WO2024164119A1 - 正极片、二次电池和用电装置 - Google Patents

正极片、二次电池和用电装置 Download PDF

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WO2024164119A1
WO2024164119A1 PCT/CN2023/074661 CN2023074661W WO2024164119A1 WO 2024164119 A1 WO2024164119 A1 WO 2024164119A1 CN 2023074661 W CN2023074661 W CN 2023074661W WO 2024164119 A1 WO2024164119 A1 WO 2024164119A1
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Prior art keywords
positive electrode
active material
electrode active
electrode sheet
sheet according
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English (en)
French (fr)
Inventor
尚义博
徐晓富
秦一鸣
潘坚福
张新羽
刘倩
叶永煌
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Contemporary Amperex Technology Co Ltd
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Contemporary Amperex Technology Co Ltd
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Priority to JP2025522246A priority Critical patent/JP2025535338A/ja
Priority to PCT/CN2023/074661 priority patent/WO2024164119A1/zh
Priority to KR1020257005500A priority patent/KR20250036923A/ko
Priority to EP23920334.2A priority patent/EP4579840A4/en
Priority to CN202380010142.3A priority patent/CN116830333B/zh
Publication of WO2024164119A1 publication Critical patent/WO2024164119A1/zh
Priority to US19/072,696 priority patent/US20250201824A1/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
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/136—Electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/364—Composites as mixtures
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—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
    • H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
    • 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
    • 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 belongs to the field of battery technology, and specifically relates to a positive electrode sheet, a secondary battery and an electrical device.
  • Lithium-ion batteries are green, environmentally friendly, high-energy, and low-carbon. They are not only used in energy storage power systems such as hydropower, thermal, wind, and solar power stations, but are also widely used in electric vehicles such as electric bicycles, electric motorcycles, and electric vehicles, as well as military equipment and aerospace and other fields. With the development of the current society, people's requirements for lithium-ion batteries are getting higher and higher, and fast charging performance and cycle performance have become important performance indicators of lithium batteries.
  • lithium-ion battery positive electrode materials mostly use ternary layered positive electrode materials, such as nickel-cobalt-manganese (NCM) system materials, but conventional NCM system materials have poor rate tolerance margins at low voltages, which will affect the battery's fast charging capability and actual available capacity.
  • NCM nickel-cobalt-manganese
  • the present application provides a positive electrode sheet, which aims to broaden the rate tolerance boundary of the positive electrode active material at high and low voltages, improve the fast charging capability, and ensure the cycle performance.
  • the first aspect of the present application provides a positive electrode sheet, wherein the positive electrode sheet comprises a positive electrode active material layer, the positive electrode active material layer comprises a first positive electrode active material and a second positive electrode active material,
  • the first positive electrode active material includes Li a Ni b Co c M 1d M 2e O f R ′ g , wherein 0.75 ⁇ a ⁇ 1.2, 0 ⁇ b ⁇ 1, 0 ⁇ c ⁇ 1, 0 ⁇ d ⁇ 1, 0 ⁇ e ⁇ 0.2, 1 ⁇ f ⁇ 2.5, 0 ⁇ g ⁇ 1, f+g ⁇ 3, M 1 is Mn element and/or Al element, M 2 includes one or more elements of Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, Sr, Sb, Y, W, and Nb, and R ′ includes one or more elements of N, F, S, and Cl;
  • the second positive electrode active material includes Li1 + xM3nMn1 -yA'yP1 - zEzO4 , wherein -0.100 ⁇ x ⁇ 0.100 , 0 ⁇ n ⁇ 1.1, 0.001 ⁇ y ⁇ 1, 0 ⁇ z ⁇ 0.100, M3 includes one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo and W, A' includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti , V, Zr, Fe, Ga, Sn, Sb, Nb and Ge, and E includes one or more elements selected from B, Si, N, S, F, Cl and Br;
  • the positive electrode sheet satisfies:
  • n (A') is the molar amount of A' in the positive electrode sheet, in mol
  • n (Ni) is the molar amount of Ni in the positive electrode sheet, in mol
  • n (Mn) is the molar amount of Mn in the positive electrode sheet, in mol
  • R is the molar amount of the positive electrode sheet in The resistance at 25°C, in ⁇ .
  • the positive electrode sheet of the first aspect of the present application has at least the following beneficial effects: (1) the rate tolerance margin of the Li a Ni b Co c M 1d M 2e O f R′ g positive electrode active material system is poor at a low SOC (state of charge, i.e., remaining capacity), while the rate tolerance margin of Li 1+x M 3n Mn 1-y A′ y P 1-z E z O 4 is poor at a high SOC.
  • the defects of the two systems can be compensated at the same time, and the rate tolerance margin at high and low SOCs can be widened, thereby improving the fast charging capability; (2) by combining the positive electrode active material Li a Ni b Co c M 1d M 2e O f R′ g with the positive electrode active material Li 1+x M 3n Mn 1-y A′ y P 1- z E z O 4 4 blending can further achieve both high energy density and good cycle performance; (3) by controlling the molar number of A' element, Ni element, and Mn element in the positive electrode sheet and the positive electrode sheet resistance to satisfy the above range, the fast charging capability and cycle performance of the positive electrode sheet can be guaranteed at the same time, and it is beneficial to obtain high energy density.
  • n (P) is the molar amount of P in the positive electrode sheet, in mol.
  • the appropriate doping ratio can be further controlled to achieve both higher energy density and better cycle performance while improving fast charging capability.
  • the second positive electrode active material has a discharge platform, and the discharge voltage of at least one of the discharge platforms is not lower than the discharge cut-off voltage of the first positive electrode active material, and is not higher than 3.5 V.
  • At least one of the following conditions is satisfied: 0.0007 ⁇ n (Ni) ⁇ 0.0016, 0.0009 ⁇ n (Mn) ⁇ 0.0016, 0.0002 ⁇ n (A′) ⁇ 0.0006.
  • 0 ⁇ R ⁇ 1.3 optionally, 0 ⁇ R ⁇ 1.
  • M1 is a Mn element.
  • Optional land By controlling Within the given range, the fast charging capability can be further improved while taking into account better cycle performance.
  • n (A′) , n (Ni) , n (Mn) and R are controlled to meet the given conditions.
  • the coating mass of the positive electrode active material layer is 15.50 mg/cm 2 to 20.78 mg/cm 2 , and can be optionally 16.80 mg/cm 2 to 18.83 mg/cm 2 .
  • the fast charging performance can be further improved, while taking into account both energy density and cycle performance.
  • the compaction density of the positive electrode active material layer is 2.4 g/cm 3 to 3.40 g/cm 3 , and may be 2.6 g/cm 3 to 3.25 g/cm 3 .
  • the Dv50 particle size of the first positive electrode active material is 2.1 ⁇ m to 6.3 ⁇ m, and can be optionally 3.5 ⁇ m to 4.9 ⁇ m.
  • the specific surface area of the first positive electrode active material is 0.3 m 2 /g to 1.2 m 2 /g, and can be optionally 0.5 m 2 /g to 0.9 m 2 /g.
  • the Dv50 particle size of the second positive electrode active material is 0.25 ⁇ m to 1.49 ⁇ m, and can be optionally 0.5 ⁇ m to 0.9 ⁇ m.
  • the specific surface area of the second positive electrode active material is 9.0 m 2 /g to 23.2 m 2 /g, and can be optionally 10.5 m 2 /g to 17.9 m 2 /g.
  • a first coating layer is provided on the surface of the first positive electrode active material, and optionally, the first coating layer includes one or more elements selected from Ti, Al, B, Nb, Zr, Si and W.
  • the thickness of the first coating layer is 20 nm to 150 nm.
  • a second coating layer is provided on the surface of the second positive electrode active material, and optionally, the second coating layer includes at least one of pyrophosphate, phosphate and carbon.
  • the thickness of the second coating layer is 10 nm to 50 nm.
  • E is at least one of B, Si, N and S.
  • A′ is composed of Fe, Ti, V and Mg. At least one of .
  • the second aspect of the present application provides a secondary battery, which includes: the positive electrode sheet of the first aspect of the present application.
  • the third aspect of the present application provides an electrical device, which includes: the positive electrode sheet of the first aspect of the present application, and/or the secondary battery described in the second aspect of the present application.
  • the "range” disclosed in the present application is defined in the form of a lower limit and/or an upper limit, and a given range is defined by selecting a lower limit and/or an upper limit, and the selected lower limit and/or the rear upper limit define the boundary of a particular range.
  • the range defined in this way can be inclusive or exclusive of the end value, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form an unambiguous range, and any lower limit can be combined with other lower limits to form an unambiguous range, and any upper limit can be combined with any other upper limit to form an unambiguous range.
  • each individually disclosed point or single value itself can be combined with any other point or single value as a lower limit or upper limit or with other lower limits or upper limits to form an unambiguous range.
  • a range of not more than 150 is listed for a specific parameter, it is also expected that 10 to 140 and 20 to 120 etc. meet the range of not more than 150.
  • the minimum range values 2.1 and 3.5 are listed, and if the maximum range values 4.9 and 6.3 are listed, the following ranges are all expected: 2.1-6.3, 2.1-4.9, 3.5-6.3, and 3.5-4.9.
  • a numerical range such as "10-50” represents an abbreviation of any real number combination between 10 and 50, where 10 and 50 are both real numbers.
  • the numerical range “20-30” means that all real numbers between “20-30” have been fully listed in this document, and "20-30” is just an abbreviation of these numerical combinations.
  • the method includes steps S1 and S2, which means that the method may include steps S1 and S2 performed sequentially, or may include steps S2 and S1 performed sequentially.
  • the method may also include steps S3, indicating that step S3 can be added to the method in any order.
  • the method may include steps S1, S2 and S3, or steps S1, S3 and S2, or steps S3, S1 and S2, etc.
  • the terms “include” and “comprising” mentioned in this application may be open-ended or closed-ended.
  • the terms “include” and “comprising” may mean that other components not listed may also be included or contained, or may only include or contain the listed components.
  • the terms “plurality” and “multiple” refer to two or more.
  • ternary layered positive electrode active materials such as NCM
  • NCM ternary layered positive electrode active materials
  • the positive electrode material of this system will have problems such as increased battery internal resistance and increased electrode polarization, which will cause the discharge voltage to reach the cut-off voltage ahead of schedule.
  • the positive electrode material of this system has a poor rate tolerance margin at low SOC, which affects the fast charging and cycle performance of the battery.
  • a first aspect of the present application provides a positive electrode sheet, wherein the positive electrode sheet includes a positive electrode active material layer, the positive electrode active material layer includes a first positive electrode active material and a second positive electrode active material, the first positive electrode active material includes Li a Ni b Co c M 1d M 2e O f R′ g , wherein 0.75 ⁇ a ⁇ 1.2, 0 ⁇ b ⁇ 1, 0 ⁇ c ⁇ 1, 0 ⁇ d ⁇ 1, 0 ⁇ e ⁇ 0.2, 1 ⁇ f ⁇ 2.5, 0 ⁇ g ⁇ 1, f+g ⁇ 3, M 1 is a Mn element and/or an Al element, M 2 includes one or more elements selected from Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, Sr, Sb, Y, W, and Nb, and R′ includes one or more elements selected from N, F, S, and Cl; the second positive electrode active material includes Li 1+x M 3n Mn 1-y A′ y P 1-z E z O 4 , wherein -0.1
  • n (A′) is the molar amount of A′ in the positive electrode sheet, in mol
  • n (Ni) is the molar amount of Ni in the positive electrode sheet, in mol
  • n (Mn) is the molar amount of Mn in the positive electrode sheet, in mol
  • R is the resistance of the positive electrode sheet at 25°C, in ⁇ .
  • the inventors of the present application have found that the layered positive electrode active material system Li a Ni b Co c M 1d M 2e Of R′ g has a poor rate tolerance margin at low SOC, while the positive electrode active material Li 1+x M 3n Mn 1-y A′ y P 1-z E z O 4 has a low-voltage discharge platform (generally not more than 3.5V) near the end of discharge.
  • the discharge platform of Li 1+x M 3n Mn 1-y A′ y P 1-z E z O 4 at low voltage can be used to make the overall discharge curve of the mixed composite positive electrode active material have a discharge platform near the end.
  • the positive electrode active material system Li 1+x M 3n Mn 1-y A′ y P 1-z E z O 4 has a low voltage discharge platform (generally not more than 3.5V) near the end of discharge.
  • A′ y P 1-z E z O 4 is also limited by the problem of poor rate tolerance boundary at high SOC.
  • the defects of the two systems can be compensated at the same time, and the rate tolerance boundary at high and low SOCs can be widened, thereby improving the fast charging capability and taking into account the cycle performance.
  • the positive electrode active material Li a Ni b Co c M 1d M 2e Of R′ g has a higher energy density
  • the positive electrode active material Li 1+x M 3n Mn 1-y A′ y P 1-z E z O 4 has higher cycle performance and safety.
  • the positive electrode active material Li 1+x M 3n Mn 1-y A′ y P 1-z E z O 4 The lattice shrinkage rate during the charge and discharge process is relatively large.
  • Mixing the positive active materials of the two systems is also beneficial to further match the expansion of the battery negative electrode sheet and improve the long-term performance of the battery; further, the inventors also found in the exploration process that a high Ni content in the positive electrode sheet is helpful to improve the battery energy density, but too high Ni content will damage the cycle performance, a high Mn content is helpful to the cycle performance, but too high will damage the battery energy density, a high A' element content is helpful to improve the cycle performance, but too high will damage the battery energy density, further, a high positive electrode sheet resistance will also affect the battery power and cycle performance, and by controlling the molar number of A' element, Ni element, and Mn element in the positive electrode sheet and the positive electrode sheet resistance to meet the range given by the above formula, it can further ensure that the positive electrode sheet and the battery have good fast charging capability and good cycle performance
  • the inventors have found through in-depth research that, on the basis of satisfying the above conditions, the positive electrode sheet of the present application can further control the molar amount and/or relative amount of elements in the positive electrode sheet, the selection of positive electrode active materials, the electrode sheet resistance, the coating amount of the electrode sheet active material layer, etc. to further improve the performance of the positive electrode sheet. That is, on the basis of satisfying the above conditions, one or more of the following conditions can also be optionally satisfied.
  • the first positive electrode active material may be partially Li a Ni b Co c M 1d M 2e O f R ′ g , or all Li a Ni b Co c M 1d M 2e O f R ′ g , wherein 0.75 ⁇ a ⁇ 1.2, 0 ⁇ b ⁇ 1, 0 ⁇ c ⁇ 1, 0 ⁇ d ⁇ 1, 0 ⁇ e ⁇ 0.2, 1 ⁇ f ⁇ 2.5, 0 ⁇ g ⁇ 1, f+g ⁇ 3, M1 is Mn element and/or Al element, M2 includes Zr, Zn, One or more elements selected from the group consisting of Cu, Cr, Mg, Fe, V, Ti, Sr, Sb, Y, W, and Nb; and R′ includes one or more elements selected from the group consisting of N, F, S, and Cl.
  • the positive electrode active material Li a Ni b Co c M 1d M 2e Of R′ g satisfies the above-given range conditions, which is more conducive to having higher energy density, good cycle performance and longer cycle life.
  • the positive electrode active material Li a Ni b Co c M 1d M 2e Of R′ g taking the nickel-cobalt-manganese ternary positive electrode active material (i.e., NCM) system as an example, increasing the nickel content can increase the volume energy density of the positive electrode material; increasing the manganese content can reduce the material cost, improve the safety and structural stability of the material, and improve the cycle performance, but too high a manganese content will destroy the layered structure of the material and reduce the specific capacity of the material; cobalt can stabilize the layered structure of the material and improve the cycle and rate performance of the material, but too high a cobalt content will lead to a decrease in the actual capacity.
