WO2020062046A1 - 正极添加剂及其制备方法、正极及其制备方法和锂离子电池 - Google Patents

正极添加剂及其制备方法、正极及其制备方法和锂离子电池 Download PDF

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WO2020062046A1
WO2020062046A1 PCT/CN2018/108383 CN2018108383W WO2020062046A1 WO 2020062046 A1 WO2020062046 A1 WO 2020062046A1 CN 2018108383 W CN2018108383 W CN 2018108383W WO 2020062046 A1 WO2020062046 A1 WO 2020062046A1
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Prior art keywords
positive electrode
carbon
iron phosphate
additive
electrode additive
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PCT/CN2018/108383
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English (en)
French (fr)
Inventor
卢威
李伟红
陈朝阳
陈立桅
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Ningbo Zhiliang New Energy Co Ltd
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Ningbo Zhiliang New Energy Co Ltd
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Priority to JP2021542236A priority Critical patent/JP7158595B2/ja
Priority to CN201880001558.8A priority patent/CN109417162B/zh
Priority to PCT/CN2018/108383 priority patent/WO2020062046A1/zh
Priority to KR1020217012856A priority patent/KR102699307B1/ko
Priority to PL18935918.5T priority patent/PL3859825T3/pl
Priority to US17/277,809 priority patent/US12100830B2/en
Priority to EP18935918.5A priority patent/EP3859825B1/en
Priority to ES18935918T priority patent/ES3014483T3/es
Publication of WO2020062046A1 publication Critical patent/WO2020062046A1/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
    • H01M4/62—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
    • 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
    • H01M4/139—Processes of manufacture
    • H01M4/1391—Processes of manufacture of electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • H—ELECTRICITY
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    • 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
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    • 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
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    • 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
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    • 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
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    • 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
    • H01M4/621—Binders
    • H01M4/622—Binders being polymers
    • H—ELECTRICITY
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    • 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
    • H01M4/621—Binders
    • H01M4/622—Binders being polymers
    • H01M4/623—Binders being polymers fluorinated polymers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the invention relates to the field of lithium ion batteries, and in particular, to a positive electrode additive and a preparation method thereof, a positive electrode and a preparation method thereof, and a lithium ion battery.
  • high nickel ternary materials such as LiNi 0.6 Co 0.2 Mn 0.2 O 2 , LiNi 0.8 Co 0.1 Mn 0.1 O 2 and nickel nickel cobalt aluminate, etc., these materials have already achieved commercial production.
  • High voltage spinel materials LiNi 0.5 Mn 1.5 O 4 and lithium-rich anode materials are under development. The use of these positive electrode materials can effectively improve the energy density of lithium ion batteries.
  • the traditional lithium cobaltate material When the traditional lithium cobaltate material is charged to 4.2V, it can release a gram capacity of 140mAh / g, and when it is charged to 4.5V, the gram capacity can reach 190mAh / g, and the operating voltage has been increased.
  • the battery in some mobile phones has been Charge the lithium cobaltate battery to 4.35V.
  • the ternary materials currently used in electric vehicle batteries are being shifted from NCM111 (LiNi 1/3 Co 1/3 Mn 1/3 O 2 ).
  • NCM523 LiNi 0.5 Co 0.2 Mn 0.3 O 2
  • NCM811 LiNi 0.8 Co 0.1 Mn 0.1 O 2
  • NCA lithium nickel cobalt aluminate
  • the interface between the positive electrode material and the organic electrolyte is unstable, and the positive electrode in the high voltage state has a high reactivity, and the battery is prone to thermal runaway, causing combustion or explosion.
  • the ternary material with the increase of the nickel content, the thermal stability of the positive electrode material rapidly decreases, which also increases a great safety hazard. When it is used in a large number of electric vehicle power battery packs, it will bring more serious problems. as a result of. Therefore, while pursuing the high energy density of the battery, how to ensure the safety of the battery has become a major challenge in the lithium ion battery industry.
  • a method for preparing a positive electrode additive, a positive electrode and a method for preparing the same, and a lithium ion battery are also provided.
  • a positive electrode additive includes 10% to 40% of carbon-coated lithium manganese iron phosphate and an organic solvent in terms of mass percentage.
  • the carbon-coated lithium manganese iron phosphate is dispersed in the organic solvent.
  • the carbon-coated lithium manganese iron phosphate has a median particle diameter of 30 nm to 100 nm.
  • a method for preparing a positive electrode additive includes the following steps: dispersing carbon-coated lithium manganese iron phosphate in an organic solvent to obtain a positive electrode additive.
  • a method for preparing a positive electrode includes the following steps:
  • a positive electrode material, a positive electrode additive, a binder, a conductive material, and N-methylpyrrolidone are mixed to obtain a positive electrode slurry, wherein the positive electrode additive is the positive electrode additive prepared by the positive electrode additive or the method for preparing the positive electrode additive.
  • the mass ratio of the positive electrode material and the carbon-coated lithium manganese iron phosphate in the positive electrode additive is 80:20 to 99: 1;
  • the positive electrode slurry is made into a positive electrode.
  • a positive electrode is prepared by the method for preparing a positive electrode.
  • a lithium-ion battery includes the above-mentioned positive electrode.
  • FIG. 1 is a flowchart of a method of manufacturing a positive electrode according to an embodiment.
  • FIG. 2a is a scanning electron microscope image of a positive electrode material on a positive electrode prepared in Comparative Example 6.
  • FIG. 2b is a scanning electron microscope image of FIG. 2a at a magnification of 10 times.
  • 3a is a scanning electron microscope image of a positive electrode material on a positive electrode prepared in Example 20.
  • FIG. 3b is a scanning electron microscope image of FIG. 3a at a magnification of 10 times.
  • FIG. 4a is a scanning electron microscope image of a positive electrode material on a positive electrode prepared in Comparative Example 7.
  • FIG. 4a is a scanning electron microscope image of a positive electrode material on a positive electrode prepared in Comparative Example 7.
  • FIG. 4b is a scanning electron microscope image of FIG. 4a at a magnification of 10 times.
  • 5a is a scanning electron microscope image of a positive electrode material on a positive electrode prepared in Example 26.
  • FIG. 5b is a scanning electron microscope image of FIG. 5a at a magnification of 10 times.
  • FIG. 6a is a scanning electron microscope image of a cathode material on a cathode prepared in Comparative Example 8.
  • FIG. 6a is a scanning electron microscope image of a cathode material on a cathode prepared in Comparative Example 8.
  • FIG. 6b is a scanning electron microscope image of FIG. 6a at a magnification of 10 times.
  • Example 7a is a scanning electron microscope image of a positive electrode material on a positive electrode prepared in Example 27.
  • FIG. 7b is a scanning electron microscope image of FIG. 7a at a magnification of 10 times.
  • FIG. 8 is an EDX spectrum of a positive electrode material on a positive electrode prepared in Example 20.
  • FIG. 8 is an EDX spectrum of a positive electrode material on a positive electrode prepared in Example 20.
  • FIG. 9 is an EDX spectrum of a positive electrode material on a positive electrode prepared in Example 26.
  • FIG. 9 is an EDX spectrum of a positive electrode material on a positive electrode prepared in Example 26.
  • FIG. 10 is an EDX spectrum of a positive electrode material on a positive electrode prepared in Example 27.
  • FIG. 10 is an EDX spectrum of a positive electrode material on a positive electrode prepared in Example 27.
  • FIG. 11 is an electrical test curve diagram of a button-type half cell assembled with the positive electrode of Example 20 and Comparative Example 6.
  • FIG. 11 is an electrical test curve diagram of a button-type half cell assembled with the positive electrode of Example 20 and Comparative Example 6.
  • FIG. 12 is an electric test curve diagram of the assembled positive battery of the positive electrode of Example 26 and Comparative Example 7.
  • FIG. 12 is an electric test curve diagram of the assembled positive battery of the positive electrode of Example 26 and Comparative Example 7.
  • FIG. 13 is an electric test curve diagram of the button type half-cell assembled with the positive electrode of Example 27 and Comparative Example 8.
  • FIG. 14 is a comparison diagram of the rate test of the button type half-cells assembled with the positive electrodes of Example 20 and Comparative Example 6.
  • FIG. 14 is a comparison diagram of the rate test of the button type half-cells assembled with the positive electrodes of Example 20 and Comparative Example 6.
  • the positive electrode additive is a dispersion liquid of lithium manganese iron phosphate, and includes 10% to 40% of carbon-coated lithium manganese iron phosphate (LMFP) and an organic solvent, carbon-coated in terms of mass percentage. Lithium manganese iron phosphate is dispersed in an organic solvent.
  • LMFP carbon-coated lithium manganese iron phosphate
  • organic solvent carbon-coated in terms of mass percentage. Lithium manganese iron phosphate is dispersed in an organic solvent.
  • the carbon-coated lithium manganese iron phosphate has a median particle diameter (D 50 ) of 30 nm to 100 nm. If the carbon-coated lithium manganese iron phosphate has a median particle diameter greater than 100 nm, it cannot cover the positive electrode material well. And it will affect the capacity of the positive electrode material, resulting in a lower capacity of the positive electrode material.
  • Carbon-coated lithium manganese iron phosphate is commercially available. Generally, the carbon mass percentage in the carbon-coated lithium manganese iron phosphate is 2% to 15%.
  • the organic solvent may be an organic solvent commonly used in the art. Specifically, the organic solvent is selected from at least one of N-methylpyrrolidone (NMP) and N, N-dimethylformamide (DMF).
  • NMP N-methylpyrrolidone
  • DMF N, N-dimethylformamide
  • the step of preparing the positive electrode additive includes: dispersing the carbon-coated lithium manganese iron phosphate in an organic solvent to obtain a carbon-coated lithium manganese iron phosphate dispersion, thereby obtaining a positive electrode additive.
  • the carbon-coated lithium manganese iron phosphate is ground in an organic solvent to disperse the carbon-coated lithium manganese iron phosphate in the organic solvent to form a dispersion.
  • the agglomerated carbon-coated lithium manganese iron phosphate is depolymerized and dispersed by grinding, so that the carbon-coated lithium manganese iron phosphate in the positive electrode additive is a primary particle, that is, the median particle diameter (D 50 ) is 30 nm to 100 nm. .
