containing polyolefin binder may include but not limited to polyvinylidene fluoride (PVDF), vinylidene fluoride copolymer or their modification (for example, carboxylic acid, Acrylic acid, acrylonitrile and other modified) derivatives, etc.
  • PVDF polyvinylidene fluoride
  • the mass percentage of the binder may be due to the poor conductivity of the binder itself, so the amount of the binder cannot be too high.
  • the type of the positive electrode collector is not specifically limited, and can be selected according to actual needs.
  • the positive current collector can usually be a layered body, and the positive current collector is usually a structure or part that can collect current.
  • the positive current collector can be various materials suitable for use as the positive current collector of the electrochemical energy storage device in the art.
  • the positive current collector may include but not limited to metal foil, more specifically may include but not limited to nickel foil and aluminum foil.
  • the present application provides a secondary battery, including a positive pole piece, a negative pole piece, a separator spaced between the positive pole piece and the negative pole piece, and an electrolyte, wherein the positive pole piece is according to the present invention Apply the positive pole piece of the first aspect.
  • the negative electrode sheet of the secondary battery generally includes a negative electrode current collector and a negative electrode active material layer located on the surface of the negative electrode current collector, and the negative electrode active material layer generally includes a negative electrode active material.
  • the negative electrode active material can be various materials suitable for the negative electrode active material of lithium secondary batteries in the art, for example, can include but not limited to graphite, soft carbon, hard carbon, carbon fiber, mesocarbon microspheres, silicon-based One or more combinations of materials, tin-based materials, lithium titanate or other metals that can form alloys with lithium.
  • the graphite can be selected from one or more combinations of artificial graphite, natural graphite and modified graphite;
  • the silicon-based material can be selected from elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon alloys A combination of one or more;
  • the tin-based material can be selected from one or more of simple tin, tin oxide, and tin alloys.
  • the negative electrode current collector is usually a structure or part that collects current.
  • the negative electrode current collector can be a variety of materials suitable for use as a lithium secondary battery negative electrode current collector in the art.
  • the negative electrode current collector can include but not It is limited to metal foil, and more specifically may include but not limited to copper foil.
  • the negative electrode sheet can also be a lithium sheet.
  • the electrolyte of the secondary battery can be various electrolytes suitable for secondary batteries in the art, for example, the electrolyte usually includes an electrolyte and a solvent, and the electrolyte usually includes a lithium salt, more specifically Yes, the lithium salt can be an inorganic lithium salt and/or an organic lithium salt, specifically including but not limited to LiPF 6 , LiBF 4 , LiN(SO 2 F) 2 (abbreviated as LiFSI), LiN(CF 3 SO 2 ) 2 (abbreviated as LiTFSI), LiClO 4 , LiAsF 6 , LiB(C 2 O 4 ) 2 (abbreviated as LiBOB), and LiBF 2 C 2 O 4 (abbreviated as LiDFOB).
  • LiPF 6 LiBF 4
  • LiN(SO 2 F) 2 abbreviated as LiFSI
  • LiTFSI LiN(CF 3 SO 2 ) 2
  • LiClO 4 LiAsF 6
  • LiB(C 2 O 4 ) 2 abbre
  • the concentration of the electrolyte may be 0.8 mol/L ⁇ 1.5 mol/L.
  • the solvent can be various solvents suitable for electrolytes of secondary batteries in the art, and the solvent of the electrolyte is usually a non-aqueous solvent, which can be an organic solvent, specifically including but not limited to ethylene carbonate, propylene carbonate One or more combinations of esters, butene carbonate, pentenyl carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate or their halogenated derivatives.
  • the separator of the secondary battery can be a variety of materials suitable for secondary battery separators in the art, for example, it can be made of, but not limited to, polyethylene, polypropylene, polyvinylidene fluoride, aramid, One or more combinations of polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester and natural fibers.
  • each of the positive electrode sheet, separator and negative electrode sheet can be a layered body, so that After being cut to the target size and stacked one by one, it can also be wound to the target size to form a battery cell, and can be further combined with an electrolyte to form a secondary battery.
  • FIG. 1 shows a perspective view of a secondary battery according to a specific embodiment of the present application
  • FIG. 2 is an exploded view of the secondary battery shown in FIG. 1
  • a secondary battery 5 according to the present application (hereinafter referred to as a battery cell 5 ) includes an outer package 51 , an electrode assembly 52 , a top cover assembly 53 and an electrolyte (not shown).
  • the electrode assembly 52 is accommodated in the casing 51, and the number of the electrode assembly 52 is not limited, and may be one or more.
  • the battery cell 5 shown in FIG. 1 is a can-type battery, but the present application is not limited thereto.
  • the battery cell 5 may be a pouch-type battery, that is, the casing 51 is replaced by a metal plastic film and the top cover is omitted. Component 53.
  • a third aspect of the present application provides a battery module, which includes the secondary battery described in the second aspect of the present application.
  • the secondary battery can be assembled into a battery module, and the battery module can contain multiple secondary batteries, and the specific number can be adjusted according to the application and capacity of the battery module.
  • FIG. 3 is a perspective view of a battery module 4 as an example. Referring to FIG. 3 , in the battery module 4 , 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 may be fixed by fasteners.
  • the battery module 4 may also include a casing having a containing space, and a plurality of secondary batteries 5 are contained in the containing space.
  • a fourth aspect of the present application provides a battery pack, which includes the battery module described in the third aspect of the present application.
  • the above-mentioned battery modules can 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.
  • FIG. 4 is a perspective view of the battery pack 1 as an example
  • FIG. 5 is an exploded view of the battery pack shown in FIG. 4 .
  • 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 cover the lower box body 3 and form a closed space for accommodating the battery module 4 .
  • Multiple battery modules 4 can be arranged in the battery box in any manner.
  • a fifth aspect of the present application provides an electric device, which includes the secondary battery described in the second aspect of the present application, or the battery module described in the third aspect of the present application, or the battery pack described in the fourth aspect of the present application.