  • NCM nickel-cobalt-manganese ternary positive electrode active material
  • M1 may be a Mn element
  • the first positive electrode active material may be a positive electrode active material of an NCM system, in which case its general formula may be LiaNibCocMndM2eOfR'g , for example , it may be a nickel - cobalt - manganese ternary layered positive electrode active material.
  • the second positive electrode active material may be partially Li1 + xM3nMn1 - yA′yP1- zEzO4 , or entirely Li1 + xM3nMn1 - yA′yP1 - zEzO4 , wherein -0.100 ⁇ x ⁇ 0.100 , 0 ⁇ n ⁇ 1.1 , 0.001 ⁇ y ⁇ 1, 0 ⁇ z ⁇ 0.100 , M 3 includes one or more elements of Zn, Al, Na, K, Mg, Nb, Mo and W, A′ includes one or more elements of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ga, Sn, Sb, Nb and Ge, and E includes one or more elements of B, Si, N, S, F, Cl and Br.
  • Doping at least one of the lithium site, manganese site and phosphorus site can help improve the performance of the positive electrode active material, for example, it can improve the interface performance, reduce the interface side reaction with the electrolyte, reduce the concentration of anti-site defects, improve the material kinetics and gram capacity, etc.
  • the particle morphology can also be improved and the compaction density can be increased.
  • the lattice volume change rate of the second positive electrode active material during the charge and discharge process is Compared with the first positive electrode active material, it is larger and can better match the volume expansion of the negative electrode during charging.
  • the manganese-doped element A' is selected from the above elements to help appropriately reduce the lattice change rate of the material during lithium insertion and extraction, improve the structural stability of the positive electrode material, reduce the dissolution of the manganese-site element and reduce the oxygen activity on the particle surface, thereby increasing the gram capacity of the material, and reducing the interface side reaction between the material and the electrolyte during use, thereby improving the cycle performance of the material, etc.;
  • the element E doped at the phosphorus position is selected from the above elements to help change the difficulty of the Mn-O bond length change, thereby improving the electronic conductivity and reducing the lithium ion migration barrier, promoting lithium ion migration, and improving the rate performance and fast charging performance; similarly, the element M3 doped at the lithium position is selected from the above elements to help improve the lattice change rate of the material and maintain the capacity of the material.
  • the positive electrode active material can have better performance.
  • the selection of the above doping elements and the values of x, n, y and z can also keep Li 1+x M 3n Mn 1-y A′ y P 1-z E z O 4 electrically neutral, and maintaining electrical neutrality can ensure that the The defects and impurities in the positive electrode active material are minimized.
  • transition metal such as manganese
  • the excess transition metal is likely to precipitate in the form of a single substance or form an impurity phase inside the lattice due to the relatively stable structure of the material system itself. Maintaining electrical neutrality can minimize such impurities.
  • ensuring the electrical neutrality of the system can also generate lithium vacancies in the positive electrode active material in some cases, thereby making the kinetic performance of the positive electrode active material more excellent.
  • existing materials such as lithium manganese phosphate, lithium iron phosphate, and lithium manganese iron phosphate that can be applied to high-voltage systems, it is more conducive to obtaining better cycle performance and high-temperature stability, as well as larger gram capacity and larger compaction density.
  • the manganese site only represents the position of the manganese element or the A' element in the lattice of the positive electrode active material Li1 + xM3nMn1 - yA'yP1- zEzO4 , but does not mean that there must be a manganese element in the manganese site.
  • the manganese element on the manganese site can be partially or completely replaced by the A' element.
  • the second positive electrode active material Li1 + xM3nMn1 - yA'yP1 - zEzO4 does not contain manganese elements.
  • the manganese site may include iron elements or iron elements and other doping elements at the same time.
  • E in the second positive electrode active material Li 1+x M 3n Mn 1-y A′ y P 1-z E z O 4 , E may include one or more elements of B, Si, N and S.
  • A′ in the second positive electrode active material Li 1+x M 3n Mn 1-y A′ y P 1-z E z O 4 , A′ may include one or more elements of Fe, Ti, V and Mg.
  • A′ may be Fe element; further optionally, A′ may be at least two elements selected from Fe, Ti, V and Mg; further optionally, A′ may be Fe element and one or more elements selected from Ti, V and Mg.
  • the second positive electrode active material Li 1+x M 3n Mn 1-y A′ y P 1-z E z O 4 can be doped at the manganese position and the phosphorus position at the same time, thereby not only effectively reducing the dissolution of the manganese element, thereby reducing the manganese ions that migrate to the negative electrode, reducing the electrolyte consumed by the decomposition of the SEI film, and improving the cycle performance and safety performance of the battery, but also promoting the adjustment of the Mn-O bond, reducing the lithium ion migration barrier, promoting lithium ion migration, and improving the rate performance and fast charging performance.
  • doping can also be performed at the lithium position, manganese position and phosphorus position at the same time, thereby further obtaining significantly improved rate performance, improved cycle performance and/or high temperature stability.
  • the numerical range of the stoichiometric number of the element of the corresponding doping site in the chemical formula is not only a limitation on the stoichiometric number of each element as the site, but also a limitation on the sum of the stoichiometric numbers of each element as the site.
  • the numerical range of the stoichiometric number of the element of the corresponding doping site in the chemical formula is not only a limitation on the stoichiometric number of each element as the site, but also a limitation on the sum of the stoichiometric numbers of each element as the site .
  • the stoichiometric numbers y 1 , y 2 ...y n of A 1 ′, A 2 ′ ...A n ′ shall each fall within the numerical range of y defined in the present application, and the sum of y 1 , y 2 ...y n shall also fall within the numerical range.
  • the numerical range of the stoichiometric numbers of M 3 and E defined in the present application also has the above meaning.
  • the value of may be 0.005, 0.01, 0.02, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, etc., or may be a range consisting of any of the above values; optionally, Alternatively, By controlling the molar number of A' element, Ni element, Mn element and the positive electrode sheet resistance to meet the given range, good fast charging capability, high energy density and good cycle performance can be further guaranteed.
  • the positive electrode sheet also satisfies: Where n (P) is the molar amount of phosphorus element P in the positive electrode, in mol.
  • the value of can be 0.2 , 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1.0, 1.05, 1.15, 1.2 , 1.25, 1.3, 1.35, 1.4, 1.45, etc., or can be a range consisting of any of the above values.
  • the first positive electrode active material Li a Ni b Co c M 1d M 2e O f R′ g has a higher specific capacity and better conductivity.
  • the first positive electrode active material Li a Ni b Co c M 1d M 2e O f R′ Increasing the Ni content in g helps to improve the battery energy density, but too high a content will damage the cycle performance; the content of the A′ element in the second positive electrode active material affects the voltage platform and cycle performance of the material.
  • a high content of the A′ element helps to improve the cycle performance, but the platform voltage will have a significant loss, which is not conducive to the battery energy density.
  • a low content of the A′ element helps to improve the platform voltage, but the material cycle performance will deteriorate.
  • Selecting a suitable content range is beneficial for the second positive electrode active material to take into account both a higher platform voltage and better cycle performance. For example, as a specific example, when the manganese position contains both manganese and iron elements, a higher manganese-iron ratio can increase the voltage platform, which is beneficial to improving the energy density of the battery.
  • the content of Ni element in the positive electrode sheet is provided by the first positive electrode active material
  • the phosphorus element is provided by the second positive electrode active material
  • the Mn element and the A' element can be provided by the first positive electrode active material and/or the second positive electrode active material.
  • the value of is within the given range, which can not only make the first positive electrode active material and the second positive electrode active material have a suitable blending ratio, but also make the second positive electrode active material have a suitable A' element content range, and obtain better cycle performance. Therefore, it can further take into account higher energy density and better cycle performance on the basis of widening the rate tolerance boundary at high and low SOC of the battery and improving the fast charging capability. Optionally, This can further improve the fast charging performance while taking into account higher energy density and better cycle performance.
  • the molar amount of each element in the positive electrode sheet can be obtained by ICP testing. For example, it can be performed by the following operation: take about 0.4g (accurate to 0.0001g) of dry positive electrode sheet or 0.1g (accurate to 0.0001g) of wet positive electrode sheet in a 30ml digestion tank, retain one digestion tank without sample as a blank sample, move the digestion tank containing the positive electrode sample into the fume hood and add 12ml of reverse aqua regia.
  • start digestion (digestion program: heat to 120°C for 6min and hold for 8min, heat to 160°C for 5min and hold for 8min, heat to 180°C for 5min and hold for 5min), cool to room temperature and take out after completion, place the digestion tank in a fume hood, slowly unscrew the nut to release the air, remove the previously installed parts one by one, transfer the solution in the digestion tank to a 100ml volumetric flask through a funnel (filter paper is required), then rinse the digestion tank with ultrapure water, and transfer the rinse liquid to the volumetric flask, use 10ml of ultrapure water for each rinse, shake the solution in the 100ml volumetric flask, use a pipette to take 1ml of the shaken solution and add it to another 100ml volumetric flask, then add ultrapure water to make up the volume (the solution reaches 100ml in total), and finally use ICP-OES to test the sample solution.
  • start digestion heat to 120°C for 6min and hold for
  • the concentrated nitric acid can be purchased from the market in the form of a concentrated nitric acid solution with a mass fraction of 68%
  • the concentrated hydrochloric acid can be purchased from the market in the form of a concentrated hydrochloric acid with a mass fraction of 68%
  • hydrogen chloride gas and ultrapure water can be added to ultrapure water in a mass proportion of 68% and 32% respectively, and the required concentrated hydrochloric acid can be obtained after complete dissolution.
  • the positive electrode sheet resistance can be tested at room temperature using a BER1300 diaphragm resistor meter, and the test steps can be as follows: (1) prepare the electrode sheet into a disc with a diameter of 22 mm; (2) place the prepared disc on the test platform of the BER1300 instrument; (3) adjust the machine test pressure to 0.4 tons, adjust the test time to 10 seconds, and start the test.
  • the obtained resistance value is the diaphragm resistance.
  • the second positive electrode active material may include one or more of the positive electrode active materials of the lithium manganese phosphate system, the lithium iron phosphate system, the lithium manganese iron phosphate system, etc. , which meet the above general formula Li1 +xM3nMn1 - yA′yP1 - zEzO4 .
  • the second positive electrode active material is Li 1+x Mn 1-y A′ y P 1-z E z O 4 , that is, lithium manganese phosphate or lithium manganese phosphate doped with at least one of the lithium site, manganese site and phosphorus site, wherein the modification of the lithium manganese phosphate in the present application can significantly reduce
  • the dissolution of manganese elements and the reduced lattice change rate are more conducive to improving the battery's cycle performance, rate performance, safety performance and increasing the battery's capacity when used in secondary batteries.
  • Li 1+x Mn 1-y A′ y P 1-z E z O 4 may include Li 1+x Mn 1- y Fe y P 1-z E z O 4.
  • lithium manganese iron phosphate has a higher voltage platform and a higher energy density when the specific capacity is the same; (iii) 0.001 ⁇ y ⁇ 0.500, 0.9 ⁇ n ⁇ 1.1, in which case the second positive electrode active material is Li 1+x M 3n Mn 1-y A′ y P 1-z E z O 4.
  • the value of y will limit the total amount of all doping elements, if y is too small, that is, the doping amount is too little, the doping element will not work, if y exceeds 0.5, it will lead to a small Mn content in the system, affecting the voltage platform of the material, and the value range of y can be selected from 0.001 to 0.500, and then from 0.25 to 0.5.
  • the stoichiometric numbers of the elements located at the same site can be the same or different, but all meet the numerical range of the stoichiometric number of each element in the chemical formula Li 1+x M 3n Mn 1-y A′ y P 1-z E z O 4 .
  • the second positive electrode active material may only include positive electrode active materials with chemical formula Li 1+x A′P 1-z E z O 4 and/or chemical formula Li 1+x Mn 1-y A′ y P 1-z E z O 4 , in which the values of x and z are independent of each other, but both satisfy the numerical range specified for the stoichiometric numbers of x and z in the chemical formula Li 1+x M 3n Mn 1-y A′ y P 1-z E z O 4 .
  • the second positive electrode active material has a discharge platform, and the discharge voltage of at least one discharge platform is not lower than the discharge cut-off voltage of the first positive electrode active material, and is not higher than 3.5V.
  • the specific stoichiometric ratio of the positive electrode active material Li 1+x M 3n Mn 1-y A′ y P 1-z E z O 4 is different, and its discharge platform may also change.
  • the second positive electrode active material is lithium iron phosphate
  • the second positive electrode active material is lithium manganese phosphate doped with manganese, such as lithium manganese iron phosphate
  • the present application by further making the second positive electrode active material have a voltage platform not higher than 3.5V, it can be further ensured that after the first positive electrode active material and the second positive electrode active material are mixed, the platform can be used to alleviate the polarization in the previous discharge process, broaden the rate tolerance boundary at high and low SOC, thereby improving the fast charging capability, taking into account the cycle performance, and improving the actual available capacity.
  • the molar amount of Ni element n (Ni) (in mol) in the positive electrode sheet satisfies: 0.0005 ⁇ n (Ni) ⁇ 0.0025, for example, n (A′) can be 0.0008, 0.001, 0.0012, 0.0014, 0.0016, 0.0018, 0.002, 0.0022, 0.0024, etc., or can be a range consisting of any of the above values; Optionally, 0.0007 ⁇ n (Ni) ⁇ 0.0016.
  • the Ni element is provided by the first positive electrode active material. The increase in the Ni element content in the first positive electrode active material helps to improve the battery energy density, but will damage the cycle performance.
  • the battery can further have both higher energy density and better cycle performance.
  • the molar amount of the Mn element n (Mn) (unit: mol) in the positive electrode sheet satisfies: 0.0005 ⁇ n (Mn) ⁇ 0.0025, for example, n (Mn) can be 0.0007, 0.001, 0.0013, 0.0015, 0.0018, 0.002, 0.0021, 0.0023, etc., or can be a range composed of any of the above values; optionally, 0.0009 ⁇ n (Mn) ⁇ 0.0016.
  • n (A') (in mol) of the A' element in the positive electrode sheet satisfies the following conditions: 0.00005 ⁇ n (A') ⁇ 0.0015, for example, n (A') can be 0.00008, 0.0001, 0.0002, 0.0003, 0.0004, 0.0005, 0.0006, 0.0007, 0.0008, 0.0009, 0.001, 0.0012, 0.0014, etc., or can be a range composed of any of the above values; Optionally, 0.0002 ⁇ n (A') ⁇ 0.0006.
  • the high energy density and good cycle performance of the battery can be further guaranteed.
  • the resistance R (in ⁇ ) of the positive electrode sheet satisfies: 0 ⁇ R ⁇ 1.3
  • the value of R can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, etc., or can be a range composed of any of the above values.
  • too high resistance of the positive electrode sheet will also affect the power performance and cycle performance of the battery
  • by controlling the value range of R within the given range it can be further beneficial to make the positive electrode sheet and the battery have better fast charging performance and cycle performance.
  • 0 ⁇ R ⁇ 1 by further controlling the value range of R within the given range, the internal resistance of the battery can be further reduced, and the fast charging performance and cycle performance can be improved.
  • the molar amounts of the Mn element and the A' element in the positive electrode sheet satisfy the following conditions:
  • the value of can be 0.03, 0.05, 0.07, 0.09, 0.1, 0.3, 0.5, 0.7, 0.9, 1.1, 1.3, 1.5, 1.7, 1.9, etc., or can be a range composed of any of the above values.
  • the content of the A' element in the second positive electrode active material affects the voltage platform and cycle performance of the material. A high content of the A' element helps to improve the cycle performance, but the platform voltage will have a significant loss, which is not conducive to the battery energy density.