  • the carbon-coated lithium manganese iron phosphate has a median particle diameter (D 50 ) of 60 nm to 80 nm.
  • D 50 median particle diameter
  • the particle size of the carbon-coated lithium manganese iron phosphate is too small, the cost is high, and the production cost of the cathode material is increased.
  • the carbon-coated lithium manganese iron phosphate in this particle size range can not only ensure that the positive electrode additive has a suitable cost, but also can cover the positive electrode material well, and the positive electrode material has a higher capacity.
  • the positive electrode additive further includes a binder having a mass percentage of 2% or less. Too much binder will affect the electrical properties of the cathode material.
  • the binder may be a binder commonly used in the art. Specifically, the binder is polyvinylidene fluoride (PVDF) or styrene-butadiene rubber (SBR).
  • PVDF polyvinylidene fluoride
  • SBR styrene-butadiene rubber
  • the positive electrode additive is prepared by the following steps: the binder and the organic solvent are stirred and mixed until completely dissolved, and then carbon-coated lithium manganese iron phosphate is added to obtain a positive electrode additive.
  • the positive electrode additive further includes an inorganic material having a mass percentage of 0.5% or less.
  • the inorganic material is selected from at least one of nanometer aluminum oxide, nanometer titanium oxide, and nanometer magnesium oxide. These inorganic materials are inert metal oxide materials.
  • the above-mentioned inorganic material can effectively block the reaction between the positive electrode material and the electrolytic solution, and can further improve safety and reliability. However, too much inorganic material will affect the gram capacity of the positive electrode material.
  • an inorganic material is also added in the step of adding carbon-coated lithium manganese iron phosphate.
  • the mass ratio of the inorganic material to the carbon-coated lithium manganese iron phosphate is 1:20 or less. Too much inorganic material will result in poor conductivity of the positive electrode material, resulting in a lower capacity of the positive electrode material.
  • the positive electrode additive further includes a conductive agent having a mass percentage of 10% or less. Too much conductive agent will reduce the effective substance content and cause a decrease in capacity.
  • the conductive agent may be a conductive agent commonly used in the art. Specifically, the conductive agent is selected from at least one of acetylene black, Ketjen black, graphene, and carbon nanotubes. These materials are all nano-carbons and are commonly used conductive agents for lithium ion batteries. These substances are used as a conductive agent. At this time, in the preparation of the positive electrode additive, a conductive agent is also added in the step of adding carbon-coated lithium manganese iron phosphate.
  • the mass percentage content of the solid in the positive electrode additive is 10% to 45%.
  • the solid content of the positive electrode additive is moderately thick. If the concentration is too high, the positive electrode additive has poor fluidity and is not easy to use; if the concentration is too low, the amount of the positive electrode additive used in the later period is excessive, resulting in waste of solvent and uneconomical. Further, the mass percentage content of the solid in the positive electrode additive is 25% to 30%.
  • the carbon-coated lithium manganese iron phosphate can be better dispersed in an organic solvent, and sedimentation is not easy to occur in the organic solvent, and the scale in the positive electrode slurry mixing process is reduced. Measurement error.
  • the carbon-coated lithium manganese iron phosphate and the conductive agent are mixed uniformly, and the conductivity of the carbon-coated lithium manganese iron phosphate can be improved, thereby improving the gram capacity of the positive electrode material. .
  • a method for preparing a positive electrode includes the following steps:
  • Step S110 mixing a positive electrode material, a positive electrode additive, a binder, a conductive material, and N-methylpyrrolidone to obtain a positive electrode slurry.
  • step S110 includes: mixing the binder with N-methylpyrrolidone under continuous stirring conditions, and then sequentially adding a conductive material, a positive electrode additive, and a positive electrode material to obtain a positive electrode slurry to make the positive electrode The slurry is mixed more evenly.
  • step S110 is not limited to the above steps.
  • the positive electrode material, the positive electrode additive, the binder, the conductive material, and the N-methylpyrrolidone may be directly mixed.
  • the cathode material may be a cathode material commonly used in the art.
  • the cathode material is selected from the group consisting of nickel-cobalt-manganese ternary material (NCM), nickel-cobalt-aluminum ternary material (NCA), lithium manganate (LiMn 2 O 4 ), and At least one of lithium cobaltate (LiCoO 2 ).
  • the structural formula of the nickel-cobalt-manganese ternary material is LiNi 1-yz Co y Mn z O 2 , 0 ⁇ y ⁇ 1, 0 ⁇ z ⁇ 1, y + z ⁇ 1.
  • the structural formula of the nickel nickel cobalt aluminate ternary material is LiNi 1-yz Co y Al z O 2 , 0 ⁇ y ⁇ 1, 0 ⁇ z ⁇ 1, y + z ⁇ 1, 1-yz ⁇ 0.8.
  • the median diameter of the positive electrode material is 3 to 20 micrometers.
  • the positive electrode additive is the foregoing positive electrode additive, and details are not described herein again.
  • the mass ratio of the positive electrode material and the carbon-coated lithium manganese iron phosphate in the positive electrode additive is 80:20 to 99: 1. If the mass ratio of the positive electrode material to the carbon-coated lithium manganese iron phosphate in the positive electrode additive is more than 99: 1, it cannot provide sufficient safety, and less than 80:20, the manufacturing cost of the positive electrode is too high, and the compaction of the positive electrode is low .
  • the amount of additives used is between 60:40 and 80:20, it can also improve the safety, but it will cause a reduction in energy density.
  • the adhesive may be a commonly used adhesive.
  • the binder is polyvinylidene fluoride.
  • the conductive material may be a conductive agent commonly used in the art.
  • the conductive material is composed of acetylene black and carbon nanotubes with a mass ratio of 1: 0.1 to 1: 2. If the mass ratio of the positive electrode material to the carbon-coated lithium manganese iron phosphate in the positive electrode additive is more than 99: 1, it cannot provide sufficient safety, and less than 80:20, the manufacturing cost of the positive electrode is too high, and the compaction of the positive electrode will be low . When the amount of additives used is between 60:40 and 80:20, it can also improve the safety, but it will cause a reduction in energy density.
  • N-methylpyrrolidone is an organic solvent.
  • the mass ratio of the total amount of carbon-coated lithium manganese iron phosphate in the positive electrode material and the positive electrode additive to the binder and the conductive material (94 to 98.49): (1.5 to 3): (0.01 to 3) .
  • Step S120 making a positive electrode slurry into a positive electrode.
  • the step of making the positive electrode slurry into a positive electrode includes: coating the positive electrode on a current collector, and then drying to obtain a positive electrode.
  • the current collector may be a positive current collector commonly used in the art, such as aluminum foil, nickel foam, and the like.
  • the method for preparing the above-mentioned positive electrode is simple to operate and easy for industrial production.
  • the method for preparing the above-mentioned positive electrode The positive electrode additive, the positive electrode material, the binder, the conductive material, and N-methylpyrrolidone are used to prepare a positive electrode slurry, and then the positive electrode slurry is made into a positive electrode to obtain the positive electrode.
  • the area of direct contact between the positive electrode material and the electrolyte is small, which reduces side reactions between the positive electrode material and the electrolyte, and reduces the dissolution of metal ions in the positive electrode material into the electrolyte, and can even puncture the lithium ion battery.
  • the positive electrode of one embodiment is prepared by the method for preparing a positive electrode described above.
  • the positive electrode not only has higher gram capacity and higher rate performance, which is beneficial to improve the energy density of the lithium ion battery, but also has better cycle performance, which is beneficial to improve the cycle life and safety performance of the lithium ion battery.
  • a lithium ion battery according to an embodiment includes the above-mentioned positive electrode.
  • the lithium-ion battery has both higher energy density, longer cycle life, and better safety performance.
  • the preparation process of the positive electrode additives of Examples 1 to 10 is as follows:
  • the preparation process of the positive electrode of this embodiment is substantially the same as that of Example 7. The difference is that the preparation of the positive electrode additive in step (1) of this embodiment is different. There are no inorganic materials, binders, and The conductive agent is prepared as follows:
  • each raw material was weighed according to Table 1.
  • the organic solvent and carbon-coated lithium manganese iron phosphate were mechanically stirred for 0.5 hours, and then sand-milled in a sand mill for 2 hours to obtain a positive electrode additive.
  • the mass percentage content of carbon in the carbon-coated lithium manganese iron phosphate used in this embodiment is the same as that in Embodiment 7.
  • the preparation process of the positive electrode of this embodiment is substantially the same as that of Example 7. The difference is that the preparation of the positive electrode additive in step (1) of this embodiment is different. There is no conductive agent and binder in the positive electrode additive of this embodiment.
  • the preparation process is as follows:
  • each raw material was weighed according to Table 1.
  • Carbon-coated lithium manganese iron phosphate and inorganic materials were added to an organic solvent, mechanically stirred for 0.5 hours, and then sand-milled in a sand mill for 2 hours to obtain Positive additive.
  • the mass percentage content of carbon in the carbon-coated lithium manganese iron phosphate used in this embodiment is the same as that in Embodiment 7.
  • the preparation process of the positive electrode of this embodiment is substantially the same as that of Example 7. The difference is that the preparation of the positive electrode additive in step (1) of this embodiment is different.
  • the positive electrode additive of this embodiment does not have inorganic materials and conductive agents. The process is as follows:
  • the preparation process of the positive electrode of this embodiment is substantially the same as that of Example 7. The difference is that the preparation of the positive electrode additive in step (1) of this embodiment is different. There is no inorganic material and binder in the positive electrode additive of this embodiment.
  • the preparation process is as follows:
  • each raw material was weighed according to Table 1.
  • the conductive agent and carbon-coated lithium manganese iron phosphate were added to the premix, mechanically stirred for 0.5 hours, and then sand-milled in a sand mill for 2 hours to obtain a positive electrode. additive.
  • the mass percentage content of carbon in the carbon-coated lithium manganese iron phosphate used in this embodiment is the same as that in Embodiment 7.
  • the preparation process of the positive electrode of this embodiment is substantially the same as that of Example 7. The difference is that the preparation of the positive electrode additive in step (1) of this embodiment is different. There is no conductive agent in the positive electrode additive of this embodiment.