  • the secondary battery, or the battery module, or the battery pack can be used as a power source of the electric device or an energy storage unit of the electric device.
  • the electric device can be, but not limited to, mobile devices (such as mobile phones, notebook computers, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.
  • the electric device can select a secondary battery, a battery module or a battery pack according to its usage requirements.
  • Fig. 6 shows a schematic diagram of an electrical device according to a specific embodiment of the present application.
  • the electric device may be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle.
  • a battery pack or battery module can be used.
  • the electric device may be a mobile phone, a tablet computer, a notebook computer, and the like.
  • the electrical device usually requires thinner and thinner, and the secondary battery of the present application can be used as a power source.
  • Inner layer coating mix the first active material of the inner layer and the second active material of the inner layer in proportion, fully stir and mix with binder (1.8%), dispersant (0.2%) and an appropriate amount of NMP, so that It forms a uniform inner layer slurry; the inner layer slurry is coated on the positive electrode current collector Al foil, and dried;
  • Outer layer coating mix the first active material of the outer layer and the second active material of the outer layer in proportion, fully stir and mix with binder (1.6%), dispersant (0.2%) and an appropriate amount of NMP, so that It forms a uniform outer layer slurry; this slurry is coated on the pole piece that has been coated with the inner layer slurry, and after drying, the positive electrode piece is cold-pressed to the designed compaction density, and the strips are used for later use.
  • Negative electrode sheet fully stir and mix the negative electrode active material graphite, conductive carbon, and binder polyvinylidene fluoride (PVDF) in an appropriate amount of water solvent at a weight ratio of 95:3:2 to form a uniform negative electrode slurry ; Coat the slurry on the Cu foil of the negative electrode current collector, and after drying, cold press the pole piece to the designed compaction density, and divide it into strips for later use.
  • PVDF polyvinylidene fluoride
  • Isolation film 12 ⁇ m PP isolation film is used.
  • Electrolyte Use lithium iron phosphate common electrolyte.
  • Shell Aluminum-plastic film is used as the shell material.
  • the positive pole piece, the separator, and the negative pole piece are wound to form a bare cell, which is packaged with an aluminum-plastic film, injected with an electrolyte, and a lithium secondary battery is obtained after formation, degassing, and high-temperature aging.
  • the test process is shown in Table 2 (where C is the rated capacity of the battery), and the test is performed with a battery with a rated capacity of 20Ah.
  • Table 3 shows the preparation parameters and performance testing data of the positive pole pieces and secondary batteries of Examples 1-15 and Comparative Examples 1-5.
  • the active material layer of the positive electrode sheet has the characteristics of double-layer and tertiary pore size distribution provided by the present invention.
  • such a double-layer tertiary pore size distribution not only ensures the ability of the micropores in the active material layer to transport lithium ions, but also makes the inner active material layer and the outer layer active.
  • the lithium ion transport capacity of the material layer is consistent; at the same time, the pore size distribution of the inner active material layer and the outer active material layer is reasonable, which avoids the occupying effect and filling effect, thereby further avoiding or reducing the secondary battery in a low temperature environment.
  • the low-temperature charge-discharge performance of the secondary battery is significantly improved due to the sharp decline in the internal lithium ion transport capacity. Therefore, the low-temperature energy retention rate and the maximum output power of the secondary batteries in the low-temperature and low-SOC state of Examples 1-15 in Table 3 are significantly better than those of Comparative Examples 1-5.
  • Comparative Example 1 the active material layer on the surface of the positive electrode sheet is single-layer coated, and there is no characteristic of tertiary pore size distribution in the active material layer coated by this single layer.
  • the inside and outside of the electrode sheet of Comparative Example 1 The kinetic properties are all poor, and the low-temperature charge and discharge performance of the secondary battery is obviously inferior to that of Examples 1-15.
  • the first-order pore diameters of the inner active material layer and the outer active material layer are too large. Although it is beneficial to electrolyte transportation, the specific surface area of the active material layer is greatly reduced, and its electrochemical active sites are relatively large. The magnitude is reduced. In Comparative Example 3, the second and third pore diameters in the inner active material layer and the outer active material layer are too large, that is, the particle diameter of the active material particles is also too large, and the kinetic performance of the large particle active material is poor. And it is more obvious at low temperature.
  • Comparative Example 4 the first-order pore diameters of the inner active material layer and the outer active material layer are too large, and the second and third pore diameters in the inner active material layer and the outer active material layer are too large, so at the same time Has the disadvantages of comparative examples 2 and 3.
  • Comparative Examples 2 to 4 although the active material layer on the surface of the positive pole piece is also double-layer coated and has a tertiary pore size distribution, the pore size distribution is unreasonable and does not effectively promote the transport of lithium ions, which cannot be avoided.
  • the internal lithium ion transport capacity of the secondary battery drops sharply in a low temperature environment, so the low temperature charge and discharge performance of the secondary battery in Comparative Examples 2 to 4 has not been improved, which is manifested in the low temperature energy retention rate and the maximum output power at low temperature and low SOC state bad.
  • the outer active material layer adopts an active material particle pore size distribution scheme with better kinetic properties.
  • the active material layer in the inner layer adopts the pore size distribution scheme of the active material particles with poor kinetic performance, so it cannot effectively promote the transport of lithium ions.
  • the maximum output power in the SOC state is even worse than that of Comparative Examples 1-4.
  • Examples 11 and 12 show the effect of the mass ratio of the first active material and the second active material in the inner active material layer and the outer active material layer on the technical effect of the present invention.
  • the mass of the active material forming the second pore size i.e. the first active material
  • the tertiary pore size i.e. the second active material
  • the compaction of the active material layer is smaller, resulting in a second The reduction in the energy density of the secondary battery.
