WO2024078414A1 - 正极补锂添加剂及其制备方法、富锂正极、二次电池 - Google Patents

正极补锂添加剂及其制备方法、富锂正极、二次电池 Download PDF

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WO2024078414A1
WO2024078414A1 PCT/CN2023/123383 CN2023123383W WO2024078414A1 WO 2024078414 A1 WO2024078414 A1 WO 2024078414A1 CN 2023123383 W CN2023123383 W CN 2023123383W WO 2024078414 A1 WO2024078414 A1 WO 2024078414A1
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lithium
positive electrode
passivation
rich
supplement additive
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PCT/CN2023/123383
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English (en)
French (fr)
Inventor
钟泽钦
万远鑫
孔令涌
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Foshan Dynanonic Innovazone New Energy Technology Co Ltd
Qujing Dynanonic Innovazone New Energy Technology Co Ltd
Shenzhen Dynanonic Innovazone New Energy Technology Co Ltd
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Foshan Dynanonic Innovazone New Energy Technology Co Ltd
Qujing Dynanonic Innovazone New Energy Technology Co Ltd
Shenzhen Dynanonic Innovazone New Energy Technology Co Ltd
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Priority to EP23876616.6A priority Critical patent/EP4601070A4/en
Publication of WO2024078414A1 publication Critical patent/WO2024078414A1/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
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G49/00—Compounds of iron
    • C01G49/0018—Mixed oxides or hydroxides
    • C01G49/0027—Mixed oxides or hydroxides containing one alkali metal
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • 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
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/4235—Safety or regulating additives or arrangements in electrodes, separators or electrolyte
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • 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
    • H01M4/52—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
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/50—Solid solutions
    • C01P2002/52—Solid solutions containing elements as dopants
    • C—CHEMISTRY; METALLURGY
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    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/50—Solid solutions
    • C01P2002/52—Solid solutions containing elements as dopants
    • C01P2002/54—Solid solutions containing elements as dopants one element only
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/60—Particles characterised by their size
    • C01P2004/61—Micrometer sized, i.e. from 1-100 micrometer
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/60—Particles characterised by their size
    • C01P2004/62—Submicrometer sized, i.e. from 0.1-1 micrometer
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
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    • C01—INORGANIC CHEMISTRY
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    • C01P2004/00—Particle morphology
    • C01P2004/80—Particles consisting of a mixture of two or more inorganic phases
    • C01P2004/82—Particles consisting of a mixture of two or more inorganic phases two phases having the same anion, e.g. both oxidic phases
    • C01P2004/84—Particles consisting of a mixture of two or more inorganic phases two phases having the same anion, e.g. both oxidic phases one phase coated with the other
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/80—Particles consisting of a mixture of two or more inorganic phases
    • C01P2004/82—Particles consisting of a mixture of two or more inorganic phases two phases having the same anion, e.g. both oxidic phases
    • C01P2004/84—Particles consisting of a mixture of two or more inorganic phases two phases having the same anion, e.g. both oxidic phases one phase coated with the other
    • C01P2004/86—Thin layer coatings, i.e. the coating thickness being less than 0.1 time the particle radius
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/40—Electric properties
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present application relates to the field of material technology, and in particular to a positive electrode lithium supplement additive and a preparation method thereof, a lithium-rich positive electrode, and a secondary battery.
  • lithium-ion batteries Since lithium-ion batteries were put on the market in 1991, they have been widely used in mobile communications, laptops and other fields because of their advantages such as high operating voltage, long cycle life, high energy density and no memory effect.
  • the energy density and cycle life of lithium-ion batteries are closely related to their first coulombic efficiency and the formation of the negative electrode solid electrolyte interface (SEI) film.
  • SEI solid electrolyte interface
  • the first charge will consume about 10% of the lithium source; when using high-capacity negative electrode materials, such as alloys (silicon, tin, etc.), oxides (silicon oxide, tin oxide, etc.) and amorphous carbon as the negative electrode, the consumption of positive electrode lithium source will be aggravated.
  • high-capacity negative electrode materials such as alloys (silicon, tin, etc.), oxides (silicon oxide, tin oxide, etc.) and amorphous carbon
  • One of the purposes of the embodiments of the present application is to provide a positive electrode lithium replenishing additive and a preparation method thereof, as well as a lithium-rich positive electrode and a secondary battery, which aims to solve the problem of poor structural stability and poor lithium replenishing effect of traditional positive electrode lithium replenishing additives to a certain extent.
  • a positive electrode lithium supplement additive comprising: a lithium-rich iron material and a passivation material in-situ bonded to the outer surface of the lithium-rich iron material; the chemical formula of the passivation material is aLi 2 O ⁇ bFe x O y , wherein 1 ⁇ x ⁇ 3, 1 ⁇ y ⁇ 4, 0.0001 ⁇ a ⁇ 0.01, and 0.0001 ⁇ b ⁇ 0.01.
  • a method for preparing a positive electrode lithium supplement additive comprising the following steps:
  • an iron source, a lithium source and a doping metal source are mixed to obtain a precursor
  • the lithium-rich iron-based material is subjected to reduction treatment to generate a passivation material in situ on the outer surface of the lithium-rich iron-based material;
  • the chemical formula of the passivation material is aLi 2 O ⁇ bFe x O y , wherein 1 ⁇ x ⁇ 3, 1 ⁇ y ⁇ 4, 0.0001 ⁇ a ⁇ 0.01, and 0.0001 ⁇ b ⁇ 0.01.
  • a lithium-rich positive electrode comprising a positive electrode active material and the positive electrode lithium replenishing additive described above or the positive electrode lithium replenishing additive prepared by the method described above.
  • a secondary battery comprising a positive electrode, a negative electrode, a separator and an electrolyte, wherein the positive electrode comprises the above-mentioned lithium-rich positive electrode.
  • the positive electrode lithium supplement additive provided by the embodiment of the present application has the beneficial effect of comprising a lithium-rich iron material and a passivation material combined on the outer surface of the lithium-rich iron material, wherein the chemical formula of the passivation material is aLi 2 O ⁇ bFe x O y , and the passivation material combined on the outer surface of the lithium-rich iron material can not only effectively prevent the lithium-rich iron material from The interface of the lithium-iron material reacts with water and carbon dioxide in the environment to form excessive residual alkali, thereby improving the moisture resistance and processing performance of the lithium-replenishing material, improving the structural stability and performance stability of the positive electrode lithium-replenishing additive, thereby improving its lithium-replenishing effect on the positive electrode and improving the battery cycle performance; and the passivation material has little effect on the migration and transmission of carriers.
  • the passivation material 0.0001 ⁇ a ⁇ 0.01, 0.0001 ⁇ b ⁇ 0.01, 1 ⁇ x ⁇ 3, 1 ⁇ y ⁇ 4, among which, if a and b are too large, the reduction strength is too high, resulting in a decrease in active components, affecting the effective utilization rate of Li; if a and b are too low, the dense layer formed is limited and the protective effect is weakened; and if the x/y ratio is higher, it means that the more Fe is reduced, the more passivation materials are combined on the outer surface of the lithium-rich iron material.
  • the lithium-rich iron in the positive electrode lithium-replenishing additive has a good lithium-replenishing effect on the positive electrode material, which can timely replenish the loss of lithium ions in the material during the charge and discharge cycle, thereby improving the cycle performance of the positive electrode material and increasing the battery life.
  • the beneficial effect of the preparation method of the positive electrode lithium supplement additive provided by the embodiment of the present application is that: after the iron source, the lithium source and the doped metal source are mixed according to the stoichiometric ratio of the elements in the lithium-rich iron-based material, the lithium-rich iron-based material can be obtained by sintering. Then, the lithium-rich iron-based material is reduced, and by reducing part of the lithium-rich iron-based material into iron and lithium oxides, a dense passivation material can be generated in situ on the outer surface of the lithium-rich iron-based material.
  • the chemical formula of the passivation material is aLi2O ⁇ bFexOy , wherein 1 ⁇ x ⁇ 3, 1 ⁇ y ⁇ 4, 0.0001 ⁇ a ⁇ 0.01 , and 0.0001 ⁇ b ⁇ 0.01.
  • the preparation method is simple in process, and the passivation material is formed in situ at the interface of the lithium-rich iron-based material, which can effectively prevent the interface from reacting with water and carbon dioxide in the environment to form excessive residual alkali, thereby improving the moisture resistance and processing performance of the lithium supplement material and improving the battery cycle performance.
  • the beneficial effect of the lithium-rich positive electrode provided by the embodiment of the present application is that: since it includes the positive electrode active material and the above-mentioned positive electrode lithium replenishing additive, the positive electrode lithium replenishing additive has good structural stability, good lithium replenishing effect, good conductivity, and is doped in the positive electrode active material, and can effectively replenish the lithium loss of the positive electrode during the operation of the battery, and the lithium replenishing effect is long-lasting. Therefore, the lithium-rich positive electrode has good cycle stability and high energy density.
  • the secondary battery provided by the embodiment of the present application has the following beneficial effects: comprising a positive electrode, a negative electrode, a separator and The electrolyte, because the positive electrode contains the above-mentioned lithium-rich positive electrode, the lithium-rich positive electrode has the characteristics of good cycle stability and high energy density, thereby improving the cycle performance and service life of the secondary battery.
  • FIG1 is a schematic flow diagram of a method for preparing a positive electrode lithium supplement additive provided in an embodiment of the present application
  • FIG. 2 is a schematic diagram of the structure of a positive electrode lithium supplement additive provided in an embodiment of the present application, wherein the figure marks are: 1—lithium-rich iron material, 2—passivation layer, 3—conductive layer.
  • the term "and/or” describes the association relationship of associated objects, indicating that there may be three relationships.
  • a and/or B can mean: A exists alone, A and B exist at the same time, and B exists alone.
  • a and B can be singular or plural.
  • the character "/" generally indicates that the associated objects are in an "or” relationship.
  • At least one means one or more
  • plural means two or more.
  • At least one of the following” or similar expressions refers to any combination of these items, including any combination of single items or plural items.
