WO2022171074A1 - 磷酸铁锂及其制备方法、锂离子电池 - Google Patents

磷酸铁锂及其制备方法、锂离子电池 Download PDF

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WO2022171074A1
WO2022171074A1 PCT/CN2022/075496 CN2022075496W WO2022171074A1 WO 2022171074 A1 WO2022171074 A1 WO 2022171074A1 CN 2022075496 W CN2022075496 W CN 2022075496W WO 2022171074 A1 WO2022171074 A1 WO 2022171074A1
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lithium
iron phosphate
source
lithium iron
preparation
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PCT/CN2022/075496
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English (en)
French (fr)
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岳海峰
郭欢
杨琛
席小兵
杨才德
黄友元
贺雪琴
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贝特瑞（天津）纳米材料制造有限公司
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Priority to EP22752235.6A priority Critical patent/EP4119498A4/en
Priority to US17/996,766 priority patent/US20230170481A1/en
Priority to JP2022562905A priority patent/JP7465369B2/ja
Publication of WO2022171074A1 publication Critical patent/WO2022171074A1/zh

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    • C—CHEMISTRY; METALLURGY
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    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B25/00—Phosphorus; Compounds thereof
    • C01B25/16—Oxyacids of phosphorus; Salts thereof
    • C01B25/26—Phosphates
    • C01B25/45—Phosphates containing plural metal, or metal and ammonium
    • 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
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/136—Electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
    • H—ELECTRICITY
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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
    • 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
    • H01M4/36—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
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    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/70—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data
    • C01P2002/72—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data by d-values or two theta-values, e.g. as X-ray diagram
    • 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
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    • C01P2004/62—Submicrometer sized, i.e. from 0.1-1 micrometer
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    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
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    • C—CHEMISTRY; METALLURGY
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    • C01P2006/40—Electric properties
    • 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
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present application relates to the technical field of lithium ion batteries, in particular to lithium iron phosphate, a preparation method thereof, and a lithium ion battery.
  • Lithium iron phosphate has attracted widespread attention since it was proposed in 1997. It occupies a place in the cathode material of lithium ion batteries with its excellent stability, high rate charging, non-toxicity and long cycle life. However, lithium iron phosphate also has obvious advantages. Defects such as low conductivity, ionic diffusivity, etc.
  • lithium iron phosphate batteries For cathode materials, low conductivity limits the performance of lithium iron phosphate batteries to a large extent.
  • methods such as carbon coating, metal doping, and adding metal particles are usually used to improve the conductivity by a few order of magnitude.
  • Conventional lithium iron phosphate is prepared by carbothermic reduction. In the carbothermic reduction of lithium iron phosphate, Fe 2+ is easily oxidized to Fe 3+ , so a reducing agent needs to be added to prevent the oxidation of Fe 2+ .
  • H2 or carbon source is often used as a reducing agent. The addition of carbon source can form a carbon coating on the surface of lithium iron phosphate to enhance the conductivity of the particles. However, the carbon coating will also cause the positive electrode. The reduction in the compaction performance of the material, which in turn leads to a reduction in the electrochemical performance.
  • Research shows that adding excess reducing agent or increasing the reaction temperature during the reaction process will lead to the delithiation behavior of lithium iron phosphate and promote the generation of Fe x P. Therefore, too high reaction temperature cannot be used in the carbothermic reduction of lithium iron phosphate.
  • the reaction temperature in the prior art is below 800 °C, which is still accompanied by the formation of a small amount of Fe x P.
  • the embodiment of the present application provides a preparation method of lithium iron phosphate, comprising the following steps:
  • the sintering atmosphere includes a mild oxidizing gas
  • the mild oxidizing gas includes carbon dioxide
  • the sintering temperature is 800°C to 900°C.
  • the gas in the sintering atmosphere contains a mild oxidizing gas, which inhibits the generation of magnetic substances, and the reduction situation that decreases with the addition of carbon dioxide to the system can be made up by increasing the temperature.
  • the elevated temperature can make the LFP/C have better crystallinity and thus the compaction performance is well improved, and the method of the present application can ensure the purity, crystallinity and electrochemical performance of lithium iron phosphate.
  • the mild oxidizing gas further includes a protective gas
  • the protective gas includes at least one of nitrogen, argon, helium and neon;
  • the mild oxidizing gas further includes a protective gas, and the volume ratio of the carbon dioxide to the protective gas is (1:99) ⁇ (99:1).
  • the total gas flow rate in the sintering atmosphere is 3L/min ⁇ 10L/min.
  • the holding time of the sintering is 2h-20h.
  • the method includes at least one of the following technical features a to d:
  • the iron source comprises at least one in iron phosphate, metallic iron, iron nitrate, iron oxide, iron chloride and ferrous oxalate;
  • the phosphorus source includes at least one of iron phosphate, ammonium monohydrogen phosphate, ammonium dihydrogen phosphate, ammonium phosphate and ferrous monohydrogen phosphate;
  • the reducing carbon source includes at least one of sucrose, glucose and polyethylene glycol
  • the lithium source is at least one of lithium carbonate, lithium phosphate, lithium hydroxide and lithium chloride.
  • the mass ratio of the iron source, lithium source, phosphorus source and carbon source is (95-105):(90-110):(95-105):(0.1-10).
  • the preparation process of the drying material includes:
  • the phosphorus source, iron source, lithium source, reducing carbon source and solvent are mixed and ground to obtain a slurry, which is dried to obtain a dry material.
  • the method also includes at least one of the following technical features a to g:
  • the method of described mixing and grinding includes any one of ball milling and sand milling;
  • the median diameter D50 of the solid particles in the slurry is 0.1 ⁇ m to 3 ⁇ m;
  • the solvent includes at least one of water and ethylene glycol
  • the solid content in the slurry is 5% to 80% of the total mass of the slurry
  • the drying mode includes any one of spray drying and evaporative drying
  • the drying temperature is 50°C ⁇ 500°C;
  • the drying time is 0.1h ⁇ 10h.
  • the embodiments of the present application provide a lithium iron phosphate material, which is prepared by the preparation method of the first aspect.
  • the lithium iron phosphate material comprises at least one of the following technical features a to d:
  • the lithium iron phosphate is an olivine structure
  • the powder compaction density of the lithium iron phosphate material is 2.1g/cm 3 to 3.3g/cm 3 ;
  • the average particle size of the lithium iron phosphate material is 0.1 ⁇ m to 5 ⁇ m;
  • the specific surface area of the lithium iron phosphate is 1 m 2 /g to 50 m 2 /g.
  • an embodiment of the present application provides a lithium ion battery, the lithium ion battery comprising the lithium iron phosphate prepared by the preparation method of the first aspect or the lithium iron phosphate of any one of the second aspect.
  • the carbon dioxide added during the calcination of the present application inhibits the formation of Fe x P, and improves the LFP/C unit mass capacity and battery reliability, because carbon dioxide gas has weak oxidizing properties at high temperatures and the oxidizing properties are insufficient.
  • Lithium iron (LFP/C) has better crystallinity and the compaction performance is thus well improved, and the method of the present application can ensure the purity, crystallinity and electrochemical performance of LiFePO 4 .
  • the lithium iron phosphate prepared by the present application in the carbothermic reduction of lithium iron phosphate, the gas in the sintering atmosphere contains mild oxidizing gas, and the mild oxidizing gas is carbon dioxide, which has high purity, crystallinity and electrochemical performance.
  • Fig. 1 is the XRD test chart of the lithium iron phosphate material prepared in Example 2 of the application;
  • FIG. 2 is an XRD test chart of the lithium iron phosphate material prepared in Comparative Example 3 of the present application.
  • lithium iron phosphate has the advantages of high rate charging, long cycle life and high stability
  • the embodiment of the present application provides a preparation method of lithium iron phosphate, comprising the following steps:
  • the sintering atmosphere includes mild oxidizing gas, the mild oxidizing gas includes carbon dioxide, and the sintering temperature is 800°C to 900°C.
  • the method of the present application can ensure the purity and crystallization of lithium iron phosphate (LFP). degree and electrochemical performance.
  • the sintering temperature is 800°C to 900°C, specifically, the sintering temperature can be 800°C, 810°C, 820°C, 830°C, 840°C, 850°C, 860°C, 870°C, 880°C, 890°C or 900°C etc., which are not specifically limited, but are not limited to the listed numerical values, and other unlisted numerical values within the numerical range are also applicable.