  • the first positive electrode active material may be a positive electrode active material of an NCM system, Li a Ni b Co c Mn d M 2e Of R′ g , such as Li a Ni b Co c Mn d Of R′ g
  • the second positive electrode active material may be a lithium manganese iron phosphate positive electrode active material doped with manganese, Li 1+x Mn 1-y A′ y P 1-z E z O 4 (0.001 ⁇ y ⁇ 0.500), such as Li 1+x Mn 1-y Fe y P 1-z E z O 4 .
  • the value range of can be 0.02-2.0, optionally 0.05-0.8, and further optionally 0.17-0.69, wherein the width of the voltage platform of the second positive electrode active material Li1 +xMn1 -yA′yP1 - zEzO4 at the end of discharge (not more than 3.5V) in the entire discharge curve is positively correlated with the stoichiometry of the A′ element in the material, and the high voltage platform can improve the energy density of the corresponding battery.
  • a high A′ content is conducive to improving the cycle performance, but the platform voltage will have a significant loss, which is not conducive to the battery energy density.
  • a low A content is conducive to improving the platform voltage, but the material cycle performance will deteriorate.
  • the value of is within the given range, which can not only further make the first positive electrode active material and the second positive electrode active material have a suitable blending ratio, but also make the second positive electrode active material have a suitable A' element content range, thereby obtaining better cycle performance, thereby further taking into account higher energy density and better cycle performance on the basis of improving fast charging capability.
  • the microelectrode is a Pt
  • the single-particle microelectrode test device mainly includes a microelectrode, a microscope, a micromanipulator and an electrochemical workstation. The microelectrode is moved by the microscope and the micromanipulator to make it contact with a single particle of the second active material.
  • the particle to be tested is used as the working electrode, and the lithium strip is used as the counter electrode and the reference electrode for electrochemical testing.
  • the charging current decreases to 0.05C
  • the constant voltage charging is terminated, and then 0.33C is discharged to a full discharge voltage of 2.5V.
  • the specific capacity-voltage curve of the discharge process is taken, with the specific capacity as the X-axis and the voltage as the Y-axis.
  • the charging capacity at 3.5V is recorded as Q3
  • the coating mass of the positive electrode active material layer can be 15.50 mg/cm 2 to 20.78 mg/cm 2 , for example, 16.0 mg/cm 2 , 16.50 mg/cm 2 , 17.0 mg/cm 2 , 17.50 mg/cm 2 , 18.0 mg/cm 2 , 18.50 mg/cm 2 , 19.0 mg/cm 2 , 19.50 mg/cm 2 , 20.0 mg/cm 2 , 20.5 mg/cm 2 , etc., or can be a range consisting of any of the above values; optionally, the coating mass of the positive electrode active material layer is 16.80 mg/cm 2 ⁇ 18.83mg/ cm2 .
  • the coating quality of the positive electrode active material layer is too low, on the one hand, it is not conducive to the improvement of the battery energy density, and on the other hand , the polarization of the pole piece will be significantly improved.
  • the improvement effect of mixing the second positive electrode active material Li1+xM3nMn1-yA′yP1-zEzO4 in the first positive electrode active material LiaNibCocM1dM2eOfR′g is not obvious, and when the coating quality of the positive electrode active material layer is too high, it will cause the degree of increase in the polarization of the pole piece to exceed the improvement effect of mixing Li1 + xM3nMn1 - yA′yP1 - zEzO4 , affecting the rate performance and fast charging performance.
  • the fast charging performance of the battery can be further improved, while taking into account both the energy density and the cycle performance.
  • the compaction density of the positive electrode active material layer is 2.4 g/cm 3 to 3.40 g/cm 3 , for example, 2.5 g/cm 3 , 2.6 g/cm 3 , 2.7 g/cm 3 , 2.8 g/cm 3 , 2.9 g/cm 3 , 3.0 g/cm 3 , 3.1 g/cm 3 , 3.2 g/cm 3 , 3.3 g/cm 3 , etc., or can be a range consisting of any of the above values.
  • the compaction density of the active material layer of the positive electrode sheet can be measured according to GB/T 24533-2009.
  • the compaction density of the positive electrode active material layer in the positive electrode sheet is too small, it is easy to cause loose contact between particles inside the electrode sheet and increase the contact resistance; while if the compaction density of the positive electrode active material layer in the positive electrode sheet is too large, it will lead to two problems. First, it is easy to cause some particles inside the electrode sheet to break/produce cracks after cold pressing. The broken particles/cracks are easy to react with the electrolyte to cause battery performance degradation. When the battery is cycled, due to the high internal pressure of the electrode sheet, the mutual compression between particles is also easy to cause particle breakage; second, the porosity of the electrode sheet decreases, and the difficulty of electrolyte infiltration increases, which is easy to cause battery performance degradation.
  • the compaction density of the active material layer of the positive electrode sheet can be 2.6g/ cm3 ⁇ 3.25g/ cm3 , which can further improve the battery cycle performance and long-term use performance.
  • the Dv50 particle size of the first positive electrode active material is 2.1 ⁇ m to 6.3 ⁇ m, for example, it can be 2.4 ⁇ m, 2.7 ⁇ m, 3.0 ⁇ m, 3.3 ⁇ m, 3.6 ⁇ m, 3.9 ⁇ m, 4.2 ⁇ m, 4.5 ⁇ m, 4.8 ⁇ m, 5.1 ⁇ m, 5.4 ⁇ m, 5.7 ⁇ m, 6.0 ⁇ m, etc., or it can be a range composed of any of the above values.
  • the Dv50 of the first positive electrode active material refers to the particle size corresponding to the cumulative volume distribution percentage of the first positive electrode active material reaching 50%.
  • the Dv50 particle size of the first positive electrode active material can be measured by laser diffraction particle size analysis, for example, with reference to the standard GB/T19077-2016, using a laser particle size analyzer (such as Malvern Master Size 3000) for measurement.
  • a laser particle size analyzer such as Malvern Master Size 3000
  • the Dv50 particle size of the first positive electrode active material within the given range, it is not only beneficial to prevent it from breaking or pulverizing during the charge and discharge process, thereby reducing the capacity loss of the battery, but also can shorten the diffusion path of active ions and increase the conduction rate of electrons, which is beneficial to improving the cycle performance of the battery; at the same time, it can also enable the active material to have suitable active sites, reduce or avoid the increase of side reactions of the material during the cycle due to too small particle size, which has a greater negative impact on the cycle performance, and the increase of active sites due to too large particle size, which has a greater negative impact on the power performance.
  • controlling the Dv50 particle size of the first positive electrode active material within the given range can further ensure that the battery has a higher energy density.
  • the Dv50 particle size of the first positive electrode active material can be It is 3.5 ⁇ m ⁇ 4.9 ⁇ m, which can further take into account high energy density, good power performance and cycle performance, and improve fast charging capability and service life.
  • the Dv50 particle size of the second positive electrode active material may be 0.25 ⁇ m to 1.49 ⁇ m, for example, 0.3 ⁇ m, 0.4 ⁇ m, 0.5 ⁇ m, 0.6 ⁇ m, 0.7 ⁇ m, 0.8 ⁇ m, 0.9 ⁇ m, 1.0 ⁇ m, 1.1 ⁇ m, 1.2 ⁇ m, 1.3 ⁇ m, 1.4 ⁇ m, etc., or may be a range consisting of any of the above values.
  • the Dv50 of the second positive electrode active material refers to the particle size corresponding to the cumulative volume distribution percentage of the second positive electrode active material reaching 50%.
  • the Dv50 particle size of the second positive electrode active material can be measured by laser diffraction particle size analysis, for example, with reference to standard GB/T19077-2016, using a laser particle size analyzer (such as Malvern Master Size 3000) for measurement.
  • a laser particle size analyzer such as Malvern Master Size 3000
  • controlling the Dv50 particle size of the second positive electrode active material within the given range it is not only beneficial to prevent it from breaking or pulverizing during the charge and discharge process, thereby reducing capacity loss, but also can shorten the diffusion path of active ions and increase the conduction rate of electrons, which is beneficial to improving the cycle performance; at the same time, it can also make the active material have suitable active sites, while taking into account the cycle performance and power performance; and, controlling the Dv50 particle size of the second positive electrode active material within the given range is also beneficial to match the Dv50 particle size range of the first positive electrode active material to achieve the expected compaction density, avoiding large gaps between the positive electrode active material particles.
  • the Dv50 particle size of the second positive electrode active material can be 0.5 ⁇ m to 0.9 ⁇ m, thereby further taking into account high energy density, good power performance and cycle performance, and improving fast charging capability and service life.
  • the specific surface area of the first positive electrode active material is 0.3m 2 / g to 1.2m 2 /g, for example, it can be 0.4m 2 / g, 0.5m 2 /g, 0.6m 2 /g, 0.7m 2 /g, 0.8m 2 / g, 0.9m 2 /g, 1.0m 2 / g, 1.1m 2 /g, etc., or it can be a range consisting of any of the above values; optionally, the specific surface area of the first positive electrode active material is 0.5m 2 /g to 0.9m 2 /g.
  • the specific surface area of the second positive electrode active material can be 9.0m2 /g to 23.2m2 /g, for example, 10m2 /g, 11m2 /g, 12m2 /g, 13m2 /g, 14m2 /g, 15m2 / g, 16m2 /g, 17m2 /g, 18m2 /g, 19m2 /g, 20m2 /g, 21m2 /g, 22m2 /g, etc., or can be a range consisting of any of the above values; optionally, the specific surface area of the second positive electrode active material can be 10.5m2 /g to 17.9m2 /g.
  • the specific surface areas of the first and second positive electrode active materials can be measured by conventional methods in the art, such as nitrogen physical adsorption method.
  • the increase in specific surface area helps to increase the active sites of the positive electrode active material, so that the material has better power performance, but these increased active sites will also increase the side reactions of the positive electrode active material during the cycle process, thereby causing the material's cycle performance to decay.
  • by controlling the specific surface area of the first positive electrode active material and the second positive electrode active material within the given range better power performance and cycle life can be further obtained, and the fast charging capability and service life can be improved.
  • a first coating layer may be provided on the surface of the first positive electrode active material.
  • the first coating layer may include one or more elements selected from Ti, Al, B, Nb, Zr, Si and W.
  • Providing a coating layer on the surface of the positive electrode active material can not only prevent the positive electrode active material from contacting with the electrolyte, thereby reducing the side reaction between the positive electrode active material and the electrolyte, but also improve the stability of the structure of the positive electrode active material, thereby improving the cycle stability and safety of the material.
  • the above elements in the first coating layer can be in the form of oxides (such as Al 2 O 3 , ZrO 2 , TiO2 , Nb2O3 , etc.
  • the first coating layer contains the above-given element range to enhance the material surface ion conductivity, improve the material rate performance and gram capacity, stabilize the material structure, avoid direct contact between the material and the electrolyte, and improve the cycle performance.
  • the thickness of the first coating layer can be 20nm to 150nm, for example, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 110nm, 120nm, 130nm, 140nm, etc., or can be a range composed of any of the above values.
  • the coating layer is sintered, the coating material will react with the lithium in the internal material, resulting in a reduction in the available active lithium in the material, and the corresponding material gram capacity is reduced.
  • the thickness of the first coating layer within the above-mentioned range, the above problems can be effectively avoided or reduced, and the rate performance of the first positive electrode active material can be effectively improved, and the surface structure of the material can be stabilized.
  • a second coating layer may be provided on the surface of the second positive electrode active material.
  • the provision of the second coating layer can not only prevent the second positive electrode active material from contacting with the electrolyte, thereby reducing the side reaction between the second positive electrode active material and the electrolyte, but also avoid or inhibit the dissolution of transition metals or doping elements in the second positive electrode active material, while improving its structural stability, thereby improving the cycle stability and safety of the positive electrode active material.
  • the second coating layer may include at least one of pyrophosphate, phosphate and carbon.
  • metal ions are difficult to migrate in pyrophosphate, and selecting pyrophosphate as the coating layer material can effectively isolate the metal ions doped in the positive electrode material from the electrolyte; further, the pyrophosphate can be selected as a crystalline pyrophosphate, and the structure of the crystalline pyrophosphate is stable.
  • As a coating layer material it can effectively inhibit the dissolution of transition metals in the active material and improve the cycle performance.
  • Phosphate coating can improve the ion transport performance of the positive electrode material, which is conducive to promoting the transmission of lithium ions; further, the phosphate can be a crystalline phosphate.
  • the crystalline phosphate and the crystalline pyrophosphate have a high lattice matching degree, good stability and excellent lithium ion conductivity.
  • Using them to coat the second positive electrode active material can improve the stability of the positive electrode active material, effectively reduce the interface side reactions of the electrolyte, and thus improve the high-temperature cycle and storage performance of the battery.
  • Carbon coating can effectively improve the conductivity and desolvation ability of the positive electrode active material.
  • Carbon materials have good electronic conductivity. When used in batteries, electrochemical reactions occur, which require the participation of electrons. In order to increase the electron transmission between particles and the electron transmission at different positions of particles, carbon with excellent conductivity can be used to coat the positive electrode active material.
  • the pyrophosphate, phosphate and carbon can be located in the same coating layer or in at least two sub-coating layers.
  • a pyrophosphate coating layer, a phosphate coating layer and a carbon coating layer can be formed in sequence on the surface of the second positive electrode active material, or a phosphate coating layer, a pyrophosphate coating layer and a carbon coating layer can be formed in sequence on the surface of the second positive electrode active material.
  • a composite coating layer of pyrophosphate and phosphate can be first formed on the surface of the second positive electrode active material, and then a carbon coating layer can be formed on the surface of the composite coating layer.
  • the thickness of the second coating layer may be 10 nm to 50 nm.
  • it may be 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, etc., or it may be a range composed of any of the above values.
  • Controlling the thickness of the second coating layer within the given range can not only effectively hinder the dissolution of transition metals or doping elements in the second positive electrode active material, and reduce the lattice change rate of the second positive electrode active material, but also avoid the coating thickness being too large to affect the migration of lithium ions and the energy density of the battery, thereby further improving the battery's kinetic performance, cycle performance and safety without sacrificing the gram capacity of the second positive electrode active material.
  • the second coating layer may include a first sub-coating layer, a second sub-coating layer and a third sub-coating layer
  • the first sub-coating layer may coat the second positive electrode active material and include crystalline pyrophosphate
  • the second sub-coating layer may include crystalline phosphate and coat the first sub-coating layer
  • the third sub-coating layer may be carbon and coat the second sub-coating layer.
  • Pyrophosphate as the first sub-coating layer can effectively isolate the metal ions doped in the second positive electrode active material from the electrolyte, and the crystalline pyrophosphate coating can effectively inhibit the dissolution of transition metals in the second positive electrode active material and improve the cycle performance;
  • the crystalline phosphate as the second sub-coating layer has a high lattice matching degree with the crystalline pyrophosphate in the first sub-coating layer, and has better stability than pyrophosphate and has excellent lithium ion conductivity, which is beneficial to improve the stability of the positive electrode active material and reduce the interface side reaction between the positive electrode active material and the electrolyte;
  • the third sub-coating layer can enhance the electron transport between particles, improve the electronic conductivity of the positive electrode active material, and effectively improve the conductivity and desolvation ability of the positive electrode active material.
  • the thickness of the first sub-coating layer can be 1nm to 10nm, such as 3nm, 4nm, 5nm, 6nm, 7nm, 8nm, 9nm, etc., or within any range of the above-mentioned arbitrary numerical values.
  • the thickness of the first sub-coating layer When the thickness of the first sub-coating layer is within the given range, it can avoid the adverse effect on the kinetic properties of the positive electrode active material that may be caused by being too thick, and can avoid the problem that the migration of transition metal ions may not be effectively hindered when it is too thin; the thickness of the second sub-coating layer can be 2nm to 15nm, such as 3nm, 4nm, 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, 11nm, 12nm, 13nm, 14nm, etc., or within any range of the above-mentioned arbitrary numerical values. The thickness of the second sub-coating layer is too large and may cause Affects the platform voltage of the overall positive electrode active material.