  • the preparation process is as follows:
  • the preparation process of the positive electrode of this embodiment is substantially the same as that of Example 7. The difference is that the preparation of the positive electrode additive in step (1) of this embodiment is different. There is no binder in the positive electrode additive of this embodiment.
  • the preparation process is as follows :
  • the manufacturing processes of the positive electrodes of Examples 17 and 18 are substantially the same as those of Example 7, except that the mass percentages of the raw materials are different. Among them, the manufacturing processes of the positive electrodes of Examples 17 and 18 are shown in Table 1. The mass percentage content of carbon in the carbon-coated lithium manganese iron phosphate used in Examples 17 and 18 is the same as in Example 7.
  • the preparation process of the positive electrode additive of Comparative Example 1 is substantially the same as that of Example 1. The difference is that the preparation of the positive electrode additive of step (1) in this embodiment is different. There is no carbon-coated manganese phosphate in the positive electrode additive of this embodiment. Iron lithium. At this time, in the positive electrode additive, the mass percentage content of the inorganic material was 10.2%, the mass percentage content of the binder was 1.5%, the mass percentage content of the conductive agent was 0.01%, and the solid content of the positive electrode additive was 11.71 wt%. . The mass percentage content of carbon in the carbon-coated lithium manganese iron phosphate used in this embodiment is the same as that in embodiment 1.
  • the preparation process of the positive electrode of Example 19 to Example 34 is as follows:
  • the binder and N-methylpyrrolidone were stirred and mixed for 30 minutes, and then the conductive material was added under the condition of continuous stirring. After stirring and mixing for 30 minutes, the examples 1 to 18 were added.
  • the obtained positive electrode additive was then added to the positive electrode material after being stirred and mixed for 30 minutes, and finally stirred and mixed for another 12 hours to obtain a positive electrode slurry.
  • the positive electrode slurry was coated on a current collector and dried at 110 ° C. to obtain a positive electrode.
  • the particle diameters of the positive electrode materials of Examples 19 to 28 are shown in Table 3.
  • the particle diameters of the positive electrode materials of Examples 29 to 36 are the same as those of Example 25.
  • A indicates the mass of the positive electrode material
  • B indicates the mass of the carbon-coated lithium manganese iron phosphate in the positive electrode additive. Then, the sum of the masses of the positive electrode material and the carbon-coated lithium manganese iron phosphate in the positive electrode additive is recorded.
  • a + B the mass ratio of the carbon-coated lithium manganese iron phosphate in the positive electrode material and the positive electrode additive is denoted as A: B; C represents the mass of the binder, D represents the mass of the conductive substance, (A + B): C: D represents the mass ratio of the total amount of carbon-coated lithium manganese iron phosphate in the positive electrode material and the positive electrode additive to the binder and the conductive material.
  • NCM (523) represents LiNi 0.5 Co 0.3 Mn 0.2 O 2
  • NCM (622) represents LiNi 0.6 Co 0.2 Mn 0.2 O 2
  • NCM (811) represents LiNi 0.8 Co 0.1 Mn 0.1 O 2 .
  • the preparation process of the positive electrode of Comparative Example 2 is substantially the same as that of Example 19, except that the positive electrode additive of Comparative Example 1 is used for the positive electrode of Comparative Example 2.
  • the binder and N-methylpyrrolidone are stirred and mixed for 30 minutes, and then the conductive material is added under continuous stirring. After stirring and mixing for 30 minutes, nano-alumina is added, and then the NCM (523) positive electrode is added after stirring and mixing for 30 minutes. The material was finally stirred and mixed for another 12 hours to obtain a positive electrode slurry.
  • the positive electrode slurry was coated on a current collector and dried at 110 ° C. to obtain a positive electrode.
  • the positive electrode material, the binder, the conductive material, and N-methylpyrrolidone were the same as those in Example 20, and the addition ratio was also the same as in Example 20.
  • the mass ratio of the positive electrode material to the alumina in Comparative Example 3 was 93: 7.
  • the sum of the mass of the positive electrode material and the alumina: the mass of the binder: the mass of the conductive substance 97: 1.5: 1.5.
  • the binder and N-methylpyrrolidone are stirred and mixed for 30 minutes, and then the conductive material is added under continuous stirring. After stirring and mixing for 30 minutes, carbon-coated lithium manganese iron phosphate is added, and then added after stirring and mixing for 30 minutes.
  • the positive electrode material was finally stirred and mixed for another 12 hours to obtain a positive electrode slurry.
  • the positive electrode slurry was coated on a current collector and dried at 110 ° C. to obtain a positive electrode.
  • the positive electrode material, the binder, the conductive material, and N-methylpyrrolidone were the same as in Example 20, and the addition ratio was also the same as in Example 20.
  • the preparation process of the positive electrode of Comparative Example 5 is as follows:
  • the carbon-coated lithium manganese iron phosphate and NCM (523) were mechanically fused for 15 minutes according to a mass ratio of 93: 7, and then a conductive agent and a binder were added to continue mechanical fusion for 15 minutes to obtain a positive electrode active material; N-methylpyrrolidone was stirred and mixed for 30 minutes, and then the conductive material was added under continuous stirring. After stirring and mixing for 30 minutes, the positive electrode active material was added, and finally stirred and mixed for 12 hours to obtain a positive electrode slurry, and the positive electrode slurry was coated. It was dried on a current collector at 110 ° C to obtain a positive electrode.
  • the conductive agent and the binder of Comparative Example 5 are the same as the conductive agent and the binder of Example 1.
  • the mass ratio of the conductive agent to the carbon-coated lithium manganese iron phosphate is 1: 14.3, and the binder and carbon are the same.
  • the coated lithium manganese iron phosphate has a mass ratio of 1:19, the binder, the conductive material, and the N-methylpyrrolidone are the same as in Example 20, and the addition ratio is also the same as in Example 20.
  • Mass: mass of the bonding substance: mass of the conductive substance 97: 1.5: 1.5.
  • the binder and N-methylpyrrolidone are stirred and mixed for 30 minutes, and then the conductive material is added under continuous stirring. After stirring and mixing for 30 minutes, NCM (523) cathode material is added. Finally, the mixture is stirred and mixed for 12 hours to obtain a positive electrode slurry.
  • the positive electrode slurry was coated on a current collector and dried at 110 ° C. to obtain a positive electrode.
  • the binder and N-methylpyrrolidone are stirred and mixed for 30 minutes, and then the conductive material is added under continuous stirring. After stirring and mixing for 30 minutes, LiMn 2 O 4 cathode material is added, and finally the mixture is stirred and mixed for 12 hours to obtain a positive electrode slurry.
  • the positive electrode slurry was coated on a current collector and dried at 110 ° C. to obtain a positive electrode.
  • the binder and N-methylpyrrolidone are stirred and mixed for 30 minutes, and then the conductive material is added under continuous stirring. After stirring and mixing for 30 minutes, LiCoO 2 cathode material is added, and finally the mixture is stirred and mixed for 12 hours to obtain a positive electrode slurry.
  • the positive electrode slurry was coated on a current collector and dried at 110 ° C to obtain a positive electrode.
  • FIG. 2a is a scanning electron microscope (SEM) image of the positive electrode material on the positive electrode prepared in Comparative Example 6, and FIG. 2b is an enlarged view of 10a at 2a.
  • SEM scanning electron microscope
  • FIG. 3a is a scanning electron microscope (SEM) image of the positive electrode material on the positive electrode prepared in Example 20.
  • FIG. 3b is an enlarged view of 10 times 3a. From the figure, it can be seen that lithium manganese iron phosphate and the conductive agent form a uniform The structure of the network layer is uniformly and densely coated on the surface of the particles of the positive electrode material, and the particle size of the lithium manganese iron phosphate is about 60 nm.
  • FIG. 4a is a scanning electron microscope image of the positive electrode material on the positive electrode prepared in Comparative Example 7, and FIG. 4b is an enlarged view of 4a, which is 10 times larger.
  • Agent, conductive material formed a uniform network layer structure.
  • Fig. 5a is a scanning electron microscope image of the positive electrode material on the positive electrode prepared in Example 26, and Fig. 5b is an enlarged view of 10 times that of 5a.
  • lithium manganese iron phosphate and the conductive agent form a uniform network layer Structure, the network layer structure is uniformly and densely coated on the irregular particle surface of the lithium manganate material, and the particle size of the lithium iron manganese phosphate is about 60 nm.
  • Fig. 6a is a scanning electron microscope image of the positive electrode material on the positive electrode prepared in Comparative Example 8, and Fig. 6b is an enlarged view of 6a at 10 times.
  • the surface of the spherical particles of the positive electrode material is covered with a layer of conductive material.
  • a uniform network layer structure is formed between conductive objects.
  • FIG. 7a is a scanning electron microscope image of the positive electrode material on the positive electrode prepared in Example 27, and FIG. 7b is an enlarged view of 10 times that of 7a.
  • the lithium manganese iron phosphate particles and the conductive agent form a uniform network Layer structure, the network layer structure is uniformly and densely coated on the surface of the spherical particles of the positive electrode material; the particle size of the lithium manganese iron phosphate is about 60 nm.
  • the positive electrode materials on the positive electrodes of Examples 19, 21 to 25, and 28 to 36 have similar morphologies to those of Examples 20, 26, and 27, and details are not described herein again.
  • the positive electrode material contains elements such as Ni, Co, Mn, Fe, O, P, and C. These three The surface of the elementary cathode material contains a lithium manganese iron phosphate component.
  • FIG. 9 is an EDX spectrum of the positive electrode material on the positive electrode prepared in Example 26. It can be seen from the figure that the positive electrode material contains elements such as Mn, Fe, O, P, and C. These illustrate the lithium manganate positive electrode material The surface is made of lithium manganese iron phosphate.
  • FIG. 10 is an EDX spectrum of the positive electrode material on the positive electrode prepared in Example 27. It can be seen from the figure that the positive electrode material contains elements such as Co, Mn, Fe, O, P, and C, which proves that lithium cobaltate
  • the surface of the positive electrode material contains a lithium manganese iron phosphate component.