  • the temperature is lower than 800°C, the obtained lithium iron phosphate has poor crystallinity and powder compaction performance.
  • the lithium iron phosphate prepared in the present application has high powder compaction performance, which is helpful to obtain high energy density.
  • sintering The temperature is 820°C ⁇ 880°C.
  • the source of carbon dioxide is not limited, for example, carbon dioxide can be directly introduced, or carbon dioxide can be generated during the preparation process by using a substance capable of producing carbon dioxide.
  • the lithium iron phosphate obtained in the above embodiment has greatly improved electrochemical performance, cycle performance, safety and crystallinity.
  • the mild oxidizing gas also includes a protective gas
  • the protective gas is at least one of nitrogen, argon, helium, and neon.
  • carbon dioxide can inhibit the formation of Fe x P
  • the protective gas controls the chemical reaction between the reaction product and the environment.
  • the volume ratio of carbon dioxide and protective gas is (1:99) ⁇ (99:1), specifically, the volume ratio of carbon dioxide to protective gas may be 1:99, 10:90, 20:80, 30:70, 40:60, 50:50, 60:40, 70:30 , 80:20, 90:10 or 99:1, etc., which are not specifically limited, but are not limited to the listed numerical values, and other unlisted numerical values within the numerical range are also applicable.
  • the volume ratio of carbon dioxide to the protective gas is (30-70):(70-30), and the volume ratio of carbon dioxide to the protective gas is within the above range, which can increase the reducing performance of the system and improve the carbonization rate of the carbon source. , thereby accelerating the reduction reaction of Fe 3+ and making Fe 3+ fully reduced, which can further improve the uniformity of the crystal structure and the compaction density of the powder.
  • the sintering process of the present application is carried out in a separate atmosphere of carbon dioxide and protective gas, which can not only improve the unit mass capacity and battery reliability of the carbon-coated lithium iron phosphate LFP/C, but also facilitate the adjustment of the redox situation of the system. Choice and flexibility.
  • the sintering is performed in a HB-Ln2060 intermittent rotary resistance furnace, and the heating rate of the sintering is 1°C/min to 10°C/min, specifically 1°C/min, 2°C/min. min, 3°C/min, 4°C/min, 5°C/min, 6°C/min, 7°C/min, 8°C/min, 9°C/min or 10°C/min etc. Not limited to the recited values, other non-recited values within this range of values are equally applicable.
  • the holding time for sintering is 2h to 20h, specifically 2h, 4h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 16h, 18h or 20h, etc.
  • the total gas flow rate in the sintering atmosphere is 3L/min ⁇ 10L/min, specifically 4L/min, 5L/min, 6L/min, 7L/min, 8L/min or 9L/min, etc., but not limited to those listed value, other non-recited values within this value range also apply.
  • the flow rates of the sintered carbon dioxide and the protective gas can be the same or different, and the two have different effects and do not affect each other. If the flow rate is too slow, the protective atmosphere cannot play a protective role; if the flow rate is too fast, the gas will destroy the powder. Take out the rotary kiln to block the pipeline.
  • the iron source of the present application includes at least one of iron phosphate, metallic iron, iron nitrate, iron oxide, iron chloride and ferrous oxalate.
  • the phosphorus source includes at least one of iron phosphate, ammonium monohydrogen phosphate, ammonium dihydrogen phosphate, ammonium phosphate and ferrous monohydrogen phosphate.
  • the reducing carbon source is at least one of sucrose, glucose and polyethylene glycol, specifically, it can be any one of sucrose, glucose and polyethylene glycol, or it can be polyethylene glycol. Combinations of ethylene glycol mixed with sucrose, polyethylene glycol mixed with glucose, polyethylene glycol mixed with sucrose, glucose, and the like.
  • the lithium source is at least one of lithium carbonate, lithium phosphate, lithium hydroxide and lithium chloride.
  • the mass ratio/molar ratio of iron source, lithium source, phosphorus source and carbon source is (95 ⁇ 105):(90 ⁇ 110):(95 ⁇ 105):(0.1 ⁇ 10 ), exemplarily, the mass ratio of iron source, lithium source, phosphorus source and carbon source may be 95:90:100:0.1, 100:100:105:5, 100:110:95:10, 105:90: 95:0.1 and 100:105:105:3, etc., are not specifically limited, but are not limited to the listed values, and other unlisted values within the numerical range are also applicable.
  • both the phosphorus source and the iron source are iron phosphate
  • the mass ratio of the iron phosphate to the reducing carbon source is (1-100):1, specifically 100:1, 90 :1, 80:1, 70:1, 65:1, 60:1, 50:1, 40:1, 30:1, 20:1, 10:1, 8:1, 5:1, 2.5:1 , 2:1, 1.6:1, 1.25:1 or 1:1, etc., which are not limited here, but are not limited to the listed values, and other unlisted values within the numerical range are also applicable.
  • the iron phosphate and reducing carbon source are controlled within the above range, the prepared material has good electrical conductivity. Too much carbon source will cause the coating to be too thick, increase the internal resistance of the material, and reduce the total amount of active substances. If the amount of carbon source added is too small, it will cause uneven carbon coating and affect the conductivity of the material.
  • the molar ratio of the lithium element in the lithium source to the iron phosphate is (0.97 ⁇ 1.1):1, and specifically, the molar ratio of the lithium element in the lithium source to the iron phosphate can be 0.97:1, 0.98:1, 1.0:1, 1.05:1 or 1.1:1, etc., are not limited here, but are not limited to the listed numerical values, and other unlisted numerical values within the numerical range are also applicable.
  • the preparation method of lithium iron phosphate comprises the following steps:
  • the phosphorus source, iron source, lithium source, reducing carbon source and solvent are mixed and ground to obtain a slurry.
  • a dry material is obtained, and the obtained dry material is heated at 800°C ⁇ 900°C Sintering under conditions for 2h to 20h to obtain lithium iron phosphate
  • the gas in the sintering atmosphere includes carbon dioxide gas and protective gas, wherein the volume ratio of carbon dioxide gas and protective gas is (1:99) ⁇ (99:1), the total The gas flow rate is 3L/min ⁇ 10L/min.
  • the method of mixing and grinding includes ball milling or sand milling. Specifically, the ball milling operation is performed in an SX-8 type ball mill.
  • the solvent includes at least one of water and ethylene glycol.
  • the median diameter D50 of the solid particles in the slurry is 0.1 ⁇ m ⁇ 3 ⁇ m, and specifically, the median diameter D50 of the solid particles in the slurry may be 0.12 ⁇ m, 0.14 ⁇ m, 0.15 ⁇ m, 0.18 ⁇ m, 0.2 ⁇ m, 0.22 ⁇ m, 0.25 ⁇ m or 0.28 ⁇ m, etc., are not limited here, but are not limited to the listed numerical values, and other unlisted numerical values within the numerical range are also applicable.
  • the method for controlling the above particle size is: ball-milling the large particles in the slurry raw material to a D50 of 0.7-0.9 ⁇ m (to make a slurry with a solid content of 53%), and ball-milling the small particles to a D50 of 0.4-0.6 ⁇ m (made into a slurry with a solid content of 20%), then mixed and finely ground to obtain a final slurry particle size D50 of 0.1 ⁇ m to 0.3 ⁇ m.
  • the solid content in the slurry is 5% to 80% of the total mass of the slurry, specifically, the solid content in the slurry is 5%, 10%, 20%, 30%, 40%, 50% or 60%, etc., are not limited here, but are not limited to the listed numerical values, and other unlisted numerical values within the numerical range are also applicable.
  • the solid content in the slurry is 10% to 60% of the total mass of the slurry.
  • the drying method is any one of spray drying and evaporative drying, specifically, the spray drying is to use a sprayer to carry out centrifugal spray drying, and the inlet temperature of the sprayer is 110 °C ⁇ 300 °C, specifically, the inlet temperature can be 120 °C, 130°C, 150°C, 180°C, 200°C, 230°C, 250°C, 280°C or 300°C, etc.
  • the outlet temperature of the sprayer is 60°C to 130°C, specifically, the outlet temperature can be 65°C, 70°C, 75°C, 80°C, 85°C, 90°C or 110°C, etc.
  • centrifugal spray drying in this application has more advantages.
  • centrifugal spray can form the required droplets more stably than two-fluid spray.
  • two-fluid spray is easy to implement airflow disturbance when the airflow speed is too fast.
  • the compaction density of the prepared lithium iron phosphate material will be low, and the electrochemical performance will be reduced.