  • the thickness of the second sub-coating layer When the thickness of the second sub-coating layer is within the given range, its surface structure is stable, the side reaction with the electrolyte is small, and the interface side reaction can be effectively reduced, thereby improving the high-temperature cycle performance and high-temperature storage performance of the battery;
  • the thickness of the third sub-coating layer can be 2nm to 25nm, such as 4nm, 6nm, 8nm, 10nm, 12nm, 14nm, 16nm, 18nm, 20nm, 22nm, 24nm, etc., or within any range of any of the above values.
  • the thickness of the third sub-coating layer When the thickness of the third sub-coating layer is within the given range, it can improve the conductivity of the positive electrode active material and the compaction density of the positive electrode sheet, while avoiding the problem of affecting the compaction density of the sheet due to excessive coating thickness when the sub-coating layer contains amorphous carbon.
  • the thickness test of each coating layer can be carried out by FIB, and the specific method may include the following steps: randomly selecting a single particle from the positive electrode active material powder to be tested, cutting a thin slice with a thickness of about 100nm from the middle position or near the middle position of the selected particle, and then performing TEM testing on the thin slice, measuring the thickness of the coating layer, measuring 3 to 5 positions, and taking the average value.
  • the second aspect of the present application provides a secondary battery, which includes: the positive electrode sheet of the first aspect of the present application.
  • a shell assembly In a secondary battery, a shell assembly, a positive electrode sheet, a negative electrode sheet, a diaphragm, and an electrolyte are generally included.
  • the positive electrode sheet, the negative electrode sheet, the diaphragm, and the electrolyte are located in a receiving cavity formed by the shell assembly.
  • the shell assembly may be an aluminum-plastic film or a metal shell assembly, and the metal shell assembly may include a square shell assembly and a cylindrical shell assembly.
  • the shell assembly is a metal shell assembly, it generally includes a shell having an opening on at least one side and a cover for sealing the opening.
  • positive electrode sheet includes the positive electrode sheet of the first aspect of the present application, it can be understood as being included in the technical scope of the battery of the fourth aspect of the present application.
  • other structural features or material selection of the positive electrode sheet, as well as the selection of the negative electrode sheet, the diaphragm, and the electrolyte can adopt conventional selections in the art, and those skilled in the art can flexibly select according to actual needs.
  • the secondary battery can be either a laminated battery or a wound battery
  • the wound battery can be either a square battery or a cylindrical battery.
  • the battery can be a cylindrical battery.
  • the positive electrode sheet, the negative electrode sheet and the separator can be stacked to form a laminated unit, or can be stacked and then wound to form a wound body.
  • the battery may be a single cell or a battery module assembled from cells.
  • the battery module may include multiple cells, and the specific number may be adjusted according to the application and capacity of the battery module.
  • the battery module may also include a packaging assembly with a receiving space, and the packaging assembly may include a bottom plate, a side plate, a cover plate, etc.
  • the above-mentioned battery modules may also be assembled into a battery pack, and the number of battery modules contained in the battery pack may be adjusted according to the application and capacity of the battery pack.
  • the present application also provides an electrical device, which includes: the positive electrode sheet of the first aspect of the present application, and/or the secondary battery of the second aspect of the present application.
  • the secondary battery such as a battery cell, a battery module or a battery pack, can be used as a power source for the electrical device or as an energy storage unit for the electrical device.
  • the electrical device may include, but is not limited to, mobile devices (such as mobile phones, laptop computers), 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, and energy storage systems.
  • the electrical device may be a vehicle.
  • the electrical device can select the specific type of battery according to its usage requirements, such as battery cells, battery modules or battery packs.
  • 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 electrical device may be a mobile phone, a tablet computer, or a laptop computer.
  • the electrical device is usually required to be thin and light, and may use a battery cell as a power source.
  • the positive electrode active material, polyvinylidene fluoride (PVDF) and conductive carbon are added to a certain amount of N-methylpyrrolidone (NMP), and the mass ratio of the positive electrode active material: polyvinylidene fluoride: conductive carbon is 90:5:5.
  • NMP N-methylpyrrolidone
  • the mixture is stirred in a drying room to form a uniform slurry with a viscosity controlled at 3000-10000 mPa ⁇ S.
  • the slurry is coated on an aluminum foil and dried to form a positive electrode sheet.
  • Graphite, sodium carboxymethyl cellulose (CMC), styrene butadiene rubber (SBR), and conductive carbon are added to a certain amount of deionized water, with the mass ratio of graphite: sodium carboxymethyl cellulose: styrene butadiene rubber: conductive carbon being 90:2:3:5, and stirred to form a uniform slurry with a viscosity controlled at 3000-10000 mPa ⁇ S.
  • the slurry is coated on a copper foil and dried to form a negative electrode sheet.
  • the prepared positive electrode sheet, negative electrode sheet and separator are made into corresponding battery cells according to the Z-shaped stacking structure, and the battery cells are vacuum dried at 90°C for 12 hours, and then the positive and negative electrode tabs are ultrasonically welded.
  • the positive electrode uses aluminum tabs and the negative electrode uses nickel tabs.
  • the positive and negative electrode tabs are located on the same side of the battery cell.
  • the battery cell after the tab welding is loaded into an aluminum-plastic film of appropriate size for top-side packaging.
  • the conventional packaging temperature is 145°C, and the electrolyte is injected (the electrolyte is 1 mol/L LiPF6/(ethylene carbonate (EC) + diethyl carbonate (DEC) + dimethyl carbonate (DMC)) (volume ratio 1:1:1) + 5wt.% fluoroethylene carbonate (FEC)), let it stand, form, age, exhaust, double seal, and capacity test to obtain the prepared soft-pack stacked battery.
  • the electrolyte is 1 mol/L LiPF6/(ethylene carbonate (EC) + diethyl carbonate (DEC) + dimethyl carbonate (DMC)) (volume ratio 1:1:1) + 5wt.% fluoroethylene carbonate (FEC)
  • the diaphragm resistance is tested using a BER1300 diaphragm resistance meter.
  • the test steps are as follows: (a) prepare the electrode into a disc with a diameter of 22 mm; (b) place the prepared disc on the test platform of the BER1300 instrument; (c) adjust the machine test pressure to 0.4 T, the test temperature to 25 ° C, and the test time to 10 s, and then start the test.
  • the obtained resistance value is the diaphragm resistance.
  • the capacity of the soft-pack laminated battery is tested.