  • the mass ratio of the active material forming the second-level pore size (i.e. the first active material) and the active material forming the third-level pore size is relatively small, due to the internal lithium ions in the large particle size active material If the transmission path is too long, it will adversely affect the kinetic performance of the secondary battery.
  • Examples 13 to 15 show the influence of the mass ratio of the conductive agent to the active material in the inner active material layer and the outer active material layer on the technical effect of the present invention. If the mass ratio of the conductive agent to the active material is too small, the conductivity will be poor, which is not conducive to the performance of the kinetic performance. Conversely, if the mass ratio of the conductive agent to the active material is too large, although the increase of the conductive agent can increase the conductivity between the active materials, thereby improving the energy retention rate of the secondary battery to a certain extent, it is not conducive to the energy retention of the secondary battery. increase in density.

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Abstract

一种正极极片，包括正极集流体和涂覆于正极集流体至少一个表面的正极活性物质层，正极活性物质层包括依次层叠的内层活性物质层和外层活性物质层；内层活性物质层具有三级孔径分布：内层第一级孔径分布为3nm～10nm，内层第二级孔径分布为10nm～100nm，内层第三级孔径分布为0.1μm～2μm，外层活性物质层具有三级孔径分布：外层第一级孔径分布为0.5nm～3nm，外层第二级孔径分布为10nm～100nm，外层第三级孔径分布为0.1μm～2μm。

Description

正极极片、二次电池、电池模组、电池包及用电装置
相关申请的交叉引用
本申请要求享有于2021年09月30日提交的名称为“正极极片、二次电池、电池模组、电池包及用电装置”的中国专利申请202111159354.7的优先权，该申请的全部内容通过引用并入本文中。
技术领域
本申请涉及电池领域，具体地讲，涉及一种正极极片、二次电池、电池模组、电池包及用电装置。
背景技术
随着二次电池在电动汽车及军工领域应用的迅速发展，其低温性能不能适应特殊低温天气或极端环境的缺点愈发得到关注。在低温条件下，二次电池的有效放电容量和有效放电量都会有明显的下降，同时其在低于-10℃的环境下的充电性能极差，这严重制约着二次电池的应用。
二次电池主要由正极极片、负极极片、隔离膜、电解液组成。处于低温环境的二次电池存在着放电电压平台下降、放电容量低、容量衰减块、倍率性能差等特点。低温性能限制了二次电池在电动汽车领域、军工领域及极端环境中的应用。因此，开发低温性能优异的二次电池是市场的迫切需求。
发明内容
鉴于背景技术中存在的问题，本申请提供一种正极极片、二次电池、电池模组、电池包及用电装置。
第一方面，本申请提供一种正极极片，包括正极集流体和涂覆于所述正极集流体至少一个表面的正极活性物质层。所述正极活性物质层依次包括层叠于所述正极集流体表面的内层活性物质层和层叠于所述内层活性物质层表面的外层活性物质层。
所述内层活性物质层具有三级孔径分布：内层第一级孔径分布为3nm～10nm，可选为6nm～10nm；内层第二级孔径分布为10nm～100nm，可选为10nm～84nm；内层第三级孔径分布为0.1μm～2μm，可选为0.1μm～1.26μm。
所述外层活性物质层具有三级孔径分布：外层第一级孔径分布为0.5nm～3nm，可选为1nm～3nm；外层第二级孔径分布为10nm～100nm，可选为60nm～100nm；外层第三级孔径分布为0.1μm～2μm，可选为 0.45μm～2μm。
相对于现有技术而言，本申请提供的正极极片的活性物质层具有双层三级孔径分布的特点。这样的双层三级孔径分布在不降低正极活性物质的质量和能量密度的前提下，不但保证了活性物质层中的微孔对锂离子的运输能力，使内层活性物质层和外层活性物质层的锂离子运输能力实现一致性；同时，内层活性物质层和外层活性物质层的孔径分布合理，避免了占位效应和填充效应，从而进一步避免或减小二次电池在低温环境下内部锂离子运输能力急剧下降的状况，使二次电池的低温充放电性能得到显著改善。