  • at least one of a, b or c or “at least one of a, b and c”
  • the size of the serial numbers of the above-mentioned processes does not mean the order of execution, some or all of the steps can be executed in parallel or sequentially, and the execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.
  • the weight of the relevant components mentioned in the embodiments of the present specification can not only refer to the specific content of each component, but also represent the proportional relationship between the weights of the components. Therefore, as long as the content of the relevant components in the embodiments of the present specification is proportionally enlarged or reduced, it is within the scope disclosed in the embodiments of the present specification.
  • the mass in the embodiments of the present specification can be ⁇ g, mg, g, kg and other mass units known in the chemical industry.
  • a first aspect of an embodiment of the present application provides a positive electrode lithium supplement additive, which includes: a lithium-rich iron material 1 and a passivation material in situ bonded to the outer surface of the lithium-rich iron material 1; the chemical formula of the passivation material is aLi2O ⁇ bFexOy , wherein 1 ⁇ x ⁇ 3, 1 ⁇ y ⁇ 4, 0.0001 ⁇ a ⁇ 0.01, and 0.0001 ⁇ b ⁇ 0.01.
  • the first aspect of the embodiment of the present application provides a positive electrode lithium supplement additive, comprising a lithium-rich iron material 1 and a passivation material bonded to the outer surface of the lithium-rich iron material 1, wherein the chemical formula of the passivation material is aLi 2 O ⁇ bFe x O y .
  • the passivation material is bonded to the outer surface of the lithium-rich iron material 1, which can not only effectively prevent the lithium-rich iron material 1 interface from reacting with water and carbon dioxide in the environment to form excessive residual alkali, but also improve the moisture resistance and processing performance of the lithium supplement material, improve the structural stability and performance stability of the positive electrode lithium supplement additive, thereby improving its lithium supplement effect on the positive electrode and improving the battery cycle performance; and the passivation material has little effect on the migration and transmission of carriers.
  • the passivation material 0.0001 ⁇ a ⁇ 0.01, 0.0001 ⁇ b ⁇ 0.01, 1 ⁇ x ⁇ 3, 1 ⁇ y ⁇ 4, where if a and b are too large, the reduction strength is too high, resulting in a decrease in active components and affecting the effective utilization rate of Li; if a and b are too low, the dense layer formed is limited and the protective effect is weakened; and if the x/y ratio is higher, it means that the more Fe is reduced, the more passivation materials are combined on the outer surface of the lithium-rich iron-based material 1.
  • the lithium-rich iron-based material in the positive electrode lithium supplement additive has a good lithium supplement effect on the positive electrode material, and can timely supplement the loss of lithium ions in the material during the charge and discharge cycle, thereby improving the cycle performance of the positive electrode material and increasing the battery life.
  • the chemical formula of the lithium-rich iron material 1 is Li c Fe d Me O f , wherein M is selected from at least one metal element of Co, Ni, Mn, V, Cu, Mo, Al, Ti, Mg, Na, Ca, Zr, Si, Zn, Cr, and P, 1 ⁇ c ⁇ 6, 0 ⁇ d ⁇ 0.99, 0 ⁇ e ⁇ 0.1, and 1 ⁇ f ⁇ 4.
  • Fe mainly plays a role in stabilizing the structure; the larger d is, the Li 5 FeO 4 structure is dominant, and the better the structural stability is.
  • the main function of M doping metal is to improve the bulk phase transmission of lithium ions, and at the same time, it can reduce the oxygen activity of oxygen released during charging and de-lithiation.
  • the larger e is, the better the effect of improving the bulk phase transmission of lithium ions.
  • the larger c is, the more lithium ions can be released in actual applications, so that the capacity of the lithium-rich iron material 1 is higher.
  • the average particle size of the lithium-rich iron-based material 1 is 100nm to 50 ⁇ m; the lithium-rich iron-based material 1 of this particle size not only has a good lithium replenishing effect, but also is conducive to the composite of the positive electrode lithium replenishing additive and the positive electrode active material, thereby improving its lithium replenishing effect.
  • the average particle size of the lithium-rich iron-based material 1 includes but is not limited to 100nm to 1 ⁇ m, 1 to 10 ⁇ m, 10 to 20 ⁇ m, 20 to 30 ⁇ m, 30 to 40 ⁇ m, 40 to 50 ⁇ m, etc.
  • the valence state of the iron ions in the passivation material is lower than the valence state of the iron ions in the lithium-rich iron-based material 1.
  • the passivation material with low-valence iron ions has better stability and has a passivation effect, preventing the interface of the lithium-rich iron-based material 1 from reacting with water and carbon dioxide in the environment to form excessive residual alkali, thereby improving the structural stability and performance stability of the positive electrode lithium supplement additive.
  • the passivation material can be directly prepared by reducing the lithium-rich iron-based material 1.
  • the low-valent state of iron ions in the passivation material is the reduced valence state corresponding to the iron ions in the lithium-rich iron-based material 1.
  • the amount of the passivation material generated by the reduction can be flexibly controlled, thereby controlling the binding effect of the passivation material on the surface of the lithium-rich iron-based material 1. It is possible to reduce and generate a portion of the passivation material on the surface of the lithium-rich iron-based material 1, or to allow the passivation material generated by the reduction to form a complete coating layer on the surface of the lithium-rich iron-based material 1.
  • the passivation material containing low-valent iron ions can be directly mixed with the lithium-rich iron-based material 1 and, after a high-temperature reaction, directly coated on the outer surface of the lithium-rich iron-based material 1.
  • the passivation material is coated on the outer surface of the lithium-rich iron-based material 1 to form a passivation layer 2.
  • the passivation material forms a dense and uniform coated passivation layer 2 on the outer surface of the lithium-rich iron-based material 1, which can more effectively prevent the interface of the lithium-rich iron-based material 1 from reacting with water and carbon dioxide in the environment to form excessive residual alkali, better improve the moisture resistance and processing properties of the lithium-replenishing material, improve the structural stability and performance stability of the positive electrode lithium-replenishing additive, thereby improving its lithium-replenishing effect on the positive electrode and improving the battery cycle performance.
  • the passivation material alone forms a continuous and dense coating layer; the passivation effect is good, and the structural stability and performance stability of the positive electrode lithium supplement additive can be significantly improved.
  • the passivation material in the passivation layer 2, is doped with other coating materials to form a dense coating layer.
  • the passivation material is doped with carbon material to form a dense coating layer.
  • the concentration of low-valent iron ions increases radially from the inside to the outside.
  • the lithium-rich iron-based material 1 can be reduced in a reducing atmosphere so that the passivation layer 2 is formed in situ on the outer surface of the lithium-rich iron-based material 1.
  • the passivation material aLi 2 O ⁇ bFe x O y is not uniformly distributed. The more fully the lithium-rich iron-based material 1 is in contact with the reducing atmosphere, the more fully it is reduced. Therefore, the content of the passivation material is increasingly enriched from the inside to the outside in the radial direction, that is, the low-valent iron ions are increasingly concentrated.
  • the concentration of iron ions in the state is also increasing, and the passivation layer 2 is becoming more and more dense.
  • This embodiment can ensure the compactness of the passivation layer 2 and the passivation effect on the material interface, and ensure the stability of the material interface relative to the environment.
  • the average thickness of the passivation layer 2 is 3 to 150 nm; this thickness can effectively avoid the generation of residual alkali and maintain the structural stability and performance stability of the lithium-rich iron-based material 1; and has little effect on the migration and transmission of carriers. If the average thickness of the passivation layer 2 is too high, it will affect the effective utilization of the active ingredients and lithium in the lithium-rich iron-based material 1; if the average thickness of the passivation layer 2 is too low, it will be unfavorable to improve the structural stability and performance stability of the lithium-rich iron-based material 1.
  • the average thickness of the passivation layer 2 includes but is not limited to 3 to 10 nm, 10 to 15 nm, 15 to 20 nm, 20 to 25 nm, 25 to 30 nm, 30 to 40 nm, 40 to 50 nm, 50 to 80 nm, 80 to 100 nm, 100 to 120 nm, 120 to 150 nm, etc.
  • the mass of the passivation material accounts for 0.01-10wt% of the total mass of the lithium-rich iron-based material 1 and the passivation material; the passivation material of this mass percentage in the positive electrode lithium supplement additive can effectively avoid the generation of residual alkali and maintain the structural stability and performance stability of the lithium-rich iron-based material 1; and has little effect on the migration and transmission of carriers. If the content of the passivation material is too low, it cannot provide good protection; if the proportion of the passivation material is too high, the overall magnetism is strong and cannot be smoothly applied to the back-end battery.
  • the mass of the passivation material accounts for 0.01-0.1wt%, 0.1-1wt%, 1-3wt%, 3-5wt%, 5-8wt%, 8-10wt%, etc. of the total mass of the lithium-rich iron-based material 1 and the passivation material.
  • the positive electrode lithium supplement additive further includes a conductive layer 3 coated on the outer surface of the passivation layer 2, and the conductive effect of the positive electrode lithium supplement additive is improved by coating the conductive layer 3 on the outer surface of the passivation layer 2.
  • the schematic diagram of the structure is shown in FIG2.
  • the conductive layer 3 includes at least one of graphene, carbon nanotubes, conductive carbon black, and conductive graphite; these carbon materials have good conductive effects and can effectively improve the positive electrode lithium supplement additive The electron transfer efficiency.
  • the average thickness of the conductive layer 3 is 50 to 150 nm, exemplarily 60 to 120 nm, exemplarily 70 to 100 nm, and the conductive layer 3 having this thickness can effectively improve the electron transfer efficiency.
  • the mass percentage of the conductive layer 3 is 0.5-10wt%. This mass percentage of the conductive layer 3 can effectively improve the electron transmission efficiency. If the mass percentage of the conductive layer 3 is too high, the content of the lithium-rich iron-based material 1 in the positive electrode lithium supplement additive is reduced, thereby affecting the lithium supplement effect; if the mass percentage of the conductive layer 3 is too low, the effect of improving the conductive performance of the positive electrode lithium supplement additive is limited. In some specific embodiments, the mass percentage of the conductive layer 3 in the positive electrode lithium supplement additive includes but is not limited to 0.5-1wt%, 1-2wt%, 2-5wt%, 5-8wt%, 8-10wt%, etc.