  • the reaction trend can be established by simulating the reaction system through preliminary thermodynamic and kinetic analysis, in which the thermodynamic data can be obtained through literature search and thermodynamic characterization to obtain the basic reactants and possible products ⁇ h f 0 s, 298.15 K (standard enthalpy of formation), S 0 s, 298.15K (standard entropy) and C p (specific heat capacity at constant pressure) to obtain the enthalpy of formation, entropy and temperature expressions, and then establish the ⁇ G (Gibbs free) of the reaction system energy), the reaction equilibrium constant k eq of each reaction formula can be obtained through the transformation of Arrhenius formula, and the mathematical method analysis is carried out in the factsage software to obtain the distribution trend of reaction products under different temperatures and atmospheres.
  • the thermodynamic data can be obtained through literature search and thermodynamic characterization to obtain the basic reactants and possible products ⁇ h f 0 s, 298.15 K (standard enthalpy of formation), S 0 s
  • thermodynamic data of reactants and products that may be formed are shown in Table 1 (standard enthalpy of formation of reactants and products in the reduction reaction, standard entropy value, wherein CO 2 , H 2 O are gas phase, others are solid phase), Table 2 (Relationship formula of specific heat capacity and temperature of reactants and products).
  • This application simulates the trend of the reaction system through thermodynamics and kinetics, and corroborates each other with the experimental scheme and establishes the optimal reaction temperature.
  • Thermodynamics and kinetics simulation can effectively reduce the amount of experiments and provide optimal reaction conditions to reduce production costs and time costs. And give theoretical support for performance improvement from a deeper level.
  • the powder compaction density of the lithium iron phosphate material is 2.1g/cm 3 -3.3g/cm 3 , such as 2.1g/cm 3 , 2.3g/cm 3 , 2.5g/cm 3 . 3 , 2.6g/cm 3 , 2.8g/cm 3 , 3.0g/cm 3 or 3.2g/cm 3 , etc., but not limited to the listed numerical values, and other unlisted numerical values within the numerical range are also applicable.
  • Lithium iron phosphate has an olivine structure.
  • the average particle size of lithium iron phosphate is 0.1 ⁇ m to 5 ⁇ m, specifically, the average particle size of lithium iron phosphate can be 0.1 ⁇ m, 0.5 ⁇ m, 1 ⁇ m, 2 ⁇ m, 3 ⁇ m, 4 ⁇ m and 5 ⁇ m, etc., which are not limited here, but not only Limitation to the recited values applies equally to other non-recited values within the range of values.
  • the specific surface area of lithium iron phosphate is 1m 2 /g ⁇ 50m 2 /g, specifically, the specific surface area of lithium iron phosphate can be 1m 2 /g, 5m 2 /g, 10m 2 /g, 20m 2 /g, 35m 2 /g and 40m 2 /g, etc., are not limited here, but are not limited to the listed numerical values, and other unlisted numerical values within the numerical range are also applicable.
  • the lithium iron phosphate material prepared in the present application is a high-temperature sintered lithium iron phosphate material, which controls the content of F x P and improves the crystallinity, powder compaction density, and electrochemical performance of the lithium iron phosphate.
  • the present application relates to a lithium ion battery.
  • the lithium ion battery includes a positive pole piece, a negative pole piece, and a separator disposed between the positive pole piece and the negative pole piece.
  • the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer, and the positive electrode active material layer may include a positive electrode active material, a conductive agent and a binder, and the positive electrode active material is lithium iron phosphate prepared by the above preparation method.
  • the positive electrode current collector can use Al foil, and similarly, other positive electrode current collectors commonly used in the art can also be used.
  • the conductive agent of the positive electrode sheet may include at least one of conductive carbon black, lamellar graphite, graphene or carbon nanotubes.
  • the binder in the positive electrode sheet can include polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, styrene-acrylate copolymer, styrene-butadiene copolymer, polyamide, polyacrylonitrile, Polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinyl acetate, polyvinylpyrrolidone, polyvinyl ether, polymethylmethacrylate, polytetrafluoroethylene or polyhexafluoropropylene at least one of them.
  • the negative pole piece includes a current collector and a negative electrode active material layer.
  • the negative electrode active material layer includes a negative electrode active material, a conductive agent, and a binder.
  • the current collector of the negative electrode sheet may include at least one of copper foil, aluminum foil, nickel foil or fluorocarbon current collector.
  • the negative electrode active material may include at least one of soft carbon, hard carbon, artificial graphite, natural graphite, amorphous carbon, silicon oxide compound, natural carbon compound, and lithium titanate.
  • Binders may include carboxymethyl cellulose (CMC), polyacrylic acid, polyvinylpyrrolidone, polyaniline, polyimide, polyamideimide, polysiloxane, polystyrene butadiene rubber, epoxy resin, At least one of polyester resin, polyurethane resin or polyfluorene.
  • CMC carboxymethyl cellulose
  • polyacrylic acid polyvinylpyrrolidone
  • polyaniline polyimide
  • polyamideimide polysiloxane
  • polystyrene butadiene rubber epoxy resin
  • At least one of polyester resin, polyurethane resin or polyfluorene At least one of polyester resin, polyurethane resin or polyfluorene.
  • the conductive agent may include at least one of conductive carbon black, Ketjen black, acetylene black, carbon nanotubes, VGCF (Vapor Grown Carbon Fiber, vapor grown carbon fiber) or graphene.
  • the separator includes at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide or aramid.
  • the polyethylene includes at least one selected from high density polyethylene, low density polyethylene or ultra-high molecular weight polyethylene.
  • polyethylene and polypropylene they have a good effect on preventing short circuits and can improve the stability of the battery through the shutdown effect.
  • the thickness of the isolation film is in the range of about 5 ⁇ m to 500 ⁇ m.
  • the lithium ion battery may further include an electrolyte.
  • the electrolyte includes, but is not limited to, dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), ethylene carbonate (EC), propylene carbonate (PC), At least two of propyl propionate (PP).
  • the electrolyte may additionally include at least one of vinylene carbonate (VC), fluoroethylene carbonate (FEC), or a dinitrile compound as an electrolyte additive.
  • the electrolyte further includes a lithium salt.
  • the positive pole piece, the separator and the negative pole piece are wound or stacked in sequence to form an electrode piece, and then packed into, for example, an aluminum plastic film for encapsulation, injected with an electrolyte, formed, and packaged, that is, to make Lithium Ion Battery. Then, the performance test and cycle test of the prepared lithium-ion battery were carried out.
  • the gas in the sintering atmosphere includes a mild oxidizing gas, which inhibits the formation of Fe x P, and with the addition of carbon dioxide, the reduction state of the system can be reduced by increasing the temperature.
  • the elevated temperature can make LFP/C have higher crystallinity and powder compaction density, and the method of the above embodiment can ensure the purity, crystallinity and electrochemical performance of LiFePO 4 ; further, changing the mild The proportion of oxidizing gas in the sintering atmosphere can easily adjust the redox situation of the system, and the addition of carbon source can have more selectivity and flexibility.
  • a preparation method of lithium iron phosphate comprising the steps:
  • step (3) The slurry obtained in step (2) is transferred to a spray dryer, the inlet temperature of the spray dryer is 240°C, the outlet temperature is 80°C, the gas flow rate is 14m 3 /h, and the peristaltic pump flow rate is 5L/h , to get the spray material;
  • a preparation method of lithium iron phosphate comprising the steps:
  • step (3) transfer the slurry obtained in step (2) to a Nilu spray dryer for centrifugal spraying, the inlet temperature of the spray dryer is 240°C, the outlet temperature is 80°C, the gas flow rate is 14m 3 /h, and the peristaltic pump The flow rate is 5L/h to obtain spray material;
  • Fig. 1 is an XRD test chart of the lithium iron phosphate material prepared in the present embodiment. It can be seen from Fig. 1 that the crystallinity of lithium iron phosphate is good, mainly because the content of Fe 3 P is controlled in the present application.
  • Example 1 The difference from Example 1 is that the volume ratio of carbon dioxide and nitrogen in step (4) is 1:9.
  • Example 1 The difference from Example 1 is that the volume ratio of carbon dioxide and nitrogen in step (4) is 9:1.
  • Example 2 The difference from Example 2 is that the volume ratio of carbon dioxide and nitrogen in step (4) is 1:9.
  • Example 2 The difference from Example 2 is that the volume ratio of carbon dioxide and nitrogen in step (4) is 9:1.