  • the positive electrode materials on the positive electrodes of Examples 19, 21 to 25, and Examples 28 to 36 have EDX spectra similar to those of Examples 20, 26, and 27, and details are not described herein again.
  • the positive electrodes of Examples 20, 26, 27 and Comparative Examples 6 to 8 were assembled into button-type half-cells, in which all the half-cells used lithium sheets as negative electrodes, and the half-cells made of the positive electrodes of Example 20 and Comparative Example 6 Charge and discharge at constant current and constant voltage at a current of 0.2C in the range of 2.75V to 4.3V.
  • the half-cells produced by the positive electrode of Example 26 and Comparative Example 7 were charged at a constant current of 0.2C in the range of 3.0V to 4.3V.
  • the constant-current charge and discharge were performed.
  • the half-cells fabricated in the positive electrode of Example 27 and Comparative Example 8 were charged and discharged at a constant current and constant voltage at a current of 0.2C in the range of 3.5V to 4.35V.
  • FIG. 11 is a graph of electrical test data of the assembled positive batteries of the positive electrodes of Example 20 and Comparative Example 6, and the half-cells produced by the positive electrodes of Example 20 and Comparative Example 6 at 0.2C have a discharge gram capacity of 163.5, respectively. mAh / g and 162.8 mAh / g; this shows that the positive electrode additive of Example 1 does not affect the electrochemical performance of the ternary lithium ion battery.
  • the electric curve of the half-cell produced by using the positive electrode of Example 20 has a small bending at the voltage platform of 3.6V to 3.4V, which should be Fe 2+ in lithium manganese iron phosphate. / Fe 3+ discharge platform, because the addition amount of the positive electrode additive of Example 2 is small, and the bending amplitude is small.
  • FIG. 12 is a graph of electrical test data of the positive electrode of Example 26 and Comparative Example 7 assembled into a button-type half cell.
  • the half cell made of the positive electrode of Example 26 and Comparative Example 7 is under a current of 0.2C.
  • the discharge specific capacities are 109.0 mAh / g and 108.9 mAh / g, respectively; this shows that the positive electrode additive of Example 8 does not affect the electrochemical performance of the lithium manganate lithium ion battery.
  • the electrical curve of Example 26 has a small bending at the voltage platform of 3.6V to 3.4V. This should be the discharge platform of Fe 2+ / Fe 3+ in lithium manganese iron phosphate, because The addition amount of the positive electrode additive is small, and the bending amplitude is small.
  • FIG. 13 is a graph of electrical test data of a button-type half cell assembled with the positive electrode of Example 27 and Comparative Example 8.
  • the half cell made of the positive electrode of Example 27 and Comparative Example 8 is under a current of 0.2C.
  • the specific discharge capacities are 160.0 mAh / g and 158.7 mAh / g, respectively; this shows that the positive electrode additive of Example 9 does not affect the electrochemical performance of the lithium cobaltate lithium ion battery.
  • the electrical curve of Example 27 has a small bending at the voltage platform of 3.6V to 3.4V. This should be the discharge platform of Fe 2+ / Fe 3+ in lithium manganese iron phosphate because The addition amount of the positive electrode additive is small, and the bending amplitude is small.
  • FIG. 14 is a comparison chart of the rate test of the assembled button-type half-cells with the positive electrodes of Example 20 and Comparative Example 6, respectively.
  • the two types of button-down batteries are respectively cycled three times with currents at 0.2C, 0.5C, 1C, and 2C rates. Charge and discharge test, and count these data into a comparison chart. It can be seen from the figure that the rate performance of Example 20 is similar to that of Comparative Example 6. This shows that the positive electrode additive of Example 2 does not affect the rate performance of the ternary lithium ion battery.
  • the positive electrodes of Examples 19, 21 to 25 and Examples 28 to 36 and Comparative Examples 2 to 5 were also assembled into button-type half-cells according to the above method.
  • Examples 19, 21 to 25 and Examples 29 to 36 and The half-cells fabricated with the positive electrodes of Comparative Examples 2 to 5 were subjected to constant current and constant voltage charging and discharging at a current of 0.2C, 1C, and 2C in the range of 2.75V to 4.3V.
  • the discharge specific capacities of the half-cells produced in the positive electrodes of Examples 19 to 36 and Comparative Examples 2 to 8 at 0.2C, 1C, and 2C are shown in Table 5.
  • the button specific half-cells assembled with the positive electrodes of Examples 19 to 36 at 0.2C, 1C, and 2C have specific discharge capacities of at least 110.3mAh / g, 100.5mAh / g, and 100.5mAh / g, respectively. 89.2mAh / g, has a higher specific discharge capacity.
  • the button specific half-cells assembled with the positive electrode of Example 25 under the currents of 0.2C, 1C, and 2C have specific discharge capacities of 198mAh / g, 186.4mAh / g, and 175.4mAh / g, respectively, and have specific ratios of Examples 26 to 36.
  • the button-type half battery assembled with a positive electrode has a higher specific discharge capacity.
  • the button-type half battery assembled from the positive electrode of Example 20 and Comparative Example 3 had the same conditions except for the different types of additives, but the button-type half battery assembled from Example 20 had a current of 0.2C, 1C, and 2C.
  • the specific discharge capacities of the battery are at least 163.9mAh / g, 153.0mAh / g, and 136.8mAh / g, respectively; and the button half batteries assembled in Comparative Example 3 have a specific discharge capacity of at least 0.2C, 1C, and 2C, respectively.
  • Example 20 140.7mAh / g, 128.2mAh / g, and 115.3mAh / g are far worse than those in Example 20 because the lithium manganese iron phosphate containing capacity is used as the additive in Example 20, while the lithium manganese iron phosphate used in Comparative Example 3 is used as the additive. It is alumina with no capacity as an additive. This is because only inorganic materials are used as the positive electrode additive to cover the positive electrode material. Although an artificial passivation layer can be formed, direct contact between the electrolyte and the positive electrode material can be reduced, the dissolution of metal ions can be suppressed, and in extreme cases, the positive electrode material and the positive electrode material can be relieved.
  • the irreversible reaction between electrolytes can make the positive electrode material have higher cycle and safety stability than the unmodified positive electrode material.
  • the inorganic material itself is inert and has no gram capacity, it will reduce the overall positive electrode material.
  • the gram capacity is used to reduce the energy density of the lithium ion battery.
  • the direct contact between the electrolyte and the positive electrode material is reduced, and the rate performance of the positive electrode material is also reduced.
  • lithium is used as a positive electrode additive, it can not only solve the safety problem of the battery, but also belong to a positive electrode active material, which can exert its capacity without significantly reducing the energy density and rate performance of the positive electrode material.
  • the gram capacity of the positive electrode material is higher and the rate performance is better; and when the positive electrode additive containing only inorganic materials or the inorganic material powder is used, the positive electrode The gram capacity of the materials is low, and the rate performance is poor.
  • Example 20 and Comparative Example 4 It can also be seen from Table 5 that the manner of introducing lithium manganese phosphate removal in Example 20 and Comparative Example 4 is different (the former is introduced as an additive and the latter is introduced as a powder), and other conditions are consistent.
  • the button half-cells assembled with the positive electrode of Example 20 at 0.2C, 1C, and 2C have specific discharge capacities of at least 163.9mAh / g, 153.0mAh / g, and 136.8mAh / g, respectively, and those assembled in Comparative Example 4
  • the discharge specific capacities of the button-type half-cells under the currents of 0.2C, 1C and 2C are only 160mAh / g, 146.8mAh / g and 132.9mAh / g, respectively.
  • the electrochemical performance was far inferior to that of Example 20.
  • the positive electrode of Comparative Example 4 had a lower gram capacity and poor rate performance.
  • the positive electrode of Example 20 had a higher gram capacity and better rate performance. This is because the primary particles of lithium manganese iron phosphate in the positive electrode additive are evenly coated on the surface of the positive electrode material, and the lithium manganese iron phosphate powder is only mixed with the positive electrode material. The former structure is conducive to improving the conductivity of the lithium manganese iron phosphate particles.
  • NCM (523) -lithium manganese iron phosphate cathode active material prepared by the fusion pre-coating method and the anode material after using lithium manganese iron phosphate anode additive have the same capacity and rate performance Basically the same.
  • the positive electrode pieces produced in Examples 20, 26, and 27 and Comparative Examples 6 to 8 were respectively made into soft-packed batteries, and the soft-packed batteries were subjected to needle punching and overcharge tests and electrical performance tests. Among them, the acupuncture results, the overcharge test results, and the gram capacity of the soft pack batteries obtained in Examples 20, 26, and 27 and Comparative Examples 6 to 8 are shown in Table 6.
  • Needle puncture test Use a smooth stainless steel needle with a diameter of 6mm for a fully-charged soft-pack battery, pierce the soft-pack battery at a speed of 2.2cm / s, and observe for 1 hour. Pass without explosion or fire.
  • the positive electrode materials on the positive electrodes of Examples 19, 20 to 25, and 28 to 36 have similar safety performance to those of Examples 20, 26, and 27, and details are not described herein again.