  • the second aspect of the embodiment of the present application provides a method for preparing a positive electrode lithium supplement additive, comprising the following steps:
  • the preparation method of the positive electrode lithium supplement additive provided in the second aspect of the embodiment of the present application is to mix the iron source, the lithium source and the doping metal source according to the stoichiometric ratio of the elements in the lithium-rich iron-based material 1, and then sinter the mixture to obtain the lithium-rich iron-based material 1. Then, the lithium-rich iron-based material 1 is subjected to a reduction treatment, and by reducing part of the lithium-rich iron-based material 1 into iron and lithium oxides, the lithium-rich iron-based material 1 can be in-situ generated on the outer surface of the lithium-rich iron-based material 1.
  • the passivation material is a dense passivation material, the chemical formula of which is aLi2O ⁇ bFexOy , wherein 1 ⁇ x ⁇ 3, 1 ⁇ y ⁇ 4, 0.0001 ⁇ a ⁇ 0.01 , and 0.0001 ⁇ b ⁇ 0.01.
  • the preparation method of the embodiment of the present application is simple in process, and the passivation material is formed in situ at the interface of the lithium-rich iron-based material 1, which can effectively prevent the interface from reacting with water and carbon dioxide in the environment to form excessive residual alkali, thereby improving the moisture resistance and processing performance of the lithium-supplementing material and enhancing the battery cycle performance.
  • the chemical formula of the lithium-rich iron material 1 is LicFedMeOf , wherein M is selected from at least one metal element of Co, Ni, Mn, V, Cu, Mo, Al, Ti, Mg, Na, Ca, Zr, Si, Zn, Cr, and P, 1 ⁇ c ⁇ 6, 0 ⁇ d ⁇ 0.99, 0 ⁇ e ⁇ 0.1, and 1 ⁇ f ⁇ 4.
  • the lithium source includes at least one of lithium nitrate, lithium carbonate, lithium acetate, lithium oxalate, lithium borate, lithium phosphate, lithium chloride, lithium hydroxide, lithium peroxide, and lithium oxide.
  • the iron source comprises an iron salt; including but not limited to ferric chloride, ferric sulfate, ferric nitrate, ferric phosphate, and the like.
  • the doping metal element source includes at least one of a Co source, a Ni source, a Mn source, a V source, a Cu source, a Mo source, an Al source, a Ti source, a Mg source, a Na source, a Ca source, a Zr source, a Si source, a Zn source, a Cr source, and a P source.
  • the form of the doping metal element source includes, but is not limited to, chlorides, nitrates, phosphates, sulfates, and the like.
  • the lithium source, iron source and doped metal element source used in the above embodiments of the present application all have good solubility, which is conducive to the preparation of lithium-rich iron-based material 1 through liquid phase sintering and other treatment methods.
  • the precursor is sintered by liquid phase sintering.
  • liquid phase sintering liquid and solid phase particles coexist.
  • the sintering temperature is higher than the melting point of the low melting point component or low melting point eutectic in the sintered body and lower than the melting point of the high melting point component. Since the liquid phase migration of the material is much faster than the solid phase diffusion, the densification speed and final density of the sintered body are greatly improved.
  • Liquid phase sintering treatment The conditions include: in an atmosphere with an oxygen concentration of 0 to 1000 ppm, heating to a temperature of 350 to 900°C at a heating rate of 100 to 400°C/h and reacting for 10 to 20 hours. The heating rate, temperature conditions, reaction time, etc. effectively ensure the reaction between various raw materials such as iron source, lithium source and doped metal source, and the various raw material components sinter under high temperature conditions to generate lithium-rich iron-based material 1 particles.
  • the conditions for reducing the lithium-rich iron-based material 1 include: treating in a reducing atmosphere at a temperature of 350 to 900°C for 0.1 to 8 hours, so that the lithium-rich iron-based material 1 at the interface of the lithium-rich iron-based material 1 is partially reduced to lithium oxide and iron oxide, and a dense passivation material is formed at the interface of the lithium-rich lithium ferrate, thereby preventing the interface from reacting with water and carbon dioxide in the environment to form excessive residual alkali, thereby improving the moisture resistance and processing performance of the lithium replenishing material, improving the stability of the positive electrode lithium replenishing additive, improving its lithium replenishing effect, and improving the battery cycle performance.
  • the reducing atmosphere includes at least one reducing gas selected from the group consisting of hydrogen, hydrocarbon gas, alcohol gas, ether gas, aldehyde gas, and ketone gas; these hydrogen or gaseous molecular hydrocarbons, alcohols, ethers, aldehydes, ketones, etc. used in the embodiments of the present application all have reducing properties, and under certain temperature and atmospheric conditions, they can partially reduce the lithium-rich iron-based material 1 at the interface of the lithium-rich iron-based material 1 into lithium oxide and iron oxide, and form a dense passivation material at the interface of the lithium-rich lithium ferrate.
  • reducing gas selected from the group consisting of hydrogen, hydrocarbon gas, alcohol gas, ether gas, aldehyde gas, and ketone gas
  • the volume percentage of the reducing gas is 0.5-60%; the reducing atmosphere can effectively ensure the reduction of the interface layer of the lithium-rich iron-based material 1, so that the lithium-rich iron-based material 1 at the interface of the lithium-rich iron-based material 1 is partially reduced to lithium oxide and iron oxide, and a dense passivation material is formed at the interface of the lithium-rich lithium ferrate. If the reducing gas content is too high, it will cause the reduction ratio of the lithium-rich iron-based material 1 to be too high, reduce the proportion of lithium-replenishing materials in the positive electrode lithium-replenishing additive, and affect the lithium replenishment effect.
  • the volume percentage of the reducing gas includes but is not limited to 0.5-10%, 10-20%, 20-40%, 40-60%, etc.
  • the generated passivation material forms a passivation layer on the outer surface of the lithium-rich iron-based material 1. 2.
  • the step S40 is further included, wherein the composite material including the lithium-rich iron material 1 and the passivation material is mixed with the conductive material, and then subjected to a heat treatment to in-situ generate a conductive layer 3 on the surface of the composite material.
  • the embodiment of the present application prepares the conductive layer 3 on the surface of the composite material to improve the conductivity of the positive electrode lithium supplement additive.
  • the conductive material includes at least one of a carbon source and a semi-carbonized carbon source.
  • the carbon source includes an organic carbon source and an inorganic carbon source, wherein the organic carbon source includes glucose, sucrose, etc., and may also be other types of organic sugars.
  • the surface of the passivation material is coated to form a conductive carbon coating layer.
  • Inorganic carbon sources include graphene, conductive carbon fibers, carbon nanotubes, etc.
  • the carbon source includes both an organic carbon source and an inorganic carbon source, and an inorganic carbon source with a better conductive effect is mixed during the pyrolysis of the organic carbon source, thereby reducing the carbon content of the conductive layer 3 and improving the conductive effect.
  • the semi-carbonized carbon source refers to a process in which a portion of the carbon source is carbonized by high-temperature treatment of the carbon source in an inert atmosphere for a period of time, and active functional groups such as hydroxyl and carboxyl groups are formed on the surface of the semi-carbonized carbon source. These active functional groups can form better bonds with Fe-O in the composite material, and the bonding effect is better, thereby better improving the structural stability of the positive electrode lithium supplement additive.
  • the conductive layer 3 includes at least one of graphene, carbon nanotubes, conductive carbon black, and conductive graphite.
  • the conditions for the heat treatment include: heat treatment in an inert atmosphere at a temperature of 300 to 400° C. for 2 to 6 hours; and allowing the conductive material to form a conductive coating layer on the surface of the composite material.
  • the mass ratio of the lithium-rich iron material 1, the passivation material and the conductive layer 3 is (93-99): (0.01-1): (0.5-8); wherein, the lithium-rich iron material 1 as the core mainly provides capacity, and if the ratio is too low, the active lithium provided is low; if the ratio is too high, the passivation is insufficient, or the conductivity is insufficient, and the lithium removal process cannot be completed well; if the passivation material is too low, it cannot play a better role.
  • the ratio of the lithium-rich iron material 1, the passivation material and the conductive layer 3 not only ensures the lithium supplement effect of the additive, but also can effectively maintain the structural stability and lithium supplement stability of the additive, and has a good conductive effect, which is beneficial to improve the cycle performance of the positive electrode material and the battery.
  • the average particle size of the lithium-rich iron-based material 1 is 100 nm to 50 ⁇ m; the lithium-rich iron-based material 1 with this particle size not only has a better lithium replenishing effect, but also is conducive to the composite of the positive electrode lithium replenishing additive and the positive electrode active material, thereby improving its lithium replenishing effect.
  • the average thickness of the passivation layer 2 is 3 to 150 nm. This thickness can effectively avoid the generation of residual alkali and maintain the structural stability and performance stability of the lithium-rich iron-based material 1 ; and has little effect on the migration and transmission of carriers.
  • the average thickness of the conductive layer 3 is 50 to 150 nm, exemplarily 60 to 120 nm, exemplarily 70 to 100 nm, and the conductive layer 3 having this thickness can effectively improve the electron transfer efficiency.
  • a third aspect of an embodiment of the present application provides a lithium-rich positive electrode, which includes a positive electrode active material and the positive electrode lithium replenishing additive mentioned above or the positive electrode lithium replenishing additive prepared by the above method.
  • the lithium-rich positive electrode provided in the third aspect of the embodiment of the present application includes a positive electrode active material and the above-mentioned positive electrode lithium supplement additive.
  • the positive electrode lithium supplement additive has good structural stability, good lithium supplement effect, good conductivity, and is doped in the positive electrode active material. It can effectively supplement the lithium loss of the positive electrode during the operation of the battery, and the lithium supplement effect is long-lasting. Therefore, the lithium-rich positive electrode has good cycle stability and high energy density.