在一些可选实施方式中，所述内层活性物质层包括内层导电剂和内层活性物质，所述外层活性物质层包括外层导电剂和外层活性物质。
其中，内层活性物质层、外层活性物质层中的第一级孔径分布的形成，可通过选择具有适当比表面积的导电剂颗粒来实现。
所述内层导电剂的比表面积为300m 2/g～1000m 2/g，可选的，所述内层导电剂的比表面积为800m 2/g～1000m 2/g。
所述外层导电剂的比表面积为1000m 2/g～2500m 2/g，可选的，所述外层导电剂的比表面积为2000m 2/g～2500m 2/g。
在一些可选实施方式中，内层活性物质层、外层活性物质层中的第二、第三级孔径分布的形成，可通过选择具有双峰粒径的活性物质颗粒混合物来实现。
在一些可选实施方式中，所述内层第一活性物质的粒径分布为24nm～600nm，可选的，所述内层第一活性物质的粒径分布为24nm～200nm；所述内层第二活性物质的粒径分布为0.25μm～13μm，可选的，所述内层第二活性物质的粒径分布为0.5μm～3μm。
所述外层第一活性物质的粒径分布为24nm～600nm，可选的，所述外层第一活性物质的粒径分布为200nm～400nm；所述外层第二活性物质的粒径分布为0.25μm～13μm，可选的，所述外层第二活性物质的粒径分布为3μm～8μm。
在一些可选实施方式中，所述内层第一活性物质的粒径不与所述内层第三级孔径重合；和/或所述外层第一活性物质的粒径不与所述外层第三级孔径重合。即：内外层中形成第二级孔径的活性物质粒径不等于第三级孔径，从而避免第一活性物质粒子的占位效应。
在一些可选实施方式中，所述内层第一活性物质和所述内层第二活性物质的质量比为(0.3～3)：1。可选的，所述内层第一活性物质和所述内层第二活性物质的质量比为(1～3)：1。
在一些可选实施方式中，所述外层第一活性物质和所述外层第二活性物质的质量比为(0.3～3)：1。可选的，所述外层第一活性物质和所述外层第二活性物质的质量比为(0.3～1)：1。
内层活性物质层、外层活性物质层中，当第一活性物质与第二活性物质的质量在上述范围内，活性物质层的层压密度及活性物质中锂离子的内部 传输路径均处于较优水平，保证低温环境中二次电池的能量密度及动力学性能。
在一些可选实施方式中，所述内层导电剂和内层活性物质的质量比为(0.3～2)：100。可选的，所述内层导电剂和内层活性物质的质量比为(1.5～2)：100。
可选的，所述外层导电剂和外层活性物质的质量比为(0.3～3)：100。可选的，所述外层导电剂和外层活性物质的质量比为(2.5～3)：100。
通过使内层活性物质层、外层活性物质层中的导电剂与活性物质的质量比在合适范围内，可使极片的导电能力和动力学性能、以及二次电池的能量密度在较优范围内。
在一些可选实施方式中，所述内层导电剂和所述外层导电剂各自独立地选自活性炭或碳纳米管。活性炭或碳纳米管既有良好的导电性又有较大比表面积，可较好地形成内层活性物质层、外层活性物质层中的第一级孔径分布。
第二方面，本申请提供一种二次电池，其包括正极极片、负极极片、间隔于正极极片和负极极片之间的隔离膜、电解液，其中，所述正极极片为根据本申请第一方面的正极极片。
第三方面，本申请提供一种电池模组，其包括本申请第二方面的二次电池。
第四方面，本申请提供一种电池包，其包括本申请第二方面的二次电池或者本申请第三方面的电池模组。
第五方面，本申请提供一种用电装置，其包括本申请第二方面的二次电池或本申请第三方面的电池模组或本申请第四方面的电池包；其中，二次电池或电池模组或电池包用作用电装置的电源或能量存储单元。
本申请提供的二次电池、电池模组、电池包和用电装置包括本申请第一方面所述的正极极片，因而至少具有与上述正极极片相同或类似的技术效果。
附图说明
图1是根据本申请一具体实施方式的二次电池的立体图；
图2是图1所示二次电池的分解图；
图3是根据本申请一具体实施方式的电池模组的立体图；
图4是根据本申请一具体实施方式的电池包的立体图；
图5是图4所示电池包的分解图；
图6是本申请一具体实施方式的用电装置的示意图。
其中，附图标记说明如下：
1电池包；
2上箱体；
3下箱体；
4电池模组；
5二次电池；
51壳体；
52电极组件；
53顶盖组件。
具体实施方式
下面将结合附图对本申请技术方案的实施方式进行详细的描述。以下实施方式仅用于更加清楚地说明本申请的技术方案，因此只作为示例，而不能以此来限制本申请的保护范围。除非另有定义，本文所使用的所有的技术和科学术语与属于本申请的技术领域的技术人员通常理解的含义相同。
在本文中提及“实施方式”意味着，结合实施方式描述的特定特征、结构或特性可以包含在本申请的至少一个实施方式中。在说明书中的各个位置出现该短语并不一定均是指相同的实施方式，也不是与其它实施方式互斥的独立的或备选的实施方式。本领域技术人员显式地和隐式地理解的是，本文所描述的实施方式可以与其它实施方式相结合。
正极极片
本申请的第一方面提供一种正极极片，包括正极集流体和涂覆于所述正极集流体至少一个表面的正极活性物质层。所述正极活性物质层依次包括层叠于所述正极集流体表面的内层活性物质层和层叠于所述内层活性物质层表面的外层活性物质层。
所述内层活性物质层具有三级孔径分布：内层第一级孔径分布为3nm～10nm，可选为6nm～10nm；内层第二级孔径分布为10nm～100nm，可选为10nm～84nm；内层第三级孔径分布为0.1μm～2μm，可选为0.1μm～1.26μm。
所述外层活性物质层具有三级孔径分布：外层第一级孔径分布为0.5nm～3nm，可选为1nm～3nm；外层第二级孔径分布为10nm～100nm，可选为60nm～100nm；外层第三级孔径分布为0.1μm～2μm，可选为0.45μm～2μm。
本申请中所述的孔径分布是指多孔固体中孔道的等效直径分布，可通过气体吸附法和/或压汞法测定，例如参照GB T 21650.1-2008《压汞法和气体吸附法测定固体材料孔径分布和孔隙度》进行检测。
