WO2023159385A1 - 正极极片及二次电池、电池模块、电池包和用电装置，及平衡电池内部电压差的方法 - Google Patents

正极极片及二次电池、电池模块、电池包和用电装置，及平衡电池内部电压差的方法 Download PDF

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WO2023159385A1
WO2023159385A1 PCT/CN2022/077451 CN2022077451W WO2023159385A1 WO 2023159385 A1 WO2023159385 A1 WO 2023159385A1 CN 2022077451 W CN2022077451 W CN 2022077451W WO 2023159385 A1 WO2023159385 A1 WO 2023159385A1
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active material
lithium
positive electrode
optionally
secondary battery
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PCT/CN2022/077451
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English (en)
French (fr)
Inventor
吴益扬
叶永煌
武宝珍
吴凯
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宁德时代新能源科技股份有限公司
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Priority to CN202280005807.7A priority Critical patent/CN116941057A/zh
Priority to PCT/CN2022/077451 priority patent/WO2023159385A1/zh
Priority to EP22902504.4A priority patent/EP4258383A1/en
Priority to JP2023536972A priority patent/JP2024510692A/ja
Priority to KR1020237019885A priority patent/KR20230128457A/ko
Priority to US18/338,690 priority patent/US20240105939A1/en
Publication of WO2023159385A1 publication Critical patent/WO2023159385A1/zh

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—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
    • 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
    • H01M4/48—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
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2220/00—Batteries for particular applications
    • H01M2220/20—Batteries in motive systems, e.g. vehicle, ship, plane
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present application relates to the technical field of lithium batteries, in particular to a positive pole piece and related secondary batteries, battery modules, battery packs and electrical devices.
  • the present application also relates to a method for balancing internal voltage differences of secondary batteries.
  • lithium-ion batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, Military equipment, aerospace and other fields.
  • energy storage power systems such as hydropower, thermal power, wind power and solar power stations, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, Military equipment, aerospace and other fields.
  • the lithium iron phosphate battery has attracted people's attention due to its characteristics of large capacity, good safety, long life, and low price.
  • problems such as inaccurate remaining power display and rapid capacity decay often occur, which seriously affect the user experience. Therefore, it is very meaningful to provide a secondary battery that has good capacity retention performance and can accurately display the remaining power.
  • This application is made in view of the above-mentioned problems, and its purpose is to provide a positive electrode sheet, so that the secondary battery using the positive electrode sheet has good capacity retention performance; at the same time, the secondary battery using the positive electrode sheet The battery can accurately display the remaining power of the secondary battery, improving user experience.
  • the present application provides a positive pole piece and a secondary battery including the same, a battery module, a battery pack and an electrical device.
  • the present application also provides a method for balancing the internal voltage difference of the secondary battery.
  • the first aspect of the present application provides a positive electrode sheet, which at least includes the following materials:
  • a first active material selected from lithium iron phosphate-based materials of the formula LiFe1- xMnxPO4 , wherein x is 0-0.8, optionally 0-0.5, more optionally 0-0.25; and
  • the second active material is selected from one or more of lithium nickel oxide, lithium manganate, lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, lithium-rich manganese base, and lithium vanadium phosphate;
  • the amount of the second active material is 10-70%, optionally 10-30%, more optionally 15-20%, based on the total mass of the first active material and the second active material.
  • the secondary battery using the positive electrode sheet described in the present application has good voltage self-balancing performance, thereby having improved capacity retention performance, and can accurately display the remaining power of the secondary battery to improve user experience.
  • the amount of the first active material is 30-90%, optionally 70-90%, more optionally 80-85%, based on the first active material and the second active The total mass of the material.
  • the mass ratio of the first active material to the second active material is 3:7 to 9:1, optionally 7:3 to 9:1, more optionally 80:20 to 85:15.
  • the first active material is lithium iron phosphate or lithium manganese iron phosphate or a mixture of lithium iron phosphate and lithium iron manganese phosphate.
  • the second active material includes at least one of lithium nickel cobalt manganate or lithium nickel cobalt aluminate.
  • the geometric center of the first active material subsection is not higher than the geometric center of the second active material subsection.
  • the charging polarization of the secondary battery applying the positive electrode sheet of the present application can be reduced, thereby reducing the heat production and temperature rise of the secondary battery, Thereby improving the safety performance and life of the battery.
  • the geometric center of the distribution of the first active material coincides with the geometric center of the distribution of the second active material; or the first active material The geometric center of the material distribution is lower than the geometric center of the distribution of the second active material.
  • the second aspect of the present application provides a method of balancing the internal voltage difference of a secondary battery, wherein a positive electrode sheet comprising at least the following materials is used:
  • a first active material selected from lithium iron phosphate-based materials of the formula LiFe1- xMnxPO4 , wherein x is 0-0.8, optionally 0-0.5, more optionally 0-0.25; and
  • the second active material is selected from one or more of lithium nickel oxide, lithium manganate, lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, lithium-rich manganese base, and lithium vanadium phosphate;
  • the amount of the second active material is 10-70%, optionally 10-30%, more optionally 15-20%, based on the total mass of the first active material and the second active material.
  • a third aspect of the present application provides a secondary battery, including the positive electrode sheet of the first aspect of the present application.
  • the secondary battery can be prepared by a method for preparing a secondary battery generally used in the art.
  • the voltage value V1 at the position corresponding to the 85% state of charge and the voltage value V2 at the position corresponding to the 60% state of charge satisfy: V1-V2 ⁇ 0.15V.
  • V1 and V2 satisfy the above relationship, it is helpful to ensure that the secondary battery has a good voltage self-balancing performance, thereby improving the capacity retention performance of the secondary battery, and at the same time correctly displaying the remaining power of the secondary battery.
  • a fourth aspect of the present application provides a battery module including the secondary battery of the third aspect of the present application.
  • the battery module can be prepared by a method for preparing a battery module commonly used in the art.
  • a fifth aspect of the present application provides a battery pack, including the battery module of the fourth aspect of the present application.
  • the battery pack can be prepared by a method for preparing a battery pack commonly used in the art.
  • a sixth aspect of the present application provides an electric device, including at least one selected from the secondary battery of the third aspect of the present application, the battery module of the fourth aspect of the present application, or the battery pack of the fifth aspect of the present application.
  • the positive pole piece includes the first active material and the second active material.
  • the organic combination of the two active materials can make the secondary battery have good voltage self-balancing performance, and the voltage inside the pole piece can be adjusted by itself. SOC (State of Charge, State of Charge) state difference, thereby improving the capacity retention performance of the secondary battery.
  • SOC State of Charge, State of Charge
  • the battery module, battery pack and electric device of the present application include the secondary battery provided by the present application, and thus have at least the same advantages as the secondary battery.
  • Fig. 1 is a schematic diagram of geometric center A of the first active material overlapping with geometric center B of the second active material (Fig. 1-1) and geometric center A being lower than geometric center B (Fig. 1-2).
  • Figure 2 is the charging curve of LFP (lithium iron phosphate) ( Figure 2-1) and the charging curve of NCM (nickel cobalt manganese) ( Figure 2-2).
  • LFP lithium iron phosphate
  • NCM nickel cobalt manganese
  • FIG. 3 is a schematic diagram of parallel connection of the unit cell 1 and the unit cell 2 .
  • Figure 4 is a graph showing the difference in SOC between unit cells 1 and 2 corresponding to the LFP series (left column) and NCM523 series (ie LiNi 0.5 Co 0.2 Mn 0.3 O 2 ) (right column) as the SOC increases.
  • FIG. 5 is a schematic diagram of a secondary battery according to an embodiment of the present application.
  • FIG. 6 is an exploded view of the secondary battery according to one embodiment of the present application shown in FIG. 5 .
  • FIG. 7 is a schematic diagram of a battery module according to an embodiment of the present application.
  • FIG. 8 is a schematic diagram of a battery pack according to an embodiment of the present application.
  • FIG. 9 is an exploded view of the battery pack according to one embodiment of the present application shown in FIG. 8 .
  • FIG. 10 is a schematic diagram of an electrical device in which a secondary battery is used as a power source according to an embodiment of the present application.
  • ranges disclosed herein are defined in terms of lower and upper limits, and a given range is defined by selecting a lower limit and an upper limit that define the boundaries of the particular range. Ranges defined in this manner may be inclusive or exclusive and may be combined arbitrarily, ie any lower limit may be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, it is understood that ranges of 60-110 and 80-120 are also contemplated. Additionally, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, the following ranges are all expected: 1-3, 1-4, 1-5, 2- 3, 2-4 and 2-5.
  • the numerical range "a-b” represents an abbreviated representation of any combination of real numbers between a and b, where a and b are both real numbers.
  • the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article, and "0-5" is only an abbreviated representation of the combination of these values.
  • a certain parameter is an integer ⁇ 2
  • the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed in sequence, and may also include steps (b) and (a) performed in sequence.
  • steps (c) means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c) , may also include steps (a), (c) and (b), may also include steps (c), (a) and (b) and so on.
  • the "comprising” and “comprising” mentioned in this application represent an open type or a closed type.
  • the “comprising” and “comprising” may mean that other components not listed may be included or included, or only listed components may be included or included.
  • the term "or” is inclusive unless otherwise stated.
  • the phrase "A or B” means “A, B, or both A and B.” More specifically, the condition "A or B” is satisfied by either of the following: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists) ; or both A and B are true (or exist).