  • Example 1 The difference from Example 1 is that the flow rates of carbon dioxide and nitrogen are both 1 L/min.
  • step (3) transfer the slurry obtained in step (2) to a Nilu spray dryer for centrifugal spraying, the inlet temperature of the spray dryer is 240°C, the outlet temperature is 80°C, the gas flow rate is 14m 3 /h, and the peristaltic pump The flow rate is 5L/h to obtain spray material;
  • step (4) the calcination temperature of the spray material in the rotary resistance furnace is 750 ° C, the temperature is kept for 10 h, and the total gas flow rate in the sintering atmosphere is adjusted to 5 L/min. Composed of nitrogen, a lithium iron phosphate material is obtained.
  • step (4) carbon dioxide is replaced with an equal amount of air.
  • step (4) the spray material is sintered at a temperature of 850° C. for 10h in a rotary furnace, and the total gas flow rate in the sintering atmosphere is adjusted to 5L/min, and the gas in the sintering atmosphere is nitrogen to obtain lithium iron phosphate material.
  • Figure 2 is the XRD test chart of the lithium iron phosphate material obtained in Comparative Example 3. It can be seen that there are weak characteristic peaks of iron phosphide, which shows that under the condition of only nitrogen gas, a large amount of reducing gas is released in combination with the carbon source, The formation of a strong reducing atmosphere will promote the formation of iron phosphide in lithium iron phosphate, thereby causing harm to the safety of lithium iron phosphate.
  • the test results are shown in Table 3:
  • Example 1 Example 3 and Example 4, and Example 2, Example 5, Example 6 and Example 8
  • an appropriate amount of carbon dioxide is introduced to form a mild
  • the oxidizing atmosphere can effectively reduce the magnetic substance of the product and improve the compaction performance of the product.
  • the more carbon dioxide content in the sintering atmosphere the more the prepared lithium iron phosphate material can improve the compaction performance and initial discharge capacity of the product. , thus illustrating the importance and flexibility of carbon dioxide in system regulation.
  • Electrochemical characterization showed that the structural change of lithium iron phosphate led to the improvement of electrochemical performance.
  • the XRD test results of lithium iron phosphate in Example 2 show that there is only a small amount of Fe x P in the lithium iron phosphate sintered in a carbon dioxide atmosphere, and the crystallinity of the obtained lithium iron phosphate is compared with that in Example 1. There is a further improvement, which proves that high temperature is conducive to the improvement of the crystallinity of lithium iron phosphate and can improve its compaction density.
  • Example 1 It can be seen from the comparison between Example 1 and Example 7 that if the flow rate is too slow, the protective atmosphere cannot play a protective role, resulting in the increase of magnetic substances in the reaction system and the decline in electrochemical performance, and the compaction performance of the product has a slight decline. Since the reduction of carbon dioxide leads to a (relative) increase in carbon monoxide content and the inhibition of carbon reduction performance, the carbonization of the system is intensified, and the compaction performance is thus reduced.
  • Comparing Example 1 with Comparative Example 1 it can be seen that in Comparative Example 1, only a small amount of Fe 3 P was produced by sintering at a temperature of 750° C. in a nitrogen atmosphere, but the compaction density was low and could not meet the demand.
  • Example 1 Comparative Example 2
  • the carbothermic reduction reaction is difficult to carry out, and the obtained products are mainly complex compounds of iron phosphate, iron oxide and lithium, which are not the products we need.