  • the positive electrode active material includes but is not limited to at least one of lithium nickel cobalt manganese, lithium nickel cobalt aluminum, lithium nickel manganese, lithium cobalt oxide, lithium iron phosphate, nickel cobalt manganese aluminum, and the like.
  • the lithium-rich positive electrode is mixed with a conductive agent, a binder, etc. in proportion to form a positive electrode slurry. After the material is prepared, it is coated on the surface of the positive current collector, rolled and dried to obtain the positive electrode sheet.
  • a fourth aspect of an embodiment of the present application is a secondary battery, which includes a positive electrode, a negative electrode, a separator and an electrolyte, wherein the positive electrode includes the above-mentioned lithium-rich positive electrode.
  • the secondary battery provided in the fourth aspect of the embodiment of the present application includes a positive electrode, a negative electrode, a separator and an electrolyte. Since the positive electrode contains the above-mentioned lithium-rich positive electrode, the lithium-rich positive electrode has the characteristics of good cycle stability and high energy density, thereby improving the cycle performance and service life of the secondary battery.
  • the negative electrode of the secondary battery includes but is not limited to carbon materials such as graphite, soft carbon (such as coke), hard carbon, or nitrides, tin-based oxides, tin-based oxides, tin alloys, and nano-negative electrode materials.
  • carbon materials such as graphite, soft carbon (such as coke), hard carbon, or nitrides, tin-based oxides, tin-based oxides, tin alloys, and nano-negative electrode materials.
  • the separator includes at least one material selected from the group consisting of polypropylene fiber, polyacrylonitrile fiber, polyvinyl formal fiber, poly(ethylene terephthalate), polyethylene terephthalate, polyamide fiber, and poly(p-phenylene terephthalamide).
  • the electrolyte includes an aqueous solution containing a soluble salt of at least one of Na + , K + , and NH 4 + .
  • Fe(NO 3 ) 3 , LiNO 3 , Li 2 O 2 , and Al(NO 3 ) 3 are provided in a molar ratio of 0.97:1:2:0.03 and mixed by high-speed shearing to obtain a precursor;
  • the core-shell structure powder and the semi-carbonized carbon source are fused at a fusion speed of 2000 rpm for 30 min; a conductive carbon coating layer is formed on the surface of the core-shell structure powder to obtain a positive electrode lithium supplement additive.
  • a positive electrode lithium supplement additive whose structure is shown in Figure 2, comprises a lithium-rich iron material core 1, a passivation layer 2 and a conductive layer 3, wherein the chemical formula of the core is Li 4.95 Fe 0.96 Al 0.03 O 3.96 , the chemical formula of the passivation material in the passivation layer 2 is 0.025Li 2 O ⁇ 0.01FeO, the thickness of the passivation layer 2 is 25nm, and the raw material of the conductive layer 3 is selected from a semi-finished carbon source containing hydroxyl groups.
  • a positive electrode lithium supplement additive whose structure is shown in Figure 2, comprises a lithium-rich iron material core 1, a passivation layer 2 and a conductive layer 3, wherein the chemical formula of the core is Li 4.985 Fe 0.967 Al 0.03 O 3.988 , the chemical formula of the passivation material in the passivation layer 2 is 0.0075Li 2 O ⁇ 0.003FeO, the thickness of the passivation layer 2 is 4nm, and the raw material of the conductive layer 3 is selected from a semi-finished carbon source containing hydroxyl groups.
  • step 4 The difference between the preparation method and Example 1 is that the reducing atmosphere in step 4 is changed to 5% SO/N 2 , and the other steps remain the same.
  • a positive electrode lithium supplement additive whose structure is shown in Figure 2, comprises a lithium-rich iron material core 1, a passivation layer 2 and a conductive layer 3, wherein the chemical formula of the core is Li 4.99 Fe 0.966 Al 0.03 O 3.989 , the chemical formula of the passivation material in the passivation layer 2 is 0.01Li 2 O ⁇ 0.004FeO, the thickness of the passivation layer 2 is 8nm, and the raw material of the conductive layer 3 is selected from a semi-finished carbon source containing hydroxyl groups.
  • step 4 The difference between the preparation method and Example 1 is that the reducing atmosphere in step 4 is changed to 5% H 2 S/N 2 , and the other steps remain the same.
  • a positive electrode lithium supplement additive whose structure is shown in Figure 2, comprises a lithium-rich iron material core 1, a passivation layer 2 and a conductive layer 3, wherein the chemical formula of the core is Li 4.9625 Fe 0.9325 Al 0.03 O 3.925 , the chemical formula of the passivation material in the passivation layer 2 is 0.0375Li 2 O ⁇ 0.015FeO, the thickness of the passivation layer 2 is 35nm, and the raw material of the conductive layer 3 is selected from a semi-finished carbon source containing hydroxyl groups.
  • step 4 The difference between the preparation method and Example 1 is that the reducing atmosphere in step 4 is changed to 5% C 2 H 2 /N 2 , and the other steps remain the same.
  • a positive electrode lithium supplement additive comprises a lithium-rich iron material core 1, a passivation layer 2 and a conductive layer 3, wherein the chemical formula of the core is Li 4.975 Fe 0.965 Al 0.03 O 3.98 , the chemical formula of the passivation material in the passivation layer 2 is 0.0125Li 2 O ⁇ 0.005FeO, and the thickness of the passivation layer 2 is 20 nm.
  • the preparation method thereof is different from that of Example 1 in that step 5 is not performed, and the other steps remain the same.
  • a positive electrode lithium supplement additive comprises a lithium-rich iron material core 1 and a coated conductive layer 3, wherein the chemical formula of the core is Li 4.975 Fe 0.965 Al 0.03 O 3.98 , and the raw material of the conductive layer 3 is selected from a semi-finished carbon source containing hydroxyl groups.
  • the preparation method thereof is different from that of Example 1 in that step 4 is not performed, and the other steps remain the same.
  • a positive electrode lithium supplement additive comprises a lithium-rich iron material core 1, a passivation layer 2 and a conductive layer 3, wherein the chemical formula of the core is Li 4.975 Fe 0.965 Al 0.03 O 3.98 , the chemical formula of the passivation material in the passivation layer 2 is Li 2 CO 3 , the thickness of the passivation layer 2 is 50 nm, and the raw material of the conductive layer 3 is selected from a semi-finished carbon source containing hydroxyl groups.
  • the difference between the preparation method and Example 1 is that the gas introduced in step 4 is 1% CO 2 /N 2 , and the passivation material formed at this time is Li 2 CO 3 passivation material with a thickness of 50 nm.
  • the positive electrode lithium supplement additives prepared in Examples 1 to 6 of the present application are The iron-based material 1 directly reduced to form the passivation layer 2, and the positive electrode lithium supplement additive coated with a carbon layer, both exhibit lower water absorption under the same test conditions, thereby improving the stability of the positive electrode lithium supplement additive.
  • the passivation layer 2 formed on the surface of the positive electrode lithium replenishing additive reduces the water absorption of the positive electrode lithium replenishing additive, improves the interface stability of the positive electrode lithium replenishing additive, is beneficial to block the contact of water/ CO2 in the air with the lithium replenishing material, reduces the environmental loss of the lithium replenishing material in the positive electrode lithium replenishing additive, fully ensures the lithium replenishing effect of the positive electrode lithium replenishing additive on the positive electrode, and improves the cycle performance of the positive electrode through the positive electrode lithium replenishing additive fully and effectively replenishing the positive electrode.
  • Positive electrode sheet The positive electrode lithium supplement additive prepared in the embodiment and the comparative example was mixed with lithium cobalt oxide in a mass ratio of 5:95 to obtain a mixture, the mixture was mixed with polyvinylidene fluoride and SP-Li in a mass ratio of 93:3:4 by ball milling and stirring to obtain a positive electrode slurry, the positive electrode slurry was coated on the surface of aluminum foil, rolled, and vacuum dried at 110° C. overnight to obtain a positive electrode sheet;
  • Negative electrode lithium metal sheet
  • Electrolyte Ethylene carbonate and ethyl methyl carbonate were mixed in a volume ratio of 3:7, and LiPF 6 was added to form an electrolyte, the concentration of LiPF 6 was 1 mol/L;
  • Lithium-ion battery assembly Lithium-ion batteries were assembled in an inert atmosphere glove box in the order of lithium metal sheet-diaphragm-electrolyte-positive electrode sheet.
  • the lithium-ion batteries corresponding to the positive electrode lithium replenishing additives in Examples 1 to 6 were batteries A1 to A6, respectively, and the lithium-ion batteries corresponding to the positive electrode lithium replenishing additives in Comparative Examples 1 to 2 were batteries B1 to B2, respectively.
  • Examples A1 to A6 of the present application use positive electrode lithium supplement additives coated with a carbon layer after directly reducing the lithium-rich iron-based material to form a passivation layer.
  • the lithium-ion battery Examples A1 to A5 show excellent first charge specific capacity, and still show a high first charge specific capacity after 24 hours, indicating that the battery has good stability. Since Example A6 is not carbon-coated, the first charge specific capacity after 24 hours decreases.
  • the positive electrode lithium supplement additive used in Comparative Example B1 has no passivation layer, and the positive electrode lithium supplement additive Li 2 CO 3 passivation layer used in Comparative Example B2 has a significantly lower first charge specific capacity, and the 24-hour first charge specific capacity decreases significantly.