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Abstract

一种正极添加剂，按照质量百分含量计，包括10％～40％的碳包覆的磷酸锰铁锂和有机溶剂，碳包覆的磷酸锰铁锂分散在有机溶剂中，碳包覆的磷酸锰铁锂的中位粒径为30纳米～100纳米。

Description

正极添加剂及其制备方法、正极及其制备方法和锂离子电池 技术领域
本发明涉及锂离子电池领域，特别是涉及一种正极添加剂及其制备方法、正极及其制备方法和锂离子电池。
背景技术
近年来，随着智能手机、平板电脑、电子手环等各类消费类电子产品日新月异、节能环保的电动交通工具市场飞速增长以及储能电池市场展露头角，作为这些产品电源的锂离子电池的市场得以飞速发展。随着锂电池应用领域与市场的爆发式增长，对锂离子电池的能量密度不断提出更高的要求，为此，在锂离子电池的正极材料端，人们开始使用高电压钴酸锂(充电电压>4.3V)、高镍三元材料如LiNi 0.6Co 0.2Mn 0.2O 2、LiNi 0.8Co 0.1Mn 0.1O 2以及镍钴铝酸锂等，这些材料都已经实现了商品化的生产，同时人们还在开发高电压尖晶石材料LiNi 0.5Mn 1.5O 4、富锂相正极材料等。这些正极材料的使用，能够有效提高锂离子电池的能量密度。
传统钴酸锂材料充电至4.2V时，能够放出140mAh/g的克容量，而充电至4.5V时，克容量发挥可以达到190mAh/g，并且工作电压有所提升，目前的部分手机中电池已经将钴酸锂电池充电至4.35V。另外，为了提升电动汽车的续航里程，并且降低电池中钴元素的用量，目前电动汽车电池中使用的三元材料正在由NCM111(LiNi 1/3Co 1/3Mn 1/3O 2)转向使用NCM523(LiNi 0.5Co 0.2Mn 0.3O 2)，并进一步向NCM811(LiNi 0.8Co 0.1Mn 0.1O 2)与NCA(镍钴铝酸锂)发展。随着正极材料中镍含量的提高，正极材料的克容量逐渐提高，这有助于提高电池的能量密度，而同时三元材料中钴含量的降低，也能够降低正极材料的原料成本。因此，可以说，目前锂离子电池正极材料正在向着高电压、高克容量的方向发展，包括提升钴酸锂材料的工作电压以及提高正极材料中的镍含量等。
但是，钴酸锂电池工作电压提升后，会造成正极材料与有机电解液的界面不稳定，而且高电压状态的正极具有很高的反应活性，电池容易产生热失控，造成燃烧或爆炸；而对于三元材料，随着镍含量的升高而正极材料的热稳定性迅速降低，也增加了很大的安全隐患，当被大量应用于电动汽车的动力电池组中，会带来更为严重的后果。因此，在追求电池高能量密度的同时，如何保证电池的安全性成为锂离子电池行业中的重大挑战。
发明内容
基于此，有必要提供一种能够使锂离子电池兼具较高的能量密度和较高的安全性能的正极添加剂。
此外，还提供一种正极添加剂的制备方法、正极及其制备方法和锂离子电池。
一种正极添加剂，按照质量百分含量计，包括10％～40％的碳包覆的磷酸锰铁锂和有机溶剂，所述碳包覆的磷酸锰铁锂分散在所述有机溶剂中，所述碳包覆的磷酸锰铁锂的中位粒径为30纳米～100纳米。
一种正极添加剂的制备方法，包括如下步骤：将碳包覆的磷酸锰铁锂分散在有机溶剂中，得到正极添加剂。
一种正极的制备方法，包括如下步骤：
将正极材料、正极添加剂、粘结物、导电物及N-甲基吡咯烷酮混合，得到正极浆料，其中，所述正极添加剂为上述正极添加剂或上述正极添加剂的制备方法制备得到的正极添加剂，所述正极材料与所述正极添加剂中的所述碳包覆的磷酸锰铁锂的质量比为80:20～99:1；及
将所述正极浆料制作成正极。
一种正极，由上述正极的制备方法制备得到。
一种锂离子电池，包括上述正极。
本发明的一个或多个实施例的细节在下面的附图和描述中提出。本发明的其它特征、目的和优点将从说明书、附图以及权利要求书变得明显。
附图说明
为了更清楚地说明本发明实施例或现有技术中的技术方案，下面将对实施例或现有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发明的一些实施例，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他实施例的附图。
图1为一实施方式的正极的制备方法的流程图。
图2a为对比例6制备的正极上的正极材料的扫描电镜图。
图2b为图2a放大10倍的扫描电镜图。
图3a为实施例20制备的正极上的正极材料的扫描电镜图。
图3b为图3a放大10倍的扫描电镜图。
图4a为对比例7制备的正极上的正极材料的扫描电镜图。
图4b为图4a放大10倍的扫描电镜图。
图5a为实施例26制备的正极上的正极材料的扫描电镜图。
图5b为图5a放大10倍的扫描电镜图。
图6a为对比例8制备的正极上的正极材料的扫描电镜图。
图6b为图6a放大10倍的扫描电镜图。
图7a为实施例27制备的正极上的正极材料的扫描电镜图。
图7b为图7a放大10倍的扫描电镜图。
图8为实施例20制备的正极上的正极材料的EDX能谱图。
图9为实施例26制备的正极上的正极材料的EDX能谱图。
图10为实施例27制备的正极上的正极材料的EDX能谱图。
图11为实施例20和对比例6的正极组装成扣式半电池的电测试曲线图。
图12为实施例26和对比例7的正极组装成扣式半电池的电测试曲线图。
图13为实施例27和对比例8的正极组装成扣式半电池的电测试曲线图。
图14为实施例20和对比例6的正极组装成扣式半电池的倍率测试对比图。
具体实施方式
为了便于理解本发明，下面将参照相关附图对本发明进行更全面的描述。
一实施方式的正极添加剂，为一种磷酸锰铁锂的分散液，按照质量百分含量计，包括10％～40％的碳包覆的磷酸锰铁锂(LMFP)和有机溶剂，碳包覆的磷酸锰铁锂分散在有机溶剂中。
其中，碳包覆的磷酸锰铁锂的中位粒径(D 50)为30nm～100nm，若碳包覆的磷酸锰铁锂的中位粒径大于100nm，无法很好地包覆正极材料，而且会影响正极材料的容量，导致正极材料的容量较低。碳包覆的磷酸锰铁锂可通过市面购买得到。通常，碳包覆的磷酸锰铁锂中的碳质量百分含量为2％～15％。
其中，有机溶剂可为本领域常用的有机溶剂。具体地，有机溶剂选自N-甲基吡咯烷酮(NMP)及N,N-二甲基甲酰胺(DMF)中的至少一种。
在其中一个实施例中，正极添加剂的制备步骤包括：将碳包覆的磷酸锰铁锂分散在有机溶剂中，以得到碳包覆的磷酸锰铁锂的分散液，从而得到正极添加剂。具体地，通过在有机溶剂中研磨碳包覆的磷酸锰铁锂，以使碳包覆的磷酸锰铁锂分散在有机溶剂中，形成分散液。即通过研磨以使团聚的碳包覆的磷酸锰铁锂解聚分散，以使正极添加剂中的碳包覆的磷酸锰铁锂为一次颗粒，即中位粒径(D 50)为30nm～100nm。
进一步地，碳包覆的磷酸锰铁锂的中位粒径(D 50)为60nm～80nm，碳包覆的磷酸锰铁锂的粒径过小，成本高，会增加正极材料的生产成本，而该粒径范围的碳包覆的磷酸锰铁锂不仅能够保证正极添加剂具有合适的成本，而且还能够很好地包覆正极材料，并是正极材料具有较高的容量。
进一步地，正极添加剂还包括质量百分含量为2％以下的粘结剂。过多的粘结剂会影响正极材料的电性能。其中，粘结剂可以为本领域常用的粘结剂。具体地，粘结剂为聚偏氟乙烯(PVDF)或丁苯橡胶(SBR)。此时，正极添加剂通过如下步骤制备得到：将粘结剂与有机溶剂搅拌混合至完全溶解，然后加入碳包覆的磷酸锰铁锂，得到正极添加剂。
进一步地，正极添加剂还包括质量百分含量为0.5％以下的无机材料，无机材料选自纳米氧化铝、纳米氧化钛及纳米氧化镁中的至少一种，这些无机材料为惰性的金属氧化物材料，上述含量的无机材料可以有效阻挡正极材料与电解液之间的反应，能进一步提高安全可靠性，然而过多的无机材料会影响正极材料克容量的发挥。此时，在制备正极添加剂时，在加入碳包覆的磷酸锰铁锂的步骤中，还加入了无机材料。
更进一步地，无机材料与碳包覆的磷酸锰铁锂的质量比为1:20以下。若无机材料过多，会导致正极材料的导电性差，致使正极材料的容量较低。
进一步地，正极添加剂还包括质量百分含量为10％以下的导电剂，导电剂过多，会降低有效物质含量，造成容量降低。其中，导电剂可以为本领域常用的导电剂。具体地，导电剂选自乙炔黑、科琴黑、石墨烯及碳纳米管中的至少一种，这些物质均为纳米碳，且为锂离子电池的常用的导电剂，因此，正极添加剂中也使用这些物质作为导电剂。此时，在制备正极添加剂时，在加入碳包覆的磷酸锰铁锂的步骤中，还加入了导电剂。
进一步地，正极添加剂中的固体的质量百分含量为10％～45％。该固含量的正极添加剂粘稠适中，若浓度过高，正极添加剂流动性差，不易使用；浓度过低，导致后期正极添加剂的用量过多，造成溶剂浪费，不经济。进一步地，正极添加剂中的固体的质量百分含量为25％～30％。
上述正极添加剂至少有以下优点：
(1)经实验发现，上述配方的正极添加剂添加到正极材料中与正极材料一同制作成正极，不仅能够降低正极上的正极材料与电解液的直接接触面积，以减少正极材料与电解液之间副反应，而减少正极材料中的金属离子溶出到电解液中，甚至还能够在锂离子电池在发生穿刺、短路、过充以及在高温等极端情况下，降低锂离子电池发生燃烧、爆炸等危险的可能性，使得锂离子电池具有较高的安全性能，同时，还能够保证正极材料具有较高的克容量和倍率性能，以使锂离子电池具有较高的能量密度。
(2)通过在正极添加剂中加入粘结剂，能将碳包覆的磷酸锰铁锂更好地分散于有机溶剂中，且在有机溶剂中不容易发生沉降，减少正极混浆过程中的称量误差。