  • manganese-rich lithium-based means a manganese-rich lithium-based material commonly used in the art, which contains two components, Li 2 MnO 3 and LiMnO 2 ,
  • the chemical formula can be abbreviated as xLiMO 2 ⁇ (1-x)Li 2 MnO 3 , where 0 ⁇ x ⁇ 1.
  • the term “voltage self-balancing” refers to the difference in voltage generated by the distribution of the state of charge in different regions of the internal electrode assembly of a single battery during the use of the prepared secondary battery. Perform automatic equalization. Good “voltage self-balancing" performance is conducive to improving the capacity retention performance of the secondary battery and improving the safety and life of the secondary battery.
  • geometric center refers to the geometric center of the position where the active material is distributed in the thickness direction of the pole piece.
  • the geometric center of the distribution of the first active material in the thickness direction of the pole piece is the geometric center A
  • the geometric center of the distribution of the second active material in the thickness direction of the pole piece is the geometric center B.
  • the inventors of the present application found in actual work that: during use of lithium iron phosphate secondary batteries, problems such as inaccurate remaining power display and rapid capacity decay often occur, which seriously affect user experience. Unexpectedly, the inventors found after a lot of attempts that the above problems can be effectively improved by adding a second active material to the lithium iron phosphate positive electrode sheet.
  • the first aspect of the present application provides a positive electrode sheet, which at least includes the following materials:
  • a first active material selected from lithium iron phosphate-based materials of the formula LiFe1- xMnxPO4 , wherein x is 0-0.8, optionally 0-0.5, more optionally 0-0.25; and
  • the second active material is selected from one or more of lithium nickel oxide, lithium manganate, lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, lithium-rich manganese base, and lithium vanadium phosphate;
  • the amount of the second active material is 10-70%, optionally 10-30%, more optionally 15-20%, based on the total mass of the first active material and the second active material.
  • the positive electrode sheet of the present application includes a first active material and a second active material.
  • the organic combination of the two active materials can make the secondary battery have good voltage self-balancing performance, and can adjust the SOC state difference inside the electrode sheet by itself, thereby improving The capacity retention performance of the secondary battery; at the same time, due to the good one-to-one correspondence between the voltage and the SOC, when the remaining power is monitored through the voltage, the remaining power can be accurately displayed and the user experience can be improved.
  • the first active material is selected from lithium iron phosphate-based materials of the formula LiFe 1-x Mn x PO 4 , wherein x is 0-0.8, optionally 0-0.5, more optionally 0 -0.25.
  • x can be selected from 0, 0.1, 0.2, 0.25, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, and the like.
  • the second active material is selected from one of lithium nickelate, lithium manganate, lithium cobaltate, lithium nickel cobalt manganate, lithium nickel cobalt aluminate, lithium-rich manganese base, and lithium vanadium phosphate. one or more species.
  • the second active material may be lithium nickel cobalt manganate, or a mixture of lithium nickel cobalt manganate and lithium nickel cobalt aluminate, or a mixture of lithium nickel cobalt manganate, lithium nickel cobalt aluminate and lithium vanadium phosphate.
  • the amount of the second active material is 10-70%, optionally 10-30%, more optionally 15-20%, based on the total amount of the first active material and the second active material quality meter.
  • the amount of the second active material can be 10%, 15%, 20%, 30%, 40%, 50%, 60% or 70%, optionally 15% or 20%.
  • the amount of the second active material is within the above range, it can be ensured that the prepared positive electrode sheet has good voltage self-balancing performance, and the capacity retention performance of the secondary battery applying the positive electrode sheet of the present application can be improved, and the remaining power can be accurately displayed at the same time .
  • the high-temperature safety performance of the second active material may be poor, so if the second active material is used in an excessive amount, it may damage the secondary battery high temperature safety performance; on the contrary, if the amount of the second active material is too small, the energy density of the secondary battery may be low.
  • the minimum content of lithium nickel cobalt manganese oxide is 5%, based on the total mass of the first active material and the second active material , the precursor is the total amount of the second active material within the range defined in the present application.
  • the minimum content of lithium nickel cobalt aluminate is 5%, based on the total mass of the first active material and the second active material , the precursor is the total amount of the second active material within the range defined in the present application.
  • the first active material is used in an amount of 30-90%, optionally 70-90%, more optionally 80-85%, based on the first active material and the second active material. The total mass of the material.
  • the energy density of the positive electrode sheet may be low; when the amount of the first active material is lower than the above range, the high temperature safety performance of the secondary battery using the positive electrode sheet may be relatively low. Difference.
  • the mass ratio of the first active material to the second active material is 3:7 to 9:1, optionally 7:3 to 9:1, more optionally 80:20 to 85:15.
  • the secondary battery using the positive electrode sheet can have good voltage self-balancing performance.
  • the positive electrode sheet comprising the above mass ratio of the first active material and the second active material has a higher energy density, and the secondary battery using the positive electrode sheet also has excellent high temperature performance.
  • the first active material is lithium iron phosphate or lithium manganese iron phosphate or a mixture of lithium iron phosphate and lithium iron manganese phosphate.
  • the second active material includes at least one of lithium nickel cobalt manganate or lithium nickel cobalt aluminate.
  • the geometric center of the first active material subsection is not higher than the geometric center of the second active material subsection.
  • the geometric center A of the distribution of the first active material coincides with the geometric center B of the distribution of the second active material, as shown in Figure 1-1 .
  • the geometric center A of the distribution of the first active material is lower than the geometric center B of the distribution of the second active material, as shown in Figures 1-2 .
  • the spatial structure design at the pole piece level also has a significant impact on the performance of lithium secondary batteries, especially for the design of pole pieces containing two or more active materials.
  • the performance of the battery can be further improved by designing the space structure of the pole piece.
  • the distribution of the geometric center of the first active material and the distribution of the geometric center of the second active material conforms to the above conditions, especially when the geometric center A of the distribution of the first active material is lower than the geometric center B of the distribution of the second active material , can reduce the charging polarization of the secondary battery using the positive electrode sheet of the present application, thereby reducing the heat generation and temperature rise of the secondary battery, and then improving the safety performance and life of the secondary battery.
  • the first active material such as lithium iron phosphate
  • the second active material such as lithium nickel cobalt manganese oxide is greatly affected by diffusion, and placing it away from the current collector can shorten the transmission path of lithium ions, thereby reducing concentration polarization during charging.
  • the first active material is lithium iron phosphate and the second active material is lithium nickel cobalt manganese oxide
  • the geometry of lithium iron phosphate The center A and the geometric center B of lithium nickel cobalt manganese oxide are coincident.
  • lithium iron phosphate and lithium nickel cobalt manganese oxide are double-layer coated, lithium iron phosphate is located on the side close to the current collector, while lithium nickel cobalt manganese oxide is located on the side away from the current collector, the position of the geometric center A is low at the geometric center B.
  • the positive electrode sheet also includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode collector, and the positive electrode film layer includes a positive electrode active material.
  • the relative position of the geometric center can be determined by conventional methods known to those skilled in the art.
  • the section morphology of pole piece can be analyzed by scanning electron microscope, and the height interval of the distribution of the first active material can be identified through the particle size, so as to determine the geometric center A; the geometric center B can be confirmed by the height interval of the distribution of the second active material.
  • the surface element analysis of the positive pole piece can be performed to form a distribution map of the characteristic elements of the active material on the cross section, and confirm the height interval of the distribution of the first active material and the distribution of the second active material, thereby confirming the geometric center A Relative positional relationship with B.
  • the positive electrode current collector has two opposing surfaces in its own thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposing surfaces of the positive electrode current collector.
  • the positive electrode current collector can be a metal foil or a composite current collector.
  • aluminum foil can be used as the metal foil.
  • the composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base.
  • the composite current collector can be formed by forming metal materials (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as polypropylene (PP), polyethylene terephthalic acid It is formed on substrates such as ethylene glycol ester (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).
  • PP polypropylene
  • PET polyethylene glycol ester
  • PBT polybutylene terephthalate
  • PS polystyrene
  • PE polyethylene
  • the positive electrode film layer may further optionally include a binder.
  • the binder may include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene At least one of ethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin.
  • the positive electrode film layer may also optionally include a conductive agent.
  • the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
  • the mass fraction of the sum of the mass of the first active material and the second active material in the positive electrode film layer is not less than 80%, optionally not less than 90%, and further optionally not lower at 95%.
  • the positive electrode sheet can be prepared in the following manner: the above-mentioned components used to prepare the positive electrode sheet, such as positive electrode active material, conductive agent, binder and any other components, are dispersed in a solvent (such as N -methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.
  • a solvent such as N -methylpyrrolidone
  • the positive electrode slurry of the first active material and the positive electrode slurry of the second active material can be prepared respectively, and the positive electrode slurry of the first active material is coated on the side close to the current collector, and the positive electrode slurry of the second active material is coated on the side close to the current collector. The positive electrode slurry of the material is coated on the side away from the current collector.
  • the inventor found in the research that lithium iron phosphate secondary batteries are prone to problems such as battery capacity attenuation and inaccurate power display during use.
  • the above-mentioned problems can be better solved.
  • the possible reason is that after adding the second active material to the first active material, the resulting secondary battery has good voltage self-balancing performance, which can better balance the voltage difference inside the secondary battery.