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Abstract

一种正极补锂添加剂及其制备方法，一种富锂正极，一种二次电池，属于材料技术领域。其中，正极补锂添加剂包括：富锂铁系材料和原位结合在所述富锂铁系材料外表面的钝化材料；所述钝化材料的化学式为aLi 2O·bFe xO y，其中，1≤x≤3，1≤y≤4，0.0001≤a≤0.01，0.0001≤b≤0.01。该正极补锂添加剂中富锂铁系内对正极材料有较好的补锂效果，能够及时补充材料在充放电循环过程中锂离子的损耗；另外，钝化材料能够有效防止界面与环境中水和二氧化碳反应导致形成过多的残碱，改善补锂材料的耐湿和加工性能，提高正极材料的循环性能，提高电池循环性能及使用寿命。

Description

正极补锂添加剂及其制备方法、富锂正极、二次电池
本申请要求于2022年10月09日在中国专利局提交的、申请号为202211225960.9、发明名称为“正极补锂添加剂及其制备方法、富锂正极、二次电池”的中国专利申请的优先权，其全部内容通过引用结合在本申请中。
技术领域
本申请涉及材料技术领域，尤其涉及一种正极补锂添加剂及其制备方法，一种富锂正极，一种二次电池。
背景技术
锂离子电池因为具有工作电压高、循环寿命长、能量密度大、无记忆效应等优势，自1991年投入市场后，迅速实现了在移动通讯、笔记本电脑等领域的广泛应用。锂离子电池的能量密度和循环寿命与其首次库伦效率和负极固体电解质界面(SEI)膜的形成密切相关，在锂离子电池的首次充电过程中，负极表面形成的SEI膜会将大量的活性锂转化成碳酸锂、氟化锂和烷基锂，从而造成富锂正极的锂损失。在使用石墨作为负极的锂离子电池体系中，首次充电会消耗约10％的锂源；当采用高比容量的负极材料，例如合金类(硅、锡等)、氧化物类(氧化硅、氧化锡等)和无定形碳等作为负极时，正极锂源的消耗将加剧。
传统技术中，通过在富锂正极中添加补锂材料，能够有效补偿锂电池的首次不可逆容量损失。然而，在研究和实际应用中发现，传统的正极补锂添加剂存在表面结构稳定性差、残碱值较高的缺点，导致在电池匀浆时易发生果冻现象。另外，在充放电过程中因材料相变、产生热量等因素易产生大量的气体，导致结构不稳定继而引发一系列副反应的发生。因此亟需开发加工性能好、补锂效果好的正极补锂添加剂。
技术问题
本申请实施例的目的之一在于：提供一种正极补锂添加剂及其制备方法，以及一种富锂正极，一种二次电池，旨在一定程度上解决传统正极补锂添加剂结构稳定性差，补锂效果差的问题。
技术解决方案
为解决上述技术问题，本申请实施例采用的技术方案是：
第一方面，提供了一种正极补锂添加剂，所述正极补锂添加剂包括：富锂铁系材料和原位结合在所述富锂铁系材料外表面的钝化材料；所述钝化材料的化学式为aLi2O·bFexOy，其中，1≤x≤3，1≤y≤4，0.0001≤a≤0.01，0.0001≤b≤0.01。
第二方面，提供了一种正极补锂添加剂的制备方法，包括以下步骤：
按照富锂铁系材料中元素化学计量比，将铁源、锂源和掺杂金属源进行混合处理，得到前驱体；
对所述前驱体进行烧结处理，得到富锂铁系材料；
对所述富锂铁系材料进行还原处理，在所述富锂铁系材料外表面原位生成钝化材料；所述钝化材料的化学式为aLi2O·bFexOy，其中，1≤x≤3，1≤y≤4，0.0001≤a≤0.01，0.0001≤b≤0.01。
第三方面，提供一种富锂正极，所述富锂正极包括正极活性材料和上述的正极补锂添加剂或者上述方法制备的正极补锂添加剂。
第四方面，提供一种二次电池，所述二次电池包括正极、负极、隔膜和电解液，其中所述正极包含有上述的富锂正极。
本申请实施例提供的正极补锂添加剂的有益效果在于：包括富锂铁系材料和结合在富锂铁系材料外表面的钝化材料，其中，钝化材料的化学式为aLi2O·bFexOy，该钝化材料结合在富锂铁系材料外表面，不但能够有效防止富 锂铁系材料界面与环境中水和二氧化碳反应导致形成过多的残碱，进而改善补锂材料的耐湿和加工性能，提高正极补锂添加剂的结构稳定性和性能稳定性，进而提高其对正极的补锂效果，提升电池循环性能；而且该钝化材料对载流子的迁移传输影响小。钝化材料中0.0001≤a≤0.01，0.0001≤b≤0.01，1≤x≤3，1≤y≤4，其中，若a、b取值过大，则还原强度过高，导致活性成分降低，影响Li有效利用率发挥；若a、b取值过低，则形成的致密层有限，保护作用减弱；而若x/y比值越高，说明Fe被还原的越多，在富锂铁系材料外表面结合的钝化材料越多。另外，正极补锂添加剂中富锂铁系内对正极材料有较好的补锂效果，能够及时补充材料在充放电循环过程中锂离子的损耗，从而提高正极材料的循环性能，提高电池使用寿命。
本申请实施例提供的正极补锂添加剂的制备方法的有益效果在于：将铁源、锂源和掺杂金属源按富锂铁系材料中元素化学计量比混合后，通过烧结处理，即可得到富锂铁系材料。然后，对富锂铁系材料进行还原处理，通过将部分富锂铁系材料还原成铁和锂的氧化物，便可在富锂铁系材料外表面原位生成致密的钝化材料，该钝化材料的化学式为aLi2O·bFexOy，其中，1≤x≤3，1≤y≤4，0.0001≤a≤0.01，0.0001≤b≤0.01。制备方法工艺简单，且在富锂铁系材料界面原位形成钝化材料，能够有效防止界面与环境中水和二氧化碳反应导致形成过多的残碱，进而改善补锂材料的耐湿和加工性能，提升电池循环性能。
本申请实施例提供的富锂正极的有益效果在于：由于包括正极活性材料和上述的正极补锂添加剂，该正极补锂添加剂结构稳定性好，补锂效果好，导电性好，掺杂在正极活性材料中，能够有效补充电池工作过程中正极的锂损耗，且补锂效果持久。因而，富锂正极循环稳定好，且能量密度高。
本申请实施例提供的二次电池的有益效果在于：包括正极、负极、隔膜和 电解液，由于正极包含有上述的富锂正极，该富锂正极具有循环稳定好，且能量密度高等特性，因而提高了二次电池的循环性能和使用寿命。
附图说明
为了更清楚地说明本申请实施例中的技术方案，下面将对实施例或示范性技术描述中所需要使用的附图作简单地介绍，显而易见地，下面描述中的附图仅仅是本申请的一些实施例，对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据这些附图获得其它的附图。
图1是本申请实施例提供的正极补锂添加剂的制备方法的流程示意图；
图2是本申请实施例提供的一种正极补锂添加剂的结构示意图，其中附图标记为：1—富锂铁系材料，2—钝化层，3—导电层。
本发明的实施方式
为了使本申请要解决的技术问题、技术方案及有益效果更加清楚明白，以下结合实施例，对本申请进行详细说明。应当理解，此处所描述的具体实施例仅仅用以解释本申请，并不用于限定本申请。
本申请中，术语“和/或”，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的情况。其中A，B可以是单数或者复数。字符“/”一般表示前后关联对象是一种“或”的关系。
本申请中，“至少一个”是指一个或者多个，“多个”是指两个或两个以上。“以下至少一项(个)”或其类似表达，是指的这些项中的任意组合，包括单项(个)或复数项(个)的任意组合。例如，“a，b或c中的至少一项(个)”，或，“a，b和c中的至少一项(个)”，均可以表示：a，b，c，a-b(即a和b)，a-c，b-c，或a-b-c，其中a，b，c分别可以是单个，也可以是多个。
应理解，在本申请的各种实施例中，上述各过程的序号的大小并不意味着执行顺序的先后，部分或全部步骤可以并行执行或先后执行，各过程的执行顺序应以其功能和内在逻辑确定，而不应对本申请实施例的实施过程构成任何限定。
在本申请实施例中使用的术语是仅仅出于描述特定实施例的目的，而非旨在限制本申请。在本申请实施例和所附权利要求书中所使用的单数形式的“一种”和“该”也旨在包括多数形式，除非上下文清楚地表示其他含义。
本申请说明书实施例中所提到的相关成分的重量不仅仅可以指代各组分的具体含量，也可以表示各组分间重量的比例关系，因此，只要是按照本申请说明书实施例相关组分的含量按比例放大或缩小均在本申请说明书实施例公开的范围之内。具体地，本申请说明书实施例中的质量可以是μg、mg、g、kg等化工领域公知的质量单位。
本申请实施例第一方面提供一种正极补锂添加剂，该正极补锂添加剂包括：富锂铁系材料1和原位结合在富锂铁系材料1外表面的钝化材料；钝化材料的化学式为aLi2O·bFexOy，其中，1≤x≤3，1≤y≤4，0.0001≤a≤0.01，0.0001≤b≤0.01。
本申请实施例第一方面提供的正极补锂添加剂，包括富锂铁系材料1和结合在富锂铁系材料1外表面的钝化材料，其中，钝化材料的化学式为aLi2O·bFexOy，该钝化材料结合在富锂铁系材料1外表面，不但能够有效防止富锂铁系材料1界面与环境中水和二氧化碳反应导致形成过多的残碱，进而改善补锂材料的耐湿和加工性能，提高正极补锂添加剂的结构稳定性和性能稳定性，进而提高其对正极的补锂效果，提升电池循环性能；而且该钝化材料对载流子的迁移传输影响小。钝化材料中0.0001≤a≤0.01，0.0001≤b≤0.01，1≤x≤3， 1≤y≤4，其中，若a、b取值过大，则还原强度过高，导致活性成分降低，影响Li有效利用率发挥；若a、b取值过低，则形成的致密层有限，保护作用减弱；而若x/y比值越高，说明Fe被还原的越多，在富锂铁系材料1外表面结合的钝化材料越多。另外，正极补锂添加剂中富锂铁系内对正极材料有较好的补锂效果，能够及时补充材料在充放电循环过程中锂离子的损耗，从而提高正极材料的循环性能，提高电池使用寿命。