  • LiFePO 4 so it is not suitable to use an atmosphere with strong oxidizing property in the carbothermic reduction atmosphere.
  • Example 1 By comparing Example 1 with Comparative Example 3, it can be seen that sintering without carbon dioxide will produce a large amount of Fe 3 P, a ferromagnetic substance with a Curie temperature of up to 1043K, while more Fe 3 P that is not successfully separated exists in the Between the grains of lithium iron phosphate, the compaction density of lithium iron phosphate decreases, the capacity decreases, and there are magnetic foreign substances that can be dissolved, which brings hidden dangers to the battery cycle and safety.
  • the present application illustrates the detailed process equipment and process flow of the present application through the above-mentioned embodiments, but the present application is not limited to the above-mentioned detailed process equipment and process flow, that is, it does not mean that the present application must rely on the above-mentioned detailed process equipment and process flow. Process flow can be implemented. Those skilled in the art should understand that any improvement to the application, the equivalent replacement of each raw material of the product of the application, the addition of auxiliary components, the selection of specific methods, etc., all fall within the scope of protection and disclosure of the application.

Abstract

本申请涉及磷酸铁锂及其制备方法、锂离子电池，所述制备方法包括：将铁源、锂源、磷源和还原性碳源的干燥料进行烧结，得到所述磷酸铁锂；其中，所述烧结气氛包括温和氧化性气体，所述温和氧化性气体包括二氧化碳，所述烧结温度为800℃～900℃。本申请磷酸铁锂在碳热还原中，烧结气氛中的气体含有温和氧化性气体，抑制了磁性物质的生成，并且随着二氧化碳的加入体系降低的还原态势可以通过提升温度来弥补，同时升高的温度可以让碳包覆磷酸铁锂拥有更好的结晶度并且压实性能因此得到很好地提升，本申请的方法可保证磷酸铁锂的纯度、结晶度和电化学性能。

Description

磷酸铁锂及其制备方法、锂离子电池
本申请要求于2021年02月09日提交中国专利局，申请号为2021101789734，申请名称为“磷酸铁锂的制备方法、磷酸铁锂材料及锂离子电池”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
本申请涉及锂离子电池技术领域，尤其涉及磷酸铁锂及其制备方法、锂离子电池。
背景技术
磷酸铁锂自1997年提出后便引起了广泛关注，其以卓越的稳定性、高倍率充电、无毒、长循环寿命的特性在锂离子电池正极材料中占据一席之地，但磷酸铁锂同样具有明显缺陷例如低电导率、离子扩散率等。
对于正极材料而言，低电导率很大程度上限制了磷酸铁锂电池的性能，为了提高磷酸铁锂的电导率通常采用碳包覆、金属参杂、添加金属粒子等方法使得电导率提升数个数量级。常规的磷酸铁锂采用碳热还原法来制备，磷酸铁锂碳热还原中，Fe 2+易氧化成Fe 3+，因此需要加入还原剂以防止Fe 2+的氧化。在磷酸铁锂的生产过程中常以H 2或者碳源作为还原剂，碳源的加入能给磷酸铁锂表面形成碳包覆从而增强颗粒的导电性，但是，碳包覆的同时也会造成正极材料压实性能的降低，进而导致电化学性能降低。
研究表明升高反应温度能提高磷酸铁锂的结晶度，进而提高压实性能。但是，磷酸铁锂碳热还原过程主要涉及Fe 3+—LiFePO 4—Fe xP(x＝1,2,3)的逐步还原过程，其中Fe xP在常温下是铁磁性物质，会造成锂离子电池的短路和自放电，所以中间态产物LiFePO 4是我们的理想态，研究表明反应过程中加入过量还原剂或提升反应温度会导致磷酸铁锂的脱锂行为发生，促进Fe xP的生成，所以在磷酸铁锂的碳热还原中不能使用过高的反应温度，现有技术中的反应温度在800℃以下，仍然伴随着少量Fe xP的生成。
可以看出，高温有利于提升磷酸铁锂的结晶度，提高压实性能，从而提升其电化学以及理化性能，但会产生更多的磁性物质，增加额外的除磁成本和降低生产效率，因此，在磷酸铁锂的碳热还原反应中，急需一种既能够提高结晶度还可以避免铁磁性物质的生成的方法。
申请内容
本申请为了克服上述缺陷，提供一种磷酸铁锂材料及其制备方法、锂离子电池，通过抑制碳热还原法中的Fe xP(x＝1,2,3)的生成，从而改善磷酸铁锂/碳的理化性能和电化学性能。
第一方面，本申请实施例提供了一种磷酸铁锂的制备方法，包括如下步骤：
将铁源、锂源、磷源和还原性碳源的干燥料进行烧结，得到所述磷酸铁锂；
其中，所述烧结气氛包括温和氧化性气体，所述温和氧化性气体包括二氧化碳，所述烧结的温度为800℃～900℃。
上述方案中，磷酸铁锂在碳热还原中，烧结气氛中的气体含有温和氧化性气体，抑制了磁性物质的生成，并且随着二氧化碳的加入体系降低的还原态势可以通过提升温度来弥补，同时升高的温度可以让LFP/C拥有更好的结晶度并且压实性能因此得到很好地提升，本申请的方法可保证磷酸铁锂的纯度、结晶度和电化学性能。
结合第一方面，所述温和氧化性气体还包括保护性气体，所述保护性气体包括氮气、氩气、氦气和氖气中至少一种；
结合第一方面，所述温和氧化性气体还包括保护性气体，所述二氧化碳与所述保护性气体的体积比为(1:99)～(99:1)。
结合第一方面，所述烧结气氛中的总气体流速为3L/min～10L/min。
结合第一方面，所述烧结的保温时间为2h～20h。
结合第一方面，所述方法包含如下技术特征a至d中至少一种：
a.所述铁源包括磷酸铁、金属铁、硝酸铁、氧化铁、氯化铁和草酸亚铁中至少一种；
b.所述磷源包括磷酸铁、磷酸一氢铵、磷酸二氢铵、磷酸铵和磷酸一氢亚铁中至少一种；
c.所述还原性碳源包括蔗糖、葡萄糖和聚乙二醇中的至少一种；
d.所述锂源为碳酸锂、磷酸锂、氢氧化锂和氯化锂中至少一种。
结合第一方面，所述铁源、锂源、磷源和碳源的质量比为(95～105):(90～110)：(95～105)：(0.1～10)。
结合第一方面，所述干燥料的制备过程包括：
将磷源、铁源、锂源、还原性碳源和溶剂混合研磨，得到浆料，干燥后得到干燥料。
结合第一方面，所述方法还包括如下技术特征a至g中至少一种：
a.所述混合研磨的方式包括球磨和砂磨中任意一种；
b.所述浆料中固体颗粒的中值粒径D50为0.1μm～3μm；
c.所述溶剂包括水和乙二醇中至少一种；
d.所述浆料中固体含量为浆料总质量的5％～80％；
e.所述干燥的方式包括喷雾干燥和蒸发干燥中的任意一种；
f.所述干燥温度为50℃～500℃；
g.所述干燥时间为0.1h～10h。
第二方面，本申请实施例提供一种磷酸铁锂材料，其通过第一方面的制备方法制备。
所述磷酸铁锂材料包含如下技术特征a至d中至少一种：
a.所述磷酸铁锂为橄榄石结构；
b.所述磷酸铁锂材料的粉体压实密度为2.1g/cm 3～3.3g/cm 3；
c.所述磷酸铁锂材料的平均粒径为0.1μm～5μm；
d.所述磷酸铁锂的比表面积为1m 2/g～50m 2/g。
第三方面，本申请实施例提供一种锂离子电池，所述锂离子电池包含第一方面所述的制备方法制备的磷酸铁锂或第二方面任一项所述的磷酸铁锂。