  • the process is as follows: 0.33C constant current charging to the full charge voltage V1 is switched to constant voltage charging. When the charging current is reduced to 0.05C, the constant voltage charging ends. Then 0.33C discharge is performed to the full discharge voltage V2. This process is repeated 3 times, and the third capacity result is taken as the basis. At the same time, the third result can be used to calculate the positive electrode gram capacity.
  • the soft-pack laminated battery is subjected to charging tests at different rates (C 1 ⁇ C 2 ⁇ C 3 ⁇ C 4 ⁇ ... ⁇ C n ). During the test, the charging rate needs to be increased from small to large.
  • the full voltage of the soft-pack laminated battery and the negative electrode voltage of the soft-pack laminated battery need to be monitored simultaneously.
  • the detailed process is as follows: the soft-pack laminated battery is charged to the full charge voltage V1 or the negative electrode voltage is 0V according to C1 , the battery SOC value at the end of charging is extracted, and then 0.33C is discharged to the full discharge voltage V2, and the above process is repeated to obtain the SOC value at the end of charging at different rates.
  • Positive electrode sheet The number of positive electrode sheets is 15; the thickness of a single-layer positive electrode sheet is 0.13 mm; the compaction density of the active material layer of the positive electrode sheet is 3.1 g/cm 3 ; the first positive electrode active material is NCM523, the Dv50 particle size of the first positive electrode active material is 4.1 ⁇ m, and the specific surface area of the first positive electrode active material is 0.6 m 2 /g; the second positive electrode active material is LiMn 0.6 Fe 0.4 PO 4 , the Dv50 particle size of the second positive electrode active material is 0.83 ⁇ m, and the specific surface area of the second positive electrode active material is 12.5 m 2 /g; the positive electrode sheet satisfies: A′ is Fe, The electrode resistance is 0.1 ⁇ .
  • Negative electrode sheet The number of layers of the negative electrode sheet is 16; the thickness of a single-layer negative electrode sheet is 0.13 mm; and the compaction density of the active material layer of the negative electrode sheet is 1.68 g/cm 3 .
  • Diaphragm The number of diaphragm layers is 16; the thickness of a single-layer diaphragm is 0.011 mm.
  • the inner thickness of the battery housing is 5.9 mm;
  • the filling coefficient of the secondary battery is 2.73 g/Ah.
  • Example 2 to 16 and Comparative Examples 1 to 4 and Example 1 The difference between Examples 2 to 16 and Comparative Examples 1 to 4 and Example 1 is that: The value of is different, which is achieved by changing the blending ratio of the first positive electrode active material and the second positive electrode active material in Examples 2 to 15 and Comparative Examples 1 to 4; and by changing the type of the second positive electrode active material in Example 16, as shown in Table 1 for details.
  • the battery design scheme of the present application can improve the cycle performance and fast charging performance of the battery.
  • the value range of is between 0.001 and 0.5
  • the cycle performance of the battery is relatively good, and the fast charging performance can also be improved.
  • the value can also be selected as 0.009 to 0.35.

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Abstract

本申请公开了正极片、二次电池和用电装置。其中，正极片包括正极活性物质层，正极活性物质层包括第一正极活性材料和第二正极活性材料，第一正极活性材料包括LiaNibCocM1dM2eOfR'g，0.75≤a≤1.2，0<b<1，0<c<1，0<d<1，0≤e≤0.2，1≤f≤2.5，0≤g≤1，f+g≤3，M1为Mn元素和/或Al元素；第二正极活性材料包括Li1+xM3nMn1-yA'yP1-zEzO4，-0.100≤x≤0.100，0≤n≤1.1，0.001≤y≤1，0≤z≤0.100，A'包括Zn、Al、Na、K、Mg、Mo、W、Ti、V、Zr、Fe、Ga、Sn、Sb、Nb和Ge中的一种或多种元素；正极片满足：0.001≤n(A')R/(n(Ni)+n(Mn)+n(A') )≤0.50，其中：n(A')、n(Ni)、n(Mn)依次为正极片中A'、Ni、Mn的摩尔量，单位为mol；R为正极片在25℃下的电阻，单位为Ω。

Description

正极片、二次电池和用电装置 技术领域
本申请属于电池技术领域，具体而言，涉及正极片、二次电池和用电装置。
背景技术
锂离子电池具有绿色、环保、高能、低碳等特点，不仅被应用于水力、火力、风力和太阳能电站等储能电源系统，还被广泛应用于电动自行车、电动摩托车、电动汽车等电动交通工具，以及军事装备和航空航天等多个领域。随着当前社会的发展，人们对于锂离子电池的要求也越来越高，快充性能和循环性能已经成为锂电池的重要能力指标。目前，锂离子电池正极材料多选用三元层状正极材料，如镍钴锰(NCM)体系材料，但常规NCM体系材料在低电压处的倍率耐受边界较差，会影响电池的快充能力和实际可用容量。
公开内容
鉴于背景技术中存在的技术问题，本申请提供一种正极片，旨在拓宽正极活性材料高低电压处的倍率耐受边界，提高快充能力，同时保证循环性能。
为了实现上述目的，本申请的第一方面提供一种正极片，其中，所述正极片包括正极活性物质层，所述正极活性物质层包括第一正极活性材料和第二正极活性材料，
所述第一正极活性材料包括LiaNibCocM1dM2eOfR′g，其中，0.75≤a≤1.2，0<b<1，0<c<1，0<d<1，0≤e≤0.2，1≤f≤2.5，0≤g≤1，f+g≤3，M1为Mn元素和/或Al元素，M2包括Zr、Zn、Cu、Cr、Mg、Fe、V、Ti、Sr、Sb、Y、W、Nb中的一种或多种元素，R′包括N、F、S、Cl中的一种或多种元素；
所述第二正极活性材料包括Li1+xM3nMn1-yA′yP1-zEzO4，其中，-0.100≤x≤0.100，0≤n≤1.1，0.001≤y≤1，0≤z≤0.100，M3包括Zn、Al、Na、K、Mg、Nb、Mo和W中的一种或多种元素，A′包括Zn、Al、Na、K、Mg、Mo、W、Ti、V、Zr、Fe、Ga、Sn、Sb、Nb和Ge中的一种或多种元素，E包括B、Si、N、S、F、Cl和Br中的一种或多种元素；
所述正极片满足：
其中：n(A′)为所述正极片中A′的摩尔量，单位为mol；n(Ni)为所述正极片中Ni的摩尔量，单位为mol；n(Mn)为所述正极片中Mn的摩尔量，单位为mol；R为所述正极片在 25℃下的电阻，单位为Ω。
与现有技术相比，本申请第一方面的正极片至少具有以下有益效果：(1)LiaNibCocM1dM2eOfR′g正极活性材料体系在低SOC(荷电状态，即剩余电量)处倍率耐受边界较差，而Li1+xM3nMn1-yA′yP1-zEzO4在高SOC处倍率耐受边界较差，通过将二者复合使用，可以同时弥补两个体系的缺陷，拓宽高低SOC处倍率耐受边界，从而提升快充能力；(2)通过将正极活性材料LiaNibCocM1dM2eOfR′g与正极活性材料Li1+xM3nMn1-yA′yP1- zEzO4掺混，还可以进一步兼具较高的高能量密度和较好的循环性能；(3)通过控制正极片中A′元素、Ni元素、Mn元素的摩尔数以及正极片电阻满足上式范围，可以同时保证正极片的快充能力和循环性能，并有利于获得高能量密度。
在本申请的一些实施方式中，可选地，其中，n(P)为所述正极片中P的摩尔量，单位为mol。通过控制在所给范围内，可以进一步控制适宜的掺杂比例，在改善快充能力的基础上兼顾较高的能量密度和较好的循环性能。
在本申请的一些实施方式中，所述第二正极活性材料包括满足以下条件至少之一的正极活性材料：(i)y＝1，n＝0，所述第二正极活性材料为Li1+xA′P1-zEzO4，A′为Fe元素，或A′为Fe元素和包括Zn、Al、Na、K、Mg、Mo、W、Ti、V、Zr、Fe、Ga、Sn、Sb、Nb和Ge中的一种或多种元素；(ii)0.001≤y≤0.500，n＝0，所述第二正极活性材料为Li1+xMn1-yA′yP1-zEzO4；(iii)0.001≤y≤0.500，0.9≤n≤1.1，所述第二正极活性材料为Li1+xM3nMn1-yA′yP1-zEzO4，可选地，所述第二正极活性材料包括：(i)Li1+xA′P1-zEzO4；和/或，(ii)Li1+xMn1-yA′yP1-zEzO4。
在本申请的一些实施方式中，所述第二正极活性材料具有放电平台，至少一个所述放电平台的放电电压不低于所述第一正极活性材料的放电截止电压，且不高于3.5V。通过满足所给条件可以进一步提升快充能力，并兼顾循环性能。
在本申请的一些实施方式中，0.0005≤n(Ni)≤0.0025，0.0005≤n(Mn)≤0.0025，0.00005≤n(A′)≤0.0015。
在本申请的一些实施方式中，满足以下条件中的至少之一：0.0007≤n(Ni)≤0.0016、0.0009≤n(Mn)≤0.0016、0.0002≤n(A′)≤0.0006。
在本申请的一些实施方式中，0<R≤1.3，可选地，0<R≤1。通过控制R在所给范围内，可以进一步降低极片内阻，改善快充性能和循环性能。
在本申请的一些实施方式中，M1为Mn元素。
在本申请的一些实施方式中，可选地，再可选 地，通过控制在所给范围内，可以进一步改善快充能力，并兼顾较好的循环性能。
在本申请的一些实施方式中，可选地，通过控制n(A′)、n(Ni)、n(Mn)和R满足所给条件，可以进一步保证良好的快充能力和较好的循环性能。
在本申请的一些实施方式中，所述正极活性物质层的涂覆质量为15.50mg/cm2～20.78mg/cm2，可选为16.80mg/cm2～18.83mg/cm2。通过控制正极活性物质层的涂覆质量在所给范围内，可以进一步改善快充性能，同时能兼顾能量密度和循环性能。
在本申请的一些实施方式中，所述正极活性物质层的压实密度为2.4g/cm3～3.40g/cm3，可选为2.6g/cm3～3.25g/cm3。
在本申请的一些实施方式中，所述第一正极活性材料的Dv50粒径为2.1μm～6.3μm，可选为3.5μm～4.9μm。
在本申请的一些实施方式中，所述第一正极活性材料的比表面积为0.3m2/g～1.2m2/g，可选为0.5m2/g～0.9m2/g。
在本申请的一些实施方式中，所述第二正极活性材料的Dv50粒径为0.25μm～1.49μm，可选为0.5μm～0.9μm。
在本申请的一些实施方式中，所述第二正极活性材料的比表面积为9.0m2/g～23.2m2/g，可选为10.5m2/g～17.9m2/g。
在本申请的一些实施方式中，所述第一正极活性材料表面设有第一包覆层，可选地，所述第一包覆层包括Ti、Al、B、Nb、Zr、Si和W中的一种或多种元素。通过设置第一包覆层可以减少第一正极活性材料与电解液之间的副反应，并提高正极活性材料结构的稳定性，改善循环性能和安全性。
在本申请的一些实施方式中，所述第一包覆层的厚度为20nm～150nm。
在本申请的一些实施方式中，所述第二正极活性材料表面设有第二包覆层，可选地，所述第二包覆层包括焦磷酸盐、磷酸盐和碳中的至少之一。通过设置第二包覆层不仅可以减少第二正极活性材料与电解液之间的副反应，还可以避免或抑制过渡金属或掺杂元素的溶出，同时提高其结构稳定性，改善循环性能和安全性。
在本申请的一些实施方式中，所述第二包覆层的厚度为10nm～50nm。
在本申请的一些实施方式中，所述第二正极活性材料中，E为包括B、Si、N和S中的至少之一。
在本申请的一些实施方式中，所述第二正极活性材料中，A′为包括Fe、Ti、V和Mg 中的至少之一。
本申请的第二方面提供了一种二次电池，其包括：本申请第一方面的正极片。
本申请的第三方面提供了一种用电装置，其包括：本申请第一方面的正极片、和/或本申请第二方面所述的二次电池。
具体实施方式
下面结合具体实施方式，进一步阐述本申请。应理解，这些具体实施方式仅用于说明本申请而不用于限制本申请的范围。
在本申请中提及“实施例”意味着，结合实施例描述的特定特征、结构或特性可以包含在本申请的至少一个实施例中。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例，也不是与其它实施例互斥的独立的或备选的实施例。本领域技术人员显式地和隐式地理解的是，本申请所描述的实施例可以与其它实施例相结合。
本申请所公开的“范围”以下限和/或上限的形式来限定，给定范围是通过选定一个下限和/或一个上限进行限定的，选定的下限和/后上限限定了特别范围的边界。这种方式进行限定的范围可以是包括端值或不包括端值的，并且可以进行任意地组合，即任意下限可以与任意上限组合形成未明确记载的范围，以及任意下限可以与其它下限组合形成未明确记载的范围，同样任意上限可以与任意其它上限组合形成未明确记载的范围。此外，每个单独公开的点或单个数值自身可以作为下限或上限与任意其它点或单个数值组合或与其它下限或上限组合形成未明确记载的范围。例如，如果针对特定参数列出了不大于150的范围，理解为10～140和20～120等满足不大于150的范围也是预料到的。此外，如果列出的最小范围值2.1和3.5，和如果列出了最大范围值4.9和6.3，则下面的范围可全部预料到：2.1～6.3、2.1～4.9、3.5～6.3和3.5～4.9。在本申请中，除非有其他说明，数值范围如“10～50”表示10到50之间的任意实数组合的缩略表示，其中10和50都是实数。例如数值范围“20～30”表示本文中已经全部列出了“20～30”之间的全部实数，“20～30”只是这些数值组合的缩略表示。