在一些实施例中，富锂铁系材料1的化学式为LicFedMeOf，其中，M选自Co、Ni、Mn、V、Cu、Mo、Al、Ti、Mg、Na、Ca、Zr、Si、Zn、Cr、P中的至少一种金属元素，1≤c≤6，0＜d≤0.99，0≤e≤0.1，1＜f＜4。其中，Fe主要起着稳定结构作用；d越大，Li5FeO4结构占主体，结构稳定性越好。M掺杂金属主要作用在于改善锂离子的体相传输，同时能够降低充电脱锂过程中释氧的氧活性。e越大，对锂离子的体相传输改善效果越好。c越大，实际应用中可脱出的锂离子越多，使得富锂铁系材料1的容量越高。
在一些实施例中，富锂铁系材料1的平均粒径为100nm～50μm；该粒径大小的富锂铁系材料1既使其有较好的补锂效果，而且有利于正极补锂添加剂与正极活性材料复合，提高其补锂效果。在一些具体实施例中，富锂铁系材料1的平均粒径包括但不限于100nm～1μm、1～10μm、10～20μm、20～30μm、30～40μm、40～50μm等。
在一些实施例中，钝化材料中铁离子的价态比富锂铁系材料1中铁离子的价态低，相对于富锂铁系材料1，低价态铁离子的钝化材料有更好的稳定性，起到钝化效果，防止富锂铁系材料1界面与环境中水和二氧化碳反应导致形成过多的残碱，提高正极补锂添加剂的结构稳定性和性能稳定性。
在一些实施例中，钝化材料可直接通过对富锂铁系材料1还原制得，在这 种情况下钝化材料中铁离子的低价态为富锂铁系材料1中铁离子相对应的还原价态。通过调节对富锂铁系材料1的还原条件，可灵活调控还原生成的钝化材料的量，从而调控钝化材料在富锂铁系材料1表面的结合效果。既可以在富锂铁系材料1表面还原生成部分钝化材料，也可以使还原生成的钝化材料在富锂铁系材料1表面形成完整的包覆层。在另一些实施例中，含低价态铁离子的钝化材料可以与富锂铁系材料1直接混合并经高温反应后，直接包覆于富锂铁系材料1外表面。
在一些实施例中，钝化材料包覆在富锂铁系材料1的外表面形成钝化层2，钝化材料在富锂铁系材料1外表面形成致密且均匀的包覆钝化层2，能够更有效的防止富锂铁系材料1界面与环境中水和二氧化碳反应导致形成过多的残碱，更好的改善补锂材料的耐湿和加工性能，提高正极补锂添加剂的结构稳定性和性能稳定性，进而提高其对正极的补锂效果，提升电池循环性能。
在一些实施例中，钝化层2中，钝化材料单独形成连续致密的包覆层；钝化效果好，可显著提高正极补锂添加剂的结构稳定性和性能稳定性。
在另一些实施例中，钝化层2中，钝化材料掺杂于其它包覆材料中共同形成致密的包覆层。钝化层2中，钝化材料掺杂碳材料形成致密的包覆层。通过在钝化层2的钝化材料中掺杂碳材料等材料，使得钝化层2具有较好钝化效果的同时能够提高钝化材料的导电性能。
在一些实施例中，钝化层2中，低价态的铁离子的浓度沿径向由内至外呈递增趋势。可以理解，可以采用还原气氛对富锂铁系材料1进行还原处理，以使得富锂铁系材料1外表面原位形成钝化层2。在该钝化层2中，钝化材料aLi2O·bFexOy并不是均匀分布的，与还原气氛接触越充分的富锂铁系材料1被还原的越充分。因此，沿径向由内至外，钝化材料的含量越来越富集，即低价 态的铁离子的浓度也越来越大，钝化层2也越来越致密。该实施例能够确保钝化层2的致密性，及对材料界面的钝化效果，保证材料界面相对环境的稳定性。
在一些实施例中，钝化层2的平均厚度为3～150nm；该厚度既能够有效避免生成残碱，维持富锂铁系材料1的结构稳定性和性能稳定性；又对载流子的迁移传输影响小。若钝化层2的平均厚度过高，则会影响富锂铁系材料1中活性成分及锂有效利用率的发挥；若钝化层2的平均厚度过低，则不利于提高富锂铁系材料1的结构稳定性和性能稳定性。在一些具体实施例中，钝化层2的平均厚度包括但不限于3～10nm、10～15nm、15～20nm、20～25nm、25～30nm、30～40nm、40～50nm、50～80nm、80～100nm、100～120nm、120～150nm等。
在一些实施例中，钝化材料的质量占富锂铁系材料1和钝化材料总质量的0.01～10wt％；正极补锂添加剂中该质量百分含量的钝化材料既能够有效避免生成残碱，维持富锂铁系材料1的结构稳定性和性能稳定性；又对载流子的迁移传输影响小。若钝化材料含量过低，则无法起到较好的保护；若钝化材料比例过高，则整体磁性较强，无法顺利应用于后端电池。该配比既确保了正极补锂添加剂的补锂效果，又能够有效维持正极补锂添加剂的结构稳定性和补锂稳定性，有利于提高正极材料及电池的循环性能。在一些具体实施例中，钝化材料的质量占富锂铁系材料1和钝化材料总质量的0.01～0.1wt％、0.1～1wt％、1～3wt％、3～5wt％、5～8wt％、8～10wt％等。
在一些实施例中，正极补锂添加剂还包括包覆在钝化层2外表面的导电层3，通过在钝化层2外面包覆导电层3，提高正极补锂添加剂的导电效果。其结构示意图如附图2所示。
在一些实施例中，导电层3包括石墨烯、碳纳米管、导电碳黑、导电石墨中的至少一种；这些碳材料均有较好的导电效果，能有效提高正极补锂添加剂 的电子传输效率。
在一些实施例中，导电层3的平均厚度为50～150nm；示例性的为60～120nm，示例性的为70～100nm，该厚度的导电层3能够有效提高电子传输效率。
在一些实施例中，正极补锂添加剂中，导电层3的质量百分含量为0.5～10wt％。该质量百分含量的导电层3能够有效提高电子传输效率。若导电层3质量百分含量过高，则降低了正极补锂添加剂中富锂铁系材料1的含量，从而会影响补锂效果；若导电层3质量百分含量过低，则对正极补锂添加剂导电性能的提升效果有限。在一些具体实施例中，正极补锂添加剂中导电层3的质量百分含量包括但不限于0.5～1wt％、1～2wt％、2～5wt％、5～8wt％、8～10wt％等。
如附图1所示，本申请实施例第二方面提供一种正极补锂添加剂的制备方法，包括以下步骤：
S10.按照富锂铁系材料1中元素化学计量比，将铁源、锂源和掺杂金属源进行混合处理，得到前驱体；
S20.对前驱体进行烧结处理，得到富锂铁系材料1；
S30.对富锂铁系材料1进行还原处理，在富锂铁系材料1外表面原位生成钝化材料；钝化材料的化学式为aLi2O·bFexOy，其中，1≤x≤3，1≤y≤4，0.0001≤a≤0.01，0.0001≤b≤0.01。
本申请实施例第二方面提供的正极补锂添加剂的制备方法，将铁源、锂源和掺杂金属源按富锂铁系材料1中元素化学计量比混合后，通过烧结处理，即可得到富锂铁系材料1。然后，对富锂铁系材料1进行还原处理，通过将部分富锂铁系材料1还原成铁和锂的氧化物，便可在富锂铁系材料1外表面原位生 成致密的钝化材料，该钝化材料的化学式为aLi2O·bFexOy，其中，1≤x≤3，1≤y≤4，0.0001≤a≤0.01，0.0001≤b≤0.01。本申请实施例制备方法工艺简单，且在富锂铁系材料1界面原位形成钝化材料，能够有效防止界面与环境中水和二氧化碳反应导致形成过多的残碱，进而改善补锂材料的耐湿和加工性能，提升电池循环性能。
在一些实施例中，上述步骤S10中，富锂铁系材料1的化学式为LicFedMeOf，其中，M选自Co、Ni、Mn、V、Cu、Mo、Al、Ti、Mg、Na、Ca、Zr、Si、Zn、Cr、P中的至少一种金属元素，1≤c≤6，0＜d≤0.99，0≤e≤0.1，1＜f＜4。
在一些实施例中，锂源包括硝酸锂、碳酸锂、醋酸锂、草酸锂、硼酸锂、磷酸锂、氯化锂、氢氧化锂、过氧化锂、氧化锂中的至少一种。
在一些实施例中，铁源包括铁盐；包括但不限于氯化铁、硫酸铁、硝酸铁、磷酸铁等。
在一些实施例中，掺杂金属元素源包括Co源、Ni源、Mn源、V源、Cu源、Mo源、Al源、Ti源、Mg源、Na源、Ca源、Zr源、Si源、Zn源、Cr源、P源中的至少一种。掺杂金属元素源的形式包括但不限于氯化物、硝酸盐、磷酸盐、硫酸盐等。
本申请上述实施例采用的锂源、铁源以及掺杂金属元素源，均有较好的溶解性，有利于通过液相烧结等处理方式制备富锂铁系材料1。
在一些实施例中，上述步骤S20中，对前驱体进行烧结处理采用液相烧结处理，液相烧结过程中有液相与固相颗粒共同存在，此时烧结温度高于烧结体中低熔成分或低熔共晶的熔点低于高熔点成分的熔点。由于物质液相迁移比固相扩散要快得多，烧结体的致密化速度和最终密度均大大提高。液相烧结处理 包括条件：在氧气浓度为0～1000ppm的气氛中，以100～400℃/h的升温速率升温至温度为350～900℃后反应10～20小时。其中，升温速率、温度条件、反应时长等有效确保了铁源、锂源和掺杂金属源等各原料之间的反应，各原料组分在高温条件下烧结反应生成富锂铁系材料1颗粒。