  • the second aspect of the present application provides a method of balancing the internal voltage difference of a secondary battery, wherein a positive electrode sheet comprising at least the following materials is used:
  • a first active material selected from lithium iron phosphate-based materials of the formula LiFe1- xMnxPO4 , wherein x is 0-0.8, optionally 0-0.5, more optionally 0-0.25; and
  • the second active material is selected from one or more of lithium nickel oxide, lithium manganate, lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, lithium-rich manganese base, and lithium vanadium phosphate;
  • the amount of the second active material is 10-70%, optionally 10-30%, more optionally 15-20%, based on the total mass of the first active material and the second active material.
  • the first active material and the second active material may have the meanings described in the section about the positive electrode sheet.
  • Lithium secondary batteries can be regarded as countless small unit batteries connected in parallel. When charging lithium secondary batteries, different unit batteries have different spatial positions, temperature/stress/electrolyte infiltration and other environmental factors that affect kinetics, resulting in different charging kinetics and different charging speeds. The unit cells in the position will cause SOC deviation.
  • unit cell 1 and unit cell 2 are connected in parallel in the model.
  • Set the temperature of unit cell 1 to 30°C the temperature of unit cell 2 is higher than the temperature of unit cell 1 (for example, higher than 5°C or higher than 10°C), and charge at different rates (for example, by 1C , 2C, 4C charging rate).
  • charge at different rates for example, by 1C , 2C, 4C charging rate.
  • the SOC difference between unit cell 1 and unit cell 2 increases continuously until the average SOC of charging reaches 80% SOC or more, the unit cell The inflection point of the SOC difference between 1 and unit cell 2 appears, indicating that the voltage self-balancing performance of the unit cell is poor, and the resulting voltage difference is not enough to adjust the difference in SOC state.
  • the SOC difference decreases with the increase of the average SOC, indicating that the voltage difference between the unit cell 1 and the unit cell 2 forms an internal self-charging state.
  • the unit battery can automatically adjust the difference in SOC state under the action of voltage difference. It can be seen that adding a second active material such as lithium nickel cobalt manganese oxide to a first active material such as lithium iron phosphate can effectively improve the voltage self-balancing performance of the secondary battery.
  • a third aspect of the present application provides a secondary battery, which includes the positive electrode sheet described in the first aspect of the present application.
  • the secondary battery can be prepared by a method generally used in the art.
  • a secondary battery typically includes a positive pole piece, a negative pole piece, an electrolyte, and a separator.
  • active ions are intercalated and extracted back and forth between the positive electrode and the negative electrode.
  • the electrolyte plays the role of conducting ions between the positive pole piece and the negative pole piece.
  • the separator is arranged between the positive pole piece and the negative pole piece, which mainly plays a role in preventing the short circuit of the positive and negative poles, and at the same time allows ions to pass through.
  • the voltage value V1 at the position corresponding to the 85% state of charge and the voltage value V2 at the position corresponding to the 60% state of charge satisfy: V1- V2 ⁇ 0.15V.
  • the secondary battery has good voltage self-balancing performance, which is beneficial to improve the capacity retention performance of the secondary battery, and at the same time correctly display the remaining power of the secondary battery.
  • the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer arranged on at least one surface of the negative electrode current collector, and the negative electrode film layer includes a negative electrode active material.
  • the negative electrode current collector has two opposing surfaces in its own thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposing surfaces of the negative electrode current collector.
  • the negative electrode current collector can use a metal foil or a composite current collector.
  • copper foil can be used as the metal foil.
  • the composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base.
  • Composite current collectors can be formed by metal materials (copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver and silver alloys, etc.) on polymer material substrates (such as polypropylene (PP), polyethylene terephthalic acid It is formed on substrates such as ethylene glycol ester (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).
  • the negative electrode active material can be a negative electrode active material known in the art for batteries.
  • the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based material, tin-based material, lithium titanate, and the like.
  • the silicon-based material may be selected from at least one of elemental silicon, silicon-oxygen compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys.
  • the tin-based material may be selected from at least one of simple tin, tin oxide compounds and tin alloys.
  • the present application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials of batteries can also be used. These negative electrode active materials may be used alone or in combination of two or more.
  • the negative electrode film layer may further optionally include a binder.
  • the binder can be selected from styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), poly At least one of methacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).
  • the negative electrode film layer may also optionally include a conductive agent.
  • the conductive agent can be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.
  • the negative electrode film layer may optionally include other additives, such as thickeners (such as sodium carboxymethylcellulose (CMC-Na)) and the like.
  • thickeners such as sodium carboxymethylcellulose (CMC-Na)
  • CMC-Na sodium carboxymethylcellulose
  • the negative electrode sheet can be prepared in the following manner: the above-mentioned components used to prepare the negative electrode sheet, such as negative electrode active material, conductive agent, binder and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.
  • a solvent such as deionized water
  • the electrolyte plays the role of conducting ions between the positive pole piece and the negative pole piece.
  • the present application has no specific limitation on the type of electrolyte, which can be selected according to requirements.
  • electrolytes can be liquid, gel or all solid.
  • the electrolyte is an electrolytic solution.
  • the electrolyte solution includes an electrolyte salt and a solvent.
  • the electrolyte salt may be selected from lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonyl imide, lithium bistrifluoromethanesulfonyl imide, trifluoromethane At least one of lithium sulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium difluorooxalate borate, lithium difluorodifluorooxalatephosphate and lithium tetrafluorooxalatephosphate.
  • the solvent may be selected from ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, Butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate At least one of ester, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.
  • the electrolyte may optionally include additives.
  • additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain performances of the battery, such as additives that improve battery overcharge performance, additives that improve high-temperature or low-temperature performance of batteries, and the like.
  • a separator is further included in the secondary battery.
  • the present application has no particular limitation on the type of the isolation membrane, and any known porous structure isolation membrane with good chemical stability and mechanical stability can be selected.
  • the material of the isolation film can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.
  • the separator can be a single-layer film or a multi-layer composite film, without any particular limitation. When the separator is a multilayer composite film, the materials of each layer may be the same or different, and there is no particular limitation.
  • the positive pole piece, the negative pole piece and the separator can be made into an electrode assembly through a winding process or a lamination process.
  • the secondary battery may include an outer package.
  • the outer package can be used to package the above-mentioned electrode assembly and electrolyte.
  • the outer packaging of the secondary battery may be a hard case, such as a hard plastic case, aluminum case, steel case, and the like.
  • the outer packaging of the secondary battery may also be a soft bag, such as a bag-type soft bag.
  • the material of the soft case may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, polybutylene succinate, and the like.
  • a fourth aspect of the present application provides a battery module including the secondary battery described in the third aspect of the present application.
  • a fifth aspect of the present application provides a battery pack, including the battery module described in the fourth aspect of the present application.
  • a sixth aspect of the present application provides an electric device, including at least one of the secondary battery of the third aspect of the present application, the battery module of the fourth aspect, or the battery pack of the fifth aspect.
  • the secondary battery, battery module, or battery pack can be used as a power source of the electric device, and can also be used as an energy storage unit of the electric device.
  • the electric devices may include mobile devices (such as mobile phones, notebook computers, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, etc.) , electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but not limited thereto.
  • a secondary battery, a battery module or a battery pack can be selected according to its use requirements.
  • FIG. 5 shows a secondary battery 5 having a square structure as an example.
  • the outer package may include a housing 51 and a cover 53 .
  • the housing 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plates enclose to form an accommodating cavity.
  • the housing 51 has an opening communicating with the accommodating cavity, and the cover plate 53 can cover the opening to close the accommodating cavity.
  • the positive pole piece, the negative pole piece and the separator can be formed into an electrode assembly 52 through a winding process or a lamination process.
  • the electrode assembly 52 is packaged in the accommodating cavity. Electrolyte is infiltrated in the electrode assembly 52 .
  • the number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.
  • the secondary battery can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.
  • FIG. 7 is a battery module 4 as an example.
  • a plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4 .
  • the plurality of secondary batteries 5 may be fixed by fasteners.
  • the battery module 4 may also include a case having a housing space in which a plurality of secondary batteries 5 are accommodated.
  • the above-mentioned battery modules can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.
  • the battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box.
  • the battery box includes an upper box body 2 and a lower box body 3 , the upper box body 2 can cover the lower box body 3 and form a closed space for accommodating the battery module 4 .
  • Multiple battery modules 4 can be arranged in the battery box in any manner.
  • FIG. 10 is an example of an electrical device.
  • the electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle.
  • a battery pack or a battery module may be used.
  • a device may be a cell phone, tablet, laptop, or the like.
  • the device is generally required to be light and thin, and a secondary battery can be used as a power source.
  • Lithium iron phosphate Gram capacity 141mAh/g NCM523 ie LiNi 0.5 Co 0.2 Mn 0.3 O 2
  • Gram capacity 170mAh/g NCA i.e. LiNi 0.8 Co 0.15 Al 0.05 O 2
  • the first active material lithium iron phosphate (calculated as LiFePO 4 ), the second active material nickel cobalt manganese oxide (NCM523 is LiNi 0.5 Co 0.2 Mn 0.3 O 2 ), binder polyvinylidene fluoride, conductive agent acetylene black according to Mix at a weight ratio of 28.8:67.2:2:2, then add N-methylpyrrolidone (NMP) as a solvent, and stir until the system is homogeneous under the action of a vacuum mixer to obtain a positive electrode slurry with a solid content of 75 wt%.