发明人认为，二次电池在低温下的粘度迅速增大，内部运输锂离子的能力急剧下降，是其在低温环境中充放电性能不佳的一个重要原因。发明人进一步提出：一方面，当正极活性物质层中存在孔径较小的微孔时，微孔成为影响锂离子运输能力的主要因素。当微孔孔径小于1个溶剂化锂离子的大小(溶剂化锂离子的直径为1nm左右)时，溶剂化锂离子无法通过微孔，锂离子运输能力极低；当微孔孔径为1～3个溶剂化锂离子的大小时，锂离子运输能力中等；当微孔孔径为4～10个溶剂化锂离子的大小时，锂离子运输能 力达到最佳。另一方面，正极极片表面的活性物质的粒度分布宽，意味着活性物质颗粒大小不一，不规则程度高，此时，大颗粒占据较大的位置，从而减少颗粒堆积形成的孔隙，形成占位效应；而小颗粒则会填充在其余颗粒堆积的孔隙中间，形成填充效应，占位效应与填充效应都不利于锂离子的运输。
基于此，本申请所提供的技术解决方案为：在正极集流体的表面形成双层涂覆的活性物质层，内层形成3nm～10nm(可选为6nm～10nm)、10nm～100nm(可选为10nm～84nm)、0.1μm-2μm(可选为0.1μm～1.26μm)三级孔径分布；外层形成0.5nm～3nm(可选为1nm～3nm)、10nm-100nm(可选为60nm～100nm)、0.1μm～2μm(可选为0.45μm～2μm)三级孔径分布。这样的双层三级孔径分布在不降低正极活性物质的质量和能量密度的前提下，不但保证了活性物质层中的微孔对锂离子的运输能力，使内层活性物质层和外层活性物质层的锂离子运输能力具有一致性；同时，内层活性物质层和外层活性物质层的孔径分布合理，避免了占位效应和填充效应，此时极片的电导率得到提升，可避免或减小二次电池在低温下内部运输锂离子能力急剧下降的状况，使二次电池的低温充放电性能得到显著改善。
进一步地，在本申请的实施方式中，所述内层活性物质层可包括内层导电剂和内层活性物质，所述外层活性物质层可包括外层导电剂和外层活性物质。
在本申请的实施方式中，内外层中的第一级孔径分布的形成，可通过选择特定比表面积范围的导电剂颗粒来实现。在一些实施方式中，所述内层导电剂的比表面积可以为300m 2/g～1000m 2/g(可选为800m 2/g～1000m 2/g)。在一些实施方式中，所述外层导电剂的比表面积可以为1000m 2/g～2500m 2/g(可选为2000m 2/g～2500m 2/g)。
本申请中所述的活性物质颗粒的比表面积可通过采用气体吸附法(BET)或压汞法进行测量。本申请中比表面积为本领域公知的含义，可以用本领域公知的仪器及方法进行测定。例如可以参照GB/T 19587-2017，采用氮气吸附比表面积分析测试方法测试，并用BET(BrunauerEmmett Teller)法计算得出，其中，氮气吸附比表面积分析测试可以通过美国Micromeritics公司的Tri-Star 3020型比表面积孔径分析测试仪进行。
在本申请的实施方式中，内外层中的第二、第三级孔径的形成，可通过选择具有双峰粒径的活性物质颗粒来实现。
在一些实施方式中，所述内层第一活性物质的粒径分布可以为24nm～600nm，可选的，所述内层第一活性物质的粒径分布可以为24nm～200nm。在一些实施方式中，所述内层第二活性物质的粒径分布可以为0.25μm～13μm，可选的，所述内层第二活性物质的粒径分布可以为0.5μm～3μm。
在一些实施方式中，所述外层第一活性物质的粒径分布可以为24nm～600nm，可选的，所述外层第一活性物质的粒径分布可以为 200nm～400nm。在一些实施方式中，所述外层第二活性物质的粒径分布可以为0.25μm～13μm，可选的，所述外层第二活性物质的粒径分布可以为3μm～8μm。
更进一步可选的，所述内层第一活性物质的粒径可不与所述内层第三级孔径重合；所述外层第一活性物质的粒径可不与所述外层第三级孔径重合。即：内外层中形成第二级孔径的活性物质粒径不等于第三级孔径，从而避免第一活性物质粒子的占位效应。
本申请中所述的粒径是指的是活性物质颗粒的等效直径，指被测活性物质颗粒与某一直径的同质球体(或球体组合)最相近时，就把该球体的直径(或球体组合)作为被测颗粒的粒径分布(或粒度分布)。本申请中可采用激光粒径分析仪检测出活性物质颗粒的粒径分布。
在一些实施方式中，所述内层第一活性物质和所述内层第二活性物质的质量比可以为(0.3～3)：1。可选的，所述内层第一活性物质和所述内层第二活性物质的质量比可以为(1～3)：1。
在一些实施方式中，所述外层第一活性物质和所述外层第二活性物质的质量比可以为(0.3～3)：1。可选的，所述外层第一活性物质和所述外层第二活性物质的质量比可以为(0.3～1)：1。
内层活性物质层和外层活性物质层中，当形成第二级孔径的活性物质(即第一活性物质)与形成第三级孔径的活性物质(即第二活性物质)的质量比过大，则导致活性物质层的压密较小，造成二次电池能量密度的降低。反之，当形成第二级孔径的活性物质(即第一活性物质)与形成第三级孔径的活性物质(即第二活性物质)的质量比过小，由于大粒径活性物质中锂离子的内部传输路径过长，对二次电池的动力学性能有不利影响。
在一些实施方式中，所述内层导电剂和内层活性物质的质量比可以为(0.3～2)：100。可选的，所述内层导电剂和内层活性物质的质量比可以为(1.5～2)：100。
在一些实施方式中，所述外层导电剂和外层活性物质的质量比可以为(0.3～3)：100；可选的，所述外层导电剂和外层活性物质的质量比可以为(2.5～3)：100。
内层活性物质层和外层活性物质层中，如导电剂与活性物质的质量比过小，则导电能力变差，不利于动力学性能的发挥。反之，如导电剂与活性物质的质量比过大，虽然导电剂的增加可增大活性物质之间导电能力，从而在一定程度上提高二次电池的能量保持率，但不利于二次电池能量密度的提升。此外，各层中导电剂的用量还和层中的活性物质材料的比表面积、导电剂的粒径有关。活性物质的比表面积越大，导电剂的粒径越大，则需要的导电剂用量也越多。在本申请中，可选为内层活性物质的粒径相对外层活性物质粒径较大，因而，内层中导电剂的用量也可选为比外层中导电剂的用量稍小。