在一些实施例中，上述步骤S30中，对富锂铁系材料1进行还原处理的条件包括：在温度为350～900℃的还原气氛中处理0.1～8小时，使富锂铁系材料1界面的富锂铁系材料1部分还原成氧化锂和氧化铁，在富锂铁酸锂界面形成致密的钝化材料，从而防止界面与环境中水和二氧化碳反应导致形成过多的残碱，进而改善补锂材料的耐湿和加工性能，提高正极补锂添加剂的稳定性，提高其补锂效果，提升电池循环性能。
在一些实施例中，还原气氛中包括氢气、烃类气体、醇类气体、醚类气体、醛类气体、酮类气体中的至少一种还原气体；本申请实施例采用的这些氢气或气态分子的烃类、醇类、醚类、醛类、酮类等均具有还原性能，在一定的温度和气氛条件下均能够将富锂铁系材料1界面的富锂铁系材料1部分还原成氧化锂和氧化铁，在富锂铁酸锂界面形成致密的钝化材料。
在一些实施例中，还原气氛中，还原气体的体积百分含量为0.5～60％；该还原气氛能够有效确保对富锂铁系材料1界面层的还原，使富锂铁系材料1界面的富锂铁系材料1部分还原成氧化锂和氧化铁，在富锂铁酸锂界面形成致密的钝化材料。若还原气体含量过高，则会导致对富锂铁系材料1还原比例过高，降低正极补锂添加剂中补锂材料的占比，影响补锂效果。在一些具体实施例中，还原气氛中，还原气体的体积百分含量包括但不限于0.5～10％、10～20％、20～40％、40～60％等。
在一些实施例中，生成的钝化材料在富锂铁系材料1的外表面形成钝化层 2。
在一些实施例中，生成钝化层2后，还包括步骤：S40，将包括富锂铁系材料1和钝化材料的复合材料与导电材料混合后，进行加热处理，在复合材料表面原位生成导电层3。本申请实施例在复合材料表面制备导电层3有利于提高正极补锂添加剂的电导性能。
在一些实施例中，导电材料包括碳源、半碳化碳源中的至少一种。在一些具体实施例中，碳源包括有机碳源和无机碳源，其中，有机碳源包括葡萄糖、蔗糖等，也可以是其他种类的有机糖类，通过对有机碳源的热解，对钝化材料表面进行包覆形成导电碳包覆层。无机碳源包括石墨烯、导电碳纤维、碳纳米管等。在一些实施例中，碳源同时包括有机碳源和无机碳源，有机碳源热解的过程中夹杂了导电效果更好的无机碳源，从而降低了导电层3碳含量，提高导电效果。在一些实施例中，半碳化碳源是指通过对碳源在惰性气氛中高温处理一段时间使部分碳源碳化，在半碳化碳源表面形成羟基、羧基等活性官能团，这些活性官能团，可以与复合材料中Fe-O之间形成更好的键合，结合效果更好，从而更好的提高正极补锂添加剂的结构稳定性。
在一些实施例中，导电层3包括石墨烯、碳纳米管、导电碳黑、导电石墨中的至少一种。
在一些实施例中，加热处理的条件包括：在温度为300～400℃的惰性气氛中热处理2～6小时；使导电材料在复合材料表面形成导电包覆层。
在一些实施例中，正极补锂添加剂中，富锂铁系材料1、钝化材料和导电层3的质量比为(93～99)：(0.01～1)：(0.5～8)；其中，富锂铁系材料1作为内核主要提供容量，比例过低则可提供的活性锂较低；比例过高则钝化不足，或者导电性不足，无法较好的完成脱锂过程；钝化材料过低则无法起到较 好的保护；比例过高则整体磁性较强，无法顺利应用于后端电池；导电层3比例过低则无法提供完整导电性，比例过高则占用无效的质量。正极补锂添加剂中，富锂铁系材料1、钝化材料和导电层3的该配比，既确保了添加剂的补锂效果，又能够有效维持添加剂的结构稳定性和补锂稳定性，且导电效果好，有利于提高正极材料及电池的循环性能。
在一些实施例中，富锂铁系材料1的平均粒径为100nm～50μm；该粒径大小的富锂铁系材料1既使其有较好的补锂效果，而且有利于正极补锂添加剂与正极活性材料复合，提高其补锂效。
在一些实施例中，钝化层2的平均厚度为3～150nm；该厚度既能够有效避免生成残碱，维持富锂铁系材料1的结构稳定性和性能稳定性；又对载流子的迁移传输影响小。
在一些实施例中，导电层3的平均厚度为50～150nm；示例性的为60～120nm，示例性的为70～100nm，该厚度的导电层3能够有效提高电子传输效率。
本申请实施例第三方面提供一种富锂正极，该富锂正极包括正极活性材料和上述的正极补锂添加剂或者上述方法制备的正极补锂添加剂。
本申请实施例第三方面提供的富锂正极，由于包括正极活性材料和上述的正极补锂添加剂，该正极补锂添加剂结构稳定性好，补锂效果好，导电性好，掺杂在正极活性材料中，能够有效补充电池工作过程中正极的锂损耗，且补锂效果持久。因而，富锂正极循环稳定好，且能量密度高。
在一些实施例中，正极活性材料包括但不限于锂镍钴锰、锂镍钴铝、锂镍锰、氧化钴锂、磷酸锂铁、镍钴锰铝等中的至少一种。
在一些实施例中，将富锂正极与导电剂、粘结剂等按比例混合制成正极浆 料后，涂覆在正集流体表面，辊压、干燥，得到正极片。
本申请实施例第四方面一种二次电池，该二次电池包括正极、负极、隔膜和电解液，其中正极包含有上述的富锂正极。
本申请实施例第四方面提供的二次电池，包括正极、负极、隔膜和电解液，由于正极包含有上述的富锂正极，该富锂正极具有循环稳定好，且能量密度高等特性，因而提高了二次电池的循环性能和使用寿命。
在一些实施例中，二次电池的负极包括但不限于石墨、软碳(如焦炭等)、硬碳等碳素材料，或者氮化物、锡基氧化物、锡基氧化物、锡合金，以及纳米负极材料等。
在一些实施例中，隔膜包括聚丙烯纤维、聚丙烯腈纤维、聚乙烯醇缩甲醛纤维、聚(乙二醇对苯二甲酸酯)、聚对苯二甲酸乙二醇酯、聚酰胺纤维、聚对苯二甲酰对苯二胺中的至少一种材料。
在一些实施例中，电解液包括含Na+、K+、NH4 +中至少一种的可溶性盐的水溶液。
为使本申请上述实施细节和操作能清楚地被本领域技术人员理解，以及本申请实施例正极补锂添加剂及其制备方法的进步性能显著的体现，以下通过多个实施例来举例说明上述技术方案。
实施例1
一种正极补锂添加剂，其结构如附图2所示，包含富锂铁系材料1内核、钝化层2和导电层3，其中，内核的化学式为Li4.975Fe0.965Al0.03O3.98，钝化层2中钝化材料的化学式为0.0125Li2O·0.005FeO(x＝1，y＝1)，钝化层2的厚度为：20nm，导电层3的原材料选自含有羟基的半成品碳源。
其制备包括步骤：
①制备过氧化锂：将过氧化氢/无水氢氧化锂按照摩尔比例为1.1：1进行搅拌混合，反应温度为100℃，反应时间为30min。之后向反应器中加入定量无水乙醇。无水乙醇和过氧化氢的体积比例为1.2；最终得到带有结晶水的过氧化锂沉淀。结晶体按照420℃焙烧5h脱出结晶水得到Li2O2；
②按照分子式中Li5Fe0.97Al0.03O4元素化学计量比，提供摩尔比为0.97：1：2：0.03的用Fe(NO3)3、LiNO3、Li2O2、Al(NO3)3进行高速剪切混合，得到前驱体；
③在氮气气氛中，转入刚玉匣钵，将前驱体以300℃/h的速率升温至850℃并保温15h，冷却后对产物进行机械破碎分级得到Li5Fe0.97Al0.03O4含锂内核；
④将上述Li5Fe0.97Al0.03O4以100℃/h的速率升温至500℃，通5％H2/N2并保温5h，得到内核为Li4.975Fe0.965Al0.03O3.98，钝化层2为0.0125Li2O·0.005FeO的核壳结构粉体；
⑤以上述粉体的20wt％比例称取葡萄糖，于氮气气氛中升温至350℃保温5h，得到半碳化碳源，该半碳化碳源表面含有羟基；
⑥在氮气气氛下，将上述核壳结构粉体与半碳化碳源进行融合处理，融合处理的速度为2000rpm，融合时间为30min；在核壳结构粉体的表面形成导电碳包覆层，得到正极补锂添加剂。
实施例2
一种正极补锂添加剂，其结构如附图2所示，包含富锂铁系材料1内核、钝化层2和导电层3，其中，内核的化学式为Li4.95Fe0.96Al0.03O3.96，钝化层2中钝化材料的化学式为0.025Li2O·0.01FeO，钝化层2的厚度为：25nm，导电层3的原材料选自含有羟基的半成品碳源。
其制备方法与实施例1的区别在于：步骤4中还原性气氛更改为 5％CO/N2，其他步骤保持一致。
实施例3
一种正极补锂添加剂，其结构如附图2所示，包含富锂铁系材料1内核、钝化层2和导电层3，其中，内核的化学式为Li4.985Fe0.967Al0.03O3.988，钝化层2中钝化材料的化学式为0.0075Li2O·0.003FeO，钝化层2的厚度为：4nm，导电层3的原材料选自含有羟基的半成品碳源。
其制备方法与实施例1的区别在于：步骤4中还原性气氛更改为5％SO/N2，其他步骤保持一致。
实施例4
一种正极补锂添加剂，其结构如附图2所示，包含富锂铁系材料1内核、钝化层2和导电层3，其中，内核的化学式为Li4.99Fe0.966Al0.03O3.989，钝化层2中钝化材料的化学式为0.01Li2O·0.004FeO，钝化层2的厚度为：8nm，导电层3的原材料选自含有羟基的半成品碳源。
其制备方法与实施例1的区别在于：步骤4中还原性气氛更改为5％H2S/N2，其他步骤保持一致。
实施例5
一种正极补锂添加剂，其结构如附图2所示，包含富锂铁系材料1内核、钝化层2和导电层3，其中，内核的化学式为Li4.9625Fe0.9325Al0.03O3.925，钝化层2中钝化材料的化学式为0.0375Li2O·0.015FeO，钝化层2的厚度为：35nm，导电层3的原材料选自含有羟基的半成品碳源。