本技术方案与现有技术相比，至少具有以下技术效果：
本申请的制备方法，本申请煅烧时加入的二氧化碳抑制了Fe xP的生成，提升了LFP/C单位质量容量和电池可靠性，因二氧化碳气体在高温时具有弱氧化性能且该氧化性不足以将二价铁离子氧化成三价铁离子，在高温(800℃～900℃)反应时的方 程式为：Fe xP+CO 2+Li 2CO 3+H 3PO 4→LiFePO 4+H 2O+CO，进而能有效抑制Fe xP生成(x＝1,2,3)，并且随着二氧化碳的加入体系降低的还原态势可以通过提升温度来弥补，同时升高的温度可以让碳包覆磷酸铁锂(LFP/C)拥有更好的结晶度并且压实性能因此得到很好地提升，本申请的方法可保证LiFePO 4的纯度、结晶度和电化学性能。
本申请制备的磷酸铁锂，磷酸铁锂在碳热还原中，烧结气氛中的气体含有温和氧化性气体，温和氧化性气体为二氧化碳，其具有较高的纯度、结晶度和电化学性能。
附图说明
下面结合附图和实施例对本申请进一步说明。
图1为本申请实施例2制备的磷酸铁锂材料的XRD测试图；
图2是本申请对比例3制备的磷酸铁锂材料的XRD测试图。
具体实施方式
为了更好的理解本申请的技术方案，下面结合附图对本申请实施例进行详细描述。
应当明确，所描述的实施例仅仅是本申请一部分实施例，而不是全部的实施例。基于本申请中的实施例，本领域普通技术人员在没有作出创造性劳动前提下所获得的所有其它实施例，都属于本申请保护的范围。
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”、“所述”和“该”也旨在包括多数形式，除非上下文清楚地表示其它含义。
应当理解，本文中使用的术语“和/或”仅仅是一种描述关联对象的关联关系，表示可以存在三种关系，例如，A和/或B，可以表示：单独存在A，同时存在A和B， 单独存在B这三种情况。另外，本文中字符“/”，一般表示前后关联对象是一种“或”的关系。
现有技术中，通过磷酸铁锂作为正极材料具有高倍率充电、长循环寿命和高稳定性的优点，常规的磷酸铁锂采用传统固相还原体系制备，其只能在相对不高的温度(现有技术一般为700～750℃)的情况下完成还原反应，且反应过程中伴随着过度还原形成Fe xP(x＝1,2,3)杂质不利于碳包覆磷酸铁锂LFP/C的电化学性能的问题，
因此，本申请实施例提供一种磷酸铁锂的制备方法，包括如下步骤：
将铁源、锂源、磷源和还原性碳源的干燥料进行烧结，得到磷酸铁锂；
其中，烧结气氛包括温和氧化性气体，温和氧化性气体包括二氧化碳，烧结温度为800℃～900℃。
上述方案中，本申请在烧结时加入的二氧化碳能够抑制杂质Fe xP(x＝1,2,3)的生成，提升了碳包覆磷酸铁锂LFP/C单位质量容量和电池可靠性，具体地，由于二氧化碳气体在高温时具有弱氧化性能且该氧化性不足以将二价铁离子氧化成三价铁离子，在高温(800℃～900℃)反应时的方程式为：Fe xP+CO 2+Li 2CO 3+H 3PO 4→LiFePO 4+H 2O+CO，进而能有效抑制Fe xP生成(x＝1,2,3)，并且随着二氧化碳的加入体系降低的还原态势可以通过提升温度来弥补，同时升高的温度可以让LFP/C拥有更好的结晶度并且压实性能因此得到很好地提升，本申请的方法可保证磷酸铁锂(LFP)的纯度、结晶度和电化学性能。
烧结的温度为800℃～900℃，具体地，烧结的温度可以是800℃、810℃、820℃、830℃、840℃、850℃、860℃、870℃、880℃、890℃或900℃等，具体不做限制，但并不仅限于所列举的数值，该数值范围内其他未列举的数值同样适用。温度低于800℃，得到的磷酸铁锂结晶度及粉体压实性能较差，本申请制备的磷酸铁锂具有高的粉体压实性能，有助于获得高能量密度，优选地，烧结温度为820℃～880℃。
作为本申请可选的技术方案，二氧化碳的来源不作限定，例如可以直接通入二氧化碳，也可以使用能够产生二氧化碳的物质在制备过程中产生二氧化碳。
上述实施方式得到的磷酸铁锂相较于常规惰性气体下碳热还原得到的磷酸铁锂，电化学性能、循环性能、安全性和结晶度都得到了大幅的提升。
作为本申请可选的技术方案，温和氧化性气体还包括保护性气体，保护性气体为 氮气、氩气、氦气和氖气中至少一种，示例性的，可以是氮气与二氧化碳组合、氩气与二氧化碳组合等等，在反应过程中，二氧化碳能够抑制Fe xP的生成，保护性气体控制反应产品与环境之间的化学反应，二氧化碳与保护性气体的体积比为(1:99)～(99:1)，具体地，二氧化碳与保护性气体的体积比可以是1：99、10：90、20：80、30：70、40：60、50：50、60：40、70：30、80：20、90：10或99：1等等，具体不做限制，但并不仅限于所列举的数值，该数值范围内其他未列举的数值同样适用。优选地，二氧化碳与保护性气体的体积比为(30～70):(70～30)，二氧化碳与保护性气体的体积比在上述范围中，能增大体系的还原性能，提高碳源碳化速率，从而加快Fe 3+还原反应以及使得Fe 3+被充分还原，可以进一步提升晶体结构的均匀性及粉体压实密度。本申请烧结过程在二氧化碳和保护性气体分氛围中进行，不仅能够提升碳包覆磷酸铁锂LFP/C单位质量容量和电池可靠性，而且方便调节体系氧化还原态势，碳源的加入具备更多选择性和灵活性。
在本申请可选的技术方案中，烧结在HB-Ln2060间歇式回转式电阻炉中进行，烧结的升温速率为1℃/min～10℃/min，具体可以是1℃/min、2℃/min、3℃/min、4℃/min、5℃/min、6℃/min、7℃/min、8℃/min、9℃/min或10℃/min等，具体不做限制，但并不仅限于所列举的数值，该数值范围内其他未列举的数值同样适用。烧结的保温时间为2h～20h，具体可以是2h、4h、6h、7h、8h、9h、10h、11h、12h、13h、14h、16h、18h或20h等，具体不做限制，但并不仅限于所列举的数值，该数值范围内其他未列举的数值同样适用。烧结气氛中的总气体流速为3L/min～10L/min，具体可以是4L/min、5L/min、6L/min、7L/min、8L/min或9L/min等，但并不仅限于所列举的数值，该数值范围内其他未列举的数值同样适用。烧结的二氧化碳和保护性气体的流速可以相同或不相同，其两者作用不同且相互不产生影响，若流速过慢，则保护气氛不能起到保护作用；若流速过快，则气体会将粉末带出回转炉堵塞管道。
在本申请可选的技术方案中，本申请的铁源包括磷酸铁、金属铁、硝酸铁、氧化铁、氯化铁和草酸亚铁中至少一种。
在本申请可选的技术方案中，磷源包括磷酸铁、磷酸一氢铵、磷酸二氢铵、磷酸铵和磷酸一氢亚铁中至少一种。
在本申请可选的技术方案中，还原性碳源为蔗糖、葡萄糖和聚乙二醇中至少一 种，具体地，可以是蔗糖、葡萄糖和聚乙二醇中任意一种，还可以是聚乙二醇和蔗糖混合、聚乙二醇与葡萄糖混合、聚乙二醇与蔗糖、葡萄糖混合等等的组合。
在本申请可选的技术方案中，锂源为碳酸锂、磷酸锂、氢氧化锂和氯化锂中至少一种。
在本申请可选的技术方案中，铁源、锂源、磷源和碳源的质量比/摩尔比为(95～105):(90～110)：(95～105)：(0.1～10)，示例性的，铁源、锂源、磷源和碳源的质量比可以是95：90：100：0.1、100：100：105：5、100：110：95：10、105：90：95：0.1和100：105：105：3等，具体不做限制，但并不仅限于所列举的数值，该数值范围内其他未列举的数值同样适用。
在本申请可选的技术方案中，优选地，磷源和铁源均为磷酸铁，磷酸铁与还原性碳源的质量比为(1～100):1，具体可以是100:1、90:1、80:1、70:1、65:1、60:1、50:1、40:1、30:1、20:1、10:1、8:1、5:1、2.5:1、2:1、1.6:1、1.25:1或1:1等，在此不作限制，但并不仅限于所列举的数值，该数值范围内其他未列举的数值同样适用。将磷酸铁与还原性碳源控制在上述范围内，制备的材料具有良好的导电性，碳源加入量太多，导致包覆层过厚，增大材料内阻，减少活性物质总量，如果碳源加入量过少，会导致碳包覆不均匀，影响材料导电性。
锂源中的锂元素与磷酸铁的摩尔比为(0.97～1.1):1，具体地，锂源中的锂元素与磷酸铁的摩尔比可以为0.97:1、0.98:1、1.0:1、1.05:1或1.1:1等，在此不作限制，但并不仅限于所列举的数值，该数值范围内其他未列举的数值同样适用。
在可选的技术方案中，磷酸铁锂的制备方法包括如下步骤：
将磷源、铁源、锂源、还原性碳源和溶剂混合研磨，得到浆料，在50℃～500℃干燥0.1h～10h后得到干燥料，将得到的干燥料在800℃～900℃条件下的烧结2h～20h，得到磷酸铁锂，烧结气氛中的气体包括二氧化碳气体和保护性气体，其中，二氧化碳气体和保护性气体体积比为(1:99)～(99:1)，总气体流速为3L/min～10L/min。
在可选的技术方案中，混合研磨的方式包括球磨或砂磨，具体地，球磨操作在SX-8型球磨机中进行。
在可选的技术方案中，溶剂包括水和乙二醇中至少一种。