  • NMP N-methylpyrrolidone
  • the slurry was uniformly coated on an aluminum foil with a thickness of 13 ⁇ m at a coating density of 19.6 mg/cm 2 , and one side was coated; after that, the positive electrode sheet of Example 1 was obtained through drying, cold pressing, and slitting.
  • Negative active material artificial graphite, conductive agent acetylene black, binder styrene-butadiene rubber (SBR), thickener carboxymethyl cellulose sodium (CMC-Na) are dissolved in the solvent according to the weight ratio of 96:1:2:1 In deionized water, stir and mix evenly to prepare negative electrode slurry.
  • the negative electrode slurry was evenly coated on the copper foil of the negative electrode current collector at a coating density of 9.7 mg/cm 2 , and then dried, cold pressed, and cut to obtain negative electrode sheets.
  • a commercially available PP-PE copolymer microporous film with a thickness of 20 ⁇ m and an average pore diameter of 80 nm was used.
  • the separator is in the middle of the positive and negative poles to play the role of isolation, and wind up to get the bare cell.
  • the bare cell is placed in the outer package, the above-mentioned electrolyte is injected and packaged to obtain a secondary battery.
  • the first positive electrode active material lithium iron phosphate (calculated as LiFePO 4 )
  • the second positive electrode active material nickel cobalt lithium manganese oxide (NCM523 is LiNi 0.5 Co 0.2 Mn 0.3 O 2 )
  • binder The weight ratios of polyvinylidene fluoride as the agent and acetylene black as the conductive agent are 38.4:57.6:2:2, 48:48:2:2, 57.6:38.4:2:2, 67.2:28.8:2:2, 76.8:19.2 :2:2, 81.6:14.4:2:2 and 86.4:9.6:2:2, and the coating densities are 19.9mg/cm 2 , 20.1mg/cm 2 , 20.4mg/cm 2 , 20.7mg/cm 2 , 20.9mg/cm 2 , 21.1mg/cm 2 and 21.2mg/cm 2 , other conditions of
  • Example 9 In addition to replacing the second positive electrode active material nickel cobalt lithium manganese oxide (NCM523, namely LiNi 0.5 Co 0.2 Mn 0.3 O 2 ) with NCA of equal mass (ie LiNi 0.8 Co 0.15 Al 0.05 O 2 ), other conditions of Example 9 were the same as Example 6 is the same.
  • NCM523 nickel cobalt lithium manganese oxide
  • NCA of equal mass
  • the first positive electrode active material lithium iron phosphate (calculated as LiFePO 4 )
  • the second positive electrode active material nickel cobalt lithium manganese oxide (NCM523 is LiNi 0.5 Co 0.2 Mn 0.3 O 2 )
  • binder The weight ratios of the agent polyvinylidene fluoride and the conductive agent acetylene black are 91.2:4.8:2:2 and 96:0:2:2 respectively, and the coating density is 21.4mg/cm 2 and 21.5mg/cm 2 respectively, Other conditions of Comparative Example 1-2 are the same as in Example 1.
  • the upper and lower limits of the service voltage of the secondary battery to be tested at 25°C are Vmax and Vmin respectively, and the nominal capacity is C0Ah. Hour. Discharge the battery to the lower limit voltage Vmin with a constant current of 0.33C0; let it stand for 30 minutes; charge the battery to the upper limit voltage Vmax with a constant current of 1C0, and then switch to constant voltage charging until the current decreases to 0.05C0. All the capacities charged in the charging process correspond to the capacity of 0% SOC-100% SOC.
  • the voltage curve of the secondary battery can be obtained by plotting the SOC% as the abscissa and the corresponding voltage during constant current charging as the ordinate.
  • the corresponding minimum initial SOC position is the voltage rise position.
  • the capacity retention performance of the secondary battery is evaluated by the 25°C fast charging cycle life/number of cycles.
  • the lithium-ion batteries prepared in Examples and Comparative Examples were charged at a rate of 2C, discharged at a rate of 1C, and continuously cycled in the range of 3%-97% SOC until the capacity of the lithium-ion battery was less than 80% of the initial capacity. %, record the number of cycles, and record it as cycle performance.
  • the 25°C fast charge cycle life/number of cycles of the secondary battery prepared by adding the second active material is better.
  • the self-balancing performance of the corresponding battery can be further improved, and the capacity retention performance can be improved.