(3)通过在正极添加剂中加入导电剂，将碳包覆的磷酸锰铁锂与导电剂混合均匀，能提高碳包覆的磷酸锰铁锂自身材料的导电性，从而提高正极材料的克容量。
如图1所示，一实施方式的正极的制备方法，包括如下步骤：
步骤S110：将正极材料、正极添加剂、粘结物、导电物及N-甲基吡咯烷酮混合，得到正极浆料。
在其中一个实施例中，步骤S110包括：在持续搅拌的条件下，将粘结物与N-甲基吡咯烷酮混合，然后依次加入导电物、正极添加剂和正极材料，得到正极浆料，以使正极浆料混合得更加均匀。
需要说明的是，步骤S110也不限于为上述步骤，例如，在另一个实施例中，还可以直接将正极材料、正极添加剂、粘结物、导电物及N-甲基吡咯烷酮搅拌混合。
其中，正极材料可以为本领域常用的正极材料，具体地，正极材料选自镍钴锰三元材料(NCM)、镍钴铝三元材料(NCA)、锰酸锂(LiMn 2O 4)及钴酸锂(LiCoO 2)中的至少一种。
其中，镍钴锰三元材料的结构通式为LiNi 1-y-zCo yMn zO 2，0<y<1，0<z<1，y+z<1。
其中，镍钴铝酸锂三元材料(NCA)的结构通式为LiNi 1-y-zCo yAl zO 2，0<y<1，0<z<1，y+z<1，1-y-z≥0.8。
进一步地，正极材料的中位粒径为3微米～20微米。
其中，正极添加剂为上述正极添加剂，在此不再赘述。正极材料与正极添加剂中的碳包覆的磷酸锰铁锂的质量比为80:20～99:1。若正极材料与正极添加剂中的碳包覆的磷酸锰铁锂的质量比大于99:1，不能提供足够安全性，小于80:20，正极的制作成本过高，而且会造成正极压实偏低。当添加剂使用量在60:40～80:20之间时，也能起到安全性改善的效果，但会造成能量密度的降低。
其中，粘结物可以为本领常用的粘结剂。具体地，粘结物为聚偏氟乙烯。
其中，导电物可以为本领域常用的导电剂。导电物为由质量比为1:0.1～1:2的乙炔黑和碳纳米管组成。若正极材料与正极添加剂中的碳包覆的磷酸锰铁锂的质量比大于99:1，不能提供足够安全性，小于80:20，正极的制作成本过高，而且会造成正极压实偏低。当添加剂使用量在60:40～80:20之间时，也能起到安全性改善的效果，但会造成能量密度的降低。
其中，N-甲基吡咯烷酮为有机溶剂。
进一步地，正极材料和正极添加剂中的碳包覆的磷酸锰铁锂的总量与粘结物、导电物三者的质量比(94～98.49):(1.5～3):(0.01～3)。
步骤S120：将正极浆料制作成正极。
具体地，将正极浆料制作成正极的步骤包括：将正极涂布在集流体上，然后干燥，得到正极。集流器可以为本领域常用的正极集流体，例如铝箔、泡沫镍等。
上述正极的制备方法至少有以下优点：
(1)上述正极的制备方法操作简单，易于工业化生产。
(2)上述正极的制备方法通过上述配方的正极添加剂与正极材料、粘结物、导电物及N-甲基吡咯烷酮共同制作正极浆料，再将该正极浆料制作成正极，使得到的正极的正极材料与电解液的直接接触面积较少，较少了正极材料与电解液之间副反应，而减少正极材料中的金属离子溶出到电解液中，甚至还能够在锂离子电池在发生穿刺、短路、过充以及在高温等极端情况下，降低锂离子电池发生燃烧、爆炸等危险的可能性，使得锂离子电池具有较高的安全性能，同时，还能够正极还具有较高的克容量和倍率性能，能够使锂离子电池具有较高的能量密度。
一实施方式的正极，由上述正极的制备方法制备得到。该正极不仅具有较高的克容量和较高的倍率性能，有利于提高锂离子电池的能量密度，而且还较好的循环性能，有利提高锂离子电池的循环寿命和安全性能。
一实施方式的锂离子电池，包括上述正极。该锂离子电池兼具较高的能量密度、较长的循环寿命和较好的安全性能。
以下为具体实施例部分(以下实施例如无特殊说明，则不含有除不可避免的杂质以外的其它未明确指出的组分。)：
实施例1～10
实施例1～10的正极添加剂的制备过程如下：
按照质量百分含量计，根据表1称取各原料；将粘结剂与有机溶剂机械搅拌混合1小时，得到预混液，然后将碳包覆的磷酸锰铁锂、无机材料和导电剂加入到预混液，机械搅拌0.5小时，再在砂磨机中砂磨2小时，以使磷酸锰铁锂、无机材料和导电剂分散在预混液中，得到正极添加剂。其中，实施例1～10中使用的碳包覆的磷酸锰铁锂中的碳的质量百分含量见表2。
表1
Figure PCTCN2018108383-appb-000001
Figure PCTCN2018108383-appb-000002
其中，表1中的“--”表示该没有该物质或物质的含量为0；且表1中的无机材料中的“物质”一列中，纳米氧化铝：纳米氧化钛＝1:1、纳米氧化钛：纳米氧化铝：纳米氧化镁＝1:3:6表示的是质量比，导电剂的“物质”一列中的碳纳米管：石墨烯＝1:1表示质量比，“有机溶剂”一列中的DMF：NMP＝1:2为质量比。
表2
Figure PCTCN2018108383-appb-000003
实施例11
本实施例的正极的制备过程与实施例7大致相同，区别在于，本实施例的步骤(1)的正极添加剂的制备有所不同，本实施例的正极添加剂中没有无机材料、粘结剂和导电剂，制备过程如下：
按照质量百分含量计，根据表1称取各原料；将有机溶剂与碳包覆的磷酸锰铁锂机械搅拌0.5小时，再在砂磨机中砂磨2小时，得到正极添加剂。其中，本实施例使用的碳包覆的磷酸锰铁锂中的碳的质量百分含量与实施例7相同。
实施例12
本实施例的正极的制备过程与实施例7大致相同，区别在于，本实施例的步骤(1)的正极添加剂的制备有所不同，本实施例的正极添加剂中没有导电剂与粘结剂，制备过程如下：
按照质量百分含量计，根据表1称取各原料；将碳包覆的磷酸锰铁锂、无机材料加入到有机溶剂中，机械搅拌0.5小时，再在砂磨机中砂磨2小时，得到正极添加剂。其中，本实施例使用的碳包覆的磷酸锰铁锂中的碳的质量百分含量与实施例7相同。
实施例13
本实施例的正极的制备过程与实施例7大致相同，区别在于，本实施例的步骤(1)的正极添加剂的制备有所不同，本实施例的正极添加剂中没有无机材料和导电剂，制备过程如下：
按照质量百分含量计，根据表1称取各原料；将粘结剂与有机溶剂机械搅拌混合1小时，得到预混液，然后将碳包覆的磷酸锰铁锂加入到预混液，机械搅拌0.5小时，再在砂磨机中砂磨2小时，得到正极添加剂。其中，本实施例使用的碳包覆的磷酸锰铁锂中的碳的质量百分含量与实施例7相同。
实施例14
本实施例的正极的制备过程与实施例7大致相同，区别在于，本实施例的步骤(1)的正极添加剂的制备有所不同，本实施例的正极添加剂中没有无机材料和粘结剂，制备过 程如下：
按照质量百分含量计，根据表1称取各原料；将导电剂和碳包覆的磷酸锰铁锂加入到预混液，机械搅拌0.5小时，再在砂磨机中砂磨2小时，得到正极添加剂。其中，本实施例使用的碳包覆的磷酸锰铁锂中的碳的质量百分含量与实施例7相同。
实施例15
本实施例的正极的制备过程与实施例7大致相同，区别在于，本实施例的步骤(1)的正极添加剂的制备有所不同，本实施例的正极添加剂中没有导电剂，制备过程如下：
按照质量百分含量计，根据表1称取各原料；将粘结剂与有机溶剂机械搅拌混合1小时，得到预混液，将无机材料和碳包覆的磷酸锰铁锂加入到预混液，机械搅拌0.5小时，再在砂磨机中砂磨2小时，得到正极添加剂。其中，本实施例使用的碳包覆的磷酸锰铁锂中的碳的质量百分含量与实施例7相同。
实施例16
本实施例的正极的制备过程与实施例7大致相同，区别在于，本实施例的步骤(1)的正极添加剂的制备有所不同，本实施例的正极添加剂中没有粘结剂，制备过程如下：
按照质量百分含量计，根据表1称取各原料；将碳包覆的磷酸锰铁锂、无机材料和导电剂加入到有机溶剂中，机械搅拌0.5小时，再在砂磨机中砂磨2小时，得到正极添加剂。其中，本实施例使用的碳包覆的磷酸锰铁锂中的碳的质量百分含量与实施例7相同。
实施例17和实施例18
实施例17和实施例18的正极的制备过程与实施例7大致相同，区别在于，各原料的质量百分含量不同，其中，实施例17和实施例18的正极的制备过程如表1所示，实施例17和实施例18使用的碳包覆的磷酸锰铁锂中的碳的质量百分含量与均实施例7相同。
对比例1
对比例1的正极添加剂的制备过程与实施例1大致相同，区别在于，本实施例的步骤(1)的正极添加剂的制备有所不同，本实施例的正极添加剂中没有碳包覆的磷酸锰铁锂。此时，正极添加剂中，无机材料的质量百分含量为10.2％，粘结剂的质量百分含量为1.5％，导电剂的质量百分含量为0.01％，正极添加剂的固含量为11.71wt％。其中，本实施例使用的碳包覆的磷酸锰铁锂中的碳的质量百分含量与实施例1相同。
实施例19～实施例34
实施例19～实施例34的正极的制备过程如下：
根据表3中的具体物质和配比，将粘结物与N-甲基吡咯烷酮搅拌混合30分钟，然后在持续搅拌的条件下加入导电物，再搅拌混合30分钟之后加入将实施例1～18制备得到的正极添加剂，接着在搅拌混合30分钟后加入正极材料，最后再搅拌混合12小时，得到正极浆料，将正极浆料涂布在集流体上，并在110℃下干燥，得到正极。其中，实施例19～28的正极材料的粒径如表3所示，实施例29～36的正极材料的粒径与实施例25相同。
表3中，A表示正极材料的质量，B表示正极添加剂中的碳包覆的磷酸锰铁锂的质量，那么，正极材料和正极添加剂中的碳包覆的磷酸锰铁锂的质量之和记作A+B，正极材料和正极添加剂中的碳包覆的磷酸锰铁锂的质量比记作A:B；C表示粘结物的质量，D表示导电物的质量，(A+B):C:D则表示正极材料和正极添加剂中的碳包覆的磷酸锰铁锂的总量与粘结物、导电物三者的质量比。