其制备方法与实施例1的区别在于：步骤4中还原性气氛更改为5％C2H2/N2，其他步骤保持一致。
实施例6
一种正极补锂添加剂，包含富锂铁系材料1内核、钝化层2和导电层3，其中，内核的化学式为Li4.975Fe0.965Al0.03O3.98，钝化层2中钝化材料的化学式为0.0125Li2O·0.005FeO，钝化层2的厚度为：20nm。
其制备方法与实施例1的区别在于：不进行步骤5处理，其他步骤保持一致。
对比例1
一种正极补锂添加剂，包含富锂铁系材料1内核和包覆导电层3，其中，内核的化学式为Li4.975Fe0.965Al0.03O3.98，导电层3的原材料选自含有羟基的半成品碳源。
其制备方法与实施例1的区别在于：不进行步骤4处理，其他步骤保持一致。
对比例2
一种正极补锂添加剂，包含富锂铁系材料1内核、钝化层2和导电层3，其中，内核的化学式为Li4.975Fe0.965Al0.03O3.98，钝化层2中钝化材料的化学式为Li2CO3，钝化层2的厚度为：50nm，导电层3的原材料选自含有羟基的半成品碳源。
其制备方法与实施例1的区别在于：步骤4通入的气体为1％CO2/N2，此时形成的钝化材料为Li2CO3钝化材料；厚度为50nm。
为了验证本申请实施例的进步性，对实施例和对比例进行如下性能测试：
1、吸附速率评估方法：
①在标准大气压下，控制房间湿度在25℃，相对湿度为20-25％；
②从手套箱中取出0.3-0.5g样品，每次取一个样品，测试完再从手套箱取下一个样品；
③将称量瓶置于十万分之一精度分析天平中，关闭舱门，清零；
④称取0.17-0.19克的待测样品于容器中，用勺子把物料摊开，使摊开的面积尽量薄而均匀，以保证测试面积不影响材料的吸水率，关闭舱门，稳定3-5s打开计时器，记录分析天平质量作为0min的数值。接下来分别记录5，10，15，20min数值，计算10-20分钟的平均吸收数据，计算含包覆层的含锂内核的吸水率。
⑤选择吸水率为0～50ppm/s的含包覆层的含锂内核作为正极补锂添加剂。
测试结果如下表1所示：
表1
由上述测试结果可知，相对于无钝化层2的对比例1，以及采用Li2CO3钝化层2的对比例2，本申请实施例1～6制备的正极补锂添加剂，通过对富锂 铁系材料1直接还原处理形成钝化层2，以及包覆有碳层的正极补锂添加剂，在相同检测条件下均表现出更低的吸水性，提高了正极补锂添加剂的稳定性。
并且，正极补锂添加剂表面形成的钝化层2，降低正极补锂添加剂的吸水性，提高了正极补锂添加剂的界面稳定性，有利于阻隔空气中的水/CO2等对补锂材料的接触，降低正极补锂添加剂中补锂材料的环境损耗，充分确保正极补锂添加剂对正极的补锂效果，通过正极补锂添加剂对正极充分且有效的补锂，提高正极的循环性能。
2、扣电评估方法：
A电池组装：
①正极极片：将实施例和对比例制备的正极补锂添加剂与钴酸锂按照5∶95的质量比混合得到混合物，将混合物与聚偏氟乙烯和SP-Li以93∶3∶4的质量比混合球磨搅拌得到正极浆料，将正极浆料涂覆在铝箔表面，辊压后，110℃下真空干燥过夜，得到正极极片；
②负极：锂金属片；
③电解液：将碳酸乙烯酯和碳酸甲乙酯以3:7的体积比混合，并加入LiPF6，形成电解液，LiPF6的浓度为1mol/L；
④隔膜：聚丙烯微孔隔。
⑤锂离子电池组装：按照锂金属片-隔膜-电解液-正极片的组装顺序在惰性气氛手套箱内组装得到锂离子电池，实施例1～6正极补锂添加剂对应的锂离子电池依次为电池A1～A6，对比例1～2正极补锂添加剂对应的锂离子电池依次为电池B1～B2。
B性能测试：
①根据实施例A1～A6、对比例A1～A2的制备过程，观察产物与匣钵粘接 情况以及匣钵稳定性。
②对实施例A1～A6、对比例A1～A2的锂离子电池的电化学性能进行测试，测试条件为：将装配好的电池在室温下放置24h后进行充放电测试，充放电电压为2.7V-4.3V。
测试结果如下表2所示：
表2
由上述测试结果可知，相对于无钝化层的对比例B1，以及采用Li2CO3形成的钝化层的对比例B2，本申请实施例A1～A6采用通过对富锂铁系材料直接还原处理形成钝化层后，包覆有碳层的正极补锂添加剂制备的锂离子电池实施例A1～A5，表现出优异的首次充电比容量，且24小时后仍表现出较高的首次充电比容量，说明电池稳定性好。实施例A6由于未进行碳包覆，24小时后首次充电比容量有所下降。而对比例B1由于采用的正极补锂添加剂无钝化层，对比例B2采用的正极补锂添加剂Li2CO3钝化层，首次充电比容量显著降低，24小时首次充电比容量显著下降。
以上仅为本申请的可选实施例而已，并不用于限制本申请。对于本领域的技术人员来说，本申请可以有各种更改和变化。凡在本申请的精神和原则之内，所作的任何修改、等同替换、改进等，均应包含在本申请的权利要求范围之内。

Claims (21)

  1. 一种正极补锂添加剂，其特征在于，所述正极补锂添加剂包括：富锂铁系材料和原位结合在所述富锂铁系材料外表面的钝化材料；所述钝化材料的化学式为aLi2O·bFexOy，其中，1≤x≤3，1≤y≤4，0.0001≤a≤0.01，0.0001≤b≤0.01。
  2. 如权利要求1所述的正极补锂添加剂，其特征在于，所述富锂铁系材料的化学式为LicFedMeOf，其中，M选自Co、Ni、Mn、V、Cu、Mo、Al、Ti、Mg、Na、Ca、Zr、Si、Zn、Cr、P中的至少一种金属元素，1≤c≤6，0＜d≤0.99，0≤e≤0.1，1＜f＜4。
  3. 如权利要求1所述的正极补锂添加剂，其特征在于，所述钝化材料中铁离子的价态比所述富锂铁系材料中铁离子的价态低。
  4. 如权利要求1所述的正极补锂添加剂，其特征在于，所述钝化材料的质量占所述富锂铁系材料和所述钝化材料总质量的0.01～10wt％。
  5. 如权利要求3所述的正极补锂添加剂，其特征在于，所述钝化材料包覆在所述富锂铁系材料的外表面形成钝化层。
  6. 如权利要求5所述的正极补锂添加剂，其特征在于，所述钝化层中，所述钝化材料单独形成连续致密的包覆层。
  7. 如权利要求6所述的正极补锂添加剂，其特征在于，所述钝化层中低价态的铁离子的浓度沿径向由内至外递增。
  8. 如权利要求5所述的正极补锂添加剂，其特征在于，所述钝化层中，所述钝化材料掺杂形成致密的包覆层。
  9. 如权利要求8所述的正极补锂添加剂，其特征在于，所述钝化层中，所述钝化材料掺杂碳材料形成致密的包覆层。
  10. 如权利要求1～9任一项所述的正极补锂添加剂，其特征在于，所述富锂铁系材料的平均粒径为100nm～50μm。
  11. 如权利要求1～9任一项所述的正极补锂添加剂，其特征在于，所述钝化层的平均厚度为3～150nm。
  12. 如权利要求1～9任一项所述的正极补锂添加剂，其特征在于，所述正极补锂添加剂还包括包覆在所述钝化层外表面的导电层。
  13. 如权利要求12所述的正极补锂添加剂，其特征在于，所述导电层包括石墨烯、碳纳米管、导电碳黑、导电石墨中的至少一种。
  14. 如权利要求12所述的正极补锂添加剂，其特征在于，所述导电层的平均厚度为50～150nm。
  15. 如权利要求12所述的正极补锂添加剂，其特征在于，所述正极补锂添加剂中，所述导电层的质量百分含量为0.5～10wt％。
  16. 一种正极补锂添加剂的制备方法，其特征在于，包括以下步骤：
    按照富锂铁系材料中元素化学计量比，将铁源、锂源和掺杂金属源进行混合处理，得到前驱体；
    对所述前驱体进行烧结处理，得到富锂铁系材料；
    对所述富锂铁系材料进行还原处理，在所述富锂铁系材料外表面原位生成钝化材料；所述钝化材料的化学式为aLi2O·bFexOy，其中，1≤x≤3，1≤y≤4，0.0001≤a≤0.01，0.0001≤b≤0.01。
  17. 如权利要求16所述的正极补锂添加剂的制备方法，其特征在于，所述富锂铁系材料的化学式为LicFedMeOf，其中，M选自Co、Ni、Mn、V、Cu、Mo、Al、Ti、Mg、Na、Ca、Zr、Si、Zn、Cr、P中的至少一种金属元素，1≤c≤6，0＜d≤0.99，0≤e≤0.1，1＜f＜4。
  18. 如权利要求17所述的正极补锂添加剂的制备方法，其特征在于，所述烧结处理采用液相烧结处理，包括条件：在氧气浓度为0～1000ppm的气氛中，以100～400℃/h的升温速率升温至温度为350～900℃后反应10～20小时。
  19. 如权利要求17所述的正极补锂添加剂的制备方法，其特征在于，所述还原处理的条件包括：在温度为350～900℃的还原气氛中处理0.1～8小时。
  20. 一种富锂正极，其特征在于，所述富锂正极包括正极活性材料和如权利要求1～15任一项所述的正极补锂添加剂或者如权利要求16～19任一项所述方法制备的正极补锂添加剂。
  21. 一种二次电池，其特征在于，所述二次电池包括正极、负极、隔膜和电解液，其中所述正极包含有如权利要求20所述的富锂正极。
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