  • the present application is not limited to the above-mentioned embodiments.
  • the above-mentioned embodiments are merely examples, and within the scope of the technical solution of the present application, embodiments that have substantially the same configuration as the technical idea and exert the same function and effect are included in the technical scope of the present application.
  • various modifications conceivable by those skilled in the art are added to the embodiments, and other forms constructed by combining some components in the embodiments are also included in the scope of the present application. .

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Abstract

提供一种正极极片，其至少包括以下物质：第一活性材料，选自式LiFe 1-xMn xPO 4的磷酸铁锂基材料， x为0-0.8，可选为0-0.5，更可选为0-0.25；和第二活性材料，其选自镍酸锂、锰酸锂、钴酸锂、镍钴锰酸锂、镍钴铝酸锂、富锂锰基、磷酸钒锂中的一种或多种；其中，第二活性材料的用量为10-70％，可选为10-30％，更可选为15-20％，基于第一活性材料和第二活性材料的总质量计；还提供包含正极极片的二次电池及其相关的电池模块、电池包和用电装置；还提供一种平衡二次电池内部电压差的方法。

Description

正极极片及二次电池、电池模块、电池包和用电装置，及平衡电池内部电压差的方法 技术领域
本申请涉及锂电池技术领域，尤其涉及一种正极极片及其相关的二次电池、电池模块、电池包和用电装置，本申请还涉及一种平衡二次电池内部电压差的方法。
背景技术
近年来，随着锂离子电池的应用范围越来越广泛，锂离子电池广泛应用于水力、火力、风力和太阳能电站等储能电源系统，以及电动工具、电动自行车、电动摩托车、电动汽车、军事装备、航空航天等多个领域。其中磷酸铁锂电池由于容量大、安全性好、寿命长、价格低廉等特性而受到人们的关注。然而，磷酸铁锂电池在使用过程中经常发生剩余电量显示不准确、容量快速衰减等问题，严重影响了用户体验。因此，提供一种具备良好的容量保持性能，并能够准确显示剩余电量的二次电池是非常有意义的。
发明内容
本申请是鉴于上述课题而进行的，其目的在于，提供一种正极极片，使得应用所述正极极片的二次电池具备良好的容量保持性能；同时，应用所述正极极片的二次电池可以准确显示二次电池的剩余电量，改善用户体验。
为达到上述目的，本申请提供了一种正极极片及包含其的二次电池、电池模块、电池包和用电装置。此外，本申请还提供一种平衡二次电池内部电压差的方法。
本申请的第一方面提供一种正极极片，其至少包括以下物质：
第一活性材料，其选自式LiFe 1-xMn xPO 4的磷酸铁锂基材料，其中x为0-0.8，可选为0-0.5，更可选为0-0.25；和
第二活性材料，其选自镍酸锂、锰酸锂、钴酸锂、镍钴锰酸锂、镍钴铝酸锂、富锂锰基、磷酸钒锂中的一种或多种；
其中，所述第二活性材料的用量为10-70％，可选为10-30％，更可选为15-20％，基于第一活性材料和第二活性材料的总质量计。
应用本申请所述正极极片的二次电池具备良好的电压自均衡性能，从而具备改善的容量保持性能，同时可准确显示二次电池的剩余电量，改善用户体验。
在任意实施方式中，可选地，所述第一活性材料的用量为30-90％，可选为70-90％，更可选为80-85％，基于第一活性材料和第二活性材料的总质量计。
在任意实施方式中，可选地，所述第一活性材料与所述第二活性材料的质量比为3∶7至9∶1，可选为7∶3至9∶1，更可选为80∶20至85∶15。
当第一活性材料与第二活性材料的质量比在上述范围内时，有利于改善应用本申请正极极片的二次电池的电压自均衡性能。
在任意实施方式中，可选地，所述第一活性材料为磷酸铁锂或磷酸锰铁锂或磷酸铁锂与磷酸锰铁锂的混合物。
在任意实施方式中，可选地，所述第二活性材料包括镍钴锰酸锂或镍钴铝酸锂中的至少一种。
在任意实施方式中，可选地，在所述正极极片的厚度方向上，所述第一活性材料分部的几何中心不高于所述第二活性材料分部的几何中心。
当第一活性材料的几何中心和第二活性材料的几何中心分布符合上述情况时，可降低应用本申请正极极片的二次电池的充电极化，从而降低二次电池的产热和升温，进而改善电池的安全性能和寿命。
在任意实施方式中，可选地，在所述正极极片的厚度方向上，所述第一活性材料分布的几何中心与所述第二活性材料分布的几何中心重合；或所述第一活性材料分布的几何中心低于第二活性材料分布的几何中心。
本申请的第二方面提供一种平衡二次电池内部电压差的方法，其中使用至少包括以下物质的正极极片：
第一活性材料，其选自式LiFe 1-xMn xPO 4的磷酸铁锂基材料，其中x为0-0.8，可选为0-0.5，更可选为0-0.25；和
第二活性材料，其选自镍酸锂、锰酸锂、钴酸锂、镍钴锰酸锂、镍钴铝酸锂、富锂锰基、磷酸钒锂中的一种或多种；
其中，所述第二活性材料的用量为10-70％，可选为10-30％，更可选为15-20％，基于第一活性材料和第二活性材料的总质量计。
本申请的第三方面提供一种二次电池，包括本申请第一方面的正极极片。二次电池可采用本领域通常使用的制备二次电池的方法制备。
在任意实施方式中，可选地，在所述二次电池的充电电压曲线中，85％荷电状态对应位置的电压值V1与60％荷电状态对应位置的电压值V2满足：V1-V2≥0.15V。
当V1和V2满足上述关系时，有助于确保二次电池具备良好的电压自均衡性能，从而改善二次电池的容量保持性能，同时正确显示二次电池的剩余电量。
本申请的第四方面提供一种电池模块，包括本申请的第三方面的二次电池。电池模块可采用本领域通常使用的制备电池模块的方法制备。
本申请的第五方面提供一种电池包，包括本申请的第四方面的电池模块。电池包可采用本领域通常使用的制备电池包的方法制备。
本申请的第六方面提供一种用电装置，包括选自本申请第三方面的二次电池、本申请第四方面的电池模块或本申请第五方面的电池包中的至少一种。
[有益效果]
在本申请的二次电池中，正极极片包括第一活性材料和第二活性材料，两种活性材料的有机结合可使得二次电池具备良好的电压自均衡性能，可自行调节极片内部的SOC(荷电状态，State of Charge)状态差异，从而改善二次电池的容量保持性能，同时由于电压与SOC 的一一对应关系较好，在通过电压监测剩余电量时，可准确显示剩余电量，改善用户体验。
本申请的电池模块、电池包和用电装置包括本申请提供的二次电池，因而至少具有与所述二次电池相同的优势。
附图说明
图1为第一活性材料的几何中心A与第二活性材料的几何中心B重合(图1-1)和几何中心A低于几何中心B(图1-2)的示意图。
图2是LFP(磷酸铁锂)的充电曲线(图2-1)和NCM(镍钴锰)的充电曲线(图2-2)。LFP的充电曲线较为平缓，NCM的充电曲线比较陡峭，电压与SOC的一一对应关系较好。
图3是单元电池1和单元电池2并联的示意图。
图4是LFP系(左列图)和NCM523系(即LiNi 0.5Co 0.2Mn 0.3O 2)(右列图)对应的单元电池1和单元电池2的SOC差异随SOC增加的曲线图。
图5是本申请一实施方式的二次电池的示意图。
图6是图5所示的本申请一实施方式的二次电池的分解图。
图7是本申请一实施方式的电池模块的示意图。
图8是本申请一实施方式的电池包的示意图。
图9是图8所示的本申请一实施方式的电池包的分解图。
图10是本申请一实施方式的二次电池用作电源的用电装置的示意图。
附图标记说明：
1电池包；2上箱体；3下箱体；4电池模块；5二次电池；51壳体；52电极组件；53顶盖组件
具体实施方式
以下，适当地参照附图详细说明具体公开了本申请的正极极片及其制造方法、二次电池、电池模块、电池包和用电装置的实施方式。但是会有省略不必要的详细说明的情况。例如，有省略对已众所周知 的事项的详细说明、实际相同结构的重复说明的情况。这是为了避免以下的说明不必要地变得冗长，便于本领域技术人员的理解。此外，附图及以下说明是为了本领域技术人员充分理解本申请而提供的，并不旨在限定权利要求书所记载的主题。
本申请所公开的“范围”以下限和上限的形式来限定，给定范围是通过选定一个下限和一个上限进行限定的，选定的下限和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，即任何下限可以与任何上限组合形成一个范围。例如，如果针对特定参数列出了60-120和80-110的范围，则理解为60-110和80-120的范围也是预料到的。此外，如果列出的最小范围值1和2，和如果列出了最大范围值3，4和5，则下面的范围可全部预料到：1-3、1-4、1-5、2-3、2-4和2-5。在本申请中，除非有其他说明，数值范围“a-b”表示a到b之间的任意实数组合的缩略表示，其中a和b都是实数。例如数值范围“0-5”表示本文中已经全部列出了“0-5”之间的全部实数，“0-5”只是这些数值组合的缩略表示。另外，当表述某个参数为≥2的整数，则相当于公开了该参数为例如整数2、3、4、5、6、7、8、9、10、11、12等。