如果没有特别的说明，本申请的所有实施方式以及可选实施方式可以相互组合形成新的技术方案，并且这样的技术方案应被认为包含在本申请的公开内容中。
如果没有特别的说明，本申请的所有技术特征以及可选技术特征可以相互组合形成新的技术方案，并且这样的技术方案应被认为包含在本申请的公开内容中。
如果没有特别的说明，本申请的所有步骤可以顺序进行，也可以随机进行，优选是顺序进行的。例如，所述方法包括步骤S1和S2，表示所述方法可包括顺序进行的步骤S1和S2，也可以包括顺序进行的步骤S2和S1。例如，所述提到所述方法还可包括步骤 S3，表示步骤S3可以任意顺序加入到所述方法，例如，所述方法可以包括步骤S1、S2和S3，也可包括步骤S1、S3和S2，也可以包括步骤S3、S1和S2等。
如果没有特别的说明，本申请所提到的“包括”和“包含”表示开放式，也可以是封闭式。例如，所述“包括”和“包含”可以表示还可以包括或包含没有列出的其他组分，也可以仅包括或包含列出的组分。另外，在本申请中，术语“多个”、“多种”是指两个或两种以上。
如果没有特别的说明，在本申请中，术语“和/或”仅仅是一种描述关联对象的关联关系，表示可以存在三种关系，例如A和/或B，可以表示：单独存在A，同时存在A和B，单独存在B这三种情况。另外，本文中字符“/”，一般表示前后关联对象是一种“或”的关系。
除非另有定义，本申请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；本申请中所使用的术语只是为了描述具体的实施例的目的，不是旨在于限制本申请；本申请的说明书和权利要求书中的术语“包括”和“具有”以及它们的任何变形，意图在于覆盖不排他的包含。除非另有说明，本申请中使用的术语具有本领域技术人员通常所理解的公知含义。除非另有说明，本申请中提到的各参数的数值可以用本领域常用的各种测量方法进行测量(例如，可以按照在本申请的实施例中给出的方法进行测试)。
目前，快充性能和循环性能已经成为锂电池的重要能力指标，目前多采用三元层状正极活性材料(如NCM)制备正极片，但该体系正极材料随着循环次数增加和放电时间的延长，会出现电池内阻增加，电极极化增大的问题，进而导致放电电压提前到达截止电压，在放电曲线在放电结束阶段时存在放电电压陡降的趋势，会出现放电提前结束，影响电池的实际可用容量的问题，即该体系的正极材料在低SOC处的倍率耐受边界较差，影响电池的快充和循环性能。
有鉴于此，本申请的第一方面提供一种正极片，其中，所述正极片包括正极活性物质层，所述正极活性物质层包括第一正极活性材料和第二正极活性材料，所述第一正极活性材料包括LiaNibCocM1dM2eOfR′g，其中，0.75≤a≤1.2，0<b<1，0<c<1，0<d<1，0≤e≤0.2，1≤f≤2.5，0≤g≤1，f+g≤3，M1为Mn元素和/或Al元素，M2包括Zr、Zn、Cu、Cr、Mg、Fe、V、Ti、Sr、Sb、Y、W、Nb中的一种或多种元素，R′包括N、F、S、Cl中的一种或多种元素；所述第二正极活性材料包括Li1+xM3nMn1-yA′yP1-zEzO4，其中，-0.100≤x≤0.100，0≤n≤1.1，0.001≤y≤1，0≤z≤0.100，M3包括Zn、Al、Na、K、Mg、Nb、Mo和W中的一种或多种元素，A′包括Zn、Al、Na、K、Mg、Mo、W、Ti、V、Zr、Fe、Ga、Sn、Sb、Nb和Ge中的一种或多种元素，E包括B、Si、N、S、F、Cl 和Br中的一种或多种元素；所述正极片满足：
其中：n(A′)为所述正极片中A′的摩尔量，单位为mol；n(Ni)为所述正极片中Ni的摩尔量，单位为mol；n(Mn)为所述正极片中Mn的摩尔量，单位为mol；R为所述正极片在25℃下的电阻，单位为Ω。
本申请的发明人发现，层状正极活性材料体系LiaNibCocM1dM2eOfR′g在低SOC处倍率耐受边界较差，而正极活性材料Li1+xM3nMn1-yA′yP1-zEzO4在放电快结束时存在有低压放电平台(普遍不大于3.5V)，通过将其与上述层状正极活性材料进行掺混，可以利用Li1+xM3nMn1-yA′yP1-zEzO4在低电压处的放电平台使掺混后的复合正极活性材料的整体放电曲线在接近结束时存在一个放电平台，当电池放电到该平台时，由于电池电压随容量变化幅度较小，因此相当于对层状正极活性材料进行一定程度的恒压放电，从而可以缓解先前在低电压处放电过程中的极化作用，改善实际可用容量；并且，正极活性材料体系Li1+xM3nMn1-yA′yP1-zEzO4还受限于在高SOC处倍率耐受边界较差的问题，通过将其与层状正极活性材料体系LiaNibCocM1dM2eOfR′g掺混使用，可以同时弥补两个体系的缺陷，拓宽高低SOC处倍率耐受边界，从而提升快充能力，并能兼顾循环性能；此外，正极活性材料LiaNibCocM1dM2eOfR′g的能量密度更高，正极活性材料Li1+xM3nMn1-yA′yP1-zEzO4的循环性能和安全性更高，通过将二者进行掺混，还可以进一步兼具较高的高能量密度和较好的循环性能，再者，正极活性材料Li1+xM3nMn1-yA′yP1-zEzO4在充放电过程中的晶格收缩率相对较大，将两种体系的正极活性材料进行掺混还有利于进一步匹配电池负极片的膨胀，改善电池的长期性能；进一步地，发明人在探索过程中还发现，正极片中Ni含量高有助于电池能量密度提升，但Ni含量过高又会损伤循环性能，Mn含量高有助于循环性能，但过高又会损伤电池能量密度，A′元素含量高有助循环性能提升，但过高又会损伤电池能量密度，进一步地，正极片电阻过高也会影响电池功率和循环性能，而通过控制正极片中A′元素、Ni元素、Mn元素的摩尔数以及正极片电阻满足上式公式所给范围，可以进一步同时保证正极片和电池具有良好的快充能力和较好的循环性能，并有利于获得高能量密度。
进一步地，发明人经深入研究还发现，本申请的正极片在满足上述条件的基础上，还可以进一步控制正极片中的元素摩尔量和/或相对用量、正极活性材料选择、极片电阻、极片活性物质层涂覆量等来进一步改善正极片的性能。即，在满足上述条件的基础上，还可选地满足下述条件中的一个或多个。
在本申请的一些实施方式中，第一正极活性材料可以部分为LiaNibCocM1dM2eOfR′g，也可以全部为LiaNibCocM1dM2eOfR′g，其中，0.75≤a≤1.2，0<b<1，0<c<1，0<d<1，0≤e≤0.2，1≤f≤2.5，0≤g≤1，f+g≤3，M1为Mn元素和/或Al元素，M2包括Zr、Zn、 Cu、Cr、Mg、Fe、V、Ti、Sr、Sb、Y、W、Nb中的一种或多种元素，R′包括N、F、S、Cl中的一种或多种元素。可选地，0.5≤b<1、0<c≤0.5、0<d≤0.5，使正极活性材料LiaNibCocM1dM2eOfR′g满足上述所给范围条件，更有利于使兼具较高的能量密度、良好的循环性能和较长的循环寿命，正极活性材料LiaNibCocM1dM2eOfR′g中，以镍钴锰三元正极活性材料(即NCM)体系为例，提高镍含量可以提高正极材料的体积能量密度；提高锰含量可以降低材料成本，提高材料的安全性和结构稳定性，改善循环性能，但过高的锰含量会破坏材料的层状结构，使材料的比容量降低；钴可以稳定材料的层状结构，提高材料的循环和倍率性能，但过高的钴含量会导致实际容量降低，通过使镍钴锰含量满足上述所给范围条件，有利于使正极片和电池具有较高的能量密度、良好的倍率性能和循环性能。可选地，M1可以为Mn元素，第一正极活性材料可以为NCM体系的正极活性材料，此时其通式可以为LiaNibCocMndM2eOfR′g，例如可以为镍钴锰三元层状正极活性材料。
在本申请的一些实施例中，第二正极活性材料可以部分为Li1+xM3nMn1-yA′yP1-zEzO4，也可以全部为Li1+xM3nMn1-yA′yP1-zEzO4，其中，-0.100≤x≤0.100，0≤n≤1.1，0.001≤y≤1，0≤z≤0.100，M3包括Zn、Al、Na、K、Mg、Nb、Mo和W中的一种或多种元素，A′包括Zn、Al、Na、K、Mg、Mo、W、Ti、V、Zr、Fe、Ga、Sn、Sb、Nb和Ge中的一种或多种元素，E包括B、Si、N、S、F、Cl和Br中的一种或多种元素，在锂位、锰位和磷位中的至少之一进行掺杂，均可以辅助提升该正极活性材料的性能，例如可以改善界面性能，降低与电解液的界面副反应，降低反位缺陷浓度，提升材料动力学性能和克容量等，同时通过对锰位掺杂元素进行调控，还可以改善颗粒形貌，提升压实密度，具体地，上述第二正极活性材料在充放电过程中的晶格体积变化率相较于第一正极活性材料较大，可以较好的匹配负极在充电过程中的体积膨胀，但若正极材料的晶格体积变化率过高又不利于锂离子的传输，锰位掺杂的元素A′选自上述元素有助于适当减小该材料在脱嵌锂过程中的晶格变化率，提高该正极材料的结构稳定性，减少锰位元素的溶出并降低颗粒表面的氧活性，进而可提高材料的克容量，并降低材料在使用过程中和电解液的界面副反应，进而提升材料的循环性能等；在磷位掺杂的元素E选自上述元素还有助于改变Mn-O键长变化的难易程度，从而改善电子电导并降低锂离子迁移势垒，促进锂离子迁移，提高倍率性能和快充性能；类似地，在锂位掺杂的元素M3选自上述元素也有助于改善材料的晶格变化率并保持材料的容量。如果x的值过小，会导致整个内核体系的含锂量降低，影响材料的克容量发挥。y值会限制所有掺杂元素的总量，影响体系中的锰含量和材料的电压平台。E元素掺杂在磷的位置，由于P-O四面体较稳定，z值过大会影响材料的稳定性。当x、y和z选自上述范围时，正极活性材料可以具有更好的性能。此外，上述掺杂元素和x、n、y、z值的选择，还可以使Li1+xM3nMn1-yA′yP1-zEzO4保持电中性，而保持电中性能够保证该 正极活性材料中的缺陷和杂相尽量少，以磷酸锰锂体系的正极活性材料为例，如果存在过量的过渡金属(例如锰)，由于该材料体系本身结构较稳定，那么多余的过渡金属很可能会以单质的形式析出，或在晶格内部形成杂相，保持电中性可使这样的杂相尽量少；另外，保证体系电中性还可以在部分情况下使正极活性材料中产生锂空位，从而使正极活性材料的动力学性能更优异。与现有可应用于高电压体系的磷酸锰锂、磷酸铁锂、磷酸锰铁锂等材料相比更有利于获得较好的循环性能和高温稳定性，以及较大的克容量和较大的压实密度。可以理解的是，本申请中所述的“锰位”掺杂中，锰位仅代表正极活性材料Li1+xM3nMn1-yA′yP1-zEzO4晶格中锰元素或A′元素的位置，而不代表锰位中一定有锰元素，锰位上的锰元素可以部分或全部被A′元素取代，例如当y值取到1时，第二正极活性材料Li1+xM3nMn1-yA′yP1-zEzO4中不含锰元素，例如此时锰位上可以包括铁元素或者同时包括铁元素与其它掺杂元素。
在本申请的一些实施方式中，第二正极活性材料Li1+xM3nMn1-yA′yP1-zEzO4中，E可以包括B、Si、N和S中的一种或多种元素，通过使磷位掺杂的元素E选自所给范围可以进一步有助于改变Mn-O键长变化的难易程度，从而改善电子电导并降低锂离子迁移势垒，促进锂离子迁移，提高材料的倍率性能和快充性能。
在本申请的一些实施方式中，第二正极活性材料Li1+xM3nMn1-yA′yP1-zEzO4中，A′可以包括Fe、Ti、V和Mg中的一种或多种元素。可选地，A′可以为Fe元素；再可选地，A′可以为选自Fe、Ti、V和Mg中的至少两种元素；又可选地，A′可以为Fe元素与选自Ti、V和Mg中的一种或多种元素。通过使锰位掺杂的元素A′选自所给范围可以进一步改善正极材料的结构稳定性、克容量、循环性能、倍率性能等，得到兼具较好循环寿命和快充性能的正极片。
在本申请的一些实施例中，第二正极活性材料Li1+xM3nMn1-yA′yP1-zEzO4中，可以在锰位和磷位同时进行掺杂，由此不仅可以有效减少锰位元素的溶出，进而减少迁移到负极的锰位离子，减少因SEI膜分解而消耗的电解液，提高电池的循环性能和安全性能，还能够促进Mn-O键调整，降低锂离子迁移势垒，促进锂离子迁移，提高倍率性能和快充性能。再可选地，还可以在锂位、锰位和磷位同时进行掺杂，由此可进一步获得明显改善的倍率性能，改善的循环性能和/或高温稳定性。
本申请中，针对上述第一正极活性材料的化学式LiaNibCocM1dM2eOfR′g和第二正极活性材料的化学式Li1+xM3nMn1-yA′yP1-zEzO4，除非另有说明，否则当某掺杂位点具有两种以上元素时，对化学式中相应掺杂位点元素的化学计量数的数值范围的限定不仅是对每种作为该位点的元素的化学计量数的限定，也是对各个作为该位点的元素的化学计量数之和的限定。例如，以第二正极活性材料Li1+xM3nMn1-yA′yP1-zEzO4的化学式为例，当A1′为两种 以上元素A1′、A2′……An′时，A1′、A2′……An′各自的化学计量数y1、y2……yn各自均需落入本申请对y限定的数值范围内，且y1、y2……yn之和也需落入该数值范围内。类似地，对于M3或E为两种以上元素的情况，本申请对M3和E化学计量数的数值范围的限定也具有上述含义。
在本申请的一些实施方式中，的值可为0.005、0.01、0.02、0.05、0.1、0.15、0.2、0.25、0.3、0.35、0.4、0.45等，或可为以上任何数值所组成的范围；可选地，再可选地，通过控制正极片中A′元素、Ni元素、Mn元素的摩尔数以及正极片电阻满足该所给范围，可以进一步保证良好的快充能力、高能量密度和较好的循环性能。
在本申请的一些实施方式中，正极片还满足：其中，n(P)为正极片中磷元素P的摩尔量，单位为mol，的值可以为0.2、0.25、0.3、0.35、0.4、0.45、0.5、0.55、0.6、0.65、0.7、0.75、0.8、0.85、0.9、0.95、1.0、1.05、1.15、1.2、1.25、1.3、1.35、1.4、1.45等，或者可以为以上任何数值所组成的范围。相对于第二正极活性材料Li1+xM3nMn1-yA′yP1-zEzO4，第一正极活性材料LiaNibCocM1dM2eOfR′g的比容量更高，导电性能好也更好，其中，第一正极活性材料LiaNibCocM1dM2eOfR′g中Ni含量的提升有助于电池能量密度的提升，但其含量过高会损伤循环性能；第二正极活性材料中A′元素的含量影响材料的电压平台和循环性能，A′元素含量高有助于循环性能改善，但平台电压会有明显损失，不利于电池能量密度，相反地，A′元素含量低有助于平台电压提升，但材料循环性能会变差，选择合适的含量范围有利于使第二正极活性材料同时兼顾较高的平台电压和较好的循环性能，例如，作为一个具体示例，当锰位同时包含锰元素和铁元素时，锰铁比较高时能够提高电压平台，有利于提高电池的能量密度，但锰铁比过高时，脱锂态大量三价锰可能会破坏固溶体结构，降低材料的比容量和循环容量保持率，导致循环性能变差，影响正极寿命。本申请中，正极片中Ni元素的含量是由第一正极活性材料提供的，磷元素是由第二正极活性材料提供的，Mn元素和A′元素可由第一正极活性材料和/或第二正极活性材料提供，本申请中在满足A′元素、Ni元素、Mn元素的摩尔数以及正极片电阻R的关系式的基础上，进一步使的值在所给范围内，不仅可以使第一正极活性材料和第二正极活性材料具有适宜的掺混比例，还可以使第二正极活性材料具有适宜的A′元素含量范围，获得较好的循环性能，由此，可以在拓宽电池高低SOC处倍率耐受边界，提升快充能力的基础上，进一步兼顾较高的能量密度和较好的循环性能。可选地， 由此可以进一步使快充性能提升的同时，兼顾较高的能量密度和较好的循环性能。
本申请中，正极片中各元素的摩尔量可通过ICP测试得到，例如，可以通过如下操作进行：取干燥正极片约0.4g(精确至0.0001g)或湿润正极片0.1g(精确至0.0001g)于30ml消解罐中，保留1个不加样品的消解罐作为空白样，将装有正极片样品的消解罐移到通风橱内加入12ml逆王水，逆王水加入时沿消解罐内壁加入，使内壁上残留样品被冲入罐底，之后依次安装顶盖，隔热套，垫片，微波消解装置，螺母，使用扳手拧紧螺母，随后打开微波消解仪，将微波消解仪中光纤传感器插入先前组装好装有样品的消解罐底部，平衡放置消解罐于微波消解仪中，开始消解(消解程序6min升温至120℃保持8min，5min升温至160℃保持8min，5min升温至180℃保持5min)，结束后冷却到室温取出，将消解罐置于通风橱内，缓慢拧开螺母放气，依次将先前安装零件取下，通过漏斗(需垫滤纸)转移消解罐中溶液到100ml容量瓶中，随后用超纯水冲洗消解罐，将冲洗液也转入容量瓶中，每次冲洗用超纯水10ml，将100ml容量瓶中溶液摇匀，使用移液枪取1ml摇匀溶液加入另一个100ml容量瓶中，随后加入超纯水定容(溶液总共达到100ml)，最后使用ICP-OES测试样品溶液。其中，配置逆王水时可以将1000ml超纯水倒入2500ml玻璃瓶中，随后依次加入750ml浓硝酸和250ml浓盐酸，搅拌均匀后待用，其中浓硝酸购买市售质量分数为68％的浓硝酸溶液即可，浓盐酸可购买市售质量分数为68％的浓盐酸，或将氯化氢气体和超纯水按质量占比分别为68％和32％将氯化氢气体加入超纯水中，完全溶解后即可得到所需浓盐酸。
本申请中，正极片电阻可以在常温下采用BER1300膜片电阻仪进行测试，测试步骤可以如下：(1)将极片制备成直径为22mm圆片；(2)将制备好的圆片放入BER1300仪器的测试平台上；(3)机器测试压力调整为0.4吨，测试时间调整为10s，开始测试即可，所得到的电阻数值即为膜片电阻。