在一些实施方式中，所述内层导电剂和所述外层导电剂可各自独立地 选自活性炭或碳纳米管。活性炭或碳纳米管既有良好的导电性又有较大比表面积，可较好地形成内层活性物质层和外层活性物质层中的第一级孔径分布。
此外，在本申请的一些实施方式中，正极活性物质的具体种类没有特别的限制，只要能满足嵌入、脱出锂离子即可。正极活性物质既可为层状结构材料，使锂离子在二维空间扩散，也可为尖晶石结构，使锂离子在三维空间扩散。可选地，正极活性物质可选自锂过渡金属氧化物、锂过渡金属氧化物添加其它过渡金属或非过渡金属或非金属得到的化合物中的一种或几种。具体地，正极活性物质可选自锂钴氧化物、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中的一种或几种。
其中，橄榄石结构的含锂磷酸盐的通式可为LiFe 1-x-yMn xM’ yPO 4，0≤x≤1，0≤y<1，0≤x+y≤1，M’可选自除Fe、Mn外的其它过渡金属元素或非过渡金属元素中的一种或几种，M’可选自Cr、Mg、Ti、Al、Zn、W、Nb、Zr中一种或几种。更可选地，橄榄石结构的含锂磷酸盐可选自磷酸铁锂、磷酸锰锂、磷酸锰铁锂中的一种或几种。
锂过渡金属氧化物可选自LiCoO 2、LiMnO 2、LiNiO 2、LiMn 2O 4、LiNi xCo yMn 1-x-yO 2、LiNi xCo yAl 1-x-yO 2、LiNi xMn 2-xO 4中的一种或几种，其中0＜x＜1、0＜y＜1、0＜x+y＜1。可选地，锂过渡金属氧化物可选自LiCoO 2、LiNi 1/3Co 1/3Mn 1/3O 2、LiNi 0.5Co 0.2Mn 0.3O 2、LiNi 0.6Co 0.2Mn 0.2O 2、LiNi 0.8Co 0.1Mn 0.1O 2、LiNi 0.8Co 0.15Mn 0.05O 2、LiNi 0.8Co 0.15Al 0.05O 2、LiNi 0.5Mn 1.5O 4、LiMn 2O 4中的一种或几种。
在本申请的一些实施方式中，正极活性物质层还可包括粘结剂，其中粘结剂的种类和含量不受具体的限制，可根据实际需求进行选择。所述粘结剂通常可包括含氟聚烯烃类粘结剂，相对于所述含氟聚烯烃类粘结剂来说，水通常是良溶剂，即所述含氟聚烯烃类粘结剂通常在水中具有良好的溶解性，例如，所述含氟聚烯烃类粘结剂可以是包括但不限于聚偏氟乙烯(PVDF)、偏氟乙烯共聚物或它们的改性(例如，羧酸、丙烯酸、丙烯腈等改性)衍生物等。在所述正极材料层中，粘结剂的质量百分比含量可以是由于粘结剂本身的导电性较差，因此粘结剂的用量不能过高。
在本申请的一些实施方式中，正极集流体的种类也不受具体的限制，可根据实际需求进行选择。正极集流体通常可以为层体，正极集流体通常是可以汇集电流的结构或零件。正极集流体可以是本领域各种适用于作为电化学储能装置正极集流体的材料。例如，正极集流体可以是包括但不限于金属箔，更具体可以是包括但不限于镍箔、铝箔。
二次电池
第二方面，本申请提供一种二次电池，包括正极极片、负极极片、间隔于正极极片和负极极片之间的隔离膜、电解液，其中，所述正极极片为根据本申请第一方面的正极极片。
在一些实施方式中，二次电池的负极极片通常包括负极集流体和位于负极集流体表面的负极活性材料层，所述负极活性材料层通常包括负极活性材料。所述负极活性材料可以是本领域各种适用于锂二次电池的负极活性材料的材料，例如，可以是包括但不限于石墨、软碳、硬碳、碳纤维、中间相碳微球、硅基材料、锡基材料、钛酸锂或其他能与锂形成合金的金属中的一种或多种的组合。其中，所述石墨可选自人造石墨、天然石墨以及改性石墨中的一种或多种的组合；所述硅基材料可选自单质硅、硅氧化合物、硅碳复合物、硅合金中的一种或多种的组合；所述锡基材料可选自单质锡、锡氧化合物、锡合金中的一种或多种的组合。所述负极集流体通常是汇集电流的结构或零件，所述负极集流体可以是本领域各种适用于作为锂二次电池负极集流体的材料，例如，所述负极集流体可以是包括但不限于金属箔，更具体可以是包括但不限于铜箔。此外，负极极片也可为锂片。
在一些实施方式中，二次电池的电解液可以是本领域各种适用于二次电池的电解液，例如，所述电解液通常包括电解质和溶剂，所述电解质通常可以包括锂盐，更具体的，所述锂盐可以是无机锂盐和/或有机锂盐，具体可以是包括但不限于LiPF 6、LiBF 4、LiN(SO 2F) 2(简写为LiFSI)、LiN(CF 3SO 2) 2(简写为LiTFSI)、LiClO 4、LiAsF 6、LiB(C 2O 4) 2(简写为LiBOB)、LiBF 2C 2O 4(简写为LiDFOB)中的一种或多种的组合。再例如，所述电解质的浓度可以为0.8mol/L～1.5mol/L。所述溶剂可以是本领域各种适用于二次电池的电解液的溶剂，所述电解液的溶剂通常为非水溶剂，可以为有机溶剂，具体可以是包括但不限于碳酸乙烯酯、碳酸丙烯酯、碳酸丁烯酯、碳酸戊烯酯、碳酸二甲酯、碳酸二乙酯、碳酸二丙酯、碳酸甲乙酯或它们的卤代衍生物中的一种或多种的组合。
在一些实施方式中，二次电池的隔离膜可以是本领域各种适用于二次电池隔离膜的材料，例如，可以是包括但不限于聚乙烯、聚丙烯、聚偏氟乙烯、芳纶、聚对苯二甲酸乙二醇酯、聚四氟乙烯、聚丙烯腈、聚酰亚胺，聚酰胺、聚酯和天然纤维中的一种或多种的组合。
在一些实施方式中，制备所述二次电池的方法对于本领域技术人员来说应该是已知的，例如，所述正极极片、隔离膜和负极极片各自都可以是层体，从而可以裁剪成目标尺寸后依次叠放，还可以卷绕至目标尺寸，以用于形成电芯，并可以进一步与电解液结合以形成二次电池。