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。
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。
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(a)和(b)，表示所述方法可包括顺序进行的步骤(a)和(b)，也可以包括顺序进行的步骤(b)和(a)。例如，所述提到所述方法还可包括步骤(c)，表示步骤(c)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(a)、(b)和(c)，也可包括步骤(a)、(c)和(b)，也可以包括步骤(c)、(a)和(b)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。
如果没有特别的说明，在本申请中，术语“或”是包括性的。举例来说，短语“A或B”表示“A，B，或A和B两者”。更具体地，以下任一条件均满足条件“A或B”：A为真(或存在)并且B为假(或不存在)；A为假(或不存在)而B为真(或存在)；或A和B都为真(或存在)。
需要说明的是，本领域技术人员理解，本文中使用的术语“富锰锂基”意指本领域中通常使用的富锰锂基材料，其含有Li 2MnO 3和LiMnO 2两种组分，化学式可简写为xLiMO 2·(1-x)Li 2MnO 3，其中0＜x＜1。
需要说明的是，在本申请中，术语“电压自均衡”是指所制得的二次电池在使用过程中，对单体电池内部电极组件不同区域位置由荷电状态分布不同产生的电压差异进行自动均衡。良好的“电压自均衡”性能有利于改善二次电池的容量保持性能，提高二次电池的安全性和寿命。
需要说明的是，在本申请中，术语“几何中心”是指活性材料在极片厚度方向上分布的位置几何中心。例如，第一活性材料在极片厚度方向上分布的位置几何中心为几何中心A，第二活性材料在极片厚度方向上分布的位置几何中心为几何中心B。
本申请发明人在实际作业中发现：磷酸铁锂二次电池在使用过程中经常发生剩余电量显示不准确、容量快速衰减等问题，严重影响了用户体验。出人意料地，发明人在进行大量尝试后发现，通过在磷酸铁锂正极极片中另外添加第二活性材料，可有效改善上述问题。
[正极极片]
本申请的第一方面提供一种正极极片，其至少包括以下物质：
第一活性材料，其选自式LiFe 1-xMn xPO 4的磷酸铁锂基材料，其 中x为0-0.8，可选为0-0.5，更可选为0-0.25；和
第二活性材料，其选自镍酸锂、锰酸锂、钴酸锂、镍钴锰酸锂、镍钴铝酸锂、富锂锰基、磷酸钒锂中的一种或多种；
其中，所述第二活性材料的用量为10-70％，可选为10-30％，更可选为15-20％，基于第一活性材料和第二活性材料的总质量计。
本申请的正极极片包括第一活性材料和第二活性材料，两种活性材料的有机结合可使得二次电池具备良好的电压自均衡性能，可自行调节极片内部的SOC状态差异，从而改善二次电池的容量保持性能；同时由于电压与SOC的一一对应关系较好，在通过电压监测剩余电量时，可准确显示剩余电量，改善用户体验。
在本申请的正极极片中，第一活性材料选自式LiFe 1-xMn xPO 4的磷酸铁锂基材料，其中x为0-0.8，可选为0-0.5，更可选为0-0.25。例如，x可选自0、0.1、0.2、0.25、0.3、0.4、0.5、0.6、0.7、0.8等。
在本申请的正极极片中，第二活性材料选自镍酸锂、锰酸锂、钴酸锂、镍钴锰酸锂、镍钴铝酸锂、富锂锰基、磷酸钒锂中的一种或多种。例如，第二活性材料可以是镍钴锰酸锂，或镍钴锰酸锂与镍钴铝酸锂的混合物，或镍钴锰酸锂、镍钴铝酸锂和磷酸钒锂的混合物。
在本申请的正极极片中，第二活性材料的用量为10-70％，可选为10-30％，更可选为15-20％，基于第一活性材料和第二活性材料的总质量计。例如，第二活性材料的用量可以是10％、15％、20％、30％、40％、50％、60％或70％，可选为15％或20％。
当第二活性材料的用量在上述范围内时，可确保制得的正极极片具有良好的电压自均衡性能，改善应用本申请正极极片的二次电池的容量保持性能，同时准确显示剩余电量。
此外，由于第一活性材料的能量密度较低，但高温安全性能良好，而第二活性材料的高温安全性能可能较差，因此，如果第二活性材料的用量过多，则可能损害二次电池的高温安全性能；相反，如果第二活性材料的用量过少，则二次电池的能量密度可能较低。
在一些实施方式中，可选地，当第二活性材料中包括镍钴锰酸锂 时，镍钴锰酸锂的最低含量为5％，基于第一活性材料和第二活性材料的总质量计，前体是第二活性材料的总用量在本申请所限定的范围内。
在一些实施方式中，可选地，当第二活性材料中包括镍钴铝酸锂时，镍钴铝酸锂的最低含量为5％，基于第一活性材料和第二活性材料的总质量计，前体是第二活性材料的总用量在本申请所限定的范围内。
在一些实施方式中，可选地，所述第一活性材料的用量为30-90％，可选为70-90％，更可选为80-85％，基于第一活性材料和第二活性材料的总质量计。
当第一活性材料的用量高于上述范围时，正极极片的能量密度可能较低；当第一活性材料的用量低于上述范围时，应用正极极片的二次电池的高温安全性能可能较差。
在一些实施方式中，可选地，所述第一活性材料与所述第二活性材料的质量比为3∶7至9∶1，可选为7∶3至9∶1，更可选为80∶20至85∶15。
通过以上述质量比将第一活性材料和第二活性材料有机结合，可使得应用正极极片的二次电池具备良好的电压自均衡性能。此外，包含上述质量比的第一活性材料和第二活性材料的正极极片具备较高的能量密度，同时应用所述正极极片的二次电池还具备优异的高温性能。
在一些实施方式中，可选地，所述第一活性材料为磷酸铁锂或磷酸锰铁锂或磷酸铁锂与磷酸锰铁锂的混合物。
在一些实施方式中，可选地，所述第二活性材料包括镍钴锰酸锂或镍钴铝酸锂中的至少一种。
在一些实施方式中，可选地，在所述正极极片的厚度方向上，所述第一活性材料分部的几何中心不高于所述第二活性材料分部的几何中心。
在一些实施方式中，可选地，在所述正极极片的厚度方向上，第 一活性材料分布的几何中心A与第二活性材料分布的几何中心B重合，如图1-1中所示。
在一些实施方式中，可选地，在所述正极极片的厚度方向上，第一活性材料分布的几何中心A低于第二活性材料分布的几何中心B，如图1-2中所示。
本领域技术人员理解，极片层面的空间结构设计也对锂二次电池的性能有显著影响，尤其是对于含有两种及以上活性材料的极片设计。通过极片空间结构设计可以进一步提升电池的性能。具体到本申请，当第一活性材料的几何中心和第二活性材料的几何中心分布符合上述情况，特别是当第一活性材料分布的几何中心A低于第二活性材料分布的几何中心B时，可降低应用本申请正极极片的二次电池的充电极化，从而降低二次电池的产热和升温，进而改善二次电池的安全性能和寿命。
对于上述改善效果，可以这样理解：第一活性材料例如磷酸铁锂受扩散影响小，将其置于靠近集流体侧，可以缩短与集流体的距离，从而减小充电过程中的欧姆极化；相比之下，第二活性材料例如镍钴锰酸锂受扩散影响大，将其置于远离集流体侧，可以缩短锂离子的传输路径，从而减小充电过程中的浓差极化。
作为示例，例如，当第一活性材料为磷酸铁锂，第二活性材料为镍钴锰酸锂时，如果磷酸铁锂和镍钴锰酸锂是直接物理混合分布的，则磷酸铁锂的几何中心A和镍钴锰酸锂的几何中心B是重合的。又如，当磷酸铁锂和镍钴锰酸锂是双层涂布时，磷酸铁锂位于靠近集流体一侧，而镍钴锰酸锂位于远离集流体一侧，则几何中心A的位置低于几何中心B的位置。
本领域技术人员理解，在本申请中，正极极片还包括正极集流体以及设置在正极集流体至少一个表面的正极膜层，所述正极膜层包括正极活性材料。
在本申请中，可通过本领域技术人员已知的常规方法来确定几何中心的相对位置。例如，可通过扫描电镜分析极片断面形貌，通过颗 粒尺寸辨识出第一活性材料分布的高度区间，从而确定几何中心A；通过第二活性材料分布的高度区间确定几何中心B，从而可以确认几何中心A和B的相对位置关系。又如，可对正极极片进行表面元素分析，从而形成活性材料特征元素在断面上的分布图，确认第一活性材料分布的高度区间和第二活性材料分布的高度区间，从而确认几何中心A和B的相对位置关系。
在本申请中，正极集流体具有在其自身厚度方向相对的两个表面，正极膜层设置在正极集流体相对的两个表面的其中任意一者或两者上。
在一些实施方式中，所述正极集流体可采用金属箔片或复合集流体。例如，作为金属箔片，可采用铝箔。复合集流体可包括高分子材料基层和形成于高分子材料基层至少一个表面上的金属层。复合集流体可通过将金属材料(铝、铝合金、镍、镍合金、钛、钛合金、银及银合金等)形成在高分子材料基材(如聚丙烯(PP)、聚对苯二甲酸乙二醇酯(PET)、聚对苯二甲酸丁二醇酯(PBT)、聚苯乙烯(PS)、聚乙烯(PE)等的基材)上而形成。
在一些实施方式中，正极膜层还可选地包括粘结剂。作为示例，所述粘结剂可以包括聚偏氟乙烯(PVDF)、聚四氟乙烯(PTFE)、偏氟乙烯-四氟乙烯-丙烯三元共聚物、偏氟乙烯-六氟丙烯-四氟乙烯三元共聚物、四氟乙烯-六氟丙烯共聚物及含氟丙烯酸酯树脂中的至少一种。
在一些实施方式中，正极膜层还可选地包括导电剂。作为示例，所述导电剂可以包括超导碳、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯及碳纳米纤维中的至少一种。
在一些实施方式中，第一活性材料和第二活性材料的质量之和在正极极片膜层中的质量分数不低于80％，可选地不低于90％，进一步可选地不低于95％。
在一些实施方式中，可以通过以下方式制备正极极片：将上述用于制备正极极片的组分，例如正极活性材料、导电剂、粘结剂和任意 其他的组分分散于溶剂(例如N-甲基吡咯烷酮)中，形成正极浆料；将正极浆料涂覆在正极集流体上，经烘干、冷压等工序后，即可得到正极极片。
在一些实施方式中，可分别制备第一活性材料的正极浆料和第二活性材料的正极浆料，并将第一活性材料的正极浆料涂布在靠近集流体一侧，将第二活性材料的正极浆料涂布在远离集流体一侧。