在可选的技术方案中，浆料中固体颗粒的中值粒径D50为0.1μm～3μm，具体地， 浆料中固体颗粒的中值粒径D50可以为0.12μm、0.14μm、0.15μm、0.18μm、0.2μm、0.22μm、0.25μm或0.28μm等，在此不做限制，但并不仅限于所列举的数值，该数值范围内其他未列举的数值同样适用。具体地，控制上述粒径的方法为：将浆料原料中的大颗粒球磨至D50为0.7～0.9μm(制成固含量为53％的浆料)，小颗粒球磨至D50为0.4～0.6μm(制成固含量为20％的浆料)，然后混合进行细磨，得到的最终浆料粒径D50为0.1μm～0.3μm。
浆料中固体含量为浆料总质量的5％～80％，具体地，浆料中固体含量为浆料总质量可以为5％、10％、20％、30％、40％、50％或60％等，在此不做限制，但并不仅限于所列举的数值，该数值范围内其他未列举的数值同样适用。优选地，浆料中固体含量为浆料总质量的10％～60％。
干燥的方式为喷雾干燥和蒸发干燥中任意一种，具体地，喷雾干燥为采用喷雾机进行离心喷雾干燥，喷雾机的进口温度为110℃～300℃，具体地，进口温度可以为120℃、130℃、150℃、180℃、200℃、230℃、250℃、280℃或300℃等。喷雾机的出口温度为60℃～130℃，具体地，出口温度可以为65℃、70℃、75℃、80℃、85℃、90℃或110℃等。本申请采用离心喷雾干燥相较于其它喷雾方式更具优势，例如离心喷雾相较于二流体喷雾能更稳定的形成所需要的液滴，如二流体喷雾在气流速度过快时容易实行气流扰动而造成甜甜圈形式以及中空的颗粒，若采用二流体喷雾干燥的方式会导致制备的磷酸铁锂材料压实密度低，电化学性能下降。
上述反应中，可通过初步的热力学和动力学分析对反应体系进行模拟获得确立反应趋势，其中热力学数据通过文献查询和热力学表征得到基础的反应物及可能的生成物的⊿h f 0 s,298.15K(标准生成焓)、S 0 s,298.15K(标准熵值)和C p(恒压比热容)从而得到生成焓及熵值和温度表达式，进而确立反应体系的⊿G(吉布斯自由能)，通过阿伦尼乌斯公式转换得到各项反应式的反应平衡常数k eq，在factsage软件中进行数学方法分析，可以得到不同温度和气氛下的反应产物分布趋势，通过如下试验结果进行参照。反应物和可能形成的生成物的热力学数据如表1(还原反应中反应物和产物的标准生成焓，标准熵值，其中CO 2、H 2O为气相，其它均为固相)、表2(反应物和产物的比热容温度关系式)所示。
表1
反应物和产物 ⊿h f 0 s,298.15K(kJ/mol) S 0 s,298.15K[J/(K×mol)]
LiFePO 4 -1591.23 136.75
Fe 2O 3 -824.2 87.332
P 2O 5 -1505.5 228.8648
Li 2CO 3 -1175.08 90.31
蔗糖 -2226.1 392.4
CO 2 -393.509 213.79
H 2O -241.818 188.84
Li 3PO 4 -2095 105
Fe 3P -164.010 114.142
Fe 2P -160.250 72.34
表2
Figure PCTCN2022075496-appb-000001
通过表1和表2计算可以得出，在上述实施例原料及参数选择范围内，可以控 制得到的磷酸铁锂材料中Fe xP的含量。
本申请通过热力学和动力学模拟反应体系趋势，并和实验方案互为佐证并且确立最佳反应温度，热力学及动力学模拟可以有效减少实验量提供最佳反应条件以此降低生产成本和时间成本，并从更深层面给出性能提升的理论支撑。
通过上述方法制备的磷酸铁锂材料，磷酸铁锂材料的粉体压实密度为2.1g/cm 3～3.3g/cm 3，例如2.1g/cm 3、2.3g/cm 3、2.5g/cm 3、2.6g/cm 3、2.8g/cm 3、3.0g/cm 3或3.2g/cm 3等，但并不仅限于所列举的数值，该数值范围内其他未列举的数值同样适用。
磷酸铁锂为橄榄石结构。
磷酸铁锂的平均粒径为0.1μm～5μm，具体地，磷酸铁锂的平均粒径可以是0.1μm、0.5μm、1μm、2μm、3μm、4μm和5μm等，在此不作限制，但并不仅限于所列举的数值，该数值范围内其他未列举的数值同样适用。
磷酸铁锂的比表面积为1m 2/g～50m 2/g，具体地，磷酸铁锂的比表面积可以是1m 2/g、5m 2/g、10m 2/g、20m 2/g、35m 2/g和40m 2/g等，在此不作限制，但并不仅限于所列举的数值，该数值范围内其他未列举的数值同样适用。
本申请制备的磷酸铁锂材料为高温烧结磷酸铁锂材料，控制了Fe xP的含量，同时提升了磷酸铁锂结晶度、粉体压实密度、以及电化学性能。
本申请一种锂离子电池，锂离子电池包括正极极片、负极极片以及设置于正极极片和负极极片之间的隔离膜。
正极极片包括正极集流体和正极活性物质层，正极活性物质层可以包括正极活性物质、导电剂和粘结剂，正极活性物质为上述制备方法制备的磷酸铁锂。
正极集流体可以采用Al箔，同样，也可以采用本领域常用的其他正极集流体。
正极极片的导电剂可以包括导电炭黑、片层石墨、石墨烯或碳纳米管中的至少一种。
正极极片中的粘结剂可以包括聚偏氟乙烯、偏氟乙烯-六氟丙烯的共聚物、苯乙烯-丙烯酸酯共聚物、苯乙烯-丁二烯共聚物、聚酰胺、聚丙烯腈、聚丙烯酸酯、聚丙烯酸、聚丙烯酸盐、羧甲基纤维素纳、聚醋酸乙烯酯、聚乙烯呲咯烷酮、聚乙烯醚、聚甲基丙烯酸甲酯、聚四氟乙烯或聚六氟丙烯中的至少一种。
负极极片包括集流体和负极活性物质层。负极活性物质层包括负极活性物质、导电剂和粘结剂。
负极极片的集流体可以包括铜箔、铝箔、镍箔或碳氟集流体中的至少一种。
负极活性物质可以包括软碳、硬碳、人造石墨、天然石墨、无定形碳、硅氧化合物、归碳化合物、钛酸锂中的至少一种。
粘结剂可以包括羧甲基纤维素(CMC)、聚丙烯酸、聚乙烯基吡咯烷酮、聚苯胺、聚酰亚胺、聚酰胺酰亚胺、聚硅氧烷、聚丁苯橡胶、环氧树脂、聚酯树脂、聚氨酯树脂或聚芴中的至少一种。
导电剂可以包括导电炭黑、科琴黑、乙炔黑、碳纳米管、VGCF(Vapor Grown Carbon Fiber，气相成长碳纤维)或石墨烯中的至少一种。
作为本申请可选的技术方案，隔离膜包括聚乙烯、聚丙烯、聚偏氟乙烯、聚对苯二甲酸乙二醇酯、聚酰亚胺或芳纶中的至少一种。例如，聚乙烯包括选自高密度聚乙烯、低密度聚乙烯或超高分子量聚乙烯中的至少一种。尤其是聚乙烯和聚丙烯，它们对防止短路具有良好的作用，并可以通过关断效应改善电池的稳定性。在一些实施例中，隔离膜的厚度在约5μm～500μm的范围内。
作为本申请可选的技术方案，锂离子电池还可以包括电解液。在一些实施例中，电解液包括但不限于碳酸二甲酯(DMC)、碳酸甲乙酯(EMC)、碳酸二乙酯(DEC)、碳酸乙烯酯(EC)、碳酸丙烯酯(PC)、丙酸丙酯(PP)中的至少两种。此外，电解液还可以额外地包括作为电解液添加剂的碳酸亚乙烯酯(VC)、氟代碳酸乙烯酯(FEC)或二腈化合物中的至少一种。在一些实施例中，电解液还包括锂盐。
本申请的锂离子电池，将正极极片、隔离膜、负极极片按顺序卷绕或堆叠成电极件，之后装入例如铝塑膜中进行封装，注入电解液，化成、封装，即制成锂离子电池。然后，对制备的锂离子电池进行性能测试及循环测试。
本申请通过改变碳热还原法烧结时候的气氛，使烧结气氛中的气体包括温和氧化性气体，抑制了Fe xP的生成，并且随着二氧化碳的加入，体系降低的还原态势可以通过提升温度来弥补，同时升高的温度可以让LFP/C拥有更高的结晶度和粉体压实密度，上述实施方式的方法可保证LiFePO 4的纯度、结晶度和电化学性能；更进一步地，改变温和氧化性气体在烧结气氛中的比例可以方便调节体系氧化还原态势，碳 源的加入就能更具备更多选择性和灵活性。
以下为本申请典型但非限制性实施例：
实施例1
一种磷酸铁锂的制备方法，包括如下步骤：
(1)取4000g磷酸铁、1000g碳酸锂、150g蔗糖、250g聚乙二醇和15.5L去离子水混合，得到浆料；
(2)取0.525L浆料球磨，将浆料中的大颗粒球磨至D50为0.8μm(固含量为53％)小颗粒球磨至D50为0.5μm(固含量为20％)，然后混合细磨浆料至D50为0.2μm(固含量40％)；
(3)将步骤(2)得到的浆料转移至喷雾干燥机中，喷雾干燥机的进口温度为240℃，出口温度为80℃，气体流速为14m 3/h，蠕动泵流速为5L/h，得到喷雾料；
(4)得到喷雾料后在回转式电阻炉中，在800℃条件下烧结10h，调节烧结气氛中的总气体流速为5L/min，烧结气氛中的气体由二氧化碳和氮气按体积比为1：1组成，为二氧化碳和氮气的流速分别为2.5L/min和2.5L/min，得到磷酸铁锂材料。
实施例2
一种磷酸铁锂的制备方法，包括如下步骤：
(1)取4000g磷酸铁、1000g碳酸锂、150g葡萄糖、250g聚乙二醇和15.5L去离子水混合，得到浆料；
(2)取0.525L浆料球磨，将浆料中的大颗粒球磨至D50为0.8μm，小颗粒球磨至D50为0.5μm，然后混合细磨浆料至D50为0.2μm；
(3)将步骤(2)得到的浆料转移至尼鲁喷雾干燥机中进行离心喷雾，喷雾干燥机的进口温度为240℃，出口温度为80℃，气体流速为14m 3/h，蠕动泵流速为5L/h，得到喷雾料；