图1示出了根据本申请一具体实施方式的二次电池的立体图，图2是图1所示二次电池的分解图。参看图1和图2，根据本申请的二次电池5(以下简称电池单体5)包括外包装51、电极组件52、顶盖组件53和电解液(未示出)。其中电极组件52收容于壳体51内，电极组件52的数量不受限制，可以为一个或多个。
需要说明的是，图1所示的电池单体5为罐型电池，但本申请并不限于此，电池单体5可以是袋型电池，即壳体51由金属塑膜替代且取消顶盖组件53。
电池模组
本申请的第三方面提供一种电池模组，其包括本申请第二方面所述的二次电池。在一些实施方式中，所述二次电池可以组装成电池模组，电池模组所含的二次电池的数量可以为多个，具体数量可根据电池模组的应用和容量来调节。图3是作为一个示例的电池模组4的立体图。参照图3，在电池模组4中，多个二次电池5可以是沿电池模组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，电池模组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。
电池包
本申请的第四方面提供一种电池包，其包括本申请第三方面所述的电池模组。在一些实施方式中，上述电池模组可以组装成电池包，电池包所含电池模组的数量可以根据电池包的应用和容量进行调节。图4是作为一个示例的电池包1的立体图，图5是图4所示电池包的分解图。参照图4和图5，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组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。多个电池模组4可以按照任意的方式排布于电池箱中。
用电装置
本申请的第五方面提供一种用电装置，其包括本申请第二方面所述的二次电池或本申请第三方面所述的电池模组或本申请第四方面所述的电池包。所述二次电池、或所述电池模组、或所述电池包可用作所述用电装置的电源或所述用电装置的能量存储单元。所述用电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。
所述用电装置可以根据其使用需求来选择二次电池、电池模组或电池包。
图6示出了根据本申请一具体实施方式的用电装置的示意图。该用电装置可以为纯电动车、混合动力电动车、或插电式混合动力电动车等。为了满足该用电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组。
作为另一个示例的用电装置可以是手机、平板电脑、笔记本电脑等。该用电装置通常要求轻薄化，可以采用本申请的二次电池作为电源。
本领域技术人员可以理解：本申请的不同实施例中对于电化学活性材料中的组分选择、组分含量和材料理化性能参数的各种限定或可选范围可以任意组合，其组合而得到的各种实施例仍然在本申请范围内，且视为本说明书公开内容的一部分。
以下结合具体实施例进一步说明本申请的优势。应理解，这些实施例 仅用于说明本申请而不用于限制本申请的范围。
正极极片及二次电池的制备
制备实施例1～15和对比例1～5的正极极片及二次电池：
1.制备正极极片：
(1)内层涂覆：将内层第一活性物质和内层第二活性物质按比例混合，与粘结剂(1.8％)、分散剂(0.2％)及适量的NMP充分搅拌混合，使其形成均匀的内层浆料；将内层浆料涂覆于正极集流体Al箔上，干燥；
(2)外层涂覆：将外层第一活性物质和外层第二活性物质按比例混合，与粘结剂(1.6％)、分散剂(0.2％)及适量的NMP充分搅拌混合，使其形成均匀的外层浆料；将此浆料涂覆于已经涂覆内层浆料的极片上面，干燥后把正极片冷压到设计压实密度，分条备用。
2.按照本领域常规方法获得负极极片、隔离膜、电解液和壳体：
负极极片：将负极活性材料石墨与导电炭、粘结剂聚偏二氟乙烯(PVDF)按95:3:2重量比在适量的水溶剂中充分搅拌混合，使其形成均匀的负极浆料；将此浆料涂覆于负极集流体Cu箔上，干燥后把极片冷压到设计压实密度，分条备用。
隔离膜：采用12μm的PP隔离膜。
电解液：采用磷酸铁锂通用电解液。
壳体：壳体材料使用铝塑膜。
3、制备二次电池：
将正极极片，隔离膜，负极极片卷绕形成裸电芯，用铝塑膜将裸电芯进行封装，注入电解液，通过化成、排气和高温老化后得到锂二次电池。
二次电池的性能检测
对实施例1～15、对比例1～5中的二次电池进行如下性能检测：
1.二次电池的低温循环能量保持率检测：
测试流程如表1所示(其中C为电芯额定容量)。
表1
Figure PCTCN2022094695-appb-000001
根据上述检测步骤得到-10℃能量保持率：-10℃能量保持率＝E1/E0。
2.低温下低SOC状态下功率性能检测：
测试流程如表2所示(其中C为电芯额定容量)，以额定容量为20Ah电芯进行测试。
表2
Figure PCTCN2022094695-appb-000002
实施例1～15和对比例1～5的正极极片、二次电池的制备参数和性能检测数据如表3所示。
表3
Figure PCTCN2022094695-appb-000003
从表3的电池性能测定数据可知，实施例1～15中，正极极片的活性物质层具有本发明所提供的双层三级孔径分布的特点。这样的双层三级孔径分布在不降低正极活性物质的质量和能量密度的前提下，不但保证了活性物质层中的微孔对锂离子的运输能力，使内层活性物质层和外层活性物质层的锂离子运输能力实现一致性；同时，内层活性物质层和外层活性物质层的孔径分布合理，避免了占位效应和填充效应，从而进一步避免或减小二次电池在低温环境下内部锂离子运输能力急剧下降的状况，使二次电池的低温充放电性能得到显著改善。因而，表3中实施例1～15中二次电池的低温能量保持率和低温低SOC状态下最大输出功率均明显优于对比例1～5。
对比例1中，正极极片表面的活性物质层为单层涂覆，且在该单层涂覆的活性物质层中也不具有三级孔径分布的特征，对比例1的极片内部和外部动力学性能均表现不佳，二次电池的低温充放电性能明显劣于实施例1～15。