[方法]
如前所述，发明人在研究中发现，磷酸铁锂二次电池在使用过程中容易发生电池容量衰减、电量显示不准确等问题。出人意料地，通过向第一活性材料中添加第二活性材料，可较好地解决上述问题。可能的原因是，在向第一活性材料中添加第二活性材料后，由此获得的二次电池具有良好的电压自均衡性能，可较好的平衡二次电池内部的电压差。
因此，本申请的第二方面提供一种平衡二次电池内部电压差的方法，其中使用至少包括以下物质的正极极片：
第一活性材料，其选自式LiFe 1-xMn xPO 4的磷酸铁锂基材料，其中x为0-0.8，可选为0-0.5，更可选为0-0.25；和
第二活性材料，其选自镍酸锂、锰酸锂、钴酸锂、镍钴锰酸锂、镍钴铝酸锂、富锂锰基、磷酸钒锂中的一种或多种；
其中，所述第二活性材料的用量为10-70％，可选为10-30％，更可选为15-20％，基于第一活性材料和第二活性材料的总质量计。
本领域技术人员理解，在本申请第二方面所述的方法中，第一活性材料和第二活性材料可具有在关于正极极片部分所述的含义。
发明人通过数学物理模型对本申请所述方法进行了模拟。锂二次电池可以看作是无数个小的单元电池并联在一起。当对锂二次电池充电时，不同的单元电池由于所处的空间位置不同，温度/应力/电解液浸润等影响动力学的环境因素不同，导致充电时动力学不同，充电速率快慢不同，不同位置的单元电池会形成SOC偏差。
如图3中所示，将单元电池1和单元电池2在模型中并联。设定单元电池1所处的温度为30℃，单元电池2所处的温度高于单元电池1所处的温度(例如高于5℃或高于10℃)，通过不同倍率充电(例如通过1C、2C、4C的充电倍率)。计算单元电池1和单元电池2的SOC差异。
如图4中所示，对于磷酸铁锂电池，随着温度差异和充电倍率增加，单元电池1和单元电池2的SOC差异不断增大，直到充电的平均SOC达到80％SOC以上时，单元电池1和单元电池2的SOC差异才出现拐点，表明单元电池的电压自均衡性能较差，产生的电压差异不足以调整SOC状态的差异。相比之下，对于镍钴锰酸锂电池，在充电平均SOC达到50％SOC左右时，SOC差异随着平均SOC增大而减小，表明单元电池1和单元电池2的电压差异形成内部自均衡，单元电池在电压差的作用下可自动调节SOC状态的差异。由此可见，向第一活性材料如磷酸铁锂中添加第二活性材料如镍钴锰酸锂可有效改善二次电池的电压自均衡性能。
[二次电池]
本申请的第三方面提供一种二次电池，其包括本申请第一方面所述的正极极片。二次电池可采用本领域通常使用的方法进行制备。
通常情况下，二次电池包括正极极片、负极极片、电解质和隔离膜。在电池充放电过程中，活性离子在正极极片和负极极片之间往返嵌入和脱出。电解质在正极极片和负极极片之间起到传导离子的作用。隔离膜设置在正极极片和负极极片之间，主要起到防止正负极短路的作用，同时可以使离子通过。
在一些实施方式中，可选地，在本申请的二次电池的充电电压曲线中，85％荷电状态对应位置的电压值V1与60％荷电状态对应位置的电压值V2满足：V1-V2≥0.15V。
当V1和V2满足上述关系时，二次电池具备良好的电压自均衡性能，有利于改善二次电池的容量保持性能，同时正确显示二次电池的剩余电量。
关于二次电池的其他部件如负极极片、电解质和隔离膜的说明如下文中所述。
[负极极片]
负极极片包括负极集流体以及设置在负极集流体至少一个表面上的负极膜层，所述负极膜层包括负极活性材料。
作为示例，负极集流体具有在其自身厚度方向相对的两个表面，负极膜层设置在负极集流体相对的两个表面中的任意一者或两者上。
在一些实施方式中，所述负极集流体可采用金属箔片或复合集流体。例如，作为金属箔片，可以采用铜箔。复合集流体可包括高分子材料基层和形成于高分子材料基层至少一个表面上的金属层。复合集流体可通过将金属材料(铜、铜合金、镍、镍合金、钛、钛合金、银及银合金等)形成在高分子材料基材(如聚丙烯(PP)、聚对苯二甲酸乙二醇酯(PET)、聚对苯二甲酸丁二醇酯(PBT)、聚苯乙烯(PS)、聚乙烯(PE)等的基材)上而形成。
在一些实施方式中，负极活性材料可采用本领域公知的用于电池的负极活性材料。作为示例，负极活性材料可包括以下材料中的至少一种：人造石墨、天然石墨、软炭、硬炭、硅基材料、锡基材料和钛酸锂等。所述硅基材料可选自单质硅、硅氧化合物、硅碳复合物、硅氮复合物以及硅合金中的至少一种。所述锡基材料可选自单质锡、锡氧化合物以及锡合金中的至少一种。但本申请并不限定于这些材料，还可以使用其他可被用作电池负极活性材料的传统材料。这些负极活性材料可以仅单独使用一种，也可以将两种以上组合使用。
在一些实施方式中，负极膜层还可选地包括粘结剂。所述粘结剂可选自丁苯橡胶(SBR)、聚丙烯酸(PAA)、聚丙烯酸钠(PAAS)、聚丙烯酰胺(PAM)、聚乙烯醇(PVA)、海藻酸钠(SA)、聚甲基丙烯酸(PMAA)及羧甲基壳聚糖(CMCS)中的至少一种。
在一些实施方式中，负极膜层还可选地包括导电剂。导电剂可选自超导碳、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯及碳纳 米纤维中的至少一种。
在一些实施方式中，负极膜层还可选地包括其他助剂，例如增稠剂(如羧甲基纤维素钠(CMC-Na))等。
在一些实施方式中，可以通过以下方式制备负极极片：将上述用于制备负极极片的组分，例如负极活性材料、导电剂、粘结剂和任意其他组分分散于溶剂(例如去离子水)中，形成负极浆料；将负极浆料涂覆在负极集流体上，经烘干、冷压等工序后，即可得到负极极片。
[电解质]
电解质在正极极片和负极极片之间起到传导离子的作用。本申请对电解质的种类没有具体的限制，可根据需求进行选择。例如，电解质可以是液态的、凝胶态的或全固态的。
在一些实施方式中，所述电解质采用电解液。所述电解液包括电解质盐和溶剂。
在一些实施方式中，电解质盐可选自六氟磷酸锂、四氟硼酸锂、高氯酸锂、六氟砷酸锂、双氟磺酰亚胺锂、双三氟甲磺酰亚胺锂、三氟甲磺酸锂、二氟磷酸锂、二氟草酸硼酸锂、二草酸硼酸锂、二氟二草酸磷酸锂及四氟草酸磷酸锂中的至少一种。
在一些实施方式中，溶剂可选自碳酸亚乙酯、碳酸亚丙酯、碳酸甲乙酯、碳酸二乙酯、碳酸二甲酯、碳酸二丙酯、碳酸甲丙酯、碳酸乙丙酯、碳酸亚丁酯、氟代碳酸亚乙酯、甲酸甲酯、乙酸甲酯、乙酸乙酯、乙酸丙酯、丙酸甲酯、丙酸乙酯、丙酸丙酯、丁酸甲酯、丁酸乙酯、1，4-丁内酯、环丁砜、二甲砜、甲乙砜及二乙砜中的至少一种。
在一些实施方式中，所述电解液还可选地包括添加剂。例如添加剂可以包括负极成膜添加剂、正极成膜添加剂，还可以包括能够改善电池某些性能的添加剂，例如改善电池过充性能的添加剂、改善电池高温或低温性能的添加剂等。
[隔离膜]
在一些实施方式中，二次电池中还包括隔离膜。本申请对隔离膜的种类没有特别的限制，可以选用任意公知的具有良好的化学稳定性和机械稳定性的多孔结构隔离膜。
在一些实施方式中，隔离膜的材质可选自玻璃纤维、无纺布、聚乙烯、聚丙烯及聚偏二氟乙烯中的至少一种。隔离膜可以是单层薄膜，也可以是多层复合薄膜，没有特别限制。在隔离膜为多层复合薄膜时，各层的材料可以相同或不同，没有特别限制。
在一些实施方式中，正极极片、负极极片和隔离膜可通过卷绕工艺或叠片工艺制成电极组件。
在一些实施方式中，二次电池可包括外包装。该外包装可用于封装上述电极组件及电解质。
在一些实施方式中，二次电池的外包装可以是硬壳，例如硬塑料壳、铝壳、钢壳等。二次电池的外包装也可以是软包，例如袋式软包。软包的材质可以是塑料，作为塑料，可列举出聚丙烯、聚对苯二甲酸丁二醇酯以及聚丁二酸丁二醇酯等。
本申请的第四方面提供一种电池模块，包括本申请第三方面所述的二次电池。
本申请的第五方面提供一种电池包，包括本申请第四方面所述的电池模块。
本申请的第六方面提供一种用电装置，包括本申请第三方面的二次电池、第四方面的电池模块或第五方面的电池包中的至少一种。所述二次电池、电池模块、或电池包可以用作所述用电装置的电源，也可以用作所述用电装置的能量存储单元。所述用电装置可以包括移动设备(例如手机、笔记本电脑等)、电动车辆(例如纯电动车、混合动力电动车、插电式混合动力电动车、电动自行车、电动踏板车、电动高尔夫球车、电动卡车等)、电气列车、船舶及卫星、储能系统等，但不限于此。
作为所述用电装置，可以根据其使用需求来选择二次电池、电池模块或电池包。
另外，以下适当参照附图对本申请的二次电池、电池模块、电池包和用电装置进行说明。
本申请对二次电池的形状没有特别的限制，其可以是圆柱形、方形或其他任意的形状。例如，图5是作为一个示例的方形结构的二次电池5。
在一些实施方式中，参照图6，外包装可包括壳体51和盖板53。其中，壳体51可包括底板和连接于底板上的侧板，底板和侧板围合形成容纳腔。壳体51具有与容纳腔连通的开口，盖板53能够盖设于所述开口，以封闭所述容纳腔。正极极片、负极极片和隔离膜可经卷绕工艺或叠片工艺形成电极组件52。电极组件52封装于所述容纳腔内。电解液浸润于电极组件52中。二次电池5所含电极组件52的数量可以为一个或多个，本领域技术人员可根据具体实际需求进行选择。
在一些实施方式中，二次电池可以组装成电池模块，电池模块所含二次电池的数量可以为一个或多个，具体数量本领域技术人员可根据电池模块的应用和容量进行选择。
图7是作为一个示例的电池模块4。参照图7，在电池模块4中，多个二次电池5可以是沿电池模块4的长度方向依次排列设置。当然，也可以按照其他任意的方式进行排布。进一步可以通过紧固件将该多个二次电池5进行固定。
可选地，电池模块4还可以包括具有容纳空间的外壳，多个二次电池5容纳于该容纳空间。
在一些实施方式中，上述电池模块还可以组装成电池包，电池包所含电池模块的数量可以为一个或多个，具体数量本领域技术人员可根据电池包的应用和容量进行选择。
图8和图9是作为一个示例的电池包1。参照图8和图9，在电池包1中可以包括电池箱和设置于电池箱中的多个电池模块4。电池箱包括上箱体2和下箱体3，上箱体2能够盖设于下箱体3，并形成用于容纳电池模块4的封闭空间。多个电池模块4可以按照任意的方式排布于电池箱中。