表3
Figure PCTCN2018108383-appb-000004
Figure PCTCN2018108383-appb-000005
其中，NCM(523)表示LiNi 0.5Co 0.3Mn 0.2O 2；NCM(622)表示LiNi 0.6Co 0.2Mn 0.2O 2；NCM(811)表示LiNi 0.8Co 0.1Mn 0.1O 2。
表4
Figure PCTCN2018108383-appb-000006
对比例2
对比例2的正极的制备过程与实施例19大致相同，区别在于，对比例2的正极用的对比例1的正极添加剂。
对比例3
对比例3的正极的制备过程具体如下：
将粘结物与N-甲基吡咯烷酮搅拌混合30分钟，然后在持续搅拌的条件下加入导电物，再搅拌混合30分钟之后加入纳米氧化铝，接着在搅拌混合30分钟后加入NCM(523)正极材料，最后再搅拌混合12小时，得到正极浆料，将正极浆料涂布在集流器上，并在110℃下干燥，得到正极。其中，正极材料、粘结物、导电物、N-甲基吡咯烷酮均与实施例20相同，且添加比例也与实施例20相同，对比例3中正极材料与氧化铝的质量比为93:7，正极材料与氧化铝的质量之和:粘结物的质量:导电物的质量＝97:1.5:1.5。
对比例4
对比例4的正极的制备过程具体如下：
将粘结物与N-甲基吡咯烷酮搅拌混合30分钟，然后在持续搅拌的条件下加入导电物，再搅拌混合30分钟之后加入碳包覆的磷酸锰铁锂，接着在搅拌混合30分钟后加入正极材料，最后再搅拌混合12小时，得到正极浆料，将正极浆料涂布在集流器上，并在110℃下干燥，得到正极。其中，正极材料、粘结物、导电物、N-甲基吡咯烷酮均与实施例20相同，且添加比例也与实施例20相同，对比例4中正极材料与碳包覆的磷酸锰铁锂的质量比为93:7，正极材料与碳包覆的磷酸锰铁锂的质量之和:粘结物的质量:导电物的质量＝97:1.5:1.5。
对比例5
对比例5的正极的制备过程具体如下：
将碳包覆的磷酸锰铁锂和NCM(523)按照质量比为93:7机械融合15分钟，然后加入导电剂和粘结剂继续机械融合15分钟，得到正极活性材料；将粘结物与N-甲基吡咯烷酮搅拌混合30分钟，然后在持续搅拌的条件下加入导电物，搅拌混合30分钟之后加入将正极活性材料，最后再搅拌混合12小时，得到正极浆料，将正极浆料涂布在集流器上，并在110℃下干燥，得到正极。其中，对比例5的导电剂和粘结剂均与实施例1的导电剂和粘结剂相同，导电剂与碳包覆的磷酸锰铁锂的质量比为1:14.3，粘结剂与碳包覆的磷酸锰铁锂的质量比1:19，粘结物、导电物、N-甲基吡咯烷酮均与实施例20相同，且添加比例也实施例20相同，对比例5中正极活性材料的质量:粘结物的质量:导电物的质量＝97:1.5:1.5。
对比例6
对比例6的正极的制备过程具体如下：
将粘结物与N-甲基吡咯烷酮搅拌混合30分钟，然后在持续搅拌的条件下加入导电物，再搅拌混合30分钟之后加入NCM(523)正极材料，最后再搅拌混合12小时，得到正极浆料，将正极浆料涂布在集流器上，并在110℃下干燥，得到正极。其中，粘结物、导电物、N-甲基吡咯烷酮均与实施例20相同，对比例6的正极材料的质量:粘结物的质量:导电物的质量＝97:1.5:1.5。
对比例7
对比例7的正极的制备过程具体如下：
将粘结物与N-甲基吡咯烷酮搅拌混合30分钟，然后在持续搅拌的条件下加入导电物，再搅拌混合30分钟之后加入LiMn 2O 4正极材料，最后再搅拌混合12小时，得到正极浆料，将正极浆料涂布在集流器上，并在110℃下干燥，得到正极。其中，粘结物、导电物、N-甲基吡咯烷酮均与实施例26相同，对比例7的正极材料的质量:粘结物的质量:导电物的质量＝97:1.5:1.5。
对比例8
对比例8的正极的制备过程具体如下：
将粘结物与N-甲基吡咯烷酮搅拌混合30分钟，然后在持续搅拌的条件下加入导电物，再搅拌混合30分钟之后加入LiCoO 2正极材料，最后再搅拌混合12小时，得到正极浆料，将正极浆料涂布在集流器上，并在110℃下干燥，得到正极。其中，粘结物、导电物、N-甲基吡咯烷酮均与实施例27相同，对比例8的正极材料的质量:粘结物的质量:导电物的质量＝97:2:1。
测试：
1、扫描电镜测试：
图2a为对比例6制备得到的正极上的正极材料的扫描电镜(SEM)图，图2b为2a放大10倍的放大图，从图中可以看出，正极材料的颗粒表面包覆了一层导电物，导电物之间形成了均匀的网络层结构。
图3a为实施例20制备得到的正极上的正极材料的(SEM)扫描电镜图，图3b为3a放大10倍的放大图，从图中可以看出，磷酸锰铁锂与导电剂形成了均匀的网络层结构，该网络层结构均匀且致密地包覆在正极材料的颗粒表面，磷酸锰铁锂的颗粒尺寸约为60nm。
图4a为对比例7制备得到的正极上的正极材料的扫描电镜图，图4b为4a放大10倍的放大图，从图中可以看出，正极材料不规则的颗粒表面包覆了一层导电剂，导电物之间形成了均匀的网络层结构。
图5a为实施例26制备得到的正极上的正极材料的扫描电镜图，图5b为5a放大10倍的放大图，从图中可以看出，磷酸锰铁锂与导电剂形成了均匀的网络层结构，该网络层结构均匀且致密地包覆在锰酸锂材料的不规则颗粒表面，磷酸锰铁锂的颗粒尺寸约为60nm。
图6a为对比例8制备得到的正极上的正极材料的扫描电镜图，图6b为6a放大10倍的放大图，从图中可以看出，正极材料的球形颗粒表面包覆了一层导电物，导电物之间形成了均匀的网络层结构。
图7a为实施例27制备得到的正极上的正极材料的扫描电镜图，图7b为7a放大10倍的放大图，从图中可以看出，磷酸锰铁锂颗粒与导电剂形成了均匀的网络层结构，该网络层结构均匀且致密地包覆在正极材料的类球形颗粒表面；磷酸锰铁锂的颗粒尺寸约为 60nm。
其中，实施例19、21～25、及实施例28～36的正极上的正极材料具有与实施例20、26及27相类似的形貌，在此不再赘述。
2、EDX测试：
图8为实施例20制备得到的正极上的正极材料的EDX能谱图，从图中可以看出，正极材料中含有Ni、Co、Mn、Fe、O、P及C等元素，这些说明三元正极材料的表面是含有磷酸锰铁锂成分的。
图9为实施例26制备得到的正极上的正极材料的EDX能谱图，从图中可以看出，正极材料内含有Mn、Fe、O、P、C等元素，这些说明锰酸锂正极材料的表面是含有磷酸锰铁锂成分的。
图10为实施例27制备得到的正极上的正极材料的EDX能谱图，从图中可以看出，正极材料内含有Co、Mn、Fe、O、P及C等元素，这证明钴酸锂正极材料表面是含有磷酸锰铁锂成分的。
其中，实施例19、21～25及实施例28～36的正极上的正极材料具有与实施例20、26及27具有相似的EDX能谱图，在此不再赘述。
3、电性能测试：
分别将实施例20、26、27和对比例6～8的正极组装成扣式半电池，其中，所有半电池均以锂片作负极，将实施例20和对比例6的正极制作的半电池在2.75V～4.3V范围内以0.2C的电流进行恒流恒压充放电，将实施例26和对比例7的正极制作的半电池在3.0V～4.3V范围内以0.2C的电流进行恒流恒压充放电，将实施例27和对比例8的正极制作的半电池在3.5V～4.35V范围内以0.2C的电流进行恒流恒压充放电。
图11为实施例20和对比例6的正极组装成扣式半电池的电测试数据曲线图，实施例20与对比例6的正极制作的半电池在0.2C电流下的放电克容量分别为163.5mAh/g和162.8mAh/g；这说明，实施例1的正极添加剂不影响三元锂离子电池的电化学性能。同时，在图中可以发现，采用了实施例20的的正极制作的半电池的电曲线在3.6V～3.4V电压平台处有一个小幅度的弯曲，这应该是磷酸锰铁锂中Fe 2+/Fe 3+的放电平台，因为实施例2的正极添加剂的加入量较少，弯曲幅度较小。
图12为实施例26和对比例7的正极组装成扣式半电池的电测试数据曲线图，从图中可以看出，实施例26与对比例7的正极制作的半电池在0.2C电流下的放电比容量分别为109.0mAh/g和108.9mAh/g；这说明，实施例8的正极添加剂不影响锰酸锂锂离子电池的电化学性能。同时，在图中可以发现，实施例26的电曲线在3.6V～3.4V电压平台处有一个小幅度的弯曲，这应该是磷酸锰铁锂中Fe 2+/Fe 3+的放电平台，因为正极添加剂的加入量较少，弯曲幅度较小。
图13为实施例27和对比例8的正极组装成扣式半电池的电测试数据曲线图，从图中可以看出，实施例27与对比例8的正极制作的半电池在0.2C电流下的放电比容量分别为160.0mAh/g和158.7mAh/g；这说明，实施例9的正极添加剂不影响钴酸锂锂离子电池的电化学性能。同时，在图中可以发现，实施例27的电曲线在3.6V～3.4V电压平台处有一 个小幅度的弯曲，这应该是磷酸锰铁锂中Fe 2+/Fe 3+的放电平台，因为正极添加剂的加入量较少，弯曲幅度较小。
图14为实施例20和对比例6的正极组装成扣式半电池的倍率测试对比图，将两种扣电分别用0.2C、0.5C、1C、2C倍率下的电流各进行循环3次的充放电测试，并将这些数据统计到对比图中。从图中可以发现，实施例20与对比例6的倍率性能相近。这说明实施例2的正极添加剂不影响三元锂离子电池的倍率性能。