对比例2中，内层活性物质层、外层活性物质层的第一级孔径过大，虽然有利于电解液运输，但是活性物质层的比表面积大幅降低，其电化学活性点位相对也大幅度降低。对比例3中，内层活性物质层、外层活性物质层中的第二、第三级孔径过大，即活性物质颗粒的粒径也偏大，大颗粒活性物质的动力学性能较差，且在低温下表现得更为明显。对比例4中，内层活性物质层、外层活性物质层的第一级孔径过大，且内层活性物质层、外层活性物质层中的第二、第三级孔径过大，因而同时具有对比例2和3的缺点。对比例2～4中，正极极片表面的活性物质层虽然也为双层涂覆且具有三级孔径分布，但孔径分布不合理，没有对锂离子的运输起到有效的促进作用，无法避免二次电池在低温环境下内部锂离子运输能力的急剧下降，因而对比例2～4中二次电池的低温充放电性能未得到改善，表现为低温能量保持率和低温低SOC状态下最大输出功率不佳。
对比例5中，正极极片表面的活性物质层虽然也为双层涂覆且具有三级孔径分布，但其外层活性物质层采用了动力学性能更好的活性物质颗粒孔径分布方案，其内层活性物质层反而采用了动力学性能较差的活性物质颗粒孔径分布方案，因而也无法实现对锂离子运输的有效的促进作用，对比例5中二次电池的低温能量保持率和低温低SOC状态下最大输出功率甚至比对比例1～4更差。
实施例11和12示出了内层活性物质层、外层活性物质层中的第一活性物质和第二活性物质的质量比对本发明技术效果的影响。当形成第二级孔径的活性物质(即第一活性物质)与形成第三级孔径的活性物质(即第二活性物质)的质量比较大，则导致活性物质层的压密较小，造成二次电池能量密度的降低。反之，当形成第二级孔径的活性物质(即第一活性物质)与形成第三级孔径的活性物质(即第二活性物质)的质量比较小，由于大粒径活性物质中锂离子的内部传输路径过长，对二次电池的动力学性能有不利影响。
实施例13～15示出了内层活性物质层、外层活性物质层中导电剂与活性物质的质量比对本发明技术效果的影响。如导电剂与活性物质的质量比过小，则导电能力变差，不利于动力学性能的发挥。反之，如导电剂与活性物质的质量比过大，虽然导电剂的增加可增大活性物质之间导电能力，从而在一定程度上提高二次电池的能量保持率，但不利于二次电池能量密度的提升。
根据上述说明书的揭示和教导，本领域技术人员还可以对上述实施方式进行变更和修改。因此，本申请并不局限于上面揭示和描述的具体实施方式，对本申请的一些修改和变更也应当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 (11)

  1. 一种正极极片，包括正极集流体和涂覆于所述正极集流体至少一个表面的正极活性物质层，其中，所述正极活性物质层依次包括层叠于所述正极集流体表面的内层活性物质层和层叠于所述内层活性物质层表面的外层活性物质层；
    所述内层活性物质层具有三级孔径分布：内层第一级孔径分布为3nm～10nm，可选为6nm～10nm；内层第二级孔径分布为10nm～100nm，可选为10nm～84nm；内层第三级孔径分布为0.1μm～2μm，可选为0.1μm～1.26μm；
    所述外层活性物质层具有三级孔径分布：外层第一级孔径分布为0.5nm～3nm，可选为1nm～3nm；外层第二级孔径分布为10nm～100nm，可选为60nm～100nm；外层第三级孔径分布为0.1μm～2μm，可选为0.45μm～2μm。
  2. 根据权利要求1所述的正极极片，其中，
    所述内层活性物质层包括内层导电剂和内层活性物质，所述内层导电剂的比表面积为300m 2/g～1000m 2/g，可选为800m 2/g～1000m 2/g；和/或，
    所述外层活性物质层包括外层导电剂和外层活性物质，所述外层导电剂的比表面积为1000m 2/g～2500m 2/g，可选为2000m 2/g～2500m 2/g。
  3. 根据权利要求1或2所述的正极极片，其中，
    所述内层活性物质包括内层第一活性物质和内层第二活性物质；所述内层第一活性物质的粒径分布为24nm～600nm，可选为24nm～200nm；所述内层第二活性物质的粒径分布为0.25μm～13μm，可选为0.5μm～3μm；和/或，
    所述外层活性物质包括外层第一活性物质和外层第二活性物质；所述外层第一活性物质的粒径分布为24nm～600nm，可选为200nm～400nm；所述外层第二活性物质的粒径分布为0.25μm～13μm，可选为3μm～8μm。
  4. 根据权利要求3所述的正极极片，其中，
    所述内层第一活性物质的粒径不与所述内层第三级孔径重合；和/或，
    所述外层第一活性物质的粒径不与所述外层第三级孔径重合。
  5. 根据权利要求2至4中任一项所述的正极极片，其中，
    所述内层导电剂和内层活性物质的质量比为(0.3～2)：100，可选为(1.5～2)：100；和/或，
    所述外层导电剂和外层活性物质的质量比为(0.3～3)：100，可选为(2.5～3)：100。
  6. 根据权利要求3至5中任一项所述的正极极片，其中，
    所述内层第一活性物质和所述内层第二活性物质的质量比为(0.3～3)：1，可选为(1～3)：1；和/或，
    所述外层第一活性物质和所述外层第二活性物质的质量比为(0.3～3)：1；可选为(0.3～1)：1。
  7. 根据权利要求2至6中任一项所述的正极极片，其中，所述内层导电剂和所述外层导电剂各自独立地选自活性炭或碳纳米管。
  8. 一种二次电池，包括权利要求1至7中任一项所述的正极极片。
  9. 一种电池模组，包括权利要求8所述的二次电池。
  10. 一种电池包，包括权利要求8所述的二次电池或权利要求9所述的电池模组。
  11. 一种用电装置，包括权利要求8所述的二次电池、或权利要求9所述的电池模组、或权利要求10所述的电池包。
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