(4)得到喷雾料后在回转式电阻炉中，在850℃条件下烧结10h，调节烧结气氛中的总气体流速为5L/min，烧结气氛中的气体由二氧化碳和氮气按体积比1：1组成，二氧化碳和氮气的流速分别为2.5L/min和2.5L/min，得到磷酸铁锂材料。
图1为本实施例制备得到的磷酸铁锂材料的XRD测试图，由图1可以看出，磷酸铁锂的结晶度好，主要原因在于本申请控制了Fe 3P的含量。
实施例3
与实施例1的区别在于，步骤(4)中所述二氧化碳和氮气的体积比为1:9。
实施例4
与实施例1的区别在于，步骤(4)中所述二氧化碳和氮气的体积比为9:1。
实施例5
与实施例2的区别在于，步骤(4)中所述二氧化碳和氮气的体积比为1:9。
实施例6
与实施例2的区别在于，步骤(4)中所述二氧化碳和氮气的体积比为9:1。
实施例7
与实施例1的区别在于，二氧化碳和氮气的流速均为1L/min。
实施例8
(1)取2120g三氧化二铁、3046g磷酸二氢铵、1000g碳酸锂、150g葡萄糖、250g聚乙二醇和15.5L去离子水混合，得到浆料；
(2)取0.525L浆料球磨，将浆料中的大颗粒球磨至D50为0.8μm，小颗粒球磨至D50为0.5μm，然后混合细磨浆料至D50为0.2μm；
(3)将步骤(2)得到的浆料转移至尼鲁喷雾干燥机中进行离心喷雾，喷雾干燥机的进口温度为240℃，出口温度为80℃，气体流速为14m 3/h，蠕动泵流速为5L/h，得到喷雾料；
(4)得到喷雾料后在回转式电阻炉中，在850℃条件下烧结10h，调节烧结气氛中的总气体流速为5L/min，烧结气氛中的气体由二氧化碳和氮气按体积比1：1组成，二氧化碳和氮气的流速分别为2.5L/min和2.5L/min，得到磷酸铁锂材料
对比例1
与实施例1的区别在于，步骤(4)：喷雾料在回转式电阻炉中煅烧温度为750℃，保温10h，调节烧结气氛中的总气体流速为5L/min，所述烧结气氛中的气体由氮气组成，得到磷酸铁锂材料。
对比例2
与实施例1的区别在于，步骤(4)中二氧化碳替换为等量的空气。
对比例3
与实施例2的区别在于，步骤(4)：喷雾料在回转炉中，进行温度为850℃的烧结10h，调节烧结气氛中的总气体流速为5L/min，所述烧结气氛中的气体为氮气，得到磷酸铁锂材料。
图2为本对比例3得到的磷酸铁锂材料的XRD测试图，可以看到有微弱的磷化铁特征峰，说明了在仅通氮气条件下，结合碳源释放出的大量还原性气体，形成强还原气氛，会促使磷酸铁锂中磷化铁的生成，从而对磷酸铁锂的安全性造成危害。
性能测试：
将各实施例和对比例得到的磷酸铁锂材料进行如下性能测试：
(1)物性指标测试：将各实施例和对比例得到的磷酸铁锂材料，分别进行粉体压实密度(采用GB/T 24533-2009)、XRD和ICP(采用GB/T 24533-2019)的测试。
(2)电化学性能测试：将各实施例和对比例得到的磷酸铁锂材料作为正极活性物质，按照正极活性物质：导电炭黑：聚偏氟乙烯(PVDF)＝90:5:5的质量比混合，以N-甲基吡咯烷酮(NMP)为溶剂混浆后涂布于铝箔上，经过90℃真空干燥得到正极极片；然后组装成扣式半电池，(其中电解液的锂盐为1mol/L的LiPF6，溶剂为碳酸乙烯酯(EC)和碳酸甲乙酯(EMC)按照体积比1:1的混合物)；将得到的电池在25±2℃环境下进行充放电测试，充放电电压范围为3.7～3.5V，电流为0.1C，记录测试数据，测试结果如表3所示：
表3
Figure PCTCN2022075496-appb-000002
Figure PCTCN2022075496-appb-000003
通过实施例1、实施例3和实施例4，以及实施例2、实施例5、实施例6和实施例8的对比可知，在磷酸铁锂碳热还原过程中，通入适量二氧化碳从而形成温和氧化性的气氛能有效降低产物磁性物质并且提升产物的压实性能，在相同条件下，烧结气氛中二氧化碳含量越多，其制备的磷酸铁锂材料越能提升产物的压实性能、首次放电容量，从而说明二氧化碳在体系调节中的重要性和灵活性。电化学表征表明磷酸铁锂结构变化导致了电化学性能的提升。
实施例2中磷酸铁锂的XRD测试结果(参见图1)显示在二氧化碳气氛中烧结的磷酸铁锂只存在少量的Fe xP，且得到的磷酸铁锂晶体结晶度相较于实施例1中有进一步提升，这证明高温有利于磷酸铁锂的结晶度提高，且能够提升其压实密度。
通过实施例1与实施例7对比可知，流速过慢，则保护气氛不能起到保护作用，导致反应体系中磁性物质增多以及电化学性能表现下降，且产品的压实性能有轻微的下降，可能由于二氧化碳的减少导致一氧化碳含量(相对)上升而抑制碳的还原性能导致体系碳化加剧，压实性能因此下降。
通过实施例1与对比例1对比可知，对比例1中在氮气气氛、750℃的温度下烧结只生成了少量的Fe 3P，但压实密度较低，无法满足需求。
通过实施例1与对比例2对比可知，在通入强氧化性气体氧气时，碳热还原反应难以进行，而得到的产物主要为磷酸铁和氧化铁与锂的复杂化合物，并非我们需要的产物LiFePO 4，故而在碳热还原法气氛不宜使用氧化性过强的气氛。
通过实施例1与对比例3对比可知，在不加二氧化碳的情况下烧结会产生大量Fe 3P这种居里温度高达1043K的铁磁性物质，而更多未成功分离的Fe 3P则存在于磷酸铁锂晶粒间，导致磷酸铁锂压实密度下降，容量降低，并且存在可溶出磁性异物，给电池循环及安全带来隐患。
申请人声明，本申请通过上述实施例来说明本申请的详细工艺设备和工艺流程， 但本申请并不局限于上述详细工艺设备和工艺流程，即不意味着本申请必须依赖上述详细工艺设备和工艺流程才能实施。所属技术领域的技术人员应该明了，对本申请的任何改进，对本申请产品各原料的等效替换及辅助成分的添加、具体方式的选择等，均落在本申请的保护范围和公开范围之内。

Claims (12)

  1. 一种磷酸铁锂的制备方法，其特征在于，包括如下步骤：
    将铁源、锂源、磷源和还原性碳源的干燥料进行烧结，得到所述磷酸铁锂；
    其中，所述烧结气氛包括温和氧化性气体，所述温和氧化性气体包括二氧化碳，所述烧结温度为800℃～900℃。
  2. 根据权利要求1所述的制备方法，其特征在于，所述温和氧化性气体还包括保护性气体，所述保护性气体包括氮气、氩气、氦气和氖气中至少一种。
  3. 根据权利要求1所述的制备方法，其特征在于，所述温和氧化性气体还包括保护性气体，所述二氧化碳与所述保护性气体的体积比为(1:99)～(99:1)。
  4. 根据权利要求1～3任一项所述的制备方法，其特征在于，所述烧结气氛中的总气体流速为3L/min～10L/min。
  5. 根据权利要求1～4任一项所述的制备方法，其特征在于，所述烧结的保温时间为2h～20h。
  6. 根据权利要求1～5任一项所述的制备方法，其特征在于，所述方法包含如下技术特征a至d中至少一种：
    a.所述铁源包括磷酸铁、金属铁、硝酸铁、氧化铁、氯化铁和草酸亚铁中至少一种；
    b.所述磷源包括磷酸铁、磷酸一氢铵、磷酸二氢铵、磷酸铵和磷酸一氢亚铁中至少一种；
    c.所述还原性碳源包括蔗糖、葡萄糖和聚乙二醇中的至少一种；
    d.所述锂源为碳酸锂、磷酸锂、氢氧化锂和氯化锂中至少一种。
  7. 根据权利要求1～6任一项所述的制备方法，其特征在于，所述铁源、锂源、磷源和碳源的质量比为(95～105):(90～110)：(95～105)：(0.1～10)。
  8. 根据权利要求1～7任一项所述的制备方法，其特征在于，所述干燥料的制备过程包括：
    将磷源、铁源、锂源、还原性碳源和溶剂混合研磨，得到浆料，干燥后得到干燥料。
  9. 根据权利要求8所述的制备方法，其特征在于，所述方法还包括如下技术特征a至g中至少一种：
    a.所述混合研磨的方式包括球磨和砂磨中任意一种；
    b.所述浆料中固体颗粒的中值粒径D50为0.1μm～3μm；
    c.所述溶剂包括水和乙二醇中至少一种；
    d.所述浆料中固体含量为浆料总质量的5％～80％；
    e.所述干燥的方式包括喷雾干燥和蒸发干燥中的任意一种；
    f.所述干燥温度为50℃～500℃；
    g.所述干燥时间为0.1h～10h。
  10. 一种磷酸铁锂材料，其特征在于，通过权利要求1～9任一项所述的方法制备得到。
  11. 根据权利要求10所述的磷酸铁锂材料，其特征在于，所述磷酸铁锂材料包含如下技术特征a至d中至少一种：
    a.所述磷酸铁锂为橄榄石结构；
    b.所述磷酸铁锂材料的粉体压实密度为2.1g/cm 3～3.3g/cm 3；
    c.所述磷酸铁锂材料的平均粒径为0.1μm～5μm；
    d.所述磷酸铁锂比表面积为1m 2/g～50m 2/g。
  12. 一种锂离子电池，其特征在于，所述锂离子电池包括正极极片、负极极片以及设置于正极极片和负极极片之间的隔离膜，所述正极极片包含权利要求1～9任一项所述的制备方法制备的磷酸铁锂或权利要求10～11任一项所述的磷酸铁锂。
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