图10是作为一个示例的用电装置。该用电装置为纯电动车、混合动力电动车、或插电式混合动力电动车等。为了满足该用电装置对二次电池的高功率和高能量密度的需求，可以采用电池包或电池模块。
作为另一个示例的装置可以是手机、平板电脑、笔记本电脑等。该装置通常要求轻薄化，可以采用二次电池作为电源。
实施例
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。
本申请实施例中涉及的正极活性材料如下表所示：
名称 规格
磷酸铁锂 克容量141mAh/g
NCM523(即LiNi 0.5Co 0.2Mn 0.3O 2) 克容量170mAh/g
NCA(即LiNi 0.8Co 0.15Al 0.05O 2) 克容量180mAh/g
实施例1
正极极片的制备
将第一活性材料磷酸铁锂(以LiFePO 4计)、第二活性材料镍钴锰酸锂(NCM523即LiNi 0.5Co 0.2Mn 0.3O 2)、粘结剂聚偏氟乙烯、导电剂乙炔黑按照重量比28.8∶67.2∶2∶2进行混合，然后加入N-甲基吡咯烷酮(NMP)作为溶剂，在真空搅拌机作用下搅拌至体系呈均一状，得到固含量为75wt％的正极浆料；将正极浆料按照19.6mg/cm 2的涂敷密度均匀涂覆于厚度为13μm的铝箔上，涂覆一面；之后经过烘干、冷压、分切，得到实施例1的正极极片。
负极极片的制备
将负极活性物质人造石墨、导电剂乙炔黑、粘结剂丁苯橡胶(SBR)、增稠剂羧甲基纤维素钠(CMC-Na)按照重量比为96∶1∶2∶1 溶于溶剂去离子水中，搅拌混合均匀后制备成负极浆料。将负极浆料按9.7mg/cm 2的涂敷密度均匀涂覆在负极集流体铜箔上，经过烘干、冷压、分切得到负极极片。
电解液
在氩气气氛手套箱中(H 2O＜0.1ppm，O 2＜0.1ppm)，将有机溶剂碳酸乙烯酯(EC)/碳酸甲乙酯(EMC)按照体积比3/7混合均匀，加入12.5重量％(基于碳酸乙烯酯/碳酸甲乙酯溶剂的重量计)LiPF6溶解于上述有机溶剂中，搅拌均匀，得到电解液。
隔离膜
使用市售的厚度为20μm、平均孔径为80nm的PP-PE共聚物微孔薄膜(来自卓高电子科技公司，型号20)。
二次电池
将正极极片、隔离膜、负极极片按顺序叠好，使隔离膜处于正负极中间起到隔离的作用，并卷绕得到裸电芯。将裸电芯置于外包装中，注入上述电解液并封装，得到二次电池。
实施例2-8
除在制备正极极片的过程中，第一正极活性材料磷酸铁锂(以LiFePO 4计)、第二正极活性材料镍钴锰酸锂(NCM523即LiNi 0.5Co 0.2Mn 0.3O 2)、粘结剂聚偏氟乙烯、导电剂乙炔黑的重量比分别为38.4∶57.6∶2∶2、48∶48∶2∶2、57.6∶38.4∶2∶2、67.2∶28.8∶2∶2、76.8∶19.2∶2∶2、81.6∶14.4∶2∶2和86.4∶9.6∶2∶2，以及涂敷密度分别为19.9mg/cm 2，20.1mg/cm 2，20.4mg/cm 2，20.7mg/cm 2，20.9mg/cm 2，21.1mg/cm 2和21.2mg/cm 2以外，实施例2-8的其他条件与实施例1相同。
实施例9
除将第二正极活性材料镍钴锰酸锂(NCM523即LiNi 0.5Co 0.2Mn 0.3O 2)替换为相等质量的NCA(即LiNi 0.8Co 0.15Al 0.05O 2)以外，实施例9的其他条件与实施例6相同。
对比例1-2
除在制备正极极片的过程中，第一正极活性材料磷酸铁锂(以LiFePO 4计)、第二正极活性材料镍钴锰酸锂(NCM523即LiNi 0.5Co 0.2Mn 0.3O 2)、粘结剂聚偏氟乙烯、导电剂乙炔黑的重量比分别为91.2∶4.8∶2∶2和96∶0∶2∶2，以及涂敷密度分别为21.4mg/cm 2和21.5mg/cm 2以外，对比例1-2的其他条件与实施例1相同。
相关参数测试方法
1.第一活性材料和第二活性材料的几何中心测试
取适量正极极片样品，通过扫描电子显微镜进行表面元素分析，形成活性材料特征元素在断面上的分布图。确认第一活性材料分布的高度区间和第二活性材料分布的高度区间，从而确认第一活性材料分布的几何中心和第二活性材料分布的几何中心的相对位置。
2.二次电池的电压曲线测试
假定待测二次电池在25℃下对应的使用电压上下限分别为Vmax和Vmin，标称容量为C0Ah，测试方法如下：将待测二次电池置于25℃恒温测试环境中，静置2小时。以0.33C0的电流恒流将电池放电至下限电压Vmin；静置30分钟；以1C0的电流恒流将电池充电至上限电压Vmax，再转恒压充电，直至电流减小到0.05C0。该充电过程中所充入的所有容量对应为0％SOC-100％SOC的容量。以SOC％为横坐标，以恒流充电过程中对应电压为纵坐标作图即得二次电池的电压曲线。
在获得的电压曲线中，在15-97％SOC区间内，当SOC增加5％，电压增大＞0.2V时，所对应的最小起始SOC位置为电压抬升位置。
3. 25℃快充循环寿命/圈数
在本申请中，通过25℃快充循环寿命/圈数来评估二次电池的容量保持性能。
在25℃下，将实施例和对比例制备的锂离子电池以2C倍率充电，以1C倍率放电，进行3％-97％SOC区间的连续循环测试，直至锂离子电池的容量小于初始容量的80％，记录循环圈数，记为循环性能。
上述实施例1～9、对比例1～2的相关参数和测试结果如下表1中所示。
表1：实施例1～9与对比例1～2的相关参数及测试结果
Figure PCTCN2022077451-appb-000001
如表1中所示，相对于仅使用第一活性材料的对比例2，添加第二活性材料所制备的二次电池的25℃快充循环寿命/圈数均更优。此外，通过进一步调整第一活性材料、第二活性材料的用量和二者的质量比，可进一步改善对应电池的自均衡性能，提高容量保持性能。
需要说明的是，本申请不限定于上述实施方式。上述实施方式仅为示例，在本申请的技术方案范围内具有与技术思想实质相同的构成、发挥相同作用效果的实施方式均包含在本申请的技术范围内。此外，在不脱离本申请主旨的范围内，对实施方式施加本领域技术人员能够想到的各种变形、将实施方式中的一部分构成要素加以组合而构筑的其它方式也包含在本申请的范围内。

Claims (13)

  1. 一种正极极片，其至少包括以下物质：
    第一活性材料，其选自式LiFe 1-xMn xPO 4的磷酸铁锂基材料，其中x为0-0.8，可选为0-0.5，更可选为0-0.25；和
    第二活性材料，其选自镍酸锂、锰酸锂、钴酸锂、镍钴锰酸锂、镍钴铝酸锂、富锂锰基、磷酸钒锂中的一种或多种；
    其中，所述第二活性材料的用量为10-70％，可选为10-30％，更可选为15-20％，基于第一活性材料和第二活性材料的总质量计。
  2. 根据权利要求1所述的正极极片，其中所述第一活性材料的用量为30-90％，可选为70-90％，更可选为80-85％，基于第一活性材料和第二活性材料的总质量计。
  3. 根据权利要求1或2所述的正极极片，其中所述第一活性材料与所述第二活性材料的质量比为3∶7至9∶1，可选为7∶3至9∶1，更可选为80∶20至85∶15。
  4. 根据权利要求1-3中任一项所述的正极极片，其中所述第一活性材料为磷酸铁锂或磷酸锰铁锂或磷酸铁锂与磷酸锰铁锂的混合物。
  5. 根据权利要求1-4中任一项所述的正极极片，其中所述第二活性材料包括镍钴锰酸锂或镍钴铝酸锂中的至少一种。
  6. 根据权利要求1-5中任一项所述的正极极片，其中
    在所述正极极片的厚度方向上，所述第一活性材料分部的几何中心不高于所述第二活性材料分部的几何中心。
  7. 根据权利要求1-6-中任一项所述的正极极片，其中
    在所述正极极片的厚度方向上，所述第一活性材料分布的几何中心与所述第二活性材料分布的几何中心重合；或
    所述第一活性材料分布的几何中心低于第二活性材料分布的几何中心。
  8. 一种平衡二次电池内部电压差的方法，其中使用至少包括以下物质的正极极片，
    第一活性材料，其选自式LiFe 1-xMn xPO 4的磷酸铁锂基材料，其中x为0-0.8，可选为0-0.5，更可选为0-0.25；和
    第二活性材料，其选自镍酸锂、锰酸锂、钴酸锂、镍钴锰酸锂、镍钴铝酸锂、富锂锰基、磷酸钒锂中的一种或多种；
    其中，所述第二活性材料的用量为10-70％，可选为10-30％，更可选为15-20％，基于第一活性材料和第二活性材料的总质量计。
  9. 一种二次电池，其包括根据权利要求1-7中任一项所述的正极极片。
  10. 根据权利要求9所述的二次电池，其中
    在所述二次电池的充电电压曲线中，85％荷电状态对应位置的电压值V1与60％荷电状态对应位置的电压值V2满足：V1-V2≥0.15V。
  11. 一种电池模块，其包括根据权利要求9或10所述的二次电池。
  12. 一种电池包，其包括根据权利要求11所述的电池模块。
  13. 一种用电装置，其包括根据权利要求9或10所述的二次电池、权利要求11所述的电池模块或权利要求12所述的电池包中的至少一种。
PCT/CN2022/077451 2022-02-23 2022-02-23 正极极片及二次电池、电池模块、电池包和用电装置，及平衡电池内部电压差的方法 WO2023159385A1 (zh)

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JP2019149368A (ja) * 2017-12-27 2019-09-05 財團法人工業技術研究院Ｉｎｄｕｓｔｒｉａｌ Ｔｅｃｈｎｏｌｏｇｙ Ｒｅｓｅａｒｃｈ Ｉｎｓｔｉｔｕｔｅ リチウムイオン電池用正極
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CN101901892A (zh) * 2009-05-26 2010-12-01 上海比亚迪有限公司 一种锂离子二次电池正极及锂离子二次电池
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