将实施例19、21～25及实施例28～36和对比例2～对比例5的正极也按照上述方法组装成扣式半电池，将实施例19、21～25及实施例29～36和和对比例2～对比例5的正极制作的半电池在2.75V～4.3V范围内以0.2C、1C及2C的电流进行恒流恒压充放电，将实施例28的正极制作的半电池在3.0V～4.3V范围内以0.2C、1C及2C的电流进行恒流恒压充放电。其中，实施例19～实施例36和对比例2～对比例8的正极制作的半电池在0.2C、1C及2C电流下的放电比容量见表5。
表5
Figure PCTCN2018108383-appb-000007
Figure PCTCN2018108383-appb-000008
从表5中可以看出，实施例19～实施例36的正极组装成的扣式半电池在0.2C、1C及2C电流下的放电比容量分别至少为110.3mAh/g、100.5mAh/g及89.2mAh/g，具有较高的放电比容量。
其中，实施例25的正极组装成的扣式半电池在0.2C、1C及2C电流下的放电比容量分别为198mAh/g、186.4mAh/g及175.4mAh/g，具有比实施例26～36的正极组装成的扣式半电池具有更高的放电比容量。
其中，实施例20和对比例3的正极组装成的扣式半电池除了添加剂种类不同外，其他条件都是一致的，但实施例20所组装的扣式半电池在0.2C、1C及2C电流下的放电比容量分别至少为163.9mAh/g、153.0mAh/g及136.8mAh/g；而对比例3所组装的扣式半电池在0.2C、1C及2C电流下的放电比容量分别至少为140.7mAh/g、128.2mAh/g及115.3mAh/g，远远差于实施例20，原因在于，实施例20中采用的是含有容量的磷酸锰铁锂做添加剂，而对比例3中采用的是没有容量的氧化铝做添加剂。这是因为仅无机材料作正极添加剂用于包覆正极材料，虽然可以形成人工钝化层，减少电解液与正极材料的直接接触，抑制金属离子的溶出，并且在极端情况下能够缓解正极材料与电解液之间的不可逆反应，能够使正极材料比未经修饰处理的正极材料具有较高的循环和安全稳定性，但是，由于无机材料本身是惰性的，无克容量，会降低正极材料整体的克容量发挥，降低锂离子电池的能量密度，同时，无机材料对正极材料表面进行包覆后，减少了电解液与正极材料的直接接触，也降低了正极材料的倍率性能；而使用磷酸锰铁锂作正极添加剂时，既可以解决电池的安全性问题，同时它自身属于一种正极活性材料，能发挥出容量，不会明显降低正极材料的能量密度和倍率性能。即使用含磷酸锰铁锂的正极添加剂或使用磷酸锰铁锂粉末后，正极材料的克容量均较高，倍率性能均较好；而使用仅含无机材料的正极添加剂或无机材料粉末后，正极材料的克容量均较低，倍率性能均较差。
从表5中还可以看出，实施例20和对比例4中除磷酸锰铁锂的引入方式不同(前者是以制成添加剂的方式，后者是以粉末方式引入)，其他条件均一致，但实施例20的正极所组装的扣式半电池在0.2C、1C及2C电流下的放电比容量分别至少为163.9mAh/g、153.0mAh/g及136.8mAh/g；而对比例4所组装的扣式半电池在0.2C、1C及2C电流下的放电比容量分别仅为160mAh/g、146.8mAh/g及132.9mAh/g，显然，对比例4的正极所组装的扣式半电池的电化学表现远不如实施例20，对比例4的正极克容量较低、倍率性能较差，实施例20的正极的克容量较高、倍率性能较好。这是由于正极添加剂中的磷酸锰铁锂一次颗粒均匀包覆在正极材料表面，而磷酸锰铁锂粉末仅与正极材料混合在一起，前者的结构有利于磷酸锰铁锂颗粒电导性的提高，提高磷酸锰铁锂的容量发挥；采用融合预包覆法制备的NCM(523)-磷酸锰铁锂正极活性材料与采用磷酸锰铁锂的正极添加剂后的正极材料的克容量发挥和倍率性能均基本一致。
4、安全性能测试：
分别将实施例20、26、27和对比例6～8制作的正极极片制作成软包电池，并对软包电池以进行针刺与过充测试和电性能测试。其中，实施例20、26、27和对比例6～8得到的软包电池的针刺结果、过充测试结果以及电流为1C下的克容量见表6。
针刺测试：将充满电的软包电池使用直径为6mm的光滑不锈钢针，以2.2cm/s的速度扎透软包电池后，观察1小时，不爆炸不起火为通过。
过充测试：将充满电的软包电池1C电流充电至规定条件的充电终止电压的1.5倍后，观察1小时，不爆炸不起火为通过。
表5
  针刺 过充 克容量(mAh/g)
对比例6 起火，冒烟 起火，冒烟 150
实施例20 无明显反应，不起火不冒烟 无明显反应，不起火不冒烟 149
对比例7 起火，冒烟 起火，冒烟 94
实施例26 无明显反应，不起火不冒烟 无明显反应，不起火不冒烟 90
对比例8 起火，冒烟 起火，冒烟 148
实施例27 无明显反应，不起火不冒烟 无明显反应，不起火不冒烟 146
从表5中可以看出，采用实施例20、26、27的正极浆料制作的软包电池的安全性测试均通过了，而采用对比例6～8的正极浆料制作的软包电池均未通过；且采用实施例20、26、27的正极浆料制作的软包电池分别具有与采用对比例8～10的正极浆料制作的软包电池相接近的克容量，这说明，实施例2、实施例8和实施例9的正极添加剂对软包电池的克容量发挥影响不大。
其中，实施例19、20～25、28～36的正极上的正极材料具有与实施例20、26、27具有相似的安全性能，在此不再赘述。
以上所述实施例的各技术特征可以进行任意的组合，为使描述简洁，未对上述实施例中的各个技术特征所有可能的组合都进行描述，然而，只要这些技术特征的组合不存在矛盾，都应当认为是本说明书记载的范围。
以上所述实施例仅表达了本发明的几种实施方式，其描述较为具体和详细，但并不能因此而理解为对发明专利范围的限制。应当指出的是，对于本领域的普通技术人员来说，在不脱离本发明构思的前提下，还可以做出若干变形和改进，这些都属于本发明的保护范围。因此，本发明专利的保护范围应以所附权利要求为准。

Claims (17)

  1. 一种正极添加剂，按照质量百分含量计，包括10％～40％的碳包覆的磷酸锰铁锂和有机溶剂，所述碳包覆的磷酸锰铁锂分散在所述有机溶剂中，所述碳包覆的磷酸锰铁锂的中位粒径为30纳米～100纳米。
  2. 根据权利要求1所述的正极添加，其特征在于，所述碳包覆的磷酸锰铁锂的中位粒径为60纳米～80纳米。
  3. 根据权利要求1所述的正极添加剂，其特征在于，还包括质量百分含量为0.5％以下的无机材料，所述无机材料选自纳米氧化铝、纳米氧化钛及纳米氧化镁中的至少一种。
  4. 根据权利要求1所述的正极添加剂，其特征在于，所述碳包覆的磷酸锰铁锂中的碳的质量百分含量为2％～15％。
  5. 根据权利要求1所述的正极添加剂，其特征在于，所述有机溶剂选自N-甲基吡咯烷酮及N,N-二甲基甲酰胺中的至少一种。
  6. 根据权利要求1所述的正极添加剂，其特征在于，还包括质量百分含量为2％以下的粘结剂。
  7. 根据权利要求6所述的正极添加剂，其特征在于，所述粘结剂为聚偏氟乙烯或丁苯橡胶。
  8. 根据权利要求1～7任一项所述的正极添加剂，其特征在于，还包括质量百分含量为10％以下的导电剂。
  9. 根据权利要求8所述的正极添加剂，其特征在于，所述导电剂选自乙炔黑、科琴黑、石墨烯及碳纳米管中的至少一种。
  10. 根据权利要求1所述的正极添加剂，其特征在于，所述正极添加剂中的固体的质量百分含量为10％～45％。
  11. 根据权利要求10所述的正极添加剂，其特征在于，所述正极添加剂中的固体的质量百分含量为25％～30％。
  12. 一种权利要求1～11任一项所述的正极添加剂的制备方法，包括如下步骤：将碳包覆的磷酸锰铁锂分散在有机溶剂中，得到正极添加剂。
  13. 一种正极的制备方法，包括如下步骤：
    将正极材料、正极添加剂、粘结物、导电物及N-甲基吡咯烷酮混合，得到正极浆料，其中，所述正极添加剂为权利要求1～11任一项所述的正极添加剂或权利要求12所述的正极添加剂的制备方法制备得到的正极添加剂，所述正极材料与所述正极添加剂中的所述碳包覆的磷酸锰铁锂的质量比为80:20～99:1；及
    将所述正极浆料制作成正极。
  14. 根据权利要求13所述的正极的制备方法，其特征在于，所述将正极材料、正极添加剂、粘结物、导电物及N-甲基吡咯烷酮混合，得到正极浆料的步骤包括：在持续搅拌的条件下，将所述粘结物与所述N-甲基吡咯烷酮混合，然后加入所述导电物、所述正极添加剂和所述正极材料，得到所述正极浆料。
  15. 根据权利要求13所述的正极的制备方法，其特征在于，所述正极材料选自镍钴锰三元材料、镍钴铝三元材料、镍锰酸锂、锰酸锂及钴酸锂中的至少一种。
  16. 一种正极，由权利要求13～15任一项所述的正极的制备方法制备得到。
  17. 一种锂离子电池，包括权利要求16所述的正极。
PCT/CN2018/108383 2018-09-28 2018-09-28 正极添加剂及其制备方法、正极及其制备方法和锂离子电池 Ceased WO2020062046A1 (zh)

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US17/277,809 US12100830B2 (en) 2018-09-28 2018-09-28 Cathode additive and preparation method therefor, cathode electrode and preparation method therefor, and lithium ion battery
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