在本申请的一些实施例中，第二正极活性材料可以包括磷酸锰锂体系、磷酸铁锂体系、磷酸锰铁锂体系等所有符合上述通式Li1+xM3nMn1-yA′yP1-zEzO4的正极活性材料中的一种或多种，例如，第二正极活性材料可以包括满足以下三个条件至少之一的正极活性材料：(i)y＝1，n＝0，此时第二正极活性材料为Li1+xA′P1-zEzO4，A′可以为Fe元素，或者A′可以为Fe元素并包括Zn、Al、Na、K、Mg、Mo、W、Ti、V、Zr、Fe、Ga、Sn、Sb、Nb和Ge中的一种或多种元素，即第二正极活性材料可以包括磷酸铁锂或有铁位(与锰位位置相同)和磷位中至少之一有掺杂的磷酸铁锂。(ii)0.001≤y≤0.500，n＝0，此时第二正极活性材料为Li1+xMn1-yA′yP1-zEzO4，即可以为磷酸锰锂或锂位、锰位和磷位中至少之一有掺杂的磷酸锰锂，其中，本申请中通过对磷酸锰锂进行改性能够实现显著降低的 锰位元素溶出以及降低的晶格变化率，其用于二次电池中，更有利于改善电池的循环性能、倍率性能、安全性能并且提高电池的容量。例如，通过在化合物LiMnPO4的锂位、锰位、磷位以特定量掺杂特定的元素，能够获得改善的倍率性能，同时减少Mn与Mn位掺杂元素的溶出，获得改善的循环性能和/或高温稳定性，并且正极活性材料的克容量和压实密度也可以得到提高，作为具体一个示例，Li1+xMn1-yA′yP1-zEzO4可以包括Li1+xMn1- yFeyP1-zEzO4，相对于磷酸铁锂，磷酸锰铁锂具有更高的电压平台，在比容量相同时其具有更高的能量密度；(iii)0.001≤y≤0.500，0.9≤n≤1.1，此时第二正极活性材料为Li1+xM3nMn1-yA′yP1-zEzO4，针对磷酸锰锂体系的第二正极活性材料，考虑到y值会限制所有掺杂元素的总量，如果y过小，即掺杂量过少，掺杂元素起不到作用，如果y超过0.5，会导致体系中的Mn含量较少，影响材料的电压平台，y的取值范围可选为0.001～0.500，再可选为0.25～0.5。需要说明的是，上述三个条件中涉及的化学式Li1+xA′P1- zEzO4、Li1+xMn1-yA′yP1-zEzO4和Li1+xM3nMn1-yA′yP1-zEzO4中，位于相同位点上的元素的化学计量数可以相同，也可以不同，但都满足化学式Li1+xM3nMn1-yA′yP1-zEzO4中对各元素的化学计量数限定的数值范围。
作为一个具体示例，第二正极活性材料可以包括满足以下两个条件至少之一的正极活性材料：(i)y＝1，n＝0，第二正极活性材料为Li1+xA′P1-zEzO4，A′为Fe元素，或A′包括Fe元素和选自Zn、Al、Na、K、Mg、Mo、W、Ti、V、Zr、Fe、Ga、Sn、Sb、Nb、Ge中的一种或多种元素；(ii)0.001≤y≤0.500，n＝0，第二正极活性材料为Li1+xMn1-yA′yP1- zEzO4。可选地，第二正极活性材料可以仅包括化学式为Li1+xA′P1-zEzO4和/或化学式为Li1+xMn1-yA′yP1-zEzO4的正极活性材料，该两个化学式中，x和z的取值各自独立，但都满足化学式Li1+xM3nMn1-yA′yP1-zEzO4中对x和z的化学计量数限定的数值范围。
在本申请的一些实施方式中，第二正极活性材料具有放电平台，至少一个放电平台的放电电压不低于第一正极活性材料的放电截止电压，且不高于3.5V。正极活性材料Li1+xM3nMn1-yA′yP1-zEzO4的具体化学计量数不同，其放电平台的也可能会发生变化，例如当第二正极活性材料为磷酸铁锂时只有一个不大于3.5V的电压平台；再例如当第二正极活性材料为具有锰位掺杂的磷酸锰锂时，如磷酸锰铁锂，会存在2个放电平台，本申请利用的是放电快结束时的电压平台。本申请中通过进一步使第二正极活性材料具有不高于3.5V的电压平台，可以进一步保证第一正极活性材料和第二正极活性材料掺混后在放电快结束时，可以利用该平台缓解先前放电过程中的极化，拓宽高低SOC处倍率耐受边界，从而提升快充能力，并兼顾循环性能，改善实际可用容量。
在本申请的一些实施方式中，正极片中Ni元素的摩尔量n(Ni)(单位为mol)满足：0.0005≤n(Ni)≤0.0025，例如n(A′)可以为0.0008、0.001、0.0012、0.0014、0.0016、 0.0018、0.002、0.0022、0.0024等，或者可以为以上任何数值所组成的范围；可选地，0.0007≤n(Ni)≤0.0016。掺混后的正极活性材料中，Ni元素是由第一正极活性材料提供的，第一正极活性材料中Ni元素含量的提升有助于电池能量密度的提升，但会损伤循环性能，本申请中通过使正极片中Ni元素的含量n(Ni)满足上述所给范围，可以进一步使电池兼具较高的能量密度和较好的循环性能。进一步地，正极片中Mn元素的摩尔量n(Mn)(单位为mol)满足：0.0005≤n(Mn)≤0.0025，例如n(Mn)可以为0.0007、0.001、0.0013、0.0015、0.0018、0.002、0.0021、0.0023等，或者可以为以上任何数值所组成的范围；可选地，0.0009≤n(Mn)≤0.0016。正极片中A′元素的摩尔量n(A′)(单位为mol)满足以下条件：0.00005≤n(A′)≤0.0015，例如n(A′)可以为0.00008、0.0001、0.0002、0.0003、0.0004、0.0005、0.0006、0.0007、0.0008、0.0009、0.001、0.0012、0.0014等，或者可以为以上任何数值所组成的范围；可选地，0.0002≤n(A′)≤0.0006。本申请中通过进一步控制A′元素和Mn元素的摩尔数在所给范围内，可以进一步保证电池的高能量密度和较好的循环性能。
在本申请的一些实施方式中，正极片的电阻R(单位为Ω)满足：0<R≤1.3，例如R的取值可以为0.1、0.2、0.3、0.4、0.5、0.6、0.7、0.8、0.9、1.0、1.1、1.2等，或者可以为以上任何数值所组成的范围，考虑到正极片电阻过高同样会影响电池的功率性能和循环性能，通过将R的取值范围控制在所给范围内，可以进一步有利于使正极片和电池具有较好的快充性能和循环性能。可选地，0<R≤1，通过将R的取值范围进一步控制在所给范围内，可以进一步降低电池内阻，改善电快充性能和循环性能。
在本申请的一些实施方式中，正极片中Mn元素和A′元素的摩尔量满足以下条件：例如的值可以为0.03、0.05、0.07、0.09、0.1、0.3、0.5、0.7、0.9、1.1、1.3、1.5、1.7、1.9等，或者可以为以上任何数值所组成的范围，第二正极活性材料中A′元素的含量影响材料的电压平台和循环性能，A′元素含量高有助于循环性能改善，但平台电压会有明显损失，不利于电池能量密度，本申请中在满足A′元素、Ni元素、Mn元素的摩尔数以及正极片电阻R的关系式的基础上，进一步使的值在所给范围内，不仅可以使第一正极活性材料和第二正极活性材料具有适宜的掺混比例，还可以使第二正极活性材料具有适宜的A′元素含量范围，获得较好的循环性能，从而可以在拓宽电池高低SOC处倍率耐受边界，提升快充能力的基础上，进一步使兼顾较高的能量密度和较好的循环性能。可选地，再可选地，通过进一步使的值在所给范围内，可以进一步使正极片同时兼顾较好的快充能力、较高的 能量密度和较好的循环性能。
作为一个具体示例，第一正极活性材料可以为NCM体系的正极活性材料LiaNibCocMndM2eOfR′g，如可以为LiaNibCocMndOfR′g，第二正极活性材料可以为具有锰位掺杂的磷酸锰铁锂正极活性材料Li1+xMn1-yA′yP1-zEzO4(0.001≤y≤0.500)，如可以为Li1+xMn1-yFeyP1-zEzO4，此时的取值范围可以为0.02～2.0，可选为0.05～0.8，再可选为0.17～0.69，其中，第二正极活性材料Li1+xMn1-yA′yP1-zEzO4在放电快结束时(不大于3.5V)的电压平台在整个放电曲线中的宽度占比与该材料中A′元素的化学计量呈正向关系，而高电压平台可以提高对应电池的能量密度，A′含量高有助于循环性能改善，但平台电压会有明显损失，不利于电池能量密度，A含量低有助于平台电压提升，但材料循环性能会变差，通过控制的值在所给范围内，不仅可以进一步使所述第一正极活性材料和所述第二正极活性材料具有适宜的掺混比例，还可以使第二正极活性材料具有适宜的A′元素含量范围，获得较好的循环性能，从而可以在提升快充能力的基础上，进一步使兼顾较高的能量密度和较好的循环性能。
其中，本申请中所述的电压平台在整个放电曲线中的宽度占比可通过单颗粒微电极法测试，具体可以通过如下操作步骤进行：将第二活性物质待分散颗粒分散在采用特殊洗液(H2SO4(98wt％):双氧水(30wt％)＝3:1(V/V))和去离子水清洗过的盖玻片上，微电极为玻璃毛细管包封的Pt微电极，Pt丝直径为10μm，端面打磨成针尖形(玻璃半径与Pt丝半径比值应小于5)，以铜丝为导线，二者之间通过导电银胶导通，单颗粒测试前，需将上述微电极置于0.5mol/L的H2SO4水溶液中进行循环伏安扫描，扫速为50mV/s，扫描电势范围为-0.22V～1.22V(vs.SCE)；单颗粒微电极测试装置主要包括微电极，显微镜，微操作手和电化学工作站，通过显微镜和微操作手移动微电极，使其与第二活性物质单个颗粒接触，随后以待测颗粒为工作电极，以锂带为对电极和参比电极进行电化学测试，电解液为1mol/L LiPF6/(EC+PC)(VEC:VPC＝1:1)；电化学测试温度为25℃，0.33C恒流充电至4.4V后转为恒压充电，当充电电流减小至0.05C时，恒压充电结束，随后0.33C放电至满放电压2.5V，取放电流程的比容量-电压曲线，以比容量为X轴，电压为Y轴，记3.5V下充电容量为Q3，记整个充电容量为Q4，电压小于3.5V的容量占比(即电压平台宽度)＝Q3/Q4。
在本申请的一些实施方式中，正极活性物质层的涂覆质量可以为15.50mg/cm2～20.78mg/cm2，例如可以为16.0mg/cm2、16.50mg/cm2、17.0mg/cm2、17.50mg/cm2、18.0mg/cm2、18.50mg/cm2、19.0mg/cm2、19.50mg/cm2、20.0mg/cm2、20.5mg/cm2等，或可以为以上任何数值所组成的范围；可选地，正极活性物质层的涂覆质量为16.80mg/cm2 ～18.83mg/cm2。其中，正极活性物质层在涂覆质量过低的情况下，一方面不利于电池能量密度的提升，另一方面极片极化会有较为明显的改善，此时在第一正极活性材料LiaNibCocM1dM2eOfR′g中掺混第二正极活性材料Li1+xM3nMn1-yA′yP1-zEzO4的改善作用不明显，而当正极活性物质层的涂覆质量过高时，又会导致极片极化增加的程度超过掺混Li1+xM3nMn1-yA′yP1-zEzO4的改善作用，影响倍率性能和快充性能。本申请中通过使正极活性物质层的涂覆质量控制在所给范围内，可以进一步改善电池的快充性能，同时能兼顾能量密度和循环性能。
在本申请的一些实施方式中，正极活性物质层的压实密度为2.4g/cm3～3.40g/cm3，例如可以为2.5g/cm3、2.6g/cm3、2.7g/cm3、2.8g/cm3、2.9g/cm3、3.0g/cm3、3.1g/cm3、3.2g/cm3、3.3g/cm3等，或者可以为以上任何数值所组成的范围。其中，正极片的活性物质层压实密度可依据GB/T 24533-2009测量。正极片中正极活性物质层的压实密度过小易导致极片内部颗粒间接触松散，接触电阻增大；而正极片中正极活性物质层的压实密度过大会导致两个问题，一是易使冷压后极片内部部分颗粒破碎/产生裂隙，破碎的颗粒/裂隙容易与电解液发生副反应引起电池性能衰减，电池循环时因为极片内部压力大，颗粒间相互挤压也容易导致颗粒破碎；二是极片孔隙率下降，电解液浸润难度增大，进而易引起电池性能衰减。本申请中通过控制正极片的活性物质层压实密度在所给范围内，更有利于改善极片的极化问题，提高电池的循环性能和长期使用性能。可选地，正极片的活性物质层压实密度可以为2.6g/cm3～3.25g/cm3，由此可以进一步使电池具有提高的循环性能和长期使用性能。
在本申请的一些实施方式中，第一正极活性材料的Dv50粒径为2.1μm～6.3μm，例如可以为2.4μm、2.7μm、3.0μm、3.3μm、3.6μm、3.9μm、4.2μm、4.5μm、4.8μm、5.1μm、5.4μm、5.7μm、6.0μm等，或者可以为以上任何数值所组成的范围。第一正极活性材料的Dv50是指第一正极活性材料累计体积分布百分数达到50％时所对应的粒径。在本申请中，第一正极活性材料的Dv50粒径可采用激光衍射粒度分析法测定，例如参照标准GB/T19077-2016，使用激光粒度分析仪(例如Malvern Master Size 3000)进行测定。本申请中通过控制第一正极活性材料的Dv50粒径在所给范围内，不仅有利于防止其在充放电过程中发生破碎或粉化，从而降低电池的容量损失，还能够缩短活性离子的扩散路径、提高电子的传导速率，有利于提高电池的循环性能；同时，还可以使活性材料具有适宜的活性位点，降低或避免因粒径过小时活性位点较多，增加材料在循环过程中的副反应，对循环性能产生较大的负面影响，和因粒径过大时活性位点较少，对功率性能产生较大的负面影响。此外，基于第一包覆层的厚度，控制第一正极活性材料的Dv50粒径在所给范围内还能够进一步保证电池具有较高的能量密度。可选地，第一正极活性材料的Dv50粒径可以 为3.5μm～4.9μm，由此可以进一步兼顾高能量密度、较好的功率性能和循环性能，改善快充能力和使用寿命。
在本申请的一些实施方式中，第二正极活性材料的Dv50粒径可为0.25μm～1.49μm，例如可以为0.3μm、0.4μm、0.5μm、0.6μm、0.7μm、0.8μm、0.9μm、1.0μm、1.1μm、1.2μm、1.3μm、1.4μm等，或者可以为以上任何数值所组成的范围。第二正极活性材料的Dv50是指第二正极活性材料累计体积分布百分数达到50％时所对应的粒径。在本申请中，第二正极活性材料的Dv50粒径可采用激光衍射粒度分析法测定，例如参照标准GB/T19077-2016，使用激光粒度分析仪(例如Malvern Master Size 3000)进行测定。本申请中通过控制第二正极活性材料的Dv50粒径在所给范围内，不仅有利于防止其在充放电过程中发生破碎或粉化，从而降低容量损失，还能够缩短活性离子的扩散路径、提高电子的传导速率，有利于提高循环性能；同时还能使活性材料具有适宜的活性位点，同时兼顾循环性能和功率性能；并且，控制第二正极活性材料的Dv50粒径在所给范围内，还有利于配合第一正极活性材料的Dv50粒径范围达到预期的压实密度，避免正极活性材料颗粒间空隙较大。可选地，第二正极活性材料的Dv50粒径可以为0.5μm～0.9μm，由此可以进一步兼顾高能量密度、较好的功率性能和循环性能，改善快充能力和使用寿命。
在本申请的一些实施方式中，第一正极活性材料的比表面积为0.3m2/g～1.2m2/g，例如可以为0.4m2/g、0.5m2/g、0.6m2/g、0.7m2/g、0.8m2/g、0.9m2/g、1.0m2/g、1.1m2/g等，或者可以为以上任何数值所组成的范围；可选地，第一正极活性材料的比表面积为0.5m2/g～0.9m2/g。进一步地，第二正极活性材料的比表面积可以为9.0m2/g～23.2m2/g，例如可以为10m2/g、11m2/g、12m2/g、13m2/g、14m2/g、15m2/g、16m2/g、17m2/g、18m2/g、19m2/g、20m2/g、21m2/g、22m2/g等，或者可以为以上任何数值所组成的范围；可选地，第二正极活性材料的比表面积可以为10.5m2/g～17.9m2/g。在本申请中，第一和第二正极活性材料的比表面积可分别采用本领域的常规方法测定，如可以采用氮物理吸附法测定。比表面积增大有助于增加正极活性材料的活性位点，使材料具有较好的功率性能，但这些增加的活性位点也会增加正极活性材料在循环过程中的副反应，从而造成材料循环性能衰减，本申请中通过控制第一正极活性材料和第二正极活性材料的比表面积在所给范围内，可以进一步获得较好的功率性能和循环寿命，提升快充能力和使用寿命。
在本申请的一些实施方式中，第一正极活性材料表面可以设有第一包覆层，可选地，第一包覆层可以包括Ti、Al、B、Nb、Zr、Si和W中的一种或多种元素。在正极活性材料表面设置包覆层不仅可以避免正极活性材料与电解液接触，从而减少正极活性材料与电解液之间的副反应，还可以提高正极活性材料结构的稳定性，进而提高材料的循环稳定性能和安全性；另外，第一包覆层中的上述元素既可以以氧化物形式(如Al2O3、ZrO2、 TiO2、Nb2O3等)提供，也可以以锂化合物等形式提供，使第一包覆层中包含上述所给元素范围可以提升材料表面离子电导率，改善材料倍率性能及克容量发挥，稳定材料结构，避免材料与电解液直接接触，改善循环性能。
在本申请的一些实施方式中，第一包覆层的厚度可以为20nm～150nm，例如可以为30nm、40nm、50nm、60nm、70nm、80nm、90nm、100nm、110nm、120nm、130nm、140nm等，或者可以为以上任何数值所组成的范围。发明人发现，当第一包覆层的厚度过薄时，其在正极活性材料使用过程中破裂/深度损伤的可能性会加大，导致对第一正极活性材料性能提升和保护的作用大幅度降低；当第一包覆层的厚度过厚时，锂离子需要更长的传输路径才能从电解液中到达活性材料体系，对活性材料性能造成较大影响，此外在包覆层烧结时，包覆用物质会与内部材料中的锂发生反应，导致材料中可用活性锂减少，相应的材料克容量降低，本申请中通过控制第一包覆层的厚度在上述所给范围内，可以有效避免或减少上述问题，有效提升第一正极活性材料的倍率性能，稳定材料表面结构。
在本申请的一些实施方式中，第二正极活性材料表面可以设有第二包覆层，第二包覆层的设置不仅可以避免第二正极活性材料与电解液接触，从而减少第二正极活性材料与电解液之间的副反应，还可以避免或抑制第二正极活性材料中过渡金属或掺杂元素的溶出，同时提高其结构稳定性，进而提高正极活性材料的循环稳定性能和安全性。可选地，第二包覆层可以包括焦磷酸盐、磷酸盐和碳中的至少之一。其中，金属离子在焦磷酸盐中难以迁移，选择焦磷酸盐作为包覆层材料可以将正极材料中掺杂的金属离子与电解液进行有效隔离；进一步地，焦磷酸盐可选为晶态的焦磷酸盐，晶态焦磷酸盐的结构稳定，作为包覆层材料能够有效抑制活性材料中过渡金属的溶出，改善循环性能。磷酸盐包覆可以改善正极材料的离子传输性能，有利于促进锂离子的传输；进一步地，磷酸盐可以为晶态的磷酸盐，晶态的磷酸盐和晶态焦磷酸盐的晶格匹配度较高，稳定性好且具有优异导锂离子的能力，用其包覆第二正极活性材料可提高正极活性材料的稳定性，使电解液的界面副反应得到有效降低，从而改善电池的高温循环及存储性能。碳包覆可有效改善正极活性材料的导电性能和去溶剂化能力，碳材料具有好的电子导电性，在电池中应用时发生的是电化学反应，需要有电子的参与，为了增加颗粒与颗粒之间的电子传输，以及颗粒不同位置的电子传输，可以使用具有优异导电性能的碳来对正极活性材料进行包覆。可以理解的是，当第二包覆层中同时包括焦磷酸盐、磷酸盐和碳时，焦磷酸盐、磷酸盐和碳既可以位于同一个包覆层中，也可以位于至少两个子包覆层中，例如可以在第二正极活性材料表面依次形成焦磷酸盐包覆层、磷酸盐包覆层和碳包覆层，也可以在第二正极活性材料表面依次形成磷酸盐包覆层、焦磷酸盐包覆层和碳包覆层，或者也可以在第二正极活性材料表面先形成焦磷酸盐和磷酸盐的复合包覆层，再在复合包覆层表面形成碳包覆层。
在本申请的一些实施方式中，第二包覆层的厚度可以为10nm～50nm。例如可以为15nm、20nm、25nm、30nm、35nm、40nm、45nm等，或者可以为以上任何数值所组成的范围。控制第二包覆层的厚度在所给范围内，不仅可以有效阻碍第二正极活性材料中过渡金属或掺杂元素的溶出，并降低第二正极活性材料的晶格变化率，还能避免包覆厚度过大影响锂离子的迁移并影响电池能量密度，进而可以在不牺牲第二正极活性材料克容量的前提下，进一步改善电池的动力学性能、循环性能和安全性。
作为一个具体示例，第二包覆层可以包括第一子包覆层、第二子包覆层和第三子包覆层，第一子包覆层可以包覆第二正极活性材料并包括晶态焦磷酸盐，第二子包覆层可以包括晶态磷酸盐并包覆第一子包覆层，第三子包覆层可以为碳并包覆第二子包覆层。焦磷酸盐作为第一子包覆层可以将第二正极活性材料中掺杂的金属离子与电解液进行有效隔离，晶态焦磷酸盐包覆能够有效抑制第二正极活性材料中过渡金属的溶出，改善循环性能；晶态磷酸盐作为第二子包覆层与第一子包覆层中的晶态焦磷酸盐的晶格匹配度较高，且稳定性好于焦磷酸盐并具有优异导锂离子的能力，有利于提高正极活性材料的稳定性，降低正极活性材料和电解液的界面副反应；第三子包覆层可以增强颗粒间的电子传输，提高正极活性材料的电子导电性，并有效改善正极活性材料的导电性能和去溶剂化能力。进一步地，第一子包覆层的厚度可以为1nm～10nm，如可以为3nm、4nm、5nm、6nm、7nm、8nm、9nm等，或在上述任意数值的任意范围内，当第一子包覆层的厚度在所给范围内时，能够避免过厚时可能产生的对正极活性材料的动力学性能的不利影响，且能够避免过薄时可能无法有效阻碍过渡金属离子的迁移的问题；第二子包覆层的厚度可以为2nm～15nm，如可以为3nm、4nm、5nm、6nm、7nm、8nm、9nm、10nm、11nm、12nm、13nm、14nm等，或在上述任意数值的任意范围内，第二子包覆层的厚度过大可能会影响正极活性材料整体的平台电压，当第二子包覆层的厚度在所给范围内时，其表面结构稳定，与电解液的副反应小，能够有效减轻界面副反应，从而提升电池的高温循环性能和高温存储性能；第三子包覆层的厚度可以为2nm～25nm，如可以为4nm、6nm、8nm、10nm、12nm、14nm、16nm、18nm、20nm、22nm、24nm等，或在上述任意数值的任意范围内，当第三子包覆层的厚度在所给范围内时，能够提升正极活性材料的电导率并且提升正极极片的压实密度，同时避免该子包覆层中含有无定形碳时因包覆厚度过大影响极片压实密度的问题。
其中，本申请中，各包覆层的厚度大小测试可以通过FIB进行，具体方法可以包括以下步骤：从待测正极活性材料粉末中随机选取单个颗粒，从所选颗粒中间位置或中间位置附近切取100nm左右厚度的薄片，然后对薄片进行TEM测试，量取包覆层的厚度，测量3～5个位置，取平均值。
本申请的第二方面提供了一种二次电池，其包括：本申请第一方面的正极片。
在二次电池中，通常包括壳体组件、正极片、负极片、隔膜、电解液，正极片、负极片、隔膜和电解液位于壳体组件形成的容纳腔内。其中，根据电池的类型不同，该壳体组件可以为铝塑膜或金属壳体组件等，金属壳体组件又可以包括方形壳体组件和圆柱形壳体组件，当壳体组件为金属壳体组件时，通常包括还包括至少一侧设有开口的壳体和用于密封该开口的盖体。不管是哪种类型的电池，只要其正极片包括本申请第一方面的正极片，即可理解为包含在本申请第四方面的电池的技术范围内。其中，除前述部分正极片的活性材料及活性物质层的压实密度等特征外，正极片的其它结构特征或材料选择，以及负极片、隔膜和电解液的选择，都可以采用本领域的常规选择，本领域技术人员可以根据实际需要灵活选择。
在本申请的一些实施方式中，所述二次电池既可以为叠片电池，也可以为卷绕电池，该卷绕电池既可以为方形电池，也可以为圆柱电池，可选地，该电池可以为圆柱电池。根据电池类型的不同，正极极片、负极极片和隔膜既可以层叠布置形成叠片单元，也可以层叠后进行卷绕，形成卷绕体。
在本申请的一些实施方式中，所述电池既可以为单个电芯，也可以为由电芯组装成的电池模块，电池模块所包括的电芯的数量可以为多个，具体数量可根据电池模块的应用和容量来调节。进一步地，电池模块还可以包括具有容纳空间的封装组件，封装组件可以包括底板、侧板和盖板等。
在本申请的一些实施方式中，上述电池模块还可以组装成电池包，电池包所含电池模块的数量可以根据电池包的应用和容量进行调节。
另外，本申请还提供了一种用电装置，其包括：本申请第一方面的正极片、和/或本申请第二方面的二次电池。
所述二次电池，如电芯、电池模块或电池包，既可以作为该用电装置的电源，也可以作为该用电装置的能量存储单元。该用电装置可以包括但不限于是移动设备(例如手机、笔记本电脑)、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。作为一个具体示例，该用电装置可以为车辆。
用电装置可以根据其使用需求来选择电池的具体种类，如可以选择电芯、电池模块或电池包。
作为一个示例，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。为了满足该用电装置对电池的高功率和高能量密度的需求，可以采用电池包或电池模块。
作为另一个示例，该用电装置可以是手机、平板电脑、笔记本电脑。该用电装置通常要求轻薄化，可以采用电芯作为电源。
以下，说明本申请的实施例。下面描述的实施例是示例性的，仅用于解释本申请，而不能理解为对本申请的限制。实施例中未注明具体技术或条件的，按照本领域内的文献所描述的技术或条件或者按照产品说明书进行。所用试剂或仪器未注明生产厂商者，均为可以通过市购获得的常规产品。
二次电池的制备和测试方法：
1、软包叠片电池：
①正极极片制备：
将正极活性物质、聚偏二氟乙烯(PVDF)、导电碳加入到一定量的N-甲基吡咯烷酮(NMP)中，正极活性物质：聚偏二氟乙烯：导电碳的质量比例为90：5：5，在干燥房中搅拌制成均匀的浆料，控制粘度为3000～10000mPa·S，在铝箔上涂敷上述浆料，经过烘干处理制成正极极片。
②负极极片制备：
将石墨、羧甲基纤维素钠(CMC)、丁苯橡胶(SBR)、导电碳加入一定量的去离子水中，石墨：羧甲基纤维素钠：丁苯橡胶：导电碳的质量比例为90：2：3：5，搅拌制成均匀的浆料，控制粘度为3000～10000mPa·S，在铜箔上涂敷上述浆料，经过烘干处理制成负极极片。
③软包叠片电池制备：
将制备好的正极极片、负极极片和隔膜(聚乙烯(PE)多孔聚合薄膜)按照Z字型叠片结构制成相应电芯，将电芯在90℃的环境下真空烘干12h，随后进行正负极极耳超声焊接，正极采用铝极耳，负极采用镍极耳，正负极极耳位于电芯同侧，将极耳焊接后的电芯装入合适尺寸的铝塑膜中进行顶侧封装，封装常规温度为145℃，注液(电解液采用为1mol/L LiPF6/(碳酸乙烯酯(EC)+碳酸二乙酯(DEC)+碳酸二甲酯(DMC))(体积比1：1：1)+5wt.％氟代碳酸乙烯酯(FEC))，静置，化成，老化，排气，二封，容量测试即可得到制备好的软包叠片电池。
2、于25℃下对制得的软包叠片电池进行循环测试：
将上述制备的软包叠片电池，在25℃恒温环境，2.5～4.4V下，按照0.5C0充电至4.4V，然后在4.4V下恒压充电至电流≤0.05C0，静置5min，然后按照1C0放电至2.5V，容量记为Cn(n＝1,2,3……)，重复上述操作，容量保持率按照Cn/C3的比值计算，当Cn/C3× 100％＝80％时，提取对应的循环圈数，作为循环能力的考查指标。
3、正极极片膜片电阻测试：
膜片电阻采用BER1300膜片电阻仪进行测试，测试步骤如下：(a)将极片制备成直径为22mm圆片；(b)将制备好的圆片放入BER1300仪器的测试平台上；(c)机器测试压力调整为0.4T，测试温度为25℃、测试时间调整为10s，开始测试即可，所得到的电阻数值即为膜片电阻。
4、10％～80％SOC充电时间实验：
首先对软包叠片电池进行容量测试，流程如下：0.33C恒流充电至满充电压V1后转为恒压充电，当充电电流减小至0.05C时，恒压充电结束，随后0.33C放电至满放电压V2，按此流程重复3次，取第3次容量结果为准，同时可使用第3次结果计算正极克容量。
对软包叠片电池进行不同倍率(C1<C2<C3<C4<……<Cn)充电测试，测试中充电倍率需由小到大，充电过程中需同时监测软包叠片电池全电电压和软包叠片电池负极电压。详细过程如下：软包叠片电池按C1充电至满充电压V1或负极电压为0V，提取充电结束时电池SOC值，然后0.33C放电至满放电压V2，重复上述过程即可得到不同倍率充电结束时的SOC值，将充电结束时SOC-倍率做散点图，拟合得到充电结束时SOC与倍率间的关系式，将20％，30％，40％，50％，60％，70％，80％带入关系式中得到相应倍率(C20％、C30％、C40％、C50％、C60％、C70％、C80％)后即可计算10％～80％SOC充电时间，10％～80％SOC充电时间＝(60/C20％+60/C30％+……+60/C80％)×10％。
实施例1
软包叠片电池中：
(i)正极片：正极片的层数为15；单层正极片的厚度为0.13mm；正极片的活性物质层压实密度为3.1g/cm3；第一正极活性物质为NCM523，第一正极活性物质的Dv50粒径为4.1μm，第一正极活性材料的比表面积为0.6m2/g；第二正极活性物质为LiMn0.6Fe0.4PO4，第二正极活性物质的Dv50粒径为0.83μm，第二正极活性材料的比表面积为12.5m2/g；正极片满足：A′为Fe，极片电阻为0.1Ω。
(ii)负极片：负极片的层数为16；单层负极片厚度为0.13mm；负极片的活性物质层压实密度为1.68g/cm3。
(iii)隔膜：隔膜的层数为16；单层隔膜的厚度为0.011mm。
(iv)电池壳体的内腔厚度为5.9mm；
(vi)二次电池的注液系数为2.73 g/Ah。
实施例2～16和对比例1～4
实施例2～16和对比例1～4与实施例1的区别在于，的取值不同，通过实施例2～15和对比例1～4中通过改变第一正极活性物质和第二正极活性物质的掺混比例实现；实施例16中通过改变第二正极活性物质的种类实现，详见表1。
对实施例1～16和对比例1～4组装的电池进行测试，测试结果详见表1。
表1实施例1～16和对比例1～4的区别及相关测试结果

结果与结论：
结合上述实施例和对比例可知，采用本申请的电池设计方案可以改善电池的循环性能和快充性能。总的来说，的取值范围在0.001～0.5范围内时，电池的循环性能相对较好，同时快充性能也能得到改善，该取值还可选为0.009～0.35。
最后应说明的是：以上各实施例仅用以说明本申请的技术方案，而非对其限制；尽管参照前述各实施例对本申请进行了详细的说明，本领域的普通技术人员应当理解：其依然可以对前述各实施例所记载的技术方案进行修改，或者对其中部分或者全部技术特征进行等同替换；而这些修改或者替换，并不使相应技术方案的本质脱离本申请各实施例技术方案的范围，其均应涵盖在本申请的权利要求和说明书的范围当中。尤其是，只要不存在结构冲突，各个实施例中所提到的各项技术特征均可以任意方式组合起来。本申请并不局限于文中公开的特定实施例，而是包括落入权利要求的范围内的所有技术方案。

Claims (24)

  1. 一种正极片，其中，所述正极片包括正极活性物质层，所述正极活性物质层包括第一正极活性材料和第二正极活性材料，
    所述第一正极活性材料包括LiaNibCocM1dM2eOfR′g，其中，0.75≤a≤1.2，0<b<1，0<c<1，0<d<1，0≤e≤0.2，1≤f≤2.5，0≤g≤1，f+g≤3，M1为Mn元素和/或Al元素，M2包括Zr、Zn、Cu、Cr、Mg、Fe、V、Ti、Sr、Sb、Y、W、Nb中的一种或多种元素，R′包括N、F、S、Cl中的一种或多种元素；
    所述第二正极活性材料包括Li1+xM3nMn1-yA′yP1-zEzO4，其中，-0.100≤x≤0.100，0≤n≤1.1，0.001≤y≤1，0≤z≤0.100，M3包括Zn、Al、Na、K、Mg、Nb、Mo和W中的一种或多种元素，A′包括Zn、Al、Na、K、Mg、Mo、W、Ti、V、Zr、Fe、Ga、Sn、Sb、Nb和Ge中的一种或多种元素，E包括B、Si、N、S、F、Cl和Br中的一种或多种元素；
    所述正极片满足：
    其中：n(A′)为所述正极片中A′的摩尔量，单位为mol；n(Ni)为所述正极片中Ni的摩尔量，单位为mol；n(Mn)为所述正极片中Mn的摩尔量，单位为mol；R为所述正极片在25℃下的电阻，单位为Ω。
  2. 根据权利要求1所述的正极片，其中，可选地，其中，n(P)为所述正极片中P的摩尔量，单位为mol。
  3. 根据权利要求1或2所述的正极片，其中，所述第二正极活性材料包括满足以下条件至少之一的正极活性材料：
    (i)y＝1，n＝0，所述第二正极活性材料为Li1+xA′P1-zEzO4，A′为Fe元素，或A′为Fe元素和包括Zn、Al、Na、K、Mg、Mo、W、Ti、V、Zr、Fe、Ga、Sn、Sb、Nb和Ge中的一种或多种元素；
    (ii)0.001≤y≤0.500，n＝0，所述第二正极活性材料为Li1+xMn1-yA′yP1-zEzO4；
    (iii)0.001≤y≤0.500，0.9≤n≤1.1，所述第二正极活性材料为Li1+xM3nMn1-yA′yP1- zEzO4，
    可选地，所述第二正极活性材料包括：(i)Li1+xA′P1-zEzO4；和/或，(ii)Li1+xMn1- yA′yP1-zEzO4。
  4. 根据权利要求1～3中任一项所述的正极片，其中，所述第二正极活性材料具有放电平台，至少一个所述放电平台的放电电压不低于所述第一正极活性材料的放电截止电 压，且不高于3.5V。
  5. 根据权利要求1～4中任一项所述的正极片，其中，
    0.0005≤n(Ni)≤0.0025，0.0005≤n(Mn)≤0.0025，0.00005≤n(A′)≤0.0015。
  6. 根据权利要求1～5中任一项所述的正极片，其中，满足以下条件中的至少之一：
    0.0007≤n(Ni)≤0.0016、0.0009≤n(Mn)≤0.0016、0.0002≤n(A′)≤0.0006。
  7. 根据权利要求1～6中任一项所述的正极片，其中，0<R≤1.3，可选地，0<R≤1。
  8. 根据权利要求1～7中任一项所述的正极片，其中，M1为Mn元素。
  9. 根据权利要求1～8中任一项所述的正极片，其中，
    可选地，再可选地，
  10. 根据权利要求1～9中任一项所述的正极片，其中，
    可选地，
  11. 根据权利要求1～10中任一项所述的正极片，其中，所述正极活性物质层的涂覆质量为15.50mg/cm2～20.78mg/cm2，可选为16.80mg/cm2～18.83mg/cm2。
  12. 根据权利要求1～11中任一项所述的正极片，其中，所述正极活性物质层的压实密度为2.4g/cm3～3.40g/cm3，可选为2.6g/cm3～3.25g/cm3。
  13. 根据权利要求1～12中任一项所述的正极片，其中，所述第一正极活性材料的Dv50粒径为2.1μm～6.3μm，可选为3.5μm～4.9μm。
  14. 根据权利要求1～13中任一项所述的正极片，其中，所述第一正极活性材料的比表面积为0.3m2/g～1.2m2/g，可选为0.5m2/g～0.9m2/g。
  15. 根据权利要求1～14中任一项所述的正极片，其中，所述第二正极活性材料的Dv50粒径为0.25μm～1.49μm，可选为0.5μm～0.9μm。
  16. 根据权利要求1～15中任一项所述的正极片，其中，所述第二正极活性材料的比表面积为9.0m2/g～23.2m2/g，可选为10.5m2/g～17.9m2/g。
  17. 根据权利要求1～16中任一项所述的正极片，其中，所述第一正极活性材料表面设有第一包覆层，可选地，所述第一包覆层包括Ti、Al、B、Nb、Zr、Si和W中的一种或多种元素。
  18. 根据权利要求17所述的正极片，其中，所述第一包覆层的厚度为20nm～150nm。
  19. 根据权利要求1～18中任一项所述的正极片，其中，所述第二正极活性材料表面设有第二包覆层，可选地，所述第二包覆层包括焦磷酸盐、磷酸盐和碳中的至少之一。
  20. 根据权利要求19所述的正极片，其中，所述第二包覆层的厚度为10nm～50nm。
  21. 根据权利要求1～20中任一项所述的正极片，其中，所述第二正极活性材料中，E为包括B、Si、N和S中的至少之一。
  22. 根据权利要求1～21中任一项所述的正极片，其中，所述第二正极活性材料中，A′为包括Fe、Ti、V和Mg中的至少之一。
  23. 一种二次电池，其中，包括权利要求1～22中任一项所述的正极片。
  24. 一种用电装置，其中，包括权利要求1～22中任一项所述的正极片、和/或权利要求23中所述的二次电池。
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